TW202413770A - Additive compositions and methods for papermaking with high-kappa furnishes - Google Patents

Abstract

A strength additive composition for papermaking processes using high-kappa furnish is disclosed. The composition comprises an aqueous media and a glyoxalated polyacrylamide (gPAM) resin having a weight average molecular weight (Mw) of at least about 5 MDa, a radius of gyration (Rg) of at least about 150nm, and a structural density (Rg/Mw) of less than about 15 nm/Mda. A method of preparing the composition is also disclosed, and may be carried out in situ during a papermaking process (i.e., as an on-site method). A process of forming paper with the composition is also disclosed, and comprises combining the composition with an aqueous suspension of cellulosic fibers, forming the cellulosic fibers into a sheet, and drying the sheet to produce a paper.

Description

Additive composition and method for making paper with high kappa furnish

The present invention relates generally to additive compounds and compositions for papermaking, and more particularly to low charge high molecular weight glyoxalated polyacrylamide (gPAM) resins optimized for high-κ furnishes, and methods of making and using the same.

Papermaking is a complex process in which paper is made from pulp (e.g. wood), water, fillers and various chemicals. Papermaking is one of the most water-intensive industries as the processes include many stages that rely on the addition of large amounts of water and aqueous solutions to cellulose fibers (i.e., the "influent stream") to obtain a furnish and ultimately separation from the furnish (i.e., the "effluent stream") to obtain the final product. During a typical papermaking process, a relatively concentrated aqueous slurry of cellulose material (i.e., the "thick stock") is diluted by the addition of water to obtain a relatively diluted slurry of cellulose material (i.e., the "weak stock"), which is used to prepare a paper web that must be dewatered to obtain the final product. The type of cellulose material varies depending on the pulp and pulping process used to prepare the furnish. For example, mechanical, chemical and/or semi-chemical pulping processes may be used to decompose and/or separate cellulose materials into individual components, including cellulose fibers, which may be further subjected to various chemical and/or mechanical processes (e.g., bleaching, screening, etc.) to prepare a given pulp.

The starting materials fed into the pulping process may also vary, and depending on the pulping process, will affect the composition and effectiveness of the prepared furnish. For example, both virgin and recycled pulp are common in the paper industry. Recycled pulp is used in products such as tissue paper because it has been pre-treated to have a higher cellulose content and lower impurities than virgin pulp produced under similar process conditions. However, the recycling process is relatively expensive compared to virgin pulp production, and the pulping and recycling processes make the fibers weaker and shorter, limiting the paper cycle time after each subsequent use. In contrast, virgin pulp is more sustainable and produces products with longer paper cycle times. However, virgin pulp requires a purification step to remove impurities, and its use may be limited due to the residual impurities (e.g., lignin, anionic waste, etc.) that remain with the fibers after the pulping process. In some cases, such as the unbleached kraft (UBK) process, the pulp includes a relatively high content of dissolved and colloidal anionic materials, resulting in a "refractory" furnish that cannot be treated using conventional methods to achieve retention, filtration, formation and/or strength goals.

Throughout the papermaking process, various chemical additives are used to improve specific properties of the process (i.e., "process additives") and/or the final product being produced (i.e., "functional additives"). Examples of process additives include defoamers and antifoaming agents, retention aids, biocides, water filtration aids, forming aids, etc. Examples of functional additives include strength additives, which are used, for example, to impart temporary wet strength (TWS), wet strength (WS) and/or dry strength (DS) to the final product.

In view of the number and complexity of the stages required in a given papermaking process, as well as the number and amounts of additives used in each stage, there is an increasing need for additives that can provide process and functional improvements to a given process. Unfortunately, however, achieving some of the improvements sought may result in a reduction in other performance factors. For example, achieving high retention can increase the strength of the final product, but it can reduce filterability and formation. The use of known high molecular weight filter aids can achieve excellent filterability and retention, but has little benefit to strength, and in some cases even leads to a reduction in strength due to excessive flocculation. Certain DS additives, such as polyamide epichlorohydrin (PAE), can provide excellent dry strength, but have little benefit to filterability and limited repulpability. Further complicating matters, the efficacy of any given solution is largely dependent on the formulation, with some of the best known dry strength and/or water removal aids failing under the required conditions, for example due to the fines content, lignin content and/or conductivity of the formulation system. For example, in the difficult formulations described above, known dry and wet strength agents typically require higher loadings, but exhibit reduced performance and often limit the repulpability of the resulting fiber. Thus, while there are solutions to address these formulation-induced performance reductions, there remains a need for additives that can provide excellent water removal and good dry strength even in the most challenging formulation systems (e.g., UBK, etc.).

One class of chemicals that is increasingly being developed for multi-purpose additive applications includes glyoxalated polyacrylamide (gPAM) resins, which have been used for many years in the paper industry as process aids, such as for improving water filtration during the papermaking process, and as functional additives, such as for imparting temporary wet strength (TWS), wet strength (WS), and dry strength (DS) to the final paper produced. Typical gPAM resins are prepared by glyoxalating polyacrylamide (PAM), i.e., by reacting glyoxal with PAM or PAM copolymers, such as copolymers prepared from acrylamide (AM) and various anionic or cationic monomers. As just one example, diallyldimethylammonium chloride (DADMAC) is a cationic monomer used to prepare poly(AM/DADMAC) copolymers, which can be used as a prepolymer in a glyoxalation reaction to obtain the corresponding gPAM resin (i.e., glyoxalated poly(AM/DADMAC)). Unfortunately, known gPAM resins have a number of disadvantages in production, storage, and use. For example, although many commercial gPAM resins are known to be excellent strength additives, such resins generally perform poorly in difficult-to-handle formulations, especially in terms of dewatering and filtration. These known gPAM resins also exhibit reduced performance in high-lignin environments and, therefore, limit their utility in difficult-to-handle formulations.

The present invention provides an additive composition for papermaking. The additive composition comprises an aqueous medium and a glyoxalated polyacrylamide (gPAM) resin, wherein the glyoxalated polyacrylamide resin has a weight average molecular weight (Mw) of at least about 5 MDa, a radius of gyration (Rg) of at least about 150 nm, and a structural density (Rg/Mw) of less than about 15 nm/Mda. The additive composition can be prepared in situ during the papermaking process (i.e., as an on-site gPAM resin).

