Toughening of polybenzoxazine by silk sericin-g-PLA/Marl biocomposites

Polylactide (PLA) is the most widely known biodegradable polymer in use today. Additionally, natural proteins in silk, sericin, have been increasingly used. This work emphasized the synthesis of a graft copolymer, Sericin-g-PLA, in the presence of surface treated marl as a filler, followed by blending with polybenzoxazine to harden the obtained biocomposite. Polybenzoxazine precursor was synthesized from aliphatic diamine, bisphenol-A, and paraformaldehyde by using the faster quasi-solventless approach with 88% yield. The synthesized polybenzoxazine precursor was blended with marl having surface modified by (3-aminopropyl) trimethoxy-silane. The chemical structures of the graft copolymer and polybenzoxazine precursor were confirmed by FTIR and NMR. The results from SEM revealed the better interfacial adhesion between the graft copolymer and the polymer matrix after modification surface of marl. The results of DSC and TGA techniques showed that graft copolymer filled with modified marl can lower the curing temperature of polybenzoxazine; meanwhile, the thermal stability was increasing. The effects of the polybenzoxazine content on the mechanical properties of the biocomposite, particularly flexural strength and impact strength, were exhibited that the biocomposite from 20% graft copolymer added modified marl with polybenzoxazine gave the highest flexural modulus and impact strength.