Preparation method of water-resistant plant starch formaldehyde-free adhesive

Abstract

The invention relates to the technical field of adhesives, and discloses a preparation method of a water-resistant plant starch formaldehyde-free adhesive, plant-based starch reacts with a DOPO flame retardant and hydrogen-containing silicone oil to obtain DOPO-silicone oil modified starch, and then the DOPO-silicone oil modified starch is added into a polyurethane emulsion to obtain the water-resistant plant starch formaldehyde-free adhesive. DOPO, a nitrogen-containing benzeneimide ring and a polysiloxane structure are introduced into a starch molecular chain, starch is used as a carbon source to form a nitrogen-phosphorus intumescent flame retardant, phosphoric acid substances, nitrogen and other non-combustible gases generated during combustion are in rapid contact with the starch, dehydration is performed to form an intumescent foam carbon layer, grafted polysiloxane is pyrolyzed to generate an inorganic silicon oxide, and the intumescent foam carbon layer is formed. The flame-retardant polyurethane adhesive has the advantages that the flame-retardant polyurethane adhesive has good flame retardancy and water resistance, and is quickly attached to an expanded foam carbon layer to form a compact and stable silicon-containing carbonized layer, so that heat transfer is effectively inhibited, and oxygen is prevented from being in contact with a polyurethane adhesive matrix, so that the flame-retardant polyurethane adhesive has good flame retardancy and water resistance.

Description

Technical Field

[0001] The invention relates to the technical field of adhesives, in particular to a method for preparing a water-resistant plant starch formaldehyde-free adhesive. Background Art

[0002] Starch is cheap, readily available, biodegradable, and has good bonding properties. It is widely used in adhesives, sizing agents, intumescent flame retardants, flocculants, etc. Since starch is highly hydrophilic and has a high water absorption rate, when used as a component of an adhesive, it will affect its water resistance and waterproofing properties. Therefore, the hydrophobic modification of starch is a research hotspot. Common modifiers include fatty acid chlorides, silicones, isocyanates and other substances. Starch has a high carbon-forming property. When combined with phosphorus-containing flame retardants, an intumescent flame retardant with excellent flame retardant effect can be obtained. It is widely used in materials such as polyurethane, epoxy resin, and polypropylene.

[0003] Polyurethane and its adhesive materials have fast curing, high bonding strength and good impact resistance, and have important applications in metal, plastic, wood, leather, etc. Chinese patent application CN117736495A discloses a flame retardant and high temperature resistant polyurethane foam material and its preparation method, which uses silicon boron modified hydroxyapatite as a high temperature resistant auxiliary agent, phosphate starch and expanded graphite oxide EGO as flame retardants to improve the flame retardant properties of polyurethane foam materials. Compared with the patent, the modified plant starch of the present invention not only improves the flame retardant properties of polyurethane, but also improves its water resistance and waterproof properties. Summary of the invention

[0004] The technical problem solved by the invention is to provide a method for preparing a water-resistant plant starch formaldehyde-free adhesive, thereby solving the problem of poor flame retardancy and water resistance of polyurethane adhesive.

[0005] The technical solution adopted by the present invention is: a method for preparing a water-resistant plant starch formaldehyde-free adhesive:

[0006] S1. Add plant-based starch to dimethyl sulfoxide, add DOPO flame retardant, N,N-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine after stirring in a nitrogen atmosphere, stir and react at 20-30°C for 18-24 hours, filter and add ethanol to the filtrate to precipitate the precipitate, filter, wash with ethanol and water in turn, and dry to obtain DOPO modified starch. The preparation reaction formula is:

[0007]

[0008] S2. Add DOPO-modified starch to N,N-dimethylformamide, add hydrogenated silicone oil after stirring, heat to 80-90°C, dropwise add isopropanol solution of chloroplatinic acid, stir and react for 5-8h, add ethanol after cooling, precipitate, filter, wash with ethanol and water in turn, and dry to obtain DOPO-silicone oil-modified starch. The preparation reaction formula is:

[0009]

[0010] S3. Add DOPO-silicone oil modified starch and defoamer into the polyurethane emulsion, stir and mix well to obtain a water-resistant plant starch formaldehyde-free adhesive.

[0011] Furthermore, the masses of DOPO flame retardant, N,N-dicyclohexylcarbodiimide and 4-dimethylaminopyridine in S1 are 50-80%, 22-35% and 26-42% of the mass of plant-based starch.

[0012] Furthermore, plant-based starch includes potato starch, corn starch, and tapioca starch.

