Bamboo yellow side single-face densified bamboo and preparation method and application thereof

Abstract

The invention belongs to the field of bamboo processing and modification, and particularly relates to a tabasheer side single-face densified bamboo and a preparation method and application thereof. The preparation method comprises the following steps that the tabasheer side of bamboo wood is placed in impregnation liquid for impregnation treatment, and the bamboo wood subjected to impregnation treatment is obtained; the impregnation liquid comprises water or a flame retardant solution; the tabasheer side of the soaked bamboo wood is preheated and softened, and the preheated and softened bamboo wood is obtained; the preheating and softening treatment temperature of the tabasheer side is kept, meanwhile, the bamboo wood subjected to preheating and softening treatment is pressurized and compressed, the bamboo wood is densified to the target thickness, and the compressed bamboo wood is obtained; and the tabasheer side and the bamboo green side of the compressed bamboo wood are subjected to hot-pressing shaping treatment at the same time, pressure relief is conducted after cooling, and the tabasheer side single-face densified bamboo wood is obtained. According to the preparation method, the tabasheer side compression and flame retardance integrated treatment of the bamboo can be achieved, the thickness and density of a bamboo compression layer can be controlled, and energy consumption and cost are greatly reduced.

Description

Technical Field

[0001] The invention belongs to the field of bamboo material processing and modification, and particularly relates to a bamboo material with a single-sided densification of the yellow side of the bamboo, and a preparation method and application thereof. Background Art

[0002] my country has extremely rich bamboo resources. Bamboo has the advantages of short growth cycle, wide distribution range and high mechanical strength. Bamboo is a natural non-homogeneous anisotropic material. It is divided into bamboo green, bamboo flesh and bamboo yellow from the outer layer to the inner layer. At the same time, it has the weaknesses of thin wall, hollow and uneven structure. These characteristics bring difficulties to the processing of bamboo. In the preparation process of bamboo boards such as bamboo composite materials, reconstructed bamboo and bamboo plywood, the split bamboo pieces are processed into unit materials or bamboo fiber bundles with rectangular cross-sections, and then glued and pressed into boards. The raw material utilization rate is low and a large amount of chemical adhesives are required, which affects the environmental protection of the material. The flattened bamboo technology, which softens, flattens and shapes the curved bamboo pieces after splitting the bamboo tube, can significantly improve the utilization rate and production efficiency of bamboo. However, as an important way to utilize bamboo in its original state, flattened bamboo inherits the natural texture and density difference characteristics of bamboo. Although it has high strength, it is uneven. The part close to the bamboo yellow side accounts for a large proportion, and the basic density and surface hardness are relatively low. Due to the asymmetry of the flattened bamboo density gradient structure, it has the problem of tile bending and deformation. In addition, flattened bamboo has the disadvantages of easy water absorption, shrinkage and swelling, low dimensional stability and poor flame retardancy, which makes it difficult to meet the requirements of high-performance materials.

[0003] Compression densification technology is an environmentally friendly and effective method to improve the structure and strength of lignocellulosic materials, and is widely used in the modification and reinforcement of low-density wood (CN116533340A, CN103753664A, CN107263657A, CN109623999A). In addition, CN114770681A reports a method for mechanical densification of bamboo by delignification, which can effectively reduce the heterogeneity of bamboo and improve its performance, but requires the use of a large amount of chemical agents for delignification and chemical cross-linking agents for modification, which increases environmental pressure, processing time and production costs. CN106881755A reports a method for densification of wood / bamboo by hot pressing combined with steam injection, which achieves the overall densification of bamboo by hot pressing combined with steam injection. However, this method has high requirements on equipment and needs to be equipped with a hot pressing plate with steam spray holes, which is difficult to operate and has high energy consumption. The document [Construction and Building Materials, 2023, 392: 132073] reports a method for overall compression and densification of flattened bamboo, where natural bamboo pieces with a moisture content of 70% are compressed radially along the stalk wall at temperatures of 170°C and 190°C to obtain a relatively uniform density of densified flattened bamboo. However, the improvement effect of the performance of the compressed flattened bamboo by this method depends on a large overall compression rate (about 44%) and a high heating temperature of the upper and lower pressing plates. The compression layer is not controllable, and the energy consumption is high. The flattened bamboo has a large material volume loss rate, which increases the production cost. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a bamboo material with a single-sided densification on the yellow side, and a preparation method and application thereof. The bamboo material with a single-sided densification on the yellow side prepared by the method provided by the present invention can realize the control of the thickness and density of the compression layer, and at the same time, only one-sided hot pressing plate needs to be heated, which can greatly save energy consumption and reduce production costs.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a single-sided densified bamboo material on the yellow side of a bamboo, comprising the following steps:

[0007] The yellow side of the bamboo is placed in an impregnation liquid for impregnation treatment to obtain an impregnation-treated bamboo; the impregnation liquid includes water or a flame retardant solution;

[0008] Performing a preheating and softening treatment on the yellow side of the impregnated bamboo material to obtain a preheating and softening bamboo material;

[0009] Maintaining the preheating and softening temperature of the yellow side of the bamboo, while pressurizing and compressing the preheating and softening bamboo material to densify the bamboo material to a target thickness, thereby obtaining a compressed bamboo material;

[0010] The yellow side and the green side of the compressed bamboo material are simultaneously subjected to hot pressing and shaping treatment, and the pressure is released after cooling to obtain the single-side densified bamboo material on the yellow side.

