A wide-width thermoplastic polyolefin anti-seepage geomembrane and its preparation method

Abstract

The present invention relates to a wide-width thermoplastic polyolefin anti-seepage geomembrane and a preparation method thereof. The preparation method comprises the following steps: after uniformly mixing a thermoplastic polyolefin composite material, feeding it into a screw extruder, melting and plasticizing it in the screw extruder, and extruding it into a mold at a low temperature for forming, and then towing it forward, naturally cooling it during the process to allow the material to complete a partial crystallization process, and then feeding it into a three-roll calender to determine its thickness, thereby obtaining a wide-width thermoplastic polyolefin anti-seepage geomembrane. The geomembrane prepared by the present invention has a width greater than or equal to 6m, a small difference in transverse and longitudinal elongation, and is suitable for high-pressure water environments.

Description

Technical Field

[0001] The invention belongs to the technical field of geomembrane preparation, and particularly relates to a wide thermoplastic polyolefin anti-seepage geomembrane and a preparation method thereof. Background Art

[0002] Water conservancy and hydropower projects are vital to the well-being of the people, and water conservation, anti-seepage, and loss reduction are paramount. Given my country's vast territory and complex topography, the construction of water conservancy and hydropower projects depends on the actual geological conditions, making anti-seepage extremely challenging. Compared to mainstream reinforced concrete and asphalt concrete materials used in water conservancy and hydropower projects, anti-seepage geomembranes made from high-molecular-weight polymers offer advantages such as excellent impermeability, strong seismic resistance, simple construction, minimal climatic impact, short construction periods, low costs, and ease of repair and replacement. These geomembranes hold great promise for anti-seepage applications in hydraulic structures.

[0003] Currently, the commonly used polymer geomembranes are mainly high-density polyethylene (HDPE) geomembrane, polyvinyl chloride (PVC) geomembrane, and thermoplastic polyolefin elastomer (TPO) geomembrane. Among them, high-density polyethylene (HDPE) geomembrane has the disadvantages of high hardness and poor construction performance. In addition, its unidirectional elongation at break is as high as over 900%, but its bidirectional elongation at break is only 90%, making it difficult to adapt to the settlement deformation and uneven base of hydraulic structures under high water pressure. It is prone to local cracking or large-area puncture, leading to concentrated leakage. Polyvinyl chloride (PVC) has excellent flexibility and good adhesion to the base layer. Its unidirectional elongation at break is only about 300%, but its bidirectional elongation at break can reach about 240%. Although its multidirectional deformation limit is more than 1 times that of HDPE geomembrane, it still does not meet the requirement of more than 650% (calculated by the depth-to-width ratio probability of local depression in the cushion layer) under high water pressure. Therefore, it is not suitable for anti-seepage treatment under high water pressure environments. Thermoplastic polyolefin elastomer (TPO) geomembrane has attracted a lot of attention due to its excellent flexibility, deformation adaptability and durability. However, due to the limitations of the extrusion process, its maximum width is currently only 3 meters. When the width increases, the geomembrane cloth will produce calendering orientation during the three-roll calendering to determine the thickness, resulting in a large difference in its longitudinal and transverse elongation, and obvious transverse unevenness. For example, when tested at position 1, the longitudinal elongation is 300-400% and the transverse elongation is 700%, while when tested at another position, the longitudinal elongation will be 500-600% and the transverse elongation will be 700%, showing serious unevenness. The current anti-seepage area of ​​water conservancy and hydropower projects is large, often hundreds of thousands of square meters. Therefore, there is an urgent need to develop a thermoplastic polyolefin elastomer (TPO) anti-seepage geomembrane with a large width, small difference in longitudinal and transverse elongation, and suitable for high-pressure water environments to improve the efficiency of anti-seepage construction. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects in the prior art and provide a wide thermoplastic polyolefin anti-seepage geomembrane and a preparation method thereof, wherein the wide thermoplastic polyolefin anti-seepage geomembrane has a width greater than or equal to 6m, has a small difference in transverse and longitudinal elongation, and can be suitable for high-pressure water environments.

[0005] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0006] A method for preparing a wide-width thermoplastic polyolefin anti-seepage geomembrane comprises the following steps:

[0007] After the thermoplastic polyolefin composite material is uniformly mixed, it is fed into a screw extruder, melted and plasticized by the screw extruder, and extruded into a mold at a low temperature for forming. It is then towed and naturally cooled during the process, so that the material completes a partial crystallization process. It then enters a three-roll calender to determine the thickness, thereby obtaining a wide-width thermoplastic polyolefin anti-seepage geomembrane. The partial crystallization process of the material of the present invention refers to the fact that after the material is formed, before entering the three-roll calender, crystallization has begun, but complete crystallization has not yet been achieved. Therefore, it is called a partial crystallization process.

[0008] As a further technical solution, after the thickness is determined by a three-roll calender, it is necessary to trim, cut to length, and roll it up to obtain a thermoplastic polyolefin anti-seepage geomembrane.

