Highly oriented polypropylene tapes exhibit excellent strength and stiffness but limited ductility. In this study, we investigated the individual and combined effects of two amorphous poly-alpha-olefins (APAOs) and titanium dioxide (TiO₂) on the structure and mechanical properties of drawn polypropylene tapes. Both APAOs reduced the specific work of drawing, while TiO₂ increased tensile strength and strain at break without reducing stiffness. The combined modifications produced the greatest improvement in ductility, particularly with the APAO containing a minor crystalline fraction and TiO₂, which increased tensile strength from 343 to 388 MPa and strain at break from 12.4 to 32.3%. X-ray diffraction revealed similarly high crystalline orientation for all compositions. Modulated differential scanning calorimetry after a standardized thermal cycle revealed an increased mobile amorphous fraction and a reduced rigid amorphous fraction, suggesting that changes in amorphous-phase constraints contribute to the improved deformability. These results demonstrate that complementary tailoring of the amorphous phase can substantially improve the strength–ductility balance of highly oriented polypropylene tapes.

Elastomeric ethylene–propylene copolymer (EPC) content is a decisive factor in the impact performance of multiphase polypropylene (PP) impact copolymers (ICPs). However, producing PP ICPs with high EPC content remains challenging because increasing EPC content raises powder stickiness, potentially leading to production problems such as fouling or sheeting. Condensed mode operation with an induced condensing agent (ICA) has recently been proposed to reduce stickiness and improve flowability. In this study, we performed bench-scale PP ICP polymerizations with n-pentane (C5) or n-heptane (C7) as ICAs to assess this approach. Both ICAs enhanced monomer solubility and the polymerization rate through co-solubility. At high EPC content, C7 improved powder flowability, whereas C5 gave stickiness comparable to or greater than that of the reference. Atomic force microscopy revealed that C7 shifted the dispersed EPC phase toward the particle core, explaining the improved flowability. In contrast to literature reports, ethylene response and EPC comonomer distribution remained unchanged. Consequently, mechanical and thermal properties were unaffected. Condensed-mode operation may therefore offer benefits only when specific ICAs, such as C7, are used in substantial amounts, limiting practical applicability because of additional purification costs.

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 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.