WO2020181092A1

WO2020181092A1 - Compositions and methods comprising wet strengthening resins

Info

Publication number: WO2020181092A1
Application number: PCT/US2020/021202
Authority: WO
Inventors: Zheng DANG; Yuping Luo; Xavier DE SEQUERA; Asko Karppi
Original assignee: Kemira Oyj; Kemira Chemicals, Inc.
Priority date: 2019-03-05
Filing date: 2020-03-05
Publication date: 2020-09-10

Abstract

The present disclosure generally relates to stable PAE resins, compositions containing and methods of use as wet strengthening agents. Use of such stable PAE resins and compositions containing for treating paper-based products and the like may result in products possessing increased wet strength compared to products made with conventional (less stable) PAE resins. Furthermore, the stable PAE resins of the present disclosure may generally be better suited for storage, e.g., at elevated temperature, compared to conventional (less stable) PAE resins.

Description

COMPOSITIONS AND METHODS COMPRISING WET STRENGTHENING RESINS

RELATED APPLICATIONS

[001] This application claims priority to U.S. Provisional Application No. 62/813,934, filed on March 5, 2019; and to Finnish Application No. 20195272, filed on April 4, 2019, the contents of which are incorporated by reference in their entirety.

FIELD OF THE ART

[002] This present disclosure generally relates to resins, compositions and articles comprising and methods of use thereof, particularly resins that are useful in the paper industry, and more particularly stable polyamidoamine-epihalohydrin resins and use thereof in products such as paper-based products.

BACKGROUND

[003] Wet strength relates to the ability of paper to retain its integrity upon wetting. This property is important for tissue, towel, napkin and other consumer products. Commonly used wet strengthening agents include polyamidoamine-epichlorohydrin resins (PAE resins). As polyamidoamine-epichlorohydrin resin comprises an active crosslinker, viscosity can increase and eventually gelation will occur during storage, in particular under conditions associated with prolonged storage time and/or conditions comprising high temperatures.

[004] Wet strength resins are often added to paper and paperboard at the time of manufacture. In the absence of wet strength resins, paper normally retains only 3% to 5% of its strength after being wetted with water. However, paper made with wet strength resin generally retains at least 10% to 50% of its strength when wet. Wet strength is useful in a wide variety of paper applications, such as toweling, milk and juice cartons, paper bags, and liner board for corrugated containers. Wet strength resins can also provide increased dry strength to paper.

[005] Conventional polyamidoamine-epichlorohydrin wet strength resins generally have a limited shelf life and stability of the resin is important for providing effective performance properties over storage time. As such, there is a continuing need for compositions and methods comprising polyamidoamine-epichlorohydrin resins that are capable of being stored stably for extended durations of time.

BRIEF SUMMARY

[006] The present disclosure generally relates to a stable polyamidoamine-epichlorohydrin (“PAE”) resin suitable for use as a wet strengthening agent, which comprises a

polyamidoamine backbone having an acid value of between about 35 to about 40. In some embodiments, the stable PAE resin may comprise a solids percentage ranging about 23-27%, 24-26% or about 25%. In some embodiments, said polyamidoamine backbone may comprise a low weight average molecular weight. In some embodiments, said polyamidoamine may comprise a weight average molecular weight of no more than about 12,000 Da or about 12,000 Da when measured by size exclusion chromatography (SEC under the conditions described by Example 1 of the present disclosure). In some embodiments, said

polyamidoamine backbone may comprise a weight average molecular weight ranging from about 3,000 Da to about 12,000 Da as measured by SEC under the conditions described by Example 1 of the present disclosure. In some embodiments, said stable PAE resin may comprise a lesser degree of charge decay, e.g., when aged at 35°C, than a conventional PAE resin. In some embodiments, said stable PAE resin may comprise a lesser degree of charge decay, e.g., after aging for 2 weeks or 4 weeks at 35°C, as compared to a conventional PAE resin. In some embodiments, said stable PAE resin may exhibit less than about 30.0%, less than about 27.5%, less than about 25.0%, less than about 22.5%, less than about 20.0%, less than about 19.0%, less than about 18.0%, or less than about 17.0% charge decay at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for

measurements, after a prolonged period of aging at 35°C. In some embodiments, said stable PAE resin may comprise an initial charge density of about 15% higher or more than the initial charge density of a conventional PAE resin at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. In some embodiments, the stable PAE resin may be produced by reacting epichlorohydrin and polyamidoamine monomers at a molar ratio of epichlorohydrin: secondary amine groups of the

polyamidoamine backbone of about 1.3 to about 1.7. In some embodiments, the stable PAE resin may be less subject to loss of viscosity over time, e.g., when subjected to elevated temperatures, e.g., about 35°C. compared to a conventional PAE resin. In some embodiments, the stable PAE resin may be produced using a combination of a weak and strong acid which are added in a weight ratio of about 1.1 or more, 1.2 or more, about 1.3 or more, 1.4 or more, 1.5 or more, or about 1.6 or more, e.g., said weak acid comprises formic acid and said strong acid comprises sulfuric acid. In some embodiments, a stable PAE resin may comprise a final pH value of the resin of from about 3.0 to about 3.4. In some embodiments, a stable PAE resin may comprise a charge decay of less than about 30.0%, less than about 27.5%, less than about 25.0%, less than about 22.5%, less than about 20.0%, less than about 19.0%, less than about 18.0%, or less than about 17.0% charge decay after a prolonged period of aging at 35°C, wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. In some embodiments, a stable PAE resin may comprise a fresh resin viscosity value of between about 150 cPs to about 200 cPs immediately or proximate to the time of synthesis, e.g., wherein said stable PAE resin comprises a viscosity value of between about 140 cPs to about 250 cPs after a prolonged period of aging at 35°C, wherein the viscosity is measured at room temperature, e.g., about 22-23 °C. In some embodiments, a stable PAE resin may comprise lower levels, i.e., a lower total content, of epichlorohydrin byproducts as compared to conventional PAE resins used as wet strength agents, e.g., wherein said stable PAE resin comprising lower levels of epichlorohydrin byproducts is synthesized using higher weight ratios of weak acid to strong acid, e.g., 1.1 or more, 1.2 or more, 1.3, or more, 1.4 or more, 1.5 or more, or 1.6 or. more, as compared to a weight ratio of 1.0 or less. In some embodiments, said stable PAE resin may comprise about 10,500 ppm or more, about 10,500 ppm or less, about 10,400 ppm or less, about 10,300 ppm or less, about 10,200 ppm or less, about 10,100 ppm or less, about 10,000 ppm or less, about 9,900 ppm or less, about 9,800 ppm or less, about 9,700 ppm or less, about 9,600 ppm or less, about 9,500 ppm or less, about 9,450 ppm or less, or about 9,400 ppm or less of epichlorohydrin byproducts following synthesis of said stable PAE resin.

[007] Also, the present disclosure generally relates to a composition suitable for use as a wet strength agent which comprises at least one stable PAE resin as described herein. The present disclosure additionally generally encompasses a paper product having improved wet strength which has been produced or treated with at least one stable PAE resin as described herein.

[008] Furthermore, the present disclosure generally relates to a method of synthesizing one or more stable PAE resins, wherein said method comprises reacting one or more

polyamidoamine backbones comprising an acid value of between about 35 to about 40 with epichlorohydrin. In some embodiments, the molar ratio of epichlorohydrin: secondary amine groups of the polyamidoamine backbone may be between about 1.3 to about 1.7. In some embodiments, said method may comprise a low-temperature hold time of about 3 hours under a 30-35°C temperature range at the beginning of the synthesis reaction. In some

embodiments, said method may include the addition of a strong acid and a weak acid. In some embodiments, said method may comprise the addition of a weight ratio of weak acid: strong acid of about 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, 1.6 or more, e.g., wherein said strong acid comprises sulfuric acid and/or said weak acid comprises formic acid. In some embodiments, said method may further comprise sequential addition of formic acid and sulfuric acid. In some embodiments, said method may comprise one or more additions of formic acid and/or one or more additions of sulfuric acid. In some embodiments, said method may result in a stable PAE resin comprising a solids percentage ranging about 23-27%, 24-26% or about 25%. In some embodiments, said method may result in a stable PAE resin comprising final resin pH of about 3.0 to about 3.4. In some embodiments, said method may result in a final resin pH of about 3.0 to about 3.4, e.g., about 3.3. In some embodiments, said method may result in lower levels, i.e., a lower total content, of epichlorohydrin byproducts as compared to when higher weight ratios of weak acid to strong acid, e.g., formic acid to sulfuric acid, are used during synthesis, e.g., compared to stable or conventional PAE resins synthesized with lower weight ratios of weak acid to strong acid, e.g., formic acid to sulfuric acid.

[009] Furthermore, the present disclosure generally relates to a method of manufacturing one or more paper products, wherein said method comprises: a. providing a composition comprising predominantly cellulose fibers; b. adding a predetermined quantity of one or more stable PAE resins as described herein; and c. forming the desired paper product. The present disclosure also generally encompasses a method for strengthening paper, comprising contacting pulp fibers with a strengthening resin comprising at least one stable PAE resins, wherein said at least one stable PAE resin is synthesized by reacting epichlorohydrin with a polyamidoamine backbone comprising an acid value of between about 35 to about 40 to produce a stable PAE resin, and at least partially curing the resin in the mixture of pulp fibers and strengthening resin to produce a paper product of enhanced strength. Additionally, the present disclosure generally relates to a stable polyamidoamine-epichlorohydrin (“PAE”) resin suitable for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a solids percentage of from about 23% to about 27%, wherein said stable PAE resin comprises an initial charge density value of about 15% higher or more than the initial charge density of a conventional PAE resin at a solution pH of about 7. Furthermore, the present disclosure generally relates to a stable polyamidoamine- epichlorohydrin (“PAE”) resin suitable for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a solids percentage of from about 23% to about 27%, wherein the stable PAE resin exhibits a charge decay of about 30.00% or less, 25.00% or less, 24.00% or less, 23.00% or less, 22.00% or less, 21.00% or less, 20.00% or less, 19.00% or less, 18.00% or less after aging, or 17.00% or less after a prolonged period of aging, e.g., aging at 35°C, wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. The present disclosure also generally encompasses a stable polyamidoamine-epichlorohydrin (“PAE”) resin suitable for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a solids percentage of from about 23% to about 27%, wherein the stable PAE resin may comprise a fresh resin viscosity of about 150 to about 200 cPs and may comprise a viscosity of about 140 to about 250 cPs after a prolonged period of aging at 35°C, wherein the viscosity is measured at room temperature, e.g., about 22-23°C. Additionally, the present disclosure generally relates to a stable polyamidoamine-epichlorohydrin (“PAE”) resin suitable for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a final resin pH of from about 3.0 to about 3.4, wherein said stable PAE resin comprises an initial charge density value of about 15% more or higher than the initial charge density of a conventional PAE resin at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. Furthermore, the present disclosure generally relates to a stable polyamidoamine-epichlorohydrin (“PAE”) resin suitable for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a final resin pH of from about 3.0 to about 3.4, wherein the stable PAE resin exhibits a charge decay of about 30.00% or less, 25.00% or less, 24.00% or less, 23.00% or less, 22.00% or less, 21.00% or less, 20.00% or less, 19.00% or less, 18.00% or less after aging, or 17.00% or less after a prolonged period of aging, e.g., aging at 35°C, wherein the pH of the solution is adjusted to a pH of 7.0 for measurements.

