A high-toughness bamboo engineering material and preparation method thereof

Abstract

The present invention discloses a high-toughness bamboo engineering material and a preparation method thereof, belonging to the field of wood processing technology. The high-toughness bamboo engineering material is based on bamboo strips or oriented bamboo fiber bundles and is cured using a modified phenolic resin as an adhesive. The modified phenolic resin comprises the following raw materials by weight: 100 parts phenol, 160-190 parts 50wt% formaldehyde solution, 2-10 parts alkaline compound, 15-20 parts glycol compound, 10-15 parts dicyandiamide, and 10-30 parts latex. The high-toughness bamboo engineering material has high toughness and is resistant to cracking, meeting the performance requirements of both indoor and outdoor engineering materials.

Description

Technical Field

[0001] The invention belongs to the technical field of wood processing, and in particular relates to a high-toughness bamboo engineering material and a preparation method thereof. Background Art

[0002] Bamboo engineering materials are made by processing bamboo into strips, fiber bundles, or strips, then reassembling or compounding them to create boards, squares, or profiles that meet engineering construction requirements. As the application of bamboo engineering materials expands, higher requirements are being placed on the material's dimensions, shape, and performance. For example, processing bamboo into structural materials often requires secondary gluing of reassembled or laminated bamboo to create large-scale components such as beams and columns with a specific cross-section. For landscape applications, bamboo is often processed into curved, shaped components with a specific curvature for styling purposes. Emerging applications for bamboo engineering materials, such as elevator handrails and guardrails, require excellent toughness and impact resistance. Currently, the adhesives used in bamboo engineering materials primarily consist of phenolic resins such as standard phenolic and resorcinol. While these adhesives offer advantages such as high strength and hardness, they also suffer from brittleness and cracking. These issues significantly limit the widespread application of bamboo engineering materials in large-scale structural materials, special-shaped landscape materials, and other specialized applications. Summary of the Invention

[0003] In order to overcome the above technical problems, the present invention proposes a high-toughness bamboo engineering material and a preparation method thereof, that is, high-elasticity phenolic resin is arranged between bamboo units to increase the toughness of the bamboo engineering material glue layer and develop a high-toughness bamboo engineering material.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A high-toughness bamboo engineering material is prepared using bamboo strips or oriented bamboo fiber bundles as basic units and cured using a modified phenolic resin as an adhesive. The modified phenolic resin comprises the following raw materials in parts by weight: 100 parts of phenol, 160-190 parts of a 50 wt.% formaldehyde aqueous solution, 2-10 parts of an alkaline compound, 15-20 parts of a glycol compound, 10-15 parts of dicyandiamide, and 10-30 parts of latex.

[0006] The bamboo strips and oriented bamboo fiber bundles are obtained by splitting 3-5 year old bamboo into bamboo chips, which are then processed into the bamboo strips and oriented bamboo fiber bundles.

[0007] Furthermore, the bamboo strips have a length of 1.5-5.0 m, a width of 15-30 mm, and a thickness of 0.5-1.5 mm.

[0008] Furthermore, the oriented bamboo fiber bundle is a sheet of bamboo material formed by interweaving bamboo fiber bundles with a diameter of 0.1-0.5 mm and a length of 20-50 mm along the grain; the oriented bamboo fiber bundle is 1.5-5.0 m long, 100-300 mm wide, and 0.2-1.5 mm thick.

[0009] Furthermore, the alkaline compound is a monovalent or divalent metal hydroxide or oxide.

[0010] Furthermore, the diol compound includes one or more of ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, dibutylene glycol, polyethylene glycol and polypropylene glycol.

[0011] Furthermore, the latex includes one or more of styrene-butadiene emulsion, styrene-acrylic emulsion, acetate-acrylic emulsion and pure acrylic emulsion.

[0012] Furthermore, the alkaline compound includes alkaline compounds that are monovalent and / or divalent metal compounds.

[0013] Furthermore, the alkaline compound is one or more of sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, calcium oxide and barium oxide.

