Infusing flax

[Eric ruttan]

Rob- Here is the material property of the flax and other fibers. If you look at the comparison you will notice that flax strength is lower than glass. That means if you want a better composite laminate, the outside layer should be glass and the inner layer flax. Much like putting CSM sandwiched by WR.

I could not find the shear properties of flax. If I can find it, I will be able to determine how thick the proportions will be.

https://library.ndsu.edu/ir/bitstre...forced Composites.pdf?sequence=3&isAllowed=yy

Suggests between 2.4 and 3.4 GPa.

Infusion resins, both epoxy and polyester don't typically have a thixitrope (silica) added, there's no need for it, it will inhibit the actual infusion process.

Hand laminating resins do have thixitropes, but they don't work nearly as well in epoxy.

Who said anything about adding?

 

[ondarvr]

Since the flax stack was thicker, and the the flax for equivalent volume is lighter, the total amount of resin was probably higher.

Plus, without knowing more details, the fiber diameter of the flax is probably greater than the glass. This leaves larger areas of resin between each fiber, which can generate more heat.

The 2 degree difference
can be accounted for in the difference in the mix ratios of two separate batches. And if it was one batch, the top and bottom half of the resin in the container can yield different gel times due incomplete mixing.

We do testing on gel times to determine the amount of time required for complete mixing.

The amount of time the resin sits in the bucket prior to infusing can also affect the peak exotherm.

And in reality, 2 degrees is well within the margin of error.

 

[gonzo]

The amount of fibers can be found by the science of circle packing. If the fibers are all the same diameter, the maximum packing will be about 90%. However, if the fibers have different diameters the packing can be higher. I think that fiberglass is probably more consistent than a natural fiber on diameter size and would have a lower packing. It would not be hard to test though.

 

[ondarvr]

Yes, but the fiber diameter comes into play. The glass is well know and comparatively consistent. Natural fibers tend to be overall much larger, and inconsistent.

Tending to be larger overall is where the voids are created.

The fiber bundles of glass are packed tightly and each fiber is straight and parallel to every other fiber.

Natural fibers don't tend to be as straight or packed as tightly.

 

[Dejay]

Thanks for sharing your tests Rob, quite interesting. So this Hermes Flax seems quite competitive to glass, ignoring the large variability.

But is there any ecological benefit? Without a biodegradable resin or with mixed in glass you don't have biodegradable waste in the end. And if it were biodegradable it could rot and would also not be a carbon sink. It seems the only thing you could do with a flax composite is burn it and capture and sequester the carbon. Wouldn't that be better than biodegradable materials?

It also seems fiberglass could be recycled or downcycled more easily. And be easier or more practical to produce with near zero carbon costs since you can make it at one location and only need a sustainable energy source (e.g. solar, nuclear).

One advantage could be that flax is more low tech and you can grow and process it on an island or anywhere without having to import it from one country. But you still need high tech resin.

The most sustainable and recyclable material right now seem to be self-reinforcing thermoplastic composites. But I think not competitive for boats (and unfashionable at the moment).

The perfect "sci-fi" solution I can imagine would be some sort of CompositeGrow(tm). Just spray some growth medium and some sort of genetically engineered microorganism or fungus into a mold and it creates the perfect nano structures and fibers and watertight foam sandwich composite.

 

[A II]

No info about flax, but once a guy had the 65' Miss OSB built out of oriented strand board, not because it's good, but because he manufactured OSB and wanted to promote it for anything. On that heavy boat with a load of resin and a lot of shielding also for strength the OSB worked well as a core.

Trawler Forum: 01-26-2011 Miss OSB (actually starts at post #3) — 04-09-2011 Miss OSB update

 

[gonzo]

Tending to be larger overall is where the voids are created.
That is not correct. Check circle packing
The fiber bundles of glass are packed tightly and each fiber is straight and parallel to every other fiber.

That depends on the type of fabric; for either fiber.

