CN113235290B - Preparation method of ether bond-linked polybasic carboxyl modified regenerated cellulose - Google Patents

Abstract

The invention discloses a preparation method of ether bond connected multi-carboxyl modified regenerated cellulose, which comprises the steps of firstly changing ester groups of cellulose acetate into hydroxyl groups through saponification reaction, then adding halogenated diethyl malonate to perform alkali catalysis etherification grafting reaction to enable halogen and the hydroxyl groups to perform grafting reaction and simultaneously hydrolyze ester groups of the halogenated diethyl malonate into carboxyl groups, and finally soaking in dilute acid solution until carboxylate is completely converted into the carboxyl groups to obtain ether bond connected multi-carboxyl modified regenerated cellulose products. According to the invention, a polybasic carboxyl group is introduced on the surface of regenerated cellulose through an in-situ etherification reaction, and the polybasic carboxyl modifier is firmly bonded and connected with the regenerated cellulose through a covalent bond-ether bond, so that carboxyl is not easy to fall off, and a cellulose acetate product is not dissolved and swelled with the increase of the introduced amount of carboxyl, can tolerate a water environment with high pH value, has higher stability and adsorption capacity in the environment, and can be used for removing heavy metal ions.

Description

A kind of preparation method of polybasic carboxyl modified regenerated cellulose connected by ether bond

technical field

The invention belongs to the field of regenerated cellulose modification, in particular to a preparation method of polybasic carboxyl modified regenerated cellulose connected by ether bonds.

Background technique

With people's attention to the ecological environment, the rapid development of various technical means for water pollution control, the removal of heavy metal ions in water has always been a research hotspot. Among them, the removal of heavy metal ions by adsorption technology is a simple and effective method. One of the most environmentally friendly methods. Studies have shown that polymer adsorbents have the advantages of high adsorption capacity and good reusability in the treatment of heavy metal polluted wastewater, and biodegradable materials are the first choice for environmentally friendly polymer adsorbents. Among them, cellulose, especially cellulose nanofibers, has outstanding performance in removing heavy metal ions.

It should be noted that pure cellulose has a weak removal capacity due to its numerous hydroxyl groups. In order to improve its adsorption capacity, functionalization is usually required to introduce carboxyl groups, sulfonic acid groups, amine groups, amide groups, thiol groups, etc. Functionalized groups that can be used as ligands. Literature "Zhang Kai,Li Zongjie,Deng Nanping,et al.Tree-likecellulose nanofiber membranes modified by citric acid for heavy metal ion(Cu ^{2 +} )removal[J].Cellulose,2019,26(2):945-958" The method of citric acid modification is used to introduce polycarboxyl groups into cellulose, but the reaction is carried out under high temperature and high pressure conditions, and the citric acid and cellulose are connected by ester bonds, which are resistant to higher acid and alkaline environments. Poor receptivity. In the document "Ricardo Chagas, Martin Gericke, Ricardo B. Ferreira, et al. Synthesis and characterization of dicarboxymethyl cellulose [J]. Cellulose, 2020, 27: 1965-1974", carboxylation of cellulose powder with sodium bromomalonate However, sodium bromomalonate is a non-commercial product, and with the increase in the degree of substitution of hydroxyl groups in cellulose, the water solubility of cellulose powder will increase, and it cannot be used as a heavy metal ion adsorbent. Therefore, it is urgent to develop a new route and new method for the preparation of heavy metal ion adsorbents with tolerance to high pH water environment, mild reaction conditions, low cost and simple process.

SUMMARY OF THE INVENTION

Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a preparation method of polycarboxyl modified regenerated cellulose connected by ether bonds.

The technical solution of the present invention to solve the technical problem is to provide a method for preparing a polycarboxylate modified regenerated cellulose connected by an ether bond, characterized in that the method comprises the following steps:

Step 1, adding the cellulose acetate product into the excess strong alkaline solution, and carrying out a saponification reaction to change the ester group of the cellulose acetate into a hydroxyl group to obtain a regenerated cellulose product;

Step 2. Mix the regenerated cellulose product obtained in step 1, the solvent and the alkali activator, and after activating the regenerated cellulose, add diethyl halogenated malonate to undergo an alkali-catalyzed etherification grafting reaction so that the halogen and the hydroxyl group are grafted. The branch reaction simultaneously hydrolyzes the ester group of the halogenated diethyl malonate into a carboxyl group to obtain the initial product;

Step 3. Wash the primary product obtained in Step 2 to remove unreacted substances and small molecular by-products to complete the purification of the primary product, and then immerse it in a dilute acid solution until the carboxylate is completely converted into a carboxyl group to obtain an ether bond-linked Polycarboxyl modified regenerated cellulose products.

