光学纯度对聚左旋乳酸结晶与熔融行为的影响

通过示差扫描量热仪(DSC)和广角X射线衍射仪(WAXD)研究了聚左旋乳酸(PLLA)的光学纯度(91.6%、93.3%、94.0%、97.0%、98.4%)对聚乳酸结晶和熔融行为的影响。 在非等温结晶过程中,随着光学纯度的提高,聚乳酸的结晶峰值温度、熔点、熔融焓均提高。 在等温结晶过程中,PLLA的半结晶时间(t_1/2)随着光学纯度的增加而减少,在结晶温度100~110 ℃区间内半结晶时间均达到最小值;含有不同光学纯度PLLA的Avrami指数n≈3,表明光学纯度的变化不能改变聚乳酸以三维球晶生长的异相成核机理。 随着光学纯度的增加,聚乳酸δ-晶型转变为α-晶型的临界温度升高。 聚乳酸的结晶和熔融行为对光学纯度具有依赖性。

Effect of Optical Purities on the Crystallization and Melting Behaviors of Poly(L-lactic acid)

In both nonisothermal and isothermal treatments, crystallization and melting behaviors of poly(L-lactic acid)(PLLA) with different optical purities(91.6%, 93.3%, 94.0%, 97.0%, 98.4%) were investigated by differential scanning calorimetery(DSC) and wide-angle X-ray diffraction(WAXD).With the increase of optical purities of PLLA, the crystallization rate, the melting enthalpy, crystallization temperature and melting point increase. The Avrami index(n) is about 3, indicating a three-dimensional spherulitic growth on heterogeneous nuclei during the isothermal process. The crystalline structure of PLLA is independent on the variation of optical purities of PLLA. However, the critical temperature for crystal formation from δ-form to α-form crystals increases during the isothermal crystallization process with optical purities increasing of PLLA. All the results show that the crystallization and melting behaviors are dependent on the optical purities of PLLA.