Compositions and methods of crosslinked kraft pulp

Abstract

To provide a pulp including crosslinked cellulose fibers and having high brightness, reactivity and intrinsic viscosity.SOLUTION: A method according to the present technique includes: forming a pulp from a cellulosic feedstock; bleaching the pulp; crosslinking cellulose fibers within the pulp while the pulp has a high consistency; and drying the pulp. Crosslinking the cellulose fibers can include exposing the fibers to a glycidyl ether crosslinker having two or more glycidyl groups and a molecular weight per epoxide within a range from 140 to 175. Another method according to the present technique includes: preparing an aqueous liquid suspension of the pulp containing chemical wood pulp fibers having been bleached and dried; crosslinking the fibers using the glycidyl ether crosslinker; and drying the pulp.SELECTED DRAWING: Figure 1

Description

Detailed Description of the Invention

[0001] Cross - Reference to Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 62 / 299,894, filed on February 25, 2016, the entire contents of which are incorporated herein by reference. To the extent that the foregoing application and / or any other material incorporated herein by reference conflicts with the present disclosure, the present disclosure takes precedence.

[0002] Technical Field The present technology relates to cellulose products (e.g., pulp) and cellulose derivatives (e.g., cellulose ethers).

[0003] Background Art Cellulose ethers (e.g., carboxymethyl cellulose, methyl cellulose, etc.) form aqueous solutions and are available in various grades mainly depending on the viscosity of these solutions. Higher - grade cellulose ethers that form more viscous aqueous solutions tend to have higher utility values than lower - grade cellulose ethers that form less viscous aqueous solutions. The ability of a given cellulose ether to form a more viscous aqueous solution is closely related to the degree of polymerization and / or other properties of the cellulose precursor from which the given cellulose ether is produced. Higher - grade cellulose ethers are conventionally produced from dissolving - grade pulp (e.g., cotton linter pulp), while medium - grade and lower - grade cellulose ethers are conventionally produced from less expensive wood pulp. The pulp grades referred to in the present disclosure are further discussed in Herbert Sixta, Handbook of Pulp, Wiley - Vch (2006), the entire contents of which are incorporated herein by reference. The degree of polymerization of most wood pulp does not exceed about 1,500. In contrast, dissolving - grade pulp often has a degree of polymerization of 2,400 or more. Unfortunately, dissolving - grade pulp tends to be expensive. Prior art attempts to modify less expensive pulp for the production of higher - grade cellulose derivatives have met with only limited success. Thus, there is a need for further innovation in this field.

[0004] Many aspects of the present technology will be better understood with reference to FIGS. 1 and 2.

Brief Description of the Drawings

[0005]

Figure 1

Figure 2

[0006] Detailed Description The method for producing pulp, related systems, and compositions according to embodiments of the present technology can at least partially address one or more problems associated with the prior art, whether or not such problems are specified herein. For example, by the method according to at least some embodiments of the present technology, low-cost pulp can serve as a precursor in the production of high-grade cellulose ethers and / or other cellulose derivatives (e.g., cellulose esters). For example, kraft pulp is considerably less expensive and more widely available than dissolving-grade pulp. However, when standard kraft pulp is used as a precursor for the production of cellulose ethers, the resulting cellulose ethers tend to be of low grade.

[0007] Desirable properties in pulp used for the production of cellulose derivatives include high brightness and high viscosity. Due to the high brightness in the pulp, the cellulose derivative produced from the pulp can be almost colorless or completely colorless. In many products made from cellulose derivatives (e.g., medical fabrics, foods, drywall, etc.), it is not desirable for the cellulose derivative to impart color to the product. Similarly, in these and other applications, it tends to be useful for the cellulose derivative to have a high viscosity while still being soluble in water. Therefore, cellulose derivatives that are almost colorless or completely colorless and have a high viscosity tend to be more expensive than cellulose derivatives with prominent color and low viscosity. Due to the high reactivity in the pulp, the efficiency of the functionalization reaction (e.g., etherification) used to convert the pulp into a cellulose derivative increases. The reactivity of the pulp is closely related to the extent to which the surface of the cellulose fibers in the pulp comes into contact with water molecules in which the functionalizing agent is distributed on the surface. As the contact between the surface of the cellulose fibers and the water molecules increases, the degree to which the pulp retains water also increases. Therefore, pulp with a higher water retention value also tends to be pulp with higher reactivity.

[0008] Some prior processes have had some success in increasing the ability of kraft pulp to produce cellulose ethers that form highly viscous aqueous solutions. Unfortunately, these prior processes have always achieved that success at the expense of other desirable properties in the cellulose ether and / or at the expense of process yield. For example, some prior processes involve reducing or eliminating bleaching during the kraft process. Pulp obtained from these processes tends to have a high lignin content and correspondingly low brightness. As a result, an undesirable color results in the cellulose ether produced from these pulps. As another example, some prior processes involve increasing hemicellulose removal from kraft pulp. However, these processes have low yields due to the removal of the bulk provided by hemicellulose. Moreover, pulp obtained from these processes tends to have low reactivity due to the conversion of the component cellulose from cellulose-I to cellulose-II. Conventional crosslinking reactions also typically reduce the water retention value (and reactivity) of the pulp. Prior processes that modify low-cost pulp, even allowing for low brightness, low yield, and / or low reactivity, have still not been able to produce pulp suitable for producing cellulose ethers that form aqueous solutions having a viscosity about the same as that of the cellulose derivative produced from high-viscosity dissolved grade ether pulp.

[0009] Methods according to at least some embodiments of the present technology include crosslinking pulp having a relatively high consistency (e.g., a consistency of 12% or more). These methods may further include crosslinking the pulp with a crosslinking agent selected to increase the water retention value of the pulp. Suitable crosslinking agents for this purpose include, for example, glycidyl ether crosslinking agents having two or more glycidyl groups and a molecular weight in the range of 140 to 175 per epoxide. It has surprisingly been found that crosslinking of relatively high consistency pulp and the use of this type of crosslinking agent renders low-cost pulp (e.g., kraft pulp) suitable for the production of high-grade cellulose derivatives with little or no associated reduction in brightness, yield, reactivity, and / or other desirable pulp properties.

[0010] Conventional uncrosslinked kraft pulp tends to have lower reactivity than other chemical pulps such as sulfite pulp (i.e., pulp made by extracting lignin from wood mainly using sulfite). However, in at least some embodiments of the present technology, crosslinked kraft pulp has relatively high reactivity. Without wishing to be bound by theory and merely as a theory, this may be due to the presence of crosslinks that uniformly add additional space between cellulose chains. Longer-chain crosslinking agents (e.g., polyglycidyl ethers) can produce crosslinked pulp with higher reactivity than shorter-chain crosslinking agents (e.g., 1,3-dichloro-2-hydroxypropanol (DCP)) under similar crosslinking conditions. Pulp crosslinked with a longer-chain crosslinking agent may have a crystallinity index lower than that of the starting material pulp and even lower than that of dissolving-grade sulfite wood pulp and cotton linter pulp. For high-viscosity ether applications, crosslinking kraft pulp instead of sulfite pulp can be advantageous in at least some cases because kraft is a more powerful pulping process than the sulfite pulping process, has a higher yield (higher hemicellulose content), is less expensive, and is more environmentally considerate. Under the same crosslinking conditions, crosslinked pulp with higher reactivity than shorter-chain crosslinking agents (e.g., 1,3-dichloro-2-hydroxypropanol (DCP)) can be produced. Pulp crosslinked with a longer-chain crosslinking agent may have a crystallinity index lower than that of the starting material pulp and even lower than that of dissolving-grade sulfite wood pulp and cotton linter pulp. For high-viscosity ether applications, crosslinking kraft pulp instead of sulfite pulp can be advantageous in at least some cases because kraft is a more powerful pulping process than the sulfite pulping process, has a higher yield (higher hemicellulose content), is less expensive, and is more environmentally considerate.

[0011] In conventional kraft processing, the pulp is maintained at a relatively low consistency (e.g., a consistency of 10% or less). As the consistency of the pulp increases, it becomes more difficult to flow the pulp through pipes and mix the pulp. Thus, any crosslinking in conventional processes for modifying kraft pulp to increase the potential for producing high-grade cellulose derivatives is also carried out at relatively low consistency. One surprising discovery relevant to at least some embodiments of the present technology is that increasing the consistency of the pulp during crosslinking can increase the water retention value of the crosslinked pulp. This discovery and / or other discoveries relevant to at least some embodiments of the present technology ultimately make it possible to produce kraft pulp that is a true alternative to expensive dissolving-grade pulp and / or a suitable extender in the production of high-grade cellulose derivatives.

[0012] Specific details of methods of making pulp, and related systems and compositions, according to some embodiments of the present technology are described herein with reference to FIGS. 1 and 2. The methods and related systems and compositions may be disclosed herein primarily or entirely in the context of modifying kraft pulp for the production of cellulose derivatives, but other contexts are within the scope of the present technology in addition to those disclosed herein. For example, the suitable features of the described methods, systems, and compositions may be carried out in the context of sulfite pulp or even in the context of dissolving-grade pulp. As another example, the suitable features of the described methods, systems, and compositions may be carried out in the context of modifying kraft pulp or other pulp for uses other than the production of cellulose derivatives, such as the manufacture of specialty paper products.

