MXPA97002304A - Procedure for the preparation of filaments and polibenza fibers - Google Patents

Abstract

A continuous process for removing polyphosphoric acid from a filament of polybenzazole absorbent material is described, which comprises: a) contacting the filament of absorbent material with water or a mixture of water and polyphosphoric acid, under conditions sufficient to reduce the phosphorus content of the filament. filament less than 10,000 ppm by weight, and then b) contacting the filament of absorbent material with an aqueous solution of an inorganic base, under conditions sufficient to convert at least 50% of the polyphosphoric acid groups present in the filament to a salt of the base and the acid. It has been found that contacting the filament of absorbent material with a solution of a base, after washing the filament to remove most of the residual phosphorus, after washing the filament to remove most of the residual phosphorus, advantageously leads to an improvement in the initial strength of the filament tension, as well as an improved retention of the tensile strength and / or the molecular weight (of the polybenzazole polymer) after being exposed to light and / or high temperatures.

Description

PROCEEDING FOR THE PREPARATION OF POLYBENZAZOL FILAMENTS AND FIBERS DESCRIPTION OF THE INVENTION This invention relates to processes for the preparation of fibers and filaments of polybenzazole fiber. The prepared fibers of polybenzoxazole (PBO) and polybenzothiazole (PBT), (hereinafter referred to as polymers of PBZ or polybenzazole) can be prepared by first extruding a solution of a polybenzazole polymer into a mineral acid (an "absorbent material" of polymer) through a die or spinner to prepare a filament of absorbent material. The filament of absorbent material is then expelled through an air gap, with or without stretching, and then coagulated in a bath comprising water or a mixture of water and a mineral acid. If a multitude of filaments are extruded simultaneously, these can then be combined into a multi-filament fiber during or after the coagulation step. The filament or fiber is then washed in a wash bath to remove most of the mineral acid, and then dried. The physical properties of such filaments and fibers, such as tensile strength, are known to be relatively high. However, further improvement of said properties is desired. In one aspect, this invention is a process for removing polyphosphoric acid from a filament of polybenzazole absorbent material, which comprises: a) contacting the filament of absorbent material with water or a mixture of water and polyphosphoric acid, under sufficient conditions to reduce the phosphorus content of the filament to less than about 10,000 ppm by weight; and then b) contacting the filament of absorbent material with an aqueous solution of an inorganic base, under conditions sufficient to convert at least about 50% of the polyphosphoric acid groups present in the filament to a salt of the base and the acid, wherein the process is operated continuously at a rate in line of at least about 50 m / minute. It has been found that contacting the filament of absorbent material with a solution of a base, after washing the filament to remove most of the residual phosphorus, advantageously leads to an improvement in the initial tensile strength of the filament, thus as to an improved retention of tensile strength and / or molecular weight (of the polybenzazole polymer) after exposure to light and / or at high temperatures, relative to methods where a base is not used. These and other advantages of the invention will be apparent from the description that follows. The filaments of polybenzazole absorbent material, for use in the process of the present invention, can be prepared by extruding a polybenzazole absorbent material through an extrusion die with a small diameter or "spinner". The polybenzazole absorbent material comprises a solution of polybenzazole polymer in polyphosphoric acid. The term "polybenzazole", as used herein, refers to polybenzoxazole ("PBO") and polybenzothiazole ("PBT"). PBO, PBT and random, sequential and block copolymers of PBO and PBT are described in references such as Wolfe and others, Liquid Crystalline Polymer Compositions, Process and Products, (Polymer, crystalline, liquid, Process and Product Compositions), USA 4,703,103 (October 27, 1987); Wolfe et al., Liquid Crvstalline Polv (2.6-benzothiazole) Composition, Process and Products, (Liquid Crystal, Poly (2,6.benzothiazole) Liquid, Process and Products, US Patent 4,533,724 (August 6, 1985); Wolfe , Liquid Crvstalline Polvmer Compositions, Processes and Products, (Polymer, crystalline, liquid compositions, Procedures and Products), US Patent 4,533,693 (August 6, 1985); Evers, Thermoxidativelv Stable Articulated p-benzobisoxazole and p-benzobisthiazole