(12) United States Patent 

Rangachari et ai. 

(54) NON-IONIC PLASTICIZER ADDITIVES FOR 

WOOD PULPS AND ABSORBENT CORES 

(75) Inventors: Krishnakumar Rangachari, Savannah; 

Kays Chinai, St. Simons Island, both 

of GA (US) 

(73) Assignee: Rayonier Products and Financial 

Services Company, Ferandina Beach, 

FL (US) 

( *) Notice: Subject to any disclaimer, the term of this 

patent is extended or adjusted under 35 

U.S.c. 154(b) by 0 days. 

(21) Appl. No.: 09/642,862 

(22) Filed: Aug. 21, 2000 

Related U.S. Application Data 

(63) Continuation-in-part of application No. 09/408,047, filed on 

Sep. 29, 1999. 

(51) Int. CI? ...................................................... A61F 13/15 

(52) U.S. CI. .......................... 604/375; 264/116; 264/122; 

264/518; 162/158 

(58) Field of Search ..................................... 264/518, 115, 

264/116, 122; 162/158; 604/375 

(56) References Cited 

2,249,118 

3,554,862 

U.S. PATENT DOCUMENTS 

7/1941 De Witt . 

1/1971 Hervey et al. ....................... 162/158 

111111 1111111111111111111111111111111111111111111111111111111111111 

US006310268Bl 

(10) Patent No.: US 6,310,268 Bl 

(45) Date of Patent: Oct. 30, 2001 

3,677,886 

3,809,604 

4,144,122 

4,303,471 

4,432,833 

4,583,980 

4,610,678 

5,516,569 

5,547,541 

5,641,561 

5,695,486 

5,776,308 

5,837,627 

5,858,172 

5,866,242 

5,916,670 

5,935,880 

7/1972 Forssblad et al. ..................... 162/72 

5/1974 Estes et al. . ... ... .... ... ... ... ... ... 162/100 

3/1979 Emanuelsson et al. ............. 162/158 

12/1981 Kemi .................................... 162/158 

2/1984 Breese .................................. 162/158 

4/1986 Schneider et al. .... ... ... ... ... ... 604/359 

9/1986 Weisman et al. .................... 604/368 

5/1996 Veith et al. ............................ 428/68 

8/1996 Hansen et al. ......................... 162/12 

6/1997 Hanson et al. ....................... 442/417 

12/1997 Broughton et al. .................. 604/374 

7/1998 Sears et al. .......................... 162/158 

11/1998 Halabisky et al. ................... 442/385 

1/1999 Sears et al. .......................... 162/158 

2/1999 Tan et al. ............................. 428/219 

6/1999 Tan et al. ............................. 428/219 

8/1999 Wang et al. ........................... 442/65 

FOREIGN PATENT DOCUMENTS 

WO 99/24667 

WO 00/36215 

A1 

5/1999 CWO). 

6/2000 CWO). 

Primary Examiner-Mary Lynn Theisen 

(74) Attorney, Agent, or Firm-Rockey, Milnamow & 

Katz, Ltd. 

(57) ABSTRACT 

Soft wood pulp sheets, soft absorbent cores, and methods for 

making the soft wood pulp sheets or soft absorbent cores by 

addition of non-ionic plasticizers before, during or after the 

pulp or core manufacturing process are disclosed. Preferred 

non-ionic plasticizers are ethers or esters such as triacetin, 

citrates or glycol derivatives. 

34 Claims, No Drawings 
US 6,310,268 Bl 

1 

NON-IONIC PLASTICIZER ADDITIVES FOR 

WOOD PULPS AND ABSORBENT CORES 

CROSS-REFERENCE TO RELATED 

APPLICATIONS 

This application is a continuation-in-part of co-pending 

U.S. patent application Ser. No. 09/408,047 filed Sep. 29, 

1999. 

FIELD OF THE INVENTION 

This invention is directed to soft wood pulp sheets, soft 

absorbent cores, and methods for making the soft wood pulp 

sheets or soft absorbent cores by addition of non-ionic 

plasticizers before, during or after the pulp or core manufacturing process. Preferred non-ionic plasticizers are ethers 

or esters such as triacetin, citrates or glycol derivatives. 

BACKGROUND OF THE INVENTION 

A wide variety of absorbent structures for use in disposable absorbent articles are known in the art. Common 

commercial absorbent articles include diapers, adult incontinence products, catamenials and bandages. These products 

are provided with various functional components for 

receiving, absorbing and retaining fluids. 

Disposable absorbent articles, such as diapers, feminine 

hygiene products, adult incontinence devices and the like 

have found widespread acceptance. To function efficiently, 

such absorbent articles must quickly absorb body fluids, 

distribute those fluids within and throughout the absorbent 

article and be capable of retaining those body fluids with 

sufficient energy to dry the surface when placed under loads. 

In addition, the absorbent article need be sufficiently soft and 

flexible so as to comfortably conform to body surfaces and 

provide close fit for lower leakage. 

2 

distribution of fluid to the absorbent core while minimizing 

spread of the fluid in this layer. 

The absorbent core is typically formulated of a cellulosic 

wood fiber matrix or pulp, which pulp is capable of absorbS ing large quantities of fluid. Absorbent cores can be designed 

in a variety of ways to enhance fluid absorption and retention 

properties. By way of example, the fluid retention characteristics of absorbent cores can be greatly enhanced by 

disposing super absorbent materials amongst fibers of the 

10 wood pulp. Superabsorbent materials are well known in the 

art as substantially water-insoluble, absorbent polymeric 

compositions that are capable of absorbing large amounts of 

fluid in relation to their weight and forming hydro gels upon 

such absorption. Absorbentarticles containing blends or 

15 mixtures of pulp and superabsorbents are known in the art. 

The distribution of superabsorbents within an absorbent 

core can be uniform or non-uniform. By way of example, 

that portion of an absorbent core proximate to the backing 

layer (farthest away from the wearer) can be formulated to 

20 contain higher levels of super absorbent than those portions 

of the core proximate the facing or acquisition layer. By way 

of further example, that portion of the core closest to the site 

of fluid entry (e.g., acquisition zone) can be formulated to 

transport (wick) fluid into surrounding portions of the core 

25 (e.g., storage zone). 

As consumer demand for less expensive and less bulky 

disposable absorbent products increases, manufacturers continue to seek effective ways to reduce size and cost without 

30 sacrificing the quality of the fluid transport properties or 

structural integrity of the products during use. Preferably, 

the disposable products should be soft, thin and absorbent. 

Unfortunately, when softness and thinness characteristics 

are improved through the use of additives known in the art, 

35 absorbency is sacrificed. Therefore, there is a need in the 

industry for manufacturing processes which produce a soft 

and thin material while maintaining the desired level of 

While absorbency. the design of individual absorbent articles varies 

depending upon use, there are certain elements or components common to such articles. The absorbent article contains a liquid pervious top sheet or facing layer, which facing 

layer is designed to be in contact with a body surface. The 

facing layer is made of a material that allows for the 

unimpeded transfer of fluid from the body into the core of 

the article. The facing layer should not absorb fluid per se 45 

and, thus, should remain dry. The article further contains a 

liquid impervious back sheet or backing layer disposed on 

the outer surface of the article and which layer is designed 

Absorbent materials, such as absorbent cores may be 

40 made from pulp in the form of sheets or board. The pulp is 

defiberized in order to manufacture an absorbent material. 

Therefore, additives which improve the characteristics of the 

absorbent end product may be added 1) to the pulp, 2) during 

the manufacture of pulp board, or 3) during manufacture of 

the absorbent core. Conventionally, for the manufacture of 

absorbent materials, softness is achieved by the addition of 

debonders to the pulp, since the softness of a pulp product 

is greatly influenced by the degree to which the constituent 

to prevent the leakage of fluid out of the article. wood pulp is debonded, i.e., the extent to which hydrogen 

50 bonds within the wood pulp are broken. For example. 

debonder is added to the pulp while the pulp is in the holding 

chests, prior to deposition of the pulp slurry on the Fourdrinier wire. The result is softer pulps or pulp products, 

Disposed between the facing layer and backing layer is an 

absorbent member referred to in the art as an absorbent core. 

The function of the absorbent core is to absorb and retain 

body fluids entering the absorbent article through the facing 

layer. Because the origin of body fluids is localized, it is 

necessary to provide a means for distributing fluid through- 55 

out the dimensions of the absorbent core to make full use of 

which typically have decreased hydrogen bonding. 

Wood pulp softness can be expressed in terms of properties such as Mullen strength (the strength of pulp or a pulp 

product, measured in kilopascals (kPa), defined in greater 

detail below), and Kamas energy (the energy required to 

convert a given amount of pulp or pulp product to a fluff 

all the available absorbent material. This is typically accomplished either by providing a distribution member disposed 

between the facing layer and absorbent core and/or altering 

the composition of the absorbent core per se. 60 material, measured in watt hours per kilogram (Wh/kg), 

defined in greater detail below). Lower values of Mullen 

strength and Kamas energy correlate to softer, increasingly 

debonded, pulp. 

