CN109575696B - Preparation method of nano-cellulose-polyurethane iridescent structural color coating for wood products - Google Patents
Preparation method of nano-cellulose-polyurethane iridescent structural color coating for wood products Download PDFInfo
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- 229920002635 polyurethane Polymers 0.000 title claims abstract description 132
- 238000009500 colour coating Methods 0.000 title claims abstract description 76
- 239000002023 wood Substances 0.000 title claims abstract description 44
- 238000002360 preparation method Methods 0.000 title claims abstract description 21
- 239000000725 suspension Substances 0.000 claims abstract description 65
- 229920002678 cellulose Polymers 0.000 claims abstract description 54
- 239000001913 cellulose Substances 0.000 claims abstract description 54
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims abstract description 48
- 238000006460 hydrolysis reaction Methods 0.000 claims abstract description 25
- 238000002156 mixing Methods 0.000 claims abstract description 25
- 229920001046 Nanocellulose Polymers 0.000 claims abstract description 24
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims abstract description 21
- 229920001131 Pulp (paper) Polymers 0.000 claims abstract description 15
- 239000011248 coating agent Substances 0.000 claims abstract description 15
- 238000000576 coating method Methods 0.000 claims abstract description 15
- 238000001035 drying Methods 0.000 claims abstract description 12
- 239000000203 mixture Substances 0.000 claims abstract description 12
- 239000004972 Polyurethane varnish Substances 0.000 claims abstract description 4
- 238000005119 centrifugation Methods 0.000 claims description 32
- 239000000047 product Substances 0.000 claims description 31
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 26
- 239000000463 material Substances 0.000 claims description 25
- 238000000502 dialysis Methods 0.000 claims description 21
- 238000003760 magnetic stirring Methods 0.000 claims description 17
- 239000006228 supernatant Substances 0.000 claims description 15
- 239000007788 liquid Substances 0.000 claims description 14
- 238000010438 heat treatment Methods 0.000 claims description 8
- 239000012528 membrane Substances 0.000 claims description 7
- 238000000034 method Methods 0.000 claims description 4
- 238000006243 chemical reaction Methods 0.000 claims description 3
- 239000003086 colorant Substances 0.000 abstract description 8
- 239000002994 raw material Substances 0.000 abstract description 4
- 230000003287 optical effect Effects 0.000 abstract description 2
- 239000007864 aqueous solution Substances 0.000 description 21
- 239000000243 solution Substances 0.000 description 15
- 238000009210 therapy by ultrasound Methods 0.000 description 8
- 239000011247 coating layer Substances 0.000 description 6
- 239000012153 distilled water Substances 0.000 description 6
- 239000002159 nanocrystal Substances 0.000 description 6
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- 229910021641 deionized water Inorganic materials 0.000 description 5
- 230000007062 hydrolysis Effects 0.000 description 5
- 239000002904 solvent Substances 0.000 description 5
- 239000010410 layer Substances 0.000 description 4
- 229910021653 sulphate ion Inorganic materials 0.000 description 4
- 235000008331 Pinus X rigitaeda Nutrition 0.000 description 3
- 235000011613 Pinus brutia Nutrition 0.000 description 3
- 241000018646 Pinus brutia Species 0.000 description 3
- 238000005034 decoration Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 239000004005 microsphere Substances 0.000 description 2
- 239000011122 softwood Substances 0.000 description 2
- 238000003756 stirring Methods 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- 239000004793 Polystyrene Substances 0.000 description 1
- 241000219000 Populus Species 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000004040 coloring Methods 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 239000002537 cosmetic Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000006221 furniture coating Substances 0.000 description 1
- 239000011121 hardwood Substances 0.000 description 1
- 230000003301 hydrolyzing effect Effects 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
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- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D101/00—Coating compositions based on cellulose, modified cellulose, or cellulose derivatives
- C09D101/02—Cellulose; Modified cellulose
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Abstract
The invention relates to a preparation method of a nano-cellulose-polyurethane iridescent structural color coating for a wood product, which comprises the following steps: 1) mixing sulfate bleached wood pulp and sulfuric acid for hydrolysis reaction to obtain nano cellulose suspension; 2) sequentially centrifuging, dialyzing and concentrating the obtained nano-cellulose suspension to obtain the nano-cellulose suspension with the mass concentration of 1-3%; 3) ultrasonically dispersing the nano cellulose suspension; 4) preparing aqueous polyurethane varnish into an aqueous polyurethane solution with the mass concentration of 5-25%; 5) and mixing the nano-cellulose suspension with the aqueous polyurethane solution, coating the mixture on the surface of a wood product, and drying to obtain the iridescent structural color coating. The advantages are that: 1) structural color coatings with different iridescent colors are obtained by adjusting the proportion of the nano-cellulose to the polyurethane, and are widely applied to color coating of furniture surfaces; 2) the coating not only has the iridescent optical characteristic of the nano-cellulose, but also has better binding force with the surface of the wood, the raw materials are easy to obtain, and the operation is simple.
