Patent Application
20140224443
This application relates generally to making high-strength paper products with specific functionalities.
Many paper applications require not only high strength but also functionalities that provide the paper article with moisture, oil and grease, mold and fire resistance, increased brightness, or other specialized functionalities like antimicrobial properties or magnetic properties. Certain of these products are currently manufactured by imparting paper a coating in a secondary process.
In one approach for adding functionality to the paper surface, the sizing process uses cooked starch solutions with additives (such as brightening agents, clays, hydrophobicizing compounds) to impart surface functionality to the paper. In the sizing process, the wet web is first dried to a pre-set moisture content and/or is re-wet to achieve uniform moisture content throughout; then the material is fed into a size press where a high loading of gelatinized starch with additives is applied to the paper surface; then the material is dried again. This process involves a number of downstream processes that can be inefficient. Inefficiencies result from the number of steps involved in preparing the substrate, cooking the starch and applying it to form the finished product. A considerable amount of energy is required for these steps, which adds to the costs of the process.
For certain paper products, functionalities can be added by incorporating additives into the fibrous matrix during the papermaking process. Particulate additives can be introduced into the paper web, substituting for some of the pulp that might be used otherwise. These particulate fillers can create, for example, a bulky final paper product that creates the impression of higher quality through its tactile properties while minimizing the use of expensive pulp. Particulate fillers can also be used to impart other specialized properties besides bulk. For example, particulate additives can include filler particles, or other particles, suitable for use in papermaking, or a final paper product can include mineral particles such as calcium carbonate, dolomite, calcium sulfate, kaolin, talc, titanium dioxide, silica, aluminum hydroxide, and the like. Particles can be formed from inorganic or organic materials, and may be solid or porous. Organic particles may be polymeric, optionally crosslinked, and may be elastomeric. A wide variety of particles known in the art can be incorporated into the finished paper product to improve performance attributes such as brightness, opacity, smoothness, ink receptivity, fire retardance, water resistance, bulk, and the like.
Precipitated Calcium Carbonate (PCC) is particularly useful as a particulate filler additive where high opacity, brightness and maintenance of caliper are required. Higher PCC contents replace expensive pulp improving the profitability of paper. Although PCC contents as high as 15% are often used in papermaking, the first pass retention of the filler is poor, so that a significant amount can be lost from the paper product during the papermaking process. The PCC that is incorporated into the paper product also leads to weaker sheets, because the particles themselves disrupt the hydrogen bonding between cellulose fibers. Higher ash content (>15%) is highly desired in the paper industry, where ash content indicates the amount of filler in a paper.
In other products, TiO2 particles are highly desired as particulate fillers to improve the opacity and brightness beyond what is achievable using PCC. The TiO2 particles due to their small size and high refractive index are capable of scattering light and improving the opacity of the paper containing them. As the TiO2 particles are many times more expensive than PCC, improvement in retention is highly desired. Although flocculants can be used to improve the retention of TiO2, the flocculated TiO2 particles do not possess the same optical properties as the individual TiO2 platelets. It would be advantageous to combine TiO2 particles with other particles to form a composite that separates individual TiO2 particles and allows them to retain their optical characteristics.
Other particulate fillers can be added to the paper product to impart specific, desirable properties. As an example, magnetic or paramagnetic particles can be incorporated into the paper to form a magnetic or a magnetizable paper. As another example, colloidal silver particles can be introduced into a paper product to impart antimicrobial properties. A large number of additives can be contemplated that are available in particulate form, including additives that impart oil or grease resistance, optical brightening, ink binding, dust control, water repellency, stiffness, biocidal properties, bioactive properties (e.g., a biomolecule for controlled release), adhesive properties, diagnostic sensing, filtration assist, targeted capture/sequestration, and the like. For particulate additives, proper distribution within the paper matrix is important. For particulate additives that are expensive, proper retention is also important. And with the addition of any additive, its impact on the strength, stiffness and bulk of the final paper product must be considered.
A variety of other additives can be used to impart desirable properties to paper products, but face some of the same challenges: retention, distribution and impact on paper quality. Some other additives used presently to impart various functionalities to paper include synthetic fibers (imparting strength and hydrophobicity and absorbency characteristics), latex colloids (imparting properties such as hydrophobicity, oil and grease resistance, mold resistance, fire retardancy, impact resistance) etc. These components have poor affinity to pulp fibers, though, owing to lack of functional groups capable of interacting with cellulose fibers. As an example, latex colloids are particularly useful for imparting resilience, barrier properties, bulk, impact resistance, damping, and the like. Latex particles that are micron or submicron sized (typically 100 nm particles) suspended in an aqueous solution are particularly suited for use in papermaking. However, latex is typically water-insoluble, and can be integrated only with great difficulty into an aqueous process like papermaking.
It is desirable, therefore, to have a process where an additive capable of delivering added functionality can be mixed with pulp fibers in the wet-end of papermaking such that the additive becomes an integral part of it. It is desirable that such additives be distributed evenly and appropriately within the paper matrix, and that the additives be retained on the product and not lost in the whitewater. It is further desirable to introduce such additives so that they preserve the strength and resiliency of the final paper product.
As an example, there exists a particular need in the art for systems and methods that incorporate and retain colloidal latex particles in the wet end so that high amounts of these fillers are dispersed uniformly in the paper providing paper with desired functionalities. These colloidal latex fillers should, desirably, be incorporated so that they are stably anchored to the pulp fibers, allowing them to expand or gelatinize during paper manufacturing without being dislodged. In this manner, the fillers can occupy the interstitial spaces between cellulose fibers more completely, improving the properties of the paper product. Furthermore, it is known that high filler content has a detrimental effect on the strength of the wet web before it is dried because the fillers act as spacers and interfere with fiber-fiber bonding. An efficient retention system that attaches the latex fillers to fibers durably in the wet web can advantageously enhance wet web strength during processing by allowing fiber-fiber bonding to proceed unimpeded.
Disclosed herein in embodiments are systems for papermaking, comprising a first population of fibers dispersed in an aqueous solution and complexed with an activator, and a second population of composite additive particles bearing a tethering material, wherein the addition of the second population to the first population attaches the composite additive particles to the fibers by the interaction of the activator and the tethering material. The first population can comprise cellulosic or synthetic fibers. The composite additive particles can comprise a particle selected from the group of a PCC particle, a TiO2 particle, a magnetic particle, and a silver colloid particle. In embodiments, the composite additive particles comprise a latex component and a starch component.
