Preparation method of bio-based composite adhesive, adhesive composition and abrasive cloth

Abstract

The invention relates to the technical field of adhesives for coated abrasive tools, and discloses a preparation method of a bio-based composite adhesive, an adhesive composition and abrasive cloth, the adhesive is prepared from the following raw materials in parts by mass: phenol, a formaldehyde solution, enzymatic hydrolysis lignin, ethylene glycol, sodium hydroxide, ammonia water, urea, boric acid, other auxiliaries and water; the preparation method comprises the steps of pre-swelling and resin synthesis. Through a pre-swelling process that ammonia water and sodium hydroxide are matched to control alkalinity, not only can complete activation of enzymatic hydrolysis lignin be achieved, but also the characteristic of low ash content of the enzymatic hydrolysis lignin can be matched, it is ensured that the adhesive has extremely low ion mobility and stable dielectric constant, the requirement of an electrostatic sand planting process is met, and accurate orientation of abrasive particles is achieved in a matched mode. The reduction of the use amount of sodium hydroxide also avoids the reduction of moisture absorption and thermal creep resistance of an adhesive layer caused by alkali metal ion residues, and solves the problem that conventional lignin is difficult to apply to the adhesive for high-precision abrasive cloth.

Description

Technical Field

[0001] This invention relates to the field of adhesives for coated abrasives, and more particularly to a method for preparing a bio-based composite adhesive, an adhesive composition, and abrasive cloth. Background Technology

[0002] Phenolic resins, due to their excellent mechanical strength, heat resistance, and chemical stability, have long been widely used as a primary adhesive in the field of coated abrasive manufacturing. In abrasive cloth manufacturing, the base layer anchors the abrasive to the surface of the cloth base material, while the top layer provides secondary reinforcement by encapsulating the abrasive. Together, they determine the grinding life of the abrasive cloth and the surface grinding quality of the workpiece. With increasing environmental awareness, the preparation of bio-based phenolic resins using bio-based resources such as lignin to replace petrochemical phenolic resources has become an important research direction for the green and low-carbon transformation of adhesives. Lignin, as a natural aromatic polymer, contains a large number of phenolic hydroxyl groups, alcoholic hydroxyl groups, and active sites in its molecular structure, and has a rigid benzene ring skeleton. Introducing it into the phenolic resin system can not only reduce costs and carbon footprint, but also endow the resin with better rigidity and thermal stability.

[0003] While numerous lignin-modified phenolic resin solutions have emerged in the current technology, their applications are mostly concentrated on improving adhesives for furniture plywood and engineered wood products. These lignin adhesives focus on shear strength and bonding ability at room temperature, but their cured products typically suffer from defects such as uneven crosslinking density, low thermal softening point, and insufficient shear modulus. They cannot withstand the high-temperature friction and high-frequency impact loads generated during grinding, making them difficult to apply directly to the field of abrasive manufacturing.

[0004] Due to its large molecular weight, complex structure, and low reactivity, lignin, when introduced into phenolic resin systems, often leads to problems such as poor system compatibility, drastic viscosity fluctuations during storage, high brittleness of the adhesive layer, and the presence of particles in the adhesive layer affecting smoothness. These drawbacks are less noticeable when used as a furniture adhesive due to the surface tolerance of the board and the relatively low dynamic stress requirements. However, for sandpaper production, particles in the adhesive directly cause uneven coating thickness and severely affect the uniformity of subsequent sanding. While processes using strong acids or alkalis at high temperatures to further decompose lignin can solve the particle inclusion problem, the complex process conditions and high costs render the utilization of lignin completely uneconomical and environmentally unprofitable.