The present invention also provides a method for preparing an additive composition ("preparation method"). The preparation method comprises preparing a cationic acrylamide (cAM) prepolymer having a cationic monomer content of less than about 3.5 mol%, and selectively glyoxalizing the cAM prepolymer in an aqueous medium to obtain a gPAM resin, thereby preparing the additive composition. The cAM prepolymer comprises a cationic monomer content of about 1 to about 3 mol%, and can exhibit a reduced solution viscosity (RSV) of about 0.5 to about 1.8 dL/g. Selectively glyoxalizing the cAM prepolymer comprises controlling the concentration of the cAM prepolymer in the aqueous medium during glyoxalization. The preparation method can be performed in situ during the papermaking process (i.e., as an on-site method).

The present invention also provides a process for forming paper with an additive composition ("process"). The process comprises: (1) providing an aqueous suspension of cellulose fibers; (2) combining the additive composition with the aqueous suspension or preparing the additive composition in the presence of the aqueous suspension; (3) forming the cellulose fibers into a sheet; and (4) drying the sheet to produce paper. The process can be performed using an aqueous suspension having a kappa value of at least about 30 and without using polyamide epichlorohydrin (PAE).

Cross-reference to related applications

This application claims priority to and all rights of U.S. Provisional Application No. 63/369,985 filed on August 1, 2022, the contents of which are incorporated herein by reference.

The following detailed description is merely illustrative in nature and is not intended to limit the compositions or methods of the present invention. Furthermore, it is not intended to be bound by any theory presented in the aforementioned prior art or in the following embodiments. For the sake of brevity, the known art related to the compositions, methods, processes and portions thereof described in the embodiments herein may not be described in detail. The various tasks and process steps described herein may be incorporated into a more comprehensive procedure or process having other steps or functionality that are not described in detail herein but are well known and readily understood by those skilled in the art. Therefore, for the sake of brevity, such known steps may be only briefly mentioned, or may be omitted entirely without providing the well-known process details.

The present invention provides additive compositions comprising high performance strength agents, and methods of making and using the additive compositions. The strength agents improve wet and dry strength and are optimized for withstanding high lignin environments, thereby enabling economical production of products using difficult to process furnishes. Thus, the additive compositions can be used to increase the strength of damask board and other products made from virgin furnishes, allowing for weight reduction, reduced purification, use of higher kappa furnishes, and other cost saving measures, while improving overall fiber yield.

The additive composition includes a glyoxalated polyacrylamide (gPAM) resin as a dry strength agent. The gPAM resin has an extremely low charge and a high molecular weight, each of which can be selectively adjusted by the method provided herein. The gPAM resin exhibits excellent performance in difficult-to-handle ingredients and provides good wet and dry strength for the product. In addition, the gPAM resin is repulpable and can therefore provide the advantage of repulpable wet strength. Therefore, the additive composition can be used in the papermaking process to provide improvements and benefits. In specific applications using difficult-to-handle ingredients, the additive composition exhibits improved performance that is superior to conventional strength additives, enabling the production of improved products, such as packaging made from unbleached kraft (UNK) virgin ingredients.

As described and demonstrated in the Examples and Examples herein, it has been unexpectedly discovered that gPAM resins with additive compositions having high weight average molecular weight (Mw), low total charge, and high density can be prepared by the methods described below. Compared to the prior art, the methods of the embodiments of the present invention eliminate the interaction between the Mw and/or charge of the product gPAM resin and the Mw and/or charge of the prepolymer used to prepare the gPAM resin. Therefore, the additive composition can provide improved functionality and performance by allowing the gPAM resin to have a selectively prepared Mw and charge without the disadvantages or deficiencies of the prior art that rely on the properties of the prepolymer to exert performance.

The additive composition comprises a gPAM resin and an aqueous medium. The aqueous medium is not particularly limited and may comprise or may be any aqueous composition that is compatible with the gPAM resin and/or the components used to prepare it. In this manner, the aqueous medium may be a water-based solution or suspension, optionally including additional components such as process water from a papermaking operation, or simply including an aqueous carrier medium used to prepare the gPAM resin.

Typically, the additive composition includes a functional amount (i.e., solid content) of gPAM resin in an aqueous medium, that is, a solid content that maximizes the amount of gPAM resin while maintaining a suitable flow state for the composition. In this sense, the gPAM resin can be present in an amount greater than 0 wt.% to less than the gel point of the gPAM resin in the aqueous medium. In some embodiments, the gPAM resin is present in an amount of about 1.2% to about 6%, such as about 1.2% to about 5%, or about 1.3% to about 4%, or about 1.4% to about 3%, or about 1.95% to about 2.45%, based on the aqueous medium (i.e., in solid %). However, as will be understood from the following method, the amount of gPAM present in the composition can depend on the amount of prepolymer used in the method.

The Mw of the gPAM resin is typically at least about 5 megaDaltons (MDa). In certain embodiments, the Mw of the gPAM resin is at least about 6 MDa, or at least about 6.5, or at least about 7, or at least about 7.5 MDa. The range of Mw is not specifically limited to values above the lower limit of the ranges mentioned (i.e., about 5 MDa or higher, or about 5.5 MDa or higher, etc.). Thus, the Mw of the gPAM resin may be in the range of about 5 to about 90 MDa, such as about 5 to about 70, or about 5 to about 50, or about 10 to about 50, or about 15 to about 50 MDa. In specific embodiments, the Mw of the gPAM resin may be higher than those Mw listed in the aforementioned ranges. Such gPAM resins are available and provide the benefits of the additive compositions disclosed herein. One skilled in the art can select a particular Mw based on the embodiments shown and described herein, for example, based on the desired use or specific application of the intended additive composition. Mw determination of gPAM resins can be performed using asymmetric flow field flow separation with multi-angle light scattering (AF4-MALS).

The radius of gyration (Rg) of the gPAM resin is typically at least about 150 nm. In some embodiments, the Rg of the gPAM resin is at least about 160 nm, such as at least about 170, or at least about 180, or at least about 190, or at least about 200 nm, or at least about 210 nm. The range of Rg is not specifically limited to values above the lower limit of the ranges mentioned (i.e., about 150 nm or higher). Thus, the Rg of the gPAM resin may be in the range of about 150 nm to about 300 nm, such as about 175 nm to about 275 nm, or about 200 nm to about 250 nm. In specific embodiments, the Rg of the gPAM resin may be higher than those Rg listed in the aforementioned ranges.

