A method for modifying bamboo integrated material by piperidine nitroxide radical oxidation interface decoupling

Abstract

The application discloses a kind of piperidine nitrogen-oxygen free radical oxidation interface decoupling non-carbonization modified bamboo chips and its preparation high durability bamboo integrated material method, belong to bamboo processing technical field.The application is with primary processing bamboo chip as base material, after pretreatment, alkali delignification, PIPO selective oxidation interface decoupling, optional oxidation end-capping, densification by hot pressing is completed non-carbonization modification, all performance comparison is completed in bamboo chip dimension and natural bamboo chip, traditional carbonized bamboo chip, then modified bamboo chip is leveled, group blank, gluing, hot-pressing gluing, curing treatment preparation high durability bamboo integrated material.The modified bamboo chip of the application does not need high-temperature carbonization, zero strength loss, axial tensile strength ≥650MPa, bending strength 400~550MPa, compared with natural bamboo chip tensile strength is increased by more than 500%, compared with traditional carbonized bamboo chip tensile strength is increased by more than 490%, while water absorption is only 3%~5%, mildew grade 0 level, insect prevention rate ≥99%, durability surpasses natural bamboo chip and carbonized bamboo chip;Based on the integrated material prepared from the bamboo chip, static bending strength ≥180MPa, far superior to national standard special product standard.The process of the application is fully adapted to existing bamboo integrated material production line, simple operation, green and environment-friendly, low cost, modified bamboo chip can be widely used for preparing structural bamboo integrated material, solves the industry pain point of traditional bamboo chip carbonization sacrificing strength.

Description

Technical Field

[0001] This invention relates to the field of bamboo processing and bamboo laminated timber preparation technology, and in particular to a densification modification method for non-carbonized bamboo chips based on PIPO (TEMPO) oxidation interface decoupling, and a process for preparing high-mechanical-performance and high-durability bamboo laminated timber using the modified bamboo chips, which is applicable to the production of bamboo laminated timber in fields such as building structures, packaging and transportation, furniture manufacturing, and outdoor engineering. Background Technology

[0002] Bamboo laminated timber, as a new type of biomass engineering material, overcomes the shortcomings of natural bamboo, such as small diameter, easy cracking, and limited size, by gluing and splicing bamboo strips. It is an important green material to replace wood and steel. The performance of bamboo strips directly determines the final quality of bamboo laminated timber. Natural bamboo strips have three major defects: First, they are rich in hemicellulose, starch, and sugar, making them susceptible to microbial erosion and mold growth, as well as insect infestation. Second, their porous cellular structure and hydrophilic hydroxyl groups in cellulose result in high water absorption and swelling rates, making them prone to deformation and cracking. Third, the large interfacial constraints between cellulose molecules lead to low stress transfer efficiency and poor mechanical properties.

[0003] To improve the durability of natural bamboo strips, the industry mainstream adopts high-temperature carbonization treatment. However, this method comes at the cost of sacrificing the core mechanical properties of bamboo strips: high temperatures cause the cellulose crystal structure to be destroyed and the fibers to become brittle. The tensile strength of carbonized bamboo strips is only about 110 MPa, and the toughness drops to 4.8 MJ / m. 3 The bending strength is approximately 120 MPa, and it still suffers from high water absorption and limited effectiveness in preventing mold and insects. In short, traditional carbonized bamboo strips cannot meet the dual requirements of high strength, high toughness, and high durability for high-end structural bamboo strips, and the mechanical properties and durability of engineered wood products made from carbonized bamboo strips are also limited.

[0004] While existing modification technologies can improve the mechanical properties of bamboo, they have the following shortcomings: First, they do not conduct a systematic performance comparison at the bamboo strip level, and do not clearly define the performance improvement of modified bamboo strips; second, the modification process is not adapted to the production process of bamboo engineered wood, which involves "preliminary processing of bamboo strips → modification → gluing". Reprocessing block-shaped modified bamboo into bamboo strips will destroy the dense structure and lead to performance degradation; third, they do not solve the durability problems of modified bamboo strips, such as water resistance and mildew resistance, nor do they provide simple and efficient post-processing techniques.

