by Nick Griffiths Haynes
As (ethical) consumers, one of the most difficult problems we face is what to do with our waste. What do we do with all of the rubbish we generate as we buy all of those products guaranteed to make our lives better? Much of the contents of our rubbish bins is quite straight forward. Kitchen scraps to compost, glass to the bottle bank, paper and card, tins and cans all slip neatly into collection bins for recycling. But what about plastic? Bottles, food wrapping and all of that packaging the shiny new toys come in?
Most roadside schemes will now take plastic bottles but not other types of plastic. Why not? And as for separating out plastics, what is the difference between PET, PP, HDLP, 03, 06 and so on? Does it really matter if they are not separated? Surely all plastic gets recycled together?
Of all the plastic that enters the waste stream each year, 67% of it is municipal waste from domestic and shop dustbins along with things like street sweepings. About 40% of the contents of the average dustbin is plastic which can take up to twice the amount of space as other rubbish. Approximately 2.8 million tonnes of plastic is thrown away each year in the UK. A survey of British beaches in 2000 found on average one item of plastic rubbish for every metre of beach.
So what are plastics and where do they come from? Plastics are made from oil. 4% of global oil production going directly into plastic manufacture each year. The oil is made into monomers, tiny molecules of (usually) carbon and hydrogen. Some of the simplest monomers used are chemicals like ethylene and ethylene glycol. Monomers are combined into long chains called polymers by one of two processes.
The first is free radical catalysis where typically a peroxide or metal catalyst is used to initiate a chain reaction that generates the polymer. This is a very quick process that generates heat.
The second method, which is much slower, is condensation. This is where two monomers are condensed together to produce a dimer. The dimers can either be condensed again to create a short polymer, or dimers and monomers can be reacted together.
The polymers are mixed with a variety of additives like pigments, plasticisers and fillers which give a particular plastic its distinctive properties.
There are two main families of plastics. Thermoplastics that can be remoulded and reshaped on heating, and Thermoset plastics that once formed are ‘set’ and cannot be reformed. Around 80% of plastics used are thermoplastics like Polyethyl terephthalate (PET),Polyvinyl chloride (PVC) and high density Polyethylene (HDPE). The remaining thermoset materials are things like Polyureas (PUs) and Phenolic or Epoxy resins.
In terms of the markings on plastic products that tell you what they are for recycling, the labelling system is purely voluntary but the internationally recognised system is shown below.
01 PETpoly ethyl terephthalate02 HDPEhigh density polyethylene03 PVCpoly vinylchloride04 LDPElow density poltethylene05 PPpolypropylene06 PSpolystyrene07 Other
The recycling of plastics is carried out in several different ways. The simplest is the recovery and reuse of raw polymer during production and the remoulding of offcuts, etc, in the manufacturing of products. Post-consumer recycling takes two main forms the choice of which is determined by a variety of factors such as the purity of the plastic, how clean it is, and how much is available.
Mechanical reprocessing is where the plastic is shredded, moulded and ground into pellets which can be sold back to manufacturers and made into new products.
Chemical reprocessing involves melting down the plastics and heating them up until the polymers break down into the monomers again. These can then be separated out and repolymerised back into fresh clean polymers.
There are a number of factors that impact on how feasible the recycling of plastics is.
Especially with mechanical reprocessing, it is important to have a clean supply of pure polymer. Plastics need to be sorted into each separate type and be free from contamination like other plastics, food residues, etc. Sorting and cleaning plastics are an essential and often costly part of the process. Even simple things like the colour of the plastic can be enough to lower the price of the recycled raw material or mean an item is rejected for recycling. The sorting of bottles has been made simpler by the use of Infra Red sorting techniques.
For recycling companies to be economically viable they need to ensure a minimum quantity of pure clean plastic to recycle. This often means that is it relatively easy for companies to bale up and send off their packaging material but extremely difficult for individual householders. This is the main reason why only plastic bottles are accepted by roadside schemes at present.
Another problem for recycling is one of the key properties of plastics that make them attractive as materials in the first place. They are strong, durable and light weight. This means that a small amount of plastic takes up a large volume making the transportation of plastics on their own expensive.
Assuming these limitations can be overcome (and they can), recycled plastics are actually cheaper than virgin plastic as a raw material, using less energy to produce and therefore contributing less to greenhouse gas emissions.
If our plastic waste is not recycled, it will either end up in landfill or be incinerated. Because of its high carbon content and the fact that it is derived from oil, plastic has a high calorific value (energy per mass unit on combustion) when compared with other fuels, so the burning of plastic and mixed waste has become a popular option. Some countries even include incineration in their recycling figures.
