The effects of endlinking network and entanglement to stress-strain relation and strain-induced crystallization of un-vulcanized and vulcanized natural rubber

Simultaneous synchrotron X-ray and stress-strain measurement of un-vulcanized natural rubber (NR) revealed that an upturn of stress at large strains and strain induced crystallization (SIC) are caused by endlinking pseudo network and entanglements. Higher pseudo network density of un-vulcanized NR shows higher modulus and larger fraction of SIC. At faster stretching speed, un-vulcanized NR shows higher stress and larger fraction of SIC. On the other hand, vulcanized NR show almost the same stress-strain relation and smaller fraction of SIC at faster stretching speed. Those different behaviors are governed by entanglements, endlinking pseudo networks in un-vulcanized NR and chemical bond networks, small amount of entanglements and endlinking networks in vulcanized NR.