Preparation of water-based fire-retardant adhesive and application method thereof

Abstract

This invention discloses the preparation and application method of a water-based flame-retardant adhesive, specifically a polyvinyl alcohol composite water-soluble adhesive system. The adhesive system is composed of polyvinyl alcohol, flame retardant, thickener, antibacterial agent, and curing agent. The adhesive specifically includes the following components by mass percentage: polyvinyl alcohol 57.5%~79.3%, flame retardant 6%~21%, thickener 0~25%, antibacterial agent 1~3%, and curing agent 0.5~1.0%. This invention provides a new approach for the research of novel environmentally friendly flame-retardant adhesives. Furthermore, by fully mixing the prepared adhesive system with waste flexible polyimide foam particles and powders, molding, compacting, curing, and drying in a mold, a composite board with both good flame retardancy and flexibility is prepared, enhancing the utilization value of foam materials and contributing to environmental protection. This invention offers advantages in the recycling of waste polyimide foam, including simpler processes, lower costs, higher recycling rates, and environmental friendliness.

Description

Technical Field

[0001] This invention relates to the field of organic polymer materials technology, and in particular to a method for preparing and applying a water-based flame-retardant adhesive. Background Technology

[0002] Polyvinyl alcohol (PVA) is a polyhydroxyl polymer compound that is soluble in hot water. Its concentrated aqueous solution exhibits strong adhesion to materials such as wood, paper, fiber, cement, and ceramics. However, the extremely poor flame retardant properties of PVA films limit its application range. Polyimide flexible foam, on the other hand, is a high-performance material that is heat-resistant, lightweight, and flame-retardant. It is mainly used in aerospace, electronic packaging, and high-temperature insulation, offering significantly superior performance compared to ordinary foams. However, during the production of polyimide flexible foam, the free-floating growth of the foam results in irregularly shaped finished products, inevitably generating a large amount of scrap. Ordinary landfilling and incineration methods are ineffective in handling this waste, making its recycling a persistent challenge. In recent years, with the implementation of environmental regulations and increased public awareness of environmental protection in my country, coupled with market opportunities and green and sustainable development policies, water-based adhesives have gained enormous development potential and hold significant research value. Using water-based polyvinyl alcohol flame-retardant composite adhesive to bond polyimide flexible foam plastics for curing and drying is a feasible method. Water-based polyvinyl alcohol flame-retardant composite adhesive uses water as a solvent, making it safe to use, eliminating the risk of fire during construction, saving resources and energy, reducing environmental pollution, and is also relatively inexpensive. It is a relatively new type of coating. By adding high-performance flame retardants to the water-based polyvinyl alcohol adhesive and utilizing the high flame-retardant properties of the polyimide flexible foam plastic itself, it is possible to recycle and reuse it.

[0003] Currently, there are very few reports on methods for treating polyimide flexible foam waste, both domestically and internationally. CN115418020 A discloses a method in which polyimide foam waste is pulverized into high-density powder and then directly mixed with dianhydride monomer, foaming agent, solvent, additives, and adhesive to form a new foaming slurry. Isocyanate is then added and stirred to obtain a polyimide foam precursor. Finally, the precursor is poured into a mold and heated to cure, resulting in recycled polyimide foam material. However, this method involves a complex pulverization process, high energy consumption, and air pollution. Furthermore, the pulverized material in the foaming slurry significantly affects the foaming and molding process, leading to numerous process and cost issues. CN 116284958 A discloses a method for producing polyimide heat-insulating and sound-absorbing panels using waste flexible foam. This method involves laying the cut waste flexible polyimide foam in a mold, mixing white and black foaming agents evenly in a spraying machine, and spraying the mixed foaming slurry onto the waste surface until all the waste is laid. The mold is then closed and placed in an oven for heating and setting, allowing the foaming slurry to foam, further bonding the waste materials and completing imidization. After cooling and demolding, recycled polyimide foam panels are obtained. This method is more refined than traditional processes, but the spraying and curing processes are more complex, energy consumption is higher, and air pollution is a concern.

