A low-formaldehyde environmental protection plywood and its preparation method

Abstract

The present invention relates to the field of plywood, and specifically to a low-formaldehyde environmental protection plywood and a preparation method thereof. The original wood is impregnated with a gelatin-sugar alcohol impregnating solution, and a modified waterborne polyurethane is used as the adhesive of the plywood, and calcium carbonate and composite montmorillonite are introduced as fillers; the montmorillonite is first coated with polydopamine and then grafted with carbonated tannins; in the preparation of the modified waterborne polyurethane, polycaprolactone polyol and isophorone diisocyanate are selected to prepare a prepolymer, N-methyldiethanolamine is added to improve the heat resistance of the polyurethane, and modified silica prepared by modifying nano-silica with isopropoxy tris(ethylenediamino-N-ethoxy) titanate and butanediol are used as chain extenders, and hydroxylated phytic acid is selected as a crosslinking agent.

Description

Technical Field

[0001] The present invention relates to the field of plywood, and specifically to a low-formaldehyde environmental protection plywood and a preparation method thereof. Background Art

[0002] Plywood is one of the three major artificial boards. It is a multi-layer board made by slicing wood segments into veneers or planing wooden squares into thin woods and gluing them with adhesives. Because of its good mechanical properties and processing properties, it is widely used in building decoration, furniture manufacturing, floor manufacturing, ship and vehicle decoration, etc.

[0003] In the existing plywood market, formaldehyde pollution has always been a hot issue. Since traditional adhesives contain a large amount of formaldehyde, the safety and environmental protection of multi-layer plywood are greatly reduced. Traditionally, long-term ventilation is usually used to remove formaldehyde, which greatly reduces the utilization rate of plywood. Therefore, the research and development of low-formaldehyde environmental protection plywood has practical significance and important economic value. Summary of the Invention

[0004] The purpose of the present invention is to provide a low-formaldehyde environmental protection plywood and a preparation method thereof to solve the problems in the prior art.

[0005] To solve the above technical problems, the present invention provides the following technical solutions:

[0006] A preparation method of a low-formaldehyde environmental protection plywood includes the following steps:

[0007] S1: Prepare a composite coating agent with composite montmorillonite, calcium carbonate, and modified waterborne polyurethane;

[0008] S2: Put the log into a gelatin-sugar alcohol impregnation solution for impregnation treatment, and dry it with gradient temperature increase to obtain a substrate;

[0009] S3: Apply the composite coating agent on the surface of the substrate, let it stand and irradiate with light, stack and combine them according to the perpendicular texture between adjacent layers, and hot press to obtain a low-formaldehyde environmental protection plywood.

[0010] Further, the working conditions of the impregnation treatment are: evacuate to -0.1 MPa and keep for 20 - 30 min, pressurize to 0.8 MPa and keep for 2 - 3 h.

[0011] Further, the working conditions of the gradient temperature increase drying are: increase the temperature to 45 °C and keep for 12 h, increase the temperature to 65 °C and keep for 12 h, increase the temperature to 103 °C and keep for 24 h.

[0012] Further, the working conditions of the hot press are: the temperature is 190 - 200 °C, the time is 6 - 8 min, and the pressure is 1.2 MPa.

[0013] Further, the composition of the gelatin-sugar alcohol impregnating solution is as follows: using deionized water as the solvent, wherein there are 63 g / L of gelatin, 204 g / L of sugar alcohol, 13 g / L of maleic anhydride, 8 g / L of sodium tetraborate, and 21 g / L of modified silica.

[0014] Further, by mass parts, the composition of the composite coating agent is as follows: 2-5 parts of composite montmorillonite, 1-3 parts of calcium carbonate, and 30-35 parts of modified waterborne polyurethane.

