Thursday, June 06, 2013

"Nature" Magazine has an Axe to Grind with "Plastic Wood"

Nature takes a couple of misguided swings at plastic decking materials in their latest issue with an article entitled " 'Plastic wood' is no green guarantee". The initial context of the article is that much of Coney Island's Boardwalk is being rebuilt with "plastic wood". What the author fails to realize in his write-up is that there are actually 2 separate types of decking materials made from plastic. One is made of just plastic, typically recycled plastic, and is most often called "polylumber". The other material is made of plastic (which may or may not be recycled) AND wood flour (sawdust) or other biobased materials. This material is called a "wood-polymer composite", since it is a composite material. (In a composite material, the additive - wood flour - reinforces the plastic. Compare this to a filled material where the additive (such as calcium carbonate or talc) weakens the material.) Unfortunately, the author refers to the materials in the article as "plastic wood", a term that really isn't used in the industry and hardly even by the general public.

But my issues with this article are about far more than petty nomenclature, as the two materials have significantly different chemical/mechanical properties. Since one of these materials has a biobased component, it can be a food source for some flora and fauna of the natural world. The other one can't. So for the author to make a blanket, undifferentiated statement degrading "plastic lumber" because labs can have "mushrooms growing on the boards" is to not recognize this difference. The broad brushstroke hits both materials, one in an entirely unfair manner. But even for the composite materials, many products are treated to prevent such growth, meaning the validity of the statement can be argued regardless of which product it is applied to. It is far below scientific standards to cite second-hand evidence of lab results in one lab as evidence of any broader trend but that is what happened here.

And then there is this howler of a statement: "But the evidence for plastic timber’s durability is thin, in part because the industry arose only about two decades ago..." Yep, 20 years of real world data is what I would call thin evidence, wouldn't you? Gosh, I need 50 years of data, no wait! 100 years! of data before I am willing to accept it. Worse, this statement completely overlooks the existence of accelerated aging as a method of testing and prediction.[*] I have helped more than one company with accelerated aging of wood-polymer composites during my career and I've seen the value of the testing. It works and does make an impact on predicting product lifetime.

By the end of the article, the author also has made a mess of the idea of tropical woods as being "sustainable" too, so I'm not even really sure what the point of the article was. I realize that this was not a peer-reviewed article and was designed for non-specialist readership. However, I would argue that the standards for accuracy should still be high since general readers are less likely to read the article critically. Unless they have been in the market for decking recently, they are unlikely to know that two types of polymer-based decking exist as alternatives to wood and that they are not the same. Would it really have been so hard for this article to clarify that concept?

[*] Long time readers will know I am a very vocal critic of accelerated aging WHEN IT IS IMPROPERLY CARRIED OUT. Done with proper diligence, it is a wonderful tool for predicting product lifetime. But anyone who thinks that they can just throw some samples into a weathering chamber and cranks up the power should stick their own head in there too.

No comments: