Polymer nanoclay composites have received significant attention due to their substantially enhanced mechanical, thermal and barrier properties. However, the effect of these nanoclays on the dynamic fracture resistance of a polymer matrix during fast fracture events has not been documented. In this study, the effect of nanoclay addition on the rapid crack propagation (RCP) resistance of high-density polyethylene (HDPE) was investigated through the high-speed double torsion test. Results showed that the addition of 1, 3, and 5% of nanoclays improved the dynamic fracture resistance under the plane strain conditions ($G_{d1}$) of HDPE up to 65%. An increase in the storage and loss modulus, and a decrease in crystallinity and melt flow index with nanoclay content was also found. Although the presence of agglomerates can hinder the enhancement of $G_{d1}$ as it promotes agglomerate fracture and debonding, the increase in energy consumption through fibrillation and crazing promoted by the nanoclay prevails, suggesting that the nanoclay’s toughening effect that has been extensively reported under quasi-static and impact tests, is also present under RCP conditions, and that the HDPE nanocomposites could be used in applications in which RCP must be prevented.

Plastic recycling in the automotive industry is a priority. In this study, the effect of adding recycled polyvinyl butyral (rPVB) from automotive windshields on the coefficient of friction (CoF) and specific wear rate (k) of a glass–fiber reinforced polyamide (PAGF) is investigated. It was found that, at 15 and 20 wt.% of rPVB, it acts as a solid lubricant, reducing CoF and k up to 27% and 70%, respectively. Microscopical analysis of the wear tracks showed that rPVB spreads over the worn tracks, forming a lubricant layer, which protects the fibers from damage. However, at lower rPVB content, fiber damage cannot be prevented as the protective lubricant layer is not formed.

Polyvinyl butyral (PVB) is a polymer resin byproduct of the automotive industry. Separation and recycling of PVB from automotive windshield production lines solve waste management issues. Recycled PVB may contribute to the development of new biomaterials, and the blending with high-density polyethylene (HDPE) broadens their usage range. Materials designed for biological applications must undergo pre-clinical safety evaluation, including in vitro biocompatibility and cytotoxicity testing. This study evaluated in vitro the biocompatibility and cytotoxicity of thick composite films made of recycled PVB (rPVB), HDPE, and composites made of concentrations of both polymers using primary peripheral blood mononuclear cells (PBMCs) from healthy donors. After culturing the PBMCs in the presence of the polymers and their blends for 24 h and seven days, no potential damage was observed, neither toxicity, nor inflammation induced in the cells. The microstructure and elemental analysis of the material revealed no potential toxicity concerns. Also, no acute release of the proinflammatory cytokines TNF-a and IL1-b was observed, nor evidence of cell death, measured by the release of nucleosomes to the extracellular medium, and no damage to the cell monolayer at 24 h nor at 7 days of culture. The stimulation with lipopolysaccharide (LPS), used here as proinflammatory control, induced the significant release of both cytokines and caused damage to the cell monolayer. In conclusion, the pure recycled PVB, pure HDPE, and their composites are safe and biocompatible.

Injection molding is a high-volume manufacturing process widely used for producing polymer components; however, its process parameters strongly influence residual stress, warpage, and the resulting mechanical performance. This work presents a comprehensive factorial design and ANOVA to evaluate the simultaneous effects of the injection temperature, packing pressure, packing time, and specimen orientation on the warpage, hardness, tensile, and flexural properties of polypropylene plates. The results demonstrate that the injection temperature and packing pressure are the dominant factors affecting the hardness and ultimate tensile strength, whereas warpage is mainly governed by the injection temperature and orientation. Under the tested conditions, certain combinations of injection temperature and packing pressure led to an improved mechanical performance; however, these adjustments also produced reductions in other properties, indicating that the balance among parameters depends on the targeted application rather than a single optimal set. Conversely, the parameter combination that produced the lowest warpage still yielded a significant increase in $E_{sec}$, indicating that reducing the warpage does not necessarily compromise the tensile stiffness. Interestingly, variations in the stress distribution between the tensile and bending tests suggest that the solidification-induced structure of the material influences its mechanical response, with specimens that showed a lower tensile strength exhibiting a comparatively higher resistance under bending. These findings provide new insights into the trade-offs between dimensional accuracy and mechanical performance and offer practical guidelines for optimizing polypropylene injection molding processes.