Crystallization of natural rubber: Its unique feature

Crystallization of natural rubber (NR) has been uniquely complicated. This review is to disentangle the complications. Low-temperature crystallization (LTC) is a difficulty when using NR during winter in the early 19th century, overcome by vulcanization. In 1925, strain-induced crystallization (SIC) was firstly reported, but it has remained obscure for long till the advent of time-resolved synchrotron X-ray. Both SIC and LTC constitute the crystallization of NR, but the two are different. SIC is the most unique feature of NR, in which the causality is too evident to be missed and "template crystallization" is proposed instead of nucleation. However, LTC is sporadic due to its dependency on nucleation. Consequently, advanced kinetic studies are needed to further elucidate NR crystallization, in particular, SIC.