Process for manufacturing a high modulus poly-p-phenylene terephthalamide fiber

High modulus, high tenacity fibers of poly-p-phenylene terephthalamide (PPD-T) are manufactured comprising a fiber heat treating process for increasing the inherent viscosity and the crystallinity index of the PPD-T. Never-dried fibers swollen with water of controlled acidity are heated beyond dryness in an atmoshphere having a flow of greater than Reynolds Number 10,000 throughout the duration of the heating.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
Poly-p-phenylene terephthalamide fibers, long known for their light weight, 
high strength, and high modulus, have found wide acceptance in a great 
number of applications requiring their unique combination of properties. 
The wide acceptance has, however, given rise to a demand and need for 
fibers having still higher strength and modulus for use in still more 
demanding applications. Fibers having decreased solubility and chemical 
reactivity and increased overall crystallinity and resistance to moisture 
regain have been sought and are in demand. 
2. Description of the Prior Art 
U.S. Pat. No. 3,869,430, issued Mar. 4, 1975 on the application of H. 
Blades, discloses fibers of poly-p-phenylene terephthalamide and processes 
for making the polymer and the fibers. That patent is particularly 
concerned with a process for heat treating such fibers after the fibers 
have been dried. That patent discloses, generally, that fibers could be 
heat treated whether wet or dry; but, in the examples, teaches heat 
treatment only of dried fibers and, elsewhere in the specification, 
cautions against heat treating fibers at excessive heat for excessive time 
with the warning that decreased tenacity and decreased polymer inherent 
viscosity will result. 
Japanese Patent Publications Nos. 55-11763 and 55-11764 published Mar. 27, 
1980, disclose fibers of poly-p-phenylene terephthalamide having high 
modulus and high tenacity but with polymer exhibiting only moderate 
inherent viscosity. The processes of those publications are particularly 
concerned with a fiber-drawing step performed after coagulating the spun 
polymer and before drying the fibers. In the drawing step, the fibers are 
actually stretched to 20 to 80 or 90% of the maximum stretch attainable 
before break. After the stretching, the fibers are dried at various times 
and at temperatures above about 300 degrees and as high as 600 degrees for 
three seconds. The inherent viscosity of the polymer of fibers so-made is 
always disclosed to be less than the inherent viscosity of the starting 
polymer and there is no suggestion that the inherent viscosity might be 
increased by any heat treatment. 
The Journal of East China Institute of Textile Science and Technology, Vol. 
10, No. 2 (1984), pp. 30-34, discloses heat treatment of fibers under very 
slight tension. There is teaching that the treatment causes decomposition, 
branching, and cross-association with accompanying increases in molecular 
weight. Neither fiber modulus nor degree of crystallinity is mentioned. 
SUMMARY OF THE INVENTION 
A process is provided by this invention for manufacturing a 
poly-p-phenylene terephthalamide fiber having high modulus and high 
tenacity wherein a wet, water-swollen, fiber is exposed to a heated 
atmosphere, and the fiber, during exposure, is subjected to a tension. The 
swollen fibers, preferably, have about 20 to 100 percent water, based on 
dried fiber material, and the atmosphere is usually heated at 500 to 660 
degrees with exposure of the fiber for 0.25 to 12 seconds. The tension on 
the fiers is about 1.5 to 4 grams per denier (gpd). There is, also, 
provision for controlling the acidity or basicity of the water-swollen 
(never-dried) fibers to affect change in the inherent viscosity and 
tenacity of the polymer during the heat treatment. Inherent viscosity of 
the polymer after the heat treatment is high; more than 5.5 and as much as 
20 or more; and is increased in the heat treatment. In order to maintain 
satisfactory process operability and product properties, the basicity is 
maintained at less than about 10 and the acidity is maintained at less 
than about 60. Basicity of less than about 2 and acidity of less than 
about 1.0 are preferred. Crystallinity Index of the heat treated polymer 
is high; at least 70% and as much as 85%. 
In one embodiment of the invention, an entrainment jet is used for 
application of hot gas to dry and treat the swollen fibers in an efficient 
and effective manner. The process is very fast and, as a result, the 
product of the jet embodiment of the process is a fiber having a 
Crystallinity Index of greater than 75%. For use of the jet embodiment, it 
is preferred that the swollen fiber should be exposed to a heated 
atmosphere at 500 to 660 centigrade degrees for about 0.25 to 3 seconds, 
and most preferably about 0.5 to 2 seconds. In the most preferable range, 
there is some allowance made for different sizes of yarns--the range is 
most preferably 0.5 to 1 second for 400 denier yarns and 0.5 to 2 seconds 
for 1200 denier yarns. 
In another embodiment of the invention, an oven is used for application of 
radiant heat to cause slower drying of the swollen fibers; and, as a 
result, the product of the oven embodiment is a fiber having an inherent 
viscosity of more than about 6.5. For use of the oven embodiment, it is 
preferred that the swollen fiber should be exposed to a heated atmosphere 
at 500 to 660 degrees for about 3 to 12 seconds, and most preferably at 
550 to 660 degrees for about 5 to 12 seconds, with less time required for 
low denier yarn at a given temperature. For purposes of this invention, 
radiant heating of the oven embodiment means that at least 75 percent of 
the heat energy absorbed by the water-swollen yarn is radiant heat energy. 
In the other embodiments, there can be combinations of the above heat 
treatment embodiments which yield high modulus, high tenacity fibers with, 
both, an increased inherent viscosity and an increased Crystallinity Index 
.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is based on a treatment of poly-p-phenylene 
terephthalamide fibers which, quite unexpectedly, gives rise to fibers of 
high modulus and Crystallinity Index while permitting controlled increase 
of the ultimate inherent viscosity. The invention permits manufacture of 
high modulus fibers of poly-p-phenylene terephthalamide, having inherent 
viscosity of greater than 6.5 and Crystallinity Index of greater than 
about 75%. 
