Patent Application
20240337070
The present disclosure relates generally to additive compounds and compositions for papermaking and, more specifically, to performance and process additives utilizing combinations of glyoxalated cationic polyacrylamides and anionic polyacrylamides, and methods of making and using the same.
Papermaking is a complex process in which paper is prepared from pulp (e.g. wood), water, filler, and various chemicals. Paper manufacturing is among the most water intensive industries, as the processes include numerous stages reliant on substantial amounts of water and aqueous solutions being added to the cellulosic fibers (i.e., the “inflow stream”) to give a furnish, and eventually separated from the furnish (i.e., the “effluent stream”) to give the final product. In the course of a typical papermaking process, a relatively concentrated aqueous slurry of cellulosic material (i.e., “thick stock”) is diluted by addition of water to give a relatively diluted slurry of cellulosic material (i.e., “thin stock”), which is used to prepare a paper web that must be dewatered to give the final product. Throughout the papermaking process, various chemical additives are employed to improve particular properties of the process (i.e., “process aids”) and/or the final product being prepared (i.e., “functional aids”). Examples of processes aids include defoamers and antifoams, retention aids, biocides, drainage aids, formation aids, etc. Examples of functional additives include strength aids, e.g. for imparting temporary wet-strength (TWS), wet-strength (WS), and/or dry-strength (DS) to the final product.
In view of the number and complexity of required stages in a given papermaking process, and the number and amounts of additives utilized in each stage, there is increasing demand for additives that provide both process and functional improvements to a given processes. Unfortunately, however, achieving some sought after improvements may lead to a decrease in other performance factors. For example, achieving high retention, which can lead to improvements in the strength of the final product, can lead to reduced drainage and formation. Using conventional high molecular weight drainage aids can dive excellent drainage and retention, but offer little to no strength benefits, and in some instances even result in a reduced strength due to over-flocculation. Certain DS aids like polyamidoepichlorohydrins (PAE) can give excellent dry strength, but offer little to no drainage benefits and have limited repulpability. Complicating matters further, the efficiency of any given solution is strongly furnish dependent, with some of the best known dry strength and/or drainage aids failing under desired conditions, e.g. due to fines content, lignin content, and/or conductivity of the furnish system. As such, while there are programs to address these furnish derived performance reductions, there is a still present need for additives that provide exceptional dewatering and good dry strength in even the most challenging furnish systems.
One category of chemicals being increasingly explored for multi-use additive application includes glyoxalated polyacrylamide (GPAM) resins, which have been utilized in the paper industry for many years as processes aids, e.g. for improving water drainage during the papermaking process, and also as functional additives, e.g. for imparting temporary wet-strength (TWS), wet-strength (WS), and dry-strength (DS) to the final paper(s) being prepared. Typical GPAM resins are prepared by glyoxalating polyacrylamides (PAM), i.e., by reacting glyoxal with a PAM or PAM copolymer, such as those prepared from acrylamide (AM) and various anionic or cationic monomers. As but one example, diallyldimethylammonium chloride (DADMAC) is a cationic monomer utilized to prepare poly(AM/DADMAC) copolymers, which may be used as a prepolymer in a glyoxalation reaction to give the corresponding GPAM resins (i.e., glyoxalated poly(AM/DADMAC)). Unfortunately, conventional GPAM resins suffer from numerous drawbacks associated with production, storage, and use. For example, while many commercial GPAM resins are known to perform as exceptional strength aids, such resins typically underperform in difficult furnishes, especially with respect to dewatering and drainage.
Anionic polyacrylamides (APAMs) can also be used as strength aids. However, due to the net charge the use of a cationic cofactor is typically required for retention of the APAM. Moreover, while the use of APAM can also allow for higher dosing of certain cationic strength aids (e.g. with low charge-demand furnishes), APAM generally has a negative and often severe effect on drainage.
A drainage-optimized additive composition for papermaking is provided. The additive composition comprises an aqueous media and a glyoxalated polyacrylamide (GPAM) resin having a weight average molecular weight (Mw) of at least about 5 MDa and a cationic monomer content of at least about 4 mol %, alternatively at least about 10 mol %. The additive composition also comprises an anionic polyacrylamide (APAM) resin having a Mw of at least about 0.25 MDa and an anionic monomer content of up to about 25 mol %. The additive composition comprises the APAM resin and the GPAM resin in a wt/wt ratio of from about 1:99 to about 1:2 (APAM:GPAM), based on the total weight of the APAM resin and the GPAM resin. The GPAM resin may be prepared in situ during a papermaking process (i.e., as an on-site GPAM resin).
A method of preparing the additive composition (the “preparation method”) is also provided, and comprises preparing a cationic acrylamide (CPAM) prepolymer, and selectively glyoxalating the CPAM prepolymer in the aqueous media to give the GPAM resin. The CPAM prepolymer has a predetermined cationic monomer content, and selectively glyoxalating the CPAM prepolymer comprises controlling the concentration of the CPAM prepolymer in the aqueous media during glyoxalation to give the GPAM with the relatively high Mw. The preparation method further comprises combining the APAM resin and the GPAM resin in a wt/wt ratio of from about 1:99 to about 1:2 (APAM:GPAM), thereby giving the additive composition. The preparation method may be carried out in situ during a papermaking process (i.e., as an on-site method).
A process of forming paper with the additive composition (the “process”) is also provided. The process comprises, as base steps, providing an aqueous suspension of cellulosic fibers, forming the cellulosic fibers into a sheet, and drying the sheet to produce a paper. The process also comprises combining the additive composition with the cellulosic fibers, either in the aqueous suspension (e.g. wet-end addition and/or in situ preparation), or applying the additive composition to the sheet once formed.
The following detailed description is merely exemplary in nature and is not intended to limit the instant composition or method. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. Conventional techniques related to the compositions, methods, processes, and portions thereof set forth in the embodiments herein may not be described in detail for the sake of brevity. Various tasks and process steps described herein may be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein for being well-known and readily appreciated by those of skill in the art. As such, in the interest of brevity, such conventional steps may only be mentioned briefly or will be omitted entirely without providing well-known process details.
A drainage-optimized additive composition is provided, along with a method of preparing and processes for implementing and using the same. The additive composition is useful in providing a functionalized polymer composition to production processes in order to provide process and/or product improvements based on the propertied of the functionalized polymers.
