A method for characterizing the molecular weight and molecular weight distribution of cellulose

Abstract

The application discloses a method for characterizing the molecular weight of cellulose. The cellulose is dissolved under mild conditions in an ionic liquid / cosolvent system. The dissolution process has no influence on the molecular weight and molecular weight distribution of the cellulose. The obtained cellulose solution is molecularly dispersed, and the molecular weight and molecular weight distribution of the cellulose are accurately characterized by GPC. Furthermore, the method is suitable for various cellulose raw materials with different molecular weights and different sources and regenerated cellulose products.

Description

Technical Field

[0001] This invention belongs to the fields of polymer chemistry and analytical chemistry, and relates to a method for characterizing the molecular weight and molecular weight distribution of cellulose. Background Technology

[0002] Cellulose is the most abundant natural polymer on Earth, and its molecular weight parameter is a key fundamental information for cellulose-based materials. Therefore, accurate characterization of cellulose molecular weight and molecular weight distribution is extremely important. Currently, directly dissolving cellulose in a special solvent is an important method for determining cellulose molecular weight and its distribution. Combined with gel permeation chromatography (GPC), this method can rapidly and directly obtain information on cellulose molecular weight and molecular weight distribution. However, the most commonly used chromatographic method based on the N,N-diethylacetamide / lithium chloride (DMAc / LiCl) system suffers from problems such as cumbersome pre-activation steps (requiring several days of high-temperature activation), difficulty in dissolving high molecular weight cellulose, and the inevitable aggregation and association of cellulose molecular chains. Even when measuring the same sample, the results obtained by different research groups vary significantly. Therefore, developing a new method for rapidly, accurately, and with high operability to characterize cellulose molecular weight and molecular weight distribution is crucial for both basic research in academia and industrial applications. Summary of the Invention

[0003] This invention provides a method for characterizing the molecular weight of cellulose, the method comprising the following steps:

[0004] (1) Preparation of cellulose solution: Cellulose is dissolved in an ionic liquid / cosolvent I system to obtain cellulose solution A; cosolvent II is added to cellulose solution A to obtain cellulose solution B;

[0005] (2) Preparation of mobile phase: Mix the ionic liquid with cosolvent I and cosolvent II, and use the resulting mixed solvent as mobile phase C;

[0006] (3) Chromatographic test: The molecular weight and molecular weight distribution of the cellulose solution B were determined by gel permeation chromatography based on the mobile phase C.

[0007] According to embodiments of the present invention, the source of the cellulose is not particularly limited; that is, the characterization method is applicable to cellulose raw materials and recycled cellulose products of various molecular weights and sources. For example, the cellulose may be one or more of microcrystalline cellulose, wood pulp, bacterial cellulose, refined cotton, viscose fiber, cellophane, cotton pulp, cellulose oligomers, etc.

[0008] According to an embodiment of the present invention, the ionic liquid is a molten salt formed by imidazole cations and carboxylic acid anions.

[0009] According to an embodiment of the present invention, the imidazole cation has a substituent group. Preferably, the substituent group may be alkyl or alkenyl, more preferably, the substituent group may be C 1-12 Alkyl, C 1-12 At least one of alkenyl groups, etc. As an example, the substituent group may be one or more of methyl, ethyl, butyl, and allyl.

[0010] Preferably, the carboxylic acid anion of the ionic liquid is at least one of formate, acetate, and propionate.

[0011] According to an embodiment of the present invention, the ionic liquid may be selected from at least one of 1-butyl-3-methylimidazolium acetate (BmimAc) and 1-ethyl-3-methylimidazolium acetate (EmimAc).

[0012] According to embodiments of the present invention, the cosolvent I and cosolvent II may be the same or different, and can be one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), pyridine, pyrrolidone, acetonitrile, dichloromethane, chloroform, propylene carbonate, dimethyl carbonate, diethyl carbonate, d-valeramide, e-caprolactam, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolinone (DMI), N,N'-dimethylacrylurea, N,N,N',N'-tetramethylurea, dimethyl sulfoxide (DMSO), sulfolane, acetylacetone, tert-butanol, tert-amyl alcohol, etc. As an example, the cosolvent I and cosolvent II can be one or more of DMSO, DMF, DMAc, and DMI, independently of each other.

[0013] According to an embodiment of the present invention, the mass concentration of cellulose in solution A is 0.1-5%. As an example, the mass concentration of cellulose in solution A can be 0.1%, 1%, 2%, 3%, or 5%.

[0014] According to an embodiment of the present invention, in solution A, the mass ratio of the ionic liquid to the cosolvent I is 1:0.5-1:10, for example, 1:0.5, 1:1, 1:2, 1:5, 1:8, or 1:10.

[0015] According to an embodiment of the present invention, the preparation process of solution A further includes stirring it until a transparent and clear solution is formed. For example, the stirring temperature is room temperature; the stirring time is 0.5h-2h, exemplarily 1h.

[0016] According to an embodiment of the present invention, the concentration of cellulose in solution B is 0.5-5 mg / mL. As an example, the concentration of cellulose in solution B can be 2 mg / mL.

[0017] According to an embodiment of the present invention, the solution B is further subjected to stirring during the preparation process. For example, the stirring temperature is room temperature; the stirring time is 0.5h-2h, exemplarily 0.5h.

[0018] According to an embodiment of the present invention, the characterization method further includes filtering solution B. For example, solution B is filtered through a filter membrane.

[0019] According to an embodiment of the present invention, in solution B, the mass ratio of the ionic liquid to the co-solvent (the total mass of co-solvent I and co-solvent II) is 1:1 to 1:100. As an example, the mass ratio of the ionic liquid to the co-solvent can be 1:20 or 1:30.

[0020] According to an embodiment of the present invention, in the mobile phase C, the mass ratio of the ionic liquid to the cosolvent (the total mass of cosolvent I and cosolvent II) is 1:1 to 1:100. As an example, the mass ratio of the ionic liquid to the cosolvent can be 1:20 or 1:30.

[0021] According to an embodiment of the present invention, the preparation of the mobile phase C further includes sonicating the mixed solvent. For example, the sonication time is 0.5h-1h, exemplarily 0.5h.

[0022] According to an embodiment of the present invention, the flow rate in the chromatographic test conditions is 0.1-2.0 mL / min.

[0023] According to an embodiment of the present invention, the ionic liquid and cosolvents I and II are both of chromatographic grade purity.

[0024] The present invention also provides the application of the above characterization method in roughly determining the proportion of high and low molecular weight cellulose in a cellulose mixture sample.

[0025] According to an embodiment of the present invention, when the cellulose mixture sample contains at least two types of cellulose with significantly different molecular weights, a broad peak is obtained by gel permeation chromatography. The relative height of the main peak and the shoulder peak in the broad peak can be used to roughly determine the proportion of high and low molecular weight cellulose in the cellulose mixture sample.

[0026] The beneficial effects of this invention are:

[0027] This invention unexpectedly reveals that cellulose can be rapidly dissolved under mild conditions in an ionic liquid / cosolvent system. Furthermore, the dissolution process has no effect on the molecular weight and molecular weight distribution of cellulose, and the resulting cellulose solution exhibits molecular-level dispersion. GPC accurately characterized the molecular weight and molecular weight distribution of cellulose. Moreover, this method is applicable to cellulose raw materials of various molecular weights and origins, as well as recycled cellulose products. Attached Figure Description

[0028] Figure 1 The image shows the GPC elution curve of the cellulose sample in Example 1.

[0029] Figure 2 The GPC elution curve of the cellulose sample in Example 2 is shown.

[0030] Figure 3 The GPC elution curve of the cellulose sample in Example 3 is shown.

[0031] Figure 4 The GPC elution curve of the cellulose sample in Example 4 is shown.

[0032] Figure 5 The GPC elution curve of the cellulose sample in Example 5 is shown.

[0033] Figure 6 The GPC elution curve of the cellulose sample in Example 6 is shown.

[0034] Figure 7 The GPC elution curve of the pullulan standard in Comparative Example 1. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0036] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0037] Example 1

[0038] 20 mg of microcrystalline cellulose was dissolved in 1 g of 1-butyl-3-methylimidazolium acetate (BmimAc) / DMSO (1:1, w / w) solvent and magnetically stirred at room temperature for 0.5 h. Then, 9.5 g of DMAc was slowly added dropwise to the above solution and stirring was continued for 0.5 h. The resulting solution was filtered through a 0.22 μm PTFE membrane into a clean sample bottle to obtain a cellulose solution with a concentration of approximately 2 mg / mL, which could be used directly for GPC testing without further processing.

