Fremgangsmåte for å stabilisere hvitheten av ligninholdige fibröse materialer, stabilisert sammensetning og fibrösematerialer som er stabilisert med denne

(Cyclo)aliphatic thiols with other hydrophilic groups, unsaturated thiols, and thiols or di- and poly-sulfides with hetero-atoms are used to prevent light-induced yellowing in lignin-containing fibre materials. Thioglycerol, dithiothreitol mercaptoacetic acid and 2- or 3-mercaptopropionic acid are not included. A method for stabilizing the degree of whiteness of lignin-containing fibre materials (LFM) against light-induced yellowing by the use of thio compounds (I) as stabilizers, in which (I) comprise: (i) thiols with aliphatic or cycloaliphatic thiol group(s) and other hydrophilic group(s) selected from -OH, -NH2, -NHR , -NR R , -COOH, -SO3H, -PO3H2 or salts of these acids and bases; (ii) thiols with (cyclo)aliphatic thiol group(s) and C=C double bond(s); (iii) thiols with thiol group(s) attached to a hetero atom; and (iv) di- or poly-sulfides with hetero atom(s) attached to the di- or poly-sulfide groups. R , R = 1-4C alkyl, 2-4C hydroxyalkyl (e.g. hydroxyethyl or dihydroxypropyl), 2-4C alkanoyl or hydroxyalkanoyl. Independent claims are also included for: (1) lignin-containing LFM with a stabilized degree of whiteness, especially paper and cardboard from mechanically-produced (thermo-mechanically or chemo-thermo-mechanically) wood pulp or high-yield pulp, containing (I) in the fibre material itself or in a layer formed by impregnation, sizing or coating; (2) compositions containing (I) in an aqueous, organic or aqueous-organic liquid or paste-like medium which can be applied by spraying or coating; and (3) UV absorbers for stabilizing the degree of whiteness of LFM, comprising compounds of formula HO-Ar-CH=C(R )-CO-R . R = H, 1-12C alkanoyl (especially acetyl, propionyl or n-butanoyl) or 1-12C alkoxycarbonyl (especially -COOCH3 or -COOC2H5); R = 1-12C alkyl, especially methyl, ethyl, n-propyl, iso-propyl or n-butyl; Ar = phenylene or naphthylene, with OH in the ortho or para position to the C=C group and optionally substituted with alkyl (preferably methyl, ethyl, n- or iso-propyl, n-, sec.- or tert.-butyl), alkoxy (preferably methoxy or ethoxy), phenyl, p-(o-)-hydroxy-phenyl, benzoyl, -COOH or -SO3H