Specifically, the additive composition comprises a glyoxalatedpolyacrylamide (GPAM) resin having a high-molecular weight and high cationic charge, which provides excellent drainage to difficult furnishes and good dry strength to products, and thus the additive composition may be utilized in papermaking processes to provide improvements and advantageous thereto. The additive composition also comprises an anionic polyacrylamide (APAM) resin, which also provides good dry strength to products and can also allow for higher dosing of cationic strength aids.
As described and demonstrated in the embodiments and examples herein, the specific combinations of the particular APAM and GPAM resins of the additive composition exhibit improved functionality and performance by providing improved strength, without the drawbacks or deficiencies associated with conventional application of APAM-based additives. Moreover, the utility and tunability of the additive composition allow for increased use cases, providing a flexible yet effective system for balancing strength and drainage properties for machine efficiency and product improvements.
The additive composition comprises an aqueous media. The aqueous media is not particularly limited, and may comprise, alternatively may be, any aqueous composition compatible with the GPAM resin, the APAM resin, and/or the components used to prepare the same, as well as the APAM resins In this fashion, the aqueous media may be a water-based solution or suspension, optionally including additional components, such as process water from a papermaking operation, or simply an aqueous carrier vehicle used in the preparation of the GPAM resin, as described below.
Typically, the additive composition comprises the GPAM resin in the aqueous media in functional amount, i.e., in a solids content that maximizes the amount of GPAM resin while maintaining a useful flowable state of the composition. In this sense, the GPAM resin may be present in an amount of from greater than 0 wt. % to less than the gel point of the GPAM resin in the aqueous media. In some embodiments, the GPAM resin is present in an amount of from about 1.2 to about 6%, such as from about 1.2 to about 5, alternatively from about 1.3 to about 4, alternatively from about 1.4 to about 3, alternatively from about 1.95 to about 2.45% based on the aqueous media (i.e., as % solids). However, as will be appreciated from the method below, the amount of GPAM present in the composition may be dependent on the amount of prepolymer utilized in the method.
The GPAM resin typically has a Mw of at least about 5 megadaltons (MDa). In certain embodiments, the GPAM resin has a Mw of at least about 6 MDa, alternatively at least about 6.5, alternatively at least about 7, alternatively at least about 7.5 MDa. The range of Mw is not particularly limited above the bottom values of these ranges noted (i.e., about 5 MDa or above, alternatively about 5.5 MDa or above, etc.). As such, the GPAM resin may have a Mw in the range of from 5 to 50 MDa, such as from 5 to 40, alternatively from 5 to 35, alternatively from 5 to 30 MDa. In specific embodiments, the GPAM resin may have a Mw higher than those listed in the aforementioned ranges. Such GPAM resins may be achieved and provide the benefits of the additive composition disclosed herein. The particular Mw can be selected by one of skill in the art in view of the embodiments shown and described herein, e.g. in view of a desired use or particular application of the additive composition being targeted.
The GPAM resin may be obtained or prepared. Typically, however, the GPAM resin is prepared at the site of use (e.g. as an “on-site” method), which will be understood by those of skill in the art. The particular properties and features of the GPAM resin, including those introduced above, will be appreciated in view of the method and components utilized in the relevant steps of the preparation method set forth herein.
In general, the GPAM resin is prepared in the aqueous media, or in another aqueous media which is formulated into the final additive composition. As such, the preparation of the GPAM resin described in detail herein may be used in addition to or in place of conventional processes known in the art.
Preparing the GPAM resin comprises glyoxalating a cationic acrylamide (CPAM) prepolymer, as described below.
The CPAM prepolymer may be prepared or obtained. In some embodiments, the method comprises preparing the CPAM prepolymer. For example, the preparation may comprise reacting an acrylamide (AM) monomer, a cationic monomer, and optionally one or more additional ethylenically unsaturated monomer(s), in the presence of a chain transfer agent. However, there are multiple methods to prepare the CPAM prepolymer, which are known in the art and may be adapted from conventional methods of preparing prepolymers suitable for glyoxalation to give a GPAM resin. Examples include free radical polymerization in water, such as via use of a redox initiating system (e.g. sodium metabisulfite and sodium persulfate). Other combinations of redox initiating systems for initiating polymerization of suitable comonomers may also be used, including other persulfate salts such as potassium persulfate or ammonium persulfate or other components such as potassium bromate. Such redox initiating systems may be used in combination with a chain transfer agent, such as a sodium hypophosphite, sodium formate, isopropanol, or mercapto compound-based chain transfer agent.
The CPAM prepolymer typically includes ionic repeat units, e.g. cationic repeat units derived from the cationic monomer. The cationic comonomer may be any cationic monomer capable of reacting through radical chain polymerization with the AM monomer and/or other monomers/comonomers to form the CPAM prepolymer.
Examples of cationic monomers include tertiary and quaternary diallyl amino derivatives, or tertiary and quaternary amino derivatives of acrylic acid or (meth)acrylic acid or acrylamide or (meth)acrylamide, vinylpyridines and quaternary vinylpyridines, or para-styrene derivatives containing tertiary or quaternary aminoderivatives. Cationic comonomers may be chosen from diallyldimethylammonium chloride (DADMAC), [2-(acrylamido)ethyl]trimethylammonium chloride, [2-(methacrylamido)ethyl]trimethylammonium chloride, [3-(acrylamido)propyl]trimethyl ammonium chloride, [3-(methacrylamido)propyl]trimethyl ammonium chloride, N-methyl-2-vinylpyridinium N-methyl-4-vinylpyridinium, p-vinylphenyltrimethylammonium chloride, p-vinylbenzyltrimethylammonium chloride, [2-(acryloyloxy)ethyl]trimethylammonium chloride, [2-(methacryloyloxy)ethyl]trimethylammonium chloride, [3-(acryloyloxy)propyl]trimethyl ammonium chloride, [3-(methacryloyloxy)propyl]trimethylammonium chloride, and combinations thereof. It is understood that mixtures of cationic comonomers can be used to the same purpose. In some embodiments, the cationic monomer includes diallyldimethylammonium chloride (DADMAC).
