CA2293513A1 - Liquid ammonia explosion treatment of wood fibers - Google Patents

Abstract

A process of forming improved cellulosic fibers is 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

LIQUID AMMONIA EXPLOSION TREATMENT
OF WOOD FIBERS
l0 FIELD OF THE INVENTION
The present invention relates to the treatment of cellulosic or wood fibers after the fiber has been separated from a natural source, such as pulp or chip. The wood fibers are non-nutritive and are lignin-free when treated in the process of the present invention. More specifically, the processed cellulosic or wood fibers are converted by high pressure liquid ammonia treatment into an improved fiber, having a desired 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.
BACKGROUND OF THE INVENTION
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 explodes through the agency of applied physical forces. In general, known explosion pulping processes may be classified into two categories:
( 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 (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.
a The best known liquid explosion processes is the so called "Masonite" process, which is described in U.S. Patents Nos. 1,655,618;
1,824,221; 1,922,313; and 2,140,189; all of which are assigned to W.H.
Mason. 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.
Liquid ammonia explosion treatments have also been used to convert raw wood sources, such as wood chips, into purified wood fiber. 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. Normally, ammonia processing is an unsuccessful method for the production of a purified wood fiber having both amorphous and crystalline regions. For example, U.S. Patent No.
5,037,663 issued to Dale, discloses treating nutritive animal feedstuff fibers under pressure with liquid ammonia for the purpose of improving the nutritive value of a feed material. For example, Dale's process affects the absorptive properties of the treated material, increasing digestibility and protein desorbtion from the feed stuff.
Dale's patent relates to treatment of wood fiber and the processing of unpurified lignin containing or nutritive containing fibrous materials.
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 relate directly to the fiber morphology. Current processes, including Dale's process, produce fibers having a limited curl index and fibers that tend to have a rough or coarse feel when evaluated by a sensory panel test according to industry accepted guidelines.
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.
a SUMMARY OF THE INVENTION
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 non-nutritive, lignin-free cellulosic fiber, charging the vessel with 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.
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 smooth, soft, silky test panel feel.
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 desirable 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 absorbent fluids.
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
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 saturated the fiber, pressure is released, which causes flashing or 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 a 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 yet the fibers retain a relatively high water retention value.
As used herein, the term "permanent fiber morphology" is defined as a fiber characteristic, which remains after the fiber has been repulped for up to 300 minutes and desirably between about 150 and 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.
A wide variety of processed or purified 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.
As used herein, the term "fiber" or "fibrous" is meant to refer to a particulate material wherein the length to diameter ratio (aspect ratio) of such particulate material is greater than about 10.
Conversely, a "nonfiber" or "nonflbrous" material is meant to refer to a particulate material wherein the length to diameter ratio of such particulate material is about 10 or less or more nearly 2 or less.
In the present invention, it is desired that the cellulosic fibers be used in a form wherein the cellulosic fibers have already been refined into a pulp. As such, the processed or purified cellulosic fibers will be 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 s cellulosic material in the form of virgin wood chips or the like. The current process is a post-pulping, cellulosic fiber modifying process, as compared to known steam explosion processes that are generally used for high-yield pulp manufacturing or waste-recycle processes.
The liquid ammonia explosion treatment process of the present invention includes the following steps: ( 1 ) charging a reaction vessel with a non-nutritive, lignin-free cellulosic fiber, (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. Any reaction vessel known to those having skill in the art may be employed in the present invention, as long as the vessel has the desired capacity and is capable of withstanding the desired pressure. Suitable reaction 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 US Patent 5,262,003, issued November 16, 1993, all of which are incorporated herein by reference in their entirety.
The cellulosic fibers present in the reaction vessel and thus used in the ammonia explosion process are desirably low yield cellulosic fibers. As used herein, "low yield" cellulosic fibers are cellulosic fibers produced by pulping processes, which yield about 85 percent or less, desirably about 80 percent or less, and more desirably about 55 percent or less. In contrast, "high yield" cellulosic fibers are those cellulosic fibers produced by pulping processes, which yield about 85 percent or greater. Such "low yield" pulping processes generally leave the resulting cellulosic fibers with relatively high levels of lignin.
The cellulosic fibers, used in the process of the present invention, may be in either a dry or a wet state. In one embodiment of the present invention, the cellulosic fibers are present in an aqueous mixture having a desired consistency. As used herein, the term "consistency" refers to the concentration of cellulosic fibers in an aqueous mixture. 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 and water present in such mixture, multiplied by 100. Desirably, the fiber/aqueous mixture has a consistency of from about 10 to about 100 weight percent, more desirably from about 20 to about 80 weight percent, and even more desirably from about 25 to about 75 weight percent cellulosic fibers, based on the total weight percent of the aqueous pulp mixture.
Desirably, the aqueous mixture is agitated, stirred, or blended to effectively disperse the cellulosic fibers throughout the water prior to its introduction into the reaction vessel.
The cellulosic fibers for use in the process of the present invention are typically mixed with an aqueous solution; however, other liquids may be used in combination with water. Desirably, the liquid phase of the aqueous mixture comprises at least about 30 weight percent water, more desirably about 50 weight percent water, even more desirably about 75 weight percent water, and even more desirably 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, and acetone. Any of the above-mentioned non-aqueous liquids may be used as long as the other liquids do not adversely effect the dispersibility of the cellulosic fibers within the aqueous mixture.