[0014] Furthermore, the preparation method of the modified phenolic resin comprises the following steps:

[0015] 1) Phenol, diol compound and the first batch of formaldehyde aqueous solution are mixed and stirred, the pH is adjusted to 3-4, and refluxed at 95-115° C. for 2-3 hours to remove condensation water and free water produced by the reaction;

[0016] 2) After the reaction is completed, the first batch of alkaline compound and the second batch of formaldehyde aqueous solution are added to adjust the pH to 7.5-8.5, and then dicyandiamide is added and reacted at 85-90° C. for 1-2 hours;

[0017] 3) Add a second batch of alkaline compound, adjust the pH to 9-10, heat the reaction at 75-85°C until the sample viscosity reaches 400-500 cps, cool to below 30°C, add latex, and stir evenly to obtain the modified phenolic resin.

[0018] Furthermore, in step 1), the molar ratio of formaldehyde to phenol in the first batch of formaldehyde aqueous solution is (0.5-1.0):1; in step 2), after the second batch of formaldehyde aqueous solution is added, the molar ratio of total formaldehyde to phenol in the system is (2.0-2.5):1.

[0019] The present invention also provides a method for preparing the high-toughness bamboo engineering material, comprising the following steps:

[0020] The modified phenolic resin is evenly coated on bamboo strips or impregnated into oriented bamboo fiber bundles. After being assembled in the direction of the grain, the bamboo strips and the oriented bamboo fiber bundles are bonded into a whole by a hot pressing process in a hot press to obtain a high-toughness bamboo engineering material.

[0021] Furthermore, the sizing amount of the modified phenolic resin is 150-250g / m 2 .

[0022] The present invention addresses the brittleness of traditional phenolic resins and synthesizes a modified high-toughness phenolic resin by combining internal toughening and external toughening in the phenolic resin molecules. Specifically:

[0023] Internal toughening: 1. A low-ratio phenol and formaldehyde aqueous solution and a glycol compound are reacted at high temperature under acidic conditions to obtain a linear phenolic resin intermediate modified by the glycol compound. Phenol and formaldehyde react under these conditions to form a flexible linear thermoplastic phenolic resin. The addition of the glycol compound forms a steric hindrance by reacting with the phenolic hydroxyl group to form an etherification reaction, making it difficult for the two ortho-hydrogens on the ether bond to participate in the reaction, thereby reducing the crosslinking density. At the same time, the glycol compound can also react with the hydroxymethyl group in the intermediate hydroxymethylphenol, so that the flexible glycol compound is bonded to the phenolic resin, reducing the crosslinking density of the resin after curing and improving the flexibility of the resin. 2. After obtaining the flexible phenolic resin intermediate modified by the glycol compound, formaldehyde aqueous solution and dicyandiamide are added and reacted under alkaline conditions. During this process, the formaldehyde aqueous solution reacts with the flexible intermediate to give the resin thermosetting properties. Dicyandiamide also participates in the reaction under these conditions and bonds to the resin to form flexible chain segments, reducing the crosslinking density and improving the flexibility of the resin.

[0024] External Toughening: After the resin is synthesized, a certain amount of latex is blended in. This latex has a low glass transition temperature and good flexibility. This blend enhances the resin's flexibility while ensuring the required strength. Furthermore, the phenolic resin produced by this process not only exhibits good flexibility but also possesses excellent bonding strength and environmental performance, meeting the performance requirements of indoor reconstituted bamboo.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention uses bamboo strips or oriented bamboo fiber bundles as basic units and a high-toughness phenolic resin modified through a combination of internal and external toughening as an adhesive to produce two types of high-toughness bamboo engineering materials: high-toughness bamboo laminates and bamboo reconstituted materials. These high-toughness bamboo engineering materials produced using this method exhibit high toughness and are resistant to cracking, meeting the performance requirements of reconstituted bamboo for indoor use. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 The bamboo strips prepared in Example 1;

[0029] Figure 2 The tangential assembly prepared in Example 1;

[0030] Figure 3 The flat-pressed bamboo laminated timber prepared in Example 1;

[0031] Figure 4 This is a graph showing the immersion and peeling performance of the flat-pressed bamboo laminated timber prepared in Example 1;

[0032] Figure 5 This is a graph showing the immersion and peeling performance of the flat-pressed bamboo laminated timber prepared in Comparative Example 1;

[0033] Figure 6 The bamboo strips prepared in Example 2;

[0034] Figure 7 The radial assembly prepared in Example 2;

