Plastics

Sources of Polymers

Polymers are made up of long chain molecules containing carbon, hydrogen and oxygen atoms, along with other chemicals such as chlorine and fluorine.

Polymers occur naturally in nature and can be derived from plant and animal sources.

They include:

Casein (derived from milk) which is still used to make buttons
Horn
Resin (from trees)
Cellulose from plants - In the case of Cellulose it is mixed with acetic acid to make Cellulose acetate which is still used today

These are classed as natural polymers as they possess a similar molecular structure to those polymers commercially used today.

Polymers are made up of single monomers which form long chain molecules called polymers. How these chains behave when heated define the type of polymer.

However, the main source of polymers are fossil fuels such as oil, gas and coal, and these give us Synthetic Polymers, which are what you more commonly know as Plastics.

Synthetic polymers can be grouped into three types:

Thermoplastic

Polymers that can be reheated/reformed. A plastic that can be repeatedly reheated and remoulded.

PET, PS, PP, PMMA

Thermosetting

A chemical reaction takes place at the point where they are formed which prevents them from being reheated, recycled or reshaped.

Formaldehyde, Resin

elastomers

Soft, flexible polymers with elastic properties. They can be distorted under pressure but will return to their original shape.

Rubber, Elastic, TPE

Thermoplastic Polymers

The number (after the abbreviation letters) refers to the number that appears in the recycle triangle logo and can be used to identify the plastic if the letters are not printed.

PET (1) - Polyethylene Terephthalate:

Clear water bottles

PE (2) (4) - Polythene & Polyethylene:

Comes in two forms: High Density

(HDPE) for buckets and Low Density (LDPE) for carrier bags.

PVC (3) - PolyVinyl Chloride:

Windows, plastic tubing, guttering and hosepipes.

PP (5) - Polypropylene:

Plastic chairs.

PS (6) - Polystyrene:

Three forms: Rigid (food packaging), High Impact (HIPS) (fridge door) and expanded (foam) for packaging.

Polyamide (7+):

Better known as Nylon and used for washers bearings, hair combs.

PMMA (7+) - Polymethyl Methacrylate:

Better known as Acrylic and used for car headlights.

PC - Polycarbonate (7+):

Used for safety glasses and a range of products that require a clear hard surface.

ABS - Acrylonitrile Butadiene Styrene (7+):

the only thermoplastic that does not begin with ‘poly’. It is a relatively modern plastic used for electrical casings on computers and phones etc.

Thermosetting polymers

Thermosetting plastics are polymers that cannot be reheated and reshaped. When the plastic is formed cross linking takes place across the long chain molecules which cannot be broken down by heat. While this means these types of plastic are good for situations where they will be subjected to heat and electricity, these types of plastics cannot be recycled.