Cellulose monoacetate, cellulose diacetate or cellulose triacetate and low-cost rapid preparation method thereof

Abstract

The invention belongs to the technical field of cellulose acetate preparation, and discloses cellulose monoacetate, cellulose diacetate or cellulose triacetate and a low-cost rapid preparation method thereof. The low-cost rapid preparation method of cellulose monoacetate, cellulose diacetate or cellulose triacetate comprises the following steps: adding a cellulose raw material, an alcohol substance, toluene and deionized water into zirconium oxide balls to obtain a prepared product, carrying out ball milling treatment on the prepared product under the protection of nitrogen, adjusting ball milling parameters to obtain a ball milling product with a low substitution degree or a high substitution degree, and carrying out high-speed ball milling on the ball milling product with the low substitution degree or the high substitution degree to obtain the cellulose monoacetate, cellulose diacetate or cellulose triacetate. Washing a ball-milled product, then performing vacuum drying to obtain carboxylated cellulose with low substitution degree or high substitution degree, sequentially adding the carboxylated cellulose with low substitution degree or high substitution degree into an alkaline aqueous solution and an acetate compound to perform transesterification, and sequentially performing washing, vacuum filtration and vacuum drying on a transesterification product to obtain carboxylated cellulose with low substitution degree or high substitution degree. The cellulose monoacetate, the cellulose diacetate or the cellulose triacetate is obtained; the production cost can be reduced, and the preparation efficiency is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cellulose acetate preparation, and particularly relates to a cellulose monoacetate, diacetate or triacetate and a low-cost and rapid preparation method thereof. Background Art

[0002] Cellulose is the most abundant biopolymer in nature, widely existing in plant cell walls. It has the characteristics of being renewable and biodegradable, and has extensive applications in the fields of textiles, membrane materials, medicine, food packaging, etc. However, due to the presence of a large number of hydrogen bonds in the cellulose molecular chain, it is highly crystallized and difficult to dissolve, which limits its further chemical modification and application development.

[0003] Cellulose acetate (CA) is one of the main derivatives of cellulose, and is usually prepared by esterification reaction to partially or completely replace the hydroxyl groups (-OH) of cellulose with acetate groups (-OCOCH3). Cellulose acetates with different degrees of substitution have different physical and chemical properties. For example, cellulose monoacetate is mainly used for water-soluble and hydrophilic materials; cellulose diacetate is used in the fields of fibers, filter membranes, cigarette filters, etc.; cellulose triacetate is mainly used for high-transparency films and optical materials.

[0004] Currently, the methods for preparing cellulose acetate in industry mainly include: the traditional acetic anhydride method, which uses acetic anhydride as the esterification reagent and reacts under the catalysis of sulfuric acid or phosphoric acid. However, this method requires the use of a high-concentration acid catalyst, the reaction environment is harsh, and side reactions are likely to occur; the homogeneous solvent method, such as the N,N-dimethylacetamide (DMAC)-lithium salt system or the ionic liquid system. However, the solvent cost is high and the recovery is difficult, which limits its large-scale application; for example, Patent CN116655809A discloses a reed-based cellulose acetate and its preparation method. This method has simple and controllable steps, but the cost of using rare earth ions is high, there is toxicity, and strong acid needs to be added, which is likely to cause equipment corrosion and the reaction time is long, etc., resulting in limited market application; for example, Patent CN119192408A discloses a method for homogeneously synthesizing cellulose acetate by using a deep eutectic solvent to catalyze cellulose. This method has problems such as difficult recovery of the deep eutectic solvent, long reaction time, and high temperature control requirements.

[0005] Therefore, developing a preparation method of cellulose acetate with low cost, high efficiency and adjustable degree of substitution is of great significance for expanding its application fields. Summary of the Invention

[0006] The object of the present invention is to provide a method for the low-cost and rapid preparation of mono-, di- or tri- cellulose acetate to overcome the problems existing in the prior art. The present invention uses natural plant cellulose as a raw material and combines the induction activation of ball milling mechanical force with the hierarchical transesterification strategy under mild conditions of normal temperature and pressure to efficiently prepare different cellulose acetates (including mono-cellulose acetate, di-cellulose acetate or tri-cellulose acetate), significantly reducing the dependence on strong acid catalysts, high-temperature and high-pressure equipment and homogeneous high-cost solvent systems in the traditional preparation process of cellulose acetate. At the same time, compared with the traditional industrial acetic anhydride method or homogeneous solvent method, the present invention has significant advantages of low cost, environmental friendliness, strong equipment adaptability, fast reaction rate and high controllability. This method provides a new technical approach and theoretical basis for the chemical modification of cellulose and the green preparation and functional regulation of cellulose acetate, and has broad industrial application prospects and great ecological and environmental significance.