[0009] As a further technical solution, the thermoplastic polyolefin composite material includes a nucleating agent;

[0010] As a further technical solution, the screw extruder adopts a vacuum double exhaust single screw extruder;

[0011] As a further technical solution, the temperature of the vacuum double-exhaust single-screw extruder is set to 170-185°C, and the melt temperature during extrusion by the vacuum double-exhaust single-screw extruder is ≤200°C;

[0012] As a further technical solution, the temperature of the mold is set to 170-185°C;

[0013] As a further technical solution, the material is naturally cooled to 120-145°C during the process to complete 40-80% of the crystallization process. Before entering the three-roll calender, the material of the present invention needs to ensure that its crystallization process has reached 40-80%. If the crystallization process is too slow, for example, in traditional technology, the material has not begun to crystallize before entering the three-roll calender, and its crystallization process will be completed entirely during the thickness setting process of the three-roll calender, which will result in large differences in the elongation at break of the extruded anti-seepage geomembrane in the transverse and longitudinal directions, and uneven elongation at break in different parts. If the material is completely crystallized (all crystallization processes are completed) before entering the three-roll calender, it will not be able to be shaped during the calendering process, and thickness control will be impossible.

[0014] As a further technical solution, the vacuum double-exhaust single-screw extruder includes a barrel mechanism, a feed port and a discharge port provided on the barrel mechanism, an extrusion screw provided in the barrel mechanism, and a motor for driving the extrusion screw to rotate;

[0015] The extrusion screw comprises a feeding section, a first compression section, a barrier section, an exhaust section, a second compression section and a homogenizing section which are sequentially arranged according to the traveling direction of the material.

[0016] As a further technical solution, two exhaust ports are provided on the barrel mechanism at positions corresponding to the exhaust sections of the extrusion screw, and the exhaust ports are connected to a water ring vacuum pump.

[0017] As a further technical solution, the extrusion screw is provided with a plurality of ring pins at the middle and rear part of the first compression section and the homogenization section;

[0018] As a further technical solution, in the homogenization section, adjacent ring pins are staggered; in the middle and rear part of the first compression section, several ring pins are positioned correspondingly in the radial direction and distributed in rows.

[0019] As a further technical solution, the diameter of the extrusion screw is ≥180 mm, and the aspect ratio is ≥38.

[0020] As a further technical solution, the barrel mechanism includes a protective shell, a barrel arranged in the protective shell, a heating module sleeved on the barrel, and a cooling fan arranged outside the protective shell and used to cool the heating module.

[0021] As a further technical solution, the heating module includes a heating coil wound around the outer wall of the barrel;

[0022] As a further technical solution, the air outlet of the heat dissipation fan is aligned with the heating coil of the corresponding heating module.

[0023] As a further technical solution, two exhaust ports are provided on the barrel at positions corresponding to the exhaust sections of the extrusion screw, and the exhaust ports are connected to a water ring vacuum pump.

[0024] As a further technical solution, a cooling coil is provided outside the barrel at a position corresponding to the feeding section.

[0025] As a further technical solution, according to the direction of material travel, the discharge port is also provided with an automatic screen changer, a metering pump, a static mixer, a distributor and a wide-width mold in sequence.

[0026] As a further technical solution, the thermoplastic polyolefin composite material comprises the following raw materials in parts by weight:

[0027] 45-75 parts of thermoplastic polyolefin resin, 10-30 parts of toughening resin, 10-30 parts of inorganic filler, 0.3-1.3 parts of antioxidant, 0.3-1.3 parts of light stabilizer, 0.1-2 parts of nucleating agent, and 0.3-3 parts of pigment.

[0028] As a further technical solution, before the thermoplastic polyolefin composite material is fed into the screw extruder, the inorganic filler, antioxidant, light stabilizer, nucleating agent, and pigment are first mixed uniformly to obtain a powder, and then the powder is mixed uniformly with a portion of the thermoplastic polyolefin resin, and then fed into a twin-screw extruder for shear blending, extrusion, and granulation, and then dried and homogenized to obtain a high-concentration powder thermoplastic polyolefin masterbatch; then the high-concentration powder thermoplastic polyolefin masterbatch, the remaining thermoplastic polyolefin resin, and the toughening resin are fed into the screw extruder;

[0029] Alternatively, before the thermoplastic polyolefin composite material is fed into the screw extruder, the inorganic filler, antioxidant, light stabilizer, nucleating agent, and pigment are first mixed evenly to obtain a powder, and the thermoplastic polyolefin resin and toughening resin are mixed evenly to obtain pellets; the powder and pellets are then fed into a twin-screw extruder for shear blending, extrusion, and granulation, and then dried and homogenized to obtain a thermoplastic polyolefin masterbatch, which is then fed into the screw extruder.

[0030] As a further technical solution, the content of powder in the high-concentration powder thermoplastic polyolefin masterbatch is 40-80%.

[0031] As a further technical solution, the setting temperature of the twin-screw extruder is 165-190°C, and the melt temperature during extrusion by the twin-screw extruder is ≤230°C.

[0032] As a further technical solution, the thermoplastic polyolefin resin includes one or more of C3 / C2 / C4 terpolymer polypropylene (reaction grade TPO) and C3 / C2 binary copolymer polypropylene;

[0033] As a further technical solution, the density of the thermoplastic polyolefin resin is 0.850-0.930 g / cm 3 , the melt index at 230°C / 2.16Kg is 0.3-3.5 g / 10min; for example, LyondellBasell's Hifax CA 10A, AdflexQ300F, Dow Chemical's Versify 2300, ExxonMobil's Vistamaxx 6102, Yanshan Petrochemical's B9302, Sinopec NS06, etc.

[0034] As a further technical solution, the density of the thermoplastic polyolefin resin is 0.87-0.89 g / cm 3, the melt index at 230°C / 2.16Kg is 0.3-1.0 g / 10min;

[0035] As a further technical solution, the toughening resin includes one or more of ethylene / α-octene random copolymer (POE), ethylene / α-butene random copolymer (POE), and ethylene / α-octene block copolymer (OBC);

[0036] As a further technical solution, the density of the toughening resin is 0.855-0.905 g / cm 3 , the melt index at 190°C / 2.16Kg is 0.3-2.0; such as Dow Chemical's Engage 8842, Infuse 9010, etc.