[0010] Additionally, the present disclosure generally pertains to a stable polyamidoamine- epichlorohydrin (“PAE”) resin suitable for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a final resin pH of from about 3.0 to about 3.4, wherein the stable PAE resin may comprise a fresh resin viscosity of about 150 to about 200 cPs and may comprise a viscosity of about 140 to about 250 cPs after a prolonged period of aging at 35°C, wherein the viscosity is measured at room temperature, e.g., about 22-23°C. The present disclosure also generally encompasses a stable

polyamidoamine-epichlorohydrin (“PAE”) resin suitable for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or are synthesized with a weight ratio of formic acid : sulfuric acid of 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.6 or more, wherein said stable PAE resin comprises an initial charge density value of about 15% higher or more than the initial charge density of a conventional PAE resin at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. Furthermore, the present disclosure generally relates to a stable polyamidoamine-epichlorohydrin (“PAE”) resin suitable for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or are synthesized with a weight ratio of formic acid : sulfuric acid of 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.6 or more, wherein the stable PAE resin exhibits a charge decay of about 30.00% or less, 25.00% or less, 24.00% or less, 23.00% or less, 22.00% or less, 21.00% or less, 20.00% or less, 19.00% or less, 18.00% or less after aging, or 17.00% or less after a prolonged period of aging, e.g., aging at 35°C, wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. Additionally, the present disclosure generally relates to a stable polyamidoamine-epichlorohydrin (“PAE”) resin suitable for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or are synthesized with a weight ratio of formic acid : sulfuric acid of 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.6 or more, wherein the stable PAE resin may comprise a fresh resin viscosity of about 150 to about 200 cPs and may comprise a viscosity of about 140 to about 250 cPs after a prolonged period of aging at 35°C, wherein the viscosity is measured at room temperature, e.g., about 22-23°C. The present disclosure also generally pertains to a stable polyamidoamine- epichlorohydrin (“PAE”) resin suitable for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a solids percentage of from about 23% to about 27%, wherein the stable PAE resin is synthesized using a weight ratio of formic acid : sulfuric acid of 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.6 or more and/or comprises a final resin pH value of 3.0 or more, 3.1 or more, 3.2 or more, 3.3 or more, or 3.4 or more.

[0011] Moreover, the present disclosure generally relates to a stable polyamidoamine- epichlorohydrin (“PAE”) resin composition suitable for use as a wet strengthening agent, comprising: a PAE resin which comprises a polyamidoamine backbone having an acid value of between about 35 to about 40 and a weight average molecular weight of no more than about 12,000 Da, preferably of about 3,000 Da to about 12,000 Da, as measured by size exclusion chromatography (SEC); and an acid. In some embodiments, the stable PAE resin may comprise a solids percentage of the PAE resin from about 23% to about 27%, preferably from about 24% to about 26%. In some embodiments, the composition may have a pH value ranging from about 3.0 to about 3.5, preferably from about 3.1 to about 3.4. In some embodiments, the acid may comprise a weak acid, preferably comprising one or more of formic acid, acetic acid, lactic acid, benzoic acid, propionic acid, citric acid, malonic acid, adipic acid, malic acid, and tartaric acid, more preferably comprising formic acid; and a strong acid, preferably comprising one or more of sulfuric acid, phosphoric acid, nitric acid, perchloric acid, hydroiodic acid, hydrochloric acid, and hydrobromic acid, more preferably comprising sulfuric acid. In some embodiments, the weight ratio of the weak acid to the strong acid may be about 1.1 or more, preferably about 1.2 or more, more preferably about 1.3 or more. In some embodiments, the PAE resin may be produced by reacting

epichlorohydrin and polyamidoamine at a molar ratio of epichlorohydrin : secondary amine groups of the polyamidoamine backbone of about 1.3 to about 1.7. In some embodiments, the composition may have a fresh resin viscosity value of between about 150 cPs to about 200 cPs, as measured at room temperature; and optionally a viscosity value of between about 140 cPs to about 250 cPs, as measured at room temperature, after a prolonged period of aging at 35°C, preferably after aging at 35°C for two weeks, more preferably after aging at 35°C for 4 weeks. In some embodiments, the PAE resin may exhibit a charge decay of less than about 30.0%, preferably less than about 25.0%, more preferably less than about 20.0%, as measured from PAE resin composition having pH adjusted to 7.0, after a prolonged period of aging at 35°C, preferably after aging at 35°C for two weeks, more preferably after aging at 35°C for 4 weeks. In some embodiments, the composition may comprise about 10,500 ppm or less, preferably about 10,200 ppm or less, more preferably about 10,000 ppm or less, of epichlorohydrin byproducts.

[0012] Furthermore, the present disclosure generally relates to a method of synthesizing one or more stable PAE resin compositions as discussed herein, wherein said method comprises reacting in an aqueous solution one or more polyamidoamine backbones having an acid value of between about 35 to about 40 and a weight average molecular weight of no more than about 12,000 Da, preferably about 3,000 Da to about 12,000 Da, as measured by size exclusion chromatography (SEC), with epichlorohydrin, and stopping the reaction by adding an acid. In some embodiments, the stable PAE resin composition may comprise a solids percentage of the PAE resin from about 23% to about 27%, preferably from about 24% to about 26%. In some embodiments, the stable PAE resin composition may have a pH value ranging from about 3.0 to about 3.5, preferably from about 3.1 to about 3.4. In some embodiments, adding the acid may comprise adding one or more additions of a weak acid, preferably comprising formic acid, and one or more additions of a strong acid, preferably comprising sulfuric acid, preferably in a weight ratio of the weak acid to the strong acid of about 1.1 or more, preferably about 1.2 or more, more preferably about 1.3 or more. In some embodiments, one or more additions of the weak acid and the strong acid may be added premixed or sequentially, preferably first adding at least one addition of the weak acid followed by at least one addition of the strong acid. In some embodiments, said method may comprise any one or more of the following steps: a. reacting the polyamidoamine backbone and the epichlorohydrin in the aqueous solution at a molar ratio of epichlorohydrin : secondary amine groups of the polyamidoamine backbone of about 1.3 to about 1.7, preferably providing a solids percentage of about 40-50%; b. at the beginning of the synthesis reaction holding the aqueous solution at about 30-35°C for more than 1 hour, preferably for about 3 hours or more, more preferably for about 3 hours to about 20 hours; c. holding the temperature for about 1 hour to about 3 horns at about 45 °C; d. adding water to dilute the solution and increasing the temperature to about 65°C; e. cooking the solution for about 3 hours at about 65°C; f. adding water to dilute the cooked solution of step e.; g. cooking the solution until reaching a viscosity of at least about 110 cPs at about 65°C; h. adding the acid in order to stop the reaction.

[0013] Moreover, the present disclosure generally relates to a method of manufacturing one or more paper products, said method comprising: a. providing a composition comprising cellulose fibers; b. adding one or more stable PAE resin compositions as discussed herein, optionally as diluted; and c. forming the desired paper product. In some embodiments, said one or more stable PAE resin composition is added at any point on a paper machine wet end at an amount ranging from about 0.1 -2.0% of dry weight of the stable PAE resin by dry weight of the paper product.

[0014] Furthermore, the present disclosure generally relates to use of a stable PAE resin composition as discussed herein for wet strengthening paper, comprising contacting pulp fibers with the optionally diluted PAE resin composition, and at least partially curing the resin. Moreover, the present disclosure generally relates to a paper product having improved wet strength, wherein the paper product has been produced or treated with at least one stable PAE resin composition as discussed herein, preferably the paper product comprising one or more of the following fiber-based products: handsheets, board-based products, beverage earners, toweling, milk and juice cartons, food trays, paper bags, liner board for corrugated containers, packaging board grade, tissue and towel grade, paper materials, paper towels, diapers, sanitary napkins, training pants, pantiliners, pee pads, dryer papers or pads, floor cleaning pads, coffee filters, air filters, litter box liners, incontinence briefs, tampons, absorbent facial tissue, absorbent bathroom tissue, napkins, wrapping paper, other paperboard products such as cartons and bag paper; an adsorbent paper-based product; single or multi-ply towel facial tissue, napkins, or bathroom tissue. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0015] Figure 1 illustrates charge decay percentage measurements that were taken during an aging experiment in accordance with Example 2.

[0016] Figure 2 illustrates viscosity measurements that were taken during an aging experiment in accordance with Example 3.

[0017] Figure 3 illustrates handsheet wet tensile strength measurements that were taken during an experiment in accordance with Example 4.

[0018] Figure 4 illustrates measurements of the total content of epichlorohydrin byproducts in various different PAE resin samples following synthesis, in accordance with Example 5.

DETAILED DESCRIPTION

DEFINITIONS

[0019] As used herein the singular forms“a”,“an”, and“the” include plural referents unless the context clearly dictates otherwise. All technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs unless clearly indicated otherwise.

[0020] As used herein, the term“monomer” generally refers to nonionic monomers, anionic monomers, cationic monomers, zwitterionic monomers, betaine monomers, and amphoteric ion pair monomers.

[0021] As used herein, the terms“polymer,”“polymers,”“polymeric,” and similar terms are used in their ordinary sense as understood by one skilled in the art, and thus may be used herein to refer to or describe a large molecule (or group of such molecules) that comprise recurring units. Polymers may be formed in various ways, including by polymerizing monomers and/or by chemically modifying one or more recurring units of a precursor- polymer. Unless otherwise specified, a polymer may comprise a“homopolymer” that may comprise substantially identical recurring units that may be formed by various methods e.g., by polymerizing a particular monomer. Unless otherwise specified, a polymer may also comprise a“copolymer” that may comprise two or more different recurring units that may be formed by, e.g., copolymerizing, two or more different monomers, and/or by chemically modifying one or more recurring units of a precursor polymer. Unless otherwise specified, a polymer or copolymer may also comprise a“terpolymer” that may comprise polymers that may comprise three or more different recurring units. The term“polymer” as used herein is intended to include both the acid form of the polymer as well as its various salts. Polymers may be amphoteric in nature, i. e. , containing both anionic and cationic substituents, although not necessarily in the same proportions.

