WO2007016769A1

WO2007016769A1 - Synergistic bleaching of lignocellulosic materials with sodium hydrosulfite and h2o-soluble phosphines or phosphonium salts

Info

Publication number: WO2007016769A1
Application number: PCT/CA2006/001281
Authority: WO
Inventors: Thomas Q. Hu; Brian R. James; Trevor Williams; John A. Schmidt; Dmitry Moiseev
Original assignee: Fpinnovations
Priority date: 2005-08-05
Filing date: 2006-08-02
Publication date: 2007-02-15

Abstract

A method for the synergistic bleaching of lignocellulosic materials is described. The method involves the treatment of lignocellulosic materials, in particular, (a) wood pulps such as stone groundwood (SGW) pulp and thermomechanical pulp (TMP), and (b) papers made from wood pulps, with sodium hydrosulfite and a water-soluble phosphine such as tris(hydroxymethyl)phosphine (THP), P(CH2OH)3, or a water-soluble phosphonium compound such as tetrakis(hydroxymethyl)phosphonium sulfate (THPS), [P(CH2OH)4]2SO4. When applied to wood pulps such as SGW pulp, the method allows the bleaching of the pulps to brightness levels higher than what can be achieved using sodium hydrosulfite or the said phosphine or phosphonium compound alone, or the bleaching of the pulps to brightness levels similar to or higher than those achieved with sodium hydrosulfite alone but at much lower sodium hydrosulfite dosages.

Description

Synergistic Bleaching of Lignocellulosic Materials with Sodium Hydrosulfite and H₂O-SoIUbIe Phosphines or Phosphonium Salts

TECHNICAL FIELD

This invention relates to the bleaching of lignocellulosic materials, in particular, to the synergistic bleaching of lignocellulosic materials.

BACKGROUND ART '

Lignocellulosic materials such as wood are the raw materials used for the production of pulps and papers. In order to make papers, lignocellulosic materials are first reduced to pulps of discrete fibres by a mechanical or chemical pulping process. In mechanical pulping, pulps are produced, with retention of lignin, mainly through the action of mechanical forces in a yield of up to about 98%. One example of a mechanical pulp is the so-called stone groundwood (SGW) pulp produced from a mechanical grinding process. In chemical pulping, pulps are produced in a yield of 45-55% through the dissolution of most of the lignin by the pulping chemicals at an elevated temperature. One example of a chemical pulp is the so-called kraft pulp produced using sodium hydroxide and sodium sulfide as the pulping chemicals.

Mechanical and chemical pulps typically have a pale-yellow and a deep brown colour, respectively. Bleaching of these pulps to a whiter colour is often needed prior to the process of papermaking. One of the oldest bleaching agents used by the pulp and paper industry is sodium hydrosulfite (dithionite). Sodium hydrosulfite has been used for decades as a bleaching agent for mechanical pulps, either alone in one-stage or with alkaline hydrogen peroxide in a two-stage, peroxide-hydrosulfite sequence, and as a bleaching and/or color stripping agent for recycled fibers such as deinked pulps and mixed office waste furnish [Ellis, in: Pulp Bleaching - Principles and Practice, Eds. Dence and Reeve, Tappi Press, Atlanta, Georgia 491-512 (1996)]. The use of sodium hydrosulfite in chemical pulp bleaching has also been well documented [Liebergott, et al, Tappi J. 67(8): 76-80 (1984); Ducharme and Nye, Proc. 1993 Tappi Pulping Conf., Atlanta, Georgia 777-798 (1993)].

DOCSMTL 2 I 58997M Although most mechanical and chemical pulps and recycled fibers respond well to sodium hydrosulfite bleaching, some do not. For example, it has recently been shown that blue-stained lodgepole pine thermomechanical pulp (TMP) made from mountain- pine beetle infested pine wood responds poorly to sodium hydrosulfite bleaching and that the blue-stained pulp can not be bleached with sodium hydrosulfite to the same brightness level as the unstained pulp [Hu, et al., Proc. 2005 PacWest Conf, Harrison Hot Springs, British Columbia (2005)]. In addition, sodium hydrosulfite bleaching generates the by-product sodium thiosulfate that is corrosive to paper machines [Garner, J. Pulp Paper Sci. 14(5): J51-57, 1984]. The amounts of sodium thiosulfate generated during sodium hydrosulfite bleaching increase rapidly with increasing dosages of sodium hydrosulfite, particularly when the dosages are above 0.75% by weight based on oven-dried (o.d.) pulp [Garner, J. Pulp Paper Sci. 14(5): J51-57, 1984].

Recently, water-soluble phosphines and phosphonium compounds such as tris(hydroxymethyl)phosphine (THP), P(CH₂OH)₃, and tetrakis(hydroxymethyl)phosphonium sulfate (THPS), [P(CH₂θH)₄]₂Sθ₄, have been found to be excellent bleaching and brightness stabilizing agents for mechanical and chemical pulps [Hu, et al., US Patent Application, US2004/0173328A1, September 9, 2004]. These new bleaching agents have a bleaching power similar to or higher than that of sodium hydrosulfite, but they can be used over a wider range of pH (4.3-9.4), temperature (20-130 ⁰C) and consistency (e.g. 1.5-20%). Consistency is the weight percentage of pulp in a pulp and water mixture. Although the incorporation of these new bleaching agents into a known, reductive bleaching agent such as sodium hydrosulfite is described, no synergistic bleaching effect from the combination of sodium hydrosulfite and the said phosphine or phosphonium compound is described or claimed.

THPS has previously been shown to be a non-hazardous biocide for the control of hydrogen sulfide emissions and the reduction of corrosion in paper mills [Haack et al, Proc. 1997 Tappi Engineering & Papermakers Conf, Tappi Press, Atlanta, Georgia,

1115-1119 (1997)]. The ability of THP and THPS to kill catalase -producing bacteria in pulping liquors used for hydrogen peroxide bleaching of wood pulps has also been reported [Bowdery et al, PCT WO 01/53602 Al, 2001].

