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Suppressing the influence of humidity in protein-based materials is central to their use in a variety of applications. It is believed that protein charge plays a key role in water uptake. Therefore, in this work, whey protein was neutralized, supercharged, and superneutralized to examine the effects of protein modification on moisture absorption in protein copolymers. The charge-modified proteins were formulated into thermoset elastomers through a three-step process: methacrylation, complexation with various surfactants, and co-polymerization with n-butyl acrylate. Compatibility of the protein and hydrophobic acrylate monomer can be tuned through changes in surfactant type, ratio between surfactant and protein, and protein charge modification. Using benzalkonium chloride as the surfactant compatibilizer, elastomers with the various modified proteins were prepared using a melt polymerization approach. Acetylation and esterification of whey protein, which neutralize charged functional groups, resulted in the reduction of the proteins' water uptake relative to unmodified whey. Once incoporated into elastomers, all copolymers regardless of protein modifications have similar moisture contents. However, elastomers with superneutralized proteins demonstrated a lowered mechanical dependence on humidity, presented as a smaller change in elongation at break and tensile strength compared to a copolymer based on non-charge modified whey. This journal is

Bio-sourced macromolecules such as cyanophycin are an attractive source for alternative, sustainable plastics. While the chemical structure and biological function of cyanophycin have been previously investigated, its material properties remain largely unexplored. This study investigates the structural, thermal, mechanical, and solution properties of cyanophycin produced from recombinant Escherichia coli . Unplasticized, it has an elastic compression modulus of about 560 MPa and undergoes brittle failure at 78 MPa. Cyanophycin exhibits thermal stability in air up to 200 °C and does not undergo glass transition within its limit of thermal stability. The polypeptide is amorphous and has no long-range ordering in the solid state. In solution, water-soluble cyanophycin is thermoresponsive, exhibiting both upper and lower critical solution temperatures. Because the feasibility of industrial scale cyanophycin production through fermentation has been well studied, an expanded understanding of its materials properties should contribute to the development of new applications for this biopolymer.

The wide use of non-biodegradable, petroleum-based plastics raises important environmental concerns, which urges finding alternatives. In this study, an alternative way to produce polymers from a renewable source&mdash, milk proteins&mdash, was investigated with the aim of replacing polyethylene. Whey protein can be obtained from whey residual, which is a by-product in the cheese-making process. Two different sources of whey protein were tested: Whey protein isolate (WPI) containing 91% protein concentration and whey protein concentrate (WPC) containing 77% protein concentration. These were methacrylated, followed by free radical polymerization with co-polymer poly(ethylene glycol) methyl ether methacrylate (PEGMA) to obtain polymer sheets. Different protein concentrations in water (11&ndash, 14 w/v%), at two protein/PEGMA mass-ratios, 20:80 and 30:70, were tested. The polymers made from WPI and WPC at a higher protein/PEGMA ratio of 30:70 had significantly better tensile strength than the one with lower protein content, by about 1&ndash, 2 MPa (the best 30:70 sample exhibited 3.8 &plusmn, 0.2 MPa and the best 20:80 sample exhibited 1.9 &plusmn, 0.4 MPa). This indicates that the ratio between the hard (protein) and soft (copolymer PEGMA) domains induce significant changes to the tensile strengths of the polymer sheets. Thermally, the WPI-based polymer samples are stable up to 277.8 &plusmn, 6.2 &deg, C and the WPC-based samples are stable up to 273.0 &plusmn, 3.4 &deg, C.