MXPA97000999A - Procedure for making short fibers depolibenza - Google Patents

Abstract

The present invention relates to a process for the preparation of a short polbenzazole fiber which comprises extruding a solution of polybenzazole polymer to form an impure filament, cutting the impure filament to a desired length and washing and drying the cut filament, forming in this way a short fiber of polibenzaz

Description

PROCEDURE FOR MAKING POLIBENZAZOL SHORT FIBERS This invention relates to a process for the preparation of short fibers with high strength and high tension modulus. More specifically, this invention relates to a process for the preparation of short fibers of polybenzazole. Short fibers are short disordered fibers or filaments that they are typically prepared by cutting a dry fiber or filament into short lengths. Such fibers are particularly useful in composite applications. It is known to prepare polybenzazole polymer filaments and fibers by extruding a polymer solution, followed by stretching, washing and drying. Extruded It is also known how to prepare short polybenzazole fibers by cutting the filament after it has been washed and while it is still wet as described in US Patent 5,164,131 However, the filaments that have been thoroughly washed are rigid and difficult to cut while Thus, it would be desirable to develop an improved process for the preparation of staple fibers. In one aspect this invention is a process for the preparation of short benzazole fibers comprising the extrusion of a polybenzazole polymer solution. to form an impure filament, cut the impure filament to a desired length and, wash and dry the cut filament, thereby forming a short polybenzazole fiber. It has been found that the process of the invention provides means for preparing short fibers which do not require the cutting of rigid, washed benzazole filaments These and other advantages of the invention will be apparent from the following description. The understanding of the invention will be facilitated by reference to the accompanying drawings in Figure 1, which is a schematic representation of one embodiment of the method of the invention and figures 2 and 3 illustrating the cutting devices useful in the method of the invention. Referring now to Figures 1, 2 and 3, Figure 1 illustrates one embodiment of the process of the invention. A solution of polybenzazole polymer in polyphospho-acid is supplied ( "impure") to a rotating head (2) through an extruder (1) The impinger is preferably passed through one or more filters and / or porous plates within the rotating head and subsequently rotated through a row (not shown) on which several holes are arranged in a circular or reticular pattern The temperature of the die surface should be as uniform as possible The impure filaments rotated from the spinneret are passed through an extinguishing chamber ( 3) located below the row and the linear speed of the impure filaments is regulated by drying rollers (4) located after the extinguishing chamber which is the fiber through the extinguishing chamber and through the air space between the extinguishing chamber and the rollers The extinguishing chamber and the air space can contain any fluid that does not remove the acid solvent or react adversely with the impure, such as air, nitrogen, argon, helium or carbon dioxide. The impure filaments are introduced sequentially into a cutting device (5) to cut them in the desired lengths. Any suitable cutting device, including conventional cutting devices such as this, can be used. as reciprocating cutters or rotary cutters Figures 2 and 3 illustrate examples of cutting devices. In Figures 2 and 3, a continuous impure filament bundle fixed to the surface of a drum (23) located after the rollers (4) is cut. ) using a cutter blade (24) Figure 2 illustrates a reciprocating type cutter and figure 3 illustrates a rotary cutter cut impure ilaments (27) are dropped as they are scraped from the drum by a scraper (25) Alternatively, the impure filaments can be frozen at a temperature at which they become brittle and then cut with a conventional cutting device as described above or cut with a grinding device. Preferably, the frozen filaments are cut or ground at a temperature below 5 ° C approximately more preferably below about 0 ° C In another embodiment the impure filaments can be cut with a high pressure steam stream If a reciprocating cutter or rotary cutter is used, the drum, the cutter Cutter and scraper are preferably made of a material