A lignin-based formaldehyde-free adhesive and its preparation method

Abstract

The present invention provides a lignin-based formaldehyde-free adhesive and a preparation method thereof. In the present invention, a turbid liquid is obtained by acid precipitation of black liquor, and the lignin concentrate obtained by centrifuging the turbid liquid can be directly used for synthesizing the formaldehyde-free adhesive without undergoing treatments such as spray drying or freeze drying, reducing the preparation cost; adding a diluent and a curing agent to the lignin concentrate can directly obtain the formaldehyde-free adhesive without modifying the lignin or synthesizing resins such as phenolic resin and urea-formaldehyde resin to obtain the adhesive, with a simple synthesis process and a simple structure, being suitable for large-scale production; for the adhesive of the present invention, the preparation raw materials do not contain formaldehyde or formaldehyde derivatives, and the adhesive obtained by this method has no risk of formaldehyde release, conforming to the concept of green chemistry; the adhesive obtained by this method has a stronger bonding strength and better performance compared with the adhesive synthesized from lignin resin.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and particularly relates to a lignin-based formaldehyde-free adhesive and a preparation method thereof. Background Art

[0002] For black liquor lignin, when using wood for papermaking, alkali recovery is carried out on the black liquor, and at the same time, lignin is burned to convert it into heat energy; mainly using wheat straw, rice straw, reed, and bagasse for papermaking, it is very difficult to carry out alkali recovery. Methods such as acid precipitation method, chemical oxidation method, electrodialysis method, spray drying method, vaporization power generation method, membrane treatment method, flocculation precipitation method, biological method, and emerging ultrasonic treatment method and photocatalytic oxidation method are used to treat it to obtain lignin, and a series of products such as adhesives, resins, and rubbers are synthesized with lignin or modified lignin.

[0003] Traditional black liquor lignin-based adhesives are all adhesives obtained by using functional groups such as hydroxyl groups contained in lignin or modified lignin to replace part of phenol and other substances to synthesize phenolic resins, urea-formaldehyde resins, epoxy resins, etc. However, since lignin is a three-dimensional network polymer with an aromatic structure, its cross-linked structure causes a large steric hindrance, making it difficult to break the bonds and connect other groups to synthesize resins. Moreover, the purification process of modified lignin has high energy consumption, the modification process has high costs, and the agents added during the synthesis of resins do not conform to the concept of green chemistry.

[0004] In view of this, a method for directly synthesizing a lignin-based formaldehyde-free adhesive with lignin is needed. Summary of the Invention

[0005] In view of this, the present invention provides a lignin-based formaldehyde-free adhesive and a preparation method thereof to solve the defects existing in the prior art.

[0006] In a first aspect, the present invention provides a lignin-based formaldehyde-free adhesive, including raw materials in parts by weight: 100 - 300 parts of lignin concentrate, 3.5 - 6 parts of diluent, 1 - 10 parts of curing agent, 1 - 30 parts of filler, and 1 - 10 parts of auxiliary agent.

[0007] Preferably, for the lignin-based formaldehyde-free adhesive, the diluent includes at least one of dioctyl phthalate, diglycidyl ether, and glycerol epoxy resin.

[0008] Preferably, for the lignin-based formaldehyde-free adhesive, the curing agent includes at least one of triethylenediamine, polyamide, lysine, and polyetheramine.

[0009] Preferably, for the lignin-based formaldehyde-free adhesive, the filler includes calcium carbonate and / or talcum powder.

[0010] Preferably, for the lignin-based formaldehyde-free adhesive, the auxiliary agent includes a flame retardant and / or a waterproof agent.

[0011] Preferably, for the lignin-based formaldehyde-free adhesive, the flame retardant includes nano magnesium hydroxide and / or nano aluminum hydroxide.

[0012] Preferably, for the lignin-based formaldehyde-free adhesive, the waterproofing agent is paraffin emulsion.

