A hydroxymethylated lignin-phenolic resin and its preparation method, and a bamboo-wood composite container floor and its production method.

Abstract

This invention relates to the field of forestry engineering technology, and more particularly to a hydroxymethylated lignin-phenolic resin and its preparation method, and a bamboo-wood composite container floor and its production method. This invention uses hydroxymethylated lignin-phenolic resin as an adhesive in combination with nano-immon clay as a functional agent to produce bamboo-wood composite container floors. This not only reduces costs but also results in lower levels of free formaldehyde and free phenol, effectively reducing environmental pollution, while simultaneously improving the mechanical properties and thermal stability of the board.

Description

Technical Field

[0001] This invention relates to the field of forestry engineering technology, and in particular to a hydroxymethylated lignin phenolic resin and its preparation method, and a bamboo-wood composite container floor and its production method. Background Technology

[0002] A container is a general term for a group of containers used to transport packaged or unpackaged goods; it is a modern form of group transport. The container floor is a crucial component and primary load-bearing element, as it directly impacts the safety and quality of transported goods, making it a focus of attention.

[0003] Currently, bamboo-wood composite panels are commonly used for container flooring. Phenolic resin is one of the most widely used adhesives in the production of engineered wood products. However, phenol, its main raw material, is expensive, and the resin releases high levels of free formaldehyde and phenol, leading to high production costs for container flooring and the release of organic pollutants such as formaldehyde and phenol, thus polluting the environment. Furthermore, the cured phenolic resin layer is brittle, resulting in insufficient mechanical properties and thermal stability of bamboo-wood composite container flooring. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a hydroxymethylated lignin phenolic resin and its preparation method, as well as a bamboo-wood composite container floor and its production method. This invention uses hydroxymethylated lignin phenolic resin as an adhesive to produce bamboo-wood composite container floors, which not only reduces costs but also results in lower levels of free formaldehyde and free phenol, effectively reducing environmental pollution, while simultaneously improving the mechanical properties and thermal stability of the board.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing hydroxymethylated lignin-phenolic resin, comprising the following steps: Lignin and a first formaldehyde solution are subjected to a first addition reaction under a first alkaline condition to obtain a first product system; the pH value of the first alkaline condition is 11.5~13; the temperature of the first addition reaction is 80~85℃ and the time is 2~3h. Phenol and resorcinol were added to the first product system to carry out a second addition reaction under a second alkaline condition to obtain a second product system; the pH value of the second alkaline condition was 11.5~12.5; the temperature of the second addition reaction was 80~85℃, and the holding time was 1.5~2h; A second formaldehyde solution is added to the second product system, and the temperature is raised to 90°C to carry out a first addition-condensation reaction, and then the temperature is lowered to 70~80°C to obtain a third product system; the holding time of the first addition-condensation reaction is 50~60 min. After adding a third formaldehyde solution to the third product system, the temperature is raised to 80°C to carry out a second addition-condensation reaction to obtain a fourth product system; the second addition-condensation reaction is carried out under a third alkaline condition with a pH value of 11.5~13; the holding time of the second addition-condensation reaction is 50~60 min. Melamine and propylene carbonate were added to the fourth product system, then the temperature was lowered to 70°C, and the reaction was maintained until the resin viscosity reached 200~350 mPa·s. The mixture was then cooled to obtain the hydroxymethylated lignin-based phenolic resin. Based on the hydroxymethylated lignin-based phenolic resin as 100% by mass, the amount of lignin is 8.6-11.4%; the amount of the first formaldehyde solution is 12-16%; the amount of phenol is 17-20%; the amount of resorcinol is 0.5-1.5%; the amount of the second formaldehyde solution is 24-32%; the amount of the third formaldehyde solution is 4-8%; the amount of melamine is 0.25-0.5%; the amount of propylene carbonate is 0.8-1.6%; and the purity of the first, second, and third formaldehyde solutions is 37%.

[0006] Preferably, the pH values ​​of the first alkaline condition, the second alkaline condition, and the third alkaline condition are adjusted by an aqueous sodium hydroxide solution, wherein the mass concentration of the aqueous sodium hydroxide solution is 30%.

[0007] Preferably, the rates of the first and second heating are independently 0.6~1.2℃ / min.

[0008] The present invention provides a hydroxymethylated lignin phenolic resin prepared by the preparation method described above, characterized in that the hydroxymethylated lignin phenolic resin has a pH value of 11.5~13, a solid content of ≥35%, a viscosity of 200~350 mPa·s, a formaldehyde release of ≤0.15%, a free phenol content of ≤0.1%, a curing temperature of 120~135℃, a curing time of 12~16 min, and a number average molecular weight of 2000~10000.

