The answer is: asphalt.
Plastic is organic polymers of high molecular mass derived from petrochemicals.
Asphalt (bitumen) is a sticky, black and highly viscous liquid or semi solid form of crude oil.
Crude oil is mixture (solution) consist of several different hydrocarbons (alkanes, alkenes...).
This hydroalkanes can be separated from mixture (crude oil) using distilation (usually fractional distillation), because they have different boiling points.