U.S. patent number 3,617,439 [Application Number 04/789,084] was granted by the patent office on 1971-11-02 for process for improving comminution pulp sheets and resulting air-laid absorbent products.
This patent grant is currently assigned to The Buckeye Cellulose Corporation. Invention is credited to Benjamin E. Chapman, Jr..
United States Patent |
3,617,439 |
Chapman, Jr. |
November 2, 1971 |
PROCESS FOR IMPROVING COMMINUTION PULP SHEETS AND RESULTING
AIR-LAID ABSORBENT PRODUCTS
Abstract
A method for producing comminution pulp sheets from cellulosic
fibers and the products resulting therefrom as pulp sheets and
air-laid absorbent batts, which method comprises impregnating the
fibers of the comminution pulp sheets with about 0.1 to 2 percent
of a selected zwitterionic surfactant, such as N-octadecyl -N, N-
dimethylammonio-12-dodecanoate either in slurry prior to or during
comminution pulp sheet formation and prior to pulp sheet drying.
The resulting comminution pulp sheet is easily and effectively
fiberized or comminuted to yield fibers from which air-laid
absorbent products are prepared, and the air-laid absorbent
products are characterized by improved bulk, resiliency and
absorbency characteristics.
Inventors: |
Chapman, Jr.; Benjamin E.
(Memphis, TN) |
Assignee: |
The Buckeye Cellulose
Corporation (Cincinnati, OH)
|
Family
ID: |
25146541 |
Appl.
No.: |
04/789,084 |
Filed: |
January 2, 1969 |
Current U.S.
Class: |
162/138; 558/27;
604/365; 162/179; 264/121; 558/29; 604/375 |
Current CPC
Class: |
A61F
13/00008 (20130101); D21C 9/005 (20130101); A61L
15/20 (20130101); D21H 17/07 (20130101); A61F
2013/00731 (20130101) |
Current International
Class: |
A61F
13/00 (20060101); A61L 15/20 (20060101); A61L
15/16 (20060101); D21C 9/00 (20060101); D21H
17/07 (20060101); D21H 17/00 (20060101); D21d
003/00 () |
Field of
Search: |
;260/501.15,404,501.13,248.5 ;162/158,179 ;128/284 ;252/DIG.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
796,279 |
|
Oct 1968 |
|
CA |
|
1,128,836 |
|
Oct 1968 |
|
GB |
|
Other References
Schwarty and Perry, Surface Active Agents, 1949 p. 172..
|
Primary Examiner: Bashore; S. Leon
Assistant Examiner: Anderson; Richard H.
Claims
Having thus described the invention, what is claimed as new and
desired to be secured by Letters Patent is:
1. A method for the manufacture of a comminution pulp sheet, which
method comprises impregnating the cellulosic fibers of said pulp
sheet, prior to final dewatering in sheet formation, with about 0.1
percent to about 2.0 percent, based on the weight of active
surfactant and the bone dry weight of said pulp sheet, of a
zwitterionic surfactant having the general structure:
wherein R.sub.1 is a alkyl or alkenyl group containing about 16 to
about 22 carbon atoms, R.sub.2 and R.sub.3 are selected from the
group consisting of hydrogen and alkyl groups containing one to two
carbon atoms, R.sub.4 is an alkylene group containing one to about
11 carbon atoms, which alkylene group can have one or more hydroxyl
groups attached to carbon atoms, and R.sub.5 is selected from the
group consisting of --COO.sup.-, --SO.sub.3 .sup.-, and --OSO.sub.3
.sup.-, whereby the comminution of said pulp sheet and the
absorbency characteristics of air-laid absorbent pads produced
therefrom are improved.
2. A method for the manufacture of a comminution pulp sheet, which
method comprises impregnating the cellulosic fibers of said pulp
sheet, prior to final dewatering in sheet formation, with about 0.1
percent to 2.0 percent of a zwitterionic surfactant selected from
the group consisting of
N-octadecyl-N,N-dimethylammonio-12-dodecanoate,
N-eicosyl-N,N-dimethylammonio-3-propane-1-sulfonate,
N-tallowalkyl-N,N-dimethylammonio-2-hydroxy-3-propane-1-sulfonate,
N-C.sub.16 -C.sub.18 alkyl (and
alkenyl)-N,N-dimethylammonioacetate, N-(2-hydroxy, C.sub.16
-C.sub.18 alkyl)-N,N-dimethylammoniacetate,
N-tallowalkyl-N,N-dimethylammonioacetate, N-soyaalkyl (and
alkenyl)-N,N-dimethylammonioacetate, N-eicosyl (and
docosyl)-N,N-dimethylammonioacetate,
N-octadecyl-N,N-dimethylammonioacetate,
N-octadecyl-N,N-dimethylammonioethylsulfate, and
N-(1-methyl,C.sub.16 -C.sub.18 alkyl)-N,N-dimethylammonioacetate,
whereby the comminution of said pulp sheet and the absorbency
characteristics of air-laid absorbent pads produced therefrom are
improved.
