阅读说明：本技术 一种3d网状高结晶度核桃壳基纳米纤维素的制备方法 (Preparation method of 3D (three-dimensional) reticular high-crystallinity walnut shell-based nanocellulose ) 是由 申烨华 李丹妮 白秋红 张路伟 李聪 陈邦 王妍 于 2021-10-25 设计创作，主要内容包括：本发明公开了一种3D网状高结晶度核桃壳基纳米纤维素的制备方法,以核桃壳为原料,将核桃壳粉碎后进行脱脂处理,再采用亚氯酸钠和冰醋酸化学处理得到综纤维素,综纤维素用氢氧化钾纯化之后得到纤维素,最后经过物理场和2,2,6,6-四甲基哌啶氧化物氧化得到三维网状结构纳米纤维素,其长径比高,结晶度可达80％。本发明工艺简单、易于实施,原材料核桃壳可再生、可降解、成本低,符合绿色可持续发展原则,同时丰富了纳米纤维素原料来源,实现废弃物资源化和可持续发展,减少对环境污染的同时,有利于提高核桃壳的利用率。(The invention discloses a preparation method of 3D (three-dimensional) net-shaped high-crystallinity walnut shell-based nanocellulose, which comprises the steps of taking walnut shells as raw materials, crushing the walnut shells, carrying out degreasing treatment, carrying out chemical treatment by adopting sodium chlorite and glacial acetic acid to obtain holocellulose, purifying the holocellulose by using potassium hydroxide to obtain cellulose, and finally oxidizing the holocellulose by using a physical field and 2,2,6, 6-tetramethylpiperidine oxide to obtain the three-dimensional net-shaped structure nanocellulose, wherein the length-diameter ratio is high, and the crystallinity can reach 80%. The method has the advantages of simple process, easy implementation, renewable and degradable raw material walnut shells, low cost, accordance with the green sustainable development principle, enrichment of the source of the raw material of the nano-cellulose, realization of the resource and sustainable development of wastes, reduction of environmental pollution and contribution to improving the utilization rate of the walnut shells.)

1. A preparation method of 3D reticular high-crystallinity walnut shell-based nanocellulose is characterized by comprising the following steps:

(1) washing, drying and crushing walnut shells, and sieving the walnut shells with a 100-200-mesh sieve to obtain walnut shell powder;

(2) wrapping walnut shell powder by using filter paper, putting the wrapped walnut shell powder into a mixed solution of toluene and absolute ethyl alcohol in a volume ratio of 2:1, extracting for 8-12 hours at 140-150 ℃, taking out a filter paper bag wrapping the walnut shell powder, and drying at room temperature to obtain degreased walnut shell powder;

(3) adding the degreased walnut shell powder obtained in the step (2) into deionized water, adding sodium chlorite and glacial acetic acid, stirring and reacting at 70-80 ℃ for 40-70 minutes, adding the sodium chlorite and the glacial acetic acid again, repeating the reaction for 3-7 times, filtering and washing to be neutral after the reaction is finished, and drying to obtain holocellulose;

(4) mixing the holocellulose obtained in the step (3) with a potassium hydroxide aqueous solution and deionized water, stirring and reacting at 70-90 ℃ for 100-150 minutes, adding the potassium hydroxide aqueous solution again, continuing to stir and react for 100-150 minutes, filtering and washing to be neutral after the reaction is finished, and drying to obtain cellulose;

(5) preparing the cellulose obtained in the step (4) into a suspension with the mass concentration of 2% -4% by using deionized water, grinding for 2-6 hours by using a planetary ball mill, diluting to the mass concentration of 0.5% -1% by using the deionized water, adding 2,2,6, 6-tetramethylpiperidine oxide, sodium bromide and sodium hypochlorite, stirring at room temperature for reaction, adjusting the pH value of a reaction solution to be 10 by using hydrochloric acid and sodium hydroxide in the reaction process, and adding the hydrochloric acid and absolute ethyl alcohol to finish the reaction when the pH value of the reaction solution is stabilized at 10 and is not changed; and (4) centrifuging and washing to obtain a precipitate, namely the three-dimensional reticular nano cellulose.

2. The method for preparing 3D reticular high-crystallinity walnut shell-based nanocellulose according to claim 1, characterized in that: in the step (3), the mass ratio of the degreased walnut shell powder to the sodium chlorite and the glacial acetic acid added each time is 1: 0.3-0.7: 0.3-0.6.

