A bamboo yellow side single-face dense bamboo material and a preparation method and application thereof

Abstract

This invention belongs to the field of bamboo processing and modification, specifically relating to a method for preparing single-sided densified bamboo with a yellow side, and its application. The preparation method provided by this invention includes the following steps: immersing the yellow side of bamboo in an impregnation solution to obtain impregnated bamboo; the impregnation solution includes water or a flame retardant solution; preheating and softening the yellow side of the impregnated bamboo to obtain preheated and softened bamboo; maintaining the preheating and softening temperature while simultaneously compressing the preheated and softened bamboo to densify it to a target thickness, obtaining compressed bamboo; and simultaneously hot-pressing and shaping the yellow and green sides of the compressed bamboo, followed by cooling and depressurization to obtain the single-sided densified bamboo with a yellow side. The preparation method of this invention can achieve integrated compression and flame retardant treatment of the yellow side of bamboo, and can also control the thickness and density of the compressed bamboo layer, significantly saving energy and cost.

Description

Technical Field

[0001] This invention belongs to the field of bamboo processing and modification, specifically relating to a method for preparing and applying bamboo with single-sided densification of the yellow side. Background Technology

[0002] my country boasts abundant bamboo resources, with bamboo possessing advantages such as a short growth cycle, wide distribution, and high mechanical strength. Bamboo is a naturally heterogeneous and anisotropic material, horizontally divided into the outer layer, inner layer, and inner layer (bamboo core, bamboo flesh, and bamboo sapwood). It also exhibits weaknesses such as thin walls, hollowness, and uneven structure, all of which pose challenges to bamboo processing. In the preparation of bamboo-based panels, reconstituted bamboo, and bamboo plywood, the process involves splitting bamboo into rectangular cross-section unit materials or bamboo fiber bundles, then applying adhesive and pressing them into panels. This method results in low raw material utilization and requires large amounts of chemical adhesives, impacting the material's environmental friendliness. Flattened bamboo technology, which involves softening, flattening, and shaping the curved bamboo strips after splitting bamboo tubes, can significantly improve bamboo utilization and production efficiency. However, flattened bamboo, as an important method of utilizing bamboo in its original state, inherits the natural texture and density variations of bamboo. While its strength is high, it is uneven, with a larger proportion near the sapwood side, resulting in relatively lower basic density and surface hardness. The asymmetry of the density gradient structure of flattened bamboo leads to its tendency to bend and deform. Furthermore, flattened bamboo suffers from drawbacks such as easy water absorption, shrinkage and swelling with moisture, low dimensional stability, and poor flame retardancy, making it difficult to meet the requirements for high-performance materials.

[0003] Compression densification technology is an environmentally friendly and effective method for improving the structure and strength of lignocellulosic materials, and it is widely used in modifying and reinforcing low-density wood (CN116533340A, CN103753664A, CN107263657A, CN109623999A). Additionally, CN108772922A reports a method for mechanically densifying bamboo through delignification. This method can effectively reduce the heterogeneity of bamboo and improve its properties, but it requires the use of large amounts of chemical agents for delignification and chemical cross-linking agents for modification, increasing environmental pressure, processing time, and production costs. CN106881755A reports a method for densifying wood / bamboo through hot pressing combined with steam injection, achieving overall densification of bamboo. However, this method has high equipment requirements, necessitating a hot press plate with steam nozzles, making operation difficult and energy consumption high. The literature [Construction and Building Materials, 2023, 392:132073] reports a method for integrally compressing and densifying flattened bamboo. Natural bamboo strips with a moisture content of 70% are radially compressed along the culm wall at temperatures of 170℃ and 190℃, resulting in denser, flattened bamboo with a relatively uniform density. However, the improved performance of this method depends on a large overall compression ratio (approximately 44%) and high heating temperatures of the upper and lower pressure plates. The compression layer lacks controllability, has high energy consumption, and exhibits significant volumetric loss, increasing production costs. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for preparing single-sided densified bamboo with the yellow side as well as its application. The method provided by this invention allows for control over the thickness and density of the compressed layer, and by requiring only heating a single-sided hot press plate, it significantly saves energy and reduces production costs.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing single-sided dense bamboo material with a yellow side, comprising the following steps:

[0007] The bamboo core is immersed in an impregnation solution to obtain impregnated bamboo; the impregnation solution includes water or a flame retardant solution.

