Adhesive for formaldehyde-free plywood and preparation method of plywood

Abstract

The invention discloses an adhesive for formaldehyde-free plywood and a preparation method of the plywood. The adhesive is prepared from the following raw materials in parts by weight: 12-18 parts of crosslinked starch, 5-10 parts of modified lignin, 3-5 parts of rosin, 2.5-4.5 parts of epoxy resin, 2-4 parts of polyurethane resin, 3.5-5.5 parts of polyvinyl alcohol, 0.3-0.6 part of nano silicon dioxide, 0.6-1 part of a silane coupling agent and 55-62 parts of water, and the sum of the raw materials in parts by weight is 100. The adhesive disclosed by the invention has good bonding strength to veneers, enables the plywood to have good water resistance, also has good elastic modulus and static bending intensity of the plywood, and also realizes the purpose of formaldehyde-free release of the adhesive.

Description

Technical Field

[0001] The invention relates to an adhesive for formaldehyde-free plywood and a method for preparing the plywood, belonging to the technical field of adhesives. Background Art

[0002] Plywood is an engineered, man-made board made from layers of veneer (thin wood veneers) glued together in a vertical, cross-laminated process. The adhesive's properties are crucial to its quality and performance during production. Therefore, the adhesive must possess strong adhesion, excellent water resistance, and be environmentally friendly to ensure plywood's adaptability to a wide range of conditions and environments.

[0003] In the plywood production process, "trialdehyde glue" is a commonly used adhesive, namely urea-formaldehyde glue, phenol-formaldehyde glue, and melamine-formaldehyde glue. As public awareness of environmental protection gradually increases and the concept of green, environmentally friendly, and healthy development continues to deepen, the development of environmentally friendly, formaldehyde-free adhesives is of great significance to the healthy development of plywood.

[0004] Biomass-based adhesives, made from natural polymers such as starch, soy protein, and lignin, are environmentally friendly. Traditional biomass-based adhesives, due to their large number of hydrophilic groups and inability to form an effective cross-linked network, have relatively weak bond strength and water resistance, making them difficult to meet the adhesive requirements of plywood production. Summary of the Invention

[0005] In order to address at least one problem existing in the above-mentioned prior art, the present invention provides an adhesive for formaldehyde-free plywood and a method for preparing plywood. The adhesive has good bonding strength to veneers, and makes the plywood have good water resistance. It also takes into account that the plywood has good elastic modulus and static bending strength, and also achieves the goal of no formaldehyde release of the adhesive.

[0006] In order to achieve the above-mentioned object, the present invention adopts the following technical scheme: a formaldehyde-free plywood adhesive, comprising the following raw materials and their weight parts, and calculated based on the sum of the weight parts of the raw materials being 100 parts: 12-18 parts of cross-linked starch, 5-10 parts of modified lignin, 3-5 parts of rosin, 2.5-4.5 parts of epoxy resin, 2-4 parts of polyurethane resin, 3.5-5.5 parts of polyvinyl alcohol, 0.3-0.6 parts of nano-silica, 0.6-1 part of silane coupling agent and 55-62 parts of water.

[0007] Preferably, the weight percentage of the polyvinyl alcohol to the weight of the cross-linked starch is 21-36%.

[0008] Preferably, the mass ratio of the epoxy resin to the polyurethane resin is 1.2 to 2.2:1.

[0009] Preferably, the weight percentage of the nano-silicon dioxide to the weight of the cross-linked starch is 1.7-4%.

[0010] Preferably, the cross-linked starch is obtained by cross-linking starch with isocyanate.

[0011] Preferably, the preparation process of the cross-linked starch is as follows: first dissolving isocyanate in ethyl acetate solvent, then adding starch and stirring to mix evenly, then heating to reflux, cross-linking reaction for 5 to 6 hours, then removing the solvent, and vacuum drying to obtain cross-linked starch.

[0012] Preferably, the mass ratio of the starch to the isocyanate and ethyl acetate is 1.45-1.65:1:5.

[0013] Preferably, the starch is sago starch, potato starch, tapioca starch, waxy corn starch, etc., preferably sago starch; the isocyanate is diphenylmethane diisocyanate, toluene diisocyanate, etc., preferably diphenylmethane diisocyanate.

[0014] Preferably, the modified lignin is obtained by modifying lignin with maleic anhydride.

[0015] Preferably, the preparation process of the modified lignin is as follows: first, lignin is dissolved in deionized water, then a 2 mol / L hydrochloric acid solution is added for precipitation, centrifuged and filtered, washed with water, and then vacuum dried to obtain pretreated lignin, and then the pretreated lignin, maleic anhydride, and 4-dimethylaminopyridine are dissolved in N,N-dimethylformamide solvent, heated to 85-95°C for reaction for 8-10 hours, and then the solvent is removed and vacuum dried to obtain modified lignin.