Compared with the prior art, the beneficial effects of the present invention are:

(1) In the present invention, polybasic carboxyl groups are introduced on the surface of regenerated cellulose through in-situ etherification reaction, and polybasic carboxyl modifier and regenerated cellulose are firmly bonded and connected by covalent bond-ether bond, carboxyl groups are not easy to fall off, and acetic acid Cellulose products will not dissolve and swell with the increase in the amount of carboxyl groups introduced, and can withstand the high pH water environment. In this environment, it has higher stability and adsorption capacity, and can be used for the removal of heavy metal ions.

(2) When cellulose acetate products use nano-micron fiber membranes, the higher specific surface area and porosity of the nano-micron fiber membranes endow the material with high adsorption performance and rapid substance transfer and diffusion in the fiber membrane, and the etherification reaction will not destroy the fiber structure.

(3) The method has the advantages of simple process, mild reaction, low post-processing cost, easy operation, good application adaptability and easy industrialization.

(4) Diethyl halomalonate as a modifying reagent is a commercial intermediate for pharmaceutical and chemical synthesis, which can be directly purchased and applied.

Description of drawings

Fig. 1 is the reaction scheme diagram of the inventive method;

Fig. 2 is the SEM image of the polycarboxyl group-modified regenerated cellulose nanofiber membrane connected by ether bond prepared in Example 1 of the present invention;

Fig. 3 is the infrared spectrogram of the polycarboxyl group-modified regenerated cellulose nano-micron fiber membrane connected by ether bond prepared in Example 1 of the present invention;

Fig. 4 is the SEM image of the polycarboxyl group-modified regenerated cellulose nanofiber membrane connected by ether bond prepared in Example 2 of the present invention;

Fig. 5 is the infrared spectrogram of the polycarboxyl group-modified regenerated cellulose nano-fiber membrane connected by ether bond obtained in Example 2 of the present invention;

Fig. 6 is the SEM image of the polycarboxyl group-modified regenerated cellulose nanofiber membrane connected by ether bond prepared in Example 3 of the present invention;

Fig. 7 is the infrared spectrogram of the polycarboxyl group-modified regenerated cellulose nano-fiber membrane connected by ether bond prepared in Example 3 of the present invention;

Fig. 8 is the SEM image of the cellulose acetate nano-micron fiber membrane prepared in Comparative Example 1 of the present invention;

Fig. 9 is the infrared spectrogram of the cellulose acetate nano-micron fiber membrane obtained by Comparative Example 1 of the present invention;

Fig. 10 is the SEM image of the regenerated cellulose nano-micron fiber membrane prepared by Comparative Example 2 of the present invention;

Figure 11 is an infrared spectrum of the regenerated cellulose nano-micron fiber membrane prepared in Comparative Example 2 of the present invention.

Detailed ways

Specific embodiments of the present invention are given below. The specific embodiments are only used to further illustrate the present invention in detail, and do not limit the protection scope of the claims of the present application.

The present invention provides a preparation method (method for short) of ether-linked polycarboxylate modified regenerated cellulose, characterized in that the method comprises the following steps:

Step 1, adding the cellulose acetate product into the excess strong alkaline solution, and performing a saponification reaction under stirring conditions to change the ester group of the cellulose acetate into a hydroxyl group to obtain a regenerated cellulose product;

Preferably, in step 1, the cellulose acetate product is a cellulose acetate film, a cellulose acetate non-woven fabric, a cellulose acetate fiber or a cellulose acetate resin;

Preferably, in step 1, the strong alkaline solution is sodium hydroxide solution, potassium hydroxide solution or calcium hydroxide solution, preferably sodium hydroxide solution;

Preferably, in step 1, the obtained regenerated cellulose product is washed to neutrality through deionized water;

Preferably, in step 1, the saponification reaction temperature is 20-30 °C, and the saponification reaction time is 12-24 h;

