Method for dissolving cellulose and method for testing molecular characteristic index
By employing physical pretreatment and a LiCl/DMAc dissolution method at a mild temperature, the problems of incomplete cellulose dissolution and severe degradation were solved, achieving a simple and efficient cellulose dissolution method and stable test results.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SATERI (SHANDONG) FIBER CO LTD
- Filing Date
- 2026-03-19
- Publication Date
- 2026-06-05
AI Technical Summary
Existing technologies for preparing cellulose test solutions suffer from problems such as severe cellulose degradation, incomplete dissolution, complex operation, and high cost, which affect the accuracy of test results.
Cellulose is pretreated using physical methods, including water soaking, freeze drying, and DMAc replacement of residual moisture. It is then mixed and dissolved with LiCl/DMAc solution at 30-50℃ to avoid high-temperature degradation and insufficient dissolution at low temperatures.
This process achieves complete dissolution of cellulose, reduces the degree of cellulose degradation, simplifies the operation process, reduces costs, and ensures the stability and accuracy of test results.
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Figure CN122149965A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the fields of polymer chemistry and analytical chemistry, and relates to a method for dissolving cellulose and a method for testing molecular property indicators. Background Technology
[0002] The molecular weight, molecular weight distribution, and intrinsic viscosity of cellulose directly affect the solubility, solution properties, and mechanical properties of materials, and are of great significance to scientific research and production practice. Gel permeation chromatography (GPC) can simultaneously obtain the molecular weight and molecular weight distribution of cellulose, while capillary viscometry is a commonly used method for determining the intrinsic viscosity of cellulose. The accuracy of both testing methods is highly dependent on a qualified cellulose test solution. A qualified cellulose test solution must meet the core requirements of complete dissolution, no significant cellulose degradation, and system stability to ensure that the test results truly reflect the inherent molecular characteristics of cellulose.
[0003] To prepare cellulose test solutions that meet the requirements, existing technologies have explored various methods.
[0004] Derivatization methods reduce intermolecular hydrogen bonding in cellulose through chemical means such as esterification and nitration, enabling solubility and compatibility testing, as illustrated in the literature (A Simple Correction Method for Determining the Molecular Weight and Distribution of Nitrocellulose by Gel Permeation Chromatography (GPC) - External Standard Method [J]. 1993, 2 (2): 34-35) and (Studies on DMSO-containing carbanilation mixtures: chemistry, oxidations and cellulose integrity [J]. Cellulose, 2007, 14: 497-511.). However, these methods are complex and difficult to operate, and cellulose degradation is easily caused during derivatization.
[0005] The direct dissolution method requires no chemical modification. It directly disperses cellulose by selecting a solvent with strong dissolving power or using high temperature conditions, as in the literature (Research progress on cellulose molecular weight measurement methods [J]. Metrology Science and Technology, 2023, 67 (4):46-56.). Among them, the LiCl / DMAc system has become a commonly used system for GPC testing and capillary viscometer testing due to its relatively good stability, as in the literature (Research and application of cellulose / LiCl / DMAc solution system [J]. Polymer Bulletin, 2010, (10): 53-59.), patent CN102061001B, and patent CN108250460B. However, in the direct dissolution method, although high temperature conditions can increase the dissolution rate, they will aggravate cellulose degradation. Although low temperature conditions can reduce degradation, there are problems such as excessive dissolution time and incomplete dissolution. Undissolved cellulose particles will directly interfere with the GPC separation effect and the accuracy of capillary viscometer testing.
[0006] Furthermore, existing technologies attempt to pretreat cellulose through activation treatments such as alkaline solution treatment and high-temperature DMAc soaking before direct dissolution to improve the dissolution effect, as illustrated in the literature (Comparison testing of methods for gel permeation chromatography of cellulose: coming closer to a standard protocol [J]. Cellulose, 2015, 22: 1591-1613.). However, this still cannot avoid cellulose degradation and adds extra steps such as washing, which not only increases the complexity and cost of operation but may also introduce impurities due to incomplete washing, affecting the stability of the test results. Summary of the Invention
[0007] The purpose of this invention is to solve the problems existing in the prior art and to provide a method for dissolving cellulose and a method for testing molecular property indicators.