[0015] Further, the preparation of the composite montmorillonite includes the following steps:

[0016] 1) Mix montmorillonite and Tris-HCl buffer solution, perform ultrasonic treatment for 15-20 min, add the mixed solution of dopamine hydrochloride and Tris-HCl buffer solution, after ultrasonic treatment for 10-15 min, keep warm at 25-30 °C for 10-12 h, centrifuge, freeze-dry, and grind to obtain polydopamine-coated montmorillonite;

[0017] 2) Mix deionized water, dimethyl carbonate, and myricetin tannin powder, heat up to 45-50 °C and keep warm in a water bath for 30-40 min, add the mixed solution of polydopamine-coated montmorillonite and deionized water, and continue to keep warm for 20-30 min to obtain the composite montmorillonite.

[0018] Further, the preparation of the modified waterborne polyurethane includes the following steps:

[0019] Mix pentaerythritol and phytic acid, heat up to 115-120 °C and keep warm for 2-3 h, perform vacuum filtration and freeze-dry to obtain hydroxylated phytic acid; heat up polycaprolactone polyol to 85-90 °C and keep warm for 2 h, cool down to 75-78 °C, under a nitrogen atmosphere, add isophorone diisocyanate, dibutyltin dilaurate, and methyl ethyl ketone, heat up to 78-82 °C and keep warm for 2 h, cool down to 30-35 °C, add N-methyldiethanolamine, modified silica, and methyl ethyl ketone and continue to keep warm for 50-70 min, heat up to 78-82 °C and add butanediol and methyl ethyl ketone, continue to keep warm for 2-3 h, cool down to 30-35 °C, adjust the pH to 6, keep warm for 20-30 min, add hydroxylated phytic acid and deionized water, stir for 2-3 h, and perform vacuum distillation to obtain the modified waterborne polyurethane.

[0020] Further, the preparation of the modified silica includes the following steps: Mix nano-silica and toluene, perform ultrasonic oscillation at 40-50 °C for 20-30 min, add isopropoxytris(ethylenediamino-N-ethoxy) titanate and perform ultrasonic oscillation for 20-30 min, heat up to 65-70 °C and keep warm for 4-5 h, centrifuge, add tert-butanol and perform ultrasonic oscillation for 8-10 min, centrifuge, let stand overnight, and perform vacuum drying to obtain the modified silica.

[0021] The beneficial effects of the present invention:

[0022] The present invention provides a low-formaldehyde environmentally friendly plywood and a preparation method thereof. The treated substrate is laminated and compounded with a composite coating agent to prepare a low-formaldehyde environmentally friendly plywood with good flame retardancy, strong impact resistance, and good hydrophobicity.

[0023] The log is impregnated with a gelatin-sugar alcohol impregnating solution. Gelatin, which is low-cost, harmless, and environmentally friendly, is selected as an inducer. Modified silica prepared by modifying nano-silica with isopropoxytri(ethylenediamino-N-ethoxy) titanate is used. Referring to biomimetic mineralization, gelatin, sugar alcohol, wood, and modified silica are combined to induce the orderly deposition of modified silica and sugar alcohol on the wood. Furfuryl alcohol reacts chemically with both the benzene ring vacancies and side chains of lignin, thereby greatly improving the mildew resistance, flame retardancy, and impact resistance of the substrate.

[0024] In order to reduce the formaldehyde release amount, modified waterborne polyurethane is used as the adhesive of the plywood in the present invention. Cubic calcium carbonate and layered montmorillonite are introduced as fillers to fill and modify the modified waterborne polyurethane. While improving its mechanical properties, its use cost is reduced; in order to make the montmorillonite disperse evenly in the waterborne polyurethane and improve its reaction activity, the montmorillonite is modified. The montmorillonite is first coated with polydopamine and then grafted with carbonated tannin to improve the uniformity of the montmorillonite dispersion. At the same time, the introduction of tannin can effectively improve the crosslinking reaction degree in the composite coating agent and enhance the bonding performance of the composite coating agent; after carbonating the tannin and introducing it, the steric hindrance of the tannin can be reduced, thereby improving its binding force with other raw materials in the composite coating agent, thereby enhancing the complexity of the crosslinking network, and thus improving the flame retardancy, sound insulation, and mechanical strength of the plywood.

