1. The preparation method of the cellulose nanocrystalline powder is characterized by comprising the following steps:

1) dispersing the cellulose nanocrystals in water, and adjusting the pH value to 7;

2) adding carboxylate into the aqueous dispersion in the step 1), and uniformly stirring;

3) adding a monomer and a ceric ammonium nitrate initiator into the system obtained in the step 2), reacting for 0.5-3 h to obtain a precipitate, and performing suction filtration, washing and drying on the precipitate to obtain the cellulose nanocrystalline powder.

2. The method for preparing cellulose nanocrystalline powder according to claim 1, wherein the cellulose nanocrystalline in step 1) is selected from one or more of hydroxylated cellulose nanocrystalline, sulfonated cellulose nanocrystalline, aldehydized cellulose nanocrystalline and carboxylated cellulose nanocrystalline.

3. The method for preparing the cellulose nanocrystalline powder according to claim 1 or 2, characterized in that, after the carboxylate is added in the step 2), the concentration of the carboxylate in the reaction system is 0.01-0.6 mmol/L, optionally 0.15-0.4 mmol/L, optionally 0.16-0.19 mmol/L.

4. The method for preparing cellulose nanocrystalline powder according to any one of claims 1 to 3, wherein the carboxylate added in step 2) is one or more selected from sodium malate, sodium oxalate, sodium acetate, sodium citrate, sodium humate, sodium succinate, disodium ethylenediamine tetraacetate, tetrasodium ethylenediamine tetraacetate, sodium glutamate, sodium glycinate, sodium alanine, sodium valine, sodium leucine, sodium lactate, sodium tartrate, sodium carboxymethylcellulose, and sodium alginate.

5. The method for preparing cellulose nanocrystalline powder according to any one of claims 1 to 4, characterized in that the monomer in step 3) is a vinyl acetate monomer.

6. The preparation method of the cellulose nanocrystalline powder according to claim 5, wherein the mass ratio of the vinyl acetate to the cellulose nanocrystalline is 1: 1-10: 1, optionally 4: 1-8: 1, optionally 4: 1-6: 1;

and/or the mass ratio of the cerium ammonium nitrate initiator to the cellulose nanocrystal is 1: 10-1: 2, optionally 1: 8-1: 4, optionally 1: 5-1: 4.

7. The method for preparing cellulose nanocrystalline powder according to any one of claims 1 to 6, characterized in that the reaction temperature in step 3) is 5 to 40 ℃, optionally 15 to 30 ℃, optionally 20 to 28 ℃.

8. A cellulose nanocrystalline powder characterized by being prepared by the method for preparing a cellulose nanocrystalline powder according to any one of claims 1 to 7.

9. The cellulose nanocrystalline powder according to claim 8, wherein the grafting ratio of the polymer on the surface of the cellulose nanocrystalline is 300-600%, and the grafting efficiency is 80-99%.

10. The use of the cellulose nanocrystalline hydrophobic powder of claim 8 or 9 in polymer processing, characterized in that: is uniformly dispersed in the polymer matrix.

Background

The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

The cellulose nanocrystal is a one-dimensional rod-shaped nanometer material derived from natural cellulose, and has large specific surface area (250-²Per g) and low density (1.5-1.6 g/cm)³) And the mechanical properties are excellent (the tensile strength is 7500MPa, the elastic modulus is 100-140GPa), and the like, and the preparation method has potential application value in the aspect of preparing light high-strength polymer-based nano composite materials. However, when the dried cellulose nanocrystal powder is melt blended with a polymer, the cellulose nanocrystal surface contains abundant hydroxyl groups, and the cellulose nanocrystal cannot be uniformly dispersed due to strong hydrogen bonding, so that the cellulose nanocrystal surface needs to be modified. Wherein, the method is an efficient method for grafting and modifying the water-phase polymer on the surface of the cellulose nanocrystal by taking ammonium ceric nitrate as an initiator.