[0013] In general, it should be understood that other methods, systems, and compositions in addition to those disclosed herein are within the scope of the present technology. For example, the methods, systems, and compositions according to embodiments of the present technology may have operations, components, relative configurations, etc. that are different from and / or additional to those disclosed herein. Moreover, those skilled in the art will understand that the methods, systems, and compositions according to embodiments of the present technology may not involve the specific operations, components, relative arrangements, etc. disclosed herein without departing from the present technology.

[0014] Test Methods and Acronyms AOX: Adsorbable Organic Halides determined by EPA Method 1650A.

[0015] Ash Content: Determined by TAPPI T 211 om-07. ASTM: American Society for Testing and Materials.

[0016] Brightness: Determined by TAPPI T 525 om-12. Capillary Viscosity: Determined by TAPPI T 230 om-99.

[0017] Carboxyl Content: Determined by TAPPI T 237 om-08. Centrifugal Capacity: Determined by the corresponding method disclosed in U.S. Patent No. 8,039,683, the entire content of which is incorporated herein by reference.

[0018] CMC: Carboxymethyl Cellulose. Roughness: Determined by the corresponding method disclosed in U.S. Patent No. 6,685,856, the entire content of which is incorporated herein by reference.

[0019] Crystallinity index: Determined by the corresponding method of Lionetto et al., "Monitoring Wood Degradation during Weathering by Cellulose Crystallinity", Materials, 5, 1910 - 1922 (2012), the entire content of which is incorporated herein by reference.

[0020] Cuen solubility: Solubility in copper ethylenediamine under the conditions of TAPPI T 254 cm - 00.

[0021] Carls index: Determined by the corresponding method disclosed in U.S. Patent No. 6,685,856, the entire content of which is incorporated herein by reference.

[0022] Degree of polymerization: The number of D - glucose monomers in the cellulose molecule measured by ASTM - D1795 - 96. The average degree of polymerization represents the average number of D - glucose molecules per cellulose polymer in the cellulose polymer population.

[0023] Degree of substitution (DS): Determined by ASTM D 1439 - 03. DWP: Dissolved wood pulp.

[0024] Falling ball (FB) viscosity: Determined by TAPPI T 254 cm - 00. Drainability: Canadian standard drainability determined by TAPPI T 227 om - 04.

[0025] Free swelling: Determined by the corresponding method disclosed in U.S. Patent No. 8,039,683, the entire content of which is incorporated herein by reference.

[0026] Hemicellulose content: The total content of mannan and xylan determined by the method described in Examples 6 and 7 of U.S. Patent No. 7,541,396, the entire content of which is incorporated herein by reference. This test is based on TAPPI T 249 cm00 using analysis by Dionex ion chromatography.

[0027] HPLC: High Performance Liquid Chromatography. Intrinsic viscosity (IV): Determined in accordance with ASTM D1795-96.

[0028] ISO: International Organization for Standardization. Copper number: Determined in accordance with ISO 302:2004.

[0029] Kink angle: Determined by the corresponding method disclosed in U.S. Patent No. 6,685,856, the entire contents of which are incorporated herein by reference.

[0030] Kink index: Determined by the corresponding method disclosed in U.S. Patent No. 6,685,856, the entire contents of which are incorporated herein by reference.

[0031] Lignin content: Determined by the methods described in Examples 6 and 7 of U.S. Patent No. 7,541,396, the entire contents of which are incorporated herein by reference.

[0032] MCA: Monochloroacetic acid. NCASI: National Council for Air and Stream Improvement.

[0033] Oven dry (OD): Dried to a moisture content of 7 wt% or less. R18: Measured in accordance with TAPPI T 235 cm-00.

[0034] Resulting CMC viscosity: Represents the viscosity of a 0.5% solution of the resulting CMC by the following resulting CMC test method.

[0035] Resulting CMC color: See the following resulting CMC test method. Resulting CMC turbidity: See the following resulting CMC test method.

[0036] TAPPI: Technical Association of the Pulp and Paper Industry. Transition metal content: determined by EPA SW-856 Method 3050, 200.8.

[0037] US EPA: United States Environmental Protection Agency. Water retention value (WRV): determined by TAPPI T UM256M (2011).

[0038] Wet bulk: determined by the corresponding method disclosed in U.S. Patent No. 8,722,797, the entire content of which is incorporated herein by reference.

[0039] WPE: weight per epoxide. Obtained CMC test method Throughout the present disclosure, the characteristics of the pulp can be characterized in terms of the "obtained CMC" characteristics. These are the characteristics of the CMC that can be produced using the pulp, and CMC serves as a representative example of cellulose derivatives. It should be understood that CMC is not the only cellulose derivative that can be produced using the pulp according to embodiments of the present technology. The obtained CMC characteristics of a given pulp described herein are determined by the following procedure. Additional details regarding this procedure can be found in Nevell T.P. and Zeronian S., Cellulose Chemistry and its Applications, Chapter 15 - Cellulose Ethers (1985), which is incorporated herein by reference in its entirety.

[0040] First, determine the degree of substitution of the pulp. If the degree of substitution of the pulp is at least 1.0, proceed as defined below. If the degree of substitution of the pulp is 1.0 or less, proceed as defined below, but use 6.4 mL (instead of 8.0 mL) of 30% NaOH solution and 2.9 g (instead of 3.6 g) of MCA. Slurry a (fibrillated) pulp sample of 3 g in 80 mL of isopropanol (oven-dried). Add 8.0 mL of 30% NaOH solution over 3 minutes. Stir the suspension at 20 °C for 1 hour. Add 3.6 g of MCA (as a 15.2 mL solution of 23.6 g of MCA / 100 mL of isopropanol) over 3 minutes. Raise the temperature to 55 °C in 25 minutes and continue stirring for 3.5 hours. Drain the resulting fibrous CMC and wash it with 70% ethanol. Neutralize the sample to pH 7.0 with acetic acid and then filter. Wash the filter cake again at 20 °C with 70% ethanol and filter. Wash one more time at 20 °C with 70% ethanol and then wash three more times at 20 °C with 100% denatured ethanol, repeating washing and filtering. Air-dry the sample to a solids content of 70 - 85% to form the resulting CMC. Test a 0.5% solution of the resulting CMC using a Brookfield viscometer with spindle 2 and 50 RPM at 20 °C in accordance with ASTM method D2196-99 to determine the resulting CMC viscosity. Test a 0.5% solution of the resulting CMC by US EPA method 180.1 to determine the resulting CMC turbidity, and a 0.013% solution of the resulting CMC is tested by NCASI method TB253 to determine the resulting CMC color.

[0041] Starting material Examples of suitable starting materials for making pulp according to embodiments of the present technology include wood and recycled paper. In at least some embodiments, the starting material is not dried. In at least some embodiments, the starting material is dried. In the wood pulp manufacturing industry, trees are conventionally classified as either hardwood or softwood by conventional methods. The pulp used as the starting material can be derived from softwood or hardwood tree species. Examples of suitable softwood tree species include spruce (e.g., white spruce and balsam spruce), pine (e.g., strobe pine and loblolly pine), fir (e.g., balsam fir), larch (e.g., tamarack), hemlock, and douglas fir (e.g., western hemlock and eastern hemlock). Examples of suitable hardwood species include acacia, alder (e.g., red alder and european alder), aspen (e.g., quaking aspen), beech, birch, oak (e.g., white oak), rubber tree (e.g., eucalyptus and populus), poplar (e.g., balsam poplar, eastern cottonwood, black cottonwood, and lombardy poplar), gum and maple (e.g., sugar maple, red maple, silver maple, and bigleaf maple).

[0042] Wood from softwood or hardwood species generally contains three main components: cellulose, hemicellulose, and lignin. Cellulose makes up approximately 50% of the plant's woody structure and is an unbranched polymer of D - glucose monomers. Individual cellulose polymer chains associate to form more densely packed fibrils, which in turn associate to form microfibrils arranged in bundles. These bundles form fibers that are visible as components of the plant cell wall when viewed at high magnification under an optical or scanning electron microscope. Cellulose is highly crystalline as a result of a wide range of intramolecular and intermolecular hydrogen bonds. Hemicellulose is a heterogeneous group of low - molecular - weight carbohydrate polymers such as xylan and mannan that are related to cellulose in wood. Hemicellulose is an amorphous branched polymer, in contrast to cellulose, which is a linear polymer. Lignin is a complex aromatic polymer that makes up about 20% - 40% of wood and, in this case, exists as an amorphous polymer.

[0043] Use and Modified Kraft Process of Un-dried Pulp As described above, some embodiments include the use of un-dried pulp as a starting material for the production of pulp according to the present disclosure. In most pulp manufacturing machines, the pulp produced by a chemical pulping process (such as the kraft process) is subsequently further delignified and whitened by a bleaching process. The bleached pulp is then dehydrated and dried for shipment. Embodiments in which un-dried pulp is used may include a modified kraft process, where the pulp produced by kraft pulping is then treated with a cross-linking agent before drying to produce a cross-linked pulp. For example, the pulp can be treated with a cross-linking agent during the bleaching process, such as between two bleaching stages, or during or after a selected bleaching stage. This approach can be advantageous in that the cross-linking step can be selectively incorporated into the standard kraft process utilized in the manufacturing machine, enabling variable manufacturing capabilities. Moreover, cross-linking agents suitable for the production of pulp according to the present disclosure generally require an aqueous medium, which is provided during the bleaching process.