3. The method for the manufacture of a sheet of claim 2 wherein the
comminution of pulp sheet is comprised of wood fibers, and said
pulp sheet is impregnated with about 0.2 percent of zwitterionic
surfactant.
4. The method for the manufacture of a comminution pulp sheet of
claim 2 wherein said pulp sheet is impregnated with a zwitterionic
surfactant by a displacement shower, prior to find dewatering in
sheet formation.
5. A method for the manufacture of a comminution pulp sheet, which
method comprises impregnating the cellulosic fibers of said pulp
sheet prior to final dewatering in sheet formation with about 0.1
percent to about 2.0 percent of
N-tallowalkyl-N,N-dimethylammonioacetate, whereby the comminution
of said pulp sheet and the absorbency characteristics of air-laid
absorbent pads produced therefrom are improved.
6. A comminution pulp sheet, the cellulosic fibers of which pulp
sheet are impregnated with about 0.1 percent to about 2.0 percent,
based on the weight of active surfactant and the bone dry weight of
said pulp sheet, of a zwitterionic surfactant having the general
structure:
wherein R.sub.1 is an alkyl or alkenyl group containing about 16 to
about 22 carbon atoms, R.sub.2 and R.sub.3 are selected from the
group consisting of hydrogen and alkyl groups containing one to two
carbon atoms, R.sub.4 is an alkylene group containing one to about
11 carbon atoms, which alkylene group can have one or more hydroxyl
groups attached to carbon atoms, and R.sub.5 is selected from the
group consisting of --COO.sup.-, --SO.sub.3 .sup.-, and --OSO.sub.3
.sup.-, whereby the comminution of said pulp sheet and the
absorbency characteristics of air-laid absorbent pads produced
therefrom are improved.
7. A comminution pulp sheet, the cellulosic fibers of which pulp
sheet are impregnated with about 0.1 percent to about 2.0 percent,
based on the weight of active surfactant and the weight of bone dry
pulp, of a zwitterionic surfactant selected from the group
consisting of N-octadecyl-N,N-dimethylammonio-12-dodecanoate,
N-eicosyl-N,N-dimethylammonio-3-propane-1-sulfonate,
N-tallowalkyl-N,N-dimethylammonio-2-hydroxy-3-propane-1-sulfonate,
N-C.sub.16 -C.sub.18 alkyl (and
alkenyl)-N,N-dimethylammonioacetate, N-(2-hydroxy,C.sub.16
-C.sub.18 alkyl)-N,N-dimethylammonioacetate,
N-tallowalkyl-N,N-dimethylammonioacetate, N-soyaalkyl (and
alkenyl)-N,N-dimethylammonioacetate, N-eicosyl (and
docosyl)-N,N-dimethylammonioacetate,
N-octadecyl-N,N-dimethylammonioacetate,
N-octadecyl-N,N-dimethylammonioethylsulfate, and
N-(1-methyl,C.sub.16 -C.sub.18 alkyl)-N,N-dimethylammonioacetate,
whereby the comminution of said pulp sheet and the absorbency
characteristics of air-laid absorbent pads produced therefrom are
improved.
8. The comminution pulp sheet of claim 7, which comminution pulp
sheet is comprised of wood fibers impregnated with about 0.2
percent of N-tallowalkyl-N,N-dimethylammonioacetate.
9. An air-laid absorbent pad produced from the comminution pulp
sheet of claim 7.
Description
BACKGROUND OF THE INVENTION
This invention relates to processes for the manufacture of
comminution pulp sheets comprised of cellulosic fibers and intended
for subsequent comminution and air laying to form absorbent fibrous
batts, pads, or sheets. The absorbent fibrous batts, pads, or
sheets are used in the structures of bandages, diapers, sanitary
napkins, tampons and like articles. More particularly, the
invention relates to the fibrous impregnation of such comminution
pulp sheets with selected zwitterionic surfactants whereby the pulp
sheets are rendered easily comminutable into predominantly whole
fibers. The air-laid batts formed therefrom substantially retain
the absorbency characteristics of conventional unimpregnated pulp
sheets and by meaningful use tests exceed the fluid inhibition and
resiliency of such air-laid batts prepared from fibers derived from
unimpregnated comminution pulp sheets. The fibrous impregnation in
the present invention is effected prior to final dewatering of the
pulp sheet in sheet formation.
Specifically, the present invention consists of a method for
impregnating the fibers of a comminution pulp sheet comprised of
wood fibers or other cellulosic fibers with effective amounts of
nitrogen containing zwitterionic surfactants more fully described
below by means of structure and chemical nomenclature
specification.
Air laying, or the process consisting of comminuting or fiberizing
pulp sheets to form a mass of individual fibers dispersed in air
and subsequent deposition of fibers on a foraminous screen to form
a batt, pad, or sheet has long been practiced with varying degrees
of success. The air-laid batts, pads, or sheets have been accorded
cohesiveness by various means including cohesive pressing, soluble
glue spraying, latex dipping and thermal setting, where
thermoplastic fibers were involved.
