Polyethylene composite geomembrane and processing technology thereof

Abstract

The invention discloses a polyethylene composite geomembrane and a processing technology thereof in the field of geosynthetic materials. The polyethylene composite geomembrane is prepared from the following raw materials: high-density polyethylene, polyethylene grafted maleic anhydride, a nano montmorillonite / low-density polyethylene composite modifier, an antioxidant, a light stabilizer and a lubricant calcium stearate. Wherein the polyethylene grafted maleic anhydride is prepared by drying high-density polyethylene, mixing the dried high-density polyethylene with maleic anhydride, an initiator and an antioxidant, and performing melt extrusion through a double-screw extruder, so that the surface polarity is improved; the nano-montmorillonite / low-density polyethylene composite modifier is prepared by ultrasonically dispersing Na-montmorillonite, adding hexadecyl trimethyl ammonium bromide, stirring, centrifugally drying to obtain organic modified montmorillonite, mixing the organic modified montmorillonite with low-density polyethylene, performing intercalation reaction, and performing twin-screw extrusion and blending, so that the barrier property is enhanced. The processing technology comprises the steps of raw material mixing, twin-screw extrusion granulation and calendaring molding, and finally the polyethylene composite geomembrane with remarkably improved interface cohesiveness, weather resistance and barrier property is prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geosynthetic materials, in particular to a polyethylene composite geomembrane and a processing technology thereof. BACKGROUND

[0002] Traditional polyethylene geomembranes have become an important foundation material in the fields of water conservancy projects, landfill sites, mine restoration, etc. due to their excellent waterproofness, tensile strength, and acid and alkali corrosion resistance. Their low cost and easy processing characteristics make them widely used in engineering, but as environmental protection requirements upgrade and application scenarios become more complex, the limitations of material performance gradually become apparent. For example, in a humid or acidic soil environment, the insufficient interfacial adhesion between the geomembrane and the medium can easily lead to slippage, affecting the stability of the impermeable layer; long-term exposure to ultraviolet light, oxygen and other environments can cause the material to be surface-powdered and the elongation at break to decrease due to photo-oxidative aging, shortening the service life; in addition, the barrier ability of the material to heavy metal ions (such as lead and cadmium) and organic pollutants (such as benzene series and petroleum hydrocarbons) is limited, making it difficult to meet the strict requirements of pollution prevention and control, limiting its further application in harsh environments.

[0003] To address the above problems, existing technologies attempt to improve performance through modification methods, but the effects are often one-sided. For example, directly adding polar fillers (such as silane coupling agent modified particles) can improve interfacial adhesion, but the poor compatibility of fillers with PE and uneven dispersion can easily lead to defects within the material, thereby reducing the tensile strength; when directly blending with nano-montmorillonite, the high surface energy of the nano-montmorillonite does not match the low surface energy of PE, causing phase separation and the formation of agglomerates that not only weaken the barrier effect but also damage the mechanical uniformity of the material; single maleic anhydride grafting modification can introduce polar groups, but the grafting rate is low and does not solve the problem of interfacial bonding of nano-fillers, limiting the improvement of weather resistance and barrier properties. Some technologies use complex processes such as high-temperature calcination and multiple chemical treatments, which not only increase production costs but also may damage the original properties of the material due to excessive processing, making it difficult to achieve large-scale application.

[0004] Therefore, there is an urgent need to develop a technical solution that simultaneously addresses weak interfacial adhesion, poor weather resistance, and insufficient barrier performance through multi-component synergistic modification. The present application improves the surface polarity of the polyethylene matrix by introducing polyethylene grafted maleic anhydride, enhances the interfacial compatibility and barrier ability by combining nano-montmorillonite / low-density polyethylene composite modifiers, and optimizes the processing technology, aiming to synergistically improve the interfacial adhesion, weather resistance, and barrier performance of polyethylene geomembranes, meeting the urgent needs of engineering applications in complex environments. SUMMARY

[0005] The present application aims to provide a polyethylene composite geomembrane and a processing technology thereof, which solves the problems of weak interfacial adhesion, easy slippage, poor weather resistance, easy aging, and insufficient barrier performance of traditional polyethylene geomembranes.

[0006] The present application realizes the above-mentioned purpose through the following technical solutions: A polyethylene composite geomembrane, according to mass percentage, raw materials thereof include: High-density polyethylene: 70-80%; Polyethylene grafted maleic anhydride: 8-12%; Nano-montmorillonite / low-density polyethylene composite modifier: 9-12%; Antioxidant: 0.15-0.25%; Light stabilizer: 0.2-0.25%; Lubricant calcium stearate: 0.3-0.5%; The preparation steps of the polyethylene grafted maleic anhydride include: A1, drying the high-density polyethylene, and uniformly mixing the high-density polyethylene with maleic anhydride, dicumyl peroxide and antioxidant 1010; A2, adding a twin-screw extruder, and melt-extruding at a barrel temperature of 185-200℃; and the extrudate is granulated by water cooling traction and a granulator.

