Thermosensitive color-changing crosslinked polyethylene pipe and preparation method thereof

Abstract

The invention provides a thermosensitive color-changing crosslinked polyethylene pipe and a preparation method thereof. The thermochromic crosslinked polyethylene pipe comprises the following components in parts by weight: 100 parts of polyethylene, 30-50 parts of epoxidized soybean oil, 0.5-2 parts of nano titanium dioxide, 3-8 parts of a compatilizer, 1.5-5 parts of a thermochromic pigment, 0.5-1.2 parts of an antioxidant and 0-3 parts of a functional additive, the cross-linking degree of the thermosensitive color-changing cross-linked polyethylene pipe is reduced from inside to outside in a gradient mode. By adding epoxidized soybean oil as a dispersing agent into a polyethylene matrix and performing interface modification through nano titanium dioxide, under the combined action, the interfacial tension between the pigment and the polyethylene matrix is reduced, the dispersing performance of the pigment in the polyethylene matrix is improved, and the heat sensitivity and mechanical strength of the crosslinked polyethylene pipe are remarkably improved; and gradient cross-linking distribution is further combined, so that the bursting pressure of the cross-linked polyethylene pipe is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and more particularly to a heat-sensitive color-changing cross-linked polyethylene pipe and a preparation method thereof. Background Art

[0002] While traditional cross-linked polyethylene (PEX) pipes offer excellent heat resistance and mechanical strength, they lack temperature indication and rely on external electronic equipment for monitoring, leading to high costs and complex operation. Existing thermochromic pipes are mostly based on polyvinyl chloride (PVC) or non-cross-linked polyethylene, which suffer from insufficient temperature resistance (<100°C), poor mechanical properties, and environmental drawbacks (including the presence of phthalate plasticizers). Consequently, existing polyethylene pipes suffer from a single function, poor temperature resistance, and environmental concerns. Furthermore, the explosion resistance of existing cross-linked polyethylene pipes needs to be improved.

[0003] Therefore, there is an urgent need to provide a heat-sensitive color-changing cross-linked polyethylene pipe with excellent comprehensive properties such as good heat resistance and good mechanical properties. Summary of the Invention

[0004] The present invention aims to address the aforementioned deficiencies of existing materials by providing a cross-linked polyethylene pipe with excellent heat resistance, mechanical properties, and thermochromic performance. By adding epoxidized soybean oil as a dispersant to the polyethylene matrix and modifying the interface with nano-titanium dioxide, the present invention reduces the interfacial tension between the pigment and the polyethylene matrix, improves the pigment's dispersion within the polyethylene matrix, and significantly enhances the cross-linked polyethylene pipe's thermal sensitivity and mechanical strength. Furthermore, the gradient cross-linking distribution further increases the cross-linked polyethylene pipe's burst pressure.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a thermochromic cross-linked polyethylene pipe, which comprises the following components in parts by weight:

[0007] 100 parts of polyethylene, 30-50 parts of epoxidized soybean oil, 0.5-2 parts of nano titanium dioxide, 3-8 parts of compatibilizer, 1.5-5 parts of thermochromic pigment, 0.5-1.2 parts of antioxidant, 0-3 parts of functional additives;

[0008] The cross-linking degree of the thermosensitive color-changing cross-linked polyethylene pipe decreases gradually from the inside to the outside.

[0009] As an embodiment of the present invention, the polyethylene includes at least one of high-density polyethylene and low-density polyethylene.

[0010] As an embodiment of the present invention, the thermochromic pigment includes a green thermochromic pigment, a yellow thermochromic pigment, and a blue thermochromic pigment, and the mass ratio is green thermochromic pigment: yellow thermochromic pigment: blue thermochromic pigment = (0.8-1.1): (0.6-0.9): (0.35-0.55).

[0011] As an embodiment of the present invention, the green thermochromic pigment includes a spiropyran pigment.

[0012] As an embodiment of the present invention, the yellow thermochromic pigment includes a fluorane pigment.

[0013] As an embodiment of the present invention, the blue thermochromic pigment includes a crystal violet lactone / bisphenol A composite pigment.

[0014] As an embodiment of the present invention, in the thermochromic cross-linked polyethylene pipe, the secondary particles of the pigment are ≤2.5 μm.

