English Abstract

Strain-Induced Crystallization and Mechanical Properties of Rubber.
1. Uniaxial Deformation and Strain-Induced Crystallization of Rubbers

Shigeyuki TOKI
Retired from Mahidol University, State University of New York at Stony Brook, Tonen Chemical and Bridgestone.
Nippon Gomu Kyokaishi,(2017),90(8),401-408 General Review in Japanese

Strain-induced crystallization (SIC) of rubber is a self-reinforcing mechanism of rubber. The phenomenon was found in 1925, however, the elucidation of it has been a controversial topic since then. In 2002, synchrotron X-ray made it possible to measure stress-strain relation and SIC simultaneously. In 2012, the time constant of SIC is revealed as less than 60 m-sec by very fast experimental facilities. SIC is created instantaneously compared to practical deformation processes.
1. SIC is a common phenomenon of rubber and rubber compounds because several rubbers such as natural rubber (NR), synthetic polyisoprene rubber (IR), butadiene rubber (BR), butyl rubber (IIR), chloroprene rubber (CR), thermoplastic elastomer (TPE) and reinforcement filled rubber perform SIC.
2. During deformation, rubber perform several phenomena such as SIC with temperature upturn, cavitation due to void or crack, creation of radical due to breakdown of network, stress softening and hardening, and limited extensibility of chains between crosslinks simultaneously. Therefore, we should distinguish each phenomenon and analyze the contributions of them to a whole rubber performance.
3. Rubber is in-homogeneous material. Synthetic rubbers may include 2-10% of hard gel, remained catalysis and anti-oxidants. Natural rubber include about 6% of non-rubber components such as protein, carbohydrate, phospholipids, metal ions and others. Sulfur vulcanization system add zinc oxide and stearic acids as catalysts. Some of carbohydrates, zinc oxide and stearic acids are crystal. Protein aggregates, phospholipids and fatty-acids micelles are non-crystalline solid materials. Those solid materials may cause stress or strain concentrated points because solid particles are unable to be deformed in liquid-like matrix. Vulcanization is a chemical reaction of solid particle such as sulfur and catalysts with polymer chains in high viscous matrix. Therefore, crosslinks are unable to be distributed homogeneously. These heterogeneity may play important role for SIC of rubber.

Keywords: Crystallization, Mechanical Properties, Rubber