阅读说明：本技术 一种纳米纤维素的超疏水改性方法 (Super-hydrophobic modification method of nano-cellulose ) 是由 惠岚峰 王凌媛 王晓迪 王宇 耿合斌 于 2021-07-23 设计创作，主要内容包括：本发明涉及纳米纤维素超疏水改性,提供了一种纳米纤维素的超疏水改性方法。该发明首先利用TEMPO/NaClO/NaBr氧化体系和超声振荡相结合的方法制备不同羧基含量的纳米纤维素,再选择表面能低的十八胺为疏水改性剂,纳米纤维中的羧基和十八胺中的氨基可通过络合反应将疏水长链接枝在纳米纤维素表面,同时,选择粘附性物质聚多巴胺涂覆在改性后的纳米纤维表面,不但可以保护与纳米纤维素接枝的十八胺长链,还能将体系中游离的十八胺吸附在纳米纤维素表面。本发明制备的疏水性纳米纤维素薄膜应用于油水分离、隔水薄膜等领域。(The invention relates to super-hydrophobic modification of nano-cellulose, and provides a super-hydrophobic modification method of nano-cellulose. According to the method, firstly, a TEMPO/NaClO/NaBr oxidation system and ultrasonic oscillation combined method is utilized to prepare nanocelluloses with different carboxyl contents, then octadecylamine with low surface energy is selected as a hydrophobic modifier, a hydrophobic long chain is grafted on the surface of the nanocellulose through a complexing reaction between carboxyl in the nanofibers and amino in the octadecylamine, and meanwhile, an adhesive substance polydopamine is selected to be coated on the surface of the modified nanocellulose, so that the octadecylamine long chain grafted with the nanocellulose can be protected, and free octadecylamine in the system can be adsorbed on the surface of the nanocellulose. The hydrophobic nano cellulose film prepared by the invention is applied to the fields of oil-water separation, water-resisting films and the like.)

1. A super-hydrophobic modification method of nano-cellulose is characterized by comprising the following steps: the method comprises the following steps:

(1) soaking the fiber pulp board in 5-10% concentration NaOH solution, defibering, PFI pulping, washing the pulp with distilled water, centrifuging and cold drying.

(2) Adjusting the concentration of the pulp sample prepared in the step (1) to 5%, carrying out oxidation pretreatment by using a TEMPO/NaClO/NaBr oxidation system, and then putting the pulp sample into a groove type ultrasonic cleaner for ultrasonic oscillation treatment to obtain a nano cellulose suspension;

(3) freeze-drying the nano-cellulose suspension prepared in the step (2) to obtain nano-cellulose powder; mixing nano cellulose powder and octadecylamine solid powder according to different mass ratios, adding an ethanol solution, adjusting the pH value by using HCl after ultrasonic dispersion, and then putting the solution into a water bath kettle at 60 ℃ for magnetic stirring reaction for 3-5 hours to obtain hydrophobic nano cellulose;

(4) and (4) blending the reaction system obtained in the step (3) with dopamine solutions with different concentrations, performing ultrasonic dispersion, and then putting the suspension into a 50 ℃ water bath kettle to stir and react for 24 hours to obtain the super-hydrophobic nano cellulose suspension with the surface coated with black viscous substances.

2. The method for preparing the green nontoxic nano cellulose super hydrophobic film according to claim 1, characterized in that: in the step (1), the pulp sample is soaked for 24 hours by using NaOH solution with the mass fraction of 5-10%.

3. The method for modifying the superhydrophobicity of the nanocellulose as claimed in claim 1, wherein: in the step (2), the adding amount of NaBr is 0.1g/g of nano-cellulose; TEMPO is added in an amount of 0.015g/g of nano-cellulose; the adding amount of NaClO is 4-12mmol/g of nano-cellulose.

4. The method for modifying the superhydrophobicity of the nanocellulose as claimed in claim 1, wherein: in the step (3), the mass ratio of the octadecylamine to the nano cellulose powder is 1: 2-1: 1-2: 1.

