Disposal of Polymers
- Polymers provide a readily available, cheap alternative to many metal, glass, paper and cardboard materials in everyday use
- The low reactivity of many polymers makes them ideal for certain uses, e.g. food packaging, but at the same time creates problems with their disposal as a lot of polymers are non-biodegradable
- There are many published articles about the environmental problems of waste plastic killing marine animals
- One method of polymer disposal continues to be the use of landfill sites
- This is not ideal and various initiatives are being introduced aiming to reduce this method of waste disposal in general as well as with specific regard to polymers
Recycling
- Polymer recycling reduces the amount of waste that it going to landfill sites
- Newer landfill sites can have a recycling point where the new waste is brought before going to into the actual landfill - this is in an effort to reduce the amount of polymers (and other recyclable materials) unnecessarily going into the waste site
- The recycling of polymers can also reduce the use of finite resources
- Lots of polymers are made from the products of cracking crude oil and it's fractions
- Recycling polymers is a time-consuming process as they have to be sorted into the different categories
- These categories are usually shown somewhere on the plastic / polymer product with the recycling symbol and numbers or abbreviations for the different polymers, e.g.:
The recycling symbol for the polyethylene terephthalate polymer
- After sorting, the polymers are chopped, washed, dried, melted and then cast into pellets ready for use
- However, mixed polymers can mean that this process is wasted as its produces an unusable mix of polymers
- Certain polymers can cause problems when recycling due to their chemical composition, e.g. PVC contains a large amount of toxic chlorine which can be released
- Modern techniques are overcoming this PVC problem by dissolving the polymer and precipitating out the recycled material
Incineration
- Some petroleum / natural gas derived polymers are still difficult to recycle
- Since they have a large amount of energy stored within the polymer chains, these polymers can be incinerated
- This process can then be used to boil water and use the water vapour to turn turbines inside a power station, in a similar fashion to coal-fired power stations
- This process still causes environmental pollution as the carbon within the polymer can be released as carbon dioxide contributing to global warming
- Other toxic waste products include hydrogen chloride and other chlorinated molecules from the combustion of PVC
Feedstock recycling
- Feedstock recycling is where waste polymers are broken down, by chemical and thermal processes, into monomers, gases and oils
- These products are then used as the raw materials in the production of new polymers and other organic chemicals
- The major benefit of feedstock recycling, compared to other methods of polymer disposal, is that it works with unsorted and unwashed polymers