CN109487546B

CN109487546B - Efficient and environment-friendly preparation method of cationic nano-fibrillated cellulose

Info

Publication number: CN109487546B
Application number: CN201811280256.7A
Authority: CN
Inventors: 刘宏治; 单鹏嘉; 赵莹
Original assignee: Zhejiang A&F University ZAFU
Current assignee: Zhejiang A&F University ZAFU
Priority date: 2018-10-30
Filing date: 2018-10-30
Publication date: 2021-04-13
Anticipated expiration: 2038-10-30
Also published as: CN109487546A

Abstract

The invention discloses a high-efficiency environment-friendly cationic nano-fibrillated cellulose preparation method, which comprises the steps of replacing corrosive strong base with a mild and environment-friendly weak base reagent as an activating agent of natural cellulose fibers in a chemical pretreatment step, carrying out quaternary ammonium salinization pretreatment on paper pulp at a medium temperature, and preparing a Q-NFC aqueous dispersion with high polymerization degree and nano-fibrillated degree and controllable surface charge content after mechanical separation. The preparation method is simple and efficient, the reaction condition is mild, the environment is protected, and the preparation method is suitable for large-scale production, and the prepared Q-NFC can be used in the fields of paper and plastic reinforcement, food packaging, paint, cosmetics, electronic materials, biological medicine, environmental purification and the like.

Description

Efficient and environment-friendly preparation method of cationic nano-fibrillated cellulose

Technical Field

The invention relates to a preparation method of cellulose, in particular to a preparation method of efficient and environment-friendly cation nano-fibrillated cellulose.

Background

With the continuous development of economy in China, the problem of resource shortage is increasingly serious. Cellulose is a macromolecular polysaccharide composed of glucose units, is mainly present in plant cell walls, and is a natural high molecular material with the largest storage capacity and the widest distribution in the world. In order to improve the utilization rate of cellulose and expand the application range, the cellulose is further processed by a physical method or a chemical method, and a large novel cellulose material, namely nano-cellulose with the diameter of less than 100nm and the length of hundreds of microns or microns can be obtained. The nanocellulose microfibrils derived from plants can be roughly classified into two types, namely, Nanocellulose (NCC) and nanofibrillated cellulose (NFC), depending on their forms and preparation methods. Unlike NCC with a rigid rod-like structure, the filaments of NFC are in a randomly entangled network form, and are more easily made into various forms of materials such as films, hydrogels, aerogels, and the like, and are applied to the fields of biomedical treatment, packaging materials, adsorption materials, and the like.

At present, the fiber can be continuously refined by a method of combining mechanical treatment or chemical pretreatment and mechanical treatment to obtain the high-length-diameter-ratio nano-fiber with the diameter of 2-60 nm and the length of several micrometers. Methods combining chemical pretreatment with mechanical treatment, as opposed to purely mechanical treatmentThe preparation method of the NFC has the advantages that the preparation energy consumption of the NFC is effectively reduced, and meanwhile, a new functional group is introduced to the surface of the fiber, so that the preparation method becomes the most widely applied NFC preparation method at present. The common pretreatment methods at present include a biological enzymolysis method, a TEMPO oxidation method, a carboxymethyl method and a periodic acid oxidation method. The surfaces of the NFC prepared by the biological enzymolysis method and the TEMPO oxidation method are provided with a certain amount of negative charges, the negative charges not only increase the mutual repulsion among fibers and are beneficial to uniform dispersion of the fibers in water, but also can be effectively combined with some groups with positive charges, so that the NFC has positive charge adsorption performance. However, the biological enzymolysis method has low preparation yield and low degree of nano fibrillation, and cannot obtain the high-transparency NFC dispersion liquid; the TEMPO oxidation method has the disadvantages of high preparation cost (TEMPO catalyst is expensive) and need of using strong oxidant (NaClO or NaClO)₂) The prepared carboxylated modified NFC product has poor thermal stability, and the dried product is not easy to redisperse in water; the carboxymethyl method needs strong alkali and a large amount of alcohol organic solvents (such as isopropanol, ethanol or methanol and the like), and the surface of the carboxymethyl method has carboxyl, so that the thermal stability is poor; the periodic acid oxidation method needs a strong oxidizing agent of sodium periodate with high toxicity and high price, and the polymerization degree of the prepared NFC is seriously reduced compared with that of the pulp raw material (especially along with the prolonging of the oxidation time). In summary, the methods are not beneficial to the industrial production of NFC.