[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0009] A method for dissolving cellulose involves first pretreating cellulose using a physical method to obtain cellulose containing DMAc (N,N-dimethylacetamide), then mixing the DMAc-containing cellulose with a LiCl / DMAc solution and dissolving it at a temperature of 30~50℃ to obtain a cellulose solution.
[0010] The physical pretreatment process is as follows: First, cellulose is soaked in water and then filtered (by vacuum filtration or centrifugation) to obtain wet cellulose. Then, the wet cellulose is freeze-dried (by first freezing with liquid nitrogen and then freeze-drying in a freeze dryer or by directly placing it in a freeze dryer) to obtain freeze-dried cellulose. Finally, DMAc is used to replace the residual moisture in the freeze-dried cellulose.
[0011] As a preferred technical solution:
[0012] The cellulose dissolution method described above uses natural cellulose fiber, bacterial cellulose, cellulose pulp, regenerated cellulose membrane, or regenerated cellulose fiber, wherein the mass fraction of α-cellulose is ≥85%. When the mass fraction of α-cellulose in cellulose is ≥85%, the cellulose purity is high and the content of impurities such as lignin is low, which is beneficial to improving the stability of the dissolution process and the reproducibility of test results.
[0013] In the cellulose dissolution method described above, when cellulose is soaked in water as a medium, the mass ratio of cellulose to water is 1:100~500, the conductivity of water is 0.05~0.1μs / cm, the soaking temperature is 30~100℃, and the soaking time is 30~60min; the moisture content of the wet cellulose after filtration is 50~100%.
[0014] When the mass ratio of cellulose to water is 1:100~500, it is beneficial to provide a sufficient wetting environment for cellulose, which not only helps to disperse it evenly but also reduces water waste. When the soaking temperature is 30~100℃, it is more in line with the operation scenario under normal pressure, requiring no special equipment and helping to adapt to wetting requirements, shortening processing time and improving efficiency. When the soaking time is 10~60min, it can be well matched with the soaking temperature, making it easier to ensure that water fully penetrates into the interior of the cellulose. When the moisture content of the filtered wet cellulose is 50~100%, it is beneficial to form uniform pores between cellulose fibers and in the amorphous region during the freeze-drying stage, creating favorable conditions for subsequent solvent diffusion and helping to improve freeze-drying efficiency.
[0015] As described above, in a method for dissolving cellulose, the moisture content of the freeze-dried cellulose is ≤3%. When the moisture content of the freeze-dried cellulose is ≤3%, the cellulose can achieve a sufficient freeze-drying effect, which is conducive to the formation of a rich and uniform pore structure. At the same time, it can significantly improve the rate and sufficiency of subsequent DMAc replacement of residual moisture.
[0016] The method for dissolving cellulose as described above, which utilizes DMAc to replace residual moisture in freeze-dried cellulose, involves mixing freeze-dried cellulose with DMAc at a mass ratio of 1:150~300, soaking at 20~35℃ for 30~90 min, and then separating the cellulose containing DMAc and the excess DMAc by centrifugation. The mass fraction of DMAc in the cellulose containing DMAc is 50~80% (the content of DMAc in the cellulose containing DMAc can be calculated by weighing).
[0017] When the mass ratio of freeze-dried cellulose to DMAc is 1:150~300, it is beneficial to match the wetting requirements of cellulose, which helps to achieve complete coating and penetration of DMAc into cellulose, and reduces waste caused by excessive solvent. When the soaking temperature is 20~35℃, no additional temperature control equipment is required, making the operation convenient, while also helping to protect the structural integrity of cellulose and avoid degradation or premature dissolution of local molecular chains. When the soaking time is 30~90min, it helps to balance the wetting effect and processing efficiency, and makes it easier to ensure that DMAc fully replaces water. When the mass fraction of DMAc in the cellulose containing DMAc is 50~80%, it is beneficial to balance the centrifugation separation efficiency and subsequent dissolution requirements, which helps to ensure the efficient progress of separation operations, and avoids the effect of excessive DMAc content on the effective concentration of LiCl in the subsequent process.
[0018] As described above, a method for dissolving cellulose involves mixing DMAc-containing cellulose with a LiCl / DMAc solution, resulting in a cellulose mass fraction of 0.5% to 1.0% in the mixture. The required mass of LiCl / DMAc solution to be added can be calculated based on the DMAc content in the DMAc-containing cellulose to achieve the desired cellulose mass fraction. When the cellulose mass fraction in the mixture is 0.5% to 1.0%, it is beneficial for maintaining a stable dilute solution state of the cellulose, which is more suitable for the detection requirements of subsequent test indicators.