[0011] Preferably, the preheating and softening is to place the impregnated bamboo material in a hot press with the lower pressing plate not heated and the upper pressing plate preheated to 120-180° C. for preheating and softening; during the preheating and softening, the yellow side of the bamboo material is in contact with the upper pressing plate; the preheating and softening time is 5-120 seconds;

[0012] During the immersion treatment, the immersion depth is 10-50% of the total thickness of the bamboo material; and the immersion time is 0.5-4 hours.

[0013] Preferably, the thickness of the bamboo material is 6-15 mm; the bamboo material includes moso bamboo, giant dragon bamboo, hemp bamboo, wheeled bamboo or pole bamboo; the bamboo material includes scored flattened bamboo, unscored flattened bamboo or standard bamboo strips.

[0014] Preferably, the flame retardant solution comprises diammonium hydrogen phosphate, boric acid, borax, glucose and water; the mass ratio of the diammonium hydrogen phosphate, boric acid and borax is (2-8):(1-5):(1-5); the molar ratio of the diammonium hydrogen phosphate and glucose is 1:1; and the mass concentration of the flame retardant solution is 5-30%.

[0015] Preferably, after the immersion treatment, the moisture content of the yellow side of the bamboo material is greater than 15%, and the moisture content of the green side of the bamboo material is 5-12%.

[0016] Preferably, the pressurization and compression is carried out in a hot press; the pressure of the pressurization and compression is 2 to 40 MPa; the pressurization and compression is preferably progressive pressurization; the progressive pressurization is to pressurize and compress the bamboo material for 1 to 5 cycles, each compression cycle includes loading for 1 to 3 seconds, holding for 5 to 20 seconds, and the loading speed is 0.1 to 2.0 mm / s; during the pressurization and compression, the thickness of the bamboo material is controlled by the thickness gauge between the hot pressing plates, and the compression rate is 10 to 50%.

[0017] Preferably, the hot pressing and shaping treatment is carried out in a hot press, the heating temperature of the yellow bamboo side is 120-180°C; the heating temperature of the green bamboo side is 130-180°C; the pressure is 2-40MPa; during the hot pressing and shaping treatment, the heat preservation and pressure holding time is 0.5-6h.

[0018] Preferably, the pressure relief after cooling is to release the pressure after cooling the upper and lower hot pressing plates of the hot press machine to a temperature of 30-50° C. by passing cold water.

[0019] The present invention also provides a bamboo material with yellow side single-sided densification prepared by the preparation method described in the above technical solution, comprising a bamboo yellow side compression layer, a core uncompressed layer and a bamboo green side uncompressed layer arranged in sequence in the thickness direction; the peak density of the bamboo yellow side compression layer is 0.8-1.5 g / cm 3 The peak density of the uncompressed layer on the green bamboo side is 0.8 to 1.2 g / cm 3 .

[0020] The present invention also provides the use of the single-sided densified bamboo material on the yellow side of the bamboo described in the above technical solution in furniture, floors, cutting boards, buildings, and interior decoration.

[0021] The invention provides a preparation method of a yellow-side single-sided densified bamboo material, comprising the following steps: placing the yellow-side of the bamboo material in an impregnation liquid for impregnation treatment to obtain the impregnation-treated bamboo material; the impregnation liquid comprises water or a flame retardant solution; preheating and softening the yellow-side of the impregnation-treated bamboo material to obtain the preheating and softening-treated bamboo material; maintaining the preheating and softening treatment temperature of the yellow-side, and simultaneously pressurizing and compressing the preheating and softening-treated bamboo material to densify the bamboo material to a target thickness to obtain the compressed bamboo material; simultaneously hot-pressing and shaping the yellow-side and the green-side of the compressed bamboo material, and releasing the pressure after cooling to obtain the yellow-side single-sided densified bamboo material.

[0022] Compared with the prior art, the bamboo yellow side single-sided densification technology described in the present invention has the following unique technical points: 1. Using water as a softener to soften the bamboo yellow side is simpler, easier and more energy-saving than high-temperature softening methods such as steam, boiling, and microwaves. The use of a flame retardant solution to soften the bamboo yellow side can achieve integrated compression and flame retardant treatment of the bamboo yellow side; 2. During the bamboo compression and densification process, the plasticity of the bamboo yellow side that is directional infiltrated increases under the action of heat. Under a low compression rate, it gradually softens with the increase of preheating time, and then realizes compression deformation fixation during the hot pressing and shaping process. The thickness and density of the compression layer can be controlled by adjusting the process parameters of preheating softening, pressurized compression, and hot pressing and shaping. 3. During the preheating and softening process, only the bamboo yellow side is heated, which can greatly save energy and reduce production costs.

