This memo is intended to respond to the unfounded concerns of those who challenge the reported performance of oxo-biodegradable polyolefins. Specifically, it will be emphasized that much of the material in the Biodegradable Products Institute's position paper on oxo-biodegradables is misleading or incorrect.
Please note that the correct descriptor is oxo-biodegradable, not the abbreviated and meaningless term oxo-degradable. The oxo-biodegradable plastics with which I am most familiar are those produced using the proprietary formulations developed by EPI Environmental Products Inc. of Vancouver, British Columbia, for polyolefins. The test data to which I refer relate, therefore, specifically to EPI-based products.
Much of the alleged confusion about the significance of the term oxo-biodegradable arises because of the incorrect assumption that biodegradability and compostability are the same process. They are not. The list of test standards, requirements and specifications discussed in the BPI position paper (ASTM, EN, ISO) refers to compostable plastics.
These documents are not relevant to oxo-biodegradable polyolefins or to any other plastics that are not intended to be composted. In contrast, the ASTM test method for biodegradability is D 5338. It has been shown repeatedly in many laboratories that EPI-based polyolefins, after oxidative degradation has occurred, are biodegradable using biometric methodology such as that described in ASTM D 5338.
This testing has shown that biodegradation of EPI-based oxo-biodegradable polyethylene reaches a level of 60 percent, albeit too slowly to qualify as compostable, and that biodegradation continues beyond that point. Of course, most post-consumer plastics are not subjected to composting anyway.
The position of New York-based BPI appears to be deliberately misleading. It correctly defines a biodegradable plastic, but goes on to state that this can only be evaluated using what it calls “accepted industry standards” which, as already noted, is a list of specifications/requirements for compostability.
This attitude is clearly unjustifiable. As soon as the standards-writing organizations have prepared performance specifications for oxo-biodegradable plastics that, like most plastics, are not designed for rapid composting, then it will be appropriate to use those standards.
The noteworthy characteristic of oxo-biodegradables is that, after use and disposal, oxidation converts bioinert plastic to hydrophilic biodegradable oxidation products. Evidence for this two-stage process has been reported in scientific literature for many years. Numerous arguments in the institute's position paper indicate confusion and uncertainty on the part of the authors. The following sentences are examples:
“In a second phase, the resulting fragments are claimed to eventually undergo biodegradation. While there is a chemical theory to support a very slow biodegradation, the absence of light, presence of moisture or very low temperatures act as a dimmer switch for the process, resulting in a very slow or absent chemical process.”
None of this makes any sense. Carbon-dioxide production from the biodegradation of oxidized PE, for example, begins soon and is reasonably rapid in biometric tests. Such tests are normally carried out without photochemical stimulus in an aqueous medium at room temperature. What is it that the institute doesn't understand here?
There can be and is no accumulation of plastics fragments in the environment from oxo-biodegradable polyolefins. The oxidative degradation of oxo-biodegradable EPI-based polyolefins converts bioinert, hydrophobic material into hydrophilic, polar chemicals (the oxidations products) that biodegrade in contact with the soil. All arable land is microbially active. That there is no risk of accumulation of persistent substances in the environment has been demonstrated in numerous peer-reviewed scientific publications over the years.
Third-party testing has shown that commercial bags made from EPI-based oxo-biodegradable PE are fully compatible with conventional plastic recycling streams. There was no reduction of physical properties in the final recycled product having up to 50 percent oxo-biodegradable PE in the feedstock.
The same study showed that commercially available plastic bags made from hydro-biodegradable material (that met the compostability requirements of ASTM D 6400) completely ruined the utility of the normal recycled plastics stream. Perhaps the institute should address that troubling issue.
Recovering the value of used plastics is acknowledged to be important from both an environmental and a practical point of view. Incineration with heat recovery and recycling are acceptable methods. In this context, it should be noted that any plastic that meets the time requirements of compostability as defined in ASTM D 6400 or, even worse, EN 13432 is converted to greenhouse gas during composting. No value can be or is recovered.
In summary, there are numerous errors in the institute's position paper, too many to deal with here. It is a misguided, confused and confusing document that does not contribute anything worthwhile. In contrast to the opinions of the institute, a great deal of evidence has been published that proves that oxo-biodegradable polyolefins based on EPI prodegradants perform as claimed, i.e., after being used and discarded these plastics will oxidize under a variety of disposal conditions and the oxidation products are indeed biodegradable. No accumulation of small particles occurs. Moreover, these oxo-biodegradable plastics can be processed with the conventional waste plastic recycling stream.
David M. Wiles
Victoria, British Columbia