Fluid can be distributed to different portions of the absorbent core by means of a transfer or acquisition layer disposed between the facing layer and core. Because of the 

proximity of such an acquisition layer to the body surface of 

the wearer, the acquisition layer should not be formed from 65 

material that retains large amounts of fluid. The purpose of 

the acquisition layer is to provide for rapid transfer and 

Many industrial pulp applications involve the conversion 

of pulp to fluff pulp by mechanical means. The efficient 

mechanical fluffing of wood pulp requires a pulp (stiff) that 

will debond to a desirable degree with minimum energy 
US 6,310,268 Bl 

3 

input and little mechanical fiber damage. Such pulp must 

have the proper bulk and degree of inter-fiber bonding. A 

hard pulp sheet will increase the energy needed to create 

fluff pulp and will therefore lead to increased fiber damage, 

while an unduly soft pulp sheet will lead to pull-out of large 5 

pieces of pulp, causing poor fluffing. 

Currently, cationic compounds are used in the manufacture of wood pulp products such as sanitary papers to yield 

4 

tensile strength of the core. Thus, use of the above steps to 

produce soft absorbent cores results in substantial increases 

in the cost of the core. 

For example, soft absorbent materials are disclosed in 

U.S. Pat. Nos. 5,866,242 and 5,916,670. However, the 

processes disclosed therein may be expensive, so it would be 

desirable to use an additive which would provide a lower 

cost alternative, if such additive could be used to treat pulps 

to provide beneficial properties to pulp, and thereafter to a product which has a soft hand feel. This is accomplished 

through the lubricating nature of the substantive softening 

molecule; less extensive inter-fiber bonding leading to 

greater bulk and the plasticizing effect of these additives. 

10 absorbent cores formed from treated pulps, without decreasing absorbency. 

There are several cationic chemical materials known for 

use to soften pulp to produce a fluff or debonded pulp. These 

cationic materials are quaternary ammonium compounds, as 

disclosed in U.S. Pat. Nos. 3,554,862; 3,677,886; 3,809,604; 

4,144,122 and 4,432,833 among others. 

There continues to be a need in the art, therefore, for a 

material that satisfies the absorbency, strength and softness 

requirements needed for use as absorbent core in disposable 

15 absorbent articles and which simultaneously provides time 

and cost savings to both the pulp manufacturer and the 

manufacturer of the absorbent article. 

Nonionic agents are also used to a limited extent to 

debond pulp in the paper industry (BEROCELL 587, available from Eka Nobel) but even they cause adverse affects on 

absorbency. It is believed that this effect is due to the 

presence of long hydrophobic side chains. 

Accordingly, it would be desirable to provide a method of 

treating pulp sheets to form fluff pulp with improved soft20 ness without sacrificing the absorbent properties of the pulp. 

Water-soluble polyhydroxy alcohols have been disclosed 

as softening agents in U.S. Pat. No. 2,249,118. Non-ionic 25 

compounds such as fatty acid esters in combination with 

cationic retention agents have been disclosed in U.S. Pat. 

No. 4,303,471 to obtain good disintegration properties for 

pulp. 

However, pulp softening and debonding, when accom- 30 

plished by the conventional treatments described above, will 

result in a material that is less absorbent. 

As an alternative to the use of additives, materials may be 

specifically engineered to obtained the desired characteristics. In addition to blending pulp with superabsorbent 35 

material, a variety of other means for improving the characteristics of pulp have been described. 

SUMMARY OF THE INVENTION 

One aspect of the invention is an absorbent core comprising from 0.1 % to 10% of at least one non-ionic plasticizer. The plasticizer may be a citrate or triacetin; the core 

may have a suppleness of greater than about 0.7 g-l; a 

density of from about 0.25 g/cc to about 0.5 g/cc; and a basis 

weight of from about 200 g/m2 to about 550 g/m2. 

Another aspect of the invention is an absorbent core 

comprising: 

from about 30 weight percent to about 90 weight percent 

of cellulosic fibers; and, 

from about 0.1 weight percent to about 10 weight percent 

of at least one non-ionic plasticizer; 

wherein said core has a suppleness of greater than about 

0.7 g-\ a density of from about 0.25 g/cc to about 0.5 

glcc and a basis weight of from about 200 glm2 to about 

550 g/m2. 

Examples of suitable plasticizers are esters or ethers. The 

One particular desirable character is the stiffness of the 

absorbent core. As the disposable hygiene products industry 

moves towards ultrathin products, stiffness of the absorbent 

core has become a critical issue. The use of mercerized fibers 

to reduce the stiffness (or improve the softness) of absorbent 

cores has been disclosed in U.S. Pat. No. 5,866,242. However these fibers arc expensive when compared to nonmercerized fibers. 

40 ethers or esters may be glycol derivatives, and the esters may 

also be citrates. Suitable glycol ethers include alkyl ethers of 

low molecular weight glycols or aryl ethers of low molecular weight glycols. Suitable glycol esters include formic 

esters of low molecular weight glycols, ethanoic esters of 

Debonding agents such as quaternary ammonium compounds can be used to produce soft pulp sheets and absorbent cores. However, as previously mentioned, the use of 

debonders result in a substantial negative impact on absorbency. 

45 low molecular weight glycols or propanoic esters of low 

molecular weight glycols. A preferred ester is triacetin. 

Preferred citrates are of the formula 

50 

There have been numerous attempts by the manufacturers 

of absorbent materials to produce core materials which arc 

highly absorbent, strong, and soft U.S. Pat. No. 4,610,678 

discloses an air-laid material containing hydrophilic fibers 

and superabsorbent material, wherein the material is air-laid 55 wherein Rl, R2 and R3 are each independently alkyl groups, 

in a dry state and compacted without the use of any added and 

binding agents. Such material, however, has low integrity 

and suffers from shake-out or loss of substantial amounts of 

superabsorbent material. U.S. Pat. No. 5,516,569 discloses 

that superabsorbent material shake-out can be reduced in 60 

air-laid absorbents by adding significant amounts of water to 

material during the air-laying process. The resultant 

material, however, is stiff of low density and has a high 

water content (>about 15 weight percent). The high stiffness 

can be reduced using embossing which requires an addi- 65 

tional processing step in the manufacturing process, but 

embossing has been shown to have a negative impact on the 

R4 is selected from the group consisting of hydrogen, 

alkyl groups and _C(O)R5, wherein R5 is an alkyl 

group. The plasticizer may be triacetin. Cellulosic 

fibers used to make the cores may be derived from at 

least one type of pulp sheet, or from a mixture of at 

least two types of pulp sheets. The core may further 

comprise from about 9.99 weight percent to about 60 

weight percent of super absorbent polymer. When the 

core contains superabsorbent polymer, the core may 

have a normalized wicking energy greater than about 

2,300 ergs/g. 
US 6,310,268 Bl 

5 

Another aspect of the invention is a method for manufacturing a softened absorbent material from cellulosic fibers 

comprising the steps of: 

a) defiberizing cellulosic fibers to form defiberized cellulosic fibers; 

b) blending said defiberized cellulosic fibers with superabsorbent material to form a blended material; 

c) depositing said blended material onto a carrier layer 

under vacuum to form a layered absorbent web; and 

d) compressing said web to form an absorbent material, 

6 

glycols. A preferred ester is triacetin. One or more non-ionic 

plasticizers may be added, as combinations of non-ionic 

plasticizers may increase the efficacy of the desired result. 

The term "citrate" as used herein refers to compounds of 

5 general formula I, 

Formula I 

10 

wherein an effective softening amount of at least one 

non-ionic plasticizer is added to at least one of said 

cellulosic fibers, said defiberized cellulosic fibers, 

said blended material, said web and said absorbent 15 

material. 

wherein Rl, R2 and R3 are each independently alkyl groups 

(each may be different, or all may be the same), and R4 is 

selected from the group consisting of hydrogen, alkyl groups 

and _C(O)R5, wherein R5 is an alkyl group. The absorbent material may be an absorbent core. If the 

plasticizer is anti-microbial, the softened absorbent wood 

pulp product is an anti-microbial, softened, absorbent wood 

pulp product. If the plasticizer is odor-preventing, the soft- 20 

ened absorbent wood pulp product is an odor-preventing, 

softened absorbent wood pulp product. 

The term "alkyl" as used herein alone or in combination 

refers to C1-C12 straight or branched, saturated or unsaturated (alkenyl, alkynyl, allyl) chain radicals derived from 

saturated hydrocarbons by the removal of one hydrogen 

atom. Representative examples of alkyl groups include 

methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, isobutyl, and tert-butyl among others. Suitable plasticizers are as defined above. The cellulosic 

fibers used to make the cores may be derived from at least 

one type of pulp sheet, or from a mixture of at least two types 25 

of pulp sheets. 

