Impact of d-isomer content on the microstructure and mechanical properties of uniaxially pre-stretched poly(lactic acid). (9th January 2020) - Chen, Yunjing
Abstract: Poly(lactic acid) with 2%, 4%, and 12% d -isomer content were selected to investigate the influence of stereoregularity on mechanical properties of uniaxially pre-stretched PLAs (ps-PLAs). The mobility of molecular chains was activated by pre-stretching because the network structures composed of cohesional entanglements were destroyed, leading to a brittle-ductile transition. The elongation at break increased to 145%, 175% and 190% at pre-stretching ratio of 0.5 for ps-PLA2, ps-PLA4 and ps-PLA12, respectively. The network structures of cohesional entanglements were easier destroyed in PLAs with more d -isomer due to the stereoregularity defects, leading to higher elongation at break. Then the elongation at break decreased with increasing pre-stretching ratio owing to the development of mesophase which might initiate crazing. The more d -isomer the less strain-induced mesophase resulting from the more active chain relaxation, and then the slower decrease of elongation at break. In addition, the modulus and strength of ps-PLAs were all increased with increasing pre-stretching ratio. Graphical abstract: Image 1 Highlights: The ductile PLAs with high strength were prepared by uniaxial pre-stretching around T g . A network structure consisting of cohesional entanglements led to the brittleness of PLAs. Disentanglement induced by pre-stretching led to the toughness of ps-PLAs. The more d -isomer the larger elongation at break but smaller modulus and strength of ps-PLAs. The more d -isomer the less strain-induced mesophase and thus the less decrease of elongation at break.