Mildew-proof process for processing bamboo wood through cooperation of low-temperature freezing and ultrasonic waves

Abstract

The invention relates to the technical field of bamboo wood treatment, in particular to a mould-proof process for treating bamboo wood through cooperation of low-temperature freezing and ultrasonic waves. The mould-proof technology comprises the following steps that bamboo wood is sequentially subjected to water immersion treatment and freeze-thaw cycle treatment, and freeze-thawed bamboo wood is obtained; and the freeze-thawed bamboo wood is subjected to ultrasonic treatment under the water bath condition, and the modified bamboo wood is obtained. According to the mildew-proof process, the water-saturated bamboos are sequentially subjected to freeze-thaw cycle treatment and ultrasonic treatment, and the freeze-thaw cycle treatment can enable water permeating pores in the bamboos to be condensed into ice crystals to cause volume expansion, so that a transverse substance transmission channel is effectively established, the permeability is improved, and meanwhile, the macroscopic mechanical integrity of the bamboos is kept. The enhanced dissolution effect of the ultrasonic cavitation effect promotes dissolution of a microbial metabolism substrate and maintains the basic integrity of a cellulose microfibril network at the same time, so that a nutrient matrix required by microbial metabolism is fundamentally eliminated, and long-acting mildew prevention is realized.

Description

Technical Field

[0001] This invention relates to the field of bamboo processing technology, specifically to a mildew prevention process for bamboo that combines low-temperature freezing with ultrasonic treatment. Background Technology

[0002] The problem of bamboo mold has become a core bottleneck restricting the upgrading of the bamboo industry. This technical challenge manifests itself primarily in the following ways: during harvesting, storage, transportation, and use, sunlight, water immersion, and temperature exposure cause localized mold growth or discoloration due to the oxidation of lignin and other substances, leading to a decrease in bamboo yield; inconsistencies in color during later production processes increase processing costs and limit product quality; and mold and subsequent decay reduce bamboo strength, resulting in low market acceptance of bamboo products. This has become a common problem facing the bamboo industry in my country and worldwide. This global industry pain point has created a chain reaction of negative effects across technology, economy, and market, severely impacting the application of bamboo products in high-end fields such as construction, transportation, and new materials.

[0003] Current bamboo anti-mildew technologies are mainly divided into two categories: physical and chemical. However, the balance between environmental friendliness and performance is a prominent issue. Physical anti-mold technology mainly involves high-temperature heat treatment, which involves pyrolyzing the sugars, starches, and other nutrient matrix of mold inside bamboo at 150-220℃, achieving a carbonization rate of over 70%. However, this method has high energy consumption and environmental problems. The energy consumption for processing each ton of bamboo is 500-800 kWh, and the carbon emission intensity is 150-200 kg CO2 / ton. It also leads to the deterioration of bamboo performance: treatment at temperatures above 160℃ causes a 15%-20% decrease in bending strength, and the color value of bamboo drops from 65-75 (L* value) of the original material to 40-50, resulting in a loss of aesthetic value.

[0004] Chemical anti-mold technologies, as shown in Chinese invention patent application number 202311551749.0, include sulfur fumigation and chemical impregnation. Sulfur fumigation uses SO2 gas to penetrate the cell cavities of bamboo, inhibiting mold metabolism; quaternary ammonium salt (ACQ) impregnation constructs a hydrophobic barrier through chemical cross-linking. Both methods also present environmental problems: sulfur fumigation releases harmful gases such as SO2, H2, and S, leaving behind >200 ppm of sulfides, causing bamboo to fail to comply with EU REACH regulations; furthermore, quaternary ammonium salt preservatives leach into the soil through rainwater, with a median lethal concentration (LC50) as low as 0.1 mg / L for aquatic organisms; chemical treatment also reduces the bending strength of bamboo by 8%–12%, and the anti-mold effect lasts only 18–24 months. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a mildew prevention process for bamboo by combining low-temperature freezing and ultrasonic treatment, which can improve the mildew prevention period of bamboo while ensuring mechanical properties.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a low-temperature freezing and ultrasonic synergistic treatment process for bamboo anti-mildew, comprising the following steps: the bamboo is subjected to water immersion treatment and freeze-thaw cycle treatment in sequence to obtain freeze-thawed bamboo; the freeze-thawed bamboo is placed under water bath conditions for ultrasonic treatment to obtain modified bamboo.