[0005] In summary, existing bamboo strip modification technologies suffer from several core problems, including the sacrifice of mechanical properties by traditional carbonization, the lack of specific performance comparisons for modified bamboo strips, the inability to balance durability and mechanical properties, and incompatibility between modification processes and engineered wood production. There is an urgent need to develop a bamboo strip modification method that does not involve carbonization, results in zero strength loss, and offers high durability. Furthermore, it is crucial to clearly define the performance comparisons of modified bamboo strips with natural bamboo strips and traditionally carbonized bamboo strips at the bamboo strip level, and then to prepare high-performance bamboo engineered wood through an appropriate gluing process. Summary of the Invention

[0006] The purpose of this invention is to address the industry pain point of traditional bamboo carbonization, which sacrifices strength for durability. It provides a non-carbonized modified bamboo chip with PIPO (TEMPO) oxidation interface decoupling and a method for preparing high-durability bamboo laminated timber. The core of this invention is to address the durability defects of natural bamboo chips from the root through non-carbonization modification via "delignification-PIPO oxidation interface decoupling-hot pressing densification" after the initial processing of the bamboo chips. This simultaneously improves the mechanical properties of the bamboo chips. Finally, a suitable gluing process is used to prepare the modified bamboo chips into high-durability bamboo laminated timber.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing high-durability bamboo laminated timber using PIPO oxidation interface decoupling and non-carbonized modified bamboo chips includes six core steps: initial processing and pretreatment of bamboo chips, alkali delignification treatment, selective oxidation modification with PIPO, optional oxidation end-capping post-treatment, hot-pressing densification modification, and preparation of bamboo laminated timber from modified bamboo chips. The modification effects of each step on the bamboo chips are as follows:

[0009] (I) Bamboo strip primary processing and pretreatment: The raw bamboo is processed into regular bamboo strips. Light grinding, oil removal and low-temperature drying are used to ensure that the surface of the bamboo strips is clean and the moisture content is controllable, so as to provide a good reaction interface for subsequent chemical modification, while avoiding excessive processing that damages the fiber structure of the bamboo strips.

[0010] (II) Alkaline delignification treatment: A composite alkaline solution of NaOH and Na2SO3 is used for mild delignification to selectively remove hemicellulose, starch and sugar from bamboo strips with a removal rate of ≥95%. At the same time, the cellulose skeleton is exposed to provide reaction sites for PIPO oxidation, and the cellulose retention rate is guaranteed to be ≥90% without damaging the bamboo strip fiber structure.

[0011] (III) Selective oxidation modification of PIPO: Using the mild oxidation system of PIPO / NaBr / NaClO, carboxyl groups are selectively introduced at the C6 position of cellulose to achieve decoupling of the interface between cellulose molecules—weakening the ordered hydrogen bond network, enhancing the flexibility and rearrangement of cellulose chains, and laying the molecular foundation for subsequent hot pressing densification; at the same time, the oxidation modification destroys the active sites for microbial attachment, thereby improving the anti-mildew and anti-insect properties of bamboo strips from the root.

[0012] (iv) Post-oxidation end-capping treatment: Soak PIPO oxidized bamboo chips in dilute acetic acid at room temperature for 30 minutes to seal excess carboxyl groups on the surface of the bamboo chips, further reducing the hygroscopicity of the bamboo chips without damaging the bamboo chip structure or affecting subsequent gluing performance, so that the water resistance of the bamboo chips is comparable to or even surpasses that of carbonized bamboo chips.

[0013] (V) Hot-pressing densification modification: In response to the molecular chain characteristics of oxidized bamboo strips, medium-temperature and medium-pressure unidirectional hot pressing is used to achieve multi-scale dense rearrangement of bamboo strips, eliminate internal macroscopic pores and micro-nano defects, make the porosity <3%, allow cellulose fibers to be tightly packed, significantly improve the mechanical properties of bamboo strips, and at the same time solve the problems of water absorption, swelling, deformation and cracking of bamboo strips from the root.

