A method for determining the impregnation properties of pulp for lyocell fibers

Abstract

The application discloses a method for determining the impregnation performance of pulp for lyocell fibers. The impregnation performance of the pulp is comprehensively determined by sequentially determining a complete impregnation time t, a liquid absorption intensity I of the pulp to an NMMO solution, and a liquid absorption rate R of the pulp to the NMMO solution.

Description

Technical Field

[0001] This invention relates to the field of lyocell fiber manufacturing, and more specifically to a method for determining the pulp impregnation performance of lyocell fibers. Background Technology

[0002] Lyocell fiber was developed in the search for alternative solvents to viscose fiber. It is a fiber produced using solvent spinning methods with dissolving pulp, cotton fiber, and N-methylmorpholine-N-oxide (NMMO) as the solvent. Because lyocell and viscose fibers have different production processes and solvent systems, their requirements for pulp also differ. Existing dissolving pulp indicators, such as methyl cellulose content, alkali solubility, and reactivity, are established for the alkali solubility system of viscose fiber pulp and cannot comprehensively reflect the actual usage requirements of lyocell fiber pulp. Therefore, it is necessary to establish an evaluation system for lyocell fiber pulp to effectively link upstream pulp products with downstream spinning performance.

[0003] Impregnation is a crucial step in the production of lyocell fibers, as only uniformly impregnated pulp can yield a clear, high-quality spinning solution during the dissolution process. Due to the lack of effective methods and standards for testing impregnation performance, the actual production process requires extensive trial and error to establish an impregnation process, inevitably leading to economic losses.

[0004] Currently, the alkali absorption process of viscose fibers can be compared to the alkali absorption value and swelling degree of viscose fibers to evaluate the impregnation performance of pulp. However, simply comparing the absorption amount and swelling degree of the impregnation solution alone cannot comprehensively reflect the impregnation performance of pulp in NMMO solution and its subsequent solubility. For example, the alkali absorption value of viscose fibers measures the percentage of swelling caused by the pulp absorbing sodium hydroxide solution, which is an indicator of the rate of alkali absorption. An excessively fast alkali absorption rate may cause blockage of the pulp capillaries, affecting its reactivity; while an excessively low alkali absorption rate indicates that the capillary gaps in the pulp are not conducive to the entry of reactants, resulting in poor uniformity of alkali cellulose formation, which may in turn lead to uneven formation of xanthate esters, ultimately resulting in poor solubility. Similarly, an excessively fast impregnation capacity will also adversely affect the solubility of pulp in NMMO, causing uneven swelling and clumping that hinders subsequent dissolution; an excessively slow impregnation capacity will affect the entry of NMMO solution into the pulp pores, reducing the homogeneity of the entire system.

[0005] Therefore, how to provide a comprehensive and reliable method for evaluating the impregnation performance of pulp for lyocell fiber is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of this, the present invention provides a method for determining the impregnation performance of pulp for lyocell fibers, which comprehensively determines the impregnation performance of pulp by using the complete impregnation time t, the pulp's absorption intensity I of NMMO solution, and the pulp's absorption rate R of NMMO solution.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for determining the impregnation performance of pulp for lyocell fibers involves comprehensively judging the impregnation performance of pulp by sequentially measuring the complete impregnation time t, the pulp's absorption intensity I of NMMO solution, and the pulp's absorption rate R of NMMO solution.

[0009] As a preferred technical solution of the above technical solution, the process of determining the complete impregnation time t includes: impregnating a known mass of pulp m0 in a constant temperature NMMO solution while stirring, collecting the filtrate of unabsorbed NMMO at regular intervals, and testing the refractive index of the collected NMMO filtrate until the refractive index of the filtrate increases, and recording the impregnation time t under this condition.

[0010] As a preferred embodiment of the above technical solution, the process for determining the absorption intensity I and absorption rate R of pulp to NMMO solution includes: immersing a known mass of pulp m0 in a constant-temperature NMMO solution of a known mass m1 while stirring; filtering and collecting the NMMO filtrate m2; calculating the ratio of the mass difference of the NMMO solution before and after immersion to the mass of the pulp (m1-m2) / m0 to obtain the absorption intensity I of the pulp to NMMO; and calculating the ratio of the absorption intensity I to the complete immersion time t to obtain the absorption rate R of the pulp to NMMO. The absorption intensity I compares the amount of NMMO solution absorbed by different pulp samples, while the absorption rate R compares the rate at which different pulp samples are immersed in the NMMO solution. By comprehensively comparing the absorption intensity I and the absorption rate R, the immersion performance of the pulp in the NMMO solution and its subsequent dissolution capacity can be evaluated more comprehensively.

