Degradable environmentally-friendly adhesive for woodworking and preparation method therefor

Abstract

The present application relates to the field of adhesives, and specifically discloses a degradable environmentally-friendly adhesive for woodworking and a preparation method therefor. The adhesive comprises the following raw materials in parts by weight: 10-20 parts of a solution in which polyvinyl alcohol is dissolved, 3-10 parts of a filler, 45-60 parts of a copolymer emulsion, 10-20 parts of a stabilizer, 1-3 parts of glycerol, and 1-4 parts of an auxiliary agent. The adhesive has a solid content of 40-50% and a viscosity of 15,000-19,000 cps (25°C). The preparation method for the adhesive comprises the following steps: stirring a copolymer emulsion, adding a stabilizer thereto and uniformly dispersing same, then adding a solution in which polyvinyl alcohol is dissolved, and performing homogenization to obtain a mixture; and adding a filler to the mixture, increasing the stirring speed until the filler is fully dispersed and the resulting colloid is homogeneous and free of visible particles, then adding glycerol, an auxiliary agent and an appropriate amount of water thereto, and stirring same until the system is homogeneous and free of bubbles. The obtained adhesive has good bonding performance, and still a has good bonding strength after being placed at a relatively high temperature for a long time.

Description

Degradable environment-friendly woodworking adhesive and preparation method thereof TECHNICAL FIELD

[0001] The present application relates to the field of adhesives, more specifically, it relates to a degradable environment-friendly woodworking adhesive and a preparation method thereof. BACKGROUND

[0002] The main water-based adhesives used in the woodworking furniture market, such as polyurethane adhesives, have excellent bonding strength and good weather resistance and are widely used, but with the increasing strictness of environmental protection and the proposal of carbon footprint and low-carbon life, the development of renewable and degradable adhesives gradually enters the planning of enterprises. At present, the traditional degradable adhesives include the following raw materials: starch 20-40 parts, sucrose 10-18 parts, pectin 5-8 parts, methyl cellulose 3-5 parts, polyvinyl alcohol 5-10 parts, nano-silicon dioxide 0.01-0.09 parts, calcium carbonate 0.02-0.08 parts, sodium hydroxide 2-5 parts, sodium dodecyl sulfate 1-3.5 parts, dibutyl phthalate 3-7 parts, butyl acrylate 1-3 parts, water 50-70 parts, and the adhesive can be obtained by mixing and stirring the above raw materials uniformly, but the initial adhesion of the obtained adhesive is poor, and the bonding strength of the adhesive decreases significantly after being placed for a period of time under the generally high temperature in summer.

[0003] SUMMARY

[0004] The present application provides a degradable environment-friendly woodworking adhesive and a preparation method thereof, and the obtained adhesive has excellent bonding performance and still has good bonding strength after being placed for a long time at a higher temperature, and the performance of the adhesive is significantly reduced by environmental factors.

[0005] In a first aspect, the present application provides a degradable environment-friendly woodworking adhesive using the following technical solution:

[0006] A degradable environment-friendly woodworking adhesive comprises the following raw materials by weight: polyvinyl alcohol solution 10-20 parts, filler 3-10 parts, copolymer emulsion 45-60 parts, stabilizer 10-20 parts, glycerol 1-3 parts, and auxiliary agent 1-4 parts.

[0007] The stabilizer comprises heat-resistant powder 3-6 parts, urea 1-3 parts, choline 0.3-1 part, water 6.5-9.5 parts, and coupling agent 0.2-0.5 parts.

[0008] The solid content of the adhesive is 40-50%, and the viscosity is 15000-19000 cps (25℃).

[0009] By adopting the above technical scheme, in the copolymer emulsion, polyvinyl alcohol molecules can interact with copolymer molecules through electrostatic force, van der Waals force and hydrogen bond and other interactions. Since the polyvinyl alcohol molecules have good water solubility, they can form a hydration layer in the emulsion water phase and can form hydrogen bonds or electrostatic interactions with the groups on the surface of the copolymer molecules or the hydrophilic groups in the raw material components, thereby realizing the superposition of intermolecular mosaic and improving the initial adhesion performance of the product.

