Formaldehyde-free bio-based environment-friendly wall cloth adhesive and preparation method thereof

Abstract

This application relates to the field of adhesive technology, specifically disclosing a formaldehyde-free, bio-based, flame-retardant, and environmentally friendly wall covering adhesive and its preparation method. It is made from the following raw materials: a bio-based crosslinking agent, a multi-component synergistic flame-retardant system, a toughening and reinforcing agent, a crosslinking initiator, a dispersant, and water. The preparation method is as follows: S1, dissolving the bio-based crosslinking agent in a portion of water to obtain a first mixture; S2, grinding and mixing the components of the multi-component synergistic flame-retardant system; S3, dispersing the toughening and reinforcing agent in the remaining water and subjecting it to ultrasonic treatment; S4, adding the pre-dispersed flame-retardant composite powder to the first mixture and mixing evenly; S5, adding the reinforcing dispersion dropwise to a second mixture, and adding the crosslinking initiator and dispersant. The wall covering adhesive of this application can be used for bonding various indoor wall coverings and wallpapers to wall substrates, and it has the advantages of being green and formaldehyde-free, having excellent flame-retardant properties, high bonding strength, and good toughness.

Description

Technical Field

[0001] This application relates to the field of adhesive technology, and more specifically, to a formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive and its preparation method. Background Technology

[0002] In the field of environmentally friendly wallpaper technology, the application of adhesives is to firmly and smoothly adhere wallpaper to the wall surface. Specifically, adhesives use environmentally friendly formulas such as modified starch, plant-based glue, or low-VOC emulsions to ensure indoor air quality. Functionally, they not only provide excellent initial tack and long-lasting bonding strength, but some high-performance products also have anti-mildew and antibacterial properties, which can inhibit the growth of bacteria caused by wall moisture, thereby extending the service life of the wallpaper and maintaining the aesthetics of the wall surface.

[0003] Environmentally friendly wallpapers are typically applied using ordinary starch glue or white glue. However, these adhesives often contain formaldehyde-based cross-linking agents to improve bonding strength or water resistance, leading to indoor air pollution. Alternatively, they may contain halogenated or other harmful flame retardants to meet flame retardant requirements, which reduces the toughness and adhesion of the adhesive layer. As a result, the wallpaper is prone to curling and peeling during use, posing safety hazards and failing to meet the comprehensive needs of modern homes for safety, environmental protection, and durability. Summary of the Invention

[0004] To address the issue that environmentally friendly wall coverings often peel off and pose safety hazards due to the use of ordinary starch glue or white glue for application, this application provides a formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive and its preparation method.

[0005] Firstly, this application provides a formaldehyde-free, bio-based, flame-retardant, and environmentally friendly wall covering adhesive, employing the following technical solution: A formaldehyde-free bio-based flame-retardant and environmentally friendly wall covering adhesive is made from the following raw materials in parts by weight: 35-55 parts of bio-based crosslinking agent; 20-40 parts of multi-component synergistic flame-retardant system; 5-15 parts of toughening and reinforcing agent; 0.5-3 parts of crosslinking initiator; 1-5 parts of dispersant; and 25-45 parts of water; wherein the bio-based crosslinking agent is at least one of modified plant protein, modified starch, or chitosan derivative.

[0006] By adopting the above technical solution, a bio-based crosslinking agent is used as the skeleton of the adhesive system. It does not contain harmful volatile substances such as formaldehyde, ensuring the environmental friendliness of the product. The multi-component synergistic flame retardant system can play a flame retardant role when heated, while the toughening and reinforcing agent improves the mechanical properties and durability of the colloid through physical reinforcement and stress dispersion. The crosslinking initiator is used to activate the active sites of the bio-based agent to form a stable three-dimensional network. At the same time, the addition of the dispersant ensures that each solid component is uniformly and stably dispersed in water, avoiding agglomeration. The final wall covering adhesive meets the requirements of high bonding strength while also having high flame retardancy and environmental friendliness.

[0007] Preferably, the multi-component synergistic flame retardant system is composed of modified ammonium polyphosphate and a bio-based char layer reinforcing agent in a mass ratio of 1:0.3 to 1:1.2; the bio-based char layer reinforcing agent is Schiff base modified tannin or a selenium-containing organic compound.

[0008] By adopting the above technical solution, the modified ammonium polyphosphate can decompose to generate polyphosphoric acid when heated, promoting the dehydration and carbonization of the substrate and releasing non-flammable gas to dilute oxygen. In the bio-based char layer reinforcing agent, the Schiff base modified tannin is rich in aromatic ring structure, which can quickly form a dense and stable expanded char layer under the catalysis of polyphosphoric acid, insulating heat and oxygen. The selenium-containing organic compound captures free radicals in the gas phase, interrupting the combustion chain reaction. The two work synergistically in the above mass ratio to achieve the combination of gas phase flame retardancy and condensed phase flame retardancy. The modified ammonium polyphosphate is the basic acid source and gas source, while the bio-based char layer reinforcing agent is an efficient char source and gas phase inhibitor. This ratio range ensures that the advantages of the two mechanisms complement each other, thereby giving the colloid more durable and efficient flame retardant properties.

