CN114907492A - Method for preparing bacterial cellulose precursor material and performing bacterial cellulose acylation reaction by using precursor material - Google Patents
Method for preparing bacterial cellulose precursor material and performing bacterial cellulose acylation reaction by using precursor material Download PDFInfo
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Abstract
A method for preparing a precursor material of bacterial cellulose and performing acylation reaction of the bacterial cellulose by using the precursor material. The invention discloses a method for preparing a bacterial fiber precursor material, which comprises the following steps: s1, providing a bacterial cellulose material; s2, reacting the bacterial cellulose material obtained in the step S1 with acid anhydride, and replacing part or all of water in the bacterial cellulose material through acid anhydride hydrolysis reaction to obtain a bacterial cellulose precursor material; according to the invention, the water in the bacterial cellulose is removed through the acid anhydride pretreatment, and the bacterial cellulose is not agglomerated to form a compact structure.
Description
Technical Field
The invention relates to the field of production process flow optimization, in particular to a bacterial cellulose precursor material and a method for performing bacterial cellulose acylation reaction by using the precursor material.
Background
Cellulose acetate, cellulose propionate and the like are important derivatives in cellulose products, and commercial cellulose acetate has the characteristics of high selectivity, strong processability and the like, and has important application in the fields of energy, textiles, electronics, medical treatment and the like.
The preparation method commonly used in industry is that cellulose powder is put into acetic acid, propionic acid and butyric acid for activation, then acid anhydride-catalyst mixed solution is added for acylation reaction, a certain amount of magnesium acetate and the like are added to stop acetylation reaction after the reaction is finished, and the separated product is deacidified, washed, precipitated, separated and dried to obtain the cellulose acetate product. A great deal of research has proved that the application of cellulose acetate which takes different celluloses as raw materials is greatly different, and the raw materials for industrially producing the cellulose acetate at present are mainly alpha-cellulose extracted from wood, and the cellulose has excellent characteristics of uniformity, large polymerization degree and the like.
Cellulose is widely available and is generally obtained from plants. In contrast, bacterial cellulose is produced by bacteria growing in a liquid sugar-containing matrix, secreted through the bacterial cell walls, and aggregated together to form bacterial cellulose. As a novel nano material, the bacterial cellulose is easy to separate and purify raw materials, the cellulose content is as high as 99.9%, the polymerization degree of the bacterial cellulose is as high as 16000, and the bacterial cellulose has excellent characteristics of high mechanical strength, high Young modulus and the like due to the high polymerization degree and crystallinity, so that the bacterial cellulose has wide prospects in various fields such as medical materials, papermaking, electronic substrates and the like.
However, the bacterial cellulose is composed of superfine fibers with the diameter of 20-100 nm, which is about 100 times as much as that of plant cellulose fibers, and due to the structural characteristics, after the bacterial cellulose is dried and dewatered, intermolecular hydrogen bonds are formed on a cellulose molecular chain, and finally a compact and compact structure is easily formed, so that the activation difficulty of the bacterial cellulose in the state is increased, and further the modification effect of the bacterial cellulose is influenced. Chinese patent 103980526B discloses a preparation method of an acetylated modified bacterial cellulose aerogel oil absorption material, wherein acetic acid bacterial cellulose is prepared by modifying bacterial cellulose microfibril with a mixed solution of pyridine and acetic anhydride. A study on acetylation modification of bacterial cellulose is published in journal of synthetic fiber industry, 1g of dry bacterial cellulose is weighed, 20mL of glacial acetic acid is added to be soaked for 24 hours, then a large amount of concentrated sulfuric acid is added to serve as a catalyst, and 20mL of acetic anhydride is added to react at a constant temperature of 70 ℃ to obtain the acetic bacterial cellulose with a substitution degree of about 2.5.
As described above, the ultrafine structure of the bacterial cellulose fibers enables the bacterial cellulose precursor material after drying treatment to form a compact structure, and the original fiber dispersion state of the bacterial cellulose cannot be restored even if the bacterial cellulose precursor material is added into water, so that activation of the bacterial cellulose precursor material requires a large amount of reagents, consumes a large amount of energy, has a long activation time, and is not uniform in swelling degree of the bacterial cellulose and limited in activation effect, and further prevents subsequent acetylation reaction, so that a great number of problems exist in the production of the acetic acid bacterial cellulose with high acetylation degree.
