The degradation of fluoroelastomers (FKM) based on different monomers, additives and curing systems was studied after exposure to rapeseed biodiesel at 100 °C and different oxygen partial pressures. The sorption of fuel in the carbon black-filled FKM terpolymer was promoted by the fuel-driven cavitation in the rubber. The bisphenol-cured rubbers swelled more in biodiesel than the peroxide-cured FKM, presumably due to the chain cleavage caused by the attack of biodiesel on the double bonds formed during the bisphenol curing. With any of the selected types of monomer, the FKM rubbers absorbed biodiesel faster and to a greater extent with increasing oxygen partial pressure due to the increase in concentration of the oxidation products of biodiesel. Water-assisted complexation of biodiesel on magnesium oxide and calcium hydroxide particles led to dehydrofluorination of FKM, resulting in an extensive fuel uptake and a decrease in the strain-at-break and the Young's modulus of the rubbers. An increase in the CH2-concentration determined by infrared spectroscopy, and the appearance of biodiesel flakes in scanning electron micrographs of the extracted rubbers, were explained as being due to the presence of insoluble biodiesel grafted onto FKM on the unsaturated sites resulting from dehydrofluorination. The extensibility of the GFLT-type FKM was the least affected on exposure to biodiesel because this rubber contained less unsaturation and metal oxide/hydroxide particles.
Concerns over the fast depletion of fossil fuels, environmental issues and stringent legislation associated with petroleum-based fuels have triggered a shift to bio-based fuels, as an alternative to meet the growing energy demand in the transportation sector. However, since conventional automobile fuel systems are adapted to petroleum-based fuels, switching to biofuels causes a severe deterioration in the performance of currently used rubber components. The degradation of the rubber materials in biofuels is complicated by the presence of different additives in biofuels and rubber compounds, by oxidation of biofuels and by the effects of thermomechanical loadings in the engine. This paper presents a comprehensive review of the effects of different types of biofuels, particularly biodiesel and bioethanol, on the physical, mechanical, morphological and thermal properties of elastomers under different exposure conditions. In addition, the literature data available on the variation of rubbers' resistance to biofuels with the changes in their monomer type and composition, cure system and additives content was also studied. The review essentially focuses on the compatibility of biofuels with acrylonitrile butadiene rubber, fluoroelastomers, polychloroprene rubber and silicon rubber, as the most commonly used automotive rubbers coming into contact with fuels during their service. The knowledge summarized in this study can help to develop a guideline on the selection of rubber for automotive parts designed to withstand biofuels.
The deterioration of acrylonitrile butadiene rubber (NBR) exposed to rapeseed biodiesel at 90 degrees C was studied. The oxidation of biodiesel and NBR during ageing was monitored by H-1 NMR and infrared spectroscopy, HPLC and titration methods. The oxidation of biodiesel was impeded in the presence of NBR, but promoted in biodiesel-exposed rubber. This was explained as being due to the migration of stabilizer from the rubber to biodiesel, the diffusion of dissolved oxygen from biodiesel into NBR and the absorption of oxidation precursors of biodiesel by the rubber. The resemblance between the anomalous sorption kinetics of biodiesel in NBR and the equilibrium benzene uptake by the aged rubbers revealed that biodiesel caused a network defect in NBR, resulting in a gradual increase in the equilibrium swelling. The cleavage of crosslinks was implausible since the Young's modulus of the rubber at low strains, disregarding an initial decrease, increased with increasing exposure time. The appearance of 'naked' carbon black particles in the scanning electron micrographs of the aged rubbers and a drastic decrease in the strain-at-break of NBR after exposure to biodiesel suggests that internal cavitation was caused by the attack of biodiesel on the acrylonitrile units of NBR.
The degradation of acrylonitrile butadiene rubber (NBR) after exposure to biodiesel at different oxygen partial pressures in an automated ageing equipment at 80 °C, and in a high-pressure autoclave at 150 °C was studied. The oxidation of biodiesel was promoted by an increase in oxygen concentration, resulting in a larger uptake of fuel in the rubber due to internal cavitation, a greater decrease in the strain-at-break of NBR due to the coalescence of cavity, and a faster increase in the crosslinking density and carbonyl index due to the promotion of the oxidation of NBR. During the high-temperature autoclave ageing, less fuel was absorbed in the rubber, because the formation of hydroperoxides and acids was impeded. The extensibility of NBR aged in the autoclave decreased only slightly due to the cleavage of rubber chains by the biodiesel attack. The degradation of NBR in the absence of carbon black was explained as being due to oxidative crosslinking. The dissolution of ZnO crystals in the acidic components of biodiesel was retarded by removing the inter-particle porosity and surface defects through heat treating star-shaped ZnO particles. The rubber containing heat-treated ZnO particles swelled less in biodiesel than a NBR filled with commercial ZnO nanoparticles, and showed a smaller decrease in the strain-at-break and less oxidative crosslinking.
The deterioration of acrylonitrile butadiene rubber (NBR), a common sealing material in automobile fuel systems, when exposed to rapeseed biodiesel and hydrotreated vegetable oil (HVO) was studied. The fuel sorption was hindered in HVO-exposed rubber by the steric constraints of bulky HVO molecules, but it was promoted in biodiesel-exposed rubber by fuel-driven cavitation in the NBR and by the increase in diffusivity of biodiesel after oxidation. The absence of a tan δ peak of the bound rubber and the appearance of carbon black particles devoid of rubber suggested that the cavitation was made possible in biodiesel-aged rubber by the detachment of bound rubber from particle surfaces. The HVO-exposed NBR showed a small decrease in strain-at-break due to the migration of plasticizer from the rubber, and a small increase in the Young’s modulus due to oxidative crosslinking. A drastic decrease in extensibility and Payne-effect amplitude of NBR on exposure to biodiesel was explained as being due to the damage caused by biodiesel to the continuous network of bound rubber-carbon black. A decrease in the ZnO crystal size with increasing exposure time suggested that the particles are gradually dissolved in the acidic components of oxidized biodiesel. The Zn2+ cations released from the dissolution of ZnO particles in biodiesel promoted the hydrolysis of the nitrile groups of NBR.
