U.S. patent number 3,902,957 [Application Number 05/348,352] was granted by the patent office on 1975-09-02 for process of making fibers.
This patent grant is currently assigned to Crown Zellerbach Corporation. Invention is credited to John H. Kozlowski.
United States Patent |
3,902,957 |
Kozlowski |
September 2, 1975 |
Process of making fibers
Abstract
An improved process of manufacturing fibers by the technique of
forming a mixture of polymer, solvent for such polymer and,
optionally, water or other flashing aids, at a temperature (flash
temperature) which is high enough to bring the polymer to a plastic
state and which will permit substantially complete vaporization of
the solvent when the mixture is flashed, flashing the mixture into
a flash zone to produce a fibrous product, and subsequently
refining the fibrous product characterized in that the fibrous
product is first passed through a primary refining zone at a
temperature above the boiling point of the solvent, and then
subjecting the fibrous product to a secondary refining. The primary
refining is effected under conditions such that only a light
defibering action is imparted to the fibrous product, and is
preferably carried out in a disc refiner having wide plate
clearances. The secondary refining is carried out under conditions
to impart a vigorous fiberillating action to the fibrous product
and provide a pulp having a drainage factor in excess of 1.0
second/gram.
Inventors: |
Kozlowski; John H. (Vancouver,
WA) |
Assignee: |
Crown Zellerbach Corporation
(San Francisco, CA)
|
Family
ID: |
23367638 |
Appl.
No.: |
05/348,352 |
Filed: |
April 5, 1973 |
Current U.S.
Class: |
162/157.5 |
Current CPC
Class: |
D21H
13/14 (20130101); D21H 5/202 (20130101); D01D
5/11 (20130101) |
Current International
Class: |
D01D
5/00 (20060101); D01D 5/11 (20060101); D21F
011/00 () |
Field of
Search: |
;162/157R,146
;264/5,13,14,121,205,209,DIG.47,DIG.8 ;260/94.9F |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Bashore; S. Leon
Assistant Examiner: Chin; Peter
Attorney, Agent or Firm: Horton; Corwin R. Teigland; Stanley
M. Howard; Robert E.
Claims
I claim:
1. In a method of producing a pulp of polymeric fibers wherein a
solution or dispersion of a polymer in a solvent at an elevated
temperature and pressure is flashed through a nozzle into a zone of
reduced pressure to form a fibrous product under conditions such
that substantially all the solvent is vaporized, the improvement
comprising adding dilution water to the fibrous product while
maintaining the fibrous product at a temperature from above the
boiling point of the solvent to 100.degree.C in order to vaporize
residual solvent, passing the fibrous product at a temperature in
such range through a primary refining zone under conditions such
that only a light defibering action is imparted to the fibrous
product, and subjecting the fibrous product to secondary refining
to produce said pulp.
2. The process of claim 1 wherein the temperature of the fibrous
product being fed to the primary refining zone is maintained
between about 70.degree. C. and 100.degree. C.
3. The process of claim 2 wherein the fibrous product is diluted
with water to a consistency between about 1% and 10% by weight
prior to primary refining.
4. The process of claim 1 wherein the primary refining is carried
out by passing the fibrous material through a double disc refiner
with the spacing between the plates set at between about 0.1 inch
and 0.25 inch.
5. The process of claim 4 wherein the discs have a relative
peripheral velocity between about 4,000 and 8,000 feet per
minute.
6. The process of claim 1 wherein the polymer is an at least
partially crystalline polyolefin.
7. The process of claim 1 wherein the polyolefin is
polyethylene.
8. The process of claim 1 wherein a dispersion of the polymer,
solvent and water at a temperature above the melt dissolution
temperature of the polymer is flashed through the nozzle.
9. The process of claim 8 wherein the dispersion additionally
contains polyvinyl alcohol.
10. The process of claim 1 wherein the fibrous product is cooled to
a temperature between about 15.degree. C. and 50.degree. C. prior
to the secondary refining.
11. The process of claim 1 wherein the secondary refining is
carried out under conditions to impart a vigorous fibrillating
action to the fibrous product to thereby produce a pulp having a
drainage factor greater than 1.0 second/gram.
12. The process of claim 10 wherein the secondary refining is
carried out by passing the cooled fibrous product at least once
through a disc refiner whose plates are spaced apart a distance
less than about 0.1 inch.
13. In a method of producing a pulp of polyolefin fibers wherein a
solution or dispersion of a polyolefin in a solvent at an elevated
temperature and pressure is flashed through a nozzle into a zone of
reduced pressure to form a fibrous product, the improvement
comprising diluting the fibrous product with water to a consistency
between about 1% and 10% by weight while maintaining the fibrous
product above the boiling point of said solvent at a temperature
between about 70.degree. C. and 100.degree. C., in order to
vaporize residual solvent passing the fibrous product at said
temperature through a primary refining zone comprised of a disc
refiner adjusted to impart only a light defibering action to the
fibrous product, and passing the fibrous product at least once
through a secondary refining zone comprised of a disc refiner
adjusted to impart a vigorous fibrillating action to the fibrous
material to thereby produce a pulp having a drainage factor greater
than 1.0 second/gram.
14. The process of claim 13 wherein the refiner plates of the
double disc refiner of said primary refining zone are spaced apart
a distance between about 0.1 and 0.25 inch.
15. The process of claim 14 wherein the discs have a relative
peripheral velocity between about 4,000 and 8,000 feet per
minute.
16. The process of claim 1 wherein the size of the fibrous product
after the primary refining step is such that at least 90% of the
product is retained on 20 plus 35 mesh screens.
Description
BACKGROUND OF THE INVENTION
Numerous processes have been proposed for preparing synthetic
fibrous materials by flashing polymer solutions or dispersions held
at high temperature and pressure into a zone of reduced pressure.
In various patent literature, such as German Offenlegungsschrift
No. 1,958,609 and Japanese patent application having publication
No. 71-34921, processes are proposed in which a polymer is
dissolved in a solvent therefor and heated under at least
autogenous pressure and then flashed into a zone of lower pressure
to thereby vaporize the solvent and form fibrous materials. In the
latter mentioned patent, the fibrous material thus formed is
quenched with a water spray at a temperature between 60.degree. C.
and 80.degree. C.
Similar processes are presented in United States patent application
Ser. NO. 295,339, filed Oct. 5, 1972, (assigned to the assignee of
the present application) and as well in German OLS NO. 2,121,512
and German OLS No. 2,144,409. In these processes a polymer
dissolved in a solvent is mixed with water or other liquid
nonsolvents for the polymer to form an emulsion of the polymer
solution in a continuous water phase and this emulsion is heated
and flashed to a reduced pressure zone to produce fibers.
Another approach is described in U.S. patent application Ser. No.
