flax composite stitch & glue

Steve W,

Scarfing is one of my concerns. Thank you for the idea, next time I will use that (with flax textile instead of glass). My other concern is that okoume is came from the other half of the world, and I am more comfortable with materials which have produced at least in the same continent. Another concern is that I am not comfortable working with glass. I find those small particles of glass floating in the air scary.

Gonzo,
my tensile strength data is not from wikipedia. They are from research papers (regarding flax composites) and matweb.com (regarding plywood).

 

Here is a picture of the specimen. The 7 numbered in the table above, an okoume, and a jute one.

The jute sample is ordinary sack textile, 320 g/m2. It is very loosely woven (counted 4 threads/cm). 5 layers is 4.3 mm with hand lamination, and 3.3 mm compressed (I have put a brick on one end of the specimen, this is the compression. With both methods there is noticeable amount of air within the laminate. This specimen is 25g for 3x20cm, which means the highest textile content (38.4%), but it is the thickest one even compressed, which tells something about the amount of air trapped.
It is also seems to be the most brittle specimen, maybe because the threads are located so far away in all directions.

The price of jute have been 1/4th of flax. This makes it economically better than the other options even accounting for the mechanical deficiencies, which I believe more due to the quality of weave, than the material itself (I guess the same stands for price). In a research paper comparing flax, hemp and jute, the jute sample had the highest tensile strength.
I guess this textile is the one which begs most for vacuum bagging or infusion, or at least compression.

Unfortunately jute is also produced in another continents. It is ridiculous that it is the cheapest textile available, and even it was the only one containing 100% of flax, hemp or jute in that shop.

 

The main difference is that fiberglass has long fibers that can span the length of the hull. Jute has short fibers .

 

Here is the thread about my current boat:
http://www.boatdesign.net/forums/wo...ation/p-v-luca-szeke-my-first-boat-33763.html

 

European flax have long enough cells (30-50 cm) so that forces along them stick 'em together enough. I guess jute and hemp are similar in this respect. What we are talking about here is essentially tensile strength, and it is comparable to E glass if we take weight ratio into account.
Yes, there are drawbacks: Natural fiber quality is more variable. At the end of the day you need twice the amount of matrix. If you want to reach (or maybe extend) the strength/weight ratio of glass you need specially woven textile from specially spun threads and vacuum baggng/infusion.
I do not say that natural fiber is the choice for boat building for anyone over glass. I am just trying to validate if it is the choice of material for me as a hobbyist with a green mindset who cares about easy and safe material handling and using local market.
(Yes, I know that the difference environmentalfriendlinesswise between glass and natural fiber composite is only that the latter can be put into the hearth in cold winters.)

 

Some more attempt with flax composite:
http://www.boatdesign.net/forums/wo...uca-szeke-my-first-boat-33763.html#post383908

And I thinking about using paper maché as a core material. Maybe a sandwich with multiple instances of 1mm paper, and 1 layer of flax. What do you think about it?

 

I would prefer cork as a core. Also does meet your requirements. (most cork is from Spain and Portugal)

 

Build has begun

I have begun building a flax composite origami boat.
As the factory which have promised to produce some textile to my specification have given up (they are just not able to do it), I have choosen the heaviest flax cloth available. It is 250g/m2.
I was also thinking about some non-flax textiles. For example ordinary linen cloth (50% cotton, 50% polysomething) seemed to be a tempting choice. Two layers would have been cheaper than one layer flax, maybe the same tensile strength, and it is much more densely woven. I have to develop some method to measure tensile strength at home.

It will be a sandwich using polistyrol foam. I have found it in the local home builder's shop, intended to be placed under parquet. It comes 2.2mm thick, 1m wide, some 15m long roll.
Styrofoam is not regarded as the best core material, and it definitely does not work with polyester. But I am using epoxy, too lazy to make paper maché, and found sourcing cork difficult. And I like the idea of a very light core.
As my handwork skills are very limited, I have started with a full size print of the layout.
One side is some 1.5m wide, so I used one and half strip of the foam, taped together with cello tape.
I taped the plan to the foam (cello tape again) and cut it with a knife.
It is very easy, especially compared to plywood. Not two runs for scratch and then cut with saw, just cut and that's all. You need a very sharp knife, because the foam is torn otherwise.
When the layout was ready, I have placed some nylon under that (the one people use to paint the house), and rolled the flax on top.
Now the fun begun: spreading epoxy on the flax everywhere where there is core.

If this will be non-flexible enough, I will make the other half in the same manner, then start sewing it together.

I attach the plan (I know it is not ideal, see http://www.boatdesign.net/forums/boat-design/placement-seat-kayak-34186.html for the same hullform but smaller one, but I build this as the experimental one anyway), and some pictures of the build.

 

I have some problem with the epoxy. It is not curing. I believe it have nothing to do with other materials I am using. The reason might be one or both of the following:
- Bad mixing ratios. I am using hypodermic syringe to measure, and the 100 ml one does have several ml of uncertainty
- Bad hardener. I always forget to stir up the hardener before measuring, and it has been the end of the batch.

I am trying to heat it with a hairdryer, but it is still tacky after 3 days.

Now I am off for a week. When I return I will continue the building, no matter what.
It is an experiment anyway

 

I've never had problems with longevity, but after 2000 mixed gallons, the culprit always turned out to be improper ratios, up to and including leaving the hardener out entirely!!! The close behind but second screw up in a busy shop is usually short mixing times. sixty good stirs per batch or at least one minute of blend time will help keep the sticky gremlins at bay.

 

It is really hard to get the mixing ratio wrong with Epoxy. It is very forgiving (compared with the esther fraction)

The shelf life of the components is not a serious problem too, they do live long.

If it does not cure even when heat is applied, I would bet the hardener was just forgotten.

 

I am sure I did not leave out hardener and that the mixing ratio was near to the specified one.
However short mixing time is a possible problem.
Thank for bringing my attention to that.

 

Interesting article in the June/July edition of Professional Boatbuilder electronic magazie - titled "Rovings - Biocomposite Boatbuilding"

Info on usage, applications and comments like "In France alone, 1/4 of all arable land would be required to grow enough Flax to replace Fibreglass re-inforcing"

Makes yer think !

 

Yeah,

about the sanity of the journalists.

 

It is a bit still tacky in some places after a week. I have cut it to shape anyway.
In some places the flax and the polystirol did not stick to each other. (first picture)
The flexibility seems to be adequate for doing origami, so I have started to sew it. (second picture)