that is resistant to acid solvent corrosion. In addition, it is important that the cutter blade maintain sharpness and not be damaged. The drum surface is preferably constructed of stainless steel number SS316 and, The cutter blade is preferably constructed of stainless steel number SS431 It is able to coat the surface of the scraper with poly (tetrafluoroethylene) to reduce friction and wear on the part The length of the impure cut filaments is preferably at least 0 1 mm, more preferably at least 1 mm, although it is preferable not greater than about 100 mm, more preferably not more than about 60 mm In the process of the invention, the impure filaments are cut to the desired length after they are rotated from the spinneret but before they are washed with a fluid that it is not solvent for the polybenzazole polymer which will dissolve and wash the acid solvent of the impure ("wash fluid"). However, the filaments can be contacted with minor amounts of such fluid, by exposing the filament to a spraying water spray or water vapor for example, without departing from the invention In such cases, the solvent content of the filament should not be reduced below 1% If the filaments are to be frozen to a temperature below about 5 ° C, the solvent content of the filament should not be reduced below about 40%, before freezing and cutting or grinding. However, the filaments are preferably not contacted with moisture before being cut, except for the atmospheric humidity present due to the humidity of the spinning environment. The filaments are then contacted with a wash fluid to extract at least a portion of the acid solvent therefrom. If the acid solvent contains phosphorus, the filaments are preferably washed to a residual phosphorus content of less than about 8000 ppm, more preferably less than about 5000 ppm. Figure 1 shows a sketch of a device that can be used to collect and transfer the Polybenzazole fibers cut using a net conveyor A wash fluid may be sprayed onto the impure filaments cut in one or more stages and the filaments are then dried. Examples of suitable washing fluids include water and mixtures of water and the solvent from which the impure is prepared, such as polyphosphatic acid The cutting of the impure filaments to the desired length in the manner described above can be collected on a conveyor belt (7) in a first wash bath (8) or they can be collected on the conveyor belt before the first wash bath and subsequently transferred from The same Preferably, at least 990% by weight, more preferably 99 5% by weight of the solvent acid present in the fiber was extracted in the wash baths In order to economically and efficiently reduce the acid solvent contained in the short fiber in a Short time, several wash baths placed in series (8, 11 and 14) can be used, as illustrated in Figure 1, although the removal of the solvent can also be carried out as a single operation in a wash bath. a series of wash baths, the concentration of the acid solvent in the individual wash baths is preferably progressively smaller from the first extraction bath to the second extraction bath, until the short fiber is finally washed in a medium having a low concentration of acid solvent It is desirable to treat the fiber in an alkaline medium with a pH of 8 to 12 before the final extraction bath to prevent deterioration of the physical properties of the fiber during the drying step Preferably, the washing fluid is water or methanol or mixtures of such fluids and the acid solvent, or superheated steam or saturated steam. The temperature of the washing fluid is preferably on the scale from 5 ° C to 100 ° C If desired, a lubricating finish oil can then be applied to the short fiber. The fiber is then dried to a low residual moisture content. An important factor in short fiber drying is the temperature selection. of drying so that the fiber can be dried as quickly as possible while minimizing the formation of holes in it, as described in FIG. Patent Procedure of E.U.A. No. 142,526, filed November 2, 1993, entitled "Method for Rapid Drying of a Polybenzazole Fiber". A single drying device or multiple drying devices can be used to dry the fiber, although preferably two or more devices are used. An example is illustrated in Figure 1. A series of two or more drying devices (15 and 18) equipped with a drying device (16 and 19) and a network conveyor (17 and 20) and the temperature can be used. inside the second drying device is preferably higher than that of the first drying device.

