Market Pulps Comprising Surface Enhanced Pulp Fibers and Methods of Making the Same

Abstract

A method of making a market pulp can include separating a slurry comprising a plurality of pulp fibers into at least first and second pulp feeds. The first pulp feed can be refined at least by, for each of one or more mechanical refiners, introducing the first pulp feed between two refining elements of the refiner and rotating at least one of the refining elements, each of the refining elements comprising a plurality of bars and a plurality of grooves, where a width of each of the bars is less than or equal to 1.3 mm and a width of each of the grooves is less than or equal to 2.5 mm. The refiner(s) can consume at least 300 kWh per ton of fiber. The refined first pulp feed and second pulp feed, which is not refined, can be combined to produce a third pulp feed that can be dried.

Claims

1. A method of making market pulp, the method comprising: separating a slurry that comprises a plurality of pulp fibers into at least a first pulp feed comprising a first plurality of pulp fibers and a second pulp feed comprising a second plurality of pulp fibers; refining the first pulp feed at least by, for each of one or more mechanical refiners: introducing the first pulp feed between two refining elements of the refiner, each of the refining elements comprising: a plurality of bars, each protruding from a surface of the refining element and having a width that is less than or equal to 1.3 millimeters (mm); and a plurality of grooves defined by the bars, each having a width that is less than or equal to 2.5 mm; and rotating at least one of the refining elements; wherein refining the first pulp feed is performed such that the refiner(s) consume at least 300 kilowatt-hours (kWh) per ton of fiber in the first pulp feed; combining the refined first pulp feed and the second pulp feed to produce a third pulp feed, wherein the second pulp feed is not refined; and drying the third pulp feed.

2. The method of claim 1, comprising directing the refined first pulp feed into a tank before combining the refined first pulp feed and the second pulp feed.

3. The method of claim 1, wherein refining the first pulp feed is performed such the refiner(s) consume at least 650 kWh per ton of fiber in the first pulp feed.

4. The method of claim 1, wherein refining the first pulp feed is performed such that each of the refiner(s) operates at a specific edge load that is between 0.1 and 0.3 Watt-seconds per meter (W.Math.s/m).

5. A method of making a market pulp, the method comprising: combining first and second pulp feeds to produce a third pulp feed, wherein: the first pulp feed comprises a first plurality of pulp fibers having a length weighted average fiber length that is greater than or equal to 0.20 millimeters (mm) and an average hydrodynamic specific surface area that is greater than or equal to 10 square meters per gram (m.sup.2/g); and the second pulp feed comprises a second plurality of pulp fibers having an average hydrodynamic specific surface area that is less than or equal to 2.0 m.sup.2/g; and drying the third pulp feed.

6. The method of claim 1, wherein combining the first and second pulp feeds is performed such that less than or equal to 10% of the fibers of the third pulp feed, by weight, are the first pulp fibers.

7. The method of claim 1, wherein the market pulp is made such that the market pulp has a basis weight that is greater than or equal to 500 grams per square meter.

8. The method of claim 1, wherein the first pulp fibers and the second pulp fibers are softwood pulp fibers.

9. The method of claim 1, wherein drying the third pulp feed is performed such that less than or equal to 15% of the market pulp, by weight, is liquid.

10. The method of claim 1, comprising baling the market pulp.

11. A market pulp comprising: a first plurality of pulp fibers having a length weighted average fiber length that is greater than or equal to 0.20 millimeters (mm) and an average hydrodynamic specific surface area that is greater than or equal to 10 square meters per gram (m.sup.2/g); and a second plurality of pulp fibers having an average hydrodynamic specific surface area that is less than or equal to 2.0 m.sup.2/g; wherein less than or equal to 15% of the market pulp, by weight, is liquid.

12. The market pulp of claim 11, wherein the market pulp has a basis weight that is greater than or equal to 500 grams per square meter.

13. The market pulp of claim 11, wherein less than or equal to 10% of the fibers of the market pulp, by weight, are the first pulp fibers.

