Application of infrared spectroscopy in the multiscale structure characterization of poly(L-lactic acid)

Poly(L-lactic acid) (PLLA) is considered as a promising candidate to substitute for commercial petrochemical-based polymers due to its renewability, biodegradability, biocompatibility, and relatively high mechanical performance. To tailor the properties of PLLA to suit different application fields, it is essential to regulate its structures at different length scales accurately. Fourier transform infrared (FTIR) spectroscopy has been shown to be a simple and efficient technique to characterize the multiscale structures of PLLA. In this review, we examine the band assignments of PLLA in different states, followed by a detailed description of important contributions made by FTIR to the structural characterization of PLLA. This includes crystal modifications, diverse phase transitions, chain orientation in different phases, crystallinity, crystallization kinetics, etc. Researchers could gain a comprehensive understanding of how FTIR is used in the study of PLLA and wish to conduct further advanced studies on the structural characterization of PLLA and other macromolecules.