Abstract
Abstract A comparative experimental study of the rheological properties of four cis-1,4 polyisoprenes, two naturally occurring and two synthetic, is reported. The two naturally occurring elastomers are from the hevea tree and guayule bush, and the synthetics are produced by alkyl lithium and Ziegler catalysts. Transient and steady state shear viscosity, stress relaxation and elongational stretching experiments were carried out at 100°C. Shear viscosity was measured using creep and constant shear rate modes in a sandwich viscometer as well as with a capillary rheometer. The hevea based elastomer has the highest viscosity and maximum relaxation time. The likeliest reasons for the higher viscosity and memory of the hevea is the presence of large amounts of gel and higher levels of long chain branching than in the other cis-1,4 polyisoprenes. Rheological measurements are also reported for compounds with 0.1 and 0.2 volume loadings of carbon black. Yield values are observed for the 0.2 loading compounds.
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