ENTANGLEMENT AND END LINKING NETWORK ON STRESS-STRAIN RELATION AND STRAIN-INDUCED CRYSTALLIZATION OF UN-VULCANIZED AND VULCANIZEDNATURAL AND SYNTHETIC RUBBERS. II

摘要

Stress-strain relation and strain-induced crystallization of un-vulcanized and vulcanized natural rubber (NR) and synthetic polyisoprene (IR) were studied using synchrotron X-ray, at varied temperatures from -50°C to +100°C. Un-vulcanized IR is polymer melt which shows viscous response with yield stress related to entanglement and no strain-induced crystallization (SIC) at room temperature. At 0°C and -25°C, un-vulcanized IR shows SIC without stress upturns. Entanglements become pivots to align chains and induce crystals. At -50°C, un-vulcanized IR increases modulus linearly from small strains since the temperature is close to its Tg. Un-vulcanized NR shows a stress upturn in stress-strain relation as the same as vulcanized NR and IR but with a permanent set (1.5 strain) therefore, un-vulcanized NR. has pseudo (natural) networks. The pseudo networks create a stress upturn in stress-strain relation and SIC. Vulcanized IR shows a stress upturn and SIC by chemical bonds network. The modulus of vulcanized NR and IR appear almost the same, however the stress of vulcanized NR beyond strain 1.0 is much higher than vulcanized IR. The different behavior of them is caused by pseudo networks and non-rubber components of NR.