The CPAM prepolymer may contain other monomer units provided in by additional ethylenically unsaturated monomer(s) in the polymerization. These monomers are typically selected to not significantly interfere with the glyoxalation process. For example, additional monomer units can be acrylates or alkyl acrylates (e.g. methacrylates, methyl methacrylate, etc.), styrene, vinyl acetates, or alkyl acrylates
Polymerization is typically carried out in an aqueous solution (e.g. in the aqueous media) at a temperature of at least about 50° C. It is sometimes advantageous to raise the temperature after the addition of all comonomers has been completed so as to reduce the level of residual monomers in the product. The pH during the reaction may be adjusted with acids or bases or with a buffer, and can be dependent on the initiator system and components used in the reaction.
Comonomers maybe added all at once or added over any length of time. If one monomer is less reactive than another, then it is advantageous to add part or all of the slower reacting monomer at the start of the polymerization, followed by a slow continuous or multiple batch wise additions of more reactive monomer. Adjusting feed rates can lead to more uniformity of the compositions of polymer chains. Likewise, initiators may be added at once or added over any length of time. To reduce the amount of residual monomer in the copolymer, is often advantageous to continue adding the initiator system for some time after all monomers have been added, or to introduce batch wise additional amounts of initiator. Controlling polymer compositional and molecular weight uniformity by controlling addition times is well known in the polymer industry.
In general, the CPAM prepolymer is prepared with a predetermined cationic monomer content (i.e., mol %). For example, the CPAM prepolymer typically comprises at least about 4 mol %, alternatively at least about 10, alternatively at least about 12, alternatively at least about 15, alternatively at least about 20 mol % of cationic monomer content (i.e., units derived from the cationic monomer). In some embodiments, the CPAM prepolymer comprises from about 12 to about 50, alternatively from about 15 to about 45, alternatively from about 18 to about 40, alternatively from about 20 to about 40 mol % of cationic monomer units. In specific embodiments, the CPAM prepolymer comprises from about 15 to about 30, alternatively from about 20 to about 30, alternatively from about 20 to about 25 mol %, of cationic monomer units. However, it will be appreciated from the description herein that the particular cationic monomer content of the CPAM prepolymer, and thus the GPAM resin, may be independently selected based on a desired use. For example, lower cationic content may be selected for use in difficult furnishes, i.e., with higher lignin content, anionic trash, etc. However, the combination of the APAM resin and GPAM resin of the present embodiments may allow for increased cationic monomer content selection as well.
As introduced above, the GPAM resin is prepared by glyoxalating a CPAM prepolymer, that is, reacting the CPAM prepolymer with glyoxal or a suitable derivative (e.g. glyoxylic acid, or a similar functionalization agent) to prepare a GPAM resin therefrom. As such, a method of preparing the GPAM resin is provided, and includes glyoxalating the CPAM (e.g. as prepolymer) to give a GPAM resin therefrom. The method may be used to selectively glyoxalate the CPAM prepolymer by controlling the concentration of CPAM prepolymer in an aqueous media during glyoxalation. In this fashion, GPAM resins having high Mw can be prepared, optionally decoupled from the Mw of the CPAM utilized as the prepolymer being glyoxalated. The CPAM Mw can be determined using relative SEC against known standards, or using other techniques known in the art. The GPAM Mw can determined by batch MALS, AF4 MALS, SEC MALS, etc., or using other techniques known in the art.
As understood in the art, the reaction the CPAM prepolymer with glyoxal may be carried out under varied conditions of time, temperature, pH, etc. Typically, the glyoxal is added quickly to the CPAM prepolymer to minimize crosslinking. Alternatively, the CPAM prepolymer can be added to the glyoxal. It is also generally understood in the art that the molecular weight of the CPAM prepolymer, and the ratio of glyoxal to acrylamide groups on the CPAM prepolymer (including any of those from the cationic monomer), may be adjusted to achieve desired levels of crosslinking and viscosity build during a glyoxalation process
The CPAM prepolymer and the glyoxal are typically reacted in a dry weight (w/w) ratio of from about 75:25 to about 95:5, such as from about 80:20 to about 90:10. In specific embodiments, a 85:15 dry weight ratio is targeted. In other embodiments, a higher glyoxal content is utilized, such as in a ratio of about 85:30 (w/w).
It is typically preferred to run the glyoxalation reaction at a higher concentration (i.e., % solids) of the CPAM to optimize the efficient use of the reaction vessel and/or to obtain a final product of with a higher GPAM concentration. However, the particular conditions will be selected in order to control the properties of the GPAM (e.g. MW, Rg, etc.) and/or GPAM composition (e.g. viscosity, etc.), which will include the degree of intermolecular crosslinking, as described herein.
In some embodiments, the glyoxalation reaction specifically comprises monitoring and selectively controlling the solids content of the reaction, in terms of the GPAM product. In other words, in such embodiments the progress of the reaction may be monitored, and the amount of GPAM being prepared may be controlled. In this fashion, the glyoxalation may be carried out as a “low-solids” process or a “high-solids” process, e.g. depending on the desired use and/or application of the GPAM being prepared. For example, when carrying out the glyoxalation reaction on-site, as described in further detail below, the glyoxalation is typically performed as a low-solids process. When the glyoxalation is carried out off-site, e.g. prior to subsequent storage and/or shipment, a high-solids process may be favored (e.g. to reduce the economics of storage, transport, etc.). In general, those of skill in the art will understand a “low-solids” process to be, in the context of the glyoxalation, any process where a significant viscosity build is not observed (i.e., a low-solids process can run practically indefinitely and not gel). In contrast, a “high-solids” process in this same context is a process where a significant viscosity build is observed and, if not quenched, will eventually reach a gel point. Therefore, it is to be appreciated that the cut off between high-solids and low-solids processes becomes dynamic and related to the identity and characteristics of the reaction components (e.g. CPAM Mw, ratio of CPAM to glyoxal, etc.). The solids value at which a process moves between a high and low solids process may be understood as the “critical concentration” of a given reaction. Accordingly, it is to be appreciated that the glyoxalation may be carried out at a high or low solids content, on site or off site, with particular processes selected by those of skill in the art. Parameters and properties of such process variations are set forth herein, but may be modified, supplemented, and/or replaced by other glyoxalation techniques known in the art. Such processes may be selected based on a desired property of the GPAM resin (e.g. Mw, viscosity, Rg, charge density, zeta potential, etc.) and/or additive composition (e.g. solids content, viscosity, etc.) being prepared, or a particular use thereof.
