An environmental stress cracking resistant polyethylene material and a method for making the same

Abstract

The application discloses an anti-environmental stress cracking polyethylene material and a preparation method thereof, and relates to the technical field of polyethylene materials, which is prepared from the following raw materials in parts by weight: 40-60 parts of high-density polyethylene, 20-30 parts of linear low-density polyethylene, 5-10 parts of polyolefin elastomer, 2-5 parts of modified polyisobutylene, 0.1-0.3 parts of PIB crosslinker, 0.05-0.1 parts of MAH homopolymer, 3-8 parts of nano calcium carbonate, 2-4 parts of modified starch, 1-3 parts of maleic anhydride grafted polyethylene, 0.3-0.8 parts of antioxidant and the like. The anti-cracking combination of the modified polyisobutylene and the PIB crosslinker and the MAH homopolymer, the elastic enhancement combination of the polyolefin elastomer and the nano calcium carbonate, and the hydrophobic combination of the hydrophobic modified sodium alginate and the microencapsulated tea tree oil are designed, so that the problems of the traditional polyethylene material, such as insufficient anti-environmental stress cracking ability, difficult balance of mechanical properties and poor hydrophobicity, are solved.

Description

Technical Field

[0001] This invention relates to the field of polyethylene material technology, specifically to a polyethylene material resistant to environmental stress cracking and its preparation method. Background Technology

[0002] Polyethylene (PE) materials are widely used in outdoor water supply and drainage pipes, food packaging containers, automotive exterior parts, and chemical storage tanks due to their excellent chemical stability, processing fluidity, and cost-effectiveness. In these practical applications, the materials must withstand complex environmental conditions over long periods: outdoor pipes must resist soil stress and rainwater immersion; food packaging must withstand humidity changes during sterilization; automotive exterior parts must withstand high and low temperature cycles and ultraviolet radiation; and chemical storage tanks must come into contact with various corrosive media. As downstream applications continuously raise the performance requirements of materials, the modification research of traditional polyethylene materials has become a key focus in the industry.

[0003] Existing polyethylene material modification technologies have the following technical problems: Traditional environmental stress cracking (ESCR) modification of polyethylene materials often relies on a single elastic component, failing to construct a synergistic anti-cracking system from the molecular interface to macroscopic properties. On the one hand, the unmodified elastic component has poor interfacial compatibility with the polyethylene matrix, and the intermolecular bonding is weak. Under the combined action of stress and environmental media, microcracks easily form at the interface. On the other hand, there is a lack of utilization of endogenous byproducts generated during the modification process. These byproducts could have improved crack resistance through elastic support and dispersion, but in traditional processes, they are often treated as impurities to be removed or ignored. This makes it difficult to break through the bottleneck in the material's crack resistance, failing to meet the requirements for long-term outdoor or humid environments. In the existing technology, the optimization of the mechanical properties of polyethylene materials often falls into the dilemma of not being able to achieve both rigidity and toughness: if flexible components such as polyolefin elastomer (POE) are added to improve impact toughness, it will lead to a significant decrease in rigidity indicators such as tensile strength and flexural modulus; if inorganic fillers such as nano-calcium carbonate and talc are introduced to enhance rigidity, the impact strength will decrease due to poor bonding between the filler and the matrix. Traditional hydrophobic modification of polyethylene materials often uses a single additive. Such additives can only form a temporary hydrophobic layer on the material surface. After long-term exposure to a humid environment or repeated friction, the hydrophobic layer is prone to peeling off or failure, causing moisture to penetrate into the material. Moisture not only causes the polyethylene molecular chains to swell and degrade, but also exacerbates the aggregation of inorganic fillers, further reducing the material's crack resistance and mechanical stability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a polyethylene material resistant to environmental stress cracking and its preparation method, thus solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, embodiments of this application provide a polyethylene material resistant to environmental stress cracking, made from the following raw materials in parts by weight: 40-60 parts high-density polyethylene, 20-30 parts linear low-density polyethylene, 5-10 parts polyolefin elastomer, 2-5 parts modified polyisobutylene, 0.1-0.3 parts PIB crosslinker, 0.05-0.1 parts MAH homopolymer, 3-8 parts nano-calcium carbonate, 2-4 parts modified starch, 1-3 parts maleic anhydride grafted polyethylene, 0.3-0.8 parts antioxidant, 0.2-0.5 parts photoaging agent, 0.3-0.8 parts calcium stearate, 0.2-0.6 parts PE wax, 0.8-1.5 parts hydrophobically modified sodium alginate, 1-2 parts microencapsulated tea tree oil, and 1-3 parts modified chitosan; Among them, PIB crosslinkers and MAH homopolymers are both byproducts in the preparation process of modified polyisobutylene.

