Crystallization of Natural Rubber
Shinzo Kohjiya, Kyoto University, Japan and Yuko Ikeda, Molecular Chemistry and Engineering, Kyoto Institute of Technology, Japan
Regrettably, crystallization of natural rubber (NR) has been uniquely complicated. This paper is a trial to solve it. Two difficulties of NR utilization in early 19th century were overcome by vulcanization, invented or discovered by C. Goodyear in 1839. Many rubber people understand that the vulcanization has afforded to realize stable rubber elasticity in many applications of NR. However, more important at that time was to prevent NR from freezing in winter. Namely, low-temperature crystallization was effectively kept off by vulcanization. This fact has not been well recognized, still now.
Strain-induced crystallization (SIC) of NR was first reported by J. R. Katz in 1925. But, SIC behaviors had remained to be elucidated for a long time until the recent usage of synchrotron X-ray, which is enabling time-resolved measurements of SIC. Unfortunately, however, kinetic study of SIC is still lacking.
Both SIC and low-temperature crystallization constitutes the crystallization of NR, but the two are different: While SIC is the most unique feature of NR and is the origin of its much distinguished physical properties among rubbery materials, low-temperature crystallization is not at all specific to NR in terms of crystallization mechanism and is still simply a nuisance in utilization of NR. These features are to be discussed in this presentation.