Description
Technical Field
The invention discloses a preparation method of a nano-cellulose-polyurethane iridescent structural color coating for a wood product, and belongs to the technical field of iridescent structural color coatings for wood products.
Background
The structural color is a physical color generated by ordered arrangement of a space structure, has stable, environment-friendly and good color rendering effect, and can be applied to the surface of a material as a coating. The structural color coating is widely applied to packaging materials, anti-counterfeiting marks, cosmetics, furniture and interior decoration.
The raw material of the nano-cellulose (NCC) is wide in cellulose source and easy to obtain. The nano-cellulose is self-assembled under natural conditions, can form structural color with iridescence characteristics, and can be used as a base material of a structural color coating of iridescence. The waterborne polyurethane is used as a waterborne polymer coating, and is widely applied to coating materials for wooden products such as furniture, floors and the like due to environmental protection and good interface compatibility.
Currently, structural color coating materials are mainly focused on silica and polystyrene microspheres. In chinese patent publication No. CN107497649A, colloidal microspheres with uniform diameters are dispersed in water to obtain an aqueous dispersion, the aqueous dispersion is atomized and deposited on a substrate to form an amorphous structure color coating, and then the amorphous structure color coating is continuously deposited on the surface of the amorphous structure color coating for multiple times to form the color-superimposed amorphous structure color coating.
However, the preparation process of the structural color coating is complicated, a structural color coating with iridescence characteristics cannot be generated, good interface compatibility and stability cannot be ensured, and the coating material cannot be applied to wood products on a large scale.
Disclosure of Invention
The invention provides a preparation method of a nano-cellulose-polyurethane iridescent structural color coating for a wood product, aiming at overcoming the defects of complicated preparation process, poor interface compatibility, poor stability and the like of the structural color coating in the prior art and providing the preparation method of the nano-cellulose-polyurethane iridescent structural color coating with good colorability and surface bonding effect in the field of furniture and floor decoration materials.
The technical solution of the invention is as follows: a preparation method of a nano-cellulose-polyurethane iridescent structural color coating for a wood product comprises the following steps:
1) mixing sulfate bleached wood pulp and sulfuric acid for hydrolysis reaction, mixing the obtained solution with water after the reaction to stop the hydrolysis reaction, and obtaining nano cellulose suspension;
2) sequentially centrifuging, dialyzing and concentrating the obtained nano-cellulose suspension to obtain the nano-cellulose suspension with the mass concentration of 1-3%;
3) ultrasonically dispersing the nano cellulose suspension with the mass concentration of 1-3% obtained in the step 2);
4) preparing aqueous polyurethane varnish into an aqueous polyurethane solution with the mass concentration of 5-25%;
5) mixing the nano cellulose suspension obtained in the step 3) with a water-based polyurethane solution, coating the mixture on the surface of a wood product, and drying to obtain the iridescent structural color coating.
The invention has the beneficial effects that:
1) according to the preparation method of the nano-cellulose-polyurethane iridescent structural color coating for the wood product, the structural color coatings with different iridescent colors can be obtained by adjusting the proportion of nano-cellulose to polyurethane, and the coating can be widely applied to color coating of furniture surfaces;
2) the nano-cellulose-polyurethane iridescent structural color coating prepared by the method not only has the optical characteristics of nano-cellulose iridescence, but also has good binding force with the surface of wood, and has the advantages of easily obtained raw materials, simple operation and good application value.
