An aldehyde-free adhesive, its preparation method and application

Abstract

The present invention discloses a formaldehyde-free adhesive and its preparation method and application, belonging to the technical field of adhesive preparation. Calculated by weight parts, the formaldehyde-free adhesive is prepared from the following raw materials: 80 to 150 parts of modified lignin solution, 10 to 30 parts of polyurethane emulsion, 15 to 35 parts of curing agent, 6 to 12 parts of modified filler, and 5 to 15 parts of flame retardant. The formaldehyde-free adhesive provided by the present invention is formaldehyde-free and has high environmental protection performance; it has certain flame retardancy and excellent mechanical properties, and has good comprehensive performance. It is suitable for the preparation process of artificial boards and has certain application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of adhesive preparation, and particularly relates to a formaldehyde-free adhesive for wood-based panels, a preparation method thereof, and an application thereof. Background Art

[0002] Wood-based panels mainly include three categories: plywood, particleboard, and fiberboard. In the processing and manufacturing process of the above wood-based panels, adhesives are inevitably used. Taking particleboard as an example, it is usually made by processing wood processing residues, logging residues, small-diameter wood, or wood plant fiber raw materials into chips, and then pressing them with an adhesive.

[0003] The adhesives used in the processing of wood-based panels are mainly urea-formaldehyde glue, phenolic glue, and melamine-formaldehyde glue. The dosage of the above "three-formaldehyde glues" accounts for about 90% of the adhesives used in the wood industry. Urea-formaldehyde glue has the largest dosage because of its low price and excellent performance. However, its water resistance is poor, especially its boiling water resistance is very poor. Most of such plywood will automatically open in boiling water for two hours. Therefore, urea-formaldehyde glue is mainly used in indoor environments with low requirements for its water resistance and weather resistance, such as for the production of particleboard, fiberboard, and plywood. Phenolic glue is an adhesive with better performance than urea-formaldehyde glue. It has good boiling water resistance, but its price is relatively high. It is mainly used in outdoor environments, such as for the production of concrete plywood formwork, and partially for the impregnation of the bottom paper in high-pressure decorative laminates. Melamine-formaldehyde glue has excellent water resistance and heat resistance, but its price is relatively high.

[0004] With the increasing emphasis on environmental protection concepts, the formaldehyde content of adhesives used in wood-based panel production has received increasing attention. During the use of the above "three-formaldehyde glues", there are more or less releases of harmful substances such as formaldehyde. Therefore, new formaldehyde-free / low-formaldehyde adhesives have received attention. At present, there are two main categories of formaldehyde-free adhesives that have been developed more. One is isocyanate glue, and the other is modified biomass glue. When isocyanate adhesive is used for the preparation of particleboard, its advantage is that it can strongly bond the shredded particleboard with a relatively high moisture content together, and no harmful substances such as formaldehyde will be released during the use of the prepared particleboard. However, the disadvantage of isocyanate adhesive is that it has no initial tackiness, and processes such as adding tackifiers are required, the operation process is complex, and the cost also increases accordingly. Modified biomass adhesives are mostly starch-based adhesives and soybean protein-based adhesives used in industrial production. Such biomass adhesives have gradually entered the field of people's research. In the prior art, for example, patent document CN107033832A provides an idea for preparing a composite adhesive using cottonseed meal, and patent document CN109517576A provides an idea for preparing an adhesive using defatted soybean meal protein powder.

[0005] Lignin is the second most abundant biomass resource after cellulose. Industrial lignin often comes from industries such as papermaking and biorefining. Strengthening the reuse of lignin resources has both economic and environmental benefits. Therefore, it is of great significance to process lignin into adhesives for the preparation of wood-based panels. For example, patent document CN117821012A provides a method for preparing adhesives using black liquor lignin; the master's thesis (Xu Wenbiao. Research on the preparation of formaldehyde-free adhesives by laccase-activated cellulose ethanol lignin [D]. Beihua University, 2015.) reports the preparation of adhesives by laccase-activated lignin. However, the above-mentioned documents only focus on the resource utilization of lignin and do not pay attention to other properties potentially required during the use of the prepared adhesives in wood-based panels, such as flame retardancy and mechanical properties.

[0006] Therefore, the present invention aims to provide an aldehyde-free adhesive with excellent properties using lignin as a raw material. Summary of the Invention

[0007] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an aldehyde-free adhesive and its preparation method and application, which is aldehyde-free and has high environmental protection; has certain flame retardancy and excellent mechanical properties, and has good comprehensive performance.

[0008] To achieve the above purpose, the present invention adopts the following technical solutions:

[0009] First, an aldehyde-free adhesive is provided, which is prepared from the following raw materials in parts by weight: 80-150 parts of modified lignin solution, 10-30 parts of polyurethane emulsion, 15-35 parts of curing agent, 6-12 parts of modified filler, 5-15 parts of flame retardant;

[0010] Among them, the preparation of the flame retardant includes the following steps:

[0011] S11. Add montmorillonite to an ethanol solvent, stir and then slowly add concentrated sulfuric acid. After the addition is completed, heat treatment is carried out under slow stirring conditions. After the treatment is completed, the ethanol solvent is completely evaporated, and then it is washed and dried to obtain pre-modified montmorillonite;

[0012] S12. Prepare an aqueous solution of poly(diallyldimethylammonium chloride) and set it aside; then add the pre-modified montmorillonite obtained in step S11 to the aqueous solution of poly(diallyldimethylammonium chloride), and stir under heating conditions; after the treatment is completed, it is centrifuged, filtered and dried to obtain modified montmorillonite;

[0013] S13. Add talc powder to water to obtain a talc powder suspension and set it aside; then add the modified montmorillonite obtained in step S12 to the talc powder suspension, stir, and then centrifuge, wash and dry to obtain the flame retardant.

[0014] In some preferred technical solutions, in step S11, the mass ratio of montmorillonite, ethanol, and concentrated sulfuric acid is 1:4 to 8:0.04 to 0.08;

[0015] The temperature of the heat treatment is 25 to 35 °C, and the treatment time is 0.5 to 4 h.

[0016] In some preferred technical solutions, in step S12, the concentration of the aqueous solution of polydiallyldimethylammonium chloride is 1.2 to 2 g / L;

[0017] The mass ratio of polydiallyldimethylammonium chloride to pre-modified montmorillonite is 0.8 to 1.5:1;

[0018] The heating temperature is 25 to 35 °C, and the stirring treatment time is 0.5 to 4 h.

[0019] In some preferred technical solutions, in step S13, the concentration of the talc powder suspension is 0.8 to 1.5 g / L;

[0020] The mass ratio of talc powder to modified montmorillonite is 0.6 to 0.8:1;

[0021] The stirring treatment temperature is 25 to 35 °C, and the treatment time is 0.5 to 2 h.

[0022] In some preferred technical solutions, the preparation of the modified lignin solution includes the following steps:

[0023] Prepare a sodium hydroxide solution and a glyoxal solution for later use; then, add straw lignin to the sodium hydroxide solution under rapid stirring, stir evenly, and then slowly add the glyoxal solution and adjust the pH value of the system to 11.5 to 12.5, and then carry out the treatment under heating conditions; after the treatment is completed, the modified lignin solution is obtained;

[0024] Among them, the concentration of the sodium hydroxide solution is 25 to 35 wt%, and the concentration of the glyoxal solution is 35 to 45 wt%;

[0025] The dosage ratio of glyoxal to straw lignin is 1:2 to 4;

[0026] The heating treatment temperature is 55 to 70 °C, and the treatment time is 2 to 8 h.

[0027] In some preferred technical solutions, the preparation of the modified filler includes the following steps:

[0028] S21. First, prepare an alumina suspension; then, add KH550 to the obtained suspension, and then carry out a heat treatment under stirring conditions; after the treatment is completed, filter and dry, and then carry out high-energy ball milling treatment to obtain material I;

[0029] S22. Add silica into the DMF solvent, stir evenly, then add KH550 and succinic anhydride, and perform heat treatment under stirring; after the treatment is completed, perform centrifugation, washing, and drying treatments to obtain Material II;

[0030] S23. Add the Material I obtained in step S21 and the Material II obtained in step S22 into deionized water respectively, stir for treatment, and after the treatment is completed, perform filtration, washing, and drying treatments to obtain the modified filler.

[0031] In some preferred technical solutions, in step S21, the concentration of the alumina suspension is 12 - 18 wt%, the mass ratio of alumina to KH550 is 100:5 - 15, the heat treatment temperature is 65 - 75 °C, and the treatment time is 0.5 - 4 h;

[0032] In step S22, the mass ratio of silica, DMF, KH550, and succinic anhydride is 1:20 - 30:5 - 10:2.5 - 4, the heat treatment temperature is 25 - 35 °C, and the treatment time is 2 - 6 h;

[0033] In step S23, the mass ratio of Material I to Material II is 1:0.5 - 2; the stirring treatment temperature is 25 - 35 °C, and the treatment time is 0.5 - 4 h.

[0034] In some preferred technical solutions, the curing agent is selected from one or two of epichlorohydrin and triethylenediamine.

[0035] Secondly, the present invention also provides a preparation method of the above - mentioned formaldehyde - free adhesive, including the following steps:

[0036] Under the condition of maintaining stirring, add the polyurethane emulsion into the modified lignin solution; after stirring evenly, add the curing agent, modified filler, and flame retardant, and stir evenly again to obtain the formaldehyde - free adhesive.

[0037] Finally, what the present invention hopes to protect is the application of the above - mentioned formaldehyde - free adhesive in many processing fields including the preparation of wood - based panels.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The formaldehyde - free adhesive provided by the present invention uses the modified lignin solution as the main raw material, supplemented by the use of a part of the polyurethane emulsion, ensuring the formaldehyde - free property of the adhesive.

[0040] The formaldehyde - free adhesive provided by the present invention uses an industrial lignin by - product as the raw material for the modified lignin solution, and specifically conducts hydroxyethylation modification. The purpose is to introduce hydroxyl groups, improving its compatibility with flame retardants and fillers. At the same time, the reaction activity of the lignin after hydroxyethylation modification is enhanced, which is beneficial to the compound use of the polyurethane emulsion system. It should be particularly emphasized that compared with the commonly used formaldehyde modification, glyoxal, the modifying substance used in the present invention, has low toxicity.

[0041] The formaldehyde - free adhesive provided by the present invention endows the adhesive with certain flame - retardant properties by introducing the use of flame retardants. Common halogen - containing flame retardants have certain toxicity. The present invention selects common montmorillonite and talc powder as the core materials of the flame retardant. Montmorillonite and talc powder both have certain flame - retardant effects. However, there are problems such as dispersibility during their use, and the direct use of them separately cannot fully exert their effects. Therefore, the present invention selects to conduct certain modification on them. Specifically, the present invention first uses concentrated sulfuric acid to pre - modify montmorillonite to remove impurities and preliminarily dredge pores; then, uses polydiallyldimethylammonium chloride to conduct secondary treatment on montmorillonite. On the one hand, it is beneficial for the intercalation treatment of montmorillonite, further improving its subsequent composite ability; on the other hand, it is beneficial to introduce positive charges and amine groups on the surface or in the pores of montmorillonite. After the above - mentioned treatment of montmorillonite, it is beneficial for talc powder (rich in hydroxyl groups and negatively charged on the surface) to form a compound system with the modified montmorillonite in various forms of action such as hydrogen bonding and positive - negative charge combination, improving the dispersibility of talc powder, reducing its agglomeration performance, and facilitating the exertion of its flame - retardant effect.

