Immobilization of Antioxidants on Rutile TiO2 Nanoparticles for Enhanced Photo- and Thermo-Oxidative Aging Resistance in Polyurethane Adhesives

The versatile polyurethane (PU) has been widely used in industrial and civil products due to the diversity of structure composition and adjustable mechanical properties. However, PU is prone to aging under UV light and thermal exposure due to its molecular structure, which includes UV-sensitive carbonyl and urethane groups as well as oxygen-susceptible ether bonds. Thus, this study proposes to modify rutile titanium dioxide (TiO 2 ) nanoparticles with 2,2′-methylenebis(6-tert-butyl-4-methyl-phenol) (antioxidant 2246) by using toluene-2,4-diisocyanate (TDI) as a molecular bridge to form a nanoscaled titanium dioxide-immobilized antioxidant, M-TiO 2 composites, and then incorporate M-TiO 2 composites into PU adhesives to achieve synergistic effects in improving their photo- and thermo-oxidative aging resistance. The results indicate that the antioxidant 2246 molecules are chemically anchoring onto the surface of the TiO 2 particles and the modified TiO 2 particles show better dispersibility in PU matrix and are more efficient in improving the lap shear strength of PU adhesives than pure TiO 2 . PU adhesives containing M-TiO 2 composites exhibits superior aging resistance during the long-time accelerated photo- and thermo-oxidative aging, because of the synergistic effects of the UV-shielding properties of titanium dioxide particles and the neutralizing free radical capacity of antioxidant 2246. Highlights Antioxidant 2246 was chemically immobilized onto TiO 2 nanoparticles. TDI functioned as a molecular bridge between TiO 2 and antioxidant 2246. Surface modification improved TiO 2 dispersibility in the PU matrix. M-TiO 2 enhanced lap shear strength of PU adhesives. M-TiO 2 improved photo- and thermo-oxidative aging resistance of PU adhesives.