[0005] Furthermore, the high-precision grinding field places higher demands on the performance of abrasive cloth. The adhesive layer of the abrasive cloth needs to possess both extremely high thermal stability and resistance to thermal creep to ensure stable support of the abrasive grains even under short-term high temperatures during high-speed grinding, thereby ensuring the grinding quality of the workpiece. Simultaneously, the high-precision electrostatic abrasive coating process places even more stringent requirements on the adhesive. First, the adhesive must possess excellent coating rheology and shear recovery capabilities to ensure good wettability of the base adhesive within a specific high viscosity range, and to achieve precise orientation and gripping of the abrasive grains through high thixotropy at the moment of abrasive coating. Second, the adhesive must possess suitable dielectric properties to prevent local breakdown or charge loss of the electrostatic field on the abrasive coating surface, thereby ensuring the precise orientation of the abrasive by the electric field force. Existing lignin-modified adhesives are insufficient to meet the requirements of high-precision abrasive cloth, limiting the application of lignin in abrasive cloth adhesives. Summary of the Invention

[0006] To address the aforementioned shortcomings, the present invention aims to provide a method for preparing a bio-based composite adhesive, an adhesive composition, and abrasive cloth, thereby solving the problem that traditional lignin modification processes cannot produce adhesives that meet the requirements for high-precision abrasive cloth.

[0007] To achieve this objective, the present invention adopts the following technical solution: A method for preparing a bio-based composite adhesive, wherein the raw materials for the adhesive, by weight parts, include: 180-240 parts of phenol 320-410 parts of 37% formaldehyde solution Enzymatic hydrolysis of lignin: 80-120 parts 12-24 parts of ethylene glycol, Sodium hydroxide 1.5 to 4 parts, 4-10 parts of 25% ammonia solution 1-3 parts urea 2-5 parts boric acid Other additives: 0.02~11.55 parts; Water as needed; The preparation method includes the following steps: Pre-swelling: According to the proportions in the raw materials, the enzymatically hydrolyzed lignin, ethylene glycol, sodium hydroxide, ammonia and water are mixed to prepare a slurry with a water content of 10-20%. After that, it is allowed to stand or stirred for 1-48 hours, and then dispersed at high speed for 0.5-1 hour to obtain the pre-swelled slurry. Synthetic resins: S1. According to the proportions in the raw materials, add water, phenol, formaldehyde solution and pre-swollen slurry to the reactor, stir and mix and heat to polymerize for 2-10 hours to obtain modified phenolic resin. S2. Vacuum decompression and exhaust gas are applied to the reactor to control the solid content of the modified phenolic resin in the reactor to be 40-75%; S3. Add urea to the reactor according to the proportion in the raw materials, and stir for 10-30 minutes. S4. Add other additives to the reactor according to the proportion of the raw materials, and cool the reactor to 20~40℃. Finally, add boric acid to the reactor to adjust the pH value to 7.5~9, and discharge the material to obtain the bio-based composite adhesive.

[0008] Preferably, in the pre-swelling step, after the materials are mixed, they are stirred in a closed system at 50~60℃ for 1~6 hours, and then dispersed at high speed to obtain a pre-swelled slurry.

[0009] Preferably, in the pre-swelling step, after the materials are mixed, they are left to stand at room temperature for 6 to 48 hours, and then dispersed at high speed to obtain a pre-swelled slurry.

[0010] Preferably, in step S2 of synthesizing the resin, the vacuum degree of vacuum decompression is -0.08 to -0.095 MPa, the temperature is 50 to 60°C, and the time is 10 to 30 minutes.

[0011] Preferably, in step S1 of synthesizing the resin, water, phenol and pre-swollen slurry are first added to the reactor, and the temperature is raised to 50~55°C. After the phenol dissolves, 10~30% of formaldehyde is added, and the temperature is raised to 55~60°C. Then, the remaining formaldehyde is slowly added dropwise over 1~3 hours. After the addition is completed, the temperature is raised to 65~75°C, and the reaction continues for 0.5~2 hours to complete the heating polymerization.

[0012] Preferably, the other additives include at least one of nonionic defoamer, antioxidant and toughening agent, wherein, by weight parts, the nonionic defoamer is 0.02 to 0.05 parts, the antioxidant is 0.1 to 0.5 parts, and the toughening agent is 1 to 5 parts.

[0013] Preferably, other adjuvants include at least one of triethanolamine and resorcinol, wherein, by weight, triethanolamine is 0.5 to 1 part and resorcinol is 2 to 5 parts.

[0014] An adhesive composition comprising an adhesive prepared using the preparation method of any one of claims 1-7, and further comprising 0.03 to 0.3 parts by weight of polyether-modified siloxane.

