Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
20 ~ 3
-- 1 --
Title
Mixed Solvent for Aramid Spinning Dopes
Background of the Invention
Field of the Invention
This invention relates to spinning dopes for
aramids and, more specifically, to such spinning dopes
using a solvent of mixed acids. The spinning dopes of
this invention utilize a combination of chlorosulfuric
acid and sulfuric acid of at least 100~ concentration
and can be spun at room temperature.
Description of the Prior Art
United States Patent Number 3,767,756 issued
October 23, 1973 discloses the use of chlorosulfonic
acid, fluorosulfonic acid, concentrated sulfuric acid,
and a combination of fluorosulfonic acid and
concentrated sulfuric acid as solvents for arhmid
spinning dopes. There is discussion, in that reference,
to the effect that dopes should be prepared and held
during spinning at as low a temperature as possible; and
dopes made using the solvent 6ystems of that patent are
spun at temperatures of at least 50C. That reference
utilizes sulfuric acid having concentrations as low as
98%,
Japanese Patent Publication ~okai 63-6108,
published January 23, 1988, on the application of Azuma
et al,, discloses that spinning dopes of
poly(p-phenylene terephthalamide) can be prepared by
dissolving the polymer in concentrated sulfuric acid
which can have any of 6everal other materials mixed with
it. Those other materials include chlorosulfuric acid,
fluorosulfuric acid, dichloroacetic acid, acetic acid,
phosphorus pentoxide, nitrobenzene, etc. There is,
al60, a general statement that the dope temperature is
in the range of room temperature to 120C.
~p_3965
-- 1 --
2 ~ 3 ~
-- 2 --
~nited States Patent Number 3,819,587 issued
June 25, 1974 disclosed, generally, that combinations of
solvents can be used to make dopes of aromatic
polyamides; and both chlorosulfonic acid and
concentrated sulfuric acid were included in the lengthy
list of such solvents.
Summary of the Invention
The present invention provides a process for
spinning aramid fibers using an anisotropic dope of
poly~p-phenylene terephthalamide) in a solvent mixture
of chlorosulfonic acid and sulfuric acid of at least
100% concentration wherein the solvent mixture is about
20 to 7Q weight percent chlorosulfonic acid based on the
solvent mixture and the spinning is conducted at less
than 40C.
The gist of this invention and what makes it
patentable resides in the discovery that anisotropic
spinning dopes or solutions of poly(p-phenylene
terephthalamide) are liquid at temperatures lower than
40C even at concentration6 of greater than 18 or as
high as 21 weight percent based on the weight of the
solution when the solvent consists of a mixture of 20 to
70 weight percent chlorosulfonic acid and 30 to 80
weight percent sulfuric acid of at least 100~
concentraSion based on the weight of the solvent
mixture. Such has not previously been known or
reported.
Detailed Description of the Invention
Poly~p-phenylene terephthalamide) tPFD-T) is a
fiber-forming polymer of excellent and renowned
qualities. It is, however, difficult to dissolve and,
once dissolved, difficult to work with. The solvents
which have previously been used to m~ke spinning dopes
have included various extremely corrosive acids and have
resulted in dopes which are solid at room temperatures.
- 2~9~8
-- 3 --
secause of the corrosive nature of the solvents and
because of the fact that even small increases in the
temperature of sulutions using such solvents yield large
increases in the degradive nature of the solvent, it has
been desirable to find solvent systems for PPD-T which
yield liquid spinning dopes at low temperatures.
Until the present invention, ani60tropic
spinning dopes of PPD-T have not been known which have
been spun at low temperatures. Dopes of the present
invention can be spun at room temperature -- about 25C.
