WO2025250645A1

WO2025250645A1 - High wet strength towel comprising non-wood fibers

Info

Publication number: WO2025250645A1
Application number: PCT/US2025/031207
Authority: WO
Inventors: Thomas G. Shannon; Zhiying E. YU; Ramon E. VERA
Original assignee: Kimberly Clark Worldwide Inc; Kimberly Clark Corp
Current assignee: Kimberly Clark Worldwide Inc; Kimberly Clark Corp
Priority date: 2024-05-29
Filing date: 2025-05-28
Publication date: 2025-12-04
Anticipated expiration: 2026-11-29

Abstract

Non-wood pulps, especially those from hesperaloe, enhance tissue durability, particularly wet durability, without affecting absorbency, strength, or softness. Hesperaloe pulps can be produced by high-yield mechanical processes that don't use chemicals. These pulps have good fiber length and moderate strength, particularly when mixed with wood pulp fibers. They also offer high wet strength efficiency, allowing tissue products to achieve a CD Wet/Dry ratio of about 0.35 to 0.55 using permanent wet strength agents. The high degree of wet strength efficiency may even be obtained without the use of softwood kraft pulp fibers.

Description

HIGH WET STRENGTH TOWEL COMPRISING NON-WOOD FIBERS

BACKGROUND OF THE DISCLOSURE

In the development and manufacture of paper products, particularly paper towels for the consumer market, it is a continual objective to improve the absorbent characteristics of the product. For cleaning up some spills, the consumer needs high absorbent capacity. For some uses, consumers want a fast rate of absorbency. For other uses, a combination of high absorbent capacity and fast absorbent rate is desired. At the same time, constraints on achieving this objective include the need to maintain or reduce costs in order to provide the consumer with the highest possible value, which in part means minimizing the amount of fiber in the product.

SUMMARY OF THE DISCLOSURE

The present inventors have successfully used non-wood pulps, particularly pulps produced from hesperaloe, to produce tissue products are both highly durable and absorbent when wetted. These benefits are achieved even when the hesperaloe fibers replace conventional wood papermaking fibers, such as Northern softwood kraft pulp (NSWK). In certain instances the hesperaloe fibers may comprise high-yield mechanical hesperaloe pulps and may be blended with conventional wood pulps to form a tissue web, which may be subsequently converted into a tissue product. The resulting tissue products retain a high degree of tensile strength when wet, such as a CD Wet/Dry ratio of about 0 30 or greater, such as about 0.35 or greater, such as about 0.40 or greater, such as from about 0.35 to about 0.55.

In addition to retaining a high degree of tensile strength when wet, the inventive tissue products have a high degree of absorbency, such as an Absorbent Capacity greater than about 7.0 g/g. Surprisingly, the improvement in wet tensile strength and absorbency may be achieved by distributing the hesperaloe pulp fibers in multiple layers of a stratified tissue web, or throughout the entire tissue web. Thus, in certain instances, the present invention provides tissue products comprising at least one tissue web or ply comprising a blend of hesperaloe pulp fibers and wood pulp fibers. In this manner the tissue web or ply may be stratified, comprising multiple layers, and the hesperaloe pulp fiber may be disposed in multiple layers, or it may be unstratified and the hesperaloe pulp fibers may be distributed throughout the web or ply.

Thus, in certain aspects the present invention provides tissue products comprising at least one tissue web or ply comprising a blend of hesperaloe pulp fibers and wood pulp fibers, where the fibers are blended such that at least a portion of the hesperaloe pulp fibers are present in the surface of the tissue product brought into contact with a user’s skin in-use. Despite having hesperaloe pulp fibers disposed in the outer surface, the inventive tissue products have an Absorbent Capacity greater than about 7.0 g/g and a CD Wet/Dry Ratio greater than about 0.35.

In still other aspects the present invention provides tissue products having relatively moderate amounts of long average fiber length kraft fibers, such as softwood kraft pulp fibers, or are substantially free from long average fiber length kraft fibers. For example, the tissue products may comprise less than about 10 wt%, based upon the total weight of the tissue product, softwood kraft pulp fibers. In other instances, the tissue products of the present invention may be substantially free from softwood kraft pulp fibers, particularly NSWK.

In other aspects the present invention provides a tissue product comprising wood pulp fibers and from about 5 to about 50 weight percent hesperaloe pulp fibers wherein the hesperaloe pulp fibers are blended with wood pulp fibers, the tissue product having an Absorbent Capacity greater than about 7.0 g/g and a CD Wet/Dry Ratio greater than about 0.35.

In still other aspects the present invention provides an uncreped through-air dried tissue product comprising at least about 20 weight percent high yield hesperaloe pulp fibers, the tissue product having a basis weight from about 30 to about 60 gsm, a GMT from about 1 ,000 to about 2,500 g/3”, a CD Wet/Dry Ratio greater than about 0.35 and an Absorbent Capacity greater than about 7.0 g/g.

In other aspects the present invention provides a multi-ply creped tissue product having a first outer surface formed by a first creped tissue ply and a second outer surface formed by a second creped tissue ply, wherein the first and second outer surfaces comprise a blend of high yield hesperaloe pulp fibers and wood pulp fibers, the product comprising from about 5% to about 50% high yield hesperaloe pulp fibers and having a GMT from about 1 ,000 to about 2,500 g/3”, a CD Wet/Dry Ratio greater than about 0.35 and an Absorbent Capacity greater than about 7.0 g/g.

In yet other aspects the present invention provides a method of manufacturing a tissue product comprising the steps of: dispersing hesperaloe pulp fiber in water to form a first fiber slurry; dispersing wood pulp fibers in water to form a second fiber slurry; adding a permanent wet strength agent to at least the first or the second fiber slurry; blending the first and the second fiber slurries together and depositing them on a moving belt to form a tissue web; drying the tissue web; and converting the tissue web into a spirally wound tissue product; wherein the spirally wound tissue product comprises from about 5% to about 60% hesperaloe pulp fibers and has a CD Wet/Dry ratio from about 0.35 to about 0.55.. DESCRIPTION OF THE DRAWINGS

Figure 1 is a graph illustrating the effect of permanent wet strength (Kymene™) add-on on wet tensile strength for handsheets comprising NSWK fibers (▲ ) and handsheets comprising high yield hesperaloe pulp fiber (•).

Figure 2 is a cross-sectional view of a blended tissue web.

Figure 3 is a cross-sectional view of a layered tissue web.

