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Marco Todeschini
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+x+x+x+x+x+xCan also confirm I have experienced this issue when playing around with these natural reinforcements. I never really gave it much thought as generally I put it down to being a different batch of reinforcement, and to be honest I like both colours, so I probably can't help much. But I would say it has nothing to do with the fibre wet-out or void content of wet-laid vs infused - I always infused. And still had the same random colour variance. I do feel it is going to have something to do with the moisture content of the fibre, as that could change layup to layup depending on the weather conditions. But it isn't really a classic 'symptom' of moisture issues. Hello Hanaldo, thank you very much for sharing your experience. I hate to look very self assured (I never am, especially with things I don't understand), but beyond a reasonable doubt ALL the samples I have done with hand-layups are light. Yesterday I did an experiment to test the incidence of temperature and moisture during the infusion. I tried to keep the mold warm, about 27 ° C, during the infusion. I was afraid that the resin, in contact with the cold mold, would take too long to cure and therefore would have a long time to penetrate deeper into the fabric. Unfortunately, even though I noticed the curing time speed up, the result remained dark. I also tried to leave the jute in a box at 35 ° C for a couple of hours, and then let the pump run for a long time before starting the infusion ... but nothing to do. I also store the pre-cut pieces of jute I use in a box with many of those tiny silica bags that come with shippings, hoping to help reduce moisture. All the dark and light parts are made with the pieces from the same box, coming form the same roll. In the answer above to Chris I saw a close correlation with the thickness (and therefore the compression) of the laminate. I will continue to investigate and I'll let you know! Thank you Hi Marco, why don't you try a different brand of infusion epoxy? Just ti be sure there is not anything in the super sap that, under full vacuum, interacts with the jute. I dont think this will be it. I was using a completely different resin on the other side of the world and I still experienced these variances. That said, at this point we sort of have no idea where to start - so this is as good a place as any. I do hope we can get to the bottom of it, I'm very intrigued now! Doing some research I found this https://www.slideshare.net/mobile/Farhanullahbaig/jute-fiber-71021585According to the article, the core of a single jute fiber is air. Please see attached pics from the article. It could therefore be that, under very high vacuum, the core of every single fiber will be filled with resin which is not happening in wet layup at lower vacuum. If my theory is right, an infusion at lower vacuum is worth trying. The article also says (par. 19) that the fiber is also sensitive to chemical agents, so trying with another resin is something I would do too.   All very interesting, however both myself and Marco have experienced the variations from an infusion result. It's not like hand layup = light coloured and infusion = dark coloured, it changes. Which would indicate that at least sometimes, the high vacuum level is not an issue. I wonder if perhaps there is another influence that means that hollow fibre in some situation is 'sealed' and doesn't get wet out, and in other situations it is open and does allow full wet out. Thing that gets me is, the colour difference is drastic. Which makes me feel like it has to be more than just the fibre wet out. If the fibres fully wet out appear as the dark colour, then surely for the fibres to appear SO much lighter when not fully wet out then it would be very noticeable in other ways as well, eg. noticeably dry fibres in a cross-sectional cut, or differences in strength between the two laminates. I don't see how that microscopic channel of air through the middle of the single fibre could possibly make such a massive difference to the colour. Thank you Massimiliano, it's very interesting! I knew that the hemp was hollow inside, but I didn't know the jute was too! Hanaldo I think it makes sense, even if the channel is microscopic: I'm much more experienced in woodworking than in composites and I can tell you that there is a drastic difference in color between woods finished with finishes that soak the grain in depth (like oil based ones) and woods finished with finishes that penetrate less deep. In both cases "deep" and "less deep" refear to microscopic measures. I think it could work in a similar way. Anyway: new day, new experiment, new failure  : yestarday I tried to come back to the good old disposable vaccum bag (the last experiments were all done with silicone bags). The infusion came very badly, probably a leak at the entrance of the resin, BUT something interesting happened: all around the part damaged by the bubbles the color is light. In that area a bridge was formed, where the air from the leak was then collected, which perhaps compressed the laminate less (returning to the thesis of less compression = lighter color).  I absolutely have to do a test by adjusting the vacuum level: 1) Do you have any advice on the lowest (but working) vacuum level to keep? 2) In my limitate experience I've always heard that infusion needs the absolute absence of leaks to work. The vacuum regulator works by entering a small controlled leak, right? How do the 2 things get along? Thank you all for your precious help!