In one embodiment of the present invention, an aqueous solution directly from a pulping and/or pulp preparation process is use in the ammonia explosion treatment of the present invention, without having to separately recover the cellulosic fibers. 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.
Also present in the reaction vessel is a volume of ammonia.
Generally, the weight ratio of ammonia to cellulosic fiber in the reaction vessel is about 1:1 to 8:1. Desirably, the weight ratio of ammonia to cellulosic fiber in the reaction vessel is from about 3:1 to 7:1. More desirably, the weight ratio of ammonia to cellulosic fiber in the reaction vessel is about 5:1. Desirably, the ammonia is charged into the vessel at sufficient pressure and temperature to maintain the ammonia in a liquid state. Generally, the pressure may range from about 100 to about 300 pounds per square inch. The high-pressure forces within the vessel enables the liquid ammonia to penetrate crystalline and amorphous regions within the cellulosic fiber. Further, the fiber modification may take place in a desired temperature range of from about 10 °C to about 100 °C.
The ammonia is allowed to saturate and reach a saturation equilibrium with the cellulosic fiber. Typically, the cellulosic fiber will contain up to about 7.0 wt%a ammonia at equilibrium based on the total weight of the saturated fiber. Desirably, the cellulosic fiber will contain from about 0.5 to about 5.0 wt% ammonia at equilibrium based on the total weight of the saturated fiber.
Once the ammonia reaches a saturation equilibrium condition with the cellulosic fibers, the reaction vessel is vented.
Generally, the time necessary to reach a saturation equilibrium condition ranges from about 0.5 minutes to about 30 minutes; however, the amount of time may be longer than 30 minutes depending on a number of factors including, but not limited to, the ammonia concentration, and the amount of ammonia and fibers present.
Desirably, 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. More desirably, 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.
In general, the higher the volume ratio of ammonia employed, the shorter the period of time necessary to achieve a desired degree of 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.
Venting of the reaction vessel rapidly depressurizes the environment surrounding the ammonia/fiber mixture. The liquid ammonia flashes into a gas, causing the ammonia-saturated wood fiber g to "explode" within the reaction vessel. The resulting fibers are changed 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.
The resultant fibers have a unique combination of permanent curl, high wet resilience and high water retention value.
The ammonia explosion 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 exploded cellulosic fibers, in addition to being modified, have been discovered to exhibit improved properties that make such exploded cellulosic fibers suitable for use in liquid absorption or liquid handling applications. After the ammonia explosion process, the treated cellulosic fibers will generally exhibit a desired level of stable curl. As such, the process of the invention generally does not require the use of any additional additives to the cellulosic fibers during the ammonia explosion process or any post-treatment steps after the ammonia explosion of the fibers to achieve the desired degree of fiber curl.
The present invention is further directed to the improved cellulosic fibers produced from the ammonia explosion treatment process described above. The resulting cellulosic fibers exhibit a desired level of stable curl. Curl of a fiber may be quantified by a curl value, which measures the fractional shortening of a fiber due to kink, 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. 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. Patent 4,898,642, incorporated herein in its entirety by reference.
The curl value of a fiber may then be calculated from the following equation:
s Curl Value = (L/I) - 1 Depending on the nature of the curl of a conventionally produced cellulosic fiber, the curl may be stable when the cellulosic fiber is dry, but may be unstable when the cellulosic fiber is wet. The cellulosic fibers prepared according to the process of the present invention have been found to exhibit a substantially stable fiber curl when wet. This property of the cellulosic fibers may be quantified by a Wet Curl value, as measured according to the test method described herein, which is a length weighted mean curl average of a designated number of fibers, such as about 4000, from a fiber sample. As such, 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. It is hereby noted that the Wet Curl value, as determined herein, is calculated by only using the necessary values for those fibers with a length of greater than about 0.4 millimeter.
As used herein, the improved cellulosic fibers considered to be effectively treated by the ammonia explosion treatment exhibit a Wet Curl value that is greater than about 0.2. Desirably, the improved cellulosic fibers exhibit a Wet Curl value of from about 0.2 to about 0.4. More desirably, the improved cellulosic fibers exhibit a Wet Curl value of from about 0.2 to about 0.35. Even more desirably, the improved cellulosic fibers exhibit a Wet Curl value of from about 0.22 to about 0.33. Even more desirably, 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.
In addition to improved Wet Curl values, the improved cellulosic fibers of the present invention exhibit a relatively high water retention value.
The treated cellulosie fibers of the present invention are suitable for use in a wide variety of applications. However, depending on the use intended for the treated cellulosic fibers, such treated cellulosic fibers may be washed with water. 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 effecting the 5 properties of the cellulosic fibers.
In one embodiment 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, 10 a bat 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 Number 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.
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; 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.
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 according to the method disclosed in the Test Methods section below. 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 s lower than a wet-laid handsheet prepared from cellulosic fibers that have not been treated according to the process of the present invention.
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.
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. Patents 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.
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:
TEST METHODS AND WEB FORMATION
PROCEDURES FOR TESTING
Wet Curl Test:
The Wet Curl value for cellulosic fibers is determined by using an instrument which rapidly, accurately, and automatically determines the quality of fibers, the instrument being available from OPTest Equipment Inc., Hawkesbury, Ontario, Canada, under the designation Fiber Quality Analyzer, OpTest Product Code DA93.