Polvmers, (Poly-linked, thermo-oxidatively stable p-benzobisoxazole and p-benzobisthiazole polymers), US Patent 4,359,567 (November 16, 1982); Tsai et al., Method for makinq heterocyclic Block Copolymer, (Method for Making a Heterocyclic Block Copolymer), U.S. Pat. 4,578,432 (March 25, 1986); 11 Ency. Poly. Sci. & Eng., Polvbenzothiazoles and Polybenzoxazoles, (Polybenzothiazoles and Polybenzoxazoles), 601 (J. Wiley &Sons 1988) and W.W. Adams et al., The Materials Science and Enqeneerinq of Ri id-Rod Polvmers (Materials of Science and Engineering of rigid bar polymers) (Materials Research Society 1989). The polybenzazole polymer can be a rigid bar, a semi-rigid bar or a flexible spring. Preferably it is a liquid-crystalline, lyotropic polymer, which forms liquid-crystalline domains in solution when its concentration exceeds a critical concentration. The intrinsic viscosity of the rigid polybenzazole polymers, in methanesulfonic acid at a temperature of 25 ° C, is preferably at least about 10 dL / g, preferably at least about 15 dL / g, and most preferably about 20 dL / g. The absorbent material must contain a sufficiently high concentration of polymer so that the polymer forms an acceptable filament after extrusion and coagulation. When the polymer is liquid-crystalline, lyotropic, then the concentration of the polymer in the absorbent material is preferably high enough to provide a liquid-crystalline absorbent material. The concentration of the polymer is preferably at least about 7% by weight, preferably at least about 10% by weight, and most preferably at least about 14% by weight. The maximum concentration is limited mainly by practical factors, such as polymer solubility and viscosity of the absorbent material. The concentration of the polymer is preferably not more than 30% by weight, and most preferably not more than about 20% by weight. Polybenzazole polymers or copolymers, and suitable absorbent materials, can be synthesized by known methods, such as those described by Wolfe et al., U.S. Pat. 4,533,693 (August 6, 1985); Sybert et al., Patent of E.U.A. 4,772,678 (September 20, 1988); Harris, patent of E.U.A. 4,847,350 (July 11, 1989); and Gregory et al., U.S. Patent. 4,089,591 (February 18, 1992). In summary, suitable monomers are reacted in a non-oxidizing acid and dehydration solution under a non-oxidizing atmosphere, with vigorous stirring and high shear at a temperature that is increased in a staggered or ramp fashion of no more than 120 °. C up to 190 ° C. The absorbent material can then be formed into a filament by extrusion through a spinner, and extracting the filament through a gap. Suitable procedures are described in the previously incorporated references, and in the patent d € E.U.A. 5,034,250. The spinner preferably contains a plurality of holes. The number of holes in the spinner and their arrangement are not critical to the invention, but it is desirable to maximize the number of holes, for economic reasons. The spinner may contain as much as 100 or 1000 or more, and may be arranged in circles, grids, or in any other desired arrangement. The spinner can be constructed of ordinary materials that will not be degraded by the absorbent material, such as stainless steel. The absorbent material in the spinner enters a gap between the spinner and the coagulation bath. The hollow is typical called an "air gap" although it does not need to contain air. The void may contain any fluid that does not induce coagulation or adverse reaction with the absorbent material, such as air, nitrogen, argon, helium or carbon dioxide. The absorbent material is preferably expelled at a rotation-ejection ratio of at least about 20., preferably as high as about 40, preferably at least about 50 and most preferably at least about 60. The spin-ejection ratio is defined in this application as the ratio between the acquisition speed of the filaments and the capillary speed (Vc) of the absorbent material in the spinner. The shear rate in the spinner hole wall is preferably in the range of 1800 to 6500 s'1. The extraction must be enough to provide a filament that has the desired diameter. In step a) of the process of the invention, the filament of absorbent material is contacted with water or a mixture of water and polyphosphoric acid, under conditions sufficient to reduce the phosphorus content of the filament to less than about 10,000 ppm by weight . This can be done in an individual operation in a washing apparatus, or the filament can travel through various baths or wash cabinets to reduce the phosphorus content to the desired level. If a mixture of water and polyphosphoric acid is used, the concentration of polyphosphoric acid in solution should be less than that contained in the filament, in order to effectively wash the filament. Said mixtures are preferably used in the