Surface modified bamboo nail as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of wood processing, and relates to a surface modified bamboo nail and a preparation method and application thereof. In the prior art, bamboo nails are easy to break and split when being pneumatically injected into wood, and the injection performance is poor; in order to solve the technical problems of insufficient connection stability after injection, rapid reduction of pulling resistance due to great environmental influence and serious influence on use durability in the prior art, the invention provides a surface modified bamboo nail which comprises a bamboo nail base body, the composite coating is formed by compounding waterborne polyurethane and intercalated zirconium phosphate nanosheets, the intercalated zirconium phosphate nanosheets are evenly dispersed in the waterborne polyurethane according to the mass fraction of 3%-5%, the surface of the bamboo nail base body is evenly covered with the coating, and the thickness ranges from 35 micrometers to 40 micrometers; the overall density of the surface modified bamboo nail ranges from 0.87 g / cm < 3 > to 0.95 g / cm < 3 >, the surface modified bamboo nail is distributed in a step-shaped decreasing mode from the surface layer to the interior, the injection performance is excellent, and connection is stable. Furthermore, the invention further provides a preparation method of the surface modified bamboo nail. Meanwhile, the invention further provides application of the surface modified bamboo nail.

Description

Technical Field

[0001] The invention belongs to the technical field of wood processing, and in particular relates to a surface-modified bamboo nail and a preparation method and application thereof. Background Art

[0002] A pneumatic coil nail gun is a highly efficient fastening tool. Its core driving mechanism relies on compressed air pushing a piston, accelerating the nail within the barrel and achieving a high initial velocity, enabling rapid penetration into the wood. During penetration, part of the nail's kinetic energy is converted into work to overcome the wood's resistance to penetration, while part is dissipated through the wood's elastic deformation and frictional heat generation. As the nail penetrates deeper into the wood, the contact area increases, significantly increasing dynamic friction and becoming the primary factor in the nail's deceleration. Ultimately, the nail's penetration depth is determined by the dynamic balance between the initial kinetic energy and frictional resistance.

[0003] However, the frictional properties between nails and wood directly affect penetration efficiency and fixation stability: Dynamic friction determines the penetration depth and speed of the nail; excessive frictional resistance can lead to incomplete penetration or nail jamming. Static friction, on the other hand, determines the pull-out resistance after the nail is fixed, affecting the long-term stability of the connection. There is a conflict between these two: lower dynamic friction facilitates penetration but may reduce clamping force; higher static friction, while enhancing fixation, may increase penetration resistance, affecting construction efficiency.

[0004] At present, pneumatic nail guns mainly use metal nails (such as carbon steel and stainless steel). Although their strength and rigidity meet the requirements, the following problems still exist: corrosion problem: metal nails are prone to rust in a humid environment, resulting in loose connections or deterioration of wood; thermal bridge effect: the high thermal conductivity of metal affects the insulation performance of buildings; environmental burden: metal nails are non-degradable and do not conform to the trend of green building and sustainable development.

[0005] As a renewable, degradable and environmentally friendly material, bamboo nails have the potential to replace metal nails. However, the mechanical properties and tribological behavior of natural bamboo make it challenging in pneumatic injection applications. The Chinese invention patent application publication number is CN113681669A, and the application date is July 27, 2021. The name is: Bamboo gun nails and their production method. The disclosed bamboo gun nails are made of multiple bamboo nails of equal thickness and width bonded in parallel in a row. The nail heads of the bamboo nails are polygonal wedge-shaped or conical, and the nail bodies of two adjacent bamboo nails are separated by adhesive. The nail tail thickness of the bamboo nail is greater than the nail body thickness, and they are square or rectangular respectively. The bamboo nails are a layered structure with a reinforcement layer and a thin bamboo sheet layer separated one by one. Although this solution has made certain improvements to bamboo nails, it still has the following shortcomings: the friction coefficient is high, and the roughness of bamboo fibers may increase the injection resistance and affect the penetration depth; the bending strength is insufficient, and bamboo nails are easily broken under high-speed impact, resulting in nailing failure; the moisture content affects stability, and bamboo may expand or contract after absorbing moisture, affecting the fixation reliability.