[0035] Figure 8 The side-pressed bamboo laminated timber prepared in Example 2;

[0036] Figure 9 The oriented bamboo fiber bundle prepared in Example 3;

[0037] Figure 10 The radial assembly prepared in Example 3;

[0038] Figure 11 The high-toughness bamboo reconstructed material prepared in Example 3;

[0039] Figure 12 This is a graph showing the immersion and peeling performance of the high-toughness bamboo reconstituted material prepared in Example 3;

[0040] Figure 13 This is the immersion and peeling performance diagram of the high-toughness bamboo reconstituted material prepared in Comparative Example 3. DETAILED DESCRIPTION

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0042] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0043] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0044] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the present invention. The present description and examples are intended to be illustrative only.

[0045] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0046] Unless otherwise specified, the "parts" described in the present invention are based on mass parts.

[0047] A high-toughness bamboo engineering material is prepared by gluing bamboo strips or oriented bamboo fiber bundles as basic units and using a modified phenolic resin as an adhesive. The bamboo strips or bamboo fiber bundles are pressed into a whole by gluing. The modified phenolic resin comprises the following raw materials in parts by weight: 100 parts of phenol, 160-190 parts of a 50 wt.% formaldehyde aqueous solution, 2-10 parts of an alkaline compound, 15-20 parts of a glycol compound, 10-15 parts of dicyandiamide, and 10-30 parts of latex.

[0048] The alkaline compound is a monovalent and / or divalent metal compound. More preferably, the alkaline compound is one or more of sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, calcium oxide, and barium oxide. Most preferably, sodium hydroxide, potassium hydroxide, and calcium oxide.

[0049] The bamboo strips and oriented bamboo fiber bundles are made by splitting 3-5 year old bamboo into bamboo chips, which are then processed into bamboo strips and oriented bamboo fiber bundles.

[0050] Bamboo strips (method 1): 3-5 year old bamboo is split into bamboo tubes with a length of 2.5m, which are then split into bamboo strips with a width of 25mm using a bamboo splitter. The bamboo strips are then planed into rectangular cross-section strips using a roughing machine. The obtained bamboo strips are placed in hot water at 60-65°C, and 30% hydrogen peroxide is added at a ratio of 5-8% of the weight of the dry bamboo strips. The mixture is heated and boiled for 6-8 hours, after which the bamboo strips are removed. The steamed bamboo strips are placed in a mesh belt dryer for drying. The temperature is 60-70°C, the drying time is 72-84 hours, and the moisture content of the bamboo slices after drying is controlled at 6-10%. The dried bamboo slices are processed by a fine planer. The upper and lower hob groups of the fine planer plane the tangential surfaces (green and yellow surfaces) of the bamboo slices flat, and the left and right vertical axis hob groups plane the radial surfaces (left and right surfaces) of the bamboo slices flat, and the bamboo slices are processed into bamboo strips with a width of 20 mm and a thickness of 1.2 mm. The width and thickness errors of the bamboo strips after fine planing are controlled within 0.1 mm.

[0051] Bamboo strips (Method 2): Split 3-5 year old bamboo into 2.5m long bamboo tubes, use a bamboo splitter to split into 25mm wide bamboo strips, use a rough planer to plan the bamboo strips into rectangular cross-section bamboo strips, put the bamboo strips into a metal basket, push them into the furnace along the track, close the furnace door, open the steam valve, make the pressure reach 0.30-0.45MPa, and maintain it for 70-90 minutes; place the carbonized bamboo strips in a mesh belt dryer for drying, and the drying temperature is 200-300℃. The temperature is 60-70°C, the drying time is 72-84h, and the moisture content of the bamboo chips after drying is controlled at 6-10%; the dried bamboo chips are processed by a fine planer, and the upper and lower hob groups of the fine planer plane the tangential surfaces (bamboo green and bamboo yellow surfaces) of the bamboo chips flat, and the left and right vertical axis hob groups plane the radial surfaces (left and right sides) of the bamboo chips flat, and the processed bamboo chips are 15mm wide and 0.8mm thick. The width and thickness errors of the bamboo chips after fine planing are controlled within 0.1mm.

[0052] Oriented bamboo fiber bundles: 3-5 year old bamboo is split into bamboo chips, which are placed in a deflaking machine for deflaking. The deflaking teeth in the deflaking machine form a series of dot-shaped or line-shaped cracks on the bamboo wall, separating the bamboo into bamboo sheets formed by interweaving bamboo fiber bundles with a diameter of 0.1-0.5 mm and a length of 20-50 mm along the grain. The oriented bamboo fiber bundles are 1.5-5.0 m long, 100-300 mm wide, and 0.2-1.5 mm thick. The oriented bamboo fiber bundles are placed in a metal basket, pushed into a furnace along a track, and then the furnace door is closed. The steam valve is opened to increase the pressure to 0.30-0.45 MPa and maintained for 70-90 minutes. The carbonized bamboo chips are placed in a mesh belt dryer for drying at a drying temperature of 60-70° C. and a drying time of 72-84 hours. After drying, the moisture content of the oriented bamboo fiber bundles is controlled to be 6-10%.

[0053] In some preferred embodiments, the bamboo strips have a length of 1.5-5.0 m, a width of 15-30 mm, and a thickness of 0.5-1.5 mm, preferably a length of 2.60 m, a width of 20 mm, and a thickness of 1.2 mm.

[0054] In some preferred embodiments, the oriented bamboo fiber bundle is a sheet of bamboo material formed by interweaving bamboo fiber bundles with a diameter of 0.1-0.5 mm and a length of 20-50 mm along the grain; the oriented bamboo fiber bundle is 1.5-5.0 m long, 100-300 mm wide, and 0.2-1.5 mm thick.

[0055] In some preferred embodiments, the diol compound includes one or more of ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, dibutylene glycol, polyethylene glycol, and polypropylene glycol, preferably diethylene glycol, propylene glycol, and butylene glycol.

[0056] In some preferred embodiments, the latex comprises one or more of styrene-butadiene emulsion, styrene-acrylic emulsion, vinyl acetate-acrylic emulsion and pure acrylic emulsion, preferably a styrene-butadiene emulsion group, a styrene-acrylic emulsion group, a vinyl acetate-acrylic emulsion group and a pure acrylic emulsion group.

[0057] In some preferred embodiments, the method for preparing the modified phenolic resin comprises the following steps:

[0058] 1) Phenol, diol compound and the first batch of formaldehyde aqueous solution are mixed and stirred, the pH is adjusted to 3-4, and refluxed at 95-115° C. for 2-3 hours to remove condensation water and free water produced by the reaction;

[0059] 2) After the reaction is completed, the first batch of alkaline compound and the second batch of formaldehyde aqueous solution are added to adjust the pH to 7.5-8.5, and then dicyandiamide is added and reacted at 85-90° C. for 1-2 hours;

[0060] 3) Add a second batch of alkaline compound, adjust the pH to 9-10, heat the reaction at 75-85°C until the sample viscosity reaches 400-500 cps, cool to below 30°C, add latex, and stir evenly to obtain the modified phenolic resin.

[0061] In some preferred embodiments, in step 1), the molar ratio of formaldehyde to phenol in the first batch of formaldehyde aqueous solution is (0.5-1.0):1; in step 2), after the second batch of formaldehyde aqueous solution is added, the molar ratio of total formaldehyde to phenol in the system is (2.0-2.5):1.

[0062] The present invention also provides a method for preparing the high-toughness bamboo engineering material, comprising the following steps:

[0063] The modified phenolic resin is evenly coated on bamboo strips or oriented bamboo fiber bundles and assembled, and then sent into a hot press. The bamboo strips and oriented bamboo fiber bundles are bonded into a whole using a lamination molding process to obtain a high-toughness bamboo engineering material.

[0064] In some preferred embodiments, the sizing amount of the modified phenolic resin is 150-250 g / m 2 , preferably, 200g / m 2 .

[0065] In the hot pressing process, there are two situations:

[0066] 1) For bamboo strips, the lamination process is as follows: first, heat the hot press plate of the hot press to 120-155°C, feed the slab onto the hot press plate, close the hot press, apply a first positive pressure of 0.1-0.5 MPa, and a lateral pressure of 0.5-1.5 MPa to ensure that the bamboo strips are tightly bonded laterally without gaps; then apply a second positive pressure of 1.0-5.0 MPa and maintain the positive pressure until the core layer temperature of the slab reaches 115-125°C; then release the positive and lateral pressures and remove the slab.

[0067] 2) For oriented bamboo fiber bundles, the lamination molding process is as follows: first, the hot press plate temperature of the hot press is heated to 40-80°C, the slab is fed into the hot press, superheated steam is introduced into the hot press plate, and the hot press plate is heated to 120-155°C. At the same time, positive pressure is applied in the hot press at a pressure of 3-8 MPa until the hot press plate contacts the thickness gauge, and the positive pressure is maintained; then, the core layer temperature of the slab is detected. When the temperature reaches 115-125°C, the heating is stopped and maintained for 10-15 minutes. Cold water is introduced into the hot press plate until the temperature drops to 40-75°C, the pressure is released, and the slab is removed.

[0068] The bamboo material used in the embodiment of the present invention is selected from moso bamboo.

[0069] Example 1 (High-toughness flat-pressed bamboo laminated timber)

[0070] 1. Processing of bamboo:

[0071] 3-5 year old bamboo is split into bamboo tubes with a length of 2.5m, which are then split into bamboo strips with a width of 25mm using a bamboo splitter. The bamboo strips are then planed into rectangular strips using a roughing machine. The obtained bamboo strips are placed in 65°C hot water, and 30% hydrogen peroxide is added at a ratio of 5% by weight of the bamboo strips. The mixture is heated and boiled for 8 hours, after which the bamboo strips are taken out. The steamed bamboo strips are placed in a mesh belt dryer for drying at a drying temperature of 70°C. The drying time is 84 hours, and the moisture content of the bamboo strips after drying is controlled at 10%; the dried bamboo strips are processed by a fine planer. The upper and lower hob groups of the fine planer plane the tangential surfaces (green and yellow surfaces) of the bamboo strips flat, and the left and right vertical axis hob groups plane the radial surfaces (left and right sides) of the bamboo strips flat. The processed bamboo strips are 2.6 meters in length, 20 mm in width, and 1.2 mm in thickness. The width and thickness errors of the bamboo strips after fine planing are controlled within 0.1 mm.

[0072] 2. The modified phenolic resin is composed of the following raw materials in parts by mass: 100 parts of phenol, 190 parts of 50 wt.% formaldehyde aqueous solution, 3 parts of sodium hydroxide, 17 parts of diethylene glycol, 13 parts of dicyandiamide and 25 parts of styrene-butadiene emulsion.

[0073] Preparation of modified phenolic resin:

[0074] 1) Add 100 parts of phenol, 17 parts of diethylene glycol, and 40 parts of formaldehyde aqueous solution into a reactor (the molar ratio of formaldehyde to phenol in the formaldehyde aqueous solution is 0.63:1), stir evenly, adjust the pH to 3.5, reflux at 100°C for 2.5 hours, and remove the condensation water and free water produced by the reaction;

[0075] 2) After the reaction is completed, 150 parts of formaldehyde aqueous solution is added, the pH is adjusted to 7.5 with 1.5 parts of sodium hydroxide, and then 13 parts of dicyandiamide is added, and the reaction is carried out at 87° C. for 1.5 hours;

[0076] 3) 1.5 parts of sodium hydroxide was added to adjust the pH to 9.0, and the mixture was heated at 80° C. until the sample viscosity reached 400 cps. The mixture was cooled to 25° C., 25 parts of styrene-butadiene emulsion was added, and the mixture was stirred evenly. The mixture was discharged to obtain the modified phenolic resin.

[0077] 3. Preparation of high-toughness bamboo engineering materials:

[0078] The prepared modified phenolic resin was evenly coated on the bamboo strips (see Figure 1 ) on the surface, the glue amount is 150g / m 2 ; Assemble the bamboo strips along the grain to form a single-layer board (see Figure 2 ), then stack three layers of single-layer boards along the grain to form a flat-pressed bamboo laminated board (see Figure 3); heat the hot pressing plate of the hot press to 155°C; place the slab on the hot pressing plate; close the hot press, apply positive pressure of 0.1MPa for the first time; apply lateral pressure of 0.5MPa to ensure that the bamboo pieces are tightly bonded laterally without gaps; apply positive pressure of 1.5MPa for the second time, and maintain the positive pressure until the core temperature of the slab reaches 120°C; release the positive and lateral pressures and remove the slab.