[0044] An example as an illustration of the modified kraft process is described below in connection with FIG. 1. Generally, kraft processing involves chemically digesting a cellulose feedstock (e.g., wood chips) in white liquor, an aqueous solution of cooking chemicals (e.g., sodium sulfide and sodium hydroxide), while raising the temperature and pressure. The cooking chemicals dissolve the lignin that binds the cellulose fibers within the feedstock to each other. When this chemical digestion is complete, the pulp is transferred to an atmospheric tank known as a "blowing tank". The contents of the blowing tank are then sent to a pulp washer where the spent cooking chemicals are separated from the pulp. The pulp then proceeds through various stages of washing and bleaching and is then compressed and dried into the final product.

[0045] The kraft process is designed to recover cooking chemicals and heat. For example, spent cooking chemicals and pulp wash water can be combined to form a dilute black liquor that is concentrated to about 55% solids in a multiple-effect evaporator system. The black liquor can then be further concentrated to 65% solids either by contacting the black liquor with flue gas from the recovery furnace in a direct contact evaporator or in an indirect contact concentrator. The concentrated black liquor can then be burned in a recovery furnace. Combustion of the organic matter dissolved in the black liquor can provide heat for generating process steam and for converting sodium sulfate to sodium sulfide. The inorganic chemicals present in the black liquor can be collected as a melt that has melted at the bottom of the furnace. The melt can be dissolved in water to form green liquor, which can then be transferred to a causticizing tank where quicklime (calcium oxide) is added and the solution can be converted back to white liquor for return to the digester system. The lime mud precipitate from the causticizing tank can be calcined in a lime kiln to regenerate the quicklime.

[0046] Figure 1 is a flowchart illustrating an exemplary method 100 of making pulp according to one embodiment of the present technology. In the exemplary embodiment, method 100 is based on the kraft process. In other embodiments, the method corresponding to method 100 may be based on other suitable processes. Referring to FIG. 1, method 100 may include a pulping process 102 and a post-pulping process 104. Within the pulping process 102, method 100 may include charging chips (block 106) and pre-steaming the chips (block 108). Steam at atmospheric pressure can be used to preheat the chips and drive out air to enhance chemical penetration. After the pre-steaming, method 100 may include adding chemicals (e.g., NaOH, Na2S, and / or other suitable chemicals) to the chips (block 110). For example, the chemicals can be added as a cooking liquor. Next, the wood chips and the cooking liquor can be injected into a digester. Inside the digester, the cooking liquor may be able to impregnate the wood chips (block 112). Good penetration of the cooking liquor can facilitate uniform cooking of the wood chips.

[0047] After impregnation, method 100 may include cooking the wood chips and the cooking liquor with co-current (block 114) and counter-current (block 116) liquor contact. In either operation, heat may be applied to the cooking liquor and the chips. Next, the wash liquor may be introduced at the bottom of the digester (block 118) so as to flow counter-currently to the cooked pulp. Cooking may end when the pulp is combined with the cooling wash liquor. After digester washing, the contents of the digester may be blown (block 120). Digester blowing may include discharging the wood and the liquor at atmospheric pressure. Discharging may occur using an amount of force sufficient to cause fiber separation. If desired, the blow tank may be equipped with a heat recovery device to reduce operating costs. Finally, the pulp may be sent from the blow tank to an external pulp washer for separation of the black liquor from the pulp (block 122).

[0048] Following the pulping process 102, the pulp may be bleached and the cellulose fibers in the pulp may be cross-linked. In the standard kraft process, bleaching is performed without cross-linking. Bleaching typically does not cause a substantial reduction in the hemicellulose content of the pulp. Instead, bleaching involves a concomitant reduction in the length and viscosity of the pulp fibers and includes further removal of residual lignin. During bleaching, the pulp may be treated with various chemicals at various stages in the bleaching facility. Those stages may be carried out in conventionally designed vessels or towers. Bleaching is typically carried out as a series of operations including one or more bleaching stages, extraction stages, other treatment stages, etc. using various bleaching agents (e.g., oxygen, chlorine dioxide, etc.). The bleaching stages may be identified in terms of the order of operations carried out therein. For example, an example of a bleaching stage is O-D-E-D. Such a bleaching stage includes an oxygen bleaching stage (the "O stage"), followed by a first chlorine dioxide bleaching stage (the "D stage "), followed by an extraction stage (the "E stage" or "EOP stage" where bleaching chemicals such as peroxide ("P") and / or oxygen ("O") are mixed with caustic for lignin removal), and a second D stage. Some additional examples of bleaching processes are described in U.S. Patent Nos. 6,331,354 and 6,605,350, the entire disclosures of which are incorporated herein by reference.

[0049] The post-pulping process 104 may include first bleaching the pulp using oxygen (block 124). Bleaching the pulp using oxygen tends to be less specific for lignin removal than bleaching the pulp using chlorine dioxide. Oxygen bleaching can be carried out under pressure in an oxygen reactor. Suitable oxygen reactors and related oxygen bleaching processes are described in U.S. Patent Nos. 4,295,925, 4,295,926, 4,298,426, and 4,295,927, the entire disclosures of which are incorporated herein by reference. The amount of oxygen added to the pulp can be in the range of 50 to 80 pounds per ton of pulp. The temperature during oxygen bleaching can be in the range of 100°C to 140°C.

[0050] After oxygen bleaching of the pulp, method 100 may include crosslinking the cellulose fibers in the pulp (block 126). In at least some cases, this includes adding a crosslinking agent to the pulp and allowing the crosslinking reaction to occur before further processing the pulp. The crosslinking agent may be selected to form relatively strong crosslinks (e.g., ether crosslinks instead of ester or ionic crosslinks). For example, relatively strong crosslinks may be preferred over weak crosslinks so that the crosslinks are less likely to be disrupted by functionalization reactions (e.g., etherification) used to form cellulose derivatives. The crosslinking agent may be added to the pulp at a weight ratio of 2:100 or more, 3:100 or more, 5:100 or more, or some other suitable lower threshold or more. The upper threshold may be the maximum amount of crosslinking agent that can be used without causing the CMC obtained from the pulp to become insoluble in water. In at least some cases, a catalyst (e.g., NaOH, zinc tetrafluoroborate, Zn(BF4)2) is present during crosslinking. Additionally or alternatively, a surfactant may be present during crosslinking, such as to facilitate the dispersion and penetration of the crosslinking agent. The surfactant may be particularly useful in relation to hydrophobic crosslinking agents.

[0051] Suitable crosslinking agents include ethers such as glycidyl ethers having two or more glycidyl groups. For example, the crosslinking agent may include a first glycidyl group, a second glycidyl group, and may include three or four linear carbon atoms between the first and second glycidyl groups. Additionally or alternatively, the crosslinking agent may have a weight average molecular weight of 500 or less (e.g., in the range of 174 - 500). Further, when the crosslinking agent is an epoxide, the crosslinking agent may have a weight of 175 or less per epoxide (e.g., in the range of 140 - 175). The crosslinking agent may have a viscosity of 500 cP or less at 25°C. In at least some embodiments, the crosslinking agent is at least partially insoluble in water. This property may be useful, for example, to increase the contact between the crosslinking agent and the cellulose fibers during the crosslinking reaction. Specific examples of suitable crosslinking agents include, among others, trimethylolethane triglycidyl ether, 1,4 - butanediol diglycidyl ether, glycerin di GlycidylExamples include ether, neopentyl glycol diglycidyl ether, glycerin polyglycidyl ether, glycerin triglycidyl ether, ethylene glycol diglycidyl ether, and trimethylolpropane triglycidyl ether.

[0052] During crosslinking, the pulp can have a temperature in the range of 50°C to 85°C. Further, the pulp can have a pH in the range of 9 to 14. As already discussed, crosslinking can be useful for increasing the pulp's ability to produce high-grade cellulose derivatives while the pulp consistency is relatively high. The pulp consistency during all or part (e.g., at least 50% by time) of the crosslinking can be at least 12% (e.g., in the range of 12% to 30%) or at least 15% (e.g., in the range of 15% to 30%). For example, the pulp consistency can be increased before crosslinking (e.g., by extruding water). When further pulp processing is performed after crosslinking, the pulp consistency can be decreased after crosslinking (e.g., by adding water). Due to the relatively high consistency and / or other factors, crosslinking can increase the reactivity of the pulp (measured by the water retention value) and the alkali resistance (measured by R18). In contrast, conventional crosslinking processes typically at least either decrease or have no effect on one or both of these desirable properties.

[0053] The cross-linked pulp according to the embodiments of the present technology can be used in combination with other technologies to increase the ability of the pulp to produce high-grade cellulose derivatives. For example, the cooking described above during the pulping process 102 can be relatively mild. When using relatively mild cooking, less lignin can be removed from the pulp than in other cases. After mild cooking, the pulp can have a kappa number of 25 - 35, indicating the presence of significant residual lignin. As another example, the bleaching and extraction described below during the post-pulping process 104 can be relatively mild. Different from the modification of the kraft process by adding strong caustic extraction and pre-hydrolysis, the aforementioned modification to the kraft process can incrementally improve the ability of kraft pulp to produce high-grade cellulose derivatives without unduly impairing brightness, yield, and / or reactivity.

