CN103320003A - Preparation method for nanometer cellulose composite waterborne polyurethane paint film on wood surface - Google Patents

Abstract

The invention provides a preparation method for a nanometer cellulose composite waterborne polyurethane paint film on a wood surface, which relates to a preparation method for a wood surface paint film. The invention aims to overcome the problems of severe pollution to the environment, high toxicity and low strength of a conventional wood surface paint film. The method comprises the following steps: 1, preparation of nanometer cellulose; 2, synthesis of a waterborne polyurethane emulsion; and 3, preparation of the nanometer cellulose composite waterborne polyurethane paint film on the wood surface. The preparation method is simple, easy to operate, environment-friendly, safe and nontoxic; Young modulus is increased by 32%, which proves strength of the waterborne polyurethane paint film is enhanced indeed; temperature corresponding to a maximum weight loss rate is 420 DEG C, which shows that heat stability of a Korean pine chip is obviously improved after the polyurethane paint film is coated on the surface of the chip.

Description

A kind of preparation method of nano-cellulose composite waterborne polyurethane paint film on wood surface

technical field

The invention relates to a method for preparing a wood surface paint film.

Background technique

Applying a layer of paint film to the wood surface will protect the wood and prolong the service life of the wood. Solvent-based polyurethane contains a large amount of organic solvents, which are toxic and seriously pollute the environment, especially in two-component polyurethane, which has a high residual solvent and high toxicity.

Water-based polyurethane means that water is mainly used as the reaction solvent instead of organic solvent in the process of preparing polyurethane. Distinguished by appearance, water-based polyurethane can be roughly divided into three categories: polyurethane dispersion, polyurethane aqueous solution, and polyurethane emulsion. The difference lies in the form of water dispersed in polyurethane macromolecular particles, and there is no exact limit. The water-soluble polyurethane mentioned in actual life production refers to polyurethane dispersion or water-based polyurethane emulsion. At present, water-based polyurethane is used as the paint film on the wood surface, which has the problem of low paint film strength.

Contents of the invention

The purpose of the present invention is to solve the problem of serious environmental pollution and high toxicity when using solvent-based polyurethane as the paint film on the surface of wood, and the problem of low strength of the paint film when using water-based polyurethane as the paint film on the surface of wood, and to provide a nano-cellulose composite on the wood surface The preparation method of waterborne polyurethane paint film.

The preparation method of wood surface nano cellulose composite waterborne polyurethane paint film, realizes according to the following steps:

1. Preparation of nanocellulose: pretreat 1.00-3.00g of bamboo pulp in a sulfuric acid solution with a mass fraction of 30%-60% for 2-4 hours, filter and wash until neutral, and then disperse the product to 400-500mL In ionized water, ultrasonically disperse for 5-10 minutes, add it to a colloid mill and grind it for 0.5-1 hour, then add it to a high-pressure homogenizer, homogenize it for 10-20 times under a pressure of 1000-1500 Bar, and then crush the product for 5-20 minutes. 15min, obtain nanocellulose colloidal solution;

2. Synthesis of water-based polyurethane emulsion: Add 50-150mL of acetone into a beaker containing 10-30g of polyethylene glycol, add 3.5g of toluene diisocyanate after complete dissolution, and drop 3-5 drops of dibutyltin dilaurate , and then transfer the solution to a three-neck flask with a reflux condenser and a mechanical stirrer, and react at 70-90°C for 1-1.5h to obtain a water-based polyurethane prepolymer, lower the temperature to 60°C, and add 0.62 g of diethylenetriamine and 0.22g of diethylene glycol, react for 2-4 hours, lower the temperature to 45°C, add 0.3g of glacial acetic acid, react for 0.5h, then lower the temperature to 20°C, add 50-150mL of distilled water , stirred until emulsified, then transferred to a rotary evaporator, and evaporated acetone to obtain a water-based polyurethane emulsion;

3. Preparation of nano-cellulose composite water-based polyurethane paint film on wood surface: Mix water-based polyurethane emulsion and nano-cellulose colloidal solution at a volume ratio of 4:1, stir magnetically to obtain a mixture system, and then put wood chips to be treated into the mixture system Soak for 20-26 hours, take it out and dry it at room temperature, and then complete the preparation of the nano-cellulose composite water-based polyurethane paint film on the wood surface.