DISCLOSURE OF THE INVENTION

It has now been discovered that synergistic bleaching of lignocellulosic materials such as wood pulps and papers can be achieved by treating the materials with sodium hydrosulfite and a water-soluble phosphine such as tris(hydroxymethyl)phosphine (THP), P(CH₂OH)₃, or a water-soluble phosphonium compound such as tetrakis(hydroxymethyl)phosphonium sulfate (THPS), [P(CH₂OH)₄]₂SO₄.

DETAILED DESCRIPTION OF THE INVENTION

This invention seeks to provide a method for the synergistic bleaching of lignocellulosic materials to brightness levels higher than what can be achieved using sodium hydrosulfite alone, and/or to brightness levels higher than or similar to those achieved with sodium hydrosulfite but at much lower dosages of sodium hydrosulfite.

In accordance with one aspect of the invention there is provided a method for the synergistic bleaching of a lignocellulosic material comprising treatment of the lignocellulosic material with sodium hydrosulfite, Na₂S₂O₄, and a water-soluble phosphine or phosphonium compound of formula (A):

n+

Y₁ R₄

R, — P- -R₅-PH-R₃ [X]" (A) R₂ Y '

wherein t is zero (ie. 0) or 1; when t = 0, R₄R₅PY₂ is absent and R₃ is bonded to the P of the RiR₂PYi group; when t = 1 , R₅ is absent, 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 (s = 1 to 12) number of 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 hydroxyl, alkyl, aryl, thio, thioether, amino, ester, amide, carboxyl, carboxylate, and/or sulfonate groups; or preferably R₅ is an alkylene group (CH₂)S (s = 1 to 4) where the carbon chain is optionally interrupted by one or two oxygen (O) atom(s); y is an integer of 1 to 5, n is an integer of 0 to 2, z is an integer of 0 to 2, m is an integer of 1 to 5;

wherein when y = l, n = z = m = 0, then X is absent; Ri, R₂ and R₃, or Ri, R₂, R₃, R₄ and R₅ groups are collectively selected such that the molecule has an overall solubility of at least 0.001 g/L; Ri, R₂ and R₃, or Ri, R₂, R₃ and R₄ are independently selected from hydrogen, optionally substituted linear or branched alkyl groups, or optionally substituted aryl groups, the optional substitution referring to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties; and Yi and Y₂ are independently absent or carboxylate moieties; and

wherein when X is present, X is an inorganic or organic anion, n, y, z and m are integers, wherein n is 1 or 2, y is <5, ie. 1 to 5; z is 1 or 2 and the value of m is < 5, ie. 1 to 5; the total charge of yn = zm; Yi is a hydroxymethyl group (CH₂OH) and t is zero or 1; Ri, R₂ and R₃, or R₁, R₂, R₃, R₄ and Y₂ are independently selected from hydrogen, a Lewis acid such as boron trifluoride (BF₃), optionally substituted linear or branched alkyl groups, or optionally substituted aryl groups, the optional substitution referring to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties. In another aspect of the invention there is provided a lignocelullosic material bleached by sodium hydrosulfite, Na₂S₂O₄, and a compound of formula (A) defined herein.

In another aspect of the invention there is provided a lignocelullosic material bleached by the method of the invention.

Thus it has now been discovered that synergistic bleaching of lignocellulosic materials such as wood pulps and papers can be achieved by treating the materials with sodium hydrosulfite, Na₂S₂O₄, and a water-soluble phosphine such as tris(hydroxymethyl)phosphine (THP), P(CH₂OH)₃, or a phosphonium compound containing at least one phosphorus hydroxyalkyl bond/linkage, for example a phosphorus hydroxymethyl bond/linkage (P-CH₂OH) such as tetrakis(hydroxymethyl)phosphonium sulfate (THPS), [P(CH₂OH)₄]₂SO₄.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

According to the present invention, synergistic bleaching of lignocellulosic materials such as mechanical wood pulps and papers can be achieved by treatment of the materials with sodium hydrosulfite, Na₂S₂O₄, and a water-soluble phosphine, preferably a water-soluble tertiary phosphine; or a phosphonium compound, preferably a quaternary phosphonium compound. In a preferred embodiment the invention is the use of sodium hydrosulfite and any phosphine or phosphonium compound that contains a P- AIk-OH fragment, such as a P-CH₂-OH fragment, wherein AIk indicates an alkylene radical which may be optionally substituted or interrupted as described herein.

Treatment or treating in the method of the invention particularly contemplates contacting the lignocellulosic material with sodium hydrosulfite, Na₂S₂O₄, and the compound of formula (A) in an aqueous medium or vehicle.

More especially, the treatment or treating contemplates bleaching the lignocellulosic material with the two agents such that the sodium hydrosulfite and the compound of formula (A) are applied simultaneously or sequentially to the lignocellulosic material and are present together in the aqueous medium during the bleaching. In other words the sodium hydrosulfite and the compound of formula (A) co-act on the lignocellulosic material to effect the bleaching.

The compounds of formula (A) have been broadly defined earlier but in particular and preferred embodiments the compounds of formula (A) have the following characteristics:

a) Yi and Y₂ are both absent, R₁, R₂ and R₃, or R₁, R₂, R₃ and R₄ are independently hydrogen, an alkyl group (R) or an ether group (OR) with R being (CH₂)_qH (q = 1 to 12) interrupted by 0 to 6 oxygen (O) atoms or secondary amino (NR') groups, and/or substituted by a zero to (2q + 1) number of hydroxyl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups. R' is either hydrogen or an optionally substituted linear or branched alkyl group or optionally substituted aryl group; wherein optional substitution refers to the presence of one or more substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties;

b) Yi and Y₂ are both absent, R], R₂ and R₃, or Ri, R₂, R₃ and R₄ are independently hydrogen, an alkyl group (R) or an ether group (OR) with R being CH₂(CH₂)_qH (q = 0 to 5) interrupted by 0 to 3 oxygen (O) atoms or secondary amino (NR') groups, and/or substituted by a zero to (2q + 1) number of hydroxyl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups;

c) Yi and Y₂ are both absent, at least one of Ri and R₂ is the same as R₃ in the molecule with R₃ being a hydroxymethyl (CH₂OH) group;

