Fiber pretreatment method for preparing binderless fiberboard

Abstract

The invention relates to the technical field of fiberboard preparation, and discloses a fiber pretreatment method for adhesive-free fiberboard preparation, which comprises the following steps: sequentially carrying out alkali treatment and oxidation treatment on wood fibers, cleaning, and dehydrating until no water is squeezed out; placing the dehydrated fibers in a stirrer, spraying a metal ion solution, and uniformly stirring; continuously spraying a catechin solution for non-covalent bond coordination, and uniformly stirring; putting the coordinated fibers into a drying oven, drying, and controlling the water content to obtain pretreated fibers; and putting the pretreated fiber into a mold for shaping, and then performing hot pressing to form a plate. Metal ions and lignin hydroxyl are bonded and coordinated through an oxidation method and then are chelated with catechin phenolic hydroxyl to form self-adhesion, meanwhile, the non-adhesive fiberboard formed by tightly interweaving and stacking the fibers can reach the national standard in mechanical strength and water absorption expansion rate, the preparation method is simple and easy to implement, raw materials are easy to obtain, and the production cost is low. The method is suitable for mass production, realizes zero formaldehyde release of the fiberboard, and is lower in cost.

Description

Technical Field

[0001] The invention relates to the technical field of fiberboard preparation, in particular to a fiber pretreatment method for preparing glue-free fiberboard. Background Art

[0002] As a core market for global fiberboard production and consumption, my country's annual fiberboard production capacity has exceeded 50 million cubic meters. The industry currently predominantly uses urea-formaldehyde resin adhesives (accounting for over 90%), but the potential formaldehyde pollution from these adhesives has long hindered industry upgrades. Alternative isocyanate adhesives face application bottlenecks such as cost surges exceeding 30% and high cracking rates on the board surface. Glueless plywood technology, with its significant advantages of zero formaldehyde emissions and a 40% reduction in carbon emissions, has become a key path to breaking through the industry's environmental constraints and cost constraints.

[0003] Developing a green pretreatment system that combines fiber activation efficiency and structural integrity, and constructing a hot pressing process model for controllable reorganization of the fiber's endogenous components have become the technical breakthrough direction for achieving a mechanical strength of glue-free fiberboard exceeding 25MPa and water resistance reaching the national standard E1 level.

[0004] The patent with publication number CN119077881A discloses a fiber pretreatment method and the application of the treated fibers, belonging to the technical field of artificial boards. The invention discloses a fiber pretreatment method and the application of the treated fibers, wherein the fibers are placed in dimethylacetamide for room temperature decomposition to obtain decomposed fibers; the decomposed fibers are then placed in a LiCl / DMAc solution for treatment, and finally squeezed to remove the reagents, washed and filtered, and dried to obtain pretreated fibers, which are then used in the preparation of glue-free plywood. After treatment with the LiCl / DMAc solution, the area of the fiber self-bonding interface is greatly increased, and the surface hydroxyl activity is also increased. During the glue-free bonding process, not only do the degradation products of hemicellulose and lignin self-bond, but the cellulose melts and regenerates to form fibrils, which form self-bonding under the action of hydrogen bonds, significantly improving the performance of the glue-free plywood. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a fiber pretreatment method for the preparation of glue-free fiberboard, aiming to solve the problems of the existing fiber preparation method for glue-free fiberboard, such as complex production process, high energy consumption, difficult chemical recycling, and high environmental load.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a fiber pretreatment method for preparing glue-free fiberboard, comprising the following steps:

[0008] The wood fibers are sequentially subjected to alkali treatment and oxidation treatment, and then washed and dehydrated until no water can be squeezed out;

[0009] Place the dehydrated fiber in a blender, spray the metal ion solution first and stir evenly;

[0010] Continue spraying the catechin solution for non-covalent coordination and stir evenly;

[0011] The coordinated fibers are placed in an oven for drying and controlling the moisture content to obtain pretreated fibers for preparing glue-free fiberboard;

[0012] The pretreated fibers are placed in a mold to be shaped, and then hot-pressed into a board to obtain a glue-free fiberboard.

[0013] As a further embodiment of the present invention, the wood fiber is sequentially subjected to alkali treatment and oxidation treatment. When dehydrated after washing, the alkali treatment temperature is 80-90°C and the alkali treatment time is 1-5 hours; the oxidation treatment temperature is 50-90°C and the oxidation treatment time is 6-24 hours, and the dehydration time is 3-5 minutes.

[0014] As a further embodiment of the present invention, the metal ion solution is one of cobalt sulfate, cobalt nitrate, cobalt chloride, calcium sulfate, calcium carbonate, and calcium chloride solution.

[0015] As a further embodiment of the present invention, the mass ratio of the dehydrated fibers to the metal ions is 100:1-60:1.

[0016] As a further embodiment of the present invention, the mass ratio of the dehydrated fiber to catechin is 100:1-40:1.

[0017] As a further embodiment of the present invention, the sprayed metal ion solution is stirred evenly, and the sprayed catechin solution is stirred evenly for non-covalent coordination. The concentration of the solution is such that water is added until the polyphenols and metal ions are completely dissolved to prevent nozzle clogging during spraying. The stirring time is 30 to 60 minutes.

[0018] As a further solution of the present invention, the coordinated fibers are placed in an oven with a moisture content controlled at 12%, an oven temperature of 65° C., and a drying time of 40 to 90 minutes.

[0019] As a further embodiment of the present invention, the wood fiber is sequentially subjected to an alkali treatment and an oxidation treatment, comprising the following steps:

[0020] The wood fibers are soaked in a chemical solution, heated, and washed to obtain oxidized fibers.

[0021] As a further embodiment of the present invention, the chemical solution is a mixed aqueous solution of potassium hydroxide, phosphate buffer solution, sodium chlorite, 2,2,6,6-tetramethylpiperidinium oxide and sodium hypochlorite.

[0022] As a further solution of the present invention, the pretreated fibers are placed in a mold for shaping and then hot pressed into a board. The hot pressing temperature is 60-150°C, the hot pressing pressure is 8-20 MPa, and the hot pressing time is 1 to 60 minutes.

[0023] As a further solution of the present invention, the internal bonding strength of the glue-free fiberboard is 0.8-2.4 MPa, the bending strength is 20-48 MPa, and the thickness expansion rate of 24h water absorption is 3% to 12%.

[0024] In a second aspect, the present invention further provides a glue-free plywood fiberboard obtained by the above-mentioned method for preparing the glue-free plywood fiberboard.

[0025] Compared with the prior art, the present invention provides a fiber pretreatment method for preparing glue-free fiberboard, which has the following beneficial effects:

[0026] The fiber pretreatment method for preparing glue-free fiberboard of the present invention removes a small amount of hemicellulose, oxidizes the metal ions to form self-adhesive fibers by bonding and coordinating with lignin hydroxyl groups, and then chelates with polyphenols to form self-adhesive fibers. The stacked glue-free fiberboards not only have mechanical strength and water absorption expansion rate that meet national standards, but also have a simple and easy preparation method, easy to obtain raw materials, suitable for mass production, and have broad application prospects. In addition, the present application achieves zero formaldehyde release of the fibers, and the prepared glue-free fiberboards are more environmentally friendly than commercial fiberboards, are superior to most of the reported fiberboards, and have the advantage of low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the treatment of dehydrated fibers in the fiber pretreatment method for preparing glue-free fiberboard according to an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of pretreated fibers obtained in a fiber pretreatment method for preparing glue-free fiberboard according to an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the specification.

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0031] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it constitute a separate or selective embodiment that is mutually exclusive with other embodiments.

[0032] See also Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a fiber pretreatment method for preparing a glue-free fiberboard, comprising the following steps:

[0033] (1) The wood fibers are sequentially subjected to alkali treatment and oxidation treatment, and then washed and dehydrated until no water can be squeezed out;

[0034] (2) Place the dehydrated fiber in a blender, spray the metal ion solution on it and stir it evenly;

[0035] (3) Continue spraying the catechin solution for non-covalent coordination and stir evenly;

[0036] (4) placing the coordinated fibers into an oven, drying them and controlling the moisture content to obtain pretreated fibers for preparing glue-free fiberboard;

[0037] (5) The pretreated fibers are placed in a mold to be shaped, and then hot-pressed into a board to obtain a glue-free fiberboard.

[0038] In the embodiment of the present application, the wood fiber can be any one or more fibers such as poplar, pine, basswood, eucalyptus, etc. Although the specific embodiment of the present application only uses poplar, eucalyptus, basswood fibers (weight 0.32-0.40g / cm 3 ) is used as an example, but this should not limit the scope of protection of this application. Those skilled in the art can choose other wood fibers to replace them according to actual conditions.

[0039] In the embodiment of the present application, the wood fiber is subjected to alkali treatment and oxidation treatment, and then cleaned and dehydrated in a dehydrator until no water can be squeezed out; the wood fiber is subjected to alkali treatment and oxidation treatment in sequence, and when dehydrated after washing, the alkali treatment temperature is 80-90°C, and the alkali treatment time is 1 to 5 hours; the oxidation treatment temperature is 50-90°C, the oxidation treatment time is 6 to 24 hours, and the dehydration time is 3 to 5 minutes.

[0040] Among them, the chemical solution used for alkali treatment can be potassium hydroxide or sodium hydroxide, and the chemical solution used for oxidation treatment can be a mixed aqueous solution of phosphate buffer solution (PBS buffer), sodium chlorite (NaClO2), 2,2,6,6-tetramethylpiperidinium oxide (TEMPO) and sodium hypochlorite solution (NaClO). Preferably, the maximum range of the chemical ratio in 2000mL of water is 40-60g of potassium hydroxide, 10-20g of phosphate buffer solution, 10-20g of sodium chlorite, 0.14-0.28g of 2,2,6,6-tetramethylpiperidinium oxide, and 2.9-5.8mL of sodium hypochlorite solution.

[0041] Among them, the alkali treatment time should not be too long to remove a small part; too low an oxidation treatment temperature will lead to insufficient reaction activity of the system, but too high a temperature will cause decomposition of the weak acid and its intermediates. Therefore, the oxidation treatment temperature is preferably 50-90°C, and the oxidation treatment time is 6 to 24 hours.

[0042] In the embodiment of the present application, the metal ion solution can be one of cobalt sulfate, cobalt nitrate, cobalt chloride, calcium sulfate, calcium carbonate, and calcium chloride solutions; the salt concentration is preferably capable of completely dissolving the metal ions.

[0043] In the embodiment of the present application, the mass ratio of the dehydrated fiber to the metal ion is 100:1-60:1, and a catechin solution is added to the obtained fiber, with a weight ratio of the fiber to the catechin of 100:1-40:1. The concentration of the catechin solution is preferably capable of completely dissolving the catechin.

[0044] The metal ion solution is sprayed and stirred evenly, and the catechin solution is sprayed for non-covalent coordination and continued to be stirred evenly. The concentration of the solution is such that water is added until the polyphenols and metal ions are completely dissolved to prevent nozzle clogging during spraying. The stirring time is 30 minutes to 60 minutes.

[0045] In the embodiment of the present application, the fiber that has completed non-covalent coordination is placed in an oven and the moisture content is controlled at 12% to obtain the fiber for preparing the glue-free fiberboard. The oven temperature is preferably 60°C and the drying time is 40 minutes to 90 minutes.

[0046] In the embodiments of the present application, the hot pressing conditions can be determined according to the existing technology, such as the hot pressing temperature can be 60-150°C, the hot pressing pressure can be 4-20 MPa, and the hot pressing time can be 30-60 min.

[0047] The glue-free fiberboard prepared in the present application has excellent mechanical properties such as internal bonding strength and bending strength. Among them, the internal bonding strength is 0.8-2.4MPa, the bending strength is 20-48MPa, and the 24h water absorption thickness expansion rate is 3% to 12%, which can meet the national standards.

[0048] The fiber pretreatment method for preparing glue-free fiberboard is described in detail below using specific examples. The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials and reagents used are commercially available unless otherwise specified.

[0049] Example 1

[0050] This embodiment provides a fiber pretreatment method for preparing a non-glue fiberboard, comprising the following steps:

[0051] Weigh the weight 0.35g / cm 3 80 g of poplar fiber was placed in a 2% potassium hydroxide solution, 1000 mL of water, and 20 g of KOH, and heated at 90°C for 2 h in a water bath for alkali treatment; when the time came, 1000 mL of water, 5.8 mL (5% available chlorine) of sodium hypochlorite, 0.28 g of TEMPO oxidant, 21 g of NaClO2, and 14 g of phosphate buffer with a pH of 6.8 to 7.0 were washed and heated at 60°C for 12 h for oxidation treatment. After the reaction is completed, 200 mL of ethanol is added to stop the reaction for 1 hour. After rinsing with clean water, the mixture is placed in a tea bag and dehydrated for 3 minutes. The mixture is poured into a blender and stirred while spraying cobalt chloride solution (first) and catechin solution (later). The mass ratio of dry fiber to cobalt chloride is 60:1 (80 g:1.3 g), and the mass ratio of dry fiber to catechin is 80:1 (80 g:1 g). The fiber is stirred for 30 minutes for chelation, and then the fiber is flattened and placed in an oven at 65°C for 30 minutes. It can then be laid in a 15 cm × 15 cm mold, compacted, and hot-pressed. The hot-pressing pressure is 10 MPa, the hot-pressing temperature is 110°C, and the pressure is released after hot-pressing for 30 minutes, and then cold-pressed for 30 minutes to obtain a glue-free fiberboard.

[0052] Example 2

[0053] This embodiment provides a fiber pretreatment method for preparing a non-glue fiberboard, comprising the following steps:

[0054] Weigh the weight 0.35g / cm 380 g of poplar fiber was placed in a 2% potassium hydroxide solution, 1000 mL of water, and 20 g of KOH, and heated at 90°C for 2 h in a water bath for alkali treatment; when the time came, 1000 mL of water, 5.8 mL (5% available chlorine) of sodium hypochlorite, 0.28 g of TEMPO oxidant, 21 g of NaClO2, and 14 g of phosphate buffer solution with a pH of 6.8 to 7.0 were washed with clean water and heated at 60°C for 24 h for oxidation treatment. After the reaction is completed, 200 mL of ethanol is added to stop the reaction for 1 hour. After rinsing with clean water, the mixture is placed in a tea bag and dehydrated for 3 minutes. The mixture is poured into a blender and stirred while spraying cobalt chloride solution (first) and catechin solution (later). The mass ratio of dry fiber to cobalt chloride is 80:1 (80 g:1 g), and the mass ratio of dry fiber to catechin is 40:1 (80 g:2 g). The fiber is stirred for 30 minutes for chelation, and then the fiber is flattened and placed in an oven at 65°C for 30 minutes. It can then be laid in a 15 cm × 15 cm mold, compacted, and hot-pressed. The hot-pressing pressure is 10 MPa, the hot-pressing temperature is 110°C, and the pressure is released after hot-pressing for 30 minutes, and then cold-pressed for 30 minutes to obtain a glue-free fiberboard.

[0055] Example 3

[0056] This embodiment provides a fiber pretreatment method for preparing a non-glue fiberboard, comprising the following steps:

[0057] Weigh the weight 0.35g / cm 3 80 g of poplar fiber was placed in a 2% potassium hydroxide solution, 1000 mL of water, and 20 g of KOH, and heated at 90°C for 2 h in a water bath for alkali treatment; when the time came, 1000 mL of water, 11.6 mL (5% available chlorine) of sodium hypochlorite, 0.56 g of TEMPO oxidant, 42 g of NaClO2, and 28 g of phosphate buffer solution with a pH of 6.8 to 7.0 were washed and heated at 60°C for 12 h for oxidation treatment. After the reaction is completed, 200 mL of ethanol is added to stop the reaction for 1 hour. After rinsing with clean water, it is put into a tea bag and dehydrated for 3 minutes; poured into a blender and stirred while spraying calcium chloride solution (first) and catechin solution (later). The mass ratio of dry fiber to calcium chloride is 60:1 (80g:1.3g), and the mass ratio of dry fiber to catechin is 80:1 (80g:1g). Chelation is carried out and stirred for 30 minutes. Then, the fiber is flattened and placed in an oven at 65°C for 30 minutes. It can be laid in a 15 cm × 15 cm mold and compacted for hot pressing treatment. The hot pressing pressure is 10 MPa and the hot pressing temperature is 140°C. After hot pressing for 30 minutes, the pressure is released and then cold pressed for 30 minutes to obtain a glue-free fiberboard.