[0037] As a further technical solution, the toughening resin has a density of 0.85-0.87 g / cm 3 g / cm 3 , an ethylene / α-octene random copolymer having a melt index of 0.3-1.0 g / 10 min at 190°C / 2.16 kg and / or a density of 0.87-0.88 g / cm 3 g / cm 3 , a melt index of 0.3-1.0 g / 10min of ethylene / α-butene random copolymer at 190°C / 2.16Kg;

[0038] As a further technical solution, the inorganic filler includes one or more of calcium carbonate, talc, calcined kaolin, and calcite.

[0039] As a further technical solution, the calcium carbonate is preferably ultrafine active heavy calcium carbonate with a bulk density of 1-1.3 g / cm 3 The average particle size (D50) is between 4.0-6.0μm. For example, Omyacarb 6 from Omya Calcium;

[0040] As a further technical solution, the antioxidant includes one or more of an organic phosphite (with low volatility and hydrolysis resistance) and a hindered phenol antioxidant; preferably, it is a compound antioxidant of an organic phosphite and a hindered phenol antioxidant; for example, BASF's Irganox B 225;

[0041] The light stabilizer is a block oligomeric hindered amine light stabilizer, such as BASF's Chimassorb 2020;

[0042] The nucleating agent is one or more of a stearate nucleating agent, a sorbitol nucleating agent, an organic phosphate nucleating agent, an aromatic amide nucleating agent, and a carboxylic acid metal salt nucleating agent; preferably, a composite nucleating agent of a stearate nucleating agent and a carboxylic acid metal salt nucleating agent having an average particle size (D50) between 1.0 and 3.0 μm;

[0043] As a further technical solution, the pigment includes one or more of titanium dioxide, carbon black, iron oxide, Prussian blue, lead silicate, monoazo, disazo, and phthalocyanine, preferably rutile TiO2.

[0044] The wide-width thermoplastic polyolefin anti-seepage geomembrane prepared by the preparation method has a width greater than or equal to 6m, a bidirectional elongation at break greater than or equal to 650% (preferably greater than or equal to 750%), a difference between the longitudinal and transverse elongation at break less than or equal to 200% (preferably less than or equal to 100%), and longitudinal and transverse tensile strengths both greater than or equal to 12MPa.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] In the preparation process of the TPO geomembrane of the present invention, the limitation of the traditional technology that the material crystallizes during the calendering and thickness setting process of the three-roll calender is broken. The crystallization temperature of the material is increased by adding a nucleating agent to the raw material. At the same time, the melt temperature during extrusion of the screw extruder is reduced by improving the structure of the screw extruder, so that most of the material is crystallized before entering the three-roll calender, avoiding the problem of excessive difference in longitudinal and transverse elongation at break of the large-width thermoplastic polyolefin anti-seepage geomembrane caused by material crystallization during the calendering and thickness setting process, reducing the difference in longitudinal and transverse elongation at break, and realizing the preparation of multi-deformation large-width thermoplastic polyolefin anti-seepage geomembrane, which can be suitable for large-width thermoplastic polyolefin anti-seepage geomembrane in high-pressure water environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a schematic structural diagram of a single-screw extruder for extruding wide-width TPO geomembrane in one embodiment of the present invention;

[0048] Figure 2 This is a schematic structural diagram of a barrel mechanism in one embodiment of the present invention;

[0049] Figure 3 A schematic structural diagram of a barrel in one embodiment of the present invention;

[0050] Figure 4 This is a schematic structural diagram of an extrusion screw in one embodiment of the present invention;

[0051] Figure 5 for Figure 4 A magnified view of point A;

[0052] Figure 6 This is a schematic structural diagram of an extrusion screw in a homogenizing section in one embodiment of the present invention;

[0053] Figure 7 1 is a cross-sectional appearance diagram of the geomembrane products of Example 1 and Comparative Example 1;

[0054] Figure 8 Surface appearance diagrams of the geomembrane products of Example 1 and Comparative Example 1;

[0055] Figure 9 The melting and crystallization temperature curves of the raw materials in Example 1 and Comparative Example 2 are shown;

[0056] Figure 10 It is a fluctuation diagram of the unidirectional elongation at break of the geomembrane products of Example 1 and Comparative Example 1 at different positions;

[0057] Figure 11 Graph showing changes in biaxial tensile stress versus strain for the geomembrane products of Example 1, Comparative Example 2, and Comparative Example 5;

[0058] Figure 12 Schematic diagram of the operation of biaxial / biaxial tensile testing instrument for biaxial elongation at break test.

[0059] exist Figure 1-2 In: 1. Barrel mechanism, 2. Cooling coil, 3. Feed port, 4. Discharge port, 5. Extrusion screw, 6. Motor, 7. Feeding section, 8. First compression section, 9. Barrier section, 10. Exhaust section, 11. Second compression section, 12. Homogenizing section, 13. Exhaust port, 14. Water ring vacuum pump, 15. Pin, 16. Protective shell, 17. Barrel, 18. Heating coil, 19. Heating module, 20. Cooling fan, 21. Automatic screen changer, 22. Metering pump, 23. Static mixer, 24. Distributor, 25. Wide-width mold, 26. Spiral groove, 27. Temperature sensor. DETAILED DESCRIPTION

[0060] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0061] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0062] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0063] The present invention will be described in further detail below with reference to the accompanying drawings.

