Stretching-Induced Crystallinity and Oligomer Dispersion for Antistatic Biodegradable PLA Films

The development of antistatic biodegradable polymers, particularly polylactic acid (PLA), is limited by the intrinsically high electrical resistance of PLA. To address this, we introduce a branched conductive PLA oligomer terminated with an aniline pentamer, mPEI-PLA-HDI-AP, and evaluate its effectiveness as a conductive additive at 15 wt % in PLA films. The roles of uniaxial (UNS), simultaneous biaxial (SIB), and sequential biaxial (SEB) stretching in controlling chain alignment and tuning film conductivity are systematically examined. Variation of stretching rates (75 and 10 mm/s) and draw ratios (2×, 3×, and 4×) reveals that high stretching rates combined with large draw ratios promote crystallization, especially in SIB and SEB processes. These conditions yield small crystallites (<20 nm) and low cold-crystallization enthalpies (<5 J/g), as confirmed by WAXD and DSC. These structural modifications significantly reduce surface electrical resistance to as low as 108 Ω. In contrast, annealed PLA/mPEI-PLA-HDI-AP films exhibit similar crystallinity but show no improvement in resistivity, indicating that both enhanced crystalline packing and improved dispersion and orientation of the conductive PLA oligomer are essential and can be achieved through optimal stretching. Overall, this work demonstrates that combining conductive PLA-based oligomers with controlled stretching effectively reduces film resistance from ∼1010 Ω to ∼108 Ω, enabling PLA films suitable for antistatic packaging applications.