Further disclosed herein, in embodiments, are methods for manufacturing a paper product, comprising activating a first population of fibers in a liquid medium with an activator, forming a second population of composite additive particles, treating the second population with a tethering material to form tether-bearing composite additive particles, wherein the tethering material is capable of interacting with the activator, adding the second population to the activated population of fibers to form a treated paper matrix, and forming the paper matrix to manufacture the paper product. In embodiments, the first population comprises cellulosic fibers or synthetic fibers. In embodiments, the composite additive particles comprise a particle selected from the group of a PCC particle, a TiO2 particle, a magnetic particle, and a silver colloid particle. In embodiments, the composite additive particles comprise a latex component and a starch component.
Also disclosed herein, in embodiments, are methods for making a paper product, comprising providing a first population of fibers and a second population of fibers, wherein the fibers have low attachable affinity for each other, activating the first population of fibers in a liquid medium with an activator, treating the second population of fibers with a tethering material to form tether-bearing fibers, wherein the tethering material is capable of interacting with the activator, adding the second population of tether-bearing fibers to the activated population of fibers to form a treated paper matrix, and forming the paper matrix to manufacture the paper product. In embodiments, at least one population of fibers comprises synthetic or cellulosic fibers. In embodiments, one of the first population and the second population comprises hardwood fibers, and the other of the first population and the second population comprises softwood fibers.
Also disclosed, in embodiments, is a fibrous web, comprising a first population of fibers and a second population of fibers, wherein an activator has been attached to the first population of fibers and a tethering material has been attached to the second population of fibers, the tethering material interacting with the activator to attach the first population of fibers to the second population of fibers as a fibrous web. Also disclosed, in embodiments, is a paper product comprising the fibrous web as described above. In embodiments, the first population of fibers in the fibrous web comprises cellulosic fibers, and the second population of fibers comprises synthetic fibers. In embodiments, the first population of fibers consists essentially of cellulosic fibers, and the second population of fibers consists essentially of synthetic fibers. In embodiments, the first population of fibers comprises one of softwood fibers or hardwood fibers, and the second population of fibers comprises the other of softwood and hardwood fibers. In embodiments, the first population of fibers comprises cellulosic fibers, and the second population of fibers comprises non-cellulosic natural fibers. In embodiments, the first population of fibers comprises one of softwood fibers or hardwood fibers, and the second population of fibers comprises the other of softwood and hardwood fibers.
In addition, disclosed herein in embodiments are methods of forming a fibrous web, comprising providing a first population of fibers, activating the first population of fibers in a liquid medium with an activator, preparing a population of composite particles, wherein the composite particles comprise a latex component and a starch component, treating the population of composite particles with a tethering material to form tether-bearing composite particles, wherein the tethering material is capable of interacting with the activator to attach the composite particles to the fibers to form particle-bearing fibers, and processing the particle-bearing fibers to gelatinize the starch component and to melt the latex component, thereby distributing the melted latex component through the fibers and binding the fibers together to form the fibrous web. The method can further comprise the steps of providing a second population of fibers, wherein the second population of fibers has low attachable affinity for the first population, activating the second population of fibers with an activator, and adding the second population of fibers to the first population of fibers either before or after the activation step for either population, wherein the population of tether-bearing composite particles attaches to the first population of fibers and the second population of fibers to form particle-bearing fibers, and wherein the processing of the particle-bearing fibers distributes the melted latex component through the first population and the second population of fibers and binds the first population and the second population of fibers together to form the fibrous web. In embodiments, paper products formed from the fibrous web described above are also disclosed.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
1. Additives for Papermaking
Disclosed herein are systems and methods for attaching additives to cellulose fibers in a paper product. As used herein, the terms “paper” and “paper product” may be applied to a wide variety of sheet-like masses, molded products, and other substrates fabricated from fibers derived from biological sources (e.g., fibrous cellulosic material), which may optionally include other fibrous elements derived from mineral sources (e.g., asbestos or glass) and/or from synthetic sources (e.g., polyamides, polyesters, rayon and polyacrylic resins). As disclosed herein, a variety of specialized additives can be attached to the fibers in the paper product.
In embodiments, the additives are combined to form composite particles, and the composite particles are attached to the cellulose fibers. Composite particles can be formed by attaching two or more additives to each other; the composite particles can then be attached to the cellulose fibers. Three steps can be performed to effect the attachment of composite particle to cellulose fibers. In one step, the cellulose fibers are modified by the attachment of an agent, called an “activating agent” or “activator” that prepares the surface of the fibers for attachment to a suitably-modified composite particle. In another step, the composite particle is formed as will be described in more detail below. The composite particle is then modified by attaching a tethering agent to the particle, where the tethering agent has a particular affinity for the activating agent attached to the paper fibers. The tether-bearing composite additive particles are then admixed with the activated fibers, so that the activating agent and the tethering agents interact: this interaction durably affixes the composite additive particles bearing the tethers to the fibers bearing the activators. In embodiments, the cellulose fibers can be treated with a cationic polymer of a specific molecular weight and composition as an activator, and the composite additive particles are treated with an anionic polymer as a tethering agent; these separately-treated populations are then combined so that the composite additive particles are attached to the pulp fibers. In embodiments, the combination of these processes can be referred to as an “Anchor-Tether-Activator,” or “ATA” system. In this system, the cellulose fibers are treated with the activator, as will be described below in more detail; the composite additive particle acts as an “anchor particle” that is treated with the tethering agent. The tether-bearing anchor particles, when mixed with the activated cellulose fibers, become attached thereto, so that the composite additive particles become durably affixed to the cellulose and appropriately distributed throughout the cellulose matrix.
In embodiments, the tethering agent also acts to attach the component additives to each other to form a composite additive particle. This use of the tethering agent can allow the creation of composite particles from components that have no intrinsic attraction to each other. For example, PCC and TiO2 can be combined to form a composite additive particle using the tethering agent as “glue” to hold the components together as a composite. Or, for example, TiO2 can be combined with another additive, such as clay, to form a composite additive particle, using the tether as a “glue” to hold the composite together. The composite additive particle, thus treated with the tethering agent, forms a tether-bearing composite particle that is affixable to the activator-treated cellulose fibers in the anchor-tether-activator system as described herein.
In embodiments, the components of the composite additive particle can be attached to each other intrinsically. In one embodiment, for example, starch granules and PCC particles can be mixed together physically to form a composite particle slurry. PCC is slightly cationic at the pH used for papermaking, which makes it easier to bond with anionic starch granules. With neutral or uncharged starch granules, PCC can be mixed at high shear to form a composite additive particle slurry that can then be modified with tethering agent.
