CA1074475A

CA1074475A - Absorbent blend of grafted polysaccharide and cellulose

Info

Publication number: CA1074475A
Application number: CA241,254A
Authority: CA
Inventors: Pronoy K. Chatterjee; Graham K. Morbey
Original assignee: Personal Products Co
Current assignee: Personal Products Co
Priority date: 1974-12-09
Filing date: 1975-12-08
Publication date: 1980-03-25
Also published as: JPS5182991A; PH11500A; ES443277A1; GB1500559A; ZM17075A1; FR2293913B1; NO754137L; SE419937B; JPS5913214B2; SE7513689L; BE836429A; AR217799A1; AU498246B2; AU8723675A; MX143982A; DE2554640A1; IN144058B; FR2293913A1; NO138747C; ATA927575A

Abstract

Absorbent Blend of Grafted Polysaccharide and Cellulose Abstract of the Disclosure A selected class of grafted polysaccharide is combined in intimate mixture with less absorbent particulate matter to form a core, said core being deposited into an absorbent product such as absorbent products such as tampons, sanitary napkins or diapers.

Description

sackground of the Invention This invention relates to absorbent bodies as used in products designed to absorb body exudates such as catame-nial napkins and tampons, diapers, surgical sponges, wound dressings and the like. These products g~nerally comprise an absorbent body enveloped by a material, at least a portion of which is permeable to body exudates. In the case of cata-menial tampons, for example, the absorbent body is generally in a highly compressed form and in some circumstances may be u~ed without the enveloping material.l In the case of diapers and sanitary napkins, the absorbent body is generally in the form of a pad sandwiched between a facing sheet and a backing sheet, the latter of which may be impermeable to body exudates.
Notwithstanding the particular configuration, it isl of course, desirable that the absorbent body have a relatively high ab-sorhency per unit weight for the aqueous based body exudate fluids.
Most commonly, absorbent bodies for these products are made of highly porous batts of wood pulp fiber and general-ly meet the criteria for products of this na~ure in that wood ~, :
pulp is absorbent, inexpensive and, in the form of loose batts,comfortable to the ultimate user~. Nevertheless, in efforts to improve these absorbent products, the art is now replete with ;
modifications of, and substitute material for, wood pulp.
One such modified material is disclosed in UOS.
Patent No. 3,256,372 dated June 14, 1966 and is described ~ ;
therein as a product produced by chemically grafting, in a -water slurry, hydrophilic polymer chains onto cellulose fibers such as wood pulp (this product hereinafter referred to as grafted cellulose). The wet fibers obtained from the slurry are then extruded into shaped porous articles and carefully dried to maintain their porous struc-ture by such special tech-~7~75i niques as freeze-drying or solvent drying. The resultan-t pro-duct is highly absorbent and is useful in such products as cigarette filters. Unfortunately, however, the extruded shapes are relatively hard, brittle and, when incorporated into a pro-duct such as a disposable diaper or a catamenial device, can cause discomfort to the user.
In our copending application Canadian application No. 241,253 filed herewith, we have disclosed the discovery that grafted cellulose, when used in comminutéd powdered form of a carefully controlled particle size may be effectively in-corporated into an absorbent body without resorting to exotic drying techniques while still obviating the gelling problem usually associated with water-swellable powders. The comminut-ed grafted c~llulose powder is then disclosed as being disposed within an absorbent body as one or more cores surrounded by less absorbent material, such as wood pulp. Thus, in a sanitary nap-kin or diaper, the grafted cellulose is provided as a central ; layer sandwiched between two layers of wood pulp ~luf. In a catamenial tampon, the grafted material is disposed in the form of central cores or strata separated by layers of compres-sed wood pulp. While this disclosure represents a great advan-ce in the art in that grafted cellulose can now be used to greatly increase the absorptivity of absorhent bodies, it will still be advantageous to make a still further increase i.n ab-sorptivity.
Summary of the Invention In accordance with the present invention, a class o~
grafted polysaccharide (including the aforementioned grafted cellulose) may be more advantageously used in an absorbent body by first combinln~ said material with less absorbent par-ticulate matter in an intimate mixture therewith and then using this mixture as at least one core in an absorhent body. In par- --3- ~

.
.. ; ..... . . .