[0042] The formaldehyde - free adhesive provided by the present invention aims to improve the comprehensive properties such as the mechanical properties of the adhesive by introducing modified fillers. Silicon dioxide and alumina are two relatively common fillers, which can enhance toughness and wear resistance. Alumina is harder and silicon dioxide is relatively softer. The combined use of the two with different hardnesses can exert the greatest effect. In the present invention, corresponding modifications are also made for their use. Specifically: for alumina, it is modified with KH550 and then subjected to high - energy ball milling. On the one hand, it ensures the dispersibility of alumina, and on the other hand, through high - energy ball milling, it improves the surface activity of alumina, facilitating subsequent compounding with silicon dioxide and improving its compatibility in the modified lignin and polyurethane emulsion; for silicon dioxide, carboxylation treatment is adopted. On the one hand, it is beneficial for the compound combination with the modified alumina, and on the other hand, it is beneficial for improving the compatibility with the modified lignin solution rich in hydroxyl groups. The two can form hydrogen bonding in the form of carboxyl - hydroxyl groups, ensuring the uniformity of dispersion. Obviously, after the treated silicon dioxide and alumina are simply blended, they can be fully dispersed and densely filled in the adhesive system, ensuring the performance of the adhesive.

[0043] In summary, the adhesive provided by the present invention is formaldehyde-free and has excellent comprehensive properties, and is suitable for the preparation of artificial boards, and can be specifically used in the production and manufacturing of artificial boards such as plywood and particleboard. Detailed Embodiments

[0044] The embodiments of the present invention are described in detail below. All the embodiments are exemplary and are intended to explain the present invention and should not be construed as a limitation to the present invention.

[0045] In the embodiments of the present invention, the straw lignin is corn straw lignin, purchased externally, and its main physical and chemical properties are: lignin content about 90%, moisture 3.4%, ash content 4.5%, and pH value 4.6.

[0046] In the present invention, the particle size of the alumina is about 100 mesh.

[0047] The high-energy ball mill used in the present invention can be a common device on the market, such as a ball mill with model TV400-6.

[0048] The concentration of the concentrated sulfuric acid used in the present invention is 96%.

[0049] The polyurethane emulsion used in the present invention can be a common emulsion type. For example, the polyurethane emulsion used in the present invention has a brand number of PU-106 and is purchased from Hefei Dibang Nano Technology Co., Ltd.

[0050] In the present invention, the molecular weight of the poly(diallyldimethylammonium chloride) is 10,000 - 20,000, and it is produced by Sigma-Aldrich Company in the United States.

[0051] The remaining silica, ethanol, talcum powder, etc. used are all purchased from the market.

[0052] Example 1

[0053] A formaldehyde-free adhesive is prepared from the following raw materials by weight: 100 g of modified lignin solution, 20 g of polyurethane emulsion, 15 g of curing agent, 10 g of modified filler, and 10 g of flame retardant;

[0054] Among them, the preparation of the flame retardant includes the following steps:

[0055] S11. Add montmorillonite to an ethanol solvent, stir and then slowly add concentrated sulfuric acid. After the addition is completed, keep stirring slowly and treat at 30°C for 2 h. After the treatment is completed, completely evaporate the ethanol solvent (by heating treatment), and then perform washing and drying treatments to obtain pre-modified montmorillonite; among them, the mass ratio of montmorillonite, ethanol, and concentrated sulfuric acid is 1:5:0.05;

[0056] S12. Prepare an aqueous solution of poly(diallyldimethylammonium chloride) with a concentration of 1.5 g / L for later use. Subsequently, add the pre-modified montmorillonite obtained in step S11 to the aqueous solution of poly(diallyldimethylammonium chloride) (the mass ratio of poly(diallyldimethylammonium chloride) to pre-modified montmorillonite is 0.85:1), and stir at 30 °C for 1.5 h. After the treatment, perform centrifugation, filtration, and drying to obtain the modified montmorillonite.

[0057] S13. Add talc powder to water to prepare a talc powder suspension with a concentration of 1 g / L for later use. Subsequently, add the modified montmorillonite obtained in step S12 to the talc powder suspension (the mass ratio of talc powder to modified montmorillonite is 0.7:1), stir at 25 °C for 1 h, and then perform centrifugation, washing, and drying to obtain the flame retardant.

[0058] Among them, the preparation of the modified lignin solution includes the following steps:

[0059] Prepare a sodium hydroxide solution and a glyoxal solution for later use. Subsequently, add straw lignin to the sodium hydroxide solution under rapid stirring, stir evenly, then slowly add the glyoxal solution and adjust the pH value of the system to 12, and then perform treatment under heating conditions. After the treatment is completed, the modified lignin solution is obtained.

[0060] Among them, the concentration of the sodium hydroxide solution is 30 wt%, and the concentration of the glyoxal solution is 36 wt%.

[0061] The dosage ratio of glyoxal to straw lignin is 1:3.

[0062] The heating treatment temperature is 60 °C, and the treatment time is 4 h.

[0063] Among them, the preparation of the modified filler includes the following steps:

[0064] S21. First, prepare a 15 wt% alumina suspension; then, add KH550 to the obtained suspension (the mass ratio of alumina to KH550 is 100:9), and then treat at 70 °C for 2 h under stirring conditions. After the treatment is completed, perform filtration and drying, and then perform high-energy ball milling treatment (35 min) to obtain material I.

