GB1570485A

GB1570485A - Absorbent material for aqueous fluids

Info

Publication number: GB1570485A
Application number: GB3430475A
Authority: GB
Original assignee: Robinson and Sons Ltd
Current assignee: Robinson and Sons Ltd
Priority date: 1975-11-18
Filing date: 1975-11-18
Publication date: 1980-07-02

Description

(54) ABSORBENT MATERIAL FOR AQUEOUS FLUIDS (71) We, ROBINSON & SONS LIM1TED, a British Company of Wheat Bridge, Chesterfield, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is concerned with an absorbent material for aqueous fluids, which is particularly but not exclusively useful in absorbent medical, surgical and sanitary articles.

Absorbent articles, such as incontinence pads, baby napkins, sanitary towels, catamenial tampons, dental and surgical tamponades, surgical dressings and breast pads, are well known. They contain a material such as cellulose fluff pulp or viscose rayon staple fibre, which absorbs fluids. Recently, it has been proposed to use hydrophilic gels as the, or one of the, absorbent materials in such articles.

However, whilst such gels have very advantageous water-absorbtive properties, there are problems in locating the gel materials in an absorbent article. For example, a typical hydrophilic gel may have a wet bult at least thirty times its dry bulk, and it is not easy so to pack and locate the gel in an article that an expansion of this nature can be accommodated. If expansion of the gel is restrained, then full use is not made of its water absorbtive properties.

Furthermore, when gel particles imbibe fluid and swell, they become mobile in the surrounding fluid and can thus "leak" from an absorbent pad, for example.

We have now devised an absorbent material in which a hydrophilic gel is accommodated within the pores of an open-cell foam. In this way, when the gel imbibes fluid and swells, it is locked within the foam and is hence substantially immobile but can still expand within the foam cells.

According to one aspect of the invention therefore, there is provided an absorbent material for aqueous fluids which comprises an open cell foam containing in the cells thereof a hydrophilic gel (as herein defined).

It is to be understood that, in the materials of the invention, the proportions of gel to foam may vary very widely. It is not essential that every cell within the foam contain gel. Indeed, when the proportion of gel is low, relatively fewer cells will generally contain gel. An even distribution of gel throughout the foam is preferred but is not essential.

The foam is preferably a fully reticulated or fully open cell material having a void volume of up to about 98%. Hydrophilic foam materials are preferred since the fluids to be absorbed are largely aqueous. Suitable materials include hydrophilic aminoplast resins, modified aminoplast resins, phenolic and modified phenolic resins and polyurethane resins, of which the following are specific examples: hydrophilic urea formaldehyde, melamine formaldehyde, benzoguanamine formaldehyde, phenol formaldehyde, melamine phenol formaldehyde, poly ester polyurethanes and polyether polyureethanes.

By "hydrophilic gel" we mean a waterinsoluble polymer which forms an elastic gel on imbibing fluid without the formation of a sol.

Such hydrophilic gels are typically capable of imbibing from 10 to 100 or more times their own weight of water, up to 60 times their own weight of urine, and up to 30 times their own weight of blood and other body exudates. The amount of fluid uptake will depend upon the degree of cross-linking, the concentration of dissolved solids, the molecular size of dissolved solids in the fluid, and the pH of the fluid. The particles of polymer swell, whilst maintaining their integral identity, and hold the imbibed fluid against release when a pressure of up to 1 tonne/m2 is applied. For practical purposes, a pressure of 200 kgslm2 is used for measuring the fluid uptake of these gels and products containing gels and absorbent media, because this is the likely pressure to be encountered by the products in medical, surgical or sanitary use.

Hydrophilic gels are prepared from either hydrophilic polymers (e.g. starch, cellulose, protein, alginate, cellulose esters) by graft polymerisation of a water-soluble monomer (e.g. acrylonitrile, acrylamide, methylacrylate) on to the polymer, followed by hydrolysis without solubilisation, or from water-soluble monomers, linear homopolymers, or linear copolymers, by sparsely cross-linking the polymer (preferably just sufficiently) to render it insoluble. The degree of cross-linking required to produce a hydrophilic gel for the purposes of absorption is typically less than 2.5% of cross-linking agent, based on the weight of the water-soluble polymer. The higher the degree of cross-linking, the less the polymer will imbibe fluid.For example, a hydrophilic gel used as an ion exchange resin, will be cross-linked at between 2.5% and 5%, and absorb up to 10 times its own weight of water (poly(sodium methacrylate) cross-linked with divinyl benzene); a hydrophilic gel for insertion in live body tissue, or for optics, which has to be milled or ground, will be cross-linked at between 5% and 10rio, and absorb up to 6 times its own weight of water (polyethylene glycolmethacrylate cross-linked with methyl methacrylate). Water-soluble polymers suitable for sparse cross-linking may also be prepared from water-insoluble monomers and polymers, by introducing hydrophilic groups (e.g. hydroxyl, carboxyl, sulphonate, etc.) after polymerisation.

