CN108977045B - Method for chemically modifying water-based wood coating by using nano-cellulose dispersed graphene - Google Patents

Abstract

A method for chemically modifying an aqueous woodenware coating by nano-cellulose dispersed graphene relates to a method for modifying an aqueous woodenware coating. The problem that the existing nano-material modified waterborne wood coating has poor nano-particle dispersibility and poor mechanical property of a waterborne paint film is solved. The method comprises the following steps: firstly, preparing nano-cellulose water solution containing hemicellulose: sequentially carrying out extraction treatment and delignification treatment on a cellulose raw material to obtain holocellulose, and then carrying out mechanical pretreatment or chemical mechanical mixing pretreatment to obtain nano-cellulose water solution containing hemicellulose; secondly, stably dispersing graphene by using nano-cellulose; and thirdly, carrying out in-situ chemical modification on the nano-cellulose dispersed graphene to obtain the waterborne wood lacquer. The method can obviously improve the mechanical properties of the waterborne wood coating, such as adhesive force, wear resistance, hardness, impact resistance and the like, and even endow the paint film with certain functions of electric conduction, heat conduction, ultraviolet resistance, aging resistance and the like. The invention is used in the field of water-based wood coatings.

Description

Method for chemically modifying waterborne wood coatings by nanocellulose dispersed graphene

technical field

The present invention relates to a method for modifying water-based wood coatings.

Background technique

Wood surface finishing is the main means of wood protection and decoration. Solvent-based paints and oil-based paints have always been the mainstream paint types in the furniture industry. However, in recent years, with the strengthening of people's awareness of environmental protection and the introduction of national mandatory policies, the application of solvent-based and oil-based coatings with high VOC emission characteristics has been greatly restricted, while environment-friendly water-based wood coatings with low VOC emission characteristics have become more and more Favored by the industry, it has become the mainstream trend in the development of wood coatings. Unfortunately, the water-based wood coatings on the market have problems such as low solid content, weak interaction between components and the substrate, resulting in mechanical properties such as film hardness, wear resistance, adhesion, and impact resistance. The UV aging resistance is generally not as good as that of oil-based coatings with mature technology, so the modification of water-based wood coatings is imperative.

In recent years, there are many methods to modify water-based wood coatings by using nanomaterials. ① The method of nanocellulose modified water-based coating, but the dispersion of nanocellulose is regulated by surfactants, the components are complex and the performance of the paint film is greatly affected by small molecular surfactants; and the coating is only added by nanocellulose. The improvement of adhesion, abrasion resistance and UV aging resistance has no positive effect. ②Using nanocellulose rod-shaped crystals to improve the mechanical properties such as hardness and wear resistance of water-based wood coatings, but due to the low aspect ratio of nanocellulose rod-shaped crystals, the mechanical properties of the paint film are not significantly improved. 3. The method of preparing super-hydrophobic wood coatings by using nano-cellulose and nano-silica sol with water-dispersed resin, but nano-cellulose loaded with nano-silica first undergoes super-hydrophobic modification, which makes it extremely compatible with water-dispersed resin. There are huge differences in properties, poor affinity between the two phases, poor interfacial compatibility, and the superhydrophobic modified nanomaterials are very easy to agglomerate, resulting in poor improvement or even decline in the mechanical properties of the coating.

In a word, the inorganic nanoparticles modified waterborne wood coatings described by the above disclosed methods have the problems of poor dispersion of nanoparticles and poor improvement of coating mechanical properties and light transmittance; while organic nanocelluloses are mostly rod-shaped nanofibers Simple crystals, low aspect ratio, and limited improvement in mechanical properties of coatings; even if nanocellulose is compounded with SiO ₂ , TiO ₂ , and (oxidized) graphene, the method used has poor affinity with the polymer matrix. , Poor dispersion in the polymer matrix leads to poor improvement of the mechanical properties of the coating.

SUMMARY OF THE INVENTION

The invention aims to solve the problem of poor dispersion of nano particles in the existing nanomaterial modified waterborne wood coatings, resulting in poor mechanical properties of waterborne paint films, and provides a method for nanocellulose dispersed graphene chemically modified waterborne wood coatings.

The method for the nanocellulose dispersed graphene chemically modified water-based wood coating of the present invention comprises the following steps:

1. Preparation of hemicellulose-containing nanocellulose aqueous dispersion:

The cellulose raw material is sequentially subjected to extraction treatment and delignification treatment to obtain holocellulose, and then to mechanical pretreatment or chemical-mechanical mixing pretreatment to obtain a hemicellulose-containing nanocellulose aqueous dispersion;

The specific steps of the extraction process described in step 1 are:

The cellulose raw material is pulverized into 90-120 mesh powder, and then subjected to benzene alcohol extraction treatment for 10-12 hours. The phenyl alcohol is a mixture of toluene and absolute ethanol in a volume ratio of 2:1.

The concrete steps of delignification treatment described in step 1 are:

① Immerse the extracted cellulose powder in a sodium chlorite solution with a mass concentration of 1% to 1.2%, adjust the pH of the solution to 4 to 5 with glacial acetic acid, and then place the solution in a constant temperature water bath at 75 to 80 °C by magnetic force. Heating and stirring for 1～1.5h;

② Immerse the cellulose powder obtained in step ① into a sodium chlorite solution with a mass concentration of 1% to 1.2%, adjust the pH of the solution to 4 to 5 with glacial acetic acid, and then magnetically heat it in a constant temperature water bath at 75 to 80°C Stir for 1～1.5h;

③ Repeat step ② 5 to 6 times to basically remove lignin, then filter and wash the obtained liquid with a Buchner funnel until the filtrate is neutral, and finally obtain holocellulose;

Or the concrete steps of delignification treatment described in step 1 are:

Immerse the extracted cellulose powder in a hydrogen peroxide solution with a mass concentration of 30% to 35%, add magnesium silicate (use magnesium silicate as a stabilizer), and stir magnetically for 48 to 52 hours at room temperature to make the lignin basically remove; then filter and wash the obtained liquid with a Buchner funnel until the filtrate is neutral, and finally obtain helocellulose; wherein the mass of magnesium silicate is 1% to 1.5% of the mass of the hydrogen peroxide solution.