[0007] To achieve the above object, the technical solutions adopted by the present invention are as follows: In the first aspect, the present invention provides a low-cost and rapid preparation method of mono-, di- or tri- cellulose acetate, comprising the following steps: Step 1, adding a cellulose raw material, an alcohol substance, toluene and deionized water into zirconia balls to obtain a prepared product; Step 2, performing ball milling treatment on the prepared product under nitrogen protection, adjusting the ball milling parameters to obtain a ball milled product with low substitution degree or high substitution degree, washing the ball milled product and then performing vacuum drying to obtain carboxylated cellulose with low substitution degree or high substitution degree; Step 3, adding the carboxylated cellulose with low substitution degree or high substitution degree into an alkaline aqueous solution and an acetate compound in sequence for transesterification reaction, washing, vacuum filtering and vacuum drying the transesterification reaction product in sequence to obtain mono-, di- or tri- cellulose acetate; Further, the cellulose raw material in Step 1 includes one of viscose filament, cotton linters or viscose staple fiber; the alcohol substance in Step 1 includes one of 1-butanol, 1-pentanol, 1-hexanol, isopentanol; the mass ratio of the cellulose raw material, the alcohol substance, toluene and deionized water in Step 1 is 1:(0.1~0.15):0.005:(0.05~0.1); the mass ratio of the cellulose raw material and zirconia balls in Step 1 is 1:(25~30); Further, the obtaining of the ball milled product with low substitution degree or high substitution degree by adjusting the ball milling parameters in Step 2 specifically includes: Performing ball milling pretreatment at a speed of 100~300 rpm for 15~20 min, and then performing ball milling at a speed of 500~600 rpm for 30~40 min to obtain a ball milled product with low substitution degree; Perform ball milling pretreatment at a rotational speed of 200 - 500 rpm for 10 - 15 min, then perform primary ball milling at a rotational speed of 700 - 1000 rpm for 60 - 180 min, and then perform secondary ball milling at a rotational speed of 300 - 500 rpm for 20 - 40 min to obtain a ball milling product with a high degree of substitution; Further, the washing in step two is specifically: repeat washing three times with absolute ethanol; the vacuum drying temperature in step two is 60 °C and the time is 4 - 6 h; Further, step three specifically includes: Immerse the carboxylated cellulose with a low degree of substitution in the first alkaline aqueous solution, stir and then add the first acetate compound for the first transesterification reaction, then wash the product of the first transesterification reaction to neutral pH, perform vacuum filtration, and then perform vacuum drying to obtain cellulose acetate monophosphate; Or, Immerse the carboxylated cellulose with a high degree of substitution in the second alkaline aqueous solution, stir and then add the second acetate compound for the second transesterification reaction, then perform vacuum filtration, add again 1 / 2 of the mass of the second alkaline aqueous solution and the second acetate compound for the third transesterification reaction, wash the product of the third transesterification reaction to neutral pH, perform vacuum filtration and vacuum drying in sequence to obtain cellulose acetate diphosphate; Or, Immerse the carboxylated cellulose with a high degree of substitution in the third alkaline aqueous solution, stir and then add the third acetate compound for the fourth transesterification reaction, perform vacuum filtration and then add 2 / 3 of the mass of the third alkaline aqueous solution and the third acetate compound for the fifth transesterification reaction, add again 1 / 3 of the mass of the third alkaline aqueous solution and the third acetate compound for the sixth transesterification reaction, wash the product of the sixth transesterification reaction to neutral pH, perform vacuum filtration and vacuum drying in sequence to obtain cellulose acetate triphosphate; Further, the mass ratio of the carboxylated cellulose with a low degree of substitution to the first alkaline aqueous solution and the first acetate compound is 1:(10 - 15):(5 - 10); the mass ratio of the carboxylated cellulose with a high degree of substitution to the second alkaline aqueous solution and the second acetate compound is 1:(10 - 15):(5 - 10); the mass ratio of the carboxylated cellulose with a high degree of substitution to the third alkaline aqueous solution and the third acetate compound is 1:(10 - 15):(5 - 10); Further, the first alkaline aqueous solution, the second alkaline aqueous solution, and the third alkaline aqueous solution each include one of sodium hydroxide, potassium hydroxide, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, and cyclohexylamine, and the concentration is 0.5 to 1.5 mol / L; the first acetate compound, the second acetate compound, and the third acetate compound each include one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isopropyl acetate, sec-butyl acetate, and isoamyl acetate; Further, the rotation speed of the stirring is 500 to 1000 rpm, and the stirring time is 1 to 2 minutes; the reaction time of the first transesterification reaction, the second transesterification reaction, the third transesterification reaction, the fourth transesterification reaction, the fifth transesterification reaction, and the sixth transesterification reaction is 5 to 10 minutes; Further, the washing is as follows: washing with deionized water and ethanol at 60 °C; the temperature of the vacuum drying is 50 °C, and the vacuum drying time is 4 to 6 hours.