[0022] As used herein the term“nonionic monomer” generally refers to a monomer that possesses a neutral charge.

[0023] As used herein, the term“anionic monomers” may refer to either anionic monomers that are substantially anionic in whole or (in equilibrium) in part, at a pH in the range of about 4.0 to about 9.0. The“anionic monomers” may be neutral at low pH (from a pH of about 2 to about 6), or to anionic monomers that are anionic at low pH.

[0024] As used herein, the term“cationic monomer” generally refers to a monomer that possesses a positive charge. As used herein, in additional to its conventional meaning in the art, the terms“mol%” and/or“mole%”, and the like, generally encompass both theoretical mol% as well as mol% as determined by an analytic technique, for example, ¹³C NMR.

[0025] As used herein, the term“PAE resin” generally refers to an aqueous composition comprising a resin synthesized by reacting one or more epihalohydrins and one or more polyamidoamine pre-polymers. Generally, the one or more epihalohydrins comprise epichlorohydrin. A“conventional PAE resin” generally comprises a resin synthesized by reacting epichlorhydrin and one or more polyamidoamine pre-polymers. Procedures for synthesizing conventional PAE resins are well known in the art. Typically, a polyamidoamine backbone is first prepared by reacting a polyalkylene polyamine and a dicarboxylic acid, a dicarboxylic acid halide, and/or a diester thereof, or may be provided as an off-the-shelf polyamidoamine backbone. In some instances, the acid residues can be aliphatic, aromatic, or aralkyl, and can contain between 3 and 12 carbon atoms. In some instances, the aliphatic acid residues can be linear or cyclic. In some instances, acid residues are adipoyl and glutaroyl. In some instances, the polyalkylene polyamine may be reacted with adipic acid. In some instances, the polyalkylene polyamine may be reacted with glutaric acid. In some instances, the polyalkylene polyamine may be reacted with any one or more of the following: adipic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, and/or diphenic acid.

Typically, polyalkylenepolyamine residues may contain at least one secondary amino group and can be tri-, tetra-, penta-, or higher amines, and can also contain another amine or other functionality. In some instances, the amino groups in the polyalkylenepolyamine can be connected by aliphatic residues such as ethylene or trimethylene groups, or aromatic residues such as phenylene, aralkyl residues such as xylyl. Polyalkylenepolyamines may include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, iminobispropylamine, and dipropylenetriamine. The polyamidoamine then reacts with epichlorohydrin in an aqueous solution. The product is diluted and neutralized to the desired solid content and pH range. Examples of procedures for preparing conventional PAE resins are generally described in U.S. Pat. Nos. 2,926,154, 3,086,961, 3,700,623, 3,772,076, 4,233,417, 4,298,639, 4,298,715, 4,341,887, 4,853,431, 5,019,606, 5,510,004, 5,644,021, 6,429,267, and 7,189,307 and are known in the art. Some instances of conventional PAE synthesis comprise the neutralization of the product with strong mineral acid such as sulfuric acid and hydrochloric acid to a pH below 3.0. The final products are generally kept at 10-30% concentration, in some instances to avoid potential gelation, such as gelation that may occur during storage and/or exposure to elevated temperatures. In some instances, conventional PAE resins may comprise a polyamidoamine backbone comprising an acid value of from about 10 to about 30. In some instances, conventional PAE resins generally may comprise a polyamidoamine backbone having a weight average molecular weight of greater than about 12,000 Da as measured by size exclusion chromatography (SEC) or gel permeation chromatography (GPC).

[0026] As used herein, the term“stable PAE resin” generally refers to a PAE resin which is synthesized using a polyamidoamine backbone that comprises an acid value of between about 35 to about 40. In some instances, said polyamidoamine backbone has a weight average molecular weight of up to or about 12,000 Da, for example, a weight average molecular weight ranging from about 3,000-12,000 Da, as measured by SEC under the conditions described by Example 1 of the present disclosure. Not wishing to be bound by theory, it is hypothesized by the inventors that a polymer backbone comprising a high acid value, e.g., about 35 or greater, and a low weight average molecular weight, e.g., from about 3,000 to about 12,000 Da, may react with epichlorohydrin such that the amine reaction of the stable PAE resin synthesis may, in some instances, go nearly to completion or even go to completion. In such instances, this reaction may result in a stable PAE that comprises a higher charge relative to other conventional PAE resins. Furthermore, such a reaction may result in a higher amount of epichlorohydrin being incorporated into the polymer backbone, which may increase the stability of said stable PAE resin relative to conventional PAE resins. [0027] In some instances, the polyamidoamine backbone may comprise a mole ratio of dibasic acid residue to polyamine residue of from about greater than 0.9 to less than 1.1, e.g., about 1.0. In some instances, the polyamidoamine backbone may comprise the product of a reaction of adipic acid with a polyalkylene polyamine. In some instances, the

polyamidoamine backbone may comprise the product of a reaction of glutaric acid with a polyalkylene polyamine. In some instances, the polyamidoamine backbone may comprise the product of a reaction of a dicarboxylic acid, a dicarboxylic acid halide, and/or a diester thereof with triethylenetetramine. In some instances, the polyamidoamine backbone may comprise the product of a reaction of a dicarboxylic acid, a dicarboxylic acid halide, and/or a diester thereof with diethylenetriamine. In some instances, the polyamidoamine backbone may comprise the product of a reaction of adipic acid with triethylenetetramine. In some instances, the polyamidoamine backbone may comprise the product of a reaction of adipic acid with diethylenetriamine. In some instances, the polyamidoamine backbone may comprise the product of a reaction of glutaric acid with triethylenetetramine. In some instances, the polyamidoamine backbone may comprise the product of a reaction of glutaric acid with diethylenetriamine. In some instances, a stable PAE resin may comprise a solids percentage of from about 20% or more to less than about 30%. In some instances, a stable PAE resin may comprise a solids percentage ranging from about 23-27% or from about 24- 26%; or about 25%. In some instances, one or more stable PAE resins may comprise the product of a reaction comprising a molar ratio of epichlorohydrin: secondary amine groups of the polyamidoamine backbone of about 1.3 to about 1.7, e.g., about 1.4. In some instances, such a molar ratio may be calculated based on the consideration that at such a low conversion the amount of reacted secondary amines may be negligible, such that the molar ratio of epichlorohydrin : secondary amine groups of the polyamidoamine backbone is the same as the epichlorohydrin : polyalkylenepolyamine molar ratio: epichlorohydrin: secondary amine =

where WECH and WPA are the weights of the epichlorohydrin and polyalkylenepolyamine, respectively, reacted with x and j, the number of carbon and nitrogen atoms of the

polyalkylenepolyamine component, respectively. In some instances, a stable PAE resin may comprise a lesser degree of charge decay e.g., when aged at 35°C, than a conventional PAE resin. In some instances, a stable PAE resin may be less subject to loss of viscosity over time, e.g., when subjected to elevated temperatures, e.g., about 35°C, compared to conventional PAE resins. In some instances, a stable PAE resin may comprise a fresh resin viscosity of between about 150 cPs to about 200 cPs immediately or proximate to the time of synthesis, wherein the viscosity is measured at room temperature, e.g., about 22-23°C. In some instances, a stable PAE resin may exhibit little to no viscosity loss after aging, e.g., aging for 2 weeks or 4 weeks at 35°C, as compared to a conventional PAE resin after aging. In some instances, a stable PAE resin may comprise a viscosity value of from about 140 cPs to about 250 cPs after a prolonged period of aging at 35°C, wherein the viscosity is measured at room temperature, e.g., about 22-23°C. In some instances, a stable PAE resin may comprise a fresh resin viscosity of about 150 to about 200 cPs and may comprise a viscosity of about 140 to about 250 cPs after a prolonged period of aging at 35°C, e.g., after 29 days of aging, wherein the viscosity is measured at room temperature, e.g., about 22-23°C. In some instances, a stable PAE resin may comprise a lesser degree of charge decay, e.g., lesser degree of charge decay after aging for 2 weeks or 4 weeks at 35°C, as compared to a conventional PAE resin. In some instances, a stable PAE resin may comprise an initial charge density of about 15% higher or more than the initial charge density of a conventional PAE resin at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. In some instances, a stable PAE resin may exhibit less than about 30.0%, less than about 27.5%, less than about 25.0%, less than about 22.5%, less than about 20.0%, less than about 19.0%, less than about 18.0% charge decay, or less than about 17.0% after aging at 35°C at e.g., after about 2 weeks of aging, wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. In some instances, a stable PAE resin may have a final pH value from about 3.0 to about 3.4. In some instances, a stable PAE resin comprising a final pH value of from about 3.0 to about 3.4 may demonstrate less charge decay after aging as compared to a conventional PAE resin, e.g., less than about 30.0%, less than about 27.5%, less than about 25.0%, less than about 22.5%, less than about 20.0%, less than about 19.0%, less than about 18.0%, or less than about 17.0% charge decay after aging at 35°C at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. In some instances, a handsheet comprising stable PAE resin, e.g., stable PAE resin comprising from about 20% to less than about 30% solids and comprising a polyamidoamine backbone comprising an acid value from about 35 to about 40, may have a greater permanent wet strength after aging as compared to a handsheet comprising a conventional PAE resin, e.g., a PAE resin comprising 30% or more solids, e.g., a PAE resin not comprising an acid value of between 35-40. In some instances, a handsheet comprising stable PAE resin may have a greater permanent wet strength after 34 days of aging at 35°C as compared to a handsheet comprising a conventional PAE resin. In some instances, a handsheet comprising aged stable PAE resin may experience less wet tensile strength loss as compared to a handsheet comprising aged conventional PAE resin, i.e., when comparing a handsheet prepared with fresh stable PAE resin and a handsheet prepared with aged stable PAE resin, the loss in wet tensile strength is less than that of the loss exhibited by comparing a handsheet prepared with fresh conventional PAE resin to a handsheet prepared with aged conventional PAE resin. In some instances, a handsheet comprising aged stable PAE resin may experience less wet tensile strength loss, e.g., the stable PAE resin is aged for 34 days at 35°C, where the loss may be measured by comparing the handsheet prepared with aged stable PAE resin to one prepared with fresh stable PAE resin, as compared to the loss in wet tensile strength exhibited by a handsheet comprising aged conventional PAE resin compared to a handsheet comprising fresh conventional PAE resin. For example, in some instances, a handsheet comprising an aged stable PAE resin aged for 34 days at 35°C may experience only about a 4.4% wet tensile strength loss when compared to a handsheet comprising a fresh stable PAE resin. In some instances, a handsheet comprising or treated with a stable PAE resin or a composition containing may experience 6.25% or less, 6.00% or less, 5.75% or less, 5.50% or less, 5.25% or less, 5.00% or less, 4.75% or less, 4.50% or less, or 4.40% or less loss of wet tensile strength when comparing a handsheet comprising fresh stable PAE resin and a handsheet comprising aged stable PAE resin. In some instances, a stable PAE resin may comprise lower levels, i.e., a lower total content, of epichlorohydrin byproducts, such as may be measured by gas chromatography (GC), as compared to conventional PAE resins used as wet

strengthening agents. In some instances, a stable PAE resin, e.g., stable PAE resin comprising from about 20% to less than about 30% solids and an acid value of between about 35 to about 40, may comprise lower levels of epichlorohydrin byproducts when higher weight ratios of weak acid to strong acid, e.g., formic acid to sulfuric acid, are used during the synthesis of said stable PAE resin batches as compared to stable or conventional PAE resins which are synthesized with lower weight ratios of weak acid to strong acid, e.g., formic acid to sulfuric acid. In some instances, a stable PAE resin, e.g., stable PAE resin comprising from about 20% to less than about 30% solids and an acid value of between about 35 to about 40, may comprise about 10,500 ppm or more, about 10,500 ppm or less, about 10,400 ppm or less, about 10,300 ppm or less, about 10,200 ppm or less, about 10,100 ppm or less, about 10,000 ppm or less, about 9,900 ppm or less, about 9,800 ppm or less, about 9,700 ppm or less, about 9,600 ppm or less, about 9,500 ppm or less, about 9,450 ppm or less, or about 9,400 ppm or less of epichlorohydrin byproducts following synthesis of said stable PAE resin.

