FLD (17/04/2014)
We spend some effort considering fibre orientation for strength. Has anyone ever considered resin orientation? The resin is just polymer chains which we infuse into the fibre and link in a completely random orientation. Whilst this gives a uniformly random matrix is this the best option? If we could align resin chains and then cure or cross link in a certain orientation could we achieve better / stronger parts? Could we 'grow' polymers through the fibre?
This is not possible for several reasons. The usual resins do not cure into individual chains, they cure into three dimensional networks producing essentially one huge molecule the size of the whole resin batch. In theory you could "walk" from one end of a part to any desired position by following the polymer backbone. The resins cannot be melted once cured, they aren't thermoplastics.
There are ways to achieve orientation in polymers, e.g. by stretching a fiber. You can do this at home with polypropylene. If you pull a strip of sheet PP it will stretch and elongate and get much stiffer due to crystallization of the polymer chains and finally it will yield and tear. But this is only possible since PP is pretty much a straight chain polymer. There are other ways to achieve orientation and a bunch of other interesting effects in certain polymers, like liquid crystals, micelle formation, phase separation in copolymers and a bunch more (don't remember right now). But none of them are terribly interesting for composites, since the strength of a composite is almost exclusively caused by the physical properties and orientation of the fibers. The physical properties of the usual cured resins are one to several orders of magnitude lower than those of the fibers, you can easily crumbe a thin cured piece of resin between two fingers, meaning even if it was possible to make the resin matrix 100% stronger the resulting composite wouldn't be any better.