[0015] Preferably, the mixture also includes 0.5 to 1.5 parts by weight of silane coupling agent.

[0016] A type of abrasive cloth includes a substrate, an abrasive, a base layer, and a coating layer. The base layer is formed on one side of the substrate, and one end of the abrasive is uniformly embedded in the base layer. The coating layer covers the abrasive and the base layer. Both the base layer and the coating layer are coated with a bio-based composite adhesive prepared by any one of claims 1-7. The bio-based composite adhesive used in the base layer has a solid content of 55-75% and a viscosity of 1500-3500 mPa•s. The bio-based composite adhesive used in the coating layer has a solid content of 40-60% and a viscosity of 500-2000 mPa•s.

[0017] The technical solution provided by this invention may include the following beneficial effects: 1. In the industrial production of ethanol, polysaccharides such as cellulose in plants are degraded under the action of enzymes. The residue remaining after ethanol production contains a large amount of lignin, and this residue, as a byproduct, is enzymatically hydrolyzed lignin. Because the reaction conditions during enzymatic hydrolysis are relatively mild, the activity of enzymatically hydrolyzed lignin is high and the ash content is low. Using enzymatically hydrolyzed lignin to replace part of phenol and reacting it with formaldehyde to prepare modified phenolic resin can increase the heat resistance of the adhesive layer formed after molding when the modified phenolic resin is used as an adhesive. This allows the adhesive layer to maintain good rigidity after heating during use and maintain a low coefficient of thermal expansion, thereby improving the sanding precision of sandpaper.

[0018] Enzymatic hydrolysis of lignin, as a bio-based raw material to replace petroleum-based phenol, can not only reduce the raw material cost of adhesives and improve their performance, but also make the originally difficult-to-degrade phenolic resin adhesives somewhat biodegradable. Furthermore, as a part of the recycling of biomass waste, the application of enzymatic hydrolysis of lignin in adhesives has important environmental significance.

[0019] 2. A pre-swelling process using ammonia and sodium hydroxide to control alkalinity is employed. A composite alkali system is constructed using a low concentration of sodium hydroxide and ammonia. A small amount of sodium hydroxide acts as an initiating alkali, providing a highly localized nucleophilic environment in the initial stage of pre-swelling, promoting the initial activation of phenol and lignin surface active sites. Subsequently, the deep swelling of lignin is completed through the penetration of ammonia. This process achieves complete activation of enzymatically hydrolyzed lignin while leveraging its low ash content. No further adjustments are needed, avoiding increased process complexity. Maintaining the ion concentration within a suitable range avoids the negative impact of excessive strong electrolytes on the system's dielectric properties, ensuring the adhesive possesses extremely low ion mobility and a stable dielectric constant, meeting the requirements of electrostatic sanding processes and facilitating precise abrasive grain orientation. Reducing the amount of sodium hydroxide also avoids moisture absorption and decreased thermal creep resistance in the adhesive layer due to residual alkali metal ions, solving the problem of conventional lignin being difficult to apply to high-precision abrasive cloth adhesives.

[0020] 3. Ethylene glycol, acting as a penetrant and solubilizer, can synergistically disrupt the hydrogen bonds of enzymatically hydrolyzed lignin during the pre-swelling stage, promoting the unfolding of its macromolecular chains and the exposure of polar groups, thereby significantly enhancing the reactivity of enzymatic hydrolysis of lignin. In modified phenolic resin systems, ethylene glycol can also improve the system's compatibility and flexibility, overcoming the defects of conventional lignin-modified bio-based resins such as brittleness and delamination.

[0021] Urea can eliminate free formaldehyde and generate urea-formaldehyde structure to further improve the rigidity of the adhesive layer; boric acid can neutralize excess alkali to adjust the pH value and further improve the heat resistance of the adhesive layer by introducing boron-oxygen bonds; these properties can further improve the sanding precision of the sandpaper. Detailed Implementation