[0028] As used herein, the term“epichlorohydrin byproducts” generally refers to the amount of unreacted epichlorohydrin, glycidol, and chlorinated hydrolysis byproducts of

epichlorohydrin, e.g., 1,3-DCP, 2,3-DCP, and 3-CPD, that remain after synthesis of a PAE resin.

[0029] As used herein, the term“charge decay” generally refers to a value that is calculated at a given solution pH value, e.g., about 7.0, as follows: (initial charge density - current charge density value) / (initial charge density *100%).

[0030] As used herein, the term“epihalohydrin” generally refers to its conventional meaning in the art, that is, any compound comprising a halogen on a carbon atom adjacent to an epoxide. In some instances, the halogen may comprise chlorine, and such a compound may be referred to as epichlorohydrin.

[0031] As used herein, the term“strong acid” generally refers to an acid that almost completely dissociates to hydrogen ion and conjugate base in aqueous solution. Strong acids generally have a pKa less than about 2.2, preferably less than or equal to about 0.

Representative strong acids include hydrochloric acid, sulfuric acid, nitric acid, perchloric acid, hydroiodic acid, phosphoric acid, and hydrobromic acid. In some instances, a strong acid may comprise sulfuric acid.

[0032] As used herein, the term“weak acid” generally refers to an acid that partly dissociates to hydrogen ion and its conjugate base in aqueous solution. Weak acids generally have a pKa greater than or equal to about 2.2. Representative weak acids include acetic acid, formic acid, lactic acid, benzoic acid, propionic acid, citric acid, malonic acid, adipic acid, malic acid, and tartaric acid. In some instances, a weak acid may comprise formic acid.

[0033] As used herein, the terms“acid value” and“acid number” generally refer to the value obtained by calculating the mass of potassium hydroxide in milligrams that is required to neutralize one gram of a given chemical substance. For example, in some instances, the acid value of a polyamidoamine backbone may be calculated by a potentiometric titration using a solution of tetrabutylammonium hydroxide (“TBAOH”). The acid value may be calculated as follows: AV = (MKOH X CTBAOH X VEq x 100)/(m x ES); where AV is the acid value of the sample in mg KOH / g dry product (polyamidoamine backbone); MKOH is the molecular weight of KOH; CTBAOH is the concentration of TBAOH; VEq is the volume in mL of TBAOH used until the equivalence point is reached; m is the amount of polyamidoamine backbone in grams; and ES is the dry content of the polyamidoamine backbone. In some instances, a stable PAE resin may comprise a polyamidoamine backbone comprising an acid value of from about 35 to about 40.

[0034] As used herein, the term“molecular weight” is given its conventional meaning in the art, with the understanding that molecular weight values of the same molecule or compound may differ based upon the analytical method used to determine the molecular weight of said molecule or compound. In some instances, the weight average molecular weight of a molecule or compound may be determined by size exclusion chromatography (SEC), especially by gel permeation chromatography (GPC).

[0035] As used herein "papermaking process" generally refers to a method of making paper products from pulp comprising forming an aqueous cellulosic papermaking furnish, draining the furnish to form a sheet, and drying the sheet. The steps of forming the papermaking furnish, draining and drying may be carried out in any conventional manner generally known in the art.

STABLE PAE RESINS, AND COMPOSITIONS AND METHODS COMPRISING

[0036] The present disclosure generally relates to a stable polyamidoamine-epichlorohydrin (PAE) resin suitable for use as a wet strengthening agent, which comprises a polyamidoamine backbone that comprises an acid value of between about 35 to about 40. In some instances, said stable PAE resin may comprise a solids percentage ranging from about 23-27% or from about 24-26%; or about 25%. In some instances, said polyamidoamine backbone may comprise a low weight average molecular weight. In some instances, said polyamidoamine backbone may comprise a weight average molecular weight of no more than about 12,000 Da when measured by SEC under the conditions described by Example 1 of the present disclosure. In some instances, said stable PAE resin may comprise a weight average molecular weight ranging from about 3,000 to about 12,000 Da, as measured by SEC under the conditions described by Example 1 of the present disclosure. In some instances, the stable PAE resin may comprise a resin synthesized by reacting one or more polyamidoamine prepolymers and epichlorohydrin. In some instances, the stable PAE resin may comprise the product of a reaction comprising a molar ratio of epichlorohydrin: secondary amine groups of the polyamidoamine backbone of about 1.3 to about 1.7, e.g., about 1.4. In some instances, the stable PAE resin may comprise an initial charge density of about 15% higher or more than the initial charge density of a conventional PAE resin at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for measurements.

[0037] In some instances, the stable PAE resin may comprise a lesser degree of charge decay, e.g., when aged at 35°C, as compared to a conventional PAE resin. In some instances, the stable PAE resin may comprise a lesser degree of charge decay, e.g., lesser degree of charge decay after aging for 2 weeks or 4 weeks at 35°C, as compared to a conventional PAE resin. In some instances, the stable PAE resin may exhibit a charge decay of about 30.00% or less, 25.00% or less, 24.00% or less, 23.00% or less, 22.00% or less, 21.00% or less, 20.00% or less, 19.00% or less, 18.00% or less after aging, or 17.00% or less after a prolonged period of aging wherein the pH of the solution is adjusted to a pH of 7.0 for measurements, e.g., aging at 35°C, e.g., the stable PAE resin may exhibit less than about 18.0% charge decay or less than about 17.0% charge decay after 2 weeks of aging at 35°C at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for measurements, e.g., the stable PAE resin may exhibit less than about 30.00% charge decay after 4 weeks of aging at 35°C. In some instances, the stable PAE resin may be produced by reacting epichlorohydrin and polyamido amine at a molar ratio of epichlorohydrin: secondary amine groups of the polyamidoamine backbone of about 1.3 to about 1.7, e.g., about 1.4. In some instances, the stable PAE resin may comprise an initial charge density value of about 15% higher or more than the initial charge density of a conventional PAE resin at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. In some instances, the stable PAE resin may be less subject to loss of viscosity over time, e.g., when subjected to elevated temperatures, e.g., about 35°C compared to conventional PAE resins.

[0038] In some instances, the stable PAE resin may be produced using a combination of a weak and strong acid which are added in a ratio which provides a buffering effect and stabilizing effect. In some instances, the stable PAE resin may have a final pH value from about 3.0 to about 3.4. In some instances, one or more stable PAE resins may have a final pH value of about 3.0 or more, 3.1 or more, 3.2 or more, 3.3 or more, or 3.4 or more. In some instances, the stable PAE resin comprising a final pH value of from about 3.0 to about 3.4 may exhibit a lesser charge decay as compared to a conventional PAE resin, e.g., less than about 30.0%, less than about 27.5%, less than about 25.0%, less than about 22.5%, less than about 20.0%, less than about 19.0%, less than about 18.0% charge decay, or less than about 17.0% charge decay after a prolonged period of aging at 35°C wherein the pH of the solution is adjusted to a pH of 7.0 for measurements, e.g., less than about 20.00% after 2 weeks at 35°C, e.g., less than about 17.00% after 2 weeks of aging at 35°C at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. In some instances, the stable PAE resin may have a final acidic pH value that prevents polymer hydrolysis, viscosity decrease, and/or performance loss in said stable PAE resins. In some instances, a stable PAE resin may comprise a viscosity value of from about 140 cPs to about 250 cPs after a prolonged period of aging at 35°C, wherein the viscosity is measured at room temperature, e.g., about 22-23°C. In some instances, a stable PAE resin may exhibit little to no viscosity loss after aging, e.g., aging for 2 weeks or 4 weeks at 35°C, as compared to a conventional PAE resin after aging. In some instances, a stable PAE resin may comprise a fresh resin viscosity of about 150 to about 200 cPs and may comprise a viscosity of about 140 to about 250 cPs after a prolonged period of aging at 35°C, e.g., after 5 days or less, 5 days or more, 10 days or more, 15 days or more, 20 days or more, 25 days or more, or 29 days or more of aging, wherein the viscosity is measured at room temperature, e.g., about 22-23°C.

[0039] In some instances, stable PAE resin may comprise lower levels, i.e., a lower total content, of epichlorohydrin byproducts, such as may be measured by GC, as compared to conventional PAE resins used as wet strength agents. For example, in some instances, stable PAE resin, e.g., PAE resin comprising from about 23% solids to about 27% solids and comprising a poly amido amine backbone comprising an acid value of between about 35 to about 40, may comprise lower levels of epichlorohydrin byproducts, such as, for example, unreacted epichlorohydrin, glycidol, and chlorinated hydrolysis byproducts of

epichlorohydrin such as 1,3-dichloropropanol (1,3-DCP), 2,3-dichloropropanol (2,3- DCP), and/or 3-chloropropanediol (3-CPD), when higher weight ratios of weak acid to strong acid, e.g., formic acid to sulfuric acid, are used during the synthesis of said stable PAE resin as compared to stable PAE resins which were synthesized with lower weight ratios of weak acid to strong acid, e.g., formic acid to sulfuric acid. For example, a stable PAE resin which is synthesized with a weight ratio of 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.6 or more of formic acid: sulfuric acid may have lower amounts epichlorohydrin byproducts as compared to a stable PAE resin synthesized with a weight ratio of formic acid: sulfuric acid of 1.0 or less. In some instances, a stable PAE resin, e.g., stable PAE resin comprising from about 20% to less than about 30% solids and an acid value of between about 35 to about 40, may comprise about 10,500 ppm or more, about 10,500 ppm or less, about 10,400 ppm or less, about 10,300 ppm or less, about 10,200 ppm or less, about 10,100 ppm or less, about 10,000 ppm or less, about 9,900 ppm or less, about 9,800 ppm or less, about 9,700 ppm or less, about 9,600 ppm or less, about 9,500 ppm or less, about 9,450 ppm or less, or about 9,400 ppm or less of epichlorohydrin byproducts following synthesis of said stable PAE resin. In some instances, the amount of epichlorohydrin byproducts may be measured by GC analysis, such as, e.g., those described in Example 5 of the present disclosure. In some embodiments, a stable PAE resins may comprise improved storage stability relative to conventional PAE resins, in particular said stable PAE resin may exhibit a lesser degree of gelation over time as compared to a conventional PAE resin stored over time in the same conditions.

