JPS6366374A - Indivisualized crosslinked fiber and its production - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to cellulosic fibers having high fluid absorption properties,
The present invention relates to absorbent structures made from such cellulosic fibers and methods of making such fibers and structures. More specifically, the present invention relates to individualization.
1zcd) Absorbent cellulosic fibers utilizing cellulosic fibers in crosslinked form, structures made from such fibers, and processes for making such fibers and absorbent structures.

[Background of the invention]

Fibers that are crosslinked in a substantially individualized form and various methods of making such fibers have been described in the art. The term "individualized crosslinked fibers" refers primarily to intrafiber (IntraNb)
cr) means cellulose fibers with chemical crosslinks. That is, cross-linking is primarily between cellulose molecules of single fibers rather than between cellulose molecules of separate fibers. Individualized crosslinked fibers are generally considered useful in absorbent product applications. In general, 3 methods for producing individualized crosslinked fibers
Two categories are reported. These methods described below include (1) dry crosslinking method, (2) aqueous solution crosslinking method,
and (3) referred to as a substantially non-aqueous crosslinking method. Absorbent structures containing the fibers themselves and individualized crosslinked fibers generally exhibit at least one significant absorbency improvement compared to conventional uncrosslinked fibers. Often this improvement in absorbency is reported in terms of absorbent capacity. Additionally, absorbent structures made from individualized crosslinked fibers generally exhibit increased wet resilience and increased dry resilience compared to absorbent structures made from uncrosslinked fibers. The term "resilience" hereinafter will mean the ability of a cellulosic fiber pad to return to its expanded state upon release of a compressive force. Dry resilience specifically refers to the ability of an absorbent structure to expand upon release of an applied compressive force while the fibers are in a substantially dry state. Wet resilience specifically refers to the ability of an absorbent structure to expand upon release of an applied compressive force while the fibers are in a humidified state. For purposes of this invention and consistency of disclosure, wet resilience will be observed and reported for absorbent structures that are saturatedly humidified.

A method for producing individualized crosslinked fibers using dry crosslinking technology is described in US Pat. No. 3,224,9%.

Individualized crosslinked fibers are produced by impregnating swollen fibers with a crosslinking agent in an aqueous solution, dehydrating the fibers, disintegrating them by mechanical action, and drying the fibers at high temperatures while the fibers are in a substantially individual state. It is produced by crosslinking. The fibers are crosslinked in a non-swollen collapsed state as a result of dehydration prior to crosslinking. Methods such as those exemplified in US Pat. No. 3,224,9% in which crosslinking occurs while the fibers are in a non-swollen collapsed state are referred to as "dry crosslinked" fiber preparation methods. Dry rack fQ g fibers are characterized by low fluid retention values (FRV). The fibers may be immersed in an aqueous solution of crosslinking agent to reduce the interfiber bonding capacity prior to performing a dry crosslinking operation similar to that described in U.S. Pat. , as suggested in U.S. Pat. No. 3,440,135.

This time-consuming pretreatment (preferably about 16-48 hours) reduces the nit (nlL) content resulting from incomplete disintegration.
It is claimed to improve quality by reducing

A method for producing aqueous solution crosslinked awls is described, for example, in U.S. Pat. No. 3,241.
．． It is disclosed in the specification of No. 553.

Individualized crosslinked fibers are made by crosslinking fibers in an aqueous solution containing a crosslinking agent and a catalyst. Fibers produced in this manner are hereinafter referred to as "aqueous crosslinked" fibers. Because of the swelling effect of water on cellulosic fibers, aqueous crosslinked fibers are crosslinked while in the non-collapsed swollen state. Compared to dry crosslinked fibers, U.S. Patent No. 3,241
Aqueous crosslinked fibers, such as those disclosed in ,553, have greater flexibility and less stiffness, and are characterized by higher fluid retention values (FRV). Absorbent structures made from aqueous crosslinked fibers exhibit lower wet and dry resilience than pads made from dry crosslinked fibers.

U.S. Pat. No. 4,035,147 teaches that by contacting dehydrated, unswollen fibers with a crosslinking agent and a catalyst in a substantially non-aqueous solution containing an amount of water that is insufficient to swell the fibers. A method of making individualized crosslinked fibers is disclosed. Crosslinking occurs when the fibers are in this substantially non-aqueous solution.

This type of process will hereinafter be referred to as a non-aqueous crosslinking process; the fibers produced thereby will be referred to as non-aqueous crosslinked W&fibers. U.S. Patent No. 4,035,1
The non-aqueous crosslinked fibers disclosed in '47 do not swell even upon prolonged contact with solutions known to those skilled in the art as swelling agents. Similar to dry crosslinked fibers, they are highly stiffened by crosslinking and absorbent structures made from them are
Exhibits relatively high wet and dry resilience.

It is believed that crosslinked fibers such as those described above are useful in low density absorbent product applications such as diapers, and also in high density absorbent product applications such as sanitary napkins. However, in view of their damage and cost, such fibers do not offer significant absorption benefits over conventional fibers and have not generated significant commercial success. Also, the commercial appeal of crosslinked fibers is low due to safety concerns. The most widely referred to cross-linking agent in the literature, formaldehyde, unfortunately causes irritation to human skin and is associated with other human safety issues. Removal of free formaldehyde in cross-linked products to sufficiently low amounts so that skin irritation and other human safety issues are avoided is hampered by both technological and economic barriers.

For example, dry crosslinked fibers and non-aqueous crosslinked fibers generally yield fibers of excessive stiffness and dry resilience;
This makes it difficult to form into dense sheets for transportation and difficult to subsequently re-fluff without fiber damage. Furthermore, when compressed in the dry state, pads made from these fibers exhibit low response to wetting. That is, once compressed in the dry state, they do not exhibit the ability to regain a substantial amount of their previous absorbent capacity when wet.

Another difficulty experienced with dry crosslinked fibers and non-aqueous crosslinked fibers is that the fibers quickly aggregate during wet forming onto perforated forming wires. This means that
This prevents the formation of wet-sheeted absorbent structures as well as the formation of dense sheets that would allow for economical transportation of the fibers to conversion plants.

Aqueous crosslinked fibers are useful in high-density absorbent pad applications such as surgical bandages, tampons, and sanitary napkins (densities typically 0.40 y/ec), but are not excessively flexible when in the wet state. , thus resulting in an absorbent structure with low wet resilience. Furthermore, when wet,
Aqueous crosslinked AT fibers become too flexible to provide structural support to the pad at low fiber densities. Therefore, the wet pad collapses and the absorbent capacity decreases.

It is an object of the present invention to provide individualized crosslinked fibers and absorbent structures made from such fibers (absorbent structures made from crosslinked fibers compared to absorbent structures made from uncrosslinked fibers). have a high level of absorbency and exhibit higher wet resilience and lower dry resilience than structures made from previously known dry crosslinked fibers and non-aqueous crosslinked fibers;
The purpose of the present invention is to provide structures that exhibit greater wet resilience and structural integrity than structures made from previously known aqueous crosslinked fibers.

Yet another object of the present invention is to provide individualized crosslinked fibers as described above and made from such fibers having improved wetting responsiveness compared to hitherto known crosslinked fibers and conventional uncrosslinked fibers. The purpose of the present invention is to provide an absorbent structure.

Additionally, it is an object of the present invention to provide commercially viable individualized crosslinked fibers and absorbent structures made from such fibers as described above that can be safely utilized near human skin. be.

Another object of the present invention is to provide an improved method of forming individualized crosslinked fibers into wet formed sheet form.

[Summary of the invention]

It has been found that the above objects can be met by individualized crosslinked fibers and incorporation of these fibers into absorbent structures as disclosed herein. Generally, these objectives and other benefits are accomplished by using about 0.0% crosslinker reacted with the MA fibers in the form of intrafiber crosslinks. 5 mol % to about 3.5 mol % (calculated = F on a molar basis of cellulose anhydroglucose) (the crosslinking agent is
(selected from the group consisting of C8 dialdehydes, 02-C8 dialdehyde acid analogs having at least one aldehyde functionality, and oligomers of such 02-C8 dialdehydes and dialdehyde acid analogs). Water retention (
It has been found that such fibers characterized by having a WHV) of less than about 60 meet the aforementioned objectives associated with individualized crosslinked fibers and provide unexpectedly good absorbent performance in absorbent structure applications. Ta. Accordingly, such fibers can be prepared by: a) providing a cellulosic fiber; and b) injecting the fiber with a C-C dialdehyde, a 02-C8 dialdehyde acid analogue, and such a 02-C8 dialdehyde and dialdehyde acid analogue. C) reacting the crosslinking agent with the fibers while maintaining the fibers in a substantially discrete form, thereby forming intrafiber crosslinks; And the fiber has a crosslinking agent of about 0.5 mol%
Approximately 3.5 mole percent (calculated on a mole basis of cellulose anhydroglucose) can be obtained by carrying out a process in which the fibers are contacted with a sufficient amount of crosslinking agent to react with the fibers to form crosslinks. The fibers are characterized by having a WRV of less than about 60 after crosslinking.

Preferably, the fibers are crosslinked while in a highly twisted state. In a most preferred embodiment, the fibers are contacted with a crosslinking agent and catalyst in an aqueous solution, dehydrated, mechanically separated into substantially side-by-side forms, then dried and crosslinked under substantially unrestrained conditions. Dehydration, mechanical separation, and drying steps allow the fibers to become highly twisted before crosslinking. The twisted state is then at least partially (but less than completely) fixed as a result of crosslinking. Alternatively, cellulosic fibers in individualized form may be treated with a water-miscible diluent such as acetic acid, which is not sufficient to swell the fibers to a level higher than that corresponding to an aqueous moisture content of 30% for an equivalent fiber. The crosslinking can be carried out in a substantially non-aqueous crosslinking solution containing no amount of water. In addition to the specific methods described above, other methods, fibers and structures made according to the invention are intended to be within the scope of the invention as defined in the claims.

