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Engineering > Polymers > Flashcards

Polymers Flashcards

1
Q

Polyemers: What are they?

A

Long molecular chains, often covalently bonded
- good insulators of electricity, heat: yet low stability, weak,

Monomers: get heated, covalant bonds break, reform with others to create a POLYME

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2
Q

Homopolymer vs copolymer and examples

A

Homopolymer (made of cust one monomer)
e.g. polyethelene, PVC, polystyrene)

Copolymer (made of two or more monomores in a singular chain (e.g ABS)

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3
Q

Addition Polymeristtion:

A

A simple polymerisation, linking monomers with inclusion of all parts of the structure: no waste
Heat and pressure are suitable catalysts

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4
Q

Condensation Polymerisation

A

Two or more dissimilar monomers react together: make polymer with a byproduct (usually water) e.g. nylon (dicarboxylic acid and a diamine)

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5
Q

Thermosets

A

Undergo a CHEMICAL change with heat. (non-resversible)

Have network structure with covalent bonds along and between chains

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5
Q

Thermoset types

A

Epoxy resins, silicone, polyurethane, polyester resins

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5
Q

Thernoset vs thermoplastic properties

A

Thermosets:
- More rigid, chemical resistance, heat resistance, structrual integrity

Thermoplastics:
- recyclanble, flexible

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5
Q

Vulcanising

A

Minimising sliding of chains that distort natural rudder items under tensile loads
- controlled breaking of some ‘spare’ multiple bonds, formation of covalent bonds

Sulphur is introduces as vulcanising agent: requires heat and pressure

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5
Q

Crystabllinity

A

In amorphous: loosely packed chains, distroted: allows light rays to pass through (can be transparent e.g ABS, acrylic, PVC_

Crystaline are highly organised,

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5
Q

Thermoplastics

A

Soften when heated, can be repeatedly melted down and reformed.

Long covalently bonded chain structures with weak secondary bonds (Van der Waal): can be made flexible and transparent)

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6
Q

CONSEQUENCES Of crystallisation

A

Destroys clarity: more opaque

Greater shrinkage,
More rigidity, stronger, higher creep + fatigue resistance

Less ductile (tighter packing of molecules restricting movement)

More difficult to bond with adhesives and solvents BUT higher chemical and stress cracking resistance
Greater resistance to wear, good for structural applications.

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6
Q

Elastomers

A

Thermosoftening polymers still with multiple bonds in their structure after polymerisation e.g. rubbers

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7
Q

Vulcanising Properties

A

No longer able to completely soften under heating: loose elasticitym but increase strength and rigitidy

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8
Q

Thermosets

A

Undergoes a permanant chemical change with heat

Have a network structure with covalent bonds along and between chains

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9
Q

Thermoset vs Thermoplastics (properties)

A

More rigid, better chemical, heat resistance and structural integrity
vs.
Thermoplastics:
- more ductile, recyclable, but weaker, transparent

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10
Q

Elastomers in transport (3 types)

A

Fillers e.g. carbon black, silica: added to natural rubber tyres to increase resistance to abrasion and tearing

NEOPRENE: synthetic rubber, e.g. flexible hoses in hydraulic brake systems, fuel systems (crosslinked with oxides of zinc or magnesium) = resistant to oils and solvent

BUTYL Rubber: synthetic, no double bonds: long life (bike tyres, tubes): airtight.

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10
Q

Elastomers properties:

A

Highly flexible, wear resistant

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11
Q

Crystalline polymers vs amorphous

A

Completely transparent, loosely packed disordered: TRANSPARENT e.g. ABS, acrylic, PVC

Highly organised, aligned, closely packed: light cannot pass thru (opaque)
E.g. polypropylene, polyethylene

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11
Q

Crystallisation properties

A

Opaque, more shrinkage (tightly packed structure)

Rigid, stronger, more fatigue and corrosion/cracking resistance: structural applications

Less ductile, harder to bond

12
Q

Vulcanising:

A

Minimises distortion under tensile loads

Breaks spare multiple bonds, makes covalent bonds
Introduce sulphur

12
Q

Modification of polymer properties

A

Increase length of chain or large group of atoms

Make material crystalline
Cross-linking
Blenndong
Orientation of molecules
Copolymerisation
Prodicomg branches
Introducing additives

12
Q

Polymer textiles

A

Polymeric materials with fibre: properties non-typical of textiles e.g. ‘shade cloth’ to protect from UV, filtration systems, seatbelts, train seat covers

13
Q

Fibre manufacturing Processes:

A

Coagulating, stretching, washing, applying finish, drying, then cutting.

