what is the chemical composition of recyclable plastic and the chemical composition of non- recyclable plastic?

Plastics contain organic polymers generally derived from petroleum.Plastics are further divided into thermoplastics and thermosetting plastics according to their properties and recyclability.

Thermoplastics include a variety of plastics which are polymers of various organic momoners such as ethane (polythene), amides(Nylon), propylene(polypropylene) etc. along with some additives. Theses can be recycled because the intermolecular interactions in these plastics spontaneously reform upon cooling.

Thermosetting plastics are the polymers which are made by a process called curing due to which they cannot be recycled. They form irreversible chemical bonds during the curing process which break down upon melting and do not reform upon cooling.For example: natural rubber which is a polymer of isoprene is cured by adding sulphur.Different polymers having different monomer units are cured to get thermosetting plastic.