Modified starch-based adhesive and preparation method thereof

Abstract

The invention relates to the field of adhesives, and discloses a modified starch-based adhesive and a preparation method thereof, the modified starch-based adhesive comprises modified starch, adipic dihydrazide and borax; the modified starch is prepared by graft copolymerization of modified nano zinc oxide, diacetone acrylamide, diallyldimethylammonium chloride and starch; the modified nano-zinc oxide is prepared by grafting a modified silane coupling agent on the surface of nano-zinc oxide, and the modified silane coupling agent is prepared by performing dehydration condensation on an intermediate prepared by reacting itaconic anhydride and phenyltris (dimethyl siloxane) silane and allylamine to prepare a double-bond grafted intermediate; then, 2-mercaptobenzothiazole, 3-mercaptopropyltriethoxysilane and the double-bond grafted intermediate are subjected to a thiol-ene click reaction, and the adhesive is prepared. According to the invention, the modified starch, the adipic dihydrazide and the borax are added, so that the adhesive is endowed with good adhesive performance, water resistance, heat resistance, antibacterial performance and flame retardant performance.

Description

Technical Field

[0001] The invention belongs to the technical field of adhesives, and in particular relates to a modified starch-based adhesive and a preparation method thereof. Background Art

[0002] Adhesives are an important raw material that is indispensable to modern industry and human life. Adhesive products and bonding technologies are developing rapidly, and the application industries are constantly expanding, which has a significant impact on high-tech science and technology and the improvement of people's daily lives. Although chemical adhesives have high bonding strength, most chemical adhesives have formaldehyde release problems, which have a significant impact on human health. With the increase of people's environmental awareness, the use of biomass as the main raw material to prepare adhesives has become one of the important research directions. Therefore, in recent years, natural materials such as starch are often used to prepare and replace chemical adhesives. Starch, as a natural polymer material, has the advantages of being renewable, biodegradable, and low-cost, and is an ideal raw material for environmentally friendly materials.

[0003] Environmentally friendly adhesives have been widely used in the fields of medical devices, packaging, printing, etc. due to their advantages such as no release of harmful substances such as formaldehyde and abundant and renewable raw materials. However, starch has the problem of weak adhesion when used as an adhesive, and its water resistance is poor due to the large number of hydrophilic hydroxyl groups contained in its chain, which limits its wide application. In addition, the starch-based adhesive is often used to bond cardboard, wood boards, etc., and sometimes it is used to hold high-temperature materials or used at high temperatures. However, traditional starch-based adhesives have poor heat resistance, and because their ingredients contain polysaccharides and proteins, they are extremely susceptible to microbial invasion, such as bacteria and fungi, which causes the adhesive to mold and degrade. The prior art directly adds inorganic flame retardants or antibacterial agents to achieve flame retardant or antibacterial effects on adhesives, but as time goes by, the flame retardants or antibacterial agents have precipitation problems, which rapidly reduce the bonding properties of the adhesive, thereby affecting the use of the adhesive. Summary of the invention

[0004] In order to solve the deficiencies mentioned in the above background technology, the purpose of the present invention is to provide a modified starch-based adhesive and a preparation method thereof, by adding modified starch, adipic acid dihydrazide and borax, the modified starch-based adhesive is endowed with good bonding properties, water resistance, heat resistance, antibacterial properties and flame retardant properties.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A modified starch-based adhesive comprises the following raw materials in parts by weight: 60-90 parts of modified starch, 10-30 parts of adipic acid dihydrazide, and 2-8 parts of borax; The modified starch is prepared by grafting and copolymerizing modified nano zinc oxide, diacetone acrylamide, diallyldimethylammonium chloride and starch; wherein the modified nano zinc oxide is prepared by grafting a modified silane coupling agent on the surface of the nano zinc oxide by chemical reaction, and the modified silane coupling agent is prepared by a double bond grafting intermediate by a dehydration condensation reaction of an intermediate prepared by a silylation reaction between itaconic anhydride and phenyltri(dimethylsiloxy)silane and allylamine, and then 2-mercaptobenzothiazole and 3-mercaptopropyltriethoxysilane are simultaneously reacted with the double bond grafting intermediate to undergo a thiol-ene click reaction to prepare the modified starch.

