Journal
EUROPEAN POLYMER JOURNAL
Volume 101, Issue -, Pages 127-139Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.eurpolymj.2018.01.031
Keywords
Poly-L-lactic acid; Uniaxial deformation; SAXS/WAXS; Crystalline morphology; Orientation
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Funding
- European Union's Horizon Maria Sklodowska-Curie RISE project 'Biaxial stretching of PLLA-WS2 nanocomposites for thinner and stronger biomedical scaffolds' [691238]
- EPSRC Centre for Doctoral Training in Molecular Analytical Science (MAS) [EP/L015307/1]
- Engineering and Physical Sciences Research Council [1743147] Funding Source: researchfish
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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 (T-d) above T-g, 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 T-d where embrittlement and eventual failure were observed as T-d 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 T-d. SAXS/WAXS data showed that strain-induced crystallization occurs on drawing, but crystallite orientation decreased with increasing T-d, due to chain relaxation at temperatures >= 30 degrees C above T-g. 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 T-d. Also, the disordered alpha' crystal form was observed post-draw at T-d between 60 and 80 degrees C, whereas T-d >= 90 degrees C, resulted in the ordered alpha crystal form directly. However, on annealing at temperatures of >= 110 degrees C, the alpha'-alpha crystal transition ensued and in all samples, an oriented lamellar macromorphology developed. Therefore, T-d 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.
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