[0007] The beneficial effects of this invention are as follows: The anti-mildew process of this invention involves subjecting saturated bamboo to freeze-thaw cycles and ultrasonic treatment in sequence. The freeze-thaw cycle treatment causes the water that has permeated the pores of the bamboo to condense into ice crystals, resulting in volume expansion. This forms a submicron-level crack network on the vascular bundle walls and thin-walled cell walls, effectively establishing lateral material transport channels, improving permeability, and triggering stress release between cell wall layers, while maintaining the macroscopic mechanical integrity of the bamboo. The enhanced dissolution effect of ultrasonic cavitation promotes the dissolution of microbial metabolic substrates (nutrient matrices such as starch) while maintaining the basic integrity of the cellulose microfibril network (the main load-bearing skeleton), achieving efficient removal of nutrients such as starch, sugars, and proteins from the bamboo, fundamentally eliminating the nutrient matrix required for microbial metabolism. Attached Figure Description

[0008] Figure 1 This is an electron microscope image of the untreated bamboo strips in Embodiment 7 of the present invention; Figure 2 This is an electron microscope image of bamboo strips subjected to low-temperature freezing treatment in Embodiment 7 of the present invention; Figure 3 This is an electron microscope image of the ultrasonically treated bamboo strips in Embodiment 7 of the present invention; Figure 4 This is an electron microscope image of bamboo strips subjected to synergistic treatment by low-temperature freezing and ultrasound in Embodiment 7 of the present invention; Figure 5 The infrared spectra of bamboo strips after being treated by the four processing methods in Embodiment 7 of the present invention; Figure 6 The X-ray diffraction patterns of bamboo strips after being treated by the four processing methods in Embodiment 7 of the present invention; Figure 7 The images show the Penicillium citrinum infection of bamboo strips after treatment using the four methods described in Embodiment 7 of the present invention. Figure 8 The images show green Trichoderma infection on bamboo strips after treatment using the four methods described in Embodiment 7 of the present invention. Detailed Implementation

[0009] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0010] A mildew-proofing process for bamboo material using a combination of low-temperature freezing and ultrasonic treatment includes the following steps: the bamboo material is subjected to water immersion treatment and freeze-thaw cycle treatment in sequence to obtain freeze-thawed bamboo material; the freeze-thawed bamboo material is placed in a water bath for ultrasonic treatment to obtain modified bamboo material.

[0011] As described above, the beneficial effects of this invention are as follows: the process of this invention does not require chemical agents, yet it can improve the anti-mold performance and strength of bamboo. The freeze-thaw cycle treatment causes the internal moisture of the bamboo to condense into ice crystals. This volume expansion process disrupts the hemicellulose and lignin structures, forming a submicron-level crack network on the vascular bundle walls and thin-walled cell walls. This effectively establishes lateral material transport channels, enhances permeability, promotes the entry of moisture into the bamboo, and triggers the release of interlayer stress in the cell walls, while maintaining the macroscopic mechanical integrity of the bamboo. Simultaneously, it promotes the hydrolysis and dissolution of extracts within the cell cavities. The freeze-thawed bamboo is then subjected to ultrasonic water bath treatment to obtain modified bamboo. The powerful shock waves and microjets of the ultrasonic cavitation effect can further break down the hemicellulose and lignin structures of the cell walls with the help of moisture, and "wash out" and "clean" out the starch, glycoproteins, and other contents within the cell cavities. This cuts off the nutrient source required for the growth and reproduction of mold and other microorganisms at the source, thereby significantly improving the anti-mold performance of the bamboo.

[0012] Furthermore, it also includes the steps of rinsing with pure water and drying in sequence after ultrasonic treatment.

[0013] Furthermore, the drying temperature is 50~60 ℃.

[0014] As can be seen from the above description, using medium and low temperature drying can reduce the cracks caused by rapid drying.

[0015] Furthermore, the specific steps of the freeze-thaw cycle treatment are as follows: freeze at a low temperature of -10 to -30 ℃ and then thaw, repeating 1 to 5 times.

[0016] Preferably, the low-temperature freezing temperature is -20 to -25 °C. More preferably, the low-temperature freezing temperature is -25 °C.

[0017] As described above, the bending mechanical properties of bamboo show a trend of first increasing and then decreasing with decreasing freezing temperature, but the change is not statistically significant. The bending elastic modulus and static bending strength of bamboo are optimal at a freezing temperature of -25℃; therefore, -25℃ was selected as the optimal low-temperature freezing temperature.

[0018] Preferably, the freeze-thaw cycle is performed 2 to 4 times. More preferably, the freeze-thaw cycle is performed 4 times.

[0019] As described above, the bending mechanical properties of bamboo initially increase and then decrease with increasing freeze-thaw cycles. The bamboo exhibits the best bending modulus of elasticity after four freeze-thaw cycles, with no statistically significant change. However, the bamboo also shows the best static bending strength after four freeze-thaw cycles, with a statistically significant change. Repeated freeze-thaw cycles allow more moisture to penetrate the bamboo, condensing into ice crystals in the vascular bundle parenchyma cells, thus forming a larger network of submicron-sized cracks. Therefore, four freeze-thaw cycles were selected as the optimal number of cycles.

[0020] Furthermore, the cryogenic freezing time is 6 to 18 hours.