Drawings
FIG. 1 is a reflection spectrum of the colors of the nano-cellulose-polyurethane iridescent structural color coating for wood products prepared by different polyurethane addition amounts in example 1.
FIG. 2 is a polarized microscope photograph of nanocellulose-polyurethane iridescent structural color coatings for wood products made with different polyurethane addition levels of example 1.
Detailed Description
A preparation method of a nano-cellulose-polyurethane iridescent structural color coating for a wood product comprises the following steps:
1) mixing sulfate bleached wood pulp and sulfuric acid for hydrolysis reaction, mixing the obtained solution with water after the reaction to stop the hydrolysis reaction, and obtaining nano cellulose suspension;
2) sequentially centrifuging, dialyzing and concentrating the obtained nano-cellulose suspension to obtain the nano-cellulose suspension with the mass concentration of 1-3%;
3) ultrasonically dispersing the nano cellulose suspension with the mass concentration of 1-3% obtained in the step 2);
4) preparing aqueous polyurethane varnish into an aqueous polyurethane solution with the mass concentration of 5-25%;
5) mixing the nano cellulose suspension obtained in the step 3) with a water-based polyurethane solution, coating the mixture on the surface of a wood product, and drying to obtain the iridescent structural color coating.
The mass concentration of the sulfuric acid in the step 1) is 70-90%, and the volume ratio of the mass of the sulfate bleached wood pulp to the volume of the sulfuric acid is (10-30) g (150-250) mL; the hydrolysis reaction is stopped by adding water with the volume 3-10 times of that of sulfuric acid at the temperature of 30-70 ℃ for 1-3 hours.
Preferably, the mass concentration of the sulfuric acid in the step 1) is 75-85%, and the volume ratio of the mass of the sulfate bleached wood pulp to the sulfuric acid is (15-25) g (180-220) mL.
Preferably, in the step 1), the hydrolysis reaction is stopped by adding water which is 5-8 times of the volume of the sulfuric acid at the temperature of 40-60 ℃ for 2-3 hours.
Standing and settling the nano-cellulose suspension for 10-30 h before centrifuging in the step 2) to obtain a supernatant and a lower turbid liquid; the supernatant was decanted off and the lower turbidity was centrifuged again.
Preferably, the centrifugation rotating speed in the step 2) is 5000-8000 rpm, the centrifugation time is 3-8 min, the centrifugation times are 2-5 times, and the pH value of the nano cellulose suspension obtained after centrifugation is 2-4.
Preferably, the centrifugation speed in the step 2) is 5000-6000 rpm, the centrifugation time is 6min, the centrifugation times are 3-4 times, and the pH value of the nano cellulose suspension obtained after centrifugation is 2-4.
The pH value of the dialyzed material in the step 2) is 5-8; the cut-off molecular weight of a dialysis membrane adopted by dialysis is 6000-12000; the dialysis time is 3-7 days.
Preferably, the pH value of the dialyzed material in the step 2) is 6-7; the cut-off molecular weight of a dialysis membrane adopted by dialysis is 8000-10000; the dialysis time is 4-6 days.
And 2) concentrating by heating in an oven at the temperature of 60-90 ℃ until the mass concentration of the nano-cellulose suspension is 1-3%.
Preferably, the concentration in the step 2) is carried out by heating and concentrating in an oven at the temperature of 70-80 ℃ until the mass concentration of the nano cellulose suspension is 1-3%.
In the step 3), the ultrasonic time is 10-30 min; the ultrasonic power is 400-600W.
Preferably, in the step 3), the ultrasonic time is 20-30 min; the ultrasonic power is 500W.
In the step 4), the mass concentration of the aqueous polyurethane solution is 10-15%, the aqueous polyurethane solution is uniformly mixed under the action of magnetic stirring, the rotating speed of the magnetic stirring is 300-600 rpm, and the time is 10-30 min.
In the step 5), the nano-cellulose suspension and the aqueous polyurethane solution are uniformly mixed under the action of magnetic stirring, wherein the rotating speed of the magnetic stirring is 500-800 rpm, and the time is 2-6 hours; the mass content of polyurethane in the mixed nano-cellulose-polyurethane iridescent structural color coating is 10-50%.