[0007] According to a preferred embodiment of the present application, the high-density polyethylene is purchased from Sinopec Yanshan Petrochemical Company, and the brand is 5000S (melt flow rate MFR = 0.8-1.2 g / 10 min, density 0.941-0.950 g / cm³).

[0008] According to a preferred embodiment of the present application, the maleic anhydride is purchased from Puyang HuiCheng Electronic Materials Co., Ltd., and is an industrial-grade solid powder (purity ≥ 99.5%, melting point 52-54℃).

[0009] According to a preferred embodiment of the present application, the dicumyl peroxide is purchased from Shanghai Jinjile Industrial Co., Ltd., and is an industrial-grade liquid (purity ≥ 98.5%, decomposition temperature ≥ 116℃).

[0010] According to a preferred embodiment of the present application, the antioxidant 1010 is purchased from Li'anlong New Material Co., Ltd., and is a white crystalline powder (purity ≥ 98.0%, melting point 110-125℃).

[0011] According to a preferred embodiment of the present application, the twin-screw extruder is purchased from Nanjing Kebeilong Koya Machinery Co., Ltd., and the model is CTE-35 (screw diameter 35 mm, length-diameter ratio L / D = 40, maximum processing temperature 350℃).

[0012] According to a preferred embodiment of the present application, the antioxidant is antioxidant 1010 purchased from Li'anlong New Material Co., Ltd., and is a white crystalline powder (purity ≥ 98.0%, melting point 110-125℃).

[0013] According to the preferred embodiment of the present application, the light stabilizer is light stabilizer GW-944, which is colorless and transparent liquid (purity ≥98.0%, density 0.98-1.02 g / cm³) and is purchased from Beijing Jia Cheng Auxiliary Research Institute.

[0014] According to the preferred embodiment of the present application, the lubricant is calcium stearate, which is white powder (calcium content 6.5-7.5%, melting point 145-155 ℃, acid value ≤3 mgKOH / g) and is purchased from Dandong Chemical Research Co., Ltd.

[0015] According to the preferred embodiment of the present application, in step A1, the drying temperature is 80-85 ℃, the drying time is 2-3 h, the mass of maleic anhydride accounts for 2.5-3% of the mass of high-density polyethylene, the mass of initiator accounts for 0.08-0.1% of the mass of high-density polyethylene, and the mass of antioxidant accounts for 0.1-0.12% of the mass of high-density polyethylene.

[0016] In the present application, high-density polyethylene (HDPE) is used as the base resin, and its linear saturated molecular chain structure endows the material with high initial tensile strength and chemical corrosion resistance. However, the weak surface polarity (only containing a small amount of C-H bonds) leads to insufficient interfacial adhesion with non-polar media (such as soil clay minerals). Polyethylene grafted maleic anhydride (PE-g-MAH) improves this defect through a melt grafting reaction. Maleic anhydride (MAH) generates free radicals under the initiation of dicumyl peroxide (DCP), attacks the methylene group on the HDPE molecular chain to form a macromolecular radical, and then the double bond of MAH copolymerizes with the HDPE radical to graft the MAH containing carboxyl (-COOH) and anhydride groups (-CO-O-CO-) onto the HDPE chain. These polar groups form hydrogen bonds or ionic bonds with the silicon hydroxyl (Si-OH), aluminum hydroxyl (Al-OH), or negatively charged Si-O - - surfaces of soil clay minerals (such as montmorillonite and illite), significantly enhancing the interfacial adhesion.

[0017] According to the preferred embodiment of the present application, in step A2, the screw rotation speed of the twin-screw extruder is 300-350 rpm.

[0018] ​According to the preferred embodiment of the present application, the preparation steps of the nanometer montmorillonite / low-density polyethylene composite modifier comprises: B1, adding sodium-based montmorillonite into deionized water, ultrasonic dispersion, then adding cetyltrimethylammonium bromide, stirring at 60-65℃, centrifugation, vacuum drying to obtain organic modified montmorillonite; B2, mixing low-density polyethylene and organic modified montmorillonite according to the mass ratio (9-9.5):1, adding benzoyl peroxide and antioxidant 1076, mixing uniformly in a high-speed mixer, then adding into a banbury mixer for reaction; finally, adding the intercalation product and the remaining high-density polyethylene according to the mass ratio 1:(4-5) into a twin-screw extruder for blending and granulation.

[0019] According to the preferred embodiment of the present application, the sodium-based montmorillonite is purchased from Zhejiang Fenghong New Material Co., Ltd., with the model FM-800 (particle size 30-50 nm, interlayer spacing 1.5-1.6 nm, purity ≥95%).

[0020] According to the preferred embodiment of the present application, the deionized water is purchased from Jiangsu Jiangyin Jianghua Microelectronic Material Co., Ltd., industrial-grade deionized water.

[0021] According to the preferred embodiment of the present application, the low-density polyethylene is purchased from Sinopec Yanshan Petrochemical Co., Ltd., with the model 1C7A (melt flow rate MFR = 1.5 g / 10 min, density 0.918-0.922 g / cm³).