DEFINITIONS

As used herein, a "tissue product” generally refers to various paper products, such as facial tissue, bath tissue, paper towels, napkins, and the like. Normally, the basis weight of a tissue product of the present invention is less than about 80 grams per square meter (gsm), in some embodiments less than about 60 gsm, and in some embodiments from about 10 to about 60 gsm and more preferably from about 20 to about 50 gsm.

As used herein, the term “layer” refers to a plurality of strata of fibers, chemical treatments, or the like within a ply.

As used herein, the terms “layered tissue web,” “multi-layered tissue web,” “multi-layered web,” and “multi-layered paper sheet,” generally refer to sheets of paper prepared from two or more layers of aqueous papermaking furnish which are preferably comprised of different fiber types. The layers are preferably formed from the deposition of separate streams of dilute fiber slurries, upon one or more endless foraminous screens. If the individual layers are initially formed on separate foraminous screens, the layers are subsequently combined (while wet) to form a layered composite web.

The term “ply” refers to a discrete product element. Individual plies may be arranged in juxtaposition to each other. The term may refer to a plurality of web-like components such as in a multiply facial tissue, bath tissue, paper towel, wipe, or napkin.

As used herein, the term “basis weight” generally refers to the bone dry weight per unit area of a tissue and is generally expressed as grams per square meter (gsm). Basis weight is measured using TAPPI test method T-220.

As used herein, the term “caliper” is the representative thickness of a single sheet (caliper of tissue products comprising two or more plies is the thickness of a single sheet of tissue product comprising all plies) measured in accordance with TAPPI test method T402 using an EMVECO 200-A Microgage automated micrometer (EMVECO, Inc., Newberg, OR). The micrometer has an anvil diameter of 2.22 inches (56.4 mm) and an anvil pressure of 132 grams per square inch (per 6.45 square centimeters) (2.0 kPa).

As used herein, the term "sheet bulk" refers to the quotient of the caliper (pm) divided by the bone dry basis weight (gsm). The resulting sheet bulk is expressed in cubic centimeters per gram (cc/g). Tissue products prepared according to the present invention generally have a sheet bulk greater than about 10 cc/g, more preferably greater than about 11 cc/g and still more preferably greater than about 12 cc/g.

As used herein, the term "fiber length” refers to the length weighted average length of fibers determined utilizing a Kajaani fiber analyzer model No. FS-100 available from Kajaani Oy Electronics, Kajaani, Finland. According to the test procedure, a pulp sample is treated with a macerating liquid to ensure that no fiber bundles or shives are present. Each pulp sample is disintegrated into hot water and diluted to an approximately 0.001 percent solution. Individual test samples are drawn in approximately 50 to 100 ml portions from the dilute solution when tested using the standard Kajaani fiber analysis test procedure. The weighted average fiber length may be expressed by the following equation: where k = maximum fiber length x, = fiber length

Hi = number of fibers having length x; n = total number of fibers measured.

As used herein, the term "hesperaloe fiber” refers to a fiber derived from a plant of the genus Hesperaloe of the family Asparagaceae including, for example, Hesperaloe funifera. The fibers are generally processed into a pulp for use in the manufacture of tissue products according to the present invention. Preferably the pulping process is a high yield pulping process. The high yield hesperaloe pulp fibers generally have a lignin content, measured as Klason lignin, from about 10 to about 15 weight percent. The terms “hesperaloe fiber” and “high yield hesperaloe pulp fiber” may be used interchangeably herein when referring to non-wood fibers incorporated into tissue products, one skilled in the art will appreciate however that when incorporating non-wood fibers into tissue products it is preferred that the fibers be processed, such as by high yield pulping.

As used herein, the term “slope” refers to slope of the line resulting from plotting tensile versus stretch and is an output of the MTS TestWorks™ in the course of determining the tensile strength as described in the Test Methods section herein. Slope is reported in the units of grams (g) per unit of sample width (inches) and is measured as the gradient of the least-squares line fitted to the load- corrected strain points falling between a specimen-generated force of 70 to 157 grams (0.687 to 1 .540 N) divided by the specimen width. Slopes are generally reported herein as having units of grams per 3 inch sample width or g/3".

As used herein, the term “geometric mean slope” (GM Slope) generally refers to the square root of the product of machine direction slope and cross-machine direction slope. GM Slope generally is expressed in units of kg.

As used herein, the terms “geometric mean tensile” and “GMT” refer to the square root of the product of the machine direction tensile strength and the cross-machine direction tensile strength of the web. While the GMT may vary tissue products prepared according to the present disclosure generally have a GMT greater than about 1 ,400 g/3”, such as from about 1 ,400 to about 2,500 g/3”.

As used herein, the term “Stiffness Index” refers to the quotient of the geometric mean tensile slope, defined as the square root of the product of the MD and CD slopes (typically having units of kg), divided by the geometric mean tensile strength (typically having units of grams per three inches). MD Tensile Slope (kg)x CD Tensile Slope(kg)

Stiffness Index = - - - x 1,000

^{J J} GMT (g/3 )

While the Stiffness Index may vary tissue products prepared according to the present disclosure generally have a Stiffness Index less than about 8.0 and more preferably less than about 6.0.

As used herein, the term “Absorbent Capacity” is a measure of the amount of water absorbed by the paper towel product in the vertical orientation and is expressed as grams of water absorbed per gram of fiber (dry weight). Absorbent Capacity is measured as described in the Test Methods section and generally has units of grams per gram (g/g). While the Absorbent Capacity may vary tissue products prepared according to the present disclosure generally have an Absorbent Capacity greater than about 6.0 g/g and more preferably greater than about 7.0 g/g.

As used herein the term “CD Wet/Dry Ratio,” refers to the ratio of the wet CD tensile strength to the dry CD tensile strength, measured as described in the Test Methods Section, below. While the CD Wet/Dry Ratio may vary, tissue products prepared as described herein generally have a CD Wet/Dry Ratio greater than about 0.28 and more preferably greater than about 0.30, such as from about 0.28 to about 0.32. Generally, the foregoing ratios may be achieved over a wide range of Wet CD Tensile. For example, for tissue towel products that require a high degree of wet tensile strength in-use the Wet CD Tensile may be about 400 g/3” or greater, such as about 425 g/3” or greater, and such as about 450 g/3” or greater, such as from about 400 g/3" to about 500 g/3”. In other instances, such as facial tissue products, which require a moderate degree of wet tensile strength, the Wet CD Tensile may be about 120 g/3” or greater, such as about 130 g/3” or greater, such as about 140 g/3” or greater, such as from about 120 g/3” to about 250 g/3”.

