US20050155732A1

US20050155732A1 - Paper making process and crosslinking compositions for use in same

Info

Publication number: US20050155732A1
Application number: US11/031,380
Authority: US
Inventors: David Capwell
Original assignee: Bercen Inc
Current assignee: Bercen Inc
Priority date: 2004-01-09
Filing date: 2005-01-07
Publication date: 2005-07-21
Also published as: WO2005071162A1; CA2545476A1

Abstract

The present invention relates to methods for manufacturing paper or paperboard with improved strength, the methods comprising the addition of an aqueous aldehyde generating compound or a glyoxal releasing compound into or onto a fiber furnish prior to drying of the paper or paperboard sheet.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention provides methods of manufacturing paper and paperboard materials having increased strength, and more particularly provides a method of making paper and paperboard materials possessing increased wet and dry strength. The methods of the invention comprise addition of a crosslinker composition comprising at least one aldehyde generating compound, or more preferably a glyoxal releasing compound, which typically is activated during the drying process of the paper making process. The aldehyde generating compound, or more preferably the glyoxal releasing compound is combined with the dilute starch prior to the wet end of the paper making process. In certain other methods of the invention the aldehyde generating compound is contacted with a preformed paper or paperboard web formed from a mixture comprising a fiber slurry and a gelatinized starch composition.
2. Background.
Industrial starch may be utilized in a wide variety of paper making applications, such as a coating binder or surface treatment for paper and paperboard materials, and as a strength and retention wet end additive in papermaking. Starch compositions are frequently prepared as an aqueous dispersion which is capable of being added to the pulp slurry. For many commercial applications starch is gelatinized prior to addition of the starch to the pulp slurry, and may be carried out by the starch provider or the paper manufacturer. Gelatinization typically occurs after starch granules are dispersed as a slurry in water and the resultant aqueous slurry is heated to a temperature of 50° C. or more, and more typically to a temperature of 95° C. or more. In certain gelatinization methods, the starch granules are heated to a temperature of more than 100° C., such as starch gelatinized using a commercial jet cooker or another pressurized steam cooker. Under such conditions starch grains tend to absorb water, swell and eventually rupture to allow starch fragments and molecules to disperse in the water. This process of rupturing and dispersion is generally referred to as “gelatinization” and is an irreversible reaction, resulting in a relatively thick starch dispersion.
The crosslinking of starch with multi-functional reagents, which are reactive with starch hydroxyl groups, is well known. Glyoxal and polyaldehyde compounds and resins have been previously utilized as crosslinkers. Simple mixing of glyoxal with a starch dispersion rapidly affords a gel. However, glyoxal is infinitely soluble in water and does not interact efficiently with other chemicals or compositions, particularly heterogeneous materials dispersed in small quantities in large volumes of water, e.g., such as gelatinized starch molecules or cellulosic fibers present in the wet-end of the paper making process. Thus, addition of glyoxal or other low molecular weight crosslinkers directly to the wet-end of the papermaking process has not been found to provide benefit to end product of the paper making process.
U.S. Pat. No. 6,303,000 issued to Floyd et al. (Floyd '000) discloses gelatinized starch compositions crosslinked with a glyoxal resin and the use of same in paper making. The crosslinked starch composition of Floyd '000 comprise the reaction product formed by heating starch with a blocked glyoxal resin such as those resins recited in U.S. Pat. No. 4,695,606 (Floyd, '606) during the gelatinization process. The heating process forms a gelatinized starch that is crosslinked by the glyoxal resin. More particularly, Floyd '000 discloses the addition of a crosslinked gelatinized starch composition to the wet end of the paper making process. In other words, prior to addition to the wet end, the starch is heated with the blocked glyoxal resin to gelatinize the starch and induce a crosslinking reaction between the glyoxal and the starch. The Floyd '000 patent further discloses that the glyoxal resin can be pre-mixed with the starch prior to the gelatinization heating step or added during the starch gelatinization process. Floyd suggests that pre-mixing the starch and blocked glyoxal resin prior to the gelation process or addition of the blocked glyoxal resin during the gelatinization process, affords superior material having improved shelf stability.
The Floyd '606 patent describes paper binder compositions comprising a mixture of an acrylic or vinyl polymer with a blocked glyoxal resins, e.g., such as the reaction product of glyoxal and a urea or a cyclic urea. More particularly, the blocked glyoxal resin is a condensation polymer of glyoxal blocked with urea, cyclic ureas such as ethylene urea, 4,5-dihydroxyethylene urea and propylene urea, carbamates, glycols, or polyols.
In Floyd '000 the addition levels of the gelatinized starch composition demonstrated to affect a significant improvement in paper or paperboard strength are relatively high at the level of 40 lb or more dry starch composition per ton of dry pulp. It is well known in the art of papermaking that significant issues may occur when relatively high levels of starch are used to produce paper, including high cost, high levels of effluent Biological Oxygen Demand (BOD), reduction in paper opacity, machine deposits, and problems with dewatering and drying the paper or paperboard leading to reduced production rates. It would thus be desirable to have paper strength compositions that are effective at lower levels of usage.
A variety of polymeric stabilizing agents have been recited which are capable of stabilizing at lest one aldehyde residue of a plurality of glyoxal compounds. More particularly a variety of polyacrylamide or copolymers of acrylamide and an unsaturated aliphatic carboxylic acid, which have a plurality of glyoxal equivalents attached to the polymer chain through pendant amide groups of the acrylamide residues.
U.S. Pat. No. 3,556,932 teaches poly(acrylamide) substituted with glyoxal, e.g., a polymer chain with —C(O)NHCH(OH)CHO side chains.
U.S. Pat. No. 5,543,446 teaches terpolymers composed of (meth)acrylamide mononomers, unsaturated aliphatic carboxylic acid monomers, and a di-or polyvinyl monomer. The terpolymers can be used to increase the wet strength of a paper web during the paper making process.
International patent publication, WO 00/11046 teaches a copolymer of acrylamide and an α,β-unsaturated carboxylic acid which has been modified with a dialdehyde such as glyoxal.
Various disclosures have been prepared which teach stabilizing glyoxal with polyacrylamide and the use of polyacrylamide/glyoxal resins in paper making processes.
As an alternative approach, it would be desirable to have a crosslinking composition including a stabilized aldehyde generating compound or a stabilized glyoxal compound that is capable of crosslinking starch molecules and/or pulp fiber particles upon application of the crosslinking composition to a paper or paperboard web. It would also be desirable to provide methods of making paper and paperboard with increased strength using such crosslinking compositions.

SUMMARY OF THE INVENTION

The present invention provides storage stabile, crosslinking compositions that include at least one glyoxal releasing compound or at least one aldehyde generating compound. These compounds facilitate a process of manufacturing paper or paperboard having improved wet and/or dry strength than previous paper or paperboard manufacturing processes. Preferably, the manufacturing processes of certain embodiments of the invention provide paper or paperboard materials with equivalent strength and a reduced basis weight when compared to paper or paperboard materials made with previous paper manufacturing processes.
In accord with the present invention, a method for manufacturing paper and paperboard materials, the method comprising the steps of:

- providing a fiber slurry and a gelatinized starch composition, each of which is suitable for use in making paper or paperboard;
- providing at least one crosslinker composition comprising at least one aldehyde generating compound capable of forming at least two or more covalent bonds to functional groups present in the starch or fiber of the web;
- mixing the gelatinized starch composition and the crosslinker composition;
- adding the mixture of gelatinized starch composition and crosslinker composition to the fiber slurry contemporaneously to mixing the gelatinized starch composition and the crosslinker composition; and
- forming the paper or paperboard sheet.

