Wet laid fiber sheet manufacturing with reactivatable binders for binding particles to fibers

Binder is applied to fibers during the production of a web on a wet laid sheet manufacturing line. Particles are bound to fibrous material by a binder that has a volatility less than water, wherein the binder has a functional group capable of forming a hydrogen bond with the fibers, and a functional group that is capable of forming a hydrogen bond or a coordinate covalent bond with the particles. The binder may be activated or reactivated by addition of heat, liquid, or mechanical energy such that fibers treated with binder may be shipped to a distribution point before particles are bound to the fibers. The binder may be a polymeric binder selected from the group consisting of polyethylene glycol, polypropylene glycol, polyacrylic acid, polyamides and polyamines, and in which the polymeric binder has a hydrogen bonding functionality or coordinate covalent bond forming functionality on each repeating unit of the polymeric binder. Alternatively, the binder may be a non-polymeric organic binder that includes a functionality such as a carboxylic acid, an alcohol, an amino acid, an amide, and an amine, wherein there are at least two such functionalities on the molecule, which may be the same or different functionality. Particles attached to the fibers in this manner are firmly adhered and are not easily dislodged. Fibrous products produced by this method include fibers to which particles are bound and may also include other fibers.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention concerns reactivatable polymeric and non-polymeric binders 
applied to fibers on a wet laid fiber sheet manufacturing line and to the 
use of such binders in binding particles to fibers. In particular 
embodiments, it concerns the reactivation and use of such fibers, 
preferably at an article manufacturing plant at a location remote from a 
pulp sheet manufacturing line to bind superabsorbent and/or other 
particles to cellulosic fibers which may then be used, for example, as 
absorbent fibers incorporated into cellulosic products. 
2. General Discussion of the Background 
Superabsorbent polymers have been developed in recent years that are 
capable of absorbing many times their own weight of liquid. These 
polymers, which are also known as water insoluble hydrogels, have been 
used to increase the absorbency of sanitary products such as diapers and 
sanitary napkins. Superabsorbent polymers are often provided in the form 
of particulate powders, granules, or fibers that are distributed 
throughout absorbent cellulosic products to increase the absorbency of the 
product. Superabsorbent particles are described, for example, in U.S. Pat. 
No. 4,160,059; U.S. Pat. No. 4,676,784; U.S. Pat. No. 4,673,402; U.S. Pat. 
No. 5,002,814; and U.S. Pat. No. 5,057,166. Products such as diapers that 
incorporate absorbent hydrogels are shown in U.S. Pat. No. 3,669,103 and 
U.S. Pat. No. 3,670,731. 
One problem with the use of superabsorbents is that the superabsorbent 
material can be physically dislodged from the cellulosic fibers of an 
absorbent product and migrate from the product. Separation of the 
superabsorbent from the product wastes the superabsorbent material and 
reduces the absorbency of the product and diminishes the effectiveness of 
the superabsorbent material. This problem was addressed in European Patent 
Application 442 185 A1, which discloses use of a polyaluminum chloride 
binder to bind an absorbent polymer to a fibrous substrate. The 
polyaluminum binder, however, suffers from the drawback of being an 
inorganic product that is not readily biodegradable. Moreover, that 
European patent does not offer any guidance for selecting binders other 
than polyaluminum chloride that would be useful in binding absorbent 
particles. 
A method of immobilizing superabsorbents is disclosed in U.S. Pat. No. 
4,410,571 in which a water swellable absorbent polymer is converted to a 
non-particulate immobilized confluent layer. Polymer particles are 
converted to a coated film by plasticizing them in a polyhydroxy organic 
compound such as glycerol, ethylene glycol, or propylene glycol. The 
superabsorbent assumes a non-particulate immobilized form that can be 
foamed onto a substrate. The individual particulate identity of the 
superabsorbent polymer is lost in this process. The confluent nature of 
the superabsorbent material can also result in gel blocking, in which 
absorption is diminished as the water swollen polymers block liquid 
passage through the film layer. 
U.S. Pat. No. 4,412,036 and U.S. Pat. No. 4,467,012 disclose absorbent 
laminates in which a hydrolyzed starch polyacrylonitrile graft copolymer 
and glycerol mixture is laminated between two tissue layers. The tissue 
layers are laminated to each other by applying external heat and pressure. 
The reaction conditions form covalent bonds between the tissue layers that 
firmly adhere the tissue layers to one another. 
Numerous other patents have described methods of applying binders to 
fibrous webs. Examples include U.S. Pat. No. 2,757,150; U.S. Pat. No. 
4,584,357; and U.S. Pat. No. 4,600,462. Such binders are not described as 
being useful in binding particulates, such as superabsorbent particles, to 
fibers. Yet other patents disclose crosslinking agents such as 
polycarboxylic acids that form covalent intrafiber bonds with 
individualized cellulose fibers, as in European Patent Application 440472 
A1; European Patent Application 427 317 A2; European Patent Application 
427 316 A2; and European Patent Application 429 112 A2. The covalent 
intrafiber bonds are formed at elevated temperatures and increase the bulk 
of cellulose fibers treated with the crosslinker. The covalent bonds 
between the fibers produce a pulp sheet that is more difficult to compress 
to conventional pulp sheet densities than in an untreated sheet. Any 
covalent crosslink bonds that form between the fibers and particles occupy 
functional groups that would otherwise be available for absorption, hence 
absorption efficiency is decreased. 
Many different types of particles other than superabsorbents may be added 
to fibers for different end uses. Antimicrobials, zeolites and fire 
retardants are but a few examples of particles that are added to fibers. 
It would be advantageous to provide a method of attaching particles that 
could be accommodated to the many different particle needs of end users. 
Moreover, it would be advantageous to reduce particulate waste in the 
attachment process, and simplify shipment of fiber products that require 
particulate addition. It would be further advantageous to bind 
particulates to fibers without requiring the shipment of bulk fibers with 
adhered particulates as shipping and excessive handling of these fibers 
subject them to mechanical impact which can dislodge some particles from 
the fibers. It would also be advantageous to incorporate binders onto 
fibers during the initial pulp sheet manufacturing process so that the 
fibers are ready for reactivation and use at a remote product 
manufacturing location. 
SUMMARY OF THE INVENTION 
The foregoing and other objects are achieved by providing fibers in a wet 
laid sheet manufacturing line, such as cellulose fibers with or without 
synthetic or other fibers being wet laid into a web or sheet. The fibers 
include those with hydrogen bonding functional sites, with or without 
other fibers, to which a binder is applied to the fibers on the wet laid 
sheet manufacturing line. The binder has a volatility less than water. The 
binder also has a functional group that forms a hydrogen bond with the 
fibers having the hydrogen bonding functional sites, and a functional 
group that is also capable of forming a hydrogen bond or a coordinate 
covalent bond with particles that have a hydrogen bonding or coordinate 
covalent bonding functionality. The binder is capable of attaching the 
particles to the fibers with the hydrogen bonding functional sites, and 
forms a bond that has been found to be resistant to mechanical disruption. 
These particles can be added to the fibers during manufacture of the 
fibrous sheet on the wet laid sheet manufacturing line. However, 
preferably the particles are not added until the fibers are processed by 
an end user during the manufacture of products. Consequently, dislodgement 
of particles from fibers during shipment of the bulk fibers is eliminated. 
In addition, customization by the end user is enhanced as the end user can 
add its desired particles to the fibers at the time the fibers are used. 
Possible degradation of particulates during shipment and the delay prior 
to incorporation into products are also minimized. A significant advantage 
of these binders is that the binders can be present on fibers in an 
inactive state at the wet laid sheet manufacturing line, then later 
activated or reactivated at a remote location (e.g. at a user's plant) to 
bind particles to the fibers. 
In this application, the term "wet laid sheet manufacturing line" means a 
manufacturing line wherein a sheet or mat of fibers is formed from a 
slurry of fibers. Typically, the slurry is deposited on a wire from a 
source, such as a headbox, and the fiber sheet is dried on the line. Thus, 
the term "wet laid sheet manufacturing line" refers to a line in which a 
sheet or mat is formed by a wet laying process. A specific example of a 
wet laid sheet manufacturing line is a pulp sheet manufacturing line of 
type wherein wood pulp or other cellulosic fluff fibers, with or without 
other fibers, is made into paper or fibrous webs. The term "pulp" refers 
in this case to fibers which include a hydrogen bonding capability, 
whether or not blended with fibers without a hydrogen bonding capability. 
For convenience, and not to be construed as a limitation, the description 
proceeds with reference at times to a pulp sheet manufacturing line as a 
specific example of a wet laid sheet manufacturing line. 
Liquid binders (which includes aqueous solutions of solid binders or neat 
liquids) can be placed on the fibers, air dried, and later reactivated by 
moistening the fibers. In the case of aqueous based binders, these binders 
can be added prior to or at the drying stage of a pulp sheet manufacturing 
line so that the drying equipment already present on such a line can dry 
these binders and fibers to the desired maximum moisture content (e.g. 
about 10% w/w water, most preferably a maximum moisture content of from 
about 6% to 8% w/w) to eliminate molding or other degradation of the 
fibers. Non-aqueous binders, such as glycerin may also be added to the 
fibers on the pulp sheet manufacturing line at any suitable location. 
However, these non-aqueous binders are most preferably added after drying 
of the pulp sheet has commenced or is complete. Consequently, water in the 
pulp sheet does not tend to interfere with the incorporation of the 
binders on the fibers. Alternatively, a dry solid binder may be added to 
the fibers on the pulp sheet manufacturing line and later activated by 
heat, the addition of a liquid, by the moisture present in the sheet on 
the line prior to drying, or otherwise. For example, certain inactive 
binders can also be activated by applying kinetic energy to the fibers 
after the binder and fibers reach an equilibrium moisture content with the 
atmosphere (hereinafter referred to as "air drying"). Kinetic energy can 
be applied to the fibers, for example, by mechanically agitating the 
binder and fibers. In yet other embodiments, the binder may be activated 
or reactivated by heating the fibers after applying the binder to the 
fibers. 
The capacity for activation or reactivation allows the binder to be applied 
to the fibers on the pulp sheet manufacturing line, with the fibers being 
then shipped to distribution points with the binder in an inactive form. 
The binder is then activated at the remote distribution point or user's 
plant where particles are added to the fibers and bound thereto. As used 
herein, binder "activation" includes both activation of previously 
inactive binders (such as solid binders in the absence of liquid) or 
reactivation of previously active binders (such as a liquid binder that 
has been air dried). 
Another advantage of the present invention is that the binder can be 
activated or reactivated in a pattern that corresponds to a desired 
distribution of particles in fibrous material. A reactivation liquid, for 
example, can be applied to target areas of a diaper that will be initially 
moistened by urine during use. Superabsorbent particles can be added to 
the activated area of the diaper and adhered almost exclusively in those 
areas where initial urine absorption is required. Targeted activation of 
binder allows particles to be efficiently and economically attached to the 
fibers, with reduced particle wastage. Moreover, targeted binder 
activation and particle adherence increases the absorptive efficiency of 
the product by diminishing excessive wicking of liquid within the plane of 
an absorptive product. 
Fibers in accordance with the present invention may have particles bound to 
the fibers with a polymeric or non-polymeric binder. The polymeric binder 
may be selected from the group consisting of polypropylene glycol (PPG), 
polyethylene glycol (PEG), polyacrylic acid (PAA), poly(caprolactone) 
diol, a polyamide, a polyamine, and copolymers thereof (for example, a 
polypropylene glycol/polyethylene glycol copolymer), wherein the polymeric 
binder has a hydrogen bonding functionality or coordinate covalent bond 
forming functionality on each repeating unit of the polymeric binder. The 
non-polymeric binder has a volatility less than water, a functional group 
that forms hydrogen bonds or coordinate covalent bonds with the particles, 
and a functional group that forms hydrogen bonds with the fibers. The 
non-polymeric binder is an organic binder, and preferably includes a 
functionality selected from the group consisting of a carboxylic acid, an 
alcohol, an aldehyde, an amino acid, an amide, and an amine, wherein there 
are at least two functionalities on the molecule selected from this group, 
and the two functionalities are the same or different. Examples of such 
binders include polyols, polyamines (a non-polymeric organic binder with 
more than one amine group), polyamides (a non-polymeric organic binder 
with more than one amide group), polyaldehydes (a non-polymeric organic 
binder with more than one aldehyde functionality), polycarboxylic acids (a 
non-polymeric organic binder with more than one carboxylic acid 
functionality), amino alcohols, hydroxy acids and other binders. These 
binders have functional groups that are capable of forming the specified 
bonds with the particles and fibers. 
More preferably, the organic non-polymeric binder is selected from the 
group consisting of glycerin, ascorbic acid, urea, glycine, 
pentaerythritol, a monosaccharide or a disaccharide, citric acid, tartaric 
acid, dipropylene glycol, glyoxal, and urea derivatives such as DMDHEU. 
Suitable saccharides include glucose, sucrose, lactose, ribose, fructose, 
mannose, arabinose, and erythrose. Each of these preferred binders is a 
non-polymeric molecule that has a plurality of hydrogen bonding 
functionalities that permit the binder to form hydrogen bonds to both the 
fibers and particles. Particularly preferred binders include those that 
can form five or six membered rings, most preferably six membered rings, 
with a functional group on the surface of the particle. 
The fibrous material to which particles are to be bound may be cellulosic 
or synthetic fibers that are capable of forming hydrogen bonds with the 
binder, while the particles are selected to be of the type that form 
hydrogen bonds or coordinate covalent bonds with the binder. It has 
unexpectedly been found that this binder system secures particles to 
fibers exceptionally well. A superior fibrous product is therefore 
produced that has improved absorbent properties as compared to unbound or 
covalently bound particles. Formation of the noncovalent bond allows 
production of a fiber product that is easily manufactured and a web that 
is easily densified, and that is readily biodegradable and disposable. 
In one preferred embodiment, an absorbent product comprises a fibrous 
cellulosic mat that contains superabsorbent hydrogel particles in 
particulate form. The superabsorbent particles form hydrogen bonds or 
coordinate covalent bonds with the binder, depending upon the binder, 
while the binder in turn forms hydrogen bonds with the hydroxyl groups of 
the cellulose fibers. These noncovalent, relatively flexible bonds between 
the binder and particles maintain the particles in contact with the 
fibers, and resist dislodgement of the particles by mechanical forces 
applied to the mat during manufacture, storage or use. The binder may 
suitably be present in an amount of from about 3 to 80 percent of the 
total weight of the product, while the particles bound to the binder and 
hence to the fibers in accordance with the present invention (via 
hydrogen/coordinate covalent bonds) may suitably be present in an amount 
of 0.05 to 80 percent, preferably 1 to 80 percent or 5 to 80 percent by 
weight. An especially suitable range of binder is 3 to 40 percent by 
weight, or 3 to 25 percent by weight, while a particularly suitable range 
of such particles is 5 to 40 percent by weight. A preferred weight ratio 
of particle to binder is 2:1 to 4:1. An example of a suitable particle is 
a superabsorbent polymer such as a starch graft polyacrylate hydrogel fine 
or larger size particle such as a granule, which forms hydrogen bonds with 
the binder. The binder also forms hydrogen bonds with the hydroxyl groups 
of the cellulose or other fibers with hydrogen bonding functional sites, 
thereby securely attaching the superabsorbent particles to the fibers. 
In binding the particles to fibers, the particles are preferably insoluble 
in the binder and therefore retain their solid particulate form following 
binding. The particles have functional groups that can form hydrogen bonds 
or coordinate covalent bonds with the binder, and the binder in turn is 
capable of forming hydrogen bonds to the fibers. 
In especially preferred embodiments, the fibers are cellulosic and the 
particles are superabsorbent particles that are bound to the binder by 
hydrogen bonds. The fibers may also be continuous or discontinuous 
synthetic or natural fibers having a hydrogen bonding functional group 
that hydrogen bonds with the binder. Rayon is another specific example of 
these types of fibers. The binder is suitably applied to the fibers in an 
amount of at least 3 percent, and preferably no more than 80 percent, by 
total weight of the particle, fiber and binder. The particles may be bound 
to the fibers at less than 150.degree. C. or without any external 
application of heat at ambient temperature (e.g., about 25.degree. C.). 
