This is an editorial article. It has no abstract.

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.

Two series of polymer blends based on post-consumer polypropylene (rPP) and tire rubber crumbs (Trc) under the trademark ECOPLASTOMER^® PP70 with a mutual ratio of components 70/30 wt%, containing 10, 20, and 30 wt% of flame retardants, have been prepared using a twin-screw extruder. The influence of commercially available silane-treated alumina trihydrate (ATH-sil) with the eco-friendly system based on melamine phosphate (MP), aluminum hydroxide (AC), and peanut shells (PS), used as flame retardant agents, on the mechanical, thermal, and flammability properties of polymer blends was assessed – the incorporation of ATH-sil results in the appearance of peaks related to OH groups in the Fouriertransform infrared spectroscopy (FTIR) spectra. Similar observations are made for the MP/AC/PS system. differential scanning calorimetry (DSC) analysis revealed that using the selected flame retardants did not impact the melting and crystallization temperatures of the polymer. Tensile strength experienced a minor decrease, particularly in compositions containing more than 20 wt% of the flame retardants, while hardness remained unaffected by their share. Both flame retardants reduced the flammability of the modified polypropylene/rubber powder blends, and the most favorable outcomes were achieved with ATH-sil; however, only when employed at a minimum of 30 wt%. The formulated MP/AC/PS system proved more adept at reducing flammability and smoke emissions at lower flame retardant levels (up to 20 wt%).

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.