Liquid ammonia explosion treatment of wood fibers

Abstract

A process of forming improved cellulosic fibers, fibrous compositions containing cellulosic fibers, and absorbent articles comprising such compositions are disclosed. In the process, liquid ammonia penetrates cellulosic fibers in a pressurized environment, and when the pressure is released, an explosive process produces cellulosic fibers having unique structure and properties. The high pressure liquid ammonia treatment introduces a significant curl into the fiber and introduces a smooth, soft, silky feel to the fiber not present in conventional cellulosic fibers. Such fibers are particularly useful in tissue, wipes, distributive layers, fiber mats, filter papers, and other porous articles.

Description

FIELD OF THE INVENTION

[0002] The present invention relates to the treatment of cellulosic or wood fibers, especially after the fiber has been separated from a natural source, such as pulp or chip. The process involves treatment of wood fibers that have had lignin reduced or eliminated therefrom as compared to their natural condition. More specifically, the processed cellulosic or wood fibers are converted by high pressure liquid ammonia treatment into an improved fiber, having a morphology that provides useful properties to cellulosic web products made therefrom, such as tissues, wipes, fibrous mats, filter papers and other related cellulosic fiber applications. The invention further relates to cellulosic fibers with improved properties and absorbent article comprising such fibers.

BACKGROUND OF THE INVENTION

[0003] High-pressure treatment processes used to treat wood chips are known. These processes basically involve rapidly moving wood chips from a high pressure environment to a lower pressure environment whereupon the wood chips literally explode through the agency of applied physical forces. In general, known explosion pulping processes may be classified into two categories:

[0004] (1) where the defibration is produced primarily by the sudden volatilization of a volatile liquid (normally liquid at ambient temperature and pressure) entrapped within the interstices of the wood chips; and

[0005] (2) where the process-associated liquids are relatively non-volatile at the operating conditions, but where the force of the explosion is augmented by the injection of a relatively insoluble gas or gas mixture at elevated pressure.

[0006] The best known liquid explosion processes is the so called “Masonite” process, which is described in U.S. Pat. Nos. 1,655,618; 1,824,221; 1,922,313; and 2,140,189. In the Masonite process, woodchips or similar cellulosic materials are pressurized by steam at pressures as high as 1000 psig (6.9 MPa). Upon sudden discharge of the wood chip/water/steam mixture from the pressurizer, the water trapped within the interstices of the wood chips flashes to steam and provides the necessary energy to produce a well defibrated pulp mass.

[0007] Liquid ammonia explosion treatments have also been used to convert raw wood sources, such as wood chips. In such a process raw wood chips are impregnated with ammonia under pressure to plasticize the chips. The mixture is then exploded resulting in a material having a coarse fibrous condition that is susceptible to purification and other processes. In addition, U.S. Pat. No. 5,037,663 issued to Dale, discloses treating cellulose fibers under pressure with liquid ammonia for the purpose of improving their nutritive value or water holding capacity.

[0008] Wood fiber technology as understood to date provides wood fibers with certain fibrous characteristics. The properties of cellulosic webs, fibrous mats, and other products made using the fibers often relate directly to various aspects of fiber morphology. Examples of such webs include, but are not limited to webs and mats used to form papers, garments, and absorbent products. There is a need for fibers that have an increased curl and that will form bulkier webs and webs that feel soft and silky to the touch.

[0009] A substantial need exists to produce a fiber having a high permanent curl index and a smooth silky feel as evaluated by typical industry sensory test panel standards.

SUMMARY OF THE INVENTION

[0010] The present invention is directed to a process for forming an improved cellulosic fiber. The process includes the steps of: charging a vessel with a composition comprising cellulosic fibrous material in which lignin levels have been reduced or eliminated as compared to natural levels; charging the vessel with liquid ammonia at sufficient pressure to cause the ammonia to penetrate the cellulose fiber thereby saturating the fiber with the ammonia, and rapidly depressurizing the ammonia-saturated fiber to substantially modify the fiber morphology.

[0011] The present invention is also directed to an improved cellulosic fiber formed by a liquid ammonia explosion process. The resulting fiber possesses improved properties related to the morphology of the fiber. In one embodiment of the invention, the resulting cellulosic fibers have a curl index of at least 0.2, and possess a smoother, softer, and more silky feel as compared to fibers that have not been treated with ammonia and as compared to fibers treated with gaseous ammonia only.

[0012] The present invention is further directed to cellulosic webs containing the improved cellulosic fibers. The increased bulk, smooth silky feel, and curl index of the improved cellulosic fibers result in the formation of cellulosic webs having beneficial properties. The cellulosic webs of the present invention may be incorporated into a variety of disposable absorbent products to provide improved bulk, softness and excellent ability to absorb fluids.

[0013] These and other features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention relates to a high-pressure ammonia treatment process and an improved cellulosic fiber made by the process. In the process of the present invention, ammonia penetrates both the crystalline and amorphous portions of the fiber material. After the ammonia has penetrated the fiber, pressure is released, which causes explosion of the ammonia-filled fiber. Treatment of cellulosic fibers with ammonia, followed by rapid decompression of the ammonia-fiber suspension, results in changes in the fibers that are related to morphological, physical and chemical changes in the components of the fibers. The “explosive” decompression results in fibers that have permanent fiber morphology changes, including kinks and curls, high relative wet resilience, and a relatively high water retention value. The invention further relates to improved fibers having Wet Curl Values of at least about 0.2. The invention further relates to compositions, structures, and articles comprising the improved fibers.

[0015] As used herein, the term “permanent fiber morphology” is defined as a fiber characteristic, which remains after the fiber has been pulped for up to about 300 minutes. As used herein, the term “transient or temporary fiber morphology” is defined as a fiber characteristic, which does not remain after the fiber has been repulped for up to 150 minutes.