As used herein the term “Wet Strength Efficiency,” refers to the CD Wet/Dry Ratio divided by the add-on amount of wet strength resin (measured in kilograms per dry metric ton of fiber) multiplied by 100 and is a measure of the amount of wet strength generated relative to dry strength normalized by the amount of wet strength added.

DETAILED DESCRIPTION OF THE DISLOSURE

The present inventors have surprisingly discovered that traditional permanent wet strength agents when used in combination with hesperaloe pulp fibers, particularly mechanically pulps hesperaloe pulp fibers, may develop a high degree of wet strength and that addition of increasing amounts of permanent wet strength continue to develop product wet strength well beyond that previously observed in products made from wood pulp fibers. Accordingly, permanent wet strength agents may be incorporated in the present tissue with a high degree of efficiency to yield products having a CD Wet/Dry ratio of about 0.25 or greater, such as about 0.30 or greater, such as about 0.0.35 or greater, such as from about 0.25 to about 0.50.

As illustrated in FIG. 1 , the addition of increasing amounts of permanent wet strength agent to the tissue products comprising hesperaloe pulp fibers results in increasing wet strength, well beyond that observed in similar products prepared from conventional wood pulp fibers. For example, the addition of a permanent wet strength agent to products made from conventional wood pulp fibers increased wet tensile strength about 350%. This increase plateaued however, with further additions of permanent wet strength having little or no additional benefit. On the other hand, the addition of permanent wet strength to products comprising hesperaloe fibers had a similar initial effect on wet strength but could be increased further with subsequent additions of permanent wet strength. In this manner, further additions of permanent wet strength agents could produce tissue products having CD Wet/Dry nearly twice that of similar products produced using conventional wood pulp fibers.

Thus, in certain instances, the use of hesperaloe pulp fibers facilitates an increase in CD Wet/Dry ratio beyond that which may be achieved using conventional wood pulp fibers. Moreover, in certain instances, the increase in CD Wet/Dry ratio may be achieved with only moderately high amounts of wet strength additive. Generally, CD Wet/Dry ratios may be achieved using from about 5 to about 50 percent, and more preferably from about 15 to about 45 percent, hesperaloe pulp fibers and from about 5 kg of wet strength resin per bone dry metric ton of fiber furnish (kg/MT) to about 10 kg/MT.

The use of hesperaloe pulp fibers does not come at the expense of tissue product absorbency. For example, tissue products of the present invention generally have an Absorbent Capacity greater than about 6.0 g/g , such as from about 6.0 to 8.0 g/g . As such the tissue products are durable when wet but are still sufficiently absorbent. This balance of absorbency and wet strength is not found in the prior art without resorting to adding latex binders or the like to the tissue product.

Further, the aforementioned wet-strength properties may be achieved with only modest additions of conventional wet-strength resin. For example, in certain embodiments the tissue products comprise less than about 15 kg of wet-strength resin per metric ton of furnish, such as from about 3 to about 15 kg, and more preferably from about 3 to about 10 kg. Rather than employ an excessive amount of wet-strength resin, the improved wet-strength properties are achieved by the addition of hesperaloe pulp fibers during the manufacture of the tissue product, such as from about 5 to about 50 percent, by weight of the product, and more preferably from about 20 to about 40 percent, by weight.

Accordingly, in certain embodiments the tissue products generally comprise pulp fibers derived from non-woody plants in the genus Hesperaloe in the family Agavaceae. Suitable species within the genus Hesperaloe include, for example H. funifera, H. noctuma, H. parviflova, and H. changii, as well as combinations thereof.

In certain preferred instances, non-wood pulps useful in preparing the products of the present invention are produced by a high yield pulping process High yield pulping processes useful for the manufacture of high yield hesperaloe pulps include, for example, mechanical pulp (MP), refiner mechanical pulp (RMP), pressurized refiner mechanical pulp (PRMP), thermomechanical pulp (TMP), high temperature TMP (HT-TMP), RTS-TMP, thermopulp, groundwood pulp (GW), stone groundwood pulp (SGW), pressure groundwood pulp (PGW), super pressure groundwood pulp (PGW-S), thermo groundwood pulp (TGW), thermo stone groundwood pulp (TSGW) or any modifications and combinations thereof. Preferably the high yield pulping process has a yield greater than about 60 percent, such as from about 60 to about 90 percent and more preferably from about 65 to about 90 percent. The foregoing yields generally refer to the yield of unbleached hesperaloe pulp fiber.

In certain instances, high yield hesperaloe pulps may be prepared as described in mechanical pulping process where the hesperaloe biomass or bagasse is treated with an alkaline phosphate prior to or during mechanical refining, such as described in PCT Application No. PCT/US2021/058196, the contents of which are incorporated herein in a manner consistent with the present invention. In other instances, high yield hesperaloe pulps may be produced using a two-stage mechanical puling process where fibrillation of the hesperaloe biomass or bagasse is carried out in first mechanical pulping stage without the addition of chemicals, such alkaline peroxide chemicals, and/or other chemicals known in the art to bleach or otherwise process lignocellulosic material into pulp or precursors of pulp. Once the hesperaloe biomass or bagasse has been refined to a freeness of about 400 mL or greater, chemicals may be introduced, such as after a first mechanical pulping stage and prior to a second stage of mechanical refining. The foregoing process not only simplifies the pulping process and reduces costs, but it also improves pulp yields and the physical properties of the resulting pulp. For example, the foregoing process may be used to produce hesperaloe pulps at yields of about 80% or greater, such as about 85% or greater, such as about 90% or greater, such as yields from about 80% to about 95%.

In still other instances, high yield hesperaloe pulps may be produced without the addition of chemicals, such alkaline peroxide chemicals, and/or other chemicals known in the art to bleach or otherwise process lignocellulosic material into pulp or precursors of pulp during mechanical refining of the pulp. The hesperaloe pulp may be produced using a process comprising the steps of: (a) providing a hesperaloe biomass; (b) cutting the 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 and at a pH ranging from 6.5 to 7.5 without the addition of chemicals to yield a refined bagasse; (e) mechanically refining the refined bagasse at a pH ranging from 6 5 to 7.5 without the addition of chemicals at a second consistency, wherein the second consistency is less than the first consistency, to yield a high yield hesperaloe pulp useful in the manufacture of tissue products of the present invention.

