2 Results and Discussion
2.1 Physical properties of the emulsion
2.2 Effect of reaction temperature
Since the reaction of isocyanate groups with active hydrogen is very sensitive to temperature, the cross-linking reaction proceeds more easily than the chain-strengthening reaction as the reaction temperature increases. At high temperatures, the system viscosity increases sharply to form a gel. The experimental reaction temperature from 80 ° C to 50 ° C conducted several tests and found that the reaction is controlled at 50 ~ 60 degrees is appropriate, in this temperature range, the reaction is relatively flat, the reaction time is about 3 hours, After a certain viscosity, uniform and transparent solution is formed, the emulsion is neutralized and emulsified.
2.3 Selection of synthetic technology
Castor oil is a hydroxy-containing glyceryl ester, a natural product that reflects previous dehydration. It has a relatively high viscosity, and the viscosity increases rapidly with the TDI reaction, and the chain of the resulting resin linearly grows with the chain extender. Tartaric acid is ground and dried. It is dissolved in a small amount of butanone and added to the system. Hydrogen atoms on the hydroxyl group react with the terminal NCO groups of the prepolymer to introduce -COOH groups into the macromolecule chain. Tartaric acid is still to a certain extent. It functions as an acidic catalyst and inhibits the crosslinking reaction from proceeding. The addition of a small amount of butanone solvent can reduce and adjust the viscosity of the system. The addition of a small amount of butanone at the same time as the aqueous alkali solution is added, and strong stirring is the key to good emulsification.
2.4 Effect of tartaric acid dosage
Tartaric acid (2,3-dihydroxybutanedioic acid) is introduced into the polyurethane molecular chain structure as a hydrophilic monomer, and the polyurethane is dispersed in water to prepare a self-emulsifying emulsion. The hydrophilic group is a hydroxyl group, so the emulsion is of an anionic type. When the amount is appropriate, the result of forming a self-emulsifying stable emulsion can be achieved under certain reaction conditions. Table 2 shows the effect of the amount of tartaric acid on the stability of the emulsion. The catalytic action of tartaric acid in the reaction has been described previously. It was found that if tartaric acid is not added or added late, the prepolymer formation reaction easily generates a gel. From Table 2, it can be seen that the amount of tartaric acid in the resin between 3.7-4.4 weight percent can produce a stable emulsion with moderate viscosity and a certain degree of fluidity.
2.5 Effect of NCO/OH Ratio
The main component of castor oil is glycerol 9-alkenyl-12-hydroxyoctadecanoic acid, which is greater than 90%. The hydroxyl value is about 163, the hydroxyl group is 4.94%, and the hydroxyl equivalent is 345. According to the hydroxy standard, castor oil can be considered to contain 70% triglyceride and 30% diglyceride with an average functionality of 2.7. Due to the large number of trifunctional components, it is also important to select the proportion of NCO/OH in the prepolymer in order to avoid cross-linking reactions, in addition to controlling the reaction temperature not to be too high. Experiments conducted at a ratio of NCO/OH=1.02 to 1.4 show that no gelling occurs when the NCO/OH is less than 1.3. In this case, the ratio of isocyanate groups to total hydroxyl groups (including chain extenders and hydrophilic monomers) is less than 0.8. This ensures that no -NCO reacts with water.
2.6 Neutralizing agent
In principle, any compound containing a basic group can be selected as a neutralizing agent. This system has been tested with commonly used alkali-sodium hydroxide, ammonia, and triethylamine as neutralizers. The emulsion particles obtained from the agent are coarse and have poor uniformity. When triethylamine is used as a neutralizer, the emulsion particles are small and appear uniform.
2.7 Water resistance
The changes in water absorption and dissolution rate of the film over time are shown in Table 3. The long-chain non-polar fatty acids of the castor oil component of the emulsion film are hydrophobic, and the water resistance of the film is reduced due to the introduction of the hydrophilic group and the hydrophilicity of the ether bond in the chain extender. In the parallel four water resistance tests, although the repeatability of the data is not good enough, the trend of the given data is the same. Take No. 1 test as an example, and see the changes of water absorption rate and dissolution rate with time, see Table 3. Table 3 shows that the water absorption and dissolution of the film tend to become gentle after one day of water immersion. Dissolved may also be free chain extenders or small molecules such as tartrates.
2.8 Emulsion Adhesive Strength Test on Different Materials
The soft material has been tested on the softness of the material between the curtain fabric, between the canvas and PVC artificial leather, the results are not ideal, the data is 2 ~ 5N/25mm, the main reason is that the adhesive is difficult to cure at room temperature, No further study of the results of heat curing. For hard materials, such as PVC hard board, aluminum plate, wood board, steel plate and other materials, the bonding strength of the adhesive to the steel plate is found to be better, and the tested shear strength is related to the temperature of the pattern heat curing. Such a substrate is 08F steel plate. Size is length X width X thickness = 10025X2, the unit is mm, lap length is 12.5mm, glue two times, open for half an hour, place at room temperature for 24 hours, flood between 120 and 200 degrees for three hours, quickly After cooling for a further 24 hours, the measured shear strength strongly depends on the curing temperature.
