CN106436414A - Method for preparing wheat straw cellulose microfibrils by auxiliary enzymatic pretreatment - Google Patents

Abstract

The invention relates to a method for preparing wheat straw cellulose microfibrils assisted by enzyme pretreatment. Firstly, the wheat straw pulp is sieved, and the fiber components retained on the sieve are collected; 1% to 5% of the fiber suspension, and then add cellulase to the fiber suspension for hydrolysis to obtain the fiber slurry after enzyme pretreatment; the amount of cellulase added is 0.5% of the absolute dry mass of the fiber component % to 25%; the fiber slurry is mechanically agitated and sheared, and then formulated into a fiber suspension with a mass concentration of 0.5 to 1.5%, which is subjected to circulation and homogenization treatment to prepare a cellulose microfibril emulsion; the cellulose microfibril emulsion The fibril emulsion is sequentially subjected to centrifugation and filtration to obtain wheat straw cellulose microfibrils. The invention can reduce the energy consumption of mechanical dissociation, is beneficial to reduce the amount of enzymes, makes the fibers in the slurry uniformly dispersed, and can successfully separate microfibrils through a high-pressure homogenizer.

Description

A method for preparing wheat straw cellulose microfibrils assisted by enzyme pretreatment

【Technical field】

The invention belongs to the field of plant cellulose biomass refining, in particular to a method for assisting preparation of wheat straw cellulose microfibrils through enzyme pretreatment.

【Background technique】

Cellulose is the most abundant renewable natural polymer in nature, widely present in natural plants such as wood, grasses, cotton and hemp. Because cellulose has some disadvantages in performance, such as poor pyrolysis performance, chemical corrosion resistance, limited strength, etc., this limits its application range. Studies have found that when the fiber diameter reaches the nanometer level, it will have many new properties, and its crystallinity, hydrophilicity, Young's modulus, strength and transparency will all be greatly improved, making it have a wider range of applications. application range. Cellulose microfibril (CMF for short) prepared from natural cellulose has been widely used in the fields of nano-devices, packaging materials, food additives, solar cells and nano-paper.

my country is a country rich in crop straw resources, and the annual output of crop straw can reach about 700 million tons, of which 22% is wheat straw. Crop straw contains a large amount of cellulose components, industrial raw material components and calorific value. Rational use of straw is conducive to the rational development of industry, agriculture and rural economy. Otherwise, direct burning of straw will not only release a large amount of gas that will seriously pollute the environment, but also cause a major waste of energy resources. If this part of cellulose can be refined to obtain high-purity nanocellulose, it will be the focus of realizing high value-added utilization of wheat straw resources.

The chemical composition, physical form and surface properties of fine miscellaneous components in wheat straw pulp (through 100 meshes, most of which are miscellaneous cells, such as parenchyma cells, epidermal cells, etc.) are very different from those of fiber cells, and the specific surface area is relatively large. Large and low degree of crystallization, strong adsorption and hydrolysis of enzymes, part of the fine components are easy to be dissolved first in the process of enzymatic hydrolysis, and consume more enzyme dosage, therefore, the research is to screen the fine components The preparation of cellulose microfibrils from the final wheat straw pulp has important practical significance for improving the preparation method and improving the product properties.

The existing technology mainly uses wood pulp as raw material to prepare cellulose microfibrils, and the simple use of mechanical high-pressure homogenization treatment to prepare cellulose microfibrils consumes a lot of energy, and the long-term strong mechanical action damages the crystal structure of the fibers, and the raw material fibers Longer, it is easy to block the high-pressure homogenizer and make the preparation process difficult to achieve continuous; the existing pretreatment combined with mechanical preparation also has certain defects and limitations, acid and alkali pretreatment require high corrosion resistance of the equipment, separation Obtaining pure CMF consumes a large amount of water and power resources, which increases the cost and environmental load; although the reaction speed of TEMPO oxidation pretreatment is fast, the width of the prepared CMF is relatively uniform, and the stability is good, but so far there is no way to recover TEMPO in industry. Catalyst, and the preparation raw material of this method is mainly kraft wood pulp after de-lignification.

