US3849529A

US3849529A - Process for drawing polybenzimidazole fibrous materials

Info

Publication number: US3849529A
Application number: US00297511A
Authority: US
Inventors: G Ferment; A Prince; P Sessa
Original assignee: Celanese Corp
Current assignee: Celanese Corp
Priority date: 1972-10-13
Filing date: 1972-10-13
Publication date: 1974-11-19
Anticipated expiration: 1991-11-19

Abstract

DRAWING

1. AN IMPROVED CONTINUOUS PROCESS FOR THE HOT DRAWING OF A CONTINUOUS LENGTH OF A POLYBENZIMIIDAZOLE FIBROUS MATERIAL CONTAINING UP TO ABOUT 100 PERCENT BY WEIGHT OF WATER, SAID DRAWING OCCURING WITHOUT FOAMING AND WITHOUT WEMPOLYING MULTIPLE PASSES OF THE FIBROUS MATERIAL THROUGH THE DRAWING ZONE OF DRAWING THE FIBROUS MATERIAL WHILE IN CONTACT WITH A HEATED SURFACE, WHICH PROCESS COMPRISES: (A) CONTINUOUSLY PASSING SAID CONTINUOUS LENGTH OF POLYBENZIMIDAZOLE FIBROUS MATERIAL IN THE DIRECTION OF ITS LENGTH, FOR A SINGLE PASS, THROUGH AN ELONGATED DRAWING ZONE CONTAINING A HEATED GASEOUS ATMOSPHERE MAINTAINED AT A TEMPERATURE OF ABOUT 400 TO 600*C., (B) CONTINUOUSLY PASSING A PREHEATED GAS INTO SAID DRAWING ZONE AT A RATE WHICH YIELDS A REYNOLD''S NUMBER WITHIN THE DRAWING ZONE OF ABOUT 50 TO 50,000 SO AS TO CONTACT SAID FIBROUS MATERIAL THEREIN, (C) DRAWING SAID FIBROUS MATERIAL IN SAID DRAWING ZONEWHILE IN CONTACT WITH SAID REPHEATED GAS AT A DRAWRATIO OF ABOUT 2:1 TO 5:1 AND AT A DRAWING SPEED OF AT LEAST 10 METERS PER MINUTE, AND (D) THEREAFTER CONTINUOUSLY WITHDRAWING FROM SAID DRAWING ZONE A STREAM OF GAS AND DRAWN POLYBENZIMIDAZOLE FIBROUS MATERIAL.

Description

Nav. 19, 1974 Q R, FERMENT ETAL 3,849,529

PROCESS lFOR DRAWING POLYBENZIMIDAZOLE FIBRous MATERIALS Filed Oct. 13, 1972 nted States Patent O Filed Oct. 13, 1972, Ser. No. 297,511 Int. Cl. B29c 17/02; D02j 1/22 U.S. Cl. 264-85 8 Claims ABSTRACT OF THE DISCLOSURE An improved process is provided for the hot drawing of a continuous length of a polybenzimidazole fibrous material on a continuous basis, without foaming, in a single pass. The fibrous material is drawn while suspended in an elongated drawing zone provided with a owing heated gaseous atmosphere wherein heat radiantly is supplied to the fibrous material from the walls of the drawing zone as well as by contact with a stream of preheated gas (aS defined). The fibrous material may optionally be supplied to the drawing zone while in association with a substantial quantity of water thereby eliminating the necessity to carry out a conventional drying step prior to hot drawing.

BACKGROUND OF THE INVENTION Heretofore continuous lengths of polybenzimidazole fibrous materials have been hot drawn (1) while in sliding contact with a hot surface, eg., a hot shoe, or (2.) while passing for a plurality of passes through a radiantly heated drawing zone in which the fibrous material is suspended. When employing either prior art drawing technique, it has been essential that the polybenzimidazole fibrous material be dried and substantially free of water prior to introduction into the drawing zone if optimum tensile properties are to be achieved. Diliiculties have been encountered with hot shoe polybenzimidazole drawing techniques because of solid deposit formation upon the hot contact surface which requires periodic cleaning, and which may result in fiber damage and decreased line stability if allowed to accumulate. Also, precise hot shoe temperature maintenance uniformity has been of prime importance. When radiant heat has been supplied to the polybenzimidazole fibrous material in prior art techniques (e.g., the process of U.S. Pat. No. 3,622,660), it has been essential that the continuous length of fibrous material be passed through the drawing zone for a plurality of passes in order to accomplish the desired degree of drawing. Such processes additionally require a complex string-up arrangement which is impractical for large scale economic production, and commonly are accompanied by the production of broken filaments.

