It is like asking how many types of food there are. Although the number of ingredients is limited, there are as many recipes as usages, each with its own composition and characteristics. For instance some plastics are:
- Able to block oxygen to protect food,
- Transparent like glass to make eye glasses or cars lights,
- Stretching and bouncing back in shape to make foam or clothes,
- Resistant to impact as used in a protective helmet…
Here, it is important to stress that all the ingredients used are registered, evaluated and authorized under REACh, the European regulation on chemicals.
In spite of this diversity, the most common grouping of plastics in either thermoplastics or thermosets is based on their reversibility.
Most thermoplastics are produced first as small pellets, which are melted by heat and formed to make all sorts of industrial and consumer products.
They can be re-melted and return to their original state – a bit like an ice cube can be melted then cooled again in a different shape.
Thermoplastics include many plastics you’re likely to be familiar with: polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyamide, polycarbonate, polyesters and others.
Generally, they are first resins, liquid or viscous, which are cured to become a solid polymer. Unlike the thermoplastics, they cannot be re-melted when heated, making it impossible to give them a new shape.
Thermosets include vulcanized synthetic rubber, acrylics, polyurethanes, melamine, silicone, epoxies, and others.
If one considers their usages, categories of plastics are many more, including for example, coatings, adhesives, foams, elastomers, covering polymers that are used in everything from the space shuttle to canned food.
As innovation marches on, scientists and engineers create new plastics to address modern needs and respond to sustainability challenges.