285,386, filed Aug. 30, 1972 now abandoned, (assigned to the
assignee of the present application) wherein a polymer solution in
which water is dispersed as a discontinuous phase is flashed to
form fibers. In this process, the water concentration is held
between 30% and 70% of the entire mixture and in forming the
mixture it is preferable to add the water to the preformed polymer
solution to insure that the water forms the discontinuous
phase.
OLS No. 2,147,461 describes a process in which molten polymer is
emulsified with water (optionally, with a minor amount of solvent
in the polymer phase) and then heated and flashed to a reduced
pressure zone to form fibers.
While many variations are evident, it is seen that the common
feature of all these fiber-making processes is the flashing into a
zone of reduced pressure of a heated mixture containing a polymer
and a solvent for such polymer. Various conditions of flashing are
suggested in the referenced processes, including temperature and
pressure ranges for the mixture to be flashed and various solvents,
flashing aids, etc. Most of the references contemplate flashing
into a zone held at atmospheric pressure. Others suggest the
possibility of flashing into a zone which is above or below
atmospheric pressure, in some cases with the application of heat in
such zone. All of these processes may lead to the production of
fibrous material. However, each suffers from the shortcoming that a
specific set of conditions of flashing, particularly with regard to
temperature and pressure, and interrelationship of such conditions
are not provided which will permit manufacture, in a practical
manner, of fibers having the optimum properties desirable for their
use as a synthetic pulp in the manufacture of paper by conventional
techniques.
Fibrous materials produced under the general process conditions
described in these references tend to be interconnected or bundled
together to an undesirable degree and the paper produced therefrom
is undesirably low in strength (e.g., tensile strength). Such
fibrous material is more difficult to separate, cut or refine in
preparation for papermaking and contains a high content of gels and
chunks of polymer which cause undesirable "fish eyes" or
transparent spots in paper manufactured therefrom.
It has recently been suggested (in U.S. patent application Ser. NO.
340,140 of H. Yonemori, filed by the present assignee on Mar. 12,
1973, and entitled "Process of Making Fibers") to overcome these
problems by providing a specific interrelated set of flashing
conditions to produce a product capable of being readily separated
and refined into an improved pulp for papermaking which has a low
content of gels and chunks and excellent drainage factor
characteristics. Briefly, that process comprises flashing into a
zone at subatmospheric pressure to provide a fibrous product having
a temperature less than 70.degree. C. and subsequently refining the
pulp at this low temperature, preferably while maintaining the pulp
under such subatmospheric conditions in order to minimize
condensation of solvent vapor. While this approach is satisfactory
from a technical point of view, it is expensive to practice
commercially because of the vacuum requirements imposed on the
system. Also, the amount of unvaporized solvent remaining in the
fibrous product after refining is such as to require further
solvent elimination measures.
BRIEF DESCRIPTION OF THE PRESENT INVENTION
The purpose of the present invention is to provide an economical
technique applicable to all of the flashing processes previously
described which will produce a pulp useful for producing synthetic
paper by conventional papermaking techniques which has surprisingly
improved properties and a low content of solvent, gels and
chunks.
Briefly, the present process comprises taking the flashed fibrous
product produced by the foregoing processes, forming an aqueous
mixture of the fibrous product while maintaining the product at a
temperature above the boiling point of the solvent(s) employed in
the solution or dispersion, passing the fibrous product at such a
temperature through a primary refining zone operated under
conditions such that the fibrous product is subjected only to a
light shredding or defibering action, and passing the fibrous
product through a secondary refining zone under conditions such
that the fibrous product is given vigorous fibrillating action.
Preferably, the fibrous product is cooled prior to secondary
refining.
DESCRIPTION OF PREFERRED EMBODIMENTS
In practicing the process of the present invention, any polymer or
copolymer may be employed which is capable of forming fibers by
conventional spinning techniques. It is preferred to employ
crystalline or partially crystalline polyolefins such as low
pressure polyethylene, isotactic or partially isotactic
polypropylene, and ethylene-propylene copolymers. Additionally,
polybutenes and polymethyl pentenes may be employed in the practice
of this invention. Crystalline or partially crystalline polyamides
and polyesters may also be used. Noncrystalline polymers such as
polycarbonates, polysulfones, polyvinyl chloride,
polymethyl-methacrylate, polyacrylonitrile and polystyrene may be
used. Mixtures of the foregoing with each other or other polymers
may also be employed.
The preferred polyolefins employed are those having an intrinsic
viscosity above about 0.7 dl/g., which for high density
polyethylene corresponds to a viscosity average molecular weight of
about 30,000 to 40,000.
The polymers employed in practicing the present process may be in
the form of dried powder or pellets or, preferably, as a wet cake,
slurry or solution of polyolefin in the reaction solvent as
obtained after polymerization.
Generally, any substituted or unsubstituted aliphatic, aromatic or
cyclic hydrocarbon which is a solvent for the polymer at elevated
temperatures and pressures, which is relatively inert under the
conditions of operation and which has a boiling point at
atmospheric pressure that is between 20.degree. C. and 100.degree.
C., preferably between 50.degree. C. and 100.degree. C., and at the
flash zone temperature less than the softening point of the polymer
may be employed in practicing the present process. Illustrative of
the solvents which may be utilized are aromatic hydrocarbons, e.g.,
pentane, hexane, heptane and their isomers and homologues;
alicyclic hydrocarbons, e.g., cyclohexane; chlorinated
hydrocarbons, e.g., methylene chloride, carbon tetrachloride and
chloroform; higher alcohols; esters; ethers, ketones; nitriles,
amides; fluorinated compounds, e.g., fluoro-hydrocarbons;
nitromethane; and mixtures of the above solvents and other solvents
having a boiling point between about 20.degree. C. and 100.degree.
C. at atmospheric pressure. The preferred solvent is hexane which
has a boiling point of 68.7.degree. C. at atmospheric pressure.
The polymer-solvent mixture may be formed by any one of several
methods. One may start with a solution of polymer in solvent as it
comes from a solution polymerization process, either at the same
concentration, diluted or concentrated. Alternatively, one may
start with a slurry of polymer particles in the solvent such as is
produced by a slurry of polymerization procedure and the
appropriate amount of water is added to the slurry or vice versa. A
further alternative would be to start with a dry polymer powder, or
granules, or a wet cake such as might be produced at some stage of
solvent removal in the polymer plant and the appropriate amount of
solvent is admixed therewith.
The polymer concentration relative to the solvent is not critical,
the solvent being present in an amount that is greater than 100% by
weight of the polymer and sufficient to give a viscosity at the
flash temperature employed that can be easily handled. Frequently,
this viscosity will be up to about 3,500 centipoises. Generally,
the polymer concentration will vary from about 2% to about 30% by
weight of the solvent plus polymer, and preferably is in the range
of about 5% to about 15%.