While in certain instances caustic or an oxidizing agent may be introduced to the process to facilitate fiber separation by the mechanical forces, such addition may not be necessary and in certain instances may be undesirable. For example, in certain instances it be desirable to produce hesperaloe pulp without the addition of caustic to improve yield and moderate the tensile strength of the resulting pulp. Without being bound by any particular theory, it is believed that omitting the addition of caustic during mechanic treatment, particularly mechanical treatment carried out a low consistency, such as consistencies of about 10% or less, particularly from about 3% to about 5%, improves pulp yield and reduces pulp tensile strength.

Although, in certain instances, a caustic or oxidizing agent may be added during processing, it is generally preferred that the hesperaloe pulp fiber is not pretreated with a sodium sulfite or the like prior to processing. For example, high yield hesperaloe pulps are generally prepared without pretreatment of the fiber with an aqueous solution of sodium sulfite, or the like, which is commonly employed in the manufacture of chemi-mechanical wood pulps.

The inventors have discovered that mechanical pulping of hesperaloe yields a pulp having a moderate fiber length, such as a fiber length of about 1 .50 mm or greater, such as from about 1 .50 to about 2.50 mm, yet a low degree of coarseness, such as less than about 10.0 mg/100m, such as from about 3.5 to about 10.0 mg/100 m. At the same time the pulp may have a moderate degree of tensile strength, such as a pulp Tensile Index of about 55 or less, such as from about 30 to about 55.

Generally, the hesperaloe pulp fibers useful in the present invention have a relatively long fiber length, such as 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 from about 1 .50 to about 2.50 mm, such as from about 1 .55 to about 2.00 mm. The hesperaloe pulp fibers may also have a fiber coarseness less than about 10.0 mg/100m, such as less than about 8.0 mg/100m, such as less than about 6.0 mg/100m, such as from about 4.0 to about 10.0 mg/100 m, such as from about 4.0 mg/100 m to about 8.0 mg/100m.

The hesperaloe pulps may also have a relatively modest degree of 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 from about 30 to about 55, such as from about 35 to about 50, such as from about 35 to about 45. In other instances, the hesperaloe pulps may have a freeness, where a higher value is indicative of pulps that are more easily dewatered, 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 from about 500 mL to about 600 mL.

In other instances, the hesperaloe pulps may 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 dispersion of the pulp in water and cause stringing or clumping when the pulp is used to manufacture wet-laid fibrous products. For example, the inventive pulps may 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 a about 0.50% or less, such as a VLF from about 0.05% to about 1 .0%. a fiber length from about 1 .50 to about 2.50. In addition to having reduced tensile strengths and relatively long fiber lengths.

In still other instances the hesperaloe pulps may have a high degree of brightness and/or low content of epidermis debris. Brightness and reduced debris are particularly important for pulps used in the manufacture of tissue products because of the need for a white, bright appearance and a low degree of linting. Accordingly, hesperaloe pulps useful in the present invention may have a Brightness of at least about 75%, more preferably at least about 78% and still more preferably at least about 80%. In other instances, the hesperaloe pulp may have a debris 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 instances, it may be desirable to remove substantially all of the debris from the pulp such that the pulp is substantially free from, or free from, debris.

In addition to the use of high yield hesperaloe pulp fiber the tissue products of the present invention are preferably prepared without the addition of binders, particularly latex binders and more specifically carboxyl-functional latex emulsion polymers, such as those described in US Patent Nos. 6,187,140 and 7,462,258. Latex binders, such as those disclosed in the foregoing references, have been used previously in the manufacture of tissue products to improve wet performance. These binders, however, add manufacturing complexity and cost. Therefore, it is desirable to produce a tissue product, such as the inventive tissues, without the use of binders and more specifically latex binders.

Further, tissues prepared according to the present disclosure are not treated with a sizing agent, such as alkyl ketene dimer (AKD) or alkenyl succinic anhydride (ASA), either during the tissue manufacturing process or after formation and drying of the tissue web. Rather, the tissue webs are prepared by adding hesperaloe fibers and in certain embodiments a wet strength resin, to the papermaking furnish prior to formation of the web, to enhance the wet-strength properties of the finished web. Unlike conventional sizing agents, which reduce the adsorption rate of water into the sheet, hesperaloe fibers and conventional wet-strength resins allow the sheet to adsorb water as intended during the end use but maintain sheet integrity and strength when wetted.

Rather than employ latex binders or sizing agents, the tissue products typically comprise a conventional wet-strength resin. Useful conventional wet strength resins include diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), epichlorhydrin resin(s), polyamide-epichlorohydrin (PAE), or any combinations thereof, or any resins to be considered in these families of resins. Particularly preferred wet strength resins are polyamide-epichlorohydrin (PAE) resins. Commonly PAE resins are formed by first reacting a polyalkylene polyamine and an aliphatic dicarboxylic acid or dicarboxylic acid derivative. A polyaminoamide made from diethylenetriamine and adipic acid or esters of dicarboxylic acid derivatives is most common. The resulting polyaminoamide is then reacted with epichlorohydrin. Useful PAE resins are sold under the tradename Kymene® (commercially available from Ashland, Inc., Covington, KY).

Table 1 illustrates the desirable increase in wet-strength properties that can be achieved via the combination of high yield hesperaloe fiber (HYH) and a conventional wet-strength resin. The samples have a basis weight of about 36 gsm and comprised a single through-air dried ply. The samples are handsheets comprising either 100% NSWK or 100% high yield hesperaloe pulp (HYH). As the table illustrates, at a constant level of wet-strength addition, a wet tensile level can be achieved via the addition of HYH.

TABLE 1

Hesperaloe pulp fibers may be used in the manufacture of several different tissue products requiring a wet strength, as well as dry durability and softness. For example, hesperaloe pulp fibers may be used in the manufacture of tissue towel products comprising a tissue web spirally wound around a core where the tissue product has xx. In other instances, the hesperaloe pulp fibers may be used in the manufacture of facial products comprising multiple tissue plies arranged in facing relation to one another to form a sheet that is folded, the facial tissue product having xx.