The monitoring of the reaction progression is not limited to any particular technique, but instead may be carried out using any known method applicable with the reaction conditions selected. For example, the reaction may be monitored according to a property directly related to the solids content of the GPAM prepared, such as the turbidity, viscosity, pH, and/or temperature of the reaction. Likewise, the reaction may be monitored according to a property indirectly related to the solids content, i.e., a property useful for monitoring the glyoxalation reaction, such as via current consumption of a circulation pump, stirrer, etc. influenced by the reaction viscosity. It is generally known that the reaction mixture will increase in viscosity as the GPAM is being prepared. Any of such properties may be monitored over time, e.g. as a difference measurement, and multiple properties may be monitored in tandem for precise value determination and control.
The concentration of the CPAM can be selectively controlled to alter the Mw of GPAM resin prepared. For example, in some embodiments, the CPAM is present in the aqueous media at an initial concentration of from about 0.9 to about 5.7%, alternatively from about 1.5 to about 2.3%. This concentration is typically defined in terms of solids, i.e., the weight percent concentration of the starting CPAM at the start of the glyoxalation reaction, that is when all of the glyoxal has been added. In general, these ranges are implemented for a low-solids process, as introduced above. In such embodiments, the GPAM resin may be prepared in the aqueous media at a solids content (%) of about A+B, where A is the initial concentration of the CPAM in the aqueous media utilized in the glyoxalation, and B is a conversion factor based on one or more of the predetermined physical properties of the CPAM or a parameter of the glyoxalation reaction itself. In this fashion, the solids content of the CPAM and the solids content of the GPAM resin may be described in view of each other. Likewise, selective glyoxalation may be understood to include selecting a desired CPAM concentration based on a desired GPAM resin solids content in the additive composition.
The GPAM resins may be adjusted to a pH of about 3 after glyoxalation reaction to improve storage stability until they are used, or may be used directly without further adjustment.
The APAM resin may be prepared or obtained. In some embodiments, the method comprises preparing the APAM resin. For example, the preparation may comprise reacting an acrylamide (AM) monomer, an anionic monomer, and optionally one or more additional ethylenically unsaturated monomer(s).
Examples of anionic monomers generally include α,β-unsaturated carboxylic acids having from 3 to 5 carbon atoms, and salts thereof. Examples include acrylic acid, methacrylic acid, itaconic acid, etc., and salts thereof. Acrylic acid and itaconic acid are typically preferred, and may be utilized as sodium or other salts forms.
Optionally a crosslinking agent (e.g. a divinyl monomer) is utilized. Moreover, amounts of cationic monomers may also be employed, as understood in the art. However, the use of cationic monomers will typically be minimized due to the charge balance of the systems in which the additive composition is typically used.
In general, there are multiple methods to prepare the APAM resin, which are known in the art and may be adapted from conventional methods of preparing suitable anionic resins for use herein. Examples include free radical polymerization, e.g. via use of a redox initiating system. Other methods include addition polymerization, anionic polymerization, emulsion solution polymerization, etc. Typically, free radical polymerization is utilized.
The APAM resin is selected or prepared with a predetermined anionic monomer content (i.e., mol %). For example, the APAM resin typically comprises about 25 mol % anionic monomer content or less, such as from about 0.1 mol % up to about 25 mol %, depending on the GPAM utilized. In some embodiments, the anionic monomer content of the APAM resin is less than about 25, alternatively less than about 20, alternatively less than about 15, alternatively less than about 12, alternatively less than about 10, alternatively less than about 8, alternatively less than about 6 mol %. However, it will be appreciated from the description herein that the particular anionic monomer content of the APAM resin may be independently selected based on a desired use, i.e., as optimized according to the embodiments herein. For example, lower anionic content may be selected for use in certain furnishes, e.g. with higher lignin content, anionic trash, etc. Alternatively higher anionic content may be employed to further charge balance the GPAM. In general, the combination of the APAM resin and GPAM resin of the present embodiments may allow for increased cationic monomer content selection, and thereby offset certain deficiencies often associated with typical APAM resins with higher anionic content.
The APAM resin typically has a Mw of at least about 0.25 megadaltons (MDa). In certain embodiments, the APAM resin has a Mw of at least about 0.5 MDa, alternatively at least about 0.75, alternatively at least about 1, alternatively at least about 1.5 MDa. The range of Mw is not particularly limited, but is impactful to the tunability of the additive composition, as shown in the examples. As such, the APAM resin may have a Mw in the range of from about 0.25 to about 5 MDa for example, such as from about 0.5 to about 4, alternatively from about 0.5 to about 3 MDa. In specific embodiments, the APAM resin may have a Mw higher than those listed in the aforementioned ranges. Such APAM resins may be achieved and provide the benefits of the additive composition disclosed herein. The particular Mw can be selected by one of skill in the art in view of the embodiments shown and described herein, e.g. in view of a desired use or particular application of the additive composition being targeted. Weight average molecular weight of the APAM resin can be determined by any suitable technique, such as size exclusion chromatography (SEC), or other methods described herein.
In general, the additive composition comprises the APAM resin and the GPAM resin in a wt./wt. ratio of from about 1:99 to about 1:2 (APAM:GPAM), i.e., a ratio based on the total weight of the APAM resin and the GPAM utilized. In this fashion, while near-equal amounts of the two resins can be employed, the APAM resin is typically used in smaller relative amounts (proportion) to the GPAM resin. The effects of the reduced APAM resin loading are shown in the examples herein, which demonstrate the tunability of the additive composition in terms of the Mw of the GPAM resin, the cationic monomer content of the GPAM resin, the Mw of the APAM resin, and the anionic monomer content of the APAM resin. In specific embodiments, the additive composition comprises the APAM resin and the GPAM resin in a wt./wt. ratio of from about 1:30 to about 1:3, alternatively of from about 1:20 to about 1:5, alternatively of from about 1:15 to about 1:7, alternatively of from about 1:12 to about 1:7 (APAM:GPAM). In some embodiments, the relative proportion of APAM utilized is consistent across all dosages of a given application, and the total dosage of the additive composition is altered to provide the desired effect. For example, in some embodiment a wt./wt. ratio of from about 1:8 to about 1:10 (APAM:GPAM) is utilized.