As another example, colloidal latex particles can interact electrostatically with granular starch of opposite charge resulting in a composite latex/starch additive particle. The composite latex-starch additive particle can then be treated with a tethering agent as described herein, and affixed to the activated cellulose fibers. When prepared and deployed in accordance with these systems and methods, such a composite latex/starch additive can then used as functional additive with appropriate chemistry to improve bonding and retention in the pulp in the wet-end of papermaking. In embodiments, the granular starch particles can be used to deliver the latex into the papermaking web so that they are distributed throughout the fibrous matrix. Attached to the starch granules by electrostatic attraction, the latex particles then become embedded uniformly in the fibrous web. As the starch granules gelatinize during the papermaking process, they further spread the attached latex particles throughout the paper and onto the surface of the paper. These latex particles, depending on their melting or softening point, may then be advantageously incorporated in the final paper product, for example, forming a film in the paper during the paper drying process or otherwise imparting desirable latex properties to the final paper product. In embodiments, starch granules encrusted with latex (i.e., the composite latex/starch additive) helps to distribute the latex throughout the fibrous sheet via gelatinization and film formation.
In embodiments, latex polymers are selected that are oppositely charged from the starch granule that is selected to form the composite. Thus, latex/starch composites are formed and stabilized by electrostatic forces. As used herein, the term “latex” refers to a lyophobic colloidal suspension of a synthetic polymer or a natural polymer (such as hydrocolloid particles of gums, methyl cellulose, CMC, and the like) in a liquid phase. The terms “latex polymer” or “latex particle” refer to the polymeric material suspended in such a colloidal suspension. Latex comprising synthetic polymers can be produced by a polymerization reaction ex vivo. Examples of synthetic latex polymers or particles include styrene-butadiene rubber, acrylonitrile butadiene styrene, acrylic polymers, polyvinyl acetate polymers, and the like.
For the uses as disclosed herein, a suitable latex can be chosen from a wide variety of polymers. Some species of latex are inert polymers (Polyvinylacetate) while some are reactive (acrylic based), capable of flowing and crosslinking in the high temperature encountered in the drying section of papermaking Latex can also be selected according to the properties of its component polymers. For example, a useful latex can be comprised of glassy polymers such as polystyrene when stiffness is required, or rubbery polymers such as styrene-butadiene copolymers, when flexibility is required. In embodiments, a cationic latex is used that can be combined with a negatively charged starch particle.
Composite starch-latex additive particles as described herein can then be attached to the fibrous matrix formed by the papermaking process. The composite starch-latex particles, however, lack strong affinity to the natural and/or synthetic fibers used to form the paper web. Hence, additional steps as disclosed herein can be performed to attach the composite starch-latex particles to the fibrous web.
In embodiments, three steps as described previously can be performed to effect this attachment. In one step, the fibers are modified by the attachment of an agent, called an “activating agent,” that prepares the surface of the fibers for attachment to a suitably-modified composite starch-latex particle. In another step, the starch-latex particle is modified by attaching a tethering agent to the particle, where the tethering agent has a particular affinity for the activating agent attached to the paper fibers. The tether-bearing starch-latex particles are then admixed with the activated fibers, so that the activating agent and the tethering agents interact: this interaction durably affixes the composite particles bearing the tethers to the fibers bearing the activators. In embodiments, these systems and methods can be used to treat fibers used in papermaking with a cationic polymer of a specific molecular weight and composition as an activator, to treat composite starch-latex granules with an anionic polymer as a tethering agent, and to combine these separately treated populations so that the starch granules are attached to the pulp fibers.
The present disclosure from time to time refers to fibers used in papermaking as “pulp fibers.” It is recognized, though, that a variety of fibers can be used in papermaking. As used herein, the term “fiber” can include natural fibers or synthetic fibers. Natural fibers can include fibers from animal sources (e.g., wool, hair, silk), fibers from plant sources (e.g., cotton, flax, jute, cellulose), and fibers from mineral sources (e.g., asbestos, glass). As used herein, the term “natural fiber” refers to a fiber or a microfiber derived from a natural source without artificial modification. Natural fibers include vegetable-derived fibers, animal-derived fibers and mineral-derived fibers. Vegetable-derived fibers can be predominately cellulosic, e.g., cotton, jute, flax, hemp, sisal, ramie, and the like. Vegetable-derived fibers can include fibers derived from seeds or seed cases, such as cotton or kapok. Vegetable-derived fibers can include fibers derived from leaves, such as sisal and agave. Vegetable-derived fibers can include fibers derived from the skin or bast surrounding the stem of a plant, such as flax, jute, kenaf, hemp, ramie, rattan, soybean fibers, vine fibers, jute, kenaf, industrial hemp, ramie, rattan, soybean fiber, and banana fibers. Vegetable-derived fibers can include fibers derived from the fruit of a plant, such as coconut fibers. Vegetable-derived fibers can include fibers derived from the stalk of a plant, such as wheat, rice, barley, bamboo, and grass. Vegetable-derived fibers can include wood fibers. Animal-derived fibers typically comprise proteins, e.g., wool, silk, mohair, and the like. Animal-derived fibers can be derived from animal hair, e.g., sheep's wool, goat hair, alpaca hair, horse hair, etc. Animal-derived fibers can be derived from animal body parts, e.g., catgut, sinew, etc. Animal-derived fibers can be collected from the dried saliva or other excretions of insects or their cocoons, e.g., silk obtained from silkworm cocoons. Animal-derived fibers can be derived from feathers of birds. Mineral-derived natural fibers are obtained from minerals. Mineral-derived fibers can be derived from asbestos. Mineral-derived fibers can be a glass or ceramic fiber, e.g., glass wool fibers, quartz fibers, aluminum oxide, silicon carbide, boron carbide, and the like.
Synthetic fibers are fibers that are manufactured in whole or in part. Synthetic fibers include artificial fibers, where a natural precursor fiber is modified to form a fiber. Cellulose can also be modified to produce cellulose acetate fibers, and can form artificial fibers such as Rayon or Lyocell. In embodiments, artificial fibers can include fibers made from cellulose substrates, for example cellulose esters (e.g., cellulose acetate), rayon, bamboo fiber, lyocells, viscose rayon, and the like. Synthetic fibers also include fibers made from non-natural sources, can include fibers made from polyesters, aramids, acrylics, nylons, polyurethane, polyolefin, polyactides, and the like. Synthetic fibers can be formed from synthetic materials that are inorganic or organic.