By "poly-p-phenylene terephthalamide" is meant the homopolymer resulting 
from mole-for-mole polymerization of p-phenylene diamine and terephthaloyl 
chloride and, also, copolymers resulting from 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. Examples of acceptable other aromatic diamines include 
m-phenylene diamine, 4,4'-diphenyldiamine, 3,3'-diphenyldiamine, 
3,4'-diphenyldiamine, 4,4'oxydiphenyldiamine, 3,3'-oxydiphenyldiamine, 
3,4'-oxydiphenyldiamine, 4,4'-sulfonyldiphenyldiamine, 
3,3'-sulfonyldiphenyldiamine, 3,4'-sulfonyldiphenyldiamine, and the like. 
Examples of acceptable other aromatic diacid chlorides include 
2,6-naphthalenedicarboxylic acid chloride, isophthaloyl chloride, 
4,4'-oxydibenzoyl chloride, 3,3'-oxydibenzoyl chloride, 3,4'-oxydibenzoyl 
chloride, 4,4'-sulfonyldibenzoyl chloride, 3,3'-sulfonyldibenzoyl 
chloride, 3,4'-sulfonyldibenzoyl chloride, 4,4'-dibenzoyl chloride, 
3,3'-dibenzoyl chloride, 3,4'-dibenzoyl chloride, and the like. 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 the other diamines and diacid chlorides have no 
reactive groups which interfere with the polymerization reaction. 
Poly-p-phenylene terephthalamide fibers which include such small amounts 
of other diacids or diamines and which are heat treated by this invention, 
may exhibit physical properties slightly different from those which would 
have been obtained had no other diacids or diamines been present. 
The polymer can be conveniently made by any of the well known 
polymerization processes such as those taught in U.S. Pat. No. 3,063,966 
and U.S. Pat. No. 3,869,429. One process for making the polymer includes 
dissolving one mole of p-phenylene diamine in a solvent system comprising 
about one mole of calcium chloride and about 2.5 liters of 
N-methyl-2-pyrrolidone and then adding one mole of terephthaloyl chloride 
with agitation and cooling. The addition of the diacid chloride is usually 
accomplished in two steps;--the first addition step being about 25-35 
weight percent of the total with the second addition step occurring after 
the system has been stirred for about 15 minutes. Cooling is applied to 
the system after the second addition step to maintain the temperature 
below about 60.degree. C. Under forces of continued agitation, the polymer 
gels and then crumbles; and, after a few hours or more, the resulting 
crumb-like polymer is ground and washed several times in water and dried 
in an oven at about 100.degree.-150.degree. C. 
Molecular weight of the polymer is dependent upon a multitude of 
conditions. For example, to obtain polymer of high molecular weight, 
reactants and solvent should be free from impurity and the water content 
of the total reaction system should be as low as possible --no more, and 
preferably less, than 0.03 weight percent. Care should be exercised to 
assure the use of equimolar amounts of the diamine and the diacid chloride 
because only a slight imbalance in the reactant materials will result in a 
polymer of low molecular weight. While it may be preferred that inorganic 
salts be added to the solvent to assist in maintaining a solution of the 
polymer as it is formed, quaternary ammonium salts have, also, been found 
to be effective in maintaining the polymer solution. Examples of useful 
quaternary ammonium salts include: methyl-tri-n-butyl ammonium chloride, 
methyl-tri-n-propyl ammonium chloride, tetra-n-propyl ammonium chloride, 
tetra-nbutyl ammonium chloride, and the like. 
Fibers are made in accordance with the present invention by extruding a 
dope of the polymer under certain conditions. The dope can be prepared by 
dissolving an adequate amount of the polymer in an appropriate solvent. 
Sulfuric acid, chlorosulfuric acid, fluorosulfuric acid and mixtures of 
these acids can be identified as appropriate solvents. Sulfuric acid is 
much the preferred solvent and must be used at a concentration of 98% or 
greater to avoid undue degradation of the polymer. The polymer should be 
dissolved in he dope in the amount of at least 30, preferably more than 
40, grams of polymer per 100 milliliters of solvent. The densities of the 
acid solvents are as follows: H.sub.2 SO.sub.4, 1.83 g/ml; HSO.sub.3 Cl, 
1.79 g/ml; and HSO.sub.3 F, 1.74 g/ml. 
Before dissolving the polymer to make the spinning dope, the polymer should 
be carefully dried to, preferably, less than one weight percent water; and 
the polymer and the solvent should be combined under dry conditions. Dopes 
should be mixed and held in the spinning process at as low a temperature 
as is practical to keep them liquid in order to reduce degradation of the 
polymer. Exposure of the dopes to temperatures of greater than 90.degree. 
C. should be minimized. 
The dope, once prepared, can be used immediately or stored for future use. 
If stored, the dope is preferably frozen and stored in solid form in an 
inert atmosphere such as under a dry nitrogen blanket. If the dope is to 
be used immediately, it can conveniently be made continuously and fed 
directly to spinnerets. Continuous preparation and immediate use minimizes 
degradation of the polymer in the spinning process. 
The dopes are, typically, solid at room temperature and behave, in 
spinning, like polymer melts. For example, a dope of 45 grams of the 
polymer with an inherent viscosity of about 5.4 in 100 milliliters of 100% 
sulfuric acid may exhibit a bulk viscosity of about 900 poises at 
105.degree. C. and about 1000 poises at 80.degree. C., measured at a shear 
rate of 20 sec.sup.-1,and would solidify an opaque solid at about 
70.degree. C. The bulk viscosity of dopes made with a particular polymer 
increases with molecular weight of the polymer for given temperatures and 
concentrations. 
Dopes can generally be extruded at any temperature where they are 
sufficiently fluid. Since the degree of degradation is dependent upon time 
and temperature, temperatures below about 120.degree. C. are usually used 
and temperatures below about 90.degree. C. are preferable. If higher 
temperatures are required or desired for any reason, processing equipment 
should be designed so that the dope is exposed to the higher temperatures 
for a minimum time. 
Dopes used to make the fibers of this invention are optically anisotropic, 
that is microscopic regions of the dope are birefringent and a bulk sample 
of the dope depolarizes plane-polarized light because the light 
transmission properties of the microscopic regions of the dope vary with 
direction. It is believed to be important that the dopes used in this 
invention must be anisotropic, at least in part. 