[0015] As an embodiment of the present invention, the epoxy value of the epoxidized soybean oil is 4.5-6%, and the iodine value is ≤3gI2 / 100g.

[0016] As an embodiment of the present invention, the compatibilizer includes PE-g-MAH.

[0017] As an embodiment of the present invention, the antioxidant includes at least one of a hindered phenol antioxidant, a phosphite antioxidant, and an ultraviolet light absorber.

[0018] As an embodiment of the present invention, the functional additive includes a silver ion antibacterial agent.

[0019] As an embodiment of the present invention, the difference in cross-linking degree between the inside and outside of the thermosensitive color-changing cross-linked polyethylene pipe is ≥10%.

[0020] The second aspect of the present invention provides a method for preparing the heat-sensitive color-changing cross-linked polyethylene pipe according to the first aspect of the present invention, comprising the following steps:

[0021] (1) According to the formula, epoxy soybean oil, thermochromic pigment, nano titanium dioxide, and compatibilizer are mixed at a temperature of T1°C and a rotation speed of R1 rpm to obtain a first mixed raw material;

[0022] (2) mixing the first mixed raw material prepared in step (1), polyethylene, antioxidant and functional additive at a temperature of T2°C and a rotation speed of R2 rpm, and extruding at 90-175°C to obtain a tube blank;

[0023] (3) irradiating the inside and outside of the pipe blank obtained in step (2) simultaneously to crosslink, so that the heat-sensitive color-changing crosslinked polyethylene pipe material is obtained, the irradiation energy of the inside of the pipe blank is E1 kGy, and the irradiation energy of the outside of the pipe blank is E2 kGy;

[0024] wherein T1 < T2, R1 < R2, and E1 > E2.

[0025] As an embodiment of the present application, T1 is ≤ 20℃.

[0026] As an embodiment of the present application, T2 is = 90-100℃.

[0027] As an embodiment of the present application, R1 is ≤ 500 rpm.

[0028] As an embodiment of the present application, R2 is ≥ 800 rpm.

[0029] As an embodiment of the present application, E1 is = 75-100 kGy.

[0030] As an embodiment of the present application, E2 is = 50-75 kGy.

[0031] As an embodiment of the present application, the extrusion in step (2) is performed in a twin-screw extruder, which comprises a feeding section, a compression section and a homogenizing section, the temperature of the feeding section is set to 90-100℃, the temperature of the compression section is set to 170-175℃, and the temperature of the homogenizing section is set to 140-145℃.

[0032] Compared with the prior art, the present application has the following beneficial effects:

[0033] In the present application, epoxy soybean oil is added as a dispersant in a polyethylene matrix, and the interface of nano-titanium dioxide is modified, which reduces the interfacial tension between the temperature-sensitive color-changing pigment and the polyethylene matrix, improves the dispersion performance of the pigment in the polyethylene matrix, and significantly improves the heat-sensitive performance and mechanical strength of the crosslinked polyethylene pipe material; further combined with gradient crosslinking distribution, the burst pressure of the crosslinked polyethylene pipe material is further improved.

[0034] The heat-sensitive color-changing crosslinked polyethylene pipe material of the present application has a color-changing response time ≤ 6.5 s, a tensile strength ≥ 35 MPa, a burst pressure ≥ 0.4 MPa, a heat-sensitive color-changing cycle life ≥ 100,000 times, and a bending fatigue life ≥ 200,000 times. DETAILED DESCRIPTION

[0035] For better explanation of the purpose, technical scheme and advantage of the present invention, the present invention will be further described below in conjunction with specific embodiment, but embodiment does not limit the present invention in any form.Unless otherwise stated, the reagent, method and equipment adopted in the present invention are conventional reagents, methods and equipment in the art.Unless otherwise stated, the reagents and materials used in the present invention are commercially available.

[0036] In the present invention, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0037] In the present invention, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Furthermore, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0038] The reagents and instruments used in the present invention without indicating the manufacturer are all conventional products that can be purchased from the market.

