Abstract
This work presents a comprehensive experimental and theoretical investigation of polylactide (PLA) nanocomposites reinforced with zinc oxide (ZnO) nanoparticles at concentrations of 0.5, 1, 3, and 5 wt.%. The dispersion state and microstructural features of ZnO within the PLA matrix were examined using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, revealing homogeneous distribution at low filler contents and progressive agglomeration at higher loadings. X-ray diffraction analysis confirms that ZnO preserves its hexagonal wurtzite crystal structure after incorporation into the polymer matrix, while composition-dependent variations in crystallite size and lattice microstrain are found to correlate with the mechanical response of the composites. Fourier-transform infrared spectroscopy indicates interfacial interactions between PLA chains and ZnO nanoparticles, as evidenced by systematic shifts in the carbonyl stretching band and associated charge redistribution. Ultraviolet–visible spectroscopy demonstrates a significant enhancement of UV-shielding performance with increasing ZnO content, accompanied by the emergence of sub-bandgap absorption tails attributed to defect-related and interfacial electronic states. Density functional theory calculations support the experimental observations by revealing interfacial charge transfer and a slight modification of the electronic structure at the PLA/ZnO interface. The results show that ZnO incorporation improves both mechanical stiffness and UV-blocking efficiency, while an optimal ZnO loading below 1 wt.% is identified to maintain mechanical integrity and minimize agglomeration-induced degradation.