14
Q

Textiles examples

A

Polyester
Nylon
Aramid
Olefins
PTFE (Teflon)

14
Q

Polyester properties and uses

A
  • strong, resilient, hydrophobic
  • helium airships, some tyres, car parts e.g. fan belts, radiator hoses
15
Q

Nylon properties and uses

A

Dry lubricant
- being replaced by PTFE
- resistant to acids, bases, oils

16
Q

Olefids

A

Polyethylene or Polypropylene fibres shaped in sheets
- waterproof, used for collapsible shelters and buildings

17
Q

PTFE (Teflon)

A

Fire resistant, stop water vapour
- filters in engines

18
Q

Aramid

A
  • nomex and Keval
  • strengthened by a bacjbone of benzene rings
  • strong BUT only low temperature uses
  • used in aircraft, bulletproofing
19
Q

Polymer Manufacturing types

A

Blow molding
Extrusion
Thermoforming
Calendaring
Rotational molding
Injection molding

20
Q

Blow moulding

A
  • thermoplastics
    1. polymer tube lowered into mold, air forces tube to shape of mold

used for making containers e.g. oil containers

21
Q

Extrusion

A
  1. Polymer granules melted, forced through die
    - good for thermosoftening ploymers
  • polymer tubing, bike cable coatings
22
Q

Thermoforming

A

Thermoplastic containers

  1. thermoplastic sheets placed over dies, make required shape
  • can be done with matching dies, vacuum or air pressure
23
Q

Calendering

A

Thermoplastic poured into cavity between rollers, plastic squeezed through
- can be embossed with patterns
- Tiles, films, curtains

24
Q

Rotational molding

A

Polymer poured into mold, centrifugal force makes hollow article

25
Q

Silicones properties, uses

A
  • Non-chemically reactive
  • Low thermal and electrical conductivity
  • Can repel water (watertight steels)
  • Electronics (low thermal and electrical conductivity properties)
  • Aviaton (sealants)
  • lubricants

THERMOSET

25
Q

Injection molding

A
  1. Polymer granules placed into hopper
  2. released into heated chamber where reciprocating screw forces metal closer to die (even heating due to screw)
  3. Forced into die, cooled then released
  • good for mass manufacturing, cheap
  • poor finish: sprue and split line evident
  • used for small thermoplastic moldings for cars and bijes
26
Q

Polyurethane Foam

A

THERMOSET
- resistant to water, oil, grease
- good specific strength
- adhesive when forming
- Thermal insulative

  • Used for insulation e.g. roofs, wine tanks, refrigeration
27
Q

Polyethylene

A

low melting temperature, tough, flexible, insulator, low density has branched chains reducing crystallinity, high density is linear

coating on outer of bike gear and brake cables

28
Q

Polycarbonate

A

High strength (resistant to impact and fracture), tough materials (can be optically transparent)
- Easily manufactured.

Lightweight, good alternative to glass
Ecofriendly processing and recyclability
Good electrical properties, UV radiation protection

3D printing, food containers, medical applications, car bumpers and headlight lenses

29
Q

Polypropylene

A

Harder then polyethelene, low density and hight heat resistance

-Packaging, automotives

29
Q

Polyvinyl chloride (PVC)

A
  • Cheap
  • Strong
  • Weather and chemical resistant
  • Strong tensile strength
  • Electrical insulation
  • Pipes, flooring, car interiors and seat coverigs, wire insulation
30
Q

Polyamide (nylon)

A
  • Chemical, oil, thermal resistant
  • Flexible
  • High wear and abrasion resistance
  • Low coefficient of friction
  • Lightweight
  • Water aborbant

Automotive parts, industrial vlaves, insulation for railway sleepers

31
Q

Acrylic (perspex)

A
  • High rigidity, weldability
  • Insulating
  • Impact, abrasion and strain resistance
  • Good surface aspect
  • High dimensional stability
  • Dashboard components, wheel covers, helmets, pipes
31
Q

Vulcanised Rubber

A
  • Elasticity
  • Weather, ozone, heat and chemical resistance
  • Abrasion, oil and aging resistance
  • Hoses, insulation, vibration dampers, tyres
32
Q
A

Engineering (10 decks)

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