Water absorption properties of phenolic laminates.

[HeinBau]

Dear reader,

We are currently manufacturing quite large panels for a scientific base from the following materials:

Skins : E-glass/phenolic (Cellobond 2027), 6mm thick
Core : Polyurethane foam, 120mm thick

The sandwhich panels are typically 7m long, 2.4m wide and 120mm thick. They are trimmed along the sides.

The question is what happens to the laminate under prolonged exposure to moisture, especially along the trimmed edges. Will we get any problems of moisture migrating along the fibes. The manufacturing technique employed is a vacuum infusion process. If so, how can we prevent moisture from migrating? Painting exposed cut fibres with resin perhaps?

There is a lot of literature available for polyester laminates, but none for phenolic laminates.

Can anybody help.

Regards
Heinrich

 

[rd78]

Heinrich-

We may have some literature on phenolic laminates that would help. These things are never exactly on point, but provide useful background. Contact me privately and I'll see if we can email something to you. r.doherty@fsengineer.com

Regards
Rick Doherty, PE

 

[Compositepro]

In the long term you will probably get cracking and degradation of the foam. The rate will depend on many environmental factors but the main problems would be temperature and humidity cycling. The foam will try to expand and contract much more than the skins. The cyclic stresses will fatigue the foam and result in what could be called microcracking, a uniform pattern of cracks. But the cracks will not be small in such a large and thick panel. These cracks do not necessarily destroy the structural integrity of your base, however. Minimizing humidity and temperature cycling in magnitude and frequency will help. So sealing the edges will help.

 

[Kiwikid]

I used to build cool rooms and freezers from polystyrene and steel skins some 25+ years ago. Given that these building had to endure 40C+ outside and -10c inside moisture was always a concern. Any moisture penetration meant that it would condense and eventually freeze blowing the panel or a joint.

A good sealant and correct application was always the key to a good moisture barrier.

Almost all the buildings I worked on then are still functioning perfectly today and some were in extreme environments. Do a good job on the seal and moisture will be the least of your worries.

Cheers
Kerry

 

[rnd2]

I can tell you this much. I personally have have phenolic resin re-enforced cotton fibre composites formed under heat and pressure left outside on the ground in the weather and, just like the original stainless steel materials left out to "rust" that after 12 years they are, apart from surface darkening, as good as the day they were made. They do not rot with long term moistuure exposure.
Phenolic resin is one of the most insoluble substances on the planet.

 

[rnd2]

I should have said fully cured phenolic resin.