Method for preparing low-VOCs type medium density fiberboard based on wood fiber hydroxyl complexing sealing technology

Abstract

The invention relates to the technical field of artificial board processing, and discloses a method for preparing a low VOCs type medium density fiberboard based on a wood fiber hydroxyl complexing sealing technology. The method comprises the following steps: firstly, carrying out steam explosion pretreatment on wood fibers, destroying the crystal structure of the wood fibers and activating hydroxyl; carrying out carboxylation and condensation polymerization on the activated fibers by adopting biomass-based polycarboxylic acid and amine compounds, and constructing complexing sites on the surfaces of the fibers; then metal ions are introduced to be subjected to a complexation reaction with the fibers, and stable sealing of hydroxyl in fiber molecules is achieved; and finally, sizing by adopting a modified bean-based protein adhesive, and carrying out paving, pre-pressing and hot press molding. Through the synergistic effect of activation, crosslinking and complexation, a VOCs release channel is blocked from the source, the formaldehyde release amount of the prepared fiberboard is smaller than or equal to 0.025 mg / m < 3 > (ENF level), the total VOCs release amount is smaller than or equal to 200 micrograms / m < 3 >, the odor level is remarkably reduced, meanwhile, the mechanical property is excellent, and outstanding environmental friendliness and practicability are achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of wood-based panel processing, and particularly relates to a method for preparing low-VOCs medium-density fiberboard based on wood fiber hydroxyl complexation sealing technology. BACKGROUND

[0002] Fiberboard is widely used in furniture manufacturing, interior decoration and other fields due to its wide raw material sources, uniform texture and good processing performance. However, traditional fiberboard production generally uses urea-formaldehyde resin (UF), phenol-formaldehyde resin (PF) and other adhesives, which can continuously release free formaldehyde for a long time, causing harm to human health and the environment. In addition, wood itself can also decompose and produce formaldehyde, acetic acid, terpenes, ketones and other volatile organic compounds (VOCs) during hot pressing, resulting in a pungent odor of the board.

[0003] To reduce the amount of formaldehyde release, people mainly adopt the following methods: (1) using modified urea-formaldehyde glue (such as adding melamine, capture agent); (2) using isocyanate (MDI) adhesive. However, method (1) cannot fundamentally solve the problem of formaldehyde release, and may introduce other pollutants; method (2) can achieve no formaldehyde addition, but MDI is expensive and easy to stick to the board during hot pressing, limiting its wide application. At the same time, these two methods do not effectively solve the problem of wood VOCs release.

[0004] To reduce the VOCs and formaldehyde content of fiberboard, the traditional process is to directly mix the adsorbent (auxiliary agent) with the raw material for pressing, such as CN 113150399 A discloses a low-odor wood-based panel and a preparation method thereof, which mixes and presses layered MXene adsorbent material with wood fiber; CN 110696140 A discloses a production method of low-odor environment-friendly wood-based panel, which directly mixes orange peel powder, tea powder and slow-release odor grade capsules with wood raw materials to prepare low-odor board. Although the addition of adsorbents can temporarily reduce VOCs and odor, the adsorption of adsorbents to odor is mainly a physical action, and is in a state of adsorption balance. With the change of temperature, humidity or other environment, formaldehyde and VOCs will eventually be released into the environment, causing adverse effects on human body. In recent years, biomass modification technology has provided a new idea for the development of ultra-low VOCs board. For example, steam explosion technology can efficiently separate fibers and degrade hemicellulose to produce active groups; biomass-based polycarboxylic acid can esterify and cross-link with cellulose hydroxyl groups to realize formaldehyde-free gluing; metal complexing agents can combine with carbonyl and carboxyl groups in wood components to fix small molecule organic compounds. However, there is no mature solution to integrate the above technologies and apply them to fiberboard preparation to solve the problems of formaldehyde and total VOCs.

[0005] Therefore, it is of great industrial value to develop a comprehensive method that can permanently seal the VOCs release source through chemical action. Summary of the Invention

[0006] In view of the above, it is necessary to provide a method for preparing low-VOC medium fiberboard based on lignocellulose hydroxyl complexation and sealing technology. By causing the hydroxyl groups of lignocellulose to undergo chemical reaction to form a sealing effect, a medium fiberboard with low VOCs, low odor and excellent mechanical properties can be prepared.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows.