A novel and facile method to produce inexpensive protein biofoams suitable for sponge applications is presented. The protein used in the study was wheat gluten (WG), readily available as a by/co-product, but the method is expected to work for other cross-linkable proteins. The foams were obtained by high-speed stirring of pristine WG powder in water at room temperature followed by drying. Glutaraldehyde was used to crosslink the foam material in order to stabilize the dispersion, reduce its tackiness and improve the strength of the final foam. The foams were of medium to high density and absorbed readily both hydrophobic and hydrophilic liquids. The foam structure, consisting primarily of an open pore/channel system, led to a remarkably fast capillary-driven (pore-filling only) uptake of a hydrophobic liquid (limonene). Essentially all uptake occurred within the first second (to ca. 90% of the dry weight). In a polar liquid (water), the rapid pore-filling occurred in parallel with a more time-dependent swelling of the foam matrix material. Further improvement in the foam strength was achieved by making a denser foam or adding TEMPO-oxidized cellulose nanofibres. Soft foams were obtained by adding glycerol.
The differential swelling and bending of multilayer polymeric films due to the dissimilar uptake of volatile organic compounds (VOCs; n-hexane, limonene) in the different layers was studied. Motions of thin polyethylene films triggered by the penetrant were investigated to learn more about how their deformation is related to VOC absorption. Single layers of metallocene or low-density polyethylene, and multilayers (2-288-layers) of these in alternating positions were considered. Single-, 24-, and 288 layer films displayed no motion when uniformly subjected to VOCs, but they could display simple curving modes when only one side of the film was wetted with a liquid VOC. Two-layer films displayed simple bending when uniformly subjected to VOCs due to the different swelling in the two layers, but when the VOC was applied to only one side of the film, more complex modes of motion as well as dynamic oscillations were observed (e.g., constant amplitude wagging at 2 Hz for ca. 50 s until all the VOC had evaporated). Diffusion modeling was used to study the transport behavior of VOCs inside the films and the different bending modes. Finally a prototype VOC sensor was developed, where the reproducible curving of the two-layer film was calibrated with n-hexane. The sensor is simple, cost-efficient, and nondestructive and requires no electricity.
This paper presents the structure and properties of two multilayered systems where polymers in adjacent layers were either miscible or immiscible. The miscible system consisted of 2, 17, 18, 24 and nominally 288 layers of alternating low-density (LDPE) and low-density/linear-low density (mPE) polyethylene layers with observed thicknesses ranging from 150 nm to 20 urn. The immiscible system consisted of 5 and 19 layer films with a combination of poly(ethylene-co-vinyl alcohol) (EVOH) (thickness: 9 and 1 gm, respectively), LDPE (17 and 7 gm) and a polyethylene adhesive (3 and 1 gm). The purpose of the multi-layering was to increase the crack growth resistance and, in the EVOH-based system, to decrease the oxygen transmission rate. Indeed, the crack growth resistance, as measured on tensile-tested notched films, increased with increasing number of layers. The thinnest polyethylene and polyethylene adhesive layers showed a clear ductile failure when fractured even in liquid nitrogen. Simultaneous synchrotron wide-angle/small-angle X-ray scattering and tensile testing indicated no new deformation features with changes in the layer thickness. The oxygen permeability was the same in the 5- and 19-layer EVOH-based films, but the uptake of n-hexane was strongly reduced in the 19-layer films, demonstrating the effective protective role of the EVOH layers. The n-hexane desorption data of the 2-layer LDPE/mPE film was successfully modeled using the diffusivities and solubilities of the single layers. Crystallization was slower and more confined in the films with thinner layers. The interlayer mixing in the melt (measured by isothermal crystallization from melts of initially layered polyethylene-based systems) was, as expected, significantly faster in the 24- and 288-multilayer films than in the 2-layer film.
A methodology was developed for qualitative assessment and characterisation of particle lossesfrom nanocomposites during service life. The methodology can be generalised to other systemswhere the material fragments during ageing and can be extended to quantitative analysis. Achamber was constructed for ageing of selected materials, which enabled effective collectionand subsequent analysis of released particles. A combination of scanning and transmissionelectron microscopy and energy dispersive X-ray spectroscopy was found to be suitable forcharacterising particles in terms of size, shape and content. The methodology was tested on acommon nanoclay composite with polypropylene as the matrix. There was no need forphysical/mechanical wear to generate particles, slow flow of air and elevated temperature ledto cracking and fragmentation of the material, and subsequent release of nanocompositeparticles containing embedded or protruding clay. The release of pure clay particles andpolypropylene particles was also detected. Using the methodology, it was observed that evenin ‘mild’ degradation conditions (pure thermo-oxidation with no wear), fillers andnanocomposite particles can be released to the environment, which is an environmental andhealth concern.
A protein-based material created from a new approach using whole defatted larvae of the Black Soldier fly is presented. The larvae turn organic waste into their own biomass with high content of protein and lipids, which can be used as animal feed or for material production. After removing the larva lipid and adding a plasticizer, the ground material was compression molded into plates/films. The lipid, rich in saturated fatty acids, can be used in applications such as lubricants. The amino acids present in the greatest amounts were the essential amino acids aspartic acid/asparagine and glutamic acid/glutamine. Infrared spectroscopy revealed that the protein material had a high amount of strongly hydrogen-bonded beta-sheets, indicative of a highly aggregated protein. To assess the moisture-protein material interactions, the moisture uptake was investigated. The moisture uptake followed a BET type III moisture sorption isotherm, which could be fitted to the Guggenheim, Anderson and de Boer (GAB) equation. GAB, in combination with cluster size analysis, revealed that the water clustered in the material already at a low moisture content and the cluster increased in size with increasing relative humidity. The clustering also led to a peak in moisture diffusivity at an intermediate moisture uptake.
A novel emulsion copolymer of vinyl acetate (VAc) and 1-hexene was synthesized at ambient pressure. The feeding technique, initiation system and reaction time of the copolymerization were optimized based on molecular characteristics such as the weight contribution of 1-hexene in the copolymer chains and glass transition temperature (T-g) as well as on bulk properties like minimum film-formation temperature (MFFT) and solid content. According to nuclear magnetic resonance spectroscopy and differential scanning calorimetry results, the combination of starve feeding and redox initiation, within a reaction time of 4h, effectively led to the copolymerization at ambient pressure between highly reactive polar VAc monomers and non-polar 1-hexene monomers of low reactivity. The copolymer showed a lower T-g and MFFT, and a reasonable solid content compared to the poly(vinyl acetate) (PVAc) homopolymer. The consumption rate, hydrolysis of acetate groups and chain transfer reactions during the polymerization were followed using infrared spectroscopy. Based on the results, the undesirable reactions between the VAc blocks were hindered by the neighbouring 1-hexene molecules. Tensile testing revealed an improvement in the toughness and elongation at break of VAc-1-hexene films compared to PVAc films.
