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... The most important property of gellan, which is at the origin of its widespread use, is its capability of forming thermo-reversible transparent gels by cooling aqueous solutions containing cations, even at low polymer concentrations. The gellan sol-gel transition is an exothermic process [12] that can occur in a range of temperature between 30 and 50 • C, depending on the specific Another appealing property of gellan is its suitability as innovative agent for wet cleaning treatments in the restoration of paper artworks [21]. In a recent work [22], it was also demonstrated that microgels based on gellan, i.e. micro-scale particles internally made by a gellan cross-linked network, offer several advantages for paper cleaning with respect to more established procedure based on wet cleaning or hydrogels systems. ...
... In addition, the softness of microgels suspensions can be adapted to the irregular surface of paper artworks, thus providing an higher efficiency. It is interesting to note that gellan hydrogels employed for paper cleaning are formed in the presence of calcium acetate [21], while gellan microgels are prepared by applying external shear upon the addition of sodium chloride [26]. It is thus important, also in the context of its cultural heritage applications, to clarify the role of cations on gellan aggregation. ...
... Figures 2A-C directly compare the images of the polymer network obtained without adding salts to the polymer suspension (G pure ) and by adding sodium chloride (G N a ) or calcium acetate (G Ca ). We focus on results for G N a (27 mM) and G Ca (2.5 mM), since these are the salt concentrations relevant for application to paper preservation for microgels [22] and hydrogels [21], respectively. ...
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Among hydrocolloids, gellan is one of the most used anionic polysaccharides, because of its capability of forming mechanically stable gels at relatively low concentrations. Despite its long-standing use and importance, the gellan aggregation mechanism is still not presently understood at the microscopic level due to the lack of atomistic information. Here we will fill this gap by reporting molecular dynamics simulations of gellan chains at different polymer and salt contents, being able to unveil the occurrence of the two steps in the process, in agreement with existing hypotheses. At first, the formation of double helices takes place, followed by the aggregation into super-structures. For both steps, the role of bivalent cations appears to be crucial, as also shown by rheology and atomic force microscopy measurements: they not only facilitate the junction of the chains into double helices, but also promote through bridging their arrangement into larger aggregates. On the other hand, monovalent cations have a much more reduced role, making it possible to form double helices only at very high salt content and not actively participating in the formation of gels. Our simulations thus offer the first complete microscopic overview of gellan aggregation and will be important for future use of gellan-based systems for a wide variety of applications, ranging from food science to art restoration.
... Full aqueous immersion could lead to an excess amount of water in paper, leading to a swelling of the amorphous zones in cellulose or migration and solubilization of some constituent elements such as inks or fillers. Hydrogels offer an alternative to aqueous immersion procedures (Barbabietola et al. 2016;Casoli et al. 2013;Iannuccelli et al. 2010;Mazzuca et al. 2014Mazzuca et al. , 2016Mazzuca et al. , 2017Micheli et al. 2016).These systems have been the subject of increasing interest in the paper conservation field over the past decade for their ability to control the amount of water released into paper during treatment. Moreover, they can absorb degradation products from paper surface, thus performing a cleaning action on paper artworks, minimizing damages. ...
... The cleaning capability of gellan gel has been studied mainly on western paper (Iannuccelli et al. 2010;Isca et al. 2015;Mazzuca et al. 2014;Micheli et al. 2016), while there seems to be few references regarding the application of gels as a potential cleaning agent for ancient Chinese paper (Liang et al. 2017;Yip 2014). Despite the significance of Chinese paper collections present in libraries, archives, and museums all around the world, there have been only few studies concerning the material composition of this paper type (Brown et al., 2017). ...
... to ensure close contact between the gel and the sample (Iannuccelli et al. 2020). Usually, on a gel of 6 cm diameter and 1 cm height a weight of 500 g was applied (Mazzuca et al. 2014). After the cleaning process (approximately 1 h, unless otherwise stated), the gel was removed manually in one step. ...
Article
Aqueous cleaning of works of art on paper is one of the most important and delicate steps in a conservation process. It allows the removal of inorganic (metals) and organic substances, such as degradation products and other contaminants. These substances are responsible for yellowing, weakening, and loss of mechanical properties of paper. In this article, the cleaning effect of gellan gum was assessed on xuan paper, a traditional Chinese paper different in composition and papermaking technology compared to many Western papers. To assess the effect of gellan gum on xuan paper, its characteristics were studied before and after cleaning utilizing non-invasive and micro-invasive techniques. Results were compared to those obtained when treating Western papers and indicated that gellan gum can be applied effectively for aqueous cleaning of xuan paper.
... In the last years, efforts have been done to determine several methodologies to clean paper artworks, preserving, at the same time, paper features. In this contest, for example, dry cleaning methodologies like mechanical abrasion involving micro blasting techniques or laser ablation are reported in literature [7][8][9][10], so as the introduction of wet techniques like solutions of nanoparticles made by sodium hydroxide or of polyamides to raise the pH of acid papers, and gel-based material [11][12][13][14][15]. Usually, the wet cleaning of paper artworks has been carried out by immersing paper sheets in a water bath; this process could be harmful for fragile and delicate artworks, because it can induce fibers weakening, loss of mechanical properties, and change in paper morphology pigments or ink fading [16]. ...
... In this contest, for example, dry cleaning methodologies like mechanical abrasion involving micro blasting techniques or laser ablation are reported in literature [7][8][9][10], so as the introduction of wet techniques like solutions of nanoparticles made by sodium hydroxide or of polyamides to raise the pH of acid papers, and gel-based material [11][12][13][14][15]. Usually, the wet cleaning of paper artworks has been carried out by immersing paper sheets in a water bath; this process could be harmful for fragile and delicate artworks, because it can induce fibers weakening, loss of mechanical properties, and change in paper morphology pigments or ink fading [16]. The use of hydrogels represents a valid alternative to this procedure because due to their retentive properties, they minimize the mentioned disadvantages [14,17,18]. In this contest, several hydrogels for cleaning paper artworks have been presented and they effectiveness reported in the literature [14,[17][18][19]. ...
... The use of hydrogels represents a valid alternative to this procedure because due to their retentive properties, they minimize the mentioned disadvantages [14,17,18]. In this contest, several hydrogels for cleaning paper artworks have been presented and they effectiveness reported in the literature [14,[17][18][19]. It should be noted, however, that the proposed hydrogels have been extensively studied and characterized mainly on ancient paper and little on modern paper. ...
Article
Hydrogel-based cleaning of paper artworks is an increasingly widespread process in the cultural heritage field. However, the search for tuned (compatible, highly retentive and not perishable) hydrogels is a challenging open question. In this paper, a complete characterization of chemical hydrogels based on polyvinyl alcohol (PVA) crosslinked with telechelic PVA and their remarkable performances as gels for cleaning paper artworks are reported. The rheological properties, porosity, water content of these gels were determined and analyzed as a function of the components concentration during synthesis. Due mechanical and retentive properties, the reported gels are optimum candidates for paper cleaning applications. The efficacy of these PVA-based gels has been demonstrated applying them on the surface of the sheets of several paper artworks, and characterizing the samples before and after the cleaning process by means of a multidisciplinary approach involving spectroscopic and chromatographic tests.
... As concern the chromatographic analysis of the material removed by the manuscripts, a sampling and extraction procedure previously described has been followed [7]. ...
... The analyses of the compounds, captured by sponges, show that all paper samples (16 manuscripts) have similar composition and similar degradation state. In details, the identified organic compounds were oxalic (t r 2.9 min), ascorbic (t r 3.8 min) and citric (t r 8.3 min) acids (Table SI 1) (Fig. 3) [6][7][8][9][10]11,12,13]. From these chromatograms, another important information was also obtained, concerning the glue used in these volumes: the broad peak at around 12 min is relative to the presence of degraded starch (as identified using of a commercial standard). ...
... Some of the most significant obtained spectra are reported in Fig. 6-8. As shown, in all cases is evident the characteristic feature of FTIR spectrum of cellulose (see Fig. S1 for comparison), that is the typical absorption bands in the region 1500-950 cm -1 due, for instance, to CO and CC stretching, CCH and OCH deformation stretching, COH and HCH bending [7,15]. Moreover, in all spectra is clearly visible the presence of carbonates, whose bands are at 1420 and 874 cm −1 . ...
Article
The conservation and restoration of paper artworks play a fundamental role in the field of our Cultural Heritage. In this contest, the characterization of paper composition as well as degradation state is fundamental to determine the suitable restoration and conservation processes for paper artworks. In this work, we present an interdisciplinary study focalized on the not-invasive characterization of a group of 16 precious Arabic-Christian manuscripts (originating from different regions of the Arabian Peninsula used in Christian environment) of XIII century, collected in the Vatican Library (Biblioteca Apostolica Vaticana – BAV, Vatican City). The aim of this study is focused onto the characterization of papers and inks compositions of these manuscripts, in order to understand if there are similarity between them, and in same way, to obtain information about the provenience of them. For this goal, several analytical techniques were applied by using portable instrumentation directly in the restoration laboratory of BAV, such as Infrared Reflectography, X-ray fluorescence and colorimetry. In addition, High Performance Liquid Chromatography with UV/VIS detection and Fourier Transform Infrared Spectroscopy were applied for the evaluation of the composition and the conservation status of these books by the analyses of the material, removed by a sampling method based on the sponges mainly used for cleaning of paper artworks. Crossing the obtained results, we can characterize the composition of the paper and the inks, used in the various manuscripts. They present the same characteristics in terms of chemical composition, not linked on the region where the book was found, underlining that the used protocol for the paper and its production were the same in the Arabic Peninsula.
... In the last years, efforts have been done to determine several methodologies to clean paper artworks, preserving, at the same time, paper features. In this contest, for example, dry cleaning methodologies like mechanical abrasion involving micro blasting techniques or laser ablation are reported in literature [7][8][9][10], so as the introduction of wet techniques like solutions of nanoparticles made by sodium hydroxide or of polyamides to raise the pH of acid papers, and gel-based material [11][12][13][14][15]. Usually, the wet cleaning of paper artworks has been carried out by immersing paper sheets in a water bath; this process could be harmful for fragile and delicate artworks, because it can induce fibers weakening, loss of mechanical properties, and change in paper morphology pigments or ink fading [16]. ...
... In this contest, for example, dry cleaning methodologies like mechanical abrasion involving micro blasting techniques or laser ablation are reported in literature [7][8][9][10], so as the introduction of wet techniques like solutions of nanoparticles made by sodium hydroxide or of polyamides to raise the pH of acid papers, and gel-based material [11][12][13][14][15]. Usually, the wet cleaning of paper artworks has been carried out by immersing paper sheets in a water bath; this process could be harmful for fragile and delicate artworks, because it can induce fibers weakening, loss of mechanical properties, and change in paper morphology pigments or ink fading [16]. The use of hydrogels represents a valid alternative to this procedure because due to their retentive properties, they minimize the mentioned disadvantages [14,17,18]. In this contest, several hydrogels for cleaning paper artworks have been presented and they effectiveness reported in the literature [14,[17][18][19]. ...
... The use of hydrogels represents a valid alternative to this procedure because due to their retentive properties, they minimize the mentioned disadvantages [14,17,18]. In this contest, several hydrogels for cleaning paper artworks have been presented and they effectiveness reported in the literature [14,[17][18][19]. It should be noted, however, that the proposed hydrogels have been extensively studied and characterized mainly on ancient paper and little on modern paper. ...
Article
Wet cleaning of paper artworks by using hydrogels is a recently proposed process in the cultural heritage field. In this contest, on one side, research has focused on more effective and tuned cleaning hydrogels; on the other, the cleaning performances of the proposed hydrogels have been studied on ancient paper and very little on modern paper. This lack of information is not negligible, since the two kinds of paper differ strongly in composition. The difference, in turn could affect the performance of cleaning gels. In this article, new chemical hydrogels were synthetized using an oxidized polyvinyl alcohol (PVA) bearing an aldehyde group at each chain end, as cross-linking agent, i.e. telechelic PVA. PVA hydrogels have been characterized as candidates for paper cleaning applications. The possibility of tuning the mechanical and retentive properties, simply by changing the ratio of two polymer concentrations, their stability and transparency, indeed, render them, potentially suitable in cultural heritage field. The cleaning capability of two hydrogels, with different PVA/telechelic PVA ratios, has been assessed both on ancient paper, than a modern one and the results have been compared. The efficacy of these hydrogels has been demonstrated characterizing the samples before and after the cleaning process by means of a multidisciplinary approach involving spectroscopic and chromatographic tests.
