CELLULOSE RAW MATERIAL AND METHOD FOR RECYCLING A CELLULOSE RAW MATERIAL FROM BLENDED TEXTILE WASTE

Abstract

A recycled cellulose raw material and a method for recycling a cellulose raw material from blended textile waste with high reliability and yielding high raw material quality is shown, the method comprising the steps in the given order: providing the blended textile waste containing at least one cellulose component and at least one synthetic polymer component, treating the blended textile waste in a non-oxidizing aqueous treatment medium in order to degrade the at least one synthetic polymer component, whereby the treatment is carried out at a temperature between 100° C. and 200° C., and obtaining the recycled cellulose raw material from the treated blended textile waste.

Claims

1. A method for recycling a cellulose raw material from blended textile waste, the method comprising the steps in the given order: a) providing the blended textile waste containing at least one cellulose component and at least one synthetic polymer component, b) treating the blended textile waste in a non-oxidizing aqueous treatment medium in order to degrade the at least one synthetic polymer component, whereby the treatment is carried out at a temperature between 100° C. and 200° C., and c) obtaining the recycled cellulose raw material from the treated blended textile waste.

2. The method according to claim 1, wherein aqueous treatment medium contains at least one hydrolyzing agent, and whereby the amount of said at least one hydrolyzing agent is adjusted to the amount of the at least one synthetic polymer component in the blended textile waste, such that the at least one synthetic polymer component is essentially fully degraded.

3. The method according to claim 2, wherein the at least one hydrolyzing agent is a base, more particularly NaOH.

4. The method according to claim 2, wherein the amount of the at least one hydrolyzing agent in the aqueous treatment medium is at least 1 mol per mol of hydrolytically cleavable bonds in the at least one synthetic polymer component.

5. The method according to claim 4, wherein the amount of the at least one hydrolyzing agent in the aqueous treatment medium is less than 3 mol per mol of hydrolytically cleavable bonds in the at least one synthetic polymer component.

6. The method according to claim 1, wherein the treatment in step b) is carried out at a temperature between 110° C. and 190° C., more particularly between 120° C. and 180° C.

7. The method according to claim 1, wherein the at least one synthetic polymer component contains a type of polyester- or polyamide-fiber.

8. The method according to claim 1, wherein the treatment in step b) is carried out under reducing conditions.

9. The method according to claim 8, wherein at least one reducing agent is present during step b).

10. The method according to claim 1, wherein after step b), the blended textile waste is subjected to at least one bleaching step, more particularly an oxidative bleaching step, at alkaline and/or acidic conditions.

11. The method according to claim 10, wherein the blended textile waste is washed and optionally pressed prior to being subjected to the bleaching step and/or between the bleaching steps.

12. The method according to claim 1, wherein the blended textile waste is comminuted and/or disintegrated prior to the treatment in step b).

13. The method according to claim 1, wherein non-fibrous scrap is at least partially removed from the blended textile waste, prior to the treatment in step b).

14. Recycled cellulose raw material, obtained through a method according to claim 1.

15. Use of a recycled cellulose raw material according to claim 14 in a method for the production of cellulosic molded bodies.

Description

MODES FOR CARRYING OUT THE INVENTION

[0040] In the following, the invention is demonstrated according to a number of embodiments.

[0041] In a first embodiment, the method for recycling a cellulose raw material from blended textile waste comprises the following steps in the given order: [0042] a) providing the blended textile waste containing at least a cellulose component and a synthetic polymer component, [0043] b) treating the blended textile waste in a non-oxidizing aqueous treatment medium in order to degrade the synthetic polymer component, whereby the treatment is carried out at a temperature between 100° C. and 200° C., and [0044] c) obtaining the recycled cellulose raw material from the treated blended textile waste.

[0045] In step a), a blended textile waste is provided, which consists of a mixture of different textile fibers, which form at least one cellulose component and at least one synthetic polymer component. Besides the cellulose and synthetic polymer component, the blended textile waste may also comprise residues of other textile fibers, such as natural protein-based fibers. The blended textile waste is a pre- and/or post-consumer textile waste as described above. The cellulose component from said textile waste comprises cellulose-based fibers, e.g. cotton-, Viscose-, Modal-, Lyocell- or Cupro-fibers. The cellulose component can then be recovered from the textile waste and recycled to a cellulose raw material which can serve to produce new regenerated cellulosic fibers. The synthetic polymer component from said textile waste on the other hand comprises non-cellulosic synthetic polymer textile fibers, such as, but not limited to, polyester- or polyamide-fibers, which can be degraded by means of hydrolyzation.