[0023] The results of the embodiment show that the present invention significantly improves the comprehensive performance of bamboo by compressing and densifying the yellow side of bamboo on one side. The peak density of the yellow side compression layer of the single-sided compressed and densified bamboo can reach up to 1.23g / cm 3 The surface hardness of the yellow side of the single-sided compressed bamboo is 21.6-26.8N / mm 2; The static bending strength of the single-sided compressed and densified bamboo is 248.1~279.0MPa; The elastic modulus of the single-sided compressed and densified bamboo is 11.5~13.6GPa. The peak density, surface hardness, static bending strength and elastic modulus of the compression layer on the yellow side of the single-sided compressed and densified bamboo are greatly improved compared with the control material. The present invention can achieve controllable compression and densification of the yellow side of the bamboo by adjusting the process parameters of preheating softening, pressurized compression and hot pressing shaping treatment, and the treatment process is green and environmentally friendly. While ensuring the natural high density of the green side, the peak density of the yellow side is increased to the same or higher than that of the green side, while retaining a certain thickness of the uncompressed layer in the core to form a structural morphology with symmetrical density distribution. The processing method of the present invention can not only effectively reduce the volume loss rate of densified bamboo and maintain the natural texture of bamboo, but also increase the density and strength of bamboo by improving the compression ratio as needed, so that bamboo can be widely used in furniture, flooring, chopping boards, construction, and interior decoration fields, and can also be further glued to prepare high-performance bamboo integrated materials and bamboo-wood composite boards, thereby promoting the green and healthy development of the bamboo industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a physical cross-sectional view of the samples in Comparative Example 1 and Example 1;

[0025] Figure 2 The SEM images of the bamboo yellow side cross-section of the samples in Comparative Example 1 and Example 1;

[0026] Figure 3 It is the cross-sectional density distribution diagram of the samples in Comparative Example 1 and Examples 1 to 4;

[0027] Figure 4 It is the cross-sectional density distribution diagram of the samples in Example 3 and Example 5;

[0028] Figure 5 It is a heat release rate curve diagram of the samples in Comparative Example 1 and Examples 3, 6, and 7;

[0029] Figure 6 It is a curve diagram of the total amount of heat release of the samples in Comparative Example 1 and Examples 3, 6, and 7;

[0030] Figure 7 It is a curve diagram of the total smoke production of the samples in Comparative Example 1 and Examples 3, 6 and 7. DETAILED DESCRIPTION

[0031] The present invention provides a method for preparing a single-sided densified bamboo material on the yellow side of a bamboo, comprising the following steps:

[0032] The yellow side of the bamboo is placed in an impregnation liquid for impregnation treatment to obtain an impregnation-treated bamboo; the impregnation liquid includes water or a flame retardant solution;

[0033] Performing a preheating and softening treatment on the yellow side of the impregnated bamboo material to obtain a preheating and softening bamboo material;

[0034] Maintaining the preheating and softening temperature of the yellow side of the bamboo, while pressurizing and compressing the preheating and softening bamboo material to densify the bamboo material to a target thickness, thereby obtaining a compressed bamboo material;

[0035] The yellow side and the green side of the compressed bamboo material are simultaneously subjected to hot pressing and shaping treatment, and the pressure is released after cooling to obtain the single-side densified bamboo material on the yellow side.

[0036] The invention places the yellow side of the bamboo material in an impregnation liquid for impregnation treatment to obtain the impregnation-treated bamboo material.

[0037] In the present invention, the thickness of the bamboo material is preferably 6 to 15 mm. In the present invention, the length and width of the bamboo material are not specifically limited, but the size of the bamboo material should be compatible with the hot press plate, including bamboo with bamboo nodes or only the internode portion. In the present invention, the bamboo species of the bamboo material preferably include moso bamboo, giant dragon bamboo, hemp bamboo, wheeled bamboo or supporting bamboo. In the present invention, the bamboo material preferably includes original bamboo board, specifically preferably includes notched flattened bamboo, unnotched flattened bamboo or standard bamboo strips.

[0038] In the present invention, the impregnation liquid includes water or a flame retardant solution.

[0039] In the present invention, the flame retardant solution preferably includes diammonium hydrogen phosphate, boric acid, borax, glucose and water; the mass concentration of the flame retardant solution is preferably 5-30%, more preferably 10-25%. In the present invention, the mass ratio of diammonium hydrogen phosphate, boric acid and borax in the flame retardant solution is preferably (2-8):(1-5):(1-5), more preferably 7:(1-2):(1-2); the molar ratio of diammonium hydrogen phosphate and glucose is preferably 1:1. In the present invention, the water is preferably deionized water, tap water or pure water. In the present invention, the temperature of the flame retardant solution is preferably 30-60°C.

[0040] In the present invention, the time of the impregnation treatment is preferably 0.5 to 4 hours, more preferably 1 to 4 hours; during the impregnation treatment, the impregnation depth is preferably 10 to 50% of the total thickness of the bamboo material, more preferably 20 to 50%, and the impregnation depth can be determined specifically according to the thickness requirement of the reference compression layer.

[0041] In the present invention, after the immersion treatment, the moisture content of the yellow side of the bamboo is preferably greater than 15%, more preferably 20-50%; the moisture content of the green side of the bamboo is preferably 5-12%, more preferably 7-10%.

[0042] After obtaining the impregnated bamboo material, the present invention performs a preheating and softening treatment on the yellow side of the impregnated bamboo material to obtain the preheating and softening bamboo material.

[0043] In the present invention, the preheating and softening is preferably carried out in a hot press, and the preheating and softening step is specifically preferably placing the impregnated bamboo material in a hot press with an unheated lower pressing plate and an upper pressing plate preheated to 120-180° C. for preheating and softening, and applying a relatively small pressure of 0.05-0.1 MPa.