The advantages of the present invention are:

1. Prepare a stable aqueous polyurethane emulsion through prepolymerization, chain extension, neutralization, emulsification and rotary evaporation, and then introduce nanocellulose prepared by high-pressure homogeneity into the emulsion system through physical blending. Coating nano-cellulose composite water-based polyurethane paint film on the wood surface. The method is simple, easy to operate, environmentally friendly, safe and non-toxic.

2, red pine wood chips, the red pine wood chips that are coated with water-based polyurethane and the surface of the gained of the present invention are coated with the red pine wood chips of nanocellulose composite water-based polyurethane paint film, Young's modulus is 71569MPa successively, 45448MPa, 60175MPa, thus can After being coated with water-based polyurethane paint film, the Young's modulus of wood chips decreased, while the surface of red pine wood chips coated with nanocellulose composite water-based polyurethane paint film increased by 32%. It shows that the introduction of nanocellulose does enhance the strength of waterborne polyurethane paint film.

3. As can be seen from the DTG diagram, the temperature corresponding to the maximum weight loss rate of the red pine wood chip is 382 ° C, and the red pine wood chip coated with water-based polyurethane and the surface of the gained surface of the present invention are coated with nano-cellulose composite water-based polyurethane paint film. For pine wood chips, the temperature corresponding to the maximum weight loss rate is 420°C, which shows that after the surface of red pine wood chips is coated with polyurethane paint film, its thermal stability is obviously improved.

Description of drawings

Fig. 1 is the Fourier transform infrared spectrogram of the red pine wood chip that the gained surface is coated with nano-cellulose composite water-based polyurethane paint film in the embodiment;

Fig. 2 is the scanning electron micrograph of sample a in the embodiment;

Fig. 3 is the scanning electron micrograph of sample b in the embodiment;

Fig. 4 is the scanning electron micrograph of sample c in the embodiment;

Fig. 5 is the sectional view of sample a, b and c in the embodiment;

Fig. 6 is the stress-strain graph of sample a, b and c in the embodiment;

Fig. 7 is the TG curve figure of sample a, b and c in the embodiment;

Fig. 8 is a DTG curve diagram of samples a, b and c in the embodiment.

Detailed ways

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

Specific embodiment one: the preparation method of nano-cellulose composite water-based polyurethane paint film on the surface of wood in this embodiment is realized in the following steps:

1. Preparation of nanocellulose: pretreat 1.00-3.00g of bamboo pulp in a sulfuric acid solution with a mass fraction of 30%-60% for 2-4 hours, filter and wash until neutral, and then disperse the product to 400-500mL In ionized water, ultrasonically disperse for 5-10 minutes, add it to a colloid mill and grind it for 0.5-1 hour, then add it to a high-pressure homogenizer, homogenize it for 10-20 times under a pressure of 1000-1500 Bar, and then crush the product for 5-20 minutes. 15min, obtain nanocellulose colloidal solution;

2. Synthesis of water-based polyurethane emulsion: Add 50-150mL of acetone into a beaker containing 10-30g of polyethylene glycol, add 3.5g of toluene diisocyanate after complete dissolution, and drop 3-5 drops of dibutyltin dilaurate , and then transfer the solution to a three-neck flask with a reflux condenser and a mechanical stirrer, and react at 70-90°C for 1-1.5h to obtain a water-based polyurethane prepolymer, lower the temperature to 60°C, and add 0.62 g of diethylenetriamine and 0.22g of diethylene glycol, react for 2-4 hours, lower the temperature to 45°C, add 0.3g of glacial acetic acid, react for 0.5h, then lower the temperature to 20°C, add 50-150mL of distilled water , stirred until emulsified, then transferred to a rotary evaporator, and evaporated acetone to obtain a water-based polyurethane emulsion;

3. Preparation of nano-cellulose composite water-based polyurethane paint film on wood surface: Mix water-based polyurethane emulsion and nano-cellulose colloidal solution at a volume ratio of 4:1, stir magnetically to obtain a mixture system, and then put wood chips to be treated into the mixture system Soak for 20-26 hours, take it out and dry it at room temperature, and then complete the preparation of the nano-cellulose composite water-based polyurethane paint film on the wood surface.

The bamboo pulp in Step 1 of this embodiment is the pulp prepared from bamboo in a paper mill.

