Process for pretreating reclaimed cotton fibers to be used in the production of molded bodies from regenerated cellulose

Abstract

A process for pretreating reclaimed cotton fibers to be used in the production of molded bodies from regenerated cellulose, characterized by effective metal reduction and adjustment of the degree of polymerization and brightness, including a metal removing stage and an oxidative bleaching stage of the reclaimed cotton fibers or pulp produced thereof. Reclaimed cotton fibers treated according to the described process may be used alone or in blends with conventional dissolving pulp as raw material for the production of molded bodies from regenerated cellulose. The process enables technically smooth, safe, and economically feasible spinning via the Viscose or Lyocell process, therefore, the current invention provides an efficient recycling pathway for cotton waste materials.

Claims

1. A process for obtaining a molded cellulose body comprising: pretreating reclaimed cotton fibers in a chemical metal removing stage and an oxidative bleaching stage; preparing a spinning dope comprising the reclaimed cotton fibers by a lyocell or viscose process to produce a regenerated cellulose; and obtaining the molded cellulose body.

2. The process according to claim 1, wherein the cotton fibers are reclaimed from pre-consumer cotton waste.

3. The process according to claim 1, wherein the cotton fibers are reclaimed from post-consumer cotton waste.

4. The process according to claim 1, wherein the reclaimed cotton fibers include pulp prepared from cotton rags.

5. The process according to claim 1, wherein the reclaimed cotton fibers are mechanically shredded, milled, or opened prior to their use.

6. The process according to claim 1, wherein the chemical metal removing stage is an acidic washing treatment and/or a treatment with a complexing agent.

7. The process according to claim 6, wherein the reclaimed cotton fibers are treated by an aqueous solution of a complexing agent.

8. The process according to claim 6, wherein both treatments are combined in one step by adding a complexing agent to the acidic washing treatment.

9. The process according to claim 1, wherein the oxidative bleaching stage comprises an oxygen bleaching treatment.

10. The process according to claim 1, wherein the oxidative bleaching stage comprises a peroxide bleaching treatment.

11. The process according to claim 1, wherein the oxidative bleaching stage comprises an ozone bleaching treatment.

12. The process according to claim 1, wherein the oxidative bleaching stage comprises a sequence of oxidative bleaching treatments selected from the group consisting of oxygen bleaching treatment, peroxide bleaching treatment and ozone bleaching treatment.

13. The process according to claim 1, wherein the molded cellulose body is produced according to the Viscose process.

14. The process according to claim 13, wherein the process conditions are chosen such that an intrinsic viscosity of the reclaimed cotton fibers after pretreating is in the range between 850 to 300 ml/g.

15. The process according to claim 14, wherein the intrinsic is in the range between 650 to 350 ml/g.

16. The process according to claim 15, wherein the intrinsic viscosity is in the range between 550 to 400 ml/g.

17. The process according to claim 13, wherein the molded body is a staple fiber, filament fiber, sponge or foil of the Viscose or Modal type.

18. The process according to claim 13, wherein the viscose process is a Modal process.

19. The process according to claim 1 wherein the molded cellulose body is produced according to the Lyocell process.

20. The process according to claim 19, wherein the process conditions are chosen such that an intrinsic viscosity of the reclaimed cotton fibers after pretreating is in the range between 650 to 300 ml/g.

21. The process according to claim 20, wherein the intrinsic viscosity is in the range between 500 to 350 ml/g.

22. The process according to claim 21, wherein the intrinsic viscosity is in the range between 440 to 360 ml/g.

23. The process according to claim 19, wherein the molded body is a staple fiber, filament fiber, sponge or foil of the Lyocell type.

24. The process according to claim 1, wherein the spinning dope further comprises dissolving pulp.

25. The process according to claim 1, wherein the resulting molded bodies are used for further processing into textile or nonwoven products.

26. The process according to claim 1, wherein the spinning dope comprises 100% reclaimed cotton fibers.

Description

EXAMPLES

Example 1

(1) A Lyocell spinning; dope was prepared from Sample 1 being untreated reclaimed cotton fibers from colored pre-consumer cotton waste material present in the form of cotton rag pulp. Said spinning dope was subjected to the Sikarex test without any pretreatment. Said spinning dope did not pass the Sikarex Test.