[Detailed description of the invention]

Cellulosic fibers of different natural sources are applicable to the present invention. Digested fibers from softwoods, hardwoods or linters are
Preferably used. Also, esparto grass, bagasse,
Fibers from wool, flax, and other lignin and cellulosic fiber sources can be utilized as raw materials in the present invention.

The fibers can be supplied in slurry, non-sheet form or sheet form.

Fibers supplied as wet laps, dry wraps or other sheet forms are preferably rendered into a non-sheet form by mechanically disintegrating the sheet (preferably before contacting the fibers with the crosslinking agent). Preferably, the fibers are also provided in a wet or humidified state. Most preferably the fibers are wet fibers. In the case of dry wrap, it is advantageous to moisten the fibers prior to mechanical disintegration to minimize fiber damage.

The optimal iron fiber source for use with the present invention will depend on the particular end use intended. Generally, valve fibers made by chemical valve processing are preferred. Fully bleached, partially bleached and unbleached fibers are applicable. It is often desirable to utilize bleached bulbs because of their superior brightness and consumer appeal. In one novel aspect of the invention, detailed below,
The fibers are partially bleached, crosslinked and then completely bleached. In the case of products such as vapor towels and absorbent pads for diapers, sanitary napkins, sanitary products and other similar absorbent paper products, we utilize fibers from Southern softwood valves due to their excellent absorbent properties What you can do is
Particularly preferred.

Crosslinking agents that can be applied to this development include 02-C8 dialdehydes, acid chains of such dialdehydes (the acid chain has at least one aldehyde group), and such dialdehydes and acid chains. Examples include body oligomers.

These compounds are present in at least two cellulose chains in a single cellulose chain or on the most closely located cellulose chains in a single fiber.
can react with hydroxyl groups.

Those familiar with the crosslinker field will recognize that the dialdehyde crosslinkers may exist or react in a variety of forms, including the acid chain and oligomeric forms. All such forms are intended to be included within the scope of this invention. Therefore, reference to a particular crosslinking agent will hereinafter mean that the particular crosslinking agent as well as other forms are present in the aqueous solution. Particular crosslinking agents contemplated for use in the present invention are glutaraldehyde, glyoxal, and glyoxylic acid.

Glutaraldehyde provides the highest level of absorbency and resilience to the fibers, is believed to be safe and non-irritating to human skin when in its reacted and cross-linked state, and is particularly desirable because it provides the most stable cross-links. preferable. It has been found that monoaldehyde compounds that do not have additional carboxyl groups, such as acetaldehyde and furfural, do not provide the absorbent structure with the desired level of absorbent capacity, resilience, and wetting responsiveness.

It has been unexpectedly discovered that superior absorbent pad performance can be obtained at substantially lower levels of crosslinking than those previously practiced. Generally, unexpectedly good results are obtained when the crosslinking agent reacted with the fibers ranges from about 0.5 mol% to about 3.5 mol% (calculated on a cellulose anhydroglucose mole basis).
obtained in the case of an absorbent pad made from individualized cross-linked fibers having a

Preferably, the crosslinking agent is contacted with the fibers in a liquid medium under conditions such that the crosslinking agent penetrates into the interior of the individual fiber structures. However, other methods of crosslinking agent treatment are within the scope of this invention, including spraying the fibers while in individualized fuzz.

Generally, the fibers will also be contacted with a suitable catalyst before crosslinking. The type, amount, and method of contacting the catalyst with the fibers will depend on the particular crosslinking process being performed. These variables are detailed below.

Once the fibers have been treated with a crosslinker and catalyst, either the fibers can be maintained in the substantial absence of interfiber bonds, i.e., to a low incidence of interfiber contacts compared to a fluff-free bulb fiber, or the fibers can be treated with interfiber bonds, especially hydrogen. The crosslinking agent is reacted with the fibers while submerged in a solution that does not facilitate bond formation. This forms crosslinks that are intrafiber in nature. Under these conditions, the crosslinking agent reacts to form crosslinks between hydroxyl groups of a single cellulose chain or between hydroxyl groups of cellulose chains located closest to a single cellulosic fiber.

Although not presented or intended to limit the scope of the invention, it is believed that the crosslinking agent reacts with the hydroxyl groups of cellulose to form hemiacecous and acetal linkages. Formation of acetal bonds, believed to be a desirable type of bond that provides stable cross-linking, is favored under acidic reaction conditions. Therefore, acid-catalyzed crosslinking conditions are highly preferred for purposes of the present invention.

The fibers are preferably "fluffed" prior to reaction of the crosslinking agent with the fibers.
mechanically disintegrated into a low-density individualized fibrous form known as Mechanical disaggregation can be accomplished by a variety of methods now known or becoming known in the art. Mechanical disaggregation is preferably accomplished by a method that minimizes knot formation and fiber damage. One type of device that has been found to be particularly useful for defibrating cellulosic fibers is the three-stage fluffing device described in US Pat. No. 3,987,968. U.S. Patent No. 3,9
No. 87,968, the fluff forming apparatus subjects humidified cellulosic bulb fibers to a combination of mechanical impact, mechanical agitation, air agitation, and a limited amount of air drying to form a substantially knot-free fluff. make. The individualized fibers imparted to them an increased degree of curl and twist compared to the amount of curl and twist naturally present in such fibers. This additional curl and twist is believed to increase the elasticity of the absorbent structure made from the finished crosslinked fibers.

Other methods applicable to disintegrate cellulosic fibers include, but are not limited to, varing.
Examples include processing in a blender and contacting the fibers tangentially with a rotating disc refiner or wire brush. Preferably, airflow is directed toward the fibers during such disintegration to assist in separating the fibers into substantially discrete forms.

Regardless of the particular mechanical equipment used to form the fluff, the fibers are preferably initially at least about 20% water.
, preferably containing about 40% to about 60% moisture,
Process mechanically.

Also, mechanical refining of consistent or partially dried fibers can be used to impart curl or twist to the fibers in addition to the curl or twist imparted as a result of mechanical disintegration.

The fibers produced according to the invention exhibit a unique combination of stiffness and resilience (-r-L, which allows absorbent structures made from the fibers to maintain high levels of absorbency). , and exhibits a high level of resilience and swelling response to wetness of the dry compressed absorbent structure.In addition to having a crosslinking level within said range, the crosslinked fibers:
It is characterized by having a water retention value (WHV) of less than about 60, preferably about 28-45 for conventional chemically bulbed papermaking fibers. The WRV of a particular fiber indicates the level of crosslinking and degree of swelling of the fiber upon crosslinking. Those skilled in the art will recognize that the more swollen the fibers are upon crosslinking, the higher the WHV will be at a given level of crosslinking.

Very highly crosslinked fibers, such as those made by the previously known dry crosslinking methods described above, have been found to have a WHV of less than about 25, generally less than about 20. Of course, the particular crosslinking method utilized will affect the WRV of the crosslinked 'a-cone. However, any method that will yield a crosslinking level and WRV within the above limits is believed to be within the scope of this invention, and is intended to be within the scope of this invention. Applicable crosslinking methods include dry crosslinking methods and non-aqueous crosslinking methods as generally discussed in the Background of the Invention. Preferred dry crosslinking methods and non-aqueous crosslinking methods within the scope of the present invention are detailed below. The aqueous crosslinking process, in which the solution causes the fibers to swell to a high degree,
This will result in fibers with a WHV greater than 0. These fibers would provide insufficient stiffness and resilience for purposes of this invention.

With specific reference to the dry crosslinking method, individualized crosslinked fibers are produced by preparing a predetermined amount of cellulosic fibers and contacting a slurry of the fibers with a crosslinking agent of the type and amount described above to form the fibers into a substantially discrete form. mechanical separation, e.g., disaggregation, maintaining the fibers in a substantially discrete form, drying the fibers, and reacting a crosslinking agent with the fibers in the presence of a catalyst to form crosslinks. Can be manufactured. In addition to the drying step, the defibration step is believed to impart additional curl.

Subsequent drying is accomplished by twisting the 'ja fibers.

Twist is enhanced by the curled geometry of the fibers. As used herein, fiber "curl" refers to the geometric curvature of the fiber about its longitudinal axis. “Yori (Lwi)
sL ) J means the rotation of the fiber around the vertical section of the longitudinal axis of the fiber. For illustrative purposes only, and without seeking to specifically limit the scope of the invention, individualized crosslinked fibers within the scope of the present invention having an average of about 6 twists per 111 fibers were observed.

Maintaining the fibers in a substantially discrete configuration during drying and crosslinking allows the fibers to be twisted during drying and thereby crosslinked in such twisted curl form. Drying the fibers under conditions that allow the fibers to twist and curl is referred to as drying the fibers under substantially unconstrained conditions. On the other hand, drying the fibers in sheet form produces dry fibers that do not twist and curl as substantially as fibers dried in individualized form. Interfiber hydrogen bonds are believed to "restraint" the relative occurrence of fiber twisting and curl formation.

There are various methods by which fibers can be contacted with crosslinking agents and catalysts. In one embodiment, the fibers are initially contacted with a solution containing both a crosslinking agent and a catalyst.

In another embodiment, the fibers are contacted with an aqueous solution of crosslinking agent and soaked prior to addition of the catalyst. Then add the catalyst.

In a third embodiment, a crosslinking agent and catalyst are added to an aqueous slurry of cellulosic fibers.

Other methods in addition to those described herein will be apparent to those skilled in the art and are intended to be included within the scope of this invention. Regardless of the particular method of contacting the fibers with the crosslinking agent and catalyst, the cellulosic fibers, crosslinking agent and catalyst are preferably mixed and/or thoroughly immersed with the fibers to ensure complete contact and contact with the individual fibers. Guarantees impregnation of individual fibers.

