Can anybody recommend a glue (perhaps a type of cyanoacrylate) for bonding carbon fibre?
I'm not looking for advice on how to do the repair itself. I just want to know what brand or type of product (e.g. high viscosity, low viscosity; or perhaps a specific specialist product) is known to give a good bond.
Thank you.
If it's a repair to something structural, simple glue won't be strong enough. The strength comes from the fibres, and if they're broken, you have a very weak spot.
In the general case, which glue to choose often depends on the characteristics not just of the material but the stresses on the join, even once you've identified a class of glues that bond well to the material.
If we consider a non-safety-critical carbon-fibre accessory, so not aerobars, but a bottle cage or a Tailfin pannier rack, the best thing is likely to be epoxy, and a slow-setting one with the parts held together by a jig while it cures. Even then, if it's carrying a load, just gluing the break shut is unlikely to be enough - but you imply you've already thought of reinforcing or building up the join.
On bike frames or even worse, forks, forget it.
The best bonding of carbon fiber comes from using a two-part, epoxy resin (polyepoxides). When the polyepoxides resin is combined with a co-reactant resin, also known as a hardener, it results in a thermosetting polymer. This has extensive cross linking of the molecules which give it good mechanical properties, including an excellent bond strength.
There are several brands and varieties of epoxy designed for use with carbon fiber. More specifically, a thixotropic resin, is good for carbon fiber. When a thixotropic resin is "worked" or stirred, the consistency becomes more fluid. When left to stand, it becomes more thick-gelatinous. Thus one can work it into the carbon fiber weave, and when the weave is put into place around a mold or repair area and left alone, the more gel-like state tends to resist running.
Here's a link to an article on epoxy and other resins and their applications.
