WO1994022936A1

WO1994022936A1 - Rapid heat treatment of liquid crystalline fibers

Info

Publication number: WO1994022936A1
Application number: PCT/US1994/000400
Authority: WO
Inventors: William M. Pleban; Cherylyn Lee; Stefanos Lepeniotis; Benjamin G. Morris, Jr.; George L. Collins
Original assignee: Hoechst Celanese Corporation
Priority date: 1993-03-26
Filing date: 1994-01-12
Publication date: 1994-10-13

Abstract

Fibers and yarns having high strength and high modulus can be made by heat treating at elevated temperatures for relatively short periods of time as-spun fibers and yarns made from liquid crystalline polyesters or poly(esteramide)s consisting essentially of monomer units derived from 6-hydroxy-2-naphthoic acid, 4-hydroxybenzoic acid, 4,4'-biphenol, terephthalic acid, and an optional aromatic aminophenol or diamine, such as the preferred p-aminophenol.

Description

Rapid Heat Treatment of Liquid Crystalline Fibers

FIELD OF THE INVENTION

This invention relates generally to fibers made from liquid crystalline polymers, and more specifically, to fibers having both high modulus and high strength made by rapid heat treatment at elevated temperatures.

BACKGROUND OF THE INVENTION

It is well known that liquid crystalline polymers can be made into fibers having high strength and high modulus. In general, the best properties are obtained by heating fibers at elevated temperatures for extended periods of time, generally 8 hours or longer.

Typically, the heat treatment increases the strength (tenacity) significantly without a corresponding increase in modulus.

Only a few references indicate that high strength can be obtained by heat treatment for less than about eight hours. For example, commonly-assigned U.S. Patent 4,574,066 discloses that liquid crystalline polymers made from 6-hydroxy-2-naphthoic acid and 4- hydroxybenzoic acid can be made into fibers whose strength is increased by heat treatment for two hours or less, provided that the polymer is made using a potassium catalyst and the final part of the polymerization is carried out at high temperatures. The patent also reports in the sentence bridging columns 7 and 8 that the strength decreases if the fiber is heat treated for too long a time. However, the data provided in the patent also show that the modulus of these fibers does not increase significantly under heat treatment conditions.

U.S. Patent 4,183,895 discloses that fibers made from liquid crystalline polymers can be made into high strength fibers by heat treatment at temperatures near the melting point of the polymer for a time in the range of 5 seconds to several hours. This heat treatment results in fibers having improved tenacity. In a few examples, the modulus also increases to some extent. In the examples of polymers containing monomer repeat units derived from naphthalene, the modulus generally is relatively unchanged after heat treatment, with the highest final modulus after heat treatment being 553 gpd.

Commonly-assigned U.S. Patent 4,473,682 describes liquid crystalline polymers containing monomer repeat units derived from 6-hydroxy-2-naphthoic acid, 4- hydroxybenzoic acid, terephthalic acid and 4,4'- biphenol. Commonly-assigned U.S. Application No. 07/687,801, now allowed, teaches polymers which have the same monomers as described in the '682 patent, plus an additional monomer unit derived from 4-aminophenol. Fibers made from the polymers in these two patents are reported in the examples to develop both high tenacity and high modulus when they are heat treated. The heat treatment times used in the examples all appear to be at least about eight hours. The '682 patent generally suggests in Column 9, lines 45-46, that heat treatment times can be on the order of a few minutes to several days, but provides no description of how high modulus and tenacity can be achieved in less than eight hours.

SUMMARY OF THE INVENTION

In view of the foregoing, it is surprising that fibers having both high strength and high modulus can be made by heat treatment of certain liquid crystalline polymers for relatively short times. Such fibers are made by melt spinning a liquid crystalline polymer consisting essentially of monomer units I, II, III, IV and optional V to yield an as-spun fiber, where

II is -o- -

IV is terephthaloyl containing up to about 25% isophthaloyl; and

V is - Y - Ar - Z -

where Ar is one or more divalent aromatic moieties selected from the group consisting of 1,3-phenylene, 1,4-phenylene, 4,4'-biphenylene, 2, 6-naphthylene and 2,7-naphthylene, Y is a divalent moiety selected from the group consisting of -NH- and -NR-, Z is a divalent moiety selected from the group consisting of -NH-, -NR-, and -0-, and R is an alkyl or aryl moiety containing 1-6 carbon atoms. Some of monomer units I-V may optionally include substituents for some of the hydrogen atoms on the aromatic ring. These substituents may be alkyl groups having 1 to 4 carbon atoms, fluorinated alkyl groups having 1 to 4 carbon atoms, alkoxy groups having 1 to 4 carbon atoms, halogen atoms, phenyl groups and mixtures thereof. The liquid crystalline polymer consists essentially of about 1 to about 15 mole % of monomer unit I, about 20 to about 70 mole % of monomer unit II, about 5 to about 40 mole % of monomer unit III, about 1 to about 40 mole % of monomer unit IV, and up to about 20 mole % of optional monomer unit V. The as-spun fiber is heat treated for a time in the range of about 0.25 hours to about 7 hours at a temperature in the range from about 80°C below the melting point of the liquid crystalline polymer up to the melting temperature of the liquid - crystalline polymer to yield a heat treated fiber having a tenacity of at least about 20 gpd and a modulus of at least about 600 gpd as measured by ASTM test method D3822-79. Fibers made by the method disclosed herein are also claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a computer-generated contour plot of the modulus and tenacity of liquid crystalline poly(esteramide) fibers that have been subjected to heat treatment after spinning as a function of the heat treatment time and heat treatment temperature. The poly(esteramide) is derived from 6-hydroxy-2-naphthoic acid (3.5 mole %) , 4-hydroxybenzoic acid (60 mole %) , 4,4'-biphenol (13.25 mole %) , terephthalic acid (18.25 mole %) and p-aminophenol (5 mole %) .