[0039] Mix BmimAc / DMSO / DMAc at a mass ratio of 1:1:19 and sonicate for 0.5 h. Use this mixture as a mobile phase for rinsing the chromatographic system. Tests can only be performed after the baseline has stabilized.

[0040] The molecular weight of the obtained cellulose solution was determined by GPC-MALLS. The GPC unit was a Waters e2695, the differential detector was a Waters 2414, the laser light scattering detector was a Wyatt DAWN HELEOS-II, the column was a PL-Mixed C, the mobile phase was BmimAc / DMSO / DMAc (1:1:19, w / w), the column temperature and detector temperature were set to 40℃, the flow rate was 0.5 mL / min, and the injection volume was 20 μL.

[0041] Test results are as follows Figure 1 As shown, the calculated absolute weight-average molecular weight of microcrystalline cellulose is 3.90 × 10⁻⁶. 4 g / mol, polydispersity index is 3.12.

[0042] Example 2

[0043] Dissolve 30 mg of wood pulp in 1 g of 1-ethyl-3-methylimidazolium acetate (EmimAc) / DMF (1:1, w / w) solvent and stir magnetically at room temperature for 1 h. Then, slowly add 14.5 g of DMF to the above solution and continue stirring for 0.5 h. Filter the resulting solution through a 0.22 μm PTFE filter into a clean sample bottle to obtain a cellulose solution with a concentration of approximately 2 mg / mL. This solution can be used directly for GPC testing without further processing.

[0044] The EmimAc / DMF was mixed at a mass ratio of 1:30 and sonicated for 0.5 h. It was then used as a mobile phase for rinsing the chromatographic system. The test could only be performed after the baseline had stabilized.

[0045] The molecular weight of the obtained cellulose solution was determined by GPC-MALLS. The GPC unit was a Waters e2695, the differential detector was a Waters 2414, the laser light scattering detector was a Wyatt DAWN HELEOS-II, the column was a PL-Mixed C, the mobile phase was EmimAc / DMF (1:30, w / w), the column temperature and detector temperature were set to 40℃, the flow rate was 0.5 mL / min, and the injection volume was 20 μL.

[0046] Test results are as follows Figure 2 As shown, the calculated absolute weight-average molecular weight of wood pulp is 5.05 × 10⁻⁶. 5 g / mol, polydispersity index is 4.22.

[0047] Example 3

[0048] 20 mg of bacterial cellulose was dissolved in 1 g of BmimAc / DMSO (1:1, w / w) solvent and magnetically stirred at room temperature for 1 h. Then, 9.5 g of DMAc was slowly added dropwise to the above solution and stirring was continued for 0.5 h. The resulting solution was filtered through a 0.22 μm PTFE membrane into a clean sample bottle to obtain a cellulose solution with a concentration of approximately 2 mg / mL, which could be used directly for GPC testing without further processing.

[0049] Mix BmimAc / DMSO / DMAc at a mass ratio of 1:1:19 and sonicate for 0.5 h. Use this mixture as a mobile phase for rinsing the chromatographic system. Tests can only be performed after the baseline has stabilized.

[0050] The molecular weight of the obtained cellulose solution was determined by GPC-MALLS. The GPC unit was a Waters e2695, the differential detector was a Waters 2414, the laser light scattering detector was a Wyatt DAWN HELEOS-II, the column was a PL-Mixed C, the mobile phase was BmimAc / DMSO / DMAc (1:1:19, w / w), the column temperature and detector temperature were set to 40℃, the flow rate was 0.5 mL / min, and the injection volume was 20 μL.

[0051] Test results are as follows Figure 3 As shown, the calculated absolute weight-average molecular weight of bacterial cellulose is 3.59 × 10⁻⁶. 5 g / mol, polydispersity index is 3.02.