[0011] As a preferred embodiment of the above technical solution, the temperature of the constant-temperature NMMO solution is 20–90°C.

[0012] As a preferred embodiment of the above technical solution, the temperature of the isothermal NMMO solution is 50–76°C.

[0013] As a preferred embodiment of the above technical solution, the mass ratio of pulp to NMMO solution is 1:10 to 1000, and the concentration of NMMO solution is 50 to 80 wt%.

[0014] As a preferred embodiment of the above technical solution, the mass ratio of pulp to NMMO solution is 1:10, and the NMMO solution concentration is 65-75 wt%.

[0015] As a preferred embodiment of the above technical solution, the pulp is one of cotton pulp, wood pulp, bamboo pulp or hemp pulp.

[0016] As a preferred embodiment of the above technical solution, the pulp is one of cotton dissolving pulp, wood dissolving pulp, bamboo dissolving pulp, or hemp dissolving pulp.

[0017] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a method for determining the impregnation performance of pulp for lyocell fiber, which can compare the differences in impregnation performance of different pulps, and grasp the impregnation performance of pulp in NMMO solution from a macroscopic perspective, which is more instructive for the formulation of production process. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 The attached figure is a schematic diagram of the impregnation device provided by the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The following embodiments all use appendices. Figure 1The apparatus shown is used for impregnation testing to determine the impregnation performance of pulp for lyocell fibers. It includes a stainless steel cylinder 1, a heating jacket 2, and a measuring cylinder 3. The cylinder 1 has a lid 4 at its top and a lid 5 at its bottom. A valve 6 is located under the bottom lid 5, and an air valve 7 is located on the lid 4. A pressurizing device can be connected to the air valve 7 to meet the requirements of pressurized filtration. A screen 8, made of stainless steel or nickel, with a pore size ≤0.180mm (≥80 mesh, or consistent with the filtration section of the corresponding lyocell spinning solution production process), is installed on the bottom lid 5. A stirring paddle 9 is installed inside the cylinder 1. A first sealing gasket 10 is located at the top of the cylinder 1, and a second sealing gasket 11 is located at the bottom of the cylinder 1 to seal and prevent material leakage. The heating jacket 2, equipped with a temperature control device, is fitted over the cylinder 1. The cylinder 1 is fixed to an iron frame 12. The measuring cylinder 3 is placed at the lower end of the cylinder 1 and is used to quantitatively measure the remaining liquid after impregnation.

[0022] Example 1

[0023] The experiment was conducted in an impregnation apparatus. 1g of softwood dissolving pulp with an average degree of polymerization of 630 was impregnated in a stainless steel cylinder containing 100g of 70wt% NMMO solution. The air valve orifice diameter was 5mm, the nickel sieve was 80 mesh, and the effective filtration diameter was 50mm. The heating mantle temperature was adjusted to maintain the NMMO solution temperature inside the cylinder at 70℃, and then maintained at 70℃. For the first 30 minutes, the NMMO solution was filtered and collected at 5-minute intervals (5min, 10min, 15min, 20min, 25min, 30min). After 30 minutes, the NMMO solution was filtered and collected at 1-minute intervals for refractive index determination. Mechanical stirring of the same intensity was maintained during the holding period, and the bottom lid was closed to prevent leakage. During filtration, stirring was stopped, the bottom lid was opened first, and then pressure was applied by closing the top lid and opening the air valve on the top lid to accelerate filtrate collection. The refractive index of the filtrate was tested until the value increased, and the holding time tmin under this condition was recorded.

[0024] The experiment was conducted in an impregnation apparatus. 1g of softwood dissolving pulp with an average degree of polymerization of 630 was impregnated in a stainless steel cylinder containing 100g of 70wt% NMMO solution. The air valve had a 5mm orifice, the nickel sieve had an 80-mesh size, and the effective filtration diameter was 50mm. The temperature of the heating mantle was adjusted to 70℃ and then kept at that temperature. During this time, mechanical stirring of the same intensity was carried out. After t min, stirring was stopped, and then the filtrate was filtered under pressure. After 100s, the mass of the filtrate collected in the graduated cylinder was recorded, and the liquid absorption intensity and absorption rate were calculated. The results are shown in Table 1 below.