[0008] In a second aspect, the present invention provides a mono-, di-, or tri-cellulose acetate obtained based on the low-cost and rapid preparation method of the above-mentioned mono-, di-, or tri-cellulose acetate.

[0009] The above technical solution has the following advantages or beneficial effects: In a first aspect, the present invention provides a low-cost and rapid preparation method of mono-, di- or tri- cellulose acetate. By using natural plant raw materials rich in cellulose as raw materials and treating the raw materials by mechanochemical conversion method, adding alcohols, non-swelling solvent toluene and deionized water, under mild conditions of normal temperature and pressure, cellulose carboxylation is achieved by means of ball milling mechanochemical conversion method. Mechanical energy is introduced into the process of cellulose molecular structure reconstruction, causing the cellulose molecular chains to break and generating active sites. Under the conditions of no metal catalyst and no chemical oxidant, high-speed shearing and frictional force are utilized to induce the dissociation of water molecules to generate hydroxyl radicals and hydrogen radicals. At the same time, alcohols act as hydroxyl donors, thereby stimulating the hydroxyl groups at the C2 / C3 / C6 positions of the cellulose molecular chains to undergo free radical-induced functional group exchange reactions; during the ball milling process, the added alcohols act as hydroxyl donor solvents and reaction media, which can promote the dispersion and activation of cellulose and at the same time participate in the functional group exchange reactions on the cellulose chains. Toluene, as a non-swelling solvent, helps to maintain the integrity of the cellulose structure and prevent the molecular chains from entangling and the reaction from getting out of control due to excessive swelling. Deionized water is activated into hydroxyl and hydrogen radicals during the ball milling process, and the radicals react with the hydroxyl groups on the cellulose chains to achieve cellulose carboxylation, obtaining carboxylated cellulose with different degrees of substitution. Then, the obtained carboxylated cellulose is immersed in an alkaline solution at room temperature and allowed to rapidly carry out transesterification reaction with acetate compounds, thereby enabling the efficient preparation of cellulose acetate with different degrees of substitution (including mono-cellulose acetate, di-cellulose acetate or tri-cellulose acetate); the present invention can reduce production costs and significantly improve the preparation efficiency, providing a new technical approach and theoretical basis for the chemical modification of cellulose and the green preparation and functional regulation of cellulose acetate, and having broad industrial application prospects and great ecological and environmental significance.

