How Plastics are formed into useful items?
Ans. The single most important property of plastics is the change that they undergo on heating. Some plastics can be softened by heating and will then harden again on cooling. This cycle of softening and hardening can be repeated many times without any appreciable change in the properties. Such plastics are termed THERMOPLASTICS. There is the other class of Plastics which soften on heating and if kept at that temperature for some time, harden irreversibly. That is, such products cannot be softened by further heating. This type is called THERMOSETTING. In thermosetting materials, chemical reaction takes place during heating and crosslinks are formed between adjoining chains. Heat causes the polymer molecules to turn flexible and if the crosslinks were not formed, the process could be repeated any number of times. On the above thermal property depends the processing of plastics i.e., formation of useful articles. The various processing techniques include: Extrusion Blow-moulding Injectio
