Hydrolytic degradation of branched PLA produced by reactive extrusion
2018
Simmons, Heather | Kontopoulou, Marianna
Reactive extrusion using dicumyl peroxide (DCP) and a tri-functional coagent, triallyl trimesate (TAM) is implemented to introduce long-chain branching (LCB) in poly(lactic acid) (PLA). The effects of this modification on the long-term hydrolysis of PLA are assessed by monitoring the mass, molar mass distributions, and thermal properties of specimens exposed to hydrolytic degradation at a temperature of 60 °C. A slow initial rate of mass loss coupled with an immediate and rapid loss in molar mass are characteristic of a bulk erosion mechanism. Significant loss is observed in all molar mass averages within the first 20 days. In LCB PLA the most drastic decrease was observed in the z-average molar mass, Mz, as a result of the cleavage of the LCB segments from the polymer chain. Degradation induced crystallinity is observed in all formulations, attributed to the combined influence of annealing and the plasticizing effect of water. Although the hydrolysis profile is altered, reactive modification does not affect negatively the degradability of LCB PLA over a 12-week period, suggesting that these modified PLAs can be used in commodity applications that require degradable polymers.
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