DE2219646C3 - Polyamide fibre and process for its production - Google Patents

Description

characterized in that the

10

Degree

Fibers have a lateral birefringence of at least 0.022.

2. Polyamide fiber according to claim 1, characterized by a thread tensile strength of at least 22 g/den kiJ and a yarn modulus of at least 900 g/den.

3. Polyamide fiber according to claim 2, characterized by an orientation angle of less than 10°.

15

20

25

The invention relates to a polyamide fiber according to the preamble of claim 1.

Such a polyamide fiber, known from example 44 of DE-OS 19 29 694, has after heat treatment a tensile strength of 17.1 g/den, an elongation at break of 2.2% and an initial modulus of 817 g/den and also a high crystallinity and a low orientation angle of 11°. However, it has no measurable lateral birefringence.

In the manufacturing process known from Example 2 of DE-OS 19 29 694, the spinning mass contains 50 g of poly(p-phenylene terephthalamide) in 450 g of solvent and has an inherent viscosity of 3.8. The spinning mass is extruded directly into an aqueous coagulating bath. During the subsequent heat treatment, the fiber is stretched to 1.06 times its original length and the tensile strength increases from 7 g/den to 13.7 g/den. The initial modulus of the threads produced using this process is 888 g/den. The tensile strength and initial modulus of this polyamide fiber is already relatively high, but for certain applications, for example fiber-reinforced composites, polyamide fibers with even higher strength and even higher modulus are required.

The invention is based on the object of achieving a combination of high tensile strength and high initial modulus in a polyamide fiber.

This object is achieved according to the invention by the features specified in the characterizing part of claim 1.

The fibers according to the invention can be produced by spinning a mass consisting essentially of poly(p-phenylene phthalate) and sulfuric acid of at least 98%, chlorosulfonic acid or fluorosulfonic acid or mixtures of these acids as solvent, into a coagulating bath and by subsequent heat treatment of the fibers at a temperature of at least 150 ⁰ C under a tension of at least 0.5 g/den, whereby

the spinning mass contains at least 30 g of poly(p-phenylene terephthalamide) in 100 ml of solvent and has an inherent viscosity such that the polyamide fibre produced has an inherent viscosity of at least 4.0,

the spinning mass is spun into a layer of an inert, non-coagulating fluid before it enters a coagulating bath,

the fibres are subsequently heat treated while maintaining a tension less than that required to stretch the fibres to 1.03 times their original length, and

the heat treatment time is such that the original tensile strength and inherent viscosity of the starting fibres are not reduced by more than 30%.

Preferably, the spinning mass contains at least 40 g of poly(p-phenyleneterephthalamide) in 100 ml of solvent.

The polyamide fiber according to the invention is particularly suitable for reinforcing plastic components, in particular for aircraft coverings, antenna coverings, ceilings and spacecraft parts. Components reinforced with the fiber according to the invention do not warp in high humidity. This property can be demonstrated by a quick test in which the component is exposed to boiling water. The composite components containing the polyamide fiber according to the invention have a high flexural modulus, a high flexural elastic limit and a high impact strength.

Preferred embodiments of the polyamide fiber are specified in claims 2 and 3.

Embodiments of the invention are explained below with reference to the drawing. It shows

Fig. 1 shows a schematic representation of a device for spinning the polyamide barrel and

Fig. 2 shows a schematic representation of a device for heat treatment of the polyamide fiber.

As shown in Fig. 1, a spinning mass is conveyed through a transfer line 1, a spinning block 2, the spinning openings of the spinneret 3 and a gas layer 5 into a circulating coagulation liquid 6 in the spinning tube 10 through which the threads 4 are guided. The strong multi-thread yarn 15 thus formed is guided under the guide member 7 and wound onto a spinning bobbin 9. The coagulation liquid 6 flows from the container 11 through the spinning tube 10 and falls into the container 12, from which it is conveyed back into the container 11 by the pump 13 through the pipe 14.

