Bonding with West Systems epoxy to plexiglass

Over the years I've noticed a few references here about epoxy not adhering well to acrylic, when doing fiberglass layups for windscreen fairings. Recently I've seen a couple of RVs where the fairing was delaminating over the top of the roll bar, and/or chipping away entirely.

On a whim I decided to try a little experiment. I bonded both canopy and windscreen to my airplane with Sikaflex 295UV, and I had some primer- Sika 209D- left over from those jobs. Technically, the primer is an adhesion promoter for the urethane. I wondered if it would improve an epoxy bond as well.

I scrounged two trimmings from a canopy, and attacked them with 60 grit sandpaper until I had a nice uniformly rough surface on each. One of them got a quick wipe with denatured alcohol, the other got wiped first with Sika 226 cleaner (now known as Sika Aktivator 205, which they specify as the first step in the bonding process), and then coated with the 209D primer. After waiting the requisite time for the primer to dry, I mixed some West 105 with 206 fast hardener. Then laid up a single layer of cloth on each piece of prepared acrylic. After that I went over to the cool antique fly-in happening around the corner from me, and hung out for several hours looking at cool old airplanes

About 8 hours later, I tried a very unscientific pull test on each part. The glass on the bare acrylic peeled off cleanly, leaving no apparent residue. The primed part didn't want to let go so easily. Pulling hard, I was able to tear a corner loose, but strands of fiberglass remained embedded in resin, still attached to the acrylic.









Obviously, an unscientific test. Among other things, I didn't wait long enough (several days, at least) to allow a proper post-cure of the epoxy. And there are concerns about applying nasty solvents to one's ?ber-expensive bubble. Duly noted. I have yet to apply the knowledge I gained, though I'm considering it since I'm about to lay up the windscreen fairing. I thought it worth sharing in case someone is interested, or wants to try it themselves.

Your mileage may vary; tax, license and dealer prep not included, etc, etc.

This is interesting and I appreciate you experimenting here. Does the 209 primer help with adhesion of fiberglass to aluminum also? Is there any problem with West epoxy getting a permanent grip on the aluminum canopy skin?

acrylic experimentation

Lars, appreciate your 'experimental' processes for our benefit.
........ acrylic is a real problem area, there seems to be little documentation on how to properly tackle all the things we need to do to it!
In all the acrylic stuff I've done in the sign business; drill, weld, glue, bend etc. I offer 2 caveats; I am a big fan of mechanical bond, so scuffing it always helps....but at some point, a coarse enough scratch becomes a potential stresspoint ( crack!)
chemical bonding agents are made for just such a purpose, but the face of the acrylic is a much different animal than the machined edge....lots of failures have been caused by solvents attacking the exposed edge of a sheet, especially when stressed ( as in a cold-formed bend).

Advice.... worth exactly what you paid!

Hysol

We plastic airplane people use HYSOL to bond dis-similiar materials. Carbon to E glas, either carbon or Eglas to aluminum, and acrylic to Eglas or carbon. All of my windows are bonded to fiberglas with Hysol...tough stuff.

Gordon

Lancair ES
N144GP

and....

clean only with alcohol. No acetone or MEK. Prep with 40 or 80 grit to scuff up.

gp

A while back when I was doing my canopy I also did a few unscientific experiments with West Systems epoxy adhesion to acrylic. My purely qualitative findings were that scuffing the acrylic surface made a huge difference. Even very fine scuffing with 200 to 400 grit.

hysol

Lancair, so I need help to understand, I could bond the first layer fiberglass fabric to the acrylic canopy, then finish the layup with epoxy like west sys. or Do I do the entire layup with Hysol? Thanks in advance

bird

Lancair Super ES said:

We plastic airplane people use HYSOL to bond dis-similiar materials...

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To clarify, I think that Lancair means the EA94xx line of epoxy adhesives from Hysol (formerly Dexter-Hysol, and currently a division of Loc-Tite).

The most popular of these is EA9430, which has probably the best peel strength of any epoxy adhesive, around 60 lbs/in. in T-peel. EA9430 and its predecessor EA9410 were used in the Schreder HP/RS-series kit sailplanes to bond wing skins to PVC foam ribs. The earlier EA9410 formulation used prior to about 1980 contained asbestos as one of the fillers, and was replaced by the non-asbestos EA9430.

Another popular Hysol epoxy is EA9460, which has better tolerance of high temperatures, but lower T-peel strength.

Thanks, Bob K.

bird said:

Lancair, so I need help to understand, I could bond the first layer fiberglass fabric to the acrylic canopy, then finish the layup with epoxy like west sys. or Do I do the entire layup with Hysol? Thanks in advance

bird

Click to expand...

I have never tried laminating with the Hysol epoxies, but I have used them to bond stuff together. And based on that experience, I think it would be pretty heinous to try to saturate fiberglass cloth with EA9430 or similar. They are thickened epoxy mixes with enough filler to make them thixotropic (non-runny), and are intended to be used for bonding, not laminating.

For a laminating resin, you want something thin and runny. Or at least thinner.

Thanks, Bob K.

bruceh said:

Does the 209 primer help with adhesion of fiberglass to aluminum also? Is there any problem with West epoxy getting a permanent grip on the aluminum canopy skin?

