POLYMERS

THREE MAIN TYPES OF PLASTIC (POLMERS)

1. Thermoplastics:

 

Thermoplastics can be heated and shaped many times. Thermoplastics will soften when it is heated and can be shaped when hot. The plastic will harden when cooled, but can be reshaped because their is no links between the polymer chains. Some common thermoplastics are ABS (acrylonitrile butadienestyrene), Nylon (polyamide), acrylic (polymethyl methacrylate), uPVC (polyvinyl chloride), polystyrene, polypropylene and cellulose acetate.

 

 

2. Thermosetting Plastics:

 

Thermosetting plastics can only be heated and shaped once. If re-heated they cannot soften as polymer chains are interlinked. Separate polymers are joined in order to form a huge polymer. The main thermosetting plastics are epoxy resin, melamine formaldehyde, polyester resin and urea formaldehyde.

 

 

3. Elastomers:

These are polymers that have good elasticity, i.e they can be distorted under pressure but will return to their original shape when the pressure is removed.

 

IMPROVING THE PROPERTIES OF PLASTICS: ADDITIVES:

• Fillers = are used to reduce the bulk of the plastic. They generally cheaper than plastics and so helps reduce costs. Examples of fillers include: sawdust, wood flour, crushed quartz and limestone. Some fillers can increase strength and hardness of the polymer by removing brittleness.
• Flame-retardants = are used to reduce the risk of combustion. Their main role is to create a chemical reaction once combustion has begun; they release agents that will stifle the combustion. An example of the use of flame-retardants is in the foams used to fill seating cushions.
• Anti-static agents = reduce the effects of static charges that could build up on a product, for example from walking on a carpet made from synthetic materials.
• Plasticiser = are added to plastics to improve the flow properties of plastics when being moulded. They also reduce the softening temperature and go some way to making the material less brittle.
• Stabilisers = are used to reduce the effects of ultraviolet light, i.e by making the plastics more resistant to being 'broken down' by sunlight. This is important both from a structural and an aesthetic point of view. Stabilisers are used in products that are exposed to a lot of sunlight (such as windows, doors and conservatory components).