According to Fig. 2, the yarn 28 produced according to Fig. 1 is guided over a tension guide 20, around a roller 21 controlled by a magnetic brake, over the idle roller 22 and the roller 24 equipped with the dynamometer 23, through a heated tube 27, which contains an insulating box 29. The yarn is pulled out of the tube 27 by the force-driven rollers 25 and is then wound onto the spool 26 under constant tension.

The fibres according to the invention can be produced by spinning a dope containing at least 30, preferably at least 40 g of polyamide per 100 ml of solvent (the volume is determined at 25°C) through a thin layer of gas (or a non-coagulating liquid such as toluene, heptane etc.) into a cold coagulating bath and

the threads are then washed, dried and heat treated. If about 98 to 100 percent sulfuric acid is used as a solvent, this corresponds to spinning dopes that contain at least 14, preferably at least 18 percent polyamide by weight. The spinning dope should contain less than 2% water.

Suitable solvents are essentially sulphuric acid (containing at least 98% H ₂ SO ₄ ), chlorosulphonic acid, fluorosulphonic acid and mixtures of these acids. The solvents may contain certain organic additives.

Additives such as halogenated alkylsulfonic acids, halogenated aromatic sulfonic acids, halogenated acetic acids, halogenated lower aliphatic alcohols and halogenated ketones or aldehydes may be present in amounts up to about 30% of the total weight of solvent and additive, depending on their particular nature. When using fluorosulfonic acid (instead of chlorosulfonic acid or sulfuric acid) or when working with low polyamide concentrations, larger amounts of additive can be added. The higher the percentage of halogen, the larger amounts of additive can be used. Trifluoromethanesulfonic acid can be present in the same amount by weight as sulfuric acid, chlorosulfonic acid or fluorosulfonic acid. Sulfones, chlorinated phenols and nitrobenzene can also be used as solvent additives, but in smaller amounts than in the case of the halogenated additives described above.

Furthermore, the usual additives such as dyes, fillers, matting agents, UV stabilizers, oxidation retarders, etc. can be incorporated into the fibers according to the invention.

In order to obtain fibers according to the invention with unusually high inherent viscosity (hereinafter also referred to as "IV"), precautions must be taken to prevent degradation of the polyamide throughout the process. The polyamide should be dry and neutral. Exposure times to temperatures above about 90 ⁰ C on the spinning dopes should be kept to a minimum and freshly spun fibers should be neutralized and thoroughly washed.

For a given spinning system (spinning dope, jet speed, spinneret, etc.), tensile strength and modulus increase with increasing ratio of the speed of the fiber withdrawn from the coagulating bath to the jet speed (»spinning draw factor«) until the fibers break. The jet speed is the average speed of the spinning dope in the spinning orifice, calculated from the volume of spinning dope passed through the spinning orifice in unit time and the cross-sectional area of the spinning orifice. The breaking elongation of the yarn decreases with increasing spinning draw factor.

The fibres are heated in a zone maintained at at least 150 ⁰ C under a tension of at least 0.5 g/den, but less than the tension required to stretch the fibres (at the temperature used) to more than 1.03 times their original length. In continuous treatment, the amount of stretching is equal to the ratio of the exit velocity from the oven to the entry velocity into the oven. Usually the stretching ratio is less than 1.02. For a given temperature, treatment time and tension are matched so that adjusted to give an apparent crystallite size of greater than 58 A (preferably greater than 70 A) and an orientation angle of not more than 13°. Thus, exposure to a temperature of 150 ⁰ C for 60 seconds under a tension of 10 g/den has proven satisfactory for a 190 den yarn. For a 400 den yarn, excellent results are obtained in a heating zone of 650 ⁰ C with treatment times of 0.6 to 1.0 seconds under a tension of 6 g/den. By extending the treatment time at 650° C to 2.4 seconds under a tension of 6 g/den, a very high modulus of 1340 g/den has been observed, but a 20 percent drop in tensile strength and a 11 percent drop in the inherent viscosity of the fiber compared to the starting fiber. Even heating zone temperatures of 800 ⁰ C or more can be used if the treatment times are short enough. The use of high temperatures and long treatment times leads to excessive degradation of the fibers and thus to a reduction in the initial tensile strength and/or inherent viscosity by 30% or more. For yarns with titres of about 400 denier or less, it is preferable to work with a heating zone temperature between about 250 and 600 ⁰ C (especially from 450 to 580 ⁰ C), treatment times of 0.3 to 5 seconds and tensions of between 1 and 8 g/denier. For yarns with titres of 700 to 1500 denier or more, temperatures 50 to 100 ⁰ C higher than the preferred temperatures given above can be used.