[0006] Preferably, the starch is a mixture of one or more of cassava starch, corn starch, potato starch and wheat starch.

[0007] Preferably, the preparation method of the modified starch comprises the following steps: starch and deionized water are placed in a reactor, stirred and gelatinized at 80-90°C for 20-40 minutes, then cooled to 45-55°C, initiator sodium bisulfite and modified nano zinc oxide are added under a nitrogen atmosphere, and then initiator ammonium persulfate, diacetone acrylamide, and diallyldimethylammonium chloride are slowly added under reflux conditions, stirred and reacted for 3-5 hours, and after the reaction is completed, the pH value of the system is adjusted to 6-7 with sodium hydroxide solution to prepare the modified starch.

[0008] Preferably, the mass ratio of the starch, sodium bisulfite, modified nano zinc oxide, ammonium persulfate, diacetone acrylamide and diallyldimethylammonium chloride is 5-10: 0.02-0.04: 0.6-1: 0.03-0.06: 0.4-1: 0.4-0.6.

[0009] Preferably, the preparation method of the modified nano zinc oxide comprises the following steps: A. Itaconic anhydride, tetrahydrofuran and chloroplatinic acid catalyst are placed in a reactor, stirred and heated to 60-75° C. under a nitrogen atmosphere, and then phenyltri(dimethylsiloxy)silane is added, the temperature is raised to 80-95° C., and the reaction is stirred for 4-6 hours. After the reaction is completed, the unreacted product is removed by rotary evaporation to prepare an intermediate; B. Take the intermediate and glacial acetic acid in a reactor, stir and mix evenly, then add allylamine dropwise under ice bath conditions, place at room temperature and stir to react for 2-3 hours, then heat to 40-50° C. under nitrogen atmosphere, reflux for 3-4 hours, and after the reaction is completed, filter, wash and dry to obtain a double bond grafted intermediate; C. Put the double bond grafting intermediate, 2-mercaptobenzothiazole, 3-mercaptopropyltriethoxysilane and tetrahydrofuran in a reactor, heat it to 50-70° C. under a nitrogen atmosphere, then add triethylamine and stir to react for 4-6 hours. After the reaction is completed, filter, wash and dry to prepare a modified silane coupling agent. D. Take nano zinc oxide, ethanol and deionized water in a reactor, disperse them evenly by ultrasonication, and use ammonia water to adjust the pH value of the system to 9-11. Then, add the modified silane coupling agent to the reactor under a nitrogen atmosphere, stir and react at 55-70°C for 3-5 hours. After the reaction is completed, centrifuge, wash and dry to prepare modified nano zinc oxide.

[0010] Preferably, in step A, the molar ratio of itaconic anhydride to phenyltri(dimethylsiloxy)silane is 3-3.2:1.

[0011] Preferably, the molar ratio of the intermediate in step B to allylamine is 1:3-3.5.

[0012] Preferably, in step C, the molar ratio of the double bond grafting intermediate, 2-mercaptobenzothiazole and 3-mercaptopropyltriethoxysilane is 1:1-1.2:1-1.2.

[0013] A method for preparing a modified starch-based adhesive comprises the following steps: weighing various raw materials by weight, stirring the modified starch and adipic acid dihydrazide at 60-80° C. for 1-2 hours, then adding borax and continuing to stir and mix for 0.5-1 hour to prepare the modified starch-based adhesive.