The term "aryl" as used herein alone or in combination 

refers to a carbocyclic aromatic group having about 6 to 12 

carbon atoms such as phenyl, naphthyl, indenyl, indanyl, 

Another aspect of the invention is a wood pulp sheet azulenyl, fluorenyl and anthracenyl. 

comprising: 

from about 90 weight percent to about 99.9 weight 

percent of cellulosic fibers; and, 

from about 0.1 weight percent to about 10 weight percent 

of at least one citrate, wherein said sheet has a defiberization energy of from about 35 to about 60 Whlkg. 

Suitable citrates are as defined above. Presently preferred 

wood pulp sheets have a wicking energy greater than about 

40,000 ergs/g, and more preferably greater than about 

60,000 ergs/g. 

Another aspect of the invention is a method for softening 

wood pulp sheets comprising the step of adding to said 

sheets an effective wood pulp sheet softening amount of at 

least one citrate of the formula 

wherein R\ R2 and R3 are each independently alkyl groups, 

and 

R4 is selected from the group consisting of hydrogen, 

alkyl groups and _C(O)R5, 

wherein R5 is an alkyl group. 

Suitable citrates are as defined above. 

DETAILED DESCRIPTION OF IRE 

INVENTION 

Definitions 

The term "non-ionic plasticizer" as used herein refers to 

compounds such as esters or ethers. The ethers or esters may 

be glycol derivatives, and the esters may also be citrates. 

Suitable glycol ethers include alkyl ethers of low molecular 

weight glycols or aryl ethers of low molecular weight 

glycols. Suitable glycol esters include formic esters of low 

molecular weight glycols, ethanoic esters of low molecular 

weight glycols or propanoic esters of low molecular weight 

The term "wood pulp" as used herein refers to a cellulosic 

material obtained from wood produced according to a pulp30 ing process including but not limited to sulfite, kraft and 

thermo mechanical pulping processes, and in which lignin 

and other cellulose pulp impurities may be removed in 

whole or in part by a process which includes but is not 

limited to an oxidation or other bleaching process, wherein 

cellulosic hydroxyl groups naturally present in the cellulosic 

35 material have not been chemically substituted or derivatized. 

Cellulose ether and acetate end-use derivative products are 

not considered wood pulp. 

The term "softened pulps" refers to fibrous end-use wood 

pulps (for example, fluff pulps) that have some chemical 

40 agent (softener) added to soften the pulp, preferably by 

reducing interfiber bonding (addition of the softener results 

in a soft pulp sheet). The chemical agents (softeners) are 

commercial products added to fluff pulps during sheet 

forming which make the pulp sheet softer and easier to fluff 

45 or defiber. The force with which pulp fibers bond is measured indirectly by measuring Mullen strength or the force 

(or energy) expended to debond or fluff a given pulp sheet. 

As used herein, the term "cellulosic fibers" refers to those 

fibers which are conventionally employed to form a web for 

50 use, for example, in absorbent articles. A wide variety of 

pulped cellulosic fibers, derived from wood and non-wood 

sources, can be used. Cellulosic fibers that can be used in the 

present invention are well known in the art and include wood 

pulp, cotton, flax and peat moss. Wood pulp is preferred. 

55 Cellulose acetate fibers are not included in this definition. 

Pulps and cores of the present invention are cellulose 

acetate-free. Pulps can be obtained from mechanical or 

chemi-mechanical, sulfite, kraft, pulping reject materials, 

organic solvent pulps, etc. Both softwood and hardwood 

60 species are useful. Softwood pulps are preferred. It is not 

necessary to treat cellulosic fibers with chemical debonding 

agents, cross-linking agents and the like for use in the 

present invention. Wood pulp is most commonly employed 

because of its availability and price. Therefore, cellulosic 

65 fibers derived primarily from wood pulp are most preferred. 

Suitable wood pulp fibers for use with the invention can 

be obtained from well-known chemical processes. The pulp 
US 6,310,268 Bl 

7 

fibers may also be processed by chemical methods, thermomechanical methods, chemithermomechanical methods, or 

combinations thereof. The preferred pulp fiber is produced 

8 

required to produce rupture of a material under certain 

experimental conditions. Mullen strength is determined on 

some of the products presented in the examples using a 

method based on TAPPIT807. A TMI Monitor Burst 1000 is 

used to measure the hydrostatic pressure required to rupture 

a pulp sheet. Mullen strength is recorded as kPa at rupture. 

The term "Kamas energy" as used herein refers to the 

energy required to convert a given amount of pulp or pulp 

product to a fluff material measured in watt hours per 

kilogram (Wh/kg). A Kamas lab hammer mill Model 

H-OI-C was used to defiberize some of the products presented in the examples. Strips of pulp sheets 5 cm wide and 

having a basis weight of 640 gsm were fed into the 

hammermill, using, 4200 rpm motor speed, 50% feeder 

speed, and an 8 mm screen. The energy required to defiberby chemical methods, either sulfate or sulfite. The preferred 

starting material is prepared from long-fiber coniferous 5 

wood species such as southern pine, Douglas fir, spruce, and 

hemlock. Other chemical pulps made from short or long 

fibered wood species, ground wood fibers, recycled or 

secondary wood pulp fibers, and bleached and unbleached 

wood pulp fibers can be used. Short wood fibers are pro- 10 

duced from hardwood species, such as eucalyptus, using 

known chemical processes or from any wood species using 

mechanical or chemithermomechanical methods. Details of 

the production of wood pulp fibers are well-known to those 

skilled in the art. 15 ize the pump sheet is recorded, and reported as Wh/kg of 

The fluff, the energy of defiberization. term "wood pulp sheet" as used herein refers to 

cellulosic fiber sheets formed using the wet-laid process. 

The sheets typically have a basis weight of between 200 and 

800 gsm and density between 0.3 to 1.0 g/cc. The pulp sheets 

are subsequently defibered in a hammermill to convert them 

into fluff pulp before being used in an absorbent product. 

Wood pulp sheets can be differentiated from tissue paper or 

paper sheets by their basis weights. Typically, tissue paper 

has a basis weight of from about 5 to about 50 gsm and paper 

sheets have basis weights of from about 47 to about 103 

gsm. Therefore, these materials have lower basis weights 

than wood pulp sheets. 

The Gurley stiffness values of the absorbent materials 

were measured using a Gurley stiffness tester (Model No 

4171E), manufactured by Gurley Precision Instruments of 

20 Troy, N.Y. The instrument measures the externally applied 

moment required to produce a given deflection of a test strip 

of specific dimensions fixed at one end and having a 

concentrated load applied to the other end. The results are 

obtained in "Gurley stiffness" values in units of milligrams. 

25 It should be noted that the higher the stiffness of the material, 

the less flexible and hence the less soft it is. 

The term "absorbent core" as used herein refers to a 

cellulosic wood fiber matrix or pulp, which pulp is capable 

of absorbing large quantities of fluid. Absorbent cores can be 30 

designed in a variety of ways to enhance fluid absorption and 

retention properties. By way of example, the fluid retention 

characteristics of absorbent cores can be greatly enhanced 

by disposing superabsorbent materials amongst fibers of the 

wood pulp. The absorbent core may be used to manufacture 35 

consumer products such as diapers, feminine hygiene products or incontinence products. 

Superabsorbent materials are well-known to those skilled 

in the art as substantially water-insoluble, absorbent polymeric compositions that are capable of absorbing large 40 

amounts of fluid in relation to their weight and forming 

hydrogels upon such absorption. 

The Methods 

One aspect of this invention is a method for obtaining a 

softened absorbent core by adding a plasticizer as a softener 

to the process stream at any convenient point in the air-laid 

manufacturing process. The process stream contains wood 

pulp as well as other additives. Production of an absorbent 

material by air-laying means is well known in the art. 

Briefly, cellulosic fibers (e.g., pulp) are processed using a 

hammermill to individualize the fibers. The individualized 

fibers are blended with SAP granules in a blending system 

and pneumatically conveyed into a series of forming heads. 

The blending and distribution of absorbent materials can be 

controlled separately for each forming head. Controlled air 

circulation and winged agitators in each chamber produce 

uniform mixture and distribution of pulp and SAP. The SAP 

can be thoroughly and homogeneously blended throughout 

the web or contained only in specific strata by distributing it 

to selected forming heads. Fibers (and SAP) from each 

forming chamber arc deposited by vacuum onto a carrier 

layer, thus forming a layered absorbent web. The web is 

subsequently compressed using calenders to achieve desirable density. The deified web is wound into a roll using 

conventional winding equipment. A forming wire can be 

covered with tissue paper to reduce the loss of material as 

the carrier layer. The tissue paper layer can be removed prior 

to calendering or incorporated into the formed material. 

Moreover, an absorbent core having improved properties 

may be obtained by post-manufacturing application of 

additive, by applying the additive to the core which results 

from the air-laid process described above. 

