A method for treating bamboo by high-temperature steam, polyethylene glycol and microwave in a ternary synergistic manner

Abstract

The application belongs to the technical field of bamboo modification processing, and discloses a method for treating bamboo by using high-temperature steam, polyethylene glycol and microwave in a ternary synergistic manner.The method comprises the following steps: sequentially performing high-temperature steam treatment, polyethylene glycol solution immersion treatment and microwave treatment on the bamboo.By using the synergistic treatment of high-temperature steam, polyethylene glycol and microwave, the bamboo is uniformly and controllably softened and toughened from the surface to the deep layer, and the flexibility processing adaptability and structural stability of the bamboo are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of bamboo modification and processing technology, specifically relating to a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol and microwave. Background Technology

[0002] my country boasts abundant bamboo resources and is a major global producer and exporter of bamboo products. Driven by national policies such as "replacing plastic with bamboo" and the "dual-carbon" strategy, bamboo, as a green, renewable, and recyclable bio-based alternative material, has shown broad application prospects in bamboo panels, structural bamboo, furniture products, and high-end consumer goods. However, natural bamboo possesses a highly dense cell wall structure, strong rigidity, and limited plasticity. This makes it prone to cracking, breakage, or deformation difficulties during deep processing such as flattening, bending, and complex shaping, becoming a key obstacle restricting the further application of bamboo towards high-performance and complex structures. Therefore, effectively controlling the microstructure and stress distribution of bamboo cell walls and improving its flexible processing performance is one of the core technological challenges for the high-quality development of the bamboo industry. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a method for the ternary synergistic treatment of bamboo using high-temperature steam, polyethylene glycol, and microwave, so as to significantly improve the flexible processing adaptability of bamboo while maintaining its structural integrity.

[0004] The objective of this invention is achieved through the following technical solution: This invention provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol and microwave, comprising: subjecting bamboo to high-temperature steam treatment, polyethylene glycol solution impregnation treatment and microwave treatment in sequence.

[0005] In some embodiments, the temperature of the high-temperature steam treatment is 100–180°C, and the time of the high-temperature steam treatment is 30–180 min.

[0006] Furthermore, the temperature of the high-temperature steam treatment is 120–160°C, and the time of the high-temperature steam treatment is 50–90 min.

[0007] In some embodiments, the mass concentration of the polyethylene glycol solution is 0.5% to 50%, and the molecular weight of the polyethylene glycol is 100 to 20,000 Da.

[0008] Furthermore, the mass concentration of the polyethylene glycol solution is 1% to 10%, and the molecular weight of the polyethylene glycol is 200 to 4000 Da.

[0009] In some embodiments, the immersion time for the polyethylene glycol solution impregnation treatment is 0.1 to 24 h.

[0010] Furthermore, the immersion time for the polyethylene glycol solution impregnation treatment is 1 to 6 hours.

[0011] In some embodiments, the power used for microwave processing is 10 to 500 W, and the microwave processing time is 1 to 120 min.

[0012] Furthermore, the power used for the microwave processing is 50 to 300 W.

[0013] Furthermore, the microwave processing time is 5 to 30 minutes.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are as follows: (1) The method for processing bamboo proposed in this invention utilizes a specific sequence of processes, namely high-temperature steam treatment, polyethylene glycol impregnation and microwave treatment, to form a synergistic effect among the three, thereby achieving a progressive enhancement of "pore opening-penetration-curing", realizing deep, uniform and controllable softening and toughening of bamboo from the surface to the interior, and significantly improving the flexible processing adaptability and structural stability of bamboo. (2) This invention changes the traditional high-energy-consumption mode of simply extending the steam time by using a specific sequence of "steam pretreatment → polyethylene glycol impregnation → microwave treatment". This sequence achieves synergistic effects of "pore opening-penetration-curing", which can achieve better modification in a shorter total working time and has significant energy-saving and high-efficiency advantages; (3) The present invention achieves stable flexibility and deformation capacity of bamboo by combining the physical effects of thermal expansion and pore expansion of high temperature steam treatment with the chemical plasticization of the reconstruction of the hydrogen bond network of cell wall by polyethylene glycol impregnation. While maintaining structural integrity, it significantly improves processing adaptability and is suitable for high-precision processing processes such as flattening, bending and complex configuration forming. Attached Figure Description

[0015] Figure 1 Infrared spectra of bamboo strips treated by the method used in Example 1 and Comparative Examples 1-5; Figure 2 Infrared spectra of bamboo strips treated by the methods used in Examples 1-4 and pure polyethylene glycol; Figure 3 Thermogravimetric analysis curves of bamboo strips treated by the methods used in Examples 1-4 are shown in Example 1. Figure 4 For Example 1, the derivative thermogravimetric curves of bamboo strips treated by the methods used in Comparative Examples 1-4 are shown. Figure 5 The image shows a scanning electron microscope (SEM) image of the cross-section of the bamboo strip obtained in Comparative Example 1. Figure 6This is a scanning electron microscope image of the cross-section of the bamboo strip after it has been processed by the method used in Example 1. Detailed Implementation

[0016] This invention provides a method for the synergistic treatment of bamboo using high-temperature steam, polyethylene glycol, and microwave, comprising the following steps: 1) Treat the bamboo in high-temperature steam at 100-180℃ for 30-180 min; 2) Soak the steam-treated bamboo in a polyethylene glycol solution with a concentration of 0.5%–50% and a molecular weight of 100–20000 Da for 0.1–24 h; 3) Microwave the soaked bamboo at a power of 10-500 W for 1-120 min.

[0017] It should be noted that the bamboo material is bamboo strips that have been radially de-emerged from the outer green and yellow layers and do not contain bamboo nodes. By removing the dense outer layers such as the outer green and yellow layers of bamboo, as well as structurally discontinuous areas such as bamboo nodes, the cross-sectional density gradient and stress concentration areas can be reduced, improving the uniformity of the softening treatment and the consistency of the finished product. This is beneficial for subsequent finishing processes such as flattening, bending, and planing. The initial moisture content of the bamboo material is 5% to 80%, preferably 10% to 40%. Within this moisture content range, the bamboo material exhibits suitable dielectric response and heat transfer behavior during steam treatment, polyethylene glycol impregnation, and microwave heating. This allows for a more uniform distribution of the softening effect in the thickness direction, avoiding insufficient heating due to excessively low moisture content or internal cracking due to excessively high moisture content, thereby improving the controllability and repeatability of the entire process.

[0018] In step 1), the temperature of the high-temperature steam is 100–180°C, but not limited to 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, or 180°C, preferably 120–160°C. Within this temperature range, the thermal expansion and pore-expanding effect of the steam can effectively open the microscopic channels of bamboo fibers and thin-walled cells, improve cell wall permeability, and initially reduce the rigidity of bamboo without excessive thermal degradation, providing a channel and pretreatment basis for the deep penetration of polyethylene glycol. The high-temperature steam treatment time is 30–180 min, but not limited to 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, 160 min, 170 min, or 180 min, preferably 50–90 min. If the processing time is too short, it is difficult to form a stable permeability enhancement and stress relaxation effect; if it is too long, it is easy to cause excessive degradation of hemicellulose and lignin. Within the optimal time range, the softening depth and cell wall structure integrity can be taken into account, providing a suitable precursor state for subsequent chemical plasticization and microwave treatment.

[0019] In step 2), the concentration of the polyethylene glycol solution is 0.5% to 50%, but is not limited to 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%, preferably 1% to 10%. Below 0.5%, the polyethylene glycol content is insufficient to form an effective hydrogen bond reconstruction network, making it difficult to significantly improve flexibility; above 50%, it easily leads to over-plasticization and localized accumulation. A concentration range of 1% to 10% is preferred, which can significantly improve the elastic modulus while moderately reducing static bending strength, achieving a comprehensive balance of "softening-toughening". The molecular weight of polyethylene glycol is 100 to 20,000 Da, not limited to 100 Da, 200 Da, 400 Da, 600 Da, 800 Da, 1000 Da, 2000 Da, 3000 Da, 4000 Da, 5000 Da, 6000 Da, 7000 Da, 8000 Da, 9000 Da, 10000 Da, 12000 Da, 14000 Da, 16000 Da, 18000 Da, 20000 Da, preferably 200 to 4000 Da. While polyethylene glycol with too low a molecular weight has good permeability, its retention capacity is insufficient, making it difficult to form a stable plasticizing network; while with too high a molecular weight, diffusion is limited and the modified area is localized. Preferably, polyethylene glycol (PEG) with a molecular weight in the range of 200–4000 can match the pore size of the cell wall, establishing a uniform “cellulose-PEG-cellulose” hydrogen bond bridging structure at the cell wall scale. The PEG soaking time is 0.1–24 h, not limited to 0.1 h, 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h, 17 h, 18 h, 19 h, 20 h, 21 h, 22 h, 23 h, or 24 h, but preferably 1–6 h. Shorter soaking times are insufficient for complete penetration from the surface to the interior, while longer soaking times reduce efficiency and may cause excessive swelling. Preferably, within the 1–6 h time range, PEG can enter the cell wall and cell cavity with the aid of pre-opened steam channels, uniformly distributing across the bamboo cross-section, achieving full reconstruction of the cell wall hydrogen bond network.

[0020] In step 3), the microwave processing power is 10–500 W, but not limited to 10 W, 20 W, 30 W, 40 W, 50 W, 60 W, 70 W, 80 W, 90 W, 100 W, 200 W, 300 W, 400 W, or 500 W; preferably 50–300 W. Lower power results in insufficient heating and softening of the bulk phase; excessively high power may lead to localized overheating, cracking, and carbonization. Preferably, within the power range of 50–300 W, microwaves can create a uniform dielectric heating effect within the bamboo, causing synergistic migration and redistribution of water and polyethylene glycol within the cell walls. The microwave treatment time ranges from 1 to 120 minutes, but is not limited to 1 minute, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, 65 minutes, 70 minutes, 80 minutes, 90 minutes, 100 minutes, 110 minutes, or 120 minutes, with 5 to 30 minutes being preferred. Too short a microwave time makes it difficult to complete the stress rearrangement and polyethylene glycol diffusion process, while too long a time will cause significant strength attenuation and internal damage. The preferred time range of 5 to 30 minutes allows microwave heating to effectively release residual stress in the cell walls and promote the uniform distribution of polyethylene glycol in the cross-sectional direction, thereby achieving high stiffness and good flexibility while maintaining a certain load-bearing capacity.