For the mechanical pretreatment described in step 1, the specific operation steps are as follows:

①Put the holocellulose into a 250mL beaker, and add deionized water until the mass fraction of holocellulose is 0.1%-0.3%

②Then use 600bar high-pressure homogenizing mechanical treatment for 30-40min to obtain a nanocellulose aqueous dispersion containing hemicellulose, in which hemicellulose accounts for 20%-30% of the mass of hemocellulose;

The chemical-mechanical mixing pretreatment described in step 1, the specific operation steps are as follows:

①Put the holocellulose into a 250mL beaker, add deionized water until the mass fraction of holocellulose is 0.1%-0.3%, then add sodium bromide and TEMPO reagent in turn, and then under magnetic stirring, add 2.5-3mL/ Add sodium hypochlorite at a speed of min, and then use sodium hydroxide with a concentration of 0.5 mol/L to adjust the pH to 10 to 10.5, and continue the reaction until the pH does not change; the mass of sodium bromide is 12% to 12% of the mass of holocellulose. 13%, the mass of TEMPO reagent is 1%-2% of the mass of holocellulose, and the mass of sodium hypochlorite is 25%-35% of the mass of holocellulose;

②After suction filtration and water washing, deionized water and sodium chlorite were added, and the pH value was adjusted to 4-5 with glacial acetic acid, and then magnetically stirred at 70-80 °C for 1-2 hours, and the carboxyl group was obtained by suction filtration and water washing. cellulose; wherein the mass ratio of deionized water and holocellulose is (95-105):3, and the mass of sodium chlorite is 25%-35% of the mass of holocellulose;

③ Then reconstitute 0.1%-0.3% carboxylated cellulose aqueous dispersion, and then mechanically disperse it by a high-speed mixer at 14,000-16,000 rpm for 20-30 minutes to obtain a hemicellulose-containing nanocellulose aqueous dispersion, in which the hemicellulose is dispersed. The cellulose accounts for 10% to 20% of the quality of the holocellulose.

The cellulose raw material described in step 1 is biomass raw material powder with a particle size of 100 mesh or more (such as wood powder, crop straw powder, waste paper, leaves, bast fiber raw materials, etc.);

2. Nanocellulose stably dispersed graphene:

①Place graphene or reduced graphene in the hemicellulose-containing nanocellulose aqueous dispersion obtained in step 1, mechanically disperse it under high-speed stirring at 14000-16000 rpm for 1-20 minutes, and then disperse under 900-1100W ultrasonic conditions 1 to 20 minutes to obtain a uniformly dispersed nanocellulose/graphene aqueous dispersion; wherein the graphene or reduced graphene is 0.1% to 0.3% of the mass of the hemicellulose-containing nanocellulose aqueous dispersion;

②Then the nanocellulose/graphene aqueous dispersion is heated under stirring conditions of 600～1000rpm to evaporate the water to obtain an aqueous dispersion with a mass concentration of 10%～20%, and then add acetone to the aqueous dispersion to make the acetone Account for 30% to 40% of the volume of the aqueous dispersion, then disperse for 1 to 20 minutes under 400 to 600W ultrasonic conditions, and then centrifuge at 8000 to 10000 rpm to obtain a precipitate;

3. Add acetone to the precipitate, then disperse under 500～600W ultrasonic conditions for 1～20min, and then centrifuge at 8000～9000rpm to obtain the precipitate; wherein the mass ratio of the precipitate to acetone is 1:(9～11);

④ Repeat step ③ for 5 to 6 times, then add acetone to the precipitate to obtain an acetone dispersion of the precipitate with a solid content of 20% to 25%;

The preparation method of the reduced graphene described in the step 2 is specifically:

The commercially available graphene oxide is placed in a commercially available hydrogen iodide solution, placed at room temperature for 20min～30min, and then washed alternately with water and ethanol for 3～5 times, wherein the water wash is 1～10min each time, and the ethanol wash is 1～10min each time. 10min to obtain reduced graphene;

3. In-situ chemical modification of nanocellulose-dispersed graphene water-based wood paint:

① Mix isophorone diisocyanate and the acetone dispersion of the precipitate obtained in step 2, stir evenly (within 0.5% of the solid content in the water-based paint), and then pour it into a dry tetrafluoroethylene solution with a stirrer and a condenser tube. In the flask, heated to 65～70℃ and reacted for 1～2h;

②Then add polypropylene glycol-2000 to the reaction system, keep 65～70℃ and react for 1.5～2h;

③ Slowly drop the acetone solution of 1,4-butanediol with a mass concentration of 15% to 25% into the reaction system, and control the dropping speed of the acetone solution of 1,4-butanediol to control the temperature of the system at 70- 80℃, the reaction is 1.5～2h;

④ Dissolve dimethylolpropionic acid with a small amount of N-methylpyrrolidone, then add it to the reaction system, control the reaction temperature to be 65～75°C, use acetone to control the viscosity of the reaction solution to be lower than 100mPa·S, and react for 3.5～ 4h;

⑤Add triethylamine into the reaction system, and neutralize the reaction for 15-20min; wherein isophorone diisocyanate, the acetone dispersion of the precipitate obtained in step 2, polypropylene glycol-2000, 1,4-butanediol The mass ratio of acetone solution, dimethylolpropionic acid and triethylamine is (50～60):(10～20):(45～60):(15～20):(5～8):(3～ 5).

⑥ Then disperse the reaction solution with a high-speed disperser to obtain an in-situ chemically modified water-based polyurethane emulsion containing hemicellulose-containing nanocellulose-dispersed graphene, which is a nano-cellulose-dispersed graphene chemically modified waterborne wood coating.

During the modification process of step 3, continuous stirring is performed.

The water-based acrylate emulsion can be added to the emulsion obtained in ⑥ to obtain a blended water-based polyurethane acrylate emulsion. Adding water-based acrylate emulsion to obtain another water-based wood coating, the properties of the two coatings are different: the water-based polyurethane emulsion is a single-component wood coating, and the blended coating has the advantages of both water-based polyurethane and acrylate.