[0013] Preferably, for the lignin-based formaldehyde-free adhesive, the preparation method of the lignin concentrate includes the following steps:

[0014] Place plant fibers in a reaction vessel, then add water and an alkali-activated cementitious material catalyst, and react at a temperature of 30-130 °C for 1-3 h. After solid-liquid separation, black liquor and delignified plant fibers are obtained;

[0015] Adjust the pH of the black liquor to 2-3, let it stand and layer, to obtain the upper supernatant and the lower turbid liquid;

[0016] Centrifuge and concentrate the lower turbid liquid to obtain the lignin concentrate.

[0017] Preferably, for the lignin-based formaldehyde-free adhesive, the alkali-activated cementitious material catalyst is composed of blast furnace slag and / or steel slag, metakaolin and / or fly ash, foundry sand, water glass, water and hydrogen peroxide;

[0018] The water glass includes sodium water glass and / or potassium water glass;

[0019] The mass ratio of the alkali-activated cementitious material catalyst to the plant fibers is 1:(7-12);

[0020] The mass ratio of the plant fibers to the water is 1:(10-20);

[0021] The mass ratio of the blast furnace slag and / or steel slag, metakaolin and / or fly ash, foundry sand, water glass, water and hydrogen peroxide is (60-90):(10-40):(10-15):(70-100):(60-110):(3-6);

[0022] Adjust the pH of the black liquor to 2-3 using an acid solution;

[0023] Centrifuge the lower turbid liquid at 6000-10000 r / min for 2-4 min to obtain the lignin concentrate; the solid content in the lignin concentrate is 9-11%.

[0024] In a second aspect, the present invention also provides a preparation method of the lignin-based formaldehyde-free adhesive, including the following steps:

[0025] Add a diluent, a curing agent, a filler, and an auxiliary agent to the lignin concentrate, and stir to obtain the lignin-based formaldehyde-free adhesive.

[0026] The present invention has the following beneficial effects compared with the prior art:

[0027] The present invention directly synthesizes a lignin-based formaldehyde-free adhesive using lignin in black liquor. Compared with traditional synthetic adhesives, it has the following advantages: (1) By acidifying the black liquor to obtain a turbid liquid, and centrifuging the turbid liquid to obtain a lignin concentrate, which can be directly used for synthesizing the adhesive without processes such as spray drying or freeze drying, reducing the preparation cost; (2) Adding a diluent and a curing agent to the concentrated lignin black liquor can directly obtain the adhesive without modifying the lignin or synthesizing resins such as phenolic resin and urea formaldehyde resin to obtain the adhesive. The synthesis process is simple, the structure is simple, and it is suitable for large-scale production; (3) The adhesive of the present invention does not contain formaldehyde or formaldehyde derivatives in its preparation raw materials. The adhesive obtained by this method does not contain harmful substances such as formaldehyde, meeting the concept of green chemistry; (4) The adhesive obtained by this method has a stronger bonding strength and better performance compared with the adhesive synthesized from lignin resin. Brief Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is a comparison chart of the bonding strength of plywoods prepared with the adhesives prepared in Example 3 and Comparative Example 1 of the present invention. Detailed Embodiments

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0031] It should be noted that the description order of the following embodiments does not limit the preferred order of the embodiments. Additionally, in the description of this application, the term "comprising" means "including but not limited to". The various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present invention; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0032] An embodiment of this application provides a lignin-based formaldehyde-free adhesive, including raw materials in parts by weight: 100 - 300 parts of lignin concentrate, 3.5 - 6 parts of diluent, 1 - 10 parts of curing agent, 1 - 30 parts of filler, and 1 - 10 parts of additive.

[0033] In some embodiments, the diluent includes at least one of dioctyl phthalate, diglycidyl ether, and glycerol epoxy resin. Specifically, the diluent, also known as the solvent, mainly serves to reduce the viscosity of the adhesive, facilitating operation, and improving the wettability and fluidity of the adhesive.

[0034] In some embodiments, the curing agent includes at least one of triethylenediamine, polyamide, lysine, and polyetheramine. The curing agent is a component that promotes the curing of the bonding substance through chemical reactions, and its properties and dosage play an important role in the performance of the adhesive.

[0035] In some embodiments, the filler includes calcium carbonate and / or talcum powder. The filler generally does not undergo chemical reactions in the adhesive. It can increase the consistency of the adhesive, reduce the coefficient of thermal expansion, decrease shrinkage, and improve the impact resistance and mechanical strength.

