PROCESS FOR THE MANUFACTURE OF A FIBER COMPRISING META-ARAMID

Abstract

A process for manufacturing a fiber including meta-aramid having a breaking tenacity of at least 300 mN/tex including the steps of preparing a spin dope including meta-aramid and sulfuric acid having a concentration of at least 80 wt % and passing the spin dope through a spinneret into a coagulation bath, wherein the spin dope has a meta-aramid concentration of at least 10 wt %. The invention also pertains to a meta-aramid fiber, a multifilament yarn, a textile sheet and protective clothing.

Claims

1. A process for manufacturing a fiber comprising meta-aramid having a breaking tenacity of at least 300 mN/tex comprising the steps of preparing a spin dope comprising meta-aramid and sulfuric acid having a concentration of at least 80 wt % and passing the spin dope through a spinneret into a coagulation bath, wherein the spin dope has a meta-aramid concentration of at least 10 wt %.

2. The process according to claim 1, wherein the fiber comprising meta-aramid has a breaking tenacity of at least 350 mN/tex.

3. The process according to claim 1, wherein the spin dope has a meta-aramid concentration in the range of 10-30 wt %.

4. The process according to claim 1, wherein the meta-aramid is co-poly(m-phenylene isophthalamide) comprising at most 5 molar % of aromatic moieties other than m-phenylene.

5. The process according to claim 1, wherein the spin dope is prepared by mixing meta-aramid and sulfuric acid.

6. The process according to claim 1, wherein the spin dope is prepared at a temperature in the range of 30 to 90° C.

7. The process according to claim 1, wherein the spin dope is passed through a gaseous medium after exiting the spinneret and before entering the coagulation bath.

8. The process according to claim 7, wherein the spin dope passes through a gaseous medium of a length in the range of 2 to 20 mm.

9. The process according to claim 1, wherein the sulfuric acid has a concentration of at least 85 wt %.

10. The process according to claim 1, wherein the fibers are heated in at least one heating step to a temperature in the range of 250 to 400° C., optionally followed by a further heating step at a temperature in the range of 250 to 400° C.

11. A meta-aramid fiber having a breaking tenacity of at least 300 mN/tex, obtainable by the process according to claim 1.

12. The meta-aramid fiber having breaking tenacity of at least 300 mN/tex and a sulfonic acid group content of at least 0.001 wt %.

13. The meta-aramid fiber according to claim 11, having a breaking tenacity of at least 350 mN/tex.

14. The meta-aramid fiber according to claim 11 having an organic solvent content below 250 ppm.

15. The meta-aramid multifilament yarn comprising the meta-aramid fiber of claim 11.

16. The meta-aramid multifilament yarn according to claim 15 wherein at least 50% of individual filaments have a round cross section such that the average ratio of [diameter of the minimum circumscribed circle] to [diameter of the maximum inscribed circle] is at most 1.3.

17. A textile sheet comprising the meta-aramid fiber of claim 11 and/or the meta-aramid multifilament yarn.

18. A protective clothing comprising the textile sheet of claim 17.

Description

EXAMPLES

[0084] Methods

[0085] 1. Mechanical Properties

[0086] The breaking tenacity, elongation at break and toughness at rupture of the meta-aramid multifilament yarns are determined according to ASTM D 7269-17.

[0087] 2. Sulfonic Acid Group Content

[0088] The sulfonic acid group content is determined by .sup.1H-NMR. 20 mg of as-spun non-heat-treated sample are dissolved in 1 mL DMSO-d6 and 550 μL thereof is transferred to a 5 mm NMR sample tube. .sup.1H NMR spectra are recorded at 300 K on a Bruker Avance III 400 MHz NMR spectrometer equipped with a BBFO-plus 5 mm broadband probe. Spectra are recorded by co-adding 64 scans with a 30° excitation pulse using a pre-scan delay of 6 s and an acquisition time of 4 s. The 1H NMR spectra obtained were referenced by setting the DMSO-d6 residual solvent signal to 2.5 ppm.