Disclosure of Invention
The invention aims to solve the problems, and provides a process for efficiently producing a bacterial cellulose precursor material.
A method of preparing a bacterial cellulose precursor material, comprising the steps of:
s1, providing a bacterial cellulose material with the water content of 60-93%;
s2, reacting the material obtained in the step S1 with acid anhydride, and replacing part or all of water in the bacterial cellulose material through acid anhydride hydrolysis reaction to obtain a bacterial cellulose precursor material.
The water content of the bacterial cellulose precursor material obtained in the step S2 is less than 20%; preferably, < 10%; more preferably, less than 5%; particularly preferably, less than 1%.
As a particularly preferred embodiment, in step S2, the amount of the acid anhydride added is in excess of the stoichiometric ratio of the acid anhydride to the water contained in the bacterial cellulose.
The excessive acid anhydride can enable water in the bacterial cellulose to be removed completely, and at the same time, surprisingly, the fatty acid hydrolyzed by the acid anhydride can replace the water in the bacterial cellulose, play a role in preventing space of agglomeration of the bacterial cellulose, and the fatty acid formed by the hydrolysis of the acid anhydride is also an acylating agent, so that the material has better effect in acylation reaction because harmful impurities can not be formed.
Preferably, the water content of the bacterial cellulose in the step S1 is 40-95%.
Bacterial cellulose is a widely used production raw material. When the raw material is used for industrial production, dehydration pretreatment needs to be carried out on the raw material. But because of the special structure, the moisture content in the bacterial cellulose subjected to dehydration pretreatment is greatly reduced. Because of lacking the space blocking effect of water molecules, the bacteria cellulose molecules have the undesired space blocking effect, but the residual water molecules still have the space blocking effect on the bacteria cellulose, so that the phenomena of polycondensation and agglomeration of the bacteria cellulose are prevented. It is understood that the control of the water content of the bacterial cellulose material in the step S1 within a proper ratio range is beneficial for the subsequent processing of the step S2;
preferably, the water content of the bacterial cellulose material obtained in the step S1 is 40% -95%; if the water content is too high, a large amount of anhydride solution is required to be added in the anhydride hydrolysis reaction of the step S2, so that the resource waste is serious; if the water content is too low, the pretreatment cost is increased, and the bacterial cellulose is agglomerated to form a compact structure, so that the subsequent acylation reaction is difficult to perform due to the structure, and the effect of the acylation reaction is influenced. Due to the superfine characteristic of the bacterial cellulose, the bacterial cellulose losing too much water forms intermolecular hydrogen bonds because the distance between cellulose molecular chains is shortened, and finally becomes a compact network structure. Although acetic anhydride can also displace water in the bacterial cellulose, too high a density can prevent a part of bound water from being displaced and can also reduce the rate of the subsequent acetylation reaction, and at this time, a further external heat source is needed to help disperse the network structure, and too low a water content is not favorable for the acetylation reaction in terms of energy utilization and reaction efficiency.
Preferably, the step S1 includes: and (3) performing water removal treatment on the bacterial cellulose to ensure that the water content of the bacterial cellulose is 60-93%.
It will be appreciated that, because of the relatively high water content of the bacterial cellulose material, the water content of the original bacterial cellulose may be more than 99%, and even up to 99.9%, and therefore, it may be advantageous to first reduce the water content using conventional drying methods prior to the removal of water using the anhydride. The water removal in the step S1 is performed to control the water content in the bacterial cellulose within a certain range, and since the bacterial cellulose with high water content is easy to store, transport and transport, the step S1 preferably includes a step of removing water.
Meanwhile, it should be understood that the water removal step of step S1 and the hydrolysis step of step S2 are performed at different times and different places, respectively, and should be considered to be within the scope of the present application.
In step S2, the hydrolysis reaction of the acid anhydride is known in the art, and the hydrolysis reaction of the acid anhydride can remove free moisture in the cellulose acetate, and at the same time, the generated fatty acid can promote the swelling effect inside the bacterial cellulose, thereby avoiding the destruction of the crystal structure of the bacterial cellulose caused by the necessity of adding an additional chemical reagent to swell the bacterial cellulose in the prior art.
