Comprehensive AQA Design Technology Unit 2 Notes

Course Overview

Welcome to AQA Design Technology Unit 2 - your guide to understanding one of the most important material groups in modern manufacturing. Polymers are everywhere in your daily life, and this unit will help you understand why designers choose specific plastics for different applications.

You'll explore two main areas: the performance characteristics that make polymers so useful, and their practical applications in real-world products. This knowledge is essential for your coursework and exams.

Tip: Focus on connecting polymer properties to everyday products you recognise - this makes the theory much easier to remember!

Performance Characteristics of Polymers

Ever wondered why your bike helmet can absorb massive impacts without cracking? It's all about mechanical properties - how materials behave when forces are applied to them.

Toughness is impact resistance, allowing materials to absorb energy without breaking. Polycarbonate cycle helmets and ABS car bumpers are perfect examples. Flexibility lets materials bend without snapping back to shape - think PVC sheets or polythene film sold in rolls.

Elasticity differs from flexibility because it involves stretching rather than bending. Elastomers like rubber and latex excel here, which is why they're used in balloons and stretchy fabrics. Plasticity allows permanent reshaping without breaking - essential for manufacturing processes.

Remember: Thermoplastics are generally more flexible, whilst thermosets tend to be rigid and brittle.

Physical Properties and Material Behaviour

Physical properties determine how polymers interact with their environment. Thermal insulation makes polymers perfect for saucepan handles and building insulation foams, whilst electrical insulation properties make them ideal for plug casings and wire coverings.

UV resistance is crucial for outdoor products. Standard ABS garden furniture fades and becomes brittle in sunlight, which is why ASA (Acrylonitrile Styrene Acrylate) was developed as a UV-resistant alternative.

Chemical resistance varies dramatically between polymers. HDPE resists bleach and chemicals so well it's used to line landfill sites, whilst PET water bottles shouldn't be reused as they may leak chemicals over time.

Key Point: A material's melting point often dictates its application - you wouldn't make a kettle handle from low-melting plastic!

Food Packaging and Transparency

Polymer food packaging isn't just about containing products - it's about preservation and safety. These materials create barriers against oxygen, microbes, and contamination whilst showing if tampering has occurred.

Transparency levels matter enormously in packaging design. Fully transparent materials like acrylic let you see contents clearly, whilst translucent materials allow light through but blur the view. Some ready meals need special films that allow microwaving whilst keeping food fresh.

The self-finishing property of polymers eliminates extra processing steps. Surface textures come directly from the mould, and colours can be added during production rather than painted afterwards.

Design Insight: EDM (electrical discharge machining) creates those textured grips on your TV remote by etching spark patterns into moulds!

Polymer Additives and Enhancement

Polymer additives transform basic plastics into high-performance materials. Think of them as ingredients that enhance specific properties for different applications.

Manufacturing additives like plasticisers improve flow during moulding, whilst thermal antioxidants prevent degradation from processing heat. Performance additives extend product lifespan - antioxidants prevent cracking and discolouration, UV stabilisers protect against sun damage.

Functional additives solve specific problems: fire retardants increase safety, antistatic additives reduce static buildup, and bio-batch additives make traditionally non-biodegradable plastics break down safely.

Environmental Focus: Biodegradability additives are increasingly important as they allow common plastics like polyethylene to decompose naturally instead of polluting food chains.

Classification and Production of Polymers

All polymers fall into two main categories: thermoplastics (can be reheated and reshaped) and thermosets (set permanently when cured). This fundamental difference affects everything from manufacturing processes to recycling possibilities.

Polymer production starts with crude oil fractional distillation, separating different fuel types by molecular size. Cracking breaks large molecules into smaller, more useful versions using heat and pressure.

Polymerisation joins these smaller molecules (monomers) into long chains called polymers. Thermoplastics have tangled, unfixed chains allowing reshaping, whilst thermosets form rigid cross-linked structures that can't be remoulded.

Recycling Reality: Thermoplastics' ability to be reheated and reshaped makes them much easier to recycle than thermosets!

Essential Thermoplastics You Need to Know

LDPE and HDPE (Low and High Density Polyethylene) are both 'polythene' but behave differently. LDPE is flexible and translucent (squeezy bottles, carrier bags), whilst HDPE is stronger and more chemical-resistant (storage boxes, chemical containers).

Polypropylene (PP) offers excellent fatigue resistance - it bends repeatedly without breaking, making it perfect for hinged lids. HIPS (High Impact Polystyrene) combines lightness with strength for yoghurt pots and disposable cutlery.

ABS provides exceptional impact strength and surface finish quality, ideal for safety helmets and appliance casings. PMMA (Acrylic) offers glass-like transparency with better impact resistance for shower trays and car lamp covers.

Study Tip: Connect each polymer's properties to products you use daily - it makes remembering their applications much easier!

Specialist Thermoplastics and Applications

Nylon was the first commercially successful synthetic polymer, famous for its self-lubricating properties and durability. From parachute cord to machine gears, its low friction coefficient makes it incredibly versatile.

PVC comes in two forms: rigid PVC for plumbing pipes and window frames, and flexible PVC (with added plasticisers) for hoses and electrical tape. Both offer excellent chemical and weather resistance.

PET (Polyethylene Terephthalate) combines food safety with recyclability, though single-use is recommended for water bottles. Its malleability suits high-speed manufacturing of complex shapes with thin walls.

Environmental Note: PET is highly recyclable but shouldn't be reused for drinking as it may leach chemicals over time.

Thermosets: Permanent Solutions

Thermosets can't be reheated and reshaped like thermoplastics, but they offer superior heat resistance and structural stability. Once cured with a catalyst, they maintain their shape even at high temperatures.

Urea Formaldehyde (UF) provides excellent heat resistance for electrical components like sockets and switches, plus works as an adhesive in MDF production. Melamine Formaldehyde (MF) offers superior scratch resistance for picnic ware and kitchen worktop laminates.

Polyester resin dominates marine applications, creating tough glass-reinforced plastic (GRP) for boat hulls when combined with glass fibres. Epoxy resin serves as a high-performance adhesive and protective coating for electronic components.

Key Difference: Thermosets cure through an exothermic reaction (generating heat), creating permanent cross-links that can't be undone by reheating.