Abstract
Mastication reduced the molecular weight of natural rubber (NR). This would affect the tensile properties and strain-induced crystallization of the rubber vulcanizates due to the structural changes of the rubber molecules. In this study, influences of mastication time on tensile response, deformation-induced crystallization, and structural effects of crosslinked NR were investigated. The crystallization behavior and structural changes during stretching were studied by means of wide angle X-ray scattering (WAXS) and small angle X-ray scattering (SAXS). Increased mastication time significantly affected modulus at specified strain and upturn point of strain-induced crystallization of the crosslinked samples while the tensile strength was influenced slightly by mastication. During stretching, degree of crystallinity at given strain was found to decrease with increasing mastication time, while the crystallite size was reduced. Moreover, the size of crosslinked network structures induced by crosslinking also decreased slightly with increasing mastication time, as suggested by SAXS measurement.
Highlights
Natural rubber (NR) has many attractive properties such as high tensile strength and extensibility, good crack growth resistance, and low heat build-up[1], it is never used in its pure form without vulcanization[2]
The crosslink density of the samples increased with mastication time
That the crosslink density increased with mastication time was later
Summary
Natural rubber (NR) has many attractive properties such as high tensile strength and extensibility, good crack growth resistance, and low heat build-up[1], it is never used in its pure form without vulcanization[2]. Since mastication is usually required, the effects of molecular weight reduction through the mastication on tensile properties and on micro-structure are of great interest for understanding the final properties of vulcanizates. Ono et al.[6] investigated the stress-strain properties and strain-induced crystallization of NR vulcanizates with different molecular weights, and reported that a higher molecular weight provided a higher level of stress at a given strain and better strain-induced crystallization ability due to the homogeneous network structures of high molecular weight rubbers. The effects of different parameters such as crosslink density, filler content, temperature and deformation rate on the final properties, crystallization behavior and microstructure of NR have been extensively investigated and are well discussed in the report[7], but how the molecular
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