Note: Descriptions are shown in the official language in which they were submitted.
WO 96/10661 PCT/US95/11229
02199 514
PROCESS FOR THE PREPARATION
OF POLYBENZAZOLE FILAMENTS AND FIBERS
This invention relates to processes for the preparation of polybenzazole fibers
5 and fiberfilaments.
Fibers prepared from polybenzoxazole (PBO) and polybenzothiazole (PBT)
(hereinafter referred to as PBZ or polybenzazole polymers) may be prepared by first extruding
a solution of polybenzazole polymer in a mineral acid (a polymer "dope") through a die or
spinneret to prepare a dope filament. The dope filament is then drawn across an air gap, with
10 or without stretching, and then coagulated in a bath comprising water or a mixture of water
and a mineral acid. If multiple filaments are extruded simultaneously, they may then be
combined into a multifilament fiber during or after the coagulation step. The filament or fiber
is then washed in a washing bath to remove most of the mineral acid, and then dried. The
physical properties of such filaments and fibers, such as tensile strength, are known to be
relatively high. However, further improvement in such properties is desirable.
In one aspect, this invention is a process for removing polyphosphoric acid from a
polybenzazole dope filament, which comprises:
(a) contacting the dope filament with water or a mixture of water and
polyphosphoric acid under conditions sufficient to reduce the phosphorous content of the
20 filament to less than about 10,000 ppm by weight; and then
(b) contacting the dope filament with an aqueous solution of an inorganic base
under conditions sufficient to convert at least about 50 percent of the polyphosphoric acid
groups present in the filament to a salt of the base and the acid,
wherein the process is run continuously at a line speed of at least about 50
25 mlminute
It has been discovered that contacting the dope filament with a solution of a base
after washing the filament to remove most of the residual phosphorous advantageously leads
to an improvement in the initial tensile strength of the f ilament, as well as improved retention
of tensile strength and/or molecular weight (of the polybenzazole polymer) following
30 exposure to light and/or high temperatures, relative to methods wherein a base is not
employed. These and other advantages of the invention are apparent from the description
which follows.
Polybenzazole dope filaments for use in the process of the present invention maybe prepared bythe extrusion of a polybenzazole dope through an extrusion die with a small
35 diameter or a "spinneret". The polybenzazole dope comprises a solution of polybenzazole
polymer in polyphosphoric acid. The term " polybenzazole " as used herein refers to
polybenzoxazole ("PBO") and polybenzothiazole ("PBT"). PBO, PBT and random, sequential
and block copolymers of PBO and PBT are described in references such as Wolfe et al., Liquid
-1 -
WO96/10661 0 2 1 9 9 5 1 4 PCr/US95/,l229
Crystalline Polvmer Compositions, Process and Products, U.S. Patent 4,703,103 (October 27,
1987); Wolfe et al., Liquid Crystalline Poly(2,6-Benzothiazole) Compositions, Process and
Products, U.S. Patent4,533,724 (August 6,1985); Wolfe, Liquid Crystalline Polymer Com-
positions, Process and Products, U.S. Patent4,533,693 (August 6,1985); Evers, Thermo-
5 -oxidatively Stable Articulated p-Benzobisoxazole and p-Benzobisthiazole Polymers, U.S.
Patent 4,359,567 (November 16,1982); Tsai et al., Method for Makinq Heterocyclic B lock
Copolymer, U.S. Patent4,578,432 (March 25,1986); 11 Ency. Poly. Sci. & Eng.,
Pol~,L,enzull,iazoles and Polybenzoxazoles, 601 (J. Wiley & Sons 1988) and W. W. Adams et al.,
The Materials Science and Enqineerinq of Riqid-Rod Polymers (Materials Research Society
10 1989). The polybenzazole polymer may be rigid rod, semi-rigid rod orflexible coil. It is
preferably a Iyotropic liquid-crystalline polymer, which forms liquid-crystalline domains in
solution when its concentration exceeds a critical concentration. The intrinsic viscosity of rigid
polybenzazole polymers in methanesulfonic acid at a temperature of 25C is preferably at least
about 10 dL/g, more preferably at least about 15 dL/g and most preferably at least about
15 20 dL/g.
