Method for detecting solubility of pulp in ionic liquid

Abstract

The invention relates to the technical field of regenerated cellulose, and provides a method for detecting the solubility of pulp in ionic liquid. Pulp is smashed and then mixed with an ionic liquid aqueous solution, then vacuum rotary evaporation is conducted, and colloid is obtained; the colloid is filtered, the filtering performance of the pulp is judged according to the weight of the colloid passing through the filter screen, meanwhile, the number of bright spots in the colloid is observed under a polarizing microscope, and the solubility of the pulp in the ionic liquid is judged according to the number of the bright spots. According to the method provided by the invention, traditional equipment is adopted, production requirements are completely simulated, and the solubility of the pulp in the ionic liquid can be rapidly and accurately detected; by adopting the method, the availability of the raw materials can be evaluated in advance, a scientific basis is provided for purchasing qualified pulp, the quality of regenerated cellulose products is guaranteed from the source, and the product quality is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of regenerated cellulose, and particularly relates to a method for detecting solubility of pulp in ionic liquid. BACKGROUND

[0002] The solvent method is the most commonly used method for preparing regenerated cellulose at present, which can avoid environmental pollution and safety hazards caused by the use of toxic reagents such as carbon disulfide in the traditional viscose method by directly dissolving natural cellulose raw materials through specific solvents.

[0003] As a new type of green organic solvent, ionic liquid has unique advantages in the solvent method. It has strong designability, excellent solubility, low vapor pressure, and recyclability, and can efficiently dissolve cellulose under mild conditions with less damage to the structure of cellulose.

[0004] In the process of preparing regenerated cellulose by using ionic liquid, pulp as the core raw material, its solubility in ionic liquid directly affects the quality and production efficiency of the regenerated cellulose product, which is a key indicator in the production process. However, current researches focus more on the detection of the solubility of ionic liquid itself, and lack effective detection methods for the solubility of pulp in ionic liquid, which makes it difficult to accurately determine whether the pulp is suitable for production, so that enterprises are difficult to evaluate the usability of the pulp through quantitative indicators when purchasing raw materials, thereby affecting the stability of product quality. SUMMARY

[0005] Therefore, the present application provides a method for detecting the solubility of pulp in ionic liquid. The method provided by the present application can quickly and accurately detect the solubility of pulp in ionic liquid by completely simulating the production requirements.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] A method for detecting the solubility of pulp in ionic liquid, comprising the following steps:

[0008] After the pulp is crushed, it is mixed with an ionic liquid aqueous solution to obtain a mixed slurry;

[0009] The mixed slurry is subjected to vacuum rotary evaporation to obtain a colloid;

[0010] The colloid is filtered for a certain period of time, the weight of the filtered colloid is detected and recorded as m; the filtration performance of the pulp is judged according to the m value; the larger the m value is, the better the filtration performance of the pulp is;

[0011] The number of bright spots in the colloid is observed under a polarizing microscope, and recorded as n; the solubility of the pulp in the ionic liquid is determined according to the value of n; the smaller the value of n, the better the solubility of the pulp in the ionic liquid.

[0012] Preferably, the degree of polymerization of the pulp is 500-2500.

[0013] Preferably, the content of water in the aqueous ionic liquid solution is 20-28wt%.

[0014] Preferably, the mass fraction of the pulp in the mixed pulp slurry is 6-11%.

[0015] Preferably, the vacuum degree of the vacuum rotary evaporation is 800-1200Pa, and the temperature is 100-125℃.

[0016] Preferably, the content of water in the colloid is less than or equal to 1.5wt%.

[0017] Preferably, the precision of the filtration is 50-100μm, and the time is 10min.

[0018] Preferably, the filtration is vacuum filtration, and the vacuum degree of the vacuum filtration is 800-1200Pa.

