Types of biodegradable polythene film
Polythene or Polyethylene film will naturally fragment and biodegrade, but it can take many decades to do this, and can in the meantime cause an environmental problem. 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=== (Trade Associations for this industry are "Biodegradable Products Institute" (BPI); European Bioplastics, and "SPIBioplastics Council"
This type is made from corn (maize), potatoes or wheat. This form of biodegradable film meets the ASTM standard (American Standard for Testing Materials) and European norm EN13432 for compostability as it degrades at least 90% within 180 days or less under specified conditions. However, actual products made with this type of film may not meet those standards.
Examples of polymers with which starch is commonly used
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
It is "compostable" under industrial conditions.
Reduced fossil fuel content (depending on loading of filler.
Much too expensive for everyday use
Source of starch can be problematic (competition against food use, rainforests being 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.
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 (OXO-BIODEGRADABLE))=== (Trade Association for this industry is the Oxo-biodegradable Plastics Association - www.biodeg.org) These films are made by blending an additive to provide an oxidative and then a biological mechanism to degrade them. This typically takes 6 months to 2 years in the environment if 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 low molecular-weight fragments that water can wet, and then these smaller oxidized molecules are biodegraded, i.e. converted into carbon dioxide, water and biomass by microorganisms. Commercial competitors and their trade associations allege that the process of biodegradation stops at a certain point, leaving fragments, but they have never established why or at what point. This is similar to the breakdown of woody plant material where lignin is broken down and forms a humus component improving the soil quality. If put in an in-vessel composting system this type of plastic will rapidly break down, but it is not currently marketed as compostable.
Pros & cons of additive based film/bag
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 (http://www.biodeg.org/position-papers/recycling/?domain=biodeg.org)
Like normal plastics they are made from a by-product of oil or natural gas, but these would be extracted whether the by-product were used to make plastic or not.
They are certified non-toxic, and safe for food-contact
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 [compostable]] products 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
Trash Bags, Garbage Bags, Compost Bags, Carrier bag, Agricultural Film, Mulch Film, produce bags, - in fact all forms of short-life plastic film packaging
BBC News: "All Tesco bags 'to be degradable dt. 10th May'06" http://news.bbc.co.uk/1/hi/uk/4758419.stm
BBC News: "Degradable carrier bags launched dt. 2nd Sep'02" http://news.bbc.co.uk/1/hi/uk/2229698.stm
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