DT Polymers Test (1.2-1.5)

what are polymers made up of

long chain molecules containing carbon, hydrogen & oxygen atoms + other chemicals like chlorine & fluorine

where do polymers come from - 2 different possibilities

1. natural polymers occur naturally in nature & can be derived from plant/anumal sources. these possess a similar molecular structure to polymers commercially used today

2. synthetic polymers are the main source today - from fossil fuels e.g. oil, gas, coal

polymers properties (x11 - 10 good, 1 bad)

• good electrical insulator

• good thermal insulator

• good strength to weight ratio

• good atmospheric/chemical resistance

• low melting temps (particularly thermoplastics)

• lighweight

• can be self coloured / opaque / transparent

• self finishing

• quite hygenic

• water resistant

• can be enhanced with fillers/plasticides/stabilisers to be made flame retardant/anti static etc

sources of synthetic polymers

gained through thermal cracking, derived from fossil fuels (particularly oil), so are carbon based

1. crude oil is broken down in oil refineries (distillation) into its component parts (fractions)

2. fractions can go through cracking - a thermal reaction that produces smaller hydrocarbons (alkanes / alkenes)

3. alkenes are unsaturated polymers and can be used to make polymers e.g. ethene used to make ethanol

synthetic polymers

have been manufactured by humans, 3 types:

1. thermoplastics can be repeatedly reheated & remoulded

2. in thermosets (thermosetting polymers) a chemical reaction takes place when they’re formed which prevents them from being reheated / reshaped

3. elastomers have good elasticity & can be distorted under pressure but will return to their original shape

how the makeup of polymers affects their properties

polymers are made of single monomers which form long chain molecules (polymers)

how these chains behave when heated define the type of polymer (thermoplastic / thermoset / elastomer)

thermoplastics

can be reheated and remoulded over & over again (recyclable)

the hydrocarbons obtained from cracking are chemically processed to make the monomers (molecules of a single compound) join together end to end to form long chains (polymers - the building blocks of all plastics)

when heated the chain molecules become flexible allowing the material to be reshaped. when cooled the become rigid & solid again

monomer

a molecule of a single compound that can be bonded to other identical molecules to form a polymer

the building blocks of polymers

polymer

the building blocks of all plastics

a large number of smaller units bonded together

a large molecule made of many repeating subunits

thermoplastics: LDPE

low density polyethylene

tough, chemical resistant, weatherproof, can be translucent, low rigidity

SWT 65°C

squeezy detergent bottles, toys, carrier bags, bin liners, packaging, food trays

thermoplastics: HDPE

high density polyethylene

weatherproof, tough, can be translucent, chemical resistant

SWT 65°C

chemical drums, jerry cans, toys, household / kitchenware, long life bags, buckets, bowls

thermoplastics: PP

polypropylene

can be translucent, chemical resistant, tough, fatigue ressitant

SWT 100°C

rope folders, folio cases, food containers, medical equipment, hinged container lids

thermoplastics: HIPS

high impact polystyrene

hard, rigid, can be translucent, tough

SWT 70°C

yoghurt pots, fridge linings, single use drink cups, toilet seats, instrument control knobs

thermoplastics: ABS

acrylonitrile butadiene styrene

extremely tough, hard, available in opaque

SWT 80°C

phone handsets, rigid luggage, domestic appliances, handles, computer housings, remote control / calculator casings

thermoplastics: PMMA

polymethyl-methacrylate aka acrylic

tough, hard, good chemical resistance, can be translucent

SWT 95°C

car light casings, CNC laser cut items, lighting units / covers, baths

thermoplastics: nylon

tough, corrosion resistant, temperature resistance, low coefficient of friction

SWT 150°C

bearings, gears, curtain rails, textiles, boil in the bag food packaging, car engine manifolds, cable ties

thermoplastics: uPVC

rigid polyvinyl chloride

rigid, opaque, tough, hard, weathering & chemical resistant, fire retardant

SWT 95°C

window frames, external doors, guttering / downpipes / water service pipes, bank cards

thermoplastics: PVC

flexible polyvinyl chloride

can be translucent, tough, flexible, weathering & chemical resistant

SWT 95°C

hose pipes, cable insulation, medical grade tubing, inflatable products, imitation leather, seat coverings

recycling symbols

numbers signify how commonly used a material is (1 common, 6 rare, 7 other)