As noted previously, the instant tissue products have a high degree of absorbent capacity such as an Absorbent Capacity greater than about 6.0 g/g, such as from about 6.0 to about 7.0 g/g and more preferably from about 6.5 to about 7.0 g/g, while also having a CD Wet/Dry Ratio greater than about 0.30, such as from about 0.30 to about 0.40 Generally, the foregoing absorbent capacities and wet strengths are achieved at basis weights from about 30 to about 60 grams per square meter (gsm) and more preferably from about 35 to about 50 gsm and still more preferably from about 40 to about 50 gsm.

In addition to having satisfactory absorbent properties, the tissue products generally have improved wet CD performance. For example, in certain embodiments the tissue products have a Wet CD Durability greater than about 1 .75, such as from about 1 .75 to about 2.5 and more preferably from about 2.0 to about 2.5. At the foregoing Wet CD Durability levels the tissue products may have a Wet CD Stretch greater than about 10.0 percent, such as greater than about 12.0, such as greater than about 14,0, such as from about 10.0 percent to about 16.0, such as from about 12.0 to about 14.0.

While having improved properties, the tissue products prepared according to the present disclosure continue to be strong enough to withstand use by a consumer. For example, inventive tissue products generally have a geometric mean tensile (GMT) greater than about 800 g/3”, such as from about 800 to about 3,000 g/3”. The GMT may be varied depending on the intended use of the tissue product and the product format, including the basis weight and the number of plies. Not only are the instant tissue products absorbent and strong enough to withstand use, they may also have a low degree of stiffness and have good hand feel. As such the tissue products may have a GM Slope less than about 10.0 kg, such as from about 4.0 to about 10.0 kg and more preferably from about 4.0 to about 8.0 kg. The foregoing GM Slopes may be achieved over a range of tensile strengths, such as a GMT ranging from about 800 g/3”, such as from about 800 to about 3,000 g/3”. As such the inventive tissue products may have a Stiffness Index less than about 8.0, such as from about 4.0 to about 8.0 and more preferably from about 4.0 to about 6.0.

Base tissue webs useful in the formation of tissue products of the present invention may be manufactured using any one of a number of well-known wet-laid papermaking processes that employ a creping step to foreshorten the web, such as, for example, creped wet pressed, modified wet pressed, or creped through-air dried (CTAD). In certain instances, basesheet may be formed using either a wet pressed or a modified wet pressed process such as those disclosed in U.S. Pat. Nos. 3,953,638, 5,324,575 and 6,080,279, the disclosures of which are incorporated herein in a manner consistent with the instant application. In these processes the embryonic tissue web is transferred to a Yankee dryer, which completes the drying process, and then creped from the Yankee surface using a doctor blade or other suitable device.

In other instances, the tissue basesheet may be manufactured by a creped through-air dried process in which the embryonic web is noncompressively dried. Suitable creped through-air dried processes include those disclosed in U.S. Pat. No. 10,240,296, the contents of which are incorporated herein in a manner consistent with the present disclosure.

In still other instances the tissue basesheet may be manufactured by a process including the step of using pressure, vacuum, or air flow through the wet web (or a combination of these) to conform the wet web into a shaped fabric and subsequently drying the shaped sheet using a Yankee dryer, or series of steam heated dryers, or some other means. Exemplary tissue manufacturing processes include, for example, ATMOS process developed by Voith or the NTT process developed by Metso; or fabric creped tissue, made using a process including the step of transferring the wet web from a carrying surface (belt, fabric, felt, or roll) moving at one speed to a fabric moving at a slower speed (at least 5 percent slower) and subsequently drying the sheet.

In one instance the manufacture of tissue basesheet comprising hesperaloe pulp fibers may be carried out using a twin wire former having a papermaking headbox that injects or deposits an aqueous suspension of papermaking fibers, including hesperaloe pulp fibers, onto a plurality of forming fabrics, such as the outer forming fabric and the inner forming fabric, thereby forming a wet tissue web. The forming process of the present disclosure may be any conventional forming process known in the papermaking industry. Such formation processes include, but are not limited to, Fourdriniers, roof formers such as suction breast roll formers, and gap formers such as twin wire formers and crescent formers.

Tissue webs made in accordance with the present disclosure can be made with a homogeneous fiber furnish or can be formed from a stratified fiber furnish producing layers within the single- or multiply tissue product. Homogeneous webs, also referred to herein as blended, may be prepared such that the various fiber furnishes are distributed throughout the web, as illustrated in FIG. 2. As shown in FIG. 1 , the web 10 may comprise a first outer surface 1 1 and second outer surface 13, one or more of the outer surfaces 10, 13 may be brought into contact with the user’s skin during use depending upon how the web 10 is converted into a finished product. The web 10 further comprises a blend of hesperaloe pulp fibers 22 and wood pulp fibers 24. The homogenous nature of the fiber furnish is such that the hesperaloe pulp fibers 22 form a portion of the first outer surface 1 1 and second outer surface 13.

The inventive tissue products may also comprise a stratified web, which may be formed using equipment known in the art, such as a multi-layered headbox. Different fiber furnishes can be used in each layer to create a layer with the desired characteristics, however, it may be desirable to distribute the hesperaloe pulp fibers in two or more layers, particularly the layers forming the outer surfaces of the web. For example, as illustrated in FIG. 3 the tissue web 10 may comprises a first outer surface 11 and second outer surface 13 and first and second outer layers, 12, 16 and a middle layer 14. The first outer layer 12 and a second outer layer 16 both contain hesperaloe pulp fibers 22 and wood pulp fibers 24. The middle layer 14 may also contain hesperaloe pulp fibers 22 and wood pulp fibers 24.

When constructing a web from a stratified fiber furnish, the relative weight of each layer may vary. For example, in one instance, when constructing a web containing three layers, each layer can be from about 15 to about 40 percent of the total weight of the web, such as from about 25 to about 35 percent of the weight of the web. Hesperaloe pulp fibers 22 may comprise from about 5 wt% to about 50 wt% of the total weight of the web and may be disposed in the first and second outer layers or may be disposed in the each of the layers in an equal amount.

Although in certain instances the papermaking fibers may be deposited in layers to provide a stratified web, the inventors have now discovered that layer is not necessary to produce tissue products having desirable properties. Accordingly, in certain instances, it may be preferable to deposit hesperaloe pulp fibers throughout the web. In those instances, where a stratified headbox is used to form the web, hesperaloe pulp fibers may be deposited in two or more, or all of, the layers. In other instances, the web may not be stratified and may simply consist of hesperaloe and wood pulp fibers, such as hardwood kraft pulp fibers, blended together. Thus, in certain instances the hesperaloe pulp fibers may be distributed throughout the web, including the outer surface of the web.