【Content of invention】

The purpose of the present invention is to overcome the problems existing in the prior art, and to provide a method for assisting the preparation of wheat straw cellulose microfibrils by enzyme pretreatment. The fibers in the slurry are evenly dispersed, which is beneficial to continuous processing with low energy consumption and pollution-free High-value utilization of crop wheat straw.

In order to achieve the above object, the present invention adopts following technical scheme:

Include the following steps:

(1) Sieving the wheat straw pulp to collect the fiber components trapped on the sieve;

(2) The fiber component obtained in step (1) is prepared into a fiber suspension with a mass concentration of 1% to 5% with a buffer, and then cellulase is added to the fiber suspension for hydrolysis to obtain enzyme pretreated Fiber slurry; wherein the amount of cellulase added is 0.5% to 25% of the absolute dry mass of the fiber component;

(3) the fiber slurry obtained in step (2) after the enzyme pretreatment is subjected to mechanical stirring and shearing;

(4) preparing the fiber slurry after mechanically agitating and shearing in step (3) into a fiber suspension with a mass concentration of 0.5 to 1.5%, and performing a circulation homogenization treatment to prepare a cellulose microfibril emulsion;

(5) Centrifuging and filtering the cellulose microfibril emulsion in sequence to obtain wheat straw cellulose microfibrils.

Further, the screen mesh in step (1) is 100 mesh.

Further, in step (2), the fiber components are soaked and swollen in water for 6-18 hours, then decomposed by a decomposer for 10-30 minutes, squeezed dry, and then formulated into a fiber suspension.

Further, the buffer used in step (2) is a phosphate buffer with a concentration of 0.05 mol/L.

Further, the cellulase used in the step (2) is a solid-state endoglucanase with an activity of 50000u/g.

Further, the hydrolysis in step (2) is carried out in a constant temperature water bath oscillating pot at 45-65° C., the oscillating frequency is 80-120 r/min, and the hydrolysis time is 30-180 minutes.

Further, in step (3), the stirring speed is 5000-10000 r/min, and the stirring time is 5-15 minutes.

Further, in the cyclic homogenization treatment in step (4), the pressure is 50-100 MPa, and the number of cycles is 10-30 times.

Further, in step (5), the cellulose microfibril emulsion is centrifuged at a rotation speed of 4000-8000 r/min for 10-30 min.

Compared with the prior art, the present invention has the following beneficial technical effects:

(1) In the method of the present invention, wheat straw pulp is used as a raw material to realize high-value reuse of crop waste and expand the source of raw materials for preparing cellulose microfibrils. (2) Chemical agents such as acid, alkali, and TEMPO catalyst are not used in the preparation process, which reduces environmental pollution, and can reduce energy consumption of mechanical dissociation, and has good economic and environmental benefits. (3) Sieving the wheat straw pulp before enzyme pretreatment is beneficial to reduce the consumption of enzyme by the miscellaneous cells in the pulp, and then carry out appropriate enzyme pretreatment and stirring and shearing treatment to make the fibers in the pulp evenly dispersed, so as to The microfibrils are successfully separated by a high-pressure homogenizer, which is convenient for continuous processing. (4) The prepared wheat straw cellulose microfibrils are in the form of milky white gel, and the microfibrils are interwoven into a network structure with a diameter of 25-100nm, a length of micron level, a large long-diameter ratio and stable performance, reaching Quality requirements for cellulose microfibrils.

【Description of drawings】

Fig. 1 is the scanning electron micrograph of the wheat straw cellulose microfibril prepared in embodiment 1 (5% of enzyme amount added, homogenized 10 times);

Fig. 2 is the scanning electron micrograph of the wheat straw cellulose microfibril prepared in comparative example 1 (without adding endoglucanase, homogenizing 10 times);

Fig. 3 is the scanning electron micrograph of the wheat straw cellulose microfibril prepared in embodiment 2 (enzyme amount 25%, homogeneous 10 times);

Fig. 4 is the fiber scanning electron microscope picture after the preparation of embodiment 3 (enzyme amount 25%, homogeneous 5 times);

Fig. 5 is the scanning electron micrograph of the wheat straw cellulose microfibril prepared in embodiment 3 (enzyme amount 25%, homogeneous 30 times);

Fig. 6 is a graph showing the appearance of cellulose microfibrils prepared in the present invention.

