CA1105831A

CA1105831A - Absorbent materials

Info

Publication number: CA1105831A
Application number: CA313,309A
Authority: CA
Inventors: John A. Bosley; Vicki Maddison; Alan A. Mckinnon
Original assignee: Unilever PLC
Current assignee: Unilever PLC
Priority date: 1977-10-18
Filing date: 1978-10-13
Publication date: 1981-07-28
Also published as: FR2406471A1; IE47456B1; DE2862250D1; DE2844956A1; IE782053L; AT369643B; AU4078178A; AU526924B2; IT7869389A0; SE7810830L; FR2406471B1; LU80384A1; IT1108485B; DK462578A; EP0001706B1; PT68666A; NO783519L; JPS5470694A; NZ188633A; BR7806853A

Abstract

- 1 - J.702/7 Canada ABSTRACT OF THE DISCLOSURE

Water-swellable particulate absorbents surface-treated with one or more polyethers containing oxyethylene and/or oxypropylene units have improved dispersibility in blood.

Description

3~

- 1 - cJ.702/7 ~BSORBEN~ MATER~ALS

This invention relates to absorbent materials, more especially absorbent materials suitable for use in absorbent disposable products such as sanitary towels or napkins and : tampons and absorbent products for surgical or medical use.
The invention also relates to processes for producing such materials and to absorbent articles containing such materials, In recent years there has been much interest in the synthesis of absorbent polymers having a high capacity *or absorbing water and body fluids, A number of different polymers have been developed some being wholly synthetic in nature and some partially svnthetic.

Among the partially synthetic absorbent polymers are those based on starch. These include the starch-acrylonitrile graft copolymers described in US Patent Sepcifications Nos. 3,997,484 (the USA as represented by the Secretary of Agriculture) and 3,661,815 (Grain Processing Corporation), and the cross-linked gelatinised starch derivatives described in Canadian Patent 1,084,914 issued to Unilever Ltd. on September 2, 1980, corres-ponding to German Offenlegungsschrift 2,702,781 (Unilever N.V.) published July 28, 1978. Other examples of partially synthetic absorbent polymers are the carboxymethylated cellulose described in US Patent Sepcification No. 3,589,364 (Buckeye Cellulose Corporation), and the carboxymethyl cellulose cross-linked by acid interesterification as described by Podlas, T.J. in INDA
Tech. Symp. 1976, 2~3 March, pp 25-39.
~' 15 Wholly synthetic absorbents include polyacrylates cross-linked with a polyamide/epichlorhydrin material as described in US Patent 4,076,673 issued February 28, 1978 (Dow Chemical Com-pany) and the potassium salts of polyacrylic acid cross-lined by aluminium ions as described in US Patent 4,090~013 issued May 16, 1978 (National Starch and Chemical Corporation).
The above materials are substantially water-insoluble and absorb many times their weight of water, urine or other aqueous body exudates. They retain a particulate character as they imbibe surrounding liquid and swell. In most cases, even with water, the swollen particles are gelatinous and tacky and form clusters. An exception is

- 2 -,~

~ 3 ~ ~ 31 cJ.702/7 the cross~ ed starch derivative described in ~bove-mentioned Canadian Patent 1 0~4 9~4,the particles of which on absorbing water are substantially non-tach7 and dry to the touch. However, e~en this s~arch derivative, as well s as the other absorbents previously referred to, has poor . dlspersibility in blood, so that when blood is brought into contact with a ma~s oP the absorben$ sig~ificant penetration . into the bed and hence absorption is extremely slow. ~he par~icles have therefore what may bé descri~ed as poor "blood wet-out~' so that on exposure to blooa the.
particulate material at the inside of a mass remains unreached by the blood. Although the mechani~m is not understood at the present time, it appear~ that the blood on initial contact with the par-ticles ~orms some sort of mass ~hich acts as a barrier to the passage oi the blood through the ~uriace layers of the particles.
An object o~ the invention i~ to provids a~ absorbent composition having improYed blood dispersibility, or I'blood ~et-out". It is als~ an object to pr~vide a process for producing such an ~mproved absorbent.
According to the invention there is provided a water swellable particulate absorbent materi~l suriace_treated to enhance its dispersibility i~ blood wlth one or more ~ polyethers o~ the formula - 25 Ho(c2H~o)a(c3~6o)b(c2H4o)c where a ~ c represents the total number of oxyethylene units and b the numbe~ of o~propylene u~its and where ' .
, ' :

