Non-wood slurry

Abstract

Disclosed are improved non-woody slurries, in particular non-woody slurries prepared from plants of the family Aspartate, and more particularly one or more plants of the genus Yucca, and methods of making the same. The method of manufacture generally includes at least one mechanical treatment stage, such as mechanical refinement, without adding chemicals to biomass or bagasse. The refined biomass and bagasse may then be treated with chemicals, such as caustic and / or oxidant, and then subjected to a second stage of mechanical treatment. The resulting non-wood slurry has a high degree of freeness, such as freeness in the range of 500 mL to 600 mL, and a relatively moderate degree of tensile strength, such as a tensile index of about 50 or less.

Description

BACKGROUND

[0001] Pulp is a lignocellulosic fibrous material prepared by chemically and / or mechanically separating cellulose fibers from a lignocellulosic or non-lignocellulosic source. Whether by mechanical, chemical, or a combination of mechanical and chemical, the pulping process reduces the source material to its constituent fibers. In addition to separating the biomass into fibers, pulping removes a portion of the lignin from the fibers, while leaving the cellulose and hemicellulose portions intact. Chemical pulping achieves this by degrading the lignin into small water-soluble molecules that can be washed away from the cellulose and hemicellulose fibers without depolymerizing them. Removing lignin has the benefit of increasing the brightness of the pulp.

[0002] Fibers derived from woody biomass generally contain a higher concentration of lignin compared to non-woody biomass. As a result, processes for pulping woody biomass, particularly for producing high brightness woody pulp, are typically highly chemically intensive. When applied to non-woody biomass, the same processes typically result in significant depolymerization of the cellulose and hemicellulose, resulting in a pulp that is too weak and unacceptably low yield. As a result, alternative pulping processes are generally required to produce non-woody pulp with sufficient strength and brightness, as well as economically viable yield.

[0003] While certain alternatives to chemically intensive pulping methods have been developed for manufacturing non-woody pulp, there remains a need in the art for methods of producing pulp with desirable properties, such as relatively long fiber length, low coarseness, low fines, good dispersibility, and high brightness. This is particularly true for non-wood materials that have leaves or stems with a cuticle layer, as their non-fibrous nature makes them challenging to pulp using conventional methods. SUMMARY

[0004] The present invention provides novel methods for pulping non-wood materials and novel pulps produced thereby. The non-woody pulps of the present invention have several beneficial properties, such as reduced tensile strength, relatively long fiber length, low coarseness, low fines, good dispersibility, high brightness, or low dirtiness. To achieve the beneficial properties, the biomass is mechanically pulped with the addition of a chemical that occurs only after the first mechanical pulping stage. The properties of the non-woody pulp can be further improved by treating the biomass to remove at least a portion of the water-soluble extractives prior to mechanical pulping.

[0005] Thus, in some cases, the present application provides a mechanical pulping method in which non-wood biomass is extracted to remove a portion of water-soluble solids, but is not otherwise subjected to chemical treatment prior to a first mechanical refining stage. Instead, chemicals such as alkali and hydrogen peroxide are added to the refined bagasse immediately after the first mechanical refining stage. In those cases in which an oxygen-based composition such as hydrogen peroxide is added to the fibrillated bagasse, a stabilizing agent can also be added. The chemically treated bagasse is then subjected to a second stage of mechanical refining to produce a primary pulp that can be subjected to further processing.

[0006] In other cases, the present application provides a method for producing a non-wood pulp using a two-stage mechanical pulping method in which fibrillation of non-wood biomass or bagasse is performed in a first mechanical pulping stage without the addition of chemicals such as alkaline peroxide chemicals and / or other chemicals known in the art to bleach or otherwise process lignocellulosic material into a pulp or pulp precursor. Chemicals are introduced to the refined bagasse after the first mechanical pulping stage and prior to a second mechanical refining stage. The above-described method not only simplifies the pulping method and reduces costs, but also improves pulp yield and the physical properties of the resulting pulp. For example, the non-wood pulp of the present application can be produced at a yield of about 80% or greater, such as about 85% or greater, such as about 90% or greater, such as a yield of about 80% to about 95%.

[0007] In other cases, the present application provides a method of making a non-wood pulp, the method comprising the steps of: (a) providing a non-wood biomass; (b) cutting the non-wood biomass to a nominal length; (c) extracting water-soluble solids from the cut biomass to produce a bagasse; (d) mechanically refining the bagasse at a first consistency to produce a refined bagasse; (e) chemically treating the refined bagasse; and (f) mechanically refining the chemically treated bagasse to produce a non-wood pulp.

[0008] In yet other cases, the present application provides a method of making a non-wood pulp, the method comprising the steps of: (a) providing a non-wood biomass; (b) cutting the non-wood biomass to a nominal length; (c) extracting water-soluble solids from the cut biomass to produce a bagasse; (d) mechanically refining the bagasse at a first consistency to produce a refined bagasse; (e) chemically treating the refined bagasse; (f) mechanically refining the refined bagasse at a second consistency, wherein the second consistency is less than the first consistency, to produce a non-wood pulp; (g) cleaning the non-wood pulp to produce a cleaned pulp; and (h) bleaching the cleaned pulp to produce a bleached non-wood pulp.

[0009] In yet other cases, the present invention provides a method of making a non-wood pulp, the method comprising the steps of: (a) providing a non-wood biomass; (b) cutting the non-wood biomass to a nominal length of less than about 20 mm; (c) extracting water soluble solids from the cut biomass; (d) washing the biomass to produce a washed biomass; (f) thickening the washed biomass to a consistency ranging from 40% to about 50%; (g) refining the thickened biomass under first refining conditions to produce a primary pulp; (f) chemically treating the primary pulp by adding hydrogen peroxide, sodium hydroxide, sodium silicate, and DTPA to the primary pulp; (g) diluting the primary pulp to produce a diluted primary pulp having a consistency ranging from about 3% to about 4%; and; (h) refining the diluted primary pulp under second refining conditions to produce a non-wood pulp. The non-wood pulp can be subjected to further processing, such as cleaning to produce a cleaned pulp, bleaching to produce a bleached pulp, or drying to produce a dried pulp.

[0010] In certain cases, after chemically treating the primary pulp, the primary pulp is reacted with a chemical additive. This reaction period can be referred to as a retention period. The retention period can be about 30 minutes or more, such as about 45 minutes or more, such as about 1 hour or more, such as about 30 minutes to 2 hours. The chemically treated pulp can be retained in an insulated container such that a temperature ranging from about 70°C to 80°C can be maintained during the retention period.

[0011] While the methods of the present invention are well suited for pulping a wide range of non-wood biomass, the methods are particularly well suited for pulping biomass derived from plants of the Asparagaceae family. Thus, in certain cases, the present invention provides a non-wood pulp comprising a plurality of fibers derived from a plant of the Asparagaceae family. The resulting pulp has one or more physical properties making them well suited for making wet-laid fiber products, such as tissue products. For example, the pulp of the present invention can have a relatively long fiber length, such as a fiber length of about 1.50 mm or more, and can be suitable for dewatering, such as having a freeness of at least about 500 mL or more, and have a moderate tensile strength, such as a tensile index of less than about 50. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a process flow diagram for a method for producing a non-wood mechanical pulp.

[0013] Figure 2 Refining curves are shown for the following three bleached pulps: (·) alkaline peroxide mechanical esparto pulp; (A) esparto pulp of the present invention, and (■) northern softwood kraft pulp.

[0014] Figure 3The following three bleached pulps are shown: (·) alkaline peroxide mechanical flax straw pulp; (A) flax straw pulp of the present invention; and (■) northern softwood kraft pulp.

[0015] Definitions

[0016] As used herein, the term "substantially free" means less than 3 wt%, or less than 2 wt%, or less than 1 wt%, or less than 0.5 wt%, or less than 0.25 wt%, or less than 0.1 wt%, or less than 0.05 wt%, or less than 0.01 wt%, and / or alternatively, free. As used herein, "free" means 0 wt%.

[0017] As used herein, the term "biomass" generally refers to organic matter derived from non-woody plants and includes whole plants and plant organs (i.e., leaves, stems, flowers, stalks, roots, etc.).

[0018] As used herein, the term "bagasse" generally refers to biomass that has been subjected to a processing step, such as, for example, pressing, grinding, compressing, or steeping, to remove a portion of the biomass water-soluble solids. Bagasse can be prepared by compressing and steeping biomass using a plug screw or other form of compression screw to extract a portion of the biomass water-soluble solids.

[0019] As used herein, the term "pulp" generally refers to a plurality of cellulosic fibers derived from biomass, the fibers having an elongated shape in which the apparent length exceeds the apparent width. Generally, pulps prepared according to the present invention are dispersible in water, have a measurable freeness, and are useful in forming handsheets.

[0020] As used herein, the term "fines" generally refers to fibrous, water-insoluble cellulosic material having an aspect ratio of about 1 to about 100, and wherein the length of the fibrous, water-insoluble material is less than about 0.2 mm. In certain instances, pulps prepared according to the present invention can comprise fines. In certain instances, the amount of fines present in a pulp prepared according to the present invention can be about 2.0% or less, such as about 1.5% or less, such as about 1.0% or less, such as about 0.5% to about 2.0%. The fines content of a pulp (on a length-weighted basis) can be measured using an OpTest Fiber Quality Analyzer-360 (OpTest Equipment, Inc., Hawkesbury, ON) as described in the Test Methods section below. Generally, the percentage of fines on a length-weighted basis is the sum of the lengths of the fines divided by the total length of the fibers and fines in the sample.