[0010] At the same time, the polyvinyl alcohol molecules also have strong hydrogen bond interaction, and can form an interpenetrating network structure under the action of the stabilizer, and the heat-resistant powder and filler are uniformly dispersed in the network structure, which not only can maintain the dispersion state of the copolymer emulsion, prevent the agglomeration and deposition of the emulsion molecules, and help to maintain the long-term stability and uniformity of the emulsion, but also can absorb and conduct heat, reduce the temperature difference driven molecular diffusion, and improve the resistance of the system to higher temperature, so that the product still has good bonding strength after being placed at a higher temperature for a long time. Glycerol can play a certain moisturizing effect and reduce the influence of environmental factors on the performance of the adhesive.

[0011] The choline contained in the stabilizer can form hydrogen bonds or ionic bonds with polyvinyl alcohol molecules, so that the mutual combination between polyvinyl alcohol molecules is enhanced, the initial adhesion performance of the product is improved, and the choline has strong surface activity, can reduce the surface tension in the emulsion system, improve the wetting performance, make the solution more easily mixed with other substances, improve the rheological performance of the emulsion, and make it have good fluidity and lubricity. Urea can also inhibit the aggregation of copolymer molecules, prevent the mutual adsorption and agglomeration of copolymer molecules in the emulsion, and improve the stability and dispersion of the emulsion.

[0012] Preferably, the filler is at least one of cassava powder, kaolin and ground calcium powder.

[0013] Further, the filler is preferably a combination of cassava powder and kaolin.

[0014] By adopting the above technical scheme, the cassava powder is mainly composed of starch, which is a degradable natural material, and contains a small amount of amino compounds, interacts with polyvinyl alcohol molecules, realizes the superposition and inlaying between molecules, and improves the initial adhesion performance of the product. Kaolin has a large specific surface area and adsorption capacity, which can increase the adhesion of the product. At the same time, kaolin has a layered structure, which can form a hydration layer with water molecules, so that the copolymer emulsion can be more stably dispersed, and the viscosity and rheological properties of the system can be improved, and the coating performance of the product can be improved. The dispersion state of kaolin itself can form a three-dimensional network structure, which can prevent the aggregation and deposition of emulsion molecules, and can help to maintain the long-term stability and uniformity of the emulsion. The three-dimensional network structure formed by the dispersion state can help the heat-resistant powder to absorb and conduct heat faster, improve the tolerance of the system at high temperature, so that the product still has good bonding strength after being placed at high temperature for a long time.

[0015] Preferably, the heat-resistant powder includes at least one of polylactic acid powder, rice husk powder, and cellulose acetate.

[0016] Further, the heat-resistant powder preferably comprises polylactic acid powder and cellulose acetate.

[0017] By adopting the above technical scheme, the polylactic acid powder, the rice husk powder, and the cellulose acetate are all degradable materials and have good heat resistance. At the same time, the cellulose acetate contains a large number of hydroxyl and acetyl functional groups, which can react with the hydroxyl functional groups in the polyvinyl alcohol molecules to form an interpenetrating network structure through hydrogen bonding. At the same time, the linear structure of cellulose acetate and the branched structure of polyvinyl alcohol can also promote the mutual penetration of the two materials to improve the bonding capacity of the product. In the copolymer emulsion, the cellulose acetate can also improve the dispersion state and stability of the copolymer emulsion molecules.

[0018] Preferably, the copolymer emulsion is at least one of vinyl acetate-ethylene copolymer emulsion, vinyl acetate-acrylate copolymer emulsion, and styrene-acrylate copolymer emulsion.

[0019] Further, the copolymer emulsion is preferably vinyl acetate-ethylene copolymer emulsion; wherein the vinyl acetate-ethylene copolymer emulsion is one of Dalian VAE, model P-5000, Guangxi Guangwei VAE, model BJ-707, and Germany Wacker VAE emulsion, model 706K, or a combination of two.

[0020] Preferably, the auxiliary agent includes 1-3 parts of plasticizer, 0.1-0.4 parts of wetting agent, 0.1-0.25 parts of preservative, and 0.1-0.35 parts of defoaming agent.

[0021] Preferably, the plasticizer includes at least one of 2,2,4-trimethylpentanediol isobutyl ester, dioctyl adipate, dioctyl sebacate, and diisononyl adipate.

[0022] Preferably, the preservative is at least one of 1,2-benzisothiazolin-3-one, 2-butyl-1,2-benzisothiazolin-3-one.

