A pressure-induced resistive carbon nanotube-modified polyolefin pipeline special material and preparation method thereof

Abstract

The invention discloses a pressure-induced resistive carbon nanotube-modified polyolefin pipeline special material, which is composed of the following raw materials in parts by weight: 20-50 parts of carbon nanotube masterbatch, 43-76.5 parts of polyolefin matrix, 3-6 parts of conductive carbon black, and 0.5-1 parts of functional additives; the carbon nanotube masterbatch is composed of the following raw materials in parts by weight: 6-12 parts of carbon nanotubes, 71-87 parts of polyolefin matrix, 6-12 parts of propylene-based elastomer toughening agent, 1-2 parts of polar monomer maleic acid monoester, and 0.02-0.1 parts of organic peroxide initiator; the carbon nanotube-modified polyolefin pipeline special material of the invention uses carbon nanotubes and nano conductive carbon black as conductive agents, and adds an elastomer toughening agent modified by maleic anhydride grafting, thereby solving the problem of high brittleness of early carbon fiber reinforced polyethylene materials; at the same time, through a three-layer co-extrusion method, the carbon nanotube-modified polyolefin pipeline special material is only placed in the middle of a composite pipeline, thereby avoiding the adverse effect of the introduction of conductive fillers on the pressure bearing capacity of the composite pipeline.

Description

Technical Field

[0001] The invention belongs to the field of carbon nanotube modified polyolefin materials, and in particular relates to a pressure-induced resistive carbon nanotube modified polyolefin pipeline special material and a preparation method thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Carbon nanotubes (CNTs) are one-dimensional nanomaterials composed of several to dozens of layers of coaxial circular tubes of carbon atoms arranged in a hexagonal pattern. The P electrons of carbon atoms on carbon nanotubes form a large range of delocalized π bonds. Due to the significant conjugation effect, carbon nanotubes have excellent electrical conductivity and are a nanocarbon material with a high aspect ratio. When CNTs are added to polymers for molding, CNTs tend to form orientation along the flow direction of the polymer melt, resulting in more anisotropic properties of the composite material.

[0004] The conventional practice for monitoring the operating status of plastic pipes is to connect an external pressure gauge to the pipeline, but monitoring the operating status of long-distance pipelines, especially buried pipelines, is a difficult problem in the industry. Installing pressure sensors, photoelectric sensors, etc. in the pipeline to transmit, collect and analyze the signals through distributed optical fibers is a popular monitoring method at present, but the investment cost of this technology is high. Patent No. ZL201910147997.6 and ZL202110042251.6 disclose a self-enhanced and self-sensing non-metallic pipeline safety protection solution using short-cut carbon fiber reinforced polyethylene (PE-CF) electrofusion joints. While improving the strength of the pipeline joints, it realizes self-monitoring of the structural damage status. This technical solution can not only monitor the operating parameters and deformation of the pipeline without external sensors (Sensor-Free), but also obtain changes in the damage status of the pipeline material itself that cannot be monitored by traditional pressure sensors, strain gauges, etc., and realize accurate assessment of the health status of the non-metallic composite pipeline structure. However, the chopped carbon fiber reinforced polyethylene (PE-CF) electrofusion joint in this technical solution has the following shortcomings: (1) Although the addition of chopped carbon fiber can increase the bursting pressure of the pipe fittings to a certain extent, it leads to greater brittleness of the pipe fittings; (2) The overall resistance of the chopped carbon fiber reinforced polyethylene (PE-CF) electrofusion joint is relatively low. When installed in an actual pipeline, the conveying medium water in the pipeline, the moisture in the environment, and the environment in the soil will affect the resistance of the chopped carbon fiber reinforced polyethylene (PE-CF) electrofusion joint. The pipe fittings need to be protected from moisture, otherwise the monitoring reliability is poor; (3) Carbon fiber is used as a conductive agent, the material cost is high, and there are problems such as complex preparation process and large equipment investment. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a pressure-induced resistive carbon nanotube-modified polyolefin pipeline special material and a preparation method thereof.

[0006] In order to achieve the above technical objectives, the technical solution adopted by the present invention is as follows:

[0007] In the first aspect of the present invention, there is provided a piezoresistive carbon nanotube-modified polyolefin pipe material, which is composed of the following raw materials in parts by weight: 20-50 parts of carbon nanotube masterbatch, 43-76.5 parts of polyolefin matrix, 3-6 parts of conductive carbon black, and 0.5-1 part of functional additive;

[0008] The carbon nanotube masterbatch is composed of the following raw materials in parts by weight: 6-15 parts of carbon nanotubes, 71-87 parts of polyolefin matrix, 6-12 parts of propylene-based elastomer toughening agent, 1-2 parts of polar monomer maleic acid monoester, and 0.02-0.1 parts of organic peroxide initiator.

[0009] The second aspect of the present invention provides a method for preparing a carbon nanotube-modified polyolefin pipe material with pressure-induced resistive switching, comprising:

[0010] The carbon nanotube masterbatch, polyolefin matrix, conductive carbon black and functional additives are uniformly mixed according to the proportion, and a twin-screw reaction extruder is used to perform melt blending, reaction and extrusion granulation.

[0011] The third aspect of the present invention provides a piezo-resistive polyolefin composite pipe, wherein the piezo-resistive polyolefin composite pipe is a three-layer co-extruded composite pipe, wherein the inner and outer layers are prepared by extrusion of polyolefin, and the middle layer is prepared by extrusion of the above-mentioned piezo-resistive carbon nanotube-modified polyolefin pipe special material;

[0012] Conductive copper wires or copper foils are wound around the surfaces of both ends of the middle layer pipe of the polyolefin composite pipe, and the conductive copper wires or copper foils are led out to the terminal posts.

[0013] A fourth aspect of the present invention provides a method for using the above-mentioned piezoresistive polyolefin composite pipeline to monitor the real-time pressure of the pipeline, comprising:

[0014] (1) Resistance-pressure curve test of pressure-induced resistance polyolefin composite pipe: a pressure-induced resistance polyolefin composite pipe of a specific length is selected, plugs are added to both ends of the polyolefin composite pipe, the terminals at both ends of the polyolefin composite pipe are connected to a resistance meter that can record resistance in real time, and the pipe is pressurized at a speed of 2-5 MPa / min until the pipe ruptures, and the resistance-pressure characteristic curve of the polyolefin composite pipe section is obtained;

[0015] (2) Real-time pressure monitoring of pipes: At the location where the pipeline operation status needs to be monitored, the above-mentioned specific length of the pressure-induced resistive polyolefin composite pipe is connected to the pipeline, and the resistance of the pressure-induced resistive polyolefin composite pipe is monitored in real time. The real-time pressure of the pipe is inferred based on the real-time resistance.

[0016] The beneficial effects of the present invention are:

[0017] (1) Carbon nanotubes, maleic acid monoester, peroxide initiator and polyolefin matrix are modified by reactive grafting to prepare carbon nanotube masterbatch. Maleic acid monoester polar monomer is grafted on polyolefin molecular chain by reaction process. The ester group and carboxyl group of grafted maleic acid monoester interact with carbonyl group and hydroxyl group on the surface of carbon nanotubes. Under the shear force of twin screw, carbon nanotubes are evenly dispersed. Then, conductive carbon black is blended and granulated. Maleic acid ester grafted on polyolefin also promotes the dispersion of conductive carbon black. Thus, a carbon nanotube modified polyolefin pipe special material which is compounded with fibrous and granular conductive agent and is pressure-sensitive is prepared.

[0018] (2) The present invention places the carbon nanotube-modified polyolefin pipe material in the middle of the polyolefin pipe by a three-layer co-extrusion method, and utilizes the pressure sensitivity of the conductive network formed by the carbon nanotubes and nano-conductive carbon black of the middle layer nanocarbon / polyolefin composition. The distance between the conductive filler carbon nanotubes and nano-conductive carbon black increases after being subjected to internal pressure, causing the resistance to increase significantly. By testing the corresponding relationship of the resistance-pressure curve of the composite pipe, the pressure in the pipeline is inferred based on the monitored resistance, and the principle of piezoresistive change is used to realize the monitoring of the pipeline operation status.

[0019] (3) The present invention places the carbon nanotube-modified polyolefin pipe special material in the middle of the polyolefin pipe by a three-layer co-extrusion method, and utilizes the high insulation properties of the inner and outer polyolefin layers to effectively avoid the interference of the transport medium in the pipe, such as water, and the moisture in the outer buried environment and overhead air on the resistance test, thereby improving the accuracy of the resistance test and thus enhancing the reliability of the composite pipeline operation status monitoring.

[0020] (4) The carbon nanotube-modified polyolefin pipe material of the present invention uses carbon nanotubes and nano-conductive carbon black as conductive agents, and adds an elastomer toughening agent modified by maleic anhydride grafting, which solves the problem of high brittleness of the previous carbon fiber reinforced polyethylene material; at the same time, through the three-layer co-extrusion method, the carbon nanotube-modified polyolefin pipe material is only placed in the middle of the composite pipe, avoiding the adverse effect of the introduction of conductive fillers on the pressure-bearing capacity of the composite pipe.

