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Plasticized polylactic acid nanocomposite films with cellulose and chitin nanocrystals prepared using extrusion and compression molding with two cooling rates: Effects on mechanical, thermal and optical properties
... Prior to degradation experiments, the samples' dry weight was measured to obtain the sample initial mass. At different time intervals (3,7,14,21,28, and 35 days), duplicate sacrificial specimens of each sample were recovered, washed, and dried until the constant was weighed. Photographs of samples were taken for visual comparison. ...
... In addition, the difference of components' surface polarity was not advantageous to obtain a good interfacial adhesion between PLA, PHB, and ChNP. Similar behaviors have been reported by other authors when they observed that the addition of chitin or cellulose nanocrystals into a PLA or PLA/PHB matrix resulted in the drastic decrease in elongation for the break values of nanocomposites [15,28,69,70]. The T g value for the neat PLA sample was found at 62 • C, while weak peaks corresponding to the exothermic crystallization and endothermic melting of PLA were observed at around 124 and 152 • C, respectively. ...
... In addition, the difference of components' surface polarity was not advantageous to obtain a good interfacial adhesion between PLA, PHB, and ChNP. Similar behaviors have been reported by other authors when they observed that the addition of chitin or cellulose nanocrystals into a PLA or PLA/PHB matrix resulted in the drastic decrease in elongation for the break values of nanocomposites [15,28,69,70]. ...
Fully bio-based poly(lactic acid) (PLA) and poly(3-hydroxybutyrate) (PHB) blends plasticized with tributyrin (TB), and their nanocomposite based on chitin nanoparticles (ChNPs) was developed using melt mixing followed by a compression molding process. The combination of PHB and ChNPs had an impact on the crystallinity of the plasticized PLA matrix, thus improving its oxygen and carbon dioxide barrier properties as well as displaying a UV light-blocking effect. The addition of 2 wt% of ChNP induced an improvement on the initial thermal degradation temperature and the overall migration behavior of blends, which had been compromised by the presence of TB. All processed materials were fully disintegrated under composting conditions, suggesting their potential application as fully biodegradable packaging materials.
... Liquid-assisted extrusion was developed for nanocomposites derived from clay suspensions and polyamide 6 (PA6) [292] and used for first time on cellulose nanocomposites by Oksman et al. in 2006 [293]. Several reports on liquid-assisted extrusion or wet feeding of cellulose have since been published [294][295][296][297][298][299][300][301][302]. ...
... In liquid-assisted extrusion processes, CNMs are suspended or dispersed in water with or without additives. This suspension is pumped into the extruder that vaporizes the liquid phase and removes it via a venting system [292,293,[295][296][297][298][299][300][301]. Karger-Kocsis et al. [292] listed several benefits of the liquidassisted feeding of nanomaterials into the extruder, including the absence of the necessity for the surface modification of the nanomaterials-thus avoiding the degradation associated with surface modifiers, reduced health risks owing to the suspension of the nanomaterials in liquid, and their improved dispersion because of 'blow-up' phenomena caused by the pressurized liquid evaporating from the melt, particularly in cases where water is used. ...
... It was also demonstrated that water-assisted extrusion does not significantly affect the molecular weight of PA6. Herrera et al. [295,299,300] studied the effect of plasticizers or dispersing aids on the dispersion of CNMs in PLA using a liquid-assisted extrusion process. They found that the addition of plasticizers such as TEC and GTA effectively enhances the dispersion of CNFs and CNCs in PLA. ...
This review paper provides a recent overview of current international research that is being conducted into the functional properties of cellulose as a nanomaterial. A particular emphasis is placed on fundamental and applied research that is being undertaken to generate applications, which are now becoming a real prospect given the developments in the field over the last 20 years. A short introduction covers the context of the work, and definitions of the different forms of cellulose nanomaterials (CNMs) that are most widely studied. We also address the terminology used for CNMs, suggesting a standard way to classify these materials. The reviews are separated out into theme areas, namely healthcare, water purification, biocomposites, and energy. Each section contains a short review of the field within the theme and summarizes recent work being undertaken by the groups represented. Topics that are covered include cellulose nanocrystals for directed growth of tissues, bacterial cellulose in healthcare, nanocellulose for drug delivery, nanocellulose for water purification, nanocellulose for thermoplastic composites, nanocellulose for structurally colored materials, transparent wood biocomposites, supercapacitors and batteries.
... 15 Ashby diagrams for the relative Young's modulus, E relative , versus relative yield strength, σ relative , for nanocomposites based on modified (◯) and raw (•) CNC, and modified (▢) and raw (▇) CNF. a Effect of processing method; b Effect of shaping process; c Effect of matrix type. The diagrams were drafted using a set of ~120 data collected from 50 articles (Kim et al. 2019;Shojaeiarani et al. 2018Shojaeiarani et al. , 2019Yano et al. 2018;Herrera et al. 2015Herrera et al. , 2016Igarashi et al. 2018;Jonoobi et al. 2012Jonoobi et al. , 2010Gan et al. 2017;Lizundia et al. 2016;Morelli et al. 2016a, b;Bondeson and Oksman 2007a, b;Nagalakshmaiah et al. 2016;Sakakibara et al. 2016;Peng et al. 2016Peng et al. , 2017Wang et al. 2018;Kassab et al. 2019;Seoane et al. 2017;Qian et al. 2018;Zhang et al. 2019Zhang et al. , 2014Leszczyńska et al. 2015;Boran et al. 2016;Iyer et al. 2015;Yang and Gardner 2011;Khoshkava and Kamal 2014;Arias et al. 2015;Johari et al. 2016;Oksman et al. 2006;Clemons 2015;Panaitescu et al. 2013;Nicharat et al. 2015;Iwamoto et al. 2014a, b;Rohner et al. 2018;Venkatraman et al. 2019;Yasim-Anuar et al. 2020;Lo Re et al. 2018;Sapkota et al. 2015;Pracella et al. 2014;Abdulkhani et al. 2014;Corrêa et al. 2014;Oguz et al. 2021;Qian and Sheng 2017;Venkatesh et al. 2022;Liu et al. 2013) respectively), yield quite similar results. The injection molding (in green) gives the best improvements, with values of E relative and σ relative ranging from 0.6 to 9.5 and 0.56 to 2.43, respectively. ...
... Open and closed symbols for modified (◯) and raw (•) CNC and modified (▢) and raw (▇) CNF. The diagrams were drafted from a set of ~120 data collected from 50 articles (Kim et al. 2019;Shojaeiarani et al. 2018Shojaeiarani et al. , 2019Yano et al. 2018;Herrera et al. 2015Herrera et al. , 2016Igarashi et al. 2018;Jonoobi et al. 2012Jonoobi et al. , 2010Gan et al. 2017;Lizundia et al. 2016;Morelli et al. 2016a, b;Oksman 2007a, 2007b;Nagalakshmaiah et al. 2016;Sakakibara et al. 2016;Peng et al. 2016Peng et al. , 2017Wang et al. 2018;Kassab et al. 2019;Seoane et al. 2017;Qian et al. 2018;Zhang et al. 2019Zhang et al. , 2014Leszczyńska et al. 2015;Boran et al. 2016;Iyer et al. 2015;Yang and Gardner 2011;Khoshkava and Kamal 2014;Arias et al. 2015;Johari et al. 2016;Oksman et al. 2006;Clemons 2015;Panaitescu et al. 2013;Nicharat et al. 2015;Iwamoto et al. 2014aIwamoto et al. , 2014bRohner et al. 2018;Venkatraman et al. 2019;Yasim-Anuar et al. 2020;Lo Re et al. 2018;Sapkota et al. 2015;Pracella et al. 2014;Abdulkhani et al. 2014;Corrêa et al. 2014;Oguz et al. 2021;Qian and Sheng 2017;Venkatesh et al. 2022;Liu et al. 2013) concentration (0.05 to 1%vol) indicated Young's moduli higher than that predicted by the model. In these systems, the Young modulus values fit the model or become lower than it as the CNM concentration increases. ...
This chapter provides a comprehensive review of the processes used to deconstruct cellulosic fibers into cellulose nanomaterials (CNM) and their use in one of the most promising applications, namely, engineered (bio)plastics. We focus on the preparation of CNM via chemical and enzymatic pretreatments and discuss the most recent developments in related areas. The mechanical processes used to isolate CNM are described, with an emphasis on their effect on morphological and strength development. We also provide a comparative analysis of the industrialization potential of the most important methods to incorporate CNM in polymeric matrices. Classical and emerging uses of CNM in engineering (bio)plastics are presented, considering (i) CNM dispersion in polymer matrices to develop nanocomposites and, (ii) CNM adsorption at interfaces in polymer blends and composites to build hierarchical structures. The dispersion/orientation state of CNM in such materials and the underlying physical–chemical phenomena related to interfacial interactions between CNM and the polymer phase are discussed. The latter takes into consideration the impact of CNM on the development of functional materials. Overall, this chapter offers essential knowledge to facilitate the conversion of cellulosic fibers into CNM and their implementation in the field of composites.
... Melt processing has been employed in numerous research projects in which nanocellulose was used as a minor component to reinforce a thermoplastic resin (Seydibeyoglu and Oksman 2008;Martínez-Sanz et al. 2012, 2013aSuzuki et al. 2013Suzuki et al. , 2014Fortunati et al. 2014;Ambrosio-Martin et al. 2015a;Arrieta et al. 2015;Ferrer et al. 2016a;Herrera et al. 2016;Lendvai et al. 2016). After emerging from the die of the extruder, the material cools below the melting point of the matrix polymer. ...
... Alternatively, researchers who want to utilize nature-based products have selected poly-(lactic acid) (Martínez-Sanz et al. 2012) or thermoplastic starch mixtures (Lendvai et al. 2016) as the matrix. Herrera et al. (2016) showed that the results were strongly affected by the rate of cooling in the case of poly-lactic acid film reinforced with CNC. Rapid cooling yielded more amorphous, transparent, and compliant films. ...
