Formaldehyde-free adhesive based on biomass material as well as preparation method and application of formaldehyde-free adhesive

Abstract

The invention belongs to the technical field of formaldehyde-free adhesives, and particularly relates to a formaldehyde-free adhesive based on a biomass material as well as a preparation method and application of the formaldehyde-free adhesive. The formaldehyde-free adhesive comprises the following raw material components in parts by mass: 50-80 parts of a biomass material, 5-20 parts of phenol, 5-15 parts of polyethylene glycol, 2-8 parts of polyol, 1-5 parts of citric acid, 2-10 parts of glyoxal and 3-8 parts of a cross-linking agent. According to the preparation method of the formaldehyde-free adhesive, phenol, polyethylene glycol and polyhydric alcohol are adopted and subjected to high-temperature treatment to generate bio-oil, then the bio-oil reacts with chemical substances such as citric acid and glyoxal, and the adhesive with a cross-linked structure is obtained; the adhesive can provide strong bonding strength on wood, straw, reed, bamboo wood and the like, and can adapt to different types of shaving board production processes.

Description

Technical Field

[0001] This invention belongs to the field of formaldehyde-free adhesive technology, and particularly relates to a formaldehyde-free adhesive based on biomass materials, its preparation method, and its application. Background Technology

[0002] Formaldehyde is a known carcinogen, and its volatilization pollutes air quality, affecting indoor air quality. Traditional adhesives contain formaldehyde, and their widespread use poses potential risks to the environment and human health. With increasing global environmental awareness, the wood adhesive industry is facing severe challenges. Therefore, developing formaldehyde-free, low-toxicity, and environmentally friendly adhesives has become an urgent need for the wood processing industry.

[0003] In recent years, with the promotion of the concept of sustainable development, biomass adhesives, as an environmentally friendly alternative material, have gradually attracted the attention of the scientific and industrial communities. Biomass adhesives are mainly synthesized using renewable plant-derived resources, such as vegetable oils, sugars, starch, cellulose, and hemicellulose, as raw materials. They possess advantages such as being non-toxic, low-pollution, and biodegradable, meeting the demands of modern society for green, environmentally friendly, and sustainable development. Biomass oils, as liquid products generated from organic matter such as plants and animals during pyrolysis and liquefaction, contain numerous active functional groups, such as phenolic hydroxyl groups, aldehyde groups, ketone groups, and carboxyl groups. These functional groups can react with other chemical reagents to form polymers with strong adhesive properties. In particular, plant-derived biomass oils (such as wood, straw, and camellia fruit shells) contain abundant phenolic hydroxyl groups and aromatic ring structures, exhibiting excellent polymerization and cross-linking properties, thus showing great potential in the development of wood adhesives. However, despite the significant advantages of biomass oil-based adhesives in terms of environmental protection and green performance, some challenges remain in practical applications.

[0004] First, the complex composition of biomass oils and their varying origins can lead to significant performance fluctuations and a lack of stability in adhesives. Second, traditional biomass oil adhesives exhibit poor bonding strength and water resistance in wet conditions, limiting their widespread application in wood processing. Finally, current catalytic and cross-linking methods for biomass liquefaction have several shortcomings. Therefore, researchers are working to optimize the structure of biomass oils and improve the overall performance of adhesives through various modification methods, such as adding cross-linking agents, catalysts, and copolymers. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a formaldehyde-free adhesive based on biomass materials, its preparation method and application.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: A formaldehyde-free adhesive based on biomass materials, wherein the raw materials of the formaldehyde-free adhesive comprise the following components by weight: 50-80 parts biomass material, 5-20 parts phenol, 5-15 parts polyethylene glycol, 2-8 parts polyol, 1-5 parts citric acid, 2-10 parts glyoxal, and 3-8 parts crosslinking agent. Phenolic biomass oils, due to their strong hydrogen bonding, can form a good bonding interface on the wood surface, improving adhesive strength. Furthermore, certain polyphenolic compounds in biomass oils can effectively enhance the UV resistance and antioxidant properties of wood products, extending the lifespan of the wood.

[0007] In this invention, polyethylene glycol, phenol, and glyoxal are selected as common solvents and active components in the biomass liquefaction reaction, aiming to synergistically impart excellent structural adhesion and reactivity to the liquefied bio-oil. Phenol, as a key polyphenol component, not only participates in the depolymerization reaction of lignin and hemicellulose in the biomass material during liquefaction but also retains its hydroxyl structure, forming a strong interfacial interaction with wood fibers through hydrogen bonds at the bonding interface, thereby significantly improving bonding strength. Simultaneously, phenol and its derivatives possess excellent antioxidant and UV-resistant properties, contributing to enhanced plywood durability and environmental stability. Polyethylene glycol and glyoxal act as plasticizers and chain transfer agents, improving the system's fluidity and dispersibility, which is beneficial for uniform application of the adhesive and the full progress of the cross-linking reaction, synergistically enhancing the adhesive's performance.

[0008] The ratio of phenol, polyethylene glycol, polyols, citric acid, and glyoxal affects the overall performance of the adhesive. When the dosage of glyoxal and citric acid is too low, the adhesive lacks sufficient cross-linking nodes, leading to low strength and poor water resistance. Conversely, excessive dosage can result in over-cross-linking or excessively high viscosity, reducing workability. Another crucial factor is the ratio of polyol to phenol and polyethylene glycol. The multiple hydroxyl groups in polyols provide additional active sites for the cross-linking reaction and regulate molecular flexibility.

[0009] Preferably, the crosslinking agent comprises polyvinyl alcohol and sodium dodecyl sulfate, and the mass ratio of polyvinyl alcohol to sodium dodecyl sulfate is 1:1-3:1; It may include: polyvinyl alcohol and tannic acid, and the mass ratio of polyvinyl alcohol to tannic acid is 2:1-3:1; The molecular weight range of the polyvinyl alcohol is 400-1700.

