A kind of preparation method of cellulose acetyl citrate

Abstract

The present invention relates to a preparation method of acetylated cellulose citrate. Jute is used as a raw material, which is crushed, alkali-treated, bleached, centrifuged, and dried. The pretreated jute fibers are added to a mixed solution of hydrochloric acid and citric acid for hydrolysis and carboxylation modification. Then, acetic anhydride is used as an acylating agent to react with the carboxylated nanocellulose, and acetylated cellulose citrate is obtained at room temperature. In the present invention, the hydroxyl group on C6 of cellulose undergoes a cross-linking esterification reaction with citric acid, and acetic anhydride is used as the acylating agent. After the hydroxyl groups in the cellulose citrate molecules are acetylated, they are blocked, thereby improving the hydrophobicity of the nanocellulose and enhancing the interfacial compatibility with the biodegradable biopolyester. The preparation process of the present invention is green and environmentally friendly, and has less negative impact on the environment during the preparation process. The acetylated cellulose citrate obtained by modification has strong hydrophobicity and effectively improves the dispersibility of nanocellulose in the biodegradable polyester.

Description

Technical Field

[0001] The invention relates to a method for preparing cellulose ester, in particular to a method for preparing cellulose citrate ester. Background Art

[0002] Cellulose is the most abundant biopolymer on earth. Nanocellulose not only has the advantages of cellulose itself, such as wide source, good biocompatibility, and high strength, but also has the characteristics of nanomaterials such as high reactivity and small size effect. Nanocellulose can replace expensive, non-biodegradable synthetic materials and is considered to be a new generation of raw materials with great potential.

[0003] Cellulose is a renewable and biodegradable green resource in nature, but because of the presence of a large number of hydroxyl groups on its molecular chain, it is very sensitive to moisture, which not only reduces the durability of cellulose materials, but also causes poor compatibility of cellulose with hydrophobic matrices and organic solvents in composite processing, and has certain processing limitations. The hydrophobic modification of cellulose is mainly divided into several aspects: chemical modification, such as esterification, etherification, graft polymerization, and solvent treatment; physical and chemical modification, such as plasma etching polymerization, electrospraying, and electrowetting; surface coating, such as sol-gel atomic layer deposition, magnetron sputtering, etc. (A brief evaluation of the above modification methods, such as the most widely used, difficult to process, etc.).

[0004] Nanocellulose has a large specific surface area and contains a large number of hydroxyl groups on its surface. Cellulose particles can easily aggregate through hydrogen bonding interactions, and it is difficult to disperse the aggregated cellulose particles by physical methods. Therefore, hydrophobic modification of nanocellulose, reducing the hydrophilicity and polarity of nanocellulose, and improving the interfacial compatibility with the hydrophobic polyester matrix are important means to prepare nanocellulose reinforced composite materials with excellent performance. Summary of the invention

[0005] The invention provides a method for preparing acetyl citrate cellulose in order to improve the hydrophobicity of nanocellulose and enhance the interfacial compatibility with hydrophobic polyester.

[0006] A method for preparing cellulose acetyl citrate, characterized in that:

[0007] The method uses jute as raw material, firstly grinds and ball-mills jute powder to obtain jute powder, and then sequentially treats with alkali, bleaches, carboxylates and acetylates to obtain acetyl citrate cellulose.

[0008] The method comprises the following steps:

[0009] (a) weighing a certain amount of jute, crushing it, and grinding it with a ball mill to obtain jute powder;

[0010] (b) weighing 20 g of the jute powder obtained in step (a) and adding it to 200 ml of sodium hydroxide solution, heating and stirring the mixture, repeating twice to remove lignin and hemicellulose therein, filtering and washing with distilled water after the reaction is completed, and centrifuging until neutral;

[0011] (c) adding the jute powder treated in step (b) into a mixed solution of NaOH and H2O2, bleaching the mixture at 60°C for 6 to 9 hours, centrifugally washing the mixture until the pH value is neutral, and drying the mixture for later use;

[0012] (d) Weigh 6 g of the product obtained by drying in step (c), add it to 300 ml of a mixed solution of hydrochloric acid and citric acid, and heat and stir; after the reaction, centrifuge and wash until the pH is neutral, and dry it at 70-85° C. for 8-15 hours to obtain carboxylated cellulose;

[0013] (e) taking 1 g of the carboxylated cellulose obtained in step (d) and mixing it with 25 ml of acetic acid solution and stirring for 20 to 40 min, then adding a mixed solution of concentrated sulfuric acid and acetic acid to the solution and stirring for 20 to 30 min; then adding acetic anhydride to the stirred and mixed solution and reacting at room temperature for 10 to 15 h;

[0014] (f) filtering the solution obtained in step (e) to remove unreacted carboxylated cellulose, and adding ice water to the filtrate while stirring to quickly terminate the reaction and obtain a white flocculent precipitate;

[0015] (g) The precipitate obtained in step (f) is washed with distilled water until it becomes neutral, and the precipitate is collected and dried to obtain a white powder, which is acetyl cellulose citrate.

