Polymers/plastics Flashcards
What are plastics?
- Are carbon-based
- Range of organic materials
What are plastics building blocks?
Monomers
What turns monomers into polymers?
Polymerization
How are plastics manufactured?
From crude oil
Whats the first synthetic material made?
Bakelite
What bakelite and example of?
Thermosetting plastic
What is electro-negativity?
The electron attracting potential of an element
What are the elements in organic polymers?
C, H, N, O, P and S
What does difference in electro-negativity determine?
Bond type
What does a big difference in electro-negativity show?
It is an ionic bond
What does a small difference in electro-negativity show?
It is a covalent bond
How is ethane denoted?
C_2H_6
What organic molecule is the start of a homologous series?
CH_4
Whats the source of all plastics?
- Crude oil
What does crude oil consist of?
- Consists predominantly of hydrocarbons
What percentage of the hydrocarbons in crude oil are aliphatic?
25%
What percentage of hydrocarbons in crude oil are aromatic?
17%
What percentage of hydrocarbons in crude oil are naphthenes?
50 %
What does increasing the number of carbons do?
Increases the boiling point in a systematic way
What is the basis of oil refining?
Separating in different fractions
What colour is crude oil?
Viscous, dark colored
What kind of boiling points do small molecules have?
low
What is an example of aromatics?
Benzene
Example of cycloalkanes?
Methyl
Example of Alkynes?
Acetylene
What is the biggest contributor to petrochemical feedstock?
Gasoline
What is petrochemical feedstock?
Petrochemical feedstock is used for manufacturing polymers
accounts for 2.7% of crude oil
What is the polymerisation of ethylene?
Polyethylene
What uses, heat, pressure and catalyst?
Polymerization
What causes the distribution of chain lengths and thus molecular weights?
Formation of macromolecules during polymerization
How is molecular weight determined?
Molecular weight determined by polymerization conditions
What has a lower molecular weight?
The increased amount of polymer
What are the two types polymers?
They can be crystalline or amorphous
What are thermoplastics?
- Become soft and melt when heated and can be moulded into a new shape that is retained on cooling
- Thermo-plastics can be reheated and remoulded many times
What are the thermosetting plastics?
- Thermosetting plastics cannot be remolded
- If reheated it will not soften
When do thermosetting plastics set?
When first cooled
What will happen to thermosetting plastics when reheated?
Will not soften
What polymers are included in thermoplastics?
Polyethylene, polystyrene, nylon
How are thermoplastics bond?
Weak intermolecular bonding
What kind of density do straight chained materials have?
High density material
How are straight chains and branched chains different?
Branched chains cannot come close together
What is the effect of side chains?-
- Side chains increase distance between the main C-C chain
- Reduced packing and reduced intermolecular attraction
What cannot happen to thermoplastics?
Cannot be reprocessed
What do thermosetting plastic polymers undergo?
A chemical reaction that locks the monomer chains
What are examples of polymers in thermosetting plastics?
Includes phenolics, various epoxy resins
What are co-polymers?
Many commercial polymers are prepared from more than one
monomer
What are the 4 most common co-polymers?
- Random
- Alternating
- Block
- Graft
What is the arrangement of normal polystyrene?
Normal polystyrene is atactic → rings are randomly arranged, irregular
What is syndiotactic?
Syndiotactic is more crystalline than atactic → rings on different sides, regular alternating pattern around the hydrocarbon backbone chain
What are some properties of polymers?
- Low melting point
- Variable molecule size
- Low compressive strength
- Low stiffness
- Low density
- High toughness
What is the area under a stress strain graph?
Absorbed energy
How much plastic produced annually world wide?
300 million tonnes per year
How much is consumption growing by in Western Europe?
4% per year in western Europe
How much of plastics is used in construction?
1/4
How can use of plastics have environmental benefits?
- Use in vehicles resulting in fuel savings
- Foam insulation
What are examples of high volume plastics?
- Polyethylene (PE)
- Polyethylene terephthalate (PET)
- Polyvinylchloride (PVC)
What is PVC used for?
- Window frames
- Pipes
What is PET used for?
- Bottles
- Food packaging
How much of plastics is used in the transport sector?
8%
What do plasticisers do?
Makes plastic mouldable at particular temps
What are some additives to polymers?
- Plasticisers
- Fillers
- Pigments
- Antioxidants
What type of polymers are ideal for application?
hard and tough
How does extrusion work?
- Granules go into extruder → plastic melt
- Barrel heated so it melts and then extruded through a nozzle
What two quantities help to generate shear heat in an extruder?
Combination of pressure and compression
How does injection moulding work?
- Load plastic pellets in the machine hopper
- Using a RAM inject melted plastic into mould
- Open the mold and eject the solidified plastic part
How does processing by compression moulding work?
- Lump of plastic and squeeze it in a mould using a plunger
What is plastic is mainly used in construction?
PVC
How much of plastic used in construction goes towards making pipes and ducts?
1/2
Where is HDPE used?
The lining system in a landfill will have a high-density polyethylene to stop leaching getting into the environment
What does HDPE stand for?
High-density polyethylene
What are characteristics of HDPE lining in landfills?
- Flexible membrane liners
- It is a thermoplastic so they are heat-sealed together
What is used for the cover of landfills?
LDPE
Why do they use LDPE as the cover in landfills?
Needs to be more flexible because waste is contracting due to degradation. There is subsidence
Where is bitumen used?
Coat roads in it and is the binder
What can be mixed into bitumen?
Aggregates
What is bitumen produced from?
Bitumen is produced from crude oil during fractional distillation
What are the features of bitumen?
Viscous liquid or solid consisting of polycyclic aromatic hydrocarbons
Bitumen is the ? oil fraction.
Heaviest
What is bitumens boiling point?
> 370˚C
What does bitumen do when heated
Softens when heated and non-volatile
What are advantages of bitumens properties?
Bitumen has excellent waterproofing and adhesive properties
How much bitumen is produced annually in Europe?
16 million tonnes per year
How much carbon and hydrogen does bitumen contain?
82-88%
8-11%
How trace metals exist as in bitumen?
Trace metals present as inorganic salts
What does the exact composition of bitumen depend on?
Exact composition depends on the crude oil and the distillation process
What are the main chemical groups in bitumen?
Asphaltenes and Maltenes
How can Maltese’s be subdivided?
Resins, aromatics, and saturates.
What is the optimum amount of filling in asphalt?
Bitumen fills the voids. Both the stone skeleton and bitumen contribute to the properties of the mix
What is the suboptimal filling in asphalt?
Too much or too little bitumen so either stone skeleton or properties dominate