[walter]

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"Coupling agents are used to provide a stable bond between two otherwise nonbonding and incompatible surfaces. In reinforced and filled plastics, the improved bond between the fibrous or particulate inorganic component and the organic matrix polymer results in greater composite strength and longer service life.
Silane coupling agents are often used to treat silica (both fumed and precipitated) treatment with great effectiveness in filled polymer systems. The silane treatment can improve processing, performance, and durability of silica-modifed product by:
* Improving adhesion between the silica and the polymer
* Improving wet-out of the silica by the polymer
* Improving dispersion of the silica in the polymer
* Improving electrical properties
* Increasing mechanical properties
* Reducing viscosity of the silica/polymer mix.."


Someone suggested just washing the aggregate in 91% Isoprolyl wound wash solution (and not messing with toxic chemicals). I tested the Isopropyl idea, and it works. I bought a bottle at Walgreen's, poured into the container and thoroughly wetted the aggregate. 7 days later it was used in a mix. Jig test shows 10% performance increase (which makes me even more inclined to use real coupling agent!)


Don't mind the pictures, poor surface finish is due to my sloppy work. I developed affection for careless, sloppy joe mixes where I just dump things into container, mix vigorously for 3 minutes then dump it into the mold :nono: No vibrocompaction either... But these mixes are as strong as my "1ksi" mix from post #1597, so why not. Top surface picture shows "peanut butter" effect, not sure if it's good or bad, I'll talk about it in a moment.

Now, there's something special about this particular mix. It's brutal (and not plasticky), with tough surface and awesome awesome sound - it really gives me chills. Like metal but without the ringing. And I'm not talking about alcohol "treatment", that has nothing to do with it. The mix itself is interesting and I would love to see it on my machine. No, I want to see it on my machine - I am not kidding. So here's the plan:


1. Start work on the mold; plan on attaching a decent vibrating motor or two. Vibrating will take care of the voids and surface finish - I don't think I would recommend going without it.

2. Use some kind of coupling agent, either BYK C-8000 or Cameron's Dow product. These things alone should be good for 10-40% in strength improvement. (Not that I really need it, I can already kill an elephant).

3. Figure out the peanut butter thing. Or just use vacuum..


The peanut butter thing is probably due to (improper) use of small aggregate. What it does it basically creates peanut butter like consistency and reduces flow. It's different from honey effect -you dump it on the surface and it just stays there. It looks puffy and lightweight, and not very serious. It does not reduce strength so it's no big deal, just a little annoyance. It may require vacuum though.
My smallest aggregate was in 0.05-0.12mm range and I read that you shouldn't just dump these tiny particles into the mix- some are using special blenders to control the process, it's some kind of rocket science. Whatever

Ok, here's the mix:

16% Epoxy
64% Quartz Aggregate
20% Zeeospheres

I mixed the epoxy with hardener, left in the pot for 10min, then added random pile of aggregate, 5 different sizes from 0.05mm to15mm (pictured below). I dumped it into the epoxy, all at once (I know you shouldn't do that). Good mixing ensued and finally Zeeospheres were added. These things are pure magic and I don't recommend going without it.

I immediately realized I had dialed the wrong "number"- my epoxy disappeared and there was not enough to wet the mix! I felt pretty stupid, but continued on with the mixing. Then, surprise.. My mix turned into cool flowy slurry. And then into peanut butter.

Conclusion: I should probably change my mixing "technique" and work on the air voids.. But the point is, I totally like the results. I would be thrilled to have it on my machine!
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