The change in Mooney viscosity (ML_(1+4)) with aging was followed for silica compounds containing various silanes.Several mechanisms for the aging stability are postulated and confirmed through experimentation.The type of silane used can cause the ML_(1+4) to increase or even decrease during aging.When bis(triethoxy silanes) are used in silica filled rubbers,the ML_(1+4) growth during aging is caused by hydrolysis.Silica-silica bridging was found to be responsible for the ML_(1+4) growth in rubber compounds containing a more thermally stable polysulfide or a sulfur-free bis(triethoxy silane).When the bis(triethoxy silane) is bis(3-triethoxysilylpropyl) tetrasulfide (TESPT),a fraction of TESPT is attached to the unsaturated rubber to give polymer-silica attachments.These attachments further enhance the hydrolytic ML_(1+4) increase during aging.Chemical coating of the silica with a monofunctional silane effectively stops the ML_(1+4) increase upon aging.The prevetion of ML_(1+4) growth is so efficient that a reduction in the ML_(1+4) can be realized by adsorption of ambient moisture.The extent of ML_(1+4) reduction caused by moisture depends on the degree of hydrophobation of the coated silicas.
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