The quaternization pretreatment is to carry out etherification reaction on hydroxyl on the surface of cellulose by using a reagent with quaternary ammonium salt groups, and the introduced positive charge groups weaken the hydrogen bond acting force among cellulose microfibrils, thereby being beneficial to the microfibrillation treatment of cellulose pulp. Compared with TO-NFC prepared by a TEMPO oxidation method which is widely researched and reported at present, Q-NFC prepared by quaternary ammonium salinization pretreatment has the advantages of good thermal stability, easiness in redispersion in water after drying, high viscosity and the like. The dried nano cellulose paper has good mechanical property and oxygen barrier property, and can be widely applied to a plurality of fields such as food packaging industry, cosmetic industry, clothing industry, environmental purification and the like.

However, in the prior Q-NFC report, the pretreatment process requires a long time quaternary ammonium salt treatment of low solid content pulp fibers under strong alkali and heating conditions (65 ℃), the quaternary ammonium salt reagent is high in dosage and sometimes needs to be supplemented with toxic organic solvents such as isopropyl alcohol, dimethyl acetamide (DMAC), dimethyl sulfoxide (DMSO) and the like (P Olszewska et al cellulose 201118,1213; Yanghui & Li group Paper and Paper Making,2013,32, 25; Chaker et al Carbohydrate Polymers 2015, 131, 224; T.Ho et al cellulose 2011,18, 1391; Pei et al Soft Matter 2013,9, 2047; Litten et al European Polymer Journal 2016,75, 116; Saini et al, Carbohydrate Polymers 2016,135,239). Therefore, the existing method for preparing cationic NFC (namely Q-NFC) has the problems that the reaction medium environment is strict, the time consumption is long, the polymerization degree (DPv) of the prepared Q-NFC product is seriously reduced compared with that of a paper pulp raw material, and the like, so that the method is not beneficial to practical industrial preparation.

Disclosure of Invention

The invention aims to provide a high-efficiency and environment-friendly method for preparing cationic nano-fibrillated cellulose aiming at the defects of the prior art.

The purpose of the invention is realized by the following technical scheme: a preparation method of high-efficiency and environment-friendly cation nano-fibrillated cellulose comprises the following steps:

(1) paper pulp pretreatment:

dissolving weak base in wet paper pulp with solid content of 10-35 wt%, continuously stirring until uniform mixing is achieved, then adding a cationic reagent, stirring until full mixing is achieved, and heating and drying the mixed pulp until constant weight is achieved; or adding dry paper pulp into a weak base aqueous solution to enable the solid content of the paper pulp to be 10-35 wt%, continuously stirring until the paper pulp is uniformly mixed, then adding a cationic reagent, stirring until the paper pulp is fully mixed, and heating and drying the mixed pulp until the weight is constant;

(2) Q-NFC preparation: and dispersing the dried slurry in deionized water, fully washing with distilled water to remove unreacted cationic reagents, carrying out mechanical treatment to obtain uniform and viscous Q-NFC aqueous dispersion, and measuring by conductivity titration to obtain the content of trimethyl ammonium chloride groups on the surface of the microfiber, wherein the content of trimethyl ammonium chloride groups on the surface of the microfiber is 0.2-1.0 mmol/g.

Further, in the step (1), the paper pulp is various types of bleached or unbleached paper pulp, including chemical pulp, chemimechanical pulp, semi-mechanical pulp, mechanical pulp and industrial waste paper pulp, and the content of lignin in the paper pulp is high or low.

Further, in the step (1), the weak base is selected from any one of urea, thiourea and melamine, or a plurality of the weak bases are mixed according to any proportion.

Further, in the step (1), weak base is dissolved in wet paper pulp with the solid content of 10-35 wt%, wherein the mass ratio of the weak base to water in the wet paper pulp is 0.1-1.2: 1, and the weak base can be completely dissolved without precipitation; the content of cationic groups on the surface of Q-NFC can be regulated and controlled by changing the addition amount of weak base.

Further, in the step (1), adding the dry paper pulp into a weak base aqueous solution, wherein the mass ratio of weak base to water in the weak base aqueous solution is 0.1-1.2: 1; the content of cationic groups on the surface of Q-NFC can be regulated and controlled by changing the addition amount of weak base.

Further, in the step (1), the cationic reagent is selected from any one of 2, 3-epoxypropyltrimethylammonium chloride (EPTAC), 3-chloro-2-hydroxypropyltrimethylammonium chloride, (2-chloroethyl) trimethylammonium chloride, or a mixture of a plurality of them in any ratio.

