METHOD FOR DECOLORING OF A TEXTILE MATERIAL

Abstract

The invention concerns a method for decoloring of a textile material, the method comprising the steps of: providing a textile material; providing an alkaline solution containing one or more anionic polyelectrolytes; treating the textile material in the alkaline solution during a treatment period; and recovering at least some of the textile material from the alkaline solution.

Claims

1. A method for decoloring of a textile material, the method comprising the steps of: providing a textile material, at least a portion of the textile material being colored; providing an alkaline solution containing one or more anionic polyelectrolytes; treating the textile material in the alkaline solution during a treatment period of at least 10 minutes at a temperature in the range of from 100 C. to 180 C.; and recovering at least some of the textile material from the alkaline solution after the treatment period.

2. The method according to claim 1, wherein the one or more anionic polyelectrolytes is/are selected from the group: carboxymethyl cellulose (CMC); carboxyalkyl ethers of cellulose, starch, amylose, amylopectin and/or natural gums; polyacrylic acid; polymaleic acid; acrylic acid maleic acid copolymer; polymethacrylic acid; polymers of naphthalene sulfonic acids; sulfonated polystyrene; and polyethylene sulfonate.

3. The method according to claim 1, wherein the one or more anionic polyelectrolytes has a concentration in the alkaline solution of at least 0.01% (weight) in relation to a dry weight of the textile material.

4. The method according to claim 3, wherein the one or more anionic polyelectrolytes has a concentration in the alkaline solution of 1.5% (weight) or less.

5. The method according to claim 1, wherein the one or more anionic polyelectrolytes comprises carboxymethyl cellulose (CMC) and wherein the concentration of the carboxymethyl cellulose (CMC) in the alkaline solution is at least 0.01% (weight) in relation to a dry weight of the textile material.

6. The method according to claim 1, wherein the alkaline solution has a pH above 11.

7. The method according to claim 1, wherein the alkaline solution has a basicity corresponding to at least 0.2 g dissolved sodium hydroxide (NaOH) per liter of the alkaline solution.

8. The method according to claim 1, wherein the alkaline solution has an effective alkali (EA) concentration of at least 0.2 g calculated as sodium hydroxide (NaOH) equivalents.

9. The method according to claim 1, wherein the alkaline solution comprises sulfide.

10. The method according to claim 8, wherein the alkaline solution has a sulfidity S (%) of at least 1%, wherein the sulfidity is calculated as S (%)=100(weight of Na.sub.2S)/(total weight of NaOH+Na.sub.2S).

11. The method according to claim 9, wherein the alkaline solution has a total content of sulfide that is at least 0.01 g per liter.

12. The method according to claim 1, wherein the alkaline solution contains industrial white liquor.

13. The method according to claim 1, wherein the treatment period is at least 30 min.

14. The method according to claim 1, wherein the alkaline solution has, at least during a portion of the treatment period, a temperature in the range of 110 C. to 180 C.

15. The method according to claim 1, wherein the textile material comprises cellulosic fibers.

16. The method according to claim 1, wherein the textile material comprises polyester fibers.

17. The method according to claim 1, wherein the method comprises the step of mechanically disintegrating the textile material before treating it in the alkaline solution.

18. A method for recycling of a textile material, wherein the method comprises steps according to claim 1.

19. A textile material recovered from a method according to claim 1.

20. (canceled)

21. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0049] In the description of the invention given below reference is made to the following figures:

[0050] FIG. 1. Reference example with sodium dithionite. The ratio k/s calculated from reflectance using D65/10.

[0051] FIG. 2. The effect of CMC in white liquor. The ratio k/s calculated from reflectance as described using D65/10.

[0052] FIG. 3. The effect of different levels of addition of CMC using white liquor (D65/10).

[0053] FIG. 4. The effect of different levels of addition of CMC using NaOH (D65/10).

[0054] FIG. 5. Effect of different types of CMC in decoloring a dyed textile mixture using white liquor with and without CMC. The ratio k/s calculated from reflectance using D65/10.

[0055] FIG. 6. Effect of added CMC in decoloring a dark blue pigmented textile using white liquor as alkali source. The ratio k/s calculated from reflectance using D65/10.

[0056] FIG. 7. Effect of added CMC in decoloring a dark blue pigmented textile comparing NaOH and white liquor (WL) as alkali source. The ratio k/s calculated from reflectance using D65/10.

