BACKGROUND: A new concept for reinforcing silica, named networked silica, was used to achieve enhanced reinforcing performance of silica and to eliminate the disadvantage of ethanol production and precure through coupling reagents in the preparation of silica-reinforced SBR compounds.
RESULTS:The networked silicas were prepared by connecting silica particles with amine and glycidoxy groups, which had been previously coupled on their surface. The networked silicas compounded in SBR showed a significant enhancement of tensile strength accompanied with a moderate increase in modulus at a high loading of 70 phr even without using any coupling reagents. Their high performance is discussed in relation to their physical and chemical properties investigated using thermogravimetry, infrared spectroscopy, ζ -potential, transmission electron microscopy and nitrogen adsorption methods.
CONCLUSION:The improved reinforcing performance of networked silicas confirmed their feasibility as reinforcing materials for the manufacture of highly stable tires. The high tensile strength achieved using the networked silicas is probably due to the physical entanglements of rubber molecules with the networks formed among silica particles.
We reviewed the accelerators, the hydrolysis and condensation reaction mechanism of bifunctional alkoxy silane, and the mechanism of zinc ion in natural rubber (NR) composites. NR composites transform into thermoset composites after vulcanization reaction with help of sulfur and accelerators. Bifunctional alkoxy silanes chemically bond between NR and inorganic silica. For alkoxy silane coupling with silica surface, hydrolysis reaction takes first and then condensation reaction with hydroxyl group in silica takes place. With help of zinc ion the reaction efficiency increases significantly. Zinc ion, a smart material that increases accelerator synergy, mechanism for improvements of interfacial adhesion between NR and silica was revisited.
A networked silica (NS) prepared by interconnecting silica particles with polymeric methylene diphenyl diisocyanate (MDI) was developed for use as a highly effective reinforcing material for rubber compounds without the need to add silane coupling agents. MDI incorporated onto the silica surface formed networks among neighboring silica particles with urethane linkages and produced NS at low cost. The TEM photographs illustrated the improved dispersion and formation of openings among the silica particles, which could allow easy intrusion of rubber molecules. The NS showed a high reinforcing performance for styrene—butadiene rubber (SBR) compounds, suggesting the possibility of replacing the silica reinforcing systems with coupling agents. Due to the absence of any silane-containing coupling agents, the NS does not suffer the disadvantages associated with coupling agents. Since the NS reinforces rubber compounds by the physical entanglement between rubber molecules and the MDI chains, high loading of the NS is more effective in enhancing the mechanical properties of rubber compounds.
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