[0021] It should be noted that the high-temperature steam treatment proposed in this invention can improve cell wall permeability, providing channels for polyethylene glycol (PEG) molecules to penetrate into the cell wall and reconstruct the hydrogen bond network; PEG impregnation can reconstruct the hydrogen bond structure inside the cell wall, achieving chemical plasticization and toughening; microwave heating treatment can promote the rapid migration and uniform distribution of PEG inside the bamboo, enabling comprehensive control of the softening process from the surface to the interior. The three mechanisms work together to effectively overcome the limitations of traditional high-temperature steam softening in terms of softening depth, uniformity, and energy consumption. While maintaining the structural integrity of the bamboo, it significantly improves its adaptability to flexible processing, making it suitable for the industrial processing needs of flattening, bending, and complex shaping of bamboo.

[0022] It should be noted that the weight of the bamboo strip itself is directly related to the parameters of the subsequent processing. For example, when the dry weight of a single bamboo strip exceeds about 15 g (about 10 times the weight of a standard bamboo strip) due to increased thickness or density, the high-temperature steam treatment time at 160℃ should not be less than 60 min in order to achieve the same treatment effect. Otherwise, problems such as insufficient polyethylene glycol penetration and substandard softening and toughening effects may occur.

[0023] There are quantitative constraints among the parameters of the three treatment methods: high-temperature steam treatment, polyethylene glycol impregnation, and microwave heating treatment. The temperature of high-temperature steam treatment (120–160℃) determines the degree of improvement in the permeability of bamboo, which in turn affects the matching of the subsequent polyethylene glycol mass concentration (1%–10%) and molecular weight (200–4000 Da); microwave treatment (50–300 W, 5–30 min) further promotes penetration and curing. The three methods work synergistically to achieve an optimized match of "pore opening-penetration-curing".

[0024] It should be noted that, unless otherwise specified, the concentrations mentioned in this application refer to mass concentrations.

[0025] The present invention will be further described in detail with reference to specific embodiments. The following embodiments can enable those skilled in the art to have a more comprehensive understanding of the present invention, but do not limit the present invention in any way.

[0026] Example 1: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave, including: Bamboo strips (3-5 year old moso bamboo from Nanping, Fujian, which were radially treated to remove the green and yellow parts of the bamboo, then cut along the fiber direction and processed into rectangular strips with dimensions of 65 mm × 14 mm × 2 mm) were placed in a high-temperature steam reactor (Beijing Zhongjiao Jinyuan Technology Co., Ltd., CEL-MPR-100 mL micro reactor) and treated at 160 ℃ for 60 min. After removal, they were immediately immersed in a 100 mL volume of polyethylene glycol (Shanghai Maclean Biochemical Technology Co., Ltd.) aqueous solution with a concentration of 5% and a molecular weight of 1500 Da for 30 min. After soaking, the bamboo strips were placed in a microwave oven (Mijia Smart Microwave Oven P1 of Chunmi Technology (Shanghai) Co., Ltd.) and heated at 128 W for 15 min. After cooling, the ternary synergistic treatment bamboo strip samples were obtained.

[0027] Example 2: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave. Compared with Example 1, the polyethylene glycol concentration is 1%, and other conditions are the same.

[0028] Example 3: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave. Compared with Example 1, the polyethylene glycol concentration is 10%, and other conditions are the same.

[0029] Example 4: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave. Compared with Example 1, the polyethylene glycol concentration is 20%, and other conditions are the same.

[0030] Example 5: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave. Compared with Example 1, the molecular weight of polyethylene glycol is 200 Da, and other conditions are the same.

[0031] Example 6: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave. Compared with Example 1, the molecular weight of polyethylene glycol is 1000 Da, and other conditions are the same.

[0032] Example 7: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave. Compared with Example 1, the molecular weight of polyethylene glycol is 2000 Da, and other conditions are the same.

[0033] Example 8: This embodiment provides a method for the ternary synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave. Compared with Example 1, the molecular weight of polyethylene glycol is 4000 Da, and other conditions are the same.

[0034] Example 9: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave. Compared with Example 1, the molecular weight of polyethylene glycol is 6000 Da, and other conditions are the same.

[0035] Example 10: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave. Compared with Embodiment 1, the treatment temperature of the high-temperature steam is 100°C, and other conditions are the same.

[0036] Example 11: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave. Compared with Embodiment 1, the treatment temperature of the high-temperature steam is 120°C, while other conditions remain the same.

[0037] Example 12: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave. Compared with Embodiment 1, the treatment temperature of the high-temperature steam is 140°C, while other conditions remain the same.

[0038] Example 13: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave. Compared with Embodiment 1, the treatment temperature of the high-temperature steam is 180°C, while other conditions remain the same.

[0039] Example 14: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol and microwave. Compared with Example 1, the microwave treatment time is 5 minutes, and other conditions are the same.

[0040] Example 15: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol and microwave. Compared with Example 1, the microwave treatment time is 10 min, and other conditions are the same.

[0041] Example 16: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol and microwave. Compared with Example 1, the microwave treatment time is 20 min, and other conditions are the same.

[0042] Example 17: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol and microwave. Compared with Example 1, the microwave treatment time is 25 min, and other conditions are the same.

[0043] Example 18: This embodiment provides a method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol and microwave. Compared with Example 1, the microwave treatment time is 30 min, and other conditions are the same.

