Preparation and use of high-polymerization-degree and high-substitution-degree cellulose formate

Abstract

A method for preparing a high-polymerization-degree and high-substitution-degree cellulose formate. The method comprises the following steps: subjecting a cellulose raw material to an immersion treatment in a molten salt hydrate, and then carrying out solid-liquid separation, wherein the separated solid phase is a cellulose slurry and is washed and dried, and the separated liquid phase is the molten salt hydrate and is recycled; dispersing the cellulose slurry in a formic acid solution to perform a reaction, adding a regeneration solvent after the reaction is finished, and then carrying out solid-liquid separation, cleaning and drying, so as to obtain a high-polymerization-degree cellulose formate; or dispersing the cellulose slurry in a formic acid solution to perform a reaction, and carrying out direct-spinning or film formation after the reaction is finished. The preparation method has mild conditions and avoids drastic degradation of cellulose during the reaction process; in addition, the obtained cellulose formate product has a high polymerization degree and a high substitution degree, and a high yield, which is 117-135% of the raw materials. Moreover, both the molten salt hydrate and the formic acid reagent used in the preparation method can be recycled.

Description

Preparation and application of cellulose formate with high degree of polymerization and high degree of substitution Technical Field

[0001] Preparation and application of cellulose formate with high degree of polymerization and high degree of substitution Background Art

[0002] Cellulose esters can be divided into organic and inorganic esters, depending on the type of acid that reacts with cellulose. Cellulose esters are commercially important biomass-modified materials with wide applications in plastics, films, fibers, coatings, and pharmaceuticals. Cellulose acetate, cellulose nitrate, and cellulose sulfate, in particular, are all industrially produced. Cellulose esters also exhibit significant potential in the pharmaceutical field.

[0003] At present, there are few reports on the research and application of cellulose formate. This is mainly because the cellulose formate prepared by the existing method has a low degree of polymerization, resulting in poor performance and no good application prospects. Generally speaking, the preparation principle of cellulose formate is: each glucose group in the cellulose macromolecule contains three alcoholic hydroxyl polar groups; in formic acid solution, the alcoholic hydroxyl groups undergo protonation reaction to produce the corresponding cellulose formate. However, due to the anti-degradation barrier effect of natural cellulose, the aforementioned protonation reaction usually requires sulfuric acid, hydrochloric acid, phosphoric acid or zinc chloride as a catalyst. Using this method, although on the one hand, cellulose formate with a high degree of substitution can be obtained, on the other hand, due to the severe degradation of cellulose during the hydrolysis process, the degree of polymerization of cellulose formate is low (<200). This further leads to poor mechanical properties when using this cellulose formate to prepare films or other materials (J. Poly. Sci.: Poly. Lett., 1986, 24(10), 495; J. Poly. Sci.: Poly. Chem., 1986, 24, 2981), making it impossible to use it in practice. Furthermore, this method also involves a reaction between cellulose and the strong acid catalyst, resulting in a product of insufficient purity, often resulting in a mixture of cellulose formate and other cellulose esters. There are also reports of direct hydrolysis of cellulose with formic acid at high temperatures; however, this high reaction temperature results in low product yields. Literature reports that reacting bleached softwood pulp with 98 wt% formic acid at 90°C for 20 hours yielded a maximum yield of only 45% (ACS Sustain. Chem. Eng., 2019, 7, 9449).

[0004] In summary, the existing cellulose formate production process suffers from low product polymerization degree, low yield, and difficulty in obtaining a pure product, significantly limiting its application. Obtaining cellulose formate with high polymer content, high degree of substitution, and high yield is a prerequisite for its widespread application. Currently, there are no reports on methods for producing cellulose formate with high polymerization degree and high yield. Technical issues

[0005] To address the problems of existing cellulose formate preparation methods, the present invention provides a method for preparing cellulose formate with a high degree of polymerization. This method not only utilizes mild conditions, avoiding severe cellulose degradation during hydrolysis, but also achieves a high cellulose formate yield of 117-135% of the raw material. Furthermore, the molten salt hydrate and formic acid reagent used in the preparation method are reusable, resulting in low production costs, broad market application prospects, and significant economic value. Technical Solutions