[0054] After cross-linking the cellulose fibers in the pulp, method 100 can include bleaching the pulp with chlorine dioxide for the first time (block 128). Chlorine dioxide bleaching tends to be more selective than oxygen bleaching with respect to lignin removal. The amount of chlorine dioxide added to the pulp can be in the range of 20 - 30 pounds per ton of pulp. The temperature during the first chlorine dioxide bleaching can be in the range of 50°C - 85°C. After first bleaching the pulp with chlorine dioxide, method 100 can include extraction (block 130) to remove lignin from the pulp. Extraction can include adding hydrogen peroxide or another suitable caustic to the pulp. The amount of hydrogen peroxide added to the pulp can be in the range of 20 - 100 pounds per ton of pulp. The temperature during extraction can be in the range of 75°C - 95°C. In contrast to strong caustic extraction for hemicellulose removal, extraction for lignin removal can be relatively mild. For example, the extraction can be an extraction that does not change the crystalline structure of the cellulose fibers.

[0055] Referring again to FIG. 1, after extraction, method 100 may include bleaching the pulp with chlorine dioxide a second time (block 132). The amount of chlorine dioxide added to the pulp can be in the range of 10 to 30 pounds per ton of pulp. The temperature during the second chlorine dioxide bleaching can be in the range of 60° C. to 90° C. Method 100 may further include additional operations other than those specifically identified in FIG. 1. For example, after any of the operations in process 104 after pulping, method 100 may include washing the pulp. This can be useful, for example, to remove carryover and increase pulp consistency, among other things.

[0056] For example, the washing operation can be used to increase pulp consistency after oxygen bleaching of the pulp and before crosslinking of the pulp. The washing operation after crosslinking of the pulp can reduce or remove carryover. An example of carryover is an adsorbable organic halide or a halogenated compound, which is typically represented as AOX and is usually expressed in parts per million (ppm) as the AOX content of the AOX level. Such organic halogens can be introduced by or with various reactants and additives during pulp production, even if a chlorine-free bleaching process that does not contain elemental chlorine is used. For example, the crosslinking agents discussed above can be a source of such organic halogens. Some crosslinking reagents can contain reaction intermediates from their respective synthesis processes. These reaction intermediates are often not effective crosslinking agents, and the intermediates are present with the pulp fibers during the crosslinking process in which the pulp fibers are exposed to the crosslinking reagent, thereby introducing organic halogens into the crosslinked pulp. The AOX content is generally not high enough to adversely affect the ability of the pulp to produce suitable cellulose ethers, but specific handling requirements regarding AOX and other carryover substances in the wastewater from the process can increase costs. Therefore, it may be desirable to reduce the AOX level and the content of other carryover substances in the crosslinked pulp to levels that are typically associated with the market pulp of the dissolving grade. Although not so high as to give rise to, the specific handling requirements regarding AOX and other carryover substances in the wastewater from the process can increase costs. Therefore, it may be desirable to reduce the AOX level and the content of other carryover substances in the crosslinked pulp to levels that are typically associated with the market pulp of the dissolving grade, among other things.

[0057] The washing operation is generally carried out using water, but any suitable washing reagent may be used. The AOX content in the crosslinked pulp can be reduced more effectively by washing with water at a higher temperature compared to a lower temperature. Without wishing to be bound by theory, this is related to the low water solubility of the crosslinking agents and their expected intermediates discussed herein, and washing at a higher temperature is thought to enhance their removal from the pulp and the removal of the associated organohalogens. Thus, some methods involve washing the crosslinked pulp fibers with water at a temperature between 30 °C and 80 °C to remove residual crosslinking agents. The washing operation may optionally include or be accompanied by high-energy dispersion of the fibers (e.g., disintegration in a Waring blender or similar mixer), which is thought to promote additional reactions between the residual crosslinking agents and the pulp fibers and also reduce the AOX content associated with the presence of the crosslinking agents. The crosslinked pulp washed in this way can exhibit a significant reduction in AOX content (e.g., up to 90%, up to 95%, or even up to 97%) compared to the crosslinked pulp not washed in this way. In some embodiments, the pulp before washing can exhibit an AOX content of up to 1000 ppm or more, while the AOX content of the pulp after washing can be 200 ppm or less, e.g., 100 ppm or less, 50 ppm or less, 20 ppm or less, etc.

[0058] The crosslinking in the embodiment illustrated by Method 100 is carried out after oxygen bleaching and before chlorine dioxide bleaching. However, in other embodiments, the crosslinking can be carried out at other corresponding times in the post-pulping process 104 described below. The bleaching and extraction operations may also be rearranged or removed in other embodiments. When "X" is defined as the crosslinking operation, the post-pulping method according to some embodiments of the present technology can be characterized by, among a very large number of other suitable variations, O-X-D-E-D (Figure 1), O-D-X-E-D, O-D-E-X, O-D-E-X-D, O-D-E-D-X, D-X-E-D-E-D, D-E-X-D-E-D, D-E-D-X-E-D, D-E-D-E-X-D, D-E-D-E-D-X, D-X-E-E-D, D-E-X-E-D, D-E-E-X-D, or D-E-E-D-X. Further, the crosslinking can be carried out during oxygen bleaching, chlorine dioxide bleaching, and / or extraction. Therefore, the post-pulping method according to some further embodiments of the present technology can be characterized by, among a very large number of other suitable variations, O / X-D-E-D, O-D / X-E-D, O-D-E / X-D, O-D-E / X, O-D-E-D / X, D / X-E-D-E-D, D-E / X-D-E-D, D-E-D / X-E-D, D-E-D-E / X-D, D-E-D-E-D / X, D / X-E-E-D, D-E / X-E-D, D-E-E / X-D, D-E-E-D / X.

[0059] After the bleaching process 104, Method 100 can include processing the pulp for use, sale, and / or transportation (block 134). For example, the pulp can be further washed, dried (e.g., flash dried), compressed, containerized for use, sale, and / or transportation, and / or otherwise, the pulp can be processed into a suitable form (e.g., sheet, veil, roll, etc.). The pulp can have a basis weight of 500 - 1200 g / m 2 and / or a density of 0.2 - 0.9 g / cm 3 of.

[0060] Use of Dry Pulp In a generally accepted model of the cell wall structure of woody materials, the cellulose microfibrils form a layered structure together with the lignin - hemicellulose matrix surrounding them. The intra - matrix and inter - microfibril voids within the lignin - hemicellulose matrix form the portion of small pores, sometimes called micropores. In chemical pulping, most of the lignin and some hemicellulose dissolve, leaving inter - layer voids that form relatively large pores, sometimes called macropores.

[0061] The fiber pore structure changes as the pulp dries. Specifically, when water is removed from the pulp during the drying process, most of the pores partially or completely collapse, resulting in a loss of pore volume. Moreover, hydrogen bonds are formed between and within the cell walls, and many of the collapsed pores are permanently maintained in that state by the hydrogen bonds. This phenomenon is known as hornification and tends to result in an irreversible decrease in the WRV of the pulp. In other words, undried pulp generally has a higher WRV compared to dried pulp (even if the dried pulp is wetted again subsequently).

[0062] Although the formation of hydrogen bonds during pulp drying tends to enhance some properties of the pulp, such as certain strength and flexibility characteristics useful in absorbent applications, dried pulp is expected to generally be less reactive compared to undried pulp. The reduced reactivity is due to the loss of pore volume by hornification, which reduces and / or delays the penetration of reactants into the fiber structure.

[0063] Thus, it is expected that dry pulp fibers would not have a void volume sufficient for the crosslinking agent to penetrate and achieve crosslinking, and thus dry pulp would not be a suitable starting material for producing the pulp according to the present disclosure. However, it has been found that dry kraft pulp is a suitable starting material for producing a crosslinked pulp that can form a high viscosity aqueous solution and produce a cellulose ether having various characteristics described herein (e.g., WRV, brightness, R18, lignin and cellulose-II content, etc.).

[0064] The approach of using dry pulp as a starting material can be advantageous in that conventional kraft market pulp is widely available, generally inexpensive, and easier to transport than undried pulp. Moreover, the use of dry pulp allows the crosslinking process to be carried out separately (instead of being related) from the pulp bleaching process, such as in a facility different from the location (or time) where the starting material is produced and / or at a different time.

[0065] An example of an embodiment as an illustration of a method of using dry pulp as a starting material will be described below in connection with FIG. 2, which is a flowchart illustrating a method 200 of making a pulp according to another embodiment of the present technology. Many of the concepts raised in the description of method 200 have been discussed in detail above with respect to method 100, and thus the discussion of method 200 can be understood by reference to such concepts, which are intended to have the same scope as those detailed elsewhere in this specification, even if the discussion is not described at the same level of detail as the following explanation. Briefly, method 200 begins at 202 by preparing an aqueous suspension of pulp comprising chemically wood pulp fibers that have already been bleached and dried. At 204, the method includes crosslinking the chemically wood pulp fibers, and at 206, the method includes drying the pulp after crosslinking. Next, the pulp is processed as market pulp for use, sale, or transportation at 208.

