CN114150521B

CN114150521B - Preparation method of hemp-based lyocell fiber pulp

Info

Publication number: CN114150521B
Application number: CN202111466520.8A
Authority: CN
Inventors: 连丹丹; 卢建军; 刘伟方; 葛超; 史晟
Original assignee: Taiyuan University of Technology
Current assignee: Taiyuan University of Technology
Priority date: 2021-12-03
Filing date: 2021-12-03
Publication date: 2023-02-10
Anticipated expiration: 2041-12-03
Also published as: CN114150521A

Abstract

The invention belongs to the technical field of textile raw material preparation, and provides a preparation method of hemp-based lyocell pulp, aiming at solving the problems of poor stability, thermal runaway and the like of a spinning solution caused by iron metal elements in the dissolving process of the pulp in NMMO at present, hemp cellulose is subjected to alkali boiling at a high temperature of 195-205 ℃ in alkali liquor, washed to be neutral by deionized water, and dried to obtain the hemp cellulose with degraded polymerization degree; then, treating the hemp cellulose with degraded polymerization degree by acid, removing iron element in the pulp to obtain hemp pulp, and treating the hemp pulp by using a chelating agent to remove the iron element in the pulp; washing, filtering and drying to obtain the hemp-based lyocell pulp. By utilizing the metal element removing process method, the iron metal element in the pulp is removed, so that the content of the iron metal element is lower than 15ppm, and the problems of poor spinning solution stability, thermal runaway and the like caused by the iron metal element are solved.

Description

Preparation method of hemp-based lyocell fiber pulp

Technical Field

The invention belongs to the technical field of textile raw material preparation, and particularly relates to a preparation method of hemp-based lyocell pulp.

Background

The lyocell fiber is a regenerated cellulose fiber prepared by mixing and heating wood, cotton and bamboo cellulose pulp serving as raw materials with N-methylmorpholine-N-oxide NMMO/water to form spinning solution and spinning by a dry method or a wet method. The solvent can be recycled, and the production process is pollution-free and environment-friendly. Has good physical and mechanical properties, wrinkle resistance and comfort. At present, most pulp raw materials for preparing the lyocell fibers are sourced from imported wood pulp, because the pulp for preparing the lyocell fibers has extremely strict requirements on indexes such as polymerization degree, ash content, metal impurity content and the like.

The dissolving process of pulp in NMMO is theoretically a pure physical process, but actually, chemical side reactions occur in the spinning dope during dissolving, which have various adverse effects. Transition metal ions in the pulp are strong inducers of homogeneous dissolution reaction in lyocell spinning solution, fe (II) or Cu (I) ions and N-methylmorpholinyl generated by redox reaction of NMMO participate in free radical reaction to accelerate the breakage of hydroxyl and glycosidic bonds in cellulose, promote the degradation of the cellulose and reduce the polymerization degree of the cellulose. Meanwhile, the decomposition process of the NMMO releases heat, the thermal stability of the cellulose solution is poor, and thermal runaway and even explosion can occur. Therefore, if the pulp meeting the requirements of the Lyocell spinning is prepared, the occurrence of side reactions in the spinning is effectively inhibited, and the reduction of the content of metal ions is a fundamental measure.

Hemp, as a long-history crop for textile use, is widely used in paper, clothing, building materials, medicine, food, oil, and the like. Industrial cannabis, also known as hemp, refers to a nontoxic utilization value of cannabis with a Tetrahydrocannabinol (THC) content of less than 0.3% in the plant, and is a 1-year-old herbaceous organism of the cannabis genus of the cannabinaceae family. As a traditional high-economic-value crop, the bast fiber has excellent advantages in the aspect of properties, is reputed as the king of natural fiber, has small fineness, high strength, good moisture absorption and sweat releasing performance and good wearability, has excellent heat resistance, antibacterial and bacteriostatic properties and ultraviolet resistance, and is a natural health-care fiber.

Hemp bast fiber consists of cellulose, hemicellulose, lignin and other impurities, wherein the cellulose content is about 57%. According to literature reports, hemp fibers contain about 200-400ppm of trace elements of iron, the presence of which is a direct cause of the inability of hemp fibers to be used for the preparation of lyocell fibers at the present stage. Hemp fiber is essentially different from wood pulp fiber, bamboo fiber, cotton fiber and the like in terms of cellulose structure, polymerization degree, impurity content and the like.