[0021] As used herein, the term "brightness" generally refers to the optical brightness of a pulp sample measured according to ISO 2470-1 :2016. Brightness is typically expressed as a percentage (%).

[0022] As used herein, the term "fines" generally refers to the amount of material retained on a MasterScreen ™ The weight percent of solids on the equipment. The amount of fines in a given pulp sample is typically measured as described in the Test Methods section below.

[0023] As used herein, the term "tensile index" generally refers to the tensile strength of a sample in units of grams force per 25.4 mm divided by the basis weight in units of grams per square meter. For a given pulp sample, the tensile index is typically measured by dispersing the pulp in water to form a handsheet (as described in the Test Methods section below), and then measuring the tensile and basis weight of the handsheet.

[0024] As used herein, the term "thickness" is the representative thickness of a pulp sheet, and is typically measured as described in the Test Methods section below. Thickness is typically in units of millimeters or micrometers.

[0025] As used herein, the term "freeness" refers to Canadian Standard Freeness (CSF) determined according to TAPPI Standard T 227 OM-94. Freeness is typically in units of milliliters (mL).

[0026] As used herein, the term "fiber length" generally refers to the length-weighted average fiber length (LWAFL) of fibers measured using an OpTest Fiber Quality Analyzer Model FQA-360 (OpTest Equipment, Inc., Hawkesbury, ON) as described in the Test Methods section below. Fiber length is typically in units of millimeters.

[0027] As used herein, the term "coarseness" generally refers to the weight of fiber per unit length measured using an OpTest Fiber Quality Analyzer-360 (OpTest Equipment, Inc., Hawkesbury, ON) as described in the Test Methods section below. Coarseness typically has units of mass per unit length, such as milligrams per 100 meters (mg / 100 meters).

[0028] As used herein, the term "very long fiber fraction" generally refers to the percentage of fibers having a length (number average fiber length) greater than 6.0 mm, and is typically determined using an OpTest Fiber Quality Analyzer-360 (OpTest Equipment, Inc., Hawkesbury, ON) as described in the Test Methods section below.

[0029] As used in this article, the term "dispersion index" typically refers to the length-weighted average fiber length (L... w ) and number-average fiber length (L n The ratio of length-weighted average fiber length (L) to fiber length distribution in a given pulp. w ) and number-average fiber length (L n The ratio of ) is typically determined using the OpTest Fiber Quality Analyzer-360 (OpTest Equipment, Inc., Hawkesbury, ON), as described in the Test Methods section below.

[0030] As used herein, when referring to the size of biomass or bagasse, the term "nominal size" generally refers to the size of a given sieve through which at least about 70% of the biomass or bagasse travels. Generally speaking, a sieve is a component capable of sieving materials according to size. Examples of sieves may include perforated plates, cylinders, etc., or wire mesh or fabric, etc. Preferred methods for screening and grading bagasse and biomass are described in the following Test Methods section.

[0031] A range may be expressed in this document as from “about” one particular value and / or to “about” another particular value. When expressing such a range, the other side includes from one particular value and / or to another particular value. Similarly, when a value is expressed as an approximation using the antecedent “about,” it should be understood that a particular value forms the other side. It should also be understood that the endpoints of each range are significant both relative to and independent of the other endpoint.

[0032] Similarly, when a value is expressed as an approximation using the antecedent “about,” it should be understood that the particular value forms on the other hand. It should also be understood that each endpoint of a range is significant both relative to and independent of the other endpoint. Unless otherwise stated, the term “about” means within 5% (e.g., within 2% or 1%) of the particular value modified by the term “about.”

[0033] Throughout this disclosure, various aspects of this disclosure may be presented in a range format. It should be understood that the range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of this disclosure. Therefore, a range description should be considered as having specifically disclosed all possible subranges and the individual numerical values ​​within that range. For example, a range such as 1 to 6 should be considered as having specifically disclosed subranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6, 3 to 6, etc., and individual numbers within that range such as 1, 2, 2.7, 3, 4, 5, 5.3, 6, and any all and part of the increments therein. This applies regardless of the width of the range.

[0034] All percentages and ratios are calculated by weight unless otherwise indicated. All percentages and ratios are calculated based on total composition unless otherwise indicated.

[0035] All component or composition levels are in reference to active levels, unless otherwise indicated, and are exclusive of impurities, for example, residual solvents or by-products, which can be present in commercially available sources of such components or compositions. DETAILED DESCRIPTION

[0036] The present invention relates to non-wood pulps and methods for making non-wood pulps, particularly non-wood pulps produced from non-wood plants of the Asparagaceae family. Of particular interest are non-wood pulps produced from plants of the genus Agave, and more particularly one or more plants selected from the group consisting of H. funifera, H. parviflora, H. nocturna, H. chiangii, H. tenuifolia, H. engelmannii, and H. malacophylla.

[0037] The non-wood pulps are preferably produced by mechanical treatment (such as refining) of non-wood biomass or bagasse. The refining is preferably performed in two separate stages, with the first refining stage being performed without the addition of chemicals prior to or during refining. In this manner, the non-wood bagasse can be substantially free of chemical additives, or free of chemical additives, during the first mechanical refining stage. Following the first mechanical refining stage, the refined bagasse is subjected to chemical treatment, such as with alkaline peroxide chemicals and / or other chemicals known in the art to bleach or otherwise process lignocellulosic materials into pulp or pulp precursors. The chemically treated and refined bagasse is then subjected to a second mechanical refining stage to produce a primary pulp.

[0038] Production of the pulp by mechanical treatment without the addition of chemicals improves overall pulp yield. In certain cases, the methods of the present invention can have a yield of about 80% or greater, such as about 85% or greater, such as about 90% or greater, such as about 80% to about 95%. Omission of chemicals during mechanical pulping generally removes less lignin, improving yield, while reducing tensile strength. Thus, the pulp produced according to the present invention can have an increased amount of lignin, as well as a low degree of tensile strength (typically measured as tensile index), as compared to pulps prepared by the addition of chemicals prior to or during mechanical refining.

[0039] Despite the omission of chemical treatment during the first mechanical refining stage, the pulp has desirable physical properties, such as a high degree of freeness, particularly as compared to other non-wood pulps and pulps made using both chemical and mechanical treatment. The improved freeness is typically accompanied by a relatively low degree of tensile strength. This combination of high freeness and low tensile strength makes the pulp of the present invention well suited for making fibrous structures, particularly low basis weight tissue paper, which requires a pulp that dries easily and produces only a moderate degree of tensile strength while maintaining a high degree of softness.

[0040] Thus, in some cases, the pulp of the present invention can have a freeness of about 500 mL or greater, such as about 510 mL or greater, such as about 525 mL or greater, such as about 550 mL or greater, such as about 500 mL to about 600 mL, with the higher values indicating that the pulp dries more easily.

[0041] The pulp can also have a relatively moderate tensile strength, such as a tensile index of about 55 or less, such as about 50 or less, such as about 45 or less, such as about 30 to about 55, such as about 35 to about 50, such as about 35 to about 45.

[0042] In some cases, the relationship between the freeness and the tensile index of the pulp of the present invention can be improved as compared to pulps made where the bagasse is chemically treated prior to mechanical treatment. For example, the pulp can have a freeness of about 500 mL or greater, such as about 510 mL or greater, such as about 525 mL or greater, such as about 500 mL to about 600 mL, and a tensile index of about 55 or less, such as about 35 to about 50. In this way, the pulp can be well suited for use in a wet-laid tissue paper making process due to the relatively high freeness and amenability to dewatering of the pulp, but yet weak enough so that they do not add an excessive amount of tensile strength to the finished tissue paper product.

[0043] In addition to having a moderate tensile strength and a high degree of freeness, the pulp typically has a relatively long fiber length, such as about 1.50 mm or greater, such as about 1.55 mm or greater, such as about 1.60 mm or greater, such as about 1.65 mm or greater, such as about 1.70 mm or greater, such as about 1.75 mm or greater, such as about 1.50 to about 2.50 mm, such as about 1.55 to about 2.00 mm.

[0044] A comparison of the physical properties of the pulp made according to the present invention to a pulp made using both chemical and mechanical treatment is shown in Table 1 below. A comparison of the tensile index and freeness of the pulp made according to the present invention to a pulp made using chemical and mechanical treatment is shown in Figure 1 .

[0045] Table 1

[0046]

[0047] In other cases, the slurry of the present application can have a moderate degree of tensile strength and a low degree of fibers having a fiber length greater than 6.0 mm, which can inhibit the dispersion of the slurry in water and cause stringing or lumps when the slurry is used to make a wet-laid fibrous product. For example, the slurry of the present application can have a tensile index of about 55 or less, such as about 50 or less; and a very long fiber fraction (VLF) of about 1.0% or less, such as about 0.75% or less, such as about 0.50% or less, such as about 0.05% to about 1.0% VLF; a fiber length of about 1.50 to about 2.50. In addition to having a reduced tensile strength and a relatively long fiber length,

[0048] Generally, the slurry of the present application is prepared from one or more non- woody plants. The slurry can include fibers derived from a single plant species, or, alternatively, fibers derived from two or more different plant species. The biomass that can be used in the present application can include a freshly harvested non-woody plant, a partially dried non-woody plant, a fully dried non-woody plant, or a combination thereof. The biomass can consist essentially of the above-ground portion of the plant, more specifically, the portion of the plant above the crown, still more preferably the leaves of the plant.