[0066] Method 200 is based on the kraft process in that, as described in connection with method 100, the dried and bleached chemical wood pulp fibers can be chemical wood pulp fibers produced by a kraft pulp process and then bleached (without crosslinking). However, the method corresponding to method 200 may use any suitably dried and bleached chemical wood pulp fibers. The aqueous suspension at 202 can be produced in any suitable manner, such as by slurrying the pulp in water at a desired consistency within a mixing device.

[0067] Once an aqueous suspension of the pulp is provided, method 200 can include crosslinking the chemical wood pulp fibers with a crosslinking agent. As in method 100, this can include adding a crosslinking agent (and optionally a catalyst) to the aqueous suspension and enabling the crosslinking reaction to occur before further processing the pulp. The crosslinking agent is an ether crosslinking agent having two or more Glycidyl groups as described above with respect to method 100, and the consistency of the aqueous suspension during all or part of the crosslinking (e.g., at least 50% over time) can be at least 12% (e.g., within the range of 12% - 30%) or at least 15% (e.g., within the range of 15% - 30%). The crosslinking agent and other features of the crosslinking step can be as described above in method 100. Glycidyl

[0068] After crosslinking, method 200 includes drying the pulp at 206. At 208, the method can include processing the pulp for use, sale, and / or transportation. Various pulp processing operations such as drying, compressing, containerizing, etc. are described above with respect to method 100.

[0069] ​Similar to method 100, method 200 may also include additional operations other than those specifically identified in FIG. 2. For example, method 200 may include washing the pulp, such as after cross-linking of the chemical wood pulp fibers and before drying the pulp. This can be useful, for example, to remove carryover by reducing the AOX content of the pulp and / or removing residual cross-linking agents and other chemicals, and increasing pulp consistency, etc. With regard to the reduction of AOX, the washing can be carried out using water at a temperature between 30° C. and 80° C., optionally in connection with high-energy dispersion of the pulp.

[0070] Blending of pulp In some embodiments, the cross-linked pulp, i.e., the pulp produced according to aspects of the present disclosure, such as by method 100 and / or 200, is combined with another pulp before being dried. The pulp according to at least some embodiments of the present technology is well-suited for use as a pulp extender that reduces the amount of expensive dissolving grade pulp required to produce a given cellulose derivative product without compromising the viscosity or other desirable properties of the product. For example, the cross-linked pulp can be blended with another pulp (e.g., a dissolving grade pulp having a cellulose content of more than 90% by oven dry weight) such that the cross-linked pulp constitutes at least 20% (e.g., at least 30%) of the oven dry weight of the resulting blended pulp. In other embodiments, the cross-linked pulp can be used without being blended with another pulp.

[0071] Cross-linked pulp properties The pulp according to embodiments of the present technology may have one or more of the following properties: An AOX content of 200 ppm or less (e.g., 100 ppm, 50 ppm, and / or 20 ppm or less).

[0072] 500 g / m 2 or more and / or 1200 g / m 2 or less basis weight. Luminance of 75% or more (e.g., 80% or 85% or more) and / or 92% or less (e.g., 88.5% or less). For example, the luminance can be in the range of 80% to 88%.

[0073] The cellulose-II structure determined by X-ray crystallography is slight (e.g., at least the cellulose-II structure is substantially absent).

[0074] Crystallization index of 80% or less (e.g., 75% or less). Less than complete Cuen solubility (e.g., insoluble or only partially soluble).

[0075] 0.20 g / cm 3 or more (e.g., 0.50, 0.55, or 0.60 g / cm 3 or more) of density.

[0076] Falling ball viscosity of 200 cP or more (e.g., 200, 300, 330, 500, 800, 1,000, 1,400, 2,000, or 3,000 cP or more). At very high degrees of crosslinking, the falling ball viscosity of the crosslinked pulp according to at least some embodiments of the present technology can be low, but the CMC viscosity obtained for these pulps can still be very high. Without wishing to be bound by theory and merely as a theory, the molecular structure of cellulose can change from linear to highly branched at high degrees of crosslinking. Cellulose having a highly branched structure can have a low falling ball viscosity but can still form a high-grade ether.

[0077] Freeness of 700 mL or more. Hemicellulose content of 6% or more (e.g., 10%, 13.5%, or 15.5% or more) and / or 20% or less (e.g., 18%, 16%, or 14% or less) by weight. For example, the hemicellulose content can be in the range of 6% to 20% by weight, in the range of 7% to 17% by weight, or in the range of 8 to 15% by weight.

[0078] Intrinsic viscosity of 1,150 mL / g or more (e.g., 1,300, 1,400, 1,500, or 2,100 mL / g or more).

[0079] A lignin content of 1.0% or less (for example, 0.75% or 0.09% or less). A mannan content of 4% or more (for example, 4%, 5%, 6%, or 7% or more). For example, the mannan content can be in the range of 4% to 8% or in the range of 5% to 7%.

[0080] An R18 of 88% or more (for example, 89% or more) and / or 92% or less (for example, 91% or 90% or less).

[0081] An obtained CMC color of 5 or less (for example, 3 or less). An obtained CMC turbidity of 25 ntu or less (for example, 5 or 0.5 ntu or less).

[0082] An obtained CMC viscosity of 59 cP or more (for example, 60, 90, 120, or 150 cP or more).

[0083] A total transition metal content of 20 ppm or less. The iron content can be 5 ppm or less. The copper content can be 2 ppm or less. The calcium content can be 150 ppm or less (for example, 60 ppm or less) and / or 30 ppm or more (for example, 50 or 70 ppm or more). Transition metals are often undesirable in pulp, for example, because they can accelerate the decomposition of cellulose in the etherification process.

[0084] A water retention value of 1.0 g / g or more (for example, 1.1, 1.2, or 1.3 g / g or more) and / or 1.4 g / g or less.

[0085] A xylan content of 4% or more (for example, 5%, 6%, or 7% or more) and / or 16% or less. For example, the xylan content can be in the range of 4% to 16%, in the range of 5% to 8%, or in the range of 6% to 7%.

Examples

[0086] The following experimental examples are provided to illustrate certain embodiments of the present disclosure. It is understood that additional embodiments not limited to the specific features described are consistent with the following experimental examples. desired.

[0087] Commercially available products for reference 9H4F: Aqualon 9H4F high viscosity (DS = 0.95) CMC from Ashland, Inc.

[0088] NB416: Pine-derived, fluff-grade kraft wood pulp obtained from the Weyerhaeuser Company mill in New Bern, NC.

[0089] NB421: Pine-derived, ether-grade kraft wood pulp obtained from the Weyerhaeuser Company mill in New Bern, NC.

[0090] PW416: Pine-derived, fluff-grade kraft wood pulp obtained from the Weyerhaeuser Company mill in Port Wentworth, GA.

[0091] Sulfite 1 and Sulfite 2: Sulfite-processed, dissolving-grade, spruce-derived pulp from Borregaard ChemCell.

[0092] The Weyerhaeuser pulps referred to herein are generally sold in sheet form (e.g., rolls or bales) or other dry forms. The following experimental examples also refer to undried samples of these pulps, such as samples obtained at various points during the bleaching process or otherwise before drying (such as from the compressed portion).

[0093] Experimental Example 1: Epoxide-crosslinked pulp The starting material for the preparation of the crosslinked pulp in this example was PW416 pulp obtained from the extraction stage (EOP) as a wet lap with a solids content of 38% (after laboratory centrifugation). The pulp was preheated to 75 °C. In plastic bags, 52.6 grams of undried (equivalent to 20 grams of OD) samples of the pulp were mixed with warm water (75 °C), various crosslinking agents, and NaOH (pH 11 - 13) at various pulp consistencies shown in Tables 1 and 2. Tables 1 and 2 list the properties of the crosslinked pulp samples and the corresponding CMCs. For comparison, the uncrosslinked PW416 pulp from the EOP stage was found to have a CMC viscosity of 42 cP obtained.

[0094] The following tests of polyepoxide crosslinking agents were carried out: GE - 30 (trimethylolpropane triglycidyl ether polymer (TMPTGE)) and GE - 31 (trimethylolethane triglycidyl ether polymer) from CVC Thermoset. Glycerin diglycidyl ether (GDE) from Aldrich. Denacol EX811 and EX810 (both ethylene glycol diglycidyl ether (EGDE)), Denacol EX313 (glycerin polyglycidyl ether (GPE)), Denacol EX314 (glycerin triglycidyl ether (GTE)), and EX612 (sorbitol polyglycidyl ether) from Nagase Chemitex. HELOXY modifier 505 (castor oil polyglycidyl ether (M505)), HELOXY modifier 48 (trimethylolpropane triglycidyl ether, M48 (TMPTGE)), HELOXY modifier 67 (1,4 - butanediol diglycidyl ether, M67 (BDDE)), and HELOXY modifier 68 (neopentyl glycol diglycidyl ether) from Momentive. D.E.R. 736 Epoxy Resin (D736) from Dow Chemical, polypropylene glycol, chloromethyloxirane polymer, diethylene glycol diglycidyl ether (DEGDE) from other suppliers, 1,3-dichloro-2-hydroxypropanol (DCP), GPE, BDDE, EGDE, and TMPTGE.