[0052] Example 4

[0053] Dissolve 20 mg of a mixture of microcrystalline cellulose and wood pulp (microcrystalline cellulose: wood pulp = 3:1 or 1:1) in 1 g of EmimAc / DMF (1:1, w / w) solvent and stir magnetically at room temperature for 0.5 h. Then, slowly add 14.5 g of DMF to the above solution and continue stirring for 0.5 h. Filter the resulting solution through a 0.22 μm PTFE membrane into a clean sample vial to obtain a cellulose solution with a concentration of approximately 2 mg / mL. This solution can be used directly for GPC testing without further processing.

[0054] The EmimAc / DMF was mixed at a mass ratio of 1:30 and sonicated for 0.5 h. It was then used as a mobile phase for rinsing the chromatographic system. The test could only be performed after the baseline had stabilized.

[0055] The molecular weight of the obtained cellulose solution was determined by GPC-MALLS. The GPC unit was a Waters e2695, the differential detector was a Waters 2414, the laser light scattering detector was a Wyatt DAWN HELEOS-II, the column was a PL-Mixed C, the mobile phase was EmimAc / DMF (1:30, w / w), the column temperature and detector temperature were set to 40℃, the flow rate was 0.5 mL / min, and the injection volume was 20 μL.

[0056] Test results are as follows Figure 4 As shown, the calculated absolute weight-average molecular weight of the mixture of microcrystalline cellulose / wood pulp = 3:1 is 1.33 × 10⁻⁶. 5 The polydispersity index is 7.15; while the absolute weight-average molecular weight of the 1:1 mixture of microcrystalline cellulose and wood pulp is 2.37 × 10⁻⁶ g / mol. 5 The concentration is g / mol, and the polydispersity index is 6.03. The relative height of the main peak and the shoulder peak can be used to roughly determine the relative content of each component in the mixture.

[0057] Example 5

[0058] 20 mg of viscose fiber was dissolved in 1 g of BmimAc / DMSO (1:1, w / w) solvent and magnetically stirred at room temperature for 0.5 h. Then, 9.5 g of DMAc was slowly added dropwise to the above solution and stirring was continued for 0.5 h. The resulting solution was filtered through a 0.22 μm PTFE membrane into a clean sample bottle to obtain a cellulose solution with a concentration of approximately 2 mg / mL, which could be used directly for GPC testing without further processing.

[0059] Mix BmimAc / DMSO / DMAc at a mass ratio of 1:1:19 and sonicate for 0.5 h. Use this mixture as a mobile phase for rinsing the chromatographic system. Tests can only be performed after the baseline has stabilized.

[0060] The molecular weight of the obtained cellulose solution was determined by GPC-MALLS. The GPC unit was a Waters e2695, the differential detector was a Waters 2414, the laser light scattering detector was a Wyatt DAWN HELEOS-II, the column was a PL-Mixed C, the mobile phase was BmimAc / DMSO / DMAc (1:1:19, w / w), the column temperature and detector temperature were set to 40℃, the flow rate was 0.5 mL / min, and the injection volume was 20 μL.

[0061] Test results are as follows Figure 5 As shown, the calculated absolute weight-average molecular weight of viscose fiber is 7.31 × 10⁻⁶. 4 g / mol, with a polydispersity index of 3.33.

[0062] Example 6

[0063] Dissolve 20 mg of cellophane in 1 g of BmimAc / DMSO (1:1, w / w) solvent and stir magnetically at room temperature for 0.5 h. Then, slowly add 9.5 g of DMAc to the above solution and continue stirring for 0.5 h. Filter the resulting solution through a 0.22 μm PTFE membrane into a clean sample bottle to obtain a cellulose solution with a concentration of approximately 2 mg / mL. This solution can be used directly for GPC testing without further processing.

[0064] Mix BmimAc / DMSO / DMAc at a mass ratio of 1:1:19 and sonicate for 0.5 h. Use this mixture as a mobile phase for rinsing the chromatographic system. Tests can only be performed after the baseline has stabilized.

[0065] The molecular weight of the obtained cellulose solution was determined by GPC-MALLS. The GPC unit was a Waters e2695, the differential detector was a Waters 2414, the laser light scattering detector was a Wyatt DAWN HELEOS-II, the column was a PL-Mixed C, the mobile phase was BmimAc / DMSO / DMAc (1:1:19, w / w), the column temperature and detector temperature were set to 40℃, the flow rate was 0.5 mL / min, and the injection volume was 20 μL.