[0006] Preferably, the method for preparing modified polyisobutylene includes the following steps: Step 1: Take polyisobutylene raw material and vacuum dry it at 60-80℃ for 1-2 hours to remove moisture from the raw material and obtain pretreated polyisobutylene; the vacuum degree of vacuum drying is -0.07 to -0.09 MPa. Step 2: Mix pretreated polyisobutylene, maleic anhydride, and initiator in a weight ratio of 100:5~8:0.3~0.5, place the mixture in a high-speed mixer, and stir at 100~120℃ for 15~25 minutes to obtain a premix; the initiator is a mixture of dicumyl peroxide and benzoyl peroxide in a mass ratio of 1:1. Step 3: The premixed material is fed into a twin-screw extruder for grafting reaction. The screw speed of the extruder is 200-300 r / min, and the extrusion temperature range is 160-190℃. After water cooling, pelletizing and drying, the reaction product is obtained as modified polyisobutylene. During the reaction, some polyisobutylene molecular chains crosslink to form PIB crosslinks, and some maleic anhydride undergoes self-polymerization to form MAH homopolymers.

[0007] Preferably, the drying process in step three is hot air drying, with a drying temperature of 80-90°C and a drying time of 2-3 hours; the grafting rate of the modified polyisobutylene is 1.2%-2.0%, and the melt flow rate is 5-15 g / 10 min.

[0008] Preferably, the antioxidant is a mixture of hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 1:1; the photoaging agent is one of benzotriazole photoaging agents UV-326 or UV-327.

[0009] Preferably, the modified starch is propylene oxide modified starch, and its preparation method is as follows: Starch and propylene oxide are mixed at a mass ratio of 100:5-10 and reacted under alkaline conditions at 40-50°C for 3-4 hours. The reaction product is neutralized, washed, and dried to obtain propylene oxide-modified starch. The degree of substitution of the modified starch is 0.05-0.1.

[0010] Preferably, the capsule wall material of the microencapsulated tea tree oil is urea-formaldehyde resin, and the mass ratio of the capsule core to the capsule wall is 1:2 to 3; the particle size of the microencapsulated tea tree oil is 3 to 8 μm, and the encapsulation rate is ≥85%.

[0011] Preferably, the hydrophobically modified sodium alginate is hexadecyltrimethylammonium bromide modified sodium alginate, and the modification method is as follows: Sodium alginate was dissolved in deionized water, and hexadecyltrimethylammonium bromide was added. The mass ratio of sodium alginate to hexadecyltrimethylammonium bromide was 100:8-12. The mixture was stirred at 50-60°C for 2-3 hours. After precipitation, filtration and drying, hydrophobic modified sodium alginate was obtained.

[0012] Preferably, the modified chitosan is acetic anhydride-modified chitosan, and the preparation steps include: Chitosan was dissolved in a 1%–2% acetic acid solution, and acetic anhydride was added. The molar ratio of chitosan to acetic anhydride was 1:0.5–1. The mixture was reacted at 30–40°C for 1–2 hours. The pH was adjusted to 7–8 with sodium hydroxide solution. After precipitation, the mixture was washed and dried to obtain modified chitosan. The degree of deacetylation of the modified chitosan was ≥80%.

[0013] Preferably, the nano-calcium carbonate has a particle size of 50–100 nm and is modified with the silane coupling agent KH-550; the modification process is as follows: Nano-calcium carbonate and KH-550 are stirred in a high-speed mixer at 80-100°C for 30-40 minutes to obtain modified nano-calcium carbonate, wherein the mass ratio of nano-calcium carbonate to KH-550 is 100:2-4.

[0014] Secondly, embodiments of this application provide a method for preparing a polyethylene material resistant to environmental stress cracking, comprising the following steps: Step 1: Weigh all raw materials according to the weight proportions. First, put high-density polyethylene, linear low-density polyethylene, and polyolefin elastomer into a high-speed mixer and stir at 120-140°C for 10-15 minutes to obtain the resin matrix material. Step 2: Add modified polyisobutylene, PIB crosslinker, MAH homopolymer, nano calcium carbonate, modified starch, and maleic anhydride grafted polyethylene to the resin matrix material, and continue stirring at 130-150℃ for 15-20 minutes to obtain the premixed main material. Step 3: Add antioxidants, photoaging agents, calcium stearate, PE wax, hydrophobically modified sodium alginate, microencapsulated tea tree oil, and modified chitosan to the premixed main ingredients, and stir at 110-130℃ for 5-10 minutes to obtain the mixture. Step four: The mixture is fed into a twin-screw extruder for extrusion granulation. The screw speed of the extruder is 180-250 r / min, and the extrusion temperature range is 170-200℃. After cooling and screening, the granules are used to obtain polyethylene material resistant to environmental stress cracking.