[0036] In some embodiments, the additive includes a flame retardant and / or a waterproofing agent.

[0037] In some embodiments, the flame retardant includes nano magnesium hydroxide and / or nano aluminum hydroxide.

[0038] In some embodiments, the waterproofing agent is paraffin emulsion.

[0039] Specifically, the flame retardant is a functional additive that imparts flame retardancy to the adhesive; the waterproofing agent is paraffin emulsion, and the waterproofing agent is a functional additive that imparts water insolubility to the adhesive.

[0040] In some embodiments, a method for preparing lignin concentrate comprises the following steps:

[0041] S1. Place plant fibers in a reaction vessel, then add water and an alkali-activated cementitious material catalyst, and react at a temperature of 30 - 130 °C for 1 - 3 h. After solid-liquid separation, black liquor and delignified plant fibers are obtained;

[0042] S2. Adjust the pH of the black liquor to 2 - 3, let it stand for stratification, and obtain the upper supernatant and the lower turbid liquid;

[0043] S3. Centrifuge and concentrate the lower turbid liquid to obtain lignin concentrate.

[0044] Specifically, in the above embodiments, the black liquor is a concentrate of plant fiber black liquor; the lignin separated by acid precipitation of plant fiber black liquor and the mixture after concentration of the solution after acid precipitation, that is, the pH of the black liquor is adjusted to 2 - 3 with 50% sulfuric acid by mass concentration until lignin is precipitated; the solid weight content of the black liquor is 9 - 11%; the solution after separating lignin from the black liquor by acid precipitation only contains high-molecular-weight lignin and can be used as a raw material for adhesives.

[0045] In some embodiments, the alkali-activated cementitious material catalyst is composed of blast furnace slag and / or steel slag, metakaolin and / or fly ash, foundry sand, water glass, water, and hydrogen peroxide;

[0046] The water glass includes sodium water glass and / or potassium water glass;

[0047] The mass ratio of the alkali-activated cementitious material catalyst to plant fibers is 1:(7 - 12);

[0048] The mass ratio of plant fibers to water is 1:(10 - 20);

[0049] The mass ratio of blast furnace slag and / or steel slag, metakaolin and / or fly ash, foundry sand, water glass, water, and hydrogen peroxide is (60 - 90):(10 - 40):(10 - 15):(70 - 100):(60 - 110):(3 - 6).

[0050] Preferably, the alkali-activated cementitious material catalyst is composed of steel slag, metakaolin, fly ash, foundry sand, water glass, water, and hydrogen peroxide; the mass ratio of steel slag, metakaolin, fly ash, foundry sand, potassium water glass, water, and hydrogen peroxide is (65 - 90):(25 - 35):(10 - 15):(85 - 98):(60 - 102):(70 - 100):(3 - 5.5).

[0051] In some embodiments, the plant fibers include woody plant fibers or herbaceous plant fibers.

[0052] In some embodiments, the woody plant fibers include eucalyptus fibers or fir fibers.

[0053] In some embodiments, the herbaceous plant fibers include bagasse fibers or rice straw fibers.

[0054] In some embodiments, the modulus of the sodium silicate is 1 - 2.

[0055] In some embodiments, the pH of the black liquor is adjusted to 2 - 3 using an acid solution; specifically, the pH of the black liquor is adjusted to 2 - 3 using concentrated hydrochloric acid with a mass concentration of 30% - 50% or concentrated sulfuric acid with a mass concentration of 50%, allowed to stand for 1 - 2 h, layered, to obtain the upper supernatant and the lower turbid liquid, and the upper supernatant is removed to obtain the lower turbid liquid; the pH of the black liquor is adjusted to 2 - 3 until lignin precipitates. The solution of the black liquor after separating lignin by acid precipitation only contains high - molecular - weight lignin and can be used as a raw material for adhesives; the lower turbid liquid contains high - molecular - weight lignin and is used to prepare adhesives.

[0056] In some embodiments, the lower turbid liquid is centrifuged at 6000 - 10000 r / min for 2 - 4 min to obtain a lignin concentrate; the solid content (weight content) in the lignin concentrate is 9 - 11%.