It is an object of the present invention to provide an improved continuous hot drawing process for a continuous length of a polybenzimidazole fibrous material.

It is a object of the present invention to provide an irnproved continuous hot drawing process for a continuous length of a polybenzimidazole fibrous material which eiiciently is carried out on a stable 'basis upon a single pass through a hot drawing zone.

It is an object of the present invention to provide an improved continuous hot drawing process for a polybenzimidazole fibrous material wherein the fibrous material fed to the drawing zone optionally may be in association with a substantial quantity of water.

`It is an object of the present invention to provide an irnproved continuous hot drawing process for a polybenzimidazole fibrous material which is conducted in the absence of contact with a hot draw surface, e.g., a hot shoe, or pin.

ice

It is a further object of the present invention to provide an improved continuous hot drawing process for a polybenzimidazole fibrous material which is capable of yielding a product of superior fiber uniformity.

It is a further object of the present invention to provide an improved continuous hot drawing process for a polybenzimidazole fibrous material which is not unduly sensitive to the maintenance of a narrowly defined drawing temperature.

These and other objects, as well as the scope, nature, and utilization of the process will be apparent from the following detailed description and appended claims.

l SUMMARY OF THE INVENTION It has been found that in a continuous process for the hot drawing of a continuous length of a polybenzimidazole fibrous material at a draw ratio of about 2:1 to 5:1 and at a drawing speed of at least l0 meters per minute improved results are achieved by:

(a) Continuously passing the continuous length of polybenzimidazole fibrous material in the direction of its length while under a longitudinal tension for a single pass through an elongated drawing zone wherein the drawing is accomplished which is provided with a heated gaseous atmosphere at a temperature of about 400 to 600 C. in which the fibrous material is suspended and in which radiant heat is supplied to the fibrous material from the walls of the drawing zone,

(b) Continuously introducing into the gaseous atmosphere of the elongated drawing zone at least one stream of preheated gas which impinges upon the moving continuous length of polybenzimidazole fibrous material within the elongated drawing zone and flows within the elongated drawing zone, and

(c) Continuously withdrawing from the gaseous atmosphere of the elongated drawing zone at least one stream of gas.

DESCRIPTION OF THE DRAWINGS FIG. l is a schematic illustration of an apparatus capable of carrying out the improved continuous hot drawing process of the present invention.

FIG. 2 is a schematic illustration of an additional apparatus capable of carrying out the improved continuous hot drawing process of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS The Starting Polymer Polybenzimidazoles are a known class of heterocyclic polymers. Typical polymers of this class and their preparation are more fully described in U.S. Pat. No. 2,895,948, U.S. Re. Pat. No. 26,065, and in the Journal of Polymer Science, vol. 50, pp. S11-539 (1961) which are herein incorporated by reference. The polybenzimidazoles consist essentially of recurring units of the following Formulas I and II. Formula I is:

wherein R is a tetravalent aromatic nucleus, preferably symmetrically substituted, with the nitrogen atoms forming the benzimidazole rings being paired upon adjacent carbon atoms, i.e., ortho carbon atoms, of the aromatic nucleus, and R is a member of the class consisting of l) an aromatic ring, (2) an alkylene group (preferably those having 4 to 8 carbon atoms), and (3) a heterocyclic ring from the class consisting of (a) pyridine, (b) pyrazine,

(c) furan, (d) quinoline, (c) thiophen, (f) pyran.

Formula II is:

wherein Z is an aromatic nucleus having the nitrogen atoms forming the benzimidazole ring paired upon adjacent carbon atoms of the aromatic nucleus.

Preferably, aromatic polybenzimidazoles are selected, e.g., polymers consisting essentially of the recurring units of Formulas I and II wherein R is an aromatic ring or a heterocyclic ring.

As set forth in U.S. Re. Pat. No. 26,065, the aromatic polybenzimidazoles having the recurring units of Formula II may be prepared by self-condensing a trifunctional aromatic compound containing only a single set of ortho disposed diamino substituents and an aromatic, preferably phenyl, carboxylate ester substituent. Exemplary of polymers of this type is poly-2,5(6)benzimidazole prepared by the autocondensation of phenyl-3,4-diaminobenzoate.