ticular, such less absorbent particulate matter, i.e., fibers, powders, etc., should be capable of being wetted, but should not swell to as great an extent as the grafted polysaccharide when exposed to aqueous systems such as body fluids. Examples of such materials are such unmodified cellulosics as wood pulp and cotton; regenerated cellulose; synthetic wettable mate-rials such as hydrophilic synthetic polymers, e.g., hydro-philic polyurethane foams, polyvinyl alcohol fibers, hydro-philic nylon, and the like.
For the purpose herein, such materials shall be termed "unmodified cellulose" it heing undPrstood that this term encompasses the equivalents thereof known to those in the art and, in fact, may include noncellulosic materials as exem-plified above as well as cellulose which has been modified -- either physically or chemically in a manner which does not dis- -advantageously affect its wettability or swellability with res-pect to the teachings of this invention.
For reasons not yet clearly understood, it has been ~; discovered that such a core, comprising a given weight of the blend of unmodified cellulosic material and grafted polysaccha-ride is substantially more absorbent than a core of an identi-cal weight of either the unmodiied cellulose or the grafted polysaccharide taken alone~.
Specifically, it has been discovered that polysaccha-ride particles having grafted thereon hydrophilic chains of carboxyl- carboxylaté/ and/or carbamide moities, when combined in an intimate mixture with unmodified cellulose to form a core, synergistically cooperate with the unmodified cellulose to great-ly enhance the ability of the core to absorb water and aqueous solution. When this core is incorporated into an absorbent body such as in products for absorbing body fluids (e.g. cata-: ' .. . . . . ..
" ' " ' - ' , ' ,' ~' , ,' , ',' ''. ' ,~ ', ', ,,, , " , ' . ', ~: , ' .

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menial nap~ins/ tampons, diapers and the like), it will yreat-ly increase the absorbency of such products.
In a preferred embodiment of this invention, the core comprises a mixture of the grafted polysaccharide particles and comminuted wood pulp. Preferably, the grafted polysaccharide is selected to have an arithmetic average particle size of from about 40 to about 1000 microns and still more preferably, from about 50 to about 500 microns in size. As used herein, the term "arithmetic average particle size" is taken to mean par-ticle size calculated from the expression:

~ ab - arithmetic average 100 particle size where "a" is weight fraction of particles expressed as a percen-tage of total weight and "b" is the average particle size for ~ -"a" expressed in microns, a method of measuring these values being described herein.
~- The unmodified cellulose constituent of the core may be in the form of powder or fiber and the arithmetic particle size may vary over a wide range, e.g., arithmetic particle si-zes of fro~ 2000 to 50 microns are suitable. It is preferred that the mixture comprise at least 10% by weight of the grafted polysaccharide material and preferably at least 20% by weight up to a maximum of about 95% by weight.
The blended core may be disposed as a central layer within an absorbent body, the remainder of which is convention-al absorbent materials. For example, when the blended core is used in a sanitary napkin or diaper, the core may be provided as a central layer sandwiched between wood pulp layers or wadded tissue layers. In the case of a catamenial tampon, the . . .
.. . . . .. . . .

f~7~ 5 core may be disposed on one or more interior layers. When the core is used in tampons of the type made by first winding a rectangular pad of wood pulp, cotton or the like, into a cylin-der and then compressing the same, the core may be applied onto the surface of the pad, and then wound with the pad prior to compressing, When used in this manner, the core particles assu-me a spiral configuration in radial cross-section.
In accordance with this invention ~here is provided in an absorbent product, an absorbent core comprising grafted polysaccharide particles in intimate mixture with less absorbent, wettable, less swellable particulate matter selected from unmo-dified cellulose or hydrophilic synthetic polymer. The grafted polysaccharide particles comprise polysaccharide having grafted thereon about 10~ by weight to about 90~ by weight hydrophilic chains of the general formula:

(C~2)q - CR - - (CH2)p~ CR2 - _ ~-`C=O - C=o . X Y
_ _ m _ n wherein R and R2 are selected from the group consisting of hydrogen and alkyl having 1 to 4 carbon atoms, X and Y are selected from the group consisting of -OH, -O(alkali metal), and -NH2, wherein m is an integer having a value of 0 to about 5000, wherein n is an integer having a value of 0 to about 5000, the sum of all m and n groups is at least 500, p is an integer having a value of 0 or 1, and q is an integer having a value of 1 to 4.~ The individual particles of the grafted poly-; saccharide have an arithmetic avérage size of from about 50 to about 500 microns. The absorbent core exhibits a fluid -':' .~ . .. .
.' .~,':

