What difference is there? Thermoplastics-thermosets!
In general, 2 kinds of plastics are used in common injection molding: Thermoplastics and theromosets.
Thermoset plastics are plastics in which the plastic softens once and when hardens cannot be remelted and recycle. Thermoset plastics form cross-links between the molecules that will not be broken down by re-heating. Old thermoset plastics were often referred to as bakelite. You might remember then as the brown colored plates that were in many households in the 1950’s. Durable, but ugly. Circuit breakers housing were also often made of this plastic. Procedures consisted mainly of loading a preform or biscuit of plastic powder into a compression molding press. The press closed, exposing the perform to high pressure and heat. The plastic then did it’s one time melt, flowed into the cavity formed for the part and solidified. Modern thermosets have been developed that eliminate the need for a perform and can be injected in a method more similar to that of thermoplastics. More aesthetically pleasing colors have also been developed. Even with the development of many engineering resin thermoplastics there are still applications that are the domain of the thremoset.
Thermoplastics can be softened and hardened many times. They form very few cross-links during the melting and cooling process. This makes them easy to recycle and reuse and therefore the darling of the modern “green” plastics base.
In future pages we will discuss various kinds of thermoplastics.