Polymers Flashcards
How are natural plastics formed ?
Natural latex is harvested by tapping a tree. This can be mixed with other things to form resins, rubbers and plastics.
What are Bioplastics made from?
Made from the starch of corn or vegetables
What are Synthetic plastics made from?
Made from finite petrochemical resources such as crude oil
How are polymers produced?
Crude oil is mined and then refined in fractional distillation, which separates the chemicals into fractions. These fractions are split into monomers which mix with chemicals to become polymers
Describe Fractional distillation
Crude oil is heated to 350 degrees then pumped into the base of the distillation tower. Crude oil vaporises and rises up the tower. As they reach there melting points the different substances of the crude oil condense. The heaviest, hardest to break molecules at bottom, lightest and easiest at top. The fractions are then siphoned off for cracking.
What is a Thermoforming polymer?
Have long chains of molecules tangled together with no mixed structure or pattern. Generally soft and flexible with shape memory.
What is a Thermosetting polymer?
More brittle than thermoplastics and are best suited to stiffer mouldings. They also have long chains of molecules, cross-linked to form a rigid molecular structure. Very hard and waterproof when solid
What is PETE
Polyethylene terephthalate - Clear, easily coloured, smooth finish (Plastic bottles)
What is HDPE
High density polyethylene - Flexible, translucent, weatherproof, tough (Hard hats)
What is PVC
Polyvinyl Chloride - Durable, tensile strength, low water absorption, chemical and flame resistance (Piping)
What is LDPE
Low density polyethylene - Tough, impact-resistant, low temp impact resistance, good chemical resistance (Water buoys)
What is PP
Polypropylene - Translucent, easily coloured, tough, good chemical and fatigue resistance (Lunch boxes)
What is PS
Polystyrene - Low cost, easy to make, easy to shape (Yoghurt pots)
Name the primary Stock forms
Sheets, Rods, Tubing
How are Plastic films used?
Used in packaging, especially in food industry. Heat sealed to be airtight and tamper proof.
What is the Gauge of a plastic
The wall thickness of a plastic
What is Expanded polystyrene used for?
EPS is used regularly as thermal insulation and food packaging.
What are Powders and Granules used for
Mainly used in plastic processing, the granules are heated into a liquid and then reformed.
What are the uses of Plastic Additives
Can adapt the platsic for different uses by adding chemicals, additives and compounds during manufacturing.
How are Tailored Plastics changed for use
Pigments and plasticises can be added to change the colour, flexibility or scent of a plastic
What are the uses of Thermoplastics
Can be woven into fabrics to make them more resistant to wear and tear.
How does 3D Printing (Laser Sintering) work
Uses as laser source to provide thermal energy and selectively fuse together particles of a powdered material. More expensive and precise
How does 3D Printing (Fused Deposition) Modelling) work
Extrudes a thermoplastic filament in a series of layers over a build plate. Cheaper and often used in schools
How does Chemical Welding work
A chemical liquid is placed between two pieces of something which then causes a chemical reaction, forcing the tiles to fuse together.
What are the advantages of Laser Cutting
A very accurate way to cut different types of thermoforming polymer sheets. Can follow an uploaded design to a very fine tolerance.
What is Kerf Allowance
What the laser removes when cutting
Explain the process of Injection Moulding
- Pellets and Granules are fed into a hopper
- Hopper feeds an Archimedes screw which drags the granules to a heater where they melt
- Melted plastic falls into the mould
- Injection cylinder fills and seals the mould
- Plastic cools in the mould and the moving plate is removed, leaving the moulded object
Explain the process of Extrusion Moulding
- Pellets and Granules are fed into a hopper
- Continuous flow of molten plastic is forced under pressure and through a die (mould).
3.Long continuous strips same shape as exit hole is created - Passed through a water tank and pull rollers to cool and solidify it
Explain the process of Blow Moulding
- A tube of heated and softened plastic is inserted into a solid mould with the mould gripping the parrison
- Air is then injected which forces the plastic to expand into the shape of the mould
- Mould is opened and finished project is trimmed
What is Rotational Moulding
Makes hollow shapes with uniform wall thickness
Powder is put in a mould and heated and rotated and then cooled while still rotating
Reasons for Surface Treatments and Finishes
Protection
Aesthetics
Functionality
Why are Spray Primer and Paints used?
Plastics are primed and sprayed with paints for aesthetics and protection from UV degradation. They are quick to apply but contain VOCs (Volatile Organic Compounds) which release hazardous fumes.
What are Vinyl Decals
Printed and cut self-adhesive vinyl can be attached to most surfaces. They are easy to make and use in projects if you have access to vinyl sticker machine and a CAD programme.
What is Flocking
When flocking fibres are bonded to statically charged materials with an adhesive
Wha are the uses of Etching and Frosting
Patterns or grooves can be etched into surfaces to make light reflect more effectively or the material can be frosted across large areas to make the plastic more opaque
What is Heat transfer printing
An image is printed onto special papers and bonded onto the surface of an object with a heat press. This is commonly used for t-shirts and mugs
What is Electroplating
Plastics are covered in a conductive layer or etched before plating. This is mainly used in the car industry
What are Rubberising sprays
A slightly textured coating with a matt finish. Sprayed onto various materials to provide grip
Why is Polishing used
Polishing is used to restore a high quality finish if the plastic becomes rough or scratched during the process
What is Hydrographic printing
Colour images are printed onto a water soluble film which floats in a tank. The object is then dipped in the tank and is coated by the film which contains an adhesive