[0016] As used herein, the terms “purification” and “purified” in reference to any fiber or fibrous composition shall mean any processes by which the lignin content of a fibrous material has been reduced or eliminated, and fibers and fibrous compositions that have undergone such processes. Examples of purification methods include, but are not limited to, certain pulping processes. Examples of pulping processes include, but are not limited to, mechanical, chemimechanical, semichemical, and chemical processes such as kraft and sulfite processes. In some embodiments, the fibers present in the vessel and thus used in the ammonia explosion process are cellulosic fibers that have been treated by a low yield pulping process. Yield in a pulping process refers to the dry weight of fibrous material after pulping as a percentage of the dry weight of the wood material used in the pulping process. Although the term “yield” is often considered in connection with pulping processes, the term is not intended to be limiting to such processes, and the present invention includes processes using fibrous materials for which lignin content has been reduced by processes other than pulping. Further, the term “yield” may be used to describe processes other than pulping processes. As used herein, “low yield” cellulosic fibers are fibers produced by processes that yield about 60 percent or less. In contrast, “high yield” cellulosic fibers are those fibers produced by processes that yield above about 60 percent or greater. As a general matter, it has been found that reducing lignin content of a fibrous material prior to liquid ammonia treatment will typically result in the addition of more curl and other beneficial characteristics to the fibers through the treatment process. Further, in some embodiments it has been found that the degree of curl and other beneficial fiber characteristics increases as the lignin content in the fibrous material decreases. In some embodiments, the fibers are produced by a process having a yield of 55 percent or less. In other embodiments, the fibers are produced by a process having a yield of 50 percent or less. In other embodiments, the fibers are produced by a process having a yield of 45 percent or less. In other embodiments, the fibers are produced by a process having a yield of 40 percent or less.

[0017] Any cellulosic fibers may be employed in the process of the present invention. Illustrative cellulosic fibers include, but are not limited to, wood and wood products, such as wood pulp fibers; non-woody, paper-making fibers from cotton, from straws and grasses, such as rice and esparto, from canes and reeds, such as bagasse, from bamboos, from stalks with bast fibers, such as jute, flax, kenaf, cannabis, linen and ramie; and from leaf fibers, such as abaca and sisal. It is also possible to use mixtures of one or more cellulosic fibers. Suitably, the cellulosic fiber used is from a wood source. Suitable wood sources include, but are not limited to, softwood sources such as pines, spruces, and firs; and hardwood sources such as oaks, eucalyptuses, poplars, beeches, and aspens. In some embodiments, fibers are mixed with other materials, including, for example, synthetic fibers and other non-cellulosic fibers.

[0018] In some embodiments of the present invention, purified cellulosic fibers are used. After sufficient purification, the cellulosic fibers are substantially in the form of individual cellulosic fibers, although such individual cellulosic fibers may be in an aggregate form such as a pulp sheet. Thus, the current process of the present invention is in contrast to known steam explosion processes that generally treat cellulosic material in the form of virgin wood chips or the like. In some embodiments, the current process can be used as a process for modifying cellulose fibers in which lignin content has been reduced or eliminated, as compared to known steam explosion processes that are generally used for processing raw wood material or waste-recycle processes. The use of purified fibers is not intended to be limiting, however, and the invention includes treatments of wood at any stage before during, or after purification.

[0019] Methods of Treating Fibers

[0020] The liquid ammonia explosion treatment process of the present invention includes the following steps: (1) charging a vessel with cellulosic fibers, (2) charging the vessel with ammonia at sufficient pressure to cause the ammonia to penetrate the cellulose fiber, and (3) rapidly depressurizing the ammonia-saturated fiber. Although the terms “vessel” and “reaction vessel” are used throughout this application, it will be understood that any type of vessel, container or enclosure known to those having skill in the art or developed in the future can be employed, as long as the vessel has sufficient capacity and is capable of withstanding the pressure of the process. As such, the terms “vessel” and “reaction vessel” are not limiting and include any such container or enclosure. Suitable vessels include, but are not limited to, reaction vessels disclosed in Canadian Patent No. 1,070,537, dated Jan. 29, 1980; Canadian Patent No. 1,070,646, dated Jan. 29, 1980; Canadian Patent No. 1,119,033, dated Mar. 2, 1982; Canadian Patent No. 1,138,708, dated Jan. 4, 1983; and U.S. Pat. No. 5,262,003, issued Nov. 16, 1993, all of which are incorporated herein by reference in their entirety.

[0021] The cellulosic fibrous compositions used in the process of the present invention may be in either a dry or a wet state at the time of processing. In one embodiment of the present invention, the cellulosic fibers are present in an aqueous mixture having a specific consistency. As used herein, the term “consistency” refers to the concentration of cellulosic fibrous compositions in an aqueous mixture. In many embodiments, the cellulosic fibrous composition has been dried or dewatered to reduce or to eliminate water content in the composition. Such processes reduce the opportunity for water to interfere with the process by causing the ammonia to form ammonium ions. In other embodiments, the cellulosic fibers for use in the process of the present invention are mixed with an aqueous solution. The consistency of a fiber-containing mixture is presented as a weight percent representing the weight amount of cellulosic fibers present in an aqueous mixture divided by the total weight amount of cellulosic fibers, water, and other components present in such mixture, multiplied by 100. In one embodiment, the mixture has a consistency of from about 10 to about 100 weight percent. In another embodiment, the mixture has a consistency ranging from about 20 to about 80 weight percent. In another embodiment, the mixture has a consistency ranging from about 25 to about 75 weight percent cellulosic fibrous composition, based on the total weight percent of the aqueous pulp mixture. In one embodiment, the fibrous composition has a consistency of about 30%. It has been found that assuring that the aqueous mixture is agitated, stirred, or blended to effectively disperse the cellulosic fibers throughout the water prior to its introduction into the vessel is beneficial in achieving uniform fiber treatment.

[0022] Where an aqueous composition is present, other liquids may be used in combination with water. In some embodiments, the liquid phase of the aqueous mixture comprises at least about 30 weight percent water. In some embodiments, the liquid phase comprises at least about 50 weight percent water. In some embodiments, the liquid phase comprises at least about 75 weight percent water. In some embodiments, the liquid phase comprises 100 weight percent water. When another liquid is employed with the water, such other suitable liquids include, but are not limited to, methanol, ethanol, isopropanol, acetone, and combinations thereof. Any liquids may be used, although it is some liquids adversely affect the dispersibility of the cellulosic fibers within the mixture.

