Compostability of Plastics and packaging: Standards on biodegradability and ecotoxicity

The first attempts to define a standard on requirements for plastics and packaging suitable to composting date back tothe middle of 90s, when ORCA (Organic Reclamation and Composting Association) in Europe and ISR-ASTM(Institute for Standard Research of ASTM) in the USA, started fundamental preliminary works. Official standardspecifications were developed shortly after. ASTM D6400 (Standard Specification for Compostable Plastics) wasoriginally published in 1999 and the European harmonised standard EN 13432 (Packaging. Requirements for packagingrecoverable through composting and biodegradation. Test scheme and evaluation criteria for the final acceptance ofpackaging) the year after.

Since 2008 also an international standard (ISO 17088 Specifications for compostable plastics)is available. The three standard specifications basically apply the same testing approach (and requirements) based on:assessment of biodegradability (90% in 180 days), assessment of disintegrability (90% in 90 days), assessment ofpossible negative effects on the final compost (ecotoxicity testing and content of metals).After 20 years from the first discussions and more than 10 years of practical application of the standards, we can nowtry to draw some conclusions, collect the voiced criticisms and restart some further dialogue (similarly to what done inthe 90s) to see if and how the current standards can be improved.Compostable plastics (that comply with the standards) are nowadays applied in specific applications (e.g. bio-wastebags, carrier bags, single use cutlery and tableware, etc.) that are finally delivered together with the bio-waste tocomposting plants. No negative reports are available to our knowledge. On the other hand, it is interesting to remarkthat lack of degradation has been found when testing materials that do not comply with the standards, whilecompostable plastics performed satisfactory.The biodegradation level (90% in 180 days) has been considered to be too low (why 90%? What about the residual10%?) or too high (compostable plastics are too fast and composting is a sort of “cold” incineration, fast converting theorganic carbon into CO2). The biodegradation rate has been considered too slow (permissive) or too fast (conservative).The ecotoxicity testing has been criticised because carried out after 3 months composting. Somebody wanted it to berepeated at different times, following the biodegradation course. All these criticisms seem not founded enough and arediscussed in this paper.However, in spite of the successful application of the above standards, we note that further reassurance on theenvironmental safety of bioplastics is progressively requested due to the higher volumes that are expected to bemarketed in the near future by the biodegradable plastic industry. In particular the interest is on the substances producedduring biodegradation that might reach soil when compost is used as fertilizer. A first attempt to address this concernhas been adopted by ISO. A recent revision of ISO 17088 requires that constituents present in amount ranging between1% and 10% are tested individually for biodegradation. The reason of this further requirement is to show that the 90%biodegradation level (instead of “100%”) does not “hide” a 10% fraction formed by some recalcitrant minorconstituents.In order to provide a further reassurance to the concerned stakeholders, an approach currently under discussion is tofocus the attention on the molecules that can be possibly generated during the first phase of degradation, when thepolymer, still outside the microbial cells, is depolymerised back to the original monomers. It should be pointed out thatsince the original polymer must show a 90% biodegradation level, all or most intermediates must be biodegradable,otherwise this limit would not be reached. Therefore, this approach focuses on substances that can be released into theenvironment in traces and can also be applied to substances other than the monomers, such as additives used to enhance polymer properties and processability.

Copyright: © European Compost Network ECN e.V.
Quelle: Orbit 2012 (Juni 2012)
Seiten: 6
Preis inkl. MwSt.: € 6,00
Autor: Dr. Francesco Degli-Innocenti

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