MXPA96004167A - Preparation of reticulated cellulosic fibers deacido policarboxilico individualiza - Google Patents

Abstract

The present invention relates to a method for preparing crosslinked, individualized cellulosic fibers having an amount of crosslinking agent of C2-C9 polycarboxylic acid which reacts therein in a crosslinked intrafiber ester linkage form, said crosslinked fibers providing a value of water retention of about 25 to 60, said method comprising the step of heating the non-crosslinked cellulosic fibers at a moisture content ranging from 0 to about 70% with 1 to 15%, by weight on a citric acid base applied to a dry fiber base of C2-C9 polycarboxylic acid crosslinking agent, and from 0.005 to 1% by weight, applied on a dry fiber basis, of active surface agent, on them, to remove any moisture content and to cause the cross-linking agent of polycarboxylic acid reacts with the cellulose fibers and forms the cross-ester between the molecules of cellulose, to provide said reticulated cellulose fibers

Description

PREPARATION OF RETICULATED CELLULOSE FIBERS WITH POLYCARBOLYLIC ACID. INDIVIDUALIZADAS FIELD OF THE INVENTION The present invention is directed to an improved process for preparing cellulosic fibers for absorbent products and products made therefrom.

BACKGROUND OF THE INVENTION Herrón et al., In the U.S. Patent. No. 5,137,537 is directed to absorbent structures comprising individualized crosslinked cellulosic fibers having between about 0.5 and 10.0 mol% of a C2-C9 polycarboxylic acid crosslinking agent, calculated on a molar basis of anhydroglucose cellulose, which reacts with said fibers in a crosslinked form of intrafiber ester bond, wherein said crosslinked fibers have a water retention value of from about 25 to about 60. The invention of Herron et al. has preferred application for high density absorbent products ( above 0.15 g / cm3), for example thin disposable diapers, feminine hygiene towels and incontinence products for adults. The preferred methods of fiber preparation in Herron et al. Involve dry curing, that is to say curing the aqueous fiber-polycarboxylic acid mixture of at least 60% consistency. A method of dry curing described in Herron et al., Comprises contacting the uncrosslinked fibers in unlimited form with the aqueous crosslinking composition to have uniform penetration and distribution of the crosslinking composition thereon, dehydrating, optionally further drying, defibrate the fibers in substantially individual form, optionally additional drying without affecting the separation of the fibers in the individual form obtained by defibration, curing to cause cross-linking to occur, and optionally washing or bleaching and washing. In a second method of dry curing described in Herron et al., The process is carried out as described in the previous paragraph except that either before or after being put in contact with the aqueous crosslinking composition, the fibers are provided in the sheet form and although in the sheet form the fibers are dried and cured, they are defibrated in substantially individual form. Considerations have been given to obtain fibers crosslinked with C2-C9 polycarboxylic acid, while minimizing the cost of its production. By eliminating washing or bleaching and washing after curing, processing and equipment costs are reduced, but the moisture content of the absorbent product is also reduced. In addition, by reducing the amount of defibration before curing, the processing and equipment costs are reduced, however, it also causes the reduction in the moisture correspondence and the reduction of the dry elasticity in the absorbent product, and causes an increase in the formation of fiber balls that provide an appearance of importance for the absorbent product.

BRIEF DESCRIPTION OF THE INVENTION It has been discovered in the present invention that the reduction of the surface tension of the aqueous crosslinking composition compounds the losses of moisture correspondence that would otherwise occur by eliminating washing or baling and washing after curing, and allows to reduce the amount of defibration before curing without loss of correspondence to moisture, as manifested by the results in the wet compressibility test described hereinafter, and without damaging the appearance, as evidenced by the results in the knuckle test and of pill, and improves dry elasticity, as manifested by the results in the 5K density test described hereinafter.

The method of the present invention is to prepare crosslinked, individualized cellulosic fibers having an effective amount of a cross-linking agent of C2-C9 polycarboxylic acid, which reacts therein in a crosslinked form of intrafiber ester and improves elasticity dry (as evidenced by the results in the 5K density test described here later), (i.e., the crosslinked fibers as described in U.S. Patent No. 5,137,537, but without improving dry elasticity), said method comprising the step of heating non-crosslinked cellulosic fibers to a moisture content varying from 0. to about 70%, preferably varying from 30 to 40%, with from 1 to 15%, by weight on a citric acid base applied on a dry fiber basis, of C2-C9 polycarboxylic acid crosslinking agent, and from 0.005 to 1% by weight applied on a dry fiber base, active surface agent, above them, to remove any moisture content and to cause the crosslinking agent of polycarboxylic acid to react with the cellulosic fibers and form crosslinking of ester between the cellulose molecules (i.e., which causes the cure), to provide said cross-linked cellulose fibers. In one embodiment, said method is carried out without washing or bleaching and washing the crosslinked fibers. The preparation of the non-crosslinked cellulose fibers at a moisture content ranging from 0 to 70%, preferably from 30 to 40%, with from 1 to 15%, by weight on a base of citric acid applied on a fiber basis dry, of C2-C9 polycarboxylic acid crosslinking agent, and from 0.005 to 1% by weight applied on a dry fiber basis, of active surface agent, above them, preferably comprises contacting the cellulosic fibers not crosslinked with an aqueous crosslinking composition containing the C2-C9 polycarboxylic acid crosslinking agent in an amount to provide 1 to 15% thereof, by weight, on a citric acid base applied on a dry fiber basis, in the fibers subjected to said heating step, and containing active surface agent in an amount to provide from 0.005 to 1% thereof, by weight, applied on a dry fiber basis, in the fibers subjected to said heating pa In a highly preferred embodiment, said contacting is carried out by transporting a sheet of uncrosslinked cellulosic fibers having a moisture content ranging from 0% to 10% through a body of said aqueous crosslinking composition contained in a carrier fastener. press rolls and through said fastener for impregnating said fiber sheet with said aqueous crosslinking composition and for producing on the output side of the fastener a sheet impregnated with fibers containing said aqueous crosslinking composition in an amount that provides 30% at 80% or more (eg, equal to 85% or 90% or equal to 95%), preferably from 40% to 70% consistency, and the fiber impregnated sheet is subjected to defibration to produce a shredded mixture that is ready for treatment in said heating step. In another embodiment, the contacting is carried out by forming a suspension of the uncrosslinked cellulose fibers in an unlimited form in the aqueous crosslinking composition, from 0.1% to 20% consistency, and soaking for approximately 1 to 240 minutes, after from which the liquid is removed from the suspension to increase the consistency to vary from 30 to 100%, to form a reduced mixture of liquid, after which the reduced mixture of liquid is subjected to defibration to form a defibrated mixture that is ready for the treatment in said heating step. As indicated above, the presence of active surface agent reduces the surface tension in the heating step, causing the increase in the moisture correspondence of the crosslinked fibers, as evidenced by the increased values in the wet compressibility test described here afterwards, to adjust the loss in this property when the steps of washing or blanching and washing after the cure are omitted. Although it is not the intention of the present to be limited by any theory as to why this occurs, it is believed that the reduced surface terrestrial prevents the shrinkage fibers during the reaction with the crosslinking agent, resulting in a more open structure in an absorbent article made of the fibers and correspondence to the higher moisture. As indicated above, the inclusion of the active surface agent to reduce the surface tension in the aqueous crosslinking composition in the contact that causes the pulp to become more easily defibrated (i.e., becomes more spongy), resulting in the reduction in the amount of defibration without the loss of correspondence to moisture in a structure made of the crosslinked fibers, as determined in the wet compressibility test described hereinafter, and with improvements in appearance, as determined in FIG. knuckle and pill test, described hereinafter. When commercially available disc cuppers are used for defibration, said inclusion of active surface agent allows reduction of the number of cuppers used to half of those otherwise required or to less than half of those otherwise required, to obtain the corresponding to the preferred humidity and with the improvement of the appearance. Although it is not the intention of the present to be limited by any theory as to why these advantages occur, it is believed that the decrease in surface tension adhesion from fiber to fiber, thereby reducing the amount of defibration to obtain the correspondence to the preferred humidity. As indicated above, the presence of the active surface agent causes the increase in dry elasticity for the crosslinked fiber products, as evidenced by the results in the 5K density test as described hereinafter. The term "individualized crosslinked fibers" is used herein to mean that the crosslinks are primarily intrafiber instead of interfiber. The term "intrafiber" means a polycarboxylic acid molecule that is reacted only with a molecule or molecules of a single fiber instead of between separate fiber molecules. The% mol of the polycarboxylic acid crosslinking agent is calculated on a molar basis of cellulose glucose anhydride which reacts with the fibers, being determined by the following procedure: first a sample of crosslinked fibers is washed with sufficient hot water to remove any unreacted crosslinking agent and the catalyst. Next, the fibers are dried to an equilibrium moisture content. The free carboxyl group content is then determined, essentially according to the T.A.P.P.I method. T237 OS-77. The% mol of the reacted polycarboxylic acid crosslinking agent is then calculated based on the considerations that a carboxylic group is left unreacted in each polycarboxylic acid molecule, that the fibers before reacting have a carboxyl content of 30 meq. / kg, and that no new carboxyls are generated on the cellulose molecules during the crosslinking process apart from the free carboxyls on the crosslinking portions, and that the molecular weight of the crosslinked pulp fibers is 162 (i.e. anhydrous glucose unit). The term "citric acid base" is used herein to mean the weight of citric acid which provides the same number of reactive carboxyl groups, as provided by the currently used polycarboxylic acid, with the carboxyl reactant groups which are the groups Carboxyxil reactants minus one per molecule. The term "reactive carboxyl groups" is defined below. The term "applied on a dry fiber basis" means that the percentage established by a relationship, where the denominator is the weight of the cellulosic fibers present if they were dry, (ie, without moisture content). The "water retention values", set forth herein, are determined by the following procedure: a sample of about 0.3 g to about 0.4 g of fibers (ie, from about 0.3 g to about a 0.4 g portion of the fibers) which the water retention value is being determined is soaked in a container covered with approximately 10 ml of distilled or deionized water at room temperature for about 15 and about 20 hours.The soaked fibers are collected on a filter and transferred to a 80 mesh wire basket, supported approximately 3.81 cm above a lower part of a 60 mesh screen of a centrifugal tube, covers the tube with a plastic cover and centrifuges the sample at a relative centrifugal force. 1,500 to 1,700 gravities for 19 to 21 minutes The centrifuged fibers are then removed from the basket and weighed. a constant weight at 105"C and returns to weigh. The water retention value (WRV) is calculated as follows: RV = (W-D) X 100 D where, = the wet weight of the centrifuged fibers; D = the dry weight of the fibers; and W-D = the weight of the water absorbed.

