High-molecular-weight and high-solid-content nitrocellulose aqueous dispersion and preparation method thereof

Abstract

The invention discloses a method for preparing a high-molecular-weight and high-solid-content nitrocellulose aqueous dispersion, which comprises the following steps: uniformly dissolving high-molecular-weight and large-mass nitrocellulose in an ethyl acetate solvent to form a homogeneous solution; the preparation method comprises the following steps: adding a nitrocellulose aqueous dispersion into a supersaturated polyvinyl alcohol solution of ethyl acetate, dropwise adding the nitrocellulose aqueous dispersion into the supersaturated polyvinyl alcohol solution of ethyl acetate through a constant-pressure dropping funnel under stirring, uniformly stirring, transferring into a high-speed homogenizer, emulsifying again, removing ethyl acetate through a rotary evaporator, and filtering through a screen to obtain the nitrocellulose aqueous dispersion. The preparation of the high-molecular-weight and high-solid-content nitrocellulose aqueous dispersion is realized by adopting an emulsification-solvent evaporation method, and the method is simple to operate, low in cost, environment-friendly, greatly adjustable in NC content and variety, and wide in application prospect.

Description

Technical Field

[0001] The invention relates to a method for preparing a nitrocellulose aqueous coating system. Background Art

[0002] Biomass-derived renewable coatings based on vegetable oils, starches and cellulose as main raw materials have attracted great attention in many fields due to their non-toxicity, biocompatibility and biodegradability. Nitrocellulose is a non-toxic and biodegradable bioplastic prepared by a highly exothermic esterification reaction between cellulose and concentrated nitric acid. Due to its excellent film-forming ability, good mechanical properties, durability, good adhesion to substrates and other special properties, it plays an increasingly important role in printing inks, adhesives, and different types of industrial coatings such as leather and wood. However, with the increasing awareness of environmental protection and safe production, traditional organic solvent-based NC coatings have been gradually replaced by low-pollution, non-flammable water-based nitrocellulose (WNC).

[0003] Previous researchers have done a lot of work on the preparation of WNC. Fatemeh Fallah et al. prepared WNC by direct mechanical emulsification and gel emulsification, respectively. The effects of solvent type, emulsification rate, storage temperature, dispersed phase viscosity and addition rate on NC particle size and WNC stability were studied. However, in the preparation process, the researchers used relatively high concentrations of emulsifiers and high-energy-consuming equipment, which greatly increased the production cost and aggravated the pollution to the environment. Sude Ma et al. used a self-emulsification method, using dimethylolpropionic acid as a hydrophilic chain extender, isophorone diisocyanate as a reactant, and triethylamine as a capping agent to introduce carboxyl groups into the nitrocellulose molecular chain, so that it spontaneously formed an emulsion with thermodynamically stable properties in the aqueous phase. Compared with other methods, the self-emulsification method avoids the use of emulsifiers and high energy input, and the prepared emulsion particles are smaller in size and more evenly distributed. However, its main disadvantages are that the preparation process is complicated, the operation is difficult, the preparation cost is high, and it is difficult to achieve real industrial application.

[0004] The inventors have found that the solvent replacement method is a simple and quick method for preparing polymer aqueous dispersions. In this method, a hydrophobic solute is first dissolved in a water-miscible organic solvent (usually ethanol, acetone or tetrahydrofuran) to form an organic phase, and then the solution is added to a certain amount of non-solvent under continuous magnetic stirring to generate a polymer nano-aqueous dispersion by means of the "Ouzo" mechanism. The solvent replacement method does not require the participation of an emulsifier, and polymer particles can be formed spontaneously without external energy input. Xia Wu et al. prepared an ethyl cellulose aqueous dispersion using the solvent replacement method. The particle size of the obtained dispersion was between 60-100 nm and showed relatively excellent stability. However, the solvent replacement method has high requirements for the type, molecular weight, concentration and type of the polymer, and the like. When the relative molecular weight of the polymer is high or the solid content of the organic solution is high, large-sized white flocs will appear in the formed aqueous dispersion, and even sedimentation will occur. This also limits the type and solid content range of nitrocellulose that can be used to prepare aqueous dispersions, and it is not universal and difficult to achieve true industrial production. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a method for preparing a high molecular weight, high solid content nitrocellulose aqueous dispersion, wherein the NC solution is prepared by an emulsification-solvent volatilization method using weakly water-soluble ethyl acetate as an organic phase, and the high molecular weight, high solid content nitrocellulose aqueous dispersion is prepared in combination with an environmentally friendly surfactant polyvinyl alcohol.

