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Plastics (Problems (Long shelf life, meaning difficult to dispose of,…
Plastics
Problems
Long shelf life, meaning difficult to dispose of
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They do not corrode or rot, meaning it is impossible to completely dispose of
Are sticky when molten, and can cause severe burns
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Thermoplastics can be recycled, but utility can be decreased with frequent heating
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Thermosets
Structure
When heated, they undergo a chemical change, increasing the melting point
Due to this chemical change, they can only be heated up once, making them not recyclable
They have strong chemical bonds, that hold the long chains together.
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Examples
Urea Formaldehyde (Bakelite) is hard and brittle and a good insulator (Used for electrical plugs, sockets, switches & toilet seats)
Melamine Formaldehyde (Formica) is scratch, water and stain resistant and is used as a laminate in kitchen work surfaces. When plasticised it is called Melamine (Used for children’s cups and dishes)
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Epoxy Resins which are mixed with a hardener and left to set. They can be used to make adhesives and flooring.
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Origins
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Made with coal or oil, separated during fractional distillation
Thermoplastics
Structure
As the plastic cools, new weak bonds form, and as no chemical reaction has taken place, it is able to be reshaped many, many times
When heated the bonds break, making it semi fluid, and easily shaped
Long chain of polymers, joined by weak bonds
Examples
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Polychloroethene / Polyvinyl chloride (PVC) can be plasticised by different amounts to make a wide range of products (window frames, gutters, disposable pens, razor handles and credit cards) It is strong, stiff and chemical and weather resistant.
Polythene
High Density Polythene (HDPE) is tough and can be blow and injection moulded, or extruded
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Acrylonitrile Butadiene Styrene (ABS) is strong, tough, scratch resistant and resists heat and chemicals. It is used in lego bricks and kitchen appliances
Polystyrene (PS) is used to make vending cups and model kits. It is light, transparent but quite brittle. It is vulcanised to make High Impact Polystyrene (HIPS) This is used for Vacuum forming in thin sheets, which are cheap and easy to work with. Expanded Polystyrene (EPS) is used as thermal insulation for packaging and food cartons. It is 90% air.
Polypropylene (PP) is versatile and flexible without breaking, and can withstand variable temperatures (crisp packets, yoghurt tubs)
Polymides (Nylon) are hard, tough and resist wear, however are hard to join (used in fabrics and combs)
Polyesters are used as fibres in textiles and in cassettes and video tapes. Polyethylene Teryphthalate (PET) is a clear, tough polyester (fizzy drinks bottles & Babies bottles)
Polycarbonates are used to make CD packaging, bus shelters and car lights. They have high strength, are transparent and are good resistors of heat and chemicals.
Polyurethane can be rubbery, rigid or flexible. It is used to make car bumpers, shoes, trainers and furniture.
Polymethylmetacrylate (PMMA) is better known as Acrylic and is often used as a glass substitute. Acrylic is strong and a good insulator, but scratches easily (used in street signs, baths and spectacles). It is suitable for Vacuum forming, line bending and blow-moulding
Elastomers
Structure
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The bonds between the chains are 'springy', giving them a rubberlike quality
Natural rubber is an example, it can be vulcanised to make ebonite
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