Method of treating cellulose pulp

Abstract

Disclosed is a method of treating cellulose pulp for use in regeneration of cellulose including the steps of: i) preparing an alkaline metal hydroxide solution having a concentration of 4-10% by weight; ii) adding cellulose pulp to form a slurry; iii) heating the slurry to a temperature of 40-100 C.; and iv) dissolving the treated cellulose pulp in an alkaline solution having a temperature within the range of 10 C. to 12 C.; wherein the percentage by weight is based on the total weight of the slurry.

Claims

1. A method of treating cellulose pulp for use in regeneration of cellulose, characterized in that said method comprises the steps of: i) preparing an alkaline metal hydroxide solution having a concentration of 4-10% by weight; ii) adding cellulose pulp to form a slurry; iii) heating said slurry to a temperature of 40-100 C.; and iv) dissolving the treated cellulose pulp in an alkaline solution having a temperature within the range of 10 C. to 12 C.; wherein the percentage by weight is based on the total weight of said slurry.

2. The method according to claim 1, wherein said slurry has a cellulose content of 3-40% by weight, based on the total weight of said slurry.

3. The method according to claim 1, wherein the cellulose content in the alkaline solution of step iv) is at least 4% by weight, based on the total weight of said slurry.

4. The method according to claim 1, wherein the cellulose pulp is a dissolving pulp.

5. The method according to claim 1, wherein the alkaline metal hydroxide solution is prepared to a concentration of 5-8% by weight, based on the total weight of said slurry.

6. The method according to claim 1, wherein the alkaline metal hydroxide is NaOH.

7. The method according to claim 1, wherein the cellulose slurry, in step iii) is heated for a time period of 0.5-24 hours.

8. The method according to claim 1, wherein said method comprises the steps of: i) preparing an alkaline metal hydroxide solution having a concentration of 4-10% by weight; ii-a) adding cellulose pulp to form a slurry having a cellulose content of 3-10% by weight; iii-a) heating said slurry from step ii-a) to a temperature of 40-100 C. for a first time period; ii-b) increasing the cellulose content in the slurry to a cellulose content of 10-40% by weight; iii-b) heating said slurry from step ii-b) to a temperature of 40-100 C. for a second time period; and iv) dissolving the treated cellulose pulp in an alkaline solution having a temperature within the range of 10 C. to 12 C.; wherein the percentages by weight are based on the total weight of said slurry.

9. The method according to claim 8, wherein said first time period is 5-30 minutes.

10. The method according to claim 8, wherein said second time period is 0.5-24 hours.

11. The method according to claim 1, wherein an accelerator is added during the treatment.

12. The method according to claim 11, wherein said accelerator comprises at least one of manganese salt, cobalt salt, ferrous(II) salt, ferric (III) salt, and copper(II) salt, and wherein said at least one accelerator is added to the cellulose pulp before adding the cellulose pulp to the prepared alkaline metal hydroxide solution to form the slurry.

13. The method according to claim 11, wherein said accelerator comprises at least one of oxygen, and peroxides, and wherein said at least one accelerator is added to the slurry in step iii).

14. The method according to claim 1, wherein said slurry in step iii) or further is subjected to an overpressure within the range of 5-15 bar.

15. The method according to claim 8, wherein said cellulose slurry in step iii-a) has a cellulose content of 4-8% by weight, based on the total weight of said slurry.

16. The method according to claim 1, wherein said cellulose slurry in step iii) has a cellulose content of 15-35% by weight, based on the total weight of said slurry.

17. The method according to claim 1, wherein said slurry, in step iii) is heated to a temperature within the range of 5090 C.

18. The method according to claim 1, wherein treated cellulose pulp, between step iii) and step iv), is subjected to swelling.

19. The method according to claim 18, wherein the swelling is performed by incubating the treated cellulose pulp in an alkaline solution at a reduced temperature of >0 C.

20. The method according to claim 1, wherein said slurry, after completion of step iii), is subjected to washing and thereafter drying.

21. A cellulose pulp treated according to the method according to claim 1.

22. The method according to claim 1, wherein the cellulose slurry, in step iii) is heated for a time period of 2-10 hours.

23. The method according to claim 8, wherein said first time period is 10-15 minutes.

24. The method according to claim 8, wherein said second time period is 2-10 hours.

25. The method according to claim 8, wherein said cellulose slurry in step iii-b) has a cellulose content of 15-35% by weight, based on the total weight of said slurry.