[0014] (vi) Preparation of bamboo laminated timber from modified bamboo strips: Based on the surface characteristics of PIPO modified bamboo strips, water-based environmentally friendly adhesives are selected, and the amount of adhesive applied and the hot pressing bonding parameters are optimized to ensure the interlayer bonding strength of the modified bamboo strips. The high-performance modified bamboo strips are bonded into high-durability bamboo laminated timber with a uniform overall structure and no delamination.

[0015] The core performance comparison of the PIPO oxidative densification modified bamboo of this invention with natural bamboo chips and traditional carbonized bamboo chips is shown in Table 1.

[0016] The modified bamboo strips prepared by this invention have the following core advantages: 1. No high-temperature carbonization is required, resulting in zero strength loss, while their durability surpasses that of natural and carbonized bamboo strips; 2. The modification process is moved forward to after the initial processing of bamboo strips, fully following the traditional production process of bamboo engineered wood, without requiring significant modifications to existing production lines. The oxidation and end-capping post-processing is cost-free, easy to operate, and suitable for large-scale production; 3. The modification process uses an aqueous reaction system, with no harmful organic solvent emissions. Hot pressing and drying are both medium-low temperature processes, resulting in energy consumption far lower than high-temperature carbonization; 4. Oxidation modification only introduces carboxyl groups at the C6 position of cellulose, retaining certain hydrophilic active groups on the bamboo strip surface. This results in excellent compatibility with water-based adhesives. Combined with optimized bonding processes, the interlayer bonding strength of the modified bamboo strips can be guaranteed, achieving efficient transfer of bamboo strip properties to engineered wood. Detailed Implementation

[0017] To make the technical solution, process parameters and performance effects of bamboo strips of the present invention clearer, a detailed description is provided below with reference to specific embodiments. The scope of protection of the present invention is not limited to the following embodiments.

[0018] Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art; all raw materials and reagents used are commercially available analytical grade or industrial grade products, of which PIPO (TEMPO, 99%), NaBr (99%), and NaClO (10%) are conventional chemical reagents, and the adhesive is commercially available water-based phenolic resin adhesive.

[0019] Unless otherwise specified, the tests on the physical and mechanical properties, mildew and insect resistance, etc. of bamboo strips and engineered wood involved in this invention are all conducted in accordance with the national standard methods of GB 15780-2026 "Test Methods for Physical and Mechanical Properties of Bamboo", GB / T 40487-2021 "Structural Bamboo Engineered Wood", and GB / T 1741-2020 "Determination of Mildew Resistance of Paint Films". All performance tests of bamboo strips are completed under the same test conditions and on bamboo strips of the same specifications to ensure the objectivity of the comparison.