Generally, any material that catalyzes the crosslinking mechanism can be utilized. Applicable catalysts include organic acids and acid salts. Particularly preferred catalysts are salts, such as the chlorides, nitrates or sulphates of aluminum, magnesium, zinc and calcium. One particular example of a preferred salt is zinc nitrate, which is also a hydrate. Other catalysts include acids such as sulfuric acid, hydrochloric acid and other mineral and organic acids. A given catalyst can be used as the sole catalytic agent or as a single catalytic agent.
It can be used in combination with the other catalysts mentioned above. It is believed that the combination of acid salts and organic acids as catalytic agents provides excellent crosslinking reaction efficiency. Unexpectedly high levels of reaction completion were observed in the case of catalytic combinations of zinc nitrate salts and organic acids such as citric acid. The use of such combinations is preferred. Mineral acids are used to adjust the pH of the fibers while in solution and in contact with the crosslinking agent, but are preferably not utilized as the main catalyst.

The optimal amounts of crosslinking agent and catalyst utilized will depend on the particular crosslinking agent utilized, reaction conditions and the particular product application intended.

Of course, the amount of catalyst preferably used will depend on the particular type and amount of crosslinking agent and the reaction conditions, particularly temperature and pH. Generally, based on technical and economic considerations, a catalyst amount of about 10% to about 50% by weight based on the fffm of crosslinking agent added to the cellulosic fibers is preferred. For purposes of illustration, if the catalyst utilized is zinc nitrate hexahydrate and the crosslinking agent is glutaraldehyde,
A catalyst amount of about 30.1 R% based on the amount of glutaraldehyde added is preferred. Most preferably, from about 5% to about 30% of citric acid, based on the weight of the glutaraldehyde.
Additionally, the aqueous portion of the cellulosic fiber slurry or crosslinker solution is brought into contact with the crosslinker and fibers at a pH of about 2 to about 5, more preferably at a pH of about 2. It is desirable to adjust the target pH to about 5 to pH 3.5.

Cellulosic fibers generally should be dehydrated and optionally dried. The optimum consistency that can be used will vary depending on the type of fluffing device utilized. In a preferred embodiment, the cellulosic fibers are dehydrated and optimally dried to about 30% to about 80% consistency. More preferably, the fibers are dehydrated and dried to a consistency level of about 40% to about 60%. Drying the fibers to these preferred ranges generally facilitates disintegration of the fibers into individualized forms without the excessive formation of knots associated with high wax content and without the high levels of fiber damage associated with lower moisture contents. will do.

By way of example, dewatering can be accomplished by methods such as mechanically pressing the pulp, centrifuging it, air drying it, and the like. Additional drying is preferably performed by methods known in the art such as air drying, flash drying, etc. under conditions that do not require the use of high temperatures for extended periods of time. Excessive high temperatures at this stage of the process may result in premature onset of crosslinking. Preferably, the temperature above about 160°C is
Not maintained for more than 2-3 seconds. Mechanical disaggregation is performed as described above.

The disintegrated fibers are then twisted at an appropriate temperature for an effective period of time to cure the crosslinking agent, ie, to react with the cellulosic fibers.

The rate and degree of crosslinking depends on the degree of dryness of the fibers, the temperature, the amount and type of catalyst and crosslinking agent, and the method utilized to twist and/or dry the fibers while crosslinking. Crosslinking at a particular temperature will occur faster for fibers at initial moisture content when achieved by continuous draft drying than when subjected to drying/twisting in a static oven. Those skilled in the art will recognize that numerous temperature-time relationships exist in the case of crosslinker curing. Normal paper drying temperature for a period of approximately 30 minutes to 60 minutes under static conditions.
For example, 120 knives (approximately 49℃) - approximately 150 knives (approximately 66℃
)] will generally provide acceptable curing efficiency for fibers having a moisture content of less than about 5%. Also, those skilled in the art will recognize that higher temperatures and air convection will reduce the time required for curing. However, the curing temperature is preferably maintained below about 160°C because exposure of the fibers to high temperatures above about 160°C can result in yellowing or other damage to the fibers.

Maximum crosslinking levels will be achieved when the fiber is wood-dry (moisture content less than about 596%). Due to the lack of water, the fibers crosslink when in a substantially non-swelling collapsed state.

Therefore, they characteristically have low fluid retention values (FRV) compared to the range applicable to the present invention. FRV means the amount of fluid (calculated on a dry fiber basis) that remains absorbed by a fiber sample that has been soaked and then centrifuged to remove interfiber fluid (FRV is further defined as
The FRV n1 law will be described later). The amount of fluid that a crosslinked fiber can absorb depends on its ability to swell upon saturation, in other words its inner diameter or volume upon swelling to a maximum amount.

This depends on the level of crosslinking. As the level of intrafiber crosslinking increases for a given fiber and method, the FRV of the fiber decreases until the fiber no longer swells when wet. Thus, the FRV value of a fiber structurally describes the physical state of the fiber at saturation. Unless otherwise specified, the FRV data presented here refers to the fiber water retention value (W
RV). Also, other fluids,
For example, saline water and synthetic urine can be advantageously utilized as analytical fluid media. Generally, the FRV of certain fibers crosslinked by methods in which curing is significantly dependent on drying, such as in this publication.
will depend primarily on the crosslinking agent and level of crosslinking. The WHV of fibers crosslinked by this dry crosslinking method with crosslinking agent amounts applicable to the present invention is generally less than about 50, about 2
5, preferably about 28 to about 45.

Approximately 0.5 mol% glutaraldehyde reacted thereon
Bleached SSK fibers having ~2.5 mole % (calculated in cellulose anhydroglucose molar groups) have a WHV of about 4
0 to about 28. It was found that the degree of bleaching and the implementation of the post-crosslinking bleaching step affect WRV. This effect is examined in detail below. Southern softwood kraft (SSK) fibers made by dry crosslinking processes known prior to the present invention have higher crosslinking levels than those described herein and have a WRV of less than about 25.

As mentioned above, such fibers are excessively stiff and
and was observed to exhibit a lower absorbent capacity than the fibers of the present invention.

In another method of making individualized crosslinked fibers by dry crosslinking, cellulosic fibers are contacted with a solution containing a crosslinking agent as described above. The fibers are provided in sheet form before or after contact with the crosslinking agent.

Preferably, the solution containing the crosslinking agent also contains one of the catalysts applicable to the dry crosslinking process. Dry the fibers while in sheet form, preferably at 20°C
Crosslinking is achieved by twisting at a temperature of about 160°C.

After crosslinking, the fibers are mechanically separated into substantially discrete forms.

This is preferably carried out by treatment with a fiber fluffing device, such as that described in U.S. Pat. Can be implemented. The individualized crosslinked fibers produced according to this sheet crosslinking method contain from about 0.5 mol 96 to about 3.5 mol % of the crosslinking agent (calculated on a molar basis of cellulose anhydroglucose; measured after disintegration) in the form of intrafiber crosslinks. with a sufficient amount of crosslinking agent to react with the fibers. Another effect of drying and crosslinking the fibers when in sheet form is that the fiber-to-fiber bond restrains the fibers from twisting and curling, resulting in increased drying. Compared to individualized crosslinked fibers produced according to a method in which the fibers are dried under substantially unconstrained conditions and then crosslinked in a twisted curl arrangement, relatively untwisted fibers produced from the sheet curing method described above (unLwisLed ) Absorbent structures made from fibers would be expected to exhibit lower wet resilience and -lower responsiveness to wetting of dry absorbent structures.

Another category of crosslinking methods applicable to the present invention are non-aqueous cure crosslinking methods. The same types of fibers that are applicable to dry crosslinking processes can be used in the production of non-aqueous crosslinked fibers. The fibers contain a sufficient amount of crosslinking agent (the reaction m of the crosslinking agent is calculated after the crosslinking reaction) such that from about 0.5 mole % to about 3.5 moles 96 of the crosslinker subsequently reacts with the fibers and a suitable catalyst. Process with. The crosslinking agent is allowed to react while the fibers are submerged in a solution that does not cause substantial swelling of the fibers.

However, the fibers can contain up to 30% water or swell in the crosslinking solution to an extent equivalent to a fiber having about 3006 water holes. It has been found that such partially swollen fiber geometries provide additional unexpected benefits as detailed below. The crosslinking solution contains a non-aqueous water-miscible polar diluent, such as, but not limited to, acetic acid, propanoic acid, or acetone. Preferred catalysts include mineral acids such as sulfuric acid, and halogen acids such as hydrochloric acid. Other applicable catalysts include salts of mineral and halogen acids, organic acids and their salts. Also,
Crosslinking solution systems applicable for use as crosslinking media include those disclosed in US Pat. No. 4,035,147. The crosslinking solution can contain some water or other fiber swelling liquid, but the amount of water is preferably 70%
% consistency seabulb fiber (30% aqueous water content) is insufficient to produce a swelling water ψ commensurate with the swelling level provided by the fiber (30% aqueous water content). Additionally, it is preferred that the water content of the crosslinking solution is less than about 10% of the total volume of the solution, excluding fibers.

An amount of water in the crosslinking solution in excess of this two reduces crosslinking efficiency and rate.

Absorption of the crosslinking agent by the fibers can be accomplished in the crosslinking solution itself, or in a pretreatment step, such as, but not limited to, saturation of the fibers with either an aqueous or non-aqueous solution containing the crosslinker. Preferably, the fibers are mechanically disintegrated into discrete forms.

This mechanical treatment can be carried out by the fiber fluffing method described in connection with the dry crosslinking method above.

It is particularly preferred to incorporate into the production of the fluff a mechanical treatment that causes the moistened cellulosic fibers to curl or twist to an extent that exceeds the fiber's natural amount of curl or twist (if any).