A template transfer method (TTM) and a fiber fixation technique were established for fiber handling and micro tensile stage mounting of aligned and non-aligned electrospun fiber mats. The custom-made template had been precut to be mounted on a variety of collectors, including a rapidly rotating collector used to align the fibers. The method eliminated need for direct physical interaction with the fiber mats before or during the tensile testing since the fiber mats were never directly clamped or removed from the original substrate. By using the TTM it was possible to measure the tensile properties of aligned poly(methyl methacrylate) (PMMA) fiber mats, which showed a 250 % increase in strength and 450 % increase in modulus as compared to a non-aligned system. The method was further evaluated for aligned PMMA fibers reinforced with cellulose (4 wt%) prepared as enzymatically derived nanofibrillated cellulose (NFC). These fibers showed an additional increase of 30 % in both tensile strength and modulus, resulting in a toughness increase of 25 %. The fracture interfaces of the PMMA-NFC fibers showed a low amount of NFC pull-outs, indicating favorable phase compatibility. The presented fiber handling technique is universal and may be applied where conservative estimates of mechanical properties need to be assessed for very thin fibers.
The preparation of superparamagnetic thin fibers by electrospinning dispersions of nanosized magnetite (Fe3O4, SPIO/USPIO) in a PMMA/PEO polymer solution is reported. The saturation magnetization and coercivity were not affected by the concentration (0, 1, 10, 20 wt%) or fiber orientation, showing hysteresis loops with high magnetization (64 A m(2) kg(-1) @ 500 kA m(-1)) and record low coercivity (20 A m(-1)). AC susceptibility measurements vs. temperature at frequencies from 60 to 2 kHz confirmed superparamagnetism. The mechanical properties were only slightly dependent on the particle concentration because the nanoparticles were separately encapsulated by the polymer. A uniform fibre fracture cross section was found at all the investigated particle contents, which suggests a strong interaction at the polymer/particle interface. A theoretical value of the magnetic low field susceptibility was calculated from the Langevin function and compared with measured values. The results show a distinct but concentration-independent anisotropy, favoring magnetization along the fiber orientation with no sign of exchange interaction, explained by complete nanoparticle separation. Superparamagnetism cannot be inferred from particle size alone, so a relevant interpretation and criterion for superparamagnetism is presented, in accordance with Neel's original definition. From the measurements, it can be concluded that magnetic characterization can be used to elucidate the material morphology beyond the resolution of available microscopy techniques (TEM and SEM).
A new type of antimicrobial, biocompatible and toughness enhanced ultra-thin fiber mats for biomedical applications is presented. The tough and porous fiber mats were obtained by electrospinning solution-blended poly (methyl methacrylate) (PMMA) and polyethylene oxide (PEO), filled with up to 25 wt % of Lanasol-a naturally occurring brominated cyclic compound that can be extracted from red sea algae. Antibacterial effectiveness was tested following the industrial Standard JIS L 1902 and under agitated medium (ASTM E2149). Even at the lowest concentrations of Lanasol, 4 wt %, a significant bactericidal effect was seen with a 4-log (99.99%) reduction in bacterial viability against S. aureus, which is one of the leading causes of hospital-acquired (nosocomial) infections in the world. The mechanical fiber toughness was insignificantly altered up to the maximum Lanasol concentration tested, and was for all fiber mats orders of magnitudes higher than electrospun fibers based on solely PMMA. This antimicrobial fiber system, relying on a dissolved antimicrobial agent (demonstrated by X-ray diffraction and Infrared (IR)-spectroscopy) rather than a dispersed and "mixed-in" solid antibacterial particle phase, presents a new concept which opens the door to tougher, stronger and more ductile antimicrobial fibers.
A missing cornerstone in the development of tough micro/nano fibre systems is an understanding of the fibre failure mechanisms, which stems from the limitation in observing the fracture of objects with dimensions one hundredth of the width of a hair strand. Tensile testing in the electron microscope is herein adopted to reveal the fracture behaviour of a novel type of toughened electrospun poly(methyl methacrylate)/poly(ethylene oxide) fibre mats for biomedical applications. These fibres showed a toughness more than two orders of magnitude greater than that of pristine PMMA fibres. The in-situ microscopy revealed that the toughness were not only dependent on the initial molecular alignment after spinning, but also on the polymer formulation that could promote further molecular orientation during the formation of micro/nano-necking. The true fibre strength was greater than 150 MPa, which was considerably higher than that of the unmodified PMMA (17 MPa). This necking phenomenon was prohibited by high aspect ratio cellulose nanocrystal fillers in the ultra-tough fibres, leading to a decrease in toughness by more than one order of magnitude. The reported necking mechanism may have broad implications also within more traditional melt-spinning research.
Conductive natural rubber (NR) nanocomposites were prepared by solvent-casting suspensions of reduced graphene oxide(rGO) or carbon nanotubes (CNTs), followed by vulcanization of the rubber composites. Both rGO and CNT were compatible as fillers in the NR as well as having sufficient intrinsic electrical conductivity for functional applications. Physical (thermal) and chemical reduction of GO were investigated, and the results of the reductions were monitored by X-ray photoelectron spectroscopy for establishing a reduction protocol that was useful for the rGO nanocomposite preparation. Field-emission scanning electron microscopy showed that both nanofillers were adequately dispersed in the main NR phase. The CNT composite displays a marked mechanical hysteresis and higher elongation at break, in comparison to the rGO composites for an equal fraction of the carbon phase. Moreover, the composite conductivity was always ca. 3-4 orders of magnitude higher for the CNT composite than for the rGO composites, the former reaching a maximum conductivity of ca. 10.5 S/m, which was explained by the more favorable geometry of the CNT versus the rGO sheets. For low current density applications though, both composites achieved the necessary percolation and showed the electrical conductivity needed for being applied as flexible conductors for a light-emitting diode.
