Method for representing degradation degree of cellulose in lyocell fiber spinning solution

Abstract

The invention discloses a method for characterizing the degradation degree of cellulose in a lyocell fiber spinning solution, and relates to the technical field of pulping, papermaking and spinning, and the method comprises the following steps: separating the cellulose in the lyocell fiber spinning solution and evaluating the degradation degree of NMMO regenerated cellulose fiber. According to the method, cellulose in the lyocell fiber spinning solution is regenerated into a form which is easily dissolved in a copper ethylenediamine solution, a method suitable for testing the polymerization degree of the NMMO regenerated cellulose fiber is constructed, and compared with the raw material cellulose fiber / pulp, the method can be used as one of methods for representing the chemical stability of the lyocell fiber spinning solution.

Description

Technical Field

[0001] The invention relates to the technical field of pulping, papermaking and textiles, and more particularly to a method for characterizing the degradation degree of cellulose in lyocell fiber spinning solution. Background Art

[0002] The aqueous solution of N-methylmorpholine-N-oxide (NMMO) can directly dissolve cellulose without any derivatization, complexation or special activation, and can replace the currently commonly used viscose fiber process to produce regenerated cellulose fibers (RCF). Usually, the spinning solution is composed of 8-20% cellulose, 75-80% NMMO solvent and 5-12% water. The ternary solution of cellulose / NMMO / water is formed at a high temperature of 90-120°C. The concentration of cellulose determines the exact composition of the solution.

[0003] The production of regenerated cellulose fibers by the NMMO route is characterized by the following steps:

[0004] ① Preparation of spinning solution: NMMO solution is mixed with pulp and stirred evenly to obtain a clear and viscous solution;

[0005] ② Dry-jet-wet spinning method: The high-viscosity spinning solution is extruded through the spinneret through the air gap into the coagulation bath (mostly a low-concentration NMMO aqueous solution);

[0006] ③ Cellulose regeneration: NMMO solvent in the dissolution liquid strip is then regenerated into continuous filaments through drawing;

[0007] ④ Wash, oil, curl, dry, cut and perform other post-processing on the regenerated cellulose fibers;

[0008] ⑤ Recover the solvent NMMO from the coagulation bath discharge liquid.

[0009] The final properties of Lyocell fibers are strongly influenced by the selected spinning parameters (e.g. spinneret and air gap dimensions, extrusion speed, draw ratio) and the properties of the spinning dope (hemicellulose content, intrinsic viscosity and concentration of cellulose, temperature, modifiers).

[0010] The choice of spinning process for lyocell fiber is directly related to the viscosity of spinning solution, and the viscosity of spinning solution is related to many factors, such as the cellulose concentration in the solution, the polymerization degree or characteristic viscosity of cellulose (hereinafter referred to as viscosity-average polymerization degree), temperature, etc., which will affect the viscosity of spinning solution. The spinning solution made of low-concentration cellulose or low-polymerization degree cellulose has a lower viscosity, which is conducive to spinning, but the economy is not good; the increase of cellulose concentration or the use of high-polymerization degree cellulose will rapidly increase the viscosity of spinning solution, and it is known that the higher polymerization degree of cellulose can significantly improve the tensile properties of the final product lyocell fiber. However, in industry, the dissolution process of cellulose in NMMO solution is usually carried out in the presence of air, accompanied by the oxidative degradation of cellulose. When the polymerization degree of degraded cellulose is small and cannot meet the requirements of high-speed spinning, different cellulose concentrations must be used to adjust the viscosity of spinning solution to adapt to different cellulose polymerization degrees.

[0011] The present invention uses the viscosity average polymerization degree and its reduction degree to indicate the degradation of cellulose in the lyocell fiber spinning solution. The characteristic viscosity of the copper ethylenediamine solution of the cellulose dissolved in the lyocell fiber spinning solution (hereinafter referred to as NMMO regenerated cellulose fiber) is measured, and then the polymerization degree of the NMMO regenerated cellulose fiber is calculated, and compared with the viscosity average polymerization degree of the raw material cellulose fiber / pulp. The difficulty of the determination method of the present invention is that the dissolution ability of copper ethylenediamine on the regenerated cellulose fiber is limited, which is specifically manifested in: the dissolution cycle is long, and the cellulose is easily degraded during the dissolution process; the structure of cellulose changes after separation from the spinning solution, from the original cellulose type I to cellulose type II, and the crystallinity will also show obvious differences due to different extraction processes, so some cellulose cannot be dissolved.