Figure 2 is a computer-generated contour plot of the modulus and tenacity of liquid crystalline polyester fibers that have been subjected to heat treatment after spinning as a function of the heat treatment time and heat treatment temperature. The polyester is derived from 6-hydroxy-2-naphthoic acid (4 mole %), 4-hydroxybenzoic acid (60 mole %), 4,4'- biphenol (18 mole %) and terephthalic acid (18 mole %) .

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred polymer composition is a polyester consisting essentially of monomer units I, II, III and IV, with monomer unit IV being terephthaloyl. Preferably, this polyester composition contains about 2 to about 10 mole % of monomer unit I, about 40 to about 70 mole % of monomer unit II, about 10 to about 30 mole % of monomer unit III, and about 10 to about 30 mole % of monomer unit IV. More preferably, the amount of monomer unit I is about 3 to about 10 mole %. A particularly preferred polyester consists essentially of about 4 mole % of monomer unit I, about 60 mole % of monomer unit II, and about 18 mole % each of monomer units III and IV. Polyesters having this composition are described in detail in commonly-assigned U.S.

Patent 4,473,682. This polyester is made by methods well known in the art, such as those disclosed in U.S. Patent 4,473,682. The preferred method is melt acidolysis polymerization. In this case, the phenolic groups are esterified to acetates, and polymerization proceeds through ester interchange as acetic acid by¬ product boils off. Thus, 6-acetoxy-2-naphthoic acid, 4-acetoxybenzoic acid, 4,4'-diacetoxybiphenyl, and terephthalic acid are the preferred reactants. Generally, it is more convenient to generate the acetates in situ by charging the monomers without prior acetylation along with a catalyst and sufficient acetic anhydride to acetylate the phenolic groups. Heating of the reactants leads first to acetylation of the phenolic groups followed by polymerization. Catalysts for melt acidolysis polymerization are well known in the art. The preferred catalyst is potassium acetate.

Polymerization occurs as the temperature is gradually increased. The final part of the polymerization is completed by heating the molten polymer under vacuum to about 350°C with stirring until the desired molecular weight is achieved, as measured by inherent viscosity. Preferably, the polymer has an inherent viscosity (I.V.) of at least about 1.0 dl/g when measured at 60°C on a 0.1% solution (w/v) in 50/50 (v/v) hexafluoroisopropanol/pentafluorophenol. More preferably, the I.V. is in the range of about 6 to 9, with about 7 being particularly preferred. A polyester with this composition has a melting point of about 355°-360°C and is melt spun in the temperature range of about 360°-375°C. Details on the melt spinning and heat treatment of this particular polymer are presented in Examples 38-59.

Another preferred composition is a poly(esteramide) consisting essentially of monomer units I, II, III, IV and V, with monomer unit IV being terephthaloyl and monomer unit V being derived from 4- aminophenol, as show ^A elow.

Monomer unit V is present in an amount of about 1 to about 20 mole % of all the monomer units. More preferably, the poly(esteramide) consists essentially of about 2 to about 10 mole % of monomer unit I, about 40 to about 70 mole % of monomer unit II, about 5 to about 30 mole % of monomer unit III, about 10 to about 30 mole % of monomer unit IV, and about 2 to about 10 mole % of monomer unit V. A particularly preferred poly(esteramide) consists essentially of about 3.5% of monomer unit I, about 60 mole % of monomer unit II, about 13.25 mole % of monomer unit III, about 18.25 mole % of monomer unit IV, and about 5 mole % of monomer unit V. The melting point of the particularly preferred poly(esteramide) is in the range of about 350°-355°C, and it is preferably melt spun in the range of about 350°C-370°C. Preferably, the inherent viscosity (I.V.) is at least about 1.0 dl/g when measured at 60°C on a 0.1% solution (w/v) in 50/50 (v/v) hexafluoroisopropanol/pentafluorophenol. More preferably, the I.V. is in the range of about 6 to 9 dl/g and most preferably is about 7 dl/g.

The preferred poly(esteramide)s are made by methods well known in the art. The preferred method is melt acidolysis polymerization, analogous to that previously described for the preferred polyester except for the presence of additional monomer unit V, derived from 4-aminophenol. This monomer unit is preferably introduced as N-acetyl-p-aminophenol. Synthesis of this and related liquid crystalline poly(esteramide)s are described in commonly-assigned U.S. Application No. 07/687,801, now allowed, and commonly-assigned U.S. Patents 4,330,457, 4,351,917 and 4,351,918. The polymers of the current invention are melt spun into fibers by conventional methods, but without the subsequent drawing steps that are utilized in the production of conventional fibers. The molten polymer is extruded through an orifice in the molten state and taken up on a reel at a sufficient speed that the fiber is drawn down to the desired size (generally about 4 to about 7 denier) . This fiber (referred to as the "as- spun" fiber) , rather than being subjected to subsequent drawing steps as is done with conventional fibers, is instead subjected to heat treatment, in which it is placed in a hot oven under an inert atmosphere (e.g., nitrogen) . The fiber is placed in the oven without applying stress. This can be done by suspending lengths of fiber between two points in the oven. Large quantities of fiber, including fiber in the form of yarn, can be heat treated by loosely winding the fiber onto a heat resistant bobbin and placing the whole bobbin in the oven.