[0057] FIG. 8. Effect of added CMC in decoloring a blue denim textile using white liquor with and without CMC. The ratio k/s calculated from reflectance using D65/10.

[0058] FIG. 9. Effect of added CMC in decoloring a dyed textile mixture using white liquor with and without CMC. The ratio k/s calculated from reflectance using D65/10.

DESCRIPTION OF EXAMPLES

[0059] In the following it will, for instance, be described some experiments showing the effects of the decoloring method as disclosed herein.

Example 1Reference Example

[0060] A polycotton bed sheet (polyester and cotton) with printed blue parts (lines) was separated into a blue-enriched fraction (by cutting out these parts). The samples were mechanically disintegrated and treated with an aqueous solution of sodium dithionite at two different pH-levels together with a reference without dithionite addition (Sample 1.3). To the sample with low pH sodium acetate, 5 g/l, was added, and to the sample with high pH sodium carbonate, 5 g/l, was added. This experiment was performed as a reference experiment since sodium dithionite is commonly used for removing color from textiles.

[0061] The treatments were performed using 5 g (dry) of textile material and a liquor to textile ratio of 40:1 liter/kg and with an addition of sodium dithionite of 2.5% on textile weight. The temperature during the treatments were 70 C. and the duration was 60 minutes. The samples were washed with water and the optical properties were evaluated using a Minolta Spectrophotometer CM-3630. The samples used for optical evaluation were prepared according to ISO 36:88. The reflectance values over the measured wavelengths (360-740 nm with spatial resolution of 10 nm) were used as such but also converted to the ratio between the light absorption coefficient (k) and the light scattering coefficient (s) using the Kubelka-Munk relation k/s=(1-R.sub.).sup.2/2/R.sub.. The benefit of recalculating to k/s is that this ratio is linearly correlated to the chromophore concentration (at the same s) which the reflectance is not. Also, the CIELAB Lab-values give important information on color and were determined. In some cases, the C/2 illuminant/observer is used (ISO-brightness etc.) but in other cases it is interesting to look at the D65-values especially in relation to fluorescent structures like optical brightening agents (due to higher amount of UV-radiation in D compared to C illuminant). The experimental details and results can be seen in Table 1. Treatment with dithionite is clearly inefficient for removing the color from the textiles.

TABLE-US-00001 TABLE 1 Experimental overview and results for Example 1. The optical properties reported were measured using C/2 illuminant and observer. Sodium R.sub.457 Material pH dithionite (%) L* a* b* Starting Enriched 71.58 82.38 7.14 9.06 material blue Sample 1.1 Enriched 5.95 YES 72.18 82.29 6.47 9.72 blue Sample 1.2 Enriched 10.65 YES 72.96 82.84 5.80 9.44 blue Sample 1.3 Enriched 6.30 NO 70.56 82.12 6.80 8.66 blue

[0062] Based on the effect on brightness (R.sub.457) and L*a*b*-values the treatments are almost without effect. When looking at the UV-VIS-absorption using k/s (FIG. 1) there is a very small effect in the visible region at longer wavelengths. The reference treatment with water is as efficient as the treatment with dithionite at lower pH but the treatment at pH 10.65 gives an additional small benefit compared to the others.

Example 2

[0063] The same material, enriched blue, was treated in autoclaves in a hot-air oven (CAS 420 Autoclave Oven, manufactured by CRS Reactor Engineering AB, Sweden, equipped with acid resistant steel 1.4433 autoclaves, with a volume of 3 liters each). The following procedure was applied: 100 g (dry) textile material was added to an alkaline aqueous solution containing 0 or 1% CMC (carboxymethyl cellulose) on textile weight in the form of Blanose 7MC (Ashland Inc.), with a liquor:textile=9:1 (kg/kg) and an effective alkali addition of 34.5% based on textile weight (diluted industrial white liquor; EA=38.3 g/l, sulfidity=34%). The heating from 25 C. to 70 C. was performed at a constant rate of 0.75 C./min. After 15 minutes stabilization of the temperature at 70 C., the temperature was raised with 0.75 C./min to the final temperature of 140 C. and holding time at maximum temperature=60 minutes. After cooling the samples were washed thoroughly with deionized water, see results in Table 2. The optical properties were evaluated as in Example 1.

