METHOD FOR PRODUCING REGENERATED CELLULOSE FIBERS FROM COTTON CONTAINING TEXTILE WASTE

Abstract

The invention relates to a method for regenerating cellulose fibers from cotton-containing textile, wherein the degree of polymerization (DP) of cellulose in cotton is reduced by using a DP decreasing agent, which is an endo-cellulase of the type EC Number 3.2.1.4, together with mechanical energy. The DP of cellulose in cotton is reduced to under 1500, which makes it particularly suitable for the following steps, especially the spinning step. The cellulose is further dissolved using cellulose solvent comprising NMMO or an aqueous mixture of NMMO and the obtained cellulose-containing liquid is subjected to a spinning process to produce cellulose fibers.

Claims

1. A method for producing regenerated cellulose fibers from cotton-containing waste textile comprising cellulose having a degree of polymerization (DP) within the range of 1500-3000, comprising the steps of: (a) decreasing the DP of cellulose from waste cotton to under 1500 by subjecting cotton-containing waste textile to an endocellulase of the type EC 3.2.1.4 and applying mechanical energy; (b) adding a cellulose solvent comprising N-methyl morpholine N-oxide (NMMO) or an aqueous mixture of NMMO to obtain a cellulose-containing liquid; and (c) subjecting the cellulose-containing liquid to a cellulose spinning process to produce cellulose fibers.

2. The method according to claim 1, wherein mechanical energy is applied simultaneously with the treatment with endocellulase.

3. The method according to claim 1, wherein applying mechanical energy comprises applying a high shearing or impact energy.

4. The method according to claim 1, wherein the cotton-containing textile comprises more than 85 wt. % cellulose, preferably -cellulose.

5. The method according to claim 1, wherein the textile comprises both cotton and synthetic fibers.

6. The method according to claim 5, wherein the synthetic fibers comprise polyethylene terephthalate, polypropylene and/or polyamides, preferably polyethylene terephthalate.

7. The method according to claim 1, comprising prior to step (a) reducing the cotton-containing textile in size to a fiber size of 5 mm or less.

8. The method according to claim 1, wherein in step (b) an anti-oxidant is added, preferably propylgallate.

9. The method according to claim 1, wherein the cellulose solvent is N-methyl morpholine N-oxide.

10. The method according to claim 1, wherein in step (c) the cellulose-containing liquid is pumped through spinnerets, following by washing and drying of the obtained fibers.

Description

EXAMPLE 1: ENZYMATIC REDUCTION OF THE DP

Method

[0034] In this example, 500 mg cellulose sample fine industrial cotton waste with an initial DP of 1967 was weighed and added into a 50 ml plastic tube. 20 ml of buffered enzyme solution (enzymes are specified below) was prepared and poured over the cellulose in the tube. The mechanical energy was supplied by adding 10 V4A steel balls with a diameter of 6 mm were added to the tube and the tube was placed into a 500 ml beaker a beaker dyeing system LABOMAT, Mathis AG. In total, two centrifuge tubes were placed in one beaker and the beaker was filled with warm water for heat transfer. The metal beakers were placed into the beaker dyeing system LABOMAT, Mathis AG. The reaction mixture was rotated for 6 hours at 40 rpm at the indicated temperature.

[0035] After the indicated time the cellulose was filtered off on a glass filter, washed with 520 ml soft water and 310 ml acetone and dried on air. The DP of the cellulose sample was then determined according to DIN 54270.

Results

[0036] When exo-acting cellulase (Cellobiohydrolase I from Hypocrea jecorina, EC Number 3.2.1.91 Sigma Aldrich, process conditions: 7.7 U for 500 mg cellulose, 100 mM acetate buffer, pH 5.0, 50 C.) is used as the enzyme, the measured DP is 1869 (5%). Hard clusters of fibers are formed and the cellulosic sample is not well dispersed in the buffer.

[0037] When endo-acting cellulase (endo-1,4--D-Glucanase from Aspergillus sp., EC Number 3.2.1.4, Sigma Aldrich, process conditions 7.7 U for 500 mg cellulose, 100 mM phosphate buffer, pH 7.0, 50 C.) is used as the enzyme, the measured DP is 1435 (27%). The cellulosic sample is finely dispersed in the buffer.

[0038] When endo-acting cellulase (EC Number 3.2.1.4, NS59006, Novozymes, process conditions: 4% on sample weight, 100 mM phosphate buffer, pH 7.0, 45 C.) is used as the enzyme, the measured DP is 1208 (39%). The cellulosic sample is finely dispersed in the buffer.

