Preparation method of microcapsule foaming bamboo fiber composite pipe with controllable structure

Abstract

The invention relates to a microcapsule foaming bamboo fiber composite pipe with a controllable structure and a preparation method of the microcapsule foaming bamboo fiber composite pipe, and belongs to the technical field of polymer composite materials. According to the method, HDPE serves as a matrix, polyphenol modified bamboo fibers, nanocellulose aerogel (CNF-A), a core-shell type microcapsule foaming agent, a compatilizer, an antioxidant, a lubricant and a light stabilizer are matched, and the light high-strength composite pipe is prepared through high-speed mixing, twin-screw melt blending and extrusion pipe making processes. Bamboo fibers are subjected to dopamine self-polymerization polyphenol modification, and interface bonding of the fibers and an HDPE matrix is remarkably improved; the CNF-A constructs a three-dimensional porous reinforced network, so that the toughness and the structural stability of the pipe are improved; the microcapsule foaming agent realizes controllable release of gas through the polyurea shell layer, so that the pipe forms a uniform and stable microporous structure, the density is effectively reduced, and the buoyancy is improved. The composite pipe has the advantages of light weight, high specific strength, excellent interface stability and good environmental tolerance, and is suitable for the marine application fields of marine cage culture pipe frames, marine ranch buoyancy structures, ecological buoys, light bearing members and the like.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a foamed composite pipe and belongs to the technical field of foamed materials and functional high polymer materials. BACKGROUND

[0002] Bamboo fiber reinforced thermoplastic composites have attracted extensive attention in the field of pipes, plates and structural parts due to their renewability, low density and good mechanical properties. Among them, HDPE-based bamboo fiber composite pipes have the advantages of wide processing window and good hydrolysis resistance, and are suitable for outdoor and water environment use. However, due to the strong hydrophilicity of natural fibers and poor interfacial compatibility, the dispersion of the fibers in the polymer matrix is insufficient, which easily leads to interfacial debonding, resulting in the attenuation of the mechanical properties of the composite and the increase of water absorption and swelling. In addition, bamboo fibers are prone to thermal degradation during high-temperature processing, which is not conducive to the stability of the long-term service performance of the material.

[0003] Existing fiber modification methods mostly use alkali treatment, silanization or esterification modification, etc. These methods have certain effect on improving the interfacial bonding, but they greatly damage the fiber structure and some chemical reagents lack environmental friendliness. In recent years, the polyphenol coating formed by the self-polymerization of dopamine has attracted attention because it can form hydrogen bonds, π-π interactions and covalent bonds with various matrices, but its application in bamboo fiber / HDPE composite pipes is still immature, especially the long-term stability in marine environment is insufficient.

[0004] On the other hand, marine net cage culture, marine ranching buoyancy structure and ecological buoy, etc. have higher requirements for pipes: the material not only needs to be lightweight and high-strength, but also needs to maintain dimensional stability in seawater, ultraviolet light and long-term humid heat environment. However, traditional high-density polyethylene pipes have high density and insufficient buoyancy; chemical blowing agents (AC, OBS, etc.) are difficult to precisely control the gas release behavior in extrusion processing, often leading to uneven cell structure, wall thickness fluctuation and mechanical property decline. At the same time, the release temperature distribution of chemical blowing agents is wide, which easily causes appearance defects of the pipe and may cause residual risk in marine service.

[0005] Microcapsule foaming technology has been used in the preparation of lightweight materials due to its controllable release temperature, closed core material and uniform cell structure, but existing core-shell microcapsules are mostly used in PP, PVC or coating systems, which have poor compatibility with HDPE-based composite materials filled with natural fibers, and easily cause weak interfacial bonding, microcapsule rupture or uneven dispersion, etc. In addition, there is little systematic research on the synergistic use of microcapsule foaming technology, bamboo fiber modification, multi-scale cellulose aerogel and compatibilizer for marine lightweight pipes in existing literature.

