Polymers

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Polymers

• A level Product Design
• Unit 2

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Whats the difference between a plastic a
polymer ?

• Plasticity is a material property not a
  material
• the ability to be shaped or formed
• Plastic Materials
• Bone
• Horn
• Clay
• Concrete
• A polymer is a certain type of material
• There are natural synthethic polymers
• We are only interested in synthetic polymers

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What is a Polymer ?

• an individual chemical molecule is called a
  monomer
• When many monomers are linked together to form a
  chain, a polymer molecule is formed
• A plastic consists of many large polymer molecules

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What is a polymer ?

• A chemical reaction forms the polymer molecule
  (makes the chain)
• polymerisation
• Normally, chains are randomly arranged and form
  a 3d pattern
• Imagine a piece of string scrunched up into a
  ball

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Polymer Properties

• Fully uncoiled, one polymer molecules chain
  length may be 10,000 times the diameter of the
  chain
• The length of the chain gives the material
  flexibility
• Many other material properties are dependent on
  the chain length
• Tg glass transition temperature
• Temperature at which polymer moves from a hard
  glass like state to a softer rubbery state

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Plastic Additives

• Polymer molecules
• Reinforcement
• Added to improve material strength properties
• Plasticizer
• Added to change natural material properties
• Makes material easier to process
• Filler
• Added to replace polymer
• Cost reduction measure
• Stabilizers
• Stop deterioriating over time
• Heat, UV, Biodegradation
• Foamants
• Increases volume
• Gives more elasticity
• under compression

Typical PVC Content
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Synthetic Polymer Categories
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Crosslinked Polymers

• Very strong
• Strong bonds between chains (crosslinks) and
  intra-chain
• Level of crosslinking determines Tg
• Thermosetting plastics (eg Araldite) are highly
  linked
• Chemical reaction forms the links
• One way process cannot be reversed
• Will not soften with heat - very high Tg
• Araldite is a tradename for a resin based polymer
• The resin is mixed with an activator to start
  curing
• Materials like rubbers are lightly crosslinked
• Tg is below freezingie. Is in a rubbery state at
  all temperatures above 0
• Below Tg, material is hard brittle (useless)

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Thermoplastics

• Strong covalent bonds
• Bonds between individual chain elements
• Weak bonds between chains
• These bonds can be easily broken with heat
• Breaking all bonds causes return to original
  shape
• Recyclable by re-heating
• Energy cost !
• Contamination is a big issue

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Thermoplastics

• Amorphous thermoplastics
• Chains are randomly entangled
• Generally transparent
• Eg. PolyCarbonate (CDs)
• Glass transition temperature (Tg) is a key
  property
• Semi-crystaline thermoplastics
• Cooling causes molecules to fold in a regular
  structure and form a crystal
• Crystal is dense and so plastic is opaque
• Eg. Polyethylene (gas and water pipes)
• Have a definate meting point (Tm)

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Semi-Crystalline Thermoplastics

• The more crystalline a material is
• The stronger it gets
• It has more resistance to solvents
• Solvents need to dissolve into a material
• Amorphous plastics have greater free space
• Higher density
• Higher modulus (stiffness)
• Higher melting point (Tm)
• The lower its transparency
• Reduced impact resistance (brittle)
• Reduced ductility
• Ability to be deformed without cracking

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Effect of temperature on thermoplastics
Tg (glass to rubber)
Tm (melting point)
Stiffness (modulus)
Temperature
Amorphous thermoplastic Semi-crystalline
thermoplastic
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Thermosetting Plastics

• 15 of plastic production
• Polyurethane
• Carpet underlay
• bed foam
• Urea formaldehyde (UF)
• Mains plugs/sockets/light switches
• Phenol Formaldehyde (PF)
• Tradename Bakelite
• Epoxy Resin
• Tradename Araldite
• Used as coatings adhesives or to form
  compositeseg. Carbon fibre
• Can cause health problems
• Melamine formaldhyde
• Work top laminates

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Sources of Polymers

• Oil (carbon)
• 4 of crude oil is used for plastics
• Sustainable sources (biopolymers)
• Wheat corn
• Carrot
• Recycling
• Difficult all recycled items must be of the same
  polymer
• Mixed plastics can be used for low level products
  such as road surfacing, wood replacement

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Carbon Based Polymers

• PolyPropylene (PP)
• Tupperware (lunch boxes)
• Poly Vinyl Chloride (PVC)
• Window frames
• PolyStyrene (PS)
• Packaging
• Yoghurt pots / vending machine cups

