CELLULOSE FIBERS

Abstract

There is provided a cellulose based fiber made of a i) cellulose dissolving pulp, and ii) a recycled cellulose textile, which is treated to swell the cellulose with a reducing additive and a) bleached with oxygen at alkaline conditions with a pH in the range 9-13.5 and/or b) bleached with ozone at acid conditions below pH 6, wherein the cellulose based fiber is manufactured with one selected from a Viscose process and a Lyocell process. Advantages include that the tensile strength of the fiber is improved and it is possible to manufacture improved cellulose fibers which comprise a fraction of recycled material.

Claims

1. A cellulose based fiber made of a i) cellulose dissolving pulp, and ii) a material made from recycled textile comprising cellulose, which is a) treated to swell the cellulose under reducing conditions together with at least one reducing additive present at least during a part of the swelling and b) treated in at least one of the following bleaching steps i) bleaching with oxygen at alkaline conditions with a pH in the range 9-13.5 and ii) bleaching with ozone at acid conditions below pH 6, wherein the steps a) and b) are carried out in sequential order and wherein the bleaching steps i) and ii) may be carried out in any order if both i) and ii) are performed, and wherein the cellulose based fiber is manufactured with one selected from a Viscose process and a Lyocell process.

2. The cellulose based fiber according to claim 1, wherein the cellulose dissolving pulp is from a virgin source.

3. The cellulose based fiber according to claim 1, wherein the cellulose dissolving pulp is of a type normally used in a Viscose process.

4. The cellulose based fiber according to claim 1, wherein the cellulose dissolving pulp is of a type normally used in a Lyocell process.

5. The cellulose based fiber according to claim 1, wherein the material made from recycled textile constitutes at least 10 wt % of the cellulose based fiber.

6. The cellulose based fiber according to claim 1, wherein the recycled textile is at least one selected from the group consisting of cotton, Lyocell, rayon, and Viscose.

7. The cellulose based fiber according to claim 1, wherein the recycled textile is cotton.

8. The cellulose based fiber according to claim 1, wherein the recycled textile is mechanically disintegrated to at least partially disintegrate the cellulose before the swelling of the cellulose.

9. The cellulose based fiber according to claim 1, wherein the pH during the swelling is in the range of 9-13.5.

10. The cellulose based fiber according to claim 1, wherein NaOH is present during the swelling in a concentration from 0.01 to 0.5 mol/l.

11. The cellulose based fiber according to claim 1, wherein the temperature during the swelling is in the range 50-100 C.

12. The cellulose based fiber according to claim 1, wherein the at least one reducing additive comprises sodium dithionite, Na.sub.2S.sub.2O.sub.4 in a concentration from 0.01 to 0.25 mol/l.

13. The cellulose based fiber according to claim 1, wherein the bleaching with oxygen at alkaline conditions is carried out at a temperature in the interval 60-120 C.

14. The cellulose based fiber according to claim 1, wherein the bleaching with oxygen at alkaline conditions is carried out during 20 minutes-24 hours.

15. The cellulose based fiber according to claim 1, wherein the bleaching with oxygen at alkaline conditions is carried out during 30 min-120 min.

16. The cellulose based fiber according to claim 1, wherein a wash is carried out before the bleaching with ozone at acid conditions.

17. The cellulose based fiber according to claim 1, wherein the material is dewatered to a water content of less than 66 wt % before the bleaching with ozone at acid conditions.

18. The cellulose based fiber according to claim 1, wherein the bleaching with ozone at acid conditions is carried out at a pH in the interval 1.5-5.

19. A method for manufacturing a cellulose based fiber, comprising the step of mixing: i) cellulose dissolving pulp, and material made from recycled textile comprising cellulose, which is a) treated to swell the cellulose under reducing conditions together with at least one reducing additive present at least during a part of the swelling and b) treated in at least one of the following bleaching steps i) bleaching with oxygen at alkaline conditions with a pH in the range 9-13.5 and ii) bleaching with ozone at acid conditions below pH 6, wherein the steps a) and b) are carried out in sequential order and wherein the bleaching steps i) and ii) may be carried out in any order if both i) and ii) are performed, and wherein the cellulose based fiber is manufactured with one selected from a Viscose process and a Lyocell process.

Description

DETAILED DESCRIPTION

[0024] Before the invention is disclosed and described in detail, it is to be understood that this invention is not limited to particular compounds, configurations, method steps, substrates, and materials disclosed herein as such compounds, configurations, method steps, substrates, and materials may vary somewhat. It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the present invention is limited only by the appended claims and equivalents thereof.