initial stages of washing, since the gradual removal of the polyphosphoric acid from a multi-filament fiber tends to improve its physical properties. Preferably, the first filament is "coagulated" in a coagulation bath containing water or a mixture of water and polyolefinic acid, which removes sufficient solvent to prevent substantial stretching of the filament during any subsequent processing. The filament can then be further washed in a multi-step process. The term "coagulation", as used herein, does not necessarily imply that the absorbent material is a liquid that flows and changes to a solid phase. The absorbent material may be at a sufficiently low temperature, so that it essentially does not flow before the coagulation step begins. The amount of solvent removed during the coagulation step will depend on the residence time of the filament in the coagulation bath, the temperature of the bath and the concentration of the solvent therein. For example, using a solution of 20% by weight of polyphosphoric acid at a temperature of about 23 ° C, a residence time of about one second, will remove approximately 70% of the solvent present in the filament. The washing of the filament may be carried out by immersing the filament in water or in a mixture of water or polyphosphoric acid (a "washing fluid"), but preferably it is carried out in a continuous process by passing the filament through a series of bathrooms or laundry cabinets. Laundry cabinets typically comprise an enclosed cabinet containing one or more rollers, in which the filaments travel a number of times, and through, before leaving the cabinet. As the filament travels around the roller, it is sprayed with a washing fluid. The washing fluid is continuously collected at the bottom of the cabinet and drained from it. Preferably, the surface of the filament is not allowed to dry after the coagulation step begins and before the washing steps are completed. By theory, without pretending the union, it is said that the wet, never dry, surface of the filament is relatively porous and provides trajectories to wash the residual phosphorus from the interior of the filament. On the other hand, it is said that the pores close when they dry and do not open even when they get wet again. The closed pores trap the residual phosphorus within the filament. The temperature of the coagulation bath is preferably at least about 10 ° C, preferably at least about 25 ° C, preferably not greater than about 50 ° C, and most preferably not greater than about 40 ° C. The residence time of the filament in the coagulation bath is preferably at least about 1 second, and most preferably no more than about 5 seconds. The concentration of acid in the coagulation bath is preferably at least about 0.5% by weight, preferably at least about 20%, preferably not more than about 40%, and most preferably not more than about 25% . For a continuous process, it is preferred to use such a low temperature and a solvent content as high as practical, so that the solvent can be removed as slowly as possible. The temperature of the washing fluids is preferably at least about 25 ° C, preferably at least about 50 ° C, and preferably not greater than about 120 ° C, most preferably not greater than about 100 ° C. . The washing fluid can also be applied in the form of steam (steam), but is more conveniently used in liquid form. The residence time of the filament in the wash baths will depend on the desired concentration of residual phosphorus in the filament, but typical residence times are in the range of 180 seconds to 300 seconds. The duration of the entire washing process, used in the first step of the process of the invention, is preferably not greater than about 200 seconds, most preferably not more than about 160 seconds. For a continuous spinning operation, the concentration of phosphorus in the filament is preferably carried as low as practical in the coagulation and washing operations, giving this for said procedures, fewer steps and higher speeds in line are desirable. It is believed that a slower reduction in phosphorus concentration in the filament provides a filament that has better physical properties. It is also believed that this result is achieved more efficiently in a continuous multi-step operation, using a series of baths or wash cabinets, reducing the acid concentration in the wash bath as the filament continues below the line of washing. Conveniently, the wash fluid residue collected after the last wash step can be used as the wash fluid in the next-to-last wash step, and so on up to the line, the wash fluid containing the highest concentration. high acid that was used in the first washing step. The concentration of acid in the baths or wash cabinets is preferably at least about 0.2% by weight, and is preferably not greater than about 40% by weight.