[0049] The slurry of the present application can be prepared from one or more non-woody plants of the Asparagaceae family. Suitable non-woody plants can include, but are not limited to, one or more plants of the genus Agave, such as Agave tequilana, A. sisalana, and A. fourcroyde; and one or more plants of the genus Hesperaloe, such as Hesperaloe amanda, H. parviflora, H. noctiflora, H. funifera, H. tunicata, H. engelmanniana, and H. fasciata. In certain cases, it can be preferred to prepare the slurry from a plant of the genus Hesperaloe, such as H. amanda, H. parviflora, H. noctiflora, H. funifera, H. tunicata, H. engelmanniana, and H. fasciata.

[0050] The slurry can be produced from non-woody plants, particularly non-seed portions of plants, more particularly leaves, and still more particularly leaves above the canopy of the plant, by processing the biomass. In some cases, water soluble solids can be removed from the non-woody biomass by compression and steeping prior to refining. Compression and steeping can also be used to remove the epidermis from the biomass, as well as to cut the biomass to a certain size prior to refining. The non-woody biomass is subjected to mechanical treatment, such as by refining, which is preferably performed in two separate stages, with the first refining stage being performed without the addition of chemicals prior to or during refining. In this manner, the non-woody bagasse can be substantially free of chemical additives, or free of chemical additives, during the first mechanical refining stage.

[0051] Following the first mechanical refining stage and prior to the second mechanical refining stage, a chemical commonly used in the art to facilitate the removal of lignin from lignocellulosic materials, such as sodium hydroxide, an oxidizing chemical, such as hydrogen peroxide or sodium peroxide, or other chemicals, such as sulfur dioxide, sodium sulfite, sodium bisulfite, or sodium dithionite, is added to the refined bagasse. In some cases, it can be preferred to treat the refined bagasse with an alkaline peroxide solution prior to the mechanical refining of the second stage. In those cases where an oxidizing chemical is added to the refined bagasse, one or more stabilizers, such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), and nitrilotriacetic acid (NTA), can also be added.

[0052] In some cases, the slurry produced according to the present application can be bleached to increase its optical properties, particularly brightness. For example, the present application provides non-woody slurry derived from plants of the genus Chamaerops having a brightness of 75% or more, such as about 77% or more, such as about 79% or more, such as about 75 to about 92%. Bleaching can be performed using any one of the well-known methods of bleaching a slurry. In some cases, it can be preferred that the bleaching be performed without the use of elemental chlorine, more preferably without the use of chlorine-containing compounds. The bleaching can be performed in one stage, or in multiple stages. In some cases, the bleaching method can preferably include at least one non-chlorine bleaching stage, although any one or more of the conventional non-chlorine bleaching stages or sequences can be used, including stages or sequences using oxygen (including oxygen delignification), ozone, peroxides, hydrosulfite, and the like.

[0053] Although some end uses can benefit from bleaching, the present application is not so limited, and the slurry of the present application can be unbleached and have a brightness of less than about 75%, such as about 50% to about 75%, such as about 55% to about 70%.

[0054] The pulp products of the present invention, although produced from non-wood fibers and by mechanical pulping, do not suffer from the same freeness problems of prior art non-wood mechanical pulps. In fact, in some cases, the pulp products of the present invention have a relatively high freeness, such as a freeness of at least about 400 mL CSF, such as at least about 450 mL CSF, such as at least about 500 mL CSF, such as from about 400 to about 700 mL CSF, such as from about 450 to about 600 mL CSF. Generally, "freeness" refers to the drainage rate of the pulp, or how "freely" the pulp will release its water. Freeness is important in papermaking because if the freeness is too low, then not enough water can be removed on the paper machine to achieve good sheet structure and strength. Generally, mechanical pulps, particularly mechanical non-wood pulps, have a low freeness due to the high fines content that inhibits drainage of the pulp when wet formed into a sheet.

[0055] The pulp products of the present invention can be provided in wet pulp sheet form, or in a dry form, such as a sheet, bale, or roll form, and can be distinguished from other fiber products, such as fiber products intended for packaging, tissue, books, magazines, letters, and the like. The thickness of the pulp sheet can range from about 0.05 cm to 0.50 cm, such as from about 0.10 cm to about 0.25 cm. The absolute dry basis weight of the pulp produced according to the present invention can range from about 200 g / m2to about 1,000 g / m2.

[0056] The pulp products of the present invention are generally subjected to further processing to convert the fibers into a final product for use by a consumer. For example, the pulp products can be produced in a sheet form having a consistency of about 40% or greater, and can subsequently be dispersed in water under agitation, pumped to a headbox and wet-laid to form a fiber web.

[0057] Figure 1 A non-limiting method for producing non-wood pulp according to the present invention is shown in FIG. 1. The method includes providing raw grass pampas biomass 10 and cutting the biomass 10 to a size using a cutting apparatus 20. As discussed in more detail below, the cutting can be accomplished in a variety of ways, and preferably results in cut biomass having a size of about 20 mm or less, such as at least about 10 mm or less. In addition to cutting, at least a portion of the water-soluble extractives are removed from the biomass prior to mechanical pulping. In some cases, such as Figure 1 As shown, the cutting and extraction of water-soluble extractives can be performed in a single stage using a screw press or the like, while washing with an extraction solvent 25 to remove water-soluble solids 27 from the biomass 10. The amount of water-soluble solids 27 removed from the biomass 10 can vary depending on the extraction method and conditions. In some cases, at least about 40%, such as at least about 50%, such as at least about 55% of the water-soluble solids are removed from the biomass prior to mechanical pulping.

[0058] With continued reference to Figure 1 The extracted and cut biomass, now generally referred to as bagasse 30, is washed 40 with a washing fluid 45. The washed bagasse 50 can be thickened to produce washed bagasse having a consistency in the range of about 1% to about 5%. The washings are typically thickened to a consistency of at least about 20%, such as at least about 30%, such as about 35% to about 45%, prior to refining in a first mechanical refiner 60 under first refining conditions to produce refined bagasse 70. The first refining conditions can be selected to cause fibrillation of the bagasse 50 and produce refined bagasse 70 having a freeness of at least about 500 mL, such as at least about 550 mL, such as about 500 mL to about 650 mL, and a yield of at least about 90%. Generally, the first refining conditions are such that the bagasse is substantially free, more preferably free, of chemical additives, such as alkaline peroxide or other chemicals typically used to remove lignin. In this manner, the first mechanical refining stage can be conducted at a bagasse pH of 6.0 to about 8.0, more preferably about 6.5 to about 7.5.

[0059] In some cases, the refined bagasse can be transferred from the first digester to a downstream process under atmospheric conditions via a transfer screw, chute, or the like. In cases where the first digester includes a pressurized enclosure, the refined bagasse can be discharged to the downstream process via a blowdown valve. Generally, upon discharge from the first mechanical refiner 6, the refined bagasse 70 is treated with an alkaline peroxide solution 75 and allowed to react under first reaction conditions prior to being subjected to a second refining stage. The refined bagasse can also be subjected to cleaning or screening to remove debris prior to the second mechanical pulping stage.

[0060] The chemically treated and refined bagasse 70 is subjected to further mechanical treatment using a second mechanical refiner 80. The consistency of the bagasse 70 during the second refining stage is generally different than the consistency of the biomass refined in the first stage and can be in the range of about 3% to about 6%. The refined bagasse 70 is pulped using the second mechanical refiner 80 under second refining conditions to produce a primary slurry 90. The primary slurry 90 can have a freeness of at least about 500 mL, such as at least about 550 mL, such as about 500 mL to about 650 mL, and a yield of at least about 90%. The primary slurry 90 can also have a brightness in the range of about 50% to about 60%.

[0061] Further processing of the primary slurry 90 can be performed. For example, as shown in FIG. 2, skin debris 105 can be removed from the primary slurry 90 by passing the slurry through a cleaning system 100 including one or more cleaners. The cleaned primary slurry 110 can then be transferred to a bleaching tower 120 and bleached by the addition of an alkaline peroxide solution 125 to produce a bleached slurry 130. Figure 1 ​

[0062] The biomass can be cut to size prior to processing, such as extraction, pressing, grinding, or pulping. In some cases, the biomass can be cut to size and cleaned immediately prior to grinding and extraction to remove water-soluble portions of the biomass. Alternatively, the biomass can be cut to size when harvested using a harvesting apparatus designed to produce biomass cuttings of a desired size, particularly an apparatus designed to cut and chip the biomass in a single operation.

