The use of PET to form drinks bottles is one of the most abundant and visible applications of plastic material in the world. Wells have developed a range of materials which can provide an oxo-biodegradable property to such bottles when the Reverte masterbatch (additive concentrate) is added to the material at the pre-form manufacturing stage.
When developing such a product there are a number of critical aspects a manufacturer such as Wells needs to consider:
It has always been clear to the Reverte team that recycling of plastics is the preferred route for these types of bottles, however we only have to look at our kerbsides, parks and countryside to see that neither recycling nor landfill is the final destination for a significant quantity of bottles. With this in mind, it is in our opinion preferable to have a product that if incorrectly disposed of, will have a shorter existence in the open environment than similar non treated articles.
Reverte for PET bottles has undergone extensive testing to determine suitability for such applications and has been used now for a number of years by Brand Owners who are concerned about global littering through the thoughtless discarding of bottles.
Many such Brand Owners are also supporters of recycling and the benefits of Reverte straddle the two camps.
Wells have conducted a number of recycling studies, examining the impact of Reverte containing bottles entering the recycling stream and we are comfortable that there is no significant effect on material quality. It is however no secret that the recycling community do not want any additives in their feedstocks, of any kind, as they would like each gram of recycled PET to be exactly the same as the last. Additives are however a necessary reality in modern plastics, whether that be to offer colour stability of soft drinks which are packaged in PET, minimise dust attraction or improve barrier properties. Many polymers and applications benefit from very small additions of additives.
Green claims and legislation vary from country to country and region to region. Wells viewpoint on this subject is that each customer must satisfy themselves of the claims they wish to make on packaging and are within the guidelines of the local market in which they wish to promote Reverte containing Oxo-biodegradable bottles.
Reverte is an Oxo-biodegradable additive and that word clearly defines the mode of action and is internationally recognised. Oxo–degradation is defined by CEN/TR15351-06 (published by the European Standards Organisation) as ‘degradation identified as resulting from oxidative cleavage of macromolecules’. Oxo-biodegradation as “degradation identified as resulting from oxidative and cell-mediated phenomena, either simultaneously or successively”.
It is incorrect to label Reverte containing PET bottles as biodegradable, and in some countries/states it is illegal and therefore should not be done, such claims will not be promoted or supported by Wells.
Natural degradation of polymers, such as PET, polyolefin’s and other polymers occurs relatively haphazardly and at a slow rate – normally measured in 100’s or 1000’s of years.
Degradation is generally instigated by exposure to heat, UV light and/or moisture. Due to how slow this process is subsequent microbial biodigestion may occur, but only when the molecular weight is sufficiently low enough, and the polymer becomes less hydrophobic.
However, microbial digestion (biodegradation) can commence if the polymer’s molecular weight can be sufficiently reduced by initial degradation.
Degradation comprises of two phases, oxidative degradation and mineralisation or biodegradation (anaerobic or aerobic dependant on environment).
Laboratory testing of the oxo-biodegradation of polymers comprises a set of tests performed consecutively on the polymer to demonstrate oxidative and biodegradation characteristics and to test for compounds toxic to plant and animal life.
The catalysed oxidation of PET can be accelerated by exposing the Reverte™ containing product to elevated temperatures in combination with the UV. Wells uses a testing environment of 50°C with a low level of UVA and UVB at 26kLy/yr to accelerate the catalysed oxidation of product containing Reverte™ for PET.
Arrhenius principles may then be applied to the results obtained at 50°C to transpose them into an indicated (real-time) result that would be expected at 20oC in an idealised environment.
FT-IR spectrometry may be used to follow the progress of the chain scission reaction by measuring the ratio of a C=0 peak to C-H peak.
It is important to note that rates may vary dependent on the exact environment which the discarded bottle may be found in. For example, if discarded in a cool dark environment the rate of oxidative degradation will be slower than when in a hot light environment. Oxidative degradation will occur in both situations (assuming oxygen present) but at different rates.
Oxidation will not occur in the absence of oxygen, although oxygen can be found at surprisingly high levels even in areas which would appear to be oxygen free, such as some layers of a landfill. It is popularly considered that a landfill disposal environment is anaerobic in nature, however it should be remembered that there is no “standard” landfill and that this may not necessarily be the case.
In general a Reverte treated bottle in the correct environment will fragment in approximately 10 years, making itself available for biodegradation.
The biodegradation (mineralisation) is the conversion of available carbon to carbon dioxide in aerobic environments or methane in anaerobic environments. This will not occur if there are no microbes present to perform such a task, or if the molecular weight has not been sufficiently reduced by the first stage of oxidation. It is clear that even grass cuttings will not biodegrade if there are no viable microbes.
The format or thickness of the bottle will also have an impact, the thicker the plastic bottle the slower the oxo-biodegradation when compared to a thinner bottle discarded in the same environment.
The choice of polymer will also have an effect, for best results the polymer should be stabiliser free, each manufacturer should check with their supplier that this is the case before proceeding.
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