Preferably, in the step 5), the nano-cellulose suspension and the aqueous polyurethane solution are uniformly mixed under the action of magnetic stirring, wherein the rotating speed of the magnetic stirring is 500-600 rpm, and the time is 3-5 hours; the mass content of polyurethane in the mixed nano-cellulose-polyurethane iridescent structural color coating is 15-30%.
In the step 5), the thickness of the nano-cellulose-polyurethane iridescent structural color coating is 5-10 microns.
Preferably, in the step 5), the thickness of the nano-cellulose-polyurethane iridescent structural color coating is 6-8 microns.
Example 1
Mixing 15g of sulfate bleached poplar wood pulp with 160mL of sulfuric acid with the mass concentration of 70%, carrying out hydrolysis reaction for 1h in a water bath at 40 ℃ at 800rpm, mixing the obtained hydrolysis material with 1500mL of distilled water, standing and settling for 10h to obtain a supernatant and a lower turbid liquid; pouring the supernatant, and centrifuging the lower-layer turbid liquid for 3 times, wherein the supernatant obtained after each centrifugation is poured, the obtained lower-layer turbid liquid is washed by distilled water, and then the next centrifugation is carried out, wherein the rotation speed of the centrifugation is 4000rpm, and the time of the single centrifugation is 6 min; dialyzing the obtained centrifugal material for 7 days by adopting a dialysis membrane with the molecular weight cutoff of 8000 to obtain a nano cellulose suspension with the pH value of 6.0; concentrating the obtained dialysis suspension in an oven at 50 ℃ until the mass concentration is 1% to obtain a chiral nematic cellulose nanocrystal suspension;
mixing 0.5g of polyurethane with 10 mL of deionized water, and carrying out ultrasonic treatment for 2 min under the power of 500W to obtain a polyurethane aqueous solution (the mass concentration is 5%);
2g of the chiral nematic cellulose nanocrystal suspension is subjected to ultrasonic treatment for 5min under the power of 500W, then the chiral nematic cellulose nanocrystal suspension is mixed with 0.05g of polyurethane aqueous solution, 0.1g of polyurethane aqueous solution, 0.15g of polyurethane aqueous solution, 0.2g of polyurethane aqueous solution and 0.25g of polyurethane aqueous solution respectively, the mixture is magnetically stirred for 1h at the rotating speed of 500rpm to obtain mixed liquor, the mixture is coated on the surface of wood respectively, and the solvent is volatilized to dry under the condition of air room temperature, so that the nano cellulose-polyurethane iridescent structural color coating with the thickness of 5 micrometers is obtained.
The mass contents of the polyurethane in the nanocellulose-polyurethane iridescent structural color coating layer were calculated to be 10%, 20%, 30%, 40% and 50%, respectively (mass content of polyurethane = mass of polyurethane/mass of nanocellulose-polyurethane iridescent structural color coating layer).
The nanocellulose-polyurethane iridescent structural color coating can be tested as follows:
the nano-cellulose-polyurethane iridescent structural color coating for the wooden products prepared by different polyurethane adding amounts of 10 percent reflects iridescent colors on the surface of wood. FIG. 1 is a reflection spectrogram of colors of nano-cellulose-polyurethane iridescent structural color coatings for wood products prepared by different polyurethane addition amounts in example 1, and it can be seen from FIG. 1 that the reflection wavelength of the nano-cellulose-polyurethane iridescent structural color coatings gradually shifts red with the increase of the polyurethane addition amount, and the reflection wavelength of the nano-cellulose-polyurethane iridescent structural color coatings is 432nm when the polyurethane addition amount is 10%; when the addition amount of the polyurethane is 50%, the reflection wavelength of the nano-cellulose-polyurethane iridescent structural color coating is 720 nm; fig. 2 is a polarizing microscope picture of nanocellulose-polyurethane iridescent structure color coatings for wood products prepared by different polyurethane addition amounts in example 1, wherein the nanocellulose-polyurethane iridescent structure color coatings have obvious birefringence characteristics, and the polarizing microscope picture of nanocellulose-polyurethane iridescent structure color coatings for wood products prepared by different polyurethane addition amounts is obviously different. Table 1 shows the surface adhesion test data of the nanocellulose-polyurethane iridescent structure color coating for wood products prepared by different polyurethane addition amounts in example 1, and the adhesion is obviously increased with the increase of the polyurethane content. The nano-cellulose-polyurethane iridescent structure color coating for the wood products, provided by the invention, has a good coloring effect and good surface bonding force, and can be applied to home decoration materials.
