CN102093484B - Method for preparing nano crystal cellulose by dissociating ZnCl2 - Google Patents

Abstract

The invention discloses a method for preparing nanocrystalline cellulose by dissociating _ZnCl2 : (1) adding cellulose raw materials into _ZnCl2 solution to form a suspension; (2) homogenizing the suspension at a high speed under heating conditions (3) Add dilute acid to the cellulose/ _ZnCl solution, control the pH value _of the solution to be less than 5, so that the cellulose is precipitated, centrifuged and separated, and the upper solution is removed , taking the lower layer of cellulose jelly for ultrasonic dispersion treatment or wet grinding to obtain nanocrystalline cellulose. The _ZnCl2 used in the present invention has the advantages of being green, stable, cheap, easy to recycle, reusable and the like. Moreover, the reaction conditions are mild, the damage to cellulose degradation is small, the equipment is less corrosive, and the operation is simple, the yield is high, the obtained nanocrystalline cellulose has a network structure, and the mechanical strength is good, which is beneficial to its application in composite materials.

Description

A method for preparing nanocrystalline cellulose by dissociation of ZnCl2

technical field

The invention relates to a preparation method of nano-crystal cellulose, in particular to a method for preparing nano-crystal cellulose by using _ZnCl2 to dissociate cellulose crystal regions.

Background technique

Cellulose is the most abundant, renewable and biodegradable natural polymer in the world, and nature can provide about 100 billion tons of cellulose every year. The use of its performance improvement and high added value has become a research hotspot at home and abroad. Cellulose can be degraded by acid hydrolysis, enzyme treatment and mechanical method to produce nanocrystalline cellulose. Nanocrystalline cellulose has many excellent properties, such as high purity, high degree of polymerization, high crystallinity, high hydrophilicity, high Young's modulus, high strength, ultrafine structure and high transparency, etc. In view of the Excellent performance, it has good potential applications in fine chemical industry, medicine, food, composite materials, new energy and other fields.

At present, the preparation of nanocrystalline cellulose reported in the literature mainly adopts strong acid hydrolysis such as sulfuric acid, which is not easy to control the degree of cellulose degradation, and is more corrosive to equipment, and post-treatment will produce a large amount of acid waste liquid, which is very polluting to the environment.

Contents of the invention

The purpose of the present invention is to provide a method for preparing nanocrystalline cellulose by using _ZnCl2 to dissociate the cellulose crystal region.

The technical scheme adopted in the present invention is:

A method for dissociating _ZnCl2 to prepare nanocrystalline cellulose, the method comprising the steps of:

(1) Add the cellulose raw material into the ZnCl ₂ solution to form a suspension;

(2) Disperse the suspension homogeneously at high speed under heating conditions to dissociate the cellulose crystallization region to obtain a transparent cellulose/ _ZnCl solution;

(3) Add dilute acid to the cellulose/ZnCl ₂ solution, control the pH value of the solution to be less than 5, precipitate the cellulose, centrifuge and separate the layers, remove the solution containing ZnCl ₂ and acid in the upper layer, and take the cellulose jelly in the lower layer. The material is subjected to ultrasonic dispersion treatment or wet grinding to obtain nanocrystalline cellulose.

The cellulose raw material in the step (1) is cotton, chemical pulp or microcrystalline cellulose.

The mass fraction of the ZnCl ₂ solution in the step (1) is 50-70%; the mass ratio of the cellulose raw material to the ZnCl ₂ solution is 1:10-30.

The heating condition in the step (2) is heating to a temperature of 80° C. to 100° C., the speed of the high-speed homogeneous dispersion is above 8000 rpm, and the dispersion time is 1 h to 4 h.

The dilute acid described in the step (3) is hydrochloric acid, sulfuric acid or phosphoric acid, preferably hydrochloric acid, the massfraction of the described dilute acid is 0.1%～10%, preferably 0.5%, the volume consumption of the described dilute acid is step (1 ) 3 to 6 times the volume of the ZnCl ₂ solution.

In the step (3), after the centrifugal layering, after removing the upper layer solution, the cellulose jelly in the lower layer is centrifuged and eluted 5 to 8 times with water, and then subjected to ultrasonic dispersion treatment or wet grinding to obtain nano Crystalline cellulose.

The frequency of the ultrasound in the step (3) is greater than 25KHz, and the dispersing process is usually carried out at a temperature of 50° C. to 80° C. for 1 to 4 hours.

The wet grinding time in the step (3) is 2 to 4 hours, and the power of the wet grinding is greater than 180W.

