Environment-friendly composite material for pipe joint and preparation method of environment-friendly composite material

Abstract

The invention relates to the technical field of high polymer material modification technologies and double-shot molding technologies, and discloses an environment-friendly composite material for pipe joints and a preparation method thereof.The method comprises the steps of raw material pretreatment, melt mixing, functional additive adding and machine shaping. The interface bonding state of the fibers and the bio-based resin is optimized in real time, uniform dispersion of the fibers in a matrix is guaranteed, the phenomenon of fiber agglomeration or interface debonding in a traditional process is avoided, the stability and consistency of the mechanical property of a composite material are guaranteed, and the structural reliability of a pipe joint product is improved; by dynamically monitoring shear heat history and melt rheological characteristics, feeding back and regulating temperature field distribution and shear strength in real time, the risk of thermal degradation of fibers is actively prevented, the performance integrity of an enhanced phase is ensured, stability control over the material processing process is synchronously achieved, performance deviation caused by process fluctuation is reduced, and the processing quality is improved. And the quality qualification rate of pipe joint batch production is improved.

Description

Technical Field

[0001] The present invention relates to the fields of polymer material modification technology and two-color injection molding technology, and specifically relates to an environmentally friendly composite material for pipe joints and a preparation method thereof. Background Art

[0002] Pipe fittings are parts that connect pipes in hydraulic systems or install pipes on hydraulic components. It is a general term for connectors that can be installed and removed in fluid pathways. Environmentally friendly composite materials are based on the requirements of green environmental protection and sustainable development, and should include composite materials with renewable biomass resources as raw materials and green high-performance composite materials.

[0003] At present, the following defects exist in the preparation process of pipe joint composite materials: the raw material selection of traditional composite materials cannot achieve dynamic control of the interface compatibility between bio-based resins and plant fibers. If the melt rheology of bio-based polyester resins does not match the dispersibility of natural plant fibers, it may cause fiber agglomeration in the matrix or interface debonding, which directly affects the stability of the mechanical properties of the material.

[0004] Therefore, an environmentally friendly composite material for pipe joints and a preparation method thereof are proposed to solve the above problems. Summary of the Invention

[0005] (1) Technical problems solved In view of the deficiencies in the prior art, the present invention provides an environmentally friendly composite material for pipe joints and a preparation method thereof, which solves the problems raised in the above-mentioned background technology.

[0006] (2) Technical solution 2. To achieve the above objectives, the present invention provides the following technical solutions: An environmentally friendly composite material for pipe joints and a method for preparing the same, comprising the following steps: Step 1: Raw material pretreatment Selecting natural plant fibers, wherein the natural plant fibers are at least one of bamboo fibers, hemp fibers, or coconut shell fibers, and having a fiber length of 0.5-3 mm, and performing alkali treatment, washing, and drying the fibers; Step 2: Melt mixing a. Add 40-60 parts by weight of bio-based polyester resin to the main feed port of a twin-screw extruder and control the temperature at 180-210°C to melt it; b. Introduce 20-35 parts by weight of pretreated natural plant fibers from the side feed port, and feed them at a screw speed of 200-400 r / min and a shear rate of 500-1500 Mix under the above conditions for 10-20 minutes to form a uniformly dispersed matrix mixture; Step 3: Adding functional additives To the matrix mixture obtained in step b, add in sequence: 8-15 parts by weight of degradable toughening agent, control the temperature to 160-190°C, and mix for 5-10 minutes; Add 5-12 parts by weight of environmentally friendly flame retardant, heat to 185-200°C, and mix for 8-15 minutes; Step 4: Processing and forming Add the mixture obtained in step 3 to an injection molding machine or molding equipment, and in the presence of 3-8 parts by mass of a processing aid, mold it at a mold temperature of 50-80°C and a pressure of 15-30 MPa, hold the pressure for 2-10 minutes, and demold to obtain a pipe joint product; Wherein, the bio-based polyester resin is at least one of polylactic acid, polyhydroxyalkanoate or polybutylene succinate; The degradable toughening agent is a blend of polycaprolactone and maleic anhydride grafted polylactic acid, with a blending mass ratio of 1:1-1:3; The environmentally friendly flame retardant is a compound of at least two of coated aluminum hydroxide, phosphorus-nitrogen intumescent flame retardant or zinc borate.