[0006] The technical solution of the present invention is a method for preparing high-polymerization degree cellulose formate or its derivatives, comprising the following steps:

[0007] (1) The cellulose raw material is immersed in molten salt hydrate, and then the solid and liquid are separated; the solid phase after separation is cellulose pulp, which is washed and dried, and the liquid phase after separation is molten salt hydrate, which is recycled. The solid content of the cellulose raw material in the molten salt hydrate is 1-20wt%, the immersion temperature is 10-50℃, and the immersion time is 1-100min. The cellulose raw material is microcrystalline cellulose, cotton pulp, dissolving pulp, ascidian cellulose or bacterial cellulose. The molten salt hydrate is Li + Mg 2+ , Ca 2+ 、Zn 2+ 、Al 3+ 、Fe 3+ and Cu 2+ One or two of the hydrates of chloride, bromide, iodide, perchlorate, nitrate and thiocyanate; the weight fraction of the inorganic salt in the molten salt hydrate is 40-70%.

[0008] This step changes the crystal form of the cellulose raw material while ensuring that the cellulose raw material does not dissolve by controlling the solid content, temperature conditions and treatment time of the cellulose raw material during the impregnation treatment. The reaction conditions are mild and the process is simple, which is of great significance for industrial production.

[0009] (2) The cellulose pulp obtained in step (1) is dispersed in a formic acid solution for reaction, and after the reaction is completed, a regeneration solvent is added, followed by solid-liquid separation and washing to obtain a high-polymerization degree cellulose formate wet material; or the cellulose pulp obtained in step (1) is dispersed in a formic acid solution for reaction, and after the reaction is completed, directly spinning or film forming. The solid content of the cellulose pulp in the formic acid solution is 1-20wt%, the concentration of the formic acid solution is 50-98%, the reaction temperature is 10-50°C, and the reaction time is 1h-72h. The regeneration solvent is water, ethanol, acetone, tert-butanol, or n-butanol.

[0010] The change in the cellulose structure in the cellulose pulp treated in step (1) enables it to react with formic acid at a lower temperature in this step, thereby avoiding severe degradation of the cellulose during the reaction. The resulting cellulose formate has the advantages of a high degree of substitution (1.0-2.0), a high degree of polymerization (300-1000), and a high yield (117-135% of the raw material). Compared with existing cellulose formate, the product performance is significantly improved, producing unexpected technical effects. This method solves the difficulties faced in actual production and has important practical application value.

[0011] Preferably, the molten salt hydrate is LiBr·3H2O, ZnCl2·4H2O, LiCl·3H2O, AlCl3·6H2O, FeCl3·6H2O, MgCl2·6H2O, CaCl2·6H2O, LiNO3·3H2O, Ca(NO3)2·4H2O, Mg(NO3)2·6H2O, LiClO4·3H2O or LiSCN·2.5H2O.

[0012] Preferably, the cellulose slurry described in step (1) is washed with water, and the resulting liquid phase is a salt solution. The molten salt hydrate is separated by chromatography or rotary evaporation, concentrated to the initial concentration, and recycled. The liquid obtained by solid-liquid separation in step (2) is a formic acid-regeneration solvent solution, which can also be recycled after being concentrated to the initial concentration. In this application, both the molten salt and formic acid can be recycled, which greatly reduces the process cost. The entire process is green, clean and sustainable, which has important practical significance for promoting the high-value utilization of cellulose.

[0013] The high-polymerization cellulose formate prepared by the aforementioned method has a degree of substitution of 1.0-2.0, a cellulose II crystal form, a degree of polymerization of 300-1000, and a yield of 117-135% of the raw material. Furthermore, the cellulose formate is soluble in formic acid, dimethyl sulfoxide, pyridine, N-methylpyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide, facilitating further processing and applications. It can also be used as an intermediate for the preparation of various cellulose derivatives. Furthermore, the high-substitution cellulose formate exhibits good interfacial compatibility with polymers (such as rubber and plastics), improving their mechanical properties and thermal stability. Furthermore, as a biodegradable regenerated cellulose ester, cellulose formate has the potential to serve as an alternative to petroleum-based materials, which is of great significance for ecological protection.

