CN113512361B - A kind of shellac with high bonding strength and preparation method thereof - Google Patents

Abstract

The invention discloses high-adhesion-strength shellac and a preparation method thereof, and belongs to the field of application of natural adhesives. The invention puts carboxylic acid and/or alcohol containing sulfydryl, shellac, initiator and solvent into a reaction vessel, and reacts for 2-48 hours under heating condition; and precipitating and filtering the product in deionized water, and drying the precipitate in a vacuum oven to obtain a purified product. The preparation method provided by the invention is easy to operate and control, efficient in reaction and easy to purify, and the obtained shellac is stable in chemical property and has high bonding performance to polar materials such as metal, wood, ceramic, glass and the like.

Description

A kind of shellac with high bonding strength and preparation method thereof

technical field

The invention belongs to the technical field of environment-friendly natural polymer adhesives, and relates to a high-bonding strength shellac and a preparation method thereof, in particular to a preparation method of high-bonding strength shellac containing multiple polar groups and the use.

Background technique

Shellac is a kind of low-molecular-weight natural resin with a molecular weight of about 900g/mol, which is prepared by removing impurities and waxes from the secretions of shellac insects, and is non-toxic to humans and animals. Dissolving shellac in absolute ethanol can form a paste solution with a certain viscosity, which can be used to adjust the viscosity of cosmetics or skin care products. Since shellac resin has a high softening point, it naturally forms a film after the ethanol in the shellac ethanol solution volatilizes. Because of this property, shellac is often used as a film former in cosmetics. In addition, shellac is also used in food preservatives, glazing agents for chocolate and other desserts, and enteric coatings for pharmaceuticals; because of its molecular structure containing chromophores, it is also often used as an environmentally friendly weakly acidic industrial dye. In addition to the above uses, shellac has good bonding strength due to the polar functional groups such as carboxyl and hydroxyl groups in the molecular structure of shellac. Shellac is mainly used as an adhesive for wood and is used in the splicing of wooden furniture.

With the improvement of people's awareness of health and environmental protection and the continuous deepening of shellac research, the application scope of shellac has become wider and wider, from the initial wood processing field to the production and processing of metal, glass, ceramic parts and other high-performance products. process. In these new application areas, the requirements for the bonding strength of shellac and substrates are becoming more and more stringent. The existing natural shellac resin is directly used as an adhesive, and its bonding strength can no longer meet the technological requirements.

SUMMARY OF THE INVENTION

In order to solve the deficiencies of the prior art, the present invention provides a shellac with high bonding strength and a preparation method thereof. The invention adopts mercapto-ene addition reaction to introduce functional groups such as carboxyl group, hydroxyl group and amine (ammonium salt) group into the shellac resin molecule, so as to improve the adhesive force between the shellac resin and the base material and obtain high bonding strength.

One of the objects of the present invention is to provide a high bonding strength shellac, the shellac includes formula I and formula II,

wherein R is selected from -(CH ₂ ) _n -COOH, -(CH ₂ ) _n' -OH, -(CH ₂ ) _n' -NH ₂ , -(CH ₂ ) _n -NH ₃ Cl, -CH(CH ₂ ) ₂ -(OH) ₂ , -CH(CH ₂ ) ₂ -(COOH) ₂ , -C ₆ H ₄ -COOH, -C ₆ H ₄ -OH,

And n, n' are integers, n=2-11, n'=2-12.

Another object of the present invention is to provide a kind of preparation method of high bonding strength shellac, comprising the following steps:

1) The shellac and the terminal mercapto compound are charged according to the molar ratio of 1:0.5-2.0 and added to the excess organic solvent, then the initiator of 1-5% of the quality of the terminal mercapto compound is added, and then nitrogen protection is introduced and heated Reaction in oil bath at 50-80°C for 2-48 hours;

in,

The shellac is shellac or white shellac,

The terminal mercapto compound is selected from HS-( _CH2 ) _n- COOH, HS-( _CH2 ) _n' -OH, HS-( _CH2 ) _{n'- NH2} , HS-( _CH2 ) _{n- NH3} Cl, HS-(CH ₂ ) _n -N(CH ₃ ) ₂ , HS-CH(CH ₂ ) ₂ -(OH) ₂ , HS-CH(CH ₂ ) ₂ -(COOH) ₂ , HS-C ₆ H ₄ -COOH, HS-C ₆ H ₄ -OH, wherein, n, n' are integers, n=2-11, n'=2-12,

The initiator is at least one of azobisisobutyronitrile, azobisisoheptanenitrile, azobiscyanovaleric acid and dimethylazobisisobutyrate;

2) After the reaction is finished, the product is added dropwise into deionized water for precipitation, and the obtained precipitate is dried in a 30° C. vacuum oven to constant weight to obtain a high-bonding strength shellac containing multiple polar groups.