Fibers of the present invention can be made using the conditions 
specifically set out in U.S. Pat. No. 3,869,429. Dopes are extruded 
through spinnerets with orifices ranging from about 0.025 to 0.25 mm in 
diameter, or perhaps slightly larger or smaller. The number, size, shape, 
and configuration of the orifices are not critical. The extruded dope is 
conducted into a coagulation bath through a noncoagulating fluid layer. 
While in the fluid layer, the extruded dope is stretched from as little as 
1 to as much as 15 times its initial length (spin stretch factor). The 
fluid layer is generally air but can be any other inert gas or even liquid 
which is a noncoagulant for the dope. The noncoagulating fluid layer is 
generally from 0.1 to 10 centimeters in thickness. 
The coagulation bath is aqueous and ranges from pure water, or brine, to as 
much as 70% sulfuric acid. Bath temperatures can range from below freezing 
to about 28.degree. C. or, perhaps, slightly higher. It is preferred that 
the temperature of the coagulation bath be kept below about 10.degree. C., 
and more preferably, below 5.degree. C., to obtain fibers with the highest 
initial strength. 
After the extruded dope has been conducted through the coagulation bath, 
the dope has coagulated into a water-swollen fiber and is ready for drying 
and heat treatment. The fiber includes about 20 to 100% percent aqueous 
coagulation medium, based on dry fiber material, and, for the purposes of 
this invention, must be thoroughly washed to remove the proper amount of 
salt and acid from the interior of the swollen fiber. It is now understood 
that fiber-washing solutions can be pure water or they can be slightly 
alkaline. Washing solutions should be such that the liquid in the interior 
of the swollen fiber should have an acidity less than 60 and preferably 
less than 10 and a basicity less than 10 and preferably less than 2 
depending upon the conditions of the heat treatment and the desired final 
inherent viscosity of the fiber product. 
It is now believed that heat treatment of never-dried poly-p-phenylene 
terephthalamide fibers results in alteration of the polymer in the fiber 
in that the heat treatment causes a complex combination of polymerization, 
depolymerization, branching and crosslinking reactions. 
At temperatures from above 500.degree. C. to about 660.degree. C., at the 
relatively short exposure times of this invention (0.25-12 sec), the 
predominant reaction is believed to be branching and cross-linking which 
lead to fibers with higher molecular weights and higher inherent 
viscosities; these reactions are believed to be catalyzed by acids. Thus, 
poly-p-phenylene terephthalamide never-dried fibers having an inherent 
viscosity of about 5.5 and containing about 9 milliequivalents of acid or 
less, showed little or no significant change in inherent viscosity when 
heated at oven temperatures of 450.degree.-500.degree. C. for 6-9 seconds. 
However, when heated at oven temperatures of 550.degree.-660.degree. C., 
these same never-dried fibers showed an unexpected and pronounced increase 
in inherent viscosity up to or greater than 6.5, and the moduli increased 
to about 1100 gpd or higher, while tenacities were maintained at 18 gpd or 
higher. By contrast, when poly-p-phenylene terephthalamide fibers 
containing about 150 milliequivalents of acid per kg of fiber were heated 
in an oven even at temperatures as low as 410.degree. C. for 5 sec, the 
inherent viscosities of the fibers were increased from about 5.5 to over 
7, while fiber tenacity deteriorated from about 25 gpd to less than 16 
gpd, below the range of interest of this invention. 
Within the range of temperatures (500.degree.-660.degree. C.) and exposure 
times (0.25-12 sec) of this invention, acidity of up to about 60 meq of 
acid per kg of yarn is acceptable. Within that acidity limit, process 
operability and product properties are acceptable. The upper limit of 60 
acidity approximately corresponds to what is believed to be the sum of 
acid groups attached to poly-p-phenylene terephthalamide polymer. The acid 
groups are made up of carboxylic acid groups and sulfonic acid groups. 
When a base such as sodium hydroxide is used in the fiber washing 
processes, it is believed that the acid groups react with and neutralize 
basic groups which are present in the fiber as a result of such washing 
processes. Above about 60 meq of acid per kg of yarn, product quality and 
processability deteriorate sharply. 
The presence of small amounts of basic material, like sodium hydroxide, in 
the never-dried poly-p-phenylene terephthalamide fibers prior to heating 
under the conditions of time and temperature of this invention appear to 
have little affect on those thermal reactions which yield high molecular 
weights and inherent viscosities. Thus, when a series of poly-p-phenylene 
terephthalamide fibers containing 1.5 milliequivalents of sodium hydroxide 
per kg of fiber were heated in an oven at 550.degree.-640.degree. C. for 
7-9 seconds, inherent viscosities were increased to from 7.0 to greater 
than 20 and moduli to from 1060 to 1244, while tenacities were maintained 
at greater than 18 gpd. At an oven temperature of 500.degree. C. for about 
9 sec, poly-p-phenylene terephthalamide fibers containing this level of 
base showed no change in inherent viscosity. At high levels of base in the 
fibers, on the other hand, inherent viscosity was sharply reduced. Thus, 
about 400 milliequivalents of sodium hydroxide in poly-p-phenylene 
terephthalamide fibers, even at oven temperature as low as 410.degree. C. 
for 5 sec, caused a dramatic drop in fiber properties to 3.0 inherent 
viscosity, 3.7 gpd tenacity and 450 gpd modulus. 
Within the range of temperatures and exposure times of this invention, 
basicity of up to about 10 meq of base per kg of yarn is acceptable. 
Within that range, process operability and product properties are 
acceptable. Above about 10 meq of base, the processability through the 
heat treatment deteriorates badly and the polymer of the fibers is 
believed to be severely degraded by that heat treatment through hydrolysis 
and depolymerization reactions. 
Very important to the operation of this invention, is the discovery that 
increased inherent viscosities result from heat treatments at temperatures 
of greater than 500.degree. C. of never-dried fibers having an acidity of 
less than 60, and preferably less than 10, milliequivalents of acid per kg 
of fiber and a basicity of less than 10, and preferably less than 2, 
milliequivalents of base per kg of fiber. 