5. The method for modifying the superhydrophobicity of the nanocellulose as claimed in claim 1, wherein: and (4) determining the concentration of the dopamine in the step (4) to be 1g/L-3 g/L.

6. Super-hydrophobic nanocellulose obtained by a method for the super-hydrophobic modification of nanocellulose according to any one of claims 1 to 5.

Technical Field

The invention relates to the field of nano-cellulose super-hydrophobic modification, in particular to a super-hydrophobic modification method of nano-cellulose.

Background

The nano-cellulose is cellulose with the diameter of 1-100 nm, and has the characteristics of cellulose, such as: the material is reproducible, degradable, good in biocompatibility, strong in chemical stability and the like; also has the advantages of high length-width ratio, high elastic modulus, high specific surface area and the like which are peculiar to the nano-scale material. Generally, the preparation method of the nanocellulose comprises a physical grinding method, a chemical hydrolysis method, a biological enzymolysis method, a chemical physical method and the like, wherein the chemical physical method is to oxidize a hydroxyl group at the C6 position in a cellulose glucose unit into a carboxyl group by a TEMPO oxidation method and prepare the nanocellulose by an auxiliary ultrasonic oscillation method, and the nanocellulose prepared by the method not only has the original active hydroxyl group, but also has the carboxyl group obtained by oxidizing the hydroxyl group at the specific position, so that the nanocellulose can react with various reagents.

In recent years, nanocellulose is rapidly developed in the fields of functional hydrogel, conductive aerogel, metal ion adsorption, bionic dressing, flexible electronics and the like, and has a wide application prospect. But also because of the existence of a large amount of hydrophilic groups, the nanocellulose material is easy to absorb moisture in the environment to cause stiffness reduction, which limits the development speed of nanocellulose. Therefore, the hydrophobic modification of the nano-cellulose is an important way for promoting the rapid development and expanding the application field of the nano-cellulose.

At present, the method for carrying out hydrophobic modification on nano-cellulose mainly comprises 1) physical adsorption modification; 2) esterification modification; 3) graft copolymerization; 4) modifying a silane coupling agent; most of the modification processes require three or more hydrophobic modifiers or organic solvents for dispersion, such as toluene, acetone, tetrahydrofuran and other toxic reagents, so that reduction of the use of the modifying reagents, improvement of the hydrophobic modification efficiency and reduction of the use of the toxic reagents are problems to be solved urgently.

According to the invention, only octadecylamine containing a hydrophobic long chain is used as a modifier, and the octadecylamine is grafted on the surface of the nanocellulose through a complex reaction between carboxyl in the nanocellulose and amino in the octadecylamine, so that the hydrophobic property of the nanocellulose is improved; and then further coating with polydopamine, so that free dopamine can be adsorbed on the surface of the nano-cellulose to achieve the super-hydrophobic effect. The method only uses ethanol and water as dispersing agents, avoids the use of toxic reagents, is a green and nontoxic hydrophobic modification method for the nano-cellulose, and has optimistic application prospect.

Disclosure of Invention

In view of the problems or defects of the prior art, the invention aims to provide a method for modifying the superhydrophobicity of the nanocellulose. According to the invention, octadecylamine containing a hydrophobic long chain is grafted on the surface of the nano-cellulose, so that the hydrophobic property of the nano-cellulose is improved, and the problem that the nano-cellulose material is easy to absorb moisture in the environment is solved.

In order to achieve the purpose, bleached sulfate hardwood pulp is used as a raw material, a TEMPO/NaClO/NaBr oxidation system is used for assisting ultrasonic oscillation to prepare nano-cellulose, nano-cellulose with different carboxyl contents is obtained by controlling reaction conditions, an octadecylamine/dopamine system is used for modifying the nano-cellulose and performing suction filtration to obtain a film, and the prepared film has good super-hydrophobic performance and friction resistance.

The technical scheme adopted by the invention is as follows:

(1) soaking the fiber pulp board in NaOH solution of certain concentration, defibering, PFI pulping, washing the pulp sample with distilled water, centrifuging and cold drying.