[0063] In some cases, the biomass can be cut to size using a forage harvester. Forage harvesters generally include a header and a cutting wheel or drum. The biomass can be directly cut by the harvester header using reciprocating knives, discs, or rotating mowers, or large saw-like blades. The header is configured such that the cutting height is above the canopy of the plant, such as about 10 cm to about 30 cm above the ground. The biomass is fed from the header to the cutting wheel. The cutting wheel is equipped with several knives affixed thereto that chop the silage and blow it out of the harvester’s chute into a wagon connected to the harvester or to another vehicle driving alongside. The configuration of the knives, the number of knives attached to the cutting wheel, and the speed of the cutting wheel determine the cut size of the biomass. For example, the harvester can be configured to produce a nominal chop length of 5 mm to about 50 mm, such as 5 mm to about 30 mm, such as about 5 mm to about 20 mm. It should be noted that the nominal chop length is set by the harvester, and the actual chop length of the material can vary depending on the consistency of the orientation of the biomass fed into the cutting wheel and other factors.

[0064] In other cases, mechanical size reduction methods, such as hammer mills, rotary shredders, shear shredders, knife choppers, barrel mills, wood chip chippers, or any other device that reduces the nominal size of the incoming biomass, can be used post-harvest to chop the biomass to a size. Prior to chopping, milling or chipping can be performed using barrel mills, horizontal mills / choppers, or simple wood chip chippers. These first stage systems typically have a large rotating drum with large blunt hammers that quickly shear or shred the material into a less dense, loose form that can be easily ground to the desired size. Large screens are often used in the first stage milling to prevent oversized material from leaving the mill chamber. These screens can have openings ranging in size from about 5 cm to about 15 cm. Chippers typically use a rotating drum with fixed knives parallel to the drum axis. The size of the chopped biomass is typically controlled by the feed rate. Once the first stage milling or chipping is complete, a hammer mill is used to grind the feedstock to the desired particle size. Hammer mills use a large rotating drum with protruding metal rods (i.e., hammers) that impact the material at high speed to break and tear the material particles. Generally, the metal rods swing freely from the drum, but fixed hammers are also common in hammer mill designs. The size of the biomass exiting the hammer mill can range from 5 mm to about 50 mm, such as 5 mm to about 30 mm, such as about 5 mm to about 20 mm.

[0065] Generally, chopping the biomass, particularly prior to pulping or bleaching the biomass, improves one or more physical properties of the resulting pulp. For example, chopping the biomass can reduce the fraction of long fibers in the pulp, making the pulp easier to disperse and suitable for making wet-laid paper products, particularly wet-laid tissue paper products. In certain cases, the reduction in the fraction of long fibers can be achieved without significantly reducing the fiber length, such that the fiber length of the pulp can be about 1.50 mm or greater, such as about 1.55 mm or greater, such as about 1.60 mm or greater, such as about 1.65 mm or greater, such as about 1.70 mm or greater, such as about 1.75 mm or greater, such as about 1.50 mm to about 2.50 mm, such as about 1.55 mm to about 2.00 mm.

[0066] Chopping the biomass prior to pulping can also reduce the fraction of pulp fibers having a fiber length of 6.0 mm or greater, referred to herein as the very long fiber fraction (VLF). For example, a pulp prepared according to the present disclosure can have a VLF of about 1.0% or less, such as 0.75% or less, such as 0.50% or less, such as 0.25% or less, such as 0.20% or less, such as 0.15% or less, such as 0.10% or less.

[0067] In other cases, cutting the biomass prior to pulping reduces the distribution or narrows the distribution of fiber lengths such that the dispersibility index is about 2.25 or less, such as about 2.10 or less, such as about 2.00 or less, such as about 1.90 or less, such as from about 1.50 to about 2.25, such as from about 1.50 to about 2.10, such as from about 1.50 to about 2.00. With a dispersibility of less than about 2.25, more preferably less than about 2.10 or less, the lengths of the fibers are relatively uniform, improving the dispersion of the pulp in water and reducing fiber clumping and webbing when forming a wet-laid paper product.

[0068] In certain cases, the biomass is treated prior to pulping to remove at least a portion of water-soluble material. The water-soluble solids can be removed using any of several well-known extraction methods, such as solvent extraction methods, particularly those using aqueous solvents, and more particularly those using aqueous polar solvents, such as water. Those skilled in the art will recognize that the ratio of extraction solvent to biomass will vary based on the solvent, the amount of biomass to be extracted, and the extraction procedure. In certain cases, the extraction solvent can be water, and the ratio of extraction solvent to biomass is from about 1 :5 to about 1 : 100, such as from about 1 :5 to about 1 :50, and more preferably from about 1 :5 to about 1 :20, based on the liters of extraction solvent to kilograms of bone dry biomass.

[0069] The pH of the extraction solvent can be between about pH 5.0 and 8.0, such as between about pH 6.0 and about 8.0, between about pH 6.5 and about 7.5. In those cases where the extraction solvent is water, the pH of the water can be between about pH 6.5 and about 7.5. When the extraction includes a draw with the crude juice, the draw can have a pH of about 4.0 to about 5.0.

[0070] In those cases where the extraction method is a batch extraction method, the duration of the extraction can range from about 0.25 hours to about 24 hours, such as, for example, from about 0.5 hours to about 2 hours, from about 1 hour to about 8 hours, or from about 1 hour to about 6 hours.

[0071] In those cases where the extraction method is a continuous method, the duration of the extraction can range from about 0.25 hours to about 5 hours, such as, for example, from about 0.5 hours to about 3 hours.

[0072] Simple aqueous extraction can be preferred for removal of water-soluble extractives, although other extraction methods are within the scope of the present invention. For example, simple water extraction of the biomass can be suitable for obtaining an insoluble biomass fraction (referred to herein as bagasse) that can be further processed according to the present invention. In other cases, the extractant solution can include a surfactant, additional solvent, or extract-containing juice in addition to water. The extract-containing juice can be from, for example, an earlier extraction step or an earlier grinding step.

[0073] In some cases, it can be preferred to combine extraction with grinding of the biomass. Rollers, screws, and other forms of presses can be used to grind the biomass. For example, the biomass can be passed between one or more press zones of opposing counter-rotating rollers to maximize mechanical removal of water-soluble fractions and production of bagasse that can be subjected to further processing as described below. When the bagasse is subjected to multiple pressings, the water-soluble fraction removed in one grinding step (often referred to as juice) can be used to wash the bagasse in subsequent grinding steps.

[0074] In some preferred cases, the biomass can be harvested and chopped to a size, ground, and extracted with an aqueous solvent to remove water-soluble extractives such as inorganic salts, sugars, polysaccharides, organic acids, and saponins. The grinding step can be performed prior to pulping using a screw press, optionally using suction, to remove water-soluble extractives and further reduce the size of the biomass. Generally, the extraction step, alone or in combination with grinding, removes at least about 25% of the water-soluble solids from the biomass, more preferably at least about 50%, still more preferably at least about 75%, such as from about 25% to about 98%, such as from about 50% to about 90%, such as from about 75% to about 90%.

[0075] Removal of water-soluble extractives from the biomass is preferably performed prior to pulping, more preferably prior to bleaching. Removal of water-soluble extractives from the biomass can improve the efficiency of pulping and / or bleaching. For example, it has been demonstrated that removal of a substantial portion of the water-soluble extractives from the primary pulp, such as at least about 85%, more preferably at least about 90%, of the water-soluble extractives, improves the brightness of the bleached pulp. In some cases, the present invention provides for removal of at least 85%, such as at least about 90%, such as at least about 95%, of the water-soluble extractives from the pulp prior to bleaching. By removing water-soluble extractives prior to bleaching, the bleached pulp can have a brightness of about 80% or more.

[0076] Alternatively, water-soluble solids can be removed from the biomass prior to pulping by diffusion. In diffusion, the biomass is contacted with a solvent to extract the water-soluble solids. Generally, the biomass is prepared by first cutting rather than shearing or pulverizing in order to minimize damage to the fibers and to avoid creating excess fines. The prepared biomass is then repeatedly washed with a solvent in a diffuser to extract the water-soluble solids from the biomass. The solvent can be any of the aforementioned solvents. An exemplary solvent is water, particularly hot water, more particularly water having a temperature of about 40 °C to about 90 °C.

[0077] Various types of diffusers are known in the art and can be suitable for use with the biomass as described herein. Suitable diffusers include ring diffusers, tower diffusers, or drum diffusers. Exemplary diffusion systems are discussed in, for example, U.S. Patent Nos. 4,182,632; 4,751,060; 5,885,539; and 6,193,805, the contents of which are hereby incorporated by reference herein to the extent consistent with the present disclosure. Numerous other diffusion methods and apparatuses for diffusion methods are known and can be suitable for use in the methods described herein. One such diffuser is a continuous loop, counter-current, shallow bed Crown Model III percolation extractor, which is commercially available from Crown Iron Works, Blaine, MN.

[0078] Alternatively, the water-soluble portion of the biomass can be removed prior to pulping by compression and steeping. Compression and steeping can be performed using multiple devices or a single compression and steeping device, such as a plug screw feeder, for example, an MSD Impressafiner® commercially available from Andritz, Inc. of Alpharetta, GA, or another device suitable for compressing and steeping the cut and washed biomass. For example, the cut biomass can be compressed by a device capable of having a compression ratio of at least 2.5 to 1, such as a 4 to 1 compression ratio, such as a 5 to 1 compression ratio, including all compression ratios therebetween, to remove the water-soluble portion and prepare the biomass for pulping. Compression ratio is defined as the ratio of the inlet volume of the compression zone to the outlet volume of the compression zone, relative. Such a compression ratio allows for sufficient pressurization of the biomass to ensure proper chemical absorption during pulping. ®

[0079] The device used for compression can further be used for steeping, or a separate device can be used for the steeping stage. Steeping allows for softening and separation of the biomass into fibers by applying a physical mechanical treatment. Steeping can also increase the surface area of the bagasse, which can be used to absorb chemicals in the subsequent pulping step.