[0021] (5) The pressure-induced resistive composite pipe of the present invention places the nanocarbon / polyolefin composition in the middle of the pipe by three-layer co-extrusion, the thickness of the middle layer is controlled to be 2-6 mm, and the length of the pressure-induced resistive composite pipe is directly controlled to be 0.1-1 meter. It is directly connected to the pipeline through common connection methods such as hot melting and electric melting, and the pressure-induced resistive composite pipe of the present invention is connected at the position where the operating status needs to be monitored. Compared with the early stage of using PE / CF materials to prepare self-reinforced and self-sensing pipe fittings, the material cost is effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0023] Figure 1 It is a schematic cross-sectional view of the inner layer and the middle layer of the three-layer co-extruded composite tube of the present invention;

[0024] Figure 2 It is a schematic diagram of the distribution of the conductive copper foil in the middle layer of the outer cylindrical surface of the three-layer co-extruded composite tube of the present invention;

[0025] Figure 3 It is a partial enlarged view of the position of the conductive copper foil of the middle layer on the outer cylindrical surface of the three-layer co-extruded composite tube of the present invention;

[0026] Figure 4 It is a cross-sectional schematic diagram of the piezoresistive polyolefin composite pipeline of the present invention;

[0027] Figure 5 It is a partial enlarged view of the joint portion of the conductive copper foil and the copper terminal of the present invention;

[0028] Figure 6 It is a schematic diagram of the structure of the copper terminal applicable to the present invention;

[0029] In the figure, 1-three-layer co-extruded composite tube, 2-polyolefin inner layer, 3-carbon nanotube modified polyolefin special material middle layer, 4-conductive copper foil, 5-polyolefin outer layer, 6-copper terminal. DETAILED DESCRIPTION

[0030] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0031] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0032] The first typical embodiment of the present invention provides a piezoresistive carbon nanotube-modified polyolefin pipe special material, wherein the raw materials are composed of the following raw materials in parts by weight: 20-50 parts of carbon nanotube masterbatch, 43-76.5 parts of polyolefin matrix, 3-6 parts of conductive carbon black, and 0.5-1 parts of functional additives;

[0033] The carbon nanotube masterbatch is composed of the following raw materials in parts by weight: 6-15 parts of carbon nanotubes, 71-87 parts of polyolefin matrix, 6-12 parts of propylene-based elastomer toughening agent, 1-2 parts of polar monomer maleic acid monoester, and 0.02-0.1 parts of organic peroxide initiator.

[0034] In one or more embodiments, the preparation method of the carbon nanotube masterbatch is: carbon nanotubes, polyolefin matrix, propylene elastomer toughening agent, polar monomer maleic acid monoester, and organic peroxide initiator are uniformly mixed according to mass ratio, and melt blending, grafting reaction, and extrusion granulation are performed using a twin-screw reaction extruder.

[0035] Preferably, the temperature of melt blending, grafting reaction and extrusion granulation is 180-210°C. At this temperature, the polyolefin molecular chain is grafted with the polar monomer of maleic acid monoester, and the ester group and carboxyl group of the grafted maleic acid monoester interact with the carbonyl group and hydroxyl group on the surface of the carbon nanotubes, thereby achieving uniform dispersion of the carbon nanotubes under the shear force of the twin screw.

[0036] In one or more embodiments, the polyolefin matrix is ​​pipeline-grade polyethylene or pipeline-grade polypropylene.

[0037] In one or more embodiments, the carbon nanotubes are one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes.

[0038] In one or more embodiments, the conductive carbon black is One of them.

[0039] In one or more embodiments, the propylene-based elastomer toughening agent is Dow Chemical's VERSIFY TM , ExxonMobil's Vistamaxx TM One of them.

[0040] In one or more embodiments, the polar monomer maleic acid monoester is one of monomethyl maleate, monoethyl maleate, monobutyl maleate, and monooctyl maleate.

[0041] In one or more embodiments, the organic peroxide is one of tert-butyl peroxide isopropylbenzene, 2,5-di-tert-butyl peroxide-2,5-dimethylhexane, and bis(tert-butyl peroxide isopropyl)benzene.

[0042] In one or more embodiments, the functional additive is one or more of an antioxidant, an ultraviolet aging agent, and a lubricant.

[0043] In one or more embodiments, the volume resistivity of the carbon nanotube-modified polyolefin pipe material is less than 1.0*10 6 Ω·cm.

[0044] A second typical embodiment of the present invention provides a method for preparing a carbon nanotube-modified polyolefin pipe material with pressure-induced resistive switching, comprising:

[0045] The carbon nanotube masterbatch, polyolefin matrix, conductive carbon black and functional additives are uniformly mixed according to the proportion, and a twin-screw reaction extruder is used to perform melt blending, reaction and extrusion granulation.

[0046] The carbon nanotube masterbatch is blended with the conductive carbon black to form granules. The maleate grafted on the polyolefin also promotes the dispersion of the conductive carbon black. Thus, a special carbon nanotube-modified polyolefin pipe material which is compounded with fibrous and granular conductive agents and is pressure-sensitive is prepared.

[0047] In one or more embodiments, the temperature of melt blending, reaction and extrusion granulation is 180-210°C.

