A heat and hydrolysis resistant polyethylene material and a method for making the same

Abstract

This invention relates to a heat- and hydrolysis-resistant polyethylene material and its preparation method, belonging to the field of polymer materials technology. The polyethylene material comprises polyethylene resin, a vinyl silane coupling agent, a composite initiation system, a modified carbodiimide anti-hydrolysis agent, a catalyst, and an antioxidant. The composite initiation system is composed of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and N-hydroxyphthalimide. The modified carbodiimide anti-hydrolysis agent is a functionalized polyethylene with carbodiimide groups and hindered phenolic antioxidant groups grafted onto the polyethylene backbone. In preparation, graft material A and functional masterbatch B are prepared separately, then mixed, granulated, and crosslinked in warm water. This invention achieves chemical bonding and fixation of the anti-hydrolysis groups through modified carbodiimide, while the composite initiation system inhibits crosslinking side reactions, giving the material heat resistance, hydrolysis resistance, and drinking water contact safety, making it suitable for water-contact components such as water pump housings in water dispensers.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more particularly to a heat-resistant and hydrolysis-resistant polyethylene material and its preparation method. Background Technology

[0002] Polyethylene (PE) is widely used in pipes, cables, packaging, and household products due to its excellent electrical insulation, chemical resistance, and processability. However, the molecular chains of ordinary thermoplastic polyethylene have a linear structure, which is prone to slippage when heated. Its long-term operating temperature is usually no more than 70°C. At the same time, its performance may deteriorate in high-temperature hot water environments due to cross-linking network hydrolysis and small molecule migration and precipitation, making it difficult to meet the comprehensive requirements of water-contact components such as water pump housings for heat resistance, hydrolysis resistance, and drinking water safety.

[0003] To overcome the aforementioned defects, existing technologies typically employ the following technical means: First, adding anti-hydrolysis agents. Commonly used anti-hydrolysis agents include carbodiimide compounds, such as N,N'-bis(2,6-diisopropylphenyl)carbodiimide, to improve the stability of the material under humid and hot environments. Second, adding initiators. Commonly used initiators include dicumyl peroxide, used to initiate silane grafting reactions.

[0004] While the aforementioned technologies have improved the performance of polyethylene to some extent, several shortcomings remain. First, existing anti-hydrolysis additives have poor compatibility with the polyethylene matrix and are prone to migration and precipitation under prolonged immersion. This not only makes the anti-hydrolysis effect difficult to maintain but also risks causing secondary pollution of drinking water. Second, traditional initiators easily induce side reactions such as cross-linking during the grafting process, producing gels that affect the integrity of the cross-linked network, thereby reducing the material's heat resistance, increasing small molecule residues, and producing odorous decomposition products. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a heat-resistant and hydrolysis-resistant polyethylene material and its preparation method. The method utilizes a modified carbodiimide anti-hydrolysis agent to achieve chemical bonding and fixation of the anti-hydrolysis groups. A composite initiation system using 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (i.e., bis(2,5-diphenyl ether)) and N-hydroxyphthalimide (NOP) inhibits cross-linking side reactions, optimizing the grafting reaction. A stepwise antioxidant addition strategy balances processing stability and grafting efficiency. The synergistic effect of these three factors results in a material that possesses heat resistance, hydrolysis resistance, and drinking water contact safety, meeting the requirements for use in water-contact components such as the water pump housing of a miniature water dispenser.

[0006] The objective of this invention can be achieved through the following technical solutions: In a first aspect, a heat-resistant and hydrolysis-resistant polyethylene material is provided, comprising the following components by weight: 100 parts of polyethylene resin; Vinylsilane coupling agent 0.5-3 parts; 0.02-0.2 parts of the composite initiation system; 0.1-1 parts of modified carbodiimide anti-hydrolysis agent; Catalyst 0.01-0.05 parts; Antioxidant 0.1-0.5 parts.

[0007] Furthermore, the polyethylene resin is a blend of high-density polyethylene and linear low-density polyethylene; the melt flow rate of the polyethylene resin is 1.0-5.0 g / 10 min; and the blending ratio of the linear low-density polyethylene is 5-30% of the total weight of the polyethylene resin.

[0008] Furthermore, the vinylsilane coupling agent is vinyltrimethoxysilane or vinyltriethoxysilane.

[0009] Furthermore, the composite initiation system is composed of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and N-hydroxyphthalimide (NOP), wherein the weight ratio of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane to N-hydroxyphthalimide is (1-5):1.

[0010] Furthermore, the modified carbodiimide antihydrolysis agent is functionalized polyethylene, which is composed of a polyethylene backbone and carbodiimide groups and hindered phenolic antioxidant groups grafted onto the polyethylene backbone; the grafting rate of the carbodiimide groups is 0.5-5 wt%, and the grafting rate of the hindered phenolic antioxidant groups is 0.5-3 wt%.

[0011] Wherein, the carbodiimide group is a carbodiimide compound containing a monovinyl group, preferably 1-allyl-3-cyclohexylcarbodiimide; The hindered phenolic antioxidant group is an acrylate compound containing a hindered phenolic structure, preferably allyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

[0012] The grafting rate is based on the weight of the modified carbodiimide antihydrolysis agent itself, i.e., the weight of the functionalized polyethylene.