(2) Adjusting the concentration of the pulp sample prepared in the step (1) to 5%, carrying out oxidation pretreatment by using a TEMPO/NaClO/NaBr oxidation system, and then putting the pulp sample into a groove type ultrasonic cleaner for ultrasonic oscillation treatment to obtain a nano cellulose suspension;

(3) freeze-drying the nano-cellulose suspension prepared in the step (2) to obtain nano-cellulose powder; mixing nano cellulose powder and octadecylamine solid powder according to different mass ratios, adding an ethanol solution, adjusting the pH value by using HCl after ultrasonic dispersion, and then putting the solution into a water bath kettle at 60 ℃ for magnetic stirring reaction for 3-5 hours to obtain hydrophobic nano cellulose;

(4) and (4) blending the reaction system obtained in the step (3) with dopamine solutions with different concentrations, performing ultrasonic dispersion, and then putting the suspension into a 50 ℃ water bath kettle to stir and react for 24 hours to obtain the super-hydrophobic nano cellulose suspension with the surface coated with black viscous substances.

Further, according to the technical scheme, in the step (1), the pulp sample is soaked in a NaOH solution with the mass fraction of 5% -10% for 24 hours. Preferably, the selected NaOH concentration is 8%.

Further, according to the technical scheme, the adding amount of NaBr in the step (2) is 0.1g/g of nano cellulose; TEMPO is added in an amount of 0.015g/g of nano-cellulose; the adding amount of NaClO is 4-12mmol/g of nano-cellulose; preferably, in the technical scheme, the adding amount of the NaClO is 8mmol/g of the nano-cellulose.

Further, in the technical scheme, the mass ratio of the octadecylamine to the nano cellulose powder in the step (3) is 1: 2-2: 1, and the used organic solvent only contains ethanol and meets the requirement of a composite green reagent. Preferably, in the technical scheme, the mass ratio of the octadecylamine to the nano cellulose powder is determined to be 1: 1.

Further, in the above technical scheme, Tris (hydroxymethyl) aminomethane (Tris) is used in the step (4) to adjust the pH of the reaction system to 8.5.

Further, in the above technical solution, the concentration of dopamine in step (4) is determined to be 1g/L-3g/L, preferably, in the above technical solution, the concentration of dopamine is determined to be 2 g/L.

The invention provides super-hydrophobic nano-cellulose prepared by the method.

Compared with the prior art, the invention relates to a super-hydrophobic modification method of nano-cellulose, and the innovation points are as follows:

(1) the fibers can be swelled by soaking with NaOH, and the structure is looser after a part of soluble cellulose and hemicellulose are removed. The soaked cellulose is beneficial to preparing the nano cellulose with high carboxyl content.

(2) According to the invention, only octadecylamine is used as a hydrophobic modifier, the super-hydrophobic effect can be achieved through a complex reaction and the surface adsorption of polydopamine, and the hydrophobic modification process only uses water and ethanol as dispersants, so that a green chemical concept is compounded.

(3) According to the invention, the viscous substance polydopamine is used, so that the polydopamine can be coated on the outer layer of the nano-cellulose grafted by octadecylamine, the effect of reinforcing the hydrophobic long chain is achieved, free octadecylamine in the system is adsorbed on the surface of the nano-cellulose, and the super-hydrophobic property of the nano-cellulose material is enhanced.

Drawings

Fig. 1 is a contact angle diagram of a nanocellulose superhydrophobic film prepared in example 5 of the present invention.

Detailed Description

The innovative features will be described more fully and clearly in order to explain the technical design of the invention. The following detailed description is to be read in connection with specific embodiments.