[0006] Therefore, the prior art still lacks a microcapsule foaming bamboo fiber composite pipe preparation technology with light weight, strength retention, interface enhancement, seawater resistance and weather resistance, especially in the field of marine engineering and offshore aquaculture structures, which needs to be further broken through. SUMMARY

[0007] A preparation method of controllable structure microcapsule foaming bamboo fiber composite pipe, comprising the following raw materials by weight: HDPE 50~70 parts Polyphenol-modified bamboo fiber 15~25 parts Nano-cellulose aerogel (CNF-A) 2~6 parts Core-shell microcapsule foaming agent 1~2 parts Compatibilizer (HDPE-g-GMA) 3~6 parts Antioxidant (168 / 1010 compound) 0.2~0.6 parts Lubricant (magnesium stearate) 0.2~0.5 parts Light stabilizer (Tinuvin944) 0.1~0.3 parts The preparation comprises the following steps: (1) HDPE, polyphenol-modified bamboo fiber, CNF-A, compatibilizer, antioxidant, lubricant and light stabilizer are mixed at high speed to obtain a premix, the premix is extruded and granulated by a twin-screw extruder (extruder section temperature: feeding section 150~165 ℃, compression section 170~185 ℃, metering section 180~195 ℃, screw rotation speed 60~100 rpm), cooled, granulated and dried to obtain a composite master batch; (2) The composite master batch is mixed with the core-shell microcapsule foaming agent and fed, the core-shell microcapsule foaming agent is slowly added through a side feeding point, the extruder section temperature is set to feeding 140~155 ℃, compression 150~165 ℃, metering 155~165 ℃, die 160~170 ℃, and the screw rotation speed is 50~90 rpm, the die adopts a sizing vacuum jacket and is cooperated with a water bath for rapid cooling and shaping to stabilize the porous structure, after the pipe is cut and placed at room temperature, the foaming bamboo fiber composite pipe is obtained.

[0008] As a preferred scheme, the preparation method of the polyphenol-modified bamboo fiber is as follows: Tris-HCl buffer solution is added to dopamine hydrochloride under stirring to obtain a dopamine working solution, bamboo fiber is slowly added to the dopamine working solution, and gentle stirring is performed, and the self-polymerization reaction is carried out at room temperature for 8 h, and the bamboo fiber is washed and dried to obtain polyphenol-modified bamboo fiber.

[0009] As a preferred scheme, the preparation method of the CNF-A is as follows: A commercial CNF suspension with a mass concentration of 2-4% is stirred uniformly and introduced into a silica gel mold, a glutaraldehyde aqueous solution with a mass concentration of 0.2-0.4 wt% is added, and a small amount of hydrochloric acid is used to adjust the pH value to 5, and the reaction is performed for 50 min, and then the CNF suspension is washed with water; a 50% ethanol solution by volume fraction is added to the mold and is replaced for 30 min, and then 70% and 100% ethanol is sequentially added to replace the 50% ethanol solution, after the replacement is completed, the CNF-A is obtained by freezing in a-80 ℃ freezer for about 4 h and freeze-drying.

[0010] As a preferred solution, the preparation method of the core-shell type microcapsule foaming agent is as follows: (1) Water phase solution preparation: a PVA solution with a mass concentration of 2-4% is prepared, a NaCl solution with a mass concentration of 0.1-0.5% is added, and the PVA is added to deionized water, and stirring is performed under the protection of N2 in an ice bath at 5-10 ℃ to obtain a water phase solution; oil phase solution preparation: the oil phase is prepared by stirring and mixing n-pentane and diphenyl methane diisocyanate (MDI); (2) Core-shell microcapsule foaming agent preparation: the oil phase is slowly dropped into the water phase solution under stirring, and a high-speed stirrer (5000-12000 rpm, 2-8 min) is used to control the oil droplet size to 5-50 μm, and a diethylenetriamine solution is quickly added to the emulsion, and the reaction is performed at 10-25 ℃ for 30-60 min, and then the temperature is increased to 40-50 ℃ for 1-2 h, after the reaction is completed, centrifugation, washing and freeze-drying are performed to obtain the core-shell microcapsule foaming agent.

[0011] As a preferred solution, the shell layer of the core-shell type microcapsule foaming agent is formed of polyurea, the core material is n-pentane, and the average particle size of the microcapsule is 10-40 μm.

[0012] As a preferred solution, the bamboo fiber composite pipe is applied in the fields of seawater net cage culture pipe racks, ocean ranching buoyancy structures, ecological floating buoys and light weight load bearing members.

[0013] The basic principle of the present application is as follows: (1) The bamboo fiber is coated with a surface polyphenol coating layer through a dopamine self-polymerization reaction, the coating layer is rich in functional groups such as amine groups, can produce hydrogen bonds, covalent bonds or polar interactions with HDPE-g-GMA, and thus the interfacial bonding strength between the fiber and the resin matrix is significantly improved.

