Should Surface Tension Test Fluids Be Stored at Reduced Temperature to Achieve Maximum Shelf Life?

Question: If chemical reactions affect the accuracy of dyne fluids, wouldn’t it be a good idea to store them in a refrigerator?

Answer: There’s no question that storing dyne solutions at a reduced temperature will slow down any chemical reactions, but that is only one factor that affects their aging or performance. There are a number of things to consider, as I’ll get to below. But first, please keep in mind that 55 to 60 dynes/cm test fluids will freeze at about +3°C (39°F), and we strongly recommend that a change of state be avoided (more information on that topic is available here). Also, in many cases low temperature storage ends up being at relatively high humidity. This can be detrimental, as there may be some degree of water vapor transmission over time from the storage environment into the bottles of test fluid (or the barrels of test markers).

For end-users of ACCU DYNE TESTTM Marker Pens and surface tension test fluids, the most critical considerations are ensuring that the test supplies and material samples are both at ambient temperature when the test is performed, and avoiding repeated temperature cycling from refrigerated to ambient. Temperature (and humidity) cycling are used in accelerated aging studies, which is enough to be said regarding that.

We’ll consider three different scenarios, and discuss the benefits and risks of refrigerated test fluid storage for each.

Some shops need to keep supplies on hand, but only use them for specific short run jobs. In this case, there may be periods of weeks or even a few months when they are not used at all, followed by short periods of relatively intense usage. In this situation, as long as it is ensured that the test markers or dyne fluids are removed from refrigeration long enough in advance – 24 hours is a nice conditioning period – then storing them refrigerated would probably be a prudent idea, especially if there is not an alternate storage area with good environmental control.

By contrast, in many industries – film extrusion, printing and converting for example – dyne testing is an ongoing requirement. In this case, the only reason to refrigerate would be if large “master” bottles (8 ounces or larger) are used to periodically replenish small bottles used for testing, or if ACCU DYNE TESTTM Marker Pens are bought in multiple sets for release to manufacturing as required. Generally speaking, we do not recommend refrigeration of inventory under these conditions, as the chance of using test supplies before they are adequately conditioned, along with the possibility of freezing and exposure to high humidity, combine to create more risk than I would care to take with sensitive reagents.

The last example would be for distributors who purchase to hold inventory for resale. In this case, it is clear that ideally it would be best to store refrigerated in a humidity-controlled environment. The most serious consideration is to make sure that the time your inventory is out of cold storage to fill orders is minimized, so its temperature stays as constant as possible.

So – what’s the quick and easy answer? Of course there is none – this is dyne testing after all, and every situation has its own unique twists – but if I had to make a blanket recommendation, I would say just store your product well sealed under normally controlled laboratory conditions in its original packaging. If your test supplies must be kept in the shop at elevated temperature or humidity, consider increasing the frequency of replenishment. Other than that, don’t worry yourself overmuch about the finer details of thermodynamics.

The Effects of Freezing Dyne Testing Solutions

Question: What happens when your test fluids freeze and then re-thaw, and why are you so concerned with avoiding this when you ship in the winter?

Answer: With regard to how freezing may affect product performance, this is a difficult question to answer, as it comes down to the inability to prove a negative. To start, let me make it clear I am not a chemist by any stretch of the imagination; my background is experimental design and quality control. So, if there are any readers out there who can comment on the chemistry of the freeze/thaw cycle on binary (plus dye) mixtures, I would love to hear from you!

I have heard a number of anecdotal reports of changes in the reactions of surface tension test fluids after they have been frozen, but cannot personally remember ever seeing an effect myself. Nevertheless, subtle changes in the mixtures could have a meaningful impact under some circumstances: Water vapor adsorption could be accelerated; leaching of polymer from the bottle at the liquid/solid interface could be increased; the dispersion of the dye in the 2-ethoxyethanol/formamide mixture could be altered. Undoubtedly a good number of other possibilities exist as well, including the potential for shortened shelf life.

The biggest problem with determining any impact on performance is that to run a comprehensive study on the effect of freezing on test accuracy, you would need to test at least a dozen different dyne levels on an almost literally limitless variety of substrates – a Herculean task at best.

So, in the interest of caution and keeping the anecdotes in mind, I feel it is best to avoid freezing dyne solutions.

But, the most pressing issue with regard to freezing is damage in transit. ACCU DYNE TESTTM Marker Pens will sometimes lose their tip seals and leak during shipping once they have been frozen. I believe that the reason for this is that shrinkage of the plastic spring that controls the release of test fluid from the tip allows seepage of test fluid during the thaw cycle. Sometimes the seal between the pen barrel and the tip leaks for similar reasons. Rarely, the same problem can manifest with bottled test fluids – especially with dropper bottles.

The short and the long of it is that, based on brand stewardship considerations and replacement costs, as well as the potential for effects on measurement accuracy, we feel it is very important to avoid allowing ACCU DYNE TESTTM Marker Pens and surface tension test fluids to freeze.