Preferably the tissue webs and products of the present invention are manufactured using a wet strength agent, particularly a permanent wet strength agent. As used herein, “wet strength agents” are materials used to immobilize the bonds between fibers in the wet state. Any material that when added to a paper web or sheet at an effective level results in providing the sheet with a wet geometric tensile strength :dry geometric tensile strength ratio in excess of 0.1 will, for purposes of this invention, be termed a wet strength agent. Typically, these materials are termed either as permanent wet strength agents or as “temporary” wet strength agents. For the purposes of differentiating permanent from temporary wet strength, permanent will be defined as those resins which, when incorporated into paper or tissue products, will provide a product that retains more than 50 percent of its original wet tensile strength after exposure to water for a period of at least five minutes, permanent wet strength agents are those which show less than 50 percent of their original wet strength after being saturated with water for five minutes. Both classes of material find application in the present invention. The amount of wet strength agent or dry strength added to the pulp fibers can be at least about 0.1 dry weight percent, more specifically about 0.2 dry weight percent or greater, and still more specifically from about 0.1 to about 3 dry weight percent, based on the dry weight of the fibers.

Useful dry strength additives include carboxymethyl cellulose resins, starch-based resins, and mixtures thereof. Examples of preferred dry strength additives include naturally derived starches, carboxymethyl cellulose and cationic modified starches such as those commercially available under the tradename REDIBOND™ (Ingredion Inc., Westcheser, IL, U.S.A.).

Suitable temporary wet strength resins include, but are not limited to, polyacrylamide resins, particularly glyoxyalated polyacrylamide resins and still more particularly cationic glyoxyalated polyacrylamide resins. Suitable temporary wet strength resins are described in U.S. Pat. Nos. 3,556,932 and 3,556,933. Useful temporary wet strength agents include those commercially available under the tradename FennoBond™ (Solenis LLC, Wilimington, DE, U.S.A).

Useful permanent wet strength agents are also well known in the art and provide a product that will retain more than 50% of its original wet strength after exposure to water for a period of at least 5 minutes. Suitable permanent wet strength agents may include polyamide-epichlorohydrin, polyacrylamides, styrene-butadiene latices; insolubilized polyvinyl alcohol; urea-formaldehyde; polyethyleneimine; chitosan polymers and mixtures thereof can be added to the papermaking furnish or to the embryonic web. Suitable types of such resins are described in U.S. Pat. Nos. 3,700,623 and 3,772,076. Particularly preferred permanent wet strength agents may be polyamide-epichlorohydrin resins, such as those available the tradename Kymene™ (Solenis LLC, Wilimington, DE, U.S.A).

TEST METHODS

Wet and Dry Tensile

Samples for tensile strength testing are prepared by cutting a 3 inches (76.2 mm) by 5 inches (127 mm) long strip in either the machine direction (MD) or cross-machine direction (CD) orientation using a JDC Precision Sample Cutter (Thwing-Albert Instrument Company, Philadelphia, PA, Model No. JDC 3-10, Ser. No. 37333). The instrument used for measuring tensile strengths is an MTS Systems Sintech 11 S, Serial No. 6233. The data acquisition software is MTS TestWorks™ for Windows Ver. 4 (MTS Systems Corp., Research Triangle Park, NC). The load cell is selected from either a 50 Newton or 100 Newton maximum, depending on the strength of the sample being tested, such that the majority of peak load values fall between 10 and 90 percent of the load cell's full scale value. The gauge length between jaws is 4 ± 0.04 inches. The jaws are operated using pneumatic-action and are rubber coated. The minimum grip face width is 3 inches (76.2 mm), and the approximate height of a jaw is 0.5 inches (12.7 mm). The crosshead speed is 10 ± 0.4 inches/min (254 ± 1 mm/min), and the break sensitivity is set at 65 percent. The sample is placed in the jaws of the instrument, centered both vertically and horizontally. The test is then started and ends when the specimen breaks. The peak load is recorded as either the "MD tensile strength” or the “CD tensile strength” of the specimen depending on the sample being tested. At least six (6) representative specimens are tested for each product, taken “as is,” and the arithmetic average of all individual specimen tests is either the MD or CD tensile strength for the product.

Wet tensile strength was measured in the same manner as dry strength except that the samples were wetted prior to testing. Specifically, in order to wet the sample, a 3"x5" tray was filled with distilled or deionized water at a temperature of approximately 23° C. The water is added to the tray to an approximate one-centimeter depth.

A 3M “Scotch-Brite” general purpose scrubbing pad is then cut to dimensions of 2.5"x4". A piece of masking tape approximately 5" long is placed along one of the 4" edges of the pad. The masking tape is used to hold the scrubbing pad.

The scrubbing pad is then placed into the water with the taped end facing up. The pad remains in the water at all times until testing is completed. The sample to be tested is placed on blotter paper that conforms to TAPPI T205. The scrubbing pad is removed from the water bath and tapped lightly three times on a screen associated with the wetting pan. The scrubbing pad is then gently placed on the sample parallel to the width of the sample in the approximate center. The scrubbing pad is held in place for approximately one second. The sample is then immediately put into the tensile tester and tested.

To calculate the wet/dry tensile strength ratio, the wet tensile strength value was divided by the dry tensile strength value.

Absorbency

As used herein, “vertical absorbent capacity” is a measure of the amount of water absorbed by a paper product (single-ply or multi-ply) or a sheet, expressed as grams of water absorbed per gram of fiber (dry weight). In particular, the vertical absorbent capacity is determined by cutting a sheet of the product to be tested (which may contain one or more plies) into a square measuring 100 millimeters by 100 millimeters (± 1 mm.) The resulting test specimen is weighed to the nearest 0.01 gram and the value is recorded as the “dry weight.” The specimen is attached to a 3-point clamping device and hung from one corner in a 3-point clamping device such that the opposite corner is lower than the rest of the specimen, then the sample and the clamp are placed into a dish of water and soaked in the water for 3 minutes (± 5 seconds). The water should be distilled or de-ionized water at a temperature of 23 ± 3°C. At the end of the soaking time, the specimen and the clamp are removed from the water. The clamping device should be such that the clamp area and pressure have minimal effect on the test result. Specifically, the clamp area should be only large enough to hold the sample and the pressure should also just be sufficient for holding the sample, while minimizing the amount of water removed from the sample during clamping. The sample specimen is allowed to drain for 3 minutes (± 5 seconds). At the end of the draining time, the specimen is removed by holding a weighing dish under the specimen and releasing it from the clamping device. The wet specimen is then weighed to the nearest 0.01 gram and the value recorded as the “wet weight”. The vertical absorbent capacity in grams per gram = [(wet weight - dry weight)/dry weight]. At least five (5) replicate measurements are made on representative samples from the same roll or box of product to yield an average vertical absorbent capacity value.