Preferred crosslinker compositions comprise one or more equivalents of an aldehyde generating compound typically comprising one or more equivalents of at least one compound having two or more aldehyde resuides. Typically preferred aldehyde generating compounds of the invention include those compounds according to any one of Formula I, II, III, VI, V or VI.
Other aspects of the invention are discussed infra.
For purposes of the present invention, the term “self-retaining starch” means any starch, that through its functionality, has the property of being retained effectively in the paper or paperboard web during the process of sheet consolidation during the papermaking process. Though not limited to the general description, this usually requires that the starch have a net cationic charge for retention on the generally anionic fibers used to make paper and paperboard.
Thus, a “self-retaining gelatinized starch” is added to the papermaking slurry at some point before consolidation of the paper web and is substantially retained or adsorbed onto the fiber components of the slurry and becomes a component of the paper or paperboard.
For the purposes of the present invention, the term “aldehyde generating compound” refers to materials that degrade at ambient or elevated temperatures upon exposure to starch, gelatinized starch, or pulp fiber to generate compounds containing two or more reactive aldehyde residues that are then available for reaction with functional groups that generally react in an aqueous environment with aldehyde groups. Moreover, the term aldehyde generating compound includes those compounds capable of generating polyaldehyde compounds upon degredation and compounds capable of generating one or more aldehyde groups in sequence such that two or more covalently connected aldehyde residues are generated during the degredation of the aldehyde generating compound. Particularly preferred aldehyde generating compounds release glyoxal or generate one or two aldehyde groups which are derived from glyoxal.
For the purposes of the present invention, the term “glyoxal releasing compound” refers to materials that degrade at ambient or elevated temperatures upon exposure to starch, gelatinized starch, or pulp fiber to generate compounds containing reactive glyoxal moieties that are then available for reaction with functional groups that generally react in an aqueous environment with glyoxal. In general, glyoxal releasing compounds are a subset of aldehyde generating compounds.
For the purposes of the present invention, the term “blocked aldehyde residue” refers to structures in which at least one aldehyde group is hindered from forming free or active aldehyde groups under storage or wet end paper making conditions. Similarly, the term “blocked glyoxal residue,” as used herein, refers to structures in which the glyoxal generating group is hindered from forming a free or active aldehyde group under the current conditions present. The term “unblocked glyoxal residue,” as used herein, refers to structures in which at least one glyxoal aldehyde residue is present as a reactive aldehyde group, i.e., a CHO group.
For the purposes of the present invention, the term “stabilizing agent” refers to any compound or combination of compounds capable of forming a linear, branched, or cyclic structure which comprises one or more equivalents of glyoxal as a part of the linear, branched or cyclic structure or as a substituent thereof. Preferred stabilizing agents are capable of masking, blocking or otherwise protecting one, or preferably, two aldehyde functional groups of glyoxal from undergoing undesired reactions prior to the drying step of the paper making process.
For the purposes of the present invention, the term “aldehyde blocking agent” refers to any compound or combination of compounds capable of masking, blocking or otherwise protecting an aldehyde functional group and preferably are capable of masking or blocking aldehyde functional groups in an aqueous environment. Typically preferred aldehyde blocking agents release or unmask the akdehyde group at elevated temperatures such as the temperature used to dry paper or paperboard.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for manufacturing paper or paperboard sheet with increased strength, the method comprising the steps of:

In preferred methods of manufacturing paper comprising pre-mixing of a gelatinized starch and the crosslinker composition and addition of the mixture to a figure slurry, the gelatinized starch composition and the crosslinker composition are mixed together in a batch process or in a continuous flow process prior to addition to the fiber slurry. In certain preferred methods of the invention the mixing of the gelatinized starch composition and the crosslinker composition occurs within less than about 1 hour prior to addition to the fiber slurry, or more preferably less than about 30 minutes or less than 10 minutes prior to addition to the fiber slurry. In certain particularly preferred embodiments, the gelatinized starch composition and the crosslinker composition are mixed together less than about 5 minutes or less than about 1 minute prior to addition to the fiber slurry.
The invention also provides a method for manufacturing paper or paperboard sheet with increased strength, the method comprising the steps of:

- providing a fiber slurry and a gelatinized starch composition, each of which is suitable for use in making paper or paperboard;
- providing at least one crosslinker composition comprising at least one aldehyde generating compound capable of forming at least two or more covalent bonds to functional groups present in the starch or fiber of the web;
- preparing a paper or paperboard web comprising pulp fiber and at least one starch prepared by mixing the gelatinized starch composition and the fiber slurry;
- contacting the web with the crosslinker composition under conditions conducive to formation at least two or more covalent bonds to functional groups present in the starch or fiber of the web.

Suitable crosslinking compositions suitable for use in the paper making methods of the present invention include one or more of the following compositions, each of which comprises one or more compounds according to Formula I, II-a, II, III, IV, V, or VI and may optionally further comprise one or more aldehyde blocking agents.
Preferred methods for manufacturing paper or paperboard sheet provided by the present invention are suitable for the preparation of paper or paperboard sheets which have increased strength. Typically the methods of the invention comprise the steps of:

Typically the gelatinized starch composition and the crosslinker composition can be mixed in any fashion such that the two reagents from an admixture prior to addition to the paper slurry. Typically, the gelatinized starch composition and the crosslinker composition are admixed in either a continuous flow process during the process of addition to the paper slurry or the reagents are admixed in a batch process prior to addition of the mixture to the paper slurry in aliquots.
In certain preferred paper making methods of the invention the gelatinized starch composition and the crosslinker composition are introduced into the paper slurry using manifold capable of delivering each reagent continuously or in regularly distributed portions over a specified time interval. More preferably, the gelatinized starch composition and the crosslinker composition are admixed in a mixing chamber which has been incorporated into the manifold which transfers gelatinized starch composition and the crosslinker composition from the reagent containers to the paper slurry delivered to the “head box” of the paper manufacturing mill. In certain other methods of the invention, the aldehyde generating compound may be administered to a fiber web during the formation or initial drying steps of the paper or paperboard making process. Typically preferred application methods include spraying of the aldehyde generating compound onto the fiber web.
In certain preferred processes of the invention the gelatinized starch composition and the crosslinker composition are admixed together in a continuous flow process prior to addition to the fiber slurry. Any device or mixing apparatus used to mix two or more fluids from two or more fluid streams to form a single fluid mixture are suitable for use in the methods of the present invention. Typically the manifold delivering the gelatinized starch composition and the crosslinker composition to the fiber slurry are combined either in a pre-mixing chamber or the manifold pipes for the gelatinized starch composition and the crosslinker composition are joined by a “T” joint, a “Y” joint or another branch point capable of mixing two or more fluid flows into a single fluid effluent.
In certain preferred methods of the invention, the gelatinized starch composition and the crosslinker composition are mixed together less than about 1 hour prior to addition to the fiber slurry. More preferably, the gelatinized starch composition and the crosslinker composition are mixed together less than about 30 minutes prior to addition to the fiber slurry or less than about 10 or about 5 minutes prior to addition to the fiber slurry.
Other preferred methods for manufacturing paper or paperboard sheet provided by the present invention are suitable for the preparation of paper or paperboard sheets which have increased strength. Typically the methods of the invention comprise the steps of:

Crosslinking compositions of the present invention comprise an aqueous solution or dispersion containing at least one aldehyde generating compound or glyoxal releasing compound that are suitable for imparting increased wet and/or dry strength to paper or paperboard. Preferred aqueous crosslinking compositions of the invention comprise at least one glyoxal releasing compound comprising at least one blocked or unblocked glyoxal residue which is capable of generating reactive aldehyde groups and/or releasing glyoxal upon contacting the glyoxal releasing compound with starch, gelatinized starch, pulp fiber or a combination thereof. Typically preferred aqueous crosslinker compositions of the invention are storage stable, particularly when stored at a temperature of 40° C. or less.
The crosslinker compositions of the present invention are particularly useful for manufacturing paper or paperboard sheet having increased strength at the same basis weight, or having the same strength with reduced basis weight. The methods for manufacturing paper or paperboard typically comprise providing a paper or paperboard web; contacting the web with at least one crosslinker composition of the present invention; and heating the paper or paperboard web at a temperature which is sufficient to dry the paper. Typically the crosslinker composition is applied to the web before the drying step or after the web has been partially dried. The paper produced by the manufacturing methods of the invention may have various desirable physical properties depending upon the order of the crosslinker composition addition step and the drying step.
Preferred crosslinker compositions for use in the methods of strengthening paper or paperboard provided by the present invention include those crosslinker compositions comprising:

- an aqueous media; and
- a monomeric or oligomeric aldehyde generating compound comprising
  - at least one equivalent of a dialdehyde or polyaldehyde compound; and
  - between 0.25 and about 5 equivalents of a stabilizing agent which is capable of reacting with two or more aldehyde residues.

In certain particularly preferred crosslinker compositions are substantially free of materials capable of irreversibly reacting with aldehyde generating compounds of the crosslinker composition. More preferably, the crosslinker compositions of the invention do not comprise starch or gelatinized starch. The invention further provides crosslinker compositions which are storage stable in the absence of starch, gelatinized starch, or pulp fiber for at least one week and reacts at a temperature of less than 100° C. to form covalent bonds with starch, gelatinized starch or pulp fiber in less than an hour.
In other preferred embodiments, the invention provides crosslinker composition which comprise an aldehyde generating compound which releases glyoxal.
In certain preferred embodiments, the crosslinker composition comprises an aldehyde generating compound having at least one stabilizing agent which is selected from linear, branched or cyclic organic molecules having at least two functional groups capable of blocking an aldehyde residue. Typically preferred stabilizing agents are selected from the group consisting of optionally substituted urea, optionally substituted thiourea, optionally substituted guanidine, optionally substituted alkylene glycol, optionally substituted α,ω-akanediol, optionally substituted poly(ethylene glycol), optionally substituted imidazolidin-2-one, optionally substituted tetrahydro-pyrimidin-2-one, and combinations thereof.
In certain particularly preferred embodiments, the stabilizing agent has a molecular weight of less than 1000 g/mol. More preferably, the stabilizing agent having a molecular weight of 1000 g/mol or less is selected from optionally substituted urea, optionally substituted thiourea, optionally substituted guanidine, optionally substituted alkylene glycol, optionally substituted α,ω-akanediol, optionally substituted poly(ethylene glycol), optionally substituted imidazolidin-2-one, optionally substituted tetrahydro-pyrimidin-2-one, and combinations thereof.
In yet other embodiments, the present invention provides crosslinking compositions which further comprise one or more aldehyde blocking compounds which are present in the crosslinking composition at between about 0 and about 20 molar % of the aldehyde generating compound. Certain preferred aldehyde blocking compounds are selected from the group consisting of C_1-20alcohols, C_2-20alkylene glycols, and C_1-20alkylamines, and the like. Particularly preferred aldehyde blocking compound include methanol, ethanol, propanol, ethylene glycol, and propylene glycol, and the like.
Certain preferred crosslinker compositions, which are suitable for use in the paper manufacturing methods of the invention, comprise an aldehyde generating compound or a glyoxal generating compound which is a compound according to Formula I:

- wherein
- Z is monovalent or divalent urea, monovalent or divalent α,ω-C_2-8alkanediol, C_2-8alkylene glycol, poly(ethylene glycol) having a molecular weight of less than about 20,000, ω-amino-α-C_2-8alkanol or Z is a 5 to 7 member optionally substituted heterocyclic group having one ring nitrogen atom, at least one additional ring heteroatom selected from N, O, or S, and zero or one oxo substitutents;
- n is 0, 1, or 2;
- m is 0 or 1;
- n′=n if m=1 or n′=0 if m=0, wherein at least one of m and n is not zero.

Other preferred crosslinker compositions, which are suitable for use in the paper manufacturing methods of the invention, comprise an aldehyde generating compound or a glyoxal releasing compound which is a compound according to Formula II:

- wherein
- A is an optionally substituted methylene group, an optionally substituted C_2-4alkylene group, or a single bond;
- B is carbonyl, thiocarbonyl, or an optionally substituted 1,2-ethylene residue;
- X₁and X₂are independently selected from the group consisting of oxygen and NR₃;
- R₁and R₂are independently selected from the group consisting of hydrogen, hydroxy, optionally substituted C_1-20alkyl, optionally substituted C_1-20alkoxy, optionally substituted urea, optionally substituted thiourea, or
- R₁and R₂, taken in combination, form a N,N′-divalent urea;
- R₃is independently selected at each occurrence of R₃from the group consisting of hydrogen, 1-hydroxy-ethan-2-al-1-yl group, or a blocked glyoxal residue.

Certain preferred crosslinker compositions of the present invention comprise an aldehyde generating compound or a glyoxal releasing compound which is a compound according to Formula II-a:

- wherein
- A is an optionally substituted methylene group, an optionally substituted C_2-4alkylene group, or a single bond;
- B is carbonyl, thiocarbonyl, or an optionally substituted 1,2-ethylene residue;
- X₁and X₂are independently selected from the group consisting of oxygen and NR₃;
- R₁and R₂are independently selected from the group consisting of hydrogen, hydroxy, optionally substituted C_1-20alkyl, optionally substituted C_1-20alkoxy, optionally substituted urea, optionally substituted thiourea, or
- R₁and R₂, taken in combination, form a N,N′-divalent urea;
- R₃is independently selected at each occurrence of R₃from the group consisting of hydrogen, optionally substituted C_1-20alkyl, and unblocked and blocked glyoxal residues, where unblocked glyoxal residue is a 1-hydroxy-2-ethanal-1-yl group and the blocked glyoxal residue is a 1-hydroxy-2-(protected aldehyde residue)-ethan-1-yl group; or
- R₃is a 1,2-dihydroxyethylene residue coupled to two rings according to Formula I; and
- wherein the aldehyde generating compound according to Formula I degrades to generate at least one equivalent of glyoxal when the crosslinking composition is contacted with starch or pulp fiber.

