Alkali inorganic binders for the production of fibre based foams

The production of fibre-based low-density foams, which can be exploited as heat and sound insulating materials, was investigated. Commercially available bio-soluble calcium–silica based fibres were used. The combined use of clot-forming (a protein-assisted foaming method) and alkaline inorganic binders with increasing complexity, such as colloidal silica, a potassium silicate aqueous solution or a synthetic alkali alumina-silicate, was evaluated for the development of completely flameproof inorganic foams. The final structures were dependent on the binding systems (colloidal suspension, salt solution or sol–gel system). On using colloidal silica, the interlocking network of fibres provided a self-supporting and uniform porous structure, which can eventually be shaped into boards, depending on the chosen application. After the burnout of organic residues at 500 °C, a final bulk density of about 190 kg/m3 was obtained, and promising sound insulation properties were achieved.