[0016] Furthermore, the particle size of the jute powder after ball milling in step (a) is 75-85 mesh.

[0017] Furthermore, the concentration of NaOH in step (b) is 1-4 mol / L.

[0018] Furthermore, the reaction temperature in step (b) is 60-80° C., and the reaction time is 2-4 hours.

[0019] Furthermore, the mixed solution of NaOH and H2O2 in step (c) is a solution prepared by mixing 1 mol / L NaOH and 24% H2O2 in a volume ratio of 1:1 to 2.

[0020] Furthermore, in step (d), the concentration of hydrochloric acid is 4-10 mol / L, the concentration of citric acid is 2-6 mol / L; and the volume ratio of hydrochloric acid to citric acid is 1:9.

[0021] Furthermore, the reaction temperature in step (d) is 70-85° C., and the reaction time is 5-7 h.

[0022] Furthermore, in step (e), the volume of acetic anhydride added is 30-35 ml, the volume of concentrated sulfuric acid is 0.07-0.11 ml, and the volume of acetic acid is 7-11 ml.

[0023] Beneficial effects of the present invention:

[0024] (1) Based on the original nanocellulose, the present invention utilizes the hydroxyl groups on cellulose C6 to react with citric acid for esterification and cross-linking. The network structure formed by cross-linking increases the connection density of the nanocellulose. After further acetylation modification, the hydrophobicity of the nanocellulose is significantly improved.

[0025] (2) The preparation process of the present invention is simple and can be operated continuously; the raw materials used are derived from biomass resources, the raw material cost is low, the operating conditions are relatively low, and the preparation process has little negative impact on the environment.

[0026] (3) The hydrophobic effect of the modified nanocellulose is stable, the agglomeration of the particles is reduced, and the interfacial compatibility with the hydrophobic polyester is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a SEM image of cellulose acetyl citrate of the present invention;

[0028] Figure 2 It is the infrared spectrum of acetyl citrate cellulose of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with specific examples, and these implementation cases are only used to illustrate the present invention and are not used to limit the scope of the present invention. In addition, after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the claims attached to this application.

[0030] Example 1

[0031] Weigh a certain amount of jute, crush it, and then use a ball mill to grind it to 80 mesh. Weigh 20g of jute powder and add it to 200ml of 1.75mol / L sodium hydroxide solution. Heat and stir the mixture at 70℃ for 3 hours. Repeat twice to remove lignin and hemicellulose. After the reaction is completed, filter it and wash it with distilled water, and centrifuge it to neutral. Add cellulose to a mixed solution of 1mol / L NaOH and 24% H2O2 in a volume ratio of 1:1. After bleaching at 60℃ for 8 hours, centrifuge and wash it until the pH is neutral, and dry it for use.

[0032] Weigh 6g of bleached cellulose and add it to 300ml of a mixed solution of 6mol / L hydrochloric acid and 3mol / L citric acid (volume ratio 1:9), and heat and stir at 80℃ for 6h. After the reaction, centrifuge and wash until the pH is neutral, and dry at 80℃ for 12 hours to obtain carboxylated nanocellulose. Take 1g of carboxylated nanocellulose and mix it with 25ml of acetic acid solution and stir for 30min, then add a mixed solution consisting of 0.07ml of concentrated sulfuric acid and 7ml of acetic acid to the solution and stir for 25min;

[0033] Add 32 mL of acetic anhydride to the solution after stirring and mixing, and react at room temperature for 14 hours. Filter the solution to remove unreacted carboxylated cellulose, and add ice water to the filtrate while stirring to quickly terminate the reaction and obtain a white flocculent precipitate. Wash the precipitate with distilled water until it is neutral, collect the precipitate and dry it to obtain a white powder, which is acetyl citrate cellulose ester. Example

[0034] Weigh a certain amount of jute, crush it, and then use a ball mill to grind it to 80 mesh. Weigh 20g of jute powder and 150ml of 2.25mol / L sodium hydroxide solution, heat and stir the mixture at 60℃ for 4 hours, repeat twice to remove lignin, hemicellulose and pigments. After the reaction is completed, filter and wash with distilled water, and centrifuge to neutral. Add cellulose to a mixed solution of 1mol / L NaOH and 24% H2O2 in a volume ratio of 1:1, bleach it at 60℃ for 8 hours, centrifuge and wash until the pH is neutral, and dry it for use.