.
' '': ' , -J.702/7 a + c or b may be zero, the amount o~ polyether being such as to permit capilla~ flow of blood through a mass of the particulate absorbent.
The molecular weight of the polyether is not critical and may vary for example over the range 300 to 6,000, The polyether may be a polyoxyethylene polymer, i.e.
a polyethylene glycol, in which case b in the above ~ormula is zero. Polyethylene glycol~ are water-soluble.
Preferred polyethylene glycols are those having a molecular weight of from 300 to 2~000.
The polyether may be a polyoxypropylene polymer, i.e.
a polypropylene glycol, in which case a + c in the above formula is ~ero. Polypropylene glycols are not ~oluble in water. Preferred polypropylene glycols are those having a molecular weight of from 400 to 2~500.
~he polyether may also be a water-soluble or a water-insoluble polyoxyethylene-polyoxypropylene block copolymer.
By a water-soluble polyether is meant one which is soluble to the extent of more than 1% in water at 25C? i. e. a solubili-ty of greater than 1 g in 100 g of water. In - water-soluble polyoxyethylene-polyoxypropylene copolymers the weight o~ the oxyethylene units exceeds about 15% by weight o~ the total compound. Suitable polyoxyethylene-polyoxypropylene block copolymers are those available commercially under the trade mark PL~RONIC, ~or example the water-soluble PLURONICS L62, L~3, L35 and F38, and the water-insoluble PLURONICS L61, L81, L101 and L121.
~: .

~ 5 ~ ~ ~ 5 ~ ?1 cJ.702/7 Preferred polyo.Yyethylene-polyoxypropylene copol~ers are those which are liquid at room temperature. Pre~erred water-soluble copolymers are those having a molecular weight of from l,000 to 3,000.
The water swellable absorbent materials which may be treated with the polyether are exemplified by the partially synthetic and wholly synthetic absorbent polymers described above. ~he water retention values of such polymers are at least 2 g/g and are usually much higher. The particulate absorbent material may be in the form of a powder, granules, flakes or fibres.

The treatment o~ the absorbent with a liquid polyether may be effected simply by directly mixing the particulate absorbent with the polyether. When a polyether is used which is solid at normal temperature it is necessary to iirst melt the polyether and then to thoroughly mix the particulate absorbent with the molten polyether. Mixtures of solid and liquid polyethers would also require to be heated to melt the solid component.
The treatment of the absorbent with the polyether may be effected by first dissolving the polyether in a suitable volatile solvent and after thoroughly mixing the absorbent with this solution, heating the mixture to drive off the solvent. ~olvents which may be used are water and the lower aliphatic alcohols, preferably ethanol or isopropanol, although any other solvent could be used which is su~ficiently volatile to permit its ready removal after ' - 6 ~ 5~ cJ.~02/7 admixture with the absorbent material~ Ho~Yever, in the case of water it is necessary to use generally larger amo~mts of ehe polyether to ensure -tha-t after treat~ent there i~ enough present on the surface of the particles o~ the absorbent to enhance blood wet-out. It may be possible to produce the surface-treatea absorbent by adding the polyether in solution in a solvent during the process of manu~acturing the absorbent. For example, in the case of the absorbent described in above-mentio~ed Canadian Patent 1 084 ~4, the starch derivative in its acid form is conveniently mixed with a solution o~ the polyether in a volatile solvent, and an alkall, e.g. sodium caxbonate or ammonium hydroxi~e, and the mixture heated to obtain as a .~ .
dry po1~der the treated starch deriva-tive in the salt form.
lS The amount of the polyether that is used for the treatment of the absorbent depends on a number of ~actors.
The amount which is suf*icient to e~fect an enhancement of the dispersibility of the absorbent in blood (i.e. the "~lood wet-out" o~ the absorbent) may vary with the ; 20 chemical type of absorbent and its physical form, e.g.
particle size, and the type and molecular weight of the polyether used in the treatment, as 1iell as on the method of treatment. In general, for a given absorbent, increasing amount~ o:E polye-ther are required as the molecular weight of the polyether employed increases. It should be noted, however, that excessive amounts of the polyether or polyether mixture inhibit blood dispersibility , ' ~ 7 - cJ.702j7 tS~