[0014] As previously mentioned, high-polymerization cellulose formate is used to prepare cellulose derivatives or cellulose formate-derived products. Specifically, the cellulose formate is dissolved in formic acid, dimethyl sulfoxide, pyridine, N-methylpyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide. The highly reactive aldehyde groups are then reacted to produce cellulose derivatives, casting to produce high-performance cellulose formate films, or spinning to produce cellulose formate filaments with high tensile strength. This is because the formate groups (i.e., formyl groups) in cellulose formate are also aldehyde groups and possess reducing properties. Aldehyde groups can be further oxidized to carboxyl groups, react with amino compounds through Schiff base reactions, or react with sodium bisulfite to introduce sulfonic acid groups. Therefore, using cellulose formate as an intermediate, further derivatization can yield cellulose products with diverse properties. Beneficial effects

[0015] Beneficial effects of the present invention:

[0016] (1) The present invention provides a novel method for preparing cellulose formate, which is simple to operate, has mild reaction conditions, and low process cost, and also has a high product yield (117-135% of the raw material), a high degree of substitution (1.0-2.0), and a high degree of polymerization (300-1000), thereby solving the bottleneck of actual production and having important practical application value.

[0017] (2) The preparation method of the present invention comprises two steps: pre-impregnation of cellulose in a molten salt hydrate system and hydrolysis with formic acid, without the use of other additives (sulfuric acid, phosphoric acid, hydrochloric acid, etc.); the obtained product has high purity and no by-products, and both the molten salt hydrate and formic acid can be recycled by a simple method, with low process cost.

[0018] (3) The cellulose formate obtained by the preparation method of the present invention has a high degree of polymerization, and a high-strength cellulose formate transparent film can be obtained by direct casting. The tensile strength of the film can reach 75-100 MPa, the transmittance can reach 91-96% (550 nm), and it has good barrier properties. High-strength cellulose formate filaments can also be obtained by spinning, and the tensile strength of the filaments can reach 1.0-1.5 cN / dtex.

[0019] (4) The cellulose formate obtained by the preparation method of the present invention is soluble in organic solvents such as formic acid, dimethyl sulfoxide, pyridine, N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide. The maximum solubility in formic acid can reach 10%, and the maximum solubility in dimethyl sulfoxide, pyridine, N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide can reach 8%. It is convenient to use the highly reactive aldehyde group to prepare cellulose derivatives, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG1 is a physical diagram of cellulose formate prepared in Example 1.

[0021] FIG2 is a physical picture of the cellulose formate film prepared in Example 1.

[0022] FIG3 is a stress-strain diagram of the cellulose formate film prepared in Example 1.

[0023] FIG4 is a graph showing the light transmittance of the cellulose formate film prepared in Example 1.

[0024] FIG5 is a diagram showing the spinning process of cellulose formate according to Example 3.

[0025] FIG6 is a physical picture of the cellulose formate filaments prepared in Example 3. Modes for Carrying Out the Invention

[0026] The present invention will be further described below with reference to the embodiments.

[0027] The present invention will be further described below with reference to the following embodiments. The feasibility of the present method is further described below with reference to specific implementation examples, but it does not mean that the present invention is limited to these examples.

[0028] Example 1: Preparation of high degree of polymerization and high degree of substitution cellulose formate

[0029] First, cotton pulp is pre-impregnated in molten salt hydrate. The cotton pulp has a solid content of 1%, and the molten salt hydrate is a 60% LiBr solution. After impregnation at 50°C for 5 minutes, the pulp is washed and dried. The recovered molten salt hydrate is then rotary evaporated and reused. The pre-impregnated pulp is then added to a 98% formic acid solution for reaction. The cotton pulp has a solid content of 1%. The reaction temperature is 30°C, and the reaction time is 72 hours. After the reaction, the wet cellulose formate is washed with water to obtain a white paste at room temperature, as shown in Figure 1. The washed formic acid is then rotary evaporated and reused.