Another aspect of this invention relates to the treatment of 

wood pulp sheets useful for making a fluff pulp preferably 

for absorbency intensive applications. Surprisingly, this 

method of treating wood pulp sheets with a softening agent 

to soften the pulp does not adversely effecting the absorbency of the material. The wood pulp sheet is treated by 

applying to the wood pulp sheet a sufficient amount of a 

The terms "superabsorbent polymer" or "SAP" as used 

herein refer to a polymeric material that is capable of 

absorbing large quantities of fluid by forming a hydrated gel. 45 

The superabsorbent polymers also can retain significant 

amounts of water under moderate pressures. Super absorbent 

polymers generally fall into three classes, namely, starch 

graft copolymers, cross-linked carboxymethylcellulose 

derivatives, and modified hydrophilic polyacrylates. 50 

Examples of such absorbent polymers are hydrolyzed 

starch-acrylonitrile graft copolymer; a neutralized starchacrylic acid graft copolymer, a saponified acrylic acid estervinyl acetate copolymer, a hydrolyzed acrylonitrile copolymer or acrylamide copolymer, a modified cross-linked 55 

polyvinyl alcohol, a neutralized self-cross-linking polyacrylic acid, a cross-linked polyacrylate salt, carboxylated 

cellulose, and a neutralized cross-linked isobutylene-maleic 

anhydride copolymer. An absorbent material of the present 

invention can contain any SAP known in the art. The SAP 60 

can be in the form of particulate matter, flakes, fibers and the 

like. Exemplary particulate forms include granules, pulverized particles, spheres, aggregates and agglomerates. Exemplary and preferred SAPs include salts of crosslinked polyacrylic acid such as sodium polyacrylate. 65 material comprising the softening agent. 

The term "Mullen strength" as used herein refers to the 

hydrostatic pressure, typically measured in kilopascals, 

Various types of wood pulp sheets were tested to measure 

the effect that the softening agents of the present invention 
US 6,310,268 Bl 

9 

had on properties including Mullen strength, Kamas energy, 

absorption time and fluid retention. It was found that citrate 

esters reduce Kamas energy, reduce Mullen strength, and 

have a negligible effect on both absorption time and fluid 

retention properties of pulp sheets. 

When the invention is practiced industrially, the softening 

agents are best applied to wood pulp sheets in an aqueous 

solution which can be made up in a holding tank or prepared 

continuously with an in-line static mixer. In the manufacture 

of absorbent pulp sheets, these agents can be added to a fiber 

slurry at the machine chest, fan pump or head box. They can 

also be applied by spray application to a wet pulp sheet or 

can be applied via a "dip and nip" procedure in which an 

evacuated but not completely dried pulp sheet is dipped into 

a solution containing the agent and subsequently pressed. 

Additionally, softening agents of the invention may be 

sprayed, rolled or printed onto one or both sides of a pulp 

sheet. 

The wood pulp used in the sheets treated by the methods 

of the present invention can also be pretreated prior to use 

with the present invention. This pretreatment may include 

physical treatment, such as subjecting the fibers to steam, or 

chemical treatment, for example, cross-linking the cellulose 

fibers using any of a variety of cross-linking agents such as 

dimethyl dihydroxyethylene urea. Cross-linking the fibers, 

for example, increases their resiliency, and thereby can 

improve their absorbency. The fibers may also be twisted or 

crimped, as desired. 

Although not to be construed as a limitation, examples of 

pretreating fibers include the application of fire retardants to 

the fibers, such as by spraying the fibers with fire-retardant 

chemicals. Specific fire-retardant chemicals include, by way 

of example, sodium borate/boric acid, urea, and ureal 

phosphates. In addition, the fibers may be pre-treated with 

surfactants or other liquids, such as water or solvents, which 

modify the surface of the fibers. These are known as 

softened or debonded fibers. Other pre-treatments include 

exposure to antimicrobials, pigments and densification or 

softening agents. Fibers pre-treated with other chemicals, 

such as thermoplastic and thermosetting resins also may be 

used. 

Wood pulp sheets may be treated for softening by spraying the softener on the sheet as it is rolled up upon formation 

in the papermaking process, or by spraying the softener as 

the rolled sheets of pulp are unrolled for further processing. 

Sheets so treated, when utilized to make an absorbent core, 

results in a softer absorbent core which retains capacity for 

liquid retention. 

The Additives 

Plasticizers such as tributyl citrate have been used in 

combination with terpolymers to form binder compositions 

to make soft absorbent webs which are capable of dispersing 

in an aqueous environment into unrecognizable pieces in 

U.S. Pat. No. 5,935,880. These binder compositions of the 

, 880 patent are used by those skilled in the art as additives 

10 

citric acid esters have been used for odor-prevention in 

sanitary hygiene products as disclosed in U.S. Pat. No. 

4,583,980. In the '980 patent, a high concentration of 

additive (12.5-37.5%) is utilized to create an additive layer 

5 in the product. By contrast, the present invention utilizes 

much lower concentrations. 

10 

Triacetin has been used as a solvent for a bonding medium 

such as cellulose acetate to form a strengthened web containing pulped cellulosic fibers as disclosed in U.S. Pat. Nos. 

5,837,627 and 5,695,486. However, when these materials 

are strengthened using a combination of cellulose acetate 

and triacetin, absorbency decreases. In the present invention, 

cellulose acetate is not contemplated to be within the definition of cellulosic fibers. 

Triacetin was first recognized to provide softening in pulp 

15 in U.S. Pat. Nos. 5,776,308 and 5,858,172. These patents 

also disclosed other non-ionic compounds such as alkyl 

ethers, aryl ethers, formic, ethanoic and propanoic esters of 

low molecular weight glycols (such as propylene glycol 

diacetate and 2-phenoxyethanol) for softening wood pulp. 

20 However, the citrate esters of the present invention have not 

been disclosed for such purposes. Moreover, the use of these 

non-ionic compounds as additives in the manufacture of 

absorbent cores has not previously been disclosed. 

Examples of suitable plasticizers are esters or ethers. The 

25 ethers or esters may be glycol derivatives, and the esters may 

also be citrates or triacetin. Suitable glycol ethers include 

alkyl ethers of low molecular weight glycols or aryl ethers 

of low molecular weight glycols. Suitable glycol esters 

include formic esters of low molecular weight glycols, 

30 ethanoic esters of low molecular weight glycols or propanoic esters of low molecular weight glycols. 

Examples of suitable citrate esters include trimethyl 

citrate, acetyl trimethyl citrate, triethyl citrate, tri-n-butyl 

citrate, acetyl triethyl citrate, acetyl tri-n-butyl citrate, acetyl 

35 tri-n-hexyl citrate, n-butyryl tri-n-hexyl citrate, acetyl tri-n-

(hexyl/octyl/decyl) citrate and acetyl tri-n-(octyl/decyl) citrate and combinations thereof among others. 

Addition of the plasticizers of the present invention 

should not decrease the relative liquid absorption rate of said 

40 absorbent material by more than 5%. 

Compounds are preferably added neat, though it should 

be noted that application of a softening agent to wood pulp 

is not limited to neat application, and can also include 

application in solution, as an emulsion, as a suspension or a 

45 dispersion. One or more of the additives described above 

may be utilized. Plasticizers may act synergistically with 

each other. Moreover, other additives which may be used in 

conjunction with the non-ionic plasticizers of the present 

invention include absorbent capacity enhancing materials 

50 such as super absorbent polymers, zeolites and activated 

carbon, brighteners such as titanium dioxide, and odor 

absorbents such as sodium bicarbonate, EDTA, zeolites, 

activated carbon and borates. Solvents can also reduce the 

dusting caused by the additives or the pulp itself because 

55 more of the fines are attached and bound to the matrix by the 

bonding medium. 

in the wet laid process, for manufacturing absorbent materials having basis weights below 125. For the present 

invention, absorbent cores are manufactured by an air-laid 60 

process, which is utilized to make materials having much 

higher basis weights. 

The effective softening amount of the additives described 

above will depend upon the system to be treated. Factors 

which will influence how much of the additive is necessary 

include the type of wood pulp utilized, particular processing 

conditions, which other additives are present, which particular additive is selected and the desired properties of the 

Citric resultant absorbent core. acid has been disclosed as a binder useful in 

combination with a densifying agent to bind particles to 

fibers in U.S. Pat. Nos. 5,641,561 and 5,547,541. However, 65 

citric acid is not a plasticizer, as it is a carboxylic acid, while 

art recognized plasticizers are esters or ethers. Additionally, 

Test Procedures & Definitions 

In the tests described hereinafter, industry-employed standard test procedures have been used. If any deviations from 
US 6,310,268 Bl 

11 

standard test procedure have been made, such deviations 

have been identified. 

12 

A decrease in stiffness was observed as the amount of 

triacetin treated pulp is increased. A control air-laid absorbent core had a stiffness of 980 mg, while the absorbent 

cores with 100% triacetin treated pulps had a stiffness of 780 

For purposes of evaluating the products obtained and 

described by the present disclosure as well as the invention 

herein, several tests were used to characterize the desirable 

fibrous wood pulp end-use performance improvements 

resulting from use of the presently disclosed softening agent 

treatment, and to describe some of the analytical properties 

5 mg. Table 1 summarizes this trend. 

