Nylon Bonding Failure

[falls]

Hi Everyone. After 11 successful pairs I have had my first major problem.
I had some topsheets done my Miller studio on white nylon abraded and treated for bonding.
In layup last night things seemed to go pretty well and the skis appear to have cured and held shape, however this morning I noticed that the edges of nylon topsheet didn't seem well bonded and the whole topsheet just peeled off like a peel ply. Not even a few spots of adhesion.

Parameters:
Room temp cure epoxy - under pressure 50psi for 12 hours
Heater running and ambient temp in room 18C
Propane torch flame treatment prior to layup (have never done this before)
Mix ratios good, mixing good. Upper glass layer perhaps slightly low epoxy, but not greatly.
Nylon bond surface appeared clean

Problems?:
Major one is that after peeling the nylon topsheet there are large white areas where the epoxy surface has gone powdery (can pick it up on your finger). This powder can be seen on the under side of the nylon also.

Top glass layer

Powdery residue


Theories:
Number one is that lower ambient temp and probably high humidity (winter - temp dropping late in day rapidly) led to amine blush forming between the glass layer and the nylon = no bonding. Even though room temp was 18C the heat sink of aluminium cat track etc maybe meant top layer was much colder (?) and this slowed curing. Also enclosed room to hold heat prob held CO2 also and this helps create amine blush.

Number two. Nylon just poorly adherent. Either factory treatment worn off during shipment and handling, or my effort at flame treatment actually ruined the flame treatment. Residue from flame acted as a release agent?

Number three - my epoxy system is not compatible with nylon even when abraded and flamed.

Number 4 - deficient epoxy volume. Upper glass layer was wet but could have been wetter probably. I just laid the topsheet plastic on this glass layer rather than wetting the underside of the topsheet (I know some people do wet the underside of the nylon). I don't think this would have led to complete failure to bond however.

Any help appreciated as I have a few more nylon topsheets on hand that I am too nervous to use now.

[MontuckyMadman]

The way I underwtand is that it is a mechanical bond. There no non compatible.
The only time this nylon doent stick is either not enough resain put on or it squeezed out.
Powdery redidu is bad.
Resin has either gone bad, wasn't mixed sufficiently either prior to dispencing or wh n mixed togwther.
Other powdery systems we h ave seen are do to incorrect ratios. Ie too much hardner.
My two cents.

[falls]

Thanks montucky.
Could be insufficient resin. Do you usually wet the underside of the topsheet?
And just to confirm you have used the abraded nylon not the fleece backed stuff?
Could be right about not mixing the resin prior to pouring from the container. I meant to do this but forgot. I think when sitting a while some resins undergo a phase separation which if not remixed would alter the chemical reaction components available.
It is a bit weird that where the glass drapes away from the core it all looks normal, but it is only where the topsheet was resting on the epoxy that it looks powdery/abnormal.

I need to run some bonding tests, which I should have done before.

[MontuckyMadman]

I skim coat eveything in a wet layup.
Yes I have used all the products. Abraded nylon, fleece backed, uhmw topsheet, tpu and pbt.
The only time the nylon peeled off like that was not enough resin or a completly non compatible substance like pe films and foils.
If you are useing the entropy it will seprate and you have to get it all in suspention again before applying.
I have been putting it in the microwave. Might not be a good idea but its a shit load quicker than a hot water bath and haven't had any problems.

[MontuckyMadman]

On second thought, that powder may just be what little bit of resin you have left.
I thought you had a bottom blanket?
Your glass looks over saturated at the edges. I think you pressed it all out.
What's your fiber to resin ratio roughly? Less than 30% resin?
It all looks dry from several thousend miles away.
Some controllers and blankets will change your results greatly.

[gozaimaas]

Your glass looks over saturated at the edges. I think you pressed it all out.
.

I thought the same thing. So much resin so far away from the core.
Did you wet the fibreglass right to the edge like that or was it dry and soaked up resin?

[falls]

Wet the glass out all the way to the edge on separate table. The squeeze out hasn't made the glass more noticeably wet than when it went in. In the pictures the excess glass you see is the lower and upper layers sitting on each other as the excess that is wider than the ski (a fair bit wider). The epoxy you see at the edges of the core I think has definitely been squeezed out.
I agree there looks to be a good amount of resin dumped at the edge of the core.
You can see some VDS that I laid on the edges of the core has squeezed out off the edge too.
The resin was pretty viscous with lower temp. Perhaps this led to pressure sludging it out to the sides and 5 hour cure leaves a long time for squeeze out.
I can see a few spots on top where there are strands of glass lifting up.

The powderiness I can't understand. But insufficient resin/too much squeeze out seems to be firming up as cause of no bonding.