[0044] In the present invention, during the preheating and softening, the yellow side of the bamboo material is preferably in contact with the upper pressing plate, and the green side of the bamboo material is in contact with the lower pressing plate. In the present invention, the preheating and softening time is preferably 5 to 120 seconds, more preferably 10 to 100 seconds. In the present invention, during the preheating and softening, once the bamboo material contacts the upper pressing plate, the press is immediately stopped from closing, and the pressure of the hot press is preferably 0.05 to 0.1 MPa, more preferably 0.05 to 0.08 MPa.

[0045] After obtaining the preheated and softened bamboo material, the present invention maintains the preheated and softened temperature of the yellow side of the bamboo, and simultaneously pressurizes and compresses the preheated and softened bamboo material to densify the bamboo material to a target thickness, thereby obtaining compressed bamboo material.

[0046] In the present invention, the compression is preferably carried out in a hot press; the pressure of the compression is preferably 2-40 MPa, more preferably 5-30 MPa; the compression is preferably progressive compression. In the present invention, the progressive compression is preferably 1-5 cycles of compression on the bamboo, each compression cycle includes loading for 1-3 seconds and holding for 5-20 seconds. In the present invention, the loading speed is preferably 0.1-2.0 mm / s, more preferably 0.5-1.2 mm / s.

[0047] In the present invention, the compression rate of the compressed bamboo is preferably 10-50%, more preferably 20-40%. In the present invention, the thickness of the compressed bamboo is preferably 3-10 mm, and the thickness is preferably controlled by a thickness gauge between the hot pressing plates.

[0048] After obtaining the compressed bamboo material, the present invention simultaneously performs hot pressing and shaping treatment on the yellow side and the green side of the compressed bamboo material, and releases the pressure after cooling to obtain the single-side densified bamboo material on the yellow side.

[0049] In the present invention, the hot pressing and shaping treatment is preferably carried out in a hot press. During the hot pressing and shaping treatment, the heating temperature of the yellow bamboo side is preferably 120-180°C, more preferably 130-160°C; the heating temperature of the green bamboo side is preferably 130-180°C, more preferably 130-160°C; the pressure is preferably 2-40MPa, more preferably 5-30MPa. In the present invention, the pressure during the hot pressing and shaping treatment is preferably the same as the pressure of the pressurized compression. In the present invention, during the hot pressing and shaping treatment, the heat preservation and pressure holding time is preferably 0.5-6h, more preferably 0.5-5h.

[0050] In the present invention, the role of hot pressing shaping treatment is: under the action of heat, moisture and force, on the one hand, the moisture inside the bamboo can be gasified and discharged from the longitudinal conveying channel of the bamboo, and the compression deformation of the bamboo can be temporarily fixed; on the other hand, by extending the heat preservation and pressure holding time, the main components of the bamboo will undergo degradation reactions when heated, causing internal molecular movement and releasing internal residual stress, thereby reducing deformation recovery and fixing the compression deformation of the bamboo.

[0051] In the present invention, the post-cooling pressure relief is preferably to pass cold water to cool the upper and lower hot pressing plates to 30-50°C, then release the pressure, the cooling rate is controlled by the flow rate of the cold water valve, and the cooling time is preferably 5-50 minutes.

[0052] In the present invention, the pressure relief after cooling can prevent defects such as bubbling and cracking caused by excessively high internal temperature of the bamboo material.

[0053] The present invention also provides a single-sided densified bamboo material on the yellow side prepared by the preparation method described in the above technical solution, comprising a compressed layer on the yellow side, a core uncompressed layer and a green side uncompressed layer arranged in sequence in the thickness direction.

[0054] In the present invention, the thickness of the compressed layer on the yellow bamboo side is preferably 2-4 mm; the thickness of the uncompressed layer on the green bamboo side is preferably 1-5 mm; the peak density of the compressed layer on the yellow bamboo side is preferably 0.8-1.5 g / cm 3 The peak density of the uncompressed layer on the green bamboo side is preferably 0.8 to 1.2 g / cm 3 .

[0055] The present invention also provides the use of the single-sided densified bamboo material on the yellow side of the bamboo described in the above technical solution in furniture, floors, cutting boards, buildings, and interior decoration.

[0056] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0057] Example 1

[0058] The processing object is a flattened bamboo board with a size of 150mm×100mm×9.3mm (length×width×thickness) and a density of 0.75g / cm 3 .

[0059] The specific processing process is as follows:

[0060] (1) The yellow side of a bamboo sample (water content 10%) was immersed in water for 1 hour. The immersion depth was 20% of the total thickness of the bamboo. After the immersion treatment, the water content of the yellow side was 20%.

[0061] (2) The soaked bamboo is placed in a hot press with the lower pressing plate not heated and the upper pressing plate preheated to 140°C, with the yellow side of the soaked bamboo facing upwards. A 6 mm thickness gauge is placed on the four sides of the pressing plate. The hot press is closed and preheated to soften for 10 seconds.

[0062] (3) The preheated and softened bamboo is subjected to progressive pressurization for a total of one compression cycle, with loading for 3 seconds and load holding for 7 seconds. The loading speed is 1.1 mm / s and the compression rate is 35%.