14. The market pulp of claim 11, wherein the first pulp fibers and the second pulp fibers are softwood pulp fibers.

15. A bale of the market pulp of claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The following drawings illustrate by way of example and not limitation. For the sake of brevity and clarity, every feature of a given structure is not always labeled in every figure in which that structure appears. Identical reference numbers do not necessarily indicate an identical structure. Rather, the same reference number may be used to indicate a similar feature or a feature with similar functionality, as may non-identical reference numbers.

[0019] FIG. 1 is a schematic of a system that can be used to make a market pulp that includes both surface enhanced pulp fibers and unrefined pulp fibers.

[0020] FIG. 2 is a schematic of two refining elements that can be used in the one or more refiners of the system of FIG. 1 to produce surface enhanced pulp fibers.

[0021] FIG. 3A is a schematic of a refining unit that can be used in the system of FIG. 1 to produce surface enhanced pulp fibers. The refining unit of FIG. 3A includes a single refiner through which a pulp feed can be recirculated.

[0022] FIG. 3B is a schematic of another refining unit that can be used in the system of FIG. 1 to produce surface enhanced pulp fibers. The refining unit of FIG. 3B includes two refiners, where a pulp feed can be recirculated through one of the refiners.

DETAILED DESCRIPTION

[0023] Referring to FIG. 1, shown is a system 10 that can be used to perform some of the present methods. While some methods are described with reference to system 10, system 10 is not limiting on those methods, which can be performed using any suitable system.

[0024] Some methods of making a market pulp include a step of separating a slurry that comprises a plurality of pulp fibers into at least first and second pulp feeds (e.g., 18 and 22). The first pulp feed can comprise a first plurality of fibers (e.g., a first portion of the slurry's pulp fibers) and the second pulp feed can comprise a second plurality of fibers (e.g., a second portion of the slurry's pulp fibers). The slurry can be contained within a reservoir (e.g., 14), and the pulp fibers of the slurry (and thus the first and second pulp fibers) can be hardwood pulp fibers (e.g., from oak, gum, maple, poplar, eucalyptus, aspen, birch, and/or the like), softwood pulp fibers (e.g., from spruce, pine, first, hemlock, redwood, and/or the like), non-wood pulp fibers (e.g., from kenaf, hemp, straws, bagasse, and/or the like), or a combination thereof. The pulp fibers of the slurry can be obtained from any suitable process, such as, for example, a chemical process (e.g., a kraft process), a mechanical process, a thermomechanical process, a chemi-thermomechanical process, and/or the like, and can be bleached or unbleached. The slurry can have any suitable consistency to promote runnability in system 10; for example, less than or equal to any one of, or between any two of, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% of the slurry, by weight, can be the pulp fibers.

[0025] Some methods include a step of refining the first pulp feed to fibrillate the first pulp fibers. The first pulp feed can be refined in a refining unit (e.g., 26) of system 10 that includes one or more mechanical refiners (e.g., 30a and/or 30b) (FIGS. 3A and 3B). Referring additionally to FIG. 2, each of the refiner(s) can comprise at least two refining elements (e.g., 34), each including a plurality of bars (e.g., 42) that extend outwardly from a surface (e.g., 38) of the refining element and define a plurality of grooves (e.g., 46). For example, each of the refiner(s) can be a disk refiner (e.g., a single-disk refiner, a double-risk refiner, or a multi-disk refiner) (e.g., in which the refining elements are refiner plates) or a conical refiner (e.g., in which the refining elements are conical refiner fillings).