As also set forth in the above-mentioned patent, the aromatic polybenzimidazoles having the recurring units of Formula I may be prepared by condensing an aromatic tetraamine compound containing a pair of orthodiamino substituents on the aromatic nucleus with a dicarboxyl compound selected from the class consisting of (a) the diphenyl ester of an aromatic dicarboxylic acid, (b) the diphenyl ester of a heterocyclic dicarboxylic acid wherein the carboxyl groups are substituents upon a carbon in a ring compound selected from the class consisting of pyridine, pyrazine, furan, quinoline, thiophene and pyran and (c) an anhydride of an aromatic dicarboxylic acid.

Examples of polybenzimidazoles which have the recurring structure of Formula I are as follows:

where the double bonds of the ethylene groups are intact in the final polymer.

The preferred polybenzimidazole for use in the present process is one prepared from poly-2,2(mphenylene)- 5,5-bibenzimidazole, the recurring unit of which is:

fr @i .l

L \N yt@ With respect to aromatic polybenzimidazoles, preferably equimolar quantities of the monomeric tetraamine and dicarboxyl compound are introduced into a first stage melt polymerization reaction zone and heated therein at a temperature above about 200 C., preferably at least 250 C., and more preferably from about 270 to 300 C. The reaction is conducted in a substantially oxygen-free atmosphere, i.e., below about 20 p.p.m. oxygen and preferably below about 8 p.p.m. oxygen, until a foamed prepolymer is formed having an inherent viscosity, expressed as deciliters per gram, of at least 0.1, and preferably from about 0.13 to 0.3, the inherent viscosity (IV.) as used herein being determined from a solution of 0.4 grams of the polymer in ml. of 97 percent H2SO4 at 25 C.

After the conclusion of the first stage reaction, which normally takes at least 0.5 hour and preferably 1 to 3 hours, the foamed prepolymer is cooled and then powdered or pulverized in any convenient manner. The resulting prepolymer powder is then introduced into a second stage polymerization reaction zone wherein it is heated under substantially oxygen-free conditions, as described above, to yield a polybenzimidazole polymer product, desirably having an LV., as measured above, of at least 0.6, e.g., 0.80 to 1.1 or more.

The temperature employed in the second stage is at least 250 C., preferably at least 325 C., and more preferably from about 350 to 425 C. The second stage reaction generally takes at least 0.5 hour, and preferably from about 1 to 4 hours or more.

A particularly preferred method for preparing the polybenzimidazole is disclosed in the aforesaid U.S. Pat. No. 3,509,108. As disclosed therein aromatic polybenzimidazoles may be prepared by initially reacting the monomer in a melt phase polymerization at a temperature above about 200 C. and a pressure above 50 p.s.i. (e.g., 300 to 600 p.s.i.) and then heating the resulting reaction product in a solid state polymerization at a temperature above about 300 C. (e.g., 350 to 500 C.) to yield the final product.

Preparation of the Continuous Length of Pibrous Material The term continuous length of polybenzimidazole fibrous material as used herein includes monofilaments, as Well as multifilament fibrous materials, such as yarn,

' strand, cable, tow, and the like. In a preferred embodiment of the process the continuous length of polybenzimidazole fibrous material is a multifilament yarn or a multifilament tow.

As is known in the art, polybenzimidazoles are generally formed into continuous lengths of fibrous materials by solution spinning, that is, by dry or Wet spinning a solution of the polymer in an appropriate solvent such as N, N-dimethylacetamide, N,Ndimethylformamide, dimethylsulfoxide or sulfuric acid (used only in wet spinning) through an opening of predetermined shape into an evaporative atmosphere for the solvent in which most of the solvent is evaporated (dry) or into a coagulation bath (wet), resulting in the polymer having the desired filamentary shape.

The polymer solutions may be prepared in accordance with known procedures, For example, sufficient polybenzimidazole may be dissolved in the solvent to yield a final solution suitable for extrusion containing from about 10 to 45 percent by weight of the polymer, based on the total weight of the solution, preferably from about 20 to 30 percent by weight.

One suitable means for dissolving the polymer in the solvent is by mixing the materials at a temperature above the atmospheric boiling point of the solvent, for example 25 to 120 C. above such boiling point, and at a pressure of 2 to 15 atmospheres for a period of l to 5 hours.