Preferred compounds of Formula II or II-a, which are suitable for use in the crosslinking compositions of the invention include those compounds in which:

- R₁and R₂are independently selected from the group consisting of hydrogen, hydroxy, methanol, ethanol, urea, or
- R₁and R₂, taken in combination, form a N,N′-divalent urea;
- R₃is independently selected at each occurrence of R₃from the group consisting of hydrogen, methyl, and ethyl, or
- R₃is an unblocked glyoxal residue or a blocked glyoxal residue selected from the group consisting of 1,2-dihydroxy-2-(C_1-4-alkoxy)-ethan-1-yl, 1,2-dihydroxy-2-(3-hydroxypropoxy)-ethan-1-yl, and 1,2-dihydroxy-2-(2-hydroxypropoxy)-ethan-1-yl.

Other preferred compounds of Formula II or II-a, which are suitable for use in the crosslinking compositions of the invention include those compounds in which:

- X₁and X₂are NR₃;
- A is a single bond;
- B is a carbonyl or thiocarbonyl group; and
- R₁and R₂are independently selected from hydroxy, C_1-6alkoxy, or blocked glyoxal residues.

Still other preferred compounds of Formula II or II-a, which are suitable for use in the crosslinking compositions of the invention include those compounds in which:

- X₁and X₂are NR₃;
- A is a 1,1-C_1-6alkylene group;
- B is a carbonyl or thiocarbonyl group;
- R₁and R₂are independently selected from hydrogen, hydroxy, or C_1-6alkoxy, and
- R₃is an unblocked glyoxal residue or a blocked glyoxal residue selected from the group consisting of 1,2-dihydroxy-2-(C_1-4-alkoxy)-ethan-1-yl, 1,2-dihydroxy-2-(3-hydroxypropoxy)-ethan-1-yl, and 1,2-dihydroxy-2-(2-hydroxypropoxy)-ethan-1-yl.

Other preferred aldehyde generating compounds provided by the invention which are suitable for use in the methods of the invention comprise substituted triaminoheteroaromatic and substituted triaminobenzene compounds according to Formula III:

- wherein
- each of X₁, X₂, and X₃are independently selected from the group consisting of CH or N; and
- R₄and R₅are independently selected at each occurrence of R₄and R₅in Formula III from the group selected from hydrogen, a 1-hydroxy-ethan-2-al-1-yl group, or a blocked glyoxal residue; or
- one or more occurrences of NR₄R₅in Formula III, taken in combination form an optionally substituted N-piperazinyl residue.

Particularly preferred compounds of Formula III include 1,3,5-triazine compounds, e.g., compounds of Formula III in which each of X₁, X₂, and X₃is nitrogen.
Other preferred compounds of Formula III include those compounds in which one or more, or preferably each occurrence of NR₄R₅, taken in combination, forms an optionally substituted N-2,3,5,6-tetrahydroxypiperazinyl residue. Particularly preferred compounds of Formula III, in which NR₄R₅, taken in combination, forms a N-2,3,5,6-tetrahydroxypiperazinyl residue include compounds of Formula IV:

- wherein
- each of X₁, X₂, and X₃are independently selected from the group consisting of CH or N; and
- R₆is independently selected at each occurrence from the group selected from optionally substituted alkyl, optionally substituted carboxamide.

Preferred aldehyde generating compounds of formula IV include those compounds in which R₆is independently selected at each occurrence from —C(O)NH₂or —C(O)NHCH(OH)CHO.
Yet other preferred aldehyde generating compounds which are suitable for use in the methods of manufacturing paper provided by the invention include those compounds according to V:

- wherein
- m is an integer from 0 to about 1000;
- A is an optionally substituted methylene group, an optionally substituted C_2-4alkylene group, or a single bond;
- B is carbonyl, thiocarbonyl, or an optionally substituted 1,2-ethylene residue;
- R₁and R₂are independently selected from the group consisting of hydrogen, hydroxy, optionally substituted C_1-20alkyl, optionally substituted C_1-20alkoxy, optionally substituted urea, optionally substituted thiourea, or
- R₁and R₂, taken in combination, form a N,N′-divalent urea;
- R₃is independently selected at each occurrence of R₃from the group consisting of hydrogen, optionally substituted C_1-20alkyl, and unblocked and blocked glyoxal residues, where unblocked glyoxal residue is a 1-hydroxy-2-ethanal-1-yl group and the blocked glyoxal residue is a 1-hydroxy-2-(protected aldehyde residue)-ethan-1-yl group; or
- R₄is a 1,2-dihydroxyethylene residue; or
- R₄is a telechelic oligiomer comprising 2n+1 glyoxal residues alternating with n groups selected from the group consisting of α,ω-alkane diols, alkylene glycols, and poly(ethylene glycol); and
- n is an integer of from 0 to about 100;
- wherein the aldehyde generating compound according to Formula II degrades to generate at least one equivalent of glyoxal when the crosslinking composition is contacted with starch or pulp fiber.

Other preferred compounds of Formula I, which are suitable for use in the crosslinking compositions of the invention include those compounds according to Formula VI:

- wherein
- p is an integer from 1 to about 1000;
- Z is independently selected at each occurrence from the group consisting of optionally substituted urea, optionally substituted thiourea, optionally substituted guanidine, optionally substituted alkylene glycol, optionally substituted α,ω-akanediol, optionally substituted poly(ethylene glycol), optionally substituted imidazolidin-2-one, and optionally substituted tetrahydro-pyrimidin-2-one;
- wherein the aldehyde generating compound according to Formula VI degrades to generate at least one equivalent of glyoxal when the crosslinking composition is contacted with starch or pulp fiber.
- R₅is hydrogen, alkoxy, hydroxyalkoxy, amino, hydroxy, mono and dialkyl amino, optionally substituted alkane diol, optionally substituted urea, or optionally substituted alkylene glycol; and
- R₆is hydrogen, optionally substituted alkyl, optionally substituted alkanoyl, optionally substituted unblocked glyoxal residue, or blocked glyoxal residues.

Certain preferred aldehyde generating compounds or glyoxal generating compounds according to Formula VI, include those compounds wherein

- Z is urea, thiourea, C_2-10α,ω-alkanediol, C_2-10alkylene glycol, poly(ethyleneglycol) having between 2 and about 100 glycol repeat units.

Certain particularly preferred aldehyde generating compounds and glyoxal generating compound, which are suitable for use in the crosslinking compositions of the present invention, include compounds of the formulae:
In accord with the present invention, a method for manufacturing paper and paperboard materials, the method comprising the steps of:

- providing a paper or paperboard web comprising pulp fiber and at least one starch;
- contacting the web with at least one crosslinker composition comprising at least one aldehyde generating compound capable of forming at least two or more covalent bonds to functional groups present in the starch or fiber of the web.