[0008] The bamboo yellow side of the impregnated bamboo is preheated and softened to obtain preheated and softened bamboo.

[0009] Maintain the preheating and softening treatment temperature on the bamboo yellow side, and simultaneously compress the preheated and softened bamboo to densify it to the target thickness, thereby obtaining compressed bamboo.

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

[0011] Preferably, the preheating and softening is performed by placing the impregnated bamboo material in a hot press with the lower platen unheated and the upper platen preheated to 120-180°C for preheating and softening; during the preheating and softening, the bamboo yellow side of the bamboo material is in contact with the upper platen; the preheating and softening time is 5-120 seconds.

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

[0013] Preferably, the thickness of the bamboo material is 6-15mm; the bamboo material includes moso bamboo, giant dragon bamboo, hemp bamboo, cart bamboo or pole bamboo; the bamboo material includes serrated flat bamboo, unserrated flat 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 diammonium hydrogen phosphate, boric acid, and borax is (2-8):(1-5):(1-5); the molar ratio of diammonium hydrogen phosphate and glucose is 1:1; and the mass concentration of the flame retardant solution is 5-30%.

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

[0016] Preferably, the pressure compression is performed in a hot press; the pressure of the pressure compression is 2–40 MPa; the pressure compression is preferably a gradual compression; the gradual compression involves compressing the bamboo material for 1–5 cycles, each compression cycle including loading for 1–3 seconds, holding for 5–20 seconds, and the loading speed is 0.1–2.0 mm / s; during the pressure compression, the thickness of the bamboo material is controlled by the thickness gauge between the hot press plates, and the compression rate is 10–50%.

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

[0018] Preferably, the pressure relief after cooling is achieved by circulating cold water to cool the upper and lower hot platens of the hot press to 30-50°C before releasing the pressure.

[0019] The present invention also provides a single-sided dense bamboo material with a yellow side prepared by the preparation method described above, comprising a compressed layer on the yellow side, an uncompressed core layer, and an uncompressed bamboo green side layer arranged sequentially in the thickness direction; the peak density of the compressed layer on the yellow side is 0.8–1.5 g / cm³. 3 The peak density of the uncompressed layer on the bamboo green side is 0.8–1.2 g / cm³. 3 .

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

[0021] This invention provides a method for preparing single-sided densified bamboo material with the yellow side, comprising the following steps: immersing the yellow side of bamboo material in an impregnation solution to obtain impregnated bamboo material; the impregnation solution includes water or a flame retardant solution; preheating and softening the yellow side of the impregnated bamboo material to obtain preheated and softened bamboo material; maintaining the preheating and softening temperature of the yellow side while simultaneously compressing the preheated and softened bamboo material to densify it to a target thickness, obtaining compressed bamboo material; simultaneously hot-pressing and shaping the yellow and green sides of the compressed bamboo material, and releasing the pressure after cooling to obtain the single-sided densified bamboo material with the yellow side.

[0022] Compared with existing technologies, the bamboo material densification technology on the single-sided bamboo yellow side described in this invention has the following unique technical advantages: 1. Using water as a softening agent to soften the bamboo yellow side is simpler, easier, and more energy-efficient than high-temperature softening methods such as steaming, boiling, and microwaves. Using a flame retardant solution to soften the bamboo yellow side allows for integrated compression and flame retardant treatment. 2. During the bamboo compression and densification process, the plasticity of the directionally impregnated bamboo yellow side increases under heat. At low compression rates, it gradually softens with increasing preheating time, and then achieves compression deformation fixation during hot pressing. Furthermore, the thickness and density of the compressed layer can be controlled by adjusting the process parameters of preheating softening, pressurization, and hot pressing. 3. During the preheating softening process, only the bamboo yellow side is heated, significantly saving energy and reducing production costs.