[0022] According to the preferred embodiment of the present application, the benzoyl peroxide is purchased from Jiangsu Qiangsheng Functional Chemical Co., Ltd., industrial-grade powder (purity ≥98.0%, decomposition temperature 105-110℃, active oxygen content ≥7.0%, suitable for initiating polymerization reaction in a banbury mixer).

[0023] According to the preferred embodiment of the present application, the antioxidant 1076 is purchased from Shanghai Petrochemical Xnir Chemical Co., Ltd., white crystalline powder (purity ≥98.0%, melting point 50-60℃, hindered phenolic antioxidant, synergistic inhibition of thermal oxidation with antioxidant 1010).

[0024] According to the preferred embodiment of the present application, the high-speed mixer is purchased from Changzhou One Step Drying Equipment Co., Ltd., model SRL-100 (volume 100 L, rotation speed 1000-1200 rpm, motor power 5.5 kW).

[0025] According to the preferred embodiment of the present application, the banbury mixer is purchased from Dalian Rubber and Plastic Machinery Co., Ltd., model X(S)M-50 (volume 50 L, temperature control range 150-200℃, rotor rotation speed 50-60 rpm, power 30 kW).

[0026] According to a preferred embodiment of the present application, the twin-screw extruder is purchased from the Coperion Group, model SHJ-35 (screw diameter 35 mm, length-diameter ratio L / D=40, maximum processing temperature 350℃, power 55kW).

[0027] According to a preferred embodiment of the present application, in step B1, the particle size of the sodium-based montmorillonite is 30-50nm, and the interlayer spacing is 1.5-1.6nm; the ultrasonic dispersion time is 30-35min, and the stirring time is 2-3h; the vacuum drying temperature is 60-65℃, and the vacuum drying time is 12-13h.

[0028] According to a preferred embodiment of the present application, in step B2, the speed of the high-speed mixer is 1000-1200rpm, and the mixing time is 5-10min; the temperature of the internal mixer is 175-180℃, the rotor speed of the internal mixer is 50-60rpm, and the reaction time in the internal mixer is 30-40min; the temperature of the twin-screw extruder is 165-190℃, and the screw speed is 400-450rpm.

[0029] In the present application, the nano-montmorillonite / low-density polyethylene composite modifier (MMT / LDPE) realizes nano-enhancement through two-step modification: first, the sodium-based montmorillonite (Na-MMT) is ultrasonically dispersed in deionized water, and the interlayer sodium ions are ion-exchanged with the hydrophobic long chain of cetyltrimethylammonium bromide (CTAB) to form organically modified montmorillonite (OMMT), the interlayer spacing of which is increased from about 1nm to 1.5-1.6nm, the quaternary ammonium cations on the surface of the sheet layer face the water phase, and the hydrophobic carbon-hydrogen chain faces the montmorillonite layer, improving the compatibility with the polymer; then, the OMMT is mixed with low-density polyethylene (LDPE) at a ratio of (9-9.5):1, and benzoyl peroxide (BPO) initiator and antioxidant 1076 are added, and after preliminary winding in a high-speed mixer, the mixture is fed into an internal mixer, BPO decomposes to generate free radicals to initiate LDPE molecular chain rupture, forming macromolecular chains containing free radicals, which react with the silicon hydroxyl (Si-OH) or aluminum hydroxyl (Al-OH) on the edge of the OMMT sheet layer to form covalent bonds or hydrogen bonds, fixing the OMMT on the LDPE chain; finally, when the MMT / LDPE composite modifier is blended with HDPE, the homologous polarity of LDPE and HDPE (both are polyethylene) disperses the OMMT sheet layer uniformly in the HDPE matrix through van der Waals force and a small amount of eutectic action, forming a continuous nano-barrier network to hinder the penetration of oxygen, water molecules and heavy metal ions.

[0030] The present application also provides a processing process for the polyethylene composite geomembrane, the steps of which include: S1, high density polyethylene, polyethylene grafted maleic anhydride, nano-montmorillonite / low density polyethylene composite modifier, antioxidant, light stabilizer, calcium stearate are weighed according to the formula proportion, and then added into a high-speed mixer and uniformly mixed; S2, the mixture is melt-extruded and granulated by a double screw extruder, to obtain a special material; the barrel temperature of the double screw extruder is 155-160 DEG C at the feeding section, 185-190 DEG C at the compression section, 205-210 DEG C at the metering section, and 215-220 DEG C at the die head; S3, the special material is calendered into a sheet by a calender; the sheet is compounded with another layer of un-compounded sheet by a hot press compounding machine, to form a double-layer structure; and the sheet is naturally cooled to below 25 DEG C.

[0031] According to the preferred embodiment of the present application, in step S1, the rotating speed of the high-speed mixer is 800-850 rpm, and the mixing time is 5-10 min.

[0032] According to the preferred embodiment of the present application, in step S2, the rotating speed of the screw of the double screw extruder is 450-500 rpm.