The as-spun fibers can be heat treated to fibers having both high modulus and high tenacity by heating them at an elevated temperature for relatively short times. It has been found that the short heat treatment times are important because the tenacity and modulus decrease after excessive heat treatment. As stated previously, heat treatment can be carried out for a period of about 0.25 to about 7 hours when the heat treatment is carried out at a temperature within about 80°C of the melting point of the polymer. This results in a fiber having a tenacity of at least about 20 gpd and a modulus of at least about 600 gpd. The upper limit for heat treatment is the melting temperature of the polymer. Because the fibers become sticky as the heat treatment temperature approaches the melting point, the practical upper limit is a few degrees below the melting point, at which temperature the fibers stick together.

More preferably, the heat treatment time is about 0.5 to about 6 hours, and the heat treatment temperature is within about 70° of the melting point of the polymer. Most preferably, the heat treatment is carried out for about 1 to about 5 hours within about 60° of the melting temperature of the polymer. Fibers treated in accordance with the more preferred heat treatment times and temperatures have a tenacity of at least about 24 gpd and a modulus of at least about 750 gpd, and those fibers treated in accordance with the most preferred heat treatment conditions have a tenacity of at least about 27 gpd and a modulus of at least about 900 gpd.

For the preferred polyester composition consisting essentially of monomer units I, II, III and IV, the fiber is preferably heat treated for about 0.25 to about 6 hours at a temperature within about 70° of the melting temperature of the polymer to yield a heat treated fiber having a tenacity of at least about 24 gpd and a modulus of at least about 750 gpd. More preferably, the fiber is heat treated for about 0.5 to about 5 hours at a temperature within about 60° to about 20° below the melting temperature of the polymer to yield a heat treated fiber having a tenacity of at least about 27 gpd and a modulus of at least about 900 gpd.

For the preferred poly(esteramide) composition consisting essentially of monomer units I, II, III, IV and V, where V is derived from p-aminophenol, the heat treatment is preferably carried out for a time in the range of about 0.5 to about 7 hours within about 70° of the melting point of the polymer to yield a fiber having a tenacity of at least about 27 gpd and a modulus of at least about 800 gpd. More preferably, the heat treatment is carried out for a time of about 1 to about 6 hours at a temperature within about 60° of the melting point of the polymer to yield a fiber having a tenacity of at least about 29 gpd and a modulus of at least about 900 gpd.

The fibers taught herein can also be made and heat treated in the form of yarns, which comprise a multiplicity of individual fibers. Yarns can also be subjected to rapid heat treatment at elevated temperatures to achieve high modulus and high tenacity. The measured properties of the yarns are in general somewhat lower than those of single filament fibers, perhaps because of a difference in test methods.

Thus, an as-spun yarn made from a liquid crystalline polymer consisting essentially of monomer units I, II, III,- IV and optional V, where monomer unit

I makes up about 1 to about 15 mole % of the polymer,

II makes up about 20 to about 70 mole % of the polymer,

III makes up about 5 to about 40 mole % of the polymer, IV makes up about 1 to about 40 mole % of the polymer, and V is present in an amount up to about 20 mole % of the polymer, can be heat treated for a time in the range of about 0.25 to about 7 hours at a temperature within about 80° of the melting point of the polymer to yield a heat treated yarn having a tenacity of at least about 18 gpd and a modulus of at least about 700 gpd as measured by ASTM test method D885. More preferably, the heat treatment is carried out for a time greater than about 0.5 hours but less than about 6 hours at a temperature within about 70° of the melting point of the liquid crystalline polymer to yield a heat treated yarn having a tenacity of at least about 19 gpd and a modulus of at least about 750 gpd.

For the preferred polyester consisting essentially of monomer units, I, II, III and IV, where IV is terephthaloyl, heat treatment of the as-spun yarn is preferably carried out for a time in the range of about 0.25 hours to about 6 hours at a temperature in the range of about 70°C below the melting point up to the melting point of the polyester to yield a heat treated yarn having tenacity of at least about 18 gpd and a modulus of at least about 700 gpd as measured by ASTM test method D885. More preferably the heat treatment is carried out for a time in the range of about 0.5 to about 5 hours at a temperature within about 60° of the melting point of the polyester to yield a heat treated yarn having a tenacity of at least about 19 gpd and a modulus of at least about 750 gpd.

For the preferred poly(esteramide) consisting essentially of monomer units I, II, III, IV and V, where IV is terephthaloyl and V is derived from p- aminophenol, where V is present in an amount of about 1 to about 20 mole % of the polymer, the heat treatment is preferably carried out for a time in the range of about 0.5 hours up to about 7 hours at a temperature within about 70° of the melting point of the polymer to yield a heat treated yarn having a tenacity of at least about 24 gpd and modulus of at least about 700 gpd as measured by ASTM test method D885. More preferably, the heat treatment is carried out for a time in the range of about 1 hour to about 6 hours at a temperature within about 60° of the melting point of the poly(esteramide) to yield a yarn having a tenacity greater than about 26 gpd and a modulus greater than about 800 gpd.

