FIBER PRODUCTION WITH SUPERCRITICAL FLUID PHASE FROM COTTON STRAW

Abstract

Disclosed is a method of obtaining regenerated cellulose fiber by using supercritical-N.sub.2O and/or supercritical-CHF.sub.3 compounds from cotton straw which are formed as thin chips mechanically.

Claims

1. A method for obtaining regenerated cellulose fiber that comprises the following steps: a) treating cotton straw which is formed as a thin chip with diluted acetic acid; b) obtaining cellulose pulp by separating hemi-cellulose part from the cotton straw treated with the diluted acetic acid solution; c) subjecting the cellulose pulp to a bleaching process in order to remove lignin from its structure; d) obtaining cellulose xanthate from cellulose macro molecules with intrinsic viscosity value; e) processing cellulose solution in neutralization (coagulation) bath and pulling out the fiber from the nozzles; characterized in comprising the following process step: allowing cellulose macro molecules to have intrinsic viscosity values by using supercritical —N.sub.2O and/or supercritical-CHF, solution during c and d process steps.

2. A method according to claim 1, characterized in that, said coagulation bath disclosed in step e comprises 6-10% by weight H.sub.2SO.sub.4, 10-30% by weight Na.sub.2SO.sub.4 and 1-4% by weight ZnSO.sub.4 mixture.

3. A method according to claim 1, characterized in that, said coagulation bath temperature disclosed in process step e is 40-60° C.

4. A method according to claim 1, characterized in that, the pulling out process disclosed in process step e is 40-80 mt/min speed.

5. A method according to claim 1, characterized in that, said supercritical-N.sub.2O solution is created at 313-353.5° K temperature, at 7-24.5 MPa pressure value and with 2.3-10% by weight.

6. A method according to claim 1, characterized in that, said supercritical-CHF.sub.3 solution is created at 26.1 C° temperature and 48 atm pressure value and with 1.6 dipole moment.

7. Regenerated cellulose fiber obtained with the method disclosed in claim 1 having 450-550 ml/g viscosity.

8. Regenerated cellulose fiber obtained with the method disclosed in claim 1 wherein the brightness is (ISO) 88-92%.

9. Regenerated cellulose fiber obtained with the method disclosed in claim 1 wherein the kappa number is <0.5.

10. Regenerated cellulose fiber obtained with said method disclosed in claim 1 wherein the R18 value is >95%.

11. Regenerated cellulose fiber obtained with the method disclosed in claim 1 wherein the R10 value is >92%.

12. Regenerated cellulose fiber obtained with the method disclosed in claim 1 having a gamma number of 30-45.

Description

FIGURES CLARIFYING THE INVENTION

[0053] FIG. 1: It is a general view of the wood cell.

[0054] FIG. 2: It is a schematic view of alpha cellulose and beta cellulose alignments.

[0055] The drawings shall not be scaled necessarily and the details that are not required for understanding the present invention can be omitted. Apart from this, elements that are at least substantially identical or at least having substantially similar functions are shown with the same numeral.

DESCRIPTION OF PART REFERENCES

[0056] A. Alfa cellulose [0057] B. Beta cellulose [0058] H. Wood cell [0059] ML. Middle layer [0060] S1. Lower layer [0061] S2. Intermediate layer [0062] S3. Upper layer [0063] P. Primary cell wall [0064] W. Rough layer

COMPOUND REFERENCE NUMBERS CLARIFYING THE INVENTION

[0065] (1) Cellulose molecule [0066] (2) Lignin fragmentation reaction [0067] (3) Reaction of the cellulose molecule with super critical fluid N.sub.2O [0068] (4) Reaction of the cellulose molecule with super critical fluid CHF.sub.3

DETAILED DESCRIPTION OF THE INVENTION

[0069] In this detailed description, the method for obtaining fiber with supercritical fluid phase from the cotton straw which is formed mechanically as a thin chip, is described only in order to clarify the subject matter and in a manner without creating any limiting effect.

