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The influence of the type of mechanical recycling of waste rubber particles on the tensile properties of waste/natural rubber blends has been investigated. The wastes originating from ground tyre rubber (GTR) had been treated by two distinct processes: cryo-grinding and high shear mixing (HSM). For both processes, the resulting composites show enhanced stiffness and strength for all strain rates and temperatures tested. This is attributed to both the reinforcing effect of the waste as well as the nucleation ability of the wastes on strain induced crystallization (SIC) in the natural rubber (NR) matrix. Cryo-grinding was shown to provide the finest particle size with an average diameter of 34 µm, while the HSM process was found to show an elastic modulus of aggregated GTR powder of 7 MPa at 1 Hz at room temperature. Within these characteristics, the NR/GTR blends using the HSM process show the best tensile performance under single loading, with the highest strength and highest ability to crystallize under strain. Under cyclic loading, NR/GTR blends using cryo-ground GTR particles show the best performance, which we ascribed to their ability to better distribute and accommodate the stress from one cycle to another owing to their finest size. Both explored recycling techniques provide the natural/waste rubber blends interesting properties such as mechanical reinforcement and strain-induced crystallization ability under various testing conditions. [ABSTRACT FROM AUTHOR]

Natural rubber is a polymer that, by inducing crystallization at a certain level of stress, contributes significantly to reducing cut and chip (CC) damage to rubber articles when exposed to harsh conditions. This unique property is dependent on several factors, including the processing conditions, the cross-linking system and the type of additives used, resulting in varying apparent cross-link density (CLD) of the cross-linked CB filled rubber. Therefore, this work focuses on the systematic investigation of CC phenomena as a function of CLDs represented by conventional (CV), semi-efficient (SEV) and efficient (EV) cross-linking systems. Rubber samples based on different cross-linking systems were prepared by varying the concentration of the accelerator N-tert-butylbenzothiazolesulfonamide (TBBS) at a constant concentration of 2.5 phr sulfur as a cross-linking agent. The different CLDs were achieved by different concentration ratios (A/S) between accelerator (A) and sulfur (S), using A/S ¼ 0.1, 0.3, 0.6 for the CV system, A/S ¼ 0.7, 1.0, 1.5, 2.0, 2.5 for the SEV system and A/S ¼ 3.0 for the EV system. First, the basic mechanical behaviour was presented as a function of CLD, with the optimal behaviour found in the range of 181–241 μmol cm-3 . The CC resistance is independent of the CLD when the rubber specimens are loaded with a normal force of 100 N. However, at higher load, the optimal range of CLD decreases rapidly from 136 to 241 μmol cm-3 . Furthermore, a significant influence of SIC on CC resistance was confirmed in the range of CLD from 181 to 241 μmol cm-3 . Moreover, in the range of CLD from 181 to 241 μmol cm-3 the predominant effect of NR on CC resistance was observed. Finally, an effect of degradation of cross-link network on CC properties due to rubber curing in the reversion has been discussed. [ABSTRACT FROM AUTHOR]

Abstract: The biaxial orientation behavior of poly(ethylene 2,5‐furandicarboxylate) (PEF) is studied in comparison to poly(ethylene terephthalate) (PET). PEF is a polyester that can be produced through similar steps as PET but using 100% biobased 2,5‐furandicarboxylic acid instead of terephthalic acid. This work highlights the stress–strain behavior of PEF during biaxial orientation at various temperatures. Strain hardening and strain‐induced crystallization in the oriented PEF samples generally appeared at higher stretch ratios for PEF than for PET at comparable molecular weight, while somewhat lower degrees of crystallinity are reached in PEF. Shrinkage in oriented PEF is found to be on par with PET in the region of the glass transition. Higher modulus and improved barrier properties, compared to PET, are found in the oriented materials when sufficiently high stretch ratios are applied in biaxial orientation. [ABSTRACT FROM AUTHOR]

Rather than an exhaustive review of the numerous reported studies of strain-induced crystallization (SIC) in natural rubber, this chapter discusses some aspects of the physical mechanisms involved that we think are fundamental for understanding crystallization kinetics and processes such as reinforcement. We mainly focus on the rich information that can be retrieved from X-ray diffraction studies. In particular, we show how easily knowledge of the strain state of the amorphous fraction can be obtained quantitatively from X-ray diffraction patterns and how informative that knowledge is. Considering, for instance, the hardening sequence observed during stretching, it is clear that no prediction of the stress level can be made without knowing both the crystalline content and the average elongation of the remaining molten chains. Particular emphasis is put on the strain relaxation effect that accompanies SIC in both static and dynamic conditions. This fundamental effect is described in the theory of SIC developed by Flory, which we present from an innovative perspective to emphasize its deep analogy to the liquidâ€˵gas phase transformation. In spite of the fact that Flory's theory has only been qualitatively verified experimentally and is limited to static and equilibrium conditions, it grasps the essential of the driving mechanisms at play. Some simple experiments are presented within this framework that should enlighten the most fundamental aspects of SIC. The crystallization kinetics underlies most aspects of SIC and is discussed in detail. Tensile impact tests, which allow conceptually simple but very informative experiments, are treated first. We try to show that the time dependence of the crystalline content is tentatively related to the mechanism of strain relaxation in a simple manner. Knowledge of crystallization kinetics is also essential for explaining the hysteretic behavior observed in dynamic conditions. Similarities and/or differences between dynamic and static SIC are discussed. [ABSTRACT FROM AUTHOR]

The crystallization behavior of polychloroprene rubber (CR) has been studied in this work. Differential scanning calorimetry (DSC) was applied to characterize the crystallization behavior. And X-ray diffraction was applied to determine the impact of crosslinking on the crystallization of CR. Synchrotron X-ray diffraction (SXRD) method was applied to study the dynamic crystalline behavior. On the basis of the experimental results, it is found that crosslinking will hamper the crystallization of CR while large strain can restore this course. And this is in accord with the Mooney-Rivlin analysis result. Detailed discussion was offered circling around this phenomenon. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

A theory of strain-crystallization of random networks comprised of stereoregular chains is developed. The crosslinks are assumed to be expelled from crystal cores. For this reason, the rubber is considered to be represented as a random eutectoid copolymer, the thermodynamics of strain crystallisation of which is described by the use of the van der Waals model of networks. The strain dependence of the maximum melting temperatures, the degree of crystallinity and the average thickness of the crystallites calculated are shown to be in fair accord with experimental data. [ABSTRACT FROM AUTHOR]