2.7 - Polymers Flashcards
Man-made polymers are referred to as ________.
plastics
What are plastics derived from?
- Coal, gas, cellulose and commonly crude oil.
- Crude oil needs to be processed before use.
What is fractional distillation?
- The process of fractional distillation separates crude oil into useful hydrocarbon products.
- The different components that are separated out are known as fractions.
- The fractions include petrol, naptha, kerosene, diesel and bitumen.
In the process of producing plastics, what happens after fractional distillation?
- A chemical called naphtha, a mix of hydrocarbons used for the production of many different plastic polymers, is vented off from the distillery column.
- This then undergoes a process called cracking so that individual hydrocarbons, called monomers, are produced.
In the process of producing plastics, what happens after the hydrocarbon is cracked?
- Monomers undergo polymerisation, which links monomers together to make a polymer chain.
- For example, a long chain of ethylene forms polyethylene which is used to make carrier bags, toys and bottles.
Give an example of a common bioplastic.
- The one of the most common plant-based polymers is polylactic acid (PLA).
- It is commonly used in a 3D printer.
- PLA is obtained from corn starch - the corn is fermented to produce lactic acid, which is polymerised to produce polylactic acid.
Why is the development and use of bioplastics important?
Bioplastics are being continually developed to combat the environmental concerns related to the non-biodegradable properties of plastic polymers.
What are the properties of thermoforming plastics?
- These are easy to mould and shape when hot.
- They can be formed into complex shapes and reformed multiple times.
- They are lightweight, strong, waterproof and corrosion resistant.
What are the properties of thermosetting plastics?
- A thermoset is irreversibly hardened and cannot be reformed.
- It makes a hard, but often brittle plastic which resists deformation.
- It has good heat and electrical resistance (good insulator) and is commonly used for electrical components, domestic plugs and switches.
- It also has good chemical resistance and structural integrity. It can be reinforced to produce a strong, durable material.
What are some ways of modifying plastics?
- Stabilisers
- Pigments
- Plasticisers
How do stabilisers modify plastics?
- Stabilisers can be added to make plastic more resistant to heat and light.
- Over time UV light degrades plastic, turning it brittle and faded.
- This has an impact on strength, and changes the surface appearance and texture.
How do pigments modify plastics?
Pigments can be added to vary the colour of plastics.
How do plasticisers modify plastics
- Plasticisers give a material improved flexibility .
- Are commonly used in PVC to improve applications such as sheathing for electrical cables and car interior trim.
What are some different stock forms that plastics are produced in?
- Film
- Granules / pellets
- Foam
- Rods / tubes
- Powder
- Sheet
What is film used for? (Stock form)
Used for packaging, bags, labels and sheeting.
What are granules / pellets used for? (Stock form)
Used for extrusion and injection moulding.
What is foam used for? (Stock form)
- Can be made flexible or rigid.
- Used for thermal insulation and packaging.
What are rods / tubes used for? (Stock form)
- Used in electrical, plumbing, garden, military and medical applications.
- Can be bent to shape.
What is powder used for? (Stock form)
- Mixes well with additives and dyes.
- Also used in resin glues, spray coating and 3D printing.
What are sheets used for? (Stock form)
- Durable and lightweight.
- Used for protective surfaces, roofing and signage.
- Can be cut to size, bent, curved or vacuum formed.
Plastic screws, nuts and bolts can be made from PVC, nylon and PET.
What are some useful properties of plastic fittings?
- Resist corrosion and don’t rust, particularly when used in wet or salty conditions.
- Made to be UV resistant.
- Flexible, rigid, lightweight and cost effective.
- Can be reinforced with metal.
- Non-conductive, so ideal for electrical use.
Why are plastic fittings more ideal than metal fittings in some conditions?
- More lightweight
- More corrosion resistant
- Non-conductive
- Cost effective
How do plastic hinges differ from metal ones?
- They resist corrosion and are lightweight.
- Plastic hinges can be reinforced with glass fibre.
- No lubrication needed due to rust not forming.
- Also resistant to solvents, sea water and temperature variation.
Exam Style Question:
Explain one advantage of using materials that are sold in standard dimensions.
[2]
- Materials are easier to obtain and likely to be stocked by many retailers.
Or
- Parts are more likely to manufactured in large numbers, making them cost effective due to economies of scale.
Describe the process of vacuum forming.
- This technique is used to shape plastic.
- It works by heating a sheet of plastic, which is then pulled by the vacuum to form around the shape or mould.
- Once the plastic has cooled and set hard it can be removed from the moulding tool.
Describe the process of 3D printing.
- The 3D printing process builds a three-dimensional object formed from reels of thermoplastic.
- 3D printers use CAD files which are converted into a series of co-ordinates called G-code that the printer will follow to build up the object in layers.
