There are three types of plastics classifications depending on their characteristics: depending on their chemical structure, their polarity and their application. Depending on their chemical structure and their temperature behaviour, plastics can be classified in thermoplastics, thermosetting plastics and elastomers.
As regards polarity, the presence of atoms of different nature causes electrons, in covalent bonds, to displace towards the most electronegative atom, creating a dipole. Polymers that contain these electronegative atoms, such as CI, O, N, F, etc. will be polar compounds, what influence in the properties of the material. If polarity increases, mechanical strength, hardness, stiffness, resistance to heat, water and humidity absorption and chemical resistance increase too, as well as polar compound permeability, such as steam, and metal stickiness and metal adhesion. While the polarity increase decreases the thermal expansion, the electrical isolation power, the tendency to accumulate electrostatic charges and the polar molecule permeability (O2, N2).
The third and last classification, depending on their application, is applied to thermoplastics. Four plastic types exist:
Commodity or standard plastics
Plastics that are manufactured and used in large quantities, due to their price and their good characteristics in many aspects. Some of these plastics are polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) or acrylonitrile-butadiene-styrene (ABS).
These are used where good structural properties are needed (transparency, self-lubrication, temperature resistance, etc.). Some plastics of this group are polyamide (PA), polyoxymethylene (POM), polycarbonate (PC), polyethylene terephthalate (PET), poly (p-phenylene ether) (PPE) and poly (polybutylene terephthalate) (PBT).
Special purpose plastics
They are plastics that have a specific property in exceptionally high level, as for example, the poly (methyl methacrylate) (PMMA) that has good transparency and light stability, or the polytetrafluoroethylene (PTFE) that has a great resistance to temperature and to chemical products.
These plastics are mostly thermoplastics with high heat resistance, this is, with a good mechanical resistance to high temperatures, specifically of more than 150°C. Polyimide (PI), polysulfone (PSU), polyether sulfone (PES), polyarylsulfone (PAS), polyphenylene sulphide (PPS) and liquid crystal polymers (LPC) belong to this group.