| abstract |
They are produced by impregnating cellulose-containing material with an aqueous solution containing alkali metal hydroxide and urea, heating the impregnated cellulose-containing material to form the cellulose carbamates and separating unreacted urea and by-products. A relatively high concentration of hydroxide is necessary for the uniform distribution of the reactants in the cellulose-containing material; on the other hand, a larger amount of hydroxide promotes the tendency of the isocyanic acid formed during heating to react and an excessive breakdown of the cellulose, so that in order to avoid hydroxide and urea losses, this with alkali metal hydroxide and urea-impregnated material is washed out one or more times with urea-containing water before heating, whereby reproducible and reliable undyed products which are not degraded too much and which are sufficiently substituted with carbamate groups in all areas are obtained. |