What sort of weight loss can I expect from poly resin in an open mould

[Bango String]

Does anyone have any idea about how much weight is lost by Styrene evaporation during an open mould lay up?

I've picked up data some about loosing 60g/sqm. Any ideas or experience?

Banjo

[gonzo]

It depends on the styrene content of the resin. Figure the percentage of styrene in weight and deduct that from the total weight of resin used in the laminate.

Originally Posted by Bango String

Does anyone have any idea about how much weight is lost by Styrene evaporation during an open mould lay up?

There is no such per m² figure! It depends on the resin you use (how much solid content) and of course on the weight of the layup. A 100gsm roving needs about 100gram of resin where a 320 gsm fabric some 320 gram of (solid) resin sucks.
So, when you have a resin with 60% solid you should calculate that 40% of the dilusive/thinner will evaporate (and should).

Regards
Richard

edited: I should type faster...........gonzo got it already

[Bango String]

Thanks, that answers a lot and would explain my 30% difference between what went in and what came out.

The next question is sometimes the difference is 28% other times it 31%. Assuming that the weight of product is constant. Will anything change the amount of VOC that escapes? Temp, Humidity, air flow over the part? time between hits? or is it a case that 100% of the VOC will always eascape?

[Fanie]

There is a weight reduction when the resin dries out, it is however neglectable. You will have more of a weight problem with your method. Hand layup means you use the same amount of resin as the glass weight, where it is ideal to have a 50% resin to glass weight ratio. Remember the resin does not contribute to strength much, like nothing.

Besides the weight, it is also costing you double the resin.

[gonzo]

The styrene content is not always exact. Are you mixing the resin?

[Fanie]

If you want to save on weight then one method would be vacuum injection. Two reason's I don't like is you use a lot of consumables and there is a chance of the process failing. Whatever you were going to save in terms of the resin the consumables gulp up. The final product however comes out about 25% lighter, since the glass is 1kg vs about 500g resin.

I am currently preparing another method of wetting the glass. I made a glass feeder that rolls the excess resin out, and the idea is to so obtain wetted glass with no excess resin, target ratio glas vs resin is also 2:1.

No consumables other than peel ply needs to be used, and the wetout is continuous, only stopping to put a full glass reel in and filling the resin up. I'm negotiating with the glass weavers to make the glass reels narrower from 1m300 so they handle and apply easier to a width of 650mm.

Originally Posted by gonzo

The styrene content is not always exact. Are you mixing the resin?

Additionally the dilutives, solvents need much longer to come out in thicker layers and low temperatures. In some poor layup you will have styrene vapor after one year! Even some "big brands" have proven that.

[Herman]

Please do remember that most of the styrene will co-cure with the polyester. The tests I have done typically show a 7% weight loss (approx). This is using DCPD resin (low styrene content of some 30-40%, and fast final cure)

Any residual uncured styrene will yellow over time, that is why polyester slowly turns brown. Also, in gelcoats, you can have the same problem, when for some reason the final cure is not achieved.

About cutting rolls of fiberglass: This should not be a problem, using the right equipment. I can direct you to a piece of equipment that works.

[gonzo]

I mean if you are mixing the resin well before taking it out of the container. The solids settle and give you different percentages of styrene