[0010] In this invention, polyvinyl alcohol (PVA) is introduced as an auxiliary modifying component to enhance the structural integrity and overall performance of liquefied oil-based adhesives. PVA molecules are rich in hydroxyl groups, enabling them to undergo esterification or acetal reactions with crosslinking agents such as glyoxal and citric acid, forming a dense three-dimensional network structure. This significantly improves the crosslinking degree and water resistance of the adhesive. Simultaneously, PVA's excellent film-forming properties and flexibility help improve the brittleness of the liquefied oil adhesive layer, enhancing its adhesion and overall mechanical strength at the wood interface. Furthermore, PVA also has good thickening and dispersing effects, which can regulate the rheological properties of the adhesive system, improve the stability and workability of the adhesive solution, and play a crucial synergistic regulatory role in the preparation and application of the adhesive.

[0011] Preferably, the biomass material includes one or more of wood, corn, rice straw, reeds, or bamboo; Preferably, the polyol includes one or more of ethylene glycol, glycerol, butanediol, isophorone diol, or 1,3-propanediol.

[0012] Introducing polyols (such as ethylene glycol, glycerol, butylene glycol, isophorone diol, and 1,3-propanediol) into the biomass liquefaction or adhesive synthesis process has multifaceted and significant synergistic enhancing effects. In particular, it forms stable chemical networks and improves system performance by interacting with reactive groups such as phenol, polyethylene glycol, and lignin and hemicellulose in biomass. By adjusting the ratio of polyvinyl alcohol, polyols, and liquefied oil, and through preparation methods such as stirring and evaporation, the viscosity and solid content range of the adhesive can be flexibly adjusted to match the application requirements of different substrates and application scenarios, achieving a harmonious balance between structure, performance, and process.

[0013] First, polyols contain multiple hydroxyl groups (–OH), which can undergo etherification or esterification reactions with biomass degradation products (such as lignin fragments, sugars, and aldehydes, ketones, and carboxyl groups in oligomers). In the presence of crosslinking agents (such as glyoxal and citric acid), they further form a crosslinked network, thereby improving the structural density and mechanical strength of the adhesive. Second, polyols possess good hydrophilicity and solubility, promoting homogeneous reactions between phenol, polyethylene glycol, and other biomass components during liquefaction. This effectively inhibits coking and non-selective condensation reactions, improving liquefaction efficiency and reaction selectivity, and enhancing the uniformity and stability of the adhesive. Furthermore, polyols can also act as plasticizers to adjust the flexibility of the adhesive, reduce internal stress in the crosslinked network, and improve the crack resistance after curing.

[0014] Therefore, polyols not only participate in chemical reactions, but also form significant synergistic effects with phenol, polyethylene glycol, and biomass materials at the levels of reaction medium, molecular connection, and performance regulation. They are an important component that cannot be ignored in the realization of high-performance bio-based adhesives.

[0015] Preferably, the viscosity of the formaldehyde-free adhesive is 500-3000 mPa·s, and the solid content is 80-100 wt%.

[0016] More preferably, the formaldehyde-free adhesive has a solid content of 80-90 wt%.

[0017] In liquefied oil adhesive systems, appropriate viscosity and solid content are key parameters for ensuring adhesive application, interfacial wettability, and final bonding performance. Based on experimental systems and practical application requirements, the viscosity should be controlled within the range of 500–3000 mPa·s, and the solid content should be maintained above 80 wt% (high moisture content due to low solid content can affect bonding). Low viscosity (500–1000 mPa·s) adhesives are suitable for highly permeable substrates (such as bamboo and soft herbaceous boards) or interfaces requiring deep wetting and penetration. These systems have high fluidity, which facilitates the adhesive's penetration into the fiber structure to form a "mechanical interlock" and enhance bonding strength. However, excessive penetration should be controlled to prevent "adhesive starvation." Medium viscosity (1000–2000 mPa·s) systems are suitable for most conventional engineered wood products (such as particleboard, plywood, and multi-layer boards), offering good application fluidity and reaction efficiency, and represent the recommended industrial adhesive parameter range. High viscosity (2000–3000 mPa·s) systems... Adhesives with a solid content of mPa·s are more suitable for heavy wood substrates or applications requiring rapid edge sealing and short-term setting. Higher solid content helps to increase the thickness of the adhesive layer and reduce evaporation shrinkage, but it requires higher quality construction equipment (such as uniformity of hot pressing and uniformity of adhesive distribution).

[0018] Preferably, the raw materials of the formaldehyde-free adhesive include the following components by weight: 50-80 parts biomass material, 5-12 parts phenol, 5-10 parts polyethylene glycol, 2-6 parts polyol, 1-3 parts citric acid, 3-8 parts glyoxal, and 3-6 parts crosslinking agent. Under the same technical concept, this application also provides a method for preparing a formaldehyde-free adhesive based on biomass materials, specifically including the following steps: (1) Mix phenol, polyethylene glycol and polyol, add biomass material and liquefy at 140-180℃ for 1-5 hours to obtain liquid biomass material; (2) Mix the liquid biomass material obtained in step (1) with citric acid and glyoxal, and stir at 60-80℃ for 0.5-2h to fully react; (3) Continue to add crosslinking agent, heat to 90-110℃, maintain for 1-3h, cool to room temperature, and obtain formaldehyde-free adhesive based on biomass materials.

[0019] This invention liquefies biomass raw materials such as wood and straw to obtain biomass oil, and then reacts it with citric acid, glyoxal, and a crosslinking agent to prepare a high-performance wood adhesive suitable for the preparation of wood and reed straw particleboard. This adhesive not only exhibits excellent bonding strength in the dry state but also significantly improves the water resistance of particleboard, adapting it to application requirements under various environmental conditions. By optimizing the reaction process and raw material ratio, this invention provides a formaldehyde-free adhesive with good green environmental protection characteristics and excellent performance. It innovatively uses straw as a raw material, offering a new solution for the green transformation of industries such as wood and bamboo processing and engineered wood products.

