An assessment on the effect of ignimbrite dust on rotomolded polyethylene composites

Abstract

Ignimbrite dust, an inorganic by-product from stone extraction, was used as a filler of rotomolded polyethylene items. The blends were prepared by dry-blending and later processed to obtain composites with different ratios of fillers, from 5 to 20 % by weight. Additionally, an azodicarbonamide-based chemical foaming agent was added to obtain foamed PE parts with the same proportions of the filler, working in this case in two layers, i.e. an external skin made of neat PE or composite, and the internal foamed layer, also made of PE or composite. Mechanical characterization showed an increase in maximum stress and elastic modulus in both bending and tensile tests when adding mineral powder to the virgin material. Impact tests showed no major differences between the neat polyethylene and the composites, which is a positive result, considering the sensitiveness of this procedure to the incorporation of foreign materials. Furthermore, a slight increase in impact resistance was observed for the composite with 10 wt% ignimbrite in the outer layer and 20 wt% ignimbrite in the foamed inner layer. Thermogravimetric tests indicated no differences between the blends used, thus keeping the thermal stability of PE even when adding mineral powder and foaming agent. The characterization was completed with thermal testing, interestingly including the modified Ångström method to determine the thermal diffusivity of the materials and the effect of the filler on the polymer matrix. Therefore, the research includes the characterization of the composite materials, providing properties not usually mentioned in the literature, helping to expand the knowledge about such composite materials beyond mechanical properties, providing a broader range of properties to offer a wider application area.