[0089] The sulfonic acid group content is calculated by the formula below and expressed in meq/kg (mmol/kg):

A.sub.sMPD=integral (singlet @ 8.97 ppm) [mol]

A.sub.meta aramid=(integral 8.86−7.08 ppm−(6*AsMPD))/8 [mol]

sMPD=(A.sub.sMPD*186.1844) [mg]

meta aramid=(A.sub.meta aramid*238.2414) [mg]

S=(sMPD/(sMPD+meta aramid))*(32.065/186.1844)*100%

Sulfonic acid group content=106*(S/100)/32.065 [meq/kg]

[0090] 3. Sulfur Content

[0091] The sulfur content may be determined by inductively coupled plasma optical emission spectrometry (ICP-OES). To 100 mg of fiber, 9 ml of concentrated nitric acid (70 wt %) is added. This mixture is exposed to microwave digestion in an Ultrawave (Milestone) until a clear liquid is obtained. The volume is adjusted to 25 ml by addition of MilliQ water. Precipitates are removed from this solution by filtration. The clear filtrate is analyzed by ICP-OES in a Perkin Elmer Optima 8300 DV apparatus. For the determination of the sulfur content emission lines at 181,972 nm and 180,669 nm wavelength are used.

[0092] 4. Organic Solvent Content

[0093] The organic solvent content is determined by gas chromatography. About 1.0 mg of fibers was collected and heated over 500° C. in an electric furnace. Gas chromatography (Shimadzu Corporation, Ltd., Model: GC-2010) was used to measure the amide solvent amount vaporized from the fiber. Subsequently, residual solvent concentration in the fiber was calculated by using the calibration curve prepared by using an amide-based solvent as a standard sample.

[0094] 5. Relative Viscosity

[0095] A polymer sample is dried at 50° C. in a vacuum oven for two hours for removal of water. The dried sample is then dissolved in sulfuric acid at room temperature overnight. The flow time of the 0.25%(w/V) sample solution in 96%(w/w) sulfuric acid was then measured at 25° C. in an Ubbelohde viscometer (e.g. Schott AVS370). Under identical conditions the flow time of the solvent was measured as well. The relative viscosity was then calculated as the ratio between the two observed flow times.

[0096] 6. Microscopy

[0097] The yarn is embedded in melted paraffin, which is left for about five minutes and solidified. Thereafter, the embedded sample is cut, vertical to the fiber axis, by a microtome to obtain a cut piece of 5 to 7 μm thick. Then, the cut piece is placed on a slide glass which is heated to melt the paraffin. Thereafter, the melt paraffin was removed by xylene and ethanol. Next, a cross-section of the fiber is observed and photographed by using an optical microscope (manufactured by NIKON CORPORATION; trade name “ECLIPSE” LV100N) to obtain a cross-sectional photograph. The magnification is selected within a range from 100 to 1000 as necessary.

[0098] 7. LOI

[0099] The limiting oxygen index (LOI) iss determined in accordance with ASTM D2863. A yarn specimen of 168000 dtex is prepared from each sample by combining the required number of yarns. The yarns are wound on a precision reel, with a yarn tension during winding of 5±3 mN/tex based on the nominal linear density of the yarn. This specimen is encircled with thin copper wire. Each specimen has a length of approximately 150 mm, a width of approximately 10±0.5 mm and a thickness of approximately 3±0.25 mm. The specimen is marked at approx. 50 mm from the end which is to be ignited. Immediately before testing, the specimen is conditioned for at least 88 hours at 23±2° C. and 50±5% relative humidity. The specimen were tested according to option A of ASTM D2863 (top surface ignition).

Example 1

[0100] Fibers were spun from a spin dope comprising a m-aramid polymer (poly(m-phenyl isophthalamide) having a relative viscosity of 1.55.

[0101] The m-aramid polymer was mixed in a Theysohn 20 mm twin screw extruder at a temperature of 85° C. and a speed of 300 rpm with 99.8 wt % sulfuric acid to a polymer concentration of 18 w/w % to obtain a spin dope.

[0102] The spin dope was processed into filaments by passing it at 55° C. through filters and at 85° C. through a spinneret, through an air gap and into a static coagulation bath (under the conditions indicated in Table 1). The coagulation bath had a temperature of 3° C.

TABLE-US-00001 TABLE 1 Settings in spinning process Spinneret openings Winding (number/diameter speed Air gap Drawing ratio Sample in μm) (m/min) (mm) in air gap 1-1 50/80 60 5 3.6 1-2 50/80 60 5 3.6

[0103] The multifilament yarns obtained after coagulation were washed and neutralized by subsequently passing them through baths of water, 0.4% NaOH and again water. The yarns were dried at 150° C. and wound on the bobbin.