[0048] A third typical embodiment of the present invention provides a piezo-resistive polyolefin composite pipe, wherein the piezo-resistive polyolefin composite pipe is a three-layer co-extruded composite pipe, wherein the inner and outer layers are prepared by extrusion of polyolefin, and the middle layer is prepared by extrusion of the above-mentioned piezo-resistive carbon nanotube-modified polyolefin pipe special material;

[0049] Conductive copper wires or copper foils are wound around the surfaces of both ends of the middle layer pipe of the polyolefin composite pipe, and the conductive copper wires or copper foils are led out to the terminal posts.

[0050] In one or more embodiments, the thickness of the piezoresistive polyolefin composite pipe is 6-120 mm;

[0051] In one or more embodiments, the thickness of the outer layer of the piezoresistive polyolefin composite pipe is 2-10 mm;

[0052] In one or more embodiments, the thickness of the middle layer of the piezoresistive polyolefin composite pipe is 2-6 mm.

[0053] In one or more embodiments, the number of turns of the conductive copper wire or copper foil is 2-10 turns;

[0054] In one or more embodiments, the conductive copper wire or copper foil wrapped around the surface of the middle layer of the polyolefin composite pipe has an interval of 0.1-0.5 mm.

[0055] A fourth typical embodiment of the present invention provides a method for using the above-mentioned piezoresistive polyolefin composite pipeline to monitor the real-time pressure of the pipeline, comprising:

[0056] (1) Resistance-pressure curve test of pressure-induced resistance polyolefin composite pipe: a pressure-induced resistance polyolefin composite pipe of a specific length is selected, plugs are added to both ends of the polyolefin composite pipe, the terminals at both ends of the polyolefin composite pipe are connected to a resistance meter that can record resistance in real time, and the pipe is pressurized at a speed of 2-5 MPa / min until the pipe ruptures, and the resistance-pressure characteristic curve of the polyolefin composite pipe section is obtained;

[0057] (2) Real-time pressure monitoring of pipes: At the location where the pipeline operation status needs to be monitored, the above-mentioned specific length of the pressure-induced resistive polyolefin composite pipe is connected to the pipeline, and the resistance of the pressure-induced resistive polyolefin composite pipe is monitored in real time. The real-time pressure of the pipe is inferred based on the real-time resistance.

[0058] In one or more embodiments, the piezoresistive polyolefin composite pipe is connected to the pipeline through a common connection method such as hot melting, electric melting, etc.

[0059] In one or more embodiments, the specific length of the piezoresistive polyolefin composite pipe is controlled to be 0.1-1 meter.

[0060] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0061] Example 1

[0062] Preparation of S1 carbon nanotube masterbatch:

[0063] 12 parts of multi-walled carbon nanotubes (NC7000, Nanocyl, Belgium), 2 parts of monoethyl maleate, and propylene elastomer (Vistamaxx TM6202, ExxonMobil) 12 parts, peroxide initiator 2,5-di-tert-butylperoxy-2,5-dimethylhexane 0.05 parts, polyethylene pipe material (QHM32F, Qilu Petrochemical) 74 parts were mixed evenly in a high mixer, and melt blending, grafting reaction and extrusion granulation were carried out at a temperature of 190°C using a twin-screw reaction extruder.

[0064] Preparation of S2 pressure-induced resistive carbon nanotube-modified polyethylene special material:

[0065] 50 parts of the carbon nanotube masterbatch in S1 (containing 12% carbon nanotubes and 12% propylene elastomer toughening agent), 3 parts of conductive carbon black (Ketjen black ECP600JD), 46.5 parts of 100-grade polyethylene pipe material (23050, Yantai Wanhua Group Co., Ltd.), and 0.5 parts of antioxidant tetra[β-(3.5-di-tert-butyl, 4-hydroxyphenyl) propionic acid] pentaerythritol ester were mixed evenly, and melt blended, reacted, and extruded and granulated using a twin-screw reaction extruder. The extrusion temperature was 200-210°C, and the speed of the extruder was 400r / min to obtain a special material for polyethylene modified by carbon nanotubes. The material melt mass flow rate was tested (190°C, 5kg weight), the material was molded, the volume resistivity was tested, and the yield strength, tensile strength, and nominal strain at break of the material were tested according to GB / T1040.2, as shown in Table 1.