[0016] Preferably, the mass ratio of the lignin to maleic anhydride and N,N-dimethylformamide is 1.15-1.35:1:4, and the amount of 4-dimethylaminopyridine is 0.1% of the amount of maleic anhydride.

[0017] Preferably, the silane coupling agent is one of silane coupling agent KH550, silane coupling agent KH560 or silane coupling agent KH570.

[0018] Preferably, the particle size of the nano-silica is 50 to 100 nm.

[0019] The present invention also provides a method for preparing an adhesive for formaldehyde-free plywood, the specific steps of which are as follows:

[0020] Sa1, grind the cross-linked starch, modified lignin, rosin, epoxy resin, and polyurethane resin through a 500-600 mesh sieve respectively and set aside;

[0021] Sa2. Mix nano-silica with an appropriate amount of water and homogenize under high pressure to form a uniformly dispersed nano-silica suspension; the amount of water added is 15 times that of nano-silica;

[0022] Sa3. Dissolve polyvinyl alcohol in the remaining water under stirring. After heating, add the ground rosin, epoxy resin, and polyurethane resin in sequence. After dissolving and dispersing them evenly, add the ground cross-linked starch and modified lignin in sequence. Dissolve and disperse them evenly to form a uniformly dispersed mixture.

[0023] Sa4. Add the nano-silica suspension and silane coupling agent to the mixture under stirring, mix well, and obtain a formaldehyde-free plywood adhesive.

[0024] Preferably, in step Sa2, the high-pressure homogenization conditions are: a pressure of 40 to 50 MPa, and a time of 5 to 10 s.

[0025] Preferably, in steps Sa3 and Sa4, the stirring speed is 300-400 rpm.

[0026] Preferably, in step Sa3, the temperature is heated to 75-85°C.

[0027] The present invention also provides a method for preparing formaldehyde-free plywood using the above adhesive, the specific steps of which are as follows:

[0028] Sb1, applying glue on the surface of the wood veneer using the above adhesive;

[0029] Sb2, assembling the odd-numbered layers of glued veneers so that the grain directions of adjacent veneers are perpendicular to each other to obtain slabs;

[0030] Sb3. The slab is first subjected to cold pressing treatment and then to hot pressing treatment to obtain formaldehyde-free plywood.

[0031] Preferably, the amount of glue applied in step Sb1 is 90 to 110 g / m 2 .

[0032] Preferably, the cold pressing conditions of step Sb3 are: pressure of 0.6-0.8 MPa, and time of 20-40 min.

[0033] Preferably, the hot pressing conditions of step Sb3 are: temperature of 165-195° C., pressure of 1.1-1.3 MPa, and time of 1.3-1.8 min / mm.

[0034] Beneficial effects of the present invention: The formaldehyde-free plywood adhesive of the present invention is based on cross-linked starch and modified lignin, and is synergistically prepared with rosin, epoxy resin, polyurethane resin, polyvinyl alcohol, nano-silica, and silane coupling agent. This not only achieves the goal of formaldehyde-free release of the adhesive, but also improves the bonding strength of the adhesive to the wood veneer and enhances the water resistance of the adhesive. The formaldehyde-free plywood adhesive of the present invention has a sizing amount of less than 100 g / m2 on the veneer. 2 Compared with traditional phenolic and urea-formaldehyde adhesives, the amount of glue applied is significantly reduced, the plywood preparation operation is easy to control, it is applicable to most woods and hot pressing equipment, and has good industrialization prospects; the formaldehyde-free plywood adhesive of the present invention has the advantages of high bonding strength, good water resistance, and green environmental protection, so that the bonding strength of the adhesive to the veneer, the elastic modulus and the static bending strength of the plywood are all higher than the national standards, and it has broad market prospects in the field of plywood manufacturing. DETAILED DESCRIPTION

[0035] The following is a clear and complete description of the technical solutions in the implementation of the present invention. The embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer.

[0036] The veneer in the present invention refers to a wood material with a thickness of approximately 0.5 to 3.5 mm obtained by peeling or slicing logs, and is used to make plywood. The veneer is selected from poplar, eucalyptus, pine, miscellaneous wood, fir, birch, basswood, crabapple, safflower, maple, elm, oak, or rubberwood, and has a moisture content of 7 to 15 wt%. In some specific embodiments, the prepared adhesive can be applied to the surface of the wood veneer using a roller coater.