[0008] A method for preparing low-VOC medium fiberboard based on lignocellulose hydroxyl complexation sealing technology includes the following steps.

[0009] (1) Steam explosion pretreatment: The wood fibers were soaked in a sodium hydroxide-urea mixture and placed in a steam explosion tank to be blasted by saturated steam to obtain activated wood fibers.

[0010] (2) Carboxylation and polycondensation treatment: The activated fiber obtained in step (1) is mixed with biomass-based polycarboxylic acid, catalyst and sodium hydroxide, and heated to carry out carboxylation reaction; then amine compounds and dehydrating agent are added, and heated to cause the carboxyl group and amino group to undergo polycondensation reaction to form amide bond.

[0011] (3) Complexation treatment: Add metal salt solution to the system after step (2), stir and adjust pH value to make the metal ions complex with the amide bonds on the fiber.

[0012] (4) Adhesive application and molding: After washing and drying the fibers treated in step (3), a modified soybean protein adhesive is applied, and the fibers are laid, pre-pressed and hot-pressed to obtain the low VOCs type medium fiberboard.

[0013] In this invention, further, in the sodium hydroxide-urea mixture in step (1), the mass concentration of sodium hydroxide is 3~6% and the mass concentration of urea is 5~15%; the conditions for the steam explosion are: pressure 1.0~3.0 MPa, pressure holding time 2~8 min.

[0014] In this invention, the biomass-based polycarboxylic acid in step (2) is one of citric acid, butanetetracarboxylic acid or polymaleic acid, and its amount is 3 to 8% of the dry fiber mass; the catalyst is any one of sodium hypophosphite, sulfuric acid, phosphoric acid, toluenesulfonic acid, potassium permanganate or nitric acid, and its amount is 0.5 to 2.5% of the dry fiber mass.

[0015] In this invention, the amount of sodium hydroxide used in step (2) is 1.0 to 3.5% of the dry fiber mass.

[0016] The oven-dried fibers mentioned are all "activated wood fibers" obtained after steam explosion pretreatment, and are in an oven-dried state.

[0017] In this invention, further, the amine compound mentioned in step (2) is any one of triethylenediamine, triethylamine, methylamine, aniline, and tetrabutylammonium bromide, and its amount is 4 to 10% of the oven-dry fiber mass; the dehydrating agent is any one of dimethylformamide, dicyclohexylcarbodiimide, and N-(triethylammonium sulfonyl)carbamate, and its amount is 2 to 7% of the oven-dry fiber mass.

[0018] In this invention, the metal salt in step (3) is one of zinc sulfate, zinc chloride or aluminum nitrate, and its amount is 1 to 3% of the dry fiber mass based on the metal ion content; the pH value of the complexation reaction is 6.5 to 7.5, and the reaction time is 15 to 30 min.

[0019] In this invention, the modified soybean protein adhesive in step (4) is prepared by the following method: adding 1.5 to 2 times the mass of warm water to soybean flour, and adding 5 to 10% of the mass of soybean flour silane coupling agent KH550 and 3 to 5% of hydrogen peroxide, and stirring and modifying at 60°C for 1.0 h; the amount of adhesive applied is 6 to 15% of the dry fiber mass.

[0020] In this invention, the hot pressing in step (4) further adopts a three-stage process: high pressure stage: pressure 1.2~1.8MPa, temperature 200~240℃; pressure holding stage: pressure 0.2~0.5MPa, temperature 175~190℃; thickness fixing stage: pressure 1.8~2.4MPa, temperature 140~180℃; the pressing plate speed is 5.0~7.5 m / min.

[0021] In this invention, the wood fiber in step (1) is one or more of fast-growing poplar, eucalyptus, fir or pine.

[0022] This invention also proposes a low-VOCs medium-density fiberboard (MDF) prepared by the method described above. Its formaldehyde emission is ≤0.025 mg / m³. 3 Total VOCs release ≤200 μg / m³ 3 .

[0023] Compared with the prior art, the present invention has at least the following beneficial effects.