[0013] Furthermore, the mass of hydrogenated silicone oil and chloroplatinic acid in S2 is 30-55% and 0.002-0.004% of the mass of DOPO modified starch.

[0014] Furthermore, the mass of the DOPO-silicone oil modified starch in S3 is 2-15% of the mass of the polyurethane emulsion.

[0015] Furthermore, the preparation method of DOPO flame retardant is:

[0016] (1) Add N-(4-aminophenyl)maleimide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (115-121% by mass of N-(4-aminophenyl)maleimide) to N,N-dimethylformamide, heat to 120-135° C. in a nitrogen atmosphere, react for 7-12 hours, cool, add ice water, precipitate, filter, wash with n-hexane, and then recrystallize from dichloromethane to obtain intermediate A.

[0017] (2) Add intermediate A and 29-34% of the mass of maleic anhydride to dichloromethane, stir and react at room temperature for 2-3 hours, rotary evaporate, wash with n-hexane, and then recrystallize in dichloromethane to obtain DOPO flame retardant. The preparation reaction formula is as follows:

[0018]

[0019] The technical effect of the present invention is as follows: the carboxyl group of the DOPO flame retardant is used to carry out an esterification reaction with the hydroxyl group of the plant starch, and the introduced olefin group is then subjected to an addition reaction with the hydrogen-containing silicone oil to obtain DOPO-silicone oil-modified starch, which is used as a hydrophobic flame retardant modifier and added to polyurethane to obtain a water-resistant plant starch formaldehyde-free adhesive. The hydrophobic benzene ring structure and polysiloxane molecular chain are introduced into the starch molecular chain, which significantly reduces the hydrophilicity of the starch, avoids the starch being added to the polyurethane adhesive to increase the hydrophilicity and water absorption of the adhesive, and at the same time, the long chain of the hydrophobic polysiloxane molecule forms a hydrophobic network in the polyurethane film matrix, which is conducive to reducing the water absorption rate and improving the water resistance and waterproof performance.

[0020] The DOPO-silicone oil modified starch of the present invention introduces DOPO, nitrogen-containing benzimide ring and polysiloxane structure into the molecular chain, uses starch as a carbon source, and forms a nitrogen-phosphorus expansion flame retardant. Since the starch matrix is ​​grafted with DOPO and nitrogen-containing benzimide ring, phosphoric acid substances, nitrogen and other non-combustible gases generated during combustion quickly contact with the starch and dehydrate to form an expansion foam carbon layer, and the grafted polysiloxane is pyrolyzed to generate inorganic silicon oxide, which is quickly attached to the expansion foam carbon layer to form a compact and stable silicon-containing carbonized layer, which effectively inhibits the transfer of heat and hinders the contact of oxygen with the polyurethane adhesive matrix, thereby showing good flame retardant performance. DETAILED DESCRIPTION

[0021] Polyurethane emulsion, model PU1179, Hefei Dibang Nanotechnology Co., Ltd. Defoamer, model silicone defoamer RKZ6004, Tianjin Ruike Chemical Trading Co., Ltd. Hydrogenated silicone oil, hydrogen content 1.5%, Yantai Shunming New Materials Co., Ltd. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, CAS registration number is 35948-25-5. N-(4-aminophenyl)maleimide, CAS registration number is 29753-26-2.

[0022] Embodiment 1:

[0023] (1) To 12 mL of N,N-dimethylformamide, 2 g of N-(4-aminophenyl)maleimide and 2.3 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added, and the mixture was heated to 135° C. in a nitrogen atmosphere for 7 h. After cooling, ice water was added to precipitate, which was filtered, washed with n-hexane, and then recrystallized from dichloromethane to obtain intermediate A.

[0024] (2) Add 3 g of intermediate A and 1.02 g of maleic anhydride to 40 mL of dichloromethane, stir and react at room temperature for 2 h, rotary evaporate, wash with n-hexane, and then recrystallize in dichloromethane to obtain DOPO flame retardant.

[0025] (3) Add 10 g of cassava starch to 500 mL of dimethyl sulfoxide, and then add 6.5 g of DOPO flame retardant, 2.8 g of N,N-dicyclohexylcarbodiimide, and 3.5 g of 4-dimethylaminopyridine in a nitrogen atmosphere after stirring. Stir and react at 20° C. for 24 h. After filtering, add ethanol to the filtrate to precipitate the precipitate, filter it, wash it with ethanol and water in turn, and dry it to obtain DOPO modified starch.