d) Yi and Y₂ are both absent, R₁, R₂ and R₃ or R₁, R₂, R₃ and R₄ are all hydroxymethyl (CH₂OH) groups; e) Yi is a hydroxymethyl group (CH₂OH) and t is zero or 1, Ri, R₂ and R₃, or Ri, R₂, R₃, R₄ and Y₂ are independently hydrogen, a Lewis acid such as boron trifluoride (BF₃), an alkyl group (R) or an ether group (OR) with R being (CH₂)_qH (q = 1 to 12) interrupted by 0 to 6 oxygen (O) atoms or secondary amino (NR') groups, and/or substituted by a zero to (2q + 1) number of hydroxyl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups. R' is either hydrogen or an optionally substituted linear or branched alkyl group or optionally substituted aryl group; wherein optional substitution refers to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties;

f) Yi is a hydroxymethyl group (CH₂OH) and t is zero or 1, Ri, R₂ and R₃, or Ri, R₂, R₃, R₄ and Y₂ are independently hydrogen, a Lewis acid such as boron trifluoride (BF₃), an alkyl group (R) or an ether group (OR) with R being CH₂(CH₂)_qH (q = 0 to 5) interrupted by 0 to 3 oxygen (O) atoms or secondary amino (NR') groups, and/or substituted by a zero to (2q + 1) number of hydroxyl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups;

g) Yi is a hydroxymethyl group (CH₂OH) and t is zero or 1, and at least one of R₃, R₄ and Y₂ is a hydroxymethyl (CH₂OH) group.

In the phosphonium compounds of formula (A) X is suitably selected from chloride, sulfate, hydroxide, hydrosulfite, phosphate, carbonate, bicarbonate, bisulfate, alkoxide, formate, acetate, citrate, oxalate, ascorbate, ethylenediaminetetraacetate or diethylenetriaminepentaacetate .

The compounds of formula (A) for use in the invention need to be water-soluble and the variables in formula (A) are selected so that the compounds (A) have an overall water solubility of at least 0.001 g/L.

Further examples of preferred phosphine and phosphonium compounds for use in the invention are indicated below: Phosphines:

Ri

The R₁, R₂ and R₃ groups being collectively selected such that the molecule has an overall solubility of at least 0.001 g/L.

Where Ri and/or R₂ are/is hydrogen; and R₃, R₃ and R₁, or R₃ and R₂, is/are selected from, optionally substituted linear or branch alkyl groups, or optionally substituted aryl groups; or Ri, R₂ and R₃ are independently selected from, optionally substituted linear or branched alkyl groups, or optionally substituted aryl groups. Where optional substitution can refer to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties.

In a more preferred embodiment R₁, R₂ and R₃ are independently an alkyl group (R) or an ether group (OR) with R being (CH₂)_qH (q = 1 to 12) interrupted by 0 to 6 oxygen (O) atoms or secondary amino (NR') groups, and/or substituted by a zero to (2q + 1) number of hydroxyl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups.

In even more preferred embodiments Ri, R₂ and R₃ are independently an alkyl group (R) or an ether group (OR) with R being CH₂(CH₂)_qH (q = 0 to 5) interrupted by 0 to 3 oxygen (O) atoms or secondary amino (NR'), and/or substituted by a zero to (2q + 1) number of hydroxyl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups. R' is either hydrogen or an optionally substituted linear or branched alkyl group or optionally substituted aryl group. Where optional substitution can refer to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties. In yet even more preferred embodiments at least one of R_{] f} R₂ and R₃ is a CH₂OH group.

In a most preferred embodiment the water-soluble phosphine is the commercially available compound, tris(hydroxymethyl)phosphine (THP), P(CH₂OH)₃.

Diphosphines and Bisphosphines:

The Ri, R₂, R₃, Re and R₇ groups being collectively selected such that the molecule has an overall solubility of at least 0.001 g/L.

Where Ri, R₂, R₃ and R₇ are independently selected from hydrogen, optionally substituted linear or branched alkyl groups, or optionally substituted aryl groups. Where optional substitution can refer to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties.

In more preferred embodiments the diphosphine compound is of C₂ or C_s symmetry. In preferred embodiments Ri, R₂, R₃ and R₇ are independently hydrogen, an alkyl group (R) or an ether group (OR) with R being (CH₂)_qH (q = 1 to 12) interrupted by 0 to 6 oxygen (O) atoms or secondary amino (NR') groups, and/or substituted by a zero to (2q + 1) number of hydroxyl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups. R' is either hydrogen or an optionally substituted linear or branched alkyl group or optionally substituted aryl group. Where optional substitution can refer to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties.

In more preferred embodiments Rj, R₂, R₃ and R₇ are independently hydrogen, an alkyl group (R) or an ether group (OR) with R being CH₂(CH₂)_qH (q = 0 to 5) interrupted by 0 to 3 oxygen (O) atoms or secondary amino (NR') groups, and/or substituted by a zero to (2q + 1) number of hydroxyl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups.

In even more preferred embodiments at least one of Ri and R_∑ is the same as R₃ in the molecule. In yet even more preferred embodiments at least one of Ri and R₂ is the same as R₃ in the molecule with R₃ being a hydroxymethyl (CH₂OH) group. In most preferred embodiments Ri, R₂, R3 and R₇ are all hydroxymethyl (CH₂OH) groups.

R₆ is absent; 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 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 hydroxyl, alkyl, aryl, thio, thioether, amino, ester, amide, carboxyl, carboxylate, and/or sulfonate groups.

In preferred embodiments R₆ is an alkylene group (CH₂)_S (s = 1 to 4), where the carbon chain is optionally interrupted by one or two oxygen (O) atom(s).

Phosphonium Compounds:

Wherein X is an inorganic or organic anion such as, but not limited to, chloride, sulfate, hydroxide, hydrosulfite, phosphate, carbonate, bicarbonate, bisulfate, alkoxide, formate, acetate, citrate, oxalate, ascorbate, ethylenediaminetetraacetate or diethylene- triaminepentaacetate, and the value of m is < 5; the total charge of yn = zm. Where R₃ is a hydroxymethyl group (CH₂OH); and R₁, R₂ and R₇ are independently selected from hydrogen, a Lewis acid such as boron trifluoride (BF₃), optionally substituted linear or branched alkyl groups, or optionally substituted aryl groups. Where optional substitution can refer to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties.