This review article was prompted by a remarkable growth in the number of scientific publications dealing with the use of nanocellulose (especially nanofibrillated cellulose (NFC), cellulose nanocrystals (CNC), and bacterial cellulose (BC)) to enhance the barrier properties and other performance attributes of new generations of packaging products. Recent research has confirmed and extended what is known about oxygen barrier and water vapor transmission performance, strength properties, and the susceptibility of nanocellulose-based films and coatings to the presence of humidity or moisture. Recent research also points to various promising strategies to prepare ecologically-friendly packaging materials, taking advantage of nanocellulose-based layers, to compete in an arena that has long been dominated by synthetic plastics. Some promising approaches entail usage of multiple layers of different materials or additives such as waxes, high-aspect ratio nano-clays, and surface-active compounds in addition to the nanocellulose material. While various high-end applications may be achieved by chemical derivatization or grafting of the nanocellulose, the current trends in research suggest that high-volume implementation will likely incorporate water-based formulations, which may include water-based dispersions or emulsions, depending on the end-uses.
... The fabrication methods for polymer-reinforced CNF composites are similar to those used for synthetic fibers and micro-sized fillers. The most commonly used manufacturing processes are extrusion (Chaitanya & Singh, 2017), internal melt-blending (Warid, 2017), injection molding (Essabir, Boujmal, Bensalah, et al., 2016), compression molding (Herrera, Salaberria, Mathew, & Oksman, 2016), rotational molding (Khanam & AlMaadeed, 2015) as well as casting (Qazanfarzadeh & Kadivar, 2016). ...
... Herrera Vargas (2017) and Dufresne (2018) revealed that CNF tends to agglomerate among themselves in a dry condition, due to the formation of hydrogen bonds during a drying process, and this leads to size increment, causing CNF to lose its nanoscale characteristic. Studies by Soulestin, Quievy, Sclavons, and Devaux (2007), Herrera, Salaberria, Mathew, and Oksman (2016), and Oksman et al. (2016b) discovered that the presence of water from the CNF helped in eliminating CNF aggregation, Feeding zone Compression zone Metering zone thus lead to homogenous CNF dispersion. In comparison to the conventional method that uses dried CNF, the use of CNF suspension as a reinforcement material is beneficial in terms of the following: (a) unnecessary surface modification of CNF, (b) no degradation of surface modifiers, (c) low health risk because the CNF is in slurry and, (d) CNF dispersion can be improved due to "blow-up" phenomena, caused by evaporation of water from the CNF during melt-processing. ...
Nanocellulose, including cellulose nanofiber (CNF), recently has received an exponential growth of interest to be used as an alternative material to replace petroleum-based materials for the production of biomaterial with low environmental impact. Owing to its superior and versatile properties; low weight, large surface area, high mechanical, and physical properties, CNF has been used for various purposes and one of them is as a reinforcement material for polymer composites. This review discusses CNF-based nanocomposites made from different kinds of polymers and the highlight is on the fabrication methods and modifications that have been carried out to enhance their properties.
... Introduction Chitin is a natural fiber that has been recently studied for its beneficial properties as reinforcing materials in biopolymers [1][2][3]. Its is abundantly found in crustacean shell, insect cuticle and cell wall of fungi. ...
... However, its brittleness and poor stability limit its industrial applications. Therefore, modification of PLA with the addition of plasticizers, coupling and antistatic agents was done as a strategy to improve its performance so that it can compete with the conventional polymers used in the packaging industry [3]. Coltelli, et al. [7] discovered that incorporating PLA with chitin nanofibrils increased the elongation of the polymer by 180%. ...
This project aimed to study the reinforcement effect of fungal chitin at different loading on chitin/PLA composite. The chitin nanofibers were extracted from three mushroom species (oyster mushroom Pleurotus ostreatus, shiitake mushroom Lentinula edodes, enoki mushroom Flammulina velutipes ) and used as a reinforcement element in PLA. The chitin/PLA composite was fabricated using a solvent-casting method followed by the hot-compress molding method. In the solvent-casting method, the chitin nanofibers were dispersed in PLA/chloroform mixture and the mixture was left for solvent evaporation. The solvent-free chitin/PLA thin film was then filled in dog bone mold before proceeded with hot-compress molding at 190°C and 70 bar. The samples with different chitin loading were tested with tensile test to study the mechanical performance of nanocomposite. The chitin/PLA composite from oyster mushroom shows the optimum result (σ= 43 MPa, E= 12 MPa) at 5% chitin loading. The increment of the chitin loading leads to a decrease in both strength and strain. However, for the samples from enoki and shitake mushrooms, the optimum chitin loading is 10% with 55 MPa and 56 MPa tensile strength, respectively. This study suggests the potential of fungal chitin as reinforcement in PLA.
... An initial weight loss centered at 80°C corresponding to adsorbed water evaporation (blue arrow), together with a wide and marked thermodegradation event occurring in the 280−405°C range originating from the degradation of 2-amino-2-deoxy-D-glucopyranose units in chitin is observed. 52 ChNFs adsorb more water (by weight) in comparison with chitin powder, and the degradation curve becomes wider for ChNFs. Besides, a char equivalent of ∼25 wt % is obtained at 650°C for ChNFs. ...
Fungal nanochitin can assist the transition from the linear fossil-based economy to a circular biobased economy given its environmental benefits over conventional crustacean-nanochitin. Its real-world implementation requires carefully assessing its toxicity so that unwanted human health and environmental issues are avoided. Accordingly, the cytotoxicity and inflammatory effects of chitin nanofibrils (ChNFs) from white mushroom is assessed. ChNFs are few nanometers in diameter, with a 75.8% N-acetylation degree, a crystallinity of 59.1%, and present a 44:56 chitin/glucan weight ratio. Studies are conducted for aqueous colloidal ChNF dispersions (0−5 mg·mL −1) and free-standing films having physically entangled ChNFs. Aqueous dispersions of chitin nanocrystals (ChNCs) isolated via hydrochloric acid hydrolysis of α-chitin powder are also evaluated for comparison. Cytotoxicity studies conducted in human fibroblasts (MRC-5 cells) and murine brain microglia (BV-2 cells) reveal a comparatively safer behavior over related biobased nanomaterials. However, a strong inflammatory response was observed when BV-2 cells were cultured in the presence of colloidal ChNFs. These novel cytotoxicity and inflammatory studies shed light on the potential of fungal ChNFs for biomedical applications.
... [42] Due to bigger (ⅮⅮ) suggests that the amino groups are concentrated more heavily within the polymer's, there are important functional groups to show the biological properties and solubility of chitosan such as [-ΝΗ2]. [43] In addition to ⅮⅮ, molecular weight (ΜԜ) is a crucial factor that affects chitosan's bioactivity. Higher (ΜԜ) chitosan rarely exhibits significant bioactivities compared to lower MW chitosan. ...
Recent studies have used more marine-origin polysaccharides since they are widely available, economical, biocompatible, and biodegradable. These characteristics promote their technological use in water treatment, tissue engineering, cancer therapy, wound dressing, drug delivery systems, and biosensors. Due to its versatility and capacity to be produced from waste marine crustaceans, chitosan is becoming more and more important in a range of fields. It is first utilized in biomedical applications due to its versatile properties, which include biocompatibility, antibacterial activity, and biodegradability. A summary of marine polysaccharides (chitosan), including its supply, chemical, biological characteristics, and uses in tissue engineering, is given in this review.
... The microscopy observation can investigate the changes in the crystal's morphology and the optical characteristics of the mixture, permitting for the assessment whether the presence of polymeric matrices affect the nature of the RUT crystals. The practicality of such technique has been demonstrated in several investigations of various drugs and their mixtures with many hydrophilic matrices (Aho et al 2017;Herrera et al. 2016). The microscopic images of all samples were provided in Fig. 1. ...
Rutin (RUT) is a phytochemical flavonoid with numerous therapeutic potentials including antihypertension, cardioprotective, neuroprotective, and anti-cancer activities. Its clinical use is inhibited due to its poor aqueous solubility and permeability over oral administration. The present study aimed to overcome these problems through micellization and entrapment of RUT in solid dispersion (SD) using Poloxamer (POL) 407 and 188 as surfactant-based matrices. The RUT/SD formulations were prepared in serial drug loading concentrations in weight percentage to the total solid. The physical properties of the formed RUT/SD solids were characterized by several methods including polarizing microscopy, differential thermal analysis (DTA), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and dissolution study. The dissolution test was performed using a paddle dissolution apparatus and samples were analyzed using UV spectrophotometry. Polarized microscope confirmed that the optical behaviors of the RUT/SD implied a formation of miscible RUT with POL matrices. The morphology of RUT/SDs varied from porous matrices with craters to smoother surfaces as a function of RUT concentrations. XRD and DTA data exhibited that RUT existed as partially amorphous. These data indicated that the higher concentration of RUT in the RUT/SD formulations, the higher amorphous proportion of the RUT in the solid state. Henceforth, this led to an increase in the percentage of dissolved RUT from the developed RUT/SD formulations at 94 to 100% compared to pure RUT at only
... Because of the deep relationship between the tunicin CNC, sticky wheat corn starch biopolymer matrix, moisture, and softener, as well as the CNC's ability to create a three-dimensional stiff network, the nanocomposites have high mechanical strength scalded water. On the other hand, the mechanical properties of the nanocomposite films increased proportionally with the nanofiller concentration, which demonstrates an effective stress transmission between the biopolymer matrix and CNC nanofiller [120,121]. ...