TABLE-US-00002 TABLE 2 Results for Example 2. The optical properties are measured using C/2 illuminant and observer. Material CMC R.sub.457 (%) L* a* b* Starting Enriched 71.58 82.38 7.14 9.06 material blue Sample Enriched NO 87.53 93.96 1.63 1.77 2.1 blue Sample Enriched YES 89.24 95.35 1.18 0.6 2.2 blue

[0064] The effect of CMC is further exemplified in FIG. 2. The reference is still clearly blue, but when CMC is added the k/s-ratio is decreased, showing much more color removal.

[0065] The same blue-enriched material used in Example 1 were used in Example 2 and the k/s-ratios of the recovered material after treatment using dithionite in Example 1, is at least an order of magnitude larger than those reported for the alkaline treatment in combination with CMC.

Example 3

[0066] To further investigate the effect of CMC another sample of blue-enriched polycotton was used with different addition levels of CMC (Blanose 7MC) was tried (0.1; 0.5 and 1% on textile weight). The experiment was performed according to the method in Example 2 and the optical properties evaluated according to the method in Example 1.

TABLE-US-00003 TABLE 3 Results for Example 3. WL stands for industrial white liquor. The optical properties reported were measured using C/2 illuminant and observer. CMC (% on textile weight R.sub.457 (%) L* a* b* Starting material 76.41 86.65 3.5 5.76 Sample 3.1 0 88.56 94.14 1.29 2.24 Sample 3.2 0.1 89.94 95.24 0.68 1.31 Sample 3.3 0.5 90.10 95.47 0.51 1.02 Sample 3.4 1 90.61 95.53 0.47 1.29

[0067] As can be seen in FIG. 3, the addition of such a small amount of CMC as 0.1% based on textile weight gives a large effect, there is a larger effect at 0.5%, but 1% does only improve the blue pigment removal to a very low degree in the short wavelengths. This show that only a rather small amount of CMC is needed to reach maximum effect.

Example 4

[0068] To further investigate the effect of CMC (Blanose 7MC) in combination with NaOH, the same material as in Example 3, consisting of blue-enriched polycotton was used. Apart from the fact that the alkali source was pure NaOH the experiments were performed according to Example 2 and the results evaluated according to Example 1.

TABLE-US-00004 TABLE 4 Results for Example 4. The optical properties reported were measured using C/2 illuminant and observer. CMC (% on textile weight R.sub.457 (%) L* a* b* Starting material 76.41 86.65 3.5 5.76 Sample 4.1 0 87.72 92.95 1.94 3.64 Sample 4.2 1 88.70 93.67 1.39 3.10

[0069] The effect of CMC is clear also in combination with pure NaOH and this is also made visual in FIG. 4, where the k/s-ratio is shown for pure NaOH with and without addition of CMC.

Example 5

[0070] Different types of CMC have different molecular weights and different degrees of substitution (DS). This influences the solubility and dispersing ability mainly due to differences in charge density. To investigate the effect of different CMC types, the following trials on another batch of enriched blue polycotton textile were performed. The experiment was performed according to the method in Example 2 but with 30 g (dry) textile material and the optical properties evaluated according to the method in Example 1. Commercial CMC grades Blanose 7LC, Blanose 7MC, Blanose 7HC from Ashland were tried together with Nymcel ZSB-10 from Noviant/CP Kelco and Niklacell P70 UC from Mare. The samples named Blanose have a degree of substitution at 0.65-0.9 with varying molecular weights (L=low molecular weight, M=medium molecular weight and H=high molecular weight). Nymcel ZSB-10 has a low degree of substitution (DS=0.2) with medium molecular weight and Niklacell P70 UC a degree of substitution of 0.5-0.65, with medium to high molecular weight. The results are summarized in Table 5 and show that all of the different types of CMC are effective in removing color.

TABLE-US-00005 TABLE 5 Results for Example 5. The optical properties reported were measured using C/2 illuminant and observer. CMC R.sub.457 (%) Line in FIG. 5 Sample 5.1 Blanose 7LC 83.70 Sample 5.2 Blanose 7MC 84.00 Sample 5.3 Blanose 7HC 81.81 Sample 5.4 Nymcel 84.01 Sample 5.5 Niklacell P70 UC 84.91 Sample 5.6 No CMC, WL 79.93

[0071] The beneficial effect of CMC is seen for all types of tested CMC with small differences between them. The highest effect is seen with Niklacell P70 UC and the smallest effect with Blanose 7HC with the remaining three in between but closer to Niklacell P70 UC.