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.
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.
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 desired 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.
Preparation of Wet-Laid Handsheet:
A 7.5 inch by 7.5 inch handsheet is prepared using the desired fiber samples by using an 8 inch by 8 inch cast bronze wet-laid handsheet former mold, available from Voith Corporation. The handsheets have a basis weight of about 60 grams per square meter. The handsheets are made using ratios of 30, 70 and 100 percent ammonia exploded recovered fibers mixed, when applicable, with an appropriate percentage of recycled fiber wet lap obtained from the Kimberly Clark Owensboro facility. The recycled fiber wet lap is the recovered product, the production of which provided the original waste sludge, which was used in the steam explosion treatment process.
A British Disintegrator mixer, available from Testing Machines, Inc, is 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 is set to zero and is turned on until the counter runs to about 600. The contents of the British Disintegrator are then poured into a vessel filled with about 8 liters of distilled water.
The handsheet former, having an approximate 12 inch deep chamber, is filled with tap water to about 5 inches below the top of the handsheet former chamber. The contents of the bucket are then poured into the handsheet former chamber where a dedicated stirrer is then used to mix the suspension in the handsheet former chamber. The stirrer is 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 is then removed and the suspension is drained through the forming screen of the handsheet former. The handsheet former is then opened and two layers of blotting paper are placed on top of the handsheet. A roller, applying the equivalent of about 308 kiloPascals of a pressure inch, is moved back and forth one along each side and the center of the formed handsheet. The blotting paper, with the formed handsheet attached, is then lifted off the forming screen. The blotting paper is then placed on a table such that the formed handsheet faced upwards. An 18 inch, 4 mesh, stainless steel screen is placed on top of the handsheet. The blotting paper, handsheet, and screen are then flipped so that the screen is on the bottom and the blotting paper is on top. The blotting paper is then peeled off of the handsheet, leaving the handsheet on the screen. The handsheet is transferred, wire side up, to the polished convex surface of an 8 inch by 8 inch dryer hot plate. A
canvas cover is placed over the convex surface and handsheet and is weighted down to prevent drying induced wrinkling. The handsheet is dried for 2 minutes and then removed for subsequent evaluation.
Bulk and Dry Densitxof an Absorbent Structure:
From a handsheet prepared according to the procedure described above, a strip of sample handsheet material, having a width of about 2 inches and a length of about 15 inches is obtained by using a textile saw available, for example, from Eastman Machine Corp., Buffalo, New York. The sample strip is cut at least about 1 inch away from the edge of the handsheet so as to avoid edge effects. The sample strip is marked in about 10 millimeter intervals using water-soluble ink.
To measure the bulk of the sample strip, a bulk meter, accurate to at least about 0.01 millimeter, such as a bulk meter available from Mitutoyo Corporation, is used. An one inch diameter platen is used to measure the bulk, with the platen being parallel to the base of the bulk meter. The bulk of the sample strip is measured in about 50 millimeter intervals along the length of the sample strip and then averaged. The average bulk of the sample strip is then used to calculate the dry density of the sample strip, using the weight and dimensions of the sample strip.
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 a 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