... It is formed by the repetition unit of (1,3)-β-D-glucose, (1,4)β-D-glucuronic acid, (1,4)β-D-glucose, and (1,4)α-L-rhamnose. 17 Interestingly, it was recently shown 34 that a shear stress applied during gelation in the presence of sodium chloride is able to rearrange the Gellan gum network into stable microgel particles, whose elasticity depends on Gellan and salt concentrations. With respect to paper cleaning, microgels could offer several advantages when compared to hydrogels: first, their reduced size may be suitable to achieve a better penetration in the porous structure of paper, where they could adsorb pollution materials and degradation byproducts in a shorter amount of time; second, the softness of the microgel suspensions could be tuned to make them easily adapt to the irregular surfaces of artifacts without inducing alteration of the latter. ...
... In order to compare the cleaning effectiveness of microgels with respect to previously established protocols, the same diagnostic measurements are performed on modern and ancient samples subjected to a Gellan gum hydrogel treatment and water bath. 17 (Top) As compared to hydrogels, the reduced sizes of microparticles are suitable to easily adapt to the irregular surfaces of the artifacts and to better penetrate in the porous structure of paper allowing a deeper cleaning in a shorter time. (Bottom) Illustration of the osmosis cleaning mechanism performed by microgels. ...
... Gellan hydrogel preparation has been performed following the protocol reported elsewhere. 17,18 2.3. Paper Samples and Cleaning Process. ...
Article
Microgel particles have emerged in the last few years as a favourite model system for fundamental science and for innovative applications ranging from industrial to biomedical fields. Despite their potentialities, no works so far have focused on the application of microgels for cultural heritage preservation. Here we show their first use for this purpose, focusing on wet paper cleaning. Exploiting their retentive properties, microgels are able to clean paper ensuring more controlled water releasing from the gel matrix, in analogy to their macroscopic counterpart, i.e., hydrogels. However, differently from these, the reduced size of microgels makes them suitable to efficiently penetrate in the porous structure of the paper and to easily adapt to the irregular surfaces of artefacts. To test their cleaning abilities, we prepare microgels made of Gellan gum, a natural and widespread material already used as a hydrogel for paper cleaning, and apply them to modern and ancient paper samples. Combining several diagnostic methods, we show that microgels performances in the removal of cellulose degradation by-products for ancient samples are superior to commonly employed hydrogels and water bath treatments. This is due to the composition and morphology of ancient paper, which facilitates microgels penetration. For modern paper cleaning performances are at least comparable to the other methods. In all cases, the application of microgels takes place on a time scale of a few minutes, opening the way for widespread use as a rapid and efficient cleaning protocol.
... Second, their action is relatively timeconsuming (about 1 h). 10,16 Despite the great attention addressed to the cleaning of ancient paper artworks, very little has been done on this issue for modern paper crafts, even if they are more fragile and tend to degrade faster, as they are composed of mechanically and/or chemically treated wood pulp instead of rags. 20,21 In this context, the characterization of modern paper, as well as the setting up of suitable procedures for their wet restoration, is almost unexplored. ...
... 20,21 In this context, the characterization of modern paper, as well as the setting up of suitable procedures for their wet restoration, is almost unexplored. 10,11,20,22 Recent articles outline the complexity and reduced efficacy of the cleaning procedure on modern paper with respect to ancient paper. 12,23 Furthermore, the removal of foxing due to modern adhesives to the paper surface is an almost unexplored field. ...
... The idea comes from the finding that successful cleaning needs an intimate contact of the material employed with both the substrate and compounds to be removed, as observed by comparing the times needed for a complete cleaning process with gellan hydrogel (1 h) or with the corresponding gellan microgels (few minutes). 10,14,15,23 It has been demonstrated that poly(vinyl alcohol) (PVA)-based hydrogels are good materials for cleaning both ancient and modern paper samples. 12,13 In addition, PVA-shelled microbubbles are very stable and acoustically active, thus representing a versatile tool to enhance the cleaning action with US. 28,29 On this basis, we defined a novel strategy for the removal of adhesives from modern paper that combines shortterm treatment based on PVA-shelled microbubbles and US treatment, followed by a final cleaning step with hydrogels made up of PVA and telechelic PVA (tel-PVA; see Scheme S1). ...
Article
Full-text available
In this work, we shed new light on ultrasound contrast agents applied to the field of cultural heritage as an invaluable fine-tune cleaning tool for paper artworks. In this context, one of the primary and challenging issues is the removal of modern adhesives from paper artifacts. Modern adhesives are synthetic polymers whose presence enhances paper degradation and worsens its optical features. A thorough analytical and high-spatial-resolution combined study was successfully performed to test the capability of poly(vinyl alcohol)-based microbubbles stimulated by a proper noninvasive 1 MHz ultrasound field exposure in removing these adhesives from paper surfaces, in the absence of volatile invasive and toxic chemicals and without damaging paper and/or leaving residues. We demonstrate that poly(vinyl alcohol)-shelled microbubbles are suitable for interacting with paper surfaces, targeting and boosting in a few minutes the nondamaging removal of adhesive particles from paper samples thanks to their peculiar shell composition together with their ultrasound dynamics.
... In particular, the effects of γ-rays treatments on cellulose and hemicellulose have been evaluated using a method involving the application of Gellan gel, coupled to an electrochemical biosensor, based on a screen-printed electrode connected with a portable instrumental setup. This tool was previously developed for cleaning paper artworks since it is suitable for in situ and in a simple way the assessment of degradation of artwork [42,43]. Gellan gel is able to remove in non-invasive way degradation products of cellulose present on the surface of wood manufacture, while the biosensor, specific for glucose, the main degradation product of this polysaccharide, offers the possibility to combine the analytical capability of the electrochemical techniques with the detection specificity, characteristic of the biosensor itself. ...
... Spectra of wood samples (as it were, without any pretreatment) were acquired on a Thermo-Scientific (mod. Is50) instrument (Thermo Scientific Inc., Madison WI), equipped with an attenuated total reflectance (ATR) diamond crystal [42]. Spectra were collected in the region between 4000 and 525 cm −1 , with 64 scans for each sample at a resolution of 2 cm −1 , by placing the samples directly on the ATR crystal. ...
... All experiments were performed in triplicate on the different wood samples. The characterization of the degradation of the wood components was carried out by normalizing the absorbance and performing a deconvolution of the bands in the range 840-1900 cm −1 , using a sum of Lorentzian/Gaussian functions [42,[49][50][51]. To this purpose the OMNIC software was employed. ...
Article
Irradiation with γ rays is widely used in the sterilization of a large variety of products and materials in the field of medical supplies, pharmaceuticals, cosmetics, food industry and cultural heritage. It is also applied on wood materials, with the purpose of improving their shelf-life, by lowering the microbial charge and hence the microbial-related deterioration rate. A fundamental issue when applying γ rays is the preservation of the chemico-physical as well as of the structural and mechanical properties of the materials irradiated, since a significant change of properties may jeopardize the use of the materials for the purpose intended. To this end, in this paper we analyzed the chemicophysical properties of four different types of wood used for the construction of musical instruments namely fir, maple, poplar and durmast oak under increasing doses of γ rays. In detail, the effect of incremental radiation doses was evaluated by comparing the results obtained by acoustic tests with those providing information at molecular level, i.e., cyclic voltammetry, linear square voltammetry and infrared spectroscopy. Moreover, in this work the glucose released as a result of the degradation of wood cellulose and hemicellulose, has been analyzed for the first time, with an innovative tool, based on the use of a Gellan gel. The integrated approach presented here, based on both traditional and innovative techniques has proven to be highly efficient in providing a complete picture of wood behavior following γ-ray irradiation, at both the macroscopic and the molecular level.
... Wet cleaning is a fundamental operation in paper artworks restoration because it allows the removal of grime, dirt and water-soluble substances arising from cellulose degradation. Wet cleaning also allows for the partial dissolution of aged glues and pastes, even if, for a complete and selective removal, specific hydrolytic enzymes are preferred [1][2][3]. ...
... The traditional cleaning procedure implies the immersion of paper artworks in water [3,4], which eventually induces the removal of sizing agents, i.e., gelatine, the spreading of inks and it also leads to the swelling of cellulose fibers, which may cause the deformation of paper after drying, leading to a significant decrease in the mechanical resistance of the cellulosic network [2,[5][6][7][8]. The usage of hydrogels could overcome the drawbacks induced by this traditional cleaning practice. ...
... Recently, physical gels based on natural polysaccharides, such as Gellan gel (Gg), have been proposed for the cleaning of paper artworks. From a rheological point of view, these hydrogels are rigid systems that can be applied and removed from paper in one step, as one body, without leaving residues on the treated surfaces [2,9,15,16]. These materials are also biocompatible (in fact they are widely used in food and medicine), and they are thus safe for operators. ...
Article
Hypothesis: Due to their highly retentive properties, innovative recently developed, semi-interpenetrated hydrogels made up of poly(vinyl pyrrolidone) (PVP) chains embedded in a poly(2-hydroxyethyl methacrylate) (p(HEMA)) network should be efficiently used as cleaning material for fragile and degraded paper artworks. In restoration practice, indeed the wet cleaning of these artworks is usually performed by immersion of paper in water, a procedure which may lead to several drawbacks, including paper fibers swelling and dissolution of water-soluble original components. Experiments: This class of gels were yet presented in literature, but their interactions with paper materials and ability to be spiked with active enzymes (as cleaning agents), have not been analyzed. To establish the suitability of these hydrogels as paper cleaning materials, first, a rheological and microstructural characterization of the gels was performed. Moreover, diffusion of macromolecules inside gels was studied using fluorescence microscopy, to check if these innovative hydrogels can be used as carriers for hydrolytic enzymes. Indeed, pastes and glues are usually found in old paper artworks, and their removal is a very delicate operation that requires a selective action, which is granted by specific hydrolytic enzymes. At the same time, spectroscopic analyses on paper samples under investigation before and after cleaning treatment has been performed, thus assessing the capabilty of these gels as cleaning materials. Findings: With the aim of demonstrating the versatility of these hydrogels, several case studies, i.e., the removal of grime and water-soluble cellulose degradation byproducts, the removal of animal glue and the removal of starch paste from real samples, are presented. Results obtained with these gels have been compared to those obtained by using another gel used for paper artworks cleaning, i.e., Gellan gel.
... Wet cleaning of ancient papers is one of the most delicate and important steps in a conservation process. Due to inherent fragility of ancient paper artworks, the cleaning of these artifacts is a very difficult task because it can cause several damages, such as loss of mechanical properties, inks or pigments fading and fibers hydroxide nanoparticle, able to raise the pH of acid papers, or gelbased material [4][5][6][7][8][9]. ...
... The application of rigid, retentive hydrogels reduces water uptake of the paper, more respectful of the original integrity of the artwork. In this context, a valid alternative to traditional paper washing by immersion is represented by Gellan gel, as pointed out in a previous work [5]. Moreover, Gellan gel could be easily loaded with hydrolytic enzymes in order to facilitate the removal of unwanted and/or dangerous materials from paper artwork like old and deteriorated adhesives that, after the enzymatic reactions, could be easily removed from the paper and absorbed by the gel. ...