[0006] In summary, how to balance the injection performance (low dynamic friction) and fixing stability (high static friction) of bamboo nails; how to improve the impact resistance of bamboo nails through surface modification to avoid breakage during pneumatic injection; and how to optimize the moisture content and density distribution of bamboo nails to ensure long-term stability in different environments are problems that need to be solved urgently in existing technologies. Summary of the Invention

[0007] 1. Technical problem to be solved by the invention

[0008] In order to solve the technical problems that bamboo nails in the prior art are prone to breaking and splitting when pneumatically injected into wood, and have poor injection performance; the connection stability is insufficient after injection, and the pull-out resistance is greatly affected by the environment and rapidly decreases, which seriously affects the durability of use, the present application provides a surface-modified bamboo nail with excellent injection performance and stable connection. Furthermore, the present invention also provides a method for preparing the surface-modified bamboo nail; at the same time, the present invention also provides the application of the surface-modified bamboo nail.

[0009] 2. Technical solution

[0010] In order to achieve the above objectives, the technical solutions provided are:

[0011] Based on the purpose of the present invention, the first aspect of the present invention provides a surface-modified bamboo nail, wherein the surface-modified bamboo nail comprises:

[0012] Bamboo nail base;

[0013] A composite coating, wherein the composite coating is composed of a waterborne polyurethane and intercalated zirconium phosphate nanosheets, wherein the intercalated zirconium phosphate nanosheets are uniformly dispersed in the waterborne polyurethane at a mass fraction of 3% to 5%, and the composite coating is uniformly covered on the surface of the bamboo nail substrate; the composite coating has a thickness of 35 μm to 40 μm;

[0014] The overall density of the surface modified bamboo nail is 0.87 g / cm 3 ~0.95g / cm 3 , and the distribution decreases in a stepped manner from the surface to the inside.

[0015] Preferably, the diameter of the surface modified bamboo nail is 3.5 mm.

[0016] According to any embodiment of the first aspect of the present invention, the surface-modified bamboo nail has a taper angle of 35° to 45°, and the tip is flush with the center of the original bamboo node.

[0017] The taper angle refers to the total angle formed by the inclined surfaces on both sides of the tip of the bamboo nail.

[0018] According to the surface-modified bamboo nail of any embodiment of the first aspect of the present invention, the surface thin-walled cells of the bamboo nail matrix are removed and the bamboo fibers are exposed.

[0019] Based on the purpose of the present invention, the second aspect of the present invention provides a method for preparing a surface-modified bamboo nail, comprising the following steps:

[0020] Preparation of composite coating: Disperse intercalated zirconium phosphate nanosheets in aqueous polyurethane at a mass fraction of 3% to 5%, stir at room temperature, and ultrasonically treat to obtain a composite coating;

[0021] Composite coating loading: spraying the composite coating onto the surface of the bamboo nail substrate at a pressure of 0.4 MPa to 0.6 MPa; after each spraying, pressurizing and twisting the bamboo nail; repeating the spraying and pressurizing and rolling several times;

[0022] Post-treatment: drying to form a uniform coating with a thickness of 35 μm to 40 μm on the surface of the bamboo nail substrate to obtain the surface-modified bamboo nail;

[0023] The overall density of the surface modified bamboo nail is 0.87 g / cm 3 ~0.95g / cm 3 , and the distribution decreases in a stepped manner from the surface to the inside.

[0024] Preferably, in the step of preparing the composite coating, the stirring time at room temperature is 1.5 h to 2.5 h, more preferably 2 h; and the ultrasonic treatment time is 25 min to 30 min, more preferably 30 min.

[0025] Preferably, in the post-treatment, the drying time is 12 hours.

[0026] According to the preparation method of any embodiment of the second aspect of the present invention, in the composite coating loading step, after each spraying, the bamboo nail is pressurized and twisted and rolled at 55°C to 65°C, with a pressure of 1MPa to 1.5MPa, a rolling speed of 1 to 3 revolutions per second, and dried for 5min to 15min; the spraying and pressurizing and rolling are repeated 2 to 4 times.