The specific relationship between Mw and Rg of gPAM resins produces an extremely dense cross-linked structure. The structural density of gPAM resins can be expressed as a ratio of Rg/Mw (nm/Mda). Specifically, gPAM resins typically exhibit a structural density of less than about 20 nm/Mda. For example, in specific embodiments, the structural density of gPAM resins is less than about 15 nm/Mda, such as less than about 14, or less than about 13, or less than about 12, or less than about 11, or less than about 10 nm/Mda. The range of Rg/Mw is not specifically limited to values below the upper limit of these mentioned ranges. Thus, the gPAM resin may have a structural density of about 1 to about 20, such as 1 to about 15, or about 1 to about 14, or about 1 to about 13, or about 1 to about 12, or about 1 to about 11, or about 1 to about 10, or about 2 to about 9 nm/Mda.

It should be understood that the specific Mw or Rg of the gPAM resin can be selected to achieve the desired structural density (Rg/Mw) and ultimate performance of the additive composition provided herein. Therefore, Mw or Rg slightly above or below the above-listed endpoints can be used to prepare gPAM resins with structural densities within one of the listed ranges. However, in general, the Mw and Rg of the gPAM resin are higher than the conventional resins, and its structural density (Rg/Mw) is lower than such conventional resins, as described in the examples herein.

Based on the methods and components used in the preparation methods described herein, the specific properties and characteristics of gPAM resins, including those described above, will be understood.

Generally, the method of preparing the additive composition comprises preparing the gPAM resin in an aqueous medium or in another aqueous medium formulated into the final additive composition. Therefore, the preparation process of the gPAM resin described in detail herein may be used in addition to or instead of the conventional methods known in the art.

The preparation of gPAM resin includes glyoxalizing cationic acrylamide (cAM) prepolymer, that is, reacting glyoxal with cAM prepolymer.

A cAM prepolymer may be prepared or obtained. In some embodiments, a method comprises preparing a cAM prepolymer. For example, the preparation process may comprise reacting an acrylamide (AM) monomer, a cationic monomer, and optionally one or more additional ethylenically unsaturated monomers in the presence of a chain transfer agent. However, there are a variety of methods for preparing cAM prepolymers that are adaptations of methods known in the art and self-learned for preparing prepolymers suitable for glyoxalation to obtain GPAM resins. Examples include free radical polymerization in water, such as by using a redox initiation system (e.g., sodium metabisulfite and sodium persulfate). Other combinations of redox initiating systems for initiating polymerization of suitable comonomers may also be used, including other persulfates such as potassium persulfate or ammonium persulfate or other components such as potassium bromate. Such redox initiating systems may be used in combination with chain transfer agents such as sodium hypophosphite, sodium formate, isopropyl alcohol or chain transfer agents based on hydroxyl compounds.

The cAM prepolymer generally includes ionic repeating units, such as cationic repeating units derived from a cationic monomer. The cationic comonomer can be any cationic monomer capable of reacting with the AM monomer and/or other monomers/comonomers via free radical chain polymerization to form the cAM prepolymer.

Examples of cationic monomers include tertiary and quaternary diallylamine derivatives, or tertiary and quaternary amine derivatives of acrylic acid or (meth)acrylic acid or acrylamide or (meth)acrylamide, vinyl pyridine and quaternary vinyl pyridine, or para-styrene derivatives containing tertiary or quaternary amine derivatives. The cationic copolymer monomer may be selected from diallyldimethylammonium chloride (DADMAC), [2-(acrylamido)ethyl]trimethylammonium chloride, [2-(methacrylamido)ethyl]trimethylammonium chloride, [3-(acrylamido)propyl]trimethylammonium chloride, [3-(methacrylamido)propyl]trimethylammonium chloride, N-methyl-2-vinylpyrrolidone, N-methyl-4-vinylpyrrolidone, p-vinylphenyltrimethylammonium chloride, p-vinylbenzyltrimethylammonium chloride, [2-(acryloyloxy)ethyl]trimethylammonium chloride, [2-(methacryloyloxy)ethyl]trimethylammonium chloride, [3-(acryloyloxy)propyl]trimethylammonium chloride, [3-(methacryloyloxy)propyl]trimethylammonium chloride, and combinations thereof. It should be understood that mixtures of cationic comonomers can be used for the same purpose. In some embodiments, the cationic monomer includes diallyldimethylammonium chloride (DADMAC).

The cationic acrylamide prepolymer may contain other monomer units provided by additional ethylenically unsaturated monomers in the polymerization. Such monomers are generally selected so as not to significantly interfere with the glyoxalation process. For example, the additional monomer units may be selected from acrylates, alkyl acrylates (e.g., methacrylate, methyl methacrylate, etc.), alkyl hydroxyacrylates, styrene, vinyl acetate, alkyl acrylamides (e.g., N-alkyl (meth) acrylamides, N,N-dialkyl (meth) acrylamides, etc.), and the like, and combinations thereof. Specific examples of such monomer units include methacrylate, octadecyl (meth)acrylate, ethyl acrylate, butyl acrylate, methyl (meth)acrylate, hydroxyethyl (meth)acrylate, 2-ethylhexyl acrylate, N-octyl (meth)acrylamide, N-tert-butylacrylamide, N-vinyl pyrrolidone, N,N'-dimethylacrylamide, styrene, vinyl acetate, 2-hydroxyethyl acrylate, acrylonitrile and the like, and combinations thereof.

In certain embodiments, anionic monomers or monomers that are later converted to anionic group-containing units are included in or as other monomers/comonomers to form cAM prepolymers. It should be understood that the term "cAM prepolymer" as used herein is not limited to cationic polymers, but simply indicates the presence of cationic monomers as described herein. Therefore, those skilled in the art will understand that, for example, when anionic monomers are used in the polymerization and/or anionic units are present in the structure of the cAM prepolymer, the cAM prepolymer itself can be amphoteric in nature. For example, in some such embodiments, one or more anionic monomers are selected from vinyl acidic compounds (e.g., acrylic acid, methacrylic acid, maleic acid, allyl sulfonic acid, vinyl sulfonic acid, itaconic acid, fumaric acid, 2-acrylamido-2-methylpropanesulfonic acid, etc.), vinyl compounds having potential anionic groups (e.g., maleic anhydride, itaconic anhydride), vinyl-containing salts (e.g., alkaline metal and/or ammonium salts of the above acidic compounds, sodium styrene sulfonate, etc.), and combinations thereof. Such anionic monomers can be collectively described as vinyl carboxylic acids and their esters or salts.

The cAM prepolymer can be prepared to have a linear or branched chain structure, and can be cross-linked or substantially non-cross-linked. It should be understood that in certain embodiments, the preparation method utilizes a chain transfer agent as described above. Therefore, it should be understood that the cAM prepolymer can also be chain-transferred, or cross-linked and chain-transferred (i.e., structured).