The wet compressibility test in the present, is a measure of the correspondence to moisture and absorbency in a structure made from the fibers for which the property is being determined, and is carried out by the following procedure: prepare a four by four square inch pad placed in air, leaving approximately 7.5 g, from the fibers that are tested. The density to the pad is adjusted to 0.2 g / cc with a press. The pad is loaded with synthetic urine at ten times its dry weight, or up to the point of saturation, whichever is less. A compression load of 0.1 PSI is applied to the pad. After about 60 seconds, during which time the pad is balanced, then the compression load is increased to 1.1 PSI. The pad is allowed to reach equilibrium and then the compression load is reduced to 0.1 PSI. The pad is then allowed to reach equilibrium, and the thickness is measured. The density for the pad is calculated at the second load of 0.1 PSI, based on the thickness measured after the pad is balanced, after the compression load is reduced to 0.1 PSI. The empty volume reported in cc / g, is then determined. The empty volume is the reciprocal of the density of the pad in number minus the volume of fiber (0.95 cc / g). This empty volume is denoted as the number compressibility in the present. Very high values indicate a greater correspondence to humidity. The knuckle and pill test herein is a measure of the number of appearance defects (fiberballs) in a structure made of the fibers for which property is determined and carried out by the following procedure: a sample of fibers that is tested (13.5 grams of dry bone) with water to form two liters (o.675% consistency). The sample is allowed to soak for a minimum of five minutes. The mixture is then transferred to a Tappi disintegrator and mixed there for 2 minutes. The mixture is then diluted to 8 liters in a bucket. 5 sheets are then made by hand (each one approximately 1.3 grams) using a manual cup (covered screw mold), ie draining the water from a pulp suspension added to the manual leaf cup, through the screw of the same, leaving a sheet in the mold, count the knuckles and pills (fibers rolled and agglutinated upwards) of the wet leaves on a light box. If a large number of knuckles and pills are present, then these are counted in square inch area and multiplied by the total area (30.65 square inches per sheet made in a Papprix manual sheet cup and 31.3 square inches per one sheet made in a Tappi manual sheet cup). The readings on the 5 handmade sheets are averaged to provide the number of knuckles and pills. Very high values indicate many defects. The 5K density test is a measure of the stiffness of the fibers and the dry elasticity of a structure made from the fibers (ie, the ability of the structure to expand by releasing the compressive force applied, while the fibers are in a substantially dry condition), and is carried out according to the following procedure: a square pad placed in air of four inches by four inches, having a mass of about 7.5 g of the fibers for which Dry elasticity is determined, and compressed in a dry state by a hydraulic press at a pressure of 5,000 psi, and the pressure is released quickly. The pad is reversed and the pressure is repeated and released. The thickness of the pad is measured after pressing with an unloaded gauge (the thickness was tested in Ames thickness). Five thickness readings are taken, one in the center and 0.001 inches in each of the four corners and the five values are averaged. The pad is cut to four inches by four and then measured. The density after pressing is then calculated as mass / (area x thickness). This density is denoted as the 5K density in the present. The lowest of the values of the 5K density test, ie the density after the pressure occurs, the greater the fiber stiffness and the greater the dry elasticity. The drip capacity test herein is a combined measure of absorbency and absorbent capacity and is carried out here by the following procedure: a square pad placed in air of four inches by four inches having a mass is prepared of approximately 7.5 g, from the fibers for which the drip capacity is being determined and is placed on a screen mesh. Synthetic urine is applied to the center of the pad at a rate of 8 ml / sec. The flow of synthetic urine is stopped when the first drops of synthetic urine escape from the bottom or side of the pad. The drip capacity of the difference in mass of the pad before and subsequent to the introduction of synthetic urine divided by the mass of the fibers, on dry granulated base. The majority of the drip capacity is, the best of the absorbing properties. The conduction velocity test of the present is a measure of the speed at which the liquid is conducted through a pad of fibers that is tested and is determined here by the following procedure: a square pad placed in air is prepared four by four inches having a mass of approximately 3.5 g and a density of 0.2 g / cc, from fibers for which the fluid conduction velocity is determined. The test is carried out in a fluid conduction velocity tester. The conduction velocity tester comprises a container, two lower electrodes with pins for inserting through a sample, two upper electrodes with pins for inserting through a sample, two vertically oriented plates for placement in the container, and a controller of time to start when either of the two adjacent pins on the lower electrodes are in liquid contact and to stop when either of the two adjacent pins on the upper electrodes are in contact with the liquid. The synthetic urine is placed in the container of the fluid conduction velocity tester to provide a one-inch depth of synthetic urine there. The fiber pad that is tested, is placed between the plates of the fluid conduction velocity tester with the lower electrode pins that are "* inserted through the total thickness of the pad 7/12 inches from the bottom of the pad and the pins of the upper electrodes being inserted through the full thickness of the pad of 2 1/12 inches, from the bottom of the pad and the assembly is inserted into the body of synthetic urine in the tester container in such a way that the lower part of a third of an inch extends towards the synthetic urine.The fluid conduction velocity in cm / s is 3.81 (the distance between the upper and lower electrodes is in centimeters), divided by the driving time from the lower electrodes in the upper electrodes as indicated by the time setter.The most extensive driving speed, the s rádida fluid conduit. The term "synthetic urine" is used herein to mean a solution prepared from water and 10 g of sodium chloride per liter of water and 0.52 ml of a 1% aqueous solution of Triton X100 (a surfactant is octylphenoxypolyethoxy ethanol, available from Rohm & Haas Co.) per liter of drinking water. Synthetic urine should be at 25 ± 1% ° C when used. The air-laid pads referred to herein are made as follows: placement in air is carried out at an air placement of approximately 120 g of fiber in a 14 by 14 inch square on a piece of tissue and a second piece of tissue, is then placed on top of the mass placed in air to form a pad. The pad is pressed and trimmed in 4 by 4 inch squares. The term "defibration" and "defiberation" are used herein to refer to any process that can be used to mechanically separate fibers into substantially individual forms, although they are already in that form, ie the stage or steps of treating mechanically the fibers, either individually or in a more compacted form, where the treatment or treatments of fiber separation in a substantially individual form if they are not already in that form, and / or impart curling and twisting to the fibers in a dry state .