The additive composition may be used to make paper, which comprises pulp and the APAM and GPAM resins. The additive composition used in paper making may lead to beneficial properties, such as, e.g. improved dry strength, temporary wet-strength, permanent wet-strength, wet-strength decay, etc., compared to the same properties when a conventional additive composition (e.g. a GPAM resin of relatively-low Mw) is used, as well as process improvements such as increased drainage speed compared to conventional additives (e.g. APAM resins along, or with conventional GPAM resins, etc.).
The additive composition may be formulated as a single composition (i.e., an aqueous composition comprising both APAM and GPAM resins). However, the GPAM resin is typically prepared in/as an aqueous composition, as described above, which may be combined with the APAM or separately employed. For example, the composition may comprise the APAM and GPAM resins as separately packaged components, which may be applied (e.g. to pulp, sheets, etc.) separately, sequentially, or at the same time.
In certain embodiments, the additive composition comprises the GPAM resin as an aqueous composition obtained directly from the glyoxalation method set forth herein, which may be added to/combined with a component comprising the APAM resin, or instead used directly (e.g. in combination with use of a separate APAM-containing component). In this fashion, as described in additional detail herein, the glyoxalation may be performed in advance of a desired time of use of the additive composition (i.e., “off-site”), or instead may be carried out at substantially the same time the additive composition is to be utilized (i.e., “on-site”). The time between formation of the GPAM resin, the reactive window thereof, the GPAM content in the additive composition, and other factors known in the art, will all be utilized to inform the practical limits on the concentration of a particular GPAM resin in the additive composition of the present embodiments.
In some embodiments, the method comprises applying the APAM resin to an aqueous suspension of cellulosic fibers (e.g. pulp) directly, separate from the GPAM resin. In such embodiments, combining the APAM resin and the GPAM resin may comprise providing the GPAM resin to the aqueous suspension of cellulosic fibers, e.g. before or after the APAM resin is applied thereto. In specific embodiments, it has been shown that application of the APAM resin before the GPAM resin provides superior results in terms of drainage and/or strength improvements. The parameters and scope of these improvements are described in further detail below.
The additive composition may be prepared and subsequently combined with a pre-formed aqueous suspension of cellulosic fibers. For example, the GPAM resin may be prepared and introduced to the suspension within a time period suitable for storage, such as within about 10, alternatively of about 8, alternatively of about 5 hours after glyoxalation. Alternatively, the additive composition may be prepared in the aqueous suspension, i.e., where the GPAM resin is prepared in-situ with the aqueous suspension. Such processes are known in the art as “on-site” processes, and are particularly suitable for use in the present embodiments. In either such instance, the APAM resin is typically introduced prior to the GPAM resin as described herein.
In the paper making process there are multiple steps, generally including: forming an aqueous suspension of cellulosic fibers; addition of additives (e.g. the additive composition) to the suspension; forming a sheet from the fibers; and drying the sheet to give the paper. Additional steps may also be employed (e.g. for tissue and towel grades, a forth step of creping or forming a structure of the paper to provide properties such as softness is typically employed). These steps and variations of the process are known to those skilled in the art.
It will be appreciated that application of the additive composition to the aqueous suspension of cellulosic fibers is typically performed as a wet-end addition, e.g. to treat a stock mixture prepared after pulping. The particular type of pulp, i.e., the particular types of cellulosic material to be treated, is not limited but may alter the particular performance characteristics of a given APM/GPAM combination. However, such alterations are not outside the scope of the present embodiments, but instead are contemplated herein as the additive composition may be tuned to optimize performance (e.g. strength, drainage), in numerous fiber compositions from virgin to recycled, as will be readily understood by those of skill in the art in view of the examples herein.
It is also understood that the additive composition may be applied in other process steps, such as via spray application to the sheet, between layers of a multi-ply product, etc. Such applications will be understood by those of skill in the art, and may be modified for use with the additive composition. Alternatively, the additive composition may be formulated or otherwise altered for use in a specific application and/or with particular equipment.
In view of the above, a process of forming paper is also provided herein. The process generally comprises:
In such embodiments, combining the additive composition with the aqueous suspension typically comprises first providing the anionic polyacrylamide (APAM) resin to the aqueous suspension, and then providing the glyoxalated polyacrylamide (GPAM) resin to the aqueous suspension.
In other embodiments, the process of forming paper comprised
In such embodiments, the APAM and GPAM resins may be applied together or separately, and sequentially or at substantially the same time (e.g. via two applicators).
As demonstrated below, the additive composition provides improved strength and maintained or improved drainage characteristics compared to conventional compositions using similar components. Specifically, as provided herein, the embodiments allow for optimization of the relative proportion of APAM:GPAM, and the additive composition provides for significant strength improvement on an equal total dosage basis relative to use of a conventional GPAM resin alone. Additionally, while drainage is usually negatively impacted by APAM usage, the specific combinations of the present embodiments allowed for drainage performance to be maintained relative to comparative use of GPAM alone.
In particular implementations, the additive composition provides dry-strength to the paper being formed. For example, in some embodiments, the paper exhibits a mechanical strength performance (e.g. as determined via ring crush testing (e.g. TAPPI T822)), that is increased by at least about 1, alternatively at least about 3, alternatively at least about 6, alternatively at least about 9%, compared to a paper prepared with a substantially similar process that is substantially free from the additive composition, or uses components outside the scope of the present embodiments.
In addition to the strength increase, the additive composition may provide an improved drainage rate, e.g. as exhibited during sheet formation. In certain embodiments, the additive composition provides a drainage time reduced by at least about 10, alternatively at least about 20, alternatively at least about 25, alternatively at least about 30%, compared to a drainage rate of a substantially similar process that is free from the additive composition all together. Likewise, the additive composition may exhibit a drainage time reduced by at least about 15, alternatively at least about 20%, alternatively at least about 25%, compared to a drainage rate of a substantially similar process that is free from the GPAM resin of the additive composition.
The paper making process introduced above may further comprise steps of drying, patterning, treating, and creping the paper to form a finished paper product. Finished paper products can include, but are not limited to, bath tissue, facial tissue, and paper towels, which are also contemplated herein.
The following examples, illustrating embodiments of this disclosure, are intended to illustrate and not to limit the invention. Unless otherwise noted, all solvents, substrates, and reagents are purchased or otherwise obtained from various commercial suppliers (e.g. Sigma-Aldrich, VWR, Alfa Aesar) and utilized as received (i.e., without further purification) or as in a form used conventionally in the art.
