Swelling Rubber to Measure Toluene Content in Gasoline

Materials View, a weekly product from Wiley which highlights an article in a Wiley journal [1] this week points to an article from the Journal of Applied Polymer Science regarding the swelling of rubber after immersion in gasoline. The swelling of rubber in a solvent is nothing new. Flory laid out some the theoretical details behind it back in the 1950's. It's a technique that I often use - usually to determine the amount of non-crosslinked material [2] and/or the relative degree of crosslinking in similar materials [3] as it is very easy to set up and run. A balance and/or a ruler, some beakers and lots of solvent is all you need. Oh one more thing - time. It typically takes 24 hours for the rubber to swell completely, although if the rubber sample is very large, it can take longer. This is usually not a problem as I can be doing other things while the samples are soaking. Heating the solvent baths can decrease the time to equilibration, but has to be used cautiously as many of the solvents that swell rubber are rather flammable.

In this particular article, the authors claim that the swelling can be used to determine the amount of toluene there is in gasoline. The researchers state in the title that toluene is an adulterant, although there is certainly evidence that toluene in fuel can be beneficial in many cases. The researchers had to rely on quite a bit of statistical analysis in order to get the results, which doesn't surprise me at all. I wonder how sensitive the test is to other nonaliphatic additives that can be added to gasoline too, such as ethanol.

I've not read the article [4] so I'm to going to be able to make extremely definitive statements about the motivations of this research, but there already is an ASTM standard (D3606) for determining the amount of toluene (and benzene too) in gasoline, this being done by GC. While I've never thought of GC as being a particularly difficult or expensive test, there might be cases were access to a GC is difficult, but I am having a hard time imagining when and where that would be. If you are in a place in the world where you care about toluene as an adulterant in gasoline, then you are not in some remote location, but instead are in a spot where electricity and the carrier gases and the money for a GC are available. Besides, this swelling test takes at least a day to run, and more importantly, is heavily reliant on the rubber test specimens being of a constant composition and crosslinking over time.

While this is a new test, it seems to me like a big step backwards in time.



[1] How come these articles are never free to read? Other publishers that have similar schemes to draw attention to certain articles have them free-to-read for at least a short period of time.
[2] The non-crosslinked material will diffuse into the excess solvent. Massing the initial sample and the what is in the bath will give you the percentage of uncrosslinked material.
[3] The larger the dimensional change in the part, the lower the degree of crosslinking.
[4] My employer doesn't have a paid subscription to the journal and I would have a very hard time telling them with a straight face to pop $35 for an article about swelling rubber in gasoline.