In the last few years, there are rising numbers for environmental waste due to factors such as plastic based food packaging that really need to get enough attention in order to prevent the issue from becoming worse and bringing disaster to society. Thus, the uses of plastic composite materials need to be reduced and need to be replaced with materials that are natural and have low degradation to preserve nature. Based on the statistics for the global, the production of plastic has been roughly calculated for passing 400 million metric tons every year and has a high probability of approaching the value of 500 million metric tons at the year of 2025 and this issue needs to be counteracted as soon as possible. Due to that, the increasing number for recent development of natural biopolymer, as an example starch, has been investigated as the substitution for the non-biodegradable biopolymer. Besides, among all biodegradable polymers, starch has been considered as promising substitution polymer due to its renewability, easy availability, and biodegradability. Apart from that, by the reinforcement from the nanocellulose, starch fiber has an increasing in terms of mechanical, barrier and thermal properties. In this review paper, we will be discussing the up-to-date development of nanocellulose fiber reinforced starch biopolymer composites throughout this century.
... [42] Due to bigger (ⅮⅮ) suggests that the amino groups are concentrated more heavily within the polymer's, there are important functional groups to show the biological properties and solubility of chitosan such as [-ΝΗ2]. [43] In addition to ⅮⅮ, molecular weight (ΜԜ) is a crucial factor that affects chitosan's bioactivity. Higher (ΜԜ) chitosan rarely exhibits significant bioactivities compared to lower MW chitosan. ...
... With regards to the non-plasticized composites, Tg increases slightly from 56.9 °C (pure PLA) to 60.9 °C (40 wt% cellulose fibers). This is consistent with previous research findings on the use of kenaf, bamboo and cotton to reinforce polymers, which can be due to the impeding of movement that the steric hindrance of cellulose fibers causes to PLA molecular chain (Eichers et al. 2022;Herrera et al. 2016). Notably, the crystallinity of PLA increased significantly from 6.8% to 37.7% with the addition of 40 wt. ...
Pulp fibers are among the most abundant and cost effective cellulose source for the fabrication of polymer-cellulose composites. A straightforward method is to impregnate pulp fibers into thermoplastic films by hot press forming. As such, tissue materials made from hard or soft wood lignin-free Kraft fibers are attractive. In this work, we prepared cellulose fiber-polylactic acid (PLA) composite films by impregnating PLA films into a 40 g/m² tissue paper texture. A PLA film was sandwiched between single and multiple layers of cellulose tissues by hot pressing, forming composite films. Up to 40 wt% cellulose could be incorporated into PLA in this way. The effect of cellulose fiber content on the composite thermomechanical properties has been studied and reported. A natural terpene, limonene, was infused into the cellulose fibers by immersion coating to produce antioxidant composites. Limonene-modified composites demonstrated long-term antioxidant release and activity for three days, verified by 2, 2-Diphenyl-1-picrylhydrazyl (DPPH), cupric ion reducing antioxidant capacity (CUPRAC) and free iron ions (Fe²⁺)/ferrozine chelating assays separately. The short-term (2 h) antioxidant activity of the biocomposites reached 50–70% levels depending on the cellulose fiber concentration for the DPPH and CUPRAC assays but remained lower at 20–55% levels in the metal chelating assay. Due to sustained release of limonene from the composites, at the end of the 5-day period, the iron chelating antioxidant activity of the composites improved reaching 75%, whereas for DPPH and CUPRAC assay, 90% activity was recorded. These biocomposite films can be used in active protective packaging of both food (fruit) and cosmetic products.
Graphical abstract
... In addition, PLA has the characteristics of light weight, large deformation, strong plasticity and low manufacturing cost, showing broad application prospects in medical and health, electronic communications, aerospace and other fields [4][5][6]. W. Yang et al. [7][8][9][10][11] blended PLA with other materials, such as lignin nanoparticles, nanocrystalline cellulose, chitin nanoparticles, and organically modified montmorillonite powder, etc. to improve its toughness and biodegradability. Malwela et al. [12] studied the degradation rate of PLA with different components. ...
Polylactic acid (PLA) has been widely used in the field of medical devices. However, few studies have been conducted on the extrusion molding of PLA micro tubes for the preparation of biodegradable vascular stents. In this paper, the extrusion die for PLA single-cavity micro tubes was designed and manufactured by micro-extrusion theory. Taking the outer diameter, wall thickness, wall thickness uniformity and ovality of micro tubes as the evaluation index, the influence of the main extrusion process parameters on the evaluation index was studied. The experimental results show that the outer diameter and wall thickness are significantly affected by screw speed, pulling speed and gas flow rate; extrusion process parameters have little influence on wall thickness uniformity and ovality within a certain range, which mainly depends on the processing accuracy and assembly accuracy of the extrusion die. However, excessively high screw speed and low gas flow rate have significant effects on ovality. Finally, according to the influence of extrusion process parameters on the evaluation index, a series of micro tubes that meet the design requirements are extruded and carved into vascular stent structures.
... PLA's ductility was increased by using only 1 % CNF combined with a plasticizer. Herrera et al. (2016) looked at PLA with cellulose and chitin nanocrystals and found that adding 1 wt. percent cellulose and chitin nanocrystals improved the mechanical properties of plasticised PLA. ...
The production of nanocellulose from cellulose-based biomaterials has increased research in nanotechnology due to their biocompatibility, biodegradability, renewability, and low toxicity. The physicochemical properties of nanocellulose produced from waste biomass have broad environmental, geotechnical, food packaging, and biomedical engineering applications. There is growing attention to advance research in producing nanocellulose based on its unique properties. Textile waste is a good source of cellulose for the development of nanocellulose. A comprehensive study on the most recent developments in the extraction of nanocellulose from textile wastes using the enzymatic assisted technique as a green functional biomaterial has rarely been subjected to extensive review. Thus, against this limitation, an extensive study on nanocellulose derived from textile wastes focusing on the enzymatic hydrolysis process, properties, and recent wide-range applications are the focus of this work. The review is concluded with their potential as novel bionanomaterials.
... Although much less studied than CNCs or CNFs, the aptitude of ChNCs to act as nucleating agent for PLLA has been demonstrated [22]. ...
In the present work, the nucleating aptitude for poly-L-(lactic acid) (PLLA) of several biobased nanoparticles (NPs) with different morphologies and surface properties, including cellulose nanofibrils with and without lignin (LCNFs and CNFs) as well as cellulose, chitin and starch nanocrystals (CNCs, ChNCs and SNCs), was investigated. A single melt-processing step using a small amount of poly(ethylene glycol) (PEG) as carrier for the NPs was adopted to prepare films with the same nanofiller content of 1 wt%. The nucleation efficiency was investigated by differential scanning calorimetry using Avrami's and Lauritzen–Hoffman's secondary nucleation theory. The crystallization half-time was found to change considerably according to the morphology and surface properties of the NPs, with the lowest time observed for CNFs and CNCs, followed by ChNCs, SNCs and LCNFs. Comparing the surface energy components of the different nucleating agents, it was found that the nanofiller with the highest γp had the lowest t1/2 and demonstrated the most effective nucleating aptitude. The evolution of the melt rheological properties of the different compositions, and the mechanical and optical properties of the films with and without a short annealing treatment were also studied.
... The CNCs were in water suspension, with a solid content of 10.3 wt%, having a crystallinity approx. 80% [28] and charge density of À0.36 mEq.g À1 . The cationic CNCs were prepared as described in our previous work from birch pulp, have a crystallinity approx. ...
Membrane filtration and affinity-based adsorption are the two most used strategies in separation technologies. Here, µm-thick multifunctional and sustainable composite membranes of electrospun cellulose acetate (CA) infused with functionalized, anionic, and cationic cellulose nanocrystals (CNCs) with enhanced wettability, tensile strength, and excellent retention capacities were designed. CNCs could uniformly impregnate into the three-dimensional CA network to effectively improve its properties. The impregnation of cationic CNCs at 0.5 wt% concentration drastically increased the tensile strength (1669%) while maintaining high permeation flux of 9400 Lm⁻²h⁻¹ which is remarkable with cellulose modified electrospun membranes. The membranes infused with anionic CNCs exhibited a particle retention efficiency of 96% for 500 nm and 77% for 100 nm latex beads whilst the cationic CNC membranes exhibited a combined particle retention strategy using selectivity and size exclusion with a retention of >81% with 100 nm latex beads and 80% with ∼50 nm silver nanoparticles. We envision that the developed multifunctional membranes can be utilized for affinity-based and size-exclusion filtration to selectively trap bacteria or substances of biological significance.
... The neat PHB sheet in Figure 9a is homogeneous, whereas multiple particles are observed in both nanocomposites in Figure 9b,c, and the number of particles increases with the ChNC concentration. The ChNC material structure is very similar (a flake-like structure), as previously reported by Herrera et al. [58]. Therefore, these particles are most likely ChNCs agglomerates that were not dispersed at the nanoscale. ...
This study focuses on the use of pilot-scale produced polyhydroxy butyrate (PHB) biopolymer and chitin nanocrystals (ChNCs) in two different concentrated (1 and 5 wt.%) nanocomposites. The nanocomposites were compounded using a twin-screw extruder and calendered into sheets. The crystallization was studied using polarized optical microscopy and differential scanning calorimetry, the thermal properties were studied using thermogravimetric analysis, the viscosity was studied using a shear rheometer, the mechanical properties were studied using conventional tensile testing, and the morphology of the prepared material was studied using optical microscopy and scanning electron microscopy. The results showed that the addition of ChNCs significantly affected the crystallization of PHB, resulting in slower crystallization, lower overall crystallinity, and smaller crystal size. Furthermore, the addition of ChNCs resulted in increased viscosity in the final formulations. The calendering process resulted in slightly aligned sheets and the nanocomposites with 5 wt.% ChNCs evaluated along the machine direction showed the highest mechanical properties, the strength increased from 24 to 33 MPa, while the transversal direction with lower initial strength at 14 MPa was improved to 21 MPa.
