Polymers Flashcards
Ethene is a starting material for …
PAINT/DEGREASER:
- ClH2CH2Cl
- 1,2-dichloroethane
ANTIFREEZE:
- HOCH2CH2OH
- ethane-1,2-diol
POLYMERS:
- e.g polythene
VINEGAR:
- 5% CH3COOH
- ethanoic acid
The manufacture of margarine
Process ~ Hardening
HYDROGENATION requirements :
- Hydrogen
- 150 degrees
- nickel catalyst
Type of reaction ~ ADDITION
- Oil partially solidifies and hardens
- vary the HARDNESS by adding different numbers of H2 molecules.
Fewer hydrogens ~ MORE SPREADABLE
More hydrogens ~ LESS SPREADABLE
Making POLYMERS & TYPE of reaction
- Two ALKENE molecules COLLIDE and their PI-BOND BREAKS.
- Each carbon atom now has an UNPAIRED electron so is a RADICAL.
- C-C bond forms between two CARBON RADICALS.
- The END carbon atoms still have an unpaired electron so more MONOMERS can add on one at a time.
Type of reaction :
ADDITION POLYMERISATION
Making Poly(ethene) in industry
Method 1 : RADICAL POLYMERISATION
Conditions:
- 200 degrees
- high pressure
Problem:
- get BRANCHED poly(ethene)
- FEWER CONTACT POINTS occur due to branches.
- WEAKER London forces
- FEWER atoms per unit volume
- Relatively LOW DENSITY
NAME ~ low density poly(ethene) or LDPE
USE ~ carrier bags due to its relatively low strength.
Making poly(ethene) in industry
Method 2 : Ziegler-Natta Process
Conditions:
- 60 degrees
- TiCl3 & Al(C2H5)2Cl catalysts
Result:
- UNBRANCHED poly(ethene)
- GREATER CONTACT POINTS due to unbranched chains.
- STRONGER London forces
- MORE atoms per unit volume
- Relatively HIGH DENSITY
NAME ~ high density poly(ethene) or HDPE
USE ~ plastic food containers and bottles due to its relatively high strength.
Why are polymers useful?
- Cheap
- Readily available
- Unreactive
- Durable
Problem with polymers?
- Non-biodegradable
- Produce toxic fumes when incinerated
Polymer Disposal:
- 85%
- 8%
- 85% is put in LANDFILL
- 5% is INCINERATED
Problems: - some plastics do not melt
- poisonous fumes can be produced
- plastics contain a large amount of CARBON which results in the greenhouse gas CO2 to be released
Polymer Disposal:
- 7%
SORTING & RECYCLING:
- Conserves finite fossil fuels
- reduces landfill waste
DIFFICULTIES:
- Labour intensive
- colourants, stabilisers and plasticisers in plastic waste can release poisonous heavy metal ions.
- POISONOUS DIOXINS can be released if PVC & HDPE are not separated , thus spoiling the recycling process.
DEVELOPMENTS:
- New optical scanning techniques can separate PET from HDPE.
RECLAMATION of polymers
- Processing of polymers into NEW PRODUCTS when they have been sorted.
- Chopped into small flakes, washed, melted and re-moulded.
- PET bottles ~ carpets, clothing & new bottles.
- HDPE ~ plastic boxes & bins
Uses of polymers: Fuel source for energy
FUEL SOURCE FOR ENERGY:
- Have a high stored energy content
- Can incinerate non-recyclable polymers to produce HEAT ENERGY.
- Use the heat energy to produce STEAM , which drives TURBINES to make ELECTRICITY.
Uses of polymers : Feedstock recycling
FEEDSTOCK RECYCLING:
- Chemical and thermal processes RECLAIM monomers, gases and oil from waste polymers.
- The polymers DO NOT have to be washed or sorted prior to the process.
- The RAW MATERIALS obtained produce NEW polymers.
Uses of polymers : Recycling of PVC (polyvinyl chloride)
DIFFICULTIES:
- high chlorine content
- toxic acidic HCl gas & toxic dioxins are released during incineration.
DEVELOPMENTS:
- PVC on electrical wiring can be SEPARATED from other polymers using SOLVENTS and then re-used.
Uses of polymers : Bioplastics
BIOPLASTICS:
Made from RENEWABLE resources such as:
- plant starch
- plant cellulose
- plant oil
- plant proteins
BENEFITS:
- biodegradable
- sustainable alternative to oil-based
polymers.
- Conserve crude oil reserves.
Uses of polymers: Biodegradable & Compostable polymers
BIODEGRADABLE are made from either:
- starch
- cellulose
- additives which alter the structure
These allow them to be BROKEN DOWN by MICROORGANISMS and environmental conditions into:
- Water
- Carbon dioxide
- Inorganic compounds
- Biomass
COMPOSTABLE:
- Degrade to give NO TOXIC or VISIBLE
residues.
Uses of polymers : Photodegradable polymers
Used when plant-based polymers cannot be used.
CARBONYL GROUPS (C=O):
- Carbonyl groups are incorporated into the backbone of the polymer.
- They absorb LIGHT ENERGY causing the polymer to break down.
ALTERNATIVELY
LIGHT SENSITIVE ADDITIVES:
- These are blended with the polymer and CATALYSE the break down of the polymer in the presence of UV light.
Photodegradable polymers in LANDFILLS are unlikely to receive sufficient EXPOSURE to light for degradation to occur.
Uses of polymers : Cracking
This process produces:
- SHORTER chain ALKANES used as FUELS
- ALKENES which make POLYMERS