[0019] In the cellulose dissolution method described above, the mass fraction of LiCl in the LiCl / DMAc solution is 8.0%~9.0% (calibrated by a refractive index meter). When the mass fraction of LiCl in the LiCl / DMAc solution is 8.0%~9.0%, it helps to efficiently promote cellulose dissolution, and the properties (such as refractive index) of the LiCl / DMAc solution are more likely to remain stable after filtration. Combined with the saturation concentration of LiCl in DMAc being 8.5% (mass fraction), this range helps cellulose achieve the optimal dissolution state.
[0020] The cellulose dissolution method described above has a dissolution time of 6-15 hours. When the dissolution time is 6-15 hours, it is beneficial to achieve the optimal balance between dissolution effect and efficiency. This not only helps to ensure that the cellulose molecular chains are fully dispersed and completely dissolved, but also significantly shortens the processing cycle. Compared with the traditional process that does not use the method of this invention, the efficiency advantage is significant.
[0021] The cellulose dissolution method described above has an average degree of polymerization of less than 1000 before dissolution, and the change rate of the average degree of polymerization of cellulose after dissolution does not exceed 5%. The average degree of polymerization of cellulose after dissolution can be verified by precipitation and regeneration of cellulose according to standard determination. A change rate of no more than 5% can be used for GPC or viscosity method testing.
[0022] The present invention also provides a method for testing the molecular properties of cellulose. First, a cellulose solution is obtained by dissolving cellulose as described in any of the preceding claims. Then, the cellulose solution is diluted with DMAc until the mass fraction of LiCl is 0.5% to 1.0% to obtain the cellulose solution to be tested. The intrinsic viscosity of the cellulose is then obtained by capillary viscometer method, or the molecular weight and molecular weight distribution of the cellulose are obtained by GPC method.
[0023] Invention principle:
[0024] This invention employs a physical pretreatment method for cellulose (soaking cellulose in water → freeze-drying → using DMAc to replace residual moisture in the freeze-dried cellulose). This allows for the efficient dissolution of cellulose using a LiCl / DMAc solution at temperatures of 30-50°C, for the following reasons:
[0025] Soaking cellulose in water allows hydrogen bonds to form between the water and the individual fibers in the cellulose. Water can fully penetrate the amorphous region of cellulose, reducing the hydrogen bonding between cellulose fibers. As a result, the cellulose swells and its volume increases.
[0026] Compared to other drying methods (such as heat drying), freeze drying can maintain the volume of water-swollen cellulose. After the water is removed, pores are left, which is beneficial to improve the subsequent solvent diffusion efficiency and dissolution efficiency.
[0027] DMAc is used to replace the residual moisture in freeze-dried cellulose. Since freeze-drying cannot completely remove the moisture in cellulose, but the residual moisture greatly affects the subsequent dissolution effect and efficiency, in order to ensure that the pores left by the previous system are not damaged and to avoid using heat drying to remove moisture, DMAc that is consistent with the solvent component of the subsequent dissolution is selected for replacement. DMAc is retained in cellulose, so that cellulose continues to be in a swollen state.
[0028] This invention utilizes LiCl / DMAc solution to efficiently dissolve cellulose at temperatures of 30-50°C. Compared to existing technologies, this avoids both cellulose degradation at high temperatures and difficulties in dissolving, excessively long dissolution times, or incomplete dissolution at low temperatures. The method of this invention exhibits low cellulose degradation, effectively dissolves cellulose, and achieves monomolecular chain dispersion in dilute solutions, meeting the requirements for testing molecular properties such as intrinsic viscosity, molecular weight, and molecular weight distribution.
[0029] Beneficial effects:
[0030] (1) The present invention achieves full dissolution of cellulose by combining physical pretreatment with dissolution under mild temperature conditions, while effectively inhibiting the degradation of cellulose during the dissolution process, thus ensuring the authenticity of the original molecular weight and molecular weight distribution of cellulose.
[0031] (2) The physical pretreatment process of the present invention does not involve chemical modification and does not require additional washing steps. It is simple to operate, reduces the complexity and cost of operation, and avoids the problem of impurities introduced by incomplete washing, thus ensuring the stability of the cellulose solution system.