[0020] Example 1

[0021] This embodiment provides a method for preparing high-durability bamboo laminated timber using PIPO oxidized non-carbonized modified bamboo strips. The specific steps are as follows: (I) Initial processing and pretreatment of bamboo strips: Select 5-year-old moso bamboo and process it into regular bamboo strips with a thickness of 6mm, a width of 30mm, and a length of 1000mm; use 300-grit sandpaper to lightly grind both sides of the bamboo strips until the texture is uniform, remove burrs, repeatedly wipe the surface of the bamboo strips with anhydrous ethanol to remove oil stains, and then place them in a 55℃ oven to dry for 15 minutes. After drying, the moisture content of the bamboo strips is 10%, resulting in clean and dry substrate bamboo strips; (II) Alkali delignification treatment: Prepare 2.5M NaOH and 0.4M... A mixed alkaline solution of Na2SO3 was used to immerse the bamboo substrate in the solution at a bath ratio of 1:20. The solution was boiled for 8 hours, with stirring every hour to ensure uniform delignification. After treatment, the bamboo substrate was repeatedly rinsed with deionized water until the surface pH reached 7. It was then dried at 65℃ to constant weight to obtain delignified bamboo substrate. The removal rates of hemicellulose, starch, and sugar were 96%, and the cellulose retention rate was 92%. (III) Selective oxidation modification with PIPO (TEMPO): An oxidation system of TEMPO / NaBr / NaClO / delignified bamboo substrate was prepared at a mass ratio of 0.2:1.0:2.0:100. A 0.5M... The system was kept at pH 10 with NaOH and kept at 60°C for 12 hours in a drying oven without stirring to ensure the integrity of the bamboo chip structure. After oxidation, the bamboo chips were washed with deionized water until neutral and then vacuum dried at 40°C for 12 hours to obtain PIPO oxidized bamboo chips with a cellulose C6 carboxyl grafting rate of 1.3 mmol / g. S3-1: Post-oxidation end-capping treatment: PIPO oxidized bamboo chips were placed in a dilute acetic acid solution with pH 5.5 and soaked at room temperature (25°C) for 30 minutes. After soaking, the bamboo chips were washed with deionized water until neutral, and then vacuum dried at 40℃ for 6 hours to obtain end-capped oxidized bamboo chips with a surface carboxyl group sealing rate of 65% and a hygroscopicity reduced by 18% compared to unend-capped bamboo chips; (iv) hot-pressing densification modification: the end-capped oxidized bamboo chips were placed in a unidirectional hot press, the hot pressing pressure was set to 6.5MPa, the hot pressing temperature was 125℃, and the pressure was held for 24 hours. After hot pressing, the bamboo chips were allowed to cool naturally to room temperature before demolding to obtain PIPO oxidized densification modified bamboo chips with a density of 1.25g / cm³. 3Thickness shrinkage rate 25%, porosity 2.8%, no cracking or warping; (V) Modified bamboo strips were used to prepare bamboo laminated timber, with commercially available soybean protein glue as the adhesive, and the glue application amount was 200g / m 2 The modified bamboo strips were coated with adhesive on both sides. The coated modified bamboo strips were then assembled into 5 layers with the same grain direction, and the layers were aligned without misalignment. The assembled bamboo strips were placed in a hot press, with a bonding pressure of 3.5 MPa, a temperature of 90℃, and a holding pressure of 12 min / layer. After bonding, the bamboo laminated timber was cured in an environment with a temperature of 23℃ and a relative humidity of 50% for 8 days. After curing, the moisture content of the laminated timber was 10%, resulting in a 5-layer structure PIPO oxidized high-durability bamboo laminated timber.

[0022] Performance test results:

[0023] 1. Bamboo strip dimensions: The modified bamboo strips of this invention have an axial tensile strength of 661 MPa and a tensile toughness of 22 MJ / m. 3 The flexural strength is 480 MPa, flexural modulus is 48 GPa, water absorption is 4.2%, porosity is 2.8%, moisture swelling rate is 1.8%, mildew grade is 0, insect resistance is 99.2%, and there is no deformation or cracking; natural bamboo strips: axial tensile strength is 102 MPa, tensile toughness is 5.5 MJ / m 3 The flexural strength is 85 MPa, flexural modulus is 15 GPa, water absorption is 18%, porosity is 30%, moisture swelling rate is 12%, mildew grade is 3, and insect resistance is 75%; traditional carbonized bamboo strips have an axial tensile strength of 110 MPa and tensile toughness of 4.8 MJ / m. 3 Flexural strength 120MPa, flexural modulus 18GPa, water absorption 15%, porosity 15%, moisture expansion rate 10%, mildew grade 2, insect resistance 85%.

[0024] 2. Dimensions of engineered wood: The engineered wood prepared by the modified bamboo strips of this invention has the following properties: static bending strength of 190MPa, elastic modulus of 15.8GPa, bonding strength of 1.3MPa, water absorption rate of 4.5%, dimensional stability of 0.35%, and no warping, mildew, or delamination after being placed at room temperature and humidity for 6 months, which is far superior to the GB / T20241-2023 premium grade standard.

[0025] Example 2

[0026] The difference between this embodiment and Embodiment 1 is that the oxidation end-capping post-treatment in step S3-1 is omitted, while the remaining steps, process parameters and bamboo strip specifications are the same as in Embodiment 1.