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re-tention greater than that of each component when tested alone. The core comprises about 10 to about 95~ by weight,of the grafted polysaccharide.
BRIEF DESCRIPTION OF THE DRAWINGS
... . ..
In the drawings:
Fig. 1 is a perspective view of an absorbent dressing or a disposable diaper embodying this invention, a portion thereof being broken away to show interior detail~
~; Fig. 2 is a cross-sectional view of the dressing or diaper oE Fig. 1 taken along line 2-2;
Fig. 3 is a perspective view of a partially rolled blank for compressing into a first catamenial tampon embodying this invention;
Fig. 4 is a perspective view of a finished tampon made from the blank of Fig. 3, a portion thereof being broken away to show interior detail;
Fig. 5 is a perspective view of a partially folded blank for compressing into a second catamenial tampon embodying !
this invention;
~; 20 Fig, 6,is a cross-sectional view of the finished tam-pon made from the blank of Fig. 5 taken thrQugh an axial plane through the tampon.
Fig, 7 is a perspective view of a catamenial sani-tary napkin embodylng this invention, a portion thereof being broken away to show interior detail; ~-Fig. 8 is a cross-sectional view of the sanitary ;~ napk1n of Fig. 7 taken along line 8-8; and Figs. 9, 10 and 11 are graphical illustrations of the synergistic effect obtained in accordance with the teach- -ings of this inventionO

' ~ ':

DESCRIPTION OF THE PREFERRED EMBODIMENTS
The Grafted Polysaccharide Water--insoluble starch or a wide variety of cellu-losic fibers can be utilized as starting materials for produc-ing the grafted polysaccharides suitable for the present inven-tion. Typically, such cellulosic fibers are: cotton, cotton linters, wood pulp, bagasse pulp, jute, rayon and the like. The polysaccharide chains are then modified by grafting thereon a hydrophilic chain of the general formula:

_ ~(CH2)q - CR - - -(CH2)p - fR
~ c o I L ~ n wherein Rl and R2 are selected from the group consisting of hy-drogen and alkyl having 1 to 4 carbon atoms, X and Y are select-ed from the group consisting of -OH, -O(alkali metal), -O(alkyl) having one to four carbon atoms, -OHNH3, and -NH2, wherein m is an integer having a value of 0 to about 5000, n is an inte-ger having a value of 0 to about 5000, the total number of m and n moiety on a chain is at least 500, p is an integer having a value of zero or 1, and q is an integer having a value of 1 to 4O
; Preferred hydrophilic chains are those selected from the group consisting of polyacrylic acid, alkali polyacrylate such as sodium or potassium polyacrylate and copolymers of -these which may be obtained, for example, by the hydrolysis of polyacrylonitrile chains. It should be understood that in the hydrolysis of polyacrylonitrile chains, some polyacryl-amide, an intermediate product, is formed and may be also pre~
sent in the final product.

.

. ' ' .

While the detailed mechanism by which the grafting oE the hydrophilic chain or chains onto a starch or a cellulo-sic backbone is not fully known, it is believed that one pO5-sibility is that grafting takes place through a free radical mechanism whereby the free radical i5 situated on the backbone which serves as a reducing agent and the hydrophilic chains is attached to the cellulosic reducing agent through a carbon linkage. The produced grafted copolymer using a cellulosic backbone is of the type:
H O~ CH O~

¦ ~ H
~J`H ~
CH2O~ H 0 wherein ~ represents the hydrophilic chain of Formula I above.
The grafted copolymer using a starch backbone is substantially similar to that represented by Formula I except that a starch backbon~ i5 present in lieu of a cellulose backbone.
The foregoing hydrophilic chains are polymers of an olefinieally unsaturated earboxylie acid or a derivative there-of with itself or with at least one other monomer copolymer- -isable therewith. The resulting polycarboxylic aeid-type poly~
mers can, for example,inelude those containing monomer units ~ sueh as aerylic aeid, aerylie anhydride, methaerylic aeid, cro- -; 20 tonic aeid, maleic aeid, itaconic acid, citraconic acid, alpha-dimethyl maleic acid, ~ -butyl maleie aeid, fumaric acid, ; aeonitie aeid, as well a~ partial salts, amides and esters thereof. Anhydrides of any of the aforesaid acids can also be employed.

~, . . .
~ . ~

P~79~75 Comonomers which can be used with the above function-al monomers include ~ olefins such as ethylene, propylene, isobutylene, l-butene, 2-butene. Further examples of comono-mers are described in commonly assigned United States Patent No. 3,889,678, dated June 17, 1975.
The initial copolymers of anhydrides with another monomer can be conver-ted to carboxyl-containing copolymers by reaction with water, and carboxylate-containing moieties, such as ammonium or alkali salts thereof, by reaction with aqueous solutions of alkali metal compounds such as sodium hydroxide, potassium hydroxide, and the like or with aqueous ammonia.
The copolymers are formed in a known manner by react-ing admixtures of the desired monomers in the presence of a peroxide catalyst in a suitable solvent for the monomers.
The obtained copolymers are conveniently identified in terms of their monomeric constituents. However, the names so applied to the copolymers refer to the molecular structure of the polymer and are not limited to the polymers prepared by the copolymerization of the specific monomers. In many instances, the identical copolymers may be prepared from other monomers and converted to the desired copolymer by a subsequent chemical reaction. ~ -A preferred hydrophilic polymer chain can be prepared by several methods known in the art. Illustrative of such methods are the follow~ng:
(1) Polymerize acrylonitrile and hydrolyze with an alkaline solution to form alkali salts of polyacrylic acid.