[0020] Preferably, the liquefaction process specifically includes: Phenol, polyethylene glycol, polyol and biomass material are mixed and stirred continuously under an inert gas atmosphere. The reaction is carried out at 140-180 °C for 1-5 h. After the reaction is completed, the mixture is quickly cooled to room temperature and transferred to a beaker. Ethanol is mixed in a volume ratio of 4-6:1 and stirred continuously for 20-40 min. The solid and liquid are separated by vacuum filtration and rotary evaporation. The resulting liquid is the liquid biomass material.

[0021] More preferably, the liquefaction temperature is 155-165 °C, and the holding time is 2-3 h. Within this range, both yield and suppression of coking can be achieved, making it more reproducible in industrial applications.

[0022] More preferably, the inert gas atmosphere is a nitrogen atmosphere.

[0023] Liquefaction technology for biomass oils is an important technique for improving their application in adhesives. Liquefaction effectively enhances the solubility, reactivity, and adhesive properties of biomass oils. The liquefaction process typically involves a chemical reaction at high temperatures, using a specific proportion of catalyst or solvent, to decompose the lignocellulose, hemicellulose, and lignin components of biomass, converting them into bio-oils containing active functional groups such as phenolic hydroxyl groups and aldehyde groups. These active functional groups play a crucial role in adhesive preparation, and through reactions with other chemical reagents, they effectively enhance the adhesive's bonding properties, mechanical properties, and water resistance.

[0024] Under the same technical concept, this application also provides an application of a formaldehyde-free adhesive based on biomass materials, including the application of the above-mentioned formaldehyde-free adhesive based on biomass materials in bonding particleboard. During use, the moisture content of the particleboard raw material is controlled at 3-5%; the solid content of the formaldehyde-free adhesive is 80-100%, and the amount of formaldehyde-free adhesive added is 8-12% of the oven-dry particleboard mass.

[0025] Preferably, when bonding particleboard with the formaldehyde-free adhesive, the formaldehyde-free adhesive is sprayed onto the surface of the particleboard material, and then hot-pressed to form a core. The hot-pressing temperature is 180-220℃, and the hot-pressing time is 3-10 minutes.

[0026] The particleboard is laid in a three-layer oriented strand board configuration, with the top and bottom outer layers as surface layers and the middle layer as the core layer. The particle size of the surface layer raw material is controlled at 1-3 mm, and the particle size of the core layer is controlled at 5-8 mm. It is pre-pressed under 0.5-0.8 MPa pressure for 20-40 seconds to form the particleboard, ensuring uniform adhesive coating and reducing the risks associated with subsequent hot-pressing and blowing. This formaldehyde-free adhesive is compatible with existing 8–12 ft continuous press production lines, enabling integrated online adhesive application, hot pressing, and edge trimming production of particleboard or oriented strand board without equipment modifications. Preferably, during the hot pressing process, the temperature is raised to 180-200℃ within 60-90 seconds, held at 200-220℃ for 120-240 seconds, and then cooled to 130-150℃ before the pressure is released.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The formaldehyde-free adhesive provided by the present invention uses biomass materials such as citric acid, polyethylene glycol, and glyoxal, and does not contain harmful substances such as formaldehyde, which meets the requirements of green environmental protection and reduces the environmental burden of traditional adhesives; the adhesive of the present invention can provide strong bonding strength for wood, straw, reeds, bamboo and other materials, and can adapt to different types of particleboard production processes; in humid environments, the adhesive can still maintain excellent bonding strength, and is particularly suitable for particleboard used in high humidity environments, and has good water resistance; in extreme environments such as high temperature and high humidity, the mechanical properties of particleboard are stable, which can ensure the long-term performance of the product during use; (2) The method for preparing the formaldehyde-free adhesive of the present invention uses phenol, polyethylene glycol and polyol, which are treated at high temperature to generate bio-oil, and then react with citric acid, glyoxal and other chemical substances to obtain an adhesive with a cross-linking structure. The cross-linking structure is based on the bio-oil rich in hydroxyl and aromatic ring structures formed by liquefaction of phenol, polyethylene glycol and polyol, which further undergoes multiple chemical reactions such as esterification, acetalization and etherification with carboxyl and aldehyde groups in citric acid and glyoxal to construct a three-dimensional network structure composed of phenolic hydroxyl, alcoholic hydroxyl and multifunctional cross-linking points. This network not only provides high-density covalent cross-linking nodes, which significantly enhances the mechanical strength and heat resistance of the adhesive, but also has good interfacial adaptability and water resistance due to the synergistic distribution of hydrophilic and hydrophobic groups in the cross-linking structure. Thus, it achieves multiple performance advantages of formaldehyde-free release, strong adhesion and environmental stability. In this bio-based adhesive system, the ratio of phenol, polyethylene glycol, polyol, citric acid, and glyoxal, as well as the temperature and time of the reaction process, jointly determine the density and performance of the crosslinking network. The most critical factors are often the molar ratio between the crosslinking agent and the reactive hydroxyl groups, and the temperature gradient during the reaction stages. The combination of reaction temperature and residence time affects the reaction rate and efficiency between hydroxyl groups and aldehyde and carboxyl groups: too short or too low a temperature leads to insufficient crosslinking, while too long or too high a temperature easily causes side reactions or decomposition. Therefore, only with appropriate crosslinking agent addition ratios, polyol ratios, and reasonable multi-stage temperature control can a high-density and uniform crosslinking network be obtained, giving the adhesive optimal mechanical strength, water resistance, and environmental stability, providing strong crosslinking strength and environmental adaptability, and solving problems such as formaldehyde release and poor water resistance that may occur during the use of traditional adhesives. (3) The bio-based adhesive of this application is used to bond particleboard. The particleboard prepared has formaldehyde release, strength and expansion rate that meet national standards. It has excellent performance and has a promising market prospect. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 Here is a photograph of the biomass liquefied oil prepared in Example 1 of this application; Figure 2 These are actual images of the formaldehyde-free adhesive prepared in Example 1 of this application; Figure 3 This is a picture of a three-layer plywood produced by applying the formaldehyde-free adhesive prepared in Example 1 of this application to plywood production; Figure 4 This is the infrared spectrum of the biomass liquefied oil prepared in Example 1 of this application; Figure 5 This is the infrared spectrum of the formaldehyde-free adhesive prepared in Example 1 of this application. Detailed Implementation

