Use of a polymer in the production of cellulosic fibres

Abstract

The present application relates to the field of regenerated cellulose fiber preparation, in particular to a use of a polymer in the preparation of lyocell fiber. The polymer is used to stabilize the cellulose spinning solution with N-methylmorpholine-N-oxide (NMMO) as solvent, so as to improve the thermal stability and / or color of the cellulose spinning solution under heating conditions. The polymer is a lactone polymer or a salt thereof, comprising at least one specific structure of repeating units (I), (II), (III) and / or (IV), and the number average molecular weight is 500 Da-500,000 Da. By adding the polymer to the cellulose spinning solution in the cellulose dissolution stage and / or the spinning solution maturation stage, the cellulose main chain rupture, the thermal degradation and / or oxidative degradation of NMMO solvent and the free radical initiated degradation reaction can be effectively inhibited, so as to reduce the spinning solution viscosity attenuation and the color increase, and improve the stability of the lyocell fiber preparation process and the consistency of the finished fiber quality.

Description

Technical Field

[0001] This invention relates to a polymer and its application in the preparation of cellulose fibers, particularly its use as a stabilizer (polymer stabilizing agent) in cellulose spinning solutions during cellulose fiber production. The polymer effectively inhibits the thermal or oxidative degradation of cellulose and its solvent, N-methylmorpholine-N-oxide (NMMO), during dissolution and spinning, thereby significantly improving the stability and color of the cellulose spinning solution and enhancing fiber quality. This invention provides a simple and efficient method to enhance the stability of the lyocell fiber production process, with broad industrial application prospects. Background Technology

[0002] Lyocell fiber is a regenerated fiber derived from natural cellulose, possessing excellent mechanical properties, biodegradability, and environmental friendliness, and is widely used in textiles, medical materials, and nonwovens. Unlike traditional viscose methods, lyocell fiber uses NMMO as a direct solvent to dissolve cellulose. The entire production process does not produce toxic byproducts, and the solvent can be recycled, thus earning it the reputation of a "green fiber." However, NMMO exhibits certain thermal instability and is prone to decomposition under high-temperature, high-shear dissolution and spinning conditions, producing degradation products such as N-methylmorpholine (MML), morpholine (ML), and formaldehyde. Furthermore, this process leads to cellulose degradation, reducing molecular weight and solution viscosity, and also causes the cellulose spinning solution to darken in color, severely affecting the appearance and properties of the finished fiber and limiting the efficiency and stability of high-quality fiber production.

[0003] To inhibit the aforementioned degradation reactions, stabilizers are typically added during the production process. Traditional small-molecule antioxidants such as propyl gallate (PG) can delay the decomposition of NMMO to some extent, but they are prone to discoloration or reaction with the system at high temperatures, leading to a darkening of the cellulose spinning solution. Hydroxylamine can also be used as a stabilizer in the cellulose / NMMO / H2O system. Its decomposition intermediates interact with active decomposition species in the system, inhibiting further degradation of the solvent and cellulose to some extent. However, hydroxylamine may also generate highly reactive free radicals during use, potentially causing cellulose molecular chain breakage, leading to a decrease in system viscosity, and posing certain safety risks, thus limiting its industrial application.

[0004] Therefore, developing novel stabilizers that simultaneously possess excellent solvent stabilization capabilities and cellulose protection while having minimal impact on the system's color has become a key technological requirement for improving the quality and process controllability of lyocell fiber preparation. Summary of the Invention

[0005] This invention relates to the field of regenerated cellulose fiber preparation, specifically to a polymer stabilizer for stabilizing cellulose spinning solution during lyocell fiber preparation and its uses.

[0006] In the preparation of lyocell fibers, a solvent system containing NMMO is typically used to dissolve and spin cellulose. However, under high temperature, high shear, and oxidative conditions, cellulose molecules are prone to degradation, and the solvent system may also undergo thermal oxidative decomposition, leading to problems such as unstable viscosity of the cellulose spinning solution, increased color, and fluctuations in the properties of the finished fiber. Existing technologies typically alleviate these problems by adding antioxidants or stabilizers, but these methods generally suffer from limited stabilization effects, insufficient color control, or adverse effects on the spinning process. In this invention, "thermal stability" refers to the comprehensive performance of effectively suppressing the viscosity change, the amount of N-methylmorpholine-N-oxide (NMMO) degradation products, and the rate of color change of the cellulose spinning solution within a certain time under the heating conditions involved in lyocell fiber preparation.