Particles may also be bound in the absence of any external application of 
pressure, or in the absence of external heat and pressure. 
In some embodiments the binder is associated with the fibers as a solid 
(for example, a dry powder or a dried liquid), and the fibers with the 
hydrogen bonding functionality contain at least 7 percent water by weight 
when the binding step is performed. This level of moisture in the fibers 
provides sufficient mobility of reactants to allow the particles and 
fibers to bind well to each other. When a liquid binder is used (for 
example, glycerin or a solution of glycine powder), the fibers suitably 
contain at least about 0.5 percent water by weight. A solid binder is 
suitably used with such fibers having 0.5 percent water by weight if the 
binder is heated above its melting point to liquefy it. A solid binder may 
be thermoplastic or meltable, such that it can be heated above its melting 
point and then cooled to fuse fibers to each other. The thermoplastic 
properties of the binder can also provide additional mechanical adherence 
between the particles and fibers. In some embodiments, a thermoplastic 
binder such as urea may be employed which can adhere particles both 
thermoplastically and with hydrogen bonding. 
It is therefore an object of the present invention to apply binder 
materials to fibers on a wet laid sheet manufacturing line, the binder 
materials being capable of binding particles to the fibers. 
Another object of the present invention is to provide fibers with binders 
which may be reactivated at a site remote from the wet laid sheet 
manufacturing line for the purpose of adhering particulate materials to 
the fibers. 
It is another object of this invention to provide improved fibers from a 
wet laid sheet manufacturing line which facilitates the binding of 
particles to fibers in a customized manner to easily allow different end 
users of the products to select and bind different types or brands of 
particles to the fibers. 
It is also an object of this invention to provide a fiber product from a 
wet laid sheet manufacturing line with enhanced particulate binding 
capabilities. 
Another object of the invention is to provide improved fiber from a wet 
laid sheet manufacturing line usable in providing absorbent products in 
which particulates are firmly bound to fibers such that the particles are 
less likely dislodged by mechanical forces. 
The invention also includes the products produced by any of the methods 
described herein. 
This invention relates to the foregoing features and objects individually 
as well as in combination. The foregoing and other features and advantages 
of the invention will become more apparent from the following detailed 
description and accompanying drawings.

DETAILED DESCRIPTION OF SEVERAL PREFERRED EMBODIMENTS OF THE INVENTION 
Processing of Fibers 
FIG. 1 illustrates a wet laid sheet manufacturing line such as a pulp sheet 
manufacturing line 10. In this manufacturing line, a pulp slurry 12 is 
delivered from a headbox 14 through a slice 16 and onto a Fourdrinier wire 
18. The pulp slurry 12 typically includes cellulose fibers such as wood 
pulp fibers and may also include synthetic or other non-cellulose fibers 
as part of the slurry. Water is drawn from the pulp deposited on wire 18 
by conventional vacuum system, not shown, leaving a deposited pulp sheet 
20 which is carried through a dewatering station 22, illustrated in this 
case as two sets of calendar rolls 24, 26 each defining a respective nip 
through which the pulp sheet or mat 20 passes. From the dewatering 
station, the pulp sheet 20 enters a drying section 30 of the pulp 
manufacturing line. In a conventional pulp sheet manufacturing line, 
drying section 30 may include multiple canister dryers with the pulp mat 
20 following a serpentine path around the respective canister dryers and 
emerging as a dried sheet or mat 32 from the outlet of the drying section 
30. Other alternate drying mechanisms, alone or in addition to canister 
dryers, may be included in the drying stage 30. The dried pulp sheet 32 
has a maximum moisture content pursuant to the manufacturer's 
specifications. Typically, the maximum moisture content is no more than 
10% by weight of the fibers and most preferably no more than about 6% to 
8% by weight. Otherwise, the fibers tend to be too damp. Unless overly 
damp fibers are immediately used, these fibers are subject to degradation 
by, for example, mold or the like. The dried sheet 32 is taken up on a 
roll 40 for transportation to a remote location, that is, one separate 
from the pulp sheet manufacturing line, such as at a user's plant for use 
in manufacturing products. Alternatively, the dried sheet 32 is collected 
in a baling apparatus 42 from which bales of the pulp 44 are obtained for 
transport to a remote location. 
A binder of the type explained in detail below is applied to the pulp sheet 
from one or more binder applying devices, one of which is indicated at 50 
in FIG. 1. Any binder applying device may be used, such as sprayers, roll 
coaters, immersion applicators or the like. Sprayers are typically easier 
to utilize and incorporate into a pulp sheet manufacturing line. As 
indicated by the arrows 52, 54 and 56, the binder may be applied at 
various locations on the pulp sheet manufacturing line, such as ahead of 
the drying stage 30 (indicated by line 52), intermediate the drying stage 
30 (as indicated by line 54), or downstream from the drying stage 30 (as 
indicated by the line 56). Water based binders, such as non-polymeric 
urea, are typically applied at a location where sufficient drying can 
still take place in the drying stage to produce a dried binder containing 
fiber sheet with no more than the maximum desired moisture content. 
Consequently, to take advantage of the drying stage 30, water based 
binders are typically applied at locations 52 or 54. At location 52, the 
water remaining in the sheet or mat 20 at this stage tends to interfere 
with the penetration of the binder into the sheet. Consequently, 
application of the binder after some drying has taken place, for example 
at location 54, is preferable. If water based binders are applied at 
location 56 in an amount which would cause the moisture content of the 
sheet to exceed the desired maximum level, an additional drying stage (not 
shown) may be included in the pulp manufacturing line to bring the 
moisture content down to the desired level. 
A non-aqueous based binder, such as glycerin, is most preferably added 
downstream from the drying stage at location 56 or during the drying stage 
as indicated by location 54. However, liquid non-aqueous binders may also 
be added at location 52 upstream of the drying stage. At this latter 
location, the water in the wet web at this point may tend to attract these 
binders into the mat or sheet as the binders tend to be hydroscopic. Since 
non-aqueous binders typically do not enhance the degradation of the 
product due to the addition of moisture to the sheet, they can be applied 
downstream from the drying stage without bringing the moisture content of 
the sheet above the desired maximum level. 
The particulate materials, selected as explained below, may be added to the 
sheet and adhered thereto by the binders on the pulp manufacturing line, 
such as indicated by the particulate applicator 60, which may comprise a 
bulk or volumetric metering device. These particles may be sprinkled, 
poured or otherwise added to the sheet. To facilitate the adherence of 
these particulates to the sheet at this location, enough moisture must 
remain in the sheet, in the case of aqueous binders, to enable the bonding 
between the particles and fibers as explained below. For non-aqueous 
binders, the particles in this case are preferably added while the binder 
is still wet or heated to facilitate the reaction. Although particles can 
be added on the pulp sheet manufacturing line in this manner, with a 
subsequent drying stage being utilized to reduce the moisture content 
following particulate addition. However, if a water based binder makes the 
fibers too wet following the addition of the particles, this is not the 
preferred approach. Also, during transportation of rolls or bales of these 
fibers, particles can become dislodged by mechanical impact during 
transport. In addition, this approach interferes with the customization of 
the fiber application at a user's location. For example, a user may want 
the capability of selecting particular types or brands of particles for 
adherence to the fibers in the user's products, without having this 
selection having been made by a pulp sheet manufacturer who incorporates 
the particles into the pulp sheet during its manufacture. Also, certain 
particles may degrade over time, making it advantageous to add such 
particles immediately prior to incorporation into products. For example, 
superabsorbent particles are susceptible to absorbing moisture from the 
atmosphere during shipment. Particles with a relatively short shelf life, 
such as certain zeolites (e.g. Abscents with odor absorbing materials 
which can become saturated with odors over time) being one example, may 
also degrade over time. Another example is zeolites with silver salts as 
antimicrobial agents which can photodegrade. Therefore, it is advantageous 
to provide a product in which the end user of the product may incorporate 
the desired particles at the time the fibers are converted into products. 
Therefore, in keeping with this preferred approach, as illustrated in FIG. 
2, the respective rolls 40 or bales 44 of binder containing fibers, 
without particles, are transported to a remote location for use by a user. 
These rolls or bales (or otherwise transported fibers, e.g. bagged, 
containerized or otherwise in bulk form) are then refiberized by a 
fiberizing apparatus 70. Although any fiberizer may be used, a typical 
fiberizing apparatus 70 is a hammermill which may be used alone or in 
conjunction with other devices such as picker rolls or the like for 
breaking up the sheet 32 or bales 42 into individual fibers. 
A particulate material adding mechanism 72 (like mechanism 30) delivers the 
desired particulate materials to the fibers at the desired location in the 
user's process. Again, the device 72 typically comprises a metering 
mechanism, although any suitable device for adding particulates to fibrous 
materials may be used. For example, the particulates may be delivered as 
indicated by line 74 to the fiberizing apparatus 70. In the case of some 
binders, agitation of fibers within the fiberizer 70, as explained in 
greater detail below, reactivates the binders and causes the particulates 
to be adhered to the fibers by the binder. Alternatively, a reactivating 
liquid, such as water, may be sprayed or otherwise applied to the fibers, 
such as from a reactivation liquid tank or source 78 by way of a sprayer 
(not shown) at location 80. The particles may then be applied, as 
indicated by line 84 to the fibers downstream from the application of the 
reactivation liquid 80. Alternatively, the particles added prior to 
location 80 are adhered to the fibers by the binder upon reactivation of 
the binder at location 80. As yet another alternative, the fiberized 
fibers are delivered to an air laying device 90 and reformed into a 
desired product such as a web indicated at 92. In the case of air laid 
fibers, the reactivation liquid may be applied to the web at location 96 
with the particles then being added at location 98 as shown with the 
reactivated binder then adhering the particles to the fibers. The 
particles may be applied at a location in the process upstream from the 
application of the reactivating liquid at location 96. In addition, the 
binder may be reactivated at specifically defined locations on the web 92, 
such as in target zones of an absorbent core of a product with the 
particles then only being applied to these target zones, thereby 
minimizing the wasting of the particulate material. The web 92, with or 
without other components of the end user's product, is then processed into 
the user's product, such as being included within a disposable diaper 100. 
Again, with this approach, the end user of the fibers may readily select 
particles to be applied to its product and may activate the binder as 
required to enhance the efficient production of the user's product. In 
addition, the user has flexibility in air laying or otherwise combining 
the binder containing fibers into a finished product with the desired 
particulates. The binder containing fibers, because the binders are all 
water soluble, are preferably not wet laid because wet laying would remove 
at least some of the binder. Not only is handling and shipping of the 
particulate containing products avoided by the manufacturer of the pulp 
sheet, enhanced adhesion of particulates to the fibers results because the 
particles are not subjected to mechanical forces between the location of 
manufacture of the fibers and the location at which the particulate 
materials are added. 
Fiber Characteristics 
In particularly preferred embodiments, the fibers being processed are 
cellulosic or synthetic fibers to which superabsorbent hydrogel polymer 
particles and/or other particles are adhered by a binder, with products 
then being made therefrom. Suitable fibers include wood pulp fibers, which 
can be obtained from well known chemical processes such as the kraft and 
sulfite processes. In these processes, the best starting material is 
prepared from long fiber coniferous wood species, such as pine, douglas 
fir, spruce and hemlock. Wood pulp fibers can also be obtained from 
mechanical processes, such as ground wood, mechanical, thermomechanical, 
chemimechanical, and chemithermomechanical pulp processes. The fibers are 
preferably elongated, for example having a length to width ratio of about 
10:1 to 5:1. 
The fibers used in the present invention also include fibers that are 
pretreated prior to the application of a binder to the fibers as explained 
below. This pretreatment may include physical treatment, such as 
subjecting the fibers to steam or chemical treatment, such as 
cross-linking the fibers. 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, non-polymeric urea, urea/phosphates, etc. In 
addition, the fibers may be pretreated with surfactants or other liquids, 
such as water or solvents, which modify the surface of the fibers. Other 
pretreatments include exposure to antimicrobials or pigments. 
The fibers may also be pretreated in a way which increases their 
wettability. For example, natural fibers may be pretreated with a liquid 
sodium silicate, as by spraying the fibers with this material, for 
pretreatment purposes. Wettability of the surface of fibers is also 
improved by subjecting the fibers to a corona discharge pretreatment in 
which electrical current is discharged through the fibers in a 
conventional manner. In the case of both synthetic fibers and wood pulp 
fibers, corona discharge pretreatment results in an oxygen functionality 
on the surface of the fibers, making them more wettable and more bondable. 
The fibers may also be pretreated with conventional cross-linking 
materials and may be twisted or crimped, as desired. Pretreating cellulose 
fibers with chemicals which result in lignin or cellulose rich fiber 
surfaces may also be performed in a conventional manner. 
Bleaching processes, such as chlorine or ozone/oxygen bleaching may be used 
in pretreating the fibers. In addition, the fibers may be pretreated, as 
by slurrying the fibers in baths containing antimicrobial solutions (such 
as solutions of antimicrobial particles as set forth below), fertilizers 
and pesticides, and/or fragrances and flavors for release over time during 
the life of the fibers. Fibers pretreated with other chemicals, such as 
thermoplastic and thermoset resins may also be used. Combinations of 
pretreatments may also be employed with the resulting pretreated fibers 
then being subjected to the application of the binder coating as explained 
below. 
Ground wood fibers, recycled or secondary wood pulp fibers, and bleached 
and unbleached wood pulp fibers can be used. Details of the production of 
wood pulp fibers are well known to those skilled in the art. These fibers 
are commercially available from a number of companies, including 
Weyerhaeuser Company, the assignee of the present invention. 
The fibers can also be any of a variety of other natural or synthetic 
fibers, however, all of the fibers to which particles are to be attached 
in accordance with the present invention include a hydrogen bonding 
functionality. This does not preclude the blending of such fibers with 
fibers lacking this characteristic. However, the fibers lacking a hydrogen 
bonding functionality will not have particles bonded thereto with the 
strength of the bonds that would be present if the fibers had a hydrogen 
bonding functionality. 
A hydrogen bond is an intermolecular force that occurs between hydrogen 
atoms that are covalently bonded to small, strongly electronegative 
elements (such as nitrogen and oxygen) and nonbonding electron pairs on 
other such electronegative elements. A hydrogen bonding functionality is a 
functional group that contains an oxygen or nitrogen atom, for example 
hydroxyls, carboxyls, ethers, esters, epoxides, carbonyls, amines, 
urethanes and others, that is capable of forming a hydrogen bond. The 
orbitals of the nonbonding electron pairs on the oxygen or nitrogen 
overlap with the relatively empty 1s orbital of the hydrogen covalently 
bonded to another nitrogen or oxygen atom. The 1s orbital of the hydrogen 
is relatively empty due to the unequal sharing of the electrons in the 
covalent bond between it and the small electronegative atom (oxygen or 
nitrogen) to which it is bound. 
Specific examples of natural fibers that contain a hydrogen bonding 
functionality include chopped silk fibers, wood pulp fibers, bagasse, 
hemp, jute, rice, wheat, bamboo, corn, sisal, cotton, flax, kenaf, peat 
moss, and mixtures thereof. Suitable synthetic fibers with hydrogen 
bonding functionalities include acrylic, polyester, carboxylated 
polyolefins, rayon and nylon. The hydrogen bonding functionality is an 
ester in acrylic fibers and a carboxylic acid in carboxylated polyolefin 
fibers, an ester in polyester, an amide in nylon, and a hydroxyl in rayon. 
Polyethylene and polypropylene would be unsuitable fibers for use in 
particle to fiber bonding in accordance with the present invention because 
they include only carbons and hydrogens without any oxygens or nitrogens 
that can participate in hydrogen bonds. 
Blends of fibers comprised of fibers with hydrogen bonding functionality 
and those without may be used with the binder bonding being strongest to 
the fibers with the prescribed functionality. Typically, the non-hydrogen 
bonding functional fibers are present in an amount of from 0-80% by weight 
of the fiber blend and most preferably in an amount of from 5% to 30% by 
weight. Blends of multiple types of fibers may also be used. 