2. The Attachment Process
a. Activation
As used herein, the term “activation” refers to the interaction of an activating material, such as a polymer, with suspended particles or fibers in a liquid medium, such as an aqueous solution. An “activator,” for example an “activator polymer,” can carry out this activation. In embodiments, high molecular weight polymers can be introduced into the particulate or fibrous dispersion as activator polymers, so that these polymers interact, or complex, with the dispersed particles or fibers. The polymer-fiber complexes interact with other similar complexes, or with other fibers, and form agglomerates.
This “activation” step can function as a pretreatment to prepare the surface of the suspended material (e.g., fibers) for further interactions in the subsequent phases of the disclosed system and methods. For example, the activation step can prepare the surface of the suspended materials to interact with other polymers that have been rationally designed to interact therewith in a subsequent “tethering” step, as described below. Not to be bound by theory, it is believed that when the suspended materials (e.g., fibers) are coated by an activating material such as a polymer, these coated materials can adopt some of the surface properties of the polymer or other coating. This altered surface character in itself can be advantageous for retention, attachment and/or dewatering.
In another embodiment, activation can be accomplished by chemical modification of the suspended material. For example, oxidants or bases/alkalis can increase the negative surface energy of fibers or particles, and acids can decrease the negative surface energy or even induce a positive surface energy on suspended material. In another embodiment, electrochemical oxidation or reduction processes can be used to affect the surface charge on the suspended materials. These chemical modifications can produce activated particulates that have a higher affinity for tethered anchor particles as described below.
Suspended materials suitable for modification, or activation, can include organic or inorganic particles, or mixtures thereof. Inorganic particles can include one or more materials such as calcium carbonate, dolomite, calcium sulfate, kaolin, talc, titanium dioxide, sand, diatomaceous earth, aluminum hydroxide, silica, other metal oxides and the like.
Organic particles can include one or more materials such as starch, modified starch, polymeric spheres (both solid and hollow), carbon based nanoparticles such as carbon nanotubes and the like. Particle sizes can range from a few nanometers to few hundred microns. In certain embodiments, macroscopic particles in the millimeter range may be suitable.
In embodiments, suspended materials may comprise materials such as lignocellulosic material, cellulosic material, minerals, vitreous material, cementitious material, carbonaceous material, plastics, elastomeric materials, and the like. In embodiments, cellulosic and lignocellulosic materials may include wood materials such as wood flakes, wood fibers, wood waste material, wood powder, lignins, wood pulp, or fibers from woody plants.
The “activation” step may be performed using flocculants or other polymeric substances. Preferably, the polymers or flocculants can be charged, including anionic or cationic polymers.
In embodiments, anionic polymers can be used, including, for example, olefinic polymers, such as polymers made from polyacrylate, polymethacrylate, partially hydrolyzed polyacrylamide, and salts, esters and copolymers thereof such as (sodium acrylate/acrylamide) copolymers, sulfonated polymers, such as sulfonated polystyrene, and salts, esters and copolymers thereof. Suitable polycations include: polyvinylamines, polyallylamines, polydiallyldimethylammoniums (e.g., the chloride salt), branched or linear polyethyleneimine, crosslinked amines (including epichlorohydrin/dimethylamine, and epichlorohydrin/alkylenediamines), quaternary ammonium substituted polymers, such as (acrylamide/dimethylaminoethylacrylate methyl chloride quat) copolymers and trimethylammoniummethylene-substituted polystyrene, and the like. Nonionic polymers suitable for hydrogen bonding interactions can include polyethylene oxide, polypropylene oxide, polyhydroxyethylacrylate, polyhydroxyethylmethacrylate, and the like. In embodiments, an activator such as polyethylene oxide can be used as an activator with a cationic tethering material in accordance with the description of tethering materials below. In embodiments, activator polymers with hydrophobic modifications can be used. Flocculants such as those sold under the trademark MAGNAFLOC® by Ciba Specialty Chemicals can be used.
In embodiments, activators such as polymers or copolymers containing carboxylate, sulfonate, phosphonate, or hydroxamate groups can be used. These groups can be incorporated in the polymer as manufactured, alternatively they can be produced by neutralization of the corresponding acid groups, or generated by hydrolysis of a precursor such as an ester, amide, anhydride, or nitrile group. The neutralization or hydrolysis step could be done on site prior to the point of use, or it could occur in situ in the process stream.
The activated suspended material (e.g., fiber) can also be an amine functionalized or modified. As used herein, the term “modified material” can include any material that has been modified by the attachment of one or more amine functional groups as described herein. The functional group on the surface of the suspended material can be from modification using a multifunctional coupling agent or a polymer. The multifunctional coupling agent can be an amino silane coupling agent as an example. These molecules can bond to a material's surface and then present their amine group for interaction with the particulate matter. In the case of a polymer, the polymer on the surface of a suspended fiber or particle can be covalently bound to the surface or interact with the surface of the particle and/or fiber using any number of other forces such as electrostatic, hydrophobic, or hydrogen bonding interactions. In the case that the polymer is covalently bound to the surface, a multifunctional coupling agent can be used such as a silane coupling agent. Suitable coupling agents include isocyano silanes and epoxy silanes as examples. A polyamine can then react with an isocyano silane or epoxy silane for example. Polyamines include polyallyl amine, polyvinyl amine, chitosan, and polyethylenimine.
In embodiments, polyamines (polymers containing primary, secondary, tertiary, and/or quaternary amines) can also self-assemble onto the surface of the suspended particles or fibers to functionalize them without the need of a coupling agent. For example, polyamines can self-assemble onto the surface of the particles or fibers through electrostatic interactions. They can also be precipitated onto the surface in the case of chitosan for example. Since chitosan is soluble in acidic aqueous conditions, it can be precipitated onto the surface of suspended material by adding a chitosan solution to the suspended material at a low pH and then raising the solution pH.
In embodiments, the amines or a majority of amines are charged. Some polyamines, such as quarternary amines are fully charged regardless of the pH. Other amines can be charged or uncharged depending on the environment. The polyamines can be charged after addition onto the suspended particles or fibers by treating them with an acid solution to protonate the amines. In embodiments, the acid solution can be non-aqueous to prevent the polyamine from going back into solution in the case where it is not covalently attached to the particle or fiber.
The polymers or particles can complex via forming one or more ionic bonds, covalent bonds, hydrogen bonding and combinations thereof, for example. Ionic complexing is preferred.