In certain preferred methods of the invention, a paper sheet is prepared by the method of manufacture. In other preferred methods of the invention, a paperboard sheet is prepared by the manufacturing method.
In certain embodiments, the crosslinker composition is contacted with the web before the drying process commences or after partial drying of the web. In certain preferred embodiments, it may be beneficial to contact the web with one or more crosslinker compositions at various times in the paper making process. For example, one or more different crosslinker compositions are contacted with the web prior to commencing the drying step and second crosslinker composition, which may be the same or different from the first crosslinker composition is contacted with the web after a first drying step partially dries the sheet.
Typically the methods of manufacture provide at least one of increased wet strength or increased dry strength of the web or the paper or paperboard sheet prepared by the method of manufacture.
Preferred crosslinker compositions which are suitable for use in the methods of the present invention include any of the crosslinker compositions provided herein or a mixture of two or more such crosslinker compositions added simultaneously or separately to the paper making process. Certain preferred crosslinker compositions suitable for use in the paper or paperboard making methods of the present invention include those compositions comprising glyoxal generating compounds or at least one compound according to Formula I, II, III, IV, V, VI or a subformula thereof.
As used herein, “alkyl” is intended to include both branched and straight-chain saturated aliphatic hydrocarbon groups, having the specified number of carbon atoms. Examples of alkyl include, but are not limited to, methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, t-butyl, n-pentyl, and s-pentyl. Preferred alkyl groups are C_1-6alkyl groups. Especially preferred alkyl groups are methyl, ethyl, propyl, butyl, and 3-pentyl. The term C_1-4alkyl as used herein includes alkyl groups consisting of 1 to 4 carbon atoms, which may contain a cyclopropyl moiety. Suitable examples are methyl, ethyl, and cyclopropylmethyl. The term “alkyl” is also intended to include cycloalkyl and cycloalkylalkyl groups where there term “cycloalkyl” is used as defined herein.
“Cycloalkyl” is intended to include saturated ring groups, having the specified number of carbon atoms, such as cyclopropyl, cyclobutyl, cyclopentyl, or cyclohexyl. Cycloalkyl groups typically will have 3 to about 8 ring members.
“Alkenyl” is intended to include hydrocarbon chains of either a straight or branched configuration comprising one or more unsaturated carbon-carbon bonds, which may occur in any stable point along the chain, such as ethenyl and propenyl. Alkenyl groups typically will have 2 to about 8 carbon atoms, more typically 2 to about 6 carbon atoms.
“Alkynyl” is intended to include hydrocarbon chains of either a straight or branched configuration comprising one or more carbon-carbon triple bonds, which may occur in any stable point along the chain, such as ethynyl and propynyl. Alkynyl groups typically will have 2 to about 8 carbon atoms, more typically 2 to about 6 carbon atoms.
“Alkoxy” represents an alkyl group as defined above with the indicated number of carbon atoms attached through an oxygen bridge. Examples of alkoxy include, but are not limited to, methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, 2-butoxy, t-butoxy, n-pentoxy, 2-pentoxy, 3-pentoxy, isopentoxy, neopentoxy, n-hexoxy, 2-hexoxy, 3-hexoxy, and 3-methylpentoxy. Alkoxy groups typically have 1 to about 8 carbon atoms, more typically 1 to about 6 carbon atoms.
In the papermaking process wood pulp is prepared, bleached if required, cleaned, and run through a series of beaters or refiners until it is a fine slush. At this point fillers and other additives, such as the gelatinized starch compositions of the invention, can be mixed in. When preparation is complete, the slush is pumped onto a fast-moving wire screen where it becomes consolidated into a continuous web or sheet of paper or paperboard.
As the consolidating web travels with the moving wire, excess water is drained away leaving a crude paper or paperboard sheet. The sheet is then squeezed between rollers or presses to remove some of the remaining water and to ensure uniform thickness and smoothness. Finally, the web is run over a series of heated rollers or heating devices to remove most of the remaining water. The paper may be “finished” in any number of ways, including but not limited to, surface treatments, calendaring, or coating. The finished paper is spooled onto ‘parent rolls’ termed the reel.

EXAMPLES

The present invention is further illustrated by the following examples which should not be construed as limiting in any way. The contents of all cited references (including literature references, issued patents, published patent applications) as cited throughout this application are hereby expressly incorporated by reference. The practice of the present invention will employ, unless otherwise indicated, conventional techniques, which are within the skill of the art. Such techniques are explained fully in the literature.
In the following example, laboratory handsheets were prepared using the MK sheet forming device in semi-automatic mode. Pulp was beaten to 300 CSF (Canadian Standard Freeness) using a laboratory beater. Additions were made to a 1% slurry of the pulp prior to addition to the headbox. Sheets (12×12″) were formed using conventional practice, pressed, and dryed at 120° C. using 2 passes through a felted rotating cylinder dryer. A pass is one rotation around the heated drum. The speed of this rotation is adjustable. For this study the rotation took 1 minute. The pulp slurries were prepared in ordinary tap water without pH adjustment. Old Corrugated Containers (OCC) was obtained from commercial box clippings.

Example 1

Preparation of a Mixture of 3,4-dihydroxy-imidazolidin-2-one and at Least one Aldehyde Blocking Compound

A 1000 ml flask was charged with glyoxal (40% in water, 145 grams, 1 mole) and the contents of the flask were stirred and warmed to 55° C. Urea (50% in water, 120 grams, 1 mole) was added to the stirred glyoxal solution over four hours at 55° C. To this mixture propylene glycol (38 grams, 0.5 moles) and a catalytic amount of sulfuric acid (98%, typically about 1 gram) was added. The reaction mixture was then heated to 70° C. for two hours to generate the product, of which the predominant reaction produce had the structure, as follows:

Example 2

Preparation of a Cyclic Glyoxal with Pendant Blocked Glyoxal Residues

A 1000 ml flask was charged with glyoxal (40% in water, 435 grams, 3 moles) and the contents of the flask were stirred and warmed to 55° C. Urea (50% in water, 120 grams, 1 mole) was added to the stirred glyoxal solution over two hours at 55° C. A catalytic amount of sulfuric acid (98%, typically about 1 gram) was added to the reaction mixture to accelerate the cyclization reaction. The reaction mixture was allowed to stir for four hours and then propylene glycol (152 grams, 2 moles) was added. The reaction mixture was then heated to 70° C. for two hours to generate the product, of which the predominant reaction produce had the structure, as follows:

Example 3

Dry Strength Evaluation of Paper Manufactured With a Gelatinized Starch Composition Comprising the Compound of Example 1 as the Glyoxal Releasing Compound

A handsheet study demonstrating strength improvements included one handsheet set prepared without a starch additive and three sets of sheets with different starch compositions. Handsheets are 15 gm (12 in×12 in). Sample 3A was a control OCC furnish with no additives. Sets 3B thru 3D were made with the identical furnish and conditions but a different starch additive was used in each set.
Set 3B contained a cationic pregelatinized potato starch (Penford PAR 6048AR, available from Penford Products, Inc.), at 10 lb/ton and is referred to herein as the “starch only” control. Set 3C was prepared with a gelatinized starch composition comprising a mixture of Penford PAR 6048AR and the glyoxal generating compound provided in Example 1. The mixture was prepared by mixing the glyoxal generating compound into the Penford PAR 6048AR (25%) at 32° C. over 1 hour with agitation. The resulting mixture had a solids content of 23.7%. by weight.

Set 3D was prepared using the same gelatinized starch composition as was used in Set 3C except that the gelatinized starch composition was prepared by mixing the glyoxal generating compound from Example 1 into a Penford PAR 6048AR at 90° C. over 30 minutes with agitation (pre-reaction process). In both 3C and 3D the glyoxal generating compound was blended into Penford PAR 6048AR at 10% by weight dry on dry. The combination was added to the OCC slurry at 10 lb/ton.

TABLE I


Sample	Description	Dry Tensile	Shelf-Life

3A	fiber control	46.04	NA
3B	starch control	47.26	6 months
3C	cold blend	57.65	3 months
3D	pre-reacted	55.72	3 weeks

The results demonstrate that the dry strength of the paperboard was improved when the glyoxal generating compound was added to the starch. Performance in terms of strength development and stability are best when the material is added to the starch under mild conditions (example 3C). Moreover, treatment of the gelatinized starch composition under the conditions of the pre-reaction process reduces the stability of the starch composition.

