Activity:
Put some hot water in a plastic bucket and try to press it. You will feel that the bucket has become comparatively soft. Now at the time of cooking try to press the handle of the pressure cooker. You observe that handle neither becomes hot nor soft, that is both the bucket and handle made of plastics show different properties. This is because the internal structures of both are different.
Thus plastics are of two types:
(a) Thermoplastic (thermally soft) i.e. it becomes soft on heating.
(b) Thermosetting plastic (thermally strong) i.e. it remains hard and retains its property even on heating.