3. The method for preparing 3D reticular high-crystallinity walnut shell-based nanocellulose according to claim 1, characterized in that: in the step (4), the mass ratio of the holocellulose to the potassium hydroxide aqueous solution to the deionized water is 1: 1-2: 40, wherein the mass concentration of the potassium hydroxide aqueous solution is 4-6%.

4. The method for preparing 3D reticular high-crystallinity walnut shell-based nanocellulose according to claim 1, characterized in that: in the step (5), the mass ratio of the cellulose to the 2,2,6, 6-tetramethylpiperidine oxide to the sodium bromide to the sodium hypochlorite is 1: 0.016-0.032: 0.1-0.2: 3-11.

Technical Field

The invention belongs to the technical field of nano-cellulose preparation, and particularly relates to a preparation method of 3D reticular high-crystallinity walnut shell-based nano-cellulose.

Background

With the rapid increase of the population, the world demand for oil crops and edible oil is rapidly increased. Walnuts are used as woody oil, form four large cultivation areas of southwest, northwest, east coast and China, and the planting area and the yield are in the first place of the world. The oil content of walnut kernel is about 70%, which is 3.5 times of soybean, and is high-grade edible oil and industrial oil, so walnut element is a name of 'woody oil material king'.

With the wide range of seed value and processing utilization of walnuts, a large amount of by-products, namely walnut shells, are generated at the same time, but the utilization rate of the walnut shells is low at present, most of the walnut shells are only used as feed or are discarded at will, the economic added value is not high, and the environment is polluted. The walnut shell is taken as a typical wood fiber biomass, contains a large amount of cellulose which can be used as a high-quality source of the cellulose, the cellulose is one of natural high polymer with most abundant content in the nature, is degradable and renewable, is easy to chemically modify, and is widely applied to various fields.

The nano-cellulose is an ultramicro fiber with the fiber diameter less than 100nm, and has a plurality of excellent characteristics, such as high strength, high crystallinity, high purity, high polymerization degree, degradability, good hydrophilicity, transparency, light weight, good biocompatibility and the like, so that the nano-cellulose has good application prospects in materials such as artificial biological tissues, biosensors, flexible electronic devices and the like. Therefore, the utilization rate of the walnut shells can be improved by extracting the cellulose from the walnut shells, the resource waste is reduced, and the economic value of the walnut shells is improved.

Disclosure of Invention

The invention aims to provide a preparation method of 3D reticular high-crystallinity walnut shell-based nanocellulose.

In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:

1. washing, drying and crushing walnut shells, and sieving the walnut shells with a 100-200-mesh sieve to obtain walnut shell powder;

2. wrapping walnut shell powder by using filter paper, putting the wrapped walnut shell powder into a mixed solution of toluene and absolute ethyl alcohol in a volume ratio of 2:1, extracting for 8-12 hours at 140-150 ℃, taking out a filter paper bag wrapping the walnut shell powder, and drying at room temperature to obtain degreased walnut shell powder;

3. adding the degreased walnut shell powder obtained in the step 2 into deionized water, adding sodium chlorite and glacial acetic acid, stirring and reacting at 70-80 ℃ for 40-70 minutes, adding the sodium chlorite and the glacial acetic acid again, repeating the reaction for 3-7 times, filtering and washing to be neutral after the reaction is finished, and drying to obtain holocellulose;

4. mixing the holocellulose obtained in the step (3) with a potassium hydroxide aqueous solution and deionized water, stirring and reacting at 70-90 ℃ for 100-150 minutes, adding the potassium hydroxide aqueous solution again, continuing to stir and react for 100-150 minutes, filtering and washing to be neutral after the reaction is finished, and drying to obtain cellulose;

5. preparing the cellulose obtained in the step (4) into a suspension with the mass concentration of 2% -4% by using deionized water, grinding for 2-6 hours by using a planetary ball mill, diluting to the mass concentration of 0.5% -1% by using the deionized water, adding 2,2,6, 6-tetramethylpiperidine oxide, sodium bromide and sodium hypochlorite, stirring at room temperature for reaction, adjusting the pH value of a reaction solution to be 10 by using hydrochloric acid and sodium hydroxide in the reaction process, and adding the hydrochloric acid and absolute ethyl alcohol to finish the reaction when the pH value of the reaction solution is stabilized at 10 and does not change any more; and (4) centrifuging and washing to obtain a precipitate, namely the three-dimensional reticular nano cellulose.

