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Lecture notes on Technical principles - UNIT 2
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Extensive and easy to understand classnotes for Unit 2 - within technical principles for paper 1. These helped me achieve an A* throughout the course.
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1️⃣ Performance characteristics of polymersMechanical properties
Are characteristics a material displays when exerted on by a force.
Examples
Toughness - determines a polymer's ability to absorb energy + deform plastically without cracking
e.g. cycle helmets ae worn to protect the head in a collision. The polymer material absorbs the energy +
breaks to dissipate the energy.
Flexibility - the ability of a material to be bent or folded without breaking
Flexible PVC sheet is often sold by roll + used for protective coverings. While film is used for
laminating.
Thermoplastics vary in their level of flexibility - often relating to their thickness.
Elasticity - material's resistance to distortion + ability to return to its original shape
Polyurethane is used in the textile industry, to produce fabrics that have good elasticity
Balloons are made from polymers called elastomers (e.g. rubber / latex)
Plasticity - the ability to be permanently deformed (shaped) + retain the deformed shape (like plastic
deformation)
Mouldability - ability to be shaped into a form
Thermoplastics are often moulded in a hot molten state, under mechanically exerted pressure (e.g.
compressed air, hydraulics or rotation)
Thermosets are often moulded in cold liquid form + cured (set) using a catalyst (hardener)
Ability to be cut + scored - depends on the hardness of the material
Acrylic is hard, easily scored + snapped. But it may chip or crack when machine cut.
HDPE + HIPS are softer and more flexible - so won't score as well. But can be cut more easily without
chipping.
Physical properties
Are the measurable characteristics a material displays
Examples
Self-finishing - no additional surface finishing is required
In manufacture, the surface of the mould, whether smooth + highly polishes or textured, will dictate the
surface finish
Pigments can be added to the polymers pre-production, removing the need for secondary surface
colouring.
,UV resistance
UV 'bleaches' the colour from polymers - like ABS which is commonly used for garden furniture.
Acrylonitrile styrene acrylate (ASA) has been developed as an alternative to ABS. It retains its colour
+ has greater UV resistance.
Also effects the polymer's mechanical properties, degrading it + making it more brittle.
Melting points
Thermoplastics become soft + pliable with heat - making them ideal to shape + mould.
Transparency + translucency - dictates how permeable a material is to light radiation (how see-through it
is)
Examples of translucent polymer uses
Replacement to glass in windows + signs
In packaging to allow the buyer to see the contents
Translucent - some light may pass through, but will be diffused + objects on the other side will not be
clear.
Opaque - impermeable to light
Resistance to chemicals
HDPE is particularly resistant to chemicals + is used to manufacture bleach bottles.
HDPE is used in large sheets, to line landfill sites: acting as a barrier between the waste + the soil.
Resistance to liquids
HDPE + PET are used in plastic water bottles
HDPE is reusable + recyclable
PET is recyclable, but should not be reused as overtime the plastic may leach chemicals into the
water.
Ability to be combined with other polymers + additives
Additives for processing
Plasticisers - enhance flow characteristics + enable polymers to be moulded at higher
temperatures
Thermal antioxidants - help to prevent oxidation due to heat exposure, during the manufacturing
process
Additives for performance
Antioxidants - reduce degradation + deterioration from exposure to air + water. They help prevent
cracking + discolouration
UV light stabilisers - help improve a material's resistance to degradation by UV light
Additives to improve function
Fire retardants
Plasticisers make materials more stretchy
Antistatic additives - are used to reduce the build up of static charge (like on clothing)
, Additives for biodegradability
Bio-batch materials - are additives that enable a thermoplastic to biodegrade. Meaning that they can be
broken down more quickly + safely by natural bacteria.
Recyclability
Reduces reliance on the production of new material from finite resources
Insulation
Thermal insulation - reduces heat transfer (especially between objects + people)
The insulating properties of polymers are utilized in saucepan handles + kitchen utensils
Polymer materials can have air trapped inside them, to create foams that are used as insulation in
packaging
Electrical insulation - a material that doesn't allow electricity to flow freely through it
Polymers are very good electrical insulators - making them useful for electrical product casings +
shields
Suitability for food packaging
Polymer films + moulded polymer sheets prolong the shelf life of food - retaining the flavour +
protecting the quality
Hygienically protect the goods inside, by creating a barrier to oxygen, tampering etc
Problematic food packaging (recyclability)
Films + bags can be heat sealed to keep the food inside airtight + fresh
Many ready meals come in film sealed black plastic trays
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