To obtain activated suspended materials, the activator could be introduced into a liquid medium through several different means. For example, a large mixing tank could be used to mix an activating material with fine particulate materials. Activated particles or fibers are produced that can be treated with one or more subsequent steps of attachment to tether-bearing anchor particles.
b. Tethering
As used herein, the term “tethering” refers to an interaction between an activated suspended particle or fiber and an additive particle, herein termed an anchor particle (as described below). The additive particle, for example, a composite additive particle, (“anchor particle”) can be treated or coated with a tethering material. The tethering material, such as a polymer, forms a complex or coating on the surface of the anchor particles such that the tethered anchor particles have an affinity for the activated suspended material. In embodiments, the selection of tether and activator materials is intended to make the two solids streams complementary so that the activated particles or fibers in the suspension become tethered, linked or otherwise attached to the anchor particle.
In accordance with these systems and methods, the tethering material acts as a complexing agent to affix the activated particles or fibers to the additive particle anchor material. In embodiments, a tethering material can be any type of material that interacts strongly with the activating material and that is connectable to an anchor particle. Composite latex-starch particles are an example of an additive particle or anchor particle that can be treated with a tethering agent.
In embodiments, various interactions such as electrostatic, hydrogen bonding or hydrophobic behavior can be used to affix an activated complex to a tethering material complexed with an anchor particle.
For use in papermaking, an anchor particle can be selected from any particulate matter that is desirably attached to cellulose fibers in the final paper product. The tether-bearing anchor particle comprising the desirable additive can then interact with the activated cellulose fibers in the wet paper stream. As an example, starch granules can be used as an anchor particle to be attached to the cellulose fibers, as is described in more detail below. Or, as described herein, composite latex-starch granules can be used as anchor particles, to be attached via tethering agents to activated fibers.
In embodiments, polymers such as linear or branched polyethyleneimine can be used as tethering materials. It would be understood that other anionic or cationic polymers could be used as tethering agents, for example polydiallyldimethylammonium chloride (poly(DADMAC)). In other embodiments, cationic tethering agents such as epichlorohydrin dimethylamine (epi/DMA), styrene maleic anhydride imide (SMAI), polyethylene imide (PEI), polyvinylamine, polyallylamine, amine-aldehyde condensates, poly(dimethylaminoethyl acrylate methyl chloride quaternary) polymers and the like can be used. Advantageously, cationic polymers useful as tethering agents can include quaternary ammonium or phosphonium groups. Advantageously, polymers with quaternary ammonium groups such as poly(DADMAC) or epi/DMA can be used as tethering agents. In other embodiments, polyvalent metal salts (e.g., calcium, magnesium, aluminum, iron salts, and the like) can be used as tethering agents. In other embodiments cationic surfactants such as dimethyldialkyl(C8-C22)ammonium halides, alkyl(C8-C22)trimethylammonium halides, alkyl(C8-C22)dimethylbenzylammonium halides, cetyl pyridinium chloride, fatty amines, protonated or quaternized fatty amines, fatty amides and alkyl phosphonium compounds can be used as tethering agents. In embodiments, polymers having hydrophobic modifications can be used as tethering agents.
The efficacy of a tethering material, however, can depend on the activating material. A high affinity between the tethering material and the activating material can lead to a strong and/or rapid interaction there between. A suitable choice for tether material is one that can remain bound to the anchor surface, but can impart surface properties that are beneficial to a strong complex formation with the activator polymer. For example, a polyanionic activator can be matched with a polycationic tether material or a polycationic activator can be matched with a polyanionic tether material. In one embodiment, a poly(sodium acrylate-co-acrylamide) activator is matched with a chitosan tether material.
In hydrogen bonding terms, a hydrogen bond donor should be used in conjunction with a hydrogen bond acceptor. In embodiments, the tether material can be complementary to the chosen activator, and both materials can possess a strong affinity to their respective deposition surfaces while retaining this surface property.
In other embodiments, cationic-anionic interactions can be arranged between activated suspended materials and tether-bearing anchor particles. The activator may be a cationic or an anionic material, as long as it has an affinity for the suspended material to which it attaches. The complementary tethering material can be selected to have affinity for the specific anchor particles being used in the system. In other embodiments, hydrophobic interactions can be employed in the activation-tethering system.
3. Retention and Incorporation in Papermaking
It is envisioned that the complexes formed from the additive or composite additive (“anchor”) particles and the activated fibrous matter can form a homogeneous part of a fibrous product like paper. In embodiments, the interactions between the activated suspended fibers and the tether-bearing anchor particles can enhance the mechanical properties of the complex that they form. For example, an activated suspended material can be durably bound to one or more tether-bearing anchor particles, so that the tether-bearing anchor particles do not segregate or move from their position on the fibers. Increased compatibility of the activated fine materials with a denser (anchor) matrix modified with the appropriate tether polymer can lead to further mechanical stability of the resulting composite material. For example, using latex-starch composites as tether-bearing anchor particles permits the latex to attach durably to the paper fibers; the gelatinization of the starch combined with the melting of the latex allows the flowable latex to permeate the paper fibers and impart desirable properties thereto. In embodiments, the latex-starch composites can be attached to fibers having low or no attachable affinity for each other, such as cellulosic fibers and synthetic fibers or two different populations of synthetic fibers, such that the melting of the latex allows the flowable latex to attach the fibers to each other to form a fibrous composite. In embodiments, such a fibrous composite may have further advantageous properties based, for example, on the elastomeric nature of the latex agent binding the fibers together. In other embodiments, the activation-tethering system disclosed herein can be applied to attach dissimilar types of cellulose fibers together, such as softwood fibers and hardwood fibers.
Most papers and paperboards attain specific physical characteristics by using a mixture of hardwood and softwood. Hardwood fibers are short in length, typically around 1 mm and with a diameter of around 20 um, resulting in a length to diameter ratio of 50:1. Softwood fibers are longer than hardwood, typically around 3 mm in length with a diameter of 30 um, resulting in a length to diameter ratio of 100:1. Softwood fibers offer high strength because of their ability to overlap and intertwine. Hardwood fibers offer good formation and improve aesthetics of the paper surface due to their small size. For a functional paper it is necessary to have adequate wet strength when it is made such that it does not break on the web and have sufficient mechanical properties (such as tensile and burst) that it could be used in its intended application (printing, photocopying for office pares and edge crush strength, stiffness and bulk for packaging applications). These mechanical properties are realized when the hardwood and softwood fibers are intimately mixed together and there is sufficient hydrogen bonding between them to enable strength and stiffness. To improve the low number of hydrogen bonds between the fibers, it is necessary to increase proximity of fibers and the number of contact points between them.