 

[rob denney]

Thanks for all the information. I am not too concerned with strength as the laminate needs to be strong enough to not need a core. So, stiffness is key. The higher resin absorption/lower sg means thicker skins for the same weight of laminate. Increasing the glass to the same thickness/stiffness would be about the same weight, use less resin and be stronger.

The samples are being tested by the local University, the results of this and other tests and boat building progress will be posted daily when there is something to report on the harryproa Yahoo chat group and weekly(ish) on Cargo Ferry Prototype – HARRYPROA http://harryproa.com/?p=3788

 

[rxcomposite]

Thank you Eric for the excellent article.

Gonzo and Ondarvr should read it as it seems they are arguing about something without the benefit of a refutable data. It all be just opinions and conjectures.

The study is done with sophisticated equipments including Scanning Electron Microscope. The cross section of the fibers are there, the resulting material properties, and the production method used.

Interesting to note that even with infusion and pressure curing, the Volume Fraction is still 35% (roughly 34% fiver content). Compared to industry standard of a similar fiber orientation, a Unidirectional glass fiber is easily capable of reaching 60% Volume Fraction (58% fiver content). This suggest that the randomness of flax fiber is just a little better than glass CSM and below that of a woven glass WR which has an equivalent 50% Volume Fraction (48% fiber content). In the article, the electron microscope showed the flax fiber orientation.

 

[rxcomposite]

Thanks for all the information. I am not too concerned with strength as the laminate needs to be strong enough to not need a core.

My suggestion to use it as "core" was to improve the laminate properties. It roughly translate to "Stacking sequence" or "Laminate schedule" wherein you place the material with a lesser property in the central portion of the laminate where it is not stressed so much, only sheared.

From the article provided by Eric, the resulting properties are there (Table 16) and can be used in Classical Lamination Theory, Lloyd's tabulated method, or ISO tabular method. The LR and ISO method can also be used for dissimilar material. For example, using abaca fibers for the outermost layer and Jute fibers for the inner/central layers.

 

[Eric ruttan]

Thank you Eric for the excellent article.

Gonzo and Ondarvr should read it as it seems they are arguing about something without the benefit of a refutable data. It all be just opinions and conjectures.

The study is done with sophisticated equipments including Scanning Electron Microscope. The cross section of the fibers are there, the resulting material properties, and the production method used.

Interesting to note that even with infusion and pressure curing, the Volume Fraction is still 35% (roughly 34% fiver content). Compared to industry standard of a similar fiber orientation, a Unidirectional glass fiber is easily capable of reaching 60% Volume Fraction (58% fiver content). This suggest that the randomness of flax fiber is just a little better than glass CSM and below that of a woven glass WR which has an equivalent 50% Volume Fraction (48% fiber content). In the article, the electron microscope showed the flax fiber orientation.

rxcomposite,
I have suggested that the comparatively small openings of the glass stack, vs the larger gaps of the flax, forces the epoxy into a thixatropic state, which seems to explain why the smaller gap of the glass stack flows epoxy much further, faster than the flax stack. And it does so with the epoxy being colder.
Perhaps it it more related to the coating (sizing) of the glass?
I am curious about your thoughts.
Can you see a way to improve the flax infusion?
Could a thixatropic additive be added to the epoxy for infusing the flax stack, thus extending the epoxy flow?

 

[ondarvr]

Thixitropes are added to resins to reduce the flow rate. Lowering the viscosity, sometimes with solvents increases the flow rate.

Depending on the resin and the method of reducing the viscosity, it can have a significant affect on the physical properties, reducing them.

 

[ondarvr]

Thank you Eric for the excellent article.

Gonzo and Ondarvr should read it as it seems they are arguing about something without the benefit of a refutable data. It all be just opinions and conjectures.
.

I live in a remote location, almost off the grid, as a result I only have satellite internet, which is sketchy at best.

So I don't click on links that require a sizable download of data unless I'm traveling or the conditions are right.

The info in the link didn't surprise me, it follows the tendencies of other natural fibers.

 

[rxcomposite]

DCockey hit the nail right on the head. It is specific heat.