[0033] According to the preferred embodiment of the present application, in step S3, the roller temperature of the calender is 170-185 DEG C, and the roller spacing is 0.6-0.7 mm; the thickness of the sheet is 0.3-2.0 mm; and the temperature of the hot press compounding machine is 180-190 DEG C, the pressure is 0.6-0.7 MPa, and the speed is 1.2-1.4 m / min.

[0034] In the present application, the antioxidant inhibits molecular chain rupture by capturing free radicals generated by thermal oxidation: hindered phenolic antioxidant 1010 provides active hydrogen atoms to capture peroxide radicals (ROO·), to generate stable phenolic oxygen radicals (ArO·), which react with hydrogen peroxide (ROOH) to decompose into harmless alcohol (ROH), to terminate the chain reaction; antioxidant 1076 synergistically expands the antioxidant temperature range. The light stabilizer (such as GW-944, hindered amine HALS) absorbs ultraviolet energy and converts into heat energy by intramolecular rearrangement (such as cyclization) to release, avoiding direct degradation of the HDPE molecular chain by ultraviolet light, and capturing free radicals to inhibit photo-oxidation chain reaction. The lubricant calcium stearate acts as an anionic surfactant, with its polar carboxylate adsorbed on the HDPE chain, and the non-polar long carbon chain facing the material surface, to reduce the friction coefficient of the melt and the processing equipment (double screw, calender roll), reduce processing heat generation and roll sticking, and ensure uniform dispersion of the material and molding of the product. Through polarity complementation, physical entanglement, chemical bonding and processing synergy, the interface adhesion, weather resistance and barrier properties are simultaneously improved.

[0035] The present application has the following advantages: The polyethylene composite geomembrane of the present application significantly improves the interfacial bonding performance through multi-component synergistic modification. The polyethylene grafted maleic anhydride added in the raw material is prepared by a melt grafting process, and the maleic anhydride groups are uniformly distributed on the surface of the polyethylene molecular chain, forming a large number of polar sites. Strong ionic or hydrogen bond interactions occur between the polar sites and the clay minerals (containing Si-O - , Al-O - , etc. negative charge groups) in the soil, sand and other media, effectively improving the interfacial slip problem caused by the weak surface polarity of the traditional PE membrane, making the bonding between the geomembrane and the medium more stable, and the structure of the impermeable layer more firm.

[0036] The introduction of nano-montmorillonite / low-density polyethylene composite modifier further enhances the weather resistance and barrier properties of the material. The organic modified montmorillonite is treated by hexadecyl trimethyl ammonium bromide intercalation, and its lamellar structure is uniformly dispersed in the matrix with the assistance of low-density polyethylene, forming a continuous nanoscale barrier network that can effectively block the penetration of small molecules such as oxygen and water molecules, delaying the performance degradation of the material due to oxidation or hydrolysis; at the same time, the montmorillonite lamellar structure has strong adsorption effect on heavy metal ions and organic pollutants, significantly reducing the migration and diffusion ability of harmful substances, and expanding the application range of the geomembrane in pollution prevention and control scenarios.

[0037] The optimization of the processing technology realizes the efficient synergy of each component and the overall improvement of the material performance. In the double screw extrusion granulation process, by controlling the temperature, speed and other parameters, the uniform mixing and melt blending of high-density polyethylene, PE-g-MAH, MMT / LDPE and additives are ensured, and the internal defects caused by poor compatibility are avoided; the calendering process combined with the optional double-layer composite structure further improves the thickness uniformity and mechanical strength of the sheet, and the finally obtained polyethylene composite geomembrane has excellent interfacial bonding, weather resistance and barrier properties, which can meet the long-term use requirements in complex environments such as water conservancy projects, landfill sites, mine restoration, etc., and the comprehensive performance is significantly better than that of the traditional single modified polyethylene geomembrane. DETAILED DESCRIPTION

[0038] The following detailed description is only used to further illustrate the present application, and cannot be understood as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0039] I. Examples Example 1 HDPE (melt flow rate MFR = 1.0 g / 10 min, grade 5000S, manufacturer SINOPEC Yanshan Petrochemical Co., Ltd.) 750 g was weighed and dried in an oven at 80°C for 2.5 hours until the water content of the material was less than 0.05%. Maleic anhydride (MAH, purity ≥ 99.5%, manufacturer Puyang Huicheng Electronic Material Co., Ltd.) 25 g, dicumyl peroxide (DCP, purity ≥ 98.5%, manufacturer Shanghai Jinjile New Material Co., Ltd.) 0.8 g, antioxidant 1010 (purity ≥ 98.0%, manufacturer Liyanlong New Material Co., Ltd.) 1.5 g were weighed and added to the dried HDPE in a high-speed mixer (model SRL-100, manufacturer Changzhou Yibudiao Drying Equipment Co., Ltd.) and mixed at a speed of 800 rpm for 5 minutes to ensure uniform dispersion of the components.