- It is also known as additive manufacturing, as the material is added in layers.
Describe the process of drape forming.
- Plastic sheet is heated to a softened state, where it can be formed over a mould.
- It takes on the shape of the mould without stretching the plastic and retains the dimensional thickness.
- It is a slow process without the need for a vacuum, so is low cost, but it does take time.
- Used for components with a gentle curve like motorcycle windscreens and bath panels.
Exam Style Question:
Describe one advantage of 3D printing in the home.
[3]
- New parts can be made when they are required.
- Well suited to one-off or small batch production of parts for personal needs.
- Useful to replace parts of domestic appliances.
- CAD files can be downloaded from the Internet and shared with others”
Describe the process of extrusion.
- Granular plastic is held in a hopper.
- It is moved by Archimedean screw along a heated tube, called the heating chamber.
- Once the polymer has been melted it is pushed through a die mould.
- This creates a continuous flow plastic in a specific shape or profile.
Describe the process of injection moulding.
- Granular plastic is held in a hopper.
- It is moved via an Archimedean screw along a heated tube, called the heating chamber.
- Once the polymer has been melted, it is pushed into a mould with a hydraulic ram. The use of the hydraulic ram ensures just enough material is injected into the mould each time.
- The mould is then cooled so that the moulded plastic can be removed.
What is injection moulding usually used for?
- Products such as bottle caps, toys and automotive parts are produced with injection moulding.
- Injection moulding can handle complex parts and shapes to produce consistent products in large quantities.
What is extrusion usually used for?
It is used for cables, pipes, mouldings and plastic films for packaging.
Processes like injection moulding can be __________ in order to increase the output rate and imorove cost effectiveness.
automanted
Describe the process of line bending.
- Line bending enables thermoplastics, like acrylic sheets, to be folded.
- A line bender heats a sheet of thermoplastic over a strip heater until it is soft.
- It can then be bent to a chosen angle. When the plastic cools, it retains the shape.
Describe the process of plastic welding.
- Heat softens the polymers and they can be joined with a plastic filler material in the form of a long thin cable.
- The heat source comes from hot gas welding guns which produces a thin jet of hot air to soften the polymers.
- Solvent plastic welding can also be used to partially dissolve the plastics, so that they can bond together.
Describe the process of resin casting.
- Liquid synthetic resin is mixed with a curing agent, poured into a mould and allowed to harden.
- Unlike extrusion or injection moulding, which forces plastic into a shape, casting relies on gravity to pull the resin in to all parts of the mould.
What is resin casting usually used for?
- Resin casting is used for industrial prototypes, precise models and moulds for dentistry.
- It also a popular with artists, jewellery makers and hobbyists.
What are the advantges and disadvantages of resin casting?
Advantages:
- Resin casting produces a strong final product.
- It is has a quick production time.
Disadvantages:
- Its use is limited to smaller scale items.
Describe the process of blow moulding.
- A tube of softened plastic, known as a parison is fed into a hollow mould.
- The parison is pinched at the bottom so it can be filled with warm air and inflates to fill the mould, taking on the shape.
- After the parison cools, the mould opens and the finished product is trimmed.
What is blow moulding usually used for?
This method is used for plastic bottles and containers.
What is a ‘chinagraph pencil’?
- A wax or grease-based pencil that can write on most non-porous surfaces.
- Used when marking out on a plastic surface like acrylic.
- Alternatively, an alcohol-based permanent marker would also work to mark a line to cut to.
What are some different tools for cutting plastics by hand?
- Coping saw
- Junior hacksaw
- File
Plastics are often referred to as ‘______________’ in that they are manufactured with their final surface.
self-finishing
Plastics can be painted. Before painting, how should the surface be prepared?
- It should be clean and free of grease.
- Fine abrasive papers rub down the surface to make it smooth and free of debris.
- A polymer specific primer can be applied.
- Paint suitable for plastics can be sprayed to produce an even finish.
What is hydro-graphic printing? (Surface finish)
- Hydro-graphic printing applies a printed design to a three-dimensional surface.
- The film containing the design is placed on the surface of water in a dipping tank.
- The pattern will curve around the surface of the product when submerged.
What are vinyl-cut decals? (Surface finish)
- Vinyl-cut decals are printed with a pattern or text onto vinyl with an adhesive backing.
- They are printed on large rolls and cut using a large format cutter into a variety of shapes.
- Commonly used on vehicles, window displays and guitars.
How are polymers affected by exposure to UV radiation?
- Polymers are affected by exposure to sunlight, UV radiation, and indoor strip fluorescent lighting.
- The surface of the material takes on a chalky white appearance, the colour fades and the material becomes brittle.
How can plastics be protected from degrading from UV radiation?
The addition of stabilisers, absorbers and UV blockers can all slow down the degradation process.
