Method of forming highly absorbent fibrous webs and resulting products

Webs are formed by mixing chemically modified cellulose fibers in a carrier and dewatering to form a mixture of gel-like consistency having a minimum of external water wherein the fibers have not lost their individual structures. This mixture is sprayed or injected into a gas stream of volume and velocity such that the individual fibers are separated. These fibers are collected into highly-absorbent webs having varying structures. Due to the rapid separation of fibers and subsequent drying, reduced interfiber hydrogen bonding takes place resulting in good tactile properties such as softness and drape. By controlling the direction and velocity of the fibers, webs can be produced having structures ranging from very dense mats to loose, fluffy batt-like products. The webs of the invention possess high absorbency, good wicking, and strength sufficient for handling. They may be used as components for wipers, surgical sponges, and personal care products such as sanitary napkins, tampons, and disposable diapers.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to highly-absorbent webs and methods of making them. 
More specifically it pertains to an improved process of forming such webs 
of chemically modified cellulose fibers that are not only highly-absorbent 
but have excellent tactile properties such as softness and drape. Such 
webs have adequate strength and controlled wicking properties making them 
particularly suitable as a component of products where it is desirable to 
draw liquids away from the surface and concentrate them in a particular 
area or location. Such applications include, by way of example and not 
limitation, disposable diapers, sanitary napkins, tampons, wipers, 
surgical sponges, and the like. 
2. Description of the Prior Art 
The chemical modification of cellulose to increase its absorbency has been 
previously described and can be considered in a broad sense to fall into 
three major classifications in terms of methods: 
(a) chemical substitution, etherization or esterification; 
(b) chemical substitution plus crosslinking; and 
(c) polymeric grafting. 
For example, U.S. Pat. No. 3,670,679 to Mitchell is directed to absorbent 
fibers formed by extruding solutions such as those prepared from a 
hydroxyalkyl cellulose. As examples of category "(a)" above, Bernardin 
U.S. Pat. Nos. 3,658,790 and 3,691,154 disclose absorbent fibers in 
batt-like mats formed from phosphorylated cellulose or its acid form and 
products incorporating them. An example of category "(b)" above is 
disclosed in U.S. Pat. No. 3,589,364 to Dean et al which discloses 
absorbent structures including crosslinked fibers of carboxymethyl 
cellulose and products made therefrom. Category "(c)" above is exemplified 
by the formation of acrylonitrile grafted cellulose absorbent fibers and 
products as disclosed in U.S. Pat. Nos. 3,194,727 to Adams et al; 
3,455,643 to Gruber et al; 3,065,041 to Sven; and 3,046,078 to Salsbury. 
U.S. Pat. No. 3,997,647 to Lassen, assigned to the assignee of the present 
invention, discloses an extrusion process for forming highly-absorbent 
filamentary webs from gel-like extrudates. These extrudates include 
swollen fibers of chemically modified cellulose which have not lost their 
individual identities. By extrusion the fibers are aligned and interbonded 
to form filaments having channels and capillaries which provide high 
absorbency and excellent wicking properties. However, the interfiber 
bonding, believed to be hydrogen bonding, produced by the method of the 
Lassen patent tends to produce a harsh, stiff web unless solvent drying or 
other special drying means are employed. Solvent drying is, of course, 
relatively expensive in terms of operating costs as well as capital 
investment required for recovery equipment. In addition, the use of 
solvents requires precautions to be taken against ecological, safety and 
health hazards. 
SUMMARY OF THE INVENTION 
The present invention is directed to an improved method for forming soft, 
drapable, highly-absorbent webs of chemically modified fibers without the 
need for solvent drying. In accordance with the present invention the 
chemically modified cellulose fibers are mixed with the imbibed solvent 
and dewatered to form a gel-like mixture having a minimum of external 
water that is sprayed or injected into a gas stream, usually air. The 
velocity and direction of the air stream are controlled so that the 
individual fibers are separated and can be collected fo form an open, 
lightly bonded web. In this manner interfiber bonding is, in the 
subsequent drying process, minimized and a soft, drapable web results. The 
density of the web may be controlled by external water content and, by 
varying the degree of fiber drying and the fiber velocity. Webs may be 
produced having a wide variety of structures from close, compact fibers to 
loose, open webs and a wide range of properties including absorbency and 
wicking rates. Increased drying rates may be obtained by high energy 
applications, such as heated air or microwaves. 
Preferred forms of chemically modified fibers include phosphorylated 
cellulose, crosslinked carboxymethyl cellulose, and acrylonitrile grafted 
cellulose. These fibers may be used alone to form highly absorbent webs or 
to enhance the properties of other fibrous webs by admixture therewith. 
Formed structures may be produced by directing the air stream onto molds, 
and laminates with reinforcing scrims or other films or fabrics can be 
constructed by appropriate application of the fibrous air stream in 
accordance with the invention. 
The webs of the present invention find particular applicability in 
improving the performance of absorbent products such as wipers, surgical 
sponges, sanitary napkins, tampons, disposable diapers, and the like.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
While the invention will be described in connection with preferred 
embodiments, it will be understood that it is not intended to limit the 
invention to those embodiments. On the contrary, it is intended to cover 
all alternatives, modifications, and equivalents as may be included within 
the spirit and scope of the invention as defined by the appended claims. 
In order to provide a complete understanding of the present invention, the 
intended meaning of certain terms used within the description will be 
stated: 
"Chemically modified cellulose" refers to cellulosic materials, the 
composition and/or structures of which have been transformed by 
derivatization in such a way as to induce a significant increase in their 
hydrophilic character. Examples of derivatization processes include 
carboxylation, phosphorylation, and grafting of acrylic segments. The 
present invention is not concerned with cellulosic solutions or other 
cellulosic compositions in which the individual fibers or other basic 
structures, themselves, lose their identity; 
"Highly absorbent" as used herein indicates that the modified cellulose 
will absorb significantly more of the liquid being used than will 
unmodified cellulose under the same conditions. It is recognized that the 
particular absorbency rating will depend not only on the specific material 
tested but on the conditions under which the measurements are made. For 
example, the absorbency of a material under pressure may be quite 
different from its absorbency in an uncompressed state; 
"Fibers" is used herein in reference to the fibers of chemically modified 
cellulose that are mixed with a swelling solvent to form the mixture used 
in the process of the invention; for cost considerations the fibers 
generally have a length preferably of about papermaking fiber size, e.g., 
about 0.02 to 0.2 inches and a diameter preferably about 0.002 to 0.003 
inches although larger fibers such as cotton linters may be used. 