[0046] The fibers of the cellulose- and synthetic polymer component are usually intrinsically intermingled in the textile waste, e.g. due to yarn-spinning, knitting and/or weaving. Thus, prior to the treatment in step b), the blended textile waste is comminuted and/or disintegrated in order to separate the fibers of the different components so as they may be treated individually and more efficiently. Additionally, non-fibrous scrap is at least partially removed from the blended textile waste, prior to the treatment in step b). Such non-fibrous scrap may result from non-fibrous solid components contained in textiles, such as buttons, zippers, decorative elements, prints, labels and/or dirt.

[0047] In another embodiment, as a pre-treatment, the blended textile waste is washed and pressed dry to remove any loose dirt prior to subjecting it to the treatment in step b).

[0048] In step b), the blended textile waste is treated in an aqueous treatment medium in order to degrade the synthetic polymer component. Thereby the blended textile waste is submerged in the aqueous treatment medium to form a suspension. Optionally, the suspension may be stirred or forcefully intermixed to improve the dispersion of the blended textile waste. The suspension is then heated to a temperature above at least 100° C., whereby the treatment of the blended textile waste is further carried out at a temperature between 100° C. and 200° C. In further embodiments, the treatment of the blended textile waste in step b) is carried out at a temperature between 110° C. and 190° C., between 120° C. and 180° C., between 125° C. and 175° C., or between 130° C. and 170° C.

[0049] In the first embodiment, the treatment medium contains a hydrolyzing agent, which is added to the aqueous treatment medium in an amount which is adjusted to the content of the synthetic polymer component in the blended textile waste. This can be done by analyzing the blended textile waste prior to the treatment in step b), thereby determining the content of the synthetic polymer component in the blended textile waste. On the basis of the determined synthetic polymer component content, the amount of hydrolyzing agent is selected such that the synthetic polymer component is essentially fully degraded during the treatment in step b).

[0050] The hydrolyzing agent in the present embodiment is a base, in particular NaOH. Thus, the non-oxidizing aqueous treatment medium is an aqueous alkaline treatment medium, and the synthetic polymer component is degraded by means of alkaline hydrolyzation. The amount of base added to the aqueous alkaline treatment medium is selected to be between 1 mol and 3 mol per mol of hydrolytically cleavable bonds in the synthetic polymer component. From the content and composition of the synthetic polymer component, the amount of hydrolytically cleavable bonds may easily be derived. If, for example, the synthetic polymer component is polyethyleneterephtalate (PET), the monomer unit has a molar weight M.sub.PET of 192.17 g/mol and comprises 2 ester bonds. Thus, the amount n.sub.bonds,PET of hydrolytically cleavable bonds of the PET-component amounts to

n.sub.bonds,PET=2.Math.M.sub.PET/M.sub.PET,  (1)

where M.sub.PET is the total mass of PET contained in the blended textile waste. This scheme may be applied mutatis mutandis to all other synthetic polymer components contained in the textile waste and subsequently added together:

n.sub.bonds=n.sub.bonds,PET+n.sub.bonds,pc2+n.sub.bonds,pc3+ . . . ,  (2)

where n.sub.bonds,pc2 and n.sub.bonds,pc3 are the amounts of hydrolytically cleavable bond of an optional second and third synthetic polymer component, determined equivalently through formula (1). Thus, as mentioned above, the amount of base (NaOH) as hydrolyzing agent n.sub.agent added to the aqueous treatment medium is between 1.Math.n.sub.bonds and 3.Math.n.sub.bonds, where n.sub.bonds refers to the total amount of hydrolytically cleavable bonds in all synthetic polymer components. Therefore, the following ratio between amount of agent and amount of bonds is satisfied:

1≤n.sub.agent/n.sub.bonds≤3.  (3)

[0051] In a further embodiments, the amount of base added to the aqueous alkaline treatment medium is selected to be at least 1.25 mol or at least 1.5 mol and at maximum 2.75 mol or 2.5 mol per mol of hydrolytically cleavable bonds in the synthetic polymer component. Thus, the amount of base added would satisfy 1.25≤n.sub.agent/n.sub.bonds≤2.75, or 1.5≤n.sub.agent/n.sub.bonds≤2.5.