[0004] Currently, how to harmlessly treat polyimide flexible foam waste and how to recycle it have become urgent problems to be solved. Summary of the Invention

[0005] This invention provides a method for preparing and applying a water-based flame-retardant adhesive to overcome the shortcomings of the prior art. It provides a method for preparing a water-based flame-retardant adhesive and utilizes it to treat polyimide soft foam waste in a harmless manner. This water-based flame-retardant adhesive is an environmentally friendly flame-retardant composite adhesive formulation that is simple to formulate, easy to prepare, has simple components, and does not contain organic solvents, thereby improving the recycling rate of waste materials.

[0006] In order to achieve the objectives of this invention, the following technologies are proposed: The first aspect proposes a water-based flame-retardant adhesive, characterized in that it comprises, by weight percentage: Polyvinyl alcohol (PVA) contains 57.5% to 79.3%. As a film-forming matrix, PVA contains a high content of hydroxyl functional groups, which can increase the adhesion of the coating. It is a resin with strong adhesion. The polymer molecular chain is an irregular flexible chain segment, which is beneficial to increasing the flexibility of the coating film.

[0007] Flame retardants 6% to 21%; Thickener 0 to 25%; Antibacterial agent 1% to 3%; Hardener 0.5% to 1%.

[0008] Furthermore, the flame retardant is one or more mixtures of dimethyl methylphosphonate (DMMP), ammonium polyphosphate (APP), aluminum diethylphosphonate, aluminum hydroxide, and magnesium hydroxide. Among these, dimethyl methylphosphonate and ammonium polyphosphate, as reactive flame retardants, can improve flame retardant performance by reacting with polyvinyl alcohol (PVA). Dimethyl methylphosphonate is a colorless, transparent liquid with a phosphorus content as high as 25%, miscible with water and various organic solvents. After hydrolysis, dimethyl methylphosphonate can undergo esterification with PVA under high-temperature conditions, thereby improving the polymer's flame retardant performance. During combustion, it produces phosphorus-containing gases that dilute the oxygen on the surface of PVA, reducing smoke release. Additionally, the phosphate groups in the structure decompose into metaphosphoric acid during heating. During combustion, metaphosphoric acid dehydrates PVA, forming a dense charred isolation layer on the surface, preventing further diffusion of oxygen and heat into the polymer matrix, thus improving the flame retardant effect of PVA. Its flame retardant mechanism can be explained as follows:

[0009] Ammonium polyphosphate can improve flame retardant properties by reacting with polyvinyl alcohol (PVA). During high-temperature thermal degradation, the ammonium polyphosphate in PVA flame-retardant adhesives degrades first with the loss of H2O and NH3. The H2O and NH3 produced during high-temperature decomposition are non-flammable gases, which can dilute the oxygen concentration and the gaseous combustibles produced by the decomposition of the polymer matrix, effectively reducing the temperature and concentration, thus exhibiting gas-phase flame retardant effects. Furthermore, the polyphosphates generated during high-temperature decomposition have high reactivity, and most of the polyphosphates crosslink with PVA, further contributing to char formation. This forms a protective char layer on the surface of the composite material, preventing further contact between gaseous combustibles and oxygen, and hindering heat transfer, thereby achieving a certain degree of condensed-phase flame retardant effect. Its flame-retardant mechanism can be explained as follows:

[0010]

[0011] Diethylphosphonic aluminum, aluminum hydroxide, and magnesium hydroxide, as additive flame retardants, can achieve both gel-phase and gas-phase flame retardant effects through high-temperature decomposition. The flame-retardant mechanism of diethylphosphonic aluminum involves both condensed-phase and gas-phase flame retardancy. Thermal decomposition transforms it into aluminum phosphate (AlPO4), which covers the surface of the burning material, isolating oxygen and promoting polymer carbonization. Furthermore, thermal decomposition generates PO· free radicals in the gas phase, capturing OH· and H· in the combustion chain reaction and converting them into HPO· and PO·, thus terminating the free radical chain reaction. Aluminum hydroxide and magnesium hydroxide have similar flame-retardant effects. During high-temperature decomposition, they release large amounts of water and absorb significant heat energy, while simultaneously diluting the oxygen content in the air, thus preventing or delaying combustion. The Al2O3 or MgO produced during combustion has a high specific surface energy and strong adsorption capacity, forming a carbonized film on the polymer surface that effectively suppresses smoke, achieving a gel-phase flame-retardant effect. However, their flame-retardant effect is relatively moderate, requiring a relatively large dosage.

