On the improvement of properties of bioplastic composites derived from wasted cottonseed protein by rational cross-linking and natural fiber reinforcement

An approach of largely improving the properties of protein-based biopolymers is reported. Cottonseed protein concentrate (CPC) purified from cottonseed protein powder waste, with a protein content of >70% and a plasticizing efficiency of 4.2, was used to produce bioplastic polymer. A prepreg consisting of relatively oriented sisal fiber (SF) was transferred into CPC matrix as reinforcement, giving rise to improved mechanical properties of CPC/SF composites. To enhance interfacial bonding forces between the fiber and polymer, dialdehyde starch, DAS, with varied content (5–30 wt%) was introduced, and the FTIR and NMR results showed that DAS can effectively bridge biomacromolecular chains and form strong chemical bonds within the crosslinked structure. This cross-linking treatment leads to the formation of tight CPC/SF interfaces with strong adhesion, as shown by microscopic images, translating into excellent mechanical performance (e.g. tensile strength 21 MPa), water resistance (e.g. water contact angle 80°) and thermal stability (e.g. glass transition temperature 104 °C) of the composites. The all green composites derived from natural resources with comparable or even superior properties to state-of-the-art biomass-based composites hold great potential for being utilized in larger industries.