The conditions for the acid anhydride hydrolysis reaction are not particularly limited, and the acid anhydride hydrolysis reaction is known in the art, and as one embodiment, bacterial cellulose having a certain water content is mixed with acid anhydride. The process parameters are not particularly limited, and known hydrolysis reaction parameters can be used in the present application under the existing anhydride hydrolysis reaction conditions, and the adjustment of conventional process parameters such as temperature, pressure and the like should be considered to be within the protection scope of the present application. The reaction can be carried out in conventional reaction vessels, such as reaction kettles and reaction tanks. It is understood that the reaction conditions that the moisture in the bacterial cellulose reacts with the acid anhydride to a reasonable range may be satisfied.
Meanwhile, the generated short-chain fatty acid can replace hydrogen bonds formed by combining water and hydroxyl groups on a glucose unit in the bacterial cellulose, so that a bacterial cellulose molecular chain is kept in a swelling and dispersing state continuously, and the step that the hydrogen bonds between cellulose molecular chains in a bacterial cellulose precursor material are damaged by adding a chemical reagent and inputting extra energy in the prior art is avoided.
Preferably, the acid anhydride is one or more of acetic anhydride, propionic anhydride and butyric anhydride. If the molecular weight of the anhydride is too large and the carbon chain is too long, the anhydride cannot enter the intermolecular of the bacterial cellulose, so that the space blocking effect is achieved;
the type of bacterial cellulose is not particularly limited, and known bacteria producing bacterial cellulose include, but are not limited to, one or more of bacteria belonging to the genus Acetobacter, bacteria belonging to the genus Agrobacterium, bacteria belonging to the genus Rhizobium, and bacteria belonging to the genus Sarcina.
The second aspect of the invention provides a bacterial cellulose precursor material, which is prepared by the preparation method of the first aspect.
In a third aspect, the present invention provides a method for acylation reaction of bacterial cellulose, comprising the steps of:
s1, providing a bacterial cellulose material with the water content of 40-95%.
S2, reacting the material obtained in the step S1 with acid anhydride, and replacing part or all of water in the bacterial cellulose material through acid anhydride hydrolysis reaction to obtain a bacterial cellulose precursor material;
and S3, mixing the bacterial cellulose precursor material obtained in the step S2 with an acylating reagent solution, and starting to react.
And S4, finishing the reaction to finally obtain the acetic acid bacteria cellulose.
Preferably, the step S1 includes: and (3) performing water removal treatment on the bacterial cellulose to ensure that the water content of the bacterial cellulose is 40-95%.
The type of bacterial cellulose is not particularly limited, and known bacteria producing bacterial cellulose include, but are not limited to, one or more of bacteria belonging to the genus Acetobacter, bacteria belonging to the genus Agrobacterium, bacteria belonging to the genus Rhizobium, and bacteria belonging to the genus Sarcina.
As a particularly preferred embodiment, in step S2, the amount of the acid anhydride added is in excess of the stoichiometric ratio of the acid anhydride to the water contained in the bacterial cellulose.
The excessive acid anhydride can enable water in the bacterial cellulose to be removed completely, and meanwhile, surprisingly, the fatty acid hydrolyzed by the acid anhydride can replace the water in the bacterial cellulose to play a role in preventing the space of the bacterial cellulose from agglomerating, and the fatty acid formed by the hydrolysis of the acid anhydride is also an acylating agent, so that the formed fatty acid participates in the acylation reaction and is consumed in the subsequent acylation reaction, and undesirable impurities cannot be formed.
Preferably, the acid anhydride is one or more of acetic anhydride, propionic anhydride and butyric anhydride.
Preferably, the anhydride is acetic anhydride.
Preferably, the anhydride is propionic anhydride.
Preferably, the anhydride is a mixture of propionic anhydride and butyric anhydride.
