Tuning the Rheological, Thermal, and Solid-State Properties of Branched PLA by Free-Radical-Mediated Reactive Extrusion

The purpose of this work is to establish structure property relations of poly(lactide) (PLA) formulations that were branched by peroxide mediated reactive extrusion, in the presence of triallyl trimesate (TAM) coagent. Based on detailed evaluations of the molar mass distributions and rheological properties we deduce that modified PLA consists of a population of linear, and long chain branched (LCB) PLA chains, depending upon the amount of the peroxide and coagent. Even though peroxide alone does not induce significant changes in the architecture, TAM is very effective in producing LCB structures, which result in substantial increases in viscosity, elasticity, as well as strain hardening characteristics. At high DCP and TAM loadings, cross-linked structures are obtained. The reactively modified formulations have higher molar mass, which results in improved Izod impact strength, whereas the rest of the properties, including their capacity to degrade hydrolytically, are maintained. Furthermore, these materials develop high amounts of crystallinity, when cooled under well-controlled conditions, revealing a nucleating effect, which promotes crystallization.