[0021] Preferably, the freeze-thaw cycle time is 6-9 hours. More preferably, the freeze-thaw cycle time is 6 hours.

[0022] As described above, the bending mechanical properties of bamboo decrease with increasing freezing time, and this change is statistically significant. The bamboo exhibits the best bending modulus of elasticity and static bending strength at a freezing time of 6 hours; therefore, a freezing time of 6 hours was selected.

[0023] Furthermore, the power of the ultrasonic treatment is 900~1300 W.

[0024] Preferably, the ultrasonic processing power is 1100~1300W. More preferably, the ultrasonic processing power is 1200W.

[0025] As described above, the bending mechanical properties of bamboo initially increase and then decrease with increasing ultrasonic power. The bending elastic modulus of bamboo is optimal at an ultrasonic power of 1200 W, and this change is statistically significant. Conversely, the static bending strength of bamboo is optimal at an ultrasonic power of 1100 W, but this change is not statistically significant. Therefore, an ultrasonic treatment power of 1200 W was selected.

[0026] Furthermore, the temperature for ultrasonic treatment is 40~60 ℃.

[0027] Preferably, the ultrasonic treatment temperature is 45~55 °C. More preferably, the ultrasonic treatment temperature is 50 °C.

[0028] As described above, the bending mechanical properties of bamboo initially increase and then decrease with increasing ultrasonic treatment temperature, but the changes are not statistically significant. The optimal ultrasonic treatment temperature for bamboo is 50 ℃, resulting in the best bending modulus and static bending strength. Therefore, 50 ℃ was selected as the optimal ultrasonic treatment temperature.

[0029] Furthermore, the ultrasonic treatment time is 20~60 min.

[0030] Preferably, the ultrasonic treatment time is 35-45 minutes. More preferably, the ultrasonic treatment time is 40 minutes.

[0031] As described above, the bending mechanical properties of bamboo initially increase and then decrease with increasing ultrasonic treatment time, but the changes are not statistically significant. The optimal ultrasonic treatment time for bamboo is 40 minutes, resulting in the best bending modulus of elasticity and static bending strength. Therefore, a treatment time of 40 minutes was selected.

[0032] Furthermore, the bamboo material is bamboo with the green and yellow parts removed radially.

[0033] Furthermore, the bamboo material that is radially removed from the green and yellow parts can be any common bamboo material form such as bamboo strips, bamboo blocks, or bamboo tubes.

[0034] Furthermore, the water immersion treatment involves soaking the bamboo in pure water until it sinks to the bottom.

[0035] As can be seen from the above description, the moisture content inside fresh bamboo is insufficient to condense enough ice crystals in the thin-walled cells of the vascular bundles to burst the cell walls and form a sufficient submicron-level fissure network. Therefore, it is necessary to soak the bamboo in pure water to form saturated bamboo.

[0036] Furthermore, the moisture content of the modified bamboo is 8-12%.

[0037] As described above, modified bamboo exhibits high bending performance at a moisture content of 8-12% and is not prone to mold.

[0038] Another technical solution adopted in this invention is: a bamboo material prepared by a mildew-proofing process using the above-mentioned low-temperature freezing and ultrasonic synergistic treatment.

[0039] As can be seen from the above description, the bamboo material prepared by the present invention has high anti-mildew properties and strength.

[0040] The raw materials and equipment used in the following embodiments are as follows: Moso bamboo: Two-year-old moso bamboo from Wuyi Mountain.

[0041] Refrigerator: Haier Group, BC / BD-142GHEPGD; Ultrasonic Cleaner: Wenzhou Hongxiang Technology; Electronic Balance: Shanghai Minqiao Precision Instrument Co., Ltd., DY202K; Constant Temperature Water Bath: Gongyi Yuhua Instrument Co., Ltd., DF-101S; Electric Heating Drying Oven: Fisford Instruments (Hebei) Co., Ltd., Model: WGL-45B; Microcomputer-Controlled Electronic Universal Laboratory Machine: Shimadzu Corporation, Japan, AGS-X; Moisture Content Analyzer: Shenzhen Jumaoyuan Technology Co., Ltd., GM605; Scanning Electron Microscope: Hitachi Ultra-High Resolution Cold Field Emission Scanning Electron Microscope, SU8600; Fourier Transform Infrared Spectrometer: Thermo Fisher Scientific, Nicolet iS5.