Compared with flax and ramie, hemp is a bast fiber, but the content, polymerization degree and single fiber structure characteristics of cellulose are different: the single fiber section in the hemp bast is distributed by a plurality of fiber cells in bundles, is separated by parenchyma cells, and has a single fiber percentage of 10%. The single fiber section in the flax bast is gathered into a fiber bundle by 10-20 fiber cells, and is separated by surrounding parenchyma cells, and the single fiber percentage is 20%. The single fiber section in ramie bast is formed by 20-80 fiber cells gathering into bundles, separated by parenchyma cells, and easily decomposed into single cells, and the single fiber percentage is 90%.

At present, the utilization methods of hemp bast fiber in industry mainly comprise a silk spinning type and a wool spinning type, and the core is degumming, carding and spinning the bast fiber. However, the hemp fiber has large bending and torsional rigidity, the fiber is not easy to cohere, the length and the fineness of the hemp fiber have great relationship with the degumming and carding process, so the length unevenness is high, the spinnability of the hemp is poor, and the pure hemp yarn has the defects of hardness, brittleness, straightness, low single strength and the like. Pure hemp yarns are not suitable for use in knitwear and tend to blend with other fibers, complementing their properties to improve yarn performance. And, a large amount of doffing is generated in the process of carding and spinning the hemp fiber, which results in the waste of raw materials. Therefore, the development of the lyocell fiber pulp prepared by using the hemp bast fiber has important technical and market values.

Disclosure of Invention

The invention provides a preparation method of hemp-based lyocell pulp, aiming at solving the problems of poor stability, thermal runaway and the like of spinning solution caused by iron metal elements in the dissolving process of the pulp in NMMO (N-methyl-cellulose), and the pulp for lyocell fibers is prepared by using degummed hemp bast fibers. Namely, the polymerization degree of the hemp cellulose under the reaction system is reduced under the specific temperature and pressure, and is controlled to be 500-600 so as to meet the spinnability of the pulp. The iron metal element in the pulp is removed by using a metal element removal process method, so that the content of the iron metal element is lower than 15ppm, and the problems of poor stability, thermal runaway and the like of the spinning solution caused by the iron metal element are solved.

The invention is realized by the following technical scheme: a method for preparing hemp-based lyocell fiber pulp comprises boiling degummed hemp bast cellulose in alkali liquor at 195-205 deg.C, washing with deionized water to neutrality, and drying to obtain polymerization degree degraded hemp cellulose; then, acid treatment is carried out on the hemp cellulose with the degraded polymerization degree, iron elements in the pulp are removed, hemp pulp is obtained, a chelating agent is used for treating the hemp pulp, and the iron elements in the pulp are removed; washing, filtering and drying to obtain the hemp-based lyocell pulp.

The method comprises the following specific steps:

(1) Degradation of polymerization degree of hemp fiber: A. alkali boiling of degummed hemp fiber: putting the fiber into a sodium hydroxide solution with the mass concentration of 5-15%, and then putting the sodium hydroxide solution mixed with the hemp fiber into a reaction kettle, wherein the bath ratio is 1:35, then placing the mixture into a homogeneous reactor, controlling the heating rate to be 5-10 ℃/min and the rotating speed to be 10-20 r/min; heating to 195-205 ℃, reacting for 1-1.5 h, taking out the reaction kettle, quenching in a water bath for 30min, and taking out the reacted product;

B. suction filtration and washing: filtering the product solution after reaction, and reserving hemp fibers; adding deionized water into hemp fiber, stirring, washing for 1min, repeating suction filtration, and washing until the filtrate is neutral; drying the obtained filter cake at 80 ℃ for 1h to obtain the degraded hemp pulp;

(2) Removing iron elements in the pulp by acid treatment: A. pretreatment of degraded hemp pulp: adding 2-4g of hemp pulp into 60-150ml of deionized water, and stirring at 400rpm for 0.5h until the pulp is uniformly dispersed;