[0032] (3) The cellulose solution prepared by the present invention meets the requirements of complete dissolution, no obvious degradation and stable system, and can be directly adapted to the GPC method for determining molecular weight and molecular weight distribution and the capillary viscometer method for determining intrinsic viscosity. Attached Figure Description
[0033] Figure 1 The GPC test spectrum of Example 1;
[0034] Figure 2 The GPC test spectrum of Example 2;
[0035] Figure 3 This is the GPC test spectrum of Example 3. Detailed Implementation
[0036] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.
[0037] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:
[0038] Average degree of polymerization: tested according to FZT 50010.3-2011 standard.
[0039] Mass fraction of α-cellulose in cellulose: tested according to FZ / T 50010.4-2011 standard.
[0040] Conductivity: Tested according to GB / T 6908-2018 standard.
[0041] GPC testing: The GPC instrument used was a Wufeng LC-100 gel permeation chromatograph with a Shimadzu RID-20A differential detector, a Shodex GPC KF-805L column, a LiCl / DMAc solution (LiCl mass fraction of 0.5%), a flow rate of 1 mL / min, a test temperature of 50℃, and a fixed injection volume of 100 μL per injection using a manual syringe. Polystyrene standards were used as standard samples. A GPC molecular weight calibration curve was plotted, and the fitted calibration curve was used to process the cellulose sample to obtain the molecular weight and molecular weight distribution of cellulose.
[0042] Example 1
[0043] A method for testing the molecular properties of cellulose, the specific steps of which are as follows:
[0044] (1) Preparation of materials
[0045] Cellulose: hardwood pulp with an average degree of polymerization of 562, of which α-cellulose accounts for 85% by mass;
[0046] Water: conductivity is 0.1 μS / cm;
[0047] DMAc: Analytical grade or chromatographic grade;
[0048] LiCl: analytical grade;
[0049] LiCl / DMAc solution: LiCl mass fraction is 8.0%.
[0050] (2) Cellulose pulp was pretreated by physical method to obtain DMAc-containing cellulose.
[0051] The physical pretreatment process is as follows: First, cellulose is soaked in water at 30℃ for 60 minutes, with a cellulose to water mass ratio of 1:100. The mixture is then pulped and dispersed, followed by filtration to obtain wet cellulose with a moisture content of 55.6%. The wet cellulose is then freeze-dried to obtain freeze-dried cellulose with a moisture content of 3.00%. The freeze-dried cellulose is then mixed with DMAc at a mass ratio of 1:150, soaked at 25℃ for 60 minutes, and then centrifuged to separate the cellulose containing DMAc from the excess DMAc.
[0052] The DMAc-containing cellulose has a DMAc mass fraction of 80.0%.
[0053] (3) Preparation of cellulose solution
[0054] Cellulose containing DMAc was mixed with LiCl / DMAc solution to obtain a mixture with a cellulose mass fraction of 0.5%. The mixture was dissolved at 30℃ for 11 hours to obtain a cellulose solution.
[0055] After dissolution, the average degree of polymerization of cellulose changed by 2%.
[0056] (4) Testing of the molecular weight and molecular weight distribution of cellulose
[0057] The cellulose solution was diluted with DMAc to a LiCl mass fraction of 0.5% to obtain the cellulose solution to be tested. The intrinsic viscosity of the cellulose was then determined using a capillary viscometer method, or the molecular weight and molecular weight distribution of the cellulose were determined using the GPC method. Figure 1 (As shown).
[0058] Comparative Example 1
[0059] A method for dissolving cellulose involves mixing cellulose (the same raw material as in Example 1) with a LiCl / DMAc solution (the same as in Example 1) to obtain a mixture (the mass fraction of cellulose is the same as in Example 1), and dissolving the mixture at a certain temperature for a period of time to obtain a cellulose solution.
[0060] The study found that if the dissolution temperature is the same as in Example 1, the dissolution time needs to be as high as 80 hours to achieve the same complete dissolution state as in Example 1; if the dissolution time is the same as in Example 1, the dissolution temperature needs to be as high as 120°C to achieve the same complete dissolution state as in Example 1. After dissolution, the average degree of polymerization of cellulose changes by 15%.
