Assessment of welded ignimbrite waste dust as a filler in rotomolded products: rheological and thermomechanical behavior of PP/ignimbrite composites

This work aims at demonstrating the potential benefits of using a mineral waste from quarries as a filler of polypropylene (PP) products obtained by rotational molding. A polypropylene matrix was dry blended with the ignimbrite dust (mainly composed of silica and alumina) in ratios up to 30% weight, obtaining well consolidated parts in all cases. However, it can be observed that, as expected, the parts with higher loadings result in a higher number of defects due to the air release hindering. The viscosity of the obtained blends was determined by oscillatory rheometry, finding that the incorporation of up to 30% of the mineral dust is not significantly affecting the viscous behavior of the material. Furthermore, the low particle size of the filler allows for a good distribution inside the PP matrix, obtaining a homogeneous material with good dispersion. The increased amount of ignimbrite results in improved storage modulus, meaning that the filler, even in dust format, is able to stiffen the matrix at high loadings (over 20%). However, increased ratios of filler also result in a lower adhesion between the filler and the matrix and reduced homogeneity of the blend.