CN109024036A - A method of preparing nano-cellulose - Google Patents

Abstract

The invention discloses a method for preparing nano-cellulose, which comprises the following steps: (1) performing cellulase treatment on lignocellulose fibers, and centrifuging to obtain enzyme treatment residues; (2) using solid organic acids to treat enzyme treatment residues Further processing; (3) After the processing in step (2), centrifuge to separate the acid in the supernatant, perform dialysis on the precipitated part, and then centrifuge after dialysis to obtain nanocellulose. The preparation of nanocellulose by cellulase-assisted solid organic acid can effectively increase the yield of nanocellulose, shorten acid hydrolysis, reduce the concentration of solid organic acid, and improve the dispersion stability of nanocellulose.

Description

A method for preparing nanocellulose

technical field

The invention belongs to the field of nanomaterials, and in particular relates to a method for preparing nanocellulose.

Background technique

Nanofibers have become a research hotspot in the field of nanomaterials due to their nanometer size, high specific surface area, low density, biodegradability, excellent mechanical strength and optical properties, and the natural regeneration of raw fiber. At present, the preparation methods of nanocellulose mainly include: chemical method, mechanical method and biological method. Among them, the chemical method mainly refers to the method of preparing nanocellulose by using chemical reagents such as high-concentration inorganic acids to treat wood fibers. The high-concentration inorganic acid method can produce uniformly sized and stably dispersed nanocellulose crystals (Cellulose Nanocrystals, CNC), but lacks an economical acid recovery method (9kg H ₂ SO4/1kg nanocellulose), and the product has low thermal stability (The initial decomposition temperature is 218°C, the initial decomposition temperature of the original fiber is 274°C), the functional modification of the product is difficult to realize (such as the introduction of sulfuric acid group) and the product yield is low (30-50%). The mechanical method mainly refers to the mechanical treatment of wood fibers with mechanical equipment such as Microflidizer or Homogenizer, so that the fibers can be cut and fibrillated, so as to separate the Cellulose Nanofibrils in the nanometer size range. The CNF prepared by the mechanical method does not require chemical reagents and has less impact on the environment, but the CNF prepared by the mechanical method has a wider particle size distribution. At the same time, the equipment required for mechanical preparation is relatively special, and the energy consumption is high. Biological preparation of nanocellulose has good biocompatibility and biodegradability, but the preparation cycle is long and energy consumption is high. Therefore, inventing a green and efficient method for preparing nanocellulose is the basis for its wide application in materials and other fields.

Contents of the invention

In view of the deficiencies of the existing problems, the purpose of the present invention is to provide a method for preparing nanocellulose, which uses cellulase to assist solid organic acids to prepare nanocellulose, so that the yield of nanocellulose is increased by 2 to 4 times, and it can effectively Reduce the concentration of solid organic acid, solid organic acid recrystallized after cooling, recyclable, green and environmental protection.

The technical scheme that the present invention solves its technical problem adopts is:

A method for preparing nanocellulose, comprising the steps of:

(1) Carry out cellulase treatment to lignocellulosic fiber earlier, centrifugal separation obtains enzyme treatment residue;

(2) Utilize solid organic acid to process the enzyme treatment residue again;

(3) After the treatment in step (2), centrifuge to separate the acid in the supernatant, dialyze the precipitated part, and then centrifuge to obtain nanocellulose. The flowchart is shown in Figure 1.

Using cellulase to assist solid organic acid to prepare nanocellulose can effectively increase the yield of nanocellulose. Without changing the amount of solid organic acid and acid hydrolysis time, the yield of nanocellulose can be increased by 2 to 4 times.

Preferably, the cellulase treatment in the step (1) uses acetic acid-sodium acetate buffer solution with a pH of 4.5 to 5.5, the treatment temperature is 45 to 55°C, the substrate concentration is 5 to 20 wt%, and placed in a constant temperature oscillator Oscillation reaction, the treatment time is 2-96 hours, the rotation speed is 150-250rpm; after the treatment, the precipitated part is centrifuged to separate the enzyme treatment residue;

Preferably, in the step (2), the temperature at which the solid organic acid is treated with the enzyme treatment residue is 90-120°C, the solid-to-liquid ratio is 1:5-1:20, and it is placed in the reactor and mechanically stirred for 0.5-6h , stirring speed 100 ~ 500rpm;

Preferably, in the step (3), after the treatment in the step (2), the supernatant and the precipitated part are centrifuged; the supernatant is mainly acid, and the solid organic acid can be recrystallized when cooled to room temperature, and recovered Utilization; the precipitated part is dialyzed to neutrality with a dialysis bag, and then centrifuged to separate the upper layer of nanocellulose.

Wherein, the cellulase is purchased from the market or prepared by itself.