Further, the method is preferably carried out according to the following steps:

(1) adding the cellulose raw material into the _ZnCl2 solution to form a suspension; the cellulose raw material is cotton, chemical pulp or microcrystalline cellulose; the mass fraction of the _ZnCl2 solution is 50-70%; The mass ratio of the cellulose raw material to the _ZnCl solution is 1:10~30;

(2) Disperse the suspension homogeneously at a high speed of 8000 rpm or more at a temperature of 80°C~100°C for 1h~4h to obtain a transparent cellulose/ZnCl ₂ solution;

(3) Add dilute acid to the cellulose/ _ZnCl2 solution, control the pH value of the solution to be less than 5, make the cellulose precipitate, centrifuge and separate layers, remove the upper layer of ZnCl2 _and acid solution, take the lower layer of cellulose jelly and After 5 to 8 times of centrifugation and elution with water, ultrasonic dispersion treatment or wet grinding is performed to obtain nanocrystalline cellulose.

In the step (3), dilute acid is added to the cellulose/ZnCl ₂ solution to precipitate the cellulose, and the pH value of the solution is kept below 5 to prevent the formation of Zn(OH) ₂ precipitation.

The invention has the advantages that _ZnCl2 is green, stable, cheap, easy to recycle, reusable and the like. The reaction conditions are mild, the damage to cellulose degradation is small, the equipment is less corrosive, and the operation is simple and the yield is high. After being treated with _ZnCl2 , the crystallization regions of cellulose are dissociated, and the hydrogen bonds between cellulose molecules are broken. At this time, the macromolecular structure of cellulose is easily destroyed, and it is easy to be broken into nanocrystalline cellulose under the action of external force. This process can be realized under certain treatment conditions, and this process is a physical action, and the reaction conditions are easy to control to avoid severe damage to the cellulose. Therefore, the yield of nanocrystalline cellulose prepared by this method is high, and the obtained nanocrystalline fiber It is a network structure and has good mechanical strength, which is conducive to its application in composite materials.

Description of drawings

Fig. 1 is a transmission electron micrograph of nanocrystalline cellulose prepared in Example 1 of the present invention (magnification ×6000).

Fig. 2 is a transmission electron micrograph of nanocrystalline cellulose prepared in Example 1 of the present invention (magnification ×60000).

Detailed ways

The following are several specific embodiments of the present invention to further illustrate the present invention, but the protection scope of the present invention is not limited thereto.

Example 1

Weigh 3g microcrystalline cellulose, add it to 30g mass fraction 65% ZnCl ₂ solvent, 80 ℃ oil bath for 1h, and at the same time disperse and homogenize at a high speed, the homogenization speed is 12000 rpm, and obtain a transparent cellulose/ZnCl ₂ solution . Add 90ml of 0.5% hydrochloric acid to the cellulose/ZnCl ₂ solution to precipitate the cellulose, centrifuge to separate layers, remove the upper layer of ZnCl ₂ and acid solution, take the lower layer of cellulose jelly, and then carry out 5 times of centrifugal elution with water After removing the dissociated cellulose jelly in the crystalline region of the lower layer and ultrasonicating at 50° C. (the frequency of the ultrasonic wave is 40 KHz) for 2 hours, nanocrystalline cellulose is obtained. It can be seen from the observation of the transmission electron microscope that the nanocrystalline microelements prepared by this method have a network structure, with a diameter of about 20-30nm and a length of 300-700nm, and a network structure. As shown in Figure 1 and Figure 2.

Example 2

Weigh 1 g of chemical pulp, add it to 30 g of 65% ZnCl ₂ solvent in mass fraction, 80 ° C oil bath for 3 h, and at the same time disperse and homogenize at a high speed, the homogenization speed is 12000 rpm, and obtain a transparent cellulose/ZnCl ₂ solution. Add 105ml of 0.5% hydrochloric acid to the cellulose/ZnCl ₂ solution to precipitate the cellulose, centrifuge to separate layers, remove the upper layer of ZnCl ₂ and acid solution, take the lower layer of cellulose jelly, and then carry out 8 times of centrifugal elution with water After removing the dissociated cellulose in the crystallization region of the lower layer and ultrasonicating at 80° C. (frequency of ultrasonic is 60 KHz) for 4 hours, nanocrystalline cellulose is obtained.

Example 3

Weigh 1 g of absorbent cotton, add it to 30 g of 65% ZnCl ₂ solvent in mass fraction, 100 ° C oil bath for 4 hours, and at the same time disperse and homogenize at a high speed, the homogenization speed is 8000 rpm, and obtain a transparent cellulose/ZnCl ₂ solution. Add 105ml of 0.5% hydrochloric acid to the cellulose/ZnCl ₂ solution to precipitate the cellulose, centrifuge to separate layers, remove the upper layer of ZnCl ₂ and acid solution, take the lower layer of cellulose jelly, and then carry out 6 times of centrifugal elution with water After removing the dissociated cellulose in the crystallization region of the lower layer and ultrasonicating at 80° C. (frequency of ultrasonic is 60 KHz) for 4 hours, nanocrystalline cellulose is obtained.