EXAMPLE

Basesheets were made using a through-air dried papermaking process commonly referred to as “uncreped through-air dried” (“UCTAD”) and generally described in US Patent No. 5,607,551 , the contents of which are incorporated herein in a manner consistent with the present invention. Base sheets with a target bone dry basis weight of about 36 grams per square meter (gsm) were produced. The base sheets were then converted into single ply towel product by calendaring and spirally winding a single ply into rolled tissue products, as described in more detail below. The inventive samples comprised a blend of high yield hesperaloe (HYH) pulp fibers and eucalyptus kraft pulp fibers (EHWK). HYH was prepared by processing the hesperaloe biomass using a two-stage screw press, which cut the biomass to a nominal size of about and 20 mm and removed about 55 wt% of the water-soluble extractives. The extracted and cut biomass was washed by mixing with water at a consistency ranging from 1 % to 5%, dewatered to a consistency of 40% to 50%, and then diluted with hot water to a consistency of about 4%. The diluted bagasse was fed to an Andritz 36- 1CP single disc refiner operating at atmospheric pressure, a temperature of about 130 F and rotational disc speed of 900 rpm.

The dewatered and pressed biomass was fed to a pressurized high consistency refiner using a feed screw and blower. An impregnation solution (2% hydrogen peroxide, 2% sodium hydroxide, 1 % sodium silicate and 0.4% DTPA) was added at the blower to allow an approximately 30-minute retention time before high consistency refining.

The impregnated biomass was fiberized in an Andritz 36-1 CP pressurized single disc refiner operating at a pressure of 30-35 psi and rotational disc speed of 1800 rpm. The refining consistency ranged from 25 to 45%.

After high consistency refining the pulp was blown to a cyclone and discharged. Blowline bleaching was carried out by the addition of a bleaching solution comprising 3% hydrogen peroxide, 1.2% sodium hydroxide, 3% sodium silicate and 0.4% DTPA at the entrance of the blowline. The retention time was approximately 1 hour.

In certain instances, after blowline bleaching, the pulp was diluted with water to a consistency of 2% and the pH was adjusted to 7.0 with the addition of sulfuric acid. The diluted pulp was passed through a pressure screen. The pressure screen has a Dolphin rotor design equipped with a PG25-03 micro-slotted screen basket having 0.1 mm slots. The screen fractioned the pulp into accepts and rejects. The rejects were sent to a Twinflo low consistency refiner for further processing. After low consistency refining, the refined pulp was combined with screening accepts and dewatered to a consistency of 20%. The primary pulp was bleached using 12% hydrogen peroxide solution, 4% NaOH, 3% NaSi, 0.5% DTPA in a single stage.

Once dried pulp was produced using a conventional drying system by dispersing wet lap pulp (approximately 75% moisture content) in a pulper for 30 minutes with agitation and then transferred to a stock tank. From the stock tank was pumped to a headbox where it was dispersed to form a mat The mat was subjected to Fourdrinier dewatering, vacuum dewatering, pressing between a pair of opposed rolls and dried by passing over a drying section consisting of three steam heated dryers. The steam loadings for the dryers were 24.5 PSI, 21 PSI, and 22 PSI and the machine speed was 100 feet per minute. The dried pulp sheet had a basis weight ranging from about 140 to about 290 gsm and a moisture content ranging from about 6% to about 7%. The fiber properties bleached HYH pulp are summarized in Table 1 , below.

TABLE 3

Tissue products were manufactured by forming a base web from EHWK and NSWK or EHWK and mechanical HYH pulp. In all instances the fiber furnishes were blended prior to dispersing the fibers to form the web. The composition of the webs is further described in Table 4, below. In those instances where the sample contained NSWK, the NSWK was subjected to batch refining at refining at 4.5 hp- days/metric ton for 3 minutes. In certain instances, CMC was also added to control strength, as indicated in Table 4, below. In all instances, a permanent wet strength agent (Kymene™, commercially available from Solenis LLC, Wilmington, DE, U.S.A) was added as indicated in Table 4, below.

TABLE 4

The tissue web was formed on a Voith Fabrics TissueForm V forming fabric, vacuum dewatered to approximately 25 percent consistency and then subjected to rush transfer at a rate of 24 percent when transferred to the transfer fabric. The transfer fabric was a Voith T807-5 (commercially available from Voith Paper, Inc., Appleton Wl). The web was then transferred to a woven through-air drying fabric having a plurality of substantially machine direction (MD) oriented ridges spaced apart from one another approximately 3.5 mm. The MD ridges were substantially continuous in the MD of the fabric and woven in a parallel, spaced apart arrangement to define valleys there between, where the valleys have a depth of about 1 .5 mm. Transfer to the through-drying fabric was done using vacuum levels of greater than 6 inches of mercury at the transfer. The web was then dried to approximately 98 percent solids before winding. The base sheet, prepared as described above, was converted into a single ply rolled towel product. Specifically, base sheet was calendered using a patterned steel roll and a 40 P&J polyurethane roll, substantially as described in US Patent No. 10,040,265, the contents of which are incorporated herein in a manner consistent with the present invention, at a load of 30 pli. The finished tissue product was subjected to physical testing, the results of which are shown in Tables 5 and 6, below.

TABLE 5

TABLE 6

The foregoing is one example of an inventive tissue product prepared according to the present disclosure. In a first embodiment the invention provides a tissue product comprising greater than about 5 weight percent high yield hesperaloe fiber having an Absorbent Capacity greater than about 7.0 g/g and a CD Wet/Dry Ratio greater than about 0.35, such as from about 0.35 to about 0.55.

In a second embodiment the invention provides the tissue product of the first embodiment having a Wet CD Durability of greater than about 1.75. In a third embodiment the invention provides the tissue product of the first embodiment having an Absorbent Capacity from about 7.0 to about 7.5 g/g, a CD Wet/Dry Ratio from about 0.30 to about 0.35.