In some embodiments, the cAM prepolymer is crosslinked, and the preparation method includes the use of a crosslinking agent. Typical examples of crosslinking agents are polyolefinic unsaturated compounds, such as methylenebis(meth)acrylamide, triallyl ammonium chloride, tetraallyl ammonium chloride, polyethylene glycol diacrylate, polyethylene glycol dimethacrylate, N-vinyl acrylamide, divinylbenzene, tetra(ethylene glycol) diacrylate, dimethylallylaminoethyl acrylate ammonium chloride, diallyloxyacetic acid, diallyl octylamide, trimethylpropane ethoxylated triacrylate, N-allyl acrylamide, N-methylallyl acrylamide, pentaerythritol triacrylate and the like, as well as salts, derivatives and combinations thereof. Other systems and reagents for crosslinking may be used instead of or in addition to the above reagents. For example, covalent crosslinking through side groups can be achieved, for example, by using ethylenically unsaturated epoxy or silane monomers, using multifunctional crosslinking agents (such as silanes, epoxies, multivalent metal compounds, etc.), or by other known crosslinking systems. In certain embodiments, the cAM prepolymer is prepared using at least one of the anionic monomer units described above and is further crosslinked by covalently bonding bonding groups using the cationic groups of the anionic monomer units.

The polymerization is usually carried out in aqueous solution (e.g., in an aqueous medium) at a temperature of at least about 50° C. It is sometimes advantageous to increase the temperature after all comonomer addition is complete in order to reduce the residual monomer content of the product. The pH during the reaction can be adjusted with acids or bases or with buffers and can depend on the initiator system and the components used in the reaction.

The comonomers may be added all at once or over any length of time. If one monomer is less reactive than another, it may be advantageous to add some or all of the slower reacting monomer at the beginning of the polymerization, followed by a slow continuous or multiple batch addition of the more reactive monomer. Adjusting the feed rate may result in a more uniform composition of the polymer chain. Similarly, the initiator may be added all at once or over any length of time. In order to reduce the amount of residual monomer in the copolymer, it is often advantageous to continue adding the initiator system for a period of time after all the monomers have been added, or to introduce additional amounts of initiator in batches. Controlling the polymer composition and molecular weight uniformity by controlling the addition time is well known in the polymer industry.

In some embodiments, the prepared cAM prepolymer has at least one predetermined physical property, such as cationic monomer content, Mw and/or reduced solution viscosity (RSV). For example, the cAM prepolymer typically comprises an extremely low charge, typically having less than about 4 mol% of cationic monomer units derived from cationic monomers. For example, in general embodiments, the cAM prepolymer comprises less than about 3.5, or less than about 3, or less than about 2.5 mol% of cationic monomer units. In some embodiments, the cAM prepolymer comprises about 0.5 to about 3.5, or about 1 to about 3.5, or about 1 to about 3, or about 1.5 to about 3, or about 1.5 to about 2.5 mol% of cationic monomer units.

The cAM prepolymers typically have a medium/high Mw of about 80 to about 130 KDa. In some embodiments, the Mw of the cAM prepolymer is about 90 to about 130 KDa, or about 90 to about 120 KDa. The Mw of the cAM prepolymer can be determined by standard procedures and methods, such as by SEC/RI.

The RSV of the cAM prepolymer is typically about 0.5 dL/g to about 1.8 dL/g, such as about 0.6 dL/g to about 1.6 dL/g. The RSV of the cAM prepolymer can be determined by standard procedures and methods, such as using a PolyVisc.

In certain embodiments, the cAM prepolymer comprises about 0.5 to about 3.5 mol% of cationic monomer units derived from a cationic monomer, has a Mw of about 80 to about 130 KDa, and exhibits a RSV of about 0.5 to about 1.8 dL. In a specific embodiment, the cAM prepolymer comprises about 1 to about 3 mol% of cationic monomer units derived from a cationic monomer, has a Mw of about 90 to about 120 KDa, and exhibits a RSV of about 0.6 to about 1.6 dL/g.

The cAM prepolymer can be characterized by other properties in addition to those described above, such as by charge density and/or zeta potential. For example, in some embodiments, the zeta potential of the cAM prepolymer at pH 7 is typically about 10 to about 30 mV. In some embodiments, the zeta potential of the cAM prepolymer at pH 7 is about 15 to about 30 mV, such as about 15 to about 30, or about 20 to about 30, or about 20 to about 25 mV. The zeta potential of the cAM prepolymer can be determined by standard procedures and methods, such as by using a Wyatt Mobius. In these or other embodiments, the charge density of the cAM prepolymer at pH 7 is typically about 0.2 to about 3 mEq/g, such as about 1 to about 3 mEq/g.

The method further comprises glyoxalizing the cAM prepolymer, i.e. reacting the cAM prepolymer with glyoxal. As illustrated in the examples herein, the method can be used to selectively glyoxalize the cAM prepolymer by controlling the concentration of the cAM prepolymer in the aqueous medium during the glyoxalization. In this way, it has been found that the above-mentioned gPAM resins with high Mw, high Rg and high structural density can be prepared, regardless of the Mw of the cAM prepolymer.

As is understood in the art, the reaction of the cAM prepolymer with glyoxal can be carried out at different times, temperatures, pH, etc. Typically, glyoxal is added to the cAM prepolymer quickly to minimize crosslinking. Alternatively, the cAM prepolymer can be added to glyoxal. Also as is commonly understood in the art, the molecular weight of the cAM prepolymer and the ratio of glyoxal to acrylamide groups on the cAM prepolymer can be adjusted to achieve the desired degree of crosslinking and viscosity build during the glyoxalization process.

The cAM prepolymer (A) and glyoxal (B) are typically reacted in a dry weight (w/w) ratio of about 75:25 to about 95:5 (A):(B), such as about 80:20 to about 90:10. The residual glyoxal content of the final gPAM resin is typically less than about 10%, or less than about 8%, or less than about 5%, based on the dry weight of the gPAM resin.