Article
Disposable non-invasive and compatible real time monitoring tool was developed in order to follow the cleaning process of paper artwork directly in situ. This tool was based on a biocompatible cleaning hydrogel coupled with flow electrochemical diagnostic tool, suitable to verify in situ and in a simple way the assessment of degradation of artwork and the efficiency of cleaning process. In this paper, the results obtained by applying this tool on a great format artwork with a lining as support, “Le Nozze di Psiche”, engraved by Diana Scultori, printed in 1613, are reported. This opera was affected by a structural and chromatic deterioration due to a strong oxidative degradation. Such deterioration was probably accelerated by the adhesive (a mixture of starch paste and animal glue) used in a previous lining intervention. In this case, the cleaning agents used are rigid hydrogels of Gellan gum, modified with hydrolytic enzymes. By using the flow sampling system, all materials removed by the gel was carried up to a thin layer cell containing a selective electrochemical biosensors, suitable to monitor both treatments, the cleaning process and the removal of lining. These were monitored, allowing understanding when both processes were completed, thus avoiding lengthy and unnecessary cleaning applications. The effectiveness of cleaning with Gellan gel was assessed quantitatively by using non-invasive optical reflectance spectroscopy by a portable instrumentation, elaborating data with an improved version of the Kubelka-Munk theory in order to recover the absorption coefficient of the cellulose fibers of “Le Nozze di Psiche”. The concentration of oxidized groups acting as chromophores was obtained by comparing the experimental optical absorption spectra to those simulated computationally by using TDDFT-based calculations. By following the cleaning with Gellan gel the results indicate a large decrease of the concentration of degradation product of cellulose. Moreover, chromatographic analysis were carried out in order to evaluate the amount of acid compound, produced during the aging and present on the graphic artwork, using the Gellan gel after cleaning step. The results obtained from the restoration of “Le Nozze di Psiche” have allowed the restorers to evaluate innovative methods for cleaning treatment of paper artworks with a highly specialized scientific-diagnostic approach.
... One practical solution for cleaning paper artworks consists in the use of agar and gellan gum gels (Domingues et al., 2013;Mazzuca et al., 2014;De Filpo et al., 2015;Cremonesi, 2016); however, the details of their functioning are still not fully known. It is known that the gradual https://doi.org/10.1016/j.ibiod.2020.104996 ...
... The solution was then poured into 60 mm diameter polystyrene Petri dishes and cooled at room temperature (RT), to form transparent membranes (Leones et al., 2012). Gellan gum hydrogels were prepared according to the protocols reported by Iannucelli et al. and Mazzuca et al., which are procedures commonly used by conservators (Iannuccelli and Sotgiu, 2010;Mazzuca et al., 2014). To prepare the hydrogel, 20 g L −1 gellan gum (Kelcogel GC-LA, CP Kelco Inc.) and 0.4 g L −1 calcium acetate (Sigma-Aldrich) were dispersed in Milli-Q water and heated under magnetic stirring up to 100°C, until complete dissolution. ...
Article
Full-text available
Fungal stains affect documents and artworks on paper all over the world, diminishing their chemical stability and compromising their readability. The present paper studies the suitability of agarose and gellan gum hydrogels to remove fungal stains from paper, using paper impregnated with alizarin as a model system to simulate the most common colorant molecules produced by fungi - polyketide quinones. The effect of pH variation on the efficacy of the gels was evaluated by UV spectrometry. The results show that the cleaning efficacy of the gels greatly depends on the gel matrix, the colorant molecules, and the pH balance of the process.
... Consequently, in the design of a restoration intervention of paper artifacts, thorough diagnostic analyses must be planned to determine their composition and to assess their degradation state [18][19][20][21][22][23][24][25][26][27][28][29]. A brief review of the paper restoration methods can be found in the Supplementary material. ...
... This technique hasve a great ability to identify functional groups and provide information on the substances found within the paper and on their degradation state. Laboratory equipment and ad-hoc accessories, such as the attenuated total reflectance (ATR), used to avoid destructive sampling or invasive approaches, provide useful information for paper materials [19,36]. However, since high performance FTIR spectrometers are not transportable in situ, it is necessary to move the artworks to the laboratory. ...
Article
We report a non-invasive and multi-analytical physico-chemical method for the characterization of paper artworks, able to identify sizing, inks, and glues and to quantify oxidative degradation by-products. The proposed methodology is mostly carried out in situ by using easy-to-use and cheap portable instrumentation for the acquisition of multispectral images, punctual ultraviolet-visible-near infrared fiber-optics reflectance spectroscopy (FORS) and punctual fiber optics fluorescence spectroscopy. Further analytical information is provided by non-invasive in-situ sampling of paper surface by using soft latex sponges, making possible laboratory chromatographic and infrared spectroscopic analyses on the aqueous sponge extracts. The proposed diagnostics method was applied to two 17th century letters written by St Francis of Sales (1567–1622), collected at the Chigi Palace in the town of Ariccia (Italy). Results show an intense oxidative degradation of the letters, also localized in water spots, and the presence of carboxylic acids by-products. Analysis of FORS spectra provided the concentration of chromophores in the paper substrate. The diagnostic method allowed the identification of gelatin sizing, the presence of starch glue in specific areas of the letters and the type of ink used in the text. Our diagnostic approach aims to offer to conservator-restorer a characterization of a paper artwork, that can be applied to other, for a correct planning of conservation interventions.
... The long used technique of surface cleaning by aqueous treatment and immersion also proved to be harmful for the albumen layer, increasing the cracking [6]. Besides, the prolonged contact with water may induce the swelling and deformation of cellulose fibers of the substrate [7]. Currently, preservation of the archival albumen photographs is maintained by storage in chemically inert enclosures with constant temperature and humidity control and occasional remote moistening [8]. ...
... For the last decade, researchers and conservators have been successfully using rigid hydrogels on the basis of polysaccharides for the cleaning of paper artworks surface [7]. Gellan gum produced by Sphingomonas elodea (ATCC 31461, previously referred to as Pseudomonas elodea [9]) consists of repeating tetrasaccharide units of glucose, glucuronic acid and rhamnose residues in a 2:1:1 ratio [10]. ...
Article
In the conservation practice of albumen photographs, wet cleaning techniques were long used to remove pollutions, gluing components, cellulose degradation products, and to reduce highlight yellowing. However, water immersion, as well as surface cleaning, enhances the cracking of the albumen layer surface. These cleaning methods are suitable for paper artworks. Whereas the conventional water treatment may cause irreversible damage of the paper structure, the use of rigid hydrogel of Gellan gum had been proposed as an alternative technique that is less destructive to the paper structure. Two wet treatments, water and Gellan gum hydrogel, were applied to the samples of original 19th century albumen photoprints. Their effect was assessed using instrumental methods, such as Fourier transform infrared spectroscopy, laser confocal microscopy, scanning electron microscopy, atomic force microscopy, and pH measurements. The effect of wet treatments on the albumen photograph surface cracking was quantified. Despite that Gellan hydrogel is very gentle and efficient tool for the restoration of paper artworks, it is as harmful for the albumen photographs surface as the conventional water surface cleaning, and therefore may be applied on the verso of the photographs solely.
... The interesting aspect and true novelty of the restoration of paper performed by the application of a protecting coating with CNCs is the reversibility of the treatment, a capability that we are able to demonstrate. To ensure this reversibility, we used a cleaning method, based on the application of a Gellan hydrogel on the paper surface; 3,4,33,34,37,38,40 the other surface of the gel is coupled with a flow sampling plate, in line with an electrochemical system designed ad hoc for sensing the amount of cellulose eventually removed from the paper surface. 3,34,37,38 Gellan hydrogel is a Gellan gum-based hydrogel, widely used for the cleaning of paper artworks. ...
... 3,34,37,38 Gellan hydrogel is a Gellan gum-based hydrogel, widely used for the cleaning of paper artworks. 3,4,33,34,37,38,40 During the cleaning process, it can be applied on paper as a rigid one body and allowed to act as a water reservoir, releasing small amounts of water in a controlled way. Water acts as a cleaning agent, removing patinas, dust, as well as byproducts of cellulose hydrolysis and oxidation from paper. ...
Article
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An innovative consolidation strategy for degraded paper is presented based on the reversible application of cellulose nanocrystals as sustainable fillers to reinforce mechanical properties and resistance to further degradation. The compatibility and efficacy of the proposed consolidation treatment are assessed first on pure cellulose paper, used as a model, by reliable techniques such as field emission scanning electron microscopy, atomic force microscopy, tensile tests, X-ray powder diffraction, and Fourier transform infrared spectroscopy, evidencing the influence of the surface functionalization of nanocellulose on the consolidation and protection effects. Then, the consolidation technique is applied to real aged paper samples from Breviarium romanum ad usum Fratrum Minorum S.P. (1738), demonstrating the promising potential of the suggested approach. Amperometric measurements, carried out with a smart electrochemical tool developed in our laboratory, demonstrate the reversibility of the proposed treatment by removal of the nanocrystalline cellulose from the paper surface with a suitable cleaning hydrogel. This completely new feature of the consolidation treatment proposed here satisfies a pivotal requisite in cultural heritage conservation because the methodological requirement for the ″reversibility″ of any conservation measure is a fundamental goal for restorers. A paper artifact, in fact, is subject to a number of natural and man-made hazards, inducing continuous degradation. With time, monitoring and consolidation actions need to be often performed to ensure conservation, and this tends to modify the status quo and compromise the artifact integrity. Removable treatments can potentially avoid erosion of the artifact integrity.
... PAAb and PAAn treatments by brushing and agar rigid gel were selected for the samples with iron-gall ink spots and performed in the pH condition of irongall ink stability in order to guarantee a more controlled treatment. In this regard, the use of rigid gels, like gellan gum and agar for preservation treatments of cultural artefacts, has been recently exploited taking advantage of their ability in spreading active species (Wolbers 2000(Wolbers , 2004Campani et al. 2007;Anzani et al. 2008;Iannuccelli and Sotgiu 2010;Cremonesi 2012;Isca 2014;Mazzuca et al. 2013Mazzuca et al. , 2014aSullivan et al. 2014). ...
Article
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A new approach to the conservation of paper manuscripts is proposed that leads to both deacidification and strengthening of paper. The study was carried out by using polyamidoamines (PAAOHs) functionalized with alcoholic groups, in their native form (PAAb) or neutralized with boric acid (PAAn). They were applied on model paper samples containing iron-gall ink spots through agar rigid gel or by brushing. Preliminary evaluation of the effects of polymer concentration, methods, and duration of application have been tested on model ink-free paper samples. The improvements induced by PAAOHs on paper samples was revealed by surface pH (evaluated in ink-free areas, inside ink spots and on the edges between them) and by measurements of alkaline reserve according to TAPPI T 553 pm-92. The results showed the different behaviour of ink-free and inked regions due to high acidity of iron gall ink. In fact, although a treatment with solutions having low concentration (i.e. 0.1 and 0.15 M) is sufficient for preserving ink-free paper samples from ageing, higher concentration of polymer (0.3 M) or extra brushing application are needed in order to get a complete deacidification of the ink spots. As a side-effect of deacidification treatments, PAAOHs promoted a significant reduction of thermo-hygrometric ageing effects and water smearing at the edge of iron-gall ink spots, as suggested by Raman spectroscopy and mechanical analyses. Graphical abstract Open image in new window
... As a comparison, we also conducted conformal contact experiments using agarose and gellan hydrogels, which are materials commonly used in the conservation of art. 10,11,51 When we compare Figure 4 with Figure S11, we find that both the agarose (G = 41 kPa) and gellan (G = 48 kPa) hydrogels made more efficient contact (Figures S9−S11), ranging from 86% to 100% for all three rough substrates, compared with elastomers of similar modulus. We ascribe this increase in conformal contact to several subtle but distinct chemical and physical differences between the elastomers and the hydrogels. ...
Article
Efficient removal of particulates from a rough surface with a soft material through a ‘press and peel’ method (i.e., an adhesion and release approach) depends on good conformal contact at the interface; a material should be sufficiently soft to maximize contact with a particle while also conforming to rough surface features to clean the entire substrate surface. Here, we investigate the use of bottlebrush networks—extremely soft elastomers composed of macromolecules with polymeric side chains—as materials for cleaning model substrates of varying roughness. Formed through free-radical polymerization of mono- and di-methacrylate functionalized polysiloxanes, these solvent-free supersoft elastomers exhibit moduli comparable to solvated gels, allowing for a lower moduli regime of elastomers to be used in contact experiments than previously possible. By varying the macromonomer to crosslinker ratio, we study the effect of modulus on conformal contact and cleaning for materials that are as soft as gels while minimizing/negating physical and/or chemical concerns that using a traditional material may involve (e.g., changes in component concentrations, solvent evaporation, syneresis). We study cleaning efficacy by quantifying the conformal contact between soft materials and rough substrates via a contact adhesion-based measurement. These results give insight into the correlation between material modulus and conformal contact with surfaces of varying feature height. Not only does a decrease in material modulus lead to improved conformal contact with rough surfaces, but it also facilitates adhesion to particulates situated on the rough surface thus aiding removal. We highlight this property control with a case study illustrating the removal of an artificial soil mixture from a rough, acrylic surface via peeling rather than rubbing, which can cause damage to delicate surfaces.