[0030] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0031] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0032] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0033] Example 1: The formaldehyde-free adhesive based on biomass materials provided in this embodiment includes the following raw materials: phenol (10g), polyethylene glycol (5g), glycerol (2g), straw powder (50g), citric acid (2g), glyoxal (3g), (PVA) (2g), sodium dodecyl sulfate (2g); the molecular weight of polyvinyl alcohol is 899. Its preparation method includes the following steps: (1) Liquefaction treatment Mix 10 g (≥ 99%) of phenol, 5 g of polyethylene glycol PEG-400 (average molecular weight 380–420), 2 g of glycerol, and 50 g of 40-mesh corn stalk powder by weight, and place in a 250 mL three-necked flask; purge with nitrogen gas for 50 mL min. - ¹ After displacement for 3 min, the mixture was stirred at 300 rpm and heated to 140 ℃ and held at that temperature for 3 h. After the reaction was complete, the system temperature was lowered to 25 ℃ by bathing in an ice-water bath for 5 min. The slurry was then transferred to a 1 L beaker, and 250 mL of 95% (v / v) ethanol was added (ethanol:total reaction volume ≈ 5:1), and the mixture was magnetically stirred for 30 min. Subsequently... Solid-liquid separation was performed by vacuum filtration using a 0.45 µm glass fiber membrane under a vacuum of 0.09 MPa; the filtrate was then cooled at 50 °C. Ethanol was removed by rotary evaporation at 0.07 MPa to obtain approximately 85 g of dark brown liquid biomass oil (83% yield based on oven-dried straw). (2) The brown liquid biomass oil obtained in step (1) is mixed with citric acid and glyoxal, and stirred at 70°C for 1 hour to react fully; (3) Continue to add crosslinking agent, heat to 100℃, keep for 2 hours, cool to room temperature, and obtain formaldehyde-free adhesive based on biomass materials; According to GB / T 2793-2021, the viscosity of the formaldehyde-free adhesive is 1510 ± 46 mPa·s, and the solid content is 84.5 ± 0.3 wt%.

[0034] Based on the selection and dosage of the above materials, the application of formaldehyde-free adhesives based on biomass materials in particleboard manufacturing mainly includes the following process steps: (1) Drying: The obtained straw fragments are sieved through an 8-10 mesh screen and sent to a drying kiln to dry the moisture content of the fragments to 4-5%; (2) Mixing and applying adhesive: according to the ratio of 1m 3 780 kg of dried straw fragments and 100 kg of adhesive are added to the finished particleboard. The adhesive is sprayed onto the surface of the straw in the form of atomization, and then sent to a drying kiln to dry the moisture content of the fragments containing adhesive to 8-10%. (3) Laying and shaping: The crushed material after mixing in step (2) is thoroughly mixed and then laid and shaped; the particleboard is laid in three layers with the outer top and bottom layers as the surface layer and the middle layer as the core layer. The particle size of the surface layer is controlled at 1-3 mm and the particle size of the core layer is controlled at 5-8 mm. It is pre-compressed at 0.5-0.8 MPa for 20-40 s. (4) Hot pressing: The laid slab is sent into the hot press for hot pressing. The temperature is raised to 200℃ within 60 s, and kept constant at 200-210℃ for 120 s. Then the temperature is lowered to 140℃ and the pressure is released. The slab is pressed to make the thickness of the 8mm thickness gauge consistent under pressure. (5) Cooling and trimming: After hot pressing, the slab is cooled to room temperature and then trimmed. (6) Stacking and sanding: Stack the trimmed slabs for 90 hours, then sand them. After inspection and grading, the finished product can be obtained.

[0035] Figure 1 This is a picture of the biomass liquefied oil prepared in Example 1 of this application.

[0036] Figure 2 This is a physical image of the formaldehyde-free adhesive prepared in Example 1 of this application.

[0037] Figure 3 This is a picture of a finished three-layer plywood product obtained by applying the formaldehyde-free adhesive prepared in Example 1 of this application to plywood production.

[0038] Figure 4 This is the infrared spectrum of the biomass liquefied oil prepared in Example 1 of this application.

[0039] Figure 5 This is the infrared spectrum of the formaldehyde-free adhesive prepared in Example 1 of this application.

[0040] The particleboard prepared above will be subjected to performance tests, and the test results are shown in Table 1 below: Table 1 Performance test results of the particleboard prepared in Example 1

[0041] Based on the quality inspection results of the products obtained from the above embodiments, it can be concluded that reed particleboard can be manufactured according to the method and process provided by the present invention.

[0042] Infrared characteristic peak tests were performed on the product of Example 1, and the results are shown in Table 2 below: Table 2 Comparison of infrared characteristic peaks between Figure 4 (liquid bio-oil) and Figure 5 (formaldehyde-free adhesive after curing)

[0043] Compared to liquid bio-oil, the curing adhesive has a curing time of 1732 cm⁻¹ -1 A significantly increased ester bond vibration peak appears, and it reaches 1250 cm⁻¹. -1 1105 cm -1 Enhanced C–O (ester) and C–O–C (acetal) stretching vibrations are observed at 3350 cm⁻¹, respectively. -1 –OH absorption is significantly reduced. These characteristics collectively confirm that the citric acid-hydroxy esterification and glyoxal-hydroxyacetal reaction construct a dense, double-covalently cross-linked network. The retained 2922 cm⁻¹ -1 Alkyl groups and 1598 / 1510 cm -1 The aromatic ring absorption indicates that the system still contains hydrophobic segments and a π-π skeleton, providing excellent water resistance and cohesive strength to the cured board.