[0037] The starch of the present invention is sago starch, potato starch, cassava starch, waxy corn starch, etc., preferably sago starch; the isocyanate is diphenylmethane diisocyanate, toluene diisocyanate, etc., preferably diphenylmethane diisocyanate.

[0038] Example 1

[0039] A method for preparing an adhesive for formaldehyde-free plywood comprises the following steps:

[0040] Step 1, preparation of cross-linked starch: first dissolve diphenylmethane diisocyanate in ethyl acetate solvent, then add sago starch and stir to mix evenly, the mass ratio of sago starch to diphenylmethane diisocyanate and ethyl acetate is 1.55:1:5, then heat to reflux, cross-link reaction for 6 hours, then remove the solvent and vacuum dry to obtain cross-linked starch;

[0041] Step 2, preparation of modified lignin: first dissolve lignin in deionized water, then add 2 mol / L hydrochloric acid solution for precipitation, centrifuge and filter, wash with water, and then vacuum dry to obtain pretreated lignin, then dissolve the pretreated lignin, maleic anhydride, and 4-dimethylaminopyridine in N,N-dimethylformamide solvent, the mass ratio of lignin to maleic anhydride and N,N-dimethylformamide is 1.25:1:4, the amount of 4-dimethylaminopyridine is 0.1% of the amount of maleic anhydride, heat to 90°C for reaction for 9 hours, then remove the solvent, and vacuum dry to obtain modified lignin.

[0042] Step 3, grinding the cross-linked starch, modified lignin, rosin, epoxy resin, and polyurethane resin through a 500-600 mesh sieve respectively for later use;

[0043] Step 4: 0.6 parts by weight of nano-silicon dioxide with a particle size of 50 to 100 nm and 9 parts by weight of water were mixed, and high-pressure homogenization was performed at a pressure of 45 MPa for 8 seconds to form a uniformly dispersed nano-silicon dioxide suspension;

[0044] Step 5: Dissolve polyvinyl alcohol in 51.5 parts by weight of water under stirring at a speed of 350 rpm, heat to 80° C., and then add 4 parts by weight of the ground rosin, 4 parts by weight of epoxy resin, and 2 parts by weight of polyurethane resin in sequence. After dissolving and dispersing them uniformly, add 18 parts by weight of the ground cross-linked starch and 5.1 parts by weight of modified lignin in sequence, dissolve and disperse them uniformly, and form a uniformly dispersed mixture.

[0045] Step 6: Add the nano-silica suspension and 0.6 parts by weight of a silane coupling agent to the mixture while stirring at a rotation speed of 350 rpm, and mix well to obtain a formaldehyde-free plywood adhesive.

[0046] The preparation method of formaldehyde-free plywood is as follows:

[0047] Step (1): Use the above adhesive to apply glue on the surface of the wood veneer, with the glue amount being 100g / m 2 ;

[0048] Step (2), assembling the odd number of glued veneers so that the wood grain directions of adjacent veneers are perpendicular to each other to obtain slabs;

[0049] Step (3): cold-press the slab at a pressure of 0.7 MPa for 30 min, and then hot-press at a temperature of 180° C. and a pressure of 1.2 MPa for 1.5 min / mm to obtain formaldehyde-free plywood.

[0050] Example 2

[0051] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 1 in that: the weight parts of the raw materials added are: 15 parts of cross-linked starch, 8 parts of modified lignin, 4.5 parts of rosin, 3.5 parts of epoxy resin, 3 parts of polyurethane resin, 4.5 parts of polyvinyl alcohol, 0.45 parts of nano-silicon dioxide with a particle size of 50 to 100 nm, 0.8 parts of a silane coupling agent, and 60.25 parts of water; the amount of water added to the nano-silicon dioxide suspension is 6.75 parts; otherwise, the preparation method is identical to that of the formaldehyde-free plywood adhesive in Example 1;

[0052] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0053] Example 3

[0054] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 1 in that: the weight of the raw materials added are: 14 parts of cross-linked starch, 9 parts of modified lignin, 3.5 parts of rosin, 4.5 parts of epoxy resin, 2 parts of polyurethane resin, 4.5 parts of polyvinyl alcohol, 0.45 parts of nano-silica with a particle size of 50 to 100 nm, 0.6 parts of a silane coupling agent, and 61.45 parts of water; the amount of water added to the nano-silica suspension is 6.75 parts; otherwise, the preparation method is identical to that of the formaldehyde-free plywood adhesive in Example 1;