[0080] ​Extracted bagasse is converted to slurry by mechanical refining using a digester having an inlet and a rotating disc within a housing. The digester can be operated in continuous or batch mode. If continuous mode is used, a single digester or multiple digesters in series or parallel can be operated. If batch mode is used, multiple digesters are operated alternately to accommodate the continuous transfer of bagasse to the digesters and the continuous feed of primary slurry from the digesters. The digesters can be in horizontal, vertical or inclined orientation.

[0081] The digesters can be operated at a range of temperatures and pressures. In some cases, when mechanical pulping is performed in two separate mechanical refining stages, the digester conditions can be varied between the two stages. For example, the temperature can be in the range of about 120°C to about 190°C for the first stage, and about 35°C to about 55°C for the second stage. Further, the digester pressure can be in the range of about 30 psi to about 35 psi for the first stage, and the second stage can be performed at atmospheric pressure.

[0082] The digester operation can be optimized by subjecting the bagasse to first and second mechanical refining stages to fibrillate the esparto bagasse without excessive cutting, fines generation or yield loss, where the first stage is performed at a first consistency and the second stage is performed at a second consistency different from the first consistency. For example, the biomass can be mechanically refined at a first condition where the biomass consistency is at least about 20%, such as at least about 30%, such as about 35% to about 45%. The refined bagasse can be discharged from the first digester, diluted and secondarily mechanically refined at a second condition where the refined bagasse consistency is about 3% to about 6%, such as about 5%, to produce a primary slurry.

[0083] After the first mechanical pulping stage, the primary slurry can be discharged from the first digester and treated with chemicals, and allowed for a retention period for chemical reactions before being transferred to the second digester for the second mechanical refining stage. The primary slurry can also be quenched, such as by cooling, when it is discharged from the first digester to the second digester. For example, the primary slurry can be cooled to below about 80°C after retention when it is transferred to or received by the digester for the second stage mechanical refining.

[0084] The second digester conditions can be maintained, such as atmospheric pressure, a consistency of about 3% to about 6%, and a temperature of about 35°C to about 55°C. The second refining is typically performed without further addition of chemicals. The primary slurry, which can have a brightness of about 50% to about 60%, can be subjected to further processing to produce a finished slurry. For example, the primary slurry can be diluted, cleaned to remove debris, and bleached to produce a bleached slurry having a brightness of about 80% or more.

[0085] In some cases, the primary pulp can be bleached by reacting the primary pulp with an alkaline peroxide chemical under conditions that allow the temperature of the primary pulp to be maintained as the pulp is transferred to the bleaching tower for secondary bleaching. If the primary pulp is discharged directly to the bleaching tower, the temperature of the primary pulp can also be thermally adjusted within the bleaching tower by the addition of liquid or gas or by the use of heat transfer components.

[0086] In some cases, the primary pulp can be transferred from the digester to the bleaching tower under atmospheric conditions by a transfer screw, chute, or the like. When the digester includes a pressurized housing, the primary pulp can be discharged to the bleaching tower via a vent valve.

[0087] The bleaching can be performed without the use of chlorine or chlorine-containing compounds. Non-chlorine oxidizing agents such as peroxides, oxygen, and / or ozone can be used to bleach the primary pulp, with the addition of cyanamide or a cyanamide salt. When the secondary bleaching includes a peroxide as the bleaching agent, the method can also include one or more stabilizers or complexing agents to avoid decomposition of the peroxide. If heavy metal salts are removed from the primary pulp by washing prior to bleaching, the addition of a stabilizer or complexing agent can be omitted.

[0088] In some cases, it can be desirable to separate the cuticle debris from the primary pulp prior to secondary bleaching. Cuticle debris is typically derived from the cuticle layer of the leaf of the biomass and can include additional layers of the cuticular epidermis. Cuticle debris can include cellulose, cutin, cutan, polysaccharides, lipids, and waxes. Cuticle debris can be hydrophobic and can have a color or hand that is undesirable in paper products. For example, cuticle debris can have a brown or yellow color and a rough hand.

[0089] The removal of cuticle debris prior to secondary bleaching can improve the efficiency of the secondary bleaching and increase the brightness of the finished pulp. Additionally, the removal of cuticle debris can improve the physical properties of paper products made with the pulp. For example, the removal of cuticle debris from the pulp can improve the hand and softness of tissue products made therefrom. In other cases, the removal of cuticle debris from the pulp can reduce lint levels in the finished product, as the typically hydrophobic debris is less well suited to bond with the cellulose fibers that form the paper product.

[0090] In some cases, the primary pulp can have a debris content of about 5 wt% or less, such as about 3 wt% or less, such as less than about 2.5 wt%, such as less than about 2.0 wt%, prior to secondary bleaching. Preferably, the primary pulp has a low debris content, so there is generally no specific lower limit to the amount of debris. However, in some cases, an amount of cuticle debris can survive the processing and the primary pulp can have a debris content of about 0.5 wt% or greater, such as about 1.0 wt% to about 5.0 wt%.

[0091] By reducing the shive prior to secondary bleaching, the resulting bleached pulp can have improved brightness and acceptable shive levels. Such pulp is well suited for the production of high brightness paper products, particularly tissue paper products that require high brightness and low lint. Thus, the bleached pulp of the present invention has a brightness of at least about 75% and a shive content of about 1.0 wt.% or less, such as about 0.90 wt.% or less, such as about 0.80 wt.% or less, such as about 0.60 wt.% or less. In certain cases, it can be desirable to remove substantially all shive from the pulp prior to bleaching, such that the bleached pulp has no detectable shive.

[0092] Non-limiting examples of apparatus that can be used to remove surface shive from the primary pulp include one or more screens, cleaners, washers, or surge tanks. In certain cases, a screen, particularly a pressure screen having a body equipped with a first screen having screen openings and a second screen having holes, such that both the screen openings and the holes can be used to screen the primary pulp, can be used to remove shive. Multiple screens can be used in many different configurations and flows.

[0093] In certain cases, it can be preferred to screen the pulp to remove shive by using a pressure screen having at least one screen opening. The screen opening can have a width dimension of about 0.3 mm or less, such as about 0.25 mm or less, such as about 0.10 mm to about 0.15 mm.

[0094] Shive can also be removed from the primary pulp by one or more conical cleaners, particularly one or more hydrocyclones. Those skilled in the art will recognize that a hydrocyclone is a general description of a cleaning device that uses centrifugal force and other fluid dynamics to separate insoluble solids based on density. Generally, conical cleaners have a geometry that provides a decreasing (cross-sectional) diameter. Multiple cleaners can be combined in various orientations so as to share a common feed chamber and a discharge chamber.

[0095] The conical cleaners can include one or more of a forward flow (conventional) cleaner, a low density cleaner, a reverse flow cleaner, a through-flow cleaner, a core-bleed cleaner, an asymmetric cleaner, and a gyratory cleaner. In certain cases, it can be preferred to use at least one low density cleaner having a diameter of about 25 cm to about 120 cm and an operating pressure drop of about 100 kPa to about 210 kPa to remove surface shive. The low density cleaner can be operated in a forward feed configuration and at a pulp consistency of about 0.5% to about 2.0%.

[0096] After cleaning, the cleaned pulp can be subjected to secondary bleaching. Secondary bleaching can be carried out at medium consistency or high consistency and can consist of one, two or three bleaching stages, depending on the desired brightness of the finished pulp. Generally, medium consistency bleaching is carried out at a pulp consistency of less than about 16%, such as from about 8% to about 16%, such as from about 8% to about 12%. On the other hand, high consistency bleaching can be carried out at a pulp consistency of about 16%, such as from about 16 to about 30%, such as from about 16 to about 22%.

[0097] Secondary bleaching can be carried out in two stages at a consistency of about 10% using an alkaline peroxide solution with or without peroxide stabilizers: sodium silicate and DTPA. In other cases, secondary bleaching can be carried out in two stages, where the first stage is carried out at a consistency of about 10% and the second stage is carried out at a consistency of about 20%, and both stages are carried out using an alkaline peroxide solution with or without peroxide stabilizers: sodium silicate and DTPA. Secondary bleaching can also be carried out in a single high consistency stage, such as a consistency of about 20%. Regardless of the number of stages or the consistency of the pulp, the total peroxide dosage can range from about 8% to about 12% and the ratio of caustic to peroxide can range from about 0.4 to about 0.6.

[0098] Secondary bleaching can be carried out at a temperature of about 75°C to about 85°C and the total retention time can range from about 1 hour to about 5 hours. The final pH of the bleached pulp can be from about 8 to about 11, more preferably from about 9 to about 10.

[0099] The bleached pulp can be fed to further processing steps, which can include a number of operations including, but not limited to, mechanical refining, screening, and washing, to produce a secondary bleached pulp suitable for end use, such as the manufacture of wet-laid paper products. For example, the bleached pulp can be diluted and refined using a twin flow non-pressurized refiner at a low consistency, such as a consistency of about 3.0% to about 5.0%. The refined bleached pulp can then be dewatered, dried, and formed into a sheet.

