Solution of PPD-T and PVP and articles made therefrom

A poly(p-phenylene terephthalamide) composition is disclosed comprising 50 to 95 weight percent PPD-T and 5 to 50 weight percent PVP along with a process for making the composition and articles made from the composition.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to preparation and use of a poly(p-phenylene 
terephthalamide) (PPD-T) combination of materials which includes PPD-T and 
polyvinyl pyrrolidone (PVP); and to processes for making shaped articles 
made from that combination. Solutions in which the combination was formed 
during polymerization of the PPD-T can be used to make the shaped 
articles. 
2. Description of the Prior Art 
European Patent Publications No. 381,172, published Sep. 8, 1990 and No. 
396,020, published Nov. 7, 1990, disclose what is termed a homogeneously 
mixed alloy of aromatic polyamides and PVP. It is said that the component 
parts of the alloys of these publications are completely miscible and 
exhibit a single glass transition temperature between those of the 
polyamide and the PVP. It is, also, stated that the PVP can be used in the 
alloy in concentrations of 2% to 98%, with 30% to 70% preferred; and that 
the PVP is not leached out of the alloy by water. The aromatic polyamides 
exemplified in those publications are substantially noncrystalline. PPD-T 
is not mentioned in those publications; and the publications contain no 
recognition of any differences between a system wherein aramids are 
polymerized in the presence of PVP and a system wherein completely 
polymerized aramids are merely dissolved in the presence of PVP. 
European Patent Publication No. 401,740, published Dec. 12, 1990 discloses 
that completely polymerized PPD-T can be dissolved with completely 
polymerized PVP to make a fiber spinning dope to spin fibers which exhibit 
the tensile properties of the PPD-T and the moisture uptake and dyeability 
properties of the PVP. 
SUMMARY OF THE INVENTION 
The present invention provides a process for polymerizing PPD-T in a 
reaction medium which includes PVP to yield a solution of PPD-T and PVP 
and a process for preparing shaped articles from such solution including 
the steps of: establishing a solvent system including PVP, N-methyl 
pyrrolidone (NMP), and an alkaline earth metal salt; placing, in reactive 
contact in the solvent system, p-phenylene diamine (PPD) and terephthaloyl 
chloride (TCl) to yield a polymerization system; agitating the 
polymerization system to yield a PPD-T composition in solution; 
neutralizing acid generated during polymerization of the PPD and TCl by 
adding an alkaline-earth metal base to the polymerization system; and 
spinning, casting, molding, fibridating, or otherwise forming the PPD-T 
composition into shaped articles. The invention is, especially, focused on 
a process for spinning fibers using the polymerization system as the 
spinning dope. 
The invention, also, provides shaped articles made in accordance with the 
above-mentioned process wherein the shaped article is a PPD-T composition 
which includes 50 to 95 weight percent PPD-T and 5 to 50 weight percent 
PVP. The shaped articles preferred in this invention are fibers, films, 
and fibrids. 
DETAILED DESCRIPTION OF THE INVENTION 
PPD-T is well-known for strength and modulus as well as for resistance to 
degradation at high temperatures. PPD-T is particularly well-known as the 
material of fibers which exhibit extremely high tensile properties. To 
make fibers and other shaped articles of PPD-T, however, has been very 
difficult due to the solvent systems which had to be used. 
To make shaped articles of PPD-T, prior to this invention, the PPD-T had to 
be prepared and isolated from the polymerization system; and, then, the 
isolated PPD-T had to be dissolved in concentrated sulfuric acid and 
promptly used to make the articles. Solubility of PPD-T in the 
polymerization system was so low that meaningful polymer concentrations 
could not be obtained; and resolution in a stronger solvent was necessary. 
Concentrated sulfuric acid was used as the solvent for the PPD-T and great 
care had to be exercised to avoid excessive corrosion and unacceptable 
degradation of the polymer. 
