Moisture‐induced anti‐plasticization of polylactic acid: Experiments and modeling
Yu Chen, Tian Tang, Cagri Ayranci
Abstract
Abstract Polylactic acid (PLA) is a biodegradable polymer derived from bio‐renewable resources. The effect of diffused water molecules on the mechanical properties of PLA, before the onset of hydrolytic degradation, has been rarely studied. In this work, PLA fibers produced by melt‐extrusion were conditioned in chambers with different levels of relative humidity (36%, 75%, and 98%), as well as immersed in distilled water. Creep tests were conducted on dry and conditioned samples and creep compliances were extracted. With the increase of moisture content, the decrease in instantaneous elastic compliance, as well as the more flattened curves in the last stage of the creep tests, indicates the existence of water‐bridge‐anti‐plasticization effect. The modified Burgers‐Reimschuessel model developed in our previous work is found to be able to predict the effect of absorbed moisture on the viscoelasticity of PLA. The present work highlights the importance of considering the moisture's anti‐plasticization effect. The proposed methodology can be adopted to evaluate the effect of moisture on the viscoelasticity of PLA for different applications.