Preferably, the polymer solutions, after suitable filtration to remove any undissolved portions, are dry spun. For example, the solutions may be extruded through a spinneret into a conventional type downdraft spinning column containing a circulating inert gas such as nitrogen, noble gases, combustion gases or superheated steam. Conveniently, the spinneret face is at a temperature offrom about 100 to 170 C., the top of the column from about 120 to 220 C., the middle of the column from about 140 to 250 C., and the bottom of the column from about 160 to 320 C. After leaving the spinning column, the continuous filamentary materials are taken up, for example, at a speed within the range of about 50 to 350 meters or more per minute. If the continuous filamentary materials are to be washed while wound on bobbins, the resulting asspun materials may be subjected to a slight steam drawing treatment at a draw ratio of from about 1.05 :1 to 1.5 :1 in order to prevent the fibers from relaxing and falling off the bobbin during the subsequent washing step. Further details with respect to a method for dry-spinning a continuous length of a polybenzimidazole fibrous material are shown in U.S. Pat. No. 3,502,576 to Bohrer et al. which is assigned to the same assignee as the present invention and is herein incorporated by reference.

The continuous length of polybenzimidazole fibrous material is next washed so as to remove at least the major portion of residual spinning solvent, e.g., so that the washed materials contain less than about 1 percent by Weight solvent based on the weight of the continuous filamentary material, and preferably so as to obtain an essentially spinning solvent-free fibrous material (i.e., a fibrous material containing less than about 0.1 percent solvent by weight). Typically, a simple water wash is employed; however, if desired, other wash materials such as acetone, methanol, methylethyl ketone and similar solvent-miscible and volatile organic solvents may be used in place of or in combination with the water. The washing operation may be conducted by collecting the polybenzimidazole fibrous material on perforated rolls or bobbins, immersing the rolls in the liquid wash bath and pressure washing the fibrous material, for example, for about 2 to 48 hours or more. Alternatively, the continuous length of polybenzimidazole fibrous material may be washed on a continuous basis by passing the fibrous material in the direction of its length through one or more liquid wash baths (e.g., for 1 to l0 minutes). Any wash technique known to those skilled in the art may be selected.

The continuous length of polybenzimidazole fibrous material may next be dried to remove the liquid wash bath by any convenient technique. For instance, the drying operation for bobbins of yarn may be conducted at a temperature of about 150 to 300 C. for about 2 to 100 hours or more. Alternatively, the continuous length of polybenzimidazole fibrous material may be dried on a continuous basis by passing the fibrous material in the direction of its length through an appropriate drying zone (e.g., an oven provided at 300 to 400 C. for 1 to 2 minutes). If drying is employed, preferably the drying temperature does not exceed about 250 C. for several hours or 400 C. for more than one minute, as above these limits degradation of the 'fiber may occur. The fibrous material may be introduced into the drawing zone (described hereafter) while in a substantially anhydrous form immediately after drying (i.e., may contain less than about 2 percent water based upon the weight of the fibrous material). As is known to those skilled in polybenzimidazole fiber technology, the fibrous material has a propensity to pick up about 10 to 13 percent moisture by weight when exposed to ambient conditions for an appreciable period of time.

It is possible, however, that the continuous length of polybenzimidazole fibrous material which is drawn in the present process be in intimate association with a substantial quantity of water when introduced into the drawing zone (described hereinafter), i.e., the fibrous material may be (l) in intimate association with its equilibrium moisture content of about 10 to 13 percent by weight based upon the weight of the fibrous material, or (2) be soaking wet and contain up to about 100 percent by weight of water based upon the weight of the fibrous material, e.g., often about 15 to about 70 percent by weight of water. When the fibrous material is provided in association with an appreciable quantity of water the drying may be surprisingly conducted simultaneously with drawing in the drawing zone (described hereafter) without foaming or sacrifice of tensile properties within the resulting drawn fibrous material. A time consuming separate drying step may accordingly be completely eliminated.

The polybenzimidazole fibrous material prior to drawing in accordance with the present process preferably possesses a denier per Ifilament of about 1 to 20, and most preferably about 3 to 16 (e.g., 3 to 6 for a multifilament tow and 8 to 16 for a multilament yarn). Multifilament yarns selected for use in the process preferably contain about 10 to 500 filaments, and most preferably about 25 to 200 filaments. A multifilament tow selected for use in the process preferably contains about 1,000 to 300,000 filaments, or more, and most preferably about 50,000 to 150,000 fil-aments. When tows containing an extremely large number of filaments are drawn in accordance with the present invention, it is preferred that the tows be supplied to the drawing zone (described hereafter) While in a flattened ribbon-like configuration.