[0027] According to the method for preparing the surface-modified bamboo nails of any embodiment of the second aspect of the present invention, the preparation process of the intercalated zirconium phosphate nanosheets is as follows:

[0028] Zirconium oxychloride octahydrate was dissolved in 3 mol / L phosphoric acid solution, refluxed at 100°C for 48 hours, washed, centrifuged, dried and then ground to obtain α-zirconium phosphate particles;

[0029] The α-zirconium phosphate particles and tetrabutylammonium hydroxide were mixed in a molar ratio of 1:1, ultrasonically dispersed for 30 minutes, and stirred for 6 hours to obtain the intercalated zirconium phosphate nanosheets.

[0030] According to the method for preparing a surface-modified bamboo nail according to any embodiment of the second aspect of the present invention, the diameter of the α-zirconium phosphate particles is 500 nm to 600 nm.

[0031] According to the method for preparing the surface-modified bamboo nails of any embodiment of the second aspect of the present invention, the synthesis of the waterborne polyurethane comprises:

[0032] After dehydration, polycaprolactone diol was reacted with isophorone diisocyanate and catalyst dibutyltin dilaurate at 80°C for 3 hours;

[0033] Dimethylol propionic acid was added for chain extension, and the mixture was emulsified after neutralization and then chain extended for the second time with ethylenediamine to obtain a waterborne polyurethane emulsion with a solid content of 30%.

[0034] Preferably, 20.0 g of polycaprolactone diol (Mn≈2000 g / moL) is added to a three-necked flask equipped with a thermometer, an electric stirring rod and a reflux condenser, and heated to 110° C. and kept warm for 2 h to remove moisture.

[0035] According to 40% hard segment content (mass fraction), 13.3 g of isophorone diisocyanate (IPDI) and 0.05 g of dibutyltin dilaurate (DBTDL) were added as catalysts and reacted at 80° C. for 3 h to generate an isocyanate-terminated prepolymer.

[0036] Subsequently, 2.7 g of dimethylolpropionic acid (DMPA) was added and the reaction was continued at 80° C. The consumption of NCO groups was monitored by dibutylamine titration until its content was lower than the theoretical value, indicating that the reaction was completed, and a waterborne polyurethane prepolymer with a hydrophilic segment was obtained.

[0037] To reduce the viscosity, 5 mL of acetone was added and the system was cooled to 50° C. Then, 1.8 g of triethylamine (TEA) was added to neutralize the carboxylic acid groups in DMPA, and the reaction was continued for 30 min.

[0038] 50g of deionized water was then quickly added, and the mixture was emulsified and dispersed under high shear. 1.2g of ethylenediamine (EDA) was then added dropwise for chain extension, and stirring was continued for 1 hour. Finally, the acetone was removed by vacuum distillation at 40°C to obtain a water-based polyurethane emulsion with a solids content of approximately 30%.

[0039] According to the method for preparing a surface-modified bamboo nail according to any embodiment of the second aspect of the present invention, the preparation process of the bamboo nail substrate is as follows:

[0040] Planing the outer green layer and inner yellow layer of the bamboo, processing them into a tapered angle of 35° to 45°, so that the tip of the bamboo nail is flush with the center of the original bamboo node, and obtaining the planed bamboo;

[0041] The surface of the planed bamboo is sandblasted by using silicon carbide abrasive with a particle size of 240, a sandblasting pressure of 0.4 MPa, a height of 10 cm, an angle of 90 degrees, and a treatment time of 10 s to 20 s, to obtain the sandblasted bamboo;

[0042] The sandblasted bamboo is dried after cleaning, to obtain the bamboo nail base.

[0043] Preferably, the outer green layer and the inner yellow layer of the bamboo are each planed by 1 mm; and the bamboo is sequentially cleaned by ultrasonic cleaning with deionized water and anhydrous ethanol for 5 min at 60 DEG C.

[0044] Based on the purpose of the present application, the third aspect of the present application provides an application of the surface-modified bamboo nail, wherein the surface-modified bamboo nail or the surface-modified bamboo nail prepared by the method is applied to the manufacture of a pneumatic nail reel.