【detailed description】

The present invention will be described in further detail below in conjunction with the accompanying drawings.

The present invention comprises the following steps:

(1) The raw material used is wheat straw pulp, which belongs to grass fiber raw material. The fiber is shorter, the width is smaller, and it contains more parenchyma cells and epidermal cells and other miscellaneous cells. Before pretreatment, the wheat straw pulp is sieved. The fine miscellaneous components are removed, and the fiber components retained on the 100-mesh sieve are collected for subsequent processing.

(2) Soak the fiber component obtained in step (1) in water for 6-18 hours, and then disperse it for 10-30 minutes through a decomposer to disperse the wheat straw pulp evenly, so that the enzyme added later can be fully mixed with the wheat straw fiber; squeeze dry Moisture, use a buffer solution with a concentration of 0.05mol/L to prepare a fiber suspension with a mass concentration of 1% to 5%, and then add cellulase that is 0.5% to 25% relative to the absolute dry mass of the fiber component for hydrolysis. The temperature in the water-bath oscillating pot is kept at 45-65°C, the oscillating frequency is 80-120r/min, and the reaction time is 30-180min. After the hydrolysis is completed, put it in a boiling water bath to boil and inactivate for 5 minutes, and then thoroughly wash with distilled water to obtain the fiber slurry after enzyme pretreatment.

Wherein the buffer in step (2) is a phosphate buffer, and the cellulase is a commercially available solid-state endoglucanase derived from Su Kehan (Weifang) Bioengineering Co., Ltd., the brand is SUKACell, and the activity It is 50000u/g.

(3) The fiber slurry obtained in step (2) after the enzyme pretreatment is subjected to appropriate mechanical stirring and shearing, the stirring speed is controlled at 5000-10000r/min, and the stirring time is 5-15min, so that the slurry is longer The fibers become shorter and the fibers are evenly dispersed, which is conducive to passing through the homogenizer smoothly.

(4) the fiber that obtains in step (3) is mixed with 100mL with distilled water, and mass concentration is 0.5～1.5% fiber suspension, through the circulation homogenization treatment of high-pressure homogenizer, control the operating pressure of high-pressure homogenizer at 50 ～100MPa, the number of cycles is 10～30 times, and the cellulose microfibril emulsion is prepared.

(5) Centrifuge the cellulose microfibril emulsion obtained in step (4) at a rotating speed of 4000 to 8000r/min for 10 to 30 minutes, take the centrifugate and filter it through a cellulose ultrafiltration membrane, and collect the solid components retained on the membrane surface , to obtain wheat straw cellulose microfibrils.

The present invention uses wheat straw pulp as a raw material, expands the raw material limitation for preparing cellulose microfibrils, sieves wheat straw fibers before high-pressure homogenization treatment, and then performs appropriate enzyme pretreatment and stirring and shearing treatment, which is beneficial to reduce The amount of enzyme used makes the slurry pass through the high-pressure homogenizer to separate the microfibrils smoothly, and the preparation process does not use chemical reagents, which can reduce energy consumption, improve product performance, reduce pollution load, and contribute to the industrial production of cellulose microfibrils .

The present invention will be described in further detail below through specific examples.

