Myth vs Reality: Does Loctite Blue damage Lexan?

[adam-21]

Does Loctite Blue really damage Lexan? Let’s find out!

I think we all agree that Lexan is strong stuff. However, let’s take a moment to show just how strong it is. Take a look at this image from this page on Lynxmotion.com. The caption for this image reads “Will it Break? No!”

Exhibit A

Next to the image is this quote from Jim, our generous host:

It really hurt holding this long enough for the camera to snap the image. When I let go it returned to it’s normal flat shape, no worse for the wear. Now Polycarbonate is not indestructible, but it is very tough. A 1/8" thick x 1/4" wide strip can be broken, but it takes several back and forth bends before it finally breaks.

Strong stuff indeed. I think we’d all agree that Jim is a credible witness for this subject matter, so let’s accept that Lexan can be bent with a great deal of force without breaking.

The Experiment

For the experiment, I took a piece of 1/8 inch thick black Lexan, 4.5 inches long by 1.5 inches wide, and applied a layer of Loctite Blue along the center. This lexan had been random-orbit sanded to give it the nice smooth scratch-resistant satin finish that is very popular. I then set the Lexan on a shelf.

After five days, I picked up the piece of Lexan and decided it was time to test it. At first I gave it just a little bend with not much force at all. I heard a cracking sound. Interesting.

I then applied more force, and … SNAP! The piece of Lexan broke in not one, but two places, and the center piece went flying across the room. Look out!

Exhibit B

http://feat.putfile.com/profilepics/main/5/a-bot-7986003341.jpg

The putfile site scaled down the image, so you can’t see it that well, but there is a noticable crazing pattern (like you would see on glazed pottery) where the Loctite was applied. And in case you are thinking it, no, the random-orbit sanding does not create a pattern like this.

The Verdict

Loctite Blue damages Lexan.

PS. Yes, I changed my login name to something more anonymous.

[evolution-2]

Locktite can do that to many types of plastic. It’s a chemical reaction.

Red, the permanent stuff, is even worse. And Locktite does serious damage to Carbon fiber. More specifically, to the resins commonly used to make sandwiched carbon fiber sheet. It will crystallize and make the carbon very brittle.

It can have the same effect on certain densities of ABS and Polypropylene.
Not that there is any reason to use locktite on plastic anyways, but if you have to use a bolt through it, and want to locktite the threads, just use a locknut. And when you apply locktite, there shouldn’t be any excess puddling around the bolt anyways. Rubbing just enough on that you can barely see the color in between the threads is enough. There’s no need for a large drop on it.

[chunga]

maybe it something that the orbital sanding had done to it

[cwkoehler]

Nice experiment dude - thanks for the info

Crazing of Polycarbonate by Cyanoacrylates Author(s): Benjamin Seidenberg and E. Mielke Contact: (301) 286-6882 Clear molded parts of Lexan (General Electric polycarbonate plastic) have been observed to develop crazing (small cracks) when exposed to Loctite (cyanoacrylate) compounds used to lock screws in place. In some cases the crazing progressed to eventual fracture of the Lexan part. One such occurrence was the subject of Alert No. GT-A-78-01 dated August 8, 1978. The Loctite compounds are acrylates that cure when air is excluded. Consequently, they may remain fluid for prolonged periods and attack the Lexan if it is under a state of tensile stress. Additionally, an excess of Loctite and slow curing conditions, contribute to the crazing problem. To prevent the crazing problem in Lexan it is recommended that: (1) cyano-acrylate compounds be avoided, (2) solvents other than ethyl or isopropylalcohol and hexane be avoided and (3) the Lexan parts be stress relieved by annealing at an elevated temperature, as recommended by General Electric.

[adam-21]

@cwkoehler

Nice experiment dude - thanks for the info

Thank you for the kind words, and the GE quote. They make Lexan, so that’s as official as it gets.

[italian_guy299]

I finally know for sure

[DCBpower]

I worked at a place that made electronic flash units and we had one customer that repeatedly damaged the equipment and always took it apart to see what happened before sending it in, obviously making it very difficult for us to see what happened. The case was made from ABS but all the screws were in brass inserts. We decided to add some red loctite after this repair and dropped it off at shipping at the end of the day all nicely packed in the box…

The next morning there were circuit boards and black crumbs in the box, the vapors ate the entire housing.