[0040] In some instances, a composition suitable for use as a wet strengthening agent may comprise one or more stable PAE resins or compositions containing as described herein. In some instances, a product, e.g., a paper product, e.g., a board-based product, e,g., a fiber- based product, having improved wet strength may be produced or treated with at least one stable PAE resin or composition containing as discussed herein. In some instances, such products, in particular paper-based products, e.g., fiber-based products, may possess improved wet strength performance as compared to a product comprising or treated with a conventional PAE resin. Such products may include, for example, fiber-based products, e.g., handsheets, board-based products, beverage carriers, toweling, milk and juice cartons, food trays, paper bags, liner board for corrugated containers, packaging board grade, and tissue and towel grade, paper materials, paper towels, diapers, sanitary napkins, training pants, pantiliners, incontinence briefs, tampons, pee pads, litter box liners, coffee filters, air filters, dryer pads, floor cleaning pads, absorbent facial tissue, absorbent bathroom tissue, napkins, wrapping paper, and other paperboard products such as cartons and bag paper. Furthermore, in some instances, one or more stable PAE resins may be used paper processing, in some instances as wet strength resins. Further examples of paper products which may comprise one or more stable PAE resins include but are not limited to packaging board grade, and tissue and towel grade, paper materials, paper towels, absorbent facial tissue, absorbent bathroom tissue, napkins, wrapping paper, and other paperboard products such as cartons and bag paper. In some instances, the one or more stable PAE resins may be incorporated into any one or more paper products at an amount ranging from about 0.1 to about 2.0% of dry weight stable PAE resin by dry weight of the paper. In some instances, the one or more stable PAE resins or composition containing may be incorporated into the papermaking furnish at any point on the wet end of the paper machine. In some instances, the one or more stable PAE resins or composition containing may also be applied from a tub size or at a size press or from showers to the dried or partially dried sheet. In some instances, desirable wet strength may be obtained by incorporating in the paper from about 0.1 to about 2.0% of dry weight stable PAE resin by dry weight of the pulp.

[0041] In some instances, a handsheet may comprise or may be treated with a stable PAE resin or a composition containing as discussed herein. In some instances, a handsheet comprising or treated with a stable PAE resin or composition containing, e.g., stable PAE resin comprising from about 23% to about 27% solids and comprising a polyamidoamine backbone comprising an acid value from about 35 to about 40, may have a greater permanent wet strength after aging as compared to a handsheet comprising or treated with a

conventional PAE resin, e.g., a PAE resin comprising 30% solids, e.g., a PAE resin comprising an acid value of less than 35. In some instances, a handsheet comprising or treated with a stable PAE resin or a composition containing may have a greater permanent wet strength after a prolonged period of aging, e.g., 10 days or more, 15 days or more, 20 days or more, 25 days or more, 30 days or more or 34 days or more, as compared to a handsheet comprising or treated with a conventional PAE resin. In some instances, a handsheet comprising or treated with a stable PAE resin or a composition containing may experience less wet tensile strength loss as compared to a handsheet comprising or treated with a conventional PAE resin, where the loss in wet tensile strength is measured by comparing a handsheet comprising fresh stable PAE resin to one comprising aged stable PAE resin, and comparing the calculated loss to that of the loss exhibited by comparing a handsheet comprising fresh conventional PAE resin to a handsheet comprising aged conventional PAE resin. In some instances, a handsheet comprising or treated with a stable PAE resin or a composition containing may experience 6.25% or less, 6.00% or less, 5.75% or less, 5.50% or less, 5.25% or less, 5.00% or less, 4.75% or less, 4.50% or less, or 4.40% or less loss of wet tensile strength when comparing a handsheet comprising fresh stable PAE resin and a handsheet comprising aged stable PAE resin.

[0042] In some instances, one or more stable PAE resins or one or more compositions containing may be used in the manufacture of paper products and absorbent paper products, e.g., as wet strengthening resins. In some instances, such products may comprise cellulose paperboard webs which comprise: (a) predominantly cellulose fibers and (b) a composition comprising one or more stable PAE resins. In some instances, one or more stable PAE resins or a composition containing may be suited for the manufacture of absorbent paper products such as single or multi-ply towel facial tissue, napkins and bathroom tissue. In some instances, the absorbent paper may be manufactured utilizing: (a) softwood fiber, hardwood fiber, recycle fiber, refined fiber or a mixture of these in an amount sufficient to form an overall furnish of from approximately 1 to 100% hardwood fiber, softwood fiber, recycle fiber, refined fiber or a mixture of these; (b) adding a predetermined quantity of a

composition comprising the one or more stable PAE resins; and (c) forming a paper product by drying on one or more drying means to a desired moisture content level, optionally about less than ten percent, e.g., 8% or less, or 7% or less.

[0043] In some instances, one or more stable PAE resins may be synthesized differently than conventional PAE resins in order to maximize the stability and utility of said one or more stable PAE resins, wherein such differences include, but are not limited to including, for example, that said one or more stable PAE resins may comprise: 1.) an increased mole ratio of epichlorohydrin to secondary amine in the pre-polymer such that the secondary amine reaction is maximized and a stable PAE resin with a higher final pH value to minimize charge decay over resin storage stages is produced; 2.) the low-temperature hold time may be increased in the beginning of the synthesis (i.e., prolong 1 hour hold to 3 hour hold or more under the 30-35°C temperature range) to effectively form the pendant chlorohydrin groups and diminish/eliminate the epichlorohydrin hydrolysis which can lead to reduced levels of epichlorohydrin by-products; and/or 3.) the blend of acid ratio of formic acid to sulfuric acid may be increased (from conventionally used weight ratio of 1.0 to 1.1 or more, 1.2 or more,

1.3 or more, 1.4 or more, 1.5 or more, or about 1.6 or more) to quench the crosslinldng reaction and to stabilize the final stable PAE resin at a higher final pH level as compared to conventional PAE resin.

[0044] In some instances, the stable PAE resin or composition or paper product containing may provide any one or more of the following properties in relation to one or more conventional PAE resins: 1.) higher levels of azetidinium content as compared to

conventional PAE resins, e.g., based on initial resin charge density values; 2.) greater thermostability; 3.) enhanced wet strength performance; 4.) higher final resin pH (pH of about 3.0 to about 3.4); 5.) less subject to change in resin cationic charge during storage; and 6.) low levels of epichlorohydrin byproducts, such as, for example, 1,3-DCP, 2,3-DCP, and 3-CPD.

[0045] In some instances, other components can be added to a composition comprising one or more stable PAE resins, such as other ionic or non-ionic polymers, for example polyvinyl alcohol (PVA), polyethylene oxide (PEO), hydroxyethylcelluloses, polydiallyldimethyl ammonium chloride (D ADM AC) polymers, polyacrylamide-based polymers, and/or glyoxylated polyacrylamide-based (GPAM) polymers, and the like, for applications such as wet strengthening applications. In some instances, one or more stable PAE resins may be blended with one or more polyacrylamide-based polymers and/or resins. In some instances, one or more stable PAE resins may be blended with one or more GPAM resins. In some instances, one or more stable PAE resins may comprise one or more polyacrylamide-based polymers, wherein said one or more polyacrylamide-based polymers may function as promoters and/or boosters. In some instances, one or more stable PAE resins may be blended with one or more GPAM resins and/or one or more polyacrylamide-based polymers, and such blends may demonstrate enhanced storage stability. In some instances, use of one or more stable PAE resins or compositions containing described herein in such blends may further improve the storage stability of the blends, in particular a lesser degree of gelation over time as the stable PAE resin ages. Moreover, in some instances, additional stabilizing compounds can be added to a composition comprising one or more stable PAE resins to further stabilize the composition. In some instances, an additional stabilizer may include non-aldehyde, low molecular weight, non-ionic, water soluble organic stabilizing compounds, optionally in combination with a water soluble, inorganic complexing metal salt. Such stabilizers are described in U.S. Patent No. 7,868,071. Such non-aldehyde, low molecular weight (i.e., a molecular weight below about 5000 Daltons, specifically below about 1000 Daltons, more specifically below about 300 Daltons), non-ionic, water soluble organic stabilizing compounds include (a) water soluble tertiary amines, such as triethanolamine, 2- dimethylamino ethanol, and aminopropyl diethanolamine, and the like; water soluble amides, and especially water soluble primary amides such as adipamide NH2C(0)(CH2)4C(0)NH2), thiourea (NH2C(S)NEh), lower molecular weight urea-formaldehyde oligomers, urea (NHhC(0)NH₂) and water soluble polyamine-urea adducts, such as the urea adduct with 3,3'- diamino-N-methyldiproplyamine, i.e., (NH₂C(0)N(H)--(CH₂)₃--N(CH₃)--(CH₂)₃N- (H)C(0)NH₂), and the like; lower molecular weight carbohydrates, including various monosaccharides, disaccharides, trisaccharides, and polysaccharides; and lower molecular- weight polyalcohols (polyols) including glycerol, sorbitol, polyvinyl alcohol and various other polyols.

[0046] In some instances, the amount of added low molecular weight, non-aldehyde, non ionic, water soluble organic stabilizing compound should not be significantly above a stoichiometric equivalent of, or a slight stoichiometric excess of the molar amount of the epichlorohydrin used in the synthesis of the stable PAE resin. In some cases, an amount of the low molecular weight, non-aldehyde, non-ionic, water soluble organic stabilizing compound of from about 0.1% to about 25% by weight based on the weight of the stable PAE resin solids, and more usually 1 to 15% by weight.