[0007] Preferably, the alkali treatment in step 1 comprises the following steps: The natural plant fiber is immersed in a sodium hydroxide solution with a mass concentration of 5%-10%, and treated at 60-80°C for 30-90 minutes. Ultrasonic waves are used to assist the treatment process at a frequency of 40kHz±5kHz. During cleaning, deionized water is used to rinse repeatedly until it becomes neutral. The drying conditions are hot air drying at 80-105℃ for 1-3 hours, and the final moisture content of the fiber is less than 1.5%.

[0008] Preferably, the natural plant fiber after alkali treatment needs to be surface modified: Immerse the dry fiber in silane coupling agent ethanol solution with a silane coupling agent concentration of 1%-5% and an ethanol concentration of 95%. Take it out after soaking for 30-60 minutes and cure it in an oven at 110-130℃ for 0.5-1.5 hours. The silane coupling agent is γ-aminopropyltriethoxysilane or γ-glycidyloxypropyltrimethoxysilane.

[0009] Preferably, the mixing process in step 2b needs to control the melt temperature window to 185°C ± 5°C, the pressure sensor monitors the barrel pressure in real time and maintains it at 8-15 MPa, and the melt flow index is controlled at 10-30 g / 10 min.

[0010] Preferably, when adding the environmentally friendly flame retardant in step 3, a staged temperature increase strategy is adopted: First, mix at 185-190℃ for 3-5min, then heat to 195-200℃ and mix for 5-10min. During the vacuum degassing stage, the vacuum degree is maintained at 0.08-0.1MPa, and the degassing time is 5-8min.

[0011] Preferably, the processing aid consists of the following components in parts by weight: Lubricant: 1-3 parts of calcium stearate or oxidized polyethylene wax; Dispersant: polyvinyl pyrrolidone or hyperbranched polyester 0.5-2 parts; Nucleating agent: 0.3-1.5 parts of phenyl zinc phosphate or talc; Anti-hydrolysis agent: 1-1.5 parts of carbodiimide compound.

[0012] Preferably, the compounding ratio of the environmentally friendly flame retardant is coated aluminum hydroxide: phosphorus nitrogen intumescent flame retardant = 2:1-4:1, or zinc borate: phosphorus nitrogen intumescent flame retardant = 1:1-1:2.

[0013] Preferably, its components include by mass: 40-60 parts of bio-based polyester resin; 20-35 parts of modified natural plant fiber; 8-15 parts of degradable toughening agent; 5-12 parts of environmentally friendly flame retardant; 3-8 parts of processing aid; The material has a biodegradability rate greater than 90%, an oxygen index greater than 28%, a tensile strength greater than 45 MPa, and an impact toughness greater than 12 kJ / m².

[0014] Preferably, the composite material meets the following performance indicators in pipe joint applications: Sealing pressure test: No leakage when maintaining pressure for 30 minutes under 1.6MPa water pressure; Corrosion resistance: After immersion in 10% NaCl solution for 30 days, the tensile strength retention rate is greater than 85%; Thermal deformation temperature is greater than 85℃; The weld strength is greater than 90% of the material's strength.

[0015] Preferably, the microstructure of the composite material comprises: The modified natural plant fiber forms a chemical bond at the interface with the bio-based polyester resin, with the coupling agent coverage exceeding 90%; The flame retardant is evenly dispersed in the matrix with a particle size of 1-5 μm, with no visible agglomeration; The toughening agent forms an island structure with an island phase diameter of 0.2-1μm and a distribution density greater than 10 5 pieces / mm².

[0016] (3) Beneficial effects Compared with the prior art, the present invention provides an environmentally friendly composite material for pipe joints and a preparation method thereof, which has the following beneficial effects: 1. In the present invention, by matching differentiated surface modification strategies for different fiber types during the pretreatment process of natural plant fibers, the interfacial bonding state between the fibers and the bio-based resin is optimized in real time, ensuring the uniform dispersion of the fibers in the matrix, avoiding fiber agglomeration or interfacial debonding in traditional processes, ensuring the stability and consistency of the mechanical properties of the composite material, and improving the structural reliability of the pipe fitting products.