For purposes of convenience, and not to be construed as a limitation, the 
following description proceeds with reference to the treatment of chemical 
wood pulp fibers. The fibers are formed into a sheet or equivalently a mat 
on a pulp sheet manufacturing line and are subjected to the application of 
a binder during the manufacture of the pulp sheet. Mats of NB 416 wood 
pulp fibers from Weyerhaeuser Company with the applied binders are a 
specific example. 
Particle Characteristics 
In accordance with the present invention, particles are added to the sheet 
or fibers before, during or following fiberization of the sheet to give 
these fibers desired properties, such as increased absorbency, 
abrasiveness, or antimicrobial activity. The particle can be any 
particulate material that has the desired property and which is capable of 
forming hydrogen bonds or coordinate covalent bonds with the binder. 
Hydrogen bonds can be formed, as discussed above, by particles that 
contain functional groups having an oxygen or nitrogen. Coordinate 
covalent bonds, in contrast, are formed by donation of a lone pair of 
electrons on one atom to an empty orbital of another atom. Coordinate 
covalent bonds differ from covalent bonds in that covalent bonds are 
formed by a pair of electrons wherein one of the electrons is donated from 
each of the atoms that participate in the bond. Particles can form 
coordinate covalent bonds if they have an empty p or d or f orbital that 
is capable of accepting a pair of electrons from the binder. 
A coordinate covalent bond occurs between a donor compound that has a lone 
pair of electrons to donate to the bond, and an acceptor that has an empty 
orbital to accept the lone pair of electrons from the donor. According to 
the Aufbau and Pauli principles, electrons occupy the lobes of atomic 
orbitals one at a time with a maximum of two electrons (with opposite 
spins) per lobe. The most basic orbital is the s orbital, which is 
available for bonding the elements in the first row of the periodic table. 
In the second row of the periodic table, electrons fill first the 2s 
orbital of Li and Be, but metals in Groups IA and IIA do not have 
sufficient affinity for electrons to participate in coordinate covalent 
bonding. Beginning with column IIIA (boron), the three p orbitals 
participate in coordinate covalent bonding and the lobes of the p orbitals 
begin to fill. Boron has one electron in one of the 2p orbitals thus 
leaving the other two p orbitals empty and available for coordinate 
covalent bonding. An example of a coordinate covalently bonded boron 
containing particle is boric acid, which is used as an astringent, 
antiseptic and fire retardant. Boric acid is shown below wherein the boron 
is coordinate covalently bonded to a polypropylene glycol (PPG) binder. 
##STR1## 
The next element, carbon, usually hybridizes to have one electron in the 
2s orbital and the three remaining electrons are singly placed in the 
three p orbitals. This leaves no lobes empty for coordinate covalent 
bonding and electron additions proceeding further across that row of the 
periodic table also leave no lobes empty. Hence, boron is the only element 
in the second row of the periodic table that is capable of forming 
coordinate covalent bonds. 
Next the third row begins to fill, and the two 3s electrons fill first in 
sodium and magnesium, but these metals in groups IA and IIA do not form 
coordinate covalent bonds as discussed above. Then aluminum, like boron, 
places one electron in one of the 3p lobes, and the two other 3p lobes are 
empty and available for coordinate covalent bonding. The same trends 
continue across the third row, but the third row elements also have 
available five 3d lobes so the potential for coordination bonding exists 
even though 3p orbitals are occupied in the third row. Hence, Al, P, S, 
and Cl are capable of accepting a pair of electrons from an electron pair 
donor to form a coordinate covalent bond. An example of this is found in 
the bonding in PCl.sub.5, aluminum trihydrate, or phosphorous 
pentasulfide. A phosphorous pentasulfide particle can be used to increase 
flammability of a product, while aluminum trihydrate is a fire retardant. 
An example of a coordinate covalently bonded aluminum compound is 
##STR2## 
wherein aluminum trihydrate is coordinate covalently bonded to a 
polypropylene glycol (PPG) polymer. 
In the next row, the 4s orbital is filled first, then the 3d lobes begin to 
fill--one electron per lobe until all have a single then a second electron 
to each lobe until all lobes are filled. However, 4p and 4f orbitals are 
also available, hence many of the transition elements are capable of 
forming coordinate covalent bonds. 
The elements that have empty orbitals that participate in coordinate 
covalent bonding include all those except the metals (which excludes 
hydrogen) in groups IA and IIA, and C, N, O, F, Ne and He. Especially 
preferred particles contain boron, aluminum, iron, rhodium, osmium, 
platinum, and palladium, particularly boron. Examples of particles in 
accordance with the present invention that are capable of coordinate 
covalent bonding are aluminum trihydrate, antimony oxide, arsenic 
disulfide, bismuth aluminate, bismuth iodide oxide, bismuth phosphate, 
bismuth subcarbonate, bismuth subgallate, cadmium salycilate, chromic 
carbonate, chromic hydroxide, chromic oxide, and chromic phosphate. All of 
the polymeric binders used in manufacturing the pulp sheet on line in 
accordance with the present invention (PPG, PAA, polyamide, polyamine and 
poly(caprolactone) diol) are are capable of donating a lone pair of 
electrons from an oxygen or nitrogen to form a coordinate covalent bond 
with a suitable particle that has an empty orbital for coordinate covalent 
bonding. 
Superabsorbent Particles 
In one disclosed embodiment the added particles are superabsorbent 
particles, which comprise polymers that swell on exposure to water and 
form a hydrated gel (hydrogel) by absorbing large amounts of water. 
Superabsorbents are defined herein as materials that exhibit the ability 
to absorb large quantities of liquid, i.e. in excess of 10 to 15 parts of 
liquid per part thereof. These superabsorbent materials generally fall 
into three classes, namely starch graft copolymers, crosslinked 
carboxymethylcellulose derivatives and modified hydrophilic polyacrylates. 
Examples of such absorbent polymers are hydrolyzed starch-acrylonitrile 
graft copolymer, a neutralized starch-acrylic acid graft copolymer, a 
saponified acrylic acid ester-vinyl acetate copolymer, a hydrolyzed 
acrylonitrile copolymer or acrylamide copolymer, a modified cross-linked 
polyvinyl alcohol, a neutralized self-crosslinking polyacrylic acid, a 
crosslinked polyacrylate salt, carboxylated cellulose, and a neutralized 
crosslinked isobutylene-maleic anhydride copolymer. Natural materials, 
such as peat, also are capable of behaving as superabsorbent particles. 
Superabsorbent particles are available commercially, for example starch 
graft polyacrylate hydrogel fines (IM 1000F) from Hoechst-Celanese of 
Portsmouth, Va., or larger particles such as granules. Other 
superabsorbent particles are marketed under the trademarks SANWET 
(supplied by Sanyo Kasei Kogyo Kabushiki Kaisha), SUMIKA GEL (supplied by 
Sumitomo Kagaku Kabushiki Kaisha and which is emulsion polymerized and 
spherical as opposed to solution polymerized ground particles), FAVOR 
(supplied by Stockhausen of Greensboro, N.C.), and NORSOCRYL (supplied by 
Atochem). The superabsorbent particles come in a variety of sizes and 
morphologies, for example IM 1000 and IM 1000F. The 1000F is finer and 
will pass through a 200 mesh screen whereas IM 1000 has particles that 
will not pass through a 60 mesh screen. Another type of superabsorbent 
particle is IM 5600 (agglomerated fines). Superabsorbent particulate 
hydrophilic polymers are also described in detail in U.S. Pat. No. 
4,102,340, which is incorporated herein by reference. That incorporated 
patent discloses hydrocolloid absorbent materials such as cross-linked 
polyacrylamides. 
Other Particles 
Many particles that form hydrogen bonds or coordinate covalent bonds are 
suitable for use with the present invention. Some such particles are 
listed in Table 1 with an indication of the function of the listed 
particles. 
TABLE I 
______________________________________ 
Particulates For Binding 
Name Function 
______________________________________ 
Aluminum Trihydrate 
Fire retardant, astringent 
Acediasulfone Antibacterial 
Agaricic acid Antiperspirant 
Alclometastone Topical anti-inflammatory 
Calcium alginate 
Topical hemostatic 
Amidomycin Fungicide 
Antimony oxide Fire retardant 
Apigenin Yellow dye, mordant 
Arsenic disulfide 
Red Pigment 
Aspirin Anti-inflammatory; antipyretic 
Azanidazole Antiprotozoal (Trichomonas) 
Azelaic acid Antiacne 
Baicalein Astringent 
Bendazac Anti-inflammatory 
Benomyl Fungicide; ascaricide 
Benzestrol Estrogen 
Benzylpenicillinic acid 
Antibacterial 
Benzylsulfamide Antibacterial 
Bergaptene Antipsoriatic 
Betasine Iodine source 
Bezitramide Narcotic analgesic 
Bibrocathol Topical antiseptic 
Bietanautine Antihistaminic 
Bifenox Herbicide 
Bifonazole Antifungal 
Binapacryl Fungicide, miticide 
Bis(p-chlorophenoxy) 
Miticide 
methane 
Bismuth aluminate 
Antacid 
Bismuth iodide oxide 
Anti-infective 
Bismuth phosphate 
Antacid; protectant 
Bismuth subcarbonate 
Topical protectant 
Bismuth subgallate 
Astringent, antacid; protectant 
Bisphenol A Fungicide 
Bitertanol Agricultural fungicide 
Bithionol Topical anti-infective 
Bromacil Herbicide 
Bromadiolone Rodenticide 
Bromcresol green 
Indicator 
Bromcresol purple 
Indicator 
Bromethalin Rodenticide 
p-Bromoacetanilide 
Analgesic; antipyretic 
3-Bromo-d-camphor 
Topical counterirritant 
Bromophos Insecticide 
Bromopropylate Acaricide 
5-Bromosalicyl- antibaterial (tuberculostatic) 
hydroxamic acid 
5-Bromosalycilic acid 
Analgesic 
acetate 
Bromosaligenin Anti-inflammatory 
Bromthymol blue Indicator 
Broxyquinoline Antiseptic; disinfectant 
Bucetin Analgesic 
Bumadizon Analgesic; anti-inflammatory; 
antipyretic 
Bupirimate Fungicide 
Busulfan Carcinogen, insect sterilant, 
antineoplastic 
Butamben Topical anesthetic 
Butrylin Insecticide 
Butylated hydroxy- 
Antioxidant (BHA) 
anisole 
Butyl paraben Pharmaceutic aid; food 
preservative 
4-tert-Butylphenyl 
Light absorber 
salicylate 
Cacotheline Indicator 
Cactinomycin Antineoplastic 
Cadmium salycilate 
Antiseptic 
Calamine Skin protectant 
Calcium carbonate 
Antacid 
Calcium saccharate 
Pharmaceutic aid 
Calcium tartrate 
Preservative; deodorant; antacid 
Cambendazole Anthelminthic 
Candicidin Topical antifungal 
Candidin Topical antifungal 
Capsaicin Topical analgesic 
Captan Fungicide; bacteriostat 
Carbadox Antimicrobial 
Carbamazepine Anticonvulsant; analgesic 
Carbarsone Antiamebic 
Carbaryl Contact insecticide 
Carbazochrome Antihemorrhagic 
salycilate 
Carbendazim Fungicide 
Carbochloral Hypnotic 
Carbophenothion Miticide; insecticide 
Carboquone Antineoplastic 
Carisoprodol Skeletal muscle relaxant 
Carthamin Dye 
Carvacrol Disinfectant 
Cephalin Local hemostatic 
Chalcomycin Antibiotic 
Chartreusin Antibiotic 
Chitin Vulnerary 
Chloramben Herbicide 
Chloramphenacol Antimicrobial 
palmitate 
Chloranil Fungicide 
Chlorbetamide Antiamebic 
Chlordimeform Insecticide 
Chlorfenac Herbicide 
Chlorfenethol Acaricide 
Chlorhexidine Topical antibacterial 
Chloroazodin Antibacterial; topical 
anesthetic 
Chlorophacinone Anticoagulant rodenticide 
p-Chlorophenol Antiseptic 
Chlorothricin Antibiotic 
Chlorotrianisene 
Estrogen 
Chloroxylenol Antiseptic; germicide 
Chlorphenesin Topical antifungal 
Chlorphenesin carbamate 
Relaxant (skeletal muscle) 
Chlorphenoxamide 
Antiamebic 
Chlorpropamide Antidiabetic 
Chlorpyrifos Insecticide 
Chlorquinaldol Topical antibacterial 
Chlorsulfuron Herbicide 
Chlorothion Insecticide 
Chlozoxazone Relaxant 
Cholesterol Pharmaceutic aid 
Chromic carbonate 
Pigment 
Chromic hydroxide 
Pigment 
Chromic oxide Abrasive 
Chromic phosphate 
Green pigment 
Chrysamminic acid 
Explosive 
Chrysarobin Antipsoriatic 
Cilastazol Antithrombotic 
Cinoxate Sunscreen agent 
______________________________________ 
Other suitable particles include proteins, vitamins zeolites and silica, 
which contain oxygen or nitrogen groups, or both. An example of a suitable 
zeolite is Abscents odor absorber available from UOP of Tarrytown, N.Y. An 
example of a suitable antimicrobial particle is chlorhexidine 
(N,N"-Bis(4-chlorophenyl)-3,12-diimino-2,4,11,13-tetraazatetradecanediimid 
amide). The list in Table I is by no means exhaustive as it can be readily 
determined for each type of particle whether it is capable of forming a 
hydrogen bond or a coordinate covalent bond. Many of the particles are 
non-absorbent, or not superabsorbent polymers. 
The particles listed in Table 1 have chemical properties that make them 
suitable for binding to fibers with the binders of the present invention. 
The listed particles are organic or inorganic compounds that have little 
or no water solubility, yet have the capacity to hydrogen bond. Water 
solubility is preferably low, for example, less than 10 g dissolves 
completely in 300 ml of water at 25.degree. C., more preferably less than 
about 1 g in 300 ml at 25.degree. C. This low solubility allows the 
particles to remain solid, and the hydrogen bonding capacity allows them 
to adhere to the fibers. Once bound, the particles substantially retain a 
discrete particulate form instead of dissolving or fusing. More of the 
particles are discrete than fused once bound. 
The amount of binder added to the fibers can vary widely, for example from 
0.05 to 80 percent of the total weight of the fibrous material, binders 
and particles. Antimicrobials such as chlorhexidine are effective in very 
low amounts, such as 0.05 percent. Superabsorbent particles are preferably 
added in an amount of 3-40 percent, especially 15-25 percent by weight. 
Polymeric Binder Characteristics 
The particles may be bound to the fibers by a water soluble polymeric 
binder selected from a predetermined group of polymeric binders that each 
have a hydrogen bonding functionality or coordinate covalent bond forming 
functionality on each repeating unit of the polymer. Again, these binders 
are applied on the wet laid sheet or pulp sheet manufacturing line. The 
pulp sheet manufacturing line refers to the manufacturing line at which 
the pulp sheet is formed and includes the locations within a plant at 
which processes (e.g. sheet formation, dewatering, drying, etc.) are 
performed prior to rolling, baling or otherwise gathering or packing the 
fiber for transport to an end use location. In accordance with the present 
invention, the predetermined groups of polymeric binders includes the set 
of binders consisting of polypropylene glycol (PPG); a PPG/PEG copolymer; 
polyacrylic acid; a polyamide such as polyglycine or another polypeptide; 
a polyamine such as polyethyleneimine or polyvinyl pyridine; or a polyol 
such as poly(caprolactone) diol. As used herein, a polymer is a 
macromolecule formed by chemical union of 5 or more identical combining 
units (monomers). A polyamine is a polymer that contains amine functional 
groups and a polyamide is a polymer that contains amide functional groups. 
Each of the binders has a hydrogen bonding or a coordinate covalent 
bonding functionality on each repeating unit (monomer) of the polymer. 
