Crab and prawn shell utilization as a source of bio-based thermoplastics through graft polymerization with acrylate monomers

To recycle crab and prawn shell wastes and prepare environment friendly thermoplastics, various acrylate monomers-methyl (meth)acrylates, ethyl (meth)acrylates, and butyl (meth)acrylates were grafted onto molecular chains of chitin and crude protein in shells. The acrylates were proved to be successfully grafted onto the demineralized shells through FTIR characterization and grafting parameters of the shell-g-polyacrylates were obtained through titration and Soxhlet extraction. Then, effects of grafting ratio and molecular structure of acrylate monomers on tensile properties and water resistance of the grafted shell thermoplastic films were surveyed. With the increase in grafting ratio of the demineralized shell-g-PMMA, tensile strength of the thermoplastic films initially increased, reached the maximum when the ratio was 31.86%, and then leveled off while both the elongation and water resistance of the film showed an increasing trend. In addition, with the increase in the alkyl chain length of ester group in acrylate unit, tensile strength and water resistance of the grafted shell film decreased continuously while tensile elongation kept increasing. As for alpha-methyl in methacrylate unit, the film prepared from the shells grafted with methacrylates had higher tensile strength and water resistance but lower elongation than the ones grafted with corresponding acrylates.