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 schematically represents a preferred method of contacting non-crosslinked fibers with an aqueous crosslinking composition. Figure 2 schematically represents a heating mode that causes moisture removal and the formation of ester crosslinks (curing) in the method herein.

DETAILED DESCRIPTION OF THE INVENTION As indicated above, the method of the present invention is to prepare individualized crosslinked cellulosic fibers having an amount having an effective amount of a C2-C9 polycarboxylic acid crosslinking agent, which reacts therein in the bonding form reticular of intrafiber ester and improves dry elasticity. The term "effective amount" is used herein to mean an amount to provide fibers that have a water retention value from about to 60. The Patent E.U.A. No. 5,137,537 indicates that it may be from about 0.5 mol% to about 10 mol% C2-C9 polycarboxylic acid crosslinking agent, calculated on a molar basis of anhydroglucose cellulose. The improved dry elasticity is a dry elasticity characterized by a 5K density of not more than 0.15 g / cm3, preferably not more than 0.12 g / cm3, typically ranging from 0.11 to 0.12 g / cm3, as compared to a density 5K higher when the benefits of the invention are not obtained. As indicated above, said method comprising the step of heating the cellulosic fibers without crosslinking to a moisture content ranging from 0 to 70%, preferably ranging from 30 to 40%, with from 1 to 15%, by weight on a citric acid base applied on a dry fiber base, C2-C9 polycarboxylic acid crosslinking agent, and from 0.005 to 1% by weight applied on a dry fiber basis, active surface agent, above them , to remove any moisture content and to cause the polycarboxylic acid crosslinking agent to react with the cellulosic fibers and form ester crosslinking between the cellulose molecules, to provide said crosslinked cellulosic fibers. In one embodiment, said method is carried out without washing or bleaching and washing the crosslinked fibers. Preferably, the C2-C9 polycarboxylic acid crosslinking agent is present in an amount of 3 to 12%, by weight on a citric acid base applied on a dry fiber basis, and the active surface agent is present in a amount of 0.01 to 0.2%, by weight applied on a dry fiber basis. Cellulosic fibers of various natural origins are applicable to the method herein. Digested fibers are preferably used from soft pulp, hard pulp or cotton waste. Esparto grass fibers, bagasse, hemp, flax or other lignáceas and sources of cellulosic fibers can also be used as raw material in the present. Typically, the fibers are wood pulp fibers made by chemical pulping processes. The fibers can be supplied in suspension, powder or in sheet form. The fibers are supplied as dry splicing, wet splicing or other laminated form can be disintegrated before contacting the fibers with the crosslinking agent, for example by stirring in water or by mechanical disintegration of the sheet. The fibers may also be provided in a wet or damp condition. Preferably, the fibers are obtained and used in the form of dry splicing. We will now refer to the crosslinking agents of C2-C9 polycarboxylic acid. These are organic acids containing two or more carboxyl groups (COOH) and from 2 to 9 carbon atoms in the chain or in the ring to which the carboxyl groups are attached; the carboxyl groups are not included when determining the number of carbon atoms in the chain or ring (for example, the acid, 1,2,3, tricarboxylic propan, would be considered to be a C3 polycarboxylic acid, which contains three carboxyl groups and the 1,2,3,4 butane tetracarboxylic acid should be considered to be a C4 polycarboxylic acid, containing four carboxyl groups). More specifically, the C2-C9 polycarboxylic acids, suitable for use as crosslinking agents in the present invention, include aliphatic and alicyclic acids, either saturated or olefinically unsaturated with at least three, and preferably more carboxylic groups per molecule or with two carboxyl groups per molecule if the carbon-carbon double bond is present alpha, beta, to one or both carboxyl groups. A further requirement is that to be reactive in the esterification of hydroxyl cellulose groups, a given carboxyl group in an aliphatic or alicyclic polycarboxylic acid, must be separated from a second carboxyl group by not less than two carbon atoms and not more than three. carbon atoms. Without being bound by the theory, from these requirements it appears that a carboxyl group which is reactive, must be capable of forming a cyclic 5- or 6-membered anhydride ring with a neighboring carboxyl group in the polycarboxylic acid molecule. Where two carboxyl groups are separated by a carbon-carbon double bond, or both are connected to the same ring, the two carboxyl groups must be in the cis configuration, in relation to each other if they are to interact in this way. Accordingly, a reactive carboxyl group is a carboxyl group separated from a second carboxyl group by not less than 2 carbon atoms and not more than 3 carbon atoms, if where two carboxyl groups are separated by a carbon-carbon double bond, or are both connected to the same ring, a reactive carboxyl group, must be in the cis configuration to another carboxyl group. In aliphatic polycarboxylic acids containing three or more carboxyl groups per molecule, a group is attached '- hydroxyl to an atom of the alpha carbon to a carboxyl group not interfering with the esterification and crosslinking of the cellulosic fibers by the acid. Therefore, polycarboxylic acids, such as citric acid (also known as 2-hydroxy-1,2,3-propanedicarboxylic acid), and monosuccinic tartrate acids, are suitable as crosslinking agents in the present invention. The aliphatic or alicyclic C2-C9 polyocarboxylic acid crosslinking agents may also contain an oxygen or sulfur atom or atoms in the chain or ring to which the carboxyl groups are attached. Accordingly, polycarboxylic acids such as oxydisuccinic acid, also known as 2, 2-oxybis (butanodicaic), thiodisuccinic acids, and the like, this means that they are included, within the scope of the invention. For purposes of the present invention, oxydisuccinic acid would be considered to be a C4 polycarboxylic acid, containing four carboxyl groups. Examples of specific polycarboxylic acids falling within the scope of the present invention include the following: maleic acid, citraconic acid, also known as methyl maleic acid, citric acid, itaconic acid, also known as methylenesulic acid, tricarboxylic acid also known as acid 1,2,3-propanedicarboxylic acid, transaconitic acid also known as trans-1-phenyl-1,2,3-tricarboxylic acid, 1,2,3,4-butane-tetracarboxylic acid, cis- 1, 2, 3, 4 acid -cyclopentantetra-carboxylic acid, mellitic acid, also known as benzenecarboxylic acid, and oxydisuccinic acid, also known as 2,2'-oxybis (butanedioic acid). The above list of specific polycarboxylic acids is for exemplary purposes only, and it is not intended that they are all included. Importantly, the crosslinking agent must be capable of reacting with at least two hydroxyl groups in the vicinity of the cellulose chains in a simple cellulosic fiber. Preferably, the C2-C9 polycarboxylic acids, used herein are aliphatic, and saturated, and contain at least three carboxylic groups per molecule. A group of preferred polycarboxylic acid agents for use with the present invention include citric acid also known as 2-hydroxy-1,2,3-propanedicarboxylic acid, 1,2,3-propanedicarboxylic acid and 1,2,3-acid. , 4 butane tetracarboxylic. Citric acid is especially preferred, because it has provided fibers with high levels of wettability, absorbency and elasticity, and is safe and non-irritating to human skin, and has provided stable crosslinking bonds. In addition, citric acid is available in large quantities at relatively low prices, thereby making it commercially feasible as the crosslinking agent. Another group of preferred crosslinking agents for use in the present invention include C2-C0 polycarboxylic acids, which contain at least one oxygen atom in the chain to which the carboxylic groups are attached. Examples of these compounds include monosuccinic tartrate acid having the structural formula and disuccinic tartrate acid that has the structural formula -: > 4 - A more detailed description of monosuccic tartrate acid, disuccinic tartrate acid, and salts thereof, can be found in Bushe et al. In U.S. Pat. No. 4,663,071, issued May 5, 1987, incorporated herein by reference. Those with knowledge in the area of polycarboxylic acids, will recognize that the crosslinking agents of C2-C9 polycarboxylic acid, aliphatic and alicyclic > "<" described above, can be reacted in a variety of ways to form the crosslinked fibers used herein, such as the free acid form, and salts thereof. Although the free acid form is preferred, all of such forms are so meant to be included within the invention plan. We now point to active surface agents.