10 Preparation of Improved Cellulosic Fibers of the Present Invention In Examples 1-4, cellulosic fiber samples were prepared by dewatering, in a laboratory centrifuge, 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 15 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 BCTMP pulp fibers, available from Tembec Inc. of Canada (Example 4). Each sample formed a mixture having a consistency of about 30 weight percent cellulosic fibers. Samples of about 100 grams were added to a laboratory ammonia explosion reactor, available from Stake Tech Ltd., Canada. The reactor had a capacity of 2 liters.
After closing the top valve, inert gas (nitrogen) was injected into the reactor along with 500 grams of liquid ammonia (5:1 NH3 to fiber ratio by mass). The reactor was maintained at a pressure of 200 psi for five minutes. The cellulosic fibers were then explosively decompressed and discharged into a container by opening the bottom valve of the reaction vessel.
The treated fiber was dried by one of two methods The first method was to rinse the fiber with water, followed by air drying and oven drying at 90 °C for one hour. The second method was to air dry the fiber without a water rinse, followed by oven drying at 90 °C
for one hour. The ammonia exploded fibers were collected for evaluation. The results of the fiber evaluations are given in Tables 1-4 below.

Formation of Handsheets From Improved Cellulosic Fibers The fibers of Examples 1-4 were used to form handsheets using the procedure described in the Test Method section above.
Testing was conducted on the handsheets. The results are set forth in Tables 1-4 below.

SAMPLE ID Example 1 (CR- 54) AMMONIA TREATMENT CONTROL GAS GAS LIQUID
LIQUID

* DRYING METHOD - AIR AIRlOVEN AIRIOVEN~
AIR

SI CONVERTED AVERAGE
TEST DATA

Specific Volume (cm~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 (J/m~2)27.35 13.53 7.19 0.51 0.77 Absorp.

(Wet) Tensile Index-(Nm/g) 0.92 0.68 0.63 0.20 0.23 (Wet) Tensile Energy(J/m~2)0.42 0.42 0.50 0.14 0.15 Absorp.

