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POLYMERS Flashcards

1
Q

How are the majority of polymers made?

A

Via fractional distillation of crude oil.

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2
Q

Which fraction of crude oil is the main one used in the production of polymers?

A

Naphtha

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3
Q

What is cracking?

A

Breaking the large hydrocarbons down into smaller, more useful forms.

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4
Q

What are the three types of polymers?

A

Thermoplastics
Thermosetting polymers
Elastomers

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5
Q

Why are polymers described as self-finishing?

A

They can be pigmented during the manufacture process to give colour and there require no additional secondary finishing process.

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6
Q

What are the stock forms that polymers are available in?

A

Granules
Sheet
Film
Rods (other extruded forms)
Tubes
Bars
Foam
Powder

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7
Q

What does is mean by the safe working temperature of polymers ?

A

The temperature seemed safe for processing without possible degradation of the polymer properties.

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8
Q

Describe low density polyethylene.

A

LDPE
Very tough, good chemical resistance, weatherproof, available in translucent, low level of rigidity.
Safe working temperature of 65 degrees
Squeeze detergent bottles, carrier bags

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9
Q

Describe high density polyethylene?

A

HDPE
Available in translucent form, weatherproof, tough, good chemical resistance.
Safe working temperature of 65 degrees.
Household and kitchenware, long life carrier bags, buckets

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10
Q

Describe polypropylene?

A

PP
Available in translucent, good chemical resistance, tough, good fatigues resistance (hinge property)
Safe working temperature of 100 degrees.
Folders, hinged container lids

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11
Q

Describe high impact polystyrene?

A

HIPS
Hard, rigid, available in translucent, tough.
Safe working temperature of 70 degrees.
Yoghurt pots, single use drink cups, toilet seats.

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12
Q

Describe acrylonitrile butadiene styrene?

A

ABS
Extremely tough, hard, available in opaque.
Safe working temperature of 80 degrees.
Rigid luggage, LEGO, remote control casings.

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13
Q

Describe polymethylmethacrylate?

A

PMMA (acrylic)
Tough, hard, good chemical resistance , available in translucent.
Sage working temperature of 95 degrees.
Car light casings, lighting units.

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14
Q

Describe nylon.

A

Tough, corrosion resistant, good temperature resistance, low coefficient of friction.
Safe working temperature of 150 degrees.
Curtain rails, textiles, cable ties

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15
Q

Describe rigid polyvinyl chloride?

A

uPVC
Rigid, opaque, tough, hard, good weathering resistance, good chemical resistance, fire retardant.
Safe wouldn’t temperature of 95 degrees.
Window frames, guttering and downpipes

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16
Q

Describe flexible polyvinyl chloride.

A

PVC
Available in translucent, tough, flexible, good weathering resistance, good chemical resistance.
Safe working temperature of 95 degrees.
Hose pipes, cable insulation, inflatable products.

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17
Q

What are the 9 thermoplastics?

A

Low density polyethylene
High density polyethylene
Polypropylene
High impact polystyrene
Acrylonitrile butadiene styrene
Polymethylmethacrylate (PMMA)
Nylon
Rigid polyvinyl chloride
Flexible polyvinyl chloride

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18
Q

What are the 4 thermosetting polymers?

A

Urea formaldehyde
Melamine formaldehyde
Polyester resin
Epoxy resin

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19
Q

Describe urea formaldehyde?

A

Hard, heat resistant, good electrical insulator, brittle
Safe working temperature of 80 degrees
Electrical fittings, adhesives

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20
Q

Describe melamine formaldehyde ?

A

Hard, opaque, tough, heat resistant, food safe, chemical resistant
Safe working temperature of 130 degrees
Decorative laminates, picnic ware, buttons

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21
Q

Describe polyester resin?

A

Rigid, heat resistant, chemical resistant, brittle
Safe working temperature of 95 degrees
Castings, car parts, chair seats

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22
Q

Describe epoxy resin?

A

Rigid, clear, hard, tough, chemical resistant
Safe working temperature of 80-120 degrees
Adhesives, encapsulation of electrical components, surface coatings

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23
Q

Are elastomers toxic or non-toxic?

A

Non-toxic
Makes it ideal for gripped surfaces touched by the skin.

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24
Q

What are the 4 elastomers?

A

Natural rubber
Butadiene rubber
Neoprene
Silicone

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25
Q

Describe natural rubber?

A

High tensile strength, low elongation, good hardness compared to other elastomers, tough, electrical insulator, good cold resistance.
Tyres, tubes, balloons.

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26
Q

Describe butadiene rubber?