[0030] According to the characterization results, the degree of substitution of the obtained cellulose formate is 2.0, the degree of polymerization is 600, and the yield is 135% of the raw material. In addition, by directly casting the formic acid solution of the obtained cellulose formate, a high-strength transparent film can be obtained, as shown in Figure 2, and the pattern and text under the film can be clearly seen. Through testing, the film has a tensile strength of 100MPa (Figure 3), a transmittance of 96% (550nm, Figure 4), and has good barrier properties (oxygen permeability coefficient 3.838E-11, moisture permeability 4.57 g / (m 2 h), and a water contact angle of 85°). In addition, the cellulose formate has a solubility of up to 10% in anhydrous formic acid and a maximum solubility of up to 8% in dimethyl sulfoxide.

[0031] Comparative Example 1: Changing the dipping temperature

[0032] First, cotton pulp is pre-impregnated in molten salt hydrate. The cotton pulp has a solid content of 1%, and the molten salt hydrate is a 60% LiBr solution. After impregnation at 90°C for 5 minutes, the pulp is washed and dried. The recovered molten salt hydrate is then rotary evaporated and reused. The pre-impregnated pulp is then added to a 98% formic acid solution with a solid content of 1%. The reaction temperature is 30°C, and the reaction time is 72 hours. After the reaction, the wet cellulose formate is washed with water, and the washed formic acid is rotary evaporated and reused.

[0033] Characterization results show that the obtained cellulose formate has a degree of substitution of 1.2, a degree of polymerization of 100, and a yield of 85% of the raw material. Furthermore, direct casting of the formic acid solution of the obtained cellulose formate failed to produce a high-strength film. This indicates that excessively high molten salt hydrate pretreatment temperatures prevent the production of cellulose formate with high degrees of substitution, high degrees of polymerization, and high yields. This is due to partial degradation of the cellulose, which reduces the degree of polymerization and yield of the cellulose formate.

[0034] Comparative Example 2: Changing the formic acid reaction temperature

[0035] First, cotton pulp is pre-impregnated in molten salt hydrate. The cotton pulp has a solids content of 1%, and the molten salt hydrate is a 60% LiBr solution. After impregnation at 50°C for 5 minutes, the pulp is washed and dried. The recovered molten salt hydrate is then rotary evaporated and reused. The pre-impregnated pulp is then added to a 98% formic acid solution with a solids content of 1%. The reaction temperature is 60°C and the reaction time is 1 hour. After the reaction, the wet cellulose formate is washed with water, and the washed formic acid is rotary evaporated and reused.

[0036] Characterization results indicate that the obtained cellulose formate has a degree of substitution of 2.1, but a degree of polymerization of only 50, resulting in a yield of 70% of the raw material. Furthermore, due to the low degree of polymerization of the obtained cellulose formate, direct casting failed to produce a film. This suggests that the reaction temperature of the molten salt pretreated slurry in formic acid was too high (over 50°C), preventing the production of high-polymerization, high-yield cellulose formate.

[0037] Example 2: Preparation of high degree of polymerization and high degree of substitution cellulose formate

[0038] First, microcrystalline cellulose is pre-impregnated in a molten salt hydrate solution containing 20% ​​cellulose solids and a 70% ZnCl₂ solution. After impregnation at 10°C for 1 minute, the slurry is washed and dried, and the recovered molten salt hydrate is rotary evaporated and reused. The pre-impregnated slurry is then added to a 50% formic acid solution containing 20% ​​cotton pulp solids for a reaction. The reaction temperature is 10°C, and the reaction time is 1 hour. After the reaction, the wet cellulose formate is washed and the washed formic acid is rotary evaporated and reused.

[0039] Characterization results indicate that the obtained cellulose formate has a degree of substitution of 1.0, a degree of polymerization of 300, and a yield of 117%. Furthermore, a high-strength film can be obtained by directly casting the formic acid solution of the obtained cellulose formate. Testing showed that the film has a tensile strength of 75 MPa, a light transmittance of 92% (550 nm), and good barrier properties (oxygen permeability coefficient of 8.037E-10, moisture permeability of 3.96 g / (m 2 h), and a water contact angle of 80°). In addition, the cellulose formate has a solubility of up to 8% in N-methylpyrrolidone.