THE CONTINUOUS HOT DRAWING The continuous length of polybenzimidazole fibrous material is drawn through the application of a longitudinal tension thereto while passing in the direction of its length for a single pass through an elongated drawing zone provided with a flowing heated gaseous atmosphere with heat being supplied to the fibrous material both by radiation and convection.

The heated gaseous atmosphere within the elongated drawing zone is maintained at a temperature of about 400 to 600 C. and, most preferably at a temperature of about 430 to 530 C. If desired, a temperature gradient substantially within the above ranges may be selected. It has been found that the present drawing process is not highly dependent upon the maintenance of a narrowly defined draw temperature for optimum results as is cornmon with hot shoe polybenzimidazole drawing techniques.

The desired temperature within the elongated drawing zone is maintained by radiant heat from the walls of the drawing zone, as well as by the continuous introduction of at least one stream of preheated gas into the elongated drawing zone `which impinges upon the moving continuous length of polybenzimidazole fibrous material. A heat source may be provided in the walls of the drawing zone, or heat may be imparted to the walls of the drawing zone solely by the stream of preheated gas. For instance, in the former embodiment variable resistance heating elements may be provided within the walls of the elongated heating zone, and the stream of gas which is introduced therein preliminarily passed over a similar heating element before entering the same. In order to maintain gas flow within the elongated heating zone at least one stream of gas is continuously withdrawn from the same. For instance, a stream of gas may be introduced at the entrance end of the elongated drawing zone, and a stream of gas allowed to egress from the exit end of the elongated drawing zone. Alternatively, -a stream of gas may be introduced at the exit end of the elongated drawing zone and withdrawn from the entrance end of the same. The preheated gas which is introduced into the elongated drawing zone is preferably at a temperature which approximates that of the desired temperature of the gaseous atmosphere of the drawing zone at the time of its introduction. The radiant heat which is supplied to the fibrous material from the walls of the heating zone serves to aid in the maintenance of the flowing gaseous atmosphere of the heating zone at the desired draw temperature.

The stream of preheated `gas is introduced at a' rate which yields a Reynolds number Within the drawing Zone 7 of 50 to 50,000, and preferably yields a Reynolds number within the drawing zone of 5,000 to 10,000.

The nature of the gaseous atmosphere provided in the elongated drawing zone is not critical to the operation of the present process. A gaseous atmosphere is preferably selected, however, which is substantially unreactive to the fibrous material passing through the same. For instance, air may conveniently serve as the gaseous atmosphere. Inert gaseous atmospheres such as nitrogen, argon, or helium may also be selected, as well as superheated steam, etc.

The draw ratio employed upon a single pass through the elongated drawing zone is about 2:1 to 5:1, and most preferably about 2:1 to 3.5:l.

The term draw ratio, as is well known, is a measure of the degree of stretching during the orientation of the fibrous material expressed as the ratio of the cross-sectional area of the undrawn material to that of the drawn material. While any of the several known ways for measuring or determining draw ratio may be employed, typically the draw ratio is found by taking the ratio of the surface speed of -a takeup roll at the exit end of the drawing zone to the surface speed of a feed or supply roll at the entrance end of the drawing zone.

The minimum hot drawing residence time, i.e., the time during which the fiber is heated while suspended in the elongated drawing zone while under a longitudinal tension, is dependent upon the single filament denier of the fibrous material, the number of filaments in the continuous length of fibrous material, and whether the fibrous material is in a substantially anhydrous form when introduced into the drawing zone. To a limited extent the drawing temperature will also have an effect as higher draw temperatures will enable the draw to be achieved in slightly shorter residence times. Simple experimentation will enable the optimum residence times to be obtained. Typically, however, when filaments of about 1 to 20 denier are present in a yarn of about l0 to 1000 filaments, residence times of about 0.05 to seconds, preferably 0.1 to 2 seconds, and more preferably 0.2 to 0.5 seconds are employed. When processing tows of about 50,000 to 150,000 filaments of l to denier per filament, typically the residence times are about .05 to seconds, preferably 1 to 15 seconds, and more preferably 3 to 10 seconds. The shorter residence times are associated primarily with anhydrous fibrous materials, smaller denier filaments, and with smaller yarns and tows.