Preferably, the fiber is dried to a moisture content of less than 30% by weight, preferably less than 20% by weight, more preferably less than 10% by weight and more preferably less than 05% by weight. first drying device is preferably at least 130 ° C, more preferably at least 150 ° C approximately, and more preferably at least 160 ° C; although it is preferable not greater than about 230 ° C, more preferably not higher than 220 ° C and, more preferably less than 210 ° C The appropriate temperature for the drying devices varies in accordance with the moisture content of the short fiber introduced to an individual drying device, although preferably not exceeding 250 ° C. The short fiber can be heated by any suitable means, such as hot air circulation or infrared heating. The atmosphere inside the drying device can be, for example, nitrogen, argon or air The short fiber dried to a desired moisture content can be thrown into a storage container (21) The polybenzazole filaments used in the process of the invention can be obtained by spinning an impurity containing a polybenzazole polymer. the present, "polybenzazole" refers to pohbenzoxazole homopolymers (PBO), pohbenzotiaz homopohomers ol (PBT) and random copolymerized block polymer, sequential or block of PBO and PBT Polymers of pohbenzoxazole, polybenzothiazole and random copolymerized, sequential or block polymers thereof are described, for example, in "Liquid Crystalline Polymer Compositions Process and Products" by Wolfe et al. US 4,703,103 (October 27, 1987), "Liquid Crystalline Polymer Compositions, Process and Products" by Wolfe et al US Patent 4,703,103 (October 27, 1987) "Liquid Crystalline Polymer Compositions Process and Products", US Patent 4, 533692 (August 6, 1985), "Liquid Crystalline Poly (2 6-benzothiazole) Composition Process and Products, US Patent 4 533 724 (August 6, 1985)," Liquid Crystalline Polymer Compositions Process and Products "US Patent 4,533693 (August 6, 1985), 'Thermooxidatively Stable Articulated p- Benzobisthiazole Polymers' by Evers, US Patent 4,539,567 (November 16, 1982); and "Method for Makíng Heterocyclic Block Copolymer" by Tsai, U.S. Pat. 4,578,432 (March 25, 1986), The structural units present in the PBZ polymer are preferably selected so that the polymer is liotropic liquid crystalline. The preferred monomer units are illustrated below in Formulas I-VIII. The polymer consists more preferably in essential form of monomer units selected from those illustrated below and, more preferably consists essentially of cis-polybenzoxazole, trans-polybenzoxazole or trans-polybenzothiazole. cis-polybenzoxazole Poly [benzo (1,2-d: 5,4-d ') bisoxazole-2,6-diyl-1,4-phenylene] trans-polybenzoxazole Poly [benzo (1, 2-d: 4,5-d ') bisoxazole-2,6-diyl-1,4-phenylene] trans-polybenzothiazole cis-polybenzothiazole AB-PBO Pol? (2,5-benzoxazole) Poly (2,5-benzothiazole) AB-PBO 25 Pol? (2,6-benzoxazole) Poh (2,6-benzothol) Polybenzazole polymers and copolymers and impure ones can be synthesized by known methods such as those described in Wolfe et al, US Patent 4,533,693 (August 6, 1985), Syebert et al, US Patent 4,772,678 (September 20, 1985). 1988) Harps, U.S. Patent 4,847,350 (July 11, 1989) and Gregory et al, U.S. Patent 5,089,591 (February 18, 1992) In summary, suitable monomers are reacted in a solution of non-oxidizing and dehydrating acid (the acid solvent) under a non-oxidizing atmosphere with vigorous mixing and high shear at a temperature that increases stepwise or ascending from no more than 120 ° C to at least 190 ° C. Suitable solvents for the preparation of the impurity polymer PBZ include cresols and non-oxidizing acids Examples of suitable acidic solvents include polyphosphocid acid methanesulfonic acid and highly concentrated sulfuric acid om ezclas thereof Preferably, the acidic solvent is polyphosphoric acid or methanesulfonic acid, although more preferably it is polyphosphoric acid. The polymer concentration in the solvent is preferably at least about 7% by weight, more preferably at least 10% by weight. weight, and more preferably at least 13% by weight The maximum concentration is limited by practical factors of handling, such as polymer solubility and impurity viscosity. The polymer concentration does not normally exceed 30% by weight, and preferably is not higher of about 20% by weight. Oxidation inhibitors, tarnish agents, coloring agents and unsightly agents can also be added to the impurity. Polybenzazole solutions can be stored for a time before spinning. However, it is particularly desirable to conduct a continuous polymerization, the direct spinning method wherein the polymerization is conducted continuously and an impure is supplied by spinning directly into a spinning device without prior storage. The process of the present invention is preferably operated in a continuous manner with a linear velocity of at least 50 meters. / minute (m / mm) The linear velocity is more preferably at least 200 m / min, more preferably at least 400 m / mm and more preferably at least 600 m / min. The following examples are given to illustrate the invention and should not be considered as limiting in any way Unless otherwise stated, all p arts and percentages are given by weight Example 1 A portion of 4,6-d? Am? No-1, 3-benzen? Dol di-hydrochloride (50 g, 0235 mol) was stirred with 200 g of pophosphophoc acid (with a phosphorus pentoxide content of 83 3% by weight) for 12 hours at 40 aC under a blanket of nitrogen. The temperature of the mixture was stirred at 60 ° C. ° C and the dechlorination was conducted under reduced pressure to about 50 mm Hg To this mixture were added tereftahco acid (390 g, 0236 mol) and 103 g of phosphorus pentoxide and the mixtures were heated under a stream of nitrogen for eight hours at 60 ° C then for nine hours at 120 ° C, then for fifteen hours at 150 ° C and then for 128 hours at 180 ° C The polybenzazole polymer solution obtained by polymerization obtained by polymerization in this manner was used as an impurity of spinning without any additional treatment