Mikael S. Hedenqvist

Diffusion of small-molecule penetrants in polyethylene: free volume and morphology

Based on desorption and permeation measurements, the diffusivity and solubility of n-hexane and oxygen have been obtained for a wide range of linear and branched polyethylenes (PEs) with crystallinities between 40 and 97% and mass-average molar masses between 103 and 106 g mol−1. The morphology and contents of crystal core (CC), crystal-core-like interfacial (ICC), liquid-like interfacial (IL) and liquid (L) components were assessed by transmission electron microscopy, Raman spectroscopy, 13C cross-polarization/magic-angle spinning nuclear magnetic resonance spectroscopy, differential scanning calorimetry, density measurements and small-angle light scattering. The penetrant solubility in the non-crystalline phases increased with increasing concentration of chain ends and chain branches. This effect was masked at certain crystallinities by the constraining effect of the crystallites. The diffusivity selectivity of oxygen over n-hexane increased strongly with increasing crystallinity and decreasing non-crystalline layer thickness, demonstrating that the crystal-induced constraint on the non-crystalline chains more efficiently retards the diffusion of larger molecules. The fractional free volume of the non-crystalline components decreased strongly with increasing crystallinity in the low-crystallinity range (<60%), above which it remained practically constant. The latter is because the constraining effect of the crystals is compensated for by the plasticizing effect of the chain ends, which leads to a constant free volume in this crystallinity range. A model, based on the Cohen-Turnbull-Fujita (CTF) model, considering the polymers to consist of four components, CC, ICC, IL and L, was applied to the diffusivity data. The branched PEs and the majority of the linear PEs could be described by the modified CTF model. However, the lowest-molar-mass linear PEs exhibited a considerably larger interfacial free volume than the other samples. Real-time Raman spectroscopy on CCl4-swollen samples showed that the changes in the CC and ICC contents during sorption were only small.

Transport properties of chitosan and whey blended with poly(ε-caprolactone) assessed by standard permeability measurements and microcalorimetry

Blends of poly(p-caprolactone) (PCL) with chitosan and a whey-protein-isolate (WPI) were prepared by solution mixing and film casting. The purpose was to increase the water vapour resistivity of ch ...

Wheat gluten polymer structures : The impact of genotype environment and processing on their functionality in various applications

ABSTRACT For a number of applications, gluten protein polymer structures are of the highest importance in determining end-use properties. The present article focuses on gluten protein structures in the wheat grain, genotype- and environment-related changes, protein structures in various applications, and their impact on quality. Protein structures in mature wheat grain or flour are strongly related to end-use properties, although influenced by genetic and environment interactions. Nitrogen availability during wheat development and genetically determined plant development rhythm are the most important parameters determining the gluten protein polymer structure, although temperature during plant development interacts with the impact of the mentioned parameters. Glutenin subunits are the main proteins incorporated in the gluten protein polymer in extracted wheat flour. During dough mixing, gliadins are also incorporated through disulfide-sulfhydryl exchange reactions. Gluten protein polymer size and complexi...

Parameters affecting the determination of transport kinetics data in highly swelling polymers above Tg

Abstract Sorption and desorption data for n-hexane–natural rubber and n-hexane–low-density polyethylene were analysed to reveal the cause of the s-shaped sorption curves frequently occurring in highly swollen polymers. The model permitted the influence of solute-concentration-dependent diffusivity, sample geometry, boundary concentrations and swelling-induced mechanical stresses on the transport data to be examined. The calculated solute diffusivity varied by several orders of magnitude, depending on the choice of parameters included in the model. The inclusion of direct mechanical stress relaxation parameters only gave a slight improvement of the fit to the experimental data. The inclusion of a time-dependent surface concentration was the only way to fit the s-shaped sorption curves for both natural rubber and low-density polyethylene. Although isotropic three-dimensional swelling of natural rubber occurred over the whole sorption transient period, this condition was unable to explain the swelling (thickness increase) of low-density polyethylene. In the latter system, a model consisting of two stages had to be adopted: stage I where the swelling was mainly one-dimensional, and stage II which occurred later and was characterized by three-dimensional swelling similar to that occurring in natural rubber. During the transient sorption period, the ratio between natural rubber and low-density polyethylene of the ratio of the thickness to cross-sectional area was close to their bulk modulus ratio, which suggests that it is the bulk modulus rather than the Youngs modulus which determines the sorption characteristics of polymers above T g .