[0013] Furthermore, the catalyst is an organic bismuth catalyst, specifically bismuth neodecanoate.

[0014] In this invention, the amount of organobismuth catalyst used is 0.01 to 0.05 parts by weight. In the crosslinking stage of step 3, the organobismuth catalyst catalyzes the hydrolysis and condensation of silane groups to form Si-O-Si crosslinking bonds. After crosslinking is completed, the catalyst remains in the material in trace amounts, and the amount of bismuth leached out is negligible.

[0015] Tests using simulated water immersion revealed bismuth ions (Bi). 3+ The leaching amount is lower than the detection limit of inductively coupled plasma mass spectrometry (ICP-MS) (<0.001 mg / L), indicating that the leaching amount of bismuth is extremely low and meets the hygiene and safety requirements for drinking water contact materials.

[0016] The present invention preferably uses an organic bismuth catalyst (bismuth neodecanoate) to achieve an environmentally friendly and low-toxicity catalytic effect.

[0017] Furthermore, the catalyst of the present invention also includes an organotin catalyst, wherein the organotin catalyst is di-n-octyltin dilaurate (DOS); the amount of di-n-octyltin dilaurate added is 0.2 to 0.3 parts.

[0018] Furthermore, the antioxidant is a compound mixture of hindered phenolic antioxidants and phosphite antioxidants, wherein the hindered phenolic antioxidant is antioxidant 1010 and the phosphite antioxidant is antioxidant 168; the weight ratio of antioxidant 1010 to antioxidant 168 is 1:1 to 3:1.

[0019] In this invention, the hindered phenolic groups grafted onto the modified carbodiimide anti-hydrolysis agent are covalently fixed within the material, providing long-lasting antioxidant protection that is not easily migrated. The added antioxidant 1010 and 168 compound system provides processing stability and additional continuous antioxidant protection. The two work synergistically to achieve full-cycle antioxidant protection of the material without affecting the grafting efficiency.

[0020] In a second aspect, a method for preparing the heat-resistant and hydrolysis-resistant polyethylene material described in the first aspect is provided, comprising the following steps: (1) After mixing polyethylene resin, vinyl silane coupling agent, composite initiation system and antioxidant accounting for 20-30% of the total weight of antioxidant, the mixture is subjected to melt grafting reaction under nitrogen protection, extruded and granulated, and dried to obtain graft material A. (2) After mixing polyethylene resin, catalyst, modified carbodiimide anti-hydrolysis agent and antioxidant accounting for 70-80% of the total weight of antioxidant, the mixture is subjected to segmented heating and melting blending, extrusion granulation, and drying to obtain functional masterbatch B. (3) Graft material A and functional masterbatch B are mixed evenly at a weight ratio of (85-95): (5-15), and then melt-blended and extruded to granulate to obtain pre-crosslinked polyethylene material; (4) The obtained pre-crosslinked polyethylene material is placed in a constant temperature water bath at 85-95℃ for crosslinking treatment for 4-8 hours. After crosslinking, it is dried in a forced-air drying oven at 80-90℃ for 4-6 hours to obtain heat-resistant and hydrolysis-resistant polyethylene material.

[0021] Furthermore, in step (1), the temperature of the melt grafting reaction is 180-200°C and the time is 1-3 minutes.

[0022] Further, in step (2), the segmented heating and melting blending is as follows: after feeding at 150-160°C, the temperature is raised to 165-170°C for blending, and the blending time is 1-3 minutes.

[0023] The beneficial effects of this invention are as follows: (1) This invention uses 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and N-hydroxyphthalimide in a specific ratio as a composite initiation system. During the grafting reaction, bis(tert-butylperoxy)hexane decomposes upon heating to generate free radicals, which initiate the grafting of vinyl silane coupling agent onto the polyethylene molecular chain, resulting in the polyethylene backbone having hydrolyzable silane groups. The functional mechanism of NOP (N-hydroxyphthalimide) is hydrogen atom transfer (HAT) regulation: NOP generates phthalimide-N-oxygen (PINO) under the initiation of the initiator DHBP. PINO has selective HAT ability on the C–H bond of polyethylene, and through polar effect and free radical concentration regulation, it synergistically enhances grafting selectivity, efficiently generates macromolecular free radical grafting sites, and improves vinyl silane grafting efficiency; at the same time, PINO does not participate in interchain coupling, thereby inhibiting crosslinking side reactions. This mechanism differs from the reversible termination (NMP) mechanism of stable free radicals such as TEMPO. It is a grafting-promoting effect based on HAT. Subsequently, under the action of an organobismuth catalyst and moisture, the silane groups grafted onto the polyethylene chain undergo hydrolysis and condensation reactions, forming a Si-O-Si three-dimensional cross-linked network structure. After cross-linking, the polyethylene molecular chain transforms from its original linear structure into a three-dimensional network structure. While linear molecular chains can deform upon heating through inter-chain slippage, the molecular chain segments in the three-dimensional network structure are connected by chemical cross-linking bonds, preventing free slippage upon heating. Therefore, the heat resistance of the material is significantly improved. Testing shows that the heat distortion temperature of the material of this invention can reach above 101.8℃, and the Vicat softening point can reach above 97.2℃. It can withstand boiling water environments and meets the usage requirements of the water pump housing of a micro water dispenser under boiling water conditions.