The heat treatment described herein is carried out under an inert atmosphere to prevent degradation of the fiber through oxidation of the polymer. Examples of suitable inert atmospheres are nitrogen, argon and helium. It may be possible during the latter stages of the heat treatment to include air in the atmosphere, as has been taught for the heat treatment of liquid crystalline polyesters in U.S. Patent 5,045,257. The use of air in place of an inert gas would offer economic advantages in processing.

The method of rapid heat treatment of liquid crystalline fibers described herein is extremely useful because it results in shorter processing times, which makes the overall process more economical. The fibers themselves are useful in applications where high modulus and high strength are required, such as ropes and reinforcements for belts.

EXAMPLE 1

This example illustrates the preparation of a particularly preferred poly(esteramide) from a 6 mole reaction mixture of 4-hydroxybenzoic acid, 6-hydroxy-2- naphthoic acid, 4,4 ' -biphenol, terephthalic acid, and N-acetyl-p-aminophenol in the ratio 60.0:3.5:13.25:18.25:5.0.

To a 2 liter "Slim Jim" flask equipped with a C- shaped 316 stainless steel stirrer, gas inlet tube, thermocouple, and a Vigreux column attached to a condenser and receiver, were added the following:

(a) 496.8 grams of 4-hydroxybenzoic acid (3.6 moles) ;

(b) 39.5 grams of 6-hydroxy-2-naphthoic acid (0.21 moles) ;

(c) 147.9 grams of 4, 4 '-biphenol (0.795 moles); (d) 181.8 grams of terephthalic acid (1.095 moles) ;

(e) 45.3 grams of N-acetyl-p-aminophenol (0.3 moles) . The flask was immersed in a sand bath and provided with means to accurately control the temperature. The flask was thoroughly purged of oxygen by evacuation and flushed with nitrogen three times, followed by slow heating in the sand bath; and

(f) 10 ml of a 1.2% (w/v) solution of potassium acetate in acetic acid (60 ppm K⁺) , which was added as a catalyst, along with 598.8 grams of acetic anhydride (2.5% excess). Acetic acid began to distill over and was collected in a graduated cylinder.

The contents of the flask were heated while stirring at a rate of 75 rpm to 152°C over a period of 111 minutes at which time 100 ml of acetic acid had been collected. The polymerization temperature was then gradually raised to 350°C over a period of 215 minutes, at which time a total of 660 ml of acetic acid had been collected. The flask was evacuated to a pressure of less than 1.0 mm at 350°C while stirring. The polymer was stirred at 350°C until the desired change in torque was achieved. During this period the polymer melt continued to increase in viscosity while the remaining acetic acid was removed from the flask. The resulting poly(esteramide) had an inherent viscosity (I.V.) of 9.0 dl/g as determined in a hexafluoroisopropanol/pentafluorophenol solution (50/50, v/v) of 0.1 percent (w/v) concentration at 60°C, and a melt viscosity of 365 poise at a shear rate of 10³ sec¹ measured at 345°C in a capillary rheometer using an orifice of 0.015 inch diameter and 1.0" length. The polymer showed a melting point (Tm) of about 355°C. The "melting point", also referred to herein as "melting temperature", is the peak of the endotherm which is oberved by differential scanning calorimetry (DSC) at a heating rate of 20°C/min for the solid to nematic phase transition. The polymer melt was optically anisotropic.

EXAMPLE 2

This example illustrates the preparation of a particularly preferred polyester from a 7 mole reaction mixture of 4-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, 4,4'-biphenol, and terephthalic acid in the mole ratio 60.0:4.0:18.0:18.0. The procedure of Example 1 was substantially repeated with the exception that the following components were charged into the flask:

(a) 579.6 grams of 4-hydroxybenzoic acid (4.2 moles) ;

(b) 53.8 grams of 6-hydroxy-2-naphthoic acid

(0.28 moles) ; (c) 233.9 grams of 4, 4 ' -biphenol (1.26 moles);

(d) 208.9 grams of terephthalic acid (1.26 moles) ; and

(e) 10 ml of a 1.2% (w/v) solution of potassium acetate in acetic acid (60 ppm K⁺) , which was added as a catalyst along with 598.8 grams of acetic anhydride (2.5 % excess) . The final reaction temperature was 355°C.

The resulting wholly aromatic polymer had an I.V. of about 9 dl/g as determined in hexafluoroisopropanol/pentafluorophenol solution (50/50, v/v) of 0.1% concentration (w/v) at 60°C and a Tm of about 360°C as measured by differential scanning calorimetry.

