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Bimodality and Increased Amount of Crosslinker Enhances Tensile Properties of the Silicone Networks Article Abstract
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Published: October 07, 2007
Bimodality and Increased Amount of Crosslinker Enhances Tensile Properties of the Silicone Networks
by Gul Bali Shah
The effect of Bimodality i.e. blending short and long chains (0 to 80 % w/w) silicone prepolymers, and that of concentration of the crosslinker on the tensile properties such as percent elongation at break (%Eb), ultimate tensile strength (UTS), 100 % modulus and elastic modulus (E) has been investigated. It was found out that the greater amount of crosslinker used for crosslinking provide an additional reinforcement to the silicone network where as bimodality further significantly accentuate this effect. Remarkably, the %Eb of the silicone networks has been found out to increase to an average of 2.4 times that of the monomodal network cured in each of the three series of bimodal networks cured with 3.9, 9.1 and 12.3% of crosslinker. The optimum property in each case was observed at about 70 mol % of P100. The over all order of sensitivity of these properties up to about 70 mol % of short chain prepolymer has been observed to be as: %Eb > UTS > 100% modulus > elastic modulus. It has been shown that in addition to the previously published reports the tensile properties are acutely dependent not only upon the degree of crosslinking and primary molecular weight but also on bimodality and amount of crosslinker concentration for preparation of the unfilled silicone polymer networks. The concept of phase inversion (or phase transition) associated with the optimum properties in polymer blends has for the first time been applied to the bimodal polymer networks. It has been observed that the maxima in tensile properties generally corresponds to phase inversion which takes place at 0.5 volume fraction (70 mol %) of short chain (P100) prepolymer which is in accordance with the literature for other systems.
http://www.e-polymers.org
e-Polymers 2007, no. 113
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