[0014] Beneficial effects of the present invention: The invention uses itaconic anhydride and phenyltri(dimethylsiloxy)silane to undergo a silylation reaction to prepare an intermediate, then uses the intermediate and allylamine to undergo a dehydration condensation reaction to prepare a double-bond grafted intermediate containing three double-bond functional groups, then uses the SH bonds in the structures of 2-mercaptobenzothiazole and 3-mercaptopropyltriethoxysilane to respectively undergo a thiol-ene click reaction with a double bond in the structure of the double-bond grafted intermediate to prepare a modified silane coupling agent with the remaining double-bond functional group, then uses the silicon hydroxyl group introduced in the structure of the modified silane coupling agent to undergo a condensation reaction with the hydroxyl group on the surface of the nano zinc oxide to prepare the modified nano zinc oxide containing the double-bond functional group. Among them, nano zinc oxide, as a multifunctional inorganic material, has ultraviolet shielding effect and good antibacterial effect. It can destroy DNA, cell membranes and proteins, leading to the death of microorganisms. The modified silane coupling agent is grafted on the surface of nano zinc oxide through a strong chemical bond, which is beneficial to improve the dispersion uniformity of nano zinc oxide and enable it to give full play to its comprehensive performance. In addition, the thiazole monomer introduced on the surface of nano zinc oxide has a hydrophobic structure and antibacterial activity, and can be used as a hydrophobic antibacterial monomer. The introduced sulfur element and silicone chain segment improve the long-term flame retardant and heat resistance of the adhesive to a certain extent.

[0015] The invention utilizes a modified silane coupling agent to perform double-bond modification on nano zinc oxide, and then grafts and copolymerizes diacetone acrylamide, diallyl dimethyl ammonium chloride and starch to prepare modified starch. Diacetone acrylamide is used as a vinyl monomer, and adipic acid dihydrazide is used to perform primary crosslinking on the modified starch. The grafted diacetone acrylamide in the modified starch can undergo ketohydrazide crosslinking with adipic acid dihydrazide, and the crosslinking reaction improves the bonding performance, has the advantage of high reaction activity, and enables the adhesive to be rapidly solidified. Borax is then added for secondary crosslinking, and the two crosslinkings strengthen the structural network between the modified starch molecules, improve the density, and block the penetration of water into the gel, thereby improving the water resistance of the starch-based adhesive. In addition, the graft crosslinking modification effectively improves the heat resistance of the adhesive, because the three-dimensional network structure formed by the crosslinking increases the interaction force between the chain segments, improves the binding energy between the molecules, and requires a higher temperature for the decomposition of the adhesive, thereby preparing an environmentally friendly modified starch-based adhesive with excellent water resistance, antibacterial performance, heat resistance and flame retardant performance. DETAILED DESCRIPTION

[0016] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] Example 1 A method for preparing modified nano zinc oxide comprises the following steps: A. 6.9 g of itaconic anhydride, 20 mL of tetrahydrofuran and 0.33 g of chloroplatinic acid catalyst were placed in a reactor, stirred and heated to 70 ° C under a nitrogen atmosphere, and then 6.6 g of phenyltri(dimethylsiloxy)silane was added, the temperature was raised to 90 ° C, and the reaction was stirred for 5 hours. After the reaction was completed, the unreacted product was removed by rotary evaporation to prepare an intermediate; B. Take 6.7g of the intermediate (Mr=666.9) and 20mL of glacial acetic acid in a reactor, stir and mix evenly, then add 1.9g of allylamine dropwise under ice bath conditions, place at room temperature and stir to react for 2h, then heat to 50°C under nitrogen atmosphere, reflux for 4h, and after the reaction is completed, filter, wash and dry to obtain a double bond grafted intermediate; C. Take 7.8g of double bond grafted intermediate (Mr=784.2), 1.7g of 2-mercaptobenzothiazole, 2.4g of 3-mercaptopropyltriethoxysilane and 100mL of tetrahydrofuran in a reactor, heat to 65°C under a nitrogen atmosphere, then add 0.5g of triethylamine and stir to react for 6h. After the reaction is completed, filter, wash and dry to prepare a modified silane coupling agent; D. Take 5g of nano zinc oxide, 90mL of ethanol and 20mL of deionized water in a reactor, disperse them evenly by ultrasonication, and adjust the pH value of the system to 10 with ammonia water. Then, add 2.1g of modified silane coupling agent to the reactor under nitrogen atmosphere, stir and react at 70°C for 4h. After the reaction is completed, centrifuge, wash and dry to prepare modified nano zinc oxide.