[0025] In the preparation of the modified waterborne polyurethane, polycaprolactone polyol and isophorone diisocyanate are selected to prepare a prepolymer. N-methyldiethanolamine is added to improve the heat resistance of the polyurethane. Modified silica prepared by modifying nano-silica with isopropoxytri(ethylenediamino-N-ethoxy) titanate and butanediol are selected as chain extenders, and hydroxylated phytic acid is selected as a crosslinking agent to greatly improve the thermal stability, hydrophobicity, and flame retardancy of the polyurethane, thereby endowing the plywood with high heat resistance and flame retardancy. Specific Embodiments

[0026] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0027] It should be noted that if there are directional indications involved in the embodiments of the present invention, such as up, down, left, right, front, and back, these directional indications are only used to explain the relative positional relationship and movement conditions between components in a specific posture. If this specific posture changes, the directional indications will also change accordingly. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the realization by those of ordinary skill in the art. When the combination of technical solutions is contradictory or cannot be realized, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0028] The technical solutions of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0029] Embodiment 1: A method for preparing a low-formaldehyde environmentally friendly plywood, comprising the following steps:

[0030] S1: Prepare a composite coating agent with composite montmorillonite, calcium carbonate, and modified waterborne polyurethane;

[0031] By mass, the composition of the composite coating agent is: 2 parts of composite montmorillonite, 1 part of calcium carbonate, and 30 parts of modified waterborne polyurethane;

[0032] The preparation of the composite montmorillonite includes the following steps:

[0033] 1) Mix 4 g of montmorillonite and 500 mL of Tris-HCl buffer solution, ultrasonically treat for 15 min, add a mixed solution of 10.5 g of dopamine hydrochloride and 800 mL of Tris-HCl buffer solution, ultrasonically treat for 10 min, then keep warm at 25 °C for 12 h, centrifuge, freeze-dry, and grind to obtain polydopamine-coated montmorillonite;

[0034] 2) Mix 4 g of deionized water, 5 g of dimethyl carbonate, and 6 g of myricetin tannin powder, heat to 45 °C and keep warm in a water bath for 40 min, add a mixed solution of 1 g of polydopamine-coated montmorillonite and 1 g of deionized water, and continue to keep warm for 20 min to obtain composite montmorillonite;

[0035] The preparation of the modified waterborne polyurethane includes the following steps:

[0036] Mix 2.18 g of pentaerythritol and 13.6 g of phytic acid, heat up to 115 °C and keep warm for 3 h, then carry out vacuum filtration and freeze-drying to obtain hydroxylated phytic acid; heat 0.1 mol of polycaprolactone polyol up to 85 °C and keep warm for 2 h, cool down to 75 °C, under a nitrogen atmosphere, add 0.44 mol of isophorone diisocyanate, 4 drops of dibutyltin dilaurate, and 10 mL of methyl ethyl ketone, heat up to 78 °C and keep warm for 2 h, cool down to 30 °C, add 0.1 mol of N-methyldiethanolamine and 4 mL of methyl ethyl ketone and continue to keep warm for 50 min, heat up to 78 °C, add 5 g of modified silica, 0.26 mol of butanediol, and 10 mL of methyl ethyl ketone, continue to keep warm for 2 h, cool down to 30 °C, adjust the pH to 6, keep warm for 20 min, add 7 g of hydroxylated phytic acid and 20 mL of deionized water, stir for 2 h, and carry out vacuum distillation to obtain modified waterborne polyurethane;

[0037] S2: Immerse the log in a gelatin-sugar alcohol impregnating solution for impregnation treatment, and carry out gradient heating and drying to obtain a substrate;

[0038] The working conditions for the impregnation treatment are: evacuate to -0.1 MPa and keep for 20 min, pressurize to 0.8 MPa and keep for 2 h;

