Process for the manufacture of polyetherketoneketone fiber

Abstract

A process for manufacturing a fiber including polyetherketoneketone including the steps of: mixing polyetherketoneketone and sulfuric acid having a concentration of at least 90 wt % to obtain a spin dope and passing the spin dope through a spinneret into a coagulation bath, wherein the polyetherketoneketone is dissolved in the sulfuric acid to a concentration of 12 to 22 wt %. Also disclosed are fibers obtainable by the process and polyetherketoneketone fibers having a sulfur content of 0.001 to 5 wt %, based on the weight of the fiber, in particular such fibers having low or high crystallinity, as well as, hybrid yarns and composite materials.

Claims

1. A process for manufacturing a polyetherketoneketone fiber comprising the steps of: mixing polyetherketoneketone and sulfuric acid having a concentration of at least 90 wt % to obtain a spin dope and passing the spin dope through a spinneret into a coagulation bath, wherein the polyetherketoneketone is dissolved in the sulfuric acid to a concentration of 12 to 22 wt %, wherein the spin dope comprises a polymer fraction and at least 60 wt % of the polymer fraction is polyetherketoneketone.

2. The process according to claim 1, wherein the polyetherketoneketone comprises repeating units represented by Formula I and Formula II:
-A-C(═O)—B—C(═O)—  I
-A-C(═O)-D-C(═O)—  II, where A is a -Ph-O-Ph- group, where Ph is a phenylene radical, B is 1,4-phenylene and D is 1,3-phenylene and wherein the ratio of repeating units represented by Formula I:Formula II is 100:0 to 0:100.

3. The process according to claim 1, wherein the polyetherketoneketone has a melting temperature T.sub.m which is at least 295° C.

4. The process according to claim 1 further comprising heating the fiber in at least one heating step to a temperature in the range of 150 to 290° C.

5. The process according to claim 4, wherein during heating step, a tension is applied which results in a drawing ratio of 1.5 to 10.

6. The process according to claim 4, wherein the fiber is heated in a second heating step to a temperature in the range of 150 to 290° C.

7. The process according to claim 6, wherein during the second heating step a tension is applied which results in a drawing ratio of the fiber of at most 1.5.

8. The process according to claim 1, wherein the fiber after coagulation is only treated with solutions having a pH of at most 11.

9. The process according to claim 1, wherein the spin dope comprises a polymer fraction and at least 70 wt % of the polymer fraction is polyetherketoneketone.

10. The process according to claim 1, wherein the spin dope comprises a polymer fraction and at least 90 wt % of the polymer fraction is polyetherketoneketone.

Description

(1) The present invention is described in more detail with reference to the figures in the annex, which show:

(2) FIG. 1: XRD patterns of PEKK fibers according to the invention. Left hand: sample 1, center: sample 1-3, right-hand: sample 1-9; and

(3) FIG. 2: Microphotograph of a PEKK fiber obtained using a melt spinning process.

(4) The invention is described more in detail in the following examples, which should not be construed to limit the scope of present invention.

EXAMPLES

(5) PEKK Fiber Prepared Using the Process of the Invention

(6) a)

(7) Fibers were spun from a spin dope comprising a PEKK polymer (Kepstan 8001 sold by Arkema France) having a melt volume index according to ISO 113 at 380° C. under 5 kg of 22 cm.sup.3/10 min, Tg=166° C., Tm=363° C., T/I ratio=80/20.

(8) The PEKK polymer was mixed in a Theysohn 20 mm twin screw extruder at a temperature of 80° C. and a speed of 300 rpm with 99.8 wt % sulfuric acid to a polymer concentration of 20 w/w % to obtain a spin dope.

(9) The spin dope was processed into filaments by passing it at 90° C. through filters and a spinneret, through an air gap and into a coagulation bath (under the conditions indicated in Table 1). The coagulation bath comprised water and had a temperature of 25° C.

(10) TABLE-US-00001 TABLE 1 Settings in spin process Spinning Drawing Spinneret openings (number * speed Air gap ratio in air Sample opening diameter in μm) (m/min) (mm) gap 1 25 * 125 90 10 4.6 2 25 * 125 50 6 3.4 3 25 * 125 50 6 5.1

(11) The filaments obtained after coagulation were washed and neutralized by subsequently passing them through baths of water, 0.2% NaOH and again water. The yarns were wound in the wet state, washed offline and dried under ambient conditions on the bobbin.