Example 1:

(1) preparing nano-cellulose: weighing 30g of oven-dried bleached sulfate hardwood pulp, soaking in 5% NaOH solution for 12 hr, defibering (20000r), pulping with PFI (4000r), washing with distilled water, centrifuging for three times (8000r/min, 20min), and cold drying for 48 hr. 5g of the cold-dried pulp was weighed and 95ml of distilled water was added to obtain a 5% strength cellulose suspension. 0.5g of NaBr, 0.06g of TEMPO and 20mmol of NaClO are added in sequence, and 0.1mol/L of HCl and 0.1mol/L of NaOH are added dropwise to control the pH value of the reaction system to be kept at 10. Placing the pulp sample into a groove type ultrasonic wave to carry out ultrasonic oscillation treatment for 3h, adding ethanol to stop reaction, carrying out centrifugal washing for three times (8000r/min, 15min), and freeze-drying to obtain nano cellulose powder;

(2) preparation of hydrophobic nanocellulose particles: weighing 2g of nano cellulose powder, and adding 25ml of distilled water; weighing 1g of octadecylamine powder, adding 75ml of ethanol, and stirring for dissolving; mixing the two solutions to obtain a reaction system with the mass ratio of the nano-cellulose powder to the octadecylamine powder being 2: 1, adjusting the pH of the system to be about 7.5 by using 0.1mol/L HCl, and putting the reaction system into a 60 ℃ water bath kettle to perform magnetic stirring reaction for 5 hours to obtain the hydrophobic nano-cellulose.

(3) Polydopamine coated hydrophobic nanocellulose: weighing 1g of dopamine solid, adding 99ml of distilled water to obtain 1g/L of dopamine solution, and adjusting the pH value of the dopamine solution to be 8.5 by using Tris (hydroxymethyl) aminomethane (Tris); and blending the solution obtained in the previous step with a dopamine solution, performing ultrasonic dispersion, then placing the suspension into a 50 ℃ water bath kettle, stirring and reacting for 24 hours, and centrifuging and cold drying the suspension to obtain the super-hydrophobic nano-cellulose with the surface coated with the black viscous substance.

Example 2:

(1) preparing nano-cellulose: weighing 30g of oven-dried bleached sulfate hardwood pulp, soaking in 8% NaOH solution for 12 hr, defibering (20000r), pulping with PFI (4000r), washing with distilled water, centrifuging for three times (8000r/min, 20min), and cold drying for 48 hr. 5g of the cold-dried pulp was weighed and 95ml of distilled water was added to obtain a 5% strength cellulose suspension. 0.5g of NaBr, 0.06g of TEMPO and 40mmol of NaClO are added in sequence, and 0.1mol/L of HCl and 0.1mol/L of NaOH are added dropwise to control the pH value of the reaction system to be kept at 10. Placing the pulp sample into a groove type ultrasonic wave to carry out ultrasonic oscillation treatment for 3h, adding ethanol to stop reaction, carrying out centrifugal washing for three times (8000r/min, 15min), and freeze-drying to obtain nano cellulose powder;

(2) preparation of hydrophobic nanocellulose particles: weighing 1g of nano cellulose powder, and adding 25ml of distilled water; weighing 2g of octadecylamine powder, adding 75ml of ethanol, and stirring for dissolving; mixing the two solutions to obtain a reaction system with the mass ratio of the nano-cellulose powder to the octadecylamine powder being 1: 2, adjusting the pH of the system to be about 7.5 by using 0.1mol/L HCl, and putting the reaction system into a 60 ℃ water bath kettle to perform magnetic stirring reaction for 4 hours to obtain the hydrophobic nano-cellulose.

(3) Polydopamine coated hydrophobic nanocellulose: weighing 3g of dopamine solid, adding 97ml of distilled water to obtain 1g/L of dopamine solution, and adjusting the pH value of the dopamine solution to be 8.5 by using Tris (hydroxymethyl) aminomethane (Tris); and blending the solution obtained in the previous step with a dopamine solution, performing ultrasonic dispersion, then placing the suspension into a 50 ℃ water bath kettle, stirring and reacting for 24 hours, and after the reaction is finished, centrifuging and cold drying the suspension to obtain the super-hydrophobic nano-cellulose with the surface coated with the black viscous substance.