[0019] Preferably, the amount of the pulp is 15g, and the standard for judging the filtration performance of the pulp according to the value of m includes: m is 0-30g, indicating that the filtration performance of the pulp is poor; 30g

[0020] Preferably, the standard for judging the solubility of the pulp in the ionic liquid according to the value of n includes: n is 0-10, indicating that the solubility of the pulp in the ionic liquid is excellent; 10

[0021] The application provides a method for detecting the solubility of pulp in ionic liquid, comprising the following steps: mixing the crushed pulp with ionic liquid aqueous solution to obtain mixed pulp; filtering the colloid in a certain time, detecting the weight of the obtained filtered colloid, and recording it as m; judging the filtering performance of the pulp according to the m value; the larger the m value is, the better the filtering performance of the pulp is; observing the number of bright spots in the colloid under a polarizing microscope, and recording it as n; judging the solubility of the pulp in ionic liquid according to the n value; the smaller the n value is, the better the solubility of the pulp in ionic liquid is. The method provided by the application can quickly and accurately detect the solubility of the pulp in ionic liquid, and the analysis is not interfered, simple and fast; the application breaks through the phenomenon that there is no test method for the raw material index in the process of dissolving cellulose by using ionic liquid solvent method, and the usability of the raw material can be evaluated in advance by using the method, so that scientific basis is provided for purchasing qualified pulp, and the quality of the regenerated cellulose product is guaranteed from the source, and the product quality is improved. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is the physical map (left) and the structural schematic diagram (right) of the filter, wherein: 1 - barrel, 2 - colloid, 3 - isolation filter screen, 4 - vacuum port;

[0023] Figure 2 It is the observation result of the colloid in example 1 under a polarizing microscope;

[0024] Figure 3 It is the observation result of the colloid in example 4 under a polarizing microscope. DETAILED DESCRIPTION

[0025] The application provides a method for detecting the solubility of pulp in ionic liquid, comprising the following steps:

[0026] Mixing the crushed pulp with ionic liquid aqueous solution to obtain mixed pulp;

[0027] Vacuum rotary evaporation is carried out on the mixed pulp to obtain a colloid;

[0028] Filtering the colloid in a certain time, detecting the weight of the obtained filtered colloid, and recording it as m; judging the filtering performance of the pulp according to the m value; the larger the m value is, the better the filtering performance of the pulp is;

[0029] Observing the number of bright spots in the colloid under a polarizing microscope, and recording it as n; judging the solubility of the pulp in ionic liquid according to the n value; the smaller the n value is, the better the solubility of the pulp in ionic liquid is.

[0030] The present application mixes the pulp after being crushed and the ionic liquid aqueous solution to obtain a mixed pulp. In the present application, the degree of polymerization of the pulp is preferably 500-2500, and can be 500, 1000, 1500, 2000 or 2500; in the present application, the impurity content of the pulp with different degrees of polymerization is also different; in the specific embodiments of the present application, the solubility of a plurality of different pulps can be detected respectively, and then the solubility is compared.

[0031] The present application does not have special requirements for the type of the pulp, and the pulp commonly used in the art can be detected by the method of the present application, such as conifer dissolving pulp, cotton pulp, etc.

[0032] The present application does not have special requirements for the crushing method, and the pulp can be crushed into a velvet-like fiber.

[0033] In the present application, after being crushed, the obtained crushed pulp is preferably balanced in moisture, and then mixed with the ionic liquid aqueous solution; the balancing of moisture is preferably: the crushed pulp is balanced for 24h under constant temperature and humidity conditions; the temperature of the constant temperature and humidity conditions is preferably 25℃, and the humidity is preferably 50%.

[0034] In the present application, the ionic liquid aqueous solution is preferably obtained by mixing ionic liquid and water; the content of water in the ionic liquid aqueous solution is preferably 20-28wt%, and can be 25wt%; the present application adds part of water to swell the fiber, and promotes the dissolution speed of the ionic liquid to the fiber.

[0035] The present application does not have special requirements for the type of the ionic liquid, and can be selected according to actual needs; in the specific embodiments of the present application, the ionic liquid is 1-allyl-3-methylimidazole chloride.

[0036] In the present application, the mass fraction of the pulp in the mixed pulp is preferably 6-11%, and can be 6.3% or 8.3%.