[0009] Preferably, the toughening and reinforcing agent is a nanomaterial with an organic-inorganic hybrid structure, wherein the nanomaterial is a graphene nanosheet modified with polyaniline or phenylphosphonic acid or a nano-calcium carbonate modified with carboxylated styrene-butadiene rubber.

[0010] By adopting the above technical solutions, the selected nanomaterials achieve strong interfacial bonding with the bio-based polymer matrix through an organic-inorganic hybrid structure. The polyaniline or phenylphosphonic acid-modified graphene nanosheets, on the one hand, hinder crack propagation with their large specific surface area and two-dimensional sheet structure, improving the strength and modulus of the adhesive layer; on the other hand, polyaniline and phenylphosphonic acid also contribute additional flame-retardant and corrosion-resistant effects. The carboxylated styrene-butadiene rubber-modified nano-calcium carbonate exists in the form of an elastomer coating rigid nanoparticles. The nano-calcium carbonate provides rigidity enhancement and dimensional stability, while the outer carboxylated styrene-butadiene rubber shell deforms under stress through its high elasticity, absorbing and dispersing energy, thereby improving the toughness, impact resistance, and adaptability to deformation of the wallpaper and substrate.

[0011] Preferably, the crosslinking initiator is epichlorohydrin or sodium trimetaphosphate, and the dispersant is sodium polyacrylate or polyethylene glycol octylphenyl ether.

[0012] By adopting the above technical solutions, the selection of crosslinking initiators is matched with the active groups of bio-based main agents; the epoxy groups of epichlorohydrin can undergo ring-opening crosslinking reactions with amino and hydroxyl groups on plant proteins or chitosan derivatives to form a network structure linked by ether bonds; sodium trimetaphosphate serves as a highly efficient esterification crosslinking agent for starch or protein hydroxyl groups, forming phosphate ester crosslinking bridges; both initiators can efficiently initiate crosslinking under mild conditions, forming stable chemical bonds, thereby improving the water resistance and bonding strength of the colloid; sodium polyacrylate provides dual stabilizing effects of steric hindrance and electrostatic repulsion in the system through its polyelectrolyte properties, making it suitable for the dispersion of inorganic nanoparticles; polyethylene glycol octylphenyl ether, as a nonionic surfactant, can reduce interfacial tension and has high wetting and dispersing effects on organically modified nanomaterials and flame retardant powders. Both can ensure the uniformity and stability of complex multiphase systems during preparation and storage.

[0013] Secondly, this application provides a method for preparing formaldehyde-free bio-based flame-retardant and environmentally friendly wall covering adhesive, using the following technical solution: A method for preparing a formaldehyde-free, bio-based, flame-retardant, and environmentally friendly wall covering adhesive includes the following steps: S1. Dissolve the bio-based crosslinking agent in a portion of water, adjust the pH value, and obtain the first mixture; S2. Grind and mix the components in the multi-component synergistic flame retardant system to obtain pre-dispersed flame retardant composite powder; S3. Disperse the toughening and reinforcing agent in the remaining water and perform ultrasonic treatment to obtain a uniform reinforcing dispersion. S4. Under stirring conditions, the pre-dispersed flame-retardant composite powder obtained in S2 is added to the first mixture obtained in S1 and mixed evenly to obtain the second mixture. S5. The reinforcing dispersion obtained in S3 is added dropwise to the second mixture obtained in S4, and a crosslinking initiator and a dispersant are added. The mixture is stirred and reacted to obtain the formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive.

[0014] By adopting the above technical solution, the preparation method follows the principle of stepwise pre-dispersion and sequential feeding, solving the problems of uniform dispersion and reaction control in complex multi-component systems. First, a bio-based main agent solution, a flame retardant premixed powder, and a toughening and reinforcing agent dispersion are prepared separately to ensure that each functional component is depolymerized or dispersed in its medium, avoiding agglomeration caused by one-time feeding. Then, the flame retardant composite powder is mixed with the main agent solution, which enables the flame retardant particles to be initially coated by the bio-based polymer, improving compatibility. Finally, the reinforcing agent dispersion is slowly added under stirring and cross-linking is initiated, so that the nano-reinforcing material can be uniformly embedded in the colloidal network during the formation process, achieving the effect of strengthening and toughening.

[0015] Preferably, before step S1, the pretreatment of the bio-based raw materials is further included: the plant protein or starch is hydrolyzed and modified under alkaline conditions at a temperature of 50-70°C and a time of 30-90 min to obtain the bio-based crosslinking agent.