26. The method according to claim 8, wherein said slurry, in step iii-a) and iii-b), is heated to a temperature within the range of 50-90 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the tensile strength for fibres from cellulose dope (A) being stretched 0%, 40% and 50%, left staple representing fibres spun in the carbonate based coagulation solution, and right staple representing fibres spun in the sulphuric acid based coagulation solution.

(2) FIG. 2 shows the tensile strength for fibres from cellulose dope (B) being stretched 0%, 40% and 50%, left staple representing fibres spun in the carbonate based coagulation solution, and right staple representing fibres spun in the sulphuric acid based coagulation solution.

(3) FIG. 3 shows the elongation (%) for fibres from cellulose dope (A) being stretched 0%, 40% and 50%, left staple representing fibres spun in the carbonate based coagulation solution, and right staple representing fibres spun in the sulphuric acid based coagulation solution.

(4) FIG. 4 shows the elongation (%) for fibres from cellulose dope (B) being stretched 0%, 40% and 50%, left staple representing fibres spun in the carbonate based coagulation solution, and right staple representing fibres spun in the sulphuric acid based coagulation solution.

(5) FIG. 5 shows the tensile strength (cN/tex) and titre (dtex) for all fibres from the tensile test of fibres from the cellulose dope (B). The staples represent the tensile strength, the triangular dots represent the carbonate titre, and the crosses represent the sulphuric acid titre.

(6) FIG. 6 shows the molecular weight distributions for the three different treated cellulose pulps. The line marked with A shows the molecular weight distribution for the cellulose pulp treated with HCl, the line marked with B shows the molecular weight distribution for the cellulose pulp treated with 8% by weight of NaOH, and the line marked with C shows the molecular weight distribution for the cellulose pulp treated with 7% by weight of NaOH.

DETAILED DESCRIPTION

(7) The present invention will now be described more fully hereinafter with reference to the accompanying drawings.

(8) The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and to fully convey the scope of the invention to the skilled addressee.

(9) When using a dissolving process with cold alkaline solution having a temperature within the range of 10 C. to 12 C. (step (iv)), some sort of treatment is necessary in order to lower the viscosity of the cellulose pulp.

(10) Commercial dissolving pulp normally has a viscosity within the range of about 400 to 1200 dm.sup.3/kg. In order to be soluble within the cold alkaline solution process, a viscosity within the range of 200 to 250 dm.sup.3/kg is preferred to provide an effective dissolving. However, a viscosity of up to about 350 dm.sup.3/kg is also a possible option.

(11) However, when treating the cellulose pulp with an alkaline solution there might be a potential risk that the metastable cellulose I is transformed into the stable cellulose II, and this transfer from cellulose I to cellulose II is irreversible. Thus, the treatment has to be balanced in order to lower the viscosity of the cellulose pulp, but not create a transformation from cellulose I into cellulose II.

(12) In the below given examples the treated cellulose pulp is tested for further use in a dissolving process with cold alkaline solution.

EXAMPLE 1

(13) Sodium hydroxide solutions, with the below in Table 1 indicated concentrations were prepared. Cellulose pulp was added to form a slurry with a cellulose content of about 5% by weight. The slurry was heated to 50 C. for 10 minutes, and thereafter the cellulose content was increased by wash pressing the slurry to a cellulose content of about 30-40% by weight.

(14) Thereafter, the slurry was heated to 50 C. The heating was stopped at varying times for different samples of the treated cellulose pulp, and the cellulose pulp was cooled to stop further lowering of the viscosity thereof. The viscosity was measured for each sample.

(15) The treated cellulose pulp was allowed to swell over night in a 6% by weight NaOH solution and a cellulose content of 5% by weight at a temperature of >0 C.

(16) Thereafter the treated cellulose pulp was dissolved in 8% by weight sodium hydroxide (NaOH), and 0.8% zinc oxide (ZnO). The cellulose content was about 5% by weight. The slurry of cellulose pulp was continuously stirred at a temperature of about 8 C. for at least 10 minutes.

(17) Dissolution was detected by light microscopy both with and without polarized light.