Increasing temperature, voltage and/or treatment time generally leads to the formation of a higher modulus in the heated fibers.

Heating can be carried out in a hot gas oven, in a liquid heating bath or by passing the yarn over hot pins, hot plates or through heating slots. The yarn should preferably be in an inert atmosphere such as nitrogen. It is convenient to heat the yarn in a dry state, but satisfactory results can also be obtained with a wet yarn which has just been washed or with a dried and then re-moistened yarn if the treatment time is extended somewhat. The treatment can be carried out in several stages, e.g. by heat treating the wet yarns in one stage and then heat treating them again in another stage under the same or different conditions. Normally the yarns are untwisted or have a very low twist during the heat treatment and may also be finished.

Suitable starting fibers have an inherent viscosity of at least 4.0, a lateral birefringence of at least 0.02, an orientation angle of less than about 22° (preferably less than about 16°), and an apparent crystallite size of less than about 12 A. Generally, the fibers have a density of at least 1.40 (preferably at least 1.44) g/cm ³ and a thread tensile strength of at least 22 g/den.

All processes known in the field of reinforced plastics can be used to produce composite materials. For example, synthetic resin moldings can be made by wrapping a core with polyamide threads soaked in a hardening resin under

tension and hardening of the resin, it is possible to produce tapes reinforced lengthwise by polyamide threads, or it is possible to process the fibres into textile fabrics in which the fibres or threads run in one or more directions and to impregnate or coat these with resins or resin solutions of suitable viscosity. The impregnated or coated products can be dried until they reach the desired degree of tackiness, or the resin can be B-stage or hardened to obtain pre-impregnated products.

Furthermore, polyamide yarns can be cut into short staple fibers for use as reinforcing agents in compression molding, injection molding, etc., or such short staple fibers can be sprayed onto appropriate molds using the well-known technique of stacked glass-reinforced plastics.

The polyamides intended for use in the invention can be prepared by reacting suitable monomers in the presence of an amide-type solvent at low temperatures as described in U.S. Patent No. 3,063,966. To obtain high molecular weight polyamides, monomers and solvents should contain as few impurities as possible and the water content of the total reaction mixture should be less than 0.03 weight percent.

Poly(p-phenyleneterephthalamide) is conveniently prepared by dissolving 1728 parts of p-phenylenediamine in a mixture of 15,200 parts of hexamethylphosphoramide and 30,400 parts of N-methylpyrrolidone, cooling the solution to 15°C in a polymerization vessel under nitrogen and then adding 3243 parts of powdered terephthalic acid chloride with rapid stirring. In 3 to 4 minutes the solution solidifies and turns into a dry, crumbly mass. If possible, stirring is continued for a further 1.5 hours with cooling in order to maintain the temperature of the product at about 25 ^° C. The polymerization is essentially quantitative and at the end the reaction mixture contains 7.5% of polymer with an inherent viscosity (hereinafter referred to as IV) of about 5.5. The inherent viscosity of the polymer can be controlled by the ratio of monomers to solvent in this production method. If the amount of monomers is reduced from 9.83% to 8.64%, a reaction mixture is obtained that contains 6.5% polyamide with an inherent viscosity of 6.0. If one starts with 11.7% monomers, the final reaction mixture contains 9.0% polymer with an IV of 2.5.