Beneficial effects of the present invention:

The invention proposes a method for in-situ chemical modification of water-based wood lacquer with nanocellulose dispersed graphene with hemicellulose, and the characteristics are as follows:

①The hemicellulose segment is short, and it is grafted on the long nanocellulose segment to form a "brush" shape with a large specific surface area; ②The hemicellulose contains more hydroxyl functional groups than cellulose, which can better absorb water in water. It is stably dispersed in the liquid and has greater hydroxyl reactivity; ③ Both cellulose and hemicellulose have a six-membered ring structure, which can have a strong "coupling" effect with the six-membered ring of graphene to form a stable combination .

This results in the following advantages:

①The nanocellulose with hemicellulose forms a strong "coupling" force with graphene, so that the graphene is coated with nanocellulose to form a stable aqueous dispersion; ②The existence of abundant hydroxyl functional groups improves the nanofiber The dispersion stability of the cellulose in the aqueous solution is conducive to the better dispersion of the nanocellulose in the polymer matrix, thereby modifying the performance of the water-based paint film; ③ The abundant hydroxyl groups facilitate the passage of the nanocellulose and the emulsion colloid polymer of the water-based paint "Hydrogen bonds" or "chemical bonds" between polar functional groups form stronger interactions, thereby better enhancing the performance of water-based paint films; ④ "brush"-shaped nanocellulose can form a dendritic bond with the polymer matrix , using the huge specific surface area and chemical/hydrogen bonding to enhance the molecular network structure of the polymer matrix, thereby theoretically improving the mechanical strength of the paint film; The specific surface area and mechanical strength of the paint film significantly improve the mechanical properties of the paint film, and through the conductive link formed by the lamellae, the paint film has certain functions such as thermal conductivity, electrical conductivity, and anti-ultraviolet aging resistance; The extraction step of nanocellulose simplifies the process flow; ⑦The hemicellulose is wrapped around the nanocellulose, and the structure is loose, which makes it easier to disperse the "hemicellulose-coated nanocellulose" when the nanocellulose is mechanically separated and extracted. ", less energy consumption, and avoids the "shear-induced short" problem of the nanocellulose molecular chain, which is beneficial to obtain nanocellulose with a higher aspect ratio, potentially increasing the specific surface area of nanocellulose, and then significantly enhancing the polymerization of the paint film. physical properties.

This method can significantly improve the mechanical properties of waterborne wood coatings such as adhesion, wear resistance, hardness, impact resistance, etc., and even endow the paint film with certain functions such as electrical conductivity, thermal conductivity, and anti-ultraviolet and aging resistance. The grade III is increased to the grade II after modification, the wear resistance is increased from 40% mass loss rate before modification to 10%~20% mass loss rate after modification, and the tensile strength is increased from 2.3% before modification. MPa increased to 3.5-4MPa after modification, hardness increased from hardness B before modification to HB-H after modification, impact resistance increased from 2.1J/m ² before modification impact toughness After modification, the impact toughness of 2.8～3.5J/m ² , the gloss is not significantly reduced, the resistance value can reach 950～1200Ω, the thermal conductivity can reach 10～20w/m·k, and the yellowing index can be reduced by 30%～ 45%. It prolongs the service life of water-based wood coatings, broadens the application range of water-based wood coatings, and increases the added value of wood products.

Types of water-based paints applicable to this method: water-based polyurethane, water-based polyurethane-modified acrylate, water-based epoxy resin, water-based epoxy resin-modified acrylate, etc.

Description of drawings

Fig. 1 is the scanning electron microscope image of the two-dimensional reduced graphene obtained in embodiment 1 step 2;

Fig. 2 is the transmission electron microscope image of the hemicellulose-containing nanocellulose composite graphene obtained in step 2 of Example 1;

Fig. 3 is the scanning electron microscope picture of the two-dimensional graphene that step 1 of embodiment 2 obtains;

4 is a transmission electron microscope image of the hemicellulose-containing nanocellulose composite graphene obtained in step 2 of Example 2.

Detailed ways

The technical solutions of the present invention are not limited to the specific embodiments listed below, but also include any combination of specific embodiments.

Embodiment 1: The method of nanocellulose dispersed graphene chemically modified water-based wood coating of the present embodiment includes the following steps:

1. Preparation of hemicellulose-containing nanocellulose aqueous dispersion:

The cellulose raw material is sequentially subjected to extraction treatment and delignification treatment to obtain holocellulose, and then to mechanical pretreatment or chemical-mechanical mixing pretreatment to obtain a hemicellulose-containing nanocellulose aqueous dispersion;

The described mechanical pretreatment, the specific operation steps are as follows:

①Add deionized water to the holocellulose until the mass fraction of the holocellulose is 0.1%-0.3%;

②Then use 600bar high-pressure homogenizing mechanical treatment for 30-40min to obtain a nanocellulose aqueous dispersion containing hemicellulose, in which hemicellulose accounts for 20%-30% of the mass of hemocellulose;

Described chemical mechanical mixing pretreatment, specific operation steps are as follows:

①Add deionized water to the holocellulose until the mass fraction of holocellulose is 0.1%-0.3%, then add sodium bromide and TEMPO reagent in turn, and then add at a rate of 2.5-3mL/min under magnetic stirring Sodium hypochlorite, then adjust the pH value to 10-10.5, and continue the reaction until the pH value does not change; the mass of sodium bromide is 12%-13% of the mass of holocellulose, and the mass of TEMPO reagent is 1%-1% of the mass of holocellulose 2%, the quality of sodium hypochlorite is 25% to 35% of the quality of holocellulose;

②After suction filtration and water washing, add deionized water and sodium chlorite to adjust the pH value to 4-5, then magnetically stir at 70-80°C for 1-2 hours, filter and wash with water to obtain carboxylated cellulose ; wherein the mass ratio of deionized water and holocellulose is (95～105): 3, and the quality of sodium chlorite is 25%～35% of the quality of holocellulose;

③ Then reconstitute 0.1%-0.3% carboxylated cellulose aqueous dispersion, and then mechanically disperse it by a high-speed mixer at 14,000-16,000 rpm for 20-30 minutes to obtain a hemicellulose-containing nanocellulose aqueous dispersion, in which the hemicellulose is dispersed. The cellulose accounts for 10% to 20% of the quality of the holocellulose;