[0012] Furthermore, the thickener is one or more of hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and polyacrylamide, which can be used as a film-forming aid. The hydroxyl and amide groups in its structure are beneficial to improving the polymerization performance, promoting the elastic deformation of the polymer, improving the dispersibility of inorganic flame retardant fillers, and increasing the consistency and water retention of the adhesive.

[0013] Furthermore, the antibacterial agent is carboxymethyl chitosan, which has film-forming properties and can form hydrogen bonds with the polymer matrix, thereby improving adhesion and film density. The amino and carboxyl groups in its molecular structure can destroy the cell membrane of microorganisms, thus having antibacterial and bacteriostatic effects and being able to inhibit mold growth for a long time.

[0014] Furthermore, the curing agent is γ-glycidyl etheroxypropyltrimethoxysilane KH560, which can reduce the agglomeration of flame retardant fillers, improve dispersibility, and reduce interfacial stress, thereby enhancing the density of the adhesive film. In addition, appropriate addition amounts can improve the water resistance, mechanical strength, and durability of the adhesive film.

[0015] The second aspect proposes a method for preparing water-based flame-retardant adhesives, including the following steps: Step 01: Dissolve polyvinyl alcohol in water at 80°C to 95°C, and then cool the water to room temperature to obtain a homogeneous aqueous solution with a solid content of 6% to 9% of the solute. Step 11: Add flame retardant, thickener, antibacterial agent and curing agent to the homogeneous aqueous solution obtained in step 01, and obtain water-based flame retardant adhesive by stirring.

[0016] The third aspect proposes a method for using a water-based flame-retardant adhesive, including the following steps: Step 02: Process the soft polyimide foam waste into polyimide foam waste granules or powder; Step 12: The water-based flame-retardant adhesive and the polyimide foam waste particles or powder obtained in step 02 are stirred and mixed at a solute mass ratio of 1:0.5 to 0.65. Step 22: Pour the mixture obtained in step 12 into a mold and compact it. Heat and cure it at 80°C to 100°C for 8 to 16 hours to obtain the recycled polyimide foam composite board material.

[0017] The advantages of the above technical solution are: The present invention provides a water-based flame-retardant adhesive with pure water as the solvent, which replaces the traditional organic solvent and avoids the pollution of the environment and the harm to human health caused by solvent volatilization.

[0018] The present invention provides a water-based flame retardant adhesive, which has good properties, high mechanical strength of coating film, strong adhesion and good flame retardant effect.

[0019] This invention is applicable to various types and densities of flexible polyimide foam. The recycling method is highly efficient, requires simple equipment, and features high recycling rate and low recycling cost. Attached Figure Description

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will now be described in further detail with reference to the accompanying drawings.

[0021] Figure 1 The vertical burning (UL-94) and flexibility test diagrams of Example 1 are shown.

[0022] Figure 2 The diagram shows the vertical burning (UL-94) and flexibility test results from Example 2.

[0023] Figure 3 The vertical burning (UL-94) and flexibility test diagrams of Example 3 are shown.

[0024] Figure 4 The vertical burning (UL-94) and flexibility test diagrams of Example 4 are shown.

[0025] Figure 5 The vertical burning (UL-94) and flexibility test diagrams of Example 5 are shown.

[0026] Figure 6 The vertical burning (UL-94) and flexibility test diagrams of Example 6 are shown. Detailed Implementation

[0028] This embodiment provides a water-based flame-retardant adhesive and a method for preparing a recycled polyimide foam composite board thereof. The water-based flame-retardant adhesive comprises the following solute components by mass percentage: polyvinyl alcohol 79.7%, dimethyl methylphosphonate 16%, polyacrylamide 0.3%, carboxymethyl chitosan 3%, and γ-glycidoxypropyltrimethoxysilane 1%.

