Biodegradable polythene film
Polyethylene or polythene film
If traditional polyethylene film is littered it can be unsightly, and a hazard to wildlife. Some people believe that making plastic shopping bags biodegradable is one way to try to allow the open litter to degrade.
Plastic recycling improves usage of resources. Biodegradable films need to be kept away from the usual recycling stream to prevent contaminating the polymers to be recycled.
If disposed of in a sanitary landfill, most traditional plastics do not readily decompose. The sterile conditions of a sealed landfill also deter degradation of biodegradable polymers.
Polyethylene is a
In the polymer industry the name is sometimes shortened to PE in a manner similar to that by which other polymers like polypropylene and polystyrene are shortened to PP and PS respectively. In the United Kingdom the polymer is commonly called polythene, although this is not recognised scientifically.
The ethene molecule (known almost universally by its common name ethylene) C2H4 is CH2=CH2, Two CH2 groups connected by a double bond, thus:
Polyethylene is created through polymerization of ethene. It can be produced through radical polymerization, anionic addition polymerization, ion coordination polymerization or cationic addition polymerization. This is because ethene does not have any substituent groups that influence the stability of the propagation head of the polymer. Each of these methods results in a different type of polyethylene.
Alternatives to biodegradable polythene film
This section is in prose. is available. (December 2016) |
Polythene or polyethylene film will naturally fragment and biodegrade, but it can take many decades to do this.[2] There are two methods to resolve this problem. One is to modify the carbon chain of polyethylene with an additive to improve its degradability and then its biodegradability; the other is to make a film with similar properties to polyethylene from a biodegradable substance such as starch. The latter are however much more expensive.
Starch based or biobased (hydrodegradable) film
This type is made from corn (maize), potatoes or wheat. This form of biodegradable film meets the
Examples of polymers made from starch
- Polycaprolactone (PCL)
- Polyvinyl alcohol (PVA)
- Polylactic acid (PLA)
The heat, moisture and aeration in an industrial composting plant are required for this type of film to biodegrade, so it will not therefore readily degrade if littered in the environment.
Pros & cons of starch based film/bag
Pros
- It is "compostable" under industrial conditions.
- Reduced fossil fuel content (depending on loading of filler.)
Cons
- Is more expensive than its non-biodegradable counterpart
- Source of rainforestsbeing cleared to grow crops for bioplastics)
- Fossil fuels are burned and CO2 produced in the agricultural production process.
- Poorer mechanical strength than additive based example – filling a starch bag with wet leaves and placing it curbside can result in the bottom falling out when a haulier picks it up.
- Often not strong enough for use in high-speed machines
- Degradation in a sealed landfill takes at least 6 months.
- Emits CO2 in aerobic conditions and methane under anaerobic conditions
- Limited Shelf life. Conditions must be respected for stockage.
- If mixed with other plastics for recycling, the recycling process is compromised.
Typical applications
Carrier bag, refusal sacks, vegetable bags, food films, agricultural films, mailing films. However, these applications are still very limited compared to those of petroleum based plastic films.
Additive based
Additives can be added to conventional polymers to make them either oxodegradable or more hydrophilic to facilitate microbial attack.
Oxodegradable
These films are made by incorporating an additive within normal polymers to provide an oxidative and then a biological mechanism to degrade them. This typically takes 6 months to 1 year in the environment with adequate exposure to oxygen Degradation is a two-stage process; first the plastic is converted by reaction with oxygen (light, heat and/or stress accelerates the process but is not essential) to hydrophilic low molecular-weight materials and then these smaller
Enhancing hydrophilicity of the polymer
These films are inherently biodegradable over a long period of time. Enhancement of the polymer by adding in additives to change the hydrophobic nature of the resin to slightly hydrophilic allows microorganisms to consume the macromolecules of the product, these products often are confused with oxobiodegradable products, but work in a different way. Enhancing of the hydrophilicity of the polymer allows fungus and bacteria to consume the polymer at a faster rate utilizing the carbon inside the polymer chain for energy. These additives attract certain microorganisms found in nature and many tests have been completed on the mixing of synthetic and biobased materials which are inherently biodegradable for enhancing the biodegradability of synthetic polymers that are not as fast to biodegrade.[8]
Pros and cons of additive based film/bag
Pros
- Much cheaper than starch-based plastics
- Can be made with normal machinery, and can be used in high speed machines, so no need to change suppliers and no loss of jobs
- Materials are well known
- Does not compete against food production
- These films look, act and perform just like their non-degradable counterparts, during their programmed service-life but then break down if discarded.
- They can be recycled with normal plastics.[9]
- They are certified non-toxic, and safe for food-contact
- Some bags degrade at about the same rate as a leaf. In fact, when used as bin liners, bags can start degrading after three or four days of being in the bin.[citation needed]
Cons
- Degradation depends on access to air
- Not designed to degrade in landfill, but can be safely landfilled. Will degrade if oxygen is present, but will NOT emit methane in landfill
- European or American (EN13432 D6400)Standards on compostableproducts are not appropriate, as not designed for composting. They should be tested according to ASTM D6954 or (as from 1 Jan 1010) UAE norm 5009:2009
- They are not suitable for PET or PVC
- Precise rate of degradation/biodegradation cannot be predicted, but will be faster than nature's wastes such as straw or twigs, and much faster than normal plastic
- Like normal plastics they are made from a by-product of oil or natural gas
- If mixed with other plastics for recycling, the recycling process is compromised.
Typical applications
Trash Bags, Garbage Bags, Compost Bags, Carrier bag, Agricultural Film, Mulch Film, produce bags, - in fact all forms of short-life plastic film packaging
See also
References
- ^ "Biodegradable Plastic enhancing hydrophilic properties". Biosphere Plastic. Retrieved 30 June 2011.
- ^ "Microbes biodegrade aromatic hydrocarbons". Biosphere Plastic. Retrieved 20 May 2011.
- ^ "Oxo-degradable plastics: do they biodegrade? In search of a definite answer | OWS". Ows.be. 20 June 2014. Retrieved 16 August 2018.
- ^ "Oxo-degradable plastics increasingly under fire in Europe – European Bioplastics e.V". European-bioplastics.org. 28 February 2017. Retrieved 16 August 2018.
- ^ "What are the Benefits and Drawbacks to Oxo-degradable Bags? - PPRC PPRC". Pprc.org. Archived from the original on 21 October 2017. Retrieved 16 August 2018.
- ^ "Environmental impact of oxo-degradable plastics". Food Packaging Forum. 24 April 2017. Retrieved 16 August 2018.
- ISBN 9789279618284. Retrieved 16 August 2018.
- ISBN 9781439851166. Retrieved 10 March 2009.
- ^ "RECYCLING OF PLASTICS". Oxobiodegradable Plastics Association. Archived from the original on 19 January 2010. Retrieved July 9, 2012.
- BBC News: "All Tesco bags 'to be degradable" 10 May 2006 http://news.bbc.co.uk/1/hi/uk/4758419.stm
- BBC News: "Degradable carrier bags launched" 2 September 2002 http://news.bbc.co.uk/1/hi/uk/2229698.stm
- Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6