[0064] Device Example

[0065] Figure 1-6The present invention shows an embodiment of a single-screw extruder for wide-width TPO geomembrane extrusion, comprising a barrel mechanism 1, a feed port 3 and a discharge port 4 disposed on the barrel mechanism 1, an extrusion screw 5 rotatably disposed within the barrel mechanism 1, and a motor 6 for driving the extrusion screw 5. The extrusion screw 5 comprises a feed section 7, a first compression section 8, a barrier section 9, an exhaust section 10, a second compression section 11, and a homogenizing section 12, which are sequentially arranged in the direction of material flow. The present invention provides an exhaust section 10 in the middle of the screw to expel bubbles from the melt, and a second compression section 11 is provided after the exhaust section 10 to re-pressurize the melt, thereby improving the uniformity and plasticization effect of the melt. The present invention improves the structure of the extrusion screw and arranges it to include a feeding section, a first compression section, a barrier section, an exhaust section, a second compression section and a homogenizing section arranged in sequence in the direction of material travel. After the material is melted in the first compression section, it enters the exhaust section through the barrier section to discharge the gas in the melt, and then re-builds pressure in the second compression section and is homogenized in the homogenizing section before being discharged. The functions of the various sections of the extrusion screw of the present invention are as follows: 1) the present invention arranges the first compression section to melt the material, 2) the barrier section in traditional technology is usually arranged between the compression section and the homogenizing section, and is used to 1) The present invention sets the barrier section between the first compression section and the exhaust section to block the unmelted material, and the barrier section can promote the discharge of bubbles while blocking the unmelted material, improve the exhaust effect, and prevent the backflow of the exhaust section material; 2) The present invention sets the exhaust section to discharge bubbles in the melt, 3) The present invention sets the second compression section after the exhaust section to build up pressure on the material for the second time, thereby improving the plasticization effect of the material and improving the uniformity and plasticization effect of the melt, 4) The present invention sets the homogenization section to homogenize the melt before extrusion to provide uniformity of the melt. In addition, the present invention also sets a number of pins in the middle and rear part of the first compression section to mix and homogenize while compressing and plasticizing, so as to promote uniform mixing of the melt, so that the melt can be preliminarily homogenized before exhausting, thereby improving the uniformity and plasticization effect of the melt. In summary, the setting order of the various sections of the present invention greatly improves the uniformity and plasticization effect of the melt, so that it can meet the production needs of large-capacity materials.

[0066] As an embodiment of the single-screw extruder for extruding wide-width TPO geomembrane of the present invention, the diameter of the extrusion screw is ≥180 mm, and the aspect ratio is ≥38.

[0067] As an embodiment of a single-screw extruder for wide-width TPO geomembrane extrusion of the present invention, the diameter of the extrusion screw 5 is 180 mm and the aspect ratio is 38; this parameter setting enables it to meet the demand for extrusion of wide-width TOP geomembranes of 6 m and above.

[0068] As an embodiment of a single-screw extruder for extruding wide-width TPO geomembrane according to the present invention, the extrusion screw 5 is provided with a plurality of ring pins 15 in the middle and rear part of the first compression section 8 and in the homogenizing section 12. The design of the pins 15 according to the present invention, especially the setting of the pins in the first compression section, further improves the mixing and plasticizing effect of the melt.

[0069] As an embodiment of the single-screw extruder for wide-width TPO geomembrane extrusion of the present invention, in the homogenizing section, adjacent ring pins 15 are staggered.

[0070] As an embodiment of a single-screw extruder for wide-width TPO geomembrane extrusion of the present invention, in the middle and rear part of the first compression section 8, several circles of pins 15 are positioned correspondingly in the radial direction and distributed in rows, and the spacing distance between adjacent circles is equal to the thread pitch of the extrusion screw of the first compression section.

[0071] As an embodiment of a single-screw extruder for wide-width TPO geomembrane extrusion according to the present invention, the barrel mechanism 1 includes a protective housing 16, a barrel 17 disposed within the protective housing 16, a heating module 19 sleeved on the barrel 17, and a cooling fan 20 disposed outside the protective housing 16 and used to cool the heating module 19. The heating module 19 is used to heat the material, and the cooling fan 20 can cool the heating module 19 when the temperature of the barrel 17 exceeds a set temperature, thereby achieving temperature control of the material.

[0072] As an embodiment of a single-screw extruder for wide-width TPO geomembrane extrusion according to the present invention, the heating module 19 includes a heating coil 18 wound around the outer wall of the barrel 17 .

[0073] As an embodiment of a single-screw extruder for wide-width TPO geomembrane extrusion of the present invention, the outer wall of the barrel 17 is provided with a plurality of spiral grooves 26 , and the heating coil 18 is wound around the outer wall of the barrel 17 along the spiral grooves 26 .

[0074] As an embodiment of a single-screw extruder for extruding a wide-width TPO geomembrane according to the present invention, the air outlet of the heat dissipation fan 20 is aligned with the heating coil 18 of the corresponding heating module 19 .