[0010] Furthermore, the present invention realizes carboxylated cellulose with different degrees of substitution by controlling ball milling parameters. The principle lies in the action of mechanical force on the cellulose molecular chain during the ball milling process. The low-speed ball milling pretreatment can preliminarily disperse and activate the cellulose, providing more active sites for subsequent reactions. High-speed ball milling, through strong mechanical shear force and impact force, promotes the breakage of the cellulose molecular chain, generating a large number of free radicals. The free radicals react with the activated water molecules, causing the hydroxyl groups on the cellulose chain to be substituted by carboxyl groups. The subsequent speed reduction treatment stabilizes the reaction process and terminates the reaction. By adjusting the rotation speed and time of ball milling, the generation amount of free radicals and the reaction degree can be controlled, thereby realizing the regulation of the degree of substitution. Low-degree-of-substitution carboxylated cellulose is mainly achieved through high-speed ball milling for a short time (low-speed ball milling pretreatment at 100 - 300 rpm for 15 - 20 min, and then high-speed ball milling at 500 - 600 rpm for 30 - 40 min), while high-degree-of-substitution carboxylated cellulose requires longer time and higher-intensity ball milling treatment (low-speed treatment at 200 - 500 rpm for 10 - 15 min, high-speed treatment at 700 - 1000 rpm for 50 - 240 min, and speed reduction treatment at 200 - 500 rpm for 20 - 40 min). Through precise control of the ball milling parameters, the substitution reaction occurs at specific positions on the cellulose chain, and thus carboxylated cellulose with different degrees of substitution is obtained.

[0011] Furthermore, by constructing a multi-stage transesterification reaction path carried out in an aqueous phase system with alkali as a rapid catalyst at room temperature, the efficient preparation of mono-, di-, or tri-acetate cellulose from low- and high-degree-of-substitution carboxylated cellulose can be realized. By adjusting the reaction material ratio, stirring rate, and reaction time, a rapid transesterification reaction can be achieved at room temperature, effectively reducing problems such as large consumption of acetic anhydride and uneven product distribution in the traditional thermal esterification process. At the same time, the present invention uses short-chain ester compounds (such as ethyl acetate, propyl acetate, etc.) to replace traditional acetic anhydride, improving the greenness and industrial adaptability of the reaction. By setting different stages of transesterification reaction, the precise synthesis of mono-acetate cellulose, di-acetate cellulose, or tri-acetate cellulose can be realized. For the preparation of di- or tri-acetate cellulose, a two-stage or three-stage progressive "batch-type" transesterification reaction design is respectively adopted. By gradually introducing acetate compounds and alkaline catalytic components, the carboxyl groups of carboxylated cellulose are fully exposed and participate in the reaction. The multi-stage progressive transesterification reaction mode not only significantly improves the degree of transesterification reaction but also effectively inhibits the occurrence of side reactions. Finally, di- or tri-acetate cellulose can be obtained according to the target requirements.

[0012] In a second aspect, the present invention also provides a cellulose monoacetate, diacetate or triacetate. By optimizing the preparation process, reducing raw material consumption, improving reaction efficiency, simplifying post-treatment steps, etc., the production cost is significantly reduced. Moreover, the carboxyl group content, acetyl group content, degree of substitution and yield of the prepared cellulose acetate are all higher, with more excellent properties, and can meet the application requirements of higher standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 FIG. is a schematic flow chart of a low-cost and rapid preparation method of a cellulose monoacetate, diacetate or triacetate of the present invention; Figure 2 FIG. is a schematic diagram of viscose filament in Example 3 of the present invention; Figure 3 FIG. is a schematic diagram of a carboxylated cellulose with a high degree of substitution in Example 3 of the present invention; Figure 4 FIG. is an infrared spectrum diagram of cellulose diacetate in Example 3 of the present invention; Figure 5 FIG. is a schematic diagram of cellulose diacetate in Example 3 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] The following further describes the present invention in detail with specific embodiments, which are explanations of the present invention rather than limitations. In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above drawings are used to distinguish similar objects, and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily need to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0015] Example 1: Refer to Figure 1, the present invention provides a low-cost and rapid preparation method of mono-, di- or tri- cellulose acetate, comprising the following steps: Step 1: Weigh 20 g of viscose filament, add 2 g of isoamyl alcohol, 0.1 g of toluene and 1 g of deionized water, mix them, put them into a zirconia ball mill tank of a ball mill, and add 500 g of zirconia balls to obtain a prepared product; Step 2: Under nitrogen protection, perform two-stage ball milling on the prepared product. First, perform low-speed pretreatment at 100 rpm for 20 min, and then adjust the speed to 500 rpm for high-speed ball milling for 40 min. After the ball milling is completed, a ball-milled product with a low degree of substitution is obtained. The ball-milled product with a low degree of substitution is repeatedly washed three times with absolute ethanol and then vacuum dried at 60 °C for 6 h to obtain carboxylated cellulose with a low degree of substitution; Step 3: Take 10 g of carboxylated cellulose with a low degree of substitution and immerse it in 100 g of 0.5 mol / L aqueous trimethylamine solution. Stir at a speed of 1000 rpm for 1 min for wetting, then add 50 g of propyl acetate, and carry out the first transesterification reaction at room temperature with continuous stirring for 5 min. After the first transesterification reaction is completed, wash the obtained first transesterification reaction product with deionized water and hot ethanol at 60 °C until the pH is neutral, then perform vacuum filtration to collect the filter cake, and vacuum dry it at 50 °C for 4 h to obtain mono-cellulose acetate.