Preferably, the organic solvent in step 1) is at least one of 1,4-dioxane, tetrahydrofuran, ethanol and methanol.

beneficial effect

Compared with the existing shellac, the high-bonding strength shellac provided by the present invention improves the cohesiveness by more than 2 times. Thirdly, the high-bonding strength shellac of the present invention improves the solubility and facilitates construction. Moreover, the high bonding strength shellac of the present invention has excellent stability, solves the problems of poor storage stability and harsh storage conditions of the existing shellac resin, and avoids economic losses and shellac caused by improper storage of the shellac resin. waste of resources.

In addition, the preparation method of the shellac resin provided by the present invention is easy to operate and control, the reaction is efficient, and the purification is easy, and the obtained high-bonding strength shellac has stable chemical properties and good storage performance.

The high bonding strength shellac containing carboxyl, hydroxyl, amine, ammonium and other polar groups provided by the present invention is used for the environment-friendly adhesive in the processing of metals, wood, ceramics, glass and other materials. use.

Description of drawings

The accompanying drawings are used to provide a further understanding of the technical solutions of the present invention, and constitute a part of the specification. They are used to explain the technical solutions of the present invention together with the specific embodiments of the present application, and do not limit the technical solutions of the present invention.

Figure 1 is the infrared spectrum (FTIR) of shellac and the product of Example 1.

Figure 2(a) is a graph showing the results of differential scanning calorimetry (DSC) measurement of shellac.

Figure 2(b) is a graph showing the results of the differential scanning calorimeter (DSC) measurement of the product of Example 1.

Figure 3 is an FTIR image of shellac and the product of Example 2.

FIG. 4 is a graph showing the results of differential scanning calorimetry (DSC) measurement of the product of Example 2. FIG.

Detailed ways

The present invention will be described in more detail below with reference to the accompanying drawings, in which preferred embodiments of the present invention are shown, and it should be understood that those skilled in the art can modify the invention described herein and still achieve the beneficial effects of the present invention. Therefore, the following description of shellac that can be used for multiple heating should be understood as widely known to those skilled in the art, and not as a limitation of the present invention.

Example 1:

Accurately weigh 1.5001 g (1.685 mmol) of shellac, dissolve it with 3.00 g of tetrahydrofuran, then add 0.0893 g (0.843 mmol) of 3-mercaptopropionic acid, and add 4.5 mg of azobisisobutyronitrile. After passing N ₂ gas for 30 min, it was put into a 60 ℃ oil bath to react for 24 h. The resulting product was precipitated with deionized water. The precipitate was collected by high-speed centrifugation and dried in a vacuum oven at 30°C to obtain the final product.

The chemical structure of shellac before and after 3-mercaptopropionic acid modification was tested by infrared spectroscopy, and the results are shown in Figure 1. Figure 1 shows that the absorption peaks of unmodified shellac at wavenumbers 1188 and 1151 cm ^-1 are in-plane bending vibration absorption peaks of carbon-hydrogen bonds (CH) in olefins; After the addition of , the double bond absorption peak here disappeared, indicating that the modification reaction was successful. At the same time, a new high-intensity absorption peak appeared at the chemical shift of 3435 cm ^-1 in Figure 1, which was the absorption peak of -OH in the carboxyl group, which proved that a highly polar carboxyl group was additionally introduced into the shellac molecule.

Differential scanning calorimeter (DSC) was used to test the thermal properties of mercaptopropionic acid before and after modification of shellac. The results are shown in Figure 2: unmodified shellac will undergo thermal polymerization of vinyl during the heating process. The reaction heat was 55.17 J/g (Fig. 2a). After modification with mercaptopropionic acid, the product obtained in Example 1 only had a glass transition temperature (79.5°C) during the heating process, and basically no thermal effect was produced (Fig. 2b), indicating that the double bond in the shellac raw material has been After consumption, it is indirectly proved that the addition and modification of shellac by mercaptopropionic acid will improve the thermal stability or storage stability of the product.

