Polymers Flashcards
How are polymers made?
Most plastics are made from crude oil. After refining, chemical reactions produce a large number of identical molecules called monomers which are then combined together to form long strands called polymers. All plastics are types of polymers.
How are bioplastics made?
Plastics can also be made from plant oils in other words from renewable materials.
Properties of polymers
• Coloured – can be produced in any colour.
• Self finishing.
• Shaped – Can be formed into unusual shapes.
• Formed – formed a number of ways.
• Cost – reasonable.
• Versatile working properties
What are thermoforming plastics?
These plastics can be re- heated and therefore shaped in various ways. They become mouldable after reheating as they do not undergo significant chemical change. The bond between the molecules is weak and become weaker when reheated, allowing reshaping. These types of plastics can be recycled.
Pros of thermoforming polymers
Highly recyclable
Aesthetically-superior finishes
High-impact resistance
Remoulding/reshaping capabilities
Chemical resistant
Eco-friendly manufacturing
Cons of thermoforming polymers
Generally more expensive than thermoset
Can melt if heated
Thermoforming polymers examples
- High-impact polystyrene (HIPS)
- High-density poly thene (HDPE)
- Polyethylene Terephthate (PET)
- Acrylic (PMMA)
- Polypropylene (PP)
- Polyvinyl Chloride (PVC)
High-impact polystyrene (HIPS) properties and uses
- Thermoforming
- Properties: glasslike in texture, has a low temperature resistance, rigid, cheap, available in many colours, can be cut and vacuum formed easily, food safe but toxic when burned.
- Uses: typically used to produce handling trays and signage, children’s toys, automotive and appliance components, CD cases and yoghurt pots
High-density polythene (HDPE) properties and uses
- Thermoforming
- Properties: flexible, wheatherproof, easy to process, strong, resists shattering, stiff, lightweight, can be recycled well and good chemical resistance
- Uses: used to manufacture numerous items, including food and beverage containers, plastic bottles, pipes, cutting boards, washing baskets and chairs
Polyethylene Terephthalate (PET) properties and uses
- Thermoforming
- Properties: easily blow moulded, good chemical resistance, smooth finish, clear, light, strong and tough
- Uses: generally used for packaging food and beverages (especially carbonated soft drinks) and for textiles/clothing
Acrilic (PMMA) properties and uses
- Thermoforming
- Properties: Excellent transparency, up to 17 times the impact resistance of ordinary glass, hard, brittle, shiny, available in many colours, weather resistance, scratches easily, can be cut, folded and polished well
- Uses: Commonly used for car headlights, visors, lenses for glasses, shatter resistant window panels and signs/displays
Polypropylene (PP) properties and uses
- Thermoforming
- Properties: Tough, strong, translucent, easily coloured, available in sheets and flexible, lightweight and good chemical and heat resistance
- Uses: uses include food packaging film, children’s toys, plastic chairs and casings
Polyvinyl chloride (PVC) properties and uses
- Thermoforming
- Properties: brittle, durable, cheap, can be matt of high gloss, an excellent insulator, good strength and good chemical and weather resistance
- Uses: It is used in plumbing, electrical cable insulation, guttering and window frames
What are thermosetting polymers
Once ‘set’ these plastics cannot be reheated to soften, shape and mould. The molecules of these plastics are cross linked in three dimensions and this is why they cannot be reshaped or recycled. The bond between the molecules is very strong.
What are the pros of thermosetting polymers
More resistant to high temperatures than thermoplastics
Highly flexible design
Thick to thin wall capabilities
Excellent aesthetic appearance
High levels of dimensional stability
Cost-effective