[0017] 2. In the present invention, by dynamically monitoring the shear heat history and melt rheological properties during the twin-screw extrusion processing stage, real-time feedback is provided to control the temperature field distribution and shear strength, actively prevent the risk of fiber thermal degradation, ensure the integrity of the reinforcement phase performance, and simultaneously achieve stability control of the material processing process, reduce performance deviations caused by process fluctuations, and improve the quality pass rate of mass production of pipe fittings.

[0018] 3. In the present invention, by accurately matching the compatibility relationship between the decomposition temperature and the processing window during the compounding stage of the flame retardant and the toughening agent, a directional distribution mechanism of the flame retardant element in the matrix is ​​established, breaking through the bottleneck of the coordinated optimization of flame retardant efficiency and mechanical properties, and simultaneously ensuring the fire safety protection capability and mechanical bearing capacity of the pipe joint product, thereby improving the environmental adaptability and service life of the composite material as a whole. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a flow chart of an environmentally friendly composite material for pipe joints and a preparation method thereof. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0021] Example 1: An environmentally friendly composite material for a pipe joint and a preparation method thereof, comprising the following steps: Step 1: Raw material pretreatment Selecting natural plant fibers, wherein the natural plant fibers are at least one of bamboo fibers, hemp fibers, or coconut shell fibers, and having a fiber length of 0.5 mm, and performing alkali treatment, washing, and drying the fibers; Step 2: Melt mixing a. Add 40 parts by mass of bio-based polyester resin to the main feed port of a twin-screw extruder and control the temperature at 180-210°C to melt it; b. 20 parts by mass of pretreated natural plant fibers were introduced from the side feed port and the screw speed was 200 r / min and the shear rate was 500 Mix under the above conditions for 10-20 minutes to form a uniformly dispersed matrix mixture; Step 3: Adding functional additives To the matrix mixture obtained in step b, add in sequence: 8 parts by mass of degradable toughening agent, control the temperature to 160°C, and mix for 5 minutes; 5 parts by mass of environmentally friendly flame retardant, heat to 18°C, and mix for 8 minutes; Step 4: Processing and forming The mixture obtained in step 3 is added to an injection molding machine or molding equipment, and in the presence of 3 parts by mass of a processing aid, molded at a mold temperature of 50° C. and a pressure of 15 MPa, with a holding time of 2 minutes, and demolded to obtain a pipe joint product; in: The bio-based polyester resin is at least one of polylactic acid, polyhydroxyalkanoate or polybutylene succinate; The biodegradable toughening agent is a blend of polycaprolactone and maleic anhydride grafted polylactic acid, with a blending mass ratio of 1:1; The environmentally friendly flame retardant is a compound of at least two of coated aluminum hydroxide, phosphorus-nitrogen intumescent flame retardant or zinc borate.

[0022] The alkali treatment in step one comprises the following steps: The natural plant fibers were immersed in a 5% sodium hydroxide solution at 60°C for 30 minutes. Ultrasonic waves were used during the treatment at a frequency of 40kHz±5kHz. During cleaning, deionized water is used to rinse repeatedly until it becomes neutral. The drying condition is hot air drying at 80°C for 1 hour, and the final moisture content of the fiber is less than 1.5%.

[0023] After alkali treatment, natural plant fibers need to be surface modified: The dried fiber was immersed in a silane coupling agent ethanol solution with a silane coupling agent concentration of 1% and an ethanol concentration of 95%. After soaking for 30 minutes, the fiber was taken out and cured in an oven at 110°C for 0.5 hours. The silane coupling agent is γ-aminopropyltriethoxysilane or γ-glycidyloxypropyltrimethoxysilane.

[0024] The mixing process in step 2b needs to control the melt temperature window to 185℃±5℃, the pressure sensor monitors the barrel pressure in real time and maintains it at 8MPa, and the melt flow index is controlled at 10g / 10min.

[0025] When adding environmentally friendly flame retardants in step 3, a staged temperature increase strategy is adopted: First, mix at 185°C for 3 minutes, then heat to 195°C and mix for 5 minutes. During the vacuum degassing stage, the vacuum degree is maintained at 0.08 MPa, and the degassing time is 5 minutes.

[0026] The processing aid is composed of the following components by weight: Lubricant: 1 part calcium stearate or oxidized polyethylene wax; Dispersant: 0.5 parts of polyvinyl pyrrolidone or hyperbranched polyester; Nucleating agent: 0.3 parts of phenyl zinc phosphate or talc; Anti-hydrolysis agent: 1 part of carbodiimide compound.

