Enthalpy relaxation of the glass of poly (l-lactic acid) of different d-isomer content and its effect on mechanical properties
Enthalpy relaxation of the glass of poly (l-lactic acid) of different d-isomer content and its effect on mechanical properties
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DOI：
10.1007/s00289-016-1854-5
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发表时间：
2017-07
期刊：
影响因子：
3.2
通讯作者：
H. M. Naeem Iqbal;Chanita Sungkapreecha;R. Androsch
中科院分区：
文献类型：
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作者：
H. M. Naeem Iqbal;Chanita Sungkapreecha;R. Androsch
用常规的差示扫描量热法分析了聚L-乳酸（PLLA）及其含有2mol%和4mol% d-异构体共聚单元的无规共聚物的玻璃化松弛。发现在PLLA链中存在高达4%的d-异构体共单元对完全无定形样品中的玻璃化弛豫动力学没有可测量的影响。在环境温度下，在以50 K/min的速率快速冷却熔体之后，为了避免结晶，玻璃弛豫在约10 min之后开始，并且在5000 min内不结束。玻璃的松弛伴随着机械性能的重大变化，因为它是由时间分辨的测量的显微压痕硬度和杨氏模量。在退火的无定形PLLA在环境温度下，显微硬度和杨氏模量增加超过40和10%，分别在约一个月的时间内，并与平衡值尚未实现，即使在这样长的退火时间。如在的情况下的弛豫动力学，无论是，绝对值和分析的机械性能的时间演变是独立的存在ofd-异构体共单元在PLLA链内的调查浓度范围内。
The relaxation of the glass of poly (l-lactic acid) (PLLA) and its random copolymers with 2 and 4 mol%d-isomer co-units has been analyzed by conventional differential scanning calorimetry. It was found that the presence of up to 4%d-isomer co-units in the PLLA chain has no measurable effect on the glass relaxation kinetics in fully amorphous samples. At ambient temperature, after rapid cooling of the melt at a rate of 50 K/min, to avoid crystallization, the glass relaxation begins after about 10 min and is not finished within 5000 min. The relaxation of the glass is accompanied by a major change of mechanical properties as it was revealed by time-resolved measurements of the micro-indentation hardness and Young’s modulus. During annealing of amorphous PLLA at ambient temperature, the microhardness and Young’s modulus increase by more than 40 and 10%, respectively, within a time period of about one month, and with an equilibrium value not yet achieved even after such a long annealing time. As in case of the enthalpy-relaxation kinetics, both, absolute values and the time evolution of the analyzed mechanical properties are independent on the presence ofd-isomer co-units in the PLLA chain within the investigated concentration range.