[0014] (2) The microcapsule is coated with a polyurea shell layer to cover the n-pentane core material, and in the extrusion molding process, the shell layer is gradually broken or changes in permeability under heat, so that the gas is released in a controlled manner, and a uniform and adjustable closed cell structure is formed.

[0015] (3) The bamboo fiber provides a macroscopic reinforcing skeleton, and the CNF aerogel provides a nanoscale three-dimensional network, and the two form a “multi-scale synergistic reinforcing system” in the matrix.

[0016] Compared with the prior art, the present application has the following beneficial effects: (1) The controllable foaming is realized by the core-shell microcapsule, the pore size distribution is more uniform, the closed pore rate is high, the hole concentration or collapse caused by the traditional chemical foaming agent is avoided, the pipe density can be reduced by 10-30%, the buoyancy is significantly improved, and the pipe is suitable for marine buoyancy components.

[0017] (2) The bamboo fiber and CNF-A multi-scale reinforcing system improves the tensile, bending and impact properties; the micro-porous structure also provides energy absorption and buffering effect, so that the pipe has the characteristics of strength, toughness and light weight, and can meet the double requirements of load bearing and fatigue resistance of net cage culture pipe frame, marine ranching floating body and the like. BRIEF DESCRIPTION OF DRAWINGS

[0018] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the accompanying drawings: Figure 1 Preparation flow chart of core-shell microcapsule foaming agent. DETAILED DESCRIPTION

[0019] The present application will be described in detail below with specific examples. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be pointed out that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made. These all belong to the protection scope of the present application. Example 1

[0020] (1) Preparation of polyphenol-modified bamboo fiber 2 L, pH 8.5 of 10 mM Tris-HCl buffer solution, under stirring, 3.0 g dopamine hydrochloride was added to obtain dopamine working solution. 100 g of dried bamboo fiber was slowly added to the above working solution, and gentle stirring was maintained to ensure that all the fibers were infiltrated. The self-polymerization reaction was carried out at room temperature for 8 h, after the reaction was completed, the bamboo fiber was taken out, washed with a large amount of deionized water until the water washing liquid color became light or close to transparent, and polyphenol-modified bamboo fiber was obtained.

[0021] (2) Preparation method of nanocellulose aerogel Take 200 g, 2 wt% concentration of commercial CNF suspension into a beaker, stir to make it fully uniform and then pour into the prepared silica gel mold. Then, slowly add 20 mL of 0.3 wt% glutaraldehyde aqueous solution, and adjust the pH of the system to 5 with a small amount of hydrochloric acid, so that it is suitable for crosslinking reaction. Keep the reaction for about 50 min, let the CNF form a three-dimensional gel network; after the reaction is completed, rinse with clean water to remove excess glutaraldehyde that does not participate in the reaction. In order to prevent the structure of aerogel from collapsing during freeze-drying, solvent replacement is needed first. Add 1000 mL of 50% ethanol solution to the mold for 30 min, then replace it with 70% and 100% ethanol in turn, and replace the water inside the gel with ethanol step by step. After the replacement is completed, the mold is placed in a-80 ℃ freezer for about 4 h to freeze the gel completely. Finally, the frozen gel is placed in a freeze-drying machine for sublimation dehydration, and a nano-cellulose aerogel with complete structure and uniform pores is obtained.

[0022] (3) Preparation of core-shell microcapsule foaming agent Water phase solution preparation: weigh 20 g of PVA and add it to water in portions, heat and stir at 80 ℃ until completely dissolved to obtain a 4% PVA solution, then cool to 10 ℃, and add 3 g of 0.2% NaCl solution. Add the above PVA solution to 1000 g of deionized water, stir under 5 ℃ ice bath and N2 protection to obtain the water phase solution. Oil phase solution preparation: the oil phase is prepared by stirring and mixing 100 g of n-pentane and 40 g of MDI, and the whole process is operated under low temperature and inert atmosphere.

[0023] Preparation of core-shell microcapsule foaming agent: slowly drop the oil phase into the water phase solution under stirring, and use a high-speed blender (10000 rpm, 5 min) to control the oil droplet size to 5-50 μm. Quickly add the diethylenetriamine solution to the emulsion to make the amine and MDI react to form a polyurea layer at the oil-water interface; first react at 20 ℃ for 50 min, then heat to 45 ℃ for 2 h to reinforce the shell layer. After the reaction is completed, centrifuge, wash, and freeze-dry to obtain the polyurea shell-pentane core microcapsule foaming agent.