The dopes of this invention ~re #pecifically
directed toward the use of PPD-T and, for purposes of
this invention, PPD-T i~ meant to include the
homopolymer resultinq from mole-for-mole polymerization
of p-phenylene diamine and terephthaloyl chloride and,
also, copolymers resulting ~rom incorporation of small
amounts of other aromatic diamine with the p-phenylene
diamine and of small amounts of other aromatic diacid
chloride with the terephthaloyl chloride. As a general
rule, other aromatic diamines and other aromatic diacid
chlorides can be used in amounts up to as much as about
10 mole percent of the p-phenylene diamine or the
terephthaloyl chloride, or perhaps slightly higher,
provided only that the other diamlnes and diacid
chlorides have no reactive group6 which interfere w~th
the polymerization reaction.
The PPD-T can be conveniently made by any of
the well known polymerization processes such as those
taught in U.S. Pat. Nos. 3,063,966; 3,869,429; or
4,308,374. PPD-T used in this invention has an inherent
viscosity of greater than about 4 dL/g. Before
preparation of spinninq dope, the PPD-T and other
ingredients should be carefully and completely dried,
preferably to less than one-half weight percent water;
the PPD-T and the solvent should be combined under dry
conditions; and the dope should be stored under dry
-- 3 --
2 ~ 3 ~
conditions. Care should be exercised to exclude
atmospheric moisture.
The sulfuric acid which is used in practice of
this invention should be at least 100% concentration to
assure that there is no water in that acid. The
sulfuric acid can be from 100~ to 103% or, perhaps, as
high as 105% concentration. The presence of moisture in
the spinning dope is believed to cause loss oi chlorine
from the chlorosulfuric acid solvent component; and such
loss of chlorine causes increase in melting temperature
of the spinning dope.
Dopes of this invention are made by dissolving
PPD-T in mixtures of chlorosulfuric acid and 6ulfuric
acid of a concentration at least 100%. The mixture of
acids is the factor which controls the acceptability of
the dope as a dope of this invention. AS a seneral
rule, it has been determined that, in solutions of PPD-T
in mixtures of chlorosulfuric acid and concentrated
sulfuric acid, the melting point of the solutions is
below about 25C when the acid mixture is from about 20
to 65 weight percent chlorosulfuric acid; and that the
melting point of such solutions is still below about
35C when the acid mixture iB as much a6 70 weight
percent chlorosulfuric acid.
The dopes of this invention are ani60tropic.
That is, microscopic regions of the dopes are
birefringent and a bulk sample of such a dope
depolarizes plane-polarized light because the light
transmission properties of the microscopic regions of
the dope vary with direction.
The above-noted melting points are
substantially independent of PPD-T concentration at
concentrations which result in anisotropic solutions.
It has been found that solutions of PPD-T are
substantially anisotropic at polymer concentrations from
about 9 to about 20 weight percent based on the solution
-- 4 --
2 ~ 3 ~
-- 5 --
at temperatures from the melting point to at least 40C.
About 21 weight percent polymer based on the solution
appears to represent the upper 601ubility limit for
PPD-T in chlorosulfuric acid/sulfuric acid mixtures,
independent of the concentration of chlorosulfuric acid
in the solvent mixture.
The melting point information provided below
for PPD-T dopes of this invention is based on use of
PPD T having an inherent viscosity of 4 dL/g at a
concentration of 18 weight percent based on the
solution.
Weight Ratio Rm. Temp.
CSA/SA- 25~C 35C
15/85 Solid Solid
20/80 Anis.~^ Anis.
25/75 Anis. Anis.
60/40 Anis. Anis.
65/35 Anis. Anis.
70/30 Solid Anis.
eO/20 Solid Solid
90/10 Solid Solid
CSA - Chlorosulfuric Acid
SA - Sulfuric Acid (100%)
~-Anis. , Anisotropic dope with fiber-forming
capability.
The dopes of this invention are prepared by
dissolving PPD-T in the desired mixture of acids. As a
general rule, the acids are combined prior to addition
of the PPD-T. In combining the acids, generally, the
chlorosulfuric ac~d is mixed into the concentrated
~ulfuric acid. The ~mall amount of heat of mixing is
more easlly dis6ipated by adding the chlorosulfuric acid
into the concentrated sulfuric acid rather than the
other way around. After the acids have been combined,
the PPD-T is added to the acids, ~lowly, with stirring.