(18) TABLE-US-00001 TABLE 1 NaOH Viscosity after (% by pretreatment Treatment time ID weight) (dm.sup.3/kg) (min) Dissolution 1 26 227 180 No dissolution was found, a lot of fibers shown in microscopic review 2 18 239 270 No proper dissolution was found, still a lot of fibers shown in microscopic review. 3 10 252 960 Dissolution was found, however some fibers remained non- dissolved.

(19) The treatments with 26% by weight and 18% by weight NaOH, respectively, resulted in no detectable dissolving of cellulose, which probably is due to the transformation of native cellulose I into the less dissolvable cellulose II.

(20) The treatment with 10% by weight worked, even though showing some fibers remaining after dissolving, but the treatment step as such required an undesirable long process time in order to reach the targeted viscosity range. Thus, the process efficiency may be improved further.

EXAMPLE 2

(21) In order to avoid the transformation of cellulose I into cellulose II, additional test was performed with lower concentrations of sodium hydroxide. However, as the process efficiency seems to decrease with decreased sodium hydroxide, an accelerator was provided to the treatment step.

(22) Sodium hydroxide solutions, with the below in Table 2 indicated concentrations was prepared. Cellulose pulp was added to form a slurry with a cellulose content of about 5% by weight. The slurry was heated to 50 C. for 10 minutes, and thereafter the cellulose content was increased by wash pressing the slurry to a cellulose content of about 30-40% by weight.

(23) Thereafter, the slurry was heated to 50 C. The heating was stopped at varying times for different samples of the treated cellulose pulp, and the cellulose pulp was cooled to stop further lowering of the viscosity thereof. The viscosity was measured for each sample.

(24) Accelerators were used in this example, pressurized O2, 5 bar or 15 bar, respectively, or a manganese salt, in form of MnSO.sub.4, in a concentration of 25 ppm or 100 ppm, respectively.

(25) When using pressurized O.sub.2 as accelerator, the treatment was made in an autoclave chamber, and the chamber was first evacuated to vacuum, and thereafter O.sub.2 was added to an overpressure of 5 bar O.sub.2 or 15 bar O.sub.2.

(26) When using manganese salt, the salt was added by applying a solution of the manganese salt to the cellulose pulp. This may be accomplished by spraying and/or mixing the solution onto/into the cellulose pulp.

(27) The treated cellulose pulp was allowed to swell over night in a 6% by weight NaOH solution and a cellulose content of 5% by weight at a temperature of >0 C.

(28) Thereafter the treated cellulose pulp was dissolved in 8% by weight sodium hydroxide (NaOH), and 0.8% zinc oxide (ZnO). The cellulose content was about 5% by weight. The slurry of cellulose pulp was continuously stirred at a temperature of about 8 C. for at least 10 minutes.

(29) Dissolution was detected by polarized light both with and without polarized light.

(30) TABLE-US-00002 TABLE 2 Viscosity NaOH after (% by pretreatment Treatment ID weight) Accelerator (dm.sup.3/kg) time (min) Dissolution 4 10 5 bar O.sub.2 219 360 Dissolution was found; some fibers remained undissolved. 5 8 15 bar O.sub.2 207 600 Dissolution was found; however some fibers remained undissolved, but less than in with 10% by weight of NaOH. 6 7 15 bar O.sub.2 230 840 Dissolution was found; however some fibers remained undissolved, but less than in with 8% by weight of NaOH. 8 6 100 ppm 234 960 Proper dissolving Mn.sup.2+ was found.

(31) The treatments with 10% by weight NaOH, 8% by weight NaOH, and 7% be weight NaOH worked, even though showing some fibers remained after dissolving.

(32) The treatments with 6% by weight NaOH provided proper dissolving, but again the treatment step as such required an undesirable long process time in order to reach the targeted viscosity range, even though using accelerators. Thus, the process efficiency may be improved further.

EXAMPLE 3

(33) In order to improve the efficiency of the treatment even further, the temperature was increased during the treatment.

(34) Thus, sodium hydroxide solutions having a concentration of 6% by weight were prepared. Cellulose pulp was added to form slurries with a cellulose content of about 5% by weight. The slurries were heated to 60 C. for 10 minutes, and thereafter the cellulose content was increased by wash pressing the slurries to a cellulose content of about 30-40% by weight.

(35) Thereafter, the slurries were heated to 60 C. The heating was stopped at varying times for different samples of the treated cellulose pulp, and the cellulose pulp was cooled to stop further lowering of the viscosity thereof. The viscosity was measured for each sample.