[0029] Specifically, the following steps are included: (1) Dissolve polyvinyl alcohol in water at 95°C and then cool it to room temperature to obtain a homogeneous aqueous solution with a solid content of 6%. Then add flame retardant dimethyl methylphosphonate, thickener polyacrylamide, antibacterial agent methyl chitosan, and curing agent γ-glycidyl etheroxypropyltrimethoxysilane according to the mass percentage of the solute. After stirring and reacting thoroughly, the water-based flame retardant adhesive is obtained.

[0030] (2) Cut (or cut) the clean soft polyimide foam waste into block particles to obtain polyimide foam waste particles for later use. (3) Use water-based flame retardant adhesive and pretreated soft polyimide foam waste at a solute mass ratio of 1:0.65 and stir thoroughly for 15 minutes; (4) Pour the well-mixed water-based flame-retardant adhesive and the soft polyimide foam waste mixture into a mold and compact it. Then heat and cure it at 100℃ for 8 hours to obtain recycled polyimide foam composite board material. It has good flexibility and flame retardancy up to V-0 level. Vertical burning (UL-94) and flexibility test diagrams are shown in the figure. Figure 1 As shown, the adhesion (GB / T 5210-2006) was measured to be 0.4 MPa, and the limiting oxygen index (LOI) was 23.5%.

[0031] Example 2 This embodiment provides a water-based flame-retardant adhesive and a method for preparing a recycled polyimide foam composite board thereof. The water-based flame-retardant adhesive comprises the following solute components by mass percentage: 64.5% polyvinyl alcohol, 8% ammonium polyphosphate, 25% hydroxymethyl cellulose, 2% carboxymethyl chitosan, and 0.5% γ-glycidoxypropyltrimethoxysilane.

[0032] Specifically, the following steps are included: (1) Dissolve polyvinyl alcohol in water at 80°C and then cool it to room temperature to obtain a homogeneous aqueous solution with a solid content of 7%. Then add flame retardant ammonium polyphosphate, thickener hydroxymethyl cellulose, antibacterial agent methyl chitosan, and curing agent γ-glycidyl etheroxypropyltrimethoxysilane according to the mass percentage of the solute. After stirring and reacting thoroughly, the water-based flame retardant adhesive is obtained.

[0033] (2) Cut (or cut) the clean soft polyimide foam waste into block particles to obtain polyimide foam waste particles for later use. (3) Use water-based flame retardant adhesive and pretreated soft polyimide foam waste at a solute mass ratio of 1:0.6 and stir thoroughly for 30 minutes; (4) Pour the well-mixed water-based flame-retardant adhesive and the soft polyimide foam waste mixture into a mold and compact it. Then heat and cure it at 90°C for 10 hours to obtain the recycled polyimide foam composite board material, which has good flexibility and flame retardancy up to V-0 level. Vertical burning (UL-94) and flexibility test diagrams are shown below. Figure 2 As shown, the adhesion (GB / T5210-2006) was measured to be 1.0 MPa, and the limiting oxygen index (LOI) was 24.5%.

[0034] Example 3 This embodiment provides a water-based flame-retardant adhesive and a method for preparing a recycled polyimide foam composite board thereof. The water-based flame-retardant adhesive comprises the following solute components by mass percentage: 57.5% polyvinyl alcohol, 21% aluminum hydroxide, 20% hydroxypropyl methylcellulose, 1% carboxymethyl chitosan, and 0.5% γ-glycidoxypropyltrimethoxysilane.

[0035] Specifically, the following steps are included: (1) Dissolve polyvinyl alcohol in water at 85°C and then cool it to room temperature to obtain a homogeneous aqueous solution with 8% solid content solute. Then add flame retardant aluminum hydroxide, thickener hydroxypropyl methylcellulose, antibacterial agent carboxymethyl chitosan, and curing agent γ-glycidyl etheroxypropyltrimethoxysilane according to the mass percentage of solute. After stirring and reacting thoroughly, the water-based flame retardant adhesive is obtained.

