Effect of humidity during laminating

[AndrewK]

Have not been able to get any further with this so did my own qualitative test.
Onto a glass laminate I laminated a set of glass strips, one side when the humidity was 55% and on the reverse side when the RH was 85%.
After curing at the same time simply pulled each tab away from the base laminate.
There were only 3 sets of tabs but in each case the 85% RH laminations failed.
Unfortunately still dont know how much weaker the 85% RH laminates were relative to the 55% RH ones.
So would still like to see research data if anyone can help.

[Herman]

Good info. Exact measurements can only be done with some equipment. There has been a design for a bending tester in PBB. One of my customers built it, and did quite some testing (do not have the data).

One of those testers is still on my wish list....

Thank you, Andrew, for your diligence. I'm hoping you can give a little more detail - test method and the difference (failure versus non failure) between the 55 and 85 test pieces.

[AndrewK]

fg1inc, my test was a very simple qualitative one, basically an interlamina peel strength.
I used an off cut glass laminate as a base, one edge I covered with packaging tape on both sides so that I could get my thumb under the strips and start the peel by pulling against each other.
The strips were 25mm wide 2 x 750gsm triaxial glass, I had 3 pairs aligned on either side of the base laminate. One side was laminated when the RH was at 55% and the other later on that evening when the RH reached 85%, surface temperature was still 20'C at this stage and above dew point.
The strips were pulled apart from each other until the weaker of the two failed.
In all three cases the 85%RH laminations failed first, these had peeled approx 30mm before the laminate failed by buckling. Failure was delamination at the first and second layer of the test strip, ie a layer of glass was stuck to the base laminate. The 55%RH side only peeled 3,5 & 8 mm by comparison.

I guess the next thing to try is as I proposed earlier by comparing test laminates laminated at low RH against opposite partners where the glass was impregnated at a low RH but laminated on to the base laminate at high RH.
ie the impregnating tent proposal.

Andrew

Thanks again Andrew, very interesting. Was the cure time different for the 2 samples?
Here in south florida we rarely see RH below 90%. I've only been in the fiberglass business for 45 years so i still have a lot to learn!!
About 25 years ago we switched all repair work from poly to epoxy and the tech types we spoke to said that epoxy was less affected by humidity than poly.

There are systems on the market adressing exactly this problem. One can buy formulations allowing for more than 80% rel. humidity, just ask your formulator (not the supplier).

Regards
Richard

[AndrewK]

You can not conclude too much from the test but it does support the literature I have read and the DNV and Australian Standard requirement that the RH is not to exceed 80% during lamination.
As I understand it the issue here is not due to epoxy and type of curing agent used but matrix reinforcement filament coupling regardless of resin type used.
I do get my resin from the formulator, they have a good range of curing agents including non blushing but still recommend a more stringent 70% RH max.

The cure schedule was not identical, the 55%RH strips had 6 hors longer cure at ambient temp, 24hrs versus 18 but this should not be an issue as I post cured for 12hrs at 70'C.

I do agree that plenty of good boats get built in high humidity locations and survive the test of time.