[0055] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0056] Example 4

[0057] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 1 in that: the weight of the raw materials added are: 12 parts of cross-linked starch, 10 parts of modified lignin, 5 parts of rosin, 4 parts of epoxy resin, 2.5 parts of polyurethane resin, 3.5 parts of polyvinyl alcohol, 0.6 parts of nano-silicon dioxide with a particle size of 50 to 100 nm, 1 part of a silane coupling agent, and 61.4 parts of water; the amount of water added to the nano-silicon dioxide suspension is 9 parts; otherwise, the preparation method is identical to that of the formaldehyde-free plywood adhesive in Example 1;

[0058] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0059] Example 5

[0060] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 1 in that: the raw materials added are as follows: 12 parts by weight of cross-linked starch, 10 parts of modified lignin, 4.6 parts of rosin, 2.5 parts of epoxy resin, 4 parts of polyurethane resin, 3.8 parts of polyvinyl alcohol, 0.5 parts of nano-silica with a particle size of 50 to 100 nm, 1 part of a silane coupling agent, and 61.6 parts of water; the amount of water added to the nano-silica suspension is 7.5 parts; otherwise, the preparation method is identical to that of the formaldehyde-free plywood adhesive in Example 1;

[0061] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0062] Example 6

[0063] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 1 in that: the weight parts of the raw materials added are: 17 parts of cross-linked starch, 8.15 parts of modified lignin, 3.5 parts of rosin, 4.5 parts of epoxy resin, 2.2 parts of polyurethane resin, 3.5 parts of polyvinyl alcohol, 0.3 parts of nano-silica with a particle size of 50 to 100 nm, 0.75 parts of a silane coupling agent, and 60.1 parts of water; the amount of water added to the nano-silica suspension is 4.5 parts; otherwise, the preparation method is identical to that of the formaldehyde-free plywood adhesive in Example 1;

[0064] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0065] Example 7

[0066] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 1 in that: the weight parts of the raw materials added are: 15 parts of cross-linked starch, 6.1 parts of modified lignin, 3.95 parts of rosin, 4 parts of epoxy resin, 2 parts of polyurethane resin, 5.5 parts of polyvinyl alcohol, 0.45 parts of nano-silicon dioxide with a particle size of 50 to 100 nm, 1 part of a silane coupling agent, and 60 parts of water; the amount of water added to the nano-silicon dioxide suspension is 6.75 parts; otherwise, the preparation method is identical to that of the formaldehyde-free plywood adhesive in Example 1;

[0067] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0068] Example 8

[0069] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 1 in that: the weight parts of the raw materials added are: 18 parts of cross-linked starch, 10 parts of modified lignin, 4 parts of rosin, 4 parts of epoxy resin, 2.5 parts of polyurethane resin, 5 parts of polyvinyl alcohol, 0.5 parts of nano-silicon dioxide with a particle size of 50 to 100 nm, 1 part of a silane coupling agent, and 55 parts of water; the amount of water added to the nano-silicon dioxide suspension is 7.5 parts; otherwise, the preparation method is identical to that of the formaldehyde-free plywood adhesive in Example 1;

[0070] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0071] Example 9

[0072] A method for preparing an adhesive for formaldehyde-free plywood comprises the following steps:

[0073] Step 1, preparation of cross-linked starch:

[0074] First, diphenylmethane diisocyanate was dissolved in ethyl acetate solvent, and then sago starch was added and stirred to mix evenly. The mass ratio of sago starch to diphenylmethane diisocyanate and ethyl acetate was 1.45:1:5. The mixture was then heated to reflux and cross-linked for 6 hours. The solvent was then removed and the mixture was dried in vacuo to obtain cross-linked starch.

[0075] Step 2, preparation of modified lignin: first dissolve lignin in deionized water, then add 2 mol / L hydrochloric acid solution for precipitation, centrifuge and filter, wash with water, and then vacuum dry to obtain pretreated lignin, then dissolve the pretreated lignin, maleic anhydride, and 4-dimethylaminopyridine in N,N-dimethylformamide solvent, the mass ratio of lignin to maleic anhydride and N,N-dimethylformamide is 1.15:1:4, the amount of 4-dimethylaminopyridine is 0.1% of the amount of maleic anhydride, heat to 85°C for reaction for 10 hours, then remove the solvent, and vacuum dry to obtain modified lignin.