[0016] By adopting the above technical solution, within the set temperature and time range, alkaline conditions can partially break the peptide bonds of proteins or the glycosidic bonds of starch, exposing more potential active groups, while appropriately reducing the molecular weight and increasing its solubility and reactivity in water. This pretreatment process lays the foundation for the subsequent efficient reaction with the crosslinking initiator, making the final crosslinked network more compact, thereby improving the adhesive strength and water resistance. The control of temperature and time parameters ensures that the degree of hydrolysis is moderate, avoiding excessive degradation that leads to excessively short molecular chains, which would affect the cohesive strength after film formation.

[0017] Preferably, in step S2, the grinding and mixing are carried out using a ball milling process with a ball milling speed of 200-500 rpm and a ball milling time of 1-4 h, so that the particle size D90 of the pre-dispersed flame retardant composite powder is ≤10 μm.

[0018] By adopting the above technical solution, ball milling is used to co-mill modified ammonium polyphosphate and bio-based char layer reinforcing agent. The purpose is not only to reduce the particle size, but also to achieve uniform mixing and tight bonding of the two components at the microscale. Under the above rotation speed and time parameters, the impact and shear force generated by the grinding media can break up powder agglomeration and make the surfaces of the two particles fully contact and produce a certain degree of mechanical fusion. The particle size D90 of the composite powder is controlled below 10 micrometers, increasing its specific surface area, so that it can be wetted and dispersed faster and better when mixed with liquid in the later stage. This pre-composite and ultrafine treatment ensures the uniform distribution of flame retardant components in the final colloid, which is the process guarantee for achieving stable, efficient and synergistic flame retardant effect.

[0019] Preferably, in step S3, the ultrasonic treatment power is 300-600W, the treatment time is 15-40min, and the absolute value of the Zeta potential of the reinforcing dispersion is controlled to be ≥30mV to ensure system stability.

[0020] By employing the above technical solution, ultrasonic dispersion of the toughening and reinforcing agent nanomaterials is a factor that prevents their agglomeration due to high surface energy. Within the aforementioned power and time range, the cavitation effect generated by ultrasound can produce local impact force and microjets, overcoming the van der Waals forces between nanoparticles, allowing them to fully deagglomerate and disperse in water. By controlling the processing parameters, the Zeta potential of the resulting dispersion reaches above 30 millivolts, indicating that the nanoparticles have a high net charge on their surface, and the particles can maintain a stable dispersion state for a long time due to strong electrostatic repulsion. Obtaining a stable nano-dispersion provides conditions for its uniform introduction into the colloidal matrix in subsequent steps, avoiding performance inhomogeneity caused by nanomaterial agglomeration.

[0021] Preferably, in step S5, the temperature of the stirring reaction is 40–80°C, the stirring speed is 500–1500 rpm, and the reaction time is 1–3 h; the viscosity of the system is controlled within the range of 500–3000 mPa·s during the reaction.

[0022] By adopting the above technical solution, this step is the stage of cross-linking network formation and final compounding of each component; the reaction temperature affects the activation energy and reaction rate of the cross-linking initiator, and within this temperature range, the cross-linking reaction can be ensured to proceed fully and smoothly; a high stirring speed ensures that the reaction system remains uniform as the viscosity gradually increases, and that heat and material transfer is sufficient, preventing local overheating or uneven cross-linking; and a certain reaction time provides sufficient time for the cross-linking network to grow and mature; at the same time, too low a viscosity will cause the adhesive to drip when applied to vertical walls and result in poor storage stability; too high a viscosity will affect the smoothness of the adhesive application and the wetting and spreading of the wallpaper.

[0023] Preferably, in step S5, after adding the crosslinking initiator, an antifoaming agent and a preservative are also added; the antifoaming agent is a polyether-modified organosilicon, and its addition amount is 0.1 to 0.5 parts; the preservative is a bio-based benzoic acid derivative, and its addition amount is 0.2 to 0.8 parts.

[0024] By adopting the above technical solutions, polyether-modified silicone defoamers can reduce the surface tension of the adhesive system, eliminate air bubbles entrained during high-speed stirring and subsequent filling, and prevent air bubbles from solidifying in the adhesive film and forming defects that affect the bonding effect and aesthetics. Meanwhile, bio-based benzoic acid derivatives, as preservatives, can inhibit the growth of mold and bacteria in residual nutrients in the adhesive during storage, ensuring the stability and safety of the product within its shelf life.

[0025] In summary, this application has the following beneficial effects: 1. Since this application uses a bio-based crosslinking agent as the backbone and is compounded with a multi-component synergistic flame retardant system, toughening and reinforcing agent, crosslinking initiator and dispersant, the bio-based agent ensures that the system is formaldehyde-free and environmentally friendly, while the flame retardant system and toughening and reinforcing agent are added for fire safety and mechanical properties respectively. Under the action of crosslinking initiator and dispersant, each component forms a uniform and stable composite system, thereby achieving the effect of making the wall covering adhesive have environmental protection, high flame retardancy, high bonding strength and toughness at the same time.