[0023] In one embodiment of the present invention, an aqueous solution directly from a pulping and/or pulp preparation process is used in the ammonia explosion treatment of the present invention. In this embodiment, the amount of water and other process conditions may need to be monitored in order to produce a suitable aqueous mixture for use in the process of the present invention. In some embodiments, the fibrous composition is fiberized, for example in a hammermill, prior to processing. While not wanting to be bound to a particular theory, it is believed that fiberizing enhances the ability of ammonia to penetrate the individual fibers by exposing a greater portion of the fiber surface area.

[0024] Also present in the vessel is a volume of ammonia, preferably liquid ammonia. The ammonia may be placed in the vessel before or after the fibrous composition, or at the same time. In some embodiments, the fibrous composition is inserted before the ammonia to assure that the fibers are immersed in ammonia. While the invention includes any range of weight ratios between ammonia and fibers, in some embodiments the weight ratio of ammonia to dry weight cellulosic fibrous composition in the reaction vessel is from about 1:1 to about 8:1. In one embodiment, the ratio is from about 3:1 to about 7:1. In another embodiment, the ratio is about 5:1. In some embodiments, the ammonia is charged into the vessel at sufficient pressure and temperature to maintain the ammonia in a liquid state. Any pressure effective to cause the ammonia to penetrate the fibers may be used. In some embodiments, pressure range is from about 100 to about 300 pounds per square inch (psi). In one embodiment, pressure is approximately 200 psi. The high-pressure forces within the vessel enables the liquid ammonia to penetrate crystalline and amorphous regions within the cellulosic fiber. The process may be performed at any temperature.

[0025] The ammonia is allowed to penetrate the fibers. Any degree of penetration is included within the present invention. In some embodiments, fibers are penetrated to saturation equilibrium. In some embodiments, saturation equilibrium involves fibers containing ammonia in an amount equal to 100% of fiber dry weight or higher. In other embodiments, the saturation equilibrium involves fibers containing ammonia in an amount equal to or less than 100% of fiber dry weight.

[0026] Similarly the time duration for which the fibers are pressurized may be any amount. In one embodiment, the time ranges from about 0.5 minutes to about 30 minutes; however, the amount of time may be shorter or longer than this duration depending on a number of factors including, but not limited to, the ammonia concentration, the pressure, and the amount of ammonia and fibers present. In some embodiments, the time necessary to reach a saturation equilibrium condition between the ammonia and the cellulosic fibers is from about 0.5 minute to about 20 minutes. In other embodiments, the time necessary to reach a saturation equilibrium condition between the ammonia and the cellulosic fibers is from about 1 minute to about 10 minutes.

[0027] In general, the higher the volume ratio of ammonia employed, the shorter the period of time necessary to achieve a specific degree of penetration or saturation, and ultimately, fiber modification. As such, it may be possible to achieve essentially equivalent degrees of fiber modification for different cellulosic fiber samples by using different combinations of reaction conditions, such as ammonia concentrations and saturation times.

[0028] The fibrous material is then rapidly depressurized by relieving the pressure from the environment surrounding the ammonia/fiber mixture. Any method of pressure release can be used. In some embodiments, depressurizing involves releasing or expelling fibers from the vessel to an environment that is not pressurized, for example by releasing the fibers through an oscillating valve. In some embodiments, the vessel continues to maintain pressure, for example in a continuous process. In other embodiments, depressurization involves venting the vessel. While not wanting to be bound to a specific theory, it is believed that, upon depressurization, the liquid ammonia flashes into a gas, causing the ammonia-saturated wood fiber to “explode” within the reaction vessel, and thereby changing the fibers morphologically, chemically and physically due to the combination of mechanical action of the process and the chemical action resulting from the penetration of the cellulosic fibers by the ammonia. In many embodiments, the resultant fibers have a unique combination of curl as part of their permanent fiber morphology, high wet resilience and high water retention value.

[0029] The process physically changes the fiber, causing the cellulosic fibers to become modified. Without intending to be bound hereby, it is believed that the ammonia explosion process causes the cellulosic fibers to undergo a curling phenomenon. The cellulosic fibers, in addition to being modified, have been discovered to exhibit improved properties that make such fibers suitable for use in liquid absorption or liquid handling applications. After the process, the treated cellulosic fibers in some embodiments will exhibit a level of curl as part of their permanent fiber morphology. In some embodiments, the curl is stable and will remain as such upon exposure to water. As such, the process of the invention generally does not require the use of any additional additives to the cellulosic fibers during the process or any post-treatment steps after the process of the fibers to achieve or to retain the fiber curl. The foregoing statement is not intended to be limiting, however, and embodiments exist in which the processes involve other steps or treatments for a variety of purposes. For example, fibers may be dried by a variety of means. Examples include, but are not limited to air drying, oven drying, drying upon a heated surfaced, and through-air drying. Rinsing may also be employed to remove ammonia from the fiber. Embodiments exist in which numerous other process steps and combinations of process steps are added.

[0030] It has been found that treatments involving liquid ammonia provide better, more dramatic results than treatments with ammonia gas. Ammonia gas treatments generally do not provide the degree of bulk enhancement or increase in softness as treatments involving liquid ammonia. Treatments with liquid ammonia generally provide fibers that will form a softer, more silky fibrous webs than fibers formed by treatments with gaseous ammonia. Higher bulk generally improves wet resilience and water retention of the resulting webs.