B. acid treatment: adding 0.1-0.2 g of oxalic acid, and uniformly stirring until the pH value of the hemp pulp liquid is 2;

C. water bath reaction: placing the hemp pulp liquid after acid treatment in a water bath at 40-90 ℃ and 400rpm for 20-60 min; then taking out and placing in cold water for intermediate-speed cooling;

D. washing and suction filtration: placing the reacted product solution into a sand core funnel, carrying out suction filtration by using a water film, reserving a product filter cake, and repeatedly washing and carrying out suction filtration for 5 times by using 20ml-40ml of oxalic acid solution with the mass concentration of 3%; then washing with 40ml deionized water, filtering repeatedly until the filtrate is neutral,

E. and (3) drying: drying the obtained product filter cake for 1h at the temperature of 80 ℃ to obtain hemp pulp;

(3) And (3) treating by using a chelating agent to remove iron elements in the pulp: a. hemp pulp pretreatment: adding 50-100ml of deionized water into 2-4g of hemp pulp, stirring at 400rpm for 0.5h until the pulp is uniformly dispersed;

b. and (3) treatment with a chelating agent: adding a chelating agent diethylene triamine pentaacetic acid into the hemp pulp dispersion liquid, wherein the mass of the chelating agent accounts for 0.2-0.4% of the total mass of the mixed liquid; then stirring the mixture in water bath at 20-60 ℃ at 400rpm for reaction for 20-50min, and cooling the mixture with cold water at a high speed after the reaction is finished;

c. washing, suction filtration and drying: filtering the reacted solution in a sand core funnel by a water film to obtain a product filter cake, and repeatedly washing and filtering the filter cake for 5 times by using 20ml-40ml of chelating agent diethylenetriamine pentaacetic acid solution with the same concentration; then repeatedly washing and filtering for 10 times by using 40ml of deionized water; the obtained filter cake was dried at 80 ℃ for 1h to obtain white hemp-based lyocell pulp.

In the invention, the hemp degumming is carried out by adopting a conventional degumming method to obtain the hemp bast cellulose. The white hemp-based lyocell fiber pulp obtained by the method has the polymerization degree of 500-600 and the iron element content of 10-14ppm. Compared with the background technology, the polymerization degree of the hemp fiber is reduced through specific high temperature and high pressure, the iron element in the pulp is removed through acid treatment and chelating agent treatment, the removal effect is obvious, the subsequent dissolving and spinning process is favorably and smoothly carried out, the method needs less reagent amount, has lower cost and is suitable for industrial production.

Drawings

FIG. 1 shows hemp cellulose pulp prepared in example 1;

FIG. 2 is a FTIR spectrum of the hemp cellulose pulp prepared in example 1;

FIG. 3 is a hemp cellulose pulp XRD pattern;

fig. 4 is a graph of hemp cellulose pulp TG.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1: a method for preparing hemp-based lyocell pulp comprises boiling degummed hemp cellulose in alkaline solution at high temperature, washing with deionized water to neutrality, and drying to obtain hemp cellulose with degraded polymerization degree; then, treating the hemp cellulose with degraded polymerization degree by acid, removing iron element in the pulp to obtain hemp pulp, and treating the hemp pulp by using a chelating agent to remove the iron element in the pulp; washing, filtering, and drying to obtain the hemp-based lyocell fiber pulp.

1. The chemical materials used were: sodium hydroxide, oxalic acid, diethylenetriamine pentaacetic acid and deionized water, wherein the combined preparation dosage is as follows: measured in grams and milliliters. 10 g. + -. 5g NaOH, 0.2 g. + -. 0.1g oxalic acid C ₂ H ₂ O ₄ ·2H ₂ O, 0.2g +/-0.1 g of diethylenetriamine pentaacetic acid C ₁₄ H ₂₃ N ₃ O ₁₀ 5000 mL +/-100 mL of deionized water H ₂ O。

2. The preparation method comprises the following steps:

(1) Selecting chemical materials: the chemical material used for preparation is selected, and the quality purity and the concentration are controlled as follows: the purity of the sodium hydroxide solid is 96 percent; the purity of the oxalic acid solid is 99.5 percent; the purity of the diethylenetriamine pentaacetic acid solid is 98.5 percent; the deionized purity is 99.9 percent.

