Question

why plastic melts on heating while steel or any other metal not?

Answer 1

Plastic melts on heating while steel or any other metal not because plastics have low ignition temperature( the point of melting) but steel or any other metals have high ignition temperature compared to plastic.
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Answer 2

Plastic has a polymeric structure panel which is responsible for its physical properties , basically , plastics are carbohydro compounds with multiple polarity within the structure but not the outside of the structures , which makes it undegradable , while on the other hand , metals and other heavy structures doesn't disassociate on heating because , while on heating plastic materials , it's molecular structures get higher thermal differences due to which it's irresistible , hence it melts down , metals can't just offer this property aslike , they have higher degree of bonding between their molecules and they can offer thermal conduction , and electric conduction too , but in case of plastics , it's not the same , they can't offer thermal and electronic conductions within them , many things are responsible for these circumstances , thermal resistance , thermal conductance , thermal differences have also many consequences , aslike , electro thermal differences , they alter the ignition temperatures and hence plastics melt down easily , but metals not

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