Graft polymerisation is readily achieved by processes well known in the polymer arts, for example acrylonitrile can be grafted on to cellulose using ceric salts as catalysts, to produce the graft copolymer cellulose-acrylonitrile.

Cross-linking may be readily effected by processes well known in the polymer arts, for example either by incorporating typically less than 2.5% of a difunctional cross-linking agent in the monomer mix, prior to polymerisation, or by cross-linking with typically less than 2.5% of a difunctional cross-linking agent, a watersoluble linear homopolymer or linear copolymer. Also, for example, cross-linking can be achieved by irradiation, with either electron or gamma rays, of either a water-soluble polymer to effect intermolecular bonds, or of two water soluble polymers, to produce an insoluble copolymer capable of absorbing more than ten times its own weight of water.

Examples of water-insoluble polymers and monomers suitable for graft polymerisation on to these polymers, to produce copolymers, have previously been mentioned. Examples of watersoluble polymers, suitable for the production ol hydrophilic gels, are:-- Vinyl polymers - e.g.

polyvinyl alcohol, polyvinyl pyrrolidone, polystyrene sulphonate, polyvinyl methyl ether, polyvinyl morpholinone.

Acrylic polymers - e.g. polyacrylamide, poly (ethyl methacrylate), poly (acrylic, methacrylic and crotonic) acids, poly (sodium acrylate), poly (hydroxy methyl acrylate), poly (glycol methacrylate).

Cyclic ether polymers - e.g. polyethylene glycol (or oxide), polypropylene glycol (or oxide).

Amino polymers - e.g. polyethylenimine.

Polysaccharides - e.g. starch, dextrin, cellulose ethers.

Copolymers - e.g. maleic anhydride with vinyl ethyl ether.

Examples of non-conjugating difunctional cross-linking agents, suitable for insolubilising the above water-soluble polymers, are methylene bisacrylamide, methacrylic acid, glycol dimethacrylate, divinyl ether, epichlorhydrin, diallylamine and ethanolamine.

The preferred hydrophilic gels for the purposes of the present invention are those based on polysaccharides, because unlike most of the other gel materials, these are not entirely derived from petroleum or oil. In particular, the hydrophilic gel described in British Patent No. 1,325,998, which is based on a saponified carboxylated starch - polyacrylonitrile graft copolymer, is especially suitable for use in this present invention.

One manner of making the absorbent material of this invention consists in intimately blending an open-cell foam with particulate hydrophilic gel in any proportions, whereby gel particles become located within the foam cells.

To obtain maximum accommodation of the gel in the foam, the foam will be in granular form and the gel particles should have a diameter of not more than half, and preferably about 1/5, of the pore diameter of the foam. In this way, the gel particles readily enter the foam cells.

The preferred foam pore diameter is from 10 tc 300 microns, the foam granules preferably being from 100 um to 1 mm in size. The hydro.

philic gel particles will generally be up to about 200 Clam, although a particle size of less than 50 pm is preferred.

Usually, not all the gel will become accommodated within the foam granules. Some gel will adhere to the outer surfaces of the granules and some will remain loose in the mixture.

There may also be some aggregation of the hydrophilic gel particles during the blending, and the aggregates will normally be too large to enter the pores in the foam.

In another method of making the absorbent material of the invention, the foam is impregnated with a liquid carrying the gel, and after impregnation the liquid is removed. In this way, gel particles are located within the pores of the foam. The carrier liquid must be one which does not cause the gel particles to swell, and generally a suspension of gel particles in a volatile organic solvent, such as for example isopropanol, is preferred.

In general, the larger the piece of foam to be impregnated with gel, the more difficult it is to achieve a high loading of gel and, for this reason, we prefer generally to use foam granules in both the above methods.