[0015] This invention provides a polyethylene material resistant to environmental stress cracking and its preparation method. It has the following beneficial effects: (1) By designing a crack-resistant combination of modified polyisobutylene and PIB crosslinker and MAH homopolymer, combined with an elastic enhancement combination of polyolefin elastomer and nano calcium carbonate, and a hydrophobic combination of hydrophobically modified sodium alginate and microencapsulated tea tree oil, a complete functional network is formed from the molecular interface to the macroscopic properties, which solves the problems of insufficient resistance to environmental stress cracking, difficulty in balancing mechanical properties and poor hydrophobicity of traditional polyethylene materials; (2) In view of the characteristics of modified polyisobutylene and by-products, a special vacuum drying pretreatment process was designed to avoid the negative impact of moisture on interfacial bonding; a step-by-step premixing process was adopted, and the resin matrix, interfacial modification components and functional additives were added in sequence to solve the problem of uneven dispersion of raw materials caused by traditional one-time mixing. (3) Through the synergistic optimization of raw materials and processes, the material has excellent resistance to environmental stress cracking, mechanical load-bearing capacity and moisture absorption capacity, and can be adapted to complex application scenarios such as outdoor pipelines, food packaging, and automotive exterior parts, breaking the limitations of the application range of traditional polyethylene materials; at the same time, the introduction of natural modified components such as modified starch and modified chitosan reduces the amount of chemical additives used, reduces the risk of harmful substances being released, and conforms to the current development direction of green and safe polymer materials, improving the environmental friendliness and safety of the material.

[0016] (4) Use natural modified components to partially replace expensive chemical additives, thereby reducing the cost of raw material procurement while ensuring material performance; reduce the agglomeration of raw materials through stepwise mixing process, thereby reducing the scrap rate caused by substandard performance and reducing resource waste in the production process. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Traditional polyethylene materials have the following problems when used in complex environments such as outdoors, in humid conditions, and in chemical media: First, they have insufficient resistance to environmental stress cracking (ESCR), and the balance between the rigidity and flexibility of the molecular chain is not good. Under long-term stress and the combined effect of environmental media, microcracks are prone to appear, leading to premature product failure. Second, modified polyisobutylene has poor compatibility with the polyethylene matrix. Unmodified polyisobutylene molecular chains are nonpolar and have weak interfacial bonding with the resin. Moreover, the PIB crosslinks and MAH homopolymers generated during the modification process are prone to agglomeration, which affects the uniformity of the material. Third, the uneven dispersion of fillers such as nano-calcium carbonate and modified starch during processing can easily lead to stress concentration points, exacerbating the risk of cracking. Fourth, the synergy between hydrophobicity and anti-aging is poor. Moisture penetration in humid environments can cause damage to the internal structure. At the same time, thermal-oxidative aging and photo-aging during outdoor use accelerate molecular chain degradation, further reducing crack resistance. Fifth, traditional preparation processes are not designed to adapt to modified polyisobutylene and by-products, resulting in uneven mixing of raw materials, insufficient thermal stability, and large fluctuations in ESCR levels between batches, making it difficult to meet the needs of stable industrial production.

[0019] To address the aforementioned problems in the prior art, this application provides a polyethylene material resistant to environmental stress cracking and its preparation method. By constructing a synergistic system of core resin, modified polyisobutylene, endogenous byproducts, and functional additives, and combining it with a process scheme of graded pretreatment of raw materials, stepwise premixing, and precise extrusion granulation, the compatibility problem between modified polyisobutylene and the matrix is ​​solved. Furthermore, the synergistic effect of PIB crosslinkers and MAH homopolymers enhances the stress cracking resistance, while also improving the material's hydrophobicity, anti-aging properties, and processing stability, making it suitable for complex environmental applications such as outdoor pipelines, packaging containers, and automotive parts.

[0020] In terms of raw material ratio, the embodiments of this application use 40%–60% high-density polyethylene (HDPE) as the main component, combined with 20%–30% linear low-density polyethylene (LLDPE), utilizing the rigidity of HDPE and the short-chain flexibility of LLDPE to synergistically balance the mechanical properties of the matrix; 2%–5% modified polyisobutylene (PIB-g-MAH) and 0.15%–0.4% endogenous byproducts (PIB crosslinker, MAH homopolymer) are introduced, the polar groups of modified polyisobutylene improve interfacial compatibility, the PIB crosslinker enhances elastic recovery ability, and the MAH homopolymer assists in dispersion and filling. The materials, including polyolefin elastomer (POE) and nano-calcium carbonate, work synergistically to improve the ESCR rating. The combination of 5%–10% POE and 3%–8% nano-calcium carbonate allows POE to form elastic micro-regions that absorb stress, while nano-calcium carbonate disperses stress concentration, further enhancing crack resistance. The addition of 1%–3% maleic anhydride-grafted polyethylene (PE-g-MAH) compatibilizer improves the interfacial bonding between inorganic fillers and organic resins. The combination of hydrophobically modified sodium alginate and microencapsulated tea tree oil creates a dual hydrophobic network, reducing moisture absorption. Antioxidants and photoaging agents are added to delay degradation, while calcium stearate and PE wax optimize processing flowability. In terms of process, a modified polyisobutylene-specific pretreatment, step-by-step feeding and mixing, and precise temperature-controlled extrusion are employed to ensure uniform raw material dispersion and avoid byproduct agglomeration and additive thermal decomposition.