2.9 In order to find the best reaction conditions, use the formal experimental design method to optimize
In the process of the same process, the same amount of castor oil, changing the four factors, the amount of A-TDI; B-chain extender type; C-tartaric acid dosage; D-reaction temperature. A factor takes four levels, and the remaining three factors take two levels. The orthogonal table L16 (215) is changed to the orthogonal table L16 (41X212) [4] so that four-level factors can be arranged on the two-level table. The specific arrangement is shown in Table 5. The inspection index is the average shear strength test results of the adhesive-bonded 08F steel plate, the unit is N/cm2, and the curing temperature is 160 degrees. The amount of castor oil for the test was 100 parts by weight. After 16 trials, evenly dispersed emulsions were produced within the range of the above four factors, and they all had good fluidity and could be directly used as adhesives for adhesive bonding of various materials. The following is an intuitive analysis of the effect of each factor on the shear strength. Table 5 shows the sum of test results corresponding to levels 1, 2, 3, and 4 in column J, respectively. Divide them by the number of trials to obtain the average test result corresponding to each level representing the factor on column J, respectively. The minimum value of the average value is subtracted from the minimum value to obtain the range difference. The extreme difference indicates that the factor has the greatest influence on the test result, while the smallest factor has the smallest influence on the test result. By comprehensive comparison, the optimal reaction conditions can be obtained. Within the scope of the test changes, the use of TDI in an amount of 29.2 parts by weight; chain extender 1.4-butanediol; tartaric acid in an amount of 4.17 parts by weight and a reaction temperature of 60 degrees is the optimum reaction conditions.
3 Conclusion
(1) A water-based system in which castor oil and toluene diisocyanate are the main raw materials, butanediol or diethylene glycol is the chain extender, tartaric acid is the hydrophilic monomer, and triethylamine is the neutralizing agent. The uniform and stable polyurethane emulsion adhesive can be made under the process conditions described herein.
(2) The adhesive strength of the adhesive has a strong dependence on the curing temperature.
(3) The preferred reaction conditions through the orthogonal experimental design method are: 100 parts by weight of castor oil; 29.2 parts by TDI; 4.17 parts by tartaric acid; 1.4-butanediol by chain extender; reaction temperature is 60 degrees.
2.1 Physical properties of the emulsion
2.2 Effect of reaction temperature
Since the reaction of isocyanate groups with active hydrogen is very sensitive to temperature, the cross-linking reaction proceeds more easily than the chain-strengthening reaction as the reaction temperature increases. At high temperatures, the system viscosity increases sharply to form a gel. The experimental reaction temperature from 80 ° C to 50 ° C conducted several tests and found that the reaction is controlled at 50 ~ 60 degrees is appropriate, in this temperature range, the reaction is relatively flat, the reaction time is about 3 hours, After a certain viscosity, uniform and transparent solution is formed, the emulsion is neutralized and emulsified.
2.3 Selection of synthetic technology
Castor oil is a hydroxy-containing glyceryl ester, a natural product that reflects previous dehydration. It has a relatively high viscosity, and the viscosity increases rapidly with the TDI reaction, and the chain of the resulting resin linearly grows with the chain extender. Tartaric acid is ground and dried. It is dissolved in a small amount of butanone and added to the system. Hydrogen atoms on the hydroxyl group react with the terminal NCO groups of the prepolymer to introduce -COOH groups into the macromolecule chain. Tartaric acid is still to a certain extent. It functions as an acidic catalyst and inhibits the crosslinking reaction from proceeding. The addition of a small amount of butanone solvent can reduce and adjust the viscosity of the system. The addition of a small amount of butanone at the same time as the aqueous alkali solution is added, and strong stirring is the key to good emulsification.
2.4 Effect of tartaric acid dosage
Tartaric acid (2,3-dihydroxybutanedioic acid) is introduced into the polyurethane molecular chain structure as a hydrophilic monomer, and the polyurethane is dispersed in water to prepare a self-emulsifying emulsion. The hydrophilic group is a hydroxyl group, so the emulsion is of an anionic type. When the amount is appropriate, the result of forming a self-emulsifying stable emulsion can be achieved under certain reaction conditions. Table 2 shows the effect of the amount of tartaric acid on the stability of the emulsion. The catalytic action of tartaric acid in the reaction has been described previously. It was found that if tartaric acid is not added or added late, the prepolymer formation reaction easily generates a gel. From Table 2, it can be seen that the amount of tartaric acid in the resin between 3.7-4.4 weight percent can produce a stable emulsion with moderate viscosity and a certain degree of fluidity.