In a further method of making the absorbent material of the invention, the open cell foam is formed in the presence of the hydrophilic gel whereby hydrophilic gel is contained within the cells of the foam. This may be effected by, for example, polymerising to form the foam in the presence of the gel.

The proportions of foam and gel in the materials of the invention may vary very widely, i.e. from 1:99 to 99:1 by weight.

Generally, there will be at least 4% by weight of gel relative to the total weight of foam and gel. By varying the proportions, the bulk density of the absorbent material can be varied. In this way (and, where necessary, by appropriate choice of the foam and gel materials themselves), bulk densities closely similar to those of conventional absorbents such as viscose rayon staple, cellulose fluff pulp, cotton shearers and cotton linters, for example, may be obtained.

By achieving a similar bulk density to these conventional absorbents, the absorbent materials of the present invention can be processed on conventional pneumatic converting machinery, and can also be blended in any proportion with one or more conventional absorbents such as cellulose fluff pulp (this is more fully described hereinafter).

By appropriate choice of the proportions of foam and gel in the absorbent materials of the invention, it is possible to obtain a material whose bulk when wet is substantially the same as its bulk when dry, without resorting to precompression of the material (which is a technique conventionally used to bring the dry bulk of a product closer to its wet bulk). It is a serious disadvantage of many conventional absorbent articles such as pads, that their wet bulk is significantly less than their dry bulk.

For example, the wet bulk of cellulose fluff pulp is only 45% of its dry bulk; cellulose wadding has a wet bulk only 55% of its dry bulk; surgical wadding viscose rayon staple fibre has a wet bulk only 60% of its dry bulk, and cotton linters has a wet bulk only 65% of its dry bulk. In practice, the manufacturer of products containing these materials has necessarily to produce a dry absorbent pad which is about twice as bulky as in its wet condition, and this results in discomfort and embarrassment for the wearer, and extra cost for the manufacturer because he has to use a larger amount of wrapping and coverstock.On the other hand, an absorbent pad of the present invention containing a blend of a hydrophilic gel and foamed resin, can be produced which wilt exhibit no significant change in bulk when it is converted from the dry to the wet state, and which, because of the high absorption characteristics of the hydrophilic gel, will only be about half as bulky as a conventional product having an equivalent absorptive capacity.

Furthermore, it is possible to arrange for the absorbent materials of the invention to have a higher bulk when wet than when dry. This is of particular interest for the production of tampons and tamponades. Using traditional materials for these products, i.e. cotton and viscose rayon, the pad has to be compressed to give a lower dry bulk. The release of the compression forces when fluid reaches the pad, gives the increased wet bulk. It is now possible to blend a hydrophilic gel and a foam such as an aminoplast resin, in varying proportions to produce the exact amount of expansion required for the tampon or tamponades.

In the past, one of the problems associated with the use of hydrophilic gels in absorbent articles has been the mobility of the gel "particles" in the swollen state whilst surrounded by fluid. This problem is substantially overcome by the absorbent material of the present invention since once the gel particles in the foam imbibe fluid and swell, they become too large to escape from the foam pores and are thus anchored within the foam. The gel can still absorb very large quantities of fluid, however, if the total pore volume of the foam is relatively large (as is highly preferred).

In an absorbent article comprising the absorbent material of the invention, the reticulated structure of the foamed resin reduces the rate of spread of fluid compared with a conventional article wherein the absorbent material is, for example, cellulose fluff pulp. This reduction in the rate of spread of fluid is particularly important in female incontinence pads and sanitary towels, for example, where leakage at the sides of the pad or towel can be a problem.

This property also allows the product to retain a dry surface much longer, and prevents soiling of clothing when pressure is applied to the product in use.

The absorbent material of the present invention may be used alone as the absorbent in an absorbent article, it being understood that in TABLE I

100% 90% 80% 70% 60% 40% 1/3 25% BLEND Foam Foam Foam Foam Foam Foam Foam Foam 100% Resin 10% 20% 30% 40% 60% 2/3 75% Gel Gel Gel Gel Gel Gel Gel Gel Dry Bulk 32 29 27 24.5 15 14 13 9 2.5 density ccslgm. ccslgm. ccslgm. ccs/gm. ccs/gm. ccs/gm. ccslpm. ccs/gm. ccslgm.