The drawing speed utilized in the present process is at least 10 meters per minute. The drawing speed is defined as the rate at which the continuous length of fibrous material is supplied to the elongated drawing zone while under a longitudinal tension. The drawing speed utilized in the present process is preferably about 10 to 30 meters per minute when drawing a tow, and preferably about to 150 meters per minute when processing a multifilament yarn.

The following examples are given as specific illustrations of the invention. It should be understood, however, that the in-vention is not limited to the specific details set forth in the examples.

EXAMPLE I A polybenzimidazole yarn, namely, poly-2,2-(mphen ylene)5,5'bibenzimidazole was selected as the examplary polybenzimidazole for -use in carrying out the process of this invention.

The polymer was formed into an as-spun yarn in the manner described in the Example I of U.S. Pat. No. 3,502,756 to Bohrer et al. More particularly, a dope of N,Ndimethylacetamide containing 23 percent by weight of the polymer was extruded through a 50hole jet into a dry spinning chamber containing nitrogen as the drying atmosphere and was stretched at a draw ratio of 1.06:1 in a steam atmosphere to form a 600/50 yarn (50 75 8 filaments making up a yarn having an overall dry denier of 600). l

The yarn was washed with water for 48 hours by batch pressure washing on a bobbin until the residual solvent content was essentially zero. The yarn was next dried to an essentially zero water content by air oven drying at C. for 72 hours.

The drawing process for the present invention was next carried out employing the apparatus of FIG. 1. More specifically, immediately after drying, the yarn 1 was withdrawn from a bobbin (not shown) and was continuously passed through a tubular elongated drawing zone 2 having a length of four feet while axially suspended therein which was provided with a flowing heated air atmosphere. The elongated drawing zone 2 had a diameter of 0.825 inch. Situated at each end of the elongated drawing zone 2 were pairs of skewed rolls 4 and 6, and 8 and 10 which maintained a longitudinal tension upon the yarn while passing through the same. The drawing zone 2 was bounded by four

draw furnace sections

12, 14, 16 and 18, each of which incorporated a variable resistance heater within its walls. A thermocouple was provided within the elongated drawing zone 2 at the center of each draw furnace section, and was connected to

gauges

20, 22, 24, and 26 from which the temperature of the air atmosphere along the elongated heating zone could be read.

A stream of preheated air was continuously introduced adjacent the entrance end of the drawing zone 2 via inlet 28 at a rate of 700 s.c.f.h. with the aid of blower 29. The air was preheated by means of Variac control 30 connected to resistance heater 32. The stream of preheated air within the drawing zone exhibited a Reynolds number of 9,900. A yarn finish was continuously applied to the drawn yarn 34 by means of transfer roller 36 adjacent the exit end of the elongated drawing zone 2.

The draw parameters utilized are summarized below:

Draw Drawing zone temperatures speed, C.) meters/ Draw Grams Run min. ratio At 20 At 22 At 24 At 2G tension The single filament properties achieved are summarized below:

Tenacity, Denier per grams per Elongation, Run filament denier percent TE 1/2 *TE 1/2=Index of fiber organization wherein T is tenacity at break ln grams per denier and E is elongation of percent extension from original length at break in tensile test. An explanation of this test and its signifilczalceligiven in the Textile Research Journal 36, No. 7, pages 593-602,

EXAMPLE II Example I was repeated with the exceptions indicated. The polybenzimidazole yarn was soaking Wet when supplied to the drawing zone 2 and contained about 60 percent water by Weight based upon the weight of the yarn. The yarn was simultaneously dried and drawn while passing through drawing zone 2.

The draw parameters utilized are summarized below:

Draw Drawing zone temperatures speed, C.) meters] Draw Grams Run rrin. ratio At 20 At 22 At 24 At 26 tension The single ilament properties achieved are summarized below:

Tenaeity, grams per denier Elongation, percent EXAMPLE III Drawing zone temperatures The single ilament properties achieved are summarized below:

Tenacity, grams per denier Denier per Elongaton, lament percent EXAMPLE IV Example III was repeated with the exception that the polybenzimidazole tow consisted of 2000 filaments having a total denier of 6000.