[0039] In a first aspect of the present invention, an embodiment of the present invention provides a heat-sensitive color-changing cross-linked polyethylene pipe comprising the following components in parts by weight:

[0040] 100 parts of polyethylene, 30-50 parts of epoxidized soybean oil, 0.5-2 parts of nano titanium dioxide, 3-8 parts of compatibilizer, 1.5-5 parts of thermochromic pigment, 0.5-1.2 parts of antioxidant, 0-3 parts of functional additives;

[0041] The cross-linking degree of the thermosensitive color-changing cross-linked polyethylene pipe decreases gradually from the inside to the outside.

[0042] The present invention reduces the interfacial tension between the thermochromic pigment and the polyethylene matrix by adding epoxy soybean oil as a dispersant and performing interface modification with nano-titanium dioxide in the polyethylene matrix, thereby improving the dispersion performance of the thermochromic pigment in the polyethylene matrix and significantly improving the thermal sensitivity and mechanical strength of the cross-linked polyethylene pipe. Furthermore, combined with the gradient cross-linking distribution, the bursting pressure of the cross-linked polyethylene pipe is further increased.

[0043] It should be emphasized that the cross-linked polyethylene pipe in the present invention refers to a formed tubular cross-linked polyethylene material.

[0044] In some embodiments of the present invention, the polyethylene includes at least one of high-density polyethylene (HDPE) and low-density polyethylene (LDPE). Polyethylene commonly used in the art for preparing pipes can be used to prepare the heat-sensitive color-changing cross-linked polyethylene pipe in the present invention.

[0045] In some embodiments of the present invention, the thermochromic pigment includes a green thermochromic pigment, a yellow thermochromic pigment, and a blue thermochromic pigment, and the mass ratio is green thermochromic pigment: yellow thermochromic pigment: blue thermochromic pigment = (0.8-1.1): (0.6-0.9): (0.35-0.55). The ratio of the three colors is controlled within this range, and a four-stage temperature response can be achieved within the range of 21-65°C - "21°C (light green) → 31°C (goose yellow) → 43°C (sky blue) → above 65°C (irreversible red and black)", and the color change with temperature is sensitive, and the color change response time with temperature is within 5s. Through the multi-color synergistic color change mechanism, the temperature resistance of the thermochromic cross-linked polyethylene pipe can be further improved, and the cyclic color change response within the temperature range of 21-65°C is greater than 100,000 times.

[0046] In some embodiments of the present invention, the green thermochromic pigment comprises a spiropyran pigment, specifically spiro[1,3,3-trimethylindole-(6'-nitrochroman)]. Spiropyran ring opening enables reversible color change between dark green and light green, with the pigment appearing dark green below 21°C and gradually shifting to light green above 21°C.

[0047] In some embodiments of the present invention, the yellow thermochromic pigment includes a fluoran pigment, specifically 3-diethylamino-6-methyl-7-phenylaminofluoran. Fluoran pigments can achieve reversible color change between light green and light yellow through temperature-induced conformational transition of fluoran.

[0048] In some embodiments of the present invention, the blue thermochromic pigment includes a crystal violet lactone / bisphenol A composite pigment, specifically a blue composite pigment composed of crystal violet lactone and bisphenol A in a mass ratio of 1:1. A reversible color change between light yellow and sky blue can be achieved through the dissociation of crystal violet lactone and bisphenol A. The presence of bisphenol A can make the color change threshold more precise (>65°C). Above the color change threshold temperature, crystal violet lactone will be permanently protonated, changing from sky blue to an irreversible reddish-black color.

[0049] The use of these organic pigments for thermochromic pigments not only improves the compatibility of thermochromic pigments with the polyethylene matrix and reduces pigment agglomeration, but also enables multi-stage reversible temperature change, resulting in more sensitive and diverse color changes. The ternary system of spiropyran-fluoran-crystal violet lactone is used to achieve four-stage color change through intermolecular energy transfer.

[0050] In some embodiments of the present invention, in the thermochromic cross-linked polyethylene pipe, the secondary particles of the thermochromic pigment are ≤2.5 μm. Within this particle size range, the pigment is not easy to agglomerate in the polyethylene matrix and has good dispersion properties, which is beneficial to improving the mechanical strength of the thermochromic cross-linked polyethylene pipe.