Wherein, cellulase refers to endoglucanase or exoglucanase or the combination of the two enzymes.

Among them, the solid organic acid means that it is in a solid state at room temperature, and it is in a molten or dissolved state after the temperature rises. After the acid hydrolysis reaction is completed, it can be precipitated when the temperature drops to room temperature, so as to realize acid recovery.

Wherein, the solid organic acid is purchased from the market.

Wherein, the solid organic acid refers to oxalic acid or maleic acid.

Wherein, the lignocellulosic raw materials applicable to the method include coniferous wood, broad-leaved wood and gramineous plants.

Beneficial effect

The present invention uses cellulase treatment combined with solid organic acid to prepare nano-cellulose, compared with the prior art, it presents the following characteristics:

(1) It can effectively shorten the acid hydrolysis time, and the yield of nanocellulose prepared by assisted solid organic acid hydrolysis for 1 hour by cellulase pretreatment is much higher than that of single solid organic acid hydrolysis for 2 hours;

(2) It can effectively reduce the concentration of solid organic acid, and the yield of nanocellulose prepared by hydrolysis of solid organic acid assisted by cellulase pretreatment is much higher than that of increasing the concentration of solid organic acid by 10% to hydrolyze nanocellulose;

(3) It can effectively improve the dispersion stability of nanocellulose. The stability of nanocellulose prepared by single solid organic acid is poor. Combined with cellulase pretreatment, it can increase the reaction degree of solid organic acid and fiber, thereby improving the stability of nanocellulose. sex.

(4) The present invention prepares nanocellulose by assisting solid organic acid with cellulase, which can effectively increase the yield of nanocellulose, shorten acid hydrolysis, reduce the concentration of solid organic acid, and improve the dispersion stability of nanocellulose.

Description of drawings

Figure 1 is a flow chart for the preparation of nanocellulose.

Fig. 2 is the thermogravimetric analysis diagram of nanocellulose obtained in Example 1.

Detailed ways

The present invention is described in further detail below in conjunction with embodiment. The reagents or instruments used are not indicated by the manufacturer, and they are all regarded as conventional products that can be purchased through the market.

The cellulase Cell I used in the following examples is a commercial enzyme provided by an enzyme preparation company, Cell II is a laboratory-made cellulase, and solid organic acids (oxalic acid, maleic acid) are purchased from Sinopharm Reagent Co., Ltd.; The bleached eucalyptus pulp used in the experiment was provided by a paper mill in Shandong. After the dry pulp board was soaked in water for 24 hours, the pulp board was decomposed and dispersed by a deflaker and placed in a refrigerator for later use.

Example 1: Cell I assists oxalic acid to prepare nanocellulose.

Put the decomposed wet slurry (5g) in a 250mL Erlenmeyer flask, add acetic acid-sodium acetate buffer (pH value 4.8) according to the substrate concentration of 5wt%, the amount of Cell I is 0.01mL/g substrate, and the conical The bottle was placed in a constant temperature shaker and gyrated at 200r/min at 50°C for 4h; after the enzymatic hydrolysis, centrifuge at 8000r/min to separate the residual fiber after enzyme treatment;

After the enzyme-treated residue fiber was freeze-dried, 4 g of fiber was taken for oxalic acid treatment, the oxalic acid concentration was 50%, the acid hydrolysis temperature was 100°C, and the acid hydrolysis time was 1 h. The oxalic acid treatment process was assisted by mechanical stirring (300 rpm); dialyzed after acid hydrolysis , followed by centrifugation to obtain nanocellulose.

Experimental results:

Cell I (0.01mL/g substrate, 4h) enzymatically treated lignocellulosic raw materials yielded 96.7%, and at lower enzyme dosage, the fiber loss during enzyme treatment was less (3.3%); Cell I assisted oxalic acid in the treatment of bleached eucalyptus Table 1 shows the yield of nanocellulose prepared from wood pulp compared with single oxalic acid treatment of bleached eucalyptus wood pulp.

Table 1 Preparation of nanocellulose from bleached eucalyptus pulp by Cell I assisted oxalic acid treatment vs single oxalic acid treatment

Experiments show that Cell I assists oxalic acid (Cell I+O50-1) to prepare nano-cellulose yield close to three times the nano-cellulose yield under the same oxalic acid concentration and time treatment; improve the oxalic acid treatment time to 2h (O50- 2) The yield is only 11.2%. When the acid concentration is increased to 60% (O60-1), the yield is only 12.6%, which is far lower than the yield of Cell I assisted oxalic acid (O50-1) to prepare nanocellulose.