The concentration of the polymer obtained by the reaction described above was 14.0% by weight and, the concentration of the solvent was 86.0% by weight (base concentration P? Os) The polymer impurity It was degassed in a double worm extruder The pressure was raised and the impure was transferred to a rotating head using a counter pump The impure tapped was extruded through a row with 668 holes an orifice diameter of 022 mm, hole length of 040 mm, entry angle of 20 degrees and an orifice density of 5 / cm The turning temperature was 165 ° C and the discharge velocity per individual orifice was 023 g / mm The distance between the row and the extinguishing chamber was 2 cm and the length of the extinguishing chamber was 20 cm The temperature of the air flow in the extinguishing chamber was 70 ° C and the air flow velocity was 0 7 m / sec The filaments were stretched by means of a pair of drying rollers placed below the face of the spinneret at a speed of 200 m / min. Next, the filaments of the fibers were guided to a ring cutter (rotary cutter) ) placed under the pair of rollers and cut into 45 mm long fibers The cut fiber filaments were collected on a conveyor belt The weight of the filaments was about 1 49 denier per filament Subsequently, the short fibers cut were They are placed inside a first wash bath containing 10% by weight aqueous polyphosphoric acid solution maintained at 22 ± 2 ° C. Subsequently, the filaments are transported through an alkaline solution bath maintained at 22d2 ° C and having a pH of 10 5 and then washed in a water bath A finishing oil was added to the short fiber and the fibers were passed through a first hot air circulation oven maintained at 190 ° C and one second hot air circulating type oven maintained at 220 ° C to dry them until the moisture content was 0.5% by weight Next, the dried short fibers were detached towards a storage container. The properties of the short fiber obtained were evaluated. The intrinsic viscosity of the polybenzazole polymer was measured by mixing a portion of the polybenzoxazole impure with water in a domestic mixer and activating the mixer several times. The polymer powder was redissolved in methanesulfonic acid and the intrinsic viscosity was measured at 30 ° C. The fiber size was measured using a Denicon machine (available from Vibroscope) after the fiber was allowed to stand for 24 hours in a constant temperature constant humidity chamber, constant humidity maintained at a temperature of 22 ° C and a humidity of 65% relative humidity The phosphorus content of the filaments was measured by an atomic spectroscopy technique. This concentration of phosphorus atom can be converted to a concentration of phosphoric acid (percentage by weight). The average phosphorus content of the fibers was 3800 ppm The tensile strength and modulus of the fibers were measured according to the Japanese industrial test method number JIS L-1013 (1981) using a Tensilon machine (available from Toyo Baldwin Co) The gauge length was 5 cm and the deformation index was 100% per minute. The average tensile strength of the fibers during 50 measurements was 5 5 Gpa, the elongation The rupture was 37% and the tension modulus was 159 Gpa. The moisture content of the filament was measured according to the following method: A fiber sample was taken before a drying device was weighed (W, ) and the sample was allowed to stand for 30 minutes in a hot air circulation oven maintained at 230 ° C. The sample was cooled to room temperature in a desiccator and a sample weight (Wf) was measured. The moisture content was calculated using the following equation CMR = (W, -Wf) / Wf x 100. An optical microscope (200X) can be used to verify the presence or absence of damage to the filament (shock bands). There were less than 5 damaged filaments per 100 filaments. The presence of shock bands can reduce the tensile strength of the short fiber after exposure to sunlight. The shock bands can be observed as dark bands on the filament, which are visible at an enlargement of 200X Example 2 A solution of 40% cis-polybenzoxasol (having an intrinsic viscosity of 30 dL / g at 25 ° C and a concentration of 0 05 g / dL in methanesulfonic acid) in polyphosphoric acid was prepared. The impure was swirled in filaments a through a row 3 mil, orifice-31 at a spinning temperature of 150 ° C The filaments were hand stretched and collected on a 952 cm spool and cut into filaments from 12 7 to 20 32 cm The filaments were immersed in liquid nitrogen for at least 30 seconds and fed into a centrifugal mill. The mill was operated on a low speed frame with a screen size of apertures of 1.8 x 1.2 mm. Liquid nitrogen was fed into the grinding chamber before and during milling to keep the chamber at a low temperature. The milled filaments were then washed in water for 2 hours and air-dried for 1 hour.

Claims (1)

1. CLAIMS A process for the preparation of a short polbenzazole fiber comprising extruding a solution of polybenzazole polymer to form an impure filament, cutting the impure filament to a desired length and washing and drying the cut filament, thereby forming a fiber polybenzazole 2 The method of claim 1, wherein the impure filament is cut with a rotary cutting device. The method of claim 1, wherein the impure filament is cut with a reciprocal cutting device. claim 1, wherein the impure filament is frozen at a temperature of less than 0 ° C before cutting. The process of claim 1, wherein the benzazole polymer is polybenzoxazole. The process of claim 1, wherein the Polybenzazole polymer is polybenzothiazole 7 The process of claim 1, wherein the cut fiber is contacted with a aqueous alkaline solution having a pH of 8 to 12 during the washing step 8 The method of claim 1 wherein the length of the cut filament is at least 0 1 mm The method of claim 1 wherein the length of the cut filament is at least 1 mm 10. The method of claim 1, wherein the length of the cut filament is not greater than 100 mm. The method of claim 1, wherein the length of the cut filament is not greater than 60 mm.