Aqueous glyoxylated polyacrylamide compositions

Abstract

An aqueous composition is provided comprising water and a cationic polymeric resin having at least one reactive aldehyde group and formed by the reaction of glyoxal with a polymer. The polymer comprises at least one acrylamide repeat unit and at least one cationic repeat unit, wherein the number of equivalents of reactive aldehyde divided by the number of equivalents of residual glyoxal is greater than about 1.2 based on the total weight of the polymer, wherein the polymer has greater than about 50 mole percent acrylamide repeat units and from about 2 to about 30 mole percent cationic repeat units prior to reaction, wherein greater than about 5 mole percent of the acrylamide repeat units are converted to reactive aldehyde groups in the cationic polymeric resin; and wherein the composition exhibits a viscosity increase of less than about 200 percent.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 133,449, filed January 4, 2021, the disclosure of which is expressly incorporated herein by reference in its entirety. Technical Field

[0003] In general, this disclosure relates to aqueous compositions comprising a glyoxylated polyacrylamide (GPAM) polymer. More specifically, this disclosure relates to a composition wherein a high level of formed aldehyde functional groups are present on the GPAM polymer, there are fewer intermolecular crosslinks between the initial cationic acrylamide polymer chains, and a lower amount of glyoxal is present in the final composition. Background Technology

[0004] Glyoxylated polyacrylamide (GPAM) resins have been used in the paper industry for many years to impart temporary wet strength, wet strength, and dry strength to the final paper. They are also known to improve drainage during the papermaking process. However, not all GPAM resins are effective at imparting wet strength to paper, and none are known to match the wet strength imparted by other wet strength chemicals such as polyamide-epioclosan (PAE) resins. Various resins and their efficiencies are described in numerous references, such as William Scott’s Principles of Wet End Chemistry (Tappi Press) or Espy, HH’s “The mechanism of wet-strength development in paper – A review,” Tappi Journal 78(4), 90-99 (1995). Although PAE resins are very effective at imparting wet strength, the wet strength they provide is permanent, meaning that the wet strength of the paper does not decrease over time when kept wet. GPAM resins are able to provide so-called temporary wet strength, which means that the strength of the wetted paper decreases over time. Therefore, there is a need for a temporary wet strength resin that provides an initial wet strength level similar to or greater than that of PAE or other permanent wet strength resins.

[0005] GPAM resins are typically formed by reacting glyoxal with the acrylamide groups of a polymer made from acrylamide-based monomers and ionic monomers. The resulting GPAM resins typically contain reactive aldehyde functional groups side-attached to the polymer. They also typically contain an excess of unreacted glyoxal. For the purposes of this patent, "GPAM resin" will refer to the composition of this patent comprising GPAM and glyoxal, and "GPAM" will refer only to the resulting acetaldehyde-acidified acrylamide polymer. Generally, high levels of reactive aldehyde functional groups side-attached to the polymer (hereinafter referred to as the polymer), or aldehyde functional groups in GPAM, or aldehyde functional groups on GPAM cannot be generated in GPAM resins because of the significant increase in viscosity and the potential for gelation during deeper acetaldehyde acidification. Furthermore, some GPAM resins have high levels of residual glyoxal, making them unsuitable for use. There is a need for GPAM resins that can have low levels of residual glyoxal while still maintaining high reactivity.

[0006] Over time, GPAM resins react slowly within the aqueous composition. The aldehyde functional groups of the GPAM resin tend to continue reacting with open acrylamide groups to form crosslinks and increase the viscosity of the aqueous composition. GPAM resins may even continue to react to form a gelled composition, leading to reduced product efficacy and ease of use.

[0007] The shelf life is described by the retention of the side-aldehyde functional groups of GPAM during aging and / or the lack of increase or minimal increase in viscosity of the GPAM resin composition. Commercially available GPAM resins may have a shelf life of only about 30 days at approximately 32°C. Viscosity increases over time until the product becomes unusable. For conventional GPAM resins, an increase in the solids content of the final aqueous composition, an increase in the level of GPAM functional groups, or an increase in storage temperature will shorten the shelf life. Therefore, there remains a need for GPAM compositions with relatively high concentrations (such as greater than 10% solids content) of high aldehyde functional groups that do not contain excessively high levels of glyoxal and are stable over time.

[0008] When paper is prepared at a pH of approximately 5.5 to 7, GPAM resins with aldehyde functional groups provide the initial wet strength of the paper. Efficiency decreases when the papermaking process is carried out at higher pH values. Therefore, there is a need for a GPAM resin that exhibits good wet strength generation efficiency under neutral or even alkaline papermaking conditions.

[0009] Furthermore, when forming GPAM resin, glyoxal reacts with the acrylamide groups of an acrylamide-based polymer. The reaction is typically carried out at a pH of approximately 8, 9.7, or 10 and at concentrations suitable for use as the final product (such as 10% solids content). In this case, the viscosity of the reaction is monitored to determine the termination point, thus preventing the GPAM from becoming overly crosslinked due to its reactive functional aldehyde groups, which increases viscosity and shortens shelf life. This viscosity monitoring process places demands on manufacturing plants. Without monitoring the reaction, gel formation can occur in the reaction vessel, leading to productivity losses. For this reason, a GPAM resin forming reaction that is stable over time is also required, significantly reducing the likelihood of gel formation in the reaction vessel and eliminating the need for extensive viscosity monitoring to determine the termination point. Summary of the Invention

[0010] This disclosure provides an aqueous composition comprising water and a cationic polymer resin having at least one reactive aldehyde group and formed by the reaction of glyoxal with a polymer. The polymer comprises at least one acrylamide repeating unit and at least one cationic repeating unit, wherein the equivalent number of reactive aldehydes divided by the equivalent number of residual glyoxal, based on the total weight of the polymer, is greater than about 1.2, preferably greater than about 1.5, and more preferably greater than about 2, wherein prior to the reaction, the polymer may have greater than about 50 mol% of acrylamide repeating units and about 2 to about 30 mol% of cationic repeating units, wherein greater than about 5 mol% of the acrylamide repeating units of the polymer are converted into reactive aldehyde groups in the cationic polymer resin.

[0011] This disclosure also provides a method for preparing an aqueous composition comprising water and a cationic polymer, the method comprising the following steps:

[0012] Polymerizing two or more monomers via free radical polymerization to form a polymer comprising at least one acrylamide repeating unit and at least one cationic repeating unit;

[0013] The acrylamide groups of the polymer are reacted with glyoxal to form a cationic polymer resin having side-attached reactive aldehyde groups, and excess glyoxal is optionally removed to form the aqueous composition.

[0014] The number of equivalent reactive aldehydes formed on the polymer, based on the total weight of the polymer, divided by the number of equivalent residual glyoxal is greater than approximately 1.2.

[0015] The step of reacting the polymer with glyoxal is carried out by adding an aqueous mixture of the polymer to a glyoxal solution such that a polymer-glyoxal reaction of greater than 50, 65, or 80 mol% occurs before approximately 100% of the polymer in the polymer mixture is added to the glyoxal solution; wherein the percentage of polymer-glyoxal reaction is defined as the approximate maximum percentage of acrylamide groups reacted after a reaction time of approximately 8 hours at approximately 22°C and approximately 8.9 with glyoxal;

[0016] In this process, after adding approximately 100% of the polymer solution to achieve a certain glyoxylation level such that at least 20 mol% of the acrylamide repeating units of the polymer are converted into reactive aldehyde groups, the reaction between the polymer and glyoxal continues, and in this process, compared to adding a glyoxal solution to the polymer solution, less viscosity increase occurs during the polymer-glyoxal reaction.

[0017] When measured at approximately 10% solids content and a pH of approximately 3.5 after aging at approximately 40°C for approximately 30 days, the composition exhibited a viscosity increase of less than approximately 50%.

[0018] This disclosure also provides a method for forming paper, the method comprising the following steps:

[0019] Provides aqueous suspensions of cellulose fibers;

[0020] An aqueous composition is added to the suspension, wherein the aqueous composition comprises:

[0021] Water; and

[0022] A cationic polymer resin having at least one reactive aldehyde group and formed by the reaction of glyoxal with a polymer;

[0023] The polymer comprises at least one acrylamide repeating unit and at least one cationic repeating unit;

[0024] Based on the total weight of the polymer, the equivalent number of reactive aldehydes divided by the equivalent number of residual glyoxal is greater than approximately 1.2.

[0025] Prior to the reaction, the polymer has more than about 50 mol% of acrylamide repeating units and about 2 to about 30 mol% of cationic repeating units;

[0026] In this process, more than about 5 mol% of the acrylamide repeating units in the polymer are converted into reactive aldehyde groups in the cationic polymer resin; and

[0027] When measured at approximately 10% solids content and a pH of approximately 3.2 after aging at approximately 40°C for approximately 30 days, the composition exhibited a viscosity increase of less than approximately 200%.

[0028] Cellulose fibers are used to form paper; and

[0029] The paper is dried to produce an initial wet tensile strength that is at least 10%, 15%, 20%, 25%, or 30% greater than that of a control paper when only about 15 mol% of the at least one acrylamide repeating unit is converted into a reactive aldehyde group. Detailed Implementation

[0030] The following detailed description of the invention is merely exemplary in nature and is not intended to limit the compositions or methods described herein. Furthermore, it is not intended to be limited by any theory presented in the foregoing background or the following detailed description. All values ​​described herein may alternatively be described as approximate values, such as ±0.1, 0.5, 1, 5, 10, 15, or even 20%, or any value or range thereof. Moreover, in various non-limiting embodiments, the use of all values ​​and ranges of values ​​(both integers and fractions) is expressly contemplated, including those values ​​set forth herein and the values ​​and ranges between those values.

[0031] The embodiments of this disclosure generally relate to GPAM compositions and methods of manufacturing the same. For the sake of brevity, conventional techniques associated with GPAM resins may not be described in detail herein. Furthermore, various tasks and process steps described herein can be combined into a more comprehensive procedure or process with additional steps or functions not described in detail herein. In particular, the various steps in the manufacture of GPAM resins are well known, and therefore, for the sake of brevity, many conventional steps are often only briefly mentioned herein or are often omitted entirely without providing well-known process details. In various embodiments, the term "solution" is used herein and can be described as a mixture in which at least 97% of the compound is soluble. In other embodiments, a solution may mean the absence of a separated phase that refracts visible light in the presence of a refractive index difference between phases. In other non-limiting embodiments, the term solution as used herein can be replaced with a mixture.

[0032] In one embodiment, this disclosure provides an aqueous composition comprising water and a cationic polymer resin having at least one reactive aldehyde group and formed by the reaction of glyoxal with a polymer. The polymer comprises at least one acrylamide repeating unit and at least one cationic repeating unit, wherein the equivalent number of reactive aldehydes divided by the equivalent number of residual glyoxal based on the total weight of the polymer is greater than about 1.2, wherein prior to the reaction, the polymer may have greater than about 50 mol% acrylamide repeating units and about 5 to about 30 mol% cationic repeating units, wherein greater than about 20 mol% of the acrylamide repeating units of the polymer are converted to reactive aldehyde groups in the cationic form; and wherein the composition exhibits a viscosity increase of less than about 200% when measured at about 10% solids content and about 3.2 after aging at about 40°C for about 30 days.

[0033] This disclosure also provides an aqueous composition comprising water and a cationic polymer resin having at least one side-attached reactive aldehyde group and formed by the reaction of glyoxal with a polymer. This polymer is described throughout this disclosure as a “prepolymer” and is distinguished from the final cationic polymer resin. For example, cationic polyacrylamide (prepolymer) prior to reaction with glyoxal differs from an acetaldehyde-acidified cationic polymer. The polymer comprises at least one acrylamide repeating unit and at least one cationic repeating unit, wherein the equivalent number of reactive aldehydes divided by the equivalent number of residual glyoxal based on the total weight of the polymer is greater than about 1.2, wherein prior to the reaction, the polymer may have more than about 50 mol% acrylamide repeating units and about 5 to about 30 mol% cationic repeating units, wherein more than about 20 mol% of the acrylamide repeating units of the polymer are converted into reactive aldehyde groups in the cationic polymer resin; optionally, the composition has at least about 4 wt% solids content, and wherein, when aged at about 40°C for about 30 days, the composition exhibits a viscosity increase of less than about 200% when measured at about 10% solids content and about 3.2.

[0034] In one embodiment, the polymer comprises at least one acrylamide repeating unit and at least one cationic repeating unit, wherein the equivalent number of reactive aldehydes divided by the equivalent number of residual glyoxal based on the total weight of the polymer is greater than about 1.2, preferably greater than about 1.5, and more preferably greater than about 2, wherein prior to the reaction, the polymer may have greater than about 50 mol% acrylamide repeating units and about 2 to about 30 mol% cationic repeating units, wherein greater than about 5 mol% of the acrylamide repeating units of the polymer are converted into reactive aldehyde groups in the cationic polymer resin; optionally, the composition has at least about 1 wt% solids content, and wherein the composition exhibits a viscosity increase of less than about 200% when measured at a pH of about 3.2 after aging at about 25°C for about 30 days. For the purposes of this disclosure, the terms “reactive,” “aldehyde reactive,” “reactive aldehyde,” “reactive aldehyde functional group,” “reactive aldehyde group,” “functional aldehyde group,” “side-reactive aldehyde group,” “side-polymer aldehyde group,” and “side-reactive aldehyde functional group” are used interchangeably and denote a side-reactive aldehyde functional group on glyoxylated polyacrylamide.