[0026] The first pulp feed can be refined at least by, for each of the refiner(s), introducing the first pulp feed between the refining elements and rotating at least one, optionally each, of the refining elements. The bars can thereby impart compression and shearing forces on the first pulp fibers to increase the fibrillation, and thus the average hydrodynamic specific surface area, thereof. To facilitate a high degree of fibrillation while mitigating undesired reductions in fiber length, each of the refining elements can have a fine bar pattern and, optionally, the refiner(s) can be operated at a low intensity (e.g., at a low specific edge load (SEL)), compared to conventional refining processes. For example, for each of the refining elements, each of the bars can have a width that is less than or equal to any one of, or between any two of, 1.3 millimeters (mm), 1.2 mm, 1.1 mm, 1.0 mm, 0.9 mm, or 0.8 mm (e.g., less than or equal to 1.3 mm or 1.0 mm) and each of the grooves can have a width that is less than or equal to any one of, or between any two of, 2.5 mm, 2.3 mm, 2.1 mm, 1.9 mm, 1.7 mm, 1.5 mm, or 1.3 mm (e.g., less than or equal to 2.5 mm, 1.6 mm, or 1.3 mm). And, refining the first pulp feed can be performed such that each of the refiner(s) operates at a SEL that is less than or equal to any one of, or between any two of, 0.70 Watt-seconds per meter (W s/m), 0.60 W.Math.s/m, 0.50 W.Math.s/m, 0.40 W.Math.s/m, 0.30 W.Math.s/m, 0.25 W.Math.s/m, 0.20 Ws/m, 0.15 W s/m, or 0.10 W.Math.s/m (e.g., between 0.1 and 0.3 W.Math.s/m or 0.1 and 0.2 W.Math.s/m).

[0027] The first pulp feed can be refined using a large amount of refining energy, compared to conventional processes, to achieve a high degree of fibrillation. For example, refining the first pulp feed can be performed such that, per ton of fiber in the first pulp feed, the refiner(s) consume greater than or equal to any one of, or between any two of, 300 kilowatt-hours (kWh), 400 kWh, 500 kWh, 600 kWh, 700 kWh, 800 kWh, 900 kWh, or 1,000 kWh (e.g., greater than or equal to 300 kWh or 650 kWh per ton of fiber in the first pulp feed). The refining energy expended can depend at least in part on the type of fibers in the first pulp feed and the desired degree of fibrillation. Without limitation, when the first pulp fibers are hardwood fibers, the refining energy can be between 300 and 650 kWh per ton of fiber and when the first pulp fibers are softwood fibers, the refining energy can be at least 650 kWh, optionally at least 1,000 kWh, per ton of fiber (e.g., because softwood fibers, which are typically longer than hardwood fibers, may be subjected to more refining than hardwood fibers before fiber shortening and fines production adversely affects fiber quality).

[0028] Such refining energies can be reached in any suitable manner. For example, each of the refiner(s) can consume, per ton of fiber in the first pulp feed, less than or equal to any one of, or between any two of, 110 kWh, 100 kWh, 90 kWh, 80 kWh, 70 kWh, 60 kWh, 50 kWh, 40 kWh, or 30 kWh each time the first pulp feed is passed through the refiner. To reach the total desired refining energy, the first pulp feed can be recirculated through at least one of the refiner(s) and/or passed through multiple refiners such that the cumulative energy consumed by the refiner(s) reaches the desired level (e.g., at least 300 kWh or 650 kWh per ton of fiber). Referring to FIG. 3A, for example, the one or more refiners can consist of a single refiner (e.g., 30a) (e.g., where, for each of the refiner's refining elements, each of the bars has a width that is less than or equal to 1.3 mm and each of the grooves has a width that is less than or equal to 1.6 mm) and the first pulp feed can be passed through the refiner a plurality of times (e.g., greater than or equal to any one of, or between any two of, 2, 6, 10, 14, 18, 22, or 26 times) until the refiner consumes the desired refining energy. Alternatively, and referring to FIG. 3B, the one or more refiners can comprise one or more first refiners (e.g., 30a) (e.g., a single first refiner) and one or more second refiners (e.g., 30b) such that the first pulp feed passes through multiple refiners. Each of the first refiner(s) can be configured to fibrillate the first pulp fibers with less refinement than the second refiner(s). For example, for each of the first refiner(s), each of the bars can have a width that is greater than or equal to 1.0 mm, each of the grooves can have a width that is greater than or equal 1.6 mm, and the first refiner can operate at a SEL between 0.2 and 0.3 Ws/m. The first pulp feed can be introduced into the second refiner(s) after passing through the first refiner(s) and, for each of the second refiner(s), each of the bars can have a width that is less than or equal to 1.0 mm, each of the grooves can have a width that is less than or equal to 1.6 mm, and the second refiner can operate at a SEL between 0.1 and 0.2 W.Math.s/m. The first pulp feed can be recirculated through at least one of the second refiner(s) (e.g., as described with respect to FIG. 3A).