The active surface agent distributed over the crosslinked titanium fibers may be a surfactant, cationic or anionic, zwitterionic, ampholitic, nonionic, water soluble agent, or combinations thereof. Nonionic surfactants are preferred. The preferred active surface agents of a group (sold under the Trade Name of Pluronic and described hereinafter), provide a surface tension at a level of 0.1% in water at 25C ranging from 42 to 53 dynes / cm. Preferred active surface active agents of another type (sold under the tradename Neoldol and described hereinafter) provide a surface tension at a level of 0.1% in water at 76 ° F of 28 to 30 dynes / cm. A class of nonionic surfactants consists of polymeric, polyoxyethylene polyoxypropylene compounds based on ethylene glycol, propylene glycol, glycerol, trimethylolpropane or ethylenediamine as the hydrogen compound of initiator reagent. Preferred surfactants in this class are the compounds formed by the ethylene oxide condensate, a hydrophobic base formed by the condensation of propylene oxide with propylene glycol. The average molecular weight of the surfactant usually varies from about 1,000 to 15,000 gr / mol and the molecular weight of the hydrophobic portion generally falls on the scale of about 900 to 4,000 gr / mol. Preferably, the average molecular weight of the surfactant varies from about 1,000 to 5,000 g / mol, the molecular weight of the hydrophobic poly (oxy-propylene) varies from 900 to 2,000 g / mol, and from the hydrophilic poly (oxyethylene) unit , an amount ranging from 10% to 80% by weight of the total molecule is present. Synthetic nonionic surfactants are commercially available by the Trade Name of Pluronic, and are supplied by Yandotte Chemicals Corporation. Especially preferred nonionic surfactants are Pluronic L31 (the average molecular weight of the surfactants of 1,100 g / mol, the molecular weight of the hydrophobic poly (oxypropylene) of 950 g / mol, and 10% of the poly (oxyethylene) unit). hydrophilic in weight in the total molecule), Pluronic L35 (average molecular weight of 1,900 g / mol, hydrophobic poly (oxypropylene) molecular weight of 950 g / mol, and 50% of the hydrophilic poly (oxyethylene) unit by weight in the total molecule), Pluronic L62 (average molecular weight of surfactant of 2,500 g / mol, hydrophobic poly (oxypropylene) molecular weight of 1,750 g / mol, and 20% of the hydrophilic poly (oxyethylene) unit by weight in the total molecule), and Pluronic F38 (average molecular weight of surfactant of 4,700 g / mol, hydrophobic poly (oxypropylene) molecular weight of 950 g / mol, 80% of the hydrophilic poly (oxyethylene) unit by weight in the molecule total). The surface tensions for aqueous solutions at 0.1% of these 25 ° C surfactants are as follows: Pluronic L31, 46.9 dynes / cm; Pluronic L35, 48.8 dynes / cm; Pluronic L62, 42.8 dynes / cm; Pluronic F38, 52.2 dynes / cm, the most preferred is Pluronic L35. Another class of nonionic surfactants consists of the condensation products of primary or secondary aliphatic alcohols or fatty acids having from 8 to 24 carbon atoms, either straight chain or branched chain configurations with from 2 to about 50 moles of ethylene oxide per mole of alcohol. Aliphatic alcohols comprising from 12 to 15 carbon atoms are preferred with from about 5 to 15, most preferably from about 6 to 8 moles of ethylene oxide per mole of aliphatic compound. Preferred surfactants are prepared from primary alcohols that are either linear such as those derived from natural fats or prepared by the Ziegler process, from ethylene, for example myristyl, cetyl, or stearyl alcohols, for example Neodoles. , (Neodol, which is a Commercial Name of Shell Chemical Company), or partially branched, such as Lutensols, (Lutensol, which is a Trade Name of BASF) and Dobanols (Dobanol which is a Commercial Name of Shell), which have approximately 25% 2-branched methyl, or Synperonics, which are understood to have approximately 50% of 2-methyls amides (Synperonic, which is a Commercial Name of ICI), or primary alcohols that have more than 50% of the branched chain structure, sold under the Trade Name of Lial, by Liquichmica . Specific examples of non-ionic surfactants falling within the scope of the invention include Neodol 23-6.5, Neodol 25-7, Dobanol 45-4, Dobanol 45-7, Dobanol 45-9, Dobanol 91-2.5, Dobanol 91- 3, Dobanol 91-4, Dobanol 91-6, Dobanol 91-8, Dobanol 23-6.5, Synperonic 6, Synperonic 14, condensation products of coconut alcohol, with an average of between 5 and 12 moles of ethylene oxide per mole of alcohol, the alkyl portion of the coconut having from 10 to 14 carbon atoms, and the condensation products of the bait alcohol, with an average of between 7 and 12 moles of ethylene oxide per mole of alcohol, the bait containing between 16 and 22 carbon atoms. The secondary alkyl alkyl ethoxylates are also suitable in the present compositions, especially those ethoxylates of the Tergitol series, having from about 9 to 15 carbon atoms in the alkyl group and up to about 11, especially from about 3 to 9 residues. of ethoxy per molecule. Especially preferred nonionic surfactants of this class are Neodol 23-6.5 which is a C12-C13 linear alcohol, ethoxylated with an average of 6.7 moles of ethylene oxide per mole of alcohol and has a molecular weight of 488 g / mol and Neodol 25-7, which is an ethoxylated C12-C15 linear alcohol with an average of 7.3 moles of ethylene oxide and has a molecular weight of 524 g / mol. The surface tension for 0.1% solutions of Neodol 23-6.5 and Neodol 25-7 at 76 F, in distilled water are respectively 28 dynes / cm and 30 dynes / cm. Another class of nonionic surfactants consists of the polyethylene oxide condensates of alkylphenols, for example condensation products of alkylphenols having an alkyl group containing from 6 to 20 carbon atoms, either in a straight chain or in a of branched chain, with ethylene oxide, said ethylene oxide, being present in equal amounts of 4 to 50 moles of ethylene oxide per mole of alkyl phenol. Preferably the alkyl phenol contains from about 8 to 18 carbon atoms in the alkyl group, and from about 6 to 15 moles of ethylene oxide per mole of alkyl phenol. The alkyl substituent in said compounds can be derived, for example, from polymerized propylene, di-isobutylene, octene and nonene. Other examples include condensates of dodecylphenol with 9 moles of ethylene oxide per mole of phenol, condensates of dinonylphenol with 11 moles of ethylene oxide per mole of phenol; condensates of nonylphenol with 11 moles of ethylene oxide per mole of phenol; condensates of nonylphenol and di-isoctylphenol with 13 moles of ethylene oxide. Another class of nonionic surfactants are ethoxylated alcohols or acids or condensates of polyoxypropylene, polyoxyethylene which are capped with propylene oxide, butylene oxide, and / or short chain alcohols and / or short chain fatty acids, for example those containing from 1 to about 5 carbon atoms, and mixtures thereof; another class of nonionic surfactants are non-ionic semi-polar surfactants including water-soluble amine oxides containing an alkyl apportion of about 10 to 18 carbon atoms, and two selected portions of group consisting of alkyl portions and hydroxyalkyl from about 1 to 3 carbon atoms; water-soluble phosphine oxides containing an alkyl portion of about 10 to 18 carbon atoms and two portions selected from the group consisting of alkyl groups and hydroxyalkyl groups, containing from about 1 to 3 carbon atoms; and its ague soluble oxides containing an alkyl portion of about 10 to 18 carbon atoms and one selected from the group consisting of alkyl and hydroxyalkyl portions of about 1 to 3 carbon atoms. Ampholytic surfactants include aliphatic derivatives, or aliphatic derivatives of heterocycle, secondary and tertiary amines in the aliphatic portion can be straight or branched chain and where one of the aliphatic substituents contains from about 8 to 18 carbon atoms and by at least one aliphatic substituent contains an anionic water solubilizing group.