The transfer of heterogeneous photocatalysis applications from the laboratory to real-life aqueous systems is challenging due to the higher density of photocatalysts compared to water, light attenuation effects in water, complicated recovery protocols, and metal pollution from metal-based photocatalysts. In this work, we overcome these obstacles by developing a buoyant Pickering photocatalyst carrier based on green cellulose nanofibers (CNFs) derived from wood. The air bubbles in the carrier were stable because the particle surfactants provided thermodynamic stability and the derived photocatalytic foams floated on water throughout the test period (4 weeks). A metal-free semiconductor photocatalyst, g-C3N4, was facilely embedded inside the foam by mixing the photocatalyst with the air-bubble suspension followed by casting and drying to produce solid foams. When tested under mild irradiation conditions (visible light, low energy LEDs) and no agitation, almost three times more dye was removed after 6 h for the floating g-C3N4-CNF nanocomposite foam, compared to the pure g-C3N4 powder residing on the bottom of a ca. 2 cm-high water pillar. The buoyancy and physicochemical properties of the carrier material were imperative to render escalated oxygenation, high photon utilization, and faster dye degradation. The reported assembly protocol is facile, general, and provides a new strategy for assembling green floating foams that can potentially carry a number of different photocatalysts.
Photonic films based on cellulose nanocrystals (CNCs) are sustainable candidates for sensors, structurally colored radiative cooling, and iridescent coatings. Such CNC-based films possess a helicoidal nanoarchitecture, which gives selective reflection with the polarization of the incident light. However, due to the hygroscopic nature of CNCs, the structural colored material changes and may be irreversibly damaged at high relative humidity. Thus, moisture protection is essential in such settings. In this work, hygroscopic CNC-based films are protected with a bioinspired synthetic plant cuticle; a strategy already adopted by real plants. The protective cuticle layers altered the reflected colors to some extent, but more importantly, they significantly reduced the water vapor permeance by more than two orders of magnitude, from 2.1 × 107 (pristine CNC/GLU film) to 12.3 × 104 g µm m−2 day−1 atm−1 (protected CNC/GLU film). This expands significantly the time window of operation for CNC/GLU films at high relative humidity.
A multi-structured architecture of artificial intelligence techniques including artificial neural network (ANN), adaptive neuro-fuzzy-inference-system (ANFIS) and genetic algorithm (GA) were developed to predict and optimize the fireproofing properties of a model intumescent flame retardant coating including ammonium polyphosphate, pentaerythritol, melamine, thermoplastic acrylic resin and liquid hydrocarbon resin. By implementing ANN on heat insulation results of coating samples, prepared based on a L16 orthogonal array, mean fireproofing time (MFPT) values were properly predicted. The predicted data were then proved to be valid through performing closeness examinations on fuzzy inference systems results regarding their experimental counterparts. However, the possible deviations tapped into phenomena like foam detachment and char cracking were alleviated by ANFIS modeling embedded with pertinent fuzzy rules based on the sole and associative practical role of used additives. The contribution of each intumescent coating component on the formulation with optimized fireproofing behavior was then explored using GA modeling. A similar optimization procedure was also conducted using conventional Taguchi experimental design but the GA based optimized intumescent coating was found to exhibit higher MFPT value than that suggested by the Taguchi method.
Integration of fiber modification step with a modern pulp mill is a resource efficient way to produce functional fibers. Motivated by the need to integrate polymer adsorption with the current pulping system, anion-specific effects in carboxymethylcellulose (CMC) adsorption have been studied. The QCM-D adsorption experiments revealed that CMC adsorption to the cellulose model surface is prone to anion-specific effects. A correlation was observed between the adsorbed CMC and the degree of hydration of the co-ions present in the magnesium salts. The presence of a chaotropic co-ion such as nitrate increased the adsorption of CMC on cellulose compared to the presence of the kosmotropic sulfate co-ion. However, anion-specificity was not significant in the case of salts containing zinc cations. The hydration of anions determines the distribution of the ions at the interface. Chaotropic ions, such as nitrates, are likely to be distributed near the chaotropic cellulose surface, causing changes in the ordering of water molecules and resulting in greater entropy gain once released from the surface, thus increasing CMC adsorption.
Engineered polymeric nanoparticles (NPs) have been comprehensively explored as potential platforms for diagnosis and targeted therapy for several diseases including cancer. Herein, we designed functional poly(acrylic acid)-b-poly(butyl acrylate) (PAA-b-PBA) NPs using reversible addition-fragmentation chain-transfer (RAFT)-mediated emulsion polymerization via polymerization-induced self-assembly (PISA). The hydrophilic PAA-macroRAFT, forming a stabilizing shell (i.e., corona), was chain-extended using the hydrophobic monomer n-butyl acrylate (n-BA), resulting in stable, monodisperse, and reproducible PAA-b-PBA NPs, typically having a diameter of 130 nm. The surface engineering of the PAA-b-PBA NP post-PISA were explored using a two-step approach. The hydrophilic NP-shell corona was modified with allyl groups under mild conditions, using allylamine in water, which resulted in stable allyl-functional NPs (allyl-NPs) suitable for further bioconjugation. The allyl-NPs were subsequently conjugated with a thiol-functional fluorescent dye (BODIPY-SH) to the allyl groups using "thiol-ene"-click chemistry, to mimic the attachment of a thiol-functional target ligand. The successful attachment of BODIPY-SH to the allyl-NPs was corroborated by UV-vis spectroscopy, showing the characteristic absorbance of the BODIPY-fluorophore at 500 nm. Despite modification of NPs with allyl groups and attachment of BODIPY-SH, the NPs retained their colloidal stability and monodispersity as indicated by DLS. This demonstrates that post-PISA functionalization is a robust method for synthesizing functional NPs. Neither the NPs nor allyl-NPs showed significant cytotoxicity toward RAW264.7 or MCF-7 cell lines, which indicates their desirable safety profile. The cellular uptake of the NPs using J774A cells in vitro was found to be time and concentration dependent. The anti-cancer drug doxorubicin was efficiently (90%) encapsulated into the PAA-b-PBA NPs during NP formation. After a small initial burst release during the first 2 h, a controlled release pattern over 7 days was observed. The present investigation demonstrates a potential method for functionalizing polymeric NP post-PISA to produce carriers designed for targeted drug delivery.