Wet Bulk 28 29 30 31 33 37 42 38 41 density c:cs/gm. ccs/grn. ccslgm. ccs/gm. ccslgm. ccs/gm. ccslgm. ccs/grn. cos/gm.

Ret. 20.0 22.0 ] 25.0 25.0 25.0 34.0 36.5 32.0 37.0 Coeff.

TABLE II

100% 75% Blend 50% Blend 45% Blend 25% Blend 100% Blend 25% Fluff 50% Fluff 55% Fluff 75% Fluff Fluff Pulp Pulp Pulp Pulp Pulp Dry Bulk 22.5 15.0 14.0 14.5 17.0 22.5 density ccs/grn. ccs/grn. ccs/gm. ccs/grn. ccs/gm. ccs/gm .

Wet Bulk 32.5 19.5 15.0 14.5 13.0 12.0 density ccs/gm. ccs/gm. ccs/gm. ccs/gm. ccs/gm . ccs/gm.

Ret. 25.0 17.0 13.0 12.5 11.5 10.5 Coeff.

TABLE III

Weight Ret. Coeff. Fluid Absorbed Rayon tampons 3.0 gms. I 13.0 39.0 rips.

(Precompressed) 1/3rd foam, 2/3rds gel 1.4 gms. 25.0 35.0 mls.

blend (Uncompressed) addition to the gel accommodated within the foam, there may be some gel on the outer surfaces of the foam and in loose admixture therewith. It is also possible however, to use the absorbent materials of the present invention together with other absorbent materials such as cotton wool, cotton linters or cellulose wadding or fluff pulp. By careful choice of the proportions of absorbent material of the invention, and conventional absorbent, it is possible to obtain products whose bulk density is either reduced, or increased, or unchanged when converted from the dry to the wet state.

The following Examples 1 and 2 show the properties of various absorbent materials of the invention together with, for comparative pur poses, the properties of the foam and of the gel.

Example 3 describes one form of absorbent article according to the invention, namely a tampon, and compares this with a conventional tampon. All the Examples are given by way of illustration only. In the Examples, wet bulk density means the bulk density of the wet absorbent material excluding the weight of the water present therein.

EXAMPLE 1 Table 1 compares blends of different proportions of a typical amino last foam resin (cast bulk density = 8 kg/m = 0.5 lbs/cu,ft; granulated or crushed bulk density = 2 lbs/ cu.ft.), and a hydrophilic gel of the carboxylated starch-acrylonitrile graft copolymer type (Polymer 35-A-100 supplies by Grain Processing Corp.).

A typical cellulose fluff pulp has the following properties: Dry bulk =22.5 ccs/gm. Wet bulk = 12.0 density density ccs/gm.

Retention coefficient = 10.5 By interpolation from Table 1, it can be seen that a blend of about 2/3rds foam resin and about 1/3rd hydrophilic gel, will have a dry bulk density which is the same as fluff pulp.

EXAMPLE 2 lhe blend of 2/3rds foam and 1/3rd gel (see Example 1) was mixed in varying proportions with cellulose fluff pulp, and the dry and wet bulk densities, and retention coefficients, were measured. The results are shown in Table II on previous page.

As can be seen, the mixture of 55% fluff pulp and 45% blend had the same bulk densities in the wet and dry states. A comparison of the bulk of the mixture with that of an amount of fluff pulp required to absorb 100 mls., is as follows: Fluff pulp: Dry Bulk - 215 ccs. Wet Bulk - 114ccs.

Dry wt. - 9.5 gms.

Gel/foam/fluff Dry Bulk - 116 ccs. Wet Bulk pulp mixture: - 116 ccs.

Dry wt. - 8.0 gms.

EXAMPLE3 Table I shows that a blend of 1/3rd foam resin, 2/3rds hydrogel, has a wet bulk of 42 ccs/gm, which is at least three times its dry bulk, and a retention coefficient of 36.5. This blend is suitable for tampons and tamponades, and tampons were made by wrapping 1 gm of this blend in a non-woven fabric. These were compared with rayon tampons for fluid absorption, with the results shown in Table III.

EXAMPLE 4 A suspension of absorbent starch (saponified carboxylated starch-polyacrylonitrile graft copolymer) was made up in isopropanol.