[0040] Example 3: Preparation of high degree of polymerization and high degree of substitution cellulose formate

[0041] First, hardwood dissolving pulp is pre-impregnated in molten salt hydrate. The pulp has a solids content of 10%, and the molten salt hydrate is a 40% ZnCl2 solution. After impregnation at 40°C for 10 minutes, the pulp is washed and dried. The recovered molten salt hydrate is then rotary evaporated and reused. The pre-impregnated pulp is then added to an 88% formic acid solution with a solids content of 5%. The reaction temperature is 50°C and the reaction time is 48 hours. After the reaction, the pulp is washed and dried to obtain a wet cellulose formate. The washed formic acid is then rotary evaporated and reused.

[0042] Characterization results indicate that the obtained cellulose formate has a degree of substitution of 1.4, a degree of polymerization of 500, and a yield of 124%. Furthermore, the resulting cellulose formate solution was spun in a 5% NaOH solution. The spinning process is shown in Figure 5. After washing and drying, cellulose formate filaments were obtained, as shown in Figure 6. Testing revealed a tensile strength of 1.5 cN / dtex. Furthermore, the solubility of this cellulose formate in N,N-dimethylformamide and N,N-dimethylacetamide reaches 8%.

[0043] Example 4: Preparation of high degree of polymerization and high degree of substitution cellulose formate

[0044] First, softwood dissolving pulp is pre-impregnated in molten salt hydrate. The pulp has a solids content of 15% and contains 40% LiBr and 10% CaCl2. After impregnation at 25°C for 80 minutes, the pulp is washed and dried. The recovered molten salt hydrate is then rotary evaporated and reused. The pre-impregnated pulp is then added to a 60% formic acid solution with a solids content of 12%. The reaction temperature is 10°C and the reaction time is 40 hours. After the reaction, the wet cellulose formate is washed and the washed formic acid is rotary evaporated and reused.

[0045] Characterization results indicate that the obtained cellulose formate has a degree of substitution of 1.8, a degree of polymerization of 450, and a yield of 129%. Furthermore, a high-strength film can be obtained by directly casting the formic acid solution of the obtained cellulose formate. Testing showed that the film had a tensile strength of 89 MPa, a light transmittance of 95% (550 nm), and good barrier properties (oxygen permeability coefficient of 2.938E-11, moisture permeability of 5.28 g / (m 2 h), with a water contact angle of 90°). In addition, the cellulose formate has a solubility of up to 10% in anhydrous formic acid and up to 8% in pyridine.

[0046] Example 5: Preparation of high degree of polymerization and high degree of substitution cellulose formate

[0047] First, ascidian cellulose is pre-impregnated in molten salt hydrate with a 5% solids content, containing 40% AlCl₃ and 10% ZnCl₂. After impregnation at 20°C for 50 minutes, the slurry is washed and dried, and the recovered molten salt hydrate is rotary evaporated and reused. The pre-impregnated slurry is then added to a 70% formic acid solution with an 8% solids content. The reaction temperature is 15°C, and the reaction time is 36 hours. After the reaction, the wet cellulose formate is washed and the washed formic acid is rotary evaporated and reused.

[0048] Characterization results indicate that the obtained cellulose formate has a degree of substitution of 1.2, a degree of polymerization of 350, and a yield of 121%. Furthermore, the resulting cellulose formate solution was spun in water and dried to produce cellulose formate filaments. Testing revealed a tensile strength of 1.0 cN / dtex. Furthermore, the cellulose formate exhibits a solubility of 8% in anhydrous formic acid and 6% in N-methylpyrrolidone.

[0049] Example 6: Preparation of high degree of polymerization and high degree of substitution cellulose formate

[0050] First, bacterial cellulose is pre-impregnated in molten salt hydrate. The slurry has a solids content of 2% and contains 30% LiCl and 40% ZnCl₂. After impregnation at 15°C for 90 minutes, the slurry is washed and dried. The recovered molten salt hydrate is then rotary evaporated and reused. The pre-impregnated slurry is then added to an 80% formic acid solution with a solids content of 15%. The reaction temperature is 40°C and the reaction time is 5 hours. After the reaction, the wet cellulose formate is washed and the washed formic acid is rotary evaporated and reused.

