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Crystallization of polylactide during impregnation with liquid CO2

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Publication date 2015
Author Plummer Christohper John George Yonghoon Yoon Garin Léo E.Manson Jan-Anders,
Project A new generation of ultra-light bio-based particleboard produced with an in-line foaming step
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Original article (peer-reviewed)

Journal Polymer Bulletin
Volume (Issue) 72(1)
Page(s) 103 - 116
Title of proceedings Polymer Bulletin
DOI 10.1007/s00289-014-1262-7

Open Access

URL http://link.springer.com/article/10.1007%2Fs00289-014-1262-7
Type of Open Access Publisher (Gold Open Access)

Abstract

The evolution of the morphology and degree of crystallinity was investigated postmortem in initially amorphous specimens of a commercial poly(DL- lactide) with a relatively low D-lactide content, after different immersion times in liquid CO2 at 10 ?C and 5 MPa. Relatively high concentrations of CO2 induced a crystalline phase that remained stable at room temperature after desorption of the CO2, but was distinct from those generally associated with melt crystallization of polylactides (PLA), as demonstrated by transmission electron microscopy and wide- angle X-ray diffraction, consistent with previous observations. Crystallinity devel- oped at the surface of the specimens within relatively short times compared with those necessary for the overall CO2 content to reach saturation, resulting in a well- defined semicrystalline layer, whose thickness increased with immersion time. This behaviour was argued to be consistent with the existence of a well-defined diffusion front, associated with a step-like CO2 concentration gradient that reflected a strong increase in the diffusivity of the CO2 with the local CO2 content. Crystallization led to a reduction in both the rate of CO2 uptake and the CO2 concentration at saturation compared with that observed for a poly(DL-lactide) with a significantly higher D- lactide content and little tendency to crystallize in the presence of liquid CO2. Assuming the CO2 to be concentrated in the amorphous regions of semicrystalline PLA, a simple model for non-linear Fickian diffusion based on data from previous desorption measurements was used to show that diffusion through the semicrys- talline surface layer should dominate impregnation kinetics in initially amorphous specimens that undergo rapid crystallization above a certain critical CO2 concen- tration, consistent with the observed rates of CO2 uptake.
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