The adhesion properties of shellac A and shellac to steel plates and glass were measured by an electronic tensile machine, and the tensile rate was set to 10 mm/min. The experimental results show that the tensile forces of unmodified shellac bonded to steel plates and glass samples are 2.25 MPa and 2.52 MPa, respectively, and the tensile shear strengths of the products of Example 1 are 4.37 MPa and 4.55 MPa, respectively, about 2 times the tensile shear strength, proving that the product can significantly improve the bond strength.

Example 2:

Accurately weigh 1.5011g (1.687mmol) shellac, dissolve it with 6.02g of 1,4-dioxane, then add 0.3650g (3.373mmol) of thioglycerol, add 3.7mg of azodiisoheptyl Nitrile. After passing N ₂ gas for 30 min, it was put into an oil bath at 80 °C for 12 h. The resulting product was precipitated with deionized water. The precipitate was collected by high-speed centrifugation and dried in a vacuum oven at 30°C to obtain the final product.

The chemical structures of shellac before and after thioglycerol modification were tested by infrared spectroscopy, and the results are shown in Figure 3. In the infrared spectrum of modified shellac, the absorption peak of -OH appeared at the chemical shift of 3200-3450 cm ^-1 , which proved that polar hydroxyl groups were introduced into the shellac molecule.

Differential scanning calorimeter (DSC) was used to test the thermal properties of thioglycerol modified shellac. The results are shown in Figure 4: the heat of vinyl polymerization of unmodified shellac during the heating process is 55.17 J/g (Fig. 2a). After modification with thioglycerol, the heat of polymerization of the product obtained in Example 2 was 3.72 J/g (Fig. 4), indicating that most of the double bonds in the shellac raw material were consumed, which indirectly proved that shellac was added with mercaptopropionic acid. The thermal stability or storage stability of the modified product will be significantly improved.

The adhesion properties of shellac A and shellac to steel plates and glass were measured by an electronic tensile machine, and the tensile rate was set to 10 mm/min. The experimental results show that the tensile forces of unmodified purple shellac bonded steel plates and glass samples are 2.25 MPa and 2.52 MPa, respectively, and the tensile shear strengths of the products of Example 4 are 4.79 MPa and 4.92 MPa, respectively, which are about the same as unmodified worms. The tensile shear strength of the adhesive is more than 2 times, which proves that the product can significantly improve the bond strength.

Example 3:

Accurately weigh 1.5007g (1.687mmol) of white shellac, dissolve it with 4.55g of methanol and ethanol (mass ratio 1:1), then add 0.1915g (1.686mmol) of 3-mercaptopropylamine hydrochloride, add 2.0 mg azobisisoheptanenitrile and 2.0 mg azobiscyanovaleric acid. After sealing, it was put into a 50°C oil bath to react for 48h. The resulting product was precipitated with deionized water. The precipitate was collected by high-speed centrifugation and dried in a vacuum oven at 30°C to obtain the final product.

The adhesion properties of shellac A and shellac to steel plates and glass were measured by an electronic tensile machine, and the tensile rate was set to 10 mm/min. The experimental results show that the tensile forces of unmodified purple shellac bonded steel plates and glass samples are 2.11 MPa and 2.34 MPa, respectively. The tensile shear strengths of the products obtained in Example 3 are 3.52 MPa and 3.58 MPa, respectively, which are approximately The tensile shear strength of the adhesive is 1.67 times, which proves that the product can significantly improve the bond strength.

Example 4:

Accurately weigh 1.5031g (1.689mmol) of white shellac, dissolve it with 6.10g of tetrahydrofuran and ethanol (mass ratio 2:1), then add 0.1844g (2.027mmol) of 3-mercaptopropylamine, add 2.0mg of azo Diisoheptanenitrile and 2.0 mg dimethyl azobisisobutyrate. After sealing, put it into a 58-60 ℃ oil bath for 24 hours. The resulting product was precipitated with deionized water. The precipitate was collected by high-speed centrifugation and dried in a vacuum oven at 30°C to obtain the final product.