[0051] In some embodiments of the present invention, the epoxy soybean oil has an epoxy value of 4.5-6% and an iodine value of ≤3gI2 / 100g. Selecting this appropriate epoxy soybean oil can better leverage its dispersant function, working in conjunction with nano-titanium dioxide to reduce the interfacial tension between the thermochromic pigment and the polyethylene matrix through interface modification, thereby improving the dispersion of the thermochromic pigment within the polyethylene matrix. This allows the thermochromic pigment to form a well-defined color-changing response network within the polyethylene matrix, achieving a rapid response to temperature changes and further enhancing the mechanical strength of the cross-linked polyethylene pipe.

[0052] In some embodiments of the present invention, the compatibilizer includes PE-g-MAH. The compatibilizer can improve the dispersion efficiency of epoxidized soybean oil. The carbonyl peak of MAH-g-PE (1720 cm -1 ) and epoxy groups of epoxidized soybean oil (910 cm -1 ) form hydrogen bonds, and the interface bonding strength is significantly improved.

[0053] In some embodiments of the present invention, the antioxidant includes at least one of a hindered phenol antioxidant, a phosphite antioxidant, and a UV absorber. The addition of an appropriate amount of antioxidant can extend the service life of polyethylene pipes in high-temperature environments (such as hot water pipelines and wire and cable insulation); it can also slightly reduce the melt viscosity of polyethylene, improving processing fluidity. Therefore, the appropriate combination and dosage of antioxidants can balance the processing stability and long-term aging resistance of polyethylene.

[0054] In some embodiments of the present invention, the functional additives include but are not limited to silver ion antimicrobial agents. Functional additives can be added according to the performance requirements of actual use.

[0055] In some embodiments of the present invention, the difference in crosslinking between the inner and outer layers of the thermochromic cross-linked polyethylene tubing is ≥10%. The inner layer (70±5%) has a significantly higher crosslinking degree than the outer layer (55±5%), creating a 10-15% crosslinking gradient. This structure allows the inner layer to withstand the primary fluid pressure while the outer layer maintains toughness, significantly increasing the burst pressure of the tubing. In this invention, crosslinking is determined according to ASTM D2765-16 (2024).

[0056] In a second aspect of the present invention, an embodiment of the present invention further provides a method for preparing the heat-sensitive color-changing cross-linked polyethylene pipe according to the first aspect of the present invention, comprising the following steps:

[0057] (1) According to the formula, epoxy soybean oil, thermochromic pigment, nano titanium dioxide, and compatibilizer are mixed at a temperature of T1°C and a rotation speed of R1 rpm to obtain a first mixed raw material;

[0058] (2) mixing the first mixed raw material prepared in step (1), polyethylene, antioxidant and functional additive at a temperature of T2°C and a rotation speed of R2 rpm, and extruding at 90-175°C to obtain a tube blank;

[0059] (3) simultaneously irradiating and cross-linking the inside and outside of the tube blank obtained in step (2) to obtain the thermochromic cross-linked polyethylene pipe, wherein the irradiation energy of the inside of the tube blank is E1 kGy, and the irradiation energy of the outside of the tube blank is E2 kGy;

[0060] Among them, T1 <T2,R1<R2,E1> E2.

[0061] In the present invention, epoxy soybean oil is used as a dispersant. The epoxy soybean oil, thermochromic pigment, nano titanium dioxide, and compatibilizer are pre-dispersed at low temperature and low speed. With the help of the compatibilizer, the epoxy soybean oil forms a stable dispersion with the nano titanium dioxide and the thermochromic pigment through physical effects such as van der Waals force and steric hindrance. The dispersion is then further dispersed and mixed into a polyethylene matrix and mixed with other remaining raw materials at high speed at high temperature. The raw materials are evenly dispersed under the shear force of the extruder and work together to improve the comprehensive performance of the thermochromic cross-linked polyethylene pipe.

[0062] By improving the dispersion process of raw materials, the dispersing effect of epoxy soybean oil can be fully utilized, and the combined effect with nano-titanium dioxide can modify the interface of polyethylene, thereby reducing the interfacial tension between the thermochromic pigment and the polyethylene matrix.

[0063] In some embodiments of the present invention, the T1 ≤ 20°C.

[0064] In some embodiments of the present invention, T2 = 90-100°C.

