Bleaching and brightness stabilization of lignocellulosic materials with water-soluble phosphines or phosphonium compounds

A method of bleaching and brightness stabilization of a lignocellulosic pulp comprising:

• i) bleaching the lignocellulosic pulp, in an aqueous medium with a water-soluble phosphine or phosphonium compound of formula (A):
• wherein t is zero or 1;
• when t=0, R4R5PY2 is absent and R3 is bonded to the P of the R1R2PY1 group;
• when t=1, R5 is absent such that there is a P—P bond, or R5 is an alkylene group (CH2)s (s=1 to 12) interrupted by 0 to 6 oxygen (O) atoms or secondary amino (NR′) groups, and/or substituted by a zero to 2s number of a hydroxyl, alkyl, aryl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups, or a phenylene group substituted by a zero to 4 number of a hydroxyl, alkyl, aryl, thio, thioether, amino, ester, amide, carboxyl, carboxylate, and/or sulfonate groups;
• m is an integer of 0 to 5 and y is an integer of 1 or more, and n and z are integers of 0 or more such that yn=zm;
• when y=1, and n=z=m=0, then X is absent;
• R1, R2 and R3, or R1, R2, R3, R4 and R5 groups are collectively selected such that said compound of formula (A) has an overall solubility of at least 0.01 g/L;
• R1, R2 and R3, or R1, R2, R3 and R4 are independently selected from hydrogen, optionally substituted linear or branched alkyl groups, or optionally substituted aryl groups, the optional substitution being the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties;
• and
• Y1 and Y2 are independently absent or a carboxylate moiety;
• or
• when X is present, X is an inorganic or organic anion, and the value of m is ≦5;
• the total charge of yn=zm;
• and
• Y1 is a hydroxymethyl group (CH2OH);
• R1, R2 and R3, or R1, R2, R3, R4 and Y2 are independently selected from hydrogen, boron trifluoride (BF3), optionally substituted linear or branched alkyl groups, or optionally substituted aryl groups, the optional substitution being the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties;
• and
• ii) stabilizing the brightness in the resulting bleached lignocellulosic pulp with said compound of formula A of said bleaching in step i).