[0051] Characterization results indicate that the obtained cellulose formate has a degree of substitution of 1.0, a degree of polymerization of 300, and a yield of 117%. Furthermore, the resulting cellulose formate solution was spun in acetone, washed, and dried to produce cellulose formate filaments. Testing revealed a tensile strength of 1.1 cN / dtex. Furthermore, the cellulose formate exhibited a solubility of 5% in N-methylpyrrolidone and 6% in N,N-dimethylacetamide.

[0052] Example 7: Preparation of high degree of polymerization and high degree of substitution cellulose formate

[0053] First, softwood dissolving pulp is pre-impregnated in molten salt hydrate. The pulp has a solids content of 1% and contains 10% LiBr and 30% MgCl2. After impregnation at 30°C for 100 minutes, the pulp is washed and dried. The recovered molten salt hydrate is then rotary evaporated and reused. The pre-impregnated pulp is then added to a 60% formic acid solution with a solids content of 10%. The reaction temperature is 50°C and the reaction time is 60 hours. After the reaction, the wet cellulose formate is washed and the washed formic acid is rotary evaporated and reused.

[0054] Characterization results indicate that the obtained cellulose formate has a degree of substitution of 1.9, a degree of polymerization of 500, and a yield of 132%. Furthermore, a high-strength film can be obtained by directly casting the formic acid solution of the obtained cellulose formate. Testing showed that the film has a tensile strength of 95 MPa, a light transmittance of 91% (550 nm), and good barrier properties (oxygen permeability coefficient of 9.378E-11, moisture permeability of 4.01 g / (m 2 h), and a water contact angle of 88°). In addition, the cellulose formate has a solubility of up to 10% in N,N-dimethylformamide and a solubility of up to 8% in pyridine.

[0055] Example 8: Preparation of high degree of polymerization and high degree of substitution cellulose formate

[0056] First, cotton pulp is pre-impregnated in molten salt hydrate. The cotton pulp has a solids content of 10%, and the molten salt hydrate contains 20% ZnCl2 and 40% LiClO4. After impregnation at 40°C for 40 minutes, the pulp is washed and dried. The recovered molten salt hydrate is then rotary evaporated and reused. The pre-impregnated pulp is then added to a 98% formic acid solution for a reaction. The cotton pulp has a solids content of 2%. The reaction temperature is 30°C and the reaction time is 10 hours. After the reaction, the wet cellulose formate is washed and the washed formic acid is rotary evaporated and reused.

[0057] Characterization results indicate that the obtained cellulose formate has a degree of substitution of 2.0, a degree of polymerization of 1000, and a yield of 135%. Furthermore, the resulting cellulose formate solution was spun in anhydrous ethanol, washed, and dried to produce cellulose formate filaments. Testing revealed a tensile strength of 1.4 cN / dtex. Furthermore, the cellulose formate exhibited a solubility of 8% in dimethyl sulfoxide and 8% in N,N-dimethylacetamide.

[0058] In summary, Examples 1-8 use cellulose formate prepared under the mild conditions described in this application, with a degree of substitution of 1.0-2.0, a yield of 117-135% of the raw material, and a degree of polymerization of 300-1000. Compared with the preparation methods in the prior art, various parameters have been significantly improved. Using the cellulose formate described above, a high-strength cellulose formate transparent film is obtained by direct casting, with a tensile strength of 75-100 MPa, a transmittance of 91-96% (550 nm), and good barrier properties. Using the cellulose formate described above, a high-strength cellulose formate filament is obtained by spinning, with a tensile strength of 1.0-1.5 cN / dtex. In addition, the aforementioned films and yarns obtained using cellulose formate have excellent water resistance and are expected to replace cellulose acetate, with broad application prospects in membrane materials, pharmaceuticals, textiles and other industries.

