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An investigation into the crystalline morphology transitions in poly-L-lactic acid (PLLA) under uniaxial deformation in the quasi-solid-state regime

Billimoria, Kharmen; Heeley, Ellen L.; Parsons, Nathan and Figiel, Łukasz (2018). An investigation into the crystalline morphology transitions in poly-L-lactic acid (PLLA) under uniaxial deformation in the quasi-solid-state regime. European Polymer Journal, 101 pp. 127–139.

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DOI (Digital Object Identifier) Link: https://doi.org/10.1016/j.eurpolymj.2018.01.031
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Abstract

The mechanical behaviour, crystalline and macromorphology structure development during uniaxial deformation and annealing of poly-L-lactic acid (PLLA), with varying strain rate and draw temperatures (Td) above Tg, have been investigated using small- and wide-angle X-ray scattering (SAXS/WAXS), microscopy, thermal and mechanical techniques. The mechanical behaviour of PLLA, was strongly dependent on Td where embrittlement and eventual failure were observed as Td was increased, during uniaxial drawing of the amorphous polymer. This was mirrored in the bulk surface morphology where crazing, microvoiding and cavitation occurred with increasing Td. SAXS/WAXS data showed that strain-induced crystallization occurs on drawing, but crystallite orientation decreased with increasing Td, due to chain relaxation at temperatures ≥30 oC above Tg. However, no long-range oriented lamellar macromorphology was observed post-draw directly and only developed in the samples that were step annealed at temperatures above Td. Also, the disordered α’ crystal form was observed post-draw at Td between 60 – 80 oC, whereas Td ≥ 90 oC, resulted in the ordered α crystal form directly. However, on annealing at temperatures of ≥110 oC, the α’- α crystal transition ensued and in all samples, an oriented lamellar macromorphology developed. Therefore, Td and post-draw annealing, have a significant influence on the mechanical properties, crystallinity and crystalline phase transformation in PLLA, which in-turn, affects the polymers medical and industrial applications.

Item Type: Journal Item
Copyright Holders: 2018 Elsevier Ltd
ISSN: 0014-3057
Keywords: poly-L-lactic acid; uniaxial deformation; SAXS/WAXS; crystalline morphology; orientation
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Life, Health and Chemical Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Research Group: Smart Materials
Item ID: 53678
Depositing User: Ellen Heeley
Date Deposited: 28 Feb 2018 15:14
Last Modified: 02 May 2018 14:39
URI: http://oro.open.ac.uk/id/eprint/53678
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