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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
European Polymer Journal ( IF 5.8 ) Pub Date : 2018-04-01 , DOI: 10.1016/j.eurpolymj.2018.01.031
Kharmen Billimoria , Ellen L. Heeley , Nathan Parsons , Łukasz Figiel

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 °C 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 and 80 °C, whereas Td ≥ 90 °C, resulted in the ordered α crystal form directly. However, on annealing at temperatures of ≥110 °C, 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.

中文翻译:

准固态状态下单轴变形下聚 L-乳酸 (PLLA) 结晶形态转变的研究

摘要 聚乳酸 (PLLA) 在单轴变形和退火过程中的机械行为、晶体和宏观形貌结构发展,具有不同的应变速率和高于 Tg 的拉伸温度 (Td),已经使用小角和广角 X 进行了研究。 -射线散射 (SAXS/WAXS)、显微镜、热和机械技术。PLLA 的机械性能强烈依赖于 Td,在无定形聚合物的单轴拉伸过程中,随着 Td 的增加,观察到脆化和最终失效。这反映在整体表面形态中,随着 Td 的增加,出现裂纹、微孔和空化。SAXS/WAXS 数据表明,拉伸时发生应变诱导结晶,但由于在高于 Tg ≥ 30 °C 的温度下链松弛,晶粒取向随着 Td 的增加而降低。然而,没有观察到直接拉伸后的长程取向层状宏观形态,仅在高于 Td 的温度下逐步退火的样品中出现。此外,在 60 到 80°C 之间的 Td 下,在拉伸后观察到无序的 α' 晶形,而 Td ≥ 90°C,直接导致有序的 α 晶形。然而,在≥ 110 °C 的温度下退火时,随后发生了 α'-α 晶体转变,并且在所有样品中都形成了定向层状宏观形态。因此,Td 和拉伸后退火对 PLLA 的机械性能、结晶度和结晶相变有显着影响,进而影响聚合物的医疗和工业应用。直接拉伸后没有观察到长程取向的层状宏观形态,仅在高于 Td 的温度下逐步退火的样品中出现。此外,在 60 到 80°C 之间的 Td 下,在拉伸后观察到无序的 α' 晶形,而 Td ≥ 90°C,直接导致有序的 α 晶形。然而,在≥ 110 °C 的温度下退火时,随后发生了 α'-α 晶体转变,并且在所有样品中都形成了定向层状宏观形态。因此,Td 和拉伸后退火对 PLLA 的机械性能、结晶度和结晶相变有显着影响,进而影响聚合物的医疗和工业应用。直接拉伸后没有观察到长程取向的层状宏观形态,仅在高于 Td 的温度下逐步退火的样品中出现。此外,在 60 到 80°C 之间的 Td 下,在拉伸后观察到无序的 α' 晶形,而 Td ≥ 90°C,直接导致有序的 α 晶形。然而,在≥ 110 °C 的温度下退火时,随后发生了 α'-α 晶体转变,并且在所有样品中都形成了定向层状宏观形态。因此,Td 和拉伸后退火对 PLLA 的机械性能、结晶度和结晶相变有显着影响,进而影响聚合物的医疗和工业应用。直接产生有序的α晶型。然而,在≥ 110 °C 的温度下退火时,随后发生了 α'-α 晶体转变,并且在所有样品中都形成了定向层状宏观形态。因此,Td 和拉伸后退火对 PLLA 的机械性能、结晶度和结晶相变有显着影响,进而影响聚合物的医疗和工业应用。直接产生有序的α晶型。然而,在≥ 110 °C 的温度下退火时,随后发生了 α'-α 晶体转变,并且在所有样品中都形成了定向层状宏观形态。因此,Td 和拉伸后退火对 PLLA 的机械性能、结晶度和结晶相变有显着影响,进而影响聚合物的医疗和工业应用。
更新日期:2018-04-01
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