The draw parameters utilized are summarized below:

Run A Draw speed, meters/min. Draw ratio Drawing zone temperatures, C.:

At 20 At 22 At 24 At 26 Grams tension The single filament properties achieved are summerized below:

Run A Denier per filament 1.5 Tenacity, grams per denier 3.9 Elongation percent 18.8 TE 1/2 17.0

EXAMPLE V 10 'Ihe draw parameters utilized are summarized below:

Run A Draw speed, meters/min. 20 Draw ratio 2:1 Drawing zone temperatures, C.:

At 26 540 At extensions 518, 540 Grams tension 500 b iIhe single lament properties achieved are summarized e ow:

Run A Denier per filament 1.63 Tenacity, grams per denier 5.25 Elongation percent 28.1 TE 1/2 27.8

EXAMPLE VI The drawing process of the present invention was carried out employing the apparatus of FIG. 2. The yarn employed was substantially identical to that described in connection with Examples I-V. The yarn 48 had been dried to an essentially zero water content and was withdrawn from a bobbin (not shown) and continuously passed through a tubular drawing zone 50 having a length of 22 inches while axially suspended therein which was provided with a flowing heated air atmosphere. The elongated drawing zone S0 had a diameter of 0.313 inch. Situated at each end of the elongated drawing zone 50 were pairs of skewed

rolls

52 and 54, and 56 and 58 which maintained a longitudinal tension upon the yarn while passing through the same. Roll 52 was provided at a surface temperature of 280 C. by an internal resistance heater. No resistance heaters were provided in the walls of the heating zone 50.

Air was continuously introduced through line 60 and was fed to

flowmeters

62 and 64. The air from owmeter 62 passed over resistance heater 66 which was actuated by controller 68 after receiving a signal from thermocouple 70. The air after passing over resistance heater 66 was passed into drawing zone 50 at 72 at a rate of about 75 s.c.f.h. The air from owmeter 64 passed over resistance heater 74 which was actuated by controller 76 after receiving a signal from thermocouple 78. The air after passing over resistance heater 74 was passed into the drawing zone 50 at 80 at a rate of about 110 s.c.f.h. via an aspirator nozzle directed toward the exit end 82 of the elongated drawing zone 50.

Approximately percent by volume of the air introduced into the drawing zone at 72 and 80 exited at 82, and about 10 percent by volume of the air introduced into the drawing zone at 72 and 80 exited at 84. The stream of preheated air produced in the drawing zone 50 exhibited a Reynolds number of about 5,400. The preheated gas heated the Walls of the drawing zone 50.

' A yarn iinish was continuously applied to the drawn yarn 86 by means of a transfer roll 88 adjacent the exit end of the elongated drawing zone 50.

The draw parameters utilized are summarized below:

The single lament properties achieved are summarized below:

Draw Drawing zone temperatures sneed, C.) inches from exit end meters] Draw Grams Run min. ratio 0 5 10 15 ?0 tension The single filament properties achieved are summarized below:

Tenacity, l Denier per grams per Elongation, Run lament denier percent TE 1/2 For comparative purposes the process of Example VII was repeated with the exception that the air flow was cut oi and stagnant heated air was provided within elongated drawing zone l50. The stagnant air within the drawing zone ranged from 450 to 530 C. and was heated solely by radiation from the hot walls of the drawing zone. The yarn passing through the drawing zone immediately broke when the air ow was terminated.

Although the invention has been .described with preferred embodiments, it is to be understood that variations and modications may be resorted to as will be apparent to those skilled in the art. Such variations and modications are to be considered within the purview and scope of the claims appended hereto. p

We claim: 1. An improved continuous process for the hot drawing of a continuous length of a polybenzimidazole brous material containing up to about 100 percent by weight of water, said drawing occurring without foaming and without employing multiple passes of the -iibrous material through the drawing zone or drawing the fibrous material while in contact with a heated surface, which process comprises:

(a) continuously passing said continuous length of polybenzimidazole fibrous material in the direction of its length, for a single pass, through an elongated drawing zone containing a heated gaseous atmosphere maintained at a temperature of about 400 to 600 C.,

(b) continuously passing a preheated gas into said drawing zone at a rate which yields a Reynolds number within the drawing zone of about 50 to 50,- 000 so as to contact said iibrous material therein,

Cil

(c) drawing said fibrous material in said drawing zone while in contact with said preheated gas at a draw ratio of about 2:1 to 5:1 and at a drawing speed of at least 10 meters per minute, and

(d) thereafter continuously withdrawing from said drawing zone a stream of gas and drawn polybenzimidazole brous material.