[0100] As an alternative, both the bleached and unbleached pulps prepared according to the present application can be formed into dry sheets or rolls. The pulp can be diluted with water, resulting in a diluted pulp, which can be pumped through a fan pump to a headbox. The diluted pulp can be supplied to the headbox at a consistency of about 0.1% to about 5% solids, such as from about 0.5% to about 3% solids by weight, such as from about 1% to about 2.5% solids by weight.

[0101] The diluted slurry can be jetted from a headbox onto a wire and partially dewatered to form a partially dewatered slurry sheet. The wire can be a foraminous continuous metal screen or plastic wire that travels in a loop. The wire can be, for example, a flat wire fourdrinier paper machine, a twin-wire former, or any combination of these. Low vacuum boxes and suction boxes can be used with the wire in a conventional manner. After dewatering on the wire, the consistency of the slurry sheet can be in the range of about 2% to about 35% solids, such as about 10% to about 30% solids.

[0102] The partially dewatered slurry sheet can be conveyed to a wet press section. In the wet press section, additional water can be pressed and vacuumed from the slurry. The wet press section can utilize a press nip system formed by rollers that are pressed against one another with the aid of press felts that support the slurry sheet and can absorb the water that is pressed. Vacuum boxes can optionally be used to apply a vacuum to the press felts to remove moisture so that when the felt returns to the press nip in the next cycle, it does not add moisture to the sheet. The wet press section can increase the consistency of the partially dewatered slurry sheet to about 40% solids or greater, such as about 50% solids or greater.

[0103] The pressed slurry can be dried through a hot dryer section. The slurry sheet can be dried in the hot dryer section at temperatures above about 100°C to remove more water. The hot dryer can include, for example, a series of internally steam-heated cylinders that evaporate the moisture of the slurry as it travels over the heated cylinders. Generally, the hot dryer increases the consistency of the pressed slurry to about 80% by weight or greater, such as about 90% by weight or greater, such as about 80% to about 95% by weight.

[0104] The dried slurry exiting the hot dryer can be in the form of a continuous dried slurry sheet, which can be combined into sheets, bales, rolls, or other forms. In certain instances, the resulting slurry sheet has a moisture content of less than about 3%, more preferably less than 20%, and still more preferably less than about 10%. The slurry sheet can be produced at any given basis weight, however, in certain instances, the slurry sheet can have a basis weight of at least about 150 grams per square meter (gsm), such as about 150 gsm to about 600 gsm, more preferably about 200 gsm to about 500 gsm.

[0105] During sheet formation, the ability of the slurry sheet to disperse in water and drain is of great importance, as if insufficient drainage occurs, the speed of the paper machine must be reduced, or the wet-formed web will not hold together on the foraminous surface. A measure of this drainage parameter is freeness, and more particularly Canadian Standard Freeness (CSF). Thus, in certain instances, the slurry prepared according to the present disclosure has a Canadian Standard Freeness (CSF) of greater than about 400 mL, and more preferably greater than about 450 mL, such as about 400 mL to about 600 mL.

[0106] The slurries produced according to the present application can have one or more improved physical properties that make them well suited for use in the manufacture of wet-laid paper products, and more particularly, wet-laid tissue paper products. The slurries of the present application can be blended with other wood and non-wood pulps as desired to form a wet-laid product having the desired attributes. The bleached pulps can include wood pulp fibers produced by any of several well-known methods, such as chemical (sulfite, kraft), thermal, mechanical, or combinations of these techniques. In some cases, the pulps of the present application can replace one or more pulps, particularly wood pulps, in a conventional papermaking furnish. For example, the pulps of the present application can replace northern bleached softwood kraft (NBSK) pulp fibers.

[0107] In some cases, the present application provides a non-wood pulp, particularly a flax pulp produced without the use of chemicals through at least one mechanical treatment stage, as described herein, having a fiber length of about 1.50 mm or greater, such as about 1.55 mm or greater, such as about 1.60 mm or greater, such as about 1.65 mm or greater, such as about 1.70 mm or greater, such as about 1.75 mm or greater, such as about 1.50 mm to about 2.50 mm, such as about 1.55 mm to about 2.00 mm. In some cases, the non-wood pulps of the present application can have a coarseness of less than about 10.0 mg / 100 m, such as less than about 9.0 mg / 100 m, such as less than about 8.0 mg / 100 m, such as less than about 7.0 mg / 100 m, such as less than about 6.0, such as less than about 5.0, such as about 4.0 mg / 100 m to about 10.0 mg / 100 m, such as about 4.0 mg / 100 m to about 8.0 mg / 100 m, such as about 4.0 mg / 100 m to about 6.0 mg / 100 m.

[0108] At the aforementioned fiber lengths, the pulps can have a moderate tensile strength, such as a tensile index of about 55 or less, such as about 50 or less, such as about 45 or less, such as about 30 to about 55, such as about 35 to about 50, such as about 35 to about 45. Moreover, the pulps can have only a moderate tensile strength even when refined. For example, as shown in FIG. 1, the pulps can have a tensile index that is less than flax pulps produced by chemical-mechanical pulping at a wide range of refining levels. Figure 2

[0109] The freeness of the pulps can also be improved by using the aforementioned chemicals during pulping. For example, as shown in FIG. 2, the pulps can have a freeness that is greater than flax pulps produced by chemical-mechanical pulping at a wide range of refining levels. Figure 3 ​As shown, the pulp of the present application can have a higher freeness at a given tensile index as compared to a pulp of a papyrus prepared by a chemical mechanical pulping process. Thus, in some cases, the non-wood pulp can have a freeness of about 500 mL or greater, such as about 525 mL or greater, such as about 550 mL or greater, such as about 500 mL to about 600 mL.

[0110] The non-wood pulp of the present application can also have a low fines content and a high freeness, such as a fines content of less than about 2.0%, more preferably less than about 1.5%, still more preferably less than about 1.0%, such as about 0.5 to about 2.0, and a freeness of about 500 mL or greater, such as about 525 mL or greater, such as about 550 mL or greater, such as about 500 mL to about 600 mL.

[0111] The non-wood pulp of the present application can also be a bleached non-wood pulp having a brightness of about 75% or greater, such as about 80% or greater, such as about 82% or greater, such as about 75% to about 92%, such as about 80% to about 90%, such as about 80% to about 85%. At the foregoing brightness levels, the pulp can have a debris content of about 1.0% by weight or less, such as about 0.90% by weight or less, such as about 0.80% by weight or less, such as about 0 to about 0.80% by weight.

[0112] In other cases, the non-wood pulp can include a low content of water soluble extractives, such as less than about 5.0% by weight of water soluble solids, more preferably less than about 3.0% by weight of water soluble solids, still more preferably less than about 2.0% by weight of water soluble solids. Removal of the water soluble extractives during processing of the non-wood biomass into a pulp can improve the bleaching of the fibers such that the bleached non-wood pulp has a low amount of water soluble solids (e.g., less than about 5.0% by weight) and a high brightness, such as at least 80% or greater, such as about 80% to about 92%.

[0113] Test Methods

[0114] Slurry Handsheet

[0115] Pulp handsheets were prepared using a Valley Ironwork laboratory handsheet former (size 8.5 inches x 8.5 inches). The pulp was mixed with distilled water to form a slurry at a ratio of 25 g of pulp (dry basis) to 2 L of water. The pulp / water mixture was subjected to defibration using a L&W defibrator model 965583 at a speed of 2975 ± 25 RPM for 5 minutes. After defibration, the mixture was further diluted by the addition of 4 L of water. A handsheet was formed using a wet laid handsheet former to a basis weight of 60 grams per square meter (gsm). The handsheet was removed from the screen, placed in a press with a blotter sheet, and pressed at a pressure of 75 pounds per square inch for 1 minute, dried on a steam dryer for 2 minutes, and finally dried in an oven. The handsheet was cut into 7.5 square inches and subjected to testing.

[0116] Fiber Properties

[0117] Fiber properties such as length, coarseness, percent fines, and fraction of very long fibers were typically determined using an OpTest Fiber Quality Analyzer-360 (OpTest Equipment, Inc., Hawkesbury, ON) according to the manufacturer’s instructions. A sample was typically prepared by first accurately weighing a sample of pulp. The sample mass can be in the range of about 10 mg to about 50 mg (dry basis), and can be taken from a handsheet or pulp sheet. The weighed sample was diluted to a known consistency (about 2 mg / l to about 10 mg / l). An aliquot of the diluted sample (typically 200 ml) was further diluted to a final volume of 600 ml and placed in the analyzer. The sample was then analyzed according to the manufacturer’s instructions, and the output of the analyzer was recorded, such as length weighted average fiber length, coarseness, length weighted fines, and a histogram showing the distribution of various fiber properties for a given sample. Generally, each reported fiber property was the average of three replicates.

[0118] The output of the Fiber Quality Analyzer was used to calculate the fraction of very long fibers (VFL), which is the sum of the number of fibers from 6 mm to 14.95 mm divided by the total number of fibers. Generally, the group data output by the instrument, which provides the number of individual fibers counted within a given fiber length range, was used to determine the VLF. The total number of individual fibers counted (N) and the total number of individual fibers counted that were 6 mm or longer in length (n) were determined from the group data. VLF = n / N*100.