[0027] The compounding ratio of the environmentally friendly flame retardant is coated aluminum hydroxide: phosphorus nitrogen intumescent flame retardant = 2:1-4:1, or zinc borate: phosphorus nitrogen intumescent flame retardant = 1:1-1:2; The phosphorus-nitrogen intumescent flame retardant is a compound of ammonium polyphosphate and melamine cyanurate, with a compounding mass ratio of 3:1.

[0028] 40 parts of bio-based polyester resin; 20 parts of modified natural plant fiber; 8 parts of degradable toughening agent; 5 parts of environmentally friendly flame retardant; 3 parts of processing aid; The material has a biodegradability rate greater than 90%, an oxygen index greater than 28%, a tensile strength greater than 45 MPa, and an impact toughness greater than 12 kJ / m².

[0029] Composite materials meet the following performance indicators in pipe fitting applications: Sealing pressure test: No leakage when maintaining pressure for 30 minutes under 1.6MPa water pressure; Corrosion resistance: After immersion in 10% NaCl solution for 30 days, the tensile strength retention rate is greater than 85%; Thermal deformation temperature is greater than 85℃; The weld strength is greater than 90% of the material's strength.

[0030] The microstructure of a composite material includes: The modified natural plant fiber forms a chemical bond at the interface with the bio-based polyester resin, with the coupling agent coverage exceeding 90%; The flame retardant is evenly dispersed in the matrix with a particle size of 1 μm, with no visible agglomeration; The toughening agent forms an island structure with an island phase diameter of 0.2 μm and a distribution density greater than 10 5 pieces / mm².

[0031] Example 2: An environmentally friendly composite material for a pipe joint and a preparation method thereof, comprising the following steps: Step 1: Raw material pretreatment Selecting natural plant fibers, wherein the natural plant fibers are at least one of bamboo fibers, hemp fibers, or coconut shell fibers, and having a fiber length of 1.5 mm, and performing alkali treatment, washing, and drying the fibers; Step 2: Melt mixing a. Add 50 parts by mass of bio-based polyester resin to the main feed port of a twin-screw extruder and control the temperature at 195°C to melt it; b. 30 parts by mass of pretreated natural plant fibers were introduced from the side feed port and the screw speed was 300 r / min and the shear rate was 1000 The mixture was mixed under the above conditions for 15 min to form a uniformly dispersed matrix mixture; Step 3: Adding functional additives To the matrix mixture obtained in step b, add in sequence: 12 parts by mass of degradable toughening agent, control the temperature to 175°C, and mix for 8 minutes; 8 parts by weight of environmentally friendly flame retardant, heat to 190°C, and mix for 12 minutes; Step 4: Processing and forming The mixture obtained in step 3 is added to an injection molding machine or molding equipment, and in the presence of 3-8 parts by mass of a processing aid, molded at a mold temperature of 65° C. and a pressure of 22 MPa, with a holding time of 6 minutes, and demolded to obtain a pipe joint product; Wherein, the bio-based polyester resin is at least one of polylactic acid, polyhydroxyalkanoate or polybutylene succinate; The biodegradable toughening agent is a blend of polycaprolactone and maleic anhydride grafted polylactic acid, with a blending mass ratio of 1:2; The environmentally friendly flame retardant is a compound of at least two of coated aluminum hydroxide, phosphorus-nitrogen intumescent flame retardant or zinc borate.

[0032] The alkali treatment in step one comprises the following steps: The natural plant fibers were immersed in a sodium hydroxide solution with a mass concentration of 8% and treated at 70°C for 60 minutes. Ultrasonic waves were used to assist the treatment at a frequency of 40kHz±5kHz. During cleaning, deionized water is used to rinse repeatedly until it becomes neutral. The drying condition is hot air drying at 95°C for 2 hours, and the final moisture content of the fiber is less than 1.5%.

[0033] After alkali treatment, natural plant fibers need to be surface modified: The dried fiber was immersed in a silane coupling agent ethanol solution with a silane coupling agent concentration of 3% and an ethanol concentration of 95%. After soaking for 45 minutes, the fiber was taken out and cured in a 120°C oven for 1 hour. The silane coupling agent is γ-aminopropyltriethoxysilane or γ-glycidyloxypropyltrimethoxysilane.