[0022] To facilitate understanding of the present invention, a more complete description is provided below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0023] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0025] A method for preparing a bio-based composite adhesive, wherein the raw materials for the adhesive, by weight parts, include: 180-240 parts of phenol 320-410 parts of 37% formaldehyde solution Enzymatic hydrolysis of lignin: 80-120 parts 12-24 parts of ethylene glycol, Sodium hydroxide 1.5 to 4 parts, 4-10 parts of 25% ammonia solution 1-3 parts urea 2-5 parts boric acid Other additives: 0.02~11.55 parts; Water as needed; The preparation method includes the following steps: Pre-swelling: According to the proportions in the raw materials, the enzymatically hydrolyzed lignin, ethylene glycol, sodium hydroxide, ammonia and water are mixed to prepare a slurry with a water content of 10-20%. After that, it is allowed to stand or stirred for 1-48 hours, and then dispersed at high speed for 0.5-1 hour to obtain the pre-swelled slurry. Synthetic resins: S1. According to the proportions in the raw materials, add water, phenol, formaldehyde solution and pre-swollen slurry to the reactor, stir and mix and heat to polymerize for 2-10 hours to obtain modified phenolic resin. S2. Vacuum decompression and exhaust gas are applied to the reactor to control the solid content of the modified phenolic resin in the reactor to be 40-75%; S3. Add urea to the reactor according to the proportion in the raw materials, and stir for 10-30 minutes. S4. Add other additives to the reactor according to the proportion of the raw materials, and cool the reactor to 20~40℃. Finally, add boric acid to the reactor to adjust the pH value to 7.5~9, and discharge the material to obtain the bio-based composite adhesive.

[0026] In the industrial production of ethanol, polysaccharides such as cellulose in plants are degraded under the action of enzymes. The residue remaining after ethanol production contains a large amount of lignin, and this residue, as a byproduct, is enzymatically hydrolyzed lignin. Because the reaction conditions during enzymatic hydrolysis are relatively mild, the activity of enzymatically hydrolyzed lignin is high and the ash content is low. Using enzymatically hydrolyzed lignin to replace part of phenol and reacting it with formaldehyde to prepare modified phenolic resin can increase the heat resistance of the adhesive layer formed after molding when the modified phenolic resin is used as an adhesive. This allows the adhesive layer to maintain good rigidity after heating during use and to maintain a low coefficient of thermal expansion, thereby improving the sanding precision of sandpaper.

[0027] Enzymatic hydrolysis of lignin, as a bio-based raw material to replace petroleum-based phenol, can not only reduce the raw material cost of adhesives and improve their performance, but also make the originally difficult-to-degrade phenolic resin adhesives somewhat biodegradable. Furthermore, as a part of the recycling of biomass waste, the application of enzymatic hydrolysis of lignin in adhesives has important environmental significance.

[0028] A pre-swelling process using ammonia and sodium hydroxide to control alkalinity involves constructing a composite alkali system with a low concentration of sodium hydroxide and ammonia. A small amount of sodium hydroxide acts as an initiating alkali, providing a highly localized nucleophilic environment in the early stages of pre-swelling to promote the initial activation of phenol and lignin surface active sites. Subsequently, the deep swelling of lignin is achieved through the penetration of ammonia. This process achieves complete activation of enzymatically hydrolyzed lignin while leveraging its low ash content. No further adjustments are needed to avoid increasing process complexity. Maintaining the ion concentration within a suitable range avoids the negative impact of excessive strong electrolytes on the system's dielectric properties, ensuring the adhesive has extremely low ion mobility and a stable dielectric constant, meeting the requirements of electrostatic sanding processes and facilitating precise abrasive grain orientation. Reducing the amount of sodium hydroxide also avoids moisture absorption and decreased thermal creep resistance in the adhesive layer due to residual alkali metal ions, solving the problem of conventional lignin being difficult to apply to high-precision abrasive cloth adhesives.

[0029] Ethylene glycol, acting as a penetrant and solubilizer, can synergistically disrupt the hydrogen bonds of enzymatically hydrolyzed lignin during the pre-swelling stage, promoting the unfolding of its macromolecular chains and the exposure of polar groups, thereby significantly enhancing the reactivity of enzymatic hydrolysis of lignin. In modified phenolic resin systems, ethylene glycol can also improve the system's compatibility and flexibility, overcoming the defects of conventional lignin-modified bio-based resins such as brittleness and delamination.

