A qualitative model for the mechanical behavior of pretreated asbestos‐epoxy composites

The aim of the present work was to investigate the effect of fiber pretreatment, fiber content, coating concentration, and also pretreatment procedure on the tensile properties of asbestos‐epoxy composites. These composites comprise materials of considerable industrial importance. Asbestos exhibits unique properties. Occasionally it is difficult to disperse asbestos properly because the individual fibrils are very small and tend to agglomerate, but there is no evidence that asbestos is not easily wetted out by all systems. However, the higher potential aspect ratio of asbestos fibers compared with glass is not always realized in practice because the fibers break in length to fine diameters. Accordingly, the very considerable new surface created makes successful wetting difficult or impossible. For this reason, asbestos was precoated with a well adhered film of poly(hexamethylene adipamide), a polymer especially compatible with the epoxy phase. The pretreatment procedure followed was based on the principles of the interfacial polymerization involving the serial application to the asbestos of two immiscible solutions of hexamethylenediamine and adipoyl chloride. Accordingly, epoxy‐nylon‐chrysotile composites were made while varying pretreated fiber volume fraction, concentration of the polyamide coating, and reactants application order. Results obtained from tensile measurements proved quite interesting: Relative modulus of elasticity and relative ultimate strength exhibited a similar behavior when correlated with the ratio of polyamide to asbestos concentration. The corresponding curves pass through distinct maxima at which severe improvement of the material performance is effected. A thorough interpretation of these results is also included.