The crumbly acidic product is vigorously stirred in a mixer or colloid mill and ground with water, and the resulting polyamide slurry is filtered. The wet polyamide is then further washed by slurrying in soft water to remove solvents and hydrochloric acid, and filtered off. This slurrying and filtration is repeated four times in succession, followed by a final wash with distilled water. To assist neutralization, a batch of the soft wash water can contain sodium carbonate or caustic soda. The polyamide is then dried at 120 to 140 ⁰ C.

Polycondensation can also be carried out by continuous mixing of the monomers.

Test procedure

The inherent viscosity (I.V.) is determined at a polyamide solution concentration of 0.5 g polyamide or fibers in 100 ml concentrated (95 to 98 percent) sulfuric acid as solvent and at a temperature of 30° C.

Method for determining the apparent crystallite size

The diffraction patterns observed vary with the chemical structure, crystallinity and the degree of order and orientation in the fiber. A measure of apparent crystallite size (ACS) is calculated from values obtained from an X-ray diffraction pattern using a reflection method in which the intensity curve is recorded using an X-ray diffractometer.

To record the diffraction pattern, an X-ray spectroscope, a width angle diffractometer and an electronic control panel are used. About 13 m of yarn is wound on a sample holder so that the yarn axis is perpendicular to the mechanical (2 &thetas;^) axis of the diffractometer. The sample holder has about 21 notches, each 0.254 mm wide, cut around the edge of the holder and a thin lead foil is glued over the bottom of the rectangular opening so that only the fibers on the top are exposed to the X-rays. Using nickel-filtered copper radiation (1.5418 A), a curve of diffracted intensity is recorded from 6° to 38° 2 &thetas; at a scanning rate of 2 &thetas; per minute, a chart speed of 12.7 mm/min, a time constant setting of 2 with 0.5° diffraction and receiving slits using a scintillation detector with a pulse height analyzer, where 2 θ is the angle between the non-diffracted and the diffracted beam The full scale of the recording device is set so that the entire diffraction curve remains on the (linear) scale but with the highest possible sensitivity and preferably so that the maximum intensity is at least 50% of the full scale deflection

The diffraction curves or diffractograms observed for the fibers according to the invention, when the sample is crystalline, consist of a pattern of several peaks, two main peaks of which lie in the range of about 17 to 25° 2θ and, for most samples, in the narrower range of 19 to 24° 2θ. In some cases one of the two peaks appears only as a kink, which ^is sufficient to determine its position. When the sample is not crystalline, a single, very broad peak is the only feature of the diffractogram. In this case, the apparent crystallite size is considered to be zero. To obtain the apparent crystallite size used here as a structural parameter, measurements are carried out on the one of the two main peaks that lies at the smaller 2 Θ value. This procedure is the following (cf. "X-Ray Diffraction Methods in Polymer Science" by Leroy E. Alexander, Wiley-Interscience Publishers (1969), Chapter 7):

First, a baseline is established on the diagram by drawing a straight line between the curve points at 9° and 36° 2 &thetas; Then, drop the plumb line from the center of the peak of the relevant peak onto the baseline and mark a point on this plumb line halfway between the peak of the peak and the

base line. Then draw a horizontal line through this midpoint. This line may intersect a shoulder of the summit or, if the minimum between the two main summits is low enough, both shoulders. The width of the summit in question at this point is obtained either by measuring the distance on the horizontal line from one shoulder to the vertical and doubling this measurement or, if possible, by measuring the distance between the two shoulders along the horizontal line. The distance is expressed as a's summit width (or "line width") in radians and is calculated by using the scale for 2θ (previously plotted on the chart) to convert the observed width in cm to degrees and finally to radians. If B is the observed line width in radians, the corrected line width is β in radians (cf. Alexander, op. cit., p. 443)

&bgr; = &igr;/&Iacgr; ² '-Iacgr;^{> τ} ,

where b is the instrument broadening in radians. The instrument broadening constant b is determined by measuring the line width of the maximum at about 28" 2 &thetas; in the diffractogram of a silicon crystal powder sample supplied by the manufacturer of the X-ray apparatus. The constant b is this line width in radians. The following instrument settings are used: scanning speed 0.1^5" 2 &thetas; per minute, time constant setting 8 and chart speed 1 "/min.