[0035] In one embodiment, this disclosure generally relates to compositions of glyoxylated cationic polymeric acrylamide (GPAM) resins, wherein a high level of formed aldehyde functional groups is present on the GPAM polymer, there are fewer intermolecular crosslinks between the initial cationic acrylamide polymer chains, and simultaneously, less glyoxal in the final mixture. Furthermore, compared to GPAM resins with compositions having different levels of aldehyde functional groups and lacking crosslinks, the GPAM resin compositions of this disclosure, when used in papermaking, provide the resulting paper with greater initial wet strength (WS) and greater total WS decay over time. Additionally, the GPAM resin compositions of this disclosure can exhibit better aging stability. In another embodiment, a method for preparing the compositions of the invention is defined. The likelihood of gelation or excessive viscosity increase occurring in said method is significantly reduced compared to previous methods.

[0036] In other non-limiting embodiments, aqueous compositions of GPAM resin optionally having a solids content of at least 4% are disclosed, wherein the GPAM in the composition has a side-reactive aldehyde group formed by the reaction of glyoxal with a polymer, wherein the polymer comprises at least one acrylamide repeating unit and at least one cationic repeating unit, wherein the molar percentage of the acrylamide repeating unit is at least 50 and the molar percentage of the cationic repeating unit is 5 to 30, and wherein the equivalent number of reactive aldehyde groups of GPAM in the composition (the number of moles of side-reactive aldehyde groups per gram of GPAM polymer) divided by the equivalent number of residual glyoxal (the number of moles of unreacted glyoxal per gram of GPAM polymer) is greater than about 1.2, and wherein at least 20 mol% of the acrylamide repeating unit of the polymer is converted to a side-reactive aldehyde group, and wherein when the aqueous composition is aged for 30 days at a pH of about 3.2 and 40°C with a solids content of 10%, a viscosity increase of less than about 200% is caused. In other embodiments, a cationic GPAM resin composition having high reactivity, low residual glyoxal levels, and excellent aging stability is disclosed. High reactivity allows 30% or 40% of the acrylamide groups in the starting polymer to be converted into side-reactive aldehyde functional groups. Furthermore, approximately 40 mol%, 50 mol%, or 60 mol% of the repeating acrylamide units in the polymer react with glyoxal. Some reactions form side-reactive aldehyde functional groups, while others form intermolecular or intramolecular crosslinks.

[0037] In other non-limiting embodiments, an aqueous composition of GPAM resin optionally having a solids content of at least 1% is disclosed, wherein the GPAM of the composition has a side-reactive aldehyde group formed by the reaction of glyoxal with a polymer, wherein the polymer comprises at least one acrylamide repeating unit and at least one cationic repeating unit, wherein the molar percentage of the acrylamide repeating unit is at least 50 and the molar percentage of the cationic repeating unit is 2 to 30, and wherein the equivalent number of reactive aldehyde groups of GPAM in the composition (the number of moles of side-reactive aldehyde groups per gram of GPAM polymer) divided by the equivalent number of residual glyoxal (the number of moles of unreacted glyoxal per gram of GPAM polymer) is greater than about 1.2, preferably greater than about 1.5, preferably greater than about 2, and wherein at least 5 mol% of the acrylamide repeating unit of the polymer is converted into a side-reactive aldehyde group, and wherein when the aqueous composition is aged for 30 days at a pH of about 3.2 and 25°C and a solids content of 10%, it causes a viscosity increase of less than about 200%.

[0038] In various embodiments, typical cationic monomers are diallyl dimethylammonium chloride (DADMAC), 2-(acryloyloxyethyl)-trimethylammonium chloride, 2-(dimethylamino)ethyl acrylate, 3-acryloylaminopropyl-trimethylammonium chloride, dimethylaminopropylacrylamide, or combinations thereof.

[0039] In various embodiments, the high functionality of GPAM imparts high initial wet strength properties to paper using the GPAM resin. However, to obtain a higher level (albeit not as high as in this disclosure) of functional groups, prior GPAM resins also implied a higher level of residual glyoxal. For this disclosure, the final level of residual glyoxal in the GPAM resin is lower compared to the aldehyde functional groups realized on GPAM. For the aqueous composition of any of the preceding claims, the molar ratio of the equivalent number of reactive aldehyde groups in the composition to the equivalent number of glyoxal in the composition is greater than about 1.3, about 1.4, or about 1.5.

[0040] In various embodiments where high levels of side-attached aldehyde functional groups and low residual levels of glyoxal are present on GPAM, this disclosure unexpectedly achieves a higher level of aging stability in the GPAM resin. Stability can be defined in various ways, including no increase in viscosity during aging or maintenance of the level of reactive aldehyde functional groups on the GPAM during aging. The stability of the GPAM polymer in the aqueous GPAM resin composition depends on the pH and solids content of the composition. For the aqueous composition of this disclosure with a solids content of 10% by weight and a pH of about 3.2, after aging at about 40°C for about 30 days, the viscosity will increase by less than 200%, or less than 150%, or less than 100%, or less than 50%, and / or the equivalent number loss of reactive aldehyde groups on the GPAM will be less than about 40 mol%, about 30 mol%, or about 20 mol%. For the aqueous GPAM resin composition with a solids content of 12% or 14% by weight, the increase in viscosity and / or the stability of the functional groups may also be real.

[0041] In one embodiment of the aqueous composition disclosed herein, after aging at about 25°C for about 30 days at a pH of about 3.2, the equivalent number loss of reactive aldehyde groups on GPAM will be less than about 40 mol%, about 30 mol%, about 20 mol%, or about 10 mol%.

[0042] The highly reactive aldehyde functional groups of GPAM in one embodiment of this disclosure are obtained by reacting glyoxal with the acrylamide groups of a starting cationic acrylamide polymer. The ratio of the molar amount of glyoxal to the molar amount of acrylamide groups on the starting polymer is critical. This ratio typically needs to be high enough to generate reactive aldehyde functional groups on the GPAM but limit the number of crosslinks formed. For the aqueous compositions of this disclosure, when glyoxal is rapidly added to the starting polymer composition during the reaction, the ratio of the molar amount of glyoxal to the molar amount of acrylamide repeating units is greater than about 0.7:1, greater than about 1:1, or greater than about 2:1.

[0043] The glyoxylation method of the starting polymer can be further defined by a reaction window (RW), which takes into account the molecular weight of the polymer, the molar ratio of glyoxal to acrylamide groups, and the solids content of the aqueous mixture of glyoxal and the polymer at the time of reaction. Not every variation of this method can be described herein, but those skilled in the art will understand these variations. For the purpose of illustratively defining the reaction window, glyoxal is added to the solution of the starting cationic acrylamide polymer and added rapidly such that all or almost all of the glyoxal is added when the glyoxylation reaction begins. The solids content, relative to the reaction composition and the reaction window, is defined as the weight percentage concentration of the starting GPAM polymer in the entire aqueous composition at the time of reaction, i.e., when all the glyoxal has been added. The higher the molecular weight of the starting polymer, the more likely the process is to result in gelation of the GPAM, i.e., excessive crosslinking, leading to the formation of components with very high molecular structures. Similarly, with increasing solids content at the time of reaction, the likelihood of intermolecular crosslinks rather than intramolecular crosslinks is greater. Excessive intermolecular crosslinking leads to gelation. Finally, the ratio of glyoxal to acrylamide groups should be sufficiently high to allow for an excess of glyoxal that drives the reaction to produce reactive aldehyde functional groups rather than crosslinking. The molecular weight of the starting polymer can be expressed as specific viscosity (RSV). For the purposes of this disclosure, in the case of rapid addition of glyoxal to the starting polymer mixture, RW is defined as the ratio of RSV multiplied by RSV multiplied by the solid content (wt%) of the cationic acrylamide polymer reacting at the start of the acetaldehyde acidification reaction, divided by the moles of glyoxal to the moles of acrylamide groups. An acceptable RW is less than about 0.14, about 0.12, or about 0.10. As described above, for the purpose of defining RW, the solid content is defined as the weight percentage of the starting cationic acrylamide polymer relative to the total aqueous composition of the reaction comprising the polymer, glyoxal, and water of the reaction mixture.

[0044] The composition and method in one embodiment of this disclosure have unexpected advantages, not only avoiding gelling during the acetaldehyde acidification reaction. The composition and method achieve the desired properties, namely, that the viscosity of the mixture does not increase rapidly during the acetaldehyde acidification process. If the viscosity increases rapidly during the reaction, even in the later stages, it can be difficult to control the viscosity and molecular weight of the final GPAM. The rapid increase in viscosity during acetaldehyde acidification means that special care should be taken during large-scale manufacturing, i.e., monitoring should be conducted to avoid the formation of a high-viscosity or gelled mixture in the reaction vessel. Within the RW of this disclosure, the GPAM reaction mixture not only does not gel, but also exhibits minimal viscosity increase, making close monitoring as required in previous GPAM resin preparations unnecessary. Even with variations in reaction time of several hours, the viscosity, molecular weight, and even the final properties of the GPAM resin used to generate the initial wet strength (WS) of the paper do not change significantly. On the one hand, the ratio of the RSV of the final GPAM resin to the RSV of the starting polymer is less than 3, or less than 2, or less than 1.5, or less than 1.2.

[0045] Different alternative methods can be followed for the reaction of glyoxal with the acrylamide groups of a cationic acrylamide polymer. Instead of adding glyoxal to the polymer or a rapid mixture of the two materials, the polymer can be added slowly to the glyoxal solution. After the polymer is slowly added to the glyoxal, the reaction can continue. This method variation yields a higher average ratio of the molar number of glyoxal to the molar number of acrylamide groups available to react with the glyoxal. The amount, rate, and properties of the polymer added to the glyoxal can ensure that at least 50% of the final reactive aldehyde groups present on the GPAM are present on the GPAM at the time of its formation before all the polymer is added to the glyoxal. The amount, rate, and properties of the polymer added to the glyoxal can ensure that at least 65% or at least 80% of the final reactive aldehyde groups are formed on the polymer before all the polymer is added to the glyoxal. Optionally, the pH of the formed GPAM is lowered to about 3.2 and some excess glyoxal is optionally removed.

[0046] In another embodiment, the GPAM composition of this disclosure is prepared by an alternative method. In the GPAM method described herein, glyoxal is added to the polymer or glyoxal and the polymer are added rapidly together and an acetaldehyde acidification reaction occurs. This alternative method involves the slow addition of the polymer to a glyoxal solution. The result is an unexpectedly increased reaction window size while achieving the same benefits of the composition and method, which are described elsewhere as part of this disclosure. In the GPAM resin of this alternative method, the use of an excess mol% of glyoxal relative to the molar number of acrylamide groups on the cationic acrylamide polymer throughout the acetaldehyde acidification reaction results in highly reactive GPAM, i.e., at least 20% of the acrylamide groups are converted to reactive aldehyde functional groups, exhibiting excellent storage stability and efficiently imparting wet strength to paper. Furthermore, in the final GPAM resin, the equivalent number of functional aldehyde groups on the GPAM divided by the equivalent number of residual glyoxal in the GPAM resin will be greater than 1.2, making the GPAM resin safer for use in papermaking. In a novel method of adding a polymer to glyoxal, known as the so-called reverse acetaldehyde acidification method, less viscosity increase occurs during the acetaldehyde acidification process compared to the rapid addition of glyoxal to the polymer. The effect is a wider reaction window, allowing the use of starting cationic acrylamide polymers with higher RSV, or allowing for higher total or final polymer solids content during the acetaldehyde acidification reaction, or allowing for a lower ratio of the molar number of glyoxal to the molar number of acrylamide groups on the cationic acrylamide polymer. For example, the alternative (reverse) method involves adding the prepolymer to glyoxal compared to a first method in which glyoxal is added to the prepolymer.

[0047] This disclosure also describes the preparation of paper utilizing temporary wet strength (WS). For example, methods for forming paper may include...

[0048] 1. Provides an aqueous suspension of cellulose fibers;

[0049] 2. Add an aqueous composition to the suspension, wherein the aqueous composition comprises the GPAM resin described in this document;

[0050] 3. To enable cellulose fibers to form paper; and

[0051] 4. Dry the paper to produce paper with an initial wet tensile strength that is at least 10%, 15%, 20%, 25%, or 30% greater than that of a control paper when only about 15 mol% of the at least one acrylamide repeating unit is converted into a reactive aldehyde group.

[0052] Paper formed by the above method can be formed, wherein the addition level of GPAM resin (on dry weight) is about 0.3%, and its initial wet strength is about 10%, about 15%, or about 20% higher than that of a comparative paper formed from an equivalent composition made of GPAM in which the degree of reaction of the acrylamide groups of the starting polymer to form GPAM is less than about 15%.

[0053] One embodiment of this disclosure comprises an aqueous mixture or solution of a cationic polymer resin having a side-reactive aldehyde functional group (a glyoxylated polyacrylamide (GPAM) formed by reacting a polymer of acrylamide and repeating cationic monomer units with glyoxal to form a reactive side-reactive aldehyde functional group on the polymer (also referred to as a reactive aldehyde group of the polymer)). The reactive cationic resin composition, referred to as glyoxylated polyacrylamide (GPAM) resin during preparation, may have at least 40%, 50%, or 55% amide groups of the initiating cationic polyacrylamide that reacts with glyoxal. Important is not only the level of reacting amide groups but also the number of side-reactive aldehyde functional groups formed in the final GPAM. A further distinction of this disclosure is that 40% to 50% to 60% of the reacting amide groups form reactive aldehyde functional groups. In one embodiment, greater than 20%, greater than 25%, or greater than 30% molar of the initiating amide groups of the cationic acrylamide polymer are present as aldehyde functional groups in the final GPAM. Some of the side polymer aldehyde groups formed by the reaction of glyoxal with the polymer can react with other polymer chains to form crosslinks, and some can undergo intramolecular reactions with the same polymer chain they belong to. Not all the glyoxal used in the acetaldehyde acidification reaction reacts with the polymer; some remains in the GPAM resin as glyoxal. Then, after the acetaldehyde acidification reaction is complete, some glyoxal can be removed. The amount of glyoxal in the final mixture of GPAM resin and water will be referred to as residual glyoxal. For the purposes of this disclosure, the final GPAM polymer has high aldehyde reactivity, and the level of residual glyoxal is relatively low compared to the level of the GPAM polymer in the GPAM resin composition, thus making the GPAM resin very effective in establishing wet strength in paper and safer to use compared to previous GPAM resins. The lower level of residual glyoxal is advantageous. Furthermore, the final GPAM resin can exhibit excellent aging stability. In addition, the final GPAM resin can impart high initial wet strength properties to paper and, in some cases, better wet strength decay compared to previous GPAM resins with lower levels of aldehyde functional groups on the GPAM.