Further, in the step (1), the mass ratio of the cationic reagent to the oven-dried paper pulp is 0.36-5.8: 1, and the content of cationic groups on the surface of Q-NFC can be regulated and controlled by changing the addition amount of the cationic reagent.

Further, in the step (1), the mixed slurry is put into an oven with the temperature of 50-150 ℃ for heating and drying until the weight is constant.

Further, in the step (2), the mechanical treatment adopts high-pressure homogenization, and the conditions of the high-pressure homogenization are as follows: the pressure is 700-900MPa, the time is 5-15 minutes, and the flow rate is 70-150 ml/min.

The invention has the beneficial effects that: according to the method, a weak alkali reagent replaces a corrosive strong alkali reagent to serve as an activating agent of the cellulose fiber, the amount of a chemical reagent used in the pulp pretreatment process is reduced, the problems that the chemical reagent is large in amount, the obtained cellulose is low in polymerization degree and the like in the existing method are solved, and the content of cationic groups on the surface of the nano cellulose is changed by regulating and controlling the preparation process. The method has the advantages of high efficiency, environmental protection, mild reaction medium environment, high DPv of products, good transparency of water dispersion and the like, and can be used for efficiently preparing high-quality Q-NFC.

Drawings

FIG. 1 is a graph comparing the transmittance curves at a wavelength of 600nm for Q-NFC dispersions (solids content of 0.2 wt%) according to examples 1 to 11 of the invention and comparative examples 1, 2 and 3.

Detailed Description

The technical solution of the present invention is not limited to the following specific embodiments, but includes any combination of the specific embodiments.

Example 1

The process for preparing Q-NFC under the weak base condition comprises the following steps:

10.8g of urea is weighed and dissolved in 10g of wet pulp, after all the urea is dissolved, 5.8g of 2, 3-epoxypropyltrimethylammonium chloride is added, and the mixture is put into a 50 ℃ oven and heated to constant weight. Then fully dispersing the dried slurry by deionized water, and then carrying out suction filtration and washing until filtrate is AgNO₃The solution was tested for the presence of no chloride ions. And finally, mechanically treating the washed slurry to obtain the transparent NFC dispersion liquid with positive charges on the surface.

Example 2

0.6g of urea is weighed and dissolved in 10g of wet bamboo pulp, after all the urea is dissolved, 0.36g of 2, 3-epoxypropyl trimethyl ammonium chloride is added, and the mixture is put into a 65 ℃ oven and heated to constant weight. Then fully dispersing the dried slurry by deionized water, and then carrying out suction filtration and washing until filtrate is AgNO₃The solution was tested for the presence of no chloride ions. And finally, mechanically treating the washed slurry to obtain the transparent NFC dispersion liquid with positive charges on the surface.

Example 3

weighing 10.8g of urea, dissolving in 9g of water, adding 1g of dry bamboo pulp into the urea aqueous solution, adding 5.8g of 2, 3-epoxypropyltrimethylammonium chloride after all the urea aqueous solution is dissolved, putting the mixture into a 65 ℃ oven, and heating to constant weight. Then fully dispersing the dried slurry by deionized water, and then carrying out suction filtration and washing until filtrate is AgNO₃The solution was tested for the presence of no chloride ions. And finally, mechanically treating the washed slurry to obtain the transparent NFC dispersion liquid with positive charges on the surface.

Example 4

0.6g of urea is weighed and dissolved in 9g of water, 1g of dry bamboo pulp is added into the urea water solution, after the complete dissolution, 5.8g of 2, 3-epoxypropyl trimethyl ammonium chloride is added, and the mixture is put into a 65 ℃ oven and heated to constant weight. Then fully dispersing the dried slurry by deionized water, and then carrying out suction filtration and washing until filtrate is AgNO₃The solution was tested for the presence of no chloride ions. And finally, mechanically treating the washed slurry to obtain the transparent NFC dispersion liquid with positive charges on the surface.

Example 5

2.3g of urea was weighed out and dissolved in 2.9g of wet pulp, after all dissolved, 2.9g of 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, and the mixture was put into a 65 ℃ oven and heated to constant weight. Then fully dispersing the dried slurry by deionized water, and then carrying out suction filtration and washing until filtrate is AgNO₃The solution was tested for the presence of no chloride ions. And finally, mechanically treating the washed slurry to obtain the transparent NFC dispersion liquid with positive charges on the surface.