... Enzymes have also been used in combination with gellan gum, which can bind the enzyme and absorb water-soluble elements through capillary action, thereby supporting enzyme activity (Fiacconi et al. 2012;Mazzuca et al. 2014). It is worth noting that results from the use of many mechanical, chemical and biological conservation measures and restoration treatments described in the literature are often contradictory, have undergone testing in oversimplified conditions or verified on too few types of materials to be considered safe and/or effective (Ďurovič and Zelinger 1993;Boudalis et al. 1996;Zou et al. 1996). ...
... It was also helpful in removing acidity from the paper as HPLC measurements showed the pH of paper increased after the treatment. This indicated that the cleaning with rigid gel was effective and did not induce any morphological changes to the paper [21]. ...
Article
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This paper is based on the explorative study aimed at furthering the understanding of cleaning of acrylic emulsion painted surfaces and evaluating the effectiveness of gel cleaning with rigid gels without affecting the original paint layer. In the present study, the gellan and agar gelling materials were exploited for cleaning acrylic emulsion painted surfaces by optimizing their rheological properties using two application methodologies. The gellan and agar gels were used on soiled and unsoiled acrylic painted surfaces and micro-photographed at 50x magnification using Dinolite digital microscope under normal, raking and ultraviolet fluorescence light. The experimental results have demonstrated better contact, no loss of water and fair cleaning results for gellan gel as compared to agar. The effectiveness of the cleaning operation was also observed using ATR-FTIR and SEM-EDX in the present study. The results can be extended for cleaning of other sensitive painted surfaces.
... Other properties and uses for gellan gum include film formation with mechanical and water vapor barrier properties (Yang, Paulson, and Nickerson 2010;Yang and Paulson 2000), e.g. application in paper cups for hot drinks and the combined use with purple sweet potato for pH monitoring (Wei et al. 2017); vehicle for ophthalmic drugs and drug release (D'Arrigo et al. 2014;Mahdi, Conway, and Smith 2014;Osmałek, Froelich, and Tasarek 2014;Prezotti, Ferreira Cury, and Evangelista 2014); gelling agent in dental and personal care (Banik, Kanari, and Upadhyay 2000); wound healing and tissue engineering (Becker 2015;Bonifacio et al. 2017;Douglas et al. 2016;Hadjizadeh and Doillon 2010); inhibition of acid corrosion of iron cast (Rajeswari et al. 2013); and the use of gellan hydrogel for paper cleaning (Mazzuca et al. 2014). ...
Article
Microbial exopolysaccharides (EPS) are an abundant and important group of compounds that can be secreted by bacteria, fungi and algae. The biotechnological production of these substances represents a faster alternative when compared to chemical and plant-derived production with the possibility of using industrial wastes as substrates, a feasible strategy after a comprehensive study of factors that may affect the synthesis by the chosen microorganism and desirable final product. Another possible difficulty could be the extraction and purification methods, a crucial part of the production of microbial polysaccharides, since different methods should be adopted. In this sense, this review aims to present the biotechnological production of microbial exopolysaccharides, exploring the production steps, optimization processes and current applications of these relevant bioproducts.
... It was also helpful in removing acidity from the paper as HPLC measurements showed the pH of paper increased after the treatment. This indicated that the cleaning with rigid gel was effective and did not induce any morphological changes to the paper [21]. ...
Article
This paper is based on the explorative study aimed at furthering the understanding of cleaning of acrylic emulsion painted surfaces and evaluating the effectiveness of gel cleaning with rigid gels without affecting the original paint layer. In the present study, the gellan and agar gelling materials were exploited for cleaning acrylic emulsion painted surfaces by optimizing their rheological properties using two application methodologies. The gellan and agar gels were used on soiled and unsoiled acrylic painted surfaces and micro-photographed at 50x magnification using Dinolite digital microscope under normal, raking and ultraviolet fluorescence light. The experimental results have demonstrated better contact, no loss of water and fair cleaning results for gellan gel as compared to agar. The effectiveness of the cleaning operation was also observed using ATR-FTIR and SEM-EDX in the present study. The results can be extended for cleaning of other sensitive painted surfaces.
... It was also helpful in removing acidity from the paper as HPLC measurements showed the pH of paper increased after the treatment. This indicated that the cleaning with rigid gel was effective and did not induce any morphological changes to the paper [21]. ...
Article
Full-text available
This paper is based on the explorative study aimed at furthering the understanding of cleaning of acrylic emulsion painted surfaces and evaluating the effectiveness of gel cleaning with rigid gels without affecting the original paint layer. In the present study, the gellan and agar gelling materials were exploited for cleaning acrylic emulsion painted surfaces by optimizing their rheological properties using two application methodologies. The gellan and agar gels were used on soiled and unsoiled acrylic painted surfaces and micro-photographed at 50x magnification using Dinolite digital microscope under normal, raking and ultraviolet fluorescence light. The experimental results have demonstrated better contact, no loss of water and fair cleaning results for gellan gel as compared to agar. The effectiveness of the cleaning operation was also observed using ATR-FTIR and SEM-EDX in the present study. The results can be extended for cleaning of other sensitive painted surfaces.
... Kelco U.S., Inc. is widely applied, which is therefore also selected for this study. Similar to the application of agarose gel, the concentration of gellan gel varies from around 2 wt% (Iannuccelli & Sotgiu, 2010;Botti et al., 2011;Mazzuca et al., 2014) to around 5 wt% (Hughes & Sullivan, 2016;Sullivan et al., 2017), while the thickness of prepared gel from 2mm to 1cm. ...
Thesis
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Old mending in bound manuscripts and rare books can cause distortions on pages or new tears right beside the mends due to their stiffness and inflexibility. Additionally, they may also interfere with the readability of the pages as sometimes they cover text and illustrations. Detaching old mending papers glued with protein-based adhesives often requires a combination of moisture and heat. Nevertheless, not only has a uniform and accurate heat application always been difficult to achieve with the common heating tools, but the accessibility to the working area is also restricted when the mends are glued close to the spine fold of a bound volume. This study aims to introduce a new heat transfer method to the removal of old mends glued with protein-based adhesives through an innovative heating device – the IMAT heater (Intelligent Mobile Accurate Thermo-Electrical Device). This device is a flexible and ultrathin heat transfer mat based on carbon nanotubes (CNTs), which was developed by the EUfunded IMAT Research Project. The IMAT heater features a rapid thermal response, a precisely controllable and stable heat regulation as well as a uniform heat distribution during a conservation treatment. Owing to its optional size, air permeability and transparency, different needs of specific applications can be met. Furthermore, due to the slight thickness and the flexibility of the mat, it is considered to be ideal when dealing with old mends glued close to the spine fold of manuscripts and rare books. Experiments with applications and evaluation of coupling the IMAT heater with various hydrogels and Gore-Tex sandwiches are performed. After the investigation, a considerable temperature-related optimization on conservation treatment utilizing the IMAT heater is verified. An optimal working pattern of combining heat transfer with moisture introduction using the IMAT heater is suggested for the future conservation work. Besides, performance of each treatment variation correlated with different humidification sandwiches and treating temperatures is characterized. Finally, conservation treatments on three historical documents from the collections of the Bavarian State Library are successfully conducted: a medieval manuscript (BSB, Clm 18199), an incunable from the early years of printing (BSB, 2 Inc.ca 1726 a) and a printed book from the 18th century (BSB, Diss. 849 d, 16).
... Among of issues involved in the protection of paper-based artifacts, cleaning is of great significance because various contaminants can damage paper-based artifacts. For example, stains can severely damage artifacts not only in value but also in corrosion; mold growth not only deteriorates the structure of the paper itself but also permanently detracts from the visual appearance of an artifact 1,2 . Therefore, cleaning of paper-based artifacts is necessary to decrease the further damage of contamination and improve the aesthetics of works. ...
Article
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Constructing methods for cleaning stains on paper artworks that meet the requirements of preservation of cultural relics are still challenging. In response to this problem, a novel electrochemical cleaning method and the preparation of corresponding electrodes were proposed. For this purpose, the conductive graphene (rGO)/polyacryamide (PAM)/montmorillonite (MMT) composite hydrogel as cathode and PbO2-based material as anode were prepared and characterized. The electrochemical cleaning efficiencies of real sample and mimicking paper artifacts were evaluated, and the effects of the electrochemical cleaning on paper itself were detected. Based on the above experiments, the following results were obtained. The composite hydrogel with attractive mechanical properties is mainly based on the hydrogen bond interactions between PAM chains and MMT. The results of cleaning efficiency revealed that the black mildew stains together with the yellowish foxing stains were almost completely eliminated within 6 min at 8 mA/cm², and various stains formed by tideline, foxing, organic dyes and drinks could be thoroughly removed at 4 mA/cm² within 5 min. In addition, the proposed cleaning method has advantages in local selectivity, easy control of cleaning course, and reusability, which represents a potential utility of this approach.
... Typical gels used in cultural heritage are both natural compounds, like cellulose ether derivatives, and synthetic products, like the so-called "Wolbers' solvent gels" [57,59] or polyacrylic acid. Adjacent to these well know gels, new natural polymeric compounds, such as Gellan and Agar, are also commonly used, in particular for water-sensitive surfaces [59][60][61]. ...
Article
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In recent years, the use and the necessity of green materials and methodologies have been promoted in the field of cultural heritage, aiming to a low impact on the operator health and the environment. For a long time, in restoration and conservation science, the main goal was searching for the most compatible solutions with the materials of the artefacts not thinking sometimes about the possible issues for the operator and/or for the environment. Recently, thanks also to an increasing attention to a respectful consumption of environmental resources and waste management, new scientific methodologies have been proposed for more sustainable and green interventions, promoting furthermore the concept of preventive conservation. The aim of this work is to present an overview about some of the most interesting technologies and methodologies already available as alternative to traditional and more invasive/dangerous restoration treatments towards artefact, operators and environment. In particular, the methods described in this paper have been critically analysed focusing on which might be the positive and negative points considering the convenience of use by the restorers and the reasons why these methods are still not well known and diffused.
... 11 One of the most delicate phases of interventive conservation is the cleaning process, which must exhibit selectivity in the treatment of unwanted layers, without compromising the original historic and artistic substrate. Current research focuses on the development of innovative cleaning materials, including microemulsions, solvents, and rigid gels, 12,13 and biological cleaning methods, such as microorganisms and hydrolytic enzymes. 14−19 Enzymes exhibit exquisite molecular recognition, 15,19,20 and have been used to remove starch paste, 18,21−23 protein-based glues and adhesives, 18,24 lipid-based compounds, 25 and aged acrylic coatings and inks 26 from historic textiles, paper, and prints, wall-paintings, and ceramic materials. ...
Article
Enzyme-based treatments are used in heritage conservation for the effective removal of glues and other damaging organic layers from the surfaces of historic and artistic works. Despite their potential, however, the application of enzymatic treatments is currently limited because of their poor efficiency and low operational and environmental stability. We demonstrate the use of α-amylase immobilized on gold nanoparticles to improve the efficacy of enzymatic treatments enhancing both the reactivity and the stability of the formulations. Gold nanoparticles coated with α-amylase exhibit significant advantages compared to free enzymes. We report up to 5× greater resistance to environmental changes, up to 2× higher efficacy toward removal of starch-based glues from textiles and deeper penetration through the fibers, without causing damage or inducing salt precipitation. These results offer exciting prospects for the development of enzymatic formulations, both for heritage conservation and the wider application of enzymes, such as in medicine, the detergent industry, and green chemistry.
... A new class of GG with improved mechanical properties are prepared using methacrylation procedures [52]. GG is an US food and drug administration (FDA) & European union (EU) [53] approved biomaterial [45,54]. The mechanical properties of GG can be improved by modifying the type and the degree of crosslinks [52]. ...