[0044] Comparative Example 1: This comparative example provides a method for processing bamboo. Compared with Example 1, the bamboo (3-5 year old moso bamboo from Nanping, Fujian) is only treated by removing the bamboo green and yellow parts radially, and then cut and processed into rectangular bamboo strips with dimensions of 65 mm × 14 mm × 2 mm along the fiber direction, without undergoing any additional treatment.

[0045] Comparative Example 2: This comparative example provides a method for treating bamboo. Compared with Example 1, only high-temperature steam treatment is performed, without polyethylene glycol impregnation and microwave treatment, while other conditions remain the same.

[0046] Comparative Example 3: This comparative example provides a method for treating bamboo. Compared with Example 1, only polyethylene glycol impregnation is performed, without high-temperature steam and microwave treatment, while other conditions remain the same.

[0047] Comparative Example 4: This comparative example provides a method for treating bamboo. Compared with Example 1, only microwave treatment is performed, without high-temperature steam and polyethylene glycol impregnation treatment, while other conditions remain the same.

[0048] Comparative Example 5: This comparative example provides a method for treating bamboo. Compared with Example 1, only water soaking is performed, without high-temperature steam, polyethylene glycol impregnation and microwave treatment. Specifically, the bamboo strips are soaked in water for 30 minutes.

[0049] Comparative Example 6: This comparative example provides a method for treating bamboo. Compared with Example 1, it uses a combination of high-temperature steam and polyethylene glycol impregnation, without microwave treatment, while keeping other conditions the same.

[0050] Comparative Example 7: This comparative example provides a method for treating bamboo. Compared with Example 1, it uses a combination of high-temperature steam and microwave treatment, without polyethylene glycol impregnation, while other conditions remain the same.

[0051] Comparative Example 8: This comparative example provides a method for treating bamboo. Compared with Example 1, it uses a combination of polyethylene glycol impregnation and microwave treatment, without high-temperature steam treatment, while keeping other conditions the same.

[0052] Comparative Example 9: This comparative example provides a method for treating bamboo, which differs from Example 1 in the order of steps. The order is: high-temperature steam → microwave → polyethylene glycol impregnation. Specifically, the bamboo strips are subjected to high-temperature steam treatment (160°C, 60 min), then microwaved (128 W, 15 min), and finally immersed in a polyethylene glycol solution (5% concentration, molecular weight 1500 Da) for 30 min, with other conditions remaining the same.

[0053] Comparative Example 10: This comparative example provides a method for treating bamboo, which differs from Example 1 in the order of steps. The order is: polyethylene glycol impregnation → high-temperature steam → microwave treatment. Specifically, bamboo strips are immersed in a polyethylene glycol solution (concentration 5%, molecular weight 1500 Da) for 30 min, then removed and subjected to high-temperature steam treatment (160°C, 60 min), and finally microwave treatment (128 W, 15 min), with other conditions remaining the same.

[0054] Comparative Example 11: This comparative example provides a method for treating bamboo, which differs from Example 1 in the order of steps. The order is: polyethylene glycol impregnation → microwave → high-temperature steam treatment. Specifically, bamboo strips are immersed in a polyethylene glycol solution (concentration 5%, molecular weight 1500 Da) for 30 min, then microwaved (128 W, 15 min), and finally steamed (160°C, 60 min), with other conditions remaining the same.

[0055] Comparative Example 12: This comparative example provides a method for treating bamboo, which differs from Example 1 in the order of steps. The order is: microwave → high-temperature steam → polyethylene glycol impregnation. Specifically, the bamboo strips are microwaved (128 W, 15 min), then subjected to high-temperature steam treatment (160°C, 60 min), and finally immersed in a polyethylene glycol solution (5% concentration, molecular weight 1500 Da) for 30 min, with other conditions remaining the same.

[0056] Comparative Example 13: This comparative example provides a method for treating bamboo, which differs from Example 1 in the order of steps. The order is: microwave treatment → polyethylene glycol impregnation → high-temperature steam treatment. Specifically, the bamboo strips are microwave-treated (128 W, 15 min), then soaked in a polyethylene glycol solution (5% concentration, molecular weight 1500 Da) for 30 min, and finally treated with high-temperature steam (160°C, 60 min), with other conditions remaining the same.

[0057] Comparative Example 14: This comparative example provides a method for treating bamboo. Compared with Example 1, only high-temperature steam treatment is performed, without polyethylene glycol impregnation and microwave treatment, and the high-temperature steam treatment time is extended to 120 min, while other conditions remain the same.