[0016] Example 2: See Figure 1 , the present invention provides a low-cost and rapid preparation method of mono-, di- or tri- cellulose acetate, comprising the following steps: Step 1: Weigh 10 g of cotton linters, add 1.5 g of 1-butanol, 0.05 g of toluene and 1 g of deionized water, mix them, put them into a zirconia ball mill tank of a ball mill, and add 300 g of zirconia balls to obtain a prepared product; Step 2: Under nitrogen protection, perform two-stage ball milling on the prepared product. First, perform low-speed pretreatment at 300 rpm for 15 min, and then adjust the speed to 600 rpm for high-speed ball milling for 30 min. After the ball milling is completed, a ball-milled product with a low degree of substitution is obtained. The ball-milled product with a low degree of substitution is repeatedly washed three times with absolute ethanol and then vacuum dried at 60 °C for 6 h to obtain carboxylated cellulose with a low degree of substitution; Step 3: Take 5 g of low-substituted carboxylated cellulose and immerse it in 75 g of 1.5 mol / L sodium hydroxide aqueous solution. Stir for 2 min at a rotation speed of 500 rpm for wetting, then add 50 g of ethyl acetate, and carry out the first transesterification reaction under room temperature conditions with continuous stirring for 10 min. After the first transesterification reaction is completed, wash the obtained first transesterification reaction product with deionized water and hot ethanol at 60 °C until the pH is neutral, then carry out vacuum filtration to collect the filter cake, and vacuum dry it at 50 °C for 4 h to obtain cellulose acetate monophosphate.

[0017] Example 3: Refer to Figure 1 , the present invention provides a low-cost and rapid preparation method of cellulose acetate mono-, di- or tri-phosphate, comprising the following steps: Step 1: Refer to Figure 2 , weigh 10 g of viscose filament, add 1.3 g of 1-pentanol, 0.05 g of toluene and 0.8 g of deionized water, mix them and put them into a zirconia ball mill tank of a ball mill, and add 280 g of zirconia balls to obtain a prepared product; Step 2: Carry out three-stage ball milling treatment on the prepared product under nitrogen protection. First, perform low-speed pretreatment at 300 rpm for 13 min, then adjust the speed to 800 rpm for high-speed ball milling for 120 min, and finally perform speed reduction treatment at 300 rpm for 30 min. After the ball milling is completed, obtain a high-substituted ball milling product. Wash the high-substituted ball milling product three times repeatedly with absolute ethanol, and then vacuum dry it at 60 °C for 5 h. Refer to Figure 3 , to obtain high-substituted carboxylated cellulose; Step 3: Take 5 g of high-substituted carboxylated cellulose and immerse it in 65 g of 1 mol / L diethylamine aqueous solution. Stir for 1.5 min at a rotation speed of 800 rpm for wetting, then add 40 g of propyl acetate, and carry out the second transesterification reaction under room temperature conditions with continuous stirring for 8 min. Then carry out vacuum filtration to collect the filter cake as the second transesterification reaction product. Add 20 g of propyl acetate and 32.5 g of diethylamine aqueous solution to the second transesterification reaction product again, and continue to carry out the third transesterification reaction under room temperature conditions with continuous stirring for 8 min. After the third transesterification reaction is completed, wash the obtained third transesterification reaction product with deionized water and hot ethanol at 60 °C until the pH is neutral, then carry out vacuum filtration to collect the filter cake, and vacuum dry it at 50 °C for 5 h. Refer to Figure 5 , to obtain cellulose acetate diphosphate.