Preferably, in the step S3, the acylating reagent is one or more of an acetylation reagent, a propionylation reagent and a butyrylation reagent;
preferably, in the step S3, the acylating agent is an acetylating agent;
preferably, in step S3, the acylating agent is a propionylating agent;
preferably, in step S3, the acylating agent is a butyrylating agent;
preferably, in step S3, the acylating agent is a mixture of a propionylating agent and a butyrylating agent;
preferably, the acid anhydride in step S2 is the same as the acid corresponding to the acylating agent in step S3.
Taking acetic anhydride as an example, acetic anhydride reacts with water to generate acetic acid, and the acetic acid can also be used as an acetylation reagent in the subsequent acetylation reaction, so that no impurities exist in the reaction, and the dehydration and acetylation reaction of the bacterial cellulose are comprehensively combined.
The process parameters of the acylation reaction are not particularly limited, and the known acetylation reaction conditions are adjusted within the protection scope of the present application without departing from the inventive concept of the present application, which is only an illustrative example and not any limitation to the protection scope, and in the step S3, the acetylation reaction temperature is-30 ℃ to 100 ℃, and the acetylation reaction time is 0.1 to 12 hours.
Preferably, the acetylating reagent solution includes a catalyst.
It is understood that the catalyst refers to a reagent which can catalyze and greatly improve the acetylation reaction efficiency of the bacterial cellulose when used in a small amount; the type of catalysis is not particularly limited, and any known catalyst capable of promoting the acetylation of cellulose can be used in the present application, by way of illustration only, and not by way of limitation of the scope of protection, and the catalyst includes, but is not limited to, one or more of sulfuric acid, perchloric acid, p-toluoyl chloride, tartaric acid, citric acid, and lithium dimethylacetamide chloride.
Particularly preferably, in the acetylation reagent, the molar ratio of the catalyst to the acetylation reagent is 0.01-0.5.
The kind of the acylating agent is not particularly limited, and any known acylating agent can be used in the present application without departing from the inventive concept of the present application, and is only an illustrative example, not any limitation to the scope of protection, and the acylating agent includes but is not limited to one or more of acetyl chloride, acetic anhydride, and acetyl iodide; the propionylation reagent comprises one or more of propionyl chloride, propionic anhydride and propionyl iodide; the butyrylating agent comprises one or more of butyryl chloride, butyric anhydride and butyryl iodide; it will be understood that the mixture of the propionylating agent and the butyrylating agent may be simply prepared by mixing the propionylating agent and the butyrylating agent in a ratio which is not particularly required herein, and that conventional adjustments to the ratio of propionylating agent to butyrylating agent in accordance with the performance requirements of known products are considered to be within the scope of the present application.
The bacterial cellulose related to the present application is particularly suitable for acetylation of bacterial cellulose, and particularly acetic anhydride is used as a hydrolysis reagent in step S2. In the preparation process of the precursor, acetic anhydride is used for removing water, so that the acetic acid generated by the reaction cannot become impurities in the acetylation reaction.
In the application, the preparation of the bacterial cellulose precursor material is to better enable the bacterial cellulose precursor material to be subjected to acetylation reaction with a catalyst-acetyl reagent, and the acetylation reaction can be efficiently carried out to produce the acetic acid bacterial cellulose by using the bacterial cellulose precursor material.
For the acetylation reaction, a method of terminating the reaction is known, and the present application does not limit this, and any known termination reaction method that can be used for acetylation reaction of bacterial cellulose can be used in the present application. It will be understood that, as an illustrative example and not as any limitation on the scope of protection, the method of terminating the reaction involves the addition of an aqueous solution of magnesium acetate.
Preferably, the reaction is terminated and a post-treatment process is included, which is not limited herein, and any known post-treatment process of cellulose acetate can be used herein, including but not limited to deacidification washing, precipitation, separation and drying.
Technical effects
Compared with the prior production process, the invention has the advantages that:
according to the method, the characteristic that the bacterial cellulose wet material is swelled and dispersed is utilized, acetic anhydride enters the bacterial cellulose wet material and reacts with water contained in the bacterial cellulose wet material to generate acetic acid, an acetylation reaction precursor material is prepared, and then acetylation reaction is further carried out. The method can save the harsh activation process and reduce the energy consumption, and has mild acetylation reaction conditions, short time and high substitution degree of the obtained acetic acid bacteria cellulose. The method is beneficial to simplifying the production flow of the acetic acid bacteria cellulose, reducing the energy consumption cost, improving the production efficiency and being suitable for industrial production.