by pre~enti~ capillary ~lo~ of blood through a mass oi the particulate absorbent. It is required that the blood ~hould be able to percolate throu~h the capillaries or spaces between the particles and thereYore these should not be blocked by the polyether. If this occurs the blood would be forced to tra~el through the mass by dif~usion alone: this is a relatively slow process and corresponds to very poor blood wet-out properties. Consequently, the .
amount o~ th~ polyether used for the treatment of the absorb0nt should not be such as to result in, ~or example, a mi~ture having a paste-like or ointment~ e consistency such as is produced by the composition described in .. E~ample 6 of British Patent Speci~ication No.1,454,055 .(Pharmacia AB).
Employing the gelatinis~d starch deri.vati~es described in above-mentioned Canadian Pa-tent ~ 08L~ 914 good re~ult~
have been obtained using as little as 1% by weight oi a polyethylene glycol having an average molecular weight o~
400 based on the weight o~ absorbent while amount~ o~ thi~
20 polyether, when mi~ed directly with the a~sorbent, abo~e about ~~ should not be used to a~oid producing an unsatis~actory oin-tment-like or pasty ~i~ture. The higher molecular weight, normally solid, polyet,hylene glycols are generally requirea to be u~ed in greater amounts than the liquid glycols. For most absorbent materials the amount of po~yethylene glycol will not normally be required to e~cee~ about ~0/0 by weight o~ the absorbent polymer ,' , ' . ~ . . . . .

' - 8 _ ~ S ~ ~ ~ cJ.702/~

when the direct method of mixing with the absorbent is employed.
The polypropylene ~lycols and the polyoxyethylene-polyoxypropylene copolymers will generally be used in 5 amounts of from about 1% to about 35% by weight, depending on their molecular weight and the nature of the absorbent.
The normally solid copolymers, having generally higher molecular weights, when used alone tend to be required to be used in relatively substantial amounts, e.g. about 25%
to about 35% by weight of the absorbent, but again the amount of the polyether required will be dependent to some extent on the chemical type and physical form of the absorbent being treated. As will be shown hereinafter, in certain cases amounts of polyether up to about 50/0 by weight of the absorbent can be used while still permitting capillary flow of blood through a mass of the particulate treated absorbent.
By treatment o~ an absorbent with a polyether in accordance with the invention one can also improve the feel to the touch of a mass of absorbent swollen with blood.
Many absorbent polymers become very ~ticky to the touch when blood is added to a mass of the particles. We have ; found that treatment with the polyether reduces this stickiness.
The treatments described do not markedly af~ect the blood retention value of an absorbent.

.~
, - ' ' ' .

- 9 - ~ 5~ cJ.702/7 The invention also relates to liquid absorbent articles containing the absorbent material o the invention. The liquid absorbent articlc may comprise a ~ibrons carrier or support for the absorben-t material, such as a woven or S umYoven material such as cotton cloth, rayon, wool, surgical gauze or paper as well as cellulosic fluf~, on or within which the absorbent material is supported. The absorbent material may be spread on the carrier or it may be mixed with loose fibres to make a composite fluff or wadding which can be enclosed between cover sheets o~
paper or cloth. The article may also be in the form of a laminate. In a particular ~orm, -the carrier comprises two sheets bet~een which the absorbent material is sandwiched. The absorbent materials o~ the invention are particularly suitable for use in sanitary to~els, napkins or tampons. The production of an absorbent article utilising a particulate absorbent material is described for'example in a~ove-mentioned ~anadian Patent ~ 084 914.
The Invention will now be illustrated by the ~ollowing example~. Percentages are by weight.
References herein to the "dry-off" o~ an absorbent re-fer to feel of the polymer -to the touch after a mass of particles of the absorbent has absorbed blood. An absorbent ~ith poor dry-off would be s-ticky to the touch , 25 whereas one with a good dry-o~f would ~eel substantially dry and non-sticky. ~Yater and urine retèntion values are gi~en to the nearest quarter o~ a unit.