[0079] Comparative Example 1

[0080] The same as Example 1, except that step 2 is omitted and ordinary phenolic resin (pure phenolic resin) is used. The viscosity of the resin is 375 cps, the solid content is 56%, and the pH is 9.6.

[0081] Table 1 shows the physical and mechanical properties of the flat-pressed bamboo laminated timber of Example 1 and Comparative Example 1 according to the test results of structural bamboo laminated timber (GB / T40487-2021). The immersion peeling performance of the bamboo base material end prepared in Example 1 and Comparative Example 1 after 28 days of water immersion is shown in Table 1. Figure 4 、 Figure 5 .

[0082] Table 1

[0083]

[0084] As can be seen from Table 1, under the same conditions of density, moisture content and static bending strength, the impact resistance of Example 1 of the present invention is improved by 90% compared with Comparative Example 1, and no peeling phenomenon occurs during use (see Figure 4 ), while in Comparative Example 1, after 28 days of water blistering, local peeling was evident between the layers (see Figure 5 ).

[0085] Example 2 (High-toughness side-pressure bamboo laminated timber)

[0086] 1. Processing of bamboo:

[0087] The five-year-old bamboo is split into bamboo tubes with a length of 5.0m, which are then split into bamboo strips with a width of 25mm using a bamboo splitting machine. The bamboo strips are then planed into rectangular bamboo strips using a roughing machine. The bamboo strips are placed in a metal basket, pushed into a furnace along a track, and the furnace door is closed. The steam valve is opened to make the pressure reach 0.35MPa and maintained for 90min. The carbonized bamboo strips are placed in a mesh belt dryer for drying at a drying temperature of 70°C and a drying time of 72h. The moisture content of the bamboo strips after drying is controlled to be 10%. The dried bamboo strips are processed using a fine planing machine. The upper and lower hob groups of the fine planing machine plan the tangential surfaces (green and yellow surfaces) of the bamboo strips, and the left and right vertical shaft hob groups plan and cut the radial surfaces (left and right sides) of the bamboo strips to be smooth. The strips are processed into bamboo strips with a length of 5.0m, a width of 15mm and a thickness of 0.8mm. The width and thickness errors of the bamboo strips after fine planing are controlled within 0.1mm.

[0088] 2. The modified phenolic resin is composed of the following raw materials in parts by mass: 100 parts of phenol, 190 parts of 50 wt% formaldehyde aqueous solution, 5 parts of potassium hydroxide, 20 parts of propylene glycol, 15 parts of dicyandiamide and 20 parts of pure acrylic emulsion.

[0089] Preparation of modified phenolic resin:

[0090] 1) Add 100 parts of phenol, 20 parts of propylene glycol, and 60 parts of a 50 wt.% formaldehyde aqueous solution into a reaction kettle (the molar ratio of formaldehyde to phenol in the formaldehyde aqueous solution is 0.94:1), stir evenly, adjust the pH to 4.0, reflux at 95°C for 3.0 hours, and remove the condensation water and free water produced by the reaction;

[0091] 2) After the reaction is completed, 130 parts of a 50 wt.% formaldehyde aqueous solution is added, the pH is adjusted to 7.5 with 2 parts of potassium hydroxide, and then 15 parts of dicyandiamide are added, and the reaction is carried out at 90° C. for 1.0 h;

[0092] 3) Add 3 parts of potassium hydroxide to adjust the pH to 9.2, heat the reaction at 80°C until the sample viscosity reaches 450 cps, cool to 30°C, add 20 parts of pure acrylic emulsion, stir evenly, and discharge to obtain modified phenolic resin.

[0093] 3. Preparation of high-toughness bamboo engineering materials:

[0094] The prepared modified phenolic resin was evenly coated on the bamboo strips (see Figure 6 ) on the surface, the glue amount is 250g / m 2 ; Assemble bamboo strips radially along the grain to form a single-layer board (see Figure 7 ), then stack three layers of single-layer boards along the grain to form a flat-pressed bamboo laminated board (see Figure 8); heat the hot pressing plate of the hot press to 155°C; place the slab on the hot pressing plate; close the hot press, apply positive pressure of 0.1MPa for the first time; apply lateral pressure of 0.5MPa to ensure that the bamboo pieces are tightly bonded laterally without gaps; apply positive pressure of 1.5MPa for the second time, and maintain the positive pressure until the core temperature of the slab reaches 120°C; release the positive and lateral pressures and remove the slab.

