"The effect of chain extender (Cex) on the molecular weight properties and hydrolytic degradation of modified PLA films (PLA--Cex) was determined and compared with PLA without Cex (PLA--Con). Effects of the Cex content and the residence time on the molecular weight were reviewed using melt blending and compression molding. A response surface methodology was applied to design the experiments and estimate the optimal conditions for obtaining the maximum weight average and number average molecular weight achieved at 1.5 wt% Cex and residence time of 17 minutes. The hydrolytic degradation experiments were run in water from 40 to 95 °C and in 50% ethanol from 40 to 85 °C. The rate of hydrolytic degradation of PLA--Cex film was estimated using mathematical models, and it was considerably lower than that of PLA--Con in all conditions. The activation energy for hydrolysis above Tg was determined using the Arrhenius equation, showing no significant difference between PLA--Cex and PLA--Con. The Vogel-Tammann-Fulcher (VTF) and the Williams-Landel-Ferry (WLF) models were used for studying the hydrolytic degradation of polymers over a broad range of temperature crossing Tg. A master curve was constructed using the time-temperature superposition principle. The experimental data at 85 °C were used to predict the degradation behavior at 40 °C. It was found that PLA--Cex would take approximately 72 percent more time than PLA--Con to degrade to soluble oligomer chains."--Page ii.
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