Synergistic UV shielding and radical scavenging: Bifunctionalized ZnAl-LDH for enhanced photothermal oxidative stability of polypropylene

Layered double hydroxides (LDHs) hold significant promise as antioxidant carriers for enhancing the aging resistance of polymers. However, their widespread application is hampered by inherent limitations such as low antioxidant loading capacity, diminished activity post-intercalation, and insufficient ultraviolet (UV) shielding. This study presents a strategic dual-modification approach: the UV absorber (UV-284) was intercalated into the ZnAl-LDH interlayers, constructing an intrinsic "UV shield" while the hindered phenolic antioxidant (AO) was covalently grafted onto the LDH surface using γ-glycidyl ether oxypropyl trimethoxysilane (KH-560) as a bridging molecule. This process successfully created a synergistic anti-aging system, denoted ULKA, which integrates both UV shielding and radical scavenging functionalities. Results demonstrate that the intercalation of UV-284 reduced the band gap of ULKA from 3.84 eV to 2.88 eV, significantly enhancing its absorption of low-energy ultraviolet light. Furthermore, the introduction of an electron-donating ester group into the antioxidant molecule increased the electron cloud density around the phenolic hydroxyl groups, thereby improving its radical capture efficiency. Incorporating merely 1 wt% of ULKA into polypropylene (PP) via melt blending yielded PP/ULKA composites with superior resistance to photo-thermal oxidation compared to both pure PP and PP containing an equivalent amount of commercial antioxidant Irganox 1010. After 600 h of UV accelerated aging, the PP/ULKA composite retained 85.94% of its impact strength and 81.76% of its elongation at break, significantly outperforming PP/1010. The oxidation induction time (OIT) of the composite reached 22.7 min. Following 28 days of thermal oxidative aging at 110 °C, the increase in the carbonyl index (CI) was merely 0.93%, far lower than the 3.5% increase observed for pure PP. XPS analysis further confirmed that the C = O /C-C intensity ratio increased by only 0.018, a value significantly lower than those of other samples. This work provides a novel design strategy and experimental foundation for developing highly efficient and migration-resistant anti-aging additives for polymers.