In one preferred embodiment water is employed as a flashing aid. In
this embodiment the water may be in a continuous phase or
discontinuous phase, depending upon the amount of water added to
the polymer-solvent mixture and the manner of addition. If the
water is to form the discontinuous phase it should be present in an
amount less than 70%. To form a continuous water phase the water
should be present in an amount greater than 30% by volume of the
mixture and preferably between 50% and 70%. The particular method
of mixing is not critical, but if it is desired to have the water
form a discontinuous phase it has been found to be advantageous to
have the solvent present prior to water addition since the solvent
or polymer solution will form the continuous phase of the mixture
to be formed. This latter approach is particularly desirable when
one employs an amount of water which is near the borderline of an
inversion occurring, i.e., at the point where the amount of water
is approaching that level where it would form the continuous phase.
Conversely, if the water is added with or before the solvent, it
will tend to form the continuous phase.
A primary function of the water is to provide energy to aid the
vaporization of the solvent during flashing since it is not
desirable to have the temperature so high that there is sufficient
energy imparted to the solvent alone to effect its complete
vaporization. However, the amount of water should not be so great
as to require the expenditure of unnecessary heat values in
attaining the desired flashing temperature, i.e., once that amount
of water required to form an aqueous solution or dispersion of the
agent having a suitable viscosity is determined, additional water
may be employed to a certain extent since it helps to lower the
mixture viscosity and aids solvent vaporization but the additional
amount need not be great.
Another function of the water is to reduce the temperature of the
fibrous mass in the zone immediately following the nozzle (flash
zone). The addition of water increases the total vapor pressure of
the system at the moment of flashing thus reducing the boiling
point of the flashing mixture. This is independent of the amount of
water employed, and very small quantities may thus be employed for
this purpose. As a practical matter, however, water would be
employed in the amount of at least about 1% by volume of the
solvent-water mixture. Lowering the boiling point of the mixture in
this fashion will assist in establishing proper temperature
conditions in the fibrous mass formed upon flashing in accordance
with this invention, as discussed in detail at a later point.
Another function of the water is to act as the carrier for a
hydrophilic water-dispersing agent for the fibers to be formed. It
has been found that it is most advantageous to have the
water-dispersing agent present during flashing and precipitation of
the fibrous polymer. An equivalent amount of the same agent added
at a later stage to the already formed fibers does not give the
same degree of dispersibility and the presence of the agent
enhances the refinability of the fibers. Therefore, the water
should be present in an amount sufficient to carry that amount of
the hydrophilic agent employed to impart to the fibrous polymer the
desired level of water dispersibility, preferably as a solution
thereof. Additional water above such minimum amount required to
carry the agent may be employed to impart a suitable viscosity to
the aqueous solution or dispersion agent, i.e., the aqueous
solution of the water-dispersion agent should not be so viscous as
to present problems of handling or incorporation into the polymer
solution as a dispersed phase. Also, the water can aid in reducing
the viscosity of the mixture to a level less than that of the
polymer solution alone, thus permitting higher polymer
concentrations.
The agents which may be added to the mixture to impart water
dispersibility to the fibrous polymer are preferably water soluble,
or partially water soluble, high molecular weight materials.
However, they may also be materials which are soluble or partially
soluble in the solvent so long as they are somewhat hydrophilic and
impart water dispersibility to the fibers. The amount of
water-dispersing agent employed may range from about 0.1% to about
15% by weight of the polymer, preferably from about 0.1% to about
5% by weight. The preferred waterdispersing agent is an at least
partially water-soluble polyvinyl alcohol (PVA) having a degree of
hydrolysis greater than about 77% and, preferably, greater than
about 88 mol. % and having a viscosity (in a 4% aqueous solution at
20.degree. C.) between about 2 and 50 centipoises. Desirably, the
PVA has a degree of polymerization in the range of 200 to 4,000 and
preferably between 300 and 1,500. If desired, the PVA may be
chemically modified to enhance its adhesion to the polymer,
dispersion and other properties. The polyvinyl alcohol is
preferably added with the water at the time the mixture is formed.
Illustrative of other water-dispersing agents that may be employed
are cationic guar, cationic starch, potato starch, methylcellulose
and Lytron 820 (a styrene-maleic acid copolymer).
Such water-dispersing agents are also advantageous in developing
the fiber properties during refining of the flashed product in
accordance with this invention, as described at a later point.
Alternatively for this purpose, such agents may be added subsequent
to flashing, such as with the dilution water for refining. It is
particularly advantageous to add at least 0.75% and preferably
between about 1 1/2% and 5% by weight of the flashed polymer of
polyvinyl alcohol, either before and/or after flashing (but prior
to refining).
The ingredients of the mixture can be placed in any suitable vessel
which is capable of being heated to an elevated temperature and
pressure. Generally, an autoclave is employed. However, when water
is added as a flashing aid it is important that the vessel employed
be equipped with a mixing or stirring device capable of keeping the
mixture in a constant state of agitation since a stable emulsion is
not formed and upon standing the mixture will quickly separate into
two distinct and separate phases.
The ingredients are then heated to a suitable temperature and
preferably agitated if water is present to form a uniform mixture
wherein water is present as a discontinuous or dispersed phase
within a continuous phase of polymer solution or as a continuous
phase with polymer solution dispersed uniformly therein, depending
upon the water concentration and mode of addition, as previously
discussed. The temperature employed is preferably above the melt
dissolution temperature of the polymer in the solvent employed. The
melt dissolution temperature of any particular solvent is
determined by placing low concentrations of the polymer (e.g., 0.1
and 1.0% by weight) into the solvent in a vial which is then sealed
and placed in an oil bath. The temperature of the oil bath is
raised slowly (e.g., 10.degree. C/hr) until the last trace of
polymer disappears. This temperature is the melt dissolution
temperature. In some instances, it may be desirable to operate at a
temperature below the melt dissolution temperature. In this case
the temperature should be high enough under the operating
conditions so that the polymer is dissolved in the solvent or at
least is in a swollen state with sufficient fluidity to be
discharged from the nozzle, i.e., in a plastic state.
Flashing is preferably carried out substantially adiabatically,
utilizing the heat (enthalpy) in the heated mixture to provide the
heat of vaporization for vaporizing substantially all of the
solvent when the mixture is discharged to the flash zone held at a
suitable lower pressure. Accordingly, for adiabatic flashing, the
temperature of the mixture prior to flashing should be high enough
to provide sufficient heat content or enthalpy for vaporization
adiabatically of substantially all solvent upon flashing to the
flash zone. However, the maximum temperature employed should be
less than the critical temperature of the solvent and/or the
decomposition temperature of the polymer.