(2) Degradation of polymerization degree of hemp fiber:

A. preparing a solution: weighing 10g of sodium hydroxide +/-0.5 g, weighing 50ml of deionized water +/-1 ml, placing the deionized water in a beaker for mixing, and stirring the mixture for 2min by using a glass rod to uniformly mix the deionized water and the deionized water for later use;

B. high-pressure alkali cooking: placing 2g of hemp fiber and 70ml of sodium hydroxide solution in a reaction kettle, wherein the bath ratio is 1:35 and then placed in a homogeneous reactor. Heating is started, the heating temperature is set to be 195 ℃, the heating rate is set to be 10 ℃/min, and the rotating speed is 10 r/min. When the temperature reached 195 deg.C, a 1.5h timer was started. And (4) closing the homogeneous reactor after 1.5h, taking out the reaction kettle, placing the reaction kettle in a water bath, quenching for 30min, and opening the cover.

C. And (3) filtering and washing with deionized water: and (3) placing the product solution after reaction in a Buchner funnel of a filter flask for suction filtration, carrying out suction filtration on the waste liquor after cooking in the filter flask, and reserving hemp fibers on a filter membrane. Adding appropriate amount of deionized water, stirring, washing for 1min, and vacuum filtering. This operation was repeated, and the filtrate was washed until it was neutral.

D. And (3) drying: putting the product filter cake into an evaporation dish, and then putting the evaporation dish into an oven for drying at the drying temperature of 80 ℃ for 1h; drying to obtain degraded hemp pulp;

(3) Removing iron elements in the pulp by acid treatment:

a. hemp pulp pretreatment: placing 2g of hemp pulp in a beaker, adding 60ml plus or minus 1ml of deionized water, placing on a magnetic stirrer, and stirring at the speed of 400rpm for 0.5h until the pulp is uniformly dispersed.

b. Acid treatment: add 0.1g oxalic acid to the beaker and mix well with stirring until ph is 2.

c. And (3) constant-temperature water bath: the beaker is placed in a water bath kettle, the water bath temperature is 60 ℃, the stirring speed is 400rpm, and the water bath time is 60min. Taking out the beaker, and placing the beaker in cold water for quick cooling.

d. Washing and suction filtration: placing the reacted product solution in a sand core funnel, carrying out suction filtration by using a water membrane, remaining a product filter cake on the filter membrane, and pumping the waste liquid into a filter bottle; washing with 20ml of oxalic acid solution with the mass concentration of 3 percent, and repeatedly carrying out suction filtration for 5 times; washing with 40ml of deionized water and suction filtration were repeated until the filtrate became neutral.

e. And (3) drying: putting the product filter cake into an evaporation dish, and then putting the evaporation dish into an oven for drying at the drying temperature of 80 ℃ for 1h; drying to obtain hemp pulp.

(4) Chelating agent treatment for removing iron element in pulp

A. Hemp pulp pretreatment: placing 2g of the processed hemp pulp in a beaker, adding 50ml +/-1 ml of deionized water, placing on a magnetic stirrer, and stirring at the speed of 400rpm for 0.5h until the pulp is uniformly dispersed.

B. And (3) treatment with a chelating agent: adding a chelating agent diethylenetriamine pentaacetic acid into the beaker, wherein the mass of the chelating agent accounts for 0.3 percent of the total mass of the mixed solution; then stirring and reacting the mixture in water bath at 40 ℃ and at 400rpm for 60min, and cooling the mixture with cold water at a high speed after the reaction is finished;

C. washing and suction filtration: placing the reacted product solution in a sand core funnel, carrying out suction filtration by using a water membrane, remaining a product filter cake on the filter membrane, and pumping the waste liquid into a filter bottle; washing with 20ml chelating agent diethylenetriamine pentaacetic acid solution with the same concentration, and repeatedly performing suction filtration for 5 times; washing with 40ml of deionized water and suction filtration were repeated 10 times.

D. And (3) drying: putting the product filter cake into an evaporation dish, and then putting the evaporation dish into an oven for drying at the drying temperature of 80 ℃ for 1h; drying to obtain hemp pulp as white solid.

