Adhesion of Silicone to Fiberglass?

What solvents are we talking about?

If the solvent in the process is the same as the solvent in the silicone you haven't got a snowball's chance, matey! That's why silicone sealants are used in domestic bathrooms: the solvent, i.e. WATER, won't touch 'em.

Not that I've had too many baths recently.... Well, not this year, anyway......

Toluene is the solvent.

To err is human.

silicon bathtub caulk has no solvent. It is high viscosity silicone polymer chains with reactive points. It comes as a high voscosity thixotropic paste and water from the air reacts with it, splitting off acetic acid and linking the chains

True. Silicone also has very poor adhesion characteristics. And fiberglass resin, unless it's perfectly mixed, will always have some reactants left over to leach out of the material and cause the silicone to fall off.

The only way I could see this working is to roughen up the fiberglass and then use some sort of barrier layer (e.g. primer) to keep the silicone away from the resin. Even then I wouldn't trust the bond to hold under tension.

To be honest I've never seen silicone adhere to fiberglass. This is why it's never used below the waterline on a boat hull.

I have done this with silicone and metal. Since silicone will not adhere to metal easily as well, we developed a mechanical bond/fastening system. First we machine the metal to have a small T-slot along the length that we want the piece to have a silicone layer. This is then sand blast lightly to make the metal slightly "porous". We then screw or glue metal forms around the prepared area to act as a form. We then pour liquid silicone into the form area and the silicone settles into the T-slots thus making a mechanical bond that the silicone can not delaminate from. I'm sure you could use the same idea with fibreglass and make it thick enough to form in some sort of slot (not necessarily a T-slot) to act as a retaining feature for the silicone.

Just a thought.

How do you get the bubbles out of the T slot, or doens't this seem to matter?

What bubbles? Bubbles in the silicone when pouring?? What do you mean?

Yes, exactly, bubbles in the silicone when it it poured into the T-channel.

Why would it bubble? Are you pouring it from 20 feet above object? I've never had bubbles in the silicone when I poured it into the metal T-slots at a slow, steady rate and a close distance to the T-slots. We even cut a sample cross section to check for porosity. Why the concern??? The process I use is NOT injection molded, just straight pour out of purchased container.

I should add that fiberglass fabric is coated with toluene diluted high consistency silicone. Adhesion is the most important property of this process. I already use silanes but, adhesion needs to be improved.

I think everyone assumed you were asking about cured, resin impregnated fiberglass, not fiberglass fabric. Cloth is the term I am accustomed to seeing. Are we talking abou the same thing?

Anyway, I've never heard of impregnating fiberglass cloth with silicone, What is the purpose if I may ask?

To produce Silicone fabric coated reinforced materials for several industries, such as automotive and aerospace.

Very interesting. I had never heard of that before. Thanks

After years of dealing with "Silicon Seal" caulking products I have come to the conclusion that the only thing silicon sticks to is it's self!

Not Fiberglass.

Not steel.

Not aluminum.

Not glass.

Not wood.

Not stone.

"Silicon Seal" is an oxymoron!

I have feared adding my 2 cents for the resulting onslaught of response I would not have time to read.

But, as I understand it; silicone is to be used as an adhesive to similar (rubberized) materials and to most (all) else it is simply a sealant.

cr3

what kind of silicone are you using? Sealant, rubber, ??

High consistency silicone peroxide cure system.

I gather the silicon does not impregnate the fiberglass cloth in the same way that resin does? I also gather that the silicon cannot penetrate the weave sufficiently from both sides to keep it from delaminating? Is that the crux of the problem?

Yes, that could be the problem.

What else might be the problem?

Some components of fiberglass like amines as treatment that inhibit adhesion.

I'm going to take a wild guess that you have researched this pretty well already and came to this group as a last resort. Being that I now understand more fully the problem and don't have any answers I will not take up any more of your time. However it has been interesting. thanks

PS I love conversing with professionals. So often they seem to know what they are talking about even if I don't have a clue and it is always enlightening

Thanks for your comments.

At first i thought "who is this idiot, trying to get silicone to stick to silicone fibres?" fibre glass cloth being just that, fine threads of silicone glass. having read above however you have an interesting problem. My second thought was making the silicon rubber stick to fibreglass sheet such as in a boat. That process depends on whether the resin is polyester or not. One type, I forget which, drys in air, the other won't set in air, consequently they add a wax to the resin whcih rises to the surface, excluding air and allowing teh resin to set. Thats why you cant stick broken buckets back together, the wax is in the way!

Have you tried the paint on sealing 'rubbers' used for bathroom showers? they stick like glue to anything and can be made very runny to soak into your fibreglass cloth. setting time is also rather quick plus they have good stand alone strenth. i believe these are a silicone formulation. If you do try them, the tools are throw aways and the can will develop quite a thick skin, like one or two inches, if you don't finish it off.

I think you should talk to some one at Dow we use a silicone sealant and it sticks to everything. Real pain to get apart. Use it to seal vinyl to glass.

I will try. Thanks for your comments.

Are you talking about fiberglass cloth, or about a fiberglass reinforced plastic. If plastic, what plastic is it? Is it Polyester, Phenolic, Epoxy, etc.?

We're talking about fiberglass cloth reinforced high consistency silicone peroxide system.

In the land of the blind the one eyed man is king.

Much of the solution to your problem will come from your material fabricating process. More to the point: consider using a calendering process to impregnate the silicone compound into the fiberglass reinforcement material (IE: fiberglass cloth, mat, woven roving, etc.) . During the calendering process you will need to run release films over the two primary drums to keep the silicone from sticking to the roller drums. The release films (IE: coated Mylar) will be used to draw the laminate through additional dimensioning rollers and ultimately through curing platens. This will result in a continuous roll of fiberglass reinforced silicone matting/cloth. It is very important however to use only "chromed" fiberglass fabric or cloth to ensure thorough bonding. Chrome finished cloths such as such as Volan A, F-16 and F-3 are heat cleaned fiberglass fabrics that are saturated in a methacrylate chromic chloride solution, cured, and washed to remove any soluble salts that were residues left from the fiberglass manufacturing process. This should aid greatly in the bonding efficiency of the silicone to the fiberglass fibers.

I hope this puts you on a path to your overall solution, however to offer any further time or information you would need to put me on your payroll. Unfortunately, I have already retired. Best of luck and I wish you great success.

Thank you so much for your advice. I will try and see what kind of results are obtained.

I found a probable solution to this problem; Maleic Anhydride will improve adhesion tremendously but the problem is how to process it without producing the fumes which are extremelly irritant to eyes and respiratory system. Is there a similar chemical with same kind of reactivity?

1. controlling to machine rpm and full curing of heat

2. you may add in adhesive highly effective tackifer compound

Would you suggest one?