[0058] The mechanical properties of bamboo samples treated using the methods employed in the examples and comparative examples were tested using an electronic universal testing machine (Jinan Wenteng Experimental Instrument Co., Ltd., WDW-50E). The static bending strength and modulus of elasticity were determined according to GB / T 15780-1995 standard. The results are shown in Table 1. Examples 1-4 investigated the effect of polyethylene glycol concentration on the static bending strength and modulus of elasticity of bamboo samples under the same high-temperature steam-polyethylene glycol-microwave ternary synergistic treatment conditions. As shown in Table 1, taking the bamboo sample from Comparative Example 1 as the baseline (static bending strength 250.4 ± 12.7 MPa, modulus of elasticity 12672.4 ± 220.4 MPa), the mechanical properties of the bamboo samples exhibited a typical concentration-dependent characteristic as the polyethylene glycol concentration increased from 1% to 20%. When the polyethylene glycol concentration was 1%, the static bending strength decreased to 207.6 ± 13.5 MPa (–17.1%), while the elastic modulus increased to 13,597.5 ± 700.7 MPa (+7.3%). This indicates that low-concentration polyethylene glycol could partially penetrate the cell wall and produce a certain degree of plasticization, but the penetration depth and the degree of hydrogen bond reconstruction were limited, and the cell wall relaxation and stiffness increase were relatively mild. When the concentration was increased to 5%, the static bending strength further decreased to 182.5 ± 10.4 MPa (–27.1%), while the elastic modulus significantly increased to 15,232.2 ± 818.9 MPa (+20.2%), and the cell wall changed from a dense and rigid structure to a flexible and high-stiff structure. When the concentration was further increased to 10% and 20%, the static bending strength rebounded to 197.6 ± 12.0 MPa and 212.1 ± 12.9 MPa, respectively, while the elastic modulus decreased to 14,623.9 ± 724.6 MPa and 13,800.7 ± 721.2 MPa, respectively. This indicates that excessively high concentrations lead to polyethylene glycol retention and localized swelling, which is detrimental to maintaining stiffness. Considering the combined results of a decrease in static bending strength of approximately 27.1% and an increase in elastic modulus of approximately 20.2%, a 5% polyethylene glycol concentration can significantly reduce stiffness, improve bendability, and maintain a high load-bearing capacity. This concentration is the preferred concentration for flattening and bending processing conditions in this invention.

[0059] Examples 1 and 5-9 were used to investigate the effect of polyethylene glycol (PEG) molecular weight on the mechanical properties of bamboo strips under the same high-temperature steam-PEG-microwave ternary synergistic treatment conditions. As shown in Table 1, using the bamboo strips in Comparative Example 1 as the baseline (static bending strength of 250.4 ± 12.7 MPa, elastic modulus of 12,672.4 ± 220.4 MPa), when the molecular weight was 200 and 1000, the static bending strength decreased to 227.9 ± 11.6 MPa and 224.9 ± 11.2 MPa, respectively, with changes of -9.0% and -10.2%; the elastic modulus increased to 13,306.0 ± 665.3 MPa and 13,736.9 ± 684.3 MPa, corresponding to +5.0% and +8.4%, indicating that low molecular weight PEG mainly plays a surface lubricating and slight plasticizing role, with limited penetration depth. At a molecular weight of 1500, the static bending strength further decreased to 182.5 ± 10.4 MPa (–27.1%), while the elastic modulus significantly increased to 15232.2 ± 818.9 MPa (+20.2%), showing the most significant strength-toughness balance among all groups. This indicates that this molecular weight matches the micropores of the cell wall well, enabling the formation of a relatively uniform hydrogen bond reconstruction and plasticizing densification network at the cell wall scale. When the molecular weight continued to increase to 2000, 4000, and 6000, the decrease in static bending strength decreased to –20.3%, –18.9%, and –15.4%, respectively, while the change in elastic modulus decreased to +10.7%, +10.1%, and +8.6%, respectively. Due to the larger molecular volume and limited diffusion of high molecular weight polyethylene glycol, the penetration was insufficient, and the modified area tended to be localized. Combining the combined performance of a static bending strength of approximately 182.5 MPa and an elastic modulus of approximately 15.2 GPa at a molecular weight of 1500, the goal of "moderately reduced strength and significantly increased stiffness" can be achieved. This is beneficial for both flattening and bending while ensuring structural load-bearing capacity, and is the preferred polyethylene glycol molecular weight in this invention.

[0060] Examples 1, 10-13 were used to investigate the effect of high-temperature steam at different temperatures on the mechanical properties of bamboo strips under the same high-temperature steam-polyethylene glycol-microwave ternary synergistic treatment conditions. Table 1 shows that the effects of high-temperature steam treatment at different temperatures on the mechanical properties of bamboo strips are significantly temperature-dependent. Using the bamboo strips from Comparative Example 1 as a baseline (static bending strength of 250.4 ± 12.7 MPa, elastic modulus of 12,672.4 ± 220.4 MPa), as the steam temperature increased from 100 ℃ to 180 ℃, the static bending strength showed a continuous decreasing trend, from 240.1 ± 12.1 MPa (–4.1%) at 100 ℃ to 156.2 ± 9.8 MPa (–37.6%) at 180 ℃. This indicates that increasing temperature gradually weakens cell wall integrity and reduces load-bearing capacity. In contrast, the modulus of elasticity showed an initial increase followed by a decrease: it gradually rose from 13,331.4 ± 320.2 MPa (+5.2%) at 100 ℃, reaching 15,232.2 ± 818.9 MPa (+20.2%) at 160 ℃, and then fell back to 13,952.3 ± 763.3 MPa (+10.1%) at 180 ℃. This indicates that high-temperature steam is beneficial for releasing internal stress in the cell walls and reconstructing the hydrogen bond network, thereby increasing the stiffness of bamboo within a certain temperature range. However, excessively high temperatures (above 160 ℃) will cause excessive degradation of hemicellulose and lignin, leading to structural deterioration. The combination of a static bending strength of approximately 182.5 MPa (a relative decrease of 27.1%) and an elastic modulus of approximately 15.2 GPa (a relative increase of 20.2%) at 160 ℃ achieves a better trade-off between softening depth, structural integrity, and stiffness enhancement, making it suitable as the recommended temperature for steam pretreatment in the method of this invention.