Preferably, in step 1, the concentration of the strong alkaline solution is 0.05-0.8 mol/L, preferably 0.1-0.5 mol/L;

Preferably, in step 1, the cellulose acetate film exists in the form of nano-micron fiber film, and the preparation process is as follows: the fiber film is spun by a multi-needle electrospinning device, and the number of needles can be determined according to the width of the receiving roll. Adjustment to increase the number of needles increases the spinning speed. The cellulose acetate and the mixed solvent form a spinning solution with a mass fraction of 17% to 21% of the cellulose acetate; the mixed solvent is N,N-dimethylformamide/acetone system or N,N-dimethylformamide/ Dichloroethane system, wherein the volume ratio of N,N-dimethylformamide to acetone or dichloroethane is 1.5-3:1 (preferably 2:1); the spinning solution is 0.4-0.8mL/h The liquid feed rate forms fibers at a spinning voltage of 18 to 25 kV, an ambient temperature of 20 to 30°C, and an ambient humidity of 50 to 90 percent. The radial direction of the roller makes a reciprocating motion, and the cellulose acetate nano-micron fiber film can be received on the surface of the roller, and it is vacuum dried at 50 ° C for 48 hours for use.

Step 2. Mix the regenerated cellulose product obtained in step 1, the solvent and the alkali activator, stir and activate the regenerated cellulose for 0.5 to 1.5 h (preferably 1 h), and then add diethyl halogenated malonate for alkali-catalyzed etherification. The grafting reaction causes the halogen and the hydroxyl to undergo a grafting reaction and the ester group of the halogenated diethylmalonate is hydrolyzed into a carboxyl group to obtain a primary product;

Preferably, in step 2, the solvent is an organic solvent containing an alkane group, preferably isopropanol, acetone, acetonitrile, dichloromethane, cyclohexane or n-hexane, more preferably isopropanol;

Preferably, in step 2, the diethyl halomalonate is diethyl bromomalonate or diethyl chloromalonate, preferably diethyl bromomalonate;

Preferably, in step 2, the alkali activator adopts a strong alkaline solution with a mass fraction of 20% to 30% (preferably 25%); the strong alkaline solution is sodium hydroxide solution, potassium hydroxide solution or hydrogen Calcium oxide solution, preferably sodium hydroxide solution;

Preferably, in step 2, the ratio of the mass of the regenerated cellulose product to the volume of the solvent is 1g:200ml～600ml (preferably 1g:400ml); the molar ratio of the regenerated cellulose product to the solute of the alkali activator is 1:3～ 50; the molar ratio of the regenerated cellulose product to the halogenated diethyl malonate is 1:1-3.

Preferably, in step 2, the alkali activator is added dropwise, and after the dropwise addition is completed, the mixture is stirred and activated for 0.5 to 1.5 hours.

Preferably, in step 2, the diethyl halomalonate is dissolved in the solvent and then added to the reaction system.

Preferably, in step 2, the etherification grafting reaction is carried out under stirring conditions for 2-12 hours, and the reaction temperature is 20-70°C.

Step 3. Wash the primary product obtained in Step 2 with a mixed solution of ethanol/deionized water to remove unreacted substances and small molecular by-products to complete the purification of the primary product, and then immerse it in a dilute acid solution until the carboxylate is completely converted. It is a carboxyl group to obtain a polycarboxylate modified regenerated cellulose product connected by ether bonds;

Preferably, in step 3, the volume ratio of ethanol to deionized water in the ethanol/deionized water mixed solution is 3 to 1:1, and the number of washings is 3 to 5 times, and each washing is 3 to 5 minutes;

Preferably, in step 3, the dilute acid solution is a protonic acid with pH=1-6 (preferably 2-4), preferably hydrochloric acid, sulfuric acid, acetic acid, phosphoric acid or nitric acid;

Preferably, in step 3, the number of times of immersion in the dilute acid solution is 3-5 times, the soaking temperature is 20-30°C, and the soaking time is 10-15 minutes each time, so as to ensure that the carboxylate is completely converted into a carboxyl group.

Preferably, in step 3, the ether-bonded polycarboxy-modified regenerated cellulose product can be washed to neutrality by deionized water.