Example 1

Sieve the wheat straw pulp, collect the fiber components trapped on the 100-mesh sieve, soak and swell with water for 12 hours, decompose for 30 minutes with a decomposer, squeeze out the water, and prepare the concentration with 0.05mol/L phosphate buffer solution 3% fiber suspension; then add domestic solid-state endoglucanase of 5% relative to the absolute dry mass of the fiber component for hydrolysis, keep the temperature at 45°C in a constant temperature water bath oscillating pot, and the oscillating frequency is 100r/min, the reaction The time is 120min. After the hydrolysis is completed, put it in a boiling water bath to boil and inactivate for 5 minutes, and then wash it thoroughly with distilled water to obtain the fiber slurry after enzyme pretreatment; then the fiber slurry is stirred by appropriate machinery, and the stirring speed is controlled at 8000r/min. 10min, and then it is prepared into 100mL of fiber suspension with a mass fraction of 0.5%. After the circulation homogenization treatment of the high-pressure homogenizer, the operating pressure of the high-pressure homogenizer is controlled at 80MPa, and the number of cycles is 10 times to prepare cellulose microfibrils. Emulsion: centrifuge the obtained cellulose microfibril emulsion at a rotating speed of 8000r/min for 30min, take the centrifugate and filter it through a cellulose ultrafiltration membrane, collect the solid components retained on the membrane surface, and obtain wheat straw cellulose microfibrils , and the scanning electron microscope picture (×100k) is shown in Figure 1.

The prepared wheat straw cellulose microfibrils have a width of 40-100 nm, a length of micron order, a crystallinity (CrI%) of 74.53, a degree of polymerization (DP) of 235, and a homogeneous energy consumption of 865.9 W·h. .

Comparative example 1: without enzyme pretreatment, direct high-pressure homogeneous treatment, other conditions are the same as embodiment 1

Sieve the wheat straw pulp, collect the fiber components trapped on the 100-mesh sieve, soak and swell with water for 12 hours, then put the fiber slurry through proper mechanical stirring, the stirring speed is controlled at 8000r/min, and the stirring time is 10min, and then Prepare 100mL of a fiber suspension with a mass fraction of 0.5%, undergo cyclic homogenization treatment with a high-pressure homogenizer, control the operating pressure of the high-pressure homogenizer at 80MPa, and cycle 10 times to prepare a cellulose microfibril emulsion; The obtained cellulose microfibril emulsion was centrifuged at a rotating speed of 8000r/min for 30min, the centrifuged liquid was filtered through a cellulose ultrafiltration membrane, and the solid components retained on the membrane surface were collected to obtain wheat straw cellulose microfibrils. The picture (×100k) is shown in Figure 2.

The prepared cellulose microfibrils: crystallinity (CrI%) 63.28, degree of polymerization (DP) 318, fiber width 50-140nm, uneven distribution, length micron order, energy consumption 1.03kW·h.

In Example 1, an endoglucanase pretreatment of 5% relative to the absolute dry mass of the fiber component was added to prepare wheat straw cellulose microfibrils; the comparative results of Comparative Example 1 and Example 1 show that, from the energy consumption measurement From the above, 1.03kW·h is greater than 865.9W·h, indicating that the energy consumption of dissociated fibers will be reduced after enzyme pretreatment, and the width range of the product cellulose microfibrils after enzyme pretreatment is narrowed, the size is more uniform, and the crystallinity is improved. performance is improved.

Example 2

Other conditions are the same as in Example 1, only the addition amount of endoglucanase is 0.5%, 2%, ... 25% and 45% relative to the absolute dry mass of the fiber component, to prepare wheat straw cellulose microfibrils, and its performance The test results are shown in Table 1 below; the scanning electron microscope pictures (×100k) of wheat straw cellulose microfibrils obtained by adding 25% enzyme and homogenizing 10 times are shown in Figure 3.

Table 1 Performance test results of wheat straw cellulose microfibrils prepared with different enzyme additions

Enzyme addition 0.5% 2% 15% 25% 30% 45% Yield (%) 93 87 68 52 48 42 Width (nm) 40～120 40～110 35～85 30～80 30～65 25～60 Crystallinity 71.68 73.53 75.76 76.86 76.32 75.13 Polymerization 287 245 221 210 189 177 Energy consumption value (W h) 955.0 794.3 813.5 672.9 634.3 624.6

From the analysis data, it can be seen that, with other conditions unchanged, with the increase of the enzyme dosage, although the performance of the product wheat straw cellulose microfibrils is improved, the width becomes more uniform, the crystallinity increases, the degree of polymerization decreases, and the dissociation energy consumption decreases. However, when the amount of enzymes increases to a certain extent, the cost of enzymes increases, the yield of cellulose microfibrils decreases, and excess enzymes can be used in a limited hydrolysis time

Endo-glucan did not exert the best effect, so considering comprehensively, the addition amount of endo-glucan is selected to be between 0.5% and 25%.