Then the apparent crystallite width corresponding to the selected reflection is given by the equation

ACS-

&Kgr;&lgr;

β cos<9

given in the

K is assigned the value 1,

&lgr; is the X-ray wavelength (in this case

1.5418 A), β is the corrected line width in radians (see above)

and θ is the Bragg angle (half of the 2 &THgr; value of the selected maximum as determined from the diffractogram).

Since the line width in these measurements is influenced not only by the crystallite size, but also by stresses and imperfections in the crystals (which are of unknown size), the measured value for the crystallite size is called "apparent"

It has been found that the values determined using this method are accurate to within ±2 A with a 95 percent probability.

Methods for the application of optical Properties for determining the lateral Birefringence in the fibers according to the invention

Preliminary observations are first made on short pieces of fiber with the transmission interference microscope to get an idea of the range of values Λ|| and n± for the refractive index . The fibers are placed in a series of "Cargille index" or refractive fluids to find the point at which the refractive index of the oil is equal to the refractive index of the fiber (least edge shift), first for Π\\ and then for O _1. The fibers according to the invention are characterized by a relatively uniform value of /in and a value ηχ which decreases somewhat towards the center of the raser.

&iacgr;&ogr; A well-aligned bundle of fibers, approximately 1 mm in diameter and 5 cm long, is then taped to a flat polytetrafluoroethylene plate . A drop of epoxy embedding resin, prepared from 94 cm ³ dodecenylsuccinic anhydride (as hardener), 75 cm ³ "Araldite 6005", 8 cm ³ dibutyl phthalate (as plasticizer), 3 cm ³ N-benzyldimethylamine (as accelerator) (the accelerator is first mixed with the "Araldite" resin, then the hardener and plasticizer are added), is placed in the center of the bundle and the assembled sample is placed in an oven at 60° C for 20 hours . During this time the embedding material flows through the bundle and polymerizes. A small section is cut from the specimen and glued to the end of a conical rod so that when the rod is placed in the clamp of a microtome, oblique sections (approximately 45° to the fiber axis) of approximately 0.2 μm thickness can be made. This cutting is best done with a microtome for ultra-thin sectioning at a cutting speed of 1 mm/sec or less. The fiber bundle should be directed in a plane perpendicular to the knife edge. Furthermore, the bundle should be at an angle of approximately 45° to the

Cutting direction should be inclined.

Sections are fished out of the microtome's water trough using a small piece of microscope cover glass for examination under the optical microscope and transferred to a microscope slide. by floating the sections on a drop of water The water is then removed with a piece of filter paper or by evaporation The slide is cut in half and both parts are placed on the tables of an interference filter microscope The piece with the section is placed in the measuring beam of the microscope and the other piece of the slide is placed in the reference beam The microscope is set to interference contrast Using

so green light (&lgr;&mdash; 0.546 µgr;) one records the distance (D%) by which the wedge compensator must be moved between black background settings and the distance (d) between black background and black sections. The analyzer should be adjusted so that its polarization direction is parallel to the short axis of the fiber sections. Then, using the approximate value of n _L determined according to the method described in the previous paragraph, one can calculate the section thickness (T) from the equation

where n« is the refractive index of the reference fluid, which in this case is air ( fr«= 1.00).
Then the cuts are placed in an oil with a

refractive index close to /J ₁ (~ 1.64), a cover glass is placed on top and the preparation is placed on the universal rotary table of a polarizing microscope. White light is used and the following calculations are based on a wavelength of λ = 0.55 μgr. The polarizer and analyzer are crossed in the 45° position and an elliptical compensator r./it with a maximum range of λ/30 is inserted into the usual compensator slot. The measurements are carried out with the naked eye using a 32x magnifying objective lens and a 6x magnifying eyepiece.