In preferred embodiments R₃ is a hydroxymethyl group (CH₂OH); and Rj, R₂ and R₇ are independently hydrogen, a Lewis acid such as boron trifluoride (BF3), an alkyl group (R) or an ether group (OR) with R being (CH₂)_qH (q = 1 to 12) interrupted by 0 to 6 oxygen (O) atoms or secondary amino (NR') groups, and/or substituted by a zero to (2q + 1) number of hydroxyl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups. R' is either hydrogen or an optionally substituted linear or branched alkyl group or optionally substituted aryl group. Where optional substitution can refer to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties.

In more preferred embodiments R₃ is a hydroxymethyl group (CH₂OH); and R₁, R₂ and R₇ are independently hydrogen, a Lewis acid such as boron trifluoride (BF₃), an alkyl group (R) or an ether group (OR) with R being CH₂(CH₂)_qH (q = 0 to 5) interrupted by 0 to 3 oxygen (O) atoms or secondary amino (NR') groups, and/or substituted by a zero to (2q + 1) number of hydroxyl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups.

In a most preferred embodiment the phosphonium compound is the commercially- available tetrakis(hydroxymethyl)phosphonium sulfate (THPS), [P(CH₂OH)₄]₂SO₄.

Diphosphonium and Bisphosphonium Compounds:

Wherein X is an inorganic or organic anion such as, but not limited to, chloride, sulfate, hydroxide, hydrosulfϊte, phosphate, carbonate, bicarbonate, bisulfate, alkoxide, formate, acetate, citrate, oxalate, ascorbate, ethylenediammetetraacetate or diethylene- triaminepentaacetate, and the value of m is < 5; the total charge of yn = zm.

Where R₃ is a hydroxymethyl group (CH₂OH); and Ri, R₂, R₄, R₇ and Rg are independently selected from hydrogen, a Lewis acid such as boron trifluoride (BF₃), optionally substituted linear or branched alkyl groups, or optionally substituted aryl groups. Where optional substitution can refer to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties.

In more preferred embodiments the diphosphonium compound is of C₂ or C_s symmetry. In preferred embodiments R₃ is a hydroxymethyl group (CH₂OH); and Ri, R₂, R₄, R₇ and Rg are independently hydrogen, a Lewis acid such as boron trifluoride (BF₃), an alkyl group (R) or an ether group (OR) with R being (CH₂)_qH (q = 1 to 12) interrupted by 0 to 6 oxygen (O) atoms or secondary amino (NR') groups, and/or substituted by a zero to (2q + 1) number of hydroxyl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups. R' is either hydrogen or an optionally substituted linear or branched alkyl group or optionally substituted aryl group. Where optional substitution can refer to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties.

In more preferred embodiments R₃ is a hydroxymethyl group (CH₂OH); and Ri, R₂, R₄, R₇ and R₈ are independently hydrogen, a Lewis acid such as boron trifluoride (BF₃), an alkyl group (R) or an ether group (OR) with R being CH₂(CH₂)_qH (q = 0 to 5) interrupted by 0 to 3 oxygen (O) atoms or secondary amino (NR') groups, and/or substituted by a zero to (2q + 1) number of hydroxyl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups.

In most preferred embodiments R₃ is a hydroxymethyl group (CH₂OH); and at least one

Of R₄, R₇ and Rg is also a hydroxymethyl (CH₂OH) group.

Especially preferred compounds of formula (A) for use in the invention include; tris(hydroxymethyl)phosphine (THP), P(CH₂OH)₃; tris(hydroxypropyl)phosphine(THPP), P(CH₂CH₂CH₂OH)₃; bis[bis(hydroxymethyl)phosphino]ethane, (HOCH₂)₂PCH₂CH₂P(CH₂OH)₂; tetrakis(hydroxymethyl)phosphonium sulfate (THPS), [P(CH₂OH)₄]₂SO₄.

Unless indicated otherwise terms indicated hereinafter have the following meanings in this specification:

i) alkyl and alkyl moieties are straight chain or branched and have 1 to 12, preferably 1 to 6 and more preferably 1 to 4 carbon atoms; alkyl moieties represent the alkyl portions of thioether, amide, ether and ester substituents; ii) aryl and aryl moieties and arylene have 6 to 14 carbon atoms and are preferably phenyl or phenylene; aryl moieties represent the aryl portions of thioether, amide, ether and ester substituents;

iii) water-soluble means, with reference to the compounds of formula (A), that the compounds have an overall water solubility of at least 0.001 g/L.

iv) synergistic bleaching with sodium hydrosulfϊte and a phosphine or phosphonium compound refers to bleaching of the lignocellulosic material to give the material an increase in brightness that is higher than the sum of the increases in brightness from separate bleaching of the material with sodium hydrosulfite and with the said phosphine or phosphonium compound.

Method of Use

Treatment of lignocellulosic materials such as wood chips, recycled fibers, pulps and papers with sodium hydrosulfϊte, Na₂S₂θ₄, and the said phosphine or phosphonium compounds of formula (A) can be carried out on chips, recycled fibers, pulps or papers over a consistency of 0.01 to 99% in a pH range of 3.0 - 10.0 and a temperature range of 20 - 170 ⁰C at various places during the manufacturing and processing of the pulps or papers, such as the impregnation or refining of wood chips in an impregnator or refiner, bleaching of the pulps in a bleach tower or any other vessels, and surface sizing or coating of papers in a size press or coater.

For the said treatment of the said lignocellulosic materials, sodium hydrosulfite either as a powder or dissolved in a solution, and the said phosphine or phosphonium compounds of formula (A) can be combined in solution and added to the said lignocellulosic materials with or without storage of the combined solution, or they can be added separately to the said lignocellulosic materials. The said phosphine or phosphonium compounds of formula (A) can also be combined with sodium hydrosulfite during the production or preparation of sodium hydrosulfite, and then added to the said lignocellulosic materials. In other words, the said phosphine or phosphonium compounds of formula (A) can be used as an additive in sodium hydrosulfϊte bleach formulation for the synergistic bleaching of the said lignocellulosic materials.

