Polymer Disposal (Edexcel IAL Chemistry)

Spec point — 5.8

Polymer Disposal

• The three main methods to dispose of plastics are:

  • Landfill waste disposal
  • Incineration / burning
  • Recycling

Landfill waste disposal

• Landfill sites are not desirable because they take up valuable land
• Since polymers are nonbiodegradable, micro-organisms such as decomposers cannot break them down
• Therefore, plastic items will not decompose for hundreds of years which causes landfill sites to fill rapidly

Incineration

• Polymers release a lot of heat energy when they burn

• However, incineration / burning of plastic is not a good solution to the waste issue as it produces the greenhouse gas carbon dioxide, which contributes to climate change

• Some polymers release toxic fumes when they burn

  • An example of this is poly(vinylchloride) which releases toxic hydrogen chloride gas when burned

  • Chemists have designed ways to remove toxic waste products like HCl before they are emitted into the atmosphere

  • The waste gases from the incinerator are scrubbed/reacted with a base or carbonate

  • The base reacts with the acidic HCl gas, neutralising it

    • eg. CaO (s) + 2HCl (aq)→CaCl₂ (aq) + H₂O (l)

Recycling

• Recycling plastic reduces the amount of water that goes to landfill sites or is burned

• It can also help to conserve crude oil reserves as less energy is required to recycle plastics than produce them

• This means that finite natural resources, such as crude oil and other fossil fuels, can be better managed as they are not being used:

  • As raw materials for plastics in the manufacture of plastics
  • To power the industrial processes to manufacture plastics

Biodegradable polymers

• Chemists have also developed biodegradable and compostable polymers

• Biodegradable polymers can be broken down over time by microorganisms

  • Common products from this process include carbon dioxide, water and other organic compounds

• The polyester and polyamide condensation polymers are considered to be biodegradable as they can be broken down using hydrolysis reactions

  • This is a major advantage over the polymers produced using alkene monomers (polyalkenes)
  • When polyesters and polyamides are taken to landfill sites, they can be broken down easily and their products used for other applications

Compostable polymers

• Compostable polymers are commonly plant-based

  • Plant starch is being used in the production of biodegradable bin liners
  • Sugar cane fibres are replacing polystyrene in the production of disposable plates and cups

• Compostable polymers degrade naturally leaving no harmful residues