[0023] The results of the embodiments show that the present invention, through single-sided compression densification of the bamboo's yellow side, significantly improves the overall performance of bamboo. The peak density of the compressed layer on the yellow side of the bamboo treated with single-sided compression densification can reach up to 1.23 g / cm³. 3 The surface hardness of the yellow side of single-sided compressed bamboo is 21.6–26.8 N / mm. 2The static bending strength of single-sided compressed bamboo is 248.1–279.0 MPa, and the elastic modulus is 11.5–13.6 GPa. The peak density, surface hardness, static bending strength, and elastic modulus of the compressed layer on the bamboo stalk side of the single-sided compressed bamboo are significantly improved compared to the control material. This invention achieves controllable compression and densification of the bamboo stalk side by adjusting the process parameters of preheating softening, pressure compression, and hot pressing shaping, and the process is environmentally friendly. While maintaining the natural high density of the bamboo stalk side, the peak density of the bamboo stalk side is increased to the same or higher level as the bamboo stalk side, while retaining a certain thickness of uncompressed layer in the core, forming a symmetrical density distribution structure. The processing method described in this invention can not only effectively reduce the volume loss rate of dense bamboo and maintain the natural texture of bamboo, but also increase the density and strength of bamboo by increasing the compression ratio as needed. This allows bamboo to be widely used in furniture, flooring, cutting boards, construction, and interior decoration. It can also be further glued to prepare high-performance bamboo engineered wood and bamboo-wood composite boards, thereby promoting the green and healthy development of the bamboo industry. Attached Figure Description

[0024] Figure 1 These are cross-sectional views of the samples from Comparative Example 1 and Example 1.

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

[0026] Figure 3 The density distribution diagrams of the samples in Comparative Example 1 and Examples 1-4 are shown.

[0027] Figure 4 These are cross-sectional density distribution diagrams of the samples from Examples 3 and 5;

[0028] Figure 5 The graphs show the heat release rate of the samples in Comparative Example 1 and Examples 3, 6, and 7.

[0029] Figure 6 The graph shows the total heat release of the samples in Comparative Example 1 and Examples 3, 6, and 7.

[0030] Figure 7 The graph shows the total smoke production curves for samples in Comparative Example 1 and Examples 3, 6, and 7. Detailed Implementation

[0031] This invention provides a method for preparing single-sided dense bamboo material with a yellow side, comprising the following steps:

[0032] The bamboo core is immersed in an impregnation solution to obtain impregnated bamboo; the impregnation solution includes water or a flame retardant solution.

[0033] The bamboo yellow side of the impregnated bamboo is preheated and softened to obtain preheated and softened bamboo.

[0034] Maintain the preheating and softening treatment temperature on the bamboo yellow side, and simultaneously compress the preheated and softened bamboo to densify it to the target thickness, thereby obtaining compressed bamboo.

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

[0036] This invention involves immersing the yellow side of bamboo in an impregnation solution to obtain impregnated bamboo.

[0037] In this invention, the thickness of the bamboo material is preferably 6-15 mm. The length and width of the bamboo material are not specifically limited, but the dimensions should be compatible with the pressing plate of the hot press, and the bamboo material includes bamboo with nodes or only the portion between the nodes. In this invention, the bamboo species preferably include moso bamboo, giant dragon bamboo, hemp bamboo, cart bamboo, or pole bamboo. In this invention, the bamboo material preferably includes unprocessed bamboo boards, specifically, serrated flat bamboo, unserrated flat bamboo, or sized bamboo strips.

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

[0039] In this invention, the flame retardant solution preferably comprises 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 this 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 to glucose is preferably 1:1. In this invention, the water is preferably deionized water, tap water, or purified water. In this invention, the temperature of the flame retardant solution is preferably 30-60°C.

[0040] In this invention, the impregnation time is preferably 0.5 to 4 hours, more preferably 1 to 4 hours; during the impregnation process, the impregnation depth is preferably 10 to 50% of the total thickness of the bamboo, more preferably 20 to 50%, and the specific impregnation depth can be determined according to the required thickness of the compression layer.