This repeating functionality may be a hydroxyl, carboxylic acid, amide, 
ether or amine. These binders are capable of forming hydrogen bonds 
because they have a functional group that contains an oxygen or a 
nitrogen. 
The polyglycol has repeating ether units with hydroxyl groups at the 
terminal ends of the molecule, and polyacrylic acid has a repeating 
carboxyl group in which a hydrogen is bound to an electronegative oxygen, 
creating a dipole that leaves the hydrogen partially positively charged. 
The polyamide (such as a polypeptide) or polyamine has a repeating NR 
group in which a hydrogen may be bound to an electronegative nitrogen that 
also leaves the hydrogen partially positively charged. The hydrogen in 
both cases can then interact with an oxygen or nitrogen on the particle or 
fiber to form a hydrogen bond that adheres the binder to the particle and 
fiber. The electronegative oxygen or nitrogen of the binder can also form 
a hydrogen bond with hydrogens on the particle or fiber that have positive 
dipoles induced by oxygens or nitrogens to which the hydrogen is attached. 
The polyamide also has a carboxyl group with an electronegative oxygen 
that can interact with hydrogen atoms in the particles or fibers. 
Thus, the polymeric binders enhance the hydrogen bonding (a) between the 
fibers and binder; and (b) in the case of particles with hydrogen bonding 
functionalities, between the binder and the particles. 
Alternatively, the polymeric binder may form a coordinate covalent bond 
with the particles and a hydrogen bond to the fibers. For example, the 
oxygen or nitrogen on the binder has an unbound pair of electrons that can 
be donated to an empty orbital in the particle to form a coordinate 
covalent bond. For example, one free pair of electrons on the oxygen or 
nitrogen can be donated to the empty p orbital of a boron containing 
particle to form a coordinate covalent bond that adheres the particle to 
the binder. The fibers themselves contain functional groups that can form 
hydrogen bonds with the binder, and allow the binder to adhere to the 
fiber. Cellulosic and synthetic fibers, for example, contain hydroxyl, 
carboxyl, amide, ether and ester groups that will hydrogen bond with the 
hydroxyl, carboxylic acid, amide or amine groups of the binder. Hence the 
polymeric binder will adhere the particle with a coordinate covalent bond 
and the fiber will adhere with a hydrogen bond. 
In some preferred embodiments, the polymeric binder is bound to both the 
fibers and the particle by hydrogen bonds. A polypropylene glycol binder, 
for example, can be used to bind polyacrylate hydrogel particles to 
cellulosic fibers. The hydroxyl and ether groups on the glycol binder 
participate in hydrogen bonding interactions with the hydroxyl groups on 
the cellulose fibers and the carboxyl groups on the polyacrylate hydrogel, 
as shown below: 
##STR3## 
Hence the binder will adhere both the particle and fiber with hydrogen 
bonds. The presence of a hydrogen bonding functionality on each repeating 
unit of the polymeric binder has been found to increase the number of 
hydrogen bonding interactions per unit mass of polymer, which provides 
superior binding efficiency and diminishes separation of particles from 
the fibers. The repeating ether functionality on the glycol binder 
provides this efficiency in the example diagrammed above. A repeating 
carboxyl group is the repeating functionality on polyacrylic acid, while 
repeating carbonyls and NR groups (wherein R is either an H or alkyl, 
preferably lower alkyl i.e. less than five carbon atoms, where the alkyls 
are normal or in an iso configuration) of the amide linkages are the 
repeating functionalities on polyamides such as polypeptides. A repeating 
amine group is present on polyamines. 
The polymeric organic binders of the present invention have been found to 
increase in binding efficiency as the length of the polymer increases, at 
least within the ranges of molecular weights that are reported in the 
examples below. This increase in binding efficiency is attributable to the 
increased number of hydrogen bonding or coordinate covalent bonding groups 
on the polymer with increasing molecular length. Each of the polymeric 
binders has a hydrogen bonding or coordinate covalent bonding 
functionality on each repeating unit of the polymer, hence longer polymers 
provide more hydrogen bonding groups or coordinate covalent bonding groups 
that can participate in hydrogen bonding interactions or coordinate 
covalent bonds. 
Although the invention is not limited to polymeric binders of particular 
molecular weights, polymeric binders having a molecular weight greater 
than 500 grams/mole are preferred because they provide attractive physical 
properties, and the solid is less volatile and more thermoplastic as 
compared to small polymeric binders. Polymeric binders with molecular 
weights greater than 4000 grams/mole are especially preferred, because 
they have minimal volatility and are less likely to evaporate from the 
fibers. In some particular embodiments, polymers with molecular weights 
between 4000 and 8000 grams/mole have been used. Polymers with molecular 
weights above 8000 may be used, but exceedingly high molecular weight 
polymers may decrease binding efficiency because of processing 
difficulties. 
Certain polymeric binders have greater binding efficiency because their 
repeating functionality is a more efficient hydrogen bonding group. It has 
been found that repeating amide groups are more efficient than repeating 
carboxyl functionalities, which are more efficient than repeating hydroxyl 
functionalities, which in turn are more efficient than amine or ether 
functionalities. Hence, polymeric binders may be preferred that have 
repeating amine or ether functionalities, more preferably repeating 
hydroxyl functionalities, and even more preferably repeating carbonyl or 
carboxyl functionalities, and most preferably repeating amide 
functionalities. Binding may occur at any pH, but is suitably performed at 
a neutral pH of 5-8, preferably 6-8, to diminish acid hydrolysis of the 
resulting fibrous product. Suitable binders may be selected from the group 
consisting of polyethylene glycol; polyethylene glycol and polypropylene 
glycol, including copolymers thereof; polyethylene glycol, polypropylene 
glycol and polyacrylic acid; polyethylene glycol, polypropylene glycol, 
polyacrylic acid, and a polyamide; polyethylene glycol, polypropylene 
glycol, polyacrylic acid, a polyamide and a polyamine; polypropylene 
glycol alone; polypropylene glycol and polyacrylic acid; polypropylene 
glycol alone; polypropylene glycol, polyacrylic acid and a polyamide; and 
polypropylene glycol, polyacrylic acid, a polyamide and a polyamine; 
polyacrylic acid alone; polyacrylic acid and a polyamide; polyacrylic 
acid, a polyamide and a polyamine; a polyamide alone; a polyamide and a 
polyamine; or a polyamine alone. 
The group consisting of polyacrylic acid, polyamide and polyamine has been 
found to have a especially good binding efficiency. Among polyamides, 
polypeptides are especially preferred. 
Non-Polymeric Binder Characteristics 
The particles may be bound to the fibers by a non-polymeric organic binder 
selected from a predetermined group of binders that each have a volatility 
less than water. Again, these binders are applied on-line during the 
manufacture of the fibrous sheet or web. The vapor pressure of the binder 
may, for example, be less than 10 mm Hg at 25.degree. C., and more 
preferably less than 1 mm Hg at 25.degree. C. The non-polymeric binder has 
a functional group that forms hydrogen bonds or coordinate covalent bonds 
with the particles. In accordance with the present invention, the 
predetermined group of non-polymeric binders may include a functionality 
such as an alcohol, a carboxylic acid, an amino acid, an amide, or an 
amine, wherein each binder includes at least two such functionalities, and 
the two functionalities are the same or different. A requirement for the 
non-polymeric binder is that it have a plurality of functional groups that 
are capable of hydrogen bonding, or at least one group that can hydrogen 
bond and at least one group that can form coordinate covalent bonds. As 
used herein, the term "non-polymeric" refers to a monomer, dimer, trimer, 
tetramer, and oligomers, although some particular non-polymeric binders 
are monomeric and dimeric, preferably monomeric. 
Particularly preferred non-polymeric organic binders are capable of forming 
five or six membered rings with a functional group on the surface of the 
particle. An example of such a binder is an amine or amino acid (for 
example, a primary amine or an amino acid such as glycine) which forms six 
membered rings by forming hydrogen bonds: 
##STR4## 
A six membered ring is also formed by the hydroxyl groups of carboxylic 
acids, alcohols, and amino acids. 
##STR5## 
A five membered ring can be formed by the binder and the functionality on 
the surface of the particle, for example 
##STR6## 
wherein the particle is SAP and the binder is an alcohol, such as a polyol 
with hydroxyl groups on adjacent carbons, for example 2,3-butanediol. 
Other alcohols that do not form a five membered ring can also be used, for 
example alcohols that do not have hydroxyl groups on adjacent carbons. 
Examples of suitable alcohols include primary, secondary or tertiary 
alcohols. 
Amino alcohol binders are alcohols that contain an amino group 
(--NR.sub.2), and include binders such as ethanolamine (2-aminoethanol), 
diglycolamine (2-(2-aminoethoxy)ethanol)). Non-polymeric polycarboxylic 
acids contain more than one carboxylic acid functional group, and include 
such binders as citric acid, propane tricarboxylic acid, maleic acid, 
butanetetracarboxylic acid, cyclopentanetetracarboxylic acid, benzene 
tetracarboxylic acid and tartaric acid. A polyol is an alcohol that 
contains a plurality of hydroxyl groups, and includes diols such as the 
glycols (dihydric alcohols) ethylene glycol, propylene glycol and 
trimethylene glycol; triols such as glycerin (1,2,3-propanetriol); and 
polyhydroxy or polycarboxylic acid compounds such as tartaric acid or 
ascorbic acid (vitamin C): 
##STR7## 
Hydroxy acid binders are acids that contain a hydroxyl group, and include 
hydroxyacetic acid (CH.sub.2 OHCOOH) and lactic, tartaric, ascorbic, 
citric, and salicylic acid. Amino acid binders include any amino acid, 
such as glycine, alanine, valine, serine, threonine, cysteine, glutamic 
acid, lysine, or .beta. alanine. Non-polymeric polyamide binders are small 
molecules (for example, monomers or dimers) that have more than one amide 
group, such as oxamide, urea and biuret. Similarly, a non-polymeric 
polyamine binder is a non-polymeric molecule that has more than one amino 
group, such as ethylene diamine, EDTA or the amino acids asparagine and 
glutamine. 
Each of the non-polymeric binders disclosed above is capable of forming 
hydrogen bonds because it has a functional group that contains an oxygen 
or nitrogen, or has oxygen or nitrogen containing groups that include a 
hydrogen. The amino alcohol, amino acid, carboxylic acid, alcohol and 
hydroxy acid all have a hydroxyl group in which a hydrogen is bound to an 
electronegative oxygen, creating a dipole that leaves the hydrogen 
partially positively charged. The amino alcohol, amino acid, amide and 
amine all have an NR group in which a hydrogen may be bound to an 
electronegative nitrogen that also leaves the hydrogen partially 
positively charged. The partially positively charged hydrogen in both 
cases then can interact with an oxygen or nitrogen on the particle or 
fiber that adheres the binder to the particle and fiber. The 
polycarboxylic acid, hydroxy acid, amino acid and amide also have a 
carboxyl group with an electronegative oxygen that can interact with 
hydrogen atoms in the particles and fibers. Similarly, electronegative 
atoms (such as oxygen or nitrogen) on the fiber or particle can interact 
with hydrogen atoms on the binder that have positive dipoles, and 
partially positive hydrogen atoms on the fiber or particle can interact 
with eleotronegative atoms on the binder. 
Several hydrogen bonding interactions of two of the binders (glycine and 
1,3-propanediol) with cellulose are shown below: 
##STR8## 
The hydrogen bonding interactions are shown as dotted lines. One such 
interaction is shown between the nitrogen of glycine and a hydrogen of an 
OH on cellulose. A hydrogen bond with glycine is also shown between an 
oxygen of the OH on glycine and the hydroxy hydrogen of an alcohol 
sidechain on cellulose. Hydrogen bonding interactions of the 
1,3-propanediol are shown in dotted lines between an oxygen on an OH group 
of the binder and a hydrogen of an OH group on the cellulose molecule. 
Another hydrogen bond is also shown between a hydrogen on an OH group of 
the glycol binder and an oxygen in an alcohol sidechain of the cellulose. 
Alternatively, the oxygen or nitrogen on the binder has an unbound pair of 
electrons that can be donated to an empty orbital in the particle to form 
a coordinate covalent bond. The free pair of electrons on the oxygen or 
nitrogen can be donated to the empty p, d or f orbital of a particle (for 
example a boron containing particle) to form a coordinate covalent bond 
that adheres the particle to the binder. The fibers themselves do not 
normally contain functional groups that can form coordinate covalent bonds 
with the binders, but hydrogen bonding interactions allow the binder to 
adhere to the fiber. Cellulosic and synthetic fibers, for example, contain 
hydroxyl, carboxyl and ester groups that will hydrogen bond with the 
hydroxyl, carboxylic acid, amide or amine groups of the binder. 
Non-cellulosic or non-synthetic fibers that have these functionalities can 
also be used, for example silk, which has an amide linkage. Hence the 
binder will adhere the particle with a coordinate covalent bond and the 
fiber with a hydrogen bond. 
In some preferred embodiments, the binder is bound to both the fibers and 
the particle by hydrogen bonds. A polyol binder, for example, can be used 
to bind polyacrylate hydrogel particles to cellulosic fibers. The hydroxyl 
groups on the polyol binder participate in hydrogen bonding interactions 
with the hydroxyl groups on the cellulose fibers and the carboxyl groups 
on the polyacrylate hydrogel. Hence the binder will adhere both the 
particle and fiber with hydrogen bonds. These hydrogen bonds provide 
excellent binding efficiency and diminish separation of bound particles 
from the fibers. 
A structural drawing is shown below in which citric acid, vitamin C and 
urea adhere polyacrylate particles to cellulose with hydrogen bonds. Some 
of the possible hydrogen bonding interactions are shown as dashed lines. 
##STR9## 
Particularly efficient hydrogen bonding binders include those with carboxyl 
groups, such as ascorbic acid, or amide groups, such as urea. Hydroxyl 
groups are also very efficient binders. Amine and ether functionalities 
are less efficient binders. 
Binders have functional groups that may be selected independently or in 
combination from the group consisting of a carboxylic acid, an alcohol, an 
amide and an amine, wherein the binder has at least two of these 
functional groups, and each of the functional groups can be the same (for 
example, a polyol, polycarboxylic and polyamine or polyamide) or different 
(for example, an amino alcohol, hydroxyamide, carboxyamide, or amino 
acid). Functional groups may also be selected independently or in 
combination from the group consisting of a carboxylic acid alone; a 
carboxylic acid and an alcohol; a carboxylic acid, an alcohol and an 
amide; a carboxylic acid, an alcohol, an amide and an amine; an alcohol 
alone; an alcohol and an amide; an alcohol, an amide and an amine; an 
amide alone; an amide and an amine; and an amine alone. 
Preferred functional groups for the non-polymeric binders may be selected 
independently or in combination from the group consisting of an amino 
alcohol, a polycarboxylic acid, a polyol, a hydroxy acid, an amino acid, 
an amide, and a polyamine. Other preferred groups of binders include an 
amino alcohol alone, an amino alcohol and a polycarboxylic acid, an amino 
alcohol, a polycarboxylic acid and a polyol; an amino alcohol, a 
polycarboxylic acid, a polyol and a hydroxy acid; an amino alcohol, a 
polycarboxylic acid, a polyol, a hydroxy acid and an amino acid; an amino 
alcohol, a polycarboxylic acid, a polyol, a hydroxy acid, an amino acid 
and an amide; a polycarboxylic acid and a polyol; a polycarboxylic acid, a 
polyol and a hydroxy acid; a polycarboxylic acid, a polyol, a hydroxy 
acid, and an amino acid; a polycarboxylic acid, a polyol, a hydroxy acid, 
an amino acid and an amide; a polycarboxylic acid, a polyol, a hydroxy 
acid, an amino acid, an amide and a polyamine; a hydroxy acid and an amino 
acid; a hydroxy acid, amino acid and amide; a hydroxy acid, amino acid, 
amide and polyamine; an amino acid and an amide; an amino acid, amide and 
a polyamine; an amide and a polyamine; an amino alcohol alone, a 
polycarboxylic acid alone, a polyol alone, a hydroxy acid alone, an amino 
acid alone, an amide alone and a polyamine alone. 