[0063] (4) The temperature of the lower pressing plate is raised to 140°C and maintained at this temperature for 0.5 h to compress and deform the bamboo in the hot press.

[0064] (5) passing cold water to quickly cool the upper and lower hot pressing plates to 30° C., and then opening the hot pressing machine to obtain the single-sided densified bamboo material on the yellow side of the bamboo.

[0065] The single-sided densified bamboo material on the yellow side obtained in this example is recorded as 140°C-1-0.5h.

[0066] Example 2

[0067] The processing object is a flattened bamboo board with a size of 150mm×100mm×9.3mm (length×width×thickness) and a density of 0.75g / cm 3 .

[0068] The specific processing process is as follows:

[0069] (1) The yellow side of a bamboo sample (water content 10%) was immersed in water for 2 hours. The immersion depth was 30% of the total thickness of the bamboo. After the immersion treatment, the water content of the yellow side was 25%.

[0070] (2) The soaked bamboo is placed in a hot press with the lower pressing plate not heated and the upper pressing plate preheated to 140°C, with the yellow side of the soaked bamboo facing upwards. A 6 mm thickness gauge is placed on the four sides of the pressing plate. The hot press is closed and preheated to soften for 30 seconds.

[0071] (3) The preheated and softened bamboo is subjected to progressive compression for a total of 2 compression cycles, each of which includes loading for 2 seconds and holding for 8 seconds. The loading speed is 0.8 mm / s and the compression rate is 35%.

[0072] (4) The temperature of the lower pressing plate is raised to 140°C and maintained at this temperature for 1.5 hours to allow the bamboo in the hot press to be compressed and deformed and fixed.

[0073] (5) passing cold water to quickly cool the upper and lower hot pressing plates to 30° C., and then opening the hot pressing machine to obtain the single-sided densified bamboo material on the yellow side of the bamboo.

[0074] The single-sided densified bamboo material on the yellow side obtained in this example is recorded as 140°C-2-1.5h.

[0075] Example 3

[0076] The processing object is a flattened bamboo board with a size of 150mm×100mm×9.3mm (length×width×thickness) and a density of 0.75g / cm 3 .

[0077] The specific processing process is as follows:

[0078] (1) The yellow side of a bamboo sample (water content 10%) was immersed in water for 3 hours. The immersion depth was 40% of the total thickness of the bamboo. After the immersion treatment, the water content of the yellow side was 28%.

[0079] (2) The soaked bamboo is placed in a hot press with the lower pressing plate not heated and the upper pressing plate preheated to 140°C, with the yellow side of the soaked bamboo facing upwards. A 6 mm thickness gauge is placed on the four sides of the pressing plate. The hot press is closed and preheated to soften for 50 seconds.

[0080] (3) The preheated and softened bamboo is subjected to progressive compression for a total of three compression cycles, each of which includes loading for 1 second and holding for 9 seconds. The loading speed is 1.1 mm / s and the compression rate is 35%.

[0081] (4) The temperature of the lower pressing plate is raised to 140°C and maintained at this temperature for 2.5 hours to allow the bamboo in the hot press to be compressed and deformed and fixed.

[0082] (5) passing cold water to quickly cool the upper and lower hot pressing plates to 30° C., and then opening the hot pressing machine to obtain the single-sided densified bamboo material on the yellow side of the bamboo.

[0083] The single-sided densified bamboo material on the yellow side obtained in this example is recorded as 140°C-3-2.5h.

[0084] Example 4

[0085] The processing object is a flattened bamboo board with a size of 150mm×100mm×9.3mm (length×width×thickness) and a density of 0.75g / cm 3 .

[0086] The specific processing process is as follows:

[0087] (1) The yellow side of a bamboo sample (water content 10%) was immersed in water for 4 hours. The immersion depth was 50% of the total thickness of the bamboo. After the immersion treatment, the water content of the yellow side was 32%.

[0088] (2) The soaked bamboo is placed in a hot press with the lower pressing plate not heated and the upper pressing plate preheated to 140°C, with the yellow side of the soaked bamboo facing upwards. A 6 mm thickness gauge is placed on the four sides of the pressing plate. The hot press is closed and preheated to soften for 70 seconds.

[0089] (3) The preheated and softened bamboo is subjected to progressive compression for a total of four compression cycles, each of which includes loading for 1 s and holding for 9 s. The loading speed is 0.8 mm / s and the compression rate is 35%.

[0090] (4) The temperature of the lower pressing plate is raised to 140°C and maintained at this temperature for 3.5 hours to allow the bamboo in the hot press to be compressed and deformed and fixed.

[0091] (5) passing cold water to quickly cool the upper and lower hot pressing plates to 30° C., and then opening the hot pressing machine to obtain the single-sided densified bamboo material on the yellow side of the bamboo.

[0092] The single-sided densified bamboo material on the yellow side obtained in this example is recorded as 140° C.-4-3.5h.

[0093] Example 5

[0094] The processing object is a flattened bamboo board with a size of 150mm×100mm×9.3mm (length×width×thickness) and a density of 0.75g / cm 3 .

[0095] The specific processing process is as follows:

[0096] (1) The yellow side of a bamboo sample (water content 10%) was immersed in water for 3 hours. The immersion depth was 40% of the total thickness of the bamboo. After the immersion treatment, the water content of the yellow side was 28%.