In particular, such air-laid products, because of the economies
involved in the relatively simple process of fiberizing and
reconstituting pulp sheets to form absorbent batts or pads by the
air lay method, have been widely used in absorbent products of a
disposable nature as set forth above. The comminution of cellulosic
fiber pulp sheets, and in particular wood pulp sheets, has in
practice been troublesome in the respect of requiring large amounts
of power, producing high noise levels and resulting in large
amounts of broken fibers and fines rather than the desired long
whole fibers.
One solution to the foregoing problems is found in U.S. Pat. No.
3,395,708, issued to Laurence R. B. Hervey and Donald K. George on
Aug. 6, 1968, which patent discloses and claims the use of a
specific class of cationic debonding agents to result in a
comminution-prone woodpulp sheet. While it is true that certain
benefits in ease of comminution and in resultant air-laid product
characteristics result from use of the cationic debonding agents
disclosed and claimed by the aforementioned patent, applicant has
found that the cationic debonding agents, for example dimethyl
dihydrogenated tallow quaternary ammonium chloride, achieve
comminution ease in a woodpulp sheet at a considerable disadvantage
to both absorbent rate and total absorbent capacity in subsequent
air-laid products. In fact, and although a woodpulp sheet without
surfactant impregnation is difficult to comminute or fiberize in
the preparation of air-carried fibrous masses to be deposited on
foraminous media in the air-laid process, the characteristics of
both absorbent rate and absorbent capacity of an air-laid pad
prepared from such material is in fact superior to that prepared
from woodpulp sheets impregnated with a cationic debonding
agent.
Most assuredly the comminution-promoting effect of the cationic
debonding agents disclosed in the aforementioned patent and in the
paper literature constitutes an improvement over the use of
unimpregnated woodpulp sheets. However, applicant has discovered
that the impregnation of woodpulp and other cellulosic sheets with
zwitterionic surfactants having particular structures imparts
comminution ease to wood pulp sheets, which comminution ease is
essentially equivalent to that imparted by the cationic debonding
agents, while substantially retaining and improving in several
respects the absorbent product characteristics of unimpregnated
woodpulp sheets.
SUMMARY OF THE INVENTION
Inasmuch as pulp sheets having a predilection toward easy
comminution into whole fibers were desired for use in the
manufacture of various types of absorbent air-laid batts, pads, and
sheets, applicant investigated his initial discovery that certain
zwitterionic surfactants when used as impregnants for woodpulp
sheets did improve the ease and completeness of comminution or
fiberization to a surprisingly high degree without engendering an
attentant prohibitive loss in subsequent air-laid pad absorbency.
Applicant discovered that the desired ease of comminution, with
attendant and subsequent air-laid pad absorbency can be achieved by
impregnating woodpulp sheets prior to final dewatering in the
formation process with a zwitterionic surfactant having the general
structure:
wherein R.sub.1 is an alkyl or alkenyl group containing about 16 to
about 22 carbon atoms, R.sub.2 and R.sub.3 are selected from the
group consisting of hydrogen and alkyl groups containing one to two
carbon atoms, R.sub.4 is an alkylene group containing one to about
11 carbon atoms, which alkylene group can have one or more hydroxyl
groups attached to carbon atoms, and R.sub.5 is selected from the
group consisting of --COO.sup.-, --SO.sub.3 .sup.-, and --OSO.sub.3
.sup.-.
In air-laid absorbent pads, applicant was surprised to discover
that the use of the aforementioned zwitterionic surfactants as
impregnants for woodpulp and other cellulosic fiber sheets resulted
in improving their comminution characteristics while providing
excellent power requirement and total absorptive capacity
characteristics with regard to both cationic impregnated woodpulp
sheets and woodpulp sheets devoid of any surfactant. The use of
zwitterionic surfactants is also enhanced, particularly in
instances where batt or pad clarity or color is a desirable
feature, by the fact that the present zwitterionic surfactants form
clear or water-white solutions for sheet impregnation. While the
present process and resultant products are primarily described in
terms of wood fiber absorbent pads, it is specifically noted that
the attendant benefits will accrue to comminution pulp sheets
prepared from other cellulosic fibers or admixtures of other
cellulosic fibers with wood fibers. Additionally, the ease of
comminution effects of the present invention are applicable to
processes other than the preparation of air-laid absorbent
structures wherein pulp sheets are comminuted, for example in the
preparation of viscose rayon by the slurry process, the preparation
of the cellulose nitrate, the preparation of cellulose acetate and
other cellulose derivatives.
Applicant was further surprised to find that the use of the
disclosed zwitterionic surfactants can be carried out, not only by
their introduction into fiber slurries prior to sheet formation,
but by displacement of the water contained in a sheet of pulp as
first formed with a displacement wash or shower on the forming
wire. The displacement shower is comprised of an aqueous solution
of the selected zwitterionic surfactant. The displacement shower
system of sheet impregnation offers desirable advantages in that it
effects economy in surfactant use, since only the displacement
shower water system and not the entire white water or slurry water
systems of a paper machine must be loaded with surfactant. Further
advantages accrue from displacement showering in that changes to
nonimpregnated woodpulp sheets are easily effected because the
entire white water system of the paper machine is not surfactant
loaded.