2. Nanocellulose stably dispersed graphene:

①Place graphene or reduced graphene in the hemicellulose-containing nanocellulose aqueous dispersion obtained in step 1, mechanically disperse it under high-speed stirring at 14000-16000 rpm for 1-20 minutes, and then disperse under 900-1100W ultrasonic conditions 1 to 20 minutes to obtain a uniformly dispersed nanocellulose/graphene aqueous dispersion; wherein the graphene or reduced graphene is 0.1% to 0.3% of the mass of the hemicellulose-containing nanocellulose aqueous dispersion;

②Then the nanocellulose/graphene aqueous dispersion is heated under stirring conditions of 600～1000rpm to evaporate the water to obtain an aqueous dispersion with a mass concentration of 10%～20%, and then add acetone to the aqueous dispersion to make the acetone Account for 30% to 40% of the volume of the aqueous dispersion, then disperse for 1 to 20 minutes under 400 to 600W ultrasonic conditions, and then centrifuge at 8000 to 10000 rpm to obtain a precipitate;

3. Add acetone to the precipitate, then disperse under 500～600W ultrasonic conditions for 1～20min, and then centrifuge at 8000～9000rpm to obtain the precipitate; wherein the mass ratio of the precipitate to acetone is 1:(9～11);

④ Repeat step ③ for 5 to 6 times, then add acetone to the precipitate to obtain an acetone dispersion of the precipitate with a solid content of 20% to 25%;

3. In-situ chemical modification of nanocellulose-dispersed graphene water-based wood paint:

① Mix isophorone diisocyanate and the acetone dispersion of the precipitate obtained in step 2, stir evenly, and then heat to 65～70℃ for 1～2h;

②Then add polypropylene glycol-2000 to the reaction system, keep 65～70℃ and react for 1.5～2h;

③ Add the acetone solution of 1,4-butanediol with a mass concentration of 15% to 25% into the reaction system dropwise, and control the dropping speed of the acetone solution of 1,4-butanediol to control the temperature of the system at 70-80 ℃, the reaction is 1.5～2h;

④ Dissolve dimethylolpropionic acid with N-methylpyrrolidone, then add it to the reaction system, control the reaction temperature to be 65-75°C, use acetone to control the viscosity of the reaction solution to be lower than 100mPa·S, and react for 3.5-4h;

⑤Add triethylamine into the reaction system, and neutralize the reaction for 15～20min;

⑥ Then disperse the reaction solution with a high-speed disperser to obtain an in-situ chemically modified water-based polyurethane emulsion containing hemicellulose-containing nanocellulose-dispersed graphene, which is a nano-cellulose-dispersed graphene chemically modified waterborne wood coating.

Embodiment 2: The difference between this embodiment and Embodiment 1 is that the specific steps of the extraction process described in Step 1 are:

The cellulose raw material is pulverized into 90-120 mesh powder, and then subjected to phenyl alcohol extraction treatment for 10-12 hours; the phenyl alcohol is a mixture of toluene and anhydrous ethanol in a volume ratio of 2:1. Others are the same as the first embodiment.

Embodiment 3: The difference between this embodiment and Embodiment 1 is that the specific steps of the delignification treatment described in Step 1 are:

① Immerse the extracted cellulose powder in a sodium chlorite solution with a mass concentration of 1% to 1.2%, adjust the pH of the solution to 4 to 5 with glacial acetic acid, and then place the solution in a constant temperature water bath at 75 to 80 °C by magnetic force. Heating and stirring for 1～1.5h;

② Immerse the cellulose powder obtained in step ① into a sodium chlorite solution with a mass concentration of 1% to 1.2%, adjust the pH of the solution to 4 to 5 with glacial acetic acid, and then magnetically heat it in a constant temperature water bath at 75 to 80°C Stir for 1～1.5h;

③ Repeat step ② 5 to 6 times to basically remove lignin, then filter and wash the obtained liquid with a Buchner funnel until the filtrate is neutral, and finally obtain holocellulose. Others are the same as the first embodiment.

Embodiment 4: The difference between this embodiment and Embodiment 1 is that the specific steps of the delignification treatment described in Step 1 are:

Immerse the extracted cellulose powder in a hydrogen peroxide solution with a mass concentration of 30% to 35%, add magnesium silicate, and stir magnetically for 48 to 52 hours at room temperature to basically remove lignin; Filtration and washing are carried out in the funnel until the filtrate is neutral, and finally the holocellulose is obtained; wherein the mass of the magnesium silicate is 1% to 1.5% of the mass of the hydrogen peroxide solution. Others are the same as the first embodiment.

Embodiment 5: The difference between this embodiment and Embodiment 1 is that the cellulose raw material described in Step 1 is a biomass raw material powder with a particle size of 100 mesh or more. Others are the same as the first embodiment.

Embodiment 6: The difference between this embodiment and Embodiment 5 is that the biomass raw material powder is wood powder, crop straw powder, waste paper, leaves or bast fiber raw materials. Others are the same as the fifth embodiment.

Embodiment 7: The difference between this embodiment and Embodiment 1 is that the preparation method of the reduced graphene described in Step 2 is specifically:

The graphene oxide is placed in a hydrogen iodide solution, placed at room temperature for 20 to 30 minutes, and then washed alternately with water and ethanol for 3 to 5 times, wherein the water is washed for 1 to 10 minutes each time, and the ethanol is washed for 1 to 10 minutes each time to obtain reduced graphene. . Others are the same as the first embodiment.

Embodiment 8: The difference between this embodiment and Embodiment 1 is that continuous stirring is performed during the modification process in step 3. Others are the same as the first embodiment.

Embodiment 9: The difference between this embodiment and Embodiment 1 is that water-based acrylate emulsion is continued to be added to the emulsion obtained in step 3 to obtain a blended water-based polyurethane acrylate emulsion. Others are the same as the first embodiment.

