Formation of Crystallites with Low Surface Energy
Résumé
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 (σe) was attempted. NR samples were quickly stretched at predetermined crystallization temperature (Tc) to a prescribed draw ratio (αs), and the wide angle X-ray diffraction patterns during the subsequent stepwise heating process were investigated. Melting temperature (Tm) was found to depend solely on αs and to be independent of Tc. Simultaneously, average crystallite size in the chain direction (〈Lc〉) was primarily determined by network-chain density and was also independent of Tc. As a result, the plot of Tm versus〈Lc〉-1 suggested that σe is negligibly low and estimated Tm is an approximation of the equilibrium melting temperature.