[0023] By adopting the technical scheme, the component selection of the copolymer emulsion and the type of the auxiliary agent are optimized, and the comprehensive quality of the product is improved.

[0024] Preferably, the concentration of the polyvinyl alcohol dissolving solution is 22-33%.

[0025] By adopting the technical scheme, the polyvinyl alcohol dissolving solution with a proper concentration is selected, the initial adhesion performance of the adhesive product is ensured, and the influence of environmental factors on the performance of the adhesive is reduced.

[0026] In a second aspect, the application provides a preparation method of the degradable and environment-friendly woodworking adhesive, which adopts the following technical scheme:

[0027] The preparation method of the degradable and environment-friendly woodworking adhesive comprises the following steps:

[0028] Urea and choline are dissolved in water to obtain a dissolving solution, a coupling agent is then added and stirred uniformly, and finally heat-resistant powder is added and mixed uniformly to obtain a stabilizer;

[0029] The copolymer emulsion is stirred, the stabilizer is uniformly dispersed, and then the polyvinyl alcohol dissolving solution is added for homogenization to obtain a mixture;

[0030] The filler is added to the mixture, and the stirring speed is increased, and after the filler is uniformly dispersed and the colloidal particles are removed, glycerol, an auxiliary agent and appropriate water are added, and the stirring is continued until the system is uniform and free of bubbles.

[0031] By adopting the technical scheme, the copolymer emulsion is first mixed uniformly with the stabilizer, and then mixed with the polyvinyl alcohol dissolving solution and the filler, which helps to improve the stability of the system and the orderly arrangement of the superposition and inlaying between molecules, and improves the comprehensive quality of the product.

[0032] In summary, the application has the following beneficial effects:

[0033] 1. The polyvinyl alcohol molecules have strong hydrogen bonding, and under the action of the stabilizer, an interpenetrating network structure can be formed, and the heat-resistant powder and the filler are uniformly dispersed in the network structure, which not only can maintain the dispersion state of the copolymer emulsion, prevent the agglomeration and deposition of the emulsion molecules, and help to maintain the long-term stability and uniformity of the emulsion, but also can absorb and conduct heat, reduce the molecular diffusion driven by temperature difference, and improve the resistance of the system to high temperature, so that the product still has good bonding strength after being placed at high temperature for a long time.

[0034] 2. The choline contained in the stabilizer can form hydrogen bonds or ionic bonds between the polyvinyl alcohol molecules, so that the mutual combination between the polyvinyl alcohol molecules is enhanced, the initial adhesion performance of the product is improved, and the choline has strong surface activity, can reduce the surface tension in the emulsion system, improve the wetting performance, make the solution easier to mix with other substances, improve the rheological performance of the emulsion, and make it have good flowability and lubricity. Urea can also inhibit the aggregation of copolymer molecules, prevent copolymer molecules from mutual adsorption and agglomeration in the emulsion, and improve the stability and dispersity of the emulsion.

[0035] 3. The cellulose acetate contains a large number of hydroxyl and acetyl functional groups, which can react with the hydroxyl functional groups in the polyvinyl alcohol molecules to form an interpenetrating network structure through hydrogen bonds, and the linear structure of cellulose acetate and the branched structure of polyvinyl alcohol can also promote the mutual penetration of the two materials to improve the bonding capacity of the product. In the copolymer emulsion, cellulose acetate can also improve the dispersion state and stability of the copolymer emulsion molecules. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a process flow diagram of the preparation method of the degradable environmentally friendly woodworking adhesive of the present application. DETAILED DESCRIPTION

[0037] The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions not mentioned in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer, and the reagents or instruments not mentioned by the manufacturer are conventional products that can be purchased on the market. Among them: the particle size of the filler is micron level, polylactic acid CAS number 26100-51-6; cellulose acetate CAS number: 9004-35-7; styrene-acrylate copolymer emulsion is specifically benzene propyl emulsion 816, CAS number 25085-34-1; wetting agent brand is OT-75, silane coupling agent type is KH550, defoaming agent is BYK defoaming agent.