Increased inherent viscosity indicates an increase in molecular weight of 
the polymer which constitutes the fiber product. Fibers of polymer having 
moderately increased molecular weight exhibit decreased solubility and, 
also, exhibit increased resistance to deterioration due to moisture and 
chemical exposure. Fibers of polymer having greatly increased molecular 
weight, such as indicated by an inherent viscosity of 20, or greater, 
exhibit complete insolubility. For most uses, the washing medium for 
practice of this invention should be neutral or slightly basic. 
The heat treatment of this invention can be carried out by various means. 
One embodiment of this invention is in the use of a fluid jet which 
conducts heated fluid, usually air, nitrogen, or steam, against the fibers 
to be heat treated. The jet is a so-called forwarding jet which has a 
fiber introduced at the back end of the jet and conducts the fiber through 
the jet and out the front in a stream of heated fluid. The jet provides 
turbulent but subsonic movement of heated gas. FIG. 1 depicts a jet which 
is effective for practice of this invention. The jet includes a fiber 
introduction back part 1, a fluid introduction body part 2, and a heat 
treating barrel extender 3. Fiber 4 is introduced into back part 1 at 
fiber feed orifice 5, is conducted through that part to heat chamber 6, 
and from there through barrel extender 3. Heated fluid is introduced into 
heat chamber 6 by means of conduits 7 which may be present around heat 
chamber 6 in any number of one or more and, if more than one, 
substantially equally spaced. 
The heated fluid and the fiber to be heat treated are conducted through 
barrel extender 3 in the same direction, at the same or different speeds. 
Some of the heated fluid also exits through the fiber feed orifice 5 in 
the back part 1 so as to avoid entrainment of cool, outside, gases. The 
speed of the heated fluid is carefully selected to provide high heat 
transfer from the fluid through the jet device. For the purpose of this 
invention, it has been concluded that a flow designated by a Reynolds 
Number of greater than about 10,000 is preferred. The Reynolds Number is 
defined by the following equation: 
##EQU1## 
wherein D=Jet diameter 
v=heated fluid velocity 
.eta.=heated fluid density 
.mu.=heated fluid viscosity 
and all dimensions for those quantities are in consistent units. 
As an example of a determination of Reynolds Number for the practice of 
this invention, there is taken the use of steam at 40 psig as the heated 
fluid. It is determined that steam under such pressure results in a flow 
of 2.0 SCFM (standard cubic feet per minute) at a temperature of about 
550.degree. C. when the jet diameter (throat) is 0.18 centimeters. The 
effective steam velocity calculates to 2.8.times.10.sup.4 centimeters per 
second. Standard tables give the density of such steam as 
9.7.times.10.sup.'4 grams per cubic centimeter and the viscosity of such 
steam as 3.0.times.10.sup.-4 poise. The Reynolds Number for this set of 
conditions is 16,000: 
##EQU2## 
Use of the jet as a means for heating fibers permits heating convectively 
at rates of approximately ten times the rate which is obtained using a 
radiant oven. 
The Reynolds Number or the degree of turbulence of gas in the jet has been 
taken to be substantially independent of the yarn or fiber moving through 
the jet. The rate of movement of the yarn or fiber through the jet is 
important only to provide the desired or required heating time. As a 
matter of fact, the turbulent flow of the heated gas can be countercurrent 
to the movement of the yarn or fiber being heat treated. 
Another embodiment of this invention is in the use of an oven which is 
fitted with a radiant heat source and which provides drying and heat 
treating energy without the high relative velocity of fibers and heating 
fluid which is associated with the jet, previously-described. The oven of 
this embodiment is usually in the form of a tube or rectangular cavity 
with dimensions much greater than the fiber to be heat treated. Heated 
fluid is introduced into the oven at a rate such that there is very little 
turbulence and the heating forces are primarily radiant in nature. FIG. 2 
depicts an oven which is effective for practice of this invention. The 
oven includes a tube 10 with fiber introduction end 11 and fiber exit end 
12. Tube 10 is contained in insulating jacket 13 and there is provision 
for introducing heated fluid into tube 10 by means of conduits 14 which 
may be present around tube 10 in any number of one or more and, if more 
than one, substantially equally spaced. 
Fiber 15 to be heat treated, is conducted through the oven at a speed 
adequate to permit drying the fiber and exposing the dried fiber to the 
proper heat energy. The heating fluid is supplied at a rate which is 
adequate to maintain a desired temperature in the oven and carry 
evaporated swelling medium away. 
The two above-described embodiments for practice of this invention differ, 
among other ways, in that the jet embodiment utilizes turbulent heated 
fluid flow with a resultant, very thin boundary layer and very high, 
substantially convective, heat transfer; the oven embodiment utilizes 
relatively slow moving, laminar, heated fluid flow with a resultant 
relatively thick boundary layer and low, substantially radiant, heat 
transfer. 
Due to the different mechanisms of heat transfer in the embodiments of this 
invention, different results can be expected as a function of the time at 
which a fiber is heated and the temperature at which the heating takes 
place. As was previously noted, use of the jet embodiment in practice of 
this invention permits manufacture of fibers having a high Crystallinity 
Index and use of the oven embodiment permits manufacture of fibers having 
a high inherent viscosity. It is believed that increasing crystallinity is 
developed in a fiber by increasing the temperature of the fiber heat 
treatment and that crystallinity is developed very quickly and is, in 
fact, developed so quickly that the degree of crystallinity is, 
practically, a matter of the maximum temperature to which the fiber has 
been exposed. 
It is, also, believed that the reactions leading to increased inherent 
viscosity are relatively slow processes compared with the rate of 
crystallization, as discussed above. When fibers are exposed to high 
temperatures for a time appreciably longer than that required for the 
increase in crystallization, the reactions leading to increased inherent 
viscosity will commence. When the rate of heating is relatively slow, 
branching and crosslinking reactions will compete with the crystallization 
reaction and limit, to some extent, the ultimate degree of crystallinity 
which can be obtained. 