[0039] The working conditions for the gradient heating and drying are: heat up to 45 °C and keep for 12 h, heat up to 65 °C and keep for 12 h, heat up to 103 °C and keep for 24 h;

[0040] The composition of the gelatin-sugar alcohol impregnating solution is: using deionized water as the solvent, including 63 g / L of gelatin, 204 g / L of sugar alcohol, 13 g / L of maleic anhydride, 8 g / L of sodium tetraborate, and 21 g / L of modified silica;

[0041] The preparation of the modified silica includes the following steps: mix 0.5 g of nano-silica and 90 mL of toluene, carry out ultrasonic oscillation at 40 °C for 30 min, add 2 g of isopropoxytris(ethylenediamino-N-ethoxy) titanate and carry out ultrasonic oscillation for 20 min, heat up to 65 °C and keep warm for 5 h, centrifuge, add 100 mL of tert-butanol and carry out ultrasonic oscillation for 8 min, centrifuge, let stand overnight, and carry out vacuum drying to obtain modified silica;

[0042] S3: Apply the composite coating agent on the surface of the substrate, let stand under sunlight for 20 min, stack and combine according to the perpendicular texture between adjacent layers, and carry out hot pressing to obtain a low-formaldehyde environmentally friendly plywood; the working conditions for hot pressing are: temperature is 190 °C, time is 8 min, and pressure is 1.2 MPa.

[0043] Example 2: A preparation method of a low-formaldehyde environmentally friendly plywood, including the following steps:

[0044] S1: Prepare a composite coating agent with composite montmorillonite, calcium carbonate, and modified waterborne polyurethane;

[0045] By mass fraction, the composition of the composite coating agent is: 3 parts of composite montmorillonite, 2 parts of calcium carbonate, and 33 parts of modified waterborne polyurethane;

[0046] The preparation of the composite montmorillonite includes the following steps:

[0047] 1) Mix 4 g of montmorillonite with 500 mL of Tris-HCl buffer solution, ultrasonically treat for 18 min, add a mixture of 10.5 g of dopamine hydrochloride and 800 mL of Tris-HCl buffer solution, ultrasonically treat for 13 min, then keep warm at 28 °C for 11 h, centrifuge, freeze-dry, and grind to obtain polydopamine-coated montmorillonite;

[0048] 2) Mix 4 g of deionized water, 5 g of dimethyl carbonate, and 6 g of myricetin tannin powder, heat up to 48 °C and keep warm in a water bath for 35 min, add a mixture of 1 g of polydopamine-coated montmorillonite and 1 g of deionized water, and continue to keep warm for 25 min to obtain the composite montmorillonite;

[0049] The preparation of the modified waterborne polyurethane includes the following steps:

[0050] Mix 2.18 g of pentaerythritol with 13.6 g of phytic acid, heat up to 118 °C and keep warm for 2.5 h, vacuum filter and freeze-dry to obtain hydroxylated phytic acid; heat 0.1 mol of polycaprolactone polyol to 88 °C and keep warm for 2 h, cool down to 76 °C, under a nitrogen atmosphere, add 0.44 mol of isophorone diisocyanate, 4 drops of dibutyltin dilaurate, and 10 mL of butanone, heat up to 80 °C and keep warm for 2 h, cool down to 33 °C, add 0.1 mol of N-methyldiethanolamine and 4 mL of butanone and continue to keep warm for 60 min, heat up to 80 °C, add 5 g of modified silica, 0.26 mol of butanediol, and 10 mL of butanone, continue to keep warm for 2.5 h, cool down to 33 °C, adjust the pH to 6, keep warm for 25 min, add 7 g of hydroxylated phytic acid and 20 mL of deionized water, stir for 2.5 h, and carry out vacuum distillation to obtain the modified waterborne polyurethane;

[0051] S2: Immerse the log in the gelatin-sugar alcohol impregnating solution for impregnation treatment, and dry it by gradient heating to obtain a substrate;