The dope should contain a high enough concentration of polymer for the
polymer to form an acceptable filament after extrusion and coagulation. When the polymer is
Iyotropic liquid-crystalline, then the concentration of polymer in the dope is preferably high
enough to provide a liquid-crystalline dope. The concentration of the polymer is preferably at
20 least about 7 weight percent, more preferably at least about 10 weight percent and most
preferably at least about 14 weight percent. The maximum concentration is limited primarily
by practical factors, such as polymer solubility and dope viscosity. The concentration of
polymer is preferably no more than 30 weight percent, and more preferably no more than
about 20 weight percent.
Suitable polybenzazole polymers or copolymers and dopes can be synthesized by
known procedures, such as those described in Wolfe et al., U.S. Patent 4,533,693 (August 6,
1985); Sybert et al., U.S. Patent 4,772,678 (September Z0,1988); Harris, U.S. Patent 4,847,350
(July 11,1989); and Gregoryetal., U.S. Patent 5,089,591 (February 18,1992). In summary,
suitable monomers are reacted in a solution of nonoxidizing and dehydrating acid under
30 nonoxidizing atmosphere with vigorous mixing and high shear at a temperature that is
increased in step-wise or ramped fashion from no more than 120C to at least 190C.
The dope may then be formed into a filament by extrusion through a spinneret,
and drawing the filament across a gap. Suitable processes are described in the references
previously incorporated and U.S. Patent 5,034,250. The spinneret preferably contains a
35 plurality of holes. The number of holes in the spinneret and their arrangement is not critical to
the invention, but it is desirable to maximize the number of holes for economic reasons. The
spinneret may contain as many as 100 or 1000 or more, and they may be arranged in circles,
grids, or in any other desired arrangement. The spinneret may be constructed out of ordinary
materials that will not be degraded by the dope, such as stainless steel.
-2-
WO 96/10661 PCT/US95/11229
-
0 2 1 9 9 5 1 4
Dope exiting the spinneret enters a gap between the spinneret and the
coagulation bath. The gap is typically called an "air gap" although it need not contain air. The
gap may contain any fluid that does not induce coagulation or react adversely with the dope,
such as air, nitrogen, argon, helium or carbon dioxide. The dope is preferably drawn to a spin-
5 -draw ratio of at least about 20, highly preferably at least about 40, more preferably at least
about 50 and most preferably at least about 60. The spin-draw ratio is defined in this
application as the ratio between the take-up velocity of the filaments and the capillary velocity
(v of the dope in the spinneret. The shear rate at the spinneret hole wall is preferably in the
range of from 1800 to 6500 s-1. The draw should be sufficient to provide a filament having the
10 desired diameter.
In step (a) of the process of the invention, the dope filament is contacted withwater or a mixture of water and polyphosphoric acid under conditions sufficient to reduce the
phosphorous content of the filament to less than about 10,000 ppm by weight. This may be
carried out as a single operation in one washing apparatus, or the filament may travel through
several baths or washing cabinets to reduce the phosphorous content to the desired level. If a
mixture of water and polyphosphoric acid is used, the concentration of polyphosphoric acid in
solution should be lower than that contained in the filament in order to effectively wash the
filament. Such mixtures are preferably used in the initial stages of washing, since gradual
removal of polyphosphoric acid from a multifilament fiber tends to improve its physical
20 properties.
