Synergistic mechanical effects of calcite micro- and nanoparticles and β-nucleation in polypropylene copolymers

Polymer chain extenders induce significant toxicity through DAF-16 and SKN-1 pathways in Caenorhabditis elegans: A comparative analysis

Polymer chain extenders, commonly used in plastic production, have garnered increasing attention due to their potential environmental impacts. However, a comprehensive understanding of their ecological risks remains largely unknown. In this study, we employed the model organism Caenorhabditis elegans to investigate toxicological profiles of ten commonly-used chain extenders. Exposure to environmentally relevant concentrations of these chain extenders (ranging from 0.1 µg L-1 to 10 mg L-1) caused significant variations in toxicity. Lethality assays demonstrated the LC50 values ranged from 92.42 µg L-1 to 1553.65 mg L-1, indicating marked differences in acute toxicity. Sublethal exposures could inhibit nematodes' growth, shorten lifespan, and induce locomotor deficits, neuronal damage, and reproductive toxicity. Molecular analyses further elucidated the involvement of the DAF-16 and SKN-1 signaling pathways, as evidenced by upregulated expression of genes including ctl-1,2,3, sod-3, gcs-1, and gst-4. It implicates these pathways in mediating oxidative stress and toxicities induced by chain extenders. Particularly, hexamethylene diisocyanate and diallyl maleate exhibited markedly high toxicity among the chain extenders, as revealed through a comparative analysis of multiple endpoints. These findings demonstrate the potential ecotoxicological risks of polymer chain extenders, and suggest the need for more rigorous environmental safety assessments.

The Influence of Glass Fiber/Glass Fiber Powder with β-Nucleating Agent on the Properties of Polypropylene

Glass fiber-reinforced polypropylene (PP/GF) has been widely used due to its high stiffness, but for some applications that need low-module characteristics, PP/GF will have limitations due to its lower toughness, so it is necessary to develop glass fiber-modified polypropylene with good stiffness–toughness balance performance. In this study, two average length glass fibers (4.5 mm and 12 mm) and glass fiber powder, combined with β-nucleating agent, were used to investigate the effects on the crystallization and mechanical properties of polypropylene. The results show that compared with glass fiber, glass fiber powder cooperates with β-nucleating agent reinforced polypropylene composite showed good stiffness–toughness balance performance, and β-crystals were found in the composite measured by Differential Scanning Calorimetry (DSC), the presence of β-crystals can improve the toughness of the composite.

Engineering Polypropylene-Calcium Sulfate (Anhydrite II) Composites: The Key Role of Zinc Ionomers via Reactive Extrusion

Polypropylene (PP) is one of the most versatile polymers widely used in packaging, textiles, automotive, and electrical applications. Melt blending of PP with micro- and/or nano-fillers is a common approach for obtaining specific end-use characteristics and major enhancements of properties. The study aims to develop high-performance composites by filling PP with CaSO₄ β-anhydrite II (AII) issued from natural gypsum. The effects of the addition of up to 40 wt.% AII into PP matrix have been deeply evaluated in terms of morphology, mechanical and thermal properties. The PP-AII composites (without any modifier) as produced with internal mixers showed enhanced thermal stability and stiffness. At high filler loadings (40% AII), there was a significant decrease in tensile strength and impact resistance; therefore, custom formulations with special reactive modifiers/compatibilizers (PP functionalized/grafted with maleic anhydride (PP-g-MA) and zinc diacrylate (ZnDA)) were developed. The study revealed that the addition of only 2% ZnDA (able to induce ionomeric character) leads to PP-AII composites characterized by improved kinetics of crystallization, remarkable thermal stability, and enhanced mechanical properties, i.e., high tensile strength, rigidity, and even rise in impact resistance. The formation of Zn ionomers and dynamic ionic crosslinks, finer dispersion of AII microparticles, and better compatibility within the polyolefinic matrix allow us to explain the recorded increase in properties. Interestingly, the PP-AII composites also exhibited significant improvements in the elastic behavior under dynamic mechanical stress and of the heat deflection temperature (HDT), thus paving the way for engineering applications. Larger experimental trials have been conducted to produce the most promising composite materials by reactive extrusion (REx) on twin-screw extruders, while evaluating their performances through various methods of analysis and processing.

Crystallinity-Based Product Design: Utilizing the Polymorphism of Isotactic PP Homo- and Copolymers

The polymorphism of isotactic polypropylene (iPP) in combination with the strong response of this polymer to nucleation can be utilized for expanding the application range of this versatile polymer. Based on three “case studies” related to β-iPP pressure pipes, ethylene-propylene (EP) random copolymers for thin-wall injection molding and transparency and sterilization resistance of cast films we demonstrate ways of combining polymer composition, nucleation and process settings to achieve the desired application performance. The importance of considering interactions between polymer design, nucleation and processing parameters for designing application properties is highlighted.