Embodiment 10: The difference between this embodiment and Embodiment 1 is that the isophorone diisocyanate in step 3, the acetone dispersion of the precipitate obtained in step 2, polypropylene glycol-2000, 1,4-butanediol The mass ratio of acetone solution, dimethylolpropionic acid and triethylamine is (50～60):(10～20):(45～60):(15～20):(5～8):(3 ~5). Others are the same as the first embodiment.

The embodiments of the present invention are described in detail below. The following embodiments are implemented on the premise of the technical solutions of the present invention, and provide detailed embodiments and specific operation processes, but the protection scope of the present invention is not limited to the following implementations example.

Example 1:

The method for the nanocellulose dispersed graphene chemically modified water-based wood coating of the present embodiment comprises the following steps:

1. Preparation of hemicellulose-containing nanocellulose aqueous dispersion: The cellulose raw materials are sequentially extracted and delignified to obtain hemocellulose fibers, and then mechanically pretreated to obtain hemicellulose-containing nanofibers. Cellulose aqueous dispersion;

The specific steps of the extraction process described in step 1 are:

The cellulose raw material was pulverized into 100 mesh powder, and then extracted with benzene alcohol for 10 hours. The phenyl alcohol is composed of toluene and absolute ethanol in a volume ratio of 2:1.

The concrete steps of delignification treatment described in step 1 are:

① Immerse the extracted cellulose powder in a sodium chlorite solution with a mass concentration of 1%, adjust the pH of the solution to 4.5 with glacial acetic acid, and then magnetically heat and stir in a constant temperature water bath at 75°C for 1 hour;

② Immerse the cellulose powder obtained in step ① in a sodium chlorite solution with a mass concentration of 1%, adjust the pH value of the solution to 4.5 with glacial acetic acid, and then magnetically heat and stir in a constant temperature water bath at 75°C for 1 hour;

③ Repeat step ② 5 times to basically remove lignin, then filter and wash the obtained liquid with a Buchner funnel until the filtrate is neutral, and finally obtain holocellulose;

For the mechanical pretreatment described in step 1, the specific operation steps are as follows:

①Put the holocellulose into a 250mL beaker, and add deionized water until the mass fraction of the holocellulose is 0.3%;

②Then use 600bar high-pressure homogenization machine for 30min to obtain the nanocellulose aqueous dispersion containing hemicellulose, in which hemicellulose accounts for 25% of the quality of the holocellulose;

The cellulose raw material described in step 1 is wood powder with a particle size of 100 mesh or more.

2. Nanocellulose stably dispersed graphene:

1. Place commercially available graphene oxide in a commercially available hydrogen iodide solution, place at room temperature for 20 minutes, and then alternately wash with water and ethanol for 3 times, each time for 10 minutes, and each for 10 minutes with ethanol to obtain reduced graphene; The reduced graphene is placed in the hemicellulose-containing nanocellulose aqueous dispersion obtained in step 1, mechanically dispersed for 20min under high-speed stirring at 15000rpm, and then dispersed for 20min under 1000W ultrasonic conditions to obtain uniformly dispersed nanocellulose/ Graphene aqueous dispersion; wherein graphene or reduced graphene is 0.1% of the mass of the hemicellulose-containing nanocellulose aqueous dispersion;

②Then the nanocellulose/graphene aqueous dispersion was heated under stirring conditions of 600 rpm to evaporate the water to obtain an aqueous dispersion with a mass concentration of 15%, and then acetone was added to the aqueous dispersion to make acetone occupy the volume of the aqueous dispersion 30%, then dispersed under 500W ultrasonic conditions for 20min, and then centrifuged at 8000rpm to obtain a precipitate;

3. Add acetone to the precipitate, then disperse under 500W ultrasonic conditions for 20min, and then centrifuge at 8000rpm to obtain the precipitate; wherein the mass ratio of the precipitate and acetone is 1:10;

④ Repeat step ③ 5 times, then add acetone to the precipitate to obtain the acetone dispersion of the precipitate, and the solid content is 25%;

3. In-situ chemical modification of nanocellulose-dispersed graphene water-based wood paint:

①Weigh 56g of isophorone diisocyanate and 10ml of the acetone dispersion of the precipitate obtained in step 2, stir evenly, pour it into a dry four-necked flask with a stirrer and a condenser, and heat it to 65°C for 1 hour;

②Weigh 50g of polypropylene glycol-2000, add it to the above reaction system, keep it at 65℃ for 1.5h;

③Weigh the acetone solution of 1,4-butanediol with a total mass of 17g, which contains 10.5g of 1,4-butanediol, and then slowly add it dropwise to the reaction solution, and control the rate of addition of acetone so that the temperature of the system is controlled at 75°C, react for 1.5h;

④Weigh 5.8g of dimethylolpropionic acid and dissolve it with a small amount of N-methylpyrrolidone, add it to the reaction solution, control the reaction temperature at 70°C, use acetone to control the viscosity of the reaction solution to be lower than 100mPa·S, and react for 3.5h ;

⑤ Weigh 4.3g of triethylamine and add it to the reaction system, and neutralize it for 15min;

⑥ Disperse the above-mentioned liquid with a high-speed disperser to obtain an in-situ chemically modified water-based polyurethane emulsion containing hemicellulose-containing nanocellulose-dispersed graphene.

Fig. 1 is the SEM image of the reduced graphene obtained in step 2 of embodiment 1, Fig. 2 is the SEM image of the nanocellulose composite graphene obtained in step 2 of embodiment 1, it can be known that the obtained two-dimensional graphene sheet side length is greater than 50um, the diameter of nanocellulose is less than 100nm, the length is greater than 50um, the nanocellulose with high aspect ratio is evenly distributed on the graphene sheet, and the surface properties of graphene are well coated and controlled, which is the subsequent enhancement and modification of the paint film. Foundation.