Preferably, the filament is first "coagulated" in a coagulation bath containing
water or a mixture of water and polyphosphoric acid, which removes enough of the solvent to
prevent substantial stretching of the filament during any subsequent processing. The filament
maythen befurtherwashed in a multi-step process. Theterm "coagulation" as used herein
25 does not necessarily imply that the dope is a f lowing liquid and changes into a solid phase. The
dope may be at a temperature low enough so that it is essentially non-flowing before the
coagulation step begins. The amount of solvent removed during the coagulation step will
depend on the residence time of the filament in the coagulation bath, the temperature of the
bath and the concentration of solvent therein. For example, using a 20 weight percent solution
30 of polyphosphoric acid at a temperature of about 23C, a residence time of about one second
will remove about 70 percent of the solvent present in the filament.
The washing of the filament may be carried out by soaking the filament in water
or a mixture of water and polyphosphoric acid (a "washing fluid"), but is preferably carried out
in a continuous process by running the f ilament through a series of baths or washing cabinets.
35 Washing cabinets typically comprise an enclosed cabinet containing one or more rolls which
the filament travels around a number of times, and across, prior to exiting the cabinet. As the
filamenttraveis around the roll, it is sprayed with a washing fluid. The washing fluid is
continuously collected in the bottom of the cabinet and drained therefrom.
-3-
WO 96/10661 PCT/US95/11229
02 1 99 5 1 4
~. , ~ ., .
Preferably, the surface of the filament is not allowed to dry after the coagulation
step starts and before the washing step(s) are completed. It is theorized, without intending to
be bound, that the wet, never-dried surface of the filament is relatively porous and provides
paths to wash residual phosphorus from inside the filament. On the other hand, it is theorized
5 that the pores close when they become dry and do not open even when they become wet
again. The closed pores trap residual phosphorus inside the filament.
The temperature of the coagulation bath is preferably at least about 1 0C, morepl eferably at least about 25C, and is preferably no greater than about 50C, more preferably
no greater than about 40C. The residence time of the filament in the coagulation bath is
10 preferably at least about 1 second, and is preferably no more than about 5 seconds. The
concentration of acid in the coagulation bath is preferably at least about 0.5 percent by weight,
more preferably at least about 20 percent, and is preferably no greater than about 40 percent,
more preferably no greater than about 25 percent. For a continuous process, it is preferable to
use as low a temperature and high a solvent content as is practical, so that the solvent may be
removed as slowly as possible.
The temperature of the washing fluid(s) are preferably at least about 25C, morepreferably at least about 50C, and is preferably no greater than about 1 20C, more preferably
no greater than about 1 00C. The washing fluid may also be applied in vapor form (steam), but
is more conveniently used in liquid form. The residence time of the filament in the washing
20 bath(s) will depend on the desired concentration of residual phosphorus in the filament, but
typical residence times are in the range of from 180 seconds to 300 seconds. The duration of
the entire washing process utilized in the first step of the process of the invention is preferably
no greater than about 200 seconds, more preferably no greater than about 160 seconds.
For a continuous spinning operation, the concentration of phosphorous in the
25 filament is preferably brought down as slowly as is practical in the coagulation and washing
operations, given that for such processes, fewer steps and higher line speeds are desirable. It is
believed that a slower reduction in the phosphorous concentration in the filament provides a
filament which has better physical properties. It is also believed that this result is more
efficiently achieved in a continuous multi-step operation, utilizing a series of baths or washing
30 cabinets, by decreasing the concentration of acid in the washing bath as the filament proceeds
down the washing line. Conveniently, the washing fluid residue collected after the last
washing step may be used as the washing fluid in the next-to-last washing step, and so forth up
the line, with washing fluid containing the highest acid concentration being used in the first
washing step. The concentration of acid in the washing baths or cabinets is preferably at least
35 about 0.2 percent by weight, and is preferably no greater than about 40 percent by weight.
The residual concentration of phosphorous in the filament after step (a) of the
process is preferably less than about 8,000 ppm, more preferably less than about 6,000 ppm,
and most preferably less than about 4,000 ppm. The residua I phosphorus content of a
-4-
WO 96/10661 PCT/US95/11229
..