[0070] N.sub.2O supercritical (SC) fluid to be used in order to obtain fiber from the cotton straw is created at 313-353° K. temperatures and 7.00-24.5 MPa pressure values with 2.3-10% by weight. The transition value of Dinitrogen monoxide (N.sub.2O) optimum supercritical value is 71 bar (7.1 Mpa) and 36.5° C. Within this environment cellulose/N.sub.2O/H.sub.2O is available. Within cellulose macro molecules included within this fluid is SC N.sub.2O—H bonds instead of H—O. When pressure and temperature is changed, because N.sub.2O does not make ionic or covalent bond with the cellulose macro molecule, it again passes to the gas phase and can be used again.

[0071] In the supercritical phase process, N.sub.2O and/or CHF.sub.3 compounds are in a fluid phase at the determined pressure and temperature, they are not in solid or gas phase. The diffusion of the compounds into the cellulose solution in supercritical phase is accelerated, penetration between the cellulose macro molecules is increased and it creates hydrogen bridge bonds with macro molecules as a solvent. In this step, on one hand partially negative charged oxygen atom in N.sub.2O and the hydrogen atom in the hydroxyl group of 6.sup.th carbon in the cellulose molecule that has partial positive charge creates bridge bond, on the other hand partially negative charged fluor atom in CHF.sub.3 and the hydrogen atom in the hydroxyl group of 6.sup.th carbon in the cellulose molecule creates bridge bond. In this step there are hydrogen bridge bonds based on the negative charge value of the oxygen atom in OH in other words hydroxyl within the cellulose macro molecule itself and between macro molecules. The oxygen in N.sub.2O with high negative value or fluor atom in CHF.sub.3 creates bridge bonds with the hydrogen atoms in the hydroxyl group by entering into the cellulose macro molecules and in this manner macro molecular bonds by means of decreasing reach to the intrinsic viscosity value. By means of the supercritical phase process, similar to the conventional NaOH reactions used in the prior art, before bond ruptures occur in the cellulose chain, polymer chain length remains the same and intrinsic viscosity value is reached.

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[0072] At the end of the process, N.sub.2O or CHF.sub.3, are passed to the gas phase again and recovered by changing supercritical pressure and temperature values.

[0073] Supercritical—CHF.sub.3 fluid at Pc 48.0 atm and at 261° C. has dipole moment (db) of 1.6. The fluor (δ−) atom is more electronegative than the oxygen (δ−) atom. Therefore the hydrogen atoms between the cellulose macro molecules and for molecules prefer to bond to the fluor atom. The bond electrons are pulled out by the atom with high electronegativity. Therefore a polarization occurs. The hydrogen that is left without electron and partially positive charged interacts with the neighbor atom with high electronegativity in an electrostatic manner, it becomes a kind of bridge atom, here this hydrogen makes hydrogen bond with the fluor atom.

[0074] CHF.sub.3 structure is a polar structure. Therefore the bond formation energy of CHF.sub.3 is lower than the bond formation energy of OH groups in the cellulose molecule with the hydrogen atom between molecules it is easier to form H δ+—F δ-bond. H δ+—F δ−

[0075] Due to the reason that CHF.sub.3 is polar and its dipole moment is 1.6; the hydrogen (δ+) atom within the hydroxyl groups bonded to the 6.sup.th carbon atom between the cellulose macro molecules and Fluor (δ−) atom make hydrogen bond. In order to realize this reaction, due to the supercritical (SC) fluid phase is Pc 48.0 atm and 26.1° C., the penetration and diffusion of CHF.sub.3 between the cellulose macro molecules will be very easy. Within this environment there is cellulose/CHF.sub.3/H2O and when the normal atmospheric pressure is available, CHF.sub.3 is recovered.

[0076] Due to CHF.sub.3 tetrahedral, N.sub.2O have linear geometric structure, their penetration between cellulose macro molecules occur more easily. N-methyl morpholine-N-oxide is 117 akb, CHF.sub.3 67 akb, N.sub.2O 44 akb. For this reason the diffusion speed of CHF.sub.3 and N.sub.2O is faster than N-methyl morpholine-N-oxide. They enter more easily and more rapidly between the cellulose macro molecules, they make the macro molecules closer and increase the crystallization degree of the polymer. At the same time the values of dry and wet elongation ratios (%) are increased by dry and wet tenacity values (cN/dtex) among mechanical features of the fiber to be obtained by increasing the polymer degree of the solution.