A principal object of this invention is, accordingly, to provide
woodpulp sheets for comminution and later formation into air-laid
absorbent pads of various types and methods for their production,
which cellulose sheets are impregnated with the zwitterionic
surfactants disclosed herein.
A further objective of the present invention is to provide
zwitterionic surfactant impregnated woodpulp sheets for comminution
and later deposition to form air-laid absorbent pads, which
woodpulp sheets exhibit a surprising ease of comminution to form
fibers for deposition into air-laid absorbent pads having improved
absorbent characteristics.
Another object of this invention is to provided improved air-laid
batts, pads, and sheets, for catamenial tampons, sanitary napkins,
surgical dressings, disposable diapers and other absorbent pads and
fibrous structures, prepared from woodpulp sheets impregnated with
the herein disclosed zwitterionic surfactants.
Yet another object of the invention is to provide comminution pulp
sheets which are easily reduced to individual fibers for use in the
production of cellulose chemicals and cellulose derivatives.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In general, applicant has found that the foregoing objectives can
be met, as before stated, by impregnating an otherwise suitable
woodpulp sheet prior to substantial water removal or drying with
zwitterionic surfactants having the general structure:
wherein R.sub.1 is an alkyl or alkenyl group containing about 16 to
about 22 carbon atoms, R.sub.2 and R.sub.3 are selected from the
group consisting of hydrogen and alkyl groups containing one to two
carbon atoms, R.sub.4 is an alkylene group containing one to about
11 carbon atoms, which alkylene group can have one or more hydroxyl
groups attached to carbon atoms, and R.sub.5 is selected from the
group consisting of --COO.sup.-, --SO.sub.3 .sup.-, and --OSO.sub.3
.sup.-.
As stated and inferred hereinbefore, impregnation of the woodpulp
sheets in the present sense envisions the introduction of
effectively distributed amounts of the herein disclosed
zwitterionic surfactants to the fibers of a woodpulp sheet during
sheet formation and prior to substantial water removal and drying.
It is noted that comminution pulp sheets in general have a fairly
high basis weight and thickness, for example a comminution pulp
sheet can have a basis weight of about 200 lbs. per ream of 500
sheets measuring 19 inches by 24 inches, and a thickness of about
0.050 inches, although the present fiberization and absorbency
effects will be noted in comminution pulp sheets of other basis
weights and thicknesses. Impregnation can be accomplished by adding
the requisite amounts of zwitterionic surfactant to holding tanks
or head boxes prior to sheet formation, however, this method of
addition is considered wasteful of the relatively high-priced
surfactants and is detrimental to continued paper formation in that
the entire white water system of the paper machine is inevitably
contaminated with surfactant. Applicant has found that one
excellent means of addition is that of adding the zwitterionic
surfactants of this invention by showering an aqueous solution of
the selected zwitterionic surfactant, using about 2 lbs. to about 6
lbs. of solution per lb. of pulp (the solution containing about
2000 lbs. of water to about 1 lb. active surfactant) onto a
comminution pulp sheet traveling on the forming wire of a paper
machine prior to substantial dewatering in the formation process. A
preferred method of spray addition, in order to effect good
surfactant distribution, is to direct a distributed system of
flooding nozzles to impinge the surfactant solution upon the head
box side of a dandy roll mounted in operative position above the
forming wire. An alternate system is to use a well-distributed
system of nonwashing sprays to accomplish surfactant addition.
This is to say that the zwitterionic surfactant addition point can
be prior to, over, or following an initial formation vacuum box or
dewatering device and can be prior to or within a dandy roll which
is positioned prior to subsequent vacuum boxes. These methods of
zwitterionic surfactant addition are preferred in order to achieve
a uniform distribution of the zwitterionic surfactant across and
through the formed sheet and allow, as an additional benefit,
adequate displacement of the initial water associated with the
formed sheet by the zwitterionic surfactant solution. Other systems
for application of the zwitterionic surfactants to comminution pulp
sheets will also be effective, if good distribution is
achieved.
Applicant states that effective amounts of zwitterionic surfactant
addition can be about 0.1 percent to about 2.0 percent preferably
0.2 percent, based on the weight of "active" zwitterionic
surfactant applied and the weight of bone dry pulp. Additions of
less than about 0.1 percent by weight of zwitterionic surfactant to
pulp sheets do not fully develop the improvement in comminution.
Additions of zwitterionic surfactant of more than about 2.0 percent
by weight do not contribute further substantial improvement to
fiberization or to the absorbent characteristics of subsequently
formed air-laid absorbent pads.