[0009] This invention provides a method for producing bamboo-wood composite container floor panels, comprising the following steps: The hydroxymethylated lignin phenolic resin described in the above scheme is diluted to a solid content of 25-35% to obtain an adhesive; the radial bamboo curtain is impregnated in the adhesive and then dried to obtain the impregnated bamboo curtain. Nano-immon clay was added to the above-mentioned hydroxymethylated lignin phenolic resin to adjust the viscosity to 2500~3000 mPa·s, resulting in a mixed adhesive; the mixed adhesive was then coated onto the surface of a wood veneer to obtain the coated veneer; the moisture content of the wood veneer before coating was 5~8%; The bamboo curtain after being impregnated with glue and the veneer after being coated with glue are assembled, pre-pressed and hot-pressed according to the process design to obtain the bamboo-wood composite container floor; the hot pressing temperature is 130~140℃, the pressure is 3~4.5MPa and the time is 30~35min.

[0010] Preferably, the nano-immon clay has a dry powder particle size of 70% < 100 nm.

[0011] Preferably, the moisture content of the bamboo curtain after impregnation and drying is 10-20%; the moisture content of the radial bamboo curtain before impregnation is 0-10%.

[0012] Preferably, the thickness of the radial bamboo curtain is 1.5~3.0mm; and the impregnation time is 180~240s.

[0013] Preferably, the amount of glue applied to the surface of the wood veneer is 210~290g / m². 2 The present invention provides a bamboo-wood composite container floor obtained by the production method described above. The bamboo-wood composite container floor has a longitudinal short-span shear force ≥8500N, a transverse short-span shear force ≥2500N, a central concentrated load ≥58000N, and a 24h water absorption thickness expansion rate ≤15%.

[0014] This invention provides a method for preparing hydroxymethylated lignin phenolic resin. Under alkaline conditions, the phenolic hydroxyl groups on the benzene ring of the lignin raw material undergo an addition reaction with formaldehyde to generate hydroxymethylated lignin. It further undergoes a condensation reaction with phenol and formaldehyde to form a three-dimensional cross-linked network structure. As an adhesive, it not only reduces the dependence on petroleum-derived raw material phenol and reduces production costs, but also has a low content of free formaldehyde and free phenol in the adhesive after the reaction, effectively reducing environmental pollution. At the same time, it can also realize the effective utilization of renewable resources (lignin).

[0015] Furthermore, in preparing hydroxymethylated lignin phenolic resin, this invention replaces part of the phenol with resorcinol, and simultaneously adds melamine and propylene carbonate, achieving rapid curing at medium and low temperatures and reducing the content of free formaldehyde and free phenol. Compared with conventional phenolic resins, the curing temperature of the hydroxymethylated lignin phenolic resin prepared by this invention can be reduced to 120-130℃ (conventionally requiring above 135℃), the curing time can be shortened to 12-16 minutes (conventionally requiring 20 minutes), and the curing efficiency is increased by 20-25%, greatly improving production efficiency and reducing energy consumption.

[0016] This invention provides a method for producing bamboo-wood composite container flooring. It uses hydroxymethylated lignin-phenolic resin as the impregnating adhesive, and then adds nano-immon clay as a functional agent to prepare a veneer adhesive. This improves the mechanical properties and thermal stability of the board, resulting in significant economic and social benefits. Related technologies typically add starch-based fillers such as flour as additives. However, after high-temperature reaction, the main components—starch (65-75%) and protein (8-15%)—undergo complex chemical changes, exhibiting thermal degradation that produces low-molecular-weight volatile substances. This leads to denaturation, loss of original elastic properties, poor thermal stability, and susceptibility to mold and deterioration in humid environments. Detailed Implementation

[0017] This invention provides a method for preparing hydroxymethylated lignin-phenolic resin, comprising the following steps: Lignin and a first formaldehyde solution are subjected to a first addition reaction under a first alkaline condition to obtain a first product system; the pH value of the first alkaline condition is 11.5~13; the temperature of the first addition reaction is 80~85℃ and the time is 2~3h. Phenol and resorcinol were added to the first product system to carry out a second addition reaction under a second alkaline condition to obtain a second product system; the pH value of the second alkaline condition was 11.5~12.5; the temperature of the second addition reaction was 80~85℃, and the holding time was 1.5~2h; A second formaldehyde solution is added to the second product system, and the temperature is raised to 90°C to carry out a first addition-condensation reaction, and then the temperature is lowered to 80°C to obtain a third product system; the holding time of the first addition-condensation reaction is 50~60 min. After adding a third formaldehyde solution to the third product system, the temperature is raised to 80°C to carry out a second addition-condensation reaction to obtain a fourth product system; the second addition-condensation reaction is carried out under a third alkaline condition with a pH value of 11.5~13; the holding time of the second addition-condensation reaction is 50~60 min. Melamine and propylene carbonate were added to the fourth product system, then the temperature was lowered to 70°C, and the reaction was maintained until the resin viscosity reached 200~350 mPa·s. The mixture was then cooled to obtain the hydroxymethylated lignin-based phenolic resin. Based on the hydroxymethylated lignin-based phenolic resin as 100% by mass, the amount of lignin is 8.6-11.4%; the amount of the first formaldehyde solution is 12-16%; the amount of phenol is 17-20%; the amount of resorcinol is 0.5-1.5%; the amount of the second formaldehyde solution is 24-32%; the amount of the third formaldehyde solution is 4-8%; the amount of melamine is 0.25-0.5%; the amount of propylene carbonate is 0.8-1.6%; and the purity of the first, second, and third formaldehyde solutions is 37%.