[0026] 2. In this application, a multi-component synergistic flame retardant system composed of modified ammonium polyphosphate and bio-based char layer reinforcing agent is preferred. The modified ammonium polyphosphate acts as an acid source and gas source when heated, promoting char formation and releasing non-combustible gases. The selected bio-based char layer reinforcing agent acts as a char source or a gas-phase free radical scavenger. The two can work synergistically when exposed to fire, that is, they jointly form a dense and expanded char layer in the condensed phase to isolate heat and oxygen, while interfering with the combustion chain reaction in the gas phase. This synergistic gas-solid phase flame retardant mechanism enables the wall covering adhesive to achieve a faster and more durable flame retardant effect than a single flame retardant, thereby improving the fire safety of the wall covering adhesive.

[0027] 3. In the method of this application, the bio-based raw materials are first subjected to controlled hydrolysis to increase their activity; then the flame retardant components are ball-milled for pre-composite and refined to ensure their dispersibility; the nano-reinforcement is ultrasonically dispersed to obtain a stable dispersion; finally, in the stirring reaction stage, the flame retardant and the main agent solution are mixed sequentially, and then the nano-reinforcement dispersion is introduced to initiate cross-linking; this process allows each functional component to be introduced into the system under suitable conditions, and the subsequent steps are based on the homogeneous medium formed by the preceding steps, so that the flame retardant particles are well coated by the polymer and the nano-reinforcement is uniformly fixed in the formed three-dimensional network structure, thereby obtaining a wall covering adhesive product with uniform component distribution, dense structure and good comprehensive performance. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the preparation method of a formaldehyde-free bio-based flame-retardant and environmentally friendly wall covering adhesive proposed in this application. Detailed Implementation

[0029] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0030] Technical concept: Environmentally friendly wallpapers are typically applied using ordinary starch glue or white glue. However, these adhesives often contain formaldehyde-based cross-linking agents to improve bonding strength or water resistance, leading to indoor air pollution. Alternatively, they may contain halogenated or other harmful flame retardants to meet flame retardant requirements, which reduces the toughness and adhesion of the adhesive layer. As a result, the wallpaper is prone to curling and peeling during use, posing safety hazards and failing to meet the comprehensive needs of modern homes for safety, environmental protection, and durability.

[0031] This application discloses a formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive and its preparation method. It is made from the following raw materials: a bio-based crosslinking agent, a multi-component synergistic flame-retardant system, a toughening and reinforcing agent, a crosslinking initiator, a dispersant, and water. The preparation method is as follows: S1, dissolve the bio-based crosslinking agent in a portion of water to obtain a first mixture; S2, grind and mix the components in the multi-component synergistic flame-retardant system; S3, disperse the toughening and reinforcing agent in the remaining water and perform ultrasonic treatment; S4, add the pre-dispersed flame-retardant composite powder to the first mixture and mix evenly; S5, add the reinforcing dispersion dropwise to a second mixture, and add the crosslinking initiator and dispersant.

[0032] This application uses a bio-based crosslinking agent as the backbone, and combines it with a multi-component synergistic flame retardant system, toughening and reinforcing agent, crosslinking initiator and dispersant. The bio-based agent ensures that the system is formaldehyde-free and environmentally friendly, while the flame retardant system and toughening and reinforcing agent are added to address fire safety and mechanical properties, respectively. Under the action of the crosslinking initiator and dispersant, the components form a uniform and stable composite system, thereby achieving the effect of making the wall covering adhesive environmentally friendly, highly flame retardant, highly adhesive and tough.

[0033] Example 1: This example provides a formaldehyde-free, bio-based, flame-retardant, and environmentally friendly wall covering adhesive, made from raw materials comprising the following parts by weight: 35 parts of bio-based crosslinking agent; 20 parts of multi-component synergistic flame retardant system; 5 parts of toughening and reinforcing agent; 0.5 parts of crosslinking initiator; 1 part of dispersant; 25 parts of water.

[0034] The multi-component synergistic flame retardant system consists of modified ammonium polyphosphate and a bio-based char layer reinforcing agent in a mass ratio of 1:0.3. The bio-based char layer reinforcing agent is Schiff base modified tannin; the toughening reinforcing agent is graphene nanosheets modified with polyaniline or phenylphosphonic acid; the crosslinking initiator is epichlorohydrin; and the dispersant is sodium polyacrylate.

[0035] The preparation method of the above-mentioned formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive is as follows: S1. Dissolve the bio-based crosslinking agent in a portion of water, adjust the pH value, and obtain the first mixture.