[0065] S22. Add silica to DMF solvent, stir evenly, then add KH550 and succinic anhydride, and treat at 25 °C for 4 h under stirring conditions. After the treatment is completed, perform centrifugation, washing, and drying to obtain material II. Among them, the mass ratio of silica, DMF, KH550, and succinic anhydride is 1:25:6:3.

[0066] S23. Add the material I obtained in step S21 and the material II obtained in step S22 to deionized water according to a mass ratio of 1:1, and perform stirring treatment (25°C, 2 h). After the treatment, perform filtration, washing, and drying treatments to obtain the modified filler.

[0067] In this embodiment, a method for preparing the above-mentioned formaldehyde-free adhesive is also provided, including the following steps: Under the condition of maintaining stirring, add a polyurethane emulsion to the modified lignin solution; after stirring evenly, add epichlorohydrin, the modified filler, and the flame retardant, and stir evenly again to obtain the formaldehyde-free adhesive.

[0068] Example 2

[0069] A formaldehyde-free adhesive is prepared from the following raw materials by weight: 100 g of modified lignin solution, 22 g of polyurethane emulsion, 16 g of curing agent, 9 g of modified filler, and 11 g of flame retardant.

[0070] Among them, the preparation of the flame retardant includes the following steps:

[0071] S11. Add montmorillonite to an ethanol solvent, stir, and then slowly add concentrated sulfuric acid. After the addition is completed, maintain slow stirring conditions and treat at 30°C for 2.5 h. After the treatment, completely evaporate the ethanol solvent (perform heat treatment), and then perform washing and drying treatments to obtain pre-modified montmorillonite; among them, the mass ratio of montmorillonite, ethanol, and concentrated sulfuric acid is 1:5:0.05.

[0072] S12. Prepare an aqueous solution of polydiallyldimethylammonium chloride with a concentration of 1.4 g / L and set it aside; then add the pre-modified montmorillonite obtained in step S11 to the aqueous solution of polydiallyldimethylammonium chloride (the mass ratio of polydiallyldimethylammonium chloride to pre-modified montmorillonite is 0.85:1), and stir at 30°C for 2 h; after the treatment, perform centrifugation, filtration, and drying treatments to obtain modified montmorillonite.

[0073] S13. Add talc powder to water to prepare a talc powder suspension with a concentration of 0.9 g / L and set it aside; then add the modified montmorillonite obtained in step S12 to the talc powder suspension (the mass ratio of talc powder to modified montmorillonite is 0.75:1), stir at 25°C for 1.5 h, and then perform centrifugation, washing, and drying treatments to obtain the flame retardant.

[0074] Among them, the preparation of the modified lignin solution includes the following steps:

[0075] Prepare sodium hydroxide solution and glyoxal solution for later use. Subsequently, add straw lignin to the sodium hydroxide solution under rapid stirring. After stirring evenly, slowly add the glyoxal solution and adjust the pH value of the system to 11.8. Then, carry out the treatment under heating conditions. After the treatment is completed, the modified lignin solution is obtained.

[0076] Among them, the concentration of the sodium hydroxide solution is 30 wt%, and the concentration of the glyoxal solution is 36 wt%.

[0077] The dosage ratio of glyoxal to straw lignin is 1:3.

[0078] The heating treatment temperature is 60 °C, and the treatment time is 4 h.

[0079] Among them, the preparation of the modified filler includes the following steps:

[0080] S21. First, prepare a 15 wt% alumina suspension. Then, add KH550 to the obtained suspension (the mass ratio of alumina to KH550 is 100:9). Subsequently, carry out the treatment at 70 °C for 2 h under stirring conditions. After the treatment is completed, carry out filtration and drying treatments, and then carry out high-energy ball milling treatment (35 min) to obtain Material I.

[0081] S22. Add silica to the DMF solvent, stir evenly, then add KH550 and succinic anhydride, and carry out the treatment at 25 °C for 4 h under stirring conditions. After the treatment is completed, carry out centrifugation, washing, and drying treatments to obtain Material II. Among them, the mass ratio of silica, DMF, KH550, and succinic anhydride is 1:25:6:3.

[0082] S23. Add Material I obtained in step S21 and Material II obtained in step S22 to deionized water according to a mass ratio of 1:1, and carry out stirring treatment (25 °C, 2 h). After the treatment is completed, carry out filtration, washing, and drying treatments to obtain the modified filler.

[0083] In this example, a preparation method of the above-mentioned formaldehyde-free adhesive is also provided, including the following steps: Under stirring conditions, add polyurethane emulsion to the modified lignin solution. After stirring evenly, add epichlorohydrin, modified filler, and flame retardant, and stir evenly again to obtain the formaldehyde-free adhesive.

[0084] Example 3

[0085] A formaldehyde-free adhesive is prepared from the following raw materials by weight: 100 g of modified lignin solution, 18 g of polyurethane emulsion, 15 g of curing agent, 11 g of modified filler, and 9 g of flame retardant.