This may be accomplished by first providing fluffing fibers in a humidified state and subjecting the fibers to a mechanical treatment, e.g. to the aforementioned method of disintegrating the fibers into substantially discrete forms, to at least partially disintegrate the fibers. This can be achieved by drying.

The relative amount of curl and twist imparted to the fibers depends, in part, on the moisture content of the fibers. Without limiting the scope of the invention, it is believed that fibers naturally twist upon drying under conditions where fiber-to-fiber contact is low, ie, when the fibers are in an individualized form. Mechanical treatment of the humidified fibers also initially causes the fibers to curl. The fibers are then dried or partially dried under substantially unconstrained conditions while the fibers are twisted. The degree of curl is enhanced by the additional amount of mechanically applied curl. The defibration fluffing step is preferably performed on a high consistency humidified valve or a valve dehydrated to about 45% to about 55% fiber consistency (measured before the start of defibration).

After disintegration, if the disintegration process has not yet resulted in fibers having a moisture content of 0% to about 3096, the fibers are
It should be dried to a moisture content of 0% to about 30% before contact with the crosslinking solution. The drying step should be carried out while the fibers are under substantially unconstrained conditions. That is, fiber-to-fiber contact should be minimized so that the inherent fiber twisting during drying is not inhibited. Both the air drying method and the flash drying method
suitable for this purpose.

The singulated fibers are then contacted with a crosslinking solution containing a water-miscible non-aqueous diluent, a crosslinker, and a catalyst.

The crosslinking solution can contain a limited amount of water. The water content of the crosslinking solution should be less than about 18%, preferably about 9%
less than

In addition, batt (bit) of fibers that are not mechanically disintegrated
) can be contacted with a crosslinking solution as described above.

The amount of crosslinker and acid catalyst used will depend on reaction conditions such as consistency, temperature, moisture in the crosslinking solution and fibers, type of crosslinker and diluent in the crosslinking solution, and desired degree of crosslinking. . Preferably, the amount of crosslinking agent used is about 0
．． 2@H% to about 10% by weight (based on the total weight of the crosslinking solution without fibers). The preferred acid catalyst content additionally depends on the acidity of the catalyst in the crosslinking solution. Good results are generally achieved with catalyst content in the crosslinking solution containing an acetic acid diluent, a preferred amount of glutaraldehyde, and a limited amount of water.
f1 (including hydrochloric acid) from about 0.3% to about 5% by weight (based on the weight of the crosslinking solution without fibers). Slurries of fibers and crosslinking solution having less than about 10 ifffiL% fiber consistency are preferred for crosslinking with the crosslinking solution.

The crosslinking reaction can be carried out at room temperature or, for accelerated reaction rates, at an elevated temperature, preferably below about 40°C.

There are various methods by which fibers can be contacted with a crosslinking solution and crosslinked in the crosslinking solution. In one embodiment, the fibers are initially contacted with a solution containing both a crosslinking agent and an acid catalyst. The fibers are immersed in a crosslinking solution, during which crosslinking occurs. In another embodiment, contacting the fiber with a diluent;
Soak before adding acid catalyst. Then add an acid catalyst,
Crosslinking then begins. Other methods in addition to those described will be apparent to those skilled in the art and are intended to be within the scope of this invention.

Preferably, the crosslinking agent and crosslinking conditions are selected to facilitate intrafiber crosslinking. Thus, it is advantageous for the crosslinking reaction to occur substantially partially after the crosslinking agent has had sufficient time to penetrate the fibers. The reaction conditions are preferably chosen to avoid immediate crosslinking unless the crosslinking agent has already penetrated the fibers. Reaction periods in which crosslinking is substantially complete in a period of about 30 minutes are preferred. It is believed that longer reaction periods provide the least marginal benefit in fiber performance. However, both shorter and longer periods, including substantially immediate crosslinking, are intended to be within the scope of this invention.

It is also contemplated that after only partial curing while in solution, the crosslinking reaction is completed later by drying or twisting treatment herein.

After the crosslinking process, the fibers are drained and washed. Preferably,
A sufficient amount of a basic material, such as caustic, is added in the cleaning step to neutralize any acid remaining in the valve. After washing, the fibers are defluidized (dcrluidizc),
Dry completely. Preferably, between the membrane fluidization step and the drying step, the fibers are subjected to a second mechanical defibration step that curls the crosslinked fibers, such as fuzz formation by defibration. Upon drying, the curled state of the fibers imparts additional twist as described above in conjunction with the curling treatment prior to contact with the crosslinking solution.

The same kink and curl inducing devices and methods described in connection with the first mechanical defibration step are applicable to this second mechanical defibration step. As used herein, the term "disaggregation" refers to any method that can be used to mechanically separate OI cones into substantially discrete forms, even though the fibers may already be provided in a substantially discrete form. Probably. "Disintegration" therefore refers to the process of mechanically treating fibers, either in discrete or more compacted form; (b) Mechanical treatment that imparts curl and twist to the fibers upon drying.

This second defibration step has been found to increase the twisted curl-like properties of the bulb after the fibers have been crosslinked. This increase in the twisted curl-like arrangement of the fibers results in increased resilience and wet response of the absorbent structure. The second defibration process can be performed on any of the crosslinked fibers described herein in a humidified state. However, it is a particular advantage of non-aqueous crosslinking methods that the second disintegration step is possible without the need for an additional drying step. This is due to the fact that the solution (in which the fibers are crosslinked) keeps the fibers flexible after crosslinking, even though it does not cause the fibers to assume an undesirable highly swollen state.

Furthermore, unexpectedly, the expansion rate of the absorbent structure, which was increased when wetting the compressed pad, was higher than that of the twisted but partially swollen fibers compared to fibers that were completely dried out of water before cross-linking. It has been found that this can be obtained in the case of structures made from fibers that are crosslinked when in a state of oxidation.

Improved results are obtained with individualized crosslinked fibers that are crosslinked under conditions that dry the fibers to about 18% to about 30% moisture prior to contact with the crosslinking solution. If the fibers are completely dried before contacting the crosslinking solution, the fibers are in a non-swollen collapsed state. The fibers do not become swollen upon contact with the crosslinking solution due to the low water content of the solution. As mentioned above, a critical aspect of the crosslinking solution is that it does not cause substantial swelling of the fibers.

However, when the diluent of the crosslinking solution is absorbed by the already swollen fibers, the fibers have effectively "dryed" the water but retain their native partially swollen state.

To explain the degree of fiber swelling, it is useful to refer again to the fluid retention value (FRV) of the 'a fibers after crosslinking. Fibers with higher FRV correspond to fibers that are crosslinked when in a higher swelling state compared to fibers that are crosslinked when in a lower swelling state (all other factors being equal).

Without limiting the scope of the invention, it is believed that partially swollen crosslinked fibers with increased FRV have greater wet resilience and wet response than crosslinked fibers when in the unswollen state.

Fibers with increased wet resilience and responsiveness to wet swell or untwist more readily when wet in an attempt to return to their natural state (unLvisL).
be able to. Note that because of the stiffness imparted by crosslinking, m-fibers can still provide structural support to saturated pads made from the fibers. The numerical FRV data described herein in connection with partially swollen crosslinked fibers would be Water Retention Value (WRV). It is believed that as the WHV increases above about 60, the stiffness of the fibers becomes insufficient to provide the desired wet resilience and wet responsiveness to support saturated absorbent structures.

In an alternative method of crosslinking fibers in solution, the fibers are first immersed in an aqueous or other fiber swelling solution, defluidized, dried to the desired level, and then loaded with catalyst and crosslinking agent as described above. Submerge in water-miscible crosslinking solution. The fibers are preferably mechanically defibrated to a fluffy texture after defluidization and prior to additional drying to obtain the enhanced twist and curl benefits described above. Mechanical disaggregation carried out after contacting the 'a 'm with the crosslinking agent volatilizes the crosslinking agent and thus potentially results in air pollution due to the crosslinking agent or high air treatment investments due to the crosslinking agent, It's not that desirable.

In a modification of the method described immediately above, the fibers are disintegrated;
The fibers are then immersed in a highly concentrated solution of a cross-linking agent and a fiber swelling diluent (preferably water). The cross-linking agent concentration is sufficiently high to inhibit water-induced swelling of the fibers. A 50% by weight aqueous solution of a crosslinking agent (preferably glutaraldehyde) has been found to be a useful solution for presoaking fibers. It is submerged in a crosslinking solution containing a polar diluent, a catalyst, and a limited amount of water, and then crosslinked as described above.

Also, as mentioned above, the crosslinked fibers can be deflownized and subjected to a second mechanical disintegration step before further processing into sheets or absorbent structures.

Pre-soaking the fibers with a cross-linker in an aqueous solution before reacting the cross-linker can be used with pads made from cross-linked fibers of the non-aqueous solution curing process in which the fibers were not T-soaked in a cross-linker-containing solution. Even by comparison, absorbent pads made from crosslinked fibers have unexpectedly high absorbency.

The crosslinked fibers formed as a result of the dry crosslinking method and the non-aqueous crosslinking method are products of the present invention.

The crosslinked fibers of the present invention can be used directly in the production of air-formed absorbent cores. Additionally, because of their stiffness and elasticity, crosslinked fibers can be wet formed into low density sheets without consolidation. This low density sheet, when subsequently dried, is directly useful as an absorbent core without further machining.

The crosslinked fibers can also be wet-formed into compacted valve seats for safe or transport to remote locations.

-q Once the individualized crosslinked fibers are made, they can be dry formed and formed directly into absorbent structures, or wet formed and formed into absorbent structures or dense valve seats. The fibers of the present invention provide six orders of magnitude of substantial performance advantages. However, it is difficult to form such fibers into a smooth wet-formed sheet using a conventional wet-sheet forming method. This is because the individualized crosslinked fibers aggregate quickly when in solution. Such flocculation can occur both in the headbox and during deposition into the porous forming wire. Attempts to sheet individualized crosslinked fibers by conventional valve sheeting methods have been found to form multiple aggregated fiber clumps. This results from the stiff twisting properties of the fibers, low levels of fiber-to-fiber bonding, and high drainage properties of the fibers once deposited onto the sheet forming wire.