[0040] The mixed material was added to a twin-screw extruder (model CTE-35, manufacturer Nanjing Kebeilong Koyama Machinery Co., Ltd.) and set to control the barrel temperature in stages: 185°C for the feeding section, 190°C for the compression section, 200°C for the metering section, and 215°C for the die head. The screw speed was set to 300 rpm. After the material completed the melt blending and grafting reaction in the twin-screw extruder, it was cooled and formed by a water-cooled traction system, then granulated by a pelletizer to obtain polyethylene grafted maleic anhydride (PE-g-MAH) particles. Next, a nano-montmorillonite / low-density polyethylene composite modifier (MMT / LDPE) was prepared. Sodium-based montmorillonite (particle size 30-50 nm, interlayer spacing 1.5-1.6 nm, manufacturer Zhejiang Fenghong New Material Co., Ltd., grade FM-800) 100 g was added to deionized water (conductivity ≤ 10 μS / cm, manufacturer Jiangsu Jiangyin Jianghua Microelectronic Material Co., Ltd.) and dispersed using an ultrasonic dispersion device (frequency 40 kHz) for 30 minutes to form a uniform suspension. Hexadecyltrimethylammonium bromide (CTAB, 3% of the mass of the montmorillonite) was added to the suspension and stirred in a 60°C constant-temperature water bath for 2 hours to promote the cation exchange reaction between the sodium ions in the interlayer of the montmorillonite and the CTAB. After stirring, the suspension was centrifuged at a speed of 8000 rpm for 10 minutes, the precipitate was collected, and then placed in a 60°C vacuum drying oven for 12 hours to remove the water, obtaining organic modified montmorillonite (OMMT).

[0041] Take low density polyethylene (LDPE, melt flow rate MFR = 1.5 g / 10 min, grade 1C7A, manufacturer SINOPEC Yanshan Petrochemical Co., Ltd.) 900 g, and OMMT 100 g in a mass ratio of 9:1 into a high-speed mixer (model SRL-100) and mix at a speed of 1000 rpm for 5 minutes. Then add benzoyl peroxide (BPO, purity ≥98.0%, manufacturer Jiangsu Qiangsheng Functional Chemical Co., Ltd.) 3 g, antioxidant 1076 (purity ≥98.0%, manufacturer Shanghai Petrochemical Xiniel Chemical Co., Ltd.) 2 g, and continue to mix for 5 minutes to make the components fully entangled. Put the mixture into a rubber mixing machine (model X(S)M-50, manufacturer Dalian Rubber and Plastics Machinery Co., Ltd.) and set the temperature to 175℃, the rotor speed to 50 rpm, and react for 30 minutes to promote the combination of the free radicals generated by the decomposition of BPO with the molecular chains of LDPE and the layers of OMMT. After the reaction is completed, put the intercalation product and the remaining HDPE 100 g into a twin-screw extruder (model SHJ-35, manufacturer Koya Equipment Group) and set the barrel temperature to 165-190℃ (165℃ for the feeding section, 175℃ for the compression section, 185℃ for the metering section, and 190℃ for the head), the screw speed to 400 rpm, and melt blend and granulate to obtain nano-montmorillonite / low density polyethylene composite modifier (MMT / LDPE) particles.

[0042] Finally, prepare a polyethylene composite geomembrane. Take HDPE 750 g, PE-g-MAH 100 g, MMT / LDPE 100 g, antioxidant 1010 1.5 g, antioxidant 1076 2.0 g (purchased from Shanghai Petrochemical Xiniel Chemical Co., Ltd.), light stabilizer GW-944 (purchased from Beijing Jia Cheng Auxiliary Research Institute) 2.0 g, calcium stearate (purchased from Dandong Chemical Research Co., Ltd.) 3.0 g according to the formula proportion, add them into a high-speed mixer (model SRL-100) and mix at a speed of 800 rpm for 5 minutes to ensure uniform dispersion of the components. Put the mixture into a twin-screw extruder (model CTE-35) and set the barrel temperature to 155-215℃ (155℃ for the feeding section, 185℃ for the compression section, 205℃ for the metering section, and 215℃ for the head), the screw speed to 450 rpm, and melt extrude and granulate to obtain a special material for composite geomembrane. Put the special material into a calender (set the roller temperature to 170℃ and the roller spacing to 0.6 mm) to make a sheet with a thickness of 1.0 mm through the calendering process. Put the sheet into a hot press compounding machine (set the temperature to 180℃, the pressure to 0.6 MPa, and the running speed to 1.2 m / min) and hot-press it with another sheet that is not compounded to form a double-layer composite geomembrane. Finally, cool the sheet to below 25℃ naturally and cut it into finished products with a width of 2 meters and a length of 100 meters per roll.

[0043] Example 2 The preparation method is the same as that of Example 1, except that 780 g of high-density polyethylene (HDPE, melt flow rate MFR = 1.0 g / 10 min, grade 5000S) is weighed and dried in an 80°C oven for 2 hours until the water content is less than 0.05%. Maleic anhydride 23 g, dicumyl peroxide 0.7 g, and antioxidant 1010 1.6 g are weighed and uniformly mixed with the dried HDPE in a high-speed mixer (800 rpm, 5 min).

