Fluidized bed combustion fly ash as filler in composite polyurethane materials

Abstract

Fly ash (FA) is a waste material having great potential as modifier of mechanical and thermal properties in polyurethane (PUR) technology. There are very few reporting the use of fluidized bed combustion (FBC) FA in the production of PUR foams. In this work, authors have used the as received FBC FA as an additive to PUR rigid foams. The composite materials containing 5, 10, 15, and 20 wt% of FA were obtained by hand mixing and casting method. Microscopic observations of both unmodified and composite foams showed a well formed, cellular structure of the rigid foam. The cell structure was uniform; most of the cells were closed, which was an important parameter influencing thermal insulation properties of PUR materials. FA was uniformly distributed within PUR matrix and placed between cells. When the content of FA in composite foams increased, cells' dimensions decreased, which suggested that FA particles acted as nucleation sites during the foam formation process. The absorption bands presented in IR spectrum of PUR foam confirmed the presence of urethane bonds in the unmodified foam material. The IR spectrum of as-received FA reconfirmed the crystalline phases recognized by XRD analysis, which were anhydrite, quartz, lime, calcite and aluminosilicate. No additional bands were observed which suggested that no chemical bonding between PUR matrix and FA particles occurred in the composite foam. The incorporation of FA into the PUR matrix, up to 10 wt%, improved the mechanical performance of the composite materials, when compared to unmodified PUR foam. Such a tendency suggested the occurrence of interfacial interactions between polymer matrix and FA particles, as well as the uniform distribution of the filler within PUR material. For all the materials analyzed, the addition of FA to PUR foam reduced both carbon content and the gross calorific value. The addition of FA improved the thermal stability of the PUR foam material (barrier effect of the FA prevented the release of gases from the foam structure).

Keywords: Chemical composition; Composites; Fly ash; Polyurethane; Thermal properties.