A reaction flask is charged with DI water, diallyldimethylammonium chloride DADMAC, a pH modifier, and chain transfer agent. To the reaction flask two external feeds are connected, one containing acrylamide, the other containing sodium metabisulfite (SMBS) and chain transfer reagent. The reaction mixture is warmed to 35° C., then ammonium persulfate (APS) and sodium bromate are added, followed by starting the feeds. The acrylamide feed is set to be added over 135 minutes, the SMBS feed is set to be added over 195 minutes. During the acrylamide feed, the reaction is gradually heated through an external heating source at ˜0.4° C./min up to 90° C. After the conclusion of the acrylamide feed, a second portion of APS is added and the reaction is held at 90° C. for one hour. The amount of DADMAC is varied as necessary to make a prepolymer with the desired amount of cationic monomer. The molecular weight (Mw) of the prepolymer is manipulated by increasing or reducing the amount of chain transfer agent as necessary. The CPAM Mw is determined using known methods, such as via relative SEC against known standards.
A CPAM prepolymer is charged to a reaction flask and diluted with DI water so the concentration of the polymer is as desired, to which is added glyoxal at 15:85 dry w:w ratio relative to the prepolymer. The pH is increased to 10.2 using dilute NaOH and this pH is maintained for the desired reaction time. After which, the reaction is quenched by reducing the pH to 4 with dilute sulfuric acid. The resulting glyoxalated cationic polyacrylamide (GPAM) is then characterized according to known methods, such as via batch mode MALS, SEC MALS, AF4 MALS, etc.
While not shown in the specific examples below, the glyoxalation may also be carried out at a higher glyoxal ratio to alter the level of GPAM glyoxalation, such as by adding glyoxal at a dry w:w ratio of about 30:80 relative to the prepolymer, to give the GPAM.
It will be understood that the cationic content of the GPAM (e.g. reported as charge, mol %), is typically based on the mol % of cationic monomer used to prepare the CPAM prepolymer itself.
A reaction flask is charged with DI water, acrylic acid, and acrylamide. Optionally, a crosslinking agent (e.g. a divinyl monomer), is added. The pH is adjusted with sulfuric acid, and the mixture is warmed to 35° C. Sodium metabisulfite (SMBS) and sodium persulfate (SPS) are added to initiate the polymerization, and the temperature is allowed to rise adiabatically. The reaction is allowed to proceed for 90 min before a second amount of SMBS is added. The reaction is continued for another 30 min. The amount of acrylic acid is varied as necessary to make a polymer with the desired amount of anionic monomer content. The molecular weight (Mw) of the polymer is manipulated by increasing or reducing the amount of initiator or crosslinking agent. The APAM Mw is determined using known methods, such as via estimation by intrinsic viscosity (IV) against known standards.
Various additive compositions are prepared using APAM and GPAM resins and analyzed. Specific parameters and properties of the APAM and GPAM resins utilized in the additive compositions are set forth in the table below.
(1) Determined by MALS
(2) Determined by SEC MALS
(3) Determined by SEC
(4) Estimated by IV
A furnish made up of OCC fibers was dispersed in water, refined to a CSF of 350-400 mL, and adjusted to a pH of 7. The water used was conditioned with calcium chloride (147 g per 1000 L) and sodium bicarbonate (84 g per 1000 L) to normal hardness, and sodium sulfate was added to adjust to a conductivity of 2000 uS/cm. To the furnish was added 2.5 wt % (dry basis) of oxidized starch (GPC D-28F). The stock was applied to the paper machine through a flow spreader (hydraulic) head box onto a fourdrinier equipped with vacuum assisted baffles to remove water and form a wet sheet. The wet sheet was then passed through two single felt presses to mechanically remove water and densify the sheet. The final water removal (drying) is carried out using electrically heated dryer cans before being wound up onto a core at the reel, targeting a basis weight of 100 lb/3000 sqft.
Ring crush was measured with a Crush Testing Machine, with the analysis performed according to TAPPI method T 822 (e.g. om-16).
Five paper machine trials (Trials A-E) were run according to the procedure above. The specific parameters and results of the paper machine trials are set forth in tables further below. All strength values are reported as the % increase vs. blank, determined via Ring Crush Test. For the performance comparisons, the examples set forth in each table were run at the same time in the same furnish.
(5)Strength improvement reported as % increase, relative to blank performance (Ring Crush)
BAPAM 3 (bead polymer)
(5)Strength improvement reported as % increase, relative to blank performance (Ring Crush)
(5)Strength improvement reported as % increase, relative to blank performance (Ring Crush)
(5)Strength improvement reported as % increase, relative to blank performance (Ring Crush)
SAPAM 1 (solution polymer)
(5)Strength improvement reported as % increase, relative to blank performance (Ring Crush)
SAPAM 1 (solution polymer)
As shown in Trial A, the additive composition using the medium charge (e.g. 12.8% cationic) GPAM demonstrate consistently increased strength performance on an equal total dosage basis. Conversely, the compositions utilizing low-normal charge (e.g. 4.1% cationic) GPAM did not achieve the strength performance levels as those using 12.8% cationic GPAM or greater. As also shown, a relatively low proportion of APAM can be used to improve the strength performance, and higher molecular weight APAM provided higher strength compared to the lower molecular weight variants. In this trial, no clear effect of APAM charge can be seen in terms of performance characteristics.
As further demonstrated in Trial B, the additive composition using the medium charge (e.g. 12.8% cationic) GPAM provide consistently increased strength performance on an equal total dosage basis. Conversely, the compositions utilizing low-normal charge (e.g. 4.1% cationic) GPAM did not achieve the strength performance levels as those using 12.8% cationic GPAM or greater. As also shown, a relatively low proportion of APAM (e.g. 1:6 and 1:9 APAM:GPAM ratios) can provide improved strength performance. These effects are further supported by the results of Trial C, which employed low-normal charge (e.g. 4.1% cationic) GPAM in combination with APAM having lower anionic charge. However, no consistent strength improvement on an equal total dose basis using the 4.1% cationic GPAM was achieved.
As shown in Trial D, the high-charge GPAM provided the additive composition with improved strength performance over lower-charged GPAM containing compositions. Surprisingly, the additive compositions using the 20.6% cationic GPAM increased strength performance relative to the GPAM alone, even at equal total dosage. Improved performance was also achieved using combinations with a relatively low proportion of APAM to GPAM, e.g. 1:9.