[0104] The properties of the yarns obtained after drying (also indicated as “as-spun”) were determined.

TABLE-US-00002 TABLE 2 Mechanical properties of the as-spun yarns Linear Breaking Elongation Toughness density tenacity at break at rupture Sample (dtex) (mN/tex) (%) (J/g) 1-1 232 195 56.3 81 1-2 237 197 56.9 83

[0105] For sample 1-1 the sulfonic acid group content was determined to be 116 meq/kg. Sample 1-1 was heat treated in a two-step process. Yarns were reeled off from the bobbin and lead through a first oven in which a draw ratio of 1.6 was applied, and through a second oven that was kept at a temperature of 333° C. and in which the draw ratio was kept at 1, the draw ratio being defined as the speed after the oven divided by the speed before the oven. The residence time in both ovens (based on the speed between the ovens) was 18.8 s.

TABLE-US-00003 TABLE 3 Mechanical properties of heat treated yarns Temperature Linear Breaking Elongation Toughness oven 1 density tenacity at break at rupture Sample (° C.) (dtex) (mN/tex) (%) (J/g) 1-1-1 305 140 325 49.0 91.8 1-1-2 315 141 304 44.1 83.4 1-1-3 325 142 317 39.5 79.0 1-1-4 335 146 273 26.9 56.1 1-1-5 345 145 276 27.8 59.7

Example 2

[0106] Fibers were spun from a spin dope comprising a m-aramid polymer having a relative viscosity of 1.55. The m-aramid polymer was mixed in a Theysohn 20 mm twin screw extruder at a temperature of 55° C. (2-1 and 2-3) or 60° C. (2-2 and 2-4) and a speed of 450 rpm with 99.8 wt % sulfuric acid to a polymer concentration of 16 wt/wt % or 17.5 wt/wt % to obtain a spin dope.

[0107] The spin dope was processed into filaments by passing it through filters and through a spinneret, through a 5 mm air gap, in which a draw ratio of 3.41 was applied, and into a static coagulation bath (under the conditions indicated in Table 4). The coagulation bath had a temperature of 5° C.

TABLE-US-00004 TABLE 4 Spinning settings example 2 Spinneret openings Polymer (number/ Draw Winding Temperature concentration diameter ratio in speed of spinneret Sample (wt/wt %) in μm) air gap (m/min) (° C.) 2-1 16 106/75 3.41 60 65 2-2 16 106/75 3.41 60 70 2-3 16 106/75 3.41 60 110 2-4 17.5 106/75 3.67 40 90

[0108] The multifilament yarns obtained after coagulation were washed and neutralized by subsequently passing them through baths of water, 0.25% NaOH and again water. The yarns were dried at 150° C. and wound on the bobbin.

[0109] The properties of the yarns obtained after drying (also indicated as “as-spun”) were determined.

TABLE-US-00005 TABLE 5 Mechanical properties of the as-spun yarns Linear Breaking Elongation Toughness density tenacity at break at rupture Sample (dtex) (mN/tex) (%) (J/g) 2-1 360 235 23 40 2-2 360 244 24 44 2-3 380 211 47 73 2-4 413 200 73 103

TABLE-US-00006 TABLE 6 Relative viscosity and sulfonic acid group content of the fiber Sulfonic acid group content Sample Relative viscosity (meq/kg) 2-1 1.52 17.6 2-2 1.52 23.5 2-3 1.48 55.6

[0110] Sample 2-3 was heat treated in a two-step process. Yarns were reeled off from the bobbin and lead through a first oven in which at a temperature of 305° C. various draw ratios were applied, and through a second oven that was kept at a temperature of 333° C. and in which the draw ratio was kept at 1, the draw ratio being defined as the speed after the oven divided by the speed before the oven. The residence time in both ovens was calculated based on the speed between both ovens. The sulfur content of sample 2-3 was determined to be 0.18 wt %.

TABLE-US-00007 TABLE 7 Heat treatment and mechanical properties of meta- aramid yarns treated in a two-step heating process Draw Residence Linear Breaking Elongation Toughness Sam- ratio in time ovens density tenacity at break at rupture ple oven 1 (s) (dtex) (mN/tex) (%) (J/g) 2-3-1 1.6 18.8 234 312 49.6 108.1 2-3-2 1.8 16.7 209 332 40.8 96.3 2-3-3 2.0 15.0 190 334 32.3 80.6 2-3-4 2.2 13.7 174 345 24.8 65.8 2-4-1 1.6 6.5 254 327 30.0 76.0

Example 3

[0111] Fibers were spun from a spin dope comprising a m-aramid polymer having a relative viscosity of 1.58.

