Adhesion of modified polymers to fibres: Maxima on adhesive strength-modifier amount curves and the causes of their appearance

Adhesion of modified polymers to fibres is considered. The dependences of the shear adhesive strength of polymer/fibre joints on the modifier content are analysed. It is shown that an increase in the adhesive strength can often be achieved by adding a component with a lower adhesive ability to the basic adhesive. As a result, a maximum strength is observed for a certain concentration range of the minor component. This paradoxical phenomenon can be explained with the use of simple qualitative reasoning, which is based on the analysis of the concentration dependences of surface and bulk properties. By the example of the ED-20 epoxy resin (analog of DGEBA), competitive processes whose superposition produces such a maximum are shown to be different for one-phase and two-phase adhesives.