"Water retention" is defined in U.S. Pat. No. 3,670,069 to Mitchell et al, 
at column 6, lines 51 to 70, as the moisture remaining in and on a rewet 
fiber specimen after it has been centrifuged 10 minutes at an acceleration 
of 1000 times normal gravitational acceleration. For most practical 
purposes, this will be substantially equivalent to the "Fiber Saturation 
Point" as later defined; 
"Free standing saline absorbency" is a measure of the normal saline 
capacity under zero load. It is determined by first placing a preweighed 
sample in 1 normal saline solution for 30 seconds. The sample is then 
removed with a spatula, allowed to drip for 30 seconds and weighed again 
wet. The saline picked up divided by the original dry sample weight is the 
free standing saline absorbency; 
"Wicking" is determined by placing a sample over concentric conductive 
rings which are fixed 1-1/16 inches apart radially. Current is applied and 
liquid added to the center of the rings at a rate of 240 milliliters per 
minute. When the liquid reaches the outer ring, the circuit is completed, 
and this time is reported as the wicking rate. This test is further 
described in the above-referenced Lassen patent; 
"Tensile" was measured using a Model TM-M Instron Tensile Tester equipped 
with a "B" cell and operated on a sample two inches wide with a jaw 
separation of 1/4 inch, a crosshead speed of 1/2 inch per minute, a full 
scale load range of from 1000 grams to 10,000 grams and a chart speed of 5 
centimeters per minute. Wet tensile results were obtained in the same 
manner on samples soaked for 30 seconds in 1 normal saline prior to 
testing; 
##EQU1## 
"Extrudate" refers to a mass of extrudable, hydrophilic, fibrous cellulosic 
material which has been swollen by the imbibition of a solvent to such an 
extent as to plasticize the individual cellulosic fibers and render them 
independently mobile. In all cases, external water content is preferably 
minimized and doses not exceed a range of .+-.5 g/g fiber of the fiber 
saturation point. 
"Dry fiber consistency" as used herein means weight percent of dry fibrous 
material. Dry weight is determined by drying samples for 2 hours at 
105.degree. C. in any of the compositions or mixtures recited. All 
percentages are by weight unless otherwise noted. 
In the process of the present invention as illustrated in FIG. 1, the first 
step is to provide chemically modified cellulose fibers. While 
commercially available products such as "Buckeye" carboxylated cellulose 
from Buckeye Corporation, for example, with modification, may be useful in 
this process, the diversity of results which may be obtained is increased 
by beginning with pulp or wood fibers and treating them by 
phosphorylation, carboxylation, or acrylonitrile substitution as set forth 
in greater detail below. 
One of the preferred types of chemically modified fibers for use in the 
present invention is phosphorylated pulp fibers. To produce such fibers 
the following process may be used although it will be recognized by those 
skilled in this art that variations and modifications of this 
phosphorylation process may also be utilized. 
The particular pulp selected to be phosphorylated is not critical; for 
example, Northern spruce pulp is readily available, generally low in cost, 
and produces very acceptable results. The pulp may be used in dry sheet 
form as supplied by pulp manufacturers. The sheets are preferably immersed 
for about 15 to 45 minutes in a reagent composition containing about 50% 
urea and about 32% phosphoric acid, for example. The purpose of this 
immersion is to distribute those reagents evenly throughout the pulp, and 
it will be apparent that the time and reagent concentration may be varied 
within wide ranges depending upon factors such as speed of operation and 
desired degree of phosphorylation. For example, to obtain 6% or better 
phosphorylation, a pickup of approximately 200% to 300% of the above 
reagent solution should be achieved. It is preferred to maintain the 
treating bath at a somewhat elevated temperature, for example, 60.degree. 
C. to 70.degree. C. to facilitate the penetration of the pulp boards. 
After immersion, the pulp is cured at a temperature within the range of 
from about 125.degree. C. to about 195.degree. C. and preferably 
180.degree. C. to 190.degree. C. Since the purpose of heating is to make 
energy available for the phosphorylation reaction, the amount of time 
required for this step depends upon the form and intensity of the applied 
energy as well as the quantity of pulp and the concentration of reagent 
therein. For example, the curing of wood pulp in an oven at 180.degree. C. 
is preferably terminated when the pulp has turned light brown in color. On 
the other hand, the curing may be greatly accelerated by the use of a 
microwave over in which case the temperature of the pulp provides an 
indication of its cure state, and the curing is terminated when the 
temperature of the pulp rises after having first maintained a generally 
constant level. The use of microwaves also generally results in somewhat 
softer webs with very little of the discoloration which results from 
standard oven curing and is preferred for these reasons as well as reduced 
cure time. 
After curing, the phosphorylated pulp is washed to remove excess reagents. 
It is then hydrolyzed with a dilute acid, preferably hydrochloric acid (2% 
to 5% by weight, for example). In some cases, depending upon the pulp 
used, hard fiber clumps may be present, and mild agitation may be used to 
break or soften them. Hydrolysis at a temperature of about 50.degree. C. 
to 90.degree. C. and preferably 60.degree. C. to 70.degree. C. for 
one-half hour to two hours is usually sufficient, after with the 
phosphorylated pulp is washed again with water. 
Ther resulting hydrolyzed phosphorylated pulp is in its acid form and next 
is converted to its salt form by contact with an excess of base, for 
example, sodium carbonate (3 to 6% by weight). Preferably this contact 
takes place under conditions of agitation for at least about 15 minutes at 
room temperature. After washing to remove excess base, the phosphorylated 
pulp is in its preferred chemically modified form. 