Article
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Over the past few decades, gellan gum (GG) has attracted substantial research interest in several fields including biomedical and clinical applications. The GG has highly versatile properties like easy bio-fabrication, tunable mechanical, cell adhesion, biocompatibility, biodegradability, drug delivery, and is easy to functionalize. These properties have put forth GG as a promising material in tissue engineering and regenerative medicine fields. Nevertheless, GG alone has poor mechanical strength, stability, and a high gelling temperature in physiological conditions. However, GG physiochemical properties can be enhanced by blending them with other polymers like chitosan, agar, sodium alginate, starch, cellulose, pullulan, polyvinyl chloride, xanthan gum, and other nanomaterials, like gold, silver, or composites. In this review article, we discuss the comprehensive overview and different strategies for the preparation of GG based biomaterial, hydrogels, and scaffolds for drug delivery, wound healing, antimicrobial activity, and cell adhesion. In addition, we have given special attention to tissue engineering applications of GG, which can be combined with another natural, synthetic polymers and nanoparticles, and other composites materials. Overall, this review article clearly presents a summary of the recent advances in research studies on GG for different biomedical applications.
... Biodegradable polymeric films represent an alternative option in food packaging because they may be obtained at low costs from renewable sources with no contribution to the environmental pollution. For these reasons, biodegradable polymers, which already encounter extensive use in several fields (Mazzuca et al., 2014), have been attracting much interest as alternatives to non-degradable polymers currently used in food packaging. Among them the most commonly used are polysaccharides such as cellulose, pullulan, agarose, starch and chitosan (Valencia-Chamorro et al., 2011;Dhall, 2013;Elsabee and Abdou, 2013). ...
Article
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The growing demand for increased fresh food shelf life as well as the need of protection against foodborne diseases urged the development of antimicrobial food packaging. Among the most efficient methods, the combination of organic–inorganic, packaging, i.e. polymer embedded metal nanoparticles proved to be highly effective. Silver nanoparticles (AgNPs), in particular, have antimicrobial, anti-fungi, anti-yeasts and anti-viral activities and can be combined with both non-degradable and edible polymers for active food packaging. The actual application of AgNPs in food packaging is regulated by EU and USA food safety authorities in a prudent way, due to the inability to make conclusive statements on their toxicity. Therefore, their use is evaluated in terms of Ag+ migration into the packed food. In this mini review, the most recent studies are reported on protection of meat, fruit and dairy products against the most common food pathogens by AgNPs-doped non-degradable and edible polymers and oils are reported.
... The oxidation of hydroxyl groups in a cellulose chain in an ambient atmosphere leads to the formation of both C=C double bonds in glucose ring and of C=O bonds (carbonyl groups), which can be further oxidized to carboxylic groups, depending on the position of the C=O bonds in cellulose chain [5,8,12]. The ratio O I = A 1640-1850 /A 1580 between the area of carbonyl bands in the range 1640-1850 cm −1 (A 1640-1850 ), representing the final oxidation stage of cellulose, and that of the band at 1580 cm −1 (A 1580 ), corresponding to the presence of intermediate species, gives information on how advanced the oxidation process is [5,10]. In contrast, the ratio O T = A 1500-2800 /A 700-3000 between the area of Raman bands of oxidized functional groups in the range 1500-2800 cm −1 (A 1500-2800 ) and the area of whole spectrum (A 700-3000 ) measures the amount of oxidation products linked to the cellulose backbone. ...
Article
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Micro-Raman and luminescence spectroscopy were combined with morphological analysis to study the conservation state of differently degraded paper samples, dated from 1873 to 2021. The aim of the work reported in this paper was to obtain ageing markers based on variations of Raman and fluorescence spectral features. Raman and luminescence spectra were acquired by scanning non-printed areas of books, and Raman and fluorescence maps were built by contrasting spectral parameters point by point, obtaining a micron-scale space resolved imaging of the degradation pattern. Complementary information on paper morphology and surface compactness were obtained by high-resolution scanning electron and atomic force microscopy. The proposed non-destructive procedure is particularly interesting for precious and ancient samples to analyze their degradation processes and to evaluate the performance and effectiveness of restoration treatments.
... It must be noticed that systems with excessively high storage moduli are not able to adapt to surface irregularities typical of painted artifacts (i.e., ≥1 mm) (20). This is further visualized in SI Appendix, Fig. S8, where FT1 PVA gels are compared to a pHEMA/PVP SIPN we previously formulated for the cleaning of artifacts (19,21) and to a gellan sheet similar to those traditionally employed in the restoration practice (47). The pHEMA/PVP gels have G′ values of 4 to 5 × 10 3 Pa (17), roughly half the modulus of a typical gellan sheet (48). ...
Article
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Significance From the earliest cave paintings of mankind, to Renaissance frescos and modern art masterpieces, the preservation of surfaces against soiling and degradation is fundamental to transfer such a vast heritage to future generations. However, traditional cleaning methods are often invasive and risky. We overcame these limitations by designing a cleaning system in the framework of colloid and materials science. We formulated twin-chain hydrogels with ideal mechanical properties, retentiveness, and interconnected porosity, allowing adhesion to rough and textured paint layers, and controlled wetting of surfaces, granting safe removal of soil. The gels were used to clean two Jackson Pollock masterpieces, recovering their visual aspect, marking a turning point in the field of conservation of important collections worldwide.
... For what concerns synthetic polymers, acrylamide hydrogels were successfully applied for the cleaning of easel paintings [14]. Their meso/nanoporosity was measured via small-angle X-ray scattering (SAXS), while the retention properties, which are very advantageous when treating water-sensitive substrates, were determined by differential scanning calorimetry (DSC) work surfaces [8,[23][24][25][26][27][28][29]. Actually, the removal of stains due to brochantite, Cu 4 (SO 4 )(OH) 6 , is an important issue in conservation of marble surfaces closely connected to bronze elements. ...
Article
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The effectiveness of Agar gels for copper stain removal from marble surfaces was systematically studied. Gels with different agar concentrations (1, 3, 5%) and different chelating agents used as additives (ethylenediaminetetraacetic acid, EDTA, and ammonium citrate tribasic, TAC) were tested on laboratory marble specimens for different contact times (30 and 60 min). For better characterization, hydrogels were lyophilised and cryogels were obtained. Systematic comparison of different formulations was feasible on cryogels and performed in terms of: (i) the morphological properties, by field-emission scanning electron microscopy (FE-SEM); (ii) the type of Cu(II)-complexes formed and their quantitative comparison by electron paramagnetic resonance (EPR) spectroscopy; (iii) the total amount of copper removed from marble surfaces, by Inductively Coupled Plasma–Optical Emission Spectrometry (ICP-OES). AgarArt 1% with TAC exhibited the highest effectiveness for copper stain removal after 60 min contact (431 μg/cm2). Such a good cleaning effectiveness can be ascribed to the co-presence of the following properties: efficient metal coordination, which is related to the additive presence, and favourable gel morphology, related both to the gel concentration and to the additive type. In fact, it was observed that both the low gel concentration and the presence of TAC are related to a narrow pore size distribution in gels, besides the possibility of copper coordination. The presence of EDTA results in a broader pore size distribution and in a lower gel strength, with respect to gels with TAC. Thus, a new procedure for studying gels was proposed, which allows to optimize the conditions for metal stain removal from built heritage.
... They demonstrated the practical advantages of gel to control electrochemical parameters on a real object. The use of gels in treatments is widespread for paintings, paper and graphic arts [20][21][22][23][24], but much less frequent for metal cultural heritage artefacts. An initial study has shown the interest of gels in the chemical cleaning of metal objects [25]. ...
Article
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Gels were used to perform localized dechlorination treatments on ferrous or copper alloy archaeological objects. Agar gel (3%w) was used as a medium for the electrolyte, a 1%w KNO3 solution. Localized electrolysis with gel was carried out using the same parameters as immersion electrolysis. To determine the end of treatment, two tools were validated: determining the quantity of chlorides present in the gels by XRF and monitoring the oxygen consumption of an object before and after treatment. This study shows that the technique results in the efficient extraction of chlorides. In the case of the stabilization of composite objects or for the localized treatment of copper objects, the use of a localized electrolytic gel treatment is a new effective solution proposed to conservators.
... Considering the promising evidences, this technique became rapidly captivating in several fields, including wall paintings and stone care [47][48][49]. Moreover, the employment of gels turned to be essential when dealing with paper or wood substrates, for which the conventional procedure by immersion into water solution was not ideal [50,51]. ...
Article
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In the general global rise of attention and research to seek greener attitudes, the field of cultural heritage (CH) makes no exception. In the last decades, an increasing number of sustainable and biologically based solutions have been proposed for the protection and care of artworks. Additionally, the safety of the target artwork and the operator must be kept as core goals. Within this scenario, new products and treatments should be explored and implemented in the common conservation praxes. Therefore, this review addressing metal heritage is aimed to report biologically derived gel formulations already proposed for this specific area as reliable tools for cleaning. Promising bio-gel-based protocols, still to be implemented in metal conservation, are also presented to promote their investigation by stakeholders in metal conservation. After an opening overview on the common practices for cleaning metallic surfaces in CH, the focus will be moved onto the potentialities of gel-alternatives and in particular of ones with a biological origin. In more detail, we displayed water-gels (i.e., hydrogels) and solvent-gels (i.e., organogels) together with particular attention to bio-solvents. The discussion is closed in light of the state-of-the-art and future perspectives.
... Biodegradable films made from polymeric materials have been utilized as an alternative for conventionally used materials for food packaging purposes. These polymeric materials are obtained from the renewable sources at an economical cost, and these do not contribute to environmental pollution owing to their biodegradable nature (Mazzuca et al., 2014). Because of their eco-friendly nature, the biodegradable polymers have been employed extensively in various fields and garnered the attention of researchers as a viable option for utilization in food packaging materials (Carbone et al., 2016). ...
... The use of gels is fully integrated into the practices of painting conservators, and there are many existing and ongoing studies on this practice [3][4][5][6][7][8][9] . The successful results of gel treatments have led to them being extended to other fields of cultural heritage conservation: polychromy [10] , paper and graphic arts [11][12][13] , textiles [ 14 , 15 ], and stone [ 16 , 17 ]. The examples are many and various, but in the field of metal conservation they are so scarce as to be practically inexistent. ...
Article
Full-text available
Currently gels or dispersions are widely used in the restoration of paintings, graphic arts, stuccoworks and stones, but their use in metal restoration is less widespread. In this study, several gels and dispersions were selected for use in metal treatments. These gels and dispersions have been tested as a support for the treatment solutions usually used for chemical treatments of metals. First, the compatibility of these physical and chemical gels or dispersions with selected treatment solutions was checked. Viscous physical gels (Xanthan gum), collagen-based physical gels (nerve glue), chemical gels (Nanorestore gels®) or dispersions (polyacrylic acid, cellulose-based compound) displayed good compatibility with acid, neutral or basic solutions. Physical peelable gels (Agar or gellan gum) displayed more limited compatibility but were more easily applied on metallic objects. Test treatments were carried out on archaeological objects: silver-plated copper alloy coins. The best post-treatment results in terms of efficiency and the overall aesthetic appearance of the object were obtained with physical peelable gels (Agar or gellan gum) containing a treatment solution (2–5%w of disodium EDTA), applied hot.
Article
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Purpose The main aim of this study is to study the effect of alkyl dimethyl benzyl ammonium chloride on removing stains, yellowness and harmful metal ions on historical printed paper, as well as the effect of this cleaner on optical and chemical properties of treated paper. Design/methodology/approach The assessments after and before treatment were carried out using digital microscopy, infrared spectroscopy (FTIR), pH measurement, color change and finally scanning electron microscopy. Findings The results showed that the concentrations used under study (1% and 3%) cleaned the paper efficiently without any observed effect on the chemical composition of cellulose, which was confirmed by IR spectra. The most stains that completely disappeared were the soil spots, also the pH values had improved significantly after treatment, which confirms that the detergent is effective in neutralizing the acidity of cellulose. Moreover, the color change revealed an increase in the chromatic lightness of the paper after treatment, which agreed with the results of the scanning electron microscopy examination, as the paper appeared free of dirt, and the fibers and bundles became more cohesive. Originality/value To the best of the authors’ knowledge, this study is a unique study, as there is no previous literature that has indicated the use of the effect of alkyl dimethyl benzyl ammonium chloride washing treatments for printed historical paper, as it was limited only to making disinfection materials and water purification products.
