期刊
EUROPEAN POLYMER JOURNAL
卷 48, 期 4, 页码 779-788出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.eurpolymj.2012.01.014
关键词
Poly(lactide); Poly(lactic acid); Oxygen permeability; Gas barrier properties; Crystallinity; Rigid amorphous fraction
The helium and oxygen gas barrier properties of poly(lactide) were investigated as a function of stereochemistry and crystallinity degree. Poly(L-lactide) and poly(D,L-lactide) films were obtained by extrusion and thermally cold crystallized in either alpha'- or alpha-crystalline form with increasing crystallinity degree. Annealing of the films at low temperatures yielded to alpha'-crystals as well as the creation of a rigid amorphous fraction in the amorphous phase. Unexpectedly, the quantity of the rigid amorphous fraction was highest in poly(L-lactide) crystallized under alpha'-form. Unexpectedly, the gas permeability increased with increasing quantity of alpha'-crystals in poly(L-lactide) and remained constant with increasing quantity of alpha'-crystals in poly(D,L-lactide). A gain in gas barrier properties was obtained upon crystallization at higher temperatures yielding alpha-crystals. The analysis of the oxygen transport parameters, in particular the diffusion and the solubility coefficient showed that the diffusion was accelerated upon crystallization, while the solubility coefficient decreased in an expected manner which led to conclude that it remained constant in the amorphous phase. The acceleration of the diffusion seems to be correlated to the occurrence of the rigid amorphous fraction, which holds larger free volume. To conclude, for optimization of poly(lactide) gas barrier properties by focussing on the decrease of the diffusion coefficient it can be suggested to work with poly(D,L-lactide) and to aim a crystallization in alpha-form avoiding the formation of a rigid amorphous fraction. (C) 2012 Elsevier Ltd. All rights reserved.
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