[0065] In some embodiments of the present invention, R1≤500 rpm.

[0066] In some embodiments of the present invention, the R2 is ≥ 800 rpm.

[0067] In some embodiments of the present invention, E1 = 75-100 kGy; E2 = 50-75 kGy. Using a high-energy electron beam to irradiate the inner surface of the tube blank can achieve a high degree of crosslinking (70 ± 5%) in the polyethylene. As the electron beam's penetration decreases with increasing irradiation depth, the polyethylene's crosslinking also gradually decreases. When the electron beam energy on both the outer and inner surfaces of the tube blank is selected within the aforementioned appropriate range, the crosslinking degree of the polyethylene in the resulting tube blank forms a radial gradient that decreases from the inside out. Combined with the distribution of epoxidized soybean oil, nano-titanium dioxide, and thermochromic pigments within the polyethylene matrix, the burst pressure of the resulting thermochromic cross-linked polyethylene pipe can be significantly increased. The crosslinking degree of the inner layer of the pipe (70 ± 5%) is significantly higher than that of the outer layer (55 ± 5%), resulting in a 10-15% crosslinking gradient. This structure allows the inner layer to withstand the primary fluid pressure while the outer layer maintains toughness, significantly increasing the pipe's burst pressure.

[0068] In some embodiments of the present invention, the extrusion described in step (2) is carried out in a twin-screw extruder, which includes a feeding section, a compression section and a homogenizing section. The temperature of the feeding section is set to 90-100°C, the temperature of the compression section is set to 170-175°C, and the temperature of the homogenizing section is set to 140-145°C.

[0069] The following are specific embodiments of the present invention.

[0070] The following is a list of some of the raw materials used in the examples of the present invention. Unless otherwise specified, all of them are commercially available products or prepared by conventional means in the art:

[0071] Polyethylene:

[0072] HDPE: DGDB-2480, density 0.952g / cm 3 , melt mass flow rate MFR = 0.8 g / 10 min at 190 ° C and 2.16 kg load, purchased from Qilu Petrochemical;

[0073] LDPE: LD100BW, density 0.922g / cm 3 , melt mass flow rate MFR = 2.0 g / 10 min at 190 ° C and 2.16 kg load, purchased from Yanshan Petrochemical;

[0074] Epoxidized soybean oil (ESO):

[0075] 1#ESO: Vikoflex 7170, epoxy value 5.8%, iodine value 1.5g I2 / 100g, purchased from Arkema;

[0076] 2#ESO: epoxidized soybean oil, epoxide value 7.0%, iodine value 4.5gI2 / 100g, purchased from Shandong Xingshun Chemical Co., Ltd.

[0077] Titanium dioxide (TiO2):

[0078] 1#n-TiO2: nano-titanium dioxide, MZT-A1, particle size 3-5 nm, purchased from Jiweinanxin Materials;

[0079] 2#n-TiO2: nano-titanium dioxide, XFIO2, particle size of 15-25 nm, purchased from Jiangsu Xianfeng Nanomaterial Technology Co., Ltd.;

[0080] 3#m-TiO2: micron-sized titanium dioxide, titanium dioxide R-666, 325 mesh (<44 μm), purchased from Bai Yuying, Yunfu, Guangdong;

[0081] n-SiO2: nano-silicon dioxide, DK-SiO2-60, particle size 60 nm, purchased from Deke Island Gold;

[0082] n-ZrO2: nano zirconium dioxide, UG-R50Y3, particle size 50 nm, purchased from Suzhou Youzi Nanomaterials Co., Ltd.;

[0083] Compatibilizer:

[0084] PE-g-MAH: ADMER PE-g-MAH AT2614E, purchased from Mitsui Chemicals;

[0085] Thermochromic pigment:

[0086] Green thermochromic pigment: spiro[1,3,3-trimethylindole-(6'-nitrochroman)], CAS No. 1498-88-0, purchased from Tianjin Seteri Technology Development Co., Ltd.

[0087] Yellow thermochromic pigment: 3-diethylamino-6-methyl-7-phenylaminofluoran, CAS No. 29512-49-0, purchased from Hubei Jusheng Technology Co., Ltd.

