RU2805062C1 - Method for obtaining cellulose thread - Google Patents

Abstract

FIELD: cellulose production.

SUBSTANCE: obtaining cellulose solutions suitable for spinning threads and obtaining cellulose threads by an alternative to viscose method. The method for obtaining cellulose thread includes hydrolytic degradation, activation of cellulose with water with further replacement of water with N,N-dimethylacetamide (DMAA), dissolution of activated cellulose at a temperature below 150°C in a mixed solvent containing DMAA and from 4 to 12 wt.% lithium chloride, spinning the thread in a wet or dry-wet way in a water-dimethylacetamide precipitation bath, followed by orientation stretching, washing, drying. Hydrolytic degradation is carried out in an acidic environment in the presence of sulfuric or nitric acid, to increase the strength and elasticity of the thread, the mixed solvent and the precipitation bath additionally contain ethylene glycol, and the orientation stretching is carried out first in air and then in a water vapor medium.

EFFECT: obtaining a cellulose thread for textile and technical purposes with a specific breaking load of 26-33.5 cN/tex, an elongation at break of 8-12%.

3 cl, 4 ex

Description

Technical field

The invention relates to the field of producing cellulose solutions suitable for spinning threads, and to the field of producing cellulose threads for textile and technical purposes using an alternative viscose method.

State of the art

Until now, the production of cellulose fibers and threads has been carried out mainly using the viscose method. Since this method has significant disadvantages, the main ones being the multi-stage nature and significant harmfulness of production, which requires very high costs for treatment facilities, many studies are aimed at finding other ways to produce cellulose threads, namely, methods for direct dissolution of cellulose without the formation of derivatives.

Direct, more environmentally friendly organic and inorganic cellulose solvents have been proposed by various researchers, including N-methylmorpholine-N-oxide (NMMO) and N,N-dimethylacetamide (DMAA), the latter being used with the addition of lithium chloride. The only one that has been mastered on an industrial scale and is an alternative to viscose is the process of producing cellulose threads from cellulose solutions in NMMO. The process has a significant advantage over viscose, but its disadvantages include the high cost of the solvent, the complexity and energy consumption of the process of cellulose dissolution and solvent regeneration.

A promising direct solvent for cellulose is DMAA with the addition of lithium chloride. Since the 80s of the 20th century, many studies have been devoted to the dissolution of cellulose in DMAA with LiCl, but the production of fibers and threads from these solutions is a significantly smaller number of works. Dissolution of cellulose is the most complex and important stage in the preparation of the spinning solution, which has a decisive influence on the quality characteristics of the resulting fibers.

Cellulose dissolves in a mixture of DMAA with LiCl when heated to a temperature of 150°C and above, but at such temperatures it undergoes significant depolymerization. As a rule, cellulose is activated before dissolution to increase its reactivity, intensify the dissolution process and improve the quality of the solution.

In Chinese application CN 101550614 A, IPC D01F 2/08, publ. 10/07/2009, cellulose pulp with a degree of polymerization of 200-1000 is crushed, activated with a solution of DMAA heated to 160°C, DMAA with KMnO ₄ or by boiling with aqueous NaOH, then washed and dried at 50°C until the water content is less than 1% . Activated cellulose is added to a DMAA solution containing 6.6-10 wt. % LiCl, heat and stir at 100°C until a gel-like state, then continue stirring for 8-12 hours at 25°C until completely dissolved. To reduce the viscosity, the solution is heated to 30-70°C and filtered at this temperature, degassed in a vacuum, the pressure is increased with nitrogen and wet-molded through a die with a hole diameter of 0.04-0.08 mm into a bath containing water, acetone, methanol, etc. at 20-80°C, the immersion time in the bath is 0.1-0.2 s, then the thread is pulled out in a water bath at 20-80°C and dried. Among the positive aspects of the method, easy control of product quality is noted, but the characteristics of the resulting threads are not indicated. The disadvantage of this process is the high temperature of the activating system.

The method for producing thread from wood cellulose proposed in the application CN 110172746 A (IPC D01F 2/00, published on August 27, 2019) includes the following steps:

- obtaining a mixed solvent by dissolving 5-10 wt. % LiCl in DMAA when heated, dissolution temperature is 100-105°C, dissolution time 3-4 hours;

- preparation of a spinning solution with a cellulose concentration of 10-20 wt. % mixing cellulose with the resulting mixed solvent in a vacuum at 105-120°C for 4-5 hours;

- spinning of threads using the dry-wet method through a spinneret with a hole diameter of 10-110 microns, a hole capillary length of 300-900 microns, a speed of 35-45 m/min through an air gap of 6-9 cm into a bath with a temperature of 3-10 ° C containing mixed solvent DMAA with LiCl obtained at the initial stage;

- washing the resulting thread by immersion in a bath with a 75-95% ethanol solution at room temperature for 3-4 hours, then in a bath of water at a temperature of 75-95°C for 2-3 hours, treatment by immersion in a bath with a lubricant with a concentration of 3 g/l at 80-85°C for 2 hours and drying.