With phosphorylated pulp or other types of chemically modified cellulose, 
when it is desired to produce a web with high wicking rates, containment 
capacity, or the ability to absorb and retain large quantities of liquid, 
the next step is preferably refining of the chemically modified pulp. 
While it is not desired that the invention be limited to any particular 
theory, it is believed that the refining breaks away the outer shell, or 
primary wall of the fiber thus allowing it to expand and absorb more 
liquid. 
When refining has been completed, the individual fibers, while retaining 
their individual identities, are in a highly swollen, gel-like form having 
a concentration preferably in the range of from 5% to 20%. At this point, 
particularly when physiological effects are to be considered, the pH of 
the fibers is adjusted to within the range of from about 4 to 9 and 
preferably 5.5 to 8 by the addition of dilute acid or base as needed. It 
will be recognized that this step may be carried out at a different time 
in the overall process or omitted entirely when dermatological factors 
need not be considered. 
As thus produced, the phosphorylated pulp mixture extrudate is sometimes 
referred to hereinafter as "standard phosphorylated extrudate". 
The dewatering step is important since it is preferred that most of the 
external water be removed so that only .+-.5 g/g of fiber of the fiber 
saturation point remains prior to spraying the mixture. It will be 
recognized that the actual consistency of the mixture with unbound water 
removed will vary with the type of chemical fiber modification and the 
prior processing history of the pulp. 
In all cases, however, as shown in FIG. 27, it is important that dewatering 
take place to the extent that external water remaining is within a range 
.+-.5 grams per gram of fiber and preferably .+-.3 grams per gram of fiber 
of the fiber saturation point as discussed in greater detail below and 
that the total water remaining be at least 4 grams per gram of fiber and 
preferably within a range .+-.3 grams per gram of fiber of the fiber 
saturation point. External water is defined as that which is removable by 
centrifuging for 30 minutes at an acceleration of 1000 times normal 
gravitational acceleration. Thus, the extrudates of the present invention 
do not embrace slurries or other compositions containing substantial 
amounts of free water such as are used in conventional papermaking 
techniques. 
Turning also now to FIG. 2, it can be seen that the extrudate 10 is 
injected by pump 11 through spray nozzle 12 in the forming section which 
facilitates the separation of the extrudate into individual fibers 16. A 
stream 14 of separated, air-borne fibers 16 is sprayed directly onto a 
collecting surface 18 which may be an endless belt driven about rolls 19. 
The direction, temperature, and velocity of air stream 14 and carrier 18 
are controlled to achieve a desired degree of fiber separation, placement 
and drying so that an undesirable amount of hydrogen bonding is avoided. 
Preferably the air stream is heated to a temperature in the range of from 
about 30.degree. C. to about 160.degree. C. for improved drying. 
Alternatively, nozzle 12 can be of the airless spray type. Fibers 16 are 
collected by means of carrier 18 as formed web 20. Vacuum box 21 may be 
used, if desired, to aid in web formation and increase the rate of fiber 
drying. This web 20 may be further dried if desired by dryer 22 and is 
illustrated as wound into rolls 24. Of course, it will be recognized that 
the resulting web from the process of the invention may be fed directly 
into apparatus for the manufacture of end use products such as sanitary 
napkins, disposable diapers, and the like. 
In FIG. 3 a web forming embodiment is illustrated in greater detail. Drying 
chamber 26 includes inlet 28 for heated air provided by blower 30 and 
heater 32. Also within drying chamber 26 is spray nozzle 12 fed with 
extrudate 10 by pump 11 and compressed air by line 34. Dried fibers 16 
exit at opening 36 with exhaust air vented at 38. The random deposition of 
fibers on carrier 18 forms a fluff batt 40 which may be further dried, if 
desired, and processed as shown in FIG. 2. The drying chamber 26 allows 
the fibers 16 to be substantially dried prior to deposition so that they 
are lighter and produce a thick, fluffy, airy mat with a high degree of 
z-direction fiber orientation. Such a web formed from phosphorylated pulp 
fibers is shown in FIGS. 6 and 7 at magnifications of 100.times. and 
1000.times., respectively. The lack of interfiber bonding and large void 
areas resulting from predrying are apparent. 
FIG. 4 illustrates an embodiment wherein the process of FIG. 2 is modified 
by adding compressed air to spray nozzle 12 and means for heating the air 
in dryer 22. The fibers 16 are wet as web 20 is formed and the web is 
dried as it passes through dryer 22. The result is a somewhat more highly 
bonded, thin mat as shown in the photomicrographs of FIGS. 8 and 9 shown 
at magnifications of 100.times. and 1000.times., respectively. FIGS. 10 
and 11 similarly illustrate the results obtained with Buckeye brand 
carboxymethyl cellulose fibers. 
FIG. 5 illustrates still a third web forming embodiment wherein partial 
drying is first obtained in primary drying chamber 26A and final drying is 
accomplished in secondary drying chamber 22A. Both dryers are supplied 
with heated air for more rapid drying. 
FIG. 12 is a microphotograph cross-section of the web of FIGS. 7 and 8 
taken at a magnification of 50.times. illustrating the layered structure 
obtainable with this embodiment of the invention. 
The invention will now be further described by way of specific examples. 
EXAMPLE 1 
A standard phosphorylated extrudate at 6.5% dry fiber consistency was 
extruded from a 20 milliliter disposable syringe acting as pump and 
reservoir using appropriate fittings into the liquid port of a pneumatic 
spray nozzle fitted for 30 psi compressed air. The pneumatic spray nozzle 
was equipped with a slotted dispersing tip and 5 milliliters of extrudate 
were manually injected through the pneumatic sprayer (Spraying Systems 
Company Model 1/4 J fitted with dispersing tip No. 125328 SS over 
dispersing head No. 2050 with a liquid port opening of 0.50 inch) to 
suspend the fibers individually. The compressed air was fed into the air 
port at room temperature. This fiber suspension was collected in a uniform 
layer of separated fibers on a 12 inch.times.12 inch.times.1/8 inch sheet 
of Teflon brand fluorinated ethylene-propylene resin, and these separated 
fibers were subsequently air dried five minutes using the high velocity 
air from the spray nozzle. The result was a fluff-like collection of 
fibers having a dry fiber consistency of 85.2%. 