This method is applicable to fibers with essentially circular cross-section.

The universal turntable is set to the zero tilt position and the sections are rotated about their vertical axis so that the long axes of the fiber sections form an angle of 45° with the polarizer and a tilt axis is set parallel to the longer and shorter axes of the sections. With the compensator off, the sections are then tilted about the axis parallel to the minor axis of the sections to the point of lowest average intensity in the sections. The sections are then tilted about the axis parallel to their major axis to the minimum intensity or until a Maltese cross appears. The amount of inclination in each axis is recorded. These angles can be used to calculate the increase in path length caused by tilting J0 (see "Manual of the Polarizing Microscope" by A. F. Hallimond, published by Coolke, Troughton and Simms Ltd, York, England, 1953); however, this is unnecessary when one considers the accuracy required. The second inclination is, however, a valuable measure of the distortion of the section. It has been found that if the inclination about its major axis is more than 20°, the sections should be judged bad and new sections should be made. &iacgr;&ogr;

The compensator is then switched on and the angle corresponding to the greatest amount of compensation required to obtain extinction along the minor axis of the section is observed. The compensator is then set to the angle "5 corresponding to the greatest amount of compensation required to obtain extinction along the major axis of the section. This angle is recorded and subtracted from the first compensator setting. This difference is recorded as 2 φ so, leaving the sign of the difference unchanged. For the purposes of the invention, the lateral birefringence (An) is calculated from the equation

To =

K λ Sin 2 Φ

55

where K is an instrument constant supplied by the manufacturer of the compensators, λ is the wavelength of the applied light (in μ), 2 Φ is the difference in compensator readings defined above, and T is the thickness of the section in μ. Positive lateral birefringence is defined as n _r > n, where n _r is the refractive index for light polarized such that the electric vector is along the radius of the fiber cross-section, while n, is the refractive index for light polarized such that the electric vector is perpendicular to the radius of the fiber cross-section.

Generally, such compensator readings of birefringence are made on 5 or 10 threads, or on as many threads as are required to obtain a representative sample of the fiber bundle, and the lateral birefringence is calculated as the average of these measurements. When viewing each section, no distortions or other anomalies caused by cutting should be apparent which would be noticeable to a person skilled in the art; however, a slight deviation of the inclination of the optical axis from its expected position is acceptable if it can be compensated for by tilting. Sections which exhibit distortions other than those here designated as acceptable should be disregarded. It may also be preferable to make a new section which exhibits no distortions or anomalies. In most cases, compensator readings taken to determine the birefringence of binaural threads are made with the inclination axes set at a constant level. However, it is conceivable that the threads in the fiber bundle may not be parallel to each other before the cuts are made, so that individual threads are cut at different angles. In this case, the procedure for setting the inclination angles (tilt angles) must be repeated for each individual fiber cut before the compensator readings are taken. As described above, any cut where the inclination about its major axis is greater than 20° is disregarded.

The accuracy of the method just described for determining the lateral birefringence Δη is ±0.003, regardless of the value of Δη, with a 90 percent confidence level.

All fibers according to the invention consisting essentially of poly(p-phenylene terephthalic acid amide) which have a substantially round cross-section and a thread titre of less than 10 denier have a Δη value of at least 0.022.

