Polymers A 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 compression Typical PVC Content

Synthetic Polymer Categories Long chain polymers Crosslinked polymers Thermoplastics Thermosetting Plastics Elastomers Semi-crystallineamorphous

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) Temperature Amorphous thermoplastic Semi-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 (< C) Hard tough antistatic. good resistance against chemicals. Poor resistance to UV-light Can be painted Min temp:-25 0 C Max Temp:80 0 C Glass Temp:110 0 C

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:-50 0 C Max Temp:170 0 C Glass transition temperature: 82 o C. Melting point: 250 o C.

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: C Max temp: C Melting point:130 0 C 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 c by adding plasticizer ◦ Makes PVC suitable for hose pipes etc Max Temp: 60 0 C Min Temp: C Glass temp (Tg):83 0 C 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 70 0 c Min temp -50 o c Melting point c Glass temp: C

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 C Min temp 0 0 C Melting point: C Glass temp:-18 0 C

Material Properties: PS Amorphous Flammable Excellent thermal insulation ◦Used in fridge linings Solid: ◦Light, Hard, Stiff, Brittle Expanded: ◦Light, Bouyant, Crumbles Min temp:-40 0 C Max temp: 60 0 c Glass transition point: C

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:5 0 C Max temp:41 0 C Glass temperature :110 0 C

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 and Care of Plastics.pdf and Care of Plastics.pdf

Guess the plastic ….

Guess the plastic …..

Guess the plastic ……

Guess the plastic ….

Answers! ABS PVC HDPE Acrylic