To mitigate the layer-to-layer adhesion challenge, crosslinks can
be created among layers. Crosslinks in polymers are traditionally
formed by chemical reactions during the initial cure of the material
or by the addition of a chemical crosslinking agent, approaches that
are impractical for this application. Alternatively, high energy
ionizing irradiation, such as electron beam, gamma, or X-ray radiation,
may be used to induce crosslinking in certain polymers.
Irradiation generates radicals on the main chain (scission) or on
side chains (crosslinking). The radicals recombine or trigger further
reactions potentially improving the adhesion between layers and
enhancing thermomechanical properties. However, scission reduces
polymer molecular weight and leads to poor properties and
should be avoided in this paradigm. Whether the chain scission or
the crosslinking is dominant during the irradiation process determines
the degree of crosslinking and thermoset behavior. This in
turn, determines whether the properties of polymeric materials are
enhanced or lowered by the irradiation.