The amount of sodium hydrosulfϊte can suitably range from 0.01 to 2.0% by weight based on oven-dried (o.d.) chip/fϊber/pulp weight, preferably at least 0.05%, more preferably at least 0.1% and most preferably from 0.2 to 1.0%, by weight. The amount of the phosphine or the phosphonium compound can suitably range from 0.001 to 2.0% by weight based on oven-dried (o.d.) chip/fiber/pulp weight, preferably at least 0.01%, more preferably at least 0.02% and most preferably from 0.05 to 1.0%, by weight. The treatment can take place over the course of between 5 minutes and 30 days.

The invention contemplates the synergistic bleaching of lignocellulosic materials such as wood pulps and papers, the pulps and papers containing the said bleached pulps.

The lignocellulosic mechanical wood pulp may be, for example, spruce SGW pulp or lodgepole pine TMP.

The lignocellulosic material may, for example, be an unbleached mechanical wood pulp or a mechanical wood pulp that has been partially or fully bleached with other bleaching chemicals such as alkaline hydrogen peroxide; or a chemical wood pulp such as unbleached kraft pulp or kraft pulp partially or fully delignifϊed and/or bleached with other delignifying and/or bleaching chemicals such as oxygen and/or chlorine dioxide.

The lignocellulosic material may also be a paper sheet containing mechanical wood pulp as the sole pulp component or as one of the pulp components.

Paper in the present specification also includes paperboard.

This invention also covers the pulp or paper produced by the use of the method and compositions described herein. EXAMPLES

The present invention is illustrated by, but not limited to, the following examples:

General Procedure A: Bleaching of Wood Pulps with Sodium Hydrosulfite

All chemicals used for the bleaching of wood pulps are in percent with respect to oven- dried (o.d.) pulp weights. Unless otherwise specified, 0.2-2.0% of sodium hydrosulfite, Na₂S₂O₄, is dissolved in a known amount of deionized (DI) water (H₂O) or a pulp mill process water, the pH of which has been adjusted to 5.0, and which when combined with a wood pulp will give a 4.0% consistency (Cs). The solution is added to the pulp (4.0-16 g o.d.) in a polyethylene bag. The air in the bag is squeezed out, and the bag is sealed and then immersed in a water-bath at 65⁰C for 1 h with manual mixing at 15 and 30 minutes. At the end of the bleaching process, the bag is removed and cooled in a cold water-bath to room temperature (-20 ⁰C). The pulp is diluted with DI H₂O to 0.5- 1.0% Cs. and filtered with filtrate being recycled once to recover the fines. The same dilution and filtration is then repeated once. The pulp is used to make handsheets (200 g/m²) according to PAPTAC Standard Test Method C.5. The ISO brightness values of the sheets are determined in a Technibrite Micro TB-IC instrument according to PAPTAC Standard Test Method E.1.

General Procedure B: Bleaching of Wood Pulps with a Phosphine or Phosphonium Compound, or with Sodium Hydrosulfite and a Phosphine or Phosphonium Compound

AU chemicals used for the bleaching of wood pulps are in percent with respect to oven- dried (o.d.) pulp weights. Unless otherwise specified, 0.05-1.0% of a phosphine or phosphonium compound is dissolved in a known amount of DI H₂O or a pulp mill process water that when combined with a wood pulp (4.0-16 g o.d.) will give a 4.0% Cs. Unless otherwise specified, the pH of the solution is adjusted to 5.0, and in the case of bleaching with sodium hydrosulfite and a phosphine or phosphonium compound, 0.2- 2.0% of sodium hydrosulfite is added. The solution is then added to the pulp in a polyethylene bag. The air in the bag is squeezed out, and the bag is sealed and then immersed in a water-bath at 65°C for 1 h with manual mixing at 15 and 30 minutes. At the end of the bleaching process, the bag is removed and cooled in a cold water-bath to room temperature (-20 ⁰C). The pulp is diluted with DI H₂O to 0.5-1.0% Cs. and filtered with filtrate being recycled once to recover the fines. The same dilution and filtration is then repeated once. The pulp is used to make handsheets (200 g/m²) according to PAPTAC Standard Test Method C.5. The ISO brightness values of the sheets are determined in a Technibrite Micro TB-IC instrument according to PAPTAC Standard Test Method E.I.

EXAMPLE 1

A spruce SGW pulp from an eastern Canadian mill (ISO brightness = 66.2%) was bleached with various amounts of sodium hydrosulfite, Na₂S₂O₄, at 4% Cs. (with the mill process water), pH 5.0 and 65 ⁰C for 1 h according to the general procedure A disclosed above. The same SGW pulp was also bleached with various amounts of THPS alone, or with various amounts OfNa₂S₂O₄ and THPS simultaneously, at 4% Cs. (with the mill process water), pH 5.0 and 65 ⁰C for 1 h according to the general procedure B disclosed above. The results are summarized in Table 1. Bleaching the

SGW pulp with 1.0% Na₂S₂O₄ gave an ISO brightness gain of 3.0 points. Bleaching the SGW pulp with 0.1% THPS gave an ISO brightness increase of 0.9 point. Bleaching the pulp simultaneously with 1.0% Na₂S₂O₄ and 0.1% THPS gave an ISO brightness gain of 5.0 points. This is considered synergistic since 5.0 > 3.0 + 0.9 = 3.9. Such synergistic bleaching made it possible to obtain a pulp with an ISO brightness of 71.2%, compared to a maximum ISO brightness of 69.2% achievable with Na₂S₂O₄. Such synergistic bleaching also made it possible to obtain an ISO brightness of 70.1% with 0.5% Of Na₂S₂O₄, compared to 1.0% OfNa₂S₂O₄ needed to reach an ISO brightness of 69.2% when Na₂S₂O₄ was used alone. Table 1. ISO brightness values of the SGW pulp (ISO brightness i = 66.2%) bleached with various amount OfNa₂S₂O₄, THPS, or Na₂S₂O₄ and THPS, and the corresponding brightness gains.

