Thermoplastics vs Thermosets
The type of plastic used to produce a specific item depends greatly on the function of that item. Die cast display cases obviously have different demands than soda bottles do. Luckily, there are polymers that are ideally suited for both.
The two distinctive classes of polymers are thermoplastics and thermosets. Thermoplastics are defined by their ability to be reheated and reshaped multiple times after they are formed. This makes them easy to process and recycle, ideal for “disposable” products. Parkesine, the very first plastic, fell into this category.
On the other hand, thermosets can only be molded or formed once. Heating alters the chemical structure in such a way that the polymer chains can’t flow past each other. This type of plastic is better suited for longer-term items such as display cases. The first synthetic plastic, Bakelite, was a thermoset. Thermosets are durable enough that early Bakelite products still exist.