(2) Polymerize methyl acrylate and hydrolyze with an alkaline solution to form alkali salts of polyacrylic acid.

(3) Polymerize ethyl acrylate and hydrolyze with an alkaline solution to form alkali salts of polyacrylic acid.

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(4) Polymerize acrylic acid or alkali salts of acry-lic acid.

(5) Polymerize methacrylonitrile and hydrolyze with acids to form polymethacrylic acid or hydrolyze with an alka-line solution to form alkali salts of polymethacrylic acid.

(6) Polymerize methacrylic acid or alkali salts of methacrylic acid.

(7) Polymerize acrylamide, optionally followed by hydrolysis.

(8) Polymerize methacrylamide, optionally followed by hydrolysis.

(9) Form copolymers of any of the above monomers or copolymerize wi'th a small amount of non-hydrolyza~le monomers. ~-Methods of graft-copolymerizing olefinicaLly unsatu-rated chains onto cellulose and starch are known in the art.
Thus, grafting of the hydrophilic material onto a starch or cellulose backbone can be accomplished slmultaneously with the formation of the hydrophilic polymeric material in an aqueous medium, because the peroxide catalyst used to copolymerize the various monomers forms a redox catalyst system in combination with a reducing agent and thus also serves to effect chain transfer onto the starch or cellulose backbone. Suitable red- ~
ucing agents for this purpose are ceric ion, ferrous ion, -cobaltic ion, (NH4)2S2O8, cuprous ion, and the like. The deslred ions can be supplied in the form of salts such as ceric ammonium nitrate, ferrous ammonium sulfate, and the like.
Graft-copolymerization of olefinically-unsaturated chains can also be effected by irradiation (ultraviolet-, gamma-, or X-radiation) or by heating in an aqueous medium in the presence ~;
of an emulsifier.
Powdered starch or cellulose fibers or pulp can be ,': . ,:: --11- , . . .

slurried in water containing a graft-copolvmerization catalyst system and the monomex or monomers added to the slurry and polymerized in situ at ambient temperature or above depending on the catalyst employed. In this manner, a portion of the Formed hydrophilic polymer may also be physically entrapped into the polysaccharide material during the polymerization process. The preparation of suitable starting materials for practicing the present invention is also illustrated in U.S.
Patent No. 3,256,372.
Hydrophilic chainS loading on the polysaccharide backbone can vary from about 10~ by weight to about 90~ by weight, and preferably is about 40 to about 80% by weight of the grafted polysaccharide.
The grafted polysaccharide produced in the aforedes-cribed manner may be dried at atmospheric pressure and in a -gaseous atmosphere so as to drive off the water. In the case of ~-the grafted cellulose, a relatively dense, non-porous, stiff, brittle and hornified material results~` It is desired to use the polysaccharide in the form of a powder having an average ~;
particle size of about S0 to about 1000 microns and preferably `~
about 7b to about S00 microns. Accordingly,lthe dried material ~ -resulting from the grafting step may, where necessary, be com-minuted into a powder using any convenient method, such as, for example, by grinding in a ball mill or by utilizing other size reduction equipment such as a micropulverizer, a Wiley (trade mark) mill, a Weber (trade mark) mill or the like.
.- ~
In accordance with the teachings of this inven-tion, the grafted polysaccharide having an arithmetic average par-ticle size of from 40 to about 1000 microns is combined, in ~ -an intimate mixture with less absorbent, wettable less swell-able particulate matter, e.g., unmodified cellulose, to form -12~