[0018] Example 2 A method for preparing modified starch comprises the following steps: Take 10g corn starch and 15mL deionized water in a reactor, place it at 85°C and stir for gelatinization for 30min, then cool it to 50°C, add 0.02g initiator sodium bisulfite and 1g modified nano zinc oxide prepared in Example 1 under a nitrogen atmosphere, then slowly add 0.04g initiator ammonium persulfate, 0.8g diacetone acrylamide, and 0.5g diallyldimethylammonium chloride under reflux conditions, stir and react for 4h, and after the reaction is completed, use sodium hydroxide solution to adjust the pH value of the system to 7 to prepare modified starch.

[0019] Example 3 A modified starch-based adhesive comprises the following raw materials in parts by weight: 65 parts of the modified starch prepared in Example 2, 12 parts of adipic acid dihydrazide, and 2 parts of borax.

[0020] The preparation method of the modified starch-based adhesive comprises the following steps: weighing each raw material by weight, stirring the modified starch and adipic acid dihydrazide at 70° C. for 1 hour, then adding borax and continuing to stir and mix for 0.5 hour to prepare the modified starch-based adhesive.

[0021] Example 4 A modified starch-based adhesive comprises the following raw materials in parts by weight: 77 parts of the modified starch prepared in Example 2, 20 parts of adipic acid dihydrazide, and 4 parts of borax.

[0022] The preparation method of the above modified starch-based adhesive is the same as that of Example 3.

[0023] Example 5 A modified starch-based adhesive comprises the following raw materials in parts by weight: 88 parts of the modified starch prepared in Example 2, 28 parts of adipic acid dihydrazide, and 7 parts of borax.

[0024] The preparation method of the above modified starch-based adhesive is the same as that of Example 3.

[0025] Comparative Example 1 A method for preparing modified starch comprises the following steps: Take 10g corn starch and 15mL deionized water in a reactor, place it at 85°C and stir for gelatinization for 30min, then cool it to 50°C, add 0.02g initiator sodium bisulfite and 1g modified nano zinc oxide prepared in Example 1 under a nitrogen atmosphere, then slowly add 0.04g initiator ammonium persulfate and 0.5g diallyldimethylammonium chloride under reflux conditions, stir and react for 4h, and after the reaction is completed, use sodium hydroxide solution to adjust the pH value of the system to 7 to prepare modified starch.

[0026] Comparative Example 2 A method for preparing modified starch comprises the following steps: Take 10g corn starch and 15mL deionized water in a reactor, place it at 85℃ and stir for gelatinization for 30min, then cool it to 50℃, add 0.02g initiator sodium bisulfite and 1g nano zinc oxide under nitrogen atmosphere, then slowly add 0.04g initiator ammonium persulfate, 0.8g diacetone acrylamide, and 0.5g diallyldimethylammonium chloride under reflux conditions, stir and react for 4h, and after the reaction is completed, use sodium hydroxide solution to adjust the pH value of the system to 7 to prepare modified starch.

[0027] Comparative Example 3 A modified starch-based adhesive comprises the following raw materials in parts by weight: 88 parts of the modified starch prepared in Comparative Example 1, 28 parts of adipic acid dihydrazide, and 7 parts of borax.

[0028] The preparation method of the above modified starch-based adhesive is the same as that of Example 3.

[0029] Comparative Example 4 A modified starch-based adhesive comprises the following raw materials in parts by weight: 88 parts of the modified starch prepared in Comparative Example 2, 28 parts of adipic acid dihydrazide, and 7 parts of borax.

[0030] The preparation method of the above modified starch-based adhesive is the same as that of Example 3.

