<p>This study highlights a gamma-assisted approach to irradiation-treated cellulose nanocrystals (CNCs) derived from cannabis stem fiber for high UV-shielding PLA composites. The CNCs obtained from sequential pre-treatment possessed high crystallinity (up to 76% CI), while gamma irradiation (5–25&#xa0;kGy at 60&#xa0;°C) reduced particle size and improved dispersion. CNC treated at 20&#xa0;kGy was selected for further study due to its favorable dispersion and retained high crystallinity (73% CI) with uniform nanoscale morphology. The optimized CNC enhanced the mechanical performance of PLA films at low loading (0.1 wt%). The addition of TiO₂ into the CNC system led to a synergistic improvement in UV-shielding performance. The PLA/CNC–TiO₂ films achieved up to 61% UV-A and 32% UV-B shielding at low filler contents (0.5–1.0 wt%). Enhanced UV absorption is attributed to the combined effects of nanoscale dispersion and interfacial interactions between CNC and TiO₂, which improve light-harvesting efficiency. In addition, this system exhibited promising UV-shielding efficiency at significantly lower filler loading compared with other hybrid systems, indicating improved filler efficiency. These results highlight an efficient and sustainable strategy for designing bio-based polymer composites with enhanced UV protection for advanced UV-shielding applications.</p> Graphical abstract <p></p>