Therefore, we provide a practical sheeting method for individualized crosslinked fibers,
Wet-formed absorbent structures and transportation/
The ability to form dense valve seats for subsequent defibration is of significant commercial interest.

Accordingly, a new method has been developed to sheet individualized crosslinked fibers that tend to aggregate in solution.

In this novel method, a H-containing slurry containing individualized cross-linked fibers is first prepared using a Fourdrlnie wire in a manner similar to conventional valve seat forming methods.
(r wire) onto a porous forming wire. However, due to the nature of individualized crosslinked fibers, these fibers are deposited on the forming wire in multiple fiber clumps. A small (at least one) stream of fluid (preferably water) is directed onto the deposited bulk fibers. Preferably, a series of showers are directed onto the fibers deposited onto the forming wire. Continuous showers are used in which the volumetric flow rate is The shower should have sufficient velocity so that the impact of the fluid on the fibers acts to suppress the formation of fiber flocculation and to disperse already formed fiber flocculation. The fiber fixation step is preferably carried out on a cylindrical screen such as a dandy roll or another device of similar function that is or becomes known in the art.Then, once fixed, the fibrous sheet is It can be dried and optionally consolidated as desired.The spacing between showers depends on the specific fiber flocking rate, the line speed of the forming wire, the drainage through the forming wire, the number of showers, and the speed and flow rate through the shower. It will change accordingly.

Preferably, the shower is close enough to the shower to avoid substantial levels of floc formation.

In addition to suppressing and dispersing the formation of fiber flocculation, the fluid showered onto the fibers provides additional liquid medium that can disperse the fibers for subsequent sheet formation. This compensates for the extremely fast drainage of the individualized crosslinked fibers. Multiple showers of decreasing volumetric flow facilitate a systematic net increase in slurry consistency while providing a repeated dispersion/suppression effect on fiber flocculation. This means that
Forms a relatively smooth, uniform deposit of fibers.

These fibers are then quickly fixed in sheet form by draining the fluid and pressing the fibers against a perforated wire, i.e., prior to reflocculation.

Compared to valve seats made from conventional uncrosslinked cellulosic fibers, valve seats made from crosslinked fibers of the present invention are more difficult to compress to conventional valve seat densities. It may therefore be desirable to combine crosslinked fibers with uncrosslinked fibers, such as those commonly used in the manufacture of absorbent cores. Valve seats containing stiffened crosslinked fibers preferably contain from about 5% to about 90% uncrosslinked cellulosic fibers, based on the total dry weight of the sheet, mixed with individualized crosslinked fibers. It is particularly preferred to incorporate from about 5% to about 3096 highly refined uncrosslinked cellulosic fibers based on the total dry weight of the sheet.

Such highly refined fibers have a filter skin level of C8F approximately 300m.
1, preferably less than C8F16Om1. The uncrosslinked fibers are preferably mixed with an aqueous slurry of individualized crosslinked fibers. This mixture can then be formed into a dense valve seat for subsequent defibration and formation of absorbent pads. The incorporation of uncrosslinked fibers facilitates compression of the valve seat into a compact form while imparting a surprisingly low loss of absorbency to the subsequently formed absorbent pad. Uncrosslinked fibers additionally increase the tensile strength of the valve seat and of absorbent structures made directly from the valve seat or from a mixture of crosslinked and uncrosslinked fibers. Regardless of whether the blend of crosslinked and uncrosslinked fibers is first made into a valve seat and then formed into an absorbent pad, or whether it is directly formed into an absorbent pad, the absorbent pad may be air-formed or wet-formed as described above. Can be made into paper.

Sheets or webs made from individualized crosslinked fibers or mixtures that also contain uncrosslinked fibers preferably have a basis weight of less than about 800 g/rrt and a density of 0.60z/ci
will have less than Without intending to limit the scope of the invention, the basis weight is from 300 g/d to about 600 g/nf and the density is 0. Wet-formed sheets having a weight of 15g1ci to about 0.30g/ctrl can be used for disposable articles such as diapers,
Particularly intended for direct application as absorbent cores in tampons and other sanitary products. Structures with basis weights and densities above these levels are most useful for subsequent milling/air forming or wet forming to form lower density/basis weight structures that are more useful in absorbent applications. I believe there is. However, such high basis weight/density structures also exhibit surprisingly high absorbency and wet response. Other applications contemplated for the fibers of the present invention include 0.1
Included are low density tissue sheets having densities that can be less than 0 g/cc.

For product applications where the crosslinked fibers are placed next to or near human skin, it may be desirable to further process the fibers to remove excess unreacted crosslinker.

Preferably, the amount of unreacted crosslinker is reduced to at least less than about 0.03% based on the dry weight of the cellulosic fibers. A series of treatments that have been found to successfully remove excess crosslinking agent include sequentially washing the crosslinked fibers, soaking the fibers in an aqueous solution for a suitable period of time, sieving the fibers, and consolidating the fibers, e.g., by centrifugation. dewatering to about 40% to about 80% cysticity, mechanically disintegrating the dehydrated fibers as described above, and air drying the fibers. This process was found to reduce residual free crosslinker content to about 0.01% to 0.15%.

In another method of reducing residual crosslinkers, easily extractable crosslinkers are removed by an alkaline wash solution.

Alkalinity is measured by basic compounds such as sodium hydroxide,
or in the form of oxidizing agents, such as chemicals commonly used as bleaching agents, such as sodium hypochlorite, and amino gold-platinum compounds, such as ammonium hydroxide, which hydrolyze hemisecure bonds to form Schiff bases. It can be introduced with The pH is preferably maintained at a level of at least about pH 7, more preferably at least about pH 9, to inhibit reversion of acetal crosslinks. It is preferable to induce decomposition of hemiacecool bonds while being neutral to acetal bonds. Therefore, extractants that operate in highly alkaline conditions are preferred. 0.01N~0
．． One cleaning treatment with IN ammonium hydroxide concentration:
A soaking time of 30 minutes to 2 hours reduces the residue content to approximately 0.000.
A decrease of 8% to about 0.0023% was observed.

It is believed that minimal additional benefit is provided for soak times greater than about 30 minutes and ammonium hydroxide concentrations greater than about 0.0 IN.

Both single-stage and multi-stage oxidations have been found to be effective methods for extracting residual crosslinker.

Available chlorine (a
v, CI+) 0.1% to av, CJ7 approx. 0.8% (
It has been found that a one-stage wash at (based on the dry weight of the fiber) reduces the amount of residual crosslinker from about 0.0015% to about 0.0025%.

In one novel approach to producing crosslinked individualized fibers, the fiber source is subjected to a conventional multi-step bleaching sequence.
e), but at an intermediate point in the sequence the bleaching process is interrupted and the fibers are crosslinked according to the invention. After curing, complete the rest of the bleaching sequence. It has been found that acceptably low crosslinker residuals of less than 0.006% can be obtained in this way. This method makes it a preferred method for producing crosslinked fibers since the capital costs and processing inconveniences of additional washing and extraction equipment and additional processes are avoided due to the combination of bleaching and residue reduction steps. Specifically, 1. ; teased. As will be obvious to those skilled in the art, the bleaching sequence carried out and the break points in the sequence for crosslinking can vary widely.

However, a multi-stage bleaching sequence in which a DEP or DEH" step follows cross-linking has been found to give desirable results (*D: chlorine dioxide, E: caustic extraction, P:
peroxide, H: sodium hypochlorite). The post-crosslinking bleaching sequence is an alkaline treatment preferably carried out at a pH greater than about pH 7, preferably greater than about pH 9.

In addition to providing an effective reduction in residual crosslinker, post-crosslinking alkaline treatment results in higher FR for equal crosslinking levels.
V (fluid retention value) was observed to facilitate fiber development. Higher FRV fibers have lower dry resilience, i.e., in the dry state, while retaining substantially the same wet resilience and moisture responsiveness as otherwise equivalent wt fibers that have been crosslinked after bleaching is complete. densification more easily. This was especially surprising given that higher FRV traditionally resulted in decreased absorbency.

The crosslinked fibers described herein are useful in a variety of absorbent articles, including but not limited to tissue sheets, disposable diapers, sanitary products, sanitary napkins, tampons, and bandages. Each of the articles has an absorbent structure containing the individualized crosslinked fibers described herein. For example, disposable diapers or similar articles having a liquid permeable topsheet, a liquid impermeable backsheet coupled to the topsheet, and an absorbent structure containing individualized crosslinked fibers are specifically contemplated. Such articles are generally described in U.S. Patent No. 3.
860.003.

Typically, absorbent cores for diapers and sanitary products are made from unstiffened powdered crosslinked cellulosic mEl, and the absorbent core has a dry density of 0.06 g/cc to about 0.12 g/cc. Upon wetting, absorbent cores typically exhibit capacity loss.

The crosslinked fibers of the present invention exhibit substantially higher fluid absorbency, such as, but not limited to, absorbent capacity and wicking action (wlckjng ) has been found to be able to be used to make absorbent cores with speed. Furthermore, these improved absorbency results can be obtained with increased levels of wet resilience. Density 0.06 g/ce to about 0.15 g supporting substantially constant capacity when wet
/cc of absorbent core, about 2.0% crosslinker on a dry cellulose anhydroglucose mole basis. It is particularly preferred to utilize crosslinked fibers having a crosslinking level of 0.96 to about 2.5 mole percent. Absorbent cores made from such 21L have a striking combination of structural integrity: compression resistance and wet resilience. The term wet resilience in this context refers to the ability of a humidifying pad to spring back to its original shape and capacity upon exposure to and release from compressive forces.