AVERAGE PHYSICAL
TEST DATA

C.S. Freeness (ml) 695 775 745 775 765 Bulk (in) 0.0062 0.00670.0068 0.01010.0102 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 (ftib/ft~2)1.873 0.927 0.493 0.035 0.053 Absorp.

(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(1/m~2)0.029 0.029 0.034 0.009 0.010 Absorp.

Porosity (Frazier)(cfm/ft~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 i (%) 72.60 72.94 73.66 73.43 71.05 I (ISO) Opacity Scattering Coefficient(m2/kg)31.49 30.51 31.45 32.73 28.12 Absorption Coefficient(mz/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 F1~RYINCi MR1 HUUS: (1) AIR = WATER RINSE TO 6-7 pH, FOLLOWED BY AIR DRYING
(2) AIR/OVEN = NO WATER RINSE; AIR DRY, THEN OVEN DRY

Table SAMPLE ID Example 2 (LL-19) AMMONIA TREATMENT CONTROL GAS LIQUID LIQUIDLIQU~I1 GAS

* DRYING METHODS - Air Air/OvenAir Air/OvenAir/Oven SI CONVERTED AGE ATA
AVER TEST
D

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(J/m2) 20.45 6.46 7.82 0.53 0.94 1.19 Absrp.

(Wet) Tensile (Nm/g) 1.06 0.86 0.81 0.26 0.30 0.35 Index (Wet) Tensile 0.97 0.83 0.86 0.21 0.23 0.42 Energy Absrp.
(J/mz) AVERAGE PHYSICALTEST
DATA

C. S. Freeness(ml) 685 725 695 750 730 720 Bulk (In) 0.00590.00650.0068 0.0092 0.00990.0094 ~

Tensile (Ibs.) 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(ftlb/ft-2)1.401 0.442 0.536 0.036 0.064 0.081 Absorp.

(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 0.067 0.057 0.059 0.015 0.016 0.028 Energy Absrp.(J/m~2) Porosity (Frazier)(cfm/ft~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 (m~2/kg)38.08 39.99 38.54 38.17 37.88 40.80 Coefficient Absorption (m~2/kg)0.18 0.20 0.27 0.17 0.24 0.29 Coefficient 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.OS 2.30 3.71 4.52 *DRYING (1) WATER RINSE
METHODS: AIR TO
= 6-7 pH, FOLLOWED
BY
AIR
DRYING

(2) O WATER DRY, AIR/OVEN RINSE; THEN
= N AIR OVEN
DRY

FOR

Table 3 SAMPLE ID Example 3 (EUCALYPTUS) AMMONIA TREATMENT CONTROL GAS GAS LIQUIDLIQUID-* DRYING METHOD - AIR AIR/OVENAIR
AIR/OVEN

Sl CONVERTED AVERAGE
TEST DATA

Specific Volume (cm~3/g)2.56 2.68 2.82 3.63 3.77 Tensile Index (Nm/g) 16.05 15.1011.54 4.38 4.95 Tensile Energy (J/m~2)5.10 5.11 3.11 0.67 1.08 Absorp.

(Wet) Tensile Index(Nm/g) 0.98 0.93 0.81 0.38 0.42 (Wet) Tensile Energy(J/m~2)0.60 0.72 0.75 0.32 0.34 Absorp.

TEST DATA

C.S. Freeness (ml) 520 580 550 Bulk (in) 0.0060 0.00630.0067 0.00860.0089 Tensile (lbs.) 5.45 5.13 3.92 1.49 1.68 Stretch (%) 1.072 1.1320.964 0.701 0.864 Tensile Energy (ftib/ft~2)0.350 0.3500.213 0.046 0.0?4 Absorp.

(Wet) Tensile (lbs.) 0.334 0.3180.275 0.129 0.143 (Wet) Stretch (%) 2.006 2.2782.744 3.012 2.698 (Wet) Tensile Energy(J/m~2)0.041 0.0490.052 0.022 0.023 Absorp.

