This is an editorial article. It has no abstract.

This is an editorial article. It has no abstract.

This study examines the combined effects of molecular modalities (unimodal, bimodal, trimodal) and biaxial stretching modes (sequential and simultaneous) on the yielding, stiffness, and necking behaviour of stretched high-density polyethylene (HDPE). Yield strength and stiffness were examined in relation to oriented material produced by drawing at linear strain rates 5.4·10^–3, 2.2·10^–2, and 8.6·10^–2 s^–1 under both stretching modes. Simultaneous stretching outperformed sequential stretching, with yield strength increasing with draw rate. Unimodal HDPE showed higher yield strength and stiffness than bimodal and trimodal grades, while trimodal HDPE had the lowest necking tendency from greater flexibility and uniformity. The highest necking tendency was observed in unimodal HDPE in strain localization analysis using the maximum strain/average strain ratio, while trimodal HDPE deformed more uniformly due to improved molecular weight distribution and strain hardening. Increasing the draw rate reduced strain localization, improving mechanical performance. Insights for optimising polyethylene materials in industry are provided by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) spectroscopy, and mechanical analyses, establishing the correlation between HDPE structure, processing, and properties.

The use of rheo-optical techniques to evaluate crystallization in polymer processing has many advantages; however, it is still little seen. Shear-induced crystallization of polyamide 6 (PA6) was here proposed and studied with these techniques. Mixtures of PA6 in a polypropylene (PP) matrix were also studied. A polarized light optical microscope, with an AxioVision system attached to its top allowing the acquisition of photos at any time during the measurement and a Linkam hot stage device to control shear and temperature, was modified to receive a specially built quantitative rheo-optical detector. Temperature was variable, characterizing non-isothermal analysis. The experiments consisted of varying the shear rate on the polymer system while collecting the respective cross-polarized transmitted light intensity response by LabVIEW software. Shear rates of 1, 10, 100 and 180 s^–1 were applied to all samples. Differential scanning calorimetry (DSC) analysis was also performed to predict crystallization behavior. PA6’s crystallization increased with the increase of shear rate; however, for the PP/PA6 mixtures under the highest rates, crystallization intensity falls from a specific temperature in which the polymer’s viscosity is not enough to maintain the structural integrity. Data related to PP/PA6 mixtures showed that shear increases crystallization if the polymer has time to organize itself.

In this research, heat-triggered triple-shape memory polymers (TSMPs) based on the ethylene-methyl acrylate copolymer (EMA)/chloroprene rubber (CR) thermoplastic vulcanizates (TPVs) were prepared by dynamic vulcanization successfully; meanwhile, an effective and facile triple-shape memory strategy was designed to realize the efficient and stable shape fixity and recovery of two temporary shapes. The field-emission scanning electron microscope images showed that EMA/CR TPV surface was a sea-island structure with the CR particle size ranging from 3 to 6 μm. Differential scanning calorimeters and X-ray diffraction were used to investigate the crystallization behavior of both EMA and CR. These served as a significant basis for the two temporary shapes: fixity and recovery. The results of triple-shape memory tests showed that the EMA/CR TPV had excellent triple-shape memory properties, where the first shape fixity ratio was higher than 89% and both the first shape recovery ratio and second shape recovery ratio could be higher than 95%. It can be observed that the EMA/CR TPV exhibited rapid shape recovery speed with the first shape recovery time of 10 s and the second shape recovery time of 20 s, respectively. This research presents a novel approach to extending the application of TPV in the field of smart devices, endowing them with excellent mechanical and triple-shape memory properties.