The residual phosphorus concentration in the filament after step a) of the process is preferably less than about 8,000 ppm, preferably less than about 6,000 ppm, and most preferably less than about 4,000 ppm. The residual phosphorus content of a substantially dry filament can be measured using X-ray fluorescence techniques, described in E.P. Bertin, Principies and Practice of X-Rav Spectrometric Analvsis - 2nd. ed. (Plenum Press 1984). The appropriate equipment is commercially available under the trade name of KEVEX 770 XRF and Philips Electronic Instruments. The filament used in the method of the invention can be combined into a multi-filament fiber at any point during the process of the invention. Preferably, however, the filaments are combined just before, or during coagulation. Since the term "filament" is used throughout this application to describe the process of the invention, the method of the invention can also be performed on a filament contained in a multi-filament fiber, using the same process parameters, as it was described here for use with an individual filament. The filament is preferably under tension during at least a part of the washing process. Most preferably, the tension is also applied throughout the coagulation and washing process, particularly when the fluid temperature is very high. The tension is preferably sufficient to prevent the filament from shrinking or relaxing. In the second step of the process of the invention, the filament of absorbent material is contacted with an aqueous solution of an inorganic base, under conditions sufficient to convert at least about 50% by weight of the acid groups present in the filament to the corresponding salt form (hereinafter "neutralization step"). This step can be done in an individual operation, or the plant can travel through several bathrooms or wash cabinets to reduce the phosphorus content to the desired level. Preferably, however, this step is carried out in an individual wash cabinet, as described above. Examples of suitable water-soluble bases include sodium hydroxide, ammonium lid oxide, sodium carbonate, and sodium bicarbonate. The percentage of acid groups, which have been converted, can be followed by any suitable technique, such as nuclear magnetic resonance (NMR) spectroscopy or Fourier transform infrared spectroscopy (FTIR). The concentration of base in the solution is preferably at least about 0.2% by weight, preferably at least about 0.4% by weight, and preferably not more than about 1.2% by weight, most preferably not more than about 0.8% by weight. weight. The duration of this second step will depend on the concentration of the base, with longer residence times required for lower concentrations, but preferably not greater than about 120 seconds, most preferably not greater than about 60 seconds. Preferably, at least about 50% of the acid groups remaining after step a), are converted to their salt form, preferably at least about 75%, and most preferably at least about 95% are thus converted. The pH of the base solution used in the neutralization step will depend on the duration of the passage, with a preferred higher pH with a shorter duration, but preferably it is in the range of 10 to 14, most preferably in the scale of 11. to 12. Since the residual base in the fiber tends to degrade the properties of the fiber, particularly if the fiber is heat treated after the neutralization step, the concentration of the base and the residence times are preferably selected to obtain a stoichiometric ratio of base: acid groups in the fiber of at least 0.5: 1.0, preferably of at least 075: 1 00, and preferably not greater than 1.5: 1.0, most preferably not greater than 1.25: 1.0, but preferably 1: 1. The stoichiometry of the process can be determined by a suitable method, such as by measuring the ratio of phosphorus to conjugate acid of the inorganic base in the fiber, after the neutralization step. For example, if sodium hydroxide is used, the phosphorus: sodium ratio in the fiber can be measured by a suitable technique such as Neutron Activation Analysis. The process of the present invention is preferably carried out in a continuous form at a line speed of at least about 50 m / minute. The line speed preferably is at least about 200 m / minute, most preferably at least about 400 m / minute and most preferably at least about 600 m / minute. After the second step of the process, if any residual base is present in the fiber, the fiber preferably is further washed with egua during a residence time of at least about 1 second to remove most of the residual base. The particular washing conditions will depend on the amount of residual base present, requiring longer residence times to remove large amounts of base. Then, the filament may be dried, heat treated, and / or wound on rolls, as desired, as described, for example, in the US patent. 5,296,185. Multiple filament fibers containing PBZ can be used in ropes, cables, fiber-reinforced mixed materials and cut-resistant garments. The following examples are presented to illustrate the invention and should not be construed as limiting in any way. Unless otherwise specified, all parts and percentages are given by weight.

