Crystallinity describes the degree of structural order in solids, and in polymers it strongly influences rheological, mechanical, thermal, and optical properties as well as degradation. In this study, we investigate how adding a xylitic brown coal fraction affects the crystallization of polylactide (PLA) and polypropylene (PP) under static and shear conditions. We characterized composites by wide-angle X-ray scattering (WAXS), Fourier transform infrared spectroscopy (FTIR), polarization light microscopy (PLM), scanning electron microscopy (SEM) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) to examine both crystallization and filler structure. Results show that the lignocellulosic filler markedly alters crystallization kinetics and supramolecular morphology. In PLA-based composites, a transcrystalline layer (TCL) developed at the interface, modifying crystallization and reducing spherulite formation. In PP, only a weak TCL developed due to limited interfacial compatibility. Under shear, PP displayed the expected acceleration of spherulite growth, while PLA showed competing mechanisms between spherulitic nucleation and TCL formation. These findings highlight the role of natural, hybrid organic–mineral fillers in tailoring polymer crystallization processes and improving composite design.

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.