[0047] In some instances, a composition comprising combinations of the one or more of the foregoing classes of stabilizers can be used. In some instances, these stabilizing compounds can be used together with a water soluble, inorganic complexing metal salt. Suitable water soluble, inorganic complexing metal salts include the water soluble salts of a complexing metal having an electron charge density greater than that of sodium, such as aluminum, zinc, calcium, chromium, iron, magnesium and lithium. In some instances, water soluble salts of these metals include the nitrates, sulfates, chlorides, and bromides. In some instances, water soluble, inorganic complexing metal salts may include zinc chloride, magnesium chloride, calcium chloride, and lithium chloride. In some instances, a water soluble, inorganic complexing metal salt may comprise aluminum sulfate, also known as alum. In some instances, on a resin weight basis, the water soluble, inorganic complexing metal salt may be beneficially added in an amount up to about 10% by weight of the stable PAE resin solids. In some instances, an amount of the water soluble, inorganic complexing metal salt of up to about 5% by weight of the stable PAE resin solids may be sufficient. In some instances, the low molecular weight non-aldehyde, non-ionic stabilizing compound and the water soluble, inorganic complexing metal salt are used in combination.

[0048] The present disclosure also generally relates to a method of synthesizing one or more stable PAE resins or compositions containing, wherein said method comprises reacting one or more polyamidoamine backbones comprising an acid value of between about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da with one or more epihalohydrins, e.g., epichlorohydrin, to produce said one or more stable PAE resins. In some instances, said one or more epihalohydrins may comprise epichlorohydrin. In some instances, the molar ratio of epichlorohydrin : secondary amine groups of the

polyamidoamine backbone is between about 1.3 to about 1.7, e.g., about 1.4. In some instances, said method may comprise a low-temperature hold time of about 3 hours or more under a 30-35°C temperature range at the beginning of the synthesis reaction. In some instances, the method may comprise the addition of a strong acid and a weak acid. In some instances, said method may comprise use of a weight ratio of weak acid : strong acid of about 1.1 or less, 1.1 or more, 1.2 or more, about 1.3 or more, or about 1.4 or more, 1.5 or more, 1.6 or more, optionally wherein said strong acid comprises sulfuric acid and/or said weak acid comprises formic acid. In some instances, said method may result in a stable PAE resin comprising higher levels of azetidinium content as compared to PAE resins not synthesized by said method, as indicated by initial resin charge density values. In some instances, said method may result in a stable PAE resin comprising a higher final resin pH, e.g., a pH of about 3.0 to about 3.4, as compared to pH ranges of conventional PAE resins, e.g., about 2.9- 3.0.

[0049] In some instances, said method may comprise a target value of from about 23% to about 27% solids, e.g., about 25%, PAE resin. In some instances, after the first stage of the synthesis reaction, the solids percentage may be about from about 40% to about 50%, e.g., about 45%. In some instances, the method for synthesizing one or more stable PAE resins may comprise: a. reacting epichlorohydrin with polyamidoamine backbone comprising an acid value of between about 35 to about 40 and/or a weight average molecular weight of from about 3,000 to about 12,000 Da at a molar ratio of about 1.3 to about 1.7 of epichlorohydrin: secondary amine groups of the polyamidoamine backbone, wherein the first stage of the reaction produces a solids percentage of from about 40% to about 50%, e.g., about 45%, and wherein the reaction is performed in an aqueous solution; b. holding the aqueous solution at about 30-35°C for about 3 hours to about 20 hours; c. holding the temperature for about 1 hour to about 3 hours at about 45°C; d. adding water to dilute the solution and increasing the temperature to about 65°C; e. cooking the solution for about 3 hours at about 65°C; f. adding water to dilute the solution of step e.; g. cooking for about 2 hours until the desired kill point viscosity is reached, e.g., about 110 cPs at about 65°C; and h. adding formic acid and/or sulfuric acid. In some instances, step. h. may comprise one or more additions of formic and sulfuric acid. In some instances, the additions of formic acid and sulfuric acid may be sequential additions. In some instances, step. h. may comprise one or more additions of formic and sulfuric acid, wherein the one or both of formic acid and sulfuric acid are added multiple times. In some instances, step h. may comprise addition of sulfuric acid, and following addition of sulfuric acid, addition of formic acid at such an amount that the weight ratio of formic acid: sulfuric acid is 1.1 or less, 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.6 or more. In some instances, step h. may comprise addition of formic acid and sulfuric acid which are pre-mixed at a desired weight ratio, e.g., 1.1 or less, 1.1 or more, 1.2 or more, 1.3. or more, 1.4 or more, 1.5 or more, or 1.6 or more of formic acid to sulfuric acid. In some instances, said method may result in a stable PAE resin comprising a solids percentage ranging about 23-27%, 24-26% or about 25%. In some instances, the stable PAE resin which results from said method may have a viscosity of about 150 to about 200 cPs, wherein the viscosity is measured at room temperature, e.g., about 22-23°C. In some instances, the method may result in a stable PAE resin comprising a final pH value from about 3.0 to about 3.4, e.g., about 3.3. In some instances, said method may result in lower levels, i.e., a lower total content, of epichlorohydrin byproducts when higher weight ratios of weak acid to strong acid, e.g., formic acid to sulfuric acid, are used during the synthesis of said stable PAE resin batches e.g., compared to stable or conventional PAE resins which were synthesized with lower weight ratios of weak acid to strong acid, e.g., formic acid to sulfuric acid. In some instances, the one or more stable PAE resins comprising lower levels of epichlorohydrin byproducts may be synthesized using higher weight ratios of weak acid to strong acid, e.g., 1.1 or more, 1.2 or more, 1.3, or more, 1.4 or more, 1.5 or more, or 1.6 or more, as compared to a weight ratio of 1.0 or less. In some instances, the one or more stable PAE resins comprising lower levels of epichlorohydrin byproducts may be synthesized using higher weight ratios of weak acid to strong acid, e.g., 1.1 or more, 1.2 or more, 1.3, or more,

1.4 or more, 1.5 or more, or 1.6 or more, as compared to a weight ratio of 1.0 or less, further wherein the one or more stable PAE resins comprising lower levels of epichlorohydrin byproducts may comprise about 10,500 ppm or more, about 10,500 ppm or less, about 10,400 ppm or less, about 10,300 ppm or less, about 10,200 ppm or less, about 10,100 ppm or less, about 10,000 ppm or less, about 9,900 ppm or less, about 9,800 ppm or less, about 9,700 ppm or less, about 9,600 ppm or less, about 9,500 ppm or less, about 9,450 ppm or less, or about 9,400 ppm or less of epichlorohydrin byproducts following synthesis of said stable PAE resin. In some instances, said method may result in a stable PAE resin or composition containing comprising any of the one or more properties of the stable PAE resins described herein.

[0050] Furthermore, the present disclosure generally relates to a method of manufacturing one or more paper products, wherein said method comprises: a. providing a composition comprising predominantly cellulose fibers; b. adding a predetermined quantity of a composition comprising one or more stable PAE resins; and c. forming the desired paper product. In some instances, the resultant product may comprise greater permanent wet tensile strength as compared to a product manufactured with a conventional PAE resin.

[0051] Moreover, the present disclosure generally relates to a method of manufacturing one or more paper products, e.g., one or more adsorbent paper products, wherein said method comprises: a. providing a composition comprising softwood fiber, hardwood fiber, recycle fiber, refined fiber, or a mixture of these in an amount sufficient to form an overall furnish of from approximately 1 to 100% hardwood fiber, softwood fiber, recycle fiber, refined fiber or a mixture of these; (b) adding a predetermined quantity of a composition comprising the one or more stable PAE resins; and (c) forming a paper product by drying on one or more drying means to a desired moisture content level. In some instances, the resultant product may comprise greater permanent wet tensile strength as compared to a product manufactured with a conventional PAE resin.

[0052] Additionally, the present disclosure generally encompasses a method for

strengthening paper, comprising contacting pulp fibers with a strengthening resin comprising at least one stable PAE resin, wherein said stable PAE resin is synthesized from reacting epichlorohydrin with a polyamidoamine backbone comprising an acid value of between about 35 to about 40 to produce a stable PAE resin, and at least partially curing the resin in the mixture of pulp fibers and strengthening resin to produce a paper product of enhanced strength.

[0053] Moreover, the present disclosure generally relates to a stable PAE resin for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a solids percentage of from about 23% to about 27%, wherein said stable PAE resin comprises an initial charge density value of about 15% higher or more than the initial charge density of a conventional PAE resin at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. The present disclosure generally encompasses a stable PAE resin for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a solids percentage of from about 23% to about 27%, wherein the stable PAE resin exhibits a charge decay of about 30.00% or less, 25.00% or less, 24.00% or less, 23.00% or less, 22.00 % or less, 21.00% or less, 20.00% or less, 19.00% or less, 18.00% or less after aging, or 17.00% or less after a prolonged period of aging wherein the pH of the solution is adjusted to a pH of 7.0 for measurements, e.g., aging at 35°C. The present disclosure generally encompasses a stable PAE resin for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a solids percentage of from about 23% to about 27%, wherein the stable PAE resin may comprise a fresh resin viscosity of about 150 to about 200 cPs and may comprise a viscosity of about 140 to about 250 cPs after a prolonged period of aging at 35°C, wherein the viscosity is measured at room temperature, e.g., about 22-23 °C.

[0054] The present disclosure generally relates to a stable PAE resin for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a final resin pH of from about 3.0 to about 3.4, wherein said stable PAE resin comprises an initial charge density value of about 15% higher or more than the initial charge density of a conventional PAE resin at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. The present disclosure also generally relates to a stable PAE resin for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a final resin pH of from about 3.0 to about 3.4, wherein the stable PAE resin exhibits a charge decay of about 30.00% or less, 25.00% or less, 24.00% or less, 23.00% or less, 22.00% or less, 21.00% or less, 20.00% or less, 19.00% or less, 18.00% or less after aging, or 17.00% or less after a prolonged period of aging wherein the pH of the solution is adjusted to a pH of 7.0 for measurements, e.g., aging at 35°C. The present disclosure further generally relates to a stable PAE resin for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a final resin pH of from about 3.0 to about 3.4, wherein the stable PAE resin may comprise a fresh resin viscosity of about 150 to about 200 cPs and may comprise a viscosity of about 140 to about 250 cPs after a prolonged period of aging at 35°C, wherein the viscosity is measured at room temperature, e.g., about 22-23°C.