[0021] The complete process steps of this application are as follows: S1: Raw material pretreatment Modified polyisobutylene, PIB crosslinker, and MAH homopolymer were vacuum dried at 70–80°C for 1.5–2.5 hours with a vacuum degree of -0.08–-0.09 MPa to remove adsorbed moisture and avoid poor interfacial bonding. After drying, the products were sealed and stored to prevent moisture absorption.

[0022] Nano-calcium carbonate modified with KH-550, modified starch, and modified chitosan were passed through a 100-120 mesh sieve, and the sieve-passing material was collected. The material was then dried at 60-70℃ for 1-1.5 hours, with the moisture content controlled to ≤0.3%, to avoid filler agglomeration and processing bubbles.

[0023] Microencapsulated tea tree oil was vacuum dried at 35–45°C for 0.8–1.2 hours with a moisture content ≤0.2% to prevent premature release of the oil due to capsule wall rupture during extrusion. Hydrophobically modified sodium alginate was passed through an 80-mesh sieve and then sealed for storage to prevent moisture absorption and reduced hydrophobicity.

[0024] The polyolefin elastomer (POE) is dried at 80-90°C for 1 hour to remove surface oil and moisture, thereby improving its compatibility with the resin matrix.

[0025] In some embodiments of this application, if the drying temperature of the modified polyisobutylene is below 70°C in step S1, the moisture removal is incomplete, which can easily lead to bubbles in the extruded strip; if it is above 80°C, its grafted structure is easily destroyed, reducing its compatibility with the matrix. The drying temperature of nano-calcium carbonate is controlled at 60–70°C, which can remove moisture while avoiding the decomposition of the surface modifier: if the temperature is too high, the KH-550 coupling agent will fail, increasing the risk of filler agglomeration; if the temperature is too low, residual moisture will lead to a decrease in interfacial bonding.

[0026] In some embodiments of this application, in step S1, if the vacuum drying time of the microencapsulated tea tree oil is less than 0.8 hours, the moisture is not completely removed, and the capsule wall is prone to rupture during high-temperature extrusion; if it is longer than 1.2 hours, the tea tree oil is prone to volatilization, reducing the hydrophobic effect. The modified chitosan should be used within 24 hours after sieving to avoid long-term exposure to moisture absorption, which would lead to a decrease in hydrophobicity.

[0027] S2: Premix Weigh out the following components by weight: high-density polyethylene, linear low-density polyethylene, polyolefin elastomer, maleic anhydride-grafted polyethylene, antioxidant, photoaging agent, calcium stearate, PE wax, and the modified polyisobutylene, PIB crosslinker, MAH homopolymer, nano-calcium carbonate, modified starch, modified chitosan, hydrophobically modified sodium alginate, and microencapsulated tea tree oil. Pour them into a high-speed mixer and stir in three steps: First, add high-density polyethylene, linear low-density polyethylene, and polyolefin elastomer, and stir for 3 minutes at a speed of 100-120 r / min and a temperature of 25-30℃ to form a uniform resin matrix. Add modified polyisobutylene, PIB crosslinker, MAH homopolymer, and maleic anhydride-grafted polyethylene, and continue stirring for 2 minutes while maintaining the rotation speed to promote interfacial bonding. Add the remaining additives and fillers, reduce the rotation speed to 80-100 r / min, and stir for 4 minutes to obtain the premixed material.

[0028] In some embodiments of this application, in step S2, the relative humidity of the mixing environment is ≤55% to avoid moisture absorption by the raw materials; the purpose of the three-step stirring is to first construct the resin matrix, then add interface modification-related components, such as modified polyisobutylene and compatibilizers, and finally add additives and fillers, which can improve the dispersion uniformity. If the stirring order is reversed, modified polyisobutylene and by-products are prone to adhere to the inner wall of the equipment, resulting in excessively high or low local concentrations, affecting the crack resistance performance; the rotation speed is controlled at 80-120 r / min, which can ensure uniform mixing and avoid the microencapsulated tea tree oil from breaking due to excessive shear force.

[0029] In some embodiments of this application, in step S2, the total mixing time is controlled at 9 minutes. If it is less than 9 minutes, the raw materials are not sufficiently dispersed; if it is more than 9 minutes, the raw materials are prone to heating up due to friction, and the modified polyisobutylene will slightly melt, affecting the subsequent extrusion processing.

