Mechanical and crystallization properties of hot runner injection molded virgin and recycled polypropylene

Abstract

As the demand for sustainable and environmentally conscious practices continues to grow, recycled plastics have become increasingly popular for plastics manufacturers. However, reprocessing these materials can result in inconsistencies in both process and product quality, leading to a loss in mechanical properties. To address this issue, this work investigates the injection molding of recycled and virgin polypropylene (PP). Using a multi‐cavity hot runner mold, correlations between processing parameters, such as melt temperature, mold temperature, pack pressure, soak time, and mechanical properties, were systematically investigated. A multivariate analysis approach was used to model the variables for each material. Results indicated significant correlations between processing, mechanical properties, and morphology. In particular, for the PP, the melt temperature affected the formation of β‐crystals and their transition to α‐crystals upon tensile testing. Different morphology was observed for the recycled polypropylene (rPP), in which crystallization was affected by polyethylene (PE) contamination. The results discuss the injection molding polymer, structure, and properties, relationship providing an approach to understanding and optimizing the mechanical properties of rPP.Highlights Polyethylene contamination in polypropylene significantly influences crystallinity. Recycling contamination reduces the polypropylene's ability to form β crystals. Virgin polypropylene mechanical properties can be tailored through processing conditions. Recycled polypropylene mechanical properties suffer at higher temperatures and residence times. Polypropylene α/β morphologies can be visualized after mechanical testing.

The Effects of Nucleating Agents and Processing on the Crystallization and Mechanical Properties of Polylactic Acid: A Review

“…Shear-induced processing techniques have been extensively investigated with other polymer materials, such as PP and PE [ 152 , 154 , 156 , 157 , 158 , 159 , 160 , 161 , 162 ]. For example, previous research from the authors showed that for PP, by increasing melt and decreasing mold temperatures, polymer chains aligned and froze with higher orientation, forming β crystals [ 163 ]. However, there is a conspicuous absence of studies concerning shear-induced technology applied to PLA and its blends.…”