[0042] Embodiment 1 of the present invention is a process for low-temperature freezing of bamboo, comprising the following steps: Fresh moso bamboo is used to prepare radially de-emergent and de-emergent bamboo strips. The bamboo strips are soaked in pure water until they sink, resulting in saturated bamboo strips. The saturated bamboo strips are divided into five batches and subjected to freezing treatment at -10℃, -15℃, -20℃, -25℃, and -30℃ for 6 hours respectively in a refrigerator. Subsequently, they are transferred to a 50℃ constant temperature water bath (temperature fluctuation ±1℃) for 1 hour to thaw, completing one freeze-thaw cycle. The strips are then rinsed with pure water for 10 minutes and dried in an electric heating drying oven (60℃) until the final moisture content stabilizes at 8%~12%, yielding modified bamboo. The bending performance test results of the obtained modified bamboo strips are shown in Table 1. During the test, the bamboo strips were cut into small rectangular strips of 200 mm × 25 mm × 8 mm for bending mechanical property testing. The bending mechanical properties were tested according to GB / T 17657-2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels" 4.7 Static bending strength and modulus of elasticity (three-point bending).

[0043] Table 1

[0044] As can be seen from Table 1, the bending modulus of elasticity and static bending strength of bamboo are significantly improved under the conditions of freezing temperature -25℃, freezing time 6h, and 1 cycle.

[0045] Embodiment 2 of the present invention is as follows: The only difference between Example 2 and Example 1 is that the water-saturated bamboo strips were frozen at -25℃ for 6h, 9h, 12h, 15h, and 18h, respectively. The bending performance test results of the obtained modified bamboo strips are shown in Table 2.

[0046] Table 2

[0047] As can be seen from Table 2, the bending modulus of elasticity and static bending strength of bamboo are significantly improved under the conditions of freezing temperature -25℃, freezing time 6h, and 1 cycle.

[0048] Embodiment 3 of the present invention is as follows: The difference between Example 3 and Example 1 is only that: the water-saturated bamboo strips were frozen at -25℃ for 6 hours, and then thawed in a 50℃ constant temperature water bath (temperature fluctuation ±1℃) for 1 hour. This freeze-thaw cycle was repeated 1, 2, 3, 4, and 5 times respectively. The bending performance test results of the obtained modified bamboo strips are shown in Table 3.

[0049] Table 3

[0050] As can be seen from Table 3, the bending modulus of elasticity and static bending strength of bamboo are significantly improved under the conditions of freezing temperature -25℃, freezing time 6h, and 4 cycles.

[0051] Embodiment four of the present invention is: an anti-mildew process for bamboo treated with ultrasonic waves, the steps of which are as follows: Bamboo strips with radially removed bamboo green and yellow layers were prepared from fresh moso bamboo. The bamboo strips were soaked in pure water until they sank, resulting in saturated bamboo strips. These saturated bamboo strips were then placed in a 50℃ constant-temperature aqueous solution and divided into five batches, treated with ultrasonic power of 900W, 1000W, 1100W, 1200W, and 1300W respectively for 30 min. The bamboo strips were then rinsed with pure water for 10 min and dried in an electric hot air drying oven (60℃) until the final moisture content stabilized at 8%~12%, yielding modified bamboo. The bending performance test results and mass loss results of the prepared modified bamboo strips are shown in Table 4. For the bending mechanical properties test, the bamboo strips were cut into small rectangular strips of 200 mm × 25 mm × 8 mm for testing. The bending mechanical properties test was conducted according to GB / T 17657-2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels" 4.7 Static bending strength and modulus of elasticity (three-point bending).

[0052] Table 4

[0053] As shown in Table 4, the flexural modulus of bamboo is most significantly improved under the conditions of ultrasonic power of 1200W, treatment temperature of 50℃ and treatment time of 30 min; the static bending strength of bamboo is most significantly improved under the conditions of ultrasonic power of 1100W, treatment temperature of 50℃ and treatment time of 30 min.

[0054] Embodiment five of the present invention is as follows: The only difference between Example 5 and Example 4 is that the ultrasonic power is 1200W, and the processing time is 20, 30, 40, 50, and 60 minutes, respectively. The bending performance test results of the obtained modified bamboo strips are shown in Table 5.

[0055] Table 5

[0056] As can be seen from Table 5, the flexural modulus and static bending strength of bamboo are significantly improved under the conditions of ultrasonic power of 1200 W, treatment temperature of 50 ℃ and treatment time of 40 min.

[0057] Embodiment six of the present invention is as follows: The only difference between Example 6 and Example 4 is that the ultrasonic power is 1200W, the processing time is 40min, and the processing temperatures are 40, 45, 50, 55, and 60 ℃, respectively. The bending performance test results of the obtained modified bamboo strips are shown in Table 6.

[0058] Table 6

[0059] As shown in Table 6, the flexural modulus of bamboo is most significantly improved under the conditions of ultrasonic power of 1200W, treatment temperature of 50℃ and treatment time of 40 min; the static bending strength of bamboo is most significantly improved under the conditions of ultrasonic power of 1200W, treatment temperature of 40℃ and treatment time of 40 min.

[0060] Embodiment 7 of the present invention describes the preparation of modified bamboo strips under different processing methods.