[0018] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0019] In this invention, lignin and a first formaldehyde solution are subjected to a first addition reaction under a first alkaline condition to obtain a first product system.

[0020] The amounts of raw materials used in each step will be explained in detail later. In this invention, the pH value of the first alkaline condition is 11.5-13, and in specific embodiments it can be 11.5, 12, 12.5 or 13. Preferably, the pH value of the first alkaline condition is controlled within the above range by adding an aqueous sodium hydroxide solution; the mass concentration of the sodium hydroxide solution is 30%. In this invention, the temperature of the first addition reaction is 80-85°C, and in specific embodiments it can be 80, 81, 82, 83, 84 or 85°C; the time of the first addition reaction is 2-3 hours, and in specific embodiments it can be 2, 2.5 or 3 hours. In this invention, the first addition reaction is preferably carried out under stirring conditions.

[0021] In the first addition reaction process of the present invention, the unoccupied phenolic hydroxyl groups on the lignin benzene ring undergo an addition reaction with formaldehyde molecules to generate hydroxymethyl lignin. These hydroxymethyl groups can undergo condensation reactions with phenol, resorcinol or other lignin active functional groups in subsequent reactions. The substitution rate of phenol by hydroxymethylated lignin can reach about 30-40%.

[0022] After obtaining the first product system, the present invention adds phenol and resorcinol to the first product system to carry out a second addition reaction under a second alkaline condition to obtain the second product system.

[0023] In this invention, the pH value of the second alkaline condition is 11.5~12.5, and in specific embodiments it can be 11.5, 12 or 12.5. Preferably, the pH value of the second alkaline condition is controlled within the above range by adding an aqueous sodium hydroxide solution; the mass concentration of the aqueous sodium hydroxide solution is 30%. In this invention, the temperature of the second addition reaction is 80~85℃, and in specific embodiments it can be 80, 81, 82, 83, 84 or 85℃; the time of the second addition reaction is 1.5~2 hours. In this invention, the second addition reaction is preferably carried out under stirring conditions. After adding phenol and resorcinol, formaldehyde undergoes an addition reaction with phenol and resorcinol under the second alkaline condition to generate polyhydroxymethylphenol, forming a mixture of monohydroxymethylphenol and polyhydroxymethylphenol. Therefore, the second product system of this invention mainly consists of a mixture of monohydroxymethylphenol and polyhydroxymethylphenol. The addition of resorcinol to replace part of the phenol in this invention helps to reduce the content of free phenol.

[0024] After obtaining the second product system, the present invention adds a second formaldehyde solution to the second product system, first heats up to 90°C to carry out a first addition-condensation reaction, and then cools down to 70~80°C to obtain the third product system.

[0025] In this invention, the first heating rate is preferably 0.6~1.2℃ / min, and in specific embodiments it can be 0.6, 0.8, 0.9, 1.0 or 1.2℃ / min. The holding time for the first addition-condensation reaction is preferably 50~60min; the first condensation reaction is preferably carried out under stirring conditions.

[0026] In the first addition-condensation reaction process of the present invention, hydroxymethylphenol can continue to undergo an addition reaction with formaldehyde to generate dihydroxymethylphenol and trihydroxymethylphenol. The mixture of hydroxymethylphenol undergoes a condensation reaction with phenol or with each other to generate a linear initial phenolic resin.

[0027] After obtaining the third product system, the present invention adds a third formaldehyde solution to the third product system, and then raises the temperature to 80°C to carry out a second addition-condensation reaction to obtain the fourth product system.

[0028] In this invention, the second heating rate is preferably 0.6~1.2℃ / min, and in specific embodiments it can be 0.6, 0.8, 0.9, 1.0 or 1.2℃ / min. In this invention, the second addition-condensation reaction is carried out under a third alkaline condition, the pH of which is 11.5~13, and in specific embodiments it can be 11.5, 12, 12.5 or 13. Preferably, the pH of the third alkaline condition is controlled within the above range by adding an aqueous sodium hydroxide solution; the mass concentration of the aqueous sodium hydroxide solution is 30%. In this invention, the temperature of the second addition-condensation reaction is 80℃, and the holding time is 50~60min. In this invention, the second addition-condensation reaction is preferably carried out under stirring conditions. In this invention, the fourth product system mainly consists of hydroxymethylphenol and a linear phenolic ester resin.

[0029] The addition reaction of formaldehyde to phenol is an exothermic reaction. To avoid excessively rapid heating, this invention adds formaldehyde in stages and slowly, and controls the rates of the first and second heating. This controls the exothermic process and reaction temperature, and solves the problem of excessively large differences in the number-average and weight-average molecular weights of the resin products from the subsequent polycondensation reaction.

[0030] After obtaining the fourth product system, the present invention adds melamine and propylene carbonate to the fourth product system, then cools to 70°C and maintains the temperature until the resin viscosity reaches 200-300 mPa·s, then cools down to obtain the hydroxymethylated lignin-based phenolic resin. In the present invention, the polycondensation reaction continues during the heat preservation reaction, causing the resin viscosity to continuously increase.