Example 2: detecting, analyzing and characterizing the polymerization degree and the iron content of the prepared hemp pulp

Firstly, measuring the polymerization degree of the hemp pulp by using a Ubbelohde viscometer with the diameter of a capillary tube of 0.80 +/-0.05 mm; the polymerization degree is measured by the Ubbelohde viscometer method: under the test conditions of temperature (25 +/-1) DEG C and relative humidity (65 +/-3)%, 250mg of pulp is weighed by an electronic balance and put into a dissolving bottle, 25ml of distilled water and 1g of copper sheet are added, and the solution is vigorously shaken for a period of time to fully swell. Then 25ml of copper ethylenediamine is taken out by a pipette and is shaken vigorously to be dissolved completely. Then the dissolved solution was poured into a viscometer for measurement, immersed in a constant temperature water bath to reach (25. + -. 1) ℃ and kept at a constant temperature for 5 minutes, the liquid level was brought to the upper scale by an ear-washing ball, and then the time required for the solution to flow from the upper scale to the lower scale was recorded in seconds to be accurate to 2 seconds. Parallel tests are carried out, and the difference of the results of the two tests cannot exceed +/-2.5%.

The relative viscosity is then calculated according to equation (1):

(1) (ii) a In the formula (I), the compound is shown in the specification,

relative viscosity, h is the viscometer constant for the measurement in negative first power seconds(s) ^-1 ），

The time taken to pass the distance between the two graduation lines.

Then from the calculated

The numerical value is found out

And calculating the viscosity rho of the tested solution according to the mass of the sample and the volume of the solution during drying. Will be provided with

Dividing the value by the value of viscosity rho to obtain the intrinsic viscosity

The unit is mL/g. The precision is two digits after decimal point, and then the precision is reduced to one digit after decimal point according to the regulation of GB/T8170.

Finally according to the average degree of polymerization

Calculating formula (2) to obtain the average polymerization degree

。

(2) (ii) a And calculating one digit after the decimal point, and trimming to an integer digit according to the GB/T8170 specification. Polymerization degree of hemp pulp obtained

=530。

Note: when in use

<1100mL/g, tolerance error<2 percent; when in use

<700mL/g, tolerance error<1 percent; when in use

>1100mL/g, allowA large error.

Secondly, measuring the iron content of the product by inductively coupled plasma atomic emission spectrometry (ICP-OES, instrument model Agilent 5110); the test method is as follows:

1. 0.2g of dry sample +6ml of concentrated HNO ₃ +2ml 30%H ₂ O ₂ Mixing, placing in polytetrafluoroethylene digestion tank, and pre-digesting at 130 deg.C for 0.5 hr.

2. The microwave digestion was carried out according to the digestion procedure shown in table 1.

TABLE 1

3. The digestion tank is opened after being cooled to room temperature, and all digestion solution is transferred (a small amount of ultrapure water is used for washing the digestion tank for 3 times, and washing liquid is combined in the volumetric flask) to a 25mL volumetric flask for constant volume.

4. Passing through a water phase filter membrane to obtain a sample solution and a blank control solution. And (4) moving the sample into a sample introduction system for testing to obtain a test result.

Table 2 shows the polymerization degree and iron content (ICP test) of the hemp cellulose pulp obtained by the preparation

As can be seen from the results of the polymerization degree and the iron content of the hemp cellulose pulp shown in the table 2, the polymerization degree of the hemp cellulose can be reduced and controlled to be 500-600 under the specific temperature, pressure and technical process, and the requirement of the Lyocell method on the polymerization degree of the pulp is met. The iron element removing process method can remove the iron metal element in the pulp to ensure that the content of the iron metal element is lower than 15ppm, and meets the requirement of the Lyocell method on the content of the iron element in the pulp.

Meanwhile, the hemp cellulose pulp obtained is shown in figure 1, and it can be seen that the pulp is composed of short fibers with uniform length, is white in color and has no redundant impurities. Fourier transformation of the resulting hemp cellulose pulpThe FTIR spectrum is measured, and the FTIR chart is shown in figure 2, 3420 cm ^-1 The broad peak belongs to the stretching vibration absorption peak of the cellulose hydroxyl functional group-OH. 1730 cm ^-1 No obvious stretching vibration peak of carbonyl (C-O) is generated, which shows that the method of the invention can remove lignin impurities in the fiber.

