The techniques of forming thermoplastics are obviously influenced by the fact that the molecules of thermoplastics do not cross-link on heating and therefore can be maintained in a softened state while being made to flow under pressure into a new shape. The properties of each thermoplastic, however, sometimes limit the nature of the possible processes in which it will be involved. Some, for example, will be flexible enough to be ejected from a mould having undercuts in it; others will be too brittle to withstand such a treatment. It is therefore preferable to know about each plastics in terms of properties and applications in order to appreciate which forming techniques may be most suited to it.
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