Example

Poly(p-phenylene terephthalic acid amide) having an inherent viscosity of 6.0 is added to 99.7% sulfuric acid at 40 ⁰ C in a water-jacketed industrial planetary mixer through the top inlet over a period of 2 minutes at a rate of 46 g of polyamide per 100 ml of acid. The mixer is closed and placed under a vacuum of 68.5 to 76 cm Hg. The temperature in the water jacket is raised to 85° C and the planetary mixer blades are started at low speed. After 12 minutes the jacket temperature is reduced to 77° C so that the solution assumes a temperature of 79 to 82° C. Mixing is then continued for a further two hours. The solution then has a bulk viscosity of 2300 P.

The spinning mass is transferred to a vessel lined with glass and equipped with a water jacket (at 90 ⁰ C). A vacuum of 69 to 76 cm Hg is applied for 30 minutes to remove all air and bubbles introduced during the transfer. The spinning mass is then removed from the vessel.

through an overhead line tightly wrapped with a water line at 90° C into a spinning block electrically heated to ⁸⁰ 0 C with a connected gear pump. The gear pump conveys the spinning dope at a metered rate through another line in the block to a spinneret pack provided with a water jacket at 80° C, which has a screen base, stainless steel felt and a spinneret of 12.7 mm diameter, which is equipped with 100 spinning openings each with a diameter of 0.051 mm. The spinning dope is spun from the spinneret at a nozzle speed of 63 m/min vertically downwards through a 5 mm thick layer of air into water at 1"C, which is located in a spinning tube as shown in Fig. 1. Samples a and c are prepared with a freely rotating roller under the spinning tube which deflects the running thread to the winding point, while sample d is spun using a ceramic rod. The yarn is wound onto a spinning bobbin at varying speeds while spraying with water at 50° C. The yarn bobbins are stored in a water tank. The bobbins are then immersed in 0.1 normal sodium bicarbonate solution and then further extracted with water at 70° C in an advancing reel extraction apparatus as described in U.S. Patent No. 2,659,225. The extracted yarn is wound up and dried on bobbins at 70° C. The properties of the dried yarn, which has an inherent viscosity of 5.2, are given in the table below for samples a, c and d prepared with spinning draw factors of 1.5, 3.4 and 4.4 respectively.

Sample e is dried under a tension of 5 g/den at 150° C. Yarn sample f is made from a polyamide with an inherent viscosity of 6.6

The inherent viscosity ranges from 4.9 (sample b) to 53 (samples f and f-1).

The well washed and dried yarns from 135 to 415 den (100 threads) are passed under different conditions through a 3.05 m long stainless steel tube with an internal diameter of 1.5 cm, which is filled with nitrogen. The conditions are shown in the table below under "Heating conditions".

where »°C« is the temperature of the tube wall in the middle of the tube, »t« is the treatment time in seconds and »span« is the tension in g/den The tube is electrically heated and housed in a vermiculite box for insulation purposes. The nitrogen flows through a tube in the box before being fed to the yarn treatment tube. The yarns are only stretched to 1.001 to 1.021 times their original length and do not come into contact with the tube walls.

Similar results are obtained by treating yarns wet from water in the same way

It is observed that the temperature for a yarn of 400 denier should be about 100° C higher than for a yarn of 200 denier, if in both cases a treatment time of 1 second is used

Composites made of epoxy resin and unidirectional fibres with a fibre content of 60 Volume percent for the fiber samples b-1, e-J b*w. M show excellent values for the flexural modulus (ASTM D790-66, Method A with some modifications), the flexural elastic limit at a bending strain of 0.02% (ASTM D790-66 (11.5) and Appendix to ASTM D638-68), tensile strength, tensile modulus and load-to-break life [time to failure under a static tensile load in the axial direction expressed as a percentage (usually 95 to 98%) of the mean absolute tensile strength of the specimen in question].

The thin (approximately 0.25 mm thick) composite samples used to determine the tensile properties show little warping after 12 hours of exposure to boiling water.

