Application of antioxidant functionalized silicas in natural rubber

Antioxidant functionalized silica was designed and prepared from N-phenyl-1, 4-phenylenediamine(PPDA), (3-Glycidyloxypropyl)trimethoxysilane and silica to improve the dispersion of silica in the rubber matrix and to avoid the volatility and extractability of the antioxidants. The reinforcement and antioxidation effects of the modified silica in natural rubber (NR) were studied and compared with those of carbon black/NR, neat silica/NR and Si69 modified silica/NR (the latter three composites added with N-(1, 3-dimethylbutyl)-N-phenyl-1, 4-phenylenediamine (4020) as antioxidant). The results show that the use of antioxidant functionalized silica can prolong the scorch time, shorten the optimum curing time, improve the dispersion of silica in NR network, and improve the mechanical properties of the composites. The tensile strength and tear strength of the antioxidant functionalized silica/NR increase with increasing PPDA grafting content. When the PPDA content reaches 5.27% (mass fraction to silica), its tensile strength increases 90% and 73% to those of the neat silica/NR and Si69 modified silica/NR, respectively, and is closed to that of the carbon black/NR; its tear strength is 5, 2.5 and 2 times of those of neat silica/NR, Si69 modified silica/NR and carbon black/NR, respectively. Furthermore, the antioxidant functionalized silica/NR composites show great resistance in thermal oxidative ageing and damp heat ageing. Their stability is improved in ozone ageing compared with those used 4020 as antioxidant.