[0030] S3: Extrusion Granulation The premixed material obtained in step S2 is fed into a twin-screw extruder, and the extrusion granulation parameters are as follows: The screw length-to-diameter ratio is 40:1, and the temperature settings for each zone are as follows: Zone 1 160-170℃, Zone 2 175-185℃, Zone 3 185-195℃, Zone 4 190-200℃, and the die head temperature 195-205℃. The main unit's rotation speed is 250–300 r / min, and the vacuum negative pressure is -0.07–-0.08 MPa; The extruded strip is cooled by water at a temperature of 20-25°C. After cooling to 40-50°C, it enters the pelletizer and is pelletized to a diameter of 2-3 mm and a length of 2-3 mm. After pelleting, the pellets are dried at 70-80℃ for 1-1.5 hours to remove surface moisture. They are then sealed in aluminum-plastic composite bags with desiccant added. The relative humidity of the storage environment is ≤50%.

[0031] In some embodiments of this application, in step S3, the extrusion temperature range is controlled between 160 and 205°C. If the temperature is below 160°C, the raw material will not melt sufficiently; if it is above 205°C, the grafted structure of the modified polyisobutylene will easily decompose, and a large amount of microencapsulated tea tree oil will rupture, leading to a decrease in crack resistance and hydrophobic properties. The main motor speed is 250–300 r / min, which can balance the shear strength and material residence time: if the speed is too high, the shear force will be too large, leading to the degradation of POE elastomer; if the speed is too low, the material will be unevenly mixed.

[0032] In some embodiments of this application, in step S3, the water cooling temperature is 20-25°C. If the water temperature is below 20°C, the material strip will cool too quickly and easily crack; if it is above 25°C, insufficient cooling will cause the particles to stick together. After the particles are dried, they need to be cooled to room temperature before packaging to avoid internal moisture condensation caused by high-temperature packaging.

[0033] In this application, the modified polyisobutylene is a maleic anhydride-grafted product with a grafting rate of 1.2%–2.0%. Its maleic anhydride groups can react with the hydroxyl groups on the surface of nano-calcium carbonate and the modified starch hydroxyl groups to enhance interfacial bonding. The PIB crosslinker can form elastic support points in the matrix, reducing residual stress. The MAH homopolymer, as a polar small molecule, can assist in dispersing nano-calcium carbonate and prevent filler agglomeration. The antioxidant is a 1:1 mass ratio of 1010 and 168, which synergistically enhances thermo-oxidative stability. The photoaging agent is UV-327, which can absorb ultraviolet rays and delay outdoor aging. Microencapsulated tea tree oil and hydrophobically modified sodium alginate work together to form a hydrophobic film on the material surface, reducing water penetration. The capsule wall of the microencapsulated tea tree oil is made of urea-formaldehyde resin with a particle size of 3–8 μm and an encapsulation rate of ≥85%.

[0034] The present application will be described in detail below with reference to specific embodiments. The total weight of raw materials in each embodiment is 100 parts. The raw material specifications and process steps are the same as those mentioned above, with only the key parameters being different. The comparative examples omit the core raw materials or use traditional processes to verify the superiority of the technical solution of the present application.

[0035] Example 1 S1: Raw material pretreatment: 3 parts of modified polyisobutylene, 0.2 parts of PIB crosslinker, and 0.07 parts of MAH homopolymer were vacuum dried at 75℃ for 2 hours with a vacuum degree of -0.085MPa; 4.5 parts of KH-550 modified nano-calcium carbonate with a particle size of 80nm; 2.8 parts of propylene oxide modified starch with a degree of substitution of 0.08; 1.8 parts of acetic anhydride modified chitosan with a degree of deacetylation of 85% were passed through a 110-mesh sieve and dried at 65℃ for 1.2 hours; 1.4 parts of microencapsulated tea tree oil with a particle size of 5μm and an encapsulation rate of 88% were vacuum dried at 40℃ for 1 hour; 1.1 parts of hydrophobically modified sodium alginate were passed through an 80-mesh sieve and sealed for later use; 7 parts of POE were dried at 85℃ for 1 hour.

[0036] S2: Premix: Weigh 50 parts HDPE, 25 parts LLDPE, 6 parts POE, 1.9 parts PE-g-MAH, 0.5 parts antioxidant, 0.3 parts photoaging agent, 0.5 parts calcium stearate, 0.93 parts PE wax, and the remaining raw materials after S1 pretreatment; mix in an environment of 28℃ and 50% relative humidity. First add HDPE, LLDPE, and POE and stir at 110r / min for 3 minutes. Then add modified polyisobutylene, PIB crosslinker, MAH homopolymer, and PE-g-MAH and stir for 2 minutes. Finally, add the remaining components and stir at 90r / min for 4 minutes to obtain the premixed material.

[0037] S3: Extrusion granulation: Twin-screw extruder with a length-to-diameter ratio of 40:1, zone 1 165℃, zone 2 180℃, zone 3 190℃, zone 4 195℃, die head 200℃; main extruder speed 280r / min, vacuum negative pressure -0.075MPa; water cooling temperature 22℃, strip cooled to 45℃ and granulated, particle size 2.5mm, length 2.5mm; granules dried at 75℃ for 1.2 hours, sealed in aluminum-plastic composite bags.

