Mechanical Decrosslinking and Reprocessing of Crosslinked Rotomolded Polypropylene Using Cryogenic-Assisted Shear Pulverization and Compression Molding

This paper presents a novel recycling approach for porous/foamed crosslinked rotomolded polypropylene (xPP) parts, originally designed for lightweight and thermal insulation. The method uses a cryogenic-assisted shear pulverization technique to produce parts by compression molding. The part’s final gel content and crosslink density were found to depend on their dicumyl peroxide (DCP) content (0–2.5 phr) and characterized in terms of their chemical, thermal, physical and mechanical properties. The results show that this recycling technique allows for an effective reprocessing of the crosslinked materials since partial decrosslinking occurs. For example, the crosslink density decreased by 64% (3.10 to 1.11 × 10−3 mol/cm3) and the gel content by 9% (84.4% to 71.2%) at 2.5 phr DCP. Reprocessing through compression molding led to a compact and partially crosslinked structure resulting in significant improvements in terms of tensile strength (1480%), tensile modulus (604%), elongation at break (8900%), Shore A hardness (19%) and Shore D hardness (32%) compared to xPP samples (at 2.5 phr). This study paves the way for the development of more sustainable recycling methods, especially for crosslinked polymers, by providing new opportunities to reuse the wastes/end-of-life materials in advanced materials and different applications.