[0095] [Table 1]

[0096] The results shown in Table 1 indicate that the polyepoxides D736 (dipropylene glycol diglycidyl ether), DEGDE (diethylene glycol diglycidyl ether), EX612 (sorbitol polyglycidyl ether), M505 (castor oil polyglycidyl ether), and PEGDE (poly(ethylene glycol) diglycidyl ether) with Mn of 525 were not good candidates for crosslinking to produce pulp with high intrinsic viscosity. Their molecules have more than five straight-chain atoms between two glycidyl ether functional groups.

[0097] Among the crosslinking agents tested that have five or more straight-chain atoms between two glycidyl ether functional groups, DEGDE and PEGDE are highly soluble in water. D736 is partially water-soluble. EX612 and M505 have only slight solubility in water (NG) but have high molecular weight (>500), high weight per epoxide (>175), and / or high viscosity (>500 cP). Therefore, at least some polyepoxides with the following properties may be useful for crosslinking pulp according to embodiments of the present technology: molecular weight of 500 or less, weight per epoxide of 175 or less, viscosity of 500 cP or less, and a molecular structure with fewer than five straight-chain carbon atoms between two glycidyl ether functional groups.

[0098] The results also showed that crosslinking agents that are well-suited for producing crosslinked pulp with high obtained CMC viscosity have fewer than five straight-chain atoms between two glycidyl ether functional groups. Without wishing to be bound by theory, these crosslinking agents may penetrate the cellulose structure more easily than crosslinking agents with longer chains.

[0099] It can be advantageous for the crosslinking agent to be water-insoluble or only partially soluble in water. A crosslinking agent that is water-insoluble or only partially soluble can, for example, more readily contact and react with cellulose fibers than a crosslinking agent that is highly soluble in water. Polyepoxides with low or no water solubility gave better results than polyepoxides with greater water solubility. For example, GPE has substantially the same structure as EX314, except that GPE is modified such that EX314 has a higher water solubility; and EGDE has the same structure as EX810, except that EGDE is modified such that EX810 has a higher water solubility. Table 2 shows additional results of using GPE (water-insoluble: Mn > 204, < 500) with EOP pulp (NB416 or PW416) at various consistencies. The intrinsic viscosity (IV*) was calculated from a model based on commercially available samples with known intrinsic viscosities. The basic data for the model can be found at the bottom of Table 2. The resulting model was IV * = 717.2ln(A) - 1817.3(R 2 = 0.9988). The results shown in Table 2 indicate that better results are obtained as the crosslinking consistency increases.

[0100]

Table 2

[0101] Experimental Example 2: Bleached EGDE Crosslinked Pulp (O-D-E-X) In this example, partially water-soluble ethylene glycol diglycidyl ether (EGDE) was used as the crosslinking agent. The starting material for the preparation of the crosslinked pulp in this example was PW416 pulp obtained from the extraction stage as a wet lap with a solids content of 38.5% (after laboratory centrifugation). A 60 gram (OD) sample of the pulp was mixed with water, EGDE, and NaOH to give a final concentration of EGDE and NaOH of 8.8% and 4.8%, respectively, with a final pulp consistency of 10%. The pulp mixture was mixed by hand for a few minutes, filtered to remove half of the liquid, and then reacted at 75°C for 2 hours. Half of the resulting crosslinked pulp was thoroughly water washed and then spun at 747 g / m 2 Grammage and 0.53g / cm 3 A sheet was produced with a density of 79.3%. The sheet had a brightness of 79.3% and a rolling ball viscosity of about 1,350 cP. The crosslinked pulp was not 100% soluble in copper ethylenediamine. The CMC from the pulp had a 0.5% solution viscosity of 86 cP (Sample 1A in Table 5). The other half of the crosslinked pulp (unwashed) was bleached with H2O2 (0.76% on dry pulp weight) at 76°C for 30 minutes (Sample 1B in Table 5). The pulp was washed and bleached to 746 g / m 2 Grammage and 0.54 g / cm 3 A sheet was produced having a density of 1,000 .001 g / m2. The pulp sheet had a brightness of 82.3% and a FB viscosity of 1,270 cP. The CMC from the pulp had a 0.5% solution viscosity of 84 cP. Other properties are summarized in Table 5.

[0102] Experimental Example 3: Bleached GTE Crosslinked Pulp (ODEXD) In this example, glycerol triglycidyl ether (GTE) was used as a crosslinking agent. The starting material for the preparation of the crosslinked pulp in this example was NB416 pulp obtained from the extraction stage (NB416 EOP) as a wet lap with a solids content of 38.5% (after laboratory centrifugation). A 60-gram (oven-dried) sample of the pulp was mixed with water, GTE, and NaOH at 75 °C for 1 hour for crosslinking. Next, the crosslinked pulp was mixed with bleaching chemicals (ClO2 or H2O2) at 75 °C for 45 minutes for reaction. The bleached samples had increased brightness (78% - 86%) and CMC viscosity (Table 3).

[0103]

Table 3

[0104] Experimental Example 4: Bleached EGDE Crosslinked Pulp (O-D-E-D-X) In this example, ethylene glycol diglycidyl ether (EGDE) was used again as a crosslinking agent. The starting material for the preparation of the crosslinked pulp in this example was NB416 pulp obtained from the extraction stage as a wet lap with a solids content of 38.5% (after laboratory centrifugation). A 60-gram (oven-dried) sample of this pulp was mixed with water, EGDE, and NaOH, with the concentrations of EGDE and NaOH being 11% and 5.4% respectively, and the pulp having a consistency of 10%. The pulp mixture was manually mixed for several minutes. Half of the liquid was filtered, and the final concentrations of EGDE and NaOH in the pulp were 4.9% and 2.7% respectively, and the pulp consistency was 20%. Next, the mixture was reacted at 80 °C for 2 hours. The resulting crosslinked pulp was thoroughly washed with water and had a basis weight of 65 g / m 2 and a basis weight of 0.65 g / cm 3A TAPPI hand sheet with a density of was produced. The sheet had a brightness of 87.8% and a falling ball viscosity of 2,710 cP. The pulp was not completely soluble in copper ethylenediamine. The CMC from the pulp had a 0.5% solution viscosity of 126 cP (Sample 2A in Table 5). The other half of the wet crosslinked pulp was treated at 75 °C for 1 hour at 10% consistency using H2O2 (1% based on the dry pulp weight) and 0.5% NaOH (0.5% based on the dry pulp weight). The bleached pulp was washed and 65 g / m 2 basis weight and 0.68 g / cm 3 A TAPPI hand sheet with a density of was produced. The crosslinked pulp had a falling ball viscosity of 283 cP and a brightness of 89.4%. The CMC from the pulp had a 0.5% solution viscosity of 107 cP (Sample 2B in Table 5).

[0105] Experimental Example 5: Crosslinking Efficacy at Various Temperatures The procedure from Experimental Example 4 was repeated to further prepare samples using EGDE as the crosslinking agent, and the final concentrations of EGDE and NaOH in the pulp were approximately 4.9% and 2.7% respectively. The pulp was crosslinked at 20% consistency. The crosslinked pulp was washed but not bleached. The falling ball viscosities and CMC characteristics of the crosslinked pulp are summarized in Table 4 below (Samples A1 - A7). Not all samples were fully soluble in copper ethylenediamine. Many crosslinked pulps did not dissolve in copper ethylenediamine.

[0106]

Table 4

[0107] For the crosslinked pulps listed in Table 4, the pulp FB viscosity was not a good indicator of the corresponding CMC viscosity, especially at very high crosslinking densities. At very high crosslinking densities, the crosslinked pulp did not dissolve completely in copper ethylenediamine, so the crosslinked pulp actually showed a low FB viscosity. However, the CMC solution viscosity from these highly crosslinked pulps was very high and the CMC solutions were clear. The intrinsic viscosity (IV) for these pulps* ) are listed in Table 4. The temperature shock on the crosslinking efficacy was clear for the crosslinking agents tested. Other crosslinking agents may have other optimal temperature ranges such as 50 °C to 85 °C.

[0108] For comparison, two commercially available high-viscosity dissolved ether grade pulps (sulfite 1 and sulfite 2) and two commercially available kraft pulps (PW416 and NB421) were made into CMCs without the first crosslinking of the pulp. These pulps were soluble in copper ethylenediamine and their pulp FB viscosity was a good indicator of their CMC viscosity. The CMC solutions from these commercially available sulfite and kraft pulps were clear, but the solution viscosities were relatively low, especially for the CMC solutions from kraft pulps. Samples 1A and 1B in Table 5 are described in Experimental Example 2 above. Samples 2A and 2B in Table 5 are described in Experimental Example 4 above. In addition to the data shown in Table 5, the CMC from Sample 1B was found to have a lignin content of 0.2 wt.%. Compared with the CMC data shown in Table 5, 9H4F was found to have a CMC color of 0.12, a 0.013% CMC turbidity of 0.12 ntu, and a 0.67% CMC turbidity of 1.1 ntu.