[0031] Fibers

[0032] The present invention is further directed to improved cellulosic fibers. In some embodiments, the cellulosic fibers exhibit a stable curl. Curl of a fiber may be quantified by a curl value, which measures the fractional shortening of a fiber due to kinks, twists, and/or bends in the fiber. For the purposes of the present invention, fiber curl value is measured by viewing the fiber in a two dimensional plane such as by light microscopy. To determine the curl value of a fiber, the projected length of a fiber, corresponding to the longest dimension of a two-dimensional rectangle encompassing the fiber, I, and the actual length of the fiber, L, are both measured. An image analysis method may be used to measure L and I. A suitable image analysis method is described in U.S. Pat. No. 4,898,642, incorporated herein in its entirety by reference. The curl value of a fiber may then be calculated from the following equation:

Curl Value (L/I)−1

[0033] Depending on the nature of the curl of a conventionally produced cellulosic fiber, the curl may remain stable when the cellulosic fiber is dry, but may be lost in whole or in part when the cellulosic fiber is wet. The cellulosic fibers prepared according to the process of the present invention have been found to maintain much of their fiber curl when wet. This property of the cellulosic fibers may be quantified by a Wet Curl value, which is simply the Curl Value when wet. Wet Curl can be measured according to the test method described herein or an equivalent test method. The method disclosed herein is a mean curl average of about 4000 fibers or more from a fiber sample. The Wet Curl value represents the summation of the individual curl values for each wet fiber in the sample multiplied by the fiber's actual length, L, divided by the summation of the actual lengths of the fibers. Wet Curl value is calculated by using only fibers with a length of about 0.4 millimeter or greater.

[0034] Another aspect of the invention is cellulosic fibers that exhibit a curl index greater than about 0.2 and a Wet Curl value that is greater than about 0.2. In one embodiment, the improved cellulosic fibers exhibit a Wet Curl value of from about 0.2 to about 0.4. In another embodiment, the improved cellulosic fibers exhibit a Wet Curl value of from about 0.2 to about 0.35. In another embodiment, the improved cellulosic fibers exhibit a Wet Curl value of from about 0.22 to about 0.33. In another embodiment, the improved cellulosic fibers exhibit a Wet Curl value of from about 0.25 to about 0.33. In contrast, cellulosic fibers that have not been treated in accordance with the present invention generally exhibit a Wet Curl value that is less than about 0.2.

[0035] In addition to improved Wet Curl values, the improved cellulosic fibers of the present invention exhibit a relatively high water retention value.

[0036] The treated cellulosic fibers of the present invention are suitable for use in a wide variety of applications. In some embodiments, depending on the use intended for the treated cellulosic fibers, the treated cellulosic fibers are washed with water, for example, to remove the ammonia. If any additional processing procedures are planned because of the specific use for which the treated cellulosic fibers are intended, other well-known recovery and post-treatment steps may be used without adversely affecting the properties of the cellulosic fibers.

[0037] In one embodiment, the fibers have a more soft, smooth, and silky feel than fibers that have not been treated with ammonia or fibers that have been treated with gaseous ammonia only.

[0038] Absorbent Compositions, Structures, and Articles

[0039] In some embodiments of the present invention, the treated cellulosic fibers, prepared according to the process of the present invention, are formed into a fibrous web for incorporation into an absorbent structure. A fibrous web may take the form of, for example, a batt of comminuted wood pulp fluff, a tissue layer, a hydroentangled pulp sheet, a mechanically softened pulp sheet, or a nonwoven fabric. An exemplary absorbent structure is described in copending U.S. Patent Application Serial No. 60/008,994, which is incorporated herein in its entirety by reference. Fibrous webs containing the improved cellulosic fibers of the present invention may be formed by an air-laying process or a wet-laid process, or by essentially any other process known to those skilled in the art for forming a fibrous web.

[0040] The cellulosic fibers treated according to the process of the present invention are particularly suited for use in disposable absorbent products such as diapers, adult incontinent products, and bed pads; catamenial devices such as sanitary napkins, and tampons; other absorbent products such as wipes, bibs, wound dressings, and surgical capes or drapes; laboratory uses such as filter papers; and tissue-based products such as facial or bathroom tissues, household towels, wipes and related products. Accordingly, the present invention further relates to disposable absorbent products comprising the cellulosic fibers treated according to the process of the present invention.

[0041] In one embodiment of the present invention, the treated fibers prepared according to the above-described process are formed into a handsheet, such as a tissue-based product. Such a handsheet may be formed by either a wet-laid or an air-laid process. A wet-laid handsheet may be prepared, for example, according to the method disclosed herein. It has been discovered that a wet-laid handsheet prepared from the treated cellulosic fibers prepared according to the above-described process may exhibit a density that is lower than a wet-laid handsheet prepared from cellulosic fibers that have not been treated according to the process of the present invention.

[0042] It has also been discovered that a wet-laid handsheet prepared from the treated cellulosic fibers of the present invention may exhibit an increased bulk and higher absorbent capacity than a wet-laid handsheet prepared from cellulosic fibers that have not been treated according to the process of the invention.

[0043] In a further embodiment of the present invention, the treated cellulosic fibers of the present invention are used as a component in a disposable absorbent product. The disposable absorbent product comprises a liquid-permeable topsheet, a backsheet attached to the liquid-permeable topsheet, and an absorbent structure positioned between the liquid-permeable topsheet and the backsheet, wherein the absorbent structure comprises treated cellulosic fibers of the present invention. The structure of the disposable absorbent products may vary depending upon the use of the final product. Exemplary disposable absorbent products are described in U.S. Pat. Nos. 4,710,187; 4,762,521; 4,770,656; and 4,798,603; all of which are incorporated herein by reference it their entirety.

[0044] The following test methods may be used to evaluate the improved cellulosic fibers produced from the ammonia explosion process of the present invention, as well as, fiber-containing webs containing such fibers:

[0045] Wet Curl Test

[0046] The Wet Curl value for cellulosic fibers is determined by using an instrument or method which accurately determines the Wet Curl value of fibers. Any device or method capable of accurately determining Wet Curl values of a sample may be used. One such instrument is available from OPTest Equipment Inc., Hawkesbury, Ontario, Canada, under the designation Fiber Quality Analyzer, OpTest Product Code DA93.

[0047] To conduct the test using the foregoing instrument, a sample of dried cellulosic fibers is obtained. The cellulosic fiber sample is poured into a 600-milliliter plastic sample beaker to be used in the Fiber Quality Analyzer. The fiber sample in the beaker is diluted with tap water until the fiber concentration in the beaker is about 10 to about 25 fibers per second for evaluation by the Fiber Quality Analyzer.

