Mechanical properties of short basalt fibre reinforced polypropylene and the effect of fibre sizing on adhesion

The focus of this study was to investigate the potential of short basalt fibre (BF) as reinforcement for polypropylene (PP) and the effect fibre sizing has on adhesion and resultant mechanical properties. Short fibre PP composites were manufactured at fibre loadings of 10, 20 and 30 wt% using fibres coated in multi-purpose epoxy based sizing and four experimental PP tailored sizings. SEM image analysis of polished composite cross-sections showed that dispersion was independent of what matrix the fibre sizing was designed for. Fibre length distribution showed the final fibre length of BF was larger than glass fibres in PP composites, which is attributed to its higher abrasive resistance. DSC revealed in general basalt does not influence the crystallinity of PP but some sizings resulted in a 2–3%increase, however, BF increases onset crystallisation temperature by ~3 °C. Tensile and flexural properties of PP can be significantly increased by up to 64% (tensile strength) and 110% (tensile modulus) through the addition of short BF with properties increasing as fibre content increases; however the impact strength simultaneously decreases. Mechanical properties were highly dependent on fibre sizing, where fibres indicating good adhesion provided the greatest increase in tensile and flexural strength but resulted in lower impact strength. Analysis of the fibre-matrix interface highlighted the significant effect sizing has on interfacial shear strength where improvements of 117% were evident. This study highlights the potential of BF as an effective reinforcement for PP while enforcing the importance and advancements of fibre sizing on promotion of adhesion.