1-3 are easily recycled in the UK

1. PET: drink bottles, produce clamshells, cooking oil, vinegar

2. HDPE: milk / shampoo bottles, detergents

3. PVC: chemical containers, packaging, piping, electrical tape

4. LDPE: plastic bags, squeeze bottles, bread bags, bin liners

5. PP: plastic bottle tops, buckets, yoghurt pots, straws, crisp packets

6. PS (polystyrene): disposable cups, takeaway containers, foam packaging, packaging ‘peanuts’

7. other e.g. acrylics, polycarbonates, nylon, fibreglass

thermosets

polymers that can’t be reheated & reshaped. good for situations where it’ll be subjected to heat / electricity, not recyclable

have long chains of molecules tangled together with no fixed pattern. when formed cross-linking takes place across the long chain molecules which can’t be broken down by heat

the most commonly used type. generally soft & flexible with shape memory

types we learn are based on the use of resin (epoxy / polyester) or formaldehyde (urea / melamine)

exothermic reactions

chemical reactions that release energy

thermosets: UF

urea formaldehyde

hard, heat resistant, electrical conductor, brittle

SWT 80°C

white electrical fittings, adhesives

thermosets: MF

melamine formaldehyde

hard, opaque, tough, heat / chemical resistant, food safe

SWT 130°C

worktop surfaces, decorative laminates, picnic ware, buttons

thermosets: polyester resin

rigid, heat / chemical resistant, brittle

SWT 95°C

boat hulls, car body parts, castings, chair seats

thermosets: epoxy resin

rigid, clear, hard, tough, chemical resistant

SWT 80-200°C

adhesive (araldite), surface coatings, encapsulation of electrical components, cardiac pacemakers, aerospace, Carbon Fibre Reinforced Polymer

1 use for each thermoset

• UF: white electrical fittings

• MF: worktop surfaces

• PR: car body parts

• ER: adhesive (araldite)

1 use for each thermoplastic

• LDPE: bin liners

• HDPE: jerry cans

• PP: medical equipment

• HIPS: yoghurt pots

• ABS: computer housings

• PMMA: laser cutting

• nylon: bearings

• uPVC: window frames

• PVC: hose pipes

elastomers

have the ability to undergo significant elastic deformation and return to their original shape once stress is removed

have links between monomers that are flexible even when cool, giving it rubber properties

2 types of elastomers

Thermoplastic Elastomers (TPEs) can be melted, moulded & solidified (like thermoplastics). can be reprocessed multiple times. have physical cross links rather than covalent (permanent) cross links (from chemical reactions)

Thermoset Elastomers (rubber) can’t be re melted / processed once cured (vulcanized) - the process is irreversible. have covalent cross links between polymer chains. all the ones we learn are this

vulcanization

hardening rubber or a similar material by treating it with sulphur at a high temperature

elastomers: natural rubber

polyisoprene

high tensile strength, low elongation, hard, tough, electrical insulator, cold resistant

tyres, belts, gaskets, footware

elastomers: BR

butadiene rubber

tough, wear / thermal resistant against friction, electrical insulator

tyres, shoe soles, water hoses

elastomers: neoprene

polychloroprene rubber

thermal / oil / chemical / weather / abrasion resistant, tough, insulator

wetsuits, laptop cases, shock absorber seals, door seals

elastomers: silicone

good flexibility at low temps, thermal / weather / extreme temp resistance, lubricating, electrical insulator, poor abrasion resistance

flexible bakewear, cooking utensils, lubricants, medical, baby bottle teats

1 use for each elastomer

• natural rubber: tyres

• BR: hoses

• neoprene: wetsuits

• silicone: cooking utensils

biopolymers

derived from living organisms, either produced by the organisms themselves (naturally occurring) or synthesised from renewable sources (synthetically made), but are always based on biological & renewable raw materials

2 types of biopolymer

natural biopolymers: directly extracted from living organisms, natural occurring e.g. cellulose (plant cell walls) chitin (exoskeletons of insects & crustaceans), silk & wool (proteins), DNA & RNA

synthetic biopolymers: synthesised using biological raw materials but through man made processes. can be produced by chemically modifying natural biopolymers / by microbial fermentation e.g. PLA (from fermented plant derived sugars) and PHA (from bacterial fermentation)

biopolymers: corn starch polymer

natural biopolymer, made from high starch vegetables (e.g. corn, potatoes, maize)

packaging products, straws, vending cups, disposable cutlery, bags, take away food containers

biopolymers: potatopak

natural biopolymer, made from potato starch

single use food items (e.g. bowls, cutlery, food trays), serviettes, packaging beads, bin bags

