Sulfobutyl ether-xanthan gum and a method for preparing the same

Abstract

The application discloses sulfobutyl ether-xanthan gum and a preparation method thereof, and the preparation steps of the sulfobutyl ether-xanthan gum include: (1) alkaline swelling of xanthan gum, (2) preparation of sulfobutyl etherizing agent, (3) sulfobutyl etherization of the xanthan gum, (4) purification and drying of the sulfobutyl ether-xanthan gum. The etherization reaction is carried out between the hydroxyl groups on the sugar unit molecules of the xanthan gum and 1,4-butanedisulfonic acid lactone, and the sulfobutyl ether-xanthan gum is prepared. The synthetic method is simple in process, low in by-products, high in conversion rate, and has a yield of 65-80%. The synthesized sulfobutyl ether-xanthan gum has the characteristics of solubilization, high viscosity and significant salt resistance, and can be used as a potential thickening agent with good thickening effect, and has a wide application prospect in the fields of food, cosmetics, textiles, medicine and oil exploitation.

Description

Technical Field

[0001] This invention relates to a sulfobutyl ether-xanthan gum and its preparation method, belonging to the field of natural polymer materials and polymer modification technology. Background Technology

[0002] Xanthan gum (XG) is a natural polymer composed of repeating pentasaccharide units, primarily consisting of two D-glucose units, two D-mannose units, and one D-glucuronic acid unit. Its average relative molecular mass is generally around 2 × 10⁻⁶. 6 -1.5×10 7 Between. The molecular structure is as follows:

[0003]

[0004] Structural formula of xanthan gum (XG)

[0005] Xanthan gum has a cellulose-like poly-β-1,4-pyranose main chain and three sugar units as side chains. The side chains consist of alternating D-glucuronic acid units and two D-mannose units, with the C2 of one D-mannose unit connected to the O atom on the C3 of the D-glucose unit in the main chain. At the C4 and C6 of some terminal D-mannose units in the side chains, a pyruvate group is attached via a ketal form of the ketone carbonyl group. Meanwhile, the C6 position of some D-mannose units near the main chain is acylated. These side chain groups play a crucial role in the structure and properties of xanthan gum; changes to these groups can significantly alter its properties.

[0006] Xanthan gum is an extracellular polysaccharide gum obtained from the metabolism of *Xanthomonas auricula-judae*, a bacterial pathogen that causes black rot in cabbage. It is a high-molecular-weight polymer. Xanthan gum's unique structure determines its excellent thickening, rheological, salt-resistant, and shear-resistant properties, as well as its excellent biocompatibility and biodegradability. Xanthan gum also possesses good suspension, emulsifying, water-soluble, thickening, and pseudoplastic properties, and is stable to heat, acids, alkalis, salts, and enzymatic reactions. It can be used as a thickener, emulsifier, stabilizer, and humectant, and is widely used in food, pharmaceuticals, cosmetics, daily chemicals, petroleum, and mining industries. However, the application of xanthan gum is limited by its natural form and properties. Therefore, chemical modification has become an important way to improve the performance of xanthan gum and broaden its application areas.

[0007] Studies have found that chemical modification can improve the solubility, stability, viscosity, and rheological properties of xanthan gum. Esterification modification increases the solubility of xanthan gum and improves its swelling power and viscosity. Etherification modification improves the solubility and rheological properties of xanthan gum, making it more suitable for applications such as drug controlled-release systems and tissue engineering. Amination modification increases the gelling properties of xanthan gum, making it more suitable as a biogelling agent and drug sustained-release carrier. Crosslinking modification improves the mechanical strength and stability of xanthan gum, increasing its application potential in tissue engineering and drug controlled-release systems.