[0119] The output of the Fiber Quality Analyzer was also used to calculate the ratio of length weighted average fiber length (L w ) to number average fiber length (L n ). L w and L n were calculated by the FQA software using the following equations: L w = (Σ (N x L)) / Σ N L n = Σ N / Σ N

[0120]

[0121] where n and L are determined by the instrument during the analysis of the sample. The ratio of the length-weighted average fiber length (L w ) to the number average fiber length (L n ) indicates the fiber length distribution of the sample. A higher ratio indicates a wider fiber length distribution. A value of 1 indicates that all fibers in the sample have the same length.

[0122] Fiber coarseness is measured using the FQA instrument and is measured "as is" without removal of fines. Consistency of pulp samples is determined using TAPPI Method T-240 or equivalent and the consistency (%) is recorded to the nearest 0.01%. Based on the measured consistency, the amount of undried sample required to yield approximately 0.015 grams of oven-dried pulp is calculated and weighed out and the weight is recorded to the nearest 0.0001 g. The weighed undried pulp is transferred to a British Pulp Disintegrator or equivalent and the total volume of the sample is diluted to 2 liters with deionized water and disintegrated at 15,000 revolutions according to the manufacturer's instructions. The disintegrated sample is further diluted with deionized water to a total volume of 5 liters ± 50 mL and the volume is recorded to the nearest 10 mL. The diluted sample is agitated by stirring and approximately 600 grams is weighed into a clean beaker. The mass of the sample weighed into the beaker is recorded to the nearest 0.1 g. The oven-dry weight of the pulp sample to be analyzed is then calculated as shown in the equation below and the fiber analysis is performed according to the manufacturer's instructions.

[0123]

[0124] Thickness

[0125] In general, dry and prepare handsheets for testing as described in TAPPI T 205 sp-02. Pulp sheets can be tested as is. Thickness is measured using a L&W Model Code SE 050 micrometer or equivalent. The micrometer has a circular foot with an area of 2.0 cm 2 at a rate of 1.0 mm / sec and a pressure of 50 kPa. In general, thickness is reported as the average of five samples.

[0126] Basis Weight

[0127] Generally, the drying and preparation of handmade paper is performed for the tests described in TAPPI T 205 sp-02. Pulp sheets can be tested as is. The oven-dry basis weight is typically measured by first cutting the sample into approximately 19.05 cm × 19.05 cm pieces using a suitable cutting tool. The cut sample is then placed on a balance in an oven preheated to 105°C ± 2°C. Once the sample weight has stabilized, the weight is recorded to an accuracy of 0.01 g. The oven-dry basis weight is equal to the measured weight (W) multiplied by 27.56.

[0128] Tensile

[0129] Generally, tensile strength is measured by forming handmade paper with a specific pulp as described herein, and then testing the resulting handmade paper. Typically, the handmade paper is dried and prepared for testing as described in TAPPI T 205 sp-02. The samples are pre-conditioned and tested under TAPPI conditions (50 ± 2% relative humidity and 72 ± 1.8℉) as described in TAPPI T 402. Tensile strength testing is performed using an MTS Systems Sintech 11S, serial number 6233 tensile testing instrument, essentially as described in TAPPI T 494 om-01. Data acquisition software is MTS TestWorks for Windows Ver. 3.10. ® (MTSSystems Corp., Research Triangle Park, NC). Typically, the tensile strength of five samples is measured and averaged. Tensile strength is usually expressed in grams per unit sample width, such as g / 25.4 mm.

[0130] Dust

[0131] MasterScreen, typically from Pulmac Systems International (Williston, VT), is used. ™ Measuring debris. MasterScreen ™ It is a low-consistency screening device designed to mechanically separate fibers from contaminants. (MasterScreen) ™ It is equipped with a sieve (part number 3390P) with a mesh size of 100µm (0.004 inches). The use of MasterScreen type instruments for screening pulp is generally described in T-274.

[0132] Approximately 5.0 oven-dry metric tons of fiber were used for analysis. Samples could be obtained from handmade paper, pulp sheets, or wet pulp sheets. 5.0 g of sample was mixed with 2 L of water and dissociated using a benchtop dissociator at 15,000 rpm prior to testing. In some cases, when the fiber length of the known sample exceeds 2 mm, a cationic loosening agent such as cationic oleoyl imidazoline could be added to the diluted sample to prevent clumping or snagging. In those cases where a loosening agent was added, it was typically added at a rate of 160 kg loosening agent / oven-dry metric ton of fiber. The sample was screened according to the manufacturer's instructions, and the sieve residue was collected in a collection cup equipped with a 150-mesh stainless steel sieve. A washing cycle was run after the initial cycle to ensure that all debris retained by the sieve was captured. Finally, the collection cup was rinsed with water, and the rinsing fluid was collected in a beaker. The waste liquid and washing fluid collected in the beaker were filtered under vacuum using a pre-weighed filter pad. The debris was collected on the filter pad and dried overnight in an oven preheated to 105°C. Weigh the dried filter pads to an accuracy of 0.01 g and calculate the weight percentage of debris. Generally, debris is reported as a percentage by weight and is the average of three samples.

[0133] Water Soluble Solids

[0134] Total biomass water-soluble solids can be extracted using accelerated solvent extraction (ASE) systems such as Dionex. ™ ASE ™ The determination was performed using a method called Thermo Fisher Scientific, Waltham, MA. Approximately 10 grams of harvested biomass was dried in an oven to constant weight, typically at 125°C for 4 hours. After drying, approximately 0.2 grams of oven-dried biomass was accurately weighed and the weight (W) was recorded. b (Accurate to 0.001 g). Water was used as the solvent, and the biomass was extracted under the conditions shown in Table 2 below. The biomass to solvent ratio was typically 100:1, and two consecutive water extraction cycles were performed.

[0135] Table 2

[0136]

[0137] At the end of the extraction process, the liquid phase was collected, vacuum dried in a warm water bath at approximately 80°C, and the weight (W) of the dried material was recorded. i (Accurate to 0.001g). Total weight of water-soluble solids (W) e The weight (W) of the solids recovered from the extraction method i ) Calculate. Then use the following equation to determine the total water-soluble solids as a percentage of oven-dry biomass:

[0138]

[0139] Size Classification

[0140] Using the Williams sieve analysis method, TMI Chip Class ™ Model 71-01 (Testing Machines Inc., New Castle, DE) was used to determine the relative size and nominal size of the biomass and bagasse, which indicates the relative proportion of biomass or bagasse retained on each of a series of screens having different sizes as described in Table 3 below, in weight percent.

[0141] Table 3

[0142]

[0143] The Williams sieve analysis method measures the lengthwise or crosswise dimension of the biomass or bagasse retained on a given screen. Two important values can be obtained from the above sieve data regarding chip uniformity. The first value is the screen size through which at least 70% of the biomass or bagasse travels, i.e., the nominal size. The second is the relative distribution of chips on each screen and the relative position of the screen at which the distribution is maximized.

[0144] Examples

[0145] The inventive pulps were prepared from Yucca filamentosa biomass using a two-stage mechanical pulping process, with chemical addition after the first mechanical pulping stage. Both bleached and unbleached pulps were prepared. The process used to prepare the exemplary pulps is summarized in Table 4 below.

[0146] Table 4

[0147]

[0148] The biomass was cut and water soluble extractives removed using a two-stage screw press that cut the biomass to a nominal size of about 6.5 and removed about 45 wt% water soluble extractives. The extracted and cut biomass was washed by mixing with water, dewatered, and then diluted to a consistency of about 40%. The biomass was fed to an Andritz 36-1CP single disc refiner operating at a pressure of 30 psi, a temperature of about 130°C, an average energy load of 190 KW, and a rotating disc speed of 1800 rpm.

[0149] After high consistency refining, the refined bagasse with a freeness of about 642 mL was blown to a cyclone and discharged. Alkaline peroxide chemicals (4.3% hydrogen peroxide, 3.3% sodium hydroxide, 2.2% sodium silicate, and 0.2% DTPA) were added at the blower to allow for a retention time of about 30 minutes prior to low consistency refining. The diluted, refined bagasse was then fed to an Antritz TwinFlow IIIB refiner, which operates at atmospheric conditions and has rotating disc refiner plates operating at 1200 rpm.

[0150] Fiber and tensile strength properties of the primary and bleached pulps are summarized in Tables 5 and 6 below. To further evaluate the physical properties of the inventive pulps, samples were refined and formed into handsheets as described herein. The handsheets were subjected to tensile and porosity testing as described herein. The results of the tensile and porosity testing are summarized in Table 8 below.

[0151] Table 5

[0152]

[0153] Table 6

[0154]

[0155] Comparative Example 1

[0156] A comparative sample of rope agave pulp was prepared using an alkaline-hydrogen peroxide mechanical process substantially as described in Example 3 of PCT Application No. PCT / US2021 / 058196. Fiber and tensile strength properties of the bleached pulp are summarized in Tables 7 and 8 below.