[0024] This invention achieves significant beneficial effects through a multi-level synergistic effect of "steam explosion-chemical cross-linking-ionic complexation", which are specifically manifested in the following aspects.

[0025] 1. This invention overcomes the limitations of traditional physical adsorption methods, achieving fundamental VOCs control through chemical means. First, steam explosion pretreatment efficiently activates the hydroxyl groups on the fiber surface, disrupting the crystalline structure of cellulose. Subsequently, biomass polycarboxylic acids and amine compounds undergo carboxylation and condensation reactions, constructing abundant amide bond complexation sites on the fiber surface. Finally, metal ions undergo a strong complexation reaction with these sites, directly sealing and immobilizing the source of VOCs release—the active hydroxyl groups—through coordinate and covalent bonds. This "chemical anchoring" mechanism is stable and persistent, unaffected by changes in environmental temperature and humidity, fundamentally solving the industry problem of easy VOCs desorption and rebound, and achieving long-term stable control of release levels.

[0026] 2. This invention combines the dual advantages of source emission reduction and neutralization / fixation. The steam explosion process effectively volatilizes and removes volatile acids, aldehydes, ketones, and terpenes originally present in the wood. Subsequent metal complexation reactions further neutralize residual acidic components. As shown in Table 3, the boards prepared by this invention can achieve an odor level of OD0-OD1 (odorless or with a barely noticeable odor), exhibiting a natural woody fragrance, completely eliminating the pungent chemical odor of traditional engineered wood products, and greatly improving the product's environmental friendliness and user experience.

[0027] 3. Particularly noteworthy is that this invention achieves ultra-low VOCs while significantly enhancing the physical and mechanical properties of the board. Steam explosion and chemical cross-linking treatments greatly increase the roughness and reactivity of the fiber surface. The ester bond cross-linking network formed by the polycarboxylic acid and cellulose molecular chains, along with the complexation bridging effect of metal ions, collectively constructs a robust fiber-fiber interface. Ultimately, this allows the board to achieve internal bond strength (IB) and static bending strength (MOR) superior to national standards even with relatively low sizing (6-15%) (see Table 3), breaking the traditional perception that "environmental protection and mechanical properties are mutually exclusive."

[0028] 4. The core raw materials used in this invention, such as citric acid, butanetetracarboxylic acid, zinc salt, and soy protein, are all environmentally friendly, renewable, or low-cost substances. The entire process is formaldehyde-free, avoiding the use of expensive and process-sensitive MDI isocyanate. The overall cost is only slightly higher than traditional urea-formaldehyde resin fiberboard, but the product's environmental protection level and performance added value are significantly improved. This invention successfully develops a new type of environmentally friendly board solution with excellent comprehensive performance, controllable cost, and easy industrialization, with extremely broad market prospects. Attached Figure Description

[0029] Figure 1 This is a process flow diagram for the preparation of low-VOCs fiberboard in Example 1. Detailed Implementation

[0030] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0031] Example 1

[0032] This embodiment proposes a method for preparing low-VOCs medium fiberboard based on lignocellulose hydroxyl complexation sealing technology, and its process flow diagram is shown below. Figure 1 As shown, the specific steps include:

[0033] (1) Steam explosion pretreatment: The wood fibers after hot grinding were soaked in a mixture of 6% sodium hydroxide and 10% urea for 1.5 h, placed in a steam explosion tank, saturated steam was introduced, and the pressure was maintained at 2.5 MPa for 5.5 min. The pressure was then released and the wood fibers were exploded instantly to obtain activated wood fibers.

[0034] (2) Carboxylation and polycondensation treatment: 100 parts by weight of the activated fiber obtained in (1) are mixed with 5.0 parts by weight of citric acid, 2.0 parts by weight of sodium hypophosphite and 1.5 parts by weight of sodium hydroxide aqueous solution. The mixture is reacted at 95 °C for 1.0 h to complete carboxylation. Then, 5.0 parts by weight of triethylenediamine is added, heated to 80 °C, and 3.0 parts by weight of dimethylformamide is added to allow the carboxyl group (-COOH) to undergo a polycondensation reaction with the amino group (-NH2) for 1.0 h to form an amide bond (-CONH-).