[0025] Table 1

[0026]

[0027] Example 2

[0028] Experiments were conducted in an impregnation apparatus. 0.5g of a self-made dissolving slurry with an average degree of polymerization of 500 was impregnated in a stainless steel cylinder containing 100g of a 75wt% NMMO solution. The air valve orifice diameter was 5mm, the nickel sieve was 80 mesh, and the effective filtration diameter was 50mm. The heating mantle temperature was adjusted to maintain the NMMO solution temperature inside the cylinder at 90℃, and then held at 90℃. For the first 30 minutes, the holding time was 5min, 10min, 15min, 20min, 25min, and 30min, and after 30min, approximately 1ml of NMMO filtrate was collected for refractive index determination. During the holding period, mechanical stirring of the same intensity was maintained, and the bottom lid was closed to prevent leakage. During filtration, stirring was stopped, the bottom lid was opened first, and then pressure was applied by closing the top lid and opening the air valve on the top lid to accelerate filtrate collection. The refractive index of the filtrate was tested until the value increased, and the holding time tmin under this condition was recorded.

[0029] Experiments were conducted in an impregnation apparatus. 0.5 g of a self-made dissolving slurry with an average degree of polymerization of 500 was impregnated in a stainless steel cylinder containing 100 g of 75 wt% NMMO solution. The air valve had a 5 mm orifice, the nickel sieve had an 80 mesh, and the effective filtration diameter was 50 mm. The temperature of the heating mantle was adjusted to bring the temperature of the cellulose NMMO solution in the cylinder to 90 °C and then kept at that temperature. During this period, mechanical stirring of the same intensity was carried out. After t min, stirring was stopped, and then the filtrate was filtered under pressure. After 100 s, when no more filtrate dripped, the mass of the filtrate collected in the graduated cylinder was recorded, and the liquid absorption intensity and liquid absorption rate were calculated. The results are shown in Table 2 below.

[0030] Table 2

[0031]

[0032] Example 3

[0033] Five g each of eucalyptus pulp, cotton pulp, and bamboo pulp with an average degree of polymerization of 600±30 were impregnated in a stainless steel cylinder containing 200 g of 80 wt% NMMO solution. The air valve had a 5 mm orifice, the nickel screen was 100 mesh, and the effective filter diameter was 50 mm. The heating mantle temperature was adjusted to bring the temperature of the cellulose NMMO solution in the cylinder to 80 °C, and then the cylinder was kept at 80 °C. For the first 30 minutes, the NMMO solution was filtered and collected every 5 minutes (5 min, 10 min, 15 min, 20 min, 25 min, and 30 min). After 30 minutes, the NMMO solution was filtered and collected every 1 minute for refractive index determination. During the heat preservation period, mechanical stirring of the same intensity was carried out, and the bottom lid was closed to prevent material leakage. When filtering, stirring was stopped, the bottom lid was opened first, and then pressure was applied by closing the top lid and opening the air valve of the top lid to accelerate the collection of the filtrate. After the refractive index of the filtrate increased, the heat preservation time t1, t2, and t3 min for eucalyptus dissolving pulp, cotton dissolving pulp, and bamboo dissolving pulp under this condition was recorded respectively.

[0034] Take 5g of eucalyptus dissolving pulp with an average degree of polymerization of 620 and impregnate it in a stainless steel cylinder containing 200g of 80wt% NMMO solution. The air valve has a 5mm orifice, the nickel screen is 100 mesh, and the effective filter diameter is 50mm. Adjust the temperature of the heating jacket to keep the temperature of the cellulose NMMO solution in the cylinder at 80℃ and keep it warm. During this period, mechanical stirring of the same intensity is carried out. After t1 min, stop stirring and then filter the filtrate under pressure. After 120s, when no more filtrate drips, record the mass of the filtrate collected in the graduated cylinder and calculate the liquid absorption intensity and liquid absorption rate.

[0035] Take 5g of cotton dissolving pulp with an average degree of polymerization of 630 and impregnate it in a stainless steel cylinder containing 200g of 80wt% NMMO solution. The air valve has a 5mm orifice, the nickel screen is 100 mesh, and the effective filter diameter is 50mm. Adjust the temperature of the heating jacket to keep the temperature of the cellulose NMMO solution in the cylinder at 80℃ and keep it warm. During this period, mechanical stirring of the same intensity is carried out. After t2 min, stop stirring and then filter the filtrate under pressure. After 120s, when no more filtrate drips, record the mass of the filtrate collected in the graduated cylinder and calculate the liquid absorption intensity and liquid absorption rate.

