polymers

• Thermoforming- plastic becomes soft and flexible when heated

  • Join to form long polymer chains (no fixed structure or pattern)
• thermoforming:

  Pros and cons: It can be repeatedly heated and moulded

  • Not suitable for hot areas or UV sensitivity
  • Each time plastic is reheated it it will try to return to its original shape (plastic memory)
  • Good surface finish can be achieved
  • Recycled easily (reused as it can reshaped)
• Thermosetting- cannot be reformed once set to shape (melamine formaldehyde)

  • Chains of polymers resulting in a (cross linked) rigid molecular structure
• thermosetting:

  Pros and cons: hard and durable with good structural rigidity

  • Can withstand high temperature
  • Good electrical insulator
  • Cannot be remoulded
  • Burns if reheated
  • Used to make composite materials
• Vacuum forming- heat plastic until softened and draping into mould. Vacuum sucks plastic into mould then is ejected from the mould.
• Blow moulding- blow into mould and set in shape.
• Injection moulding- injecting softened plastic into mould (can make complicated shapes)
• High Impact Polystyrene (HIPS)

  • flexible, lightweight, impact resistant, easily moldable, gloss finished 
  • Not very recyclable 
  • Example: expanded foam polystyrene (protect product packaging)
  • Suitable for food containers
  • (SELF FINISHING)
• Acrylic (polymethyl-methacrylate)- Versatile and tough 

  • Scratches and easily and become brittle if thin
  • Acrylic fibres in clothing
  • Seen in sportswear, swimwear
  • Good insulator
  • Negative: not recyclable
• Polyester resin- viscous, clear polyester solution

  • Hardened resin is tough and high abrasion resistance
  • Suitable for embedding objects (jewellery making)
  • Resin replicas (anatomical models)
• Composite adhesive- polyester resin used in composite materials 

  • Lightweight and waterproof 
  • release agent is used for non stick purposes
  • Used to adhere layers fibreglass
  • Used in making boats, vehicle parts 
• Urea formaldehyde (UF)- good electrical insulator

  • Paper industry: improve tear strength
  • Timber industry: UFresin to bind particles
  • Promote easy care and anti wrinkle properties in fabrics
• Plastic properties- 

  • Self finishing 
  • Tough (impact resistant)
  • electrical, thermal insulator
• Electrical insulator- prevent short circuit and ensure safety

  • Flexible PVC coating in UF
  • Thermoset plastics are used so they won't melt
• Biodegradable polymers- made of plants

  • Plants are used for polymers instead of food (specially for LICs)
  • Thermoplastic
  • Suitable for takeaway box, non toxic, high melting point (able to injection mould)