[0007] The inventors have discovered that a polymer with specific structural characteristics and molecular weight range, when added to the cellulose spinning solution during the preparation of lyocell fibers, can achieve synergistic stabilization of both the cellulose dissolution system and the solvent system without significantly affecting the system's performance. This polymer not only effectively inhibits the degradation behavior of cellulose molecules during dissolution and spinning but also significantly reduces the degradation rate of the NMMO solvent under processing conditions, thereby improving system stability.

[0008] Specifically, the polymer stabilizer described in this invention exhibits the following technical effects in the lyocell fiber preparation system: (1) Under high temperature dissolution and spinning conditions, reduce the rate of viscosity decay of cellulose spinning solution over time and improve the viscosity stability of the solution system. (2) Inhibiting the degradation reaction of cellulose molecular chains helps maintain the degree of polymerization of cellulose and the mechanical properties of the fibers obtained therefrom. (3) Significantly inhibits the thermal oxidative degradation of NMMO solvent during processing, reduces the rate of color increase in the system, and improves the appearance of the solution; (4) It helps to improve the stability of the spinning process and improve the consistency of the finished Lyocell fiber quality.

[0009] Therefore, by introducing the above-mentioned polymer stabilizer into the lyocell fiber preparation system, the present invention achieves dual stabilization of the cellulose dissolving system and the NMMO solvent system, overcoming the problems of easy degradation and difficulty in color control in the prior art, and has good prospects for industrial application. Attached Figure Description

[0010] Figure 1Effect curves of different stabilizers on the viscosity of cellulose solution over time Detailed Implementation

[0011] The number-average molecular weight (Mn) of the polymer described in this invention was determined by gel permeation chromatography (GPC). The sample was dissolved in a 10 wt% sodium hydroxide aqueous solution at 80°C, neutralized with 1 mol / L hydrochloric acid, and diluted to approximately 0.2 wt% as the test solution. The test used a 0.1 mol / L NaCl aqueous solution as the mobile phase at a flow rate of 0.8 mL / min, and detected using a differential refractive index detector. Molecular weight was calibrated using polyethylene glycol / polyethylene oxide standards. The obtained molecular weight is the apparent number-average molecular weight relative to the standards.

[0012] Example 1: Inhibitory effect of polymer on NMMO solvent degradation Cellulose pulp (cellulose content >98%, degree of polymerization approximately 660) was mixed with an 85% (w / w) aqueous solution of N-methylmorpholine-N-oxide (NMMO) and a 0.01% (w / w) stabilizer in a glass reaction vessel, adjusting the cellulose mass fraction in the mixture to 10%. The stabilizers included a blank control, propyl gallate (PG), and samples of the polymer stabilizer of this invention with different molecular weights (polymer A, Mn = 38000 Da; polymer B, Mn = 53000 Da; wherein A / B have the same chemical structure, differing only in number average molecular weight). The mixture was heated and stirred under the following conditions: Condition 1: Heat at 100℃ for 3 hours; Condition 2: Heat at 120℃ for 1 hour.

[0013] After the samples were processed, the content of N-methylmorpholine (MML), the degradation product of NMMO, was determined by high-performance liquid chromatography (HPLC). The results are shown in Table 1.

[0014] Table 1. Effects of different stabilizers on the MML content of NMMO degradation products. Stability test conditions Blank control Added propyl gallate (PG) Add polymer A Add polymer B 100℃，3h 49 μg / kg 45 μg / kg 31 μg / kg 32 μg / kg 120℃，1h 101 μg / kg 65 μg / kg 44 μg / kg 45 μg / kg The results showed that the system with the polymer of this invention effectively suppressed MML formation under both temperature conditions, exhibiting excellent NMMO thermal stability. Polymers of different molecular weights significantly outperformed the blank control and small molecule stabilizers.

[0015] Example 2: Effect of polymers on the viscosity stability of cellulose solutions Cellulose pulp (cellulose content >98%, degree of polymerization approximately 660), 85% NMMO aqueous solution (by mass), and 0.01% stabilizer were mixed at 100°C to obtain a cellulose spinning solution with a cellulose mass fraction of 5%. The stabilizers also included a blank control, propyl gallate, and polymers A and B (polymer A, Mn = 38000 Da; polymer B, Mn = 53000 Da; where A and B have the same chemical structure, differing only in number average molecular weight).

[0016] Sample viscosity was measured using a Brookfield viscometer at a constant oil bath temperature of 100°C ± 0.2°C. To minimize interference from evaporation and oxidation, the sample surface was covered with aluminum foil and preheated in the oil bath for 1 minute before measurement. Test results are as follows: Figure 1 As shown.

[0017] The results showed that, under the same treatment conditions, the viscosity of the cellulose spinning solution in the blank control system (without stabilizer) decreased significantly over time, indicating viscosity loss during heating. In the system with added PG, the viscosity decrease trend slowed, showing that it had a certain improving effect on viscosity stability. The viscosity of the systems with added polymers A or B remained relatively stable, with significantly smaller changes than those in the blank control and PG systems.