[0055] The present disclosure also generally relates to a stable PAE resin for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or are synthesized with a weight ratio of formic acid : sulfuric acid of 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.6 or more, wherein said stable PAE resin comprises an initial charge density value of about 15% higher or more than the initial charge density of a conventional PAE resin at a solution pH of about 7.0, i.e., wherein the pH of the solution is adjusted to a pH of 7.0 for measurements. The present disclosure also generally relates to a stable PAE resin for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or are synthesized with a weight ratio of formic acid : sulfuric acid of 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.6 or more, wherein the stable PAE resin exhibits a charge decay of about 30.00% or less, 25.00% or less, 24.00% or less, 23.00% or less, 22.00% or less,

21.00% or less, 20.00% or less, 19.00% or less, 18.00% or less after aging, or 17.00% or less after a prolonged period of aging wherein the pH of the solution is adjusted to a pH of 7.0 for measurements, e.g., aging at 35°C. The present disclosure further generally relates to a stable PAE resin for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or are synthesized with a weight ratio of formic acid : sulfuric acid of 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.6 or more, wherein the stable PAE resin may comprise a fresh resin viscosity of about 150 to about 200 cPs and may comprise a viscosity of about 140 to about 250 cPs after a prolonged period of aging at 35°C, wherein the viscosity is measured at room temperature, e.g., about 22-23 °C.

[0056] The present disclosure further generally encompasses a stable PAE resin for use as a wet strengthening agent comprising a polyamidoamine backbone comprising an acid value of about 35 to about 40 and/or a weight average molecular weight of about 3,000 to about 12,000 Da (as measured by SEC under the conditions described by Example 1 of the present disclosure) and/or a solids percentage of from about 23% to about 27%, wherein the stable PAE resin is synthesized using a weight ratio of formic acid : sulfuric acid of 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.6 or more and/or comprises a final resin pH value of 3.0 or more, 3.1 or more, 3.2 or more, 3.3 or more, or 3.4 or more. EXAMPLES

[0057] Example 1: PAE Resin Manufacturing Process

[0058] In this example, a stable PAE resin and a conventional wet strength PAE resin (conventional PAE resin A) were manufactured according to the methods described below. The composition of each the stable PAE resin and the conventional PAE resin are presented in Table 1 and Table 2, respectively.

TABLE 1 - STABLE PAE RESIN COMPOSITION

TABLE 2 - CONVENTIONAL PAE RESIN A COMPOSITION

[0059] The weight average molecular weight of the polyamidoamine backbone of the stable PAE resin was determined by performing size-exclusion chromatography (SEC) using Malvern Panalytical OMNISEC system. Eluent was a buffer solution containing 0.3125 M CH3COOH + 0.3125 M CIlaCOONa, and a flow rate of 0.5 mL/min at 35°C was used. The column set consisted of three columns (a TSKgel PWXL guard column and two TSKgel GMPWXL columns). A refractive index detector was used for detection. The molecular weights and PDIs were determined using conventional (column) calibration with

polyethylene oxide)/poly(ethylene glycol) narrow molecular weight distribution standards (Polymer Standards Service). The injection volume was 50 pL with a sample concentration of between 0.1 - 4 mg/mL depending on the sample. Ethylene glycol (lmg/mL) was used as a flow marker. Results were calculated using the OMNISEC software from Malvern. The weight average molecular weight of the polyamidoamine backbone was determined to be approximately 4,200 Da ( see Table 3).

[0060] The acid value of the polyamidoamine backbone of the stable PAE resin was determined as follows. An automatic titrator (Dosimat 716; MetroOhm AG) and a Solvotrode combined pH electrode (MetroOhm AG) were used for the titration to determine the equivalence point. A fresh 0.1N solution of Tetrabutylammonium Hydroxide (TBAOH) (ACROS Organics from ThermoFisher Scientific) in toluene/methanol was used for the nonaqueous titration. A sample of the polyamidoamine backbone was prepared by combining 0.75 g polyamidoamine backbone (diluted to 30.2% dry content from 60% dry content), 0.50 ml, methanol, 0.50 mL isopropanol, and two drops of phenolphthalein solution. Following sample preparation, the titrator was initiated, and the Solvotrode electrode and the Dosimeter were introduced to the beaker containing the sample. The titration using TBAOH was performed, and the equivalence point determined based on the results of the titration. The acid value of the polyamidoamine backbone was then calculated as follows: AV = (MKOH x CTBAOH x V_Eq x 100)/(m x ES); where AV is the acid value of the sample in mg KOH / g dry product (polyamidoamine backbone); MKOH is the molecular weight of KOH; CTBAOH is the concentration of TBAOH; V_Eq is the volume in mL of TBAOH used until the equivalence point is reached; m is the amount of polyamidoamine backbone in grams; and ES is the dry content of the polyamidoamine backbone. The acid value was determined to be 37.9 for the polyamidoamine backbone of the stable PAE resin of Table 1 (see Table 3).

TABLE 3 - POLYAMIDOAMINE BACKBONE WEIGHT AVERAGE MOLECULAR

WEIGHT AND ACID VALUE

[0061] The stable PAE resin composition presented in Table 1 was prepared as follows for a 1,000 gram batch with a target of 25% solids. 243.33 grams of polyamidoamine backbone comprising an acid value of 37.9 and a weight average molecular weight of 4,200 Da was reacted with 89.22 grams of epichlorohydrin in water, which resulted in a solids percentage of 45% after the first stage reaction. Next, the reaction mixture was held for 3 hours at a temperature ranging from 30-35°C. Following the 3 hour hold, the temperature was increased to 45°C and held for 1 hour, after which water was added, and then the temperature was increased to 65°C. The temperature was held at 65°C for approximately 3 hours, at which point water was added for further dilution and cooking proceeded at 65°C for an additional approximately 2 hours until the kill point was achieved. Once the kill point was achieved (110 cPs at 65°C for the Stable PAE resin of Table 1), the reaction was killed by addition of sulfuric acid and formic acid. This process resulted in a final stable PAE resin having a viscosity of about between 150-200 cPs, where the viscosity was measured at room temperature (about 22-23°C). The final resin pH was from about 3.2-3.3, the final solids content 25%, and the ratio of epichlorohydrin: secondary amine groups was about 140 mole%.

[0062] Conventional PAE resin A of the composition presented in Table 2 was prepared as follows for a 1 ,000 gram batch with a target of 30% solids. 310.26 grams of polyamidoamine backbone were reacted with 100.90 grams of epichlorohydrin in water, which resulted in a solids percentage of 31% after the first stage of the reaction. Next, the reaction mixture was held for 1 hour at 30-35°C, after which the temperature was raised to 55°C within 10 min. Following the temperature increase, the mixture was cooked for about 6 hours to the kill point viscosity of 125 cPs at 55°C. This process resulted in a final PAE resin having a viscosity of about 140-160 cPs, where the viscosity was measured at room temperature (about 22-23 °C). The final resin pH was about 2.9-3.0, the final solids content 30%, and the ratio of epichlorohydrin: secondary amine groups was about 125 mole%.

[0063] Example 2: PAE Resin Comparison - Charge Stability

[0064] The charge decay of stable PAE resin and conventional PAE resin A were compared at various different final resin pH values. Samples of each of the resins were aged at 35°C for 2 weeks prior to charge decay analysis. Batches of stable PAE resin were prepared with final pH values of either 3.0, 3.2, 3.3, or 3.4. Conventional PAE resin A had a final resin pH value of about 2.9, following the 2 week aging at 35°C. The charge decay values were calculated as follows: (initial charge density - current charge density value) / (initial charge density *100%). The charge density values for use in calculating the charge decay values were measured as follows. A Mutek PCD 05 was used to determine the cationic charge density value of the stable PAE and conventional PAE resin A. The PAE sample (either stable PAE resin or conventional PAE resin A) was diluted to the concentration of 0.025%. The pH value of the 0.025% solution was then adjusted to pH 7.0±0.2 by using 0.1 N NaOH. The pH value of a 0.001 N standard PYSK solution was also adjusted to pH 7.0±0.2. 10.00 gram the solution containing either the stable PAE resin or the conventional PAE resin A was transferred to the measuring cell of PCD 05 and then titrated by the standard PVSK solution. At the end of titration, record the volume of PVSK titer in mL. The PAE charge density can be calculated by the eqn.

[0065] Three (3) replicates of titration were conducted and the average value and the standard deviation were obtained. From the average value of charge density the charge decay values were calculated.

[0066] As shown in Figure 1, the stable PAE resin demonstrated low charge decay after aging for 2 weeks at 35 °C. In particular, stable PAE resin had a charge decay of less than 24% at a final resin pH value of 3.2; a charge decay of less than about 21.00% at a final resin pH value of about 3.3, and a charge decay of less than about 17.00% at a final resin pH value of about 3.4 (see Figure 1). Moreover, the stable PAE resin exhibited a lower charge decay at final resin pH values of 3.2, 3.3, and 3.4 as compared to conventional PAE resin A (see

Figure 1).

[0067] Example 3: PAE Resin Comparison - Viscosity

[0068] In the present example, the viscosity was compared for stable PAE resin of Example 1 and conventional PAE resin (conventional PAE resin A) of Example 1.

[0069] Samples of each of stable PAE resin and conventional PAE resin A were prepared. Samples of each were aged for up to 30 days at 35°C, and the viscosity of each of the samples was measured at the end of the aging process. Viscosity was measured using a Brookfiled Viscometer, DV2T, with a #62 spindle and a spindle rotation speed of 60 RPM. The viscosity of each of the samples was measured at room temperature (about 22-23 °C) [0070] As shown in Figure 2, stable PAE resin demonstrated a high viscosity after 29 days of aging. In particular, stable PAE resin had a fresh resin viscosity value of about 190 CPS, and a viscosity value of about 190 cPs after about 29 days of aging, and demonstrated a viscosity range of from about 140 cPs to about 190 cPs over the course of the 29 days of aging {see Figure 2).

[0071] Example 4: PAE Resin Comparison - Handsheet Strength

[0072] In the present example, handsheets which comprised either stable PAE resin or conventional PAE resin A at the dosage of 5 # dry resin/ton of Example 1 were compared for their wet tensile strength. The handsheets comprised standard lab pulp with a 50/50 SW/HW bleached virgin fiber. The thick stock was diluted with synthetic water treated with 150 ppm of sulfate and 35 ppm of calcium ion. The pH was then adjusted to about 7.5. Handsheets (80 g/m²) were prepared using a Dynamic Sheet Former. Sheets were pressed with a pneumatic roll press set at 15 psi and drum-dried for 60 seconds at 240°F. The sheets were post cured in a forced air oven at 105°C for 5 minutes. Prior to the paper testing, the paper samples were conditioned overnight in a Tappi standard lab with constant temperature at 23°C and humidity at 50% R.H.

[0073] The paper sheet was cut to 1 inch wide strip for initial wet tensile (IWT)

measurements. This method was based on TAPPI TEST Method T456 (this test method is generally used to determine the wet tensile strength of paper and paperboard immediately after deionized water is brushed onto both sides of a paper sample). Eight measurements were taken per condition, and the average value and standard deviation were obtained and reported in Figure 3. A Thwing- Albert QC3A tensile tester was used for measuring the IWT values of the handsheet samples comprising stable PAE resin and the handsheet samples comprising conventional PAE resin A.