Example 3:

(1) preparing nano-cellulose: weighing 30g of oven-dried bleached sulfate hardwood pulp, soaking in 10% NaOH solution for 12 hr, defibering (20000r), pulping with PFI (4000r), washing with distilled water, centrifuging for three times (8000r/min, 20min), and cold drying for 48 hr. 5g of the cold-dried pulp was weighed and 95ml of distilled water was added to obtain a 5% strength cellulose suspension. 0.5g of NaBr, 0.06g of TEMPO and 60mmol of NaClO are added in sequence, and 0.1mol/L of HCl and 0.1mol/L of NaOH are added dropwise to control the pH value of the reaction system to be kept at 10. Placing the pulp sample into a groove type ultrasonic wave to carry out ultrasonic oscillation treatment for 3h, adding ethanol to stop reaction, carrying out centrifugal washing for three times (8000r/min, 15min), and freeze-drying to obtain nano cellulose powder;

(2) preparation of hydrophobic nanocellulose particles: weighing 1g of nano cellulose powder, and adding 25ml of distilled water; weighing 1g of octadecylamine powder, adding 75ml of ethanol, and stirring for dissolving; mixing the two solutions to obtain a reaction system with the mass ratio of the nano-cellulose powder to the octadecylamine powder being 1: 1, adjusting the pH of the system to be about 7.5 by using 0.1mol/L HCl, and putting the reaction system into a 60 ℃ water bath kettle to perform magnetic stirring reaction for 3 hours to obtain the hydrophobic nano-cellulose.

(3) Polydopamine coated hydrophobic nanocellulose: weighing 2g of dopamine solid, adding 98ml of distilled water to obtain 2g/L of dopamine solution, and adjusting the pH value of the dopamine solution to be 8.5 by using Tris (hydroxymethyl) aminomethane (Tris); and blending the solution obtained in the previous step with a dopamine solution, performing ultrasonic dispersion, then placing the suspension into a 50 ℃ water bath kettle, stirring and reacting for 24 hours, and after the reaction is finished, centrifuging and cold drying the suspension to obtain the super-hydrophobic nano-cellulose with the surface coated with the black viscous substance.

Example 4:

(1) preparing nano-cellulose: weighing 30g of oven-dried bleached sulfate hardwood pulp, soaking in 8% NaOH solution for 12 hr, defibering (20000r), pulping with PFI (4000r), washing with distilled water, centrifuging for three times (8000r/min, 20min), and cold drying for 48 hr. 5g of the cold-dried pulp was weighed and 95ml of distilled water was added to obtain a 5% strength cellulose suspension. 0.5g of NaBr, 0.06g of TEMPO and 60mmol of NaClO are added in sequence, and 0.1mol/L of HCl and 0.1mol/L of NaOH are added dropwise to control the pH value of the reaction system to be kept at 10. Placing the pulp sample into a groove type ultrasonic wave to carry out ultrasonic oscillation treatment for 3h, adding ethanol to stop reaction, carrying out centrifugal washing for three times (8000r/min, 15min), and freeze-drying to obtain nano cellulose powder;

(2) preparation of hydrophobic nanocellulose particles: weighing 1g of nano cellulose powder, and adding 25ml of distilled water; weighing 2g of octadecylamine powder, adding 75ml of ethanol, and stirring for dissolving; mixing the two solutions to obtain a reaction system with the mass ratio of the nano-cellulose powder to the octadecylamine powder being 1: 2, adjusting the pH of the system to be about 7.5 by using 0.1mol/L HCl, and putting the reaction system into a 60 ℃ water bath kettle to perform magnetic stirring reaction for 5 hours to obtain the hydrophobic nano-cellulose.

(3) Polydopamine coated hydrophobic nanocellulose: weighing 3g of dopamine solid, adding 97ml of distilled water to obtain 1g/L of dopamine solution, and adjusting the pH value of the dopamine solution to be 8.5 by using Tris (hydroxymethyl) aminomethane (Tris); and blending the solution obtained in the previous step with a dopamine solution, performing ultrasonic dispersion, then placing the suspension into a 50 ℃ water bath kettle, stirring and reacting for 24 hours, and after the reaction is finished, centrifuging and cold drying the suspension to obtain the super-hydrophobic nano-cellulose with the surface coated with the black viscous substance.

