Surface Modification Of Silica And Its Application In Rubber

Surface modification of silica can improve its reinforcement effect in rubber. Anothernoticeable subject in the rubber industry is how to prolong serve life of vulcanizates. In thiswork, antioxidant coupling agent was grafted onto silica surface to obtain antioxidantfunctionalized silica, and then they were incorporated into styrene-butadiene rubber (SBR) ornatural rubber (NR) to test their reinforcement and ageing properties.(3-Glycidyloxy-propyl)trimethoxysilane (A187) reacted with N-phenyl-1,4-phenylenedi-amine(PPDA) to synthesize antioxidant coupling agent. The structure of the product wascharacterized by~1H-NMR, HPLC-MS, and FTIR. Then the product was used to modify silicasurface to prepare antioxidant functionalized silica. The result of XPS, TGA and TEM showedthat PPDA was successfully grafted onto the silica surface, which reduced the amount ofsilanol groups and adsorbed water on silica surface. The grafting density rapidly increasedwith the increasing amount of coupling agent at first, and then the increasing tendencyslowdown and got to a plateau. The dispersion of the modified silica in organic solvent wasmuch better.The reinforcement and anti-ageing properties of antioxidant functionalized silica forSBR were studied. It was found that the processing and mechanical properties of thevulcanizates were both the best when50phr fillers were incorporated into SBR. Antioxidantfunctionalized silica filled SBR were then compared with those filled with carbon black, neatsilica, bis(3-triethoxysilylpropyl)tetrasulfane (Si69) modified silica, or A187modifiedsilica. RPA results showed that the torque, optimum cure time and Payne effect of antioxidantfunctionalized silica filled vulcanizates decreased compared to that of neat silica filledcompound; moreover, its compatibility with rubber and dispersion in matrix were improved.The mechanical properties increased with increasing grafting density of the antioxidant, andwere similar to that of vulcanizates filled with carbon black or Si69modified silica; however,properties of A187modified silica filled vulcanizate were poor. Thermal oxidative and dampheat ageing tests showed that the antioxidant functionalized silica filled vulcanizates weremuch more stable than the vulcanizates added with antioxidant4020. Their tensile strength,elongation at break and the retention after ageing were better than the references. However, their anti-ozone ageing property was a litter poor.At last, the antioxidant functionalized silica was used in NR. Similar to SBR composites,RPA results showed that the torque and filler-filler interaction of antioxidant functionalizedsilica/NR compounds declined, and its compatibility with rubber and dispersion in matrixwere improved. The optimum cure time was almost the same as that of carbon black filled NRbut much shorter than those of neat silica or Si69modified silica filled compounds. Thetensile strength of antioxidant functionalized silica/NR vulcanizates increased with increasinggrafting density of antioxidant, and it was almost the same as that of carbon black filledvulcanizate. The tensile strength of A187modified silica filled vulcanizate followed and wasbetter than that of Si69modified silica filled vulcanizate. The elongation at break of theantioxidant functionalized silica/NR vulcanizates was preceded only by that of neat silicafilled vulcanizate and their content of bound rubber was more than that of carbon black filledvulcanizate, indicating that antioxidant functionalized silica had strong interaction with NRmatrix. Thermal oxidative, ozone and damp heat ageing tests showed that the antioxidantfunctionalized silica filled NR was much more stable than the vulcanizates added withantioxidant4020. Their tensile strength, elongation at break and the retention after ageingwere better than those of the references.