|Carbon Black Reinforcement
of Rubbers No.7:
Strain-Induced Crystallization and Self-Reinforcement of NR: (2)A New Model and Concept for the Self-Reinforcement of NR
Polymer Engineering Design
Nippon Gomu Kyokaishi,(2004),77(12),420-426 General Review in Japanese
The author introduces the assumption that first, vulcanized rubber consists of the inhomogeneous structures, discontinuous cross-linked phase and continuous uncross-linked phase. Secondly, the strain-induced crystallization takes place in the uncross-linked phase of NR whose volume fraction is about 25% in the system. In the uncross-linked phase under large extension, molecular flows and orientation occur due to the high compression given by surrounded cross-linked hard rubber phases. As extension increases, the crystallization spreads over the uncross-linked phases, thus the uncross-linked phase is regenerated from its original soft uncross-linked rubber to the hard and strong super-network made of small crystals and extended molecules. The strand network supports the major part of heavy stress of the system and generates the upturn of the stress. The strength of the strand(true stress)becomes about 1.6 GPa in failure, absolutely the same value as that of polypropylene fiber.
Natural rubber, Strain-induced crystallization, Inhomogeneous cross-linked structures, Super-network, Self-reinforcement