VISCOELASTICITY OF RUBBER-RESIN MIXTURES

In the reported experiments, the dynamic viscoelastic response of blends in various proportions of natural rubber with each of two tackifier resins a poly ( beta -pinene) and a pentaerythritol ester of hydrogenated rosin, has been investigated. Results are presented in the from of master curves of the modulus G prime //r and the viscosity eta prime //r against frequency. The two resins show remarkably similar behavior in modifying the viscoelastic behavior of the rubber; the most obvious effects of increasing resin concentration are (a) a displacement of the transition zone toward lower frequencies, (b) a reduction in width and eventual elimination of the ″rubbery plateau,″ and (c) a displacement of the terminal zone in the direction of higher frequencies. Quantitative analysis of the results, using relaxation time spectra, lends support to the iso-free-volume theory of the glassy state and shows a correlation between fractional free volume and monomeric friction coefficient.