O 2 1 9 9 5 1 4
substantially dry filament may be measured using X-ray fluorescence techniques described in
E.P. Bertin, Princi,oles and Practice of X-Rav Spectrometric Analysis - Second Ed. (Plenum Press
1984). Suitable equipment is commercially available underthe trade name KEVEX 770 XRF and
from Philips Electronic Instruments.
The filament utilized in the process of the invention may be combined into a
multifilament fiber at any point during the process of the invention. Preferably, however, the
filaments are combined just prior to, or during, coagulation. While the term "filament" is used
throughout this application to describe the process of the invention, the process of the
invention may of course also be carried out on a filament contained in a multifilament fiber,
10 utilizing the same process parameters as described herein for use with a single filament.
The fi lament is p~ eferably under tension d uring at least part of the washing
process. More preferably, tension is also applied throughoutthe coagulation and washing
process, particularly when the fluid temperature is very high. The tension is preferably
sufficient to prevent the f ilament from shrinking or relaxing.
In the second step of the process of the invention, the dope filament is contacted
with an aqueous solution of an inorganic base under conditions sufficient to convert at least
about 50 percent of the acid groups present in the filament to the corresponding salt form
(hereafter "neutralization step"). This step may likewise be carried out in a single operation, or
the filament may travel through several baths or washing cabinets to reduce the phosphorous
20 content to the desired level. Preferably, however, this step is carried out in a single washing
cabinet as described above. Examples of suitable water-soluble bases include sodium
hydroxide, ammonium hydroxide, sodium carbonate, and sodium bicarbonate. The
percentage of acid groups which have been converted may be followed by any suitable
technique, such as nuclear magnetic resonance spectroscopy (NMR) or Fourier transform
25 infrared spectroscopy (FTIR~.
The concentration of base in the solution is preferably at least about 0.2 weight
percent, more preferably at least about 0.4 weight percent, and is preferably no greater than
about 1.2 weight percent, more preferably no greater than about 0.8 weight percent. The
duration of this second step will depend on the concentration of the base, with longer
30 residence times required for lower concentrations, but is preferably no greater than about 120
seconds, more preferably no greater than about 60 seconds. Preferably at least about 50
percent of the acid groups remaining after step (a) are converted to their salt form, more
preferably at least about 75 percent, and most preferably at least about 95 percent are so
converted. The preferred pH of the base solution used in the neutralization step will depend
35 on the duration of the step, with a higher pH preferred with a shorter duration, but is
preferably in the range of from 10 to 14, more preferably in the range of from 1 1 to 12.
Since residual base in the fiber tends to degrade the properties of the fiber,
particularly if the fiber is heat-treated after the neutralization step, the concentration of base
-5-
WO96/10661 0 2 1 99 5 1 4
and residence times are preferably selected to achieve a stoichiometric ratio of base: acid
groups in the fiber of at least 0.5:1.0, more preferably at least 0.75:1.00, and is preferably no
greater than 1.5:1.0, more preferably no greater than 1.25:1.0, but is most pr~ferably 1:1. The
stoichiometry of the process can be determined by a suitable method, such as by measuring the
5 ratio of phosphorous to the conjugate acid of the inorganic base in the fiber after the
neutralization step. For example, if sodium hydroxide is used, the ratio of phosphorous:sodium
in the fiber may be measured by a suitable technique such as Neutron Activation Analysis.
The process of the present invention is preferably run in a continuous fashion
with a line speed of at least about 50 m/minute. The line speed is highly preferably at least
10 about 200 mlminute, more preferably at least about 400 m/minute and most preferably at least
about 600 mlminute.
Following the second step of the process, if any residual base is present in thefiber, the fiber is preferably washed further with water for a residence time of at least about 1
second to remove most of the residual base. The particular washing conditions will depend on
the amount of residual base present, with longer residence times required to remove greater
amounts of base. Thereafter, the filament may be dried, heat-treated, and/or wound on rolls
as desired, as described, for example, in U.S. Patent 5,296,185. Multifilament fibers containing
PBZ polymers may be used in ropes, cables, fiber-reinforced composites and cut-resistant
clothing.