In view of the above, it can be understood that practice of the jet 
embodiment, with its rapid heat transfer and high rate of heating, yields 
heat treated fibers with substantially increased crystallinity and an 
inherent viscosity which has been increased only slightly. It can, 
further, be understood that practice of the oven embodiment, with its 
relatively slow heat transfer and slow rate of heating, yields heat 
treated fibers with dramatically increased inherent viscosity and a 
crystallinity which has been increased to a lesser degree. 
The description of this invention is directed toward the use of fibers 
which have been newly-spun and never dried to less than 20 percent 
moisture prior to operation of the heat treating process. It is believed 
that previously-dried fibers cannot successfully be heat treated by this 
process because the heat treatment is effective when performed on the 
polymer molecules at the time that they are being dried and ordered into a 
compact fiber structure. 
The following test procedures represent descriptions of methods used to 
evaluate the fibers prepared, in the Examples, as exemplifying the instant 
invention. 
TEST PROCEDURES 
Inherent Viscosity 
Inherent Viscosity (IV) is defined by the equation: 
EQU IV=ln(.eta.rel)/c 
where c is the concentration (0.5 gram of polymer in 100 ml of solvent) of 
the polymer solution and .eta.rel (relative viscosity) is the ratio 
between the flow times of the polymer solution and the solvent as measured 
at 30.degree. C. in a capillary viscometer. The inherent viscosity values 
reported and specified herein are determined using concentrated sulfuric 
acid (96% H.sub.2 SO.sub.4). Inherent viscosities reported as 20 dl/g or 
greater are indications that the polymer being tested is insoluble. Fibers 
of this invention can be insoluble. Tensile Properties 
Yarns tested for tensile properties are, first, conditioned and, then, 
twisted to a twist multiplier of 1.1. The twist multiplier (TM) of a yarn 
is defined as: 
##EQU3## 
The yarns tested in Examples 1-16 and 25-33 were conditioned at 25.degree. 
C., 55% relative humidity for a minimum of 14 hours and the tensile tests 
were conducted at those conditions. The yarns tested in Examples 17-24 
were conditioned at 21.degree. C., 65% relative humidity for 48 hours and 
the tensile tests were conducted at those conditions. 
Tenacity (breaking tenacity), elongation (breaking elongation), and modulus 
are determined by breaking test yarns on an Instron tester (Instron 
Engineering Corp., Canton, Mass.). 
Tenacity and elongation are determined in accordance with ASTM D2101-1985 
using sample yarn lengths of 25.4 cm and a rate of 50% strain/min. 
The modulus for a yarn from Examples 1-16 and 25-33 was calculated from the 
slope of the secant at 0 and 1% strains on the stress-strain curve and is 
equal to the stress in grams at 1% strain (absolute) times 100, divided by 
the test yarn denier. 
The modulus for a yarn from Examples 17-24 was calculated from the slope of 
a line running between the points where the stress-strain curve intersects 
the lines, parallel to the strain axis, which represent 22 and 27% of full 
load to break (Full scale to break for 400 denier yarns was 20 pounds and 
for 1200 denier yarns was 100 pounds). Results from tests of the two 
methods for determining modulus are believed to be substantially 
equivalent. For purposes of determining yarn moduli in claim conformance, 
the method of Examples 1-16 and 25-33 will be used. 
Denier 
The denier of a yarn is determined by weighing a known length of the yarn. 
Denier is defined as the weight, in grams, of 9000 meters of the yarn. 
In actual practice, the measured denier of a yarn sample, test conditions 
and sample identification are fed into a computer before the start of a 
test; the computer records the load-elongation curve of the yarn as it is 
broken and then calculates the properties. 
Yarn Moisture 
The amount of moisture included in a test yarn is determined by drying a 
weighed amount of wet yarn at 160.degree. C. for 1 hour and then dividing 
the weight of the water removed by the weight of the dry yarn and 
multiplying by 100. 
Acidity and Basicity of Yarn 
Residual acid or base in a yarn sample was determined by boiling a weighed, 
wet, yarn sample (about 20 grams) for one hour in about 200 ml deionized 
water and about 15 ml 0.1 N sodium hydroxide, and then titrating the 
solution to neutrality (pH 7.0) with standardized aqueous HCl. The dry 
weight basis of the yarn sample was determined after rinsing the yarn 
several times with water and oven drying. The acidity or basicity was 
calculated as milliequivalents of acid or base per kilogram of dry yarn. 
The amount of sodium hydroxide added to the solution must be such that the 
pH of the system remains at pH 11.0 to 11.5 throughout the boiling step of 
the test. 
Moisture Regain 
The moisture regain of a yarn is the amount of moisture absorbed in a 
period of 24 hours at 70.degree. F. and 5% relative humidity, expressed as 
a percentage of the dry weight of the fiber. Dry weight of the fiber is 
determined after heating the fiber at 105-110.degree. C. for at least two 
hours and cooling it in a dessicator. 
Apparent Crystallite Size and Crystallinity Index 
Apparent Crystallite Size and Crystallinity Index for poly-p-phenylene 
terephthalamide fibers are derived from X-ray diffractograms of the fiber 
materials. Apparent Crystallite size is calculated from measurements of 
the half-height peak width of the diffraction peak at about 23.degree. 
(2.THETA.), corrected only for instrumental broadening. All other 
broadening effects are assumed to be a result of crystallite size. 
The diffraction pattern of poly-p-phenylene terephthalamide is 
characterized by the X-ray peaks occurring at about 20.degree. and 
23.degree. (2.THETA.). As crystallinity increases, the relative overlap of 
these peaks decreases as the intensity of the crystalline peaks increases. 
The Crystallinity Index of poly-p-phenylene terephthalamide is defined as 
the ratio of the difference between the intensity values of the peak at 
about 23.degree. and the minimum of the valley at about 22.degree. to the 
peak intensity at about 23.degree., expressed as percent. It is an 
empirical value and must not be interpreted as percent crystallinity. 