It is also possible to carry out the flashing to some extent in a
nonadiabatic fashion, for example, by the addition of heat to the
material as it is flashed from the nozzle. For instance, low
pressure steam (e.g., below 20 psig) or water at about 100.degree.
C. may be added to the fibrous noodle in the flashing zone as by
injection thereof in a conduit immediately following the flash
nozzle into which the flashed noodle is also injected. In this
case, the flashing temperature should be chosen so the heat content
in the mixture to be flashed plus the heat added to the flashed
material is sufficient to vaporize substantially all of the solvent
in the flash zone.
The pressure employed in the vessel containing the heated mixture
is preferably substantially autogenous although pressures higher
than autogenous may be employed. It may be desirable, particularly
in batch operations, to employ an inert gas such as nitrogen during
the flashing operation to maintain substantially autogenous
pressure in the vessel and thus maintain the velocity of the
mixture through the nozzle at a fairly constant level.
Flashing is preferably effected through a nozzle which has a
substantial longitudinal dimension in order to efficiently impart
shear to the mixture (particularly the polymer component thereof)
immediately prior to flashing. Such shearing action aids fiber
formation and enhances fiber properties for papermaking purposes.
The nozzle may be circular or noncircular in cross-section and may
be an annulus.
The flash zone is maintained at a pressure which, in conjunction
with the other conditions of flashing are selected so that the
temperature of the flashed product is almost immediately lowered in
the flash zone, by evaporation of substantially all of the solvent
(and a portion of the flashing aids, if employed), to a temperature
below the softening temperature of the polymer, preferably below
about 100.degree. C., but above the boiling temperature of the
solvent(s) employed and preferably above about 70.degree. C.
In a typical flashing procedure in accordance with this invention,
vaporization may be substantially complete 10 to 100 cm downstream
of the nozzle. However, this can vary widely depending on the flow
velocity, flash zone pressure, flash temperature, solvent, etc.
Importantly, in the mixture to be flashed, all of the components of
the mixture and the concentration of each in the mixture are chosen
with respect to the heat capacity of each, with respect to the heat
of vaporization of each component which will be volatilized in
flashing, and with respect to the flash temperature chosen so as to
produce in the flashed product a temperature above the boiling
point of the solvent and preferably between about 70.degree. C. and
about 100.degree. C. upon flashing of the mixture into the flash
zone. Expressed in another way, the heat content of the mixture to
be flashed and the heat to be removed through vaporization of the
vaporizable components (solvent and any flashing aids vaporized, if
employed) should be adjusted so that the residual heat in the
flashed product, after removal of the heat of vaporization of the
vaporized components, will impart a temperature in the flashed
product which is between about 70.degree. C. and 100.degree. C.
Selection of the appropriate flashing temperature and of the
components of the mixture and their concentrations for this purpose
will depend upon the pressure selected for the flash zone and the
amount of heat added to the flash material during flashing if the
flashing is performed nonadiabatically. Preferably, the flash zone
is at substantially atmospheric pressure, i.e., between about 600
and 800 mm Hg. If the flash temperature is too high or if the
components of the flash mixture and their concentrations with
respect to their heat capacity and heat of vaporization (for the
vaporizable components) are improperly chosen, the temperature of
the flashed product, upon substantially complete evaporation of the
solvent, will remain above 100.degree. C. If the flash temperature
is too low, or, again, the components are improperly chosen with
respect to heat capacity and heat of vaporization, there will be
incomplete evaporation of the solvent. For the purpose of this
invention appropriate selection of these variable parameters,
namely, the flash temperature, components and concentrations
thereof in the flash mixture, may be determined for a given
pressure condition in the flash zone by making a heat balance for
the flashing operation which will produce the desired noodle
temperature below 100.degree. C. Advantageously, these variable
parameters may be selected so as to satisfy the following equation:
##EQU1## Q.sub.p = Enthalpy of polymer(s) in flash mixture Q.sub.s
= Enthalpy of solvent(s) in flash mixture
Q.sub.f = Enthalpy of flashing aid(s) in flash mixture
Q.sub.na = Heat added to flashing mixture (if nonadiabatic)
V.sub.s = Enthalpy of vaporization of solvent vaporized
V.sub.f = Enthalpy of vaporization of flashing aids vaporized (if
any)
W.sub.p = Weight of polymer in the flashed product
C'.sub.p = Heat capacity of polymer in flashed product
W'.sub.f = Weight respectively, of the flashing aids, adjuvants,
and/or nonvolatile components other than polymer in the flashed
product (if any)
C'.sub.f = Heat capacity of the respective flashing aids,
adjuvants, and/or nonvolatile components other than polymer in the
flashed product (if any)
and where such enthalpy values are based on the same temperature
datum plane and the heat capacities are those applicable between
such datum plane and the temperature of the flashed product.
In using this formula, the heat capacity values and Weights of the
flash components may be substituted into this formula, for example,
as follows for the specific case where a single polymer, solvent
and flashing aid are present in the flash mixture: ##EQU2## where
the additional terms are: W.sub.s = Weight of the solvent in the
flash mixture
C.sub.s = Heat capacity of the solvent in the flash mixture
W.sub.f = Weight of the flashing aid in the flash mixture
C.sub.f = Heat capacity of the flashing aid in the flash
mixture
C.sub.p = Heat capacity of the polymer in the flash mixture
H.sub.f = Heat of vaporization of solvent under flash
conditions
H.sub.s = Heat of vaporization of flashing aid under flash
conditions
T.sub.f = Flash temperature, .degree.C.
and where the indicated heat capacities are those applicable
between the flash temperatures and the previously mentioned
temperature datum plane.
In practice, the heat capacity and enthalpy of vaporization values
for the desired components can be substituted into this equation.
Then, a flash temperature and the concentrations of the flash
mixture components may be selected relative to each other to
satisfy the equation for a desired flashed product temperature. For
ease of calculation it can be useful to program these variables for
computer analysis to select the desired components and flash
temperature.
It is not necessary to actually measure the noodle temperature
(which is a cumbersome procedure under the flash zone conditions).
All that is necessary for control purposes is to maintain the
indicated parameters for the flash procedure at values that satisfy
this equation for the noodle temperature which is desired. Of
course, the various parameters should also satisfy the other
conditions for proper flashing as previously discussed, e.g., the
flash temperature should be above the melt dissolution temperature,
substantially all of the solvent should be vaporized, etc.
While it is desirable to have the temperature of the fibrous
product or noodle at a temperature between about 70.degree. C. and
100.degree. C. after flashing in order to insure vaporization of as
much of the solvent as possible, the temperature can be raised to
this range by suitable means prior to primary refining. As will be
discussed more below, primary refining is carried out at a
temperature above the boiling point of the solvent and preferably
within the range of about 70.degree. C. to 100.degree. C. in order
to vaporize any residual solvent left in the noodle.