[0088] Blue thermochromic pigment: a mixture of crystal violet lactone and bisphenol A in a mass ratio of 1:1, wherein crystal violet lactone (analytical grade) was purchased from Tokyo Chemical Industry Co., Ltd.; bisphenol A (analytical grade) was purchased from Tianjin Guangfu Fine Chemical Research Institute;

[0089] Inorganic pigment VO 2： CAS number 12036-21-4, Jikang SS-V50, purchased from Hangzhou Jikang New Materials Co., Ltd.;

[0090] Antioxidant:

[0091] Antioxidant 1010: commercially available;

[0092] Antioxidant 168: Commercially available;

[0093] UV absorber: UV531, commercially available;

[0094] Functional additive:

[0095] Silver ion antibacterial agent: silver-loaded zirconium phosphate, IONPURE AG300, purchased from SINOCHEM.

[0096] Examples 1 to 6, Comparative Examples 1 to 5

[0097] A series of thermochromic cross-linked polyethylene pipes are provided. The pipe formula (including raw material types and weight amounts) is detailed in Table 1. The preparation method includes the following steps:

[0098] (1) According to the formula, epoxy soybean oil, thermochromic pigment, nano titanium dioxide (or corresponding nano oxide, micron-sized titanium dioxide), and compatibilizer are pre-mixed in a mixer at a temperature of T1 = 15° C. and a rotation speed of R1 = 400 rpm to obtain a first mixed raw material;

[0099] (2) The first mixed raw material, polyethylene, antioxidant and functional additive prepared in step (1) are further mixed at a temperature of T2 = 95°C and a rotation speed of R2 = 1000 rpm, and the mixed raw material is added to a twin-screw extruder, the screw speed is set to 250 rpm, the temperature of the feed section of the twin-screw extruder is set to 95°C, the temperature of the compression section is set to 172°C, and the temperature of the homogenization section is set to 142°C; extrusion molding is performed; wherein the compression section temperature (172°C is lower than 180-220°C of conventional PEX) protects the heat-sensitive pigment from decomposition through low-temperature high-shear plasticization;

[0100] (3) Gradient cross-linking and molding

[0101] The discharge port of the twin-screw extruder is combined with PCL dynamic traction (traction rate is 20±0.1mm / s) and spray water tank temperature control (water tank controls the temperature in the range of 25-32°C) cooling technology to cool and shape the tube blank; at the same time, electron beam irradiation cross-linking is performed inside and outside the tube blank, wherein the electron beam dose inside the tube blank is E1=100kGy, and the electron beam dose outside the tube blank is E2=75kGy.

[0102] Table 1

[0103]

[0104] Examples 7 to 10

[0105] A series of thermochromic cross-linked polyethylene pipes were provided, which were prepared according to the method of Example 1. The difference from Example 1 was that the total amount of the thermochromic pigment remained unchanged, and the usage ratio of the three colors of the thermochromic pigment was changed (see Table 2 for details). For example, Example 7 in Table 2 shows that the total weight of the thermochromic pigment (green + yellow + blue) was the same as in Example 1, which was 2.1 parts by weight, and the ratio of green:yellow:blue was 0.8:0.9:0.55.

[0106] Table 2

[0107]

[0108] Comparative Example 6

[0109] A thermochromic cross-linked polyethylene pipe is provided, which is prepared by referring to the method of Example 1. The difference from Example 1 is that the types and amounts of raw materials are the same as those in Example 1. In the preparation method, in step (3), the electron beam dose inside the tube blank is E1=75kGy, and the electron beam dose outside the tube blank is E2=100kGy (i.e., E1 <E2,交联度由内向外梯度增大)。

[0110] Comparative Example 7

[0111] A thermochromic cross-linked polyethylene pipe is provided, which is prepared according to the method of Example 1. The difference from Example 1 is that the pigment is replaced by an inorganic pigment VO2 in equal parts by weight.

[0112] Performance Testing

[0113] The following performance tests were conducted on the heat-sensitive color-changing cross-linked polyethylene pipes prepared in the above examples and comparative examples:

[0114] 1. Uniformity of raw material dispersion in pipes

[0115] The thermochromic cross-linked polyethylene pipe was subjected to liquid nitrogen brittle fracture, and the average size (μm) of the secondary particles of the pigment in the brittle fracture section was observed using a scanning electron microscope (SEM). The test results are detailed in Table 3.