-- 5 --
2~9~ ~
Solution is most easily effected if the PPD-T is in
finely-divided form. The temperature of the system
should be maintained as low as possible to minimize loss
of chlorine from the solvent system.
The dopes, once prepared, can be used
immediately or stored for future use. Even though the
dopes are liquid at low temperature, if they are stored,
they should be frozen and stored in solid form in an
inert atmosphere 6uch as under a dry nitrogen blanket.
If the dopes are to be used immediately, they can
conveniently be made continuously and fed directly to
spinnerets. Continuous preparation and immediate use
minimizes even the slight degradation of the PPD-T
encountered in the low temperature spinning process.
Spinning the dopes of this invention is
accomplished in accordance with well known spinning
processes with the exception that the spinning can be
conducted at very low temperatures. For example, the
teachings of United States Patent No. 3,767,756 can be
followed for spinning fibers from the dopes of this
invention; but, due to the use of the combination of
chlorosulfuric acid and sulfuric acid in this invention,
the spinning can be accomplished at less than 40C.
Test Procedures
Inherent Visc06ity (IV) - Inherent viscosity is
defined by
ln(nr.l )
IV - ----------
c
where c is concentration (0.5 grams polymer in 100
milliliters of solvent), ~r~l iS the ratio of the flow
times of polymer solution and solvent as determined at
30C in a capillary viscometer. For all inherent
viscosities reported herein, the solvent is concentrated
sulfuric acid (95-98%, by weight, HzS~
Linear Density - The standard for linear density
-- 6 --
2 0 ~
herein is denier (D~ expressed as weight in grams of a
9000 meter le~gth and calculated from the measured
weight of a shorter length (for example, 90
centimeters). Linear density in SI units, is dtex, and
is calculated from the equation
dtex - 1.111 (D).
Tensile Properties - Break Tenacity (T), percent
elongation (E), and initial modulus (M) for yarns are
computed from the output of a digitized laboratory
stress/strain tester according to ASTM D2101, Part 25,
1968 and as described in U.S. Patent No. 3,B69,429 from
Column 10, line 60 to Column 11, line 28 using a testing
rate of 50% elongation per minute. Unless otherwise
indicated, "tenacity" means break tenacity of yarn and
"modulus" means initial modulus of yarn. Both T and M
are initially determined in units of grams per (initial)
der,ier and are converted to SI units (dN/tex) by
multiplication with 0.883.
Description of the Preferred Embodiments
Example
This example demonstrates preparation and
low temperature spinning of a PPD-T spinning dope using
a mixture of chlorosulfuric acid and sulfuric acid of at
least 100% concentration.
Chlorosulfuric acid ~50 weight parts) wa8
added, with agitation, to 100.05% sulfuric acid (50
weight parts) in a closed container purged with an
inert, dry gas. After mixing the acids for a few
minutes, 22 weight parts of finely-divided PPD-T of
inherent viscosity 6.1 were added over the course of 3
minutes, with continued agitation. Agitation was
continued for about 9 hours with no external heating.
The temperature of the dope over the time of continued
agitation was from 29C to 33C due to the heat
2 ~ 3 ~
-- 8
generated by mixing. ~ vacuum was drawn on the dope
during the last 15 minutes of agitation and for an
additional 10 minutes after agitation was stopped.
The dope was spun at 25DC without further
deareation. A first fiber sample was spun using a
spinneret with 10 holes of 4 mils diameter. The
throughput rate was 0.801 milliliters per minute and the
spin was conducted through an air gap of 0.25 inch into
an ice water coagulation bath. The yarn was collected
at 32 meters per minute.
A second fiber sample was spun at the same
conditions, using the same ~pinneret, at twice the
throughput rate and at a collectlon rate of 70 meters
per minute.
The fiber properties were as follows:
First Second
Denier 58 67
Tenacity (gpd) 19.6 18.9
Elongation (%) 5.3 5.4
Modulus (gpd) 286 287