The concentration of the cAM prepolymer is selectively controlled during the glyoxalation to obtain a high Mw gPAM resin. For example, in typical embodiments, the cAM prepolymer is present in the aqueous medium at an initial concentration of less than about 4%, or less than about 3%, or less than about 2% (w/w). In certain embodiments, the prepolymer is present in the aqueous medium at an initial concentration of about 0.5% to about 4%, or about 0.5% to about 3%, or about 0.5% to about 2.5%, or about 0.5% to about 2%, or about 1% to about 2%. This concentration is typically defined in terms of solids, that is, the weight percent concentration of the starting cAM prepolymer at the beginning of the glyoxalation reaction (i.e., when all of the glyoxal has been added). In this way, the solids content of the cAM prepolymer and the solids content of the gPAM resin can be described with reference to each other. Likewise, selective glyoxalation can be understood to include selecting the desired cAM prepolymer concentration based on the desired gPAM resin solids content in the addition composition.

In some embodiments, the concentration of glyoxal and the concentration of the cAM prepolymer during the glyoxalation are selectively controlled simultaneously. For example, in a particular embodiment, the concentration of glyoxal in the aqueous medium is about 0.1% to about 1% (w/w). In some embodiments, the concentration of glyoxal is about 0.1% to about 0.5%, or about 0.2% to about 0.3%.

gPAM resin can be adjusted to about pH 3 after the glyoxalation reaction to improve its storage stability before use, or it can be used directly without further adjustment.

The additive composition can be used in papermaking, for example, for making paper or board products. In particular, the additive composition can be used to treat pulp or fibers in the form of furnish, web, sheet, etc. with a gPAM resin. The additive composition used in papermaking can provide beneficial properties such as improved dry strength, temporary wet strength, permanent wet strength, wet strength degradation, etc., compared to the same properties when using conventional gPAM resins (i.e., having a relatively low Mw).

There are a number of steps in the papermaking process, generally including: forming an aqueous suspension of cellulose fibers; adding an additive (e.g., an additive composition) to the suspension; forming a sheet from the fibers; and drying the sheet to obtain paper. Additional steps may also be employed (e.g., for towel and facial tissue grades, steps of crimping or forming the paper structure are often employed to obtain properties such as softness). Furthermore, the addition of additives (e.g., additive compositions) may be performed after the sheet is formed. Such steps and variations of the process are known to those skilled in the art. The additive composition, which is a strength aid, may be added during any one or more appropriate steps in the papermaking process, such as after pulping and before drying.

In summary, the present invention also provides a process for preparing paper or paperboard. The process generally comprises: (1) providing an aqueous suspension of cellulose fibers; (2) treating the cellulose fibers with an additive composition; (3) forming the cellulose fibers into a sheet; and (4) drying the sheet to produce paper.

In some embodiments, the method utilizes difficult furnishes, i.e., furnishes with a relatively high lignin content and possibly other dissolved and/or suspended colloidal anionic materials. For example, the additive composition is particularly useful for high-κ furnishes, i.e., furnishes with a kappa value of at least 25, or at least 30 for pulp. In certain embodiments, the process comprises treating cellulose fibers of a pulp with a kappa value of at least 30, or at least 32, or at least 35, or at least 40.

The term "κ" as used herein in the context of a process should be understood in accordance with the known meaning of the industry standard κ value. It should therefore be understood that the κ value is a key test method used to determine the content/level of residual lignin in a sample of finished pulp or in-process pulp. In this way, the κ value can be used to measure the integrity of a given pulping process and can be used to characterize and/or differentiate types of pulps based on relative lignin content. There is no specific restriction on the type of pulp when determining the κ value, with recognized standards applicable to determining the κ value of various pulps (including chemical, semi-chemical, unbleached, semi-bleached and bleached varieties).

The kappa value of a given furnish may be determined by using a strong oxidizing agent (e.g., potassium permanganate) which reacts with lignin and certain other organic impurities remaining in the pulp at various stages of the process in small quantities. The kappa value of a particular sample may be determined manually (e.g., by laboratory reaction and analysis) or by using an automated instrument suitable for measuring kappa values. It will be appreciated that a given procedure and/or instrument may need to be validated against the specific circumstances of a given standard in order to determine whether the results are consistent with the standard itself. Examples of kappa values include test method TAPPI/ANSI T 236 om-13 (November 2013), provided by the Technical Association of the Pulp & Paper Industry Inc (TAPPI) and approved by the American National Standards Institute (ANSI). As written, the TAPPI/ANSI T 236 om-13 standard is intended for laboratory testing of pulp. However, it should be recognized that kappa values are widely used in pulp and paper mills as in-process tests and are modified in some cases.

Typically, Kappa values are reported as values between 1 and 100. However, values above 100 may be determined, but it should be understood that the precision of a given test may be reduced when Kappa values exceed 100. Section 16 of the TAPPI/ANSI T 236 om-13 standard provides information about how certain departures from the standard may have unintended or unexpected effects on data accuracy, precision, or both.

In some cases, the Kappa value can be used to quantify or at least approximately quantify the lignin content of a particular pulp sample. For example, for pulps with a total yield of less than 70%, the Kappa value has an approximately linear relationship with Klason lignin and the chlorine value, so the Kappa value determined according to the TAPPI/ANSI T 236 om-13 standard can be used to estimate the percentage of Klason lignin in the sample according to the equation Lignin content (%) = Kappa value × 0.13. However, it should be understood that there is no universal and clear relationship between the Kappa value and the exact content of lignin or other organic impurities in the pulp. In fact, any such relationship may vary due to the wood species, pulping process, and delignification process used to obtain the specific pulp prepared. Therefore, when the Kappa value is used to determine an exact numerical value for the amount of lignin present in a particular furnish (such as the furnishes suitable for use in embodiments of the present invention), a more accurate relationship can be established by testing the pulp therein according to methods and procedures widely known in the art.

The aqueous suspension of cellulose fibers may contain virgin and/or recycled fibers. In some embodiments, the aqueous suspension contains at least 30% virgin fibers, such as at least 70%, or at least 90%, or at least 95%, or at least 99% virgin fibers (w/w) based on the total weight of the cellulose fibers in the suspension. In some such embodiments, the aqueous suspension is unbleached kraft (UBK) virgin furnish.

In some embodiments, the aqueous suspension comprises regenerated fibers. The amount of regenerated fibers may vary and may be used to supplement virgin fibers or as a primary fiber source in the aqueous suspension. Therefore, based on the total weight of cellulose fibers in the suspension, the aqueous suspension may contain at least 1%, or at least 5%, or at least 10%, or at least 20%, or at least 30%, or at least 50%, or at least 75% regenerated fibers (w/w) in an amount comprising virgin fibers. In some embodiments, the aqueous suspension is composed of regenerated fibers (e.g., as 100% regenerated furnish and/or for 100% regenerated furnishing plants). It should be understood that regenerated fibers may be derived from miscellaneous waste paper, old corrugated cardboard (OCC), etc.

