Effects of montmorillonite (MMT) on the crystallization behavior of poly (L-lactic acid) (PLLA) by variable-temperature FTIR coupled with difference spectrometry, PCMW2D and 2DCOS analyses

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(-1)) 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 degrees C and 116-152 degrees C, 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 alpha'- and the alpha'-PLLAs based on 2DCOS results. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

The effect of montmorillonite on the crystallization behavior of poly(L-lactic acid) was studied using variable-temperature FTIR spectroscopy. The results showed that the addition of a small amount of montmorillonite delayed the cold crystallization of the poly(L-lactic acid), while a larger amount advanced the cold crystallization. However, the introduction of montmorillonite did not affect the phase transition order of the poly(L-lactic acid).