[0076] Step 3, grinding the cross-linked starch, modified lignin, rosin, epoxy resin, and polyurethane resin through a 500-600 mesh sieve respectively for later use;

[0077] Step 4: 0.6 parts by weight of nano-silicon dioxide with a particle size of 50 to 100 nm and 9 parts by weight of water were mixed, and high-pressure homogenization was performed at a pressure of 40 MPa for 10 seconds to form a uniformly dispersed nano-silicon dioxide suspension;

[0078] Step 5: Dissolve polyvinyl alcohol in 51.55 parts by weight of water under stirring at a speed of 300 rpm, heat to 75°C, and then add 3.5 parts by weight of the ground rosin, 4.5 parts by weight of epoxy resin, and 3.3 parts by weight of polyurethane resin in sequence. After dissolving and dispersing them evenly, add 14 parts by weight of the ground cross-linked starch and 9 parts by weight of modified lignin in sequence, dissolve and disperse them evenly, and form a uniformly dispersed mixture.

[0079] Step 6: Add the nano-silica suspension and 0.6 parts by weight of a silane coupling agent to the mixture while stirring at a rotation speed of 300 rpm, and mix well to obtain a formaldehyde-free plywood adhesive.

[0080] The preparation method of formaldehyde-free plywood is as follows:

[0081] Step (1): Use the above adhesive to apply glue on the surface of the wood veneer, with the glue amount being 90g / m 2 ;

[0082] Step (2), assembling the odd number of glued veneers so that the wood grain directions of adjacent veneers are perpendicular to each other to obtain slabs;

[0083] Step (3): cold-press the slab at a pressure of 0.6 MPa for 40 min, and then hot-press at a temperature of 165° C. and a pressure of 1.3 MPa for 1.3 min / mm to obtain formaldehyde-free plywood.

[0084] Example 10

[0085] A method for preparing an adhesive for formaldehyde-free plywood comprises the following steps:

[0086] Step 1, preparation of cross-linked starch: first dissolve diphenylmethane diisocyanate in ethyl acetate solvent, then add sago starch and stir to mix evenly, the mass ratio of sago starch to diphenylmethane diisocyanate and ethyl acetate is 1.65:1:5, then heat to reflux, cross-link reaction for 6 hours, then remove the solvent and vacuum dry to obtain cross-linked starch;

[0087] Step 2, preparation of modified lignin: first dissolve lignin in deionized water, then add 2 mol / L hydrochloric acid solution for precipitation, centrifuge and filter, wash with water, and then vacuum dry to obtain pretreated lignin, then dissolve the pretreated lignin, maleic anhydride, and 4-dimethylaminopyridine in N,N-dimethylformamide solvent, the mass ratio of lignin to maleic anhydride and N,N-dimethylformamide is 1.35:1:4, the amount of 4-dimethylaminopyridine is 0.1% of the amount of maleic anhydride, heat to 95°C for reaction for 8 hours, then remove the solvent, and vacuum dry to obtain modified lignin.

[0088] Step 3, grinding the cross-linked starch, modified lignin, rosin, epoxy resin, and polyurethane resin through a 500-600 mesh sieve respectively for later use;

[0089] Step 4: 0.31 parts by weight of nano-silicon dioxide with a particle size of 50 to 100 nm and 4.65 parts by weight of water were mixed, and high-pressure homogenization was performed at a pressure of 55 MPa for 5 seconds to form a uniformly dispersed nano-silicon dioxide suspension;

[0090] Step 5: Dissolve polyvinyl alcohol in 54.34 parts by weight of water under stirring at a speed of 450 rpm, heat to 85° C., and then add 4.5 parts by weight of the ground rosin, 4.5 parts by weight of epoxy resin, and 2.2 parts by weight of polyurethane resin in sequence. After dissolving and dispersing them uniformly, add 18 parts by weight of the ground cross-linked starch and 5 parts by weight of modified lignin in sequence, dissolve and disperse them uniformly, and form a uniformly dispersed mixture.

[0091] Step 6: Add the nano-silica suspension and 1 part by weight of a silane coupling agent to the mixture while stirring at a rotation speed of 450 rpm, and mix well to obtain a formaldehyde-free plywood adhesive.

[0092] The preparation method of formaldehyde-free plywood is as follows:

[0093] Step (1): Use the above adhesive to apply glue on the surface of the wood veneer, with the glue amount being 110 g / m 2 ;

[0094] Step (2), assembling the odd number of glued veneers so that the wood grain directions of adjacent veneers are perpendicular to each other to obtain slabs;

[0095] Step (3): cold-press the slab at a pressure of 0.8 MPa for 20 min, and then hot-press at a temperature of 190° C. and a pressure of 1.1 MPa for 1.8 min / mm to obtain formaldehyde-free plywood.

