Bag stack resin absorption – a data point!
So I was working on a video about really basic pre-preg – and making Laminates Sample #2 and #4 at the same time. Because my basement is not a fussy place, I used dry peel ply (crinkly nasty old dry peel ply actually) as the first layer of my consumable stack of sample #2. I removed the peel ply from the already-trimmed (1’x1′) panel and weighed it because I was curious. Then I carefully cut a one square foot dry sample of the same plain nylon peel ply – with the red stripes. I think this is Airtech, but I’m not 100% sure.
The dry sample weighed 10g and the sample that absorbed resin weighed 13g. So: 3g or resin per square foot, about 11 square feet (10.764 you nerds) per square meter. 3 x 11 =33. Now I don’t know if that three on the scale is 2.51g or 3.49g… but it’s a range. (I went back and weighed it again later – see below – and the absorbed resin weighed 5g – probably need to look into that scale!) This means that this peel ply absorbs 30-50g of (this) resin per square meter.
This makes sense if the peel ply is 100-120g per square meter, a 35% resin ratio would be 35-40 extra grams. My mental go-to estimate is 50g per square meter (don’t remember where it came from!) – so it’s nice I’m in a reasonable place given these observations and my questionable measurements. Maybe I’ll try some larger samples and other resins to see if we can science this up a bit!
So if your pre-preg laminate can afford 35g-50g of resin per square meter – go ahead and forget that pre-preg peel ply. And the resin you bleed off – well that’s up to you. But if you use perforated release film (and out of an autoclave, you should) it’ll be something!
Now on to breather. In Laminate Sample #4 – a 3mm QI prepreg panel, I had 4oz breather that was nearly fully saturated. I weighed a square foot of this and at the same time re-weighed the peel ply sample from above. I’m not sure why it (or if it actually!) got heavier, but here’s the new resin estimate for the peel ply (left) and the resin uptake estimate for the breather (right):
Yikes! The breather soaked up 333 grams per square meter of resin. It may have been slightly less, again with the scale giving non-repeatable measurements. But still, that’s a lot! This laminate had a total of 1783g of resin per square meter. The bleed from peel ply and breather was about 375g. That’s about 20% of the resin available in the laminate. The calculated resin ration went from 37% to 32%. I will measure the thickness and weight of the panel when I get it trimmed up and report back.