[0024] (2) The present invention introduces a modified carbodiimide anti-hydrolysis agent into the formulation. The anti-hydrolysis agent has polyethylene as the main chain, on which carbodiimide groups (–N=C=N–) and hindered phenolic antioxidant groups are covalently grafted. The Si-O-Si bonds in the silane crosslinking network may be hydrolyzed and broken in a high-temperature hot water environment, producing silanol groups (Si-OH). The carbodiimide groups can react with the silanol groups to generate stable urea derivatives, thereby inhibiting the hydrolytic degradation of the crosslinking network. The hydrolysis resistance of the carbodiimide group is achieved through the following mechanism: the carbodiimide group can react with trace carboxylic acid sites generated by the thermal oxidative degradation of polyethylene material to form an N-acylurea structure, eliminating acidic centers that may catalyze the hydrolysis of Si-O-Si bonds; the covalently grafted carbodiimide / hindered phenolic bifunctional sites are all hydrophobic structures, which can reduce the local water content at the siloxane crosslinking nodes; the carbodiimide group is covalently grafted onto the polyethylene backbone to achieve chemical bonding and fixation of the hydrolysis-resistant group, preventing the migration and precipitation of small molecules and ensuring long-term performance. This mechanism differs from the classic mechanism of polyester systems and is an innovative application of this invention in the polyethylene silane crosslinking system. Simultaneously, the hindered phenolic antioxidant groups provide antioxidant protection, inhibiting the thermal oxidative degradation of the material and reducing the generation of acidic species such as carboxylic acids from the source, while the carbodiimide group inhibits the hydrolytic degradation of the crosslinking network by reacting with silanol groups and trace carboxylic acids generated by thermal oxidation. After being soaked in hot water at 95℃, the material retains more than 87.5% of its tensile strength and has excellent hydrolysis resistance.

[0025] (3) This invention ensures the safety of drinking water contact from three levels: First, it uses an organic bismuth catalyst, in which the content of controlled heavy metals such as lead, tin, and mercury meets the relevant regulatory limits, and the bismuth ion leaching amount tested by simulated water immersion is below the detection limit (<0.001 mg / L), meeting the hygiene and safety requirements for drinking water contact materials; second, the anti-hydrolysis groups in the modified carbodiimide anti-hydrolysis agent are covalently grafted onto the polyethylene main chain, and will not migrate or precipitate into drinking water in the form of free small molecules; finally, the composite initiation system makes the grafting reaction more controllable, reduces the residue of small molecule byproducts, and reduces potential precipitates from the source. The three dimensions work together to ensure that the material is not likely to release harmful substances into drinking water during use.

[0026] (4) This invention adopts a two-step preparation process, which separates the preparation of silane grafting reaction and catalytic crosslinking functional masterbatch, avoiding premature crosslinking caused by the presence of catalyst during grafting, thus giving grafted material A good storage stability. In the stepwise antioxidant addition strategy, only a small amount of antioxidant accounting for 20-30% of the total antioxidant weight is added in step (1), which avoids the inhibition of grafting reaction by excessive antioxidant while ensuring processing thermal stability; in step (2), the remaining 70-80% of antioxidant is added to ensure that the finished product has excellent long-term thermal and oxygen aging protection capability. Step (2) adopts a segmented heating strategy of feeding at 150-160℃ and then heating to 165-170℃, which further avoids the risk of premature crosslinking caused by catalyst. The entire process can be realized in a conventional twin-screw extruder and warm water crosslinking equipment. It has a wide process window, is easy to operate, has good batch stability, and has good prospects for industrial promotion and application. Detailed Implementation

[0027] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0028] Preparation example: Preparation of modified carbodiimide anti-hydrolysis agent 1. Raw material pretreatment Linear low-density polyethylene (LLDPE, melt flow rate 2.0 g / 10 min) was dried in a vacuum drying oven at 80 °C for 5 hours and set aside for later use. Similarly, the polymerizable monomer containing hindered phenolic groups (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) was dried in a vacuum drying oven at 80 °C for 5 hours and set aside for later use. The polymerizable monomer containing carbodiimide groups (1-allyl-3-cyclohexylcarbodiimide) was dried to constant weight in a vacuum desiccator at room temperature and set aside for later use.

[0029] 2. Preparation of monomers containing carbodiimide groups In this preparation example, 1-allyl-3-cyclohexylcarbodiimide (also known as N-allyl-N'-cyclohexylcarbodiimide) is used as a polymerizable monomer containing a carbodiimide group. The method for preparing carbodiimide from substituted thiourea by desulfurization in an HTIB (hydroxytoluenesulfonyl iodobenzene) / triethylamine system is described in the paper "Preparation Process and Application Research of Substituted Thiourea". This preparation example follows this synthetic principle, using allylamine and cyclohexylamine as raw materials, and performs cross-oxidative coupling in an iodine / triethylamine system to prepare the target product.