[0112] The m-aramid polymer was mixed in a Clextral 53 mm twin screw extruder at a temperature of 45° C. and a speed of 250 rpm with 99.8 wt % sulfuric acid to a polymer concentration of 12 wt/wt % to obtain a spin dope.

[0113] The spin dope was processed into filaments by passing it at 50° C. through filters and at 50° C. through a spinneret containing 1000 capillaries of 65 μm diameter, through an air gap, in which the filaments were drawn by a factor of 2.9, and into a falling jet coagulation bath (under the conditions indicated in Table 1). The coagulation bath had a temperature of 5° C.

[0114] The multifilament yarns obtained after coagulation were washed and neutralized by subsequently passing them through baths of water, 0.35% NaOH and again water. The yarns were dried on a godet at 160° C. Optionally the yarns were hot drawn on heated godets and wound on the bobbin.

TABLE-US-00008 TABLE 8 Settings in spinning process Hot drawing 1: Hot drawing 2: Drying speed (m/min)/ speed (m/min)/ godet temperature (° C.)/ temperature (° C.)/ speed Air gap residence time residence time Sample (m/min) (mm) (s) (s) 3-1 100 13 — — 3-2 100 11 — — 3-3 100 9 — — 3-4 100 13 160/270/0.66 160/285/0.66 3-5 100 11 160/270/0.66 160/285/0.66 3-6 100 9 100/270/0.26 160/305/1.32 3-7 100 13 155/180/0.17 155/285/1.35

[0115] The properties of the yarns obtained were determined and are shown in table 9.

TABLE-US-00009 TABLE 9 Mechanical properties yarns Linear Breaking Elongation Toughness density tenacity at break at rupture Sample (dtex) (mN/tex) (%) (J/g) 3-1 2625 155 65.0 79.6 3-2 2598 167 51.4 71.4 3-3 2598 173 49.8 68.7 3-4 1593 276 26.9 56.2 3-5 1586 294 26.3 57.3 3-6 1597 273 27.4 59.6 3-7 1650 282 23.7 53.9

Example 4

[0116] Fibers were spun from a spin dope comprising a meta-aramid polymer having a relative viscosity of 1.55. The m-aramid polymer was mixed in a Theysohn 20 mm twin screw extruder at a temperature of 60° C. and a speed of 450 rpm with 99.8 wt % sulfuric acid to a polymer concentration of 16 wt/wt % to obtain a spin dope. The spin dope was processed into filaments by passing it through filters and through a spinneret, through a 5 mm air gap, in which a draw ratio of 2.08 was applied, and into a dynamic coagulation bath (under the conditions indicated in Table 10). The coagulation bath had a temperature of 5° C. After the coagulation bath the yarns were wet drawn between 2 roller sets.

TABLE-US-00010 TABLE 10 Settings in spinning process Spinneret openings Tempera- Speed Wet (number/ ture of Air Drawing after co- drawing diameter spinneret gap ratio in agulation ratio Sample in μm) (° C.) (mm) air gap (m/min) (—) 4-1 106/65 110 5 2.08 40 1 4-2 106/65 110 5 2.08 40 1.2 4-3 106/65 110 5 2.08 40 1.3 4-4 106/65 110 5 2.08 40 1.4 4-5 106/65 105 5 40 1.2 4-6 106/65 105 5 40 1.2

[0117] The multifilament yarns obtained after coagulation and wet drawing were washed and neutralized by subsequently passing them through baths of water, 0.25% NaOH and again water. The yarns were dried at 150° C. and wound on the bobbin.

[0118] The properties of the yarns obtained after drying (also indicated as “as-spun”) were determined.

TABLE-US-00011 TABLE 11 Mechanical properties of the as-spun yarns Linear Breaking Elongation Toughness density tenacity at break at rupture Sample (dtex) (mN/tex) (%) (J/g) 4-1 480 157 105 122 4-2 430 176 98 124 4-3 390 196 84 120 4-4 363 202 67 100

[0119] Sample 4-2 was heat treated in a two-step process. Yarns were reeled off from the bobbin and lead through a first oven in which at a temperature of 315° C. a draw ratio of 1 was applied, and through a second oven that was kept at a temperature of 315° C. and in which the draw ratio was varied, the draw ratio being defined as the speed after the oven divided by the speed before the oven.