Pieces of polyurethane foam, about 2mm thick were impregnated with the suspension and then dried. Whilst the penetration of gel into the foam cells was not very high, the treated foam still had a useful water-absorption ratio. For example, one specimen of volume 9 cc (97% voids) weighed 0.2 gms. dry (before impregnation), and took up 0.2 gm. gel. The gelimpregnated dry specimen imbibed 7 gm. water (drip and shake free) whereas an identical specimen of foam not containing gel imbibed only 3 gm. water.

Test Methods All the above mentioned tests (except the tests on tampons), i.e. dry and wet bulk density, and retention coefficient, were performed under a pressure of 200 kgs/m2. A calibrated cylinder was used which contained a removable piston capable of exerting a pressure, on the material under test, equivalent to 200 kgs/m2 - The retention coefficient of the material under test was obtained by dividing the figure obtained for the increase in weight of the sample due to fluid uptake by the dry weight of the sample. The retention coefficient on the tampons (Table III) was calculated by determining the fluid absorbed, using the drip and drain method.

The absorbent materials of the invention are particularly, but not exclusively, useful in absorbent medical, surgical and sanitory articles.

In general, they may be incorporated in such articles in the same way that conventional absorbents are incorporated in conventional such articles.

In order that the invention may be more fully understood, reference is made to the accompanying drawings in which: Figure 1 is a perspective view of one form of baby diaper according to the present invention Figure 2 is a section on the line II-II of Figure 1; Figure 3 shows an alternative construction, in section similar to Figure 2; and Figure 4 illustrates one process for making the diaper of Figures 1 and 2.

Referring to the drawings, Figures 1 and 2 show a baby diaper comprising an outer envelope 38 of water-permeable sheet material closed at each end and along the seam 42. Within the envelope is a random mixture of fluffed cellulose pulp (50) and granules foam/gel absorbent material of the invention (52). The proportions of pulp and foam/gel are preferably such that the loss of volume of the pulp when wetted is counterbalanced by a corresponding increase in volume of the foam/gel material.

The diaper of Figure 3 has a sandwich construction in which the foam/gel of the invention (52) is sandwiched between two layers (50, 51) of fluffed cellulose pulp. Again, the proportions of pulp and foam/gel are preferably such that the bulk of the diaper is substantially unchanged when it is wetted.

Referring to Figure 4, foam in block form (1) is fed by a conveyor system (2) into a granulator (3) where it is broken into small pieces and passes into a further section (4) where it is further refined into small granules. Such equipment is well-known and the small granules are passed by means of the air current thus created into a separator (5) where the particles lose velocity and fall downwards, while the air is dissipated upwards. The separator acts as a store for the granulated foam, which collects at the bottom of the container as at (6). The bottom of the separator includes a metering device (7) which is illustrated in simple form whereby rotation of the metering device feeds substantially steady quantities of foam granules into a duct 13 along which it is drawn under the influence of suction fan 14 to merge with the delivery from a metering device (15). Meter.

ing device 15 delivers regular quantities of gel material (16) (contained within a hopper 17) to combine with the granulated foam, and the two materials travel together under the influence of the suction fan (14) and are delivered via duct 18 into the inlet of a mixer (19) which typically includes a paddle type rotor and screen (20) to ensure sufficient inter-mixing.

The foam gel mixture is drawn through from the mixer via duct 21, to combine with the outputs from a pulveriser (9) the purpose of which will be presently described.

The equipment is shown in simple diagram matical form. A reel of cellulose (8) is drawn into a pulveriser (9) which is provided for the purpose of pulverising cellulose pulp to produce a fluffed pulp to finally mix the ingredients prior to depositing in a manner to be described.

A toothed rotor 11 contacts the advancing web of cellulose pulp (12) and disintegrates the material into a fine fluff, the degree of fineness having some relationship to the rate of advance of the web (12) and the speed of the rotor (11).

By virtue of the current of air generated by such equipment, the fluffed material is fed away from the pulveriser and joins the metered foam granules at junction 23 via duct 22, becoming moderately inter-mixed therewith, and this inter-mixed materials proceeds by further ducting (24) to a further mixer (25) with a grid (26).