Example 4

Dry Strength Evaluation of Paper Manufactured with a Gelatinized Starch Composition Comprising the Compound of Example 2 as the Glyoxal Generating Compound

A handsheet study demonstrating strength improvements included one handsheet set prepared without a starch additive and three sets of sheets with different starch compositions. Handsheets are 15 gm (12 in×12 in). Sample 4A was a control OCC furnish with no additives. Sets 4B thru 4D were made with the identical furnish and conditions but a different starch additive was used in each set.
Set 4B contained a cationic pregelatinized potato starch (Penford PAR 6048AR), at 10 lb/ton and is referred to herein as the “starch only” control. Set 4C was prepared with a gelatinized starch composition comprising a mixture of Penford PAR 6048AR and the glyoxal generating compound provided in Example 2. The mixture was prepared by mixing the glyoxal generating compound into the Penford PAR 6048AR (25%) at 32° C. over 1 hour with agitation. The resulting mixture had a solids content of 23.7% by weight.

Set 4D was prepared using the same gelatinized starch composition as was used in Set 4C except that the gelatinized starch composition was prepared by mixing the glyoxal generating compound from Example 2 into Penford PAR 6048AR at 90° C. over 30 minutes with agitation (pre-reaction process). In both 4C and 4D the glyoxal generating compound was blended into Penford PAR 6048AR at 10% by weight dry on dry. The combination was added to the OCC slurry at 10 lb/ton.

TABLE II


Sample	Description	Dry Tensile	Shelf-Life

4A	fiber control	46.04	NA
4B	starch control	47.26	6 months
4C	cold blend	52.47	1.5 days
4D	pre-reacted	ND	<1 hour

The results demonstrate that the dry strength of the paperboard was improved when the glyoxal generating compound of Example 2 was added to the gelatinized starch composition. Performance in terms of strength development and stability were best when the material was added to the starch under the mild conditions (example 4C). Treatment of the gelatinized starch composition with harsh conditions, such as those of set 4D, resulted in a gelatinized starch composition that was not usable for use in commercial applications, due in part to a short shelf life.

Example 5

Preparation of Cyclic Amide with Pendent Blocked Glyoxal Units

Sodium bicarbonate (7.5 grams) was introduced into a sealed nitrogen filled round bottom flask fixed with heating, cooling, reflux, distillation, pH probe, temperature probe and constant pressure addition apparatus. Formaldehyde (37% in water, 172 grams, 2 moles) was then added to the flask. Propionaldehyde (116 grams, 2 moles) was then slowly added to the reaction mixture over 2 hours at 30° C. Upon complete addition of the propionaldehyde, the reaction solution was heated to 45° C. for 4 hours. Urea (120 grs (2 moles)) was then added and the temperature of the reaction mixture increased to 60° C. for 2 hours. Residual raw materials and a small amounts of reaction by-products were then removed from the reaction flask by vacuum distillation. Sulfuric acid (98%, 6.25 grams) was added to the material remaining in the flask after distillation and the reaction mixture was held at 60° C. for 4 hours.
Glyoxal (40% by weight in water; 290 grams, 2 moles) and propylene glycol (152 grams, 2 moles) were added sequentially at 55° C. to the reaction mixture. The reaction mixture was allowed to stir for an hour after complete addition of each reagent, e.g., glyoxal and propylene glycol.
The reaction mixture was returned to room temperature and the pH was adjusted to about 6.5 by addition of sodium bicarbonate. The predominate glyoxal generating compound formed by the reaction is represented by the structure, as follows:

Example 6

Dry Strength Evaluation of Paper Manufactured with a Gelatinized Starch Composition Comprising the Compound of Example 5 as the Glyoxal Releasing Compound

A handsheet study demonstrating strength improvements included one handsheet prepared without a starch additive and three sets of sheets with different starch compositions. Handsheets are 15 gm (12 in×12 in). Sample 6A was a control OCC furnish with no additives. Sets 6B thru 6D were made with the identical furnish and conditions but a different starch additive was used in each set.
Set 6B contained a cationic pregelatinized potato starch (Penford PAR 6048AR), at 10 lb/ton and is referred to herein as the “starch only” control. Set 6C was prepared with a gelatinized starch composition comprising a mixture of Penford PAR 6048AR and the glyoxal generating compound provided in Example 5. The mixture was prepared by mixing the glyoxal generating compound into the Penford PAR 6048AR (25%) at 32° C. over 1 hour with agitation. The resulting mixture had a solids of 23.7%.

Set 6D was prepared using the same gelatinized starch composition as was used in Set 6C except that the gelatinized starch composition was prepared by mixing the glyoxal generating compound from Example 5 into Penford PAR 6048AR at 90° C. over 30 minutes with agitation (pre-reaction process). In both 6C and 6D the glyoxal generating compound was blended into Penford PAR 6048AR at 10% by weight dry on dry. The combination was added to the OCC slurry at 10 lb/ton.

TABLE III


Sample	Description	Dry Tensile	Shelf-Life

6A	fiber control	46.04	NA
6B	starch control	47.26	6 months
6C	cold blend	57.47	1 month
6D	pre-reacted	56.41	5 days

Example 7

Production Scale Paper Manufactured using a Gelatinized Starch Composition in which the Glyoxal Generating Compound is the Compound Provided by Example 1

A 10 tote trial of a gelatinized starch composition was prepared by mixing the comprising a glyoxal generating compound provided by Example 1 and Penford PAR 6048AR cationic potato starch (7%:93% by weight of glyoxal generating compound:starch) to give a final combined concentration of 21% (less than 3000 cps). The gelatinized starch composition was added to the paper making process at several locations in the wet end of the paper making process, such as the suction side of the machine chest fan pump and the suction side of the pressure screen. During this trial the average dosage rate of the gelatinized starch composition was about 10 pounds per ton.
The paper manufacturing method using the gelatinized starch composition having a glyoxal generating compound provided by Example 1 provides the following benefits: (1) reduced the basis weight of the paperboard by approximately 1.5%; (2) increased the speed of the machine by approximately 6%; (3) maintained the ring crush and Mullen test parameters of the paperboard while the speed was increased and the basis weight was reduced; (4) increased drainage from the consolidated web; (5) reduced filler machine chest turbidity; and (6) reduced white water turbidity.

Example 8

Preparation of a Cyclic Glyoxal Compound with Pendant Glyoxal Residues and no Aldehyde Blocking

A 1000 ml flask was charged with glyoxal (40% in water, 435 grams, 3 moles) and sulfuric acid (98%, 2 grs) and was stirred and warmed to 65° C. Urea (50% in water, 120 grams, 1 mole) was added to the stirred glyoxal solution over four hours at 65° C. The reaction mixture was held for two hours at 70° C. to generate the product, of which the predominant reaction product had the structure, as follows:

Example 9

Demonstration of Stability for Glyoxal Generating Compounds in a Self-Retaining Starch Solution

Penford PAR 6048AR cationic potato starch was blended with the glyoxal generating compounds taken from example 1, 5, and 8. In addition, unreacted/unblocked glyoxal was used as a comparison. The blending was done at ambient temperature and for 30 minutes. The blend ratio and starch solids are listed in Table IV. A Brookfield RV viscometer (spindle #5/10 rpm/25° C.) was used to measure the viscosity.