[0029] Such high-energy refining (e.g., at least 300 kWh per ton of fiber) performed using refining elements having a fine bar pattern (e.g., any of those described above) and/or at low intensity (e.g., at a SEL between 0.1 and 0.3 W.Math.s/m) can yield larger increases in the average hydrodynamic specific area of the first pulp fibers than conventional refining processes while mitigating reductions in fiber length. For example, the first pulp feed can be refined such that the average hydrodynamic specific surface area of the first pulp fibers increases by at least 300% (e.g., at least 700%) while the length weighted average fiber length of the first pulp fibers decreases by less than 30%. To illustrate, the fibrillated first pulp fibers, referred to herein as “surface enhanced pulp fibers” (SEPF), can have a length weighted average fiber length that is greater than or equal to any one of, or between any two of, 0.20 millimeters (mm), 0.30 mm, 0.40 mm, 0.50 mm, 0.60 mm, 0.70 mm, 0.80 mm, 0.90 mm, 1.0 mm, 1.5 mm, or 2.0 mm (e.g., greater than or equal to 0.20 mm, 0.30 mm, or 0.40 mm or between 1.0 mm and 2.0 mm), and an average hydrodynamic specific surface area that is greater than or equal to any one of, or between any two of, 10 square meters per gram (m.sup.2/g), 12 m.sup.2/g, 14 m.sup.2/g, 16 m.sup.2/g, 18 m.sup.2/g, 20 m.sup.2/g, or larger (e.g., greater than or equal to 10 m.sup.2/g). Optionally, the number of SEPF can be at least 12,000 per milligram on an oven-dry basis (e.g., based on a sample of the SEPF that is dried in an oven set at 105° C. for 24 hours). A description of SEPF and processes by which SEPF can be made are set forth in further detail in U.S. patent application Ser. No. 13/836,760, filed Mar. 15, 2013, and published as Pub. No. US 2014/0057105 on Feb. 27, 2014, which is hereby incorporated by reference. The SEPF, due at least in part to their large average hydrodynamic specific surface area, can improve the wet-web strength and/or dry strength of a paper product to a greater extent than conventionally-refined fibers when incorporated therein.

[0030] The market pulp can be produced for transportation to a separate mill where the market pulp can be rehydrated, repulped, and used to form a paper product. As such, the market pulp preferably has a low moisture content to reduce transportation costs and a composition that facilitates the rehydration thereof. The market pulp can include the SEPF such that a paper product produced therefrom can attain the above-described improvements in strength; however the SEPF can have a comparatively high water retention value (WRV), which may render the SEPF difficult to dry (e.g., may require a large amount of energy for drying), particularly because the market pulp can have a high basis weight compared to paper products (e.g., a basis weight that is at least 500 grams per square meter (gsm)). And, the SEPF can be difficult to rehydrate because of the SEPF's physical characteristics (e.g., the large average hydrodynamic specific surface area thereof).

[0031] To address these challenges and facilitate production of a low moisture content, rehydratable market pulp comprising SEPF, some methods include a step of combining the refined first pulp feed and the second pulp feed to produce a third pulp feed (e.g., 62) that can be used to make the market pulp. The second pulp feed can be unrefined; for example, the second pulp fibers can have an average hydrodynamic specific surface area that is less than or equal to any one of, or between any two of, 2.4 m.sup.2/g, 2.2 m.sup.2/g, 2.0 m.sup.2/g, 1.8 m.sup.2/g, 1.6 m.sup.2/g, 1.4 m.sup.2/g, 1.2 m.sup.2/g, 1.0 m.sup.2/g, 0.8 m.sup.2/g, or 0.6 m.sup.2/g (e.g., less than or equal to 2.0 m.sup.2/g). The combination of SEPF and unrefined pulp fibers in the third pulp feed can promote the dryability thereof, e.g., such that the third pulp feed can be dried to a greater extent than a pulp feed whose pulp fibers comprise SEPF alone or in combination with conventionally-refined fibers, at least for a given amount energy used to dry the third pulp feed.

