On the effects of creep-induced crystallization and dipolar rotation on PLLA's electrical and electromechanical properties

The development of biocompatible piezoelectric materials is crucial for advancing biomedical devices and sustainable electronics. This study investigates how crystalline structure and molecular orientation in electrospun poly(L-lactic acid) (PLLA) scaffolds determine electromechanical properties through a systematic analysis of thermomechanical creep-induced crystallization. Our investigation demonstrates that PLLA's piezoelectric response is strongly correlated with stress-induced molecular dipole reorientation, specifically the constructive alignment of CdbndO dipoles, as supported by a quantitative correlation between dipole alignment, crystallinity, and d₃₃. This finding challenges previous assumptions regarding the dominant role of crystallization in PLLA's electrical properties. Through quantitative correlation of thermal, electromechanical, and spectroscopic data, we establish a clear decoupling between crystallinity and piezoelectric response: while the applied creep regime drives a continuous, monotonic increase in bulk crystallinity (progressing from 24% to 70% over 12 h), the macroscopic piezoelectric response exhibits non-monotonic behavior. Specifically, an optimized 6-h processing window yields a peak d₃₃ value of 1.2 pC/N (from an initial 0.8 pC/N), which correlates directly with FT-IR-based mathematical deconvolution revealing an intramolecular shift toward perpendicular tg and gt conformers. At longer creep durations, this optimal dipole alignment relaxes, coinciding with a reduction in d₃₃ despite continued increases in crystallinity, further supporting the decoupled behavior. These results demonstrate that while crystallization is necessary, it plays a secondary role by providing a rigid morphological framework that stabilizes the electroactive dipole configuration; optimal piezoelectric performance requires both sufficient crystallinity and favorable dipole alignment. Furthermore, we establish that this microstructural evolution enhances piezoelectric properties without transitioning to ferroelectric behavior or significantly altering the frequency-dependent impedance response. These insights advance the fundamental understanding of structure–property relationships in semicrystalline biopolymers, positioning purely organic, additive-free PLLA as a promising candidate for biodegradable electronics and advanced tissue engineering platforms where dipole alignment significantly influences electromechanical response.