TABLE IV


10% Active Starch Solids
15% Active crosslinker

Crosslinker
Viscosity	Glyoxal	Example #1	Example #8	Example #5

2 Hours	Gel (0.5 hr)	300 cPs	Gel (0.5 hr)	350 cPs
4 Hours	Gel	300 cPs	Gel	300 cPs
6 Hours	Gel	300 cPs	Gel	300 cPs
8 Hours	Gel	300 cPs	Gel	300 cPs
24 Hours	Gel	300 cPs	Gel	300 cPs

The results in Table IV demonstrate that the blocked aldehyde containing compounds of type demonstrated in Examples 1 and 5 can produce stable mixtures with starch while unblocked aldehyde containing compounds, like that of example 8, and glyoxal will not produce stable mixtures with starch.
The disclosures of all articles and references mentioned in this application, including patents, are incorporated herein by reference.
The invention and the manner and process of making and using it, are now described in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains, to make and use the same. It is to be understood that the foregoing describes preferred embodiments of the present invention and that modifications may be made therein without departing from the spirit or scope of the present invention as set forth in the claims. To particularly point out and distinctly claim the subject matter regarded as invention, the following claims conclude this specification.

Claims

1. A method for manufacturing paper or paperboard sheet with increased strength, the method comprising the steps of:

providing a fiber slurry and a gelatinized starch composition, each of which is suitable for use in making paper or paperboard;

providing at least one crosslinker composition comprising at least one aldehyde generating compound capable of forming at least two or more covalent bonds to functional groups present in the starch or fiber of the web;

mixing the gelatinized starch composition and the crosslinker composition;

adding the mixture of gelatinized starch composition and crosslinker composition to the fiber slurry contemporaneously to mixing the gelatinized starch composition and the crosslinker composition; and

forming the paper or paperboard sheet.

2. The method of claim 1, wherein the gelatinized starch composition and the crosslinker composition are mixed together in a batch process prior to addition to the fiber slurry.

3. The method of claim 1, wherein the gelatinized starch composition and the crosslinker composition are mixed together in a continuous flow process prior to addition to the fiber slurry.

4. The method of claim 1, wherein the gelatinized starch composition and the crosslinker composition are mixed together less than about 1 hour prior to addition to the fiber slurry.

5. The method of claim 1, wherein the gelatinized starch composition and the crosslinker composition are mixed together less than about 30 minutes prior to addition to the fiber slurry.

6. The method of claim 1, wherein the gelatinized starch composition and the crosslinker composition are mixed together less than about 10 minutes prior to addition to the fiber slurry.

7. The method of claim 1, wherein the gelatinized starch composition and the crosslinker composition are mixed together less than about 1 minute prior to addition to the fiber slurry.

8. The method of claim 1, wherein a paper sheet is prepared by the method of manufacture.

9. The method of claim 1, wherein a paperboard sheet is prepared by the method of manufacture.

10. The method of claim 1, wherein the starch is self-retaining.

11. The method of claim 10, wherein the starch is a cationic starch.

12. The method of claim 10, wherein the starch is pregelatinized self-retaining starch selected from potato, corn or wheat starch.

13. The method of claim 1, wherein the crosslinker composition comprises between about 0.001% to about 80% aldehyde generating compound by weight in an aqueous media.

14. The method of claim 13, wherein the crosslinker composition does not comprise starch or gelatinized starch.

15. The method of claim 13, wherein the crosslinker composition is stable in the absence of starch, gelatinized starch, or pulp fiber for at least one week and reacts at a temperature of greater than about 25° C. to form covalent bonds with starch, gelatinized starch or pulp fiber in less than an hour.

16. The method of claim 13, wherein the crosslinker composition comprises at least one equivalent of a compound having at least two aldehyde residues and between about 0.25 and about 5 equivalents of one or more stabilizing compounds.

17. The method of claim 16, wherein the compound having at least two aldehyde residues is glyoxal.

18. The method of claim 16, wherein the stabilizing agent is a linear, branched or cyclic organic molecule having at least two functional groups capable of blocking an aldehyde residue.

19. The method of any one of claims 1 through 18, wherein the crosslinker composition further comprises at least one aldehyde blocking agent.

20. The method of claim 19, wherein the crosslinker composition comprises at least 0.1 molar equivalent of aldehybe blocking agent relative to the aldehyde generating compound.

21. The method of claim 19, wherein the crosslinker composition comprises at least one aldehyde blocking agent selected from urea, thiourea, amines, alkanols, alkane diols, and alkylene glycols.

22. The method of claim 1, wherein the aldehyde generating compound is a compound of Formula I:

wherein

Z is monovalent or divalent urea, monovalent or divalent α,ω-C_2-8alkanediol, C_2-8alkylene glycol, poly(ethylene glycol) having a molecular weight of less than about 20,000, ω-amino-α-C_2-8alkanol or Z is a 5 to 7 member optionally substituted heterocyclic group having one ring nitrogen atom, at least one additional ring heteroatom selected from N, O, or S, and zero or one oxo substitutents;

n is 0, 1, or 2;

m is 0 or 1;

n′=n if m=1 or n′=0 if m=0, wherein at least one of m and n is not zero.

23. The method of claim 1, wherein the aldehyde generating compound is a compound of Formula II:

wherein

A is an optionally substituted methylene group, an optionally substituted C_2-4alkylene group, or a single bond;

B is carbonyl, thiocarbonyl, or an optionally substituted 1,2-ethylene residue;

X₁and X₂are independently selected from the group consisting of oxygen and NR₃;

R₁and R₂are independently selected from the group consisting of hydrogen, hydroxy, optionally substituted C_1-20alkyl, optionally substituted C_1-20alkoxy, optionally substituted urea, optionally substituted thiourea, or

R₁and R₂, taken in combination, form a N,N′-divalent urea;

R₃is independently selected at each occurrence of R₃from the group consisting of hydrogen, 1-hydroxy-ethan-2-al-1-yl group, or a blocked glyoxal residue.

24. The method of claim 1, wherein the aldehyde generating compound is a compound of Formula III:

wherein

each of X₁, X₂, and X₃are independently selected from the group consisting of CH or N; and

R₄and R₅are independently selected at each occurrence of R₄and R₅in Formula III from the group selected from hydrogen, a 1-hydroxy-ethan-2-al-1-yl group, or a blocked glyoxal residue; or

one or more occurrences of NR₄R₅in Formula III, taken in combination form an optionally substituted N-piperazinyl residue.

25. The method of claim 24, wherein each of X₁, X₂, and X₃is nitrogen.

26. The method of claim 24, wherein one or more occurrences of NR₄R₅in Formula III, taken in combination form an optionally substituted N-2,3,5,6-tetrahydroxypiperazinyl residue.

27. The method of claim 24, wherein the aldehyde generating compound is a compound of Formula IV:

wherein

R₆is independently selected at each occurrence from the group selected from optionally substituted alkyl, optionally substituted carboxamide.

28. The method of claim 27, wherein R₆is independently selected at each occurrence from —C(O)NH₂or —C(O)NHCH(OH)CHO.

29. A method for manufacturing paper or paperboard sheet with increased strength, the method comprising the steps of:

preparing a paper or paperboard web comprising pulp fiber and at least one starch prepared by mixing the gelatinized starch composition and the fiber slurry;

contacting the web with the crosslinker composition under conditions conducive to formation at least two or more covalent bonds to functional groups present in the starch or fiber of the web.