[0061] Examples 1, 14-18 were used to investigate the effects of different microwave treatment times on the static bending strength and modulus of elasticity of bamboo. Table 1 shows that, using the bamboo strips from Comparative Example 1 as a baseline (static bending strength 250.4 ± 12.7 MPa, modulus of elasticity 12672.4 ± 220.4 MPa), after pretreatment with high-temperature steam and polyethylene glycol impregnation at 160 ℃, the static bending strength of the bamboo gradually decreased as the microwave heating time increased from 5 min to 30 min, with a change ranging from -6.2% (5 min) to -43.8% (30 min). This indicates that excessively long microwave treatment times lead to further damage to the bamboo cell walls, reducing its load-bearing capacity. However, the modulus of elasticity showed a trend of first increasing and then decreasing. Initial microwave heating (5–15 min) effectively improved stiffness, reaching a maximum value of 15232.2 ± 818.9 MPa (+20.2%) at 15 min, indicating that the stress release and hydrogen bond network reconstruction effects within the cell walls were most significant at this time. As the microwave treatment time further increased (20–30 min), although the elastic modulus remained higher than that of untreated bamboo strips, a downward trend began to emerge, with increases of +17.9%, +12.4%, and +8.3%, respectively. Considering the equilibrium point of approximately 182.5 MPa for static bending strength and approximately 15.2 GPa for elastic modulus at 15 min, this microwave heating time avoids a significant decrease in strength after 20 min while achieving the highest stiffness gain. It is the preferred microwave heating time that balances softening effect, structural safety, and stability in subsequent hot pressing.

[0062] Furthermore, as shown in Table 1, in Example 1 of the present invention, after being treated with high-temperature steam, polyethylene glycol impregnation and microwave ternary synergistic treatment, compared with the bamboo strip in Comparative Example 1 (static bending strength of 250.4±12.7 MPa, elastic modulus of 12672.4±220.4 MPa), the static bending strength decreased to 182.5±10.4 MPa (–27.1%), and the elastic modulus increased to 15232.2±818.9 MPa (+20.2%). While the load-bearing capacity decreased slightly, the elastic modulus increased and the structure changed from brittle fracture to collapse deformation. The overall performance is a synergistic optimization of stiffness and toughness, which is more conducive to flattening and bending. High-temperature steam treatment alone (Comparative Example 2) reduced the static bending strength to 170.5 ± 8.3 MPa (–31.9%) and the elastic modulus to 11,139.0 ± 531.8 MPa (–12.1%), with both strength and stiffness decreasing simultaneously. Although softening was significant, the structure remained brittle. Microwave treatment alone (Comparative Example 4) resulted in a static bending strength of 229.4 ± 10.8 MPa (–8.4%) and an elastic modulus that decreased to 10,796.9 ± 538.1 MPa (–14.8%), indicating a significant risk of stiffness degradation. Polyethylene glycol impregnation (Comparative Example 3) and the polyethylene glycol-microwave combination (Comparative Example 8) increased the static bending strength to 271.2 ± 12.1 MPa and 278.9 ± 12.9 MPa, respectively, and the elastic modulus to 13,584.8 ± 617.7 MPa and 13,850.9 ± 660.6 MPa, respectively, corresponding to a strength increase of +8.3% to +11.4% and a stiffness increase of +7.2% to +9.3%. However, the material is relatively hard, which is not conducive to flattening and large curvature bending. The steam-polyethylene glycol binary treatment (Comparative Example 6) had a static bending strength of 235.6 ± 8.4 MPa (–5.9%) and an elastic modulus of 13,356.7 ± 630.3 MPa (+5.4%), with relatively mild softening and stiffness improvement. In a comprehensive comparison, only the ternary synergistic bamboo achieved significant toughening and controllable softening at the same level of static bending strength of about 182.5 MPa and elastic modulus of about 15.2 GPa. It is the optimal treatment solution for the flattening, bending and complex forming requirements of bamboo.

[0063] As shown in Table 1, Comparative Examples 9-13 were used to verify the criticality of the step sequence. The results showed that, under the same processing parameters, any change in the sequence of "high-temperature steam → PEG impregnation → microwave" led to a significant deterioration in performance. Using the bamboo strips in Comparative Example 1 as a baseline (static bending strength of 250.4 ± 12.7 MPa, elastic modulus of 12,672.4 ± 220.4 MPa), compared to Example 1 (elastic modulus +20.2%, static bending strength -27.1%), the increase in elastic modulus of the bamboo strips treated by the method used in Comparative Examples 9-13 was only +1.2% to +6.3%, indicating a sharp decline in stiffness improvement. Simultaneously, the decrease in static bending strength (-7.6% to -15.0%) was generally smaller, which precisely reflects insufficient polyethylene glycol penetration and plasticization, proving insufficient modification depth. The mechanism lies in the fact that the sequence in Example 1 formed a synergistic chain of "steam opening → deep polyethylene glycol penetration → microwave curing". Changing the order disrupts this chain: for example, microwaving or steaming before microwaving (Comparative Examples 9, 12, and 13) leads to pore closure and hinders permeation; impregnation with polyethylene glycol followed by high-temperature treatment (Comparative Examples 10 and 11) easily causes the loss of effective components. The above data strongly demonstrate the necessity and irreplaceability of the specific step sequence of this invention for achieving deep synergistic modification.