[0012] After consulting the literature and conducting experiments, it is known that changes in the composition and temperature of the coagulation bath will change the structure of the resulting regenerated cellulose fiber. The primary structure of cellulose remains basically unchanged before and after regeneration, and the dissolution process is mainly a physical process. The regeneration method mainly affects the crystal structure of cellulose. By regulating the regeneration conditions of the cellulose solution, regenerated cellulose with different crystal structures can be obtained. For example, when regenerated in water and acid, the cellulose solution is directly regenerated to obtain cellulose II crystal form, and the polarity of the regenerator has a significant effect on the crystal form and crystallinity of the regenerated cellulose. When regenerated in water, the crystallinity can reach 57%, and amorphous cellulose is directly regenerated in ethanol. Inspired by this, the present invention changes the composition and temperature of the non-cellulose solvent and regulates the regeneration conditions of the cellulose solution to achieve the regeneration of cellulose in the lyocell fiber spinning solution into a form that is easily soluble in a copper ethylenediamine solution, and then dissolves it in a copper ethylenediamine solution, records the outflow time of the sample in a capillary viscometer, and compares it with the raw cellulose fiber / pulp.

[0013] In addition, the process of using ionic liquids for cellulose processing adopts the same technology as the NMMO process, and is therefore also classified as a Lyocell type process. The method of the present invention can also be used to characterize the degree of degradation of the cellulose dissolved in its spinning solution. Summary of the invention

[0014] In view of this, the present invention provides a method for characterizing the degree of cellulose degradation in lyocell fiber spinning solution, which helps to control the viscosity of the spinning solution and the viscosity-average polymerization degree of the raw cellulose fiber / pulp to optimize the preparation of the spinning solution, so that the near-end spinning process has greater variability.

[0015] To achieve the above object, the present invention adopts the following technical solution:

[0016] Improving the dissolution efficiency of NMMO regenerated cellulose fiber in copper ethylenediamine solution can quickly and accurately determine the viscosity average polymerization degree of NMMO regenerated cellulose fiber and compare it with raw cellulose fiber / pulp, specifically comprising the following steps:

[0017] a) separating cellulose from the lyocell fiber spinning solution: mixing the spinning solution with a non-cellulose solvent and removing all solvent residues to obtain NMMO regenerated cellulose fibers that are as pure and dry as possible;

[0018] b) Evaluation of the degree of degradation of NMMO regenerated cellulose fiber: Determine the intrinsic viscosity of the copper ethylenediamine solution of the raw cellulose fiber, pulp and NMMO regenerated cellulose fiber, and then calculate the degree of polymerization; compare the degree of reduction of the average degree of polymerization of the two.

[0019] The non-cellulose solvent includes, but is not limited to, toluene, chloroform, carbon tetrachloride, pentane, hexane, ethanol, isopropanol, acetone, glacial acetic acid, and deionized water. The cellulose is regenerated by a solvent-non-solvent replacement method, and the non-cellulose solvent used is one or more of these solvents.

[0020] The non-cellulose solvent may be heated or cooled to increase the solubility of the dissolving solvent.

[0021] In order to obtain the purest regenerated cellulose fibers possible, the regenerated cellulose fibers can be washed / separated multiple times with non-cellulose solvents, or the Soxhlet extraction method can be used for multiple extractions; stirring or physical field effects (such as ultrasound, microwaves, etc.) can be used to enhance the controllable preparation of the crystal form.

[0022] The NMMO regenerated cellulose fiber is dried in an oven (temperature ≤ 60°C), naturally air-dried or freeze-dried, and then stored in a desiccator or a sealed plastic bag.

[0023] When measuring the intrinsic viscosity of copper ethylenediamine solution of raw cellulose fiber / pulp and NMMO regenerated cellulose fiber, the preparation of the two test solutions should be consistent to reduce operational errors.

[0024] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a method for characterizing the degradation degree of cellulose in lyocell fiber spinning solution, which has the following beneficial effects:

[0025] The present invention adopts the measurement method of viscosity-average polymerization degree to construct a method suitable for testing the polymerization degree of NMMO regenerated cellulose fiber, regenerates the cellulose in the lyocell fiber spinning solution into a form that is easily soluble in a copper ethylenediamine solution, and explores a method for quickly determining the polymerization degree of cellulose in the lyocell fiber spinning solution by a viscosity method, so as to select suitable cellulose fiber / pulp raw materials and select and control the process conditions for preparing and purifying cellulose fiber / pulp in the research on developing lyocell fiber. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] The determination method of viscosity average polymerization degree refers to GB / T 1548-2016, which measures the intrinsic viscosity of raw cellulose fiber / pulp and NMMO regenerated cellulose fiber in copper ethylenediamine solution and calculates their polymerization degree. After the molecular weight of cellulose is determined by gel chromatography, the weight average molecular weight (M w ) as the main indicator, because it can better reflect the characteristics of macromolecules. w / 180 to calculate the degree of polymerization (the molecular weight of glucose is 180).