[0031] The purpose of adding melamine in this invention is to reduce free formaldehyde and free phenol; the addition of acrylate carbonate in this invention can lower the curing temperature, increase the curing rate, and achieve medium-low temperature curing of hydroxymethylated lignin phenolic resin.

[0032] In this invention, based on the hydroxymethylated lignin-based phenolic resin as 100% by mass, the amount of lignin used is 8.6% to 11.4%, and in specific embodiments it can be 8.6%, 9%, 9.5%, 10%, 10.5%, 11%, or 11.4%; the amount of the first formaldehyde solution used is 12% to 16%, and in specific embodiments it can be 12%, 13%, 14%, 15%, or 16%; the amount of phenol used is 17% to 20%, and in specific embodiments it can be 17%, 18%, 19%, or 20%; the amount of resorcinol used is 0.5% to 1.5%, and in specific embodiments it can be 0.5%, 0.7%, 1.0%, 1.2%, or... 1.5%; the amount of the second formaldehyde solution is 24-32%, and in specific embodiments it can be 24%, 26%, 28%, 30% or 32%; the amount of the third formaldehyde solution is 4-8%, and in specific embodiments it can be 4%, 5%, 6%, 7% or 85%; the amount of melamine is 0.25-0.5%, and in specific embodiments it can be 0.25%, 0.3%, 0.4% or 0.5%; the amount of propylene carbonate is 0.8-1.6%, and in specific embodiments it can be 0.8%, 1.0%, 1.2%, 1.4% or 1.6%; the purity of the first formaldehyde solution, the second formaldehyde solution and the third formaldehyde solution is 37%.

[0033] The present invention provides a hydroxymethylated lignin phenolic resin prepared by the preparation method described above. The hydroxymethylated lignin phenolic resin has a pH value of 11.5~13, a solid content of ≥35%, a viscosity of 200~350 mpa·s, a formaldehyde release of ≤0.15%, a free phenol content of ≤0.1%, a curing temperature of 120~135℃, a curing time of 12~16 min, and a number average molecular weight of 2000~10000.

[0034] This invention provides the application of the hydroxymethylated lignin phenolic resin described above in the preparation of bamboo-wood composite boards.

[0035] This invention provides a method for producing bamboo-wood composite container floor panels, comprising the following steps: The above-mentioned hydroxymethylated lignin phenolic resin was diluted to a concentration of 25-35% to obtain an adhesive; the radial bamboo curtain was impregnated with the adhesive and then dried to obtain the impregnated bamboo curtain. Nano-immon clay was added to the above-mentioned hydroxymethylated lignin phenolic resin to adjust the viscosity to 2500~3000 mPa·s, resulting in a mixed adhesive; the mixed adhesive was then coated onto the surface of a wood veneer to obtain the coated veneer; the moisture content of the wood veneer before coating was 5~8%; The bamboo curtain after being impregnated with glue and the veneer after being coated with glue are assembled, pre-pressed and hot-pressed according to the process design to obtain the bamboo-wood composite container floor; the hot pressing temperature is 130~140℃ and the time is 30~35min.

[0036] The present invention dilutes the above-mentioned hydroxymethylated lignin phenolic resin to a solid content of 25-35% to obtain an adhesive.

[0037] In this invention, the diluent used for dilution is preferably water. In specific embodiments, the solid content after dilution can be 25%, 28%, 30%, 32%, or 35%.

[0038] After obtaining the adhesive, the present invention impregnates the radial bamboo curtain with the adhesive, and then removes and dries it to obtain the impregnated bamboo curtain.

[0039] In this invention, the moisture content of the radial bamboo curtain is preferably 0-10%, and in specific embodiments it can be 0, 2, 4, 6, 8, or 10%; the thickness of the radial bamboo curtain is preferably 1.5-3.0 mm, and in specific embodiments it can be 1.5, 2.0, 2.5, or 3.0 mm. In this invention, the impregnation time is preferably 180-240 s, and in specific embodiments it can be 180, 190, 200, 210, 220, 230, or 240 s. This invention does not impose a special limitation on the drying method; a drying method well known in the art can be used, such as: air-drying after resin application followed by drying in a tunnel kiln. In this invention, the moisture content of the dried, impregnated bamboo curtain is preferably 10-20%, and in specific embodiments it can be 10, 12, 14, 16, 18, or 20%.

[0040] In this invention, nano-immon clay is added to the above-mentioned hydroxymethylated lignin phenolic resin to adjust the viscosity to 2500~3000 mPa·s, thereby obtaining a mixed adhesive.

[0041] In this invention, the nano-immon clay preferably has a dry powder particle size of 70% <100nm; the preparation method of the nano-immon clay preferably includes the following steps: using a high energy density medium stirring mill to perform ultrafine grinding of the immon clay (RI / S) slurry, so that the immon clay achieves a dry powder particle size of 70% <100nm, and then drying to obtain the nano-immon clay.