[0044] The mixture is added to a twin-screw extruder (cylinder temperature 185-200°C, screw speed 350 rpm) for melt extrusion, water-cooled traction, and pelletization to obtain PE-g-MAH particles. MMT / LDPE is prepared as follows: sodium-based montmorillonite 105 g is ultrasonically dispersed for 35 min, CTAB (3%) is added and stirred at 60°C for 2.5 hours, and then centrifuged and dried for 13 hours to obtain OMMT; LDPE 855 g is mixed with OMMT 105 g, BPO 3.2 g, and antioxidant 1076 2.1 g, and then high-speed mixed (1000 rpm, 5 min) and then densified (178°C, 50 rpm, 35 min), and then blended with the remaining HDPE 90 g in a twin-screw extruder (165-190°C, 420 rpm) for pelletization to obtain MMT / LDPE particles. HDPE 780 g, PE-g-MAH 80 g, MMT / LDPE 100 g, antioxidant 1010 1.6 g, antioxidant 1076 2.0 g, light stabilizer GW-944 2.0 g, and calcium stearate 3.0 g are weighed according to the formula, high-speed mixed (800 rpm, 5 min), and then extruded in a twin-screw extruder (cylinder temperature 155-220°C, screw speed 480 rpm) for pelletization; calendered (175°C, 0.65 mm) and then hot-pressed (185°C, 0.65 MPa, 1.3 m / min) to obtain a double-layer composite geomembrane.

[0045] Example 3 The preparation method is the same as that of Example 1, except that 780 g of high-density polyethylene (HDPE, melt flow rate MFR = 1.0 g / 10 min, grade 5000S) is weighed and dried in an 80°C oven for 2 hours until the water content is less than 0.05%. Maleic anhydride 23 g, dicumyl peroxide 0.7 g, and antioxidant 1010 1.6 g are weighed and uniformly mixed with the dried HDPE in a high-speed mixer (800 rpm, 5 min).

[0046] The mixture was added into a twin-screw extruder (cylinder temperature 185-200°C, screw rotation speed 320 rpm) for melt extrusion, water-cooling traction, and granulation to obtain PE-g-MAH granules. Preparation of MMT / LDPE: 110 g of sodium-based montmorillonite was ultrasonically dispersed for 35 minutes, 65°C stirring was performed for 3 hours after the addition of CTAB (3%), and OMMT was obtained by centrifugal drying for 12.5 hours; 825 g of LDPE was mixed with 110 g of OMMT, 3.3 g of BPO and 2.2 g of antioxidant 1076 were added, high-speed mixing (1000 rpm, 5 minutes) was performed, followed by banburying (180°C, 50 rpm, 40 minutes), and then 110 g of remaining HDPE (mass ratio 1:5) was twin-screw blended (165-190°C, 450 rpm) to obtain MMT / LDPE granules.

[0047] HDPE 700 g, PE-g-MAH 120 g, MMT / LDPE 120 g, antioxidant 1010 1.8 g, antioxidant 1076 2.0 g, light stabilizer GW-944 2.0 g, and calcium stearate 3.0 g were weighed according to the formula, high-speed mixing (800 rpm, 8 minutes) was performed, followed by twin-screw extrusion (cylinder temperature 155-220°C, screw rotation speed 500 rpm) to obtain granules; calendering (180°C, 0.7 mm) was performed, followed by hot-pressing compounding (190°C, 0.7 MPa, 1.4 m / min) to obtain a double-layer composite geomembrane.

[0048] Comparative Example 1 The preparation method was the same as in Example 1, except that 800 g of HDPE (not grafted), 200 g of ordinary HDPE (not modified), 100 g of MMT / LDPE, 2.0 g of antioxidant 1010, 2.5 g of antioxidant 1076, 2.5 g of light stabilizer GW-944, and 3.5 g of calcium stearate were weighed, mixed, and then twin-screw extruded (cylinder temperature 155-220°C, screw rotation speed 450 rpm) to obtain granules; calendering (170°C, 0.6 mm) was performed, followed by hot-pressing compounding (180°C, 0.6 MPa, 1.2 m / min) to obtain a double-layer geomembrane.

[0049] Comparative Example 2 The preparation method was the same as in Example 1, except that 750 g of HDPE, 100 g of PE-g-MAH, 100 g of ordinary LDPE (not modified), 1.5 g of antioxidant 1010, 2.0 g of antioxidant 1076, 2.0 g of light stabilizer GW-944, and 3.0 g of calcium stearate were weighed, mixed, and then twin-screw extruded (cylinder temperature 155-220°C, screw rotation speed 450 rpm) to obtain granules; calendering (170°C, 0.6 mm) was performed, followed by hot-pressing compounding (180°C, 0.6 MPa, 1.2 m / min) to obtain a double-layer geomembrane.

[0050] Comparative Example 3 The preparation method is the same as that of Example 1, except that 750 g of HDPE, 100 g of PE-g-MAH, 100 g of unmodified montmorillonite (without CTAB intercalation and LDPE compounding), 1.5 g of antioxidant 1010, 2.0 g of antioxidant 1076, 2.0 g of light stabilizer GW-944, and 3.0 g of calcium stearate are weighed, mixed, and then extruded by a twin-screw extruder (cylinder temperature 155-220°C, screw rotation speed 450 rpm / min) to form pellets; after calendering (170°C, 0.6 mm), hot pressing compounding (180°C, 0.6 MPa, 1.2 m / min) is performed, and the double-layer geomembrane is obtained after cooling.