TABLE 1
Example 2
Mixing 20g of sulfate bleached pine wood pulp with 180mL of sulfuric acid with the mass concentration of 80%, performing hydrolysis reaction in a water bath at 50 ℃ for 2h at 700rpm, mixing the obtained hydrolysis material with 2000mL of distilled water, standing and settling for 20h to obtain a supernatant and a lower turbid liquid; pouring the supernatant, and centrifuging the lower-layer turbid liquid for 4 times, wherein the supernatant obtained after each centrifugation is poured, the obtained lower-layer turbid liquid is washed by distilled water, and then the next centrifugation is carried out, the rotation speed of the centrifugation is 5000rpm, and the time of the single centrifugation is 7 min; dialyzing the obtained centrifugal material for 5 days by using a dialysis membrane with the molecular weight cutoff of 9000 to obtain a nano cellulose suspension with the pH value of 5.0; concentrating the obtained dialysis suspension in an oven at the temperature of 60 ℃ until the mass concentration is 2% to obtain a nano cellulose suspension;
mixing 1g of polyurethane with 10 mL of deionized water, and carrying out ultrasonic treatment for 2 min under the power of 500W to obtain a polyurethane aqueous solution (the mass concentration is 10%);
and (2) carrying out ultrasonic treatment on 2g of the nano-cellulose suspension for 3min under the power of 400W, then respectively mixing the nano-cellulose suspension with 0.05g of polyurethane aqueous solution, 0.1g of polyurethane aqueous solution, 0.15g of polyurethane aqueous solution, 0.2g of polyurethane aqueous solution and 0.25g of polyurethane aqueous solution, magnetically stirring the mixture at the rotating speed of 500rpm for 1h to obtain mixed liquor, respectively coating the mixture on the surface of wood, and volatilizing the solvent at the room temperature of air to obtain a nano-cellulose-polyurethane iridescent structural color coating with the thickness of 6 mu m.
The mass contents of the polyurethane in the nanocellulose-polyurethane iridescent structural color coating layer were calculated to be 10%, 20%, 30%, 40% and 50%, respectively (mass content of polyurethane = mass of polyurethane/mass of nanocellulose-polyurethane iridescent structural color coating layer).
The nanocellulose-polyurethane iridescent structural color coating was tested and the results were substantially in accordance with example 1.
Example 3
Mixing 25g of sulfate bleached fir wood pulp with 200mL of sulfuric acid with the mass concentration of 80%, performing hydrolysis reaction in a water bath at 60 ℃ for 3h at 800rpm, mixing the obtained hydrolysis material with 2000mL of distilled water, standing and settling for 30h to obtain a supernatant and a lower turbid liquid; pouring the supernatant, and centrifuging the lower turbid liquid for 5 times, wherein the supernatant obtained after each centrifugation is poured, the obtained lower turbid liquid is washed by distilled water, and then the next centrifugation is carried out, the rotation speed of the centrifugation is 6000rpm, and the time of the single centrifugation is 8 min; dialyzing the obtained centrifugal material by using a dialysis membrane with the molecular weight cutoff of 10000 for 6 days to obtain a nano cellulose suspension with the pH value of 6.0; concentrating the obtained dialysis suspension in an oven at 70 ℃ until the mass concentration is 3% to obtain a nano cellulose suspension;
mixing 1g of polyurethane with 10 mL of deionized water, and carrying out ultrasonic treatment for 2 min under the power of 500W to obtain a polyurethane aqueous solution (the mass concentration is 10%);
and (2) carrying out ultrasonic treatment on 3g of the nano-cellulose suspension for 3min under the power of 400W, then respectively mixing the nano-cellulose suspension with 0.1g of polyurethane aqueous solution, 0.225g of polyurethane aqueous solution, 0.385g of polyurethane aqueous solution, 0.6g of polyurethane aqueous solution and 0.9g of polyurethane aqueous solution, carrying out magnetic stirring at the rotating speed of 600rpm for 2h to obtain a mixed solution, coating the mixture on the surface of wood, and volatilizing the solvent at the room temperature of air to obtain a nano-cellulose-polyurethane iridescent structural color coating with the thickness of 10 mu m.