Detailed Description
The following embodiments of the present invention will be described in more detail by way of specific embodiments, but it is only used to illustrate some embodiments of the present invention, and should not be construed as limiting the scope of the present invention.
Example 1
S1, adding 50g of bacterial cellulose wet material with the water content of 90% into a reaction container with a stirrer, adding acetic anhydride capable of displacing 44.5g of water, and stirring for 45min to obtain a bacterial cellulose precursor solution (the water displaced in the precursor solution is 100% of water in the wet material).
S2, adding an acetic anhydride-concentrated sulfuric acid mixed reagent into the precursor material obtained in the step S1, wherein the consumption of concentrated sulfuric acid is 0.5mL, the consumption of acetic anhydride is 20mL, and the reaction time is 2 h.
And S3, adding a magnesium acetate aqueous solution to terminate the reaction, pouring the mixture in the three-neck flask into deionized water when the temperature of the three-neck flask is reduced to room temperature, collecting precipitated precipitate, washing with a large amount of clear water, stopping after the pH value of the filtrate is greater than 6.5, and drying the washed precipitate in an oven to obtain a bacterial cellulose acetylation reaction product.
The degree of substitution of the reaction product was tested according to (national standard HG/T3021-1999), the main operating steps are as follows:
firstly crushing the acetic acid bacteria cellulose, drying the crushed acetic acid bacteria cellulose in an oven at 105 ℃ for 60min, weighing about 1.500g of dried acetic acid bacteria cellulose powder, adding the weighed acetic acid bacteria cellulose powder into a 250mL flask, and adding about 65mL of acetone to dissolve the acetic acid bacteria cellulose powder; then, 25.00mL of 1M NaOH solution is added and stirred for 3 h; the walls and stopper were then rinsed with 50mL of distilled water, and 25.00mL of 0.5M H added 2 SO 4 Solution and about 0.5mL of phenolphthalein reagent; titrate with 0.5M sodium hydroxide solution until red color appears, record V 1 The unit is mL. A blank experiment was conducted and the above steps were repeated without the addition of vinegar tablets and a record of 0Titration amount V of 500M sodium hydroxide solution 2 . The degree of substitution is calculated by the following formula:
wherein m is 1 The mass of the acetic acid bacteria cellulose powder weighed for the substitution degree test, AV is the mass of acetic acid contained in 100g of acetic acid bacteria cellulose; DS is the number of acetyl groups contained in each unit ring, and its upper limit value is 3.
The product yield of the bacterial cellulose acetylation reaction is calculated according to the following formula:
wherein m is 2 The mass m of the acetic acid bacteria cellulose collected after the reaction is finished 3 The mass of the bacterial cellulose put into reaction.
The degree of substitution of the acetic acid bacterial cellulose obtained in example 1 was 2.91, and the yield was 93%.
Example 2
S1, adding 10g of bacterial cellulose with a water content of 70% into a reaction container with a stirrer, adding acetic anhydride capable of replacing 6.65g of water, and stirring for 15min to obtain a bacterial cellulose precursor material (the water replaced in the precursor solution is 95% of water in the wet material).
S2, adding a dimethylacetamide-lithium chloride-acetic anhydride mixed reagent into the precursor material obtained in the step S1, wherein the dosage of the ionic liquid dimethylacetamide-lithium chloride is 60 mL (the lithium chloride accounts for 0.4%), the dosage of the acetic anhydride is 12mL, and the reaction time is 1.5 h.
And S3, adding a magnesium acetate aqueous solution to terminate the reaction, pouring the mixture in the three-neck flask into distilled water when the temperature of the three-neck flask is reduced to room temperature, collecting precipitated precipitate, washing with a large amount of clear water, stopping after the pH value of the filtrate is greater than 6.5, and drying the washed precipitate in an oven to obtain a bacterial cellulose acetylation reaction product.
The degree of substitution of the acetic acid bacterial cellulose obtained in example 2 was 2.73, and the yield was 89%.
