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Synergistic effects and mechanism of hazardous chlorinated aromatic hydrocarbon formation during plastics combustion: A multiscale study
Summary
This study examines the synergistic toxic effects of chlorinated aromatic compounds released from plastic materials during degradation or incineration. The researchers investigated how these hazardous compounds interact to produce combined toxicity greater than individual exposures. Findings highlight the compounded health and environmental risks posed by chlorinated byproducts from plastic waste.
The combustion of waste plastics provides critical insights for researchers addressing environmental challenges. This study systematically investigates the combustion behavior, reaction kinetics, and mechanisms of polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), and their ternary blend (PP:PS:PVC). Headspace gas chromatography–mass spectrometry analysis showed that the emitted volatile organic compounds ranged from volatile to semi-volatile regimes, with saturation mass concentrations spanning 0 μg·m−3 < log10C0 < 10 μg·m−3. Co-combustion substantially increased the relative abundance of oxygenated species, such as aldehydes, ketones, esters, and acids, compared with single-component plastics. Two-dimensional correlation spectroscopy indicated that the order of gas evolution was: gaseous acids, residual functional groups, aldehydes, ketones, esters, and, finally, aliphatic hydrocarbons, suggesting premature oxidation in the blend. Iso-conversional kinetic analysis showed that PVC had a significant catalytic effect, reducing the activation energy for PVC dehydrochlorination by approximately 40 kJ·mol−1 and for residual carbon oxidation by about 100 kJ·mol−1 in the blend compared with pure PVC. Cone calorimetry showed that PS had the highest total smoke release (3,188 m2·m−2) and PVC produced the highest carbon monoxide yield (0.192 kg·kg−1), indicating a greater hazard. The ternary blend showed an increased carbon monoxide yield of 0.183 kg·kg−1 compared with either PP or PS alone. Reactive force field simulations provided atomic-level evidence that PVC-derived chlorine radicals attack PP and PS chains, accelerate radical-driven oxidation, and promote the formation of chlorinated aromatics, such as chlorostyrene (C8H7Cl). These findings provide a theoretical basis for developing sustainable strategies for waste plastic combustion and pollution control.