Enthalpy relaxation and embrittlement of Poly(L-lactide) during physical aging
Enthalpy relaxation and embrittlement of Poly(L-lactide) during physical aging
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DOI：
10.1021/ma071737c
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发表时间：
2007-12-25
期刊：
影响因子：
5.5
通讯作者：
Inoue, Yoshio
中科院分区：
文献类型：
--
作者：
Pan, Pengju;Zhu, Bo;Inoue, Yoshio
采用差示扫描量热法（DSC）、动态力学热分析（DMTA）和拉伸试验研究了聚L-乳酸（PLLA）在玻璃化转变温度（T-g）以下的热焓松弛行为及其对力学性能的影响。玻璃化转变区的热焓损失（OH）和吸热峰温度（Tp）均随老化时间（t（a））的对数线性增加。在DSC结果的基础上，对热焓松弛过程进行了动力学分析，得到了PLLA的动力学参数：40 ℃热焓松弛速率β（H）= 1.77 J g（-1）/decade，表观活化能Δ h *= 1107 KJ mol（-1）。此外，对聚DL-乳酸（PDLLA）的焓松弛动力学分析表明，PDLLA的AV值与PLLA的AV值相似。此外，研究发现，PLLA的强度和模量逐渐增加，相反，他们的韧性急剧下降，在物理老化过程中。经40 ℃ × 1008h时效处理后，试样的屈服强度和拉伸模量分别比未时效试样提高了18.8%和23.1%。此外，PLLA的断裂应变随着在25 ℃下老化24小时从超过300%降低到约6%。此外，通过扫描电子显微镜评估的断口形貌检查表明，PLLA的断裂从“韧性”的物理老化过程中的“诱导”的方式改变。物理老化中延展性的下降与聚合物链从无序形态到更有序形态的重排相关。
The enthalpy relaxation behavior of Poly(L-lactide) (PLLA) below glass transition temperature (T-g) and its effects on the mechanical properties were studied using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and tensile test. Both the enthalpy loss OH) and peak endothermic temperature (T-p) in the glass transition region show a linear increase with the logarithm of aging time (t(a)). On the basis of DSC results, the kinetics of the enthalpy relaxation process were analyzed, and the kinetic parameters of PLLA were obtained: relaxation rate of enthalpy at 40 degrees C beta(H) = 1.77 J g(-1) per decade, and apparent activation energy Delta h* = 1107 KJ mol(-1). Besides, analysis on the kinetic of enthalpy relaxation for poly(DL-lactide) (PDLLA) shows that the AV value of PDLLA is similar to that of PLLA. Moreover, it was found that the strength and modulus of PLLA increase gradually;, on the contrary, them toughness reduces dramatically during the physical aging. The yield strength and tensile modulus increased respectively 18.8% and 23.1% after being aged at 40 degrees C for 1008 h, as compared to the unaged sample. Also, the fracture strain of PLLA decreased from more than 300% to about 6% with aging at 25 degrees C for 24 h. Moreover, the fractographic examination evaluated by scanning electron microscopy showed that the fracture of PLLA changed from the "ductile" to "inductile" manner during physical aging. The drop of ductility in physical aging is correlated to the rearrangement of polymer chains from disordered to more ordered morphology.