[0042] In this invention, the ultrafine grinding is preferably performed using a high-energy-density media stirring mill; the ultrafine grinding time is preferably 2 hours; the grinding media used for ultrafine grinding is Y₂O₃-stabilized ZrO₂ ceramic microspheres with a bead diameter of 0.6~0.8 mm. In this invention, illite clay is a transitional mineral form of montmorillonite to illite during diagenesis, and it is widely distributed in various geological bodies such as soils, rock weathering crusts, modern marine and lacustrine sediments, various sedimentary rocks from the Cenozoic to Paleozoic eras, as well as hydrothermal veins and volcanic sediments. In this invention, the illite clay used is a commercially available product.

[0043] This invention utilizes nano-immon clay to replace organic fillers such as flour and corn flour that have long been used in the engineered wood products industry. It serves as a resin viscosity modifier, saves grain resources, reduces production costs, and improves the bonding performance and weather resistance of the boards.

[0044] In this invention, the amount of nano-immon clay used is sufficient to make the viscosity of the mixed adhesive reach 2500~3000 mpa·s. In specific embodiments, the viscosity of the mixed adhesive can be 2500, 2600, 2700, 2800, 2900 or 3000 mpa·s.

[0045] After obtaining the mixed adhesive, the present invention applies the mixed adhesive to the surface of the wood veneer to obtain the veneer after adhesive application.

[0046] In this invention, the wood veneer preferably comprises rubberwood veneer; the moisture content of the wood veneer before gluing is preferably 5-8%, and in specific embodiments it can be 5, 6, 7, or 8%; the coating preferably includes brushing. In this invention, the amount of glue applied to the surface of the wood veneer is preferably 210-290 g / m². 2 In specific embodiments, the values ​​can be 210, 220, 230, 240, 250, 260, 270, 280, or 290 g / m³. 2 .

[0047] After obtaining the impregnated bamboo curtain and the coated veneer, the present invention assembles, pre-presses and hot-presses the impregnated bamboo curtain and coated veneer according to the process design to obtain the bamboo-wood composite container floor.

[0048] The present invention does not have special requirements for the implementation process of the preform assembly and pre-pressing; any implementation process well known in the art can be used. In the present invention, the preform assembly preferably also uses a wooden veneer. For example, a pine veneer with a thickness of 1.0~2.0mm can be used.

[0049] In this invention, the hot-pressing temperature is 130~140℃, and the time is 30~35 minutes. In specific embodiments, the hot-pressing temperature can be 130, 135, or 140℃. The hot-pressing pressure is preferably 3~4.5 MPa, and in specific embodiments, it can be 3, 3.5, 4.0, or 4.5 MPa. In this invention, the compression ratio after pre-pressing and hot-pressing is preferably 20~25%.

[0050] This invention provides a bamboo-wood composite container floor obtained by the production method described above, which has good mechanical properties and thermal stability. Specifically, the bamboo-wood composite container floor has a longitudinal short-span shear force ≥8500N, a transverse short-span shear force ≥2500N, a central concentrated load ≥58000N, and a 24-hour water absorption thickness expansion rate ≤15%.

[0051] The following detailed descriptions, in conjunction with embodiments, illustrate the hydroxymethylated lignin phenolic resin and its preparation method and application, as well as the bamboo-wood composite container floor and its production method provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0052] The mass fractions in the following examples refer to the mass fractions of hydroxymethylated lignin-based phenolic resins.

[0053] Example 1 1. Preparation of hydroxymethylated lignin-phenolic resin: (1) One-time feeding: Place 8.6% lignin, 12% formaldehyde solution (purity 37%) and sodium hydroxide aqueous solution (sodium hydroxide aqueous solution mass concentration 30%) in the reactor, control the pH to 12, and stir at 80℃ for 2h; (2) Secondary feeding: Slowly add 20% phenol and 0.5% resorcinol and sodium hydroxide aqueous solution to the reactor, control the pH of the system to 11.5, and continue the reaction at 80℃ for 1.5h; (3) Three feedings: Slowly add 32% formaldehyde solution, control the heating rate at 0.6℃ / min, finish feeding at 75℃, gradually increase the temperature to 90℃, keep the temperature for 50min, and then cool down to 80℃; (4) Four additions: Slowly add 4% formaldehyde solution to the system, control the heating rate at 0.6℃ / min, add sodium hydroxide aqueous solution, control the pH at 11.5, and stir at 80℃ for 50min; (5) Endpoint control: Add 0.25% melamine and 0.8% propylene carbonate to the obtained system, then cool down to 70°C, keep the reaction at the temperature for 50 min, control the resin viscosity to reach 250 mpa·s, cool down, and discharge the material to obtain hydroxymethylated lignin-based phenolic resin. The main properties of the hydroxymethylated lignin-based phenolic resin adhesive are: pH 11.5, solids content ≥35%, rotational viscosity of 250 mPa·s at 23℃, formaldehyde release 0.12%, free phenol content 0.08%, curing temperature 120℃, curing time 12 min, and number average molecular weight 3000.

