Ultra thin sheet metal as moisture barrier in plastic composite.

[SeaSpark]

There have been a couple of active threads lately which evolved in a discussion about the durability of plastic composite materials.

One of the key factors in detoration seems to be moisture ingress into the laminate. No plastic material is completely "waterproof" or "dampproof" this is also why in packaging materials for food a very thin aluminium layer is applied.

Would it not be possible to apply a very thin sheet of aluminium to the outside of a plastic composite hull? Either in mold or afterwards via vacuum bagging? It could also be strips like in cold moulded wood building. If a transparent epoxy coating is applied as a last layer you would end up with a shiny aluminium hull (no to my taste but people seem to like it) Aluminium sheets can be anodised in any color (or crome if you want). Anodising also makes any other coating unnecessary. Scratches can be fixed by "gluing" a ultra thin sheet over the affected (filled) area.

Comments welcome.

[DanishBagger]

That seems like a nifty idea.

Just a couple of questions from an amateur:

If the hull is mainly CF, wouldn't it be a bad idea to use aluminium as the barrier-sheet, isn't that just introducing another, just as vital, parameter to the composite orgy?

Also, how about those mylar bags for wine, is that also covered in aluminium or is that something else (because if it is different, maybe that could be used)?

[SeaSpark]

isn't that just introducing another, just as vital, parameter to the composite orgy?

Epoxy is said to adhese well to most metals, as a very thin outer layer it does not play a role in structural strength. Don't see many problems.

Also, how about those mylar bags for wine, is that also covered in aluminium or is that something else

The bags i have seen had an aluminium film, as with most food products this is mostly to keep oxigen from reacting with the product.

[SeaSpark]

How about titanium film as last (first?) layer, titanium has good antifouling properties and unlike copper does not corrode. It is a very scratch resistant metal with a beautiful shine. It's expencive but in thin film material costs are not high, don't know how difficult it is to produce titanium film though.

From wikipedia about titanium epoxy composite A6 airplane wings i understand epoxy and titanium mix well:

After a series of wing-fatigue problems, about 85% of the fleet was fitted with new graphite/epoxy/titanium/aluminum composite wings

[DanishBagger]

Originally Posted by SeaSpark

Epoxy is said to adhese well to most metals, as a very thin outer layer it does not play a role in structural strength. Don't see many problems.

I meant problems as in "corrosion". CF+Alu?

The bags i have seen had an aluminium film, as with most food products this is mostly to keep oxigen from reacting with the product.

Oh, so it _is_ alu-foil on there. I was thinking that since it is oxygen proof, it's propably also waterproof. But if that is indeed alu, then one should be able to somehow spray it on, or is it indeed a "sheet".

Heh, I just had an image in my head of someone using those ktichen aluminium rolls, covering an entire boat in it, painting it over with epoxy.

[DanishBagger]

Originally Posted by SeaSpark

How about titanium film as last (first?) layer, titanium has good antifouling properties and unlike copper does not corrode. It is a very scratch resistant metal with a beautiful shine. It's expencive but in thin film material costs are not high, don't know how difficult it is to produce titanium film though.

From wikipedia about titanium epoxy composite A6 airplane wings i understand epoxy and titanium mix well:

Ah, titanium - I love titanium, I wish I could buy tonnes of it (litterally).

Anyways, I did a search for titanium film, and it turns out that you need argon, vacuum, and several other gasses (and the danger of explosions), however, I tried searching for titanium foil, which aren't measured in microns, but you can get at thicknesses around 0.001", and sheets which begins at around 0.01".

However, although titanium has all these great properties, and if you make it like one would do cold-moulding, _and_ covered it with epoxy, you would end up with an epoxy outer layer, and if so, I don't see the purpose, except for puncture resistance and moisture barrier.

I wonder if you could put it on in strips while vacuumbagging, and therefore get the titanium to be the outermost layer. At 0.001" it should be easily enough formed, methinks.

http://www.espi-metals.com/metals/cattitanium.htm


EDIT: I haven't tried (yet), but from the litterature, it seems that epoxy has a hard time adhering to aluminium. Apparently you have to rough up the surface quite a bit and then give it an acid bath of some sorts, and then - instantly _ cover it with epoxy before it has a chance to oxidise. I wonder if titanium would have the same problem?