Low Loading Nitrogen‐Doped Carbon Quantum Dots as Melt Processable UV ‐Shielding Additives for Transparent PET Films With Enhanced

ABSTRACT

Polyethylene terephthalate (PET) films are widely used in packaging, optical and electronic applications because of their high transparency and processability. However, their practical use under ultraviolet (UV) radiation is limited by low UV‐A shielding capability and poor long‐term UV‐aging resistance. In this study, nitrogen‐doped carbon quantum dots (N‐CQDs) were synthesized from citric acid and polyethyleneimine via a hydrothermal method and then incorporated into PET by melt blending to fabricate transparent composite films. The strong UV absorption and excellent thermal stability of N‐CQDs enabled them to be promising UV‐shielding nano‐additives during PET melt processing. The UV‐shielding performance of the composite films improved progressively with increasing N‐CQDs loading. At 0.5 wt% N‐CQDs, the composite films exhibited UV transmittance below 3% and a visible light transmittance above 97%. In accelerated UV‐aging tests, they showed significantly improved UV‐aging resistance compared with pure PET. Notably, the 0.3 wt% N‐CQDs composite film retained 63.9% of tensile strength and 41.7% of elongation at break after 600 h of UV irradiation, which were higher than those of pure PET. SEM observations further confirmed that N‐CQDs loading alleviated UV‐induced surface cracking. Thus, low loading N‐CQDs are effective melt‐processable UV‐shielding nano‐additives for improving PET films while preserving optical transparency.