[0054] In one embodiment, the GPAM resin disclosed herein has a higher level of reactive aldehyde groups compared to previous GPAM resins. Therefore, they can provide improved initial wet strength for paper containing them compared to GPAM resins with lower levels of aldehyde functional groups. In one embodiment, the GPAM resin offers improved safety and storage stability and is easier to manufacture using the glyoxylation process.

[0055] Hercobond, from Solenis LLC, has a reactive aldehyde content of 1.76 meq / g and in which only about 16% of the acrylamide groups are converted into reactive aldehyde functional groups. TM Compared to currently commercially available GPAM resins such as 1194, this GPAM resin, based on a weight percentage added to paper under equivalent conditions, produces an initial wet strength that is 10%, 15%, 20%, 25%, or 30% higher. Unbound by theory, the increase in initial paper wet strength (WS) is believed to be due to a higher level of reactive aldehyde functional groups. It was also unexpectedly found that, compared to commercially available 1194 products, this GPAM resin exhibits a greater percentage decrease in wet strength over time while the paper remains wet. However, in the tests specified below, typical GPAM resins (including commercially available controls) show a decrease in wet strength of approximately 55% over time, while this GPAM resin provides a decrease of approximately 5% or more, or approximately 60%. Both higher strength and a greater level of decrease are desirable properties. Uniquely, this disclosure combines improved safety, improved storage stability, and ease of manufacture with respect to the acetaldehyde oxidation method.

[0056] The papermaking process generally involves three steps. The first step is to form an aqueous suspension of cellulose fibers. The second step is to add additives, such as those disclosed herein, to the suspension. The third step is to form and dry the paper. For tissue and towel grades, the fourth step is to crease or form the paper structure to provide various properties such as softness. These steps can be modified by those skilled in the art.

[0057] In one embodiment, the reactive cationic resin of this disclosure can be added to the papermaking process at any point in the current process of adding reinforcing resins, and the resin is typically added to the paper as an aqueous composition. In one embodiment, the GPAM resin of this disclosure can be added at any time before, during, or after paper formation. For example, the resin can be added before or after pulp refining, on the suction side of the machine pulp tank, at the fan pump or headbox, or by spraying or foaming onto wet web. The resin can also be added to preformed paper by application to dry paper via trough sizing or spraying. In most industrial papermaking, the resin is typically added as an aqueous composition on the suction side of the machine pulp tank or at the fan pump or headbox. Various amounts of resin can be used. Those skilled in the art can readily determine the actual amount of resin used in the paper.

[0058] Some GPAM resins used in the manufacture of GPAM resins have low levels of residual glyoxal. In this disclosure, when referring to GPAM or GPAM resin, the reactive aldehyde functional group will be referred to as a reactive group or functional group. Existing GPAM resins with even slightly higher levels of reactive aldehyde functional groups have higher levels of residual glyoxal (as a percentage of the GPAM polymer) compared to previous GPAM resins. The functional group level of this GPAM is higher than that of such previous GPAM resins, and due to the higher functional group level, this GPAM resin is more efficient in producing (i.e., imparting) higher initial wet strength in the final treated paper. However, at the same time, in the GPAM of this disclosure, the level of residual glyoxal is lower for a given level of GPAM functional groups and for the level of initial wet strength per unit amount of GPAM in the paper (i.e., its efficiency). This can be traced back to the ratio of the amount of reactive aldehyde groups to the level of glyoxal in the final GPAM. This level can be expressed based on the equivalent number of repeating units in the GPAM polymer, i.e., the millimoles of reactive aldehyde functional groups or the moles of glyoxal for a given weight of GPAM polymer. The ratio of the equivalent number of reactive aldehyde groups to the equivalent number of residual glyoxal defines the safety factor (SF). For the purposes of this disclosure, in one embodiment, the equivalent number of reactive aldehyde groups in the composition divided by the equivalent number of residual glyoxal is typically greater than 1.2, or greater than 1.3, or greater than 1.4, or greater than 1.5.

[0059] Water-soluble aldehydes, such as glyoxal, exist in aqueous solutions in various forms, such as hydrated monomers, hydrated dimers, or oligomers. These forms can be considered as existing as the basic aldehyde structure. The molar concentration of an aldehyde group or compound includes the residual aldehyde on the polymer and the molar concentration of aldehyde-based functional groups, based on the aldehyde in its simplest form—unhydrated, unchained, or not in any other form. The meq of the aldehyde functional group in the polymer can be measured by NMR. The level of glyoxal (considering all its various forms) can be measured by titration.

[0060] Additionally, in embodiments of this disclosure, the glyoxal level in the GPAM resin (i.e., GPAM polymer with glyoxal) can be less than 10% by weight.

[0061] GPAM resins in water with relatively high solids content (e.g., greater than about 8 or 10% by weight) typically have poor shelf life. Over time and after manufacturing, they tend to exhibit increased viscosity and loss of side-reactive aldehyde functional groups. Their viscosity often increases, even reaching the gel point. Existing aqueous GPAM resin compositions with relatively high solids content (e.g., 10%) may have a shelf life of less than 30 days at 30°C, after which they become too thick to use on paper machines. In one embodiment, another aspect of this disclosure provides improved storage stability while maintaining high reactivity and / or high efficiency. Shelf life is a description of the stability of GPAM resin over time, and the presence or absence of stability can be described and measured by altering the viscosity of the GPAM resin, altering the aldehyde functional groups of the GPAM, altering the homogeneity of the GPAM resin, or altering the efficiency with which the GPAM resin imparts initial wet strength to paper. The viscosity of the aqueous GPAM composition at a solids content greater than 8% by weight or greater than 10% by weight is such that when aged at 40°C in a sealed container for more than 1 month or more than 2 months, the viscosity increase is no more than 200%, 100%, 50%, 30%, or 20%, respectively, with stability determined at the optimal pH. This is not theoretically sound, but is believed to be due to the tendency of reactive aldehydes to react with free groups (such as amide groups) to further generate crosslinks. In this resin, the modification of the prepolymer groups reactive to the aldehyde is complete or nearly complete, meaning that the reaction rate and extent are significantly slowed under normal conditions under which the reaction can occur. The GPAM resins of this disclosure exhibit very little or no viscosity increase upon aging, and they lose reactivity at a very slow rate. Those skilled in the art will understand how changing the active solids content (i.e., the weight % of the GPAM polymer) and the temperature and pH of the aqueous GPAM resin composition affects stability. Compared to other aqueous GPAM resin compositions with relatively high solids content, the stability of the inventive aqueous GPAM resin composition is significantly improved under normal storage conditions for such compositions. What is even more surprising about this aqueous GPAM composition is the absence of high levels of residual glyoxal (i.e., unreacted glyoxal) in the aqueous composition. Again, without being bound by theory, but in one embodiment, the relatively long storage stability of the GPAM of this disclosure is unexpected, as this is contrary to the previously held finding that GPAM resins with increased reactivity and / or low levels of residual starting glyoxal in the final mixture / solution tend to result in shorter shelf lives. While higher levels of reactivity are said to cause more reaction in the final product upon aging, resulting in increased viscosity, low levels of glyoxal, such as less than 10% by weight based on the GPAM polymer, are expected to reverse the glyoxal reaction that occurs during the formulation of the GPAM resin.For the purposes of this disclosure, this reversal did not occur as rapidly as expected during aging tests. At lower pH values, such as 2 to 4, 2.5 to 3.5, 3 to 3.5, or 2.8 to 3.2, reversal tends to occur slowly. Reversal and stability can be pH-dependent, and an advantage of this disclosure is observed when comparing multiple GPAMs with equivalent pH values. Stability allows for a reduction in the level of GPAM aldehyde functional groups of less than 50%, less than 40%, less than 30%, less than 20%, less than 10%, or less than 5% after aging at 40°C for more than 1 month or more than 2 months. Stability allows for at least 98% of the GPAM resin to remain physically homogeneous after aging at 40°C for more than 1 month or more than 2 months. Stability allows for the efficiency with which the GPAM resin imparts initial wet strength to the paper (wet strength per % of GPAM resin retained in the paper) to remain at least 50% of its original value or at least 70% of its original value after aging at 40°C for more than 1 month or more than 2 months.

[0062] Reactions associated with stability loss are slowed by lowering the pH of the GPAM resin composition. While some instability and reversal of the aldehyde reaction may occur at higher pH values, such as above 7, when free glyoxal levels are low, the relative amounts occurring are less than with previous GPAM resins having equivalent solids content. In one embodiment of this disclosure, the pH reduction is eliminated, and the stability of the GPAM resin composition is improved to more than twice the stability length of previous GPAM resins with a solids content of at least 8% at equivalent pH.

[0063] The GPAM compositions disclosed herein begin with the preparation of a polymer that can react with glyoxal to form a reactive aldehyde functional group. The polymer to be reacted has groups that can react with glyoxal. These groups can be any groups known in the art. For example, a dialdehyde-reactive comonomer can be used to form the reactive cationic resin of this disclosure. In another embodiment, any dialdehyde-reactive comonomer can be used, which is capable of reacting with a cationic comonomer via free radical chain polymerization to form a dialdehyde-reactive comonomer. In one embodiment, the dialdehyde-reactive comonomer is typically acrylamide.

[0064] The polymer also contains repeating ionic units. The typical ionic charge is cationic. In one embodiment, the cationic comonomer used to form the reactive cationic resin of this disclosure can be any cationic monomer capable of reacting with a dialdehyde reactive comonomer via free radical chain polymerization to form a dialdehyde reactive copolymer. The cationic monomer includes tertiary and quaternary diallylamino derivatives, or tertiary and quaternary amino derivatives of acrylic acid or (meth)acrylic acid or acrylamide or (meth)acrylamide, vinylpyridine and quaternary vinylpyridine, or p-styrene derivatives containing tertiary or quaternary amino derivatives.

[0065] The cationic comonomer may be selected from the following members: diallyl dimethyl ammonium chloride (DADMAC), [2-(acrylamido)ethyl]trimethyl ammonium chloride, [2-(methacrylamido)ethyl]trimethyl ammonium chloride, [3-(acrylamido)propyl]trimethyl ammonium chloride, [3-(methacryloylamino)propyl]trimethyl ammonium chloride, N-methyl-2-vinylpyridinium, N-methyl-4-vinylpyridinium, p-vinylphenyltrimethyl ammonium chloride, p-vinylbenzyltrimethyl ammonium chloride, [2-(acryloyloxy)ethyl]trimethyl ammonium chloride, [2-(methacryloyloxy)ethyl]trimethyl ammonium chloride, [3-(acryloyloxy)propyl]trimethyl ammonium chloride, [3-(methacryloyloxy)propyl]trimethyl ammonium chloride, and combinations thereof.

[0066] Mixtures of cationic comonomers can be used for the same purpose. Typically, cationic comonomers are not reactive to dialdehydes under alkaline conditions (e.g., pH greater than 7).

[0067] A typical cationic comonomer is diallyl dimethyl ammonium chloride (DADMAC). It should be understood that mixtures of cationic comonomers can be used for the same purpose. Generally, cationic comonomers are not reactive to glyoxal under alkaline conditions (i.e., pH greater than 7). Typical levels of cationic monomers, measured in moles, are at least 2%, at least 5%, at least 10%, or at least 15% of the starting polymer.

[0068] Based on the molar amount of the prepolymer used to form the GPAM resin, the amount of acrylamide is typically at least 50% to 95%, 60% to 90%, or 65% to 90%.

[0069] The reactive aldehyde functional repeating unit originates from the reaction of glyoxal with acrylamide. Glyoxal is a typical aldehyde compound. Glyoxal can react primarily by reacting only once, rather than twice, to form side-attached reactive aldehyde functional groups. When glyoxal reacts twice, the reaction can be an intermolecular crosslink between polymer chains, or the two reactions can occur intramolecularly within the same polymer chain. The ratio of single to double reactions can be greater than 1:1, or greater than 1.5:1, or greater than 2:1, or greater than 2.5:1, or greater than 3:1. Higher ratios result in greater GPAM reactive aldehyde functionality and less GPAM crosslinking. Crosslinking leads to an increase in viscosity during acetaldehyde acidification. Furthermore, the ratio of intramolecular to intermolecular reactions in double reactions is greater than 1:2, greater than 1:1, greater than 2:1, or greater than 3:1.

[0070] When using GPAM resins in the papermaking process, other chemicals may be added. For example, small amounts of cationic polymers may be used to neutralize anionic substances in the pulp. Additionally, detackers may be added to soften the paper. Cellulose derivatives such as carboxymethyl cellulose or various types of starch, or synthetic polymers such as polyacrylamide copolymers, or permanent wet strength resins such as polyamidoamine-epimercohydrin resins may also be added. Other additives may be added, such as those commonly used in papermaking, such as mineral fillers or aluminum sulfate. Compounds that improve paper softness may be added. Such materials are well known in paper used in paper grades containing GPAM resins and are described in general papermaking literature and articles. They may affect the properties of GPAM resins by altering retention or pH. However, this disclosure offers performance advantages under similar conditions compared to other GPAM resins.