To achieve this, softwood fibers are subjected to refining processes that enhance their surface area, induces fibrillation and overall improves the contact area between hardwood and softwood fibers. Refining crushes the lumens of softwood cellulose fibers, changing them from a cylindrical shape into a ribbon shape. There are several benefits to refining: the flat fibers result in a flatter paper surface; the fibrils created from refining result in more sites for hydrogen bonding; the ratio of softwood and hardwood can be variably adjusted as necessary because of the increase in hydrogen bonding and good bond formation. Without refining, softwood fibers have a low attachable affinity to hardwood fibers. Refining, by increasing the surface area available for hydrogen bonding in the softwood fibers, improves the attachable affinity of softwood fibers to hardwood fibers so that they can be attached to each other to form functional paper products.
But refining also creates problems: the increased hydrogen bonding causes poor drainage on the paper machine; the additional residence time in a refiner is costly; the crushed lumen results in a significant decrease in caliper per basis weight. Thus there exists a need to improve the bonding between hardwood and softwood fibers without employing the refining process, or with less intensive refining. Techniques as disclosed herein, described in more detail below, can attach the dissimilar hardwood and softwood fibers to each other without refining, thereby decreasing or eliminating the exposure of the fibers to the refining process.
Hardwood fibers and unrefined softwood fibers are examples of dissimilar fibers having low attachable affinity to each other. In embodiments, other fibers dissimilar to cellulosic fibers can be introduced into the paper product to improve functionalities and attain certain features. Certain of these dissimilar fibers can have a low attachable affinity for the cellulosic fibers, such that the fibers do not coalesce during papermaking to make a functional paper product (i.e., one having adequate wet strength when it is made such that it does not break on the web and having sufficient mechanical properties (e.g., tensile and burst strength) allowing it to be used its intended application). Examples of dissimilar fibers having a low attachable affinity to cellulosic fibers can include vegetable stalk fibers, bast fibers and seed hull fibers. Vegetable stalk fibers such as sugarcane, bamboo, cereal straw (wheat, rye, oats, barley, rice), switchgrass, papyrus, corn, cotton, and sorghum have length to diameter ratios similar to softwood or hardwood, but often with high variation and have a high proportion of thin-walled cells. Bast fibers such as hemp, jute, kenaf, and flax are significantly more robust than stalk fibers but still have a high variation of length and diameter. Vegetable stalk and bast fibers are relatively inexpensive and most require only a year to reach full maturity (compared to wood which is in the range of 15-50 years). Economically, it would be advantageous to use vegetable stalk and bast fibers as fillers in combination with cellulosic fibers to form paper products. Use of the systems and methods disclosed herein can allow these fibers (e.g., vegetable stalk and bast fibers) having low attachable affinity to be formed into paper products with cellulosic fibers. As used herein, the term “low attachable affinity” also applies to fibers that have no attachable affinity to each other.
Dissimilar populations of fibers, such as a population of hardwood fibers and a population of softwood fibers, or a population of cellulosic fibers and a population of non-cellulosic (natural or synthetic) fibers can be attached to each other by treating one population with an activator, and the other population with a tethering agent, and combining the two treated populations. Dissimilar fibers where the native attachment of one fiber population to the other fiber population does not allow the two populations to coalesce during papermaking to make a functional paper product (i.e., one having adequate wet strength when it is made such that it does not break on the web and having sufficient mechanical properties (e.g., tensile and burst strength) allowing it to be used its intended application) are considered to be fiber populations having low attachable affinity. At the low end of the attachable affinity continuum are those fibers, such as cellulosic and hydrophobic synthetic fibers (e.g., olefinic, polyamide, polyester fibers, and the like) that have minimal or no attachable affinity for each other.
The interaction of the activator and the tethering agent forms a durable complex binding the two dissimilar fiber populations together, overcoming the tendency of fiber populations with low attachable affinity to form inadequate paper products, and reinforcing the attachment of fiber populations with a higher attachable affinity to each other. In an exemplary embodiment of two populations of dissimilar fibers with low attachable affinity, hardwood fibers can be treated with a tethering agent and softwood fibers can be treated with an activator, or vice versa. Using the activator-tether system in this way can save the time, energy and expense associated with processing the softwood fibers as is currently done. These two treated populations can be combined to form a paper product, attaching the hardwood and the softwood fibers together without the need to subject the softwood fibers to the refining process. Similarly, cellulosic fibers can be treated with an activator, and hydrophobic synthetic fibers can be treated with a tethering agent or vice versa: this represents another example of two dissimilar fiber populations having low or no attachable affinity to each other.
These two treated populations of dissimilar fibers can be combined to form a paper product, attaching (for example) the cellulosic and the non-cellulosic fibers together to form a paper product having specialized properties. As an example, cotton seed hull fibers (both staple and linter) are significantly longer than softwood fibers with relatively low variability in length and diameter, and can offer high strength to specialty papers (i.e. currency), but are very expensive. Hull fibers, typically high in lignin and/or inorganic content are dissimilar to cellulose, and they represent low affinity attachable fibers. Their attachment to cellulosic fibers can be improved by using the systems and methods disclosed herein, allowing fewer of these fibers to be used for forming a high performance product. Advantageously, hull fibers can be used as high performance additives, in combination with cellulosic fibers to form paper products.
For papermaking, cationic and anionic polymers for activators and tethering agents (respectively) can be selected from a wide variety of available polymers, as described above. In embodiments, starch granules used to form starch-latex composites can be used in their native state, or they can be modified with short amine side-groups, with amine polymers, or with hydrophobic side groups (each a “modified starch”). The presence of amines on the surface of the starch granules can help in attaching an anionic tethering polymer.
For activating the cellulose fibers, cationic polymers can be used. The polycation can be linked to the fiber surface using a coupling agent, for example a bifunctional crosslinking agent such as a carbonyldiimidazole or a silane, or the polyamine can self-assemble onto the surface of the cellulose fiber through electrostatic, hydrogen bonding, or hydrophobic interactions. In embodiments, the polyamine can spontaneously self-assemble onto the fiber surface or it can be precipitated onto the surface. For example, in embodiments, chitosan can be precipitated on the surface of the cellulose fibers to activate them. Because chitosan is soluble only in an acidic solution, it can be added to a cellulose fiber dispersion at an acidic pH, and then can be precipitated onto the surface of the cellulose fibers by slowly adding base to the dispersion until chitosan is no longer soluble. In embodiments, a difunctional crosslinking agent can be used to attach the polycation to the fiber, by reacting with both the polycation and the fiber.
In other embodiments, a polycation such as a polyamine can be added directly to the fiber dispersion or slurry. For example, the addition level of the polycation can be between about 0.01% to 5.0% (based on the weight of the fiber), e.g., between 0.1% to 2%. For example, if the cellulose fiber population is treated with a polyamine like poly(DADMAC), a separately treated population of tether-bearing starch granules can be mixed in thereafter, resulting in the attachment of the starch-latex composites to the cellulose fibers by the interaction of the activator polymer and the tether polymer. In embodiments, starch-latex composites can be treated with a variety of anionic polymers, such as anionic polyacrylamide, which then act as tethers.