[0036] The process includes pretreatment of the bio-based raw materials before step S1: the plant protein is hydrolyzed and modified under alkaline conditions at a temperature of 50°C for 30 minutes to obtain the bio-based crosslinking agent. In step S1, the pH value is adjusted to 8.5.

[0037] S2. Grind and mix the components in the multi-component synergistic flame retardant system to obtain pre-dispersed flame retardant composite powder.

[0038] The grinding and mixing process uses ball milling at a speed of 200 rpm for 1 hour, which makes the particle size D90 of the pre-dispersed flame retardant composite powder less than or equal to 10 micrometers.

[0039] S3. Disperse the toughening and reinforcing agent in the remaining water and perform ultrasonic treatment to obtain a uniform reinforcing dispersion.

[0040] The ultrasonic treatment power was 300W, the treatment time was 15 minutes, and the absolute value of the Zeta potential of the reinforcing dispersion was controlled at 30 mV to ensure the stability of the system.

[0041] S4. Under stirring conditions, the pre-dispersed flame-retardant composite powder obtained in S2 is added to the first mixture obtained in S1 and mixed evenly to obtain the second mixture.

[0042] S5. Add the reinforcing dispersion obtained in S3 to the second mixture obtained in S4, and add the crosslinking initiator and dispersant. Stir the reaction to obtain formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive.

[0043] The reaction temperature was 40℃, the stirring speed was 500 rpm, and the reaction time was 1 hour. The viscosity of the system was controlled within the range of 500 mPa·s during the reaction. After adding the crosslinking initiator, an antifoaming agent and a preservative were also added. The antifoaming agent was polyether-modified organosilicon, and its addition amount was 0.1 parts. The preservative was a bio-based benzoic acid derivative, and its addition amount was 0.2 parts.

[0044] Example 2: This example provides a formaldehyde-free, bio-based, flame-retardant, and environmentally friendly wall covering adhesive, made from raw materials comprising the following parts by weight: 45 parts of bio-based crosslinking agent; 30 parts of multi-component synergistic flame retardant system; 10 parts of toughening and reinforcing agent; 1.8 parts of crosslinking initiator; 3 parts of dispersant; 35 parts of water.

[0045] The multi-component synergistic flame retardant system consists of modified ammonium polyphosphate and a bio-based char layer reinforcing agent in a mass ratio of 1:0.75. The bio-based char layer reinforcing agent is a selenium-containing organic compound. The toughening reinforcing agent is carboxylated styrene-butadiene rubber modified nano-calcium carbonate. The crosslinking initiator is sodium trimetaphosphate, and the dispersant is polyethylene glycol octylphenyl ether.

[0046] The preparation method of the above-mentioned formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive is as follows: S1. Dissolve the bio-based crosslinking agent in a portion of water, adjust the pH value, and obtain the first mixture.

[0047] The process includes pretreatment of the bio-based raw materials before step S1: starch is hydrolyzed and modified under alkaline conditions at a temperature of 60°C for 60 minutes to obtain the bio-based crosslinking agent. In step S1, the pH value is adjusted to 9.5.

[0048] S2. Grind and mix the components in the multi-component synergistic flame retardant system to obtain pre-dispersed flame retardant composite powder.

[0049] The grinding and mixing process uses ball milling at a speed of 350 rpm for 2.5 hours, which makes the particle size D90 of the pre-dispersed flame retardant composite powder less than or equal to 10 micrometers.

[0050] S3. Disperse the toughening and reinforcing agent in the remaining water and perform ultrasonic treatment to obtain a uniform reinforcing dispersion.

[0051] The ultrasonic treatment power was 450W, the treatment time was 28 minutes, and the absolute value of the Zeta potential of the reinforcing dispersion was controlled at 40 mV to ensure the stability of the system.

[0052] S4. Under stirring conditions, the pre-dispersed flame-retardant composite powder obtained in S2 is added to the first mixture obtained in S1 and mixed evenly to obtain the second mixture.

[0053] S5. Add the reinforcing dispersion obtained in S3 to the second mixture obtained in S4, and add the crosslinking initiator and dispersant. Stir the reaction to obtain formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive.

[0054] The reaction temperature was 60℃, the stirring speed was 1000 rpm, and the reaction time was 2 hours. The viscosity of the system was controlled within the range of 1750 mPa·s during the reaction. After adding the crosslinking initiator, an antifoaming agent and a preservative were also added. The antifoaming agent was polyether-modified organosilicon, and its addition amount was 0.3 parts. The preservative was a bio-based benzoic acid derivative, and its addition amount was 0.5 parts.

[0055] Example 3: This example provides a formaldehyde-free, bio-based, flame-retardant, and environmentally friendly wall covering adhesive, made from raw materials comprising the following parts by weight: 55 parts of bio-based crosslinking agent; 40 parts of multi-component synergistic flame retardant system; 15 parts of toughening and reinforcing agent; 3 parts of crosslinking initiator; 5 parts of dispersant; 45 parts of water.