Engineered polymeric nanoparticles (NPs) have been comprehensively explored as potential platforms for diagnosis and targeted therapy for several diseases including cancer. Herein, we designed functional poly(acrylic acid)-b-poly(butyl acrylate) (PAA-b-PBA) NPs using reversible addition-fragmentation chain-transfer (RAFT)-mediated emulsion polymerization via polymerization-induced self-assembly (PISA). The hydrophilic PAA-macroRAFT, forming a stabilizing shell (i.e. corona), was chain-extended using the hydrophobic monomer n-butyl acrylate (n-BA), resulting in stable, monodisperse and reproducible PAA-b-PBA NPs, typically having a diameter of 130 nm. Two approaches of surface engineering of the PAA-b-PBA NPs post-PISA were explored; a two-step and a one-step approach. In the two-step approach, the hydrophilic NP-shell corona was modified with allyl-groups under mild conditions using allylamine in water which resulted in stable allyl-functional NPs (allyl-NPs) suitable for further bio-conjugation. Their versatility was investigated by the subsequent conjugation of a thiol-functional fluorescent dye (BODIPY-SH) to the allyl-groups using click chemistry, in order to mimic the attachment of a thiol-functional target ligand. The average size and size distribution of the corresponding NPs did not change after BODIPY-conjugation. Neither the NPs nor allyl-NPs showed significant cytotoxicity towards RAW264.7 or MCF-7 cell lines, which indicates their desirable safety profile. A one-step approach to concurrently conjugate allyl-groups and a fluorescent dye (FITC) to the preformed PAA-b-PBA NPs was investigated. The cellular uptake of the FITC-NPs using J774A cells in vitro was found to be time- and concentration-dependent. The anti-cancer drug, doxorubicin, was efficiently (90%) encapsulated into the PAA-b-PBA NPs during NP formation. After a small burst release during the first two hours, a controlled release pattern over 7 days was observed. The present investigation demonstrates a potential method to functionalize polymeric NPs post-PISA to produce targeted drug delivery carriers.
Lignocellulosic biomass is the most abundantly available resource in nature. However, its potential as a replacement of oil in plastic production has not been fully exploited. To reduce the carbon footprint, the use of lignocellulose biomass to produce bio-based plastics is attracting increasing global interest. The aim of this review article is to systematically summarize the recent advancements of the development of lignocellulose materials that possess thermoplastic properties, meaning they can be processed/shaped by common plastic processing techniques. The approaches used for modification of lignocellulose biomass and the properties of the modified materials, as well as factors affecting the properties of these, are discussed. The regulatory aspects and policy directions of bio-based plastics, including thermoplastic lignocellulose, are also mentioned. Current challenges of producing thermoplastic lignocellulose and the way forward to solve this are also explored.
Carbon based fillers have attracted a great deal of interest in polymer composites because of their ability to beneficially alter properties at low filler concentration, good interfacial bonding with polymer, availability in different forms, etc. The property alteration of polymer composites makes them versatile for applications in various fields, such as constructions, microelectronics, biomedical, and so on. Devastations due to building fire stress the importance of flame-retardant polymer composites, since they are directly related to human life conservation and safety. Thus, in this review, the significance of carbon-based flame-retardants for polymers is introduced. The effects of a wide variety of carbon-based material addition (such as fullerene, CNTs, graphene, graphite, and so on) on reaction-to-fire of the polymer composites are reviewed and the focus is dedicated to biochar-based reinforcements for use in flame retardant polymer composites. Additionally, the most widely used flammability measuring techniques for polymeric composites are presented. Finally, the key factors and different methods that are used for property enhancement are concluded and the scope for future work is discussed.
The oxygen, carbon dioxide, and water-transport properties of a uniaxially oriented aliphatic polyketone were determined. The polyketone was drawn to 5-10 times its original length. The transport properties were related to changes in crystallinity estimated by differential scanning calorimetry and density measurements and by changes in the molecular and crystal orientation assessed by, respectively, infrared and X-ray spectroscopy. The film structures were characterized by confocal scanning laser microscopy and scanning electron microscopy. Stress-strain tests on the drawn specimens enabled the impacts of orientation on the transport and mechanical properties to be compared. A draw-induced increase in crystallinity and molecular orientation yielded permeabilities at a draw ratio of 10 that were 30-40% of the original value, and the percentage decrease was basically independent of the type of gas/vapor molecule. Also, the diffusivities of oxygen and carbon dioxide decreased by an order of magnitude. The fact that the amorphous permeability was peaking at a draw ratio of about 5 was a consequence of a peak in amorphous solubility, which was very high for oxygen and absent for water. It was suggested that the peak in solubility was mainly caused by the destruction of the polymer hydrogen-bond network during drawing and crystal reorientation. The impact of structural reorganization within the polymer and presence of surface valleys seemed to have less impact on the mechanical properties than on the transport properties. This suggested that transport data are more sensitive than mechanical data in probing material defects and changes in molecular packing and morphology.
Unfilled cross-linked poly(dimethyl siloxane) (PDMS) is a weak material and is generally filled with high levels of particulate fillers such as silica, calcium carbonate and carbon black to improve its mechanical properties. The use of fibrous fillers such as electrospun nanofibres and multi-walled carbon nanotubes as fillers for PDMS has not been widely studied. In this study anew copolymer, polyacrylonitrile-graft-poly(dimethyl siloxane) (PAN-g-PDMS), is used as fibrous filler for PDMS. The graft copolymer is electrospun to produce the fibre filler material. It is shown how the PDMS content of the graft copolymer provides increased compatibility with silicone matrices and excellent dispersion of the fibre fillers throughout a silicone matrix. It is also shown that it is possible to include multi-walled carbon nanotubes in the electrospun fibres which are subsequently dispersed in the PDMS matrix. Fibre mats were used in the non-woven and the aligned forms. The differently prepared fibre composites have significantly different mechanical properties. Conventional composites using fibrous fillers usually show increased strength and stiffness but usually with a resultant loss of strain. In the case of the composites produced in this study there is a dramatic improvement in the extensibility of the non-woven PAN-g-PDMS fibre mat filled silicone films of up to 470%.
Glycerol-plasticized wheat gluten was explored for producing soft high-density biofoams using dry upscalable extrusion (avoiding purposely added water). The largest pore size was obtained when using the food grade ammonium bicarbonate (ABC) as blowing agent, also resulting in the highest saline liquid uptake. Foams were, however, also obtained without adding a blowing agent, possibly due to a rapid moisture uptake by the dried protein powder when fed to the extruder. ABC's low decomposition temperature enabled extrusion of the material at a temperature as low as 70 °C, well below the protein aggregation temperature. Sodium bicarbonate (SBC), the most common food-grade blowing agent, did not yield the same high foam qualities. SBC's alkalinity, and the need to use a higher processing temperature (120 °C), resulted in high protein cross-linking and aggregation. The results show the potential of an energy-efficient and industrially upscalable low-temperature foam extrusion process for competitive production of sustainable biofoams using inexpensive and readily available protein obtained from industrial biomass (wheat gluten).