In a third embodiment the present invention provides the tissue product of the first or the second embodiments having a GMT from about 1200 to about 2600 g/3”. In a fourth embodiment the present invention provides the tissue product of any one of the first through the third embodiments having a Stiffness Index from about 4.0 to about 6.0.

In a fifth embodiment the present invention provides the tissue product of any one of the first through the fourth embodiments having a basis weight from about 34 to about 60 gsm.

In a sixth embodiment the present invention provides the tissue product of any one of the first through the fifth embodiments having wet CD stretch greater than about 10.0 percent, such as from about 10.0 to about 16.0 percent.

In a seventh embodiment the present invention provides the tissue product of any one of the first through the sixth embodiments wherein the tissue product comprises a single-ply multi-layered web having a first, a second and a third layer.

In an eighth embodiment the present invention provides the tissue product of any one of the first through the seventh embodiments wherein the tissue product comprises from about 20 to about 50 weight percent high yield hesperaloe fiber.

In a ninth embodiment the present invention provides the tissue product of any one of the first through the eighth embodiments wherein the tissue product comprises at least one through-air dried tissue web.

In a tenth embodiment the present invention provides the tissue product of any one of the first through the ninth embodiments wherein the tissue product comprises at least one multi-layered through- air dried tissue web.

In an eleventh embodiment the present invention provides the tissue product of any one of the first through the tenth embodiments wherein the permanent wet strength agent is a polyamideepichlorohydrin resin.

In a twelfth embodiment the present invention provides a method of manufacturing a tissue web comprising the steps of: dispersing hesperaloe pulp fiber in water to form a first fiber slurry; dispersing wood pulp fibers in water to form a second fiber slurry; adding a permanent wet strength agent to at least the first or the second fiber slurry; blending the first and the second fiber slurries together and depositing them on a moving belt to form a tissue web; drying the tissue web; and converting the tissue web into a spirally wound tissue product; wherein the spirally wound tissue product comprises from about 5% to about 60% hesperaloe pulp fibers and has a CD Wet/Dry ratio from about 0.35 to about 0.55.

In thirteenth embodiment the present invention provides the method of the twelfth embodiment wherein the amount of permanent wet strength agent added is about 15 kg of wet-strength resin per metric ton of furnish, such as from about 3 to about 15 kg, and more preferably from about 3 to about 10 kg. In certain preferred embodiments the permanent wet strength agent is a polyamide-epichlorohydrin resin.

In a fourteenth embodiment the present invention provides the method of the twelfth or thirteenth embodiments wherein the amount of hesperaloe pulp fibers comprise from about 5 to about 50 percent, by weight of the product, and more preferably from about 20 to about 40 percent, by weight of the product.

In another embodiment the present invention provides a tissue product of any of the foregoing embodiments wherein the tissue product comprises one, two or three plies. In certain embodiments each of the tissue plies may be manufactured in a substantially similar manner.

Claims

WHAT IS CLAIMED IS:

1. A tissue product comprising a homogenous blend of wood pulp fibers, hesperaloe pulp fibers and a permanent wet strength agent, wherein the tissue product has a CD Wet/Dry ratio from about 0.35 to about 0.55.

2. The tissue product of claim 1 comprising from about 20 wt% to about 40 wt% hesperaloe pulp fibers.

3. The tissue product of claim 1 wherein the product is substantially free from softwood kraft pulp fibers.

4. The tissue product of claim 1 wherein the product is substantially free from Northern softwood kraft pulp fibers.

5. The tissue product of claim 1 comprising high yield hesperaloe pulp fibers and hardwood kraft pulp fibers.

6. The tissue product of claim 1 wherein the amount of permanent wet strength is a polyamideepichlorohydrin resin and the amount to permanent wet strength agent ranges from about 3 to about 10 kg per ton of hesperaloe and wood pulp fiber.

7. The tissue product of claim 1 having a geometric mean tensile strength (GMT) from about 1 ,000 to about 3,000 g/3”.

8. The tissue product of claim 1 having a Stiffness Index from about 4.0 to about 6.0.

9. The tissue product of claim 1 having a basis weight from about 30 to about 60 grams per square meter (gsm) and Absorbent Capacity from about 6.0 to about 7.0 g/g.

10. The tissue product of claim 1 having a Wet Burst of at least about 350 gf.

11 . The tissue product of claim 1 having a Wet CD Durability from about 1 .75 to about 2.5.

12. The tissue product of claim 1 having a basis weight from about 30 to about 60 gsm, a GM Slope from about 4.0 to about 10 kg and a GMT from about 1 ,200 to about 2,200 g/3”.

13. The tissue product of claim 1 wherein the tissue product comprises two plies and each ply is a through-air dried tissue ply.

14. The tissue product of claim 1 wherein the tissue product comprises a single uncreped through-air dried tissue ply.

15. The tissue product of claim 1 wherein the first ply is a creped tissue ply and the tissue product further comprises a second creped tissue ply, the first and second creped tissue plies each having an outer surface comprising a blend of high yield hesperaloe pulp fibers and wood pulp fibers, the product having CD Wet Tensile Strength from about 120 g/3” to about 300 g/3”.

16. The tissue product of claim 15 wherein each of the plies have a per-ply basis weight from about 12.0 to about 16.0 grams per square meter.

17. A method of manufacturing a tissue web comprising the steps of: a. dispersing hesperaloe pulp fiber in water to form a first fiber slurry; b. dispersing wood pulp fibers in water to form a second fiber slurry; c. adding a permanent wet strength agent to at least the first or the second fiber slurry; d. blending the first and the second fiber slurries together and depositing them on a moving belt to form a tissue web; e. drying the tissue web; and f. converting the tissue web into a spirally wound tissue product; wherein the spirally wound tissue product comprises from about 5% to about 60% hesperaloe pulp fibers and has a CD Wet/Dry ratio from about 0.35 to about 0.55.

18. The method of claim 17 wherein the hesperaloe pulp fibers have been produced by mechanically refining hesperaloe biomass without the addition of chemicals.

19. The method of claim 18 wherein the hesperaloe pulp fibers have a Fiber Length of at least about 1.50 mm and Coarseness from about 3.5 to about 6.0 mg/100 m.

20. The method of claim 17 wherein the wood pulp fibers comprise eucalyptus kraft pulp fibers and the product is substantially free from Northern softwood kraft pulp fibers.