Example 4

Weigh 5 g of chemical pulp, add it to 150 g of 65% ZnCl ₂ solvent in mass fraction, 80 ° C oil bath for 3 h, and at the same time disperse and homogenize at a high speed, and the homogenization speed is 10,000 rpm to obtain a transparent cellulose/ZnCl ₂ solution. Add 450ml of 0.5% hydrochloric acid to the cellulose/ZnCl ₂ solution to precipitate the cellulose, centrifuge to separate layers, remove the upper layer of ZnCl ₂ and acid solution, take the lower layer of cellulose jelly, and then carry out 8 times of centrifugal elution with water , after 4 hours of wet ball milling (wet milling power is 4KW) of dissociated cellulose in the crystallization area of the lower layer, nanocrystalline cellulose is obtained.

Example 5

Weigh 5g of absorbent cotton, add it to 150g of 65% ZnCl ₂ solvent in mass fraction, 90°C oil bath for 4 hours, and at the same time disperse and homogenize at a high speed, the homogenization speed is 12000 rpm, and obtain a transparent cellulose/ZnCl ₂ solution. Add 450ml of 0.5% hydrochloric acid to the cellulose/ZnCl ₂ solution to precipitate the cellulose, centrifuge to separate layers, remove the upper layer of ZnCl ₂ and acid solution, take the lower layer of cellulose jelly, and then carry out 8 times of centrifugal elution with water , take off the dissociated cellulose in the crystallization area of the lower layer and wet ball mill (wet milling power is 4KW) for 5 hours to obtain nanocrystalline cellulose.

Claims (7)

1. A ZnCl _Dissociation prepares the method for nanocrystalline cellulose, it is characterized in that, described method comprises the steps: (1) Add the cellulose raw material to the ZnCl ₂ solution to form a suspension; the mass fraction of the ZnCl ₂ solution is 50-70%; the mass ratio of the cellulose raw material to the ZnCl ₂ solution is 1:10- 30; (2) Disperse the suspension at a high speed and homogeneously under heating conditions to obtain a transparent cellulose/ _ZnCl solution; the speed of the high-speed homogeneous dispersion is above 8000 rpm, and the dispersion time is 1h to 4h; (3) Dilute acid is added to the cellulose/ _ZnCl2 solution, the pH value of the control solution is less than 5, the cellulose is separated out, centrifuged and layered, the upper layer solution is removed, and the lower layer of cellulose jelly is carried out by ultrasonic dispersion or wet grinding to obtain nanocrystalline cellulose; the dilute acid is hydrochloric acid, sulfuric acid or phosphoric acid, the mass fraction of the dilute acid is 0.1% to 10%, and the volumetric dosage of the dilute acid is ZnCl in step (1). ₂ 3 to 6 times the volume of the solution. 2. The method according to claim 1, characterized in that the cellulose raw material in the step (1) is cotton, chemical pulp or microcrystalline cellulose. 3. The method according to claim 1, characterized in that the heating condition in the step (2) is heating to a temperature of 80°C to 100°C. 4. The method according to claim 1, characterized in that in the step (3), the centrifugal layer is removed, and after the upper solution is removed, the cellulose jelly in the lower layer is then centrifugally washed with water for 5 to 8 times. Then, ultrasonic dispersion treatment or wet grinding is carried out to obtain nanocrystalline cellulose. 5. The method according to claim 1, characterized in that the frequency of the ultrasound in the step (3) is greater than 25 KHz, and the dispersion treatment is at a temperature of 50° C. to 80° C. for 1 to 4 hours. 6. The method according to claim 1, characterized in that the wet grinding time in the step (3) is 2 to 4 hours, and the power of the wet grinding is greater than 180W. 7. according to the method described in claim 1, it is characterized in that described method is carried out according to the following steps: (1) adding the cellulose raw material into the _ZnCl2 solution to form a suspension; the cellulose raw material is cotton, chemical pulp or microcrystalline cellulose; the mass fraction of the _ZnCl2 solution is 50-70%; The mass ratio of the cellulose raw material to the _ZnCl2 solution is 1:10-30; (2) Disperse the suspension homogeneously at a high speed of 8000 rpm or more at a temperature of 80°C to 100°C for 1h to 4h to obtain a transparent cellulose/ZnCl ₂ solution; (3) Add dilute acid to the cellulose/ _ZnCl2 solution, control the pH value of the solution to be less than 5, precipitate the cellulose, centrifuge and separate layers, remove the upper solution, take the lower layer of cellulose jelly, and then carry out 5~ After 8 times of centrifugation and elution, ultrasonic dispersion treatment or wet grinding is performed to obtain nanocrystalline cellulose.

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