[0038] EXAMPLE

[0039] Example 1

[0040] A degradable environmentally friendly woodworking adhesive, comprising the following raw materials: polyvinyl alcohol solution 10 kg, filler 3 kg, vinyl acetate-acrylate copolymer emulsion 45 kg, stabilizer 10 kg, glycerol 3 kg, plasticizer dioctyl adipate 1 kg, wetting agent 0.1 kg, preservative 1,2-benzisothiazolin-3-one 0.1 kg; defoaming agent 0.35 kg;

[0041] The stabilizer comprises heat-resistant powder 3kg, urea 1kg, choline 0.3kg, water 6.5kg, and silane coupling agent 0.2kg;

[0042] The filler is cassava powder, the heat-resistant powder comprises polylactic acid powder and rice husk powder in a mass ratio of 2:1, and the concentration of the polyvinyl alcohol solution is 33%.

[0043] A preparation method of a degradable environment-friendly woodworking adhesive comprises the following steps:

[0044] Urea and choline are dissolved in water to obtain a solution, a coupling agent is then added and stirred uniformly, and finally heat-resistant powder is added and mixed uniformly to obtain a stabilizer;

[0045] The copolymer emulsion is stirred at a stirring speed of 60r / min for 10 minutes, the stabilizer is uniformly dispersed, the polyvinyl alcohol solution is added for homogenization, the homogenization speed is 100r / min, and the homogenization time is 30 minutes;

[0046] The filler is added to the mixture, and the stirring speed is increased to 120r / min, after the filler is uniformly dispersed and no particles are generated, glycerol, plasticizer, wetting agent, preservative, defoaming agent and appropriate amount of water are added, and the system is stirred until it is uniform and free of air bubbles; the obtained adhesive has a solid content of 40% and a viscosity of 19000cps (25℃).

[0047] Example 2

[0048] A degradable environment-friendly woodworking adhesive comprises the following raw materials: polyvinyl alcohol solution 20kg, filler 10kg, styrene-acrylate copolymer emulsion 60kg, stabilizer 20kg, glycerol 1kg, plasticizer dioctyl sebacate 3kg, wetting agent 0.4kg, preservative 2-butyl-1,2-benzisothiazolin-3-one 0.25kg, and defoaming agent 0.1kg.

[0049] The stabilizer comprises heat-resistant powder 6kg, urea 3kg, choline 1kg, water 9.5kg, and silane coupling agent 0.5kg, and the concentration of the polyvinyl alcohol solution is 22%.

[0050] The filler comprises kaolin and heavy calcium powder in a mass ratio of 1:1, and the heat-resistant powder is rice husk powder.

[0051] A preparation method of a degradable environment-friendly woodworking adhesive comprises the following steps:

[0052] Urea and choline are dissolved in water to obtain a solution, a coupling agent is then added and stirred uniformly, and finally heat-resistant powder is added and mixed uniformly to obtain a stabilizer;

[0053] Stir the copolymer emulsion, stirring speed 60 rpm, stirring for 10 minutes, add stabilizer evenly dispersed, then add polyvinyl alcohol solution to homogenize to obtain the mixture; homogenization speed is 100 rpm, time is 30 min;

[0054] Add fillers to the mixture and increase the stirring speed to 120 rpm, and then add glycerol, plasticizer, wetting agent, preservative, defoamer and appropriate amount of water after the fillers are fully dispersed and the colloids are evenly distributed without particles; the obtained adhesive has a solid content of 50% and a viscosity of 15000 cps (25°C).

[0055] Example 3

[0056] The difference from Example 1 is that the degradable environmentally friendly woodworking adhesive comprises the following raw materials: polyvinyl alcohol solution 15 kg, fillers 7 kg, vinyl acetate-ethylene copolymer emulsion 53 kg, stabilizer 17 kg, glycerol 2.2 kg, plasticizer sebacic acid dioctyl ester 1.5 kg, wetting agent 0.2 kg, preservative 2-butyl-1,2-benzisothiazolin-3-one 0.15 kg; defoamer 0.14 kg; the concentration of polyvinyl alcohol solution is 28%, the solid content of the adhesive is 45%, and the viscosity is 17000 cps (25°C); the rest is the same as Example 1.

[0057] Example 4

[0058] The difference from Example 3 is that the fillers include quartz powder, kaolin and heavy calcium powder in a mass ratio of 0.6:1:2, and the rest is the same as Example 3.