[0052] The working conditions for the impregnation treatment are: evacuate to -0.1 MPa and keep for 25 min, pressurize to 0.8 MPa and keep for 2.5 h;

[0053] The working conditions for the gradient heating drying are: heat up to 45 °C and keep for 12 h, heat up to 65 °C and keep for 12 h, heat up to 103 °C and keep for 24 h;

[0054] The composition of the gelatin-sugar alcohol impregnating solution is as follows: using deionized water as the solvent, where there is 63 g / L of gelatin, 204 g / L of sugar alcohol, 13 g / L of maleic anhydride, 8 g / L of sodium tetraborate, and 21 g / L of modified silica;

[0055] The preparation of the modified silica includes the following steps: Mix 0.5 g of nano-silica and 90 mL of toluene, ultrasonically oscillate at 45 °C for 25 min, add 2 g of isopropoxytris(ethylenediamino-N-ethoxy) titanate and ultrasonically oscillate for 25 min, raise the temperature to 68 °C and keep warm for 4.5 h, centrifuge, add 100 mL of tert-butanol and ultrasonically oscillate for 9 min, centrifuge, let stand overnight, and vacuum dry to obtain the modified silica;

[0056] S3: Apply the composite coating agent on the surface of the substrate, let it stand under sunlight for 20 min, stack and combine them according to the perpendicular texture between adjacent layers, and hot press to obtain a low-formaldehyde environmentally friendly plywood; The working conditions of the hot press are: temperature 195 °C, time 7 min, pressure 1.2 MPa.

[0057] Example 3: A preparation method of a low-formaldehyde environmentally friendly plywood, including the following steps:

[0058] S1: Prepare a composite coating agent with composite montmorillonite, calcium carbonate, and modified waterborne polyurethane;

[0059] By mass, the composition of the composite coating agent is: 5 parts of composite montmorillonite, 3 parts of calcium carbonate, and 35 parts of modified waterborne polyurethane;

[0060] The preparation of the composite montmorillonite includes the following steps:

[0061] 1) Mix 4 g of montmorillonite and 500 mL of Tris-HCl buffer solution, ultrasonically process for 20 min, add a mixture of 10.5 g of dopamine hydrochloride and 800 mL of Tris-HCl buffer solution, ultrasonically process for 15 min, then keep warm at 30 °C for 10 h, centrifuge, freeze-dry, and grind to obtain poly-dopamine-coated montmorillonite;

[0062] 2) Mix 4 g of deionized water, 5 g of dimethyl carbonate, and 6 g of myricetin tannin powder, raise the temperature to 50 °C and keep warm in a water bath for 30 min, add a mixture of 1 g of poly-dopamine-coated montmorillonite and 1 g of deionized water, and continue to keep warm for 30 min to obtain the composite montmorillonite;

[0063] The preparation of the modified waterborne polyurethane includes the following steps:

[0064] Mix 2.18 g of pentaerythritol and 13.6 g of phytic acid, heat up to 120 °C and keep warm for 2 h, then perform vacuum filtration and freeze-drying to obtain hydroxylated phytic acid; heat 0.1 mol of polycaprolactone polyol up to 90 °C and keep warm for 2 h, cool down to 78 °C, under a nitrogen atmosphere, add 0.44 mol of isophorone diisocyanate, 4 drops of dibutyltin dilaurate, and 10 mL of butanone, heat up to 82 °C and keep warm for 2 h, cool down to 35 °C, add 0.1 mol of N-methyldiethanolamine and 4 mL of butanone and continue to keep warm for 70 min, heat up to 82 °C, add 5 g of modified silica, 0.26 mol of butanediol, and 10 mL of butanone, continue to keep warm for 3 h, cool down to 35 °C, adjust the pH to 6, keep warm for 30 min, add 7 g of hydroxylated phytic acid and 20 mL of deionized water, stir for 3 h, and perform vacuum distillation to obtain modified waterborne polyurethane;