It should be understood that, as described above and illustrated in the examples herein, steps (2) and (3) may be performed in any order. However, typically, the additive composition will be used in the wet end of the papermaking process. For example, in some embodiments, treating the cellulosic fibers with the additive composition comprises adding the additive composition to a furnish or a processed form thereof (e.g., thick paper stock), such as in the flow system of a paper machine. Alternatively, treating the cellulosic fibers with the additive composition may comprise adding the additive composition.

The additive composition can be prepared and then combined with a preformed aqueous suspension of cellulose fibers. For example, a gPAM resin can be prepared and introduced into the suspension within a time period suitable for storage, such as within about 10, or about 8, or about 5 hours after glyoxalization. Alternatively, the additive composition can be prepared in the aqueous suspension, i.e., the gPAM resin is prepared in situ with the aqueous suspension. Such processes are referred to in the art as "in-situ" processes and are particularly suitable for embodiments of the present invention.

As described above, the papermaking process may further include the steps of drying, patterning, treating, and crimping the paper to form a finished paper product. The finished paper product may include, but is not limited to, paper, tissue, paperboard, and the like. For example, in some embodiments, the process includes treating an unbleached kraft (UBK) virgin furnish with an additive composition. In these or other embodiments, the sample is used to prepare virgin damask paperboard. Other products such as premium paper, corrugated paper, boxboard, etc. may be prepared similarly. Examples

The following examples (illustrative embodiments of the present invention) are intended to illustrate and not limit the present invention. Unless otherwise noted, all solvents, substrates, and reagents were purchased or otherwise obtained from various commercial suppliers (e.g., Sigma-Aldrich, VWR, Alfa Aesar) and used as received (i.e., without further purification) or in a form commonly used in the art.

General cationic acrylate cAM Synthesis of prepolymer

A reaction flask was charged with deionized water, diallyldimethylammonium chloride (DADMAC), a pH adjuster, and a chain transfer agent. The reaction flask was connected to two external feed ports, one containing acrylamide and the other containing sodium metabisulfite (SMBS) and a chain transfer agent. The reaction mixture was heated to 35°C, followed by the addition of ammonium persulfate (APS) and sodium bromate, and the feeds were then started. The acrylamide feed was set to be added over 135 minutes, and the SMBS feed was set to be added over 195 minutes. During the acrylamide feed, the reactants were gradually heated to 90°C at a rate of approximately 0.4°C/min via an external heating source. After the acrylamide feed was complete, a second portion of APS was added and the reaction was held at 90°C for one hour. The amount of DADMAC was varied as needed to produce a prepolymer with the desired amount of cationic monomer. The molecular weight of the prepolymer was manipulated as needed by increasing or decreasing the amount of chain transfer agent.

cAM Prepolymer 1 ( PP1 ) Synthesis

A four-neck round-bottom flask (hereinafter referred to as the reaction flask) equipped with an overhead stirrer, a nitrogen bubbler, and a temperature probe was charged with deionized water (112 g) and 65% DADMAC (4.510 g, 0.017 mol), adipic acid (0.277 g, 0.0019 mol), and 1.08% sodium hypophosphite (SHP) solution (4.43 g, 0.000462 mol), followed by nitrogen bubbling. A single-neck round-bottom flask was charged with 50% acrylamide (120.60 g, 0.847 mol), 40% Trilon-C solution (0.484 g, 0.00038 mol) was added thereto, and connected to a peristaltic pump (ACM feed). A trigger solution containing 3.5% SMBS solution (4.81 g, 0.00088 mol) and 1.5% SHP solution (4.43 g, 0.000462 mol) was loaded into a 10 mL syringe and placed in a syringe pump (feed 1). A 15% sodium bromate solution (0.5820 g, 0.00057 mol) and a 15% ammonium persulfate solution (0.3583 g, 0.000235 mol) were charged into the reaction flask, and the ACM feed (set to 0.89 mL/min) and feed 1 (set to 3.86 mL/h) were immediately started thereafter. The polymerization reaction was allowed to react adiabatically for 1 hour, followed by heating at 0.7°C/min for 75 minutes. After the ACM feed was complete (135 min), the nitrogen bubbler was removed from the reaction solution and 15% APS solution (2.22 g, 0.00146 mol) was added to start the burn. The temperature was maintained at 90 °C for one hour, during which time Feed 1 was completed. The reaction was then cooled to below 50 °C and transferred to a sample jar.

cAM Prepolymer 2 ( PP2 ) Synthesis

A four-neck round-bottom flask (hereinafter referred to as the reaction flask) equipped with an overhead stirrer, a nitrogen bubbler, and a temperature probe was charged with deionized water (87 g) and 65% DADMAC (10.02 g, 0.04 mol), adipic acid (0.277 g, 0.0019 mol), and 1.5% sodium hypophosphite (SHP) solution (5.13 g, 0.000726 mol), followed by nitrogen bubbling. A single-neck round-bottom flask was charged with 50% acrylamide (138.34 g, 0.938 mol), 40% Trilon-C solution (0.484 g, 0.00038 mol) was added thereto, and connected to a peristaltic pump (ACM feed). A trigger solution containing 3.5% SMBS solution (5.44 g, 0.0010 mol) and 1.5% SHP solution (5.13 g, 0.000726 mol) was loaded into a 10 mL syringe and placed in a syringe pump (Feed 1). A 15% sodium bromate solution (0.6590 g, 0.000655 mol) and a 15% ammonium persulfate solution (0.4057 g, 0.00027 mol) were charged to the reaction flask, and the ACM feed (set to 1.02 mL/min) and feed 1 (set to 4.37 mL/h) were immediately started. The polymerization reaction was allowed to react adiabatically for 1 hour, followed by heating at 0.7°C/min for 75 minutes. After the ACM feed was complete (135 min), the nitrogen bubbler was removed from the reaction solution and 15% APS solution (2.52 g, 0.0017 mol) was added to start the burn. The temperature was maintained at 90 °C for one hour, during which time Feed 1 was completed. The reaction was then cooled to below 50 °C and transferred to a sample jar.

General Glyoxalation Procedure

The prepolymer (PP) was charged to a reaction flask and diluted with deionized water to the desired polymer concentration, to which glyoxal was added at a 15:85 dry w:w ratio relative to the prepolymer. The turbidity of the solution was collected to indicate the starting turbidity. The pH was raised to 10.2 using dilute NaOH, and this pH was maintained and the turbidity was measured every 2 minutes. Once the turbidity increased to the desired amount, the reaction was quenched by lowering the pH to 4 with dilute sulfuric acid.