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I don't know. I've bonded with West 105 directly to scuffed (60 grit, my go-to grade) and cleaned alclad with good results. Epoxy in general seems to bond pretty well to aluminum, at least in my experience. J-B Weld, for example, is tenacious. I've literally reassembled a shattered motorcycle clutch cover with the stuff- it held up for years.

flyboy1963 said:

chemical bonding agents are made for just such a purpose, but the face of the acrylic is a much different animal than the machined edge....lots of failures have been caused by solvents attacking the exposed edge of a sheet, especially when stressed ( as in a cold-formed bend).

Click to expand...

See below. If you read the MSDS for Sika 209D, you'll say never get that stuff on acrylic. Yet it seems to be ok. But I'm an engineer, not a chemist

Lancair Super ES said:

We plastic airplane people use HYSOL to bond dis-similiar materials. Carbon to E glas, either carbon or Eglas to aluminum, and acrylic to Eglas or carbon. All of my windows are bonded to fiberglas with Hysol...tough stuff.

Click to expand...

"Hysol" covers a pretty broad spectrum of products. Which one, or ones, are you using? I'm a plastic airplane ignoramus, no offense meant by the question.

Lancair Super ES said:

clean only with alcohol. No acetone or MEK. Prep with 40 or 80 grit to scuff up.

Click to expand...

Yep. 60 grit, in my case.

It turns out that Sika's "Aktivator" is mostly alcohol, with some titanium compound thrown in, per the MSDS.

The primer, on the other hand, includes evil stuff like isocyanates and MEK, again according to the MSDS.

Despite that, it's a product intended to be used on acrylic, targeted at the marine industry. It's been around for years as part of Sika's acrylic window bonding system. Broad anecdotal evidence in the marine industry suggests that it doesn't harm the plastic, or at least that its use doesn't lead to crazing or cracking. The record in aviation is a lot more limited, and we are using it primarily on thermally formed, as opposed to flat, surfaces, so there are bound to be some internal stresses in the material- in principle a bad thing when the plastic is exposed to solvents. I've read about at least one cracked canopy that had been installed with Sikaflex, but it doesn't seem to be widespread. Several members here have reported years and hundreds of hours of use with Sika-bonded canopies (implying the use of the primer), crack-free.

Note that I'm not suggesting, recommending, advocating or promoting the use of Sika's products in general, or more specifically, Sika's primer as an adhesion promoter. Especially for materials other than its intended use. There may be other primers/adhesion promoters that would work just as well that are more benign. Or use nothing. Or a different epoxy altogether But, since some folks here have reported adhesion issues with West epoxy (which is what Van's recommends in their instructions for this purpose) on acrylic, I thought it would be interesting to see if adhesion could be improved chemically.

Bob Kuykendall said:

To clarify, I think that Lancair means the EA94xx line of epoxy adhesives from Hysol (formerly Dexter-Hysol, and currently a division of Loc-Tite).

The most popular of these is EA9430, which has probably the best peel strength of any epoxy adhesive, around 60 lbs/in. in T-peel. EA9430 and its predecessor EA9410 were used in the Schreder HP/RS-series kit sailplanes to bond wing skins to PVC foam ribs. The earlier EA9410 formulation used prior to about 1980 contained asbestos as one of the fillers, and was replaced by the non-asbestos EA9430.

Another popular Hysol epoxy is EA9460, which has better tolerance of high temperatures, but lower T-peel strength.

Thanks, Bob K.

Click to expand...

Thanks for the clarification, Bob.

For the record, I'm no expert- merely an amateur trying to solve a problem and learn a few things along the way.

Having recently seen some really crappy-looking delaminations of windscreen fairings on slider RVs, I'm hoping to avoid that.

Don't Use 5200

The marine adhesive by 3M called 5200 is sometimes recommended for attaching the canopy to the frame.

This was used in several locations on my boat. The boat was stored out of the water, and being a Colorado boat, that meant that water or humidity wasn't a factor - especially since these particular joints were above the water line.

The materials were copper to fiberglass and fiberglass to fiberglass.

What I learned was that 5200 lasts about ten years, more or less, before debonding. It was worse than merely debonding, though - the 5200 had deteriorated and crumbled.

It's not something I'd recommend for the canopy/frame joint.

Dave

Reviving this thread - - I just helped a friend bond the windscreen with West 105/206 on his 10. A pretty big job - two guys 4.5 hrs. He mentioned after were done, that he had heard that West Systems tech reps said the adhesion to plexiglass was low. I was surprised, and decided to do some searching. Among technical docs, I came across this post.

Now to the OP - Lars, did you eventually use the adhesion promoter for your canopy attachment? What was the final result of your investigation? It certainly looked promising and I was just thinking of doing a similar test with some scraps before I do my 7 tip up bonding. Others?

I recall one poster here laid his windshield fiberglass on with separating media (packing tape ?). Then he pulled the fiberglass fairing off, final finished it and bonded it to the windshield with SIKAflex, just like he bonded the skirts on.
That seems like the ultimate in fit, finish and attachment? His pictures were inspiring.