Development of New Systems Based on Hydrotalcites for Stabilization and Deacidification of Paper Information Carriers
Abstract
This study focuses on the effectiveness of a new substance in stabilizing paper information carriers - hydrotalcite applied to the paper in a partially polar environment. The effect of modification on the stabilization of paper during accelerated aging was investigated by measuring chemical (surface pH, rate of glycosidic bond cleavage), mechanical (coefficient of the relative increase of the lifetime for folding endurance), optical (colorimetry - CIE L*a*b*), and spectral (FTIR) properties. Three types of hydrotalcites differing in composition, particle size, and preparation conditions, were tested and compared. After the modification, all the properties of acidic test papers improved. The most promising type of hydrotalcite was prepared under the nucleation action of citric acid. The atomic ratio of Mg2+ to Al3+ of this hydrotalcite was equal to 5. Modification by this hydrotalcite led to an increase in surface pH by 1.3 to 2.7 units.
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Hydrotalcite samples were prepared in the form of powder and/or sol under different conditions and characterised by various techniques. A suitable system of liquid carriers consisting of perfluoroheptane, isopropanol, and water (PFH-IPA-H 2 O) was chosen to apply HTlcs as deacidifying agents on paper. The areas of miscibility and immiscibility in the PFH-IPA-H 2 O system were determined at a temperature of 25 °C. The properties of HTlcs dispersed in the prepared solvent were measured. The size of the particles was determined by optical microscopy with image analysis. The average particle size ranges from 1 µm to 2 µm. The settling speed of particles in the prepared colloidal systems was monitored using turbidimetry. Sols in the mixture of solvents had uniformly dispersed particles that settled slowly. The effect of the prepared colloidal HTlcs dispersions on the properties of the paper, specifically the pH of its surface, was also tested. Hydrotalcites in the form of a sol with a ratio of magnesium to aluminium of 5:1 were found to be promising candidates for deacidification. The use of surfactant additives in the preparation of HTlcs did not positively affect the properties of the paper.
The degradation of cellulose is an important factor influencing its mechanical, optical, physical, and chemical properties and, hence, the lifetime of paper in libraries and archival collections. Regardless of the complexity of the paper material, the main chemical pathways for its degradation are hydrolysis and oxidation. This study presents an overview of the analytical techniques employed in the evaluation of the hydrolysis and oxidation processes; these techniques include size-exclusion chromatography, Fourier-transform infrared and ultraviolet–visible spectroscopy, and X-ray diffraction. This paper aims to determine the extent to which these instrumental methods are useful for studying the aforementioned processes and for which lignin contents. It also highlights how atmospheric humidity could affect the cellulose structure in paper containing lignin. It was found that humidity causes significant changes in the cellulose chain lengths and that a high lignin content in paper could suppress some cellulose degradation pathways. This knowledge can be applied to developing strategies and selective chemical treatments preventing the consequences of paper ageing.
The present contribution evaluates the methods of degradation and stabilization of alum-containing paper with a focus on the alkaline environment achieved by deacidification procedures. In terms of reviewed subjects, the contribution focuses on alum-rosin sized paper, which is still used as a carrier of knowledge and information; however, it also mentions cellulose itself and other brands of paper. The contribution summarizes the results on the homogeneity of the distribution of alum and rosin in the paper mass and on the paper surface. It provides the knowledge gained in the field of alkaline hydrolysis and oxidation with special regard to transition metal species. It shows the values of alkaline reserves achieved in the main mass-deacidification processes. On the basis of the acquired knowledge, the contribution emphasizes the procedures of paper stabilization. Criteria of “increased mechanical permanence and lifetime prolongation” adopted to evaluate and compare the efficacy of individual mass-deacidification processes were applied and corresponding data are introduced. The contribution also draws attention to the existence of open issues in the area of paper degradation and stabilization.
Deacidification refers to chemical treatments meant to slow down the acid hydrolysis and embrittlement of books and paper documents that had been printed on acidic paper. From the early 1800s up to about 1990, papermakers used aluminum sulfate, an acidic compound, in most printing papers. Certain deacidification methods use non-aqueous media to distribute alkaline mineral particles such as MgO within the pages of the treated books. Evidence is considered here as to whether or not the proximity of alkaline particles within such documents is sufficient to neutralize the acidic species present. Because much evidence suggests incomplete neutralization, a second focus concerns what to do next in cases where books already have been treated with a non-aqueous dispersion system. Based on the literature, the neutralization of acidic species within such paper can be completed by partial moistening, by high humidity and pressure, by water condensation, as well as by optional treatments to enhance paper strength and a final drying step.
Determination of degradation compounds of aged and deacidified papers requires an application of sev-eral analytical methods, including chromatographic and electrophoretic ones. Paper and paper extracts are very complex samples. Therefore, application of sample preparation methods is mostly involved in process of analysis. Sampling and sample preparation techniques provide transfer of analytes from a solid sample or from the gas phase (vapour) that exists above a solid sample into the extraction medium. Many extraction techniques were introduced, including conventional and advanced extractions utilizing water or organic extraction solvents, sampling tubes with adsorbents or fibre, often with the precon-centration of analytes. Passive sampling and solid-phase microextraction approaches were introduced as non-invasive techniques in the analysis of historical books and monitoring of indoor air in libraries and archives. This mini-review summarizes the sampling and sample preparation methods as well as new trends applicable in the analysis of degradation compounds of aged and deacidified papers.