Article
Fully biodegradable novel bio-based organogels were developed for removing aged protective films from the surfaces of paintings, aiming at providing effective cleaning tools, easily controllable by reducing the solvent permeation into underlying paint layers and not dangerous for human health and the environment. The gels were based on poly-3-hydroxybutyrate (PHB) as gelling agent, γ-valerolactone (GVL) as solvent and triethyl citrate (TEC) as plasticizer. PHB-gels were able to completely remove protective varnishes on real oil paintings, without affecting the pictorial layer and leaving negligible residues after the application. Moreover, the gels showed good mechanical and handling properties, they were fully composed by non-toxic ingredients and resulted readily biodegradable in water, therefore easily disposable after the use.
Article
Texture modifying abilities of whey protein microparticles are expected to be dependent on pH during heat-induced aggregation of whey protein in the microparticulation process. Therefore, whey protein microparticles were prepared at either pH 5.5 or 6.8 and their effects on small and large deformation properties of gellan gels containing whey protein microparticles as fillers were investigated. The majority of whey protein microparticles had diameters around 2 μm. Atomic force microscopy images showed that whey protein microparticles prepared at pH 6.8 partially collapsed and flatted by air-drying, while those prepared at pH 5.5 did not. The Young's modulus of filled gels adjusted to pH 5.5 decreased by the addition of whey protein microparticles, while those of filled gels adjusted to pH 6.8 increased with increasing volume fraction of filler particles. These results suggest that filler particles were weakly bonded to gel matrices at pH 5.5 but strongly at pH 6.8. Whey protein microparticles prepared at pH 5.5 showed more enhanced increases in the Young's modulus than those prepared at pH 6.8 at volume fractions between 0.2 and 0.4, indicating that microparticles prepared at pH 5.5 were mechanically stronger. The fracture stress of filled gels showed trends somewhat similar to those of the Young's modulus, while their fracture strains decreased by the addition of whey protein microparticles in all examined conditions, indicating that the primary effect of these filler particles was to enhance the brittleness of filled gels.
Article
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Organo- and hydrogels have been proposed in the restoration field to treat different types of surfaces. The possibility to retain solvents and to have a controlled and superficial action allowed to use these materials for the removal of very thin layers applied on ancient historical objects, when the under paint layers are particularly delicate and water sensitive. In the last years, an increased attention has been devoted to the proposal of more healthy products to guarantee the safeguard of the operators. Few attention has been devoted to the development of green methods which foresee the use of renewable and biodegradable materials. The aim of this paper is to test a green organo-gel for the cleaning of water sensitive surfaces like varnished egg tempera paintings. The gel has been tested experimented on mock ups varnished with natural and synthetic materials and has been validated on a small portion of a Cimabue painting for the removal of two varnishes applied on two different test areas of the painting.
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Gellan gum (GG), a linear negatively charged exopolysaccharide,is biodegradable and non-toxic in nature. It produces hard and translucent gel in the presence of metallic ions which is stable at low pH. However, GG has poor mechanical strength, poor stability in physiological conditions, high gelling temperature and small temperature window.Therefore,it is blended with different polymers such as agar, chitosan, cellulose, sodium alginate, starch, pectin, polyanaline, pullulan, polyvinyl chloride, and xanthan gum. In this article, a comprehensive overview of combination of GG with natural and synthetic polymers/compounds and their applications in biomedical field involving drug delivery system, insulin delivery, wound healing and gene therapy, is presented. It also describes the utilization of GG based materials in food and petroleum industry. All the technical scientific issues have been addressed; highlighting the recent advancement.
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Effect of silver nanoparticles on MMA/HEMA behavior in enhancing and restoring the lost chemical bonds of paper was estimated in the current study through the study of mechanical strengths (tensile and elongation), infrared spectrum and environmental microscopic examination. The results of tensile strength and elongation rate showed the effectiveness of nanoparticles in supporting paper properties under the influence of accelerated aging via the bond at 1630 cm⁻¹ that is responsible for the bonds of silver ions and cellulose. Simultaneously, the micrographs showed that the type of fiber walls impacted the effectiveness of the copolymer where the completely pure cellulose cells absorbed the copolymer, while the presence of lignin reduced the absorption which helped create interface cross-links between fibers via the adsorbed copolymer on the surface.
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Due to the favorable retention power and viscosity, the hydrogel that is loaded with an aqueous detergent, represents a promising cleaning tool for removing the foreign matters such as polymer adhesive, starch paste, and animal glue from paper artworks. However, it is still challenging to eliminate other stains, including organic dyes, commercial drinks, foxing, and mildew. Herein, we present an alternative methodology, translucent hydrogel-containing electrolyte-based electrochemical cleaning (EC), which incorporates electrochemical reactions into the hydrogel-based cleaning process using the extremely tough and translucent alginate/polyacrylamide hydrogel as cathode and PbO2 as anode. The proposed approach is generally applicable to eliminate different stains such as organic dyes, commercial drinks, mildew, and foxing from paper under several mA/cm² and a few minutes in a small controlled area. For the excellent mechanical strength, the hydrogel electrode can be reused for several times without losing its efficiency and easily peeled-off from paper as one body without any gel residues after cleaning. We further demonstrate the effect of EC on the treated paper, including the morphology, degree of polymerization, crystal structure, and mechanical properties. We conclude that the influence of EC on the paper is slight under the mild treatment.
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The mechanism, the effectiveness, and the potential damage during limewash removal from wall painting models were evaluated for agar gels and water-based pads constituted by ArbocelTM BWW 40 cellulosic fibre. Cleaning materials in different formulations were compared: pure and with additives (ethylenediaminetetraacetic acid, EDTA, and ammonium citrate tribasic, TAC) in different percentages (2% and 3%). The cleaning action was evaluated on laboratory model samples, prepared with hematite a fresco and an egg-based tempera with limewash overlayers. Calcium and iron extracted by cleaning materials were quantified by inductively coupled plasma-mass spectrometry (ICP-MS). The potential damage to the hematite painting layers was also studied by electron paramagnetic resonance (EPR) spectroscopy. A visual observation of the limewash detachment induced by the overall cleaning was also performed. Results suggest that limewash removal mainly occurs by aqueous solution release from the cleaning system, with subsequent layer wetting, probable layer swelling, weakening and complete or partial detachment. A stronger limewash adhesion on the hydrophilic fresco surface than on tempera, was observed. None of the used cleaning materials resulted harmful to the integrity of the hematite layer underneath the limewash. A small damage in terms of extracted iron was detected in the cleaning systems after direct contact with fresco and tempera hematite layers; a “protective” effect by the tempera layer was observed for the pigment, due to the organic binder and triggered by the hydrophobic content of the egg-based medium. Cleaning materials with additives are more harmful than pure materials, with a greater coordinating ability for EDTA than for TAC, which increases with chelator percentage. Data suggest a more efficient backward transportation of aqueous solutions containing calcium and iron ions towards gels with respect to cellulose, due to their smallest pore size. All these results lead to operative suggestions: for fresco painting layers, pure gel allows both a good limewash removal and a lack of damage on the hematite layers. Instead, for tempera layers a good limewash removal and a negligible damage on the pigment was shown by gel, both pure and additivated with TAC, and pure cellulose. Therefore, the present study allows to identify proper characterization methods for evaluating effectiveness and damage in limewash removal and to give useful suggestions for the planning of repeated cleaning operations on a real polychrome object.
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Copper complexes with different ligands (ethylenediaminetetraacetic acid, EDTA, ammonium citrate tribasic, TAC, and alanine, ALA) were studied in aqueous solutions and hydrogels with the aim of setting the optimal conditions for copper stain removal from marble by agar gels, with damage minimization. The stoichiometry and stability of copper complexes were monitored by ultraviolet-visible (UV-Vis) spectroscopy and the symmetry of Cu(II) centers in the different gel formulations was studied by electron paramagnetic resonance (EPR) spectroscopy. Cleaning effectiveness in optimized conditions was verified on marble laboratory specimens through color variations and by determining copper on gels by inductively coupled plasma-mass spectrometry (ICP-MS). Two copper complexes with TAC were identified, one having the known stoichiometry 1:1, and the other 1:2, Cu(TAC)2, never observed before. The stability of all the complexes at different pH was observed to increase with pH. At pH 10.0, the gel’s effectiveness in removing copper salts from marble was the highest in the presence of ALA, followed by EDTA, TAC, and pure agar gel. Limited damage to the marble surface was observed when gels with added EDTA and TAC were employed, whereas agar gel with ALA was determined to be the most efficient and safe cleaning material.
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The study discusses a new smart cleaner for archeological paper based on a sodium dodecyl sulfate (SDS) micro-emulsion. Archeological paper samples from different manuscripts from three Egyptian museums were collected. The samples were cleaned with SDS to remove the stains, the dust, and the yellowing. The treated surfaces were investigated using the visual assessment by video microscope, pH measurement, SEM with EDX, and infrared spectroscopy. The results revealed that SDS micro-emulsion cleaned the paper surface deeply, without any harmful effect on its chemical structure. The video microscope confirmed that SDS can be an effective agent for removing the stains and disfiguring from paper fibers with an observed reduction of the yellowing. Moreover, SEM confirmed that SDS can be acted as an inhibitor to some species of fungi which disappeared completely after cleaning; the action depends on the fact that the active agent in SDS can rupture the covalent bonding between the protein structures in organism cells. Furthermore, no fading or flaking was observed in the ink particles after cleaning; on the contrary, the brightness retention of inks particles increased. No changes in the typical vibrations of paper were detected after cleaning except a significant increase in (O–H) stretching intensity which proves the efficacy of the current cleaning agent in enhancing the chemical structure of treated paper via the hydration process which can increase the physical strength for the cellulosic manuscripts.
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In China, alum-gelatin aqueous solution is historically used to prevent falling off of mineral pigments from paintings and to enhance strength of their paper matrices in the restoration process. However, after a long period of time of preservation, alum-gelatin aqueous solution applied to paintings will hydrolyze and produce free acid, which accelerates aging. To resolve this issue, instead of using alum-gelatin aqueous solution, here we report a new method of using a water-borne fluoropolymer coating to protect paintings. This coating is applied to simulated paintings, and their influences are systematically examined on the antipeeling property of pigment, mechanical properties, thermal stability, chromaticity, surface morphology, and water contact angle. Our results show that the applied coating slightly affects the appearance of the painting without falling off of pigment observed. Moreover, the coating increases the tensile strength and folding endurance of the paper because the polymer fills into the porous structure of paper fibers and covers pigment particles from SEM analysis. The treated painting retains moderate hydrophilicity, which facilitates removal of degradation substances from the paintings by water cleaning and the subsequent mounting procedure. Moreover, this coating is successfully applied to repairing a set of real ancient Chinese paintings of Yuan Dynasty (1271∼1368 A.D.), with practical acceptance. Our work provides a facile yet effective solution to conservation of ancient paintings by applying the modern fluoropolymers.
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Biomaterials centered infection or implant associated infection play critical roles in all areas of medicine with implantable devices. The widespread over use of antibiotics has caused severe bacteria resistance and even super bugs. Therefore, the development of anti-infection implantable devices with non-antibiotic based new antimicrobial agents is indeed a priority for all of us. In this study, antimicrobial composite meshes were fabricated with broad-spectrum antimicrobial peptides (AMPs). Macroporous polypropylene mesh with poly-caprolactone electrospun nanosheet was utilized as substrate to load antimicrobial peptides and gellan gum presented as a media to gel with AMPs. Different amount of AMPs was loaded onto gellan gum to determine the appropriate dose. The surface morphologies, fourier transform infrared spectroscopy spectra, in vitro release profiles, mechanical performances, in vitro antimicrobial properties and cytocompatibility of composite scaffolds were evaluated. Results showed that AMPs were loaded into the meshes successfully and the in vitro release of AMPs in PBS was prolonged and less than 60 % peptides were released in 10 days. The mechanical properties of composite meshes were also within the scope of several commercial surgical meshes. Composite meshes with AMPs loading amount of over 3 mg/cm2 showed inhibition against both Gram-negative and Gram-positive bacteria effectively while presented no toxicity to mammalian cells even at a loading amount of 10 mg/cm2. These results demonstrate a new simple and practicable method to offer antimicrobial properties to medical devices for hernia repair.