[0054] 2. Nano-sizing treatment of Immon clay: (1) Crush the blocky Yimon clay, mix it with water at a ratio of 1:2 to make a slurry, and soak it for 15 minutes; (2) The soaked Immon clay slurry is mashed; (3) The Yimeng clay slurry was ultra-finely ground for 2 hours using a high energy density media stirring mill. The grinding media used was Y2O3 stabilized ZrO2 ceramic microspheres (bead diameter 0.6~0.8mm). (4) The ground slurry is dried and dispersed to obtain nano-Imon clay dry powder.

[0055] 3. Application of bamboo-wood composite container flooring: (1) The radial bamboo curtain with a thickness of 2.0 mm has a moisture content of 6% after drying. Prepare an adhesive for impregnating the radial bamboo curtain, control the impregnation concentration of hydroxymethylated lignin-based phenolic resin to be 25%, and immerse the bamboo curtain in the prepared lignin-modified phenolic resin adhesive for 180 seconds. After impregnation, drain the adhesive, air dry, and dry in a tunnel kiln until the moisture content is 12%. (2) The pine veneer with a thickness of 1.0 mm and the rubberwood veneer with a thickness of 1.7 mm had a moisture content of 6% after drying. The mixed adhesive needed for the veneer was prepared by slowly adding 5% nano-immon clay to the hydroxymethylated lignin-based phenolic resin adhesive to adjust the adhesive viscosity to 2500 mPa·s. The mixed adhesive was then evenly applied to the veneer surface at a coating weight of 210 g / m². 2 The bamboo mats, after being impregnated with glue, and the veneers, after being assembled, pre-pressed, and hot-pressed, are made into box panels, with the compression rate of the panels controlled at 25%. The main technical parameters are: hot-pressing unit pressure 3MPa, hot-pressing temperature 130℃, and hot-pressing time 30min.

[0056] The product's physical and mechanical properties were tested according to the bamboo-wood composite container floor standards T / CSF 009-2019 and GB / T17657-2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels". The main performance indicators are: short-span shear force (longitudinal) 9550N, short-span shear force (transverse) 2830N, central concentrated load ≥59570N, and 24-hour water absorption thickness expansion rate of 12%.

[0057] Example 2 1. The preparation process of hydroxymethylated lignin-phenolic resin includes the following steps: (1) One-time feeding: Place 10% lignin, 14% formaldehyde solution (purity 37%) and sodium hydroxide aqueous solution (sodium hydroxide aqueous solution mass concentration 30%) in the reactor, control the pH to 12, and stir at 80℃ for 2.5h; (2) Secondary feeding: Slowly add phenol with a mass fraction of 18%, resorcinol with a mass fraction of 1.0%, and sodium hydroxide aqueous solution to the reactor, control the pH of the system to 11.5, and continue the reaction for 2 hours; (3) Three feedings: Slowly add 27% formaldehyde solution, control the heating rate at 1.0℃ / min, finish feeding at 80℃, gradually increase the temperature to 90℃, keep the temperature for 55min, and then cool down to 80℃; (4) Four additions: Slowly add 4% formaldehyde solution to the system, control the heating rate at 1.0℃ / min, add sodium hydroxide aqueous solution, control the pH at 12, and stir at 80℃ for 55min; (5) Endpoint control: Add 0.4% melamine and 1.2% propylene carbonate to the obtained system, cool to 70℃, and keep the reaction at that temperature for 55 min. Control the resin viscosity to reach 230 mPa·s, cool down, and discharge to obtain hydroxymethylated lignin-based phenolic resin adhesive; (6) The main properties of hydroxymethylated lignin-based phenolic resin adhesive are: pH 12, solid content ≥35%, rotational viscosity of 230 mPa·s at 23℃, formaldehyde release 0.12%, free phenol content 0.09%, curing temperature 125℃, curing time 14 min, and number average molecular weight of 6000.

[0058] 2. Nano-sizing treatment of Immon clay: Same as Example 1.

[0059] 3. Application of bamboo-wood composite container flooring: (1) The radial bamboo curtain with a thickness of 2.0 mm had a moisture content of 7% after drying. A glue for impregnating the radial bamboo curtain was prepared, and the impregnation concentration of hydroxymethylated lignin-modified phenolic resin was controlled at 30%. The bamboo curtain was then immersed in the prepared lignin-modified phenolic resin adhesive for 240 seconds. After impregnation, the glue was drained, air-dried, and then dried in a tunnel kiln until the moisture content reached 15%. Samples were taken to test the glue content. (2) The pine veneer with a thickness of 1.0 mm and the rubberwood veneer with a thickness of 1.7 mm had a moisture content of 7% after drying. The mixed adhesive required for the veneer was prepared by slowly adding 15% nano-immon clay (NI / S) to the hydroxymethylated lignin-based phenolic resin adhesive to adjust the adhesive viscosity to 2800 mPa·s, and then uniformly brushing it onto the veneer surface at a coating weight of 210 g / m². 2 The bamboo mats, after being impregnated with glue, and the veneers, after being assembled, pre-pressed, and hot-pressed, are made into box panels, with the compression rate of the panels controlled at 25%. The main technical parameters are: hot-pressing unit pressure 4MPa, hot-pressing temperature 135℃, and hot-pressing time 35min.