The disadvantage of this process is the use of LiCl in the precipitation bath and the duration of the washing and oiling process; the characteristics of the resulting threads are also not given.

One of the first publications devoted to the production of molded cellulose products, in particular threads, by direct dissolution of cellulose in a mixture of DMAA with LiCl, are patents US 4302252 B2 (MPC C08B 1/00, C08J 3/09, C08K 3/16, publ. 11.24. 1981) and US 4352770 B2 (MPC C08B 1/00, D01F 2/02, published 10/05/1982), which we took as a prototype. An important aspect of the invention is the preliminary activation of cellulose in a polar environment (water, steam, liquid ammonia, DMAA, DMSO, etc.), with further removal of any polar environment other than DMAA to a concentration of less than 5%. Activation ensures swelling of cellulose, opening of its pores and access of solvent. Dissolution is carried out in DMAA, 1-methyl-2-pyrrolidinone and their mixtures with the addition of 3 to 15 wt. % LiCl at temperatures well below 150°C down to room temperature. In the case of cellulose activation in DMAA, the process is carried out by heating to 150°C or higher, with further cooling to a temperature below 100°C and adding LiCl for dissolution. It is also proposed to dissolve cellulose without prior activation in DMAA, 1-methyl-2-pyrrolidinone, or their mixtures with the addition of 3 to 15 wt. % LiCl and water with further evaporation until the water content is less than 5%. The thread is formed from solutions containing up to 16 wt. % cellulose by a wet or dry-wet method into a bath containing water, lower monohydric alcohol, acetonitrile, tetrahydrofuran and mixtures thereof at room temperature. One of the examples shows the parameters for obtaining a thread: spinneret drawing 1.655, plasticizing drawing 78%, washing with water at 65-70°C, spinning, abrasion treatment and drying at 100°C for several hours. The result is a thread having the following characteristics: linear density 1.23 denier (0.137 tex); specific breaking load under standard conditions is 3.74 g/denier (33 cN/tex), in a wet state - 2.64 g/denier (23 cN/tex); elongation at break in conditioned conditions is 6.2%, in wet condition - 8.7%; wet elastic modulus 1.4 g/denier (19 kgf/mm ² ) at 5% elongation. However, the resulting thread has a low elongation at break, which is a disadvantage of this method.

Disclosure of the Invention

The purpose of the present invention is to develop a technological, reproducible, industrial-scale method for producing cellulose thread for textile and technical purposes from wood cellulose.

The set goal is achieved by a set and sequence of operations, both at the stage of cellulose activation and at the stages of dissolving and spinning the thread. Activation and preparation for dissolution includes the following operations: 1. Treatment of pre-crushed cellulose with 4-10% aqueous solutions of mineral acids (sulfuric, nitric) at a temperature of 70-98°C for 0.5-2.0 hours, at which hydrolytic destruction, which makes it possible to obtain cellulose with an optimal degree of polymerization for further dissolution and molding.

2. Washing hydrolyzed cellulose with distilled water to neutralize the acid, remove impurities, low molecular weight fractions and continue activation of cellulose with water, squeezing excess water to a residual moisture content of 55-60%.

3. Treatment of cellulose with DMAA for 30 minutes. at a mass ratio of cellulose and DMAA of 1:8 to replace water and spin.

Activation carried out in this way can significantly reduce energy consumption when dissolving cellulose by reducing the temperature and duration of the process.

Activated cellulose is dissolved in a mixture of DMAA with LiCl and ethylene glycol, the concentration of LiCl in DMAA is 4-12 wt. %, the concentration of ethylene glycol is 0.4-1.0% by weight of DMAA with LiCl. The dissolution is first carried out at room temperature (17-22°C) without stirring for 2-6 hours, then the mixture is stirred at a temperature of 80-98°C for 3-5 hours to obtain a homogeneous, transparent spinning solution.

An important aspect of the invention is the addition of ethylene glycol to the solvent system, which makes it possible to increase the physical and mechanical properties of the resulting cellulose thread. The properties of the cellulose solution are stable, the degree of polymerization does not decrease, which ensures the stability of the molding process and guarantees the production of a thread with stable physical and mechanical properties and increased elongation.

The resulting cellulose solution has a concentration of 4-10% and, after filtration and deairing, can be used for spinning threads.

The thread is formed both wet and dry-wet through spinnerets with hole diameters from 0.08 to 0.12 mm into a water-dimethylacetamide precipitation bath containing 0-30 wt. % DMAA and 0.02-0.5 wt. % ethylene glycol at a temperature of 10-50°C.