7~

a core usable in absorbent bodies such as sanitary tampons, napkins, diapers and the like. The unmodified cellulose may be for example, comminuted wood pulp, cotton, rayon (regener-ated cellulose), or the like. The particles of the unmod~fied cellulose may vary over a wide range of sizes and shapes encompassing both fibers and powders. For example, comminuted wood pulp fibers having a particle size of~ about 1500 microns are usable as well as fine ground wood pulp powder having a particle size of 50 microns.
10It has been discovered that when the grafted poly-saccharide is chosen to lie within the size limitation pres- -cribed herein, mixtures of the grafted polysaccharide and un-modified cellulose will exhibit absorption capacities exceed-ing the expected contribution of each component, this expected contribution being based on the ability of each component to -absorb fluid when acting alone. While this synergistic effect is apparent at essentially all proportlons of the components, it becomes markedly evident when at least about 10% by weight to about 95~ by weight of the grafted polysaccharide is em-ployed, and more particularly, when about 20~ to 95% by weight of grafted polysaccharide is employed.
The intimate blending of the components may be accom-plished by use of many, now available, powder blender, such as twin shell blenders, single or double core blenders, hammer mill or ball mill blenders. The resulting mixture may be intro-duced as a highly absorbent core in an absorbent product. A1~
ternatively, the loose mixture obtained Erom the blending pro-cess may be compressed into a formed body which can be disposed as a core into an absorbent product. Where desirable, the mix-ture, either in the compressed form or in the loose form maybe adhered to a substrate such as tissue paper or a nonwoven 7~i fabric, so as to facilitate handling when incorporating this highly absorbent mixture into products. Many other variations will occur to those skilled in the art in view of the teach-ings herein.
Incorporation of Grafted Cellulose in Absorbent sOdies Referring now to the drawings, in Figs. 1 and 2, an adsorbent dressing or disposable diaper 10 is provided with a porous facing sheet Ll which can be, for example, gauze, tissue or a nonwoven fabric.' A moisture-impermeable backing sheet 12 is provided preferably made of a thin-gauge polyolefin or poly- ;~
ester sheet such as a polyethylene or polyethylene terephthalate film. It will be understood by one skilled in the art that the impermeable backing sheet is used where a dry surface is re- -quired such as in a diaper or dressing. In circumstances where this is not necessary, such as in a surgical sponge, the backing sheet may be of a permeable material such as, for example, the same material as the facing sheet. The facing and backing sheets are adhered together along common edges 13 with a suit-able, preferably water-insoluble, adhesive or may alternatively be heat-sealed if thermoplastic materials are used in the sealing area~
Sandwiched between the facing sheet 11 and the back-ing sheet 12 is an absorbent body 14 in the form of a planar laminate. The absorbent body 14 comprises a first layer 16 of absorbent material which may for example, be wadded tissue, cotton fiber, rayon fiber, wood pulp or any of a wide variety of such absorbent materials. A second layer 18 of absorbent ~ -.~ ~
material lies on the opposite face of the absorbent body 14 and may be composed of the same material as that of the first layer 16. In accordance with this invention, disposed between ; layers 16 and 18 is an absorbent core 20 comprising an inti~
'~

~14-:~7~7~ ~

mate mixture of the highly absorbent grafted polysaccharide 22 of this inven-tion and unmodified cellulose material 24 e.g., comminuted wood pulp. The grafted polysaccharide may be for example, cellulose having hydrophilic chains such as poly-acrylamide-sodium polyacrylate copolymer chains, polyacrylic acid-sodium polyacrylate copolymer chains or the like and is comminuted to an arithmetic average particle size of from 50 to 1000 microns, for example, 300 microns. The grafted cellu lose may be combined with comminuted wood pulp fibers having -an arithmetic average particle size of, for example, 1000 microns in proportions of grafted cellulose of from 10 to 95%
by weight, for example, 50~ by weight. The core 20 may be emplaced within the absorbent body by simply being deposited in a relatively loose body onto the layer 16 with layer 18 being then laid thereon. Alternatively, the core may be ad-hered to a substrate or compressed into a body which has subs-tantial structural integrity and provided in the form of a long riibbon of core material. This ribbon along with ribbons of the other two absorbent layers 16 and 18 may be registered together and then cut into the individual absorbent bodies such as absorbent body 14.
Irrespective of the method or form for fabricating the absorbent body 14 comprising the core 20 of this invention, the resulting core has a capacity for absorbing aqueous fluids e.g., water, salt solutions, urine, or other body fluids, which greatly exceeds that of an equal weight of either the unmodified cellulose or the grafted polysaccharide when each is taken alone. As a result, a highly absorbent product results.
In Figs. 3 and 4 of the drawings, the invention is illustrated as embodied in a catamenial tampon. Shown in Fig.
3 is an elongated pad 17 of absorbent material such as wood ,;, ..: :

.. . , . i , , . . : ~ , ,. ......................... . : .
.. .. . . . .