Zutionionic surfactants include derivatives of aliphatic, phosphonium and sulfonium quaternary ammonium compounds, in which one of the aliphatic substituents contains from about 8 to 18 carbon atoms. Useful anionic surfactants include water soluble salts of higher fatty acids, i.e., soaps. These include alkali metal soaps, such as sodium, potassium, ammonium, and alkylolammonium salts of higher fatty acids containing from about 8 to 24 carbon atoms and preferably from about 12 to 18 carbon atoms. Soaps can be made by direct saponification of oil grease or by neutralization of free fatty acids. Particularly useful are the sodium and potassium salts of the fatty acid mixtures, derived from coconut oil and bait, that is, coconut soap and sodium or potassium bait. Useful anionic surfactants also include water-soluble salts, preferably the alkali metal, ammonium and alkylolammonium salts of organic sulfuric reaction products, which have in their molecular structure an alkyl group consisting of about 20 carbon atoms. carbon and a sulfonic acid or a sulfuric acid ester group. (Included in the term "alkyl" is the alkyl portion of acyl groups), examples of this group of synthetic surfactants, are sodium alkyl potassium sulfate, especially those obtained by sulfation of higher alcohols (carbon atoms C8- C18, such as those produced by the reduction of the glycerides of the bait or coconut oil, and the alkylbenzene potassium sulfonates, in which the alkyl group contains from about 9 to 15 carbon atoms, straight chain or chain configuration branched, for example, those of the type described in US Patent Nos. 2,220,099 and ** -2,477,383. Particularly valuable are linear straight-chain alkylbenzene sulfonates in which the average number of carbon atoms in the alkyl group is about 11 to 13, abbreviated as C11-C13 LAS Other anionic surfactants herein, are the glyceryl alkyl sodium sulfonates, sodium ially those ethers of higher alcohols derived from coconut oil and bait; the fatty acid monoglyceride sulfates and sulphonates of sodium coconut oil; potassium or sodium salts of ether sulfates, of ethylene oxide alkylphenol containing about 1 to 10 units of ethylene oxide per molecule and where the alkyl groups contain from about 8 to 12 carbon atoms; sodium or potassium salts of alkyl ethylene oxide ether sulfate containing from about 1 to 10 ethylene oxide units per molecule, and wherein the alkyl group contains from about 10 to about 20 carbon atoms. Other anionic surfactants useful herein, include water soluble salts of alphasulfonated fatty acid esters containing from about 6 to 20 carbon atoms in the fatty acid group and from about 1 to 10 carbon atoms in the ester group; water-soluble salts of 2-acyloxyalkano-sulfonic acids containing from about 2 to 9 carbon atoms in the acyl group and from about 9 to 23 carbon atoms in the alkane portion; water-soluble salts of sulfonates of olefin and paraffin containing from about 12 to 20 carbon atoms, and alean beta-alkyloxy sulphonates containing from about 1 to about 30 carbon atoms in the alkyl group and from about 8 to 20 carbon atoms in the alkane portion The cationic surfactants herein comprise a variety of compounds characterized by one or more hydrophobic organic groups in the cation and generally by a quaternary nitrogen associated with the acid radical., are also considered quaternary nitrogen compounds. Suitable anions are halides, methyl sulfate and hydroxyl. Tertiary salines may have characteristics similar to cationic surfactants in solutions of PH values of less than about 8.5. A more complete description of these and other cationic surfactants useful herein can be found in the US patent. No. 4,228,044, Cambre, issued October 14, 1980, incorporated herein by reference. As previously indicated, the active surface agent is preferably applied to the cellulosic fibers before the crosslinking reactions occur with the C2-C9 polycarboxylic acid crosslinking agent. Most preferably, the individualized crosslinked cellulosic fibers with active surface agent therein are prepared in a process comprising curing the uncrosslinked cellulosic fibers with from 1% to 15%, preferably 3% to 12%, of crosslinking agent. of C2-C9 polycarboxylic acids, by weight on the basis of citric acid applied on a dry fiber basis, and from about 0.005% to 1%, preferably from 0.01% to 0.2% of active surface active agent by weight, applied on a dry fiber base, on it, to cause the polycarboxylic acid crosslinking agent to react with the cellulosic fibers and form ester crosslinking between the celluloses molecules, to form said crosslinked cellulosic fibers with active surface agent therein, without washing of the crosslinked fibers or the bleaching and washing of the crosslinked fibers. As indicated above, the preparation of the non-crosslinked cellulosic fibers with C2-C9 polycarboxylic acid and active surface agent thereon, for the heating step of the present, preferably comprises contacting the non-crosslinked cellulosic fibers with a aqueous crosslinking composition containing the C2-C9 polycarboxylic acid crosslinking agent in an amount to provide from 1 to 15% thereof, by weight, on a citric acid base applied on a dry fiber basis, in the* fibers subjected to said heating step and containing active surface agent in the amount to provide 0.005 to 1% thereof, by weight, applied on a dry fiber basis, in the fibers subjected to said heating step. Preferably, the C2-C9 polycarboxylic acid crosslinking agent is present in the aqueous crosslinking composition in an amount to provide 3 to 12% thereof, by weight, on a base of citric acid applied on a fiber base. dry, in the fibers subjected to said heating step. The highest amount of said crosslinking agent present in the fibers subjected to the heating step, the greatest amount of crosslinking is obtained. Preferably, the active surface agent is present in the aqueous crosslinking composition in an amount to provide 0.01 to 0.2% thereof, by weight, applied on a dry fiber basis, in the fibers subjected to the heating step. If the active agent is used insufficiently, the benefits of the invention are not obtained. If too much active surface agent is used, the rate of fluid conduction in the product made of crosslinked fibers can be reduced to an undesirable level. The pH for the aqueous crosslinking composition can be, for example, from 1 to 5.0. PH below 1 is corrosive to the processing equipment. PHs above 5 provide an impractically slow reaction rate. The esterification reaction will not occur at alkaline pH. The increase in pH reduces the reaction rate. Most preferably, the pH varies from 1.5 to 3.5. The pH is easily adjusted upwards if necessary by the addition of a base, for example, sodium hydroxide. The catalyst is preferably included in said aqueous crosslinking composition to increase the speed of the crosslinking reaction and to protect the gloss. The catalyst can be any that catalyzes the crosslinking reactions. Applicable catalysts include, for example, alkali metal hypophosphites, alkali metal phosphites, alkali metal polyphosphates, alkali metal phosphates, and alkali metal sulfates. Especially preferred catalysts are alkali metal hypophosphites, alkali metal polyphosphates, and alkali metal sulfates. The mechanism of the catalysis is known, although the catalysts may be functioning as regulating agents, keeping the pH levels within the desired scales. A more complete list of catalysts useful herein can be found in Welch et al., U.S. Pat. No. 4,820,307, issued April 1989, incorporated herein by reference. The selected catalyst can be used as the catalyst agent alone, or in combination with one or more other catalysts. The amount of catalyst preferably used is, of course, dependent on the particular type and amount of crosslinking agent and the reaction conditions of the cure, especially temperature and pH. In general, based on technical and economic considerations, catalyst levels of between about 5% by weight and about 80% by weight are preferred based on the weight of the crosslinking agent added to the cellulosic fibers. For example purposes, in the case where the catalyst used is sodium hypophosphite and the crosslinking agent is citric acid, a catalyst level of about 25% by weight, based on the amount of citric acid added, is preferred. The contacting of the cellulosic fibers with the aqueous crosslinking composition must be carried out in order to obtain uniform distribution and penetration of the crosslinking composition onto the fibers. Preferably contacting the crosslinked cellulose fibers with the aqueous crosslinking composition is carried out as illustrated schematically in Figure 1. With reference to Figure 1, a sheet of crosslinked cellulosic fibers is transported along a line of passage 10 in the direction indicated by the head of arrow 12 by the rotation of pressure rollers 14 in the directions indicated by arrows 16. A body of composition Aqueous crosslinking 18 is maintained in the holder between the rollers. The fiber sheet is transported through the body of the aqueous crosslinking composition to impregnate the fiber sheets with the aqueous crosslinking composition. The uncrosslinked cellulosic fiber sheet enters the body of aqueous crosslinking composition which normally has a moisture content ranging from 0 to 10%. The time of the fiber sheet in the body of the aqueous crosslinking composition is determined by the speed of rotation of the rolls 14, and the pressure of the rolls 14 is exerted on the fiber sheet passing therethrough, are regulated such that the appropriate amount of C2-C9 polycarboxylic acid crosslinking agent and the active surface agent as specified here above are present on the fibers for the heating step. Preferably, this is carried out to provide on the fiber sheet exiting the press rolls, an amount of aqueous crosslinking composition that provides a consistency of 30 to 80% or more (e.g., up to 85 or 90% or still 95%), preferably from 40 to 70%, depending on the initial moisture content, and the concentration of the crosslinking agent and the active surface agent, in the aqueous crosslinking composition, preferably to provide an object consistency for the treatment in the heating step. The speed of the press cylinder is normally regulated to provide a time interval of the uncrosslinked fiber sheet within the body of the aqueous crosslinking composition ranging from 0.005 to 60 seconds, preferably from 0.05 to 5 seconds. In a less preferred alternate embodiment, the sheet of non-crosslinked fibers is impregnated with the aqueous crosslinking composition to provide the foregoing consistencies, by spraying. In any case, the liquid content of the impregnated sheet is optionally adjusted by pressure mechanically and / or by air drying. The sheet impregnated with fibers, with optional adjustment of liquid content as mentioned above, is preferably subjected to defibration before treatment in the heating step. Preferably, the defibration is done by a method where knot formation and distress are minimized, and fiber damage. Typically, a commercially available disk refiner is used. Another type of device that has been found to be useful for defibrating cellulosic fibers is the three-stage sponge device, described in US Pat. No. 3,987,968, issued to D.R. Moore and 0. A. Shields, October 26, 1976, said patent being incorporated herein by reference in this disclosure. The sponge device described in described in the patent E.U.A. No. 3,987,968 subjected the wet cellulosic pulp fibers to a combination of mechanical impact, mechanical agitation, agitation with air and a limited amount of air drying to create a substantially knot-free fluff. Other applicable methods of defibration include, but are not limited to, treatment in a Waring softener, which makes tangential contact with the fibers with a rotating wire brush and a hammer mill. Preferably, a stream of air is directed to the fibers during said defibration to assist in the separation of the fibers in substantially individualized form. In spite of the particular mechanical device used to form the fluff, the fibers are preferably mechanically treated as initially containing between about 40% and 70% moisture. The individualized fibers have imparted to this an improved degree of twisting and curling in relation to the amount of twist and curl naturally present in such fibers. It is believed that this additional twisted and curled improves the elastic character of the structures made from the