The ammonium ceric nitrate can be mixed with C in cellulose₂And C₃The hydroxyl group is complexed, single electron transfer is carried out, and free radicals are generated on the surface of the cellulose nanocrystal, so that chain initiation and chain growth are generated on the surface of the cellulose nanocrystal, and the grafting rate and the grafting efficiency are higher. However, the ammonium cerium nitrate initiation system suffers from the following problems: 1) ammonium ceric nitrate is easy to hydrolyze in water, and a large amount of strong acid needs to be added into the system in order to inhibit the hydrolysis, which undoubtedly causes certain acid pollution to the environment; 2) currently, only petroleum-based polymers are graftable in cerium ammonium nitrate initiation systems, which undermines the advantages of cellulose nanocrystals as biobased materials. The polyvinyl acetate is derived from renewable biological resourcesThe polymer of origin, the monomer vinyl acetate of which can be synthesized by bioethanol. However, polyvinyl acetate is difficult to graft on the surface of cellulose nanocrystals. On the one hand, vinyl acetate monomers are easily hydrolyzed under a strongly acidic environment to lose the ability to polymerize. On the other hand, vinyl acetate radicals generated during polymerization are very reactive and are highly susceptible to chain transfer and chain termination reactions. Acetaldehyde generated by hydrolysis of vinyl acetate under acidic conditions can be used as a chain transfer agent to further promote chain transfer, which undoubtedly greatly reduces the grafting rate and grafting efficiency of polyvinyl acetate on the surface of the cellulose nanocrystal, so that the cellulose nanocrystal is subjected to irreversible agglomeration in powder.

Disclosure of Invention

Object of the Invention

In order to solve the problems that in the prior art, ammonium ceric nitrate initiates a monomer to graft and modify cellulose nanocrystalline, the monomer needs to be carried out in a strong acid environment, and some monomers are easy to hydrolyze in the strong acid environment and lose polymerization capacity, the invention provides cellulose nanocrystalline powder, a preparation method and application thereof.

Solution scheme

In order to achieve the purpose of the present invention, an embodiment of the present invention provides a method for preparing cellulose nanocrystalline powder, including the following steps:

1) dispersing the cellulose nanocrystals in water, and adjusting the pH value to 7;

2) adding carboxylate into the aqueous dispersion in the step 1), and uniformly stirring;

3) adding a monomer and a ceric ammonium nitrate initiator into the system obtained in the step 2), reacting for 0.5-3 h to obtain a precipitate, and performing suction filtration, washing and drying on the precipitate to obtain the cellulose nanocrystalline powder.

The preparation method has universality, is suitable for various vinyl monomers, and is particularly suitable for polymer monomers which are easy to hydrolyze in strong acid environment.

Further, the cellulose nanocrystals in step 1) are selected from one or more of hydroxylated cellulose nanocrystals, sulfonated cellulose nanocrystals, aldehydic cellulose nanocrystals and carboxylated cellulose nanocrystals.

Further, after the carboxylate is added in the step 2), the concentration of the carboxylate in the reaction system is 0.01-0.6 mmol/L, optionally 0.15-0.4 mmol/L, optionally 0.16-0.19 mmol/L.

Further, the carboxylate added in the step 2) is one or more selected from sodium malate, sodium oxalate, sodium acetate, sodium citrate, sodium humate, sodium succinate, disodium ethylene diamine tetraacetate, tetrasodium ethylene diamine tetraacetate, sodium glutamate, sodium glycinate, sodium alanine, sodium valine, sodium leucine, sodium lactate, sodium tartrate, sodium carboxymethylcellulose and sodium alginate.

Further, the monomer in the step 3) is vinyl acetate monomer.

Further, the mass ratio of the vinyl acetate to the cellulose nanocrystal is 1: 1-10: 1, optionally 4: 1-8: 1, optionally 4: 1-6: 1.

Further, the mass ratio of the cerium ammonium nitrate initiator to the cellulose nanocrystal is 1: 10-1: 2, optionally 1: 8-1: 4, optionally 1: 5-1: 4.

Further, the reaction temperature in the step 3) is room temperature, and may be 5 to 40 ℃, optionally 15 to 30 ℃, optionally 20 to 28 ℃.

On the other hand, the cellulose nanocrystalline powder is prepared by the preparation method of the cellulose nanocrystalline powder.

Furthermore, the grafting rate of the polymer on the surface of the cellulose nanocrystal is 300-600%, and the grafting efficiency is 80-99%.

In another aspect, the application of the cellulose nanocrystalline hydrophobic powder in polymer processing is provided, and the cellulose nanocrystalline hydrophobic powder is uniformly dispersed in a polymer matrix.