[0056] The multi-component synergistic flame retardant system consists of modified ammonium polyphosphate and a bio-based char layer reinforcing agent in a mass ratio of 1:1.2. The bio-based char layer reinforcing agent is Schiff base-modified tannin. The toughening and reinforcing agent is graphene nanosheets modified with polyaniline or phenylphosphonic acid. The crosslinking initiator is epichlorohydrin, and the dispersant is sodium polyacrylate.

[0057] The preparation method of the above-mentioned formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive is as follows: S1. Dissolve the bio-based crosslinking agent in a portion of water, adjust the pH value, and obtain the first mixture.

[0058] The process includes pretreatment of the bio-based raw materials before step S1: the plant protein is hydrolyzed and modified under alkaline conditions at a temperature of 70°C for 90 minutes to obtain the bio-based crosslinking agent. In step S1, the pH value is adjusted to 10.5.

[0059] S2. Grind and mix the components in the multi-component synergistic flame retardant system to obtain pre-dispersed flame retardant composite powder.

[0060] The grinding and mixing process uses ball milling at a speed of 500 rpm for 4 hours, which makes the particle size D90 of the pre-dispersed flame retardant composite powder less than or equal to 10 micrometers.

[0061] S3. Disperse the toughening and reinforcing agent in the remaining water and perform ultrasonic treatment to obtain a uniform reinforcing dispersion.

[0062] The ultrasonic treatment power was 600W, the treatment time was 40 minutes, and the absolute value of the Zeta potential of the reinforcing dispersion was controlled at 50 mV to ensure the stability of the system.

[0063] S4. Under stirring conditions, the pre-dispersed flame-retardant composite powder obtained in S2 is added to the first mixture obtained in S1 and mixed evenly to obtain the second mixture.

[0064] S5. Add the reinforcing dispersion obtained in S3 to the second mixture obtained in S4, and add the crosslinking initiator and dispersant. Stir the reaction to obtain formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive.

[0065] The reaction temperature was 80℃, the stirring speed was 1500 rpm, and the reaction time was 3 hours. The viscosity of the system was controlled within the range of 3000 mPa·s during the reaction. After adding the crosslinking initiator, an antifoaming agent and a preservative were also added. The antifoaming agent was polyether-modified organosilicon, and its addition amount was 0.5 parts. The preservative was a bio-based benzoic acid derivative, and its addition amount was 0.8 parts.

[0066] Comparative Example 1: This comparative example is based on the content of Example 1, except that the amount of the bio-based crosslinking agent is changed from 35 parts to 20 parts, and the rest is the same as Example 1.

[0067] Comparative Example 2: This comparative example refers to the content of Example 1, except that the total amount of the multi-component synergistic flame retardant system is changed from 20 parts to 10 parts, and the rest of the content is the same as Example 1.

[0068] Comparative Example 3: This comparative example is the same as that in Example 1, except that the amount of toughening and reinforcing agent is changed from 5 parts to 2 parts. The rest of the content is the same as that in Example 1.

[0069] Comparative Example 4: This comparative example is the same as that in Example 1, except that the amount of crosslinking initiator is changed from 0.5 parts to 0.2 parts. The rest of the content is the same as that in Example 1.

[0070] Comparative Example 5: This comparative example refers to the content of Example 1, except that the mass ratio of modified ammonium polyphosphate to bio-based char layer reinforcing agent in the multi-component synergistic flame retardant system is changed from 1:0.3 to 1:0.1, and the rest is the same as Example 1.

[0071] Comparative Example 6: This comparative example refers to the content of Example 1, except that in step S3, the power of the ultrasonic treatment is changed from 300W to 200W, and the treatment time is changed from 15 minutes to 5 minutes. The rest of the content is the same as that of Example 1.

[0072] Performance testing Sample preparation: Weigh and prepare the formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive samples to be tested according to the formulations and preparation methods described in Examples 1-3 and Comparative Examples 1-6; After all samples are left to stand and mature for 24 hours in a standard test environment of 23±2℃ and 50±5% relative humidity, they are evenly coated on the specified substrate according to the requirements of each test item, and wall coverings of specified specifications are pasted or samples are prepared. After curing to the specified age, the samples are prepared to meet the requirements of the corresponding test standards.

[0073] Environmental performance testing: A sample coated with adhesive and with wallpaper pasted on is placed in a sealed desiccator of a specific size and sealed for a specified time under certain temperature conditions. Subsequently, the formaldehyde content captured in the absorbent liquid inside the desiccator is quantitatively determined using analytical methods such as spectrophotometry or high-performance liquid chromatography. The formaldehyde release per unit area or unit mass of adhesive is calculated, and this indicator reflects the safety of the product during use in indoor environments. This test is conducted in accordance with the test method for formaldehyde release in the national standard GB18583-2008 "Limits of Hazardous Substances in Adhesives for Interior Decoration and Renovation Materials".