... Some of the other applications are as automotive components, biomedical and insulation foam. It has a low degree of crystallisation and is susceptible to ageing at ambient temperature [117]. PLAs have been promoted as a greener substitute to polyolefins, but their lifecycle requires considerable amount of energy resulting in a lower carbon balance compared to polyolefins [102]. ...
The ever rising problems associated with petroleum derived fuels and chemicals have contributed to establish an alternative platform for generation of bio-based fuels and value added materials. In this point of view, cellulosic biorefinery has attracted considerable and growing attention to develop a vast variety of platform chemicals, biofuels and other biomaterials. Biofuels are gifted products from biorefinery that can be implemented globally to reduce the gasoline consumption and related greenhouse gas emissions. Because of their abundant availability, different types of lignocellulosic raw materials can effectively be utilized to generate a wide range of value-added products in a cost effective manner. Future challenges exist is optimising the cost of biorefinery processing. To overcome the limitations of biorefinery, novel technologies should be integrated to produce more high quality platform chemicals and other biomaterials. This article provides an insight to the production of different value added products from cellulosic biorefinery including its commercial challenges and economic feasibility.
... Differently, uniform CN dispersion within hydrophobic polymers, including biodegradable polyesters, like polylactic acid (PLA), in the molten state is difficult to achieve due to the inefficient molecular interactions, which lead to CN segregation and ultimately result in mechanical embrittlement [18]. In the last years, some studies have investigated CN/PLA nanocomposites, pointing out the beneficial role of compatibilizing agents, in particular poly(ethylene glycol) (PEG) and high molecular weight poly(ethylene oxide) (PEO) [19][20][21][22]. According to the premixing methods, CN/PLA nanocomposites have shown ameliorated mechanical properties, as well as improved anti-inflammatory and antimicrobial activity [23][24][25]. ...
Chitin nanofibrils (CNs) are an emerging bio-based nanomaterial. Due to nanometric size and high crystallinity, CNs lose the allergenic features of chitin and interestingly acquire anti-inflammatory activity. Here we investigate the possible advantageous use of CNs in tympanic membrane (TM) scaffolds, as they are usually implanted inside highly inflamed tissue environment due to underlying infectious pathologies. In this study, the applications of CNs in TM scaffolds were twofold. A nanocomposite was used, consisting of poly (ethylene oxide terephthalate)/(polybutylene terephthalate) (PEOT/PBT) copolymer loaded with CN/polyethylene glycol (PEG) pre-composite at 50/50 (w/w %) weight ratio, and electrospun into fiber scaffolds, which were coated by CNs from crustacean or fungal sources via electrospray. The degradation behavior of the scaffolds was investigated during 4 months at 37 °C in an otitis-simulating fluid. In vitro tests were performed using cell types to mimic the eardrum, i.e., human mesenchymal stem cells (hMSCs) for connective, and human dermal keratinocytes (HaCaT cells) for epithelial tissues. HMSCs were able to colonize the scaffolds and produce collagen type I. The inflammatory response of HaCaT cells in contact with the CN-coated scaffolds was investigated, revealing a marked downregulation of the pro-inflammatory cytokines. CN-coated PEOT/PBT/(CN/PEG 50:50) scaffolds showed a significant indirect antimicrobial activity.
Petroleum-derived packaging materials commonly lack biodegradability, posing significant environmental and health concerns. As a result, there is a growing focus among researchers on developing innovative, biodegradable, and safe food packaging films. In this study, films based on a natural biopolymer gellan gum (GG) reinforced with chitosan nanoparticles (CNPs) were developed using a solvent casting technique. The CNPs, with an average size of 34 nm, were synthesized via ionic gelation using sodium tripolyphosphate (TPP) as a gelating agent. The structure–property relationship of these bionanocomposite films was examined by analyzing their microstructure, thermal behavior, mechanical strength, UV resistance, optical properties, and water barrier characteristics. Compared to pure GG films, the composite films exhibited improved thermal stability, mechanical strength, and barrier properties against water and UV radiation. Increasing the CNPs loading from 0 to 9 wt% resulted in decreased transparency and optical band gaps, from 87.73 to 42.15 and from 5.6048 to 5.3706 eV, respectively. Notably, GG films loaded with 1 wt% CNPs demonstrated the highest tensile strength and thermal stability. Moreover, water absorption, water vapor permeability, and equilibrium moisture content decreased as CNPs loading increased from 0 to 9 wt%. These findings suggest the potential of GG/CNP bionanocomposite films as sustainable packaging materials for the food industry.
Bio‐based waste from households and industries is a big problem for the world, however, turning it into valuable composite materials can offer a promising approach to deal with it. It involves the conversion of waste from different bio‐based sources such as cellulose waste from farming and forestry leftovers, chitin waste from seafood and mushrooms, and keratin waste from hair, nails, and feathers into natural fibers. These fibers are then effectively mixed with other materials to create composite materials having unique properties, such as high strength and stiffness, good thermal and electrical conductivity, and better barrier properties. Developing these materials is not just good for the environment because it reduces landfill waste and the reliance on non‐renewable resources, but it can also make economic sense for producers. In this review, the basic compounds of natural fibers and the development of composite materials from them are explored and discussed in detail. Furthermore, their chemical and mechanical properties are discussed and summarized. In the final section, a brief overview of the challenges and the future research needed in this fast‐evolving field is given.
Polylactic acid (PLA) is a widely recognized sustainable alternative to conventional petroleum-based plastics for food packaging. To enhance its properties that currently trail those of conventional packaging materials, the addition of chitin nanocrystals (ChNC) has been considered. This has led, amongst others to stronger materials. For their ultimate application, it is also important to evaluate these materials in terms of food safety and environmental impact. In this study, we investigate the biodegradation of and migration from ChNC/PLA nanocomposites. The solution casting method was used to prepare PLA and ChNC/PLA nanocomposites, and overall migration (OM) tests were carried out with food simulants (10 % ethanol and isooctane). Additionally, we evaluated the biodegradability (crude chitin powder, ChNC, and nanocomposites) based on ISO norm no 14851:2019. The OM tests demonstrated that the migration levels from ChNC-PLA composites were below the allowed limit (60 mg/kg). The biodegradability of ChNC was comparable to that of crude chitin powder and microcrystalline cellulose, and interestingly, when incorporated in PLA films did not impact the biodegradability of PLA in a negative way. In summary, the migration and biodegradation of ChNC/PLA nanocomposites exhibit encouraging potential for their future utilization in food packaging.
Porous sandwich structure (foam) is a prerequisite in the field of construction, aerospace, and automotive sector, due to its energy-absorbing characteristics and sound-absorbing properties. The porous structure was previously difficult to manufacture, but is now feasible, thanks to additive manufacturing process or 3D printing technology. Complex shapes and structure can be produced by the novel production technique such as fused deposition modeling (FDM) known as three-dimensional printing. These studies emphasized the importance of porous structure, particularly foams, for the construction industry, automobile sector and aerospace industries for its high performance, light-weightiness, shock absorbing properties, etc. In this article, we convey the different processes as well as their main features which can be used to fabricate the foam structure having various topologies such as open cells and closed cells, with different fundamental designs and materials such as polymer, ceramic, and metals, with a particular emphasis on metallic and polymeric materials. In this regard, a comparison between the traditional foam manufacturing techniques and additively 3D printed foam structure was made, to study the various complexities associated with such method of fabrication and attempts to integrate such study have been divided into four categories: (1) architected porous structures, (2) conventional and 3D methods of polymeric and metallic foam construction, (3) foam lattice design and characterization, and lastly (4) foam properties and applications.
Using polysaccharide nanocrystals such as chitin nanocrystals (ChNCs) as nanofiller for biodegradable aliphatic polymers is an attractive way of developing all-degradable nanocomposites. Crystallization study is vital for well regulating final performance of these type polymeric nanocomposites. In this work, ChNCs were incorporated with the poly(l-lactide)/poly(d-lactide) blends and as-obtained nanocomposites were used as target samples for the study. The results showed that ChNCs acted as nucleating agent, promoting the formation of stereocomplex (SC) crystallites and accelerating overall crystallization kinetics as a result. Therefore, the nanocomposites possessed higher SC crystallization temperatures and lower apparent activation energy as compared to the blend. However, the formation of homocrystallites (HC) was dominated by nucleation effect of SC crystallites and accordingly, the fraction of SC crystallites reduced more or less in the presence of ChNCs, despite the nanocomposites possessed higher rate of HC crystallization. This study also provided valuable information on accessing more applications of ChNCs to be used as SC nucleator for polylactide.
Chitin-based nanoparticles are polysaccharide materials that can be produced from a waste stream of the seafood industry: crustacean shells. These nanoparticles have received exponentially growing attention, especially in the field of medicine and agriculture owing to their renewable origin, biodegradability, facile modification, and functionality adjustment. Due to their exceptional mechanical strength and high surface area, chitin-based nanoparticles are ideal candidates for reinforcing biodegradable plastics to ultimately replace traditional plastics. This review discusses the preparation methods for chitin-based nanoparticles and their applications. Special focus is on biodegradable plastics for food packaging making use of the features that can be created by the chitin-based nanoparticles.
Natural fiber-reinforced polymer composites (NFPCs) have gained limelight in many applications during the recent years, owing to their availability, as well as superior mechanical characteristics, cost-effectiveness, biodegradability, and lightweight. A comprehensive understanding of the manufacturing methods, proeprties and characteristics of natural fibers pave way for begetting a wide spectrum of applications for the NFPCs in automobile, aerospace, electronics, and other engineering fields. The current review article is about natural fiber-reinforced composites, the commonly used fabrication methods, including fiber pre-treatments, and numerous intermediate steps added to achieve improved bonding, processability of these composites, their properties and application prospects. Various state-of-the-art methods like additive manufacturing, vaccum bag molding, and autoclave has also been discussed. The mechanical properties obtained through various fiber reinforcements in accordance with process parameters has a substantial impact in the industrial applications of NFPCs. The tribological applications of NFPCs are becoming increasingly important in order to deal with the mechanical and chemical wear and tear during their service life in contact applications. Flammability behavior and biodegradability assessment of NFPCs are important for high-temperature and outdoor environmental applications of these materials. The review also includes a comprehensive discussion about the trending applications and future prospects for NFPCs.