In the step 3, the mass ratio of the degreased walnut shell powder to the sodium chlorite and the glacial acetic acid added each time is preferably 1: 0.3-0.7: 0.3-0.6.

In the step 4, the mass ratio of the holocellulose to the potassium hydroxide aqueous solution to the deionized water is preferably 1:1 to 2:40, wherein the mass concentration of the potassium hydroxide aqueous solution is 4 to 6 percent.

In the step 5, the mass ratio of the cellulose to the 2,2,6, 6-tetramethylpiperidine oxide to the sodium bromide to the sodium hypochlorite is preferably 1:0.016 to 0.032:0.1 to 0.2:3 to 11.

The invention has the following beneficial effects:

1. the invention takes the woody oil tree seed walnut shell as the raw material for preparing the cellulose, the walnut shell is the main byproduct of the walnut industry, and the walnut shell as the raw material for preparing the cellulose can effectively improve the economic value of the walnut, is beneficial to the high-value utilization of the walnut, improves the utilization rate of the walnut shell and increases the added value of the walnut shell.

2. The invention has simple process, low requirement on equipment, low energy consumption and easy realization of industrialization.

3. The nano-cellulose prepared by the method has the advantages of small diameter, large negative charge on the surface, small diameter, high length-diameter ratio, and three-dimensional network structure, and most of the fiber diameter is distributed between 5nm and 30 nm.

4. The crystallinity of the nano-cellulose obtained by the method is high and reaches more than 80 percent, and the crystallinity exceeds that of commercial cellulose, and the performance is excellent.

Drawings

FIG. 1 is a transmission electron micrograph of nanocellulose prepared in example 1.

Fig. 2 is an atomic force microscope image of nanocellulose prepared in example 1.

Fig. 3 is a diameter statistical chart of the nanocellulose fibers prepared in example 1.

Fig. 4 is an XRD comparison pattern of nanocelluloses prepared by examples 1, 2, 3, 4, 5 and commercial cellulose.

FIG. 5 is a transmission electron micrograph of the nanocellulose prepared in example 3.

FIG. 6 is a transmission electron micrograph of nanocellulose prepared in example 4.

FIG. 7 is a transmission electron micrograph of nanocellulose prepared in example 5.

Detailed Description

The invention will be further described in detail with reference to the following figures and examples, but the scope of the invention is not limited to these examples.

Example 1

1. Washing walnut shells, drying, crushing, and sieving with a 200-mesh sieve to obtain walnut shell powder.

2. Wrapping 5g of walnut shell powder by using filter paper, putting the wrapped walnut shell powder into 150mL of mixed solution of toluene and absolute ethyl alcohol in a volume ratio of 2:1, extracting for 12 hours at 145 ℃ to remove pigments and lipid substances, taking out a filter paper bag wrapping the walnut shell powder, and drying for 12 hours at room temperature to obtain the degreased walnut shell powder.

3. Adding 5g of degreased walnut shell powder into 200g of deionized water, adding 2.8g of sodium chlorite and 2g of glacial acetic acid, carrying out water bath heating at 75 ℃, stirring, reacting for 1 hour, adding 2.8g of sodium chlorite and 2g of glacial acetic acid again, continuing to react for 1 hour, repeating the steps for 5 times, and reacting for 6 hours. After the reaction is finished, deionized water is used for filtering and washing to be neutral, and drying is carried out at 80 ℃ to obtain the holocellulose.

4. Mixing 5g of holocellulose, 5g of a 5% by mass potassium hydroxide aqueous solution and 200g of deionized water, heating in a water bath at 90 ℃, stirring, reacting for 2 hours, adding 5g of a 5% by mass potassium hydroxide aqueous solution again, and continuing to stir and react for 2 hours. And filtering and washing the mixture to be neutral by using deionized water after the reaction is finished, and freezing and drying the mixture to obtain the cellulose.

5. Preparing the cellulose obtained in the step 4 into a suspension with the mass concentration of 2% by deionized water, performing one-way operation by using a planetary ball mill, mechanically grinding for 4 hours at the rotating speed of 400 revolutions per minute, diluting the suspension with the deionized water until the mass concentration is 0.5%, taking 200g of diluent, adding 0.032g of 2,2,6, 6-tetramethylpiperidine oxide, 0.2g of sodium bromide and 7.1g of sodium hypochlorite, performing magnetic stirring reaction at room temperature, adjusting the pH value of the reaction solution to be 10 by using hydrochloric acid and sodium hydroxide in the reaction process, and adding 0.1mol/L of hydrochloric acid and absolute ethyl alcohol to finish the reaction when the pH value of the reaction solution is stabilized at 10 and does not change any more; centrifuging and washing at 10000rpm for 5 times to obtain precipitate, namely the three-dimensional reticular nano cellulose.