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pulpl cotton, rayon, or the like having a generally rectanyular shape and illustrated as formed into a cylinder ~y rollin~ from one end to the other in a direction parallel to the longitu-dinal sides of the pad. In accordance this aspect of the in-vention, prior to rolling, a thin layer of the intimate mix-ture of grafted polysaccharide material 22 and unmodified cellulose 24 is applied to the surface o~ the rectangulàr pad so that upon rolling, the layer ~orms core 20, as viewed in radial cross-section. The rolled pad is then compressed in ~-`
a die to the desired tampon shape 23 as is illustrated in Fig.
4. The tampon is provided with the usual withdrawal string 26 which may be sewn through the removal end of the tampon or applied by other means known in the art, such as being looped or tied around the rectangular pad 17 prior to rolling.
The core 20 exhibi-ts an absorbency which far exceeds that of an equal weight of either the polysaccharide or the unmodified cellulose taken alone and accordingly, greatly in-creases the absorbency of the tampon.
Figs. 5 and 6 illustrate another embodiment of this invention in a catamenial tampon. A rectangular pad 27 of wood pulp, for example, is laid upon a porous nonwoven cellu- ~ O
losic fabric cover 25 and has a core 28 of the herein pre-scribed intimate mixture of grafted pol~saccharide and un-modified cellulose applied to one surface. The pad 27 with the nonwoven cover 25 is then folded about its longitudinal center and folded once more into a U-shaped blank, as illus~
trated in Fig. 5. The blank is then placed in a c~lindrical die and compressed radially and/or longitudinally into the desired tampon shape 30 as shown in Fig~ 6. A withdrawal string 34 is provided at the withdrawal end o~ the compressed tampon 30 and may be attached in a manner similar to that prescribed above, i.e., sewn on, looped or tied around the ~. : . . . , :

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pad 27 prior to folding, etc. The finished tampon 30 will then comprise centrally located core of 28 surrounded by com-pressed layers of wood pulp 36 which in turn are held in place by the nonwoven cover 25.
Figs. 7 and 8 illustrate the invention embodied in a sanitary napkin 37. An absorben-t pad 38 comprised of, for example, wood pulp is enveloped by a liquid permeable wrapper 40 which extends at both ends beyond the pad so as to provide attachment tabs 42 and 44. A liquid impermeable sheet 46 is sandwiched, on one surface of the pad, between the pad and the wrapper and may extend, at least partially over the sides of the pad. The impermeable sheet may be for example, a poly-ethylene film. In a central portion of the pad 38, there is interposed, a core ~8 of the herein prescribed intimate mix- -ture of grafted polysaccharide and unmodified cellulose.
It will be appreciated by one skilled in the art that man~ variations of the above embodiments are possible while still remaining within the scope of this invention.~ For example, in each of the above embodiments, a core is provided generally in the form of a continuous layer having planar di-mensions equal to that o~ the absorbent body. It is apparent however, that this is not essential and that the core may take many different configurations such as discontinuous layers or for that matter, the intimate mixture of grated poly-saccharide and unmodified cellulose may take various shapes such as spheres, fibers, or irregularly shaped particles, the ;
important consideration being that the components are in an intimate mixture and within the size and proportions prescribed herein. When these teachings are adhered to, it will be found that irrespective of the final form which the core takes, the absorbency of the core surpasses that of an equal weight of : ,. . . . . . . .
..

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its components taken alone.
The invention will be more fully understood from a consideration of the following examples wherein cores, prepared with various components in various proportions are tested to illustrate the surprising absorbent properties taught herein.
As used in these examples, the arithmetic average particle size for a mass of absorbent material is determined by using a pulse type Sonic Sifter manufactured by the Allan-Bradley Company of Milwaukee, Wisconsin and designated by them as Model L3P (trademark). The sifter is provided with a series of vertically arranged screens for passing particles of 500 420, 355, 250, 125, ~0, 63, 38 and 20 microns respectively.
A one gram sample of the material tested is run for ten minutes at a sift amplitude of 6 and a pulse amplitude of 3. The weight, as a percentage of the 1 gram sample, remaining on ; each screen after ten minutes is determlned and reported as "a". The arithmetic average of that screen size and the screen size immediately above it is reported as "b". The arithmetic .
average particle size is then calculated as:

; 20 -100 The summation being taken for all of the screens.
EX~MPLE 1 A quantity of grafted cellulose is prepared in accord-ance with the methods described herein.
The grafted cellulose is a copolymer of cellulose and hydrophilic chains, said chains having the structure:

--F 2 1 1 ~CH2 CH
C = O - O
ONa m NH 2 n . . . : .~ ~ . - , . .