[0052] The aqueous alkaline treatment medium serves to swell the cellulose component in order to open the structure of the cellulosic fibers and thereby remove unwanted substances contained therein, such as colors, dyes, resins or other textile finishing chemicals. Further, the synthetic polymer component gets degraded, i.e. hydralized, in the aqueous alkaline treatment medium. During said degradation, the synthetic polymer component is destroyed while the cellulose component is essentially left unaltered. PET-fibers of the first synthetic polymer component, as described above, are split up in to their constituents ethylene glycol and terephtalic acid by cleaving the ester bonds in the PET-chain molecules. The NaOH molecules are thereby consumed by the reaction and the subsequent formation of terephthalic acid disodium salt (disodium terephtalate C.sub.8H.sub.4Na.sub.2O.sub.4), leaving only a small amount of NaOH molecules in excess.

[0053] In step c), a recycled cellulose raw material is finally obtained from the treated blended textile waste. In the present embodiment, the cellulose raw material is obtained by separating the swelled cellulose component from all the non-cellulosic constituents, such as the degraded synthetic polymer component. Such separation can be easily performed, e.g. by filtration of the suspension.

[0054] In a second embodiment, steps a) to c) are performed as described above for the first embodiment. Additionally, the treatment in step b) is carried out under reducing conditions. Thereby, at least one reducing agent is present in the aqueous alkaline medium and thus in the suspension. The reducing agent is preferably chosen from sodium dithionite (Na.sub.2S.sub.2O.sub.4) or thiourea dioxide (CH.sub.4N.sub.2O.sub.2S) and is present in the alkaline medium in a concentration from 1 to 100 g, such as between 25 and 75 g, per kg of blended textile waste.

[0055] In a third embodiment, additionally to the steps in the first or second embodiment above, the blended textile waste is subjected to at least one bleaching step after the treatment in step b). The bleaching steps can either be at alkaline and/or acidic conditions. Preferably the treatment in step b) is followed by at least one oxidative bleaching step. Therefore, it is preferable that the blended textile waste is washed and optionally pressed prior to being subjected to the bleaching step to neutralize the conditions of the preceding treatment and improve the efficiency of the following bleaching step.

EXAMPLES

[0056] In the following examples, embodiments of the invention are illustrated in further detail, without limiting the scope of the invention in any matter.

[0057] In all demonstrated examples, a method for producing a recycled cellulose raw material according to the present invention was applied to the blended textile waste, where several parameters of the treatment are varied throughout the examples. In all examples, the composition of the textile waste was first determined by means of NIR-spectroscopy (near-infrared spectroscopy). After the treatment, the obtained recycled cellulose raw material was separated from the spent aqueous treatment solution through a Buchner funnel and again analyzed by means of NIR-spectroscopy to determine its composition (e.g. content of residual synthetic polymer component). Similarly, the spent aqueous treatment solution was analyzed to determine the content of excess treatment agents (e.g. hydrolyzing agent/base). From the determined compositions of the recycled cellulose raw material, the synthetic polymer component reduction and the cellulose component yield were determined.

Examples A to C

[0058] Examples A, B and C show the results of a method for producing a recycled cellulose raw material, where a blended textile waste from bed linens with a composition of 61.1% cellulose component and 37.9% synthetic polymer component was used. The cellulose component was composed of cotton fibers and the synthetic polymer component was composed of PET fibers. Content of other components included in the textile waste was below 0.1%. In all four examples, the blended textile waste was comminuted and subsequently treated in an alkaline aqueous treatment medium, where NaOH was used as a hydrolyzing agent. The temperature during the treatment of step b) was held at 150° C. for different durations. Additionally, NaOH concentrations were varied between 70 g/kg and 110 g/kg of blended textile waste. All NaOH concentrations were chosen, such that after the treatment of the blended textile waste in the aqueous alkaline treatment medium, no residual NaOH was present in the spent aqueous treatment medium.

[0059] The results of the Examples A to C are summarized in Table 1.

Examples D to G

[0060] In examples D, E, F and G, a method for producing a recycled cellulose raw material was employed equivalently as for examples A to C. In examples D and F, a mixed blended textile waste with a composition of 84% cellulose component and 16% synthetic polymer component was used. The cellulose component was composed of cotton fibers and the synthetic polymer component was composed of PET fibers. In examples E and G a blended textile waste from white shirts was used, which comprised 88.2% cellulose component and 11.8% synthetic polymer component. Contents of other residual components in all examples were determined to be below 0.1%. In all four examples, the blended textile waste was comminuted and subsequently treated in an alkaline aqueous treatment medium, where NaOH was used as a hydrolyzing agent. In examples D, E and G, the temperature during the treatment of step b) was held at 150° C. for different durations between 60 min and 180 min. In example F, the temperature was held at 130° C. for a duration of 150 min. The NaOH concentrations in all examples E to G were varied between 100 g/kg and 200 g/kg of blended textile waste, such that the ratio between amount of base and amount of hydrolytically cleavable bonds (n.sub.agent/n.sub.bonds) was between approximately 1.5 and 4. Thus, residual NaOH was present in the spent aqueous treatment medium after obtaining the recycled cellulose raw material.