crosslinked fibers. The result of the defibration is referred to herein as the defibrated mixture. The defibrated mixture is easy for the heating step. The impregnated sheet can be treated, for example, in a pre-trigger (for example, a screw conveyor) to disintegrate it, before the defibration. In examples of this method, a fiber sheet of 0-10% moisture content (eg, 6% moisture content is transported through the body of the crosslinking composition to produce on the output side of the rolls , a sheet of fibers impregnated with 60% consistency or 80% consistency that is subjected to defibration or a sheet of fibers impregnated with 40% consistency that is dried with air at 60% consistency and then undergoes defiberization) a less preferred alternate embodiment, the impregnated fiber sheet is treated in the heating step without prior disintegration as described above, to produce a sheet of crosslinked cellulosic fibers, which optionally are subjected to defibration after the heating step. The contact of the non-crosslinked cellulose fibers with the aqueous crosslinking composition can also be carried out by forming a suspension of the non-crosslinked fibers in an unlimited form in the aqueous crosslinking composition, of consistency ranging from 0.1% to 20%, very preferably from 2% to 15%, and maintaining the suspension for about 1 to 240 minutes, preferably for 5 to 60 minutes. The suspension can be formed, for example, by causing a dry overlap sheet to disintegrate by agitating it in the aqueous crosslinking composition. The step of removing the liquid is normally close to being carried out to increase the consistency of a suitable stage for the heating step. This is preferably carried out by dehydrating "'" "(removing the liquid) to provide a consistency ranging from about 30% to 80%, most preferably ranging from about 40% to 50%, and optionally after further drying. By way of example, dehydration can be carried out by such methods as pressure or centrifugation mechanically.The product of dehydration is typically denoted as cake.Changing now to the stage where the cake can be further dried.This is typically taken to This is to provide a consistency within a consistency range of about 35% to 80%, preferably to provide a consistency ranging from 50% to 70%, and is preferably made under conditions such that the use of high temperatures is not required. for an extended period of time, for example, by a method known in the art as air drying. high and the time in this step can result in the drying of the fibers beyond 80% consistency, thus possibly producing an undesirable amount of damage to the fiber during a subsequent defibration. The term "reduced liquid mixture" as used herein refers to the product of the liquid removal step. The reduced liquid mixture is typically subjected to defibration performed as described above with respect to an impregnated sheet, except that the reduced liquid mixture is subjected to defibration in place of the impregnated sheet. The result of the defibration is referred to herein as the defibrated mixture. The defibrated mixture or the reduced mixture of liquid in the case where defibration is omitted, is ready for the heating step. Referring now to the heating of uncrosslinked cellulosic fibers at a moisture content ranging from 0 to about 70%, preferably ranging from 30 to 40%, with from 1 to 15%, preferably from 3 to 12%, by weight on a citric acid base applied on a dry fiber base, of C2-C9 polycarboxylic acid crosslinking agent, and from 0.005 to 1%, preferably 0.01 to 0.2%, by weight applied on a dry fiber basis , of active surface agent, above them, to remove any moisture content and to cause the crosslinking agent of polycarboxylic acid to react with the cellulosic fibers and form ester crosslinking between the cellulose molecules to provide said cross-linked cellulose fibers . In the case of fibers treated in an unlimited way, for example, defibrated fibers (fluff), a part of removal of the water content of the heating step can be carried out in a first apparatus to dry to a consistency ranging from 60% to 100%, for example, by a method known in the art as instant drying. This is carried out by transporting the fibers in a hot air stream, for example, at an inlet air temperature ranging from 93 ° C to 399 ° C, preferably at an air inlet temperature of 149 ° C at 288 ° C, until the object consistency is reached. This imparts an additional twist and twist to the fibers while the water is removed from them. Although, the amount of water removed by this drying step can be varied, it is believed that instant drying at high consistencies on the scale of 60% to 100% provides a higher level of twisted and curled fiber that makes instant drying a a consistency at the bottom of the scale 60% -100%. In preferred embodiments, the fibers are dried to approximately 85% -95% consistency. The instant drying of the fibers to a consistency, such as 85% -95%, in a larger part of the 60% -100% scale, reduces the amount of drying that must be carried out following the instant drying. The subsequent part of the heating step, or all of the heating step if instantaneous drying is omitted, may involve heating for a period ranging from 5 seconds to 2 hours at a temperature ranging from 120 ° C to 280 ° C ( temperature of the air in the heater), preferably at a temperature ranging from 145 ° C to 190 ° C (air temperature in the heater) for a period ranging from 2 to 60 minutes in a continuous air apparatus through drying / curing (the hot air passes perpendicularly through a traveling bed of fibers) or in a static oven (the fibers and the air remains immobile is a container with a static heating medium), or other heating apparatus, to remove any remaining moisture content and cause the crosslinking reaction that occurs to rigidify the fibers as a result of intrafiber crosslinking. The heating should be such that the temperature of the fibers does not exceed approximately 227 ° C since the fibers can explode in flames at this temperature. The aggregate is heated for an effective period of time to remove any remaining moisture content and cause the crosslinking agent to react with the cellulosic fibers. The extent of the reaction depends on the drying of the fiber, the time in the heating apparatus, the temperature of the air in the heating apparatus, the pH, the amount of the crosslinking agent and the method used to heat. Cross-linking at a particular temperature will occur at a higher value for fibers of a certain initial moisture content with drying / curing of air through, continuous, than with drying / curing in a static oven. Those skilled in the art will recognize that there are countless temperature-time relationships. The temperature from about 140 ° C to about 165 ° C (air temperature in the heating apparatus) for periods of between about 30 minutes and 60 minutes, under static atmospheric conditions will generally provide acceptable drying / curing efficiencies for fibers having contents humidity less than 10%. It will also be appreciated by those skilled in the art that at elevated temperatures and forced air convection (air heating through) the time required decreases. Accordingly, temperatures that range from about 170 ° C to about 190 ° C (air temperature in the heating apparatus) for periods of between about 2 minutes and 20 minutes, in an air-through furnace will also generally provide acceptable efficiencies drying / curing for fibers that have moisture contents of less than 10%. In an alternative to complete the heating after an initial instantaneous drying step, the instant drying and curing (or only curing, if the instant drying provides 100% consistency of the effluent) are carried out in the apparatus as described in Figure 2. With reference to Figure 2, a stream 20 of air and fibers of 90 to 100% consistency, from an instant dryer, are drawn to a cyclone separator 22 that separates the air and fibers, discharging the air upwards. as indicated by the arrow 26 to a duct discharging into a duct 30. Hot air (e.g. 400oF) from an oven is directed to duct 30 which contains at least one U-shaped portion, as described, to provide a travel path that provides sufficient residence time to cause the removal of any moisture content and to cause the crosslinking reaction occurring between the fibers and the crosslinking agent of C2-C9 polycarboxylic acid. The duct 30 discharges into a cyclonic separator 33 that separates air and fibers, discharging the air upward as indicated by arrow 34 and the cross-linked, dried, cellulosic fibers downward as indicated by arrow 36. If needed or desired, cause additional cross-linking which occurs, for example, in an oven Subsequent air through or static oven. The apparatus for the initial instantaneous drying step can also be of the same type of apparatus as described in Figure 2 in such a way that two or more assemblies for said apparatuses are used in series as required by the need to provide fresh dry air during the course of drying and curing. The resultant crosslinked fibers (i.e., produced by any of the alternatives described above for the application of the heating step to the fibers in an unlimited form) are optionally moistened, for example, by spraying with water to provide a moisture content of 5 to 10%. fifteen%. This makes the fibers more resistant to damage that are at risk of occurring due to subsequent handling or due to processing in the manufacture of absorbent products from the fibers. Referring now to the case where the heating step is carried out on the fibers in the sheet form to dry the fibers and cause the crosslinking reactions to occur. The same times and temperatures are applied as described above for the fibers in unlimited form. Preferably, heating is carried out at 145 ° C to 190 ° C (air temperature in the heating apparatus) for 2 to 60 minutes. After curing, the crosslinked fibers are optionally wetted at a moisture content of 5 to 15% to provide resistance to handling damage and optionally converted to substantially individualized form. The conversion to the individualized form can be carried out using a commercially available disc refiner or by treatment with a fiber spreading apparatus, such as that described in the U.S. Patent. No. 3,987,968, incorporated herein by reference. One effect of curing in the sheet form is that the fiber to fiber bond restricts the twist and curl fibers compared to where the individualized crosslinked fibers are made with curing under substantially unrestricted conditions. Fibers made in this manner would be expected to provide structures exhibiting lower absorbency and wettability than in the case of fibers cured in an unrestricted manner. Another embodiment is similar as the embodiments described above except that the steps of (a) washing or (b) blanching and washing are included. The advantage of the invention in this embodiment lies in the reduced requirements for defibration with a particular correspondence to humidity and improved dry elasticity. A washing sequence comprises allowing the fibers to soak in an aqueous wash solution for a considerable time, for example 30 minutes to 1 hour, filtering the fibers, dehydrating the fibers, for example centrifuging, at a consistency of between about 50% and approximately 80%, defibrating dehydrated fibers and drying with air. Preferably, a sufficient amount of acidic substance is added to the wash solution to maintain the wash solution at a pH of less than about 7 to inhibit the reversal of crosslinking. This washing sequence has been found to reduce the free, residual crosslinking agent content. Any bleaching is normally carried out without a substantial decrease in the content of the C2-C9 polycarboxylic acid moiety. This is done, for example, by using an acid bleaching agent, for example, chlorine dioxide. An example of bleaching with chlorine dioxide is as follows: the crosslinked fibers are mixed with water to provide 10% consistency (10 grams of fiber to 90 grams of water). The chlorine dioxide is added to the mixture to obtain 3% available chlorine. This mixture is maintained at 70oC for 180 minutes. Then the mixture is dehydrated by centrifugation, washed and dried. The invention is illustrated by the following examples. In all the examples and reference examples, the WRV of the resulting fibers is about 35. In the examples, wet compressibility, 5K densities, knuckles and pills, drip capacities and fluid conduction velocity, are determined as is stable here later.