There are some serious drawbacks. Firstly with this option, you are essentially burning a non-renewable fuel - even if the fuel had a previous use, it was still oil to begin with. The addavies and traces of the catalysts used in the production of the plastics often contain heavy metals and other toxins which are released as the plolymers break down, either out of the stack, or to be concentrated in the ash. The polymer chains themselves, when incompletely combusted, can form highly carcinogenic compounds (as do all carbon fuels, even wood). The monomers are sometimes pollutants in their own right.
Biodegradable plastics have been seen as an answer to some of the problems arising from the disposal of regular plastics. These are often made from plant starches, instead of petrochemicals, that are polymerised in the same ways to give plastics which are broken down in the natural environment. All plastics are susceptible to UV light making them brittle and this effect has been enhanced in some biodegradable by adding chemicals to the polymer chains. Unfortunately these materials still contain all the potentially toxic additives and catalyst traces that are found in conventional plastics. These can leach into ground water as the polymers break down and they still look unsightly when left abandoned in the park or on the beach!
The UK performs badly when compared to its European neighbours in terms of recycling.
Countries like Germany, Norway and Sweden that are very good at recycling tend to have laws that place responsibility on producers and distributors for packaging recycling, as well as incentive schemes to encourage people to dispose of their waste in the right way. Their kerbside schemes are often better too. In Germany the bins are segmented to make the sorting of the rubbish simpler when collected. The European Union does have legislation in place setting targets for recycling, however the way the are implemented is up to the individual members - and the UK government has been criticized for hindering recycling by the way it has set out to meet these targets.
Although Ireland is not one of the best recyclers is does give a good example of what can be achieved with simple changes. In Ireland they used to get through a staggering 1.2 billion plastic bags per year, an average of 300 bags per person. In 2002 a fee of €0.15 per bag was introduced to promote the use of reusable shopping bags. Three months after the introduction of this fee, disposable bag use had dropped by 90% and an income of €3.5 million had been generated.
The recycling of plastics does not need to be complicated. Separate your plastics and clean them. Take part in recycling schemes. Buy recycled products.
Nick Griffiths Haynes
September 2005
As (ethical) consumers, one of the most difficult problems we face is what to do with our waste. What do we do with all of the rubbish we generate as we buy all of those products guaranteed to make our lives better? Much of the contents of our rubbish bins is quite straight forward. Kitchen scraps to compost, glass to the bottle bank, paper and card, tins and cans all slip neatly into collection bins for recycling. But what about plastic? Bottles, food wrapping and all of that packaging the shiny new toys come in?
Most roadside schemes will now take plastic bottles but not other types of plastic. Why not? And as for separating out plastics, what is the difference between PET, PP, HDLP, 03, 06 and so on? Does it really matter if they are not separated? Surely all plastic gets recycled together?
Of all the plastic that enters the waste stream each year, 67% of it is municipal waste from domestic and shop dustbins along with things like street sweepings. About 40% of the contents of the average dustbin is plastic which can take up to twice the amount of space as other rubbish. Approximately 2.8 million tonnes of plastic is thrown away each year in the UK. A survey of British beaches in 2000 found on average one item of plastic rubbish for every metre of beach.
So what are plastics and where do they come from? Plastics are made from oil. 4% of global oil production going directly into plastic manufacture each year. The oil is made into monomers, tiny molecules of (usually) carbon and hydrogen. Some of the simplest monomers used are chemicals like ethylene and ethylene glycol. Monomers are combined into long chains called polymers by one of two processes.
The first is free radical catalysis where typically a peroxide or metal catalyst is used to initiate a chain reaction that generates the polymer. This is a very quick process that generates heat.
The second method, which is much slower, is condensation. This is where two monomers are condensed together to produce a dimer. The dimers can either be condensed again to create a short polymer, or dimers and monomers can be reacted together.
The polymers are mixed with a variety of additives like pigments, plasticisers and fillers which give a particular plastic its distinctive properties.
There are two main families of plastics. Thermoplastics that can be remoulded and reshaped on heating, and Thermoset plastics that once formed are ‘set’ and cannot be reformed. Around 80% of plastics used are thermoplastics like Polyethyl terephthalate (PET),Polyvinyl chloride (PVC) and high density Polyethylene (HDPE). The remaining thermoset materials are things like Polyureas (PUs) and Phenolic or Epoxy resins.
