Biodegradable polythene film

Conventionally, plastics are made of petrochemicals. These are heavily used worldwide – mainly in packaging and household applications. The benefits of low production costs, light weight, strength, relative imperviousness to gas and water, clarity, and printability are highly regarded, but the final disposal of used flexible plastics causes problems. If plastic film is not recycled or disposed of correctly it can be a significant source of litter and can create problems in waste management. If disposed of by landfill, the plastics (even the small amount of plastic film) worsen the shortage of landfill sites. Typical plastic films can be incinerated and the heat can be used. Some believe that making plastic bags biodegradable is one way to try to ease the task of waste reduction.

Types of biodegradable polythene film
There are two main methods for making normal polythene into a biodegradable film:

Starch based or biobased (hydrodegradable) film
This 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.

Examples of polymers with which starch is commonly used:
The heat, moisture and aeration one gets in a compost pile are required for this type of biodegradable film to biodegrade.
 * Polycaprolactone (PCL)
 * Polyvinyl alcohol (PVA)
 * Polylactic acid (PLA)

Pros

 * Litter is biodegradable and compostable. Biodegradable means the material will be degraded into small pieces that can be absorbed by microorganisms and transformed into CO2, H2O, energy and neutral residue.
 * Reduced fossil fuel content (depending on loading of filler)
 * Faster degradation of litter
 * No net increase of carbon dioxide in global ecosystem

Cons

 * Source of starch can be problematic (competition against food use, rainforests being cleared to grow crops for bioplastics)
 * 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 hauler picks it up. However, some biodegradable and compostable films are now very close to polyethylene or polypropylene, depending on the starch used.
 * Degradation in a sealed landfill takes at least 6 months.
 * Limited Shelf life. Some conditions must be respected for stockage.
 * Some need to be composted in industrial facilities because the temperature of the compost needs to be at 58°C. Others ( OK-compost) are home composting (temperature 20°C).
 * If mixed with other plastics for recycling, the value of recycling is reduced.

Typical application area
Carrier bag, refusal sacks, vegetable bags, food films, agricultural films, mailing films. The list of application cannot be exhaustive as new developments appear each month following the evolution of bio polymers. However, these applications are still very limited compare to those of petroleum based plastic films.

Additive based (oxodegradable/photodegradable)
These films are made by blending an additive to provide a UV / oxidative and/or biological mechanism to degrade them. This typically takes 6 months to 2 years in a landfill site. According to people who develop this process, degradation is a two stage process; first the plastic is converted by reaction with oxygen (light, heat and/or stress) to molecular fragments that water can wet, and then these smaller oxidized molecules are biodegraded, i.e. converted into carbon dioxide, water and biomass by microorganisms. But complete biodegradation, i.e. transformation by micro-organisms in energy, CO2 and H2O, has never been established. Indeed, at the end of degradation, the small particles are still too big to be absorbed and transformed by micro-organisms. If put in a compost, the oxo degradables are only another source of pollution (cf International Biodegradable Polymers Association and Working groups).

Pros

 * Much cheaper than starch-based plastics
 * Materials are well known
 * Do not compete against food use
 * These films look, act and perform just like their non-degradable counterparts, except that they are weaker and break down after being discarded.

Cons

 * Made using fossil fuel (contributes to global warming through the release of carbon dioxide)
 * Degradation in a sealed landfill is very slow.
 * Degradation depends on conditions of heat, light, stress, air etc
 * No biodegradability established, which means cannot be absorb by micro-organisms. Pollution is not visible but exists.
 * They do not comply with European Norms on compostable products
 * If mixed with other plastics for recycling, the value of recycling is reduced.

Typical applications
Trash Bags, Garbage Bags, Compost Bags, Carrier bag, Agricultural Film, Mulch Film