[0058] Example 4

[0059] This embodiment provides a fiber pretreatment method for preparing a non-glue fiberboard, comprising the following steps:

[0060] Weigh the weight 0.32g / cm 3 80 g of eucalyptus fiber was placed in a 2% potassium hydroxide solution, 1000 mL of water, and 20 g of KOH, and heated at 90°C for 2 h in a water bath for alkaline treatment; when the time was up, 1000 mL of water, 11.6 mL of (5% available chlorine) sodium hypochlorite, 0.56 g of TEMPO oxidant, 42 g of NaClO2, and 28 g of phosphate buffer solution with a pH of 6.8-7.0 were washed and heated at 60°C for 12 h for oxidation treatment. After the reaction is completed, 200 mL of ethanol is added to stop the reaction for 1 hour. After rinsing with clean water, it is put into a tea bag and dehydrated for 3 minutes; poured into a blender and stirred while spraying calcium chloride solution (first) and catechin solution (later). The mass ratio of dry fiber to calcium chloride is 60:1 (80g:1.3g), and the mass ratio of dry fiber to catechin is 40:1 (80g:2g). Chelation is carried out and stirred for 30 minutes. Then, the fiber is flattened and placed in an oven at 65°C for 30 minutes. It can be laid in a 15 cm × 15 cm mold and compacted for hot pressing treatment. The hot pressing pressure is 10 MPa and the hot pressing temperature is 140°C. After hot pressing for 30 minutes, the pressure is released and then cold pressed for 30 minutes to obtain a glue-free fiberboard.

[0061] Example 5

[0062] This embodiment provides a fiber pretreatment method for preparing a non-glue fiberboard, comprising the following steps:

[0063] Weigh the weight 0.32g / cm 3 60 g of eucalyptus fiber was placed in a 2% potassium hydroxide solution, 1000 mL of water, and 20 g of KOH, and heated at 90°C for 2 h in a water bath for alkaline treatment; when the time was up, 1000 mL of water, 11.6 mL of (5% available chlorine) sodium hypochlorite, 0.56 g of TEMPO oxidant, 42 g of NaClO2, and 28 g of phosphate buffer solution with a pH of 6.8-7.0 were washed with clean water and heated at 60°C for 12 h for oxidation treatment. After the reaction is completed, 200 mL of ethanol is added to stop the reaction for 1 hour. After rinsing with clean water, it is put into a tea bag and dehydrated for 3 minutes; poured into a blender and stirred while spraying calcium chloride solution (first) and catechin solution (later). The mass ratio of dry fiber to calcium chloride is 60:1 (80g:1.3g), and the mass ratio of dry fiber to catechin is 60:1 (80g:1.3g). Chelation is carried out and stirred for 30 minutes. Then, the fiber is flattened and placed in an oven at 65°C for 30 minutes. It can be laid in a 15 cm × 15 cm mold and compacted for hot pressing treatment. The hot pressing pressure is 20 MPa and the hot pressing temperature is 140°C. After hot pressing for 30 minutes, the pressure is released and then cold pressed for 30 minutes to obtain a glue-free fiberboard.

[0064] Comparative Example 1

[0065] Weigh the weight 0.32g / cm 3 60g of eucalyptus fiber was placed in a 2% potassium hydroxide solution, 1000mL of water, and 20g of KOH, and heated in a water bath at 90°C for 2h for alkali treatment. After washing with clean water, 1000mL of water, 11.6mL of sodium hypochlorite (5% available chlorine), 0.56g of TEMPO oxidant, 42g of NaClO2, and 28g of phosphate buffer (pH 6.8-7.0) were added and heated at 60°C for 12h for oxidation treatment. After the reaction was completed, 200mL of ethanol was added to stop the reaction for 1h. The fiber was rinsed with clean water and then placed in a tea bag for dehydration for 3min. The fiber was then laid flat and placed in an oven at 65°C for 10min. It was then laid in a 15cm x 15cm mold, compacted, and hot-pressed at 20MPa and 140°C. After 30min of hot pressing, the pressure was released and then cold-pressed for 30min to produce a non-adhesive fiberboard.

[0066] Experimental performance test

[0067] The fibers used in the preparation of the glue-free fiberboards prepared in Examples 1 to 5 and Comparative Example 1 were laid in a 15 cm x 15 cm mold, compacted and hot-pressed, and then subjected to relevant performance testing. The testing included preparing specimens in accordance with the test standard GB / T 17657-2022, "Test methods for physical and chemical properties of wood-based panels and veneered wood-based panels," and conducting tests on internal bond strength, flexural strength, and 24-hour water absorption thickness expansion. The performance met the national standard GB / T 11718-2021, "Medium Density Fiberboard."

[0068] Table 1 Performance test results

[0069]

[0070] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

[0071] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

[0072] It will be understood that in the development of any actual embodiment, as in any engineering or design project, numerous implementation-specific decisions may be made. Such a development effort may be complex and time-consuming, but for those of ordinary skill having the benefit of this disclosure, the development effort will be a routine task of design, fabrication, and production without undue experimentation.

[0073] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A fiber pretreatment method for preparing glue-free fiberboard, characterized in that: The following steps are involved: The wood fibers are sequentially subjected to alkali treatment and oxidation treatment, and then washed and dehydrated until no water can be squeezed out; Place the dehydrated fiber in a blender, spray the metal ion solution first and stir evenly; Continue spraying the catechin solution for non-covalent coordination and stir evenly; The coordinated fibers are placed in an oven for drying and controlling the moisture content to obtain pretreated fibers for preparing glue-free fiberboard; The pretreated fibers are placed in a mold to be shaped, and then hot-pressed into a board to obtain a glue-free fiberboard.

2. A fiber pretreatment method for preparing glue-free fiberboard according to claim 1, characterized in that: The wood fiber is sequentially subjected to alkali treatment and oxidation treatment. When dehydrated after washing, the alkali treatment temperature is 80-90°C and the alkali treatment time is 1-5 hours; the oxidation treatment temperature is 50-90°C, the oxidation treatment time is 6-24 hours, and the dehydration time is 3-5 minutes.

3. The fiber pretreatment method for preparing glue-free fiberboard according to claim 2, characterized in that: The wood fiber is sequentially subjected to an alkali treatment and an oxidation treatment, comprising the following steps: The wood fibers are soaked in a chemical solution, heated, and washed to obtain oxidized fibers.

4. The fiber pretreatment method for preparing glue-free fiberboard according to claim 3, characterized in that: The chemical solution is a mixed aqueous solution of potassium hydroxide, phosphate buffer solution, sodium chlorite, 2,2,6,6-tetramethylpiperidinium oxide and sodium hypochlorite.

5. The fiber pretreatment method for preparing glue-free fiberboard according to claim 1, characterized in that: The metal ion solution is one of cobalt sulfate, cobalt nitrate, cobalt chloride, calcium sulfate, calcium carbonate, and calcium chloride solution.

6. The fiber pretreatment method for preparing glue-free fiberboard according to claim 5, characterized in that: The mass ratio of the dehydrated fiber to the metal ion is 100:1-60:

1.

7. The fiber pretreatment method for preparing glue-free fiberboard according to claim 6, characterized in that: The mass ratio of the dehydrated fiber to catechin is 100:1-40:

1.

8. A fiber pretreatment method for preparing glue-free fiberboard according to claim 7, wherein the sprayed metal ion solution is stirred evenly, and the sprayed catechin solution is stirred evenly for non-covalent coordination, the solution concentration is such that water is added until the polyphenols and metal ions are completely dissolved to prevent nozzle clogging during spraying, and the stirring time is 30 minutes to 60 minutes.

9. The fiber pretreatment method for preparing glue-free fiberboard according to claim 1, characterized in that: The coordinated fibers are placed in an oven with a moisture content controlled at 12%, an oven temperature at 65° C., and a drying time of 40 to 90 minutes.

10. The fiber pretreatment method for preparing glue-free fiberboard according to claim 9, characterized in that: The pretreated fibers are placed in a mold for shaping and then hot-pressed into a board. The hot-pressing temperature is 60-150° C., the hot-pressing pressure is 8-20 MPa, and the hot-pressing time is 1-60 minutes.

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