4.1.11 Polymers - Dealing with polymer waste

4.1.11 Polymers - Dealing with polymer waste

1. Synthetic polymers are very important for everyday life to to them being so versatile

   • They have many uses from clothing to materials in cars
   • We regard this type of material as disposable
   • Addition polymerisation are saturated organic compounds so are v. stable so don't get attacked by environmental conditions or pathogens
     • So plastic remains unchanged for many years
   • A time may come when we can't make plastics we are so reliant on
     • Addition polymers are made from compounds available during processing of crude oil
       • Crude oil is non-renewable and we are using it faster than our planet can make it

2. Polymer waste

   • Over 10% of household waste is plastic
   • Plastics are disposed of in many ways:
   • Landfill, Combustion (with electrical generation), Reusing, Recycling, Using as organic feedstock

3. Landfills

   • Large holes are dug into landscape
     • Holes are lined so no contaminants can seep in
     • Rubbish is put into the holes and compacted
       • Once holes are full, it is capped and landscaped
     • After rubbish is buried, conditions change from normal atmospheric to anaerobic with limited supply of H2O
       • This reduces rate of decomposition of biodegradable materials
       • Many plastics are non-biodegradable so the waste doesn't brake down and becomes dangerous to wildlife

4. Combustion

   • Plastic are mainly organic and can be burnt
     • They contain large amts, of C so combustion releases CO2 which is a greenhouse gas and linked to climate change
     • Depending on the plastic, other toxic/polluting gases can be made (e.g.HCl)
       • These harmful gases are removed by gas scrubbers where a base (e.g. CaO) neutralises acidic gas
     • Plastics have a high calorific value they can be burnt in power stations
       • Chemical energy transferred drives turbines and generates electricity

5. Reusing

   • Some plastics can be reused for the same function many times e.g. a drink bottle

6. Recycling

   • For recycling to occur plastics must be sorted into different types which is expensive as it is labour intensive or requires high tech to automate the process
     • Plastics are cleans, melted and reshaped into new products
     • Limited market as companies are concerned about the quality and cleanliness of recycled products

7. Organic feedstock

   • After the waste plastic is sorted, chemical reactions take place to break plastic polymers into small organic molecules
     • Allows the recovered chemicals to be used in other industrial reactions

8. Biodegradable polymers

   • Sometimes a biodegradable polymer (like plant starch) is mixed with an addition polymer (like poly(ethene)) so that over time the starch breaks down making polymer chains small and the material can biodegrade
   • However, these small pieces of addition polymers can still cause hazard to the ecosystem
   • The new material is bioplastic if only the biodegradable polymer is used
   • Plant starch= makes bin bags= starch can be derived from sustainable farming methods so its carbon neutral
   • To be fully compotable= plastic must decompose landfill material as quickly as compost would with grass clippings
     • Only products should be CO2, H2O, inorganic compounds and biomass
   • A substance like poly(lactic acid) can decompose in around 180 days and is used for making cold drink cups and wrapping of fresh fruit

9. Photodegradable polymers

   • Photodegradable plastics break down chemically using energy with wavelengths similar to light
     • Once the polymer is exposed to light it begins to break down and cannot be stopped
       • Photodegradable plastics in landfill are not exposed to sufficient light to degrade
   • Either addition polymers with bonds within their structure that are weakened by absorption of light
   • Or they have an additive affected by light which weakens the bonds in the polymer