[0096] Comparative Example 1

[0097] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 1 in that: the weight parts of the raw materials added are: 18.5 parts of cross-linked starch, 5.05 parts of modified lignin, 4 parts of rosin, 2.3 parts of epoxy resin, 1.5 parts of polyurethane resin, 5.5 parts of polyvinyl alcohol, 0.35 parts of nano-silica with a particle size of 50 to 100 nm, 0.8 parts of a silane coupling agent, and 62 parts of water; the amount of water added to the nano-silica suspension is 5.25 parts; otherwise, the preparation method is identical to that of the formaldehyde-free plywood adhesive in Example 1;

[0098] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0099] Comparative Example 2

[0100] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 4 in that: the weight parts of the raw materials added are: 11.5 parts of cross-linked starch, 10 parts of modified lignin, 5 parts of rosin, 5 parts of epoxy resin, 4.5 parts of polyurethane resin, 3.5 parts of polyvinyl alcohol, 0.3 parts of nano-silica with a particle size of 50 to 100 nm, 1 part of a silane coupling agent, and 59.2 parts of water; the amount of water added to the nano-silica suspension is 4.5 parts; otherwise, the preparation method is identical to that of the formaldehyde-free plywood adhesive in Example 4;

[0101] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 4.

[0102] Comparative Example 3

[0103] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 4 in that: the weight parts of the raw materials added are: 11.5 parts of cross-linked starch, 10.5 parts of modified lignin, 5 parts of rosin, 4 parts of epoxy resin, 2.5 parts of polyurethane resin, 3.5 parts of polyvinyl alcohol, 0.4 parts of nano-silica with a particle size of 50 to 100 nm, 1 part of a silane coupling agent, and 61.6 parts of water; the amount of water added to the nano-silica suspension is 6 parts; otherwise, the preparation method is identical to that of the formaldehyde-free plywood adhesive in Example 4;

[0104] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 4.

[0105] Comparative Example 4

[0106] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 3 in that: the weight parts of the added raw materials are: 14 parts of cross-linked starch, 9 parts of modified lignin, 3.5 parts of rosin, 4.5 parts of epoxy resin, 2.5 parts of polyurethane resin, 4.5 parts of polyvinyl alcohol, 0 parts of nano-silica, 0.6 parts of silane coupling agent, and 61.4 parts of water; step 4 is omitted; and the nano-silica suspension is not added in step 5. Otherwise, the preparation method is identical to that of the formaldehyde-free plywood adhesive in Example 3.

[0107] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 3.

[0108] Comparative Example 5

[0109] A method for preparing an adhesive for formaldehyde-free plywood, which differs from Example 3 in that: the particle size of the nano-silicon dioxide is 10 to 20 nm;

[0110] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0111] Comparative Example 6

[0112] A method for preparing an adhesive for formaldehyde-free plywood, which differs from Example 3 in that: the particle size of the nano-silicon dioxide is 150 to 200 nm;

[0113] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0114] Comparative Example 7

[0115] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 1 in that: the weight parts of the raw materials added are: 18.5 parts of cross-linked starch, 5.1 parts of modified lignin, 4 parts of rosin, 4 parts of epoxy resin, 2 parts of polyurethane resin, 5.5 parts of polyvinyl alcohol, 0.4 parts of nano-silica with a particle size of 50-100 nm, 0 parts of silane coupling agent, and 61 parts of water; the amount of water added to the nano-silica suspension is 6 parts; otherwise, the preparation method is identical to that of the formaldehyde-free plywood adhesive in Example 1;

[0116] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0117] Comparative Example 8

[0118] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 1 in that sago starch replaces cross-linked starch; Step 1 is omitted, and the remaining steps are identical to those of Example 1.

[0119] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0120] Comparative Example 9

[0121] A method for preparing a formaldehyde-free plywood adhesive, which differs from Example 1 in that lignin is used instead of modified lignin; Step 2 is omitted, and the remaining steps are identical to those of Example 1.

[0122] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0123] Comparative Example 10

[0124] A method for preparing an adhesive for formaldehyde-free plywood, which differs from Example 1 in that: in the modified lignin in step 2, the mass ratio of lignin to maleic anhydride and N,N-dimethylformamide is 1:1.25:4;

[0125] The preparation method of the formaldehyde-free plywood is exactly the same as that of Example 1.

[0126] Comparative Example 11

[0127] The preparation method of a formaldehyde-free plywood adhesive is exactly the same as that of Example 1;

[0128] The preparation method of the formaldehyde-free plywood is the same as that of Example 1 except that the hot pressing treatment is performed at a temperature of 180° C. and a pressure of 1.2 MPa for 1.2 min / mm.

[0129] Comparative Example 12

[0130] The preparation method of a formaldehyde-free plywood adhesive is exactly the same as that of Example 1;

[0131] The preparation method of the formaldehyde-free plywood is the same as that of Example 1 except that the plywood is subjected to hot pressing at a temperature of 180° C. and a pressure of 1 MPa for 1.5 min / mm.