[0024] (4) Preparation of controllable structure microcapsule foamed bamboo fiber composite pipe The preparation method of controllable structure microcapsule foamed bamboo fiber composite pipe comprises the following raw materials by weight: HDPE 60 parts Polyphenol-modified bamboo fiber 20 parts Nano-cellulose aerogel (CNF-A) 4 parts Core-shell microcapsule foaming agent 2 parts Compatibilizer (HDPE-g-GMA) 4 parts Antioxidant (168 / 1010 complex) 0.4 parts Lubricant (magnesium stearate) 0.3 parts Light stabilizer (Tinuvin 944) 0.2 parts First, dry mix HDPE, dried polyphenol-modified bamboo fiber, CNF-A, compatibilizer (HDPE-g-GMA), antioxidant (168 / 1010), lubricant, and light stabilizer in a high-speed mixer for 10 min to obtain a uniform premix. The premix is granulated by a twin-screw extruder to improve dispersion (extruder section temperature: feed section 160℃, compression section 175℃, metering section 185℃; screw speed 100 rpm), and the extrudate is cooled by water bath and dried in a 60℃ vacuum drying oven to obtain a composite master batch. The master batch is mixed with the core-shell microcapsule blowing agent when extruding the pipe, and the core-shell microcapsule blowing agent is slowly added through the side feeding point to avoid high temperature rupture; the extruder section temperature is set to feed 140℃, compression 155℃, metering 160℃, die 165℃ (so that the microcapsules release gas to form closed pores at the die / mandrel), and the screw speed is 90 rpm. The mold uses a constant diameter vacuum jacket and is combined with a water bath for rapid cooling and setting to stabilize the porous structure. After extrusion, the pipe is cut and placed at room temperature to obtain a controllable structure microcapsule foaming bamboo fiber composite pipe.

[0025] The physical and chemical properties of the microcapsule foaming bamboo fiber composite pipe prepared in Example 1 are shown in Table 1. The bamboo fiber composite pipe has a low density of 0.712 g·cm -3 , an open porosity of 26.12%, a tensile strength of 35.1 MPa, an elongation at break of 156.2%, and excellent anti-aging performance with no serious powdering on the surface and little size change after 1000 h of accelerated aging test.

[0026] Table 1 Physical and chemical properties of microcapsule foaming bamboo fiber composite pipe Parameters Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Density (g-cm -3 ) 0.712 0.725 0.721 0.732 0.716 0.811 Open porosity (vol% ) 26.12 27.91 26.33 26.41 26.21 22.11 Tensile strength (MPa) 35.1 36.4 36.2 28.9 30.1 36.1 Elongation at break (%) 156.2 160.1 163.3 140.2 145.1 152.4 Anti-aging performance (1000h) No severe powdering on the surface, little change in size No severe powdering on the surface, little change in size No severe powdering on the surface, little change in size No severe powdering on the surface, little change in size No severe powdering on the surface, little change in size No severe powdering on the surface, little change in size Example 2

[0027] A method for preparing a controllable structure microcapsule foaming bamboo fiber composite pipe, comprising the following raw materials by weight: HDPE 50 parts Polyphenol-modified bamboo fiber 15 parts Nanocellulose aerogel (CNF-A) 2 parts Core-shell microcapsule blowing agent 1.5 parts Compatibilizer (HDPE-g-GMA) 4 parts Antioxidant (168 / 1010 compound) 0.3 parts Lubricant (magnesium stearate) 0.5 parts Light stabilizer (Tinuvin 944) 0.1 parts HDPE, polyphenol-modified bamboo fiber, CNF-A, compatibilizer, antioxidant, lubricant and light stabilizer were high-speed mixed to obtain a premix. The premix was extruded and granulated by a twin-screw extruder (extruder section temperature: feeding section 155 ℃, compression section 170 ℃, metering section 180 ℃; screw rotation speed 80 rpm), cooled, granulated and dried to obtain a composite master batch. The composite master batch was mixed with the core-shell microcapsule blowing agent and fed into the extruder, and the core-shell microcapsule blowing agent was slowly added through a side feeding point. The extruder section temperature was set to feeding 145 ℃, compression 155 ℃, metering 165 ℃, and die 165 ℃, and the screw rotation speed was 90 rpm. The mold used a sizing vacuum jacket and was combined with a water bath for rapid cooling and shaping to stabilize the porous structure. After extrusion, the pipe material was cut and placed at room temperature to obtain a foamed bamboo fiber composite pipe material. The bamboo fiber composite pipe material has a low density of 0.725 g·cm -3 and an open porosity of 27.91%, a tensile strength of 36.1 MPa, an elongation at break of 160.1%, and excellent anti-aging performance with no serious powdering on the surface and small size change after 1000 h of accelerated aging test. Example 3