[0074] Referring now to Figure 3, samples were prepared with either fresh resin or resin aged at 35°C for 34 days, and then the handsheet samples were compared to one another. Handsheets comprising conventional PAE resin A lost about 24% wet tensile strength as measured by initial wet tensile strength values (IWT) when comparing handsheets prepared with fresh conventional PAE resin to handsheets prepared with aged conventional PAE resin. By contrast, handsheets comprising stable PAE resin lost only about 4.4% IWT when comparing handsheets prepared with fresh stable PAE resin to handsheets prepared with aged stable PAE resin.

[0075] Example 5: Epichlorohydrin Byproducts Analysis

[0076] In the present example, analysis of the total content of epichlorohydrin byproducts was performed on various different samples of stable PAE resin, wherein each of the samples were stabilized by various different acid blends in accordance with the table presented in Figure 4 ( see Figure 4). The stable PAE resin samples where prepared as generally described in Example 1, only that different weight ratios of formic acid to sulfuric acid were used during synthesis of each of the 7 samples: 0.75, 1.0, 1.1, 1.4, and 1.6 ( see Figure 4). The final pH of the stable PAE resin samples was either 3.2, 3.3, or 3.4 ( see Figure 4).

Epichlorohydrin included unreacted epichlorohydrin, glycidol, and chlorinated hydrolysis byproducts of epichlorohydrin: 1,3-DCP, 2,3-DCP, and 3-CPD.

[0077] Analysis of the amount of epichlorohydrin byproducts, including unreacted epichlorohydrin, glycidol, and chlorinated hydrolysis byproducts of epichlorohydrin: 1,3- DCP, 2,3-DCP, and 3-CPD, was performed by gas chromatography (GC). The

epichlorohydrin, glycidol, 1,3-DCP, 2,3-DCP, and 3-CPD were extracted from an aqueous resin sample using a chloroform: 2-propanol (1 :1, v/v) solvent mixture, and quantified using 1,3-dichloroacetone as an internal standard. A flame ionization detector was used with a capillary configuration and splitless injection. The carrier gas was hydrogen. The FID used hydrogen at 45 mL/min and air at 450 mL/min at 250°C. The oven program was follows: equilibration time - 2.0 min, initial value - 65°C, initial time - 4.00 min, rate 1 - 20.00°C/min; step 2, initial value - 125°C, hold time - 2.50 min., rate 2 - 20.00°C/min; step 3, initial value 150°C, hold time - 2.00 min, rate 3 - 20.00°C/min; step 4, initial value - 175°C, hold time - 2.00 min; total run time 16.00 min.

[0078] Samples were prepared as follows. 10 grams of sample was measured into a scintillation vial using a plastic syringe. A 5 mL aliquot of internal standard (1,3

dichloroacetone) was then added, and the vial was placed on a stir plate and extracted for 1 hour. After the extraction was complete, the sample was allowed to rest for 10 minutes, and then 2 mL of the extract was drawn into a pipette. The extract was then injected into the GC for analysis. The expected retention times of each of the components to be analyzed was as follows: epichlorohydrin - 3.7 minutes; glycidol - 7.2 minutes; 1,3-dichloroacetone (internal standard) - 9.4 minutes; 1,3-DCP - 11.0 minutes; 2,3-DCP - 12.1 minutes; 3-CPD - 15.4 minutes.

[0079] The total content of epichlorohydrin byproducts in the samples of stable PAE resins was measured in ppm. The unit ppm was used as a dimensionless measure of the low levels (concentrations) of epichlorohydrin byproducts in the total weight of stable PAE resin.

[0080] Figure 4 shows the total content of epichlorohydrin byproducts, which included unreacted epichlorohydrin, glycidol, and chlorinated hydrolysis byproducts of

epichlorohydrin: 1,3-DCP, 2,3-DCP, and 3-CPD, that were comprised by stable PAE resin samples following synthesis. The results in Figure 4 demonstrate that generally lower total content of epichlorohydrin byproducts were obtained at the higher weight ratios of formic acid: sulfuric acid which were used during the synthesis of each of the stable PAE resin batches; for example, weight ratios of 1.1, 1.4, and 1.6 comprised less total epichlorohydrin byproducts as compared to weight ratios of 1.0 or 0.75.

[0081] In the preceding disclosure which includes the examples, different procedures and various steps have been described. It will, however, be evident that various modifications and changes may be made thereto, and additional procedures may be implemented, without departing from the broader scope of the procedures as set forth in the claims that follow.

Claims

1. A stable polyamidoamine-epichlorohydrin (“PAE”) resin composition suitable for use as a wet strengthening agent, comprising: a PAE resin which comprises a

polyamidoamine backbone having an acid value of between about 35 to about 40 and a weight average molecular weight of no more than about 12,000 Da, preferably of about 3,000 Da to about 12,000 Da, as measured by size exclusion chromatography (SEC); and an acid.

2. The stable PAE resin composition of claim 1, comprising a solids percentage of the PAE resin from about 23% to about 27%, preferably from about 24% to about 26%.

3. The stable PAE resin composition of claim 1 or 2, wherein the composition has a pH value ranging from about 3.0 to about 3.5, preferably from about 3.1 to about 3.4.

4. The stable PAE resin composition according to any of claims 1 to 3, wherein the acid comprises a weak acid, preferably comprising one or more of formic acid, acetic acid, lactic acid, benzoic acid, propionic acid, citric acid, malonic acid, adipic acid, malic acid, and tartaric acid, more preferably comprising formic acid; and a strong acid, preferably comprising one or more of sulfuric acid, phosphoric acid, nitric acid, perchloric acid, hydroiodic acid, hydrochloric acid, and hydrobromic acid, more preferably comprising sulfuric acid.

5. The stable PAE resin composition according to claim 4, wherein the weight ratio of the weak acid to the strong acid is about 1.1 or more, preferably about 1.2 or more, more preferably about 1.3 or more.

6. The stable PAE resin composition according to any of claims 1 to 5, wherein the PAE resin is produced by reacting epichlorohydrin and polyamidoamine at a molar ratio of epichlorohydrin : secondary amine groups of the polyamidoamine backbone of about 1.3 to about 1.7.

7. The stable PAE resin composition according to any of claims 1 to 6, wherein the

composition has a fresh resin viscosity value of between about 150 cPs to about 200 cPs, as measured at room temperature; and optionally a viscosity value of between about 140 cPs to about 250 cPs, as measured at room temperature, after a prolonged period of aging at 35°C, preferably after aging at 35°C for two weeks, more preferably after aging at 35°C for 4 weeks.

8. The stable PAE resin composition according to any of claims 1 to 7, wherein the PAE resin exhibits a charge decay of less than about 30.0%, preferably less than about 25.0%, more preferably less than about 20.0%, as measured from PAE resin composition having pH adjusted to 7.0, after a prolonged period of aging at 35°C, preferably after aging at 35°C for two weeks, more preferably after aging at 35°C for 4 weeks.

9. The stable PAE resin composition according to any of claims 1 to 8, wherein the composition comprises about 10,500 ppm or less, preferably about 10,200 ppm or less, more preferably about 10,000 ppm or less, of epichlorohydrin byproducts.

10. A method of synthesizing one or more stable PAE resin compositions according to any of claims 1 to 9, wherein said method comprises reacting in an aqueous solution one or more polyamidoamine backbones having an acid value of between about 35 to about 40 and a weight average molecular weight of no more than about 12,000 Da, preferably about 3,000 Da to about 12,000 Da, as measured by size exclusion chromatography (SEC), with epichlorohydrin, and stopping the reaction by adding an acid.

11. The method according to claim 10, wherein the stable PAE resin composition

comprises a solids percentage of the PAE resin from about 23% to about 27%, preferably from about 24% to about 26%.

12. The method according to claim 10 or 11, wherein the stable PAE resin composition has a pH value ranging from about 3.0 to about 3.5, preferably from about 3.1 to about 3.4.

13. The method according to any of claims 10 to 12, wherein adding the acid comprises adding one or more additions of a weak acid, preferably comprising formic acid, and one or more additions of a strong acid, preferably comprising sulfuric acid, preferably in a weight ratio of the weak acid to the strong acid of about 1.1 or more, preferably about 1.2 or more, more preferably about 1.3 or more.

14. The method according to claim 13, wherein one or more additions of the weak acid and the strong acid are added pre-mixed or sequentially, preferably first adding at least one addition of the weak acid followed by at least one addition of the strong acid.

15. The method according to any of claims 10 to 14, comprising one or more of the

following steps: a. reacting the polyamidoamine backbone and the epichlorohydrin in the aqueous solution at a molar ratio of epichlorohydrin : secondary amine groups of the polyamidoamine backbone of about 1.3 to about 1.7, preferably providing a solids percentage of about 40-50%; b. at the beginning of the synthesis reaction holding the aqueous solution at about 30-35°C for more than 1 hour, preferably for about 3 hours or more, more preferably for about 3 hours to about 20 hours; c. holding the temperature for about 1 hour to about 3 hours at about 45°C; d. adding water to dilute the solution and increasing the temperature to about 65°C; e. cooking the solution for about 3 hours at about 65°C; f. adding water to dilute the cooked solution of step e.; g. cooking the solution until reaching a viscosity of at least about 110 cPs at about 65°C; h. adding the acid in order to stop the reaction.

16. A method of manufacturing one or more paper products, said method comprising: a. providing a composition comprising cellulose fibers; b. adding one or more stable PAE resin compositions according to any of claims 1-9, optionally as diluted; and c. forming the desired paper product.

17. The method according to claim 16, wherein said one or more stable PAE resin

composition is added at any point on a paper machine wet end at an amount ranging from about 0.1-2.0% of dry weight of the stable PAE resin by dry weight of the paper product.

18. Use of a stable PAE resin composition according to any of claims 1 to 9 for wet strengthening paper, comprising contacting pulp fibers with the optionally diluted PAE resin composition, and at least partially curing the resin.

19. A paper product having improved wet strength, wherein the paper product has been produced or treated with at least one stable PAE resin composition according to any one of claims 1-9, preferably the paper product comprising one or more of the following fiber-based products: handsheets, board-based products, beverage carriers, toweling, milk and juice cartons, food trays, paper bags, liner board for corrugated containers, packaging board grade, tissue and towel grade, paper materials, paper towels, diapers, sanitary napkins, training pants, pantiliners, pee pads, dryer papers or pads, floor cleaning pads, coffee filters, air filters, litter box liners, incontinence briefs, tampons, absorbent facial tissue, absorbent bathroom tissue, napkins, wrapping paper, other paperboard products such as cartons and bag paper; an adsorbent paper- based product; single or multi-ply towel facial tissue, napkins, or bathroom tissue.