[0006] The above technical purpose of the present invention relates to the following scheme: a method for preparing a high molecular weight, high solid content nitrocellulose aqueous dispersion, characterized in that: a magnetic stirrer is used to uniformly dissolve the high molecular weight, large mass nitrocellulose in an ethyl acetate solvent to form a homogeneous solution; then it is added dropwise to a supersaturated polyvinyl alcohol solution of ethyl acetate through a constant pressure dropping funnel under stirring, after uniform stirring, it is transferred to a high-speed homogenizer for re-emulsification, and then the ethyl acetate is driven off by a rotary evaporator, and the nitrocellulose aqueous dispersion is obtained by sieve filtration.

[0007] The method comprises the following steps: 1) Preparation of oil phase: Add a certain amount of nitrocellulose to a certain amount of ethyl acetate, and continuously stir and dissolve at a certain temperature to form a yellow viscous solution as the oil phase; 2) Preparation of aqueous phase: adding a certain amount of polyvinyl alcohol into deionized water and stirring to dissolve at a certain temperature, then pouring a certain amount of ethyl acetate into the aqueous solution of polyvinyl alcohol to form a saturated aqueous solution of polyvinyl alcohol in ethyl acetate as the aqueous phase; 3) Preparation of crude emulsion: add a certain amount of water phase to container A, continue stirring, take a certain amount of oil phase, and drop it into the water phase under stirring; after the dropwise addition is completed, continue stirring for a certain period of time; remove container A and cool it to room temperature to obtain a crude emulsion; 4) Preparation of fine emulsion: The crude emulsion is transferred into container B, and the crude emulsion is homogenized in an ice water bath by controlling the rotor speed using a high-speed homogenizer to obtain a fine emulsion; 5) Removal of ethyl acetate: The homogenized fine emulsion is transferred to a rotary evaporator and evaporated under reduced pressure until there is no organic solvent phase in the emulsion. Then, the nitrocellulose aqueous dispersion is filtered through a nylon mesh.

[0008] Furthermore, in step 1, the weight average molecular weight of the nitrocellulose is 395800-604900; the concentration of nitrocellulose in the yellow viscous solution is 30 mg / mL-60 mg / mL; the stirring temperature is 45-55° C., and the stirring time is 7-9 h.

[0009] Furthermore, in step 2, 200-1000 mg of 1788 polyvinyl alcohol is added to 18-22 mL of deionized water and stirred at 80-90° C. for 6-8 h to dissolve, and then 9-10 wt % (mass fraction of deionized water) of ethyl acetate is poured into the aqueous solution of polyvinyl alcohol to form a saturated aqueous solution of polyvinyl alcohol in ethyl acetate.

[0010] Furthermore, in step 3), 18-20 mL of the aqueous phase is added to container A, and the stirring speed is maintained at 800-900 r / min; 6.7-20 mL of the oil phase is added to container C, and the dropping speed is controlled to be 1.5-2 s per drop; after the dropping is completed, stirring is continued for 1-2 h.

[0011] Furthermore, in step 4, the rotor speed of the homogenizer is controlled to be 10000-22000 r / min, and the homogenization time is 1-7 min; Furthermore, in step 5, the vacuum degree of the rotary evaporator is 0.098-0.1 MPa, the water bath temperature is 35-45°C, the rotation speed is 100-130 r / min, and the filtration is performed with a nylon gauze of 150-200 mesh.

