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PolymersA level Product Design
Unit 2
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
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
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
Polymer Properties
Fully uncoiled, one polymer molecule’s 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
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 compressionTypical PVC Content
Synthetic Polymer Categories
Long chain polymers
Crosslinked polymers
Thermoplastics
ThermosettingPlastics
Elastomers
Semi-crystalline amorphous
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 freezing
ie. Is in a rubbery state at all temperatures above 0◦ Below Tg, material is hard & brittle (useless)
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
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)
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
Effect of temperature on thermoplastics
Tg(glass to rubber)
Tm(melting point)
Stiffness(modulus)
TemperatureAmorphous thermoplasticSemi-crystalline thermoplastic
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 composites
eg. Carbon fibre◦ Can cause health problems
Melamine formaldhyde◦ Work top laminates◦ Office furniture
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
Carbon Based Polymers
PolyPropylene (PP)◦ Tupperware (lunch boxes)
Poly Vinyl Chloride (PVC)◦ Window frames
PolyStyrene (PS)◦ Packaging◦ Yoghurt pots / vending machine cups
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
◦ Carbonation makes HDPE unsuitable
◦ Space blankets
ABS (Acrylonitrile Butadiene Styrene)
◦ Car batteries
◦ Calculators / mobile phones
◦ Safety helmets
Material Properties: ABS
Amorphous
Good resistance against medium temperatures (< 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
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. Melting point: 250oC.
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
◦ Milk bottles
◦ trays and tanks
◦ pipe fittings, wear plates, hinges
◦ cutting boards.
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)
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
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
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
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
Some acrylic Products
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 ?
Plastic is itself a fuel and can be incinerated◦ Toxic fumes are a consequence
Plastic can also be manufactured into a synthetic oil
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
Useful Web Sites
http://www.dynalabcorp.com/files/Use and Care of Plastics.pdf
Guess the plastic ….
Guess the plastic …..
Guess the plastic ……
Guess the plastic ….
Answers!
ABS
PVC
HDPE
Acrylic