Example 2

(2) Another Lyocell spinning dope was prepared from Sample 2 being untreated reclaimed cotton fibers from indigo dyed pre-consumer Denim waste material. Due to the high viscosity of the reclaimed fibers a fibrous cellulose NMMO mixture was obtained, not suitable as spinning dope. Said fibrous cellulose NMMO mixture was subjected to the Sikarex test. Said mixture did not pass the Sikarex Test.

Example 3

(3) Sample 3 being reclaimed cotton fibers from colored pre-consumer cotton waste material present in the form of cotton rag pulp was subjected to an acidic washing treatment according to the current invention. Acidic washing was performed at pH 3 at a temperature of 60 C. for 15 min. The sample was dewatered and washed with deionised water. Sample 3 was then subjected to oxidative bleaching by hydrogen peroxide according to the current invention. Hydrogen peroxide bleaching was performed at pH 10.6 for 60 min at 80 C. The dose of H.sub.2O.sub.2 was 10 kg/odtp. 1 kg Mg.sup.2/odtp was added in the form of Mg(SO.sub.4) as bleaching auxiliary. Finally, the sample was dewatered, washed with deionised water and air dried.

(4) After subjecting sample 3 to said treatments the sample is referred to as sample 3 A-P. The metals content was effectively lowered such that spinning dopes prepared from sample 3 A-P successfully passed the Sikarex test. The intrinsic viscosity of sample 3 A-P was adjusted to 390 ml/g and the brightness was increased to 85.7% ISO. (1) A Lyocell spinning dope was prepared from a mixture of 10% Sample 3 A-P and 90% conventional dissolving pulp. Said spinning dope was used to produce regenerated cellulosic fibers of the Lyocell type by treating them according to the Lyocell process, as generally known to a person skilled in the art e.g. from EP 0356419 B1 and EP 0671492 B1. Corresponding fiber data are presented in Table 1.

Example 4

(5) Sample 3 was subjected to an acidic washing treatment according to the current invention as described in Example 3. Sample 3 was then subjected to oxidative bleaching by ozone according to the current invention. Ozone bleaching was performed at pH 2.5 for a reaction time of 10 s at 50 C. The dose of O.sub.3 was 2.9 kg/odtp. Finally, the sample was dewatered, washed with deionised water and air dried.

(6) After subjecting sample 3 to said treatments the sample is referred to as sample 3 A-Z. The metals content was effectively lowered such that spinning dopes prepared from sample 3 A-Z successfully passed the Sikarex test. The intrinsic viscosity of sample 3 A-Z was adjusted to 371 ml/g and the brightness was increased to 82.4% ISO.

Example 5

(7) Sample 4 being reclaimed cotton fibers from colored pre-consumer cotton waste material present in the form of cotton rag pulp was subjected to oxidative bleaching by hydrogen peroxide according to the current invention. Sample 4 was then subjected to an acidic washing treatment according to the current invention. Finally, the sample was dewatered, washed with deionised water and air dried.

(8) After subjecting sample 4 to said treatments the sample is referred to as sample 4 P-A. The metals content was effectively lowered such that spinning dopes prepared from sample 4 P-A successfully passed the Sikarex test. The intrinsic viscosity of sample 4 P-A was adjusted to 372 ml/g and the brightness was increased to 82.1% ISO. (1) A Lyocell spinning dope was prepared from 100% Sample 4 P-A. Said spinning dope was used to produce regenerated cellulosic fibers of the Lyocell type by treating them according to the Lyocell process. Corresponding fiber data are presented in Table 1. (2) A Viscose spinning dope was prepared from 100% Sample 4 P-A. Said spinning dope was used to produce regenerated cellulosic fibers of the Viscose type by treating them according to the Viscose process, as generally known to a person skilled in the art, e.g. from Gtze, Chemiefasern nach dem Viskoseverfahren, 1967. Corresponding fiber data are presented in Table 1. (3) A Viscose spinning dope was prepared from a mixture of 20% Sample 4 P-A and 80% conventional dissolving pulp. Said spinning dope was used to produce regenerated cellulosic fibers of the Viscose type by treating them according to the Viscose process. Corresponding fiber data are presented in Table 1.