[0066] Test results are as follows Figure 6 As shown, the calculated absolute weight-average molecular weight of the cellophane is 1.09 × 10⁻⁶. 5 g / mol, polydispersity index is 3.80.

[0067] Comparative Example 1

[0068] 20 mg of pullulan standard (molecular weight calibrated as 8.05 × 10⁻⁶) was added. 5 9.5 g of pullulan (g / mol) was dissolved in 1 g of BmimAc / DMSO (1:1, w / w) solvent and magnetically stirred at room temperature for 0.5 h. Then, 9.5 g of DMAc was slowly added dropwise to the above solution and stirring was continued for 0.5 h. The resulting solution was filtered through a 0.22 μm PTFE membrane into a clean sample vial to obtain a pullulan solution with a concentration of approximately 2 mg / mL, which could be used directly for GPC testing without further aging.

[0069] Mix BmimAc / DMSO / DMAc at a mass ratio of 1:1:19 and sonicate for 0.5 h. Use this mixture as a mobile phase for rinsing the chromatographic system. Tests can only be performed after the baseline has stabilized.

[0070] The molecular weight of the obtained pullulan solution was determined by GPC-MALLS. The GPC unit was a Waters e2695, the differential detector was a Waters 2414, the laser light scattering detector was a Wyatt DAWN HELEOS-II, the column was a PL-Mixed C, the mobile phase was BmimAc / DMSO / DMAc (1:1:19, w / w), the column temperature and detector temperature were set to 40℃, the flow rate was 0.5 mL / min, and the injection volume was 20 μL.

[0071] Test results are as follows Figure 7 As shown, the calculated absolute weight-average molecular weight of the pullulan standard is 8.04 × 10⁻⁶. 5 The polydispersity index is 1.13. The calculated absolute weight-average molecular weight of pullulan standard is very close to its molecular weight calibration value, indicating that the method of this invention can accurately characterize the molecular weight and molecular weight distribution of cellulose.

[0072] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for characterizing the molecular weight of cellulose, comprising the following steps: (1) Preparation of a cellulose solution: cellulose is dissolved in an ionic liquid / co-solvent I system to obtain a cellulose solution A; co-solvent II is added to the cellulose solution A to obtain a cellulose solution B, and the cellulose solution B is filtered through a filter membrane; (2) Preparation of a mobile phase: ionic liquid is mixed with co-solvent I and co-solvent II, and the resulting mixed solvent is used as a mobile phase C; (3) Chromatographic test: the cellulose solution B is subjected to determination of the molecular weight and molecular weight distribution of cellulose by gel permeation chromatography based on the mobile phase C; wherein: when the ionic liquid is 1 butyl 3 methylimidazole acetate (BmimAc), the co-solvent I is dimethyl sulfoxide (DMSO) and the co-solvent II is N,N-dimethylacetamide (DMAc); in the ionic liquid / co-solvent I system, BmimAc / DMSO = 1:1, w / w; in the cellulose solution B, the mass of ionic liquid: the total mass of co-solvent I and co-solvent II is 1:20; in the mobile phase C, the mass ratio of BmimAc / DMSO / DMAc is 1:1:19; when the ionic liquid is 1 ethyl 3 methylimidazolium acetate (EmimAc), the cosolvent I, cosolvent II are both N,N-dimethylformamide (DMF); in the ionic liquid / co-solvent I system, EmimAc / DMF = 1:1, w / w; in the cellulose solution B, the mass of ionic liquid: the total mass of co-solvent I and co-solvent II is 1:30; in the mobile phase C, the mass ratio of EmimAc / DMF is 1:

30.

2. The characterization method of claim 1, wherein, The cellulose is a mixture of one or more of microcrystalline cellulose, wood pulp, bacterial cellulose, purified cotton, viscose fiber, glass paper, cotton pulp, and cellulose oligomers.

3. The characterization method of claim 1, wherein, The mass concentration of cellulose in the solution A is 0.1-5%.

4. The characterization method according to any one of claims 1-3, characterized in that, In the solution B, the concentration of cellulose is 0.5-5 mg / mL.

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