Advantageous effects

(1) The preparation method is not limited by the surface functional groups of the cellulose nanocrystals, and has universality on the cellulose nanocrystals with different surface functional groups.

(2) When the monomer is vinyl acetate from a biological base as the monomer, the acid-free reaction condition inhibits the chain transfer reaction in the hydrolysis and polymerization processes of the vinyl acetate monomer, so that the polyvinyl acetate can realize high monomer conversion rate, grafting rate and grafting efficiency on the surface of the cellulose nanocrystal in a ceric ammonium nitrate aqueous phase initiation system. The powder obtained after drying the cellulose nanocrystal grafted and modified by the polyvinyl acetate can be thermally processed with the polymer and uniformly dispersed.

(3) The cellulose nanocrystal can spontaneously precipitate from water in the modification process, has a self-purification effect, and does not need dialysis and impurity removal on cellulose nanocrystal suspension before modification. The modification process is carried out in a water system, and is green and environment-friendly.

(4) At present, petroleum-based polymers can be initiated and grafted by ammonium ceric nitrate, so that the advantage of cellulose nanocrystals as bio-based nano materials is destroyed. The invention provides a method for initiating a bio-based monomer to graft and modify cellulose nanocrystals under a water-phase acid-free condition. According to the method, a very small amount of carboxylate is added into a cerium ammonium nitrate initiation system, and the hydrolysis of cerium ions in water is inhibited through the complexing action of the carboxylate and the cerium ions, so that the effects of stabilizing the cerium ions and ensuring the initiation activity are achieved.

Drawings

One or more embodiments are illustrated by the corresponding figures in the drawings, which are not meant to be limiting. The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

FIG. 1 is a photograph of a polyvinyl acetate graft-modified cellulose nanocrystal powder prepared in example 1 of the present invention;

FIG. 2 is an IR spectrum of polyvinyl acetate graft-modified cellulose nanocrystals prepared in example 1 of the present invention and comparative example 1. Of these, 1735 and 1238cm^-1The absorption peaks are respectively the ester group of the polyvinyl acetate and the absorption peak of C-O-C.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. Throughout the specification and claims, unless explicitly stated otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or component but not the exclusion of any other element or component.

Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a better understanding of the present invention. It will be understood by those skilled in the art that the present invention may be practiced without some of these specific details. In some embodiments, materials, elements, methods, means, and the like that are well known to those skilled in the art are not described in detail in order to not unnecessarily obscure the present invention.

The method for calculating the monomer conversion rate, the grafting rate and the grafting efficiency comprises the following steps:

example 1

20mL of a 1% sulfonated cellulose nanocrystal aqueous suspension and 7mg of sodium malate were added to a three-necked flask, and the pH was adjusted to 7. 0.05g of ammonium ceric nitrate and 1g of vinyl acetate were added to the system after sonication. Fully stirring, reacting at 25 ℃ for 2h, taking out, washing, and drying in a forced air drying oven to obtain white cellulose nanocrystalline powder. Wherein the conversion rate of the vinyl acetate is 80%, the grafting rate of the polyvinyl acetate on the surface of the cellulose nanocrystal is 350%, and the grafting efficiency is 87%. The obtained cellulose nanocrystalline powder is shown in fig. 1.

Example 2

The used raw material amount and the process flow are the same as those of the example 1, except that the hydroxylated cellulose nanocrystal is selected as the substrate, and the white cellulose nanocrystal powder is obtained. Wherein the conversion rate of the vinyl acetate is 75 percent, the grafting rate of the polyvinyl acetate on the surface of the cellulose nanocrystal is 300 percent, and the grafting efficiency is 80 percent.

Example 3

The used raw material dosage and the process flow are the same as the example 1, except that the aldehyde cellulose nanocrystalline is selected as the substrate, and the white cellulose nanocrystalline powder is obtained. Wherein the conversion rate of the vinyl acetate is 82%, the grafting rate of the polyvinyl acetate on the surface of the cellulose nanocrystal is 360%, and the grafting efficiency is 88%.

Example 4

The used raw material dosage and the process flow are the same as those of the example 1, except that the sodium malate is replaced by the sodium citrate to obtain the white cellulose nanocrystalline powder. Wherein the conversion rate of the vinyl acetate is 86%, the grafting rate of the polyvinyl acetate on the surface of the cellulose nanocrystal is 380%, and the grafting efficiency is 88%.