Gaseous acetic acid is formed under conditions of storage of historic paper objects. Its presence not only promotes hydrolytic cleavage of cellulose, but also causes acetylation of the cellulosic material to very small degree. The acetylation reaction proceeds under ambient conditions and without catalyst. Different analytical methods were used to prove the presence of organic acetates on cellulosic paper matrices. DESI-MS in combination with ²H-isotopic labeling showed the presence of sugar fragments with different acetylation patterns. A method based on Zemplen saponification was applied and worked also in the presence of a large excess of acetic acid and/or inorganic acetates. The acetylation effect was quantified for model papers and original, naturally aged paper samples. While cellulose acetylation was clearly proven to be another general pathway of paper aging, further studies of this acetylation phenomenon are needed with regard to conservational aspects and suitable paper storage conditions.
This contribution presents a brief overview of the deacidification and preservation of aged cellulosic objects. Aqueous, organic liquid and air - solid/liquid systems are discussed. The global aim of all these techniques is to deliver alkaline species to acidic sites in the volume of the paper, to neutralize them and to create the so-called alkaline reserve, which ensures a significant decrease in further degradation. The success of this process strongly depends on mass transport phenomena. The simplest example of such a process uses aqueous liquid-based systems (e.g., hydrogen carbonate as a base); however, damage of the paper sheets can occur due to the effects of water. Organic liquid processes with dissolved organometallic compounds are much more compatible with paper, however, they are more sensitive to process parameters, e.g., wetness in the pre-dried material, contact time and post-treatment parameters (humidity, concentration of CO2, temperature, time). When solid particles are used (most frequently MgO), the situation is even more complicated, because of the dissolution of the solid particles, diffusion into the body of the paper sheet and the reactions with acidic sites. Several approaches to modelling and optimization of deacidification procedures are outlined in this paper.
The tensile test is the most widely used method for testing the mechanical characteristics of orally disintegrating films (ODFs). The other available test is the folding endurance (FE) test, which is more suitable for clarifying the actual strength during the manufacturing and dosing. However, the FE test is performed manually, and the FE number it generates has not been adequately analyzed as an index. The aim of this studies were to establish an automatic method for determining the FE number, and to compare the resulting FE numbers with the tensile properties. For this purpose, a desktop-model endurance test machine was used. First, the operating conditions-i.e., the folding angle, the folding speed and the weight requirement were optimized using ODF models. Secondly, the FE of ODFs prepared from three film formers (HPMC, HPC, and PVA) and with insoluble particles (calcium carbonate), plasticizers (glycerin) and APIs (acetaminophen), was evaluated and compared with the tensile properties. Lastly, the commercial ODFs were investigated. The results showed that our automatic system could be successfully used to determine the FE characteristics of ODFs. FE was suggested to relate to not only the strength but also the elongation during the tensile test.
Although efficient and inexpensive, conventional viscometry to determine cellulose’s average degree of polymerization (DP) may mislead the final DP because cellulose degradation occurs in the used solvents, which consist of alkaline amino complexes of transition metals, such as cupri-ethylenediamine (CED). For oxidatively damaged pulps or celluloses, viscosity-DP determinations may be more inaccurate because alkali-induced β-elimination reactions render such oxidized celluloses even more vulnerable. Despite the risk identified in many studies, a systematic investigation of the parameters affecting the viscosity-DP assessed by reliable analytics is still required. Here, a new approach evaluating CED’s effects on oxidized cellulosics was used (i.e., immediate pulp regeneration after dissolution in CED). In-depth molecular features characterization (e.g., absolute molar masses, oxidized groups´ profiling related to molecular weight distribution) by gel permeation chromatography (GPC) coupled with fluorescence and multiangle laser light scattering (MALLS) enlightened the behavior of oxidized celluloses and the influencing parameters during dissolution in CED.
Hydrotalcites are layered double hydroxides (LDHs) of the anionic clay family. They can be obtained by synthesis, with high purity and controlled stoichiometry but with much larger preparation efforts and costs with respect to natural ores. Their properties can be tailored by changing the metals of the layer, or by inserting proper inorganic or organic anions. The reason of the few industrial applications of LDHs might be the difficulty of scaling up their synthesis and anion exchange methods, requiring often cumbersome procedures for filtering, recovery and purification of the final products. Recently, huge efforts were made to obtain facile and easily scalable preparation methods, especially favoured by the almost complete elimination of solvents and water-based procedures. The structures of the nanocomposites were studied by several techniques, from electron microscopy and diffraction to X-ray powder diffraction (the unique structural techniques able to face the low crystallinity of these materials) coupled with others, to obtain an exhaustive view of LDHs structure and reactivity. These advancements and the perspectives of larger LDHs industrial applications are described.