Strain-induced crystallization in cis- and trans-polyisoprene blends

Strain-induced crystallization (SIC) is studied in blends of cis-1, 4-polyisoprene (Hevea rubber) and synthetic trans-1, 4-polyisoprene (t-PI). Uncrosslinked solution blends were uniaxially stretched at room temperature, and the dependence of stress and birefringence on time, elongation, and t-PI content was analyzed. Stress and birefringence follow power-law decays. The rates of relaxation decrease with elongation and t-PI content, and the rates of stress relaxation are higher than the rates of birefringence relaxation for the blends studied here. At high elongation, stress- and birefringence-strain plots exhibit the drastic increase ascribed to strain-induced crystallization. With increasing amounts of t-PI, the onset of the SIC phenomenon occurs at smaller elongations.