[0066] Preparation of S3 three-layer co-extruded carbon nanotube-modified polyethylene tube:

[0067] The PE100 grade pipe material (YGH041T, Shanghai Petrochemical) is extruded into an inner core tube at a temperature of 195° C., and then a 3-4 mm middle layer of the pressure-induced resistive carbon nanotube-modified polyethylene special material in S2 is extruded on the inner core tube. According to needs, 3-5 turns of copper foil are wrapped around the surface of the carbon nanotube-modified polyethylene special material every 50 cm to lead out the monitoring terminal. The PE100 grade pipe material (YGH041T, Shanghai Petrochemical) is then co-extruded to obtain a three-layer co-extruded composite pipe with a thickness of 10 mm and a pressure bearing capacity of 1.6 MPa. A pipe section with a length of 50 cm and detection terminals led out from the middle layer at both ends is taken, and a resistance meter capable of recording resistance in real time is connected to the terminal. Plugs are added to both ends of the three-layer co-extruded carbon nanotube-modified polyethylene pipe, and the pipe is blasted at a pressurization rate of 3 MPa / min to obtain a resistance-pressure curve of the three-layer co-extruded carbon nanotube-modified polyethylene pipe, wherein the resistance without pressure is R0 and the resistance during blasting is R M , R M / R0 is defined as the sensitivity, R M The larger the / R0, the higher the sensitivity of the detection.

[0068] Comparative Example 1

[0069] Preparation of S1 carbon nanotube masterbatch (without initiator):

[0070] Multi-walled carbon nanotubes (NC7000, Belgium Nanocyl) 12 parts, monoethyl maleate 2 parts, propylene elastomer (Vistamaxx TM 6202, ExxonMobil) 12 parts and polyethylene pipe material (QHM32F, Qilu Petrochemical) 74 parts were mixed evenly in a high-speed mixer, and melt blending, grafting reaction and extrusion granulation were carried out at a temperature of 190°C using a twin-screw reaction extruder.

[0071] The preparation of S2 piezo-resistive carbon nanotube-modified polyethylene special material and the preparation of S3 three-layer co-extruded carbon nanotube-modified polyethylene tube are the same as in Example 1.

[0072] Comparative Example 2

[0073] Preparation of S1 carbon nanotube masterbatch (without monoethyl maleate):

[0074] 12 parts of multi-walled carbon nanotubes (NC7000, Nanocyl, Belgium), propylene-based elastomer (Vistamaxx TM 6202, ExxonMobil) 12 parts, peroxide initiator 2,5-di-tert-butylperoxy-2,5-dimethylhexane 0.05 parts, polyethylene pipe material (QHM32F, Qilu Petrochemical) 74 parts, are mixed evenly with a high-speed mixer, and melt blended, grafted and extruded into granules at a temperature of 190°C using a twin-screw reaction extruder.

[0075] The preparation of S2 piezo-resistive carbon nanotube-modified polyethylene special material and the preparation of S3 three-layer co-extruded carbon nanotube-modified polyethylene tube are the same as in Example 1.

[0076] Comparative Example 3

[0077] Preparation of S1 carbon nanotube masterbatch (without adding propylene-based elastomer)

[0078] 12 parts of multi-walled carbon nanotubes (NC7000, Nanocyl, Belgium), 2 parts of monoethyl maleate, 0.05 parts of peroxide initiator 2,5-di-tert-butylperoxy-2,5-dimethylhexane, and 86 parts of polyethylene pipe material (QHM32F, Qilu Petrochemical) were mixed evenly with a high-speed mixer, and melt blended, grafted, and extruded into granules at a temperature of 190°C using a twin-screw reaction extruder.

[0079] The preparation of S2 piezo-resistive carbon nanotube-modified polyethylene special material and the preparation of S3 three-layer co-extruded carbon nanotube-modified polyethylene tube are the same as in Example 1.

[0080] Comparative Example 4 (adding only carbon nanotubes without adding conductive carbon black)

[0081] Preparation of S1 carbon nanotube masterbatch:

[0082] 18 parts of multi-walled carbon nanotubes (NC7000, Nanocyl, Belgium), 2 parts of monoethyl maleate, and propylene elastomer (Vistamaxx TM 6202, ExxonMobil) 12 parts, peroxide initiator 2,5-di-tert-butylperoxy-2,5-dimethylhexane 0.05 parts, polyethylene pipe material (QHM32F, Qilu Petrochemical) 68 parts, mixed evenly with a high-speed mixer, and melt blended, grafted, and extruded at 190°C using a twin-screw reaction extruder.

[0083] Preparation of S2 pressure-induced resistive carbon nanotube-modified polyethylene special material:

[0084] 50 parts of the carbon nanotube masterbatch in S1 (containing 18% carbon nanotubes and 12% propylene elastomer toughening agent), 49.5 parts of 100-grade polyethylene pipe material (23050, Yantai Wanhua Group Co., Ltd.), and 0.5 parts of antioxidant tetra[β-(3.5-di-tert-butyl, 4-hydroxyphenyl) propionic acid] pentaerythritol ester were mixed evenly, and melt blended, reacted, and extruded and granulated using a twin-screw reaction extruder. The extrusion temperature was 200-210°C, and the speed of the extruder was 400r / min to obtain a special material for polyethylene modified by carbon nanotubes. The material melt mass flow rate was tested (190°C, 5kg weight), the material was molded, the volume resistivity was tested, and the yield strength, tensile strength, and nominal strain at break of the material were tested according to GB / T1040.2, as shown in Table 1.