The obtained nanocellulose is characterized by adopting a transmission electron microscope, and the result is shown in the figure 1-4. As can be seen from FIG. 1, the prepared nano cellulose fibers are interconnected, have a three-dimensional network-like structure and uniform fiber diameters, and the fibers are mutually crosslinked as can be seen from the atomic force microscope image of FIG. 2. As can be seen from FIG. 3, the diameter is distributed between 5-30 nm, mainly between 10-15 nm, and the prepared nano-cellulose has small diameter and high length-diameter ratio. The nano-cellulose is dispersed in deionized water, and the Zeta potential of the nano-cellulose dispersion liquid obtained by detection is-31.74 mV, which indicates that the surface of the nano-cellulose dispersion liquid has a large amount of negative charges, and the prepared nano-cellulose is relatively stable. According to the XRD comparison pattern of fig. 4, the crystallinity of the commercial nanocellulose was calculated to be 77.17%, and the crystallinity of the nanocellulose prepared in this example was 80.31%, which was significantly higher than that of the commercial nanocellulose.

Example 2

In step 5 of this example, 200g of the diluted solution was added with 0.032g of 2,2,6, 6-tetramethylpiperidine oxide, 0.2g of sodium bromide, and 3.56g of sodium hypochlorite, and the other steps were the same as in example 1 to obtain three-dimensional reticulated nanocellulose. From FIG. 4, it can be calculated that the crystallinity of the nanocellulose prepared by this example is 83.32%, which is higher than the crystallinity of the commercial nanocellulose, and the Zeta potential of the nanocellulose dispersion is-48.00 mV, which indicates that the nanocellulose prepared is relatively stable with a large amount of negative charges on the surface.

Example 3

In step 5 of this example, 200g of the diluted solution was added with 0.032g of 2,2,6, 6-tetramethylpiperidine oxide, 0.2g of sodium bromide and 10.65g of sodium hypochlorite, and the other steps were the same as in example 1 to obtain three-dimensional reticulated nanocellulose. As can be seen from FIG. 5, the cellulose fibers are interconnected and staggered, have a net structure, the fiber diameter is below 50nm, and reach the nanometer level, and from FIG. 4, it can be calculated that the crystallinity of the nanocellulose prepared by the present example is 84.84%, which is higher than the crystallinity of the commercial nanocellulose, and the Zeta potential of the nanocellulose dispersion is-30.47 mV, which indicates that the surface has a large amount of negative charges, and the prepared nanocellulose is relatively stable.

Example 4

In step 5 of this example, the cellulose obtained in step 4 was prepared into a suspension with a mass concentration of 2% with deionized water, and mechanically ground for 3 hours at a rotation speed of 400 rpm by using a planetary ball mill operating in one direction, and the other steps were the same as those of example 1, to obtain three-dimensional network nanocellulose. As can be seen from FIG. 6, the fibers are mutually crosslinked to form a three-dimensional network structure, the diameter of the fibers is below 50nm and reaches the nanometer level, and it can be calculated from FIG. 4 that the crystallinity of the nano-cellulose prepared by the present example is 82.84%, which is higher than the crystallinity of commercial nano-cellulose, and the Zeta potential of the nano-cellulose dispersion is-23.89 mV, which indicates that the surface has a large amount of negative charges, and the prepared nano-cellulose is relatively stable.

Example 5

In step 5 of this example, the cellulose obtained in step 4 was prepared into a suspension with a mass concentration of 2% with deionized water, and mechanically ground for 2 hours at a rotation speed of 400 rpm by using a planetary ball mill operating in one direction, and the other steps were the same as those of example 1, to obtain three-dimensional network nanocellulose. As can be seen from fig. 7, after the treatment under the conditions of this example, a network structure begins to appear, and the fibers gradually become fine, and the diameter is below 100nm, which reaches the nanometer level, and from fig. 4, it can be calculated that the crystallinity of the nanocellulose prepared by this example is 87.49%, which is higher than the crystallinity of the commercial nanocellulose.