The transmission electron micrographs of O50-1 and Cell I+O50-1 showed that cellulase-assisted solid organic acid treatment can effectively improve the dispersion stability of nanocellulose and improve the shape and size of nanofibers. The thermogravimetric analysis diagram is shown in Figure 2. Cellulase treatment will not reduce the thermal stability of nanofibers. The thermal stability of nanocellulose prepared by cellulose-assisted solid organic acid treatment is much higher than that of traditional high-concentration inorganic acid nanocellulose. .

Example 2: Cell I assists maleic acid to prepare nanocellulose.

Put the decomposed wet slurry (5g) in a 250mL Erlenmeyer flask, add acetic acid-sodium acetate buffer (pH value 4.8) according to the substrate concentration of 5wt%, the amount of Cell I is 0.01mL/g substrate, and the conical The bottle was placed in a constant temperature shaker and oscillated at 200r/min at 50°C for 4h; after the enzymatic hydrolysis, centrifuge at 8000r/min to separate the residual fiber after enzyme treatment.

After the enzyme-treated residue fibers were freeze-dried, 4g of fibers were taken for maleic acid treatment, the concentration of maleic acid was 60%, the acid hydrolysis temperature was 100°C, the acid hydrolysis time was 1h, and the maleic acid treatment process was assisted by mechanical stirring (300rpm) . After acid hydrolysis, dialysis was performed, followed by centrifugation to obtain nanocellulose.

Experimental results:

Cell I (0.01mL/g substrate, 4h) enzymatically treated lignocellulosic raw material yield was 96.7%, and at lower enzyme dosage, the fiber loss during enzyme treatment was less (3.3%); Cell I assisted maleic acid treatment The yield of nanocellulose prepared from bleached eucalyptus pulp compared with single maleic acid treatment is shown in Table 2.

Table 2 Preparation of nanocellulose from bleached eucalyptus pulp by Cell I assisted maleic acid treatment vs single maleic acid treatment

Experiments show that the yield of nanocellulose prepared by Cell I assisted maleic acid (Cell I+M60-1) is 3.8 times that of nanocellulose yield under the same maleic acid concentration and time treatment; Time to 2h (M60-2) yield is only 8.2%, increase the acid concentration to 70% (M70-1) yield is only 9.0%, far below Cell I assisted maleic acid (M60-1) to prepare nanocellulose Yield.

Example 3: Cell II assists oxalic acid to prepare nanocellulose.

Place the decomposed wet slurry (5g) in a 250mL conical flask, add acetic acid-sodium acetate buffer solution (pH value 4.8) according to the substrate concentration of 5wt%, the amount of Cell II is 0.01mL/g substrate, and the conical The bottle was placed in a constant temperature shaker and oscillating at 200r/min at 50°C for 24h; after the enzymatic hydrolysis, centrifuge at 8000r/min to separate the residual fiber after enzyme treatment.

After the enzyme-treated residue fiber was freeze-dried, 4 g of fiber was taken for oxalic acid treatment, the oxalic acid concentration was 50%, the acid hydrolysis temperature was 100°C, and the acid hydrolysis time was 1 h. The oxalic acid treatment process was assisted by mechanical stirring (300 rpm); dialyzed after acid hydrolysis , followed by centrifugation to obtain nanocellulose.

Experimental results:

Cell II (0.01mL/g substrate, 24h) enzymatic treatment of lignocellulosic raw materials yielded 95.6%, and at lower enzyme dosage, the fiber loss during enzyme treatment was less (4.4%); Cell II assisted oxalic acid in the treatment of bleached eucalyptus Table 3 shows the yield of nanocellulose prepared from wood pulp compared with single oxalic acid treatment of bleached eucalyptus wood pulp.

Table 3 Preparation of nanocellulose from bleached eucalyptus pulp by Cell II assisted oxalic acid treatment vs single oxalic acid treatment

Experiments show that the yield of nanocellulose prepared by Cell II assisted oxalic acid (Cell II+O50-1) is three times that of the nanocellulose yield under the same oxalic acid concentration and time treatment; improve the oxalic acid treatment time to 2h (O50- 2) The yield is only 11.2%, and the yield of increasing the acid concentration to 60% (O60-1) is only 12.6%, which is far lower than the yield of Cell I assisted oxalic acid (O50-1) to prepare nanocellulose.

Example 4: Cell II assists maleic acid to prepare nanocellulose.

Place the decomposed wet slurry (5g) in a 250mL conical flask, add acetic acid-sodium acetate buffer solution (pH value 4.8) according to the substrate concentration of 5wt%, the amount of Cell II is 0.01mL/g substrate, and the conical The bottle was placed in a constant temperature shaker and oscillating at 200r/min at 50°C for 24h; after the enzymatic hydrolysis, centrifuge at 8000r/min to separate the residual fiber after enzyme treatment.

