Plastics

Plastics

Plastics are a common material used today. Examples of plastic products:

a) .........................................................b)..........................................................c) .........................................................d) .........................................................

Few plastics were used prior to the 1940’s. All but a few plastics are manufactured (synthetic). They are distinguished from other materials by the vast number of atoms in a single molecule. Because of this fact plastics are known as MACROMOLECULES. (Macro meaning large)

(History of Plastics http://www.bpf.co.uk/bpfindustry/History_of_Plastics.cfm )

Plastics

Natural plastics

Examples of natural plastics:

Animal horns – Caesin (Glue)

Animal milk – formaldehyde (Glue)

Insects- shellac (French Polish)

Plants - Bitumen (Roads, flat roofs)

Plants – Cellulose (Table tennis balls)

Trees – Latex (Rubber)

Plastics

French Polish

Bitumen

Cellulose

Rubber

Plastics

Plastics

SourcesAll plastics are made from carbon based resources which were once living plants and animals. These include:

OILPETROLCOAL.WOODGAS

Plastics

Processing

The refining of plastics from the type of sources mentioned above involves a complex and expensive process called POLYMERIZATION

Polymerization involves:i) The raw material, oil for example, being broken down

into a gas.

ii) These gases are further broken down into single molecules called MONOMERS

iii) These monomers are then joined together in the process of polymerization. This new compound is called a POLYMER

Plastics

Classification

Plastics fall into two main categories:

THERMOSETTING PLASTICS

and

THERMOPLASTICS

(Types of Plastics) http://www.bpf.co.uk/bpfindustry/plastics_materials.cfm

Plastics

Thermosetting plastics

These are plastics which have strong cross bonds between the molecules. Such strong bonding means that once the plastic has been heated and formed IT CANNOT BE REHEATED AND REFORMED.Because of this fact, plastics are a good material to use when ............ is involved.

Examples of thermosetting plastic products are:a) ..................................b)..................................c) .................................

Thermosetting plastics mostly have complicated names which are difficult to remember!

Plastics

Thermoplastics

These plastics account for about 75% of all plastics used. These plastics are made from molecules with few cross bonds. This formation of molecules allows the plastic to be heated and formed and reheated and reformed.

Examples of Thermoplastics are:

a) ................................

b).................................

c) ................................

If the plastic has a name that sounds familiar e.g. acrylic or polythene it will most likely be a thermoplastic.

Plastics

Plastic memory

One other property thermoplastic has is it’s ability to return to it’s original shape when reheated. This property is called plastic memory because it appears to remember the shape it was before it was formed.

Plastics

Thermoplastic Uses

Polyester (PES) Fibers, textiles

Polyethylene terephthalate (PET) Plastic bottles, food packaging

Polyethylene (PE) Plastic bags, bottles

High density polyethylene (HDPE) Detergent bottles, recycling bins

Polyvinyl chloride (PVC) Pipes, guttering

Low density polyethylene (LDPE) Plastic bags, 6 pack rings

Polypropylene (PP) Bottle tops, dishware

High impact polystyrene (HIPS)

Nylon Toothbrush bristles, fishing line

Acrylonitrile butadiene styrene (ABS) Electrical casings, computers etc

Polycarbonate (PC) Safety glasses

Polymethylmethacrylate (PMMA) Signs

Polyurethane (PU) Cushioning foams

Plastics

Thermosetting plastic Uses

Urea formaldehyde Plugs

Melamine fomaldehyde Worktop surfaces

Epoxy resin Glue

Plastics

Forming plastics

All plastics require heat to form them. The temperature required to form them is relatively low 100-200oC.

Vacuum forming

A sheet of plastic is clamped over a mould and heated until soft. A vacuum is created around the mould, “sucking” the plastic onto the mould. Examples ...................., ................http://www.bpf.co.uk/downloads/files/vacuumform1.swf

Plastics

Injection moulding

Plastic granules or powder is fed into a hopper and melted in a heated screw mechanism. The mechanism forces the molten plastic into a mould (injected) . Cool air or water is then passed through the mould to cool the plastic component before release. Examples: ................,................http://www.bpf.co.uk/downloads/files/InjectionMoulding.swf

Plastics

Extrusion

Like injection moulding, plastic granules are heated and melted and then injected through a “die” ( a plate with the shape you wish to produce) This process produces long lengths of thermoplastics with the same cross section

Plastics

Blow moulding

Plastic sheets are clamped and heated. Air is then blown into the machine blowing the plastic sheet into the required shape.

http://www.bpf.co.uk/downloads/files/InjectionBlowMoulding.swf

Plastics

Rotational moulding

Rotational moulding is also known as rotomoulding or spin casting. It is a method of moulding large empty vessels such as compost bins and sit on kayaks. Plastic powder is put into a mould which is then heated and rotated around 3 axis. As the plastic is heated it coats the inside of the mould. http://www.bpf.co.uk/Plastipedia/Processes/Rotational_Moulding.aspx

Plastics

Forming thermosetting plastics

Thermosetting plastics can be moulded using the following methods:

• Reactive injection moulding• Extrusion moulding• Compression moulding• Spin moulding

Plastics

Compression moulding

Compound or blend is placed in mould and heated under pressure. When reaction is complete, product is cooled and ejected.APPLICATIONSElectrical switch and fuse boxes. Domestic electrical equipment microwave containers and tableware.