The mixture after thorough inter-mixing escapes through the perforated plate 26, being assisted by a suction fan (27), into a depositing chamber (28). The depositing chamber is of well-known type and has means for taking the water-permeable carrier web (29) of the diaper construction of Figure 2 from a reel (30) and passing it over a mesh belt (31), where the pulverised mixture is deposited on to the travelling web (29). It is usual in such depositing means to have a suction applied underneath the mesh belt as illustrated by a suction chamber (32) to which suction is applied by ducting (33) from a suction fan (34).The suction fan passes the air into the separator (5) together with any small amount of pulverised material which might have passed through the carrier web (29) and the mesh belt (31), the carried over pulverised material being deposited in the separator chamber for re-use, the adulteration being of only minor degree.

The carrier web (31) with its layer of pulverised mixture passes through a rotary cutter system (35) where it is cut into individual lengths appropriate to the diaper. These cut lengths pass into an accelerator belt and roller system (36) and (37) to produce a required gap between the cut lengths, suitable for the end seal shape illustrated by Figure 1, in which there is no pulverised material present in the end sealing area. Simultaneously, a web of cover material (38) is drawn from a reel (39) and applied continuously to the spaced cut lengths via the belt (37) and the cover is then folded to form an overlapping envelope illustrated in Figures 2 and 3 by means of folder plate system (40).Immediately before folding is completed, a jet of hot-melt adhesive is applied by ahot melt jet system (41) between the overlapping joints as illustrated at (42) in Figures 2 and 3 and also at (42) in Figure 1. There is thus formed a continuous sheath of cover material (38) with lengths of pulverised material spaced apart lengthwise therein which pass to a cutter/embosser system (43) which operates in strict timed relationship with the cutter (35). This cutter/embosser system serves to seal areas in between the pulverised lengths by physical pressure, or more advantageously by making use of heat sealing properties of a cover which can be appropriately provided. Simultaneously with the embossing, a pressure cutter will sever individual lengths to produce individual diapers sealed at each end and along the longitudinal overlapping joint.The individual diapers pass into a further accelerator belt system (44) and (45) producing spacing between individual diapers to enable a stacking system (46) which is conveniently illustrated by a plunger (47) operating in strict timed relationship with the cutter embosser (43) and the cutter (35) so that diapers are placed in face to back relationship with each other out of the belt system. It is common practice for the diapers to be held by belts engaging only with the edges thereof to enable the plunger to pull the diaper out of the belt system for stacking.

As illustrated, the diapers are marshalled into a track (48) which curves into the horizontal position enabling selected counts to be extracted for packing as required.

The construction of Figure 3 may be made in a similar way. The constituent layers of fluff pulp cellulose (50) and (51) and the sandwiched layer of foam gel mix (52) can be produced by multiple depositing stations embodying the general principles illustrated for the construction of Figure 2.

By way of example only, in the above described method, one suitable foam is a urea formaldehyde foam having a pore size of 10 to 300 microns and about 97% voids. The foam granules are preferably 0.1 mm to 1 mm in size.

A suitable gel is a saponified carboxylated starch-polyacrylonitrile graft copolymer of particle size below about 50 microns. The proportions of such materials, by weight, in the diaper produced are preferably 15% gel, 30% foam and 55% pulverised cellulose. Such a mix has a reasonably constant wet and dry bulk.

In making the absorbent materials of the invention, it can be advantageous to include a wetting agent. In use of the materials, the presence of the wetting agent speeds up the rate of wetting and swelling of the hydrophilic gel.

There are many suitable wetting agents, one example being Lissapol N ("Lissapol" is a registered trade mark).

It may also be advantageous to include in the materials of the invention a bacteriostatic agent. Certain quaternary ammonium compounds, such as cetyl trimethyl-ammonium bromide (Cetrimide) act both as bacteriostats and as wetting agents, and these substances can be included in the materials of the invention.

The addition of wetting agents and/or bacteriostats (and/or other similar additives) can be achieved in various ways. For example, referring to the process illustrated in Figure 4, a predetermined amount of the additive in powder form may be added at point A, i.e.

between the gel metering device and the suction fan 14. The additive is thus mixed with the gel and foam prior to combination with the pulverised pulp. Alternatively, an aqueous or alcoholic (for example) solution of the additive could be applied either upstream of the foam granulator, or at point B on the advancing web of cellulose pulp 12.

WHAT WE CLAIM IS: 1. An absorbent material for aqueous fluids, which comprises an open cell foam containing, within the cells thereof, a hydrophilic gel (as herein defined).

2. A material according to claim 1, wherein the gel has been made by graft polymerisation of a water-soluble monomer on a hydrophilic polymer.