[0034] The mixing process in step 2b needs to control the melt temperature window to 185℃±5℃, the pressure sensor monitors the barrel pressure in real time and maintains it at 12MPa, and the melt flow index is controlled at 20g / 10min.

[0035] When adding environmentally friendly flame retardants in step 3, a staged temperature increase strategy is adopted: First, mix at 188°C for 4 minutes, then heat to 198°C and mix for 8 minutes. During the vacuum degassing stage, the vacuum degree is maintained at 0.09 MPa, and the degassing time is 7 minutes.

[0036] The processing aid is composed of the following components by weight: Lubricant: 2 parts of calcium stearate or oxidized polyethylene wax; Dispersant: 1 part of polyvinyl pyrrolidone or hyperbranched polyester; Nucleating agent: 1 part of phenyl zinc phosphate or talc; Anti-hydrolysis agent: 1.2 parts of carbodiimide compound.

[0037] The compounding ratio of the environmentally friendly flame retardant is coated aluminum hydroxide: phosphorus nitrogen intumescent flame retardant = 2:1-4:1, or zinc borate: phosphorus nitrogen intumescent flame retardant = 1:1-1:2; The phosphorus-nitrogen intumescent flame retardant is a compound of ammonium polyphosphate and melamine cyanurate, with a compounding mass ratio of 3:1.

[0038] 50 parts of bio-based polyester resin; 30 parts of modified natural plant fiber; 12 parts of degradable toughening agent; 8 parts of environmentally friendly flame retardant; 5 parts of processing aid; The material has a biodegradability rate greater than 90%, an oxygen index greater than 28%, a tensile strength greater than 45 MPa, and an impact toughness greater than 12 kJ / m².

[0039] Composite materials meet the following performance indicators in pipe fitting applications: Sealing pressure test: No leakage when maintaining pressure for 30 minutes under 1.6MPa water pressure; Corrosion resistance: After immersion in 10% NaCl solution for 30 days, the tensile strength retention rate is greater than 85%; Thermal deformation temperature is greater than 85℃; The weld strength is greater than 90% of the material's strength.

[0040] The microstructure of a composite material includes: The modified natural plant fiber forms a chemical bond at the interface with the bio-based polyester resin, with the coupling agent coverage exceeding 90%; The flame retardant is evenly dispersed in the matrix with a particle size of 3 μm, with no visible agglomeration; The toughening agent forms an island structure with an island phase diameter of 0.6 μm and a distribution density greater than 10 5 pieces / mm².

[0041] Example 3: An environmentally friendly composite material for a pipe joint and a preparation method thereof, comprising the following steps: Step 1: Raw material pretreatment Selecting natural plant fibers, wherein the natural plant fibers are at least one of bamboo fibers, hemp fibers, or coconut shell fibers, and having a fiber length of 3 mm, and performing alkali treatment, washing, and drying the fibers; Step 2: Melt mixing a. Add 60 parts by mass of bio-based polyester resin to the main feed port of a twin-screw extruder and control the temperature at 180-210°C to melt it; b. 35 parts by mass of pretreated natural plant fibers were introduced from the side feed port and the screw speed was 400 r / min and the shear rate was 1500 The mixture was mixed under the above conditions for 20 min to form a uniformly dispersed matrix mixture; Step 3: Adding functional additives To the matrix mixture obtained in step b, add in sequence: 15 parts by weight of degradable toughening agent, control the temperature down to 190°C, and mix for 10 minutes; 12 parts by mass of environmentally friendly flame retardant, heated to 200°C, and mixed for 15 minutes; Step 4: Processing and forming The mixture obtained in step 3 is added to an injection molding machine or molding equipment, and in the presence of 8 parts by mass of a processing aid, molded at a mold temperature of 80° C. and a pressure of 30 MPa, with a holding time of 10 minutes, and demolded to obtain a pipe joint product; Wherein, the bio-based polyester resin is at least one of polylactic acid, polyhydroxyalkanoate or polybutylene succinate; The biodegradable toughening agent is a blend of polycaprolactone and maleic anhydride grafted polylactic acid, with a blending mass ratio of 1:3; The environmentally friendly flame retardant is a compound of at least two of coated aluminum hydroxide, phosphorus-nitrogen intumescent flame retardant or zinc borate.