(36) The accelerators used in this example were pressurized O.sub.2 at 15 bar, and a manganese salt, in form of MnSO.sub.4, in a concentration of 100 ppm, or a combination thereof.

(37) The treated cellulose pulp was allowed to swell over night in a 6% by weight NaOH solution and a cellulose content of 5% by weight at a temperature of >0 C.

(38) Thereafter the treated cellulose pulp was dissolved in 8% by weight sodium hydroxide (NaOH), and 0.8% zinc oxide (ZnO). The cellulose content was about 5% by weight. The slurry of cellulose pulp was continuously stirred at a temperature of about 8 C. for at least 10 minutes.

(39) Dissolution was detected by polarized light both with and without polarized light.

(40) TABLE-US-00003 TABLE 3 NaOH Viscosity after (% by pretreatment Treatment ID weight) Accelerator (dm.sup.3/kg) time (min) Dissolution 11 6 15 bar O.sub.2 230 480 Proper dissolving was found. 12 6 100 ppm 241 480 Proper Mn.sup.2+ dissolving was found. 13 6 15 bar O.sub.2 254 480 Proper and dissolving was 100 ppm found. Mn.sup.2+

(41) The treatments with 6% by weight NaOH, provided proper dissolving, and the targeted viscosity range was reached within a reasonable process time of about 5-8 hours treatment.

EXAMPLE 4

(42) Two different cellulose dopes (A) and (B), prepared according to below, were both spun in two different ways (carbonate based coagulation and sulphuric acid based coagulation) and the properties of the produced fibers were tested.

(43) Cellulose dope (A) was produced by preparing a sodium hydroxide solution having a concentration of 6% by weight were prepared. Cellulose pulp was added to form a slurry with a cellulose content of about 5% by weight. The slurry was heated to 60 C. for 10 minutes, and thereafter the cellulose content was increased by wash pressing the slurry to a cellulose content of about 30-40% by weight.

(44) Thereafter, the slurry was pressurised to 15 bar with O.sub.2, and was heated to 60 C. for 9 hours. The measured viscosity for the treated cellulose pulp was 213 dm.sup.3/kg. The treated cellulose pulp was allowed to swell over night in a 6% by weight NaOH solution and a cellulose content of 5% by weight at a temperature of >0 C.

(45) Cellulose dope (B) was produced by preparing a sodium hydroxide solution having a concentration of 6% by weight were prepared. Cellulose pulp was added to form a slurry with a cellulose content of about 5% by weight. The slurry was heated to 60 C. for 10 minutes, and thereafter the cellulose content was increased by dewatering the slurry to a cellulose content of about 30-40% by weight.

(46) Thereafter, the slurry was pressurised to 15 bar with O.sub.2, and was heated to 60 C. for 8 hours. The measured viscosity for the treated cellulose pulp was 238 dm.sup.3/kg. The treated cellulose pulp was allowed to swell over night in a 6% by weight NaOH solution and a cellulose content of 5% by weight at a temperature of >0 C.

(47) The swollen treated cellulose pulps ((A) and (B)) were thereafter dissolved in 8% by weight sodium hydroxide (NaOH), and 0.8% zinc oxide (ZnO). The cellulose content was about 5% by weight. The slurry of cellulose pulp was continuously stirred at a temperature of about 8 C. for at least 10 minutes.

(48) Thereafter one part of the cellulose dope (A) and one part of the cellulose dope (B) was each coagulated in a carbonate based coagulation solution comprising 24% by weight Na.sub.2CO.sub.3 and 4% by weight NaOH at 30 C., and another part of the cellulose dope (A) and another part of the cellulose dope (B) was each coagulated in a sulphuric acid based coagulation solution comprising 15% by weight Na.sub.2SO.sub.4 and 10% by weight of H.sub.2SO.sub.4 at room temperature. The cellulose dope was added in a flow speed of 4.2 ml/min, which corresponds to 8.3 m/min of non-stretched fiber.

(49) After spinning, the fibers were transferred to a stretch solution comprising water with a temperature of about 75 C. The fibres from the carbonate based coagulation as well as fibres from the sulphuric acid based coagulation were stretched from 0 to 100%. After stretching, the fibres were washed, and thereafter allowed to rest in deionised water for one day. The fibres were dried at 105 C. for 1 hour and thereafter allowed to acclimate in a climate chamber before tensile tests.