[0071] In various embodiments, the uniqueness of the GPAM resin of this disclosure is made possible by a novel method. Therefore, the method is another aspect of this disclosure. In various embodiments, the composition of this disclosure is most conveniently prepared by three steps. In the first step, a prepolymer composition to be reacted with glyoxal is prepared. In the second step, the resulting polymer is reacted with glyoxal to produce a reactive resin, and the pH of the reactive resin is adjusted. The third step is to remove some excess (residual) glyoxal.

[0072] Step 1: Prepolymerization

[0073] There are several methods for preparing the prepolymers of this disclosure. One method is to carry out free radical polymerization in water. One option for free radical polymerization is to use a redox initiation system, such as a combination of sodium metabisulfite and sodium persulfate. Those skilled in the art will know that the desired final polymer has a relatively low and controlled molecular weight for the next step of this method. The level of residual monomers should be low. The molecular weight can be monitored by specific viscosity (RSV) or by size exclusion chromatography (SEC).

[0074] Many other combinations of redox initiation systems can also be used to initiate the polymerization of comonomers to form copolymers for the resins of this disclosure, including other persulfates such as potassium persulfate or ammonium persulfate, or other components such as potassium bromate. Some of these redox initiation systems can be used in combination with chain transfer agents such as sodium hypophosphite or sodium formate or isopropanol or mercapto compounds or sodium metabisulfite. Any initiator and chain transfer compound known in the art can be used.

[0075] Polymerization is typically carried out in aqueous solution at a temperature of at least about 25°C or at least about 45°C, usually between about 50°C and about 90°C. Sometimes it is advantageous to raise the temperature after all comonomers have been added in order to reduce the residual monomer content in the product. The pH during the reaction may depend on the initiator used and may be adjusted with acid or base or with a buffer.

[0076] Comonomers can be added all at once or over any period of time. If one monomer is less reactive than another, it is advantageous to add some or all of the slower-reacting monomer at the start of polymerization, followed by slow, continuous, or multiple batches of the more reactive monomer. Adjusting the feed rate can make the polymer chain composition more uniform. Similarly, initiators can be added all at once or over any period of time. To reduce the amount of residual monomer in the copolymer, it is generally advantageous to continue adding the initiator system over a period of time after all monomers have been added, or to introduce additional amounts of initiator in batches. Those skilled in the art will understand that controlling the addition time controls the consistency of polymer composition and molecular weight.

[0077] The molecular weight of the final prepolymer can be controlled by varying polymerization conditions such as monomer concentration, initiator concentration, and chain transfer agent concentration using any method known in the art. Similarly, the oxygen level in the reaction mixture can be varied, but oxygen is typically removed from the reaction mixture. As known in the art, the molecular weight can also be varied by adding a monomer having multiple reactive vinyl groups or by post-treatment of the formed polymer. In various embodiments, the amount of the desired cationic comonomer in the polymer of this disclosure is, in one embodiment, at least 2 mol% or at least 5 mol% or at least 10 mol% or at least 15 mol% and less than 35 mol% or less than 30 mol%.

[0078] Aldehyde functionalization:

[0079] To produce the reactive ionomer of this disclosure, the prepolymer can be reacted with glyoxal. The reaction of acrylamide-containing polymers with glyoxal is typically carried out under weakly alkaline to neutral conditions, typically between pH 7.0-11, pH 7.0-10.5, pH 7.5-9.8, or pH 8.0-10.5. Glyoxal is rapidly added to the prepolymer to minimize crosslinking. Alternatively, in another aspect of this disclosure, a solution of the prepolymer can be added to glyoxal. The latter method minimizes crosslinking and viscosity increase in the final GPAM resin by maintaining a large excess of aldehyde groups for an extended period for the amide groups. This is described in more detail below. The aldehyde reaction is typically carried out between about 15°C and about 40°C, between 18°C ​​and 30°C, or between 19°C and 23°C.

[0080] The reaction solids content (i.e., the solids content of the cationic acrylamide polymer at the start of the reaction), the molecular weight of the prepolymer, and the ratio of glyoxal to acrylamide groups on the starting cationic acrylamide polymer (also known as the prepolymer) are crucial. In one embodiment, the objective of this disclosure is to produce a high level of reactive aldehyde functional groups on the final GPAM polymer without generating excessive intermolecular crosslinks or an excessive increase in the molecular weight of the final aqueous GPAM resin composition, and consequently, an excessive increase in viscosity. Intermolecular crosslinks tend to lead to excessive or rapid viscosity increases, potentially causing gel formation during the reaction or in the final polymer, where higher molecular weights reduce the stability (shelf life) of the final product. Limiting intermolecular crosslinks also reduces the viscosity increase during the reaction, eliminating the need for careful monitoring of the reaction. However, some intermolecular crosslinks may be required to construct a higher molecular weight final GPAM resin. In one embodiment, this disclosure achieves a unique balance between the high reactivity of the final polymer, the weight percentage of the GPAM polymer in the final aqueous GPAM composition, the level of residues (unreacted glyoxal in the composition), and the aging stability of the composition. The high reactivity of the final polymer can result in higher wet strength in paper made from the final composition of this disclosure, and in one embodiment, maintains a high level of wet strength degradation while achieving greater wet strength. In one embodiment, the unique balance of this disclosure begins with the unique reaction conditions of the prepolymer molecular weight, the ratio of glyoxal to acrylamide groups from the prepolymer, and the concentration of the GPAM polymer during the reaction. The balance of advantages of the final GPAM composition begins with the presence of certain reaction conditions. In one embodiment, these unique conditions can be defined as the reaction window (RW).

[0081] Unbound by theory, previous GPAM resins relied on increasing the polymer molecular weight to achieve higher strength values ​​in the final paper, while in many embodiments this disclosure relies on a high level of reactivity. The reaction conditions in this disclosure contribute to the ability of the reaction to proceed without excessive viscosity increase or without a viscosity increase that is too rapid. The viscosity increase during the aldehyde reaction arises from the increase in molecular weight due to intermolecular crosslinking of the polymer molecules. Some increase in molecular weight and some increase in viscosity are acceptable. What is acceptable is defined by RW. Three factors tend to control the overall level of crosslinking, intermolecular crosslinking, and final reactivity. These three factors include 1) the concentration of the starting cationic acrylamide polymer, i.e., its solids content, 2) the molecular weight of the starting cationic acrylamide polymer, and 3) the ratio of the number of moles of glyoxal used in the reaction to the number of moles of acrylamide groups in the cationic acrylamide polymer used in the reaction. The correct combination of these factors used to obtain the present disclosure, and the given method, will define what can be called RW.

[0082] In one embodiment, RW is suitable for a method of adding glyoxal to a prepolymer solution. Another aspect of this disclosure is the slow addition of the prepolymer solution to a glyoxal solution. In the case of relatively rapid addition of glyoxal to the prepolymer as disclosed in this disclosure, it is believed, but not bound by theory, that excess glyoxal during the reaction process can rapidly cap many amide groups. It has been found that adding low levels of glyoxal or adding it slowly so that only a small amount reacts at the beginning of the process results in higher viscosity and a greater tendency to form gelled polymers. Conversely, when the level of reacting amide groups is higher, the viscosity increase is less because the chance of crosslinking due to a second reaction of glyoxal is lower.

[0083] Unbound by theory, the polymer concentration during the reaction, i.e., the reaction solids content, strongly influences the level of interaction between polymer chains, or in other words, the level of overlap between different polymer molecules in the solution. In very dilute solutions below the so-called critical solution concentration, the degree of overlap between polymer chains does not affect the viscosity of the solution. At higher solids contents, polymer chains overlap and become entangled, and viscosity becomes more concentration-dependent. The higher the concentration, the more different polymer chains are adjacent to each other. Therefore, conducting the reaction at lower solids contents reduces the amount of crosslinking (intermolecular crosslinking) between polymers, while favoring the number of intramolecular reactions within polymer chains and potentially favoring the single reaction of glyoxal with the polyacrylamide polymer, resulting in the polymer with side-attached aldehyde functional groups. It is desirable to prepare GPAM resin with a high final GPAM concentration. This increases the capacity and utilization of the reaction vessel and reduces the transportation and storage costs of the GPAM resin. Therefore, it is desirable to conduct the acetaldehyde acidification reaction at a higher solids content level, i.e., at a higher total starting cationic acrylamide polymer, i.e., prepolymer concentration. The usable concentration will depend on the molecular weight of the prepolymer and the ratio of glyoxal to acrylamide groups. As mentioned above, the usable solids content can be defined by the RW (Responsibility Weight). Conducting the reaction at a higher solids content can also be used to determine how the solids content affects intermolecular crosslinking, thereby achieving the desired increase in the final GPAM molecular weight. Finally, the ability to adjust the solids content of the reaction can be used to influence the relative amounts of intermolecular and intramolecular crosslinking. The more isolated the polymer chains, the higher the percentage of intramolecular reaction relative to intermolecular reaction.

[0084] The second part is the molecular weight of the prepolymer used to form the GPAM resin. Using a lower molecular weight prepolymer for the aldehyde reaction reduces the number of crosslinks between polymer molecules. The molecular weight of the prepolymer can be high or low and still achieve targets such as high reactivity and initial wet strength, which often depends on two other factors of the RW.

[0085] The third part concerns the ratio of reactive aldehyde groups of glyoxal to the functional groups on the prepolymer that react with the aldehyde. In one embodiment, this can be considered as the ratio of the molar number of glyoxal to the molar number of acrylamide groups in the prepolymer. Adding excess glyoxal beyond a certain level leads to more single reactions of glyoxal, resulting in more final reactive functional groups. Surprisingly, there is an upper limit to the percentage of acrylamide groups in the prepolymer that tend to react with glyoxal to form reactive aldehyde functional groups. This limit is less than 100% of the acrylamide groups reacting. Assuming the reaction is completed at a solids content of about 10%, this limit is about 45%, where the total acrylamide groups reacting are limited to about 60 to 70%, and the maximum percentage of groups reacting with glyoxal without a second reaction is also about 60 to 70%. Not bound by theory, however, there may be steric hindrance to the complete functionalization of the polymer by glyoxal. This determines a point where the percentage of reacting acrylamide groups tends to stop increasing or the rate at which they occur becomes negligible. The polymer of this disclosure reacts with the aldehyde group to the maximum possible extent. The ratio of aldehyde to available functional groups exceeds the amount required to achieve complete reaction. The ratio of glyoxal to acrylamide may be important for obtaining GPAM resins, which often depend on the RW (reacting temperature).

[0086] The balance of these three factors determines the RW. These three factors are: 1) the solids content, i.e., concentration, of the prepolymer at the start of the reaction; 2) the molecular weight of the prepolymer; and 3) the ratio of the moles of glyoxal to the moles of acrylamide groups on the prepolymer. The goal is again to obtain a relatively high level of aldehyde functional groups on GPAM, which results in a relatively high level of initial wet strength imparted to the GPAM-added paper, and a nearly uncontrolled increase in viscosity of the acetaldehyde acidification reaction mixture; the final aqueous GPAM resin composition has a high solids content and good storage stability. In one embodiment, where glyoxal is added to the prepolymer at a relatively rapid, stable rate (e.g., within 15 minutes or less), the RW can be defined as: the concentration of the prepolymer in the reaction composition at the start of the aldehyde reaction (expressed as a weight percentage) multiplied by the molecular weight of the prepolymer described by the RSV, multiplied by the RSV again, and divided by the ratio of the moles of added glyoxal to the moles of acrylamide groups on the starting cationic acrylamide polymer. For this example, it is assumed that the glyoxal molecule is a dialdehyde compound and that the prepolymer contains repeating units of acrylamide and cationic monomers. The solids content in the RW calculation is the weight % concentration (solids content) of the prepolymer resin at the start of the reaction. The ratio of the number of moles of glyoxal added to the reaction to the number of moles of acrylamide groups on the prepolymer before the reaction begins is used. Finally, the molecular weight is the molecular weight of the prepolymer before the reaction occurs, expressed by RSV (this method is described elsewhere in this application). It is also assumed that the residual monomers in the prepolymer are very few, making the RSV measurement accurate.

[0087] In various implementation schemes, RW = (RSV x RSV x solids content) / the ratio of glyoxal to acrylamide.

[0088] In one implementation, RW can be less than 0.14, or less than 0.12, or less than 0.1. For this value, it is assumed that an acrylamide-based prepolymer and glyoxal are used and that the prepolymer is completely water-soluble.

[0089] In one embodiment, the acrylamide polymer, i.e., the prepolymer, that can be glyoxylated can have a polydispersity of less than 4 and a compositional variation that produces a glass transition temperature range of less than 30°C from start to finish. It is known that when industrially manufactured, the various polymer chains of the polymer can have wide molecular weights and wide ranges of composition. The polymer should be considered as a whole rather than individual polymer chains. However, in various embodiments, at least 80%, at least 90%, or at least 95% of the reaction process will fall within the range of RW (Responsibility Variable). When reaction conditions change, it is impossible to define every aspect of the RW variables. Those skilled in the art of polymerization and glyoxylation will understand the consequences of various variables such as pH or temperature during the glyoxylation reaction or the molecular weight distribution or compositional consistency of the initial acrylamide polymer.

[0090] In one embodiment of this disclosure, when glyoxal is added to the prepolymer solution, the solids content, i.e., the concentration of the prepolymer, as defined in RW, can be about 5% to 20%, or 7% to 15%, or 8 to 13% by weight. In one embodiment of this disclosure, the RSV of the prepolymer can be about 0.07 to 1.5, or about 0.07 to 1.0, or 0.08 to 0.7, or 0.09 to 0.4 dL / g dry weight. In one embodiment of this disclosure, the molar ratio of glyoxal to acrylamide groups can be about 0.65 to 3, or 0.7 to 2.5, or 0.8 to 2.