: ' -`1 lo - ~5~.~1 cJ.70217 Examples 1 to 9 Potato starch (1,000 g) was slurried in water (950 ml) containing epichlorhydrin (8.~ ml; l.OQ~o epichlorhydrin by weight of starch). Sodium hydroxide (5 g) in water ~50 ml) was added with stirring and the mi~ture was applied to a heated roller via a feeder roller to form a layer on the surface of the roller of about 0.5 mm thickness. The roller itself was heated using steam at 3.77 bars (140C).
The cross-linked starch derivative was removed from the roller as a flake material to yield 91~ g of product. The soluble content of the product was found to be 2~.0 mg/g and the product was found to have a bed volume o~ 13.5 ml/g.
Since about half of the epichlorhydrin was lost by evaporation from the heated roller the degree of substitution of the cross-linking groups was about 0.01.
- ~odium hydroxide (3~ g) in water (66 ml) followed by monochloracetic acid (39 g) in water (11 ml) was slowly added with stirring to the cross-linked potato starch (100 g~ as prepared above. The mixture was aged overnight in a polythene bag. The theoretical degree of substitution was 0.67.
The moist carboxymethyl derivative was dispersed in 10 times its weight of lN hydrochloric acid and soaked for 15 minutes and then filtered. The gel cake was repeatedly dispersed in water and ~iltered until the filtrate was substantially free o~ chloride ions. Ammonium hydroxide~
specific gravity 0.910 (~0 ml) was mixed with the water-., .

~ ~ ~ ~ cJ.702/7 swollen washed cake before drying in a forced air oven(70 C) and milling (2 mm ~creen). The milled product has a water retention value of 20.00 g/g, a urine retention ~alue of 10~25 g/g, a ~olubility of 0.3/0 and a bed volume of 51 ml/g.
Various polyethylene glycols were used to treat the control material prepared as described above. In the case of the liquid polyethylene glycols in Examples 1 to 5 the~e were added to the absorbent with thorough mixing.
For the normally solid polyethylene glycols used in Examples 6 to 9, these were melted in a glass di~h and the control absorbent material mixed with the molten polyether whil~t maintaining the mixture ju5t above the melting point of the polyether. ~he percentage~ of the poly-ethylene glycol~ added which are given in ~able I are ba~edon the weight of the control material. I~ each case the treated absorbent was of particulate form.

~ cJ.702/7 TABLE I
Example Po1yethylene Glycol Molecular Wei~ht~/0 Added

3 ~00

4 ~00 5 7 1,000 5 8 1,500 10 9 4,000 10 The products of Examples 1 to 9 each showed a marked improvement in blood wet-out and dry-off compared to the control material to which no addition had been made.
The ability of an absorbent to be wet-out by blood was assessed by placing 1-2 g of the absorbent to be treated on a watch glass and adding to it 1-3 ml of blood. In the cases where the absorbent had been treated with a poly-ethylene glycol the blood rapidly penetrated the mass of particles whereas in the case of the control material the blood only very slowly, if at all, penetrated the mass to reach the particles in the interior of the mass.
Examples 10 to 16 These e~amples illustrate the use of a mixture of liquid and solid polyethylene glycols.

~5~
- 13 - cJ.70217 A mixture of 2 parts by weight of a solid polyethylene glycol of molecular weight 1,500 and 1 part by weight of a liquid polyethylene glycol of molecular weight ~00 was heated to ju~t melt the solid component. Various amounts of the control absorbent material as described above with reference to Examples 1 to 9 were thoroughly mixed with the liquid mixture of polyethers.
The percentage~ of the polyether mixture ba~ed on the weight of the control absorbent are given below in Table II.
TABLE II
Example /0 Polyether Mixture 1~ 30 Comparative Example A 50 Comparative Example B 60 In the ca~e of each of Examples 10 to 16 the treated polymer, which was in particulate form, had a fast blood wet-out. In the case of Comparative Examples A and B, these mixtures did not absorb blood, the amount of poly-ether being so great in these cases that capillary flow ofblood between particle~ of the absorbent was prevent. The mixturé of polyether and absorbent in the case of each of , .