[0036] (2) Cut (or cut) the clean soft polyimide foam waste into block particles to obtain polyimide foam waste particles for later use. (3) Use water-based flame retardant adhesive and pretreated soft polyimide foam waste at a solute mass ratio of 1:0.5 and stir thoroughly for 30 minutes; (4) Pour the well-mixed water-based flame-retardant adhesive and the soft polyimide foam waste mixture into a mold and compact it. Then heat and cure it at 80℃ for 16 hours to obtain the recycled polyimide foam composite board material, which has a certain degree of flexibility and flame retardancy up to V-0 level. Vertical burning (UL-94) and flexibility test diagrams are shown below. Figure 3 As shown, the adhesion (GB / T 5210-2006) was measured to be 0.7 MPa, and the limiting oxygen index (LOI) was 23.8%.

[0037] Example 4 This embodiment provides a water-based flame-retardant adhesive and a method for preparing a recycled polyimide foam composite board thereof. The water-based flame-retardant adhesive comprises the following solute components by mass percentage: 66.5% polyvinyl alcohol, 6% aluminum diethylphosphinate, 25% hydroxyethyl cellulose, 2% carboxymethyl chitosan, and 0.5% γ-glycidyl etheroxypropyltrimethoxysilane.

[0038] Specifically, the following steps are included: (1) Dissolve polyvinyl alcohol in water at 85°C and then cool it to room temperature to obtain a homogeneous aqueous solution with 8% solid content solute. Then add flame retardant aluminum diethylphosphinate, thickener hydroxyethyl cellulose, antibacterial agent carboxymethyl chitosan, and curing agent γ-glycidyl etheroxypropyltrimethoxysilane according to the mass percentage of solute. After stirring and reacting thoroughly, the water-based flame retardant adhesive is obtained.

[0039] (2) Cut (or cut) the soft polyimide foam waste into block particles, or put the soft polyimide foam waste into a crusher for crushing, and mix the polyimide foam waste particles and powder in a mass ratio of 1:1 for later use. (3) Use water-based flame retardant adhesive and pretreated soft polyimide foam waste at a solute mass ratio of 1:0.6 and stir thoroughly for 30 minutes; (4) Pour the well-mixed water-based flame-retardant adhesive and the soft polyimide foam waste mixture into a mold and compact it. Then heat and cure at 85°C for 12 hours to obtain recycled polyimide foam composite board material, which has good flexibility and flame retardancy up to V-0 level. Vertical burning (UL-94) and flexibility test diagrams are shown below. Figure 4 As shown, the adhesion (GB / T5210-2006) was measured to be 1.1 MPa, and the limiting oxygen index (LOI) was 23.6%.

[0040] Example 5 This embodiment 5 provides a water-based flame-retardant adhesive and a method for preparing the recycled polyimide foam composite board. The water-based flame-retardant adhesive comprises the following components by mass percentage: 58.5% polyvinyl alcohol, 10% dimethyl methylphosphonate, 5% magnesium hydroxide, 25% hydroxyethyl cellulose, 1% carboxymethyl chitosan, and 0.5% γ-glycidyl etheroxypropyltrimethoxysilane.

[0041] Specifically, the following steps are included: (1) Dissolve polyvinyl alcohol in water at 85°C and then cool it to room temperature to obtain a homogeneous aqueous solution with a solid content of 9%. Then add flame retardant dimethyl methylphosphonate and magnesium hydroxide, thickener hydroxypropyl methylcellulose, antibacterial agent carboxymethyl chitosan, and curing agent γ-glycidyl etheroxypropyltrimethoxysilane according to the mass percentage of the solute. After stirring and reacting thoroughly, the water-based flame retardant adhesive is obtained.

[0042] (2) Put the soft polyimide foam waste into a pulverizer for pulverization to obtain polyimide foam waste powder for later use; (3) Use water-based flame retardant adhesive and pretreated soft polyimide foam waste at a solute mass ratio of 1:0.65 and stir thoroughly for 30 minutes; (4) Pour the well-mixed water-based flame-retardant adhesive and the soft polyimide foam waste mixture into a mold and compact it. Then heat and cure it at 85°C for 12 hours to obtain the recycled polyimide foam composite board material. It has good flexibility and flame retardancy up to V-0 level. Vertical burning (UL-94) and flexibility test diagrams are shown below. Figure 5 As shown, the adhesion (GB / T 5210-2006) was measured to be 0.4 MPa, and the limiting oxygen index (LOI) was 25%.