[0091] One advantageous embodiment involves a sufficient excess of glyoxal to achieve high glyoxylation and aldehyde reactivity without gelation. Another set of advantageous conditions includes an excess level of glyoxal and a molecular weight of the GPAM prepolymer such that the reaction reaches the limit of the amount of aldehyde reacting with the acrylamide groups and does not gel even when the reaction is allowed to continue for an extended period. In some embodiments, the reaction tends not to gel even without monitoring viscosity changes. This represents a significant advantage in the manufacturing process by eliminating the need to monitor viscosity and eliminating the possibility of gelation occurring in the reactor. It is also advantageous that less viscosity increase occurs during the reaction of glyoxal with the prepolymer compared to the formation of conventional GPAM resins. The reaction time can even vary for several hours without significant changes in viscosity, molecular weight, or even the final properties of the GPAM resin used to generate the initial WS in paper. On the one hand, the ratio of the RSV of the final GPAM resin to the RSV of the starting polymer is less than 3, or less than 2, or less than 1.5, or less than 1.2.

[0092] It is also advantageous to carry out the glyoxylation reaction at a higher concentration (i.e., solid content) of the prepolymer to optimize the efficient use of the reactor vessel and obtain a final product with a higher GPAM concentration.

[0093] In another non-limiting embodiment, the GPAM resin remains water-soluble under high levels of reaction with glyoxal, such as reactive polymer groups such as acrylamide groups, greater than about 55% and greater than about 60%, greater than about 65%, and greater than about 70%.

[0094] In other embodiments, the method includes removing excess glyoxal at the end of the reaction or from the final product. Methods well-known in the chemical manufacturing field, such as membrane filtration, can be used. After removing excess glyoxal and adjusting the pH, the final GPAM resin may have a solids content of about 2 to 25%, about 5 to 20%, about 7 to 15%, or about 8 to 13% by weight. After removing excess glyoxal and adjusting the pH, the residual glyoxal level may be less than about 15% or less than about 13% or less than about 10% or less than about 5% or less than about 2% or less than about 1% by weight of the final GPAM polymer, or after removing excess glyoxal and adjusting the pH, the residual glyoxal level may be less than about 1.2% or less than about 1% or less than about 0.8% or less than about 0.5% or less than about 0.2% or less than about 0.1% by weight of the final GPAM resin composition.

[0095] In another aspect of this disclosure, the process of reacting glyoxal with the prepolymer can be modified to give different reaction windows. In one set of embodiments, glyoxal is added to a cationic acrylamide prepolymer. In another embodiment, different GPAM compositions can be obtained, for example, by reversing the order of addition in a controlled manner. In particular, the prepolymer solution can be slowly added to the glyoxal solution or added in stages to the glyoxal solution to produce different GPAM compositions. The added components and residual glyoxal levels in the compositions can be the same or different. Not bound by theory, what varies significantly is the distribution of acetaldehyde acidification and intermolecular crosslinking within the GPAM resin. Furthermore, the concentration of the reacting polymer or GPAM resin can be readily adjusted during the process, and this ratio can also be changed during the process. The relative yield (RW) can be increased by diluting the reaction as it proceeds, resulting in a lower concentration of prepolymer in the later stages where intermolecular crosslinking is more likely to occur. Similarly, changing this ratio so that adding more glyoxal in the later stages of the reaction when there is a greater chance of crosslinking can increase the RW. It is impossible to describe every variation in the addition time and rate of the acetaldehyde acidification reaction. For the purposes of this disclosure, there are two types. The first, to which the extensive discussion above applies, is the prior art of adding glyoxal to a polymer solution. The second is a different embodiment of this disclosure, in which a prepolymer is added to glyoxal.

[0096] In this alternative method of slowly adding the prepolymer to a glyoxal solution, the initial glyoxal to acrylamide ratio tends to start at a higher value. For example, when only one-tenth of the prepolymer is mixed with glyoxal, the glyoxal to acrylamide ratio can be, for example, ten times higher than when all of the glyoxal is added to the prepolymer at once. Therefore, at the start of this improved method, a high degree of acetaldehyde acidification and very little (if any) intermolecular or even intramolecular crosslinking can be achieved. The amount, rate, and properties of the polymer added to the glyoxal can ensure that at least 50% of the final reactive aldehyde groups to be present on the final GPAM are present on the formed GPAM before all the polymer is added to the glyoxal. The amount, rate, and properties of the polymer added to the glyoxal can ensure that at least about 65% or at least about 80% of the polymer is formed with final reactive aldehyde groups before all the polymer is added to the glyoxal. In the alternative acetaldehyde acidification process described herein, the pH of the GPAM can be reduced to 3.2, and some excess glyoxal can be removed.

[0097] As more polymer is added, this ratio remains favorable for the formation of reactive aldehyde groups until most of the glyoxal has been used and the remaining amount is below the aforementioned amount. The process can continue to generate a portion of GPAM that can have a higher molecular weight due to crosslinking. Surprisingly, this reversal method results in a lower overall viscosity increase in the final GPAM resin compared to using the same prepolymer, glyoxal ratio, and solids content as defined in the RW.

[0098] An alternative is to switch to a different prepolymer near the end of the reaction process when there is limited glyoxal available for the reaction. If the second prepolymer can have a low RSV, the reaction window remains open, resulting in a smaller chance of gelation. The overall effect of the various embodiments is an improved ability to operate with higher molecular weight polymers or at higher prepolymer concentrations or with a lower overall glyoxal to acrylamide ratio.

[0099] In the GPAM resin produced by this alternative method, the use of glyoxal in excess mol% relative to the acrylamide groups on the cationic acrylamide polymer throughout the acetaldehyde acidification reaction results in highly reactive GPAM, with at least 20% of the acrylamide groups forming reactive aldehyde functional groups. This leads to excellent storage stability and efficient imparting of wet strength to paper. Furthermore, in the final GPAM resin, the equivalent number of functional aldehyde groups on the GPAM divided by the equivalent number of residual glyoxal in the GPAM resin will be greater than 1.2, making the GPAM resin safer for use in papermaking. In the new method of adding the polymer to glyoxal, the so-called reverse acetaldehyde acidification method, less viscosity increase occurs during the acetaldehyde acidification process compared to the rapid addition of glyoxal to the polymer. The effect is an expanded reaction window, allowing the use of starting cationic acrylamide polymers with higher RSV, or allowing for higher total polymer solids or final polymer solids during the acetaldehyde acidification reaction, or allowing for a lower ratio of the molar amount of glyoxal to the molar amount of acrylamide groups on the cationic acrylamide polymer.

[0100] Purification process

[0101] In various embodiments, the method includes a step of removing excess glyoxal. In one embodiment, the method utilizes a membrane filter for removing lower molecular weight materials. The size of the membrane opening can be adjusted. For example, an Amicon ultrafiltration unit can be used with a membrane with a rejection value of approximately 1000 g / mol. Membrane technology is described in detail in various references, such as Dead End Membrane Filtration ENE 806 Laboratory Feasibility Studies in Environmental Engineering Spring 2006, reported by Ahsan Munir, Instructor: Dr. Syed A. Hashsham (PID: A37589962), which is expressly incorporated herein by reference in various non-limiting embodiments. The device can be from Amicon or Several companies have obtained [the technology / resources]. Membrane filtration technologies described in U.S. Patents 7,932,349 and 8,101,710 can be used to remove excess residual glyoxal via processes such as percolation, the entire contents of which are expressly incorporated herein by reference. The filtration process can be carried out without excessive shear forces, which would either tear the polymer chains or generate excessive heat, leading to the loss of functional groups. Alternatively, glyoxal can be separated from the polymer by precipitating the polymer in water, washing the polymer in water, and dissolving the polymer in water. Other methods for removing excess glyoxal known in industry can be used.

[0102] Characterization methods

[0103] The molecular weight of the prepolymer (the polymer to be functionalized with glyoxal) may be important relative to the RW. In this paper, the molecular weight can be expressed as the specific viscosity (“RSV”) of 1% of the material at 25°C (in a 1M aqueous solution of NH4Cl).

[0104] The relative viscosity (RSV) of GPAM or GPAM resin can be determined using the following method. The RSV of a 1% material composition (in a 1M NH4Cl aqueous solution) is determined at 25°C using both a Ubbelohde viscometer and a Brinkmann viscometer. The flow time of the 1% material solution and the pure solvent is measured, and the relative viscosity (Nrel) is calculated. The specific viscosity is calculated from the relative viscosity. This method is based on ASTM D446. ​​The unit of RSV is dL / g dry weight.

[0105] Several instruments are available for determining RSV. For example, the Cannon MiniPV instrument, the Ubbelohde Viscometer tube (available from Visco Systems, Yonkers, NY), or the Brinkmann Viscotimer C (available from Brinkmann Instruments Inc., Cantiague Rd., Westbury, NY 11590) can be used. For this work, the sample was kept at a constant temperature of 25 ± 0.1 °C using an oil bath.

[0106] The solids content of an aqueous GPAM resin composition or prepolymer or acetaldehyde acidification reaction mixture can be measured by various standard methods, such as heating a 0.1g sample in an aluminum pan in an oven at 110°C until there is no noticeable weight loss, or using a moisture balance, such as a moisture balance manufactured by Mettler.

[0107] Viscosity during the acetaldehyde acidification reaction can be monitored to understand the progress of the reaction. The viscosity of the reaction mixture can be measured using a tube flow viscometer, where the time it takes for a specific volume of GPAM resin composition to be discharged through a tube is measured. Typically, the tube size is chosen such that the discharge time between two marks on the tube is approximately 5 seconds for a flow of 5 ml of composition at the start of the reaction. For the examples of this disclosure, the same tube viscometer is used in all these examples. The viscosity is recorded as “flow viscosity” in seconds. The final viscosity may increase by approximately 10 times. The viscosity change from start to finish and the rate of change from one measurement to another are recorded. The reaction composition in the reaction vessel is tested by drawing a small amount of the mixture into the viscometer and immediately testing the viscosity. A rapid increase within minutes may indicate that GPAM is rapidly crosslinking and may soon gel. As the viscosity increases slowly and steadily, GPAM can easily reach higher levels of crosslinking. When almost no viscosity increase occurs, the reaction can have minimal crosslinking formation and can proceed for a specific time rather than by monitoring viscosity.

[0108] To measure the level of free glyoxal in an acrylamide sample acidified with acetaldehyde, a reactive polymer mixture is reacted to form an adduct with UV absorbance. The UV absorbance at 295 nm is then measured to give the glyoxal level. The reaction with glyoxal is carried out by dilution with water and reaction with Girard's reagent T (99%, CAS No. 123-46-6) at pH 2.9 and 40°C. This reagent reacts with the α-dicarbonyl functional group of glyoxal. The glyoxal thus obtained for use in the reaction (typically a 40% solution) is used to calibrate the method. Sodium formate buffer is prepared by mixing 4.3 ml of formic acid with enough glyoxal-free water to achieve a total liquid volume of 1 liter. The pH is adjusted to 2.9 with 10 M sodium hydroxide solution (also glyoxal-free) under stirring. 1 ml of this mixture is mixed with 2 mg of Girard's reagent T. Fresh solutions are prepared for testing. As a glyoxal reference, 0.1 mL of glyoxal was added to a 50 mL volumetric flask (tare weight) and the weight was recorded to the nearest 0.0001 g. The flask was then filled to the mark with glyoxal-free water. The sample was tested using a calibration sample and an acetaldehyde-acidified polymer solution. 0.1 mL (accurate to 0.0001 g) of the sample was added to the vial, followed by 25 mL of glyoxal-free water. Then, 0.05 mL of this solution was removed and mixed with 10 mL of Girard solution. The mixture was heated at 40 °C for 30 minutes. The sample was then transferred to a cuvette and the UV absorbance was determined.

[0109] In various implementation schemes, a high level of aldehyde reactivity is the focus. The reactivity level and the level of glyoxal that has reacted twice can be measured by protons or... 13C10 NMR analysis was used for measurement. The proton assay determined the extent to which acrylamide reacted with glyoxal to form a reactive aldehyde (single reaction of glyoxal) and also determined the total extent of reaction between acrylamide and glyoxal (single and double reactions of glyoxal). The equipment used in this work was an FT-NMR spectrometer equipped with a reverse 5mm probe and a 1H operating frequency of 400 MHz or higher. Reagents could be dimethyl sulfoxide d6, 99.9% atomic deuterium and deuterium oxide, 99.9% atomic D. Two methods were used to obtain the most accurate results.

[0110] 1. The first method measures acetaldehyde-treated resin in the receiving state with the addition of d6-DMSO. This method provides the level of reacted acrylamide groups based on acrylamide residues in the polymer. The total reaction of acrylamide groups is based on amide matrix atoms, and the sample pH must be in the acidic range, i.e., approximately 3.0 to 3.5. When the byproduct concentration is high, the intensity of the byproduct signal tends to potentially overlap and affect the integration of the NMR signal. Therefore, measures can be taken to remove byproducts, such as using percolation membrane filtration processes.

[0111] 2. The second method utilizes a mixture of the reacted polymer and D2O, and provides better accuracy for the single reaction of glyoxal with acrylamide. The total amount of acrylamide reacting with glyoxal is derived from the integral of all amide and hydroxyl protons. Glyoxal byproducts are typically removed via a percolation membrane filtration process to obtain a fairly accurate integral. The results of each process can be combined. Furthermore, an internal standard can be added.