Blending poly (lactic acid) (PLA) with cellulose nanocrystals (CNCs) to fabricate nanocomposites is a valuable strategy to improve the properties of PLA without sacrificing its biodegradability. However, the nucleation and reinforcing mechanisms of CNCs for semi-crystalline PLA matrix are still elusive in melt-processed PLA/CNC nanocomposites. Herein, poly (vinyl acetate) (PVAc) chains were grafted onto the surface of CNCs via an efficient radical polymerization in an aqueous medium, making CNCs suitable for conventional melting processing techniques. It is found that the dispersion state of CNCs in the PLA matrix and the interface interaction between PLA and CNCs can be tailored by varying the PVAc grafting density. Further studies show that well-dispersed CNCs play a positive role in reinforcing PLA. But unexpectedly, the nucleation effect is suppressed even though the homogeneous dispersion of CNCs is achieved with higher PVAc grafting density because the rich PVAc chains at the interface dilute the PLA chains, thus hindering the nucleation and spherulite growth of PLA. This research sheds light on the nucleation and reinforcing mechanisms of polymer grafted CNCs, and will provide theoretical guidance for the industrialization of high-performance bio-based nanocomposites.
In the context of today’s needs for environmental sustainability, it is important to develop new materials that are based on renewable resources and biodegrade at the end of their life. Bioplastics reinforced by agricultural waste have the potential to cause a revolution in many industrial applications. This paper reports the physical properties and crystallization kinetics of biocomposite films based on poly(L-lactic acid) (PLLA) and 10 wt.% of spent coffee grounds (SCG). To enhance adhesion between the PLLA matrix and SCG particles, a compatibilizing agent based on itaconic anhydride (IA)-grafted PLLA (PLLA-g-IA) was prepared by reactive extrusion using dicumyl peroxide (DCP). Furthermore, due to the intended application of the film in the packaging industry, the organic plasticizer acetyl tributyl citrate (ATBC) is used to improve processing and increase ductility. The crystallization behavior and thermal properties were observed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Crystallinity degree increased from 3,5 (neat PLLA) up to 48% (PLLA/PLLA-g-IA/ATBC/SCG) at the highest cooling rate. The physical properties were evaluated by tensile testing and dynamic mechanical analysis (DMA). The combination of the compatibilizer, SCG, and ATBC led to a synergistic effect that positively influenced the supramolecular structure, internal damping, and overall ductility of the composite films.
Poly(lactic acid)-poly(hydroxybutyrate) (PLA-PHB)-based nanocomposite films were prepared with bio-based additives (CNCs and ChNCs) and oligomer lactic acid (OLA) compatibilizer using extrusion and then blown to films at pilot scale. The aim was to identify suitable material formulations and nanocomposite production processes for film production at a larger scale targeting food packaging applications. The film-blowing process for both the PLA-PHB blend and CNC-nanocomposite was unstable and led to non-homogeneous films with wrinkles and creases, while the blowing of the ChNC-nanocomposite was stable and resulted in a smooth and homogeneous film. The optical microscopy of the blown nanocomposite films indicated well-dispersed chitin nanocrystals while the cellulose crystals were agglomerated to micrometer-size particles. The addition of the ChNCs also resulted in the improved mechanical performance of the PLA-PHB blend due to well-dispersed crystals in the nanoscale as well as the interaction between biopolymers and the chitin nanocrystals. The strength increased from 27 MPa to 37 MPa compared to the PLA-PHB blend and showed almost 36 times higher elongation at break resulting in 10 times tougher material. Finally, the nanocomposite film with ChNCs showed improved oxygen barrier performance as well as faster degradation, indicating its potential exploitation for packaging applications.
Food industry has been criticized for use of non-biodegradable, non-eco-friendly, and toxic production methods, materials and treatment strategies. The main concern is plastic pollution in the food industry. Food grade plastics like polyethylene terephthalate, polypropylene, high- and low-density polyethylene, and polycarbonate are FDA approved for use with food contactable materials; they are very widely used polymers due to their ease in manufacture, performance, property modulation, and easy disposal. However, versatile as they may be, they are non-biodegradable which leads to their accumulation in the ecosystem resulting in serious ecological and health issues. A better alternative to such materials is the use of nature derived polymers having characteristics similar to conventional plastics. This creates an arena for edible and biodegradable biopolymers in food production and packaging. These polymers can be classified as agricultural, marine, and animal based on their origin. Such polymers have applicability as coating materials, films, and packaging materials or preservative and protective materials. The ability to form films of these polymers is used in food packaging and delivery of bioactive substances such as drugs and nutraceuticals. Reinforcing polymer with micro- or nano-fillers and introduction of nano-technology in the food sector has shown prospective use in food processing, packaging, and food biosensors for pathogen detection, while 3D printing has given rise to novel works that provide food based on customized nutrition and requirements providing enhancement in overall standard of living. This review elaborates and compiles the aforementioned research objectives that include the role of biopolymers in the food industry.
In this work, a series of hydroxy-terminated oxalamide derivatives containing different aliphatic spacer lengths (OXA-n, HO-(CH 2 ) n -NHCOCONH-(CH 2 ) n -OH , n=2, 4, 6) were designed as initiators for L-lactide ring-opening polymerization and then...
Polylactic acid (PLA) is a biopolymer that has potential for use in food packaging applications; however, its low crystallinity and poor gas barrier properties limit its use. This study aimed to increase the understanding of the structure property relation of biopolymer blends and their nanocomposites. The crystallinity of the final materials and their effect on barrier properties was studied. Two strategies were performed: first, different concentrations of poly(hydroxybutyrate) (PHB; 10, 25, and 50 wt %) were compounded with PLA to facilitate the PHB spherulite development, and then, for further increase of the overall crystallinity, glycerol triacetate (GTA) functionalized chitin nanocrystals (ChNCs) were added. The PLA:PHB blend with 25 wt % PHB showed the formation of many very small PHB spherulites with the highest PHB crystallinity among the examined compositions and was selected as the matrix for the ChNC nanocomposites. Then, ChNCs with different concentrations (0.5, 1, and 2 wt %) were added to the 75:25 PLA:PHB blend using the liquid-assisted extrusion process in the presence of GTA. The addition of the ChNCs resulted in an improvement in the crystallization rate and degree of PHB crystallinity as well as mechanical properties. The nanocomposite with the highest crystallinity resulted in greatly decreased oxygen (O) and carbon dioxide (CO2) permeability and increased the overall mechanical properties compared to the blend with GTA. This study shows that the addition ChNCs in PLA:PHB can be a possible way to reach suitable gas barrier properties for food packaging films.
About 1/3rd of produced food goes to waste, and amongst others, advanced packaging concepts need to be developed to prevent this from happening. Here, we target the antioxidative functionality of food packaging to thus address food oxidation without the need for the addition of antioxidants to the food product, which is not desirable from a consumer point of view. Chitin nanocrystals (ChNC) have been shown to be promising bio-fillers for improving the mechanical strength of biodegradable plastics, but their potential as active components in plastic films is rather unexplored. In the current study, we investigate the antioxidant activity of chitin nanocrystals as such and as part of polylactic acid (PLA) films. This investigation was conducted using DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging activity. Chitin nanocrystals produced via acid hydrolysis showed five times higher activity compared to crude chitin powder. When using these crystals as part of a polylactic acid film (either inside or on top), in both scenarios, antioxidant activity was found, but the effect was considerably greater when the particles were at the surface of the film. This is an important proof of the principle that it is possible to create biodegradable plastics with additional functionality through the addition of ChNC.
The environmental pollution concerns provoked by non‐biodegradable packaging materials along with guaranteed safety demand of the consumer, food products of high quality, ready‐to‐eat concept, and extended shelf life have played an important role to develop eco‐friendly food packaging materials using polymer nanocomposites. In addition, antioxidant and antimicrobial properties of these materials are very related to food packaging applications. Over the last decades, polymer nanocomposite materials alternative to non‐biodegradable plastic packaging materials open an opportunity in terms of biodegradability, biocompatibility, non‐toxicity, high performance, and cost‐effective nanocomposite materials. In this chapter, an overview of the application of polymer nanocomposites used most widely in food packaging along with the properties of these materials is reviewed.
The objective of this work was to develop biodegradable films by mixing gelatin/carboxymethylcellulose (FG/CMC) and gelatin/polyvinyl alcohol (FG/PVOH) and to evaluate the effect of adding these polymers on the properties of fish gelatin films. The films FG/CMC and FG/PVOH were produced in the proportions 90/10, 80/20 and 70/30 and characterized their physical, chemical and functional properties. The addition of CMC and PVOH improved the mechanical strength, barrier property and water solubility of gelatin films. FG/CMC films showed greater tensile strength and greater solubility than FG/PVOH. The maximum concentration of CMC promoted the highest mechanical resistance, while the highest PVOH content produced the film with the lowest solubility. The proposed mixing systems proved to be adequate to improve the properties of fish gelatin films, with potential for application in the packaging sector.