[0075] As an embodiment of a single-screw extruder for extruding wide-width TPO geomembrane according to the present invention, two exhaust ports 13 are provided on the barrel 17 at positions corresponding to the exhaust section 10 of the extrusion screw 5, and the exhaust port 13 is connected to a water ring vacuum pump 14. Conventional screw extruders, even if an exhaust section is provided, only have one exhaust port. However, the present invention provides two exhaust ports on the barrel of the exhaust section, and a water ring vacuum pump is provided at the exhaust port. On the one hand, this design can provide a larger exhaust volume, accelerate the discharge of gas in the melt, and avoid defects such as pits in the product caused by residual bubbles. On the other hand, it can promote the cooling of the melt and solve the problem of melt temperature rise caused by shear force, thereby reducing the temperature during the extrusion of wide-width TPO geomembrane. The two factors work together to greatly reduce the melt defects of the TPO filler system compared to a traditional single-screw extruder that is simply scaled up.

[0076] As an embodiment of the single-screw extruder for extruding wide-width TPO geomembrane of the present invention, a temperature sensor 27 is further provided on the barrel mechanism for detecting the temperature of the material.

[0077] As an embodiment of a single-screw extruder for wide-width TPO geomembrane extrusion according to the present invention, a cooling coil 2 is provided outside the barrel 17 at a position corresponding to the feeding section. Since the material is usually fed by a conveyor, and the conveyor generates shear heat during the material conveying process, resulting in an excessively high temperature of the material entering the extruder, the cooling coil 2 is provided at the feeding section of the extruder to cool the material entering the extruder, thereby preventing the excessively high temperature of the material entering the extruder from affecting the temperature control of the barrel 17, thereby causing product defects.

[0078] As an embodiment of a single-screw extruder for wide-width TPO geomembrane extrusion of the present invention, according to the direction of material travel, the discharge port 4 is further provided with an automatic screen changer 21, a metering pump 22, a static mixer 23, a distributor 24 and a wide-width mold 25 in sequence.

[0079] As an embodiment of the single-screw extruder for wide-width TPO geomembrane extrusion of the present invention, the width of the wide-width mold is greater than or equal to 6m.

[0080] In summary, the present invention adjusts the diameter and aspect ratio of the extrusion screw, the functions and sequence of each section of the screw, and sets two exhaust ports and a water ring vacuum pump. While greatly improving the capacity of the single-screw extruder, it ensures the mixing and plasticizing effects of the melt and reduces the temperature during melt extrusion, making it suitable for the extrusion of wide TPO geomembranes greater than or equal to 6m. In addition, it is also beneficial to the discharge of bubbles in the melt, avoiding product defects caused by residual bubbles in the melt. Example 1

[0081] A wide-width thermoplastic polyolefin anti-seepage geomembrane, comprising the following raw materials in parts by weight:

[0082] The preparation method comprises the following steps:

[0083] Step 1: Preparation of high-concentration powdered thermoplastic polyolefin masterbatch:

[0084] First, the inorganic filler, antioxidant, light stabilizer, nucleating agent and pigment are mixed evenly to obtain powder, and then the powder is mixed evenly with part of the thermoplastic polyolefin resin, and then sent into a twin-screw extruder for shear blending and extrusion granulation to obtain a high-concentration powder thermoplastic polyolefin masterbatch (powder content is 50%).

[0085] The setting temperature of the twin-screw extruder is 165-190°C, and the melt temperature of the twin-screw extruder during extrusion (when the material just leaves the screw, that is, the material at the discharge port) is ≤230°C.

[0086] Step 2: Preparation of geomembrane:

[0087] The high-concentration powdered thermoplastic polyolefin masterbatch prepared in step 1, the remaining thermoplastic polyolefin resin and the toughening resin are fed into the vacuum double-venting single-screw extruder described in the equipment embodiment, melted and plasticized in the vacuum double-venting single-screw extruder, and extruded into a 6.5m wide flat extrusion die for forming. After being pulled forward, the extruder is naturally cooled to 120-145 degrees Celsius during the process, and the crystallization of the material is carried out to 40-80%. After that, the extruder enters a three-roll calender for thickness setting, and then undergoes trimming, fixed-length cutting, winding, and packaging to obtain a wide-width thermoplastic polyolefin anti-seepage geomembrane (width 6m);

[0088] The temperature of the vacuum double-exhaust single-screw extruder is set to 170-185°C, and the melt temperature of the vacuum double-exhaust single-screw extruder during extrusion (when the material just leaves the screw, that is, the material at the discharge port) is ≤200°C; the temperature of the mold is set to 170-185°C. Example 2

[0089] A wide-width thermoplastic polyolefin anti-seepage geomembrane, comprising the following raw materials in parts by weight:

[0090] The preparation method comprises the following steps:

[0091] Step 1, preparation of thermoplastic polyolefin masterbatch: first, inorganic filler, antioxidant, light stabilizer, nucleating agent, and pigment are uniformly mixed to obtain powder, and thermoplastic polyolefin resin and toughening resin are uniformly mixed to obtain pellets; then the powder and pellets are fed into a twin-screw extruder for shear blending, extrusion and pelletization, and dried and homogenized to obtain thermoplastic polyolefin masterbatch;

[0092] Step 2: Geomembrane preparation:

[0093] The thermoplastic polyolefin masterbatch prepared in step 1 is fed into the vacuum double-venting single-screw extruder described in the equipment embodiment, melted and plasticized in the vacuum double-venting single-screw extruder, and extruded into a 6.5m wide flat extrusion die for forming. After being pulled forward, it is naturally cooled to 120-145 degrees Celsius during the process, so that the crystallization of the material reaches 40-80%, and then enters a three-roll calender for thickness setting, and then undergoes trimming, fixed-length cutting, winding, and packaging to obtain a wide-width thermoplastic polyolefin anti-seepage geomembrane (width 6m);