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

[0042] After obtaining the impregnated bamboo, the present invention preheats and softens the yellow side of the impregnated bamboo to obtain preheated and softened bamboo.

[0043] In this invention, the preheating and softening is preferably carried out in a hot press. Specifically, the preheating and softening step is preferably to place the impregnated bamboo material in a hot press with the lower platen unheated and the upper platen preheated to 120-180°C for preheating and softening, and apply a small pressure of 0.05-0.1 MPa.

[0044] In this invention, during the preheating and softening process, it is preferable that the yellow side of the bamboo contacts the upper pressure plate, and the green side contacts the lower pressure plate. In this invention, the preheating and softening time is preferably 5–120 seconds, more preferably 10–100 seconds. In this invention, during the preheating and softening process, the press is stopped immediately once the bamboo contacts the upper pressure plate; at this time, the pressure of the hot press is preferably 0.05–0.1 MPa, more preferably 0.05–0.08 MPa.

[0045] After obtaining the preheated and softened bamboo, the present invention maintains the preheating and softening temperature on the bamboo yellow side, and simultaneously compresses the preheated and softened bamboo to densify it to the target thickness, thereby obtaining compressed bamboo.

[0046] In this invention, the pressure compression is preferably performed in a hot press; the pressure of the pressure compression is preferably 2–40 MPa, more preferably 5–30 MPa; the pressure compression is preferably performed gradually. In this invention, the gradual pressure compression is preferably performed on the bamboo material for 1–5 cycles of pressure compression, each compression cycle including loading for 1–3 seconds and holding for 5–20 seconds. In this invention, the loading speed is preferably 0.1–2.0 mm / s, more preferably 0.5–1.2 mm / s.

[0047] In this invention, the compression rate of the bamboo material under pressure is preferably 10-50%, more preferably 20-40%. In this invention, the thickness of the bamboo material after pressure compression is preferably 3-10 mm, and the thickness is preferably controlled by a thickness gauge between the hot press plates.

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

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

[0050] In this invention, the hot pressing and shaping treatment serves two purposes: under the action of heat, moisture, and force, on the one hand, the moisture inside the bamboo can be vaporized and discharged from the longitudinal transport 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 reaction when heated, causing internal molecular movement, releasing internal residual stress, thereby reducing deformation recovery and fixing the compression deformation of the bamboo.

[0051] In this invention, the depressurization after cooling is preferably achieved by circulating cold water to cool the upper and lower hot plates of the hot plate to 30-50°C before depressurization. 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 this invention, depressurization after cooling can prevent defects such as bubbling and cracking caused by excessively high internal temperature of bamboo.

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

[0054] In this invention, the thickness of the compressed layer on the bamboo yellow side is preferably 2-4 mm; the thickness of the uncompressed layer on the bamboo green side is preferably 1-5 mm; and the peak density of the compressed layer on the bamboo yellow side is preferably 0.8-1.5 g / cm³. 3 The peak density of the uncompressed layer on the bamboo green side is preferably 0.8–1.2 g / cm³. 3 .

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

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

[0057] Example 1

[0058] The material being processed is flattened bamboo board, measuring 150mm × 100mm × 9.3mm (length × width × thickness), with a density of 0.75g / cm³. 3 .

[0059] The specific processing procedure is as follows:

[0060] (1) Immerse the bamboo sample (moisture content 10%) on the yellow side in water for 1 hour. The immersion depth is 20% of the total thickness of the bamboo. After immersion, the moisture content of the yellow side is 20%.

[0061] (2) Place the soaked bamboo in a hot press with the lower platen unheated and the upper platen preheated to 140°C. The bamboo yellow side of the soaked bamboo should face up. Place a 6mm thick gauge on the four sides of the platen, close the hot press, and preheat and soften for 10 seconds.

[0062] (3) The preheated and softened bamboo is gradually pressurized for one compression cycle, with a loading time of 3 seconds and a holding time of 7 seconds. The loading speed is 1.1 mm / s and the compression rate is 35%.