[0031] Performance Testing The modified starch-based adhesives prepared in Examples 3-5 and Comparative Examples 3-4 were subjected to performance tests: (1) Shear strength test: The modified starch-based adhesive was used to bond the wood boards, and the shear strength of the wood boards during tension was tested using a texture analyzer to characterize the bonding performance of the adhesive. Specifically, according to GB / T 33333-2016, a 38 mm × 25 mm × 1 mm Paulownia wood board was selected as the bonding substrate, and the adhesive was evenly coated on the surface of each wood board (10 mm × 25 mm). After coating, the wood board was pressed under a certain pressure (1 kg) for 1 min to ensure that the adhesive was evenly distributed. After the pressing was completed, the sample was immediately placed in an oven preheated to 80 ° C and kept at this temperature for 12 h. After the treatment, the sample was transferred to a closed environment at room temperature and a relative humidity of 50% for 24 h to balance the moisture. After the moisture balance, the shear strength of the sample was tested in a dry state (without water immersion) and a wet state (the sample was immersed in water at 25 ° C for 2 h). The tensile rate of the texture analyzer was set to 0.5 mm / s. The data results are shown in Table 1.

[0032] (2) Heat resistance test: A thermogravimetric analyzer was used to detect the thermal decomposition behavior of the modified starch-based adhesive samples. The test was carried out in a nitrogen atmosphere. The heating rate was set at 10°C / min and the samples were heated from 30°C to 700°C. The initial decomposition temperature of the adhesive samples was recorded and their heat resistance was evaluated. Generally speaking, the higher the initial decomposition temperature, the stronger the heat resistance. The data results are shown in Table 1.

[0033] (3) Antibacterial activity test: The antibacterial activity was tested by the inhibition zone method. Staphylococcus aureus and Escherichia coli were inoculated into nutrient broth, incubated overnight at 37°C, and the bacterial suspension was diluted to 10 8 CFU / mL, accurately take 40 μL of bacterial solution and evenly spread it on the solidified agar medium, then take a modified starch-based adhesive sample with a diameter of about 6 mm and place it in the center of the agar plate, and culture it at 37 ° C for 24 h. The antibacterial activity is characterized by measuring the diameter of the inhibition zone. The data results are shown in Table 1.

[0034] (4) Flame retardant performance test: The limiting oxygen index (LOI) is defined as the minimum oxygen volume concentration percentage required for a material to maintain combustion in a mixed gas flow of oxygen and nitrogen. It is intended to characterize the ease with which a material can be ignited and extinguished. The test method is carried out in accordance with ISO 4589-2-1996 and is measured using an oxygen index meter. The data results are shown in Table 1.

[0035] Table 1 Test results of sample performance

[0036] It can be seen from the data in Table 1 that the modified starch-based adhesives prepared in Examples 3-5 of the present invention have good bonding properties, water resistance, heat resistance, antibacterial properties and flame retardant properties. Among them, the modified starch added in Comparative Example 3 is not grafted with diacetone acrylamide, and its measured dry shear strength, wet shear strength and initial decomposition temperature are lower than those of Examples 3-5. The reason is that the cross-linking reaction improves the bonding performance and strengthens the structural network between the modified starch molecules, so that the decomposition of the adhesive requires a higher temperature, and at the same time, it can block the penetration of water into the gel. In Comparative Example 4, nano zinc oxide is not modified, and its measured initial decomposition temperature, Escherichia coli inhibition zone diameter, Staphylococcus aureus inhibition zone diameter and limiting oxygen index are lower than those of Examples 3-5. The reason is that the heat resistance and flame retardant properties are reduced due to the lack of sulfur elements and silicone segments in the modified starch structure, and the antibacterial properties are reduced due to the lack of thiazole monomers.

[0037] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0038] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A modified starch-based adhesive, characterized in that: The method comprises the following raw materials in parts by weight: 60-90 parts of modified starch, 10-30 parts of adipic acid dihydrazide, and 2-8 parts of borax; The modified starch is prepared by grafting and copolymerizing modified nano zinc oxide, diacetone acrylamide, diallyldimethylammonium chloride and starch; wherein the modified nano zinc oxide is prepared by grafting a modified silane coupling agent on the surface of the nano zinc oxide by chemical reaction, and the modified silane coupling agent is prepared by a double bond grafting intermediate by a dehydration condensation reaction of an intermediate prepared by a silylation reaction between itaconic anhydride and phenyltri(dimethylsiloxy)silane and allylamine, and then 2-mercaptobenzothiazole and 3-mercaptopropyltriethoxysilane are simultaneously reacted with the double bond grafting intermediate to undergo a thiol-ene click reaction to prepare the modified starch.