[0061] Fresh moso bamboo was used to prepare radially strips with the outer green and inner yellow parts removed. The bamboo strips were then subjected to the following treatments: 1. Untreated: Bamboo strips were placed in an electric heating drying oven (60℃) and dried until the final moisture content stabilized at 8%-12% to obtain untreated bamboo strips, which served as the control group; 2. Soak bamboo strips in pure water until they sink to obtain saturated bamboo strips; freeze the saturated bamboo strips in a refrigerator at -25℃ for 6 hours, then thaw them in a 50℃ constant temperature water bath (temperature fluctuation ±1℃) for 1 hour. Repeat the above freeze-thaw cycle 4 times, rinse with pure water for 10 minutes, and dry in an electric heating drying oven (60℃) until the final moisture content stabilizes at 8%~12% to obtain low-temperature frozen bamboo strips. 3. Soak the bamboo strips in pure water until they sink to obtain saturated bamboo strips; place the bamboo strips in a 50℃ constant temperature aqueous solution and treat them under ultrasonic power of 1200W for 40 minutes; take out the bamboo strips, rinse them with pure water for 10 minutes, and place them in an electric heating drying oven (60℃) to dry them until the final moisture content stabilizes at 8%~12%, thus obtaining ultrasonically treated bamboo strips. 4. Soak bamboo strips in pure water until they sink to obtain saturated bamboo strips; freeze the saturated bamboo strips at -25℃ for 6 hours in a refrigerator, then thaw them in a 50℃ constant temperature water bath (temperature fluctuation ±1℃) for 1 hour, repeat the freeze-thaw cycle 4 times, rinse with pure water for 10 minutes to obtain low-temperature frozen bamboo strips; place the low-temperature frozen bamboo strips in a 50℃ constant temperature aqueous solution and treat them with an ultrasonic power of 1200W for 40 minutes; remove the bamboo strips and rinse them with pure water for 10 minutes, then place them in an electric heating drying oven (60℃) to dry until the final moisture content stabilizes at 8%~12%, to obtain bamboo strips treated with low-temperature freezing and ultrasonic synergy.

[0062] The following tests were performed on the bamboo strips mentioned above: (1) The bending mechanical properties of bamboo strips after the above four treatment methods were tested. The test results are shown in Table 7. During the test, the bamboo strips were cut into small rectangular strips of 200 mm × 25 mm × 8 mm for bending mechanical property testing.

[0063] Table 7

[0064] As shown in Table 7, when bamboo is treated with the modification scheme of this invention—a combination of low-temperature freezing and ultrasonic treatment—the flexural modulus and static bending strength of the bamboo strips are both higher than those of untreated bamboo, bamboo strips treated with low-temperature freezing alone, and bamboo strips treated with ultrasonic treatment. Using the modification scheme of this invention, the overall flexural performance of the bamboo strips reaches its optimal level, with the flexural modulus increasing by 19.68% and the static bending strength increasing by 21.77% compared to the original bamboo.

[0065] (2) The morphological results of bamboo strips treated by the above four methods were tested using electron microscopy. The test results are shown in [the table below]. Figures 1 to 4 ,in, Figure 1 This is an electron microscope image of untreated bamboo strips. Figure 2 This is an electron microscope image of bamboo strips subjected to cryogenic treatment. Figure 3 Electron micrograph of ultrasonically treated bamboo strips. Figure 4 Electron micrograph of bamboo strips subjected to synergistic cryogenic freezing and ultrasonic treatment. Figures 1 to 3 This is a 600x magnified image. Figure 4 This is an image magnified 800 times.

[0066] pass Figure 1 and Figure 2 In comparison, the intracellular contents of bamboo cells were significantly reduced after cryogenic treatment. This indicates that after cryogenic treatment, starch, sugars, proteins, and some impurities inside the bamboo leach out along with the water. This is because cryogenic treatment induces a water-absorbing phase transition and expansion in the bamboo, forming a submicron-level fissure network on the vascular bundle walls and thin-walled cell walls, effectively establishing lateral material transport channels, thus improving permeability while maintaining the macroscopic mechanical integrity of the bamboo. Figure 1 and Figure 3 The comparison shows that after ultrasonic treatment, the cells of bamboo shrink, the intercellular spaces increase, the cell walls become loose, and the contents of the cell cavities are significantly reduced. This is because the powerful shock waves and microjets of ultrasonic cavitation can effectively break down the hemicellulose and lignin structures of the cell walls, forming a multi-level porous structure. This promotes the dissolution of microbial metabolic substrates (nutrient matrices such as starch) while maintaining the basic integrity of the cellulose microfibril network (the main load-bearing framework). Figure 1 and Figure 4The comparison shows that some contents within the cell lumen have essentially disappeared, the intercellular spaces have increased, and the cell walls have become looser. This is mainly due to the combined effects of low temperature and ultrasonic cavitation, which significantly damages the hemicellulose and lignin in the cell walls, opening the transverse material transport channels within the bamboo. The powerful shock waves and microjets of ultrasonic cavitation effectively break down the cell structure, "washing away" and dissolving contents such as starch and glycoproteins. In summary, the combined low-temperature / ultrasonic treatment of bamboo can degrade hemicellulose and lignin, making the cell walls porous and fluffy, forming a submicron-level transverse fissure network. This allows microbial metabolic substrates (nutrient matrices such as starch) to dissolve, while maintaining the basic integrity of the cellulose microfibril network (the main load-bearing framework), thereby preserving the physical and mechanical properties of bamboo.

