Epoxy is the cured end product of epoxy resins, as well as a colloquial name for the epoxide functional group. Epoxy resins, also known as polyepoxides are a class of reactive prepolymers and polymers that contain epoxide groups. They may be reacted (cross-linked) either with themselves or with a wide range of co-reactants (hardeners). The cross-linking reaction is commonly referred to as curing.

The first commercial attempts to prepare resins from epichlorohydrin were made in 1927 in the United States. Credit for the first synthesis of bisphenol-A-based epoxy resins is shared by Dr. Pierre Castan of Switzerland and Dr. S.O. Greenlee of the United States in 1936.

The most common epoxy resins are based on reacting epichlorohydrin (ECH) with bisphenol A, resulting in a different chemical substance known as bisphenol A diglycidyl ether. Bisphenol A-based resins are the most widely commercialized resins!

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Why make them so thin?

In short, carbon fibers are manufactured through the stabilization, carbonization and graphitization of a precursor (generally polyacrylonitrile or petroleum pitch). The crystal structure of graphite consists of sp2 hybridized carbon atoms arranged two-dimensionally in a honeycomb structure in the x-y plane. The layers, termed graphene layers, are stacked parallel to each other in a 3D structure.

A precursor with a smaller fiber diameter allows for a higher graphitization degree. In other words, the carbon fiber will have greater graphite content. This way, the probability of having a concentration of defects in the 3D structure is considerably reduced. That is why the mechanical properties of fibers are inversely proportional to their filament diameter.

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