The nanocellulose colloidal solution in Step 1 of this embodiment is freeze-dried to obtain solid nanocellulose for future use.

The remaining mixture system after soaking the wood chips to be treated in Step 3 of this embodiment is freeze-dried to obtain a solid for future use.

The wood chip to be treated in the third step of this embodiment is the wood that is cut into the desired size and prepared on the surface with a nanocellulose composite water-based polyurethane paint film.

Embodiment 2: This embodiment differs from Embodiment 1 in that in step 1, 2.00 g of bamboo pulp is pretreated in a sulfuric acid solution with a mass fraction of 45% for 3 hours. Other steps and parameters are the same as those in Embodiment 1.

Specific embodiment 3: The difference between this embodiment and specific embodiment 1 or 2 is that the product in step 1 is dispersed into 450mL deionized water, ultrasonically dispersed for 8min, then added to a colloid mill for grinding for 0.7h, and then added to a high-pressure homogenizer , homogenized 15 times under a pressure of 1200 Bar, and then the product was subjected to cell disruption for 10 min. Other steps and parameters are the same as those in Embodiment 1 or Embodiment 2.

Embodiment 4: This embodiment differs from Embodiments 1 to 3 in that in Step 2, toluene diisocyanate and polyethylene glycol need to be dehydrated at 40-50° C. for 10-16 hours before use. Other steps and parameters are the same as those in Embodiments 1 to 3.

Embodiment 5: This embodiment is different from Embodiment 1 to Embodiment 4 in that in step 2, 100 mL of acetone is added to a beaker containing 20 g of polyethylene glycol. Other steps and parameters are the same as in one of the specific embodiments 1 to 4.

Specific embodiment six: the difference between this embodiment and one of specific embodiments one to five is that in step two, 4 drops of dibutyltin dilaurate are added dropwise. Other steps and parameters are the same as one of the specific embodiments 1 to 5.

Embodiment 7: This embodiment is different from Embodiment 1 to Embodiment 6 in that the reaction is carried out at 80° C. for 1.2 h in step 2. Other steps and parameters are the same as one of the specific embodiments 1 to 6.

Embodiment 8: The difference between this embodiment and one of Embodiments 1 to 7 is that in step 2, the wood chips to be treated are put into the mixture system and soaked for 24 hours. Other steps and parameters are the same as one of the specific embodiments 1 to 7.

Embodiment 9: This embodiment differs from Embodiment 1 to Embodiment 8 in that the rotating speed of magnetic stirring in step 3 is 600 r/min, and the stirring time is 1.5 h. Other steps and parameters are the same as those in Embodiments 1 to 8.

Example:

The preparation method of wood surface nano cellulose composite waterborne polyurethane paint film, realizes according to the following steps:

1. Preparation of nanocellulose: Pretreat 2.00g of bamboo pulp in a sulfuric acid solution with a mass fraction of 30% for 2h, filter and wash until neutral, then disperse the product in 450mL of deionized water, ultrasonically disperse for 5min and then add to Grind in a colloid mill for 0.5h, then add it to a high-pressure homogenizer, homogenize it 15 times under a pressure of 1500Bar, and then disrupt the cells of the product for 10min to obtain a nanocellulose colloidal solution;

2. Synthesis of water-based polyurethane emulsion: Add 100mL of acetone into a beaker containing 20g of polyethylene glycol, add 3.5g of toluene diisocyanate after it is completely dissolved, drop 4 drops of dibutyltin dilaurate, and then transfer the solution to In a three-neck flask with a reflux condenser and a mechanical stirrer, react at 80°C for 1.5h to obtain a water-based polyurethane prepolymer, lower the temperature to 60°C, and add 0.62g of diethylenetriamine and 0.22g of Diethylene glycol, react for 2-4 hours, lower the temperature to 45°C, add 0.3g of glacial acetic acid, react for 0.5h, then lower the temperature to 20°C, add 100mL of distilled water, stir until emulsification, and then transfer to a rotary evaporator , steam out acetone to obtain water-based polyurethane emulsion;

3. Preparation of nano-cellulose composite water-based polyurethane paint film on wood surface: Mix water-based polyurethane emulsion and nano-cellulose colloidal solution at a volume ratio of 4:1, stir magnetically to obtain a mixture system, and then put wood chips to be treated into the mixture system Soak for 24 hours, take it out, and dry it at room temperature to complete the preparation of the nanocellulose composite water-based polyurethane paint film on the wood surface.

