Plastic Material Melt & Mould Temperatures

Understanding a plastic's melt and mould temperature is usually straightforward, but a few other factors are worth keeping in mind.

As plastic is heated and melts, thermal expansion causes it to take up more space. Pressure plays a part too, since the level of atmospheric or applied pressure can suppress or accelerate that expansion, shifting the effective melt or mould temperature in a given setup.

Impurities in a material cause melting point depression. A simple parallel is gritting roads in winter, where added salt lowers the temperature at which ice melts.

Crystalline polymers, made of highly ordered syndiotactic and isotactic chains, tend to have more defined melting points that can be targeted reliably to achieve the same result at a set temperature.

Amorphous polymers, made of disordered atactic chains, have no such structure, so their melting behaviour is less predictable and is better described as a range than a single point.