[0094] The temperature of the vacuum double-exhaust single-screw extruder is set to 170-185°C, and the melt temperature of the vacuum double-exhaust single-screw extruder during extrusion (when the material just leaves the screw, that is, the material at the discharge port) is ≤200°C; the temperature of the mold is set to 170-185°C. Example 3

[0095] A wide-width thermoplastic polyolefin anti-seepage geomembrane, comprising the following raw materials in parts by weight:

[0096] The preparation method is the same as that in Example 1. Comparative Example 1

[0097] A wide thermoplastic polyolefin anti-seepage geomembrane comprises the following raw materials in parts by weight: the same as in Example 1;

[0098] Its preparation method is the same as that of Example 1, except that, in the geomembrane preparation process in step 2, a separate single-screw extruder is used to replace the vacuum double-exhaust single-screw extruder of Example 1 for melt plasticization. The plasticization quality of the TPO geomembrane extruded by the separate single-screw extruder is poor, and due to its lack of exhaust design, the air mixed in during the raw material mixing process cannot be discharged in time, and defects such as pores and cavities are easily formed inside the product. Comparative Example 2

[0099] A wide-width thermoplastic polyolefin anti-seepage geomembrane comprises the following raw materials in parts by weight: the same as Example 2, except that no nucleating agent is added;

[0100] The preparation method is the same as that in Example 1.

[0101] Due to the removal of the nucleating agent, the geomembrane in this comparative example did not begin to crystallize before reaching the three-roll calender, although the material temperature was the same as that in Example 2; instead, the material completed the main crystallization during the thickness setting process of the three-roll calender. Comparative Example 3

[0102] A wide-width thermoplastic polyolefin anti-seepage geomembrane (width 6m), comprising the following raw materials in parts by weight: the same as in Example 1;

[0103] The preparation method is the same as that of Example 1, except that, in the step 2, during the preparation of the geomembrane, a conventional twin-screw extruder is used to replace the vacuum double-exhaust single-screw extruder of Example 1 for melt plasticization, wherein the barrel temperature of the twin-screw extruder is set to 165-190°C, and the temperature of the mold is set to 180-185°C. The melt temperature of the geomembrane raw material before entering the mold is about 30°C higher than that of Example 1, and is between 200-230°C; since the temperature of the material during extrusion is higher than that of Example 1, when the equipment spacing remains unchanged, the temperature of the geomembrane when it reaches the three-roll calender is also higher than that of Example 1, and is 150-175°C; at this time, the material has not begun to crystallize, and the crystallization process of the material is completed during the thickness setting process of the three-roll calender. Comparative Example 4

[0104] A wide-width thermoplastic polyolefin anti-seepage geomembrane (width 6m), comprising the following raw materials in parts by weight: the same as in Example 1, except that no nucleating agent is added;

[0105] The preparation method is the same as that of Example 1, except that, in the step 2, during the preparation of the geomembrane, a twin-screw extruder is used to replace the vacuum double-exhaust single-screw extruder of Example 1 for melt plasticization, wherein the barrel temperature of the twin-screw extruder is set to 165-190°C, and the temperature of the mold is set to 180-185°C. The melt temperature of the geomembrane raw material before entering the mold is about 30°C higher than that of Example 1 after shearing, plasticizing and conveying through the twin-screw extruder; since the temperature of the material during extrusion is higher than that of Example 1, when the equipment spacing remains unchanged, the temperature of the geomembrane when it reaches the three-roll calender is also higher than that of Example 1, at 150-175°C; since no nucleating agent is added, the crystallization temperature of the material is about 20°C lower than that of Example 1; at this time, the material has not begun to crystallize, and the main crystallization process of the material is completed during the thickness setting process of the three-roll calender. Comparative Example 5

[0106] Commercially available TPO homogeneous waterproof membrane for building roofs. Comparative Example 6

[0107] A polyolefin elastomer (POE) anti-seepage geomembrane comprises the following raw materials in parts by weight:

[0108] The preparation method is the same as that of Example 1, except that the product strength is low due to the excessive amount of POE added. Comparative Example 7

[0109] Commercially available HDPE geomembrane. Comparative Example 8

[0110] Commercially available PVC geomembrane.

[0111] Effect Example 1: Appearance Inspection

[0112] The geomembranes prepared in Example 1 and Comparative Example 1 were inspected for appearance. The surface and cross-section of the geomembranes were visually observed. The results are shown in Table 1. Figure 7-8 ;

[0113] from Figure 7-8 From the comparison, it can be seen that the vacuum double-exhaust single-screw extruder adopted in the present invention has good melting and plasticizing quality, and the prepared geomembrane has a smooth and flat surface, a dense cross-section and no pores; while the separation single-screw extruder in the traditional technology has poor plasticizing quality for extrude TPO geomembrane, and due to its lack of exhaust design, the air mixed in during the raw material mixing process cannot be discharged in time, and defects such as pores and cavities are easily formed inside the product.

[0114] Effect example 2: Crystallization temperature detection

[0115] The crystallization temperature of the raw materials used in Example 1 and Comparative Example 2 was tested, and the results are shown in FIG. Figure 9 ;

[0116] Crystallization Temperature Method: Test using a differential scanning calorimeter (DSC). A 5-10 mg sample was placed in a standard aluminum crucible under a nitrogen atmosphere. A heating and cooling program was established: the sample was heated to 200°C and then cooled to 0°C at a rate of 10°C / min. Heat flow curves were collected during the cooling process. The peak exothermic temperature during the cooling process was measured as the peak crystallization temperature.

