THE EFFECT OF CURING OF UNSATURATED POLYESTER RESIN ON THE DYNAMIC RELAXATION-TIME

The effect of hot curing of unsaturated polyester resin on the dynamic relaxation time was studied using dielectric measurements along with two dynamic mechanical measurement methods. It was found that the dyna mic response during cure was a material frequency dependent property a nd did not depend on the measurement method. All relaxation times, mea sured during cure, by all three measurement methods used, converged to a single equation: tau(t)(av) = at(b) where t = curing time, a, b = c onstants. The increase of the relaxation time during cure followed the same trend as a friction factor, which was found to increase with con version. The crosslinking density was found to increase slowly with co nversion, while the relaxation time increased exponentially. These two different modes of behavior during cure explain the high resolution o f dynamic measurements as a cure monitoring tool, which can easily det ect small curing changes. This behavior of the relaxation time was exp lained by the sharp rise of activation energy due to a parallel decrea se of free volume at high conversion.