Example 6

0.1g of urea is weighed out and dissolved in 2.9g of wet pulp, after all the urea is dissolved, 5.8g of 2, 3-epoxypropyltrimethylammonium chloride is added, and the mixture is put into an oven at 100 ℃ and heated to constant weight. Then fully dispersing the dried slurry by deionized water, and then carrying out suction filtration and washing until filtrate is AgNO₃The solution was tested for the presence of no chloride ions. And finally, mechanically treating the washed slurry to obtain the transparent NFC dispersion liquid with positive charges on the surface.

Example 7

weighing 2.3g of urea, dissolving the urea in 2.9g of water, adding 1g of dry bamboo pulp into the urea aqueous solution, adding 1.4g of 2, 3-epoxypropyltrimethylammonium chloride after all the urea is dissolved, and putting the mixture into an oven at 100 ℃ and heating to constant weight. Then fully dispersing the dried slurry by deionized water, and then carrying out suction filtration and washing until filtrate is AgNO₃The solution was tested for the presence of no chloride ions. And finally, mechanically treating the washed slurry to obtain the transparent NFC dispersion liquid with positive charges on the surface.

Example 8

0.1g of urea is weighed out and dissolved in 2.9g of water, 1g of dry paper pulp is added into the urea aqueous solution, after complete dissolution, 5.8g of 2, 3-epoxypropyltrimethylammonium chloride is added, and the mixture is put into an oven at 100 ℃ and heated to constant weight. Then fully dispersing the dried slurry by deionized water, and then carrying out suction filtration and washing until filtrate is AgNO₃The solution was tested for the presence of no chloride ions. And finally, mechanically treating the washed slurry to obtain the transparent NFC dispersion liquid with positive charges on the surface.

Example 9

1.4g of urea is weighed and dissolved in 3.3g of wet pulp, after all the urea is dissolved, 5.8g of 2, 3-epoxypropyltrimethylammonium chloride is added, and the mixture is put into an oven at 150 ℃ and heated to constant weight. Then fully dispersing the dried slurry by deionized water, and then carrying out suction filtration and washing until filtrate is AgNO₃The solution was tested for the presence of no chloride ions. And finally, mechanically treating the washed slurry to obtain the transparent NFC dispersion liquid with positive charges on the surface.

Example 10

weighing 2.7g of thiourea, dissolving in 3.3g of wet pulp, adding 2.9g of 2, 3-epoxypropyltrimethylammonium chloride after all the thiourea is dissolved, and putting the mixture into an oven at 100 ℃ to heat to constant weight. The dry is then dried with deionized waterFully dispersing the dried slurry, and performing suction filtration and washing until the filtrate is subjected to AgNO₃The solution was tested for the presence of no chloride ions. And finally, mechanically treating the washed slurry to obtain the transparent NFC dispersion liquid with positive charges on the surface.

Example 11

2.4g of urea is weighed and dissolved in 5g of wet pulp, after all the urea is dissolved, 1.4g of 2, 3-epoxypropyltrimethylammonium chloride is added, and the mixture is put into an oven at 100 ℃ and heated to constant weight. Then fully dispersing the dried slurry by deionized water, and then carrying out suction filtration and washing until filtrate is AgNO₃The solution was tested for the presence of no chloride ions. And finally, mechanically treating the washed slurry to obtain the transparent NFC dispersion liquid with positive charges on the surface.

Comparative example 1

The process for preparing high-charge Q-NFC under the conditions of strong alkali and high temperature is as follows:

1g of dry bamboo pulp was blended with a 5% NaOH aqueous solution to make the solid content of the bamboo pulp 5%, and then 29g of 2, 3-epoxypropyltrimethylammonium chloride was added and stirred at 65 ℃ for 8 hours. The pH of the mixed slurry was then adjusted to 7 with 0.1M hydrochloric acid and the slurry was washed thoroughly with deionized water until no significant chloride ions were present in the filtrate. And finally, mechanically treating the washed slurry to obtain the NFC dispersion liquid with positive charges on the surface.

Comparative example 2

The process for preparing low-charge Q-NFC under the conditions of strong alkali and high temperature is as follows:

1g of dry bamboo pulp was blended with a 5% NaOH aqueous solution to make the solid content of the bamboo pulp 5 wt%, and then 5.8g of 2, 3-epoxypropyltrimethylammonium chloride was added and stirred at 65 ℃ for 8 hours. The pH of the mixed slurry was then adjusted to 7 with 0.1M hydrochloric acid and the slurry was washed thoroughly with deionized water until no significant chloride ions were present in the filtrate. And finally, mechanically treating the washed slurry to obtain the NFC dispersion liquid with positive charges on the surface.

