epoxy adhesive and mineral oil

[aursuta]

this question is about the long-term interaction of cured epoxy and food-grade mineral oil.

i am a sculptor and worked with a glass-casting studio to produce large-size hollow sculptures that were intended to contain alcohol indefinitely. the sculptures were cast in sections which were joined together with a specialty epoxy adhesive called H-XTAL. we made a test with cured epoxy that was soaked in liquor (40% alcohol); after 3 months the epoxy seemed slighty soft. i am researching other liquids that could fill the sculptures without affecting the epoxy. i am wondering whether mineral oil would be a viable substitute - or would a solution of distilled water and antifreeze work? ideally once the sculptures are sealed, the liquid would stay inside for ever.

many thanks in advance for any suggestions.

[bowcoastie]

Good day Andra,

Looking at the product specification sheet, the H-XTAL is a specialty epoxy that is designed for gluing glass pieces together with a refractive index very similar to that of glass. I suspect that in order to achieve this, the resin has to have other properties that are not as good as regular epoxies. To that end, the chemical compatibility charts for epoxies such as Epoxy - Chemical Resistance list the compatibility of different chemicals. On the chart ethyl alcohol is listed ad compatible only a room temperature.

As the epoxy you have chosen is probably less chemically resistant I would choose isopropyl alcohol / water mix as a filling fluid. There are others on the list that would work such as kerosene but I suspect a flammable filling fluid would be undesirable. How low a freeze resistance resistance do you need? You can choose a mixture of isopropyl and water that is freeze resistant and has a higher flash point. The following table can guide you on the freeze point protection and flash point for a given mixture: Isopropanol (2-Propanol) based Freeze Protected Water Solutions.

With Regards,

Bruce Williams

[wjfreeman]

Bruce Williams made good suggestions.

I am unfamiliar with H-XTAL, but know it is used in applications where optical clarity and non-yellowing is important. In my work years ago with commercial epoxy resins, many of the cured properties depend, in part, on the catalyst and cure conditions. Maximum cross-linking is what you are looking for to yield the most chemical resistance, though there may be trade-offs with respect to thermal expansion, modulus properties, and possibly refractive index for your application.

In this regard, I would first try a series of tests where you try to achieve a complete cure (i.e., cross-linked product.) This will be the sweet spot for the most chemically robust product.

There are a number of tests that can estimate the cure in a test sample, including thermal analysis of the glass transition temperature, or, if casting bars, the heat deflection temperature (HDT). The old HDT test of my era is difficult to set up and measure. In this regard, however, you can check the ASTM literature (ASTM International - Standards Worldwide) for more appropriate test procedures.

In any case, you should contact the manufacturer with your question (Contact - HXTAL NYL-1HXTAL NYL-1). Be sure to describe in detail your method of curing the resin giving exact amounts and times etc.

Walter J. Freeman

[burton]

Andra,

I'm quite familiar with the HXTAL-NYL product, at least as it existed for the first few decades of manufacture, and I've also done much work with epoxy systems of many types. When fully cured at a one to one stoichiometry, epoxies are rather polar materials that will sorb polar molecules, especially small ones like water, alcohols, acetone, methylene dichloride etc. I expect the material to be much more impervious to mineral oil and if the oil itself is color stable over long times in a sealed environment (as most mineral oils are) I think that that would be fine to use. I do not recommend the water and antifreeze approach. I'm on LinkedIn, should you wish to follow-up. Indeed you should, as Walter suggested, make sure that the epoxy formulation is mixed at the right ratios and is fully cured to its ultimate Tg to get the best durability. This could involve warming the item for long times, so there may be tradeoffs.

Bruce L. Burton