[0035] Weigh 6g of bleached cellulose and add it to 200ml of a mixed solution of 10mol / L hydrochloric acid and 6mol / L citric acid in a volume ratio of 1:9, and heat and stir at 85℃ for 5h. After the reaction is completed, centrifuge and wash until the pH is neutral, and dry at 85℃ for 10 hours to obtain carboxylated nanocellulose. Take 1g of carboxylated nanocellulose and mix it with 25ml of acetic acid solution and stir for 30min, then add a mixed solution consisting of 0.08ml of concentrated sulfuric acid and 8ml of acetic acid to the solution and stir for 25min;

[0036] Add 30 mL of acetic anhydride to the solution after stirring and mixing, and react at room temperature for 15 hours. Filter the solution to remove unreacted carboxylated cellulose, and add ice water to the filtrate while stirring to quickly terminate the reaction and obtain a white flocculent precipitate. Wash the precipitate with distilled water until it is neutral, collect the precipitate and dry it to obtain a white powder, which is acetyl citrate cellulose ester. Example

[0037] Weigh a certain amount of jute, crush it, and then use a ball mill to grind it to 80 mesh. Weigh 20g of jute powder and 100ml of 3mol / L sodium hydroxide solution, heat and stir the mixture at 80℃ for 2 hours, repeat twice to remove lignin, hemicellulose and pigments. After the reaction is completed, filter and wash with distilled water, and centrifuge to neutral. Add cellulose to a mixed solution of 1mol / L NaOH and 24% H2O2 in a volume ratio of 1:1, bleach it at 60℃ for 8 hours, centrifuge and wash until the pH is neutral, and dry it for use.

[0038] Weigh 6g of bleached cellulose and add it to 250ml of a mixed solution of 8mol / L hydrochloric acid and 4mol / L citric acid in a volume ratio of 1:9, and heat and stir at 70℃ for 7h. After the reaction is completed, centrifuge and wash until the pH is neutral, and dry at 90℃ for 8 hours to obtain carboxylated nanocellulose. Take 1g of carboxylated nanocellulose and mix it with 20ml of acetic acid solution and stir for 30min, then add a mixed solution consisting of 0.1ml of concentrated sulfuric acid and 10ml of acetic acid to the solution and stir for 20min;

[0039] Add 35 mL of acetic anhydride to the solution after stirring and mixing, and react at room temperature for 10 hours. Filter the solution to remove unreacted carboxylated cellulose, and add ice water to the filtrate while stirring to quickly terminate the reaction and obtain a white flocculent precipitate. Wash the precipitate with distilled water until it is neutral, collect the precipitate and dry it to obtain a white powder, which is acetyl citrate cellulose ester. Example

[0040] Weigh a certain amount of jute, crush it, and then use a ball mill to grind it to 80 mesh. Weigh 20g of jute powder and 100ml of 4mol / L sodium hydroxide solution, heat and stir the mixture at 65℃ for 3.5 hours, repeat twice to remove lignin, hemicellulose and pigments. After the reaction is completed, filter and wash with distilled water, and centrifuge to neutral. Add cellulose to a mixed solution of 1mol / L NaOH and 24% H2O2 in a volume ratio of 1:1, bleach it at 60℃ for 8 hours, centrifuge and wash until the pH is neutral, and dry it for use.

[0041] Weigh 6g of bleached cellulose and add it to 250ml of a mixed solution of 4mol / L hydrochloric acid and 2mol / L citric acid in a volume ratio of 1:9, and heat and stir at 75℃ for 6.5h. After the reaction is completed, centrifuge and wash until the pH is neutral, and dry at 90℃ for 8 hours to obtain carboxylated nanocellulose. Take 1g of carboxylated nanocellulose and mix it with 20ml of acetic acid solution and stir for 30min, then add a mixed solution consisting of 0.09ml of concentrated sulfuric acid and 9ml of acetic acid to the solution and stir for 20min;

[0042] Add 33 mL of acetic anhydride to the solution after stirring and mixing, and react at room temperature for 13 hours. Filter the solution to remove unreacted carboxylated cellulose, and add ice water to the filtrate while stirring to quickly terminate the reaction and obtain a white flocculent precipitate. Wash the precipitate with distilled water until it is neutral, collect the precipitate and dry it to obtain a white powder, which is acetyl citrate cellulose ester. Example

[0043] Weigh a certain amount of jute, crush it, and then use a ball mill to grind it to 80 mesh. Weigh 20g of jute powder and 100ml of 1mol / L sodium hydroxide solution, heat and stir the mixture at 75℃ for 2.5 hours, repeat twice to remove lignin, hemicellulose and pigments. After the reaction is completed, filter and wash with distilled water, and centrifuge to neutral. Add cellulose to a mixed solution of 1mol / L NaOH and 24% H2O2 in a volume ratio of 1:1, bleach it at 60℃ for 8 hours, centrifuge and wash until the pH is neutral, and dry it for use.

