Plastics usually man made i.e synthetic are basically long chain of hydrocarbon chain of polymers developed from petrochemicals. Since plastics are produced from polymers, polymers which are a chain of monomers are produced from crudeoil, petroleum, natural gas or coal. Due to the absence of free mobileelectrons , plastics are poor conductors of heat and electricity.
Since Plastics are made up of stickymaterials like crude oil which act as poisons and repel water to get attached with plasticdebris and are often harmful for the petroleum based objects in sea.