Commentary from Wells Plastics Ltd on:
“Evaluation of Biodegradation-Promoting Additives for Plastics” Susan E.M. Selke et al
American Chemical Society, 27th Feb 2015
The following commentary expresses the opinion of Wells Plastics Ltd to the study described in the above paper with regards to that data pertaining to tests conducted which utilised Reverte™ oxo-biodegradable additive masterbatch, unless otherwise stated.
Wells Plastics Ltd agreed to participate in the study and discussed the proposed protocol at length both in person with Dr Selke at MSU prior to the commencement of the study and also in extensive written communication during the study. This commentary provides firstly a general overview followed by a review of specific aspects of the study as reported in the above paper.
Wells Plastics met the study team at MSU in April 2011 where it became apparent that they did not understand the basic concepts of the oxo-biodegradation process produced by Reverte™, which is designed to provide a stable, inert shelf-life and useful functioning life, then oxo-biodegrade the polymer should it be littered into the open environment. The necessity for abiotic oxidation of the polymer structure prior to biodegradation, which would not be provided in the simulated industrial composting, anaerobic and burial in soil test conditions proposed, to produce a significantly reduced Mw and altered chemical functionality, as would occur in the open environment, to enable subsequent biodegradation was addressed through technical presentations and extensive written communications.
It was explained that the test protocol would only demonstrate the inert, stable nature of the polymer materials when subjected to these environments – environments for which the Reverte™ oxo-biodegradable additive was not designed to be functional. The unsuitability of the test regimes was acknowledged and accepted by Dr Selke, however no amendments to the proposed tests were made. Additionally, the authors do not refer to this accepted, unsuitability in the study paper above.
At the SPE Global Plastics Environmental Conference, Orlando, Florida in March 2014, Wells Plastics, together with Symphony Environmental, expressed their concerns over the inappropriate methodology, validity of test results and subsequent conclusions drawn by the study team from this project, to Dr. Selke following her presentation of a paper titled “Independent Study on the Claims of Oxobiodegradable Additives”. As is evident these issues were not considered for the amendment of future publications.
Regarding more specific details of the published paper, the following comments can be made with regards to factual inaccuracies, and short-comings in methodology. It is noted here that the paper is replete with statements which misrepresent the actuality and not supported with referenced work. The more salient issues are discussed below.
The study utilised Reverte™ in the test materials at 1wt% and 5wt%, despite extensive, acknowledged, explanations that Reverte™ is designed for 1% addition rate and the addition of more would have the effect of enhanced stabilisation of the test films.
The authors seem to have a poor understanding of the legislative position in some countries/continents. Legislation in the UAE only permits the use of oxo-biodegradable plastics not compostable as well. While legislation in the UK (specifically EU) is with regards to the reduction in use of all single-use carrier bags – including biodegradable – not a ban on oxo-biodegradable plastic.
The results presented for the anaerobic degradation testing only provide comparison of total evolved gas and are not normalised to the amount of material used. A specific size of test material is described as being cut from the films to be used in these trials, therefore a consistent weight of material was used. It would be expected therefore that the rate of gas generation at 50°C would be greater at 35°C. However, the graphs presented in Figures 1a-d indicate the opposite for both PE and PET, indicating an inconsistency in either the test inoculum or application of the test method, or both.
The results presented for the aerobic degradation are invalid, when the requirements of internationally recognised test standards for these conditions are considered, as the biodegradation for the cellulose control is required to be a minimum of 70% in 45 days, which is not achieved for any of the tests involving the externally supplied additives, as illustrated in Figures 2b & d. Additionally, the cellulose biodegradation curves are very erratic in nature, dipping after 60 days. Again this suggests issues with the activity of the inoculum employed or application of the test method, or both.
The testing performed by burial in soil again provides no insight into the functionality of Reverte™ for its designed environment. An oxo-biodegradable plastic which has not been subjected to any oxidative pre-treatment and is denied access to oxygen in order to bring about abiotic Mw reduction and alter the chemical functionality of the lower molecular weight species formed will not biodegrade in this in the short timescale subjected to in this environment, i.e. an oxo-biodegradable plastics would behave no differently than a commercially available “compostable” in this environment.
The testing performed where oxidation was performed by exposure to UVA at elevated temperature involved Symphony Environmental product and as such detailed analysis of this will no doubt be provided by Symphony. However, it should be noted that the Mw was only reduced to 31.4kDa, the requirement of ASTM D6954-04 (2013) is a minimum of 5kDa. Additionally, the polydispersity index of this material following exposure was 5.7. Although no figure was provided for the polydispersity index of the material prior to oxidative degradation, 5.7 is high and our experience indicates that significant radiation induced cross-linking has occurred which would probably have left the test material with a high gel content. The PE powder used for further testing by the study team is irrelevant as this is reactor powder which has been produced with the low Mw (i.e. commercially available PE wax powder) and is of the same unoxidised nature as normal higher Mw PE.
In conclusion therefore, Wells Plastics find this study as reported in this paper to be of no academic or technical value whatsoever and provides no useful addition to the understanding of the application of Reverte™. The paper, by not referring to the presentations and information provided and the discussions held, provides a misleading commentary regarding the application of oxo-biodegradable technology. It is akin to taking a table tennis ball into the deep ocean, finding it crushes under the pressure and concluding that it is not a table tennis ball!
The shortcomings of the study with regards to its application to oxo-biodegradable Reverte™ additive masterbatch were extensively discussed with the study group, and Dr Selke in person, on numerous occasions, and were acknowledged and accepted by Dr Selke. If the MSU team had considered all the information provided to them, both verbally and in written form, and had properly learned about the design environment for Reverte™ then they could have saved 4 years work and many thousands of dollars by not performing this worthless study.
It may be considered, that had the issues raised by Wells Plastics and others regarding the methodology and the flaws in the validity of the test results obtained, as detailed above, been referenced in this paper, then the peer review panel would have also been presented with a more complete view of the study and technology of oxo-biodegradable polymers and judged its worthiness for publication accordingly.