The following examples are given to illustrate the invention and should not be
interpreted as limiting it in any way. Unless stated otherwise, all parts and percentages are
given by weight.
Examples 1-10
A 14 weight percent solution of polybenzoxazole ("PBO") in polyphosphoric acid
25 ("PPA"; available from Eastman Kodak Company) with intrinsic viscosity between 30 to 34
(measured in methanesulfonic acid at 23C) was prepared. PBO filaments were extruded at a
temperature between 165~C out of a 180 micron spinneret with 42 holes into a coagulation
bath, and combined into a multifilament fiber. A glass shroud was placed in the air gap,
between the spinneret face and the surface of the coagulation bath liquid in order to minimize
30 air currents in the air gap. The filaments were produced by using a shear rate at the spinneret
hole wall of about 3500 s-1. The spin-draw ratio utilized is 44, with a fiber take-up speed of 200
m/minute. The resulting filaments had a denier of 1.5 denier per filament and a diameter of
1 1. 5 m icrons.
The fibers were coagulated in a bath of water and polyphosphoric acid having an
35 acid content of about 20 percent by weight. The residence time in the coagulation stage was
about 0.5 seconds and the temperature was about 1 0C. The fibers were then washed off-line
with water (as comparative examples), or in a three-step process using water, a 0.05 weight
-
WO 96/10661 PCT/US95/11229
percent aqueous solution of sodium hydroxide, and water, using a washing temperature of
about 23C.
After washing, the fiber was dried under nitrogen at room temperature (23C) foran additional 48 hours. A portion of the samples were heat-set through a nitrogen-purged
5 tube furnace with a residence time of 2 seconds at 600C. A constant tension of about
3.5 g/denier was maintained on the fiber during heat setting.
Residual phosphorus was measured using X-ray fluorescence on a Philips
PW1404/DY685sequentialspectrometerwithscandiumX-raytubesandfibersampleswhich
had been pressed into a pellet for analysis. The tensile strength retention and intrinsic viscosity
10 of each fiber was then measured, both before and after heat-treatment. The retention of
tensile strength (TSR), defined as (photo-aged tensile ~Lreng ll ,/initial tensile strength) x 100
percent, was used for expressing the retention of tensile strength after photo-aging, although
separate samples were used for each measurement. Photo-aging was carried out in an Atlas
Model Ci65A weatherometer with a xenon lamp and borosilicate filter. Fiber strands were
mounted on sample holders and photo-exposed in the weatherometer. The exposure was 765
doewatt/m2 with a 300 to 800 nm wave length for a total of 100 hours.
The procedure used for measurement of tensile strength was as follows: Tensile
properties were measured in accordance with ASTM D-2101, on an Instron 4201 universal
testing machine. A 10 pound load cell was used with a crosshead speed of 1.0 inches/minute,
20 and a gauge length of 10.0 inches. Tensile data was obtained on the 42-f ilament fibers with a
twist factor of 6 to 7. The intrinsic viscosity (IV) of the fiber samples was measured by dissolving
them in methanesulfonic acid, and measuring the intrinsic viscosity at 23C.
Each number reported in the table is an average over ten samples, and different
fiber samples were used to measure the as-spun and heat-treated properties of the fiber. All of
25 the fiber samples for which data is shown in Table I were taken from the same roll of fiber, at
sequential locations along the roll. That is, the samples used for Comparative Example 1 were
taken from the portion of the roll adjacent to the samples used in Example 2, and so forth. The
results are given in Table 1.