[0059] Moreover, compared with the prior art, the preparation method described in the present application does not require the use of other additives (e.g., sulfuric acid, phosphoric acid, hydrochloric acid, etc.), the resulting product has no by-products, and both the molten salt hydrate and formic acid can be recycled by a simple method. The process cost is low, and unexpected results have been achieved, which is of great significance for industrial production.

Claims

1. A method for preparing high-polymerization-degree-of-substitution cellulose formate or its derivatives, characterized in that: The following steps are involved: (1) The cellulose raw material is immersed in a molten salt hydrate, and then the solid-liquid separation is performed; the solid phase after separation is the cellulose pulp, which is washed and dried, and the liquid phase after separation is the molten salt hydrate, which is recycled; the solid content of the cellulose raw material in the molten salt hydrate is 1-20wt%, and the immersion temperature is 10-50°C; (2) The cellulose pulp obtained in step (1) is dispersed in a formic acid solution for reaction, and after the reaction is completed, a regeneration solvent is added, and then the solid-liquid separation and washing are performed to obtain a high-polymerization degree cellulose formate wet material; Alternatively, the cellulose pulp obtained in step (1) is dispersed in a formic acid solution for reaction, and after the reaction is completed, it is directly spun or formed into a film.

2. The preparation method according to claim 1, characterized in that: In step (1), the cellulose raw material is immersed in the molten salt hydrate for 1-100 minutes; in step (2), the solid content of the cellulose pulp in the formic acid solution is 1-20wt%, the concentration of the formic acid solution is 50-98%, the reaction temperature is 10-50°C, and the reaction time is 1h-72h.

3. The preparation method according to claim 2, characterized in that: The molten salt hydrate is Li + Mg 2+ , Ca 2+ 、Zn 2+ 、Al 3+ , Fe 3+ and Cu 2+ One or two of the hydrates of chloride, bromide, iodide, perchlorate, nitrate and thiocyanate; the weight fraction of the inorganic salt in the molten salt hydrate is 40-70%.

4. The preparation method according to claim 3, characterized in that: The molten salt hydrate is LiBr·3H2O, ZnCl2·4H2O, LiCl·3H2O, AlCl3·6H2O, FeCl3·6H2O, MgCl2·6H2O, CaCl2·6H2O, LiNO3·3H2O, Ca(NO3)2·4H2O, Mg(NO3)2·6H2O, LiClO4·3H2O or LiSCN·2.5H2O.

5. The preparation method according to claim 2, characterized in that: The cellulose raw material is microcrystalline cellulose, cotton pulp, dissolving pulp, ascidian cellulose or bacterial cellulose.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The cellulose pulp described in step (1) is washed with water, and the obtained liquid phase is a salt solution, which is concentrated to the initial concentration and reused; the regeneration solvent described in step (2) is water, ethanol, acetone, tert-butanol or n-butanol; the separated liquid is a formic acid-regeneration solvent solution, which is concentrated to the initial concentration and then reused.

7. Cellulose formate with high degree of polymerization and high degree of substitution prepared by any one of claims 1 to 6.

8. The high-polymerization-degree-and-high-substitution-degree cellulose formate according to claim 7, characterized in that: The cellulose formate has a substitution degree of 1.0-2.0, a crystal form of cellulose II, and a polymerization degree of 300-1000; the cellulose formate is soluble in formic acid, dimethyl sulfoxide, pyridine, N-methylpyrrolidone, N,N-dimethylformamide or N,N-dimethylacetamide.

9. The use of high-polymerization-degree-of-substitution cellulose formate according to claim 7 or 8, characterized in that: The cellulose formate is used for preparing cellulose derivatives or cellulose formate derived products.

10. The use of high-polymerization-degree-and-high-substitution-degree cellulose formate according to claim 7 or 8, characterized in that: Specifically, the cellulose formate is dissolved in formic acid, dimethyl sulfoxide or pyridine, and then a cellulose derivative is obtained by using a highly reactive aldehyde reaction, a cellulose formate film is obtained by a casting method, or a cellulose formate filament is obtained by a spinning method.

Images