The XRD pattern 3 of the hemp cellulose pulp obtained by the preparation can be seen, the 2 theta angles corresponding to the characteristic diffraction peaks are respectively 14.88, 16.04 and 22.55, the diffraction peaks corresponding to the (101) and (002) planes are typical cellulose crystal form I, and the requirement of the lyocell method on the pulp crystal form is met.

As can be seen from the TG atlas of the prepared hemp cellulose pulp in figure 4, the initial decomposition temperature of the cellulose pulp is about 330 ℃, and the thermal stability is better.

Example 3: a method for preparing hemp-based lyocell fiber pulp, the concentration of sodium hydroxide solution is 5%, the heating rate of alkali boiling temperature is 5 ℃/min, and the rotating speed is 15 r/min; heating to 200 ℃, reacting for 1h, adding 60ml of deionized water into 3g of hemp pulp, adding 0.15g of oxalic acid, and carrying out water bath on the hemp pulp liquid subjected to acid treatment at 400rpm for 40min in 60 ℃; the mass of the chelating agent accounts for 0.2 percent of the total mass of the mixed solution; the reaction was then carried out in a water bath at 20 ℃ for 50min with stirring at 400rpm, and the procedure was otherwise as described in example 1.

Example 4: a method for preparing hemp-based lyocell fiber pulp, wherein the concentration of sodium hydroxide solution is 10%, the heating rate of alkaline boiling temperature is 8 ℃/min, and the rotating speed is 10 r/min; heating to 205 ℃, reacting for 1.2h, adding 150ml of deionized water into 4g of hemp pulp, adding 0.2g of oxalic acid, and carrying out water bath for 60min at 400rpm in water bath at 40 ℃ for the hemp pulp liquid subjected to acid treatment; the mass of the chelating agent accounts for 0.3 percent of the total mass of the mixed solution; the reaction was then stirred at 400rpm in a water bath at 40 ℃ for 30min, and the rest of the procedure was the same as that described in example 1.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of hemp-based lyocell fiber pulp is characterized in that: boiling degummed hemp bast cellulose in alkali liquor at a high temperature of 195-205 ℃, washing with deionized water to be neutral, and drying to obtain the hemp cellulose with degraded polymerization degree; then, treating the hemp cellulose with degraded polymerization degree by acid, removing iron element in the pulp to obtain hemp pulp, and treating the hemp pulp by using a chelating agent to remove the iron element in the pulp; washing, filtering and drying to obtain the hemp-based lyocell fiber pulp;

the method comprises the following specific steps:

(1) Degradation of polymerization degree of hemp fiber: A. alkali boiling of degummed hemp fiber: placing the hemp fiber in a sodium hydroxide solution with the mass concentration of 5-15%, and then placing the sodium hydroxide solution mixed with the hemp fiber in a reaction kettle, wherein the bath ratio is 1:35, then placing the mixture into a homogeneous reactor, controlling the heating rate to be 5-10 ℃/min and the rotating speed to be 10-20 r/min; heating to 195-205 ℃, reacting for 1.5-1 h, taking out the reaction kettle, quenching in a water bath for 30min, and taking out the reacted product;

B. and (3) suction filtration and washing: carrying out suction filtration on the product solution after reaction, and reserving hemp fibers; adding deionized water into hemp fiber, stirring, washing for 1min, repeating suction filtration, and washing until the filtrate is neutral; drying the obtained filter cake at 80 ℃ for 1h to obtain the degraded hemp pulp;

b. and (3) treatment with a chelating agent: adding a chelating agent diethylenetriamine pentaacetic acid into the hemp pulp dispersion liquid, wherein the mass of the chelating agent accounts for 0.2-0.4% of the total mass of the mixed liquid; then stirring the mixture in water bath at 20-60 ℃ at 400rpm for reaction for 20-50min, and cooling the mixture with cold water at a high speed after the reaction is finished;