7~ii and accounting for appxoximately 50% by weight of the grafted cellulose with the n moieties accounting for less than 5~ by weight of -the structure. The grafted cellulose is then divided into portionis, each of which is ground in a ball mill for various time intervals to produce comminuted portions of varying arith-metic average particle sizes. A first series of intimate mix-tures are prepared by blending material from each of the com-minuted portions with unmodified cellulose in varying propor-tions of the grafted to the unmodified cellulose. The unmodi-fied cellulose is fully bleached Southern Pine Kraft wood pulp obtained from the Buckeye Cellulose Co., and is comminuted in - ~ -a Wiley (trademark)-Mill using a 60 mesh screen to an average particle size of about 1500 microns. A series of pellets are ~: -prepared from each of the blends by pressing a 0.5 gram sample under a pressure of 2,000 psi in a Perkins-Elner KBr (trade- -~
mark) pellet press for two minutes. The length and diameter of the pellets are measured using a Federal thickness gauge and the actual weight of the pellets is determined. -The absorption properties of each of ~hese pellets ~;
is tested by allowing the pellet to absor~ water for a fixed period of time and then centrifuging the sample to remove un-retained water, this being accomplished in the folIowing manner.
A centrifuge filter tube is tared and t~e bottom ; æealed with a syringe cap in a manner such that the cap will be pulled off under a centrifugal force. Twenty milliliters ~ :: .. .
of distilled water are added to the tube and the pellet being tested is placed therein. The pellet is allowed to absorb the :: ~
water for a 30 second period after which the centrifuge is started. The sample is centrifuged at a speed of 2000 rpm 3~ for 10 minutes and the tube is then weighed to determine the weight of water absorbed and retained.
,..,:
.

,. . .

~ ~ . ~ . .: . .... .

A specific description of each sample and the results of the test (presented as milliliters of water absorbed and retained per mllligram of sample) is reported in Table I and graphically illustrated in Fig. 9.
TABLE I
Fluid Retention of Grafted Cellulose and Unmodified Woo~ Pulp of 1500 Micron Size ~Fluid Retentlon (ml/mg) Grafted Cellulose Particle Size ~Microns) : 311~ 102 71.2 49.6 44.2 % ~y Weight of Grafted Cellulose in Sample _ -0 1-89 1.8~ 1089 1.89 1.89 5.72 - 5.02` - 1.99 ;~ -

10.12 6.07 5.06 3.93 2.18 ~"
13.06 - 5.48 - 2.03 ~ .
100 3.88 3.39 - 2.69 1.84 As both the above table and ~'ig. 9 clearly show, for any given particle size of the grafted cellulose, -the components of the blend cooperate synergistically so as to increase fluid retention beyond the contribution of each component if acting along, i.e., referring to Fig. 9, the 1uid retention of the blends is greater than the value obtained by drawing a straight line through the retention values for zero and 100~ grafted cellulose. This efEect in each case increases to a point at `
which the fluid retention of the blend is greater than the ~-value oE the most absorbent component when acting alone. It is also apparent from the data, that the synergistic effect is greatly enhanced with increasing particle size for the grafted cellulose. Thus, for example, while synergism is evident in particle sizes as small a5 44.2 microns, the effect is rela-tively small (an eleven percent increase in retention at its highest point over that of the most absorbent component) when compared with particle sizes of 311 microns (a 500~ increase).

Absorbent cores of pellets are prepared in accordance with the procedures of ~xample 1 with the exception that the un-modified cellulose employed is a powdered, bleached, finely ground wood pulp having an average particle size of about 60 ; microns and obtained from the Brown Co., of Berlin, N.H. and : :
sold by them under the trade màrk Solka-floc. These pellets are tested for fluid retention in accordance with the procedures of Example 1 and a specific description of the samples and test results are reported in Table II with the results being ~ : .
graphically represented in Fig. 10.
TABLE II
Fluid Retention of Grafted ~11 ~ ~ ~ A
.
of 60 Micron Size Fluid Retention ml/m~

Grafted Cellulose Particle Size (Microns) : 311 102 71.2 49.6 44.2 ~

~ by Weight Grafted Cellulose ~:
~; in Sample 0 2.06 2.06 2.06 2.06 2.06 5.44 - 7.57 3.76 1.80 :: .
10.39 11.32 11.36 2.58 1.81 13039 . - - 2.71 1.93 100 3.88 3.39 - 2.69 1.84 ~ .
As in Example 1, the synergistic effect of blends of the grafted cellulose and the unmodified cellulose is evident from the above data. .
EXAMPLE 3 ;
Sample pellets are again prepared in accordance with -the methods described in Example 1 with the exception that the grafted polysaccharide is a copolymer of starch and hydrophi-lic chains, said chains having the structure:

~ 2 IH ~ - ~CH2~ CH
L 1~ L 1= i ~
OK m NH2 n and accounting for approximately 50% by weigh-t of the grafted starch with the n moieties accounting for less than 5% by weight of the structure. The procedure of Example 2 is follow-~ -ed using various blends of the grafted starch having an arithmetic average particle size of 63.3 microns in combina-tion with the Solka-floc (Trade Mark) wood pulp described in Example 2. The samples tested and the results of these tests are reported in Table III below and graphically illustrated in Fig. 11.
TABLE III -Fluid Retention of Grafted Starch and Unmodified Wood Pulp Pellet Composition Fluid Retention ..-- _. : .
% Wood Pulp ~ Grafted Starch ~69 Microns? ~ cr~A~ ) ml/m~

0 100 3.4 ; 25 75 3.94 16.18 100 0 1.91 :~
As in the foregoing examples, the synergistic effect of the blends of grafted starch and unmodified cellulose is evident.