[0035] (3) Complexation treatment: Add 2.5 parts by weight of zinc chloride metal salt solution to the fiber system after step (2), stir the reaction for 20 min, adjust the pH of the system to 6.8, so that the metal ions can undergo a complexation reaction with the amide bonds on the fiber.

[0036] (4) Sizing and molding: After washing the fiber treated in step (3), dry it to a moisture content of 9%, and then apply modified soybean protein adhesive (the modified soybean protein adhesive is prepared by adding 1.6 times its mass of warm water to soybean powder, and adding 8% of the soybean powder mass of silane coupling agent KH550 and 4% of hydrogen peroxide, and stirring and modifying at 60℃ for 1.0 h; the sizing amount is 10% of the oven-dry fiber mass), the sizing amount is 12% of the oven-dry fiber mass, and after mechanical laying and pre-pressing, it is molded by a three-stage hot pressing process of high pressure section, pressure holding section and thickness fixing section, wherein, high pressure section: pressure 1.4 MPa, temperature 230 ℃; pressure holding section: pressure 0.3 MPa, temperature 180 ℃; thickness fixing section: pressure 2.0 MPa, temperature 150 ℃; pressing plate speed 6.0 m / min.

[0037] Example 2

[0038] This embodiment proposes a method for preparing low-VOCs medium fiberboard based on lignocellulose hydroxyl complexation sealing technology, which specifically includes the following steps.

[0039] (1) Steam explosion pretreatment: The wood fibers after hot grinding were soaked in a mixture of 5% sodium hydroxide and 12% urea for 2.0 h, placed in a steam explosion tank, saturated steam was introduced, and the pressure was maintained at 2.0 MPa for 6.0 min. The pressure was then released and the wood fibers were exploded instantly to obtain activated wood fibers.

[0040] (2) Carboxylation and polycondensation treatment: 100 parts by weight of the activated fiber obtained in (1) were mixed with 6.5 parts by weight of butanetetracarboxylic acid, 2.0 parts by weight of sulfuric acid and 2.0 parts by weight of sodium hydroxide aqueous solution. The mixture was reacted at 110 °C for 0.8 h to complete carboxylation. Then 5.0 parts by weight of methylamine were added and heated to 70 °C. 3.0 parts by weight of dicyclohexylcarbodiimide were added to allow the carboxyl group (-COOH) to undergo a polycondensation reaction with the amino group (-NH2) for 0.6 h to form an amide bond (-CONH-).

[0041] (3) Complexation treatment: Add 2.0 parts by weight of zinc sulfate metal salt solution to the fiber system after step (2), stir the reaction for 25 min, adjust the pH of the system to 7.0, so that the metal ions can undergo a complexation reaction with the amide bonds on the fiber.

[0042] (4) Sizing and molding: After washing the fiber treated in step (3), dry it to a moisture content of 8%, and then apply modified soybean protein adhesive (the modified soybean protein adhesive is prepared by adding 1.5 times its mass of warm water to soybean powder, and adding 5% of the soybean powder mass of silane coupling agent KH550 and 3% of hydrogen peroxide, and stirring and modifying at 60℃ for 1.0 h; the sizing amount is 6% of the oven-dry fiber mass), the sizing amount is 10% of the oven-dry fiber mass, and after mechanical laying and pre-pressing, it is molded by a three-stage hot pressing process of high pressure section, pressure holding section and thickness fixing section, wherein, high pressure section: pressure 1.5 MPa, temperature 220 ℃; pressure holding section: pressure 0.4 MPa, temperature 175 ℃; thickness fixing section: pressure 1.9 MPa, temperature 165 ℃; pressing plate speed 6.5 m / min.

[0043] Example 3

[0044] This embodiment proposes a method for preparing low-VOCs medium fiberboard based on lignocellulose hydroxyl complexation sealing technology, which specifically includes the following steps.

[0045] (1) Steam explosion pretreatment: The wood fibers after hot grinding were soaked in a mixture of 4% sodium hydroxide and 15% urea for 1.0 h, placed in a steam explosion tank, saturated steam was introduced, and the pressure was maintained at 1.8 MPa for 5.0 min. The pressure was then released and the wood fibers were exploded instantly to obtain activated wood fibers.