[0086] Among them, the preparation of the flame retardant includes the following steps:

[0087] S11. Add montmorillonite to an ethanol solvent, stir, and then slowly add concentrated sulfuric acid. After the addition is complete, maintain slow stirring and treat at 30 °C for 2 h. After the treatment is completed, completely evaporate the ethanol solvent (by heat treatment), and then perform washing and drying treatments to obtain pre-modified montmorillonite. Among them, the mass ratio of montmorillonite, ethanol, and concentrated sulfuric acid is 1:5:0.05;

[0088] S12. Prepare an aqueous solution of poly(diallyldimethylammonium chloride) with a concentration of 1.4 g / L for standby. Then add the pre-modified montmorillonite obtained in step S11 to the aqueous solution of poly(diallyldimethylammonium chloride) (the mass ratio of poly(diallyldimethylammonium chloride) to pre-modified montmorillonite is 0.85:1), and stir at 30 °C for 1.5 h. After the treatment is completed, perform centrifugation, filtration, and drying treatments to obtain modified montmorillonite;

[0089] S13. Add talcum powder to water to prepare a talcum powder suspension with a concentration of 1 g / L for standby. Then, add the modified montmorillonite obtained in step S12 to the talcum powder suspension (the mass ratio of talcum powder to modified montmorillonite is 0.75:1), stir at 25 °C for 1.5 h, and then perform centrifugation, washing, and drying treatments to obtain the flame retardant.

[0090] Among them, the preparation of the modified lignin solution includes the following steps:

[0091] Prepare a sodium hydroxide solution and a glyoxal solution for standby. Then, add straw lignin to the sodium hydroxide solution under rapid stirring, stir evenly, slowly add the glyoxal solution, and adjust the pH value of the system to 12. Then perform treatment under heating conditions. After the treatment is completed, obtain the modified lignin solution;

[0092] Among them, the concentration of the sodium hydroxide solution is 30 wt%, and the concentration of the glyoxal solution is 36 wt%;

[0093] The dosage ratio of glyoxal to straw lignin is 1:3;

[0094] The heating treatment temperature is 60 °C, and the treatment time is 4 h.

[0095] Among them, the preparation of the modified filler includes the following steps:

[0096] S21. First, prepare a 15 wt% alumina suspension; then, add KH550 to the obtained suspension (the mass ratio of alumina to KH550 is 100:9), and then treat at 70 °C for 2 h under stirring conditions. After the treatment is completed, perform filtration and drying treatments, and then perform high-energy ball milling treatment (35 min) to obtain material I;

[0097] S22. Add silica to the DMF solvent. After stirring evenly, add KH550 and succinic anhydride, and process under stirring conditions at 25 °C for 4 h. After the treatment is completed, perform centrifugation, washing, and drying treatments to obtain Material II. Among them, the mass ratio of silica, DMF, KH550, and succinic anhydride is 1:25:6:3.

[0098] S23. According to the mass ratio of 1:1, add the Material I obtained in step S21 and the Material II obtained in step S22 to deionized water respectively, and perform stirring treatment (25 °C, 2 h). After the treatment is completed, perform filtration, washing, and drying treatments to obtain the modified filler.

[0099] In this embodiment, a preparation method of the above-mentioned formaldehyde-free glue is also provided, including the following steps: Under the condition of maintaining stirring, add polyurethane emulsion to the modified lignin solution. After stirring evenly, add epichlorohydrin, modified filler, and flame retardant, and stir evenly again to obtain the formaldehyde-free adhesive.

[0100] Comparative Example 1

[0101] Compared with Example 1, this comparative example cancels step S11. Specifically, this comparative example provides a formaldehyde-free adhesive, which is prepared from the following raw materials by weight: 100 g of modified lignin solution, 20 g of polyurethane emulsion, 15 g of curing agent, 10 g of modified filler, and 10 g of flame retardant.

[0102] Among them, the preparation of the flame retardant includes the following steps:

[0103] S11. Prepare an aqueous solution of polydiallyldimethylammonium chloride with a concentration of 1.5 g / L for standby. Subsequently, add montmorillonite to the aqueous solution of polydiallyldimethylammonium chloride (the mass ratio of polydiallyldimethylammonium chloride to montmorillonite is 0.85:1), and perform stirring treatment at 30 °C for 1.5 h. After the treatment is completed, perform centrifugation, filtration, and drying treatments to obtain modified montmorillonite.

[0104] S12. Add talc powder to water to prepare a talc powder suspension with a concentration of 1 g / L for standby. Subsequently, add the modified montmorillonite obtained in step S11 to the talc powder suspension (the mass ratio of talc powder to modified montmorillonite is 0.7:1), perform stirring treatment at 25 °C for 1 h, and then perform centrifugation, washing, and drying treatments to obtain the flame retardant.

[0105] Among them, the preparation of the modified lignin solution includes the following steps:

[0106] Prepare sodium hydroxide solution and glyoxal solution for later use. Subsequently, add straw lignin to the sodium hydroxide solution under rapid stirring. After stirring evenly, slowly add the glyoxal solution and adjust the pH value of the system to 12. Then, carry out the treatment under heating conditions. After the treatment is completed, the modified lignin solution is obtained.

[0107] Among them, the concentration of the sodium hydroxide solution is 30 wt%, and the concentration of the glyoxal solution is 36 wt%.

[0108] The dosage ratio of glyoxal to straw lignin is 1:3.

[0109] The heating treatment temperature is 60 °C, and the treatment time is 4 h.

[0110] Among them, the preparation of the modified filler includes the following steps:

[0111] S21: First, prepare a 15 wt% alumina suspension. Then, add KH550 to the obtained suspension (the mass ratio of alumina to KH550 is 100:9). Subsequently, carry out the treatment at 70 °C for 2 h under stirring conditions. After the treatment is completed, carry out filtration and drying treatments, and then carry out high-energy ball milling treatment (35 min) to obtain Material I.

[0112] S22: Add silica to the DMF solvent, stir evenly, then add KH550 and succinic anhydride, and carry out the treatment at 25 °C for 4 h under stirring conditions. After the treatment is completed, carry out centrifugation, washing, and drying treatments to obtain Material II. Among them, the mass ratio of silica, DMF, KH550, and succinic anhydride is 1:25:6:3.