[0018] Refer to Figure 4 , which is the infrared spectrum diagram of cellulose acetate diphosphate, 3400 - 3600 cm -There is a broad peak at ¹, which is related to the O-H stretching vibration and corresponds to the unreacted hydroxyl groups (-OH) in the cellulose backbone; 1700-1750 cm - At ¹ is the characteristic absorption peak of the carbonyl (C=O) stretching vibration, 1200-1300 cm - The absorption peak at ¹ is for the C-O stretching vibration, indicating that the cellulose acetate contains ester bonds (-COO-).

[0019] Example 4: See Figure 1 , the present invention provides a low-cost and rapid preparation method for mono-, di- or tri-cellulose acetate, comprising the following steps: Step 1, weigh 15 g of viscose staple fiber, add 1.5 g of isoamyl alcohol, 0.075 g of toluene and 0.75 g of deionized water, mix them and put them into a zirconia ball milling tank of a ball mill, and add 375 g of zirconia balls to obtain a prepared product; Step 2, under nitrogen protection, perform three-stage ball milling on the prepared product. First, pre-treat it at a low speed of 200 rpm for 15 min, then adjust the speed to 700 rpm for high-speed ball milling for 180 min, and finally reduce the speed to 300 rpm for 40 min. After the ball milling is completed, a ball-milled product with a high degree of substitution is obtained. The ball-milled product with a high degree of substitution is repeatedly washed three times with absolute ethanol and then vacuum dried at 60 °C for 4 h to obtain carboxylated cellulose with a high degree of substitution; Step 3, take 8 g of carboxylated cellulose with a high degree of substitution and immerse it in 80 g of 1 mol / L cyclohexylamine aqueous solution. Stir it at a speed of 500 rpm for 2 min for wetting, then add 40 g of isopropyl acetate, and carry out the second transesterification reaction at room temperature with continuous stirring for 5 min. Then, perform vacuum filtration to collect the filter cake as the product of the second transesterification reaction. Add 20 g of isopropyl acetate and 40 g of cyclohexylamine aqueous solution to the product of the second transesterification reaction again, and continue to carry out the third transesterification reaction at room temperature with continuous stirring for 8 min. After the third transesterification reaction is completed, wash the obtained product of the third transesterification reaction with deionized water and hot ethanol at 60 °C until the pH is neutral, then perform vacuum filtration to collect the filter cake, and vacuum dry it at 50 °C for 5 h to obtain di-cellulose acetate.

[0020] Example 5: See Figure 1 , the present invention provides a low-cost and rapid preparation method for mono-, di- or tri-cellulose acetate, comprising the following steps: Step 1, weigh 10 g of cotton linters, add 1.2 g of 1-pentanol, 0.05 g of toluene and 0.7 g of deionized water, mix them and put them into a zirconia ball milling tank of a ball mill, and add 270 g of zirconia balls to obtain a prepared product; Step 2: Under nitrogen protection, the prepared product is subjected to three-stage ball milling. First, it is pre-treated at a low speed of 400 rpm for 12 min, then the speed is adjusted to 900 rpm for high-speed ball milling for 100 min, and finally it is decelerated at 400 rpm for 30 min. After the ball milling is completed, a ball-milled product with a high degree of substitution is obtained. The ball-milled product with a high degree of substitution is repeatedly washed three times with absolute ethanol and then vacuum-dried at 60 °C for 4 h to obtain carboxylated cellulose with a high degree of substitution; Step 3: Take 5 g of carboxylated cellulose with a high degree of substitution and immerse it in 60 g of 1.2 mol / L diethylamine aqueous solution. Stir at a speed of 900 rpm for 1.3 min for wetting, then add 35 g of isopropyl acetate, and carry out the fourth transesterification reaction under room temperature conditions with continuous stirring for 7 min. Then, vacuum filtration is carried out to collect the filter cake as the product of the fourth transesterification reaction. Add 23.3 g of isopropyl acetate and 40 g of diethylamine aqueous solution to the product of the fourth transesterification reaction again, and continue to carry out the fifth transesterification reaction under room temperature conditions with continuous stirring for 7 min to obtain the product of the fifth transesterification reaction. Then, add 11.7 g of isopropyl acetate and 20 g of diethylamine aqueous solution to the product of the fifth transesterification reaction, and continue to carry out the sixth transesterification reaction under room temperature conditions with continuous stirring for 7 min. After the sixth transesterification reaction is completed, wash the obtained product of the sixth transesterification reaction with deionized water and hot ethanol at 60 °C until the pH is neutral, carry out vacuum filtration to collect the filter cake, and vacuum-dry it at 50 °C for 6 h to obtain cellulose triacetate.

