Role of film formers in glass fibre reinforced polypropylene - new insights and relation to mechanical properties

The adhesion strength between reinforcing glass fibres and polypropylene matrix can be improved by introduction of acidic groups due to matrix modification and by creation of a strong interphase between the components. In this paper, we consider two different sizings consisting of γ-aminopropyltriethoxysilane (APS) as silane coupling agent and either polyurethane (PU) dispersion or polypropylene (PP) dispersion as film former. The adhesion strength determined using pull-out tests showed a strong dependence on the film former. Both the variation of adhesion strengths and interphase modulus determined using nanoindentation were found to be consistent with the macromechanical properties of glass fibre reinforced polypropylene. The interphase design provided simultaneous increase in the tensile strength and the impact toughness of the composites. The results of acoustic emission and fractography confirm the different performance due to the interphase design. Failure mechanisms such as matrix deformation and fibre matrix debonding influenced by the different film formers proved to be the origin of different mechanical results, whereas fibre tensile strengths did not differ.