[0116] 2. Thermosensitive color changing performance

[0117] The prepared thermochromic cross-linked polyethylene pipe was placed in a temperature chamber and subjected to an accelerated aging test according to the standard "ISO 4892-3:2016". The temperature of the temperature chamber was set at 15°C as the starting temperature, and the heating rate was set at 10°C / min. After heating to 70°C, the temperature was naturally cooled, and this cycle was repeated. The average color change response time (s) of the color change of the thermochromic cross-linked polyethylene pipe during the initial heating process was recorded; the thermochromic cycle life (unit: 10,000 times) of the thermochromic cross-linked polyethylene pipe was fitted using the function N = (ln(1-F))^{-1 / β}×η. In the functional relationship,

[0118] F is the failure probability. In this invention, 10 groups of pipes from the same batch and formula were tested. The number of failed pipes was recorded as X, and F = X / 10. In the thermal color change test, failure was considered if any of the following conditions occurred: 1) color change response time > 10s; 2) color change function was lost, such as color irreversibility or inability to change according to temperature range;

[0119] η represents the characteristic life, which is the number of cycles when the failure probability reaches 63.2%;

[0120] β = 1.8, which is the shape parameter, obtained based on the Weibull distribution, can characterize and correct the failure mode;

[0121] 3. Mechanical properties

[0122] (1) Burst pressure (MPa): Tested in accordance with GB / T 6111-2018. Test conditions are:

[0123] Medium: water (viscosity compensation factor 1.02);

[0124] Temperature: 23±1℃;

[0125] Pressure increase rate: 0.4 MPa / min (until the pipe ruptures);

[0126] Pressure holding stage: maintain pressure at 0.3 MPa for 60 seconds (simulating actual water hammer effect);

[0127] (2) Tensile strength (MPa): The test was conducted in accordance with the standard GBT1040.1-2006. The test conditions were as follows: the specimen type was a V-shaped dumbbell; the test temperature was 23±0.5°C; the tensile rate was 50 mm / min; before the test, the pipe was annealed at 70°C for 2 h to eliminate internal stress;

[0128] (3) Bending fatigue life (10,000 times): Tested in accordance with ASTM D790-2017. Test conditions are:

[0129] Loading method: three-point bending (span = 6 × pipe wall thickness);

[0130] Deformation: 10% strain (simulated pipeline installation bending state);

[0131] Frequency: 1 Hz;

[0132] Termination condition: visible cracks or discoloration on the surface of the pipe material;

[0133] Environment: 40℃ water bath (accelerated stress relaxation);

[0134] The test results are shown in Table 3:

[0135] Table 3

[0136]

[0137]

[0138] The above results show that:

[0139] The present application reduces the interfacial tension between the temperature-sensitive discoloring pigment and the polyethylene matrix by adding epoxy soybean oil as a dispersant and interfacial modification of nano-titanium dioxide in the polyethylene matrix, which improves the dispersion performance of the pigment in the polyethylene matrix, significantly improves the thermal sensitivity and mechanical strength of the cross-linked polyethylene pipe material, and further improves the burst pressure of the cross-linked polyethylene pipe material by combining with gradient cross-linking distribution.

[0140] The thermal discoloration cross-linked polyethylene pipe material of the present application has a discoloration response time ≤6.5s, a tensile strength ≥35MPa, a burst pressure ≥0.4MPa, a thermal discoloration cycle life ≥100,000 times, and a bending fatigue life ≥200,000 times.

[0141] In Comparative Examples 1-5, due to different raw material combinations, the pigment is not uniformly dispersed, agglomeration occurs, the secondary particles of the pigment are >2.5μm, and the mechanical strength and discoloration cycle performance are significantly deteriorated.

[0142] The gradient cross-linking direction of Comparative Example 6 is opposite to that of Example 1, and the outer layer of high cross-linking leads to brittle fracture, resulting in a decrease in burst pressure from 0.52MPa in Example 1 to 0.31MPa in Comparative Example 6, a decrease of 40% in burst pressure, and a decrease of 50% in bending fatigue life.