REFERENCE EXAMPLE 1 Three hundred grams (on a dry bone base, i.e., moisture free base) are dispersed from soft southern pulp Kraft fibers in the form of dry splice sheets, in an aqueous solution containing 551.57 gr. of citric acid, 137.89 of sodium hyposphosphite, and 63 gr. of sodium hydroxide, submerging and mixing with a wheel mixer, to form a 2.5% consistency suspension. The fibers were soaked in the suspension for approximately 30 min. This mixture was centrifuged to provide a dehydrated cake of approximately 44% consistency. The dehydrated cake, which contains about 6% by weight of citric acid on a dry fiber basis, was dried with air at approximately 50% consistency. The air dried cake was fluffed in a disk refiner at a speed of 60 g / min, dried instantaneously to a consistency of 90% and heated for 6 min. at an air temperature of 350 degrees Fahrenheit in an air oven through, and then it is cooled with air with a fan to less than 150 oF. There was neither washed nor bleached after healing. The results of the test indicate a wet compressibility of 6.6 cm3 / g, a 5K density of 0.137 g / cm3, 157 knuckles and pills, a drip capacity of 11.3 g / g and a fluid conduction velocity of 0.79 cm / sec .

Reference Example 2 Esterified fibers were prepared as in the example I reference, except that the speed through the disk refiner was 180 g / min. The test results indicate a compressibility in number of 6.6 cm3 / gr. a density 5% of 0.144g / cm3, 567 knuckles and pills, a drip capacity of 10.6 g / g, and a fluid conduction velocity of 0.73 cm / sec.

Example I Esterified fibers were prepared as in reference example I, except that Pluronic L35 was included. The dehydrated cake contained about 6% by weight of citric acid on a dry fiber basis, and about 0.075% Pluronic L35 on a dry fiber basis. The results of the test indicate a number compressibility of 7.1 cm3 / g, a 5K density of 0.12 g / cm3, 7 knuckles and pills, a drip capacity of 11.3 g / g and a fluid conduction velocity of 0.55 cm / sec.

Example II Esterified fibers were prepared as in reference example II, except that 2.30 gr. of Pluronic L35 to provide 0.025% Pluronic L35 in the dehydrated cake on a dry fiber basis. The test results indicate a compressibility in number of 6.92 cm3 / gr, a 5K density of 0.116 gr / cm3, 17.8 knuckles and pills, a drip capacity of 11.68 gr / gr and a fluid conduction velocity of 0.59 cm / sec .

Example III Esterified fibers were prepared, as in Example II, except that 4.60 g of Pluronic L35 was included to provide 0.05% Pluronic L35 in the dehydrated cake on a dry fiber basis. The test results indicate a compressibility in number of 7.25 cm3 / gr, a 5K density of 0.118 gr / cm3, 4.6 knuckles and pills, a drip capacity of 12.55 gr / gr and a fluid conduction velocity of 0.53 cm / sec .

Example IV Esterified fibers were prepared, as in Example II, except that 6.89 g of Pluronic L35 was included to provide 0.075% Pluronic L35 in the dehydrated cake on a dry fiber basis. The test results indicate a number compressibility of 7.31 cm3 / gr, a 5K density of 0.113. gr / cm3, 6.8 knuckles and pills, a drip capacity of 12.73 gr / gr and a fluid conduction velocity of 0.64 cm / sec.

Example V Esterified fibers were prepared, as in Example II, except that 9.19 gr of Pluronic L35 was included to provide 0.10% Pluronic L35 in the dehydrated cake on a dry fiber basis. The test results indicate a compressibility in number of 7.05 cm3 / gr, a 5K density of 0.115. gr / cm3, a drip capacity of 11.55 gr / gr and a fluid conduction velocity of 0.55 cm / sec.

Example VI Esterified fibers were prepared, as in Example II, except that 6.89 g of Pluronic L31 was included to provide 0.075% Pluronic L31 in the dehydrated cake on a dry fiber basis. The test results indicate a compressibility in number of 7.05 cm3 / gr, a 5K density of 0.114. gr / cm3, 3.6. knuckles and pills, a drip capacity of 10.87 gr / gr and a fluid conduction velocity of 0.61 cm / sec.

Example VII Esterified fibers were prepared, as in Example II, except that 4.60 g of Pluronic F38 was included to provide 0.05% Pluronic F38 in the dehydrated cake on a dry fiber basis. The test results indicate a compressibility in number of 7.38 cm3 / gr, a 5K density of 0.123 gr / cm3, 6.4 knuckles and pills, a drip capacity of 11.77 gr / gr and a fluid conduction velocity of 0.65 cm / sec .