(50) The tensile tests were performed with a Vibroskop/Vibrodyn (Lenzing Instruments). The measurements were performed with the fibre length of 20 mm, test speed 20 mm/min and damper weight 100 mg. 10 measurements were performed on each sample. From the tensile tests, tensile strength (cN/tex), elongation (%), and titre was obtained. Titre is a measure of linear density and is measured in tex, wherein 1 tex equals 1 mg/m.

(51) FIG. 1 shows the tensile strength for fibres from cellulose dope (A) being stretched 0%, 40% and 50%, left staple representing fibres spun in the carbonate based coagulation solution, and right staple representing fibres spun in the sulphuric acid based coagulation solution.

(52) FIG. 2 shows the tensile strength for fibres from cellulose dope (B) being stretched 0%, 40% and 50%, left staple representing fibres spun in the carbonate based coagulation solution, and right staple representing fibres spun in the sulphuric acid based coagulation solution.

(53) FIG. 3 shows the elongation (%) for fibres from cellulose dope (A) being stretched 0%, 40% and 50%, left staple representing fibres spun in the carbonate based coagulation solution, and right staple representing fibres spun in the sulphuric acid based coagulation solution.

(54) FIG. 4 shows the elongation (%) for fibres from cellulose dope (B) being stretched 0%, 40% and 50%, left staple representing fibres spun in the carbonate based coagulation solution, and right staple representing fibres spun in the sulphuric acid based coagulation solution.

(55) As seen from FIGS. 1-4, the carbonate based coagulation solution provided a somewhat higher tensile strength for fibres from cellulose dope (A) as well as from cellulose dope (B), than the sulphuric acid based coagulation solution. However, elongation was higher with the sulphuric acid based coagulation solution than with the carbonate based coagulation solution.

(56) FIG. 5 shows the tensile strength (cN/tex) and titre (dtex) for all fibres from the tensile test of fibres from the cellulose dope (B). The staples represent the tensile strength, the triangular dots represent the carbonate titre, and the crosses represent the sulphuric acid titre. With the cellulose dope (B), the fibres spun from the carbonate based coagulation solution was possible to elongate to about 60%, thereafter the fibres ruptured. However, the fibres spun from the sulphuric acid based coagulation solution, was possible to elongate to about 100%, when some fibres starter to rupture. However, maximum tensile strength was reached with an elongation of about 50%.

EXAMPLE 5

(57) A comparison between a cellulose pulp prepared according to prior art (HCl treatment; a treatment at 90 C., pH 1, a cellulose pulp content of 5% by weight, and 72.9 kg HCl/tonnage cellulose pulp) having a viscosity of 210 dm.sup.3/kg, and the cellulose pulp prepared with 8% by weight of NaOH (ID 5 above) and 7% by weight of NaOH (ID 6 above) was performed in order to study the molecular weight distribution for the different cellulose pulp solutions. Size-exclusion chromatography analysis was used for this comparison.

(58) FIG. 6 shows the molecular weight distributions for the three different treated cellulose pulps. The line marked with A shows the molecular weight distribution for the cellulose pulp treated with HCl, the line marked with B shows the molecular weight distribution for the cellulose pulp treated with 8% by weight of NaOH, and the line marked with C shows the molecular weight distribution for the cellulose pulp treated with 7% by weight of NaOH. As is evident from FIG. 6, the molecular weight distribution for the two cellulose pulps treated with NaOH provide for a narrower molecular weight distribution than the cellulose pulp treated with HCl.

(59) In table 4 below the molecular weight and polydispersity index for the three different treated cellulose pulps are given. Polydispersity index is a measure of the molecular weight distribution, the lower value, the narrower molecular weight distribution.

(60) TABLE-US-00004 TABLE 4 Treated Polydispersity Index Cellulose pulp M.sub.w (kDa) M.sub.w/M.sub.n 7% by weight NaOH 73.6 2.1 8% by weight NaOH 66.0 1.9 HCl 66.9 3.6

(61) When the treated cellulose pulp has a narrower molecular weight distribution the fiber properties is influences positively, e.g. by enabling spinning from a cellulose dope with less cellulose content.

(62) The skilled person realises that a number of modifications of the embodiments described herein are possible without departing from the scope of the invention, which is defined in the appended claims.