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Q-talk 99 - Epoxy for Homebuilts

In this article I will compare the higher performing epoxy resins that are readily available to the homebuilder. I have done the best that I can to acquire comparative data from each of the manufacturers. I had to make direct calls to PTM&W and to Martin G. Scheufler Kunstharzprodukte GMBH (MGS) to acquire the mechanical data that is reported here. The data on all the Gougeon Brothers material, WEST System and ProSet systems are easily available on their web site, including MSDS's for each of the products.

The Three Resins

The first two epoxy products are available from Aircraft Spruce and Specialty Company (AS&S) while the ProSet is available direct from Gougeon or the distributors that they list on their web site (prosetepoxy. com). PTM&W does not have a web site, but some of the information is posted by another source(http://pages.sbcglobal.net/ccanedy/aeropoxy_main.html). I can thank Scot Stettler, for his support in providing all the information that is reported in the table.

MSG has a web site (www. mgs-online. com), but the information is incomplete, as the data given in PDF files are really only for one resin system, despite the hotlinks they show for all the resin systems. When one clicks on each of these only the PDF files for the L160 resin is available. The L160 product is not offered by AS&S. Further, they do not use the American Society of Testing and Materials International (ASTM) test methods as the standard for material properties they use the German D.E.N, standard. I will discuss the product further.

It is common practice in the industry to report product data in terms of just the resin properties alone. This is referred to as "neat" properties. Data reported in this manner can then be provided in a standard format that results in a meaningful comparison.

When the properties are then reported in the neat terms then one will observe that the mechanical properties are understandably lower than the properties that would result from a fiber reinforced laminate. The properties for the two U.S. epoxies are tested in accordance with the ASTM, but the German MGS material property data was published relative to their D.E.N, standards. It is similar in the test approach doesn't give appropriate comparative results, but it is used in the table below to as a trend in the material performance. There is no way for me to know the differences in the two standards without actually reviewing a written procedure, but the best way certainly would to evaluate the MGS the material under the ASTM test procedures that are listed in the spreadsheets below. This is not an exercise that I'm inclined to do though, as it takes a lot of time to prepare and evaluate the materials. I can report that Brian Martinez (Q200 Pilot, Quartz Hill, CA) is currently using the 285 / 287 MGS epoxy system to construct a Defiant and he has been very pleased with the results.

I did attempt to contact the MGS Company directly and spoke with Mr..Kaffee of their technical staff. The language barrier and different test standard did make it a little difficult to get all the information that I was looking for so I could not come to a complete understanding why all the data on their web site was based on the one L160 material system. This would imply that all the systems perform the same way, which I cannot believe. The data then given in the materials tables is not for the 285 system. The paragraph below is extracted directly from the Aircraft Spruce catalog and so I thought that it would be helpful to comment on it for added insight:

"MGS epoxy resins are approved for the production of certificated aircraft parts. The 335 and 285 systems are especially suited for homebuilders because of their long shelf lives, excellent workability, physiological friendliness, adjustable cure rates and excellent static and dynamic strength characteristics. Both systems are available with fast and slow hardeners which can be blended with each other in any proportion to provide the desired working life and cure cycle. Pot lives and working times can be adjusted from fifteen minutes, using the fast hardeners, to six hours, when the slow hardeners are employed. Once the hardeners have been blended, the specified resin to hardener mixing ratio must be maintained. Components of the 335 system should not be mixed with those of the 285 system. With both systems, if only the slowest hardener is used, the cure times should be extended to a few days, otherwise some brittleness may be noted. While room temperature curing results in good properties when the faster hardener combinations are used, some curing at elevated temperatures or post curing will result in the highest achievable strength and Tg, with the slower blends. Even unfavorable low temperature and high humidity conditions in the work environment will not effect the quality of the product and high gloss, uncontaminated, tack free surfaces are achievable every time. The resins do not contain any unreactive dilutants which with many systems result in de-gassing and bubbling of the painted finish. The MGS resins do NOT contain aromatic amines. While proper processing practices should be maintained, the physiological friendliness of these systems have been demonstrated by many years of production experience. The 285 system has slightly higher physicals than the 335 and will also achieve a higher maximum Tg after post curing. While the 335 is more viscous than the 285, after mixing with the appropriate hardeners, their viscosities are comparable. These systems are used in the construction of the Cozy, Diamond, Cirrus and other aircraft."

But wait, there's more. Continued in Q-Talk issue 100

You can order a printed copy of Q-talk #99 by using the Q-talk Back Issue Order Page.