While applicant has not completely explained the mechanism by which
the presently disclosed zwitterionic surfactants accomplish their
beneficial action and further does not wish to be bound by theory,
a general and simplified explanation is that the fibrous surfaces
and surfactant are attracted together by electrical forces
operating in the aqueous phase of the pulp slurry. The absorption,
chemisorption, or substantive reaction which follows such
attraction blocks bonding sites which would otherwise result in
"hydrogen bonds" in the finally dried pulp sheets. In this manner
the zwitterionic surfactant is attracted to the fiber surfaces, and
the subsequent sheet strength or fiberization characteristics are
an indication of the ability of the surfactant to (1) migrate to
the fiber, (2) attach to the fiber, and (3) prevent hydrogen or
other bonding mechanisms which normally result in the cohesion of
fibers to form the type of fibrous sheets which are referred to
collectively as paper. It is likely that the zwitterionic
surfactants, due to their structure, provide a larger number of
substantive bonds of lesser strength on fibers and provide fibers
of lower surface hydrophobicity than do cationic surfactants.
Having stated that the disclosed zwitterionic surfactants give rise
to improved ease of comminution in comminution pulp sheets,
applicant reemphasizes that incorporation of the zwitterionic
surfactants in comminution pulp results in subsequent air-laid
absorbent pads having the general characteristics of substantially
improved absorbency and loft or bulk properties relative to
air-laid absorbent pads prepared from either untreated woodpulp
fibers or cationic impregnated wood fibers. Suitable examples of
specific zwitterionic surfactants for use in the present invention
are: ##SPC1##
In testing the comminution pulps prepared according to the process
of the present invention, applicant has made use of several
definitive testing procedures. These are designated as the Quick
Disintegration, Tappi T-233 (Clark Classification), Absorptive
Capacity, Cellulose Absorbency (drip method), Bulk Fiber Sink,
Wicking (embossed fiber batts) and Loft tests.
In the Quick Disintegration test, pulp sheet samples are
conditioned over night at 50 percent relative humidity and
72.degree. F. The conditioned pulp sheet samples are then cut into
1 inch by 1 inch squares. A whole number of squares weighing 10 to
12 grams is weighed and the weight recorded to constitute a sample.
The weighed sample of 1 inch by 1 inch squares is placed into a
Waring Blender (Model No. CB-5) with dull blades and whizzed at the
lowest speed (16,500 r.p.m.) for 15 seconds. The resulting fibers
are placed, without densification, on the top of a standard 14-mesh
screen placed between two airtight chambers. Compressed air is
introduced into the top chamber to violently agitate, but not
further comminute the fibers, while the lower chamber is provided
with a vacuum system for removing fibers which pass through the
screen. The compressed air and vacuum system acting in conjunction
provide a 52 mm. Hg differential through the screen, which pressure
differential is applied for 2 minutes. The fraction of fiber
remaining on the top of the 14-mesh screen and the fraction falling
through are then recovered and weighed. The percentage of total
fiber weight remaining on the 14-mesh screen is recorded. At least
two, and preferably 10, replicate Quick Disintegration tests are
made, and their mathematical average is recorded as the test
result.
The standard Tappi T-233 test method is a Clark fiber
classification. As modified slightly by the applicant, this test is
run as set forth in Tappi methods with the exception that a Clark
classifier (Catalog No. 218-1, Ser. No. 18572) is employed in
classification and the Clark method of classification is followed.
The weight percentage of the sample retained on the standard
14-mesh screen is recorded as the test result.
The Absorptive Capacity test employed by applicant determines the
absorptive capacity of air-laid pads in the as-formed state and
under mild compression stress. The Absorptive Capacity test is
carried out on a 5 inch by 5 inch stainless steel plate inclined at
an angle of 15 percent with the horizontal. A 4 inch by 4 inch
stainless steel cover plate, provided with weights to result in a
total loading of 16 lbs., or 1 p.s.i., applied on a 4 inch by 4
inch sample placed between the plates, is also provided. In
carrying out the test, applicant prepares eleven 4 inch by 4 inch
air-laid pads whose basis weight varies in definite increments of
0.10 grams from 2.00 grams to 3.00 grams with an allowed tolerance
in individual air-laid pads of .+-.0.02 grams. The weight of the
individual pads is recorded as W.sub.1. For convenience in handling
during testing, the air-laid pads are formed on a sheet of tissue,
covered with a second tissue, and cohesively pressed in a dry state
at 0.56 p.s.i. The basis weight and absorptive capacity of the
covering tissue under loaded and unloaded test compressive
conditions is determined by tissue tests performed on the same
equipment. The basis weight and absorptive capacity of the covering
tissue is cancelled out of the test results by the method used in
test calculation.
In carrying out the Absorptive Capacity test each of the 11
prepared and weighed air-laid pads is open end, single wrapped with
a 4 inch by 9 inch piece of 1 mm. thickness polyethylene film
secured with pressure-sensitive tape. The wrapped sample is placed
on a 1/8-inch thick, 5 inch by 5 inch hard rubber plate, and the
weight of the rubber plate together with wrapped sample pad is
recorded as W.sub.2. The rubber plate with the wrapped sample
thereon is placed on the inclined plate, so that the tape-secured
side of the sample is up, and the open ends of the wrapped sample
are aligned toward the top and bottom of the inclined plate.
