Abstract: Fire retardant cellulosic material comprises from 0.4 to 2.0% by weight of tin and from 0.4 to 8.0% by weight of boron based on the weight of the cellulosic material. The fire retardant material is prepared in a two-stage or a one-stage process. The two-stage process comprises impregnation of the material with an alkaline solution of an alkali metal stannate or stannite, followed by impregnation with an aqueous solution of boric acid and drying. The one-stage process comprises impregnation of the material with a stable aqueous colloidal suspension of hydrous tin oxide stabilized with an alkali metal salt of boric acid having a pH in the range of from 4 to 8, followed by drying.

Abstract: A process for the preparation of a fire-retardant material which comprises a particulate inorganic filler (other than a tin compound) coated with a layer of divalent metal hydroxystannate or a divalent metal stannate, which process comprises the steps of: (i) forming a slurry of the particulate inorganic filler in an aqueous solution of an alkali hydroxystannate, also containing a divalent metal oxide dissolved therein; (ii) reacting the slurry from step (i) with a hydrolysing agent, or a water-soluble source of a divalent metal, to form a layer of a divalent metal hydroxystannate on the surface of the filler, and (iii) optionally, heating the filler coat with hydroxystannate in step (ii) in order to convert it to the corresponding divalent metal stannate.