CONTINUOUS PROCESS FOR RECYCLING

Abstract

A continuous process for the recycling of aramid fiber comprising the following steps: combining aramid fibrous material including non-continuous aramid fibers with sulfuric acid to obtain a spin dope comprising aramid, and processing the spin dope including aramid into a continuous aramid fiber. The invention also pertains to a continuous aramid fiber, preferably obtainable by said process, and to a multifilament yarn including the continuous aramid fiber.

Claims

1. A continuous process for the recycling of aramid fiber comprising the following steps: combining aramid fibrous material comprising non-continuous aramid fibers with sulfuric acid to obtain a spin dope comprising aramid, and processing the spin dope comprising aramid into a continuous aramid fiber.

2. The process of claim 1 wherein the spin dope comprising aramid comprises aramid other than the aramid derived from the non-continuous aramid fibers.

3. The process of claim 1 wherein the aramid fibrous material comprises virgin aramid polymer.

4. The process according to any one of the preceding claim 1, wherein the non-continuous aramid fiber comprises as least one of aramid short-cut, aramid pulp, aramid fibril and aramid fibrid.

5. The process of claim 4, wherein the aramid short-cut has a length in the range of 0.1 to 20 mm.

6. The process according to claim 1 wherein the sulfuric acid is liquid or solid.

7. The process according to claim 1 wherein the aramid fibrous material or part thereof is subjected to movement to agglomerate the aramid fibrous material before combining the agglomerated aramid fibrous material with sulfuric acid.

8. The process according to claim 7 wherein the movement is selected from stirring, shifting, tumbling, shaking, vibrating, falling, turning, cyclone mixing and vortex mixing or any combination thereof.

9. The process according to claim 1, wherein aramid is para-aramid.

10. The process according to claim 1 wherein the non-continuous aramid fiber provides 1 to 99 wt % of the total amount of aramid in the spin dope comprising aramid.

11. The process according to claim 2 wherein the aramid fibrous material is a solid pre-mix of non-continuous aramid fiber and virgin aramid polymer.

12. The process according to claim 2 wherein aramid fibrous material, sulfuric acid and virgin aramid polymer are combined with sulfuric acid to obtain a spin dope.

13. The process according to claim 2 comprising the steps of: combining aramid fibrous material comprising non-continuous aramid fibers with sulfuric acid to obtain a first spin dope comprising aramid, combining virgin aramid polymer and sulfuric acid to obtain a second spin dope comprising aramid, combining the first spin dope and the second spin dope, and processing the combination of the first spin dope and the second spin dope into a continuous aramid fiber.

14. A continuous aramid fiber obtainable by the process according to claim 1.

15. A continuous aramid fiber according to claim 14 comprising a polymer blend comprising a non-aramid polymer and at least 1 wt % and at most 99 wt % of meta-aramid (based on the weight of the fiber).

16. A continuous aramid fiber comprising a polymer blend comprising a non-aramid polymer and at least 1 wt % and at most 99 wt % meta-aramid (based on the weight of the fiber).

17. The continuous aramid fiber according to claim 14 comprising a polymer blend comprising 50 to 98 wt % of meta-aramid, 1 to 49 wt % of para-aramid and 1 to 49 wt % of a non-aramid.

18. The continuous aramid fiber according to claim 17, wherein the non-aramid polymer is selected from at least one of a natural polymer, a regenerated polymer, a thermoplastic polymer and a rigid rod polymer other than aramid.

19. The continuous aramid fiber according to claim 17 wherein the non-aramid polymer is selected from polyester, polyamide or acrylic polymer.

20. The continuous aramid fiber according to claim 14 comprising a dye, preferably a cationic dye.

21. The continuous aramid fiber according to claim 14 having a sulfonic acid group content of at least 0.001 wt % (mass/mass fiber).

22. The continuous aramid fiber according to claim 14 having an organic solvent content of below 250 ppm.

23. A multifilament yarn comprising the continuous aramid fiber of claim 14.

24. A textile sheet, preferably a fabric, comprising the multifilament yarn of claim 23.

25. A protective clothing comprising the textile sheet of claim 24.

26. A textile sheet, comprising the continuous aramid fiber of claim 14.

Description

Example 1: Dissolving and Respinning of Dried Pulp

[0137] Aramid pulp (Twaron® pulp type 1092) was dried to a moisture content of <1.5%. This dried pulp was used for the preparation of spin dope having an aramid concentration of ca. 19.8 wt % by mixing with 99.8% solid sulfuric acid. Mixing was performed in a Nauta mixer (Hosokawa, 1000 L) for 20 hours. Mixing was started at a temperature of 8° C. and during mixing the temperature increased to a final temperature of 20° C. (spin dope 1)

[0138] In the same way, an aramid spin dope was prepared by combining virgin aramid polymer (p-phenylene terephthalamide) and sulfuric acid (spin dope 2).

[0139] From both spin dopes and from a 50:50 mixture of both spin dopes, multifilament aramid yarn was spun using a dry-jet wet spinning process. This was done by dosing the solid spin dopes into a kneader where it is heated to 85° C. to obtain a liquid spin dope. In the kneader, the dope is transported to the outlet where it is fed to a series of pumps. After filtration, the liquid spin dope is extruded through a spinneret containing 1000 holes of 59 μm into air where it is drawn, and immediately afterwards into a coagulation bath. After their coagulation the filaments formed were removed from the coagulation bath, washed, neutralized, washed again, dried and taken up on a bobbin. The yarn was spun with a linear density of ca. 930 dtex.