[0061] The results of the Examples E to G are summarized in Table 1.

Example H

[0062] In example H, a method for producing a recycled cellulose raw material was employed equivalently as for the above mentioned examples A to G, whereby a blended textile waste from shirts with a composition of 81.4% cellulose component and 18.6% synthetic polymer component was used. The cellulose component was composed of cotton fibers and the synthetic polymer component was composed of PET fibers. The content of other residual components was below 0.1%. The blended textile waste was comminuted and subsequently treated in an alkaline aqueous treatment medium, where NaOH was used as a hydrolyzing agent. Additionally, in example H, the treatment in step b) was carried out under reducing conditions, whereby sodium dithionite (Na2S2O4) was used as a reducing agent in the aqueous treatment medium in a concentration of 50 g/kg of blended textile waste. The temperature during the treatment was held at 130° C. for a duration of 120 min. The NaOH was selected to 150 g/kg of blended textile waste.

[0063] The results of example H are shown in Table 2.

Comparative Examples U, V and W

[0064] For comparison, in examples U, V and W, a method for producing a recycled cellulose raw material was employed in a similar manner as described above, however, where the temperature during the treatment was held below 100° C. In the examples U to W, blended textile wastes from mixed sources with different compositions were used: in example U, the blended textile waste comprised 76.5% cellulose component and 23.5% synthetic polymer component; in example V, the blended textile waste comprised 84.0% cellulose component and 16.0% polymer component; and in example W, the blended textile waste comprised 89.8% cellulose component and 10.2% synthetic polymer component. Content of other residual components in all examples U to W were below 0.1%. In all three comparative examples, the blended textile waste was comminuted and subsequently treated in an alkaline aqueous treatment medium, where NaOH was used as a hydrolyzing agent, with a temperature during the treatment of step b) of 90° C. for a duration of 120 min. In examples V and W, additionally, the treatment in step b) was carried out under reducing conditions, whereby sodium dithionite (Na.sub.2S.sub.2O.sub.4) was used as a reducing agent in the aqueous treatment medium in a concentration of 50 g/kg of blended textile waste.

[0065] The results of comparative examples U, V and W are summarized in Table 2.

TABLE-US-00001 Examples A to G A B C D E F G Blended textile waste: Cotton content [wt.-%] 62.1 62.1 62.1 84.0 88.2 84.0 88.2 PET content [wt.-%] 37.9 37.9 37.9 16.0 11.8 16.0 11.8 other [wt.-%] <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 Treatment conditions: temperature [° C.] 150 150 150 150 150 130 150 duration [min] 150 90 210 150 180 150 60 NaOH conc. [g/kg] 70 110 110 100 100 200 200 n.sub.agent/n.sub.bonds 0.44 0.70 0.70 1.50 2.03 3.00 4.07 Cellulose raw material PET content [wt.-%] 27.6 27.6 33.1 <0.4 <0.7 <0.5 <0.7 PET reduction [%] 12.7 27.2 36.7 >97.5 >94.0 >97.0 >94.0 Cellulose yield [%] 78.3 96.0 96.7 90.2 86.9 90.5 89.4 Intrinsic viscosity [ml/g] 637 659 622 821 776 911 826 Excess NaOH [g/l] — — — 0.4 1.0 8.8 10.8

TABLE-US-00002 TABLE 2 Example H and comparative examples U to W U V W H (comp.) (comp.) (comp.) Textile waste: Cotton content [wt.-%] 81.4 76.5 84.0 89.8 PET content [wt.-%] 18.6 23.5 16.0 10.2 Other [wt.-%] <0.1 <0.1 <0.1 <0.1 Alkaline treatment: Temperature [° C.] 130 90 90 90 Duration [min] 120 120 120 120 NaOH conc. [g/kg] 15.0 15.0 15.0 15.0 n.sub.agent / n.sub.bonds 1.94 1.53 2.25 3.53 Reducing agent [g/kg] 50 — 50 50 Cellulose raw material PET content [wt.-%] 4.3 20.2 13.1 9.5 PET reduction [%] 81.1 22.1 28.9 16.4 Cellulose yield [%] 96.2 94.6 89.9 90.4