[0077] The Method for Obtaining Fiber with the Supercritical Fluid Phase: [0078] The cotton straw is transformed into thin chips mechanically, [0079] The cotton straw chip is waited during 30 minutes 170° C. in a diluted acetic acid solution in autoclave (Acetic acid reaches from 90° C. to 170° C. in 2.67° C./minute), [0080] After the cotton straw chip is treated with diluted acetic acid solution, it is treated with sodium sulfide (NaS.sub.2) and sodium hydroxide (NaOH) at 165° C. during 120 minutes and its hemi-cellulose section is separated and 92.7% cellulose pulp is obtained (Kappa number of the obtained pulp is 11.4, its whiteness degree is approximately 45%), [0081] In order to remove lignin within the cellulose pulp structure, first it is treated under 5 bar pressure and 100° C. with NaOH and MgSO4, then treated at 65° C. during 60 minutes treated with ClO.sub.2, then treated at 75° C. during 90 minutes with NaOH and H.sub.2O.sub.2, at the last phase treated at 80° C. with ClO.sub.2 during 180 minutes and 120 minutes, subjected to bleaching process (after the bleaching process Kappa number is 1, whiteness degree reaches to 89%), [0082] The cellulose macro molecules are reached to intrinsic values by using supercritical-N.sub.2O and/or supercritical-CHF.sub.3 solution, [0083] The cellulose macro molecules in intrinsic viscosity value is waited at 50° C. during 220 minutes in 18% NaOH and subsequently it is treated at 32° C. with 36% CS.sub.2 solution and the cellulose xanthate occurs, [0084] The cellulose xanthate solution is subjected to neutralization (coagulation) bath at 40-60° C. that includes 6-10% by weight H.sub.2SO.sub.4, 10-30% by weight NaSO.sub.4 and 1-4% by weight ZnSO.sub.4 mixture and the fiber is pulled out from the nozzles with 40-80 mt/dk pullout velocity.

[0085] The viscosity of the regenerated cellulose fiber obtained by means of the abovementioned method is 450-550 ml/g, its brightness is (ISO) 88-92%, its kappa number is <0.5.

[0086] On one hand R18 value shows the ratio of the cellulose which is dissolved in the cellulose pulp within 18% NaOH aqueous solvent; on the other hand R10 values shows the cellulose ration which is dissolved in the cellulose pulp within 10% NaOH aqueous solvent. In the regenerated cellulose fiber obtained by means of the abovementioned method, R18 value is >95%, R10 value is >92%.

[0087] The number of xanthate group created by each 100 molecules of glucose monomers that forms the cellulose macro molecule with CS.sub.2 gives gamma number. The gamma number of the regenerated cellulose fiber which is obtained by means of the method of the present invention is between 30-45.

[0088] Supercritical phase process is used instead of the process named as aging process in the conventional processes used in the present state of the art and waiting process of the cellulose solution whose lignin is removed with NaOH during 240-300 minutes. Therefore instinctive viscosity which is appropriate to viscose pullout is caught.

REFERENCES

[0089] 1—C. Ververis, K. Georghiou, N. Christodoulakis, P. Santas, R. Santas, Fiber dimensions, lignin and cellulose content of various plant materials and their suitability for paper production, Industrial Crops and Products, Volume 19, Issue 3, May 2004, Pages 245-254, [0090] 2—Zawawi Daud, Mohd Zainuri Mohd Hatta, Angzzas Sari Mohd Kassim, Halizah Awang, Ashuvila Mohd Aripin, Analysis the chemical composition and fiber morphology structure of corn stalk, Australian Journal of Basic and Applied Sciences 7(9):401-405, [0091] 3—Ahmet Tutus, Ahmet Cenk Ezici and Saim Ates, Chemical, morphological and anatomical properties and evaluation of cotton stalks (Gossypium hirsutum I.) in pulp industry, Scientific Research and Essays, Vol. 5(12), pp. 1553-1560, June 2010