[0030] Allylamine (0.1 mol, approximately 5.7 g) and cyclohexylamine (0.1 mol, approximately 9.9 g) were dissolved in dry dichloromethane (approximately 80 mL), and triethylamine (0.2 mol, approximately 20.2 g) was added. The mixture was cooled to 0–5 °C in an ice bath, and a solution of iodine (I₂, 0.1 mol, approximately 25.4 g) in dry dichloromethane (approximately 50 mL) was slowly added dropwise, maintaining the temperature below 10 °C during the addition. After the addition was complete, the mixture was brought to room temperature and stirred for 6 hours. The reaction progress was monitored by TLC (developing solvent: petroleum ether / ethyl acetate = 5:1, UV lamp at 254 nm). After the reaction was complete, the mixture was washed 2–3 times with saturated sodium thiosulfate solution (with thorough shaking each time until the organic phase was colorless and transparent), once with saturated sodium bicarbonate solution, and once with saturated brine. The organic layer was dried with anhydrous sodium sulfate. After filtration, the solvent was removed by vacuum distillation. The crude product was purified by vacuum distillation, and the fraction collected at 104-105℃ / 10mmHg was obtained to yield 1-allyl-3-cyclohexylcarbodiimide.

[0031] The above operations should be performed in a fume hood, and operators should wear protective gloves, protective clothing, and goggles.

[0032] Using nuclear magnetic resonance hydrogen spectroscopy (NMR) 1 H NMR and carbon spectroscopy (H NMR) 13 The structure of the product was confirmed by C NMR.

[0033] 1-Allyl-3-cyclohexylcarbodiimide (CAS 62490-37-3, C 10 H 16 N2) 1 H NMR (400MHz, CDCl3, ppm) δ5.88(ddt,1H), 5.24(dd,1H), 5.17(dd,1H), 4.02(dd,2H), 3.95(tt,1H), 1.85(m,2H), 1.70(m,2H), 1.30–1.45(m,4H), 1.15-1.25(m,2H) 13 C NMR (100MHz, CDCl3, ppm) δ134.6, 128.8, 117.4, 57.0, 52.6, 34.0, 25.1, 24.5ppm in, 13 The signal at δ 128.8 ppm in C NMR is a characteristic absorption peak of the central carbon of the carbodiimide group (-N=C=N-), combined with... 1 The complete disappearance of the proton signal of the primary amine -NH2 in the 1H NMR confirmed that the product was 1-allyl-3-cyclohexylcarbodiimide.

[0034] 3. Preparation of monomers containing hindered phenolic groups In this preparation example, allyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is used as a polymerizable monomer containing hindered phenolic groups, and its preparation method is as follows: In existing technologies such as “Synthesis and Performance Study of Reactive Antioxidants” and “Synthesis and Uses of Antioxidant 3052”, there are methods for synthesizing similar hindered phenolic acrylates. This preparation example follows the principle of these methods, using 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid and allyl alcohol as raw materials, and prepares the target product by esterification reaction under acid catalysis.

[0035] 0.05 mol (approx. 14.0 g) of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid, 0.55 mol (approx. 32.0 g) of allyl alcohol, 0.02 g of hydroquinone monomethyl ether (MEHQ), 0.03 mL of concentrated sulfuric acid (98%), and 50 mL of toluene were added to a three-necked flask equipped with a water separator, and nitrogen gas was introduced for protection. The mixture was heated to reflux, and the aqueous phase was continuously separated by the azeotropic effect of toluene and water. The oil bath temperature was controlled at 110–120 °C, and the reaction time was 5 hours. After the reaction was completed, the reaction solution was cooled to room temperature and transferred to a separatory funnel. The solution was washed successively with 5% sodium carbonate solution and repeatedly washed with deionized water until neutral. The organic layer was separated. The organic layer was dried with anhydrous magnesium sulfate, filtered, and then distilled under reduced pressure to remove toluene and unreacted allyl alcohol. The residue was purified by column chromatography (elution with petroleum ether / ethyl acetate at a gradient of 10:1 to 5:1) to give allyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

[0036] use 1 H NMR and 13 The structure of the product was confirmed by C NMR.

[0037] 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate allyl ester (C 20 H 30 O3, MW 318.45) 1 H NMR (400MHz, CDCl3, ppm) δ7.00(s,2H), 5.90(ddt,1H), 5.28(dd,1H), 5.22(dd,1H), 5.08(s,1H), 4.60(d,2H), 2.62(t,2H), 2.55(t,2H), 1.45(s,18H).

[0038] 13C NMR (100MHz, CDCl3, ppm) δ173.2, 152.3, 136.3, 135.6, 131.2, 125.0, 118.1, 65.5, 34.5, 31.8, 30.9, 30.3ppm in, 13 The signal at δ 173.2 ppm in the C NMR is the characteristic absorption peak of the ester carbonyl group, combined with 1 The newly observed allyl characteristic signal (δ 5.90, 5.28, 5.22, 4.60) in ¹H NMR confirmed that the product was allyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, indicating that the esterification reaction was successful.

[0039] 4. Melt grafting 100 parts of dried linear low-density polyethylene, 3 parts of 1-allyl-3-cyclohexylcarbodiimide, 2 parts of allyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and 0.05 parts of organic peroxide initiator (2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane) were added to a high-speed mixer and mixed evenly. The mixture was then fed into a twin-screw extruder for a melt grafting reaction. The reaction temperature was 180–190°C, the screw speed was 250 rpm, and the reaction time was 2 minutes. The residence time was strictly controlled to avoid thermal decomposition of the carbodiimide groups. The mixture was then extruded and granulated to obtain the modified carbodiimide anti-hydrolysis agent.