2. An improved continuous hot drawing process according to claim 1 wherein said polybenzimidazole fibrous material consists essentially of recurring units of the formula:

/N N\ C/ \R/ N N 1i il wherein R is a tetravalent aromatic nucleus, with the nitrogen atoms forming the benzimidazole rings upon adjacent carbon atoms of said aromatic nucleus, and R' is selected from the group consisting of (1) an aromatic ring, (2) an alkylene group having from 4 to 8 carbon atoms, and (3) a heterocyclic ring selected from the group consisting of (a) pyridine, (b) pyrazine, (c) furan, (d) quinoline, (e) thiophene, and (f) pyran.

3. An improved continuous hot drawing process according to claim 2 wherein said preheated gas is air.

4. An improved continuous hot drawing process according to claim 2 wherein said preheated gas is nitrogen.

S. An improved continuous hot drawing process according to claim 2 wherein said polybenzimidazole fibrous material contains between about 15 and about 70 percent by weight of water.

6. An improved continuous hot drawing process according to claim 5 wherein said drawing zone is maintained at a temperature of about 430 to 530 C.; wherein said continuous length of polybenzimidazole fibrous material is drawn at a draw ratio of about 2:1 to 35:1; and wherein said preheated gas is introduced into said elongated drawing zone at a rate which yields a Reynolds number of about 5,000 to 10,000.

7, An improved continuous hot drawing process according to claim 6 wherein said preheated gas is air.

8. An improved continuous hot drawing process according to claim 7 wherein said polybenzimidazole fibrous material is poly2,2(mphenylene) 5,5'bibenzimidazole.

References Cited UNITED STATES PATENTS 3,584,104 6/1971 Bohrer et al. 264-205 3,564,835 2/1971 Keefe, Jr. et al. 264--290 N 3,622,660 11/1971 Ecker et al. p 264-290 R 3,723,592 3/1973 Bohrer et al. 264-290 R 3,541,199 11/1970 Bohrer et al. 264--290 R 3,657,411 4/1972 Bohrer et al. l 264-290 R ROBERT F. WHITE, Rrimary Examiner I. B. LOWE, Assistant Examiner U.S. Cl. X.R. 264-290 R, Dig. 73'

Claims

1. AN IMPROVED CONTINUOUS PROCESS FOR THE HOT DRAWING OF A CONTINUOUS LENGTH OF A POLYBENZIMIIDAZOLE FIBROUS MATERIAL CONTAINING UP TO ABOUT 100 PERCENT BY WEIGHT OF WATER, SAID DRAWING OCCURING WITHOUT FOAMING AND WITHOUT WEMPOLYING MULTIPLE PASSES OF THE FIBROUS MATERIAL THROUGH THE DRAWING ZONE OF DRAWING THE FIBROUS MATERIAL WHILE IN CONTACT WITH A HEATED SURFACE, WHICH PROCESS COMPRISES: (A) CONTINUOUSLY PASSING SAID CONTINUOUS LENGTH OF POLYBENZIMIDAZOLE FIBROUS MATERIAL IN THE DIRECTION OF ITS LENGTH, FOR A SINGLE PASS, THROUGH AN ELONGATED DRAWING ZONE CONTAINING A HEATED GASEOUS ATMOSPHERE MAINTAINED AT A TEMPERATURE OF ABOUT 400 TO 600*C., (B) CONTINUOUSLY PASSING A PREHEATED GAS INTO SAID DRAWING ZONE AT A RATE WHICH YIELDS A REYNOLD''S NUMBER WITHIN THE DRAWING ZONE OF ABOUT 50 TO 50,000 SO AS TO CONTACT SAID FIBROUS MATERIAL THEREIN, (C) DRAWING SAID FIBROUS MATERIAL IN SAID DRAWING ZONEWHILE IN CONTACT WITH SAID REPHEATED GAS AT A DRAWRATIO OF ABOUT 2:1 TO 5:1 AND AT A DRAWING SPEED OF AT LEAST 10 METERS PER MINUTE, AND (D) THEREAFTER CONTINUOUSLY WITHDRAWING FROM SAID DRAWING ZONE A STREAM OF GAS AND DRAWN POLYBENZIMIDAZOLE FIBROUS MATERIAL.