[0140] The mechanical properties for the three multifilament yarns were determined according to ASTM D7269 after conditioning at 20° C. and 65% relative humidity for 14 hours in accordance with ASTM D1776. The results are shown in table 1.

TABLE-US-00001 TABLE 1 Properties of multifilament yarns Tenacity Modu- Elongation at Break lus at Sample Aramid origin (mN/tex) (GPa) Break (%) 1 (comp.) 100% virgin 2547 105 3.2 aramid polymer 2 (inv.) 50% aramid 2570 107 3.2 pulp/50% virgin aramid polymer 3 (inv.) 100% aramid 2513 107 3.2 pulp

[0141] The results presented in Table 1 show that yarn prepared from a spin dope made from aramid pulp or based on a mixture of aramid pulp and virgin aramid polymer has comparable properties to yarns prepared from a spin dope based on virgin aramid polymer. This shows the effectiveness of this recycling approach.

Example 2

[0142] An aramid spin dope was prepared based on a solid pre-mix of 6 mm short-cut aramid fiber (Twaron®, T1080) with virgin aramid polymer (p-phenylene terephthalamide) in a 1:1 ratio. Equal amounts of 6 mm short-cut aramid fiber and virgin aramid polymer were weighed in a barrel which was placed on a rollerbank for 64 h. After, the mixture was used for the preparation of spin dope having an aramid concentration of ca. 19.8 wt % by mixing with 99.8% solid sulfuric acid. Mixing was performed in a Nauta mixer (Hosokawa, 1000 L) for 20 hours. Mixing was started at a temperature of 8° C. and during mixing the temperature increased to a final temperature of 20° C. (spin dope 3)

[0143] Furthermore, an aramid spin dope was prepared in a similar fashion by combining 100% 6 mm short-cut aramid fiber, instead of the 1:1 mixture of 6 mm short-cut aramid fiber and virgin aramid polymer, and sulfuric acid (spin dope 4).

[0144] From spin dope 2 (100% virgin aramid polymer), spin dope 3, and spin dope 4 multifilament yarns were spun in the same way as for example 1. Again, the mechanical properties of the yarns were determined. The mechanical properties are shown in table 2.

TABLE-US-00002 TABLE 2 Properties of multifilament yarn Tenacity Modu- Elongation at Break lus at Sample Aramid origin (mN/tex) (GPa) Break (%) 1 (comp.) 100% virgin 2547 105 3.2 aramid polymer 4 (inv.) 50% aramid short- 2508 106 3.2 cut/50% virgin aramid polymer 5 (inv.) 100% aramid 2307 93 3.3 short-cut

[0145] The results in Table 2 again show that a spin dope comprising recycled aramid fiber may yield multifilament yarn with mechanical properties comparable to multifilament yarn prepared from 100% virgin aramid polymer.

Example 3

[0146] This example demonstrates the recycling of fabrics made from a mix of fibers, in this particular instance made of 93 wt % meta-aramid fibers, 5 wt % para-aramid fiber, and 2 wt % acrylic-based antistatic fiber. The fabric was shredded into small pieces having a maximum dimension of 20 mm. Subsequently, liquid sulfuric acid was added to the fibers and using a SpeedMixer (DAC 800) the fibers were dissolved to prepare batches of spin dope based on 16 wt % fiber. Mixing was done for 90 seconds at 1400 rpm to maintain a maximum temperature of 60° C.

[0147] Several batches of spin dope were combined in a vessel (spin dope 5). The spin dope was continuously fed to a twin screw extruder where it was heated to 35° C.

[0148] After the extruder, the liquid spin dope was filtered and extruded through a spinneret containing 106 holes of 65 μm into air where it was drawn, and immediately afterwards into a coagulation bath. After their coagulation the filaments formed were removed from the coagulation bath, washed, neutralized, washed again, dried, heat treated at ˜280° C. and taken up on a bobbin. After coagulation, during washing, and during heat treatment drawing was applied.

[0149] The mechanical properties of the multifilament yarn produced in this way are shown in table 3.

TABLE-US-00003 TABLE 3 Mechanical properties of multifilament yarn from recycled aramid-hybrid fabric Tenacity Linear Elongation at Break Density at Sample Aramid origin (mN/tex) (dtex) Break (%) 6 (inv.) Shredded fabric 343 233 21.3 consisting of 93% meta-aramid, 5% para-aramid, and 2% acrylic-based antistatic fiber

[0150] The results of Table 3 show that a fabric consisting of a mix of fibers made of different polymers, among them fibers containing aramid, can be spun into a filament yarn with properties suitable in various applications.

[0151] When dyed, the fibers obtained by this process show improved penetration of dye throughout the filament cross section, as shown by FIG. 1 in comparison to regular meta-aramid fibers (Teijinconex® Neo). FIG. 1 shows cross sectional images of recycled yarn before dyeing (left image, sample 6) and after dyeing with a blue dye (middle image). The right image shows a regular meta-aramid fiber (Teijinconex® Neo) obtained from virgin meta-aramid polymer (no recycling) and dyed with the same dye as sample 6. From FIG. 1 can be observed that when dyeing the recycled fiber, the dye penetrates all the way to the core of the filaments. In contrast, when dyeing the regular meta-aramid fiber the core of the filaments remains undyed.