X-ray diffraction patterns of yarn samples are obtained with an X-ray 
diffractometer (Philips Electronic Instruments; ct. no. PW1075/00) in 
reflection mode. Intensity data are measured with a rate meter and 
recorded either on a strip-chart or by a computerized data 
collection-reduction system. The diffraction patterns were obtained using 
the instrumental settings: 
Scanning Speed 1.degree., 20 per minute; 
Time Constant 2; 
Scan Range 6.degree. to 38.degree., 2.theta.; and 
Pulse Height Analyzer, "Differential". 
For the 23.degree. peak, the position of the half-maximum peak height is 
calculated and the 2.theta. value for this intensity measured on the high 
angle side. The difference between this 2.theta. value and the value at 
maximum peak height is multiplied by two to give the peak breadth at half 
height and is converted to degrees (1 in=4.degree.). The peak breadth is 
converted to Apparent Crystal Size through the use of tables relating the 
two parameters. 
The Crystallinity Index is calculated from the following formula: 
##EQU4## 
where A=Peak at about 23.degree., 
C=Minimum of valley at about 22.degree., and 
D=Baseline at about 23.degree.. 
Description of the Preferred Embodiments 
Preparation of Poly-p-phenylene Terephthalamide Polymer 
Poly-p-phenylene terephthalamide polymer was prepared by dissolving 1,728 
parts of p-phenylenediamine (PPD) in a mixture of 27,166 parts of 
N-methylpyrrolidone (NMP) and 2,478 parts of calcium chloride cooling to 
about 15.degree. C. in a polymer kettle blanketed with nitrogen and then 
adding 3,243 parts of molten terephthaloyl chloride (TCl) with rapid 
stirring. The solution gelled in 3 to 4 minutes. The stirring was 
continued for 1.5 hours with cooling to keep the temperature below 
25.degree. C. The reaction mass formed a crumb-like product. The 
crumb-like product was ground into small particles which were then 
slurried with: a 23% NaOH solution; a wash liquor made up of 3 parts water 
and one part NMP; and, finally, water. 
The slurry was then rinsed a final time with water and the washed polymer 
product was dewatered and dried at 100.degree. C. in dry air. The dry 
polymer product had an inherent viscosity (IV) of 6.3, and contained less 
than 0.6% NMP, less than 440 PPM Ca++, less than 550 PPM Cl-, and less 
than 1% water. 
Spinning and heat treating of fibers are extremely complicated processes. 
Evaluation of fibers with duplication of test results is often difficult. 
In the examples of the invention which follow, there are a few yarns with 
test results outside of limits set for the physical properties of yarns at 
the edge of the present invention. Such test results outside of the limits 
set for the invention are few and are generally no farther outside the 
limits than the expected experimental error. 
EXAMPLE 1 
This Example describes the preparation of a series of yarns from 
poly-p-phenylene terephthalamide like that above-prepare which yarns 
differ from each other primarily in denier and moisture content. 
An anisotropic spinning solution was prepared by dissolving the polymer in 
100.1% sulfuric acid so as to produce a 19.3 wt. percent solution. The 
spinning solution was extruded through a spinneret at about 74.degree. C. 
into a 4 mm air gap followed by a coagulating bath of 10% aqueous sulfuric 
acid maintained at a temperature of 3.degree. C. in which overflowing bath 
liquid passed downwardly through an orifice along with the filaments. The 
spinneret had 134 to 1000 spinning holes (depending on the denier) of 
0.064 millimeter diameter. The filaments were in contact with the 
coagulating bath liquid for about 0.025 seconds. The filaments were 
separated from the coagulating liquid, forwarded at various speeds 
(300-475 ypm) depending on the yarn denier desired and washed in two 
stages. In the first stage, water having a temperature of 15.degree. C. 
was sprayed on the yarns to remove most of the acid. In the second stage, 
an aqueous solution of sodium hydroxide was sprayed on the yarns followed 
by a spray of water. In the second stage, the temperature of the liquid 
sprays was 15.degree. C. Residual acid or base in the yarns was determined 
as milliequivalents per kg of yarn. The exterior of the yarns was stripped 
of excess water and yarns were either wound up without drying (yarn 
moisture of about 85%) or they were partially dried on a steam-heated roll 
to as low as 35 weight percent yarn moisture based on dried fiber 
material. The polymer in the yarns so prepared had an inherent viscosity 
of 5.4 to 5.6. Properties of the series of yarns so produced are given in 
Table 1. The yarns of this Example, A-G, differed from each other in 
denier, yarn moisture, and acidity or basicity. 
TABLE 1 
__________________________________________________________________________ 
Acidity(A) 
Forward- or 
ing Yarn Basicity(B) 
Speed Moisture 
Inh. 
Ten. 
Modulus 
(meg./kg. 
Item 
(ypm) 
Denier 
(%) Vis. 
(gpd) 
(gpd) 
of yarn) 
__________________________________________________________________________ 
A 450 2130 
85 5.5 
24.3 
513 6.30 (A) 
B 450 2130 
50 5.5 
24.4 
523 8.65 (A) 
C 300 1140 
85 5.5 
26.2 
545 5.50 (A) 
D 300 1140 
35 5.6 
26.7 
532 1.46 (B) 
E 475 400 
85 5.5 
26.5 
553 8.50 (A) 
F 400 200 
85 5.4 
22.6 
554 -- 
G 1140 
85 5.5 
24.6 
436 -- 
__________________________________________________________________________ 
EXAMPLES 2-11 
These Examples describe the preparation of a series of high modulus, high 
tenacity, and high inherent viscosity poly-p-phenylene terephthalamide 
yarns by heat-treating the yarns of Example 1 (items A-F) in an oven. 
Each of the wet yarns of Example 1 was tensioned and heat-treated in a 40 
ft oven for a given time, temperature and tension. Yarn speeds were in the 
range of 75-200 ypm and were selected to give the desired residence times. 
The oven was electrically heated and heated the yarns primarily by radiant 
heat and, only partially, by convective heat. The oven was continuously 
purged with nitrogen preheated to oven temperature, which, combined with 
steam from the drying yarn, created a nitrogen/steam atmosphere. The yarn 
leaving the oven was advanced by a set of water-cooled rolls during which 
the yarn temperature was reduced to about 25.degree. C. The oven treating 
conditions for Examples 2-11 are given in Table 2, while the properties of 
the heat treated yarns are given in Table 3. 
