Thermoplastic cellulose ester compositions and sheet materials made thereof

Thermoplastic compositions comprise a cellulose ester of a paraffinic monocarboxylic acid containing 2-4 carbon atoms plasticized with a plasticizer containing chlorine, said compositions containing also titanium dioxide and a thermoset resinous condensation product of formaldehyde and urea or melamine. The proportion of the synthetic resin may be 0.5 to 5 per cent, preferably 1 to 3 per cent, by weight of the cellulose derivative. The plasticizer may be a chlorine-containing ester of phosphoric acid, e.g. tri-(monochlorethyl phosphate). Additional plasticizers not containing chlorine may be included, e.g. dimethyl and diethyl phthalates (preferably in conjunction with a minor proportion, e.g. 25 per cent, of triphenyl phosphate), dibutyl phthalate or tartrate, triacetin, triethyl or acetyl triethyl citrate, and methyl-phthalyl or ethyl phthalyl ethyl glycolate. The synthetic resin may be a condensation product of formaldehyde and melamine in molar proportions between 6 : 1 and 1 : 1, and particularly between 2 : 1 and 1 : 1. The compositions are particularly useful for the production of non-fibrous sheeting by the block process and other methods and for the production by moulding or extrusion of other shaped articles. In an example sheets of a composition consisting of 100 parts of cellulose acetate of acetyl value (expressed as acetic acid) 51 to 53 per cent, 40 parts of tri-(monochlorethyl) phosphate, 0.06 part of titanium dioxide (anatase), and 2.0 parts of a finely ground thermoset condensation product of formaldehyde and melamine in molar proportions of 4 : 3 are prepared by the block process, and from a pair of such sheets a single, wire-reinforced sheet is formed by heating and pressing the sheets moistened with solvent with a sheet of wire fabric between them. Sheets may be similarly produced using cellulose acetate of higher acetyl value, e.g. 53 to 56 per cent, and the anatase may be replaced by the rutile form of titanium dioxide, preferably containing small proportions of zinc oxide (0.25 to 1.0 per cent), of aluminium oxide (1.5 to 2 per cent) and of silica 0.5 to 0.7 per cent), to inhibit change of the rutile to anatase. The synthetic resin inhibits the deterioration of the sheeting on exposure to the weather. The Provisional Specification refers also to compositions in which plasticizers not containing chlorine are used alone and in which thermoset condensation products of formaldehyde with melamine derivatives such as methylol melamine and