[0045] Any embodiment of any aspect of the present application can be combined with other embodiments without contradiction. In addition, any technical feature in any embodiment of any aspect of the present application can be applied to the technical feature in other embodiments without contradiction.

[0046] Any technical feature possessed by any aspect of the present application or any embodiment of the aspect is also applicable to other embodiments or other aspects without contradiction, and of course, the corresponding features can be appropriately modified when applicable to each other. The various aspects and features of the present application are further described below.

[0047] 3. Beneficial effects

[0048] Compared with the prior art, the technical solution provided by the present application has the following beneficial effects:

[0049] (1) The surface-modified bamboo nail prepared by the method of the present application has a significantly reduced surface friction coefficient (from 0.57 to 0.27-0.31), making the bamboo nail easier to shoot into wood; the indentation hardness is increased by more than 31% (from 4312 N to 5639 N-5834 N), effectively preventing breakage and splitting when shooting; a stepped density distribution of 0.87 g / cm 3 -0.95 g / cm 3 is formed, the high-density structure of the outer layer ensures the pullout resistance (more than 1500 N), while the internal moderate flexibility avoids brittle fracture; the fiber distribution of the tip of the bamboo nail is optimized after special treatment, and the cracking rate is reduced when shooting; the pullout resistance retention rate is high after the dry-wet cycle test, and the environmental stability is significantly improved.

[0050] (2) The preparation method of the surface-modified bamboo nail of the present invention: sandblasting (0.4MPa, 10s-20s) accurately removes thin-walled cells, thereby simultaneously improving the surface hardness and enhancing the coating adhesion; zirconium phosphate intercalation modification (3%-5% by mass) is compounded with waterborne polyurethane to form a uniform dispersion system under room temperature stirring and ultrasonic action; a pressurized rolling process (1MPa-1.5MPa, 60°C) accurately controls the coating thickness to 35μm-40μm, while constructing a gradient density structure; bamboo node alignment processing (tapering angle 35°-45°) and step-by-step drying (60°C, 12h) synergistically ensure the optimization of fiber orientation. The entire set of process parameters are controllable.

[0051] (3) Application of the surface-modified bamboo nails of the present invention: The surface-modified bamboo nails are used to prepare air gun nails, and the success rate of shooting into 20 mm radiata pine is greatly improved compared with the unmodified ones; the shooting depth under the same air pressure is increased, and there is no splitting phenomenon; the pull-out resistance is improved compared with the unmodified bamboo nails, reaching 1509N~-1587N; when used in a humid environment, the connection performance attenuation rate is reduced, which is far better than that of metal nails. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0053] Example 1

[0054] The preparation method of the surface-modified bamboo nail of this embodiment comprises the following steps:

[0055] S1. Preparation of bamboo nail substrate: planing the outer green layer and inner yellow layer of bamboo 1mm each, processed into a sharp angle of 40 °, so that the tip of the bamboo nail is flush with the center of the original bamboo node, to obtain bamboo after planing;

[0056] The surface of the planed bamboo was sandblasted using silicon carbide abrasive with a particle size of 240 at a pressure of 0.4 MPa, a height of 10 cm, an angle of 90°, and a treatment time of 10 seconds to obtain sandblasted bamboo.

[0057] The bamboo after sandblasting was cleaned with deionized water and anhydrous ethanol in sequence for 5 minutes by ultrasonic cleaning, and air-dried at 60° C. to obtain the bamboo nail matrix.

[0058] S2. Preparation of intercalated zirconium phosphate nanosheets: zirconium oxychloride octahydrate was dissolved in 3 mol / L phosphoric acid solution, refluxed at 100 ° C for 48h, washed, centrifuged, dried and ground to obtain α-zirconium phosphate particles, the α-zirconium phosphate particles having a diameter of 500nm to 600nm;

[0059] The α-zirconium phosphate particles and tetrabutylammonium hydroxide were mixed in a molar ratio of 1:1, ultrasonically dispersed for 30 minutes, and stirred for 6 hours to obtain the intercalated zirconium phosphate nanosheets.