During flashing, the polymer is precipitated as a fibrous product
or "noodle," which is a loose aggregation of fibers which is
usually continuous. The fibrous product is collected in a suitable
receiving vessel, preferably one which permits the vaporized
solvent to be separated therefrom.
The fibrous product in the receiving vessel may be either
substantially "dry" if flashed from a polyolefin solution or as an
aqueous slurry if flashed from a dispersion or emulsion employing
water as a flashing aid. However, in both cases a certain amount of
unflashed residual solvent will remain with the fibrous product and
it is therefore important that the temperature of the fibrous
product be kept high enough to continue the vaporization of the
solvent.
In the copending application of H. Vonemori referred to above, it
was discovered that improved products were obtained by refining the
fibrous product at relatively low temperatures, and to minimize
condensation and/or retention of the sovlent, the vapor separation
zone and the refining zone were desirably maintained under
subatmospheric pressure.
The present invention resides in the discovery that similarly
improved products can be obtained with a smaller amount of retained
solvent by carrying out the refining of the fibrous product while
it is maintained at an elevated temperature above the boiling point
of the solvent if the fibrous product first passed through a
primary refining zone under conditions such that only a light
defibering or shredding action is imparted to the fibrous product.
By defibering or shredding action, it is meant that the noodle is
subjected to forces just sufficient to pull it apart into a fibrous
mass which, at a consistency between about 1% and 10% by weight, is
pumpable. If the fibrous product is subjected to more than such
light defibering or shredding action while at elevated
temperatures, the ultimate fiber and sheet properties are
detrimentally affected, as will be shown in the examples.
Prior to passing the fibrous product through such primary refining
zone, dilution water is added to the receiving vessel to provide an
aqueous slurry of the fibrous product having an appropriate
consistency. Typically, the consistency of the aqueous slurry is
between about 1 to 10% by weight of the fibrous material, although
high consistencies between about 10% and 60% by weight may be
employed by using screw feeding or similar feeding means. The
dilution water temperature should be such as to provide an aqueous
slurry of noodle having a temperature above the boiling point of
the solvent at the pressure employed (normally 1 atmosphere), and
preferably between about 70.degree. C. and 100.degree. C.
The aqueous slurry of fibrous product at an appropriate consistency
and temperature is then passed through the primary refining zone to
effect the desired defibering or shredding action on the material.
In its preferred form, the primary refining zone is a disc refiner
of the type conventionally employed in the papermaking art and may
be a single or double rotating disc refiner. However, the refiner
is operated to impart only a light defibering or shredding action
to the fiberous product passing therethrough. This is accomplished
by preferably employing plates having narrow bars, that is, bars
having a width up to about 0.5 inch, and by spacing the plates
relatively far apart, that is, a plate clearance distance between
about 0.1 and 0.25 inch. The moving disc or discs are rotated at
speeds to provide relative peripheral velocities between about
4,000 and 8,000 feet per minute. The size of the discs may be any
of those normally employed in the papermaking art.
The defibering or shredding action referred to may be characterized
by the amount of fibrous material retained on the 20 plus 35-mesh
screens after primary refining when the fibrous material is
classified in accordance with TAPPI Standard Test T-233 SU64. At
least about 90% of the fibrous material should be retained on the
20 plus 35-mesh screens; if less than this amount is retained, the
refining action has been too vigorous. Generally, the amount of
work done on the fibrous material during primary refining will be
less than about 0.1 kilowatt-hour/kilogram.
While the primary refining is preferably accomplished by use of a
disc refiner as discussed above, it may be accomplished in other
devices such as Claflin refiners, Hollander beaters, Dynapulpers,
hydrapulpers, etc., it only being necessary to impart a defibering
or shredding action which will still permit at least about 90% of
the fibrous material to be retained on a 20 plus 35-mesh
screen.
While normally and preferably the amount of work to provide the
light brushing action is imparted to the fibrous product by one
pass through a disc refiner operated, as discussed previously,
multiple passes may be employed as long as the total work imparted
to the fibrous product by all the passes does not cause more than
the defibering or shredding action just discussed.
The aqueous slurry of fibrous product resulting from the primary
refining operation drops from the bottom of the disc refiner into a
receiving vessel which may be purged with an inert gas such as
nitrogen to remove solvent vaporized during the primary refining
step. The fibrous product is preferably cooled to a temperature
below 70.degree. C. by any suitable method, such as use of cooling
coils, adding dilution water or sitting, and the cooled pulp is
then subjected to secondary refining. Alternatively, the pulp may
be cooled and thickened for storage and/or shipment, and the
secondary refining may be accomplished at a much later date with
the same beneficial results.
The secondary refining is preferably carried out in a disc refiner
employing refiner conditions which impart a vigorous fibrillating
action to the fibrous product which optimizes the fiber papermaking
characteristics. The precise conditions employed in this secondary
refining need not be gone into in detail since the skilled
papermaker can optimize the type of plates, disc spacing, disc
velocity and power output to develop optimum properties for the
particular product to be produced from the fibers.
For purposes of illustration, the secondary refining may be carried
out with refiner plates having a plate spacing less than 0.1 inch
(2500 microns), and desirably between about zero and 0.01 inch (250
microns), and a disc peripheral velocity of between about 4,000 and
8,000 feet per minute. Multiple passes through one or more refiners
may be employed. Instead of disc refiners, one may employ any
conventional refining device and refine the pulp in a known manner
to optimize properties.
The secondary refining is conducted under conditions such that the
drainage factors of the resulting pulp is greater than 1.0
seconds/grams. Also, after secondary refining the pulp will be
retained to the extent of less than 90% and generally less than 50%
by weight on the 20 plus 35-mesh screens.
By employing the refining sequence just described, i.e., a
defibering- or shredding-type primary refining of the fibrous
noodle at an elevated temperature followed by secondary refining,
preferably at a reduced temperature, a pulp is produced having
superior qualities. In this respect, one indication of the
improvement of the fibers made by the process of the present
invention is the drainage factor of such fibers as compared to
fibers of similar classified fiber length which are made using
parameters outside the present invention. The drainage factor is a
measure of the drainage characteristics of a fiber when a slurry
thereof is placed on a foraminous surface. For synthetic fibers of
similar fiber length made by the flashing process, important
strength properties thereof correlate generally with their drainage
factor. For a fiber pulp having the same classified fiber length,
various strength properties of paper made therefrom increase with
the drainage factor of such fibers.
Another indication of improvement of the fibers made in accordance
with this invention is their slenderness relative to fibers
prepared by typical conventional technique. It is desirable to
produce fibers which are relatively thin (or of low coarseness) as
these fibers will impart higher opacity, density and better
formation to the paper prepared therefrom.