[0027] Performance test results:

[0028] 1. Bamboo strip dimensions: The modified bamboo strips of this invention have an axial tensile strength of 658 MPa and a tensile toughness of 21.8 MJ / m. 3It has a bending strength of 475 MPa, a bending modulus of 47.5 GPa, a water absorption rate of 4.8%, a porosity of 2.9%, a moisture expansion rate of 2.0%, a mildew grade of 0, an insect resistance rate of 99%, and no deformation or cracking. Compared with natural bamboo strips, its tensile strength is increased by 545% and its toughness is increased by 296%. Compared with traditional carbonized bamboo strips, its tensile strength is increased by 498% and its toughness is increased by 354%.

[0029] 2. Dimensions of laminated timber: The laminated timber prepared by the modified bamboo strips of this invention has the following properties: static bending strength of 188MPa, elastic modulus of 15.5GPa, bonding strength of 1.28MPa, water absorption rate of 5.0%, and dimensional stability of 0.4%, which meet the national standard for premium grade products.

[0030] Example 3

[0031] The difference between this embodiment and Example 1 is as follows: (ii) the alkaline solution is 2.0M NaOH + 0.3M Na2SO3, boiled for 6 hours, with a bath ratio of 1:15; (iii) the oxidation temperature is 55℃, the oxidation time is 20 hours, and the carboxyl grafting rate is 1.2 mmol / g; (iv) the hot pressing pressure is 6.0 MPa, the hot pressing temperature is 120℃, and the pressure is maintained for 20 hours; the remaining steps and bamboo strip specifications are the same as in Example 1.

[0032] Performance test results:

[0033] 1. Bamboo strip dimensions: The modified bamboo strips of this invention have an axial tensile strength of 652 MPa and a tensile toughness of 20.5 MJ / m. 3 Flexural strength 420MPa, flexural modulus 45GPa, water absorption 4.5%, porosity 2.9%, moisture expansion rate 1.9%, mildew grade 0, insect resistance 99%.

[0034] 2. Dimensions of laminated timber: The laminated timber prepared by the modified bamboo strips of this invention has the following properties: static bending strength of 182MPa, elastic modulus of 15.0GPa, bonding strength of 1.25MPa, water absorption rate of 4.8%, and dimensional stability of 0.45%, which meet the national standard for premium grade products.

[0035] Comparative Example

[0036] All bamboo strip specifications and testing conditions for the comparative examples were consistent with those of Example 1 to ensure the objectivity of the bamboo strip dimensional comparison. The laminated timber preparation process was also consistent with that of Example 1.

[0037] Comparative Example 1: Natural Bamboo Strips

[0038] The bamboo strips from Example 1 (I) were used directly as test samples without any modification such as delignification, oxidation, or densification. Natural bamboo laminated timber was prepared directly from these natural bamboo strips using the process described in Example 1.

[0039] Performance test results:

[0040] 1. Bamboo strip dimensions: Axial tensile strength 102MPa, tensile toughness 5.5MJ / m 3 Flexural strength 85MPa, flexural modulus 15GPa, water absorption 18%, porosity 30%, moisture expansion rate 12%, mildew grade 3, insect resistance 75%, extremely prone to deformation and cracking.

[0041] 2. Dimensions of engineered wood: static bending strength 90MPa, elastic modulus 8.5GPa, bonding strength 1.1MPa, water absorption rate 17%, dimensional stability 2.5%, slight warping and mold growth appear after 1 month of storage.

[0042] Comparative Example 2: Delignified hot-pressed bamboo strips without PIPO oxidation

[0043] The difference from Example 1 is that the selective oxidation modification of PIPO in (iii) is omitted, and the delignified bamboo strips in (ii) are directly subjected to hot pressing densification in (iv) to obtain delignified hot-pressed bamboo strips, which are then used to prepare engineered wood.

[0044] Performance test results:

[0045] 1. Bamboo strip dimensions: Axial tensile strength 305MPa, tensile toughness 8.2MJ / m 3 The flexural strength is 150 MPa, flexural modulus is 22 GPa, water absorption rate is 8%, porosity is 8%, moisture swelling rate is 5%, mildew grade is 1, and insect resistance rate is 85%. Compared with the modified bamboo strips of Example 1 of this invention, the mechanical properties are significantly reduced, proving that the interface decoupling of PIPO oxidation is the core of the leapfrog improvement of the mechanical properties of bamboo strips.