[0051] II. Performance Test The materials prepared in Examples 1-3 and Comparative Examples 1-3 above are subjected to performance tests according to the following methods: 1. Interfacial bonding strength test: a tensile test method is used. A geomembrane sample with a size of 50 mm x 50 mm x 0.5 mm is tightly attached to dry soil (clay mineral content ≥ 60%, water content 15%) of the same size, and is pulled vertically at a constant speed on a universal material testing machine (model: Instron 5967, loading rate 10 mm / min), and the maximum pulling force (F) is recorded. The interfacial bonding strength (σ) is calculated by the formula: σ = F / (πr²), where r is the radius of the sample (25 mm). Five parallel samples are tested for each group, and the average value is taken.

[0052] 2. Weather resistance test (elongation at break after UV aging): the geomembrane sample is placed in an ultraviolet aging box (model: Q-Lab QUV / SE, irradiance 0.89 W / m², wavelength 340 nm) for continuous irradiation for 500 hours. After aging, the sample is taken out and adjusted in a standard environment (23°C, 50% RH) for 24 hours. The electronic universal testing machine (model: Zwick Z020, tensile speed 50 mm / min) is used to test the elongation at break (ε), and the calculation formula is: ε = (L-L0) / L0 x 100%, where L is the gauge length at break, and L0 is the initial gauge length (100 mm). Five parallel samples are tested for each group, and the average value is taken.

[0053] 3. Barrier performance test (heavy metal ion adsorption rate): a standard solution of Pb 2+ , Cd 2+ with a concentration of 100 mg / L (100 mL) is prepared, 0.1 g of the geomembrane sample is added, sealed, and placed in a constant temperature oscillator (model: THZ-82, rotation speed 150 rpm, temperature 25°C) for 24 hours. The supernatant is taken and the remaining Pb2+ Cd 2+ The adsorption rate (η) was calculated according to the formula: η = (C0-C1) / C0x100%, wherein C0is the initial concentration (100 mg / L). Three parallel samples were tested for each group of samples, and the average value was taken.

[0054] 4. Mechanical property test (tensile strength, tear strength): an electronic universal testing machine (model: ZwickZ020) was used to test the tensile strength (σ_t) according to the GB / T 1040.3-2006 standard, the tensile rate was 50 mm / min, and the sample size was 150 mm x 15 mm x 0.5 mm; the tear strength (τ) was tested according to the GB / T 3903.3-2011 standard, the tear rate was 50 mm / min, and the sample size was 100 mm x 10 mm x 0.5 mm. Five parallel samples were tested for each group of samples, and the average value was taken.

[0055] Performance test results: Table 1: Performance test results of each example and comparative example

[0056] As can be seen from Table 1, by means of two-component modification and process optimization, the application effectively solves the problems of weak interfacial adhesion and easy slippage, poor weather resistance and easy aging, insufficient barrier performance and difficulty in blocking harmful substances of traditional polyethylene geomembranes. The specific analysis is as follows: the traditional polyethylene geomembrane has weak surface polarity, and the interfacial adhesion with soil, sand and other media is insufficient, which is easy to cause slippage and lead to the failure of the impermeable layer; the molecular chain is easily attacked by ultraviolet light and oxygen, causing thermal oxidative aging and photo-oxidative degradation, and the elongation at break significantly decreases after long-term exposure, and the service life is shortened; at the same time, the barrier ability to heavy metal ions and organic pollutants is limited, and it is difficult to meet the pollution control requirements.

[0057] In the present application, examples 1-3 by adding polyethylene graft maleic anhydride, the molecular chain of carboxyl and anhydride group and clay mineral in soil of silicon hydroxyl, aluminum hydroxyl form strong polar interaction (such as hydrogen bond or ionic bond), interface bonding strength is higher than traditional geomembrane (comparative example 1 without PE-g-MAH only 0.6MPa) to 1.0-1.2MPa, significantly enhanced the stability of the medium bonding, solved the easy slip problem.For weather resistance, examples 1-3 by introducing nano montmorillonite / low density polyethylene composite modifier (MMT / LDPE), its organic modified montmorillonite (OMMT) layer is uniformly dispersed in the matrix under the assistance of low density polyethylene (LDPE), form continuous nano barrier network, effectively hinder the penetration of oxygen, water molecules and ultraviolet light.After UV aging for 500 hours, the elongation at break of examples 1-3 still maintains 82-88%, far higher than comparative example 2 (without MMT / LDPE only 65%), indicating that the material anti-aging ability is significantly improved.About the barrier properties, the MMT / LDPE composite modifier of examples 1-3, the montmorillonite layer has strong adsorption effect (adsorption rate of 85-92%) on Pb 2+ 、Cd 2+ And other heavy metal ions, far more than the comparative example (unmodified montmorillonite or without MMT / LDPE only 65-80%), effectively block the migration and diffusion of harmful substances, meet the pollution prevention and control demand.In addition, the tensile strength (26-28MPa) and tear strength (50-55kN / m) of examples 1-3 are better than those of comparative example (18-22MPa, 38-45kN / m), indicating that the overall mechanical stability of the material is improved by the synergistic modification of each component, further ensuring its long-term use performance in complex environment.In summary, the present application improves the comprehensive performance of polyethylene geomembrane by multi-component synergistic modification and process optimization, solves the key defects of traditional products.