[0048] An empty plastic sample beaker is filled with tap water and placed in the Fiber Quality Analyzer test chamber. The <System Check> button of the Fiber Quality Analyzer is then pushed. If the plastic sample beaker filled with tap water is properly placed in the test chamber, the <OK> button of the Fiber Quality Analyzer is then pushed. The Fiber Quality Analyzer then performs a self-test. If a warning is not displayed on the screen after the self-test, the machine is ready to test the fiber sample.

[0049] The plastic sample beaker filled with tap water is removed from the test chamber and replaced with the fiber sample beaker. The <Measure> button of the Fiber Quality Analyzer is then pushed. The <New Measurement> button of the Fiber Quality Analyzer is then pushed. An identification of the fiber sample is then typed into the Fiber Quality Analyzer. The <OK> button of the Fiber Quality Analyzer is then pushed. The <Options> button of the Fiber Quality Analyzer is then pushed. The fiber count is set at 4,000, although any higher number may be used. The parameters of scaling of a graph to be printed out may be set automatically or to desired values. The <Previous> button of the Fiber Quality Analyzer is then pushed. The <Start> button of the Fiber Quality Analyzer is then pushed. If the fiber sample beaker is property placed in the test chamber, the <OK> button of the Fiber Quality Analyzer is then pushed. The Fiber Quality Analyzer then begins testing and displays the fibers passing through the flow cell. The Fiber Quality Analyzer also displays the fiber frequency passing through the flow cell, which is about 10 to about 25 fibers per second. If the fiber frequency is outside of this range, the <Stop> button of the Fiber Quality Analyzer should be pushed and the fiber sample should be diluted or have more fibers added to bring the fiber frequency within the desired range. If the fiber frequency is sufficient, the Fiber Quality Analyzer tests the fiber sample until it has reached a count of 4000 fibers, or the desired number, at which time the Fiber Quality Analyzer automatically stops. The <Results> button of the Fiber Quality Analyzer is then pushed. The Fiber Quality Analyzer calculates the Wet Curl value of the fiber sample, which prints out by pushing the <Done> button of the Fiber Quality Analyzer.

[0050] The present invention is further illustrated by the following examples, which are not to be construed in any way as imposing limitations upon the scope thereof On the contrary, it is to be clearly understood that resort may be had to various other embodiments, modifications, and equivalents thereof, which, after reading the description herein, may suggest themselves to those skilled in the art without departing from the spirit of the present invention.

EXAMPLES 1-4

Preparation of Improved Cellulosic Fibers of the Present Invention

[0051] In Examples 1-4, cellulosic fiber samples were prepared by dewatering various pulp types in a laboratory centrifuge. Each Example refers to a different type of pulp. The four Examples include: a southern softwood kraft pulp, available from U.S. Alliance Coosa Pines Corporation under the designation CR54 southern softwood kraft pulp (Example 1); a northern softwood kraft pulp, available from Kimberly-Clark Corporation under the designation LL-19 northern softwood kraft pulp (Example 2); a Eucalyptus pulp, available from Celulose Nipo-Brasileira S. A. of Brazil (Example 3); and bleached chemi-thermo-mechanical pulp (BCTMP) pulp fibers, made with northern softwood fibers and available from Tembec Inc. of Canada (Example 4). BCTMP fibers have significantly higher lignin contents than kraft pulps, thus providing an illustration of the relationship between lignin levels and the efficacy of the process. Fiber samples for each of the four examples formed a mixture having a consistency of about 30 weight percent cellulosic fibers, with the remaining 70 weight percent was primarily an aqueous liquid.

[0052] For each Example, numerous samples of about 100 grams were prepared and treated using a variety of protocols. For each Example, different categories of samples were prepared reflecting five different treatment protocols. The five categories were: (A) Control; (B) Gas treated, rinsed; (C) Gas treated, unrinsed; (D) Liquid treated, rinsed; and (E) Liquid treated, unrinsed. The five treatment protocols are set forth below.

[0053] A) Treatment Protocol for Control Samples

[0054] The control sample was a dried fibrous composition, used to form handsheets in the form as received from the supplier, without any ammonia treatment.

[0055] B) Treatment Protocol for Gas Treated, Rinsed Samples

[0056] Samples comprising approximately 100 grams fibers by dry weight were placed in a cylindrical laboratory ammonia explosion reactor available from Stake Technology Ltd., Norval, Ontario, Canada. The reactor had a capacity of 2 liters. The top valve of the reactor was closed such that the reactor was sealed. Gaseous ammonia was then injected into the reactor until the internal pressure of the reactor reached about 110 psi and additional ammonia was added as necessary to maintain the 110 psi pressure for five minutes. The cellulosic fibers were then explosively decompressed and discharged into a container by opening the bottom valve of the reaction vessel. Prior to drying, the treated fibers were rinsed with water until the fibers exhibited a pH between about 6 and about 7. Fibers were dried without rinsing.

[0057] C) Treatment Protocol for Gas Treated, Unrinsed Samples

[0058] Samples weighing approximately 100 grams were placed in a laboratory ammonia explosion reactor, available from Stake Technology Ltd., Norval, Ontario, Canada. The reactor had a capacity of 2 liters. The top valve of the reactor was closed such that the reactor was sealed. Gaseous ammonia until the internal pressure of the reactor reached about 110 psi and additional ammonia was added as necessary to maintain the 110 psi pressure for five minutes. The cellulosic fibers were then explosively decompressed and discharged into a container by opening the bottom valve of the reaction vessel. Fibers were dried without rinsing.