[0085] The preparation of S3 three-layer co-extruded carbon nanotube-modified polyethylene tube is the same as in Example 1.

[0086] Comparative Example 5 (no carbon nanotubes added, only conductive carbon black added)

[0087] Preparation of S1 carbon nanotube masterbatch:

[0088] 2 parts of monoethyl maleate, propylene elastomer (Vistamaxx TM 6202, ExxonMobil) 12 parts, peroxide initiator 2,5-di-tert-butylperoxy-2,5-dimethylhexane 0.05 parts, polyethylene pipe material (QHM32F, Qilu Petrochemical) 86 parts, are mixed evenly with a high-speed mixer, and melt blended, grafted and extruded into granules at a temperature of 190°C using a twin-screw reaction extruder.

[0089] Preparation of S2 pressure-induced resistive carbon nanotube-modified polyethylene special material:

[0090] 50 parts of the carbon nanotube masterbatch in S1 (containing 0 carbon nanotubes and 12% propylene elastomer toughening agent), 9 parts of conductive carbon black (Ketjen black ECP600JD), 40.5 parts of 100-grade polyethylene pipe material (23050, Yantai Wanhua Group Co., Ltd.), and 0.5 parts of antioxidant tetra[β-(3.5-di-tert-butyl, 4-hydroxyphenyl) propionic acid] pentaerythritol ester were mixed evenly, and melt blended, reacted, and extruded and granulated using a twin-screw reaction extruder. The extrusion temperature was 200-210°C, and the speed of the extruder was 400r / min to obtain a special material for polyethylene modified by carbon nanotubes. The material melt mass flow rate was tested (190°C, 5kg weight), the material was molded, the volume resistivity was tested, and the yield strength, tensile strength, and nominal strain at break of the material were tested according to GB / T1040.2, as shown in Table 1.

[0091] The preparation of S3 three-layer co-extruded carbon nanotube-modified polyethylene tube is the same as in Example 1.

[0092] Example 2

[0093] Preparation of S1 carbon nanotube masterbatch:

[0094] 6 parts of multi-walled carbon nanotubes (GT210, Shandong Dazhan Nanomaterials Co., Ltd.), 1 part of monoethyl maleate, 1 part of propylene elastomer (VERSIFY TM 2400, Dow Chemical) 6 parts, peroxide initiator di(tert-butylperoxyisopropyl)benzene 0.1 parts, polypropylene pipe material (4220, Yanshan Petrochemical) 87 parts, are mixed evenly with a high-speed mixer, and melt blended, grafted and extruded into granules at a temperature of 200°C using a twin-screw reaction extruder.

[0095] Preparation of S2 pressure-induced resistive carbon nanotube-modified polypropylene special material:

[0096] 50 parts of the carbon nanotube masterbatch in S1 (containing 6% carbon nanotubes and 6% propylene-based elastomer toughening agent), 6 parts of conductive carbon black (Ketjen Black ECP600JD), 43 parts of polypropylene pipe material (4220, Yanshan Petrochemical), 0.6 parts of antioxidant 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and 0.4 parts of light stabilizer 944 were mixed evenly, and melt blended, reacted, and extruded into granules using a twin-screw reaction extruder. The extrusion temperature was 190° C. and the speed of the extruder was 420 r / min to obtain a carbon nanotube-modified polypropylene special material. The material melt mass flow rate was tested (230°C, 2.16 kg weight), the material was compression molded, and the volume resistivity was tested. The yield strength, tensile strength, and nominal strain at break of the material were tested according to GB / T1040.2, as shown in Table 1 for details.

[0097] Preparation of S3 three-layer co-extruded carbon nanotube-modified polypropylene tube:

[0098] The polypropylene pipe material (4220, Yanshan Petrochemical) is extruded into an inner core tube at a temperature of 195° C., and then a 3-4 mm middle layer of the pressure-induced resistive carbon nanotube-modified polypropylene special material in S2 is extruded on the inner core tube. According to needs, 3-5 turns of copper foil are wrapped around the surface of the carbon nanotube-modified polypropylene special material every 50 cm to lead out the monitoring terminal. The polypropylene pipe material (4220, Yanshan Petrochemical) is then co-extruded to obtain a three-layer co-extruded composite pipe with a thickness of 10 mm and a pressure resistance of 1.6 MPa. A pipe section with a length of 50 cm and detection terminals led out from the middle layer at both ends is taken, and a resistance meter capable of recording resistance in real time is connected to the terminal. Plugs are added to both ends of the three-layer co-extruded carbon nanotube-modified polyethylene pipe, and the pipe is blasted at a pressurization rate of 3 MPa / min to obtain a resistance-pressure curve of the three-layer co-extruded carbon nanotube-modified polyethylene pipe, wherein the resistance without pressure is R0 and the resistance during blasting is R M , R M / R0 is defined as the sensitivity, R M The larger the / R0, the higher the sensitivity of the detection.

[0099] The mechanical properties of the carbon nanotube modified polyolefin special material obtained through the above examples and comparative examples and the surface resistance, flame retardancy and appearance performance data of the anti-tube are shown in Table 1:

[0100] Table 1 Performance data of carbon nanotube modified special materials and three-layer co-extruded tubes

[0101]

[0102]

[0103] From the performance data of Examples 1-2 and Comparative Examples 1-5 shown in the above table, it can be seen that:

[0104] The volume resistivity of Example 1-2 of the present invention is less than 1.0*10 6 Ω·cm, the tensile strength is greater than 20MPa, the elongation at break is greater than 500%, and the volume resistivity of comparative examples 1, 2, and 5 is greater than 1.0*10 6 Ω·cm, the tensile strength of comparative examples 1-5 is less than 20MPa, and the elongation at break is less than 500%, indicating that the carbon nanotube-modified polyolefin special material of the present invention has the physical properties of small surface resistance and excellent mechanical properties, and has better antistatic properties than the comparative examples.

[0105] Through the tensile strength and elongation at break of Example 1 of the present invention and Comparative Examples 1-5, it can be obtained that the mechanical properties of the present invention are greater than those of Comparative Examples 1-5, indicating that the carbon nanotube-modified polyolefin special material prepared by modifying carbon nanotubes by grafting polar monomers in Example 1-2 of the present invention solves the problem of high brittleness of the material caused by the addition of conductive agents.

[0106] Compared with comparative examples 1-2, embodiment 1 of the present invention has better comprehensive performance of tensile strength and breaking strength, lower volume resistivity, and higher pressure monitoring sensitivity applied to three-layer co-extruded composite pipes, indicating that the carbon nanotube-modified polyolefin special material prepared by the present invention has better dispersibility, better performance and better applicability after the carbon nanotubes are grafted and modified with maleic acid monoester and dispersed.

[0107] By comparing Example 1 and Comparative Example 3, it can be seen that if no propylene-based elastomer is added in the first step of the reaction grafting polar monomer, the cross-linking side reaction caused by peroxide will lead to a problem of too low melt mass flow rate. The carbon nanotube-modified polyolefin special material of the present invention adds propylene-based elastomer in the first step of the carbon nanotube grafting dispersion process. Under the action of the peroxide initiator, the propylene-based elastomer can avoid the problem of too low melt mass flow rate caused by excessive cross-linking of polyethylene to a certain extent through the degradation of the propylene-based chain segment. At the same time, the introduction of the propylene elastomer can toughen the system and avoid the problems of high brittleness and high elongation at break of the special material.

[0108] By comparing Example 1 with Comparative Example 4, it can be seen that the R0 of the three-layer co-extruded tube prepared by adding only carbon nanotubes as the conductive agent is higher is mainly due to the high aspect ratio structure of the carbon nanotubes themselves. During the extrusion process, the carbon nanotubes have a tendency to be oriented in the extrusion direction, causing R0 to increase. The monitoring sensitivity R M / R0 is also relatively low, mainly because there are only fibrous carbon nanotubes in the system, but no granular conductive carbon black.

[0109] By comparing Example 1 with Comparative Example 5, it can be seen that the conductive agent is only added with granular conductive carbon black, and the R0 of the prepared three-layer co-extruded tube is higher, mainly because the conductive carbon black itself is a granular structure, and a higher addition ratio is required to form a conductive network relative to the fibrous carbon nanotubes; the monitoring sensitivity R of Comparative Example 5 is M / R0 is also low.

[0110] By comparing Examples 1 and 2 with Comparative Examples 1-5, it can be seen that the embodiments of the present invention solve the problem of the difficulty in dispersing carbon nanotubes in a low-flow matrix by reverse grafting polar monomer grafting reaction and adding degradable propylene elastomer during the preparation of carbon nanotube masterbatch. At the same time, the fibrous carbon nanotubes and granular conductive carbon black synergistically form a pressure-sensitive conductive network, and the prepared carbon nanotube-modified polyolefin special material is applied to the middle layer of a three-layer co-extruded pipe, which makes full use of the characteristic that the resistance of the middle layer is sensitive to the distance of the conductive network after being pressed to realize the monitoring of the pipeline operation pressure.

[0111] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A pressure-induced resistive carbon nanotube-modified polyolefin pipe material, characterized in that: The method is composed of the following raw materials in parts by weight: 20-50 parts of carbon nanotube masterbatch, 43-76.5 parts of polyolefin matrix, 3-6 parts of conductive carbon black, and 0.5-1 part of functional additive; The carbon nanotube masterbatch is composed of the following raw materials in parts by weight: 6-15 parts of carbon nanotubes, 71-87 parts of polyolefin matrix, 6-12 parts of propylene-based elastomer toughening agent, 1-2 parts of polar monomer maleic acid monoester, and 0.02-0.1 parts of organic peroxide initiator.

