The main ingredient in most plastic material is a derivative from crude oil and natural gas.
There are many different types of plastics – clear, cloudy, solid colour, flexible, rigid, soft, etc.
Plastic products are often a polymer resin which is then then mixed with a blend of additives (See polymer vs. plastic). The additives are important as each of them are used to provide plastic with targeted optimum properties such as toughness, flexibility, elasticity, colour or to make them safer and hygienic to use for a particular application (ref).
What type of plastic a product is made from can be sometimes be identified by looking at the number at the bottom of plastic containers. Some of the main types of plastic and the parent monomer is given below (Table 1). This table shows the types of plastic and the monomers that make up the plastic.
Table 1. Main polymer types, monomers and its chemical structures
Resin identification code
|
Polymers
|
Monomers
|
♳
PETE
|
Polyethylene terephthalate (PET)
|
Ethylene glycol and Dimethyl terephthalate
|
♴
HDPE
|
High-density polyethylene
(HDPE)
|
Ethylene (CH2=CH2)
*(lesser branching between polymer chains)
|
♵
PVC
|
Polyvinyl chloride
(PVC)
|
Vinyl chloride (CH2=CH-Cl)
|
♶
LDPE
|
Low-density polyethylene
(LDPE)
|
Ethylene (CH2=CH2)
*(excessive branching)
|
♷
PP
|
Polypropylene
(PP)
|
Propylene (CH3-CH=CH2)
|
♸
PS
|
Polystyrene
(PS)
|
Styrene
|
♹
Others
|
Other plastics including acrylic, polycarbonates, polylactic acid (PLA), fibres, nylon
|
Different monomers are used for a particular polymer.
For instance, PLA made from Lactic acid
|
*The monomer used in LDPE and HDPE is ethylene but there is a difference in the degree of branching.