[0065] S2: Immerse the log in a gelatin-sugar alcohol impregnating solution for impregnation treatment, and perform gradient heating and drying to obtain a substrate;

[0066] The working conditions for the impregnation treatment are: evacuate to -0.1 MPa and hold for 30 min, pressurize to 0.8 MPa and hold for 3 h;

[0067] The working conditions for the gradient heating and drying are: heat up to 45 °C and hold for 12 h, heat up to 65 °C and hold for 12 h, heat up to 103 °C and hold for 24 h;

[0068] The composition of the gelatin-sugar alcohol impregnating solution is: using deionized water as the solvent, including 63 g / L of gelatin, 204 g / L of sugar alcohol, 13 g / L of maleic anhydride, 8 g / L of sodium tetraborate, and 21 g / L of modified silica;

[0069] The preparation of the modified silica includes the following steps: mix 0.5 g of nano-silica and 90 mL of toluene, perform ultrasonic oscillation at 50 °C for 20 min, add 2 g of isopropoxytris(ethylenediamino-N-ethoxy) titanate and perform ultrasonic oscillation for 30 min, heat up to 70 °C and keep warm for 4 h, centrifuge, add 100 mL of tert-butanol and perform ultrasonic oscillation for 10 min, centrifuge, let stand overnight, and perform vacuum drying to obtain modified silica;

[0070] S3: Apply the composite coating agent on the surface of the substrate, let it stand under sunlight for 20 min, stack and combine it according to the perpendicular texture between adjacent layers, and perform hot pressing to obtain a low-formaldehyde environmentally friendly plywood; the working conditions for the hot pressing are: temperature is 200 °C, time is 6 min, and pressure is 1.2 MPa.

[0071] Comparative Example 1: Take Example 3 as the control group, replace the composite montmorillonite with montmorillonite, and the other processes are normal.

[0072] Comparative Example 2: Take Example 3 as the control group, without adding modified silica, and the other processes are normal.

[0073] Comparative Example 3: Taking Example 3 as the control group, hydroxylated phytic acid was not added, and other processes were normal.

[0074] Comparative Example 4: Taking Example 3 as the control group, poplar was used to replace the substrate, and other processes were normal.

[0075] In the above examples and comparative examples, the thickness of the substrate was 1.9 mm, the thickness of the composite coating agent formed on the surface of the substrate was 50 μm, the composite coating agent was coated on one side of the intermediate layer substrate and double-coated on the substrates on the upper and lower surfaces of the plywood, and the number of laminations was 6.

[0076] Source of raw materials:

[0077] The log was poplar veneer, the tree species was Populus ussuriensis, the thickness was 1.8 mm, the density was 0.39 g / cm 3 , the moisture content was 6 - 8%, purchased from the market; Myrica rubra tannin powder (70%): Guangxi Baise Forest Chemical General Factory; Isopropoxytri(ethylenediamino-N-ethoxy) titanate 65380-84-9: Nanjing Nengde New Material Technology Co., Ltd.; Polycaprolactone polyol 002: Hubei Chengfeng Chemical Co., Ltd.; Calcium carbonate C111986, Montmorillonite M109698, Tris-HCl buffer T301499, Dopamine hydrochloride D103111, Dimethyl carbonate D433123, Pentaerythritol P349787, Phytic acid P350767, Isophorone diisocyanate I109582, Dibutyltin dilaurate D100274, N-Methyldiethanolamine M105603, Butanediol B110394, Gelatin G108394, Sugar alcohol X100092, Maleic anhydride M116389, Sodium tetraborate S112464, Nano-silica S433693: Aladdin Reagent; tert-Butanol, Methyl ethyl ketone, Toluene, analytical pure: Reagents of Sinopharm Group.