Compared to cores made from untreated fibers and previously known crosslinked fibers, absorbent cores made from the fibers of the present invention regain a substantially greater portion of their original capacity upon release of wet compressive forces. Dew.

In another preferred embodiment, the individualized crosslinked fibers are formed into an air-formed or wet-formed (and subsequently dried) absorbent core and the absorbent core is compressed to a dry density that is less than the equilibrium wet density of the pad. Equilibrium wet density is the density of the pad calculated on a dry fiber basis when the pad is fully saturated with fluid. When the fibers are formed into an absorbent core having a dry density lower than the equilibrium wet density, upon wetting to saturation, the core will collapse to the equilibrium wet density. Alternatively, when the fibers are formed into an absorbent core having a dry density higher than the equilibrium wet density, upon wetting to saturation, the core will expand to the equilibrium wet density. Pads made from the fibers of the present invention exhibit substantially lower equilibrium wet densities than pads made from conventional fluff fibers. The fibers of the present invention can be compressed to a density higher than the equilibrium wet density to form a thin pad, which, upon wetting, expands by expanding its absorbent capacity to that obtained in the case of uncrosslinked fibers. will increase to a significantly higher degree than

Particularly high absorbency, wet resilience and wet response, calculated on a dry cellulose mole basis, are approximately 0.7
Crosslinking levels of 5 mole % to about 1.25 mole % can be obtained. Preferably, such fibers are formed into an absorbent core having a dry density higher than the equilibrium wet density. Preferably, the absorbent core has a density of about 0.12 g/cc
~0.60 g/cc, and the corresponding equilibrium wet density is lower than that of the dry compressed pad. Also preferably, the absorbent core has a density of about 0. 12 g/cc to about 0.40 g/cc, and the corresponding equilibrium wet density is about 0.08 g/cc to about 0.12 g/cc;
Lower density than dry compressed wick. Crosslinking level 2.0 mol%~
Compared to crosslinked fibers with about 2.5 mol%, the former fibers have lower stiffness, thereby making them suitable for compaction into high density ranges.

The former fibers also have higher wetting responsiveness because they spring open at a faster rate and to a greater extent than fibers with crosslinking levels in the range of 2.0 mol% to 2.5 mol%. but have higher wet resilience and retain most of their absorption capacity. However, just as low density absorbent structures can be made from crosslinked fibers with lower crosslinking levels, absorbent structures in the high density range can be made from crosslinked fibers in the higher crosslinking level range. should be recognized. Improved performance compared to previously known individualized crosslinked fibers is obtained in the case of all such structures.

While the foregoing discussion encompasses preferred embodiments for high-density absorbent structures and low-density absorbent structures, various combinations of absorbent structure density and crosslinker amount within the scope of the disclosure herein may include It should be appreciated that this will provide superior absorbent properties and absorbent structure integrity compared to conventional cellulosic fibers and previously known crosslinked fibers. Such embodiments are intended to be included within the scope of this invention.

Method for Measuring Fluid Retention Value The water retention of cellulosic fibers was measured using the following method.

About 0.3 g to about 0.4 g of the fiber sample is placed in a covered container containing 100 ml of distilled water or deionized fishing rod at room temperature.
Soak for 5 to about 20 hours. The soaked fibers are collected on a strainer and transferred to an 80 mesh wire basket supported by a 60 mesh centrifuge tube. Cover the tube with a plastic cover and test the sample at a relative centrifugal force of 1500-1700G for 19~
Centrifuge for 21 minutes. The centrifuged fibers are then removed from the basket and weighed. The weighed fibers are dried at 105° C. to a constant weight and reweighed. Calculate the water retention using the following formula.

(W-D) D (where W is the wet weight of the centrifuged fibers, D is the dry weight of the fibers, and W-D is the weight of absorbed water) Method for measuring drip capacity: Drip absorbent core
) Capacity was measured. Drip capacity was used as a combined measure of wick absorption capacity and absorption rate.

Place approximately 7.5 g of a 4 inch x 4 inch (about 102 mm x about 102 mm) absorbent pad onto the sieve mesh.

Synthetic urine is applied to the center of the pad at a rate of 8 ml/sec.

Synthetic urine flow is stopped when the first drop of synthetic urine escapes from the bottom or sides of the pad. The drip capacity is calculated by the difference in mass of the pad before and after introduction of synthetic urine + mass of fiber (bone dry basis).

Wet compressibility of the absorbent structure was measured using the following method. Wet compressibility was utilized as a measure of wet compressibility, wet structural integrity, and wet resilience of the absorbent core.

Prepare a 7.5 g 4 inch x 4 inch (about 102 mm x about 102 mm) square pad, measure its thickness, and calculate its density. Load the pad with synthetic urine to 10 times its dry weight or to its saturation point (whichever is less). 0. Apply a 1 PSI compressive load to the pad. about 6
After 0 seconds (at which time the pad is in equilibrium), the thickness of the pad is determined 7111. The compressive load is then increased to 1.1 PSI, the pad is balanced and the thickness is measured. Then, the compressive load was reduced to 0. Reduce to IP Sl, equilibrate the pad and re-set the thickness to 4-1. Return the density to the original 0. 1 PSI load, 1. IPSI load and 0. Calculate for the pad at IPSI load (0, referred to as IPSIR (Psi recombination) load). Then, the void volume Hk (
cc/g) is measured for each respective pressure load. Void capacity is wetted pad density - fiber capacity (0
, 95cc/g). O, IPSI and 1
．． IPSI void volume is a useful indicator of wet compressibility and wet structural integrity. Higher void volume for normal initial pad densities indicates greater wet compressibility and greater wet structural integrity. O,IPSI
Void capacity and 0. The difference between the IPSIR void capacitance is
Useful for comparing the wet resilience of absorbent pads.

A smaller difference between the 0,IPSI and O,IPSIR void volumes indicates higher wetting resilience.

It has also been found that the callper difference between a dry pad and a saturated pad prior to compression is a useful indicator of the pad's responsiveness to wetting.

The dry compressibility of the absorbent core was measured using the n1 standard method for dry compressibility. Dry compressibility was utilized as a measure of the dry resilience of the core.

4 inches x 4 inches (approximately 102+) with a mass of 7.5
am Flip the pad and repeat the press. The thickness of the pad is measured with an unloaded calibus before and after pressing. The density before and after pressing is then calculated as mass/(area×thickness).

A larger difference between the pre-press and post-press densities indicates lower drying resilience.

The following method was utilized to determine the amount of glutaraldehyde reacted to form intrafiber crosslinks with the cellulose component of the individualized glutaraldehyde crosslinked fibers.

Sample o of individualized crosslinked fibers, INHcn* is extracted.

The extract is separated from the fibers and the same extraction/separation procedure is then repeated three additional times for each sample. The extract from each extraction was separately separated into 2,4-dinitrophenylhydrazone (DNP).
Mix with an aqueous solution of H).

The reaction is allowed to proceed for 15 minutes, after which a volume of chloroform is added to the mixture. Mix the reaction mixture for an additional 45 minutes. Separate the chloroform and aqueous layers in a branch funnel. The amount of glutaraldehyde was determined by converting the chloroform layer to DNP by high pressure liquid chromatography (HPLC).
Determined by analysis for H derivatives.

The chromatography conditions for HPLC analysis used were:
It was as follows. Column: c-18 reverse phase, detector: 3
UV at 60m+x, mobile phase methanol:water 80:2
'O1 flow rate 1 ml/min, measurement: peak height. Calibration curves for peak height and glutaraldehyde content range from 0 to 25
It was obtained by measuring the HPLC peak heights of five standard solutions with known amounts of glutaraldehyde in ppm.

Each of the four chloroform phases of each fiber sample was analyzed by HPLC, the peak heights were measured, and the corresponding amount of glutaraldehyde was determined from the calibration curve.

The glutaraldehyde concentrations for each extraction were then summed and divided by the fiber sample ffi amount (on a dry fiber basis) to give the glutaraldehyde content on a fiber weight basis.

Two glutaraldehyde peaks were present for each HPLC chromatogram. Either peak can be used as long as the same peak is used throughout the method.

Example 1 This example shows the effect of different amounts of the crosslinker, glutaraldehyde, on the absorbency and resilience of absorbent pads made from individualized crosslinked fibers.

Individualized crosslinked fibers were made by dry crosslinking method.

For each sample, a predetermined amount of wet Southern Softwood Kraft (SSK) bulb was prepared. The fiber is hydrated whole leopard 62
．． 496 (equivalent to a consistency of 37.6%). The slurry is made of glutaraldehyde.
Predetermined amount of 0% aqueous solution and 30% (ff of glutaraldehyde)
(for 1ffi) of zinc nitrate hexahydrate and deionized water and enough INH to lower the slurry pH to about 3.7.
It was prepared by adding CR to a solution containing CR.

The fibers are soaked in the slurry for 20 minutes and then dehydrated by centrifugation to reduce the fiber consistency to about 34% to about 35%.
And so. The dehydrated fibers were then air-dried by blowing through a dryer using room temperature air to achieve a fiber consistency of about 55% to about 56%. U.S. Patent No. 3.987,
The air-dried fibers were defibrated using a three-stage fluffing device as described in the '968 patent. The disintegrated fibers were placed in trays and cured for 45 minutes in an essentially static drying oven at 145°C. Crosslinking was completed in the oven during this period. Place the cross-linked individualized fibers on a mesh sieve and
℃ water, soaked in 60℃ water with 1% consistency for 1 hour, sieved, washed again with approx. 20℃ water,
It was centrifuged to a fiber consistency of 60%, defibrated in a three-stage fluffing apparatus as described above, and thoroughly dried in a static drying oven at 105° C. for 4 hours. The dried fibers were air formed to form an absorbent pad.