Example 3
S1, adding 20g of bacterial cellulose with water content of 85% into a reaction container with a stirrer, adding acetic anhydride capable of replacing 15.3g of water, and stirring for 30min to obtain a bacterial cellulose precursor material (the water replaced in the precursor solution is 90% of water in the wet material).
S2, adjusting the temperature of the precursor material obtained in the step S1 to 25 ℃, and adding a toluene-perchloric acid mixed reagent, wherein the dosage of perchloric acid is 1.2mL, the dosage of acetic anhydride is 15mL, and the reaction time is 0.5 min.
And S3, adding a magnesium acetate aqueous solution to terminate the reaction, pouring the mixture in the three-neck flask into deionized water when the temperature of the three-neck flask is reduced to room temperature, collecting precipitated precipitate, washing with a large amount of clear water, stopping after the pH value of the filtrate is greater than 6.5, and drying the washed precipitate in an oven to obtain a bacterial cellulose acetylation reaction product.
The degree of substitution of the acetic acid bacterial cellulose obtained in example 3 was 2.77, and the yield was 84%.
Example 4
S1, adding 10g of bacterial cellulose with a water content of 60% into a reaction container with a stirrer, adding acetic anhydride capable of replacing 5.1g of water, and stirring for 20min to obtain a bacterial cellulose precursor solution (the water replaced in the precursor solution is 85% of water in wet materials).
S2, heating the precursor solution obtained in the step S1 to 80 ℃, and adding an acetic anhydride-iodine mixed reagent, wherein the iodine dosage is 0.4mL, the acetic anhydride dosage is 20mL, and the reaction time is 1 h.
And S3, adding a magnesium acetate aqueous solution to terminate the reaction, pouring the mixture in the three-neck flask into deionized water when the temperature of the three-neck flask is reduced to room temperature, collecting precipitated precipitate, washing with a large amount of clear water, stopping after the pH value of the filtrate is greater than 6.5, and drying the washed precipitate in an oven to obtain a bacterial cellulose acetylation reaction product.
The degree of substitution of the acetic acid bacterial cellulose obtained in example 4 was 2.71, and the yield was 82%.
Example 5
S1, adding 8g of bacterial cellulose with the water content of 60% into a reaction container with a stirrer, adding acetic anhydride capable of replacing 4.32g of water, and stirring for 50min to obtain a bacterial cellulose precursor solution (the water replaced in the precursor solution is 90% of water in a wet material).
S2, raising the temperature of the precursor solution obtained in the step S1 to 70 ℃, adding 0.32mL of propionic anhydride-butyric anhydride-sulfuric acid mixed reagent, wherein the dosages of acetic anhydride and butyric anhydride are both 12.8mL, and the reaction time is 1.5 h.
And S3, adding a magnesium acetate aqueous solution to terminate the reaction, pouring the mixture in the three-neck flask into deionized water when the temperature of the three-neck flask is reduced to room temperature, collecting the precipitated precipitate, washing with a large amount of clear water, stopping after the pH value of the filtrate is greater than 6.5, and drying the washed precipitate in a drying oven to obtain a bacterial cellulose propionylation reaction product.
The degree of substitution of propionyl and the degree of substitution of butyryl were 0.77 and 1.70, respectively, and the total degree of substitution was 2.47, respectively, and the yield was 89%, respectively, for the propionic acid bacterial cellulosics obtained in example 5
Example 6
S1, adding 10g of bacterial cellulose with a water content of 80% into a reaction container with a stirrer, adding acetic anhydride capable of replacing 7.6g of water, and stirring for 15min to obtain a bacterial cellulose precursor solution (the water replaced in the precursor solution is 95% of water in wet materials).
S2, raising the temperature of the precursor solution obtained in the step S1 to 50 ℃, and adding an acetic anhydride-propionic anhydride-butyric anhydride-sulfuric acid reagent, wherein the dosage of sulfuric acid is 0.2mL, the dosages of acetic anhydride, propionic anhydride and butyric anhydride are all 8mL, and the reaction time is 2 h.
And S3, adding a magnesium acetate aqueous solution to terminate the reaction, pouring the mixture in the three-neck flask into deionized water when the temperature of the three-neck flask is reduced to room temperature, collecting precipitated precipitate, washing with a large amount of clear water, stopping after the pH value of the filtrate is greater than 6.5, and drying the washed precipitate in an oven to obtain a bacterial cellulose butyrylation reaction product.