[0037] After obtaining the mixed pulp, the present application performs vacuum rotary evaporation on the mixed pulp to obtain a colloid. In the present application, the vacuum degree of the vacuum rotary evaporation is preferably 800-1200Pa, more preferably 1000Pa, and the temperature is preferably 100-125℃, more preferably 125℃; the water content of the colloid is preferably less than or equal to 1.5wt%, more preferably less than or equal to 1wt%. The present application dehydrates through the rotary evaporation process to make the cellulose dissolve in the ionic liquid.

[0038] The colloid is filtered for a certain time, the weight of the obtained filtered colloid (i.e. the colloid passing through the filter screen) is detected and recorded as m; the filterability of the pulp is determined according to the value of m; the larger the value of m is, the better the filterability of the pulp is. In the present application, the better filterability means the less insoluble impurities in the pulp; the precision of the filtration is preferably 50-100 μm, and the filtration time is preferably 10 min; in the present application, the filtration time is controlled to be 10 min, and the filterability is determined according to the mass of the colloid passing through the filter screen within 10 min; the filtration is preferably vacuum filtration; the vacuum degree of the vacuum filtration is preferably 800-1200 Pa, and more preferably 1000 Pa. In the specific embodiments of the present application, the filtration is preferably performed using a filter; the filter preferably comprises a material barrel and a separation filter screen arranged at the bottom of the material barrel; the diameter of the filter barrel is preferably 50 cm; when vacuum filtration is performed, the colloid is placed in the material barrel of the filter, and a colloid receiving device is placed at the bottom of the separation filter screen; the sidewall of the colloid receiving device is provided with a vacuum suction port; the vacuum suction port is connected with a vacuum suction device to perform vacuum filtration; the actual picture and structural schematic diagram of the filter are shown in Figure 1 In the specific embodiments of the present application, the filter is preferably subjected to constant temperature treatment before filtration; the temperature of the constant temperature treatment is preferably the same as that of the vacuum rotary evaporation.

[0039] In the present application, the amount of the pulp is 15 g, and the standard for determining the filterability of the pulp according to the value of m includes: m is 0-30 g, indicating that the filterability of the pulp is poor; 30 g < m ≤ 50 g, indicating that the filterability of the pulp is general; 50 g < m ≤ 80 g, indicating that the filterability of the pulp is good; and m > 80 g, indicating that the filterability of the pulp is excellent. The determination standard of the filterability is specifically shown in Table 1:

[0040] Table 1: Determination standard of filterability

[0041] Colloidal weight filtered 0-30g 30 g < m < 50 g 50 g < m < 80 g m > 80 g Filtering performance Bad Average Good Excellent

[0042] After obtaining the colloid, the number of bright spots in the colloid (the colloid before filtration) is observed under a polarizing microscope and recorded as n; the solubility of the pulp in the ionic liquid is determined according to the value of n; the smaller the value of n is, the better the solubility of the pulp in the ionic liquid is. In the present application, the bright spots are the undissolved cellulose, which exhibits crystal characteristics under the polarizing microscope. In the specific embodiments of the present application, the colloid obtained by vacuum rotary evaporation is preferably randomly sampled and observed; specifically, a glass rod is used to sample, one drop of the sample is added on a glass slide, a cover glass is used to flatten it, and then the sample is placed under a polarizing microscope for observation; the number of bright spots in one field of view is determined, and the average value of the parallel test for three times is taken as the value of n.

[0043] In the present application, the standard for judging the solubility of pulp in ionic liquid according to the value of n includes: n is 0-10, indicating that the solubility of pulp in ionic liquid is superior, 10

[0044] Table 2 Solubility judgment standard

[0045] Number of highlights 0 - 10 10 < n < 30 30 < n < 50 50 < n < 60 n > 60 Dissolution performance Excellent dissolution Good dissolution Average dissolution Poor dissolution Insoluble

[0046] The technical solutions in the present application will be described clearly and completely in combination with the embodiments in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0047] The filter used in the following embodiments has the structure as shown in Figure 1 The diameter of the filter cartridge is 50 cm.