In nature, chitin is organized in hierarchical structures composed of nanoscale building blocks that show outstanding mechanical and optical properties attractive for nanomaterial design. For applications that benefit from a maximized interface such as nanocomposites and Pickering emulsions, individualized chitin nanocrystals (ChNCs) are of interest. However, when extracted in water suspension, their individualization is affected by ChNC self-assembly, requiring a large amount of water (above 90%) for ChNC transport and stock, which limits their widespread use. To master their individualization upon drying and after regeneration, we herein report a waterborne topochemical one-pot acid hydrolysis/Fischer esterification to extract ChNCs from chitin and simultaneously decorate their surface with lactate or butyrate moieties. Controlled reaction conditions were designed to obtain nanocrystals of a comparable aspect ratio of about 30 and a degree of modification of about 30% of the ChNC surface, under the rationale to assess the only effect of the topochemistry on ChNC supramolecular organization. The rheological analysis coupled with polarized light imaging shows how the nematic structuring is hindered by both surface ester moieties. The increased viscosity and elasticity of the modified ChNC colloids indicate a gel-like phase, where typical ChNC clusters of liquid crystalline phases are disrupted. Pickering emulsions have been prepared from lyophilized nanocrystals as a proof of concept. Our results demonstrate that only the emulsions stabilized by the modified ChNCs have excellent stability over time, highlighting that their individualization can be regenerated from the dry state.
Nanocellulose has emerged as one of the most significant green materials of the modern era over the last few years. Nanocellulose with nanometer widths are nature-based materials with unique and potentially valuable characteristics. These new nanocelluloses open up to natural polymer cellulose the strongly developing range of sustainable materials, nanocomposites, and medical and life sciences devices. The growing interest in nanocellulose materials is a result of their excellent properties, e.g., abundance, good mechanical properties, high aspect ratio, biocompatible, and renewable materials. Nanocellulose is getting prominence in some applications; biomedical engineering, material science, pharmaceuticals, cosmetics, foods, and packaging. This chapter discusses the nanocellulose preparation, characterization, functionalization, important fundamental aspects, and potential applications.
Walnut kernels represent no more than 50–60% of the total weight of the fruit, so the sum of walnut shells generated every year is immense. Nonetheless, these shells could be further valorised for the extraction of their main constituents following a biorefinery scheme. Hence, the objective of this work was an integral valorisation of walnut shells, which involved a sequential organosolv delignification (200 °C, 90 min, 70/30 v/v EtOH/H2O, LSR 6:1) and several posterior non-isothermal hydrothermal treatments (180, 195 and 210 °C, LSR 8:1). Moreover, the spent solids after the aforementioned treatments were evaluated as possible sources of cellulose nanocrystals. The results showed that the sequential organosolv delignifications presented relative lignin yields up to 60%, which leaded to lignins that just differed on their molecular weight distributions. The hydrothermal treatments were efficient for the removal of still present hemicelluloses (14.7–71.8%), and permitted a successful cellulose nanocrystal obtaining whereas the spent solid from the delignification stages did not. Thus, this study presented an innovative strategy for the integral valorisation of walnut shells.
Book Chapter_Mechanical Properties of PLA/Cellulose Composites
Extrusion can be considered not only as an effective technology for processing agricultural raw materials into feed and food products, but also as a thermo-mechanical method for modification of the chemical properties of biopolymers. Carbohydrates are the most represented class of organic compounds in raw materials processed by the agro-industrial complex. The assessment of the influence of the processing factor on the final physicochemical and technological properties of various types of carbohydrates included in the chemical composition of raw materials or used as mono-ingredients is an actual task for the food industry. The review considers the issues of extrusion modification of starch in terms of the difference in the properties of amylose and amylopectin as well as the presence of lipids and organic acids in the reaction system. Processes of macromolecular degradation, gelatinization, esterification and the formation of new chemical bonds in dependence on the conditions of extrusion and the composition of mixtures are discussed. The results of studies of the influence of extrusion cooking on the changes in the physicochemical properties of non-starchy polysaccharides, cellulose, araboxylans, inulin, pectin, chitosan, and gums of various origins are presented. It has been shown that extrusion and varying of its operating regimes can significantly affect the nutritional value of extrudates including changing the glycemic index, inactivating antinutritional factors, or increasing their content in extrudates.
In this study, magnetic polymer nanocomposite comprising of polylactide, liquified natural rubber and different loadings of NiZn ferrite nanoparticles was prepared using ultrasonication-assisted melt compounding method. The fabrication process has involved the ultrasonication treatment of the nanocomposite for 1 and 2 hours. The influence of ultrasonication on the dispersion degree of the nanoparticles and its reflection on the behaviour of PLA/LNR/NiZn nanocomposites was evaluated. The tensile properties showed an improvement when the nanocomposites were treated for 1 and 2 h, with optimum values obtained at 4 wt% of nanofiller loading. Similarly, the optimum values of Tg, Tc and Tm obtained from DSC analysis was found for sample ultrasonically treated for 1 h with highest crystallinity increment of 55.16% as compared to untreated sample of the same nanofiller loading. Moreover, the statistical analysis based on TGA and SEM results revealed that the nanocomposite treated ultrasonically for 1 h had better nanofiller dispersion as compared to its counterparts with 0 and 2 h treatment periods. These findings, as confirmed by magnetic testing, formed solid evidence that the optimal behaviour of PLA/LNR/NiZn nanocomposites was attained with ultrasonication treatment of 1 h with potential applications in areas served by soft magnetic materials.
Analyzing and finding solution for the natural deformities from the natural sources is the need of the hour for the scientific community. One such natural source that is the target for the researchers is chitin. This is obtained from the crustaceans, invertebrates, insects, etc. Chitin on deacetylation produced an important derivative chitosan. Both chitin and chitosan exhibits remarkable properties such as nontoxic, biocompatible, biodegradable, antimicrobial, etc. In spite of this, there are some limitations. To remove these limitations, they are mostly combined with organic or inorganic fillers to enhance the properties. Chitosan readily undergoes modification or combination with other substances than chitin to form different nanocomposites which can be applied for variety of applications from wound healing to biosensors. Thus, chitin/chitosan forms a versatile polymer in the hands of researchers to be tailor-made into a desired function by combining with suitable fillers.
The mechanical and thermal properties of semicrystalline (sc) and amorphous (a) poly(lactic acid), PLA, and poly(butylene adipate-co-terephthalate), PBAT, and their nanocomposites containing 1 and 3 wt% CNCs, prepared through solvent casting methods using one (N,N-dimethylformamide [DMF]) or two (dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF)) solvents were analyzed. Differential scanning calorimetry (DSC) showed that the total amount of crystals of the scPLA/CNC nanocomposites increased, whereas it decreased in the PBAT/CNC systems. In both cases, the crystallization temperature increased with CNC content. In tensile experiments, the Young modulus and yield strength of all nanocomposites were found to increase by incorporating CNCs, more significantly for the samples prepared using one solvent. The elongation at break of both PLA nanocomposites increased when prepared via one solvent, while it decreased for the two solvent methods as well as for PBAT nanocomposites prepared by both methods. The impact properties of the samples prepared by the two solvent methods decreased. In contrast, for the one solvent method, incorporating 3 wt% CNCs improved the impact properties by 32% and 9% in scPLA and aPLA, respectively, but decreased by 4% in PBAT nanocomposites. Also, in dynamic mechanical thermal analysis (DMA) the storage modulus of scPLA and PBAT/CNC systems increased significantly, especially in the rubbery region (5–85 MPa and 105–155 MPa, respectively). Using a percolation model, the strength of the percolating CNC was found to be dependent on temperature and affected by traces of solvent mostly in the scPLA nanocomposites.
This study details the fabrication and foaming of melt-blended polylactide (PLA) and chitin composites. The chitin used for compounding was as-received, as chitin nanowhiskers and as chitin nanowhiskers with a compatibilizing agent. The chitin nanowhiskers were produced by an acid-hydrolysis technique and their morphology was examined with transmission electron microscopy. The composite morphology was characterized with scanning electron microscopy and was related to the observed thermal, rheological, and mechanical behaviors of the composites. Chitin was found to decrease the thermal stability of the composites. Addition of chitin was also found to reduce the viscosity of the composites, which is believed to be because of the hydrolysis of PLA during melt blending of chitin in suspension. The stiffness of the composites was found to increase with increasing chitin content while the strength was found to decrease. Porous PLA—chitin composites were produced by a two-step batch-foaming technique, and the expansion behavior was correlated with the visco-elastic observations. The statistical significance of chitin type and composition dependence on the mechanical properties and foam morphologies were evaluated.
A novel composite material containing 2 wt% of cellulose nanofibers well dispersed in PLA matrix, both materials being biodegradable, was prepared and studied. Biodegradable composites with 2 and 20 wt% of cellulose fibers with standard diameters were also obtained and examined for comparison. The nanocomposite exhibited markedly higher storage modulus as compared to neat PLA and the composite with the same content of cellulose standard fibers. In addition, yield strength of the nanocomposite was improved in comparison with neat PLA, especially at elevated temperature of 45 °C, at which it was higher by 50%. No negative effect of standard fibers and nanofibers on molar mass of PLA matrix was observed. Moreover, the composite materials, including the nanocomposite, did not show weight loss up to 300 °C.
Compounding of nanocomposites using twin-screw extrusion is a process whereby nanocellulosic materials are mixed with a polymer melt. The process can be scaled up to produce cellulose nanocomposites for industrial-scale use. This process method may also allow nanocomposites to be easily injection molded or compression molded. Our aim has been to develop a cellulose nanocomposite processing method using two specific processing routes: (i) liquid feeding of the nanomaterials into the extruder and (ii) preparation of a master batch which is diluted to the desired concentration during a compounding process. The prepared nanocomposites have usually been compression molded to sheets or injection molded to samples. The studies on nanocomposite structure and properties have enabled optimization of the process as well as improved performance. Depending on the extent of separation of cellulose nanocrystals or nanofibers in the liquid medium and the interaction of nanocelluloses with the polymer matrix, different types of nanocomposites have been obtained: composites with aggregated nanocelluloses, partially dispersed nanocellulose, or fully dispersed nanocelluloses. Ultimately, the objective of these studies has been to produce nanocomposites with good mechanical properties, thermal stability, and transparency and at the same time develop an energy-efficient and cost-effective processing methodology.
