Abstract
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—milk proteins—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 (11–14 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 1–2 MPa (the best 30:70 sample exhibited 3.8 ± 0.2 MPa and the best 20:80 sample exhibited 1.9 ± 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 ± 6.2 °C and the WPC-based samples are stable up to 273.0 ± 3.4 °C.
Highlights
Raw materials from renewable and agricultural sources have been proposed to produce plastics for food packaging and shopping bags for many years [1,2]
Since some of the renewable materials, which are mainly plant-based, are first generation feedstocks, which compete with the food security, utilizing second-generation feedstocks is the preferable option. One such option is the production of plastics from whey proteins, which can be obtained from the by-product/residues of cheese-making processes and expired dairy products
Whey protein concentrate (WPC) that contains 77% protein, as per supplier information, was purchased from the supplier Natur-Drogeriet based in Hørning, Denmark, while whey protein isolate (WPI) that contains 91% protein, was purchased from the BiPro company (Eden Prairie, Minnesota, USA)
Summary
Raw materials from renewable and agricultural sources have been proposed to produce plastics for food packaging and shopping bags for many years [1,2]. Since some of the renewable materials, which are mainly plant-based, are first generation feedstocks, which compete with the food security, utilizing second-generation feedstocks (biomaterials which are by-products, residues, or wastes from other processes) is the preferable option. One such option is the production of plastics from whey proteins, which can be obtained from the by-product/residues of cheese-making processes and expired dairy products. Cow and goat milk mainly consist of 80% casein proteins and 20% whey proteins [3]. Known as serum proteins [4], consist of several globular
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