Porosity (Frazier)(cfm/ft~2)81.0 101.495.0 411.3 351.3 AVERAGE OPTICAL 87.85 86.6584.23 88.58 85.40 TEST DATA

(ISO) Brightness (%) (ISO) Opacity (%) 82.70 82.7384.27 80.48 81.77 Scattering Coefficient(m~2/kg)54.61 53.4655.42 48.99 49.16 Absorption Coefficient(m~2/kg)0.20 0.23 0.31 0.17 0.26 L* (%) 96.75 96.5196.00 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 *DRYING METHODS: ( 1) AIR = WATER RINSE TO 6-7 pH, FOLLOWED BY AIR DRYING
(2) AIR/OVEN = NO WATER RINSE; AIR DRY, THEN OVEN DRY AT

a Table SAMPLE ID Example (BCTMP) S AMMONIA TREATMENT CONTROL GAS GAS LIQUIDLIQUID
-* DRYING METHOD -- AIR AIRlOVENAIR AIRlOVEN

SI CONVERTED AVERAGE
TEST DATA

10 Specific Volume (cm~3/g)3.91 4.91 3.84 5.84 4.65 Tensile Index (Nm/g) 28.74 15.4430.39 6.31 14.74 Tensile Energy (J/m~2)17.45 5.84 18.73 2.24 7.29 Absorp.

(Wet) Tensile (Nm/g) 1.00 0.67 1.27 0.38 0.48 Index (Wet) Tensile (J/m~2)0.23 0.20 0.32 0.20 0.38 Energy Absorp.

AVERAGE PHYSICAL
TEST DATA

C.S. Freeness (ml) 570 730 600 745 695 Bulk (in) 0.0092 0.01160.0091 0.01380.0110 Tensile (lbs.) 9.77 5.25 10.33 2.15 5.01 20 Stretch (%.) 1.782 1.2401.821 1.198 1.530 Tensile Energy (ftib/ft~2)1.195 0.4001.283 0.153 0.499 Absorp.

(Wet) Tensile (Ibs.) 0.340 0.2280.433 0.129 0.165 (Wet) Stretch (%) 0.865 1.0800.975 1.777 2.147 (Wet) Tensile (J/m~2)0.016 0.0140.022 0.014 0.026 Energy Absorp.

Porosity (Frazier)(cfmlft~2)138.2 614.1125.5 >747 399.5 AVERAGE OPTICAL
TEST DATA

(ISO) Brightness (%) 74.32 53.2253.41 53.40 59.89 (ISO) Opacity (%) 78.40 86.3287.02 84.42 84.59 Scattering Coefficient(m~2/kg)36.76 33.3635.52 30.27 36.09 Absorption Coefficient(m~2/kg)0.41 2.06 2.00 1.95 1.35 L* (%) 94.37 87.2387.77 86.97 89.91 a* (%) -1.85 -0.01-0-22 0.07 -0.80 b* (%) 9.91 16.5817.30 16.01 14.71 *DRYING AIR 7 AIR NG
METHODS: = WATER pH, DRYI
(1) RINSE FOLLOWED
TO BY

(2) AIR/OVENNO WATER INSE;
= R AIR
DRY, THEN
OVEN
DRY
AT

FOR

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 (21)

1. A process for forming an improved cellulosic fiber, the process comprising the steps of:
charging a vessel with a non-nutritive, lignin-free cellulosic fiber;
charging the vessel with ammonia at a pressure sufficient to cause the ammonia to penetrate the cellulosic fiber thereby saturating the fiber with ammonia; and rapidly depressurizing the ammonia-saturated fiber to form the improved cellulosic fiber.

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 the cellulosic fiber.

3. The process of Claim 1, wherein the fiber is saturated with ammonia 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 fiber are present in a weight ratio of ammonia to cellulosic fiber of from about 1:1 to about 8:1.

5. The process of Claim 1, wherein the cellulosic fiber 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 during processing ranges from 100 to 300 psi.

8. The process of Claim 1, further comprising forming the non-nutritive, lignin-free cellulosic fiber in a pulping process.

9. An improved cellulosic fiber made according to the process of Claim 1.

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

11. An improved 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 an improved 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.