[0057] Based on the same inventive concept, the present invention also provides a method for preparing the above - mentioned lignin - based formaldehyde - free adhesive, which includes the following steps: adding a diluent, a curing agent, a filler, and an auxiliary agent to the lignin concentrate, and stirring to obtain the lignin - based formaldehyde - free adhesive.

[0058] In some embodiments, a diluent, a curing agent, a filler, and an auxiliary agent are added to the lignin concentrate, and stirred at 20 - 25 °C for 5 - 10 min to obtain the lignin - based formaldehyde - free adhesive.

[0059] The present invention proposes a method in which a turbid liquid is obtained by acid precipitation of black liquor, and the turbid liquid is centrifuged to obtain a lignin concentrate that can be directly used for synthesizing a formaldehyde - free adhesive, and it is applied to board adhesives, showing excellent bonding strength. Moreover, this synthesis method does not require modification of lignin, nor does it require addition of harmful substances such as formaldehyde, conforms to the concept of green chemistry, and has a simple process, easy operation, low cost, effectively realizing the high - value utilization of black liquor lignin.

[0060] The preparation principle of the lignin-based formaldehyde-free adhesive of the present invention is as follows: the black liquor is acidified to obtain a turbid liquid, the turbid liquid is centrifuged to obtain a lignin concentrate, and the lignin in the lignin concentrate contains abundant functional group structures such as phenolic hydroxyl groups and alcoholic hydroxyl groups, which crosslink with the amino groups in the diluent and curing agent under hot pressing conditions. The filler increases the solid content of the adhesive. The van der Waals force and the intermolecular hydrogen bond interaction increase as the distance decreases, strengthening the intermolecular crosslinking. The inorganic flame retardant and waterproofing agent make the performance of the adhesive stronger.

[0061] In some embodiments, a diluent, a curing agent, a filler, and an auxiliary agent are added to the lignin concentrate, and stirred at 20-25 °C for 5-10 min to obtain a lignin-based formaldehyde-free adhesive.

[0062] The method for directly synthesizing a lignin-based formaldehyde-free adhesive using lignin in black liquor of the present invention has the following advantages compared with traditional synthetic adhesives: (1) by acidifying the black liquor to obtain a turbid liquid, and centrifuging the turbid liquid to obtain a lignin concentrate, which can be directly used for synthesizing an adhesive without undergoing treatments such as spray drying or freeze drying, reducing the preparation cost; (2) adding a diluent and a curing agent to the lignin concentrate can directly obtain an adhesive without modifying the lignin or synthesizing resins such as phenolic resin and urea resin to obtain an adhesive. The synthesis process is simple, the structure is simple, and it is suitable for large-scale production; (3) the adhesive of the present invention does not contain formaldehyde or formaldehyde derivatives in its preparation raw materials, and the adhesive obtained by this method does not contain harmful substances such as formaldehyde, meeting the concept of green chemistry; (4) the adhesive obtained by this method has stronger bonding strength and better performance compared with the adhesive synthesized from lignin resin.

[0063] The usage method of the lignin-based formaldehyde-free adhesive of the present invention is as follows: the lignin-based formaldehyde-free adhesive prepared by the present invention is applied at 80-200 g / m 2 scraped on poplar veneer to obtain three-layer plywood, hot pressed at 0.5-2 MPa and 110-150 °C for 8-15 min, left standing in a ventilated place for 48 h, then cut into specimens with a specified length of (100±1) mm and width of (25±1) mm according to the physical and chemical properties test methods for wood-based panels and decorative wood-based panels (GB / T 17657-2022). After cutting the length of the shear surface according to the surface board thickness, the length and width of the shear surface are accurately measured with a vernier caliper. After treating the specimens, the bonding strength of the specimens is measured with a universal testing machine. The bonding strength of the dry board specimens is 3-5 MPa, the bonding strength of the specimens impregnated with cold water at (20±3) °C is 2.4-3.6 MPa, the bonding strength of the specimens impregnated with hot water at (63±3) °C for 3 h is 1.4-2.8 MPa, and the bonding strength of the specimens after boiling water impregnation - drying - boiling water impregnation is 0.9-2.1 MPa.