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Massimiliano
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Group: Forum Members
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+x+x+x+x+x+x+xCan also confirm I have experienced this issue when playing around with these natural reinforcements. I never really gave it much thought as generally I put it down to being a different batch of reinforcement, and to be honest I like both colours, so I probably can't help much. But I would say it has nothing to do with the fibre wet-out or void content of wet-laid vs infused - I always infused. And still had the same random colour variance. I do feel it is going to have something to do with the moisture content of the fibre, as that could change layup to layup depending on the weather conditions. But it isn't really a classic 'symptom' of moisture issues. Hello Hanaldo, thank you very much for sharing your experience. I hate to look very self assured (I never am, especially with things I don't understand), but beyond a reasonable doubt ALL the samples I have done with hand-layups are light. Yesterday I did an experiment to test the incidence of temperature and moisture during the infusion. I tried to keep the mold warm, about 27 ° C, during the infusion. I was afraid that the resin, in contact with the cold mold, would take too long to cure and therefore would have a long time to penetrate deeper into the fabric. Unfortunately, even though I noticed the curing time speed up, the result remained dark. I also tried to leave the jute in a box at 35 ° C for a couple of hours, and then let the pump run for a long time before starting the infusion ... but nothing to do. I also store the pre-cut pieces of jute I use in a box with many of those tiny silica bags that come with shippings, hoping to help reduce moisture. All the dark and light parts are made with the pieces from the same box, coming form the same roll. In the answer above to Chris I saw a close correlation with the thickness (and therefore the compression) of the laminate. I will continue to investigate and I'll let you know! Thank you Hi Marco, why don't you try a different brand of infusion epoxy? Just ti be sure there is not anything in the super sap that, under full vacuum, interacts with the jute. I dont think this will be it. I was using a completely different resin on the other side of the world and I still experienced these variances. That said, at this point we sort of have no idea where to start - so this is as good a place as any. I do hope we can get to the bottom of it, I'm very intrigued now! Doing some research I found this https://www.slideshare.net/mobile/Farhanullahbaig/jute-fiber-71021585According to the article, the core of a single jute fiber is air. Please see attached pics from the article. It could therefore be that, under very high vacuum, the core of every single fiber will be filled with resin which is not happening in wet layup at lower vacuum. If my theory is right, an infusion at lower vacuum is worth trying. The article also says (par. 19) that the fiber is also sensitive to chemical agents, so trying with another resin is something I would do too. All very interesting, however both myself and Marco have experienced the variations from an infusion result. It's not like hand layup = light coloured and infusion = dark coloured, it changes. Which would indicate that at least sometimes, the high vacuum level is not an issue. I wonder if perhaps there is another influence that means that hollow fibre in some situation is 'sealed' and doesn't get wet out, and in other situations it is open and does allow full wet out. Thing that gets me is, the colour difference is drastic. Which makes me feel like it has to be more than just the fibre wet out. If the fibres fully wet out appear as the dark colour, then surely for the fibres to appear SO much lighter when not fully wet out then it would be very noticeable in other ways as well, eg. noticeably dry fibres in a cross-sectional cut, or differences in strength between the two laminates. I don't see how that microscopic channel of air through the middle of the single fibre could possibly make such a massive difference to the colour. Thank you Massimiliano, it's very interesting! I knew that the hemp was hollow inside, but I didn't know the jute was too! Hanaldo I think it makes sense, even if the channel is microscopic: I'm much more experienced in woodworking than in composites and I can tell you that there is a drastic difference in color between woods finished with finishes that soak the grain in depth (like oil based ones) and woods finished with finishes that penetrate less deep. In both cases "deep" and "less deep" refear to microscopic measures. I think it could work in a similar way. Anyway: new day, new experiment, new failure : yestarday I tried to come back to the good old disposable vaccum bag (the last experiments were all done with silicone bags). The infusion came very badly, probably a leak at the entrance of the resin, BUT something interesting happened: all around the part damaged by the bubbles the color is light. In that area a bridge was formed, where the air from the leak was then collected, which perhaps compressed the laminate less (returning to the thesis of less compression = lighter color). I absolutely have to do a test by adjusting the vacuum level: 1) Do you have any advice on the lowest (but working) vacuum level to keep? 2) In my limitate experience I've always heard that infusion needs the absolute absence of leaks to work. The vacuum regulator works by entering a small controlled leak, right? How do the 2 things get along? Thank you all for your precious help! I have at work a 1000x microscope, if you like send me two small samples of light and dark result and I will be able to check if the channels are full in the dark sample and light in the light sample. If you are interested, send me your details by pm so I can contact you.