The adhesion properties of shellac A and shellac to steel plates and glass were measured by an electronic tensile machine, and the tensile rate was set to 10 mm/min. The experimental results show that the tensile forces of unmodified shellac bonded to steel plates and glass samples are 2.11 MPa and 2.34 MPa, respectively, and the tensile shear strengths of the products of Example 4 are 5.81 MPa and 5.96 MPa, respectively, which are about the same as unmodified shellac. 3 times the tensile shear strength, which proves that the product can significantly improve the bond strength.

Embodiments 1-4 are products obtained by modification of carboxyl group, hydroxyl group, amine group and ammonium group respectively, and the above specific examples also prove that the obtained high bonding strength shellac significantly improves the bonding performance, compared with the existing ones. The adhesiveness of shellac is increased by more than 2 times, because the shellac prepared by the present invention contains more carboxyl, hydroxyl, amine and ammonium groups and other groups, which can significantly improve its adhesive strength on metal and other substrates. It can meet the requirements of shellac bonding strength for processing technology such as large-sized metal parts and glass ceramic products. Moreover, the introduction of polar groups into the shellac with high adhesive strength of the present invention can significantly improve the solubility of the shellac and facilitate construction. On the other hand, the present invention adopts a mercapto-ene addition reaction to completely convert the terpene double bond in the shellac resin structure into a saturated carbon-carbon single bond, thereby solving the problems such as poor storage stability and harsh storage conditions of the shellac resin. , to avoid the economic loss and waste of shellac resources caused by improper storage of shellac resin.

Therefore, the high bonding strength shellac provided by the present invention containing a plurality of polar groups such as carboxyl group, hydroxyl group, amine group, ammonium group, etc. agent use.

The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above-mentioned embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention. These equivalent transformations All belong to the protection scope of the present invention. In addition, it should be noted that each specific technical feature described in the above-mentioned specific implementation manner may be combined in any suitable manner under the circumstance that there is no contradiction. In order to avoid unnecessary repetition, the present invention will not describe various possible combinations. In addition, the various embodiments of the present invention can also be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the contents disclosed in the present invention.

Claims (3)

1. a high bonding strength shellac, is characterized in that described shellac comprises formula I and formula II,

Formula I

Formula II wherein R is selected from -(CH ₂ ) _n -COOH, -(CH ₂ ) _n' -OH, -(CH ₂ ) _n' -NH ₂ , -(CH ₂ ) _n -NH ₃ Cl, -CH(CH ₂ ) _2- (OH) ₂ , -CH(CH ₂ ) ₂ -(COOH) ₂ , -C ₆ H ₄ -COOH, -C ₆ H ₄ -OH, and n, n' are integers, n=2- 11, n'=2-12. 2. a preparation method of high bonding strength shellac is characterized in that comprising the following steps: 1) The shellac and the terminal mercapto compound are charged according to the molar ratio of 1:0.5-2.0 and added to the excess organic solvent, and then the initiator of 1-5% by mass of the terminal mercapto compound is added, and then nitrogen protection and heating are introduced. Reaction in oil bath at 50-80 ℃ for 2-48 hours; in, The shellac is shellac or white shellac, The terminal mercapto compound is selected from HS-( _CH2 ) _n- COOH, HS-( _CH2 ) _n' -OH, HS-( _CH2 ) _{n'- NH2} , HS-( _CH2 ) _{n- NH3} Cl, HS-(CH ₂ ) _n -N(CH ₃ ) ₂ , HS-CH(CH ₂ ) ₂ -(OH) ₂ , HS-CH(CH ₂ ) ₂ -(COOH) ₂ , HS-C ₆ H ₄ -COOH, HS-C ₆ H ₄ -OH, wherein, n, n' are integers, n=2-11, n'=2-12, The initiator is at least one of azobisisobutyronitrile, azobisisoheptanenitrile, azobiscyanovaleric acid and dimethylazobisisobutyrate; 2) After the reaction, the product was added dropwise to deionized water for precipitation, and the obtained precipitate was dried in a vacuum oven at 30°C to a constant weight to obtain shellac with multiple polar groups with high adhesive strength. 3. The preparation method according to claim 2, wherein the organic solvent in step 1) is at least one of 1,4-dioxane, tetrahydrofuran, ethanol, and methanol.

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