Suppleness values are derived from the stiffness values, 

obtained as described above. Suppleness and stiffness are 

inversely proportional, and a higher suppleness value is 

more desirable for an absorbent material. To obtain a value of the pulp products. A summary of these tests and definitions follows: 

"Pulp 1" is an untreated southern pine kraft pulp sold by 

Rainier Inc. for use in applications requiring high 

absorbency. 

10 for suppleness, stiffness is divided by one thousand, and the 

resulting number is inverted. 

"Pulp 2" is a southern pine kraft pulp which has been 

treated with softener triacetin of the present invention. 15 

"Pulp 3" is a southern pine kraft pulp which has been 

treated with softener triethyl citrate of the present 

invention. 

"Pulp 4" is a cold caustic treated, mercerized fiber available from Rayonier Inc. 

"Pulp 5" is a southern pine kraft pulp available from 

Rayonier Inc. which has been treated with a cationic 

(quaternary ammonium salt) deb onder. 

To measure the absorbent capacity and rate of absorbency 

of absorbent materials, a radial wicking test was performed 

on Gravimetric Absorbency Test equipment. Maximum 

capacity is first measured, and then the time to reach 25%, 

50% and 75% of saturation is recorded. Radial wicking 

results provided in Table 2 showed no negative impact on 

absorbency properties by including triacetin treated pulps, 

since the absorbent properties of Core A (no added triacetin) 

20 were comparable to Core D (having 100% of 1% triacetin 

treated pulp). Therefore this example shows that at a 1 % 

triacetin charge, the stiffness of absorbent cores can be 

reduced by 20%. 

"Pulp 6" is a southern pine kraft pulp which has been 

treated with softener tri-n-butyl citrate of the present 25 

invention. 

Several experiments were conducted to demonstrate the 

effects of triacetin on the aforementioned debonding and 

absorbency properties of wood pulp, and on absorbent cores 

made therefrom. 30 

The absorbent cores were generated using the bench scale 

dry forming system. The bench-scale dry-forming system 

(BSDFS) is used to produce 12-inch diameter absorbent 

cores. This system allows the user to vary the number of 

layers, amount of superabsorbent polymer (SAP), pulp type 35 

and content, basis weight and density of the absorbent cores 

formed. The BSDFS can be used to produce multi-layered 

air-laid handsheets and mimics a large-scale air-laid pilot 

plant. The system comprises of a KAMAS CELLTM to 

defiberize the pulp, a 100-mesh, 12" forming wire in a 40 

vacuum forming head, a SAP dosing system, compaction 

roll for initial densification of web and a heated press for 

final densification and bonding. The absorbent cores used 

herein comprised four layers: a bottom layer of tissue, 

followed by two layers of pulp and SAP, and a final top layer 45 

of pulp. The tissue utilized was Tissue Grade 3008, available 

from Cellu Tissue Corporation of East Hartford, Connecticut. The SAP utilized was in the form of particles sold under 

the designation No. 7440, available from Stockhausen 

GmbH of Krefeld, Germany. 50 

Gurley stiffness was measured using 3.5"x1" strips. 

Radial wicking tests were carried out on 2" circular pads 

using a Gravimetric Absorbency Test System (GATS) instrument. 

EXAMPLE 1 

Triacetin (available from Eastmann Chemical Co.) was 

applied to several pulp sheets of Pulp 1 by spraying directly 

55 

on the sheets (1% oven-dried charge). Pulp sheets thus 

treated were referred to as Pulp 2. The treated Pulp 2 and 60 

non-treated Pulp 1 were combined at different ratios (0, 

33%,66% and 100%) to make air-laid absorbent cores. The 

cores contained 55% SAP. These cores were tested to obtain 

1 

TABLE 1 

Corel Pulp 2 (%)/Pulp 1 (%) Stiffness (mg) Suppleness (l/g) 

A 01100 983 1.02 

B 33/66 954 1.05 

C 66/33 768 1.30 

0 10010 784 1.28 

~ basis weight for each sample was 520 gsm, density 0.3 glee. 

TABLE 2 

Effect of using various ratios of Pulp 1 and triacetin treated Pulp 2 on 

radial wicking properties of absorbent cores (Density"" 0.30 glee) 

Average 

Amount of 1 % triacetin pulp: 0%, Core A 

Maximum Capacity (gig) 20.4 

T25 (s) 12.5 

T~W n6 T75 (s) 246.1 

Amount of 1 % triacetin pulp: 33%, Core B 

Maximum Capacity (gig) 21.1 

T25 (s) 14.0 

T~W ~.5 

T75 (s) 255.6 

Amount of 1 % triacetin pulp: 66%, Core C 

Maximum Capacity (gig) 21.6 

T~W D~ 

T50 (s) 82.8 

T75 (s) 240.4 

Amount of 1 % triacetin pulp: 100%, Core 0 

Maximum Capacity (gig) 

T25 (s) 

T50 (s) 

T75 (s) 

EXAMPLE 2 

20.4 

D.9 

81.4 

233.3 

a stiffness value on a Gurley Precision Electronic Bending A second group of experiments involved determining the 

Resistance Tester. The stiffness value indicates the softness 65 effect of density on softness of air-laid absorbent cores. Each 

of the material, with a lower stiffness value indicating a core contained 55% SAP. Air-laid absorbent cores were 

more soft material. generated from four different pulp grades, and tested accord-
US 6,310,268 Bl 

13 

ing to the following procedure. Typically, absorbent cores 

made in the lab have a density of approximately 0.3 glcc. To 

achieve greater density, a fiat press was used to lower 

thickness, thereby increasing density. Pressed samples were 

tested for stiffness. The fiat press was also used to compress 

radial wicking samples from the cores to around 0.39 glcc to 

simulate production run densities. As indicated in Table 3, 

density resulted in an increase in stiffness for all the samples 

studied. Overall the cores containing triacetin treated pulps 

had a significantly lower stiffness when compared to the 

samples of Pulp 1. It was also observed that this decrease in 

stiffness is maintained irrespective of the density. 

TABLE 3 

Stiffness vs Density 

Density Stiffness Suppleness 

Sample' % Treatment (glcc) (mg) (l/g) 

Pulp 1 none 0.327 888 1.13 

0.375 1043 0.96 

0.431 1201 0.83 

Pulp 4 none 0.296 496 2.02 

0.341 498 2.01 

0.356 574 1.74 

Pulp 5 0.25 % debonder 0.301 522 1.92 

0.393 593 1.69 

0.42 695 1.44 

Pulp 22 3% triacetin 0.293 482 2.07 

0.368 552 1.81 

0.429 630 1.59 

,~ basis weight of 520 gsm 

2~ 3% charge of triacetin on oven-dried pulp 

EXAMPLE 3 

14 

densified to a density of 0.18 (g/cc). After spraying a known 

quantity of triacetin (in this case 2.5% based on oven-dried 

pulp in the core), the core was allowed to sit in a 

temperature-controlled room for 2 hours. After this, the core 

5 was densified to a density of 0.3 glcc and the stiffness was 

measured. 

The result from this experiment is shown in Table 5, 

which illustrates that spraying triacetin directly on an air10 laid absorbent core also results in a reduction in stiffness. 

TABLE 5 

Effects of Spraying Plasticizer on Formed Absorbent Core 

15 Sample Stiffness(mg) Suppleness (l/g) 

20 

Core made from Pulp 1, no triacetin 

Core made from Pulp 1 with 2.5% 

triacetin added to core 

888 

492 

EXAMPLE 5 

1.13 

2.03 

To determine the softening effects of citrate esters, triethyl 

25 citrate was applied to Pulp 1 at a 3% oven-dried charge. The 

treated pulp (Pulp 3) was then utilized to generate air-laid 

absorbent cores. These cores were tested for stiffness 

according to the procedure described in Example 1. The 

results (Table 6) show that triethyl citrate (obtained from 

30 Morfiex Inc. of Greensboro, Ga.) behaves very similar to 

triacetin in reducing the stiffness of the absorbent core. 

TABLE 6 

The effect of varying the amount of triacetin applied to the 35 Effect of Citrate Added to Pulp on Absorbent Core Produced Therefrom 

pulp was tested by applying varying amounts of triacetin to 

Pulp 1 pulp sheets. The amount of triacetin charged on 

oven-dried pulp was varied from 0, 1%, 1.5%,2.0,3.0%,5% 

and 10%. Air-laid absorbent cores were made then made by 

using these treated pulp sheets. Each core contained 55% 

SAP. Stiffness of these sheets was then tested according to 

the procedure described in Example 1. 