2. The modified starch-based adhesive according to claim 1, characterized in that The starch is a mixture of one or more of cassava starch, corn starch, potato starch and wheat starch.

3. The modified starch-based adhesive according to claim 1, characterized in that The preparation method of the modified starch comprises the following steps: starch and deionized water are placed in a reactor, stirred and gelatinized at 80-90°C for 20-40 minutes, then cooled to 45-55°C, initiator sodium bisulfite and modified nano zinc oxide are added under nitrogen atmosphere, then initiator ammonium persulfate, diacetone acrylamide and diallyldimethylammonium chloride are slowly added under reflux conditions, stirred and reacted for 3-5 hours, and after the reaction is completed, the pH value of the system is adjusted to 6-7 with a sodium hydroxide solution to prepare the modified starch.

4. The modified starch-based adhesive according to claim 3, characterized in that The mass ratio of the starch, sodium bisulfite, modified nano zinc oxide, ammonium persulfate, diacetone acrylamide and diallyl dimethyl ammonium chloride is 5-10: 0.02-0.04: 0.6-1: 0.03-0.06: 0.4-1: 0.4-0.

6.

5. The modified starch-based adhesive according to claim 3, characterized in that The preparation method of the modified nano zinc oxide comprises the following steps: A. Itaconic anhydride, tetrahydrofuran and chloroplatinic acid catalyst are placed in a reactor, stirred and heated to 60-75° C. under a nitrogen atmosphere, and then phenyltri(dimethylsiloxy)silane is added, the temperature is raised to 80-95° C., and the reaction is stirred for 4-6 hours. After the reaction is completed, the unreacted product is removed by rotary evaporation to prepare an intermediate; B. Take the intermediate and glacial acetic acid in a reactor, stir and mix evenly, then add allylamine dropwise under ice bath conditions, place at room temperature and stir to react for 2-3 hours, then heat to 40-50° C. under nitrogen atmosphere, reflux for 3-4 hours, and after the reaction is completed, filter, wash and dry to obtain a double bond grafted intermediate; C. Put the double bond grafting intermediate, 2-mercaptobenzothiazole, 3-mercaptopropyltriethoxysilane and tetrahydrofuran in a reactor, heat it to 50-70° C. under a nitrogen atmosphere, then add triethylamine and stir to react for 4-6 hours. After the reaction is completed, filter, wash and dry to prepare a modified silane coupling agent. D. Take nano zinc oxide, ethanol and deionized water in a reactor, disperse them evenly by ultrasonication, and use ammonia water to adjust the pH value of the system to 9-11. Then, add the modified silane coupling agent to the reactor under a nitrogen atmosphere, stir and react at 55-70°C for 3-5 hours. After the reaction is completed, centrifuge, wash and dry to prepare modified nano zinc oxide.

6. The modified starch-based adhesive according to claim 5, characterized in that In the step A, the molar ratio of itaconic anhydride to phenyltri(dimethylsiloxy)silane is 3-3.2:

1.

7. The modified starch-based adhesive according to claim 5, characterized in that The molar ratio of the intermediate in step B to allylamine is 1:3-3.

5.

8. The modified starch-based adhesive according to claim 5, characterized in that In the step C, the molar ratio of the double bond grafting intermediate, 2-mercaptobenzothiazole and 3-mercaptopropyltriethoxysilane is 1:1-1.2:1-1.

2.

9. A method for preparing a modified starch-based adhesive according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: weighing various raw materials by weight, stirring the modified starch and adipic acid dihydrazide at 60-80°C for 1-2 hours, then adding borax and continuing to stir and mix for 0.5-1 hour to prepare a modified starch-based adhesive.

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