[0095] Comparative Example 2

[0096] The same as Example 2, except that step 2 is omitted and a conventional phenolic resin for artificial panels is used. The resin has a viscosity of 100 cps, a solid content of 44%, and a pH of 11.

[0097] Table 2 shows the physical and mechanical properties of the side-pressed bamboo laminated timber of Example 2 of the present invention and Comparative Example 2 tested according to the standard for structural bamboo laminated timber (GB / T40487-2021).

[0098] Table 2

[0099]

[0100]

[0101] As can be seen from Table 2, under the conditions of the same density, moisture content and static bending strength, the impact resistance of Example 2 of the present invention is improved by 75% compared with Comparative Example 2. After 28 days of circulated water blistering, the samples after Example 2 did not show any peeling phenomenon during use, while Comparative Example 3 showed obvious peeling phenomenon between the layers after 28 days of circulated water blistering.

[0102] Example 3 (High-toughness bamboo reconstituted material)

[0103] 1. Processing of bamboo:

[0104] Three-year-old bamboo is split into bamboo chips, which are placed in a deflaking machine for deflaking. The deflaking teeth in the deflaking machine are used to form a series of dot-shaped or line-shaped cracks on the bamboo wall, so that the bamboo is separated into sheet-shaped bamboo materials formed by bamboo fiber bundles with a diameter of 0.5 mm and a length of 20-50 mm interwoven along the grain. The oriented bamboo fiber bundles are 2.6 m long, 150-250 mm wide, and 0.6-1.0 mm thick. The oriented bamboo fiber bundles are placed in a metal basket, pushed into a furnace along a track, and then the furnace door is closed. The steam valve is opened to increase the pressure to 0.45 MPa and maintained for 90 minutes. The carbonized bamboo chips are placed in a mesh belt dryer for drying at a drying temperature of 70° C. and a drying time of 72 hours. After drying, the moisture content of the oriented bamboo fiber bundles is controlled to be 8%.

[0105] 2. The modified phenolic resin is composed of the following raw materials in parts by mass: 100 parts of phenol, 180 parts of 50 wt.% formaldehyde aqueous solution, 2 parts of sodium hydroxide and 8 parts of calcium oxide, 15 parts of butanediol, 10 parts of dicyandiamide and 30 parts of styrene acrylic emulsion.

[0106] Preparation of modified phenolic resin:

[0107] 1) Add 100 parts of phenol, 15 parts of butanediol, and 35 parts of formaldehyde aqueous solution into a reactor (the molar ratio of formaldehyde to phenol in the formaldehyde aqueous solution is 0.55:1), stir evenly, adjust the pH to 3.5, reflux at 110°C for 2.0 hours, and remove the condensation water and free water produced by the reaction;

[0108] 2) After the reaction is completed, 145 parts of formaldehyde aqueous solution is added, the pH is adjusted to 8.0 with 2 parts of sodium hydroxide, and then 10 parts of dicyandiamide are added, and the reaction is carried out at 85° C. for 2.0 hours;

[0109] 3) Add 8 parts of calcium oxide to adjust the pH to 9.6, heat the reaction at 80°C until the sample viscosity reaches 485 cps, cool to 35°C, add 30 parts of pure acrylic emulsion, stir evenly, and discharge to obtain modified phenolic resin.

[0110] 3. Preparation of high-toughness bamboo recombinant materials:

[0111] The modified phenolic resin was evenly impregnated into the oriented bamboo fiber bundles (see Figure 9 ) on the surface, the glue amount is 150g / m 2 ; The oriented bamboo fiber bundles are assembled in the radial direction along the grain and a single-layer board is formed by weaving technology (see Figure 10 ), and then stack 5 layers of single-layer boards along the grain to form a bamboo recombinant material blank (see Figure 11 ); heat the hot pressing plate of the hot press to 60°C; place the slab on the hot pressing plate; close the hot press, introduce superheated steam into the hot pressing plate of the hot press, heat the hot pressing plate of the hot press to 135°C, and at the same time, apply positive pressure in the hot press, the pressure is 6MPa, until the hot pressing plate contacts the thickness gauge, maintain the positive pressure; then, detect the temperature of the core layer of the slab, when the temperature reaches 120°C, stop the heating, keep it for 10 minutes, introduce cold water into the hot pressing plate of the hot press until the temperature drops to 60°C, release the pressure, and take out the slab.