[0059] D) Treatment Protocol for Liquid Treated, Rinsed Samples

[0060] Samples weighing approximately 100 grams were placed in a laboratory ammonia explosion reactor, available from Stake Technology Ltd., Norval, Ontario, Canada. The reactor had a capacity of 2 liters. The top valve of the reactor was closed such that the reactor was sealed. 500 grams of liquid ammonia (5:1 NH3 to fiber ratio by mass) was then pumped into the reactor. Inert gas (nitrogen) was then injected as needed to attain a pressure of 200 psi. The 200 psi pressure was then held for five minutes. The cellulosic fibers were then explosively decompressed and discharged into a container by opening the bottom valve of the reaction vessel. Prior to drying, the treated fibers were rinsed with water until the fibers exhibited a pH between about 6 and about 7.

[0061] E) Treatment Protocol for Liquid Treated, Unrinsed Dried Samples

[0062] Samples weighing approximately 100 grams were placed in a laboratory ammonia explosion reactor, available from Stake Technology Ltd., Norval, Ontario, Canada. The reactor had a capacity of 2 liters. The top valve of the reactor was closed such that the reactor was sealed. 500 grams of liquid ammonia (5:1 NH3 to fiber ratio by mass) was then pumped into the reactor. Inert gas (nitrogen) was then injected as needed to attain as needed to attain a pressure of 200 psi. The 200 psi pressure was then held for five minutes. The cellulosic fibers were then explosively decompressed and discharged into a container by opening the bottom valve of the reaction vessel. Fibers were then dried without rinsing.

[0063] Additional Testing and Results.

[0064] The fibers of Examples 1-4 were used to form handsheets. A 7.5 inch by 7.5 inch handsheet was prepared using fiber samples by using an 8 inch by 8 inch cast bronze wet-laid handsheet former mold, available from Voith Corporation. The handsheets had a basis weight of about 60 grams per square meter. The handsheets were made using 100 percent ammonia exploded fibers. A British Disintegrator mixer, available from Testing Machines, Inc., was filled with about 2 liters of distilled water at room temperature (23° C.) and about 45.0 grams of the fiber sample. The counter on the British Disintegrator was set to zero and was turned on until the counter runs to about 1500. The contents of the British Disintegrator were then poured into a vessel filled with about 8 liters of distilled water.

[0065] The handsheet former, having an approximate 8 inch deep chamber, was filled with tap water to about 2 inches below the top of the handsheet former chamber. The contents of the bucket were then poured into the handsheet former chamber where a dedicated stirrer was then used to mix the suspension in the handsheet former chamber. The stirrer was moved slowly up and down 6 times to cause small vortexes, but to avoid causing large vortexes, in the square pattern of the handsheet former. The stirrer was then removed and the suspension is drained through the forming screen of the handsheet former. The handsheet former was then opened and two layers of blotting paper were placed on top of the handsheet. A roller, applying the equivalent of about 308 kiloPascals of pressure per inch, was moved back and forth one along each side and the center of the formed handsheet. The blotting paper, with the formed handsheet attached, was then lifted off the forming screen. Two additional sheets of blotting paper were then placed on top of the blotting paper already upon the formed handsheet and another additional sheet was placed underneath the handsheet. The stack containing the handsheet and sheets of blotting paper was then transferred to a hydraulic press (available from Voith Corporation) and pressed at a pressure of 75 psia for one minute. The stack was then placed on a table, where the blotting papers were removed. The handsheet was then transferred, wire side up, to the polished convex surface of an 8 inch by 8 inch dryer hot plate. A canvas cover was placed over the convex surface and handsheet and was weighted down to prevent drying induced wrinkling. The handsheet was dried for 2 minutes and then removed for subsequent evaluation.

[0066] Testing was then conducted on the handsheets. The results are set forth in Tables 1-4 below. Each of the four tables corresponds to the sample (fiber type) bearing the same number. The data rows under the heading “SI CONVERTED AVERAGE TEST DATA” refer to test data expressed in appropriate units of measurement. The data rows under the heading “AVERAGE PHYSICAL TEST DATA” refer to raw data from which the SI CONVERTED AVERAGE test data were calculated. All conversions of raw data were made according to the test methods listed.

[0067] The data presented in the following tables were calculated with the test methods provided below. References to TAPPI methods refer to methods issued by the Technical Association of the Pulp and Paper Industry. References to “TECHNIBRITE Manual” refer to testing according the test manual accompanying the TECHNIBRITE Micro TB-1C testing instrument, available from Technidyne Corporation, New Albany, Ind.

Data                          Test Method Used
Specific Volume               TAPPI method P220-om88
Tensile Index                 TAPPI method P494-om88
Tensile Energy Absorption     TAPPI method P494-om88
Wet Tensile Index             TAPPI method P494-om88
Wet Tensile Energy Absorption TAPPI method P494-om88
(ISO) Brightness              TECHNIBRITE Manual
(ISO) Opacity                 TECHNIBRITE Manual
Scattering Coefficient        TECHNIBRITE Manual
Absorption Coefficient        TECHNIBRITE Manual
L                             TECHNIBRITE Manual
a                             TECHNIBRITE Manual
b                             TECHNIBRITE Manual
The reference to “Wet” Tensile Strength or Tensile Energy Absorption simply refers to the fact that the handsheet was saturated with water when tested.

[0068]

