B. Polymers Flashcards by Mia Hickman

What is the difference between thermoforming and thermosetting polymers?

Thermosetting plastics undergo a chemical change and once formed, cannot be reformed. Thermoforming plastics can be reshaped multiple times

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Why are thermoforming plastics able to be reshaped?

TF plastics are loosely entangled with very few cross links, allowing the chains to slide past each other when heated.

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Why can’t thermosetting plastics be reshaped?

TS plastics have rigid cross-linked polymer chains that set when heated and cannot be reformed.

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Which polymers are thermoforming?

Polypropylene (PP)
High density polyethylene (HDPE)
High impact polystyrene (HIPS)
Polyethylene terephthalate (PET)
Acrylic (PMMA)
Polyvinyl chloride (PVC)

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Which polymers are thermosetting?

Polyester resin (PR)
Urea formaldehyde (UF)
Epoxy Resin (ER)
Phenol formaldehyde (PF)
Melamine formaldehyde (MF)

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What are the uses of Polypropylene (PP)?

Uses: Kitchen, medical properties, rope

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What are the properties of Polypropylene (PP)?

Thermoforming

Properties: Flexible, tough, lightweight, food safe

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What are the properties of Acrylic (PMMA)?

Thermoforming

Properties: Tough but brittle when thin. Easily scratched, formed and bonded

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What are the uses of Acrylic (PMMA)?

Uses: Car lights, alternative to glass, modern baths, clothing

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What are the properties of High density polyethylene (HDPE)?

Thermoforming

Properties: Lightweight, rip and chemical resistant

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What are the uses of High density polyethylene (HDPE)?

Uses: Milk bottles, pipes, crates, wheelie bins

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What are the properties of High impact polystyrene (HIPS)?

Thermoforming

Properties: Flexible, impact resistant, lightweight, (can be) food safe

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What are the uses of High impact polystyrene (HIPS)?

Uses: Yoghurt pots, vacuum forming

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What are the uses of polyethylene terephthalate (PET)?

Thermoforming

Properties: Blow moulded, chemically resistant, fully recyclable

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What are the uses of polyethylene terephthalate (PET)?

Uses: Drinks bottles, food containers, yarn

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What are the properties of Polyvinyl chloride (PVC)?

Thermoforming

Properties: Flexible, easily extruded, tough and resistant to chemicals

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What are the uses of Polyvinyl chloride (PVC)?

Uses: Raincoats, pipes, electrical tape

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What are the properties of Polyester resin (PR)?

Thermosetting

Properties: Good electrical insulator, hard

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What happens when glass is added to Polyester resin (PR)?

PR becomes tough when mixed with glass strands to form Glass reinforced plastic (GRP)

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What are the uses of Polyester resin (PR)?

Encapsulation (think microfibre), boat halls (as GRP)

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What are the properties of Urea formaldehyde (UF)?

Thermosetting

Uses: High tensile strength, heat resistant, electrical insulator, hard, brittle, easily injection moulded

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What are the uses of Urea formaldehyde (UF)?

Uses: Adhesives for binding particle boards, decorative laminates, electrical casings

What are the properties of Epoxy resin (ER)?

Thermosetting

Properties: Good strength to weight ratio, electrical insulator, heat resistant

What are the uses of Epoxy resin?

Uses: Bonding waterproof coatings, electronic circuit boards

What are the properties of Phenol formaldehyde (PF)?

Thermosetting Properties: Heat resistant, electrical insulator

What are the uses of Phenol formaldehyde (PF)?

Uses: Heat resistant handles, electrical components, snooker balls

What are the properties of Melamine formaldehyde (MF)?

Thermosetting Properties: Lightweight, hard but brittle

What are the uses of Melamine formaldehyde (MF)?

Uses: Worktops, surfaces, some kitchenware

Why are TS polymers more difficult to recycle than TF polymers?

- The molecular structure of TS plastic is more rigid, making them difficult to reform once 'set' - When TS plastic is reheated, it tends to burn rather than melt

What properties do thermoforming plastics have?

- Easy to mould when hot - Can be formed into complex shapes - Lightweight - Strong - Waterproof - Corrosion resistant - Good strength to weight ratio - Can be injection moulded

What properties of thermosetting plastics have?

- Irreversibly hardened and cannot be reformed - Good heat, chemical and electrical resistance - Structural integrity - Can be reinforced

What do stabilisers do?

Make plastic more resistant to heat and light

What impact does UV light have on plastic?

UV light degrades plastic, turning it brittle and faded. Impacts strength and surface texture

What do plasticisers do?

Give a material improved flexibility

What do plasticisers do when added to PVC?

Improve applications such as sheathing for electrical cables and car interior trim

What are the main stock forms that polymers come in?

Film Granules/pellets Foam Rods/tubes Powder Sheets

What is film (SF) used for?

Packaging, bags, labels and sheeting

What are granules and pellets (SF) used for?

Extrusion and injection moulding

What is foam (SF) used for?

Thermal insulation and packaging. Can be flexible or rigid

What are rods and tubes (SF) used for?

Electrical, plumbing, garden, military and medical applications

What is plastic powder (SF) used for?

Resin glues, spray coating and 38 printing. Mixes well with additives and dyes

What are plastic sheets (SF) used for?

Protective surfaces, roofing and signage. Can be cut to size, bent, curved and vacuum formed.

How does vacuum forming work?

1. A plastic sheet is placed above the mould and clamped 2. The electric heater is turned on to warm the plastic until it becomes flexible 3. The air is vacuumed out below the plastic and mould, pulling the plastic to shape around the mould

How does extrusion work?

A continuous flow of molten plastic is pushed through a die to produce a specific shape or profile

What is extrusion used for?

Cables, pipes, mouldings and plastic films for packaging

How does injection moulding work?

1. Molten plastic is injected into a mould using an Archimedes screw 2. The plastic cools and hardens into the shape of the mould

What sort of product is injection moulding used to make?

Bottle caps, toys, automotive parts, toothbrushes

What are the benefits of injection moulding?

- Can handle complex parts and shapes to produce consistent products in large quantities - The process can be automated for a high output rate - Cost efficient

What is resin casting used to make?

Industrial prototypes, precise models, moulds for dentistry, art and jewellery-makers

How does resin casting work?

1. Liquid synthetic resin is mixed with a curing agent 2. The resin is poured into a mould and allowed to harden 3. Relies on gravity to pull the resin into all parts of the mould

What are the advantages and disadvantages of resin casting?

Pros: - Produces a strong final product - Quick production and setting time Cons: - Use is limited to smaller scale items

What sort of product is blow moulding used to make?

Plastic bottles and containers

How does blow moulding work?

1. Heated plastic is extruded into a hollow tube 2. The mould closes to grip the parison 3. Compressed air inflates the parison 4. The parison fills the mould and cools 5. The mould opens and the finished product is trimmed