[0112] Comparative Example 3

[0113] The same as Example 3, except that step 2 is omitted and ordinary phenolic resin for container bottom plates is used. The resin has a viscosity of 300 cps, a solid content of 48%, and a pH of 12.

[0114] Table 3 shows the physical and mechanical properties of the high-toughness bamboo reconstructed materials of Example 3 and Comparative Example 3 of the present invention tested in accordance with "Reconstructed Bamboo for Structural Use" (LY / T3194-2020).

[0115] Table 3

[0116]

[0117] As can be seen from Table 3, under the same conditions of density, moisture content and static bending strength, the impact resistance of Example 3 of the present invention is improved by 48% compared with Comparative Example 3. After 28 days of water immersion, the sample prepared in Example 3 did not show any peeling phenomenon during use (see Figure 12 ), while in comparative example 3, after 28 days of water blistering, the layers showed obvious peeling (see Figure 13 ).

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-toughness bamboo engineering material, characterized in that: The method comprises the following steps: using an oriented bamboo fiber bundle as a basic unit and a modified phenolic resin as an adhesive, and pressing the oriented bamboo fiber bundle into a whole; wherein the modified phenolic resin comprises the following raw materials in parts by weight: 100 parts of phenol, 160-190 parts of a 50 wt.% formaldehyde solution, 2-10 parts of an alkaline compound, 15-20 parts of a glycol compound, 10-15 parts of dicyandiamide, and 10-30 parts of latex; The diol compound includes one or more of ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, dibutylene glycol, polyethylene glycol and polypropylene glycol; The latex includes one or more of styrene-butadiene emulsion, styrene-acrylic emulsion, acetate-acrylic emulsion and pure acrylic emulsion; The alkaline compound includes a monovalent and / or divalent metal compound; The preparation method of the modified phenolic resin comprises the following steps: 1) Mix and stir phenol, glycol compound and the first batch of formaldehyde aqueous solution, adjust the pH to 3-4, and heat under reflux for 2-3 hours at a heating temperature of 95-115°C; 2) After the reaction is complete, add the first batch of alkaline compound and the second batch of formaldehyde aqueous solution, adjust the pH to 7.5-8.5, then add dicyandiamide and react at 85-90°C for 1-2 hours; 3) Add the second batch of alkaline compound, adjust the pH to 9-10, react at 75-85°C until the product viscosity reaches 400-500 cps, cool to 10-40°C, and finally add latex and stir evenly to obtain the modified phenolic resin; In step 1), the molar ratio of formaldehyde to phenol after the first batch of formaldehyde aqueous solution is added is (0.5-1.0):1; in step 2), after the second batch of formaldehyde aqueous solution is added, the molar ratio of total formaldehyde to phenol in the system is (2.0-2.5):

1.

2. The high-toughness bamboo engineering material according to claim 1, characterized in that: The oriented bamboo fiber bundle is a sheet of bamboo material formed by weaving bamboo fiber bundles with a diameter of 0.1-0.5 mm and a length of 20-50 mm along the grain; the oriented bamboo fiber bundle has a length of 1.5-5.0 m, a width of 100-300 mm, and a thickness of 0.2-1.5 mm.

3. A method for preparing the high-toughness bamboo engineering material according to any one of claims 1 to 2, characterized in that: The following steps are involved: The modified phenolic resin is evenly impregnated into the oriented bamboo fiber bundles, and after being assembled in the direction of the grain, the oriented bamboo fiber bundles are bonded into a whole by a hot pressing process in a hot press to obtain a high-toughness bamboo engineering material.

4. The method for preparing high-toughness bamboo engineering materials according to claim 3, characterized in that: The sizing amount of the modified phenolic resin is 150-250g / m 2 .

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