Sample' Stiffness(mg) Suppleness (l/g) 

Core made from Pulp 1, no triethyl 888 1.13 

citrate 

40 Core made from Pulp 3, 3% triethyl 

citrate added to pulp 

401 2.49 

Core made from Pulp 2, 3.1 % 481 2.08 

triacetin added to pulp 

Increasing the amount of triacetin charge resulted in an 

overall decrease in stiffness. This trend can be seen in Table ,~ each sample contained 55% SAP, had a basis weight of 520 gsm and a 

4, which illustrates that nearly a 50% reduction in stiffness 45 density of 0.3 glcc 

was obtained. 

TABLE 4 

Effects of Amount of Triacetin in Pulp on Stiffness of Absorbent Core' 

% Triacetin Stiffness (mg) Suppleness (l/g) 

0 888 1.13 

1 785 1.27 

1.5 543 1.84 

2.0 440 2.27 

3.1 481 2.08 

5 475 2.11 

10 430 2.33 

,~ basis weight of 520 gsm and density of 0.30 g/cc 

EXAMPLE 4 

In this example, triacetin was sprayed directly onto an 

absorbent core made using the BSDFS described previously. 

The absorbent core was made using untreated Pulp 1. Each 

core contained 55% SAP, and had a basis weight of 520 gsm. 

The spraying with triacetin was done after the core had been 

EXAMPLE 6 

To compare the softening ability of citrate esters to 

50 triacetin in pulp, the following experiments were performed. 

The citrate esters were obtained from Morfwex, Inc of 

Greensboro, N.C. 

To apply the additive to the pulp, 12-inch square sheets of 

55 Pulp 1 at a basis weight of 640 gsm were weighed and a 

calculated mass of plasticizer was sprayed evenly across one 

side of the sheet. Each pulp sheet was placed in a separate 

bag and allowed to sit overnight. Next, Kamas energy was 

determined for each sample, in order to characterize the 

60 amount of energy required to break a sheet. 

The results are provided in Table 7 (low charge of 

plasticizer) and Table 8 (higher charge of plasticizer). All 

three of the tested plasticizers reduced Kamas energy by 

65 about 35% when compared to the untreated Pulp 1, from 60 

to 38 Whlkg. The leftover half of each pulp sheet from the 

Kamas energy test was used in the Mullen strength test. 
US 6,310,268 Bl 

15 

TABLE 7 

Plasticizer Kamas Energy 

Sample (%) (Wh/kg) 

Pulp 1 00.0 59.76 

Pulp 2 0.27 53.35 

Pulp 2 0.52 47.00 

Pulp 2 0.74 38.36 

Pulp 1 0.00 59.76 

Pulp 3 0.26 47.22 

Pulp 3 0.55 44.35 

Pulp 3 0.74 39.12 

Pulp 1 0.00 59.76 

Pulp 6 0.27 47.09 

Pulp 6 0.48 40.07 

Pulp 6 0.71 41.47 

Pulp 6 0.99 39.10 

Pulp 5, 0.25% 44.48 

debonder 

TABLE 8 

Plasticizer Kamas Energy 

Sample (%) (Wh/kg) 

Pulp 1 00.0 59.76 

Pulp 2 1.03 39.18 

Pulp 2 2.00 38.89 

Pulp 2 3.00 35.44 

Pulp 1 0.00 59.76 

Pulp 3 1.00 39.92 

Pulp 3 2.02 36.97 

Pulp 3 3.00 34.90 

Pulp 1 0.00 59.76 

Pulp 6 2.01 36.97 

Pulp 6 2.94 36.78 

Pulp 5, 0.5% 31.14 

debonder 

EXAMPLE 7 

Mullen Strength 

(kPa) 

1091.73 

896.30 

832.80 

848.20 

1091.73 

920.60 

845.00 

840.80 

1091.73 

909.60 

924.70 

871.60 

907.70 

Mullen Strength 

(kPa) 

1091.73 

757.17 

792.03 

706.83 

1091.73 

834.50 

762.43 

785.43 

1091.73 

860.80 

825.37 

16 

to overcome the negative suction force in order to absorb 

fluid. The positive force results from the capillary pressure 

of the fiber. As the absorbent material picks up fluid, the 

positive pressure decreases. A point is reached when the 

5 positive force necessary to counter-balance the suction force 

insufficient. This point is referred to as equilibrium absorbency and represents the cessation of absorption. The hydrostatic pressure is systematically increased from 3 mm to 45 

cm of water, and the equilibrium absorbency at the 40 cm 

10 hydrostatic tension value is measured. At a hydrostatic 

tension value of about 3 mm of water, the fiber network is 

completely saturated with the test fluid. At the hydrostatic 

tension value of about 40 cm of water the maximum 

retention is measured. The confining load on the sample was 

15 0.05 psi, to ensure contact between the sample and test cell. 

A schematic illustration of an instrument used to obtain 

measurements for this characterization is described in u.S. 

Pat. No. 5,916,670. The instrument comprises a fluid source 

as well as an adjustable sample compartment. The fluid 

20 source comprises a constant-level fluid reservoir in conjunction with a supply reservoir. The entire fluid reservoir 

component is placed on a balance to allow for determination 

of the mass of the fluid lost or gained by the fluid reservoir. 

The fluid source is connected via a tube to the adjustable 

25 sample compartment. The adjustable single port compartment (available from M-K Systems of Danvers, Mass.) 

comprises a solid support on which is placed a filter paper 

(Whatman #5) and a sample of absorbent material. The solid 

support mechanism together with the filter and sample are 

30 attached to a device which allows for raising and lowering 

of the sample height relative to the height of the fluid in the 

fluid reservoir. When the level of the sample in the sample 

compartment is the same as the level of the constant level 

fluid reservoir, there is no hydrostatic pressure head applied 

35 to the sample. As the sample level is raised above the level 

of fluid in the constant level reservoir, a negative hydrostatic 

pressure head is applied to the sample. The magnitude of the 

hydrostatic pressure head is equal to the difference in height 

between the sample and the fluid reservoir as measured in The procedure for measuring stiffness and suppleness 

described in Example 1 was utilized to compare pulps 

treated in accordance with the present invention to commercially available pulps. Each sample had a basis weight of 

320 gsm and contained no SAP. Table 9 illustrates that the 

cores made with the plasticizer treated pulps had a significantly lower stiffness when compared to the untreated 45 

sample. Also the core made with the debonded pulp had 

comparable stiffness to the cores made with plasticized 

pulps. 

40 centimeters. 

Following the procedure described above, the various 

samples of absorptive material were placed in the instrument 

and fluid absorption was measured over a range of hydrostatic pressures. Each sample had a basis weight of 320 gsm 

and contained no SAP. The equilibrium absorbency at the 

highest negative hydrostatic head was reported as Retention 

in gig in Table 10. 

TABLE 9 

Pulp 1 Pulp 5 

% Treatment none 0.25% debonder 

Density (glee) 0.28 0.31 

Stiffness (mg) 732 291 

Suppleness (g-l) 1.4 3.4 

EXAMPLE 8 

50 

Pulp 2 

3% triacetin 

0.27 

345 

2.9 55 

The cores made with the debonded pulp had a significantly lower retention when compared to the untreated and 

plasticized samples. Therefore the cores made with plasticized pulps have a significantly lower stiffness without any 

negative impact on absorbent properties, unlike the cores 

made with the debonded pulps. 

TABLE 10 

Pulp 1 Pulp 5 Pulp 2 Pulp 3 

% Treatment None 0.25% 3% 3% Triethyl 

Various absorptive materials of the present invention were 

examined to determine their ability to absorb fluids against 

a negative hydrostatic pressure gradient, utilizing the following procedure. 

60 Density (glee) 

Retention (gig) 

0.17 

3.93 

Debonder 

0.18 

1.94 

Triacetin Citrate 

0.17 0.15 

3.56 3.76 

Absorbency of the sample is measured at negative hydrostatic pressure, i.e., negative hydrostatic head. The negative 65 

hydrostatic pressure exerts a suction force on the sample. 

The absorbent material needs to have enough positive force 

EXAMPLE 9 

Wicking properties of the material were measured using a 

GATS system manufactured by M/K Systems of Danvers, 
US 6,310,268 Bl 

17 

Mass. to determine the values for 45° wicking. The set up of 

the test is described in detail in U.S. Pat. No. 5,916,670, 

hereby incorporated by reference. A 45° wicking test cell is 

attached to the absorption measurement device. The test cell 

essentially consists of a circular fluid supply unit for the test 

sample and 45° ramps. The fluid supply unit has a rectangular trough and liquid level is maintained at the constant 

height by the measuring unit. 

To perform the test, a sample of the absorbent material to 

5 

10 

18 

than the cores formed using debonded pulps. 