[0042] The alkali treatment in step one comprises the following steps: The natural plant fibers were immersed in a sodium hydroxide solution with a mass concentration of 10% and treated at 80°C for 90 minutes. Ultrasonic waves were used to assist the treatment at a frequency of 40kHz±5kHz. During cleaning, deionized water is used to rinse repeatedly until it becomes neutral. The drying condition is hot air drying at 105°C for 3 hours, and the final moisture content of the fiber is less than 1.5%.

[0043] After alkali treatment, natural plant fibers need to be surface modified: The dried fiber was immersed in a silane coupling agent ethanol solution with a silane coupling agent concentration of 5% and an ethanol concentration of 95%. After soaking for 60 minutes, the fiber was taken out and cured in an oven at 130°C for 1.5 hours. The silane coupling agent is γ-aminopropyltriethoxysilane or γ-glycidyloxypropyltrimethoxysilane.

[0044] The mixing process in step 2b needs to control the melt temperature window to 185℃±5℃, the pressure sensor monitors the barrel pressure in real time and maintains it at 15MPa, and the melt flow index is controlled at 30g / 10min.

[0045] When adding environmentally friendly flame retardants in step 3, a staged temperature increase strategy is adopted: First, mix at 190°C for 5 minutes, then heat to 200°C and mix for 10 minutes. During the vacuum degassing stage, the vacuum degree is maintained at 0.1 MPa, and the degassing time is 8 minutes.

[0046] The processing aid is composed of the following components by weight: Lubricant: 3 parts of calcium stearate or oxidized polyethylene wax; Dispersant: 2 parts of polyvinyl pyrrolidone or hyperbranched polyester; Nucleating agent: 1.5 parts of phenyl zinc phosphate or talc; Anti-hydrolysis agent: 1.5 parts of carbodiimide compound.

[0047] The compounding ratio of the environmentally friendly flame retardant is coated aluminum hydroxide: phosphorus nitrogen intumescent flame retardant = 2:1-4:1, or zinc borate: phosphorus nitrogen intumescent flame retardant = 1:1-1:2; The phosphorus-nitrogen intumescent flame retardant is a compound of ammonium polyphosphate and melamine cyanurate, with a compounding mass ratio of 3:1.

[0048] 60 parts of bio-based polyester resin; 35 parts of modified natural plant fiber; 15 parts of degradable toughening agent; 12 parts of environmentally friendly flame retardant; 8 parts of processing aid; The material has a biodegradability rate greater than 90%, an oxygen index greater than 28%, a tensile strength greater than 45 MPa, and an impact toughness greater than 12 kJ / m².

[0049] Composite materials meet the following performance indicators in pipe fitting applications: Sealing pressure test: No leakage when maintaining pressure for 30 minutes under 1.6MPa water pressure; Corrosion resistance: After immersion in 10% NaCl solution for 30 days, the tensile strength retention rate is greater than 85%; Thermal deformation temperature is greater than 85℃; The weld strength is greater than 90% of the material's strength.

[0050] The microstructure of a composite material includes: The modified natural plant fiber forms a chemical bond at the interface with the bio-based polyester resin, with the coupling agent coverage exceeding 90%; The flame retardant is evenly dispersed in the matrix with a particle size of 5 μm, with no visible agglomeration; The toughening agent forms an island structure with an island phase diameter of 1 μm and a distribution density greater than 10 5 pieces / mm².

[0051] Comparative Example 1: The difference between this comparative example and Examples 1 to 3 is that no degradable toughening agent is added in the melt mixing stage.

[0052] Comparative Example 2: The difference between this comparative example and Examples 1 to 3 is that no environmentally friendly flame retardant is added during the functional additive addition stage.

[0053] Comparative Example 3: This comparative example differs from Examples 1 to 3 in that: in this comparative example, no surface modification treatment is performed on the natural plant fiber.

[0054] Comparative Example 4: The difference between this comparative example and Examples 1 to 3 is that no processing aid is added during the molding process in this comparative example.