[0036] Take 5g of bamboo dissolving pulp with an average degree of polymerization of 580 and impregnate it in a stainless steel cylinder containing 200g of 80wt% NMMO solution. The air valve has a 5mm orifice, the nickel screen is 100 mesh, and the effective filter diameter is 50mm. Adjust the temperature of the heating jacket to keep the temperature of the cellulose NMMO solution in the cylinder at 80℃ and keep it warm. During this period, mechanical stirring of the same intensity is carried out. After t3 min, stop stirring and then filter the filtrate under pressure. After 120s, when no more filtrate drips, record the mass of the filtrate collected in the graduated cylinder and calculate the liquid absorption intensity and liquid absorption rate.

[0037] The results are shown in Table 3 below;

[0038] Table 3

[0039]

[0040]

[0041] Example 4

[0042] Two g of poplar dissolving pulp with average degrees of polymerization of 450, 550, and 650 were impregnated in a stainless steel cylinder containing 100 g of 70 wt% NMMO solution. The air valve had a 5 mm orifice, the nickel screen was 80 mesh, and the effective filtration diameter was 50 mm. The temperature of the heating mantle was adjusted to bring the temperature of the cellulose NMMO solution in the cylinder to 80 °C, and then the cylinder was kept at 80 °C. For the first 30 minutes, the NMMO solution was filtered and collected every 5 minutes (5 min, 10 min, 15 min, 20 min, 25 min, and 30 min). After 30 minutes, the NMMO solution was filtered and collected every 1 minute for refractive index determination. During the heat preservation period, mechanical stirring of the same intensity was carried out, and the bottom lid was closed to prevent material leakage. When filtering, stirring was stopped, the bottom lid was opened first, and then pressure was applied by closing the top lid and opening the air valve of the top lid to accelerate the collection of the filtrate. After the refractive index of the filtrate was tested and the value increased, the heat preservation time t4, t5, and t6 min of eucalyptus dissolving pulp, cotton dissolving pulp, and bamboo dissolving pulp under this state were recorded respectively.

[0043] Take 2g of poplar dissolving pulp with an average degree of polymerization of 450 and impregnate it in a stainless steel cylinder containing 100g of 70wt% NMMO solution. The air valve has a 5mm orifice, the nickel screen is 80 mesh, and the effective filter diameter is 50mm. Adjust the temperature of the heating jacket to keep the temperature of the cellulose NMMO solution in the cylinder at 80℃ and keep it warm. During this period, mechanical stirring of the same intensity is carried out. After t4 min, stop stirring and then filter the filtrate under pressure. After 100s, when no more filtrate drips, record the mass of the filtrate collected in the graduated cylinder and calculate the liquid absorption intensity and liquid absorption rate.

[0044] Take 2g of poplar dissolving pulp with an average degree of polymerization of 550 and impregnate it in a stainless steel cylinder containing 100g of 70wt% NMMO solution. The air valve has a 5mm orifice, the nickel screen is 80 mesh, and the effective filter diameter is 50mm. Adjust the temperature of the heating jacket to keep the temperature of the cellulose NMMO solution in the cylinder at 80℃ and keep it warm. During this period, mechanical stirring of the same intensity is carried out. After t5 min, stop stirring and then filter the filtrate under pressure. After 100s, when no more filtrate drips, record the mass of the filtrate collected in the graduated cylinder and calculate the liquid absorption intensity and liquid absorption rate.

[0045] Take 2g of poplar dissolving pulp with an average degree of polymerization of 650 and impregnate it in a stainless steel cylinder containing 100g of 70wt% NMMO solution. The air valve has a 5mm orifice, the nickel screen is 80 mesh, and the effective filter diameter is 50mm. Adjust the temperature of the heating jacket to keep the temperature of the cellulose NMMO solution in the cylinder at 80℃ and keep it warm. During this period, mechanical stirring of the same intensity is carried out. After t6 min, stop stirring and then filter the filtrate under pressure. After 100s, when no more filtrate drips, record the mass of the filtrate collected in the graduated cylinder and calculate the liquid absorption intensity and liquid absorption rate.

[0046] The results are shown in Table 4 below;

[0047] Table 4

[0048]

[0049] Example 5

[0050] Experiments were conducted in an impregnation apparatus. 3g of a factory-prepared dissolving slurry with an average degree of polymerization of 400 was impregnated in a stainless steel cylinder containing 200g of a 65wt% NMMO solution. The air valve orifice diameter was 5mm, the nickel sieve was 80 mesh, and the effective filtration diameter was 50mm. The heating mantle temperature was adjusted to maintain the NMMO solution temperature inside the cylinder at 50℃, and then maintained at 50℃. For the first 30 minutes, the NMMO solution was filtered and collected at 5-minute intervals (5min, 10min, 15min, 20min, 25min, 30min). After 30 minutes, the NMMO solution was filtered and collected at 1-minute intervals for refractive index determination. Mechanical stirring of the same intensity was maintained during the holding period, and the bottom lid was closed to prevent leakage. During filtration, stirring was stopped, the bottom lid was opened first, and then pressure was applied by closing the top lid and opening the air valve on the top lid to accelerate filtrate collection. The refractive index of the filtrate was tested until it increased, and the holding time (tmin) under this condition was recorded.