Morphology and structure test method of nano-micro fiber membrane:

1. Morphology test: Scanning electron microscope (SEM) was used to observe the morphology and structure of the product, and a SEM picture with a magnification of 2000× was obtained.

2. Structure test: Fourier transform infrared spectrometer (FTIR) was used to scan the product, the scanning range was 4000-500 cm ^-1 , the scanning accuracy was 2 cm ^-1 , and each sample was scanned 16 times.

3. Heavy metal ion adsorption test: (1) Prepare Cu ²⁺ standard solutions with different concentration gradients by diluting to constant volume, and scan the solution with a UV-Vis spectrophotometer, and record the maximum absorption wavelength (861.5nm) The absorbance (Abs) value under the conditions, the concentration and absorbance values were linearly fitted, and the corresponding fitting equation was obtained. (2) Prepare a certain volume of Cu ²⁺ solution with a concentration of 200 mg/L, add the products respectively, conduct vibration adsorption at 25 ° C and 100 rpm, and take samples at certain intervals, measure the absorbance (Abs) value until equilibrium, The corresponding real-time concentration of Cu ²⁺ and the corresponding adsorption amount were calculated based on the fitting equation.

Example 1

(1) Spinning cellulose acetate nano-micron fiber membrane: using multi-needle electrospinning equipment to spin the fiber membrane, wherein, the mass fraction of cellulose acetate in the spinning solution is 19%, and the soluble volume ratio is 2: 1 of N,N-dimethylformamide/acetone mixed solvent; the spinning solution was formed into fibers at a spinning rate of 0.6 mL/h under the conditions of 20kV spinning voltage, 25°C and 70% ambient humidity, spinning needle Make a reciprocating motion along the radial direction of the receiving roller at a horizontal distance of 10 cm from the grounded receiving roller, and the cellulose acetate nano-micron fiber film can be received on the surface of the roller, and vacuum-dried at 50 ° C for 48 hours for use;

(2) Preparation of regenerated cellulose nano-micron fiber membrane: 0.25g of dry cellulose acetate nano-micron fiber membrane was immersed in 100ml of sodium hydroxide aqueous solution with a concentration of 0.5mol/L, and the saponification reaction was carried out under stirring conditions for 12h, and the reaction was completed. The regenerated cellulose nano-fiber membrane is then obtained, which is then washed with deionized water until neutral;

(3) The regenerated cellulose nano-micron fiber membrane is subjected to etherification and grafting modification reaction to obtain the initial product: immerse 0.15g of the regenerated cellulose nano-micron fiber membrane in 60 ml of isopropanol to make the quality of the regenerated cellulose nano-micron fiber membrane equal to that of isopropyl alcohol. The volume ratio of propanol is 1g:400ml; 21.6g of sodium hydroxide aqueous solution with a mass fraction of 25% is added dropwise under stirring conditions, so that the molar ratio of regenerated cellulose nanofiber membrane and sodium hydroxide is 1:45, Continue stirring for 1 h; then add a solution of diethyl bromomalonate (4.0 g, 92% purity) dissolved in 10 ml of isopropanol at 60°C, in which the regenerated cellulose nano-micron fiber membrane and bromomalonic acid The molar ratio of diethyl ester was 1:3, and the etherification grafting reaction was carried out under stirring conditions for 2h;

(4) The initial product was washed 3 times with ethanol/water mixed solution for 5 min each time, then immersed in the dilute hydrochloric acid solution of pH=4 for 3 times, 10 min each time, washed with deionized water until neutral, and dried A polycarboxyl modified regenerated cellulose nanofiber membrane linked by ether bonds is obtained.

It can be seen from Figure 2 that the fiber structure of the membrane after saponification reaction and 2h etherification graft modification reaction is not damaged.

As can be seen from Figure 3, compared with Comparative Example 2, a new characteristic absorption peak appeared in the infrared spectrum at 1730cm ^-1 (-COOH), indicating that the alkali-catalyzed etherification reaction was successfully completed on the surface of the regenerated cellulose nanofiber membrane. , the polycarboxyl group was introduced into the regenerated cellulose.

In the heavy metal ion adsorption test, the adsorption of Cu ²⁺ by the polycarboxyl modified regenerated cellulose nanofiber membrane linked by ether bonds reached the adsorption equilibrium within 1.5h, and the maximum adsorption amount was 40.0 mg/g.

