jueves, 25 de agosto de 2011

Biomaterials, compost and biodegradation of single-use bags

Every year, more o less by the end of my annual holidays, I reach the same conclusion: Writing a blog is not a matter of time but of discipline. Every year I start my holidays planning to upload 3 entries every week… but my summer activities do not allow me… they are much more interesting than preaching about environment, safety, REACH or IPPC.

This year I have made something new, fifty per cent business and fifty per cent pleasure. I met Lucia Castro Díaz in Santiago de Compostela, one of those days of Santiago’s true weather, raining softly and quiet. We had talked through Internet many times and we share many worries and interests, but last Monday was the first time we met personally. We had breakfast in a café in the very heart of Santiago’s old quarter, in Rua del Vilar, at 08:30 am, when tourists haven’t already waked up and on streets you just can see some early birds peregrines, wearing their back bag and trekking boots.

Lucia got a Dphil in Materials at the Oxford University. Her thesis was about degradation of Polyethylene exposed to environment and, although her professional skills are deployed in a wide range of matters, she is a very specialist in polymeric materials.

As you can guess, we talked about many matters, I can’t avoid my natural curiosity and whenever I have the opportunity to talk to people “who knows” I ask for advice in matters I am concerned about.

In this occasion, what I was wondering about is the meaning of the Second Additional Provision of Law 22/2011 of 28 July, waste and contaminated soils: Replacing single-use bags.

The Provision dictates the complete ban of single-use bags “non biodegradable” in Spain by 2018 and declares that for the purposes of this rule the definition of “Biodegradation” shall be applied is those included in the norm EN 13432:2000 "Requirements for packaging recoverable through composting and biodegradation- Test scheme and evaluation criteria for the final acceptance of packaging"

My concern was specifically about the term "biodegradable", term of very common use, easily and usually misuse to confuse or at least to "distract".

The Spanish law, once again, makes the mistake of include the version year in the statement of the norm. The norm may be revised any given year and that number will change… omitting that data, the quote is equally correct and avoid any future confusion… but, any way, the European norm EN 13432 resolves the definition of “biodegradable” by defining the characteristics a material must own in order to be known as "compostable" and, therefore, recycled through composting of organic solid waste.

In fact all materials are, one way or another “biodegradables”, is just a matter of time elapsed. A steel beam may need hundred of years to disappear by the effect of environment but it will do it for sure. It is obvious that steel is not a biodegradable material… How quick must degradation of a material be to be considered as “degradable”?

One of the most elemental principles of chemistry announced by Antoine Lavoisier says “Rien ne se perd, rien ne se crée, tout se transforme”, “Matter can neither be created nor destroyed, only transformed” (Traité Elémentaire de Chimie, 1789). Every transformation has a result. If we destroy plastics in a blender we are able to “degrade” the material in minuscule particles but it is obvious that this “plastic powder” is not degraded enough to be released in environment… How small must be the result of degradation?

In my modest opinion, “compostable” is one step beyond “biodegradable” and something may be biodegradable and may not be able to reach quality enough to be useful in agriculture as compost. A biodegradable material is not necessarily compostable, because it must also disintegrate during the composting cycle. On the other hand, a material which breaks during composting into microscopic pieces which are then not fully biodegradable it is also not compostable, but EN 13432 is clear aligning both meanings.

The description of the compostability criteria is vital because materials not compatible with composting can decrease the final quality of compost and make it not suitable for agriculture and, as a result, commercially not acceptable. In fact, this norm is a reference point for the producers of compost.

According to the EN-13432, the characteristics of a compostable matter are:

"Biodegradability", understood as the capability of the compostable material to be converted into CO2 under the action of micro-organisms. This property is measured with a laboratory standard test method under EN-14046 (Packaging. Evaluation of the ultimate aerobic biodegradability and disintegration of packaging materials under controlled composting conditions. Method by analysis of released carbon dioxide). In order to show complete biodegradability, a biodegradation level of at least 90% must be reached in less than 6 months.