[0112] The integrals obtained between 0.4 and 2.8 ppm correspond to the measurement of all polymer backbone protons; the integrals obtained between 2.8 and 3.9 ppm correspond to the level of DADMAC protons given (when DADMAC is used in the polymer); the integrals obtained between 4.77 and 4.97 ppm correspond to the level of dihydroxymethyl protons given from the single reaction of glyoxal with acrylamide; the integrals obtained between 4.95 and 5.9 ppm correspond to the measurement of all amide hydroxyl protons given from both the single and double reactions of glyoxal with acrylamide groups; and the integrals obtained between 7.75 and 9.25 ppm correspond to the level of providing all amide matrix protons.

[0113] The stability of the final GPAM resin can be monitored by aging the sealed sample in an oven at 32°C, 40°C, or 50°C, and then measuring the changes in the level of reactive aldehyde functional groups and the sample viscosity over time.

[0114] In various additional non-limiting embodiments, the method includes the step of adding glyoxal to the polymer solution at a rate that ensures complete addition before the final glyoxal-acrylamide reaction reaches 5%. In other embodiments, glyoxal is added to the polymer solution. In further embodiments, excess glyoxal is optionally removed, for example, by membrane separation. In other embodiments, the mentioned glyoxal level is based on the glyoxal level at which no reaction has occurred.

[0115] In other embodiments, the degree of reaction between glyoxal and the acrylamide groups of the polymer is such that at least 40% of the acrylamide groups are converted into reactive aldehyde functional groups; the at least one cationic repeating unit is formed from one or more of diallyl dimethylammonium chloride (DADMAC), 2-(acryloyloxyethyl)-trimethylammonium chloride, 2-(dimethylamino)ethyl acrylate, 3-acryloylaminopropyl-trimethylammonium chloride, dimethylaminopropylacrylamide, or combinations thereof; greater than about 60 mol% of the acrylamide repeating unit of the polymer reacts with glyoxal; the molar ratio of the equivalent number of reactive aldehyde groups to the equivalent number of glyoxal groups in the composition is... The composition contains about 10% by weight of a cationic resin with a pH of about 3.2 and exhibits a loss of less than about 10 mol% of the equivalent number of reactive aldehyde groups after aging at about 40°C for about 30 days; the composition contains about 10% by weight of a cationic resin with a pH of about 3.2 and exhibits a viscosity increase of less than about 50% after aging at about 40°C for about 30 days; the composition contains about 10% by weight of a cationic resin with a pH of about 3.2 and exhibits an increase of less than about 30% of the equivalent number of free glyoxal after aging at about 40°C for about 30 days; and the composition has a solids content of at least about 14%. In the relevant embodiments, based on the level where no reaction occurs, the ratio of the molar number of glyoxal to the molar number of the at least acrylamide repeating units of the starting cationic polymer is greater than about 2:1; greater than about 60 mol% of the acrylamide repeating units of the polymer react with glyoxal; and the molar ratio of the equivalent number of reactive aldehyde groups in the GPAM resin composition to the equivalent number of glyoxal in the composition is greater than about 1.5.

[0116] Additional Implementation Plan

[0117] This disclosure also provides a method for forming paper, the method comprising the following steps:

[0118] Provides aqueous suspensions of cellulose fibers;

[0119] An aqueous composition is added to a suspension, wherein the aqueous composition comprises:

[0120] Water; and

[0121] A cationic polymer resin having at least one reactive aldehyde group and formed by the reaction of glyoxal with a polymer;

[0122] The polymer comprises at least one acrylamide repeating unit and at least one cationic repeating unit;

[0123] Wherein, based on the total weight of the polymer, the equivalent number of reactive aldehydes divided by the equivalent number of residual glyoxal is greater than about 1.2, preferably greater than about 1.5, and more preferably greater than about 2;

[0124] Prior to the reaction, the polymer has more than about 50 mol% of acrylamide repeating units and about 2 to about 30 mol% of cationic repeating units;

[0125] In this process, more than about 5 mol% of the acrylamide repeating units in the polymer are converted into reactive aldehyde groups in the cationic polymer resin.

[0126] Cellulose fibers are used to form paper; and

[0127] The paper is dried to produce an initial wet tensile strength that is at least 10%, 15%, 20%, 25%, or 30% greater than that of a control paper when only about 15 mol% of the at least one acrylamide repeating unit is converted into a reactive aldehyde group.

[0128] Example

[0129] Example 1 - Comparative Reference GPAM Resin

[0130] This embodiment provides a typical method and results for GPAM temporary wet strength resin.

[0131] Step 1

[0132] A polymer was prepared from acrylamide (AM) and diallyl dimethyl ammonium chloride (DADMAC). 4.9 g of a 65% by weight aqueous solution of DADMAC (0.0197 mol) and 17.6 g of water were added to a flask and bubbled under nitrogen. The solution was heated to 65 °C and maintained at that temperature. 61.9 g of a 43% by weight aqueous solution of AM (0.375 mmol) was added to the flask under nitrogen atmosphere. AM was added at a constant rate over 90 minutes. 1.57 g of a 12.1% sodium persulfate solution and 4.05 g of a 37% sodium metabisulfite solution were added to the same flask. The latter two solutions were added at a constant rate over 100 minutes. The initiator solution was bubbled under nitrogen before addition. The reaction was stopped after 150 minutes. The final solids content of the polymer composition was determined to be 35%. The RSV of the polymer was determined to be 0.118 dL / g dry weight.

[0133] Step 2

[0134] 21.8 g of prepolymer solution was placed in a flask at 20 °C. 70.4 g of water was added. 5.6 g of a 40% glyoxal aqueous solution was added. The initial molar ratio of glyoxal to AM groups before the acetaldehyde acidification reaction was 0.4 moles of glyoxal to 1 mole of acrylamide groups on the polymer. The pH of the reaction was immediately adjusted to 8.7 with a 4% sodium hydroxide solution and maintained at pH 8.7 until the flow viscosity in a 1.48 mm inner diameter tube increased to 22 seconds. Using the same method, the initial viscosity was approximately 6 seconds. Further extension of the reaction would lead to polymer gelation. The reaction was terminated by lowering the pH to 3.3 with a 20% sulfuric acid solution.

[0135] NMR spectroscopy analysis of the final GPAM polymer revealed that 15 mol% of acrylamide groups were modified to have reactive aldehyde functional groups. This means that, on average, 15% * 0.95, or 14%, of the monomer units per polymer chain have reactive aldehyde functional groups. Therefore, if the average length of the polymer chain is 30 monomer units, approximately 4.2 monomer units will have aldehyde functional groups on average. In the case of two glyoxal reactions (two aldehyde groups), intramolecular or intermolecular crosslinks are formed. In this example, the reaction was carried out at a level that formed 7.6 mol% of the initial number of AM groups or 7.2% of all monomer units. For this sample, the reactivity of the final polymer was 1.6 meq / g. The calculation is as follows: The average molecular weight of the repeating units on the polymer is 0.05 * 161.5 + 0.95 * 71.08 = 75.6 g / mol. 0.14 mol of glyoxal was added to this. For each, 58 g / mol is added to the average molecular weight of each repeating unit of the polymer. Also added to the polymer is 0.072 / 2 of the glyoxal from the two reactions, meaning an additional 0.036 * 58 is added to the average molecular weight of the repeating unit. The final average molecular weight of each repeating unit of the polymer is 85.8 g. Therefore, each 85.8 g contains 0.14 mol of reactive aldehyde groups, or 1.6 meq / g of reactive aldehyde groups.

[0136] To calculate meq / g, assume the molecular weight of the repeating unit with aldehyde reactivity from the single-reaction glyoxal is 133.6 g / mol, where glyoxal is in a basic aldehyde form. Assuming glyoxal is reacted twice, 58 g of glyoxal units are added to both monomer units, and the average weight of each monomer unit is therefore 75.6 + 29 = 104.6. This can be considered as the presence of 5 mol% DADMAC groups, 14 mol% acrylamide groups with aldehyde functional groups, 7.2 mol% acrylamide groups with glyoxal crosslinking, and 95 - 14 - 7.2 = 73.8 mol% acrylamide groups. End groups are not included in the calculation. 0.05 * 161.5 + 0.14 * 133.6 + 0.072 * 104.6 + 0.738 * 71.08 = 86.7; 0.14 mol / 86.7 g = 00016 equivalents / gram, or 1.6 meq / g.

[0137] For this embodiment, a sample of the aqueous GPAM resin composition with a 10% solids content has a Brookfield viscosity of approximately 10 cps at 22°C.

[0138] At the start of the reaction, the prepolymer concentration (i.e., the solids content as defined in the RW) was approximately 7.8% by weight. The RSV was 0.118 dL / g dry weight.

[0139] In this embodiment, the RW is 0.118 * 0.118 * 7.8% / 0.4 = 0.27.

[0140] The residual glyoxal level in the 10% solution was measured to be 0.9% by weight. Therefore, the residual glyoxal is 1.6 meq / g. The SF is 1.6 / 1.6, which is approximately 1.0.

[0141] Example 2: GPAM with higher SF within RW

[0142] Step 1 Aggregation

[0143] AM:DADMAC is a polymer of 80:20

[0144] Acrylamide polymers were prepared as follows: 93.3 g of water, 31.8 g of 65% DADMAC aqueous solution, and 15.6 g of 50% acrylamide aqueous solution were added to a reaction vessel. The solution was bubbled with nitrogen for 30 minutes. A nitrogen layer was then maintained for the remainder of the reaction. The contents were heated to 45°C. When the temperature reached 45°C, 4 ml of 5% sodium persulfate solution and 4 ml of 10% sodium metabisulfite solution were added. Then, 69.4 g of each solution was added at a steady rate over 345 minutes. The initiator solution was bubbled with nitrogen before use. The monomer mixture was also added when the vessel temperature reached 45°C. A mixture of 97.4 g of 50% acrylamide solution and 26.1 g of 65% DADMAC solution was added after 195 minutes. After reaching 45°C in 210 to 240 minutes, an additional 15.6 g of acrylamide solution was added. After the addition of the initiator and monomer mixture began, the temperature was raised to 55°C and maintained at that temperature for 345 minutes. The temperature was then raised to 70°C and maintained for 90 minutes. During the reaction, the pH was adjusted to 6 several times at equal intervals using sodium bicarbonate solution. The reaction was then cooled to room temperature and stored for later use. The measured specific viscosity (RSV) of the polymer mixture with 1% solids content was 0.114 dL / g dry weight.

[0145] Step 2: Acidification with glyoxylate

[0146] In a reaction flask, 250 g of a 10% polymer aqueous solution was prepared, and the pH of the polymer described in this example was raised to 8.9 using a 10% NaOH solution. Within seconds, 48.7 g of a 40% glyoxal aqueous solution was added to the flask. The molar ratio of glyoxal to acrylamide was 1.5. This means the ratio of aldehyde groups to acrylamide groups was 3.0. The mixture was stirred for 4.5 hours while maintaining the pH at 8.9 using a 10% NaOH solution. The pH was then lowered to 3.2 using a 10% sulfuric acid solution. The RW was 0.073 (obtained from a solids content of 8.37, an RSV of 0.114, and a ratio of 1.5). During the reaction, the flow viscosity increased from 4 to 6 over 6 hours. In other words, the reaction was stable, did not readily gel, and did not require monitoring at the plant.

[0147] In this embodiment, the reactivity of the GPAM resin was measured by proton NMR spectroscopy using the same method described in this document and used in Example 1. The ratio of the number of moles of reacted AM groups to the total number of moles of AM was determined. The number of moles of reacted AM groups was then determined based on the theoretical number of moles of AM in the polymer.

[0148] For the aqueous GPAM resin composition, some excess glyoxal was removed by membrane filtration at 1000 g / mol. The final solids content after filtration was 4.41% by weight, and the glyoxal level was 0.49% by weight. The glyoxal / total solids ratio (meq / g) was 1000*(0.49 / 58) / 4.41 = 1.91. The RSV of the reacted and filtered polymer was 0.143 dL / g dry weight.

[0149] For this embodiment, the safety factor, i.e., the meq / g of reactive aldehyde and the meq / g of residual glyoxal, is 2.84 / 1.91 = 1.49, compared to only 1.0 in Example 1.

[0150] For this example, the level (mol%) of aldehyde functional groups in each polymer repeating unit was 31.9%, and the level of intermolecularly or intramolecularly crosslinked acrylamide-based repeating units was 18.7%. The ratio of reactive aldehyde AM groups to crosslinked AM group portions was 31.9 to 18.7, or a ratio of 1.7. Despite the presence of significant crosslinking, the flow viscosity showed almost no increase during the acetaldehyde acidification reaction. This was an unexpected result. Furthermore, in Example 2, more acrylamide groups reacted with glyoxal compared to Example 1, but the increase in flow viscosity was smaller. This was also an unexpected result. The relatively small reaction window for the increase in flow viscosity is defined by this and other results.

[0151] The wet strength properties of the final GPAM resin were compared with those of Example 1, and the results are listed in the table below. Paper samples were prepared on a Noble and Woods hand-made paper forming machine using the following procedure.