[0064] The following further illustrates the lignin-based formaldehyde-free adhesive of the present application and its preparation method with specific embodiments. This part further explains the content of the present invention in combination with specific embodiments, but should not be construed as a limitation to the present invention. Unless otherwise specified, the technical means adopted in the embodiments are conventional means well-known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0065] Example 1

[0066] The embodiment of the present application provides a lignin-based formaldehyde-free adhesive, including the following raw materials in parts by weight: 150 parts of lignin concentrate, 3.5 parts of diluent, 1.8 parts of curing agent, 8 parts of filler, and 3 parts of auxiliary agent;

[0067] Among them, the diluent is dioctyl phthalate;

[0068] The curing agent is triethylenediamine;

[0069] The filler is calcium carbonate;

[0070] The auxiliary agent is paraffin emulsion, and the paraffin emulsion is purchased from Keim-additec Company, model: E-342 / 45;

[0071] The preparation method of the lignin concentrate includes the following steps:

[0072] S1. Place the plant fiber in a reaction vessel, then add water and an alkali-activated cementitious material catalyst, and react at a temperature of 90 °C for 2 h. After solid-liquid separation, black liquor and delignified plant fiber are obtained;

[0073] S2. Add HCl with a mass concentration of 40% to the black liquor to adjust the pH of the black liquor to 2.5, let it stand for 2 h, and layer it to obtain the upper supernatant and the lower turbid liquid. Skim off the supernatant and collect the lower turbid liquid;

[0074] S3. Centrifuge the lower turbid liquid in S2 at a centrifugation rate of 8000 r / min for 3 min to obtain the lignin concentrate; the solid content (weight content) of the lignin concentrate is 9.8%;

[0075] Among them, the alkali-activated cementitious material catalyst is obtained by mixing steel slag, metakaolin, fly ash, foundry sand, potassium silicate, water, and hydrogen peroxide in a mass ratio of 65:35:10:98:102:70:5.5;

[0076] In the step of placing the plant fiber in a reaction vessel and then adding water and an alkali-activated cementitious material catalyst, the mass ratio of the alkali-activated cementitious material catalyst to the plant fiber is 1:12, and the mass ratio of the plant fiber to water is 1:20;

[0077] The plant fiber used is eucalyptus fiber;

[0078] The modulus of the potassium silicate water glass used is 2.

[0079] The embodiment of the present application also provides a preparation method of the above lignin-based formaldehyde-free adhesive, including the following steps:

[0080] S1. Add 3.5 parts by weight of diluent, 1.8 parts by weight of curing agent, 8 parts by weight of filler, and 3 parts by weight of auxiliary agent to 150 parts by weight of lignin concentrate, stir at 25°C for 5 min to obtain a lignin-based formaldehyde-free adhesive.

[0081] Apply the lignin-based formaldehyde-free adhesive prepared in Example 1 at 150 g / m 2 Scrape it on poplar veneer to obtain a three-layer plywood, hot press it at 1 MPa and 130°C for 10 min, let it stand in a ventilated place for 48 h, then cut it into test pieces with a specified length of (100 ± 1) mm and width of (25 ± 1) mm according to the physical and chemical properties test methods for wood-based panels and decorated wood-based panels (GB / T 17657-2022). After cutting the length of the shear surface according to the surface board thickness, accurately measure the length and width of the shear surface with a vernier caliper. After treating the test pieces, measure the bonding strength of the test pieces with a universal testing machine. The bonding strength of the dry board test pieces is about 4.2 MPa, the bonding strength of the test pieces impregnated with cold water at (20 ± 3)°C is about 2.6 MPa, the bonding strength of the test pieces impregnated with hot water at (63 ± 3)°C for 3 h is about 2.3 MPa, and the bonding strength of the test pieces after being impregnated with boiling water - dried - impregnated with boiling water is about 1.4 MPa. At the same time, test the combustion grade of the test pieces according to GB8624-2012. Example 2

[0082] The embodiment of the present application provides a lignin-based formaldehyde-free adhesive, including the following raw materials in parts by weight: 160 parts of lignin concentrate, 4 parts of diluent, 2.3 parts of curing agent, 12 parts of filler, and 4 parts of auxiliary agent;