[0064] To further verify the processing efficiency advantage of this application, the performance of bamboo strips after the ternary synergistic treatment (total time 105 min) in Example 1 was compared with that after a single high-temperature steam treatment for 120 min (Comparative Example 14). Taking the bamboo strips in Comparative Example 1 as the benchmark (static bending strength of 250.4 ± 12.7 MPa, elastic modulus of 12,672.4 ± 220.4 MPa), the static bending strength of the bamboo strips obtained by the treatment method of Comparative Example 14 was 151.3 MPa (-39.6%), and the elastic modulus was 10,418.6 MPa (-17.8%). Compared with Comparative Example 14, the processing time of the ternary synergistic treatment (total time 105 min) in Example 1 of this application was shortened by 15 min, the decrease in static bending strength was reduced from -39.6% to -27.1%, and the elastic modulus was increased from -17.8% to +20.2%, indicating that this application achieved a softening-toughening synergistic effect that cannot be achieved by a single steam extended treatment in a shorter time. The above results further confirm that the present invention, through ternary synergistic processing, not only significantly outperforms conventional single steam processing in terms of technical effect, but also has obvious advantages in terms of processing efficiency.

[0065] Table 1

[0066] Furthermore, the present invention has performed a series of characterizations on the bamboo strips treated by the methods used in the embodiments and comparative examples: The bamboo strips treated with the methods used in Example 1 and Comparative Examples 1-5 were characterized by infrared (Thermo Fisher / Nicoleti S50) imaging, and the results are as follows: Figure 1 As shown, the OH peak (3400 cm⁻¹) of the bamboo strips treated by the method used in Example 1 is... -1 Significant redshift and broadening, –CH2 (2900 cm⁻¹) -1 The double peaks are the strongest, COC (1100 cm). -1 The enhanced splitting of the peaks, forming a "cellulose-polyethylene glycol complex network" fingerprint, indicates that the rigid hydrogen bonds between cellulose molecules are reconstructed by "cellulose-polyethylene glycol-cellulose" bridging hydrogen bonds. The bamboo strips treated using the method in Comparative Example 5 only showed a peak splitting at 3400 cm⁻¹. -1 The bamboo strips treated with steam alone (Comparative Example 2) showed only partial hydrolysis and swelling, while those treated with microwave alone (Comparative Example 4) were close to the untreated bamboo strips (Comparative Example 1). The bamboo strips treated with polyethylene glycol alone (Comparative Example 3) showed moderate and unsplit peaks, indicating only surface adsorption. In summary, it can be seen that only through the synergistic effect of "steam channel opening + deep polyethylene glycol penetration + microwave enhanced diffusion" can the overall cell wall hydrogen bond network be reconstructed, achieving physical-chemical softening and toughening.

[0067] Figure 2 Infrared spectra of bamboo strips treated with different polyethylene glycol mass fractions (1%, 5%, 10%, 20%) in Examples 1-4 and pure polyethylene glycol. With increasing content, the OH peak (3400 cm⁻¹)... -1 Overall redshift and broadening: At a mass fraction of 1%, only a slight change was observed, indicating limited penetration and hydrogen bond reconstruction; the sample treated with a mass fraction of 5% showed a redshift of approximately 15 cm. -1 The widest peak indicates that the cell wall has been reconstructed from a single cellulose-cellulose hydrogen bond network to a multi-type hydrogen bond network. As the mass fraction continues to increase to 10% and 20%, the red shift and peak width increase slow down, indicating more accumulation of polyethylene glycol. (At –CH2 (2920 / 2850 cm⁻¹)) -1 In the bimodal region, the peak intensity of bamboo strips is weak at a mass fraction of 1%, clear and moderate at a mass fraction of 5%, while the peak intensity is close to that of pure polyethylene glycol at mass fractions of 10% and 20%, reflecting the presence of a packed phase at high concentrations. (1150–1000 cm⁻¹) -1 In the region, the 1110 cm² of the sample treated with a mass fraction of 5% -1 Peak broadening and overlap with the splitting of the cellulose CO peak are most pronounced. At high concentrations (PEG mass concentration exceeding 5%, such as 10% or 20%), the main effect is increased strength, while the splitting no longer enhances the effect. Combined with mechanical results, a mass fraction below 5% indicates insufficient modification, while a mass fraction above 5% results in over-plasticization and a decrease in stiffness. A polyethylene glycol concentration of approximately 5% achieves the optimal balance between softening and toughening.

[0068] Figure 3 Thermogravimetric analysis (Mettler Toledo, TGA / DSC 3+) curves of bamboo strips treated with the methods used in Examples 1-4 are shown in Example 1. Weight loss before 100℃ was less than 5%, indicating the removal of adsorbed water, demonstrating that the ternary synergistic treatment (Example 1) does not impair room-temperature thermal stability. The main degradation zone for hemicellulose and cellulose is between 250 and 380℃. The ternary synergistic treatment slightly increased the initial temperature of the main decomposition of the bamboo strips and resulted in a steeper weight loss, indicating that the cell wall changed from a multiphase disordered structure to a more homogeneous polyethylene glycol-cellulose network, and the pyrolysis changed from dispersed to synergistic. At 800℃, the bamboo strips obtained from the ternary synergistic treatment had the lowest char content (mass fraction) (approximately 10%–12%), with the remainder around 15%–20%. This indicates that the polyethylene glycol chains preferentially cleave and pull on more complete cellulose breakage and volatilization, inhibiting the formation of inert carbon skeletons, corresponding to the softening optimization state of "slightly increased stability at medium and low temperatures and easier complete cleavage at high temperatures."