[0040] 5. Grafting rate control and measurement By adjusting the feed amounts of polymerizable monomers containing carbodiimide groups and polymerizable monomers containing hindered phenolic groups, the grafting rate of carbodiimide groups can be controlled within the range of 0.5–5 wt%, and the grafting rate of hindered phenolic antioxidant groups within the range of 0.5–3 wt%, respectively. The grafting rate of the product obtained in this preparation example was determined by infrared spectroscopy (internal standard method). The grafted product was used to prepare a thin film sample with uniform thickness using a hot-pressing method, and infrared absorption spectra were collected. The characteristic absorption peak of the carbodiimide group is located at approximately 2110–2140 cm⁻¹. -1 The characteristic absorption peak of the hindered phenolic benzene ring skeleton is located at approximately 1500–1600 cm⁻¹. -1 The peak of the methylene scissor vibration in the polyethylene backbone (approximately 1460 cm⁻¹) was determined by the scissor vibration of the methylene group in the polyethylene backbone. -1 The absorbance ratio of the characteristic peak to the internal standard peak is calculated. A standard curve is established using standard samples with known grafting rates. The grafting rate can be calculated by substituting the absorbance ratio of the sample to be tested into the standard curve.

[0041] Example 1 This embodiment provides a heat-resistant and hydrolysis-resistant polyethylene material and its preparation method. The formulation is as follows, by weight: 100 parts of polyethylene resin (HDPE and LLDPE blend, HDPE:LLDPE = 82.5:17.5); 1.8 parts of vinyltrimethoxysilane; 0.11 parts of composite initiator system (bis(2,5-dimethyl)propionate and NOP in a 3:1 ratio); 0.55 parts of modified carbodiimide anti-hydrolysis agent; 0.03 parts of bismuth neodecanoate catalyst; 0.3 parts of antioxidant (1010 and 168 in a 2:1 ratio).

[0042] The preparation method is as follows: (1) After mixing polyethylene resin, vinyltrimethoxysilane, composite initiation system and antioxidant accounting for 25% of the total weight of antioxidant (i.e., 0.075 parts), a melt grafting reaction was carried out under nitrogen protection at a reaction temperature of 190°C for 2 minutes. The mixture was then extruded, granulated, and dried to obtain graft material A. (2) After mixing polyethylene resin, bismuth neodecanoate catalyst, modified carbodiimide antihydrolysis agent and antioxidant accounting for 75% of the total weight of antioxidant (i.e. 0.225 parts), the mixture is added to a twin-screw extruder for segmented heating and melt blending. The feed temperature is 155°C, and then the temperature is raised to 167°C for mixing, extrusion granulation, and drying to obtain functional masterbatch B. (3) Graft material A and functional masterbatch B are mixed evenly at a weight ratio of 90:10, and then melt-blended and extruded to granulate to obtain pre-crosslinked polyethylene material.

[0043] (4) The obtained pre-crosslinked polyethylene material is placed in a constant temperature water bath at 90°C for 6 hours for crosslinking treatment. After crosslinking, it is dried in a forced-air drying oven at 85°C for 5 hours to obtain heat-resistant and hydrolysis-resistant polyethylene material.

[0044] The exhaust gases generated in steps (1) and (2) are collected and then treated by activated carbon adsorption and alkaline absorption before being discharged.

[0045] Example 2 This embodiment provides a heat-resistant and hydrolysis-resistant polyethylene material and its preparation method. The formulation is as follows, by weight: 100 parts of polyethylene resin (HDPE and LLDPE blend, HDPE:LLDPE = 95:5); 0.8 parts of vinyltrimethoxysilane; 0.05 parts of composite initiator system (bis(2-diphenyltrimethoxysilane) and NOP in a 2:1 ratio); 0.1 parts of modified carbodiimide anti-hydrolysis agent; 0.01 parts of bismuth neodecanoate catalyst; 0.1 parts of antioxidant (1010 and 168 in a 1:1 ratio).

[0046] The preparation method is as follows: (1) After mixing polyethylene resin, vinyltrimethoxysilane, composite initiation system and antioxidant accounting for 20% of the total weight of antioxidant (i.e., 0.02 parts), a melt grafting reaction was carried out under nitrogen protection at a reaction temperature of 185°C for 3 minutes. The mixture was then extruded, granulated, and dried to obtain graft material A. (2) After mixing polyethylene resin, bismuth neodecanoate catalyst, modified carbodiimide anti-hydrolysis agent and antioxidant accounting for 80% of the total weight of antioxidant (i.e., 0.08 parts), the mixture is added to a twin-screw extruder for segmented heating and melt blending. The feed temperature is 150°C, and then the temperature is raised to 165°C for mixing. The mixing time is 3 minutes. The mixture is then extruded, granulated, and dried to obtain functional masterbatch B. (3) Graft material A and functional masterbatch B are mixed evenly at a weight ratio of 95:5, and then melt-blended and extruded to granulate to obtain pre-crosslinked polyethylene material; (4) The obtained pre-crosslinked polyethylene material was placed in a constant temperature water bath at 85°C for crosslinking treatment for 8 hours. After crosslinking, it was dried in a forced-air drying oven at 80°C for 6 hours to obtain heat-resistant and hydrolysis-resistant polyethylene material.

[0047] Example 3 This embodiment provides a heat-resistant and hydrolysis-resistant polyethylene material and its preparation method. The formulation is as follows, by weight: 100 parts of polyethylene resin (HDPE and LLDPE blend, HDPE:LLDPE = 70:30); 3.0 parts of vinyltrimethoxysilane; 0.2 parts of composite initiator system (bis(2,5-diphenyltrimethylammonium chloride) and NOP in a 5:1 ratio); 1.0 part of modified carbodiimide anti-hydrolysis agent; 0.05 parts of bismuth neodecanoate catalyst; 0.5 parts of antioxidant (1010 and 168 in a 3:1 ratio).

[0048] The preparation method is as follows: (1) After mixing polyethylene resin, vinyltrimethoxysilane, composite initiation system and antioxidant accounting for 30% of the total weight of antioxidant (i.e., 0.15 parts), a melt grafting reaction is carried out under nitrogen protection at a reaction temperature of 195°C for 1 minute. The mixture is then extruded, granulated, and dried to obtain graft material A. (2) After mixing polyethylene resin, bismuth neodecanoate catalyst, modified carbodiimide anti-hydrolysis agent and antioxidant accounting for 70% of the total weight of antioxidant (i.e., 0.35 parts), the mixture is added to a twin-screw extruder for segmented heating and melt blending. The feed temperature is 160°C, and then the temperature is raised to 170°C for mixing. The mixing time is 1 minute. The mixture is then extruded, granulated, and dried to obtain functional masterbatch B. (3) Graft material A and functional masterbatch B are mixed evenly at a weight ratio of 85:15, and then melt-blended and extruded to obtain pre-crosslinked polyethylene material.

[0049] (4) The obtained pre-crosslinked polyethylene material is placed in a constant temperature water bath at 95°C for crosslinking treatment for 4 hours. After crosslinking, it is dried in a forced-air drying oven at 90°C for 4 hours to obtain heat-resistant and hydrolysis-resistant polyethylene material.

[0050] Example 4 This embodiment provides a heat-resistant and hydrolysis-resistant polyethylene material and its preparation method. The formulation is as follows, by weight: 100 parts of polyethylene resin (HDPE and LLDPE blend, HDPE:LLDPE = 82.5:17.5); 1.8 parts of vinyltrimethoxysilane; 0.11 parts of composite initiator system (bis(2,5-dimethylsiloxane) and NOP in a 3:1 ratio); 0.55 parts of modified carbodiimide anti-hydrolysis agent; 0.2 parts of di-n-octyltin dilaurate; 0.3 parts of antioxidant (1010 and 168 in a 2:1 ratio).

[0051] The preparation method is as follows: (1) After mixing polyethylene resin, vinyltrimethoxysilane, composite initiation system and antioxidant accounting for 25% of the total weight of antioxidant (i.e., 0.075 parts), a melt grafting reaction was carried out under nitrogen protection at a reaction temperature of 190°C for 2 minutes. The mixture was then extruded, granulated, and dried to obtain graft material A. (2) After the polyethylene resin, dioctyltin dilaurate, modified carbodiimide anti-hydrolysis agent and antioxidant accounting for 75% of the total weight of antioxidant (i.e., 0.225 parts) are mixed and dispersed evenly, the mixture is added to a twin-screw extruder for segmented heating and melt blending. The feed temperature is 155°C, and then the temperature is raised to 167°C for mixing, extrusion granulation, and drying to obtain functional masterbatch B; (3) Graft material A and functional masterbatch B are mixed evenly at a weight ratio of 90:10, and then melt-blended and extruded to granulate to obtain pre-crosslinked polyethylene material.

[0052] (4) The obtained pre-crosslinked polyethylene material is placed in a constant temperature water bath at 90°C for 6 hours for crosslinking treatment. After crosslinking, it is dried in a forced-air drying oven at 85°C for 5 hours to obtain heat-resistant and hydrolysis-resistant polyethylene material.

[0053] Comparative Example 1 Based on Example 1, the modified carbodiimide antihydrolysis agent is grafted with only carbodiimide and not with hindered phenol, and the rest is the same as in Example 1.

[0054] Comparative Example 2 Based on Example 1, the modified carbodiimide antihydrolysis agent is grafted with only hindered phenols and not with carbodiimide, and the rest is the same as in Example 1.

[0055] Comparative Example 3 Based on Example 1, the modified carbodiimide anti-hydrolysis agent was replaced with N,N'-bis(2,6-diisopropylphenyl)carbodiimide, and the rest was the same as in Example 1.

[0056] Comparative Example 4 Based on Example 1, the composite initiation system was replaced with dicumyl peroxide (DCP), and the rest was the same as in Example 1.

[0057] Comparative Example 5 Based on Example 1, only double 25 is added, and NOP is not added; otherwise, it is the same as Example 1.

[0058] Comparative Example 6 Based on Example 1, the modified carbodiimide anti-hydrolysis agent and the composite initiation system were added simultaneously in step (1), and the rest was the same as in Example 1.

[0059] Comparative Example 7 Based on Example 1, the ratio of 25% to NOP is 10:1, and the rest is the same as in Example 1.

[0060] Comparative Example 8 Based on Example 1, the ratio of 25:NOP is 1:3, and the rest is the same as in Example 1.

[0061] Comparative Example 9 Based on Example 1, all the antioxidants in step (1) were added, and the rest was the same as in Example 1.

[0062] Comparative Example 10 Based on Example 1, the amount of antioxidant added in step (1) is 70-80%, the amount of antioxidant added in step (2) is 20%-30%, and the rest is the same as in Example 1.

[0063] Performance testing The present invention verifies the heat resistance, hydrolysis resistance, and water safety and environmental performance of the polyethylene materials prepared in Examples 1-4 and Comparative Examples 1-10 through the following performance tests.

[0064] I. Testing Methods (1) Referring to GB / T 1634.2 standard, the heat distortion temperature (HDT) was tested using a bending stress of 1.82 MPa; referring to GB / T 1633 standard, the Vicat softening point (VST) was tested using the A50 method. The heat distortion temperature is an important indicator for measuring the ability of a material to resist deformation under the combined action of heat and load. The Vicat softening point measures the ability of a material to resist heat deformation under a lower load (10 N), and is more sensitive to changes in the degree of crosslinking of polyethylene materials.

[0065] (2) Referring to the test principle of GB / T 12000 and considering the actual application scenario of this invention, the sample was immersed in water at 95℃±2℃ for 240h. Samples were taken before and after immersion. The tensile strength was tested according to GB / T 1040.2 standard, and the tensile strength retention rate was calculated using the following formula: Tensile strength retention rate (%) = (Tensile strength after aging / Tensile strength before aging) × 100%, Tensile strength retention rate is a core indicator for evaluating the hydrolysis resistance of materials, directly reflecting the material's ability to resist molecular chain hydrolysis and breakage and the destruction of the integrity of the cross-linked network structure under long-term immersion in high-temperature hot water.

[0066] (3) Referring to GB / T 17219 standard, immerse the sample in soaking water that meets the standard requirements for 24h±1h, and prepare a blank control soaking water at the same time. The test items include: (1) Increase in heavy metals: Based on GB / T 5750.6 and GB / T 17219 standards, the increase in five heavy metal elements (lead (Pb), cadmium (Cd), mercury (Hg), arsenic (As), and tin (Sn) in the water after immersion was measured relative to the blank control water. Lead, cadmium, mercury, arsenic, and tin are toxicological indicators specified in the drinking water hygiene standards and have clear biological toxicity. The detection was performed using inductively coupled plasma mass spectrometry (ICP-MS), and the method detection limit met the detection accuracy requirements of GB / T 17219 standard. In Table 1, the increase in the five elements is expressed as "increase in heavy metals". When the increase in the five elements is lower than the detection limit, it is expressed as "<0.001 mg / L".

[0067] (2) Increase in Total Organic Carbon (TOC): In accordance with GB / T 5750.7 and GB / T 17219 standards, the increase in total organic carbon content in the soaking water relative to the blank control water was determined using a total organic carbon analyzer. TOC is a comprehensive indicator for evaluating the degree of organic pollution in water, reflecting the total amount of organic matter (such as unreacted silane coupling agent residues, antioxidants and their decomposition products, polyethylene oligomers, surface free matter or reaction products of modified carbodiimide antihydrolysis agents, etc.) released into the water by the material.

[0068] The test results were determined according to GB / T 17219 standard, wherein the increase in arsenic was ≤0.001 mg / L, the increase in cadmium was ≤0.0005 mg / L, the increase in lead was ≤0.001 mg / L, the increase in mercury was ≤0.0001 mg / L, the increase in tin was ≤0.002 mg / L, and the increase in total organic carbon (TOC) was ≤1 mg / L.

[0069] II. Test Results The performance test results of Examples 1-4 and Comparative Examples 1-10 are shown in Table 1.

[0070] Table 1 Performance test results of Examples 1-4 and Comparative Examples 1-10

[0071] Note: The increase in heavy metals refers to the increase in lead, cadmium, mercury, and arsenic relative to the blank control water. "<0.001 mg / L" indicates that the increase in all four elements is below the detection limit. GB / T 17219 standard limits (increase): Arsenic ≤0.001 mg / L, Cadmium ≤0.0005 mg / L, Lead ≤0.001 mg / L, Mercury ≤0.0001 mg / L, Tin ≤0.002 mg / L; TOC ≤1 mg / L.

[0072] The results showed that the polyethylene materials prepared in Examples 1-4 exhibited excellent performance in all performance indicators. The heat distortion temperature was above 101.8℃, the Vicat softening point was above 97.2℃, and after immersion in 95℃ hot water for 240 hours, the tensile strength retention rate was above 87.5%. In the water safety immersion test, the increase in heavy metals (lead, cadmium, mercury, arsenic, and tin) was below the detection limit (<0.001 mg / L), and the increase in TOC was below 0.3 mg / L. This invention achieves the chemical bonding and fixation of anti-hydrolysis groups through a modified carbodiimide anti-hydrolysis agent, and through its synergistic effect with the composite initiation system and the stepwise addition strategy of antioxidants, achieves a balance between heat resistance, hydrolysis resistance, and water safety.