Example 5

The used raw material amount and the process flow are the same as those of the example 1, except that the sodium malate is replaced by the sodium oxalate to obtain the white cellulose nanocrystalline powder. Wherein the conversion rate of the vinyl acetate is 76%, the grafting rate of the polyvinyl acetate on the surface of the cellulose nanocrystal is 270%, and the grafting efficiency is 71%.

Example 6

The used raw material amount and the process flow are the same as those of the example 1, except that the carboxylated cellulose nanocrystal is selected as the substrate, wherein the carboxyl content of the carboxylated cellulose nanocrystal substrate is 0.2mmol/g, and the white cellulose nanocrystal powder is obtained. Wherein the conversion rate of the vinyl acetate is 82%, the grafting rate of the polyvinyl acetate on the surface of the cellulose nanocrystal is 340%, and the grafting efficiency is 83%.

Comparative example 1

The types, the amounts and the process flow of the used raw materials are the same as those of the example 1, except that the system does not contain sodium malate, and the product is dried to obtain hard blocks. Wherein the conversion rate of the vinyl acetate is 20%, the grafting rate of the polyvinyl acetate on the surface of the cellulose nanocrystal is 5%, and the grafting efficiency is 5%.

The comparative example shows a lower grafting ratio, which is further illustrated by the fact that the ammonium cerium nitrate hydrolyzes at a pH of 7 when no carboxylate is added to the reaction system.

The polyvinyl acetate graft-modified cellulose nanocrystals prepared in example 1 and comparative example 1 were examined and the infrared spectrum is shown in fig. 2, which shows that the polyvinyl acetate graft-modified cellulose nanocrystals had a higher grafting rate on the surface of the cellulose nanocrystals after the addition of sodium malate.

Comparative example 2

The types, the amounts and the process flow of the used raw materials are the same as those of the example 1, except that the pH of the system is adjusted to 2, and the product is dried to obtain hard blocks. Wherein the conversion rate of the vinyl acetate is 10 percent, the grafting rate of the polyvinyl acetate on the surface of the cellulose nanocrystal is 5 percent, and the grafting efficiency is 10 percent.

The lower grafting ratio in this comparative example indicates that vinyl acetate is easily decomposed under acidic conditions and polymerization is difficult to achieve.

Comparative example 3

The raw material dosage and the process flow are the same as those of the example 1, except that the carboxylated cellulose nanocrystalline is selected as the substrate under the condition of not adding sodium malate, and the product is dried to obtain hard blocks. Wherein the conversion rate of the vinyl acetate is 65%, the grafting rate of the polyvinyl acetate on the surface of the cellulose nanocrystal is 26%, and the grafting efficiency is 8%.

The grafting rate and grafting efficiency in this comparative example were lower, indicating that the cerium ions stabilized by small molecule carboxylates have higher initiating ability, while cerium ions stabilized by carboxylated cellulose nanocrystals have lower grafting rate and grafting efficiency due to the large steric hindrance and weak mobility due to the M element.

Comparative example 4

The used raw material amount and the process flow are the same as those of the example 1, except that the carboxylated cellulose nanocrystalline is selected as the substrate and sodium malate is not added, wherein the carboxyl content of the carboxylated cellulose nanocrystalline is 1.2mmol/g, and the product is dried to obtain hard blocks. Wherein the conversion rate of the vinyl acetate is 20%, the grafting rate of the polyvinyl acetate on the surface of the cellulose nanocrystal is 3%, and the grafting efficiency is 3%.

This comparative example illustrates that the addition of ammonium cerium nitrate results in ionic crosslinking of the cellulose nanocrystals and precipitation from water at higher carboxyl content on the surface of the carboxylated cellulose nanocrystals, affecting the uniformity of grafting and the initiating ability of ammonium cerium nitrate.

The invention can realize the polymer grafting modification of ammonium ceric nitrate on the surfaces of cellulose nanocrystals with different surface functional groups under the acid-free condition. The acid-free condition leads the bio-based monomer-vinyl acetate to carry out graft polymerization on the surface of the cellulose nanocrystal, and has higher monomer conversion rate, grafting rate and grafting efficiency. The powder obtained after drying the cellulose nanocrystal grafted and modified by the polyvinyl acetate can be thermally processed with the polymer and uniformly dispersed.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.