After the enzyme-treated residue fibers were freeze-dried, 4g of fibers were taken for maleic acid treatment, the concentration of maleic acid was 60%, the acid hydrolysis temperature was 100°C, the acid hydrolysis time was 1h, and the maleic acid treatment process was assisted by mechanical stirring (300rpm) . After acid hydrolysis, dialysis was performed, followed by centrifugation to obtain nanocellulose.

Experimental results:

Cell II (0.01mL/g substrate, 24h) enzymatically treated lignocellulosic raw materials yielded 95.6%, and at lower enzyme dosage, the fiber loss during enzyme treatment was less (4.4%); Cell II assisted maleic acid treatment The yield of nanocellulose prepared from bleached eucalyptus pulp compared with single maleic acid treatment is shown in Table 4.

Table 4 Preparation of nanocellulose from bleached eucalyptus pulp by Cell I assisted oxalic acid treatment vs single maleic acid treatment

Experiments show that the yield of nanocellulose prepared by Cell II assisted maleic acid (Cell II+M60-1) is 3.6 times that of the nanocellulose yield under the same maleic acid concentration and time treatment; increase the maleic acid treatment time To 2h (M60-2) yield is only 8.2%, increase the acid concentration to 70% (M70-1) yield is only 9.0%, far lower than Cell II assisted maleic acid (M60-1) to prepare nanocellulose Rate.

Comparative Example 5: Preparation of nanocellulose with oxalic acid.

Dry the decomposed wet pulp in an oven at 50°C, take 4g of fiber for oxalic acid treatment. Process-assisted mechanical stirring (300rpm); dialysis after acid hydrolysis, followed by centrifugation to obtain nanocellulose.

Experimental results:

The yield of nanocellulose prepared from bleached eucalyptus pulp treated with single oxalic acid is shown in Table 5.

Table 5 Preparation of nanocellulose from bleached eucalyptus pulp treated with oxalic acid

Experiments show that with the increase of oxalic acid concentration, the CNC yield increases gradually, the oxalic acid concentration increases by 20%, the acid hydrolysis time increases from 1h to 2h, and the CNC yield only increases by 10%.

Comparative Example 6: Preparation of nanocellulose with maleic acid.

Place the decomposed wet pulp in an oven at 50°C for drying, take 4g of fiber and process it with maleic acid. 2h, the maleic acid treatment process assisted mechanical stirring (300rpm). After acid hydrolysis, dialysis was performed, followed by centrifugation to obtain nanocellulose.

Experimental results:

The yield of nanocellulose prepared from bleached eucalyptus pulp treated with single maleic acid is shown in Table 6.

Table 6 Preparation of nanocellulose from bleached eucalyptus pulp treated with maleic acid

Experiments show that with the increase of the maleic acid concentration, the CNC yield increases gradually, the maleic acid concentration increases from 50% to 70%, and when the acid hydrolysis time increases from 1h to 2h, the CNC yield only increases by 5.3%.

The protection content of the present invention is not limited to the above embodiments. Without departing from the spirit and scope of the inventive concept, changes and advantages that can be conceived by those skilled in the art are all included in the present invention, and the appended claims are the protection scope.

Claims (5)

1. a kind of method for preparing nano-cellulose, which comprises the steps of:

(1) cellulase processing first is carried out to lignocellulose fiber, is centrifugated to obtain enzymatic treatment residue；

(2) enzymatic treatment residue is handled again using solid organic acid；

(3) in step (2) after treatment, the acid being centrifugated out in supernatant dialyses to sediment fraction, after dialysis again It is centrifugated up to nano-cellulose.

2. the method according to claim 1 for preparing nano-cellulose, which is characterized in that cellulose in the step (1) Enzymatic treatment uses the Acetic acid-sodium acetate buffer of pH 4.5 ~ 5.5, and treatment temperature is 45 ~ 55 DEG C, and concentration of substrate is 5 ~ 20 Wt% is placed in oscillating reactions in constant temperature oscillator, and the processing time is 2 ~ 96 h；After treatment, being centrifugated out sediment fraction is Enzymatic treatment residue.

3. the method according to claim 1 for preparing nano-cellulose, which is characterized in that there is solid in the step (2) The temperature that machine acid handles enzymatic treatment residue again is 90 ~ 120 DEG C, and solid-to-liquid ratio is 1:5 ~ 1:20, is placed in machine in reactor Tool stirs 0.5 ~ 6 h.

4. the method according to claim 3 for preparing nano-cellulose, which is characterized in that there is solid in the step (2) Machine acid is oxalic acid or maleic acid.

5. the method according to claim 1 for preparing nano-cellulose, which is characterized in that in the step (3), in step (2) after treatment is centrifugated out supernatant liquor and sediment fraction；Supernatant liquor is cooled to room temperature and can recrystallize solid and have Machine acid, recycles；Sediment fraction is dialysed using bag filter to neutrality, then is centrifugated out upper layer nano-cellulose.