Bio Composite Flax Fibers!

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#1

Hello everyone!
Lately I’m working with Vacuum bag infusion of Flax fibers, I’m infusing with PE resin. The pieces are small, 35x45 cm.

The layout is basically 5 layers of woven flax, 1 layer of peel ply, spiral tubes of inlet resin and vacuum are wrapped in a bleeder cloth and positioned above a layer of 3 times folded mesh and this mesh is positioned in touch with the fibers… (The picture shows this layout, but instead of the mesh I was using a low density glass fiber… but I found that the mesh works better)

The problem is that the velocity of infusion is really slow and I’m not sure if this is the best layout for it… So if you have any suggestion about it I will appreciate!

Thanks!

#2

What are you using, flax from lineo or brands/mctechnics supplied (selcom I believe)?

Flax from Lineo is great stuff, but I would only use it in wet layup or as prepreg(flaxply)
The sizing isn’t meant for infusion, not enough permeability. The selcom flax can be used for infusing, from what I’ve heard.

#3

Actually I’m using flax from NetComposites, UK.
It is a woven 2x2 (as you can see in the picture)

#4

And you are only depending on the flax for infusion permeability, or do you also have a layer of mesh over the flax? If not, I am not surprised the infusion is slow.

Also, you do use infusion grade resin? (probably, otherwise the infusion would stall after a couple of cms.

#5

I tried with and without mesh over the flax… the problem is that when I tried with the mesh the final composite showed some dry spots (picture). So I was thinking that was because with the mesh it goes faster above and don’t infuse very well under it…

I’m not sure which kind of mesh I have here but is like this one in the picture…

When using the mesh above the flax, it is better to put the spiral inlets above it or under it? Between the peel ply and the mesh?

Thanks!

#6

and yes! I’m using a infusion grade resin… with smaller samples it goes quite ok.

#7

1: why is your resin pooling in the first pic?
2: is that plywood? Is it coated and sealed? If not, that could be a reason for the bubbles in your part.
3: putting the spiral above, or below does not matter, as long as you have the spiral touching the mesh, and the mesh goes across the fabric, and then you have a way for the air/resin to get from the farbic, to the vacuum port (such as a layer of peelply, glass, or breather, touching the part and the vacuum port)
4: if your gel time is long enough, you can not use any mesh, or slightly clamp the resin line to slow the flow down. You can also trim the mesh undersize, to allow the trapped voids to escape, before your part is fully filled.
5: keep your resin bucket BELOW the part!!! (See question 1) This way, the resin will not pool, and trap any air pockets. The resin should be sucked through the fabric, not just dumped into/onto it.

#8

The results in the pic of the cured sheet are typical for too fast mesh, and too little vacuum.

Try getting a better vacuum (needs good vacuum integrity of mould and consumables, and a good pump) and try MTI hose. (you can contact Brands Structural Products in NL or MC Technics in Belgium for that)

For vacuum pumps see www.vacuumsystemen.com

#9

Thanks riff42! I had this resin pool and I didn’t know why, I was keeping the bucket at same level of the part… And it is really a good idea to just clamp a little bit the resin line to slow down the infusion!

About the question 2, no it is not plywood, are just layers of woven flax.

The last part I did, I didnt use any mesh above it, just in the spiral tubes (pic). It is better to put the spiral tubes like a did, or put them directly on the part, in this case above the peel-ply?

thanks

#10

I was using -0.55 BAR, because I was told that with deeper vacuum you can have some gas from the styrene on the resin…

But I think on this case was because of the mesh, so I will try to clamp the resin tube a little bit as was suggested before…

#11

When you asked about the plywood you meant the mould? hahaha, sorry I get it wrong

No above it I have a glass plate :slight_smile:

#12

Go higher on the vacuum. If you have gas, it can usually be directed to either water in the flax (boil it off with a high vacuum) or H2O2 in your peroxide. Use a good quality. Water in the peroxide is also a possibility.

#13

To make sure, you should put the flax fabrics for drying in oven before the infusion. Something like 1h @ 100 degC. Than there will be less water vapor trapped in the laminate.