[0032] The refined first pulp feed and second pulp feed can be combined such that at least a majority of the pulp fibers in the third pulp feed are unrefined, which can facilitate drying. For example, the refined first pulp feed and the second pulp feed can be combined such that less than or equal to any one of, or between any two of, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% (e.g., less than or equal to 10% or between 1% and 10%) of the fibers of the third pulp feed, by weight, are the first pulp fibers (e.g., the SEPF) and/or greater than or equal to any one of, or between any two of, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, or 99% (e.g., greater than or equal to 90%) of the fibers of the third pulp feed, by weight, are the second pulp fibers (e.g., the unrefined pulp fibers). Some methods comprise directing the refined first pulp feed into a tank (e.g. 58) before combining the refined first pulp feed and the second pulp feed. The refined first pulp feed can be temporarily stored in and metered from the tank (e.g., to facilitate mixing of the desired proportions of SEPF and unrefined pulp fibers).

[0033] While, as shown, the refined first pulp feed and the second pulp feed originate from a common source (e.g., the slurry), in other embodiments the first and second pulp feeds can originate from different sources. In such embodiments, the first pulp fibers (e.g., the SEPF) and second pulp fibers (e.g., the unrefined pulp fibers) can be of the same type (e.g., hardwood pulp fibers, softwood pulp fibers, or non-wood pulp fibers) or of different types.

[0034] Some methods include a step of drying the third pulp feed in a drying unit (e.g., 66) to produce the market pulp. The third pulp feed can be dried in any suitable manner, such as, for example, by draining (e.g., on a wire onto which the third pulp feed is deposited), pressing, and/or heating (e.g., with heated air) the third pulp feed. Substantially all of the moisture of the third pulp feed can be removed when it is dried. For example, drying the third pulp feed can be performed such that less than or equal to any one of, or between any two of, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, or 10% (e.g., less than or equal to 15% or 10%) of the market pulp, by weight, is liquid. As described above, the presence of unrefined pulp fibers in addition to the SEPF in the third pulp feed can facilitate drying such that the market pulp can achieve such low moisture contents and/or the energy required to do so, thereby reducing the costs of transporting the market pulp.

[0035] The market pulp can be processed further in a packaging unit (e.g., 70) to prepare the market pulp for transport. Some methods include a step of baling the market pulp (e.g., to produce one or more bales of the market pulp). For example, the third pulp feed can be dried such that the market pulp forms a sheet and the sheet can be cut into smaller sheets (e.g., having dimensions suitable for shipment) that can be stacked and baled. In other embodiments, however, the market pulp can be wound onto a roll.

[0036] The market pulp can be made such that the market pulp has a basis weight that is greater than or equal to any one of, or between any two of, 500 gsm, 600 gsm, 700 gsm, 800 gsm, 900 gsm, 1,000 gsm, 1,100 gsm, 1,200 gsm, 1,300 gsm, 1,400 gsm, or 1,500 gsm. And the produced market pulp can have any of the relative proportions of the first pulp fibers (e.g., SEPF) and second pulp fibers (e.g., unrefined pulp fibers) described above with reference to the third pulp feed. For example, less than or equal to any one of, or between any two of, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% (e.g., less than or equal to 10% or between 1% and 10%) of the fibers of the market pulp, by weight, can be the first pulp fibers and/or greater than or equal to any one of, or between any two of, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, or 99% (e.g., greater than or equal to 90%) of the fibers of the market pulp, by weight, can be the second pulp fibers. The second (e.g., unrefined) pulp fibers can facilitate rehydration of the market pulp such that the market pulp can be repulped and used to form a paper product. The market pulp can accordingly provide a cost-effective mechanism by which SEPF can be delivered to a separate mill and used in a papermaking process.

[0037] The above specification and examples provide a complete description of the structure and use of illustrative embodiments. Although certain embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this invention. As such, the various illustrative embodiments of the products, systems, and methods are not intended to be limited to the particular forms disclosed. Rather, they include all modifications and alternatives falling within the scope of the claims, and embodiments other than the one shown may include some or all of the features of the depicted embodiment. For example, elements may be omitted or combined as a unitary structure, and/or connections may be substituted. Further, where appropriate, aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples having comparable or different properties and/or functions, and addressing the same or different problems. Similarly, it will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments.

[0038] The claims are not intended to include, and should not be interpreted to include, means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively.