1 Materials and processed- polymers Flashcards
Thermoplastics
thermoplastics are made up of long chains of molecules and these chains are held together by small cross links. The polymer chains are held together by mutual attraction called Van der Waals forces. When a thermoplastic is heated, the bonds between the chains of molecules weaken and become pliable. This means that the Here the map shows where Norwich is in comparison to the UK with the scale of 1:6101227. Norwich is represented by a red pinpoint on the map. can be shaped and formed. Once the heat is removed and the plastic cools down the chains reposition and the plastic becomes hard. This means that a thermoplastic can be heated and shaped many times making it suitable for recycling.
Thermoplastic polymers are widely used in commercial packaging. Once heated, a thermoplastic can be formed into a variety of interesting shapes using different forming techniques such a blow moulding. The main advantages of using thermoplastics in commercial packaging are that they are: lightweight and versatile; strong, tough, rigid, durable, and impact and water resistant; easily formed and moulded; easily printed on; inexpensive; recyclable.
Can you give examples of thermoplastics?
Acrylic Polyethylene Polyethylene terephthalate (PET) Polyvinyl chloride (PVC) Polypropylene (PP) Acrylonitrile butadiene styrene (ABS)
Thermosetting Plastics
Unlike thermoplastics, thermosetting plastics once formed cannot be reheated and changed. The molecules in thermosetting plastics link side-to-side and end-to-end. This linking is referred to as covalent bonding and the result of this bonding is a very rigid structure.
Can you give examples of thermosetting plastics?
Epoxy resins (ER) Urea formaldehyde (UF) Polyester resin (PR)
Elastomers
An elastomer is a polymer with viscoelasticity; viscosity and elasticity.
Elastomers
Types of:
Rubber
Polyurethanes
Neoprene
Silicon
Polymers in Packaging
Polymers used in packaging can be identified by an internationally recognised coding system moulded into the base of the package or printed on the label. This system enables polymers to be easily identified and sorted prior to recycling.
Acrylic
Advantages range of colours durable good electrical insulator machines and polishes well can be transparent, translucent or opaque
Disadvantages
scratches easily
brittle
uses signs covers of storage boxes aircraft canopies covers for car lights wash basins and baths
polyethylene terephthalate (PET)
advantages hard stiff strong dimensionally stable absorbs little water good gas barrier properties good chemical resistance high impact resistance high tensile strength
disadvantages
degrades from exposure to uv light
can discolour
uses
fizzy drinks bottles
containers for food
Polyvinyl chloride PVC
advantages stiff hard tough lightweight good chemical resistance
disadvantages poor weather ability easily scratched uses pipes guttering bottles window frames
polypropylene PP
advantages low density high stiffness high resitance chemical inertness steam barrier good transparency good impact/ rigidity balance
Disadvantages
degrades from exposure to uv light
is flammable
doesn’t bond well with paint
uses
medical syringes
carpets
kitchenware
acrylonitrile butadiene styrene ABS
advantages impact strength tough hard light durable good surface finish resists chemicals
disadvantages
not weather resistant
and is opaque
uses casings for kitchen equipment toys telephones car components tool handles
Urea formaldehyde UF
advantages stiff hard brittle scratch resistant stain resistant high tensile strength can be coloured high surface hardness
disadvantages
toxic fumes are given off when it cures
Urea formaldehyde UF
electrical
advantages stiff hard brittle scratch resistant stain resistant high tensile strength can be coloured high surface hardness
disadvantages
toxic fumes are given off when it cures
uses tableware worktop laminates buttons electrical castings
Rubber
Properties
can be produced synthetically
Occurs in the sap of several varieties of plants
uses car tyres rubber gloves toys paints shoe soles tubes and hoses