The pad was compressed using a hydraulic press to a density of 0.10 g/cc. The pads were tested for absorbency, resilience and glutaraldehyde responsiveness according to the methods described herein. The reacted glutaraldehyde is reported in mole % calculated on dry fiber cellulose anhydroglucose. The results are reported in Table 1.

Table 1 Glutaralde WHV Drip Wet Compressible Sample Human (mol%) Volume No. Addition/Reaction (%) (8ml/sec)
(cc/g)Cl7g) 0.1PS
I 1.1Psl O, ]PSIR107079,
2N/A 10.88 8.04 B, 4
B2 1.7310.44 51.0 6.98 1
1.25 5.72 6.57* 3 N/A10.50 48.3 N
/A N/A N/A N/A4 2
．． 0910.82 46.7 N/A 11.2
5 6.05 [i, 095 3.1870.9
9 3B, 3 15.72 12.04
6.09 B, 8136 4.15/1.54j
5.0 15.4 [) 13.34 8.
88 8.227 8.48/1.99 32.
8 12.87 13.34 B, 93
8.318 8.42/2.75 33.2
1B, 95 13.13 7.38 8. (
i79 8U9/2.32 29.2 13.
59 12.5B 8.51 7.9010
12, Bo/3.32 27.7 13.4
7 12.04 θ, 63 7.82*
Taken from a separate sample of fibers N/A Unavailability Example 2 Individualized crosslinked fibers of Example 1 with a dry fiber density of 0.20 Z/CC
It was formed into a dry paper-making absorbent barad with a

The pads were swollen upon wetting with synthetic urine under unrestrained conditions during the performance of the drip capacitance method. The pads were then tested for absorbency, resilience and structural integrity according to the wet compression measurement method described above.

The results are reported in Table 2. Drip capacity and wet compressibility increased significantly at 0.50 mol% glutaraldehyde.

Table 2 Drip capacity Wet compressible sample (8ml/sec) k (cc/g)1
4.56 8.95 54g 5.9
02 7.84 B, 31 4.80
5.723*11.05 11.71 8.83
7.314 9.85 g, 90
5.11 B, 105 12.23 11
．． 87 13.35 7.5% 13.37
10.54 B, 04 7.257 1
1.09 9JO5,67B, 928 12
．． 04 9.69 5.72 8.8[i9
7.99 9.80 5.50
B, 7410 3.57 9.25 5
．． 50 8.4 (i* EXAMPLE 3 EXAMPLE 3 FROM A SEPARATE SAMPLE OF FIBER The amount of extractable crosslinker was determined by soaking the fiber samples in deionized water at 40°C for 1 hour at a consistency of 2.5%.The amount of glutaraldehyde extracted by water was determined by HPLC. and reported as extractable glutaraldehyde on a dry fiber weight basis.The fibers were crosslinked by a dry crosslinking method.

A Southern softwood craft valve (SSK) was prepared.

The bulb fibers were partially bleached by the following bleaching sequence steps. Chlorination (C) = 3-4% consistency slurry was converted to available chlorine (av, c
N) Treatment at approx. 5% for 30 minutes; Caustic extraction: 12% consistency slurry at approx. 74°C with 1.4 g of NaOH
/l treatment for 60 minutes; and hypochlorite treatment (H) =
12% consistency slurry at pH 11-11.5
．． At 38°C to 60°C, Elretho
) Whiteness 60-65 and viscosity 15.5-16.5c
Treat for 60 minutes with enough sodium hypochlorite to give p. Partially bleached fibers were processed into individualized crosslinked fibers according to the method described in Example 1 utilizing glutaraldehyde as a crosslinking agent. The fiber contains 2.2 glutaraldehyde, calculated on a dry fiber cellulose anhydroglucose molar basis.
It held 9 mol%. Typically, such fibers contain up to 11,000 pp of extractable glutaraldehyde.
(0,1%).

Bleaching of the partially bleached individualized fibers is then carried out using chlorine dioxide (D
) / Extraction (E) 7 Sodium hypochlorite (H) Order (D
Continue with EH) and complete. In the chlorine dioxide step (D), the individualized crosslinked fibers were soaked in a 10% consistency aqueous slurry that also contained sufficient sodium chlorite to provide 2% available chlorine on a dry fiber weight basis. After mixing, the pH of the slurry is adjusted to p by adding HCg.
The pH was lowered to about 2.5 and then the pH was lowered by addition of NaOH.
Raised it to 4,4. The valve slurry was then placed in a 70°C oven for 2.5 hours, sieved, rinsed with water to a neutral pH, and centrifuged to a consistency of 61.4.
%.

In the extraction step, a 10% consistency aqueous slurry of dehydrated fibers was prepared with NaOH0 in an oven at 40°C.
, 33g/g of water for 1.5 hours. The fibers were then sieved, rinsed with water to a neutral pH, and centrifuged to a consistency of 62.4%.

Finally, for the sodium hypochlorite stage (H),
A 10% consistency slurry of fibers was prepared containing sufficient sodium hypochlorite to provide 1.5% available chlorine on a dry fiber weight basis. The slurry was mixed and twisted in an oven at 50° C. for 1 hour. The fibers were then sieved, rinsed to pH 5.0 and centrifuged to a consistency of 62.4%. Air dry the dehydrated fibers,
It was fluffed and completely dried in an oven at 105°C for 1 hour. The amount of extractable glutaraldehyde in the fully bleached individualized crosslinked fibers was 25 ppm (0,0025%). This is significantly less than the maximum amount of extractable glutaraldehyde believed to be acceptable for applications in which the fibers are utilized near human skin.

Also, pads made from fibers that are partially bleached, cross-linked, and then fully bleached have unexpectedly higher fluid retention values and wicking rates than individualized fibers that are fully bleached and then cross-linked. It was found to have at least equivalent drip capacity and wet resilience. However, as a result of the higher WHV, fibers crosslinked at the midpoint of the bleaching sequence were more compressible in the dry state.

Substantially equivalent results were obtained when a peroxide bleaching step (P) was used in place of the final hypochlorite step (H). In the P stage, the 10% consistency dis-slurry was treated with 0.5% hydrogen peroxide (on a dry weight basis) for 90 minutes at pH 11-11.5.80°C.

Example 4 This example shows the effect of mixing an organic acid and an inorganic salt catalyst on the level of crosslinking reaction completion. The fibers were crosslinked using a dry crosslinking method.

A first sample of individualized crosslinked fibers was prepared as in Example 1. 4.0 mol% glutaraldehyde was retained after dehydration.

Analytical measurements of the fibers after crosslinking showed that the amount of glutaraldehyde reacted on the fibers was 1.58 mol% (reaction completion rate was approximately 37%).
%).

A second sample of the individualized crosslinked fibers was prepared as described in this example, except that in addition to the zinc nitrate catalyst, citric acid in an amount equal to 10% by weight of the glutaraldehyde was mixed with the zinc nitrate in the valve slurry as an additional catalyst. Prepared in the same manner as the first sample. Analysis 71P1 of the fibers after crosslinking shows that the amount of glutaraldehyde reacted on the fibers was 2.45 mol% (corresponding to about 61% reaction completion rate; molar basis), i.e. compared to the unmixed zinc nitrate catalyst sample. It was shown that the increase in reaction completion was 55.1%.

Example 5 This example disclosed the use of a small amount of gluoxylic acid, a dialdehyde acid analog having one aldehyde group, in a dry crosslinking process as described in Example 1.

Estimated glyoxylic acid reacted with cellulosic fibers1.
A fibrous slurry of wet SSK was prepared containing sufficient glyoxylic acid and zinc nitrate hexahydrate catalyst to provide 2% (on a molar basis of cellulose anhydroglucose). The centrifuged fibers had a fiber consistency of about 38% and contained about 1,06% glyoxyl by weight on a dry fiber basis. The catalyst to crosslinker ratio was approximately 0.30. pH of slurry at the start of crosslinking
was approximately 2.16. The fibers were singulated and crosslinked according to the method described in Example 1.

In the second sample, 0.53% by weight of glyoxyl (
(based on dry fiber weight) was added to the fibers to give an estimated quantitative 0.6 mole percent (calculated on a mole basis of cellulose anhydroglucose) of glyoxylic acid reacted with the fibers. Individualized crosslinked fibers were prepared according to the sample described immediately above, except that the slurry pH at the start of crosslinking was about 2.35.

Absorbent structures with densities of 0.1 g/ce and 0.2 g/cc were made from individualized crosslinked fibers as in Example 2.

The pad's drip capacity, O,IPSI, wet compressibility at 1.1 Psi and O,IPSIR, and wick action were significantly greater than absorbent structures of similar density made from regular uncrosslinked fibers. .

Example 6 This example discloses a method for making individualized crosslinked fibers by a non-aqueous cure crosslinking process in which the fibers are crosslinked in a substantially non-swelling collapsed state.

Undried SSK bleached fibers are prepared and dried to a fiber weight consistency of about 67%. U.S. Patent No. 3.987,
The fibers are mechanically disintegrated using a three-stage fluffing device such as that described in the '968 patent. The disintegrated fibers are then completely dried at 105° C. for 4 hours. Then,
The dried fibers are placed in a 10% consistency slurry of crosslinking solution and fibers. The crosslinking solution includes a 50% glutaraldehyde solution from about 0.5% to about 6.0% by weight,
An additional amount of 1.5% to about 13% by weight of water, acid catalyst (H
Cfi or H2S04) about 0.3% by weight to about 3.0f
Contains 1m% f and the remainder of acetic acid.

The fibers are maintained in the crosslinking solution at a temperature of about 25 DEG C. for 0.5 to 6 hours, with predominantly intrafiber crosslinks being formed. The fibers are then washed with cold water, centrifuged to a fiber consistency of about 60% to about 65% by weight, defibrated in a three-stage fluffer, and dried at 105° C. for 4 hours. Such fibers will generally have from about 0.5 mole % to about 3.5 mole % (based on cellulose anhydroglucose moles) of crosslinker reacted therein.