More specifically, the functionalities of the non-polymeric binder may be 
selected from the group of glycerin (a polyol), ascorbic acid (a 
polycarboxylic acid and a hydroxy acid), urea (a polyamide), glycine (an 
amino acid), pentaerythritol (a polyol), a monosaccharide, a disaccharide 
(a polyhydric alcohol), as well as citric acid, tartaric acid, dipropylene 
glycol, and urea derivatives such as DMDHEU. Suitable subgroupings of 
these binders include glycerin alone; glycerin and ascorbic acid; 
glycerin, ascorbic acid and urea; glycerin, ascorbic acid, urea and 
glycine; glycerin, ascorbic acid, urea, glycine and pentaerythritol; 
glycine, ascorbic acid, urea, glycine, pentaerythritol and a 
monosaccharide; glycerin, ascorbic acid, urea, glycine, pentaerythritol, a 
monosaccharide and a disaccharide; ascorbic acid alone; ascorbic acid and 
urea; ascorbic acid, urea and glycine; ascorbic acid, urea, glycine and 
pentaerythritol; ascorbic acid, urea, glycine, pentaerythritol and a 
monosaccharide; ascorbic acid, urea, glycine, pentaerythritol, 
monosaccharide and a disaccharide; urea alone; urea and glycine; urea, 
glycine and pentaerythritol; urea, qlycine, pentaerythritol and a 
monosaccharide; urea, glycine, pentaerythritol, a monosaccharide and a 
disaccharide; glycine alone; glycine and pentaerythritol; glycine, 
pentaerythritol and a monosaccharide; glycine, pentaerythritol, a 
monosaccharide and a disaccharide; pentaerythritol alone; pentaerythritol 
and a monosaccharide; pentaerythritol, a monosaccharide and a 
disaccharide; a monosaccharide alone; a monosaccharide and a disaccharide; 
and a disaccharide alone. 
Process Advantages 
The binders of the present invention also provide numerous process 
advantages. Binding of particles to the fibers can occur, for example, 
without external application of heat. Hence particle binding may occur at 
ambient temperature if desired. This aspect of the present invention is 
therefore distinct from prior art crosslinking processes in which elevated 
temperatures are required to covalently crosslink cellulose groups to one 
another. Moreover, the binders of the present invention have the advantage 
of being reactivatable by addition of a liquid solvent such as water. 
Hence, a liquid binder (which would include a solution of a solid or 
liquid binder, or a binder that has a melting point below room 
temperature) can be applied to a cellulose mat on the pulp sheet 
manufacturing line 10 (FIG. 1) in the absence of the particles to be bound 
and the binder dried, for example, until it reaches an equilibrium 
moisture content with the moisture in the ambient air. Thereafter, at a 
remote location or less preferably on line, the binder may be activated to 
adhere the selected particles to the fibers. Alternatively, the binder can 
be applied as a solid, for example as particles or a powder e.g., at the 
user's plant). At a later stage of processing, water or another liquid is 
added to those portions of a mat containing binder and fibers where 
particulate binding is desired. The particles may then be added to the mat 
and adhered to fibers of those portions of the mat that have been 
moistened. Alternatively, the particles may be added to the mat prior to 
activation of the binder. 
The binders may be liquids at room temperature (such as glycerin), or 
liquid solutions of binders that are solids at room temperature (for 
example, an aqueous solution of glycine), or liquid hot melts of solid 
binders. Solid binders may be added to fibers in particulate form, for 
example, by sprinkling binder particles on the fibers. 
The binding reaction of the present invention can occur across a broad 
range of pH without requiring a catalyst. A suitable pH range without a 
catalyst is 1-14, but preferred ranges are 5-8 or 6-8 because such neutral 
pH ranges will produce fibrous products (such as cellulose products) that 
are less prone to damage by acid hydrolysis. 
The moisture content of the fibers during the binding reaction is 0.5-50%, 
suitably 5-40%, and most preferably 5-20% water by weight of the fibers, 
binder and particle. A moisture content greater than 20%, more preferably 
greater than 30%, or in the range of 20-50%, more preferably 30-50%, 
interferes with the formation of covalent bonds in the production of high 
bulk fibers. Particles may be added to the fibers (e.g., blended with 
fibers in fiberizer 70 or during air laying) such that the particles are 
distributed throughout a fibrous product without being confined to a 
surface of the product. The particles can be distributed throughout the 
depth of a fiber product or in varying concentrations throughout the 
product, such as a mat or web. 
The binder is suitably present in the treated fibers in an amount of at 
least 3 percent and no more than 80 percent by weight of the fibers, 
particles, and binder ("percent by weight"). In especially preferred 
embodiments, the binder is present in an amount of 5-30 percent by weight. 
Below about 3 percent, an insufficient amount of binder is present to 
achieve adequate binding, while using excessive amounts of binder can 
introduce unnecessary expense into the binding process. High percentages 
of binder can also cause processing problems because the binder material 
transfers to equipment surfaces. 
Thermoplastic binders may also be used to help bind fibers to each other 
and particles to fibers. The binder that has the hydrogen bonding or 
coordinate covalent bonding functionalities may itself be thermoplastic. 
Some of the polymeric binders used in the present invention have the 
advantage of being thermoplastic solids. Hence fibers treated in 
accordance with the present invention can be thermobonded by elevating the 
fiber temperature above the melting temperature of the binder to melt the 
thermoplastic binder and thermoplastically bind the fibers to each other 
and the fibers to the particles. Alternatively, an auxiliary or second 
binder can be applied to the fibers as a solid or liquid at room 
temperature, and the temperature of the second binder elevated above its 
melting point to thermobond the fibers and particles. The auxiliary binder 
may be applied to the fibers either before or after the primary binder is 
applied on the pulp sheet manufacturing line, but before thermobonding. 
The binders used in the present invention may be used with fibers that have 
substantial intrafiber covalent crosslinks (such as HBA available from 
Weyerhaeuser) or fibers which are substantially free of intrafiber 
covalent crosslinking. Examples of individualized intrafiber crosslinked 
fibers are seen in European Patent Applications 440 472 A1 and 427 317 A2, 
which produce products that those publications describe as being 
substantially free of interfiber bonds. Those fibers have been 
individualized and then cured in the presence of a crosslinking material 
at an elevated temperature to produce high bulk fibers having intrafiber 
covalent crosslinks. The fibers of the present invention do not need to be 
processed as in those European applications to eliminate interfiber bonds. 
Binders of the present invention can therefore be used with natural fibers 
that have substantial interfiber bonding, which is defined as fibers that 
have not been processed as in European Applications 440 472 A1 and 427 317 
A2 to substantially eliminate interfiber bonds. Cellulose fibers that have 
not been so processed are substantially free of intrafiber bonds. 
Although intrafiber covalent crosslinking is not required for the present 
invention, such high bulk fibers can be used with the binders disclosed 
herein. However, although they could be, these fibers are not typically 
blended with other fibers in a slurry in a headbox of a wet laid sheet 
manufacturing line. Fibers that have high bulk from intrafiber covalent 
crosslinks are prepared by individualizing the fibers and curing them at 
an elevated temperature (above 150.degree. C.) in the presence of a 
crosslinking material such as citric acid. Initial application of the 
binder on such high bulk fibers may occur after the curing step and on the 
wet laid sheet manufacturing line, particularly if the binder is capable 
of functioning as a crosslinking material. The binders disclosed herein 
that can also crosslink are polyols, polycarboxylic acids, and polyamines 
(both polymeric and nonpolymeric binders that have more than one amine 
group); none of the other specifically disclosed binders are known to form 
covalent, intrafiber ester bonds. 
Binding is performed under conditions that favor formation of hydrogen 
bonds or coordinate covalent bonds, and discourage formation of covalent 
bonds. Conditions that favor covalent bonds are those disclosed in U.S. 
Pat. No. 4,412,036 and U.S. Pat. No. 4,467,012 wherein particle and binder 
would be laminated between tissue layers under high temperature and 
pressure to form laminated adherent tissue layers. That patent teaches 
that minimal adhesion occurs at 200 pli (pounds per linear inch, as in a 
calendar press) if no external heat is supplied, but adhesion improves as 
the reaction temperature increases. Improved adhesion of the tissue layers 
occurs because of enhanced covalent bonding as the temperature increases. 
Conditions that favor covalent bond formation are also shown in European 
Patent Applications 440 472 A1; 427 317 A2; 427 316 A2; and 429 112 A2. 
These European publications use polycarboxylic acid crosslinkers, and 
require elevated temperatures (for example above 145.degree. C.) and 
acidic conditions (pH less than 7) to promote formation of intrafiber 
covalent ester bonds and inhibit reversion of the ester bonds. The present 
invention, in contrast, can form hydrogen or coordinate covalent bonds 
below 145.degree. C., below 100.degree. C., and even at room temperature. 
The binders of the present invention can also bind particles to fibers 
under neutral or alkaline conditions, i.e., at a pH above 7, but 
preferably at a pH of 5-8 or 7-8. 
The intrafiber covalent bond forming processes described in the above 
European publications require formation of an anhydride that then reacts 
with a hydroxy group on cellulose to form a covalent ester bond. The 
presence of more than about 15% water by weight in the fibers interferes 
with formation of the anhydride and inhibits covalent bond formation. 
Hence, in processes that use binders that are also crosslinkers 
(polycarboxylic acid, polyols and polyamines) as binders in the present 
invention, the fibers should contain at least 15% water by weight if the 
particles and binder are present in the fibers when curing occurs. The 
water inhibits covalent bond formation, and prevents all of the binder 
from being used to form covalent intrafiber crosslinks. Hence, some of the 
binder remains available to form the non-covalent bonds with the particles 
and produce ease of densification in fiber products made by the process of 
the present invention. 
The present invention, in contrast, produces a product under conditions 
that favor formation of hydrogen or coordinate covalent bonds. Hence, the 
particles can be bound to the fibers in the absence of the external 
application of heat or pressure. Particles may also be bound and the 
resulting fiber product densified, for example at less than 200 pli (about 
8000 psi), or less than 100 pli (about 4000 psi), in the absence of 
external application of heat to produce a product in which a substantial 
portion of the particles are bound by non-covalent bonds (hydrogen or 
coordinate covalent bonds). A substantial portion of particles bound by 
non-covalent bonds means at least half of the particles are bound by other 
than covalent bonds, for example by hydrogen or coordinate covalent bonds. 
In yet other examples, particles may be bound in the absence of external 
application of pressure, but at elevated temperatures. 
In particularly preferred embodiments, the particles are substantially 
entirely bound to the fibers non-covalently. 
Binding Examples for Polymeric Binders 
Several examples are given below illustrating use of the polymeric binders 
of the present invention to attach superabsorbent particles to southern 
bleached kraft pulp. 
EXAMPLE I 
Southern bleached kraft fibers may be slurried in a headbox and delivered 
to a Fourdrinier wire to form a sheet. Following drying of the resulting 
mat to a 10 w/w % moisture content, a polyethylene glycol binder (100 
grams/100 ml deionized water average molecular weight=4,600; supplied by 
Union Carbide Corporation of Danbury, Conn.) may be sprayed onto the mat 
as a binder. The application rate being 100 grams polyethylene glycol per 
321 grams (dry weight) fibers. Thereafter, the web or mat is dried and 
then, at a separate location, starch graft polyacrylate hydrogel fines (IM 
1000F; supplied by Hoechst-Celanese of Portsmouth, Va.) may be blended 
with the binder coated fibers. These superabsorbent particles are added at 
the rate of 435 grams per 321 grams of fibers. The mixed fiber and 
particle mass may then be airlaid and thermobonded at 140.degree. C. for 
one minute to produce a web containing 40% superabsorbent particles (SAP) 
attached to the individualized fibers. The polyethylene glycol has a low 
melting point, hence raising the temperature to 140.degree. C. melts the 
binder and allows it to flow over the fibers and particles to enhance 
hydrogen bonding interactions and provide mechanical encapsulation that 
further binds the fibers and particles. This is an example of activating a 
solid binder by heating it, without liquid addition. 
EXAMPLE II 
The same procedure as in Example I, except without the thermobonding step, 
may be repeated utilizing other binders, such as 154 grams of a 65% 
solution of polyacrylic acid (average molecular weight=2,000; supplied by 
Aldrich Chemical Company of Milwaukee, Wis.) diluted with 100 ml of 
deionized water per 321 grams (dry weight) wood pulp. Other hydrogels may 
be used, such as 435 grams of polyacrylate hydrogel (FAVOR 800 supplied by 
Stockhausen of Greensboro, N.C.) per 321 grams pulp. 
EXAMPLE III 
As another example, using the process of Example I without the 
thermobonding step, the binder may be 100 grams of polyglycine (molecular 
weight=5,000-5,000; supplied as a dry powder by Sigma Chemical Company of 
St. Louis, Miss.) diluted with 100 ml of deionized water is sprayed per 
321 grams (dry weight) wood pulp. The resulting product may be dried and 
fed into a hammermill with a three-eights inch round hole screen. Then 435 
grams of starch graft polyacrylate hydrogel fines (IM 1000F; supplied by 
Hoechst-Celanese of Portsmouth, Va.) per 321 grams (dry weight) wood pulp 
is added and mixed. The mixture is shunted to an airlay line to produce a 
web containing 40% SAP attached to the fibers. 
EXAMPLE IV 
As yet another example, prepared in accordance with Example I, but without 
the thermobonding step, the binder may be 200 grams of a 50% solution of 
polyethyleneimine (molecular weight=50,000-100,000; supplied by ICN 
Biomedicals, Inc. of Costa Mesa, Calif.), or polyvinyl pyridine per 321 
grams (dry weight) wood pulp. Then 435 grams of starch graft polyacrylate 
hydrogel fines (IM 1000F; supplied by Hoechst-Celanese of Portsmouth, Va.) 
is added per 321 grams (dry weight) fibers and mixed. The resulting 
product is dried and fed into a hammermill with a three-eighths inch round 
hole screen and shunted to an airlay line to produce a web containing 40% 
SAP attached to the fibers. 
The classes of polymeric binders that encompass those described in Examples 
I-IV are especially preferred over other multiple hydrogen bonding 
functionality polymers for a number of reasons. One important reason is 
that their functionalities produce very strong, effective hydrogen 
bonding. Other important reasons include their relative lack of reactivity 
(as compared with polyaldehydes or polyisocyanates) and their low toxicity 
(again, as compared with polyaldehydes or polyisocyanates). 
EXAMPLE V 
As previously described, repetition of a hydrogen bonding group on each 
repeating unit of a polymer has been found to produce a binder that 
provides superior binding of particles to fibers, as compared to polymeric 
binders in which the hydrogen bonding functionality is not present on all 
the repeating units. This example shows the difference in binding 
efficiency between a 20% carboxylated polymer and a 100% carboxylated 
polymer. Bound samples have been prepared by air entraining 321 grams of 
southern bleached kraft fluff in a blender-like mixing device with the 
binder being sprayed onto the entrained fluff, using a 20% carboxylated 
ethylene acrylic acid copolymer and a 100% carboxylated PAA. 435 grams of 
IM 1000F superabsorbent particles were added to the binder treated fibers 
while the binder was wet and mixed. The samples were removed and dried 
overnight in a fume hood. The resulting samples were fed respectively to a 
Fitz hammermill with a three-eights inch round hole screen and shunted to 
a small M & J airlay line to produce webs having 40% SAP attached to the 
fibers. A sample containing each binder was subjected to the same 
mechanical agitation (to simulate machine processing required to make a 
web), screened through a descending series of sieves to remove unattached 
SAP, and subjected to an absorbent capacity test (less attached SAP would 
result in a lower absorbent capacity). The result of the test was measured 
by weighing the unabsorbed liquid (0.9% saline) from a standardized 
insult, hence a lower number indicates more liquid absorbed or higher 
absorbent capacity. 