[0008] Chemical modification methods for xanthan gum mainly include esterification, etherification, amination, and crosslinking. Esterification is the most common method, involving the conversion of the hydroxyl group to an ester group through reaction with acid anhydrides or esters. For example, Tao Yongzhen et al. (CN119119515A) prepared carboxymethylated xanthan gum and sulfated xanthan gum by esterification with chloroacetic acid and chlorosulfonic acid. Esterification modification can alter the solubility, thermal stability, and structure of xanthan gum. Etherification involves reacting the hydroxyl group of xanthan gum with an etherifying agent to form ether bonds. Etherification modification can improve the solubility and solvent stability of xanthan gum. Tan Tianwei et al. (CN105820264A) prepared cationic modified xanthan gum by etherification with quaternary ammonium salt etherifying agents. Amination involves reacting the hydroxyl groups of xanthan gum with amines to introduce amino groups or ammonium salts. Amination modification can increase the cation exchange capacity and gelling properties of xanthan gum. CN106832035A Tan Yebang et al. prepared a hydrophobically associating cationic xanthan gum by reacting it with glycidyl dodecyl dimethyl ammonium chloride as a modifier. CN106749736A Lu Yongjun et al. prepared cross-linked amphoteric xanthan gum by reacting it with xanthan gum using 3-chloro-2-hydroxypropyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltriethylammonium chloride, and 3-chloro-2-hydroxypropyltripropylammonium chloride as raw materials. Cross-linking introduces cross-linked structures into the xanthan gum molecule, either internally or intermolecularly. CN115612113A Zheng Bin et al. prepared xanthan gum with long alkyl chains by polymerizing it with acrylamide-2-methylpropanesulfonic acid, acrylic acid, and N-vinylpyrrolidone.

[0009] The main problem at present is that the chemical modification of xanthan gum has a limited number of modifying groups, which cannot meet the special performance requirements of xanthan gum in special industries. Summary of the Invention

[0010] To address the problems existing in the prior art, the present invention aims to provide a sulfobutyl ether-xanthan gum and its preparation method, providing more options for special industries with specific requirements for xanthan gum performance.

[0011] The present invention provides a method for preparing sulfobutyl ether-xanthan gum, and the synthetic route is as follows.

[0012]

[0013] Synthetic route of sulfonyl ether-xanthan gum

[0014] The preparation method includes the following steps:

[0015] 1) Alkali swelling of xanthan gum: Disperse xanthan gum in an alkaline solution and stir at room temperature for 1.5-2 hours. Then add alcohol and continue stirring for 1-2 hours to obtain an alkaline swelling solution of xanthan gum.

[0016] 2) Preparation of sulfobutyl etherifying agent: Under stirring, add emulsifying agent to a mixture of 1,4-butyric acid lactone and water to prepare sulfobutyl etherifying agent;

[0017] 3) Sulfobutyl etherification reaction of xanthan gum: Under vigorous stirring, sulfobutyl etherifying agent is added dropwise to xanthan gum alkaline swelling solution. The dropwise addition process is maintained for 4-7 hours, and the pH value of the system is maintained at 8.0-9.0. The reaction temperature is controlled at 50-65℃. After the dropwise addition is completed, the reaction continues for another 4-8 hours. After cooling to room temperature, xanthan gum sulfobutyl etherification reaction solution is obtained.

[0018] 4) Purification and drying of sulfobutyl ether-xanthan gum: The concentrated solution obtained by removing alcohol and part of water from the above etherification reaction solution by rotary evaporator is slowly added in batches to 3-8 times the volume of hot ethanol solution, stirred for at least 2 hours, cooled to room temperature, filtered and washed with ethanol to obtain a white or light yellow solid, dried in an oven, pulverized and sieved to obtain sulfobutyl ether-xanthan gum.

[0019] In step 1), the alkali swelling of xanthan gum is carried out by the following steps: the alkali in the alkali swelling solution is sodium hydroxide, potassium hydroxide or sodium carbonate; the alcohol is methanol, ethanol or isopropanol; the mass concentration of the alkali solution is 5-10%; the volume ratio of the alkali solution to the alcohol is 1:1-2.5; and the mass ratio of xanthan gum (grams) to the total volume (milliliters) of the alkali swelling solution is 1:25-50.

[0020] Furthermore, the alcohol is preferably isopropanol, the alkali is preferably sodium hydroxide, the mass concentration of the alkali solution is preferably 10%, and the volume ratio of the alkali solution to the alcohol is preferably 1:1.5; the mass (grams) ratio of xanthan gum to the total volume (milliliters) of the alkali swelling solution is preferably 1:25-35.

[0021] In step 2) of the preparation of the sulfobutyl etherifying agent, the emulsifying agent is selected from sodium dodecyl sulfonate or sodium dodecylbenzene sulfonate, or nonionic surfactants such as polyoxyethylene fatty acid esters, polyoxyethylene fatty alcohol ethers and fatty acid glycerides. The mass ratio of 1,4-butyrolactone, water and emulsifying agent is 1:0.5-0.8:0.01-0.05.

[0022] Furthermore, the mass ratio of the 1,4-butyrolactone, water, and emulsifying agent is 1:0.6-0.7:0.02-0.025, and the emulsifying agent is sodium dodecyl sulfonate or sodium dodecylbenzene sulfonate.