TABLE-US-00012 TABLE 12 Heat treatment and mechanical properties of meta- aramid yarns treated in a two step heating process Linear Breaking Elongation Toughness Draw ratio density tenacity at break at rupture Sample in oven 2 (dtex) (mN/tex) (%) (J/g) 4-2-1 2.06 189 353 30 80 4-2-2 2.2 168 395 26 78 4-2-3 2.3 158 409 22 66 4-5-1 2.08 201 343 28 71 4-6-1 2.08 199 310 31 72

Example 5

[0120] Fibers were spun from a spin dope comprising a meta-aramid polymer having a relative viscosity of 1.55. The m-aramid polymer was mixed in a Theysohn 20 mm twin screw extruder at a temperature of 50° C. and a speed of 300 rpm with 99.8 wt % sulfuric acid to a polymer concentration of 16 wt/wt % to obtain a spin dope. The spin dope was processed into filaments by passing it through filters and through a spinneret containing 106 capillaries with a diameter of 65 μm, maintained at temperature of around 75° C., through a 10 mm air gap, in which a draw ratio of 1.95 was applied, and into a dynamic coagulation bath. The speed after the coagulation bath was 40 m/min. After the coagulation bath the yarns were wet drawn 1.4 times between 2 roller sets. The yarns obtained after coagulation and wet drawing were washed and neutralized by subsequently passing them through baths of water, 0.25% NaOH and again water. The yarns were dried on a roller set at 220° C. The yarns moved to 2 successive roller sets, of which the settings are indicated in table 13.

TABLE-US-00013 TABLE 13 Settings in spinning and hot drawing process Coagulation First roller Second roller bath Drying set temperature set temperature temperature temperature (° C.)/drawing (° C.)/drawing Sample (° C.) (° C.) ratio (—) ratio (—) 5-1 2 220 295/1.7 295/1.3  5-2 3 220 290/1.6 290/1.35

[0121] The yarns were wound on a bobbin. The mechanical properties of the yarn are shown in table 14.

TABLE-US-00014 TABLE 14 Mechanical properties of the yarns Linear Breaking Elongation density tenacity at break Sample (dtex) (mN/tex) (%) 5-1 199 488 18.6 5-2 197 501 15.6

Example 6

Organic Solvent Content

[0122] The NMP and DMAc content of commercially available TeijinConex® B, Nomex® and Yantai Tayho Advanced Materials' meta-aramid yarn was determined by gas chromatography. The results are shown in table 13. Yarn according to the invention does not comprise organic solvent.

TABLE-US-00015 TABLE 15 organic solvent content NMP DMAc Sample Sample type (wt %/wt) (wt %/wt) Comparative 1 Multifilament yarn n.d. 1.2  (Nomex ®) Comparative 2 Staple fiber 1.9 n.d. (TeijinConex ® B) Comparative 3 Staple fiber n.d. 0.28 (Yantai) n.d. = not determined

Example 7

Cross Section of Filaments

[0123] Micrographs of embedded bundles of comparative samples 1 to 3 (as used in example 6) and a meta-aramid yarn according to the invention were prepared. The micrographs depicting the cross section of the filaments are shown in FIG. 1. Panel a) shows a cross section of filaments of comparative sample 1, panel b) of comparative sample 2, panel c) of comparative sample 3 and panel d) of the meta-aramid yarn according to the invention.

[0124] As can be seen from the comparison, the filaments of the current invention have an even, round cross section, while the comparative filaments have an oblong cross section or a cross sections of varying diameter.

Example 8

Limiting Oxygen Index

[0125] The LOI of meta-aramid yarns according to the invention and commercially available meta-aramid yarn was determined. The results are shown in table 14.

TABLE-US-00016 TABLE 16 LOI of meta-aramid yarns according to the invention and commercially available meta-aramid yarns. Sample LOI (% O.sub.2) 2-1 35 2-3 38 Comparative 2 (TeijinConex ® B) 32 4-5-1 33 4-6-1 35

[0126] The data show that the samples according to the invention have a higher LOI value than the comparative sample according to the prior art.