Large-size bamboo composite engineering material and preparation method and application thereof

Abstract

The application relates to the technical field of composite materials and engineering materials, in particular to a large-size bamboo composite engineering material and a preparation method and application thereof, which comprises a main body part and a reinforcing layer; the main body part is composed of a plurality of bamboo composite units through lateral gluing and / or longitudinal lengthening; the reinforcing layer is arranged at the bottom of the main body part; the reinforcing layer is composed of at least one end head defibration and recombination bamboo unit; the end head defibration and recombination bamboo unit is longitudinally spliced by a plurality of bamboo piece units, and the two ends of the bamboo piece unit are provided with defibration and recombination joints. The end head local defibration and recombination mode is adopted, the bamboo unit is infinitely lengthened, the problem that the material density is too large and the weight is too heavy caused by full defibration is avoided, the material light weight and high strength characteristics are ensured, and the balance between the mechanical properties and practicability is considered.

Description

Technical Field

[0001] This invention relates to the field of composite materials and engineering materials technology, specifically to a large-size bamboo composite engineered wood suitable for structural materials, and particularly to a large-size bamboo composite material whose bending strength is improved by setting a loosening and reorganizing joint in the tension layer, as well as its preparation method and application. Background Technology

[0002] Bamboo, as a fast-growing and high-strength biomass material, is an ideal raw material for building structural engineering. Processing bamboo into large-size engineering materials through flattening, modularization, splicing, and lamination is an important way to realize the high-value utilization of bamboo in building structures.

[0003] CN201810678239.2 discloses "A method for preparing seamless, infinitely extendable, directional reconstituted bamboo building materials." This technology processes the ends of unit bamboo boards into stepped lap joints, performs low-temperature plasma treatment, and then applies adhesive to achieve infinite extension of bamboo boards. The resulting product has high strength and hardness. The GB / T17657-2013 testing standard used in this scheme is mainly applicable to the evaluation of the basic physical and mechanical properties of small-sized specimens, and is difficult to truly reflect the mechanical behavior of materials as full-scale engineering components under actual stress. For structural materials such as large-span beams and columns, the performance data of small specimens cannot effectively predict practical problems such as complex stress distribution and amplified defect effects in full-scale components. CN202111283016.4 discloses "A large-scale bamboo integrated engineering material and its manufacturing method." This technology cuts finger tenons at both ends of bamboo strip units and extends them end to end, then assembles and hot-presses them into large-scale materials, realizing the longitudinal extension and large-scale utilization of bamboo. However, this method explicitly employs the traditional finger-jointing process. In practical applications, especially under bending conditions, finger-joint interfaces are often the location of stress concentration and the first point of failure, limiting the full realization of the material's overall mechanical properties. CN202010005222.8 discloses "A large-format high-strength weather-resistant bamboo-wood composite material and its manufacturing method." This technology combines impregnated bamboo curtain units with wood veneers through longitudinal continuous splicing and crisscrossing assembly, improving the material's lateral bonding strength and dimensional stability. Although this method is innovative in structural design, it does not address the reinforcement mechanism of the longitudinal splicing interface itself; the interface between bamboo curtain units remains a key constraint on the material's continuity and strength. CN221090155U discloses a reconstituted bamboo board, which achieves longitudinal splicing of bamboo bundles by loosening and overlapping the ends of all bamboo bundles and then hot-pressing them, thus producing large-size boards. However, this solution involves completely unbundling all units to solve the overall lengthening problem, which destroys the original texture and structural integrity of the bamboo strips / boards. At the same time, after all unbundling and repressing, the overall density is likely to increase significantly, making it impossible to achieve a lightweight and high-strength design based on the original bamboo structure.