Distilled and aerated water from an overhead reservoir is
distributed on the rubber plate above, outside of and running down
into the top end of the wrapped sample at the rate of 500 ml. per
minute for 1 minute. Then, beginning at the top and sides of the
rubber plate, all excess water outside the wrapped sample is
blotted up with absorbent blotting paper, taking care not to touch
the wrapped sample pad on either open end. The rubber plate with
wrapped sample thereon is then removed from the inclined plate, and
the rubber plate is carefully wiped dry in a horizontal position.
The weight of the dry rubber plate with wet wrapped sample is then
recorded as W.sub.3.
The rubber plate with wet wrapped sample thereon is immediately
returned to its original position in the inclined plate, and the
stainless steel cover plate is gently applied thereto to result in
a 1 p.s.i. loading on the wet sample. The 1 p.s.i. cover plate
loading is maintained for 45 seconds while excess water is blotted
from the rubber plate, as detailed above. The stainless steel cover
plate is then removed, and the rubber plate with wet sample thereon
is again wiped dry in a horizontal position. The weight of the
rubber plate with pressed wrapped wet sample thereon is recorded as
W.sub.4.
The rubber plate and pressed wrapped wet sample is immediately
returned to its original position on the inclined plate and
resaturated with 500 ml. of water for 1 minute, as was originally
done. Again, the excess water on the rubber plate around the sample
is blotted up with the previous precautions, and the rubber plate
is wiped dry in a horizontal position. The final weight of the
rubber plate with wet precompressed and resaturated wrapped sample
thereon is recorded as W.sub.5.
In the foregoing manner the initial zero load wet weight (W.sub.3)
the 1 p.s.i. loaded weight (W.sub.4) and the precompressed zero
load weight (W.sub.5), with tare of tape secured polyethylene wrap,
tissue and rubber plate are determined for the 11 samples.
The weight determinations W.sub.1-5 are determined separately for
the tissue used as covering for the tested air-laid pads so that
the tissue absorptive capacity can be eliminated from the air-laid
pad absorbent capacity in calculating the test results. The
combined tissue bottom and top cover sheets (32 sq. in. per pad)
used in the present determinations had a total weight of 0.39
grams. The absorptive capacity of the tissue under test conditions
was 12.80 grams H.sub.2 O/gram tissue under initial zero p.s.i.
loading, 5.52 grams H.sub.2 O/gram tissue under 1 p.s.i. loading
and 9.23 grams H.sub.2 O/gram tissue under final zero p.s.i.
loading. Having determined the W.sub.1-5 weights for the 11 samples
and separate tissue data, the absorptive capacity of the air-laid
pads is calculated according to the following formulas,
wherein:
W.sub.1 = weight air-laid pad with tissue, grams
W.sub.2 = weight polyethylene wrapped air-laid pad, tissue and
rubber plate, grams
W.sub.3 = initial zero p.s.i. wet weight of tissue-backed wrapped
air-laid pad and rubber plate, grams
W.sub.4 = 1 p.s.i. wet weight of tissue-backed wrapped air-laid pad
and rubber plate, grams
W.sub.5 = final zero p.s.i. wet weight of tissue-backed wrapped
air-laid pad and rubber plate, grams
A.sub.0 = absorptive capacity of air-laid pad alone under initial
zero p.s.i. load, grams H.sub.2 O/gram of pad weight
A.sub.1 = absorptive capacity of air-laid pad alone under initial 1
p.s.i. load, grams H.sub.2 O/gram of pad weight
A.sub.f = absorptive capacity of air-laid pad alone under final
zero p.s.i. load, grams H.sub.2 O/gram of pad weight ##SPC2##
The determination of A.sub.0, A.sub.1, and A.sub.f for the 11
samples is considered desirable versus a single determination.
Statistical determinations on replicate tests have revealed that
the 11-sample arrangement detailed above allows both paired T-test
and average T-test determinations to be made for comparison of the
various absorptive results to determine confidence limits; all of
which confidence limits are in excess of 90 percent and most of
which exceed 99 percent.
The Cellulose Absorbency test (drip method) is carried out by
preparing three 4 inch by 4 inch tissue-backed, air-laid pads as
for the Absorptive Capacity test above, except that the air-laid
pad weights are not graduated and have a weight of about 2 grams to
about 3 grams. The top and bottom tissue sheets are carefully
stripped from the air-laid pads as prepared. The tissue weights and
absorbent capacities are thereby eliminated from the calculations
in this Cellulose Absorbency test; the weight in grams of the
air-laid pad, without tissue covering, is recorded.
The prepared air-laid pad is then placed on a horizontally oriented
and supported piece of 1/2-inch-square mesh, galvanized hardware
cloth. An overhead gravity-flow reservoir containing aerated
distilled water and equipped with a 1/4-inch rubber tubing for
delivery thereof is provided. The 1/4-inch rubber tubing is
provided with a pinch clamp which is adjusted to give a controlled
flow rate of 60 ml. per minute. The waterflow is directed to the
center of the horizontal sample from the tubing tip positioned 1
inch above the sample pad. Waterflow is continued until the first
drop of water is observed to drip from the bottom side of the
supported sample pad. The time elapsed in seconds between first
waterflow and first drip is recorded and is equal to the grams of
water absorbed by the pad under the Cellulose Absorbency test
conditions. The test results are reported as grams H.sub.2 O
absorbed per gram pad weight, as calculated by multiplying the
seconds of waterflow by the grams of H.sub.2 O flowing per second
to first drip and dividing the result by the weight of the sample
pad in grams. The results for the three pads are calculated
individually and mathematically averaged to record a test result.
