Surface properties and fibre-matrix adhesion of man-made cellulose epoxy composites - Influence on impact properties

To reveal a possible explanation for this effect the fibre surface properties were investigated more closely. AFM measurements showed no differences in fibre surface topologies. However the physico-chemical properties of the fibre types differ. IGC measurements showed that the standard Cordenka fibre without avivage (“std wo a.”) possesses a slightly higher specific surface energy and base number (Kb) than the CR fibres without avivage (“CR wo a.”) resulting in a better adhesion to the highly polar epoxy. This is also shown by the pair specific interaction parameters (Isp) and the work of adhesion. Both are clearly higher for the epoxy - “std wo a.” pair. Accordingly the measured fibre pull-out lengths of the CR fibres are one order of magnitude higher than of the std suggesting a weaker interfacial shear strength between the CR fibres and epoxy. Within the same fibre type the samples without avivage show longer pull-out lengths. As a weaker fibre-matrix adhesion causes stronger crack deflection and energy dissipation these results correspond well with the previously measured Charpy impact strengths.