As shown in Trial E, using additive compositions with high and low charge APAM in combination with 12.8% cationic GPAM, decreasing the APAM proportion can be used to improve the strength performance of the additive composition even when a low-charge APAM is employed. It is also shown that the delivered GPAM (i.e., GPAM 4) can be employed in the additive composition and achieve adequate strength performance when optimized according to the embodiments herein.
A vacuum drainage test was performed using a Dynamic Drainage Analyzer (DDA). Old corrugated container (OCC) was refined to a CSF of ˜350-400 mL and then diluted with DI water to a consistency of 0.9%. To the diluted pulp was added calcium chloride (147 g per 1000 L), sodium bicarbonate (84 g per 1000 L), and sodium sulfate (added until the solution conductivity reached ˜2000 S/cm). The pH of the pulp was adjusted to 7 using concentrated sulfuric acid, followed by the addition of 2.5 wt % (dry basis) of oxidized starch (GPC D-28F). Drainage time was measured using a Dynamic Drainage Analyzer 4 instrument from PulpEye. A 60-mesh screen with a 95 mm cross-sectional filtration diameter was used. The analyzer applies a 300 mbar vacuum and measures the time between application of vacuum and the vacuum break point, or when air breaks through the thickening fiber mat. To perform the test, 750 mL of furnish was charged into the sample receptacle and the pulp was stirred. After 15 seconds of stirring, the polymer additive was charged to the stirring pulp slurry, and the stirring was continued for an additional 10 seconds. The instrument then stops stirring, applies vacuum, and records the pressure vs. time, i.e., to determine the amount of time it takes to reach the vacuum break point.
Two drainage trials (Trial F & Trial G) were run according to the DDA procedure above. The specific parameters and results of the drainage trials are set forth in the tables below. All drainage values are reported as the % reduction in drainage time vs. blank. A negative value indicates that drainage time was longer than the blank. For the performance comparisons, the examples set forth in each table were run at the same time in the same furnish.
(6)% Drainage time improvement reported as % decrease, relative to blank
BAPAM 3 (bead polymer)
(6)% Drainage time improvement reported as % decrease, relative to blank
SAPAM 1 (solution polymer)
As shown in Trials F-G, usage of APAM severely reduced drainage performance of additive compositions using low and normal/medium charge (e.g. 4.1% and 12.8% cationic) GPAMs. However, lower proportions of APAM result in less of a negative effect on drainage, and the use of lower charge APAM in the additive composition results in less of a negative effect on drainage. Notably, embodiments of the additive composition comprising high-charge, high molecular weight GPAM provide stable (i.e., non-reduced) drainage performance when APAM is employed prior to the GPAM.
As demonstrated in the Example above, the additive composition comprising the combinations of on-site GPAM and APAM with varying charge densities and molecular weights are optimized in OCC to maximize strength and minimize negative effects on drainage performance. The relative proportion of APAM:GPAM in the additive composition also optimized, along with the application procedure concerning the effects of addition order for the GPAM and APAM resins employed.
As shown, significant strength improvement is provided by the additive composition comprising APAM-GPAM combinations on an equal total dosage relative to the GPAM alone. While drainage may be negatively impacted, some combinations provide the additive composition with drainage performance maintained relative to GPAM alone. Other unexpected effects were also discovered during the example trials reported above.
For example, it can be seen that drainage performance is almost always negatively affected by APAM use, even at low APAM:GPAM proportions, compared to the use of GPAM alone. A notable solution to this was found via application of the additive composition using a high charge, high molecular weight GPAM (i.e., GPAM 3) in a second addition step, following application of the APAM component in a first addition step.
It was also shown that increasing the cationic charge of the GPAM resulted in increased strength performance of the additive composition. Conversely, when drainage was negatively affected, reducing APAM charge typically resulted in less of a negative effect (i.e., lower APAM charge reduced the reduction in draining performance seen).
It was also found that increasing the molecular weight of the APAM resulted in increased strength performance of the additive composition. This effect was also demonstrated with the use of APAM beads (i.e., APAMs 3-5), which typically comprise higher molecular weight resins and generally performed better than the solution-state APAMs of the same charge.
In specific implementations, a relatively low proportion of APAM to GPAM was shown to provide balanced performance in achieving improved strength and drainage performance. For example, a proportion of 1:9 APAM:GPAM is demonstrated in the examples with good results.
It was also shown that addition order of the components when utilizing the additive composition could improve performance, as well as being useful for selectively tailoring performance between strength and drainage. For example, first application of the APAM (i.e., before the GPAM) resulted in better drainage performance, while second application of the APAM (i.e., after the GPAM) resulted in better strength performance. However, it was surprisingly found that, while second application of the APAM always negatively impacted drainage performance, either addition order of the APAM and GPAM components resulted in better strength performance than GPAM alone (i.e., compared at the same total dosage for GPAMs, with medium or high charge).
Two paper trials (Trial H & Trial I), were conducted to prepare paper samples for repulping analysis. The specific parameters and results of the paper machine trials are set forth in the tables below.
SAPAM 1 (solution polymer)
Repulping performance was assessed via index classification (The Brecht-Zippel method, or Blue Glass Pulping Index) to determine the quality of the repulping slurry in 15 minute intervals until fully repulped. The repulping was performed via a repulping apparatus (Waring Blender, equipped with a glass jar, blade, and jar cover) fitted with a temperature controller and a motor controller with a timer. Samples of paper totaling approximately 18 grams were cut into ˜1″ square pieces. Approximately 342 grams of water was added to the blender jar such that the consistency of the final pulp slurry would be 5%. The temperature of the water was brought to 125° F. The paper pieces were added, allowed to soak for 5 minutes, and then repulped with a shear rate of 1500 rpm at 125° F. for 15 minutes. A spoonful of the slurry was removed, added to 100 mL of water in a plastic cup, mixed, and poured on top of blue glass. The sample was then visually assessed against a Brecht-Zippel Blue Glass Index standard and graded to an index point that most closely resembled the pulp sample, on a scale of 1-9 according to the index table below:
The repulping was continued in 15 minute intervals until 120 minutes had elapsed or the slurry was completely repulped (i.e., graded at Index No. 9).