Development of packaging materials based on bio-nanocomposites for food and other food contact surfaces is expected to grow in the next decade with the current focus on exploring alternatives to petroleum and emphasis on reducing environmental impact. In this context, this chapter reviews recent advancements related to biodegradable polymer nanocomposites. The chapter discusses various techniques that have been used for developing cost-effective bio-based packaging materials with optimum material properties. The biodegradable polymers addressed in this chapter include polylactide (PLA), poly (hydroxyalkanoate)s (PHA) such as poly(ß-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and natural renewable polymers such as starch, and proteins. Special emphasis is given to the advantages of using clays as nanofiller, in order to improve the mechanical and the barrier properties of these biopolymeric matrices. New natural nanofillers such as cellulose and chitin nanofibers or starch nanocrystals are also addressed.
This paper describes the thermal and mechanical properties of nanocomposites based on polylactic acid (PLA) and microfibrillated cellulose (MFC). The primary objective of this study was to improve the storage modulus of PLA at a high temperature. MFC and PLA were mixed in an organic solvent with various fiber contents up to 20 wt%, followed by drying, kneading and hot pressing into sheets. The nanocomposites were prepared in two different states, fully amorphous and crystallized. Differential scanning calorimetry (DSC) measurements revealed that the presence of MFC accelerates the crystallization of PLA. The tensile modulus and strength of neat PLA were improved with an increase of MFC content in both amorphous and crystallized states. The addition of 20 wt% of MFC in PLA improved the storage modulus of crystallized PLA at a high temperature (120 °C) from 293 MPa to 1034 MPa.
An empirical method for determining the crystallinity of native cellulose was studied with an x-ray diffractometer using the focusing and transmission techniques. The influence of fluctuations in the primary radiation and in the counting and recording processes have been determined. The intensity of the 002 interference and the amor phous scatter at 2θ = 18° was measured. The percent crystalline material in the total cellulose was expressed by an x-ray "crystallinity index." This was done for cotton cellulose decrystallized with aqueous solutions containing from 70% to nominally 100% ethylamine. The x-ray "crystallinity index" was correlated with acid hydrolysis crys tallinity, moisture regain, density, leveling-off degree of polymerization values, and infrared absorbance values for each sample. The results indicate that the crystallinity index is a time-saving empirical measure of relative crystallinity. The precision of the crystallinity index in terms of the several crystallinity criteria is given. Based on over 40 samples for which acid hydrolysis crystallinity values were available, the standard error was 6.5%.
Nanocomposite materials were obtained from a colloidal suspension of high aspect ratio P chitin whiskers as the reinforcing phase and poly(caprolactone) as the matrix. The chitin whiskers, prepared by acid hydrolysis of Riftia tubes, consisted of slender parallelepiped rods with an aspect ratio close to 120. A procedure was optimized to prepare a latex of poly(caprolactone). After mixing and stirring the two aqueous suspensions, solid films were obtained by either freeze-drying and hot-pressing or casting and evaporating the preparations. An amorphous poly(styrene-co-butyl acrylate) latex was also used as a model matrix. The thermal and mechanical properties of the resulting films were evaluated, The reinforcing effect of chitin whiskers is discussed on the basis of different types of mechanical models, and it is concluded that these whiskers form a rigid network assumed to be governed by a percolation mechanism. The formation of this network allows the thermal stabilization of the material for temperatures higher than the melting temperature of the poly(caprolactone).
To improve the toughness of PLA, poly(lactic acid) (PLA)/organically modified rectorite (OREC) nanocomposites were prepared via the melt-extrusion method. A partially exfoliated and partially intercalated structure was confirmed by WAXD and TEM. The crystallization behaviors of neat PLA and nanocomposite were studied by POM and DSC, and it was found that OREC had a great effect on the overall crystallization rate and spherulitic texture of PLA. The presence of OREC could toughen PLA greatly. For example, when 1 wt.% OREC was added, the elongation at break of the nanocomposite was increased to 210%. The toughening mechanism was analyzed through the observation of the inner structure of the tensile test bar using SEM.
This review is devoted to the advances in the modification of the strength and toughness of semi-crystalline polymers. Past efforts to obtain ultra-strength polymeric fibers are discussed, including the role of entanglements. The role of crystal plasticity in achieving high toughness is addressed. Two possibilities of the modification of crystal plasticity are described: increase in the crystal thickness and a reduction in the number of mobile dislocations in polymer crystals. Cavitation during deformation arising from mechanical mismatch between differently oriented stacks of lamellae contributes to toughness by activation of other mechanisms of plastic deformation of a material and to the plastic response of a polymer. It is shown that internal cavitation, although augmenting the toughness, greatly reduces the strength of the material. Two examples of efficient toughening in multicomponent polypropylene systems connected with cavitation are described, and attempts to produce highly oriented materials with thickness larger than fibers are reported.
Nanocomposite materials obtained from chitin whiskers and polycaprolactone (PCL) were produced by evaporation, freeze drying and melt-compounding in a mini-extruder followed by hot pressing. Chitin whiskers were obtained from crab shell by removing the protein matrix that held them in the shell structure. The chitin whiskers obtained in this way were characterised with fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). The thermal, tensile and dynamic mechanical properties of the composites were also investigated. The thermal stability of the nanocomposites was higher than that of the pure PCL, as revealed by thermogravimetric analysis (TGA). The highest increase in Young's moduli was obtained for a chitin whisker content of 10 wt%. Higher chitin whisker contents resulted in a more brittle failure behaviour of the nanocomposites which was accompanied by a reduced tensile strength and elongation at break. Melt-compounded specimens showed improved mechanical properties compared with those processed by evaporation and freeze drying techniques.
A new type of microcrystalline polymer prepared by aggregation has been discussed. The effect of the parameters of the preparation process on the properties of microcrystalline chitosan in hydrogel and solid forms has been studied using also microscopy and spectroscopy. The product obtained according to the method discussed shows the average molecular weight within a range 2.2–5.0 X 105, WRVs ≈ 260–520%, WRVg ≈ 700–1000%, and CrI up to 95%.
The aim of this work has been to study the crystallization behavior of composites based on polylactic acid (PLA) and three different types of cellulose reinforcements, viz., microcrystalline cellulose (MCC), cellulose fibers (CFs), and wood flour (WF). The primary interest was to determine how the size, chemical composition, and the surface topography of cellulosic materials affect the crystallization of PLA. The studied composite materials were compounded using a twin-screw extruder and injection-molded to test samples. The content of cellulose reinforcements were 25% by weight. The MCC and WF were shown to have a better nucleating ability than CFs based on differential scanning calorimetry and optical microscopy studies. It is difficult to visualize that transcrystallization will occur during melting process and this process is influenced by the morphological and chemical characteristics of the reinforcement. Bulk crystallization seems to be mainly dependent on the processing temperature. The cold crystallization process was shown to improve the thermal stability and storage modulus of the composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 300–310, 2006
The important industrial problem of slow crystallization of poly(l-lactide) (PLLA) is addressed by the use of cellulose nanocrystals as biobased nucleation reagents. Cellulose nanocrystals (CNC) were prepared by acid hydrolysis of cotton and additionally functionalized by partial silylation through reactions with n-dodecyldimethylchlorosilane in toluene. Such silylated cellulose nanocrystals (SCNC) were dispersible in tetrahydrofuran and chloroform, and formed stable suspensions. Nanocomposite films of PLLA and CNC or SCNC were prepared by solution casting. The effects of surface silylation of cellulose nanocrystals on morphology, non-isothermal and isothermal crystallization behavior, and mechanical properties of these truly nanostructured composites were investigated. The unmodified CNC formed aggregates in the composites, whereas the SCNC were well-dispersed and individualized in PLLA. As a result, the tensile modulus and tensile strength of the PLLA/SCNC nanocomposite films were more than 20% higher than for pure PLLA with only 1 wt.% SCNC, due to crystallinity effects and fine dispersion.
The aim of this study was to develop cellulose nanofiber (CNF) reinforced polylactic acid (PLA) by twin screw extrusion. Nanocomposites were prepared by premixing a master batch with high concentration of CNFs in PLA and diluting to final concentrations (1, 3, 5 wt.%) during the extrusion. Morphology, mechanical and dynamic mechanical properties (DMA) were studied theoretically and experimentally to see how different CNF concentrations affected the composites’ properties. The tensile modulus and strength increased from 2.9 GPa to 3.6 GPa and from 58 MPa to 71 MPa, respectively, for nanocomposites with 5 wt.% CNF. The DMA results were also positive; the storage modulus increased for all nanocomposites compared to PLA; being more significant in the high temperature region (70 °C). The addition of nanofibers shifted the tan delta peak towards higher temperatures. The tan delta peak of the PLA shifted from 70 °C to 76 °C for composites with 5 wt.% CNF.
Polylactic acid (PLA) nanocomposites were prepared using cellulose nanowhiskers (CNW) as a reinforcing element in order to
asses the value of this filler to reduce the gas and vapour permeability of the biopolyester matrix. The nanocomposites were
prepared by incorporating 1, 2, 3 and 5 wt% of the CNW into the PLA matrix by a chloroform solution casting method. The morphology,
thermal and mechanical behaviour and permeability of the films were investigated. The CNW prepared by acid hydrolysis of highly
purified alpha cellulose microfibers, resulted in nanofibers of 60–160nm in length and of 10–20nm in thickness. The results
indicated that the nanofiller was well dispersed in the PLA matrix, did not impair the thermal stability of this but induced
the formation of some crystallinity, most likely transcrystallinity. CNW prepared by freeze drying exhibited in the nanocomposites
better morphology and properties than their solvent exchanged counterparts. Interestingly, the water permeability of nanocomposites
of PLA decreased with the addition of CNW prepared by freeze drying by up to 82% and the oxygen permeability by up to 90%.
Optimum barrier enhancement was found for composites containing loadings of CNW below 3 wt%. Typical modelling of barrier
and mechanical properties failed to describe the behaviour of the composites and appropriate discussion regarding this aspect
was also carried out. From the results, CNW exhibit novel significant potential in coatings, membranes and food agrobased
packaging applications.