The dried fibers are air formed to form an absorbent structure and hydraulically pressed to a density of 0.10 g/ec or 0.20 g/cc or as desired, similar to the pad formed in Example 1.2. can be compressed to different densities.

Example 7 This example discloses a method for making individualized crosslinked fibers by a non-aqueous cure crosslinking process in which the fibers are partially, but not completely, crosslinked in a swollen state.

The undried SSK fibers are first dried prior to disintegration to give a fiber consistency of 50 to 55% by weight, and the disintegrated fibers have a moisture content of about 18% to about 30% by weight as a result of such disintegration.
The method followed is the same as that described in Example 6, except drying to % by weight and applying an additional drying step if necessary.

The fibers in partially swollen form are then crosslinked as in Example 6, washed, centrifuged, disintegrated and dried.

Compared to the crosslinked fibers of Example 6, the partially swollen crosslinked fibers of this example with substantially equivalent amounts of glutaraldehyde have a higher WHV and produce absorbent structures with higher drip capacity and wet compressibility. make.

Example 8 This example discloses a method for making individualized crosslinked fibers by a non-aqueous crosslinking process in which the fibers are pre-soaked in a highly concentrated aqueous solution containing glutaraldehyde prior to crosslinking in a substantially non-aqueous crosslinking solution.

The undried SSK fibers were mechanically separated using a disintegrating device as described in U.S. Pat.
0% by weight for about 2 minutes to about 30 minutes. The fibers are then mechanically pressed to provide partially swollen glutaraldehyde-impregnated fibers. The fibers are then crosslinked in the presence of a catalyst as in Example 6, washed, centrifuged, disintegrated and dried. Example 6 with equivalent crosslinking level
Compared to the crosslinked fibers of Example 1 and 7, the fibers of this example created absorbent structures with higher drip capacity and wet compressibility.

Example 9 Individualized crosslinked fibers were prepared according to the method described in Example 7.

The crosslinking solution contained 2% glutaraldehyde, 0.29% H2S04, 3% water, remainder acetic acid for samples 1 and 2; 0.5% glutaraldehyde for sample 3.4.
, H2S040.6%, water 1.2%, and acetic acid balance. The moisture content of the fibers entering the crosslinking solution was 30% for sample 1.2 and 18% for samples 3 and 4.

Glutaraldehyde reacted with the fibers to form crosslinks. WHV, drip capacity and recombined wet compressibility (0.1 PSIR) were measured and reported in Table 3 below.

Table 3 1 30 3.2 0.1055
N/A 8.42 30 3.2 0.2G5
5 14.4 7.73 18 1.6
0.1048 N/A N/A4 11i
1.6 Q, 2046 12.6 7.2N/A
Unavailable Example 10 The purpose of this example is to illustrate the production of wet-sheet formed sheets containing individualized crosslinked fibers.

Individualized crosslinked fiber 90 made according to the method described in Example 1
Regular uncrosslinked fiber with less than 96 Toro wood bark 100C8F! A 0.55% consistency slurry of a blend of fibers containing 110% and
4 meshes were deposited on autorene forming wire. The paper flow rate from the head box is 430k.
g/min. Immediately after deposition, a series of five water streams of decreasing flow rate were directed onto the fibers. The five water streams gave a cumulative flow ratio of 85 kg water/kg bone dry (b, d, ) fiber.

The showers were showered onto the fibers through a circular device spaced apart within a length area of about 1 m, all parallel to the direction of movement of the forming wire and across the width of the forming wire.

Approximate % of flow to total flow in each case of shower
and the flow rates through the device were as follows: Shower 1: 37% of total flow rate, 170 m/min; Shower 2:
36% of total flow rate, 165 m/min; Shower 3: 13% of total flow rate, 61 m/min; Shower 4: 9% of total flow rate, 41
m/min; Shower 5: 5% of the total flow rate, 20 m/min.

Immediately after the fifth shower, the fibers were fixed by treatment with a cylindrical sieve roll known in the art as a dandy roll. Dandy Roll uses fibers (high consistency when fixed).
slurry form) was pressed against a forming wire to fix the fibers in the form of a wet sheet. The sheet is
The appearance was similar to a normal fibrous valve seat.

The scope of the invention should be defined according to the claims.

Applicant's agent: Mr. Sato Procedural amendment book gong September s, 1986

Claims (12)

[Claims] 1. Individualized crosslinked cellulosic fibers, wherein the cellulosic fibers are in substantially discrete form and the crosslinking agent is reacted with the fibers in an intrafiber crosslinked form from 0.5 mol % to
3.5 mol % (calculated on a molar basis of cellulose anhydroglucose), said crosslinking agent is a C_2-C_8 dialdehyde, a C_2 with at least one aldehyde group.
~C_8 dialdehyde acid analogs, and oligomers of said dialdehydes and dialdehyde acid analogs, said fibers having a water retention value (WRV) of less than 60. . 2. 2. The fiber according to claim 1, wherein the fiber has from 0.75 mol% to 2.5 mol% (calculated on a molar basis of cellulose anhydroglucose) of crosslinking agent reacted therewith in the form of intrafiber crosslinking. Individualized crosslinked fibers. 3. 3. The individualized crosslinked fiber of claim 1 or 2, wherein the crosslinking agent is selected from the group consisting of glutaraldehyde, glyoxal, and glyoxylic acid. 4. 4. The individualized crosslinked fiber of claim 3, wherein the crosslinking agent is glutaraldehyde. 5. The individualized crosslinked fiber according to claim 2, 3 or 4, wherein the WRV is 28-50. 6. In producing individualized crosslinked cellulosic fibers, a. preparing cellulose fibers; b. contacting the fiber with a crosslinking agent selected from the group consisting of C_2-C_8 dialdehydes, C_2-C_8 dialdehyde acid analogs having at least one aldehyde group, and oligomers of the dialdehydes and dialdehyde acid analogs; c. reacting the crosslinking agent with the fibers in the substantial absence of interfiber bonds to form intrafiber crosslinks, wherein the fibers contain from 0.5 mol% to 3.5 mol% of the crosslinking agent (cellulose anhydride). (calculated on a molar glucose basis) is contacted with a crosslinking agent in an amount sufficient to react with the fibers to form intrafiber crosslinks, and the fibers have a WRV of less than 60 after crosslinking. Method for producing crosslinked cellulose fibers. 7. In producing individualized twisted crosslinked cellulosic fibers, a. preparing cellulose fibers; b. A solution containing a crosslinking agent selected from the group consisting of C_2-C_8 dialdehydes, C_2-C_8 dialdehyde acid analogs having at least one aldehyde group, and oligomers of said dialdehydes and dialdehyde acid analogs. c. mechanically separating said fibers into substantially discrete forms; d. drying the fibers while the fibers are in a substantially discrete form and reacting the crosslinking agent with the fibers to form crosslinks to form intrafiber crosslinks; contacting a sufficient amount of crosslinking agent to react with the fibers to form intrafiber crosslinks from 0.5 mol% to 3.5 mol% (calculated on a molar basis of cellulose anhydroglucose) of the crosslinking agent; A method for producing individualized twisted cross-linked cellulose fibers characterized by: 8. In producing individualized twisted crosslinked cellulosic fibers, a. preparing cellulose fibers; b. The fibers are crosslinked with a crosslinking agent selected from the group consisting of C_2-C_8 dialdehydes, C_2-C_8 dialdehyde acid analogs having at least one aldehyde group, and oligomers of said dialdehydes and dialdehyde acid analogs. contacting with a solution; c. reacting the crosslinking agent with the fibers in the substantial absence of interfiber bonds to form intrafiber crosslinking bonds, and from 0.5 mol% to 3.5 mol% crosslinking agent.
(calculated on a molar basis of cellulose anhydroglucose) is contacted with the fibers in an amount sufficient to react with the fibers to form intrafiber crosslinks, and the crosslinker is a water-miscible polar diluent. and the fibers in 30% water by weight.
individualized twisted crosslinked cellulosic fibers characterized in that the fibers are reacted with said fibers in a crosslinking solution containing an amount of water not sufficient to cause the fibers to swell to a higher level than the corresponding swelling level of the fibers containing said fibers. manufacturing method. 9. In producing individualized crosslinked cellulosic fibers, a. preparing cellulose fibers; b. The fibers are treated in an aqueous solution with a C_2-C_8 dialdehyde, a C_2-C_8 having at least one aldehyde group.
8 dialdehyde acid analogs, and oligomers of said dialdehydes and dialdehyde acid analogs, said solution containing a sufficient amount of cross-linking agent such that said fibers do not swell substantially. c. defluidizing the fibers and drying the fibers to a moisture content of less than 30% by weight (relative to the total weight of the fibers); d. contacting the fiber with a solution containing a polar water-miscible diluent and an amount of water not sufficient to cause the fiber to swell beyond a degree of swelling corresponding to a fiber having a water content of 30% by weight; , e. reacting the crosslinking agent with the fibers to form intrafiber crosslinking bonds, and from 0.5 mol% to 3.5 mol% crosslinking agent.
an individualized crosslinked cellulosic fiber, wherein an amount of crosslinking agent (calculated on a molar basis of cellulose anhydroglucose) reacts with the fiber to form an intrafiber crosslinking agent in contact with the fiber. manufacturing method. 10. The method for producing individualized crosslinked cellulosic fibers according to claim 6, 7, 8 or 9, wherein the crosslinking agent is glutaraldehyde. 11. Claims 6 and 7, wherein 0.75 mol% to 2.5 mol% (calculated on a cellulose anhydroglucose mole basis) of crosslinking agent reacts with the fibers to form intrafiber crosslinks. A method for producing individualized crosslinked cellulosic fibers according to item 8, 9, or 10. 12. An individualized crosslinked fiber produced by the method according to claim 6, 7, 8, 9, 10, or 11.