[0060] S3. Preparation of waterborne polyurethane: 20.0 g of polycaprolactone diol (Mn≈2000 g / moL) was added to a three-necked flask equipped with a thermometer, an electric stirring rod and a reflux condenser, and heated to 110° C. and kept warm for 2 h to remove moisture.

[0061] According to 40% hard segment content (mass fraction), 13.3 g of isophorone diisocyanate (IPDI) and 0.05 g of dibutyltin dilaurate (DBTDL) were added as catalysts and reacted at 80° C. for 3 h to generate an isocyanate-terminated prepolymer.

[0062] Subsequently, 2.7 g of dimethylolpropionic acid (DMPA) was added and the reaction was continued at 80° C. The consumption of NCO groups was monitored by dibutylamine titration until its content was lower than the theoretical value, indicating that the reaction was completed, and a waterborne polyurethane prepolymer with a hydrophilic segment was obtained.

[0063] To reduce the viscosity, 5 mL of acetone was added and the system was cooled to 50° C. Then, 1.8 g of triethylamine (TEA) was added to neutralize the carboxylic acid groups in DMPA, and the reaction was continued for 30 min.

[0064] 50g of deionized water was then quickly added, and the mixture was emulsified and dispersed under high shear. 1.2g of ethylenediamine (EDA) was then added dropwise for chain extension, and stirring was continued for 1 hour. Finally, the acetone was removed by vacuum distillation at 40°C to obtain a water-based polyurethane emulsion with a solids content of approximately 30%.

[0065] S4. Preparation of composite coating: Disperse intercalated zirconium phosphate nanosheets in aqueous polyurethane at a mass fraction of 3%, stir at room temperature for 2 h, and ultrasonically treat for 30 min to obtain a composite coating.

[0066] S5. Composite coating loading: The composite coating was sprayed on the surface of the bamboo nail substrate at a pressure of 0.5 MPa; after each spraying, the bamboo nail was pressurized and twisted and rolled dry at 60°C and 1 MPa (2 rpm, 10 min); the spraying and pressurized rolling were repeated twice.

[0067] S6. Post-treatment: Drying for 12 hours to obtain the surface-modified bamboo nail.

[0068] The surface-modified bamboo nail prepared in this example has a coating thickness of 36.1 μm and an overall density of 0.87 g / cm 3, indentation hardness 5639N (increased by 31%), surface friction coefficient 0.29 (original 0.57), pull-out strength 1509N (maintained above 1500N after dry-wet cycles).

[0069] Example 2

[0070] The preparation method of the surface-modified bamboo nail of this embodiment is basically the same as that of Example 1, except that the addition amount of the intercalated zirconium phosphate is 5%, the spraying is performed 4 times, and the rolling pressure is 1 MPa.

[0071] The surface modified bamboo nail prepared in this example has a coating thickness of 39.6 μm and an overall density of 0.94 g / cm 3 , indentation hardness 5834N, friction coefficient 0.31, pull-out strength 1535N (maintained above 1500N after dry-wet cycles).

[0072] Example 3

[0073] The preparation method of the surface-modified bamboo nails of this embodiment is basically the same as that of Example 1, except that the amount of intercalated zirconium phosphate added is 4%, the sandblasting time is 15 seconds, the spraying is performed 3 times, and the rolling pressure is 1.5 MPa.

[0074] The surface modified bamboo nail prepared in this example has a coating thickness of 38.5 μm and an overall density of 0.91 g / cm 3 , indentation hardness 5771N, friction coefficient 0.31, pull-out strength 1526N (maintained above 1500N after dry-wet cycles).

[0075] Example 4

[0076] The preparation method of the surface-modified bamboo nails of this embodiment is basically the same as that of Example 1, except that the taper angle is 45°, the sandblasting time is 20 seconds, and the rolling pressure is 1.5 MPa.

[0077] The surface modified bamboo nail prepared in this example has a coating thickness of 35.9 μm and an overall density of 0.92 g / cm 3 , indentation hardness 5678N, friction coefficient 0.27, pull-out strength 1587N (maintained above 1500N after dry-wet cycles).