[0038] Example 2-10 Examples 2-10 are based on Example 1, with only one key parameter changed, while all other conditions remain completely the same. Specific differences are shown in Table 1. Table 1. Differences in parameters for Examples 1-10 ; Comparative Examples 1-5 Comparative Examples 1-5, based on Example 1, verify the necessity of the technical solution of this application by omitting core raw materials, replacing key components, or adopting traditional processes. Specific parameter differences are shown in Table 2. Table 2 Comparative Examples 1-5 Parameter Differences Table ; Performance testing and results analysis 1. Detection Indicators and Methods The environmental stress cracking resistant polyethylene materials prepared in Examples 1-10 and Comparative Examples 1-5 were tested for their core performance according to the following standards: Environmental stress cracking time (ESCR): Refer to GB / T 1842-2008, use the bending method, test temperature 50℃, immersion medium is 10% Igepal CO-630 solution, and record the time when the sample cracks. Tensile strength: Refer to GB / T 1040.2-2006, tensile rate 50 mm / min, test ambient temperature 23℃; Impact strength of simply supported beam: Refer to GB / T 1043.1-2008, impact velocity 3.5m / s, test ambient temperature 23℃; Moisture absorption rate: Refer to GB / T 1034-2008, and calculate the mass change rate after being placed at 23℃ and 85% relative humidity for 48 hours; Water contact angle: Refer to GB / T 30693-2014, drop volume 5μL, and use a contact angle measuring instrument to test the material surface; Impact strength retention rate after thermo-oxidative aging: Refer to GB / T 7141-2008, place in an aging chamber at 100℃ for 168h, test the impact strength after aging, and calculate the retention rate: strength after aging / strength before aging × 100%.

[0039] 2. Performance test results The performance test results of each embodiment and comparative example are shown in Table 3: Table 3 Performance test results of Examples 1-10 and Comparative Examples 1-5 ; Analysis of performance impact patterns: 1. The effect of high-density polyethylene (HDPE) fraction Example 2: Due to the reduced HDPE content and insufficient matrix rigidity, the tensile strength decreased to 29.5 MPa, the ESCR time was shortened to 1080 h, and the impact strength was 16.8 kJ / m. 2 ; Example 3: Excessive HDPE content leads to decreased matrix flexibility and a drop in impact strength to 15.3 kJ / m. 2 Although the tensile strength was increased to 35.2 MPa, the ESCR time was only 1120 h. This is because excessive rigidity can easily lead to stress concentration, which in turn reduces the crack resistance. Conclusion: 50 parts HDPE is the optimal formulation, which can balance rigidity and flexibility, and achieve optimal ESCR time, tensile strength and impact strength.

[0040] 2. Effect of the amount of modified polyisobutylene Example 4: Due to insufficient modified polyisobutylene, the interfacial compatibility and elastic support were inadequate, resulting in an ESCR time of 950 h and an impact strength of 17.2 kJ / m. 2 ; Example 5: With excess modified polyisobutylene, the ESCR time was increased to 1320 h and the impact strength was 19.2 kJ / m. 2 However, the tensile strength decreased to 30.8 MPa, which was due to the excessive elastic component diluting the rigidity of the matrix; Conclusion: Three parts of modified polyisobutylene can best exert the effects of interface modification and elastic support, while taking into account both crack resistance and rigidity.

[0041] 3. Effect of polyolefin elastomer (POE) content Example 6: Insufficient POE results in a small number of elastic micro-regions, weak stress absorption capacity, ESCR time of 1020h, and impact strength of 16.1kJ / m. 2 ; Example 7: Excessive POE caused an excessive decrease in matrix rigidity, with tensile strength dropping to 28.9 MPa, despite an ESCR time of 1380 h and an impact strength of 20.5 kJ / m. 2 However, it cannot meet the rigidity requirements of structural components; Conclusion: POE 7 can achieve a balance between stress absorption and rigidity, making it suitable for most application scenarios.

[0042] 4. Effect of drying temperature on modified polyisobutylene Example 8: Incomplete moisture removal resulted in a slight decrease in interfacial adhesion; ESCR time was 1180 h; impact strength was 18.1 kJ / m. 2 ; Example 9: When the temperature is close to the upper limit of the tolerance of the modified polyisobutylene graft structure, the grafting rate decreases slightly, the ESCR time is 1210h, and the tensile strength is 32.5MPa. Conclusion: 75℃ is the optimal drying temperature, which can completely remove water and protect the grafted structure.

[0043] 5. The Influence of Stirring Method Example 10: Uneven raw material dispersion, local agglomeration of modified polyisobutylene and by-products, ESCR time 1050h, tensile strength 30.2MPa, impact strength 16.5kJ / m 2 ; Conclusion: The stepwise stirring method, which involves first mixing the matrix, then the interfacial components, and finally the additives, can improve the dispersion uniformity and is a key process to ensure performance.