The Cellulose Absorbency test (drip method) constitutes a different
procedural method for determining initial zero-loading absorptive
capacity.
The Bulk Fiber Sink test measures the rate of water absorption into
comminuted cellulose fibers at a bulk density of 0.05 grams/cubic
centimeter. The selected cellulose bulk density is substantially
equivalent to the bulk density of a cellulose fiber pad as formed
in conventional air-laying procedures. The Bulk Fiber Sink test has
advantage in that it is convenient, fast and reproducible to
confidence limits of 99.9 percent.
In carrying out the Bulk Fiber Sink test a plexiglass tube having
an ID of 1.5 inches, an OD of 1.75 inches and a length of 12 inches
is fixed in a vertical position. The plexiglass tube is provided
with a 20-mesh screen for foraminously closing its bottom end. The
plexiglass tube is loaded with 16.9 grams of comminuted cellulose
fibers in a volume of 338 cubic centimeters to result in the test
bulk density of 0.05 grams/cubic centimeter. Plexiglass tube
loading is accomplished by taking small undensified increments of
comminuted cellulose fibers and introducing them into the
plexiglass tube to provide 16.9 grams of sample; the sample is then
lightly compacted to result in the specified bulk density.
After tube loading, a 1,000 ml. graduated Pyrex cylinder is filled
to the 800 ml. mark with distilled aerated water at 72 .+-.
2.degree. F. The fiber-loaded plexiglass tube is then positioned
vertically with its screen one-half inch above the water surface in
the Pyrex graduated cylinder; the plexiglass tube is then released.
The time in seconds from release to complete submersion of the
compacted cellulose fibers within the plexiglass tube is recorded.
Ten replicate tests are run with new fillings of distilled aerated
water in the graduated cylinder and newly loaded comminuted fiber
samples. The mathematical average of time for submersion in seconds
for the 10 tests is recorded as the test result.
The Embossed Pad Wicking test measures the time for water to
proceed under the impetus of capillary action along a vertically
oriented zigzag linear embossed region, with a total length of 5.6
inches, in a tissue-backed air-laid pad. The zigzag embossed line
has a width of about one-thirtysecond inch. The zigzag linear
embossed region is formed by part of an enclosed rectilinear
embossing pattern formed by two sets of parallel embossed lines.
The embossed lines in each set are spaced 1 inch apart, and the
intersections of the lines in the two sets have included angles of
53.2.degree. and 126.8.degree. where they cross. A sample cut to
include an unbroken zigzag embossed line and oriented so that the
126.8.degree. included angles are vertically opposed is held by a
clip in a vertical position. The bottom one-eighth inch of the
sample resides in an aerated distilled-water reservoir maintained
at 72 .+-. 2.degree. F. The time in seconds, from first dipping,
for water to proceed vertically and upwardly by capillary action
for a total vertical distance of 2.5 inches, along a zigzag
embossed line length of 5.6 inches, is observed and recorded.
The tissue-covered air-laid pads for the Embossed Pad Wicking test
are prepared in the same manner as pads for the Absorptive Capacity
test with exception that six pads having a weight per 4 inch by 4
inch pad of 2 to 3 grams are prepared. These tissue-covered pads
are then embossed with the pattern described above by use of an
embossing platen on which the test pad and 0.002 inch metal shim
for final plate clearance are laid. The pad is then pressed in a
hydraulic press (Carver Press pressure of 20,000 p.s.i.g.) to
emboss the pattern on the pad. The water is changed after each six
samples, and the mathematical average time in seconds for the six
samples is taken as the test result.
The Loft test, which determines the bulk density of an air-laid pad
with tissue backing, is carried out by preparing 4 inch by 4 inch
tissue-backed pads as in the Absorptive Capacity test, with the
exception that 10 pads are prepared at a 2- to 3-gram tissue-backed
pad weight. The 10 pads are stacked and the height measured. The
volume is then taken as 4 inches .times. 4 inches .times. the stack
height in inches and converted to cubic centimeters. The bulk
density (neglecting the neglible volume of the thin tissue backing
sheets) is equal to the weight of the 10-pad stack minus 3.9 grams
of tissue weight divided by the determined volume in cubic
centimeters. A lower bulk density figure is indicative of greater
bulk or loft.
The cellulose fibers used to prepare air-laid pads in the foregoing
test procedures can be prepared by hammer-milling comminution pulp
sheets in a mill equipped with an 8-mesh screen plate and dull
hammers to avoid fiber cutting. A Sprout-Waldron mill was also used
effectively to prepare cellulose fibers for test purposes.