A

Tough, excellent wear resistance against friction, good thermal resistance against friction, electrical insulator.
Vehicle tyres, shoe soles, water hoses

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27
Q

Describe neoprene?

A

Good thermal resistance, toughness, good oil and chemical resistance, excellent weather resistance, good abrasion resistance, electrical insulator.
Wetsuits, laptop cases, wire insulation

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28
Q

Describe silicone?

A

Good flexibility at low temperatures, poor abrasion resistance, good thermal resistance and resistance to temperature extremes, good weather resistance, good lubricating qualities, electrical insulator.
Flexible ice cube trays, bakeware, cooking utensils

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29
Q

What are the 2 additives that help to make the polymer flow more easily into the mould?

A
  1. Lubricants
  2. Thermal antioxidants
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30
Q

What is the additive used to enhance aesthetics?

A

pigments

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31
Q

What are the 4 additives used to improve produce function?

A
  1. antistatics
  2. flame retardants
  3. plasticisers
  4. fillers
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32
Q

What are the 2 additives used to prolong life (prevent degradation)?

A
  1. antioxidants
  2. UV light stabilisers
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33
Q

What are the 2 additives used to encourage degradation?

A
  1. biodegradable plasticisers
  2. bio-batch additives
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34
Q

What do lubricants do?

A

The addition of wax or calcium stearate reduces the viscosity of the molten polymer, making it less sticky, allowing more intricate shapes to be formed.
They can also allow the moulding temperature to be lowered, saving energy during the manufacturing process.

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35
Q

What do thermal antioxidants do?

A

these help to prevent the polymer oxidising or discolouring due to excessive heat during processing.

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36
Q

What do pigments do?

A

these are tiny particles that are mixed into the polymer in its molten state to give colour to the final processed product.

37
Q

what do antistatics do?

A

Due to their poor electrical conductivity, plastics are used for insulating products. This insulating property can lead up to a build-up of static electrical charge, which attracts dirt and dust. The addition of antistatics improves the surface conductivity by attracting moisture from the room surroundings, therefore reducing static charge.

38
Q

What do flame retardants do?

A

Bromine, chlorine, phosphorus or metal, when added to polymers reduce the likelihood of combustion or the spread of fire. This is particularly important in products exposed to heat, such as car engine components or potential electrical fires such as plug sockets.

39
Q

What do plasticisers do?

A

These are added to allow plastics to become less hard and brittle at room temperature use.
They are added to LDPE in the manufacture of food wrap, allowing the wrap to be stretched over the food product.
They also help in processing because they allow polymers to be easily formed at higher temperatures.

40
Q

What do fillers do?

A

To provide bulk for the product (meaning less polymer is required) and to improve the polymer properties.
Commonly used fillers are sawdust and wood flour as well as mineral fillers such as chalk, clay and calcium carbonate. Sawdust and flour provide bulk, therefore reducing the amount of polymer required for the product. Mineral fillers can help to increase the thermal conductivity of the polymer, meaning they will heat up and cool down more quickly, giving shorter mould cycle times.

41
Q

What do antioxidants do?

A

They help to reduce the environmental deterioration of the polymer from exposure to oxygen in the air.
Polymer degradation can lead to increased brittleness, surface cracks and pigment discolouration.

42
Q

What do UV light stabilisers do?

A

They prevent the polymer chains from being broken down by sunlight. UV attack causes the polymer to lose colour and become more brittle.

43
Q

What do biodegradable plasticisers do?

A

Similar to plasticisers used to enhance processing, these make the polymer more flexible, softer and easier to break down, which means a faster degradation time.

44
Q

What do bio-batch additives do?

A

Oxy-degradable (degrade in the presence of oxygen), photodegradable (degrade when exposed to UV light) and hydro-degradable (degrade in the presence of water) additives can be added to polymers to help recue the degradation time from hundreds of years to a few years or even months.

45
Q

What products are made using vacuum forming?

A

lightweight trays
box inserts and liners
coffee cups
yoghurt pots

46
Q

What type of production does vacuum forming use and why?

A

It is normally limited to to small-scale batch production due to it being a slow process.
However, if a larger scale of production is required, moulds can be made from cast and machined aluminium.

47
Q

What is the process of vacuum forming?

A
  1. The mould is placed on the bed of the machine, which is called the platen. The platen is lowered to the bottom of the machine.
  2. Polymer sheet is clamped over the mould and a heater is pulled over the polymer sheet.
  3. When the polymer sheet has softened, the platen is raised into the polymer and the heat is removed.
  4. The vacuum pump is switched on, which sucks the polymer onto the mould.
  5. Once the polymer has cooled and returned to a solidified state, the platen is lowered and vacuum switched off.
  6. The mould is removed from the moulding. Excess polymer is then trimmed off.
48
Q

What products are made from thermoforming?