EXAMPLE 2 
Example 1 was repeated except that the fiber collection was dried for 2 
minutes with air at a temperature of 85.degree. C. from a Master Appliance 
laboratory hot air heat gun (Model No HG301J). The resulting fluff-like 
collection of fibers had a dry fiber consistency of 86.5%. 
EXAMPLE 3 
The extrudate of Example 1 was spread by the use of a doctor blade system 
in a thin film approximately 0.1 inch thick and gradually dried for 18 
hours at a temperature of 105.degree. C. in a circulating Blue "M" oven. 
The resulting sheet was harsh, crust-like, and slowly rewettable being 
partially swollen under microscopic observation when wet. 
EXAMPLE 4 
A standard phosphorylated extrudate was suspended in a slurry of acetone 
and solvent dried in the manner described in the above-referenced 
Bernardin patent. The resulting mat of solvent dried fibers was soft, 
flexible, rapidly rewettable and highly swollen under microscopic 
observation when wet. 
EXAMPLE 5 
A crosslinked carboxymethyl cellulose extrudate having 3.0% dry fiber 
consistency was prepared by mixing 1.0 gram of dry fluff Buckeye Cellulose 
Company (CLD SR-447) fibers in 32.3 grams of distilled water. This 
extrudate was formed into a web using a pneumatic spray nozzle and dried 
as in Example 1. The resulting collection of fibers was soft, fluff-like, 
very slowly rewettable and extremely swollen under microscopic observation 
when wet. The dry fiber consistency of the resulting web was 81.3%. 
EXAMPLE 6 
Example 2 was repeated using the carboxymethyl cellulose extrudate of 
Example 5. The resulting collection of fibers was soft, fluff-like, very 
slowly rewettable and extremely swollen under microscopic observation when 
wet. The mat had a dry fiber consistency of 82.7%. 
EXAMPLE 7 
Example 3 was repeated using the carboxymethyl cellulose extrudate of 
Example 5. The resulting sheet was harsh and crust-like, extremely slow to 
rewet but eventually highly swollen under microscopic observation when 
wet. 
EXAMPLE 8 
A sample of crosslinked carboxymethyl cellulose from Buckeye Cellulose 
Company (SR44) as received from the supplier, previously solvent dried. 
This soft fluff was very slowly wettable and extremely swollen under 
microscopic observation when wet. 
The following Table 1 summarizes the foregoing Examples and the results of 
1000 G retention tests performed with water and saline solutions. 
Table 1 
______________________________________ 
1000 G Retention 
Drying (grams/gram) 
Example 
Pulp Method Water Saline 
______________________________________ 
1 Phosphoryl- 
Present invention 
10.49 3.49 
ated High velocity air 
2 Phosphoryl- 
Present invention 
8.27 3.17 
ated Heated air 
3 Phosphoryl- 
Air drying of thick 
3.51 2.16 
ated film of extrudate 
4 Phosphoryl- 
Acetone drying of 
8.77 3.52 
ated fibrous mat 
5 CMC Present invention 
49.76 20.83 
High velocity air 
6 " Present invention 
35.90 15.72 
Heated air 
7 " Air drying of thick 
21.47 13.53 
film of extrudate 
8 " As received from 
67.97 18.72 
supplier 
______________________________________ 
As the foregoing Examples demonstrate, materials produced according to the 
invention (Examples 1, 2, 5 and 6) exhibit absorbent characteristics 
essentially equal to those of the same fibers dried according to 
solvent-drying techniques and far superior to those air dried in a thick 
film (Examples 3 and 7). They further demonstrate that in accordance with 
the invention highly absorbent fibers can be individually suspended 
through the use of pneumatic sprayers, air sprayers, centrifugal sprayers, 
and the like. Thus, highly absorbent fibers in a desirable soft, flexible 
mat form can be prepared without requiring solvent-drying techniques, 
producing significant savings in cost and handling over traditional drying 
routes. The results for Example 8, while showing high absorbency are for a 
fluff form, not a web. 
The following Examples demonstrate, through alternative embodiments, the 
variety of results obtainable in accordance with the present invention. 
EXAMPLE 9 
A standard phosphorylated extrudate at 6.5% dry fiber consistency was 
extruded from a 20 milliliter syringe through a 16 gauge (I.D.=0.046 inch) 
needle and into an air line supplying air at room temperature and pressure 
at 15 psi. The sprayer was hand operated at about 1 foot above a 
collecting surface and the individual suspended fibers were directed into 
a separate air stream at a temperature of 85.degree. C. from a distance of 
about 1 foot to the collecting surface. The partially dried fibers were 
collected on a sheet of 0.25 oz/yd.sup.2 spunbonded polypropylene 
available under the trademark EVOLUTION which was placed over a vacuum box 
with laboratory vacuum applied. The web was substantially dried as 
collected to form an airy, mat-like structure. Sixty milliliters of 
extrudate were sprayed and dried over a 15 minute interval. This structure 
had a dry fiber consistency of 83.2% and the following characteristics: 
Thickness--0.56 centimeters, 
Bulk density--0.031 gram/cubic centimeter, 
Free standing saline absorbency--33.1 grams liquid/gram fiber, 
1000 G water retention--3.93 grams liquid/gram fiber, 
1000 G saline retention--3.00 grams liquid/gram fiber, 
Wicking time--0.12 minutes, 
As is tensile--830 grams/centimeter, 
As is breaking length--474 meters, 
Wet Tensile--43 grams/centimeter, and 
Wet breaking length--25 meters. 