[0046] (2) Carboxylation and polycondensation treatment: 100 parts by weight of the activated fiber obtained in (1) were mixed with 5.0 parts by weight of polymaleic acid, 2.0 parts by weight of sodium hypophosphite and 1.5 parts by weight of sodium hydroxide aqueous solution. The mixture was reacted at 95 °C for 0.8 h to complete carboxylation. Then, 7.0 parts by weight of triethylenediamine was added and heated to 90 °C. 3.0 parts by weight of N-(triethylammonium sulfonyl)carbamate was added to allow the carboxyl group (-COOH) to undergo a polycondensation reaction with the amino group (-NH2) for 1.0 h to form an amide bond (-CONH-).

[0047] (3) Complexation treatment: Add 2.5 parts by weight of zinc chloride metal salt solution to the fiber system after step (2), stir the reaction for 20 min, adjust the pH of the system to 7.0, so that the metal ions can undergo a complexation reaction with the amide bonds on the fiber.

[0048] (4) Sizing and molding: After washing the fiber treated in step (3), dry it to a moisture content of 8%, and then apply modified soybean protein adhesive (the modified soybean protein adhesive is prepared by adding 1.6 times its mass of warm water to soybean powder, and adding 6% of the soybean powder mass of silane coupling agent KH550 and 5% of hydrogen peroxide, and stirring and modifying at 60℃ for 1.0 h; the sizing amount is 9% of the oven-dry fiber mass), the sizing amount is 12% of the oven-dry fiber mass, and after mechanical laying and pre-pressing, it is molded by a three-stage hot pressing process of high pressure section, pressure holding section and thickness fixing section, wherein, high pressure section: pressure 1.8 MPa, temperature 210 ℃; pressure holding section: pressure 0.3 MPa, temperature 190 ℃; thickness fixing section: pressure 1.8 MPa, temperature 170 ℃; pressing plate speed 6.0 m / min.

[0049] Example 4

[0050] This embodiment proposes a method for preparing low-VOCs medium fiberboard based on lignocellulose hydroxyl complexation sealing technology, which specifically includes the following steps.

[0051] (1) Steam explosion pretreatment: The wood fibers after hot grinding were soaked in a mixture of 6% sodium hydroxide and 10% urea for 1.5 h, placed in a steam explosion tank, saturated steam was introduced, and the pressure was maintained at 3.0 MPa for 3.5 min. The pressure was then released and the wood fibers were exploded instantly to obtain activated wood fibers.

[0052] (2) Carboxylation and polycondensation treatment: 100 parts by weight of the activated fiber obtained in (1) were mixed with 5.5 parts by weight of citric acid, 2.0 parts by weight of toluenesulfonic acid and 2.5 parts by weight of sodium hydroxide aqueous solution. The mixture was reacted at 105 °C for 0.8 h to complete carboxylation. Then 7.0 parts by weight of aniline were added and heated to 80 °C. 5.0 parts by weight of dimethylformamide were added to allow the carboxyl group (-COOH) to undergo a polycondensation reaction with the amino group (-NH2) for 0.8 h to form an amide bond (-CONH-).

[0053] (3) Complexation treatment: Add 1.5 parts by weight of aluminum nitrate metal salt solution to the fiber system after step (2), stir the reaction for 25 min, adjust the pH of the system to 6.9, so that the metal ions can undergo a complexation reaction with the amide bonds on the fiber.

[0054] (4) Sizing and molding: After washing the fiber treated in step (3), dry it to a moisture content of 10%, and then apply modified soybean protein adhesive (the modified soybean protein adhesive is prepared by adding warm water with a mass of 2 times to soybean powder, and adding 10% of the soybean powder mass of silane coupling agent KH550 and 5% of hydrogen peroxide, and stirring and modifying at 60°C for 1.0 h; the sizing amount is 15% of the oven-dry fiber mass). The sizing amount is 9% of the oven-dry fiber mass. After mechanical laying and pre-pressing, it is molded by a three-stage hot pressing process of high pressure section, pressure holding section and thickness fixing section. Among them, high pressure section: pressure 1.5 MPa, temperature 220 ℃; pressure holding section: pressure 0.4 MPa, temperature 175 ℃; thickness fixing section: pressure 2.2 MPa, temperature 175 ℃; pressing speed 6.5 m / min.