The nanocellulose-dispersed graphene chemically modified water-based wood coating and the unmodified wood coating obtained in Example 1 were applied to the maple surface by spraying with a spraying amount of 120 ^g /m , respectively, and dried at 30 ° C for 72 h. , obtain the nano-cellulose dispersed graphene chemically modified water-based wood paint paint film and the unmodified wood paint paint film obtained in Example 1, according to the national standard GBT-17657-2013 "wood-based panel and decorative wood-based panel physical and chemical properties test method. 》Test the mechanical properties and gloss of the two paint films. The results show that the hardness of the nanocellulose-dispersed graphene chemically modified water-based wood coating paint film obtained in Example 1 is improved from the B level before modification to the HB level, and the wear resistance is improved from the 40% mass loss rate before modification. To a mass loss rate of 15% after modification, the adhesion was improved from grade III before modification to grade II after modification, and the impact toughness was improved from 2.1J/m ² before modification to 3.5 after modification. J/m ² , the tensile strength is increased from 2.3MPa before modification to 3.7MPa after modification, the gloss is only decreased from 86.2 to 78.5, the paint film has certain electrical conductivity (resistance value 1100Ω), thermal conductivity (thermal conductivity up to 15w/mk) and anti-ultraviolet and anti-aging (yellow index is reduced by 35%); and as a control, the hardness of the water-based wood paint film modified with pure nanocellulose dispersed graphene is increased from the B level before modification by B～ Grade HB, the wear resistance is increased from 40% mass loss rate before modification to 35% mass loss rate after modification, and the adhesion is increased from grade III before modification to grade III-II after modification. Impact toughness increased from 2.1J/m ² before modification to 2.6J/m ² after modification, tensile strength increased from 2.3MPa before modification to 2.9MPa after modification, and gloss decreased only from 86.2% To 82%, the paint film has certain electrical conductivity (resistance value 1820Ω), thermal conductivity (thermal conductivity up to 14w/mk) and anti-ultraviolet and aging resistance (46% reduction in yellow index), indicating that the use of hemicellulose-containing nanocellulose The method of dispersing graphene can effectively improve the comprehensive performance of water-based wood coatings, and the comprehensive effect of graphene-modified water-based wood coatings is better than that of pure nanocellulose dispersed graphene.

Example 2:

The method for the nanocellulose dispersed graphene chemically modified water-based wood coating of the present embodiment comprises the following steps:

1. Preparation of hemicellulose-containing nanocellulose aqueous dispersion: the cellulose raw materials are sequentially extracted and delignified to obtain hemocellulose fibers, and then chemical-mechanical mixing pretreatment is performed to obtain hemicellulose-containing The nanocellulose aqueous dispersion;

The specific steps of the extraction process described in step 1 are:

The cellulose raw material was pulverized into 100 mesh powder, and then extracted with benzene alcohol for 10 hours. The phenyl alcohol is composed of toluene and absolute ethanol in a volume ratio of 2:1.

The concrete steps of delignification treatment described in step 1 are:

Immerse the extracted cellulose powder in a hydrogen peroxide solution with a mass concentration of 30%, add magnesium silicate (using magnesium silicate as a stabilizer), and stir magnetically for 48 hours at room temperature to basically remove lignin; then the obtained The obtained liquid is filtered and washed with a Buchner funnel until the filtrate is neutral, and finally the holocellulose is obtained; wherein the mass of magnesium silicate is 1% of the mass of the hydrogen peroxide solution.

The chemical-mechanical mixing pretreatment described in step 1, the specific operation steps are as follows:

①Put the holocellulose into a 250mL beaker, add deionized water until the mass fraction of holocellulose is 0.3%, then add sodium bromide and TEMPO reagent in turn, and then under magnetic stirring, at a rate of 2.5mL/min Add sodium hypochlorite, and then use sodium hydroxide with a concentration of 0.5mol/L to adjust the pH value to 10, and continue the reaction until the pH value does not change; the mass of sodium bromide is 12%.5% of the mass of holocellulose, and the mass of TEMPO reagent The mass is 1.25% of the mass of the holocellulose, and the mass of the sodium hypochlorite is 30% of the mass of the holocellulose;

②After suction filtration and water washing, deionized water and sodium chlorite were added, and the pH value was adjusted to 4.5 with glacial acetic acid, and then magnetically stirred at 70 °C for 1 hour, and the carboxylated cellulose was obtained by suction filtration and water washing; The mass ratio of ionized water and holocellulose is 100:3, and the mass of sodium chlorite is 30% of the mass of holocellulose;

③ Then reconstitute 0.3% carboxylated cellulose aqueous dispersion, and then mechanically disperse it by a high-speed mixer at 15,000 rpm for 20 minutes to obtain a hemicellulose-containing nanocellulose aqueous dispersion, in which hemicellulose accounts for 30% of the total cellulose mass. 18%.

The cellulose raw material described in the first step is wheat straw powder with a particle size of more than 100 meshes.

2. Nanocellulose stably dispersed graphene:

①Place commercially available graphene in the hemicellulose-containing nanocellulose aqueous dispersion obtained in step 1, mechanically disperse it under high-speed stirring at 15,000 rpm for 20 minutes, and then disperse it under 1,000 W ultrasonic conditions for 20 minutes to obtain uniformly dispersed nano- Cellulose/graphene aqueous dispersion; wherein graphene or reduced graphene is 0.1% of the mass of the hemicellulose-containing nanocellulose aqueous dispersion;

②Then the nanocellulose/graphene aqueous dispersion was heated under stirring conditions of 600 rpm to evaporate the water to obtain an aqueous dispersion with a mass concentration of 15%, and then acetone was added to the aqueous dispersion to make acetone occupy the volume of the aqueous dispersion 30%, then dispersed under 500W ultrasonic conditions for 20min, and then centrifuged at 8000rpm to obtain a precipitate;

3. Add acetone to the precipitate, then disperse under 500W ultrasonic conditions for 20min, and then centrifuge at 8000rpm to obtain the precipitate; wherein the mass ratio of the precipitate and acetone is 1:10;

④ Repeat step ③ 5 times, then add acetone to the precipitate to obtain the acetone dispersion of the precipitate, and the solid content is 25%;

3. In-situ chemical modification of nanocellulose-dispersed graphene water-based wood paint:

①Weigh 56g of isophorone diisocyanate and 10ml of the acetone dispersion of the precipitate obtained in step 2, stir evenly, pour it into a dry four-necked flask with a stirrer and a condenser, and heat it to 65°C for 1 hour;

②Weigh 50g of polypropylene glycol-2000, add it to the above reaction system, keep it at 65℃ for 1.5h;

③Weigh the acetone solution of 1,4-butanediol with a total mass of 17g, which contains 10.5g of 1,4-butanediol, and then slowly add it dropwise to the reaction solution, and control the rate of addition of acetone so that the temperature of the system is controlled at 75°C, react for 1.5h;

④Weigh 5.8g of dimethylolpropionic acid and dissolve it with a small amount of N-methylpyrrolidone, add it to the reaction solution, control the reaction temperature at 70°C, use acetone to control the viscosity of the reaction solution to be lower than 100mPa·S, and react for 3.5h ;

⑤ Weigh 4.3g of triethylamine and add it to the reaction system, and neutralize it for 15min;

⑥ Disperse the above-mentioned liquid with a high-speed disperser to obtain an in-situ chemically modified water-based polyurethane emulsion containing hemicellulose-containing nanocellulose-dispersed graphene.