[0012] The container A is a 100 mL single-mouth round-bottom flask; the container B is a 100 mL beaker; and the container C is a 25 mL constant pressure dropping funnel.

[0013] On the other hand, the present invention provides a high-molecular-weight, high-solid-content nitrocellulose aqueous dispersion, which is prepared by the following method: using a magnetic stirrer to uniformly dissolve high-molecular-weight, large-mass nitrocellulose in an ethyl acetate solvent to form a homogeneous solution; then dropping the solution into a supersaturated polyvinyl alcohol solution of ethyl acetate through a constant-pressure dropping funnel under stirring, stirring evenly, transferring the solution into a high-speed homogenizer for re-emulsification, then using a rotary evaporator to drive off the ethyl acetate, and filtering through a sieve to obtain the nitrocellulose aqueous dispersion.

[0014] The weight average molecular weight of the nitrocellulose is 395800-604900.

[0015] Compared with the prior art, the present invention has the following significant advantages: (1) Compared with the traditional solvent-based NC coating system, the aqueous dispersion prepared by the present invention is more environmentally friendly and green, and is also safer, reducing the problems of complex post-processing and high production costs caused by the use of organic solvents.

[0016] (2) Compared with commercially available nitrocellulose-based aqueous dispersions and those reported in the literature, the nitrocellulose aqueous dispersion provided by the present invention has a simple preparation process, does not require nitrogen protection and complex chemical reactions, has good product reproducibility, is conducive to industrial production, and has a high solid content and a wide range of nitrocellulose options.

[0017] (3) The entire product of the aqueous dispersion prepared by the present invention contains only two substances, polyvinyl alcohol and nitrocellulose, and does not require the participation of components such as emulsifiers. At the same time, the film-forming integrity and storage stability of the aqueous dispersion are also improved.

[0018] (4) The high molecular weight, high solid content nitrocellulose aqueous dispersion provided by the present invention has the characteristics of stable storage, no odor, low viscosity, high solid content, etc. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without carrying out creative work are within the scope of protection of the present invention.

[0020] Technologies, methods, and apparatus known to ordinary technicians in the relevant field may not be discussed in detail, but where appropriate, such technologies, methods, and apparatus should be considered part of the authorization specification.

[0021] The experimental methods or test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are obtained from conventional commercial channels or prepared by conventional methods unless otherwise specified.

[0022] Example 1: Aqueous nitrocellulose dispersions obtained with different nitrocellulose oil phase concentrations (1) 600, 800, 1000, and 1200 mg of nitrocellulose (weight average molecular weight of about 434500) were added to 20 mL of ethyl acetate, and stirred at 50 °C for 8 h using a magnetic stirrer to form an oil phase; (2) Take 700 mg of 1788 type polyvinyl alcohol and add it to 20 mL of deionized water and stir it at 90 °C for 6 h to dissolve. Then, pour 10 wt% (mass fraction of deionized water) of ethyl acetate into the polyvinyl alcohol aqueous solution to form a saturated aqueous solution of polyvinyl alcohol in ethyl acetate as the aqueous phase.

[0023] (3) Take 20 mL of the aqueous phase and add it to a 100 mL single-mouth round-bottom flask, put in a magnetic rod, keep the stirring speed at 900 r / min, take 10 mL of the oil phase and add it to a 25 mL constant pressure dropping funnel, and control the dropping speed to 2 s per drop. After the addition is completed, continue stirring for 1 h. Remove the single-mouth round-bottom flask and cool it to room temperature to obtain a crude emulsion.

[0024] (4) Transfer the crude emulsion into a 100 mL beaker and homogenize the crude emulsion in an ice water bath for 5 min using a high-speed homogenizer with the rotor speed controlled at 16,000 r / min.

[0025] (5) The homogenized miniemulsion was transferred to a rotary evaporator and evaporated under reduced pressure at a vacuum degree of 0.1 MPa, a water bath temperature of 45°C, and a rotation speed of 130 r / min until there was no residual smell of ethyl acetate in the emulsion. The emulsion was then taken out and filtered through a 200-mesh nylon mesh to obtain a blue-glowing nitrocellulose aqueous dispersion.