EXAMPLES 3-8

A poly(esteramide) sample made by the method of Example 1 but having an I.V. of about 7 dl/g was made into single filament fibers of about 5 dpf by extruding the molten polymer at a temperature of about 355°C through a single hole with a diameter of 5 mils and a length of 7 mils and winding the fiber onto a bobbin at a take-up rate of about 800 m/min. The tensile properties of the as-spun fibers were measured using ASTM test method D3822-79 with a one inch gauge length and a strain rate of 20%/min. The tensile properties were 8.51 gpd tenacity, 1.49% elongation, 609 gpd modulus. The fiber samples were then subjected to various heat treatment cycles to test the effects of heat treatment on properties. The heat treatment experiments were carried out by placing the fiber samples on metal racks that allowed about six inches of span between the points where the fiber samples were mounted. The samples were mounted with enough slack that they were subjected to no stress other than gravity. The racks were placed into a nitrogen purged oven and heated for varying periods of time. The tensile properties were then measured using the same test method but with a three inch gauge length for comparison with the properties of the as-spun fiber. The results obtained by heat treating the fiber at 270°C are shown in Table 1. The results obtained by heat treating the fiber at 305°C are shown in Table 2.

olv(ester 7 °

tment of Polv(esteramide. at 305°C

The data in Tables 1 and 2 illustrate that better modulus and tenacity were obtained at the higher heat treatment temperature and that they were obtained in a much shorter time. In this experiment, the properties were best after 2-4 hours of heat treatment at 305°C, and the modulus and tenacity were unchanged or decreasing after a total heat treatment of 6 hours.

EXAMPLES 9-30

A large series of poly(esteramide) fiber samples were heat treated under varying conditions for purposes of comparing their tensile properties. The poly(esteramide) was again synthesized by the method of Example 1 except that the polymerization was stopped when the polymer had an I.V. of about 7 dl/g. The fiber examples were melt spun and then heat treated using the method described in Examples 3-8. For this set of experiments, the heat-up time from room temperature to the heat treatment temperature was also varied. The tensile properties of the heat-treated fiber samples were again measured. The data are presented in Table 3. It can be seen from the data in Table 3 that the highest tenacities (greater than 30 gpd) were obtained when the heat treatment temperature was in the range of about 305°-320°C and was held there for 2.8-5.2 hours. The highest modulus values (above 1000 gpd) were obtained when the heat treatment temperature was in the range of about 295°-320°C and was held there for 2-5.2 hours.

Table 3. Heat Treatment of Poly(esteramide)

Temp. (°C)

314 305 305 296 305 305 305 320 296 296 305 305 314 314 296 290 314 300 300 300 335

335

A full factorial regression analysis was carried out on the data presented in Table 3 using a data regression program (RS/Discover^® , obtained from Bolt, Bernek and Newman, Inc., Cambridge, MA). Several features are apparent from the computer analysis. First, the heat-up time makes some difference in the final fiber properties. However, the properties depend more significantly on the heat treatment temperature and/or the time that the fibers were subjected to heat treatment (the heat treatment time) . Second, the modulus and tenacity change differently with respect to heat treatment time and temperature, but both reach a maximum value and then decrease with time at the temperatures that yield the best properties. This is most easily seen in the computer-generated contour plot showing tenacity and modulus as a function of heat treatment time and heat treatment temperature (see Figure 1) .

In the contour plot in Figure 1, the heat-up time was 30 minutes. The tenacities of the fiber samples in Figure 1 show up as a series of approximately concentric ellipses. The highest tenacity predicted by the computer model is about 32 gpd, which occurs with a heat treatment temperature of about 316° to 332°C for a time of about 3.0 to about 4.8 hours. At times or temperatures outside this range, the tenacity is lower. Similarly, the modulus, which appears as a series of approximately vertical lines is at or above 1000 gpd at times in the range of about 3.0 to 5.4 hours at any temperature shown in the plot (about 290°-335°C) . Some important trends are apparent in the computer-generated plots and in the data. Both the modulus and tenacity increase rapidly at fairly high temperatures but then decrease with further heat treatment. The contour plot and the data in Tables 1-3 lead to the conclusion that heat treatment at high temperatures for relatively short times leads to excellent tensile properties, with modulus greater than about 800 gpd, preferably above about 900 gpd, and most preferably greater than about 1000 gpd, and with tenacity greater than about 27 gpd, preferably above about 29 gpd, and most preferably above about 31 gpd. To achieve these desirable properties, heat treatment times are in the range of about 0.5 to less than about 7 hours, preferably in the range of about 1 to about 6 hours, and most preferably in the range of about 2.5 to about 5 hours. Heat treatment temperatures should be in the range of about 290°C up to the melting point of the fiber (or the temperature at which the fibers stick together) , preferably in the range of about 300°C up to the melting point of the fiber (or the temperature at which the fibers become sticky) , and most preferably in the range of about 310°C to about 335°C.

EXAMPLES 31-37

A polyester sample made by the method of Example 2 was extruded into single filament fibers at a temperature of about 360°C using the same method as in Examples 3-8. The tensile properties of the as-spun fibers were measured using ASTM test method D3822-79 as previously described. The fiber samples were heat treated at 270°C and 305°C for various times using the method described in Examples 3-8. The data for the heat treatment experiments are presented in Tables 4 and 5. It can be seen from the data in the tables that much higher tensile properties are reached at the higher heat treatment temperature and that these properties are reached rapidly at that temperature (within about 4 hours) and then level off.

Table 5. Heat Treatment of Polvester at 305°C

Time Tenacity Modulus

Exam le (hrs) ⁽α^pd⁾ (σpd) As-spun 0 8.7 654

35 2 26.9 916

36 4 29.7 1013

37 6 29.4

1014 EXAMPLES 38-59

A full factorial computer regression study of the dependence of tensile properties on the heat-up time, the heat treatment time and the heat treatment temperature was carried out using the method described in Examples 9-30. The fiber samples used in these experiments were made from the polyester that was made according to the procedure of Example 2. The polymer in these experiments had an I.V. of about 7. The fiber samples were spun at about 360°C using the same method as in Examples 3-8. The fiber samples generally ranged in size from about 5.8 to 6.7 dpf. The tensile properties of the various heat treated samples are presented in Table 6.