[0026] (4) Add 8 g of DOPO-modified starch to 500 mL of N,N-dimethylformamide, add 3.5 g of hydrogenated silicone oil after stirring, heat to 90°C, dropwise add 0.4 mL of isopropanol solution containing 0.36 mg of chloroplatinic acid, stir for 6 h, add ethanol after cooling, precipitate, filter, wash with ethanol and water in turn, and dry to obtain DOPO-silicone oil-modified starch.

[0027] (5) Add 2 g of DOPO-silicone oil-modified starch and 0.6 g of defoaming agent to 100 g of polyurethane emulsion, stir and mix well to obtain a water-resistant plant starch formaldehyde-free adhesive.

[0028] Embodiment 2:

[0029] (1) To 15 mL of N,N-dimethylformamide, 2 g of N-(4-aminophenyl)maleimide and 2.42 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide were added, and the mixture was heated to 120° C. in a nitrogen atmosphere. The mixture was reacted for 12 h. After cooling, ice water was added to precipitate. The precipitate was filtered, washed with n-hexane, and then recrystallized from dichloromethane to obtain intermediate A.

[0030] (2) Add 3 g of intermediate A and 0.87 g of maleic anhydride to 30 mL of dichloromethane, stir and react at room temperature for 3 h, rotary evaporate, wash with n-hexane, and then recrystallize in dichloromethane to obtain DOPO flame retardant.

[0031] (3) 10 g of potato starch was added to 600 mL of dimethyl sulfoxide, and then 8 g of DOPO flame retardant, 3.5 g of N,N-dicyclohexylcarbodiimide, and 4.2 g of 4-dimethylaminopyridine were added after stirring in a nitrogen atmosphere. The mixture was stirred at 20° C. for 24 h. After filtering, ethanol was added to the filtrate to precipitate the precipitate, which was filtered, washed with ethanol and water in turn, and dried to obtain DOPO modified starch.

[0032] (4) Add 8 g of DOPO-modified starch to 500 mL of N,N-dimethylformamide, add 4.4 g of hydrogenated silicone oil after stirring, heat to 80°C, dropwise add 0.4 mL of isopropanol solution containing 0.32 mg of chloroplatinic acid, stir and react for 8 h, add ethanol after cooling, precipitate, filter, wash with ethanol and water in turn, and dry to obtain DOPO-silicone oil-modified starch.

[0033] (5) Add 8 g of DOPO-silicone oil-modified starch and 1 g of defoamer to 100 g of polyurethane emulsion, stir and mix well to obtain a water-resistant plant starch formaldehyde-free adhesive.

[0034] Embodiment 3:

[0035] (3) 10 g of corn starch was added to 500 mL of dimethyl sulfoxide, and then 5 g of DOPO flame retardant (prepared according to the method of Example 1), 2.2 g of N,N-dicyclohexylcarbodiimide, and 2.6 g of 4-dimethylaminopyridine were added after stirring in a nitrogen atmosphere. The mixture was stirred at 30° C. for 18 h. After filtering, ethanol was added to the filtrate to precipitate the precipitate, which was filtered, washed with ethanol and water in turn, and dried to obtain DOPO modified starch.

[0036] (4) Add 8 g of DOPO-modified starch to 400 mL of N,N-dimethylformamide, add 2.4 g of hydrogenated silicone oil after stirring, heat to 90°C, dropwise add 0.4 mL of isopropanol solution containing 0.16 mg of chloroplatinic acid, stir for 5 h, add ethanol after cooling, precipitate, filter, wash with ethanol and water in turn, and dry to obtain DOPO-silicone oil-modified starch.

[0037] (5) Add 15 g of DOPO-silicone oil-modified starch and 1 g of defoamer to 100 g of polyurethane emulsion, stir and mix well to obtain a water-resistant plant starch formaldehyde-free adhesive.

[0038] Comparative Example 1:

[0039] (1) Add 0.6 g of defoamer to 100 g of polyurethane emulsion and stir to mix well to obtain an adhesive.

[0040] Comparative Example 2:

[0041] (1) Add 2 g of cassava starch and 0.6 g of defoamer to 100 g of polyurethane emulsion, stir and mix, and obtain a water-resistant plant starch formaldehyde-free adhesive.

[0042] Comparative Example 3:

[0043] (1) Add 2 g of DOPO modified starch (prepared according to the method of Example 1) and 0.6 g of defoamer to 100 g of polyurethane emulsion, stir and mix, and obtain a water-resistant plant starch formaldehyde-free adhesive.

[0044] Comparative Example 4:

[0045] (1) 10 g of cassava starch and 6.5 g of DOPO flame retardant were stirred and mixed to obtain a DOPO-starch blend.