EXAMPLES 1-10 A solution was prepared with 14% by weight of polybenzoxazole ("PBO") in polyphosphoric acid ("PPA" available from Eastman Kodak Company) with an intrinsic viscosity of between 30 and 34 (measured in metsnesulfonic acid at 23 ° C). The PBO filaments were extruded at a temperature of 165 ° C out of a spinner of 180 micras with 42 stems in a coagulation bath, and were combined into a multi-filament fiber. A glass cover was placed in the air gap, between the face of the spinner and the liquid surface of the coagulation bath, in order to minimize air currents in the air gap. The filaments were produced using a shear rate, at the spinner hole wall, of about 3500 s'1. The rotation-extraction ratio used is 44, with a fiber entry speed of 200 m / minute. The resulting filaments had a denier of 1.5 denier per filament and a diameter of 11.5 microns. The fibers were coagulated in a water and polyphosphoric acid bath, having an acid content of about 20% by weight. The residence time in the coagulation stage was approximately 0.5 seconds and the temperature was approximately 10 ° C. Then, the fibers were washed in line with water (as the comparative examples), or in a three step process using water, an aqueous solution of 0.05% by weight of sodium hydroxide, and water, using a washing temperature of about 23 ° C. After washing, the fiber was dried under nitrogen at room temperature (23 ° C) for an additional 48 hours. A portion of the samples was fixed with heat through a nitrogen purged tube furnace, with a residence time of 2 seconds at 600 ° C. A constant tension of approximately 3.5 g / denier was maintained on the fiber during heat fixation. The residual phosphorus was measured using X-ray fluorescence in a Philips PW1404 / DY685 sequential spectrometer, with scandium X-ray tubes and fiber samples that had been compressed into a pellet for analysis. Then, the retention of the tensile strength and the intrinsic viscosity of each fiber were measured, both before and after the heat treatment. The retention of the tensile strength (TSR), defined as (resistance to photo-dampening tension / resistance to initial tension) x 100%, was used to express the retention of the tensile strength after photoaction, although they were used Samples separately for each measurement. The photo-aging was carried out in a Ci65A Atlas climate measuring instrument, with a xenon lamp and a borosilicate filter. The fiber strands were mounted on supports and photoexposed in the weather meter. The exposure was 765 doewatt / m, with a wavelength of 300 to 800 nm, for a total of 100 hours. The procedure used to measure the tensile strength was as follows: the tensile properties were measured according to ASTM D-2101, on an Instron 4201 universal test machine. A cell with a load of 4.54 kg was used with a speed crossed of 2.54 cm / minute and a length of caliber of 25.4 cm. Stress data were obtained on 42 filament fibers with a torsion factor of 6 to 7. The intrinsic viscosity (IV) of the fiber samples was measured by dissolving them in methanesulfonic acid, and the intrinsic viscosity was measured at 23 ° C. . Each number reported in the table is an average of ten samples, and different fiber samples were used to measure the properties of how they were spun and treated with heat from the fiber. All fiber samples, for which the data are shown in Table I, were taken from the same fiber roll, in sequential locations along the roll. That is, the samples used for Comparative Example 1 were taken from the portion of the roller adjacent to the samples used in Example 2, and so on. The results are presented in Table I TABLE I P- Residual phosphorus content, parts per million by weight. TSR- Retention of the tensile strength (% of resistance to tension retained after the climate measurement treatment).