[0043] Example 6 This embodiment provides a water-based flame-retardant adhesive and a method for preparing a recycled polyimide foam composite board thereof. The water-based flame-retardant adhesive comprises the following solute components by mass percentage: 61.2% polyvinyl alcohol, 10% dimethyl methylphosphonate, 5% aluminum hydroxide, 20% hydroxyethyl cellulose, 3% carboxymethyl chitosan, and 0.8% γ-glycidoxypropyltrimethoxysilane.

[0044] Specifically, the following steps are included: (1) Dissolve polyvinyl alcohol in water at 90°C and then cool it to room temperature to obtain a homogeneous aqueous solution with 8% solid content solute. Then add flame retardant dimethyl methylphosphonate and aluminum hydroxide, thickener hydroxyethyl cellulose, antibacterial agent carboxymethyl chitosan, and curing agent γ-glycidyl etheroxypropyltrimethoxysilane according to the mass percentage of solute. After stirring and reacting thoroughly, the water-based flame retardant adhesive is obtained.

[0045] (2) Cut (or cut) the soft polyimide foam waste into block particles, or put the soft polyimide foam waste into a crusher for crushing, and mix the polyimide foam waste particles and powder in a mass ratio of 1:1 for later use. (3) Use water-based flame retardant adhesive and pretreated soft polyimide foam waste at a solute mass ratio of 1:0.5 and stir thoroughly for 30 minutes; (4) Pour the well-mixed water-based flame-retardant adhesive and the soft polyimide foam waste mixture into a mold and compact it. Then heat and cure it at 85°C for 12 hours to obtain the recycled polyimide foam composite board material. It has good flexibility and flame retardancy up to V-0 level. Vertical burning (UL-94) and flexibility test diagrams are shown below. Figure 6As shown, the adhesion (GB / T 5210-2006) was measured to be 0.3 MPa, and the limiting oxygen index (LOI) was 24%.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. An aqueous fire-retardant adhesive, characterized by, By weight percentage, including: Polyvinyl alcohol 57.5% to 79.3%; Flame retardants 6% to 21%; Thickener 0.3% to 25%; Antibacterial agent 1% to 3%; Hardener 0.5% to 1%.

2. The water-based flame-retardant adhesive according to claim 1, characterized in that, The flame retardant is one or a mixture of dimethyl methylphosphonate (DMMP), ammonium polyphosphate (APP), aluminum diethylphosphonate, aluminum hydroxide, and magnesium hydroxide.

3. The water-based fire-retardant adhesive according to claim 1, wherein The thickener is one or more of hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, and polyacrylamide.

4. The water-based fire-retardant adhesive according to claim 1, wherein The antibacterial agent is carboxymethyl chitosan.

5. The water-based fire-retardant adhesive according to claim 1, wherein The curing agent is γ-glycidyl etheroxypropyltrimethoxysilane KH560.

6. A process for the preparation of the aqueous fire-retardant adhesive according to any one of claims 1 to 5, characterized in that, Including the following steps: Step 01: Dissolve polyvinyl alcohol in water at 80°C to 95°C, and then cool the water to room temperature to obtain a homogeneous aqueous solution with a solid content of 6% to 9% of the solute. Step 11: Add flame retardant, thickener, antibacterial agent and curing agent to the homogeneous aqueous solution obtained in step 01, and obtain water-based flame retardant adhesive by stirring.

7. A method of using the water-based flame-retardant adhesive as described in any one of claims 1 to 5, characterized in that, Including the following steps: Step 02: Process the soft polyimide foam waste into polyimide foam waste granules or powder; Step 12: The water-based flame-retardant adhesive and the polyimide foam waste particles or powder obtained in Step 02 are stirred and mixed at a solute mass ratio of 1:0.5 to 0.

65. Step 22: Pour the mixture obtained in step 12 into a mold and compact it. Heat and cure it at 80°C to 100°C for 8 to 16 hours to obtain the recycled polyimide foam composite board material.

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