[0028] A method for preparing a controllable structure microcapsule foamed bamboo fiber composite pipe material, comprising the following raw materials by weight: HDPE 55 parts Polyphenol-modified bamboo fiber 18 parts Nanocellulose aerogel (CNF-A) 1.5 parts Core-shell microcapsule blowing agent 2 parts Compatibilizer (HDPE-g-GMA) 3 parts Antioxidant (168 / 1010 compound) 0.35 parts Lubricant (magnesium stearate) 0.4 parts Light stabilizer (Tinuvin 944) 0.2 parts HDPE, polyphenol-modified bamboo fiber, CNF-A, compatibilizer, antioxidant, lubricant and light stabilizer were high-speed mixed to obtain a premix. The premix was extruded and granulated by a twin-screw extruder (extruder section temperature: 160 ℃ for feeding section, 170 ℃ for compression section, 180 ℃ for metering section; screw rotation speed: 80 rpm) to obtain a composite master batch. The composite master batch was mixed with the core-shell microcapsule foaming agent and fed into the extruder, and the core-shell microcapsule foaming agent was slowly added through a side feeding point. The extruder section temperature was set to 145 ℃ for feeding, 155 ℃ for compression, 165 ℃ for metering and 165 ℃ for die, and the screw rotation speed was 90 rpm. A constant diameter vacuum jacket was used in the mold, and water bath rapid cooling was used for shaping to stabilize the porous structure. After extrusion, the pipe material was cut and placed at room temperature to obtain a foamed bamboo fiber composite pipe material. The bamboo fiber composite pipe material has a low density of 0.721 g·cm -3 and an open porosity of 26.33%, a tensile strength of 36.2 MPa, an elongation at break of 163.3%, and still exhibits excellent anti-aging performance with no serious powdering on the surface and small size change after 1000 h of accelerated aging test. Comparative Example 1

[0029] Unlike Example 1, the bamboo fiber in the formula is not modified by polyphenol, and the bamboo fiber is directly used in the formula to obtain a foamed bamboo fiber pipe material. The density and open porosity of the pipe material are 0.732 g·cm -3 and 26.41%, respectively, and the tensile strength and elongation at break are 28.9 MPa and 140.2%, respectively. Compared with Example 1, it is found that the tensile strength and elongation at break of the pipe material are significantly reduced. This is mainly because the unmodified bamboo fiber surface lacks sufficient active groups, and the interfacial bonding force between the HDPE matrix and the compatibilizer is weak. The fiber slips and interfacial debonding easily occur in the matrix, which significantly reduces the stress transfer efficiency. At the same time, the fiber dispersion is poor, and the local stress concentration is aggravated, thereby reducing the overall mechanical properties of the material. Comparative Example 2

[0030] Unlike Example 1, no CNF-A is added in the formula of Comparative Example 2. The density and open porosity of the foamed bamboo fiber composite pipe material obtained are 0.716 g·cm -3 and 26.21%, respectively, and the tensile strength and elongation at break are 30.1 MPa and 145.1%, respectively. Compared with Example 1, the tensile strength and elongation at break are both reduced. This is mainly because the three-dimensional nanometer network structure provided by CNF-A is lacking, and the strength of the pore wall and the overall skeleton support ability in the matrix are reduced, making the material more prone to micro-crack accumulation and rapid fracture under external load, resulting in a decrease in mechanical properties. Comparative Example 3

[0031] Different from the formulation in Example 1, the amount of microcapsule foaming agent in the formulation is 0.5 parts, and the density of the final foamed bamboo fiber composite pipe increases, and the opening rate decreases. Mainly because the amount of microcapsule foaming agent is insufficient, the amount of foaming gas released is low, it is difficult to form a sufficient number of stable bubbles in the melt, resulting in a decrease in the overall foaming ratio, and finally the pipe density increases, the pore structure is relatively compact, and the opening rate decreases accordingly.

