Formation of Crystallites with Low Surface Energy

摘要

In order to demonstrate that lower surface energies of bundle-like crystals have a dominant effect for the enhancement of strain-induced crystallization of natural rubber (NR), an estimation of the end-surface energy (σ_(e) ) was attempted. NR samples were quickly stretched at predetermined crystallization temperature (T_(c) ) to a prescribed draw ratio (α_(s) ), and the wide angle X-ray diffraction patterns during the subsequent stepwise heating process were investigated. Melting temperature (T_(m) ) was found to depend solely on α_(s) and to be independent of T_(c) . Simultaneously, average crystallite size in the chain direction (〈L_(ｃ) 〉) was primarily determined by network-chain density and was also independent of T_(c) . As a result, the plot of T_(m) versus〈L_(ｃ) 〉~(-1 )suggested that σ_(e) is negligibly low and estimated T_(m) is an approximation of the equilibrium melting temperature.