EXAMPLE 2: SYNERGISTIC EFFECT OF ENZYMES AND MECHANICAL ACTION

Method

[0039] In this experiment, 500 mg cellulose sample fine industrial cotton waste with an initial DP of 1740 was weighed and added into a 50 ml plastic tube. 20 ml of buffered enzyme solution (enzymes are specified below) was prepared and poured over the cellulose in the tube. The mechanical energy was supplied by adding 10 V4A stainless steel balls with a diameter of 6 mm were added to the tube and the tube was placed into a 500 ml beaker a beaker dyeing system LABOMAT, Mathis AG. In total, two centrifuge tubes were placed in one beaker and the beaker was filled with warm water for heat transfer. The metal beakers were placed into the beaker dyeing system LABOMAT, Mathis AG. The reaction mixture was rotated for 6 hours at 40 rpm at the indicated temperature.

[0040] After the indicated time the cellulose was filtered off on a glass filter, washed with 520 ml soft water and 310 ml acetone and dried on air. The DP of the cellulose sample was then determined according to DIN 54270.

[0041] When endo-acting cellulase (EC Number 3.2.1.4, NS59006, Novozymes, process conditions: 4% on sample weight, 500 mM phosphate buffer, pH 7.0, 45 C.) is used as the enzyme, without 10 V4A steel balls the measured DP is 1538 (12%). The cellulosic sample is hardly dispersed in the buffer.

[0042] When no enzyme is added to the tube the measured DP after the treatment with the 10 V4A steel balls is 1672 (4%). Hard clusters of fibers are formed and the cellulosic sample is not well dispersed in the buffer.

[0043] It can be concluded that only the combined action of enzyme and mechanical action on cotton waste textile results in a significant reduction of the degree of polymerization of the cellulose contained therein. The synergistic action of enzyme and mechanical action is also required to achieve a finely dispersed sample in the reaction mixture.

EXAMPLE 3: FIBER SIZE REDUCTION

[0044] White towels containing 901% cellulosic material and 101% polyester, were used as a substrate for milling. The fiber length before milling is equal to cotton and PET fiber length in yarn for towels (approximately 15 to 40 mm). The fiber length after milling is equal to the screen of the mill. In this case the screen size was 4 mm. A mill from Alpine was used. Other suitable mills include Alpine Rotoplex granulator or a shredder like Alpine DuraLine. Important is a screen of the desired size (<5 mm). Even smaller fiber sizes could be realized with mills like Alpine Fine Cutting Mill AFS.

EXAMPLE 4: EFFECT OF FIBER LENGTH ON DISSOLUTION OF CELLULOSE FIBERS IN NMMO

[0045] In a typical experiment, cellulose waste fibers with different fiber length and DP 1200-1300 were dried for 60 minutes at 100 C. 2.0 g of the cellulose waste was stirred overnight in 50 ml demineralized water. The next morning the cellulose waste was filtered off and added into a 250 ml three necked round-bottom flask equipped with an overhead stirrer and vacuum distillation equipment. 40 g of a NMMO solution in water (50 wt. %) and 10 mg of propylgallate were added into the flask. The mixture was stirred at low speed and heated to 100 C. The water in the mixture was distilled off by the use of a variable under pressure.

[0046] The final percentage of cellulose in NMMOxH.sub.2O was: 2 g cellulose in 23 g NMMOxH.sub.2O=8%.

Results

[0047] For the fiber length of 20-50 mm: winding of the long fibers around the axis of the overhead stirrer hamper dissolving the material. This material can still be identified as fibers with naked eye and on a microscope picture that was taken from the solution.

[0048] For the fiber length of <4 mm: the material is finely dispersed in the NMMO solution. After dissolution the solution is homogeneous without solid parts. No fibers can be identified in a microscope picture.

The experiments were repeated on a larger scale.

Method

[0049] The solution preparation took place in a laboratory kneader, starting from an aqueous suspension of the pressed out pulp in 50 wt-% aqueous NMMO through removal of the water by means of heating, shearing and vacuum during the solution process (75-99 C. mass temperature, 770-40 mbar vacuum, 5-15 rpm). After this dissolution step and water removal, an after-dissolution time of 1 h for further homogenization of the dope followed (90 C. mass temperature, 260 mbar, 15 rpm).

[0050] Material with fiber length5 mm (here: 5-20 mm) (DP 482): The preparation of 13.4% cellulose/NMMO solutions on larger scale with cellulosic material having a fiber length5 mm gave rise to major problems during dissolution even causing deformation of the stirring equipment through the formation of fiber clusters in the mixture.

[0051] Material with fiber length4 mm (DP 460): After enzymatic treatment of the material from the first experiment the material had a shorter fiber length4 mm. This material caused no problems like cluster formations or winding of fibers around the stirring equipment during dissolution and showed improved processability.