TABLE 12 

Pulp 1 Pulp 5 Pulp 5 Pulp 2 Pulp 3 

% Treatment None 0.25% 0.5% 3% 3% Triethyl 

Debonder Debonder Triacetin citrate 

Density 0.18 0.20 0.19 0.20 0.20 

(glee) 

T25 (s) 4.1 7.5 6.3 4.4 3.2 

T50 (s) 9.7 17.5 15.7 10.6 10.2 

T75 (s) 17.7 29.1 29.0 18.5 18.4 

EXAMPLE 11 

To compare the use of triacetin of the present invention to 

conventional additives which combine triacetin and cellulose acetate to achieve a different type of material, the 

following experiment was performed. Absorbent cores were 

made using cellulose acetate (CA) and triacetin in combination with Pulp 1. The CA fibers (1'h", 1.8 Denier) were 

obtained from Eastman Chemical Company. All cores were 

made at 520 gsm with 55% SAP. The control sample did not 

contain any CA and triacetin. In Core 1, the fiber make-up 

be characterized having dimension of 1"x12" was prepared. 

The sample was marked every inch along the length of the 

sample. The sample was then placed on the ramp of the test 

cell ensuring that one of the edges of the sample dips into the 

trough. The test was conducted for thirty minutes, after 

which time the sample was removed and cut along the 15 

marked distances. The cut pieces were placed into preweighed aluminum weighing dishes. The weighing dish, 

containing wet samples, was weighed again and then ovendried to a constant weight. By conducting a proper mass 

balance on the data, absorbency of the sample was deter- 20 

mined at every inch. For each sample, the amount of fluid 

absorbed per gram of sample was plotted against distance 

from the origin (source of fluid). The area under the curve 

was calculated using the following formula: 25 comprised of 92% Pulp 1 and 8% CA fibers. In Core 2, the 

fiber make-up comprised of 89% Pulp 1, 8% CA fibers and 

3% Triacetin. Core 3 was an absorbent core was also made 

with Pulp 2 (treated with 3% triacetin). The absorbent cores 

tested were comprised of a tissue layer at the bottom, 

[(y,)(X2-X,)+0.5(Y2-y,)(X2-X,)+(Y2) (X3-X2)+ 

0.5(Y3-Y2)(X3-X2)+ ... +(Yn) xn-xn_,)+ 

O.5(Yn-Yn_') (xn-xn_,)], 

where Xi is distance at the i

th inch and Y i is absorbency at 

the i

th inch. 

This area was then multiplied by the gravitational constant (981 cm/s2) and the sine of 45° to result in the work 

value of ergs/g. A higher value for 45° wicking energy 

indicates greater absorbency. The total amount of liquid 

absorbed by the strip divided by the weight of the strip gives 

the efficiency in gig. 

Each sample had a basis weight of 320 gsm and contained 

30 followed by two layers of pulp and SAP and then a top layer 

of fluff pulp. In the treated samples, CA and triacetin were 

added to the bottom two layers. The CA fibers were added 

through the hammer mill along with the wood pulp. In Core 

2, the triacetin was sprayed on to the absorbent core after 

35 addition of the CA fibers. The samples so formed were 

evaluated using the GATS 45° Wicking test procedure 

described in Example 9. 

no SAP. Table 11 shows that the cores made with the 

debonded pulp had significantly lower wicking properties 

when compared to the untreated and plasticized samples. 40 

Thus the cores made with plasticized pulps have a significantly lower stiffness without any negative impact on 45° 

wicking, unlike the cores made with the debonded pulps. 

Table 13 shows that, using CA in combination with 

triacetin in the formation of an absorbent core results in a 

negative impact on absorbent properties. On the other hand, 

Core 3 made with just the triacetin treated pulp of the present 

invention, did not show any negative impact on absorbent 

properties when compared to control sample. 

TABLE 11 

Pulp 1 Pulp 5 Pulp 5 Pulp 2 Pulp 3 

% Treatment None 0.25% 0.5% 3% 3% 

Debonder Debonder Triacetin Triethyl 

citrate 

Density 0.37 0.36 0.36 0.33 0.33 

(glee) 

Efficiency 3.7 1.6 1.56 4.0 3.1 

(gig) 

Energy 67752 35359 31463 65926 42226 

(ergs/g) 

EXAMPLE 10 

GATS Radical Wicking was carried out on the above 

samples in accordance with the procedure described in 

Example 1 to determine the rate of absorbency for each 

sample and to determine whether there were any differences 

between the cores made using the plasticizer treated pulps 

and debonded pulps. Each sample had a basis weight of 320 

gsm and contained no SAP. The results are presented in 

Table 12, which shows that the absorbent cores formed using 

plasticizer-treated pulps have a better rate of absorbency 

45 

50 

55 

TABLE 13 

Core 2 Core 3 

Corel (With CA+ (With 3% 

Control (WithCA) triacetin) triacetin) 

Density (glee) 0.4 0.4 0.4 0.39 

Efficiency (gig) 8.1 7.8 7.5 8.2 

Energy (ergs/g) 119095 107365 110000 122000 

EXAMPLE 12 

Absorbent cores were generated using the air-laid process 

at a pilot facility, and various pulps, treated as indicated in 

Table 14. The air-laid system consisted of two forming 

heads. In the first forming head a mixture of pulp and SAP 

60 was added whereas in the second forming head only pulp 

was added. After air-laying the pulp and SAP on the carrier 

layer (comprising of a tissue) the resultant web was heat 

calendered to achieve the target density. Resultant cores had 

a total amount of SAP of 40%, and the target basis weight 

65 of the absorbent core and tissue was 400 gsm. 

Gurley stiffness measurements were carried out on the 

absorbent cores generated using these pulp samples, follow-
US 6,310,268 Bl 

19 20 

dividing the 45° wicking energy values by the percentage of 

superabsorbent polymer present in the absorbent core. The 

results in Table 17 illustrate that cores formed from 

plasticizer-treated pulps have comparable wicking perforing the procedure described in Example 1. The results of 

Table 14 indicate that use of plasticizer in treated pulps can 

result in a substantial decrease in the stiffness of the absorbent cores. Similar decreases in stiffness can also be 

obtained by using pulps treated with debonders. 5 mance to cores formed from untreated pulps. 

The 45° wicking energy values were obtained according 

TABLE 16 to the procedure described in Example 9. The normalized 

wicking energy values in Table 15 were calculated by 

dividing the 45° wicking energy values by the percentage of 

superabsorbent polymer present in the absorbent core. The 

results of Table 15 illustrate that cores containing plasticizertreated pulps exhibit a significantly better wicking performance than cores containing debonder-treated pulps. Also, 

the wicking performance of some of the absorbent cores 

containing plasticized pulps is comparable to the cores 15 

containing untreated pulps. 

Pulp 

10 Sample ID Treatment 

Basis 

Weight 

(gsm) 

Density 

(g/ee) 

Stiffness 

(mg) 

Suppleness 

(l/g) 

TABLE 14 

Density Stiffness Suppleness 

Sample ID Pulp Pulp Treatment (glee) (mg) (l/g) 

Sample A none 0.29 803 1.24 

Sample B 4 caustic-treated 0.28 511 1.90 

Sample C 2 1 % triacetin 0.32 583 1.72 

Sample D 2 3% triacetin 0.30 448 2.23 

Sample E 3 1% triethyl citrate 0.30 442 2.26 

Sample F 7 1% acetyl triethyl 0.31 390 2.56 

citrate 

Sample G 5 0.25% debonder 0.32 513 1.95 

TABLE 15 

Normalized 

45° Wieking Wicking 

Pulp Density energy energy 

Sample ID Pulp Treatment (g/ee) (ergs/g) (ergs/g) 

Sample A none 0.29 142614 3565 

Sample B 4 Caustic 0.28 112559 2814 

treated 

Sample C 2 1% 0.32 134064 3352 

triacetin 

Sample D 2 3% 0.30 112260 2807 

triacetin 

Sample E 3 1% triethyl 0.30 97518 2438 

citrate 

Sample F 7 1% acetyl 0.31 98728 2469 

triethyl 

citrate 

Sample G 5 0.25% 0.32 81510 2038 

deb onder 

EXAMPLE 13 

Absorbent cores were generated using the air-laid process 

at a commercial scale machine facility under the following 

conditions. The air-laid system consisted of three forming 

heads. In the first two forming heads a mixture of pulp and 

SAP was added whereas in the third forming head only pulp 

was added. After air-laying the pulp and SAP on the carrier 

layer (comprising of a tissue) the resultant web was heat 

calendered to achieve the target density. Resultant cores had 

Sample H 

Sample I 

83% 

pulp 1 

and 

17% 

pulp 4 

100% 

pulp 2 

containing 

1% 

triacetin 

515 

504 

0.36 1053 0.95 

0.35 625 1.6 

20 Sample J 83% 

pulp 2 

538 0.37 660 1.51 

25 

30 

35 

40 

45 

Sample ID 

Sample H 

Sample I 

Sample J 

containing 

1% 

triacetin 

and 

17% 

pulp 1 

Pulp 

Treatment 

83% pulp 1 and 

17% pulp 4 

100% pulp 2 

containing 1 % 

triacetin 

83% pulp 2 

containing 1 % 

triacetin and 

17% pulp 1 

TABLE 17 

Basis 

Weight 

(gsm) 

515 

504 

538 

Density 

(glee) 

0.36 

0.34 

0.33 

EXAMPLE 14 

45° Normalized 

Wicking Wicking 

energy energy 

(ergs/g) (ergs/g) 

158356 2879 

134773 2450 

130044 2364 

Absorbent cores were generated using the air-laid process 

at a commercial scale machine facility under the following 

conditions: The air-laid system consisted of three forming 

heads. In the first two forming heads a mixture of pulp and 

50 SAP was added whereas in the third forming head only pulp 

was added. After air-laying the pulp and SAP on the carrier 

layer (comprising of a tissue) the resultant web was heat 

calendered to achieve the target density. Resultant cores had 

a total amount of SAP of 30%, and the target basis weight 

of the absorbent core and tissue was 200 gsm. 55 

The results of Table 18 illustrate that cores formed from 

plasticizer-treated pulps have comparable wicking performance to cores formed from untreated pulps. 

a total amount of SAP of 55%, and the target basis weight 60 

of the absorbent core and tissue was 500 gsm. 