[0021] Example 6: See Figure 1 , the present invention provides a low-cost and rapid preparation method for mono-, di- or tri-cellulose acetate, comprising the following steps: Step 1: Weigh 16 g of viscose staple fiber, add 2.4 g of 1-butanol, 0.08 g of toluene and 1.6 g of deionized water, mix them and load them into a zirconia ball milling tank of a ball mill, and add 480 g of zirconia balls to obtain a prepared product; Step 2: Under nitrogen protection, the prepared product is subjected to three-stage ball milling. First, it is pre-treated at a low speed of 500 rpm for 10 min, then the speed is adjusted to 1000 rpm for high-speed ball milling for 60 min, and finally it is decelerated at 500 rpm for 40 min. After the ball milling is completed, a ball-milled product with a high degree of substitution is obtained. The ball-milled product with a high degree of substitution is repeatedly washed three times with absolute ethanol and then vacuum-dried at 60 °C for 6 h to obtain carboxylated cellulose with a high degree of substitution; Step 3: Immerse 9 g of highly substituted carboxylated cellulose into 90 g of 1.5 mol / L sodium hydroxide aqueous solution, stir for 1 min at a rotation speed of 1000 rpm for wetting, then add 90 g of isopentyl acetate, carry out the fourth transesterification reaction under room temperature conditions with continuous stirring for 10 min, then perform vacuum filtration to collect the filter cake as the product of the fourth transesterification reaction. Add 60 g of isopentyl acetate and 60 g of sodium hydroxide aqueous solution to the product of the fourth transesterification reaction again, continue to carry out the fifth transesterification reaction under room temperature conditions with continuous stirring for 10 min to obtain the product of the fifth transesterification reaction. Then add 30 g of isopentyl acetate and 30 g of sodium hydroxide aqueous solution to the product of the fifth transesterification reaction, continue to carry out the sixth transesterification reaction under room temperature conditions with continuous stirring for 10 min. After the sixth transesterification reaction ends, wash the obtained product of the sixth transesterification reaction with deionized water and hot ethanol at 60 °C until the pH is neutral, perform vacuum filtration to collect the filter cake, and dry it under vacuum at 50 °C for 6 h to obtain cellulose triacetate.

[0022] Table 1 Content of carboxylation and acetyl group, degree of substitution and yield of Examples 1-6

[0023] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-cost and rapid preparation method of cellulose monoacetate, diacetate or triacetate, characterized in that, It includes the following steps: S1. Add cellulose raw material, alcohol, toluene and deionized water into zirconia balls to obtain a preparation product; S2. Under nitrogen protection, perform ball milling on the preparation product. By adjusting the ball milling parameters, obtain a ball milling product with low or high substitution degree. After washing the ball milling product, perform vacuum drying to obtain carboxylated cellulose with low or high substitution degree; S3. Add carboxylated cellulose with low or high substitution degree into an alkaline aqueous solution and an acetate compound in sequence for transesterification reaction. After washing, vacuum filtration and vacuum drying of the transesterification reaction product in sequence, obtain mono-, di- or tri-acetate cellulose.

2. A low-cost and rapid preparation method of cellulose monoacetate, diacetate or triacetate according to claim 1, characterized in that, The cellulose raw material in S1 includes one of viscose filament, cotton linter or viscose staple fiber; the alcohol in S1 includes one of 1-butanol, 1-pentanol, 1-hexanol, isoamyl alcohol; the mass ratio of the cellulose raw material, alcohol, toluene and deionized water in S1 is 1:(0.1~0.15):0.005:(0.05~0.1); the mass ratio of the cellulose raw material and zirconia balls in S1 is 1:(25~30).