[0109]

Table 5

[0110] Experimental Example 6: X-ray Diffraction of Pulp X-ray diffraction scans were performed on high-viscosity dissolved wood pulp, cotton linter pulp, commercially available kraft pulp (NB421), pulp from the extraction stage of the kraft process, and the corresponding crosslinked pulp according to embodiments of the present technology. The crosslinked pulp was found to have peaks above 15° and between 21.5° and 22.5°, and to have the same cellulose-I crystal structure as the starting material pulp. The main peaks for the crosslinked pulp were slightly shifted to higher diffraction angles (bleached pulp was 21.5° - 22.4°, extraction stage pulp was 21.7° - 22.2°). The cellulose-II crystal structure has peaks at 12.5° and between 20° and 21.5°. For cellulose-I, the peaks at diffraction angles of 22° and 18° are the crystalline and amorphous peaks, respectively. For cellulose-II, the peaks at diffraction angles of 19° and 15° are the crystalline and amorphous peaks, respectively. Table 6 summarizes the X-ray diffraction data.

[0111]

Table 6

[0112] Experimental Example 7: Drainability and Other Properties of Crosslinked Pulp Kraft 1 was prepared using the same procedure as Sample 1A in Experimental Example 2, except that the EGDE concentration was 4.6% and the NaOH concentration was 2.2%. Tests were performed on the crosslinked pulp for drainability and brightness. The results are listed in Table 7. The crosslinked pulp had a brightness and drainability similar to those of the starting material pulp and thus similar drainage properties.

[0113]

Table 7

[0114] The CMC from the crosslinked kraft pulp also had higher free swelling and centrifugation capacity than commercially available non-crosslinked ether-grade pulp from the sulfite process (sulfite 2) or the kraft process (NB421).

[0115] Experimental Example 8: WRV, Wet Bulk, and Other Properties of Crosslinked Pulps For wet bulk and other properties, more crosslinked pulp samples were tested. The results of this test are shown in Table 8. The samples tested were based on the samples described in European Patent Application Publication No. 0399564 (Sample 1) and U.S. Patent No. 8,722,797 ( Sample 2), the entire contents of which are incorporated herein by reference. Sample 1 is a 1,3-dichloro-2-hydroxypropanol (DCP) crosslinked kraft pulp. Sample 2 is a polycarboxylic acid crosslinked kraft pulp.

[0116] Kraft A was prepared in the same procedure as Sample 1A in Experimental Example 2, except that the pulp consistency was 16%, the EGDE concentration was 4.6% based on the dry weight of the pulp, and the NaOH concentration was 2.2%. The wet bulk and volume of the Kraft 1 pulp were lower than those of Samples 1 and 2 and were similar to those of normal fluff pulp (NB416). However, the Kraft 1 pulp produced a higher CMC solution viscosity than both normal fluff pulp and Sample 1. Sample 2 had a lower R18 than the uncrosslinked control pulp due to the breakdown of relatively weak ester crosslinks. The Kraft 1 sample and Sample 1 had a higher R18 than the uncrosslinked control pulp because the ether crosslinks were relatively stable during the R18 test process. Sample 1 was overcrosslinked and thus unsuitable for producing cellulose ethers.

[0117] [Table 8]

[0118] Experimental Example 9: HPLC Spectrum of Hydrolyzed Crosslinked Pulp Kraft A from Experimental Example 8 was hydrolyzed for HPLC testing. New sugar peaks were observed, indicating crosslinks between cellulose fibers in the sample.

[0119] Experimental Example 10: Metals in Crosslinked Pulp and DCM Extraction Residue Additional samples were prepared using the procedure of Experimental Example 4, except that the concentrations of the final crosslinking agent and NaOH were 4.7% and 2.6% respectively. The consistency was 19% and the temperature was 75 °C. The reaction times are listed in Table 9. After washing the pulp, tests for metal content, ball drop viscosity, and CMC viscosity obtained were performed.

[0120]

Table 9

[0121] Low calcium content and low transition metal content can be important for certain end uses. DCM residues from the crosslinked pulp were also tested. The crosslinked pulp was found to have less than 0.01% extractives. Regular bleached pulp without crosslinking also had less than 0.01% DCM extractives. The IR spectrum for the residue showed no crosslinking agent.

[0122] Experimental Example 11: Fiber form Scanning electron microscopy analysis of the crosslinked pulp showed earlywood pine. Fiber analysis showed that crosslinking changed the fiber form. The coarseness, curl index, and kink index of the crosslinked pulp increased with crosslinking consistency (Table 10). Higher coarseness, curl, and kink can be desirable, for example, to increase fiber accessibility during the derivatization reaction.

[0123]

Table 10

[0124] Experimental Example 12: Process for preparing crosslinked cellulose The PW416 pulp was obtained from the extraction stage as a wet lap with a solids content of 38% (after laboratory centrifugation). A 20-gram (OD) sample of this pulp was preheated to 80 °C and mixed in a plastic bag with warm water (80 °C), a crosslinking agent, and NaOH, with the final concentrations of the crosslinking agent and NaOH being 2.0% and 2.3%, respectively. The pulp consistencies were 10, 15, and 20% to produce Samples L, M, and N. All crosslinked mixtures had a pH greater than 11. Crosslinking was allowed to occur for 2 hours.

[0125] The NB421 pulp (fully bleached, undried) from couch trim was obtained as a wet lap with a solids content of 32.8%. Using this pulp, Samples O, P, and Q were prepared. Using the same procedure as described above for Samples L, M, and N, Samples O, P, and Q had corresponding consistencies of 10, 15, and 20%, respectively. Sample R had a crosslinking temperature of 60 °C. The characteristics of these samples are shown in Table 11 along with the characteristics of a control pulp from factory production. Crosslinking was allowed to occur for 2 hours. The viscosities of 0.67% CMC and 1.33% CMC are shown in Table 11, while elsewhere in this disclosure, the 0.5% CMC viscosity is provided.

[0126]

Table 11

[0127] Under specific conditions (e.g., 15 - 20% pulp consistency), crosslinked kraft pulp can have a considerably higher (e.g., greater than 100%) falling ball viscosity than the starting pulp. These crosslinked kraft pulps were not 100% soluble in Cuen. However, surprisingly, these crosslinked pulps were found to produce water - soluble CMC solutions with higher viscosities than CMC solutions produced from NB421 kraft pulp, which is clear and has a falling ball viscosity of 242 cP. The crosslinked pulps had not undergone extraction and thus had a high hemicellulose content and a cellulose - I crystal structure like standard kraft pulp. The crosslinked and bleached kraft pulp had a high brightness. The crosslinked pulp from the extraction stage also had a high brightness. Crosslinking can advantageously be carried out at a high pulp consistency (e.g., 11 - 30%), using a pH of 9 - 14, and at a temperature of 50 - 85 °C.

[0128] Experimental Example 13: Intrinsic Viscosity of Pulp and Shear Rate of the Resulting CMC Three control pulps (sulfite 1, sulfite 2, and cotton linter), one commercial pulp (Aqualon 9H4F from Ashland Company), and two crosslinked kraft pulps (kraft A and kraft B prepared as kraft 2 in Table 2 except that the consistency was 17%) were used to form 1% and 0.5% CMC solutions. The intrinsic viscosities of the CMC solutions from these pulps at various shear rates are shown in Table 12.

[0129]

Table 12

[0130] Experimental Example 14: Washing Procedure and AOX Content The AOX content of pulp indicates the amount of adsorbable organic halides (or halogenated compounds) it contains. By way of reference, the AOX content of two different samples of NB421 (having a SCAN IV of 1460 ml / g) was found to be 2.8 and 5.3 ppm, respectively. The AOX content of a commercially available cotton linter pulp having a SCAN IV of 1760 ml / g was found to be 4.6 ppm. Although no higher AOX levels were found to be associated with any detrimental effects on the desired properties of the crosslinked pulp or the resulting CMC produced therefrom, AOX contents higher than those typically found in high-purity pulp can represent downstream costs in the treatment and handling of the water used during pulp processing.

[0131] A sample of undried NB416 kraft wood pulp (Weyerhaeuser Company) containing undried fibers equivalent to 80 g of OD fibers and having a falling ball viscosity of 200 cP, a hemicellulose content of 15%, an ISO brightness of 86% and an R18 content of 87.5% was heated to 75 °C in a plastic bag. To the pulp was added a mixture of warm water (75 °C), a crosslinking agent (GTE), and NaOH sufficient to produce a pulp consistency of 19%, at NaOH and GTE dosages of 4.9% and 7.4% (based on the OD weight of the pulp), respectively. The mixture was placed in an oven at 75 °C for 1 hour to react.

[0132] After the crosslinking reaction, the mixture was dispersed in a Waring blender, then neutralized with acetic acid, washed, and then filtered twice with cold water (about 20 °C) to obtain a wet pulp, which was then centrifuged before being air dried.

[0133] The AOX content of the crosslinked pulp was determined to be 32 ppm. The R18 value of the pulp was 92%. CMC was prepared from the crosslinked pulp. The 0.5% CMC solution was found to have an intrinsic viscosity of 230 cP.

[0134] The same procedure was repeated except that the crosslinked pulp was manually stirred before neutralization and washing instead of being disintegrated in the Waring blender. Using these various washing operations the crosslinked pulp produced had an AOX content of 1050 ppm.

[0135] The same procedure was repeated once more except that the final pulp consistency was 12% and the washing operation included manual stirring instead of high-energy dispersion in the Waring blender. The crosslinked pulp produced in this way had an AOX content of 724 ppm.