TABLE 2 
______________________________________ 
HEAT TREATING CONDITIONS 
Feed Yarn 
Example 1, Oven Temp. Heating Time 
Tension 
Example 
Item (.degree.C.) 
(Sec.) (gpd) 
______________________________________ 
2 A 660 8.0 3.0 
3 B 640 10.7 3.0 
4 C 600 6.7 2.0 
5 C 625 6.7 2.0 
6 D 550 8.9 2.0 
7 D 600 8.9 2.0 
8 D 640 6.7 2.0 
9 E 550 4.0 2.2 
10 E 600 6.0 2.2 
11 F 540 5.0 1.8 
______________________________________ 
TABLE 3 
______________________________________ 
HEAT-TREATED YARN PROPERTIES 
Denier 
of Elong. Cryst- 
Mois- 
Ex- Treat- Tena- Mod- at Inh. allinity 
ture 
am- ed city ulus Break Vis Index Regain 
ple Yarn (gpd) (gpd) (%) (dl/g) 
(%) (%) 
______________________________________ 
2 2110 18.7 1142 1.5 &gt;20.0 72 -- 
3 2087 18.6 1136 1.6 13.9 72 -- 
4 1112 21.0 1101 1.8 7.0 72 1.2 
5 1100 19.6 1193 1.6 8.8 73 1.0 
6 1130 21.9 1061 1.9 7.0 70 -- 
7 1124 19.7 1166 1.6 15.0 72 -- 
8 1117 18.8 1244 1.5 &gt;20.0 74 -- 
9 369 22.4 1094 1.9 6.4 73 -- 
10 371 19.1 1261 1.5 14.2 74 0.9 
11 188 19.9 1102 1.7 6.3 72 -- 
______________________________________ 
These examples indicate that the poly-p-phenylene terephthalamide yarns of 
this invention with moduli greater than about 1100 gpd, inherent 
viscosities greater than about 6.5, tenacities greater than 18 gpd, and 
crystallinity indices at least 70%, were prepared using the following oven 
heating conditions: oven temperature greater than 500.degree. C. 
(preferably 550-660C.), heating times 4-11 sec., and tension 1.5-3.0 gpd. 
Note that the polymers of Examples 2 and 8 are insoluble. 
EXAMPLE 12 
A 380 denier, poly-p-phenylene terephthalamide yarn with 85% yarn moisture 
(feed yarn, Example 1E, Table 1) was heat-treated in an oven at 
640.degree. C. for 5.75 seconds by the same general procedure of Examples 
2-11, except that the tension, during heating, was only 0.75 gpd. The yarn 
so produced exhibited a tenacity of 15.8 gpd and a modulus of 1045 gpd. At 
a tension of about 2 gpd, the modulus of the yarn of this Example 12 would 
have been expected to be greater than 1250 gpd and the tenacity greater 
than 18 gpd for the time and , temperature utilized (see Example 10 in 
Tables 2 & 3 for comparison). 
EXAMPLES 13-16 
These Examples describe the oven heat-treatment of 400 and 1140 denier 
poly-p-phenylene terephthalamide yarns at less than the preferred 
temperatures. 
Feed yarns (Example 1, Items C, D & E) were heat-treated in an oven by the 
same general manner as in Examples 2-11, except that the temperatures were 
450-500.degree. C. Specific heating conditions for each Example, 13 
through 16, are listed in Table 4. Heat-treated yarn properties are given 
in Table 5. None of the yarns of these examples exhibit the combination of 
modulus/inherent viscosity/tenacity/crystallinity index which represent 
the yarns of this invention; that is, both the moduli and inherent 
viscosities fall below the desired range. 
TABLE 4 
______________________________________ 
Feed Yarn Yarn Oven Heating 
Example 1 Moist- Temp. Time Tension 
Example 
Item ure (70) (.degree.C.) 
(sec.) (gpd) 
______________________________________ 
13 E 85 450 6.0 2.2 
14 E 85 500 6.0 2.2 
15 C 85 500 8.9 2.0 
16 D 35 500 8.9 2.0 
______________________________________ 
TABLE 5 
______________________________________ 
Elong. Mois- 
Tena- Mod- at Inh./ ture 
Exam- city ulus Break Vis. C.I. Regain 
ple Denier (gpd) (gpd) (%) (dl/g) 
(%) (%) 
______________________________________ 
13 370 23.4 1058 2.1 5.2 70 1.2 
14 373 22.5 103 2.0 5.4 70 1.5 
15 1119 23.2 986 2.2 5.5 70 -- 
16 1141 23.0 1005 2.2 5.7 68 -- 
______________________________________ 
EXAMPLES 17-22 
These Examples describe the preparation of a series of high modulus, high 
tenacity and highly crystalline poly-p-phenylene terephthalamide yarns by 
heat-treating never-dried feed yarns under tension in a forwarding jet. 
For each of these Examples, yarn from Example 1, Item E for all Examples 
except 18 and Item G for Example 18, above, was immersed in water. An end 
from the immersed yarn was passed through a tension gate and onto a feed 
roll. The resulting yarn moisture was about 100%. From the feed roll, the 
yarn was passed through a forwarding jet of the type shown in FIG. 1 with 
a barrel extender which made the overall length of the jet eight inches. 
In the jet, the yarn was dried and heat-treated with superheated steam or 
heated air, depending on the specific Example. From the jet, the yarn was 
passed over a draw roll so as to maintain tension on the yarn (between 2 
and 4 gpd depending on the Example) in the heat-treating zone, and thence 
to a wind-up roll. Water was applied to the yarn just after the jet to 
reduce static bloom. Table 6 contains the specific feed yarn and jet 
conditions used for each Example, while Table 7 provides the properties of 
the heat-treated yarns so produced. 
The yarns of Examples 17-22 exhibit a combination of high modulus (greater 
than 1100 gpd), high tenacity (greater than 18 gpd) and high crystallinity 
(crystallinity index, at least 76%), and Apparent Crystal Size, at least 
74 .ANG.). 