biopolymers: biopol

aka polyhydroxybutrate (PHB)

natural biopolymer, made from bacteria growth in cultures + an additive to promote degradation, usually 1% added to thermoplastics

packaging products (e.g. film, carrier bags), vending cups, nappies, surgical stitches, pill coverings

biopolymers: PLA

polylactide acid

synthetic biopolymer, made from corn kernels or cane sugar fermented to produce lactic acid then synthesised

packaging, single use bottles, carrier bags, plant pots, disposable nappies, medical sutures, 3D printing

biopolymers: PHA

polyhydroyalkanoate

natural biopolymer, made from bacteria grown in cultures, fully compostable

packaging, sow release medication patches, films, screws, bone plates

biopolymers: lactide

synthetic biopolymer, fully compostable, water soluble, PLA / cellulose based

biomedics, slow release medication, bone repair fixings, detergent washing sachets

biopolymers: glycolide

synthetic biopolymer, fully compostable, PLA & cellulose based

food film, bags, packaging wrap, bin bags, agricultural ground sheets, flower wrap

1 use for each biopolymer

• corn starch polymer: disposable cuterly

• potatopak: packaging beads

• biopol: nappies

• PLA: 3d printing

• PHA: screws

• lactide: bone repair fixings

• glycolide: bin bags

stock forms: sheet

a flat expanse of material that may be of varying thickness

used for creating rigid structures, can be cut & shaped, used in creation of enclosures & signs etc where a flat sturdy material is needed

e.g. polycarbonate, acrylic, ABS

can be cut, drilled, bent with heat, joined together e.g. through gluing / fastening with screws

manufactured using extrusion and cast

stock forms: rod + other extruded forms

long continuous profiles with consistent cross sections

used in making parts & components for a wide variety of products

e.g. nylon, teflon

can be machined (cut / drilled / turned) into required components

manufactured using extrusion

stock forms: film

very thin flexible sheets of plastic

used for packaging, surface protection and aesthetic enhancements

e.g. polyethylene & polypropylene

can be sealed, printed on & laminated

manufactured using calendaring

stock forms: foam

a lightweight material filled with gas bubbles

used for insulation, cushioning & packaging

e.g. polyurethane, polystyrene

can be cut & shaped easily with basic tools

manufactured using injection moulding or block moulding

stock forms: granules

tiny pellets of grains of plastic

used in injection moulding & other moulding processes

almost any polymer can be in granule form e.g. PET, PVC, PP

can be melted & formed into different shapes using moulding techniques

stock forms: powder

polymer in powder form

used in processes like powder coating, rotational moulding & 3D printing

e.g. polyester, polyamide

can be heated & fused to form a continuous layer / shape

process aids (additives to make polymers easier & cheaper to process)

make the polymer flow more easily (processing often involves melting & reforming granules)

lubricants (e.g. wax) make polymers less ‘sticky’ and help it flow easier when moulding

thermal antioxidants prevent the polymer from discolouring due to heat

pigments (tiny particles mixed into polymer) give colour to the final product

additives to improve product function: antistatic agents

reduce / eliminate the buildup of static electricity on the surface of polymers, which can attract dust / hinder processing / lead to hazardous discharges

they dissipate the static charge by making the surface slightly conductive by migrating to the surface & absorbing moisture from the air / by being intrinsically conductive

widely used in packaging material for electronic components, clean rooms, or products where static charge buildup is undesirable

additives to improve product function: flame retardants

reduce the flammability of polymers. function by promoting the formation of a protective char layer / releasing non combustible gases / interfering chemically with the combustion process

essential where fire resistance is critical e.g. in construction materials, electronic casings & furniture

additives to improve product function: plasticisers

increase polymers’ flexibility, workability or extensibility. reduce intermolecular forces between polymer chains allowing them to slide past one another more easily

used in PVC to make products like flexible tubing, vinyl flooring & flexible toys

additives to improve product function: fillers

improve polymer properties / decrease product cost, can be organic or inorganic compound

reinforce / modify the polymer’s properties. some (e.g. talc / glass fibres) can increase stiffness / strength, others enhance visual aesthetics / decrease cost by being a bulking agent

common in most polymer products

additives to prolong life / prevent degradation: antioxidants

protect against oxidative degradation (cause by oxygen presence), which can lead to a breakdown of polymer chains, compromising the material’s properties. 2 types:

1. primary antioxidants (aka radical scavengers) donate hydrogen atoms to reactive free radicals in the polymer matrix, making them stable