[0046] 2. Dimensions of engineered wood: static bending strength 120MPa, elastic modulus 10.5GPa, bonding strength 1.15MPa, water absorption 7.5%.

[0047] Comparative Example 3: Modified block bamboo material was then processed into bamboo strips.

[0048] The difference from Example 1 is that: the bamboo is first processed into 80mm×18mm×6mm block bamboo material, and after modification by (II), (III), and (IV), it is processed into 6mm thick bamboo strips of the same specifications as in Example 1 to obtain modified bamboo strips, and at the same time, the bamboo strips are used to prepare engineered wood.

[0049] Performance test results:

[0050] 1. Bamboo strip dimensions: Axial tensile strength 280MPa, tensile toughness 7.8MJ / m 3 The flexural strength is 145 MPa, the flexural modulus is 20 GPa, the water absorption rate is 7.5%, and the porosity is 7%.

[0051] 2. Dimensions of engineered wood: static bending strength 115MPa, elastic modulus 10.0GPa, bonding strength 1.1MPa, performance is far lower than that of the product of this invention.

[0052] Comparative Example 4: Traditional High-Temperature Carbonized Bamboo Strips

[0053] The difference from Example 1 is that the modification processes (II), (III), and (IV) are omitted. The bamboo substrate of (I) is placed in a carbonization furnace and carbonized at 200°C for 4 hours using the industry's conventional process to obtain traditional carbonized bamboo. At the same time, the carbonized bamboo is used to prepare traditional carbonized bamboo laminated timber according to the process of Example 1.

[0054] Performance test results:

[0055] 1. Bamboo strip dimensions: Axial tensile strength 110MPa, tensile toughness 4.8MJ / m 3 The flexural strength is 120 MPa, the flexural modulus is 18 GPa, the water absorption rate is 15%, the porosity is 15%, the moisture swelling rate is 10%, the mildew grade is 2, the insect resistance rate is 85%, it is easy to deform and crack, and the bamboo strips are brittle; compared with the modified bamboo strips of Example 1 of this invention, the tensile strength is only 16.6% and the toughness is only 21.8%.

[0056] 2. Dimensions of engineered wood: static bending strength 120MPa, elastic modulus 9.5GPa, bonding strength 1.0MPa, water absorption 14%, dimensional stability 1.8%.

[0057] Test case

[0058] A comprehensive performance comparison test was conducted on the PIPO oxidative densification modified bamboo strips, natural bamboo strips, and traditional carbonized bamboo strips prepared in Example 1 of this invention. A comparative test was also conducted on the laminated timber prepared from the three types of bamboo strips. All tests followed national standard methods, and the results are shown in Table 2. Attached Figure Description

[0059] Figure 1 A schematic diagram of the process flow for PIPO oxidative modification of bamboo chips; it sequentially shows the entire process of natural bamboo chips undergoing pretreatment, alkaline delignification, PIPO catalytic oxidation, oxidative end-capping, and hot-pressing densification to obtain modified bamboo chips, which are then glued together to prepare bamboo laminated timber. The diagram clearly presents the material changes and core reagent system in each process step.

[0060] Figure 2 A schematic diagram of the PIPO (TEMPO) catalytic oxidation cycle mechanism is presented, demonstrating the catalytic cycle process of piperidine nitric oxide radical → ammonium oxycation → hydroxypiperidine, as well as the selective conversion reaction of the primary hydroxyl group at the C6 position of cellulose to the carboxyl group, clarifying the molecular mechanism of oxidative modification.

[0061] Figure 3: Schematic diagram of multi-scale structural changes inside bamboo strips; compare the internal structures of natural bamboo strips, delignified bamboo strips, PIPO oxidized bamboo strips, and hot-pressed densified modified bamboo strips to show the evolution from a porous and loose structure to a dense and ordered structure, as well as the rearrangement and porosity elimination process of cellulose microfibrils.