[0067] (3) The infrared spectra of bamboo strips treated by the above four methods were tested, and the test results are shown in the figure. Figure 5 . Figure 5 (a) shows untreated bamboo strips, (b) shows bamboo strips treated with cryogenic freezing, (c) shows bamboo strips treated with ultrasonic waves, and (d) shows bamboo strips treated with a combination of cryogenic freezing and ultrasonic waves.

[0068] contrast Figure 5 Figures a and b show that the bamboo after low-temperature freezing treatment reaches a depth of 3420 cm. -1 The sharpening and blue shift of the nearby OH stretching vibration peak also indicates that low-temperature freezing treatment disrupts the hydrogen bond network of bamboo. When ice crystals form and melt, the existing hydrogen bonds between cellulose and hemicellulose molecules are broken, potentially forming new and more free hydroxyl groups. After treatment, the peak at 1740 cm⁻¹... -1 The intensity of the C=O stretching vibration peaks attributable to the acetyl and glucuronic acid groups in hemicellulose was significantly weakened, directly indicating that freeze-thaw treatment led to partial degradation or deacetylation of hemicellulose. The formation of ice crystals exerts physical stress on the cell wall, making amorphous polysaccharides like hemicellulose more susceptible to hydrolysis and destruction. After treatment, at 1505 cm⁻¹... -1 The intensity of the aromatic ring skeleton vibration peak at 1265 cm⁻¹ decreased slightly. -1 The intensity of the guaiac ring vibration peak at 1160 cm⁻¹ was also significantly weakened, indicating that the structure of lignin was affected by freeze-thaw cycles. Although lignin is a relatively stable three-dimensional network macromolecule, the physical stress generated by freeze-thaw cycles may break its linkages (LCCs) with carbohydrates, or cause some lignin molecules to rearrange or undergo slight degradation. After treatment, the intensity of the guaiac ring vibration peak at 1160 cm⁻¹ was significantly weakened. -1 (COC asymmetric stretching) and 895 cm -1 The peaks in the cellulose crystalline region (due to β-glycosidic bond vibration) showed little change, indicating that the crystalline structure of cellulose was well preserved during freeze-thaw cycles. (1055 cm⁻¹) -1and 1030 cm -1 Minor changes in the region may reflect slight variations in the amorphous regions of cellulose or hemicellulose, but the overall structure remains intact. After treatment, 1640 cm⁻¹ -1 The significantly weakened absorption peaks of C=O (amide I band) or C=C vibrations, representing starch, sugars, proteins, etc., within the cell lumen, strongly indicate that starch, glycoproteins, and other substances within the cell lumen were dissolved or degraded during the freeze-thaw process. The repeated formation and melting of ice crystals disrupted the cellular structures storing these substances, leading to their loss.

[0069] The above results indicate that low-temperature freezing treatment did not significantly damage the cell wall cellulose skeleton structure. Instead, it effectively established lateral material transport channels by breaking down hemicellulose and lignin to form a submicron-level fissure network on the vascular bundle wall and thin-walled cell wall, thereby improving permeability and promoting the degradation and dissolution of substances such as starch, sugar, and protein in the cell cavity while maintaining the macroscopic mechanical integrity of bamboo.