[0004] In summary, while existing technologies have made progress in longitudinal splicing and structural composite applications of bamboo, they have all failed to effectively address the following core issues: First, the joint strength formed during the splicing process is significantly lower than that of the bamboo itself, becoming a weak point in large-sized components under stress. This results in the overall mechanical properties of the material (especially bending resistance) failing to meet the requirements for high-standard building structural materials. Second, the excessive thinning, full-bundle overlapping, or recombination processes adopted to achieve splicing destroy the natural fiber continuity and microstructure of the original bamboo, leading to a significant increase in material density and weight, and the loss of the inherent lightweight and high-strength characteristics of the original bamboo structure. In other words, existing technologies either sacrifice strength at the joint or sacrifice lightweight for splicing, failing to simultaneously achieve the dual goals of "high-strength splicing" and "low-density retention," thus limiting the potential for high-value and lightweight applications of bamboo in building structures. Summary of the Invention

[0005] To address the problems of low strength of finger joints and substandard bending performance in existing large-size bamboo laminated timber, this invention provides a large-size bamboo composite engineering material, its preparation method, and its application. This material has a reasonable structural design, excellent mechanical properties, and especially significantly improved bending strength.

[0006] A large-size bamboo composite engineering material includes a main body and a reinforcing layer; the main body is composed of multiple bamboo composite units formed by lateral gluing and / or longitudinal splicing; the reinforcing layer is disposed at the bottom of the main body, that is, the outermost layer that bears bending tensile stress in the service state; The reinforcing layer is composed of at least one end-reconstructed bamboo unit; the end-reconstructed bamboo unit is formed by longitudinally splicing multiple bamboo strip units, and the two ends of the bamboo strip unit have reconstructed joints.

[0007] Furthermore, the loosened and reconstituted joint is formed by loosening the ends of the bamboo strip unit to form a loose fiber structure, then impregnating it with adhesive, and then interleaving and reconstituted the end fibers of two adjacent bamboo strip units in the overlapping area and hot-pressing to form an enhanced overlapping structure with a fiber density higher than that of the bamboo strip unit body.

[0008] Furthermore, the length of the sparse treatment is 20-50 mm.

[0009] The bamboo strip unit is a flat bamboo veneer or a bamboo strip, preferably a flat bamboo veneer.

[0010] The main body is composed of a first composite unit and a second composite unit; the first composite unit is composed of two bamboo strip units with their yellow bamboo surfaces facing each other; the second composite unit is composed of two first composite units that have undergone a first four-sided planing process with their green bamboo surfaces facing each other, and a first buffer layer is set between them.

[0011] The main body is formed by joining multiple second composite units together through a comb-tooth finger joint structure, then laterally splicing and laminating them together, and a second buffer layer is provided between adjacent second composite units.

[0012] Wherein, the first buffer layer and / or the second buffer layer are wood veneers impregnated with phenolic resin.

[0013] The preparation method of the large-size bamboo composite engineering material of the present invention includes the following steps: Step 1: Preparation of end-capped reconstituted bamboo units: a. End thinning: Take a bamboo strip unit and mechanically thin it within a length range of 20-50mm from both ends; b. Impregnation: Impregnate the loosened ends with phenolic resin adhesive; the solid content of the phenolic resin adhesive is 30-35%, and the impregnation amount of the loosened part is controlled at 10-12%; c. Overlapping and reassembly: Overlap the loosened ends of two bamboo strip units along the length direction, so that the loose high-strength fiber bundles interweave and intertwine with each other; d. Curing and molding: Hot pressing is applied to the overlapping area to cure the phenolic resin and form a loosened and reconstituted joint; Step 2: Preparation of the main body: e. Glue the bamboo strip units together in pairs with the bamboo yellow side facing each other to obtain the first composite unit of "1+1"; f. Perform a first light four-sided planing on the first composite unit to remove the surface bamboo green layer; g. Two first composite units, which have been planed on all four sides, are placed with their bamboo green surfaces facing each other, and a wood veneer impregnated with phenolic resin is laid in the middle as a buffer layer. They are then glued together to obtain a "2+2" second composite unit. h. Perform a second light four-sided planing on the second composite unit; i. Multiple second composite units are joined together using a comb-tooth finger joint structure to obtain a long unit; j. Multiple long units are laterally spliced ​​and / or laminated and glued together, with the finger joints of adjacent long units in each layer staggered, and phenolic resin-impregnated wood veneer is laid between adjacent long units as a buffer layer to form the main body blank. Step 3: Overall Composite Processing At least one end-reconstituted bamboo unit obtained in step one is used as a reinforcing layer and attached to the bottom of the main body blank obtained in step two. The whole is then pressurized and composited to firmly bond them together to obtain the final product.