Generally, the set of operating parameters of the present invention
will result in improved fiber properties such as thinness and
drainage factor compared with fibers prepared using typical
conventional parameters. Because other process variables in
addition to the specific parameters of this invention also
influence fiber properties (e.g., flash nozzle size and
configuration, polymer type and molecular weight, solvent, flashing
aids, dispersants, etc.), such resulting fiber comparisons are
appropriately made with the other process variables held
constant.
For the same reason, i.e., the influence of other process
conditions besides the parameters specific to this invention on the
resulting fiber properties, no absolute fiber property values can
be assigned to the fibers which may be prepared by the process of
this invention. However, with appropriate selection of all
parameters, it has been found that pulps can be produced in
accordance with this invention which have a drainage factor in
excess of 1 and as high as 50 to 100 seconds per gram and which
have an average coarseness below 15 decigrex (as measured by TAPPI
Text 234 SU 67) and frequently between 1 and 10 decigrex (m/100 m).
For papermaking use, a drainage factor between 2 and 10 may be the
preferred range as an appropriate balance between increased
strength and ease of water removal from the fibers. Higher drainage
factors can be obtained and may be useful where the enhanced
strength is more important than rapid water removal.
In the accompanying drawing, the FIG. 1 represents a schematic
representation of apparatus suitable for use in carrying out the
process of this invention, and FIG. 2 is a detailed representation
of the flash nozzle schematically shown in FIG. 1.
In FIG. 1, 1 is a steam-jacketed vessel, provided with an agitator
1a, which may be charged with solvent, polymer (or polymer
solution) and, if desired, flashing aids such as water. Conduit 2
is provided at the bottom of vessel 1 in communication with flash
nozzle 3 through shut-off valve 4 (preferably a ball valve). As
seen in FIG. 2 flash nozzle 3 has a substantially smaller diameter
than conduit 2. After the mixture is heated to the desired
temperature and agitated, if necessary, to dissolve the polymer
and/or disperse the flashing aids, valve 4 is opened and the
mixture thus formed is forwarded from vessel 1 through flashing
nozzle 3 under autogenous pressure of the heated mixture. As the
mixture discharges from vessel 1, nitrogen or other inert gas may
be introduced into the head space thereof through line 5 in order
to maintain the pressure in the vessel at autogenous or higher
pressure. The mixture is flashed through nozzle 3 into the flash
zone which is comprised of a vapor separation vessel such as
cyclone 6, and connecting conduit 7. Conduit 7 is a pipe having an
internal cross-sectional area larger than that of flash nozzle 3
and of sufficient internal diameter to permit rapid, unrestricted
passage of the flashed noodle to cyclone 6 and preferably has an
internal cross-sectional area many times larger than that of the
nozzle 3. Optionally, low pressure steam may be introduced into
conduit 7 through line 8 located shortly beyond flash nozzle 3 to
aid in the vaporization of solvent from the precipitated
noodle.
Vaporized solvent and water leaving cyclone 6 pass through line 21
to a solvent recovery unit (not shown).
The flashed fibrous noodle entering cyclone 6 through conduit 7,
together with the unvaporized portion of water or other flashing
aid present, passed downward through conduit 9 into primary disc
refiner 10 where it is lightly shredded. Conduit 11 is provided for
introduction of dilution water at an appropriate temperature to
form a mixture or slurry with the fibrous material having an
appropriate consistency for disc refining.
The lightly shredded material leaving the primary refiner 10 passes
through conduit 12 to first receiving tank 13. Nitrogen is
introduced into tank 13 through line 14 which sweeps out solvent
vapors which are removed via suitable means not shown.
The water slurry of refined fibers is cooled, either by letting the
slurry sit in tank 13 for an appropriate time or by other means.
The slurry may be withdrawn from receiving tank 13 through line 15
utilizing pump 16, for secondary refining in disc refiner 17. The
fibrous slurry leaving secondary refiner 17 passes through conduit
18 to second receiving tank 19 where it is collected prior to
further processing for shipment or for papermaking use. If desired,
the fibrous slurry leaving refiner 17 may be recycled through line
20 for one or more additional passes through refiner 17.
The fibers after refining may be diluted to a suitable consistency
and made into synthetic paper webs, either alone or blended with
normal cellulose papermaking fibers. Alternatively, the fibers can
be dewatered, pressed into bales, stored and shipped to the
ultimate user. The secondary refining previously referred to can be
carried out by the ultimate user
The illustrated apparatus may be operated on a batch basis as
described or on a continuous basis by continuously feeding vessel 1
with polymer solution and any flashing aids desired at flow rates
to maintain the appropriate mixture in the vessel for flashing,
while heating the vessel to maintain the mixture at the appropriate
flash temperature. In order to insure unifrom dispersion of
flashing aids, it may be desirable to place an in-line mixing
device in line 2 between vessel 1 and flash nozzle 3.
Optionally, instead of using a stirred heated vessel such as vessel
1, it is also possible to prepare the mixture on a continuous basis
by blending a polymer solution with any flashing aids desired (as
by adding superheated water) continuously in an in-line mixing
device just prior to flashing through a nozzle. It is also possible
to utilize an in-line mixer.
The following examples will illustrate the invention:
EXAMPLE 1
The apparatus employed in this example is that illustrated in the
drawing and previously described. The dissolution vessel 1 was a
two-gallon stirred autoclave equipped with five 4-inch impellers on
a single shaft rotated at 1,000 rpm.
The vessel was charged with 0.32 Kg of polyethylene (Mitsui 2200P)
having an intrinsic viscosity ).eta.) of 1.4 dl/gram and 4.0 liters
of n-hexane. The vessel was sealed and the contents raised to a
temperature of 143.degree. C. For liters of water containing 2% by
weight of 88% hydrolyzed polyvinyl alchol (Moviol 30-88 made by
Farbwerke Hoechst AG) based on the polyethylene at a temperature of
143.degree. C. was then pumped into the vessel under agitation. The
vessel was pressurized with nitrogen to maintain a pressure of 160
psig. The heated contents were then flashed through a nozzle 3
having a diameter of 0.07 inch (1.75 mm) and a length of 1 1/8
inches (28.125 mm) into receiving vessel 6. Low pressure steam (10
psig) was introduced into conduit 7 via line 8 at a point 3 inches
downstream of nozzle 3. Dilution water at a temperature of
93.degree. C. was introduced into receiving vessel 6 to provide a
slurry having a consistency of about 1.0% by weight and a
temperature between 85.degree. C. and 93.degree. C. The aqueous
fibrous slurry was then passed through a primary refining zone
consisting of a Sprout Waldron single disc refiner having 12-inch
plates (Pattern C29-78B) and a plate clearance of 0.150 inch. The
moving disc was operated at 1,750 rpm (peripheral velocity of 5,495
feet per minute). The refiner had been preheated with dilution
water and steam before refiner start-up and setting of plate
clearances.