[0025] It must be noted that, as used in this specification and the appended claims, the singular forms a, an and the include plural referents unless the context clearly dictates otherwise.

[0026] If nothing else is defined, any terms and scientific terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains.

[0027] Solution is used herein to denote a homogeneous mixture comprising at least one substance dissolved in a solvent.

[0028] The term decolourisation should be understood to mean a loss of absorbance at one or more wavelengths of light of the contaminant. Typically, decolourisation involves loss of absorbance at one or more visible wavelengths of light. Furthermore, decolourisation may be partial or complete.

[0029] The term cellulosic material as used herein refers to all natural cellulosic forms (cotton, linen, jute, etc.) and all regenerated cellulosic forms such as rayon. In particular all textiles comprising cellulose are encompassed including textiles comprising treated and modified cellulose.

[0030] By dissolving pulp (which is sometimes also called dissolving cellulose or cellulose dissolving pulp), is meant a bleached wood pulp or cotton linters that has a high cellulose content (90 wt % or more). It has special properties including as a high level of brightness and uniform molecular-weight distribution. Dissolving pulp is so named because it is not made into paper, but dissolved either in a solvent or by derivatization into a homogeneous solution, which makes it completely chemically accessible and removes any remaining fibrous structure.

[0031] In a first aspect there is provided a cellulose based fiber made of a i) cellulose dissolving pulp, and ii) a material made from recycled textile comprising cellulose, which is treated to swell the cellulose under reducing conditions together with at least one reducing additive present at least during a part of the swelling and treated in at least one of the following bleaching steps a) bleaching with oxygen at alkaline conditions with a pH in the range 9-13.5 and b) bleaching with ozone at acid conditions below pH 6, wherein the cellulose based fiber is manufactured with one selected from a Viscose process and a Lyocell process.

[0032] In one embodiment the cellulose dissolving pulp is from a virgin source. In one embodiment the cellulose dissolving pulp is of a type normally used in a Viscose process. In another embodiment the cellulose dissolving pulp is of a type normally used in a Lyocell process.

[0033] In one embodiment the material made from recycled textile constitutes at least 10 wt % of the cellulose based fiber. In an alternative embodiment the material made from recycled textile constitutes at least 7 wt % of the cellulose based fiber. In an alternative embodiment the material made from recycled textile constitutes at least 15 wt % of the cellulose based fiber. In an alternative embodiment the material made from recycled textile constitutes at least 20 wt % of the cellulose based fiber. The material made from recycled textile is the special type of recycled cellulose textile treated as described. The amount of cellulose based fiber is calculated by weight of cellulose based fiber in relation to the total weight of the cellulose based fiber.

[0034] The material made from recycled textile is manufactured according to the following scheme: [0035] a. providing at least one textile material comprising cellulose, [0036] b. treating the material to swell the cellulose, under reducing conditions, wherein at least one reducing agent is present at least during a part of the swelling, [0037] c. performing at least one of the following two bleaching steps in any order
i.bleaching the material with oxygen at alkaline conditions with a pH in the range 9-13.5, and
ii.bleaching the material with ozone at acid conditions below pH 6.

[0038] The steps a), b), and c) should be carried out in sequential order, with the proviso that the at least one bleaching step c) i) and c) ii) can be carried out in any order.

[0039] In one embodiment the at least one textile is at least one selected from the group consisting of cotton, Lyocell, rayon, and Viscose. In one embodiment the at least one textile is cotton. It has been shown that textiles comprising cellulose such as cotton can suitably be recycled using the present method. Mixtures of different types of textiles are also encompassed as long as at least a part of the textiles comprise cellulose.

[0040] In one embodiment the textile is mechanically disintegrated before step b) so that the textile is at least partially disintegrated in order to improve the subsequent steps. In one embodiment the textile is mechanically disintegrated in a shredder before step b). Other methods of disintegrating the textiles are also encompassed. The shredding and disintegration creates a larger surface of the material so that the subsequent steps are facilitated.

[0041] In one embodiment the pH during step b) is in the range of 9-13.5. In another embodiment the pH during step b) is in the range of 11-13.3. The swelling is thus in these embodiments carried out under alkaline pH. In one embodiment NaOH is present during step b) in a concentration from 0.01 to 0.5 mol/l. NaOH has the advantage of being a cost efficient way of raising the pH.

[0042] In one embodiment the temperature during step b) is in the range 50-100 C.