[0014] Compared with the prior art, the large-size bamboo composite engineering material of the present invention, its preparation method and application have at least the following beneficial effects: (1) This invention sets end-capped reconstituted bamboo units at the bottom layer under tension. Due to the removal of weak phase structures such as thin-walled cells in the bamboo during the capping process, the joints retain high-strength fiber bundles. After impregnation and reconstitution, the fiber density or bulk density reaches 1-2 times that of the bamboo itself, and the tensile strength exceeds that of the bamboo. This fundamentally solves the problem of traditional finger joints or lap joints being weak points, and significantly improves the bending resistance of large-sized materials.

[0015] (2) The present invention adopts the design concept of "local reinforcement", and uses end-to-end bamboo strip units for targeted reinforcement only in the outermost layer at the bottom where the bending tensile stress is the greatest. This method only performs local disassembly and recombination at the ends, which not only realizes the infinite extension of bamboo units, but also avoids the problems of excessive density and weight caused by overall disassembly and recombination, thus taking into account the dual requirements of lightweight and high strength.

[0016] (3) The loosening and recombining joint realizes the continuity and interweaving of high-strength bamboo fiber, which can more effectively transfer and disperse stress, avoid stress concentration, and improve the structural stability and reliability of the material.

[0017] (4) The present invention uses wood veneer impregnated with phenolic resin as a buffer layer, which not only buffers the stress between bamboo materials, but also forms a high-strength adhesive interface with bamboo materials, ensuring the integrity of the overall structure. Attached Figure Description

[0018] The accompanying drawings in this application are intended to supplement the textual description in the specification with graphics, and to further explain the technical solution of this application. They do not constitute an undue limitation on this application.

[0019] Figure 1 This is a structural schematic diagram of a large-size bamboo composite engineering material.

[0020] Figure 2 This is a photograph of the specimen during tensile failure, as shown in the example.

[0021] Figure 3 This is a photograph of the comparative specimen at the point of tensile failure.

[0022] Explanation of reference numerals in the attached drawings: 1-Buffer layer, 2-Comb-tooth finger joint structure, 3-Comb-tooth finger joint structure, 4-First composite unit, 5-Second composite unit, 6-Reinforcing layer, 7-Relaxation and reassembly joint. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, but the present invention is not limited thereto.

[0024] Example Combination Figure 1As shown, a specific method for preparing a large-size bamboo composite engineering material is as follows: Step 1: Prepare a flat bamboo veneer with dimensions of 1300mm in length, 130mm in width, and 13.5mm in thickness. Prepare a 2mm thick poplar veneer and impregnate it with phenolic resin at a resin content of 15%.

[0025] Step 2: Preparation of end-reconstructed bamboo units (reinforcing layer 6): a. Take a bamboo veneer, flatten it, and loosen it within a 40mm length range at both ends; b. Immerse the loosened end in a phenolic resin solution with a solid content of 30%, controlling the resin impregnation amount of the loosened part to be 12%; c. Overlap the loosened ends of the two processed bamboo veneers by 40mm to allow the loose high-strength fiber bundles to fully interweave; d. Place the overlapped bamboo strips into a hot press and press them at 140℃ and 3MPa for 15 minutes to cure the resin and form a continuous end-reconstructed bamboo unit. Then, follow the method in step c to extend one more bamboo flattening unit, extending the total length to approximately 3800mm.