30. The method of claim 29, wherein the method of manufacture further comprises the step of drying the paper or paperboard web.

31. The method of claim 30, wherein the crosslinker composition is contacted with the web prior to the drying process.

32. The method of claim 30, wherein the crosslinker composition is contacted with the paper or paperboard web after the drying step has removed at least a portion of moisture from the paper or paperboard web.

33. The method of claim 29, wherein the crosslinker composition increases at least one of the wet strength or the dry strength of the paper or paperboard prepared by the method of manufacture.

34. The method of claim 1, wherein the crosslinker composition comprises between about 0.001% to about 80% aldehyde generating compound by weight in an aqueous media.

35. The method of claim 34, wherein the crosslinker composition does not comprise starch or gelatinized starch.

36. The method of claim 34, wherein the crosslinker composition is stable in the absence of starch, gelatinized starch, or pulp fiber for at least one week and reacts at a temperature of greater than about 25° C. to form covalent bonds with starch, gelatinized starch or pulp fiber in less than an hour.

37. The method of claim 34, wherein the crosslinker composition comprises at least one equivalent of a compound having at least two aldehyde residues and between about 0.25 and about 5 equivalents of one or more stabilizing compounds.

38. The method of claim 37, wherein the compound having at least two aldehyde residues is glyoxal.

39. The method of claim 37, wherein the stabilizing agent is a linear, branched or cyclic organic molecule having at least two functional groups capable of blocking an aldehyde residue.

40. The method of any one of claims 29 through 39, wherein the crosslinker composition further comprises at least one aldehyde blocking agent.

41. The method of claim 40, wherein the crosslinker composition comprises at least 0.1 molar equivalent of aldehybe blocking agent relative to the aldehyde generating compound.

42. The method of claim 40, wherein the crosslinker composition comprises at least one aldehyde blocking agent selected from urea, thiourea, amines, alkanols, alkane diols, and alkylene glycols.

43. The method of claim 29, wherein the aldehyde generating compound is a compound of Formula I:

wherein

n is 0, 1, or 2;

m is 0 or 1;

n′=n if m=1 or n′=0 if m=0, wherein at least one of m and p is not zero.

44. The method of claim 29, wherein the aldehyde generating compound is a compound of Formula II:

wherein

B is carbonyl, thiocarbonyl, or an optionally substituted 1,2-ethylene residue;

R₁and R₂, taken in combination, form a N,N′-divalent urea;

45. The method of claim 29, wherein the aldehyde generating compound is a compound of Formula III:

wherein

46. The method of claim 45, wherein each of X₁, X₂, and X₃is nitrogen.

47. The method of claim 45, wherein one or more occurrences of NR₄R₅in Formula III, taken in combination form an optionally substituted N-2,3,5,6-tetrahydroxypiperazinyl residue.

48. The method of claim 45, wherein the aldehyde generating compound is a compound of Formula IV:

wherein

49. The method of claim 48, wherein R₆is independently selected at each occurrence from —C(O)NH₂or —C(O)NHCH(OH)CHO.

50. The method of claim 29, wherein the glyoxal generating compound is a compound according to Formula II-a:

wherein

B is carbonyl, thiocarbonyl, or an optionally substituted 1,2-ethylene residue;

R₁and R₂, taken in combination, form a N,N′-divalent urea;

R₃is independently selected at each occurrence of R₃from the group consisting of hydrogen, optionally substituted C_1-20alkyl, and unblocked and blocked glyoxal residues, where unblocked glyoxal residue is a 1-hydroxy-2-ethanal-1-yl group and the blocked glyoxal residue is a 1-hydroxy-2-(protected aldehyde residue)-ethan-1-yl group; or

R₃is a 1,2-dihydroxyethylene residue coupled to two rings according to Formula I; and

wherein the aldehyde generating compound according to Formula I degrades to generate at least one equivalent of glyoxal when the crosslinking composition is contacted with starch or pulp fiber.

51. The method of claim 50, wherein

R₁and R₂are independently selected from the group consisting of hydrogen, hydroxy, methanol, ethanol, urea, or

R₁and R₂, taken in combination, form a N,N′-divalent urea;

R₃is independently selected at each occurrence of R₃from the group consisting of hydrogen, methyl, and ethyl, or

R₃is an unblocked glyoxal residue or a blocked glyoxal residue selected from the group consisting of 1,2-dihydroxy-2-(C_1-4-alkoxy)-ethan-1-yl, 1,2-dihydroxy-2-(3-hydroxypropoxy)-ethan-1-yl, and 1,2-dihydroxy-2-(2-hydroxypropoxy)-ethan-1-yl.

52. The method of claim 50, wherein

X₁and X₂are NR₃;

A is a single bond;

B is a carbonyl or thiocarbonyl group; and

R₁and R₂are independently selected from hydroxy, C_1-6alkoxy, or blocked glyoxal residues.

53. The method of claim 50, wherein

X₁and X₂are NR₃;

A is a 1,1-C_1-6alkylene group;

B is a carbonyl or thiocarbonyl group;

R₁and R₂are independently selected from hydrogen, hydroxy, C_1-6alkoxy, and

54. The method of claim 50, wherein the glyoxal generating compound is a compound according to Formula V:

wherein

m is an integer from 0 to about 1000;

B is carbonyl, thiocarbonyl, or an optionally substituted 1,2-ethylene residue;

R₁and R₂are independently selected from the group consisting of hydrogen, hydroxyl, optionally substituted C_1-20alkyl, optionally substituted C_1-20alkoxy, optionally substituted urea, optionally substituted thiourea, or

R₁and R₂, taken in combination, form a N,N′-divalent urea;

R₄is a 1,2-dihydroxyethylene residue; or

R₄is a telechelic oligiomer comprising 2n+1 glyoxal residues alternating with n groups selected from the group consisting of α,ω-alkane diols, alkylene glycols, and poly(ethylene glycol); and

n is an integer of from 0 to about 100;

wherein the aldehyde generating compound according to Formula V degrades to generate at least one equivalent of glyoxal when the crosslinking composition is contacted with starch or pulp fiber.

55. The method of claim 50, wherein the glyoxal generating compound is a compound according to Formula VI:

wherein

p is an integer from 1 to about 1000;

Z is independently selected at each occurrence from the group consisting of optionally substituted urea, optionally substituted thiourea, optionally substituted guanidine, optionally substituted alkylene glycol, optionally substituted α,ω-akanediol, optionally substituted poly(ethylene glycol), optionally substituted imidazolidin-2-one, and optionally substituted tetrahydro-pyrimidin-2-one;

wherein the aldehyde generating compound according to Formula VI degrades to generate at least one equivalent of glyoxal when the crosslinking composition is contacted with starch or pulp fiber.

R₅is hydrogen, alkoxy, hydroxyalkoxy, amino, hydroxy, mono and dialkyl amino, optionally substituted alkane diol, optionally substituted urea, or optionally substituted alkylene glycol; and

R₆is hydrogen, optionally substituted alkyl, optionally substituted alkanoyl, optionally substituted unblocked glyoxal residue, or blocked glyoxal residues.

56. The method of claim 55, wherein

Z is urea, thiourea, C_2-10α,ω-alkanediol, C_2-10alkylene glycol, or poly(ethyleneglycol) having between 2 and about 100 glycol repeat units;