Example 3

Other conditions are the same as in Example 1, only the amount of enzyme added is changed to 25% of the absolute dry mass of the relative fiber component, and the number of cycles of homogenization is successively 5, 10, 20, 30 and 40 times to prepare wheat straw cellulose microfibrils. Wherein the scanning electron microscope picture (×10k) of the wheat straw cellulose that adds enzyme amount 25%, homogeneous 5 times obtains is as shown in accompanying drawing 4, adds enzyme amount 25%, the wheat straw cellulose microfibril that homogenizes 30 times obtains The scanning electron microscope picture (×100k) is shown in Figure 5.

The results showed that: when the number of homogenization was 5 times, the surface of the wheat straw fiber was obviously divided and fluffed, the fiber became shorter, and the microfibril structure was exposed, but the microfibrils were not completely dissociated; with the increase of the number of homogenization, When the number of homogenization is 10 times, the width of wheat straw cellulose microfibrils is 30-80nm, the degree of crystallinity (CrI%) is 76.86, the degree of polymerization (DP) is 210, and the energy consumption is 672.9W·h. When the number of times is 30, the width of the prepared wheat straw cellulose microfibrils is 25-40nm, the distribution is uniform, the crystallinity (CrI%) is 69.87, the degree of polymerization (DP) is 165, and the energy consumption is 1.449kW·h. The analysis of the data shows that, with other conditions unchanged, with the increase of homogenization times, the wheat straw fibers are gradually dissociated into wheat straw cellulose microfibrils, and the width of the cellulose microfibrils gradually becomes narrower and the distribution is more uniform. The performance is improved, but the dissociation energy consumption will gradually increase, resulting in an increase in production costs. Comprehensive consideration, choose the number of homogenization in 10 to 30 times.

From the experimental results prepared in Examples 1 to 3, it can be seen that the preparation method of the present invention can reduce energy consumption and improve product performance, and the obtained wheat straw cellulose microfibrils present milky white gel, as shown in Figure 6; Fibrils interweave to form a network structure with a diameter of 25-100nm, a length of micron level, a relatively large length and diameter, and stable performance, which meets the quality requirements of cellulose microfibrils.

Example 4

Sieve the wheat straw pulp, collect the fiber components trapped on the 100-mesh sieve, soak and swell with water for 6 hours, decompose for 25 minutes with a decomposer, squeeze out the water, and prepare the concentration with 0.05mol/L phosphate buffer solution 2% fiber suspension; then add domestic solid-state endoglucanase of 10% relative to the dry weight of the fiber component for hydrolysis, keep the temperature at 50°C in a constant temperature water bath oscillating pot, and the oscillating frequency is 120r/min, the reaction The time is 60 minutes. After the hydrolysis is completed, put it in a boiling water bath to boil and inactivate for 5 minutes, and then wash it thoroughly with distilled water to obtain the fiber slurry after enzyme pretreatment; then, the fiber slurry is stirred by appropriate machinery, and the stirring speed is controlled at 6000r/min. 5min, then be prepared into 100mL of fiber suspension with a mass fraction of 1%, through the circulation homogenization treatment of the high-pressure homogenizer, the operating pressure of the high-pressure homogenizer is controlled at 50MPa, and the number of cycles is 15 times to prepare cellulose microfibrils Emulsion: centrifuge the obtained cellulose microfibril emulsion at a speed of 7000r/min for 20min, take the centrifugate and filter it through a cellulose ultrafiltration membrane, collect the solid components retained on the membrane surface, and obtain wheat straw cellulose microfibrils .