Table 6. Heat Treatment of Polvester

Heat Treatment

Time (hrs) Temp. (°C)

5.2 314

4.0 305

5.2 296

4.0 305

2.0 305

4.0 320

2.8 296

5.2 296

4.0 305

6.0 305

5.2 314

2.8 314

2.8 296

4.0 290

2.8 314

1.0 335

1.0 300

1.0 300

The computer regression analysis showed the same trends as were observed in the poly(esteramide) . The heat-up time had some effect on the tensile properties. The heat treatment time and heat treatment temperature were much more important in determining the fiber tensile properties. A contour plot of the tenacity and modulus as a function of heat treatment time and temperature is shown in Figure 2 (the heat-up time was 30 minutes). As was the case with poly(esteramide) , the tenacity response surface based on the computer model appears as a series of approximately concentric ellipses, with the highest tenacities (29 gpd) being obtained in about 1.5 to 4.5 hours at about 305°C to about 330°C. The modulus appears to be highest at very short heat treatment times. Heat treatment for about an hour or less at any temperature on the plot (290°- 340°C) results in a modulus of greater than about 950 gpd.

This computer-generated plot indicates that high heat treatment temperatures result in excellent fiber tensile properties within relatively short times. It also illustrates that excessive heat treatment results in poorer tensile properties. It appears from the data and the computer-generated plot that a short heat treatment cycle at high temperatures will result in a single filament fiber having a tenacity of at least about 24 gpd, preferably at least about 27 gpd, and most preferably at least about 29 gpd, and a modulus of at least about 750 gpd, preferably at least about 900 gpd, and most preferably at least about 1000 gpd.' The plot and data suggest that the heat treatment time should be in the range of about 0.25 to about 6 hours, preferably in the range of about 0.5 to about 5 hours, and most preferably in the range of about 1.5 to about 4 hours. Heat treatment temperatures should be in the range of about 290°C up to the melting temperature of the fiber (or the temperature at which the fibers become sticky) , preferably in the range of about 300° to about 340°C, and most preferably in the range of about 310°C to about 330°C.

EXAMPLES 60-64

A poly(esteramide) sample having the composition of Example 1 was made into a yarn (200 denier/40 filament) by extruding the molten polymer at a temperature of 369°C through a 40 hole x 0.005"diameter x 0.007" length spinneret. The yarn was taken up at a rate of about 2500 fpm. The tensile properties of the as-spun yarns were measured using ASTM test method D885 using a ten inch gauge length, 2.5 twists per inch and a 10% strain rate. The yarn samples were then subjected to various heat treatment cycles to test the effects of heat treatment on yarn properties. The heat treatment experiments were carried out by winding the yarn onto heat-resistant bobbins with low tension. The bobbins were placed into a nitrogen purged oven and heated. The tensile properties were then measured for comparison with the properties of the as-spun yarn. The results are shown in Table 7. Table 7. Tensile Properties of Polv(esteramide) Yarn

It is apparent from the data in Table 7 that the yarn samples, like the single filament fiber samples, show a significant increase in modulus upon heat treatment for 4 hours at 310°C. The properties obtained by heat treatment for 4 hours at 310°C are in general as high or higher than the properties obtained by heat treatment for much longer periods of time. The tensile properties measured for the yarns are somewhat lower than those measured for single filament fibers, probably because the tensile properties of yarns and fibers are measured using different test methods. By analogy with single filament test data, it appears that heat treatment for about 0.5 to less than about 7 hours at temperatures greater than about 290°C yield heat treated yarns having tenacity greater than about 24 gpd and modulus greater than about 700 gpd. Preferably, heat treatment in the range of about 1 hour to about 6 hours at a temperature greater than about 300°C yields a heat treated yarn having a tenacity greater than about 26 gpd and a modulus greater than about 800 gpd.

EXAMPLES 65-69

A polyester sample was made into a yarn (200 denier/40 filament) by extruding the molten polymer at a temperature of 364°C through a 40 hole x 0.005" diameter x 0.007" length spinneret. The yarn was taken up at a rate of about 2500 fpm. The tensile properties of the as-spun yarns were measured using ASTM test method D885 using a ten inch gauge length, 2.5 twists per inch and a 10% strain rate. The yarn samples were then subjected to various heat treatment cycles to test the effects of heat treatment on yarn properties. The heat treatment experiments were carried out by winding the yarn onto heat-resistant bobbins with low tension. The bobbins were placed into a nitrogen purged oven and heated. The tensile properties were then measured for comparison with the properties of the as-spun yarn. The results are shown in Table 8.

Table 8. Tensile Properties of Polvester Yarn

It is apparent from the data in Table 8 that the polyester yarn achieves excellent modulus and tenacity within 4 hours of heat treatment. In this case, the properties neither fall nor increase significantly after 4 hours. The tensile properties of the yarns are somewhat lower than the tensile properties measured for single filament fibers. The difference again may be the result of the use of a different test method for fibers than for yarns. By analogy with the single filament fiber, it appears that heat treatment of a yarn for abou 0.25 to about 6 hours at a temperature greater than about 290°C yields a yarn having tenacity greater than about 18 gpd and a modulus greater than about 700 gpd. Preferably, heat treatment of a yarn made from the liquid crystalline polyester for a time in the range of about 0.5 to about 5 hours at a temperature greater than about 300°C yields a yarn having a tenacity greater than about 19 gpd and a modulus greater than about 750 gpd.