EXAMPLES 23-24 
These two examples describe the preparation of poly-p-phenylene 
terephthalamide yarns by the jet heat-treating procedures described in 
Examples 17-22, except that the exposure times at 500.degree. C. were too 
long and too short, respectively, to give yarns with the desired 
combination of properties. Processing conditions are given in Table 6 and 
yarn properties in Table 7. At the short heating time of 0.5 sec. at 
500.degree. C. for Example 25, both the modulus (1053 gpd) and 
crystallinity properties (Crystallinity Index, 72%; Apparent Crystal Size, 
71 .ANG.) of the yarn were outside of the desired range. At the long 
heating time of 2.5 sec. at 500.degree. C., the yarn tenacity (16.7 gpd) 
fell below the desired range. 
TABLE 6 
__________________________________________________________________________ 
Mois- 
ture Resi- 
on Yarn Gas Flow Ten- dence 
Rey- 
Exam- 
Yarn 
Speed 
Gas Press. 
Temp. 
Rate sion Time 
nolds 
ple (%) (m/m) 
Atm. 
(psig) 
(.degree.C.) 
(SCFM) 
(gpd) 
(sec) 
(.times.1000) 
__________________________________________________________________________ 
17 100 17 air 40 550 1.9 4.0 0.7 22 
18 100 17 steam 
80 600 2.7 3.8 0.7 26 
19 100 25 steam 
40 600 1.8 2.0 0.5 14 
20 100 50 steam 
40 600 1.8 2.2 0.25 
14 
21 100 15 steam 
40 500 2.0 2.0 0.8 18 
22 100 10 steam 
40 500 2.0 2.0 1.3 18 
23 100 5 steam 
40 500 2.0 2.0 2.5 18 
24 100 25 steam 
40 500 2.0 2.0 0.5 18 
__________________________________________________________________________ 
TABLE 7 
__________________________________________________________________________ 
Appar. 
Mois- 
Ten- 
Break 
Modu- 
Crystal. 
Crystal. 
ture 
Inherent 
Exam- acity 
Elong. 
lus Index 
Size Regain 
Viscos. 
ple Denier 
(gpd) 
(%) (gpd) 
(%) (.ANG.) 
(%) (dl/g) 
__________________________________________________________________________ 
17 377 18.6 
1.5 1141 
79 78 1.2 5.7 
18 1165 
19.7 
1.5 1304 
76 74 1.0 5.5 
19 375 20.2 
1.5 1278 
76 77 1.1 6.7 
20 363 19.1 
1.4 1268 
77 78 1.1 5.4 
21 376 18.1 
1.5 1125 
76 74 1.4 5.8 
22 377 18.3 
1.5 1145 
77 76 1.4 6.0 
23 372 16.7 
1.4 1183 
77 77 1.2 6.0 
24 370 19.0 
1.7 1053 
72 71 2.4 5.0 
__________________________________________________________________________ 
EXAMPLES 25-33 AND COMISON EXAMPLES C1-C7 
Examples 25-33 and Comparison Examples C1-C7 describe the preparation of a 
series of poly-p-phenylene terephthalamide yarns using rinsing and washing 
processes which result in varying levels of acidity and basicity. 
A series of nominally 400 denier (267 filaments per yarn) poly-p-phenylene 
terephthalamide yarns was prepared as described in Example 1 except that 
the second stage of washing for yarns in this series was varied from water 
sprays to sprays of caustic solution with increasing concentration of 
sodium hydroxide ranging from 0.1 to 1.8%, followed by sprays of water or 
caustic solution with concentrations ranging from 0.01 to 0.5%. Residual 
acid or base in the yarns ranged from as high as 136 meq of acid per kg of 
yarn, through essentially neutral yarns, to as high as 106 meq of base per 
kg of yarn. The exterior of the yarns was stripped of excess water and the 
yarns were wound up without drying (yarn moisture of about 85%). 
The yarns prepared as above were tensioned and heat-treated in an oven (17 
in long) at 600.degree. C. for 5.7 sec at a tension of 2.0-2.5 gpd. The 
properties of the yarn before and after heat treatment are given in Table 
8. 
It can be seen from Table 8 that yarns having acidity levels up to acidity 
of about 60 (Examples 25-30) gave acceptable processability during oven 
heating, high modulus, good strength retention and high inherent 
viscosity. Above acidity of about 60, yarn processability deteriorated 
abruptly, such that the yarn broke under processing tensions and could not 
be strung up (Comparison Examples C1-C3). 
On the basic side, spun yarns with basicity up to about 10 could be 
successfully processed, and the properties of the resulting oven-treated 
yarns were acceptable (Examples 31-33). At basicity of greater than about 
10, yarn properties and processability deteriorated (Comparison Examples 
C4-C7). 
TABLE 8 
______________________________________ 
Before Heating 
Acidity Opera- After Heating 
Ex- or basi- Inher. bility Strgth 
Inher. 
am- city Viscos. during Mod. Reten. 
Viscos. 
ple (Meg/kg) (dl/g) heating (gpd) (%) (dl/g) 
______________________________________ 
C1 136 Acid 5.4 Oven -- -- -- 
breaks 
Can't 
string up 
C2 123 " 5.2 " -- -- -- 
C3 " Oven 5.6 " -- -- -- 
25 54 " 5.7 Acceptable 
1160 73 &gt;20 
26 42 " 5.6 " 1180 68 17.0 
27 24 " 5.2 " 1150 64 16.5 
28 21 " 5.9 " 1170 66 9.5 
29 7 " 5.7 " 1180 58 10.5 
30 4 " 5.1 " 1151 60 8.5 
31 2 base 5.3 " 1064 54 8.8 
32 4 " 5.6 " 1140 58 8.7 
33 8 " 5.7 " 1084 50 8.2 
C4 14 " 4.5 Oven -- -- -- 
breaks 
Can't 
string up 
C5 23 " 5.4 Poor 1103 48 7.0 
process 
continuity 
C6 63 " 4.8 " 1061 50 4.3 
C7 106 " 5.8 Oven -- -- -- 
breaks 
Can't 
string up 
______________________________________