[0136] Experimental Example 15: Use of Dry Pulp An 80 g OD sample of dry NB416 kraft wood pulp (Weyerhaeuser Company) having a falling ball viscosity of 200 cP, a hemicellulose content of 15%, an ISO brightness of 86% and an R18 content of 87.5% was heated to 75 °C in a plastic bag. To the pulp, a mixture of warm water (75 °C), crosslinking agent (M67), and NaOH sufficient to produce a pulp consistency of 12.9% was added at NaOH and M67 dosages of 5.0% and 7.5% (based on the OD weight of the pulp), respectively. The mixture was placed in an oven at 75 °C for 1 hour and reacted.

[0137] After the crosslinking reaction, the mixture was neutralized with acetic acid, washed, and then filtered twice using warm water (about 50 °C) to obtain a wet pulp, which was then centrifuged before being air dried.

[0138] The AOX content of the crosslinked pulp was determined to be 7.8 ppm. The WRV of the pulp was 1.17 g / g, and the R18 value of the pulp was 91.3%. The lignin content was found to be less than 1%, and the pulp had no cellulose-II structure. CMC was prepared from the crosslinked pulp. The 0.5% CMC solution was found to have an intrinsic viscosity of 89 cP and an equivalent SCAN IV of 1438 ml / g.

[0139] The same procedure was repeated except that the crosslinked pulp was dried at a temperature of 100 °C. The WRV of the pulp was 1.01 g / g, and the CMC viscosity obtained was 82 cP.

[0140] Conclusion This disclosure is not intended to be exhaustive or to limit the technology to the exact forms disclosed herein. Specific embodiments are disclosed herein for illustrative purposes, but as will be recognized by those of ordinary skill in the art, various equivalent modifications can be made without departing from the technology. In some cases, well-known structures and functions are not shown and / or are not described in detail in order to avoid unnecessarily obscuring the description of embodiments of the technology. Method steps may be presented herein in a particular order, but in alternative embodiments the steps may have a different suitable order. Similarly, specific aspects of the technology disclosed in the context of a particular embodiment may be combined with or deleted from other embodiments. Further, advantages associated with a particular embodiment may be disclosed in the context of those embodiments, while other embodiments may also exhibit such advantages, and not all embodiments are necessarily shown to have such advantages or other advantages disclosed herein within the scope of the technology.

[0141] Throughout this disclosure, the singular terms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Similarly, the use of "or" in such listings is to be construed to include (a) any single item listed, (b) all of the items listed, or (c) any combination of the items listed, unless clearly limited to mean only a single item excluding other items in a listing of two or more items. Additionally, terms such as "comprising" are used throughout this disclosure to mean including at least the recited feature, with any more of the same features and / or one or more additional No types of features are excluded. It should be understood that such terms do not indicate an absolute situation judgment. References in this specification to "one embodiment", "an embodiment", or similar designs mean that the specific features, structures, operations, or characteristics described in connection with the embodiment may be included in at least one embodiment of the present technology. Therefore, the appearance of such phrases or explicit expressions in this specification does not necessarily mean that all of them indicate the same embodiment. Furthermore, various specific features, structures, operations, or characteristics may be combined in any suitable manner in one or more embodiments of the present technology.

Claims

1. forming pulp from a cellulose feedstock; bleaching the pulp; crosslinking the cellulose fibers in the pulp while the pulp has a consistency of 12% or more; drying the pulp after bleaching the pulp and after crosslinking the cellulose fibers comprising a method of making pulp, wherein the dried pulp has a carboxymethyl cellulose (CMC) viscosity of 60 centipoise (cP) or more, wherein bleaching the pulp comprises increasing the brightness of the pulp to a brightness of 75% or more, wherein crosslinking the cellulose fibers comprises increasing the water retention value (WRV) of the pulp to 1.18 g / g or more by crosslinking the cellulose fibers, wherein crosslinking the cellulose fibers comprises exposing the cellulose fibers to a glycidyl ether crosslinking agent having two or more glycidyl groups, wherein the obtained CMC is slurrying the pulp in isopropanol, adding a predetermined amount of 30% NaOH solution according to the degree of substitution of the pulp and a predetermined amount of monochloroacetic acid according to the degree of substitution of the pulp to a suspension containing the slurried pulp, stirring the suspension to obtain fibrous CMC, washing the obtained fibrous CMC with 70% ethanol, drying the washed fibrous CMC, and is obtained by a method comprising wherein the degree of substitution is determined according to ASTM D 1439-03, wherein the obtained CMC viscosity is tested in accordance with ASTM 15 method D2196-99 using a viscometer with spindle 2 at 50 RPM and 20 °C for a 0.5% solution of the obtained CMC.

2. The method according to claim 1, wherein crosslinking the cellulose fibers comprises crosslinking the cellulose fibers while the pulp has a consistency of 15% or more.

3. The method according to claim 1 or claim 2, wherein bleaching the pulp comprises bleaching the pulp by a kraft bleaching process.

4. The method according to any one of claims 1 to 3, wherein bleaching the pulp comprises oxygen bleaching the pulp.

5. The method according to claim 4, wherein bleaching the pulp comprises bleaching the pulp with chlorine dioxide after bleaching the pulp with oxygen.

6. The method according to any one of claims 1 to 5, wherein crosslinking the cellulose fibers comprises exposing the cellulose fibers to a crosslinking agent that is at least partially insoluble in water.

7. The method according to claim 6, wherein the crosslinking agent has a weight average molecular weight in the range of 174 to 500.

8. The method according to any one of claims 1 to 7, wherein the glycidyl ether crosslinking agent has a molecular weight in the range of 140 to 175 per epoxide.

9. The method according to any one of claims 6 to 8, wherein the crosslinking agent comprises a first glycidyl group, a second glycidyl group, and three or four linear carbon atoms between the first and second glycidyl groups.

10. The method according to any one of claims 1 to 9, further comprising blending the pulp with a dissolving grade pulp having a cellulose content of more than 90% by oven dry weight after crosslinking the cellulose fibers to form a blended pulp, wherein drying the pulp comprises drying the blended pulp.

11. The method according to any one of claims 1 to 10, further comprising washing the pulp with water at a temperature in the range of 30°C to 80°C after crosslinking the cellulose fibers and before drying the pulp.

12. The method according to claim 11, wherein washing the pulp further comprises high energy dispersion of the cellulose fibers.

13. After crosslinking the cellulose fibers and before washing the pulp, the pulp has a certain adsorbable organic halide (AOX) content, The method according to claim 11 or claim 12, wherein washing the pulp reduces the AOX content of the pulp.

14. The method according to claim 13, wherein washing the pulp reduces the AOX content of the pulp by at least 90%.

15. Crosslinking the bleached cellulose fibers with a polyepoxide crosslinking agent; Drying the pulp after crosslinking the cellulose fibers comprising, A method for producing pulp, wherein the dried pulp has a carboxymethyl cellulose (CMC) viscosity of 60 centipoises or more. The obtained CMC is slurrying the pulp in isopropanol adding a predetermined amount of 30% NaOH solution according to the degree of substitution of the pulp and a predetermined amount of monochloroacetic acid according to the degree of substitution of the pulp to the suspension containing the slurried pulp stirring the suspension to obtain fibrous CMC washing the obtained fibrous CMC with 70% ethanol drying the washed fibrous CMC, and is obtained by a method including the degree of substitution is determined by ASTM D 1439-03 the obtained CMC viscosity is tested in accordance with ASTM 15 method D2196-99 by using a 0.5% solution of the obtained CMC with spindle 2 at 50 RPM and 20 °C using a viscometer, method

16. preparing an aqueous suspension of pulp, wherein the pulp contains chemically wood pulp fibers that have been pre-bleached and dried crosslinking the chemically wood pulp fibers with a glycidyl ether crosslinking agent having two or more glycidyl groups drying the pulp after crosslinking the chemically wood pulp fibers including the dried pulp has a water retention value of 1.0 g / g or more, a method for producing pulp the water retention value of the dried pulp is determined by TAPPI T UM256M (2011), method 。

17. forming pulp from a cellulose feedstock oxygen bleaching the pulp chlorine bleaching the pulp in a first chlorine bleaching step crosslinking the cellulose fibers in the pulp with a polyepoxide, wherein the crosslinking is carried out in an extraction stage chlorine bleaching the pulp in a second chlorine bleaching step drying the pulp after bleaching the pulp and after crosslinking the cellulose fibers including the dried pulp has an obtained carboxymethyl cellulose (CMC) viscosity of 60 centipoises or more, a method for producing pulp the obtained CMC is slurrying the pulp in isopropanol adding a predetermined amount of 30% NaOH solution according to the degree of substitution of the pulp and a predetermined amount of monochloroacetic acid according to the degree of substitution of the pulp to the suspension containing the slurried pulp stirring the suspension to obtain fibrous CMC Washing the obtained fibrous CMC with 70% ethanol, Drying the washed fibrous CMC, and is obtained by a method including the above steps, The degree of substitution is determined by ASTM D 1439-03, The obtained CMC viscosity is tested by using a 0.5% solution of the obtained CMC with spindle 2 at 50 RPM and 20 °C using a viscometer in accordance with ASTM 15 method D2196-99.

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