It is to be understood that the above-described embodiments of the invention are illustrative only and that modification throughout may occur to one skilled in the art. Accordingly, this invention is not to be regarded as limited to the embodiments disclosed herein.

Claims

WE CLAIM:

1. A method of making a fiber having high strength and high modulus, comprising the steps of:

(a) melt spinning a liquid crystalline polymer consisting essentially of monomer units I, II, III, IV and optional V to yield an as-spun fiber, where

IV is terephthaloyl containing up to about 25% isophthaloyl; and

V is - Y - Ar - Z -

wherein Ar is one or more divalent aromatic moieties selected from the group consisting of 1,3-phenylene, 1,4-phenylene, 4,4'-biphenylene, 2,6-naphthylene and 2,7-naphthylene, Y is a divalent moiety selected from the group consisting of -NH- and -NR-, Z is a divalent moiety selected from the group consisting of -NH-, -NR-, and -0-, and R is an alkyl or aryl moiety containing 1-6 carbon atoms;

wherein some of monomer units I-V may optionally include substituents for some of the hydrogen atoms on the aromatic ring selected from the group consisting of alkyl groups having 1 to 4 carbon atoms, fluorinated alkyl groups having 1 to 4 carbon atoms, alkoxy groups having 1 to 4 carbon atoms, halogen atoms, phenyl groups and mixtures thereof;

wherein said liquid crystalline polymer consists essentially of about 1 to about 15 mole % of said monomer unit I, about 20 to about 70 mole % of said monomer unit II, about 5 to about 40 mole % of said monomer unit III, about 1 to about 40 mole % of said monomer unit IV, and up to about 20 mole % of said monomer unit V; and

(b) heat treating said as-spun fiber for a time in the range of about 0.25 hours up to about 7 hours at a temperature within about 80°C of the melting point of said liquid crystalline polymer to yield a heat treated fiber having a tenacity of at least about 20 gpd and a modulus of at least about 600 gpd as measured by ASTM test method D3822-79.

2. A method of making a fiber having high strength and high modulus as recited in Claim 1, wherein said step of heat treating said as-spun fiber is carried out for a time greater than about 0.5 hours up to about 6 hours at a temperature within about 70° of the melting point of said liquid crystalline polymer to yield said heat treated fiber.

3. A method of making a fiber having high strength and high modulus as recited in Claim 2, wherein said heat treated fiber has a tenacity of at least about 24 gpd and a modulus of at least about 750 gpd.

4. A method of making a fiber having high strength and high modulus as recited in Claim 1, wherein said step of heat treating said as-spun fiber is carried out for a time greater than about 1 hour up to about 5 hours at a temperature within about 60° of the melting point of said liquid crystalline polymer to yield said heat treated fiber.

5. A method of making a fiber having high strength and high modulus as recited in Claim 4, wherein said heat treated fiber has a tenacity of at least about 27 gpd and a modulus of at least about 900 gpd.

6. A method of making a fiber having high strength and high modulus as recited in Claim 1, wherein said liquid crystalline polymer consists essentially of said monomer units I, II, III and IV, wherein said monomer unit IV is terephthaloyl.

7. A method of making a fiber having high strength and high modulus as recited in Claim 6, wherein said liquid crystalline polymer consists essentially of about 2 to about 10 mole % of said monomer unit I, about 40 to about 70 mole % of said monomer unit II, about 10 to about 30 mole % of said monomer unit III, and about 10 to about 30 mole % of said monomer unit IV.

8. A method of making a fiber having high strength and high modulus as recited in Claim 6, wherein said step of heat treating said as-spun fiber is carried out for a time of at least about 0.5 hours up to about 5 hours at a temperature in the range of about 60° below the melting point of said liquid crystalline polymer to about 20° below the melting point of said liquid crystalline polymer to yield a heat treated fiber having a tenacity of at least about 27 gpd and a modulus of at least about 900 gpd.

9. A method of making a fiber having high strength and high modulus as recited in Claim 6, wherein said liquid crystalline polymer consists essentially of about 4 mole % of said monomer unit I, about 60 mole % of said monomer unit II, about 18 mole % of said monomer unit III, and about 18 mole % of said monomer unit IV, wherein said step of heat treating said as-spun fiber is carried out for a time in the range of about 0.25 hours to about 6 hours at a temperature in the range of about 290°C up to the melting point of said fiber to yield a heat treated fiber having a tenacity of at least about 24 gpd and a modulus of at least about 750 gpd.

10. A method of making a fiber having high strength and high modulus as recited in Claim 1, wherein said liquid crystalline polymer consists essentially of monomer units I, II, III, IV, and V, wherein said monomer unit IV is terephthaloyl and said monomer unit V is

the amount of said monomer unit V being about 1 mole % to about 20 mole % of said liquid crystalline polymer.

11. A method of making a fiber having high strength and high modulus as recited in Claim 10, wherein said step of heat treating said as-spun fiber is carried out for a time of at least about 0.5 hours but less than about 7 hours at a temperature within about 70° of the melting point of said liquid crystalline polymer to yield a heat treated fiber having a tenacity of at least about 27 gpd and a modulus of at least about 800 gpd.