[0051] Experiments were conducted in an impregnation apparatus. 3g of a factory-prepared dissolving slurry with an average degree of polymerization of 400 was impregnated in a stainless steel cylinder containing 200g of 65wt% NMMO solution. The air valve had a 5mm orifice, the nickel sieve had an 80-mesh size, and the effective filtration diameter was 50mm. The temperature of the heating mantle was adjusted to 50℃ and then maintained at that temperature, accompanied by mechanical stirring of the same intensity. After t min, stirring was stopped, and the filtrate was then filtered under pressure. After 100s, when no more filtrate dripped, the mass of the filtrate collected in the graduated cylinder was recorded, and the liquid absorption intensity and absorption rate were calculated. The results are shown in Table 5 below.

[0052] Table 5

[0053]

[0054] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0055] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those 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 invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for determining the impregnation properties of pulp for lyocell fibers, characterized in that, Impregnation tests were performed on the following structures: The apparatus for determining the impregnation performance of pulp for lyocell fiber includes a stainless steel cylinder 1, a heating jacket 2, and a measuring cylinder 3. The cylinder 1 has a lid 4 at its top and a lid 5 at its bottom. A valve 6 is located under the bottom lid 5, and an air valve 7 is located on the lid 4. A pressurizing device can be connected to the air valve 7 to meet the requirements of pressurized filtration. A screen 8, made of stainless steel or nickel with a pore size ≤0.180mm, is installed on the bottom lid 5. A stirring paddle 9 is installed inside the cylinder 1. A sealing gasket 10 is located at the top of the cylinder 1, and a second sealing gasket 11 is located at the bottom of the cylinder 1 for sealing and preventing material leakage. The heating jacket 2, equipped with a temperature control device, is fitted over the cylinder 1. The cylinder 1 is fixed to an iron frame 12. The measuring cylinder 3 is placed at the lower end of the cylinder 1 for quantitatively measuring the remaining liquid after impregnation. The impregnation performance of pulp was comprehensively determined by measuring the complete impregnation time t, the pulp's absorption intensity I of NMMO solution, and the pulp's absorption rate R of NMMO solution. The process of determining the complete impregnation time t includes: impregnating a known mass of pulp m0 in a constant-temperature NMMO solution while stirring, collecting the filtrate of unabsorbed NMMO at intervals, and testing the refractive index of the collected NMMO filtrate until the refractive index of the filtrate increases, and recording the impregnation time t under this condition. The process for determining the absorption intensity I and absorption rate R of pulp to NMMO solution includes: immersing a known mass of pulp m0 in a constant-temperature NMMO solution of a known mass m1 while stirring, filtering and collecting the NMMO filtrate m2; calculating the ratio of the mass difference of the NMMO solution before and after immersion to the mass of the pulp (m1-m2) / m0 to obtain the absorption intensity I of the pulp to NMMO; and calculating the ratio of the absorption intensity I to the complete immersion time t to obtain the absorption rate R of the pulp to NMMO.

2. The method for determining the impregnation performance of pulp for lyocell fibers according to claim 1, characterized in that, The temperature of the isothermal NMMO solution is 20–90 °C.

3. The method for determining the impregnation performance of pulp for lyocell fibers according to claim 2, characterized in that, The temperature of the isothermal NMMO solution is 50–76 °C.

4. The method for determining the impregnation properties of pulp for lyocell fibers according to claim 3, characterized in that, The mass ratio of pulp to NMMO solution is 1:10 to 1000, and the concentration of NMMO solution is 50 to 80 wt%.

5. The method for determining the impregnation properties of pulp for lyocell fibers according to claim 4, characterized in that, The mass ratio of pulp to NMMO solution is 1:10, and the NMMO solution concentration is 65-75 wt%.

6. The method for determining the impregnation properties of pulp for lyocell fibers according to claim 5, characterized in that, The pulp is one of cotton pulp, wood pulp, bamboo pulp, or hemp pulp.

7. The method for determining the impregnation properties of pulp for lyocell fibers according to claim 6, characterized in that, The pulp is one of cotton dissolving pulp, wood dissolving pulp, bamboo dissolving pulp, or hemp dissolving pulp.

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