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Types of Biodegradable Films

 

Understanding what are Biodegradable Films!

 

The Basics (Polyethylene/PE)

Polyethylene is created through polymerization of ethene. It can be produced through radical 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.

 

Polyethylene and Biodegradability

Polyethylene or polythene film bidegrades naturally, albeit over a long period of time. Methods are available to make it more degradable under certain conditions of sunlight, moisture, oxygen, and composting and enhancement of biodegradation by reducing the hydrophobic polymer and increasing hydrophilic properties.

If traditional polyethylene film is littered it can be unsightly, and a hazard to wildlife. Some people believe that making plastic shopping bags is one way to try to allow the open litter to degrade.

 

Biodegradable process

Polythene or polyethylene film will naturally fragment and biodegrade, but it can take many decades to do this.

There are two methods to resolve this problem.

  1. Modify the carbon chain of polyethylene with an additive to improve its degrade ability and then its biodegradability.
  1. To make a film with similar properties to polyethylene from a biodegradable substance such as starch.

 

Types of biodegradable polythene film

There are 2 major types of biodegradable polythene films viz:

1) Biobased/Compost

2) Additive Based (Oxo Biodegradable)    

             

1) Starch based/Compostable/ Biobased (hydrodegradable) film

A bit more expensive type of plastic film. 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 90 days or less at 140 degrees F. However, actual products made with this type of film may not meet those standards.

Examples of polymers made from starch are:

  • 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 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.
  • 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.
  • 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.

 

2) Additive based Biodegradable film/bag

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 oxidized molecules are biodegraded, i.e. converted into carbon dioxide and biomass by naturally occurring microorganism.

There is however a lot of controversy about these types of bags. The complete biodegradation is disputed and claimed not to take place.

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.
  • They are certified non-toxic, and safe for food-contact

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
  • 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.

 

Biodegradable Vs. Compostable


Biodegradable and compostable are terms used when describing organic materials breaking down in a specific environment. Both terms are often used when defining environmentally friendly products and are often misused!

                                                                             
Compostable plastics are biodegradable in composting conditions, while other plastics degrade in the soil (landfills or anaerobic digestors).

It is important to note that compostability is a characteristic of a product, packaging or associated component that allows it to biodegrade under specific conditions (e.g. a certain temperature, timeframe, etc.). Hence, the primary difference between compostable and biodegradable is that compostable plastics are biodegradable in composting conditions, while other plastics degrade in the soil (landfills or anaerobic digestors).

 

Compostable is always biodegradable .  Biodegradable is not always compostable

 

 

 

 

References/Source:

https://en.wikipedia.org/wiki/Biodegradable_polythene_film

https://omnexus.specialchem.com/polymer-properties/properties/biodegradable

 

 

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