Polymers

Sources, classification & manufacture of thermoplastics

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  • Created by: saraswati
  • Created on: 01-05-09 12:29

PLASTICS

plastics..can be natural & synthetic

  • versatile often requiring little surface finishing
  • can be vacuum formed, injection moulded & blow moulded
  • essentially 3 types:

1) Thermoplastics - can be reformed by applying heat (plastic memory)

2) Thermosetting - can't be reformed using heat

3) Elastomers - display elastic properties eg rubber

Thermoplastic are often used as packaging as they share common properties:

  • lightwieght
  • low cost
  • recyclable
  • can be printed on
  • water-resistant
  • impact resistant
  • tough & durable

MANUFACTURE: crude oil is refined in fractioning tower to make hydrocarbon naphtha, it's cracked into monomers, these link up to form long chains through polymerisation.

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PET - POLYETHLENE TERAPHTHALATE

Recycling ID: 1

PROPERTIES

  • excellent transparacy
  • very tough
  • impenetrable to gases
  • can withstand wide range of temperatures

USES

  • fizzy drinks bottles
  • food containers
  • microwaveable food trays

ADVANTAGES

  • glass-like transparacy allows products to be seen
  • doesnt affect flavour of food products
  • ideal for use as packaging for oven ready or microwavable products
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HDPE - HIGH DENSITY POLYTHENE

Recycling ID: 2

PROPERTIES

  • excellent chemical resistance
  • good barrier to water

USES

  • bottles & containers for washin up liquids
  • cosmetic bottles
  • thin sheet packaging

ADVANTAGES

  • very suitable for containers designed to hold a wide range of liquids which need to be tough durable & flexible
  • very common form of packaging
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PVC - POLYVINYL CHLORIDE

Recycling ID: 3

PROPERTIES

  • rigid - can be flexible if plasticiers are added
  • excellent chemical resistance
  • good barrier to water/weather/gases

USES

  • shrink wrapping & cling film
  • blister packaging
  • packaging for toiletries, pharmaceutical products
  • food
  • confectionary
  • water
  • fruit juices

ADVANTAGES

  • versatile can be used for wide range of products
  • chemical resistance makes PVC suitable for batteries or pharmaceutical products
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LDPE - LOW DENSITY POLYETHYLENE

Recycling ID : 4

PROPERTIES

  • soft
  • flexible
  • excellent chemical resistance
  • good barrier to water but not gases

USES

  • stretch wrapping
  • liquid proof coatings for card (eg milk cartons)
  • carrier & other plastic bags

ADVANTAGES

  • when combined with card it becomes very versatile & cost effective material
  • plastic bags perform well as an inexpensive method of producing a thin protective layer for a wide range of goods
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PP - POLYPROPYLENE

Recycling ID : 5

PROPERTIES

  • very flexible
  • withstand repeated folding
  • can be steralised

USES

  • food containers
  • bags for dry food products
  • bottle crates
  • slot-together boxes
  • yogurt & margarine tubs
  • sweet & snack wrappers
  • video cases

ADVANTAGES

  • excellent chemical reistance (so PP can be used where other plastics cant
  • extremely tough & durable (so wont break if dropped)
  • flexible & resistance to fatigue (so material can be manufactured into boxes with 'intergral' hinges which can be folded repeatedly without snapping or tearing
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PS - POLYSTYRENE (rigid type eg HIPS, HDPS, LDPS)

Recycling ID : 6

PROPERTIES

  • wide range of colours (inc transparent)
  • stiff & hard
  • can be made impact resistance

USES

  • yogurt pots
  • CD cases
  • disposable cups & cutlery
  • bubble packs
  • prototype & architectural model

ADVANTAGES

  • very suitable for vacuum forming
  • very suitable for tough, durable & flexible containers desinged to hold wide range of liquids
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PS - POLYSTYRENE (expanded eg styrofoam)

Recycling ID : 6

PROPERTIES

  • limited range of colours usually white
  • impact resistance
  • good heat insulator
  • durable
  • very buoyant on water
  • low water absorption

USES

  • take-away packaging
  • egg cartons
  • fruit, veg & meat trays
  • hot drinks cup
  • protective packaging for electrical goods
  • expanded polystyrene 'peanuts' are used to pack void spaces in boxes to prevent products moving in transit

ADVANTAGES

  • doesnt add significant weight
  • good heat insulator so it's good for hot food products
  • excellent protective layer to absorb impact, preventing damage to valuable & fragile products
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ACRYLIC - POLYMETHYLMETHACRYLATE

Recycling ID : 7

PROPERTIES

  • wide range of bright colours
  • glossy finish
  • hard
  • brittle
  • rigid
  • heavy

USES

  • high quality containers or closures for perfume products
  • signage
  • windows point of sale display

ADVANTAGES

  • availiable in a wide range of bright colours with a hard,glossy surface finish making it ideal for signage & products which require visual impact
  • little finishing required
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THERMOSETTING PLASTICS

  • set with heat & therafter have little plasticity
  • during polymerisation the molecules link side to side & end to end
  • covalent bond
  • becomes stiff & rigid
  • cant be reformed
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THERMOPLASTIC

  • long tangled chains of molecules, with limited number of smaller cross links
  • weak van der waals forces
  • heat weakens the bond, the material becomes pliable & easier to mould
  • when heat is removed the chains reposition & becomes stiff
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POLYESTER RESIN

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