[0078] Example 5

[0079] The preparation method of the surface-modified bamboo nails in this embodiment is basically the same as that in Example 1, except that the α-zirconium phosphate used is purchased from Mianzhu Yaolong Chemical Co., Ltd. and has a diameter of 500 nm.

[0080] The surface-modified bamboo nail prepared in this example has the same performance as that of Example 1.

[0081] At the same time, based on the surface-modified bamboo nails of Examples 1-5 provided by the present invention, any of the surface-modified bamboo nails can be used to prepare pneumatic coiled nails.

[0082] Comparative Example 1

[0083] The preparation method of the bamboo nail of this comparative example is basically the same as that of Example 4, except that no sandblasting is performed. The thickness of the bamboo nail coating obtained is 36.8 μm, and the overall density is 0.93 g / cm 3 , indentation hardness 5613N, friction coefficient 0.42, and the surface is obviously uneven.

[0084] Comparative Example 2

[0085] The preparation method of the bamboo nail of this comparative example is basically the same as that of Example 4, except that the tip of the bamboo nail is not parallel to the original bamboo node. The thickness of the bamboo nail coating is 35.9 μm and the overall density is 0.92 g / cm 3 , indentation hardness 5678N, friction coefficient 0.27, in actual application, splitting occurs and injection cannot be performed.

[0086] Comparative Example 3

[0087] The preparation method of the bamboo nail of this comparative example is basically the same as that of Example 4, except that the roller drying is not used (it is instead left to stand at normal pressure). The thickness of the bamboo nail coating is 42.3 μm, and the overall density is 0.72 g / cm 3 , indentation hardness 4832N, friction coefficient 0.51, surface roughness and injection depth significantly reduced.

[0088] (Note: All tests were performed on 20mm thick radiata pine as the substrate under standard environmental conditions.)

[0089] From the examples and comparative examples, it can be seen that:

[0090] (1) Penetration Performance: This application significantly reduces the surface friction coefficient of bamboo nails (from 0.57 to 0.27-0.31) by modifying the water-based polyurethane coating with intercalated zirconium phosphate nanosheets. Simultaneously, through sandblasting and gradient density structure design, the indentation hardness is increased by more than 31% (from 4312N to 5639N-5834N). Tests show that the modified bamboo nails can easily penetrate 20mm thick radiata pine wood without splitting, solving the technical problem of natural bamboo nails being difficult to penetrate and prone to breaking.

[0091] (2) Connection stability: The modified bamboo nails showed excellent pull-out resistance (1509N~1587N), and the pull-out resistance remained above 1500N after the dry-wet cycle, which was more than 3 times higher than that of the unmodified bamboo nails. This is due to the stepped density structure (0.87g / cm 3 ~0.95g / cm 3) and optimized bamboo fiber distribution morphology, effectively overcoming the defect of traditional bamboo nails that the pull-out strength drops sharply with environmental changes.

[0092] (3) Process synergy: The synergy of sandblasting pretreatment (Comparative Example 1), bamboo joint alignment processing (Comparative Example 2) and roller drying process (Comparative Example 3) is crucial. The lack of any one of the processes will lead to an increase in friction coefficient (0.42-0.51), uneven density distribution (0.72 g / cm 3 ) or injection failure, verifying the necessity of each step of this method.

[0093] The surface-modified bamboo nail preparation method proposed in this application utilizes an intercalated zirconium phosphate-polyurethane composite coating and gradient density structure control. While maintaining the environmentally friendly properties of bamboo nails, it successfully addresses key technical challenges such as poor pneumatic injection performance and insufficient connection stability. Compared to metal nails, this bamboo nail offers advantages such as corrosion resistance, making it suitable for demanding applications such as green construction.

Claims

1. Surface modified bamboo nails, characterized by: The surface modified bamboo nail comprises: Bamboo nail base; A composite coating, wherein the composite coating is composed of a waterborne polyurethane and intercalated zirconium phosphate nanosheets, wherein the intercalated zirconium phosphate nanosheets are uniformly dispersed in the waterborne polyurethane at a mass fraction of 3% to 5%, and the composite coating is uniformly covered on the surface of the bamboo nail substrate; the composite coating has a thickness of 35 μm to 40 μm; The overall density of the surface modified bamboo nail is 0.87 g / cm 3 ~0.95g / cm 3 , and the distribution decreases in a stepped manner from the surface to the inside.