There was an article about this in Professional Boatbuilder's magazine a long time ago where they investigated why large panels tends to curl up and have uneven curing,

Let us digress a bit. When polymer or epoxy is mixed, a chemical chain reaction starts. The byproduct of this is heat and continuous to rise until it reaches a peak exothermic reaction at which point the gelcoat starts to gel. This peak exotherm is critical to achieve as it ensures that the resin will cure properly. It is indicated in the manufacturers data sheet.

Rob was laminating glass and flax. While I do not know what material his laminating table is, I can assume that it is the difference in peak exotherm that he is observing. Glass fiber is an insulator, has a high specific heat and absorbs less resin. Flax is in the wood category, specific heat is lower and has a high resin content. It is safe to assume then that the glass part did not absorb much heat while the flax part absorbed part of the heat while the heat from the resin is still dominant. This can be validated if a thermal gun is used to measure the heat on both sides during the peak exotherm stage. A Barcoll hardness tester will confirm if both sides cured properly.

Speaking of heat, the reverse is expected of gel coat sprayed on a glass or fiberglass mold, an insulator. As the heat rises, it is trapped in the gelcoat to mold side. On the surface exposed to air, the heat radiates to the atmosphere robbing the gel coat of exotherm. This becomes pronounced on large surface area mold and thinly sprayed gelcoat. It is physics. A large surface area dissipates heat. The cure for this is to bump up the cobalt and MEKP when spraying hulls and monitor the process using a thermal gun. If the mold is metal, it is preheated. Metal will absorb the heat away from the gelcoat reducing the heat build up.

 

[Eric ruttan]

DCockey hit the nail right on the head. It is specific heat.

There was an article about this in Professional Boatbuilder's magazine a long time ago where they investigated why large panels tends to curl up and have uneven curing,

Let us digress a bit. When polymer or epoxy is mixed, a chemical chain reaction starts. The byproduct of this is heat and continuous to rise until it reaches a peak exothermic reaction at which point the gelcoat starts to gel. This peak exotherm is critical to achieve as it ensures that the resin will cure properly. It is indicated in the manufacturers data sheet.

Rob was laminating glass and flax. While I do not know what material his laminating table is, I can assume that it is the difference in peak exotherm that he is observing. Glass fiber is an insulator, has a high specific heat and absorbs less resin. Flax is in the wood category, specific heat is lower and has a high resin content. It is safe to assume then that the glass part did not absorb much heat while the flax part absorbed part of the heat while the heat from the resin is still dominant. This can be validated if a thermal gun is used to measure the heat on both sides during the peak exotherm stage. A Barcoll hardness tester will confirm if both sides cured properly.

Speaking of heat, the reverse is expected of gel coat sprayed on a glass or fiberglass mold, an insulator. As the heat rises, it is trapped in the gelcoat to mold side. On the surface exposed to air, the heat radiates to the atmosphere robbing the gel coat of exotherm. This becomes pronounced on large surface area mold and thinly sprayed gelcoat. It is physics. A large surface area dissipates heat. The cure for this is to bump up the cobalt and MEKP when spraying hulls and monitor the process using a thermal gun. If the mold is metal, it is preheated. Metal will absorb the heat away from the gelcoat reducing the heat build up.

rxcomposite;
I have read this several times. I find your reply very confusing.

Glass has higher specific heat and higher density. I cannot say if glass is 'insulative' but I can say glass is much less insulative than flax, which has less specific heat and less density. Which explains why Rob observed the stack temp/epoxy get a much higher temp quicker on the flax stack.

If we assume the glass is more insulative than flax, how did the glass stack stay cooler?

But this response seems to be non responsive to my inquiry.
Why did the vacuum infusion flow so much further with the glass than the flax?
Secondary to that is how does one get better flow with the flax stack.
Typically we expect warm epoxy flowing through larger holes to flow further. The exact opposite happened here. Cooler epoxy flowed through smaller holes further and faster.

I suggest the glass stack forced the epoxy into a thixatropic state, which made it flow much better than its viscosity suggests.