Thermochemical conversion of bioplastics: Evolved gas analysis and kinetics factors for polylactic acid (PLA) - waste biomass mixture

Polylactic acid (PLA) is the highest produced bioplastic globally but facing end-life disposal challenges. Pyrolysis proves to be a viable option, but the recovered product profile is not desirable in terms of quality and value. Date Pits (DP), a waste byproduct chemically rich with lignocellulosic fragments, can provide unique carbon-rich precursors which are highly desirable in the pyrolysis process. This study aims to investigate the synergistic effect of DP addition on PLA pyrolysis products. Thermogravimetric data demonstrates that PLA mixing with DP promotes char formation, initiates degradation at lower temperatures, and decreases the peak decomposition temperature (T_p) from 362 °C to 343 °C. Primary pyrolysis occurs in the range of (200–400 °C) with 75.5 % weight loss and low heating rate shifts T_p toward lower temperatures by averting the development of the thermal lag effect. Chemical structure analysis through FTIR shows that DP addition promotes controlled volatile release through PLA depolymerization hence yielding more uniformed and distinguished peaks for hydroxyl, phenols, and ester-containing groups. Moreover, it promoted free radical reactions that enhanced lactide recovery by restricting aldehyde formation. GCMS profiling indicates that pure PLA pyrolysis majorly yieldes lactide (3,6-Dimethyl-1,4-dioxane-2,5-dione). While the copyrolysis with date pits diversifies this product profile with the production of hydrocarbons (heptane and decane), aromatics (xylene, toluene and styrene), and furans which are highly valued in biorefineries, as drop-in fuels and in petrochemical industries. Kinetic analysis shows that the PLA/DP co-pyrolysis mixture reduces activation energies (E_a) by 18 % and also reduces the thermodynamic parameters.