[0055] Example 5

[0056] This embodiment proposes a method for preparing low-VOCs medium fiberboard based on lignocellulose hydroxyl complexation sealing technology, which specifically includes the following steps.

[0057] (1) Steam explosion pretreatment: The wood fibers after hot grinding were soaked in a mixture of 6% sodium hydroxide and 10% urea for 2.0 h, placed in a steam explosion tank, saturated steam was introduced, and the pressure was maintained at 2.0 MPa for 5.0 min. The pressure was then released and the wood fibers were exploded instantly to obtain activated wood fibers.

[0058] (2) Carboxylation and polycondensation treatment: 100 parts by weight of the activated fiber obtained in (1) were mixed with 7.5 parts by weight of butanetetracarboxylic acid, 1.8 parts by weight of potassium permanganate and 1.5 parts by weight of sodium hydroxide aqueous solution. The mixture was reacted at 120 °C for 0.5 h to complete carboxylation. Then, 7.0 parts by weight of triethylenediamine was added and heated to 80 °C. 5.0 parts by weight of dimethylformamide were added to allow the carboxyl group (-COOH) to undergo a polycondensation reaction with the amino group (-NH2) for 0.5 h to form an amide bond (-CONH-).

[0059] (3) Complexation treatment: Add 2.0 parts by weight of zinc chloride metal salt solution to the fiber system after step (2), stir the reaction for 30 min, adjust the pH of the system to 6.8, so that the metal ions can undergo a complexation reaction with the amide bonds on the fiber.

[0060] (4) Sizing and molding: After washing the fiber treated in step (3), dry it to a moisture content of 9%, and then apply modified soybean protein adhesive (the modified soybean protein adhesive is prepared by adding 1.7 times its mass of warm water to soybean powder, and adding 6% of the soybean powder mass of silane coupling agent KH550 and 3% of hydrogen peroxide, and stirring and modifying at 60℃ for 1.0 h; the sizing amount is 8% of the oven-dry fiber mass), the sizing amount is 14% of the oven-dry fiber mass, and after mechanical laying and pre-pressing, it is formed by a three-stage hot pressing process of high pressure section, pressure holding section and thickness fixing section, wherein, high pressure section: pressure 1.6 MPa, temperature 230 ℃; pressure holding section: pressure 0.3 MPa, temperature 190℃; thickness fixing section: pressure 2.2 MPa, temperature 165 ℃; pressing plate speed 7.0 m / min.

[0061] Example 6

[0062] This embodiment proposes a method for preparing low-VOCs medium fiberboard based on lignocellulose hydroxyl complexation sealing technology, which specifically includes the following steps.

[0063] (1) Steam explosion pretreatment: The wood fibers after hot grinding were soaked in a mixture of 6% sodium hydroxide and 10% urea for 3.0 h, placed in a steam explosion tank, saturated steam was introduced, and the pressure was maintained at 3.0 MPa for 2.5 min. The pressure was then released and the wood fibers were exploded instantly to obtain activated wood fibers.

[0064] (2) Carboxylation and polycondensation treatment: 100 parts by weight of the activated fiber obtained in (1) were mixed with 7.5 parts by weight of citric acid, 1.8 parts by weight of nitric acid and 1.5 parts by weight of sodium hydroxide aqueous solution, and reacted at 100 °C for 0.8 h to complete carboxylation. Then 5.0 parts by weight of tetrabutylammonium bromide were added, heated to 85 °C, and 5.0 parts by weight of dimethylformamide were added to allow the carboxyl group (-COOH) and amino group (-NH2) to undergo polycondensation reaction for 1.0 h to form amide bond (-CONH-).

[0065] (3) Complexation treatment: Add 2.0 parts by weight of zinc chloride metal salt solution to the fiber system after step (2), stir the reaction for 18 min, adjust the pH of the system to 7.2, so that the metal ions can undergo a complexation reaction with the amide bonds on the fiber.