Example 2

Steps (1), (2) and (4) of this embodiment are respectively the same as steps (1), (2) and (4) of embodiment 1, and the etherification grafting reaction time of step (3) is 3h.

It can be seen from Figure 4 that the fiber structure of the membrane after saponification reaction and 3h etherification graft modification reaction is not damaged.

As can be seen from Figure 5, compared with Comparative Example 2, a new characteristic absorption peak appears in the infrared spectrum at 1730cm ^-1 (-COOH), indicating that the alkali-catalyzed etherification reaction was successfully completed on the surface of the regenerated cellulose nanofiber membrane. , the polycarboxyl group was introduced into the regenerated cellulose.

In the heavy metal ion adsorption test, the adsorption of Cu ²⁺ by the polycarboxylate modified regenerated cellulose nanofiber membrane linked by ether bonds reached the adsorption equilibrium after 2.0h, and the maximum adsorption amount was 66.7 mg/g.

Example 3

Steps (1), (2) and (4) of this embodiment are respectively the same as steps (1), (2) and (4) of embodiment 1, and the etherification grafting reaction time of step (3) is 4h.

It can be seen from Figure 6 that the fiber structure of the membrane after saponification reaction and 4h etherification graft modification reaction is not damaged.

As can be seen from Figure 7, compared with Comparative Example 2, a new characteristic absorption peak appeared in the infrared spectrum at 1730cm ^-1 (-COOH), indicating that the alkali-catalyzed etherification reaction was successfully completed on the surface of the regenerated cellulose nanofiber membrane. , the polycarboxyl group was introduced into the regenerated cellulose.

In the heavy metal ion adsorption test, the adsorption of Cu ²⁺ by the polycarboxylate modified regenerated cellulose nanofiber membrane linked by ether bonds reached the adsorption equilibrium after 2.0h, and the maximum adsorption amount was 86.7 mg/g.

Comparative Example 1

This comparative example only adopts step (1) of Example 1 to obtain a cellulose acetate nano-micron fiber membrane.

It can be seen from FIG. 8 that the average fiber diameter in the cellulose acetate nano-micron fiber membrane is about 2.6 μm.

It can be seen from FIG. 9 that characteristic absorption peaks are displayed at 1218 cm ^-1 (CO), 1362 cm ^-1 (C-CH ₃ ), 1735 cm ^-1 (C=O), and 3461 cm ^-1 (-OH), respectively.

In the heavy metal ion adsorption test, the adsorption of Cu ²⁺ by cellulose acetate nano-micron fiber membrane reached the adsorption equilibrium after 1.0h, and the maximum adsorption capacity was 23.3 mg/g.

Comparative Example 2

In this comparative example, only steps (1) and (2) of Example 1 are used to obtain a regenerated cellulose nano-micron fiber membrane.

It can be seen from Figure 10 that the fiber structure of the regenerated cellulose nano-micron fiber membrane is not damaged after the saponification reaction.

It can be seen from Figure 11 that, compared with Comparative Example 1, the characteristic absorption peaks at 1362 cm ^-1 (C-CH ₃ ) and 1735 cm ^-1 (C=O) disappear, and the absorption peak at 3461 cm ^-1 is lower The wavenumber direction shifted to 3330 cm ^-1 , indicating that the ester group in cellulose acetate was completely hydrolyzed.

In the heavy metal ion adsorption test, the adsorption of Cu ²⁺ by the regenerated cellulose nano-micron fiber membrane reached the adsorption equilibrium in 0.5h, and the maximum adsorption amount was 10.0 mg/g.

What is not described in the present invention applies to the prior art.

