Reply from:

     NEAL LANGERMAN

     (619) 990-4908

In a former life, I used to formulate lithographic press washes.  As VOC restrictions tightened, various fractions of mineral spirits, aromatic distillates, glycol ethers, and terpenes were replaced at first by heavy paraffinic distillates, such as Paraffinic 100.  It was cheap and VOCs only had to be reduced so much.  As VOC levels continued to drop, though, more active "solids" were sought in an effort to maintain some semblance of efficacy, and chemicals like t-butylated biphenyls and especially fatty acid methyl esters (FAMEs) were utilized.

Some of these FAMEs were based on high-oleic acids or occasionally even "fully" saturated starting materials like coconut.  Of course, soy methyl ester (SME) quickly gained traction due to economics, and it didn't take long before printers started experiencing rag fires, similarly to what was not uncommonly seen with D-limonene–based press washes years before.  We quickly began adding a solution of TBHQ—the same antioxidant that SME manufacturers would typically use—to our formulas with very high SME content, and the problem went away.  We never determined what concentration of SME became problematic or how much TBHQ solved the problem.  We went big with the AO and the rag fires stopped.

Fast forward 10 years, and I'm tasked with formulating an immersion cleaner, which would benefit greatly from the inclusion of SME.  While the application isn't quite the same—nobody should be dipping rags into the product…but that doesn't mean they won't—I'm still concerned with the potential for spontaneous combustion (SC).  I can't just add a line item of TBHQ to the formula as we're going to solicit bids for toll blending, and side mixing a solution of TBHQ to add to the bulk blend isn't practical.

All that ^ is to preface a few questions.  1) Does anyone have any specific information on SC of unsaturated FAMEs that I could peruse?  Upstream suppliers haven't been especially helpful, and I didn't see anything particularly relevant on the web at a glance.  2) Where can I find oily rag storage recommendations and/or requirements?  I have to assume there's an NPFA standard addressing that.  And 3) does anyone have any suggestions for testing the potential for SC in the lab?  I have zero analytical equipment and cannot directly test for oxidation or oxygen uptake.  Though it doesn't mimic field conditions, I can cook various mixtures in a standard gravity oven and check for darkening.  I can also throw oily rags in a steel bucket and put them in the hot Texas sun, though I do prefer not to start any rag fires if at all possible.

Congratulations if you made it down this far and thanks in advance if you're going to contribute something helpful! 

Dan