Synergistic UV photostabilization of linear low-density polyethylene films by alumina/silica-coated TiO2 and hindered amine light stabilizers (HALS)

Linear Low-Density Polyethylene (LLDPE) films are widely used in outdoor applications. Nevertheless, they are susceptible to photooxidative degradation under prolonged ultraviolet exposure, resulting in embrittlement, discoloration, and loss of mechanical integrity. In this study, we investigated the synergistic UV-stabilization effect of systems composed of pigment-grade titanium dioxide (TiO 2 ) coated with alumina and silica (Al 2 O 3 /SiO 2 ), and hindered amine light stabilizers (HALS) in an LLDPE matrix. LLDPE films, including unreinforced control and composites containing surface-modified TiO 2 (and combined with HALS), were prepared via melt compounding. Photostabilization resistance was assessed by monitoring the carbonyl index (CI) using Fourier transform infrared spectroscopy, and by measuring the retention of tensile properties after 1200 h of QUV-A irradiation in an accelerated weathering test. Results demonstrated that photocatalytic activity was significantly suppressed by Al 2 O 3 /SiO 2 -coated TiO 2 , thereby reducing the formation of oxidative degradation products. Moreover, the addition of HALS further enhanced stabilization by scavenging free radicals formed during photooxidation. This dual-stabilization approach exhibited superior UV resistance, with the HALS-TiO 2 (Al 2 O 3 /SiO 2 ) system, maintaining over 90% tensile strength and elongation at break, and restriction of carbonyl index to only 0.01 after 600 h of UV irradiation, compared to 1.26 for pure LLDPE. This work highlights the critical role of surface-passivated pigments in combination with organic stabilizers in the design of durable LLDPE-based materials for long-term UV resistant applications.