[0061] Compared with Example 1, Comparative Example 1 showed a significant increase in dissolution time or dissolution temperature. This is because Comparative Example 1 did not perform physical pretreatment on cellulose, so the hydrogen bond network between cellulose fibers was not destroyed, the fibers were not dispersed, and a rich pore structure was not formed inside. As a result, the solvent (LiCl / DMAc solution) could not penetrate into the fiber interior, and the dissolution rate was greatly reduced. High temperature was required to overcome the structural resistance and achieve dissolution. However, high temperature conditions would significantly aggravate the thermal degradation of cellulose, and the change rate of polymerization degree would increase significantly.
[0062] Comparative Example 2
[0063] A method for testing molecular properties of cellulose differs from Example 1 in that: in step (2), freeze drying is replaced by natural air drying.
[0064] The dissolution time in step (3) of Comparative Example 2 is 96 hours.
[0065] Compared with Example 1, Comparative Example 2 showed a significant increase in dissolution time. This is because natural air drying instead of freeze drying prevented the formation of a rich and uniform pore structure inside the cellulose, hindering the solvent from penetrating into the fiber and thus increasing the dissolution time.
[0066] Comparative Example 3
[0067] A method for testing molecular properties of cellulose differs from Example 1 in that: in step (2), after freeze-drying, the freeze-dried cellulose is no longer soaked in DMAc, and a cellulose solution is prepared directly from the freeze-dried cellulose.
[0068] The dissolution time in step (3) of Comparative Example 3 was 72 hours.
[0069] Compared with Example 1, Comparative Example 3 showed a significant increase in dissolution time. This is because Comparative Example 3 did not undergo DMAc replacement of residual moisture, and the freeze-dried cellulose still contained 2.62% moisture. This residual moisture slowed down the dissolution rate of cellulose. At the same time, the presence of moisture caused local aggregation of cellulose molecular chains, reduced the dispersibility of molecular chains, and affected the dissolution effect and the accuracy of subsequent molecular property tests.
[0070] Example 2
[0071] A method for testing the molecular properties of cellulose, the specific steps of which are as follows:
[0072] (1) Preparation of materials
[0073] Cellulose: Lyocell fiber, with an average degree of polymerization of 498, of which α-cellulose accounts for 96% by mass;
[0074] Water: conductivity is 0.1 μS / cm;
[0075] DMAc: Analytical grade or chromatographic grade;
[0076] LiCl: analytical grade;
[0077] LiCl / DMAc solution: LiCl mass fraction is 9.0%.
[0078] (2) Cellulose is pretreated by physical methods to obtain DMAc-containing cellulose.
[0079] The physical pretreatment process is as follows: First, cellulose is soaked in water at 50℃ for 30 minutes with a cellulose to water mass ratio of 1:250. Then, it is filtered to obtain wet cellulose with a water content of 58.8%. The wet cellulose is then freeze-dried to obtain freeze-dried cellulose with a water content of 1.83%. The freeze-dried cellulose is then mixed with DMAc at a mass ratio of 1:300 and soaked at 25℃ for 30 minutes. Finally, the cellulose containing DMAc and the excess DMAc are separated by centrifugation.
[0080] The DMAc-containing cellulose contains 50.0% DMAc by mass.
[0081] (3) Preparation of cellulose solution
[0082] Cellulose containing DMAc was mixed with LiCl / DMAc solution to obtain a mixture with a cellulose mass fraction of 1%. The mixture was dissolved at 30℃ for 12 hours to obtain a cellulose solution.
[0083] After dissolution, the average degree of polymerization of cellulose changed by 2%.
[0084] (4) Testing of the molecular weight and molecular weight distribution of cellulose
[0085] The cellulose solution was diluted with DMAc to a LiCl mass fraction of 0.5% to obtain the cellulose solution to be tested. The intrinsic viscosity of the cellulose was then determined using a capillary viscometer method, or the molecular weight and molecular weight distribution of the cellulose were determined using the GPC method. Figure 2 (As shown).
[0086] Example 3
[0087] A method for testing the molecular properties of cellulose, the specific steps of which are as follows:
[0088] (1) Preparation of materials
[0089] Cellulose: cotton fiber with an average degree of polymerization of 973, of which α-cellulose accounts for 92.0% by mass.
