Degradable

Degradable plastic are oil based and break down through chemical reactions rather than the activity of micro-organisms, so they can degrade in an anaerobic environment into water, CO2, biomass and trace elements.

Degradable plastic includes all classes of degradable plastic including the biodegradable and compostable. However, plastic that is not biodegradable or compostable usually use the label “Degradable plastic”. Most of the products using the label “ Degradable plastic”, degrade as a result of physical and chemical impact (fracture into smaller pieces of plastic). Biological activity is not a significant part of the degradation of these products.

Biodegradable

Any organic substance capable of being broken down by micro-organisms in the presence of oxygen (aerobic) to carbon dioxide , water biomass and mineral salts or any other elements that are present (Mineralisation). Alternatively, any organic substance able to be broken down without the presence of oxygen (anaerobic) to carbon dioxide, methane, water and biomass over a period of time (up to 2-3 years in a landfill).

The definition of biodegradability is important to keep in mind because materials that remain after biodegradation are generally safe, as they have been broken down into elemental compounds such as:

Many of the inaccurately labeled “biodegradable” products do actually experience a significant chemical breakdown. Yet that degradation is incomplete. This lack of a full organic decomposition is the reason companies cannot claim biodegradability of certain products.

The materials we use every day degrade and biodegrade slowly over time; it’s a part of life. However, when inaccurately labeled “biodegradable” materials inadvertently go through municipal composting facilities, they ca ncontaminate water and soil because of the chemical compounds they leave behind.

Additionally, there is a common misunderstanding that products labeled “biodegradable” (even properly labeled ones) will decompose in the landfill and are therefore better for the environment. However, due to the oxygen-poor and dry conditions associated with most landfills, rather than decompose, materials tend to stay relatively well preserved.

Here’s an example: A landfill study project conducted by the University of Arizona dug through more than 20 landfills across North America, and found “hundreds of undecomposed hot dogs, corn starch and lettuce dating back to the 1960s.” How did they know how old the food was, you ask? They used some of the still readable 2,425 newspapers they found to get the exact dates.

This is why commercial composting is a crucial step for biodegradable products to be environmentally effective. Once biodegradable products hit the landfill, they are as good as any other trash material.

Oxo-biodegradable

A very small amount of pro-degradant additive is introduced into the conventional manufacturing process, thereby changing the behavior of the plastic. The plastic should be consumed by bacteria and fungi after the additive has reduced the molecular structure to a level which permits living micro-organisms access to the carbon and hydrogen. The material has then ceased to be a plastic and has become a food source. This process should continue until the material has biodegraded to nothing more than CO2, water and humus. It does not leave fragments of petro-polymers in the soil.

Oxo-biodegradable plastics are currently made from naptha, which is a by product of oil refining, and oil is of course a finite resource. To read more, click here.

Hydro-biodegradable

Hydro biodegradation is initiated by hydrolysis and in the depths of a landfill hydrobiodegradable plastics generate copious quantities of methane by anaerobic biodegradation. Methane is 23 times more potent for global warming than CO2.

Hydrobiodegradable plastics are not genuinely renewable because the process of making them from crops is itself a significant user of hydrocarbon energy and a producer therefore of greenhouse gases. They are sometimes described as made from “non-food” crops, but are in fact usually made from food crops.

Photo-biodegradable

In photo-biodegradable plastics the structure of the polymer is altered by UV light in sunlight so that it is now amenable to biodegradation. In other words, the plastics contain an additive which causes the plastic to degrade under conditions of ultraviolet light and oxygen, degrading the chemical bond or link in the polymer or chemical structure of a plastic.

Compostable

Compostable matter should not produce any toxic material and should be able to support plant life. Compostable items are made from plant materials such as corn, potato, cellulose, soy and sugar and are capable of being broken down by aerobic and anaerobic means to make compost. (Aerobic: in the presence of air); Anaerobic: in the absence of air)

Water Soluble

Polymer capable of dissolving in water.

Biomass

The term biomass means any plant-derived organic matter. Biomass available for energy on a sustainable basis includes herbaceous and woody energy crops, agricultural food and feed crops, agricultural crop wastes and residues, wood wastes and residues, aquatic plants, and other waste materials including some municipal wastes.

Bio-plastics

Biomass-based plastics are derived from renewable resources. To read more, click here.

A very small amount of pro-degradant additive is introduced into the conventional manufacturing process, thereby changing the behavior of the plastic. The plastic should be consumed by bacteria and fungi after the additive has reduced the molecular structure to a level which permits living micro organisms access to the carbon and hydrogen. The material has then ceased to be a plastic and has become a food source. This process should continue until the material has biodegraded to nothing more than CO2, water and humus. It does not leave fragments of petro polymers in the soil.
Oxo biodegradable plastics are currently made from naptha, which is a by product of oil refining, and oil is of course a finite resource.

Defra (Department for Environment, Food and Rural Affairs) in the UK commissioned Loughborough University to review the environmental effects of oxo-degradable plastics.

In particular, to assess:

• The extent to which and timefram/e within which oxo-degradable plastics degrade or biodegrade
• The effects of the degradation or biodegradation of oxo-degradable plastics in the natural environment (e.g. soil, water) and different disposal facilities (e.g. recycling, industrial composting).

The study was carried out over 12 month period, involving an in-depth review of current research as well as consultation with manufacturers, retailers, trade bodies and waste treatment industries. Policy representatives and experts from DECC, Defra, the National Non-Food Crop Centre (NNFCC) and the Waste and Resources Action Programme (WRAP) have been involved throughout the research.

Downloads:

UK Assessing Envir Impacts of Oxo-degradable Plastics across their Life Cycle Jan 2010

UK, Defra, Enviro Impact of Oxo-degradable Plastics Jan 2010

UK, Defra, Oxodegradable Plastics Q&A

To see the final report click here. 

Other reading on this issue:

The use of oxo-degradable additives - It has been said that we should aim to improve the quality of the environment, not just protect it. New technology is one way of achieving this. But do the drawbacks of some technologies overshadow their advantages? An interesting view appeared in a recent copy of ICIS Connect Magazine (www.icis.com)

The plastics recycling industry and biodegradable films. SAPRO insists that the use of biodegradable additives in plastic film be stopped immediately.