[0030] Urea can eliminate free formaldehyde and generate urea-formaldehyde structure to further improve the rigidity of the adhesive layer; boric acid can neutralize excess alkali to adjust the pH value and further improve the heat resistance of the adhesive layer by introducing boron-oxygen bonds; these properties can further improve the sanding precision of the sandpaper.

[0031] Preferably, in the pre-swelling step, after the materials are mixed, they are stirred in a closed system at 50~60℃ for 1~6 hours, and then dispersed at high speed to obtain a pre-swelled slurry.

[0032] In one embodiment, heating is used to improve pre-swelling efficiency, and a sealed environment is used to prevent ammonia volatilization.

[0033] Preferably, in the pre-swelling step, after the materials are mixed, they are left to stand at room temperature for 6 to 48 hours, and then dispersed at high speed to obtain a pre-swelled slurry.

[0034] In another embodiment, a simpler process is used, which ensures complete swelling of enzymatically hydrolyzed lignin through prolonged soaking.

[0035] Preferably, in step S2 of synthesizing the resin, the vacuum degree of vacuum decompression is -0.08 to -0.095 MPa, the temperature is 50 to 60°C, and the time is 10 to 30 minutes.

[0036] The high-vacuum, low-temperature drainage and degassing process is adopted. By lowering the boiling point of the system, moisture and volatiles are rapidly removed at a temperature lower than that of the resin's violent cross-linking reaction. This increases the solid content while reducing the content of free small molecules in the system, eliminating microbubbles and pinhole defects caused by the large-scale escape of residual monomers.

[0037] Preferably, in step S1 of synthesizing the resin, water, phenol and pre-swollen slurry are first added to the reactor, and the temperature is raised to 50~55°C. After the phenol dissolves, 10~30% of formaldehyde is added, and the temperature is raised to 55~60°C. Then, the remaining formaldehyde is slowly added dropwise over 1~3 hours. After the addition is completed, the temperature is raised to 65~75°C, and the reaction continues for 0.5~2 hours to complete the heating polymerization.

[0038] In a specific embodiment, a temperature-controlled reactor with a water-cooled jacket is used for precise temperature control.

[0039] By controlling the method of formaldehyde addition, the problem of explosive polymerization caused by the exothermic reaction of formaldehyde under high pH conditions is avoided. Through a reduced amount of sodium hydroxide catalysis combined with a stepwise dropwise formaldehyde addition process, a mild condensation polymerization of phenol, formaldehyde, and enzymatically hydrolyzed lignin is induced. This not only effectively inhibits the degradation of enzymatically hydrolyzed lignin at high temperatures, ensuring the integrity of the bio-based framework, but also, by controlling the reaction rate, yields a modified phenolic resin with a narrow molecular weight distribution and stable rheology. This results in adhesives with excellent microstructure smoothness and resistance to thermal creep.

[0040] Preferably, the other additives include at least one of nonionic defoamer, antioxidant and toughening agent, wherein, by weight parts, the nonionic defoamer is 0.02 to 0.05 parts, the antioxidant is 0.1 to 0.5 parts, and the toughening agent is 1 to 5 parts.

[0041] Nonionic defoamers effectively break down microbubbles generated during pre-processing, preventing the formation of micro-cavities after curing and ensuring that the sandpaper does not chip during grinding, thus guaranteeing the continuity of the sanded surface. In a specific embodiment, the nonionic defoamer used is acetylenic glycol, which, through its excellent dynamic wetting properties and compatibility with the system, ensures the physical stability and rheological consistency of the adhesive containing enzymatically hydrolyzed lignin during long-term storage. The antioxidant used is triphenyl phosphite, which inhibits oxidation and ensures the long-term stability of the adhesive performance. The toughening agent used is polyethylene glycol PEG400, which improves the toughness of the adhesive layer and prevents the sandpaper from breaking and shedding sand when folded.

[0042] Preferably, other adjuvants include at least one of triethanolamine and resorcinol, wherein, by weight, triethanolamine is 0.5 to 1 part and resorcinol is 2 to 5 parts.

[0043] Triethanolamine, as a weak organic base, can synergistically form a more stable pH buffer system with boric acid, further improving the storage stability of adhesives. Resorcinol has higher activity than phenol; supplementing with an appropriate amount of resorcinol can bind with enzymatically hydrolyzed lignin, reduce free formaldehyde, increase the initial tack of the adhesive, and improve the density of the adhesive layer.

