Antidegradation and reinforcement effects of phenyltrimethoxysilane- or N-[3-(trimethoxysilyl)propyl]aniline-modified silica particles in natural rubber composites

• Silica was surface modified with PhTMS or ATMS via a sol–gel reaction.
• Modified silica showed a decreased interfacial adhesion energy.
• Modified silica showed an enhanced free radical scavenging activity.
• Modified silica improved the mechanical properties, thermal stability and ozone resistance in NR vulcanizates.

The modification of silica particles with phenyltrimethoxysilane or N-[3-(trimethoxysilyl)propyl]aniline via a sol–gel reaction was performed in order to improve the dispersion of silica and antidegradation in natural rubber (NR). The functional groups on the modified silica surface were characterized by Fourier transform infrared spectroscopy, while the morphology was evaluated by scanning and transmission electron microscopy. The surface properties and antioxidant activity of the modified silica particles were determined by the water contact angle and 2, 2-diphenyl-1-picrylhydrazyl assay, respectively. The modified silica particles exhibited a higher hydrophobicity and a decreased interfacial adhesion energy compared with the unmodified silica particles. The modified silica particles were then incorporated into NR. The better dispersion of the modified silica particles than the unmodified ones in the NR matrix resulted in improved mechanical properties in terms of the modulus at 300% elongation (2.9 ± 0.02 MPa), hardness (52.5 ± 0.2 Shore A), abrasion resistance (241 ± 8 mm3) and compression set (20.2 ± 0.6%). In addition, the inclusion of the modified silica particles in the NR matrix gave a high initial temperature of decomposition and retarded the ozone-induced degradation compared with the NR filled with unmodified silica particles.

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