[0055] The performance tests of the environmentally friendly composite materials for pipe joints prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were conducted. The test items and test methods are as follows: Tensile strength test: using a universal material testing machine, according to GB / T 1040.2-2006 "Determination of tensile properties of plastics"; Biodegradation rate test: bury in a soil environment with a temperature of 25℃±2℃ and a humidity of 60%±5% for 180 days, and calculate the percentage of mass loss; Oxygen index test: In a nitrogen and oxygen mixture, with an initial oxygen concentration of 21%, adjust the oxygen concentration until the sample continues to burn for 80 mm or 180 seconds; Water absorption test: completely immerse the sample in deionized water at a constant temperature of 25°C for 48 hours, then take it out and wipe off the surface moisture; Melt flow index test: The mass of the melt passing through a standard die every 10 minutes is measured at 190°C and a load of 2.16 kg.

[0056] The test data of the pipe joint composite materials prepared in Examples 1-3 and Comparative Examples 1-4 are recorded in the following table: By comparing and analyzing the data in the table, it can be seen that the environmentally friendly composite materials for pipe joints prepared by the process in Examples 1-3 have significantly better performance than the materials prepared by the process in Comparative Examples 1-4. This shows that the bio-based polyester resin forms a chemically bonded interface with the surface-modified plant fiber through molecular chain entanglement in the molten state, thereby enhancing the stress transfer efficiency between the fiber and the matrix; the degradable toughening agent induces shear yield of the matrix through the island structure dispersed phase, can absorb impact energy, and inhibit the crack propagation path, thereby improving the fracture resistance of the composite material; at the same time, the lubricating component in the processing aid reduces the melt viscosity, optimizes the filler dispersion state, and the nucleating agent induces the resin to form a microcrystalline structure, which synergistically improves the processing fluidity and dimensional stability of the material.

[0057] During the construction of the flame retardant system, the coated aluminum hydroxide decomposes when heated to release crystalline water, absorbing a large amount of heat from the combustion zone. The phosphorus-nitrogen flame retardant generates a free radical scavenger in the gas phase and forms an expanded carbon layer in the condensed phase. The dual effects block the combustion chain reaction. The coupling layer formed at the interface of the surface-modified fiber blocks the water penetration channel, and the hydrophobic groups are arranged in a direction to construct a waterproof barrier, inhibiting the erosion of moisture on the mechanical properties of the material.

[0058] Comparing and analyzing the relevant data in the table shows that the environmentally friendly composite material for pipe joints prepared by the present invention not only exhibits excellent mechanical strength, flame retardancy, and water resistance, but also achieves efficient biodegradability. This demonstrates that the process for preparing the environmentally friendly composite material for pipe joints provided by the present invention has a broader market prospect and is more suitable for promotion.

[0059] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0060] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an environmentally friendly composite material for a pipe joint, characterized by: The following steps are involved: Step 1: Raw material pretreatment Selecting natural plant fibers, wherein the natural plant fibers are at least one of bamboo fibers, hemp fibers, or coconut shell fibers, and having a fiber length of 0.5-3 mm, and performing alkali treatment, washing, and drying the fibers; Step 2: Melt mixing a. Add 40-60 parts by weight of bio-based polyester resin to the main feed port of a twin-screw extruder and control the temperature at 180-210°C to melt it; b. Introduce 20-35 parts by weight of pretreated natural plant fibers from the side feed port, and feed them at a screw speed of 200-400 r / min and a shear rate of 500-1500 Mix under the above conditions for 10-20 minutes to form a uniformly dispersed matrix mixture; Step 3: Adding functional additives To the matrix mixture obtained in step b, add in sequence: 8-15 parts by weight of degradable toughening agent, control the temperature to 160-190°C, and mix for 5-10 minutes; Add 5-12 parts by weight of environmentally friendly flame retardant, heat to 185-200°C, and mix for 8-15 minutes; Step 4: Processing and forming Add the mixture obtained in step 3 to an injection molding machine or molding equipment, and in the presence of 3-8 parts by mass of a processing aid, mold it at a mold temperature of 50-80°C and a pressure of 15-30 MPa, hold the pressure for 2-10 minutes, and demold to obtain a pipe joint product; Wherein, the bio-based polyester resin is at least one of polylactic acid, polyhydroxyalkanoate or polybutylene succinate; The degradable toughening agent is a blend of polycaprolactone and maleic anhydride grafted polylactic acid, with a blending mass ratio of 1:1-1:3; The environmentally friendly flame retardant is a compound of at least two of coated aluminum hydroxide, phosphorus-nitrogen intumescent flame retardant or zinc borate.