[0044] An adhesive composition comprising an adhesive prepared using the preparation method of any one of claims 1-7, and further comprising 0.03 to 0.3 parts by weight of polyether-modified siloxane.

[0045] Adding polyether-modified siloxane before use can further fine-tune the surface tension and viscosity of the adhesive to accommodate changes in application temperature, humidity, substrate, and abrasive specifications, ensuring that the adhesive has suitable leveling and wetting properties during application.

[0046] Preferably, the mixture also includes 0.5 to 1.5 parts by weight of silane coupling agent.

[0047] Adding a silane coupling agent before using the adhesive can improve the bond strength between the adhesive and the abrasive. In specific embodiments, KH550 or KH570 is used as the silane coupling agent.

[0048] It should be noted that polyether-modified siloxanes and silane coupling agents are relatively unstable in aqueous and alkaline adhesive systems. If added in advance, they are prone to hydrolysis and condensation side reactions during long-term storage. This not only leads to the loss of the intended regulating effect but also significantly alters the adhesive's viscosity, affecting its workability. Therefore, preparing and using the mixture immediately before application maximizes the reactivity of the polyether-modified siloxanes and silane coupling agents.

[0049] A type of abrasive cloth includes a substrate, an abrasive, a base layer, and a coating layer. The base layer is formed on one side of the substrate, and one end of the abrasive is uniformly embedded in the base layer. The coating layer covers the abrasive and the base layer. Both the base layer and the coating layer are coated with a bio-based composite adhesive prepared by any one of claims 1-7. The bio-based composite adhesive used in the base layer has a solid content of 55-75% and a viscosity of 1500-3500 mPa•s. The bio-based composite adhesive used in the coating layer has a solid content of 40-60% and a viscosity of 500-2000 mPa•s.

[0050] In a specific embodiment, an electrostatic sand-coating device is used in conjunction with the adhesive of this solution to prepare the abrasive cloth. Adhesives with different solid contents are combined with polyether-modified siloxanes and silane coupling agents to adjust the adhesive to a suitable viscosity, facilitating the mixing of abrasives of different grit sizes. By using the adhesive of this solution, both the base layer and the coating layer exhibit excellent heat resistance. Compared to using conventional adhesives, the abrasive cloth of the same specifications prepared using this solution exhibits less fluctuation in grinding accuracy, making it more suitable for high-precision grinding processes.

[0051] As a simple adjustment, the base coat and top coat can be prepared separately with different formulations and solid contents to achieve lower usage costs. Alternatively, the same high-solid-content adhesive can be used, diluted with water, alcohol, or other compatible organic solvents to adjust the solid content and viscosity before application. Fillers or other functional additives can also be added to the base coat and top coat to further adjust the adhesive's performance. For example, adding heavy calcium carbonate to the base coat adhesive increases the hardness of the adhesive layer and reduces curing shrinkage; adding calcined kaolin to the base coat improves the heat resistance and insulation of the adhesive layer. Furthermore, adding zinc stearate or cryolite to the base coat and top coat adhesives can act as a lubricant, improving grinding precision.