[0074] Flame retardant performance testing: First, according to the oxygen index test standard, the adhesive is made into a sample of a specified size, vertically fixed in a combustion chamber, and a controlled concentration of oxygen-nitrogen mixed gas flow is introduced. The minimum oxygen concentration required for the sample to maintain stable combustion for a specified time or length is measured, which is the limiting oxygen index. The higher the value, the less flammable the material is. Second, according to the vertical combustion test standard, a sample of a specific substrate coated with adhesive is vertically suspended, and its lower end is ignited with a specified flame for a specified time. The afterflame time, smoldering time, and damage length of the sample are observed and recorded to evaluate the flame resistance of the adhesive under simulated real fire source. The oxygen index test is conducted according to the national standard GB / T2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test"; the vertical combustion test is conducted according to the national standard GB / T5455-2014 "Determination of Vertical Damage Length, Smoldering Time and Afterflame Time of Textiles" or equivalent flame propagation test methods for building materials.

[0075] Bond strength test: Apply the wallpaper adhesive evenly to a standard cement mortar board or other specified substrate, then adhere the wallpaper or test block of the specified size. After curing for the specified number of days under standard curing conditions, use a suitable tensile testing machine to apply a tensile force perpendicular to the bonding surface at a constant rate until the sample fails. Record the maximum tensile force value and calculate the tensile bond strength based on the bonded area. This data directly reflects the firmness with which the adhesive fixes the wallpaper to the substrate. This test is conducted according to the test method for bond strength in the national standard GB / T9779-2015 "Multi-Layer Architectural Coatings" or the industry-standard test method for the bond strength of wallpaper adhesives.

[0076] Durability testing: Based on the bond strength test specimens after standard curing, the specimens are completely immersed in water at 23±2℃ for a certain period of time and then removed. The surface moisture is wiped off with a damp cloth, and after standing for a period of time under standard test conditions, the tensile bond strength after immersion is immediately measured according to the above bond strength test method. The bond strength retention rate is obtained by calculating the ratio of the strength after immersion to the initial strength under standard curing conditions. The higher the value, the better the water resistance and durability of the adhesive. This test is usually performed in accordance with the water resistance test section of the national standard GB / T9779-2015 or relevant building material adhesive standards.

[0077] Table 1: Test Results of Environmental Performance and Flame Retardant Performance

[0078] Table 2: Test results of bond strength and durability

[0079] Example Conclusion: As can be seen from Examples 1-3 and Comparative Example 1, and Table 1, a sufficient amount of bio-based crosslinking agent is the basis for ensuring the formation of a stable three-dimensional crosslinked network in the colloid. As a skeleton component of the adhesive, it not only provides excellent initial adhesion but also effectively seals water molecule channels through sufficient crosslinking reaction, thereby giving the product high bonding strength and excellent water resistance and durability. Conversely, insufficient agent will lead to a loose network structure and deterioration of various properties. As can be seen from Examples 1-3 and Comparative Example 2, and Table 1, the total amount of the multi-component synergistic flame retardant system is the factor that determines the fire safety level of the product. Sufficient flame retardant components can quickly form a fully covered and high-strength expanded char layer when the material is heated, effectively isolating heat and oxygen, thereby constructing an efficient physical barrier. The reduction in the amount of flame retardant in Comparative Example 2 leads to defects in the flame retardant barrier, causing the limiting oxygen index of the material to decrease, making the flame spread more easily and causing greater damage. As can be seen from Examples 1-3 and Comparative Example 3, and Table 1, the addition of the toughening and reinforcing agent can ensure the improvement of the overall performance of the colloid. Through nanoscale dispersion and interfacial strengthening, it can not only effectively transfer and disperse stress, avoiding brittle failure of the adhesive layer caused by stress concentration, thereby improving the bonding strength, but also enhance the density of the cured adhesive layer, prevent moisture intrusion, and improve water resistance. In Comparative Example 3, the amount of the agent was insufficient, which weakened the toughness and durability of the adhesive layer. Based on Examples 1-3 and Comparative Example 4, and in conjunction with Table 1, it can be seen that an appropriate amount of crosslinking initiator is the factor that activates and completes the effective crosslinking reaction of the bio-based main agent. It ensures that the active groups react fully under suitable conditions to form a highly crosslinked network structure. This dense structure not only directly contributes to high bonding strength but also reduces the migration and release of small molecules and improves the water resistance of the colloid. In Comparative Example 4, the initiator was insufficient, resulting in an incomplete crosslinking reaction, which ultimately prevented the adhesive from achieving optimal bonding, environmental protection, and durability performance. Based on Examples 1-3 and Comparative Example 5 and Table 1, it can be seen that the char layer reinforcing agent can promote the formation of a denser and stronger char protective layer when heated, which complements the gas-phase flame retardant and catalytic char formation effects of ammonium polyphosphate. In Comparative Example 5, the proportion of char layer reinforcing agent is too low, which weakens the synergistic effect of the two, reduces the quality of the formed char layer, and leads to a decrease in flame retardant performance. As can be seen from Examples 1-3 and Comparative Example 6, and Table 1, sufficient dispersion can ensure that nanoparticles or sheets are uniformly distributed in the system, avoiding agglomeration, thereby maximizing their specific surface area and reinforcing effect. In Comparative Example 6, insufficient dispersion led to a significant reduction in the effective role of the reinforcing agent, failing to fully exert its toughening and interfacial bonding effects, resulting in a loss of mechanical properties and durability of the final product.