Graphene oxide (GO) was used in this study as a template to successfully synthesize silicon oxide (SiOx) based 2D-nanomaterials, adapting the same morphological features as the GO sheets. By performing a controlled condensation reaction using low concentrations of GO (<0.5 wt%), the study shows how to obtain 2D-nanoflakes, consisting of GO-flakes coated with a silica precursor that were ca. 500 nm in lateral diameter and ca. 1.5 nm in thickness. XPS revealed that the silanes had linked covalently with the GO sheets at the expense of the oxygen groups present on the GO surface. The GO template was shown to be fully removable through thermal treatment without affecting the nanoflake morphology of the pure SiOx-material, providing a methodology for large-scale preparation of SiOx-based 2D nanosheets with nearly identical dimensions as the GO template. The formation of SiOx sheets using a GO template was investigated for two different silane precursors, (3-aminopropyl) triethoxysilane (APTES) and tetraethyl orthosilicate (TEOS), showing that both precursors were capable of accurately templating the graphene oxide template. Molecular modeling revealed that the choice of silane affected the number of layers coated on the GO sheets. Furthermore, rheological measurements showed that the relative viscosity was significantly affected by the specific surface area of the synthesized particles. The protocol used showed the ability to synthesize these types of nanoparticles using a common aqueous alcohol solvent, and yield larger amounts (∼1 g) of SiOx-sheets than what has been previously reported.
This is the first study on freeze-dried foams prepared from glutenin- and gliadin-rich fractions of wheat gluten and blends thereof. It was found that the foam density and stiffness could be controlled by a suitable choice of the glutenin/gliadin ratio. The glutenin-rich samples had the highest foam densities and the density decreased with increasing gliadin content. The compression modulus also decreased with increasing gliadin content, which was explained by the decrease in foam density, a more open porosity and the more aggregated/polymerized structure in the presence of glutenin. IR and SE-HPLC revealed that the least aggregated foams were those consisting only of the gliadin-rich fraction. Confocal laser scanning microscopy revealed the presence of both HMW-glutenin and gliadin (to a certain extent probably resisting the ethanol extraction process) in the glutenin-rich foams. SAXS indicated that the gliadin-rich fraction contributed with weakly correlated protein aggregates with a characteristic distance of 40-43 Å.
This Article reports the influence of the protein network structure on the mechanical properties of foams produced from commercial wheat gluten using freeze-drying. Foams were produced from alkaline aqueous solutions at various gluten concentrations with or without glycerol, modified with bacterial cellulose nanosized fibers, or both. The results showed that 20 wt % glycerol was sufficient for plasticization, yielding foams with low modulus and high strain recovery. It was found that when fibers were mixed into the foams, a small but insignificant increase in elastic modulus was achieved, and the foam structure became more homogeneous. SEM indicated that the compatibility between the fibers and the matrix was good, with fibers acting as bridges in the cell walls. IR spectroscopy and SE-HPLC revealed a relatively low degree of aggregation, which was highest in the presence of glycerol. Confocal laser scanning microscopy revealed distinct differences in HMW-glutenin subunits and gliadin distributions for all of the different samples.
Freeze-dried wheat gluten foams were evaluated with respect to their thermal and fire-retardant properties, which are important for insulation applications. The thermal properties were assessed by differential scanning calorimetry, the laser flash method and a hot plate method. The unplasticised foam showed a similar specific heat capacity, a lower thermal diffusivity and a slightly higher thermal conductivity than conventional rigid polystyrene and polyurethane insulation foams. Interestingly, the thermal conductivity was similar to that of closed cell polyethylene and glass-wool insulation materials. Cone calorimetry showed that, compared to a polyurethane foam, both unplasticised and glycerol-plasticised foams had a significantly longer time to ignition, a lower effective heat of combustion and a higher char content. Overall, the unplasticised foam showed better fire-proof properties than the plasticized foam. The UL 94 test revealed that the unplasticised foam did not drip (form droplets of low viscous material) and, although the burning times varied, self-extinguished after flame removal. To conclude both the insulation and fire-retardant properties were very promising for the wheat gluten foam.
A new way of producing rigid or semi-rigid foams from vital wheat gluten using a freeze-drying process is reported. Water/gluten-based mixtures were frozen and freeze-dried. Different foam structures were obtained by varying the mixing process and wheat gluten concentration, or by adding glycerol or bacterial cellulose nanofibers. MIP revealed that the foams had mainly an open porosity peaking at 93%. The average pore diameter ranged between 20 and 73 mm; the sample with the highest wheat gluten concentration and no plasticizer had the smallest pores. Immersion tests with limonene revealed that the foams rapidly soaked up the liquid. An especially interesting feature of the low-wheat-concentration foams was the "in situ'' created soft-top-rigid-bottom foams.
We use a recently developed scanning probe technique to image with high spatial resolution the injection and extraction of charge around individual surface-modified aluminum oxide nanoparticles embedded in a low-density polyethylene (LDPE) matrix. We find that the experimental results are consistent with a simple band structure model where localized electronic states are available in the band gap (trap states) in the vicinity of the nanoparticles. This work offers experimental support to a previously proposed mechanism for enhanced insulating properties of nanocomposite LDPE and provides a powerful experimental tool to further investigate such properties.
NIR spectroscopy in the transmission mode and thermogravimetric analysis were used to predict diffusion of water into polyamide 6,6 samples immersed in water at 40, 60, 75 and 90degreesC for different periods of time. The sorption curves between 40 and 75 were sigmoidal indicating that the surface concentration was time dependent. The sorption curves were readily fitted by the use of a time-dependent surface concentration and a water-concentration-dependent diffusivity. The zero-concentration water diffusivity decreased non-linearly and the activation energy of diffusion increased from 24 to 58 kJ mol(-1), with decreasing temperature. The surface concentration relaxation time decreased rapidly. The sorption of water in thick polyamide samples was readily characterized by FT-NIR spectroscopy. The accuracy and feasibility of this method was similar to conventional thermogravimetric methods. The greatest advantage of FT-NIR, however, is the possibility of detecting and monitoring the moisture concentration on-line and in a non-destructive way.
Biocomposites based on wheat gluten and reinforced with carbon fibers were produced in line with the strive to replace fossil-based plastics with microplastic-free alternatives with competing mechanical properties. The materials were first extruded/compounded and then successfully injection molded, making the setup adequate for the current industrial processing of composite plastics. Furthermore, the materials were manufactured at very low extrusion and injection temperatures (70 and 140 degrees C, respectively), saving energy compared to the compounding of commodity plastics. The sole addition of 10 vol % fibers increased yield strength and stiffness by a factor of 2-4 with good adhesion to the protein. The biocomposites were also shown to be biodegradable, lixiviating into innocuous molecules for nature, which is the next step in the development of sustainable bioplastics. The results show that an industrial protein coproduct reinforced with strong fibers can be processed using common plastic processing techniques. The enhanced mechanical performance of the reinforced protein-based matrix herein also contributes to research addressing the production of safe materials with properties matching those of traditional fossil-based plastics.
