Interphase modification and characterisation in p-aramid/ glass fibre epoxy model composites

In this thesis different approaches of surface modifications on glass and p-aramid fibres were investigated and the consequences on the adhesion between reinforcing fibres and matrix material were evaluated by means of mechanical testing methods.The single-fibre fragmentation test (SFFT) a widely used micromechanical testing method was enhanced to allow a detailed characterisation of interphases in fibre-reinforced composites. A video based analysing method of the SFFT enables a direct monitoring of the fragmentation process of the embedded fibre. This permits to draw conclusions about the load transmission between matrix and fibre. With a second developed analysing method scanning and examination of a tested specimen at high magnification in different illumination modes is facilitated. This approach allows an exact identification and analysis of fibre failure types and interfacial phenomena.Differently surface treated glass fibres were investigated with the SFFT and based on investigated fragmentation processes as well as observed fibre failure types strong influences of the surface treatments on fibre-matrix adhesion were proven. In order to activate the fibre surface of p-aramid fibres washed or plasma treated fibres were dip-coated with quaternised polyethylenimine (PEI)-based primer polymers in an aqueous solution. Through electrokinetical measurements the adsorption behaviour of the synthesised PEI-derivatives was investigated and evaluated depending on pH, polymer concentration in the solution, fibre pretreatment and degree of quaternisation of the primer polymer. The mechanical characterisation of surface treated p-aramid fibres was performed with SFFTs and fibre bundle pull-out (BPO) tests. These mechanical tests illustrated the characteristic fracture behaviour of p-aramid fibres and identified it as disturbing factor for a distinct evaluation of the SFFT. The results of the BPO tests reflected the problematic observations of the SFFTs. However, analysis of the fracture surfaces of tested specimens gave a qualitative, visual impression of the fracture behaviour and indicated a slightly improved fibre-matrix adhesion for PEI-coated fibres in comparison to cleaned standard fibres.In another series of experiments p-aramid fibres were coated with poly(styrene-co-glycidyl methacrylate) particles with the objective to enhance the adhesion and consequently also the load transmission between fibre and matrix. The optimal conditions for the coating procedure with nanoparticles were determined by performing coating experiments at varying conditions and subsequent electron microscopical analysis of the coated fibre material. A positive influence of the nanoparticles on fibre-matrix adhesion was demonstrated by means of SFFTs, BPO tests and tensile tests