[0026] The prepared aqueous dispersion was tested for particle size, and the test results are shown in Table 1. From the results, it can be seen that the method provided by the present invention can ensure that a stable aqueous dispersion can be formed when the nitrocellulose oil phase concentration is as high as 30 mg / mL to 60 mg / mL, breaking through the concentration threshold of the traditional solvent replacement method for preparing NC aqueous dispersions, and realizing the preparation of high solid content nitrocellulose aqueous dispersions.

[0027] Table 1 Average particle size of nitrocellulose aqueous dispersion obtained with different nitrocellulose oil phase concentrations

[0028] Example 2: Aqueous nitrocellulose dispersions obtained from different nitrocellulose molecular weights (1) 1000 mg of nitrocellulose with weight average molecular weights of 395800, 434500, 467400, 470600, and 604900 were added to 20 mL of ethyl acetate and stirred at 50 °C for 8 h using a magnetic stirrer to form an oil phase; (2) Take 700 mg of 1788 type polyvinyl alcohol and add it to 20 mL of deionized water and stir it at 90 °C for 6 h to dissolve. Then, pour 10 wt% (mass fraction of deionized water) of ethyl acetate into the polyvinyl alcohol aqueous solution to form a saturated aqueous solution of polyvinyl alcohol in ethyl acetate as the aqueous phase.

[0029] (3) Take 20 mL of the aqueous phase and add it to a 100 mL single-mouth round-bottom flask, put in a magnetic rod, keep the stirring speed at 900 r / min, take 10 mL of the oil phase and add it to a 25 mL constant pressure dropping funnel, and control the dropping speed to 2 s per drop. After the addition is completed, continue stirring for 1 h. Remove the single-mouth round-bottom flask and cool it to room temperature to obtain a crude emulsion.

[0030] (4) Transfer the crude emulsion into a 100 mL beaker and homogenize the crude emulsion in an ice water bath for 5 min using a high-speed homogenizer with the rotor speed controlled at 16,000 r / min.

[0031] (5) The homogenized miniemulsion was transferred to a rotary evaporator and evaporated under reduced pressure at a vacuum degree of 0.1 MPa, a water bath temperature of 45°C, and a rotation speed of 130 r / min until there was no residual smell of ethyl acetate in the emulsion. The emulsion was then taken out and filtered through a 200-mesh nylon mesh to obtain a blue-glowing nitrocellulose aqueous dispersion.

[0032] The prepared aqueous dispersion was tested for particle size, and the test results are shown in Table 2. From the results, it can be seen that the method provided by the present invention can ensure that the nitrocellulose molecular weight can still form a stable aqueous dispersion when it is as high as 395800-604900, breaking through the problems of too low molecular weight and poor product coating performance of the NC aqueous dispersion prepared by the traditional solvent replacement method, and realizing the preparation of high molecular weight nitrocellulose aqueous dispersion.

[0033] Table 2 Average particle size of nitrocellulose aqueous dispersions obtained with different nitrocellulose molecular weights

Claims

1. A method for preparing a high molecular weight, high solid content nitrocellulose aqueous dispersion, characterized in that: The high molecular weight and large mass nitrocellulose is uniformly dissolved in ethyl acetate solvent to form a homogeneous solution; then it is added dropwise to a supersaturated polyvinyl alcohol solution of ethyl acetate, stirred evenly, and then emulsified again, and then the ethyl acetate is driven off and filtered to obtain a nitrocellulose aqueous dispersion.

