The term ‘Oxobiodegradability’ is a hybridisation of two words, oxidation and biodegradability. It defines clearly a two step process initiated in this case by the Reverte® additive to degrade the polymer chain (break up) and make it available for biodegradability within the environment when a treated item has finished its useful life.
The phase of oxidation reduces the molecular weight and introduces oxygen into the structure. This process transforms the polymer from long strands to much smaller lengths. By reducing the chain length of the polymer the material loses its physical strength and elongation properties making it brittle and none ‘plastic’. The biodegradability aspect refers to the conversion of these lower molecular weight species by bacteria into biomass, CO2 and H2O in an aerobic environment, or in the case of an anaerobic environment, CH4.
Reverte® is introduced to a plastic article such as a check out bag at the manufacturing stage, the complex formulation is dosed in at a very low level, and the carefully developed complex additive package within Reverte® is now within the plastic at a predetermined amount.
The Reverte® oxo-biodegradable additive family are well suited to a wide range of processes and applications, have extensive food contact status and have been used for many years to provide a reliable and reproducible oxo-biodegradable profile around the world.
The key attribute of the Reverte® technology is the degradation profile and how it compares with a more conventional ‘oxo-biodegradable material’.
Wells Plastics laboratories measure the first stage of degradation (oxidation) using carbonyl indexing and embrittlement point determination, processes which have been developed and exploited at Wells for many years and are now adopted by the industry.
The growth of the carbonyl index relates to the level of oxygen which has been incorporated into the polymer and wherever a carbonyl group is introduced the polymer undergoes a chain scission, i.e. a molecular weight reduction and a change in its physical and chemical properties.
The more carbonyls introduced the further removed it becomes from its polymeric nature. Once a critical point has been achieved in carbonyl index the polymer loses its flexibility and breaks apart under the minutest of stresses. At this time it is considered to be at its ‘embrittlement point’.
What makes Reverte® stand out is the profile of degradation, the curve plotted of carbonyl index versus time starts off very flat with a period of no change in the carbonyl index over time. This period is known as the ‘dwell time’ another phrase coined by Wells Plastics.
After the dwell time has been passed the degradation then proceeds rapidly until the embrittlement point is reached and beyond that the plastic falls apart.
The molecular weight is lowered and the material available for biodigestion.
Biodegradability of a Reverte® treated film occurs once the molecular weight is below 5000.
At this level the polymer no longer exists and is a wide range of discrete oxidised species. Bacteria and fungi find these species suitable for a source of carbon and can be assimilated into the lifecycle resulting in the formation of biomass and CO2 under aerobic conditions.
Biodegradation can only occur (whether this is for Reverte® plastics or for grass cuttings) in environments which have warmth, bacterial activity and moisture. This fact is often overlooked when marketing oxo-biodegradable or hydrobiodegradable materials.
Oxo-Biodegradable Plastic Products Life Cycle
Bio-plastic: Superior Advantage with No loss of Product Performance
Our bio-plastic processes ensure all the strength and convenience of conventional plastic plus environment-friendly degradability. Below is the comparison between the two:
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