[0052] Example 1 According to parts by weight, the raw materials of the adhesive include: 240 parts of phenol 380 portions of 37% formaldehyde solution 80 parts of lignin were enzymatically hydrolyzed. 12 parts ethylene glycol, Two parts sodium hydroxide, 6 parts of 25% ammonia solution 2 parts urea 3 parts boric acid Water as needed; Pre-swelling: According to the proportions in the raw materials, the enzymatic hydrolyzed lignin, ethylene glycol, sodium hydroxide, ammonia and water are stirred and mixed to prepare a slurry with a water content of 10-20%. After that, it is left to stand at room temperature for 24 hours, and then dispersed at high speed for 0.5 hours to obtain the pre-swelled slurry. Synthetic resins: S1. According to the proportions in the raw materials, first add water, phenol and pre-swollen slurry into the reaction vessel, heat to 50°C, and after the phenol dissolves, first add 20% formaldehyde, heat to 60°C, and then slowly add the remaining formaldehyde dropwise over 2 hours. After the dropwise addition is complete, heat to 75°C and continue the reaction for 1 hour to obtain modified phenolic resin. S2. Vacuum decompression and exhaust are applied to the reactor. The vacuum degree is -0.09 MPa, the temperature is 60℃, and the time is 25 minutes. The solid content of the modified phenolic resin in the reactor is controlled to be 70%. S3. Add urea to the reactor according to the proportion in the raw materials and stir for 30 minutes. S4. According to the proportion in the raw materials, add other additives to the reaction vessel, cool the reaction vessel to 40°C, and finally add the pre-prepared boric acid solution to the reaction vessel to adjust the pH value to 8.5. Discharge the material to obtain the first adhesive. Preparation of sandpaper: Take an appropriate amount of the first adhesive mentioned above, add 0.3 parts of polyether-modified siloxane and 1 part of silane coupling agent KH550, stir well and preheat to 40°C, then apply it to the substrate fabric. Then use an electrostatic sand planting device to implant abrasive particles into the adhesive coated on the substrate fabric. The abrasive particles are 180-mesh zirconium corundum. After coating, gradually raise the temperature to 105°C, the adhesive cures to form a base layer, and then cool to below 50°C. Take an appropriate amount of the first adhesive mentioned above, add 1 part of silane coupling agent KH550, and dilute with water to a solid content of 40%. Stir well and preheat to 40°C. Apply the mixture to the base layer and abrasive. After coating, gradually raise the temperature to 130°C. The adhesive will cure to form a coating layer. Finally, cool to room temperature to obtain the sandpaper.

[0053] Example 2 The difference from Example 1 is that, according to the parts by mass, 240 parts of phenol in the raw materials of the adhesive are replaced with 200 parts, and 80 parts of enzymatically hydrolyzed lignin are replaced with 100 parts. Example 3 The difference from Example 1 is that, according to the parts by mass, 240 parts of phenol in the raw materials of the adhesive are replaced with 180 parts, and 80 parts of enzymatically hydrolyzed lignin are replaced with 120 parts. Comparative Example 1 The difference from Example 1 is that the pre-swelling step is omitted. Instead, in step S1 of resin synthesis, water, phenol, enzymatically hydrolyzed lignin, ethylene glycol, sodium hydroxide, and ammonia are added to the reaction vessel according to the proportions in the raw materials.

[0054] Comparative Example 2 The difference from Comparative Example 1 is that commercially available sodium lignin sulfonate was used instead of enzymatically hydrolyzed lignin.

[0055] Referring to section 5.1 of "JB / T 10155-2012 Test Method for Grinding Performance of Coated Abrasives, Abrasive Cloth, and Abrasive Paper", the abrasive cloths prepared in Examples 1-3 and Comparative Examples 1-2 were tested. Workpieces made of 304 stainless steel were used as test bars. Grinding was paused for 2 minutes every 5 minutes for natural cooling, and the surface roughness of the ground surface was recorded once. The test results are shown in Table 1 below: Table 1. Surface roughness Ra / μm of the workpiece after dry grinding test

[0056] The test results show that Examples 1-3 all have good grinding precision, with Examples 1 and 2 exhibiting even higher precision. Example 3, using a higher proportion of enzymatically hydrolyzed lignin, achieves a better service life, maintaining good precision even after 35 minutes. Comparative Example 1, lacking pre-swelling, suffers from poor abrasive orientation precision, resulting in poor surface roughness of the workpiece after grinding. While stability is acceptable within 15 minutes, precision gradually deteriorates afterward. Comparative Example 2 uses conventional sodium lignin sulfonate, which, despite its good water solubility and ability to integrate well into the adhesive without pre-swelling, introduces a large number of free ions, affecting the adhesive's dielectric properties. This significantly impacts the orientation precision of electrostatic abrasive placement, leading to lower grinding precision in the prepared abrasive cloth, with a marked deterioration in precision after 15 minutes.