[0048] Embodiment 1

[0049] S1, Pulp preparation: the pulp with a polymerization degree of 1000 (conifer dissolving pulp) is crushed, and is balanced for 24 h under the condition of temperature 25℃ and humidity 50%, and then 15 g of the pulp is weighed for use;

[0050] S2, Material mixing: 220 g of ionic liquid aqueous solution with water content of 25wt% is added to 15 g of the pulp, to obtain mixed pulp; wherein the ionic liquid is 1-allyl-3-methyl imidazole chloride;

[0051] S3, Preparation of colloid: the mixed pulp is added to a round-bottom flask, and rotary evaporation is carried out under the condition of vacuum of 1000 pa, and the evaporation temperature is 100℃, and the evaporation is carried out until the water content of the colloid is 0.7wt%;

[0052] S4, the colloid prepared in step S3 is added to a filter which has been thermostated at 100℃, and is filtered for 10 min, and the filtering precision is 50μm, and the weight of the filtered colloid is weighed as 77 g.

[0053] S5, Detection: a glass rod is dipped in the colloid prepared in step S3, and one drop of the sample is added to the surface of a glass slide, and is flattened with a cover glass, and is placed under a polarizing microscope for observation; the parallel test is carried out for 3 times, and the average value is taken, and the result shows that the number of bright spots is 14, and the observation result is as shown in Figure 2 .

[0054] S6, Conclusion: The above results show that the pulp has good filtration performance and good solubility.

[0055] Example 2

[0056] S1, Pulp preparation: The pulp with a degree of polymerization of 2000 (needle dissolution pulp) was crushed and equilibrated at a temperature of 25°C and a humidity of 50% for 24 hours. 15 g of the pulp was weighed and prepared for use;

[0057] S2, Material mixing: 220 g of an aqueous ionic liquid solution with a water content of 25 wt% was added to 15 g of the pulp to obtain a mixed pulp; the ionic liquid was 1-allyl-3-methylimidazolium chloride;

[0058] S3, Preparation of the colloid: the mixed pulp was added to a round-bottom flask and rotary evaporation was performed under a vacuum of 1000 pa, at an evaporation temperature of 100°C, until the water content of the colloid was 0.6 wt%;

[0059] S4, The colloid prepared in step S3 was added to a filter that had been thermostated at 100°C for 10 minutes, with a filtration accuracy of 50 μm. The weight of the filtered colloid was 39 g;

[0060] S5, Detection: a glass rod was dipped in the colloid prepared in step S3, and one drop of the sample was added to the surface of a glass slide. After being flattened with a cover glass, the sample was placed under a polarizing microscope for observation. The average value was obtained by parallel testing three times. The results showed that the number of bright spots was 93;

[0061] S6, Conclusion: The above results show that the pulp has general filtration performance, but poor solubility, and is a non-dissolution pulp.

[0062] Example 3

[0063] S1, Pulp preparation: The pulp with a degree of polymerization of 1500 (needle dissolution pulp) was crushed and equilibrated at a temperature of 25°C and a humidity of 50% for 24 hours. 15 g of the pulp was weighed and prepared for use;

[0064] S2, Material mixing: 220 g of an aqueous ionic liquid solution with a water content of 25 wt% was added to 15 g of the pulp to obtain a mixed pulp; the ionic liquid was 1-allyl-3-methylimidazolium chloride;

[0065] S3, Preparation of the colloid: the mixed pulp was added to a round-bottom flask and rotary evaporation was performed under a vacuum of 1000 pa, at an evaporation temperature of 100°C, until the water content of the colloid was 0.8 wt%;

[0066] S4, The colloid prepared in step S3 was added to a filter that had been thermostated at 100°C for 10 minutes, with a filtration accuracy of 50 μm. The weight of the filtered colloid was 63 g.

[0067] S5, detection: the glass rod dipped in the colloid prepared in step S3, a drop of sample was added to the surface of the slide, and then the slide was placed under a polarizing microscope after being flattened with a cover glass. The number of bright spots was 71 after parallel testing three times and taking the average value.

[0068] S6, conclusion: the above results show that the pulp has good filtering performance but poor dissolving performance, and is a pulp with poor dissolving performance.