~5~1 ~ cJ.702/~

Comparative Examples A and B was no-t particulate but rather was a continous ointment-like mass.
Exa~ple~ 17 and_18 Polypropylene glycol, MW 2,025, was added directly, with thorough mixing, to the control absorbent material as de~cribed above with reference to Examples 1 to 9. In the case of Example 17 the amount was 6% and in the case of Example 18 loo,h, both percentages being by weight of the unmodified control material. In both cases the blood wet-out and dry-off of the absorbent was improved compared to the unmodi~ied absorbent.
Examples 19 to 25 Variou~ water-soluble polyoxyethylene-polyoxypropylene copolymers were mixed with the control absorbent material as described above with reference to Examples 1 to 9.
Details of the copolymers used are gi~en in Table III.
The copolymers employed in Examples 19 to 2~ were liquids and that employed in Example 25 was a solid.

- 15 _ ~ ~3L cJ.702/7

5, ~ oooo~oo 'C ,~ ~,~ ~ ~C"
~1 o ~
o P~
o s~
~p~ oooo~oo a~ ,~ ~ u~ o o o u, b~ U~
_~ . ~ ~q~C~C~lC7 G~
C~ ,~ o ,Y_ _ _ ..
p ~ bO ~ C)_I ~ ~1 ~I C`
O ~ rl ~ O
5~ o ~ o ,1 P ~,Q
~o ~o s~
P
,~ ooooooo ~ t~o ~ ~ o o U~ o j:7 C~ ~U~ D O
~ C~ ~ ~_ _ _ _ .~ _ _ H H _1 ~rl~1 H H C`l ~I C~ 1 H S X

O

C~
H
O
P

~1 G~ O ~ l:`1 U~ O

~o `~ 'I
., - 16 - ~ cJ.702/7 The particulate products o~ E~amples 19 to 25 each ~howed a marked improvement in blood wet-out and dry-off compared to the control material to which no addition had been made, Example 26 to 28 These examples illu~trate the treatment of an absorbent with a solution of a water-soluble polyether.
A solution of a polyether in a solvent was added to the wa~hed cake prior to the addition of ammonium hydroxide in the preparative procedure described above with reference to Examples 1 to 9.
The polyethers and solvents employed together with the percentage weight of the polyether based on the weight o~ the dry untrea-ted absorbent are given below in Table IV.
TABLE IV
Example Polyether Solvent ! Polyether 26Polyethylene glycol Water 30 27Polyethylene glycol Water 50 MW 1,500 28 PLURONIC L43 Isopropanol 8 The treated products, like the ~mtreated product, were obtained as a powder. They had in each case improved blood wet-out and dry-of~ properties compared to the untreated absorbent.

- 17 _ '~ 3~ cJ.70217 Examples ~9 and 30 The preparation described in Examples 1 to ~ was repeated as far as the production of the washed acid cake which was divided into three equal portions. Polypropylene s glycol, molecular weight 2,025, dissolved in isopropanol (20 ml) was added to a portion (238 g) of the washed acid cake. Ammonium hydroxide, ~pecific gravity 0.910, (25 mls) was then mixed in before drying in a forced air oven (70C) and milling (2 mm screen).
The amount of polypropylene glycol added expressed as a percentage of the weight of a dried control product to which no polypropylene glycol was added, together with the water and urine reten-tion values of the resultant products and of the control product are given in Table V.
TABLE V

Water Urine /0 Polypropylene Retention Retention Example Glycol _ Value (~/~) Value (~
2g 14 22.25 8.75 30 21 17,75 7,50 Control 0 17.50 9.25 The particulate materials o~ Examples 29 and 30 had much better blood wet-out than the particulate control material containing no polypropylene glycol. The treated absorbents of Examples 29 and 30 also showed a good dry-off whereas blood formed a sticky matt when added to the control material.

;

q~
- 18 - cJ.702/7 Examples 31 to 39 Washed acid cake IYaS prepared as described in Examples 1 to 9. ~ range of polyether materials was added as described in Table VI in the stated percentage ba~ed on the weight of the dried control material. ~he polyethers were dissolved in isopropanol to aid their admi~ture with the absorbent, prior to ammoniation.
TABLE VI
E~ample Additive 1031 Polypropylene glycol, MW 400 32 " " " 5 33 " " " 9 34 " " MW 1,025 " " MW 2,025 7 1536 Pluronic L61, MW 2,000 6 37 " L81, MW 2,750 7 38 " L101, MW 3,800 5 39 " L121, MW 4,400 7 The Pluronic materials used in Examples 36 to 39 are water-insoluble polyoxyethylene polyoxypropylene block copolymers of the formula H0(C2~40)a(c3~60)b(c2H40)cH
where in each case a + c is such that the total weight of the polyoxyethylene units is about 10% by weight of the total compound and b is such that the molecular weights of 25 the polyoxypropylene units for tne grades 161, L81, L101 and L121 are about 1,750, 2,250, 3,250 and 4,000 respectively.