Example 5

Sieve the wheat straw pulp, collect the fiber components trapped on the 100-mesh sieve, soak and swell with water for 18 hours, then disperse it with a decomposer for 10 minutes, squeeze out the water, and prepare the concentration with 0.05mol/L phosphate buffer solution. 4% fiber suspension; then add domestic solid-state endoglucanase of 15% relative to the absolute dry mass of the fiber component for hydrolysis, keep the temperature at 55°C in a constant temperature water bath oscillating pot, and the oscillation frequency is 110r/min, and the reaction The time is 90 minutes. After the hydrolysis is completed, put it in a boiling water bath to boil and inactivate for 5 minutes, and then wash it thoroughly with distilled water to obtain the fiber slurry after enzyme pretreatment; then, the fiber slurry is stirred by appropriate machinery, and the stirring speed is controlled at 5000r/min. 8min, and then it is prepared into 100mL of fiber suspension with a mass fraction of 1.5%. After the circulation homogenization treatment of the high-pressure homogenizer, the operating pressure of the high-pressure homogenizer is controlled at 100MPa, and the number of cycles is 25 times to prepare cellulose microfibrils. Emulsion: centrifuge the obtained cellulose microfibril emulsion at a speed of 6000r/min for 25min, take the centrifugate and filter it through a cellulose ultrafiltration membrane, collect the solid components retained on the membrane surface, and obtain wheat straw cellulose microfibrils .

Example 6

Sieve the wheat straw pulp, collect the fiber components trapped on the 100-mesh sieve, soak and swell with water for 10 hours, decompose for 15 minutes with a decomposer, squeeze out the water, and prepare the concentration with 0.05mol/L phosphate buffer solution. 5% fiber suspension; then add domestic solid-state endoglucanase of 20% relative to the dry weight of the fiber component for hydrolysis, keep the temperature at 60°C in a constant temperature water bath oscillating pot, and the oscillation frequency is 90r/min, and the reaction The time is 30 minutes. After the hydrolysis is completed, put it in a boiling water bath to boil and inactivate for 5 minutes, and then fully wash with distilled water to obtain the fiber slurry after enzyme pretreatment; then the fiber slurry is properly mechanically stirred, and the stirring speed is controlled at 10000r/min. 12min, then it is prepared into 100mL of fiber suspension with a mass fraction of 1.2%. After the circulation homogenization treatment of the high-pressure homogenizer, the operating pressure of the high-pressure homogenizer is controlled at 90MPa, and the number of cycles is 18 times to prepare cellulose microfibrils. Emulsion: centrifuge the obtained cellulose microfibril emulsion at a rotating speed of 5000r/min for 15min, take the centrifugate and filter it through a cellulose ultrafiltration membrane, collect the solid components intercepted on the membrane surface, and obtain wheat straw cellulose microfibrils .

Example 7

Sieve the wheat straw pulp, collect the fiber components trapped on the 100-mesh sieve, soak and swell with water for 15 hours, then disperse it with a decomposer for 20 minutes, squeeze out the water, and prepare a concentration of 0.05mol/L with phosphate buffer solution 1% fiber suspension; then add domestic solid-state endoglucanase of 8% relative to the absolute dry mass of the fiber component for hydrolysis, keep the temperature at 65°C in a constant temperature water bath oscillating pot, and the oscillating frequency is 80r/min, the reaction The time is 180min. After the hydrolysis is completed, put it in a boiling water bath to boil and inactivate for 5 minutes, and then wash it thoroughly with distilled water to obtain the fiber slurry after enzyme pretreatment; then, the fiber slurry is stirred by appropriate machinery, and the stirring speed is controlled at 9000r/min. 15min, then it is prepared into 100mL of fiber suspension with a mass fraction of 0.8%. After the circulation homogenization treatment of the high-pressure homogenizer, the operating pressure of the high-pressure homogenizer is controlled at 60MPa, and the number of cycles is 20 times to prepare cellulose microfibrils. Emulsion: centrifuge the obtained cellulose microfibril emulsion at a rotating speed of 4000r/min for 10min, take the centrifugate and filter it through a cellulose ultrafiltration membrane, collect the solid components intercepted on the membrane surface, and obtain wheat straw cellulose microfibrils .