Starch that is to be treated in accordance with these systems and methods can be further derivatized or coated with moieties that impart desirable properties, e.g., hydrophobicity, oleophobicity or both. Starches thus modified may be also termed “modified starches.” Preferred oil resistant coating formulations are aqueous solutions of cellulose derivatives such as methylcellulose, ethyl cellulose, propyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, ethylhydroxypropyl cellulose, and ethylhydroxyethyl cellulose, cellulose acetate butyrate, which may further comprise polyvinyl alcohol and/or its derivatives. Another group of preferred oil resistant coating compositions are latex emulsions such as the emulsions of polystyrene, styrene-acrylonitrile copolymer, carboxylated styrene-butadiene copolymer, ethylene-vinyl chloride copolymer, styrene-acrylic copolymer, polyvinyl acetate, ethylene-vinyl acetate copolymer, and vinyl acetate-acrylic copolymer. The starch granule thus coated with grease resistant formulations could be attached to the activated pulp fibers via tethering, such that the surface segregation of the starch granule will modify the surface of the paper product.
In embodiments, the presence of hydrophobic starch also improves the hydrophobicity of the resulting paper without needing an internal sizing such as alkyl succinic anhydride (ASA), alkyl ketene dimer (AKD) or Rosin. The gelatinized hydrophobic starch sizes the entire thickness of the paper. This property is useful in reducing the coating requirements in making coated sheets. The coating applied using a roller or a metering bar or any such methods, would remain on the surface of the paper and not impregnate the bulk of the paper thus needing less coating to achieve the same amount of gloss and surface finish.
In other embodiments, the addition of a coating agent to the starch can improve its mechanical properties such as bending stiffness or tensile strength, or could improve its optical properties (e.g., TiO2 nanoparticles bound to starch).
Materials
A 0.5% slurry was prepared by blending 3.5% by weight softwood and hardwood pulp mixture (in the ratio of 20:80) in water.
A 0.5% slurry was prepared by blending 22.5% recycled brown pulp in water.
Handsheets were prepared using a Mark V Dynamic Paper Chemistry Jar and HandSheet Mold from Paper Chemistry Laboratory, Inc. (Larchmont, N.Y.). Handsheets were prepared without addition of polymers as controls, using the pulps prepared as described in Example 1 and 2. Handsheets were prepared with the addition of polymers as experimental samples, as described below.
For preparing each experimental handsheet, the appropriate volume of 0.5% pulp slurry prepared in accordance with Examples 1 or 2 (as applicable) was activated with up to 2% of the selected polymer(s) (based on dry weight), as described below in more detail. Polymer additions were performed at 5 minute intervals. This polymer-containing slurry was diluted with up to 3 L of water and added to the handsheet maker, where it was mixed at a rate of 1100 RPM for 5 seconds, 700 RPM for 5 seconds, and 400 RPM for 5 seconds. The water was then drained off. The subsequent sheet was then transferred off of the wire, pressed and dried.
For preparing sheets containing low melting point synthetic fibers PEFYB-00620, PEFYB-ONL490, PEFYB-00Y600, as described below in Example 9, the sheets were dried as described above and then heated further to ensure melting of the synthetic fibers.
Tensile tests were conducted on control and experimental samples using an Instron 3343. Samples of handsheets for tensile testing were initially cut into 1 in wide strips with a paper cutter, and then attached within the Instron 3343. The gauge length region was set at 4 in and the crosshead speed was 1 in/minute. Thickness was measured to provide stress data as was the weight to be able to normalize the data by weight of samples. The strips were tested to failure with an appropriate load cell. At least three strips from each control or experimental handsheet sample were tested and the values were averaged together.
StaLok 300 cationic starch was dispersed in water in slurry form such that the solids content was about 20%. COSEAL 30061A anionic latex was added to the cationic starch, up to 50% by weight of starch. The latex is spontaneously self-assembled on the starch surface resulting in a clear solution when the starch settles down. By contrast, the latex solution without starch remains milky white, as shown in
StaLok 300 cationic starch was dispersed in water in slurry form such that the solids content was about 20%. COSEAL 30061A anionic latex was added to the cationic starch, up to 50% by weight of starch. Latex-coated starch composite particles were formed, which acted as “anchor particles.” MagnaFloc 919 was then added 0.1% by weight as a tethering agent.
800 mL of a 0.5% pulp slurry prepared in accordance with Example 1 or 2 (as applicable) was initially provided. The pulp slurry was activated with 0.1% by fiber weight polyDADMAC. Separately, latex-coated cationic starch granules were prepared as a slurry in accordance with Example 5 (i.e., a non-tether-bearing starch slurry), and tethered latex-coated cationic starch granules were prepared as a slurry in accordance with Example 6 (i.e., a tether-bearing starch slurry). Each slurry was mixed for 5 minutes individually and then the pulp slurry was combined with a non-tether-bearing or a tether-bearing starch slurry and mixed for another 5 minutes using an overhead stirrer. Handsheets were then produced by the method in Example 3. The final basis weight was approximately 80 gsm for these handsheets.
PEFYB-00620, PEFYB-0NL490, PEFYB-00Y600, and PES/Nylon Bicomponent Fibers (and mixtures of two or more of the previous) were dispersed in water in slurry form such that the solids content was about 20%. In samples containing a tether, MagnaFloc 919 was then added 0.1% by weight as a tethering agent.
800 mL of a 0.5% pulp slurry prepared in accordance with Example 1 or 2 (as applicable) was initially provided. The pulp slurry was activated with 0.1% by fiber weight polyDADMAC. Separately, synthetic fibers with and with and without tethers were prepared in accordance with Example 8, so that their performance could be compared with the performance of the samples prepared with the activated pulp and tethered synthetic fibers. Each slurry was mixed for 5 minutes and then combined and mixed for another 5 minutes using an overhead stirrer. Handsheets were then produced by the method in Example 3. The final basis weight was approximately 80 gsm for these handsheets.
CG-10 was added to water to make a 1% by weight slurry of chitosan. Strong acid was added dropwise to the slurry with stirring until the solution reached a pH of 2.5 and the chitosan was dissolved.
PEFYB-00620, PEFYB-0NL490, PEFYB-00Y600, and PES/Nylon Bicomponent Fibers (and mixtures of two or more of the previous) were dispersed in water in slurry form such that the solids content was about 20%. A strong acid was then added to the slurry to bring the pH below 2.5. The solution in Example 10 was added to the synthetic fiber slurry so that the chitosan was 1% by weight of the synthetic fibers. The pH was then raised back to 8-9 with a strong base to precipitate any unbound chitosan.