[0132] Performance test: The viscosity of the adhesive was tested at a temperature of 35°C according to GB / T 2794-2022, and the results are shown in Table 1. The mechanical properties and formaldehyde emission tests were conducted according to GB / T17657-2022, and the mechanical properties and formaldehyde emission of the three-layer veneer are shown in Table 2. The elastic modulus and static bending strength of the five-layer veneer are shown in Table 3.

[0133] Table 1 Adhesives

[0134] Viscosity (mPa·s) Viscosity (mPa·s) Example 1 17865 Comparative Example 1 11302 Example 2 17560 Comparative Example 2 12547 Example 3 16982 Comparative Example 3 12975 Example 4 16454 Comparative Example 4 11784 Example 5 16132 Comparative Example 5 12687 Example 6 16317 Comparative Example 6 17120 Example 7 17275 Comparative Example 7 9565 Example 8 18647 Comparative Example 8 8560 Example 9 18371 Comparative Example 9 8241 Example 10 18243 / /

[0135] Table 2 Mechanical properties and formaldehyde emission of three-layer veneer

[0136]

[0137]

[0138] Table 3 Elastic modulus and static bending strength of five-layer veneer

[0139]

[0140]

[0141] As can be seen from Tables 1 to 3 above, the formaldehyde-free plywood adhesive of the present invention is based on cross-linked starch and modified lignin, and rosin, epoxy resin, polyurethane resin, polyvinyl alcohol, nano-silica, and silane coupling agent are added to cooperate with each other, and the effects of the components are enhanced by an appropriate amount of raw material compounding system, thereby achieving the goal of formaldehyde-free release of the adhesive, with a viscosity of 90 to 110 g / m 2The veneer is glued with a certain amount of glue to prepare plywood, the adhesive has good bonding strength to the wood veneer, and makes the plywood have good water resistance, and also takes into account that the plywood has good elastic modulus and static bending strength; the adhesive prepared by the present invention is a formaldehyde-free plywood adhesive of green bio-based source, which can be applied to most wood and hot pressing equipment, and has good industrialization prospects; through the examples, it is further found that in the appropriate raw material compounding system of the present invention, the weight of polyvinyl alcohol is controlled to be 21-36% of the weight of cross-linked starch, the mass ratio of epoxy resin to polyurethane resin is 1.2-2.2:1, and the weight of nano-silica is controlled to be 1.7-4% of the weight of cross-linked starch, the reinforcing effect between the components is further improved, the veneer has higher bonding strength, the plywood has better water resistance, and the elastic modulus and static bending strength of the plywood are further improved.

[0142] Compared with the embodiments, in Comparative Example 1, there is too much cross-linked starch and too little epoxy resin and polyurethane resin, in Comparative Example 2, there is too little cross-linked starch and too much epoxy resin and polyurethane resin, and in Comparative Example 3, there is too much cross-linked starch and too little modified lignin, which weakens the interaction between the components, reduces the viscosity of the adhesive, affects the bonding strength of the adhesive to the veneer, and also reduces the water resistance, elastic modulus and static bending strength of the plywood; in Comparative Example 4, no nano-silica is added, and in Comparative Example 7, no silane coupling is added, the interaction between the components is reduced, the viscosity of the adhesive is reduced, the bonding strength of the adhesive to the veneer is reduced, and the water resistance of the plywood is significantly reduced, and the elastic modulus and static bending strength of the plywood are also affected; in Comparative Example 5, the particle size of nano-silica is too small, and the nano-silica with too small a particle size is too small. The nano-silica agglomerates, which greatly reduces the viscosity of the adhesive, affects the bonding strength of the adhesive to the veneer, and further reduces the water resistance of the plywood; the particle size of the nano-silica in Comparative Example 5 is too large. Although the viscosity of the adhesive is reduced to a small extent, the effect of the nano-silica pile adhesive with too large a particle size on enhancing the bonding strength of the veneer is poor; the use of untreated sago starch in Comparative Example 8 and the use of unmodified lignin in Comparative Example 9 weaken the network cross-linking structure of the adhesive, greatly reducing the bonding strength and water resistance of the adhesive to the veneer; the too low hot pressing time (1.2 min / mm) in Comparative Example 10 and the too low hot pressing pressure (1 MPa) in Comparative Example 11 will reduce the bonding strength of the adhesive to the veneer and also affect the elastic modulus and static bending strength of the plywood.

