Monday, January 13, 2014

Still Proposing Changes to the Resin Identification Codes

Last June I discussed the proposed changes to the Resin Identification Codes, the 7 numbers that appear on many plastic articles inside a triangle of chasing arrows. At that time the ASTM International committee was proposing changes that I thought were insane. Plastic News is now reporting that saner heads are beginning to rule. But only to some degree.

For instance, they scrapped the idea of moving beyond the 7 numbers already in place. While there are vastly more resins produced and used than just 7, keep in mind that the numbers 1 through 6 were assigned to the "Big 6" resins, ones that make up about 3/4 of all plastics used [1]. Adding more numbers to account for additional resins is letting the tail wag the dog. All the "other" resins are just scrapings off the plate. But furthermore, once you go down that rabbit hole, there is no coming back. The committee discover that in China they have far more than just the 7 numbers and in fact have over 100 numbers! Who is really going to sort through that many codes? Thank goodness the committee is leaving the number of numbers to 7.

But on the other hand, the committee is toying with the addition of "extensions" to the numbers:
"Consideration is now being given to adding extensions to those abbreviations to further identify variations and characteristics of the seven resin groups now identified through the coding system. This could help reclaimers better identify and sort the plastics for recycling...An extension, for example, could identify if a resin has a high melt flow or low melt flow, information that could help recyclers."
While knowing melt flow [2] can be helpful, just looking at the plastic would allow someone with a little bit of processing knowledge or training to know if it is high or low melt flow. Is it a thin film? Low melt flow. Is it a bottle cap? High melt flow. And so on. But even more than that, not all resins are classified by melt flow. PET for instance, is specified by inherent viscosity (I.V.) and there is not a melt flow test standard for PVC. So how will that be addressed?

As it is, many of the currently available recycled resins are already based on a particle article for input, such as PET bottles, which means that they are already being sorted on that basis. It's far easier to look at a pile of plastic trash and pull out the PET bottles. You could easily get grade school kids to be nearly 100% effective (not that I am advocating child labor!). So how is squinting at all the codes and makes sure that only the #1.2 resins were pulled from the #1.3 resins going to help that?

Leave well enough alone. I still think that the committee is tinkering with something that just doesn't need it.

[1] The numbers weren't assigned in any particular order however. HDPE (#2) is a much bigger volume product that PET (#1) is, but that "misordering" doesn't bother me. Since there is no assurance that the volume of the plastics would be the same in the future, keeping them number in order of produced volume would lead to nothing but problems.

[2] Melt flow is a tested property of a material and is the number of grams of molten resin that will flow out of a specified orifice in 10 minutes under a specified amount of pressure. A high melt flow material has low viscosity and vice versa.

Previous Years

No comments: