Water-resistant formaldehyde-free high-density fiberboard and preparation method thereof

Abstract

The present invention relates to the field of fiberboard manufacturing technology, and specifically discloses a preparation method of a water-resistant formaldehyde-free high-density fiberboard, including: preparation of wood fiber; modification of bamboo green fiber using a phenolic-photocatalyst mixture to prepare a reinforcing material; raw material mixing and sizing paving: wood fiber, reinforcing material, adhesive, additive, waterproofing agent, and inorganic gelling material are evenly mixed, and paving and forming to obtain a slab; the slab is hot-pressed to obtain a water-resistant formaldehyde-free high-density fiberboard. The water-resistant formaldehyde-free high-density fiberboard of the present invention utilizes a low molecular weight phenolic resin and a photocatalyst to modify bamboo green fiber, utilizes the high density, high hydrophobicity, and high mechanical properties of the bamboo green fiber to improve the mechanical properties and water resistance of the fiberboard, and solves the problems of low strength, poor water resistance, and low density of the current formaldehyde-free fiberboard.

Description

Technical Field

[0001] The present invention relates to the technical field of fiberboard manufacturing, in particular to a water-resistant formaldehyde-free high-density fiberboard and a preparation method thereof. Background Art

[0002] Fiberboard is a man-made board made from wood or other plant-based fibers, bonded with a urea-formaldehyde resin adhesive. It boasts a wide range of advantages, including uniform material quality, minimal longitudinal and transverse strength differences, and resistance to cracking. However, fiberboard made with urea-formaldehyde resin can emit harmful substances such as formaldehyde and phenol during use, posing a threat to human health and polluting the air. With the advancement of social development and growing environmental awareness, demands for fiberboard to minimize harmful emissions are becoming increasingly stringent. Currently, formaldehyde-free fiberboard has been introduced to reduce formaldehyde emissions. Formaldehyde-free fiberboard primarily uses isocyanate as an adhesive. However, using isocyanate alone can result in low internal bond strength, brittleness, poor water resistance, and poor milling performance. Furthermore, fiberboard readily absorbs moisture when exposed to air, leading to severe deformation. These factors significantly limit its application.

[0003] Chinese patent application publication number CN115707739A discloses a method for preparing water-resistant fiberboard. To address the poor water resistance and low mechanical strength of existing fiberboards, the method uses modified wood fibers mixed with a flame retardant, bentonite, and kaolin, and then a compounded adhesive to produce the fiberboard. The resulting fiberboard exhibits a static bending strength of 32.3-33.4 MPa and a thickness expansion upon water absorption of 5.7-6.5%. However, its strength and water resistance are relatively low, and the adhesive contains a high level of the harmful substance phenol. Chinese patent application publication number CN107779165A discloses a process for producing formaldehyde-free fiberboard. This process utilizes a biomass-based formaldehyde-free adhesive based on a protein-based natural polymer. The resulting fiberboard exhibits low formaldehyde emissions, but its strength and water resistance require further improvement.

[0004] Phenolic resin (PF) is a high-molecular-weight compound obtained by the polycondensation of phenols and aldehydes under acidic or alkaline conditions. It is one of the earliest synthetic resins to achieve industrial production worldwide. As one of the primary adhesives used in the production of wood-based panels, phenolic resin exhibits excellent heat and water resistance and good bonding strength. Furthermore, the thermal degradation of phenolic resin is related to the position of the methylene groups. The methylene groups in phenolic resin undergo thermal degradation in two stages: in the temperature range of 350-450°C, the decomposition primarily occurs at the ortho-ortho (o-o') and ortho-para (op) positions, while in the temperature range of 400-620°C, the decomposition occurs at the para-para (p-p') position. The p-p' position has a thermal decomposition temperature approximately 50°C higher than the o-o' position. Therefore, phenolic resin does not readily release formaldehyde. Furthermore, low-molecular-weight phenolic resin impregnated fibers not only penetrates the cell wall, enhancing fiber mechanical and bonding properties, but also exhibits lower formaldehyde emissions. Currently, phenolic fiberboards are mostly prepared with phenolic resins with higher molecular weight. Although they have better temperature resistance, chemical resistance and mechanical properties, they release higher formaldehyde.

[0005] Bamboo, the "world's second largest forest," possesses excellent mechanical strength, leading to increasing research into new composite materials using bamboo and wood. However, bamboo currently is used in board materials after removing the green part. Due to the unique structure of bamboo, the green part has greater strength and density than other parts of the bamboo. Furthermore, the green part of bamboo is rich in hydrophobic silica. Using green in wood-based panels is expected to improve their strength and hydrophobicity. However, green is difficult to glue, and its presence significantly reduces the bonding strength of the board, limiting its application in fiberboard.

[0006] The present invention utilizes low molecular weight phenolic resin and photocatalyst to modify bamboo green fiber, utilizes low molecular weight phenolic resin to impregnate bamboo green fiber, improves the gluing ability of bamboo green fiber, utilizes photocatalyst and ultraviolet irradiation to remove the trace formaldehyde that may volatilize in low molecular weight phenolic resin at the same time, prepares water-resistant formaldehyde-free high-density fiberboard, and solves the problems of low strength, poor water resistance and low density of current formaldehyde-free fiberboard. Summary of the Invention

[0007] The present invention aims to provide a water-resistant formaldehyde-free high-density fiberboard and a preparation method thereof. The invention utilizes a low molecular weight phenolic resin and a photocatalyst to modify bamboo green fiber. The high density, high hydrophobicity, and high mechanical properties of the bamboo green fiber are utilized to improve the mechanical properties and water resistance of the fiberboard, thereby solving the problems of low strength, poor water resistance, and low density of current formaldehyde-free fiberboard. The specific technical solution is as follows:

[0008] A method for preparing a water-resistant formaldehyde-free high-density fiberboard comprises the following steps:

[0009] (1) Preparation of wood fiber;

[0010] (2) preparing a reinforcement material, comprising the following steps:

[0011] ① By weight, 80 to 100 parts of a low molecular weight phenolic resin and 8 to 12 parts of a photocatalyst solution are mixed to obtain a phenolic-photocatalyst mixture;

[0012] ② Split the bamboo longitudinally and take 20% of the bamboo close to the green side to obtain the green part of the bamboo;

[0013] ③ The green bamboo part obtained in step ② is chipped, screened, steamed and softened, and hot-grinded to obtain green bamboo fiber;

[0014] ④ Take 10 to 20 parts of the phenolic-photocatalyst mixture obtained in step ① and 1 to 2 parts of the bamboo green fiber obtained in step ③ and soak them evenly for 2 to 4 minutes. Finally, remove the bamboo green fiber after ultraviolet irradiation for 4 to 6 minutes to obtain a reinforced material;

[0015] (3) Mixing and sizing the raw materials and paving: by weight, evenly mix 100-200 parts of the wood fiber obtained in step (1) and 20-40 parts of the reinforcing material obtained in step (2) with 10-20 parts of an adhesive, 2-7 parts of an auxiliary agent, 5-20 parts of a waterproofing agent, and 1-8 parts of an inorganic gelling material, and pave and shape the slab;

[0016] (4) hot pressing the slab obtained in step (3) to obtain a water-resistant formaldehyde-free high-density fiberboard.

[0017] Preferably, in the above-mentioned method for preparing water-resistant formaldehyde-free high-density fiberboard, in step (1), the preparation of wood fiber is specifically as follows: one or more of eucalyptus, poplar, pine, and hard miscellaneous wood is chipped, screened, steamed and softened, hot ground, and dried to obtain wood fiber.

[0018] Preferably, in the above-mentioned method for preparing water-resistant formaldehyde-free high-density fiberboard, the moisture content of the wood fiber is 5-12%.

[0019] Preferably, in the above-mentioned method for preparing water-resistant formaldehyde-free high-density fiberboard, the low-molecular-weight phenolic resin has a molecular weight of 300-500 and a solid content of 20%.

[0020] Preferably, in the above-mentioned method for preparing water-resistant formaldehyde-free high-density fiberboard, the photocatalyst is one or more of titanium dioxide, zinc monoxide, ferric oxide, zinc dioxide, zinc sulfide, and silicon dioxide.

[0021] Preferably, in the above-mentioned method for preparing water-resistant formaldehyde-free high-density fiberboard, in step ③, the moisture content of the bamboo green fiber is 5-12%.

[0022] Preferably, in the above-mentioned method for preparing water-resistant formaldehyde-free high-density fiberboard, the adhesive is isocyanate glue.

[0023] Preferably, in the above-mentioned method for preparing water-resistant formaldehyde-free high-density fiberboard, in the step (4), the hot pressing process parameters are: hot pressing temperature of 160-220°C, hot pressing time of 3-5 minutes, and hot pressing pressure of 1-8 MPa.

[0024] Preferably, in the above-mentioned preparation method of water-resistant formaldehyde-free high-density fiberboard, the auxiliary agent is one or more of polyvinyl alcohol, polyether polyol, and isopropyl alcohol; the waterproofing agent is paraffin, and the inorganic gelling material is one or more of aluminum dihydrogen phosphate, sodium silicate, magnesium sulfate, magnesium chloride or calcium oxide.

[0025] A water-resistant formaldehyde-free high-density fiberboard prepared by the above-mentioned preparation method of the water-resistant formaldehyde-free high-density fiberboard.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The preparation method of the water-resistant formaldehyde-free high-density fiberboard of the present invention has low formaldehyde emission and is green and environmentally friendly. It also has the characteristics of high density and good water resistance, and has good mechanical processing properties such as milling and grooving. The mechanical properties such as internal bonding strength, static bending strength, and elastic modulus are improved, which is conducive to the promotion and application of fiberboard.

[0028] 2. In the preparation method of the water-resistant formaldehyde-free high-density fiberboard of the present invention, a low-molecular-weight phenolic resin and a photocatalyst solution are blended and impregnated into bamboo green fibers to prepare a reinforcing material, thereby increasing the bonding strength of the bamboo green fibers. At the same time, the high density, high strength and hydrophobicity of the bamboo green fibers are utilized to prepare the water-resistant formaldehyde-free high-density fiberboard. The low-molecular-weight phenolic resin and the photocatalyst are blended and impregnated into the bamboo green fibers, and ultraviolet irradiation is utilized to remove trace formaldehyde that may volatilize in the low-molecular-weight phenolic resin. The high density, high hydrophobicity and high mechanical properties of the bamboo green fibers are utilized as a reinforcing material to improve the mechanical properties of the fiberboard. At the same time, the hydrophobic silica rich in the green part of the bamboo material and the waterproofing agent paraffin are utilized to work together to improve the water resistance of the fiberboard.

[0029] 3. In the preparation method of the water-resistant, formaldehyde-free high-density fiberboard of the present invention, the addition of an alcohol additive enhances the stability of the isocyanate during the reaction and delays the reaction of the isocyanate adhesive, thereby improving the fiber bonding effect and the mechanical properties of the board. The addition of an inorganic gelling material enhances initial adhesion, increases the bonding strength of the fiber mat, reduces the pre-compression rebound rate of the mat, and increases the formed density of the board. DETAILED DESCRIPTION

[0030] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. Unless otherwise defined, all technical terms used hereinafter have the same meaning as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or can be prepared by existing methods.

[0031] Example 1

[0032] A method for preparing a water-resistant formaldehyde-free high-density fiberboard comprises the following steps:

[0033] (1) Preparation of wood fiber: Eucalyptus wood is chipped, screened, steamed and softened, hot ground, and dried to obtain wood fiber with a moisture content of 8-10%;

[0034] (2) preparing a reinforcement material, comprising the following steps:

[0035] ① By weight, 90 parts of low molecular weight phenolic resin were mixed with 10 parts of titanium dioxide solution. Titanium dioxide was purchased from Degussa Nano and prepared with distilled water to a solid content of 10%. The low molecular weight phenolic resin was purchased from Nasonmei with a solid content of 20% and a molecular weight of 300 to 500 to obtain a phenolic-photocatalyst mixture.

[0036] ② Split the bamboo longitudinally and take 20% of the bamboo close to the green side to obtain the green part of the bamboo;

[0037] ③ The green bamboo part obtained in step ② is chipped, screened, steamed and softened, and hot-milled to obtain green bamboo fiber, wherein the moisture content of the green bamboo fiber is 8-10%;

[0038] ④ Take 10 parts of the phenolic-photocatalyst mixture obtained in step ① and 1 part of the bamboo green fiber obtained in step ③ and soak them evenly for 3 minutes. Finally, remove the bamboo green fiber after ultraviolet irradiation for 5 minutes to obtain a reinforced material;

[0039] (3) Mixing and gluing raw materials for paving: 100 parts of the wood fiber obtained in step (1) and 20 parts of the reinforcing material obtained in step (2) are uniformly mixed with 10 parts of isocyanate, 2 parts of polyvinyl alcohol, 5 parts of paraffin wax, and 3 parts of sodium silicate, and paved to form a slab;

[0040] (4) The slab obtained in step (3) is hot-pressed for 5 minutes at a hot-pressing temperature of 180° C. and a hot-pressing pressure of 6 MPa to obtain a water-resistant formaldehyde-free high-density fiberboard.

[0041] Example 2

[0042] The difference between this embodiment and embodiment 1 is that the weight parts of the reinforcing material in step (3) are replaced by 40 parts from 20 parts, and the other steps and parameters are the same as those in embodiment 1.

[0043] Example 3

[0044] The difference between this embodiment and embodiment 1 is that the weight of wood fiber in step (3) is replaced by 200 parts instead of 100 parts, and the other steps and parameters are the same as those in embodiment 1.

[0045] Example 4

[0046] The difference between this embodiment and embodiment 1 is that the weight parts of isocyanate in step (3) are replaced by 20 parts from 10 parts, and the other steps and parameters are the same as those in embodiment 1.

[0047] Example 5

[0048] The difference between this embodiment and embodiment 4 is that the weight of the reinforcing material in step (3) is replaced by 40 parts from 20 parts, and the other steps and parameters are the same as those in embodiment 4.

[0049] Comparative Example 1

[0050] A method for preparing a water-resistant formaldehyde-free high-density fiberboard comprises the following steps:

[0051] (1) Preparation of wood fiber: Eucalyptus wood is chipped, screened, steamed and softened, hot ground, and dried to obtain wood fiber with a moisture content of 8-10%;

[0052] (2) preparing a reinforcement material, comprising the following steps:

[0053] ① By weight, 90 parts of a low molecular weight phenolic resin and 10 parts of a titanium dioxide solution were mixed to obtain a phenolic-titanium dioxide mixture;

[0054] ② Split the bamboo longitudinally and take 80% of the bamboo away from the green side to obtain the bamboo part without the green part;

[0055] ③ The bamboo material portion obtained in step ② from which the green bamboo is removed is chipped, screened, steamed and softened, and hot-grinded to obtain the green bamboo fiber;

[0056] ④ Take 10 parts of the phenolic-titanium dioxide mixture obtained in step ① and 1 part of the de-greened bamboo fiber obtained in step ③ and soak them evenly for 2 to 4 minutes. Finally, after ultraviolet irradiation for 5 minutes, remove the de-greened bamboo fiber to obtain a reinforced material;

[0057] (3) Mixing and sizing raw materials: by weight, evenly mix 20 parts of the reinforcing material obtained in step (1) with 10 parts of isocyanate, 2 parts of polyvinyl alcohol, 5 parts of paraffin wax, and 3 parts of sodium silicate, and lay them to form a slab.

[0058] (4) The slab obtained in step (3) is hot-pressed for 5 minutes at a hot-pressing temperature of 180° C. and a hot-pressing pressure of 6 MPa to obtain a water-resistant formaldehyde-free high-density fiberboard.

[0059] Comparative Example 2

[0060] A method for preparing a water-resistant formaldehyde-free high-density fiberboard comprises the following steps:

[0061] (1) Preparation of wood fiber: Eucalyptus wood is chipped, screened, steamed and softened, hot ground, and dried to obtain wood fiber with a moisture content of 8-10%;

[0062] (2) Mixing and gluing raw materials and paving: 100 parts of the wood fiber obtained in step (1) are uniformly mixed with 10 parts of isocyanate, 2 parts of polyvinyl alcohol, 5 parts of paraffin wax and 3 parts of sodium silicate by weight, and paved to form a slab.

[0063] (3) The slab obtained in step (2) is hot-pressed for 5 minutes at a hot-pressing temperature of 180° C. and a hot-pressing pressure of 6 MPa to obtain a water-resistant formaldehyde-free high-density fiberboard.

[0064] Comparative Example 3

[0065] A method for preparing a water-resistant formaldehyde-free high-density fiberboard comprises the following steps:

[0066] (1) Preparation of wood fiber: Eucalyptus wood is chipped, screened, steamed and softened, hot ground, and dried to obtain wood fiber with a moisture content of 8-10%;

[0067] (2) splitting the bamboo longitudinally, taking 20% ​​of the bamboo close to the green side of the bamboo to obtain the green part of the bamboo; chipping, screening, steaming and softening the green part, and hot grinding the green part to obtain green fiber, the moisture content of the green fiber is 8-10%;

[0068] (3) Mixing and sizing raw materials for paving: 100 parts of the wood fiber obtained in step (1) and 20 parts of the bamboo fiber obtained in step (2) are uniformly mixed with 10 parts of isocyanate, 2 parts of polyvinyl alcohol, 5 parts of paraffin wax, and 3 parts of sodium silicate, and paved to form a slab;

[0069] (4) The slab obtained in step (3) is hot-pressed for 5 minutes at a hot-pressing temperature of 180° C. and a hot-pressing pressure of 6 MPa to obtain a water-resistant formaldehyde-free high-density fiberboard.

[0070] The 18 mm thick fiberboards prepared according to the preparation methods of Examples 1 to 5 and Comparative Examples 1 to 3 were tested for mechanical properties, water resistance, etc. with reference to GB / T 17657-2013 "Test methods for physical and chemical properties of wood-based panels and veneer wood-based panels". The formaldehyde emission was measured using a 1 m 3 The test was carried out using the climate chamber method. The test results are shown in Table 1. The formaldehyde emissions of the fiberboards all reached the formaldehyde-free level.

[0071] Table 1 Performance data of fiberboard prepared in the examples of the present invention and comparative examples

[0072]

[0073]

[0074] As can be seen in Table 1, the fiberboards of the present invention significantly outperform those of the comparative examples, with most performance indicators meeting the requirements for high-density fiberboards in the GB / T 31765-2015 standard for wet-type high-density fiberboard. Examples 2 and 5 showed the highest density and static flexural strength, due to their large proportion of bamboo green fiber. Comparative Example 2, which does not contain bamboo, had the lowest density and static flexural strength. Examples 4 and 5 showed the highest internal bonding strength, which is related to their high proportion of isocyanate. However, a comparison between Example 1 and Comparative Example 2 shows that the fiberboard exhibits higher internal bonding strength when the reinforcing material and isocyanate interact. Regarding the water absorption thickness expansion rate, Examples 2 and 5 showed the lowest, while Comparative Examples 1 and 2 showed the highest, indicating that the presence of bamboo green fiber improves the water resistance of the fiberboard. In summary, the invention utilizes a low molecular weight phenolic resin and a titanium dioxide standard solution to blend and impregnate bamboo green fibers to prepare a reinforcing material. This increases the bonding strength of the bamboo green fibers while utilizing the high density, high strength, and hydrophobicity of the bamboo green fibers to prepare a water-resistant, formaldehyde-free, high-density fiberboard. The low molecular weight phenolic resin and a titanium dioxide photocatalyst are blended and impregnated into the bamboo green fibers, and ultraviolet irradiation is used to remove trace formaldehyde that may volatilize from the low molecular weight phenolic resin. The high density, high hydrophobicity, and high mechanical properties of the bamboo green fibers are utilized as a reinforcing material to improve the mechanical properties of the fiberboard. Furthermore, the hydrophobic silica rich in the green portion of the bamboo material interacts with the waterproofing agent paraffin to improve the water resistance of the fiberboard. This overcomes the problems of poor water resistance, low bonding strength, and poor bending resistance of existing fiberboards. The fiberboard of the invention is environmentally friendly and has the characteristics of low formaldehyde emission, high density, high bonding strength, and good water resistance.

[0075] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing a water-resistant formaldehyde-free high-density fiberboard, characterized in that: The following steps are involved: (1) Preparation of wood fiber; (2) preparing a reinforcement material, comprising the following steps: ① By weight, 80 to 100 parts of a low molecular weight phenolic resin and 8 to 12 parts of a photocatalyst solution are mixed to obtain a phenolic-photocatalyst mixture; the low molecular weight phenolic resin has a molecular weight of 300 to 500 and a solid content of 20%; ② Split the bamboo longitudinally and take 20% of the bamboo close to the green side to obtain the green part of the bamboo; ③ The green bamboo part obtained in step ② is chipped, screened, steamed and softened, and hot-grinded to obtain green bamboo fiber; ④ Take 10 to 20 parts of the phenolic-photocatalyst mixture obtained in step ① and 1 to 2 parts of the bamboo green fiber obtained in step ③ and soak them evenly for 2 to 4 minutes. Finally, remove the bamboo green fiber after ultraviolet irradiation for 4 to 6 minutes to obtain a reinforced material; (3) Mixing and gluing raw materials for paving: by weight, evenly mix 100-200 parts of the wood fiber obtained in step (1) and 20-40 parts of the reinforcing material obtained in step (2) with 10-20 parts of an adhesive, 2-7 parts of an auxiliary agent, 5-20 parts of a waterproofing agent, and 1-8 parts of an inorganic gelling material, wherein the adhesive is an isocyanate adhesive, and paving and forming the slab; (4) hot pressing the slab obtained in step (3) to obtain a water-resistant formaldehyde-free high-density fiberboard.

2. The method for preparing a water-resistant formaldehyde-free high-density fiberboard according to claim 1, characterized in that: In the step (1), the preparation of wood fiber is specifically as follows: one or more of eucalyptus, poplar, pine, and hard miscellaneous wood is chipped, screened, steamed and softened, hot-grinded, and dried to obtain wood fiber.

3. The method for preparing a water-resistant formaldehyde-free high-density fiberboard according to claim 2, characterized in that: The moisture content of the wood fiber is 5-12%.

4. The method for preparing a water-resistant formaldehyde-free high-density fiberboard according to claim 1, characterized in that: The photocatalyst is one or more of titanium dioxide, zinc monoxide, ferric oxide, zinc dioxide, zinc sulfide, and silicon dioxide.

5. The method for preparing a water-resistant formaldehyde-free high-density fiberboard according to claim 1, characterized in that: In the step ③, the moisture content of the bamboo green fiber is 5-12%.

6. The method for preparing a water-resistant formaldehyde-free high-density fiberboard according to claim 1, characterized in that: The auxiliary agent is one or more of polyvinyl alcohol, polyether polyol, and isopropyl alcohol; the waterproofing agent is paraffin; and the inorganic gelling material is one or more of aluminum dihydrogen phosphate, sodium silicate, magnesium sulfate, magnesium chloride, or calcium oxide.

7. The method for preparing a water-resistant formaldehyde-free high-density fiberboard according to claim 1, characterized in that: In the step (4), the hot pressing process parameters are: hot pressing temperature of 160-220° C., hot pressing time of 3-5 min, and hot pressing pressure of 1-8 MPa.

8. A water-resistant formaldehyde-free high-density fiberboard prepared by the method for preparing a water-resistant formaldehyde-free high-density fiberboard according to any one of claims 1 to 7.

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