Example 6

[0072] To exemplify the effect of the treatment on pigment-colored textiles an Example of a commercial pigmented cotton shirt was procured (Stenstrms Navy Pigment Dyed Polo Shirt, Art nr: 4400112480190), mechanically disintegrated, and treated according to the procedure in Example 2, but with g (dry) textile material.

[0073] After the treatment the resulting material was washed, and the optical properties evaluated according to the method in Example 1. As can be seen in Table 6 and FIGS. 6, a clear beneficial effect of the added CMC was noted. In FIG. 7 the addition of HS in the WL show an improved effect compared to when only treating the textile with pure NaOH.

TABLE-US-00006 TABLE 6 Results for Example 6. The optical properties reported were measured using C/2 illuminant and observer. R.sub.457 Material CMC Alkali (%) L* a* b* Sample 6.1 Untreated 8.72 27.30 0.21 13.93 Dark blue Sample 6.2 Dark blue NO WL 82.43 94.31 0.35 2.71 Sample 6.3 Dark blue YES WL 83.02 94.56 0.40 2.70 Sample 6.4 Dark blue YES NaOH 79.92 93.42 0.14 3.17

Example 7

[0074] In order to investigate the influence of the treatment on textile colored by other dyes than pigments a denim textile and a mixture of many common and dyed textiles were treated with white liquor with and without CMC. The same procedure as in Example 2 was used to treat the samples, but with 40 g (dry) textile material, and the analysis of the optical properties was performed according to the procedure in Example 1. As can be seen in FIGS. 8 and 9 the effect of CMC is significant and positive also for these colored materials.

TABLE-US-00007 TABLE 7 Sample list for Example 7. The optical properties reported were measured using C/2 illuminant and observer. Material CMC R.sub.457 (%) Starting material Denim 18.37 Sample 7.1 Denim NO 23.40 Sample 7.2 Denim YES 26.57 Starting material Mixture 8.72 Sample 7.3 Mixture NO 19.33 Sample 7.4 Mixture YES 20.63

[0075] Examples of Industrial Processes

[0076] In one example the decoloring method as disclosed herein forms part of a method for recycling of reclaimed textile material. The recycling method may additionally provide for separation and recovery of a cellulosic part from a material blend of polyester and cellulose, making use of CMC so as to provide for decoloring.

[0077] In this exemplified process the following apply: [0078] Textile material: a mix of reclaimed textile material including around 50% polyester and around 50% cotton; a portion of the textile material to be treated is colored; [0079] Mechanical treatment for disintegration of the textile material [0080] Volume of alkaline aqueous solution in relation to dry weight of textile material: 9:1 (i.e. 9 l/kg); [0081] Concentration of certain species in the alkaline solution: effective alkali concentration (NaOH): 38 g/l; sulfidity S (%) 36%; CMC 1% (weight) in relation to the dry weight of the textile material; [0082] The alkali used in the treatment originates from white liquor obtained from a Kraft pulp process; [0083] The process/method includes a step of adding CMC to the alkaline solution so as to obtain the desired concentration. [0084] The temperature during treatment of the textile material in the alkaline solution containing CMC is adjusted to around 140 C. [0085] The treatment period can be adapted to the particular situation, but in a typical industrial situation the temperature is maintained at 140 C. for 1-2 hours. [0086] After the treatment period, the recovered fibers are separated from the treatment solution. [0087] The process/method may also include additional cleaning and/or purification process steps for handling of the recovered cellulose-containing textile material, such as bleaching of a recovered cellulosic part, washing, screening and adjustment of a degree of polymerization of the recovered cellulosic part, and drying.

[0088] The recovered cellulose-containing textile material can be used to produce molded bodies, such as fibers, to produce new textile material.

[0089] Various variations of the above example are possible. For instance, the aqueous treatment solution may be a mix of white and black liquor obtained from the Kraft pulp process. Moreover, instead of obtaining the alkaline solution from a Kraft pulp process, it is possible to obtain the alkaline solution by dissolution of sodium hydroxide and sodium sulfide salts. Further, as an alternative or complement to CMC, the solution may contain one or more other polyelectrolyte(s). Also, other concentrations of the species in the alkaline solution may be used and e.g., treatment temperature and time can be varied and adjusted to the particular application.

[0090] The invention is not limited by the embodiments described above but can be modified in various ways within the scope of the claims.