[0060] The product's physical and mechanical properties were tested according to the bamboo-wood composite container floor standards T / CSF 009-2019 and GB / T17657-2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels". The main performance indicators are: short-span shear force (longitudinal) 11620N, short-span shear force (transverse) 3290N, central concentrated load 65410N, and 24-hour water absorption thickness expansion rate of 10%.

[0061] Example 3 1. The preparation process of hydroxymethylated lignin-phenolic resin includes the following steps: (1) One-time feeding: 11% lignin, 16% formaldehyde solution (purity 37%) and 8% sodium hydroxide aqueous solution (sodium hydroxide aqueous solution mass concentration 30%) were placed in the reactor, the pH was controlled at 13, and the mixture was stirred at 85℃ for 3h. (2) Secondary feeding: Slowly add phenol with a mass fraction of 17%, resorcinol with a mass fraction of 1.5%, and sodium hydroxide to the reactor, control the pH of the system to 12.5, and continue the reaction for 2 hours; (3) Three feedings: Slowly add 24% formaldehyde solution, control the heating rate at 1.2℃ / min, finish feeding at 85℃, gradually increase the temperature to 90℃, keep the temperature for 60min, and then cool down to 80℃; (4) Four additions: Slowly add 5% formaldehyde solution to the system, control the heating rate at 1.2℃ / min, add sodium hydroxide aqueous solution, control the pH at 13, and stir at 80℃ for 50~60min; (5) Endpoint control: Add 0.5% melamine and 1.6% propylene carbonate to the obtained system, cool to 70℃, and keep the reaction at that temperature for 60 min. Control the resin viscosity to reach 280 mPa·s, cool down, and discharge to obtain hydroxymethylated lignin-based phenolic resin; (6) The main properties of hydroxymethylated lignin-based phenolic resin are: pH 13, solid content ≥35%, rotational viscosity of 280 mPa·s at 23℃, formaldehyde release 0.11%, free phenol content 0.08%, curing temperature 130℃, curing time 16 min, and number average molecular weight of 9000.

[0062] 2. Nano-sizing treatment of Immon clay: Same as Example 1.

[0063] 3. Application of bamboo-wood composite container flooring: (1) The radial bamboo curtain with a thickness of 2.0 mm has a moisture content of 9% after drying. Prepare the adhesive for impregnating the radial bamboo curtain, control the impregnation concentration of hydroxymethylated lignin-based phenolic resin to be 35%, and immerse the bamboo curtain in the prepared lignin-modified phenolic resin adhesive for 240 seconds. After impregnation, drain the adhesive, air dry, and dry in a tunnel kiln until the moisture content is 20%. (2) After drying, the pine veneer with a thickness of 1.0 mm and the rubberwood veneer with a thickness of 1.7 mm have a moisture content of 7%. To prepare the mixed adhesive for the veneer, 20% nano-immon clay (NI / S) is slowly added to the hydroxymethylated lignin-based phenolic resin adhesive to adjust the adhesive viscosity to 3000 mPa·s. The mixed adhesive is then evenly brushed onto the veneer surface with a coating amount of 250 g / m³. 2 The bamboo mats, after being impregnated with glue, and the veneers, after being assembled, pre-pressed, and hot-pressed, are made into box panels, with the compression rate of the panels controlled at 25%. The main technical parameters are: hot-pressing unit pressure 4.5MPa, hot-pressing temperature 135℃, and hot-pressing time 35min.

[0064] The product's physical and mechanical properties were tested according to the bamboo-wood composite container floor standards T / CSF 009-2019 and GB / T17657-2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels". The main performance indicators are: short-span shear force (longitudinal) 11230N, short-span shear force (transverse) 3120N, central concentrated load 75300N, and 24-hour water absorption thickness expansion rate of 13%.

[0065] Comparative Example 1 The only difference from Example 1 is the use of commercially available phenolic resin and the replacement of nano-immon clay with flour as the viscosity modifier, adjusting the adhesive viscosity to 3000 mPa·s. Otherwise, the results are the same as in Example 1. Compared to Example 1, Comparative Example 1 exhibits significantly lower thermal stability. Comparative Example 1 uses starch-based fillers such as flour as additives. Under high temperatures of around 200-300°C, starch and protein undergo thermal degradation, generating low-molecular-weight volatile substances. Simultaneously, the starch denatures and loses its original elastic properties, ultimately resulting in poor thermal stability of the board. In contrast, the nano-immon clay used in Example 1 typically has a decomposition temperature above 600°C, exhibiting extremely high thermal stability.

[0066] Table 1. Performance of bamboo-wood composite container flooring prepared in the examples and comparative examples.

[0067] As shown in Table 1, the mechanical properties of the bamboo-wood composite container floor are significantly improved by using hydroxymethylated lignin phenolic resin instead of traditional phenolic resin as an adhesive and combining it with nano-immon clay as a viscosity modifier.

[0068] Table 2. Properties of hydroxymethylated lignin-based phenolic resin and conventional phenolic resin prepared in the examples.