[0078] Performance test: Flame retardancy: Refer to the UL-94 test for combustion grade; Impact resistance: Refer to ASTM D143-14, the sample was cut into 30 mm in length and 20 mm in width, the pendulum energy was 100 J, and the span-to-thickness ratio was 12:1; Hydrophobicity: Characterized by water contact angle, and 4 μL of distilled water was used for testing; Formaldehyde release: Determined with reference to GB18580-2017, and the specific data are shown in Table 1;

[0079] Table 1

[0080] Flame retardant grade <![CDATA[Impact strength (kJ / m 2 )]]> Water contact angle (°) <![CDATA[Formaldehyde emission limit (mg / m 3 )]]> Example 1 V-0 81.5 128 0.004 Example 2 V-0 82.1 129 0.003 Example 3 V-0 82.6 131 0.002 Comparative Example 1 V-1 66.3 / / Comparative Example 2 V-1 60.2 / / Comparative Example 3 V-1 73.7 / / Comparative Example 4 V-0 52.9 / /

[0081] Examples 1 - 3 were plywoods prepared according to the present invention, and the formaldehyde release limits in Examples 1 - 3 were 0.002 - 0.004 mg / m 3 , lower than 0.009 mg / m 3, meeting the health requirements; the flame retardancy grades in Examples 1 - 3 are all V - 0, indicating good flame retardancy; the impact strength in Examples 1 - 3 is 81.5 - 82.6 kJ / m 2 , indicating strong impact resistance; the water contact angle in Examples 1 - 3 is 128 - 131°, indicating a hydrophobic surface and good self - cleaning and decontamination properties; " / " in Table 1 indicates that this item was not tested.

[0082] Comparing Example 3 with Comparative Example 1, it can be seen that in order to disperse montmorillonite evenly in waterborne polyurethane and improve its reactivity, the montmorillonite is modified. The montmorillonite is first coated with polydopamine and then grafted with carbonated tannin to improve the uniformity of montmorillonite dispersion. At the same time, the introduction of tannin can effectively increase the degree of cross - linking reaction in the adhesive and enhance the bonding performance of the composite coating agent; after carbonating the tannin and introducing it, the steric hindrance of tannin can be reduced, thereby improving its binding force with other raw materials in the adhesive, enhancing the complexity of the cross - linked network, and thus improving the flame retardancy and mechanical strength of the plywood.

[0083] Comparing Example 3 with Comparative Example 2 and Comparative Example 3, it can be seen that in the preparation of modified waterborne polyurethane, polycaprolactone polyol and isophorone diisocyanate are selected to prepare the prepolymer, N - methyldiethanolamine is added to improve the heat resistance of the polyurethane, and modified silica prepared by modifying nano - silica with isopropoxytri(ethylenediamino - N - ethoxy) titanate and butanediol are used as chain extenders, and hydroxylated phytic acid is selected as the cross - linker to greatly improve the thermal stability, hydrophobicity and flame retardancy of the polyurethane, thereby endowing the plywood with high heat resistance and flame retardancy.

[0084] Comparing Example 3 with Comparative Example 4, it can be seen that the log is impregnated with a gelatin - sugar alcohol impregnating solution. Gelatin, which is inexpensive, harmless and environmentally friendly, is selected as the inducer. Referring to biomimetic mineralization, gelatin, sugar alcohol, wood and modified silica are combined to induce the orderly deposition of modified silica and sugar alcohol on the wood, thereby greatly improving the mildew resistance, flame retardancy and impact resistance of the substrate.