3. A low-cost and rapid preparation method of cellulose monoacetate, diacetate or triacetate according to claim 1, characterized in that, In S2, obtaining a ball milling product with low or high substitution degree by adjusting the ball milling parameters specifically includes: Perform ball milling pretreatment at a speed of 100~300 rpm for 15~20 min, and then perform ball milling at a speed of 500~600 rpm for 30~40 min to obtain a ball milling product with low substitution degree; Perform ball milling pretreatment at a speed of 200~500 rpm for 10~15 min, then perform primary ball milling at a speed of 700~1000 rpm for 60~180 min, and then perform secondary ball milling at a speed of 300~500 rpm for 20~40 min to obtain a ball milling product with high substitution degree.

4. A low-cost and rapid preparation method of cellulose monoacetate, diacetate or triacetate according to claim 1, characterized in that, The washing in S2 is specifically: repeat washing three times with absolute ethanol; the vacuum drying temperature in S2 is 60 °C and the time is 4~6 h.

5. A low-cost and rapid preparation method of cellulose monoacetate, diacetate or triacetate according to claim 1, characterized in that, S3 specifically includes: Immerse carboxylated cellulose with low substitution degree into the first alkaline aqueous solution, stir and then add the first acetate compound for the first transesterification reaction. Then wash the first transesterification reaction product until the pH is neutral, perform vacuum filtration, and then perform vacuum drying to obtain mono-acetate cellulose; Or, Immerse carboxylated cellulose with high substitution degree into the second alkaline aqueous solution, stir and then add the second acetate compound for the second transesterification reaction. Then perform vacuum filtration, add again 1 / 2 of the mass of the second alkaline aqueous solution and the second acetate compound for the third transesterification reaction. Wash the third transesterification reaction product until the pH is neutral, perform vacuum filtration and vacuum drying in sequence to obtain di-acetate cellulose; Or, Immerse the carboxylated cellulose with a high degree of substitution in a third alkaline aqueous solution, stir it, add a third acetate compound for the fourth transesterification reaction, perform vacuum filtration, add 2 / 3 of the mass of the third alkaline aqueous solution and the third acetate compound for the fifth transesterification reaction, and add 1 / 3 of the mass of the third alkaline aqueous solution and the third acetate compound again for the sixth transesterification reaction. Wash the product of the sixth transesterification reaction until the pH is neutral, perform vacuum filtration and vacuum drying in sequence to obtain cellulose triacetate.

6. A low-cost and rapid preparation method of cellulose monoacetate, diacetate or triacetate according to claim 5, characterized in that, The mass ratio of the carboxylated cellulose with a low degree of substitution to the first alkaline aqueous solution and the first acetate compound is 1:(10 - 15):(5 - 10); the mass ratio of the carboxylated cellulose with a high degree of substitution to the second alkaline aqueous solution and the second acetate compound is 1:(10 - 15):(5 - 10); the mass ratio of the carboxylated cellulose with a high degree of substitution to the third alkaline aqueous solution and the third acetate compound is 1:(10 - 15):(5 - 10).

7. A low-cost and rapid preparation method of cellulose monoacetate, diacetate or triacetate according to claim 5, characterized in that, The first alkaline aqueous solution, the second alkaline aqueous solution and the third alkaline aqueous solution each include one of sodium hydroxide, potassium hydroxide, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, cyclohexylamine, and the concentration is 0.5 - 1.5 mol / L; the first acetate compound, the second acetate compound and the third acetate compound each include one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, isopropyl acetate, sec-butyl acetate, isoamyl acetate.

8. A low-cost and rapid preparation method of cellulose monoacetate, diacetate or triacetate according to claim 5, characterized in that, The rotation speed of the stirring is 500 - 1000 rpm, and the stirring time is 1 - 2 min; the time of the first transesterification reaction, the second transesterification reaction, the third transesterification reaction, the fourth transesterification reaction, the fifth transesterification reaction and the sixth transesterification reaction is 5 - 10 min.

9. A low-cost and rapid preparation method of cellulose monoacetate, diacetate or triacetate according to claim 5, characterized in that, The washing is all carried out by using deionized water and ethanol at 60 °C for washing; the temperature of the vacuum drying is 50 °C, and the time of the vacuum drying is 4 - 6 h.

10. A cellulose mono-, di- or triacetate, characterized in that, It is obtained by the low-cost and rapid preparation method of cellulose monoacetate, diacetate or triacetate according to any one of the above claims 1 - 9.

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