(12) The properties of the filaments obtained after drying (also indicated as “as-spun”) were determined.

(13) The mechanical properties were determined according to ASTM D3822-07 “Standard test methods for tensile properties of single textile fibers” (20 mm gage length, 10 specimen) after conditioning the samples at 20° C. and 65% relative humidity for 14 hours in accordance with ASTM D1776 “Practice for conditioning and testing textiles”.

(14) The relative crystallinity of one as-spun yarn and two heat-treated yarns was determined by XRD measurements, carried out using a P4 diffractometer with Histar area detector, using graphite-monochromated CuKα radiation and 0.5 mm collimator.

(15) The sample-detector distance is 7.7 cm (calibrated using corundum). The data were corrected for detector non-uniformity, spatial distortion and air scattering according to standard GADSS procedures.

(16) The sample was mounted in the measuring position of the diffractometer as a bundle of parallel filaments.

(17) Crystallinity determination was carried out using the External Crystallinity method as available in GADDS V 4.1.36 from Bruker.

(18) Parameters used in the crystallinity determination: background region: 2θ-range 11-27°, χ-range 133-227°; crystalline region: 2θ-range 11-28°, χ-range 79-101°.

(19) The filament properties are shown in Table 2.

(20) TABLE-US-00002 TABLE 2 Filament properties of as-spun fiber LD BT crystallinity Sample (dtex/fil.) (mN/tex) EAB (%) TEB (J/g) (%) 1 7.9 97 194 141 19.6 2 9.3 92 220 150 n.d. 3 6.3 93 255 172 n.d. LD: linear density, BT: breaking tenacity, EAB: elongation at break, TEB: tensile energy to break

(21) Fibers of sample 1 were subjected to a one-step heat treatment in N.sub.2 atmosphere in an oven, at different conditions with regard to temperature and drawing ratio, the latter being realized by varying the entry and exit speed of the yarn.

(22) The treatment conditions and the properties of the filaments after heat treatment are shown in Table 3.

(23) TABLE-US-00003 TABLE 3 Properties of as-spun and heat-treated filaments Sam- Temp. LD BT EAB TEB crystallinity ple (° C.) DR (dtex/fil.) (mN/tex) (%) (J/g) (%) 1 (as- — — 7.9 97 194 141 19.6 spun) 1-1 160 2 4.0 243 74 133 n.d. 1-2 160 2.5 3.3 285 34 78 n.d. 1-3 160 3 2.8 365 15 44 66.0 1-4 200 2 4.0 247 53 103 n.d. 1-5 200 2.5 3.3 295 30 70 n.d. 1-6 200 3 2.8 374 10 27 n.d. 1-7 250 2 4.1 256 45 91 n.d. 1-8 250 2.5 3.3 325 19 46 n.d. 1-9 250 3 2.7 391 8 21 74.7 Temp.: temperature used during heating step, DR: tension applied during heating step to result in drawing ratio as indicated, LD: linear density, BT: breaking tenacity, EAB: elongation at break, TEB: tensile energy to break, n.d.: not determined

(24) The left-hand image of FIG. 1 shows the XRD pattern of sample 1, the centre image that of sample 1-3 and the right-hand image that of sample 1-9. As can be concluded from the XRD patterns, with an increase of the temperature of heat treatment, part of the amorphous material crystallizes into a well-developed crystal structure showing 3D crystalline order while at the same time the crystallite size increases.

(25) The method to determine crystallinity as described for the current invention results in a relative crystallinity. The as-spun PEKK yarn (sample 1) would have a much lower crystallinity if the absolute crystallinity was determined. This can be explained by the observation that the amorphous scattering shows orientation, as can be concluded by inspecting the XRD pattern of sample 1 in FIG. 1.

(26) b)

(27) Fibers were spun similarly to samples 1-3 from a spin dope comprising a PEKK polymer (Kepstan 7002 PF sold by Arkema France) having a melt volume index according to ISO 113 at 380° C./1 kg of 5.4 cm.sup.3/10 min., Tg=158° C., Tm=333° C., T/I ratio=70/30.

(28) The PEKK 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 20 wt/wt % to obtain a spin dope.