EXAMPLE 10 
Example 9 was repeated except that only 20 milliliters of extrudate were 
sprayed and dried over a 5 minute interval. This structure had a dry fiber 
consistency of 83.7% and the following characteristics: 
Thickness--0.13 centimeters, 
Bulk density--0.047 gram/cubic centimeter, 
Free standing saline absorbency--43.6 grams liquid/gram fiber 
1000 G water retention--6.82 grams/liquid/gram fiber, 
1000 G saline retention--2.92 grams liquid/gram fiber, 
Wicking time--0.35 minute, 
As is tensile--150 grams/centimeter, 
As is breaking length--246 meters, 
Wet tensile--4 grams/centimeter, and 
Wet breaking length--6 meters. 
EXAMPLE 11 
Example 9 was repeated except that the collecting surface was EVOLUTION 
spunbonded polypropylene placed on a flat solid surface, and the fibers 
were directed at an upward 45.degree. angle to allow the individually 
suspended fibers to arch upward and then fall softly downward (a distance 
of approximately 3 feet) to the collecting surface. Two laboratory heat 
guns were positioned to blow air at a temperature of 85.degree. C. across 
this collecting surface. Approximately 200 milliliters of extrudate were 
sprayed and dried over a 30 minute interval. The resulting structure had a 
dry fiber consistency of 87.9% and the following characteristics: 
Thickness--0.22 centimeters, 
Bulk density--0.11 gram/cubic centimeters, 
Free standing saline absorbency--28.9 grams liquid/gram fiber, 
1000 G water retention--6.41 grams liquid/gram fiber 
1000 G saline retention--2.51 grams liquid/gram fiber, 
Wicking time--very slow, 
As is tensile--96 grams/centimeter, 
As is breaking length--384 meters, 
Wet tensile--not measurable, and 
Wet breaking length--not measurable. 
EXAMPLE 12 
Example 11 was repeated except that the collecting surface was a 12 
inch.times.12 inch copper collecting wire (200 mesh) and the fibers were 
allowed to fall softly in their wet state. This structure was placed in a 
Blue "M" oven set at 105.degree. C. and dried for five minutes. The 
resulting structure had a dry fiber consistency of 82.5% and the following 
characteristics: 
Thickness--0.18 centimeters, 
Bulk density--0.012 gram/cubic centimeter, 
Free standing saline absorbency--29.3 grams liquid/gram fiber, 
1000 G water retention--6.47 grams liquid/gram fiber, 
1000 G saline retention--2.16 grams liquid/grams fiber, 
Wicking time--very slow, 
As is tensile--59 grams/centimeter, 
As is breaking length--281 meters, 
Wet tensile and wet breaking length not measurable. 
EXAMPLE 13 
A sample of web was prepared according to the procedure described in the 
above-mentioned Lassen patent using the extrudate described in Example 4. 
The resulting web had a dry fiber consistency of 85% and the following 
characteristics: 
Thickness--0.48 centimeters, 
Bulk density--0.033 gram/cubic centimeters, 
Free standing saline absorbency--20.5 grams/gram, 
1000 G water retention--7.86 grams liquid/gram fiber, 
1000 G saline retention--3.69 grams liquid/gram fiber, 
Wicking time--0.90 minutes, 
As is tensile (M.D.)--70 grams/centimeter, 
As is breaking length (M.D.)--43 meters, 
Wet tensile and wet breaking length not measurable. 
As can be seen, the present invention is exemplified by Examples 9, 10, 11 
and 12 can be used to produce a web similar to solvent-dried material in 
thickness, bulk density, and saline wicking rate. More importantly, it can 
also be seen that the materials formed by this invention possess a greater 
free standing saline absorbency (33.1 grams/gram as compared to only 20.5 
grams/gram of solvent-dried material--Example 13) and superior web and dry 
tensile properties (830 grams/centimeter compared to only 70 
grams/centimeter for the solvent-dried material plus a wet tensile of 43 
grams/centimeter compared to the fact that this property was not 
measurable by standard techniques used on the Instron Tensile Tester with 
the solvent-dried material). Example 11 demonstrates a material having 
considerably lower bulk density and strength as well as showing the effect 
of velocity of the sprayed fibers on the type of structure which is formed 
on the collecting surface. This material has similar physical 
characteristics to that of the material produced by Example 12. In Example 
11, the fibers were partially dried as sprayed and subsequently dried as 
collected on the collecting surface. In Example 12 a still lesser degree 
of initial drying was obtained since the fibers were sprayed wet without 
an auxiliary drying air stream as in Example 11. The result was a wet, 
open structure with a thickness of approximately 3/8 inch. This web was 
placed in a circulating oven to dry. These examples of the present 
invention show similar characteristics to airformed paper products but 
with surprising strength and absorbency. 
EXAMPLE 14 
Phosphorylated pulp as in Example 1 was pumped at a pressure of 300 psig by 
means of a Zenith Model BPB4391 pump through a TEJET tip No. SS6501 to 
form an airless spray onto black blotting paper under ambient conditions. 
A somewhat flaky web was formed. Under higher pressures a more uniform web 
would be expected. 
In a further embodiment the present invention may provide an improved 
material combining chemically modified fibers with other highly absorbent 
materials. For example, acrylonitrile grafted starch granules have been 
available but present difficulties in handling and incorporation into 
absorbent products due to dusting, sifting and positioning problems 
related to the free flowing nature of such materials. By combining these 
granular or powder materials having a mesh size from about 14 to 400, for 
example, with chemically modified fibers prior to complete drying an 
integrated composite material is formed that can be handled and reduces 
dusting problems. The following examples demonstrate this embodiment. 
EXAMPLE 15 
Phosphorylated pulp having 7.2% phosphorous and a consistency of 10.5% 
fibers was sprayed from a pressurized reservoir to a Zenith laboratory 
metering unit (Model 175G) equipped with a type BPB (1.7 cc/revolution) 
spinning pump through a high pressure hose to a Spraying Systems Company 
1/4 J pneumatic nozzle fitted with a 60100 fluid cap and 125328 air cap. 