[0044] 6. Comparative Performance Difference Analysis Comparative Example 1: Lacking the core crack-resistant component, the ESCR time is only 580 h, and the impact strength is 13.8 kJ / m. 2 This demonstrates that modified polyisobutylene, PIB crosslinkers, and MAH homopolymers are the core components for improving crack resistance. Comparative Example 2: Unmodified polyisobutylene has poor compatibility with the matrix, ESCR time of 720 h, and impact strength of 14.5 kJ / m. 2 To verify the interfacial modification value of modified polyisobutylene; Comparative Example 3: With the absence of hydrophobic network, the moisture absorption rate increased to 0.68%, and the water contact angle decreased to 78.5°, demonstrating the synergistic hydrophobic effect of hydrophobically modified sodium alginate and microencapsulated tea tree oil. Comparative Example 4: Uneven dispersion resulted in an ESCR time of 980 h and an impact strength of 15.8 kJ / m. 2 This highlights the necessity of a stepwise mixing process; Comparative Example 5: Insufficient elastic support and stress dispersion, ESCR time 850h, impact strength 12.3kJ / m 2 This study verified the synergistic enhancement effect of POE and nano-calcium carbonate.

[0045] This application's embodiments construct a crack-resistant core system consisting of modified polyisobutylene, PIB crosslinkers, and MAH homopolymers, which synergistically improve the ESCR time to 1250 hours; combined with an elastic-reinforcing system of POE and nano-calcium carbonate, the impact strength reaches 18.5 kJ / m. 2The dual hydrophobic network of hydrophobically modified sodium alginate and microencapsulated tea tree oil reduces the moisture absorption rate to 0.32%, achieving synergistic optimization of crack resistance, mechanical properties, and hydrophobicity.

[0046] This application's embodiments are designed with a special pretreatment and stepwise premixing process for vacuum drying at 70-80℃ for modified polyisobutylene and by-products, which solves the problem of uneven dispersion in traditional processes, making the ESCR time fluctuation range ≤5.6%, far lower than the 16% of traditional processes, and meeting the batch stability requirements of industrial continuous production.

[0047] The material in this application embodiment has an ESCR time ≥1250h, tensile strength ≥32.8MPa, and moisture absorption ≤0.32%, making it suitable for complex scenarios such as outdoor pipelines, food packaging, and automotive exterior parts. This expands the application range of traditional polyethylene materials by more than 40%. Furthermore, the introduction of natural components such as modified starch and modified chitosan reduces the amount of chemical additives used and lowers the risk of precipitation, which is in line with the trend of green material development.

[0048] The embodiments of this application partially replace expensive chemical additives with natural modified components, reducing raw material costs by 8% to 12%; at the same time, the step-by-step process reduces the scrap rate caused by agglomeration and performance fluctuations, improving overall production efficiency by more than 15%, thus balancing performance and economy.

[0049] In summary, the specific implementation method of this application demonstrates the innovation, stability and practicality of the environmental stress cracking resistant polyethylene material and its preparation method through a complete logical chain of pain point analysis, scheme design, process optimization, performance verification and rule summarization. It not only solves the core problems of insufficient crack resistance, uneven dispersion and poor hydrophobic aging resistance of traditional polyethylene materials, but also provides an industrializable technical path for the application of polymer materials in complex environments.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A polyethylene material resistant to environmental stress cracking, comprising the following raw materials in parts by weight: 40-60 parts high-density polyethylene, 20-30 parts linear low-density polyethylene, 5-10 parts polyolefin elastomer, 2-5 parts modified polyisobutylene, 0.1-0.3 parts PIB crosslinker, 0.05-0.1 parts MAH homopolymer, 3-8 parts nano-calcium carbonate, 2-4 parts modified starch, 1-3 parts maleic anhydride grafted polyethylene, 0.3-0.8 parts antioxidant, 0.2-0.5 parts photoaging agent, 0.3-0.8 parts calcium stearate, 0.2-0.6 parts PE wax, 0.8-1.5 parts hydrophobically modified sodium alginate, 1-2 parts microencapsulated tea tree oil, and 1-3 parts modified chitosan; in, The PIB crosslinker and MAH homopolymer are both byproducts of the preparation process of modified polyisobutylene.

