A significant effect of moisture occurs because epoxies (and I assume phenolics) absorb moisture in humid environments. If the resin requires an elevated temperature cure that can lead to porosity as the moisture boils off. Many people think that applying vacuum draws out the steam bubbles, but in reality the low pressure causes the bubbles to expand. The Federal Aviation Administration has an Advisory Circular which sets limits for humidity and temperature for manufacture of composite aircraft parts see Advisory Circular 21-26 para 8a(2) a.
Phenolic resin also creates water and formaldehyde during the curing process which is why bump or burp cycles are ususally used. I have noticed trends with ambient conditions both heat and humidity. I hope this helps.
Hi All.... Thanks for ur reply, currently working in gulf where its summer now, so humidity is too high and vary from time to time....here we r processing phenolic with acid catalyst... In some products we r getting more porosity and in some it was good its not consistant and after curing there are more color differance in the laminates....why so...,