Comparative example 3

The process for preparing low-charge Q-NFC under the conditions of low alkali concentration and high temperature is as follows:

1g of dry bamboo pulp was blended with a 1% NaOH aqueous solution to make the solid content of the bamboo pulp 5 wt%, and then 5.8g of 2, 3-epoxypropyltrimethylammonium chloride was added and stirred at 65 ℃ for 8 hours. The pH of the mixed slurry was then adjusted to 7 with 0.1M hydrochloric acid and the slurry was washed thoroughly with deionized water until no significant chloride ions were present in the filtrate. And finally, mechanically treating the washed slurry to obtain the NFC dispersion liquid with positive charges on the surface.

Comparative example 4

The process for preparing Q-NFC under the conditions of weak base and room temperature is as follows:

2.7g of urea is weighed and dissolved in 3.3g of wet paper pulp, after all the urea is dissolved, 2.9g of 2, 3-epoxypropyltrimethylammonium chloride is added, and the reaction is carried out at room temperature. Then, deionized water is used for fully dispersing the mixed slurry, and then the mixed slurry is filtered, filtered and washed until filtrate is AgNO₃The solution was tested for the presence of no chloride ions. Finally, the washed slurry is mechanically treated, and the target product cannot be obtained.

Table 1. preparation process of Q-NFC under weak base condition and corresponding performance parameters thereof

The calculation formula of the trimethyl ammonium chloride group content in Q-NFC is as follows:

in the formula: v is AgNO consumed in the titration process₃A total volume (L); c_AgNO3Is AgNO₃Molar concentration of the solution (mmol/L); m is the exact mass (g) of the dried Q-NFC sample to be weighed.

The above-mentioned embodiments are further described in detail for the purpose of illustrating the invention, and it should be understood that any modification, equivalent replacement or improvement made within the spirit and principle of the invention should be included in the scope of the invention.

Claims

1. A preparation method of high-efficiency and environment-friendly cation nano-fibrillated cellulose is characterized by comprising the following steps:

(1) paper pulp pretreatment:

dissolving weak base in wet paper pulp with solid content of 10-35 wt%, continuously stirring until uniform mixing is achieved, then adding a cationic reagent, stirring until full mixing is achieved, and putting the mixed pulp into a 50-150 ℃ drying oven for heating and drying until constant weight is achieved; or adding the dried paper pulp into a weak base aqueous solution to enable the solid content of the paper pulp to be 10-35 wt%, continuously stirring until the solid content is uniformly mixed, then adding a cationic reagent, stirring until the mixture is fully mixed, and putting the mixed slurry into a drying oven at 50-150 ℃ for heating and drying until the weight is constant;

(2) Q-NFC preparation: and dispersing the dried slurry in deionized water, fully washing with distilled water to remove unreacted cationic reagents, and mechanically treating to obtain a uniform and viscous Q-NFC aqueous dispersion.

2. The method of claim 1, wherein the method comprises the following steps: in the step (1), the paper pulp is various bleached or unbleached paper pulp; the pulp is selected from chemical pulp, chemimechanical pulp, semi-mechanical pulp, mechanical pulp and industrial waste pulp.

3. The method of claim 1, wherein the method comprises the following steps: in the step (1), the weak base is selected from any one of urea, thiourea and melamine, or a plurality of the weak bases are mixed according to any proportion.

4. The method of claim 1, wherein the method comprises the following steps: in the step (1), weak base is dissolved in wet paper pulp with the solid content of 10-35 wt%, wherein the mass ratio of the weak base to water in the wet paper pulp is 0.1-1.2: 1, and the weak base can be completely dissolved and cannot be separated out.

5. The method of claim 1, wherein the method comprises the following steps: in the step (1), adding the dry paper pulp into a weak base aqueous solution, wherein the mass ratio of weak base to water in the weak base aqueous solution is 0.1-1.2: 1.

6. The method of claim 1, wherein the method comprises the following steps: in the step (1), the cationic reagent is selected from any one of 2, 3-epoxypropyltrimethylammonium chloride (EPTAC), 3-chloro-2-hydroxypropyltrimethylammonium chloride, (2-chloroethyl) trimethylammonium chloride, or a mixture of a plurality of the above in any proportion.

7. The method of claim 1, wherein the method comprises the following steps: in the step (1), the mass ratio of the cationic reagent to the dry paper pulp is 0.36-5.8: 1.

8. The method of claim 1, wherein the method comprises the following steps: in the step (2), the mechanical treatment adopts high-pressure homogenization, and the conditions of the high-pressure homogenization are as follows: the pressure is 700-900MPa, the time is 5-15 minutes, and the flow rate is 70-150 ml/min.