[0143] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be embodied in other specific forms without departing from the spirit and essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

[0144] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A formaldehyde-free plywood adhesive, characterized in that: The invention comprises the following raw materials and their weight parts, and the total weight parts of the raw materials is 100 parts: 12-18 parts of cross-linked starch, 5-10 parts of modified lignin, 3-5 parts of rosin, 2.5-4.5 parts of epoxy resin, 2-4 parts of polyurethane resin, 3.5-5.5 parts of polyvinyl alcohol, 0.3-0.6 parts of nano-silicon dioxide, 0.6-1 parts of silane coupling agent and 55-62 parts of water; The cross-linked starch is obtained by cross-linking starch with isocyanate; The modified lignin is obtained by modifying lignin with maleic anhydride.

2. The formaldehyde-free plywood adhesive according to claim 1, characterized in that: The weight percentage of the polyvinyl alcohol to the weight of the cross-linked starch is 21-36%.

3. The formaldehyde-free plywood adhesive according to claim 1, characterized in that: The mass ratio of the epoxy resin to the polyurethane resin is 1.2 to 2.2:

1.

4. The formaldehyde-free plywood adhesive according to claim 1, characterized in that: The weight percentage of the nano silicon dioxide to the weight of the cross-linked starch is 1.7-4%.

5. The formaldehyde-free plywood adhesive according to claim 1, characterized in that: The preparation process of the cross-linked starch is as follows: first dissolving isocyanate in ethyl acetate solvent, then adding starch and stirring to mix evenly, then heating to reflux, cross-linking reaction for 5 to 6 hours, then removing the solvent, and vacuum drying to obtain cross-linked starch; The mass ratio of the starch to the isocyanate and ethyl acetate is 1.45-1.65:1:

5.

6. The formaldehyde-free plywood adhesive according to claim 1, characterized in that: The preparation process of the modified lignin is as follows: first, lignin is dissolved in deionized water, then a 2 mol / L hydrochloric acid solution is added for precipitation, centrifugation and filtration, water washing, and vacuum drying to obtain pretreated lignin, then the pretreated lignin, maleic anhydride, and 4-dimethylaminopyridine are dissolved in N,N-dimethylformamide solvent, heated to 85-95° C. for reaction for 8-10 hours, and then the solvent is removed and vacuum drying is performed to obtain modified lignin; The mass ratio of lignin to maleic anhydride and N,N-dimethylformamide is 1.15-1.35:1:4, and the amount of 4-dimethylaminopyridine is 0.1% of the amount of maleic anhydride.

7. A method for preparing the formaldehyde-free adhesive for plywood according to claim 1, characterized in that: The specific steps are as follows: Said Sa1, grind the cross-linked starch, modified lignin, rosin, epoxy resin, and polyurethane resin respectively through a 500-600 mesh sieve and set aside; Sa2. Mix nano-silica with an appropriate amount of water and homogenize under high pressure to form a uniformly dispersed nano-silica suspension; the amount of water added is 15 times that of nano-silica; Sa3. Dissolve polyvinyl alcohol in the remaining water under stirring. After heating, add the ground rosin, epoxy resin, and polyurethane resin in sequence. After dissolving and dispersing them evenly, add the ground cross-linked starch and modified lignin in sequence. Dissolve and disperse them evenly to form a uniformly dispersed mixture. Sa4. Add the nano-silica suspension and silane coupling agent to the mixture under stirring, mix well, and obtain a formaldehyde-free plywood adhesive.

8. The method for preparing the formaldehyde-free adhesive for plywood according to claim 7, characterized in that: In step Sa2, the high-pressure homogenization conditions are: a pressure of 40 to 50 MPa and a time of 5 to 10 seconds; in steps Sa3 and Sa4, the stirring speed is 300 to 400 rpm; in step Sa3, the temperature is heated to 75 to 85°C.

9. A method for preparing formaldehyde-free plywood, characterized in that: The specific steps are as follows: Sb1. Applying sizing on the surface of a wood veneer using the adhesive according to any one of claims 1 to 8; Sb2, assembling the odd-numbered layers of glued veneers so that the grain directions of adjacent veneers are perpendicular to each other to obtain slabs; Sb3. The slab is first subjected to cold pressing treatment and then to hot pressing treatment to obtain formaldehyde-free plywood.

10. The method for preparing formaldehyde-free plywood according to claim 9, characterized in that: The amount of glue applied in step Sb1 is 90-110 g / m 2 ; Cold pressing conditions of step Sb3: pressure of 0.6~0.8MPa, time of 20~40min; hot pressing conditions of step Sb3: temperature of 165~195℃, pressure of 1.1~1.3MPa, time of 1.3~1.8min / mm.

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