[0070] contrast Figure 5 From a and c, we can see that the bamboo material after ultrasonic treatment reaches a depth of 3420 cm. -1 The significantly increased intensity of the nearby broad peaks is mainly due to the "cavitation effect" generated by ultrasound in the liquid, which drastically disrupts the hydrogen bond network within the bamboo, producing more free hydroxyl groups. Simultaneously, the treatment process may make the bamboo more absorbent of water, or the degradation of chemical components may generate new hydroxyl groups, leading to a significant enhancement of -OH absorption. After treatment, at 1740 cm⁻¹... -1 The peak intensities of the acetyl and glucuronic acid groups, which are associated with hemicellulose, were significantly reduced, directly indicating that ultrasonic treatment led to drastic degradation of the hemicellulose. The extreme local conditions (high temperature, high pressure, strong shear force) generated by cavitation were sufficient to cause hemicellulose chain breakage and hydrolysis. After treatment, at 1505 cm⁻¹ -1 The intensity of the aromatic ring skeleton vibration peak at 1265 cm⁻¹ decreased significantly. -1 The sharp decrease or even disappearance of the guaiac ring vibrational peak at 1160 cm⁻¹ indicates that lignin is a rigid three-dimensional network structure, but is highly sensitive to high-energy mechanical shocks and free radical reactions caused by cavitation effects. These effects can break key bonds such as β-O-4 and even disrupt the benzene ring structure, leading to the depolymerization of lignin macromolecules. After treatment, the 1160 cm⁻¹ peak intensity... -1 (COC, crystallization zone characteristics) and 895 cm -1 The peak variation for (β-glycosidic bond) is relatively small, at 1370 cm⁻¹. -1 (CH bend) and 1055 cm -1 ¹ / 1030 cm -1The intensity and shape of peaks such as (CO stretching) may change slightly, further demonstrating the extremely high stability of the crystalline regions of cellulose, which can resist the mechanical impact of ultrasound. However, in the amorphous regions, the cellulose chains are more loosely arranged, and ultrasound may cause the chains in these regions to break or rearrange, leading to a peak at 1370 cm⁻¹. -1 And slight changes in the CO stretching region. After treatment, 1640 cm -1 The significant weakening of the absorption peaks nearby indicates that the powerful shock waves and microjets of ultrasonic cavitation can effectively break down cell structures, "washing out" and "cleaning out" contents such as starch and glycoproteins, resulting in a decrease in the intensity of their characteristic peaks.

[0071] contrast Figure 5 As can be seen from b and c, low-temperature freezing treatment is mainly physical stress (ice crystal compression), with relatively mild chemical changes; while ultrasonic treatment is a physical-chemical synergistic process, its cavitation effect brings strong mechanical force and may induce chemical reactions, thus its destructive effect on stable components such as lignin is more significant.

[0072] Figure 5 The figure d indicates that the synergistic effect of low-temperature freezing treatment inducing water adsorption phase change expansion and ultrasonic cavitation in bamboo can effectively disrupt the hydrogen bond network between lignin and hemicellulose in the cell wall, causing hemicellulose and lignin to dissolve and be removed. This forms a sub-transverse slit network between the cell walls, allowing the nutrient matrix such as starch in the cell cavity to dissolve and be removed, while maintaining the basic integrity of the cellulose microfibril network (the main load-bearing skeleton), thus preserving the physical and mechanical properties of bamboo.

[0073] (4) Test the XRD (X-ray diffraction) curves of bamboo strips after the above four treatment methods. The test results are shown in the figure. Figure 6 . Figure 6 (a) shows untreated bamboo strips, (b) shows freeze-treated bamboo strips, (c) shows ultrasonically treated bamboo strips, and (d) shows bamboo strips treated with a combination of freeze-treatment and ultrasonic treatment.

[0074] Calculations using the Segal method show that the CrI value (crystallinity) of bamboo treated with low-temperature freezing is significantly higher than that of untreated bamboo. This is not due to the formation of new crystalline structures, but rather to the selective destruction of amorphous regions, resulting in an increase in the relative proportion of crystalline regions in the overall structure. When water freezes in the micropores and gaps of bamboo cell walls, the resulting expansion stress first acts on the amorphous regions, which have weaker mechanical strength. Due to their loose, non-oriented structure, the amorphous portions of hemicellulose and cellulose are more prone to chain breakage, degradation, and delamination during repeated freeze-thaw cycles. The crystalline regions of cellulose, with their regular molecular chain arrangement and dense hydrogen bond network, possess higher mechanical strength and stability, and are better able to resist the physical stress generated by freeze-thaw cycles. As some amorphous components degrade and are destroyed, the relative content of crystalline regions in the overall bamboo increases, thus manifesting as a significant increase in the crystallinity index in the XRD pattern. This conclusion is consistent with the observation of the characteristic peak of hemicellulose (1740 cm⁻¹) in FTIR. -1 The results of the weakening effect are completely consistent, jointly confirming the degradation effect of freeze-thaw treatment on the amorphous components of bamboo. The CrI value of bamboo treated with ultrasound was also significantly higher than that of untreated bamboo, with an increase that may be comparable to or even greater than that of freeze treatment, mainly attributed to the drastic degradation of the amorphous regions. The extreme local conditions (high temperature, high pressure, strong shear force) generated by the collapse of cavitation bubbles can efficiently degrade and strip components in the amorphous regions, especially hemicellulose and lignin. This conclusion is consistent with the hemicellulose peak observed in the infrared spectrum (1740 cm⁻¹). -1 ) and lignin peaks (1510, 1265 cm) -1 The results of the significant reduction corroborate each other, and the removal of the amorphous matrix directly led to an increase in the relative proportion of the crystalline region.