[0117] from Figure 9 It can be seen that under the conditions of the present invention, the melting crystallization peak temperature of the raw material in a stress-free state is about 118 degrees, and under the conditions of Comparative Example 2, the melting crystallization peak temperature of the raw material in a stress-free state is about 98°C. The addition of a nucleating agent in the present invention helps to increase the melting crystallization temperature of the raw material, laying the foundation for achieving most of the crystallization of the material before entering the three-roll mill.

[0118] Effect Example 3: Performance Testing

[0119] The performance of the geomembranes of the embodiments and comparative examples was tested, and the results are shown in Tables 1 and Figure 10-11 ;

[0120] The testing indicators and methods are as follows:

[0121] 1) Transverse or longitudinal elongation at break test: Conduct the test in accordance with Method B in GB / T 328.9-2007, using dumbbell-type I specimens conforming to GB / T 528-2009, at a tensile speed of (250±50) mm / min.

[0122] 2) Right-angle tear strength test: The test was conducted in accordance with GB / T 529-2008, using the non-cut right-angle tear method and a tensile speed of (250±50) mm / min.

[0123] 3) Bidirectional elongation at break test: Cut a 100mm×100mm square specimen and use Figure 12 The biaxial / biaxial tensile tester shown here secures the specimen with four identical pneumatic grips on two perpendicular axes and places it at the center of the test for biaxial elongation at break. The pneumatic grips are 50 cm wide, with a 55 cm spacing between the grips. Equibiaxial tension (simultaneous stretching in two perpendicular directions at the same rate) is employed at a rate of (250 ± 50) mm / min. The biaxial elongation at break is calculated as the average ratio of the grip displacement in both directions to the initial grip spacing.

[0124] 4) Fluctuation of unidirectional elongation at break at different positions along the width of the product: Several test points were taken at equal intervals across a width of 6 meters to measure the unidirectional elongation at break. The fluctuation of the unidirectional elongation at break at each position was evaluated. The results are shown in the table below. Figure 10 ;

[0125] 5) Comparison of biaxial tensile properties: Figure 11 The biaxial / biaxial tensile tester was used to test the biaxial elongation at break of the sample, and the biaxial tensile stress-biaxial tensile strain curve was drawn. The results are shown in Figure 11 .

[0126] 2. Results and Analysis

[0127] Table 1

[0128]

[0129] Note: / indicates not tested;

[0130] From Table 1 and Figure 10-11 The data shows that:

[0131] 1) The geomembranes prepared in Examples 1-3 of the present invention have better performance in all aspects, and the difference in longitudinal / transverse elongation at break is small. The tensile strength and bidirectional elongation at break are also better than those of the comparative examples with the same width. This is because in the process of preparing wide-width geomembranes, the present invention increases the melting and crystallization temperature of the raw materials by adding a nucleating agent, and reduces the extrusion temperature of the material by a vacuum double-exhaust single-screw extruder. This ensures that most of the material crystallizes before entering the three-roll calendering and thickness setting machine without changing the distance between the extrusion die and the three-roll calendering and thickness setting machine, thereby providing the performance of the geomembrane of the present invention in all aspects, especially reducing the difference in longitudinal / transverse elongation at break.

[0132] 2) In Comparative Example 2, since no nucleating agent is added, the temperature of the raw material melting and crystallization is higher than that of Example 1. As a result, the material does not begin to crystallize before reaching the three-roll calender, but completes the main crystallization process during the thickness setting process of the three-roll calender, resulting in large differences in its longitudinal / transverse elongation at break, and large fluctuations in the unidirectional elongation at break of each part.

[0133] 3) Comparative Example 3 uses a traditional twin-screw extruder to replace the vacuum double-exhaust single-screw extruder of the present invention. Since the shear temperature rise of the twin-screw is greater than that of the single-screw, the temperature of the twin-screw extruder during material extrusion is higher than that of the vacuum double-exhaust single-screw extruder of the present invention, resulting in a higher melt temperature during material extrusion, which is about 30°C higher than that of Example 1 and is between 200-230°C. The high extrusion temperature has the following defects: on the one hand, the high temperature causes partial decomposition of the material, thereby reducing the strength (tensile strength, right-angle tear strength) of the product (see the comparison between Comparative Example 2 and Comparative Example 4); on the other hand, the defect is: since the temperature during material extrusion is higher than that of Example 1, when the equipment spacing remains unchanged, the temperature of the geomembrane when it reaches the three-roll calender is also higher than that of Example 1, which is 150-175°C. At this time, the material has not started to crystallize, and the main crystallization process of the material is completed during the thickness setting process of the three-roll calender, resulting in a large difference in the elongation at break of the product in the transverse and longitudinal directions.

[0134] 4) In order to reduce the difference in longitudinal / transverse elongation at break of the product and improve the bidirectional elongation at break of the product, the amount of POE added in the formula was increased in Comparative Example 6. However, the excessive amount of POE added resulted in a decrease in the strength of the product, making it impossible to prepare a geomembrane that met the requirements.