2. The method for preparing an environmentally friendly composite material for a pipe joint according to claim 1, characterized in that: The alkali treatment in step 1 comprises the following steps: The natural plant fiber is immersed in a sodium hydroxide solution with a mass concentration of 5%-10%, and treated at 60-80°C for 30-90 minutes. Ultrasonic waves are used to assist the treatment process at a frequency of 40kHz±5kHz. During cleaning, deionized water is used to rinse repeatedly until it becomes neutral. The drying conditions are hot air drying at 80-105℃ for 1-3 hours, and the final moisture content of the fiber is less than 1.5%.

3. The method for preparing an environmentally friendly composite material for a pipe joint according to claim 1, characterized in that: The natural plant fiber after the alkali treatment needs to be surface modified: Immerse the dry fiber in silane coupling agent ethanol solution with a silane coupling agent concentration of 1%-5% and an ethanol concentration of 95%. Take it out after soaking for 30-60 minutes and cure it in an oven at 110-130℃ for 0.5-1.5 hours. The silane coupling agent is γ-aminopropyltriethoxysilane or γ-glycidyloxypropyltrimethoxysilane.

4. The method for preparing an environmentally friendly composite material for a pipe joint according to claim 1, characterized in that: The mixing process in step 2b needs to control the melt temperature window to 185°C ± 5°C, the pressure sensor monitors the barrel pressure in real time and maintains it at 8-15 MPa, and the melt flow index is controlled at 10-30 g / 10 min.

5. The method for preparing an environmentally friendly composite material for a pipe joint according to claim 1, characterized in that: When adding the environmentally friendly flame retardant in step 3, a staged temperature increase strategy is adopted: First, mix at 185-190℃ for 3-5min, then heat to 195-200℃ and mix for 5-10min. During the vacuum degassing stage, the vacuum degree is maintained at 0.08-0.1MPa, and the degassing time is 5-8min.

6. The method for preparing an environmentally friendly composite material for a pipe joint according to claim 1, characterized in that: The processing aid is composed of the following components by weight: Lubricant: 1-3 parts of calcium stearate or oxidized polyethylene wax; Dispersant: polyvinyl pyrrolidone or hyperbranched polyester 0.5-2 parts; Nucleating agent: 0.3-1.5 parts of phenyl zinc phosphate or talc; Anti-hydrolysis agent: 1-1.5 parts of carbodiimide compound.

7. The method for preparing an environmentally friendly composite material for a pipe joint according to claim 1, characterized in that: The compounding ratio of the environmentally friendly flame retardant is coated aluminum hydroxide: phosphorus nitrogen intumescent flame retardant = 2:1-4:1, or zinc borate: phosphorus nitrogen intumescent flame retardant = 1:1-1:2; The phosphorus-nitrogen intumescent flame retardant is a compound of ammonium polyphosphate and melamine cyanurate, with a compounding mass ratio of 3:

1.

8. An environmentally friendly composite material for pipe joints, characterized by: Its components by mass include: 40-60 parts of bio-based polyester resin; 20-35 parts of modified natural plant fiber; 8-15 parts of degradable toughening agent; 5-12 parts of environmentally friendly flame retardant; 3-8 parts of processing aid; The material has a biodegradability rate greater than 90%, an oxygen index greater than 28%, a tensile strength greater than 45 MPa, and an impact toughness greater than 12 kJ / m².

9. The environmentally friendly composite material for pipe joints according to claim 8, characterized in that: The composite material meets the following performance indicators in pipe joint applications: Sealing pressure test: No leakage when maintaining pressure for 30 minutes under 1.6MPa water pressure; Corrosion resistance: After immersion in 10% NaCl solution for 30 days, the tensile strength retention rate is greater than 85%; Thermal deformation temperature is greater than 85℃; The weld strength is greater than 90% of the material's strength.

10. The environmentally friendly composite material for pipe joints according to claim 8, characterized in that: The microstructure of the composite material comprises: The modified natural plant fiber forms a chemical bond at the interface with the bio-based polyester resin, with the coupling agent coverage exceeding 90%; The flame retardant is evenly dispersed in the matrix with a particle size of 1-5 μm, with no visible agglomeration; The toughening agent forms an island structure with an island phase diameter of 0.2-1μm and a distribution density greater than 10 5 pieces / mm².

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