Polyolefins are extensively used in single-use applications, creating significant environmental burdens upon disposal. Although pyrolysis represents a promising route for converting waste polyolefins into valuable monomers and fuels, its commercialization faces obstacles due to feedstock heterogeneity that negatively impacts product quality and reactor health. Major sources of heterogeneity include embedded additives, foreign impurities, polymer aging, and structural diversity among polymer types and grades. To study these effects, virgin polyethylene compounded with common additives (fillers, pigments, and other functional additives) was pyrolyzed. Results showed that inorganic additives, like talc, kaolin, CaCO₃, TiO₂, carbon black, and zinc stearate, enhanced polymer cracking to increase lighter hydrocarbons, aromatics, and carbon residues. In contrast, antioxidants and stabilizers inhibited depolymerization, producing heavier hydrocarbons. During catalytic pyrolysis with HZSM-5 zeolite, additives strongly enhanced aromatics and catalytic coking, especially during direct contact between plastics and catalysts. However, the transport of additive-derived inorganics and degradation products can lead to reactor fouling and catalyst deactivation over time. The additive study was further extended to investigate the pyrolysis of post-consumer waste polyolefins (HDPE, LDPE/LLDPE, PP, mixed) at different grades (rigid vs. films). Comprehensive feedstock characterization—including organic and inorganic elemental composition, molecular weight distribution, branching, antioxidant content, aging, and thermal stability—was correlated with pyrolysis kinetics and product yields. PP waste contained more tertiary carbons due to their methyl groups, followed by LLDPE and LDPE due to branching. Furthermore, films contained more inorganics and were more aged than rigid plastics. Film-grade polyolefins and mixed plastics also contained oxygenated polymers, forming oxygenated pyrolysates. Statistical analyses identified that inorganics, short-chain branching, and aging significantly lowered product molecular weights, whereas antioxidants and long-chain branching modestly increased heavier products. This research highlights critical distinctions between virgin and post-consumer plastics, polyolefins types/grades, and the economic implications of feedstock variability in industrial-scale chemical recycling and upcycling processes.