[0152] Prepare pulp blends for papermaking. It is a mixture of 70% hardwood and 30% softwood, with a consistency of 3-4% and refined to a Canadian Standard Freeness of 500. Handmade paper is produced from this pulp and additives using standard hard water at pH 6 on a Noble and Wood forming machine. Wet strength chemicals are added to the mixing tank. The resulting paper is 8 inches x 8 inches in size and weighs approximately 2.6 g when fully dried (approximately 60 g / m² paper, also known as 40 lb paper, meaning 3000 square feet of paper weighs 40 lbs). These papers are aged for at least one week. The paper is cut into 0.75-inch strips with a 1 / 4-inch hole added in the middle to define the location of failure during tensile testing. The tensile strength of the paper strips after wetting with water for different durations is determined. Six paper samples are measured for each sample at each wetting time. The decay in wet strength is expressed as a percentage of the decay after wetting for two different durations, compared to the wet strength after 3 seconds of wetting. For the absorbent paper of this embodiment, three seconds is selected as the wetting time length to obtain the initial or initial wet strength value. During the strength test, this 3-second measurement is automatically controlled by a computer. When stating or comparing the wet strength values ​​of the treated paper, a baseline value can be subtracted, defined as the strength of an equivalent paper without GPAM added after wetting for 2 hours. The baseline of the paper sample in the embodiments of this disclosure is approximately 0.8 Newtons per half-inch width.

[0153] For each embodiment, the level of GPAM added to the paper was 0.35% of the dry pulp weight on a dry basis. The results are as follows.

[0154]

[0155] WS = Wet Strength (Newtons / half-inch width)

[0156] The result of Example 2 is GPAM with higher reactivity and higher wet strength, while being more stable during manufacturing, eliminating the need for viscosity monitoring during the reaction. The RW is 0.073, compared to 0.27 for Example 1.

[0157] The GPAM of Example 2 is also safer to use because there is less residual reactive glyoxal and therefore less glyoxal is added to the paper during its use for a given final wet strength. Furthermore, the GPAM of Example 2 unexpectedly provides a higher level of wet strength attenuation—59%, compared to 52% in Example 1.

[0158] Example 3: Polymer with an AM:DADMAC ratio of 80:20

[0159] Step 1: Aggregation

[0160] Acrylamide polymers were prepared in a manner similar to that of Example 2, except that the initiator level was adjusted to obtain a final RSV of 0.143 dL / g dry weight and a measured weight-average molecular weight of 27,000.

[0161] Step 2: Acidification with glyoxylate

[0162] The polymer from this example was subjected to acetaldehyde acidification in a manner similar to that of Examples 2 and 3. 250 g of a 10% aqueous polymer solution was prepared. The pH was raised to 8.9 using a 10% NaOH solution. 65.5 g of a 40% glyoxal aqueous solution and 200 g of water were added. The mixture was stirred for 6 hours while maintaining the pH at 8.9 using a 15% NaOH solution. After reacting for 6 hours, the pH was then lowered to 3.2 using a 10% sulfuric acid solution. The initial polymer solids content was 4.85%. The molar ratio of glyoxal to acrylamide groups was 2.0. The relative yield (RW) was 0.143 * 0.143 * 4.85 / 2.0 = 0.050.

[0163] During the acetaldehyde acidification reaction, the flow viscosity increases from 5 to 6. Therefore, the reaction becomes extremely stable over time and is thus consistent with this low RW. Monitoring the increase in viscosity is unnecessary in a production environment.

[0164] NMR spectroscopy measurements revealed that the final GPAM possessed 33.0% molar reactive aldehyde functional groups. The amount of acrylamide reacting with glyoxal in the two reactions was 14.2%. Therefore, the reactivity was 2.97 meq / g.

[0165] The one from Solenis is called Hercobond TM The wet strength properties of commercially available GPAM resins, specifically 1194 resin (1194), were compared, and their characteristics were very similar to those of the GPAM resin in Example 1. The papermaking and testing conditions were very similar to those in Examples 1 and 2. The results are listed in the table below.

[0166]

[0167] WS = Wet Strength (Newtons / half-inch width)

[0168] The highly reactive GPAM of this embodiment has a low RW and is very stable during glyoxylation. It has a high level of aldehyde reactivity and provides improved wet strength and large wet strength decay.

[0169] Example 4

[0170] Glyoxylation of the polymer from Example 2

[0171] 250 g of a 10% polymer aqueous solution was prepared from the polymer of Example 2. The pH was raised to 8.9 using a 10% NaOH solution. 39.06 g of a 40% glyoxal aqueous solution and 117.17 g of water were added. The ratio of glyoxal to acrylamide groups was 1.2. The mixture was stirred for 4.5 hours while maintaining the pH at 8.9 using a 10% NaOH solution. During the 4.5-hour reaction, the flow viscosity increased from 4 to 10 at a slow rate. The flow viscosity remained at 10 for the last 47 minutes. Rapid gelation or excessive viscosity increase was not possible. After 4.5 hours of reaction, the pH was then lowered to 3.2 using a 10% sulfuric acid solution. The solids content, as defined in RW, i.e., the concentration of the prepolymer at the start of the reaction, was 6.15%. At the end of the acetaldehyde acidification process, i.e., after pH adjustment, the solids content of the aqueous GPAM resin was 10.1%, and the residual glyoxal level was 1.69%. Excess glyoxal was then removed by filtration through a 1000 g / mol membrane, resulting in a solids content of 4.03% and a glyoxal content of 0.46%. The RSV of the filtered GPAM mixture was 0.189 dL / g dry weight. The reactive aldehyde content was 41.4 mol% of the acrylamide groups, and therefore 33.1% of all repeating units. The level of acrylamide groups converted to crosslinks (intermolecular and intramolecular) was 21.9%, and therefore 17.5% of all repeating units. The milliequivalent of reactive groups was 2.59. The milliequivalent of glyoxal was 1.97.

[0172] RW is 6.15*0.114*0.114 / 1.2=0.067.

[0173] SF is 1.31.

[0174] The wet strength properties of the final GPAM resin were compared with those of the GPAM in Example 1, and the tests were conducted at the same time intervals as those for the GPAM in Examples 1 and 2. The results are listed in the table below.

[0175]

[0176] WS = Wet Strength (Newtons / half-inch width)

[0177] Compared to the GPAM of Example 1, the GPAM of Example 3 has higher reactivity, higher wet strength, greater attenuation, is easier to acetaldehyde-oxidize, and is safer.

[0178] Example 5

[0179] Similar to Examples 3 and 4, the same prepolymer from Example 3 was acidified with acetaldehyde using three different ratios of glyoxal to acrylamide. The ratios were 1.7, 1.5, and 1.25. The solids content of the prepolymer at the start of the reaction was 5.82, 6.12, and 6.25, respectively. The table below lists the respective RW, as well as the increase in flow viscosity, meq / g of reactive aldehyde groups, meq of glyoxal, and RSV of the samples after excess glyoxal was removed by membrane filtration.

[0180]

[0181] As the ratio of glyoxal to acrylamide decreases, the flow viscosity (RW) increases, thus increasing the flow viscosity during the reaction.

[0182] As with the previous examples, the wet strength of the paper made from each type of GPAM was tested. The results are shown in the table below.

[0183]

[0184] WS = Wet Strength (Newtons / half-inch width)

[0185]

[0186] WS = Wet Strength (Newtons / half-inch width)

[0187] The GPAM resin disclosed herein exhibits higher wet strength. Wet strength decay remains good and is superior to the control sample. Dry strength is also improved. The sample achieves a high level of reactivity but remains stable during acetaldehyde oxidation without requiring monitoring. While the flow viscosity increases significantly during acetaldehyde oxidation when the ratio of glyoxal to acrylamide groups decreases, the rate of viscosity increase remains lower compared to previous GPAM resins. This difference is consistent with the increase in the RW value. The GPAM resin of this disclosure is again safer to use than the control sample with a safety factor of approximately 1.

[0188] The aging stability of the samples in this embodiment was also tested. The aqueous GPAM resin composition was adjusted to a solids content of 8%, and equal volumes of the composition were placed in a clean, sealed container. The samples were then stored at 50°C for up to 9 days. The relationship between flow viscosity and aging time (in days) was monitored. The effect of aging on the flow viscosity of the samples is shown below.

[0189] sky 1194 1.7X 1.5X 1.25X 0 9 11 12 11 1 9 11 12 11 2 9 11 12 11 5 11 11 11 9 6 12 9 12 7 7 12 9 10 6 8 19 8 10 6 9 114 8 10 6

[0190] The control sample began to show a rapid increase in flow viscosity after 8 days, while the new GPAM resin did not show any increase in viscosity with aging.

[0191] Reactivity was measured before aging and 9 days after aging (in meq / g). The changes are shown in the table below.

[0192] sky 1.7X 1.5X 0 2.37 2.24 9 2.47 2.42

[0193] For the new resin, the method exhibits a slight increase in aldehyde functional groups on the polymer.

[0194] The samples were also aged at 10% solids content and 40°C. The changes in flow viscosity and residual glyoxal level are shown in the table below.

[0195]

[0196]

[0197] Given that previous GPAM resins were known to have a service life of no more than about 30 days in hot weather (such as 32°C), this GPAM resin exhibits very little viscosity increase after 31 days at 40°C, and for the third resin, the viscosity increase is even small or near zero after 61 days. Similarly, the level of glyoxal produced by the reversal of the acetaldehyde acidification reaction is relatively small. This is unexpected and inventive. In various embodiments, the aqueous composition comprises about 10% by weight of a cationic resin with a pH of about 3.2, and exhibits an increase in the equivalent number of free glyoxal of less than about 30%, 25%, 20%, 15%, 10%, etc., after aging at about 40°C for about 30 days.

[0198] Example 6 – Reaction Window

[0199] Following a similar procedure to the above embodiments, various prepolymers were prepared and subjected to glyoxylation. Some were stable during the glyoxylation process, while others were unstable. The reaction window was defined by the results.

[0200]

[0201]

[0202]

[0203] The samples in the table above illustrate that when the reaction window is greater than approximately 0.1, the samples exhibit a significant increase in flow viscosity during glyoxylation, and in many cases, the reaction stops at shorter glyoxylation times. The defined reaction window is not perfect, but it can serve as a guide.

[0204] Example 7 – Reaction Window

[0205] Following a similar procedure to the above embodiments, various prepolymers were prepared and subjected to glyoxylation. Some were stable during the glyoxylation process, while others were unstable. The reaction window was defined by the results.

[0206]

[0207] Example 8 - Comparison of temporary wet strength of GPAM resin

[0208] The same procedure described above was used to test the paper additives that impart wet strength. For each embodiment, the level of GPAM added to the paper was 0.35% on a dry basis.

[0209]

[0210]

[0211] WS = Wet Strength (Newtons / half-inch width)

[0212] Example 9

[0213] As described above, there are alternative methods for preparing the GPAM resin of this disclosure. In these alternative methods, glyoxal is in significant excess relative to the acrylamide groups on the polymer at the start of the reaction between glyoxal and the acrylamide polymer. This is achieved by slowly adding the polymer to the glyoxal solution instead of adding the glyoxal directly to the polymer solution. As a result, a high percentage of the prepolymer approaches or reaches its maximum level of reaction with glyoxal during most of the reaction process, while minimal crosslinking is present. The reaction can be stopped shortly after the polymer addition is complete, or it can be continued as far as possible while maintaining the objectives of this disclosure. Surprisingly, for a given polymer RSV and the ratio of glyoxal to acrylamide groups, the increase in flow viscosity during this process is less than when glyoxal is added directly to the polymer solution.

[0214] Furthermore, in this disclosure and another aspect of the alternative method, two different prepolymers can be added, wherein the initial prepolymer added to the glyoxal can have a higher RSV when a high level of unreacted glyoxal still exists, and a second prepolymer with a lower RSV is added when the level of excess glyoxal decreases due to reaction with the first prepolymer. By adding the polymer with a lower RSV later in the process, crosslinking and therefore the occurrence of flow viscosity increases can be reduced. In another aspect, the polymer is added near the end of the reaction to utilize the excess glyoxal. In another aspect of the alternative method, at least 50% or at least 60% of the reaction between glyoxal and the acrylamide groups will occur before all the polymer has been added.

[0215] All the advantages and safety factors (SF) of the previously described compositions are achieved in the alternatives, but the RSV range of the prepolymers becomes larger.

[0216] As in the examples above, an acrylamide polymer was prepared. It contained 80 mol% acrylamide and 20 mol% DADMAC. The polymer's RSV was 0.140 dL / g dry weight.

[0217] Sample A

[0218] A similar acetaldehyde acidification procedure as described in the above embodiments was performed, wherein the molar ratio of glyoxal to acrylamide groups on the starting polymer was 1.50. Glyoxal was rapidly added to the polymer solution. After all the glyoxal had been added, the solids content of the prepolymer at the start of the acetaldehyde acidification reaction was 6.12%, as defined in RW (RW = 0.08). During the reaction, the flow viscosity increased from 5 to 47 and continued to increase with reaction time. The reaction was stopped after 4 hours and 53 minutes to prevent gelation of the reaction solution. The reaction was terminated by lowering the pH to 3.2 with a sulfuric acid solution.

[0219] Sample B

[0220] Then, an alternative glyaldehyde acidification procedure was used. A 25% polymer solution was prepared without pH adjustment. 302.8 g of a 6.33% glyoxal solution was added to a reaction flask. The pH was adjusted to 8.8 with a 10% NaOH solution. The reaction flask was kept at 22°C, and the pH was monitored. During the reaction, the pH was maintained at 8.9 by steadily adding 10% NaOH solution. 100 g of polymer solution was slowly added to the glyoxal solution at a constant rate over 2.5 hours. After all the polymer was added, the reaction continued and was finally stopped after 5 hours by lowering the pH. The flow viscosity was measured periodically. The reaction was then kept at 22°C and the pH at 8.9 throughout the entire reaction period. The flask was stirred throughout the reaction time. During the 5-hour reaction time, the viscosity increased from 3 to 19. The solids content of the RW prepolymer was 6.12%.

[0221] Each reaction product was membrane filtered to remove excess glyoxal. As shown in the previous examples, the paper samples were tested using the final GPAM sample. The temporary wet strength properties of the paper samples were then evaluated, and the results are provided in the table below.

