Sustainable Basalt Fibers vs. Traditional Glass Fibers: Comparative Study on Thermal Properties and Flow Behavior of Polyamide 66-Based Composites

In this work, basalt fibers (BF) have been investigated as possible natural and sustain- able replacements for the common synthetic mineral filler—glass fibers (GF)—used in polyamide 66 matrix (PA66). Composites have been prepared at two different fiber concentrations (15 and 25 wt.%, respectively) by melt blending. The developed systems have been mainly characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), capillary rheology, and scanning electron microscopy (SEM). The kinetic parameters to thermal degradation through the Coats–Redfern method allowed us to attest a negligible effect of fiber type on thermal stability of the developed systems. Composites incorporating 15 wt.% of fiber content possessed the highest activation energy (≥230 kJ/mol). The introduction of BF and GF in PA 66 polymer, regardless of content, always led to an increase in crystallization and melting temperatures, and to a similar reduction in crystallinity degree and glass transition temperature. The shear viscosity of the basic polymer increased by the addition of fillers, particularly at low shear rate, with a pronounced effect in the case of basal fibers. A slightly higher shear thinning behavior of BF/PA66 with respect to GF/PA66 composites was confirmed by fitting the flow curves through the power law model. Finally, a worsening in fiber dispersion, by increasing the content in the matrix, and a weak compatibility between the two phases constituting the materials were highlighted through SEM micrographs.