Affecting glass fibre surfaces and composite properties by two stage sizing application

The influence of sizing constituent distribution on the properties of sized glass fibres (GFs) and corresponding polypropylene (PP) composites was studied by two-stage sizing application, i.e. applying silane coupling agent and polymeric film former at separate stages and with different sequences, in comparison with one-stage sizing application usually used. Surface properties of sized GFs and transverse tensile strength of unidirectional GF reinforced composites were studied using various surface and interface analysis methods and tensile testing, respectively. Two-stage technology achieved sized GFs with lower loss-on-ignition (LOI) and resulted in poor fibre-matrix adhesion strength. However, applying silane coupling agent at the first sizing stage with an increased roller speed achieved sized GFs with lower LOI but composites with mechanical properties quite close to those of composites based on one-stage technology. Moreover, the difference in surface properties of sized GFs is discussed in terms of the wetting ability difference of sizing constituents and the interactions between sizing components