For comparative testing, comminution sheets of Southern pine
bleached fiber woodpulp were formed and dried to have a basis
weight, at a 5 percent by weight moisture content, of 210 lbs. per
ream of 500 sheets measuring 19 inches by 24 inches. The sheet had
an average thickness of 0.050 inches. During the formation of the
pulp sheets on the Fourdrinier wire of the paper machine they were
passed under a dandy roll, whereon a distribution system of showers
delivered approximately 300 g.p.m. of an aqueous solution
containing 0.0005 lbs. of active surfactant per pound of aqueous
solution. This amount of surfactant resulted in a pulp sheet
containing about 0.2 percent active surfactant by weight based on
the weight of bone dry pulp. The paper machine sheet speed was 300
f.p.m. For comparison, comminution pulp sheets were prepared
containing the stated amount of the zwitterionic surfactant,
N-tallowalkyl-N,N-dimethylammonioacetate (supplied under the trade
name Culveram TDG by Culver Chemical Co.) and the cationic
surfactant, dimethyl dihydrogenated tallow alkyl quaternary
ammonium chloride, (supplied under the trade name Formonyte 1703 by
the Foremost Chemical Products Co.). Indentical comminution pulp
sheets containing no surfactant were also prepared. The described
tests were performed on the compared comminution pulp sheets, and
the test results are tabulated in table I below. ##SPC3##
In reviewing the comminution and absorbency data tabulated in table
I, it is noted that the results of the Quick Disintegration test
illustrate that the zwitterionic surfactant-impregnated sample was
easily comminuted or fiberized to retain only 21.9 percent of the
sample on the standard 14-mesh screen. The fiberization of the
zwitterionic surfactant impregnated sample, as measured by
percentage was better than twice as complete as the Standard Pulp
sample without surfactant and was significantly improved over the
cationic surfactant-impregnated sample.
The results of the Tappi T-233 test illustrate that the Standard
Pulp sample without surfactant was not only incompletely fiberized,
but was, in part, reduced in fiber length by comminution; since
51.4 percent of the sample was retained on the standard 14-mesh
screen prior to fiberization, and only 44.4 percent of the sample
was retained after fiberization. The Tappi T-233 test illustrates
that the zwitterionic surfactant impregnated sample not only
provided ease of comminution as shown by the Quick Disintegration
test results, but the fibers of the zwitterionic
surfactant-impregnated sample resisted shortening in fiberization.
The Tappi T-233 test result (51.5 percent) for the
zwitterionic-impregnated sample was substantially the same as the
Tappi T-233 test result (51.4 percent) for the Standard Pulp sample
prior to fiberization, illustrating that no substantial change in
fiber classification, i.e. fiber length distribution, occurred.
Taken together, Quick Disintegration and Tappi T-233 test results
illustrate the comminution superiority of the zwitterionic
surfactant-impregnated sample over the Standard and cationic
surfactant-impregnated samples.
Having established the comminution superiority of the
zwitterionic-impregnated sample, it is apparent that so great an
advantage in the use of the zwitterionic impregnated pulp sheets
exists in comminution that only the absorbency characteristics of
surfactant-impregnated pulp sheets should be further considered,
although comparison test results are presented for the Standard
Pulp sheet for completeness.
The test results presented for the Absorptive Capacity test
illustrate an overall advantage for the zwitterionic
surfactant-impregnated sample over both the Standard Pulp sheet and
the cationic surfactant-impregnated sample; the superiority of
zwitterionic surfactant impregnation is also illustrated by the
results of the Cellulose Absorbency test.
The results tabulated for the Bulk Fiber Sink and Wicking tests
illustrate the clear superiority of zwitterionic surfactant
impregnation over cationic surfactant impregnation in pulp sheet
samples which otherwise exhibit the characteristic of improved
comminution. The tabulated results of the Loft test illustrate the
superiority of the zwitterionic-impregnated sample in the bulk and
resiliency properties desirable in absorbent disposable batts, pads
and sheets.
Standard Pulp sheets impregnated, at both the 0.1 and 2.0 percent
by weight of active (or 100 percent surfactant in a formulation)
surfactant based on the weight of bone dry pulp, with the
zwitterionic surfactants
N-tallowalkyl-N,N-dimethylammonio-2-hydroxy-3-propane-1-sulfonate,
N-eicosyl (and docosyl)-N,N-dimethylammonioacetate and
N-octadecyl-N,N-dimethylammonioethylsulfate will exhibit similar
comminution, absorbency and bulk characteristics to those
impregnated with N-tallowalkyl-N,N-dimethylammonioacetate, as do
pulp sheets impregnated with other zwitterionic surfactants having
the herein disclosed structures. The absorbent air-laid pads
comprised of zwitterionic surfactant impregnated fibers have
specific utility in bandages, diapers, sanitary napkins, tampons
and like articles.
While preferred embodiments of the invention have been described,
the descriptions are intended to be illustrative only, and it is to
be understood that many variations which will be readily apparent
to those skilled in the art may be made without departing from the
spirit and scope of the inventive contribution to the art, as
defined by the appended claims.
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