Claims (10)

1. the preparation method of the polybasic carboxyl modified regenerated cellulose connected by ether bond, is characterized in that, this method may further comprise the steps: Step 1, adding the cellulose acetate product into the excess strong alkaline solution, and carrying out a saponification reaction to change the ester group of the cellulose acetate into a hydroxyl group to obtain a regenerated cellulose product; The cellulose acetate product is a cellulose acetate film, a cellulose acetate non-woven fabric, a cellulose acetate fiber or a cellulose acetate resin; Step 2. Mix the regenerated cellulose product obtained in step 1, the solvent and the alkali activator, and after activating the regenerated cellulose, add diethyl halogenated malonate to undergo an alkali-catalyzed etherification grafting reaction so that the halogen and the hydroxyl group are grafted. The branch reaction simultaneously hydrolyzes the ester group of the halogenated diethyl malonate into a carboxyl group to obtain the initial product; Step 3. Wash the primary product obtained in Step 2 to remove unreacted substances and small molecular by-products to complete the purification of the primary product, and then immerse it in a dilute acid solution until the carboxylate is completely converted into a carboxyl group to obtain an ether bond-linked Polycarboxyl modified regenerated cellulose products. 2. the preparation method of the polycarboxylate modified regenerated cellulose of ether bond connection according to claim 1, is characterized in that, in step 1, described cellulose acetate membrane exists in the form of nano-micron fiber membrane, and preparation process is as follows : Multi-needle electrospinning equipment is used to spin the fiber membrane; cellulose acetate and mixed solvent form a spinning solution with a mass fraction of cellulose acetate of 17% to 21%; mixed solvent is N,N-dimethylformaldehyde Amide/acetone system or N,N-dimethylformamide/dichloroethane system, wherein the volume ratio of N,N-dimethylformamide to acetone or dichloroethane is 1.5 to 3:1; spinning The liquid forms fibers at a liquid feed rate of 0.4-0.8mL/h under the conditions of a spinning voltage of 18-25kV, an ambient temperature of 20-30°C and an ambient humidity of 50%-90%, and the spinning needle is at a distance from the grounded receiving roller. At a horizontal distance of 10-15 cm, a reciprocating motion is performed along the radial direction of the receiving roller, and the cellulose acetate nano-micron fiber film is received on the surface of the roller. 3. the preparation method of the polybasic carboxyl modified regenerated cellulose of ether bond connection according to claim 1, is characterized in that, in step 1, described strong alkaline solution is sodium hydroxide solution, potassium hydroxide solution or hydrogen Calcium oxide solution, the concentration is 0.05～0.8mol/L. 4. The preparation method of ether-linked polycarboxylate-modified regenerated cellulose according to claim 1, wherein in step 1, the temperature of the saponification reaction is 20-30°C, the time is 12-24h, and the stirring conditions Down. 5. the preparation method of the polybasic carboxyl modified regenerated cellulose connected by ether bond according to claim 1, is characterized in that, in step 2, described solvent is the organic solvent containing alkane group; The acid diethyl ester is diethyl bromomalonate or diethyl chloromalonate; the alkali activator adopts sodium hydroxide solution, potassium hydroxide solution or hydroxide solution with a mass fraction of 20% to 30% calcium solution. 6. the preparation method of the polycarboxylate modified regenerated cellulose connected by ether bond according to claim 1, is characterized in that, in step 2, the ratio of the quality of the regenerated cellulose product to the volume of the solvent is 1g:200ml～600ml ; The molar ratio of the regenerated cellulose product to the solute of the alkali activator is 1:3 to 50; the molar ratio of the regenerated cellulose product to the diethyl halogenated malonate is 1:1 to 3. 7. The preparation method of ether-linked polycarboxylate-modified regenerated cellulose according to claim 1, wherein in step 2, the conditions for activating the regenerated cellulose are: activation under stirring conditions for 0.5-1.5 h; The chemical grafting reaction is carried out under stirring conditions for 2 to 12 hours, and the reaction temperature is 20 to 70 °C. 8. the preparation method of the polybasic carboxyl-modified regenerated cellulose linked by ether bond according to claim 1, is characterized in that, in step 3, wash adopts the mixed solution of ethanol/deionized water, wherein the mixing solution of ethanol and deionized water The volume ratio is 3 to 1:1, and the number of washings is 3 to 5 times, and each wash is 3 to 5 minutes. 9 . The method for preparing ether-linked polycarboxylate-modified regenerated cellulose according to claim 1 , wherein, in step 3, the dilute acid solution is a protonic acid with pH=1-6. 10 . 10. The preparation method of ether-linked polycarboxylate-modified regenerated cellulose according to claim 1, wherein in step 3, the number of times of immersion in dilute acid solution is 3 to 5 times, and the immersion temperature is 20 ～30℃, soaking time 10～15min each time.

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