The mass contents of the polyurethane in the nanocellulose-polyurethane iridescent structural color coating layer were calculated to be 10%, 20%, 30%, 40% and 50%, respectively (mass content of polyurethane = mass of polyurethane/mass of nanocellulose-polyurethane iridescent structural color coating layer).
The nanocellulose-polyurethane iridescent structural color coatings were tested and the results were substantially in accordance with example 1.
From the above embodiments, it can be seen that the nanocellulose-polyurethane iridescent structural color coating provided by the invention not only has the iridescent characteristics of nanocellulose, but also has good interface bonding characteristics of polyurethane, has different iridescent colors under different nanocellulose and polyurethane proportions, can be applied to decorative materials such as furniture, floors and the like, and is easy to obtain raw materials and simple to operate.
Example 3
The invention aims to provide a nano-cellulose-polyurethane iridescent structural color coating for a wood product, and a preparation method and application thereof, wherein the preparation method comprises the following steps:
mixing sulfate bleached wood pulp and sulfuric acid for hydrolysis reaction to obtain a suspension of nano cellulose;
sequentially centrifuging, washing and concentrating the nano-cellulose suspension to obtain a nano-cellulose suspension with the mass concentration of 1-3%;
and mixing the nano-cellulose suspension with a polyurethane aqueous solution, coating the mixture on the surface of wood, and drying to obtain the nano-cellulose-polyurethane iridescent structural color coating.
According to the invention, sulfate bleached wood pulp and sulfuric acid are mixed for hydrolysis reaction to obtain the suspension of the nano cellulose. In the present invention, the sulfate bleached wood pulp preferably comprises sulfate bleached softwood pulp and sulfate bleached hardwood pulp; the sulphate bleached softwood pulp preferably comprises sulphate bleached pine pulp or sulphate bleached fir pulp, more preferably sulphate bleached pine pulp.
The mass concentration of the sulfuric acid is preferably 70-90%, and more preferably 75-85%. In the invention, the volume ratio of the mass of the sulfate bleached wood pulp to the volume of the sulfuric acid is preferably (10-30) g, (150-250) mL, and more preferably (15-25) g, (180-220) mL.
In the invention, the temperature of the hydrolysis reaction is preferably 30-70 ℃, and more preferably 40-60 ℃; the temperature of the hydrolysis reaction is preferably achieved by heating in a water bath. In the invention, the time of the hydrolysis reaction is preferably 1-3 h, and more preferably 2-3 h.
After the hydrolysis reaction is completed, the hydrolysis solution is preferably mixed with water, so that the hydrolysis reaction is stopped, and the cellulose nanocrystal suspension is obtained. In the invention, the adding volume of the water is preferably 3-10 times of the volume of the sulfuric acid, and more preferably 5-8 times.
After the nano-cellulose suspension is obtained, the nano-cellulose suspension is sequentially centrifuged, dialyzed and concentrated to obtain the nano-cellulose suspension with the mass concentration of 1-3%. The present invention preferably removes the residual sulfuric acid in the cellulose nanocrystal suspension by centrifugation.
In the invention, the pH value of the nano-cellulose suspension obtained after centrifugation is preferably 2-4. Before the centrifugation, the nano-cellulose suspension is preferably kept stand and settled to obtain a supernatant and a lower turbid liquid; and pouring out the supernatant liquid, and centrifuging the lower turbid liquid. In the invention, the standing and settling time is preferably 10-30 h, more preferably 15-25 h, and most preferably 20 h. In the invention, the centrifugation time is preferably 2-5 times, and more preferably 3-4 h; the rotating speed of the centrifugation is preferably 4000-8000 rpm, more preferably 5000-6000 rpm, and most preferably 6000 rpm; the time of single centrifugation is preferably 3-8 min, and more preferably 6 min.