"Disintegrability" or fragmentation and loss of visibility in the final compost (absence of visual pollution). It is measured in a pilot scale composting test under EN-14045 (Packaging. Evaluation of the disintegration of packaging materials in practical oriented tests under defined composting conditions). Specimens of the test material are composted with biowaste for 3 months. The final compost is then screened with a 2 mm sieve. The mass of test material residues with dimensions> 2 mm shall be less than 10% of the original mass.

Absence of negative effects on the composting process. Verified with the pilot scale composting test and, finally, low levels of heavy metals.

Each of these points is considered necessary for the definition of compostability but it is not sufficient alone.

The first question that arises is: Spanish Law aims than by 2018 all single-use bags will be completely compostable or fulfilling the definition of biodegradable included in EN-13432 may be enough? (The quality of compost, and specifically the amount of heavy metals, is key in this matter).

The second one, the question I made to Lucia, is: Is there any material in market with quality enough to be useful as single-use bags that fulfill all compostability criteria included in EN-13432?... I doubted it.

I am going to take out my crystal ball once again: I think that, except revolutionary changes in materials, market is not going to accept single-use bags capable of fulfill neither the definition of biodegradable neither the complete compostability criteria and consumers will opt for multiple-use bags…. But, then, a new question springs… How many “uses” of a bag are necessary not to be considered as “single-use”?... Are two "uses" enough?.. are 15 "uses" enough?... ANAIP is very clear about that point, and so do is AENOR.

But… can anyone be completely sure what a consumer is going to do with a plastic bag intended to be multiple-use?... well, I can’t… What do you think?... Lucia, any advice?

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1 comentario:

lucía dijo...

Como siempre, una entrada muy acertada y además me nombras en ella, que es un honor. Sobre el tema de biodegradable/compostable/renovable he publicado ya un post, porque es un tema que genera muchas dudas. Puedes verla aquí: http://www.mundomaterial.eu/2008/12/01/terminologia-de-los-bioplasticos/
Ya en ella distingo entre biodegradable y oxodegradable. Además he preguntado y me han comentado que aunque algunas de las compañías que comercializan los aditivos que convierten los plásticos tradicionales, el polietileno en este caso, en oxodegradables dicen que sí son biodegradables, ninguno ha pasado el test oficial de biodegradabilidad ni ha aportado resultados sólidos que lo demuestren. Vamos, que no va a ser posible añadirle un aditivo a las bolsas para que se conviertan en biodegradables y pasen el test.
En cuanto a las bolsas de materiales renovables, hay varios factores a tener en cuenta. Primero, los bioplásticos que se utilizan ahora para hacer bolsas son en realidad mezclas basadas en almidón pero que siguen usando poliésteres derivados del petróleo para conseguir tener las propiedades mínimas requeridas. Las mezclas suelen ser 70/30 renovable/petroquímico. Esto no deber ser un impedimento, ya que dentro de poco serán 100% renovables. También es cierto que el polietileno ya es producido 100% de fuentes renovables en Brasil, a partir de caña de azúcar, por Braskem. Pero sigue siendo más caro que el procedente de petróleo. Segundo, las bolsas renovables que vemos en la actualidad en los supermercados, a base de almidón, siguen sin tener unas propiedades idénticas a las tradicionales. En particular, tiene que mejorar la "tear propagation", es decir, que se rompen más fácilmente.
Y tercero, una de las preocupaciones con la introducción de bioplásticos en la cadena de valor es que son difíciles de distinguir de los plásticos tradicionales. Esto puede llevar a error en el consumidor, que los va a tirar en el contenedor amarillo, contaminando la cadena de reciclaje. Además de que en España sigue habiendo muy pocos lugares con plantas de compostaje.
Para más información, también podéis leer el artículo sobre las bolsas de mi blog:
Este es un debate que no va a terminar pronto. Seguirán apareciendo alternativas a los plásticos tradicionales, el mercado de los bioplásticos sigue creciendo a un 20% cada año, mientras los plásticos están sobre un 2-3%. Considero que centrarse únicamente en las bolsas es un poco demagógico, pero para que veais que España no es la única, el último enlace es de un mapa mundial con todas las otras prohibiciones: