Lg. Boretti et al., Effect of tetramethylthiuram disulphide on bis(triethoxysilylpropyl)tetrasulphane as coupling agent for silica in polyisoprene, PLAS RUB C, 29(3), 2000, pp. 144-148
Polyisoprene was compounded with 30 phr unmodified silica and with silica i
n the presence of modifiers bis(triethoxysilyrpropyl)tetrasulphane (TESPT)
and the unsymmetric polysulphide formed on reaction of TESPT with tetrameth
ylthiuram disulphide. The modifiers improved bound rubber formation and the
green strength characteristics of compounds compared with compounds with u
nmodified silica. However, the use of the unsymmetric polysulphide, part of
which could react with hydroxy groups on the silica surface and part of wh
ich contains an accelerator moiety, gave only a marginal improvement in bou
nd rubber formation and green strength, compared with compounds in which si
lica is modified with TESPT alone. Heating at 150 degrees C is essential to
improve bound rubber Formation and it ensures that essentially all of the
bound rubber, formed in the presence of modifiers, is firmly held to the su
rface, swelling in an ammonia atmosphere giving no further solublisation of
rubber compared with normal swelling. Chain end radicals, formed during mi
xing, play no role in bound rubber formation. PRC/1604.