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