[0097] (2) The soaked bamboo is placed in a hot press with the lower pressing plate not heated and the upper pressing plate preheated to 160°C, with the yellow side of the soaked bamboo facing upwards. A 6 mm thickness gauge is placed on the four sides of the pressing plate. The hot press is closed and preheated to soften for 50 seconds.

[0098] (3) Intermittent pressurization was performed using the press control program for a total of three compression cycles. Each compression cycle included loading for 1 s and holding for 9 s. The loading speed was 1.1 mm / s and the compression rate was 35%.

[0099] (4) The temperature of the lower pressing plate is raised to 160°C and maintained at this temperature for 2.5 hours to allow the bamboo in the hot press to be compressed and deformed and fixed.

[0100] (5) passing cold water to quickly cool the upper and lower hot pressing plates to 30° C., and then opening the hot pressing machine to obtain the single-sided densified bamboo material on the yellow side of the bamboo.

[0101] The single-sided densified bamboo material on the yellow side obtained in this example is recorded as 160°C-3-2.5h.

[0102] Example 6

[0103] In this embodiment, the medium for impregnating and softening the bamboo is a flame retardant solution. The moisture content of the yellow side of the bamboo after the impregnation treatment is 26%, and the rest is the same as in Example 3, wherein the flame retardant solution contains diammonium hydrogen phosphate, boric acid, and borax in a mass ratio of 7:1.5:1.5, the molar ratio of glucose to diammonium hydrogen phosphate is 1:1, and the mass fraction of the flame retardant solution is 10%.

[0104] The obtained single-sided densified bamboo material on the yellow side is recorded as FR10%-140℃.

[0105] Example 7

[0106] In this embodiment, the medium for impregnating and softening the bamboo is a flame retardant solution. The moisture content of the yellow side of the bamboo after the impregnation treatment is 25%, and the rest is the same as Example 3, wherein the flame retardant solution contains diammonium hydrogen phosphate, boric acid, and borax in a mass ratio of 7:1.5:1.5, the molar ratio of glucose to diammonium hydrogen phosphate is 1:1, and the mass fraction of the flame retardant solution is 20%.

[0107] The obtained single-sided densified bamboo material on the yellow side of the bamboo is recorded as FR20%-140℃.

[0108] Comparative Example 1

[0109] The flattened bamboo boards (control materials) without any treatment were directly tested for performance, including micromorphology (SEM), cross-sectional density, surface hardness, static bending strength, etc.

[0110] Density: 0.75g / cm 3 The specifications are 150mm×100mm×9.3mm (length×width×thickness), and the initial moisture content is 10%.

[0111] Comparative Example 2

[0112] The processing object is a flattened bamboo board with a size of 150mm×100mm×9.3mm (length×width×thickness) and a density of 0.75g / cm 3 .

[0113] The specific processing process is as follows:

[0114] (1) The yellow side of a bamboo sample (water content 10%) was immersed in water for 3 hours. The immersion depth was 40% of the total thickness of the bamboo. After the immersion treatment, the water content of the yellow side was 28%.

[0115] (2) The soaked bamboo is placed in a hot press with the lower pressing plate not heated and the upper pressing plate preheated to 140°C, with the yellow side of the soaked bamboo facing upwards. A 6 mm thickness gauge is placed on the four sides of the pressing plate. The hot press is closed and preheated to soften for 50 seconds.

[0116] (3) The preheated and softened bamboo is subjected to progressive compression for a total of three compression cycles, each of which includes loading for 1 second and holding for 9 seconds. The loading speed is 1.1 mm / s and the compression rate is 35%.

[0117] (4) passing cold water to quickly cool the upper and lower hot pressing plates to 30° C., and then opening the hot pressing machine to obtain the single-sided densified bamboo material on the yellow side of the bamboo.

[0118] The single-sided densified bamboo material on the yellow side obtained in this comparative example was recorded as 140°C-3-0h.

[0119] Figure 1 It is a physical cross-sectional view of the samples in Comparative Example 1 and Example 1, wherein Figure 1 (a) is the control material in Comparative Example 1; Figure 2 (b) is the bamboo material with single-sided densification on the yellow side in Example 1. Figure 1 It can be seen that the organizational structure of the bamboo cross section in Comparative Example 1 presents a typical gradient structure, and the vascular bundle tissue ratio decreases from the green side to the yellow side along the thickness direction of the bamboo. The vascular bundles on the green side are smaller and more densely distributed; the vascular bundles on the yellow side are larger and more sparsely distributed. The overall thickness of the bamboo material with single-sided densification on the yellow side in Example 1 becomes thinner, the upper and lower surfaces are smoother, the cell morphology on the yellow side changes, and the tissue gap decreases, but the original organizational structure of the bamboo is still maintained.