2. The surface-modified bamboo nail according to claim 1, characterized in that: The surface modified bamboo nail has a sharpening angle of 35° to 45°, and the tip is flush with the center of the original bamboo node.

3. The surface-modified bamboo nail according to any one of claims 1 or 2, characterized in that: The bamboo nail matrix removes surface thin-walled cells and exposes bamboo fibers.

4. A method for preparing surface-modified bamboo nails, characterized in that: The steps include: Preparation of composite coating: Disperse intercalated zirconium phosphate nanosheets in aqueous polyurethane at a mass fraction of 3% to 5%, stir at room temperature, and ultrasonically treat to obtain a composite coating; Composite coating loading: spraying the composite coating onto the surface of the bamboo nail substrate at a pressure of 0.4 MPa to 0.6 MPa; after each spraying, pressurizing and twisting the bamboo nail; repeating the spraying and pressurizing and rolling several times; Post-treatment: drying to form a uniform coating with a thickness of 35 μm to 40 μm on the surface of the bamboo nail substrate to obtain the surface-modified bamboo nail; The overall density of the surface modified bamboo nail is 0.87 g / cm 3 ~0.95g / cm 3 , and the distribution decreases in a stepped manner from the surface to the inside.

5. The method for preparing the surface-modified bamboo nail according to claim 4, characterized in that: In the composite coating loading step, after each spraying, the bamboo nail is pressurized and twisted and rolled at 55° C. to 65° C., with a pressure of 1 MPa to 1.5 MPa and a rolling speed of 1 to 3 revolutions per second, and dried for 5 to 15 minutes; the spraying and pressurizing and rolling are repeated 2 to 4 times.

6. The method for preparing the surface-modified bamboo nail according to claim 4, wherein: The preparation process of the intercalated zirconium phosphate nanosheets is as follows: Zirconium oxychloride octahydrate was dissolved in 3 mol / L phosphoric acid solution, refluxed at 100°C for 48 hours, washed, centrifuged, dried and then ground to obtain α-zirconium phosphate particles; The α-zirconium phosphate particles and tetrabutylammonium hydroxide were mixed in a molar ratio of 1:1, ultrasonically dispersed for 30 minutes, and stirred for 6 hours to obtain the intercalated zirconium phosphate nanosheets.

7. The method for preparing the surface-modified bamboo nail according to claim 6, wherein: The diameter of the α-zirconium phosphate particles is 500nm to 600nm.

8. The method for preparing surface-modified bamboo nails according to claim 4, wherein: The synthesis of the waterborne polyurethane comprises: After dehydration, polycaprolactone diol was reacted with isophorone diisocyanate and catalyst dibutyltin dilaurate at 80°C for 3 hours; Dimethylol propionic acid was added for chain extension, and the mixture was emulsified after neutralization and then chain extended for the second time with ethylenediamine to obtain a waterborne polyurethane emulsion with a solid content of 30%.

9. The method for preparing the surface-modified bamboo nail according to any one of claims 4 to 8, characterized in that: The preparation process of the bamboo nail matrix is ​​as follows: Planing the outer green layer and inner yellow layer of the bamboo, processing them into a sharp angle of 35° to 45°, so that the tip of the bamboo nail is flush with the center of the original bamboo node, and obtaining the planed bamboo; The surface of the planed bamboo is sandblasted with silicon carbide abrasive having a particle size of 240 at a pressure of 0.4 MPa, a height of 10 cm, an angle of 90°, and a treatment time of 10 to 20 seconds to obtain sandblasted bamboo; After cleaning, the sandblasted bamboo is air-dried to obtain the bamboo nail matrix.

10. Application of surface modified bamboo nails, characterized by: The surface-modified bamboo nail according to any one of claims 1 to 3, or the surface-modified bamboo nail prepared by the method according to any one of claims 4 to 9, is used in the manufacture of pneumatic coiled nails.