[0083] Among them, the diluent is diglycidyl ether;

[0084] The curing agent includes polyamide and lysine, and the mass ratio of polyamide to lysine is 1:1;

[0085] The filler is talcum powder;

[0086] The auxiliary agent is nano-aluminum hydroxide (average particle size is 50 nm);

[0087] The preparation method of the lignin concentrate includes the following steps:

[0088] S1. Place the plant fiber in a reaction vessel, then add water and an alkali-activated gelling material catalyst, react at a temperature of 130°C for 2 h, and after solid-liquid separation, obtain black liquor and delignified plant fiber;

[0089] S2. Add HCl with a mass concentration of 40% to the black liquor to adjust the pH of the black liquor to 3, let it stand for 1 h, separate the layers to obtain the upper supernatant and the lower turbid liquid, skim off the supernatant, and collect the lower turbid liquid;

[0090] S3. Centrifuge the lower turbid liquid in S2 at a centrifuge speed of 8000 r / min for 3 min to obtain a lignin concentrate; the solid content (weight content) of the lignin concentrate is 10.2%;

[0091] Among them, the alkali-activated cementitious material catalyst is obtained by mixing steel slag, metakaolin, fly ash, foundry sand, sodium silicate, water, and hydrogen peroxide in a mass ratio of 90:25:15:90:60:100:3;

[0092] In the step of placing the plant fiber in the reaction vessel and then adding water and the alkali-activated cementitious material catalyst, the mass ratio of the alkali-activated cementitious material catalyst to the plant fiber is 1:7, and the mass ratio of the plant fiber to water is 1:15;

[0093] The plant fiber used is eucalyptus fiber;

[0094] The modulus of the sodium silicate used is 1.8.

[0095] The embodiment of the present application also provides a preparation method of the above lignin-based formaldehyde-free adhesive, including the following steps:

[0096] S1. Add 4 parts by weight of diluent, 2.3 parts by weight of curing agent, 12 parts by weight of filler, and 4 parts by weight of auxiliary agent to 160 parts by weight of lignin concentrate, and stir at 25 °C for 5 min to obtain a lignin-based formaldehyde-free adhesive.

[0097] Apply the lignin-based formaldehyde-free adhesive prepared in Example 2 at 180 g / m 2 Scrape it on the poplar veneer to obtain a three-layer plywood, hot press it at 1 MPa and 130 °C for 10 min, let it stand in a ventilated place for 48 h, then cut it into test pieces with a specified length of (100 ± 1) mm and a width of (25 ± 1) mm according to the physical and chemical properties test method for wood-based panels and decorative wood-based panels (GB / T 17657-2022). After cutting the length of the shear surface according to the surface board thickness, accurately measure the length and width of the shear surface with a vernier caliper. After processing the test pieces, measure the bonding strength of the test pieces with a universal testing machine. The bonding strength of the dry board test pieces is about 4.4 MPa, the bonding strength of the test pieces impregnated with cold water at (20 ± 3) °C is about 2.8 MPa, the bonding strength of the test pieces impregnated with hot water at (63 ± 3) °C for 3 h is about 2.6 MPa, and the bonding strength of the test pieces after boiling water impregnation - drying - boiling water impregnation is about 1.5 MPa. At the same time, test the combustion grade of the test pieces according to GB8624-2012.

[0098] Example 3

[0099] An embodiment of the present application provides a lignin-based formaldehyde-free adhesive, which comprises the following raw materials in parts by weight: 200 parts of lignin concentrate, 6 parts of diluent, 4 parts of curing agent, 20 parts of filler, and 7 parts of auxiliary agent;

[0100] Among them, the diluent is glycerol epoxy resin;

[0101] The curing agent is polyetheramine;

[0102] The filler is calcium carbonate;

[0103] The auxiliary agent is nano magnesium hydroxide (average particle size is 50nm);

[0104] The preparation method of the lignin concentrate comprises the following steps:

[0105] S1. Place plant fibers in a reaction vessel, then add water and an alkali-activated cementitious material catalyst, and react at a temperature of 100°C for 2.5 h. After solid-liquid separation, black liquor and delignified plant fibers are obtained;

