Textile fiber-reinforced anionic polyamide-6 composites. Part II: Investigation on interfacial bond formation by short beam shear test

In order to manufacture thicker, larger and more integrated thermoplastic composite parts, a vacuum infusion process has been developed at the Delft University of Technology using a reactive resin called anionic polyamide-6 (APA-6). For these composites fiber-to-matrix bonding follows a similar mechanism as the formation of branch points in the neat APA-6 resin: de-blocking of the activator results in free isocyanate groups, which can form urea links with the aminosilanes on the glass surface. It will be shown that in general a higher mould temperature results in a stronger interface, but that at the same time a reduction in crystallinity weakens the matrix, which makes a compromise inevitable. In order to improve the interface strength at lower processing temperatures, the use of (i) activators that are capable of interfacial bonding at lower temperatures, and (ii) mixtures containing various activators is explored. It will be demonstrated that stronger bonding of the activators with the fibers does not automatically improve the mechanical properties of the composite.