In this investigation, polypropylene (PP) and low-density polyethylene (LDPE) were used in liquefaction experiments using tetralin and benzene as solvents. The temperature of the reaction vessel was increased to 450°C at 10 °C/min, with an isothermal reaction time of 60 minutes. This study investigated the influence of feed material and choice of solvent on conversion values and liquid yield composition during liquefaction experiments. Results showed that differences in the molecular structure of polypropylene and low-density polyethylene significantly affected conversion. Tetralin liquefaction yielded conversion values of 97.0% for PP and 23.8% for LDPE, while benzene liquefaction yielded conversion values of 98.5% for PP and 97.5% for LDPE at 450°C. Benzene liquefaction of PP and LDPE produced liquid fractions comprising alkanes and alkenes. Furthermore, it was found that benzene acted as a hydrogen-donor solvent, which was supported by the presence of biphenyl in the liquid fraction derived from benzene liquefaction. Overall, PP and LDPE demonstrated potential for high conversion to liquid products in liquefaction experiments conducted at 425–450°C.