[0059] Example 5

[0060] The difference from Example 3 is that the fillers include cassava powder and kaolin in a mass ratio of 2:1, and the rest is the same as Example 3.

[0061] Example 6

[0062] The difference from Example 5 is that the heat-resistant powder includes polylactic acid powder and cellulose acetate in a mass ratio of 1:1, and the rest is the same as Example 5.

[0063] Example 7

[0064] The difference from Example 6 is that the preparation method of the degradable environmentally friendly woodworking adhesive comprises the following steps:

[0065] Dissolve urea and choline in water to obtain a solution, then add a coupling agent and stir evenly, and finally add heat-resistant powder to obtain a stabilizer;

[0066] Stir the copolymer emulsion, add stabilizer, polyvinyl alcohol solution and filler to homogenize to obtain the mixture; the concentration of the polyvinyl alcohol solution is 18%;

[0067] Add glycerol, plasticizer, wetting agent, preservative, defoamer and appropriate amount of water to the mixture, stir until the system is uniform and free of air bubbles, and obtain the adhesive with solid content of 47% and viscosity of 16000 cps (25°C); the rest is the same as example 6.

[0068] Comparative Example

[0069] Comparative Example 1

[0070] The difference from example 6 is that the polyvinyl alcohol solution is replaced by acrylic emulsion, and the rest is the same as example 6.

[0071] Comparative Example 2

[0072] The difference from example 6 is that the stabilizer is replaced by heat-resistant powder, and the rest is the same as example 6.

[0073] Comparative Example 3

[0074] The difference from example 6 is that the heat-resistant powder is selected as mica powder, and the rest is the same as example 6.

[0075] Comparative Example 4

[0076] The difference from example 6 is that the adhesive solid content is 30% and the viscosity is 11000 cps (25°C).

[0077] Performance test

[0078] The adhesives obtained from examples 1-7 and comparative examples 1-4 are used for initial bonding strength test of plate and honeycomb paper in furniture industry, the bonding area is 20mm x 20mm, and the results are recorded in table 1.

[0079] The adhesives obtained from examples 1-7 and comparative examples 1-4 are placed at a temperature of 55°C for 3 months, the appearance of the product is observed, whether there is delamination, agglomeration, sedimentation phenomenon, and the bonding strength test of plate and honeycomb paper is carried out again, and the bonding strength reduction rate of the adhesive product after placement is calculated, and the results are recorded in table 1.

[0080] Table 1

[0081] It can be seen from Examples 1-7 and Table 1 that the adhesive prepared from the raw material components of the present application has excellent bonding performance, and no obvious change in appearance after being placed at a high temperature for a long time, good heat resistance and stability, and the adhesive after being placed at a high temperature still has good bonding strength, low bonding performance decline rate, and the performance of the adhesive is significantly reduced by environmental factors.

[0082] It can be seen from Examples 1 and Comparative Examples 1-3 and Table 1 that the comprehensive performance of the products is significantly reduced in the comparative examples, which do not contain polyvinyl alcohol solution and directly add acrylic emulsion, in Comparative Example 2, the stabilizer is replaced by heat-resistant powder, and in Comparative Example 3, the heat-resistant powder is replaced by mica powder. This is because in the copolymer emulsion, polyvinyl alcohol molecules can interact with copolymer molecules through electrostatic force, van der Waals force and hydrogen bonding, etc. Since the polyvinyl alcohol molecules have good water solubility, they can form a hydration layer in the emulsion water phase and form hydrogen bonds or electrostatic interactions with the groups on the surface of the copolymer molecules or the hydrophilic groups in the raw material components, thereby realizing the superposition of intermolecular mosaic and improving the initial adhesion of the product. At the same time, the polyvinyl alcohol molecules also have strong hydrogen bonding between them, and under the action of the stabilizer, they can form an interpenetrating network structure, and the heat-resistant powder and filler are uniformly dispersed in the network structure. Not only can it maintain the dispersion state of the copolymer emulsion, prevent the agglomeration and deposition of the emulsion molecules, help to maintain the long-term stability and uniformity of the emulsion, but also can absorb and conduct heat, reduce the molecular diffusion driven by temperature difference, and improve the resistance of the system to high temperature. The choline contained in the stabilizer can form hydrogen bonds or ionic bonds with the polyvinyl alcohol molecules, so that the mutual combination between the polyvinyl alcohol molecules is enhanced, the initial adhesion of the product is improved, and the choline has strong surface activity, which can reduce the surface tension of the emulsion system, improve its wetting performance, make the solution easier to mix with other substances, improve the rheological properties of the emulsion, and make it have good fluidity and lubricity. Urea can also inhibit the aggregation of copolymer molecules, prevent the mutual adsorption and agglomeration of copolymer molecules in the emulsion, and improve the stability and dispersity of the emulsion. Therefore, the polyvinyl alcohol solution, copolymer emulsion, and stabilizer and filler complement each other, have synergistic effect, and together improve the initial adhesion of the adhesive and give the product excellent stability, so that the adhesive after being placed at a high temperature still has good bonding strength.