[0113] S23: Add Material I obtained in step S21 and Material II obtained in step S22 to deionized water according to a mass ratio of 1:1, and carry out stirring treatment (25 °C, 2 h). After the treatment is completed, carry out filtration, washing, and drying treatments to obtain the modified filler.

[0114] In this comparative example, a preparation method of the above-mentioned formaldehyde-free glue is also provided, including the following steps: Under stirring conditions, add polyurethane emulsion to the modified lignin solution. After stirring evenly, add epichlorohydrin, modified filler, and flame retardant, and stir evenly again to obtain the formaldehyde-free adhesive.

[0115] Comparative Example 2

[0116] Compared with Example 1, this comparative example cancels step S12. Specifically, this comparative example provides a formaldehyde-free adhesive, which is prepared from the following raw materials by weight: 100 g of modified lignin solution, 20 g of polyurethane emulsion, 15 g of curing agent, 10 g of modified filler, and 10 g of flame retardant.

[0117] Among them, the preparation of the flame retardant includes the following steps:

[0118] S11. Add montmorillonite to an ethanol solvent, stir, and then slowly add concentrated sulfuric acid. After the addition is complete, maintain slow stirring conditions and treat at 30 °C for 2 h. After the treatment is completed, completely evaporate the ethanol solvent (by heat treatment), and then perform washing and drying treatments to obtain pre-modified montmorillonite; wherein, the mass ratio of montmorillonite, ethanol, and concentrated sulfuric acid is 1:5:0.05;

[0119] S13. Add talcum powder to water to prepare a talcum powder suspension with a concentration of 1 g / L for standby; subsequently, add the pre-modified montmorillonite obtained in step S11 to the talcum powder suspension (the mass ratio of talcum powder to pre-modified montmorillonite is 0.7:1). After stirring at 25 °C for 1 h, perform centrifugation, washing, and drying treatments to obtain the flame retardant.

[0120] Among them, the preparation of the modified lignin solution includes the following steps:

[0121] Prepare a sodium hydroxide solution and a glyoxal solution for standby; subsequently, add straw lignin to the sodium hydroxide solution under rapid stirring conditions. After stirring evenly, slowly add the glyoxal solution and adjust the pH value of the system to 12, and then perform treatment under heating conditions; after the treatment is completed, the modified lignin solution is obtained;

[0122] Among them, the concentration of the sodium hydroxide solution is 30 wt%, and the concentration of the glyoxal solution is 36 wt%;

[0123] The dosage ratio of glyoxal to straw lignin is 1:3;

[0124] The heating treatment temperature is 60 °C, and the treatment time is 4 h.

[0125] Among them, the preparation of the modified filler includes the following steps:

[0126] S21. First, prepare a 15 wt% alumina suspension; then, add KH550 to the obtained suspension (the mass ratio of alumina to KH550 is 100:9), and then treat at 70 °C for 2 h under stirring conditions; after the treatment is completed, perform filtration and drying treatments, and then perform high-energy ball milling treatment (35 min) to obtain material I;

[0127] S22. Add silica to a DMF solvent, stir evenly, then add KH550 and succinic anhydride, and treat at 25 °C for 4 h under stirring conditions; after the treatment is completed, perform centrifugation, washing, and drying treatments to obtain material II; wherein, the mass ratio of silica, DMF, KH550, and succinic anhydride is 1:25:6:3;

[0128] S23. Add the material Ⅰ obtained in step S21 and the material Ⅱ obtained in step S22 to deionized water according to the mass ratio of 1:1, and stir (at 25 °C for 2 h). After the treatment, filter, wash, and dry to obtain the modified filler.

[0129] In this comparative example, a method for preparing the above-mentioned formaldehyde-free adhesive is also provided, which includes the following steps: Under stirring conditions, add polyurethane emulsion to the modified lignin solution; after stirring evenly, add epichlorohydrin, modified filler, and flame retardant, and stir evenly again to obtain the formaldehyde-free adhesive.

[0130] Comparative Example 3

[0131] Compared with Example 1, this comparative example cancels step S21. Specifically, this comparative example provides a formaldehyde-free adhesive, which is prepared from the following raw materials by weight: 100 g of modified lignin solution, 20 g of polyurethane emulsion, 15 g of curing agent, 10 g of modified filler, and 10 g of flame retardant.

[0132] Among them, the preparation of the flame retardant includes the following steps:

[0133] S11. Add montmorillonite to an ethanol solvent, stir and then slowly add concentrated sulfuric acid. After the addition is complete, keep stirring slowly and treat at 30 °C for 2 h. After the treatment, completely evaporate the ethanol solvent (by heating treatment), and then wash and dry to obtain pre-modified montmorillonite; among them, the mass ratio of montmorillonite, ethanol, and concentrated sulfuric acid is 1:5:0.05.

[0134] S12. Prepare an aqueous solution of poly(diallyldimethylammonium chloride) with a concentration of 1.5 g / L for standby; then add the pre-modified montmorillonite obtained in step S11 to the aqueous solution of poly(diallyldimethylammonium chloride) (the mass ratio of poly(diallyldimethylammonium chloride) to pre-modified montmorillonite is 0.85:1), and stir at 30 °C for 1.5 h; after the treatment, centrifuge, filter, and dry to obtain modified montmorillonite.

[0135] S13. Add talc powder to water to prepare a talc powder suspension with a concentration of 1 g / L for standby; then add the modified montmorillonite obtained in step S12 to the talc powder suspension (the mass ratio of talc powder to modified montmorillonite is 0.7:1), stir at 25 °C for 1 h, and then centrifuge, wash, and dry to obtain the flame retardant.

