Question

State true or false.
Polystyrene and PVC are thermoplastics.

Answer 1

Thermoplastics can be molded again and again in order to give different shapes according to requirement but thermosetting plastics are the one which cannot be melted and shows a chemical change when subjected to heat.

Complete answer:
Properties like molded, extruded or pressed and on the other hand, light weight, durable and flexible, cost effective production make the plastic usage widespread in contemporary society. Plastics are used in packaging purposes, in automobiles, utensils manufacture, medical devices, construction, etc.
On the basis of we can say quality or remodeling, plastics is of two types namely thermoplastics and thermosetting plastics. The thermoplastics are the plastics which do not show a chemical reaction when they are subjected to high heat. This is why they are being molded again and again to use the same plastic for various purposes by making different shapes of it after molding. Generally, these thermoplastics have polymer mass of about 20000 to 50000 amu. Examples of thermoplastics are polyethylene, polypropylene, polystyrene and polyvinyl chloride. Thus, basically thermoplastics are the one which can be molded again and again because even if they are subjected to heat, they do not show a chemical change and thereby can be given different shapes as per requirement. But on the other hand, in case of preparation of thermosetting polymer, such process is said to be irreversible because once such plastics are formed or solidified, they cannot be converted back to the same condition to form a different structure. This is due to the chemical reaction shown by thermosetting polymers under high heat conditions which leads to formation of a different chemical compound. So, these cannot be molded again and again to form different shapes of the same plastic, but instead of it there formation is an irreversible process. Examples of thermosetting polymers are vulcanization of rubber.

Thus, the correct answer is true.

Note:
Polyisoprene of rubber before heating is tacky and slightly runny material but when it is subjected to heat along with sulphur, the product becomes rigid and non tacky. This is due to a chemical change which changes the plastic when subject to heat. Thus, such examples are of thermosetting plastics.