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Art restoration poses many challenges for scientists and conservators, as any restorative action can lead to lasting modification or damage to the original artefact. Recent interest in gel encapsulation has grown due to the ability to control the cleaning action; yet the restoration of modern paints such as acrylic-based systems still presents issues due to their extremely high sensitivity to most solvents. Herein, the preparation of dual physically and chemically crosslinked hydrogels based on regenerated cellulose and cinnamoyl-modified gelatin is demonstrated. These dual crosslinked hydrogels show increased mechanical strength and enhanced water retention compared to pure physically crosslinked hydrogels. When applied to acrylic-based paint surfaces, the dual crosslinked hydrogels extract a smaller amount of hydrophilic additives (albeit still leading to swelling within the paint film) versus physically crosslinked gels. It is anticipated that this dual crosslinking approach can be broadly applied to prepare gels for conservation of cultural heritage artefacts.
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Handmade paper is a major carrier and restoration material of traditional Chinese ancient books, calligraphies, and paintings. In this study, we carried out a Raman spectroscopy analysis of 18 types of handmade paper samples. The main components of the handmade paper were cellulose and lignin, according to the wavenumber and Raman vibration assignment. We divided its Raman spectrum into eight subbands. Five machine learning models were employed: principal component analysis (PCA), partial least squares (PLS), support vector machine (SVM), k‐nearest neighbors (KNN), and random forest (RF). The Raman spectral data were normalized, and the fluorescence envelope was subtracted using the airPLS algorithm to obtain four types of data, raw, normalized, defluorescence, and fluorescence data. An RF variable importance analysis of data processing showed that data normalization eliminated the intensity differences of fluorescence signals caused by lignin, which contained important information of raw materials and papermaking technology, let alone the data defluorescence. The data processing also reduced the importance of the average variables in almost all spectral bands. Nevertheless, the data processing is worthwhile because it significantly improves the accuracy of machine learning, and the information loss does not affect the prediction. Using the machine learning models of PCA, PLS, and SVM combined with linear regression (LR), KNN, and RF, the classification and prediction of handmade paper samples were realized. For almost all processed data, including the fluorescence data, PCA‐LR had the highest classification and prediction accuracy (R2 = 1) in almost all spectral bands. PLS‐LR and SVM‐LR had the second‐highest accuracies (R2 = 0.4–0.9), whereas KNN and RF had the lowest accuracies (R2 = 0.1–0.4) for full band spectral data. Our results suggest that the abundant information contained in Raman spectroscopy combined with powerful machine learning models could inspire further studies on handmade paper and related cultural relics. We measured the Raman spectra of 18 types of handmade paper samples, and constructed five machine‐learning models, namely, PCA‐LS, PLS‐LS, SVM‐LS, KNN, and RF, to evaluate the role of data processing and to classify and predict the samples. It shows that data processing resulted in the loss of fluorescence‐related features. Nevertheless, data processing greatly improved the accuracy of machine learning. PCA‐LR has the highest classification and prediction accuracy (R2 = 1). R2 = 0.4–0.9 for PLS‐LS and SVM‐LS. R2 = 0.1–0.4 for KNN and RF.
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Within the framework of the EU INTERREG IIIA project between Slovenia and Austria about the Vine cultural track of the archduke John from Graz to Maribor, which has included also a conservation treatment of the rare collection of 126 illustrations dated 1820 to 1850 representing paintings on paper in a gouache technique of types and sorts of grapevine which were serving as a teaching aid. The 126 originals are the only preserved illustrations of the types of vine that were grown in the area of present-day Slovenia of the Duchy of Styria before the vines were destroyed by phylloxera. The paper presents the results of non-destructive and non invasive analysis of paper as a support to the illustrations. Results were obtained from non-destructive permissible observation and analytical techniques of characterization, such as structural properties, microscopic, optical, and colorimetric and qualitative analysis on selected originals. The results served as a base to determine further conservation and preservation treatments of the exceptional gouache collection.
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Archive and library materials are an important part of our national cultural heritage. In order to identify appropriate methods for the conservation and restoration of suchmaterials, it is important to establish the current physical-chemical state of the artifactand how it can be influenced by the chemical reactions it meets with. The degree of crystallinity and orientation of the paper fibers has a significant influence on its mechanical properties. Many chemical and physical reactions can increase amorphousareas and susceptibility to biological attack, thus making the paper more brittle. Spectroscopy is one of the most powerful tools for the characterization of paper materials and for the identification of degradation products. This paper describesthe application of FTIR and Micro-Raman spectroscopy for the characterization of cellulosic materials.
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The impact of aqueous treatments on the strength properties of Whatman filter paper and five historic papers were investigated. The results showed the statistically significant decrease of tensile strength of Whatman paper and four of the historic papers due to the treatments. They also showed mixed trends concerning folding endurance and tensile energy absorption. Possible explanations for the strength decrease are proposed and long-term implications are discussed on the basis of different strength decrease scenarios. It is suggested that aqueous treatments should be applied only when necessary and that they should be followed by consolidation. The importance of strength and especially tensile tests is emphasized, as they can register changes that cannot be detected by chemical methods. It is suggested that the lack of a preconditioning step can result in misleading conclusions concerning the folding endurance of treated samples.
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The application of a new class of organogels as cleaning tools for painted surfaces is described. It combines some of the most attractive features of cleaning liquids and normal gels while diminishing the deleterious characteristics of both. Thus, the ‘latent’ gellant, polyethyleneimine (PEI), reacts with CO2 at room temperature in solutions of several organic liquids to produce an ammonium carbamate form (PEICO2). This charged species organizes itself into 3D polymer networks which immobilize the liquids as gels. The properties of the original solution (i.e. a free-flowing liquid) are re-established immediately after addition of a small amount of a weak acid which displaces the CO2 molecules and makes the PEI chains positively charged. The visual changes are substantiated by rheological analyses. Results from analytical tests to determine the utility of these gels as cleaning tools for painted surfaces of historical and artistic interest, have been obtained from contact angle and FTIR measurements as well as visual comparisons of the surfaces before and after application of the gels. The analyses indicate that the PEICO2-based organogels were very effective in removing different surface patinas from painted supports. A surface layer of dammar was completely removed from a test canvas with oil paint, an aged painting from the XIX century, and a XV century oil-on-wood panel attributed to Mariotto di Cristoforo. Finally, a surface acrylic polymeric resin (used in a restoration performed during the 1960s) was also successfully removed from Renaissance wall paintings decorating the Santa Maria della Scala Sacristy in Siena, Italy. The isothermally rheoreversible gel approach described in this work represents a new, highly versatile, and very efficient method for removing aged surface patinas from works of art.
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In this paper, we present the results of a literature survey concerning the methodology and criteria used for the evaluation of paper conservation interventions. Important issues that are reviewed include: Accelerated ageing: theoretical principles, most common methods, standards and conditions (temperature and relative humidity). Experimental setup: sample selection and preparation, planning of the experiments. Methods for the evaluation of paper properties: established methods already in use, various methods that have been sparingly used and methods that have never been used but have the potential to evolve and apply to specific problems of the evaluation. Criteria of effectiveness of the intervention. A selection of the most important relevant publications of the last 30 years and the methods yielded by the survey are presented in table format.
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a b s t r a c t The procedures for making and applying a new family of high viscosity aqueous polymeric dispersions based on poly(vinyl alcohol)-borax (PVA-borax) matrices are presented. A specific system of this type has been used to remove an oxidized varnish coating from the surface of "Coronation of the Virgin with Saints", a 15th century egg tempera painting on wood by Neri di Bicci (Florence, 1418–1492). FTIR spectra showed that the oxidized varnish was constituted of highly aged shellac resin. Good cleaning performance was attained when the liquid portion of the dispersion consisted of a mixture of water and acetone. Rheological investigations indicate that the acetone content does not affect the mechanical properties of the polymeric dispersion. Those mechanical properties permit easy removal of the cleaning agent simply by peeling it from the surface by means of a forceps or spatula once it has carried out its cleaning function. Optical microscopic and FTIR investigations show that the cleaning agent is able to remove the oxidized varnish coating from the surface of the Neri di Bicci painting without leaving detectable residues.
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The research has been focusing on some connection between the chemical composition of the papers obtained by Fourier transform infrared (FTIR) spectroscopy and the nature of the fillers, determined by energy dispersion X-ray fluorescence (EDXRF) spectroscopy. The present paper corroborates the FTIR and EDXRF results obtained for some historical papers from books of the XIX-th and XX-th centuries, from private collections. These analytical results allowed a first approximation of technological paper composition and of the age determination of the samples. This analytical method can elaborate some properly methods for paper documents preservation, taking into account the aging and degradation processes of the historical paper.
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Paper-based artworks are among the most valuable assets for transmission of knowledge. Historical paper is composed of different polysaccharides (e.g. cellulose), binders, and glues. During aging all of these components undergo several degradation processes, as a result of external and intrinsic causes, and these can compromise the state of conservation of the document. In this work, application of a new biotechnological strategy for paper artefact preservation is reported. By making use of innovative and non-invasive materials, for example appropriate hydrogels, in combination with selective electrochemical biosensors, it is possible to simultaneously verify the degradation condition of the paper artwork and then to efficiently clean it, while monitoring the process of removal of both pollution and degradation products. In this paper, we focus on specific examples in which such techniques have been applied to paper artworks and that illustrate the advantages and potential of this biotechnology compared with the traditional paper-cleaning methods currently in use. Figure Scheme of cleaning treatment of old paper and determination of the interested analyte using Flow Injection Analysis system (FIA) with integrated electrochemical biosensor
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The Italian dialect poet Cesare Pascarella travelled all around the world, noting down in notebooks his keen and caustic observations, and drawing sketches that are a visual reportage of his journeys. The sketches were mounted as a random collage over acidic cardboards that were exposed to direct sunlight in his studio. Their poor state of conservation is related to the use of modern paper: chemical instability of raw materials caused acidification and strong oxidation of the support, with intense yellowing of the surfaces and brittleness of the paper. To ensure future preservation of the drawings, chemical stabilisation with simultaneous alcoholic treatment by deacidification (calcium propionate) and reduction (borane tert-butylamine complex) appeared necessary. To verify its applicability, it was indispensible to characterise the support and identify the nature of all the graphic media. The use of Raman, Infrared, X-ray fluorescence spectroscopies and scanning electron microscopy coupled with X-ray microanalysis allowed us to clear the problems related to the different penetration depth of each analytical technique and the different responses of pigments/dyes to each spectroscopy. The palette, how it varied along the journeys, the different supports used and preparations were completely identified showing a choice of colours compatible with the reduction treatment. Figure Top: Drawing A12. Left: before chemical stabilisation and conservation treatment. Right: after chemical deacidification/reduction and the final conservation intervention. Bottom Left: SEM image of the paper composition of drawing A19. Bottom right: Raman spectra of the paper support of drawing B6 before and after the reduction treatment. On the top, the spectra without baseline correction; on the bottom, the spectrum after reduction is compared with a standard spectrum of pure cellulose paper that shows a perfect recovery of the original structure of the paper after the chemical treatment.
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The works of art and artifacts that constitute our cultural heritage are subject to deterioration, both from internal and from external factors. Surfaces that interact with the environment are the most prone to aging and decay; accordingly, soiling is a prime factor in the degradation of surfaces and the attendant disfigurement of a piece. Coatings that were originally intended to protect or contribute aesthetically to an artwork should be removed if they begin to have a destructive impact on its appearance or surface chemistry.
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Innovative hydrogels obtained by physical and chemical crosslinking of deacylated Gellan gum have been characterized in terms of water uptake, rheological properties and compressibility, and the behaviour of the tested materials, according to the type of the obtained network, is thoroughly discussed. The release from the various gels of loaded model molecules of different steric hindrance was also investigated and the trend of the release profiles has been related to the structures proposed for the physical and the chemical hydrogel.