The results of the repulpability assessment, reported as the Index No. grading of each sample at the time internal given, are set forth in the tables below:
The effect on repulpability of different APAM:GPAM proportions using the 12.8% cationic GPAM (GPAM 2) and the 18% anionic APAM (APAM 2) was assessed in Trial H. Conventional additive compositions are known for decreased repulpability, potentially due to build of permanent wet strength via incorporation of the additives. As shown above, however, the compositions of the present embodiments shown to increase strength and drainage performance do not reduce the repulpability of the paper prepared therewith.
The effect on repulpability of different addition orders using the 20.6% cationic GPAM (GPAM 3) and the 25% anionic APAM (APAM 1, solution polymer) was assessed in Trial I. In each instance, the additive composition provided in any order of addition maintained the repulpability of the GPAM component used alone.
At the dosages assessed, the additive composition of the present embodiments provides superior tailorable properties of strength and drainage, without sacrificing repulpability.
A furnish made up of OCC fibers was obtained from a commercial paper mill and dispersed in whitewater obtained from the same paper mill. The CSF was measured to be 550 mL. The conductivity of the water was measured to be 3542 uS/cm, and the pH was measured to be 6.8. The stock was applied to the paper machine through a flow spreader (hydraulic) head box onto a fourdrinier equipped with vacuum assisted baffles to remove water and form a wet sheet. The wet sheet was then passed through two single felt presses to mechanically remove water and densify the sheet. The final water removal (drying) is carried out using electrically heated dryer cans before being wound up onto a core at the reel, targeting a basis weight of 93 lb/3000 sqft.
Ring crush was measured with a Crush Testing Machine, with the analysis performed according to TAPPI method T 822 (e.g. om-16).
A paper machine trials (Trial J) was run according to the procedure above. The specific parameters and results of the paper machine trial are set forth in the table below. All strength values are reported as the % increase vs. blank, determined via Ring Crush Test. Each example set forth in the table was run at the same time in the same furnish.
(5)Strength improvement reported as % increase, relative to blank performance (Ring Crush)
SAPAM 1 (solution polymer)
Various formulations of the additive composition were assessed in Trial J, which was conducted using commercial furnish and whitewater from a commercial paper mill in order to more-closely simulate commercial conditions. In particular, commercial furnish has higher amounts of soluble lignin, higher conductivity, different salt mixtures, and expected amounts of anionic trash, which each influence additive performance.
As shown, the additive composition demonstrated improved strength performance over the controls, even in the difficult furnish. Improved performance was indicated with higher charge APAM, which was not as apparent from the trials conducted in the synthetic furnish. As such, the present embodiments demonstrate the tunable performance across a wide range of conditions, where increased charge and/or molecular weight of the APAM component may be selected to maintain improved performance in various furnish requirements. Moreover, it was also demonstrated that the combination of specific components in the additive composition provides superior strength performance over GPAM used alone at the same GPAM dosage. Accordingly, the present embodiments provide a solution for applications that require strength, drainage, and repulpability benefits of additives, but which are limited to cationic loading due to charge flipping and runnability concerns. The present compositions provide a charge-balanced solutions, which are believed to allow for higher overall GPAM dosing, that are capable of improving strength and drainage, without sacrificing repulpability or runability.
In view of the above, the additive composition can be readily envisioned for use in enhancing machine productivity. Additionally, the additive composition may be used to give good dry strength. In view of the particular tunability of the additive composition, however, it will be readily understood that the specific combination of the relatively high-molecular weight and medium-to-high charge GPAM combined with the relatively high-molecular weight and low charge APAM provides the additive composition with unique tunability for achieving improved and balanced performance characteristics that may be exploited to prepare numerous paper products.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims. Moreover, all combinations of the aforementioned components, compositions, method steps, formulation steps, etc. are hereby expressly contemplated for use herein in various non-limiting embodiments even if such combinations are not expressly described in the same or similar paragraphs.
With respect to any Markush groups relied upon herein for describing particular features or aspects of various embodiments, different, special, and/or unexpected results may be obtained from each member of the respective Markush group independent from all other Markush members. Each member of a Markush group may be relied upon individually and or in combination and provides adequate support for specific embodiments within the scope of the appended claims.
Further, any ranges and subranges relied upon in describing various embodiments of the present invention independently and collectively fall within the scope of the appended claims, and are understood to describe and contemplate all ranges including whole and/or fractional values therein, even if such values are not expressly written herein. One of skill in the art readily recognizes that the ranges and subranges enumerated herein sufficiently describe and enable various embodiments of the present invention, and such ranges and subranges may be further delineated into relevant halves, thirds, quarters, fifths, and so on. As just one example, a range “of from 0.1 to 0.9” may be further delineated into a lower third, i.e., from 0.1 to 0.3, a middle third, i.e., from 0.4 to 0.6, and an upper third, i.e., from 0.7 to 0.9, which individually and collectively are within the scope of the appended claims, and may be relied upon individually and/or collectively and provide adequate support for specific embodiments within the scope of the appended claims. In addition, with respect to the language which defines or modifies a range, such as “at least,” “greater than,” “less than,” “no more than,” and the like, it is to be understood that such language includes subranges and/or an upper or lower limit. As another example, a range of “at least 10” inherently includes a subrange of from at least 10 to 35, a subrange of from at least 10 to 25, a subrange of from 25 to 35, and so on, and each subrange may be relied upon individually and/or collectively and provides adequate support for specific embodiments within the scope of the appended claims. An individual number within a disclosed range may be relied upon and provides adequate support for specific embodiments within the scope of the appended claims. For example, a range “of from 1 to 9” includes various individual integers, such as 3, as well as individual numbers including a decimal point (or fraction), such as 4.1, which may be relied upon and provide adequate support for specific embodiments within the scope of the appended claims. Lastly, it will be understood that the term “about” with regard to any of the particular numbers and ranges described herein is used to designate values within standard error, equivalent function, efficacy, final loading, etc., as understood by those of skill in the art with relevant conventional techniques and processes for formulation and/or utilizing compounds and compositions such as those described herein. As such, the term “about” may designate a value within 10, alternatively within 5, alternatively within 1, alternatively within 0.5, alternatively within 0.1, % of the enumerated value or range.
While the present disclosure has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications will be obvious to those skilled in the art. The appended claims and this disclosure generally should be construed to cover all such obvious forms and modifications, which are within the true scope of the present disclosure.
This application claims priority to and all benefits of U.S. Provisional Application No. 63/494,201, filed Apr. 4, 2023, the content of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63494201 | Apr 2023 | US |