The functionalization of inexpensive potato protein concentrate (PPC) is presented as a simple and easily scalable method to produce bio-based superabsorbent powders. Five nontoxic acylating agents were evaluated at different reaction temperatures for solvent-free acylation of the protein. The best results were obtained for succinic anhydride (SA) and a reaction temperature of 140 degrees C. These conditions resulted in efficient functionalization that provided formation of a useful network, which allowed high uptake of fluids and little material disintegration during the uptake, that is, due to protein hydrolysis during the functionalization. The SA-acylated PPC showed increased water and saline swelling capacities of 600 and 60%, respectively, as compared to untreated PPC. The acylated potato protein also showed a saline liquid holding capacity of approximately 50% after centrifugation at 1230 rpm for 3 min, as well as a significant blood swelling capacity of 530%. This blood swelling represents more than 50% of that of a commercial fossil-based superabsorbent (SAP) used for blood absorption in sanitary health products. The swelling properties of these inexpensive protein-based acylated materials highlight their potential as sustainable SAP materials (from industrial side-streams) in applications such as daily care products that are currently dominated by fossil-based SAPs.
Functionalized wheat gluten (WG) protein particles with the ability to absorb fluids within the superabsorbent range are presented. Ethyleneditetraacetic dianhydride (EDTAD), a nontoxic acylation agent, was used for the functionalization of the WG protein at higher protein content than previously reported and no additional chemical cross-linking. The 150-550 μm protein particles had 50-150 nm nanopores induced by drying. The EDTAD treated WG were able to absorb 22, 5, and 3 times of, respectively, water, saline and blood, per gram of dry material (g/g), corresponding to 1000, 150 and 100% higher values than for the as-received WG powder. The liquid retention capacity after centrifugation revealed that almost 50% of the saline liquid was retained within the protein network, which is similar to that for petroleum-based superabsorbent polymers (SAPs). An advantageous feature of these biobased particulate materials is that the maximum swelling is obtained within the first 10 min of exposure, that is, in contrast to many commercial SAP alternatives. The large swelling in a denaturation agent (6 M urea) solution (about 32 g/g) suggests that the secondary entangled/folded structure of the protein restricts protein network expansion and when disrupted allows the absorption of even higher amounts of liquid. The increased liquid uptake, utilization of inexpensive protein coproducts, easy scalable protocols, and absence of any toxic chemicals make these new WG-based SAP particles an interesting alternative to petroleum-based SAP in, for example, absorbent disposable hygiene products.
Superabsorbent materials can absorb many times their weight in water, but are commonly derived from petroleum. Here, acylation of coagulated potato protein concentrate or soluble potato protein fruit juice yields an effective, mould-resistant, and biodegradable superabsorbent polymer. Superabsorbent polymers (SAP) are a central component of hygiene and medical products requiring high liquid swelling, but these SAP are commonly derived from petroleum resources. Here, we show that sustainable and biodegradable SAP can be produced by acylation of the agricultural potato protein side-stream (PPC) with a non-toxic dianhydride (EDTAD). Treatment of the PPC yields a material with a water swelling capacity of ca. 2400%, which is ten times greater than the untreated PPC. Acylation was also performed on waste potato fruit juice (PFJ), i.e. before the industrial treatment to precipitate the PPC. The use of PFJ for the acylation implies a saving of 320 000 tons as CO2 in greenhouse gas emissions per year by avoiding the industrial drying of the PFJ to obtain the PPC. The acylated PPC shows biodegradation and resistance to mould growth. The possibilities to produce a biodegradable SAP from the PPC allows for future fabrication of environment-friendly and disposable daily-care products, e.g. diapers and sanitary pads.
Replacing the current mainly fossil-based, disposable, and non-biodegradable sanitary products with sustainable, functional alternatives is an industry priority. Suggested biobased alternatives require evaluation of their actual impact on greenhouse gas (GHG) emissions. We evaluated GHG emissions of biobased baby diapers as the most consumed sanitary product, using a biodegradable functionalized protein superabsorbent polymer (bioSAP) and compared them with currently used fossil-based counterparts. Assessment of the diapers also included estimated GHG emissions from the production of the biobased components, transport, and end-of-life combustion of these items. It was shown that only a few of the biobased diaper alternatives resulted in lower GHG emissions than commercial diapers containing fossil-based materials. At the same time, it was demonstrated that the production of the bioSAP via chemical modification of a protein raw material is the primary GHG contributor, with 78% of the total emissions. Reduction of the GHG contribution of the bioSAP production was achieved via a proposed recycling route of the functionalization agent, reducing the GHG emissions by 13% than if no recycling was carried out. Overall, we demonstrated that reduced and competitive GHG emissions could be achieved in sanitary articles using biobased materials, thereby contributing to a sanitary industry producing disposable products with less environmental pollution while allowing customers to keep their current consumption patterns.
The production of porous wheat gluten (WG) absorbent materials by means of extrusion processing is presented for the future development of sustainable superabsorbent polymers (SAPs). Different temperatures, formulations, and WG compositions were used to determine a useful protocol that provides the best combination of porosity and water swelling properties. The most optimal formulation was based on 50 wt.% WG in water that was processed at 80 degrees C as a mixture, which provided a porous core structure with a denser outer shell. As a green foaming agent, food-grade sodium bicarbonate was added during the processing, which allowed the formation of a more open porous material. This extruded WG material was able to swell 280% in water and, due to the open-cell structure, 28% with non-polar limonene. The results are paving the way towards production of porous bio macromolecular structures with high polar/non-polar liquid uptake, using extrusion as a solvent free and energy efficient production technique without toxic reagents.