TABLE 18 

45° Normalized Gurley stiffness measurements were carried out on the 

absorbent cores generated using these pulp samples, following the procedure described in Example 1. 

The 45° wicking energy values were obtained according 

to the procedure described in Example 9. The normalized 

wicking energy values in Table 17 were calculated by 

Sample ID 

65 Sample K 

Basis 

Pulp Weight 

Treatment (gsm) 

83% pulp 1 203 

and 17% pulp 4 

Wicking Wicking 

Density energy energy 

(glee) (ergs/g) (ergs/g) 

0.30 110046 3668 
US 6,310,268 Bl 

21 

TABLE 1S-continued 

45° 

Basis Wicking 

Pulp Weight Density energy 

Sample ID Treatment (gsm) (glee) (ergs/g) 

Sample L 100% pulp 2 215 0.31 101229 

containing 

1 % triacetin 

Sample M 83% pulp 2 211 0.29 106015 

containing 

1 % triacetin 

and 17% pulp 1 

Normalized 

Wicking 

energy 

(ergs/g) 

3374 

3534 

5 

10 

22 

9. The core of claim 8 wherein said citrate IS of the 

formula 

wherein Rl, R2 and R3 are each independently alkyl groups, 

and 

R4 is selected from the group consisting of hydrogen, 

alkyl groups and _C(O)R5, 

wherein R5 is an alkyl group. 

All references cited arc hereby incorporated by reference. 15 10. The core of claim 8 wherein said core has a wicking 

energy greater than about 40,000 ergs/g. The present invention is illustrated by way of the foregoing description and examples. The foregoing description 

is intended as a non-limiting illustration, since many variations will become apparent to those skilled in the art in view 

thereof. It is intended that all such variations within the 20 

11. The core of claim 8 wherein said core has a wicking 

energy greater than about 60,000 ergs/g. 

12. An absorbent core comprising: 

from about 30 weight percent to about 90 weight percent 

of cellulosic fibers; from about 9.99 weight percent to 

about 60 weight percent of superabsorbent polymer; 

from about 0.1 weight percent to about 10 weight 

percent of at least one non-ionic plasticizer; wherein 

said core has a suppleness of greater than about 0.7 g-l; 

a density of from about 0.25 g/cc to about 0.5 g/cc and 

scope and spirit of the appended claims be embraced 

thereby. 

Changes can be made in the composition, operation and 

arrangement of the method of the present invention 

described herein without departing from the concept and 25 

scope of the invention as defined in the following claims. a basis weight of from about 200 g/m2 to about 550 

glm2 . 

We claim: 

1. A wood pulp sheet comprising: 

from about 90 weight percent to about 99.9 weight 30 

percent of cellulosic fibers; and, 

13. The core of claim 12 wherein said plasticizer is 

selected from the group consisting of esters and ethers. 

14. The core of claim 13 wherein said ethers are glycol 

derivatives. from about 0.1 weight percent to about 10 weight 

percent of at least one citrate 

wherein said sheet has a defiberization energy of from 

about 35 to about 60 Whlkg. 

2. The sheet of claim 1 wherein said citrate is of the 

formula 

15. The core of claim 14 wherein said glycol derivatives 

are selected from the group consisting of alkyl ethers of low 

35 molecular weight glycols and aryl ethers of low molecular 

weight glycols. 

16. The core of claim 13 wherein said esters are selected 

from the group consisting of formic esters of low molecular 

weight glycols, ethanoic esters of low molecular weight 

40 glycols, propanoic esters of low molecular weight glycols 

and citrates. 

17. The core of claim 13 wherein said plasticizer is 

triacetin. 

18. The core of claim 16 wherein said citrates are of the wherein R\ R2 and R3 are each independently alkyl groups, and 45 formula 

R4 is selected from the group consisting of hydrogen, 

alkyl groups and _C(O)R5, 

wherein R5 is an alkyl group. 

3. An absorbent core comprising from 0.1 % to 10% of at 50 

least one non-ionic plasticizer. 

4. The core of claim 3 wherein said plasticizer is a citrate 

or triacetin. 

5. The core of claim 3 having a suppleness of greater than 

about 0.7 g-l. 

6. The core of claim 3 having a density of from about 0.25 

g/cc to about 0.5 g/cc. 

7. The core of claim 3 having a basis weight of from about 

200 glm2 to about 550 glm2

. 

8. An absorbent core comprising: 

from about 90 weight percent to about 99.9 weight 

percent of cellulosic fibers; and, 

from about 0.1 weight percent to about 10 weight percent 

of at least one citrate 

wherein said core has a suppleness of greater than about 0.7 

g-\ a density of from about 0.25 g/cc to about 0.5 glcc and 

a basis weight of from about 200 glm2 to about 550 glm2

. 

wherein Rl, R2 and R3 are each independently alkyl groups, 

and 

55 R4 is selected from the group consisting of hydrogen, 

alkyl groups and _C(O)R5, 

wherein R5 is an alkyl group. 

19. The core of claim 12 wherein said cellulosic fibers are 

derived from at least one type of pulp sheet. 

60 20. The core of claim 12 wherein said cellulosic fibers are 

derived from a mixture of at least two types of pulp sheets. 

21. The core of claim 12 wherein said core has a normalized wicking energy greater than about 2,300 ergs/g. 

22. A method for manufacturing a softened absorbent 

65 material from cellulosic fibers comprising the steps of: 

a) defiberizing cellulosic fibers to form defiberized cellulosic fibers; 
US 6,310,268 Bl 

23 

b) blending said defiberized cellulosic fibers with superabsorbent material to form a blended material; 

c) depositing said blended material onto a carrier layer 

under vacuum to form a layered absorbent web; and 

d) compressing said web to form an absorbent material, 5 

wherein an effective softening amount of at least one nonionic plasticizer is added to at least one of said cellulosic 

fibers, said defiberized cellulosic fibers, said blended 

material, said web and said absorbent material. 

23. The method of claim 22 wherein said absorbent 10 

material is an absorbent core. 

24 

31. The method of claim 29 wherein said citrates are of 

the formula 

wherein R\ R2 and R3 are each independently alkyl groups, 

and 

R4 is selected from the grow consisting of hydrogen, 

alkyl groups and -C(O)R , 

wherein R5 is an alkyl group. 

24. The method of claim 22 wherein said plasticizer is 

anti-microbial and said softened absorbent wood pulp product is an anti-microbial, softened, absorbent wood pulp 

product. 

32. The method of claim 22 wherein said cellulosic fibers 

15 are derived from at least one type of pulp sheet. 

33. The method of claim 32 wherein said cellulosic fibers 

are derived from a mixture of at least two types of pulp 

sheets. 

25. The method of claim 22 wherein said plasticizer is 

odor-preventing and said softened absorbent wood pulp 

product is an odor-preventing, softened absorbent wood 

pulp product. 

26. The method of claim 22 wherein said plasticizer is 

selected from the group consisting of esters and ethers. 

34. A method for softening wood pulp sheets comprising 

20 the step of adding to said sheets an effective wood pulp sheet 

softening amount of at least one citrate of the formula 

27. The method of claim 26 wherein said ethers are glycol 

derivatives. 

28. The method of claim 27 wherein said glycol derivatives are selected from the group consisting of alkyl ethers 25 

of low molecular weight glycols and aryl ethers of low 

molecular weight glycols. 

29. The method of claim 26 wherein said esters are 

selected from the group consisting of formic esters of low 

molecular weight glycols, ethanoic esters of low molecular 30 

weight glycols, propanoic esters of low molecular weight 

glycols and citrates. 

30. The method of claim 22 wherein said plasticizer is 

triacetin. 

wherein Rl, R2 and R3 are each independently alkyl groups, 

and 

R4 is selected from the grow consisting of hydrogen, 

alkyl groups and -C(O)R , 

wherein R5 is an alkyl group. 

* * * * *