TABLE 1
RESULTS FOR EXAMPLE 1
SAMPLE ID	Example 1 (CR-54)
TREATMENT PROTOCOL	A	B	C	D	E
AMMONIA TREATMENT	CONTROL	GAS	GAS	LIQUID	LIQUID
RINSING	n/a	YES	NO	YES	NO
PFI REVOLUTIONS	0	0	0	0	0
SI CONVERTED AVERAGE TEST DATA
Specific Volume	(cm{circumflex over ( )}3/g)	2.63	2.83	2.90	4.30	4.31
Tensile Index	(Nm/g)	26.91	19.34	15.15	2.91	3.93
Tensile Energy Absorp.	(J/m{circumflex over ( )}2)	27.35	13.53	7.19	0.51	0.77
(Wet) Tensile Index	(Nm/g)	0.92	0.68	0.63	0.20	0.23
(Wet) Tensile Energy Absorp.	(J/m{circumflex over ( )}2)	0.42	0.42	0.50	0.14	0.15
AVERAGE PHYSICAL TEST DATA
C.S. Freeness	(ml)	695	775	745	775	765
Bulk	(in)	0.0062	0.0067	0.0068	0.0101	0.0102
Tensile	(lbs)	9.15	6.58	5.15	0.99	1.34
Stretch	(%)	2.598	1.883	1.410	0.779	0.821
Tensile Energy Absorp.	(ftib/ft{circumflex over ( )}2)	1.873	0.927	0.493	0.035	0.053
(Wet) Tensile	(lbs)	0.313	0.231	0.213	0.068	0.079
(Wet) Stretch	(%)	1.587	2.143	2.481	2.875	2.717
(Wet) Tensile Energy Absorp.	(J/m{circumflex over ( )}2)	0.029	0.029	0.034	0.009	0.010
Porosity (Frazier)	(cfm/ft{circumflex over ( )}2)	145.5	161.2	189.2	>747	586.1
AVERAGE OPTICAL TEST DATA
(ISO) Brightness	(%)	85.55	82.23	82.28	85.66	88.21
(ISO) Opacity	(%)	72.60	72.94	73.66	73.43	71.05
Scattering Coefficient (m2/kg)	31.49	30.51	31.45	32.73	28.12
Absorption Coefficient (m2/kg)	0.21	0.27	0.28	0.21	0.26
L*	(%)	95.67	94.97	94.99	95.73	94.86
a*	(%)	−0.60	−0.59	−0.53	−0.61	−0.52
b*	(%)	2.85	4.14	4.12	2.83	3.96

[0069]

TABLE 2
RESULTS FOR EXAMPLE 2
SAMPLE ID	Example 2 (LL-19)
TREATMENT PROTOCOL	A	B	C	D	E	E
AMMONIA TREATMENT	CONTROL	GAS	GAS	LIQUID	LIQUID	LIQUID
RINSING	n/a	YES	NO	YES	NO	NO
PFI REVOLUTIONS	0	0	0	0	0	0
SI CONVERTED AVERAGE TEST DATA
Specific Volume	(cm3/g)	2.52	2.75	2.87	3.90	4.19	3.99
Tensile Index	(Nm/g)	24.34	14.19	16.60	3.11	4.14	4.73
Tensile Energy Absrp.	(J/m2)	20.45	6.46	7.82	0.53	0.94	1.19
(Wet) Tensile Index	(Nm/g)	1.06	0.86	0.81	0.26	0.30	0.35
(Wet) Tensile Energy Absrp.	(J/m2)	0.97	0.83	0.86	0.21	0.23	0.42
AVERAGE PHYSICAL TEST DATA
C.S. Freeness	(ml)	685	725	695	750	730	720
Bulk	(In)	0.0059	0.0065	0.0068	0.0092	0.0099	0.0094
Tensile	(lbs.)	8.27	4.82	5.64	1.06	1.41	1.61
Stretch	(%)	2.197	1.377	1.409	0.803	0.897	0.947
Tensile Energy Absorp.	(ftlb/ft-2)	1.401	0.442	0.536	0.036	0.064	0.081
(Wet) Tensile (lbs.)	0.360	0.292	0.277	0.089	0.101	0.119
(Wet) Stretch	(%)	2.608	2.793	2.906	3.360	3.105	3.903
(Wet) Tensile Energy Absrp.	(J/m{circumflex over ( )}2)	0.067	0.057	0.059	0.015	0.016	0.028
Porosity (Frazier)	(cfm/ft{circumflex over ( )}2)	78.1	163.1	141.0	470.3	489.2	452.2
AVERAGE OPTICAL TEST DATA
(ISO) Brightness	(%)	87.88	86.80	83.60	88-07	84.53	82.86
(ISO) Opacity	(%)	76.00	77.35	77.60	75.82	76.85	78.91
Scattering Coefficient	(m{circumflex over ( )}2/kg)	38.08	39.99	38.54	38.17	37.88	40.80
Absorption Coefficient	(m{circumflex over ( )}2/kg)	0.18	0.20	0.27	0.17	0.24	0.29
L*	(%)	96.32	96.17	95.52	96.45	95.74	95.50
a*	(%)	−0.46	−0.48	−0.47	−0.47	−0.48	−0.38
b*	(%)	2.19	2.70	4.05	2.30	3.71	4.52

[0070]

TABLE 3
RESULTS FOR EXAMPLE 3
SAMPLE ID	Example 3 (EUCALYPTUS)
TREATMENT PROTOCOL	A	B	C	D	E
AMMONIA TREATMENT	CONTROL	GAS	GAS	LIQUID	LIQUID
RINSING	n/a	YES	NO	YES	NO
PFI REVOLUTIONS	0	0	0	0	0
SI CONVERTED AVERAGETEST DATA
Specific Volume	(cm{circumflex over ( )}3/g)	2.56	2.68	2.82	3.63	3.77
Tensile Index	(Nm/g)	16.05	15.10	11.54	4.38	4.95
Tensile Energy Absorp.	(J/m{circumflex over ( )}2)	5.10	5.11	3.11	0.67	1.08
(Wet) Tensile Index	(Nm/g)	0.98	0.93	0.81	0.38	0.42
(Wet) Tensile Energy Absorp.	(J/m{circumflex over ( )}2)	0.60	0.72	0.75	0.32	0.34
AVERAGE PHYSICAL TEST DATA
C.S. Freeness	(ml)	520	580	550	650	650
Bulk	(in)	0.0060	0.0063	0.0067	0.0086	0.0089
Tensile	(lbs.)	5.45	5.13	3.92	1.49	1.68
Stretch	(%)	1.072	1.132	0.964	0.701	0.864
Tensile Energy Absorp.	(ftib/ft2)	0.350	0.350	0.213	0.046	0.074
(Wet) Tensile	(lbs.)	0.334	0.318	0.275	0.129	0.143
(Wet) Stretch	(%)	2.006	2.278	2.744	3.012	2.698
(Wet) Tensile Energy Absorp.	(J/m{circumflex over ( )}2)	0.041	0.049	0.052	0.022	0.023
Porosity (Frazier)	(cfm/ft2)	81.0	101.4	95.0	411.3	351.3
AVERAGE OPTICAL TEST DATA
(ISO) Brightness	(%)	87.85	86.65	84.23	88.58	85.40
(ISO) Opacity	(%)	82.70	82.73	84.27	80.48	81.77
Scattering Coefficient	(m2/kg)	54.61	53.46	55.42	48.99	49.16
Absorption Coefficient	(m2/kg)	0.20	0.23	0.31	0.17	0.26
L*	(%)	96.75	96.51	96.00	96.83	96.12
a*	(%)	−0.43	−0.43	−0.37	−0.40	−0.30
b*	(%)	2.99	3.45	4.35	2.54	3.69