PPD-T is the primary polymer in practice of this invention. By PPD-T 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 diacid chlorides 
with the terephthaloyl chloride and other diamines with the p-phenylene 
diamine. As a general rule, other diamines and other 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 diamines and diacid chlorides have no 
reactive groups which interfere with the polymerization reaction. PPD-T, 
also, means copolymers resulting from incorporation of other aromatic 
diamines and other aromatic diacid chlorides such as, for example, 
2,6-naphthaloyl chloride or choro- or dichloroterephthaloyl chloride; 
provided, only, that the other aromatic diamines and aromatic diacid 
chlorides be present in amounts which permit preparation of anisotropic 
solutions. 
Preparation of PPD-T has generally been performed by addition of the 
reactive polymerization components to a solvent system to make a 
polymerization system from which the PPD-T precipitates as the 
polymerization proceeds. The solvent and polymerization systems have 
generally included a salt which was believed to increase the solubility of 
the para-aramid. Even so, until the present invention, the solubility of 
the PPD-T in the polymerization system was not great enough to permit use 
of the polymerization system, itself, to make shaped articles of the 
PPD-T. Preparation of PPD-T is described in U.S. Pat. Nos. 3,869,429; 
4,308,374; and 4,698,414. 
In practice of this invention, PVP is added to the solvent system or the 
polymerization system; and, the presence of the PVP, for reasons not 
entirely understood, permits the PPD-T to remain in solution to a 
concentration far beyond the maximum concentration of PPD-T usually 
experienced in the past. By PVP is meant the polymer which results from 
linear polymerization of monomer units of N-vinyl-2-pyrrolidone and 
includes small amounts of comonomers which may be present in 
concentrations below those which do not interfere with the interaction of 
the PVP with the PPD-T. 
It has been determined that PVP of nearly any molecular weight can be used 
in practice of this invention. PVP of molecular weights ranging from as 
little as about 5000 to as much as about 1,000,000 have been used and all 
have resulted in shaped articles exhibiting the benefits of the present 
invention. PVP of very high molecular weight yields spinning dopes of high 
viscosity. PVP with a molecular weight of about 10,000 to about 360,000 is 
preferred. 
Although, as stated, not entirely understood, it is believed that, during 
polymerization of PPD-T in the presence of PVP, the PVP forms a complex 
with PPD-T; and the complex combination of PPD-T and PVP forms a mass of 
the polymers, combined but capable of acting separately. The PPD-T 
composition of this invention is a heterogeneous but intimate combination 
of PPD-T and PVP; and, due to the rigid rod nature of the PPD-T, may be 
unique in the character of the combination. It is believed that PVP, as a 
more or less solid form of the NMP solvent, is attracted by the PPD-T; but 
does not breach the PPD-T crystal structure. PVP appears to form a complex 
with PPD-T up to a saturation concentration of about 50 weight percent PVP 
based on the total weight of the composition. At concentrations below the 
saturation, PVP appears to be bound by a framework of the PPD-T crystal 
structure; and above the saturation concentration, there is free, 
unassociated PVP in the composition. At all concentrations of PVP, the 
PPD-T is present in the composition as an individual phase of crystalline 
material. 
Studies have shown that the PPD-T unit cell dimensions are substantially 
unchanged over all concentrations of PVP in PPD-T. The unit cell 
dimensions of pure PPD-T, as found in PPD-T compositions including PVP, 
confirms that PPD-T and PVP are present in the compositions as independent 
materials in two phases. 
As additional verification of the heterogeneous, two-phase, nature of the 
PPD-T/PVP composition of this invention, films of the composition at all 
concentrations of PVP are opaque; and transmission electron microscope 
inspection of samples of the composition at all concentrations of PVP 
reveal two separate phases of material. 
Many of the qualities of the shaped articles of this invention are 
controlled or altered by the amount of PVP present in amounts from 5 to 50 
weight percent based on weight of the PPD-T combination. The lower limit 
is a limit of practicality because, although the benefits of the invention 
will be present at any concentration of PVP, the benefits are difficult to 
measure at concentrations of less than about 10 weight percent. 