In the invention, the pH value of the dialyzed material obtained after dialysis is preferably 5-8, and more preferably 6-7. In the invention, the cut-off molecular weight of a dialysis membrane adopted by dialysis is preferably 6000-12000, and more preferably 8000-10000; the dialysis time is preferably 3 to 7 days, and more preferably 4 to 6 days. The invention further purifies the centrifugal material obtained after centrifugation by dialysis to remove the residual sulfuric acid.
The invention preferably adopts heating concentration, and the heating temperature is preferably 60-90 ℃, and more preferably 70-80 ℃; in the embodiment of the invention, the concentration is carried out in an oven at the temperature of 60-90 ℃. The invention has no special requirement on the heating time, and can concentrate the washed materials to meet the requirement of mass concentration. The method comprises the steps of hydrolyzing sulfate bleached wood pulp by using sulfuric acid, wherein the surface of the nano-cellulose obtained after hydrolysis contains a certain amount of negative charges; the mass concentration of the nano-cellulose suspension obtained after dialysis is about 0.5%, the mass concentration of the nano-cellulose suspension obtained after washing is up to 1-3% through concentration, and under the condition of the mass concentration, the nano-cellulose is self-assembled under the action of surface negative charges, so that the anisotropic nano-cellulose suspension is obtained.
And after obtaining the nano-cellulose suspension, carrying out ultrasonic treatment on the nano-cellulose suspension to enable the cellulose nanocrystals to be more dispersed. In the invention, the time of the ultrasonic treatment is preferably 10-30 min, and more preferably 20-30 min; the power of the ultrasonic wave is preferably 400-600W, and more preferably 500W.
The nano-cellulose suspension and the polyurethane aqueous solution are mixed and then coated on the surface of furniture wood, and the structural color coatings with different iridescent colors are obtained after drying. In the present invention, the mass concentration of the aqueous polyurethane solution is 5 to 25%, more preferably 10 to 15%, and most preferably 10%. The preparation method of the polyurethane aqueous solution is not particularly limited, and the technical scheme of preparing the solution, which is well known by the technical personnel in the field, can be adopted; in the embodiment of the invention, the polyurethane is mixed with deionized water, and the polyurethane and the deionized water are uniformly mixed under the action of magnetic stirring. The magnetic stirring time is preferably 10-30 min, and more preferably 10-20 min; the rotation speed of the magnetic stirring is preferably 300-600 rpm, and more preferably 400-500 rpm.
In the invention, the mass content of polyurethane in the nano-cellulose-polyurethane iridescent structural color coating is 10-50%. Preferably 10 to 30%. In the present invention, the mixing of the nanocellulose suspension and the aqueous polyurethane solution is preferably performed under stirring conditions, more preferably under magnetic stirring conditions; the magnetic stirring time is preferably 2-6 h, and more preferably 3-5 h; the rotating speed of the magnetic stirring is preferably 500-800 rpm, and more preferably 500-600 rpm.
The coating of the present invention is not particularly limited, and a film-forming method known to those skilled in the art may be used. The nanocellulose-polyurethane mixture is preferably coated directly on the surface of wood for wood products. In the invention, the drying temperature is preferably 20-40 ℃; in the examples of the present invention, drying is carried out in particular at room temperature, i.e. without additional heating or cooling. The drying environment is not particularly limited, and the drying can be carried out in an air state; the invention has no specific requirement on the drying time, and can completely remove the solvent. In the embodiment of the invention, the mixture is uniformly coated on the surface of wood for wood products, and the wood is dried; the present invention has no particular requirement on the size of the wood. According to the invention, the solvent in the mixed material can be naturally volatilized through drying in the air at room temperature, so that the iridescent structural color formed by assembling the nano-cellulose is retained to the maximum extent.
The invention provides a nano-cellulose-polyurethane iridescent structural color coating prepared by the preparation method in the technical scheme, which comprises a nano-cellulose iridescent structural color coating base material and polyurethane doped in the base material. In the invention, the mass content of the polyurethane in the nano-cellulose-polyurethane iridescent structural color coating is preferably 10-50%, and more preferably 10-30%. In the invention, the thickness of the nano cellulose-polyurethane iridescent structural color coating for the wood product is preferably 5-10 μm, and more preferably 6-8 μm.