The pulp slurry was then subjected to secondary refining by passing
it at a temperature of 76.degree.-80.degree. C. once through the
same disic refiner with the plate spacing set at 0.025 inch and
once through at 0.010 inch, then twice through at 0.002 inch.
The resulting pulp had a drainage factor of 4.6 seconds/gram and a
fiber fraction on the 20 plus 35-mesh screen of 38.4% Handsheets
were made from the pulp in accordance with TAPPI Standard Test
T-205M-58 with modified wet pressing (400 psig). The handsheets
were tested and had the following properties:
Basis weight, g/m.sup.2 61.2 Breaking length, Km 0.56 Tensile
Energy Absorption, Kg-cm/cm.sup.2 0.009 Scott Internal Bond,
Kg-cm/cm.sup.2 .times. 10.sup.-.sup.3 59 Scattering coefficient
1834
In the foregoing example and subsequent examples, the sheet
density, basis weight and caliper were determined by TAPPI Standard
T-220, tear strength by TAPPI Standard T-414, opacity by TAPPI
Standard T-425 m-60, fiber fractionation by TAPPI Standard
T-233-SU64, coarseness by TAPPI Standard T-234 SU67, and tensile
strength, stretch, tensile energy absorption and breaking length
were determined by TAPPI Standard T-494. Scattering coefficient was
determined in accordance with the procedure described in the book
by Deane B. Judd, "Color and Business Science Industry," pp 314-329
(1961) John Wiley and Sons.
The Scott Internal Bond was determined by employing the Scott
instrument under the standard procedure.
The drainage factor in this and following examples was determined
substantially in accordance with TAPPI Test T221 OS-63 with a
slight modification in the method of calculation. Briefly,
approximately ten grams of a fiber sample is weighed and dispersed
in water. The slurry is then added to the standard sheet mold and
water added to the mark. The slurry is stirred by four up-and-down
strokes of the standard stirrer, which is then removed. The water
temperature in the mold is measured and the drainage valve opened.
The time between the opening of the valve and the first sound of
suction is noted. The procedure is repeated with water only (no
fiber) in the sheet mold and the temperature and drainage time
noted. The drainage factor in seconds per gram is then calculated
as follows: ##EQU3## where DF = Drainage factor, seconds/gram
D = Drainage time with pulp in mold, seconds
d = Drainage time without pulp in mold, seconds
V.sub.T = Viscosity of water at temperature T
w = weight of fibers employed in test, grams
The quantity (1/V.sub.T - 1) is tabulated in the aforementioned
TAPPI Test T221 OS-63. This quantity is multiplied by 0.3 which has
been empirically determined for the present fibers.
Comparative Example 1
In order to show the improvement in fiber properties obtained by
subjecting a fibrous noodle to a light defibering action at an
elevated temperature rather than a rigorous fibrillating action,
Example 1 was repeated, except that the primary refining was
accomplished by passing the fibrous noodle through the refiner with
the plates set only 0.005 inch apart. The pulp was then passed once
through a secondary refining zone as in Example 1. The resulting
pulp had a fiber fraction on the 20 plus 35-mesh screen of 36.4%
and a drainage factor of only 1.4 seconds/gram compared to 4.6
seconds/gram for the pulp of Example 1. The lower drainage factor
is indicative of a fiber which will form a much weaker sheet, as
shown from the handsheet data set forth in the following table. The
handsheets were made as in Example 1:
Property 100% ______________________________________ Breaking
length, Km 0.22 Tensile Energy Absorption, Kg-cm/cm.sup.2 0.001
Scott Internal Bond, Kg-cm/cm.sup.2 .times. 10.sup..sup.-3 31
Scattering Coefficient 1529
______________________________________
EXAMPLE 2
Example 1 was repeated except that the slurry was cooled to
37.degree.-43.degree. C. prior to secondary refining. After one
pass of secondary refining the resulting pulp had a drainage factor
of 5.0 seconds/gram and a fiber fraction on the 20 plus 35-mesh
screen of 36.4%. Handsheets were made as in Example 1 and had the
following properties:
______________________________________ Property 100% *50/50 Blend
______________________________________ Breaking Length, Km 0.77 2.2
Tensile Energy Absorption, Kg-cm/cm.sup.2 0.028 0.023 Scott
Internal Bond, Kg-cm/cm.sup.2 .times. 10.sup..sup.-3 74 140
Scattering Coefficient 1973 1196
______________________________________ *The 50/50 Blend refers to a
blend of the polyethylene fibers with bleached alder kraft pulp
having a Canadian Standard Freeness of 150 cc.
EXAMPLE 3
The same general procedure as employed in Example 1 was repeated
employing a polyvinyl alcohol made by Farbwerke Hoechst AG (Moviol
30-98) that is 98% hydrolyzed and has a viscosity (4% by weight
aqueous solution at 20.degree. C.) of 3 to 5 centipoises. Runs 1
and 2 were subjected to primary refining in the refiner described
in Example 1 at a plate clearance of 0.150 inch. Run 1 was
subjected to one pass of secondary refining at a plate clearance of
0.005 inch and two passes at a plate clearance of 0.002 inch at a
temperature of 76.degree.-77.degree. C. Run 2 was subjected to one
pass of secondary refining at a plate clearance of 0.005 and three
passes at a plate clearance of 0.002 inch at a temperature of
30.degree.-39.degree. C. Run 3, a comparison, was subjected to
primary refining at a plate clearance of 0.005 inch and two passes
of secondary refining at a plate clearance of 0.002 inch at a
temperature of 75.degree.-82.degree. C. Handsheets (both 100% and
50/50 blends) were made as in Example 1 and tested. The properties
of the fibers and handsheets were as follows:
Comparison Property Run 1 Run 2 Run 3
__________________________________________________________________________
Drainage Factor, sec/g. 3.2 5.2 1.5 % on 20 + 35-mesh screen 31.1
40.2 32 100% Handsheets Basis Weight, g/m.sup.2 60.4 59.4 59.2
Breaking Length, Km 0.60 0.86 0.32 Tensile Energy Absorption,
Kg-cm/cm.sup.2 0.012 0.026 0.002 Scott Internal Bond,
Kg-cm/cm.sup.2 .times. 10.sup..sup.-3 60 106 40 Scattering
Coefficient 1267 1276 1301 50/50 Handsheets Basis Weight, g/m.sup.2
58.2 61.8 60.0 Breaking Length, Km 2.67 2.84 2.82 Tensile Energy
Absorption, Kg-cm/cm.sup.2 0.037 0.05 0.04 Scott Internal Bond,
Kg-cm/cm.sup.2 .times. 10.sup..sup.-3 158 164 174 Scattering
Coefficient 704 703 707
__________________________________________________________________________
EXAMPLE 4
The same general procedure as employed in Example 1 was repeated
employing a polyvinyl alcohol made by Farbwerke Hoechst AG (Moviol
75-88) that is 88% hydrolyzed and has a viscosity (4% by weight
aqueous solution at 20.degree. C.) of 20-25 centipoises. Runs 1 and
2 were subjected to primary refining in the refiner described in
Example 1 at a plate clearance of 0.150 inch. Run 1 was subjected
to one pass of secondary refining at a plate clearance of 0.005
inch and two passes of secondary refining at a plate clearance of
0.002 inch at a temperature of 77.degree.-80.degree. C. Run 2 was
subjected to one pass of secondary refining at a plate clearance of
0.005 inch and three passes of secondary refining at a plate
clearance of 0.002 inch at a temperature of 33.degree.-41.degree.
