College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, China.
Analysis & Test Center, Beijing University of Chemical Technology, Beijing 100029, China.
Spectrochim Acta A Mol Biomol Spectrosc. 2022 Sep 5;277:121289. doi: 10.1016/j.saa.2022.121289. Epub 2022 Apr 21.
Effects of montmorillonite (MMT) on the crystallization behavior of poly(L-lactic acid) (PLLA) were investigated by variable-temperature FTIR spectroscopy. The variations of carbonyl band (1800-1720 cm) of different PLLA/MMT nanocomposites were focused due to its strong intensity and the involved abundant structure information. Difference spectrometry was used to evaluate the structural variations of PLLA after introducing MMT, and perturbation correlation moving window two-dimensional analysis (PCMW2D) split the temperature range into two sub-regions, i.e., 32-116 ℃ and 116-152 ℃, on the basis of the spectral variation. Two-dimensional correlation spectroscopy (2DCOS) was further applied to such sub-regions in order to find the change order between varied PLLA polymorphs. The results showed that less addition of MMT (≤3%) would lead to a well-exfoliated structure, which not only had no nucleation effect for PLLA, but also delayed the cold crystallization to a higher temperature compared with the one of pure PLLA. However, a higher addition of MMT (≥5%) would lead to an intercalated structure, which acted as a nucleating agent and thus advanced the cold crystallization to a lower temperature. Nevertheless, the introduction of MMT cannot affect the phase transition order between the amorphous, the intermediate, the α'- and the α'-PLLAs based on 2DCOS results.
采用变温傅里叶变换红外光谱法研究了蒙脱土（MMT）对聚 L-乳酸（PLLA）结晶行为的影响。由于羰基带（1800-1720cm）的强度较高且涉及丰富的结构信息，因此聚焦于不同 PLLA/MMT 纳米复合材料的羰基带变化。差谱法用于评估引入 MMT 后 PLLA 的结构变化，并且基于光谱变化，扰动相关移动窗口二维分析（PCMW2D）将温度范围分为两个子区域，即 32-116℃和 116-152℃。进一步将二维相关光谱法（2DCOS）应用于这些子区域，以确定变化的 PLLA 多晶型物之间的变化顺序。结果表明，少量添加 MMT（≤3%）会导致良好的剥离结构，这不仅对 PLLA 没有成核作用，而且与纯 PLLA 相比，还会将冷结晶延迟到更高的温度。然而，较高含量的 MMT（≥5%）会导致插层结构，其作为成核剂，从而将冷结晶推进到较低的温度。然而，根据 2DCOS 结果，引入 MMT 不会影响无定形相、中间相、α'-和α'-PLLA 之间的相转变顺序。