Na₂S₂O₄ THPS ISO Brightness ISO Brightness Gain (% o.d. pulp) (% o.d. pulp) (%) (points)

0.5 68.6 2.4 1.0 69.2 3.0 2.0 69.1 2.9

0.1 67.1 0.9 0.5 68.3 2.1

0.5 0.1 70.1 3.9 1.0 0.1 71.2 5.0

EXAMPLE 2

A laboratory-prepared, lodgepole pine TMP (ISO brightness = 54.2%) was bleached with various amounts of sodium hydrosulfite, Na₂S₂O₄, at 4% Cs. (with DI H₂O), pH 5.0 and 65 ⁰C for 1 h according to the general procedure A disclosed above. The same TMP was also bleached with various amounts of THPS alone, or with various amounts OfNa₂S₂O₄ and THPS simultaneously, at 4% Cs. (with DI H₂O), pH 5.0 and 65 ⁰C for 1 h according to the general procedure B disclosed above. The results are summarized in Table 2. Bleaching the TMP with 0.5% Na₂S₂O₄ gave an ISO brightness gain of 2.0 points. Bleaching the TMP with 0.1% THPS gave an ISO brightness increase of 1.2 points. Bleaching the pulp simultaneously with 0.5% Na₂S₂O₄ and 0.1% THPS gave a brightness gain of 3.5 points. This is considered synergistic because 3.5 > 2.0 + 1.2 = 3.2.

Table 2. ISO brightness values of the TMP bleached with various amount Of Na₂S₂O₄,

THPS, or Na₂S₂O₄ and THPS, and the corresponding brightness gains.

Na₂S₂O₄ THPS ISO Brightness ISO Brightness Gain

(% o.d. pulp) (% o.d. pulp) (%) (points)

0.5 - 56.2 2.0

1.0 - 58.1 3.9 0.1 55.4 1.2 0.5 57.1 2.9

0.5 0.1 57.7 3.5

EXAMPLE 3

A laboratory-prepared, lodgepole pine TMP (ISO brightness = 54.2%) was bleached with 0.5% Na₂S₂O₄ at 4% Cs. and 65 ⁰C for 1 h according to the general procedure A disclosed above except that a pH 6.0 acetate buffer was used. The same TMP was also bleached with 0.1% THPS alone, or with 0.5% Na₂S₂O₄ and 0.1% THPS simultaneously, at 4% Cs. and 65 ⁰C for 1 h according to the general procedure B disclosed above except that a pH 6.0 acetate buffer was used. The results are summarized in Table 3. Bleaching the TMP with 0.5% Na₂S₂O₄ and with 0.1% THPS, respectively, at buffered pH 6.0 gave an ISO brightness gain of 2.8 and 1.0 points. Bleaching the pulp simultaneously with 0.5% Na₂S₂O₄ and 0.1% THPS at buffered pH 6.0 gave a brightness gain of 4.5 points. This is considered synergistic because 4.5 > 2.8 + 1.0 = 3.8.

Table 3. . ISO brightness values of the TMP bleached with 0.5% Na₂S₂O₄, 0.1% THPS, or 0.5% Na₂S₂O₄ and 0.1% THPS at buffered pH 6.0, and the corresponding brightness gains.

0.5 57.0 2.8

0.1 55.2 1.0 0.5 0.1 58.7 4.5

EXAMPLE 4

A hemlock chemithermomechanical (CTMP) pulp from a western Canadian mill (ISO brightness = 55.6%) was bleached with various amounts of sodium hydrosulfite, Na₂S₂θ₄, at 5% Cs. (with the mill process water), pH 5.0 and 60 ⁰C for 1 h according to the general procedure A disclosed above except that the pulp slurry was preheated at 60 ⁰C for 10 minutes before the addition of Na₂S₂CV The same CTMP pulp was also bleached with 0.1% THPS alone, or with 1.0% Na₂S₂O₄ and 0.1% THPS simultaneously, at 5% Cs. (with the mill process water), pH 5.0 and 60 ⁰C for 1 h according to the general procedure B disclosed above except that the pulp slurry was preheated at 60 ⁰C for 10 minutes before the addition of THPS, or Na₂S₂O₄ and THPS. The results are summarized in Table 4. Bleaching the CTMP pulp with 1.0% Na₂S₂O₄ gave an ISO brightness gain of 5.6 points. Bleaching the CTMP pulp with 0.1 % THPS gave an ISO brightness increase of 1.3 points. Bleaching the pulp simultaneously with 1.0% Na₂S₂O₄ and 0.1 % THPS gave an ISO brightness gain of 7.3 points. This is considered synergistic because 7.3 > 5.6 + 1.3 = 6.9. Such synergistic bleaching made it possible to obtain a pulp with an ISO brightness of 62.9%, compared to a maximum ISO brightness of 61.5% achievable with 1.2% Na₂S₂O₄.

Table 4. ISO brightness values of the CTMP pulp (ISO brightness = 55.6%) bleached with various amount OfNa₂S₂O₄, 0.1% THPS, or 1.0% Na₂S₂O₄ and 0.1% THPS, and the corresponding brightness gains.

0.8 59.8 4.2 1.0 - 61.2 5.6 1.2 61.5 5.9 1.4 61.2 5.6

- 0.1 56.9 1.3

1.0 0.1 62.9 7.3 EXAMPLE 5

A laboratory-prepared, lodgepole pine TMP (ISO brightness = 54.2%) was bleached with 1.0% sodium hydrosulfite, Na₂S₂O₄, at 4% Cs. and 65 ⁰C for 1 h according to the general procedure A disclosed above except that a pH 5.0 acetate buffer was used and that in one of the bleaching experiments the Na₂S₂O₄ solution was stored under N₂ at room temperature (-23 ⁰C) for 2 h before it was added to the pulp. The same TMP pulp was also bleached with 1.0% Na₂S₂O₄ and 0.1% THPS simultaneously, at 4% Cs. and 65 ⁰C for 1 h according to the general procedure B disclosed above except that a pH 5.0 acetate buffer was used and that in one of the bleaching experiments the solution of Na₂S₂O₄ and THPS was stored under N₂ at room temperature (~23 ⁰C) for 2 h before it was added to the pulp. The results are summarized in Table 5. Combining THPS with Na₂S₂O₄ and using them for bleaching gave a higher ISO brightness gain than using Na₂S₂O₄ alone. In addition, it allowed the storage of the bleach solution at -23 ⁰C for 2 h before it was added to the pulp without decreasing the bleaching ability of the solution.