(29) The spin dope was processed into filaments by passing it at 50° C. through filters and at 65° C. through a spinneret (number and diameter of spinneret openings is indicated below), through an air gap and into a coagulation bath. The coagulation bath contained water.

(30) TABLE-US-00004 TABLE 4 Settings in spin process Spinning Drawing Spinneret openings (number * speed Air gap ratio in air Sample opening diameter in μm) (m/min) (mm) gap 4  25 * 125 50 4 4.96 5 106 * 59 55 4 4.43 6 106 * 59 65 2 3.72

(31) The filament yarn obtained after coagulation was washed with water online. The yarns of samples 4 and 5 were neutralized with 0.25 wt % of NaOH. All samples were washed a second time with water. The yarns were dried online, heat treated at 150° C. for 5 seconds (samples 4 and 5) or 7 seconds (sample 6) and wound on a bobbin.

(32) The mechanical properties of the yarns after drying and heating were determined according to ASTM D3822-07 “Standard test methods for tensile properties of single textile fibers” (20 mm gage length, 10 specimen) after conditioning the samples at 20° C. and 65% relative humidity for 14 hours in accordance with ASTM D1776 “Practice for conditioning and testing textiles”. The sulfur content of the fibers was determined by XRF (as described above).

(33) TABLE-US-00005 TABLE 5 Properties of heat treated yarns LD Sulfur of yarn Filament BT TEB content Sample (dtex) number (mN/tex) EAB (%) (J/g) (%) 4 230 25 112 52 51 0.28 5 240 106 135 135 125 0.17 6 178 106 175 164 88 0.13 LD: linear density, BT: breaking tenacity, EAB: elongation at break, TEB: tensile energy to break

(34) The filaments of all samples have a round shape (determined by microscopy of cross sections of the yarns). Especially the filaments of sample 6 have an even round shape.

(35) Evaluation of the PEKK Fibers

(36) The stability of the PEKK in the melt was evaluated for the PEKK fibers produced as explained above using rheological measurements.

(37) PEKK fibers were obtained according to the process described under b) above, and were then melted and maintained during 30 minutes at 380° C. under nitrogen flush, before measuring their viscosity using a model PHYSICA MCR302-CTD450 rheometer with parallel plate geometry (at 1 Hz using plates with a diameter of 25 mm). In particular, fiber sample 5 (neutralized and washed) was tested and a fiber sample similar to sample 6 (referred to as sample 8; no neutralization, only washing with water). As a reference (sample 7), the viscosity of the PEKK polymer used to produce the fibers was measured in the same manner, after melting the polymer and maintaining it at 380° C. under nitrogen for 30 min.

(38) The variation in viscosity is expressed as a percentage of the melt viscosity of the PEKK used to produce the fibers, submitted to the 30 minutes heat treatment. This protocol allows to evaluate the thermal stability of the fibers in the melt in stringent conditions.

(39) The results are shown in table 6 below.

(40) TABLE-US-00006 TABLE 6 Heat stability of PEKK polymer and fibers in terms of melt viscosity Neutralization Melt and washing viscosity Variation Sample PEKK procedure (Pa .Math. s) (%) 7 Kepstan 7002 — 1270 — (polymer) PF 5 (fiber) Kepstan 7002 Washing with 4540 257 PF water, neutralization with 0.25 wt. % NaOH, washing with water 8 (fiber) Kepstan 7002 Washing 2360 135 PF withwater, no neutralization, washing with water

(41) The results above show that fibers which were not neutralized and only washed with water were substantially more stable in the melt compared to fibers which are neutralized and washed. Accordingly, fibers only washed with water (without neutralization) may be used for applications with harsher requirements in terms of heat stability.

(42) These results show that the composition of the neutralization and/or washing solution is an important factor for obtaining fibers that are sufficiently stable in the melt to be used in applications such as commingling applications for instance.

Comparative Example

(43) PEKK Fiber Obtained Using Melt Spinning

(44) The PEKK polymer used in sample 1 was melt spun at 400° C. using a DSM microcompounder and a DSM fiber conditioning unit.

(45) As apparent from FIG. 2, the fibers obtained by melt spinning have an uneven surface with several defects. Without wishing to be bound by this theory, it is presently assumed that the defects correspond to regions where the polymer has formed a gel following thermal degradation and subsequent crosslinking.

(46) The average fiber diameter of the fibers obtained was 140 μm.