Authors: Maria Laura Di Lorenzo Paolo Rubino Romain Luijkx Marion Hélou
Publish Date: 2013/10/09
Volume: 292, Issue: 2, Pages: 399-409
Abstract
The influence of chain structure on crystal polymorphism of polylactic acid PLA with high llactic acid content 978–100 is detailed in this contribution Upon usual processing conditions of PLA only α and α′ crystals grow which makes these two polymorphs of major interest for research The two crystal modifications have similar chain packing which complicates their quantitative analysis by diffraction methods The two crystal modifications are instead easily identified by analysis of the crystallization kinetics which varies not only with temperature but also with crystal polymorphism The dependence of the rate of ordering on temperature shows two distinct maxima around 105–110 and 120–125 °C which are related to growth of α′ and α crystals respectively Addition of dlactic acid counits leads to a decrease of the overall crystallization rate of PLA as well as of the rate of spherulite growth G of both the crystal modifications The relative crystallization rates of α and α′ forms are highly affected by stereoregularity especially in the PLA grades that have a high crystallization rate A high dlactic acid content results not only in an overall slower crystal growth but also in a varied temperature range where each of the two crystal modifications prevail with a shift to lower temperatures of both the maxima of the G vs temperature plots indicating that inclusion of dlactic acid units in the PLA chain affects crystallization rate of both α and α′ crystal modifications
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