[0136] Among them, the preparation of the modified lignin solution includes the following steps:

[0137] Prepare sodium hydroxide solution and glyoxal solution for later use. Subsequently, add straw lignin to the sodium hydroxide solution under rapid stirring. After stirring evenly, slowly add the glyoxal solution and adjust the pH value of the system to 12, and then carry out the treatment under heating conditions. After the treatment is completed, the modified lignin solution is obtained.

[0138] Among them, the concentration of the sodium hydroxide solution is 30 wt%, and the concentration of the glyoxal solution is 36 wt%.

[0139] The dosage ratio of glyoxal to straw lignin is 1:3.

[0140] The heating treatment temperature is 60 °C, and the treatment time is 4 h.

[0141] Among them, the preparation of the modified filler includes the following steps:

[0142] S21: Add silicon dioxide to the DMF solvent, stir evenly, then add KH550 and succinic anhydride, and carry out the treatment at 25 °C under stirring conditions for 4 h. After the treatment is completed, carry out centrifugation, washing, and drying treatments to obtain Material II. Among them, the mass ratio of silicon dioxide, DMF, KH550, and succinic anhydride is 1:25:6:3.

[0143] S22: Add alumina (the dosage is the same as in Example 1) and Material II obtained in Step S21 to deionized water respectively, stir and treat (at 25 °C for 2 h). After the treatment is completed, carry out filtration, washing, and drying treatments to obtain the modified filler.

[0144] In this comparative example, a preparation method of the above-mentioned formaldehyde-free glue is also provided, including the following steps: Under the condition of maintaining stirring, add polyurethane emulsion to the modified lignin solution. After stirring evenly, add epichlorohydrin, modified filler, and flame retardant, and stir evenly again to obtain the formaldehyde-free adhesive.

[0145] Comparative Example 4

[0146] Compared with Example 1, this comparative example cancels Step S22. Specifically, this comparative example provides a formaldehyde-free adhesive, which is prepared from the following raw materials by weight: 100 g of modified lignin solution, 20 g of polyurethane emulsion, 15 g of curing agent, 10 g of modified filler, and 10 g of flame retardant.

[0147] Among them, the preparation of the flame retardant includes the following steps:

[0148] S11. Add montmorillonite to ethanol solvent, stir, and then slowly add concentrated sulfuric acid. After the addition is complete, maintain slow stirring and treat at 30 °C for 2 h. After the treatment is completed, completely evaporate the ethanol solvent (by heating treatment), and then carry out washing and drying treatments to obtain pre-modified montmorillonite; wherein, the mass ratio of montmorillonite, ethanol, and concentrated sulfuric acid is 1:5:0.05;

[0149] S12. Prepare an aqueous solution of polydiallyldimethylammonium chloride with a concentration of 1.5 g / L for standby; then add the pre-modified montmorillonite obtained in step S11 to the aqueous solution of polydiallyldimethylammonium chloride (the mass ratio of polydiallyldimethylammonium chloride to pre-modified montmorillonite is 0.85:1), and stir at 30 °C for 1.5 h; after the treatment is completed, carry out centrifugation, filtration, and drying treatments to obtain modified montmorillonite;

[0150] S13. Add talcum powder to water to prepare a talcum powder suspension with a concentration of 1 g / L for standby; then, add the modified montmorillonite obtained in step S12 to the talcum powder suspension (the mass ratio of talcum powder to modified montmorillonite is 0.7:1), stir at 25 °C for 1 h, and then carry out centrifugation, washing, and drying treatments to obtain the flame retardant.

[0151] Among them, the preparation of the modified lignin solution includes the following steps:

[0152] Prepare sodium hydroxide solution and glyoxal solution for standby; then, add straw lignin to the sodium hydroxide solution under rapid stirring, stir evenly, slowly add the glyoxal solution, and adjust the pH value of the system to 12, and then carry out treatment under heating conditions; after the treatment is completed, the modified lignin solution is obtained;

[0153] Among them, the concentration of the sodium hydroxide solution is 30 wt%, and the concentration of the glyoxal solution is 36 wt%;

[0154] The dosage ratio of glyoxal to straw lignin is 1:3;

[0155] The heating treatment temperature is 60 °C, and the treatment time is 4 h.

[0156] Among them, the preparation of the modified filler includes the following steps:

[0157] S21. First, prepare a 15 wt% alumina suspension; then, add KH550 to the obtained suspension (the mass ratio of alumina to KH550 is 100:9), and then treat at 70 °C for 2 h under stirring conditions; after the treatment is completed, carry out filtration and drying treatments, and then carry out high-energy ball milling treatment (35 min) to obtain material I;

[0158] S22. Add the obtained Material I in Step S22 and silica into deionized water respectively, and perform stirring treatment (25°C, 2 h). After the treatment, perform filtration, washing, and drying treatments to obtain the modified filler.

[0159] In this comparative example, a preparation method of the above-mentioned formaldehyde-free glue is also provided, including the following steps: Under the condition of maintaining stirring, add polyurethane emulsion to the modified lignin solution; after stirring evenly, add epichlorohydrin, modified filler, and flame retardant, and stir evenly again to obtain the formaldehyde-free adhesive.

[0160] Apply the adhesives prepared in Example 1 and Comparative Examples 1-4 on poplar veneer (270 mm × 270 mm × 1.6 mm) at a double-sided glue spreading amount of 400 g / m 2 , and perform hot pressing (hot pressing temperature 135°C, hot pressing pressure 1.3 MPa, time 6 min) to obtain three-layer plywood. Then, perform performance tests on the above three-layer plywood as follows:

[0161] Refer to GB / T17657-2022 for the test of bonding strength. Among them, after cold water immersion (25°C, 24 h) or hot water immersion (63°C, 3 h) treatment, dry thoroughly at 73°C, and then perform the test of bonding strength.

