Characterization of polyhydroxyalkanoate-based composites derived from waste cooking oil and agricultural surplus

Abstract

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), member of the polyhydroxyalkanoate family, was generated from waste vegetable oil in a lab-scale bioreactor and filled with pistachio shell (S) flour to produce fully agro-industrial waste derived biodegradable low-cost composites via melt mixing. To improve the interfacial interaction, maleic anhydride (MA) grafted PHBV (PHBV-MA) was used as a compatibilizer and pretreatment of S (TS) was realized with silanization+alkalization process. The effects of filler percentage, compatibilizer, and S modification on the mechanical, thermal, morphological, water absorption, and biodegradability properties of the composite were studied. The crystallization percentage and temperature of PHBV were found to be higher in the composites, as compared with neat PHBV, due to nucleation effect of S/TS fillers. The increased tensile strength/modulus were achieved with composites including both PHBV-MA compatibilizer and TS filler. The PHBV/PHBV-MA/TS composite reinforced with 40% TS filler increased the tensile strength and modulus of the neat PHBV by 62.1% and 45.3%, respectively. Morphological analysis revealed that samples containing PHBV-MA, or TS, have better surface wetting and interfacial adhesion than those without. The biodegradation of composites was studied over a 180 days of burial in soil. Biodegradation increased in tandem with the increase of the filler ratio in the PHBV composite from 20% to 40%. Biocomposites with 40% S/TS filler lost more than 90% of their weight, while the neat PHBV lost only 23.5%. Water absorption studies confirmed the biodegradability findings, with TS slightly reducing absorption capacity among the 40% filled samples due to the hydrophobicity effect of the silanization pretreatment.