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A composition comprising

• (I) a polyisocyanate which has
• .alpha.) a content of isocyanate groups of 10-700 milliequivalents per 100 g of polyisocyanate,
• .beta.) an average NCO functionality of .gtoreq.1.0,
• .gamma.) a content of ethylene oxide units of 0 to 30% by weight, based on the polyisocyanate, the polyethylene oxide chain having an average molecular weight (number-average) of 100-3500, and
• .delta.) a content of tertiary amino groups and/or ammonium groups of 50-5000 milliequivalents per 100 g of polyisocyanate,
• and at least one member selected from the group consisting of
• (II) a naturally occurring polymer selected from the group consisting of
• starch, cellulose, hemicellulose, chitosans, xanthans, agar, galactomannans, carrageenan, pectin, aligantes, plant gum and derivatives thereof,
• (III) a polysiloxane graft copolymer of
• a) 40 to 70% by weight of a polysiloxane, as the graft substrate, terminated by hydroxyl groups and containing v mol % of recurring units of the formula ##STR21## and w mol % of recurring units of the formula ##STR22## wherein R.sup.1a represents alkyl radicals having 1 to 24 C atoms or aryl radicals having 6 to 10 C atoms,
• R.sup.2a represents unbranched or branched alkylene radicals having 1 to 8 C atoms and
• R.sup.3a represents alkyl radicals having 1 to 24 C atoms, aryl radicals having 6 to 10 C atoms, alkoxy radicals having 1 to 6 C atoms or a hydroxyl group or
• R.sup.2a and R.sup.3a, together with the Si atom, form a trivalent 5- or 6-membered ring with an unbranched or branched alkylene radical having 4 to 8 C atoms and
• v is 80 to 99 mol % and
• w is 1 to 20 mol % where v+w gives 100 mol %,
• and the viscosity, measured at 25.degree. C., of the OH-terminated polysiloxane is between 100 and 100,000 mPa.s, and
• (b) 30 to 60% by weight of graft monomers selected from the group consisting of styrene, .alpha.-methylstyrene, (meth)acrylic acid esters, (meth)acrylonitrile and mixtures of these monomers, one or more vinyl monomers of the formula ##STR23## wherein R.sup.4a represents an H atom or a methyl group,
• R.sup.5a represents an unbranched or branched alkylene group having 1 to 18 C atoms,
• Y represents an H atom or the groups --OH or C.sub.1 -C.sub.4 -alkoxy and
• Z represents a group --OH or --NR.sub.2.sup.4a,
• (IV) a water-dilutable synthetic polymer obtainable by polymerization of olefinically unsaturated dicarboxylic acid anhydrides with other unsaturated monomers, structural units of the formula ##STR24## being formed, b) subsequent partial reaction with a monohydric alcohol R--OH (2 to 50%) and
• c) reaction of the COOH groups obtained in b) with an epoxide compound to the extent of 10-95% and neutralization of the remaining COOH groups with a base, and
• (V) a cationic polymer containing hydroxyl groups, obtainable by polymerization of monomer mixtures of
• a) at least 5% by weight of styrene and/or .alpha.-methylstyrene, methacrylonitrile, acrylonitrile or mixtures of these monomers,
• b) at least 5% by weight of (meth)acrylic acid esters of monofunctional alcohols having 1 to 12 C atoms,
• c) 0.1 to 35% by weight of one or more vinyl monomers of the formula ##STR25## wherein R.sup.1a represents an H atom or a methyl group,
• R.sup.2a represents an unbranched or branched alkylene radical having 1 to 18 C atoms,
• Y represents an H atom or the groups --OR.sup.5a and
• Z represents a group --OH or --NR.sup.3a R.sup.4a, wherein R.sup.3a, R.sup.4a and R.sup.5a represent hydrogen or an alkyl radical having 1 to 4 C atoms and the sum of a)+b)+c) is 100% by weight,
• or said polyisocynate and said naturally occurring polymer and at least one member selected from the group consisting of said polysiloxane graft copolymer, said water-dilutable synthetic polymer and said cationic polymer.