[0066] (4) Sizing and molding: After washing the fiber treated in step (3), dry it to a moisture content of 10%, and then apply modified soybean protein adhesive (the modified soybean protein adhesive is prepared by adding 1.5 times its mass of warm water to soybean powder, and adding 10% of the soybean powder mass of silane coupling agent KH550 and 5% of hydrogen peroxide, and stirring and modifying at 60°C for 1.0 h; the sizing amount is 15% of the oven-dry fiber mass). After mechanical laying and pre-pressing, it is molded by a three-stage hot pressing process of high pressure section, pressure holding section and thickness fixing section. The high pressure section has a pressure of 1.8 MPa and a temperature of 210 ℃; the pressure holding section has a pressure of 0.4 MPa and a temperature of 175 ℃; the thickness fixing section has a pressure of 2.4 MPa and a temperature of 165 ℃; the pressing speed is 6.5 m / min.

[0067] Comparative Example 1.

[0068] Comparative Example 1 is the same as Example 1, except that it does not include steps (1) steam explosion pretreatment, (2) carboxylation, polycondensation treatment and (3) complexation treatment. Only step (4) sizing and molding is the same as in Example 1.

[0069] Comparative Example 2.

[0070] Comparative Example 2 is the same as Example 1, except that it does not include steps (2) carboxylation, polycondensation treatment and (3) complexation treatment. Steps (1) steam explosion pretreatment and (4) sizing and molding are the same as in Example 1.

[0071] Comparative Example 3.

[0072] Comparative Example 1 is the same as Example 1, except that Comparative Example 1 does not have (3) complexation treatment. Steps (1) steam explosion pretreatment, (2) carboxylation, polycondensation treatment and (4) sizing and molding are the same as in Example 1.

[0073] Experiment and results analysis.

[0074] 1. Testing methods.

[0075] (1) Odor level: The odor level is determined according to GB / T44689-2024 "Odor classification and evaluation method of wood-based panels and their products". The odor level, description and label are shown in Table 1.

[0076]

[0077] (2) Mechanical properties: Physical and chemical properties were tested according to GB / T17657-2022 "Test methods for physical and chemical properties of wood-based panels and decorative panels".

[0078] (3) Formaldehyde emission: The formaldehyde emission was tested according to GB / T39600-2021 "Classification of Formaldehyde Emission of Wood-based Panels and Their Products".

[0079] (4) VOCs emission test and grade determination: The test shall be conducted in accordance with GB / T29899-2024 "Test method for volatile organic compound emission in wood-based panels and their products - small release chamber method" and graded in accordance with GB / T44690-2024 "Classification of volatile organic compound emission in wood-based panels and their products", and the grading requirements are shown in Table 2.

[0080]

[0081] 2. The test results are shown in Table 3.

[0082]

[0083] As shown in Table 3, the mechanical properties, odor level, formaldehyde release, and VOCs release of the fiberboards prepared in Examples 1-6 are all superior to those of the comparative examples 1-3. This demonstrates that the combined approach of steam explosion pretreatment, fiber hydroxyl crosslinking, and fiber complexation of the present invention can effectively solve the complex and comprehensive problems of "VOCs release," "odor," and "mechanical properties" in fiberboard. On the one hand, steam explosion pretreatment can effectively volatilize and remove some volatile aldehydes, ketones, acids, and terpenes from wood fibers, further neutralizing acidic components for subsequent complexation reactions, resulting in finished boards with a natural woody fragrance and no irritating chemical odor. Meanwhile, its esterification crosslinking efficiency with polycarboxylic acids is significantly higher than that of ordinary fibers. The ester bonds formed after crosslinking and the remaining carboxyl groups provide richer complexing sites for subsequent metal ions, thus achieving a stronger "anchoring" ability for VOC molecules. Combined with the complexing and fixing effect of metal ions, it effectively captures and blocks formaldehyde and VOCs produced by the decomposition of wood itself, ensuring that the formaldehyde release of the board is consistently below 0.025 mg / m³ (ENF grade), and the total VOC release is reduced by more than 50%, enabling the fiberboard to reach Grade I product status, suitable for places with high air quality requirements. Furthermore, this method modifies the surface of wood fiber materials, improving the compatibility of wood units with adhesives, enhancing their bonding strength, and improving the interweaving performance between wood fibers. Mechanical interlocking between the wood fibers results in a tighter bond. Ultimately, this gives the engineered wood product both low VOCs and low odor properties, as well as excellent mechanical properties.