Example 6

(9) Sample 4 after being bleached by hydrogen peroxide was subjected to an acidic washing treatment simultaneously adding a complexing agent in low concentration according to the current invention. The treatment was performed at pH 3 at a temperature of 60 C. for 30 min, EDTA was added as said complexing agent, the concentration was 2 kg/odtp. Finally, the sample was dewatered, washed with deionised water and air dried.

(10) After subjecting sample 4 to said treatments the sample is referred to as sample 4 P-AQ. The metals content was effectively lowered such that spinning dopes prepared from sample 4 P-A successfully passed the Sikarex test. The intrinsic viscosity of sample 4 P-AQ was adjusted to 366 ml/g and the brightness was increased to 84.5% ISO.

Example 7

(11) Sample 5 being reclaimed cotton fibers from colored pre-consumer cotton waste material present in the form of cotton rag pulp was subjected to oxidative bleaching by hydrogen peroxide according to the current invention. Sample 5 was then subjected to an acidic washing treatment according to the current invention. Finally, the sample was &watered, washed with deionised water and air dried.

(12) After subjecting sample 5 to said treatments the sample is referred to as sample 5 P-A. The metals content was effectively lowered such that spinning dopes prepared from sample 5 P-A successfully passed the Sikarex test. The intrinsic viscosity of sample 5 P-A was adjusted to 612 ml/g and the brightness was increased to 80.9% ISO. (1) A Viscose spinning dope was prepared from 100% Sample 5 P-A. Said spinning dope was used to produce regenerated cellulosic fibers of the Modal type by treating them according to the Modal process, as generally known to a person skilled in the art, e.g. from AT 287905. Corresponding fiber data are presented in Table 1.

Example 8

(13) Sample 6 being untreated reclaimed cotton fibers from indigo dyed pre-consumer Denim waste material was subjected to alkaline cooking similar to CRP production. Subsequently sample 6 was subjected to an acidic washing treatment according to the current invention. Then sample 6 was subjected to an oxidative bleaching sequence according to the current invention. The bleaching sequence consisted of a Z-stage followed by a P-stage. The Z-stage was performed at pH 2.5 for a reaction time of 10 s at 50 C. The dose of O.sub.3 was 5.2 kg/odtp. The P-stage bleaching was performed at pH 10.5 for 30 min at 80 C. The dose of H.sub.2O.sub.2 was 10 kg/odtp. 1 kg Mg.sup.2+/odtp was added in the form of Mg(SO.sub.4) as bleaching auxiliary. Finally, the sample was dewatered, washed with deionised water and air dried.

(14) After subjecting sample 6 to said treatments the sample is referred to as sample 6 A-Z-P. The metals content was effectively lowered such that spinning dopes prepared from sample 6 A-Z-P successfully passed the Sikarex test. The intrinsic viscosity of sample 6 A-Z-P was adjusted to 498 ml/g and the brightness was increased to 90.3% ISO.

(15) TABLE-US-00001 TABLE 1 Fiber data % % reclaimed standard Sample for cotton dissolving Fiber Titer FFk FDk spinning dope fibers pulp type [dtex] [cN/tex] [%] Reference 0 100 Viscose 1.3 27.3 17.7 Sample 4 P-A 100 0 Viscose 1.3 27.6 18.1 Sample 4 P-A 20 80 Viscose 1.3 27.2 17.5 Reference 0 100 Lyocell 1.3 41.4 10.4 Sample 4 P-A 100 0 Lyocell 1.3 43.0 9.5 Sample 3 A-P 10 90 Lyocell 1.3 35.7 10.5 Reference 0 100 Modal 1.3 26.5 14.1 Sample 5a 100 0 Modal 1.3 30.4 14.3