In step 2 of this example, toluene diisocyanate and polyethylene glycol need to be dehydrated at 45° C. for 12 hours before use.

Wood chips to be treated in the present embodiment step 3 are long 120mm, wide 15mm, thick 0.341mm red pine wood chips.

The present embodiment gained surface is coated with the red pine wood chip of nano-cellulose composite water-based polyurethane paint film, its Fourier transform infrared spectrogram, as shown in Figure 1, NCC is nano-cellulose, and WPU is water-based polyurethane solid, and WPU/ NCC is a nanocellulose composite waterborne polyurethane solid. It can be seen from the NCC spectrum that the absorption peak around 3300cm ^-1 is the -OH stretching vibration peak, and the absorption peak around 1050cm ^-1 is the COC stretching vibration peak. Comparing the spectra of WPU and WPU/NCC, it can be seen that there is almost no difference between the two, indicating that the nanocellulose is well wrapped by water-based polyurethane, and its spectrum is not reflected in the composite system, and there is no appearance at around 2300cm ^-1 - The absorption peak of NCO indicates that -NCO in the raw material has completely participated in the reaction; at the same time, there is an obvious C=O absorption peak of carbamate at 1735cm ^-1 , indicating that carbamate is indeed generated, and at 2900cm ^- The methylene absorption peak at about ¹ , and the stretching vibration peak of the basic skeleton of the benzene ring at 1450-1600 cm ^-1 are also clearly reflected in the spectrogram.

Blank reference: red pine wood chips, that is, sample a; its scanning electron microscope image is shown in Figure 2.

Comparative experiment: replace the nano-cellulose colloid solution with deionized water, and the red pine wood chip coated with water-based polyurethane, that is, sample b; its scanning electron microscope image is shown in Figure 3.

The red pine wood chips whose surface is coated with nanocellulose composite water-based polyurethane paint film in this embodiment, i.e. sample c; its scanning electron microscope picture is shown in FIG. 4 .

In Figure 2, you can clearly see the grain and pits of the red pine wood chip. Comparing Figure 3 and Figure 4, it can be seen that there is indeed a layer of paint film on the red pine wood chip. , the paint film in Figure 4 is smoother, and the viscosity is also significantly greater than that in Figure 3, indicating that the addition of nanocellulose can indeed thicken the water-based polyurethane to a certain extent, and can make the surface of the sample smoother.

The fracture diagrams of samples a, b and c are shown in Figure 5. During the stretching process, the samples did not show obvious plastic deformation before fracture, so they all belong to brittle fracture; the fracture shape of sample a is due to the During the stretching process, the sample may be torn directly along the pit pattern due to its thinness, while samples b and c are due to the fact that the water-based polyurethane paint film coated on the surface of the wood chip directly blocks the grain of the wood chip itself. The hole texture, brittle fracture occurred in the process of stress.

The stress-strain curves of samples a, b and c are shown in Figure 6. The stress-strain curves can be obtained. The Young’s modulus of samples a, b and c are 71569MPa, 45448MPa and 60175MPa in turn, and it can be concluded that the coating After coating the water-based polyurethane paint film, the Young's modulus of the wood chips decreased, while the surface of the red pine wood chips coated with nano-cellulose composite water-based polyurethane paint film increased by 32%, indicating that the nano-cellulose The introduction of does enhance the strength of waterborne polyurethane paint film.

The TG curves of samples a, b and c are shown in Figure 7. It can be seen from the TG diagram that the thermogravimetric curves of the samples are all in three stages, the first stage is 50-150°C; for a, the The stage belongs to the dehydration stage, and for b and c, the dehydration may also include the volatilization of small organic molecules adsorbed in the waterborne polyurethane. The second stage is 150-290°C. This stage is a platform, the sample does not lose weight, and the quality remains basically constant. The third stage is 290-470°C. This stage is mainly the decomposition of the sample, accompanied by the loss of hydrogen and oxygen atoms and some carbon atoms, and the sample loses weight quickly. After 470°C, the reaction ends, and the residual amount remains basically unchanged.