The invention provides application of the nano-cellulose-polyurethane iridescent structural color coating in the scheme in furniture coating materials. The nano-cellulose-polyurethane iridescent structural color coating provided by the invention has the iridescent characteristic of nano-cellulose and the good interface bonding characteristic of polyurethane, has different iridescent colors under different ratios of nano-cellulose to polyurethane, and can be applied to decorative materials such as furniture, floors and the like.
Claims (7)
1. A preparation method of a nano-cellulose-polyurethane iridescent structural color coating for a wood product is characterized by comprising the following steps:
1) mixing sulfate bleached wood pulp and sulfuric acid for hydrolysis reaction, mixing the obtained solution with water after the reaction to stop the hydrolysis reaction, and obtaining nano cellulose suspension;
2) sequentially centrifuging, dialyzing and concentrating the obtained nano-cellulose suspension to obtain the nano-cellulose suspension with the mass concentration of 1-3%;
3) ultrasonically dispersing the nano cellulose suspension obtained in the step 2);
4) preparing aqueous polyurethane varnish into an aqueous polyurethane solution with the mass concentration of 5-25%; wherein the mass concentration of the aqueous polyurethane solution is 10-15%, the aqueous polyurethane solution is uniformly mixed under the action of magnetic stirring, the rotating speed of the magnetic stirring is 300-600 rpm, and the time is 10-30 min;
5) mixing the nano cellulose suspension obtained in the step 3) with an aqueous polyurethane solution, coating the mixture on the surface of a wood product, and drying to obtain an iridescent structural color coating; the nano-cellulose suspension and the aqueous polyurethane solution are uniformly mixed under the action of magnetic stirring, wherein the rotating speed of the magnetic stirring is 500-800 rpm, and the time is 2-6 hours; the mass content of polyurethane in the mixed nano-cellulose-polyurethane iridescent structural color coating is 10-50%, and the thickness of the coating is 5-10 mu m.
2. The preparation method of the nano-cellulose-polyurethane iridescent structural color coating for the wood products according to the claim 1 is characterized in that the mass concentration of the sulfuric acid in the step 1) is 70-90%, and the volume ratio of the mass of the sulfate bleached wood pulp to the sulfuric acid is (10-30) g: (150-250) mL; the hydrolysis reaction is stopped by adding water with the volume 3-10 times of that of sulfuric acid at the temperature of 30-70 ℃ for 1-3 hours.
3. The preparation method of the nano-cellulose-polyurethane iridescent structural color coating for the wood products according to the claim 1 is characterized in that before the centrifugation in the step 2), the nano-cellulose suspension is kept stand and settled for 10-30 h to obtain a supernatant and a lower turbid liquid; the supernatant was decanted off and the lower turbidity was centrifuged again.
4. The preparation method of the nano-cellulose-polyurethane iridescent structural color coating for the wood products according to the claim 1 is characterized in that the centrifugation speed in the step 2) is 5000-8000 rpm, the centrifugation time is 3-8 min, the centrifugation times are 2-5 times, and the pH value of the nano-cellulose suspension obtained after centrifugation is 2-4.
5. The preparation method of the nano-cellulose-polyurethane iridescent structural color coating for the wood products according to claim 1, characterized in that the pH value of the dialyzed material in the step 2) is 5-8; the cut-off molecular weight of a dialysis membrane adopted by dialysis is 6000-12000; the dialysis time is 3-7 days.
6. The method for preparing the nano-cellulose-polyurethane iridescent structural color coating for the wood products according to the claim 1, characterized in that the concentration in the step 2) is heating concentration in an oven with the temperature of 60-90 ℃ until the mass concentration of the nano-cellulose suspension is 1-3%.
7. The preparation method of the nano-cellulose-polyurethane iridescent structural color coating for the wood products according to the claim 1 is characterized in that in the step 3), the ultrasonic time is 10-30 min; the ultrasonic power is 400-600W.
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