[0083] It can be seen from Example 6 and Comparative Example 4 and Table 1 that the final solid content and viscosity of the adhesive product also have a great influence on the comprehensive performance of the product. If the solid content of the adhesive is too low and the viscosity is too small, it will result in poor initial adhesion of the product, and after being placed at a high temperature for a period of time, the stability will be poor and agglomeration will occur. Therefore, it is also very important to control the solid content and viscosity of the adhesive during the preparation of the product.

[0084] The embodiments are only illustrative of the present application, and are not intended to limit the present application. Those skilled in the art can make modifications to the embodiments according to the present application without creative contribution, as long as the modifications are within the scope of the claims of the present application.

Claims

1. A degradable environment-friendly wood adhesive, characterized in that, The raw materials include the following components by weight: polyvinyl alcohol solution 10-20 parts, filler 3-10 parts, copolymer emulsion 45-60 parts, stabilizer 10-20 parts, glycerol 1-3 parts, and auxiliary agent 1-4 parts; The stabilizer includes heat-resistant powder 3-6 parts, urea 1-3 parts, choline 0.3-1 part, water 6.5-9.5 parts, and coupling agent 0.2-0.5 parts; The adhesive has a solid content of 40-50% and a viscosity of 15000-19000 cps at 25°C.

2. The degradable eco-friendly wood adhesive according to claim 1, characterized in that: The filler is at least one of cassava powder, kaolin, and ground calcium carbonate.

3. The degradable eco-friendly wood adhesive according to claim 1, characterized in that: The heat-resistant powder includes at least one of polylactic acid powder, rice husk powder, and cellulose acetate.

4. The degradable eco-friendly wood adhesive according to claim 1, characterized in that: The copolymer emulsion is at least one of vinyl acetate-ethylene copolymer emulsion, vinyl acetate-acrylate copolymer emulsion, and styrene-acrylate copolymer emulsion.

5. The degradable eco-friendly wood adhesive according to claim 1, characterized in that: The auxiliary agent includes plasticizer 1-3 parts, wetting agent 0.1-0.4 parts, preservative 0.1-0.25 parts, and defoaming agent 0.1-0.35 parts.

6. The degradable eco-friendly wood adhesive according to claim 5, characterized in that: The plasticizer includes at least one of 2,2,4-trimethylpentanediol isobutyl ester, dioctyl adipate, dioctyl sebacate, and diisononyl adipate.

7. The degradable eco-friendly wood adhesive according to claim 5, characterized in that: The preservative is at least one of 1,2-benzisothiazolin-3-one and 2-butyl-1,2-benzisothiazolin-3-one.

8. The degradable eco-friendly wood adhesive according to claim 1, characterized in that: The concentration of the polyvinyl alcohol solution is 22-33%.

9. The process for the preparation of the degradable eco-friendly wood adhesive according to any one of claims 1 to 8, characterized in that: The method includes the following steps: The urea and choline are dissolved in water to obtain a solution, the coupling agent is then added and stirred until uniform, and finally the heat-resistant powder is added and mixed until uniform to obtain the stabilizer; The copolymer emulsion is stirred, the stabilizer is added and uniformly dispersed, and then the polyvinyl alcohol solution is added and homogenized to obtain the mixture; The filler is added to the mixture and the stirring speed is increased, and after the filler is fully dispersed and the colloid is uniform without particles, the glycerol, auxiliary agent, and appropriate amount of water are added and stirred until the system is uniform and free of air bubbles.

Images