[0069] Note: In this invention, the curing time was measured with reference to GB / T 14074-2017, and the curing temperature was measured with reference to GB / T 32681-2016.

[0070] As shown in Table 2, compared with conventional phenolic resin, the curing temperature of hydroxymethylated lignin-based phenolic resin adhesive can be reduced to 120~130℃ (compared to the conventional requirement of above 135℃), the curing time can be shortened to 12~16min (compared to the conventional requirement of 20min), and the curing efficiency can be increased by 20~25%, which greatly improves production efficiency and reduces energy consumption.

[0071] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing hydroxymethylated lignin-phenolic resin, characterized in that, Includes the following steps: Lignin and a first formaldehyde solution are subjected to a first addition reaction under a first alkaline condition to obtain a first product system; the pH value of the first alkaline condition is 11.5~13; the temperature of the first addition reaction is 80~85℃ and the time is 2~3h. Phenol and resorcinol were added to the first product system to carry out a second addition reaction under a second alkaline condition to obtain a second product system; the pH value of the second alkaline condition was 11.5~12.5; the temperature of the second addition reaction was 80~85℃, and the holding time was 1.5~2h; A second formaldehyde solution is added to the second product system, and the temperature is raised to 90°C to carry out a first addition-condensation reaction, and then the temperature is lowered to 70~80°C to obtain a third product system; the holding time of the first addition-condensation reaction is 50~60 min. After adding a third formaldehyde solution to the third product system, the temperature is raised to 80°C to carry out a second addition-condensation reaction to obtain a fourth product system; the second addition-condensation reaction is carried out under a third alkaline condition with a pH value of 11.5~13; the holding time of the second addition-condensation reaction is 50~60 min. Melamine and propylene carbonate were added to the fourth product system, then the temperature was lowered to 70°C, and the reaction was maintained until the resin viscosity reached 200~350 mPa·s. The mixture was then cooled to obtain the hydroxymethylated lignin-based phenolic resin. Based on the hydroxymethylated lignin-based phenolic resin as 100% by mass, the amount of lignin is 8.6-11.4%; the amount of the first formaldehyde solution is 12-16%; the amount of phenol is 17-20%; the amount of resorcinol is 0.5-1.5%; the amount of the second formaldehyde solution is 24-32%; the amount of the third formaldehyde solution is 4-8%; the amount of melamine is 0.25-0.5%; the amount of propylene carbonate is 0.8-1.6%; and the purity of the first, second, and third formaldehyde solutions is 37%.

2. The preparation method according to claim 1, characterized in that, The pH values ​​of the first, second, and third alkaline conditions are adjusted by an aqueous sodium hydroxide solution with a mass concentration of 30%.

3. The preparation method according to claim 1, characterized in that, The rates of the first and second heating are independently 0.6~1.2℃ / min.

4. The hydroxymethylated lignin-phenolic resin prepared by the preparation method according to any one of claims 1 to 3, characterized in that, The hydroxymethylated lignin-phenolic resin has a pH value of 11.5~13, a solid content of ≥35%, a viscosity of 200~350 mPa·s, a formaldehyde release of ≤0.15%, a free phenol content of ≤0.1%, a curing temperature of 120~135℃, a curing time of 12~16 min, and a number average molecular weight of 2000~10000.

5. A method for producing a bamboo-wood composite container floor, characterized in that, Includes the following steps: The hydroxymethylated lignin phenolic resin of claim 4 is diluted to a solid content of 25-35% to obtain an adhesive; the radial bamboo curtain is impregnated in the adhesive and then dried to obtain the impregnated bamboo curtain. Nano-immon clay was added to the hydroxymethylated lignin phenolic resin according to claim 3 to adjust the viscosity to 2500~3000 mpa·s, resulting in a mixed adhesive; the mixed adhesive was then coated onto the surface of a wood veneer to obtain a coated veneer; the moisture content of the wood veneer before coating was 5~8%; The bamboo curtain after being impregnated with glue and the veneer after being coated with glue are assembled, pre-pressed and hot-pressed according to the process design to obtain the bamboo-wood composite container floor; the hot pressing temperature is 130~140℃, the pressure is 3~4.5MPa and the time is 30~35min.

6. The production method according to claim 5, characterized in that, The nano-Imon clay has a dry powder particle size of 70% <100nm.

7. The production method according to claim 5, characterized in that, The moisture content of the bamboo mat after impregnation and drying is 10-20%; the moisture content of the radial bamboo mat before impregnation is 0-10%.

8. The production method according to claim 5 or 7, characterized in that, The thickness of the radial bamboo curtain is 1.5~3.0mm; the impregnation time is 180~240s.

9. The production method according to claim 5, characterized in that, The amount of glue applied to the surface of the wood veneer is 210~290g / m². 2 .

10. The bamboo-wood composite container floor obtained by the production method according to any one of claims 5 to 9, characterized in that, The bamboo-wood composite container floor has a longitudinal short-span shear force ≥8500N, a transverse short-span shear force ≥2500N, a central concentrated load ≥58000N, and a 24-hour water absorption thickness expansion rate ≤15%.

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