The formed thread is first subjected to orientation stretching in air by 10-30%, then in water vapor by 30-110%, washed from solvent residues, dried at a temperature of 105°C, subjected to abrasion treatment and wound onto a bobbin. Orientation drawing in a water vapor environment helps to increase the strength of the thread.

The entire set and sequence of operations makes it possible to obtain cellulose thread for textile and technical purposes with a specific breaking load of 26-33.5 cN/tex, and an elongation at break of 8-12%.

Carrying out the invention

Example 1. Pre-crushed cellulose is treated with a 10% aqueous solution of sulfuric acid at a temperature of 98°C for 1.0 hour. Then the cellulose is washed with distilled water to a neutral environment and squeezed out of excess water using a water ring pump to a residual moisture content of 50%. To replace water in the pores of cellulose, it is treated twice with DMAA for 30 minutes. The mass ratio of cellulose and DMAA is 1:8.

Activated cellulose is dissolved in a mixture of DMAA with LiCl, and the concentration of LiCl in DMAA is 8 wt. %. The dissolution is first carried out at room temperature 20-22°C without stirring for 2 hours, then the mixture is stirred at a temperature of 98°C for 5 hours to obtain a homogeneous spinning solution. The resulting solution with a concentration of 5% is filtered and deaerated.

The thread is wet-spun through a spinneret with a hole diameter of 0.08 mm into an aqueous precipitation bath at a temperature of 20°C. The formed thread is first subjected to orientation stretching in air by 10%, then in water vapor by 30%, washed from solvent residues, dried at a temperature of 105°C, subjected to abrasion treatment and wound onto a bobbin. The resulting thread has a specific breaking load of 19 cN/tex, and an elongation at break of 8.8%.

Example 2. The preparation and activation of cellulose is carried out as in example 1. Activated cellulose is dissolved in a mixture of DMAA with LiCl and ethylene glycol, and the concentration of LiCl in DMAA is 8 wt. %, and the concentration of ethylene glycol is 0.4% by weight of DMAA with LiCl. The dissolution is first carried out at room temperature 20-22°C without stirring for 2 hours, then the mixture is stirred at a temperature of 98°C for 5 hours to obtain a homogeneous spinning solution. The resulting solution with a concentration of 5% is filtered and deaerated.

The thread is wet-spun through a spinneret with a hole diameter of 0.08 mm into a precipitation bath at a temperature of 20°C containing water. The formed thread is first subjected to orientation stretching in air by 10%, then in water vapor by 30%, washed from solvent residues, dried at a temperature of 105°C, subjected to abrasion treatment and wound onto a bobbin. The resulting thread has a specific breaking load of 26 cN/tex, and an elongation at break of 12.1%.

Example 3. The preparation and activation of cellulose is carried out as in example 1.

The dissolution is carried out as in example 2, with the concentration of ethylene glycol being 0.7% by weight of DMAA with LiCl.

The threads are formed using the wet method through a spinneret with a hole diameter of 0.08 mm into a precipitation bath at a temperature of 30°C containing an aqueous solution of 0.5 wt. % ethylene glycol. The formed thread is first subjected to orientation stretching in air by 20%, then in a water vapor environment by 100%, washed from solvent residues, dried at a temperature of 105°C, subjected to abrasion treatment and wound onto a bobbin. The resulting thread has a specific breaking load of 33.5 cN/tex, and an elongation at break of 11.4%.

Example 4. Preparation, activation and dissolution of cellulose are carried out as in example 3. The threads are formed using the wet method through a spinneret with a hole diameter of 0.08 mm into a precipitation bath at a temperature of 30°C containing an aqueous solution of DMAA up to 30 wt. % The formed thread is first subjected to orientation stretching in air by 30%, then in water vapor by 110%, washed from solvent residues, dried at a temperature of 105°C, subjected to abrasion treatment and wound onto a bobbin. The resulting thread has a specific breaking load of 30 cN/tex, and an elongation at break of 9.4%.

Claims (3)

1. A method for producing cellulose thread from wood cellulose, including hydrolytic destruction, activation of cellulose with water with further replacement of water with N,N-dimethylacetamide (DMAA), dissolution of activated cellulose at a temperature below 150°C in a mixed solvent containing DMAA and from 4 to 12 wt. % lithium chloride, spinning the thread using a wet or dry-wet method in a water-dimethylacetamide precipitation bath, followed by orientation stretching, washing, drying, characterized in that hydrolytic destruction is carried out in an acidic environment in the presence of sulfuric or nitric acid, to increase the strength and elasticity of the thread the mixed solvent and precipitation bath additionally contain ethylene glycol, and the orientation hood is carried out in two stages: first in air and then in water vapor. 2. The method according to claim 1, characterized in that the content of ethylene glycol in the mixed solvent is 0.4-1.0 wt. % 3. The method according to claim 1, characterized in that the content of ethylene glycol in the precipitation bath is 0.02-0.5 wt. %