[0073] Compared to the examples, Comparative Example 1, which only grafted carbodiimide without grafting hindered phenol, retained 82.4% of its tensile strength. Comparative Example 2, which only grafted hindered phenol without grafting carbodiimide, retained 65.8% of its tensile strength, with an increase of 0.48 mg / L in heavy metals (lead) and 1.12 mg / L in TOC. Comparative Example 3, which replaced the modified carbodiimide anti-hydrolysis agent with N,N'-bis(2,6-diisopropylphenyl)carbodiimide, retained 73.5% of its tensile strength, with an increase of 0.12 mg / L in heavy metals (lead) and 0.72 mg / L in TOC. In Comparative Example 4, when DCP was used instead of the composite initiator system, the heat distortion temperature was 98.5℃, the Vicat softening point was 92.8℃, and the tensile strength retention rate was 66.3%. In Comparative Example 5, when only bis(2,5-diphenyltrimethylammonium chloride) was added without NOP, the heat distortion temperature was 97.2℃, the Vicat softening point was 90.6℃, and the tensile strength retention rate was 65.8%. In Comparative Example 6, when the modified carbodiimide anti-hydrolysis agent and the composite initiator system were added simultaneously in stage S1, the tensile strength retention rate was 72.1%, and the TOC increase was 0.55 mg / L. In Comparative Examples 7-8, when the ratio of bis(2,5-diphenyltrimethylammonium chloride) to NOP deviated from the optimal range, all performance characteristics were lower than those of the examples. In Comparative Examples 9-10, when the antioxidant was added in one step or the addition amount was reversed, the tensile strength retention rates were 68.5% and 66.2%, respectively, both significantly lower than those of the examples.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A heat-resistant and hydrolysis-resistant polyethylene material, characterized in that, By weight, it includes the following components: 100 parts of polyethylene resin; Vinylsilane coupling agent 0.5-3 parts; 0.02-0.2 parts of the composite initiation system; 0.1-1 parts of modified carbodiimide anti-hydrolysis agent; Catalyst 0.01-0.05 parts; Antioxidant 0.1-0.5 parts.

2. The heat-resistant and hydrolysis-resistant polyethylene material according to claim 1, characterized in that, The polyethylene resin is a blend of high-density polyethylene and linear low-density polyethylene; the melt flow rate of the polyethylene resin is 1.0-5.0 g / 10 min; the blending ratio of the linear low-density polyethylene is 5-30% of the total weight of the polyethylene resin.

3. The heat-resistant and hydrolysis-resistant polyethylene material according to claim 1, characterized in that, The vinyl silane coupling agent is vinyltrimethoxysilane or vinyltriethoxysilane.

4. The heat-resistant and hydrolysis-resistant polyethylene material according to claim 1, characterized in that, The composite initiation system is composed of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and N-hydroxyphthalimide, wherein the weight ratio of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane to N-hydroxyphthalimide is (1-5):

1.

5. The heat-resistant and hydrolysis-resistant polyethylene material according to claim 1, characterized in that, The modified carbodiimide antihydrolysis agent is a functionalized polyethylene, which is composed of a polyethylene backbone and carbodiimide groups and hindered phenolic antioxidant groups grafted onto the polyethylene backbone; the grafting rate of the carbodiimide groups is 0.5-5 wt%, and the grafting rate of the hindered phenolic antioxidant groups is 0.5-3 wt%.

6. The heat-resistant and hydrolysis-resistant polyethylene material according to claim 1, characterized in that, The catalyst is an organic bismuth catalyst, and the organic bismuth catalyst is bismuth neodecanoate.

7. The heat-resistant and hydrolysis-resistant polyethylene material according to claim 1, characterized in that, The antioxidant is a mixture of hindered phenolic antioxidants and phosphite antioxidants, wherein the hindered phenolic antioxidant is antioxidant 1010 and the phosphite antioxidant is antioxidant 168; the weight ratio of antioxidant 1010 to antioxidant 168 is 1:1 to 3:

1.

8. A method for preparing a heat-resistant and hydrolysis-resistant polyethylene material as described in any one of claims 1-7, characterized in that, Includes the following steps: (1) After mixing polyethylene resin, vinyl silane coupling agent, composite initiation system and antioxidant accounting for 20-30% of the total weight of antioxidant, the mixture is subjected to melt grafting reaction under nitrogen protection, extruded and granulated, and dried to obtain graft material A. (2) After mixing polyethylene resin, catalyst, modified carbodiimide anti-hydrolysis agent and antioxidant accounting for 70-80% of the total weight of antioxidant, the mixture is subjected to segmented heating and melting blending, extrusion granulation, and drying to obtain functional masterbatch B. (3) Graft material A and functional masterbatch B are mixed evenly, and then melt-blended and extruded to granulate to obtain pre-crosslinked polyethylene material; (4) The obtained pre-crosslinked polyethylene material is placed in a constant temperature water bath at 85-95℃ for crosslinking treatment for 4-8 hours. After crosslinking, it is dried in a forced-air drying oven at 80-90℃ for 4-6 hours to obtain heat-resistant and hydrolysis-resistant polyethylene material.

9. The method for preparing the heat-resistant and hydrolysis-resistant polyethylene material according to claim 8, characterized in that, In step (1), the melting grafting reaction temperature is 180-200°C and the time is 1-3 minutes.

10. The method for preparing the heat-resistant and hydrolysis-resistant polyethylene material according to claim 8, characterized in that, In step (2), the segmented heating and melting blending is as follows: after feeding at 150-160°C, the temperature is raised to 165-170°C for blending, and the blending time is 1-3 minutes.

Images