[0222]

[0223] This alternative to glyoxylation results in less increase in flow viscosity during the glyoxylation process, allowing for greater flexibility in the process—for example, the reaction can be carried out at a higher solids content to produce the final polymer solution, or the ratio of glyoxal to acrylamide groups can be reduced. This alternative method of adding the polymer to glyoxal also produces GPAM resins with initial wet strength similar to that of the method of adding glyoxal to the polymer.

[0224] Example 10

[0225] A polymer with 80 mol% acrylamide and 20% DADMAC was prepared. The RSV was 0.169 dL / g dry weight. As shown in Example 6, it would be difficult to acetaldehyde-acidify this polymer with a glyoxal to acrylamide ratio of 1.5 and an RW solids content of 6.6% by the previously described method when glyoxal was added to the polymer solution. The RW value was 0.123. During acetaldehyde acidification, the reaction stopped after 82 minutes because the flow viscosity increased from 5 seconds to 33 seconds. The acetaldehyde acidification was repeated by the same method described in Example 9, but with the polymer solution slowly added to the glyoxal solution instead of adding glyoxal directly to the polymer. The polymer was added after 2.5 hours, and the reaction continued for another 1.5 hours. Based on the polymer concentration (as if unreacted) when all the polymer was added, the prepolymer and reaction solids content were the same. By this reversal method, the flow viscosity increased from an initial value of 2 to a final value of 11 seconds. When glyoxal is added to a polymer, the polymer, which is not easily acetaldehyde-oxidized, is easily acetaldehyde-oxidized.

[0226] During the reaction time, the flow viscosity, as measured in the previous examples, increased very little in the first 2.5 hours, then increased more rapidly. After 4 hours, the viscosity increased from an initial value of 3 to 40. In Example 6, a very similar reaction, carried out by adding glyoxal to the polymer, stopped after 82 minutes due to a rapid increase in viscosity. This alternative method allows for a much larger degree of reaction.

[0227] GPAM produced via this reversal method is filtered through a membrane to reduce residual glyoxal levels, and then used as an additive in papermaking using the same method described in the examples above. GPAM produced via this alternative method is then compared with Hercobond, a commercially available product from Solenis. TM The 1194 resin was compared. The wet strength values ​​of the paper are shown in the table below.

[0228]

[0229] WS = Wet Strength (Newtons / half-inch width)

[0230] This alternative glyoxylation method allows for better glyoxylation of acrylamide polymers with higher molecular weights (higher RSV) and produces products with excellent initial and temporary wet strength properties.

[0231] Example 11

[0232] To perform membrane separation of GPAM resin, a membrane with NP010 (Microdyn Nadir) was used. TM The VSEP series L-type device uses a polyethersulfone (PES) membrane with a nominal molecular weight cutoff of 1000 Daltons. Both are available from New Logic Research, Inc., Minden, NV. Detailed procedures for this device are described in the operating manual (version 2.1; dated March 1996) provided by New Logic International, the entire contents of which are explicitly incorporated herein by reference. The contents of the feed tank are continuously cooled to maintain the temperature between 20°C and 25°C. A pH probe is also inserted into the feed tank, and 10% by weight of sulfuric acid is added dropwise to the feed tank as needed to maintain the pH between 3.0 and 3.8. The process begins with 15 kg of GPAM resin in the feed tank with a solids content of 2% by weight. The GPAM resin is Hercobond. TM Plus 555 dry strength additive (available from Solenis, manufactured according to the procedure of Example 1 in U.S. Patent 7,875,676). Start the VSEP unit and maintain the operating pressure at 400 psi. Remove permeate to concentrate the solids in the feed tank while maintaining the temperature and pH of the feed tank. Continuously record the weight of the collected permeate. Concentrate the feed tank to a solids content of 4% by weight. Collect a permeate sample before processing the residue and set the feed solution aside. Add an additional 15 kg of GPAM resin with a solids content of 2% by weight to the feed tank and concentrate it to a solids content of 4% by weight in the same manner as described above. Then combine the two GPAM resin solutions, both with a solids content of 4% by weight, in the feed tank and collect a sample of the GPAM resin solution.

[0233] The GPAM resin solution was then concentrated from 4% by weight to 6% by weight while maintaining the temperature and pH. Again, the operating pressure was 400 psi and the weight of the collected permeate was continuously recorded. Once the GPAM resin solution reached 6% by weight, a permeate sample was collected before processing the residue. A sample of the 6% by weight GPAM resin solution was also collected. The GPAM resin solution was then progressively concentrated to 8% and 10% by weight solids, following the same procedure used to concentrate the GPAM resin solution from 4% by weight to 6% by weight solids, collecting samples of both permeate and GPAM resin solution.

[0234] The starting GPAM resin and the GPAM resin samples from membrane separation were stabilized by adding 500 ppm potassium sorbate (potassium sorbate dry weight relative to GPAM resin wet weight) and adjusting the pH to 3.2 with a 10% sulfuric acid aqueous solution. The samples were then aged at 4°C, 25°C, and 32°C using a 4°C refrigerator and incubators at 25°C and 32°C (for precise temperature control). Viscosity stability was monitored at 25°C using Brookfield viscometers. For GPAM resin samples with Brookfield viscometers greater than 10 cps, an LV series viscometer (available from Brookfield Engineering Laboratories, 11 Commerce Blvd., Middleboro, MA 02346) and a No. 1 rotor at 60 rpm were used. For GPAM resin samples with Brookfield viscometers less than 15 cps, a modified LV series Brookfield viscometer from UL was used at 25°C with a UL(00) rotor at 30 rpm.

[0235] Brookfield viscosity and glyoxal results are detailed in the table below. Cells with no value indicate that no measurement was performed.

[0236]

[0237]

[0238]

[0239] In the above text, (a) indicates that the viscosity (in cps) was measured using a modified UL LV series Brookfield viscometer at 30 rpm with a 00 rotor.

[0240] In the above text, (b) indicates that the viscosity (in cps) was measured using an LV series Brookfield viscometer at 60 rpm with rotor No. 1.

[0241] In the above text, (c) refers to the initial Hercobond. TM Plus 555 dry strength additive (starting material, sm) value.

[0242] These results indicate that GPAM resins (e.g., Hercobond) TMPlus 555 dry-strength additive can be concentrated via membrane separation to remove glyoxal while still exhibiting gel stability comparable to commercially available GPAM resins. Concentration via membrane separation did not significantly reduce the amount of side-conjugated reactive aldehyde functional groups, nor did it lead to a significant increase in residual glyoxal during aging. These results also suggest that percolation processes can be used to reduce residual glyoxal and low molecular weight oligomers.

[0243] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be understood that numerous variations exist. It should also be understood that the at least one exemplary embodiment is merely illustrative and is not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing detailed description is intended to provide those skilled in the art with a convenient roadmap for implementing the exemplary embodiments. It should be understood that various changes can be made to the function and arrangement of the elements described in the exemplary embodiments without departing from the scope set forth in the appended claims.

Claims

1. An aqueous composition comprising: Water; and A cationic polymer resin having at least one reactive aldehyde group and formed by the reaction of glyoxal with a polymer; The polymer comprises at least one acrylamide repeating unit and at least one cationic repeating unit; Where, based on the total weight of the polymer, the equivalent number of reactive aldehydes divided by the equivalent number of residual glyoxal is greater than 1.2; Prior to the reaction, the polymer has more than 50 mol% of acrylamide repeating units and 2 to 30 mol% of cationic repeating units; In this process, more than 5 mol% of the acrylamide repeating units in the polymer are converted into reactive aldehyde groups in the cationic polymer resin; The aqueous composition, after aging at 40°C for 30 days, showed a loss of less than 40 mol% of the equivalent number of reactive aldehyde groups when measured at 10% solids content and pH 3.

2.

2. The aqueous composition according to claim 1, wherein when measured at 10% solids content and pH 3.2 after aging at 25°C for 30 days, the composition exhibits a viscosity increase of less than 200%.

3. The aqueous composition according to claim 1, wherein the equivalent number of reactive aldehydes divided by the equivalent number of residual glyoxal based on the total weight of the polymer is greater than 2.

4. The aqueous composition according to claim 1, wherein after aging at 25°C for 30 days, the loss of the equivalent number of reactive aldehyde groups on the cationic polymer resin is less than 40 mol%.

5. The aqueous composition according to claim 1, wherein after aging at 25°C for 30 days, the loss of the equivalent number of reactive aldehyde groups on the cationic polymer resin is less than 20 mol%.

6. The aqueous composition according to claim 1, wherein after aging at 25°C for 30 days, the loss of the equivalent number of reactive aldehyde groups on the cationic polymer resin is less than 10 mol%.

7. The aqueous composition according to any one of claims 1-6, wherein the glyoxal reacts with the acrylamide groups of the polymer to such an extent that at least 30% of the acrylamide groups are converted into reactive aldehyde functional groups.

8. The aqueous composition according to any one of claims 1-6, wherein the at least one cationic repeating unit is formed from one or more of the following substances: diallyl dimethyl ammonium chloride (DADMAC), 2-(acryloyloxyethyl)-trimethyl ammonium chloride, 2-(dimethylamino)ethyl acrylate, 3-acryloylaminopropyl-trimethyl ammonium chloride, dimethylaminopropylacrylamide, or a combination thereof.

9. The aqueous composition according to any one of claims 1-6, wherein greater than 40 mol% of the acrylamide repeating unit of the polymer reacts with glyoxal.

10. The aqueous composition according to any one of claims 1-6, comprising 10% by weight of the cationic polymer resin at pH 3.2, and exhibiting a loss of less than 40 mol% of the equivalent number of reactive aldehyde groups after aging at 40°C for 30 days.

11. The aqueous composition according to any one of claims 1-6, comprising 10% by weight of the cationic polymer resin having a pH of 3.2, and exhibiting a 30% increase in the equivalent number of free glyoxal after aging at 40°C for 30 days.

12. The aqueous composition according to any one of claims 1-6, wherein the molar ratio of the equivalent number of reactive aldehyde groups in the cationic polymer resin to the equivalent number of glyoxal in the composition is greater than 1.

5.

13. A method for preparing the aqueous composition according to any one of claims 1-12, the method comprising the following steps: Polymerizing two or more monomers via free radical polymerization to form a polymer comprising at least one acrylamide repeating unit and at least one cationic repeating unit; The acrylamide groups of the polymer are reacted with glyoxal to form a cationic polymer resin having side-attached reactive aldehyde groups, and excess glyoxal is optionally removed to form the aqueous composition. Where the equivalent number of reactive aldehydes formed on the polymer, based on the total weight of the polymer, divided by the equivalent number of residual glyoxal, is greater than 1.2; The step of reacting the polymer with glyoxal is carried out by adding an aqueous mixture of the polymer to a glyoxal solution such that a polymer-glyoxal reaction of greater than 50 mol% occurs before 100% of the polymer in the polymer mixture is added to the glyoxal in the solution; wherein the percentage of polymer-glyoxal reaction is defined as the maximum percentage of acrylamide groups after a reaction time of 8 hours with glyoxal at 22°C and pH 8.

9. In this process, after adding 100% of the polymer in solution to achieve a certain glyoxylation level such that at least 20 mol% of the acrylamide repeating units of the polymer are converted into reactive aldehyde groups, the reaction of the polymer with glyoxal continues, and wherein less viscosity increase occurs during the polymer-glyoxal reaction compared to adding a glyoxal solution to the polymer solution. When measured at 10% solids content and pH 3.5 after aging at 40°C for 30 days, the composition exhibited a viscosity increase of less than 50%.

14. The method of claim 13, wherein the step of reacting the polymer with glyoxal is carried out by adding an aqueous mixture of the polymer to a glyoxal solution such that a final polymer-glyoxal reaction of greater than 65 mol% occurs before 100% of the polymer in solution is added to the glyoxal mixture.

15. A method for forming paper, the method comprising the following steps: Provides aqueous suspensions of cellulose fibers; Add the aqueous composition of any one of claims 1-12 to the suspension; Cellulose fibers are used to form paper; and The paper was dried to produce an initial wet tensile strength that was at least 10% greater than that of the control paper when only 15 mol% of the at least one acrylamide repeating unit was converted into a reactive aldehyde group.

16. The method of claim 15, wherein the dried paper produces an initial wet tensile strength at least 30% greater than that of a control paper when only 15 mol% of the at least one acrylamide repeating unit is converted to a reactive aldehyde group.

17. The aqueous composition according to claim 1, wherein... The degree of reaction between glyoxal and the acrylamide groups of the polymer results in at least 40% of the acrylamide groups being converted into reactive aldehyde functional groups. The at least one cationic repeating unit is formed from one or more of the following substances: diallyl dimethyl ammonium chloride (DADMAC), 2-(acryloyloxyethyl)-trimethyl ammonium chloride, 2-(dimethylamino)ethyl acrylate, 3-acryloylaminopropyl-trimethyl ammonium chloride, dimethylaminopropylacrylamide, or a combination thereof. More than 60 mol% of the polymer's acrylamide repeating units react with glyoxal; The molar ratio of the equivalent number of reactive aldehyde groups to the equivalent number of glyoxal groups in the composition is greater than 1.5; and wherein... The composition comprises 10% by weight of the cationic polymer resin at pH 3.2 and exhibits a loss of less than 10 mol% of the equivalent number of reactive aldehyde groups after aging at 40°C for 30 days. The composition comprises 10% by weight of the cationic polymer resin with a pH of 3.2 and exhibits a viscosity increase of less than 50% after aging at 40°C for 30 days. The composition comprises 10% by weight of the cationic polymer resin at pH 3.2, and exhibits an increase of less than 30% in the equivalent number of free glyoxal after aging at 40°C for 30 days; and The composition has a solids content of at least 14%.

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