[0043] In one embodiment the at least one reducing additive comprises sodium dithionite, Na.sub.2S.sub.2O.sub.4. In other embodiments other reducing additives are used. In one embodiment sodium dithionite, Na.sub.2S.sub.2O.sub.4 is present during step b) in a concentration from 0.01 to 0.25 mol/l.

[0044] During the bleaching step c) the chain length of cellulose is reduced together with other effects on the material. The bleaching is in one embodiment step c) i) only. In another embodiment the bleaching is step c) ii) only. In yet another embodiment the bleaching comprises both step c) i) and step c) ii) carried out in any order. I.e. in one embodiment the bleaching comprises step c) i) followed by step c) ii) and in an alternative embodiment the bleaching comprises step c) ii) followed by step c) i).

[0045] In one embodiment the bleaching in step c)-i) is carried out at a temperature in the interval 60-120 C.

[0046] In one embodiment, wherein the bleaching in step c)-i) is carried out during 20 minutes-24 hours. In one embodiment the upper limit is about two hours, however in an alternative embodiment extended bleaching is carried out, this is referred to as aging. In one embodiment the bleaching in step c)-i) is carried out during 30 min-120 min.

[0047] In one embodiment a wash is carried out before step c) ii). Since step c) ii) is carried out at low pH and when the preceding step is carried out at high pH it is an advantage to wash before the pH is lowered in step c) ii). In one embodiment the material is dewatered to a water content of less than 66 wt % before step c) ii). This step also serves to minimize the carry-over of liquid with high pH to the step with low pH. In one embodiment the pH during step c) ii) is in the interval pH 1.5-5.

[0048] The cellulose is recovered after step c). The recovered cellulose is mixed in the dissolving pulp and used for making a cellulose fiber.

[0049] In a second aspect there is provided a method for manufacturing a cellulose based fiber, comprising the step of mixing:

[0050] i) cellulose dissolving pulp, and [0051] ii) a material made from recycled textile comprising cellulose, which is treated to swell the cellulose under reducing conditions together with at least one reducing additive present at least during a part of the swelling and treated in at least one of the following bleaching steps a) bleaching with oxygen at alkaline conditions with a pH in the range 9-13.5 and b) bleaching with ozone at acid conditions below pH 6, [0052] wherein the cellulose based fiber is manufactured with one selected from a Viscose process and a Lyocell process.

[0053] In one embodiment the cellulose based fiber is manufactured with a Lyocell process. A skilled person is aware of both the Viscose process and the Lyocell process and can carry out those processes.

[0054] Other features and uses of the invention and their associated advantages will be evident to a person skilled in the art upon reading this description and the appended examples.

[0055] It is to be understood that this invention is not limited to the particular embodiments shown here. The following examples are provided for illustrative purposes and are not intended to limit the scope of the invention since the scope of the present invention is limited only by the appended claims and equivalents thereof.

EXAMPLES

[0056] The recycled material from textiles is called re:newcell pulp and it was manufactured using the following scheme:

[0057] Cotton linters were cut into small pieces.

[0058] The material was mixed together with NaOH until a pH of 12 was reached and with an addition of sodium dithionite, Na.sub.2S.sub.2O.sub.4 in a swelling step. The reductive treatment during swelling was carried out at 85 C. for 30 minutes. Thereafter the material was washed and dried at 60 C.

[0059] Subsequently ozone treatment was carried out at low pH by treating in 1% H.sub.2SO.sub.4 for 15 min followed by ozone treatment for 5 min.

[0060] Dissolving pulp was obtained from Sdra Cell in a grade called Sdra orange. It has been formulated to meet the needs of the Lyocell process in which pulp is treated directly with a solvent as opposed to the more common Viscose process which requires a chemical reaction to dissolve cellulose. The process demands a high level of purity. Its alkali resistance is over 96% while viscosity is low, which is important for the final textile fiber's properties and good runnability at the customer's end.

[0061] Fibers were made from Sdra orange mixed with various degrees of re:newcell pulp as well as from 100% re:newcell. The fibers were made using the Lyocell process: Laboratory dissolution tests were carried out using different blend ratios of the delivered cellulose samples as well as different cellulose concentrations in the cellulose direct dissolution agent N-methylmorpholine-N-oxide monohydrate (NMMO). For blending, the necessary amounts of both cellulose samples were suspended and disintegrated commonly in water using an Ultra-Turrax tool. Then, the excess of water was pressed out and the blending pulp samples were suspended in 50 wt-% aqueous NMMO. The solution preparation took place using a laboratory kneader through removal of the water by