[0080] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A formaldehyde-free, bio-based, flame-retardant, and environmentally friendly wall covering adhesive, characterized in that, It is made from raw materials comprising the following parts by weight: 35-55 parts of bio-based crosslinking agent; 20-40 parts of multi-component synergistic flame retardant system; 5-15 parts of toughening and reinforcing agent; 0.5-3 parts of crosslinking initiator; 1-5 parts of dispersant; and 25-45 parts of water; wherein the bio-based crosslinking agent is at least one of modified plant protein, modified starch, or chitosan derivative.

2. The formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive according to claim 1, characterized in that, The multi-component synergistic flame retardant system is composed of modified ammonium polyphosphate and a bio-based char layer reinforcing agent in a mass ratio of 1:0.3 to 1:1.2; the bio-based char layer reinforcing agent is Schiff base modified tannin or selenium-containing organic compound.

3. The formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive according to claim 1, characterized in that, The toughening and reinforcing agent is a nanomaterial with an organic-inorganic hybrid structure, wherein the nanomaterial is a graphene nanosheet modified with polyaniline or phenylphosphonic acid or a nano-calcium carbonate modified with carboxylated styrene-butadiene rubber.

4. The formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive according to claim 1, characterized in that, The crosslinking initiator is epichlorohydrin or sodium trimetaphosphate, and the dispersant is sodium polyacrylate or polyethylene glycol octylphenyl ether.

5. A method for preparing a formaldehyde-free, bio-based, flame-retardant, and environmentally friendly wall covering adhesive, characterized in that, The formaldehyde-free, bio-based, flame-retardant, and environmentally friendly wall covering adhesive according to any one of claims 1-4 comprises the following steps: S1. Dissolve the bio-based crosslinking agent in a portion of water, adjust the pH value, and obtain the first mixture; S2. Grind and mix the components in the multi-component synergistic flame retardant system to obtain pre-dispersed flame retardant composite powder; S3. Disperse the toughening and reinforcing agent in the remaining water and perform ultrasonic treatment to obtain a uniform reinforcing dispersion. S4. Under stirring conditions, the pre-dispersed flame-retardant composite powder obtained in S2 is added to the first mixture obtained in S1 and mixed evenly to obtain the second mixture. S5. The reinforcing dispersion obtained in S3 is added dropwise to the second mixture obtained in S4, and a crosslinking initiator and a dispersant are added. The mixture is stirred and reacted to obtain the formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive.

6. The preparation method of a formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive according to claim 5, characterized in that, Before step S1, the pretreatment of the bio-based raw materials is also included: the plant protein or starch is hydrolyzed and modified under alkaline conditions at a temperature of 50-70°C and a time of 30-90 min to obtain the bio-based crosslinking agent.

7. The preparation method of a formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive according to claim 5, characterized in that, In step S2, the grinding and mixing are carried out by ball milling, with a ball milling speed of 200-500 rpm and a ball milling time of 1-4 h, so that the particle size D90 of the pre-dispersed flame retardant composite powder is ≤10 μm.

8. The preparation method of a formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive according to claim 5, characterized in that, In step S3, the ultrasonic treatment power is 300-600W, the treatment time is 15-40min, and the absolute value of the Zeta potential of the reinforcing dispersion is controlled to be ≥30mV to ensure system stability.

9. The method for preparing a formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive according to claim 5, characterized in that, In step S5, the temperature of the stirring reaction is 40–80℃, the stirring speed is 500–1500 rpm, and the reaction time is 1–3 h; the viscosity of the system is controlled within the range of 500–3000 mPa·s during the reaction.

10. The method for preparing a formaldehyde-free bio-based flame-retardant environmentally friendly wall covering adhesive according to claim 5, characterized in that, In step S5, after adding the crosslinking initiator, an antifoaming agent and a preservative are also added; the antifoaming agent is a polyether-modified organosilicon, and its addition amount is 0.1 to 0.5 parts; the preservative is a bio-based benzoic acid derivative, and its addition amount is 0.2 to 0.8 parts.

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