(76e) Hydrolytic Degradation of Polylactide and Production of Water-Soluble Hydrolyzate Species

Authors: 
Cairncross, R. A., Drexel University
Tschirner, U., University of Minnesota
Wojdyla, D., University of Minnesota


Poly Lactic Acid (PLA) is a biodegradable, highly versatile, aliphatic polyester which can be produced from 100% renewable, natural resources offering great promise in a wide range of commodity applications. Moisture management, and its relationship to degradation in biopolymers such as PLA, is extremely important during manufacturing, shipping, storage and end-use applications. Some of the major technical challenges to widespread acceptance of biopolymers such as PLA are difficulties achieving mechanical and barrier properties comparable to conventional synthetic polymers while maintaining biodegradability.

The overall scope of the ongoing research is to investigate how degradation depends on polymer structure parameters, temperature, and water content. As a first step in this study, experiments were performed on moisture sorption and degradation of PLA. Two time series of degradation experiments were performed on PLA simultaneously. PLA samples were subjected to varying degrees of degradation by soaking in deionized and deuterated water for number of days. The hydrolyzate containing the degraded products was analyzed using simple acid-base titration to determine the molecular weight using the number of acid end groups and confirmed using NMR. The polymer (solid phase) was also characterized for molecular weight distribution using HPLC and moisture content as a function of degradation using gravimetric methods. Under conditions approximating industrial composting ? 80ºC and immersion in water ? significant degradation of PLA was observed, especially after 2-3 days. Degradation leads to an increase in hydrophilic end groups on PLA, an increase in moisture sorption, and decrease in pH of the hydrolyzate. The experimental measurements of molecular weight of hydrolyzate and residual polymer were used to confirm the possible the reaction mechanism and the possible dominance of end-group scission during degradation.

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