The effects of hydration on the solvation, diffusivity, solubility, and permeability of oxygen molecules in sustainable, biodegradable chitosan/chitin food packaging films were studied via molecular dynamics and confined random walk simulations. With increasing hydration, the membrane has a more homogeneous water distribution with the polymer chains being fully solvated. The diffusivity increased by a factor of 4 for oxygen molecules and by an order of magnitude for water with increasing the humidity. To calculate the Henry's constant and solubility of oxygen in the membranes with changing hydration, the excess chemical potential was calculated via free energy perturbation, thermodynamic integration and direct particle deletion methods. The simulations predicted a higher solubility and permeability for the lower humidity, in contradiction to experimental results. All three methods for calculating the solubility were in good agreement. It was found that the Coulombic interactions in the potential caused the oxygen to bind too strongly to the protonated amine group. Insight from this work will help guide molecular modeling of chitosan/chitin membranes, specifically permeability measurements for small solute molecules. Efforts to chemically tailor chitosan/chitin membranes to favor discrete as opposed to continuous aqueous domains could reduce oxygen permeability.

Chitosan containing nanofibrous filter media has the advantage of filtering material based on both its size and functionality. They can be potentially applicable in a wide variety of filtration applications ranging from water purification media to air filter media. We have fabricated nanofibrous filter media by electrospinning of chitosan/PEO blend solutions onto a spunbonded non-woven polypropylene substrate. Filter media with varying fiber diameter and filter basis weight were obtained. Heavy metal binding, anti-microbial and physical filtrations efficiencies of these chitosan based filter media were studied and correlated with the surface chemistry and physical characteristics of these nanofibrous filter media. Filtration efficiency of the nanofiber mats was strongly related to the size of the fibers and its surface chitosan content. Hexavalent chromium binding capacities up to 35mg chromium/g chitosan were exhibited by chitosan based nanofibrous filter media along with a 2–3log reduction in Escherichia coli bacteria cfu.

To take advantage of the unique characteristics of the wood flour by combining them with plastic in conventional panel pressing methods, a wet process was developed to make composites using polypropylene and steam-exploded (SE) flour from small-diameter loblolly pine. Wet-laid wood flour/polymer composites were fabricated using a standard TAPPI handsheet method followed by compression molding. The variables that may affect the product properties were investigated using an orthogonal test design. The results revealed that the modulus of elasticity (MOE) of composites increased, while modulus of rupture (MOR) decreased with increasing SE wood flour content. Both MOE and MOR of the composites increased with maleic anhydride grafted polypropylene content. Dynamic mechanical analyzer and differential scanning calorimetry measurement gave insight into the structure of these composites, and scanning electron microscope was used to characterize the interfacial adhesion.

Films formed by blending of two polymers usually have modified physical and mechanical properties compared to films made of the individual components. Our preliminary studies indicated that incorporation of chitosan in polyethylene oxide (PEO) films may provide additional functionality to the PEO films and may decrease their tendency to spherulitic crystallization. The objective of this study was to determine the correlation between chitosan/PEO weight ratio and the physical, mechanical, and antibacterial properties of corresponding films. Films with chitosan/PEO weight ratios from 100/0 to 50/50 in 10% increments were characterized by measuring thickness, puncture strength (PS), tensile strength (TS), elongation at break (%E), water vapor permeability (WVP), and water solubility (WS). Additionally, the films were examined by polarized microscopy, wide-angle X-ray diffraction (WAXD), and Fourier transform infrared (FTIR) spectroscopy, and their antibacterial properties were tested against Escherichia coli. The chitosan fraction contributes to antimicrobial effect of the films, decreases tendency to spherulitic crystallization of PEO, and enhances puncture and tensile strength of the films, while addition of the PEO results in thinner films with lower water vapor permeability. Films with 90/10 blend ratio of chitosan/PEO showed the most satisfactory PS, TS, %E, and antibacterial properties of all tested ratios.

Nonwoven fiber mats of chitosan with potential applications in air and water filtration were successfully made by electrospinning of chitosan and poly(ethyleneoxide) (PEO) blend solutions. Electrospinning of pure chitosan was hindered by its limited solubility in aqueous acids and high degree of inter- and intrachain hydrogen bonding. Nanometer-sized fibers with fiber diameter as low as 80 +/- 35 nm without bead defects were made by electrospinning high molecular weight chitosan/PEO (95:5) blends. Fiber formation was characterized by fiber shape and size and was found to be strongly governed by the polymer molecular weight, blend ratios, polymer concentration, choice of solvent, and degree of deacetylation of chitosan. Weight fractions of polymers in the electrospun nonwoven fibers mats were determined by thermal gravimetric analysis and were similar to ratio of polymers in the blend solution. Surface properties of fiber mats were determined by measuring the binding efficiency of toxic heavy metal ions like chromium, and they were found to be related with fiber composition and structure.

We report the formation of non-woven fibers without bead defects by electrospinning blend solutions of chitosan and polyacrylamide (PAAm) with blend ratios varying from 75wt% to 90wt% chitosan using a modified electrospinning unit wherein polymer solutions can be spun at temperatures greater than ambient up to 100°C. Electrospinning at elevated temperature leads to further expansion of the processing window, by producing fibers with fewer defects at higher chitosan weight percentage in the blends. Effects of varying blend ratios, spinning temperatures, and molecular weights on fiber formation were studied and optimum conditions for formation of uniform non-woven fiber mats with potential applications for air and water filtration were obtained. Uniform bead-less fiber mats with fiber diameter as low as 307±67nm were formed by spinning 90% chitosan in blend solutions at 70°C.

Beetle-killed loblolly pine chips were steam-exploded (SE) with a severity factor of 4.8 in a batch reactor into a fibrous mass followed by a sieve step to remove oversize pieces (> 16 mesh). The sieved SE fibers (< 16 mesh) contained 5%-10% water-soluble materials and were mainly composed of fiber fragments with lignin droplets on their surfaces. Composites were prepared by firstly compounding sieved SE fibers and polypropylene (PP) with or without maleic anhydride grafted polypropylene (MAPP) as a compatibilizer, and then by compression-molding the mixtures at 195 degrees C. The MOE of the composites increased greatly, and the yield stress sigma(y), was decreased slightly by inclusion of 50% SE fibers with no compatibilizer. Addition of 2.5% MAPP improved significantly the flexural properties of the composites, especially the sigma(y) which was eventually superior to that of neat PP. DMA and DSC measurements revealed that the SE fibers increased the crystallinity of PP by forming more crystalline fractions around wood fibers or fiber fragments. Addition of MAPP resulted in a reduction in the damping and an increase in the heat of fusion of the PP in the composites, Suggesting a stronger interface between the matrix and SE fibers. The better interfacial adhesion was also demonstrated by SEM observations showing fiber breakage occurring on the fractured surfaces of the PP composites with MAPP as a compatibilizer.

Two-step etching procedures have been developed for binary polymer blends of linear low density polyethylene (LLDPE) with high density polyethylene (HDPE), and for blends of atactic and syndiotactic polystyrene. For both cases, two different etchants have been identified for the component neat polymers; sequential etching has been employed to reveal the distribution of the component polymers within the blend. It is believed that similar procedures may be applicable to other blend systems. (C) 1998 Elsevier Science Ltd. All rights reserved.