The upper limit represents the concentration at which some qualities of the 
shaped-article begin to deteriorate due to the presence of excess PVP. It 
should be recognized that PVP is not known to be an outstanding or even 
impressive shaped-article forming material; and that, even though its 
presence in shaped-articles in combination with PPD-T yields 
shaped-articles of excellent and entirely unexpected improvements, there 
is a concentration for the PVP above which some qualities of the shaped 
articles are not acceptable. It is believed that above about 50 weight 
percent of PVP, based on the PPD-T combination, PVP is irreversibly 
leached from the shaped-article into the coagulation bath during 
manufacture. 
The solvent system of this invention utilizes N-methyl-2-pyrrolidone (NMP) 
as a solvent liquid and requires PVP to be dissolved therein. As stated, 
the PVP is dissolved in the NMP in an amount which will yield a final 
polymer product having from 5 to 50, weight, percent PVP, based on the 
PPD-T combination. As a general rule, the PVP can be dissolved in the NMP 
at all concentrations; but, at very high concentrations of PVP, the 
viscosity becomes unmanageable. 
It is optional but preferred that the solvent system should include a salt 
which serves as an aid to maintaining the polymer in solution. The salt is 
generally an alkaline earth halide; and is usually calcium chloride. PVP 
does not readily dissolve in a solution of the calcium chloride in NMP. 
The solvent system is conveniently made by, first, preparing a solution of 
the PVP in NMP and, then, adding the salt to that solution. While the 
order of addition of the PVP may be important to assure that the PVP 
remains dissolved in the system, the PVP can, also, be added after 
addition to the system of one of the reactive polymerization species. 
To make the PPD-T combination, the PPD is generally added to the solvent 
system and, after agitation to assure complete dissolution, the TCl is 
placed in reactive contact with the PPD by adding it to the solvent 
system. The agitation is continued for a time to substantially complete 
the polymerization reaction to yield PPD-T in solution. The reactive 
polymerization species are added to the solvent system in amounts which 
will result in a PPD-T concentration, at the end of the polymerization 
reaction, of 4 to 15, weight, percent PPD-T based on total weight of the 
polymerization system. The PPD-T which is made by the process of this 
invention can have an inherent viscosity from 1 to 7, and preferably has 
an inherent viscosity above 2. PPD-T of high inherent viscosity can be 
made only if all components of the polymerization reaction system are 
scrupulously dry during polymerization of the PPD-T. 
In order to make a PPD-T solution appropriate for use in making the shaped 
articles of this invention, a basic neutralizing material is added to the 
polymerization system to neutralize the acid which was generated during 
the polymerization reaction. The neutralizing material is generally an 
alkaline earth metal base, for example, oxide, hydroxide, carbonate, or 
hydride, and is preferably calcium oxide. 
The solution of this invention is anisotropic and sulfuric acid-free. The 
solution can be used for casting films or making pulp, molding articles, 
spinning fibers, and the like. An effective solution should generally 
include 6 to 16 grams of polymer per 100 grams of solution. To experience 
the benefit of this invention, the polymer in the solution should be 
greater than about 10 weight percent and less than about 50 weight percent 
PVP, based on the weight of the PPD-T combination. The fibers of this 
invention are considered to be made from the combination of PVP and PPD-T; 
and the usual additives such as dyes, fillers, delusterants, UV 
stabilizers, antioxidants, flame retardants, and the like can be 
incorporated into the combination of PVP and PPD-T which constitutes the 
fibers. Fibers can be spun in accordance with well-known spinning 
procedures, such as those taught in U.S. Pat. No. 3,767,756 issued Oct. 
23, 1973 on the application of Blades--incorporated herein by reference. 
Solutions of this invention can be used, spun, extruded, cast, molded and 
the like at any temperature at which they are liquid or at any temperature 
at which the polymer remains in solution. 
The resulting solution can, also, be used to make PPD-T composition 
fibrids. Fibrids are very small fiber-like particles which are made by 
combining the resulting solution, under vigorous forces of agitation, with 
a liquid which is miscible with the solvent of the resulting solution but 
which does not dissolve the PPD-T composition. Water is often used as the 
liquid in fibrid making processes. 