[0044] Weigh 6g of bleached cellulose and add it to 250ml of a mixed solution of 7mol / L hydrochloric acid and 3.5mol / L citric acid in a volume ratio of 1:9, and heat and stir at 78℃ for 6h. After the reaction is completed, centrifuge and wash until the pH is neutral, and dry at 90℃ for 8 hours to obtain carboxylated nanocellulose. Take 1g of carboxylated nanocellulose and mix it with 20ml of acetic acid solution and stir for 30min, then add a mixed solution consisting of 0.11ml of concentrated sulfuric acid and 11ml of acetic acid to the solution and stir for 20min;

[0045] Add 34 mL of acetic anhydride to the solution after stirring and mixing, and react at room temperature for 11 hours. Filter the solution to remove unreacted carboxylated cellulose, and add ice water to the filtrate while stirring to quickly terminate the reaction and obtain a white flocculent precipitate. Wash the precipitate with distilled water until it is neutral, collect the precipitate and dry it to obtain a white powder, which is acetyl citrate cellulose ester.

[0046] The properties of the acetyl citrate cellulose ester prepared by the present invention are characterized, as shown in FIG. Figure 1 and Figure 2 As shown in the figure, the SEM image shows that the nano-scale spherical acetyl citrate cellulose ester was successfully prepared; the infrared spectrum shows that the C=O group is at 1735cm -1 A strong absorption peak appears at 1211 cm -1 A strong absorption peak appeared at the position where the hydroxyl groups on the cellulose citrate were acetylated, and acetyl cellulose citrate was successfully prepared. It has broad application prospects as an auxiliary agent in the reinforcement and toughening modification of degradable polyester.

Claims

1. A method for preparing cellulose acetyl citrate, characterized in that: The method uses jute as raw material, firstly crushes and ball-mills jute powder, then sequentially treats with alkali, bleaches, carboxylates and acetylates to obtain acetyl citrate cellulose. The method specifically comprises the following steps: (a) weighing a certain amount of jute, crushing it, and grinding it with a ball mill to obtain jute powder; (b) weighing 20 g of the jute powder obtained in step (a) and adding it to 200 ml of sodium hydroxide solution, heating and stirring the mixture, repeating twice to remove lignin and hemicellulose therein, filtering and washing with distilled water after the reaction is completed, and centrifuging until neutral; (c) adding the jute powder treated in step (b) into a mixed solution of NaOH and H2O2, bleaching the mixture at 60°C for 6 to 9 hours, centrifugally washing the mixture until the pH value is neutral, and drying the mixture for later use; (d) Weigh 6 g of the product obtained by drying in step (c), add it to 300 ml of a mixed solution of hydrochloric acid and citric acid, and heat and stir; after the reaction, centrifuge and wash until the pH is neutral, and dry it at 70-85° C. for 8-15 hours to obtain carboxylated cellulose; (e) taking 1 g of the carboxylated cellulose obtained in step (d) and mixing it with 25 ml of acetic acid solution and stirring for 20 to 40 min, then adding a mixed solution of concentrated sulfuric acid and acetic acid to the solution and stirring for 20 to 30 min; then adding acetic anhydride to the stirred and mixed solution and reacting at room temperature for 10 to 15 h; (f) filtering the solution obtained in step (e) to remove unreacted carboxylated cellulose, and adding ice water to the filtrate while stirring to quickly terminate the reaction and obtain a white flocculent precipitate; (g) The precipitate obtained in step (f) is washed with distilled water until it becomes neutral, and the precipitate is collected and dried to obtain a white powder, which is acetyl cellulose citrate.

2. The preparation method according to claim 1, characterized in that The particle size of the jute powder after grinding in the ball mill in step (a) is 75-85 mesh.

3. The preparation method according to claim 1, characterized in that The concentration of NaOH in step (b) is 1-4 mol / L.

4. The preparation method according to claim 1, characterized in that The reaction temperature in step (b) is 60-80° C., and the reaction time is 2-4 hours.

5. The preparation method according to claim 1, characterized in that The mixed solution of NaOH and H2O2 in step (c) is a solution prepared by mixing 1 mol / L NaOH and 24% H2O2 in a volume ratio of 1:1 to 2.

6. The preparation method according to claim 1, characterized in that In step (d), the concentration of hydrochloric acid is 4-10 mol / L, the concentration of citric acid is 2-6 mol / L; and the volume ratio of hydrochloric acid to citric acid is 1:

9.

7. The preparation method according to claim 1, characterized in that The reaction temperature in step (d) is 70-85° C., and the reaction time is 5-7 h.

8. The preparation method according to claim 1, characterized in that In step (e), the volume of acetic anhydride added is 30-35 ml, the volume of concentrated sulfuric acid is 0.07-0.11 ml, and the volume of acetic acid is 7-11 ml.

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