[0044] Example 2: The formaldehyde-free adhesive based on biomass materials provided in this embodiment includes the following raw materials: phenol (12g), polyethylene glycol (6g), glycerol (3g), reed powder (60g), citric acid (2.5g), glyoxal (5.0g), polyvinyl alcohol (PVA) (3g), and tannic acid (1g).

[0045] The viscosity of the formaldehyde-free adhesive is 1,675 ± 38 mPa·s, and the solid content is 85.1 ± 0.3 wt%.

[0046] Its preparation method includes the following steps: (1) Phenol, polyethylene glycol, glycerol and 40-mesh corn stalk powder are mixed by mass and placed in a 250 mL three-necked flask; nitrogen gas is introduced into the flask at a rate of 50 mL / min. -¹ After displacement for 3 min, the mixture was stirred at 300 rpm and heated to 140 ℃ and held at that temperature for 3 h. After the reaction was complete, the mixture was cooled to 25 ℃ in an ice-water bath for 5 min. The slurry was then transferred to a 1 L beaker, and 250 mL of 95% (v / v) ethanol was added (ethanol:total reaction volume ≈ 5:1). The mixture was magnetically stirred for 30 min. Subsequently... Solid-liquid separation was performed by vacuum filtration using a 0.45 µm glass fiber membrane under a vacuum of 0.09 MPa; the filtrate was then cooled at 50 °C. Ethanol was removed by rotary evaporation at 0.07 MPa to obtain approximately 85 g of dark brown liquid biomass oil (83% yield based on oven-dried straw). (2) The liquid biomass material obtained in step (1) is mixed with citric acid and glyoxal and stirred at 75°C for 1.5 h to react completely; (3) Continue to add crosslinking agent, heat to 100°C, maintain for 2.5 h, cool to room temperature, and obtain formaldehyde-free adhesive based on biomass materials.

[0047] The preparation method of straw particleboard is the same as in Example 1.

[0048] Example 3: The formaldehyde-free adhesive based on biomass materials provided in this embodiment includes the following raw materials: phenol (15g), polyethylene glycol (7g), ethylene glycol (4g), straw powder (70g), citric acid (2.5g), glyoxal (2g), polyvinyl alcohol (PVA) (4g), and tannic acid (2g).

[0049] The viscosity of the formaldehyde-free adhesive is 1335 ± 40 mPa·s, and the solid content is 83.9 ± 0.3 wt%.

[0050] Its preparation method includes the following steps: (1) Phenol, polyethylene glycol, glycerol and 40-mesh corn stalk powder are mixed by mass and placed in a 250 mL three-necked flask; nitrogen gas is introduced into the flask at a rate of 50 mL / min. - ¹ After displacement for 3 min, the mixture was stirred at 300 rpm and heated to 160 ℃ and held at that temperature for 5 h. After the reaction was complete, the mixture was cooled to 25 ℃ in an ice-water bath for 5 min. The slurry was then transferred to a 1 L beaker, and 250 mL of 95% (v / v) ethanol was added (ethanol:total reaction volume ≈ 5:1). The mixture was magnetically stirred for 30 min. Subsequently... Solid-liquid separation was performed by vacuum filtration using a 0.45 µm glass fiber membrane under a vacuum of 0.09 MPa; the filtrate was then cooled at 50 °C. Ethanol was removed by rotary evaporation at 0.07 MPa to obtain approximately 85 g of dark brown liquid biomass oil (83% yield based on oven-dried straw).

[0051] (2) The liquid biomass material obtained in step (1) is mixed with citric acid and glyoxal, and stirred at 80°C for 2 hours to react completely; (3) Continue to add crosslinking agent, heat to 110°C, keep for 3 hours, cool to room temperature, and obtain formaldehyde-free adhesive based on biomass materials.

[0052] The preparation method of straw particleboard is the same as in Example 1.

[0053] Example 4: The formaldehyde-free adhesive based on biomass materials provided in this embodiment includes the following raw materials: phenol (8g), polyethylene glycol (5g), butanediol (3g), reed powder (55g), citric acid (2g), glyoxal (6g), polyvinyl alcohol (PVA) (2g), and tannic acid (1g).

[0054] The viscosity of the formaldehyde-free adhesive is 1180 ± 35 mPa·s, and the solid content is 82.5 ± 0.3 wt%.

[0055] Its preparation method includes the following steps: (1) Phenol, polyethylene glycol, glycerol and 40-mesh corn stalk powder are mixed by mass and placed in a 250 mL three-necked flask; nitrogen gas is introduced into the flask at a rate of 50 mL / min. - ¹ After displacement for 3 min, the mixture was stirred at 300 rpm and heated to 150 ℃ and held at that temperature for 3 h. After the reaction was complete, the mixture was cooled to 25 ℃ in an ice-water bath for 5 min. The slurry was then transferred to a 1 L beaker, and 250 mL of 95% (v / v) ethanol was added (ethanol:total reaction volume ≈ 5:1). The mixture was magnetically stirred for 30 min. Subsequently... Solid-liquid separation was performed by vacuum filtration using a 0.45 µm glass fiber membrane under a vacuum of 0.09 MPa; the filtrate was then cooled at 50 °C. Ethanol was removed by rotary evaporation at 0.07 MPa to obtain approximately 85 g of dark brown liquid biomass oil (83% yield based on oven-dried straw).

