Hysteresis Contributions in Carbon Black-Filled Rubbers Containing Conventional and Tin End-Modified Polymers

Abstract

Abstract A methodology was developed to estimate individual hysteresis contributions arising from the carbon black network, polymer free chain ends and effective polymer network chains. The estimation technique was applied to rubber compounds formulated with linear polymers of varied number-average molecular weight (Mn) from each of three different series. The three series corresponded to polymers modified with either zero, one or two tin ends per chain. In general, the relative hysteresis contributions depend on strain amplitude and Mn. For unmodified polymers at strain amplitudes from 0.02 to 0.07, and with Mn in the neighborhood of 150 kg/mole, each of the three hysteresis sources contributes about one-third of the total tan δ. With respect to shear loss modulus (G″), the carbon black network contributes about 60%, while free chain ends and the effective polymer network chains each contribute about 20%. At the same Mn and strain conditions, tin end-modified polymers reduce G″ and tan δ by as much as 60%, in comparison to their unmodified counterparts. The benefit is achieved primarily through reductions of up to 85% in the carbon black network contribution to hysteresis. Since the hysteresis contribution from free chain ends is not reduced so much by tin end-modification, the greatest potential for additional tan δ benefits lies in further free chain end reduction. In addition, it was found that tin end-modification has no measurable effect on the hysteresis contribution from effective network chains. Further, the analysis showed that an ineffective polymer network chain provides approximately ten times the hysteresis and one-half the elasticity of an effective network chain, at the test conditions of the current study. In general, the quantitative results, and some qualitative results as well, will change with compound composition and with temperature. Consequently, the development of a methodology, one that allows estimation of individual hysteresis contributions from different sources, is a major component of the present study.