Example 5:

(1) preparing nano-cellulose: weighing 30g of oven-dried bleached sulfate hardwood pulp, soaking in 10% NaOH solution for 12 hr, defibering (20000r), pulping with PFI (4000r), washing with distilled water, centrifuging for three times (8000r/min, 20min), and cold drying for 48 hr. 5g of the cold-dried pulp was weighed and 95ml of distilled water was added to obtain a 5% strength cellulose suspension. 0.5g of NaBr, 0.06g of TEMPO and 40mmol of NaClO are added in sequence, and 0.1mol/L of HCl and 0.1mol/L of NaOH are added dropwise to control the pH value of the reaction system to be kept at 10. Placing the pulp sample into a groove type ultrasonic wave to carry out ultrasonic oscillation treatment for 3h, adding ethanol to stop reaction, carrying out centrifugal washing for three times (8000r/min, 15min), and freeze-drying to obtain nano cellulose powder;

(2) preparation of hydrophobic nanocellulose particles: weighing 1g of nano cellulose powder, and adding 25ml of distilled water; weighing 1g of octadecylamine powder, adding 75ml of ethanol, and stirring for dissolving; mixing the two solutions to obtain a reaction system with the mass ratio of the nano-cellulose powder to the octadecylamine powder being 1: 1, adjusting the pH of the system to be about 7.5 by using 0.1mol/L HCl, and putting the reaction system into a 60 ℃ water bath kettle to perform magnetic stirring reaction for 4 hours to obtain the hydrophobic nano-cellulose.

(3) Polydopamine coated hydrophobic nanocellulose: weighing 2g of dopamine solid, adding 98ml of distilled water to obtain 2g/L of dopamine solution, and adjusting the pH value of the dopamine solution to be 8.5 by using Tris (hydroxymethyl) aminomethane (Tris); and blending the solution obtained in the previous step with a dopamine solution, performing ultrasonic dispersion, then placing the suspension into a 50 ℃ water bath kettle, stirring and reacting for 24 hours, and after the reaction is finished, centrifuging and cold drying the suspension to obtain the super-hydrophobic nano-cellulose with the surface coated with the black viscous substance.

Example 6:

(1) preparing nano-cellulose: weighing 30g of oven-dried bleached sulfate hardwood pulp, soaking in 10% NaOH solution for 12 hr, defibering (20000r), pulping with PFI (4000r), washing with distilled water, centrifuging for three times (8000r/min, 20min), and cold drying for 48 hr. 5g of the cold-dried pulp was weighed and 95ml of distilled water was added to obtain a 5% strength cellulose suspension. 0.5g of NaBr, 0.06g of TEMPO and 20mmol of NaClO are added in sequence, and 0.1mol/L of HCl and 0.1mol/L of NaOH are added dropwise to control the pH value of the reaction system to be kept at 10. Placing the pulp sample into a groove type ultrasonic wave to carry out ultrasonic oscillation treatment for 3h, adding ethanol to stop reaction, carrying out centrifugal washing for three times (8000r/min, 15min), and freeze-drying to obtain nano cellulose powder;

(2) preparation of hydrophobic nanocellulose particles: weighing 1g of nano cellulose powder, and adding 25ml of distilled water; weighing 1g of octadecylamine powder, adding 75ml of ethanol, and stirring for dissolving; mixing the two solutions to obtain a reaction system with the mass ratio of the nano-cellulose powder to the octadecylamine powder being 1: 1, adjusting the pH of the system to be about 7.5 by using 0.1mol/L HCl, and putting the reaction system into a 60 ℃ water bath kettle to perform magnetic stirring reaction for 4 hours to obtain the hydrophobic nano-cellulose.

(3) Polydopamine coated hydrophobic nanocellulose: weighing 2g of dopamine solid, adding 98ml of distilled water to obtain 2g/L of dopamine solution, and adjusting the pH value of the dopamine solution to be 8.5 by using Tris (hydroxymethyl) aminomethane (Tris); and blending the solution obtained in the previous step with a dopamine solution, performing ultrasonic dispersion, then placing the suspension into a 50 ℃ water bath kettle, stirring and reacting for 24 hours, and after the reaction is finished, centrifuging and cold drying the suspension to obtain the super-hydrophobic nano-cellulose with the surface coated with the black viscous substance.