GPAM 1 Synthesis

GPAM 1 was prepared from PP1 according to the general glyoxalation procedure above. A 1.6% PP1 concentration and a 0.28% glyoxal concentration were used and the reaction was quenched after the turbidity increased by 15 NTU from the initial reading.

GPAM 2 Synthesis

GPAM 2 was prepared with PP2 according to the general glyoxalation procedure above. A 1.7% PP2 concentration and a 0.3% glyoxal concentration were used and the reaction was quenched after the turbidity increased by 10 NTU from the initial reading.

Determination of polymer properties

Prepolymer RSV was measured using PolyVisc in 1 M Ammonium Chloride at 0.25 dL/g. gPAM Mw was measured using AF4-MALS. The parameters and properties of PP1, PP2, GPAM 1 and GPAM 2 are described in Table 1 below.

Table 1 DADMAC (mol%) PP RSV (dL/g) gPAM Mw (MDa) gPAM Rg (nm) Rg/Mw (nm/Mda) Turbidity change (δNTU) GPAM 1 2 0.93 33 216 6.545 15 GPAM 2 4.1 0.95 2.04 120.2 58.922 12

As shown, GPAM 1 is a gPAM resin according to an embodiment of the present invention, and GPAM 2 is a comparative gPAM resin.

In other examples shown below, a commercially available gPAM resin was used and named "GPAM 3".

Hand sheet preparation method ( HS Trial 1 To test 5 )

Unbleached virgin kraft pulp was from a commercial mill and was purified as is in a recirculating pulper until the CSF was between 550 mL and 650 mL. A noble wood handsheet mold was used to produce the handsheets. The amount of pulp required to form ten 90 lb/1000 sqft sheets was added to a proportioner and diluted to 8 L using conditioned water (pH 5; 2000 us/cm). 8 lb/ton of GPAM was added, followed by 0.25 lb/ton of commercial cPAM retention aid, and finally 7.5 lb/ton of 50% alum, with approximately 30 seconds between each addition. Sheets were made by dewatering the required amount of treated pulp using a forming wire and a deckle box, then pressing the sheet (60 PSI), and finally drying the sheet on a drum dryer (about 118°C). A total of eight sheets were made for each condition. Each condition was repeated at least once, resulting in a total of 16 sheets for each condition. For HS Run 3, Indulin-C was added to the proportioner along with a commercial defoamer (0.25 lb/ton) before adding chemical additives. The sheets were then aged in a controlled atmosphere chamber (50% relative humidity; 23°C) for at least 48 hours before testing. The parameters for HS Runs 1 to 5 are further described in Tables 2 to 3 below.

Experimental paper machine

A furnish made of unbleached kraft fiber from a commercial mill was dispersed in water adjusted to pH 4.5 and the dispersed fiber was treated with additives at any or all points described as the thick stock pump inlet and outlet, the wet end flow system in the order of mixers 1 to 4, the thin stock fan pump inlet, outlet and dilution. GPAM was applied at an equivalent dosage of 8 lb/ton at mixer 3, and commercial sizing agent and alum were added at an equivalent dosage of 3 lb/ton and 4.5 lb/ton, respectively, at the fan pump outlet. The stock was applied to the paper machine through a straightening roll (hydraulic) high-level stock box to a Fourdrinier paper machine equipped with three vacuum-assisted baffles to remove water, thereby forming a wet sheet. The wet sheet then passed through two single felt presses to mechanically remove water and densify the sheet. Final dewatering (drying) was performed using eleven electrically heated drying cans before winding onto reel cores with a target basis weight of 125 lb/1000 sqft. The parameters of the experimental paper machine are further described in Tables 2-3 below.

Mechanical strength performance of paper

Ring compression was measured using TAPPI method T 822 om-16 with a Testing Machines Inc. Model 17-76-00-0001. STFI was measured using TAPPI method T 826 om-21 with a Buchel BV Short Stroke Compression Tester Model 17-34-00-0001. Burst resistance (Mullen Burst) was measured according to standard TAPPI method T 807 om-16 with a B. F. Perkins Model C Mullen Tester. Wet paper burst resistance was measured in a manner similar to T 807 om-16, but after soaking the paper for 2 hours. For the experimental paper machine, the machine direction processing performance of STFI and the cross direction processing performance of ring compression were tested and reported. All strength performance data are normalized to basis weight and reported relative to the performance of a blank sample treated with all additives except gPAM. Based on the above measurement results, the parameters and performance of HS Tests 1 to 5 and the experimental paper machine test are described in Tables 2 and 3 below.

Table 2 Examples κ Freeness(mL) Added soluble lignin (ppm) HS test 1 32 602 - HS Test 2 32 602 - HS Test 3 32 602 600 HS test 4 80 552 - HS Test 5 102 632 - Experimental paper machine 80 552 -

table 3 Ring Press - Improvement compared to blank Burst strength (dry paper) - Improvement compared to blank Burst strength (wet paper) - Improvement compared to blank Examples GPAM 1 GPAM 2 GPAM 3 GPAM 1 GPAM 3 GPAM 1 GPAM 3 HS test 1 122% 118% 108% - - - - HS Test 2 116% - 113% - - - - HS Test 3 107% 104% 102% - - - - HS test 4 108% - 103% - - - - HS Test 5 112% 110% 107% - - - - Experimental paper machine 124% - 116% 131% 126% 169% 158%

As shown in Tables 2 and 3 above, GPAM 1 exhibited increased performance in the ring crush test relative to the comparative gPAM compositions (i.e., GPAM 2 and GPAM 3) when used in formulations with a kappa value of 32 (HS Runs 1-3), even in the presence of soluble lignin. As shown in HS Runs 4-5, this increase in performance was true even in higher kappa formulations.

When used in a pilot paper machine test, GPAM 1 exhibited improved but comparable dry strength performance relative to the comparative gPAM composition (i.e., GPAM 3). However, GPAM 1 exhibited significant improvements in wet strength performance relative to the comparative gPAM composition. Previously, only combinations of wet strength agents (such as the known gPAM and PAE) could demonstrate such improvements in wet strength under similar conditions. The present embodiments achieve superior results without the deleterious effects of PAE use, such as reduced repulpability.