[0157] Table 7

[0158]

[0159] Table 8

[0160]

[0161] Comparative Examples 3 and 4

[0162] Comparative samples of stringy yucca pulp were prepared using a three-stage non-wood pulping process commercially available from Taizen America (Macon, GA). The pulping process included both mechanical action and chemical treatment to defibrillate the plant material and produce pulp. Generally, the fibers were cut to a nominal size of about 20 mm using a guillotine cutter. The cut fibers were fed to a mechanical beater and diluted with water to a consistency of about 40%. The beaten fibers were fed to a kneader and the consistency was adjusted to about 30%. The beaten fibers were mechanically pulped by adding 7% NaOH to a first kneading cylinder and 5% H2O2 to a second kneading cylinder. The resulting pulp was washed and screened. The fiber and tensile strength properties of the unbleached pulp (Comparative Example 2) are summarized in Table 9 below. A portion of the unbleached pulp was bleached with hydrogen peroxide. The fiber and tensile strength properties of the bleached pulp (Comparative Example 3) are summarized in Table 9 below.

[0163] Table 9

[0164]

[0165] While the application has been described in detail with respect to specific embodiments thereof, it will be appreciated that those skilled in the art, upon attaining an understanding of the foregoing, can readily conceive of alterations, variations and equivalents thereof. Accordingly, the scope of the present application should be assessed as that of the appended claims and any equivalents thereof, as well as the following embodiments:

[0166] Embodiment 1 : A method for preparing pulp from a non-woody species, the method comprising the steps of: (a) cutting the non-woody species; (b) removing at least a portion of water-soluble solids from the non-woody species to produce extracted bagasse; (c) washing the extracted bagasse to produce washed bagasse having a first consistency; (d) mechanically refining the washed bagasse under first refining conditions to produce a primary pulp, wherein step (d) is substantially free of added chemicals; (e) chemically treating the primary pulp with caustic and optionally an oxidizing agent; (f) diluting the primary pulp to produce a diluted primary pulp having a consistency in the range of about 3% to about 4%; and; (g) refining the diluted primary pulp under second refining conditions to produce a non-wood pulp.

[0167] Embodiment 2: A method for preparing a pulp from non-woody biomass, the method comprising the steps of: (a) providing non-woody biomass; (b) cutting the non-woody biomass to a nominal length; (c) extracting water-soluble solids from the cut biomass to produce bagasse; (d) mechanically refining the bagasse at a first consistency to produce refined bagasse; (e) chemically treating the refined bagasse with caustic and optionally an oxidizing agent; (f) mechanically refining the chemically treated refined bagasse at a second consistency, wherein the second consistency is less than the first consistency, to produce non-woody pulp; (f) cleaning the non-woody pulp to produce cleaned pulp; and (h) bleaching the cleaned pulp to produce bleached non-woody pulp.

[0168] Embodiment 3: A method for preparing a pulp from non-woody biomass, the method comprising the steps of: (a) providing non-woody biomass; (b) cutting the non-woody biomass to a nominal length of less than about 20 mm; (c) extracting water-soluble solids from the cut biomass; (e) refining the washed biomass under first refining conditions to produce a primary pulp; (f) chemically treating the primary pulp with caustic and optionally an oxidizing agent; (g) diluting the primary pulp to produce a diluted primary pulp having a consistency in the range of about 3% to about 4%; and (h) refining the diluted primary pulp under second refining conditions to produce non-woody pulp. The non-woody pulp can be subjected to further processing, such as cleaning to produce cleaned pulp, bleaching to produce bleached pulp, or drying to produce dried pulp.

[0169] Embodiment 4: The method of any of the preceding embodiments, wherein the pulp yield is at least about 90%.

[0170] Embodiment 5: The method of any of the preceding embodiments, wherein the pulp has a fiber length of about 1.50 mm to about 2.50 mm and / or a coarseness of about 4.0 mg / 100 m to about 10.0 mg / 100 m.

[0171] Embodiment 6: The method of any of the preceding embodiments, wherein the pulp has a tensile index of less than 50, such as about 45 or less, such as about 30 to about 55, such as about 35 to about 50, such as about 35 to about 45.

[0172] Embodiment 7: The method of any of the preceding embodiments, wherein the biomass comprises one or more plants of the Chlorogalum genus.

[0173] Embodiment 8: The method of any of the preceding embodiments, wherein the biomass comprises one or more plants selected from the group consisting of Yucca filifera, Yucca smalliana, Yucca night-blooming, Yucca jonesii, Yucca linearifolia, Yucca engelmamii, and Yucca recurvifolia.

[0174] Embodiment 9: The method of any of the preceding embodiments, wherein the slurry has a freeness of about 400 mL to about 600 mL.

[0175] Embodiment 10: The method of any of the preceding embodiments, wherein the slurry has a fines content of less than about 2.0% and a freeness of about 400 mL or greater.

[0176] Embodiment 11 : The method of any of the preceding embodiments, wherein the slurry has a very long fiber (VFL) content of about 0.10% or less.

[0177] Embodiment 12: The method of any of the preceding embodiments, wherein the slurry is a substantially dry sheet having a moisture content of about 10% or less and a sheet bulk of at least about 2.0 cc / g.

[0178] Embodiment 13: The method of any of the preceding embodiments, wherein the slurry has a dispersibility index of about 2.00 or less, such as about 1.50 to about 2.00.

[0179] Embodiment 14: A high yield non-wood pulp comprising a plurality of fibers derived from one or more plants of the genus Yucca and having a fiber length of about 1.50 mm or greater, a tensile index of less than 50, and a freeness of about 500 mL or greater.

[0180] Embodiment 15: The pulp of Embodiment 14 having a brightness of at least about 75% and a debris content of less than about 1% or less.

[0181] Embodiment 16: The pulp of Embodiment 14 or 15 having a fiber length of about 1.50 mm to about 2.50 mm and a tensile index of about 35 to about 50, such as about 35 to about 45.

[0182] Embodiment 17: The pulp of any of Embodiments 14 to 16 having a coarseness of less than about 10.0 mg / 100 m.

[0183] Embodiment 18: The pulp of any of Embodiments 14 to 17 having a freeness of about 500 mL to about 600 mL.

[0184] Embodiment 10: The slurry of any one of embodiments 14-18 having a fines content of less than about 2.0% and a freeness of about 525 mL or greater.

[0185] Embodiment 20: The slurry of any one of embodiments 14-19 having a very long fiber (VFL) content of about 0.10% or less.

Claims

1. A high-yield non-wood pulp comprising a variety of fibers derived from one or more plants of the genus *Tetracentron sinense* and having a fiber length of about 1.50 mm or greater, a tensile index of less than about 50, and a freeness of about 500 mL or greater.

2. The high-yield non-wood pulp according to claim 1, wherein the high-yield non-wood pulp has a brightness of at least about 756% and less than about 1% or less of debris.

3. The high-yield non-wood pulp according to claim 1, wherein the high-yield non-wood pulp has a fiber length of about 1.50 mm to about 2.50 mm.

4. The high-yield non-wood pulp according to claim 1, wherein the high-yield non-wood pulp has a coarseness of less than about 10.0 mg / 100 m.

5. The high-yield non-wood pulp according to claim 1, wherein the high-yield non-wood pulp has a freeness of about 500 mL to about 600 mL.

6. The high-yield non-wood pulp according to claim 1, wherein the high-yield non-wood pulp has a fine particle content of less than about 2.0% and a freeness of about 525 mL or greater.

7. The high-yield non-wood pulp according to claim 1, wherein the high-yield non-wood pulp has an extremely long fiber (VFL) content of about 0.10% or less.

8. A method for manufacturing a non-wood pulp, the method comprising the following steps: a. Provide non-woody biomass derived from Asparagaceae plants; b. Feeding the non-woody biomass into a refining machine, the refining machine including a refining disc, the refining disc being enclosed in a housing having an inlet and an outlet; c. The non-lignobiomass is refined under first refining conditions having a pH in the range of 6.5 to 7.5 to produce primary pulp; d. Chemically treat the primary slurry with caustic alkali and optionally an oxidizing agent; d. The chemically treated primary slurry is fed into a refining machine, the refining machine including a refining disc enclosed in a housing having an inlet and an outlet; as well as f. Refining the chemically treated primary pulp under second refining conditions to produce a secondary pulp.

9. The method of claim 8, further comprising the step of cleaning the secondary slurry to produce a cleaned slurry having less than about 5% debris.

10. The method according to claim 8, the method further comprising the step of bleaching the secondary slurry.

11. The method of claim 10, wherein the bleaching step comprises adding a sodium hydroxide alkaline peroxide solution to the secondary slurry.

12. The method of claim 10, further comprising the step of selectively cutting the biomass.

13. The method of claim 10, further comprising the step of extracting water-soluble solids from the biomass.

14. The method of claim 10, wherein the step of chemically treating the primary slurry is carried out at a temperature of about 80°C to about 90°C for at least 30 minutes.

15. The method according to claim 8, wherein the biomass is derived from one or more plants of the genus Yucca.

16. The method according to claim 15, wherein the one or more plants are selected from: Yucca cordifolia, Yucca davidii, Yucca noctiflori, Yucca jangii, Yucca slenderii, Yucca Engelmannii, and Yucca velutipes.

17. The method of claim 8, wherein the first refining conditions include a biomass consistency in the range of about 8% to about 12%, and the second refining conditions include a primary slurry having a consistency in the range of about 3% to about 4%.

18. The method of claim 8, wherein the slurry yield is at least about 90%.

19. The method of claim 8, wherein the primary slurry is substantially free of chemical additives.

20. The method of claim 8, wherein the high-yield slurry has a fiber length of about 1.50 mm or greater, a tensile index of less than about 50, and a freeness of about 500 mL or greater.

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