[0028] Example 1

[0029] The oligomeric cotton pulp provided by a cotton pulp factory in Xinjiang Uygur Autonomous Region was used as the raw pulp to prepare a lyocell fiber spinning solution containing a composite stabilizer. The composite stabilizer was a mixture of 0.1% hydroxylamine, 1.0% sodium hydroxide and 0.2% propyl gallate. The viscosity average polymerization degree of the raw cellulose fiber, pulp and NMMO regenerated cellulose fiber was tested.

[0030]

[0031]

[0032] Example 2

[0033] Acidic sulfite dissolving pulp provided by a pulp mill in the United States was used as the raw pulp to prepare Lyocell fiber spinning solution without stabilizer (i.e. cellulose / NMMO / water ternary system), and the viscosity average polymerization degree of the raw cellulose fiber / pulp and NMMO regenerated cellulose fiber was tested.

[0034]

[0035] Example 3

[0036] The pre-hydrolyzed kraft dissolving pulp provided by a pulp mill in Brazil was used as the raw pulp to prepare the lyocell fiber spinning solution with 0.3% propyl gallate as the single stabilizer. The viscosity average polymerization degree of the raw cellulose fiber / pulp and NMMO regenerated cellulose fiber was tested.

[0037]

[0038]

[0039] Summary: The viscosity average polymerization degree test method after improvement, the viscosity average polymerization degree of raw cellulose fiber / pulp and NMMO regenerated cellulose fiber is close to the polymerization degree calculated by the weight average molecular weight determined by gel chromatography, but the viscosity method greatly shortens the test time, and the use of stabilizer does not affect the solubility of NMMO regenerated cellulose fiber in copper ethylenediamine solution; the degradation degree test shows that the use of NMMO reduces the polymerization degree of cellulose, and the polymerization degree of cellulose fiber before and after dissolution of Examples 1 to 3 retains 60 to 80% of the original polymerization degree, and may be reduced more in the case of low polymerization degree samples. There are many factors that affect the degradation of cellulose in spinning solution. The degradation degree test of the present invention can compare the slight differences between samples (relative to the apparent viscosity change of spinning solution), and has obvious advantages in operability (relative to gel chromatography) and accuracy.

[0040] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for characterizing the degree of degradation of cellulose in a lyocell fiber spinning solution, characterized in that: Improving the dissolution efficiency of NMMO regenerated cellulose fiber in copper ethylenediamine solution can quickly and accurately determine the viscosity average polymerization degree of NMMO regenerated cellulose fiber and compare it with raw cellulose fiber / pulp, specifically comprising the following steps: a) separating cellulose from the lyocell fiber spinning solution: mixing the spinning solution with a non-cellulose solvent and removing all solvent residues to obtain NMMO regenerated cellulose fibers that are as pure and dry as possible; b) Evaluation of the degradation degree of NMMO regenerated cellulose fiber: The intrinsic viscosity of the copper ethylenediamine solution of the raw cellulose fiber / pulp and the NMMO regenerated cellulose fiber is measured, and the degree of polymerization is calculated; and the degree of reduction of the viscosity average degree of polymerization of the two is compared.

2. A method for characterizing the degree of degradation of cellulose in lyocell fiber spinning solution according to claim 1, characterized in that: The non-cellulose solvents include but are not limited to toluene, chloroform, carbon tetrachloride, pentane, hexane, ethanol, isopropanol, acetone, glacial acetic acid, and deionized water. The cellulose is regenerated by a solvent-non-solvent replacement method, and the non-cellulose solvents used are one or more of them.

3. The method for characterizing the degree of degradation of cellulose in lyocell fiber spinning solution according to claim 1, characterized in that: The non-cellulose solvent may be heated or cooled to increase the solubility of the dissolving solvent.

4. The method for characterizing the degree of degradation of cellulose in lyocell fiber spinning solution according to claim 1, characterized in that: In order to obtain the purest possible regenerated cellulose fibers, the regenerated cellulose fibers can be washed / separated multiple times with non-cellulose solvents, or the Soxhlet extraction method can be used for multiple extractions; stirring or physical field effects (such as ultrasound, microwaves, etc.) can be used to enhance the controllable preparation of the crystal form.

5. The method for characterizing the degree of degradation of cellulose in lyocell fiber spinning solution according to claim 1, characterized in that: The NMMO regenerated cellulose fiber is dried in an oven (temperature ≤ 60°C), naturally air-dried or freeze-dried, and then stored in a desiccator or a sealed plastic bag.

6. The method for characterizing the degree of degradation of cellulose in lyocell fiber spinning solution according to claim 1, characterized in that: When determining the intrinsic viscosity of the copper ethylenediamine solution of raw cellulose fiber / pulp and NMMO regenerated cellulose fiber, the preparation of the two test solutions should be consistent to reduce operational errors.

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