The nozzle was mounted 18 inches above a forming wire with the flat spray 
air cap aligned in the cross direction and the nozzle tilted at an angle 
of about 60.degree. from vertical. The gel was pumped into the nozzle and 
pneumatically sprayed. From a Syntron vibrator pan General Mills polymer 
502S granules were allowed to free fall about 15 inches into the fiber 
spray and the composite material collected on a forming wire. After 
through drying at 30.degree. C., a sheet of 5% phosphorylated fibers and 
95% granules by weight was formed having high tensile strength (361 g/cm), 
1000 G saline retention of 25.4 g/g, density 0.15 g/cc, and a thickness of 
0.25 cm. 
Example 16 
Phosphorylated pulp (8.3% phosphorous) gel having a consistency of 10.2% 
solids was sprayed as in Example 15, and Grain Processing polymer 35-A-100 
was sifted from a separatory funnel into the spray at the outlet of the 
spray cap. After collecting on a fourdrinier wire and through drying at 
70.degree. C. a composite containing 10% phosphorylated fibers and 90% 
polymer was formed having a tensile strength of 35 g/cm, 1000 G saline 
retention of 12.1 g/g, density of 0.08 g/cc and thickness of 0.22 cm. 
EXAMPLE 17 
Carboxymethyl cellulose (Hercules Aqualon "R") fiber gel was mixed with 
water to 1% consistency and dewatered to 7.8% consistency. It was sprayed 
as in Example 15 and mixed at the spray nozzle with General Mills polymer 
502S added with a Vibra Screw feeder (Model SCR-20). The composite was 
through dried at 30.degree. C. and resulted in a web containing 17% fibers 
and 83% granules having a tensile of 220 g/cm, a 1000 G saline retention 
value of 28.5 g/g, density of 0.09 g/cc and a thickness of 0.19 cm. 
EXAMPLE 18 
Unrefined 700 Canadian Standard Freeness phosphorylated pulp gel having a 
7.0% phosphorous, and a consistency of 6.7% solids (fiber saturation point 
4.5 g/g, total water content 14 g/g) was pumped from a pressurized 
reservoir to a Zenith Laboratory metering unit Type 1-QF equipped with a 
type BPB (1.7 cc/revolution) spinning pump and then through a high 
pressure hose to a Spraying Systems Company 1/4 J pneumatic nozzle fitted 
with a 100150 fluid cap and a 189 351 air cap. The nozzle was mounted 40 
inches above a centerline from a 19 inch wide forming wire with the 
pneumatic nozzle flat spray air cap aligned in the cross direction and 
nozzle aligned so that the fibers were sprayed directly downward toward 
the forming wire which was traveling at 8 inches/minute. Sufficient 
compressed air was used to just separate the gel into fibers with minimum 
excess air. The Zenith pumping unit was set at 35 (equivalent to 250 
RPM's). Approximately 4 lineal feet of undried web was produced. This was 
then run through a 4 foot long tunnel type through dryer approximately 10 
feet from the spray nozzle. The through dryer was set at 100.degree. C. 
The web was very difficult to dry, but after 25 minutes of visual 
inspection it was dry. The resulting web, as shown in FIG. 13, magnified 
12.times., was crusty and not acceptable for most applications. 
EXAMPLE 19 
Example 18 was repeated except that the pulp gel was at 8.7% consistency 
(total water 10.5 g/g); 12 psi was used to pneumatically separate the gel 
fibers, and the web was through dried in 11 minutes. A poor quality web 
resulted as shown in FIG. 14, magnified 12.times.. 
EXAMPLE 20 
Example 18 was repeated except that the pulp gel was at 13.0% consistency 
(total water 6.7 g/g); 30 psi was used to pneumatically separate the gel 
fibers and the web was through dried in 6 minutes. A good quality web 
resulted as shown in FIG. 15, at 12.times.. 
EXAMPLE 21 
Example 18 was repeated except that the pulp gel was at 18.4% consistency 
(total water: 4.4 g/g); 65 psi was used to pneumatically separate the gel 
fibers, and the web was through dried in 1 minute. An excellent quality 
web, foam-like in appearance, resulted as shown in FIG. 16, at 12.times.. 
EXAMPLE 22 
Example 18 was repeated except that the pulp gel was refined to 400 
Canadian Standard Freeness. This was sprayed at 6.7% consistency (total 
water: 14 g/g, fiber saturation point: 8.5 g/g) 5 psi was used to 
pneumatically separate the gel fibers and the web was through dried in 21 
minutes. The web quality was very poor and crust-like in appearance as 
shown in FIG. 17, magnified 12.times.. 
EXAMPLE 23 
Example 22 was repeated except that the pulp gel was at 8.7% consistency 
(total water: 10.5 g/g); 15 psi was used to pneumatically separate the gel 
fibers and the web was through dried in 10 minutes. Although the external 
water content was within the preferred range, a somewhat crusty web 
resulted as shown in FIG. 18, magnified 12.times., possibly due to the 
high degree of refining. 
EXAMPLE 24 
Example 22 was repeated except that the pulp gel was at 10.0% consistency 
(total water: 9.0 g/g); 43 psi was used to pneumatically separate the gel 
fibers and the web was through dried in 6 minutes. A good quality web 
resulted as shown in FIG. 19, magnified 12.times.. 
EXAMPLE 25 
Example 22 was repeated, except that the pulp gel was at 13.0% consistency 
(total water: 6.7 g/g, dewatered by vacuum); 32 psi was used to 
pneumatically separate the gel fibers and the web was through dried in 6 
minutes. A good web, foam-like in appearance, was obtained as shown in 
FIG. 20, magnified 12.times.. 
EXAMPLE 26 
Example 18 was repeated except that the pulp gel was carboxymethyl 
cellulose (Hercules Aqualon "R"). It was sprayed at 3.2% consistency 
(total water: 30 g/g, fiber saturation point: 16.5 g/g); 23 psi was used 
to pneumatically separate the gel fibers; the forming wire was run at 4 
inches per minute; and the web was through dried in 25 minutes. A poor 
web, very board-like, was obtained as shown in FIG. 21, magnified 
12.times.. 