[0075] (5) Test the anti-mildew properties of bamboo strips treated by the above four methods. The results of the Penicillium citrinum test are shown in [the table below]. Figure 7 The results of the green Trichoderma test are shown in [link to test]. Figure 8 The anti-mold performance was tested according to GB / T 18261-2013 "Test Method for the Efficacy of Anti-mold Agents in Controlling Molds and Discoloration Fungi on Wood". Figure 7 and 8 (a) shows untreated bamboo strips, (b) shows freeze-treated bamboo strips, (c) shows ultrasonically treated bamboo strips, and (d) shows bamboo strips treated with a combination of freeze-treatment and ultrasonic treatment.

[0076] Depend on Figure 7 and 8It can be seen that untreated bamboo showed obvious mold growth on day 7 of the test, and the mold became increasingly pronounced as the test time increased, eventually completely covering the bamboo by day 28. In comparison, low-temperature freezing treated bamboo showed sporadic mold growth after 28 days; ultrasonically treated bamboo also showed sporadic mold growth after 28 days; and bamboo treated with a combination of freezing and ultrasonic treatment showed virtually no mold infection after 28 days. This indicates that low-temperature freezing, ultrasonic treatment, and the combined freezing and ultrasonic treatment can all significantly improve the mold resistance of bamboo.

[0077] In summary, the bamboo processing technology provided by this invention first involves freezing the bamboo at -25°C, causing the internal moisture to condense into ice crystals. This volume expansion process disrupts the hemicellulose and lignin structures, forming a submicron-level network of fissures in the vascular bundle walls and thin-walled cell walls. This effectively establishes lateral material transport channels, enhances permeability, promotes water penetration into the bamboo, and triggers stress release between cell wall layers, while maintaining the macroscopic mechanical integrity of the bamboo. The frozen-thawed bamboo is then subjected to ultrasonic treatment to obtain modified bamboo. The powerful shock waves and microjets from the ultrasonic cavitation effect further break down the hemicellulose and lignin structures in the cell walls with the help of moisture, and "wash out" and "clean" out contents such as starch and glycoproteins within the cell cavities. This cuts off the nutrient source needed for the growth and reproduction of mold and other microorganisms at the source, thereby significantly improving the bamboo's anti-mold properties. Furthermore, both cryogenic freezing and ultrasonic treatment improve the flexural modulus (stiffness) and static bending strength of bamboo. This means that the mechanical properties of bamboo mainly depend on the orientation and crystallinity of cellulose microfibrils, rather than the strength of "binders" such as hemicellulose and lignin. While degrading amorphous components, cryogenic freezing and ultrasonic treatment may also cause a certain degree of shrinkage and densification of the cell walls, strengthening the main load-bearing framework and optimizing stress transmission. A denser structure means more chemical bonds per unit volume, thus improving strength and stiffness, but at the cost of decreased toughness and increased brittleness.

[0078] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A mildew-proofing process for bamboo materials using a combination of low-temperature freezing and ultrasonic treatment, characterized in that, Includes the following steps: Bamboo is subjected to water immersion treatment and freeze-thaw cycle treatment in sequence to obtain freeze-thawed bamboo; the freeze-thawed bamboo is then subjected to ultrasonic treatment under water bath conditions to obtain modified bamboo.

2. The anti-mildew process for bamboo material by synergistic treatment of low-temperature freezing and ultrasound according to claim 1, characterized in that, It also includes the steps of rinsing with pure water and drying in sequence after ultrasonic treatment.

3. The anti-mildew process for bamboo material by synergistic treatment of low-temperature freezing and ultrasound according to claim 2, characterized in that, The drying temperature is 50~60℃.

4. The anti-mildew process for bamboo material by synergistic treatment of low-temperature freezing and ultrasound according to claim 1, characterized in that, The specific steps of the freeze-thaw cycle treatment are as follows: freeze at a low temperature of -10 to -30 ℃ and then thaw, repeating 1 to 5 times.

5. The anti-mildew process for bamboo material subjected to synergistic treatment of low-temperature freezing and ultrasonic waves according to claim 4, characterized in that, The cryogenic freezing time is 6 to 18 hours.

6. The anti-mildew process for bamboo material by synergistic treatment of low-temperature freezing and ultrasound according to claim 1, characterized in that, The power of the ultrasonic treatment is 900~1300 W.

7. The anti-mildew process for bamboo material by synergistic treatment of low-temperature freezing and ultrasound according to claim 1, characterized in that, The temperature of the ultrasonic treatment is 40~60℃.

8. The anti-mildew process for bamboo material by synergistic treatment of low-temperature freezing and ultrasonic waves according to claim 1, characterized in that, The bamboo material is bamboo with the outer green and inner yellow parts removed radially.

9. The anti-mildew process for bamboo material by synergistic treatment of low-temperature freezing and ultrasonic waves according to claim 1, characterized in that, The water immersion treatment involves soaking the bamboo in pure water until it sinks into the pure water.

10. The anti-mildew process for bamboo material by synergistic treatment of low-temperature freezing and ultrasound according to claim 1, characterized in that, The modified bamboo has a moisture content of 8-12%.

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