Properties of extruded vital wheat gluten sheets with sodium hydroxide and salicylic acid

This paper presents a novel approach to improve the barrier and mechanical properties of extruded glycerol-plasticized vital wheat gluten sheets. The sheets were extruded with a single screw extruder at alkaline conditions using 3-5 wt % NaOH. Salicylic acid (SA), known to improve the extrudability of wheat gluten, was also added alone or in combination with NaOH. Oxygen transmission rate and volatile mass measurements, tensile tests, protein solubility, glycerol migration, infrared spectroscopy, and electrophoresis were used to assess the properties of the extrudate. Electrophoresis showed that the gluten/glycerol sheet and the sheet with 3 wt % NaOH and 1 wt % SA contained the same building blocks in terms of proteins and protein subunits, although the protein solubility in these samples was different. The oxygen barrier, at dry conditions, was improved significantly with the addition of NaOH. On the other hand, the addition of salicylic acid yielded poorer barrier properties. The extrudate was placed on a blotting paper and its aging properties were investigated during the first 120 days. It was observed that the extrudate with 3 wt % NaOH had the most suitable combination of properties (low oxygen permeability, large strain at break, and relatively small aging-induced changes in mechanical properties); the reason is probably due to low plasticizer migration and an optimal protein aggregation/polymerization.

Influence of citric acid and curing on moisture sorption, diffusion and permeability of starch films

Starch films with different amounts of citric acid produced by solution casting were subjected to different curing temperatures and compared with films plasticized with glycerol. The films were tested in a controlled moisture generator, which enabled the moisture sorption to be measured and the diffusion coefficient and water vapor permeability to be calculated. It was shown that increasing the amount of citric acid added led to a reduction in the equilibrium moisture content, diffusion coefficient and water vapor permeability of the films, the values of which were all considerably lower than the values obtained for the films plasticized by glycerol. It was also seen that curing the film with 30 pph citric acid at 150°C led to a significant reduction in the equilibrium moisture content, the diffusion coefficient and the water vapor permeability at high relative humidity which suggests that crosslinking occurred. The calculated water vapor permeability data were comparable with the value obtained with direct measurements.

Structure and morphology of wheat gluten films: from polymeric protein aggregates toward superstructure arrangements.

Evaluation of structure and morphology of extruded wheat gluten (WG) films showed WG protein assemblies elucidated on a range of length scales from nano (4.4 Å and 9 to 10 Å, up to 70 Å) to micro (10 μm). The presence of NaOH in WG films induced a tetragonal structure with unit cell parameters, a = 51.85 Å and c = 40.65 Å, whereas NH(4)OH resulted in a bidimensional hexagonal close-packed (HCP) structure with a lattice parameter of 70 Å. In the WG films with NH(4)OH, a highly polymerized protein pattern with intimately mixed glutenins and gliadins bounded through SH/SS interchange reactions was found. A large content of β-sheet structures was also found in these films, and the film structure was oriented in the extrusion direction. In conclusion, this study highlights complexities of the supramolecular structures and conformations of wheat gluten polymeric proteins in biofilms not previously reported for biobased materials.

Mechanical Properties and Network Structure of Wheat Gluten Foams

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.

Transport properties of hyperbranched and dendrimer-like star polymers

Moisture transport properties were assessed by sorption and desorption measurements on hydroxyl-functional hyperbranched polyesters based on 2,2-bis(methylol) propionic acid (bis-MPA) as AB(2)-mono ...

Injection-molded nanocomposites and materials based on wheat gluten

This is, to our knowledge, the first study of the injection molding of materials where wheat gluten (WG) is the main component. In addition to a plasticizer (glycerol), 5 wt.% natural montmorillonite clay was added. X-ray indicated intercalated clay and transmission electron microscopy indicated locally good clay platelet dispersion. Prior to feeding into the injection molder, the material was first compression molded into plates and pelletized. The filling of the circular mold via the central gate was characterized by a divergent flow yielding, in general, a stronger and stiffer material in the circumferential direction. It was observed that 20-30 wt.% glycerol yielded the best combination of processability and mechanical properties. The clay yielded improved processability, plate homogeneity and tensile stiffness. IR spectroscopy and protein solubility indicated that the injection molding process yielded a highly aggregated structure. The overall conclusion was that injection molding is a very promising method for producing WG objects.