TEST METHODS 
Inherent Viscosity. 
Inherent Viscosity (IV) is defined by the equation: 
EQU IV=ln(h.sub.rel)/c 
where c is the concentration (0.5 gram of polymer in 100 ml of solvent) of 
the PPD-T in the polymer solution and hrel(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). 
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: 
TM=(twists/inch)/(5315/denier of yarn).sup.-1/2 
The yarns to be tested are conditioned at 25.degree. C., 55% relative 
humidity for a minimum of 14 hours and the tensile tests are 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, elongation, and initial modulus, as defined in ASTM D2101-1985, 
are determined using yarn gage lengths of 25.4 cm and an elongation rate 
of 50% strain/minute. The modulus is calculated from the slope of the 
stress-strain curve at 1% strain and is equal to the stress in grams at 1% 
strain (absolute) times 100, divided by the test yarn denier. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the Examples which follow, all parts are by weight unless specifically 
stated to be otherwise.

EXAMPLE 1 
In this example, a PPD-T composition was made in accordance with this 
invention. 
In a reaction vessel, a solvent system was established by dissolving 12.5 
parts calcium chloride in 147.5 parts NMP--both carefully and completely 
dried. 9.329 parts p-phenylene diamine were dissolved in the solvent 
system with agitation. 25 parts of a solution of 5 parts of PVP (molecular 
weight, 40,000) in 20 parts of NMP were added to the stirring system. 
The stirring system was cooled to 5.degree. C. degrees in an ice water 
bath; and, while maintaining the agitation and the ice water bath, 6.145 
parts of terephthaloyl chloride were added to the polymerization system. 
After stirring for about 5 minutes, the vessel was removed from the ice 
water bath and 11.413 parts of terephthaloyl chloride were added to the 
stirring polymerization system. The system was stirred for an additional 5 
minutes; and 4.83 parts calcium oxide, slurried in 50 parts NMP, were 
added to neutralize HCl generated during the polymerization reaction. 
The neutralized system was stirred for an additional 60 minutes to 
substantially complete the polymerization reaction. The resulting product 
included a PPD-T composition made up of PPD-T and PVP which, when 
isolated, exhibited an inherent viscosity of 3.2. The inherent viscosity 
of the combination is, of course, much different from the inherent 
viscosity of either one of the PPD-T or PVP, alone. The resulting 
polymerization system was an anisotropic solution of para-aramid 
composition of 9.57% concentration; and, viewed in terms of PPD-T, only, 
had a concentration of 8%. 
A film was cast on a glass plate from a portion of the anisotropic solution 
using a doctor knife with a 0.25 mm opening. The glass plate was placed in 
a vacuum oven set at 130.degree. C. overnight to evaporate the solvent 
from the film. A highly opaque film was formed on the glass plate. The 
glass plate, with the film, was placed in room temperature water to 
extract residual solvent as well as calcium chloride from the film. The 
film was dried in a convection oven set at 120.degree. C. The resulting 
film was highly opaque and was very strong in the direction of casting. 
The film was weak transverse to the direction of casting, thus, indicating 
the anisotropic nature of the solution and the resulting film product. 
Fibrids were prepared from a portion of the anisotropic solution by 
introducing the solution, under vigorous forces of agitation, into a bath 
of water to cause precipitation of the poly(p-phenylene terephthalamide) 
into fibrid form. 
Fibers were spun from a portion of the anisotropic solution by extruding 
the solution directly into water at a temperature of about 18.degree. C. 
The fibers were washed and dried and exhibited a tenacity of 3.7 grams per 
denier, an elongation to break of 4.9%, and an initial modulus of 236 
grams per denier. 
EXAMPLE 2 
Example 1 was repeated except that the solvent system was made up of 23.4 
parts calcium chloride in 276.6 parts NMP and 55 parts of that solution 
were used in the polymerization reaction. All other aspects of this 
Example were the same as in Example 1. 
The PPD-T composition, when isolated, exhibited an inherent viscosity of 
5.86 and the resulting polymerization system was an anisotropic solution 
of para-aramid composition of 7.54 % concentration; and viewed in terms of 
PPD-T, only, had a concentration of 5.38%. 