2. The carbon nanotube-modified polyolefin pipe material according to claim 1, characterized in that: The preparation method of the carbon nanotube masterbatch is as follows: carbon nanotubes, polyolefin matrix, propylene-based elastomer toughening agent, polar monomer maleic acid monoester, and organic peroxide initiator are uniformly mixed according to mass ratio, and melt blended, grafted, and extruded and granulated by a twin-screw reaction extruder.

3. The carbon nanotube-modified polyolefin pipe material according to claim 2, characterized in that: The temperature of the melt blending, grafting reaction and extrusion granulation is 180-210°C.

4. The carbon nanotube-modified polyolefin pipe material according to claim 1, characterized in that: The polyolefin matrix is ​​pipeline-grade polyethylene or pipeline-grade polypropylene; Or, the carbon nanotubes are one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes; Or, the conductive carbon black is one of CHEZACARB® and Ketjenblack®; Or, the propylene-based elastomer toughening agent is one of Dow Chemical's VERSIFY™ and ExxonMobil's Vistamaxx™; Or, the polar monomer maleic acid monoester is one of monomethyl maleate, monoethyl maleate, monobutyl maleate, and monooctyl maleate; Or, the organic peroxide is one of tert-butyl peroxide isopropyl benzene, 2,5-di-tert-butyl peroxide-2,5-dimethylhexane, and bis(tert-butyl peroxide isopropyl)benzene; Or, the functional additive is one or more of an antioxidant, an ultraviolet aging agent, and a lubricant.

5. The carbon nanotube-modified polyolefin pipe material according to claim 1, characterized in that: The volume resistivity of the carbon nanotube-modified polyolefin pipeline material is less than 1.0*10 6 Ω·cm.

6. The method for preparing a piezo-resistive carbon nanotube-modified polyolefin pipe material according to any one of claims 1 to 5, characterized in that: include: The carbon nanotube masterbatch, polyolefin matrix, conductive carbon black and functional additives are uniformly mixed according to the proportion, and a twin-screw reaction extruder is used to perform melt blending, reaction and extrusion granulation.

7. The preparation method according to claim 6, characterized in that: The temperature of the melt blending, reaction and extrusion granulation is 180-210°C.

8. A polyolefin composite pipe with pressure-induced resistance change, characterized in that: The piezo-resistive polyolefin composite pipe is a three-layer co-extruded composite pipe, wherein the inner and outer layers are prepared by extrusion of polyolefin, and the middle layer is prepared by extrusion of the piezo-resistive carbon nanotube-modified polyolefin pipe special material according to any one of claims 1 to 5; Conductive copper wires or copper foils are wound around the surfaces of both ends of the middle layer pipe of the polyolefin composite pipe, and the conductive copper wires or copper foils are led out to the terminal posts.

9. The polyolefin composite pipe according to claim 8, characterized in that: The thickness of the piezoresistive polyolefin composite pipe is 6-120mm; Or, the thickness of the outer layer of the piezoresistive polyolefin composite pipe is 2-10 mm; Or, the thickness of the middle layer of the piezoresistive polyolefin composite pipe is 2-6 mm; Or, the number of turns of the conductive copper wire or copper foil is 2-10; Alternatively, the conductive copper wires or copper foils wound on the surface of the middle layer of the polyolefin composite pipe are spaced at a distance of 0.1-0.5 mm.

10. A method for monitoring the real-time pressure of a pipe material using the polyolefin composite pipe according to claim 8, characterized in that: include: (1) Resistance-pressure curve test of pressure-induced resistive polyolefin composite pipe: a specific length of pressure-induced resistive polyolefin composite pipe is selected, plugs are added to both ends of the polyolefin composite pipe, the terminals at both ends of the polyolefin composite pipe are connected to a resistance meter that can record resistance in real time, and the pipe is pressurized at a speed of 2-5 MPa / min until the pipe ruptures, and the resistance-pressure characteristic curve of the polyolefin composite pipe section is obtained; (2) Real-time pressure monitoring of pipes: At the location where the pipeline operation status needs to be monitored, the above-mentioned specific length of pressure-induced resistive polyolefin composite pipe is connected to the pipeline, and the resistance of the pressure-induced resistive polyolefin composite pipe is monitored in real time. The real-time pressure of the pipe is inferred based on the real-time resistance.

11. The method for monitoring the real-time pressure of a pipe according to claim 10, characterized in that: The pressure-induced resistance polyolefin composite pipe is connected to the pipeline by a universal connection method of hot melting or electric melting; Alternatively, the specific length of the piezoresistive polyolefin composite pipe is controlled within a range of 0.1-1 meter.

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