[0063] (4) Raise the temperature of the lower platen to 140℃ and keep it warm and pressurized for 0.5h to compress and deform the bamboo material inside the hot press.

[0064] (5) Turn on cold water to quickly cool the upper and lower hot press plates to 30°C, turn on the hot press, and obtain bamboo material with one side of the yellow side being dense.

[0065] The bamboo material with single-sided densification on the yellow side obtained in this embodiment is recorded as 140℃-1-0.5h.

[0066] Example 2

[0067] The material being processed is flattened bamboo board, measuring 150mm × 100mm × 9.3mm (length × width × thickness), with a density of 0.75g / cm³. 3 .

[0068] The specific processing procedure is as follows:

[0069] (1) Immerse the bamboo sample (moisture content 10%) on the yellow side in water for 2 hours. The immersion depth is 30% of the total thickness of the bamboo. After immersion, the moisture content of the yellow side is 25%.

[0070] (2) Place the soaked bamboo in a hot press with the lower platen unheated and the upper platen preheated to 140°C. The bamboo yellow side of the soaked bamboo should face up. Place a 6mm thick gauge on the four sides of the platen, close the hot press, and preheat and soften for 30 seconds.

[0071] (3) The preheated and softened bamboo is gradually pressurized in two compression cycles. Each compression cycle includes 2 seconds of loading and 8 seconds of holding. The loading speed is 0.8 mm / s and the compression rate is 35%.

[0072] (4) Raise the temperature of the lower platen to 140℃ and keep it warm and pressurized for 1.5 hours to compress and deform the bamboo material inside the hot press.

[0073] (5) Turn on cold water to quickly cool the upper and lower hot press plates to 30°C, turn on the hot press, and obtain bamboo material with one side of the yellow side being dense.

[0074] The bamboo material with single-sided densification on the yellow side obtained in this embodiment is recorded as 140℃-2-1.5h.

[0075] Example 3

[0076] The material being processed is flattened bamboo board, measuring 150mm × 100mm × 9.3mm (length × width × thickness), with a density of 0.75g / cm³. 3 .

[0077] The specific processing procedure is as follows:

[0078] (1) Immerse the bamboo sample (moisture content 10%) on the yellow side in water for 3 hours. The immersion depth is 40% of the total thickness of the bamboo. After immersion, the moisture content of the yellow side is 28%.

[0079] (2) Place the soaked bamboo in a hot press with the lower platen unheated and the upper platen preheated to 140°C. The bamboo yellow side of the soaked bamboo should face up. Place a 6mm thick gauge on the four sides of the platen, close the hot press, and preheat and soften for 50 seconds.

[0080] (3) The preheated and softened bamboo is gradually pressurized in three compression cycles. Each compression cycle includes 1 second of loading and 9 seconds of holding. The loading speed is 1.1 mm / s and the compression rate is 35%.

[0081] (4) Raise the temperature of the lower platen to 140℃ and keep it warm and pressurized for 2.5 hours to compress and deform the bamboo material inside the hot press.

[0082] (5) Turn on cold water to quickly cool the upper and lower hot press plates to 30°C, turn on the hot press, and obtain bamboo material with one side of the yellow side being dense.

[0083] The bamboo material with single-sided densification on the yellow side obtained in this embodiment is recorded as 140℃-3-2.5h.

[0084] Example 4

[0085] The material being processed is flattened bamboo board, measuring 150mm × 100mm × 9.3mm (length × width × thickness), with a density of 0.75g / cm³. 3 .

[0086] The specific processing procedure is as follows:

[0087] (1) Immerse the bamboo sample (moisture content 10%) on the yellow side in water for 4 hours. The immersion depth is 50% of the total thickness of the bamboo. After immersion, the moisture content of the yellow side is 32%.

[0088] (2) Place the soaked bamboo in a hot press with the lower platen unheated and the upper platen preheated to 140°C. The bamboo yellow side of the soaked bamboo should face up. Place a 6mm thick gauge on the four sides of the platen, close the hot press, and preheat and soften for 70 seconds.