COMISON EXAMPLE 1 
In this Example, [poly(2,2-Bis[4-(4-aminophenoxy)phenylpropane 
terephthalamide)] (BAPP-T) polymer was prepared in the presence of PVP. 
BAPP-T is an aromatic polyamide copolymer and, in combination with PVP, 
yields a completely homogeneous solution of the components and does not 
yield an anisotropic polymerization solution. Moreover, shaped articles of 
this BAPP-T/PVP combination are clear and evidence the miscibility and 
homogeneity of the components as compared with the heterogeneity of 
PPD-T/PVP composition of the present invention. 
In a reaction vessel, a solvent system was established by dissolving 9.0 
parts of PVP (molecular weight 40,000) in 221 parts of NMP--both carefully 
and completely dried. Into the solvent system was added 16.42 parts of 
BAPP 2,2-Bis[4-(4-aminophenoxy)phenylpropane[BAPP], flake and the mixture 
was stirred until all of BAPP flake was completely dissolved. That 
solution was cooled to about 15.degree. C. and 7.9 parts terephthalic acid 
dichloride were added to the mixture, with stirring. The temperature rose 
during the reaction and the mixture was then heated, additionally, to 
50.degree. C. While continuing the stirring, 0.21 part of terephthalic 
acid dichloride was added to complete the polymerization. Finally, 0.2 
part benzoyl chloride was added to react any remaining amino end groups; 
and, after one-half hour, 2.25 parts calcium oxide were added to 
neutralize hydrogen chloride generated during the course of the 
polymerization. The resulting solution was light yellow in color but 
transparent which was indication of the isotropic nature of the solution. 
The calculated resulting polymer composition was 70%, by weight, BAPP-T 
and 30%, by weight, PVP. 
A film was cast on a glass plate from a portion of the polymerization 
solution using a doctor knife with a 0.25 mm opening. The glass plate was 
placed in a vacuum oven set at 130.degree. C. overnight to evaporate the 
solvent from the film. Transparent film was formed on the glass plate. The 
glass plate, with the film, was placed in room temperature water to 
extract residual solvent as well as calcium chloride from the film. The 
film was dried in a convection oven set at 120.degree. C. 
The film was crystal clear indicating homogeneous blend of BAPP-T and PVP. 
COMISON EXAMPLE 2 
In this example, fully polymerized BAPP-T and fully polymerized PVP were 
combined to yield solutions of the materials and films were cast from 
these solutions. To make BAPP-T, the same procedure as in Comparison 
Example 1 was used except that PVP was not added to the system. The 
resulting BAPP-T polymer solution was clear but slightly yellow in color. 
The BAPP-T was isolated by pouring the polymerization solution into 
vigorously agitated water, washing several times in water, and then drying 
in a vacuum at 120.degree. C. 
Various concentrations of BAPP-T/PVP blend solutions were prepared by 
adding dried BAPP-T polymer flake prepared above and PVP(40,000 in MW) 
powder to 25 parts of NMP in small glass bottles. The contents were shaken 
at room temperature until all solids are completely dissolved. Films were 
made from these solutions according to the procedures in Comparison 
Example 1. The results are described in the following table: 
TABLE 
______________________________________ 
Run 
Num- BAPP-T PVP % % Solution 
Film 
ber Wt. Parts 
Wt. Parts 
BAPP-T PVP Clarity 
Clarity 
______________________________________ 
2-1 1.50 0.0 100 0 Clear Clear 
2-2 1.50 0.5 75 25 Clear Clear 
2-3 1.50 1.0 60 40 Clear Clear 
2-4 1.50 1.5 50 50 Clear Clear 
2-5 1.50 3.0 33 67 Clear Clear 
2-6 1.50 4.5 25 75 Clear Clear 
2-7 0.00 5.0 0 100 Clear Clear 
______________________________________ 
The films were also examined by transmission electron microscopy and no 
indication of multiple phases was found for any of the compositions.