[0162] Refer to GB / T14656-2009 to perform the flame retardancy test on the above three-layer plywood.

[0163] Refer to GB / T17657-2022 to perform the water resistance test on the above three-layer plywood, and record the 24 h water absorption rate result.

[0164] Refer to GB / T17657-2022 to detect the formaldehyde release amount of the above three-layer plywood.

[0165] The test results are shown in Table 1.

[0166] Table 1

[0167]

[0168]

[0169] As can be seen from Table 1, the plywood prepared with the formaldehyde-free adhesive provided by the present invention has good mechanical properties, good flame retardancy, good water resistance, and excellent comprehensive performance.

[0170] The foregoing has shown and described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and what is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. An aldehyde-free adhesive, characterized in that, It is prepared from the following raw materials in parts by weight: 80 to 150 parts of modified lignin solution, 10 to 30 parts of polyurethane emulsion, 15 to 35 parts of curing agent, 6 to 12 parts of modified filler, and 5 to 15 parts of flame retardant; Among them, the preparation of the flame retardant includes the following steps: S11. Add montmorillonite to an ethanol solvent, stir, and then slowly add concentrated sulfuric acid. After the addition is completed, heat under slow stirring conditions. After the treatment is completed, completely evaporate the ethanol solvent, and then perform washing and drying treatments to obtain pre-modified montmorillonite; S12. Prepare an aqueous solution of poly(diallyldimethylammonium chloride) for standby; then add the pre-modified montmorillonite obtained in step S11 to the aqueous solution of poly(diallyldimethylammonium chloride), and stir under heating conditions; after the treatment is completed, perform centrifugation, filtration, and drying treatments to obtain modified montmorillonite; S13. Add talcum powder to water to prepare a talcum powder suspension for standby; then add the modified montmorillonite obtained in step S12 to the talcum powder suspension, stir, and then perform centrifugation, washing, and drying treatments to obtain the flame retardant; Among them, the preparation of the modified filler includes the following steps: S21. First, prepare an alumina suspension; then, add KH550 to the obtained suspension, and then heat under stirring conditions; after the treatment is completed, perform filtration and drying treatments, and then perform high-energy ball milling treatment to obtain material I; S22. Add silicon dioxide to a DMF solvent, stir evenly, then add KH550 and succinic anhydride, and heat under stirring conditions; after the treatment is completed, perform centrifugation, washing, and drying treatments to obtain material II; S23. Add the material I obtained in step S21 and the material II obtained in step S22 to deionized water respectively, stir, and after the treatment is completed, perform filtration, washing, and drying treatments to obtain the modified filler.

2. The non-formaldehyde adhesive according to claim 1, characterized in that, In step S11, the mass ratio of montmorillonite, ethanol, and concentrated sulfuric acid is 1:4 to 8:0.04 to 0.08; The heating treatment temperature is 25 to 35 °C, and the treatment time is 0.5 to 4 h.

3. The non-formaldehyde adhesive according to claim 1, characterized in that, In step S12, the concentration of the aqueous solution of poly(diallyldimethylammonium chloride) is 1.2 to 2 g / L; The mass ratio of poly(diallyldimethylammonium chloride) to pre-modified montmorillonite is 0.8 to 1.5:1; The heating temperature is 25 to 35 °C, and the stirring treatment time is 0.5 to 4 h.

4. The non-formaldehyde adhesive according to claim 1, characterized in that, In step S13, the concentration of the talcum powder suspension is 0.8 to 1.5 g / L; The mass ratio of talcum powder to modified montmorillonite is 0.6 to 0.8:1; The stirring treatment temperature is 25 to 35 °C, and the treatment time is 0.5 to 2 h.

5. The non-formaldehyde adhesive according to claim 1, characterized in that, The preparation of the modified lignin solution includes the following steps: Prepare a sodium hydroxide solution and a glyoxal solution for standby; then, add straw lignin to the sodium hydroxide solution under rapid stirring conditions, stir evenly, then slowly add the glyoxal solution and adjust the pH value of the system to 11.5 to 12.5, and then perform treatment under heating conditions; after the treatment is completed, obtain the modified lignin solution; Among them, the concentration of the sodium hydroxide solution is 25 to 35 wt%, and the concentration of the glyoxal solution is 35 to 45 wt%; The dosage ratio of glyoxal to straw lignin is 1:2 - 4; The heat treatment temperature is 55 - 70 °C, and the treatment time is 2 - 8 h.

6. The non-formaldehyde adhesive according to claim 1, wherein In step S21, the concentration of the alumina suspension is 12 - 18 wt%, the mass ratio of alumina to KH550 is 100:5 - 15, the heat treatment temperature is 65 - 75 °C, and the treatment time is 0.5 - 4 h; In step S22, the mass ratio of silica, DMF, KH550 and succinic anhydride is 1:20 - 30:5 - 10:2.5 - 4, the heat treatment temperature is 25 - 35 °C, and the treatment time is 2 - 6 h; In step S23, the mass ratio of material I to material II is 1:0.5 - 2; the stirring treatment temperature is 25 - 35 °C, and the treatment time is 0.5 - 4 h.

7. The non-formaldehyde adhesive according to claim 1, characterized in that The curing agent is selected from one or two of epichlorohydrin and triethylenediamine.

8. A method for preparing the formaldehyde-free adhesive according to any one of claims 1 to 7, characterized in that, It includes the following steps: Under the condition of keeping stirring, add the polyurethane emulsion to the modified lignin solution; after stirring evenly, add the curing agent, modified filler and flame retardant, and stir evenly again to obtain the formaldehyde-free adhesive.

9. The application of the formaldehyde-free adhesive according to any one of claims 1 - 7 in the preparation of wood-based panels.

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