Plastics are used throughout various industries. They are also tested and proven safe for food, medical, farming and many other applications. Plastics can be reused and will eventually degrade to H2O and CO2 but can take many decades. Normal plastics do not meet any degradability or biodegradability standards. It can be recycled, although stabilisers will normally be required to replace properties lost during the recycling process. Plastic is made from a by-product of oil, which means that nobody is importing additional oil to make plastic.
Degradable plastics are plastics that will break down and degrade within a much shorter period of time, usually from 3 months to 5 years depending on the type of degradable plastic it belongs to.
It is important to distinguish between the different types of biodegradable plastic as their costs and uses are very different, as well as the pros and cons of using them. There are 3 main types of biodegradable plastic available but most commonly used by consumers are the oxo-biodegradables and hydro-biodegradables.
The technology is based on a very small amount of pro-degradant additive being introduced into the manufacturing process, thereby changing the behaviour of the plastic. Degradation begins when the programmed service life is over (as controlled by the additive formulation) and the product is no longer required.
The plastic does not just fragment, but will 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. It is therefore “biodegradable.” This process continues until the material has biodegraded to nothing more than CO2, water, and humus, and it does not leave fragments of petro-polymers in the soil. Oxo-biodegradable plastic passes all the usual ecotoxicity tests, including seed germination, plant growth and organism survival (daphnia, earthworms) tests carried out in accordance with ON S 2200 and ON S 2300 national standards.
Oxo-biodegradable film has been certified as safe for long-term contact with any food type at temperatures up to 40°C, and oxo-biodegradable bags are being bought and distributed by the UK Soil Association, and used for direct contact with organic food products.
Hydro-biodegradation is initiated by hydrolysis. Some plastics in this category have a high starch content and it is sometimes said that this justifies the claim that they are made from renewable resources. However, many of them contain up to 50% of synthetic plastic derived from oil, and others (e.g. some aliphatic polyesters) are entirely based on oil-derived intermediates. Genetically-modified crops may also have been used in the manufacture of hydro-biodegradable plastics.
Hydro-biodegradable plastics are not genuinely “renewable” because the process of making them from crops is itself a significant user of fossil-fuel energy and a producer therefore of greenhouse gases. Fossil fuels are burned in the autoclaves used to ferment and polymerise material synthesised from biochemically produced intermediates (e.g. polylactic acid from carbohydrates etc); and by the agricultural machinery and road vehicles employed; also by the manufacture and transport of fertilisers and pesticides. They are sometimes described as made from “non-food” crops, but are in fact usually made from food crops.
A disproportionate amount of land would be required to produce sufficient raw material to replace conventional plastic products, and a huge amount of water, which is in such short supply in so many parts of the world. Residues from some native starches can be seriously toxic; bitter cassava for example (tapioca) has a high level of hydro-cyanic glucoside present, which has to be removed by careful washing. During growth the plant is toxic to wildlife. Cassava is exhaustive of potash.
These react to ultra-violet light, but unless they are also oxo-biodegradable they will not degrade in a landfill, a sewer, or other dark environment, or if heavily overprinted.
|Oxo-Biodegradable Plastics||Hydro-Biodegradable Plastics|
|3 months to 5 years for degradation||3 months for degradation|
|Modified from conventional plastics by adding special additives||Made from fossil-derived polymers and starch|
|Can be recycled as part of a normal plastic waste-stream||Damages recyclate unless extracted from feedstock|
|Can be made from recyclate||Cannot be made from recyclate|
|Emits CO2 slowly while degrading||Emits CO2 rapidly while degrading. As 90% of it must convert to CO2 within 180 days in order to comply with the Standards for compostable plasitc, these plastics contribute to climate change but do not improve the soil.|
|Inert deep in landfill||Emits methane deep in landfill|
|No change in machinery and workforce||Requires special machinery|
|Suitable for use in high-speed machinery||Usually not suitable|
|Compostable in-vessel||Compostable (but not for home composting)|
|Little or no on-cost||Four or five times more expensive than conventional plastic|
|Same strength as conventional plastic||Weaker than conventional plastic (unless mixed with oil-based plastic)|
|Same weight as conventional plastic||Thicker and Heavier|
|Degrades anywhere on land or sea||Degrades only in high-microbial environment|
|Programmable Lifespan||Lifespan cannot be controlled|
|No genetically modified ingredients||Possibility of GM ingredients|
|Safe for food contact||Safe for food contact|
|No PCB’s Organo-chlorines, or “heavy metals”||No PCB’s Organo-chlorines, or “heavy metals”|
|Can be incinerated with high energy-recovery||Can be incinerated, but lower calorific value|
|Production uses no fertilisers, pesticides or water||Production uses fertilisers, pesticides and water|
|No limit on availability of feedstock||Limited availability of feedstock|
|Demand for oxo-biodegradable plastics does not drive up cost of fuel for vehicles||Demand for hydro-biodegradable plastics drives up price of human and animal foodstuffs|