In testing wood pulp fiber webs made in this manner with binder applied to 
dried fibers at a location remote from a pulp sheet manufacturing line, a 
sample of the 20% carboxylated polymer (15% of the total mix) gave a 
beaker test result of 19.5 grams. A similar sample of polypropylene glycol 
gave a result of about 20.0 grams. However, the hydrogen bonding 
functionality of PPG is not as efficient as the carboxyl functionality of 
PAA. A similar sample of polyacrylic acid (100% carboxyl functionality of 
PAA) gave a result of 11.3 grams. A comparison of the 20% and 100% 
carboxylated polymers shows a substantial increase in SAP binding 
efficiency, as measured by an increase in absorbency of the product. These 
same results are expected when the binders are applied on a pulp sheet 
manufacturing line with particles added at a remote location from the 
line. 
Non-Polymeric Binding Examples 
Several examples are given below to illustrate the use of several 
non-polymeric organic binders of the present invention to attach 
superabsorbent particles to southern bleached kraft pulp. 
EXAMPLE VI 
A mat of southern bleached kraft fluff on a pulp manufacturing line may be 
dried and sprayed with glycerin at location 56 (FIG. 1) (96%, USP; 
supplied by Dow Chemical Co. of Midland, Mich.) to provide a pulp sheet 
with 30% binder to the weight of binder and fibers. Then starch graft 
polyacrylate hydrogel fines (IM 1000F; supplied by Hoechst-Celanese of 
Portsmouth, VA) may be added to a fiberizer at a remote location (FIG. 2) 
and mixed with the fluff containing the binder. Although variable, the 
particles may be added in an amount to comprise 50% by weight particles to 
the total weight of the particles, fibers and binder. The fiberizer 
mechanically activates the binder to cause the adherence of the particles 
to the fibers. The material may then be fed into a Danweb airlay machine 
to form a web containing bound 50% IM 1000F that would be substantially 
immobile in the web because the particles are bound to the fibers instead 
of mechanically entrapped by the matrix. 
EXAMPLE VII 
A southern bleached kraft fluff pulp sheet on a pulp manufacturing line may 
be sprayed with a 50% solution of glycine at location 54 in FIG. 1, in 
this case midway through the drying stage 30, (supplied as a dry powder by 
Aldrich of Milwaukee, Wis.) and dried on the line. The binder containing 
sheet may be shipped to a remote location and moisture added to provide, 
for example, a 17-21% moisture content. This sheet may then be fed into a 
hammermill. Starch graft polyacrylate hydrogel fines (IM 1000F; supplied 
by Hoechst-Celanese of Portsmouth, Va.) may simultaneously be added to the 
mill by a screw feed device, mixed with the fluff, shunted to an airlay 
forming machine and airlaid to form a web. The resulting web would contain 
20% SAP attached to the fibers substantially uniformly throughout the web 
without being confined to the surface of the web. 
EXAMPLE VIII 
A southern bleached kraft fluff pulp sheet on a pulp manufacturing line may 
be sprinkled with solid particulate pentaerythritol (supplied by Aldrich 
of Milwaukee, Wis.) at location 52 (FIG. 1). The sheet may be moistened to 
a moisture content of, for example, 17-21% and may be fed into a 
hammermill. The sheet is dried online and shipped to a remote location. 
Starch graft polyacrylate hydrogel fines (IM 1000F; supplied by 
Hoechst-Celanese of Portsmouth, Va.) may simultaneously be added to the 
mill by a screw feed device and mixed with the fluff. The resulting fibers 
with adhered particulate may be shunted to an airlay forming machine and 
airlaid to form a web. The resulting web would contain 20% SAP attached to 
the fibers. 
EXAMPLE IX 
A southern bleached kraft fluff pulp sheet on a pulp manufacturing line may 
be sprayed with a 50% solution of lactose at location 54 and dried. The 
binder treated sheet may then be fed into a hammermill at a remote 
location. The sheet may be defiberized and the resulting fibers shunted to 
an airlay line, and airlaid into a web. As the web emerges, target zones 
of the web may then be misted with water to raise the moisture content to 
17-21%. Five gram aliquots of starch graft polyacrylate hydrogel fines (IM 
1000F; supplied by Hoechst-Celanese of Portsmouth, Va.) may then be sifted 
onto the target zones. The resulting web would have target zones with 5 
grams of SAP attached to the fibers of each target zone. Portions of the 
web that were not targeted for application of the reactivating liquid 
(water) would not adhere the particles well. This is an example of 
activating the binder in a target zone at a remote location from the pulp 
sheet manufacturing line so that SAP primarily adheres to the target areas 
where the binder is activated. Target zone application of SAP can be 
advantageous because it reduces the cost of the product to provide SAP 
only in areas of a product where the SAP is needed, for example, the 
crotch area of a diaper. Placement of SAP in the area where a liquid 
insult is expected also decreases the necessity for wicking liquid to a 
SAP impregnated region. This is an advantage because the requirement for 
wicking can increase liquid leakage in an absorbent product such as a 
diaper. 
EXAMPLE X 
A southern bleached kraft sheet on a pulp manufacturing line may be sprayed 
with glycerin (96%, USP; supplied by Dow of Midland, Mich.) at location 56 
(FIG. 1). Abscents (an odor absorbing zeolite supplied by UOP of 
Tarrytown, N.Y.) may be added to the sheet and mixed in a fiberizing 
device at a remote location (see FIG. 2) to provide a homogenous mixture. 
The material may then be airlaid into a web which would be of fibers with 
adhered Abscents. The particulate retention would compare favorably to 
particulate retention with latex binders under similar conditions. 
Product Characteristics 
The following examples illustrate how SAP retention, pad integrity, 
wettability, bulk and liquid retention are affected by applying the 
glycerin binder in accordance with the present invention. In each of the 
following Examples XI-XVIII, the binder was applied to dried fibers in a 
test lab separate from a pulp sheet manufacturing line. However, the 
results are expected to be the same if the binder were applied on the pulp 
sheet manufacturing line with the particles being added at another 
location. 
EXAMPLE XI 
Superabsorbent particles were bound to cellulose fibers with a glycerin 
binder. More specifically, 321 grams of dried NB 416 fluff from 
Weyerhaeuser Company was air entrained in a blender like mixing device and 
sprayed with 100 grams of the glycerin in 100 ml of deionized water. Then 
435 grams of superabsorbent particles were mixed with the fibers and 
binder and allowed to air dry overnight in a fume hood. For purposes of 
comparison, superabsorbent particles were bound to a separate sample of 
cellulose fibers using a polyvinyl acetate (PVAc) binder that was about 3% 
carboxylated, that is only about 3% of the PVA monomers were carboxylated. 
Binding was performed as above in this Example XI, but PVAc was 
substituted for glycerin. A 100 gram sample of the glycerin and PVAc 
treated fluff with attached SAP was fed into a fan that was connected by a 
hose to a small cyclone mounted on top of a material containment box. This 
was done in an effort to simulate forces of mechanical agitation the fluff 
would encounter during the airlay process. After collection in the 
material containment device, fiber with attached SAP was removed and 
weighed. A five gram sample of the fiber with attached SAP was then placed 
in a column of sieves with decreasing mesh sizes and subjected to a 
shaking and thumping action for ten minutes in order to further dislodge 
any poorly attached SAP. Unattached or poorly attached SAP sifted through 
screens having a range of 5-60 mesh, while the fiber with well attached 
SAP remained on the 5 mesh screen. 
A 2.00 gram sample of the fibers that remained near the top of the sieve 
column was then placed in a 75 ml sample of 0.9% saline for exactly one 
minute. After that minute, the liquid that was not absorbed was poured off 
into a separate, tared beaker and weighed. The relative amounts of liquid 
absorbed is indicative of the amounts of SAP bound to the fiber. Fiber 
retaining higher amounts of SAP tend to absorb more water and give a 
smaller amount of liquid not absorbed. 
These results are shown in Table I: 
TABLE I 
______________________________________ 
Glycerin Binder 
Comparing SAP Retention with Glycerin and PVAc Binders 
Binder Beaker result 
______________________________________ 
40-504 22.8 g 
(PVAc) 
3666H 22.0 g 
(PVAc) 
Glycerin 5.5 g 
______________________________________ 
Table I illustrates that the glycerin binder provides a product that has an 
absorbency increase of 400% compared to the PVAc binder. A substantial 
portion of this improvement is believed to be due to better adhesion 
between the fibers and SAP, such that the particles are not dislodged from 
the fibers. 
EXAMPLE XII 
Pad integrity was compared in fibrous products that used no binder and a 
glycerin binder at 7% and 11% by weight. Each of these binders was used to 
bind SAP to fibers as in Example XI, and properties of the pad were 
measured and are shown in Table II: 
TABLE II 
______________________________________ 
Tensile Results 
Sample Basis Weight 
Density Tensile Index 
______________________________________ 
Pad integrity (low density): 
NB-416 464 gsm 0.12 g/cc 0.257 Nm/g 
(control) 
NB-416/7% 437.6 gsm 0.126 g/cc 0.288 Nm/g 
Glycerin 
NB-416/11% 
402.5 gsm 0.135 g/cc 0.538 Nm/g 
Glycerin 
Pad Integrity (high density): 
NB-416 482.1 gsm 0.218 g/cc 0.475 Nm/g 
(control 
NB-416/7% 460.7 gsm 0.219 g/cc 0.882 Nm/g 
Glycerin 
NB-416/11% 
421.6 gsm 0.248 g/cc 1.536 Nm/g 
Glycerin 
______________________________________ 
The glycerin binder in this example produced a product that had a higher 
tensile index than an untreated product. The increased tensile strength 
was especially enhanced in the densified product. 
EXAMPLE XIII 
The effect of binders on the wettability and bulk of fibers was tested 
using the following fibers: NB-316 (a standard southern bleached kraft 
pulp with no binder); GNB 25% (a standard southern bleached kraft pulp 
with 25% glycerin (entrained and sprayed); HBA (a high bulk intrafiber 
crosslinked fiber available from the Weyerhaeuser Company that contains 
intrafiber covalent crosslinks); and GHBA (HBA fibers treated with a 
glycerin binder) in amounts of 12.5% and 25% by weight. Results are given 
in Tables III and IV. 
FAQ time was determined by airlaying a specific quantity (4.00 grams) of 
the fluff to be tested into a clear plastic tube that was fitted with a 
screen at one end. The fluff and tube were then placed into a well in the 
test device and a metal plunger was lowered onto the fluff and the pad's 
bulk calculated. Water then flowed from underneath the pad, passed through 
the screen and wicked up through the pad. Absorbency time was measured 
from when the liquid makes contact with the bottom screen until the water 
completes an electrical circuit by contacting the foot of the plunger 
resting on top of the pad. Lower absorbency times indicate better 
absorbency. Since the absorption of the liquid by the pad was accompanied 
with some collapse of the pad's structure, the bulk of the wet pad was ten 
recalculated. The amount of liquid absorbed was then measured and a gram 
per gram capacity for the material was calculated. 
Table III gives FAQ time as a measure of wettability. A lower FAQ time 
indicates a product that is more absorbent and wicks faster. Table IV 
gives wet bulk of fibers and the adjusted bulk of the fibers. The adjusted 
bulk is a calculated number obtained by dividing the bulk by the actual 
percent of pulp in the sample. 
TABLE III 
______________________________________ 
Wettability 
Fiber FAQ time 
______________________________________ 
NB-316 3.0 sec 
GNB 25% 3.2 sec 
HBA 13.5 sec 
GHBA 12.5% 4.5 sec 
GHBA 25% 0.4 sec 
______________________________________ 
TABLE IV 
______________________________________ 
Bulk 
Fiber Wet Bulk Adjusted Bulk 
______________________________________ 
NB-316 12.7 cc/g 
12.7 cc/g 
GNB 25% 10.9 cc/g 
14.5 cc/g 
HBA 19.4 cc/g 
19.4 cc/g 
GHBA 12.5% 16.1 cc/g 
18.4 cc/g 
GHBA 25% 14.9 cc/g 
19.9 cc/g 
______________________________________ 
The low FAQ times (Table III) in the glycerin treated fibers (GNB, GHBA) 
show that wettability is as good as the untreated fiber (NB-316). The GHBA 
25% had significantly better wettability than untreated HBA. Bulk of 
glycerin treated fibers (Table IV) was not significantly decreased or 
changed at all levels of glycerin binder on a fiber to fiber comparison 
basis. 
EXAMPLE XIV 
Liquid retention of bound fibers was determined and compared to fibers in 
which no binder was added. NB-316 is a pulp sheet available from 
Weyerhaeuser Company in which no binder is used. HBA is described in 
Example X. HBA/Gly SAP was an HBA fiber that was bound with glycerin (12% 
binder, 48% fiber) and which contained 40% SAP particles. NB-316/Gly SAP 
is NB-316 fibers to which glycerin and SAP fibers were added. 
The procedure for determining liquid retention was to weigh triplicate 
small portions (near 0.2 grams) of samples to the nearest 0.0001 gram and 
then heat seal the small portions inside an envelope of a heat sealable 
nonwoven tea bag. The samples were then immersed in an excess of 0.9% 
saline for thirty minutes, then drained by suspending them from a clip for 
fifteen minutes. The samples were weighed to determine the amount of 
liquid absorbed. The grams of liquid absorbed per gram of sample was 
calculated and the samples were spun in a centrifuge for one minute. The 
samples were then reweighed and a percent liquid retention was calculated. 
Results are shown in the following Table V: 
TABLE V 
______________________________________ 
Liquid Retention (after centrifuge) 
Fiber/Binder % Retention 
______________________________________ 
NB-316/none less than 1% 
HBA/none less than 1% 
HBA/Gly SAP 23% 
NB-316/Gly SAP 31.5% 
______________________________________ 
The results in Table V illustrate that fibers that have SAP bound to them 
retain liquid well, while fibers without SAP retain liquid poorly. The 
glycerin binders provided excellent adherence of SAP to the fibers. 
EXAMPLE XV 
Auxiliary Binder 
As previously described, an auxiliary binder can be used in addition to the 
non-polymeric binders of the present invention. A 321 gram amount of a 
southern bleached kraft fiber (NB-416, supplied by Weyerhaeuser) was air 
entrained in a blenderlike mixing device and sprayed with 212.8 grams of a 
polyvinylacetate latex (PN-3666H, supplied by H B Fuller of Minneapolis, 
Minn.). While still mixing, 438 grams of a water swellable polyacrylate 
hydrogel (Favorsab 800, supplied by Stockhausen of Greensboro, N.C.) was 
added and the resulting mixture was then sprayed with 100 grams of a 50% 
solution of glycerin (supplied by Dow of Midland, Mich.). The blender was 
then stopped and the mixture was vacuumed from the blender and placed in a 
fume hood to air dry overnight. The dried product was then airlaid into a 
6" diameter pad in a laboratory padformer, pressed to a density of 
approximately 0.077 g/cc, and thermobonded at 140.degree. C. for thirty 
seconds. The resulting pads had 40% bound SAP and improved tensile 
strength as compared to untreated fluff with SAP and as also compared to 
binder treated fluff with SAP without the auxiliary binder. 
Tensile strength was highest with polyvinylacetate alone, followed by a 
combination of polyvinylacetate and glycerin, then glycerin alone. Lowest 
tensile strength was seen with no binder at all. 
EXAMPLE XVI 
Binders of the present invention may be used to bind particles to pulp 
fibers that contain synthetic thermobonding fibers. In this example, 
KittyHawk pulp (available from Weyerhaeuser Company) is a mixture of NB316 
southern bleached kraft and 22% polyethylene thermoplastic binder fibers. 
The KittyHawk pulp may be used to produce a pulp web, to which binder is 
added with SAP then being bound to the kraft fibers as described in 
Example III. Webs with these fibers with adhered SAP may then be passed 
through a thermobonder to soften the polyethylene fibers and fuse the 
fibers of the web to each other to increase web strength. 
EXAMPLE XVII 
Solid sample .sup.13 C NMR spectra were obtained on cellulose fibers 
treated with ascorbic acid to bind SAP to the fibers. An NMR spectra was 
also obtained on L-ascorbic acid. In both cases, separate spectra were 
acquired using recovery delays of 1 sec and 5 sec between acquisitions. 