[0069] Figure 4 The thermogravimetric curves (TGA) of bamboo strips treated using the methods employed in Examples 1-4 are shown in Example 1. The small peaks near 100℃ for each sample indicate the removal of adsorbed water, with little difference between samples. Significant differences are observed in the main decomposition region between 250 and 380℃. The untreated bamboo strips (Comparative Example 1), the bamboo strips treated only with steam (Comparative Example 2), and the bamboo strips treated only with microwaves (Comparative Example 4) exhibit a broad main peak with a low-temperature shoulder peak at approximately 330℃, indicating stepwise degradation of multiple components and structural heterogeneity within a wide temperature range. The bamboo strips treated only with polyethylene glycol (Comparative Example 3) show a slightly forward-shifted and passivated main peak, reflecting only the easy degradation of polyethylene glycol. The bamboo strips obtained through ternary synergistic treatment (Example 1) show a slightly shifted main peak towards the high-temperature side, with increased peak height and decreased half-peak width, and a compressed low-temperature shoulder peak, indicating that hemicellulose and cellulose degradation are locked within a narrow temperature range and proceed synergistically. Figure 3 The slight increase in initial temperature and the decrease in residual char rate correspond to each other, indicating that the uniform composite network makes thermal decomposition more concentrated and efficient, which is strong thermodynamic evidence for softening and toughening.

[0070] The morphology, cell wall thickness and gaps, and polyethylene glycol filling of the bamboo strip cross-section were analyzed using scanning electron microscopy (TESCAN MIRA LMS, Czech Republic) (the cross-section of the bamboo strip needs to be cut and sputtered with gold before the test). Figure 5 The image shows a scanning electron microscope (SEM) image of a cross-section of untreated bamboo (Comparative Example 1). The image reveals a multi-layered secondary cell wall with a dense structure and clear boundaries. Most cell cavities are regularly hollow with open openings. The mesoglea layer is tightly packed without stratification or damage, reflecting a highly ordered cellulose microfibrils and a strong hydrogen bond network. The rigid honeycomb structure composed of numerous hollow thin-walled cavities causes stress concentration at the cavity edges, resulting in high resistance and easy splitting during planing and flattening. This results in bamboo exhibiting high strength but also brittleness and difficulty in flattening. Figure 6The image shows a scanning electron microscope (SEM) image of the cross-section of bamboo strips obtained after ternary synergistic treatment (Example 1). The cell walls change from dense to relatively loose, exhibiting interlayer cleavage, sheet-like peeling, and weakening of the mesoglea layer. Many originally hollow cavities are flattened and collapsed, with the cavity openings covered by wall fragments or filling phases, exhibiting a sealed or semi-sealed morphology. A continuous dense phase is visible within the cavities and intercellular layers. This indicates that under the influence of steam-driven channel opening and microwave-assisted penetration, polyethylene glycol enters the cell walls and cavities, acting as a "filler + adhesive" for the hollow structure. This transforms the easily brittle large hollow cavities into collapsible, slippery sealed / filled cavities, improving the deformation path and energy dissipation capacity, thus facilitating softening and flattening.

[0071] In summary, the ternary synergistic treatment transforms bamboo from a "hollow rigid honeycomb" to a "end-sealed / filled, collapsible cell cavity + flexible wall layer." Under the hydrogen bond reconstruction and structural filling effect of polyethylene glycol, the cell wall transforms from a rigid and brittle skeleton into a plastic and energy-consuming composite network. This is consistent with the mechanical result of "significantly improved elastic modulus and moderately reduced static bending strength" in ternary synergistic bamboo. The mechanism of ternary synergistic softening and toughening of bamboo in this invention is verified from both structural and thermal behavior perspectives.

[0072] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for the synergistic treatment of bamboo by high-temperature steam, polyethylene glycol, and microwave, characterized in that, include: The bamboo was subjected to high-temperature steam treatment, polyethylene glycol solution impregnation treatment, and microwave treatment in sequence.

2. The method according to claim 1, characterized in that, The temperature of the high-temperature steam treatment is 100–180°C, and the time of the high-temperature steam treatment is 30–180 min.

3. The method according to claim 2, characterized in that, The temperature of the high-temperature steam treatment is 120–160°C, and the time of the high-temperature steam treatment is 50–90 min.

4. The method according to claim 1, characterized in that, The polyethylene glycol solution has a mass concentration of 0.5% to 50%, and the polyethylene glycol has a molecular weight of 100 to 20,000 Da.

5. The method according to claim 4, characterized in that, The polyethylene glycol solution has a mass concentration of 1% to 10%, and the polyethylene glycol has a molecular weight of 200 to 4000 Da.

6. The method according to claim 1, characterized in that, The immersion time for the polyethylene glycol solution impregnation treatment is 0.1 to 24 hours.

7. The method according to claim 6, characterized in that, The immersion time for the polyethylene glycol solution impregnation treatment is 1 to 6 hours.

8. The method according to claim 1, characterized in that, The power used for microwave processing is 10–500 W, and the microwave processing time is 1–120 min.

9. The method according to claim 8, characterized in that, The power used for microwave processing is 50–300 W.

10. The method according to claim 8, characterized in that, The microwave processing time is 5 to 30 minutes.

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