[0069] Example 4

[0070] S1, pulp preparation: the pulp with a degree of polymerization of 2500 (needle dissolution pulp) was crushed, and then was balanced for 24 hours at a temperature of 25°C and a humidity of 50%, and 15g of the pulp was weighed for use;

[0071] S2, material mixing: 220g of an aqueous solution of an ionic liquid with a water content of 25wt% was added to 15g of the pulp, to obtain mixed pulp; the ionic liquid was 1-allyl-3-methylimidazole chloride;

[0072] S3, preparation of the colloid: the mixed pulp was added to a round-bottom flask, and then rotary evaporation was performed under a vacuum condition of 1000pa, the evaporation temperature was 100°C, and the evaporation was performed until the water content of the colloid was 0.8wt%.

[0073] S4, the colloid prepared in step S3 was added to a filter which had been thermostated at 100°C, and then was filtered for 10 minutes, the filtering precision was 50μm, and the weight of the filtered colloid was 23g.

[0074] S5, detection: the glass rod dipped in the colloid prepared in step S3, a drop of sample was added to the surface of the slide, and then the slide was placed under a polarizing microscope after being flattened with a cover glass. The number of bright spots was 71 after parallel testing three times and taking the average value. Figure 3

[0075] S6, conclusion: the above results show that the pulp has poor filtering performance and is a pulp which cannot be dissolved.

[0076] In summary, the present application provides a method for detecting the dissolving performance of pulp in an ionic liquid, the pulp and an aqueous solution of an ionic liquid are subjected to vacuum dehydration and dissolution, the obtained colloid is subjected to vacuum suction filtration through a filter screen, the dissolving performance of the pulp is determined according to the weight of the colloid obtained within a certain time, and the dissolving quality of the colloid is further determined by using a polarizing microscope due to the different viscosities of pulps with different degrees of polymerization after dissolution. The detection speed of the present application is fast, and the actual situation of the production process can be truly reflected.

[0077] ​The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A method for detecting the solubility of pulp in ionic liquids, characterized in that, Includes the following steps: The pulp is pulverized and then mixed with an aqueous solution of an ionic liquid to obtain a mixed pulp. The mixed slurry was subjected to vacuum rotary evaporation to obtain a colloid; The colloid is filtered within a certain time, and the weight of the filtered colloid is measured and recorded as m. The filtration performance of the pulp is judged based on the value of m. The larger the value of m, the better the filtration performance of the pulp. The number of bright spots in the colloid is observed under a polarizing microscope and denoted as n; the solubility of the pulp in the ionic liquid is determined based on the value of n; the smaller the value of n, the better the solubility of the pulp in the ionic liquid.

2. The method according to claim 1, characterized in that, The degree of polymerization of the pulp is 500 to 2500.

3. The method according to claim 1, characterized in that, The water content in the aqueous solution of the ionic liquid is 20–28 wt%.

4. The method according to claim 1, characterized in that, The mass fraction of pulp in the mixed slurry is 6-11%.

5. The method according to claim 1, characterized in that, The vacuum degree of the vacuum rotary evaporation is 800-1200 Pa, and the temperature is 100-125℃.

6. The method according to claim 1, characterized in that, The moisture content of the colloid is less than or equal to 1.5 wt%.

7. The method according to claim 1, characterized in that, The filtration accuracy is 50–100 μm, and the time is 10 min.

8. The method according to claim 1 or 7, characterized in that, The filtration is a vacuum filtration; the vacuum degree of the vacuum filtration is 800-1200 Pa.

9. The method according to claim 1 or 7, characterized in that, The amount of pulp used is 15g. The standard for judging the filtration performance of pulp based on the m value includes: m is 0~30g, indicating poor filtration performance of pulp; 30g<m≤50g, indicating average filtration performance of pulp; 50g<m≤80g, indicating good filtration performance of pulp; m>80g, indicating excellent filtration performance of pulp.

10. The method according to claim 1, characterized in that, The criteria for judging the solubility of pulp in ionic liquids based on the n value are as follows: n = 0-10 indicates excellent solubility of pulp in ionic liquids; 10 < n ≤ 30 indicates good solubility of pulp in ionic liquids; 30 < n ≤ 50 indicates average solubility of pulp in ionic liquids; 50 < n ≤ 60 indicates poor solubility of pulp in ionic liquids; and n > 60 indicates that pulp is insoluble in ionic liquids.

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