WO 96/10661 PCT/US95111229
0 2 1 9 9 5 1 4
Table I
Example No. Washing Process ~ P (ppm) A-S H-T A-S H-T
-1 (Comp.)Water (20) 5000 71 83 24.3 19.3
2 Water (5) 4200 81 86 26.3 24.1
NaOH (5)
Water (10)
3 (Comp.)Water(20) 5100 73 84 23.2 18.5
4 Water (5) 4500 83 88 25.4 24.1
NaOH (5)
Water (10)
5 (Comp.)Water (20) 4400 71 84 23.5 19.4
6 Water (5) 4500 85 90 25.6 24.5
NaOH (5)
Water (10)
7 (Comp.)Water (20) 4400 72 82 23.3 19.1
8 Water (5) 4800 81 87 25.5 23.5
NaOH (5)
Water (10)
9 (Comp.)Water(20) 5000 76 84 23.0 19.4
Water (5) 4000 82 89 25.8 24.0
NaOH (5)
Water (10)
P - Residual phosphorous content, parts per million by weight
TSR - Tensile strength retention (% of tensile strength retained after
Weatherometer treatment)
IV - Intrinsic viscosity
A-S - as-spun fiber; H-T- heat-treated fiber
~ - shown in the table as the residence time in the washing bath, in minutes
(Comp.) - Comparative Example - not an example of the invention
The data showed that the tensile strength retention of the fibers was improved
when the fibers were neutralized using sodium hydroxide.
30 Examples 11-13
Using the method described in Examples 1-10, fiber samples comprised of
filaments with a denier of 1.5 denier per filament and a diameter of 11.5 microns were
prepared, coagulated in water for 1 second, washed in water for 10 minutes, and contacted
with a 0.1 N aqueous solution of a base for 10 minutes. In Example 12, the samples were
35 subsequently washed with water at room temperature for 24 hours. The tensile strength of the
samples were measured, and heat-treatment was carried out, as described in Examples 1-10.
The residual sodium and phosphorous content of the fiber was also shown (Na), as measured by
Neutron Activation Analysis. The data is shown in Tables lla and llb.
-8-
WO 96/10661 PCT/US95/11229
Table lla
Example Base 2nd Wash P (ppm) Na (ppm)
11 NaOH No 5000 9000
12 NaOH Yes 2400 940
13 Na2CO3 No 5300 14000
Table llb
Example TS (A-S) TM (A-S)TS (H-T) (TH-MT) IV (A-S)
11 790 28.5 583 39.3 34
12 810 29.6 685 42.4 37
13 780 28 504 43 35
TS (A-S) - tensile strength, as spun, ksi (1000 psi = 1 ksi)
TM(A-S)-tensilemodulus,asspun,msi(1x106psi = 1 msi)
TS (H-S) - tensile strength, heat-treated, ksi
TM (H-S) - tensile modulus, heat-treated, msi
IV (A-S) - intrinsic viscosity, as spun
20 Examples 14-20
Using the method described in Examples 1 - 10 (with the exception that the
filaments were spun through a spinneret having 166 holes and were coagulated for 1 second in
a bath containing 20 percent by weight PPA and the filaments were spun at a rate of 100
m/minute), fiber samples comprised of filaments having a denier of 1.5 denier per filament and
25 a diameter of 11.5 microns were prepared, coagulated, and washed for a period of time
sufficient to give the residual levels of phosphorous shown in Table lll. The samples were then
contacted with a 0.1 N aqueous solution of a base for 5 m inutes. Steam-jet heat-treatment was
perror")ed at about 545C at a line speed of 40 m/minute and a residence time of 1.5 seconds,
applying a tension of about 5.5 g/denier. Examples 14-16 are comparative exampleswherein
30 the fiber was not contacted with a base. The residual sodium content of the fiber was also
shown (Na), as measured by Neutron Activation Analysis. The tensile strength of the fibers was
measured as described in Examples 1-10. The data is shown in Table lll.
WO 96/10661 PCT/US95/11229
0 2 1 9 9 5 1 4
2 ~ ~ ~ ~
N
~ o
-----__
~ u~
rr~ h'~ ~ _ _ _ _
>
-
.~ .
-
o
o Q
X
o
E o o o o o u~ u .
- O O o u O ~J r~
o -- -- --
x
.
E * * * I` co ~ o ~
u
- 10 -