The peaks in the treated fiber spectrum were assigned readily to the 
components: SAP polyacrylate carboxyl (185 ppm) and backbone (50-30 ppm) 
carbons; cellulose (106, 90, 84, 76, 73 and 66 ppm); and ascorbic acid 
ring carbons C-1, C-2 and C-3 (175, 119 and 156/153 ppm, respectively); 
the other ascorbic acid carbons are in the cellulose region, two of them 
being resolved at 69 and 61 ppm. The ascorbic acid carbon chemical shifts 
in this ternary mixture were essentially identical (.+-.0.2 ppm) to their 
values in pure ascorbic acid. This indicated that the ascorbic acid in the 
treated fibers had undergone no gross structural changes, such as total 
neutralization, oxidation or ring opening. 
The signal-accumulation rates observed at the two different recovery delay 
times showed that the proton spins in pure ascorbic acid relaxed after 
excitation much more slowly than they did in the ternary mixture. As shown 
in the following table, slow relaxation yields higher signal strength at 
the long recovery delay relative to the short one. The fast proton 
spin-lattice relaxation in the coated fibers indicated that the ascorbic 
acid in this system is held more tightly in place (i.e., is less mobile) 
than in the bulk acid. The ascorbic acid is apparently held tightly by one 
or both of the other two components, cellulose and SAP, and not by other 
ascorbic acid molecules. 
If the bonding were purely ionic, involving ascorbate ion and an acrylic 
acid unit in the SAP, then the NMR of the treated fibers would show the 
ascorbic acid in the salt form. NMR reference spectra were found of the 
acid and its salt in aqueous solution, and C-3 is seen to shift 
dramatically on ionization of its OH group: 156 ppm in the acid to 176 ppm 
in the salt. Thus, since the NMR spectrum of the ternary mixture contains 
the peaks at around 156 ppm, the ascorbic acid in this system is not 
ionized. 
The infrared spectra, however, point to substantial disruption in the 
structure of the ring OH groups, comparing pure ascorbic acid with the 
treated fibers, with the ascorbic acid in the mixture resembling ascorbate 
salts in having some of the OH stretching bands missing. 
Looking at acidities, ascorbic and polyacrylic acids have nearly identical 
pK.sub.a values (4.2 vs 5, respectively). They are both typical strong 
organic acids with weak conjugate bases. Thus, there is no compelling 
reason for one of these acids to be neutralized (ionized) by the conjugate 
base of the other acid. Rather, there should be a strong tendency for an 
ascorbic acid and an acrylate ion to share a hydrogen ion between them, 
resulting in a long hydrogen bond between partially ionic ascorbic and 
acrylic acid units. This sharing of hydrogen ions would certainly be 
reflected in the IR spectrum, yet satisfies the NMR data by not invoking 
full ionization of ascorbic acid. The spectroscopic data are fully 
consistent with a hydrogen bonding mechanism between ascorbic acid and an 
acrylate unit in the superabsorber. 
______________________________________ 
Acrylic Acid NMR Amplitude Ratios at Different 
Recovery Delay Times. 
Signal Ratio, 5 sec/1 sec 
Peak Freq., ppm 
Treated Fibers 
Pure Acid 
______________________________________ 
176 1.99 5.21 
156 1.92 -- 
153 1.80 5.35 
119 2.10 4.26 
______________________________________ 
EXAMPLE XVIII 
Fibers With Superabsorber And Ascorbic Acid 
Infrared Analysis 
Infrared transmission spectra of the untreated NB316 pulp, the treated 
NB316 pulp, ascorbic acid, and the IM 100F superabsorber were prepared. 
Then, a subtraction spectrum representing the treated pulp minus the 
untreated control was obtained. 
Examination of that subtraction spectrum indicated several infrared bands 
that were obviously associated with the ascorbic acid. They were evident 
at 1755, .about.1690 (shifted slightly from 1660-1670), 868, 821, and 756 
wavenumbers (cm.sup.-1). However, several other bands that were prominent 
in the ascorbic acid spectrum were absent in that subtraction spectrum. 
They included the following: 3525, 3410, 3318, 1319, 1119, and 1026 
cm.sup.-1. 
The higher frequency bands (3300-3600 cm.sup.-1) in ascorbic acid are 
indicative of bonded OH groups. The infrared bands at 1319, 1119, and 1026 
cm.sup.-1 may also be associated with OH vibrations. Consequently, the IR 
suggested that the subtraction spectrum reflected primarily a loss of the 
OH groups that were attached directly to the ring. A likely possibility is 
that the OH groups were replaced by sodium. The only other major band in 
the subtraction spectrum was located at 1589 cm.sup.-1. This was probably 
due to the superabsorber C.dbd.O which had shifted to a slightly higher 
frequency (from 1562 cm.sup.-1). 
EXAMPLE XIX 
Activation 
The binders of the present invention have the advantage of being 
activatable by addition of liquid or by heating. "Activation" includes 
activating a previously inactive binder (e.g., by adding liquid to a 
solid) or reactivating a previously active binder (e.g., by adding liquid 
to a dried liquid binder) on the fibers. Hence, a liquid binder can be 
applied to a cellulose mat on the pulp sheet manufacturing line, in the 
absence of the particles to be bound. The binder is then dried or allowed 
to dry, for example until the binder and fiber reach an equilibrium 
moisture content with ambient air. Alternatively, the binder can be 
applied as a solid, for example, particles sprinkled onto a fiber mat on 
the pulp line. In this case, preferably the pulp sheet still contains 
sufficient moisture to adhere the particles of binder to the fibers. Also, 
the pulp sheet may have sufficient heat to adhere thermoplastic binder 
particles to the fibers. At a later stage of processing, the binder is 
activated, e.g. by using a liquid such as water. The particulates may then 
be added, and the binder secures the particulates to the fibers. This 
subsequent processing of the fibers to attach the particles can occur, for 
example, at a separate location from the location where the binder was 
applied to the fibers. Therefore, manufacturers of products can add 
particulates of interest (e.g., superabsorbent particles or fibers; 
antimicrobial particles, etc.) at the place of manufacture of the end 
products that incorporate the treated fibers. Also, more than one type of 
particulate material may be added, if desired. 
It has also been found that some of the binders of the present invention 
can be reactivated by mechanical agitation. For example, glycerin binder 
may be applied to fibrous cellulose. The glycerin binder may be allowed to 
dry overnight, and the fibers then mechanically agitated in the presence 
of superabsorbent particles to reactivate the glycerin binder and bind the 
particles to the fibers. Mechanical agitation may take place, for example, 
in a defiberizer where a sheet or mat of glycerin treated cellulose fibers 
are defiberized while being intimately mixed with SAP that is bound to the 
fibers by the mechanical agitation. 
Binder Activation Examples 
Binder reactivation in the present invention allows binder to be added to 
fibers either before or after particles are added to the fibers. The 
binder is subsequently activated by addition of liquid, heat, or 
agitation, and particles are bound to the fibers. The particles may be 
added to the fibers either before binder activation, after binder 
activation, or simultaneous with activation. If SAP is to be added to 
cellulose fibers, for example, the binder may be applied to a pulp sheet 
during its manufacture with the pulp sheet being subsequently fiberized, 
for example at a user's plant. A liquid such as water may be added to the 
pulp before or after fiberization, and SAP may be added before or after 
water addition, or simultaneously with the water. If SAP is added after 
water addition, the SAP should be applied to the fibers prior to complete 
evaporation of the added water from the fibers. 
Activation can be of all the fibers, or only portions of the fibers, such 
as target zones or portions of the mat where particulate binding is 
desired. The particles may then be added to the mat and adhered to the 
target zones of the mat which have been activated. In some embodiments, 
the binder is applied as a solid and heated during a later processing 
stage to activate the binder by softening it such that it binds the 
particles to the fibers. The particles may be added in a pattern 
corresponding to a desired distribution of particles in the fibrous 
material. Most commonly, however, activation is accomplished by moistening 
a targeted area of the product into which an inactive (dry or dried) 
binder has already been introduced. 
In yet other embodiments, the binder is applied to the fiber mat and then 
activated by subsequently applying kinetic energy to the fibers. Neat 
polypropylene glycol (MW 2000) binder, for example, may be sprayed on the 
fiber mat and allowed to air dry. Desired particles may then be added to 
the fibers (e.g. at a user's plant) as the fibers are mechanically 
agitated in a blender or defiberizer to kinetically activate the binder 
and bind the particles to the fibers. For kinetic activation, the binder 
may be added as a liquid or a solid to the fibers. In the case of liquid 
addition, the liquid is allowed to air dry, and then reactivated by 
mechanically agitating the fibers and binder. In the case of solid binder 
addition, the binder is applied as a solid, and then moistened (for 
example, to a total fiber moisture content of about 7%) and then 
mechanically agitated. 
Activation of the binder may be performed prior to adding the particles, 
subsequent to adding the partices, or simultaneously with addition of the 
particles. Once the binder is activated, it adheres a substantial portion 
of the particles to the fibers, wherein "a substantial portion" refers to 
about half of the particles present in the fibers, at least where the 
particles are not added in excess. 
In embodiments in which the binder is applied to the fibers as a solid, the 
activating step can comprise applying a liquid to the fibers after the 
binder has been applied to the fibers. 
The activating step is preferably performed after the curing step is 
complete, if a curing step is to be performed. 
The following example will illustrate several specific applications of the 
activation process, and are not intended to limit the invention to the 
disclosed methods. 
EXAMPLE XX 
The method of Example I above could be modified such that the SAP is not 
added until after the web is heated to 140.degree. C. A solid polyethylene 
glycol/polypropylene glycol copolymer could be substituted for the PRG of 
Example I, and it would melt well below 140.degree. C., and in its liquid 
form bind the SAP to the fibers. The SAP could be applied randomly across 
the heated product, or applied specifically to a targeted zone of the 
product where enhanced absorbency is specifically desired. 
EXAMPLE XXI 
A southern kraft pulp sheet could be immersed or sprayed on the pulp sheet 
manufacturing line with a 65% solution of polyacrylic acid diluted with 
deionized water. The sheet may then be misted with water at a remote 
location to raise its moisture content to, for example, 17-20% as it is 
fed into a hammermill. Polyacrylate hydrogel particles of FAVOR 800 
supplied by Stockhausen may simultaneously be added to the mill by a screw 
feed device, mixed with the fluff, shunted to an M & J airlay forming 
machine and airlaid to form a web containing bound SAP throughout the web, 
i.e., without being confined to a surface of the web. Mixing SAP 
throughout the fluff helps produce a product in which SAP is homogeneously 
or randomly distributed, which diminishes problems of gel blocking. 
EXAMPLE XXII 
A KittyHawk pulp sheet (from the Weyerhaeuser Co., containing 22% synthetic 
fiber) on a pulp sheet manufacturing line may be immersed into or sprayed 
with a 10% by weight solution of polyglycine. The sheet may then be fed 
into a hammermill at a remote location defiberized, shunted to an airlay 
line, and airlaid into a web. As the web emerges, circular target zones of 
the web may be misted with water from a spray bottle to raise the moisture 
content to 17-21% in the target zone. Five gram aliquots of starch graft 
polyacrylate hydrogel fines (IM 1000F; supplied by Hoechst-Celanese of 
Portsmouth, Va.) may be subsequently sifted onto the target zones to yield 
a web with SAP bound in target zones. The SAP does not form a confluent 
layer, but is instead present in particulate form on and below the surface 
of the web. 
EXAMPLE XXIII 
A southern bleached kraft fluff pulp sheet may be sprayed with a 50% 
solution of polyglycine and dried. The sheet may be fed to a hammermill 
with liquid added to bring the moisture content to 17-21%. Starch graft 
polyacrylate hydrogel fines (IM 10000F; supplied by Hoechst-Celanese of 
Portsmouth, Va.) may simultaneously be added to the mill by a screw feed 
device as the sheet is fed into the hammermill, mixed with the fluff, 
shunted to an airlay forming machine and airlaid to form a web. The fines 
would be intimately mixed with the fluff in the fibermill and bound to the 
fibers by the polyglycine binder to produce a web with particles 
distributed throughout its width, and not restricted to a superficial 
surface. 
EXAMPLE XXIV 
A southern bleached kraft pulp sheet on a pulp manufacturing line may be 
immersed into or sprayed with a 2% by mass solution of ascorbic acid 
(supplied as a dry powder by Aldrich Chemical Co. of Milwaukee, Wis.). The 
sheet may be dried and sufficient ascorbic acid may be added to provide 7% 
by weight ascorbic acid. The sheet may be misted with water at a remote 
location from the line to raise its moisture content to 17-20% as it is 
fed into a hammermill. Misting with water reactivates the binder prior to 
addition of superabsorbent particles (SAP). Starch graft polyacrylate 
hydrogel fines (IM 1000F supplied by Hoechst-Celanese of Portsmouth, Va.) 
may then be added as SAP to the hammermill by a screw feed device, mixed 
with the fluff, shunted to an airlay forming machine and airlaid to form a 
web. The resulting web would contain 20% SAP attached to the fibers by the 
binder. 
EXAMPLE XXV 
A KittyHawk pulp sheet on a pulp sheet manufacturing line may be immersed 
into or sprayed with a 10% by weight solution of urea (supplied by Aldrich 
of Milwaukee, Wis.). The sheet may be dried. Sufficient urea may be added 
to provide 30% by weight urea. The sheet may be fed (see FIG. 2) into a 
hammermill, defiberized, shunted to an airlay line, and airlaid into a 
web. As the web emerges, the binder in the dried web may be reactivated by 
misting target zones of the web with deionized water in a circular pattern 
from a sprayer to raise the moisture content of the web at the target 
zones to 17-21%. Five gram aliquots of polyacrylate hydrogel (FAVOR 800 
supplied by Stockhausen of Greensboro, N.C.) may subsequently be sifted 
onto each reactivated target zone. The web that results would contain 
target zones with 5 grams of SAP attached to the fibers in each target 
zone. Alternative spray patterns could be provided by selecting spray 
heads or different control devices that mist different patterns. 
Thermoplastic Binders 
An auxiliary binder may also be used to help bind fibers to each other 
above the melting point of the auxiliary binder. The auxiliary binder may 
be a solid thermoplastic material that is applied to the fibers and 
softened by elevating the temperature during the binding step to above the 
softening temperature of the auxiliary binder. The auxiliary binder is 
thereby temporarily softened, rendered more fluid (which for purposes of 
convenience may be referred to as auxiliary binder melting) and 
subsequently resolidified as the temperature cools, which 
thermoplastically binds the fibers to each other, and the particles to the 
fibers. The auxiliary binder may also contain a hydrogen bonding 
functionality that hydrogen bonds the particles to the fiber. Examples of 
auxiliary binders that are thermoplastic and also contain hydrogen bonding 
groups include ethylene vinyl alcohol, polyvinyl acetate, acrylates, 
polycarbonates, polyesters and polyamides. Further information about the 
use of such auxiliary binders can be found in U.S. Pat. No. 5,057,166. 
The auxiliary or second binder can be added to the fibers, either before or 
after a first binder, to help bind the fibers to each other and provide 
additional binding between the fibers and particles. A suitable second 
binder would be a thermoplastic or thermosetting binder. In the case of 
thermoplastic polymers, the polymers may be a material which remains 
permanently thermoplastic. Alternatively, such polymers may be a material 
which is partially or fully crosslinkable, with or without an external 
catalyst, into a thermosetting type polymer. As a few specific examples, 
suitable thermoplastic binders can be made of the following materials: 
ethylene vinyl alcohol 
polyvinyl acetate 
acrylic 
polyvinyl acetate acrylate 
acrylates 
polyvinyl dichloride 
ethylene vinyl acetate 
ethylene vinyl chloride 
polyvinyl chloride 
styrene 
styrene acrylate 
styrene/butadiene 
styrene/acrylonitrile 
butadiene/acrylonitrile 
acrylonitrile/butadiene/styrene 
ethylene acrylic acid 
polyethylene 
urethanes 
polycarbonate 
polyphenylene oxide 
polypropylene 
polyesters 
polyimides 
In addition, a few specific examples of thermoset binders include those 
made of the following materials: 
epoxy 
phenolic 
bismaleimide 
polyimide 
melamine/formaldehyde 
polyester 
urethanes 
urea 
urea/formaldehyde 
More than one of these materials may be used to treat the fibers. For 
example, a first coating or sheath of a thermoset material may be used 
followed by a second coating of a thermoplastic material. The 
superabsorbent particles or other particles are then typically adhered to 
the outer binder material. During subsequent use of the fibers to make 
products, the thermoplastic material may be heated to its softening or 
tack temperature without raising the thermoset material to its curing 
temperature. The remaining thermoset material permits subsequent heating 
of the fibers to cure the thermoset material during further processing. 