I put water on the bonding sides of the other nylon topsheets and it seems to bead together rather than sheet.

[falls]

Montucky.
I have a blanket. Was doing top heat but started getting annoyed with camber irregularities with this single side heat. Reverted to room temp epoxy.

1 piece of triax I use weighs about 250g and we usually wet out with 250g of mixed resin/hardener.

How does heat cure change squeeze out? Cures more quickly = less time for squeeze out?

[vinman]

I'd say depends on how hot things get. The resin will be less viscous when hot and squeeze out faster initially then once it gels up will slow down or stop.

As you say 5 hrs is a long time for squeeze out but some guys go 24 hrs under pressure. What is the gel time on your resin?

How do you measure your resin?

Could the nylon have been dirty or contaminated in any way?

[falls]

Resin gets weighed on digital scale that reads to the gram.
Splashes of epoxy pretty firm after 3 hours. Suggested cure 5 hours at 25C. They got pressed for 12+ hours.
Stats say thin laminate open time is 2 hours. I'd say this is about right.
Tops were fresh out of a USPS box from miller. I did flame them with a propane flame so could have been soot? But didn't visualise any discolouration or other contamination.

I think squeeze out the likely cause. It's just I would have thought I should have got at least a small amount of adhesion.

I think I can sand and repress with a wood veneer. Just a bit worried about the strength of the upper glass layer. And disappointed because I had the topsheets done for a friend.

[vinman]

Hmmm. Head scratcher for sure.

Do you think your glass is too dry as well?

[falls]

yeah I think realistically it looks too dry.
The first picture makes it look pretty bad. The white areas however on the R ski are a powdery deposit on the surface of the glass/resin.

Squeeze out def involved, but maybe the epoxy did something weird too.

I will try and find some time to do some test bonds with the epoxy, glass and nylon to see if I can get it to stick

[Richuk]

Fall, it looks like Amine blush. Flow shouldn't really be an issue at 50 psi - subject to viscosity. The view of the tip/tail section suggests the new epoxy is reasonably comparable, as it hasn't flooded out of the cassette.

The movement of the VDS is more to do with excess resin ... could be dispersal within the fabric prior to pressing or a low pressure point allowing the resin to pool, flow and carry the VDS.

If you're around 60/40 resin fibre ratio, the fibre won't be dry. The cure/blush may be giving you a false positive. Hope the tests go well - it might be worth giving the supplier a call.

[falls]

Thanks Rich
I did email the epoxy supplier and this was the reply

Hi Tim,

Sorry to hear you've had some problems. I think the issue relates to the nylon, as its not recommended to bond with epoxy. Most of the base surfaces on skis and boards like this I have seen have a fabric melted half into the plastic, with the other half of the fabric like a fur and proud to allow bonding. The bases I have seen bonded with epoxy have been polyethylene (p-tex) which responds to flame treatment. I don't believe nylon responds to flame treatment for any bonding applications.

I'm pretty sure the powdery layer will be residual nylon.

There could be bloom on the surface but it would be a low probability. Ideally just before pressing, the wet-out fabric should be agitated with a roller to disturb the surface. Bloom is at its worst in cool, moist conditions with excess CO2.

My recommendation is to run with polyethylene and not use nylon. If you'd like to persist with the nylon, I can see it being a problem - the only option would be a very coarse sand, which essentially increases the bonding area. Even this may not be satisfactory. Sanding to an 80 grit finish on the fibreglass and then rebonding will be fine.

I hope this information assists.

Kind regards

[falls]

I did a bonding test last night
Resin doesn't appear to show any sign of crystallisation.
Resin cured satisfactorily.
Method was wetting a piece of glass out fully then placing topsheet pieces on the glass and clamping between 2 sheets of MDF with clamps and some heavy books on top.
Left heater on overnight. Seemed to cure free epoxy fine so don't think temp was a problem.

Used pieces of the topsheet that didn't bond and some pieces of a new topsheet. Some pieces I applied epoxy to the bonding side and some I didn't (like when I did the layup).

Looked OK when removed from pressing


Levered corners up with a screwdriver as some epoxy had flooded over the top at the edges.

Once levered up all pieces peeled again with very little adhesion.
No epoxy or glass fibres evident on the bonding side of the nylon. Looks like before it was laid up.

Peeled off the glass (white areas where have chipped with screwdriver)


Bonding side of nylon


All these pieces were flame treated with propane torch so it is possible the propane torch is leaving a residue or my technique is no good.
Peeling of topsheet can be done just with gentle pulling. No need to wedge the screwdriver in to pull it off.

Probably should do another test without any flaming.