800 mL of a 0.5% pulp slurry prepared in accordance with Example 1 or 2 (as applicable) was initially provided. Separately, chitosan-coated synthetic fibers were prepared as a slurry in accordance with Example 11, where chitosan exemplifies a tethering agent. Each slurry preparation was mixed for 5 minutes, then samples of the uncoated pulp slurry were combined with the chitosan-coated synthetic fibers slurry and mixed for another 5 minutes using an overhead stirrer. Handsheets were then produced by the method in Example 3. The final basis weight was approximately 80 gsm for these handsheets.
Handsheet samples were prepared from activated pulp in accordance with Example 7, where the amount of latex-coated and tether-bearing latex-coated starch (StaLok 300) was 4.25% of the solids weight. The latex-coated starch had been coated with COSEAL 30061A in accordance with Example 5. The tether-bearing latex-coated starch had been coated with COSEAL30061A and then tethered with MagnaFloc 919 in accordance with Example 6. Control handsheets were also prepared in accordance with Example 3 (no activation) using the latex-coated starch particles of Example 5 (no tether). Strength data was gathered from handsheet samples made with: (1) activated pulp and tether-bearing latex-coated samples (“ATA treated”), (2) activated pulp and non-tether-bearing latex-coated particles, and (3) non-activated pulp and non-tether-bearing latex-coated particles. For ATA-treated samples, the tether used on the starch was 0.1% MagnaFloc 919 by solids and the activator on the pulp was 0.1% polyDADMAC by solids. The max load for each sample was measured using an Instron as in Example 4. Data were normalized by the mass to show load contribution per overall solids weight. Graph 1 (
The hydrophobicity improvement with the samples above was also examined. Using handsheet samples prepared as in Example 7, hydrophobicity was tested by depositing a 25 microliter water droplet on the surface of the paper and recording the time for the droplet to completely absorbed by the paper. The results of the hydrophobicity tests are shown in Table 1 (
Samples were prepared as in Example 9, where the amount of tether-bearing synthetic fibers were a total of 15% of the solids weight. The tether-bearing synthetic fibers had been prepared in accordance with Example 8. Samples were made both with activator and tether and without either activator or tether. For ATA-treated samples, the tether used on the synthetic fibers was 0.1% MagnaFloc 919 by solids and the activator on the pulp was 0.1% polyDADMAC by solids. The max load for each sample was measured using an Instron as in Example 4. Data were normalized by the mass to show load contribution per overall solids weight. Graph 2 (
Samples were prepared as in Example 12, where the amount of chitosan-coated synthetic fibers were a total of 15% of the solids weight. The chitosan-coated synthetic fibers had been prepared in accordance with Example 11. The max load for each sample was measured using an Instron as in Example 4. Data were normalized by the mass to show load contribution per overall solids weight. Graph 3 (
A 0.5% slurry was prepared by blending 93% solids content softwood in water.
PCC and Pearl Starch (and mixtures of the two) were dispersed in water in slurry form such that the solids content was about 20%. In samples containing a tether, MagnaFloc 919 was then added 0.05% by weight of solids as a tethering agent.
600 mL of a 0.5% pulp slurry prepared in accordance with Example 16 was initially provided. The pulp slurry was activated with 0.1% by fiber weight polyDADMAC. Separately, starch, PCC, and tethered starch/PCC were prepared as a slurry in accordance with Example 17. Each slurry was mixed for 5 minutes and then combined and mixed for another 5 minutes using an overhead stirrer. Handsheets were then produced by the method in Example 16. The final basis weight was approximately 60 gsm for these handsheets.
Samples were prepared as in Example 18, where the amount of PCC, Pearl Starch, tether-bearing pearl starch and PCC was between 5% and 30% of the solids weight. The tethered PCC with pearl starch had been prepared with MagnaFloc 919 in accordance with Example 17. Samples were made with both activator and tether or with neither activator nor tether. For ATA-treated samples, the tether used on the dry-mixed pearl starch and PCC and was 0.05% MagnaFloc 919 by solids and the activator on the pulp was 0.1% polyDADMAC by solids. The max load for each sample was measured using an Instron as in Example 16. Data were normalized by the mass to show load contribution per overall solids weight. Graph 4 (
Iron (III) Oxide particles were dispersed in water in slurry form such that the solids content was about 20%. In samples containing a tether, MagnaFloc 919 was then added 0.05% by weight of solids as a tethering agent.
600 mL of a 0.5% pulp slurry prepared in accordance with Example 16 was initially provided. The pulp slurry was activated with 0.1% by fiber weight polyDADMAC. Separately, Iron (III) Oxide with and without tether were prepared as a slurry in accordance with Example 20. Each slurry was mixed for 5 minutes and then combined and mixed for another 5 minutes using an overhead stirrer. Handsheets were then produced by the method in Example 16. The final basis weight was approximately 60 gsm for these handsheets.
1″ by 2″ pieces of handsheets with iron (III) oxide prepared in Example 21 were held to a ceramic magnet to verify holdout of Iron (III) Oxide in the sheet. Sheets containing as little as 5% Iron (III) oxide by solids weight held onto the magnet with no other support.
3.5% solids unrefined softwood pulp was diluted with water to 1% solids. 0.1% polyDADMAC by weight of softwood solids was added to the slurry and mixed gently for 30 seconds. The activated slurry was then diluted with water down to 0.5% solids.
3.5% solids unrefined hardwood pulp was diluted with water to 1% solids. 0.1% MagnaFloc 919 by weight of hardwood solids was added to the slurry and mixed gently for 30 seconds. The tethered slurry was then diluted with water down to 0.5% solids.
260 mL each of 0.5% solids activated softwood and tethered hardwood pulp as described in Examples 5 and 6 were combined and mixed for 5 minutes. Handsheets were then produced by the method in Example 3. The final basis weight was approximately 80 gsm for these handsheets.
While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
This application is a continuation of International Application No. PCT/US12/53098, which designated the United States and was filed on Aug. 30, 2012, published in English, which claims the benefit of U.S. Provisional Application Ser. No. 61/530,260, filed Sep. 1, 2011 and U.S. Provisional Application Ser. No. 61/660,146, filed Jun. 15, 2012. The entire contents of the above applications are incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 61530260 | Sep 2011 | US | |
| 61660146 | Jun 2012 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US12/53098 | Aug 2012 | US |
| Child | 14192253 | US |