[0089] (3) The preheated and softened bamboo is gradually pressurized in a total of 4 compression cycles. Each compression cycle includes 1 second of loading and 9 seconds of holding. The loading speed is 0.8 mm / s and the compression rate is 35%.

[0090] (4) Raise the temperature of the lower platen to 140℃ and keep it warm and pressurized for 3.5 hours to compress and deform the bamboo material inside the hot press.

[0091] (5) Turn on cold water to quickly cool the upper and lower hot press plates to 30°C, turn on the hot press, and obtain bamboo material with one side of the yellow side being dense.

[0092] The bamboo material with single-sided densification on the yellow side obtained in this embodiment is recorded as 140℃-4-3.5h.

[0093] Example 5

[0094] The material being processed is flattened bamboo board, measuring 150mm × 100mm × 9.3mm (length × width × thickness), with a density of 0.75g / cm³. 3 .

[0095] The specific processing procedure is as follows:

[0096] (1) Immerse the bamboo sample (moisture content 10%) on the yellow side in water for 3 hours. The immersion depth is 40% of the total thickness of the bamboo. After immersion, the moisture content of the yellow side is 28%.

[0097] (2) Place the soaked bamboo in a hot press with the lower platen unheated and the upper platen preheated to 160°C. The bamboo yellow side of the soaked bamboo should face up. Place a 6mm thick gauge on the four sides of the platen, close the hot press, and preheat and soften for 50 seconds.

[0098] (3) Intermittent pressurization is performed using the press control program. There are a total of 3 compression cycles. Each compression cycle includes 1 second of loading and 9 seconds of holding. The loading speed is 1.1 mm / s and the compression rate is 35%.

[0099] (4) Raise the temperature of the lower platen to 160℃ and keep it warm and pressurized for 2.5 hours to compress and deform the bamboo material inside the hot press.

[0100] (5) Turn on cold water to quickly cool the upper and lower hot press plates to 30°C, turn on the hot press, and obtain bamboo material with one side of the yellow side being dense.

[0101] The bamboo material with single-sided densification on the yellow side obtained in this embodiment is recorded as 160℃-3-2.5h.

[0102] Example 6

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

[0104] The resulting bamboo material with single-sided densification on the yellow side is denoted as FR10%-140℃.

[0105] Example 7

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

[0107] The resulting bamboo material with single-sided densification on the yellow side is denoted as FR20%-140℃.

[0108] Comparative Example 1

[0109] Untreated bamboo flattened into bamboo boards (control material) were directly subjected to performance tests, including microstructure (SEM), cross-sectional density, surface hardness, static bending strength, etc.

[0110] The density is 0.75 g / cm³. 3 The dimensions are 150mm×100mm×9.3mm (length×width×thickness), and the initial moisture content is 10%.

[0111] Comparative Example 2

[0112] The material being processed is flattened bamboo board, measuring 150mm × 100mm × 9.3mm (length × width × thickness), with a density of 0.75g / cm³. 3 .

[0113] The specific processing procedure is as follows:

[0114] (1) Immerse the bamboo sample (moisture content 10%) on the yellow side in water for 3 hours. The immersion depth is 40% of the total thickness of the bamboo. After immersion, the moisture content of the yellow side is 28%.

[0115] (2) Place the soaked bamboo in a hot press with the lower platen unheated and the upper platen preheated to 140°C. The bamboo yellow side of the soaked bamboo should face up. Place a 6mm thick gauge on the four sides of the platen, close the hot press, and preheat and soften for 50 seconds.

[0116] (3) The preheated and softened bamboo is gradually pressurized in three compression cycles. Each compression cycle includes 1 second of loading and 9 seconds of holding. The loading speed is 1.1 mm / s and the compression rate is 35%.

[0117] (4) Turn on cold water to quickly cool the upper and lower hot press plates to 30°C, turn on the hot press, and obtain bamboo material with one side of the yellow side being dense.

[0118] The bamboo material obtained in this comparative example with single-sided densification on the yellow side is recorded as 140℃-3-0h.