[0057] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0058] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a bio-based composite adhesive, characterized in that, According to parts by weight, the raw materials of the adhesive include: 180-240 parts of phenol 320-410 parts of 37% formaldehyde solution Enzymatic hydrolysis of lignin: 80-120 parts 12-24 parts of ethylene glycol, Sodium hydroxide 1.5 to 4 parts, 4-10 parts of 25% ammonia solution 1-3 parts urea 2-5 parts boric acid Other additives: 0.02~11.55 parts; Water as needed; The preparation method includes the following steps: Pre-swelling: According to the proportions in the raw materials, the enzymatically hydrolyzed lignin, ethylene glycol, sodium hydroxide, ammonia and water are mixed to prepare a slurry with a water content of 10-20%. After that, it is allowed to stand or stirred for 1-48 hours, and then dispersed at high speed for 0.5-1 hour to obtain the pre-swelled slurry. Synthetic resins: S1. According to the proportions in the raw materials, add water, phenol, formaldehyde solution and pre-swollen slurry to the reactor, stir and mix and heat to polymerize for 2-10 hours to obtain modified phenolic resin. S2. Vacuum decompression and exhaust gas are applied to the reactor to control the solid content of the modified phenolic resin in the reactor to be 40-75%; S3. Add urea to the reactor according to the proportion in the raw materials, and stir for 10-30 minutes. S4. Add other additives to the reactor according to the proportion of the raw materials, and cool the reactor to 20~40℃. Finally, add boric acid to the reactor to adjust the pH value to 7.5~9, and discharge the material to obtain the bio-based composite adhesive.

2. The method for preparing a bio-based composite adhesive according to claim 1, characterized in that: In the pre-swelling step, after the materials are mixed, they are stirred in a closed system at 50~60℃ for 1~6 hours, and then dispersed at high speed to obtain a pre-swelled slurry.

3. The method for preparing a bio-based composite adhesive according to claim 1, characterized in that: In the pre-swelling step, after the materials are mixed, they are left to stand at room temperature for 6 to 48 hours, and then dispersed at high speed to obtain a pre-swelled slurry.

4. The method for preparing a bio-based composite adhesive according to claim 1, characterized in that: In step S2 of resin synthesis, the vacuum pressure is -0.08 to -0.095 MPa, the temperature is 50 to 60°C, and the time is 10 to 30 minutes.

5. The method for preparing a bio-based composite adhesive according to claim 1, characterized in that: In step S1 of the resin synthesis, water, phenol and pre-swollen slurry are first added to the reactor and heated to 50-55°C. After the phenol dissolves, 10-30% formaldehyde is added and the temperature is raised to 55-60°C. Then, the remaining formaldehyde is slowly added dropwise over 1-3 hours. After the addition is complete, the temperature is raised to 65-75°C and the reaction continues for 0.5-2 hours to complete the heating polymerization.

6. The method for preparing a bio-based composite adhesive according to claim 1, characterized in that: Other additives include at least one of nonionic defoamer, antioxidant and toughening agent, wherein, by weight, the nonionic defoamer is 0.02 to 0.05 parts, the antioxidant is 0.1 to 0.5 parts, and the toughening agent is 1 to 5 parts.

7. The method for preparing a bio-based composite adhesive according to claim 1, characterized in that: Other adjuvants include at least one of triethanolamine and resorcinol, wherein, by weight, triethanolamine is 0.5 to 1 part and resorcinol is 2 to 5 parts.

8. An adhesive composition, characterized in that: The adhesive, including those prepared using the preparation method of any one of claims 1-7, further comprises, by weight, 0.03 to 0.3 parts of polyether-modified siloxane.

9. The adhesive composition according to claim 8, characterized in that: According to the mass fraction, it also includes 0.5 to 1.5 parts of silane coupling agent.

10. A type of abrasive cloth, characterized in that: The invention comprises a substrate, an abrasive, a base layer, and a cover layer. The base layer is formed on one side of the substrate, one end of the abrasive is uniformly embedded in the base layer, and the cover layer covers the abrasive and the base layer. Both the base layer and the cover layer are coated with a bio-based composite adhesive prepared by any one of claims 1-7. The bio-based composite adhesive used in the base layer has a solid content of 55-75% and a viscosity of 1500-3500 mPa•s, while the bio-based composite adhesive used in the cover layer has a solid content of 40-60% and a viscosity of 500-2000 mPa•s.

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