Detection of fast and slow crystallization processes in instantaneously-strained samples of cis-1,4-polyisoprene

Abstract

Cross-linked samples of natural rubber (NR) and synthetic cis-1,4-polyisoprene (IR) were instantaneously expanded to a predetermined strain ratio,  s , using a newly-designed high-speed tensile tester. Crystallization behavior after the cessation of deformation was investigated. The high-cycle wide angle X-ray diffraction (WAXD) measurements could successfully reveal the drastic progress of crystallization within the first a few hundred milliseconds. Quantitative analysis of diffraction intensity clarified coexistence of fast and slow crystallization processes; time constants  f and  s , and amplitude I f and I s , respectively, were estimated for these processes. The values of  f were in the range of 50 to 200 ms, while  s ranged between 2.5 and 4.5 s. Almost linear dependence of I f and I s on  s was clarified. The crystallite size in the directions both parallel and perpendicular to the stretching direction decreased with the increase in timeaveraged nominal stress. The crystal lattice deformed almost linearly with the average nominal stress. For the fast process, correlation between crystallization and stress relaxation was not recognized, while linear relationship between them was found for the slow process. In every case, strain-induced crystallization was found to be the major origin of stress relaxation. Based on the results, effects of strain on crystallization of polymer melt were discussed.

Kinetics of strain-induced crystallization in natural rubber: A diffusion-controlled rate law

“…Although the general mechanism is thought to be the same, the crystallinity is typically lower in synthetic isoprene rubber [11,12,3]. This suggests that the natural network in NR, formed by proteins and lipids being attached to functionalized chain ends, supports the formation of crystallites [39,40,41].…”

“…The first experiments of this kind were performed by Dunning in 1967 [10]. Within the last decade, Tosaka reported a two-step crystallization mechanism, occurring on time scales of 0.1 s and 4 s [11,12]. In our previous work, we proposed a two step mechanism consisting of a nucleation step and a growth step, the latter of which is dominated by the mobility of crystallizable chain segments.…”

Formation of Crystallites with Low Surface Energy

“…The two-dimensional wide-angle X-ray diffraction (WAXD) patterns were recorded by a conventional Xray instrument (Nano-Viewer operated at 40 kV, 30 mA, Rigaku Co., Ltd.), in which a custom-made tensile tester was placed [28]. This tensile tester can control specimen temperature between ca.…”

The effect of strain-induced crystallization (SIC) on the physical properties of natural rubber (NR)

“…Polyhedral crystal may be related to TiC and aciform crystal may be induced by strain (and thence SiC). The two-step crystallization during stress relaxation has been characterized by Tosaka et al (2006Tosaka et al ( , 2012. In the first stage, the extended low molecular weight chains form a crystalline nucleus, while in the second stage, amorphous molecules attach to the nucleus and the crystal grows.…”

“…In the case of an ideal rubber, which is composed of an elastic network, no stress relaxation should occur, since no viscous component should exist. To distinguish between the viscous term and the effect of SIC in vulcanized NR, quick stretching is necessary (Tosaka, 2009;Tosaka et al, 2006Tosaka et al, , 2012. When the entire specimen is deformed uniformly at a strain rate of 25 min -1 , the overall changes of stress and corresponding WAXD intensities are measured by synchrotron X-ray.…”