Hi northsea junkie,
Your linked essay didn't cover the difference between the bonding of epoxy to carbon vs. the epoxy to kevlar.
i am no chemist, but i was told by someone that i trust that the reason kevlar fuzzes up when you sand it is because there is only a mechanical bond, whereas carbon and glass have the mechanical and chemical bond. Also i have been told that the reason epoxy has part A and part B is because the part B isn't really a hardener like polyester has a hardener (also called catalyst). Ploy will go off eventually w/no hardener, but part A of epoxy will never harden on it's own.
Sure a sanded and unfinished surface of carbon will soak a minute amount of water, but exposed kevlar soaks water like sponge, plus you can't get it very smooth like you can with carbon. It's no big deal to put an unfinished board on the water that has exposed carbon or glass, but if there was any exposed kevlar the board would prolly be ruined. Bury the kevlar deep if you insist on using it because if you hit it while sanding you just created another step.
The plastic sheeting trick that i mentioned works really well for laminating areas about the size of a rudder or smaller. You will be amazed at the amount of air that you can squeegee out, and the surface is shinny when you peel the plastic. Also i have found that using clear surfboard epoxy which has uv inhibitors tends to save time in the long run. It's not the strongest epoxy but is good enough for most purposes, and some surfboard epoxies are better than others.
The fibers do most of the work, but there are resins with extremely good properties that will add a lot to the strength of the part.
The rule for kevlar is bury it deep. It soaks up water and only forms a mechanical bond whereas carbon forms a chemical bond with the epoxy.
First I like to show you some explanation about how epoxies and polyesters do work:
epoxy and polyesters The cloth in a laminate will always suck up some water when the surface is damaged. (That's why they fill themselves with resin too)
Glass, carbon, kevlar or whatever, it makes no difference.
If the carbon molecules of the carboncloth really are bonded in the epoxy molecules during the hardening (the polymerisation), like you said, then this should mean less stable (disturbed)epoxy molecules.
The strenght of a laminate is largely determined by the fibers in the cloth you use. The resin only keeps all the fibers together; to be more precise, holds them at their fixed position to each other.
It fills the space between the fibres and fills them and holds them internally.