[0119] Figure 1 The images shown are cross-sectional views of the samples from Comparative Example 1 and Example 1. Figure 1 (a) is the control material in Comparative Example 1; Figure 1 (b) is the bamboo material with single-sided densification on the yellow side in Example 1. Figure 1 It can be seen that the cross-sectional structure of the bamboo in Comparative Example 1 exhibits a typical gradient structure. The proportion of vascular bundle tissue decreases from the green bamboo side to the yellow bamboo side along the thickness direction of the bamboo. The vascular bundles on the green bamboo side are smaller and more densely distributed, while the vascular bundles on the yellow bamboo side are larger and more sparsely distributed. In Example 1, the overall thickness of the bamboo with single-sided compaction on the yellow bamboo side is thinner, the upper and lower surfaces are smoother, the cell morphology on the yellow bamboo side changes, and the interstitial spaces decrease, but the original tissue structure of the bamboo is still maintained.

[0120] Figure 2 The images show SEM images of the bamboo yellow side cross sections of the samples in Comparative Example 1 and Example 1. 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 is evident that the thin-walled cell morphology of bamboo undergoes significant changes during single-sided densification on the yellow side. From the green side to the yellow side, the degree of cell cavity deformation gradually increases, and the volume of cell cavities and vessels is compressed and reduced. During the densification process on the yellow side, the cell walls deform, mainly because the amorphous cellulose, hemicellulose, and lignin matrix transform from a glassy state to a rubbery state. This achieves compression strengthening modification of the yellow side, increasing its density and surface hardness, thereby enhancing its mechanical properties.

[0121] Figure 3 This is a cross-sectional density distribution diagram of the samples in Comparative Example 1 and Examples 1-4. Figure 4 This is a cross-sectional density distribution diagram of the samples from Examples 3 and 5. (From...) Figures 3-4 It can be seen that the density of the control material (bamboo in Comparative Example 1) gradually decreases from the green side to the yellow side. The thickness of the bamboo material with single-sided densification on the yellow side becomes thinner, and the cross-sectional density curve shows a symmetrical structure. The density on the yellow side increases significantly, approaching the density on the green side, indicating that single-sided densification of bamboo material on the yellow side was successfully prepared under the conditions of this invention.

[0122] By using a press control program to preheat and progressively pressurize the bamboo pith side, the peak shape of the density distribution curve of the compressed layer on the bamboo pith side can be effectively controlled. When the preheating time is short and the number of pressurizations is few, the density distribution curve of the effective compacted layer on the bamboo pith side exhibits a narrow and sharp density peak. As the preheating time increases and the number of pressurizations increases, more heat is transferred from the hot press plate to the inner layer of the bamboo pith side, the softened area on the bamboo pith side increases, the density distribution curve of the effective compacted layer on the bamboo pith side gradually widens, the density gradually increases, and the distance between the peak density and the surface of the compressed side gradually increases. As the hot pressing temperature increases, more heat is transferred from the hot press plate to the inner layer of the bamboo pith side, the degree of softening of the inner layer of the bamboo pith side increases, making it easier to compact, thereby increasing the thickness of the total compacted layer and increasing the peak density, which can reach up to 1.23 g / cm³. 3 The density is significantly higher than that of the bamboo green side. This increased density plays a crucial role in improving the overall performance of bamboo.

[0123] The physical and mechanical properties of bamboo with single-sided compaction on the yellow side were characterized, and the results are shown in Table 1. Table 1 shows that the water absorption deformation recovery rate of bamboo with single-sided compaction on the yellow side decreases with increasing hot-pressing temperature or prolonged hot-pressing time. The water absorption deformation recovery rate of bamboo with single-sided compaction on the yellow side without hot-pressing treatment (Comparative Example 2) was 17.5%. When the hot-pressing temperature was 140℃, the water absorption deformation recovery rate ranged from 6.6% to 11.2%; when the hot-pressing temperature was 160℃, the water absorption deformation recovery rate decreased to 4.3%, indicating that hot-pressing is an effective method for fixing the compression deformation of bamboo with single-sided compaction on the yellow side.