The thread properties of samples e-1, f and f-1 are determined at four breaks; the thread properties of samples b and b-1 are determined at seven and five breaks respectively

By heating a yarn similar to sample c for a period of 3 seconds at 400° C under a tension of 0.7 g/den, a fiber having a yarn tensile strength of 20.8 g/den, a yarn elongation at break of 2.2%, an initial yarn modulus of 908 g/den, an orientation angle of 12.6°, an apparent crystallite size of 91 A, a ratio of apparent crystallite size to orientation angle of 7.2 and a density of 1.45 g/cm ³ is obtained.

sample Heating conditions A.C.S.») A.C.S. O.A.*),° density °C-f-Span O.A.·) Ä 20.0
9.7 g/ ^cm3 a
a-1 without heating
250-6-6 2.2
6.2 45
60 15.6
9.4 1.45
1.45 b-1 without heating
350-1.5-4 2.6
7.4 41
70 13.9
9.5 1.45
1.46 C
c-1 without heating
250-6-4 3.5
6.2 49
59 11.5
9.7
9.8 1.45
1.46 d
d-1
d-2 without heating
250-3-6
550-6-2 4.3
6.4
12 49
62
118 1.45
1.46
1.47

continuation

14

sample

Heating conditions C-i-Span

A.C.S.-) O.A.')

A.C.S Ä

Density g/cm"

e dried at 150C

e-1 400-3-l·

f without heating

f-1 350-1.5-6.5

*) A.C.S. = Apparent crystallite size.

O.A. = Orientation angle!

41 80

50 84

13.5 8.8

11.2 7.9

1.45 1.45

1.45 1.45

Continuation -ler table

sample Cam properties &eegr; E*) Wed*) = Tensile strength in g/den.
= Elongation at break in %.
= Initial module in g/den.
= Toughness in g/den.
= Thread titer, den. Tou') DPF*) the ,9
,8th Thread properties E Wed Tou Ten*) 3.9
2.3 547
917 0.39
0.24 ,4
,4
,3 Ten 5.6
3.8 570
770 0.73
0.50 a
a-1 21.2
21.4 3.3
2.2 649
1019 0.34
0.24 415 3.7
394 3.9 ,8th
,8th 26
24 4.4
3.3 570
890 0.54
0.45 b
b-1 22.0
22.3 3.2
2.2 727
1080 0.35
0.27 196 2.0
179 1.8 ,9
1.8 25
26 4.8
3.7 680
890 0.67
0.58 C
c-1 22.8
23.1 2.8
2.0
1.3 948
1175
1394 0.34
0.23
0.11 190 1
178 ] 27
_29 4.3
3.5
2.1 680
830
1030 0.62
0.50
0.24 d
d-1
d-2 24.8
22.5
16.8 2.9
1.9 862
1080 0.35
0.19 135
136
136 27
28
22 2.7 890 0.31 e
e-1 23.6
20.5 3.2
2.1 779
1130 0.39
0.25 184
179 22 4.8
3.7 710
920 0.76
0.62 r
f-1 25.1
23.9 191
177 31
32 *) Ten
E
Wed
Tou
DPF

The fibers in the table above have the following values for lateral birefringence (Aj.

sample

a
a-1 0.045
0.035 b
b-1 0.025
0.054 C
c-1 0.035
0.042

sample -*» d 0.044 d-1 0.045 d-2 0.048 e *) e-1 0.045 e 0.031 f-1 0.053 ) Due to the manufacturing process, the properties of this Sample and the corresponding value of the sample e-1 kanr the value ±&rdquor; for this sample with at least 0.02 be taken.

1 sheet of drawings

Claims (1)

Patent claims: L Polyamide fibre of high tensile strength and high modulus with a density of at least 1.40 g/cm ³ , consisting essentially of poly(p-phenylene terephthalamide) with an inherent viscosity of at least 4.0, crystalline regions with an apparent crystallite size of more than 58 Å, an orientation angle of not more than 13° and a ratio of the apparent crystallite size to the orientation angle of at least