[0026] Step 3: Preparation of the main body: a. Lay the two bamboo pieces flat with the yellow bamboo side facing each other, and apply 150g / m² of coating. 2 Phenolic resin, after assembly, is hot-pressed and cured to obtain the "1+1" first composite unit 4; b. Perform the first four-sided planing on the first composite unit 4, with a planing amount of about 0.5mm, to remove some of the bamboo green; c. Place the two planed first composite units 4 with their bamboo green surfaces facing each other, lay a layer of wood veneer impregnated with phenolic resin in the middle, apply glue, and then hot-press the assembled blanks to obtain the "2+2" second composite unit 5. d. Perform a second four-sided planing on the second composite unit 5, with a planing amount of approximately 0.5 mm, to make its dimensions regular; e. Machining comb teeth into the ends of 3 or 4 second composite units 5, with a tooth depth of 22.5 mm, a tooth tip thickness of 1.35 mm, and a tooth spacing of 5.6 mm, and then stretching them longitudinally after applying glue, forming long units through the comb tooth finger joint structure (2, 3); f. Multiple long units are laminated to form a blank, with the interfaces of adjacent layers staggered. Phenolic resin-impregnated wood veneer is laid between each layer as a buffer layer 1 to form the main blank.

[0027] Step 4: Overall Composite Processing a. Using the single-layer end-reconstructed bamboo unit (reinforcing layer 6) obtained in step two as the bottom layer, assemble it with the main body blank obtained in step three. Apply 150g / m² of coating to the bonding surface between the reinforcing layer and the main body.2 Resorcinol-formaldehyde resin; b. The entire billet is fed into a cold press. The cold pressing conditions are: temperature > 20℃, time > 6h, and pressure 2MPa. c. After cold pressing, the material undergoes aging, edge trimming, and sanding to obtain a finished product measuring 3800×125×125mm. The overall density of the material is measured to be 0.76g / cm³. 3 .

[0028] Full-scale mechanical property tests were conducted on the finished products according to the China Engineering Construction Standardization Association standard T / CECS10138-2021 "Engineering Bamboo Materials". The results showed that tensile failure of the specimens did not occur at any of the seven disintegration and reconstitution joints (e.g., Figure 2 As shown), the parallel bending strength is 85 MPa, the parallel bending modulus is 13100 MPa, the parallel tensile strength is 135 MPa, the parallel compressive strength is 79 MPa, the parallel shear strength is 9.0 MPa, and the transverse compressive strength is 28.8 MPa.

[0029] Comparative Example This comparative example illustrates the mechanical properties of bamboo composite engineering materials when using a traditional finger-joint structure without a layer of loosened and reconstituted bamboo unit reinforcement.

[0030] Similar to Example 1, except that in step four, the single-layer end-reconstructed bamboo unit (reinforcing layer) was not used as the bottom layer, the comparative example used the main body blanks for all blanks.

[0031] The entire blank was fed into a cold press under the following conditions: temperature > 20℃, time > 6 hours, and pressure 2 MPa. After cold pressing, the blank was left to rest, trimmed, and sanded to obtain a finished product measuring 3800×125×125 mm. The overall density of the material was measured to be 0.76 g / cm³. 3 .

[0032] Full-scale mechanical property tests were conducted on the finished products according to the China Engineering Construction Standardization Association standard T / CECS10138-2021 "Engineering Bamboo Materials". The results showed that tensile failure of the specimens occurred at the bottom finger joint interface (e.g., ...). Figure 3 As shown), the flexural strength parallel to the grain is 60.0 MPa, the flexural modulus parallel to the grain is 12500 MPa, the tensile strength parallel to the grain is 122 MPa, the compressive strength parallel to the grain is 75 MPa, the shear strength parallel to the grain is 8.2 MPa, and the compressive strength across the grain is 27.2 MPa.

[0033] A comparison of the test results from the examples and the comparative examples shows that: In the embodiment, the end-reconstruction joint of the present invention was used, and the failure of the specimen did not occur at the joint; in the comparative example, a traditional finger joint was used, and the failure of the specimen occurred at the finger joint interface.

[0034] The bending strength of the embodiment meets and exceeds the standard requirements, while the bending strength of the comparative embodiment is far below the standard requirements. This fully demonstrates that the present invention achieves a significant improvement in interface strength by loosening and recombining the joint, thus eliminating it as a weakness in the overall material performance.

[0035] The reconstituted joint of the present invention achieves the technical effect of "interface strength exceeding that of the parent material" by partially removing the weak phase structure, retaining the high-strength fiber bundles, and increasing the fiber density, fundamentally solving the long-standing problem of weak finger joints in the prior art.

[0036] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A large-size bamboo composite engineering material, characterized in that: It includes a main body and a reinforcing layer; the main body is composed of multiple bamboo composite units that are laterally glued and / or longitudinally extended; the reinforcing layer is located at the bottom of the main body, that is, the outermost layer that bears bending tensile stress in the use state; The reinforcing layer is composed of at least one end-reconstructed bamboo unit; the end-reconstructed bamboo unit is formed by longitudinally splicing multiple bamboo strip units, and the two ends of the bamboo strip unit have reconstructed joints.

2. The large-size bamboo composite engineering material according to claim 1, characterized in that: The loosened and recombined joint is formed by loosening the ends of the bamboo strip units to form a loose fiber structure, then impregnating them with adhesive, and then interleaving and recombining the end fibers of two adjacent bamboo strip units in the overlapping area and hot-pressing to form an enhanced overlapping structure with a fiber density higher than that of the bamboo strip unit body.

3. The large-size bamboo composite engineering material according to claim 2, characterized in that: The length of the scavenging process is 20-50 mm.

4. The large-size bamboo composite engineering material according to claim 1, characterized in that: The bamboo strip unit is a flat bamboo veneer or a bamboo strip.

5. The large-size bamboo composite engineering material according to claim 1, characterized in that: The main body is composed of a first composite unit and a second composite unit; the first composite unit is composed of two bamboo strip units with the yellow bamboo side facing each other; the second composite unit is composed of two first composite units that have undergone the first four-sided planing treatment with the green bamboo side facing each other, and a buffer layer is set between them.

6. The large-size bamboo composite engineering material according to claim 5, characterized in that: The main body is formed by joining multiple second composite units together through a comb-tooth finger joint structure, then laterally splicing and laminating them together, and a buffer layer is provided between adjacent second composite units.

7. The large-size bamboo composite engineering material according to claim 5 or 6, characterized in that, The buffer layer is a wood veneer impregnated with phenolic resin.

8. A method for preparing large-size bamboo composite engineering materials according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Preparation of end-capped reconstituted bamboo units: a. End thinning: Take a bamboo strip unit and mechanically thin it at both ends; b. Impregnation: Impregnate the loosened ends with phenolic resin adhesive; c. Overlapping and reassembly: Overlap the loosened ends of two bamboo strip units along the length direction, so that the loose high-strength fiber bundles interweave and intertwine with each other; d. Curing and molding: Hot pressing is applied to the overlapping area to cure the phenolic resin and form a loosened and reconstituted joint; Step 2: Preparation of the main body: e. Glue the bamboo strip units together in pairs with the bamboo yellow side facing each other to obtain the "1+1" first composite unit; f. Perform a first light four-sided planing on the first composite unit to remove the surface bamboo green layer; g. Two first composite units, which have been planed on all four sides, are placed with their bamboo green surfaces facing each other, and a wood veneer impregnated with phenolic resin is laid in the middle as a buffer layer. They are then glued together to obtain a "2+2" second composite unit. h. Perform a second light four-sided planing on the second composite unit; i. Multiple second composite units are joined together using a comb-tooth finger joint structure to obtain a long unit; j. Multiple long units are laterally spliced ​​and / or laminated and glued together, with the finger joints of adjacent long units in each layer staggered, and phenolic resin-impregnated wood veneer is laid between adjacent long units as a buffer layer to form the main body blank. Step 3: Overall Composite Processing At least one end-reconstituted bamboo unit obtained in step one is used as a reinforcing layer and attached to the bottom of the main body blank obtained in step two. The whole is then pressurized and composited to firmly bond them together to obtain the final product.

9. The method for preparing large-size bamboo composite engineering materials according to claim 8, characterized in that: In step one, the end thinning is a mechanical thinning process performed on both ends of the bamboo strip unit within a length range of 20-50mm.

10. The application of the high-performance large-size bamboo composite engineering material according to any one of claims 1-7 in building structures.

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