12. A method of making a fiber having high strength and high modulus as recited in Claim 10, wherein said step of heat treating said as-spun fiber is carried out for a time of at least about 1 hour but less than about 6 hours at a temperature within about 60° of the melting point of said liquid crystalline polymer to yield a heat treated fiber having a tenacity of at least about 29 gpd and a modulus of at least about 900 gpd.

13. A method of making a fiber having high strength and high modulus as recited in Claim 10, wherein said liquid crystalline polymer consists essentially of about 2 to about 10 mole % of said monomer unit I, about 40 to about 70 mole % of said monomer unit II, about 5 to about 30 mole % of said monomer unit III, about 10 to about 30 mole % of said monomer unit IV, and about 2 to about 10 mole % of said monomer unit V.

14. A method of making a fiber having high strength and high modulus as recited in Claim 10, wherein said liquid crystalline polymer consists essentially of about 3.5 mole % of said monomer unit I, about 60 mole % of said monomer unit II, about 13.25 mole % of said monomer unit III, about 18.25 mole % of said monomer unit IV, and about 5 mole % of said monomer unit V, wherein said step of heat treating said as-spun fiber is carried out for a time in the range of about 0.5 up to about 7 hours at a temperature in the range of about 290°C up to the melting temperature of said fiber to yield a heat treated fiber having a tenacity of at least about 27 gpd and a modulus of at least about 800 gpd.

15. A fiber having high strength and high modulus made by the method of Claim 1.

16. A fiber having high strength and high modulus made by the method of Claim 3.

17. A fiber having high strength and high modulus made by the method of Claim 7.

18. A fiber having high strength and high modulus made by the method of Claim 9.

19. A fiber having high strength and high modulus made by the method of Claim 10.

20. A fiber having high strength and high modulus made by the method of Claim 14.

21. A method of making a yarn having high strength and high modulus, comprising the steps of:

(a) melt spinning a liquid crystalline polymer consisting essentially of monomer units I, II, III, IV and optional V to yield an as-spun yarn, where

IV is terephthaloyl containing up to about 25% isophthaloyl; and V is - Y - Ar - Z -

wherein Ar is one or more divalent aromatic moieties selected from the group consisting of 1,3-phenylene, 1, -phenylene, 4,4'-biphenylene, 2,6-naphthylene and 2,7-naphthylene, Y is a divalent moiety selected from the group consisting of -NH- and -NR-, Z is a divalent moiety selected from the group consisting of -NH-, -NR-, and -O-, and R is an alkyl or aryl moiety containing 1-6 carbon atoms;

(b) heat treating said as-spun yarn for a time in the range of about 0.25 hours up to about 7 hours at a temperature within about 80°C of the melting point of said liquid crystalline polymer to yield a heat treated yarn having a tenacity of at least about 18 gpd and a modulus of at least about 700 gpd as measured by ASTM test method D885.

22. A method of making a yarn having high strength and high modulus as recited in Claim 21, wherein said liquid crystalline polymer consists essentially of said monomer units I, II, III and IV, where said monomer unit IV is terephthaloyl, wherein said step of heat treating said as-spun yarn is carried out for a time in the range of about 0.25 hours to about 6 hours at a temperature within about 70° of the melting temperature of said liquid crystalline polymer.

23. A method of making a yarn having high strength and high modulus as recited in Claim 21, wherein said liquid crystalline polymer consists essentially of about 4 mole % of said monomer unit I, about 60 mole % of said monomer unit II, about 18 mole % of said monomer unit III, and about 18 mole % of said monomer unit IV, where said monomer unit IV is terephthaloyl, wherein said step of heat treating said as-spun yarn is carried out for a time in the range of about 0.25 hours to about 6 hours at a temperature in the range of about 290°C up to the melting point of said liquid crystalline polymer to yield a heat treated yarn having a tenacity of at least about 18 gpd and a modulus of at least about 700 gpd, as measured by ASTM test method D885.

24. A method of making a yarn having high strength and high modulus as recited in Claim 21, wherein said liquid crystalline polymer consists essentially of monomer units I, II, III, IV, ana. V, wherein said monomer unit IV is terephthaloyl and said monomer unit V is

the amount of said monomer unit V being about 1 mole % to about 20 mole % of said liquid crystalline polymer, wherein said step of heat treating said as-spun yarn is carried out for a time of at least about 0.5 hours up to about 7 hours at a temperature within about 70° of the melting point of said liquid crystalline polymer to yield a heat treated yarn having a tenacity of at least about 24 gpd and a modulus of at least about 700 gpd.

25. A method of making a yarn having high strength and high modulus as recited in Claim 24, wherein said liquid crystalline polymer consists essentially of about 3.5 mole % of said monomer unit I, about 60 mole % of said monomer unit II, about 13.25 mole % of said monomer unit III, about 18.25 mole % of said monomer unit IV, and about 5 mole % of said monomer unit V, wherein said step of heat treating said as-spun yarn is carried out for a time in the range of about 0.5 but less than about 7 hours at a temperature in the range of about 290°C up to the melting temperature of said liquid crystalline polymer to yield a heat treated fiber having a tenacity of at least about 24 gpd and a modulus of at least about 700 gpd.

26. A yarn having high strength and high modulus made by the method of Claim 21.