[0135] The above-described embodiments are only preferred embodiments of the present invention and are not exhaustive of all feasible implementations of the present invention. For those skilled in the art, any obvious modifications made thereto without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a wide-width thermoplastic polyolefin anti-seepage geomembrane, characterized in that: The steps include: After the thermoplastic polyolefin composite material is evenly mixed, it is sent to the screw extruder, melted and plasticized by the screw extruder, and extruded into the mold at low temperature to form. It is then pulled forward and naturally cooled during the process to complete the partial crystallization process of the material. It then enters the three-roll calender to determine the thickness, thus obtaining a wide-width thermoplastic polyolefin anti-seepage geomembrane. The thermoplastic polyolefin composite material includes a nucleating agent; The screw extruder adopts a vacuum double-exhaust single-screw extruder.

2. The method for preparing a wide-width thermoplastic polyolefin anti-seepage geomembrane according to claim 1, characterized in that: After the thickness is determined by the three-roll calender, it is necessary to trim, cut to length, and roll it up to obtain the thermoplastic polyolefin anti-seepage geomembrane.

3. The method for preparing a wide-width thermoplastic polyolefin anti-seepage geomembrane according to claim 1, characterized in that: The temperature of the vacuum double-exhaust single-screw extruder is set to 170-185°C, and the melt temperature during extrusion by the vacuum double-exhaust single-screw extruder is ≤200°C; the temperature of the mold is set to 170-185°C; During the process of natural cooling, the material crystallization process is completed by 40-80%.

4. The method for preparing a wide-width thermoplastic polyolefin anti-seepage geomembrane according to claim 3, characterized in that: The vacuum double-exhaust single-screw extruder comprises a barrel mechanism (1), a feed port (3) and a discharge port (4) arranged on the barrel mechanism (1), an extrusion screw (5) arranged in the barrel mechanism (1) for rotating, and a motor (6) for driving the extrusion screw (5) to rotate; The extrusion screw comprises a feeding section (7), a first compression section (8), a barrier section (9), an exhaust section (10), a second compression section (11) and a homogenizing section (12) which are sequentially arranged according to the direction of travel of the material; Two exhaust ports (13) are provided at positions on the barrel mechanism corresponding to the exhaust section (10) of the extrusion screw (5), and the exhaust ports (13) are connected to a water ring vacuum pump (14).

5. The method for preparing a wide-width thermoplastic polyolefin anti-seepage geomembrane according to claim 4, characterized in that: The extrusion screw (5) is provided with a plurality of ring pins (15) on the middle and rear part of the first compression section (8) and the homogenization section (12); The diameter of the extrusion screw (5) is ≥180 mm, and the aspect ratio is ≥38.

6. The method for preparing a wide-width thermoplastic polyolefin anti-seepage geomembrane according to claim 1, characterized in that: The thermoplastic polyolefin composite material comprises the following raw materials in parts by weight: 45-75 parts of thermoplastic polyolefin resin, 10-30 parts of toughening resin, 10-30 parts of inorganic filler, 0.3-1.3 parts of antioxidant, 0.3-1.3 parts of light stabilizer, 0.1-2 parts of nucleating agent, and 0.3-3 parts of pigment.

7. The method for preparing a wide-width thermoplastic polyolefin anti-seepage geomembrane according to claim 6, characterized in that: Before feeding the thermoplastic polyolefin composite material into the screw extruder, the inorganic filler, antioxidant, light stabilizer, nucleating agent and pigment are first mixed uniformly to obtain a powder. The powder is then mixed uniformly with a portion of the thermoplastic polyolefin resin and then fed into a twin-screw extruder for shear blending, extrusion and granulation. The mixture is then dried and homogenized to obtain a high-concentration powdered thermoplastic polyolefin masterbatch. The high-concentration powdered thermoplastic polyolefin masterbatch, the remaining thermoplastic polyolefin resin and the toughening resin are then fed into the screw extruder. Alternatively, before the thermoplastic polyolefin composite material is fed into the screw extruder, the inorganic filler, antioxidant, light stabilizer, nucleating agent, and pigment are first mixed evenly to obtain a powder, and the thermoplastic polyolefin resin and toughening resin are mixed evenly to obtain pellets; the powder and pellets are then fed into a twin-screw extruder for shear blending, extrusion, and granulation, and then dried and homogenized to obtain a thermoplastic polyolefin masterbatch, which is then fed into the screw extruder.

8. The method for preparing a wide-width thermoplastic polyolefin anti-seepage geomembrane according to claim 7, characterized in that: The setting temperature of the twin-screw extruder is 165-190° C., and the melt temperature during extrusion by the twin-screw extruder is ≤230° C.

9. The method for preparing a wide-width thermoplastic polyolefin anti-seepage geomembrane according to claim 6, characterized in that: Thermoplastic polyolefin resin includes one or more of C3 / C2 / C4 terpolymer polypropylene and C3 / C2 binary copolymer polypropylene; The toughening resin includes one or more of ethylene / α-octene random copolymer, ethylene / α-butene random copolymer, and ethylene / α-octene block copolymer; The inorganic filler includes one or more of calcium carbonate, talc, calcined kaolin, and calcite. The antioxidant includes one or more of organic phosphites and hindered phenol antioxidants; The light stabilizer is a block oligomeric hindered amine light stabilizer; The nucleating agent is one or more of a stearate nucleating agent, a sorbitol nucleating agent, an organic phosphate nucleating agent, an aromatic amide nucleating agent, and a carboxylic acid metal salt nucleating agent; The pigment includes one or more of titanium dioxide, carbon black, iron oxide, Prussian blue, lead silicate, monoazo, disazo, and phthalocyanine.

10. A wide thermoplastic polyolefin anti-seepage geomembrane prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The width of the wide-width thermoplastic polyolefin anti-seepage geomembrane is greater than or equal to 6m.

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