[0106] S2. Add HCl with a mass concentration of 40% to the black liquor to adjust the pH of the black liquor to 2.5, let it stand for 2 h, and layer it to obtain the upper supernatant and the lower turbid liquid. Skim off the supernatant and collect the lower turbid liquid;

[0107] S3. Centrifuge the lower turbid liquid in S2 at a centrifugation rate of 8000 r / min for 3 min to obtain the lignin concentrate; the solid content (weight content) of the lignin concentrate is 10.0%;

[0108] Among them, the alkali-activated cementitious material catalyst is obtained by mixing steel slag, metakaolin, fly ash, foundry sand, sodium silicate, water, and hydrogen peroxide with a mass ratio of 80:30:12:85:90:80:3;

[0109] In the step of placing plant fibers in a reaction vessel and then adding water and an alkali-activated cementitious material catalyst, the mass ratio of the alkali-activated cementitious material catalyst to plant fibers is 1:7, and the mass ratio of plant fibers to water is 1:10;

[0110] The plant fibers used are eucalyptus fibers;

[0111] The modulus of the sodium silicate used is 1.8.

[0112] An embodiment of the present application also provides a preparation method of the above-mentioned lignin-based formaldehyde-free adhesive, which comprises the following steps:

[0113] S1. Add 6 parts by weight of diluent, 4 parts by weight of curing agent, 20 parts by weight of filler, and 7 parts by weight of auxiliary agent to 200 parts by weight of lignin concentrate, and stir at 25 °C for 5 min to obtain a lignin-based formaldehyde-free adhesive.

[0114] Apply the lignin-based formaldehyde-free adhesive prepared in Example 3 at 200 g / m 2 Scrape it on poplar veneer to obtain a three-layer plywood. Hot press it at 1 MPa and 130 °C for 10 min, and let it stand in a ventilated place for 48 h. Then cut it into test pieces with a specified length of (100 ± 1) mm and width of (25 ± 1) mm according to the physical and chemical properties test methods for wood-based panels and veneered wood-based panels (GB / T 17657-2022). After cutting the length of the shear surface according to the surface board thickness, accurately measure the length and width of the shear surface with a vernier caliper. After treating the test pieces, measure the bonding strength of the test pieces with a universal testing machine. The bonding strength of the dry board test pieces is about 4.9 MPa, the bonding strength of the test pieces impregnated with cold water at (20 ± 3) °C is about 3.5 MPa, the bonding strength of the test pieces impregnated with hot water at (63 ± 3) °C for 3 h is about 2.5 MPa, and the bonding strength of the test pieces after boiling water impregnation - drying - boiling water impregnation is about 1.9 MPa. At the same time, test the combustion grade of the test pieces according to GB8624-2012.

[0115] Comparative Example 1

[0116] This comparative example provides a preparation method of an adhesive, including the following steps:

[0117] S1. Add commercial alkali lignin (AL) (purchased from Zibo Yinghe Chemical Co., Ltd., molecular weight 1000 - 10000) to water to prepare a lignin concentrate with a mass fraction of 10%;

[0118] S2. Add 6 parts by weight of diluent, 4 parts by weight of curing agent, 20 parts by weight of filler, and 7 parts by weight of auxiliary agent to 200 parts by weight of the lignin concentrate in S1, and stir at 25 °C for 5 min to obtain an adhesive;

[0119] Among them, the diluent is glycerol epoxy resin;

[0120] The curing agent is polyetheramine;

[0121] The filler is calcium carbonate.

[0122] Apply the adhesive prepared in Comparative Example 1 at 200 g / m 2It is scraped on poplar veneer to obtain three-layer plywood, hot-pressed at 1 MPa and 130 °C for 10 min, left standing in a ventilated place for 48 h, and then cut into specimens with a specified length of (100 ± 1) mm and a width of (25 ± 1) mm according to the physical and chemical properties test methods for wood-based panels and veneered wood-based panels (GB / T 17657-2022). After cutting the length of the shear surface according to the surface board thickness, the length and width of the shear surface are accurately measured with a vernier caliper. After processing the specimens, the bonding strength of the specimens is measured with a universal testing machine. The bonding strength of the dry board specimens is about 2.4 MPa, and the bonding strength of the specimens impregnated with cold water at (20 ± 3) °C is about 1 MPa.