A

bath
fruit punnets
cake boxes
sandwich boxes

49
Q

What is the process of thermoforming?

A

A very similar process to vacuum forming, except there is an additional mould that is pressed onto the surface of the polymer sheet at the same time as the vacuum is applied, sucking the polymer down on to the mould below. The two moulds trap the softened polymer in between them, giving extra detail to the moulding.

50
Q

What products are made using the calendering process?

A

thin polymer sheet and film

51
Q

What type of production system does calendering use?

A

continuous

52
Q

What is the process of calendering?

A
  1. It works by heating pellets of thermoplastics so that it melts into a dough-like consistency.
  2. It is then extruded between a series of heated rollers so that it becomes squashed and stretched to make it thinner.
  3. It is then finished on colling rollers, before being chopped into standard stock sheet sizes, or in the case of polymer film, it is rolled up for storage and distribution.
53
Q

What products are made using line bending?

A

acrylic boxes
shelves
point of sale displays

54
Q

What type of production is line bending suitable for and why?

A

one-off or limited batch production because it is quite slow and is a labour intensive process.

55
Q

What is the process of line bending?

A
  1. Turn on the strip heater.
  2. Place the thermoplastic on the strip heater, aligning the heated strip with where you want the bend.
  3. Ensure that you keep turning over the plastic to heat both sides evenly and avoid burning the plastic and making it bubble.
  4. Once the plastic is hot enough to bend easily, place it in the jig to create the required angle for the product and allow it to cool.
56
Q

What products does the lamination process make?

A

3D products from fibre-glass composites such as glass-reinforced plastic.
boats
yachts
kayaks
trains

57
Q

What is the process of lamination for moulding glass-reinforced plastic?

A
  1. A mould or former in the shape of the product is prepared. This might be made from timber, manufactured boards or high density foam.
  2. The mould is coated with a release agent such as wax or PVA, or is covered with parcel tape.
  3. A top layer of gel coat is applied. The gel coat of polyester resin often mixed with a pigment to give a colour to the moulding. The resin might also have additives included to prevent degradation from UV and hydrolysis.
  4. Fibreglass matting is cut to size and laid over the former. Polyester resin is brushed onto the matting and a small roller is used to push out any air bubbles that may form and to smooth out the matting (this process is called stippling). The matting is available in a range of stock forms including chopped strand, woven and ‘tissue’, which is a fine grade matting for covering the surface.
  5. Step 3 is repeated until the desired thickness is achieved, and fine tissue matting is used on the top layers. A vacuum bag may be used to compress the layers of GRP before it sets.
  6. The GRP is allowed to set.
58
Q

What products are injection moulded?

A

vacuum cleaners
clip fastenings
screw posts
battery housing
circuit board holders
(complex parts)

59
Q

What type of production does injection moulding use and why?

A

large-scale mass production or continuous production, due to the high costs of the equipment and the moulds.

60
Q

What is the process of injection moulding?

A
  1. Thermoplastic granules are poured into the hopper.
  2. An archimedian screw is rotated by a motor. This pulls the granules through the chamber and past electric heaters.
  3. The heaters melt the granules of polymer.
  4. When a sufficient charge if polymer has melted and formed at the end of the screw, a hydraulic ram forces the screw thread forward. This injects the polymer into the mould.
  5. The mould is water cooled, which enables the molten polymer to harden quickly.
  6. The mould opens and ejector pins push the moulding out.
  7. Any excess polymer is trimmed off the moulding. Formers and jigs may be used to maintain the dimensional accuracy of the moulding while it cools and hardens completely.
61
Q

What products use the blow moulding process?

A

bottles
wide range of hollow products

62
Q

Which polymers are used for blow moulding?

A

PET
LDPE
HDPE
PP

63
Q

What type of production does blow moulding use and why?

A

continuous production due to the high set-up costs associated with the equipment and moulds

64
Q

What is the process of blow moulding?

A
  1. The polymer is fed into the hopper.
  2. Sn Archimedean screw pulls the polymer through a heated section, melting the polymer.
  3. The melted polymer is extruded as a tube, which is called ‘parison’.
  4. The mould sides close around the parison and air is injected into the mould, forcing the polymer to the sides.
  5. The polymer is allowed to cool for a few seconds, the mould opens and the finished bottle is ejected.
65
Q

What are the two types of blow moulding?

A

parison
preform

66
Q

What types of products are made using rotational moulding?