[0090] Water: conductivity is 0.1 μS / cm;
[0091] DMAc: Analytical grade or chromatographic grade;
[0092] LiCl: analytical grade;
[0093] LiCl / DMAc solution: LiCl mass fraction is 9.0%.
[0094] (2) Cellulose is pretreated by physical methods to obtain DMAc-containing cellulose.
[0095] The physical pretreatment process is as follows: First, cellulose is soaked in water at 100℃ for 40 minutes with a cellulose to water mass ratio of 1:500. Then, it is filtered to obtain wet cellulose with a water content of 92.2%. The wet cellulose is then freeze-dried to obtain freeze-dried cellulose with a water content of 2.08%. The freeze-dried cellulose is then mixed with DMAc at a mass ratio of 1:200 and soaked at 35℃ for 90 minutes. Finally, the cellulose containing DMAc and the excess DMAc are separated by centrifugation.
[0096] The DMAc-containing cellulose has a DMAc mass fraction of 78.2%.
[0097] (3) Preparation of cellulose solution
[0098] Cellulose containing DMAc was mixed with LiCl / DMAc solution to obtain a mixture with a cellulose mass fraction of 0.5%. The mixture was dissolved at 50℃ for 15 h to obtain a cellulose solution.
[0099] After dissolution, the average degree of polymerization of cellulose changed by 5%.
[0100] (4) Testing of the molecular weight and molecular weight distribution of cellulose
[0101] The cellulose solution was diluted with DMAc to a LiCl mass fraction of 0.5% to obtain the cellulose solution to be tested. The intrinsic viscosity of the cellulose was then determined using a capillary viscometer method, or the molecular weight and molecular weight distribution of the cellulose were determined using the GPC method. Figure 3 (As shown).
[0102] Example 4
[0103] A method for testing the molecular properties of cellulose, the specific steps of which are as follows:
[0104] (1) Preparation of materials
[0105] Cellulose: Acetobacter xylinum cellulose with an average degree of polymerization of 262, of which α-cellulose accounts for 100% by mass;
[0106] Water: conductivity is 0.1 μS / cm;
[0107] DMAc: Analytical grade or chromatographic grade;
[0108] LiCl: analytical grade;
[0109] LiCl / DMAc solution: LiCl mass fraction is 8.0%.
[0110] (2) Cellulose is pretreated by physical methods to obtain DMAc-containing cellulose.
[0111] The physical pretreatment process is as follows: First, cellulose is soaked in water at 60℃ for 10 minutes, with a cellulose to water mass ratio of 1:300. The mixture is then pulped and dispersed, followed by filtration to obtain wet cellulose with a moisture content of 86.2%. The wet cellulose is then freeze-dried to obtain freeze-dried cellulose with a moisture content of 2.12%. The freeze-dried cellulose is then mixed with DMAc at a mass ratio of 1:300, soaked at 30℃ for 90 minutes, and then centrifuged to separate the cellulose containing DMAc from the excess DMAc.
[0112] The DMAc-containing cellulose has a DMAc mass fraction of 72.2%.
[0113] (3) Preparation of cellulose solution
[0114] Cellulose containing DMAc was mixed with LiCl / DMAc solution to obtain a mixture with a cellulose mass fraction of 1%. The mixture was dissolved at 40℃ for 6 hours to obtain a cellulose solution.
[0115] After dissolution, the average degree of polymerization of cellulose changed by 2%.
[0116] (4) Testing of the molecular weight and molecular weight distribution of cellulose
[0117] The cellulose solution was diluted with DMAc to a mass fraction of 0.5% for LiCl to obtain the cellulose solution to be tested. The intrinsic viscosity of the cellulose was then measured using a capillary viscometer method, or the molecular weight and molecular weight distribution of the cellulose were measured using the GPC method.
[0118] Example 5
[0119] A method for testing the molecular properties of cellulose, the specific steps of which are as follows:
[0120] (1) Preparation of materials
[0121] Cellulose: Lyocell cellulose membrane with an average degree of polymerization of 425, of which α-cellulose accounts for 98% by mass;
[0122] Water: conductivity is 0.1 μS / cm;
[0123] DMAc: Analytical grade or chromatographic grade;
[0124] LiCl: analytical grade;
[0125] LiCl / DMAc solution: LiCl mass fraction is 8.5%.