The DTG curves of samples a, b, and c are shown in Figure 8. It can be seen from the DTG graph that the temperature corresponding to the maximum weight loss rate of sample a is 382 ° C, while the temperature corresponding to the maximum weight loss rate of samples b and c is 420 ° C. It shows that after the surface of the red pine wood chip is coated with a polyurethane paint film, its thermal stability is obviously improved, and the addition of nanocellulose has little effect on its thermal stability.

Claims (9)

1. a kind of preparation method of wood surface nano cellulose composite waterborne polyurethane paint film is characterized in that it realizes by the following steps: 1. Preparation of nanocellulose: pretreat 1.00-3.00g of bamboo pulp in a sulfuric acid solution with a mass fraction of 30%-60% for 2-4 hours, filter and wash until neutral, and then disperse the product to 400-500mL In ionized water, ultrasonically disperse for 5-10 minutes, add it to a colloid mill and grind it for 0.5-1 hour, then add it to a high-pressure homogenizer, homogenize it for 10-20 times under a pressure of 1000-1500 Bar, and then crush the product for 5-20 minutes. 15min, obtain nanocellulose colloidal solution; 2. Synthesis of water-based polyurethane emulsion: Add 50-150mL of acetone into a beaker containing 10-30g of polyethylene glycol, add 3.5g of toluene diisocyanate after complete dissolution, and drop 3-5 drops of dibutyltin dilaurate , and then transfer the solution to a three-neck flask with a reflux condenser and a mechanical stirrer, and react at 70-90°C for 1-1.5h to obtain a water-based polyurethane prepolymer, lower the temperature to 60°C, and add 0.62 g of diethylenetriamine and 0.22g of diethylene glycol, react for 2-4 hours, lower the temperature to 45°C, add 0.3g of glacial acetic acid, react for 0.5h, then lower the temperature to 20°C, add 50-150mL of distilled water , stirred until emulsified, then transferred to a rotary evaporator, and evaporated acetone to obtain a water-based polyurethane emulsion; 3. Preparation of nano-cellulose composite water-based polyurethane paint film on wood surface: Mix water-based polyurethane emulsion and nano-cellulose colloidal solution at a volume ratio of 4:1, stir magnetically to obtain a mixture system, and then put wood chips to be treated into the mixture system Soak for 20-26 hours, take it out and dry it at room temperature, and then complete the preparation of the nano-cellulose composite water-based polyurethane paint film on the wood surface. 2. the preparation method of a kind of wood surface nano-cellulose composite water-based polyurethane paint film according to claim 1 is characterized in that in step 1, 2.00g bamboo pulp is pretreated 3h in the sulfuric acid solution of 45% in mass fraction. 3. according to the preparation method of claim 1 or 2 described a kind of wood surface nanocellulose composite water-based polyurethane paint film, it is characterized in that product is dispersed in 450mL deionized water in step 1, joins in the colloid mill after ultrasonic dispersion 8min Grinding for 0.7 h, then adding to a high-pressure homogenizer, homogenizing 15 times under a pressure of 1200 Bar, and then subjecting the product to cell disruption for 10 min. 4. The preparation method of a kind of wood surface nanocellulose composite water-based polyurethane paint film according to claim 3, it is characterized in that in step 2, toluene diisocyanate and polyethylene glycol need to be heated at 40～50 ℃ respectively before use Under dehydration treatment for 10-16 hours. 5. the preparation method of a kind of wood surface nanocellulose composite waterborne polyurethane paint film according to claim 4 is characterized in that 100mL acetone is added in the beaker that fills 20g Polyethylene Glycol in step 2. 6. the preparation method of a kind of wood surface nanocellulose composite waterborne polyurethane paint film according to claim 5 is characterized in that in step 2, drips 4 dibutyltin dilaurates. 7. The preparation method of a kind of wood surface nanocellulose composite water-based polyurethane paint film according to claim 6, characterized in that in step 2, react at 80°C for 1.2h. 8. the preparation method of a kind of wood surface nanocellulose composite water-based polyurethane paint film according to claim 7, it is characterized in that in step 2, wood chips to be treated are put into the mixture system and soaked for 24h. 9. the preparation method of a kind of wood surface nanocellulose composite water-based polyurethane paint film according to claim 8, it is characterized in that the rotating speed of magnetic stirring in step 3 is 600r/min, and stirring time is 1.5h.

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