A

traffic cones
kayaks
water tanks
children’s play equipment

67
Q

What types of polymers are used for rotational moulding?

A

HDPE
PP

68
Q

What type of production is normally used for rotational moulding and why?

A

large-scale batch or mass production due to the high set-up costs

69
Q

What is the process of rotational moulding?

A
  1. Polymer powder or granules are loaded into a mould, which is clamped and sealed.
  2. The mould is transferred to an oven where it is heated to 260-370 degrees Celsius, depending on the polymer being used. The mould is rotated slowly (fewer than 20 rotations per minute) around two axes, and as the polymer is heated, it coats the inside of the mould.
  3. Once the polymer has achieved the correct thickness, the mould is cooled. Usually a fan and/or water is used to cool the polymer.
  4. When the polymer has solidified, the part will shrink slightly, allowing it to be removed.
70
Q

What products are made from extrusion?

A

solid rod
hollow tubes
angles sections

71
Q

What type of production does extrusion use?

A

Continuous

72
Q

What is the process of extrusion?

A
  1. Polymer granules are loaded into the hopper.
  2. the Archimedean screw moves the polymer granules past the heaters.
  3. The heaters soften the polymer.
  4. When sufficient polymer has melted, the hydraulic ram pushes the Archimedean screw, forcing the polymer through a steel die. The shape of the die determines the shape of the extrusion.
  5. The extrusion may be supported by rollers as it leaves the die and is cooled by water or air.
  6. The extrusion is then cut to the desired length.
73
Q

What polymers are used for compression moulding?

A

thermosetting polymers such as urea formaldehyde and melamine formaldehyde.

74
Q

What products are made from compression moulding using urea formaldehyde?

A

electrical light fittings
switches
electrical plugs

75
Q

What products are made from compression moulding using melamine formaldehyde?

A

polymer plates, bowls and mugs for picnic sets
children’s table sets

76
Q

What is the process of compression moulding?

A
  1. A ‘slug’ of pre-weighed thermoset polymer is inserted into the pre-heated moulds.
  2. The moulds are closed and hydraulic pressure is applied. The pressure ensures that the polymer takes the shape of the mould.
  3. The moulds remain closed while cross-linking takes place and the thermoset ‘cures’.
  4. When the moulding has cured, the machine opens and the product is removed.
  5. Excess polymer known as ‘flash’ is removed.
77
Q

What are the 3 types of finishes that you can apply to polymers?

A
  1. adding colour in the moulding process
  2. acrylic spray finished
  3. overmouldings
78
Q

How can you add colour to the polymer in the moulding process?

A

Pigments are tiny particles, which are added to the polymer to create a particular colour. The pigment can be added to the polymer during the manufacturing process or they can be added during the manufacture of the polymer stock form.

79
Q

What are some examples of smart pigments?

A

Thermochromic (change colour at specific temperatures)
Phosphorescent (glow in the dark)

80
Q

Why are acrylic spray paints used on polymers?

A

enhance aesthetics and improve product function
it can also protect against the effects of UV light and weathering

81
Q

Why are acrylic spray paints appropriate to use on polymers?

A

It is fast-drying, water soluble paint that becomes water resistant when dry.

82
Q

In what industry are acrylic spray paints used a lot for mass customisation?

A

Car manufacturers as it allows the customers to choose their preferred colours for the different components of the car.

83
Q

What is overmoulding?

A

it is moulding a second polymer over specific parts of a product.

84
Q

Why is overmoulding used?

A

It is primarily used to provide areas of grip or texture or to highlight different colours for different component parts on products.

85
Q

What is an example of a product that has overmouldings?

A

A toothbrush made from PP would have a TPE overmoulding to provide an area of grip on the handle.

86
Q

What are the two ways of producing an overmoulding?

A
  1. Use two injection moulding moulds
  2. Twin shot injection moulding
87
Q

Using two injection moulding moulds is one way of producing an overmould. How does it work?

A

One mould is made for the product, for example toothbrush body, and one mould is for the grip areas. The toothbrush body is injection moulded and then the product is placed into a second mould and the grip is injection moulded onto the body.

88
Q

Twin shot injection moulding is one way of producing an overmoulding. How does it work?

A

This process uses an injection moulding machine with a mould designed to produce the product in one cycle. The mould has two separate component cavities and can be rotated through 180 degrees so that they line up with the twin injection points.
First, the moulded part, for example the toothbrush body, is created in the first mould cavity. The mould then opens slightly and rotates 180 degrees to secondary position. The mould closes again and the second injection applies the overmould, for example the grip on the toothbrush body.

DT (7 decks)

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