2. secondary antioxidants (aka peroxide decomposers) decompose peroxides (primary products of oxidation) into non reactive compounds

used in many products to increase shelf life & maintain performance, especially those exposed to air / high temps for prolonged periods

additives to prolong life / prevent degradation: antioxidants

used to protect from degradation caused by UV radiation (from the sun) which can break down polymer chains & lead to discolouration & loss of material properties. 2 types:

1. UV absorbers (UVA) absorb UV and convert it to harmless thermal energy, preventing the UV from penetrating the polymer and initiating degradation

2. Hindered Amine Light Stabilisers (HALS) neutralise free radicals in the polymer matrix due to exposure to UV. don’t absorb UV but rather counteract the effects of the degradation process

essential for outdoor applications e.g. garden furniture, automotive parts & agricultural films. ensure the material stays durable & retains its appearance + mechanical properties over time despite sunlight exposure

additives to encourage degradation

biogradeable plasticisers enhance processing & make the polymer more flexible, softer & easier to break down, meaning a faster degradation time

bio-batch additives make the polymer break down in certain conditions:

• oxy-degradable polymers degrade over time in the presence of oxygen, often used in single use items e.g. plastic carrier bags & food packaging

• photodegradable polymers degrade when exposed to UV light

• hydro-degradable polymers degrade in the presence of water

these polymers can be engineered to last from a few weeks / months to many years & won’t contribute long term to landfill issues

polymers processes

polymers are perhaps the most formed material in the workshop due to the east with which they can be turned into a liquid / softened and back to a solid at relatively low temps

polymer processes rely on polymers being heated up until it becomes plastic (flexible enough to form) but never liquid

vacuum forming

process involving heating up a sheet of plastic (we use HIPS) and raising a former / pattern up through the plastic while removing the air below to create a vacuum, causing atmospheric pressure outside the vacuum to force the plastic down onto the former

thermoforming

used to mould additional detail into the surface of polymer sheets e.g. baths, food packaging (e.g. fruit punnets), cake & sandwich boxes

typically only used in industrial products (slow process) but fine detail like embossed logos & lettering can be added

similar to vacuum forming except there’s an additional mould that’s pressed onto the surface of the polymer sheet at the same time as the vacuum is applied. the 2 moulds trap the softened polymer between them, giving the mould extra detail

calendaring

material is passed thru a series of rollers to thin it out & achieve a consistent thickness

1. raw material (plastic/rubber) is heated to reach a malleable state

2. material is fed between rollers

3. material passes thru the series of rollers, each set closer together to gradually reduce its thickness

4. final rollers can have specific textures / treatments to put a surface finish / properties onto the material

5. the material is cooled and can be cut into sheets / rolls / shapes

calendaring is commonly used for producing sheets of materials / films / coatings. highly effective for creating consistent high quality layers of material that are wound into rolls for easy storage & transport

line bending

involves heating up a small area of a plastic sheet so it can be folded / bent like paper. usually done around a former, most suitable for one off / limited batch production as it’s slow & labour intensive

injection moulding

used to create complex, high volume parts out of molten materials, commonly plastics

1. plastic pellets are fed into a heating chamber where they become molten

2. molten material is injected into a mould cavity under high pressure

3. the material cools inside the mould, taking its shape

4. once solid the moulded part is injected & the process repeats

versatile technique that allows for intricate designs & high production volumes. can be used in all products, small / large

blow moulding

used for creating hollow objects (eg bottles). starts similar to injection moulding but the moulding part is different:

1. a tube of molten plastic (parison) is extruded into the mould cavity

2. high pressure air is blown into the parison, inflating it to conform to the shape of the mould

3. the material cools & solidifies in the mould, retaining its intended design features

4. the object is ejected from the mould & prepped for post production processes

used for producing containers, bottles & other hollow structures. valued for a combo of speed, flexibility & efficiency so is ideal for creating hollow objects at scale

rotational moulding

aka roto moulding, used to create large, hollow, one piece items from plastic

1. a predetermined amount of plastic powder is placed in the mould

2. the mould is heated while being rotated along 2 perpendicular axes

3. the heat melts the plastic powder & the rotation ensures the molten material coast the interior of the mould uniformly

4. the mould is cooled, letting the material solidify into the intended shape

5. once cooled the hollow object is taken out of the mould for post-production modifications & finishing

particularly effective for creating large complex geometrically challenging hollow items like tanks, slides & bins. design flexibility, uniform wall thickness, can produce stress free parts