Although at least one exemplary embodiment has been presented in the foregoing detailed description, it should be understood that there are numerous variations. It should also be understood that one or more exemplary embodiments are merely examples and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing detailed description will provide a convenient roadmap for implementing the exemplary embodiments for those skilled in the art. It should be understood that various changes may be made to the functions and configurations of the elements described in the exemplary embodiments without departing from the scope set forth in the accompanying claims. In addition, all combinations of the foregoing components, compositions, method steps, formulation steps, etc. are hereby expressly contemplated for use in various non-limiting embodiments, even if such combinations are not expressly described in the same or similar paragraphs.

With respect to reliance herein on any Markush group to describe particular features or aspects of various embodiments, different, special and/or unexpected results may be obtained from each member of the respective Markush group independent of all other Markush members. Each member of the Markush group may be relied upon individually and/or in combination and provides sufficient support for specific embodiments that fall within the scope of the appended claims.

In addition, any ranges and sub-ranges relied upon in describing various embodiments of the present invention are independently and collectively within the scope of the accompanying patent applications and should be understood to describe and cover all ranges, including integer values and/or fractional values therein, even if such values are not explicitly written herein. Those skilled in the art will readily recognize that the ranges and sub-ranges listed herein fully describe and enable various embodiments of the present invention to be performed, and that such ranges and sub-ranges may be further described as relevant halves, thirds, quarters, fifths, etc. As just one example, the range of "0.1 to 0.9" can be further described as the lower third (i.e., 0.1 to 0.3), the middle third (i.e., 0.4 to 0.6), and the upper third (i.e., 0.7 to 0.9), which are individually and collectively within the scope of the appended claims and can individually and/or collectively serve as the basis for and provide sufficient support for specific embodiments within the scope of the appended claims. In addition, with respect to language defining or modifying a range, such as "at least," "greater than," "less than," "not more than," and similar language, it should be understood that such language includes sub-ranges and/or upper or lower limits. As another example, a range of "at least 10" inherently includes a sub-range of at least 10 to 35, a sub-range of at least 10 to 25, a sub-range of 25 to 35, etc., and each sub-range may individually and/or collectively serve as a basis and provide adequate support for specific embodiments within the scope of the accompanying claims. Individual numbers within the disclosed ranges may serve as a basis and provide adequate support for specific embodiments within the scope of the accompanying claims. For example, a range of "1 to 9" includes individual integers, such as 3, and individual numbers including decimal points (or fractions), such as 4.1, which may serve as a basis and provide adequate support for specific embodiments within the scope of the accompanying claims. Finally, it should be understood that the term "about" with respect to any specific number and range described herein is used to indicate values within standard error, equivalent function, efficacy, final load, etc., as understood by those skilled in the art for formulating and/or utilizing the compounds and compositions described herein. Thus, the term "about" can indicate a value within 10%, or within 5%, or within 1%, or within 0.5%, or within 0.1% of the recited value or range.

Although the invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications will be apparent to those skilled in the art. The appended claims and the invention should generally be construed to cover all such obvious forms and modifications within the true scope of the invention.

Claims (10)

An additive composition for papermaking, comprising: an aqueous medium; and a glyoxalated polyacrylamide (gPAM) resin having a weight average molecular weight (Mw) of at least about 5 MDa, a radius of gyration (Rg) of at least about 150 nm, and a structural density (Rg/Mw) of less than about 15 nm/Mda. The additive composition of claim 1, wherein the glyoxalated polyacrylamide resin comprises the reaction product of (A) a cationic acrylamide (cAM) prepolymer and (B) glyoxal in an aqueous medium, and wherein: (i) the cAM prepolymer (A) is present in the aqueous medium at an initial concentration of about 0.5 to about 4 wt.%; (ii) the cAM prepolymer (A) and the glyoxal (B) are reacted at a dry weight (w/w) ratio of about 75:25 to about 95:5 (A):(B); or (iii) both (i) and (ii). The additive composition of claim 2, wherein the weight average molecular weight (Mw) of the glyoxalated polyacrylamide (gPAM) resin is at least about 6 MDa, wherein the cAM prepolymer (A) is present in the aqueous medium at an initial concentration of about 1 to about 2.5 wt.%, and wherein the cAM prepolymer (A) and the glyoxal (B) are reacted at a dry weight (w/w) ratio of about 80:20 to about 90:10 (A):(B). The additive composition of claim 2, wherein the cAM prepolymer (A) comprises the reaction product of the following components: (A1) acrylamide (AM) monomer; (A2) cationic monomer; and optionally, (A3) one or more additional olefinically unsaturated monomers; wherein the cAM prepolymer (A) comprises about 0.5 to about 3.5 mol% or about 1 to about 3 mol% of cationic monomer units derived from the cationic monomer (A2). The additive composition of claim 4, wherein: (i) the AM monomer (A1) comprises acrylamide; (ii) the cationic monomer (A2) comprises diallyldimethylammonium chloride (DADMAC); (iii) the one or more additional olefinically unsaturated monomers (A3), when present, are selected from styrene, alkyl acrylates, vinyl acetate and vinyl carboxylic acids, esters or salts thereof; or (iv) any combination of (i) to (iii). The additive composition of any one of claims 2 to 5, wherein the cAM prepolymer (A) has a reduced solution viscosity (RSV) of about 0.5 dL/g to about 1.8 dL/g. A method for preparing an additive composition for papermaking, comprising: I) preparing a cationic acrylamide (cAM) prepolymer having a cationic monomer content of less than about 3.5 mol%; and II) selectively glyoxalizing the cAM prepolymer by controlling the concentration of the cAM prepolymer in an aqueous medium during glyoxalization to obtain a glyoxalated polyacrylamide (gPAM) resin having a weight average molecular weight (Mw) of at least about 5 MDa, a radius of gyration (Rg) of at least about 150 nm, and a structural density (Rg/Mw) of less than about 15 nm/Mda. A method for forming paper, the method comprising: (1)    providing an aqueous suspension of cellulose fibers; (2)    combining the additive composition of claim 1 with the aqueous suspension; (3)    forming the cellulose fibers into a sheet; and (4)    drying the sheet to produce paper. The method of claim 8, wherein the aqueous suspension of cellulose fibers: (i) has a κ value of at least about 30; (ii) comprises unbleached kraft (UBK) virgin fibers; (iii) comprises recycled fibers; (iv) is substantially free of polyamide epichlorohydrin (PAE); or (v) any combination of (i) to (iv). The method of any of claims 8 or 9, wherein the gPAM resin is prepared in situ within about 5 hours after combining the additive composition with the aqueous suspension.