KeywordsCellulose-Nanobiocomposites-Mass transport properties-PLA
The aim of this study was to produce biodegradable polylactic acid/cellulose whisker nanocomposites by compounding extrusion and investigate the possibility to use polyvinyl alcohol to improve the dispersion of whiskers in the matrix. Two feeding methods of polyvinyl alcohol and cellulose nanowhiskers were used and evaluated, dry-mixing with polylactic acid prior extrusion or pumping as suspension directly into the extruder. Various microscopic techniques, tensile testing, and dynamic mechanical thermal analysis were used to study the structure and properties of the nanocomposites. Due to immiscibility of the polymers, phase separation occurred with a continuous polylactic acid phase and a discontinuous polyvinyl alcohol phase. The whiskers were primarily located in the polyvinyl alcohol phase and only a negligible amount was located in the polylactic acid phase. This inadequate dispersion of whiskers in the polylactic acid phase was probably the reason why no improvements in thermal properties were seen for the nanocomposites. The relative small improvements in tensile modulus, tensile strength, and elongation to break for the nanocomposites also indicated that it was principally the polyvinyl alcohol phase that was reinforced with whiskers but not the polylactic acid phase.
Plasticization of semicrystalline poly(l-lactide) (PLA) with a new plasticizer – poly(propylene glycol) (PPG) is described. PLA was plasticized with PPG with nominal Mw of 425 g/mol (PPG4) and 1000 g/mol (PPG1) and crystallized. The plasticization decreased Tg, which was reflected in a lower yield stress and improved elongation at break. The crystallization in the blends was accompanied by a phase separation facilitated by an increase of plasticizer concentration in the amorphous phase and by annealing of blends at crystallization temperature. The ultimate properties of the blends with high plasticizer contents correlated with the acceleration of spherulite growth rate that reflected accumulation of plasticizer in front of growing spherulites causing weakness of interspherulitic boundaries. In PLA/PPG1 blends the phase separation was the most intense leading to the formation of PPG1 droplets, which facilitated plastic deformation of the blends that enabled to achieve the elongation at break of about 90–100% for 10 and 12.5 wt% PPG1 content in spite of relatively high Tg of PLA rich phase of the respective blends, 46.1–47.6 °C. Poly(ethylene glycol) (PEG), long known as a plasticizer for PLA, with nominal Mw of 600 g/mol, was also used to plasticize PLA for comparison.
Poly(lactic acid) (PLA) is an aliphatic polyester made up of lactic acid (2-hydroxy propionic acid) building blocks. It is also a biodegradable and compostable thermoplastic derived from renewable plant sources, such as starch and sugar. Historically, the uses of PLA have been mainly limited to biomedical areas due to its bioabsorbable characteristics. Over the past decade, the discovery of new polymerization routes which allow the economical production of high molecular weight PLA, along with the elevated environmental awareness of the general public, have resulted in an expanded use of PLA for consumer goods and packaging applications. Because PLA is compostable and derived from renewable sources, it has been considered as one of the solutions to alleviate solid waste disposal problems and to lessen the dependence on petroleum-based plastics for packaging materials. Although PLA can be processed on standard converting equipment with minimal modifications, its unique material properties must be taken into consideration in order to optimize the conversion of PLA to molded parts, films, foams, and fibers. In this article, structural, thermal, crystallization, and rheological properties of PLA are reviewed in relation to its converting processes. Specific process technologies discussed are extrusion, injection molding, injection stretch blow molding, casting, blown film, thermoforming, foaming, blending, fiber spinning, and compounding.
α-Chitin whisker-reinforced chitosan nanocomposite films were prepared by solution-casting technique. The α-chitin whiskers were prepared by acid hydrolysis of α-chitin from shrimp shells. The length of the as-prepared whiskers ranged between 150 and 800 nm, while the width ranged between 5 and 70 nm, with the average values being about 417 and 33 nm, respectively. The addition of α-chitin whiskers did not affect much the thermal stability and the apparent degree of crystallinity of the chitosan matrix. The tensile strength of α-chitin whisker-reinforced chitosan films increased from that of the pure chitosan film with initial increase in the whisker content to reach a maximum at the whisker content of 2.96 wt% and decreased gradually with further increase in the whisker content, while the percentage of elongation at break decreased from that of the pure chitosan with initial increase in the whisker content and leveled off when the whisker content was greater than or equal to 2.96 wt%. Both the addition of α-chitin whiskers and heat treatment helped improve water resistance, leading to decreased percentage of weight loss and percentage degree of swelling, of the nanocomposite films.
Cellulose whiskers separated from commercially available microcrystalline cellulose (MCC) and polylactic acid (PLA) were used to develop novel nanostructured biocomposites by compounding extrusion. MCC was treated with N,N-dimethylacetamide (DMAc) containing lithium chloride (LiCl) in order to swell the MCC and partly separate the cellulose whiskers. The suspension of whiskers was pumped into the polymer melt during the extrusion process. Different microscopy techniques, thermogravimetric analysis, X-ray diffraction and mechanical testing were used to study the structure and properties of the whiskers and composites. The results showed that DMAc/LiCl can be used as swelling/separation agent for MCC but seems to cause degradation of the composites at high temperature processing. The structure of composites was made up of partly separated nanowhiskers when PEG was used as processing aid. The mechanical properties of nanocomposites were improved and compared to reference material the elongation to break was increased about 800% for one material combination. The future studies will be focused on process optimization, dispersion of nanowhiskers and finding a more suitable pumping medium to avoid thermal degradation of the composite.
In this paper, different strategies to promote PLA crystallization were investigated with the objective of increasing the crystalline content under typical polymer processing conditions. The effect of heterogeneous nucleation was assessed by adding talc, sodium stearate and calcium lactate as potential nucleating agents. The PLA chain mobility was increased by adding up to 10 wt% acetyl triethyl citrate and polyethylene glycol as plasticizers. The crystallization kinetics were studied using DSC analysis under both isothermal and non-isothermal conditions. The isothermal data showed that talc is highly effective in nucleating the PLA in the 80-120 degrees C temperature range. In the non-isothermal DSC experiments, the crystallinity developed upon cooling was systematically studied at cooling rates of 10, 20, 40, and 80 degrees C/min. The non-isothermal data showed that the combination of nucleant and plasticizer is necessary to develop significant crystallinity at high cooling rates. The nucleated and/or plasticized PLA samples were injection molded and the effect of mold temperature on crystallinity was determined. It was possible to mold the PLA formulations using mold temperatures either below 40 degrees C or greater than 60 degrees C. At low temperature, the molded parts were nearly amorphous while at high mold temperatures, the PLA formulation with proper nucleation and plasticization was shown to achieve crystallinity levels up to 40%, close to the maximum crystalline content of the material. Tensile mechanical properties and temperature resistance of these amorphous and semi-crystalline materials were examined. Crown Copyright (c) 2007 Published by Elsevier Ltd. All rights reserved.
This study is aimed at developing and characterizing cross-linked bionanocomposites for membrane applications using chitosan as the matrix, chitin nanocrystals as the functional phase, and gluteraldehyde as the cross-linker. The nanocomposites' chemistry and morphology were examined by estimation of gel content, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and atomic force microscopy (AFM), whereby the occurrence of cross-linking and nanoscale dispersion of chitin in the matrix was confirmed. Besides, cross-linking and chitin whiskers content were both found to impact the water uptake mechanism. Cross-linking provided dimensional stability in acidic medium and significantly decreased the equilibrium water uptake. Incorporation of chitin nanocrystals provided increased permeation selectivity to chitosan in neutral and acidic medium.
The purpose of this study was to chemically modify the surface of chitin whiskers and to investigate the effect of the incorporation of these modified whiskers into a natural rubber (NR) matrix on the properties of the ensuing nanocomposite. Different chemical coupling agents were tested, namely, phenyl isocyanate (PI), alkenyl succinic anhydride (ASA) (Accosize 18 from American Cyanamid), and 3-isopropenyl-alpha,alpha'-dimethylbenzyl isocyanate (TMI). The extent of chemical modification was evaluated by Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and surface energy analysis. After chemical modification, nanocomposite films were obtained using a toluene natural rubber solution in which the whiskers were dispersed. Their mechanical properties were found to be inferior to those of unmodified chitin/NR composites presented in our previous study. In fact, even though there is an increase in filler-matrix interaction as a result of chemical modification of the chitin whiskers, this does not contribute to the improvement in the mechanical properties of the resulting nanocomposite. It is concluded that this loss of performance is due to the partial destruction of the three-dimensional network of chitin whiskers assumed to be present in the unmodified composites.
When used as fillers in polymer composites, the thermostability of cellulose crystals is important. Sulfate groups, introduced during hydrolysis with sulfuric acid, are suspected to diminish the thermostability. To elucidate the relationship between the hydrolysis conditions, the number of sulfate groups introduced, and the thermal degradation behavior of cellulose crystals, bacterial cellulose was hydrolyzed with sulfuric acid under different hydrolysis conditions. The number of sulfate groups in the crystals was determined by potentiometric titration. The thermal degradation behavior was investigated by thermogravimetric analysis. The sulfate group content increased with acid concentration, acid-to-cellulose ratio, and hydrolysis time. Even at low levels, the sulfate groups caused a significant decrease in degradation temperatures and an increase in char fraction confirming that the sulfate groups act as flame retardants. Profile analysis of the derivative thermogravimetric curves indicated thermal separation of the degradation reactions by the sulfate groups into low- and high-temperature processes. The Broido method was used to determine activation energies for the degradation processes. The activation energies were lower at larger amounts of sulfate groups suggesting a catalytic effect on the degradation reactions. For high thermostability in the crystals, low acid concentrations, small acid-to-cellulose ratios, and short hydrolysis times should be used.
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