[0023] In step 3) the sulfonated butyl etherification reaction of xanthan gum, the mass ratio of xanthan gum in the alkali swelling solution to 1,4-butyrosulactone in the sulfonated butyl etherifying agent is 1:1-1.5, the reaction temperature is 55-65℃, and the sulfonated butyl etherifying agent is added dropwise for 4-6 hours. After the addition is complete, the reaction continues for 4-7 hours.

[0024] Furthermore, the mass ratio of xanthan gum in the alkali swelling solution to 1,4-butyrosulactone in the sulfobutyl etherifying agent is preferably 1:1.5, the reaction temperature is preferably 60°C, the sulfobutyl etherifying agent is added dropwise for preferably 5-6 hours, and the reaction continues for preferably 5-6 hours after the addition is completed.

[0025] In step 4) purification and drying of sulfonyl xanthan gum, the volume ratio of concentrated solution to hot ethanol solution is 1:3-5, the temperature of hot ethanol solution is 50-70℃, the concentration of hot ethanol solution is 75-95%, and the drying temperature is 60-80℃.

[0026] Furthermore, the volume ratio of the concentrated solution to the hot ethanol solution is preferably 1:5, the temperature of the hot ethanol solution is preferably 65°C, the concentration of the hot ethanol solution is preferably 80%, and the drying temperature is preferably 75°C.

[0027] The advantages of this invention compared to the prior art are as follows:

[0028] Due to the poor solubility of 1,4-butyrosulactone, it is difficult to achieve etherification with xanthan gum under normal conditions. Therefore, no method for preparing sulfobutyl ether-modified xanthan gum has been reported in the literature to date. The method for preparing sulfobutyl ether-xanthan gum provided by this invention changes the mixing degree of reactants in the reaction system by using an emulsifying surfactant, so that the poorly soluble xanthan gum and 1,4-butyrosulactone can react fully, reducing the occurrence of side reactions, and thus obtaining sulfobutyl ether-xanthan gum.

[0029] The successful preparation of sulfobutyl ether-xanthan gum by this invention can provide more options for special industries with special requirements for xanthan gum performance. Attached Figure Description

[0030] Figure 1 Xanthan gum and sulfobutyl ether - Xanthan gum 1 H NMR spectrum (VANCE Ⅲ-600MHz, D2O)

[0031] Figure 2 Solubility experiment of xanthan gum and sulfobutyl ether-xanthan gum under different pH conditions

[0032] Figure 3 Viscosity test of xanthan gum and sulfobutyl ether-xanthan gum under different pH conditions

[0033] Figure 4 Xanthan gum and sulfobutyl ether - Viscosity experiment of xanthan gum in different NaCl salt solutions

[0034] Figure 5 Effect of CaCl2 on the viscosity of sulfobutyl ether-xanthan gum in 5% NaCl salt solution

[0035] Figure 6 Stability test of sulfobutyl ether-xanthan gum in 5% sodium chloride + 5% calcium chloride solution Detailed Implementation

[0036] Example 1

[0037] In a 500 mL round-bottom flask, 8 g of xanthan gum was added in portions to 100 mL of 10% sodium hydroxide solution with rapid stirring. The mixture was stirred for 2 hours, then 150 mL of isopropanol was added, and stirring continued for another 30 minutes. Next, a sulfobutyl etherifying agent solution prepared from 12 g of 1,4-butyrolactone, 8 mL of water, and 0.25 g of sodium dodecyl sulfonate was slowly added dropwise through a dropping funnel over 6 hours. The pH of the system was maintained at approximately 8.0-9.0 by adding sodium hydroxide solution. The temperature was then raised to 60 °C, and the reaction continued for another 6 hours after the addition was complete. The mixture was then cooled to room temperature. The alcohol medium was removed from the reaction solution under reduced pressure using a rotary evaporator. The concentrated solution was slowly added in portions to 5 times its volume of 80% ethanol solution at 65 °C, stirred for 2 hours, cooled to room temperature, filtered, and washed with 95% ethanol to obtain a white solid. This solid was dried in a 75 °C oven, pulverized, and sieved to obtain purified sulfobutyl ether-xanthan gum. The yield was 78%.

