Mechanism of Intermolecular Hydrogen Bonding Changes in the Blend Crystallization of Polylactic Acid Revealed by Terahertz Spectroscopy

The design of high-performance stereocomplex poly(lactic acid) (SC-PLA) materials relies on the hydrogen bond interactions between enantiomers. However, the formation of SC is often influenced by homocrystallite (HC), and the underlying interaction mechanism remains unclear due to limitations in characterization techniques. Terahertz (THz) spectroscopy can probe the HC lattice periodicity and SC hydrogen bonding. Here, this method is employed to study the temperature-dependent crystallization dynamics of PLA blends. At lower temperatures, the THz peak associated with SC hydrogen bonding exhibits an anomalous blue-shift that deviates from crystallinity relationships. This is attributed to the β crystal formed under constrained crystallization occupying a certain space but lacking hydrogen bonding, thus weakening the hydrogen bond strength of the system. Furthermore, specific THz parameters have the ability to characterize SC crystallinity, especially the peak height at 1.45 THz. This work reveals the effect of the conformational transition on hydrogen bonding and provides new insights into the quantitative characterization of SC in multicomponent systems.