[0143] In Comparative Example 7, inorganic pigments that cannot reversibly discolor are used, and the dispersion is not uniform, resulting in a significant deterioration in mechanical strength.

[0144] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A thermosensitive color-changing cross-linked polyethylene pipe, characterized in that: The thermosensitive color-changing cross-linked polyethylene pipe comprises the following components in parts by weight: 100 parts of polyethylene, 30-50 parts of epoxidized soybean oil, 0.5-2 parts of nano titanium dioxide, 3-8 parts of compatibilizer, 1.5-5 parts of thermochromic pigment, 0.5-1.2 parts of antioxidant, 0-3 parts of functional additives; The cross-linking degree of the thermosensitive color-changing cross-linked polyethylene pipe decreases gradually from the inside to the outside.

2. The thermochromic cross-linked polyethylene pipe according to claim 1, characterized in that: The polyethylene includes at least one of high-density polyethylene and low-density polyethylene.

3. The thermosensitive color-changing cross-linked polyethylene pipe according to claim 1, characterized in that: The thermochromic pigment includes a green thermochromic pigment, a yellow thermochromic pigment, and a blue thermochromic pigment, and the mass ratio of the green thermochromic pigment: the yellow thermochromic pigment: the blue thermochromic pigment is (0.8-1.1): (0.6-0.9): (0.35-0.55).

4. The thermosensitive color-changing cross-linked polyethylene pipe according to claim 3, characterized in that: Meet at least one of the following conditions: (1) The green thermochromic pigment includes a spiropyran pigment; (2) The yellow thermochromic pigment includes a fluorane pigment; (3) The blue thermochromic pigment includes a crystal violet lactone / bisphenol A composite pigment.

5. The thermosensitive color-changing cross-linked polyethylene pipe according to claim 1, characterized in that: In the thermochromic cross-linked polyethylene pipe, the secondary particles of the thermochromic pigment are ≤2.5 μm.

6. The thermosensitive color-changing cross-linked polyethylene pipe according to claim 1, characterized in that: The epoxy value of the epoxy soybean oil is 4.5-6%, and the iodine value is ≤3gI2 / 100g.

7. The thermochromic cross-linked polyethylene pipe according to claim 1, characterized in that: Satisfy at least one of the following characteristics: (1) The compatibilizer includes PE-g-MAH; (2) The antioxidant includes at least one of a hindered phenol antioxidant, a phosphite antioxidant, and an ultraviolet light absorber; (3) The functional additive includes a silver ion antibacterial agent.

8. The thermosensitive color-changing cross-linked polyethylene pipe according to claim 1, characterized in that: The difference in cross-linking degree between the inside and outside of the thermosensitive color-changing cross-linked polyethylene pipe is ≥10%.

9. The method for preparing a thermochromic cross-linked polyethylene pipe according to any one of claims 1 to 8, characterized in that: The steps include: (1) According to the formula, epoxy soybean oil, thermochromic pigment, nano titanium dioxide, and compatibilizer are mixed at a temperature of T1°C and a rotation speed of R1 rpm to obtain a first mixed raw material; (2) mixing the first mixed raw material prepared in step (1), polyethylene, antioxidant and functional additive at a temperature of T2°C and a rotation speed of R2 rpm, and extruding at 90-175°C to obtain a tube blank; (3) simultaneously irradiating and cross-linking the inside and outside of the tube blank obtained in step (2) to obtain the thermochromic cross-linked polyethylene pipe, wherein the irradiation energy of the inside of the tube blank is E1 kGy, and the irradiation energy of the outside of the tube blank is E2 kGy; Among them, T1 <T2,R1<R2,E1> E2.

10. The method for preparing a thermosensitive color-changing cross-linked polyethylene pipe according to claim 9, characterized in that: Meet at least one of the following conditions: (1)T1≤20℃； (2)T2＝90～100℃； (3) R1≤500rpm; (4) R2 ≥ 800 rpm; (5) E1 = 75-100 kGy; (6) E2 = 50-75 kGy; (7) In step (2), the extrusion is carried out in a twin-screw extruder, which includes a feeding section, a compression section and a homogenizing section. The temperature of the feeding section is set to 90-100°C, the temperature of the compression section is set to 170-175°C, and the temperature of the homogenizing section is set to 140-145°C.

Images