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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]

Conventional biaxial testing and free stretch blow molding (ISBM) of preforms were conducted in parallel to analyze the biaxial behavior of PET and the resulting strain-induced crystallization (SIC) under bi-axial conditions. Stretch blowing has promoted complex loading paths combining most of the simple paths used at the laboratory scale, which are analyzed locally using marked preforms. The time-temperature superposition principle is shown to apply under biaxial conditions up to high strain, which has facilitated the definition of experimental sets and mechanical comparisons. X-ray diffraction was used to analyze the crystal microstructure and texture. In ISBM, the texture is not a simple image of the final deformation state in terms of orientation. The organized phase that is induced is probably an imperfect crystal capable of evolving in time and the strain hardening under biaxial conditions could be a gradual phenomenon as in uniaxial stress. A scenario is proposed. [Display omitted] • Strain Induced Crystallization. • Time-Temperature superposition principle. • Bi axial tension. • ISBM. [ABSTRACT FROM AUTHOR]

Poly(glycolide-co-caprolactone) (PGCL) has become a novice to the bioresorbable suture owing to the synergistic properties taken from the homo-polyglycolide (PGA) and polycaprolactone (PCL) such as excellent bioresorption and flexibility. In addition to under conventional monotonic loading, the understanding of mechanical responses of PGCL copolymers under complex loading conditions such as cyclic and stress relaxation is crucial for its application as a surgical suture. Consequently, the present work focuses on evaluating the mechanical responses of PGCL sutures under monotonic, cyclic, and stress relaxation loading conditions. Under monotonic loading, the stress-strain behavior of the PGCL suture was found to be non-linear with noticeable strain-rate dependence. Under cyclic loading, inelastic responses including stress-softening, hysteresis and permanent set were observed. During cyclic loading, both stress-softening and hysteresis were found to increase with the maximum strain. In multi-step stress relaxation, the PGCL sutures were observed to exhibit a strong viscoelastic response. In an attempt to describe the relationship between the stress-relaxation and strain-induced crystallization (SIC) occurring during the loading and relaxation processes, a schematic illustration of the conformational change of polymer chains in PGCL sutures was proposed in this work. Results showed that SIC was dependent on the strain level as well as the loading and relaxation durations. The inelastic phenomena observed in PGCL sutures can be thus correlated to the combined effect of stress relaxation and SIC. [Display omitted] • Stress-softening, hysteresis, and permanent set in the cyclic response. • Strong viscoelastic response in multi-step and single-step stress relaxation. • Strain-induced crystallization occurs during loading and stress relaxation. • Schematic illustrations of the conformational changes of polymer chains in PGCL sutures. [ABSTRACT FROM AUTHOR]

This study aims at enlightening the kinetics and the nature of the precursor for crystallization in strain induced crystallization (SIC) of PET, combining ex situ and in situ X-ray diffraction on well controlled tensile experiments. Attention is paid too to annealing to assess "stability" of the phases that are generated. It is concluded that SIC in PET consists in the appearance of ordered entities the periodicities of which are those of crystal. Strain hardening corresponds to perfectioning without leading to actual crystal under tension. The kinetics of formation can be directly related to the stress, whatever the set on tensile conditions (temperature, strain rate). However, microstructure of PET can evolve after loading in case of annealing. [Display omitted] • Strain Induced Crystallization. • Time-Temperature superposition principle. • Comparison to PEF. • Role of chain architecture of PET. [ABSTRACT FROM AUTHOR]