[0084] Finally, it should be noted that the above embodiments are only used to describe preferred embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various modifications and improvements made to the technical solutions of the present invention by means of modifications or equivalent substitutions are all within the scope of protection claimed by the present invention.

Claims

1. A method for preparing low VOCs type medium density fiberboard based on wood fiber hydroxyl complex sealing technology, characterized in that, It comprises the following steps: (1) Steam explosion pretreatment: soak the lignocellulose with sodium hydroxide-urea mixed solution, put it into the steam explosion tank and introduce saturated steam to perform explosion treatment, and obtain activated lignocellulose; (2) Carboxylation and polycondensation treatment: mix the activated fiber obtained in step (1) with biomass-based polycarboxylic acid, catalyst and sodium hydroxide, heat to perform carboxylation reaction; then add amine compound and dehydrating agent, heat to make carboxyl and amino group polycondensation reaction to form amide bond; (3) Complex treatment: add metal salt solution to the system treated in step (2), stir and adjust pH value, so that metal ion and amide bond on the fiber occur complex reaction; (4) Gluing and forming: after water washing and drying the fiber treated in step (3), apply modified soy-based protein adhesive, lay, pre-press and hot-press to obtain the low VOCs type medium density fiberboard.

2. The method of claim 1, wherein, In step (1), the mass concentration of sodium hydroxide in the sodium hydroxide-urea mixed solution is 3-6%, and the mass concentration of urea is 5-15%; the steam explosion conditions are: pressure 1.0-3.0 MPa, pressure holding time 2-8 min.

3. The method of claim 1, wherein, In step (2), the biomass-based polycarboxylic acid is one of citric acid, butane tetracarboxylic acid or polymaleic acid, and its amount is 3-8% of the mass of the absolute dry fiber; the catalyst is any one of sodium hypophosphite, sulfuric acid, phosphoric acid, toluenesulfonic acid, potassium permanganate and nitric acid, and its amount is 0.5-2.5% of the mass of the absolute dry fiber.

4. The method of claim 1, wherein, In step (2), the amount of sodium hydroxide is 1.0-3.5% of the mass of the absolute dry fiber.

5. The method of claim 1, wherein, In step (2), the amine compound is any one of triethylenediamine, triethylamine, methylamine, aniline and tetrabutylammonium bromide, and its amount is 4-10% of the mass of the absolute dry fiber; the dehydrating agent is any one of dimethylformamide, dicyclohexyl carbodiimide and N-(triethylammonium sulfonyl) methyl carbamate, and its amount is 2-7% of the mass of the absolute dry fiber.

6. The method of claim 1, wherein, In step (3), the metal salt is one of zinc sulfate, zinc chloride or aluminum nitrate, and its amount is 1-3% of the mass of the absolute dry fiber in terms of metal ions; the pH value of the complex reaction is 6.5-7.5, and the reaction time is 15-30 min.

7. The method of claim 1, wherein, In step (4), the modified soy-based protein adhesive is prepared by the following method: add water with a mass of 1.5-2 times of the mass of the soy powder to the soy powder, and add silane coupling agent KH550 with a mass of 5-10% of the mass of the soy powder and hydrogen peroxide with a mass of 3-5% of the mass of the soy powder, stir at 60°C for 1.0 h to obtain the modified soy powder; the gluing amount is 6-15% of the mass of the absolute dry fiber.

8. The method of claim 1, wherein, In step (4), the hot pressing adopts a three-stage process: High pressure section: pressure 1.2-1.8 MPa, temperature 200-240°C; Pressure holding section: pressure 0.2-0.5 MPa, temperature 175-190°C; Thickness setting section: pressure 1.8-2.4 MPa, temperature 140-180°C; The pressing plate speed of the hot pressing is 5.0-7.5 m / min.

9. The method of claim 1, wherein, In step (1), the lignocellulose is one or a mixture of fast-growing poplar, eucalyptus, fir or pine.

10. A low VOCs medium density fiberboard prepared by the method of any one of claims 1 to 9.

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