. --' `:

: . :

,~
~: ' . ' ' ' :

- 19 ~ cJo 702/7 The particulate products obtained from Examples 31 to 39 ~howed a marked improvement in blood wet-out and dry-off compared to the control material containing no additive.
Example 40 Example 1 was repeated as far as the preparation of the washed acid cake. Polypropylene glycol, MW 2,025 (6 g) dissolved in isopropanol (20 ml) was mixed into the acid cake (800 g). A solution of sodium carbonate (16.2 g) in water (100 ~1) was added before drying in a forced air oven (70C) and milling (2 mm screen).
The particulate product obtained had improved blood wet-out and dry-off compared to a control material containing no additive. The product had a water retention . ~
value of 19.50 g/g and a urine retention value of 9.75 g/g.
; 15 The corresponding values for the control material were 22.50 g/g and 10.75 g/g.
Examples 41 to 44 Polyethylene glycol, molecular weight 400, was added directly with thorough mixing to absorbent materials as described in Table VII each of which had a water retention value greater than 2 g/g. In each case the blood wet-out and dry-off of the absorbent was improved compared to the respective unmodified absorbent.

:

' .
.:-,.

- 2~ cJ.702/7 TABLE VII
,xampleAbsorbent~'0 Polyethylene ~lycol, MW 400 ~1Ab~orbellt A 5 42 Absorbent B 30 43 Absorbent C 30 ~4 Absorbent D 3 Absorbent A was the potassium salt of a polyacrylic acid cross-lin~ed by aluminium ions available commercially from National Starch Corporation under the trade name Permasorb and generally described in above-mentioned U.S. Patent 4 090 013.
Absorbent B was a carboxymethylated cellulose cross-linked by intermolecular e~terification and available from Hercules Corporation under the trade name SPX 115~ and generally described by Podlas, T.J. in INDA Tech. Symp.
1976, 2_3 March, pp 25-39. It i~ a particulate fibrous material.
Absorbent C was a hydrolysed starch-polyacrylonitrile graft copolymer available from the Grain Processing 2n Corporation under the trade name Polymer 35_A_100 and generally described in US Patent No.3,661,815.
Absorben-t D was a starch-polyacryloni-trile graf-t copolymer prepared in accordance with -the process described : in US Pa-tent No,3,9Sl,100.
In the case of Examples 42 and 43 the polyethylene glycol caused some agglomeration of the particles.

i~. . . _, .

33~
- 21 - cJ.702/7 Examples 45 to 56 The liquid polyoxyethylene-polyoxvpropylene block copolymers commercially available under the trade name~
PLURI)NIC L42 and PLURONIC L81 were added with thorough 5 mixing to absorbent materials as identified in Tables VIII
and IX each of which had a water retention value greater than 2 g/g. The percentage of the copolymers added is ~ based on the weight of the untreated absorbent, In each !:. case the blood wet-out was improved compared to the 10untreated material.
TABLE VIII
Example AbsorbentC,~ PLURONIC L42 i 46 B 30 ' 1547 C 35 ': 49 E 7 ': 50 F 40 TABLE IX

,, 20Example Absorbent~ PLURONIC IJ81 . 52 B 30 ' . 53 C 35 .:. 54 D 3 - ` 255'; E 7 :~-! ~ -:, - 2'~ - cJ.702/7 Ab~orbent E was a carboxymethy7.ated ccllulose cro~s-linked by intermolecular esterification and a~ailable m~
commercially from Hercules Corporation under the trade ~-Aqualon R an~ generally de~cribed in the artic].e by Podlas, T.J. referred to above.
Absorbent F was a hydroly~ed starch-polyacrylonitrile graft copolymer available from General Mills Inc., under the trade name SGP-502S and generally described in US
Patent NoO3,997,484.
xamples 57 to 61 Polypropylene glycol, MW 2,025, was added directly, with thorough mixing, to absorbent materials as described in Table X. In all cases the b~.ood wet out and dry-off of the particulate treated absorbents was improved compared to the unmodified absorbents.
T.ABLE X
Example Absorbent~ Polypropylene glycol Gl F 40 Comparative Example C
A cro~s-linked dextran having a water retention valu~
of about 2,5 g/, wa~ employed to make a produc-t in a.ccordance with Example 6 of British Patent Specifi~ation No.1,4a4,055 (Pharmacia AB) and having the following composition:

- 23 - ~ 5~i cJ,702/7 Polyethylene glycol MW 400 ~14.3 Polyethylene glycol MW 1,500 28.6 Cro~s-linked dextran (Sephadex (~-25) 5~.1 . .
The two polyethylene glyool products were first heated together to form a melt to which dry particles of the cros~-linked dextran were added with stirring. The mixture was then cooled.
To the mixture, which had the consistency of an ointment, drop~ of blood were added. The mixture absorbed blood very ~lowly, the rate being diffu~ion controlled.
It did not swell or show dry-off properties. The poly-ethylene glycol mixture i~ pre~ent in such amount that the interparticle pore~ are blocked preventing capillary flow of the blood between the par-ticles.
~ 6~0t~5 ~de ~( .. , ~ .

-

Claims

J.702/7 (CA) The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A substantially water-insoluble polymeric absorbent material consisting of water-swellable particles surface-treated to enhance its dispersibility in blood with one or more polyethers of the formula Ho(C2H4O)a(C3H6O)b(C2H4O)CH
where ? + ? represents the total number of oxyethylene units and ? the number of oxypropylene units and where ? + ? or ?
may be zero, the amount of polyether being such as to permit capillary flow of blood through a mass of the particulate absorbent; wherein:
a. said water-swellable particulate absorbent material has a water retention value of at least 2 g/g; and b. said polyether has a molecular weight of about 300 to about 6,000,

2. An absorbent material as claimed in Claim 1, wherein the polyether is a liquid.

3. An absorbent material as claimed in Claim 1, wherein the polyether is a polyethylene glycol or a polypropylene glycol.

4. An absorbent material as claimed in Claim 1, wherein the polyether is a polyoxyethylene-polyoxypropylene block copolymer.

5. An absorbent material as claimed in any of Claims 1 to 3, wherein the polyether is a polyethylene glycol and the absorbent is treated with an amount of the polyether of from 1 to 30% by weight of the untreated absorbent.

6. An absorbent material as claimed in any of Claims 1 to 3, wherein the polyether is a polypropylene glycol and the absorbent is treated with an amount of the polyether of from 1 to 35% by weight of the untreated absorbent.

J.702/7(CA)

7. An absorbent material as claimed in any of Claims 1 to 3, wherein the polyether is a polyoxyethylene-polyoxypropylene block copolymer and the absorbent is treated with an amount of the polyether of from 1 to 35% by weight of the untreated absorbent.

8. A method of producing a substantially water-insoluble polymeric absorbent material consisting of water-swellable particles having enhanced dispersibility in blood, comprising contacting the absorbent material with one or more polyethers of the formula HO(C2H4O)a(C3H6O)b(C2H4O)CH
where a? + ? represents the total number of oxyethylene units and ? the number of oxypropylene units and where ? + ? or ? may be zero, to form a coating of polyether on the surface of the particles, the amount of polyether employed being such as to permit capillary flow of blood through a mass of the treated particulate absorbent; wherein:
a. said water-swellable particulate absorbent material has a water retention value of at least 2 g/g; and b. said polyether has a molecular weight of about 300 to about 6,000.

9. A method as claimed in Claim 8, comprising intimately mixing the particulate absorbent material with one or more liquid or liquefied polyethers of the formula given in Claim 8.

10. A method as claimed in Claim 8, comprising intimately mixing the particulate absorbent material with a solution in a volatile solvent of one or more polyethers of the formula given in Claim 8 and then removing the solvent.

11. A liquid absorbent article containing a water-swellable particulate absorbent material as claimed in any of Claims 1 to 3.

J.702/7(CA)

12. A sanitary towel or tampon containing a water-swellable particulate absorbent material as claimed in any of Claims 1 to 3.