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In a comparative evaluation of seven procedures for determination of pH of paper, 55 different paper and pulp samples were used. Six procedures were based on cold extraction and subsequent determination of extract pH, either using a variety of combined pH electrodes or using a mixture of coloured acid/base indicators. One procedure involved impregnation of the sample with a solution of indicators and subsequent spectrophotometric determination of pH of air-dry samples. The correlation of determinations showed that most extraction methods give comparable data for acidic samples, with the exception of gelatine surface-sized samples. For samples with alkaline aqueous extracts, the effect of atmospheric CO2 and slow dissolution of earth-alkali metal carbonates should be taken into account, which is not the case with any of the standardised methods for determination of paper pH. Since CO2 enters into equilibria as a weak acid, it will decrease the equilibrium pH of solutions of CaCO3 and MgCO3, the difference amounting to more than 1.5 pH units. A new procedure is therefore proposed for determination of pH of alkaline papers basing on rapid equilibration with CO2 and dissolution of carbonates. The repeatability of determinations is satisfactory, providing data with standard deviation less than 0.15 pH units. A discussion of the concept of paper pH follows, in view of the role of water content in air-dry paper and implications on stability of paper. The different procedures are compared in view of sample consumption, measurement repeatability and systematic error.
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Until now, only acids introduced in the manufacture of paper and those absorbed from the environment have been believed mainly responsible for the degradation of paper. Experimental evidence is presented to show that significant concentrations of several organic acids are spontaneously generated in the natural aging of all cellulose-based papers, including alkaline papers. Easily detectable concentrations of formic (methanoic), acetic (ethanoic), lactic, glycolic, oxalic and a few other as yet unidentified acids accumulate within a few months of manufacture in paper stored under ambient conditions. It is proposed that the formation of weak organic acids from the oxidation of carbohydrate fragments comprises an essential element of a mechanism for the aging of cellulose. Oxidation and acid hydrolysis reactions reinforce each other in this reaction mechanism to promote an ever-accelerating degradative process. Based upon these findings, a new accelerated aging test for paper has been developed that shows a greater similarity to natural aging than presently accepted accelerated aging methods.
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Chemical mutagenesis or exposure to antibiotic stress of Sphingomonas paucimobilis ATCC 31461 and R40 have been used to isolate mutants producing modified gellan gum polysaccharides. N.m.r. and conventional carbohydrate analysis methods have been used to characterise these polysaccharides. The 1H and 13C n.m.r. spectra of gellan gum have been fully assigned and the anomeric regions have been shown to be very sensitive to the type and location of non-carbohydrate substituents. Analysis of the gellan gum mutants suggests that they differ in the nature of acetate and glycerate substitution. Such gellan-related polysaccharides have been used to test the selective effect of acyl substituents on the gelation of gellan gum.
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The Application of Carbopol Poultices on Paper Objects The polyacrylic acid Carbopol has been employed for several years as a gel formative. Characteristics and the ageing process of Carbopol gels are discussed in the light of their application on paper. Investigations showed that neutralizing agents which are necessary to achieve gel formation, are migrating with the moisture to the substrate to which the gel is applied. Special attention is drawn to the behavior of (organic) amines used as neutralizing agents.
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The effect of three washing methods is compared with regard to the removal of acid compounds from aged paper: immersion washing, blotter washing, and suction table washing with the aid of ultrasonic mist. The authors identify and quantify the organic acids (acetic-, lactic-, malic-, oxalic- and succinic acid) and inorganic anions (Br(-), Cl(-), SO(4)(2-), NO(2)(-)) present in the wash water after the end of the washing operation. In this study, immersion washing was most effective, followed by the application of ultrasonic mist on the suction table in the case of thin and porous papers. Suction table washing was ineffective for the treatment of thick and dense papers. Blotter washing showed the lowest effectiveness with regard to the removal of organic acids, especially oxalic acid, from paper.
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This study concentrated upon refining an in-situ FTIR method to study accelerated ageing of paper under controlled conditions. The standardisation method applying the CH band at 2900cm−1 allowed comparison of different samples from various experiments. To distinguish the features present in the spectra in the carbonyl region coming from carbonyl vibrations not disturbed by water vibrations, bound water present in paper was desorbed and the spectra were recorded at an elevated temperature. An oxidation index of paper defined as a ratio of integrals of bands at 1730cm−1 to that at 1620cm−1 has proved amenable to follow the degradation of cellulose aged under various conditions. The boundary conditions of experiments selected by us were able to discriminate between hydrolysis of glycosidic bonds and oxidation of carbon atoms in a glycopyranose anomer. Following the changes of the spectrum in the carbonyl range proceeding with oxidation time various intermediates of the cellulose partial oxidation were distinguished starting from the least oxidized monocarbonyl groups, through diketones to aldehydes and carboxyls. Assuming a parallel–consecutive mechanism of the cellulose oxidation the spectra were resolved by fitting with multiple Gaussian–Lorentzian functions.
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Gellan gum gels formed with potassium and calcium ions were investigated by the pulsed field gradient (PFG) stimulated echo NMR method. The structure of the gel network of the gellan gum gel was discussed on the basis of the interbarrier distance, a, the permeability of the barrier, p, and the actual diffusion coefficient of water, D0. These structural parameters were estimated by the analysis of the restricted diffusion of water in the gel network. Three different types of gel, namely, weak gel, true gel and brittle gel, were obtained at various concentrations of the gel-promoting cation. Interestingly, the topological structure of the network in each type of gel as reflected by the structural parameters is identical in K+-bridged gels and Ca2+-bridged gels, although the absolute concentration of the cation needed to form the different network types is quite different. It is assumed that the binding structures at the crosslink and at the bridge between the helices are different between the type of cation. Nevertheless, structural properties of the network such as the average distance between junction zones and the permeability of the junction zone were independent of the type of gel-promoting cation. The change in the overall gel architecture formed by the junction zones in the gelation process seems to be identical in the cases of monovalent and divalent cations and the difference is only the gel-forming efficacy of cations.
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Infrared spectra of paper samples often show many overlapped bands in the most significant region of 1400-1900 cm-1. The digital deconvolution reveals the underlying information, as shown by some examples of both authentic items and reference samples, appositely prepared. The IR absorbance of oxidized groups (both unconjugated and conjugated) in cellulose, as well as gelatine, rosin and lignin can be detected with the deconvolution technique even in the presence of the broad band at ∼1630 cm-1 due to adsorbed water. The deconvolution technique allows a rough identification of the mechanism of degradation which leads to yellowing and browning of the paper samples.
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The evolution of papermaking from XII century, in Europe, was characterized by continuous changes of fibrous and non-fibrous materials as cellulose, wood pulp, sizing agents, fillers and coatings. In this study, the composition of many ancient paper documents is analysed by means of non-destructive Fourier Transform Infrared Spectroscopy (FTIR) in order to identify the main components of paper and to evaluate the presence of other compounds. The substances that cannot be detected by FTIR analysis are also underlined. The goal of this work is to set up an FTIR database for diagnostic purposes and to identify optimal spectral ranges useful for chemometric
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Hard and softwood and wood constituent polymers (cellulose and lignin) were studied using Fourier transform infrared (FTIR) spectroscopy. The hollocellulose-to-lignin ratio was estimated for some of the timber species. The structural difference between Klason lignin isolated from softwood (Pinus roxberghii and cupressus lusitanica) and hard wood (Acacia auriculaeformis and Eucalyptus tereticornis) species was studied. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1969–1975, 1999
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Four samples of gellan gum in sodium form, with equivalent average molar mass but with different acyl contents, were investigated using atomic force microscopy (AFM) and dynamic viscoelasticity measurements. The investigation was carried out at concentrations which form local molecular assemblies, including associations, networks, and gels. AFM showed that continuous network structures developed mainly through end-to-end type inter-helical associations rather than side-by-side type ones in the presence of potassium without significant increase in the vertical height on the image. Although end-to-end type inter-helical associations certainly occurred, continuous network structures did not develop in the absence of potassium. In the presence of the cation, the formation of continuous network structures could relate to the rheological thermal hysteresis between the sol-to-gel and the gel-to-sol transitions and to the dynamic storage modulus at 20 °C for gellan gum with lower acyl contents. During gelation, acyl groups increase the flexibility of the molecular bundles, inhibiting associations between the backbones when the added potassium minimizes the electrostatic repulsion. Also, acyl groups lower the charge density of the molecular bundles, which would promote associations in the absence of the cation or the stabilization of the double helix (especially via glycerate groups). This would increase the elasticity of the gelled system in the absence of the cation. Our results point to the fibrous model of gelation rather than the conventional model that assumes distinct junction zones with disordered flexible polymer chains connecting adjacent junction zones.
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The study presents an overview of the chromatographic (SEC), spectroscopic (FTIR, UV/VIS), viscometric (DP) and chemical methods (titration, pH) used for the evaluation of the degradation progress of various kinds of paper under various conditions. The methods were chosen to follow different routes of paper degradation. Model paper samples represented boundary paper types from pure cellulose cotton paper, through softwood to low quality acidic, sized groundwood paper The accelerated ageing conditions were adjusted to achieve maximum effect (climatic chamber RH 59%, 90oC) and also to mimic the environment inside books (closed vials). The results were settled on the literature data on the degradation mechanisms and compared in terms of the paper types and ageing conditions. The estimators of coupled de-polymerisation and oxidation have been proposed based on the correlation between SEC, UV/VIS and titrative coppper number determination. The overall oxidation index derived from FTIR results was shown to correlate with the summary –CHO and –COOH concentration determined by titrative methods.
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A solid-phase extraction (SPE) method was adapted to perform brewed coffee sample clean-up for seven organic acids (acetic, citric, formic, malic, pyruvic, quinic and succinic) and caffeine determination by reversed-phase UV high performance liquid chromatography (RP/UV-HPLC). For all analytes the method showed good precision and linearity and, as an application, 20 brewed coffee samples from the two types of coffee (robusta vs. arabica) were tested. Brewed coffee samples were prepared according to ISO 6668 [1991. Green coffee—preparation of samples for use in sensory analysis] and the results were compared to sensory evaluation obtained from a panel of coffee tasters. Robusta coffee demonstrated the highest content of caffeine. Total acid content varied with coffee type and also with the geographic origin of the green coffee. Roasting conditions also seem to affect final acidity in brewed coffee for both coffee types analysed.
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The effects of monovalent cation and anion species on the conformation of gellan chains in aqueous solutions were examined by optical rotation (OR) and fluorescence anisotropy measurements. The OR measurement suggested that a cation species with a large ionic radius aggregates the gellan chains to form supramolecular structures that have negative optical rotations even in the solution state. The anion species F− lowered the coil–helix transition temperature and suppressed the aggregation of gellan chains, while the anion species Cl−, Br−, and I− showed no influence on the coil–helix transition temperature or the aggregation behavior. The coil–helix transition of gellan chains was affected by the cation concentration rather than by the type of cation species; however, the latter was the predominant factor with respect to the aggregation of gellan chains.
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Effects of cations on the network formation of the microbial polysaccharide gellan were investigated using atomic force microscopy (AFM). Aqueous dispersions of gellan with various cations were spread onto freshly cleaved mica surfaces and visualized in air using the alternating current cyclic contact mode. AFM images of tetramethylammonium salt of gellan revealed branched rod-like structures, the heights of which are uniformly ca. 0.5 nm, suggesting the absence of the side-by-side aggregation of double helices. Adding KCl, CsCl, and CaCl2 promoted interhelical aggregation, evident from increases in the heights of fibrous aggregates of gellan double helices up to 2–3 nm, resulting in the formation of local network structures in the presence of CsCl and macroscopically percolated network structures in the presence of CaCl2. The surfaces of bulk gellan gels containing KCl and CsCl were imaged under respective salt solutions using the direct current contact mode, revealing fairly straight and stationary network strands.
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The rheological and thermal properties of sodium form gellan gum solutions with and without sodium chloride, potassium chloride, calcium chloride and magnesium chloride were studied by dynamic viscoelastic measurement and differential scanning calorimetry. Temperature dependence of the loss modulus for gellan gum solutions of lower concentrations without salt showed a one step-like change at a certain temperature, however that for concentrated gellan gum solutions (>2.0%) showed two step-like changes. The higher temperature process Thc may be attributed to the helix-coil transition and found in between the exothermic and endothermic peak temperatures Ts and Tm observed in cooling and heating DSC curves, while the lower temperature process Tsg may be attributed to the sol-gel transition. Temperature dependence for gellan gum solutions of higher concentrations (>3.2%) showed a large hysteresis, moreover, the temperature at which the loss shear modulus G″ showed the second step decrease shifted to higher temperatures with increasing concentration of gellan gum. The cooling or heating DSC curves for gellan gum solutions of lower concentrations showed a single exothermic or endothermic peak, and both exothermic peak t