2. The polyethylene material resistant to environmental stress cracking according to claim 1, characterized in that, The method for preparing the modified polyisobutylene includes the following steps: Step 1: Take polyisobutylene raw material and vacuum dry it at 60-80℃ for 1-2 hours to remove moisture from the raw material and obtain pretreated polyisobutylene; the vacuum degree of the vacuum drying is -0.07 to -0.09 MPa. Step 2: Mix pretreated polyisobutylene, maleic anhydride, and initiator in a weight ratio of 100:5~8:0.3~0.5, place the mixture in a high-speed mixer, and stir at 100~120℃ for 15~25 minutes to obtain a premix; the initiator is a compound of dicumyl peroxide and benzoyl peroxide in a mass ratio of 1:

1. Step 3: The premixed material is fed into a twin-screw extruder for grafting reaction. The screw speed of the extruder is 200-300 r / min, and the extrusion temperature range is 160-190℃. After water cooling, pelletizing and drying, the reaction product is obtained as modified polyisobutylene. During the reaction, some polyisobutylene molecular chains crosslink to form PIB crosslinks, and some maleic anhydride undergoes self-polymerization to form MAH homopolymers.

3. The polyethylene material resistant to environmental stress cracking according to claim 2, characterized in that, The drying process in step three is hot air drying, with a drying temperature of 80-90℃ and a drying time of 2-3 hours; the grafting rate of the modified polyisobutylene is 1.2%-2.0%, and the melt flow rate is 5-15 g / 10 min.

4. The polyethylene material resistant to environmental stress cracking according to claim 1, characterized in that, The antioxidant is prepared by compounding hindered phenolic antioxidant 1010 and phosphite antioxidant 168 in a mass ratio of 1:1; the photoaging agent is one of benzotriazole photoaging agents UV-326 or UV-327.

5. A polyethylene material resistant to environmental stress cracking according to claim 1, characterized in that, The modified starch is propylene oxide modified starch, and its preparation method is as follows: Starch and propylene oxide are mixed at a mass ratio of 100:5-10 and reacted under alkaline conditions at 40-50°C for 3-4 hours. The reaction product is neutralized, washed, and dried to obtain propylene oxide-modified starch. The degree of substitution of the modified starch is 0.05-0.

1.

6. A polyethylene material resistant to environmental stress cracking according to claim 1, characterized in that, The capsule wall material of the microencapsulated tea tree oil is urea-formaldehyde resin, and the mass ratio of the capsule core to the capsule wall is 1:2 to 3; the particle size of the microencapsulated tea tree oil is 3 to 8 μm, and the encapsulation rate is ≥85%.

7. A polyethylene material resistant to environmental stress cracking according to claim 1, characterized in that, The hydrophobically modified sodium alginate is hexadecyltrimethylammonium bromide modified sodium alginate, and the modification method is as follows: Sodium alginate was dissolved in deionized water, and hexadecyltrimethylammonium bromide was added. The mass ratio of sodium alginate to hexadecyltrimethylammonium bromide was 100:8-12. The mixture was stirred at 50-60°C for 2-3 hours. After precipitation, filtration and drying, hydrophobic modified sodium alginate was obtained.

8. A polyethylene material resistant to environmental stress cracking according to claim 1, characterized in that, The modified chitosan is acetic anhydride-modified chitosan, and the preparation steps include: Chitosan was dissolved in a 1%–2% acetic acid solution, and acetic anhydride was added. The molar ratio of chitosan to acetic anhydride was 1:0.5–1. The mixture was reacted at 30–40°C for 1–2 hours. The pH was adjusted to 7–8 with sodium hydroxide solution. After precipitation, the mixture was washed and dried to obtain modified chitosan. The degree of deacetylation of the modified chitosan was ≥80%.

9. A polyethylene material resistant to environmental stress cracking according to claim 1, characterized in that, The nano-calcium carbonate has a particle size of 50–100 nm and is modified with silane coupling agent KH-550; the modification process is as follows: Nano-calcium carbonate and KH-550 are stirred in a high-speed mixer at 80-100°C for 30-40 minutes to obtain modified nano-calcium carbonate, wherein the mass ratio of nano-calcium carbonate to KH-550 is 100:2-4.

10. A method for preparing a polyethylene material resistant to environmental stress cracking as described in any one of claims 1 to 9, characterized in that, Includes the following steps: Step 1: Weigh all raw materials according to the weight proportions. First, put high-density polyethylene, linear low-density polyethylene, and polyolefin elastomer into a high-speed mixer and stir at 120-140°C for 10-15 minutes to obtain the resin matrix material. Step 2: Add modified polyisobutylene, PIB crosslinker, MAH homopolymer, nano calcium carbonate, modified starch, and maleic anhydride grafted polyethylene to the resin matrix material, and continue stirring at 130-150°C for 15-20 minutes to obtain the premixed main material. Step 3: Add antioxidant, photoaging agent, calcium stearate, PE wax, hydrophobically modified sodium alginate, microencapsulated tea tree oil, and modified chitosan to the premixed main material, and stir at 110-130°C for 5-10 minutes to obtain the mixture. Step four: The mixture is fed into a twin-screw extruder for extrusion granulation. The screw speed of the extruder is 180-250 r / min, and the extrusion temperature range is 170-200℃. After cooling and screening, the granules are used to obtain polyethylene material resistant to environmental stress cracking.