[0046] (2) 8 g of DOPO-starch blend and 3.5 g of hydrogenated silicone oil were stirred and mixed to obtain a DOPO-silicone oil-starch blend.

[0047] (3) Add 2 g of DOPO-silicone oil-starch blend and 0.6 g of defoamer to 100 g of polyurethane emulsion, stir and mix well to obtain a water-resistant plant starch formaldehyde-free adhesive.

[0048] Comparative Example 5:

[0049] (1) 8 g of DOPO-modified starch and 3.5 g of hydrogenated silicone oil were stirred and mixed to obtain a silicone oil-DOPO-modified starch blend.

[0050] (2) Add 2 g of silicone oil-DOPO modified starch blend and 0.6 g of defoaming agent to 100 g of polyurethane emulsion, stir and mix well to obtain a water-resistant plant starch formaldehyde-free adhesive.

[0051] The tensile shear strength of the adhesive was tested according to GB / T 7124-2008 standard. The substrate was steel sheet to steel sheet, the curing temperature was 70°C, the time was 6 hours, and then placed at room temperature for 24 hours for testing.

[0052] The adhesive was cast into a mold, vacuum degassed, and then dried and cured at 80°C for 8 hours, weighed, placed in water, and soaked for 48 hours. The film was taken out, the surface moisture was wiped off, and weighed to calculate the water absorption rate. Water absorption rate = (mass after water absorption - mass before water absorption) / mass before water absorption × 100%.

[0053] The oxygen index of the film sample was tested according to GB / T 2406.1-2008 standard.

[0054] The vertical burning performance of the film sample was tested according to the UL94 method.

[0055]

[0056]

[0057] After testing, the adhesive prepared in each embodiment has a lower water absorption rate, a high limiting oxygen index, and UL94 reaches V-0 grade, has better water resistance and flame retardancy, and maintains good tensile shear strength and bonding performance. This is mainly because DOPO-silicone oil-modified starch is added, and hydrophobic benzene ring structures and polysiloxane molecular chains are introduced into the starch molecular chain, which significantly reduces the hydrophilicity of starch and avoids the addition of starch to the polyurethane adhesive to increase the hydrophilicity and water absorption of the adhesive. At the same time, the long chain of hydrophobic polysiloxane molecules forms a hydrophobic network in the polyurethane film matrix, which is beneficial to reduce water absorption and improve water resistance. After the starch is grafted and modified, DOPO, nitrogen-containing benzoimide ring and polysiloxane structure are introduced into the molecular chain, and starch is used as a carbon source to form a nitrogen-phosphorus expansion flame retardant. Since the starch matrix is ​​grafted with DOPO and nitrogen-containing benzoimide ring, the phosphoric acid substances, nitrogen and other non-combustible gases generated during combustion quickly come into contact with the starch, dehydrated to form an expanded foam carbon layer, and the grafted polysiloxane is pyrolyzed to generate inorganic silicon oxide, which quickly adheres to the expanded foam carbon layer to form a tight and stable silicon-containing carbonized layer, which effectively inhibits the transfer of heat and hinders the contact between oxygen and the polyurethane adhesive matrix, thereby showing good flame retardant properties.

[0058] In Comparative Example 2, only starch was added. Since starch has good hydrophilicity, the water absorption rate of the adhesive increased, the water resistance became poor, and the flame retardancy was very poor.

[0059] Compared with Example 1, Comparative Example 3 adds DOPO-modified starch, and the hydrophobicity of the starch becomes greater. When added to the polyurethane adhesive, the water absorption rate of the adhesive does not increase significantly. At the same time, the starch is grafted with DOPO and nitrogen-containing benzoimide rings to form a nitrogen-phosphorus expansion flame retardant. The phosphoric acid substances, nitrogen and other non-combustible gases generated during combustion quickly come into contact with the starch and dehydrate to form an expanded foam carbon layer, which can improve the flame retardant properties of the adhesive, increase the limiting oxygen index, and achieve the UL94 grade of V-2.