[0126] (2) Cellulose is pretreated by physical methods to obtain DMAc-containing cellulose.
[0127] The physical pretreatment process is as follows: First, cellulose is soaked in water at 80℃ for 60 minutes with a cellulose to water mass ratio of 1:500. Then, it is filtered to obtain wet cellulose with a water content of 98.2%. The wet cellulose is then freeze-dried to obtain freeze-dried cellulose with a water content of 1.89%. The freeze-dried cellulose is then mixed with DMAc at a mass ratio of 1:300 and soaked at 35℃ for 60 minutes. Finally, the cellulose containing DMAc and the excess DMAc are separated by centrifugation.
[0128] The DMAc-containing cellulose has a DMAc mass fraction of 63.8%.
[0129] (3) Preparation of cellulose solution
[0130] Cellulose containing DMAc was mixed with LiCl / DMAc solution to obtain a mixture with a cellulose mass fraction of 0.5%. The mixture was dissolved at 30℃ for 12 hours to obtain a cellulose solution.
[0131] After dissolution, the average degree of polymerization of cellulose changed by 5%.
[0132] (4) Testing of the molecular weight and molecular weight distribution of cellulose
[0133] The cellulose solution was diluted with DMAc to a mass fraction of 0.5% for LiCl to obtain the cellulose solution to be tested. The intrinsic viscosity of the cellulose was then measured using a capillary viscometer method, or the molecular weight and molecular weight distribution of the cellulose were measured using the GPC method.
Claims
1. A method for dissolving cellulose, characterized in that, First, cellulose is pretreated by physical method to obtain cellulose containing DMAc. Then, the DMAc-containing cellulose is mixed with LiCl / DMAc solution and dissolved at a temperature of 30~50℃ to obtain cellulose solution. The physical pretreatment process is as follows: first, cellulose is soaked in water as a medium and then filtered to obtain wet cellulose. Then, the wet cellulose is freeze-dried to obtain freeze-dried cellulose. Finally, DMAc is used to replace the residual moisture in the freeze-dried cellulose.
2. The method for dissolving cellulose according to claim 1, characterized in that, Cellulose is natural cellulose fiber, cellulose pulp, bacterial cellulose, regenerated cellulose membrane or regenerated cellulose fiber, wherein the mass fraction of α cellulose is ≥85%.
3. The method for dissolving cellulose according to claim 1, characterized in that, When cellulose is soaked in water, the mass ratio of cellulose to water is 1:100~500, the soaking temperature is 30~100℃, and the soaking time is 10~60min; the moisture content of the wet cellulose is 50~100%.
4. The method for dissolving cellulose according to claim 3, characterized in that, The moisture content of freeze-dried cellulose is ≤3%.
5. The method for dissolving cellulose according to claim 4, characterized in that, The process of using DMAc to replace the residual moisture in freeze-dried cellulose is as follows: freeze-dried cellulose and DMAc are mixed at a mass ratio of 1:150~300, soaked at 20~35℃ for 30~90 min, and then the cellulose containing DMAc and the excess DMAc are separated by centrifugation; the mass fraction of DMAc in the cellulose containing DMAc is 50~80%.
6. The method for dissolving cellulose according to claim 1, characterized in that, Cellulose containing DMAc was mixed with LiCl / DMAc solution, and the mass fraction of cellulose in the mixture was 0.5%~1.0%.
7. The method for dissolving cellulose according to claim 1, characterized in that, The mass fraction of LiCl in the LiCl / DMAc solution is 8.0%~9.0%.
8. The method for dissolving cellulose according to claim 1, characterized in that, The dissolution time is 6~15 hours.
9. The method for dissolving cellulose according to claim 1, characterized in that, Before dissolution, the average degree of polymerization of cellulose was less than 1000, and after dissolution, the rate of change of the average degree of polymerization of cellulose did not exceed 5%.
10. A method for testing the molecular properties of cellulose, characterized in that, First, a cellulose solution is obtained by dissolving cellulose according to any one of claims 1 to 9. Then, the cellulose solution is diluted with DMAc to a mass fraction of LiCl of 0.5% to 1.0% to obtain a cellulose solution to be tested. The intrinsic viscosity of the cellulose is then obtained by capillary viscometer method, or the molecular weight and molecular weight distribution of the cellulose are obtained by GPC method.