[0038] The hydroxyl groups on the sugar unit molecules in the xanthan gum structure can interact with 1,4-butyryl lactone via S... N 2. Etherification reaction. Generally, the primary hydroxyl groups on sugar molecules preferentially etherify with 1,4-butyryl lactone, but secondary hydroxyl groups can also etherify with 1,4-butyryl lactone. Therefore, xanthan gum and 1,4-butyryl lactone can be etherified at different positions by forming etherification reactions at the primary and secondary hydroxyl groups on the sugar molecule to prepare sulfobutyl ether-xanthan gum. The structure of the purified sulfobutyl ether-xanthan gum was characterized by nuclear magnetic resonance (see [link to nuclear magnetic resonance image]). Figure 1 Comparison of xanthan gum and sulfobutyl ether-xanthan gum 1The ¹H NMR spectrum of sulfobutyl ether-xanthan gum showed two new peaks between δ 2.88 and 1.68-1.75, which were attributed to two hydrogens on the -CH2- group near the -SO3- of the substituent group and four hydrogens on the -CH2- group at the center of the substituent group, respectively. The peak integration ratio was 1:2, consistent with theoretical calculations. The chemical shift of the two hydrogens on the -CH2- group near the ether bond and the proton peak on the xanthan gum skeleton appeared in the range of 3.20-4.25 (δ 1.19 is the peak of the -CH3- group of the residual trace solvent alcohol). Furthermore, the sulfobutyl ether-xanthan gum had been purified by a large amount of ethanol, eliminating the ring-opening byproducts formed by 1,4-butyryl lactone with water and alcohol, confirming that the sulfobutyl ether is incorporated into the xanthan gum molecule.

[0039] Sulfobutyl ether-xanthan gum introduces sulfonic acid-containing side chains into the xanthan gum structure, increasing the water solubility of xanthan gum. The solubility of xanthan gum and sulfobutyl ether-xanthan gum in water was observed at 20℃. Solubility increased by 10-15% within the pH ranges of 2.1, 6.5, and 11.8 (see...). Figure 2 ).

[0040] Sulfobutyl ether-xanthan gum introduces flexible side chains into the xanthan gum structure, broadening the three-dimensional spatial structure of the xanthan gum matrix and increasing its viscosity. The viscosities of 0.25% xanthan gum and sulfobutyl ether-xanthan gum in water at pH values ​​of 2.1, 5.2, 6.5, 8.3, and 11.8 were measured at 20℃. The results showed that the viscosity of sulfobutyl ether-xanthan gum was significantly higher than that of xanthan gum, especially at higher pH conditions, with an increase of approximately 15% or more (see...). Figure 3 ).

[0041] Sulfonyl ether-xanthan gum introduces a soft side chain containing sulfonic acid groups into the xanthan gum structure, increasing the solubility of the xanthan gum matrix and its complexing ability with metal ions. Experimental results show that both xanthan gum and sulfonyl ether-xanthan gum exhibit good salt resistance at 20℃ (see...). Figure 4 It can be seen that the viscosity of 0.25% sulfobutyl ether-xanthan gum is almost unaffected in both a 5% sodium chloride solution and a mixed solution of 5% sodium chloride and 5% calcium chloride, and the addition of calcium chloride does not cause precipitation. Therefore, this indicates that sulfobutyl ether-xanthan gum exhibits superior salt resistance and is adaptable to most water quality conditions (see...). Figure 5 ).

[0042] The colloid formed by sulfobutyl ether-xanthan gum exhibits good stability. Experimental results show that in a 5% sodium chloride + 5% calcium chloride mixed solution at 20℃, the viscosity of 0.25% sulfobutyl ether-xanthan gum shows almost no significant change over 24 days (see [link to experimental results]). Figure 6 ).

[0043] Example 2

[0044] In a 500 mL round-bottom flask, 8 g of xanthan gum was added in portions to 80 mL of 10% sodium hydroxide solution with rapid stirring. The mixture was stirred for 1.5 hours, then 150 mL of isopropanol was added, and stirring continued for another 30 minutes. Next, a sulfobutyl etherifying agent solution prepared from 15 g of 1,4-butyrolactone, 10 mL of water, and 0.3 g of sodium dodecyl sulfonate was slowly added dropwise through a dropping funnel over 5 hours. The pH of the system was maintained at approximately 8.0-9.0 by adding sodium hydroxide solution. The temperature was then raised to 60 °C, and the reaction continued for 5.5 hours after the addition was complete. The mixture was then cooled to room temperature. The alcohol medium was removed from the reaction solution under reduced pressure using a rotary evaporator. The concentrated solution was slowly added in portions to four times its volume of 80% ethanol solution at 65 °C, and stirred for 2 hours. After cooling to room temperature, the solution was filtered and washed with 95% ethanol to obtain a white solid. This solid was dried in a 75 °C oven, pulverized, and sieved to obtain purified sulfobutyl ether-xanthan gum. The yield was 67%.

