Interface Interfacial bonding

B. Degradation of the fiber-matrix interface resulting in loss of adhesion and interfacial bond strength. 

The major unknown in the cathodic delamination process is the mechanism by which the interfacial bond is broken. Alkaline attack of the polymer, surface energy considerations, and attack of the oxide at the interface have all been proposed, but none of the available evidence allows an unequivocal answer. 

Adherent films would not necessarily require formation of covalent bonds at the Interface, since localized lntermolecul u dispersion forces that u e operative In the adsorption of coatings (with good wetting properties) should provide stable interfacial bond conditions. Among candidate materials which could fulfill the requirements of good adhesion and substrate protection from moisture are epoxy-modified polyurethanes and epoxy-siloxane polymers. 

Goan, J.C.. Prosen, S.P. (1969). Interfacial bonding in graphite fiber-resin composites. In Interfaces in Composites. ASTM STP 452, ASTM, Philadelphia, PA, pp. 3-26. 

With a strong interfacial bond, when a fiber fractures, the high stresses in the matrix near the broken ends are relieved by the formation of a short radial crack in the resin. There is no interfacial debonding and corresponding friction at a sheared interface, but rather, the load is transferred to the fiber by elastic deformation of the resin. The lack of adhesive failure in this case is responsible for the relatively low emission observed. 

Some disadvantages include the following. When carbamates react with acidic substances, carbon dioxide is released. This could result in the formation of bubbles (flaws) at an interface and concomitant weakening of the interfacial bond. The insolubility of a carbamate salt in organic media could retard coupling reactions. The stability of the carbamate salt under nonacidic conditions could retard or inhibit coupling reactions. 

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