Alternatively, the thermoset material may be cured at the same time the 
thermoplastic material is heated by heating the fibers to the curing 
temperature of the thermoset with the thermoplastic material also being 
heated to its tack temperature. 
Certain types of binders enhance the fire resistance of the treated fibers, 
and thereby products made from these fibers. For example, polyvinyl 
chloride, polyvinyl dichloride, ethylene vinyl chloride and phenolic are 
fire retardant. 
Surfactants may also be included in the liquid binder as desired. Other 
materials may also be mixed with the liquid binder to impart desired 
characteristics to the treated fibers. For example, particulate material, 
such as pigments, may also be included in the binder for application to 
the fibers. 
EXAMPLE XXVI 
As previously described, an auxiliary binder can be used in addition to the 
polymeric binders of the present invention. A 3210 gram amount of southern 
bleached kraft binder (NB-416, supplied by Weyerhaeuser Company) is air 
entrained in a blenderlike mixing device and sprayed with 2128 grams of a 
polyvinyl acetate latex (PN-3666H, supplied by H.B. Fuller of Minneapolis, 
Minn.). This binder may also be applied to the kraft fluff in mat form on 
a pulp sheet manufacturing line. While still mixing, 4073 grams of a water 
swellable polyacrylate hydrogel (IM 1000-60, supplied by Hoechst-Celanese 
of Portsmouth, Va.) is added and the resulting mixture is then sprayed 
with 1160 grams of a 50% solution of polypropylene glycol (supplied by 
Union Carbide of Danbury, Conn.). The blender is then stopped and the 
mixture was shunted into a flash tube dryer. The dried product is then 
airlaid as a 16 inch wide web on a Danweb airlay machine, pressed to a 
density of approximately 0.15 g/cc, and thermobonded at 140.degree. C. for 
thirty seconds. The resulting web would have 40% bound SAP and improved 
tensile strength (as compared to untreated fluff With SAP). 
Application of Binder 
The binders of the present invention can be added to the fibers in any 
convenient manner. One such procedure is to spray the binder or binders on 
a web of the fibers that is conveyed past a sprayer on the pulp sheet 
manufacturing line. Another procedure is to roll coat the web with the 
binder. Relatively high viscosity binders, such as glycerin, are easier to 
roll coat than to spray. The binder would be added downstream in the 
process from the headbox because binder would be wasted if added to the 
slurry in the headbox, or for that matter, prior to the initial dewatering 
zone of the process at the wire. For solid binders, blending of the fiber 
and binder may also be accomplished by sprinkling onto or otherwise 
comingling the binders with the fibers. The fibers may also be sprayed or 
immersed in the binder, or binder particles may be applied thereto. These 
fibers can, while still wet in the case of a liquid binder or following 
reactivation of a liquid or solid, be combined with the particles. The 
fibers can also be allowed to dry for later reactivation with a 
reactivation liquid and combined with the particles at that time. 
Particles may be added from conventional volumetric feeders in a 
hammermill or from injectors on a pulp sheet manufacturing line such as a 
paper making line. 
Composite Absorbent Product 
In accordance with the present invention, absorbent structures may be made 
from the fibers, with the bound particulates, in accordance with the 
present invention. These articles may be composite structures (e.g., made 
of plural materials). For example, the articles may have a core of plural 
types of fibers, or fiber layers, with or without covering materials. 
These products are capable of absorbing significant quantities of water 
and other fluids, such as urine and body fluids. Such products include, 
but are not limited to, disposable diapers, sanitary napkins, incontinent 
pads, towels and the like. 
As best shown in FIGS. 3 and 4, an absorbent towel 200 may have a core 216 
with a cover sheet 232 and a backing sheet 234. The core 216 may be 
comprised of fibers with the binders of the present invention and 
particulate materials, such as superabsorbent particles secured to the 
fibers by the binder. The fibers that contain the binder may be blended 
with other fibers as well in the core. Cover sheet 232 is made of any 
suitable material, including liquid permeable, nonwoven materials, which 
will readily permit the passage of liquid through the cover sheet to the 
absorbent pad 216. The following list of liquid permeable materials is 
provided by way of example only: nonwoven sheets of polypropylene, rayon, 
nylon fibers, polyester fibers, and blends thereof. A specifically 
preferred cover sheet material for wipes is a 70% rayon/30% polyester 
blend having a basis weight of 21.5 grams/m.sup.2, available from the 
Scott Paper Company. 
The backing sheet 234 may be, but is not necessarily, made of a liquid 
impermeable material, including but not limited to, films of polyethylene, 
polypropylene and polyester and blends thereof along with nylon and 
polyvinyl chloride films, A specifically preferred backing sheet material 
is a polyethylene film from Dow Chemical Company. 
FIGS. 3-4 illustrate an absorbent pad structure which may be formed from 
fibers of the present invention, whether or not they are blended with 
other fibers. FIGS. 1 and 2 represent an absorbent pad having a heat 
embossed screen pattern. Pads having no pattern may also be used. A pad 
having a cover sheet and a backing sheet may be formed, for example, by 
placing a square fiber piece cut from the sheet onto a corresponding 
precut backing sheet. A corresponding precut cover sheet is placed over 
the top of the fiber on the backing sheet. This assembly may then be 
adhesively bonded. 
With reference to FIGS. 5-8, absorbent structures in the form of bandages 
or dressings are shown. In FIGS. 5 and 6, a bandage 410 for application to 
a wound to absorb blood and other bodily fluids is shown. An absorbent pad 
216 (FIG. 6) is securely mounted to an exterior or pad mounting surface 
414 of a backing strip 416. Any suitable mounting or securing means may be 
used to affix pad 216 to the surface 414 of the strip 416. However, it is 
preferable for surface 414 to be coated with an adhesive so that the pad 
216 may be adhesively mounted in place. An exemplary adhesive is ethylene 
vinyl acetate adhesive. It is also desirable for the overall surface 418 
of backing strip 416 to be coated with a conventional adhesive. Surface 
418 is the surface which is affixed to the area of the skin surrounding 
the wound. Conventional "peel-back" tabs may be used to protect the 
adhesive coating and pad 216 until the bandage is to be applied. This type 
of backing strip is well known in the art. 
The backing strip 416 may be of any known flexible material suitable for 
application to the skin. It is preferable for the strip 416 to be of a 
material which is impermeable to the passage of liquid so that fluid from 
a wound is contained by the bandage. However, the strip 416 may be 
apertured or otherwise breathable to permit air to reach the wound to 
promote the healing process. A specific example of a suitable backing 
strip 416 is a polyethylene film. 
As in the other structures described, a variety of combinations of 
antimicrobials and other particles may be used in such a bandage. Again, 
however, the particles are adhered securely in place when the particles 
have a hydrogen bonding or a coordinate covalent bonding functionality, 
the fibers to which these particles are bound have a hydrogen bonding 
functionality, and wherein the binder is selected from the group 
consisting of a polypropylene glycol, a polypropylene glycol/polyethylene 
glycol copolymer, polyacrylic acid, a polyamide, or a polyamine and the 
polymeric binder has a hydrogen bonding or a coordinate covalent bond 
forming functionality on each repeating unit of the binder. Two different 
particles, such as antimicrobials in particulate form, may be adhered to 
the same fiber. In the alternative, each different type of antimicrobial 
particle or other particle may be adhered separately to different fibers. 
Also, blends of fibers may be included in absorbent structures such as pad 
216. For example, these blends may include fibers with adhered 
antimicrobial (one or more antimicrobials) particles and adhered 
superabsorbent particles; fibers with one or more antimicrobial particles 
without superabsorbent particles blended with fibers having adhered 
superabsorbent particles with or without antimicrobial particles; and 
combinations of such fibers with untreated fibers and/or binder coated 
fibers without superabsorbent particles or antimicrobial particles. In 
addition, other particles, such as anticoagulants or hemostatics may be 
attached to the fibers. 
The absorbent pad 216 of bandage 410 may also include a cover sheet 420. 
Cover sheet 420 is typically made of any suitable material which will 
readily permit the passage of liquid through the cover sheet to the 
absorbent pad 216, such as nonwoven fiber webs of fibers such as, for 
example, rayon, nylon, polyester, propylene and blends thereof. One 
specifically preferred cover sheet material is a 70 percent rayon/30 
percent polyester blend having a basis weight of 18 g/m.sup.2 from Scott 
Paper Company. 
The dressing 216 shown in FIGS. 7 and 8 illustrates fibers 421 placed 
within an enclosure 422. Enclosure 422 has at least one liquid permeable 
surface through which fluid or liquid may pass to be absorbed by the 
fibers. The enclosure containing the loose fibers may be secured to the 
skin using adhesive tape, for example. Again, the fibers 421 preferably 
include antimicrobial particles attached to at least some of the fibers. 
FIGS. 9 and 10 illustrate fibers of the present invention incorporated into 
a feminine hygiene appliance such as a feminine pad or tampon. In this 
case, the feminine pad 510 is illustrated as having a cover sheet 512. The 
loose fibers having adhered antimicrobial particles, which may 
alternatively be in the form of a pad, are included within the interior of 
the feminine appliance as indicated at 216 in FIG. 4. The cover 512 is 
preferably liquid permeable so that bodily fluids may reach the interior 
of the pad for purposes of absorption. The cover 512 may be wrapped around 
the core 216 (as indicated by edges 514, 515). A backing sheet 516, 
preferably of a liquid impermeable material, may be adhered to the edges 
514, 515 at the underside of the core. An adhesive containing strip, such 
as indicated at 520, which may have a peelable or removable cover, may be 
mounted to the backing sheet 516 for use in adhering the pad, for example 
to a user's undergarment, during use. 
FIGS. 11 and 12 illustrate a conventional disposable diaper 550 with a core 
552 which is comprised of fibers of the present invention with adhered 
superabsorbent particulate materials. These particulate materials may be 
confined to a target zone (for example, the front portion of a diaper 
indicated at 556) or of a heavier concentration in the target zone. This 
can be accomplished by airlaying fibers of the present invention in such a 
zone. Also, the core may be reactivated by melting the binder or 
moistening the target zone with water. The superabsorbent particles may be 
sprinkled on or otherwise applied to this wetted zone. As the zone dries, 
the particles are adhered in place. 
Densification 
The products such as described above, as well as webs of the fibers of the 
present invention, can also be densified by external application of 
pressure to the web. The web of Example II, for instance, could be 
densified by passing it through a set of calendar rolls set at 60 and 90 
pli (pounds per linear inch, as in a calendar press) respectively to yield 
sheets with increased densities. Densification may alternatively be 
provided by compaction rolls or presses. The present inventors have found 
that densification is facilitated in the products treated with the 
polymeric organic binders of the present invention. Products that are 
treated with the binders of the present invention require less heat and 
pressure than untreated fibers to densify to a given density. 
Densification is preferably performed to produce a product that has a 
density of about 0.1 to 0.7 g/cc, more preferably 0.1 to 0.3 g/cc. 
An example of densification using some of the binders of the present 
invention is given below: 
EXAMPLE XXVII 
Any of the products of the present invention can be formed into 550 
gram/square meter sheets, six inches in diameter, in a laboratory 
padformer. Those pads are then passed through a set of calendar rolls set 
at 60 and 90 pli, respectively to yield sheets with densities of 0.3 and 
0.5 g/cc. 
EXAMPLE XXVIII 
CCF pulp (Weyerhaeuser Company), containing 40% SAP by weight, was coated 
with 12.5% glycerin, air laid, and densified to 0.3 g/cc. Densification to 
this product density required 60 psi for the glycerin coated fibers. In 
comparison, NB-316 fibers that were not coated with glycerin required 
densification at 200 psi to reach a 0.3 g/cc density. Absorbent capacity 
was higher for the coated fibers. This comparison indicates that the 
fibers with glycerin bound SAP were more easily densified than the fibers 
that were not coated with the binder. 
EXAMPLE XXIX 
A 50 gram amount of polypropylene glycol is diluted with 50 grams deionized 
water. The resulting solution is sprayed on 321 grams of an intrafiber 
crosslinked cellulose fluff (HBA from Weyerhaeuser Company of Tacoma, 
Wash.) that was air entrained in a blender like mixing device. While the 
HBA fiber is still damp, 438 grams of IM 1000F (supplied by 
Hoechst-Celanese, of Portsmouth, Va.) is added to the mixture. The 
resultant mixture is then vacuumed from the blender and spread on a 
counter to dry overnight. Then 550 gram/square meter handsheets, six 
inches in diameter, are made in a laboratory padformer. Those pads are 
then pressed at 2000 and 3000 psi (or 60 and 90 pli in a calendar roll), 
respectively, to yield sheets with densities of 0.3 and 0.5 g/cc. 
Alternatively, pads of untreated HBA blended with 45% IM 1000F would 
require heating to 100.degree. C. and pressures between 8,000 and 11,000 
psi to produce pads of similar densities. The same results are expected if 
the binder is applied to HBA fiber while making this fiber into a sheet on 
a pulp sheet manufacturing line. 
Particulate Binding 
FIG. 13 shows an isolated, enlarged cellulose fiber 600 with SAP particles 
602 bound to it by a binder of the present invention. This drawing 
illustrates an example of the SAP retaining its discrete particulate form 
following binding to the fibers. Some particle to particle fusion may 
occur in accordance with this invention, but maintenance of a discrete 
particulate form excludes formation of a completely confluent film in 
which the particles lose their particulate identity. Such a confluent film 
produces gel blocking that interferes with efficient liquid absorption 
into the fibers. 
The shown fiber 600 is elongated, and has an aspect ratio (ratio of length 
to width) of about 10:1. 
FIG. 14 shows the particles 602 distributed substantially uniformly 
throughout the depth 604 of a pad 606. The particles are also shown 
adhering to all the surfaces of the pad. Particles may be distributed in 
any desired pattern throughout the pad in accordance with this invention, 
and need not necessarily adhere to all surfaces or be distributed 
throughout the volume of the mat, or distributed uniformly. 
Electron Photomicrographs 
An electron photomicrograph of superabsorbent particles (SAP) bound to 
cellulose fibers with an ascorbic acid binder is shown in FIG. 15. The SAP 
is at the left margin of the photograph, and is fused to the fiber which 
occupies the central portion of the photomicrograph. The particle is seen 
to be fused to the fiber, and the fiber has undergone some shear damage 
that resulted in a fracture of the fiber. It is significant that the fiber 
has experienced shear damage while the particle has remained fused to the 
fiber, because this indicates that the particle-fiber bond formed by the 
ascorbic acid is very strong and resilient, resisting mechanical 
disruption. 
FIG. 16A-D shows several electron photomicrographs that illustrate 
individual particles bound to fibers with a lactose binder. FIG. 16C, for 
example, shows that SAP retains its individual particulate form when 
adhered to the fiber with a lactose binder. The particles do not form a 
fused confluent mass without particulate identity. 
Fiber Mixtures 
The fibers of the present invention, such as fiber 600, can be mixed with 
other types of fibers, such as that disclosed in U.S. Pat. No. 5,057,166 
which is incorporated herein by reference in its entirety. The latex 
coated fibers of that patent can be mixed with the fibers of the present 
invention to produce an absorbent product that has characteristics of both 
types of fibers. 
Having illustrated and described the principles of the invention in many 
preferred embodiments, it should be apparent to those skilled in the art 
that the invention can be modified in arrangement and detail without 
departing from such principles. We claim all modifications coming within 
the spirit and scope of the following claims.