Example VIII Esterified fibers were prepared, as in Example II, except that 9.19 gr of Pluronic L62 was included to provide 0.10% Pluronic L62 in the dehydrated cake on a dry fiber basis. The test results indicate a compressibility in number of 7.33 cm3 / gr, a 5K density of 0.117 gr / cm3, 3.8 knuckles and pills, a drip capacity of 10.85 gr / gr and a fluid conduction velocity of 0.45 cm / sec Example IX Cross-linked fibers of southern soft pulp kraft fibers were prepared using citric acid as the crosslinking agent and neodol 26 / 6.5 as the active surface agent. In the preparation, a suspension with 2.5% consistency having a pH of 3 was formed from 200 gr. dry bone pulp, 367.7 gr. of citric acid and 20.2 of neodol 23-6.5 and sodium hydroxide. After approximately 30 min. of soaking, the mixture is centrifuged to a consistency of 46.9%. The resulting dehydrated cake contains 5.33% by weight of citric acid and approximately 0.33% of neodol 23-6.5 on a dry fiber basis. The dehydrated cake was fluffed in a disc refiner at a speed of 60g / min. An instant dryer attached to the disc refiner reduces the moisture content to provide 92.9% consistency of the mixture, then the heating was carried out on the mixture of 92.9% consistency for 8 min. at an air temperature of 370oF, in a gas oven Proctor & Sch artz. The product was rinsed for 5 min. in cold water, soaked in water at 60oC for one hour, rinsed for 5 minutes in cold water, centrifuged for 5 minutes, and dried with air at 90% consistency. The test indicates a 5K density of 0.109g / cm3 3.5 knuckles and pills and a drip capacity of 14.3 g / g.

Example X Esterified fibers were prepared as in Example IX, except that the active surface agent is neodol 25-7, the dehydration was 43.9 of consistency, the dehydrated cake contains 6.02% by weight of citric acid and 0.33% of neodol 25-7 about a dry fiber base, the dehydrated cake was dried with air at 46% consistency and the cake dried with air. The test indicates a density of 5K of 0.106 g / cm3, 12.2 knuckles and pills and a drip capacity of 13.9 g / g.

Example XI Esterified fibers were made using the system described in Figure 1 having rollers one foot in diameter and 6 feet wide. The dry splice of the soft pulp of the south kraft of an initial moisture content of 6% (94% consistency). The aqueous crosslinking composition contains citric acid, Pluronic L35, sodium hypophosphate and sodium hydroxide to adjust the pH to 3. The speed of the roll is such that the residence time of the fibers of the dry sheet in the composition Aqueous crosslinking is 0.1 sec. The typical pressure in the press roll holder is 45 psi and 45 pounds per linear inch. The consistency of the sheet on the output side of the press rolls is approximately 60%. The sheet exiting the press rolls contains 6% by weight of citric acid on a dry fiber basis and 0.075% by weight of Pluronic L35 on a dry fiber basis. The impregnated sheet is first destroyed in pieces and then sponged in a disc refiner. The instant drying is subsequently carried out at 90% consistency. The drying and further curing is carried out in the system of figure 2, using air at 40oF. If required, additional heating may be carried out in an air-heating apparatus through, or in a static oven maintained at an air temperature of about 350oF. In an alternate process, the esterified fibers are prepared as described, except that the consistency of the sheet exiting the press rolls is about 40% and the impregnated sheet is dried with air at 60% consistency prior to foaming. In both cases, results similar to those obtained in Example I are obtained.

Variations will be obvious to those skilled in the art. Therefore, the invention is defined by the claims.

Claims (13)

NOVELTY OF THE INVENTION CLAIMS

1. A method for preparing individualized crosslinked cellulosic fibers having an amount of C2-C9 polycarboxylic acid crosslinking agent that reacts therein in a crosslinked form of intrafiber ester linkage, providing said crosslinked fibers with a water retention value from about 25 to 60, said method comprising the step of heating the non-crosslinked cellulosic fibers at a moisture content ranging from 0 to about 70% with 15%, by weight on a base of citric acid applied on a fiber basis dry of C2-C9 polycarboxylic acid crosslinking agent, and from 0.005 to 1% by weight, applied on a dry fiber basis, of active surface agent, on them, to remove any moisture content and to cause the agent of crosslinking of polycarboxylic acid react with the cellulose fibers and form the ester lattice between the cellulose molecules, for proportion said crosslinked cellulose fibers.

2. The method according to claim 1, further characterized in that the non-crosslinked fibers are subjected to the heating step, having a moisture content of 30 to 40%, the uncrosslinked cellulosic fibers have from 3 to 12%, by weight on a base of citric acid applied on a dry fiber base, of cross-linking agent of C2-C9 polycarboxylic acid, and of 0.01 to 0.2%, by weight applied on a dry fiber basis, of active surface agent, on them , the C2-C9 polycarboxylic acid crosslinking agent is citric acid and the active surface agent is a nonionic surfactant.

3. The method according to claim 2, further characterized in that the nonionic surfactant is one that is formed by the condensation of ethylene oxide with a hydrophobic base, formed by the condensation of propylene oxide with propylene glycol.

4. The method according to claim 2, further characterized in that the nonionic surfactant is the condensation product of C2-C15 aliphatic alcohol, with 5 to 15 moles of ethylene oxide.

The method according to claim 1, further characterized in that the fibers are not crosslinked at a moisture content ranging from 0 to about 70% with from 1 to 15%, by weight on a base of citric acid applied on a basis of dry fiber of C2-C9 polycarboxylic acid crosslinking agent, and from 0.005 to 1% by weight, applied on a dry fiber basis, of active surface active agent, on them, is prepared in a process comprising putting into contact the non-crosslinked cellulosic fibers with an aqueous crosslinking composition containing C2-C9 polycarboxylic acid crosslinking agent, and surface active agents, in appropriate amounts to provide the amounts of these agents in the fibers subjected to heating, and subsequently before of heating, defiber to provide a defibrated mixture, with or without liquid removal between contacting and defibration.

The method according to claim 5, further characterized in that the heating step comprises instantaneous drying of the defibrated mixture to dry the defrosted mixture to a consistency of between 60% and 100%.

7. The method according to claim 6, further characterized in that the instant drying is 85 to 95% consistency.

8. The method according to claim 6, further characterized in that the product resulting from the instant drying is heated for a period that varies from 5 sec. to 2 hrs. at an air temperature of 120oC to 280oC to remove any remaining moisture content and cause crosslinking to occur.

The method according to claim 5, further characterized in that said contacting is carried out by transporting a sheet of uncrosslinked cellulosic fibers having a moisture content of 0.10% through a body of said aqueous crosslinking composition.contained in a fastener of the press rolls and through said fasteners impregnate said fiber sheet with said aqueous crosslinking composition, and to produce on the outlet side of the fastener a fiber impregnated sheet containing said aqueous crosslinking composition in an amount to provide 30 to 80% consistency, and the impregnated fiber sheets are subjected to defibration to produce a desfribrated mixture that is ready for treatment in the heating step.

The method according to claim 5, further characterized in that the contacting is carried out by forming a suspension of uncrosslinked cellulosic fibers in an unlimited form in the aqueous crosslinking composition, from 0.1 to 20% consistency and soaking by about 1 to 240 min., after which the liquid is removed from the suspension to increase the consistency from 30 to 100% to form a reduced mixture in liquid, after which the reduced mixture in liquid is subjected to defibration to forming a defibrated mixture that is ready for the treatment in the heating stage.

The method according to claim 1, further characterized in that it is carried out without washing or bleaching and washing the crosslinked fibers.

12. The product made by the process of claim 11 having a 5K density not greater than 0.15 gr / cm3.

13. The product made by the process of claim 1 having a density of not more than 0.15 gr / cm3. EXTRACT OF THE DISCLOSURE In the preparation of individualized polycarboxylic acid crosslinked fibers, the requirements to obtain a correspondence to the particular humidity and maintain the satisfactory absorbency properties, even without washing or bleaching and washing, are reduced, and an improved dry elasticity is obtained, using a solution of reduced surface tension of polycarboxylic acid crosslinking agent.