Physicochemical characterisation and pyrolysis evaluation of simulated, pre-sorted heterogeneous laboratory plastic mixtures for chemicals and energy recovery

Laboratory plastic wastes comprise diverse polymers, copolymers, and both organic and inorganic additives, resulting in substantial compositional heterogeneity. Despite this variability, these materials remain energy-dense feedstocks suitable for thermochemical conversion by pyrolysis. This study evaluates ten simulated heterogeneous laboratory plastic streams (P1-P10) prepared using site-specific procurement data, homogenised by cryogenic milling and characterised to enable comparison between measured feedstock compositional characteristics and pyrolysis behaviour. Batch pyrolysis was conducted under uniform conditions (450 °C, 60 min, 20 g), and product yields, compositions, and physicochemical properties were quantified to assess energy distribution and utilisation potential. All feedstocks generated high liquid yields (73.2–95.3 wt%), accompanied by gases (1.9–14.0 wt%) and solid residues (0.4–17.6 wt%). The resulting oils exhibited high heating values (34.4–42.9 MJ kg−1) and low viscosities (0.71–3.01 cP at 25 °C), supporting potential use in fuel blending and chemical recovery. GC–MS analysis revealed compositional diversity, with oils dominated by single-ring aromatics, aliphatic, cycloaliphatic, or long-chain hydrocarbons, reflecting feedstock differences. Gas heating values ranged from 14.0 to 31.2 MJ kg−1. Solid residues contained high fixed carbon but variable ash contents, indicating differing additive loadings. Ash contents were determined using ICP-OES and SEM-EDS, to identify major inorganic constituents, while additional tests examined whether plastic derived ash influenced pyrolysis of virgin HDPE, but showed negligible changes in product distributions and oil compositions. Multivariate analyses (including one-way ANOVA, principal component analysis (PCA) and hierarchical cluster analysis (HCA)) demonstrated that feedstock heterogeneity strongly governed product quality and energy partitioning. However, the batch pyrolysis conditions used in this work and feedstock diversity may constrain broader applicability, indicating future work must incorporate more real-world variability and diverse additive chemistries around processing of laboratory plastic waste streams.