The development of fully natural wheat gluten foams showing rapid and high uptake of water, sheep blood, and saline solution, while maintaining high mechanical stability in the swollen state, is presented. Genipin was added as a natural and polar cross-linker to increase the polarity of the protein chains, whereas cellulose nanofibers (CNFs) were added as a reinforcement/stiffener of the foams, alone or in combination with the genipin. The presence of only genipin resulted in a foam that absorbed up to 25 g of water per gram of foam and a more than 15 g uptake in only 8 min. In contrast, with CNF alone, it was not possible to maintain the mechanical stability of the foam during the water uptake and the protein foam disintegrated. The combination of CNF and genipin yielded a material with the best mechanical stability of the tested samples. In the latter case, the foam could be compressed repeatedly more than 80% without displaying any structural damage. The results revealed that a strong network had formed between the wheat gluten matrix, genipin, and cellulose in the foam structure. A unique feature of the absorbent/foam, in contrast to commercial superabsorbents, was that it was able to rapidly absorb nonpolar liquids (here, n-heptane) due to the open-cell structure. The capillary-driven absorption due to the open-cell structure, the high liquid absorption in the cell walls, and the mechanical properties (both in dry and swollen states) of these natural foams make them interesting as a sustainable replacement for a range of petroleum-based foam materials, including absorbent hygiene products such as sanitary pads.
This study evaluated the effect of the wheat gluten (WG) separation process and transglutaminase (TG) microbial source on WG dough quality, and opportunities to use these factors to tailor dough quality. Two types of gluten (harshly and mildly separated), two types of TG (commercial and novel SB6), and three TG concentrations were evaluated for effects on dough mixing properties, protein structure and solubility. Mildly separated gluten improved dough development parameters, resulting into higher values of most compared with harshly separated gluten. Despite more strongly cross-linked proteins being found in the harshly separated gluten, both gluten types showed similar levels of cross-linking at optimum mixing time, although differences in the secondary protein structure were indicated. Thus, disulfide-sulfhydryl exchange reactions were found to be promoted by mixing, although restrictions on establishment of new bonds because of prior cross-links in the material were clearly indicated. Degree of polymerization in doughs made from mildly separated gluten increased to varying extents with TG addition depending on TG source and concentration. Thus, for the first time, we show that an appropriate combination of WG separation procedure and TG source can be used to tailor gluten dough end-use properties.
The popularity of transglutaminase (TG) by the food industry and the variation in functionality of this enzyme from different origins, prompted us to isolate and evaluate a high-yielding TG strain. Through the statistical approaches, Plackett-Burman and response surface methodology, a low cost fermentation media was obtained to produce 6.074 +/- 0.019 U mL(-1) of TG from a novel source; Streptomyces sp. CBMAI 1617 (SB6). Its potential exploitation was compared to commonly used TG, from Streptomyces mobaraensis. Biochemical and FT-IR studies indicated differences between SB6 and commercial TG (Biobond (TM) TG-M). Additions of TG to wheat protein and flour based doughs revealed that the dough stretching depended on the wheat protein fraction, TG amount and its origin. A higher degree of cross-linking of glutenins and of inclusion of gliadin in the polymers was seen for SB6 as compared to commercial TG. Thus, our results support the potential of SB6 to tailor wheat protein properties within various food applications.
Gluten proteins are highly impacting the quality of various gluten-based products, and transglutaminases (TGs) are used to influence the protein cross-linking. In this study we monitored the interplay of "harsh" and "mild" gluten processing for dough mixing and pasta-like sheet production and TGs from a commercial and newly sourced bacteria (SB6). Despite the harshly separated gluten presenting strongly cross-linked proteins in the beginning of the mixing, similar levels of polymerization were achieved at the optimum mixing time but with differences in the secondary protein structure. TG addition increased polymerization in wheat doughs, possibly as a result of increased glutenin polymerization, while gliadins become more soluble with SB6. This enzyme also dramatically increased polymerization in mild gluten. These results show that an adequate investigation when using TGs and gluten from various origins is necessary to adequately predict the quality in various gluten-based products, thus, of great relevance to the food industry. Industrial relevance: Currently, there is a mounting trend towards the modification of gluten proteins to improve technological features and functionality. In breadmaking, when weak Hour (low protein content) is used or general stabilization is desired for technological purposes, additives can be used to stabilize the gluten protein matrix. The use of transglutaminase (TG) has grown in popularity as they promote specific cross-linking between residues of glutamine and lysine in proteins. Another way of improving dough functionality is by increasing the oxidation of disulfide groups by adding gluten which is a co-product of the starch industry. Industrial production of gluten includes the use of heating and shear forces, which may impact gluten dough-forming ability. Thus, increased understanding of the interplay of gluten processing and the impact of choice of the TG origin in gluten dough quality is highly applicable in food industry.
A new type of chitosan and wheat gluten biofoam is presented. The pore structure achieved relied solely on the specific mixing and phase distribution when a film was cast from an aqueous mixture of chitosan/wheat gluten solution, in the absence of any chemical blowing agent, porogen or expanding gas. The foam was obtained when the liquid phase was removed by vacuum drying, without the need for the traditional freeze-drying that is frequently used for pore formation. Soft foam samples could be prepared with stiffnesses from 0.3 to 1.2 MPa and a high rebound resilience (64 and 94% at compressive strains of 80 and 20%, respectively). The foams were relatively ductile and did not require any plasticiser to allow for in-plane deformation (20% compression) and smaller bending. Only open pores with sizes of the order of 70-80 μm were observed by microscopy. The density of all the foams was ∼50 kg m-3, due to the high porosity (96% air). The foams showed a rapid and large uptake of both non-polar (limonene) and polar (water) liquids. When immersed in these liquids for 1 second, the maximum uptake recorded was 40 times the initial mass of the foam for limonene and 8 times for water.
The purpose of this study was to study the transport of monocarboxylic acids in chitosan films, since this is important for understanding and predicting the drying kinetics of chitosan from aqueous solutions. Despite the wealth of data on chitosan films prepared from aqueous monocarboxylic acid solutions, this transport has not been reported. Chitosan films were exposed to formic, acetic, propionic and butyric acid vapours, it was found that the rate of uptake decreased with increasing molecular size. The equilibration time was unexpectedly long, especially for propionic and butyric acid, nine months. A clear two-stage uptake curve was observed for propionic acid. Evidently, the rate of uptake was determined by acid-induced changes in the material. X-ray diffraction and infrared spectroscopy indicated that the structure of the chitosan acetate and buffered chitosan films changed during exposure to acid and during the subsequent drying. The dried films previously exposed to the acid showed less crystalline features than the original material and a novel repeating structure possibly involving acid molecules. The molar mass of the chitosan decreased on exposure to acid but tensile tests revealed that the films were always ductile. The films exposed to acid vapour (propionic and butyric acid) for the longest period of time were insoluble in the size-exclusion chromatography eluent, and they were also the most ductile/extensible of all samples studied.