[0060] Compared with Example 1, Comparative Example 4 adds a blend of starch, DOPO flame retardant, and hydrogenated silicone oil to a polyurethane matrix. The starch is not hydrophobically modified and has a relatively high hydrophilicity. However, due to the addition of hydrophobic hydrogenated silicone oil, the water absorption rate of the polyurethane adhesive is not significantly improved. In addition, the starch matrix is ​​not grafted with DOPO, nitrogen-containing benzimide ring, and polysiloxane structure, resulting in the inability of phosphoric acid substances, nitrogen, and other non-combustible gases generated during combustion to quickly contact the starch, resulting in the starch not being quickly dehydrated to form an expanded foam carbon layer, and the polysiloxane being pyrolyzed to generate inorganic silicon oxides, which are not quickly attached to the surface of the expanded foam carbon layer, and the silicon-containing carbonized layer is not well formed, resulting in poor flame retardancy of the adhesive, a lower limiting oxygen index than Example 1, and a UL94 grade of only V-1, which is lower than Example 1.

[0061] Comparative Example 5 added a blend of DOPO-modified starch and hydrogenated silicone oil, but the starch was not grafted with polysiloxane molecular chains, and the inorganic silicon oxide generated during combustion did not quickly adhere to the surface of the expanded foam carbon layer, and the silicon-containing carbonized layer was not well formed, resulting in poor flame retardancy, which resulted in the limiting oxygen index of the adhesive being lower than that of Example 1. In addition, the starch was not grafted with hydrophobic polysiloxane molecular chains, resulting in the hydrophilicity of the DOPO-modified starch being greater than that of the DOPO-silicone oil-modified starch of Example 1, and the water absorption rate of the polyurethane adhesive being greater than that of Example 1.

Claims

1. A method for preparing a water-resistant plant starch formaldehyde-free adhesive, characterized in that: The preparation method is as follows: S1, adding plant-based starch to dimethyl sulfoxide, adding DOPO flame retardant, N,N-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine after stirring in a nitrogen atmosphere, filtering after the reaction, adding ethanol to the filtrate, precipitating a precipitate, filtering, washing, and drying to obtain DOPO modified starch; S2, adding DOPO-modified starch to N,N-dimethylformamide, adding hydrogenated silicone oil after stirring, heating to the reaction temperature, dropping an isopropanol solution of chloroplatinic acid, stirring for reaction, cooling, adding ethanol, precipitating a precipitate, filtering, washing, and drying to obtain DOPO-silicone oil-modified starch; S3. Add DOPO-silicone oil modified starch and defoamer into the polyurethane emulsion, stir and mix well to obtain a water-resistant plant starch formaldehyde-free adhesive.

2. The method for preparing the water-resistant plant starch formaldehyde-free adhesive according to claim 1, characterized in that: The masses of DOPO flame retardant, N,N-dicyclohexylcarbodiimide and 4-dimethylaminopyridine in S1 are 50-80%, 22-35% and 26-42% of the mass of plant-based starch, respectively.

3. The method for preparing the water-resistant plant starch formaldehyde-free adhesive according to claim 2, characterized in that: The plant-based starch includes potato starch, corn starch, and tapioca starch.

4. The method for preparing the water-resistant plant starch formaldehyde-free adhesive according to claim 1, characterized in that: The reaction temperature in S1 is 20-30°C and the reaction time is 18-24h.

5. The method for preparing the water-resistant plant starch formaldehyde-free adhesive according to claim 1, characterized in that: The mass of hydrogenated silicone oil and chloroplatinic acid in S2 is 30-55% and 0.002-0.004% of the mass of DOPO modified starch.

6. The method for preparing the water-resistant plant starch formaldehyde-free adhesive according to claim 1, characterized in that: The reaction temperature in S2 is 80-90°C and the reaction time is 5-8h.

7. The method for preparing the water-resistant plant starch formaldehyde-free adhesive according to claim 1, characterized in that: The mass of the DOPO-silicone oil modified starch in S3 is 2-15% of the mass of the polyurethane emulsion.

8. The method for preparing the water-resistant plant starch formaldehyde-free adhesive according to claim 1, characterized in that: The preparation method of the DOPO flame retardant is: (1) Add N-(4-aminophenyl)maleimide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to N,N-dimethylformamide, heat to 120-135° C. in a nitrogen atmosphere, react for 7-12 hours, cool, add ice water, precipitate, wash, and recrystallize to obtain intermediate A; (2) Add intermediate A and maleic anhydride to dichloromethane, stir and react at room temperature for 2-3 hours, rotary evaporate, wash, and recrystallize to obtain DOPO flame retardant.

9. The method for preparing the water-resistant plant starch formaldehyde-free adhesive according to claim 8, characterized in that: The mass of the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is 115-121% of the mass of N-(4-aminophenyl)maleimide.

10. The method for preparing the water-resistant plant starch formaldehyde-free adhesive according to claim 8, characterized in that: The mass of the maleic anhydride is 29-34% of the mass of the intermediate.

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