Strain-Induced Crystallization of Natural Rubber and Cross-Link Densities Heterogeneities

• Published in: Macromolecules Vol. 47; no. 16; pp. 5815 - 5824
• Main Authors: Candau, Nicolas, Laghmach, Rabia, Chazeau, Laurent, Chenal, Jean-Marc, Gauthier, Catherine, Biben, Thierry, Munch, Etienne
• Format: Journal Article
• Language: English
• Published: American Chemical Society 26.08.2014
• Subjects: Engineering Sciences; Materials; Loading and unloading; Unloading; Crystallite size; Chains; Straininduced crystallization; Cross-link densities; Crystallinity index; Nucleation and growth; Cyclic deformations; Complex networks; Thermodynamic description; Nucleation process; Rubber; Strain rate
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma5006843

Strain-induced crystallization (SIC) of natural rubber (NR) is characterized during a cyclic deformation at room temperature and low strain rate (∼10–3 s–1) using in situ wide angle X-rays scattering (WAXS) measurements. The crystallinity index (CI) and average size of the crystallites in the three main directions are measured during loading and unloading. A scenario describing SIC is then proposed, assuming that SIC corresponds to the successive appearance of crystallite populations whose nucleation and growth depend on the local network density. From this scenario, a methodology, coupling experimental observations and thermodynamic description is developed to determine the distribution of the network chain density associated with the size of a corresponding crystallite population. Finally, complex cyclic tests are performed. They suggest the existence of a memory effect in the chains involved in crystallization, which eases the nucleation process of the crystallites.