Thermal degradation/hydrogenation of commodity plastics and characterization of their liquefaction products

The aim of this work is to establish thermal degradation behavior of polymers and polymer mixtures and non-catalytic liquefaction of low density polyethylene (LDPE) under different conditions followed by characterization of the products. The polymers investigated for thermal degradation studies are poly(vinylchloride) (PVC), polyethylene terephthalate (PET), and LDPE. TGA data was used to select liquefaction temperature for LDPE and other polymer(s). Thermal degradation rates were measured using weight loss during isothermal thermogravimetry experiments. Apparent first-order degradation constants were used to compare the results. The thermal degradation of single polymers were different from that of the mixture of polymers. Two different homopolymer samples showed different patterns of thermal degradation. The presence of a swelling agent (such as tetralin) affected the degradation rate and the product distribution. LDPE was liquefied at various temperatures and hydrogen pressures and the liquid products were characterized in terms of hydrocarbon fractions. Increasing the liquefaction temperature from 420 to 440°C, increased the oil yield from 10 to 59% (60 min, 800 psig H₂, tetralin). Increasing H₂ pressure lowered the viscosity of the oils by increasing the < C₁₄ fraction but did not affect the oil yield. The recovered solid polymer fraction showed significant reduction in molecular weight and polydispersity, and increases in crystallinity and melting temperature (T_m). All these variations were due to the direct result of liquefaction and subsequent extraction of the products by different solvents.