[0058] The above examples only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as limiting the scope of the present patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of variations and improvements can be made, which are within the scope of protection of the present application.

Claims

1. A polyethylene geomembrane, characterized by, Raw materials include, by mass percentage: High-density polyethylene: 70-80%; Polyethylene grafted maleic anhydride: 8-12%; Nano-montmorillonite / low-density polyethylene composite modifier: 9-12%; Antioxidant: 0.15-0.25%; Light stabilizer: 0.2-0.25%; Lubricant calcium stearate: 0.3-0.5%; The preparation of the polyethylene grafted maleic anhydride includes: A1, drying high-density polyethylene, mixing with maleic anhydride, dicumyl peroxide and antioxidant 1010 uniformly; A2, adding a twin-screw extruder, melting and extruding at a barrel temperature of 185-200℃; the extrudate is water-cooled, drawn, and granulated by a granulator.

2. The polyethylene geomembrane according to claim 1, characterized in that, In step A1, the drying temperature is 80-85℃, and the drying time is 2-3h; the mass of maleic anhydride accounts for 2.5-3% of the mass of high-density polyethylene; the mass of initiator accounts for 0.08-0.1% of the mass of high-density polyethylene; the mass of antioxidant accounts for 0.1-0.12% of the mass of high-density polyethylene.

3. The polyethylene geomembrane according to claim 1, wherein In step A2, the screw rotation speed of the twin-screw extruder is 300-350rpm.

4. The polyethylene geomembrane according to claim 1, wherein The preparation of the nano-montmorillonite / low-density polyethylene composite modifier includes: B1, taking sodium-based montmorillonite and adding it to deionized water, ultrasonic dispersion, then adding cetyltrimethylammonium bromide, stirring at 60-65℃, centrifugation, and vacuum drying to obtain organically modified montmorillonite; B2, mixing low-density polyethylene with organically modified montmorillonite at a mass ratio of (9-9.5):1, adding benzoyl peroxide and antioxidant 1076, mixing uniformly in a high-speed mixer, and then adding a banbury mixer for reaction; finally, adding the intercalation product and the remaining high-density polyethylene at a mass ratio of 1:(4-5) into a twin-screw extruder for blending and granulation.

5. The polyethylene geomembrane according to claim 1, wherein In step B1, the particle size of the sodium-based montmorillonite is 30-50nm, and the interlayer spacing is 1.5-1.6nm; the ultrasonic dispersion time is 30-35min, and the stirring time is 2-3h; the vacuum drying temperature is 60-65℃, and the vacuum drying time is 12-13h.

6. The polyethylene geomembrane according to claim 1, wherein In step B2, the rotation speed of the high-speed mixer is 1000-1200rpm, and the mixing time is 5-10min; the temperature of the banbury mixer is 175-180℃, the rotor rotation speed of the banbury mixer is 50-60rpm, and the reaction time in the banbury mixer is 30-40min; the temperature of the twin-screw extruder is 165-190℃, and the screw rotation speed is 400-450rpm.

7. A process for the production of a polyethylene geomembrane according to any one of claims 1 to 5, characterized in that the steps It includes: S1, high-density polyethylene, polyethylene grafted maleic anhydride, nano-montmorillonite / low-density polyethylene composite modifier, antioxidant, light stabilizer, and calcium stearate are weighed according to the formula ratio, and then added into a high-speed mixer and mixed uniformly; S2, the mixture is melted and extruded by a twin-screw extruder to obtain a special material; the barrel temperature of the twin-screw extruder is 155-160℃ for the feeding section, 185-190℃ for the compression section, 205-210℃ for the metering section, and 215-220℃ for the head; S3, the special material is calendered into a sheet by a calender; the sheet is compounded with another layer of un-compounded sheet by a hot press compounding machine to form a double-layer structure; the sheet is naturally cooled to below 25℃.

8. The process of claim 7, wherein, In step S1, the speed of the high-speed mixer is 800-850 rpm, and the mixing time is 5-10 min.

9. The process of claim 7, wherein, In step S2, the screw speed of the twin-screw extruder is 450-500 rpm.

10. The process of claim 7, wherein, In step S3, the roller temperature of the calender is 170-185 ℃, the roll gap is 0.6-0.7 mm; the thickness of the sheet is 0.3-2.0 mm; the temperature of the hot-pressing compound machine is 180-190 ℃, the pressure is 0.6-0.7 MPa, and the speed is 1.2-1.4 m / min.

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