Abstract: The present invention relates to a method of dyeing a substrate with a reactive dyestuff in supercritical or near supercritical carbon dioxide, said substrate being selected from the group consisting of cellulose fibres; modified cellulose fibres; protein fibres; synthetic fibres and any combination thereof, wherein the method comprises dyeing said substrate by contacting the substrate with supercritical or near supercritical carbon dioxide containing a reactive dyestuff and one or more acids in a concentration of at least 0.05 mol.

Abstract: The present invention relates to a method of dyeing a substrate with a reactive dyestuff in supercritical or near supercritical carbon dioxide, said substrate being selected from the group consisting of cellulose fibres, modified cellulose fibres, protein fibres and of synthetic fibres, or any combination thereof, wherein the method comprises the subsequent steps of: pre-treating the substrate by wetting the substrate with a fluid medium containing at least 10 wt. %, preferably at least 40 wt. % of one or more organic hydrogen bond acceptor compounds selected from the group consisting of C1-C6 alkanols, dimethyl sulfoxide, dimethylformamide, acetone, butan-2-one, dimethyl ether, methyl acetate and ethyl acetate; dyeing the substrate by contacting the pre-treated substrate with supercritical or near supercritical carbon dioxide containing a reactive dyestuff.