[0120] Figure 2 The SEM images of the bamboo yellow side cross-section of the samples in Comparative Example 1 and Example 1 are shown in FIG. Figure 2 (a) is the control material in Comparative Example 1; Figure 2 (b) is the bamboo material with single-sided densification on the yellow side in Example 1. Figure 2 It can be seen that the morphology of the thin-walled cells of the bamboo material with single-sided densification on the yellow side of the bamboo changes significantly. From the green side to the yellow side of the bamboo, the deformation degree of the cell cavity gradually increases, and the volume of the cell cavity and the vessel is compressed and reduced. During the densification process of the yellow side of the bamboo, the cell wall on the yellow side of the bamboo is deformed, mainly because the amorphous cellulose, hemicellulose and lignin matrix changes from the glassy state to the rubbery state, realizing the compression strengthening modification of the yellow side of the bamboo, increasing the density and surface hardness of the yellow side of the bamboo, and thus enhancing its mechanical properties.

[0121] Figure 3 is the cross-sectional density distribution diagram of the samples in Comparative Example 1 and Examples 1 to 4, Figure 4 3 and 5 are cross-sectional density distribution diagrams of the samples. Figures 3-4 It can be seen that the density of the control material (bamboo material of comparative example 1) gradually decreases from the green bamboo side to the yellow bamboo side. The thickness of the single-sided densified bamboo material on the yellow bamboo side becomes thinner, and the cross-sectional density curve presents a symmetrical structural morphology. The density on the yellow bamboo side increases significantly and is close to the density on the green bamboo side, indicating that the single-sided densified bamboo material on the yellow bamboo side is successfully prepared under the conditions of the present invention.

[0122] By using the press control program to preheat the yellow side of the bamboo and perform multiple progressive pressurizations, the peak shape of the density distribution curve of the compressed layer on the yellow side of the bamboo can be effectively controlled. When the preheating time is short and the number of pressurizations is small, the density distribution curve of the effective dense layer on the yellow side of the bamboo presents a narrow and sharp density peak. As the preheating time increases and the number of pressurizations increases, the amount of heat transferred from the hot pressing plate to the inner layer of the yellow side of the bamboo increases, the softened area on the yellow side of the bamboo increases, the density distribution curve of the effective dense layer on the yellow side of the bamboo gradually widens, the density gradually increases, and the distance of the peak density from the surface of the compressed side gradually increases. As the hot pressing temperature increases, the amount of heat transferred from the hot pressing plate to the inner layer of the yellow side of the bamboo increases, the degree of softening of the inner layer of the yellow side of the bamboo increases, and it is easier to be compacted, thereby increasing the thickness of the total dense layer and increasing the peak density, up to 1.23g / cm 3 , which is significantly higher than the density of the green side. The increase in density plays an important role in improving the comprehensive performance of bamboo.

[0123] The physical and mechanical properties of the bamboo material with one-sided densification on the yellow side of the bamboo are characterized, and the results are shown in Table 1. From the results in Table 1, it can be seen that with the increase of the hot pressing temperature or the extension of the hot pressing shaping time, the water absorption deformation recovery rate of the bamboo material with one-sided densification on the yellow side of the bamboo is reduced. The water absorption deformation recovery rate of the bamboo material with one-sided densification on the yellow side of the bamboo that has not been subjected to hot pressing shaping treatment (Comparative Example 2) is 17.5%. When the hot pressing shaping temperature is 140°C, the water absorption deformation recovery rate ranges from 6.6 to 11.2%; when the hot pressing shaping temperature is 160°C, the water absorption deformation recovery rate is reduced to 4.3%, indicating that the hot press shaping treatment is an effective method for fixing the compression deformation of the bamboo material with one-sided compression densification on the yellow side of the bamboo.

[0124] Table 2 and Figures 5 to 7 The cone calorimeter test data of the bamboo yellow side single-sided densification bamboo prepared in Comparative Example 1 and Examples 3, 6, and 7 are shown in Table 2 and Figures 5 to 7 It can be seen that the ignition time (TTI) of the control material is 19s and the peak heat release rate (PHRR) is 714.9kW / m 2 The total heat release (THR) is as high as 73.3MJ / m 2 , total smoke production (TSP) up to 3.24m 2. The single-sided densification treatment of the yellow side of bamboo did not significantly reduce the peak heat release rate, total heat release and total smoke production of the bamboo, but the ignition time (140℃-3-2.5h) was delayed by 4s, and the time for the peak heat release rate to appear was delayed by 115s. The ignition time of bamboo treated with integrated flame retardancy and single-sided densification of the yellow side (FR10%-140℃ and FR20%-140℃) was further delayed, and the peak heat release rate was reduced by 60.2%, the total heat release was reduced by 39.8%, and the total smoke production was reduced by 55.9%. In summary, the technology of the present invention can significantly improve the flame retardant properties of the bamboo with single-sided densification on the yellow side of the bamboo while ensuring that the bamboo has good physical and mechanical properties and dimensional stability.