The butyric acid bacterial cellulose obtained in example 6 had a degree of substitution of butyryl group of 0.26, a degree of substitution of propionyl group of 0.67, a degree of substitution of acetyl group of 1.62, a total degree of substitution of 2.55, and a yield of 83%.
Comparative example 1
S1, putting the wet bacterial cellulose material into a 120 ℃ oven to be dried to constant weight, wherein the bacterial cellulose is an absolutely dry material. 2g of the bacterial cellulose absolute dry material is added into a reaction vessel with stirring.
S2, adding 8mL of acetic acid into the absolute dry material prepared in the step S1, activating at 60 ℃ for 2h, adding a mixed solution of 0.2mL of concentrated sulfuric acid and 8mL of acetic anhydride, and reacting at 60 ℃ for 2 h.
And S3, adding a magnesium acetate aqueous solution to terminate the reaction, pouring the mixture in the three-neck flask into deionized water when the temperature of the three-neck flask is reduced to room temperature, collecting precipitated precipitate, washing with a large amount of clear water, stopping after the pH value of the filtrate is greater than 6.5, and drying the washed precipitate in an oven to obtain a bacterial cellulose acetylation reaction product.
The cellulose acetate obtained in comparative example 1 had a degree of substitution of 0.57 and a yield of 66%.
Comparative example 2
S1, adding 5g of bacterial cellulose wet material with the water content of 20% into a reaction container with a stirrer, adding acetic anhydride capable of replacing 0.8g of water, and stirring for 30min at 60 ℃ to obtain a bacterial cellulose precursor solution (the water replaced in the precursor solution is 90% of the water in the wet material).
S2, adding a tartaric acid-acetic anhydride mixed reagent into the precursor solution obtained in the step S1, and reacting at 90 ℃ for 1h, wherein the dosage of tartaric acid is 2g, and the dosage of acetic anhydride is 12 mL.
And S3, adding a magnesium acetate aqueous solution to terminate the reaction, pouring the mixture in the three-neck flask into deionized water when the temperature of the three-neck flask is reduced to room temperature, collecting precipitated precipitate, washing with a large amount of clear water, stopping after the pH value of the filtrate is greater than 6.5, and drying the washed precipitate in an oven to obtain a bacterial cellulose acetylation reaction product.
The substitution degree of the acetic acid bacterial cellulose obtained in comparative example 2 was 0.92, and the yield was 59%.
Comparative example 3
S1, putting 2.5g of a bacterial cellulose wet material with the water content of 30% into water, soaking for 24h, taking out, increasing the water content to 60%, adding acetic anhydride capable of replacing 3.938g of water, and stirring for 30min to obtain a bacterial cellulose precursor solution (the water replaced in the precursor solution is 90% of the water in the wet material).
S2, heating the temperature of the precursor solution obtained in the step S1 to 45 ℃, and adding an acetic anhydride-concentrated sulfuric acid mixed reagent, wherein the consumption of the concentrated sulfuric acid is 0.5mL, the consumption of the acetic anhydride is 6mL, and the reaction time is 2 h.
S3, adding a magnesium acetate aqueous solution to terminate the reaction, pouring the mixture in the flask into deionized water when the temperature of the three-neck flask is reduced to room temperature, collecting precipitated precipitates, washing with a large amount of clear water, stopping after the pH value of the filtrate is greater than 6.5, and drying the washed precipitates in an oven to obtain a bacterial cellulose acetylation reaction product.
The substitution degree of the acetic acid bacterial cellulose obtained in comparative example 3 was 1.02, and the yield was 61%.
It can be seen from the above embodiments that, through the reaction between acetic anhydride and water in the wet bacterial cellulose material, the generated acetic acid can effectively replace water in the wet bacterial cellulose material, so that the bacterial cellulose is always in a swelling state, and the problems that in the prior art, the bacterial cellulose must be activated by harsh pretreatment conditions, and the activation effect is limited, so that the subsequent acylation (including acetylation, propionylation, and butyrylation) reactions are more severe, the substitution degree of the acetic acid bacterial cellulose is low, and the product yield is poor are overcome.