2.5 Effect of NCO/OH Ratio
The main component of castor oil is glycerol 9-alkenyl-12-hydroxyoctadecanoic acid, which is greater than 90%. The hydroxyl value is about 163, the hydroxyl group is 4.94%, and the hydroxyl equivalent is 345. According to the hydroxy standard, castor oil can be considered to contain 70% triglyceride and 30% diglyceride with an average functionality of 2.7. Due to the large number of trifunctional components, it is also important to select the proportion of NCO/OH in the prepolymer in order to avoid cross-linking reactions, in addition to controlling the reaction temperature not to be too high. Experiments conducted at a ratio of NCO/OH=1.02 to 1.4 show that no gelling occurs when the NCO/OH is less than 1.3. In this case, the ratio of isocyanate groups to total hydroxyl groups (including chain extenders and hydrophilic monomers) is less than 0.8. This ensures that no -NCO reacts with water.
2.6 Neutralizing agent
In principle, any compound containing a basic group can be selected as a neutralizing agent. This system has been tested with commonly used alkali-sodium hydroxide, ammonia, and triethylamine as neutralizers. The emulsion particles obtained from the agent are coarse and have poor uniformity. When triethylamine is used as a neutralizer, the emulsion particles are small and appear uniform.
2.7 Water resistance
The changes in water absorption and dissolution rate of the film over time are shown in Table 3. The long-chain non-polar fatty acids of the castor oil component of the emulsion film are hydrophobic, and the water resistance of the film is reduced due to the introduction of the hydrophilic group and the hydrophilicity of the ether bond in the chain extender. In the parallel four water resistance tests, although the repeatability of the data is not good enough, the trend of the given data is the same. Take No. 1 test as an example, and see the changes of water absorption rate and dissolution rate with time, see Table 3. Table 3 shows that the water absorption and dissolution of the film tend to become gentle after one day of water immersion. Dissolved may also be free chain extenders or small molecules such as tartrates.
2.8 Emulsion Adhesive Strength Test on Different Materials
The soft material has been tested on the softness of the material between the curtain fabric, between the canvas and PVC artificial leather, the results are not ideal, the data is 2 ~ 5N/25mm, the main reason is that the adhesive is difficult to cure at room temperature, No further study of the results of heat curing. For hard materials, such as PVC hard board, aluminum plate, wood board, steel plate and other materials, the bonding strength of the adhesive to the steel plate is found to be better, and the tested shear strength is related to the temperature of the pattern heat curing. Such a substrate is 08F steel plate. Size is length X width X thickness = 10025X2, the unit is mm, lap length is 12.5mm, glue two times, open for half an hour, place at room temperature for 24 hours, flood between 120 and 200 degrees for three hours, quickly After cooling for a further 24 hours, the measured shear strength strongly depends on the curing temperature.
2.9 In order to find the best reaction conditions, use the formal experimental design method to optimize
In the process of the same process, the same amount of castor oil, changing the four factors, the amount of A-TDI; B-chain extender type; C-tartaric acid dosage; D-reaction temperature. A factor takes four levels, and the remaining three factors take two levels. The orthogonal table L16 (215) is changed to the orthogonal table L16 (41X212) [4] so that four-level factors can be arranged on the two-level table. The specific arrangement is shown in Table 5. The inspection index is the average shear strength test results of the adhesive-bonded 08F steel plate, the unit is N/cm2, and the curing temperature is 160 degrees. The amount of castor oil for the test was 100 parts by weight. After 16 trials, evenly dispersed emulsions were produced within the range of the above four factors, and they all had good fluidity and could be directly used as adhesives for adhesive bonding of various materials. The following is an intuitive analysis of the effect of each factor on the shear strength. Table 5 shows the sum of test results corresponding to levels 1, 2, 3, and 4 in column J, respectively. Divide them by the number of trials to obtain the average test result corresponding to each level representing the factor on column J, respectively. The minimum value of the average value is subtracted from the minimum value to obtain the range difference. The extreme difference indicates that the factor has the greatest influence on the test result, while the smallest factor has the smallest influence on the test result. By comprehensive comparison, the optimal reaction conditions can be obtained. Within the scope of the test changes, the use of TDI in an amount of 29.2 parts by weight; chain extender 1.4-butanediol; tartaric acid in an amount of 4.17 parts by weight and a reaction temperature of 60 degrees is the optimum reaction conditions.
3 Conclusion
(1) A water-based system in which castor oil and toluene diisocyanate are the main raw materials, butanediol or diethylene glycol is the chain extender, tartaric acid is the hydrophilic monomer, and triethylamine is the neutralizing agent. The uniform and stable polyurethane emulsion adhesive can be made under the process conditions described herein.
(2) The adhesive strength of the adhesive has a strong dependence on the curing temperature.
(3) The preferred reaction conditions through the orthogonal experimental design method are: 100 parts by weight of castor oil; 29.2 parts by TDI; 4.17 parts by tartaric acid; 1.4-butanediol by chain extender; reaction temperature is 60 degrees.
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