[0124] Table 2 and Figures 5-7 The cone calorimeter test data for the bamboo yellow side-densified bamboo prepared in Comparative Example 1 and Examples 3, 6, and 7 are shown in Table 2 and Figures 5-7 It can be seen that the ignition time (TTI) of the reference material is 19 s, and the peak heat release rate (PHRR) is 714.9 kW / m². 2 The total heat release (THR) is as high as 73.3 MJ / m³. 2 The total total smoke production (TSP) reached 3.24 m³. 2The single-sided densification treatment on the yellow side of bamboo did not significantly reduce the peak heat release rate, total heat release, and total smoke production of bamboo, but it delayed the ignition time (140℃-3-2.5h) by 4 seconds and the time to the peak heat release rate by 115 seconds. The integrated flame-retardant and single-sided densification treatment on the yellow side of bamboo (FR10%-140℃ and FR20%-140℃) further delayed the ignition time, reduced the peak heat release rate by 60.2%, reduced the total heat release by 39.8%, and reduced the total smoke production by 55.9%. In summary, the technology of this invention can significantly improve the flame-retardant performance of bamboo treated with single-sided densification on the yellow side while ensuring good physical and mechanical properties and dimensional stability.

[0125] Table 1. Test results of physical and mechanical properties

[0126]

[0127]

[0128] Table 2. Cone calorimeter test data of the bamboo yellow side-densified bamboo 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 FR 10% - 140℃ 25 404.2 (Peak time: 285s) 56.8 2.27 FR 20% - 140℃ 28 284.8 (Peak time: 290s) 44.1 1.43

[0130] Through the comparison of the above embodiments and comparative examples, it can be seen that the bamboo material with single-sided compaction on the yellow side prepared by the method of the present invention exhibits significantly improved dimensional stability and mechanical strength, as well as increased density and surface hardness on the yellow side. This method involves directional compression reinforcement of the lower-density yellow side of the bamboo, offering advantages over traditional integral compressed bamboo material in terms of high hardness and light weight. It significantly reduces the volumetric loss rate of compressed bamboo material and is simple, environmentally friendly, and energy-efficient. By controlling the process parameters of preheating softening treatment, pressurization, and hot-pressing shaping treatment, the thickness and density of the compressed layer on the yellow side can be controlled. While maintaining the high density of the natural bamboo green side, the density, surface hardness, and mechanical strength of the yellow side are directionally improved. Furthermore, by impregnating and softening the bamboo material with a flame retardant solution as needed, the flame retardant performance of the single-sided compaction on the yellow side of the bamboo material is significantly improved while ensuring good physical and mechanical properties and dimensional stability. This broadens the application fields of flattened bamboo and other natural bamboo materials, and is expected to be applied in structural and non-structural fields such as construction and interior decoration.

[0131] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing bamboo material with single-sided densification of the yellow side, comprising the following steps: The material being processed is a flattened bamboo board, measuring 150mm in length, 100mm in width, and 9.3mm in thickness, with a density of 0.75g / cm³. 3 ; (1) The bamboo sample with a moisture content of 10% was immersed in the yellow side of the flame retardant solution for 3 hours. The immersion depth was 40% of the total thickness of the bamboo. After immersion, the moisture content of the yellow side of the bamboo was 25%. The flame retardant solution was composed of 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 was 1:

1. The mass fraction of the flame retardant solution was 20%. (2) Place the soaked bamboo in a hot press with the lower platen unheated and the upper platen preheated to 140°C, with the bamboo yellow side facing up. Place a 6mm thick gauge on the four sides of the platen, close the hot press, and preheat and soften for 50 seconds. (3) The preheated and softened bamboo is gradually pressurized in three compression cycles. Each compression cycle includes 1 second of loading and 9 seconds of holding. The loading speed is 1.1 mm / s and the compression rate is 35%. (4) Raise the temperature of the lower pressure plate to 140℃ and keep it warm and pressurized for 2.5 hours to compress and deform the bamboo material inside the hot press and fix it. (5) Turn on cold water to quickly cool the upper and lower hot press plates to 30°C, turn on the hot press, and obtain bamboo material with one side of the yellow side being dense.

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