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Carbon Based Polymers

• Acrylic
• Paint
• Point of sale displays
• Baths
• Car lights
• HDPE (High Density PE)
• Bottles (biggest application)
• milk bottles (largest bottle sector)
• LDPE (low Density PE)
• Supermarket carrier bags
• Packaging film (eg. cling film)
• Washing up liquid bottles
• PET (PE Terephthalate)
• fizzy drinks bottles

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Material Properties ABS

• Amorphous
• Good resistance against medium temperatures (lt
  1000C)
• Hard
• tough
• antistatic.
• good resistance against chemicals.
• Poor resistance to UV-light
• Can be painted
• Min temp -250C
• Max Temp 800C
• Glass Temp 1100C

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Material Properties PET

• Very light
• AKA Polyester
• Can stand high tensile stress
• Often used for magnetic tape
• hard, stiff, strong
• dimensionally stable
• absorbs very little water
• good chemical resistance except to alkalis
• Medium resistance to UV
• most commonly recycled plastic
• drinks bottles are made from PET
• Semi-crystaline
• Must be rapid cooled to make it amorphous
  transparent
• Can degrade become discoloured during heat
  treatment
• Adds an unwanted flavour to food (can be
  compensated for at addition cost)
• Min Temp -500C
• Max Temp 1700C
• Glass transition temperature 82oC.

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Material Properties HDPE

• Excellent for any food related products
• Not microwaveable
• Machines extremely well (cut, bond, drill etc.)
• Good chemical resistance
• Good impact resistance
• light weight
• Poor UV tolerance
• very low moisture absorption
• high tensile strength
• Not a good candidate for gluing.
• Primarily used for blow moulding
• Colours fade over time
• Min Temp -1000C
• Max temp 1100C
• Melting point 1300C
• Glass temp -95
• Applications

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Material Properties PVC

• Amorphous (transparent)
• Is typically coloured to make opaque
• Good UV resistance
• Excellent chemical resistance
• glue able and weld able
• easily machine able heat bends nicely
• Stiff
• Tough
• hard
• Tg can be reduced down to -400c by adding
  plasticizer
• Makes PVC suitable for hose pipes etc
• Max Temp 600C
• Min Temp -250C
• Glass temp (Tg) 830C

PVC Applications (2000)
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Material Properties LDPE

• Lower density chemical resistance than HDPE
• More transparent than HDPE
• Less expensive than HDPE
• Colours fade over time
• Poor UV tolerance
• Very soft pliable
• Max temp 700c
• Min temp -50oc
• Melting point 1200c
• Glass temp -1100C

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Material Properties PP

• Poor UV resistance
• Translucent (semi-crystaline)
• Rigid
• Very light
• Excellent chemical resistance
• food storage applications
• Medical applications (syringes)
• Carpets
• Microwaveable
• Max temp 1350C
• Min temp 00C
• Melting point 1700C
• Glass temp -180C

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Material Properties PS

• Amorphous
• Flammable
• Excellent thermal insulation
• Used in fridge linings
• Solid
• Light, Hard, Stiff, Brittle
• Expanded
• Light, Bouyant, Crumbles
• Min temp -400C
• Max temp 600c
• Glass transition point 1000C

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Material Properties Acrylic

• amporphous
• Trade names perspex plexiglass
• Weather resistant (Can withstand sunlight for
  long durations)
• Difficult to recycle
• Can be done but is very expensive (not cost
  effective)
• Stiff (Flexible compared to glass)
• Less breakable than glass
• Scratches easily
• brittle
• Resistant to most chemicals and industrial fumes
• Can be cut by various methods
• Corrosion resistant
• Good electrical insulator
• Min Temp 50C
• Max temp 410C
• Glass temperature 1100C

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Some acrylic Products
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Issues

• Safety
• Many chemical plastisizers contain oestrogen
• Gender bending chemical
• Some plastics (eg. PET) degrade emit cancerous
  material over time
• Life Cycle
• Carbon based plastics take thousands of years to
  degrade
• Biodegradeable plastics are being researched now
• Sustainability
• What would land used to grow organic polymers
  normally be used for ?
• Are organic polymers at the expense of food grade
  crop ?
• Today a 500ML water bottle takes 3 fl/oz of
  crude oil to produce ( energy to manufacture)
• Energy for manufacture
• All polymers (apart from elastomers) require heat
  to make them plastic
• All plastics must be sorted and washed before
  being recycled
• Where does this energy come from ?

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Issues

• Sources of rubbish (2006)

• Plastic mining of landfill sites may become a
  future industry
• The price of plastic is linked to the price of oil

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Useful Web Sites

• http//www.dynalabcorp.com/files/Use and Care of
  Plastics.pdf

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Guess the plastic .
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Guess the plastic ..
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Guess the plastic
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Guess the plastic .
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Answers!
HDPE
ABS
PVC
Acrylic