In terms of the markings on plastic products that tell you what they are for recycling, the labelling system is purely voluntary but the internationally recognised system is shown below.
01 PETpoly ethyl terephthalate02 HDPEhigh density polyethylene03 PVCpoly vinylchloride04 LDPElow density poltethylene05 PPpolypropylene06 PSpolystyrene07 Other
The recycling of plastics is carried out in several different ways. The simplest is the recovery and reuse of raw polymer during production and the remoulding of offcuts, etc, in the manufacturing of products. Post-consumer recycling takes two main forms the choice of which is determined by a variety of factors such as the purity of the plastic, how clean it is, and how much is available.
Mechanical reprocessing is where the plastic is shredded, moulded and ground into pellets which can be sold back to manufacturers and made into new products.
Chemical reprocessing involves melting down the plastics and heating them up until the polymers break down into the monomers again. These can then be separated out and repolymerised back into fresh clean polymers.
There are a number of factors that impact on how feasible the recycling of plastics is.
Especially with mechanical reprocessing, it is important to have a clean supply of pure polymer. Plastics need to be sorted into each separate type and be free from contamination like other plastics, food residues, etc. Sorting and cleaning plastics are an essential and often costly part of the process. Even simple things like the colour of the plastic can be enough to lower the price of the recycled raw material or mean an item is rejected for recycling. The sorting of bottles has been made simpler by the use of Infra Red sorting techniques.
For recycling companies to be economically viable they need to ensure a minimum quantity of pure clean plastic to recycle. This often means that is it relatively easy for companies to bale up and send off their packaging material but extremely difficult for individual householders. This is the main reason why only plastic bottles are accepted by roadside schemes at present.
Another problem for recycling is one of the key properties of plastics that make them attractive as materials in the first place. They are strong, durable and light weight. This means that a small amount of plastic takes up a large volume making the transportation of plastics on their own expensive.
Assuming these limitations can be overcome (and they can), recycled plastics are actually cheaper than virgin plastic as a raw material, using less energy to produce and therefore contributing less to greenhouse gas emissions.
If our plastic waste is not recycled, it will either end up in landfill or be incinerated. Because of its high carbon content and the fact that it is derived from oil, plastic has a high calorific value (energy per mass unit on combustion) when compared with other fuels, so the burning of plastic and mixed waste has become a popular option. Some countries even include incineration in their recycling figures.
There are some serious drawbacks. Firstly with this option, you are essentially burning a non-renewable fuel - even if the fuel had a previous use, it was still oil to begin with. The addavies and traces of the catalysts used in the production of the plastics often contain heavy metals and other toxins which are released as the plolymers break down, either out of the stack, or to be concentrated in the ash. The polymer chains themselves, when incompletely combusted, can form highly carcinogenic compounds (as do all carbon fuels, even wood). The monomers are sometimes pollutants in their own right.
Biodegradable plastics have been seen as an answer to some of the problems arising from the disposal of regular plastics. These are often made from plant starches, instead of petrochemicals, that are polymerised in the same ways to give plastics which are broken down in the natural environment. All plastics are susceptible to UV light making them brittle and this effect has been enhanced in some biodegradable by adding chemicals to the polymer chains. Unfortunately these materials still contain all the potentially toxic additives and catalyst traces that are found in conventional plastics. These can leach into ground water as the polymers break down and they still look unsightly when left abandoned in the park or on the beach!
The UK performs badly when compared to its European neighbours in terms of recycling.
Countries like Germany, Norway and Sweden that are very good at recycling tend to have laws that place responsibility on producers and distributors for packaging recycling, as well as incentive schemes to encourage people to dispose of their waste in the right way. Their kerbside schemes are often better too. In Germany the bins are segmented to make the sorting of the rubbish simpler when collected. The European Union does have legislation in place setting targets for recycling, however the way the are implemented is up to the individual members - and the UK government has been criticized for hindering recycling by the way it has set out to meet these targets.
Although Ireland is not one of the best recyclers is does give a good example of what can be achieved with simple changes. In Ireland they used to get through a staggering 1.2 billion plastic bags per year, an average of 300 bags per person. In 2002 a fee of €0.15 per bag was introduced to promote the use of reusable shopping bags. Three months after the introduction of this fee, disposable bag use had dropped by 90% and an income of €3.5 million had been generated.
The recycling of plastics does not need to be complicated. Separate your plastics and clean them. Take part in recycling schemes. Buy recycled products.
Nick Griffiths Haynes
September 2005
