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 degrees) and thermal stability (e.g. glass transition temperature 104 degrees 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.