[0056] (2) The liquid biomass material obtained in step (1) is mixed with citric acid and glyoxal, and stirred at 80°C for 1 hour to fully react; (3) Continue to add crosslinking agent, heat to 90°C, maintain for 2 hours, cool to room temperature, and obtain formaldehyde-free adhesive based on biomass materials.

[0057] The preparation method of straw particleboard is the same as in Example 1.

[0058] Example 5: The formaldehyde-free adhesive based on biomass materials provided in this embodiment includes the following raw materials: phenol (20g), polyethylene glycol (6g), glycerol (2g), straw powder (65g), citric acid (2.5g), glyoxal (4g), polyvinyl alcohol (PVA) (4g), and tannic acid (2g).

[0059] The viscosity of the formaldehyde-free adhesive is 1880 ± 60 mPa·s, and the solid content is 86.2 ± 0.3 wt%.

[0060] Its preparation method includes the following steps: (1) Phenol, polyethylene glycol, glycerol and 40-mesh corn stalk powder are mixed by mass and placed in a 250 mL three-necked flask; nitrogen gas is introduced into the flask at a rate of 50 mL / min. - ¹ After displacement for 3 min, the mixture was stirred at 300 rpm and heated to 150 ℃ and held at that temperature for 3 h. After the reaction was complete, the mixture was cooled to 25 ℃ in an ice-water bath for 5 min. The slurry was then transferred to a 1 L beaker, and 250 mL of 95% (v / v) ethanol was added (ethanol:total reaction volume ≈ 5:1). The mixture was magnetically stirred for 30 min. Subsequently... Solid-liquid separation was performed by vacuum filtration using a 0.45 µm glass fiber membrane under a vacuum of 0.09 MPa; the filtrate was then cooled at 50 °C. Ethanol was removed by rotary evaporation at 0.07 MPa to obtain approximately 85 g of dark brown liquid biomass oil (83% yield based on oven-dried straw).

[0061] (2) The liquid biomass material obtained in step (1) is mixed with citric acid and glyoxal, and stirred at 78°C for 1.5 h to react completely; (3) Continue to add crosslinking agent, heat to 105°C, keep for 2 hours, cool to room temperature, and obtain formaldehyde-free adhesive based on biomass materials.

[0062] The preparation method of straw particleboard is the same as in Example 1.

[0063] Example 6: The formaldehyde-free adhesive based on biomass materials provided in this embodiment includes the following raw materials: phenol (16g), polyethylene glycol (8g), glycerol (5g), straw powder (80g), citric acid (3g), glyoxal (6g), polyvinyl alcohol (PVA) (5g), and tannic acid (2g).

[0064] The viscosity of the formaldehyde-free adhesive is 1720 ± 50 mPa·s, and the solid content is 85.7 ± 0.4 wt%.

[0065] Its preparation method includes the following steps: (1) Phenol, polyethylene glycol, glycerol and 40-mesh corn stalk powder are mixed by mass and placed in a 250 mL three-necked flask; nitrogen gas is introduced into the flask at a rate of 50 mL / min. - ¹ After displacement for 3 min, the mixture was stirred at 300 rpm and heated to 170 ℃ and held at that temperature for 4 h. After the reaction was complete, the mixture was cooled to 25 ℃ in an ice-water bath for 5 min. The slurry was then transferred to a 1 L beaker, and 250 mL of 95% (v / v) ethanol was added (ethanol:total reaction volume ≈ 5:1). The mixture was magnetically stirred for 30 min. Subsequently... Solid-liquid separation was performed by vacuum filtration using a 0.45 µm glass fiber membrane under a vacuum of 0.09 MPa; the filtrate was then cooled at 50 °C. Ethanol was removed by rotary evaporation at 0.07 MPa to obtain approximately 85 g of dark brown liquid biomass oil (83% yield based on oven-dried straw).

[0066] (2) The liquid biomass material obtained in step (1) is mixed with citric acid and glyoxal and stirred at 70°C for 1.5 h to react completely; (3) Continue to add crosslinking agent, heat to 100°C, keep for 3 hours, cool to room temperature, and obtain formaldehyde-free adhesive based on biomass materials.

[0067] The preparation method of straw particleboard is the same as in Example 1.

[0068] Example 7: The formaldehyde-free adhesive based on biomass materials provided in this embodiment includes the following raw materials: phenol (18g), polyethylene glycol (7g), glycerol (5g), straw powder (75g), citric acid (2g), glyoxal (5.5g), polyvinyl alcohol (PVA) (4g), and tannic acid (2g).

[0069] The viscosity of the formaldehyde-free adhesive is 1590 ± 45 mPa·s, and the solid content is 84.8 ± 0.3 wt%.

[0070] Its preparation method includes the following steps: (1) Phenol, polyethylene glycol, glycerol and 40-mesh corn stalk powder are mixed by mass and placed in a 250 mL three-necked flask; nitrogen gas is introduced into the flask at a rate of 50 mL / min. -¹ After displacement for 3 min, the mixture was stirred at 300 rpm and heated to 170 ℃ and held at that temperature for 4 h. After the reaction was complete, the mixture was cooled to 25 ℃ in an ice-water bath for 5 min. The slurry was then transferred to a 1 L beaker, and 250 mL of 95% (v / v) ethanol was added (ethanol:total reaction volume ≈ 5:1). The mixture was magnetically stirred for 30 min. Subsequently... Solid-liquid separation was performed by vacuum filtration using a 0.45 µm glass fiber membrane under a vacuum of 0.09 MPa; the filtrate was then cooled at 50 °C. Ethanol was removed by rotary evaporation at 0.07 MPa to obtain approximately 85 g of dark brown liquid biomass oil (83% yield based on oven-dried straw).

[0071] (2) The liquid biomass material obtained in step (1) is mixed with citric acid and glyoxal, and stirred at 80°C for 1 hour to fully react; (3) Continue to add crosslinking agent, heat to 95°C, maintain for 2.5h, cool to room temperature, and obtain formaldehyde-free adhesive based on biomass materials.