The invention discloses a method for preparing wheat straw cellulose microfibrils assisted by enzyme pretreatment. The method is to select wheat straw pulp as raw material, sieve out fine and impurity components, soak the obtained fiber components in water, and then add relative fiber components. Cellulase with 0.5% to 25% of absolute dry mass is hydrolyzed, and treated in a oscillating water bath at 45 to 65°C for 30 to 180 minutes to obtain fiber slurry after enzyme pretreatment; after proper stirring and shearing, it passes through a high pressure homogenizer The mechanical dissociation effect of the homogenization cycle is 10 to 30 times to obtain the wheat straw cellulose microfibril emulsion, which is collected by filtration through a cellulose ultrafiltration membrane to obtain a milky white gelatinous wheat straw cellulose microfibril product. The cellulose microfibrils are prepared from wheat straw fiber through the method of the present invention, which is conducive to expanding the source of fiber raw materials, alleviating resource waste and environmental pollution caused by direct burning of wheat straw straw, and realizing high-value reuse of crop waste. Moreover, it can reduce the energy consumption of mechanical dissociation, reduce environmental pollution, improve product performance, and have good economic and environmental benefits. At the same time, the invention properly pretreats the wheat straw fiber before the high-pressure homogenization treatment, overcomes some defects in the prior art, and is beneficial to the further optimization of the cellulose microfibril preparation technology and energy saving and environmental protection.

Claims (9)

1. a kind of enzyme pretreatment assists the method for preparing wheat straw cellulose microfibril, it is characterized in that: comprise the following steps: (1) Sieving the wheat straw pulp to collect the fiber components trapped on the sieve; (2) The fiber component obtained in step (1) is prepared into a fiber suspension with a mass concentration of 1% to 5% with a buffer, and then cellulase is added to the fiber suspension for hydrolysis to obtain enzyme pretreated Fiber slurry; wherein the amount of cellulase added is 0.5% to 25% of the absolute dry mass of the fiber component; (3) the fiber slurry obtained in step (2) after the enzyme pretreatment is subjected to mechanical stirring and shearing; (4) preparing the fiber slurry after mechanically agitating and shearing in step (3) into a fiber suspension with a mass concentration of 0.5 to 1.5%, and performing a circulation homogenization treatment to prepare a cellulose microfibril emulsion; (5) Centrifuging and filtering the cellulose microfibril emulsion in sequence to obtain wheat straw cellulose microfibrils. 2. A kind of enzyme pretreatment-assisted method for preparing wheat straw cellulose microfibrils according to claim 1, characterized in that: the sieve in step (1) is 100 mesh. 3. A method for preparing wheat straw cellulose microfibrils assisted by enzyme pretreatment according to claim 1, characterized in that: in step (2), the fiber components are first soaked and swelled in water for 6-18 hours, and then decomposed by a decomposer After 10-30 minutes, squeeze out the water and make a fiber suspension. 4. A method for preparing wheat straw cellulose microfibrils assisted by enzyme pretreatment according to claim 1, characterized in that: the buffer used in step (2) is a phosphate buffer with a concentration of 0.05mol/L. 5. a kind of enzyme pretreatment according to claim 1 assists the method for preparing wheat straw cellulose microfibril, it is characterized in that: what cellulase adopts in step (2) is that activity is the solid-state endoglucose of 50000u/g Glycanase. 6. A method for assisting preparation of wheat straw cellulose microfibrils by enzyme pretreatment according to claim 1, characterized in that: the hydrolysis in step (2) is carried out in a constant temperature water bath oscillating pot at 45-65°C, The oscillation frequency is 80-120r/min, and the hydrolysis time is 30-180min. 7. A method for preparing wheat straw cellulose microfibrils assisted by enzyme pretreatment according to claim 1, characterized in that: in step (3), the stirring speed is 5000-10000r/min, and the stirring time is 5-15min. 8. A method for preparing wheat straw cellulose microfibrils assisted by enzyme pretreatment according to claim 1, characterized in that: in the circulation homogenization treatment of step (4), the pressure is 50-100 MPa, and the number of cycles is 10 ~30 times. 9. A method for preparing wheat straw cellulose microfibrils assisted by enzyme pretreatment according to claim 1, characterized in that: in step (5), the cellulose microfibril emulsion is centrifuged at a rotating speed of 4000 to 8000r/min Separation for 10-30 minutes.