[0062] Table 1 Comparison of properties of different bamboo strips Axial tensile strength (MPa) 102 110 ≥650 <![CDATA[tensile toughness (MJ / m 3 )]]> 5.5 4.8 ≥20 Bending strength (MPa) 85 120 400～550 Flexural modulus (GPa) 15 18 ≥45 Water absorption rate (%) 18 12-18 3～5 Porosity (%) 30 15 ＜3 Moisture swelling rate (%) 12 8-12 1～2 Mold level Level 3 Level 2-3 Level 0 Insect control rate (%) 75 85 ≥99 Deformation and cracking characteristics Extremely easy easy Almost none

[0063] Table 2 Comparison of Core Performance Aspects of Laminated Materials

Claims

1. A method for modifying bamboo by decoupling the interface of piperidine nitroxide radical (PIPO) oxidation, characterized in that, Using pre-processed bamboo strips as the substrate, interface decoupling and densification modification are performed without high-temperature carbonization. The modified bamboo strips are then glued together to prepare bamboo laminated timber, including the following steps: (I) Bamboo strip primary processing and pretreatment: raw bamboo is processed into regular bamboo strips, and after surface treatment, clean and dry modified base material bamboo strips are obtained. (ii) Alkaline delignification treatment: The bamboo substrate from step S1 is placed in an alkaline delignification system to remove non-carrying components such as hemicellulose, starch, and sugar, exposing the cellulose skeleton. After washing and drying, delignified bamboo chips are obtained. (III) Selective oxidation modification of PIPO: The delignified bamboo chips from step S2 are placed in the PIPO / NaBr / NaClO oxidation system for carboxylation modification to achieve decoupling of the interface between cellulose molecules. After washing and drying, PIPO oxidized bamboo chips are obtained. S3-1: Oxidation end-capping post-treatment: The PIPO oxidized bamboo chips from step S3 are immersed in dilute acetic acid solution at room temperature to seal the surface carboxyl groups. After washing and drying, end-capped oxidized bamboo chips are obtained. (iv) Hot pressing densification modification: The PIPO oxidized bamboo strips of step S3 or the end-capped oxidized bamboo strips of step S3-1 are subjected to hot pressing densification treatment to achieve multi-scale structural densification rearrangement of bamboo strips and obtain PIPO oxidized densification modified bamboo strips. (V) Modified bamboo strips are used to prepare bamboo laminated timber. The modified bamboo strips from step S4 are leveled, assembled, glued, hot-pressed and cured to obtain PIPO oxidized and densified bamboo laminated timber with high mechanical properties and high durability.

2. The method according to claim 1, characterized in that... (i) The raw bamboo is 3-5 year old moso bamboo, which is initially processed into bamboo strips with a thickness of 5-8 mm, a width of 20-50 mm, and a length to be cut as needed; the surface treatment is to lightly sand both sides of the bamboo strips with 200-400 grit sandpaper until the texture is uniform, remove burrs and surface scum, wipe off oil stains with anhydrous ethanol, and then dry at 50-60℃ for 10-20 minutes. After drying, the moisture content of the bamboo strips is controlled at 8%-12%.

3. The method according to claim 1, characterized in that... (ii) The alkaline delignification system is a mixed aqueous solution of 2.0-2.5M NaOH and 0.3-0.4M Na2SO3, and the ratio of bamboo chips to alkaline solution is 1:15-1:

20. The treatment method is to boil for 6-8 hours, stirring once every 1 hour to ensure uniform delignification. After treatment, the bamboo chips are repeatedly rinsed with deionized water until the pH of the bamboo chip surface is 7-8, and dried at 60-70℃ to constant weight. The cellulose retention rate of the delignified bamboo chips is ≥90%, and the removal rate of hemicellulose, starch and sugar is ≥95%.

4. The method according to claim 1, characterized in that... (III) In this process, the PIPO is a piperidine nitrogen-oxygen radical catalyst, preferably TEMPO (2,2,6,6-tetramethylpiperidine-1-oxygen radical); in the PIPO / NaBr / NaClO oxidation system, the mass ratio of PIPO, NaBr, NaClO to delignified bamboo chips is 0.2∶1.0∶2.0∶100; during the oxidation treatment, 0.5M NaOH is used to continuously maintain the pH of the system at 9.5~10.5, the treatment temperature is 55~60℃, and the treatment time is constant at 12h in the drying oven, without stirring throughout to ensure the structural integrity of the bamboo chips; after oxidation, the chips are washed with deionized water until neutral, and then vacuum dried at 40~45℃ for 12~16h, resulting in oxidized bamboo chips with a C6 carboxyl grafting rate of cellulose ≥1.2mmol / g.