C. Run 3, a comparison, was subjected to one pass of primary
refining at a plate clearance of 0.005 inch. Handsheets (both 100%
and 50/50 blends) were made and tested as in Example 1. The
properties of the fibers and handsheets were as follows:
Comparison Property Run 1 Run 2 Run 3
__________________________________________________________________________
Drainage Factor, sec/g. 2.2 2.8 1.2 % on 20 + 35-mesh screen 36.6
30.4 36.4 100% Handsheets Basis Weight, g/m.sup.2 57.9 59.7 62.1
Breaking Length, Km 0.63 0.80 0.28 Tensile Energy Absorption,
Kg-cm/cm.sup.2 0.013 0.019 0.002 Scott Internal Bond,
Kg-cm/cm.sup.2 .times. 10.sup..sup.-3 70 94 42 Scattering
Coefficient 1492 1454 1291 50/50 Handsheets Basis Weight, g/m.sup.2
60.4 59.7 59.7 Breaking Length, Km 2.73 2.87 2.26 Tensile Energy
Absorption, Kg-cm/cm.sup.2 0.035 0.047 0.028 Scott Internal Bond,
Kg-cm/cm.sup.2 151 163 141 Scattering Coefficient 889 873 765
__________________________________________________________________________
EXAMPLE 5
The same general procedure as employed in Example 1 was repeated
employing a polyvinyl alcohol made by Farbwerke Hoechst AG (Moviol
75-98) that is 98% hydrolyzed and has a viscosity (4% by weight
aqueous solution at 20.degree. C.) of 25-30 centipoises. Runs 1 and
2 were subjected to primary refining in the refiner described in
Example 1 at a plate clearance of 0.150 inch. Run 1 was subjected
to one pass of secondary refining at a plate clearance of 0.005
inch and two passes at a plate clearance of 0.002 inch at a
temperature of 76.degree.-90.degree. C. Run 2 was subjected to one
pass of secondary refining at a plate clearance of 0.005 and three
passes at a plate clearance of 0.002 inch at a temperature of
40.degree.-42.degree. C. Run 3, a comparison, was subjected to
primary refining at a plate clearance of 0.005 inch and one pass of
secondary refining at a plate clearance of 0.002 inch at a
temperature of 83.degree. C. Handsheets (both 100% and 50/50
blends) were made and tested as in Example 1. The properties of the
fibers and handsheets were as follows:
Comparison Property Run 1 Run 2 Run 3
__________________________________________________________________________
Drainage Factor, sec/g. 2.3 2.8 1.8 % on 20 + 35-mesh screen 38.0
46.8 30.8 100% Handsheets Basis Weight, g/m.sup.2 58.9 62.5 59.5
Breaking Length, Km 0.55 0.77 0.35 Tensile Energy Absorption,
Kg-cm/cm.sup.2 0.007 0.012 0.004 Scott Internal Bond,
Kg-cm/cm.sup.2 .times. 10.sup..sup.-3 65 121 42 Scattering
Coefficient 1266 1111 1045 50/50 Handsheets Basis Weight, g/m.sup.2
59.4 58.9 59.1 Breaking Length, Km 2.81 2.94 2.43 Tensile Energy
Absorption, kg-cm/cm.sup.2 0.045 0.05 0.04 Scott Internal Bond,
Kg-cm/cm.sup.2 .times. 10.sup..sup.-3 170 199 165 Scattering
Coefficient 667 658 615
__________________________________________________________________________
EXAMPLE 6
Example 1 was repeated except that the polyvinyl alcohol was
Gelvatol 20/30 (made by Monsanto and is 88% hydrolyzed), the vessel
was pressurized to 190 psig and the heated contents flashed through
a nozzle having a diameter of 2.5 mm and a length of 28.4 mm. In
the first run, low pressure steam at 5 psig was introduced into
conduit 7 via line 8, and in the second run the steam pressure was
10 psig. Run 1 was subjected to primary refining with the plate
clearance set at 0.100 inch and run 2 was subjected to primary
refining with the plate clearance set at 0.250 inch. Run 3, a
comparison, was subjected to primary refining at a plate clearance
of 0.005 inch. All runs were subjected to one pass of secondary
refining with the plate clearance set at 0.005 inch and at a
temperature of about 40.degree. C. The resulting pulp had the
following properties:
Comparison Property Run 1 Run 2 Run 3
______________________________________ Drainage Factor, sec/g. 6.4
87.3 0.57 Surface Area, m.sup.2 /g 11.3 -- -- (gas adsorption) % on
20 + 35-mesh screen 20 -- --
______________________________________
Handsheets (both 100% and 50/50 blends) were made from the pulp of
run 1 and tested as in Example 1. The properties were as
follows:
Property 100% 50/50 Blend ______________________________________
Basis Weight, g/m.sup.2 59.1 58.2 Tensile, Kg/15 mm 1.19 2.51
Breaking Length, Km 1.345 2.874 Tensile Energy Absorption,
Kg-cm/cm.sup.2 0.056 0.034 Scott Internal Bond, Kg-cm/cm.sup.2
.times. 10.sup..sup.-3 114 149 Opacity, % (TAPPI corrected) 97.8
95.0 ______________________________________
EXAMPLE 7
Example 6 was repeated except that 5% by weight polyvinyl alcohol
(based on the weight of the polyethylene) was employed in the
dissolution vessel rather than 2%. After one pass of primary
refining at a plate clearance of 0.250 inch and one pass of
secondary refining at a clearance of 0.005 inch the resulting pulp
had a drainage factor of 15.7 seconds/gram. This example
illustrates that higher percentages of the aqueous dispersing agent
polyvinyl alcohol may be employed, if desired.
* * * * *