⑦ Continue adding water-based acrylate emulsion to the emulsion obtained in ⑥ according to the ratio of solid content of 1:1 to obtain a blended water-based polyurethane acrylate emulsion.

FIG. 3 is the SEM image of the reduced graphene obtained in the second step of Example 2, and FIG. 4 is the SEM image of the nanocellulose composite graphene obtained in the second step of Example 2. It can be seen that the side length of the obtained two-dimensional graphene sheet is greater than 500um, the diameter of the nanocellulose is less than 100nm, the length is greater than 10um, and the nanocellulose with high aspect ratio is evenly distributed on the graphene sheet, which is well coated and controlled. The surface properties of graphene lay the foundation for the subsequent enhancement of the modified paint film.

The nanocellulose-dispersed graphene chemically modified water-based wood coating and the unmodified wood coating obtained in Example ² were applied to the maple surface by spraying with a spraying amount of 120g/m , respectively, and after drying at 30 ° C for 72h , obtain the nano-cellulose dispersed graphene chemically modified water-based wood paint paint film and unmodified wood paint paint film obtained in Example 2; 》Test the mechanical properties and gloss of the two paint films. The results show that the hardness of the nanocellulose-dispersed graphene chemically modified water-based wood coating paint film obtained in Example 2 is increased from the B level before the modification to the HB level, and the wear resistance is increased from the 40% mass loss rate before the modification. To the mass loss rate of 18% after modification, the adhesion is improved from the level III before modification to the level II after modification, and the impact toughness is increased from ^2.1J /m2 before modification to 3.3 after modification. J/m ² , the tensile strength increased from 2.3MPa before modification to 3.5MPa after modification, and the gloss decreased from 86.2 to 77. The paint film had certain electrical conductivity (resistance value 1200Ω) and thermal conductivity (thermal conductivity reached 14w/mk) and anti-ultraviolet and anti-aging (yellow index is reduced by 37%); and as a control, the hardness of the water-based wood paint film modified with pure nanocellulose dispersed graphene is increased from the B level before modification by B～ Grade HB, the wear resistance is increased from 40% mass loss rate before modification to 35% mass loss rate after modification, and the adhesion is increased from grade III before modification to grade III-II after modification. ^The impact toughness is increased from ^2.1J /m2 before modification to 2.6J/m2 after modification, the tensile strength is increased from 2.3MPa before modification to 2.9MPa after modification, and the gloss is increased by 86.2% only dropped to 82%, the paint film has certain electrical conductivity (resistance value 1820Ω), thermal conductivity (thermal conductivity up to 14w/mk) and anti-ultraviolet and anti-aging (yellow index reduced by 46%) functions, indicating that hemicellulose-containing The nanocellulose-dispersed graphene method can effectively improve the comprehensive performance of water-based wood coatings, which is better than the comprehensive effect of pure nano-cellulose-dispersed graphene modified water-based wood coatings.

Claims (10)