Table 5. ISO brightness values of the TMP (ISO brightness = 54.2%) bleached with 1.0% Na₂S₂O₄, or 1.0% Na₂S₂O₄ and 0.1 % THPS at buffered pH 5.0 with or without the storage of the bleach solution under N₂ at ~23 ⁰C for 2 h, and the corresponding brightness gains.

Na₂S₂O₄ THPS Storage ISO Brightness ISO Brightness Gain (% o.d. pulp) (% o.d. pulp) (%) (points)

1.0 - No 60.7 6.5

1.0 - Yes 58.3 4.1

1.0 0.1 No 61.6 7.4

1.0 0.1 Yes 61.6 7.4

EXAMPLE 6

A laboratory-prepared, lodgepole pine TMP (ISO brightness = 54.2%) was bleached with 1.0% Na₂S₂O₄ at 4% Cs. and 65 ⁰C for 1 h according to the general procedure A disclosed above except that a pH 5.0 acetate buffer was used. The same TMP pulp was also bleached with 1.0% Na₂S₂O₄ and 0.1% THPS simultaneously, at 4% Cs. and 65 ⁰C for 1 h according to the general procedure B disclosed above except that a pH 5.0 acetate buffer was used and that in one of the bleaching experiments THPS and Na₂S₂O₄ were added separately and sequentially to the pulp. The results are summarized in Table 6. THPS and Na₂S₂O₄ can be combined and then added to the pulp, or they can be added to the pulp separately to bleach the pulp to a higher ISO brightness than Na₂S₂O₄.

Table 6. ISO brightness values of the TMP (ISO brightness = 54.2%) bleached with 1.0% Na₂S₂O₄, or 1.0% Na₂S₂O₄ and 0.1 % THPS at buffered pH 5.0 with or without the storage of the bleach solution under N₂ at -23 ⁰C for 2 h, and the corresponding brightness gains.

Na₂S₂O₄ THPS Order of addition ISO^" ISO Brightness

(% o.d. pulp) (% o.d. pulp) Brightness (%) Gain (points) fδ - - 6OJ 6^~5

1.0 0.1 Simultaneously 61.6 7.4 1.0 0.1 THPS then Na₂S₂O₄ 62.3 8.1

EXAMPLE 7

A softwood (mainly spruce) thermomechanical (TMP) pulp from an Eastern Canadian mill (ISO brightness = 54.4%) was bleached with 0.95% sodium hydrosulfite, Na₂S₂O₄, at 4.6% Cs. (with the mill process water), pH 4.3 and 80 ⁰C for 40 minutes according to the general procedure A disclosed above except that the pulp slurry was preheated at 80 ⁰C for 10 minutes before the addition OfNa₂S₂O₄. The same TMP pulp was also bleached with 0.1% THPS alone, or with 0.95% Na₂S₂O₄ and 0.1% THPS simultaneously, at 4.6% Cs. (with the mill process water), pH 4.3 and 80 ⁰C for 40 minutes according to the general procedure B disclosed above except that the pulp slurry was preheated at 80 ⁰C for 10 minutes before the addition of THPS, or Na₂S₂O₄ and THPS. The results are summarized in Table 7. Bleaching the TMP pulp with 0.95% Na₂S₂O₄ gave an ISO brightness gain of 5.9 points. Bleaching the TMP pulp with 0.1% THPS gave an ISO brightness increase of 1.2 points. Bleaching the pulp simultaneously with 0.95% Na₂S₂O₄ and 0.1% THPS gave an ISO brightness gain of 8.2 points. This is considered synergistic because 8.2 > 5.9 + 1.2 = 7.1.

Table 7. ISO brightness values of the TMP pulp (ISO brightness = 54.4%) bleached with 0.95% Na₂S₂O₄, 0.1% THPS, and "0.95% Na₂S₂O₄ and 0.1% THPS", respectively, and the corresponding brightness gains.

Na₂S₂O₄ THPS ISO Brightness ISO Brightness Gain

(% o.d. pulp) (% o.d. pulp) (%) (points)

0.95 - 60.3 5.9

0.1 55.6 1.2

EXAMPLE 8

A deinked mixed office waste (MOW) pulp from an Eastern Canadian mill (ISO brightness = 72.8%) was bleached with 0.5% sodium hydrosulfite, Na₂S₂O₄, at 10% Cs. (with the mill process water), pH 8.0 (pulp initial pH) and 56 ⁰C for 1.8 hours according to the general procedure A disclosed above except that the pulp slurry was preheated at 56 ⁰C for 10 minutes before the addition OfNa₂S₂O₄. The same deinked MOW pulp was also bleached with 0.1% THPS alone, or with 0.5% Na₂S₂O₄ and 0.1% THPS simultaneously, at 10% Cs. (with the mill process water), pH 8.0 (pulp initial pH) and 56 ⁰C for 1.8 hours according to the general procedure B disclosed above except that the pulp slurry was preheated at 56 ⁰C for 10 minutes before the addition of THPS, or Na₂S₂O₄ and THPS. The results are summarized in Table 8. Bleaching the deinked MOW pulp with 0.5% Na₂S₂O₄ gave an ISO brightness gain of 7.2 points. Bleaching the deinked MOW pulp with 0.1% THPS gave an ISO brightness increase of 1.0 point. Bleaching the pulp simultaneously with 0.5% Na₂S₂O₄ and 0.1 % THPS gave an ISO brightness gain of 8.9 points. This is considered synergistic because 8.9 > 7.2 + 1.0 = 8.2. Table 8. ISO brightness values of the deinked MOW pulp (ISO brightness = 72.8%) bleached with 0.5% Na₂S₂O₄, 0.1% THPS, and "0.5% Na₂S₂O₄ and 0.1% THPS", respectively, and the corresponding brightness gains.