EXAMPLE 27 
Example 26 as repeated except that the pulp gel was at 4.0% consistency 
(total water: 24.0 g/g); 35 psi was used to pneumatically separate the gel 
fibers; the forming wire was at 8 inches/minute and the web was through 
dried in 6 minutes. A poor web resulted as shown in FIG. 22, at 12.times.. 
EXAMPLE 28 
Example 26 was repeated except that the pulp gel was at 5.0% consistency 
(total water: 19.0 g/g); 12 psi was used to pneumatically separate the gel 
fibers; the forming wire was run at 3 inches per minute; and the web was 
through dried in 3 minutes. A good web resulted as shown in FIG. 23, at 
12.times.. 
EXAMPLE 29 
Example 26 was repeated except that the gel was at 5.8% consistency (total 
water: 16.4 g/g); 25 psi was used to pneumatically separate the gel 
fibers; the forming wire was run at 2 inches per minute and the web was 
through dried in 1 minute. A good web resulted as shown in FIG. 24, at 
12.times.. 
EXAMPLE 30 
Example 22 was repeated except that 60 psi was used to pneumatically 
separate gel instead of 5 psi; the gel feed pump was set at 3 instead of 
35; the forming wire was stopped due to reduced feed rate in order to 
allow sprayed fibers to build-up a reasonable basis weight so 
approximately 1 lineal foot of web was produced. The web was through dried 
in 1 minute. The web was very soft. Much drying occurred during formation 
due to the high ratio of air to gel during spraying which results in the 
material being formed at or near the fiber saturation point in spite of 
the high gel water content. Similar results are shown in e.g. Example 1. 
The web had a 17.1% consistency prior to through drying. FIG. 25 shows the 
web of this Example, magnified 12.times.. 
The results of these Examples are further illustrated in Table 2. As shown, 
good (soft, noncrusty) webs can be produced by selecting a combination of 
consistency, flow and drying conditions to achieve maximum fiber 
separation requiring a minimum of subsequent drying. As shown in FIG. 28, 
preferred web densities after drying are in the range of about 0.015 to 
0.050 grams/cc with the range of about 0.015 to 0.040 especially 
preferred. 
Table 2 
__________________________________________________________________________ 
Normal- 
ized Normal- 
Spray Thick- 
ized 
Web ness Tensile 
Fiber Prior to Centi- 
Kg/ Thru 
Satura- 
Base Gel Thru meters 
15 mm Drying 
tion Grams Drying At A At A Time 
Modified 
Point 
H.sub.2 O/ 
% % Basis Basis 
Basis At 
Photoegree. 
Cellulose 
900 "G" 
Gram Consis- 
Consis- 
Weight 
Density 
Weight 
Weight 
Stretch 
C. Refer- 
Ex. 
Type g/g Fiber 
tency 
tency 
g/m.sup.2 
g/cc 200 g/m.sup.2 
200 g/m.sup.2 
% Minutes 
ence 
__________________________________________________________________________ 
18 Phosphory- 
4.5 14.0 6.7 6.9 163 .083 .24 1.7 .86 25 113 
lated 
Unrefined 
19 Phosphory- 
4.5 10.5 8.7 9.1 182 .047 .43 1.9 .87 11 14 
lated 
Unrefined 
20 Phosphory- 
4.5 6.7 13.0 -- 184 .028 .72 1.9 4.52 6 15 
lated 
Unrefined 
21 Phosphory- 
4.5 4.4 18.4 -- 85 .016 1.28 1.1 8.05 1 16 
lated 
Unrefined 
22 Phosphory- 
8.5 14.0 6.7 6.8 150 .065 .31 3.6 .77 21 17 
lated 
Refined 
23 Phosphory- 
8.5 10.5 8.7 9.2 127 .058 .34 3.1 2.64 10 18 
lated 
Refined 
24 Phosphory- 
8.5 9.0 10.0 -- 198 .030 .66 1.4 2.67 6 19 
lated 
Refined 
25 Phosphory- 
8.5 6.7 13.0 -- 177 .033 .59 1.4 2.77 6 20 
lated 
Refined 
26 CMC 16.5 30.0 3.2 3.4 162 .050 .40 2.9 1.99 25 21 
Unrefined 
27 CMC 16.5 24.0 4.0 4.2 113 .051 .39 2.4 2.82 8 22 
Unrefined 
28 CMC 16.5 19.0 5.0 5.1 149 .035 .57 2.5 3.00 6 23 
Unrefined 
29 CMC 16.5 16.4 5.8 6.1 182 .034 .59 1.5 3.72 3 24 
Unrefined 
30 Phosphory- 
8.5 14.0 6.7 17.1 65 .015 1.33 1.8 13.86 
1 25 
lated 
Refined 
__________________________________________________________________________ 
While it is not desired to limit the invention to any particular theory, 
the following is offered as a possible explanation of the results 
obtained. 
When dry cellulosic fibers are immersed in water, the water will penetrate 
into the fiber wall causing it to swell. The swelling will continue until 
the stresses within the fiber wall are in equilibrium with the capillary 
forces which tend to drive the water into the fiber wall. The water 
content of completely saturated fibers is calld the fiber saturation point 
("FSP") and is commonly expressed in grams of water per gram of dry 
fibers. FIG. 26 illustrates the fiber saturation points of representative 
materials of the invention. 
Thus, when fibers are immersed in water part of the water is contained 
within the fiber walls and the remainder is among the fibers and within 
the lumens. For the purpose of this discussion the water contained within 
the fiber walls is called internal water while the water outside the 
fibers is called external water. FIGS. 27 and 28 describe external and 
internal water contents for the representative materials including 
preferred ranges. 
The most accurate method for determining the fiber saturation point is the 
solute exclusion technique. Dry fibers are immersed in an aqueous solution 
of a dextran of which the molecules are too large to penetrate into the 
capillaries of the fiber walls. Water is imbibed by the fibers excluding 
the solute. From the measured increase of the solute concentration of the 
ambient dextran solution, the weight of imbibed water i.e. the fiber 
saturation point can be calculated. 