[0085] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention. All equivalent structural transformations made using the description of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A preparation method of a low-formaldehyde environmental protection plywood, characterized in that It includes the following steps: S1: Prepare a composite coating agent using composite montmorillonite, calcium carbonate, and modified waterborne polyurethane; S2: Immerse the log in a gelatin-sugar alcohol immersion solution, perform gradient heating and drying to obtain a substrate; S3: Apply the composite coating agent on the surface of the substrate, let it stand and be irradiated with light, stack and combine them layer by layer with the textures perpendicular to each other between adjacent layers, and perform hot pressing to obtain a low-formaldehyde environmentally friendly plywood; The preparation of the composite montmorillonite includes the following steps: 1) Mix montmorillonite and Tris-HCl buffer solution, perform ultrasonic treatment for 15 - 20 min, add a mixed solution of hydrochloric acid dopamine and Tris-HCl buffer solution, after ultrasonic treatment for 10 - 15 min, keep it at 25 - 30 °C for 10 - 12 h, centrifuge, freeze-dry, and grind to obtain polydopamine-coated montmorillonite; 2) Mix deionized water, dimethyl carbonate, and myricetin tannin powder, heat it to 45 - 50 °C and keep it in a water bath for 30 - 40 min, add a mixed solution of polydopamine-coated montmorillonite and deionized water, and continue to keep it for 20 - 30 min to obtain the composite montmorillonite; The composition of the gelatin-sugar alcohol immersion solution is: using deionized water as the solvent, where gelatin is 63 g / L, sugar alcohol is 204 g / L, maleic anhydride is 13 g / L, sodium tetraborate is 8 g / L, and modified silica is 21 g / L; The preparation of the modified waterborne polyurethane includes the following steps: Mix pentaerythritol and phytic acid, heat it to 115 - 120 °C and keep it for 2 - 3 h, perform vacuum filtration and freeze-dry to obtain hydroxylated phytic acid; heat the polycaprolactone polyol to 85 - 90 °C and keep it for 2 h, cool it to 75 - 78 °C, under a nitrogen atmosphere, add isophorone diisocyanate, dibutyltin dilaurate, and methyl ethyl ketone, heat it to 78 - 82 °C and keep it for 2 h, cool it to 30 - 35 °C, add N-methyldiethanolamine, modified silica, and methyl ethyl ketone and continue to keep it for 50 - 70 min, heat it to 78 - 82 °C and add butanediol and methyl ethyl ketone, continue to keep it for 2 - 3 h, cool it to 30 - 35 °C, adjust the pH to 6, keep it for 20 - 30 min, add a mixed solution of hydroxylated phytic acid and deionized water, stir for 2 - 3 h, and perform reduced pressure distillation to obtain the modified waterborne polyurethane; The preparation of the modified silica includes the following steps: Mix nano-silica and toluene, perform ultrasonic oscillation at 40 - 50 °C for 20 - 30 min, add isopropoxy tris(ethylenediamino-N-ethoxy) titanate and perform ultrasonic oscillation for 20 - 30 min, heat it to 65 - 70 °C and keep it for 4 - 5 h, centrifuge, add tert-butanol and perform ultrasonic oscillation for 8 - 10 min, centrifuge, let it stand overnight, and perform vacuum drying to obtain the modified silica.

2. The preparation method of a low-formaldehyde environmental protection plywood according to claim 1, characterized in that, The working conditions for the immersion treatment are: evacuate to -0.1 MPa and keep it for 20 - 30 min, pressurize to 0.8 MPa and keep it for 2 - 3 h.

3. The preparation method of a low-formaldehyde environmentally friendly plywood according to claim 1, characterized in that, The working conditions for the gradient heating and drying are: heat it to 45 °C and keep it for 12 h, heat it to 65 °C and keep it for 12 h, heat it to 103 °C and keep it for 24 h.

4. The preparation method of a low-formaldehyde environmental protection plywood according to claim 1, characterized in that, The working conditions for the hot pressing are: temperature is 190 - 200 °C, time is 6 - 8 min, and pressure is 1.2 MPa.

5. The preparation method of a low-formaldehyde environmentally friendly plywood according to claim 1, characterized in that, By mass fraction, the composition of the composite coating agent is: 2-5 parts of composite montmorillonite, 1-3 parts of calcium carbonate, and 30-35 parts of modified waterborne polyurethane.

6. A low-formaldehyde environmental protection plywood, characterized in that, Prepared by the preparation method according to any one of claims 1-5.