IV- intrinsic viscosity. A-S- Fiber as it was spun; H-T- Fiber treated with heat. * - Shown in the chart as the residence time in the wash bath, in minutes. (Com p.) - Comparative example-is not an example of the invention.

The data showed that the retention of tensile strength d € 1 fibers was improved when the fibers were neutralized with sodium hydroxide.

EXAMPLES 11-13 Using the method described in Examples 1-10, fiber samples composed of filaments with a denier of 1.5 denier per filament, and a diameter of 11.5 microns, were coagulated in water for 1 second, washed in water for 10 minutes. and they were contacted with 0.1 N of aqueous solution of a bain e for 10 minutes. In Example 12, the samples were subsequently washed with water at room temperature for 24 hours. The tensile strength of the samples was measured, and the heat treatment was carried out, as described in Examples 1-10. The residual sodium and phosphorus content of the fiber (Na) was also shown, as measured by Neutron Activation Analysis. The data is shown in Tables Ha and llb.

TABLE Ha TABLE llb TS (AS) - Stress resistance, as spun, ksi (1000 psi = 1 ksi) TM (AS) - Stress module, as spun, msi (1 x 106 psi = 1msi) TS (HS) - Resistance to tension, heat treated, ksi TM (HS) - Stress module, heat treated, msi IV (AS) - Intrinsic viscosity, as spun EXAMPLES 14-20 Using the method described in Examples 1-10 (with the exception that the filaments were spun through a spinner having 166 holes and were coagulated for 1 second in a bath containing 20% by weight of PPA, and the filaments were yarns at a speed of 100 m / minute), fiber samples composed of filaments having a denier of 1.5 denier per filament and a diameter of 11.5 microns were prepared, coagulated and washed for a sufficient period to present the residual levels of phosphorus shown in Table III. Then, the samples were contacted with 0.1 N of an eicuous solution of a base for 5 minutes. A heat treatment with steam jet was carried out at approximately 545 ° C, at a line speed of 40 m / minute and a residence time of 1.5 seconds, applying a tension of approximately 5.5 g / den. Examples 14-16 are comparative examples, wherein the fiber was not contacted with a base. The residual sodium content of the fiber was also shown (Na), as measured by Neutron Activation Analysis. The tensile strength of the fibers was measured as described in Examples 1-10. The data is shown in Table III.

TABLE III Comparative example - not an example of the invention.

Claims (4)

1. CLAIMS 1 - . 1 - A process for removing polyphosphoric acid from a filament of polybenzazole absorbent material, which comprises: a) contacting the filament of absorbent material with water or a mixture of water and polyphosphoric acid, under conditions sufficient to reduce the content of phosphorus of the filament to less than about 10,000 ppm by weight; and then b) contacting the filament of absorbent material with an aqueous solution of an inorganic base, under conditions sufficient to convert at least about 50% of the polyphosphoric acid groups present in the filament to a salt of the base and the acid, wherein the process is operated continuously at a line speed of at least about 50 m / minute.
2. 2. The method of claim 1, wherein step a) comprises the sequential steps of (1) coagulating the filament in a coagulation bath, and (2) washing the filament in at least one separate wash bath.
3. 3. The method of claim 2, wherein the residence time of the filament in the coagulation bath is at least 1 second and not more than 5 seconds.
4. 4. The method of claim 2, wherein the cumulative residence time of the filament in the wash baths is not greater than 200 seconds. 5 - . 5 - The method of claim 1, wherein the residual phosphorus concentration, in the filament after step a), is less than 8,000 ppm 6 - The method of claim 1, wherein at least 75% of the acid groups, which remain after step a), are converted to their salt form in step b) The process of claim 1, wherein at least 95% of the acid groups, which remain after in step a), sin converted to its salt form in step b) 8 - The method of claim 1, wherein the process is operated continuously at a line speed of at least 200 m / minute 9 - The procedure of claim 1, wherein the fiber is washed with water during a residence time of at least 1 second after step b) The process of claim 1, wherein the ratio is tequiometic of base acid groups, in the fiber in step b), it is less than 1 25 1 0