This method of determining the fiber saturation point is very laborious and 
it has been shown [Scallan and Carles, "Svensk Papperstidning" 75 (1972) 
(609-703)], that a very good correlation exists between fiber saturation 
point values as determined by the solute exclusion technique and the water 
retention values ("WRV") of most fiber samples after being subjected to a 
centrifugal force of 900 G's for one-half hour. 
When by some chemical means hydrophilic groups are introduced onto the 
surface and within the amorphus regions of cellulosic fibers (e.g. 
phosphorylation) the fibers will absorb more water with a consequent 
increase in the fiber saturation point as described in the addendum to the 
above mentioned Scallan and Carles article. Beating and refining also 
increases the fiber saturation point of fibers. The fiber saturation point 
(or water retention value) of woodpulp fibers is rarely in excess of 2 
grams/gram. For dried and reslushed pulp fibers the fiber saturation point 
is not larger than one gram/gram. 
The fiber saturation points of some chemically modified hydrophilic fibers 
are shown in Table 3. 
Table 3 
______________________________________ 
External Water 
FSP Gram/Gram at 5% 
Material Gram/Gram Consistency 
______________________________________ 
Phosphorylated Fiber 
4.5 14.5 
(unbeaten) 
Phosphorylated Fiber 
8.5 10.5 
(beaten) 
Carboxymethyl cellulose 
16.5 2.5 
(Aqualon - R) 
(unbeaten) 
Woodpulp (average) 
1.5 17.5 
______________________________________ 
Data in Table 3 shows that the chemically modified fibers contain more 
internal water (higher fiber saturation point) than the woodpulp fibers. 
Thus, at e.g. 5% consistency (95 grams water/5 grams of fibers) the 
quantity of external water varies with the fiber saturation point as is 
shown in Table 3, second column. 
Because of the different amounts of external water, Aqualon R at 5% 
consistency is a gel with plastic characteristics while woodpulp is a free 
flowing slurry. The phosphorylated fibers have properties in between these 
two extremes. 
The webs formed in accordance with the invention are characterized by a 
structure having an airy, mat-like appearance with (1) high absorbency, 
(2) controllable wicking or distribution properties, (3) controllable dry 
strength properties which can vary from a fluff-like mat to a soft, 
tissue-like sheet to a tough, flexible foam-like sheet and (4) 
controllable wet strength. 
The present invention thus provides an improved highly absorbent material 
and process for making it having the following advantages: 
1. No solvent drying is needed to retain the wicking and absorbent 
characteristics of the highly absorbent fibers--this produces a 
significant cost savings; 
2. Internal fiber bonding is easily controlled within the webs by 
regulating the amount of hydrogen bonding between individual fibers in the 
drying stage with the following results: 
(a) by minimizing external water in sprayed fibers, the collected fibers 
form a bulky, loosely-bound mat of physically entangled fibers; 
(b) by partially drying all fibers before the collecting surface and 
subsequently drying them on the collecting surface, an airy mat of tacked 
fibers is formed with high strength, flexibility, and softness; 
3. A means is provided for incorporating granular materials; 
4. The liquid capacity of the web includes the increased interfiber 
capillary capacity as well as the swelled fiber capacity; 
5. The fibers can be aligned or randomized by varying the angle of the 
spray pattern in relation to the collection surface with the following 
results: 
(a) by spraying directly downward toward the collecting surface the fibers 
are randomized in orientation; 
(b) by spraying on a sharp angle to the collecting surface the majority of 
the fibers are oriented in the spray direction; 
6. When using an extrudate containing phosphorylated fibers, the flame 
retardant properties are particularly attractive for spray drying in 
heated air without flash fire danger. 
The process of the invention is susceptible to various modifications 
including spraying extrudable fibers into a high velocity heated air 
stream such as a through dryer nozzle and collecting the dried fibers on a 
continuous wire to produce a new web in-line, spraying extrudable fibers 
onto a continuous collecting surface and drying the structure in a through 
dryer to produce a new web in-line, and spraying extrudable fibers into a 
heated cyclone, flash drying them, and collecting them onto a continuous 
surface to produce a new web in-line. 
The process of the invention can also be used to integrate mechanically 
various materials with the highly absorbent fibers. For example, 
pre-mixing the materials into the extrudate and spraying this into a high 
velocity heated air stream such as through dryer nozzle and collecting the 
dried fibers on a continuous wire will produce an integrated web. Spraying 
extrudable fibers into one side of a high velocity heated air stream such 
as a through dryer nozzle and blowing picked roll pulp, for example, 
fibers into the other side of the high velocity heated air stream and 
collecting the integrated dried fibers on a continuous wire will produce 
an all air formed web in-line. Spraying extrudable fibers into a heated 
cyclone, flash drying them, blowing them through the blower unit of a roll 
pulp picker unit while picking a roll of pulp and collecting the 
integrated dried fibers on a continuous wire will produce an integrated 
web in-line. Spraying extrudable fibers into a melt-blowing process as 
described, for example, in U.S. Pat. No. 3,849,241 to Buntin et al will 
simultaneously dry and integrate the highly absorbent fibers into the melt 
blown web utilizing high velocity heated air of the melt blown process. 
These and other examples of the present invention will be apparent to those 
skilled in the art. The foregoing are illustrative of the highly 
absorbent, airy mat-like structures which can be produced in accordance 
with the invention by controlling the interfiber bonding during air 
drying. There are numerous possibilities for producing new highly 
absorbent webs in accordance with the invention in a continuous manner for 
use as a component for end use products. The highly absorbent benefits can 
be utilized such as in sanitary napkins, tampons, disposable diapers, 
wipers, and other like products. 
Thus, it is apparent that there has been provided in accordance with the 
invention a process for producing highly absorbent webs and resulting 
materials that fully satisfy the objects, aims and advantages as set forth 
above. While the invention has been described in conjunction with specific 
embodiments thereof, it is evident that many alternatives, modifications, 
and variations will be apparent to those skilled in the art in light of 
the foregoing description. Accordingly, it is intended to embrace all such 
alternatives, modifications and variations as fall within the spirit and 
broad scope of the appended claims.