Study of Strain-Induced Crystallization and Enzymatic Degradation of Drawn Poly(L-lactic acid) (PLLA) Films
Study of Strain-Induced Crystallization and Enzymatic Degradation of Drawn Poly(L-lactic acid) (PLLA) Films
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DOI：
10.1021/ma301482j
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发表时间：
2012-09-25
期刊：
影响因子：
5.5
通讯作者：
Vasanthan, Nadarajah
中科院分区：
文献类型：
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作者：
Rangari, Deepika;Vasanthan, Nadarajah
采用恒应变速率拉伸法对低结晶度的聚乳酸（PLLA）熔融压膜进行了结晶化。应变诱导的结晶和酶降解的拉伸PLLA膜的蛋白酶K的存在下，在37摄氏度进行了研究，使用重量损失测量，差示扫描量热法（DSC），和傅里叶变换红外（FTIR）光谱。结果表明，拉伸对结晶度、分子取向和酶降解有显著影响。选择921和956 cm（-1）处谱带的吸光度比（A（921）/A（956））来确定应变诱导结晶和水解期间的结构变化。DSC结晶度和A（921）/A（956）随拉伸倍数的增加而增加。由于我们无法获得921和956 cm（-1）处谱带的跃迁矩角，因此比较了二色性比。结果发现，在较低的拉伸比下，结晶取向发展迅速，而非晶取向发展缓慢得多。报道了退火的PLLA膜的酶降解，并且令人惊讶地，对于取向的PLLA膜的酶降解观察到相当不同的结果。拉伸的PLLA膜的降解程度低于未拉伸的熔融压制的PLLA膜。拉伸PLLA膜的DSC结晶度和A（921）/A（956）随降解时间增加而增加，表明结晶相随降解而增加。这表明，降解发生在自由和受限制的非晶区的情况下，拉伸PLLA膜，而它只发生在退火的未取向的PLLA膜中的自由非晶区。
Poly(lactic acid) (PLLA) melt-pressed films with low crystallinity were crystallized by stretching at a constant strain rate. The strain-induced crystallization and enzymatic degradation of drawn PLLA films in the presence of proteinase K at 37 degrees C was investigated using weight loss measurements, differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. The results show that drawing has a significant effect on the crystallinity, molecular orientation, and enzymatic degradation. The absorbance ratio of the bands at 921 and 956 cm(-1) (A(921)/A(956)) was chosen to determine the structural changes during strain-induced crystallization and hydrolysis. The DSC crystallinity and A(921)/A(956) showed an increase with the draw ratio. Since we were unable to obtain the transition moment angle for the bands at 921 and 956 cm(-1), the dichroic ratios were compared. It was found that the crystalline orientation develops rapidly at lower draw ratios whereas the amorphous orientation develops much more slowly. The enzymatic degradation of annealed PLLA films was reported, and surprisingly, quite different results were observed for the enzymatic degradation of oriented PLLA films. The extent of degradation was lower for the drawn PLLA film than for the undrawn melt-pressed PLLA film. The DSC crystallinity and A(921)/A(956) of drawn PLLA films increased with the degradation time, suggesting an increase in the crystalline phase with degradation. This reveals that degradation occurs in both the free and the restricted amorphous region in the case of drawn PLLA films, whereas it occurs only in the free amorphous region in annealed unoriented PLLA films.