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Hanaldo
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Group: Forum Members
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+xHanaldo I think it makes sense, even if the channel is microscopic: I'm much more experienced in woodworking than in composites and I can tell you that there is a drastic difference in color between woods finished with finishes that soak the grain in depth (like oil based ones) and woods finished with finishes that penetrate less deep. In both cases "deep" and "less deep" refear to microscopic measures. I think it could work in a similar way. Anyway: new day, new experiment, new failure : yestarday I tried to come back to the good old disposable vaccum bag (the last experiments were all done with silicone bags). The infusion came very badly, probably a leak at the entrance of the resin, BUT something interesting happened: all around the part damaged by the bubbles the color is light. In that area a bridge was formed, where the air from the leak was then collected, which perhaps compressed the laminate less (returning to the thesis of less compression = lighter color). I absolutely have to do a test by adjusting the vacuum level: 1) Do you have any advice on the lowest (but working) vacuum level to keep? 2) In my limitate experience I've always heard that infusion needs the absolute absence of leaks to work. The vacuum regulator works by entering a small controlled leak, right? How do the 2 things get along? Sure, but composites lamination is very different to coating wood, even if the natural fibres have similarities. What we are really suggesting here is that the fibres do not wet out properly when hand laminating. That has massive consequences on the finished laminate, not just colour difference. Do you notice any differences otherwise; does it feel a bit dry to cut, is it a bit lightweight, is it flimsier than the infused panels? I think it is important to understand that hand lamination, unless done very poorly, doesn't effect how wet out the fibres are. A hand lamination resin will have very good fibre penetration, and unless you go very lean and don't apply enough resin then it will wet out the fibres. The only difference should be in void content and fibre consolidation, a hand laminated panel will include significantly more air in the layup than an infused panel and the fibres should be pressed tighter together with less space for resin (and voids) between the fibres. The actual centre of the fibre itself, if that can be wet out when infused then it should also be wet out when wet-laid. I feel the fibre compaction is the more likely explanation. Theoretically the infused laminates should have a higher density per cubic mm than the hand laid laminates. Less space for resin and voids would also mean less space for light refraction I would think. The caveat - we are still kind of ignoring the fact we have both had lighter coloured results from infusion. Perhaps hand laminated seems to always result in a light coloured part, but infused does not always result in a dark coloured part. So what changes between those samples? If I had a bit more time I would do some experiments myself. Maybe on the weekend I will get a chance.
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Marco Todeschini
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Group: Forum Members
Posts: 7,
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+x+xHanaldo I think it makes sense, even if the channel is microscopic: I'm much more experienced in woodworking than in composites and I can tell you that there is a drastic difference in color between woods finished with finishes that soak the grain in depth (like oil based ones) and woods finished with finishes that penetrate less deep. In both cases "deep" and "less deep" refear to microscopic measures. I think it could work in a similar way. Anyway: new day, new experiment, new failure : yestarday I tried to come back to the good old disposable vaccum bag (the last experiments were all done with silicone bags). The infusion came very badly, probably a leak at the entrance of the resin, BUT something interesting happened: all around the part damaged by the bubbles the color is light. In that area a bridge was formed, where the air from the leak was then collected, which perhaps compressed the laminate less (returning to the thesis of less compression = lighter color). I absolutely have to do a test by adjusting the vacuum level: 1) Do you have any advice on the lowest (but working) vacuum level to keep? 2) In my limitate experience I've always heard that infusion needs the absolute absence of leaks to work. The vacuum regulator works by entering a small controlled leak, right? How do the 2 things get along? Sure, but composites lamination is very different to coating wood, even if the natural fibres have similarities. What we are really suggesting here is that the fibres do not wet out properly when hand laminating. That has massive consequences on the finished laminate, not just colour difference. Do you notice any differences otherwise; does it feel a bit dry to cut, is it a bit lightweight, is it flimsier than the infused panels? I think it is important to understand that hand lamination, unless done very poorly, doesn't effect how wet out the fibres are. A hand lamination resin will have very good fibre penetration, and unless you go very lean and don't apply enough resin then it will wet out the fibres. The only difference should be in void content and fibre consolidation, a hand laminated panel will include significantly more air in the layup than an infused panel and the fibres should be pressed tighter together with less space for resin (and voids) between the fibres. The actual centre of the fibre itself, if that can be wet out when infused then it should also be wet out when wet-laid. I feel the fibre compaction is the more likely explanation. Theoretically the infused laminates should have a higher density per cubic mm than the hand laid laminates. Less space for resin and voids would also mean less space for light refraction I would think. The caveat - we are still kind of ignoring the fact we have both had lighter coloured results from infusion. Perhaps hand laminated seems to always result in a light coloured part, but infused does not always result in a dark coloured part. So what changes between those samples? If I had a bit more time I would do some experiments myself. Maybe on the weekend I will get a chance. Thank you Hanaldo, you clarified my ideas about hand lamination quite a lot. Actually I can't find any big structural differences between dark and light laminates, and as you say, any resin lack should have significant negative effects... I tried to make an infusion to 0.6 vacuum: it was a failure because the resin was too slow and started curing during it, but at least it seems to show that lower vacuum level>>less compression of the fibres>>lighter color. (you can see it in the center).  I would like to ask if your infusions with different darkness were made with the same vacuum level. I'm afraid that, even with the same vacuum level, this problem can occur just for a different arrangment of flow mesh, peelply, etc ... that makes the bag more prone to push against the jute. (this would explain the reason of the color changes BEFORE I bought the vacuum regulator) For this reason I'd like to understand the logic and then apply it to a reusable silicone vacuum bag. (about silicone bags, I will try to make one with a larger offset and a higher shore value, so that it is more difficult to it to push against the jute)
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Hanaldo
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Yeh I always infuse at full vacuum, Ive never reduced the vacuum level other than maybe letting a bit more resin in on cosmetic components. So I was getting variations even at full vacuum with full consolidation and the same resin.
So I still feel something is changing layup to layup. But I never tried to figure out what that was. So if you are saying the peel ply and mesh layup changes things, I could probably see that. The bagging stack can influence the consolidation level. Perhaps it is worth putting a layer of breather cloth in as well? It will absolutely waste a bulk of resin, but it would reduce the fibre compaction too.
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