[0071]

TABLE 4
RESULTS FOR EXAMPLE 4
SAMPLE ID	Example 4 (BCTMP)
TREATMENT PROTOCOL	A	B	C	D	E
AMMONIA TREATMENT	CONTROL	GAS	GAS	LIQUID	LIQUID
RINSING	n/a	YES	NO	YES	NO
PFI REVOLUTIONS	0	0	0	0	0
SI CONVERTED AVERAGE TEST DATA
Specific Volume	(cm{circumflex over ( )}3/g)	3.91	4.91	3.84	5.84	4.65
Tensile Index	(Nm/g)	28.74	15.44	30.39	6.31	14.74
Tensile Energy Absorp.	(J/m{circumflex over ( )}2)	17.45	5.84	18.73	2.24	7.29
(Wet) Tensile Index	(Nm/g)	1.00	0.67	1.27	0.38	0.48
(Wet) Tensile Energy Absorp.	(J/m{circumflex over ( )}2)	0.23	0.20	0.32	0.20	0.38
AVERAGE PHYSICAL TEST DATA
C.S. Freeness	(ml)	570	730	600	745	695
Bulk	(in)	0.0092	0.0116	0.0091	0.0138	0.0110
Tensile	(lbs.)	9.77	5.25	10.33	2.15	5.01
Stretch	(%)	1.782	1.240	1.821	1.198	1.530
Tensile Energy Absorp.	(ftib/ft{circumflex over ( )}2)	1.195	0.400	1.283	0.153	0.499
(Wet) Tensile	(lbs.)	0.340	0.228	0.433	0.129	0.165
(Wet) Stretch	(%)	0.865	1.080	0.975	1.777	2.147
(Wet) Tensile Energy Absorp.	(J/m{circumflex over ( )}2)	0.016	0.014	0.022	0.014	0.026
Porosity (Frazier)	(cfm/ft{circumflex over ( )}2)	138.2	614.1	125.5	>747	399.5
AVERAGE OPTICAL TEST DATA
(ISO) Brightness	(%)	74.32	53.22	53.41	53.40	59.89
(ISO) Opacity	(%)	78.40	86.32	87.02	84.42	84.59
Scattering Coefficient	(m{circumflex over ( )}2/kg)	36.76	33.36	35.52	30.27	36.09
Absorption Coefficient	(m{circumflex over ( )}2/kg)	0.41	2.06	2.00	1.95	1.35
L*	(%)	94.37	87.23	87.77	86.97	89.91
a*	(%)	−1.85	−0.01	−0-22	0.07	−0.80
b*	(%)	9.91	16.58	17.30	16.01	14.71

[0072] The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

Claims

1. A process comprising: providing a cellulosic fibrous material, said fibrous material having been processed such that the lignin content has been reduced therein; charging a vessel with a composition comprising said cellulosic fibrous material; charging the vessel with ammonia at a pressure sufficient to cause the ammonia to penetrate cellulosic fibers in the cellulosic fibrous material; and rapidly depressurizing the fibrous material.

2. The process of claim 1, wherein the vessel is charged with ammonia at a pressure sufficient to cause the ammonia to penetrate crystalline and amorphous portions of at least some cellulosic fibers.

3. The process of claim 1, wherein, after charging the vessel with ammonia, the ammonia and fibrous material are retained in the vessel for a period of time ranging from about 0.5 to about 30 minutes.

4. The process of claim 1, wherein the ammonia and cellulosic fibrous material are present in a weight ratio of ammonia to cellulosic fibrous material of from about 1:1 to about 8:1.

5. The process of claim 1, wherein the cellulosic fibrous material is in an aqueous mixture prior to saturation with ammonia.

6. The process of claim 5, wherein the aqueous mixture comprises about 10 to about 80 weight percent fibers.

7. The process of claim 1, wherein the pressure ranges from about 100 to about 300 psi.

8. The process of claim 1, wherein the lignin content in the cellulosic fibrous material has been eliminated through a pulping process.

9. A cellulosic fiber made according to the process of claim 1.

10. A disposable absorbent product comprising the fiber of claim 9.

11. A cellulosic fiber having a curl index of greater than 0.2; and a Wet Curl Value of at least 0.2.

12. The fiber of claim 11, wherein the fiber has a curl index from about 0.2 to about 0.4.

13. The fiber of claim 11, wherein the fiber is formed from wood, cotton, straw, grass, cane, reed, bamboo, stalks with bast fibers, leaf fibers or a combination thereof.

14. The fiber of claim 13, wherein the fiber comprises wood.

15. A fiber-containing web or fabric comprising the fiber of claim 11.

16. A disposable absorbent product comprising the fiber of claim 11.

17. A disposable absorbent product comprising a cellulosic fiber, wherein the fiber has a curl index of greater than 0.2.

18. The disposable absorbent product of claim 17, wherein the fiber has a curl index from about 0.2 to about 0.4.

19. The disposable absorbent product of claim 17, wherein the product is a diaper, adult incontinent product, bed pad, catamenial device, wound dressing, surgical cape, surgical drape or tissue-based product.

20. The disposable absorbent product of claim 17, wherein the product is a handsheet.

21. The disposable absorbent product of claim 17, wherein the product comprises: a topsheet; a backsheet; and an absorbent structure positioned between the topsheet and the backsheet, wherein the absorbent structure comprises said fiber.