2. The method for preparing a high molecular weight, high solid content nitrocellulose aqueous dispersion according to claim 1, characterized in that: The method comprises the following steps: 1) Preparation of oil phase: Add a certain amount of nitrocellulose to a certain amount of ethyl acetate, and continuously stir and dissolve at a certain temperature to form a yellow viscous solution as the oil phase; 2) Preparation of aqueous phase: adding a certain amount of polyvinyl alcohol into deionized water and stirring to dissolve at a certain temperature, then pouring a certain amount of ethyl acetate into the aqueous solution of polyvinyl alcohol to form a saturated aqueous solution of polyvinyl alcohol in ethyl acetate as the aqueous phase; 3) Preparation of crude emulsion: add a certain amount of water phase to container A, continue stirring, take a certain amount of oil phase, and drop it into the water phase under stirring; after the dropwise addition is completed, continue stirring for a certain period of time; remove container A and cool it to room temperature to obtain a crude emulsion; 4) Preparation of fine emulsion: The crude emulsion is transferred into container B, and the crude emulsion is homogenized in an ice water bath by controlling the rotor speed using a high-speed homogenizer to obtain a fine emulsion; 5) Removal of ethyl acetate: The homogenized fine emulsion is transferred to a rotary evaporator and evaporated under reduced pressure until there is no organic solvent phase in the emulsion. Then, the nitrocellulose aqueous dispersion is filtered through a nylon mesh.

3. The method for preparing a high molecular weight, high solid content nitrocellulose aqueous dispersion according to claim 2, characterized in that: In the step 1), the weight average molecular weight of the nitrocellulose is 395800-604900; the concentration of the nitrocellulose in the yellow viscous solution is 30 mg / mL-60 mg / mL; the stirring temperature is 45-55° C., and the stirring time is 7-9 h.

4. The method for preparing a high molecular weight, high solid content nitrocellulose aqueous dispersion according to claim 2, characterized in that: In the step 2), 200-1000 mg of polyvinyl alcohol is added to 18-22 mL of deionized water and stirred at 80-90° C. for 6-8 h to dissolve, and then ethyl acetate accounting for 9-10 wt % of the mass fraction of deionized water is poured into the polyvinyl alcohol aqueous solution to form a saturated aqueous solution of polyvinyl alcohol in ethyl acetate.

5. The method for preparing a high molecular weight, high solid content nitrocellulose aqueous dispersion according to claim 2, characterized in that: In step 3), 18-20 mL of the aqueous phase is added to container A, and the stirring speed is maintained at 800-900 r / min; 6.7-20 mL of the oil phase is added to container C, and the dropping speed is controlled to be 1.5-2 s per drop; after the dropping is completed, stirring is continued for 1-2 hours.

6. The method for preparing a high molecular weight, high solid content nitrocellulose aqueous dispersion according to claim 2, characterized in that: In step 4), the rotor speed of the homogenizer is controlled to be 10000-22000 r / min, and the homogenization time is 1-7 min.

7. The method for preparing a high molecular weight, high solid content nitrocellulose aqueous dispersion according to claim 2, characterized in that: In the step 5), the vacuum degree of the rotary evaporator is 0.098-0.1 MPa, the water bath temperature is 35-45°C, the rotation speed is 100-130 r / min, and the filtration is performed with a nylon gauze of 150-200 mesh.

8. The method for preparing a high molecular weight, high solid content nitrocellulose aqueous dispersion according to claim 5, characterized in that: The container A is a 100 mL single-necked round-bottom flask; The container B is a 100 mL beaker; The container C is a 25 mL constant pressure dropping funnel.

9. A high molecular weight, high solid content nitrocellulose aqueous dispersion, characterized in that: The preparation method is as follows: high molecular weight and large mass nitrocellulose is uniformly dissolved in ethyl acetate solvent to form a homogeneous solution; then it is added dropwise to a supersaturated polyvinyl alcohol solution of ethyl acetate through a constant pressure dropping funnel under stirring, after being uniformly stirred, it is transferred to a high-speed homogenizer for re-emulsification, and then the ethyl acetate is driven off by a rotary evaporator, and the nitrocellulose water dispersion is obtained by sieve filtration.

10. The high molecular weight, high solid content nitrocellulose aqueous dispersion according to claim 9, characterized in that: The weight average molecular weight of the nitrocellulose is 395800-604900.

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