[0032] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the specific implementation described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application.

Claims

1. A method for preparing a controllable structure microcapsule foamed bamboo fiber composite pipe, comprising the following raw materials in parts by weight: HDPE 50~70 parts 15-25 parts of polyphenol-modified bamboo fiber Nanocellulose aerogel CNF-A 2-6 parts 1-2 parts of core-shell microcapsule foaming agent Compatibilizer HDPE-g-GMA 3~6 parts Antioxidant 168 / 1010 0.2~0.6 parts Lubricant: 0.2-0.5 parts magnesium stearate Light stabilizer Tinuvin 944: 0.1-0.3 parts The preparation includes the following steps: (1) HDPE, polyphenol-modified bamboo fiber, CNF-A, compatibilizer, antioxidant, lubricant and light stabilizer are mixed at high speed to obtain a premix. The premix is ​​extruded and granulated by a twin-screw extruder. The temperature of the extruder sections is: 150-165 ℃ in the feeding section, 170-185 ℃ in the compression section and 180-195 ℃ in the metering section. The screw speed is 60-100 rpm. The composite masterbatch is obtained by cooling, pelletizing and drying. (2) Extrusion tube making: The composite masterbatch and the core-shell microcapsule foaming agent are mixed and fed into the machine. The core-shell microcapsule foaming agent is slowly added through the side feeding point. The extruder segment temperature is set to feed 140-155 ℃, compression 150-165 ℃, metering 155-165 ℃, and die 160-170 ℃. The screw speed is 50-90 rpm. The die adopts a sizing vacuum sleeve and is combined with water bath for rapid cooling and shaping to stabilize the porous structure. After demolding, the tube is cut and placed at room temperature to obtain microcapsule foamed bamboo fiber composite tube. The preparation method of the polyphenol-modified bamboo fiber is as follows: Tris-HCl buffer was added to dopamine hydrochloride under stirring to obtain dopamine working solution. Bamboo fiber was slowly added to dopamine working solution and gently stirred. The self-polymerization reaction was carried out at room temperature for 8 h. The bamboo fiber was washed and dried to obtain polyphenol modified bamboo fiber. The preparation method of CNF-A is as follows: A commercial CNF suspension with a mass concentration of 2-4% was stirred evenly and poured into a silicone mold. A glutaraldehyde aqueous solution with a mass concentration of 0.2-0.4 wt% was added, and the pH was adjusted to 5 with a small amount of hydrochloric acid. The mixture was reacted for 50 min and then washed with water. A 50% ethanol solution was added to the mold to replace the ethanol for 30 min. The solution was then discarded and replaced with 70% and 100% ethanol in turn. After the replacement was completed, the mixture was frozen in a freezer at -80 ℃ and freeze-dried to obtain CNF-A. The preparation method of the core-shell microcapsule foaming agent is as follows: (1) Preparation of aqueous solution: Prepare a PVA solution with a mass concentration of 2-4%, add a NaCl solution with a mass concentration of 0.1-0.5%, add PVA to deionized water, and stir under ice bath and N2 protection at 5-10 ℃ to obtain an aqueous solution; Preparation of oil solution: mix n-pentane and diphenylmethane diisocyanate MDI by stirring. (2) Preparation of core-shell microcapsule foaming agent: Under stirring conditions, the oil phase solution was slowly added dropwise to the aqueous phase solution, and the droplet size was adjusted to 5-50 μm using a high-speed stirrer (5000-12000 rpm, 2-8 min). The diethylenetriamine solution was rapidly added dropwise to the emulsion. The reaction was first carried out at 10-25 ℃ for 30-60 min, and then heated to 40-50 ℃ and kept at 1-2 h. After the reaction was completed, the mixture was centrifuged, washed, and freeze-dried to obtain the core-shell microcapsule foaming agent.

2. The method for preparing a controllable structure microcapsule foamed bamboo fiber composite pipe as described in claim 1, characterized in that, The shell of the core-shell microcapsule foaming agent is formed of polyurea, the core material is n-pentane, and the average particle size of the microcapsules is 10-40 μm.

3. The method for preparing a controllable structure microcapsule foamed bamboo fiber composite pipe as described in claim 1, characterized in that, The bamboo fiber composite pipe is used in fields such as marine cage aquaculture pipe racks, marine ranch buoyancy structures, ecological pontoons, and lightweight load-bearing components.

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