Crystallization Behavior of PLA in Zein‐Based Biocomposite Films and Its Functional Performance for Food Packaging

In this study, PLA/Zein composite films were fabricated via solvent casting by blending polylactic acid (PLA) with the plant‐derived protein Zein. Zein acted as a heterogeneous nucleating agent, significantly accelerating PLA crystallization by promoting molecular chain rearrangement. This behavior was confirmed by attenuated total reflectance Fourier‐transform infrared spectroscopy (ATR‐FTIR), polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). At a Zein content of 30 wt%, the crystallinity of the composite film increased by 152.4% compared to neat PLA, along with improvements in tensile strength, elongation at break, and UV‐shielding performance. The introduction of Zein increased heterogeneous nucleation sites, reduced crystal size, and lowered both the glass transition and cold crystallization temperatures, facilitating rapid crystal growth and inducing ordered folding and stacking of PLA chains. In addition, the incorporation of cinnamaldehyde (CA) imparted antibacterial activity and further enhanced UV‐blocking capacity. The PLA/Zein30‐CA5 composite film exhibited nearly zero UV transmittance in the 200–350 nm range. Overall, these results suggest that the bio‐based PLA/Zein/CA composite films hold promising potential for use in active food packaging.