[0072] Table 3 Performance of the finished boards obtained in Examples 2-7

[0073] Comparative Example 1: No cross-linking agent added (no PVA, no SDS, no tannic acid) Formulation differences: The crosslinking agent was omitted; otherwise, it remained the same as in Example 1. The amount of glyoxal used was 3 g (consistent with Example 1). The preparation method includes the following steps: (1) Liquefaction: Mix 10 g of phenol, 5 g of PEG-400, 2 g of glycerol, and 50 g of 40-mesh straw powder by weight, and purge with nitrogen gas (N250 mL·min). - ¹The mixture was replaced for 3 min, stirred at 300 rpm, heated to 140 ℃, and held at that temperature for 3 h. After the reaction was complete, the system temperature was lowered to 25 ℃ by bathing in an ice-water bath for 5 min. The slurry was then transferred to a 1 L beaker and treated according to the ethanol precipitation, filtration, and rotary evaporation conditions in Example 1 to obtain liquid biomass oil.

[0074] (2) Modification: The liquid biomass oil obtained in step (1) is mixed with 2 g of citric acid and 3 g of glyoxal and stirred at 70 °C for 1 h.

[0075] (3) Crosslinking: Do not add PVA, SDS or tannic acid; heat to 100 ℃, keep for 2 hours, and cool to obtain adhesive.

[0076] (4) Particleboard: Particleboard is manufactured according to the manufacturing method of steps (1)-(6) of Example 1; the amount of solid adhesive applied is consistent with that of Example 1.

[0077] Results and conclusions: See Table 4; compared with Example 1, IB decreased to 0.31 MPa, TS 24 h increased to 16.4%, and IB dropped to 0.045 MPa after boiling, indicating that the lack of crosslinking phase led to a significant deterioration in bonding and water resistance.

[0078] Comparative Example 2: Replacing citric acid with urea (to verify "not formaldehyde-free") Formula differences: 2 g of citric acid was replaced with 2 g of urea; 3 g of glyoxal; 2 g of PVA and 2 g of SDS were retained, and the rest were the same as in Example 1. The preparation method includes the following steps: (1) Liquefaction: Same as in Example 1 (140 ℃×3 h). (2) Modification: The obtained biomass oil + 2 g of urea + 3 g of glyoxal were stirred at 70 ℃ for 1 h. (3) Crosslinking: 2 g of PVA and 2 g of SDS were added; 100 ℃×2 h were cooled to obtain glue. (4) Particleboard: Same as in Example 1. Results and conclusions: See "Table 4"; the mechanical properties were acceptable (IB 0.56MPa), but the formaldehyde release increased to 0.32 mg / 100 g, and the IB decreased after boiling (0.060 MPa), which did not meet the "formaldehyde-free" design goal.

[0079] Comparative Example 3: Reduction of liquefaction severity (110 ℃ × 1 h) Formula differences: The formula is the same as in Example 1; only the liquefaction conditions are changed to 110 °C × 1 h.

[0080] Specific steps: (1) Liquefaction: Mix 10 g of phenol (≥ 99%), 5 g of polyethylene glycol PEG-400 (average molecular weight 380–420), 2 g of glycerol and 50 g of 40 mesh corn stalk powder by mass, and place in a 250 mL three-necked flask; purge with 50 mL of nitrogen gas. - ¹ After displacement for 3 min, the temperature was raised to 110 ℃ by stirring at 300 rpm and kept constant for 1 h. After the reaction was completed, the system temperature was lowered to 25 ℃ by ice water bath for 5 min. The slurry was then transferred to a 1 L beaker. The subsequent ethanol precipitation, filtration and rotary evaporation were the same as in Example 1. (2) Modification: biomass oil + citric acid 2 g + glyoxal 3 g, 70 ℃ × 1 h. (3) Crosslinking: PVA 2 g and SDS 2 g were added; 100 ℃ × 2 h. (4) Particleboard: same as in Example 1. Results and conclusions: see “Table 4”; IB decreased to 0.42 MPa, TS 24h rose to 12.0%, indicating that insufficient liquefaction led to uneven resin phase and poor interfacial bonding.

[0081] Comparative Example 4: Polyethylene glycol (PEG-400)-free Formulation differences: PEG-400 0 g; the rest is the same as in Example 1 (citric acid 2 g, glyoxal 3 g, PVA 2 g, SDS 2 g). Specific steps: (1) Liquefaction: Mix 10 g of phenol, 2 g of glycerol and 50 g of straw powder and place in a 250 mL three-necked flask; purge with 50 mL of nitrogen gas. - ¹ After displacement for 3 min, the temperature was raised to 140 ℃ with stirring at 300 rpm and held at that temperature for 3 h. The post-treatment was the same as in Example 1. (2) Modification and crosslinking: Same as in Example 1 (70 ℃ × 1 h; 100 ℃ × 2 h). (3) Particleboard: Same as in Example 1. Results and conclusions: See “Table 4”; IB 0.48 MPa, TS 24 h 9.8%, lower than in Example 1, indicating that PEG has a positive effect on wetting, spreading and network densification.

[0082] Comparative Example 5: No citric acid Formula differences: Citric acid 0 g; the rest is the same as in Example 1 (glyoxal 3 g, PVA 2 g, SDS 2 g). Specific steps: (1) Liquefaction: Same as in Example 1.

[0083] (2) Modification: Biomass oil + 3 g of glyoxal, 70 ℃×1 h (without citric acid). (3) Crosslinking: Add 2 g of PVA and 2 g of SDS; 100 ℃ × 2 h.

[0084] (4) Particleboard: Same as in Example 1.

[0085] Results and conclusions: see Table 4; IB 0.44 MPa, IB after boiling 0.060 MPa, significantly lower than in Example 1, demonstrating that the esterification bridging / multi-point hydrogen bonds provided by citric acid are crucial to water resistance.