Claims

1. A method for preparing sulfobutyl ether-xanthan gum, characterized in that, Includes the following steps: 1) Disperse xanthan gum in an alkaline solution and stir at room temperature for 1.5-2 hours. Then add alcohol and continue stirring for 1-2 hours to obtain xanthan gum alkaline swelling solution. 2) Under stirring, add an emulsifying agent to a mixture of 1,4-butyric acid lactone and water to prepare a sulfobutyl etherifying agent; 3) Under vigorous stirring, add sulfobutyl etherifying agent dropwise to the xanthan gum alkali swelling solution. The dropwise addition process is maintained for 4-7 hours, and the pH value of the system is maintained at 8.0-9.

0. Control the reaction temperature at 50-65℃. After the dropwise addition is completed, continue the reaction for 4-8 hours. Cool to room temperature and place to obtain xanthan gum sulfobutyl etherification reaction solution. 4) Remove the alcohol and some water from the above etherification reaction solution by rotary evaporator to obtain a concentrated solution. Add the concentrated solution slowly in batches to 3-8 times the volume of hot ethanol solution, stir for at least 2 hours, cool to room temperature, filter, wash with ethanol to obtain a white or light yellow solid, dry in an oven, pulverize and sieve to obtain sulfobutyl ether-xanthan gum.

2. The method for preparing sulfobutyl ether-xanthan gum according to claim 1, characterized in that, In step 1), the alkali in the alkali swelling solution is sodium hydroxide, potassium hydroxide, or sodium carbonate; the alcohol is methanol, ethanol, or isopropanol; the mass concentration of the alkali solution is 5-10%, and the volume ratio of the alkali solution to the alcohol is 1:1-2.5; the mass ratio of xanthan gum (grams) to the total volume (milliliters) of the alkali swelling solution is 1:25-50.

3. The method for preparing sulfobutyl ether-xanthan gum according to claim 2, characterized in that, The alcohol is isopropanol, the alkali is sodium hydroxide, the mass concentration of the alkali solution is 10%, and the volume ratio of the alkali solution to the alcohol is 1:1.5; the mass ratio of xanthan gum (grams) to the total volume (milliliters) of the alkali swelling solution is 1:25-35.

4. The method for preparing sulfobutyl ether-xanthan gum according to claim 1, characterized in that, In step 2), the mass ratio of 1,4-butyrolactone, water, and emulsifying agent is 1:0.5-0.8:0.01-0.05, and the emulsifying agent is sodium dodecyl sulfonate or sodium dodecylbenzene sulfonate.

5. The method for preparing sulfobutyl ether-xanthan gum according to claim 4, characterized in that, The mass ratio of 1,4-butyryl lactone, water, and emulsifying agent is 1:0.6-0.7:0.02-0.025, and the emulsifying agent is sodium dodecyl sulfonate.

6. The method for preparing sulfobutyl ether-xanthan gum according to claim 1, characterized in that, In step 3), the mass ratio of xanthan gum in the alkali swelling solution to 1,4-butyrosulactone in the sulfobutyl etherifying agent is 1:1-1.5, the reaction temperature is 55-65℃, and the sulfobutyl etherifying agent is added dropwise for 4-6 hours; after the addition is completed, the reaction continues for 4-7 hours.

7. The method for preparing sulfobutyl ether-xanthan gum according to claim 6, characterized in that, The mass ratio of xanthan gum in the alkali swelling solution to 1,4-butyrosulactone in the sulfobutyl etherifying agent is 1:1.5, the reaction temperature is 60℃, and the sulfobutyl etherifying agent is added dropwise for 5-6 hours; after the addition is completed, the reaction continues for another 5-6 hours.

8. The method for preparing sulfobutyl ether-xanthan gum according to claim 1, characterized in that, In step 4), the volume ratio of the concentrated liquid to the hot ethanol solution is 1:3-5, the temperature of the hot ethanol solution is 50-70℃, the concentration of the hot ethanol solution is 75-95%, and the drying temperature is 60-80℃.

9. The method for preparing sulfobutyl ether-xanthan gum according to claim 8, characterized in that, The volume ratio of the concentrated liquid to the hot ethanol solution is 1:5, the temperature of the hot ethanol solution is 65°C, the concentration of the hot ethanol solution is 80%, and the drying temperature is 75°C.

10. Sulfobutyl ether-xanthan gum prepared by any one of claims 1-9.

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