[0125] Table 1 Physical and mechanical properties test results

[0126]

[0127]

[0128] Table 2 Cone calorimeter test data of bamboo materials with single-sided densification on the yellow side prepared in Comparative Example 1 and Examples 3, 6, and 7

[0129] sample TTI(s) <![CDATA[PHRR(kW / m 2 )]]> <![CDATA[THR(MJ / m 2 )]]> <![CDATA[TSP(m 2 )]]> Reference material 19 714.9 (peak time: 160s) 73.3 3.24 140℃-3-2.5h 23 696.4 (peak time: 275s) 71.5 3.29 FR10%-140℃ 25 404.2 (peak time: 285s) 56.8 2.27 FR20%-140℃ 28 284.8 (peak time: 290s) 44.1 1.43

[0130] By comparing the above embodiments and comparative examples, it can be seen that the bamboo material with single-sided densification on the yellow side of the bamboo prepared by the method of the present invention has greatly improved dimensional stability and mechanical strength, and the density and surface hardness of the yellow side of the bamboo are improved. The method performs directional compression and reinforcement on the yellow side of the bamboo with lower density. Compared with the traditional overall compressed bamboo material, it has the advantages of high hardness and light weight, significantly reduces the volume loss rate of the compressed bamboo material, and is simple and easy to operate, green and environmentally friendly, and has lower energy consumption. The thickness and density of the compressed layer on the yellow side of the bamboo can be controlled by controlling the process parameters of preheating softening treatment, pressurized compression and hot pressing shaping treatment. While maintaining the high density of the green side of the natural bamboo material, the density, surface hardness and mechanical strength of the yellow side of the bamboo are directional. In addition, the bamboo material is impregnated and softened with a flame retardant solution as needed, and the flame retardant properties of the single-sided densification bamboo material on the yellow side of the bamboo are significantly improved under the premise of ensuring good physical and mechanical properties and dimensional stability, which broadens the application field of original bamboo materials such as flattened bamboo, and is expected to be applied to structural and non-structural fields such as construction and interior decoration.

[0131] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing bamboo material with single-sided densification on the yellow side of bamboo, characterized in that: The following steps are involved: The yellow side of the bamboo is placed in an impregnation liquid for impregnation treatment to obtain an impregnation-treated bamboo; the impregnation liquid includes water or a flame retardant solution; Performing a preheating and softening treatment on the yellow side of the impregnated bamboo material to obtain a preheating and softening bamboo material; Maintaining the preheating and softening temperature of the yellow side of the bamboo, while pressurizing and compressing the preheating and softening bamboo material to densify the bamboo material to a target thickness, thereby obtaining a compressed bamboo material; The yellow side and the green side of the compressed bamboo material are simultaneously subjected to hot pressing and shaping treatment, and the pressure is released after cooling to obtain the single-side densified bamboo material on the yellow side.

2. The preparation method according to claim 1, characterized in that The preheating and softening is to place the impregnated bamboo material in a hot press with an unheated lower pressing plate and an upper pressing plate preheated to 120-180° C. for preheating and softening, and apply a relatively small pressure of 0.05-0.1 MPa; during the preheating and softening, the yellow side of the bamboo material contacts the upper pressing plate, and the green side contacts the lower pressing plate; the preheating and softening time is 5-120 seconds; During the immersion treatment, the immersion depth is 10-50% of the total thickness of the bamboo material; and the immersion time is 0.5-4 hours.

3. The preparation method according to claim 1, characterized in that: The thickness of the bamboo material is 6-15 mm; the bamboo species of the bamboo material include moso bamboo, giant dragon bamboo, hemp bamboo, wheeled bamboo or pole bamboo; the bamboo material includes scored flattened bamboo, unscored flattened bamboo or standard bamboo strips.

4. The preparation method according to claim 1, characterized in that: The flame retardant solution comprises diammonium hydrogen phosphate, boric acid, borax, glucose and water; the mass ratio of the diammonium hydrogen phosphate, boric acid and borax is (2-8):(1-5):(1-5); the molar ratio of the diammonium hydrogen phosphate and glucose is 1:1; and the mass concentration of the flame retardant solution is 5-30%.

5. The preparation method according to claim 1, characterized in that: After the immersion treatment, the moisture content of the yellow side of the bamboo material is greater than 15%, and the moisture content of the green side of the bamboo material is 5-12%.

6. The preparation method according to claim 1, characterized in that: The pressurization and compression is carried out in a hot press; the pressure of the pressurization and compression is 2 to 40 MPa; the pressurization and compression is progressive pressurization; the progressive pressurization is to pressurize and compress the bamboo material for 1 to 5 cycles, each compression cycle includes loading for 1 to 3 seconds, holding for 5 to 20 seconds, and the loading speed is 0.1 to 2.0 mm / s; during the pressurization and compression, the thickness of the bamboo material is controlled by a thickness gauge between the hot pressing plates, and the compression rate is 10 to 50%.

7. The preparation method according to claim 1, characterized in that: The hot pressing shaping treatment is carried out in a hot press, the heating temperature of the yellow bamboo side is 120-180°C; the heating temperature of the green bamboo side is 130-180°C; the pressure is 2-40MPa; during the hot pressing shaping treatment, the heat preservation and pressure holding time is 0.5-6h.

8. The preparation method according to claim 7, characterized in that: The post-cooling pressure relief is to release the pressure after passing cold water to cool the upper and lower hot pressing plates of the hot press to 30-50° C.

9. The bamboo material with single-sided densification on the yellow side prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The invention comprises a bamboo yellow side compressed layer, a core uncompressed layer and a bamboo green side uncompressed layer arranged in sequence in the thickness direction; the peak density of the bamboo yellow side compressed layer is 0.8-1.5 g / cm 3 The peak density of the uncompressed layer on the green bamboo side is 0.8 to 1.2 g / cm 3 .

10. Use of the bamboo material with single-sided densification on the yellow side of the bamboo as claimed in claim 9 in furniture, flooring, cutting boards, construction and interior decoration.

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