[0086] Comparative Example 6: Phenol-free Formula differences: 0 g phenol; the rest are the same as in Example 1 (5 g PEG-400, 2 g glycerol, 2 g citric acid, 3 g g glyoxal, 2 g PVA, 2 g SDS, 50 g straw powder).

[0087] Specific steps: (1) Liquefaction: PEG-400 / glycerol and straw powder were reacted at 140 °C for 3 h, and the post-treatment was the same as in Example 1.

[0088] (2) Modification and crosslinking: Same as Example 1 (70 ℃×1 h; 100 ℃×2 h).

[0089] (3) Particleboard: Same as in Example 1.

[0090] Results and conclusions: See Table 4; IB only 0.33 MPa, TS 24 h 15.1%, the worst among all controls, indicating that phenol participates in carbon skeleton reforming and water-resistant carbon layer formation, and makes a significant contribution to strength and water resistance.

[0091] Detection methods and statistics Standards: GB / T 17657 (Physical Mechanics), GB / T 11718-2009 Medium Density Fiberboard (Particleboard), GB / T4897-2015 (Bond Strength of Wood-based Panels); Formaldehyde emission is measured by the desiccator method (mg / 100 g).

[0092] Statistics: MOR and TS 24 h is set to n=5; IB and IB after boiling are set to n=8; expressed as "mean ± standard deviation".

[0093] Density: Target 0.70 g·cm³ -3 Tolerances are controlled according to standards.

[0094] Table 4 Performance test results of particleboard prepared in the comparative example

[0095] The results showed that the comparative example had significantly higher formaldehyde release, lower bonding strength, and higher water absorption swelling rate compared to the example, demonstrating that the preparation method of this application effectively solved the formaldehyde pollution problem while maintaining the original formaldehyde levels.

[0096] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A formaldehyde-free adhesive based on biomass materials, characterized in that, The raw materials of the formaldehyde-free adhesive include the following components by weight: 50-80 parts biomass material, 5-20 parts phenol, 5-15 parts polyethylene glycol, 2-8 parts polyol, 1-5 parts citric acid, 2-10 parts glyoxal, and 3-8 parts crosslinking agent.

2. The formaldehyde-free adhesive as described in claim 1, characterized in that, The crosslinking agent includes polyvinyl alcohol and sodium dodecyl sulfate, and the mass ratio of polyvinyl alcohol to sodium dodecyl sulfate is 1:1-3:1; It may include: polyvinyl alcohol and tannic acid, and the mass ratio of polyvinyl alcohol to tannic acid is 2:1-3:1; The molecular weight range of the polyvinyl alcohol is 400-1700.

3. The formaldehyde-free adhesive as described in claim 1, characterized in that, The biomass material includes one or more of wood, corn, rice straw, reeds or bamboo; the polyol includes one or more of ethylene glycol, glycerol, butanediol, isophorone diol or 1,3-propanediol.

4. The formaldehyde-free adhesive as described in claim 1, characterized in that, The formaldehyde-free adhesive has a viscosity of 500-3000 mPa·s and a solid content of 80-100 wt%.

5. The formaldehyde-free adhesive as described in claim 1, characterized in that, The raw materials of the formaldehyde-free adhesive include the following components by weight: 50-80 parts biomass material, 5-12 parts phenol, 5-10 parts polyethylene glycol, 2-6 parts polyol, 1-3 parts citric acid, 3-8 parts glyoxal, and 3-6 parts crosslinking agent.

6. A method for preparing a formaldehyde-free adhesive based on biomass materials, characterized in that, Specifically, the following steps are included: (1) Mix phenol, polyethylene glycol and polyol, add biomass material and liquefy at 140-180℃ for 1-5 hours to obtain liquid biomass material; (2) Mix the liquid biomass material obtained in step (1) with citric acid and glyoxal, and stir at 60-80℃ for 0.5-2h to fully react; (3) Continue to add crosslinking agent, heat to 90-110℃, maintain for 1-3h, cool to room temperature, and obtain formaldehyde-free adhesive based on biomass materials.

7. The preparation method according to claim 6, characterized in that, The liquefaction process specifically includes: Phenol, polyethylene glycol, polyol and biomass material are mixed and stirred continuously under an inert gas atmosphere. The reaction is carried out at 140-180 ℃ for 1-5 h. After the reaction is completed, it is quickly cooled to room temperature and ethanol is mixed at a volume ratio of 4-6:

1. After stirring continuously for 20-40 min, the solid and liquid are separated by vacuum filtration and rotary evaporation. The resulting liquid is the liquid biomass material.

8. An application of a formaldehyde-free adhesive based on biomass materials, characterized in that, The formaldehyde-free adhesive based on biomass materials prepared by any one of the preparation methods of claims 6-7 or as described in any one of claims 1-5 is used to bond particleboard. When using it, the moisture content of the particleboard raw material is controlled at 8-10%; the solid content of the formaldehyde-free adhesive is 80-100%; and the amount of formaldehyde-free adhesive added is 8-12% of the dry particleboard mass.

9. The application as described in claim 8, characterized in that, When bonding particleboard with the formaldehyde-free adhesive, the formaldehyde-free adhesive is sprayed onto the surface of the particleboard material and hot-pressed. The hot-pressing temperature is 180-220℃ and the hot-pressing time is 3-10 minutes. The particleboard is laid in three oriented layers, with the top and bottom outer layers being the surface layer and the middle layer being the core layer. The particle size of the surface layer raw material is controlled at 1-3 mm, and the particle size of the core layer is controlled at 5-8 mm. It is pre-compressed under a pressure of 0.5-0.8 MPa for 20-40 s to form the particleboard.

10. The application as described in claim 9, characterized in that, During the hot pressing process, the temperature is raised to 180-200℃ within 60-90 seconds, held at 200-220℃ for 120-240 seconds, and then cooled to 130-150℃ before the pressure is released.

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