[0018] Example 3: The effect of polymer on improving the color of cellulose solution The colorimetric test was performed using an improved method based on the GB / T 22295-2008 standard: Cellulose pulp spinning solution was heated at 100°C for 3 hours, then poured into a preheated 10 mm optical path colorimetric tube while still hot, maintaining a temperature of approximately 90-100°C. Gardner colorimetry (grades 1-18, where 1 is nearly colorless and 18 is dark brown) was determined using a standard white light source and visual inspection by trained personnel. Each group was measured three times, with an error of ±1 grade. This colorimetric test method was used to compare the color change trends of different samples under the same test conditions, reflecting the differences in the colorimetric control effects of different stabilizers on the cellulose-NMMO system. The results are shown in Table 2.

[0019] Table 2. Effects of different stabilizers on Gardner color of cellulose spinning solution Stability test conditions Blank control Added propyl gallate (PG) Add polymer A Add polymer B Gardner Colorimetric Index (100℃, 3h) 15 16 11 12 The results showed that the color of the cellulose spinning solution was significantly improved after adding polymer A or polymer B, and the Gardner color was significantly lower than that of the blank control and the PG system, indicating that the polymer stabilizer of the present invention can effectively inhibit the color increase of the system during high-temperature treatment.

Claims

1. The use of a polymer in the preparation process of cellulose fibers, characterized in that, The polymer is used to stabilize cellulose spinning solutions using N-methylmorpholine-N-oxide (NMMO) as a solvent in the production of lyocell fibers, in order to improve the thermal stability and / or color of the cellulose spinning solution, wherein the polymer is a lactone polymer or a salt thereof.

2. The use according to claim 1, wherein, The lactone polymer or its salt comprises at least one repeating unit (I), repeating unit (II), repeating unit (III) and / or repeating unit (IV) as shown below: Repeating unit (I): Among them, R 1 R 2 R 3 and R 4 Each of the following, in each occurrence, is independently selected from H, unsubstituted C1-C8 alkyl, substituted C1-C8 alkyl, wherein the substituent is selected from carboxyl, hydroxyl, C3-C8 cycloalkyl, C1-C8 alkoxy; and / or Repeating unit (II): ; and / or Repeating unit (III): In each occurrence of R5 and R6, the substituent is independently selected from H, unsubstituted C1-C8 alkyl, or substituted C1-C8 alkyl, wherein the substituent is selected from carboxyl, hydroxyl, C3-C8 cycloalkyl, or C1-C8 alkoxy. M, in each occurrence, is independently selected from H, alkali metal ions (e.g., Na), + K + ), or ammonium ions (NH4+) + H or alkali metal ions (e.g., Na) are preferred. + K + ); and / or Repeating unit (IV): M 1 and M 2 Each of these, in each occurrence, is independently selected from H, alkali metal ions (e.g., Na+). + K + ), or ammonium ions (NH4+) + H or alkali metal ions (e.g., Na) are preferred. + K + ).

3. The use according to claim 2, characterized in that, The repeating units (I), (II), (III) and / or (IV) may all be identical to form a single repeating unit polymer, or may be composed of two or more different repeating units to form a copolymer, wherein the repeating units are connected by random copolymerization, block copolymerization, gradient copolymerization or any combination thereof.

4. The use according to any one of claims 1-3, wherein, The number-average molecular weight (Mn) of the polymer is from 500 Da to 500,000 Da, preferably from 2,000 Da to 200,000 Da.

5. The use according to any one of claims 1-4, wherein, The amount of the polymer used is 0.001 wt% to 1 wt% based on the total mass of the cellulose spinning solution, preferably 0.005 wt% to 0.5 wt%.

6. The use according to any one of claims 1-5, wherein, The polymer is added to the cellulose spinning solution during the cellulose dissolution stage and / or the spinning solution maturation stage.

7. The use according to any one of claims 1-6, wherein, The cellulose spinning solution exhibits good thermal stability at 80–120 °C, preferably at 90–110 °C.

8. The use according to any one of claims 1-7, wherein, The polymer is used to inhibit the degradation and / or color deepening of the cellulose spinning solution under high temperature conditions.

9. The use according to any one of claims 1-8, wherein, The polymer is used to inhibit one or more of the following degradation processes: cellulose backbone breakage, thermal degradation and / or oxidative degradation of NMMO solvent, and free radical-initiated degradation reactions.

10. The use according to claims 1-9, wherein, The polymer can be a combination of different number-average molecular weights, which can be used to improve the viscosity stability and color performance of cellulose spinning solution.

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