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

作者：Billimoria Kharmen; Heeley Ellen L^*; Parsons Nathan; Figiel Lukasz

来源：European Polymer Journal, 2018, 101: 127-139.

DOI：10.1016/j.eurpolymj.2018.01.031

• Poly-L-lactic acid
• Uniaxial deformation
• SAXS/WAXS
• Crystalline morphology
• Orientation

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.

• 出版日期2018-4