0.5 - 80.0 7.2

- 0.1 73.8 1.0

0.5 0.1 81.7 8.9

Claims

1. A method of bleaching lignocellulosic material comprising treatment of the lignocellulosic material with sodium hydrosulfϊte, Na₂S₂θ₄, and a water-soluble phosphine or phosphonium compound of formula (A):

z [Xf (A)

wherein t is zero or 1 ; when t = 0, R₄R₅PY₂ is absent and R₃ is bonded to the P of the R]R₂PYi group; when t = 1, R₅ is absent, 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

(s = 1 to 12) number of 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 hydroxyl, alkyl, aryl, thio, thioether, amino, ester, amide, carboxyl, carboxylate, and/or sulfonate groups; or preferably R₅ is an alkylene group (CH₂)S (s =

1 to 4) where the carbon chain is optionally interrupted by one or two oxygen (O) atom(s); y is an integer of 1 to 5, n is an integer of 0 to 2, z is an integer of 0 to 2, m is an integer of 1 to 5;

wherein when y = l, n = z = m = 0, X is absent; R₁, R₂ and R₃, or R₁, R₂, R₃, R₄ and R₅ groups are collectively selected such that the molecule has an overall solubility of at least 0.001 g/L; R₁, R₂ and R₃, or Rj, R₂, R₃ and R₄ are independently selected from hydrogen, optionally substituted linear or branched alkyl groups, or optionally substituted aryl groups, the optional substitution referring to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties; and Yi and Y₂ are independently absent or carboxylate moieties; and

wherein when X is present, X is an inorganic or organic anion, n, y, z and m are integers, wherein n is 1 or 2, y is <5, z is 1 or 2 and the value of m is <5; the total charge of yn = zm; Yi is a hydroxymethyl group (CH₂OH) and t is zero or 1; R], R₂ and R₃, or Ri, 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 referring to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties.

2. A method according to claim 1 , wherein said compound of formula (A) is tris(hydroxymethyl)phosphme, P(CH₂OH)₃.

3. A method according to claim 1 , wherein said compound of formula (A) is a tetrakis(hydroxymethyl)phosphonium sulfate (THPS), [P(CH₂OH)₄J₂SO₄.

4. A method according to claim 1 , 2 or 3, wherein said lignocellulosic material is a mechanical wood pulp.

5. A method according to claim 1, 2 or 3, wherein said lignocellulosic material is a mechanical wood pulp that has been partially or fully bleached with alkaline hydrogen peroxide.

6. A method according to claim 1, 2 or 3, wherein said lignocellulosic material is a chemical wood pulp partially or fully delignifϊced and/or bleached with oxygen and/or chlorine dioxide.

7. A method according to claim 1 , 2 or 3, wherein said lignocellulosic material is a recycled pulp.

8. A method according to any one of claims 1 to 7, wherein the treatment is conducted in an aqueous medium at a pH of 3.0 - 10.0, a temperature of 20 - 170 ⁰C and a consistency of 0.01 - 99% for 5 minutes to 30 days with charges of sodium hydrosulfite being 0.01 to 2.0% and the phosphorus compound being 0.001 to 1.0% by weight, based on the oven-dried (o.d.) weight of the lignocellulosic material.

9. A method according to any one of claims 1 to 8, wherein the bleaching is conducted in a single-stage or multi-stage in one or more than one bleach tower, pulp mixer, a storage vessel, an agitated tank or any other stock preparation vessels of a paper machine, or any other vessels suitable for performing the treatment of the pulp.

10. A method according to any one of claims 1 to 9, wherein the treatment of the lignocellulosic material with sodium hydrosulfite and the phosphorus compound is achieved by adding sodium hydrosulfite and the phosphorus compound simultaneously to the lignocellulosic material.

1 1. A method according to any one of claims 1 to 9, wherein the treatment of the lignocellulosic material with sodium hydrosulfite and the phosphorus compound is achieved by adding the phosphorus compound and sodium hydrosulfite sequentially to the lignocellulosic material.

12. A bleached lignocellulosic material comprising lignocellulosic material treated with sodium hydrosulfite, Na₂S₂O₄, and a water-soluble phosphine or phosphonium compound of formula (A):

n+

Y, R₄

R₁- P-f-R₅— P-J-R₃ [Xf (A) t

R, Y.

wherein t is zero or 1 ; when t = 0, R₄R₅PY₂ is absent and R₃ is bonded to the P of the RiR₂PYi group; when t = 1 , R₅ is absent, 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

wherein when y = l, n = z = m = 0, X is absent; Ri, R₂ and R₃, or Rj, R₂, R₃, R₄ and R₅ groups are collectively selected such that the molecule has an overall solubility of at least 0.001 g/L; Ri, R₂ and R₃, or Rj, R₂, R₃ and R₄ are independently selected from hydrogen, optionally substituted linear or branched alkyl groups, or optionally substituted aryl groups, the optional substitution referring to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties; and Yi and Y₂ are independently absent or carboxylate moieties; and

wherein when X is present, X is an inorganic or organic anion, n, y, z and m are integers, wherein n is 1 or 2, y is <5, z is 1 or 2 and the value of m is <5; the total charge of yn = zm; Yi is a hydroxymethyl group (CH₂OH) and t is zero or 1; Ri, R₂ and R₃, or Ri, 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 referring to the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties.

13. A material according to claim 12, wherein said compound of formula (A) is tris(hydroxymethyl)phosphme, P(CH₂OH)₃.

14. A material according to claim 12, wherein said compound of formula (A) is a tetrakis(hydroxymethyl)phosphonium sulfate (THPS), [P(CH₂OH)₄]₂SO₄.

15. A pulp of bleached lignocellulosic material as defined in claim 12, 13 or 14.

16. A paper sheet containing a pulp of claim 15.