3. A material according to claim 2, wherein the water-soluble monomer is acrylonitrile, acrylamide, or methyl methacrylate, and the hydrophilic polymer is starch, cellulose, a protein, an alginate or a cellulose ester.

4. A material according to claim 1, wherein the gel has been made by cross-linking a water-soluble copolymer just sufficiently to render it water-insoluble.

5. A material according to claim 1, wherein the gel has been made by introducing hydrophilic groups into a water-insoluble polymer.

6. A material according to claim 1, wherein the gel is a polysaccharide-based gel.

7. A material according to claim 6, wherein the gel is a saponified carboxylated starchpolyacrylonitrile graft copolymer.

8. A material according to any preceding claim, wherein the cells of the foam have a diamteer of from 10 to 300 microns.

9. A material according to any preceding claim, wherein the foam is selected from hydrophilic aminoplast resins, modified aminoplast resins, phenolic and modified phenolic resins and polyurethane resins.

10. A material according to claim 9, wherein the foam is a hydrophilic urea formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, phenol formaldehyde resin, melamine phenol formaldehyde resin, polyester polyurethane resin or poiyether polyurethane resin.

11. A material according to any preceding claim, which also includes a wetting agent and/or a bacteriostat.

12. An absorbent material according to claim 1, substantially as herein described in any of the Examples.

13. A method of making an absorbent material as claimed in claim 1, which comprises intimately blending an open cell foam with particulate hydrophilic gel (as herein defined) whereby gel particles become located within the foam cells.

14. A method according to claim 13, wherein the foam is in granular form and the gel particles are of a diameter not exceeding half the average cell diameter of the foam.

15. A method according to claim 14, wherein the foam granules are from 100 um.

to 1 mm in size and the cell diameter is from 10 to 300 microns, and wherein the gel particles have a particle size less than 50,us.

16. A method of making an absorbent material as claimed in claim 1, which comprises impregnating an open cell foam with a liquid carrying a hydrophilic gel, the liquid being one which does not cause the gel particles to swell, and then removing the liquid to leave hydrophilic gel within the cells of the foam.

17. A method according to claim 16, wherein the said liquid is a volatile organic solvent.

18. A method according to claim 16, substantially as herein described in Example 4.

19. An absorbent material for aqueous fluids when produced by the method of any of claims 13 to 18.

20. An absorbent article which includes an absorbent material as claimed in any of claims 1 to 12 or 19.

21. An article according to claim 20, which also includes, in addition to the said absorbent material claimed in any of claim 1 to 12 or 19, a further adsorbent material.

22. An article according to claim 21, wherein the said further absorbent material is cotton wool, cotton linters, cellulose wadding or fluff pulp.

23. An article according to claim 21 or 22 wherein the proportions of absorbent material and further absorbent material, and the proportions of gel and open cell foam are such the the volume of the article when dry is substantially the same as when it is wet.

24. An incontinence pad, a baby napkin, a sanitary towel, a catamenial tampon, a dental or surgical tamponade, a surgical dressing or a breast pad, which comprises an absorbent material as claimed in any of claims 1 to 12 or 19.

25. A baby napkin substantially as herein described with referenee to Figures 1 and 2 or Figure 3 of the accompanying drawings.

26. A method of making a baby napkin according to claim 24 substantially as herein described with reference to Figure 4 of the accompanying drawings.

27. A method of making an absorbent material as claimed in claim 1, which comprises forming an open cell foam in the presence of a hydrophilic gel (as herein defined) whereby hydrophilic gel is contained within the cells of the foam.

28. An absorbent material produced by the method of claim 27.

29. An absorbent article containing a material as claimed in claim 28.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. powder form may be added at point A, i.e. between the gel metering device and the suction fan 14. The additive is thus mixed with the gel and foam prior to combination with the pulverised pulp. Alternatively, an aqueous or alcoholic (for example) solution of the additive could be applied either upstream of the foam granulator, or at point B on the advancing web of cellulose pulp 12. WHAT WE CLAIM IS:

1. An absorbent material for aqueous fluids, which comprises an open cell foam containing, within the cells thereof, a hydrophilic gel (as herein defined).

15. A method according to claim 14, wherein the foam granules are from 100 um.

28. An absorbent material produced by the method of claim 27.

29. An absorbent article containing a material as claimed in claim 28.