Rheological analysis of peroxide radical-induced modification of microalgae-based polymer composite

Abstract

In this study, the effect of peroxide radical-induced chemical modification on microalgae (Chlorella sp. HS2)/ polymer (ethylene-vinyl acetate, EVA) composite is investigated based on rheological and mechanical measurements, morphological observations, FT-IR, and gel tests. Generation of macromolecular clusters throughout the composite according to gelation of HS2/EVA, reflecting in linear viscoelasticity of composite. Rheological analysis characterizes the gelation kinetics of crosslinking or grafting reaction of dicumyl peroxide (DCP) radicals to HS2 and EVA matrix by identifying the gel time (tg) and gelation fractal dimension (df). DCP radicals require tg of 440 s for EVA while it delays to 1200s for HS2/EVA. The fractal dimension (df) of EVA/HS2/DCP is 2.37, decreasing from 2.42 for EVA/DCP, meaning that the reaction between radical and HS2 retard the growth of macromolecular clusters throughout the composite by gelation. The addition of HS2 significantly affects the gelation kinetics of radicals, delaying the gelation as well as its growth. Correspondingly, when DCP radicals have sufficient reaction time (> 1200 s) to induce grafting, both the tensile strength and modulus of EVA/HS2/DCP composite are significantly improved, meaning that the grafting reaction of DCP radicals between HS2 and EVA coherently improves the interfacial interaction and mechanical tensile properties. This study suggests a radical reaction as a method to improve the mechanical performance of a microalgae-based polymer composite by inducing interfacial bonding between microalgae and polymer. It will increase the potential of microalgae as a promising biomass filler for the fabrication of eco-friendly polymer composite.