Sample pellets are prepared in accordance with the methods described in Example 1 with the exception that the grafted polysaccharide is a copolymer of cellulose and a poly-mer chain comprising a combination of ionic and nonionic .
;

moieties, said chain having the structure - -CH CH - -CH ~ CH - .
C=O C=O ~ ', X m _ 2 5 n --wherein said chains account for about 80~ by weight of the grafted polysaccharide, said m moieties accounting for about ~.
31~ by weight. The X group, in about 95~ by weight of the m moiety is ONa and, in about 5~ of said m moiety is _ NH2.
The procedure of Example 2 is followed using various blends of the grafted cellulose copolymer having an arithmetic -.
average particle size of 64.6 microns in combination with the Solka-floc (trade mark) wood pulp described in Example 2. The samples tested and the results of these tests are reported in Table IV below and graphically illustrated in Fig. 11. .~ :
TABLE I~
:: , Fluid Retention of Grafted Cellulo5~ 58c8LY~E~g~d unmodified .: ,- , :
r~ r~ ~t.~
% Wood PUlp % Grafted Cellulose ml/mg ` :(69 Microns) Copolymers (63.3) : ~ Microns .
~ 100 O ' 1 . 91 : : ' ' ,' ' :-~ 20 50 50 9.46 6.49 . 0 100 6.70 . .
Again, as in the foregoing examples, the synergistic effect of the blend of grafted cellulose blended with unmodi- .
fied cellulose is noted.

: -- ,

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an absorbent product, an absorbent core comprising grafted polysaccharide particles in intimate mixture with less absorbent, wettable, less swellable particulate matter selected from unmodified cellulose or hydrophilic synthetic polymer, said grafted polysaccharide particles comprising polysaccharide having grafted thereon about 10% by weight to about 90% by weight hydrophilic chains of the general formula:

wherein R1 and R2 are selected from the group consisting of hydrogen and alkyl having 1 to 4 carbon atoms, X and Y are select-ed from the group consisting of -OH, -O(alkali metal), and -NH2, wherein m is an integer having a value of 0 to about 5000, wherein n is an integer having a value of 0 to about 5000, the sum of all m and n groups is at least 500, p is an integer having a value of 0 or 1, and q is an integer having a value of 1 to 4:
the individual particles of said grafted polysaccharide having an arithmetic average size of from about 50 to about 500 microns;
said absorbent core exhibiting a fluid retention greater than that of each component when tested alone, said core comprising about 10 to about 95%, by weight, of the grafted polysaccharide.

2. The absorbent product defined in claim 1 wherein said less absorbent, wettable, less swellable particulate matter is unmodified cellulose.

3. The product of claim 2 wherein said unmodified cellulose is wood pulp.

4. The product of claim 2 wherein said unmodified cellulose is regenerated cellulose.

5. The product of claim 1 wherein said polysaccharide is cellulose.

5. The product of claim 1 wherein said polysaccharide is starch.

7. The product of claim 1 wherein the hydrophilic chains are selected from the group consisting of polyacrylic acid, alkali polyacrylate, polyacrylamide and copolymers of these.

8. The product of claim 7, wherein the hydrophilic chains comprise alkali polyacrylate.

9. The product of claim 7, wherein the hydrophilic chains are copolymers of polyacrylamide and sodium polyacrylate.

10. A diaper comprising the absorbent product of claim 1 wherein said absorbent product is in the form of a planar pad having said core disposed therein, said planar pad being sandwich-ed between a facing sheet and a backing sheet, at least one of which is fluid permeable.

11. A sanitary napkin comprising the absorbent product of claim 1 wherein said absorbent product is in the form of a planar pad having said core disposed therein, said planar pad being sandwiched between a facing sheet and a backing sheet, at least one of which is fluid permeable.

12. The napkin of claim 11 wherein said backing sheet and said facing sheet are formed from a continuous cover sheet 13. A tampon comprising the absorbent product of claim 1 wherein said absorbent product is substantially in the form of a cylinder having said core disposed therein.

14. The tampon of claim 13 wherein said absorbent body comprises a pad of absorbent material having said core laid thereon, said pad being rolled into cylindrical form and compressed into final tampon shape.

15. The tampon of claim 14 wherein said absorbent body comprises a pad of absorbent material having said core laid thereon, said pad being folded upon itself and said folded pad being compressed into the final tampon shape.