[0123] The bonding strengths of the plywoods prepared with the lignin-based formaldehyde-free adhesives prepared in Examples 1 to 3 are shown in Table 1 below.

[0124] Table 1 - Bonding strengths of plywoods prepared with the lignin-based formaldehyde-free adhesives prepared in Examples 1 to 3

[0125]

[0126] As can be seen from Table 1, the lignin-based formaldehyde-free adhesive prepared in the present invention has a relatively high bonding strength, and still maintains a relatively high bonding strength after being impregnated with cold water, hot water, and boiling water, indicating that the adhesive prepared in the present invention has good water resistance. In addition, compared with Example 1 without a flame retardant, Examples 2 and 3 with a flame retardant added have a higher combustion performance grade, that is, they meet the Class A standard of the combustion performance of building materials and products in GB8624-2012.

[0127] The comparison of the bonding strengths of the plywoods prepared with the adhesives prepared in Example 3 and Comparative Example 1 is as Figure 1 shown.

[0128] Figure 1 In this Work, it represents the plywood prepared with the adhesive in Example 3, Figure 1 In AL, it represents the plywood prepared with the adhesive prepared in Comparative Example 1; Dry strength represents the dry board strength, and Wet strength represents the cold water impregnation strength.

[0129] As can be seen from Figure 1, all the specimens exceed the standard for the bonding strength of the board in GB / T 9846-2015 (≥0.7 MPa). The lignin-based formaldehyde-free adhesive prepared in the present invention has a relatively high bonding strength (dry board and wet board) compared with the adhesive prepared with commercial alkali lignin.

[0130] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A lignin-based formaldehyde-free adhesive, characterized in that, Comprising raw materials in parts by weight: 200 parts of lignin concentrate, 6 parts of diluent, 4 parts of curing agent, 20 parts of filler, 7 parts of auxiliary agent; Among them, the diluent is glycerol epoxy resin; The curing agent is polyetheramine; The filler is calcium carbonate; The auxiliary agent is nano magnesium hydroxide with an average particle size of 50 nm; The preparation method of the lignin concentrate includes the following steps: S1. Place plant fibers in a reaction vessel, then add water and an alkali-activated cementitious material catalyst, and react at a temperature of 100 °C for 2.5 h. After solid-liquid separation, black liquor and delignified plant fibers are obtained; S2. Add HCl with a mass concentration of 40% to the black liquor to adjust the pH of the black liquor to 2.5, let it stand for 2 h, layer, obtain the upper supernatant and the lower turbid liquid, skim off the supernatant, and collect the lower turbid liquid; S3. Centrifuge the lower turbid liquid in S2 at a centrifugation rate of 8000 r / min for 3 min to obtain the lignin concentrate; the solid content of the lignin concentrate is 10.0%; Among them, the alkali-activated cementitious material catalyst is obtained by mixing steel slag, metakaolin, fly ash, foundry sand, sodium silicate, water, and hydrogen peroxide in a mass ratio of 80:30:12:85:90:80:3; In the step of placing plant fibers in a reaction vessel and then adding water and an alkali-activated cementitious material catalyst, the mass ratio of the alkali-activated cementitious material catalyst to plant fibers is 1:7, and the mass ratio of plant fibers to water is 1:10; The plant fibers used are eucalyptus fibers; The modulus of the sodium silicate used is 1.8; Add 6 parts by weight of diluent, 4 parts by weight of curing agent, 20 parts by weight of filler, and 7 parts by weight of auxiliary agent to 200 parts by weight of lignin concentrate, and stir at 25 °C for 5 min to obtain a lignin-based formaldehyde-free adhesive.

2. A preparation method of the lignin-based formaldehyde-free adhesive as described in claim 1, characterized in that, Including the following steps: Add 6 parts by weight of diluent, 4 parts by weight of curing agent, 20 parts by weight of filler, and 7 parts by weight of auxiliary agent to 200 parts by weight of lignin concentrate, and stir at 25 °C for 5 min to obtain a lignin-based formaldehyde-free adhesive.

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