From the above examples and comparative example analysis, it is found that it is advantageous to perform the acid anhydride hydrolysis reaction of bacterial cellulose to provide an appropriate water content. In comparative example 2, the bacterial cellulose with low water content forms hydrogen bonds among fibers due to the removal of water among the fibers, so that the bacterial cellulose forms a compact and compact structure, the fibers cannot keep a dispersion state, and the catalyst and acetic anhydride are difficult to enter the bacterial cellulose to generate acetylation reaction.
The comparative example 3 shows that when the bacterial cellulose with low water content is put into water to improve the water content of the bacterial cellulose again, although the edge of the bacterial cellulose slightly swells, the effect is limited, and the reaction efficiency is poor, which indicates that after the bacterial cellulose loses water to form a compact structure, the water content of the bacterial cellulose is not improved enough to restore the bacterial cellulose to a dispersion state by only adding water.
Compared with the acetic acid bacteria cellulose prepared by the traditional method, the hydrolysis reaction of acid anhydride is utilized, the formed short-chain fatty acid is used for replacing water, so that the bacteria cellulose can not form a compact structure while the water content is reduced, the process efficiency is improved, and the substitution degree of a finished product is high.
Claims (9)
1. A method of preparing a bacterial cellulose precursor material, comprising the steps of:
s1, providing a bacterial cellulose material;
s2, reacting the material obtained in the step S1 with acid anhydride, and replacing part or all of water in the bacterial cellulose material through acid anhydride hydrolysis reaction to obtain a bacterial cellulose precursor material.
2. A method of preparing a bacterial cellulose precursor according to claim 1, wherein the water content of the bacterial cellulose precursor material obtained in step S2 is < 20%, preferably < 10%; more preferably, less than 5%; particularly preferably, < 1%.
3. The method for preparing a bacterial cellulose precursor according to claim 1, wherein the acid anhydride is added in an excess amount compared to the stoichiometric ratio of the acid anhydride to the water contained in the bacterial cellulose in step S2.
Preferably, the acid anhydride is one or more of acetic anhydride, propionic anhydride and butyric anhydride.
4. The method for preparing a bacterial cellulose precursor according to claim 1, wherein the water content of the bacterial cellulose in step S1 is 40-95%.
5. A bacterial cellulose precursor material, characterized in that it is prepared by a method according to any one of claims 1 to 4.
6. A method for acylation reaction of bacterial cellulose, comprising the steps of:
s1, providing a bacterial cellulose material;
s2, reacting the material obtained in the step S1 with acid anhydride, and replacing part or all of water in the bacterial cellulose material through acid anhydride hydrolysis reaction to obtain a bacterial cellulose precursor material;
and S3, mixing the bacterial cellulose precursor material obtained in the step S2 with an acylating reagent solution, and starting to react.
And S4, finishing the reaction to finally obtain the acetic acid bacterial cellulose.
7. The method for acylation reaction of bacterial cellulose according to claim 6, wherein the water content of the bacterial cellulose in step S1 is 40-95%.
8. The method for acylation reaction of bacterial cellulose according to claim 6, wherein in step S2, the amount of the acid anhydride added is in excess of the stoichiometric ratio of the acid anhydride to the water contained in the bacterial cellulose.
9. The method for acylation reaction of bacterial cellulose according to claim 6, wherein the acid anhydride is one or more of acetic anhydride, propionic anhydride and butyric anhydride.
Preferably, the anhydride is acetic anhydride.
Preferably, the anhydride is propionic anhydride.
Preferably, the anhydride is a mixture of propionic anhydride and butyric anhydride.
Preferably, in the step S3, the acylating reagent is one or more of an acetylation reagent, a propionylation reagent and a butyrylation reagent;
preferably, in the step S3, the acylating agent is an acetylating agent;
preferably, in step S3, the acylating agent is a propionylating agent;
preferably, in step S3, the acylating agent is a butyrylating agent;
preferably, in step S3, the acylating agent is a mixture of a propionylating agent and a butyrylating agent;
preferably, the acid anhydride in step S2 is the same as the acid corresponding to the acylating agent in step S3.
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