5. The method according to claim 1, characterized in that, In S3-1, the pH of the dilute acetic acid solution is 5-6, the soaking temperature is room temperature (20-30℃), and the soaking time is 30 min. After soaking, it is washed with deionized water until neutral, and then vacuum dried at 40-45℃ for 6-8 h. After end-sealing, the carboxyl group sealing rate on the surface of the bamboo strip is ≥60%, and the hygroscopicity is further reduced by 15-20% compared with the unsealed bamboo strip. It does not damage the bamboo strip structure and does not affect the subsequent gluing performance.

6. The method according to claim 1, characterized in that... In step (iv), the hot-pressing densification treatment is a unidirectional hot-pressing process, with a hot-pressing pressure of 6.0–6.5 MPa, a hot-pressing temperature of 120–130 °C, and a holding time of 20–24 h. After hot pressing, the material is allowed to cool naturally to room temperature before demolding; the resulting modified bamboo strips have a density ≥1.2 g / cm³. 3 Thickness shrinkage rate is 20% to 30%, porosity is <3%, and there is no cracking or warping.

7. The method according to claim 1, characterized in that... (v) In the process of applying the adhesive, the adhesive used is one of soybean protein glue, water-based phenolic resin glue, or bamboo-derived bio-glue, and the amount of adhesive applied is 180-220 g / m³. 2 The gluing method is double-sided gluing; the assembly is to assemble modified bamboo strips with the same or staggered grain, the number of layers is set as needed, and the layers are aligned without misalignment; the hot-pressing bonding process parameters are pressure 3.0~4.0MPa, temperature 80~100℃, and holding time 10~15min / layer; the curing treatment is to place the glued bamboo laminated timber in an environment with a temperature of 20~25℃ and a relative humidity of 40%~60% for 7~10 days, and the moisture content of the laminated timber is controlled at 8%~12% after curing.

8. PIPO oxidative densification non-carbonization modified bamboo strips prepared by the method according to any one of claims 1 to 7.

9. The modified bamboo strip according to claim 8, characterized in that, The modified bamboo strips have an axial tensile strength ≥650MPa and a tensile toughness ≥20MJ / m. 3 The flexural strength is 400-550 MPa, and the flexural modulus is ≥45 GPa. Compared with natural bamboo strips, the tensile strength is increased by more than 500% and the toughness is increased by more than 300%. Compared with traditional carbonized bamboo strips, the tensile strength is increased by more than 490% and the toughness is increased by more than 500%. The modified bamboo strips have a water absorption rate of 3%-5%, a mold grade of 0 (no mold), an insect resistance rate of ≥99%, a porosity of <3%, a moisture swelling rate of ≈1-2%, and almost no deformation or cracking.

10. PIPO oxidized densified high-durability bamboo laminated timber prepared by the method according to any one of claims 1 to 7.

11. The bamboo laminated timber according to claim 10, characterized in that, The bamboo laminated timber has a static bending strength ≥180MPa, an elastic modulus ≥15GPa, and a bonding strength ≥1.2MPa, all of which are superior to the GB / T 40487-2021 "Structural Bamboo Laminated Timber" premium grade standard. Compared with natural bamboo laminated timber, the static bending strength is increased by more than 100%, and compared with traditional carbonized bamboo laminated timber, the static bending strength is increased by more than 50%. The laminated timber has a uniform overall structure, without delamination, bubbling, or cracking. The water absorption rate is 3% to 5%. After being placed in a normal temperature and humidity environment for 6 months, the dimensional stability is ≤0.5%, with no warping or deformation, and the mildew grade is 0.

12. The modification method proposed in this patent is applicable to various engineering bamboo materials processed from bamboo units, including bamboo laminated timber and bamboo reconstituted timber.

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