1. the method for nano-cellulose dispersed graphene chemically modified water-based wood coatings, is characterized in that the method may further comprise the steps: 1. Preparation of hemicellulose-containing nanocellulose aqueous dispersion : The cellulose raw material is sequentially subjected to extraction treatment and delignification treatment to obtain holocellulose, and then to mechanical pretreatment or chemical-mechanical mixing pretreatment to obtain a hemicellulose-containing nanocellulose aqueous dispersion ; The described mechanical pretreatment, the specific operation steps are as follows: ①Add deionized water to the holocellulose until the mass fraction of the holocellulose is 0.1%-0.3%; ②Then use 600bar high-pressure homogenizing mechanical treatment for 30-40min to obtain a nanocellulose aqueous dispersion containing hemicellulose, in which hemicellulose accounts for 20%-30% of the mass of hemocellulose; Described chemical mechanical mixing pretreatment, specific operation steps are as follows: ①Add deionized water to the holocellulose until the mass fraction of holocellulose is 0.1%-0.3%, then add sodium bromide and TEMPO reagent in turn, and then add at a rate of 2.5-3mL/min under magnetic stirring Sodium hypochlorite, and then adjust the pH value to 10-10.5, and continue to react until the pH value does not change; the quality of sodium bromide is 12%-13% of the quality of holocellulose, and the quality of TEMPO reagent is 1%-1% of the mass of holocellulose 2%, the quality of sodium hypochlorite is 25% to 35% of the quality of holocellulose; ②After suction filtration and water washing, add deionized water and sodium chlorite to adjust the pH value to 4-5, then magnetically stir at 70-80°C for 1-2 hours, filter and wash with water to obtain carboxylated cellulose ; wherein the mass ratio of deionized water and holocellulose is (95～105): 3, and the quality of sodium chlorite is 25%～35% of the quality of holocellulose; ③ Then reconstitute 0.1%-0.3% carboxylated cellulose aqueous dispersion, and then mechanically disperse it by a high-speed mixer at 14,000-16,000 rpm for 20-30 minutes to obtain a hemicellulose-containing nanocellulose aqueous dispersion, in which the hemicellulose is dispersed. The cellulose accounts for 10% to 20% of the quality of the holocellulose; 2. Nanocellulose stably dispersed graphene: ①Place graphene or reduced graphene in the hemicellulose-containing nanocellulose aqueous dispersion obtained in step 1, mechanically disperse it under high-speed stirring at 14000-16000 rpm for 1-20 minutes, and then disperse under 900-1100W ultrasonic conditions 1 to 20 minutes to obtain a uniformly dispersed nanocellulose/graphene aqueous dispersion; wherein the graphene or reduced graphene is 0.1% to 0.3% of the mass of the hemicellulose-containing nanocellulose aqueous dispersion ; ②Then the nanocellulose/graphene aqueous dispersion is heated under stirring conditions of 600～1000rpm to evaporate the water to obtain an aqueous dispersion with a mass concentration of 10%～20%, and then add acetone to the aqueous dispersion to make the acetone Account for 30% to 40% of the volume of the aqueous dispersion, then disperse for 1 to 20 minutes under 400 to 600W ultrasonic conditions, and then centrifuge at 8000 to 10000 rpm to obtain a precipitate; 3. Add acetone to the precipitate, then disperse under 500～600W ultrasonic conditions for 1～20min, and then centrifuge at 8000～9000rpm to obtain the precipitate; wherein the mass ratio of the precipitate to acetone is 1:(9～11); ④ Repeat step ③ for 5 to 6 times, then add acetone to the precipitate to obtain an acetone dispersion of the precipitate with a solid content of 20% to 25%; 3. In-situ chemical modification of nanocellulose-dispersed graphene water-based wood paint: ① Mix isophorone diisocyanate and the acetone dispersion of the precipitate obtained in step 2, stir evenly, and then heat to 65～70℃ for 1～2h; ②Then add polypropylene glycol-2000 to the reaction system, keep 65～70℃ and react for 1.5～2h; ③ Add the acetone solution of 1,4-butanediol with a mass concentration of 15% to 25% into the reaction system dropwise, and control the dropping speed of the acetone solution of 1,4-butanediol to control the temperature of the system at 70-80 ℃, the reaction is 1.5～2h; ④ Dissolve dimethylolpropionic acid with N-methylpyrrolidone, then add it to the reaction system, control the reaction temperature to be 65-75°C, use acetone to control the viscosity of the reaction solution to be lower than 100mPa·s, and react for 3.5-4h; ⑤Add triethylamine into the reaction system, and neutralize the reaction for 15～20min; ⑥ Then disperse the reaction solution with a high-speed disperser to obtain an in-situ chemically modified water-based polyurethane emulsion containing hemicellulose-containing nanocellulose-dispersed graphene, which is a nano-cellulose-dispersed graphene chemically modified waterborne wood coating. 2. the method for nanocellulose dispersion graphene chemically modified water-based wood coating according to claim 1, is characterized in that: the concrete steps of extracting described in step 1 are: The cellulose raw material is pulverized into 90-120 mesh powder, and then subjected to phenyl alcohol extraction treatment for 10-12 hours; the phenyl alcohol is a mixture of toluene and anhydrous ethanol in a volume ratio of 2:1. 3. the method for nano-cellulose dispersed graphene chemically modified water-based wood coating according to claim 1, is characterized in that: the concrete steps of delignification described in step 1 are: ① Immerse the extracted cellulose powder in a sodium chlorite solution with a mass concentration of 1% to 1.2%, adjust the pH of the solution to 4 to 5 with glacial acetic acid, and then place the solution in a constant temperature water bath at 75 to 80 °C by magnetic force. Heating and stirring for 1～1.5h; ② Immerse the cellulose powder obtained in step ① into a sodium chlorite solution with a mass concentration of 1% to 1.2%, adjust the pH of the solution to 4 to 5 with glacial acetic acid, and then magnetically heat it in a constant temperature water bath at 75 to 80°C Stir for 1～1.5h; ③ Repeat step ② 5-6 times to basically remove lignin, then filter and wash the obtained liquid with a Buchner funnel until the filtrate is neutral, and finally obtain holocellulose. 4. the method for nano-cellulose dispersed graphene chemically modified water-based wood coating according to claim 1, is characterized in that: the concrete steps of delignification treatment described in step 1 are: Immerse the extracted cellulose powder in a hydrogen peroxide solution with a mass concentration of 30% to 35%, add magnesium silicate, and stir magnetically for 48 to 52 hours at room temperature to basically remove lignin; Filtration and washing are carried out in the funnel until the filtrate is neutral, and finally the holocellulose is obtained; wherein the mass of the magnesium silicate is 1% to 1.5% of the mass of the hydrogen peroxide solution. 5. the method for nano-cellulose dispersed graphene chemically modified water-based wood coating according to claim 1, is characterized in that: the cellulose raw material described in step 1 is the biomass raw material powder that granularity is more than 100 meshes. 6. the method for nanocellulose dispersion graphene chemically modified waterborne wood coating according to claim 5, is characterized in that: described biomass raw material powder is wood powder, crop straw powder, waste paper, leaf or bast fiber raw material. 7. the method for nano-cellulose dispersed graphene chemically modified water-based wood coating according to claim 1, is characterized in that: the preparation method of reduced graphene described in the step 2 is specially: The graphene oxide is placed in a hydrogen iodide solution, placed at room temperature for 20 to 30 minutes, and then washed alternately with water and ethanol for 3 to 5 times, wherein the water is washed for 1 to 10 minutes each time, and the ethanol is washed for 1 to 10 minutes each time to obtain reduced graphene. . 8. the method for nano-cellulose dispersed graphene chemically modified water-based wood coating according to claim 1, is characterized in that: continuously stirs in the modification process of step 3. 9. the method for nanocellulose dispersion graphene chemically modified water-based wood coating according to claim 1, it is characterized in that: in the emulsion that step 3 obtains, also continue to add water-based acrylate emulsion, obtain blending water-based polyurethane acrylate lotion. 10. the method for nanocellulose dispersion graphene chemically modified water-based wood coating according to claim 1, is characterized in that: the acetone dispersion of the precipitate obtained by isophorone diisocyanate in step 3, step 2, polymer The mass ratio of propylene glycol-2000, 1,4-butanediol in acetone, dimethylolpropionic acid and triethylamine is (50～60):(10～20):(45～60):(15～ 20): (5-8): (3-5).

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