A peroxide cross-linked polyethylene pipe and its preparation method and preparation system

Abstract

The present invention provides a peroxide-crosslinked polyethylene pipe and a preparation method and system thereof, belonging to the technical field of polyethylene pipes. The peroxide-crosslinked polyethylene pipe of the present invention utilizes high-density polyethylene and ultra-low-density polyethylene, combined with an antioxidant and a lubricant, to enhance the peroxide-crosslinked polyethylene pipe's heat resistance, flexibility, creep resistance, environmental stress cracking resistance, radiation resistance, and oxidation resistance. Furthermore, the addition of a borate-containing polymer to the co-crosslinking agent enhances the peroxide-crosslinked polyethylene pipe's crosslinking uniformity, radiation resistance, heat resistance, durability, aging resistance, and mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of polyethylene pipes, and in particular to a peroxide cross-linked polyethylene pipe and a preparation method and a preparation system thereof. Background Art

[0002] Peroxide-cross-linked polyethylene (PE-Xa) pipes are made of high-density polyethylene as the main raw material. Through the action of cross-linking agents, the linear macromolecular structure is transformed into a spatial network structure, which effectively compensates for the shortcomings of ordinary polyethylene pipes such as low heat deformation temperature, creep resistance and insufficient rigidity. It has good heat resistance, pressure resistance and resistance to environmental stress cracking, and is widely used in many fields. However, the existing peroxide cross-linked polyethylene pipe preparation technology has many shortcomings. The cross-linking reaction is difficult to control accurately, which can easily lead to uneven cross-linking, making the local performance of the pipe unstable and affecting the overall service life and reliability. At the same time, traditional preparation methods rely on specific equipment, with high energy consumption and high cost. Moreover, the cross-linked structure of some pipes is easily damaged under long-term high temperature and high pressure environments, and the performance is significantly reduced. Summary of the Invention

[0003] The purpose of the present disclosure is to overcome the deficiencies of the prior art and to provide a peroxide cross-linked polyethylene pipe and a preparation method and system thereof.

[0004] To achieve the above objectives, the technical solutions adopted in this disclosure are:

[0005] In a first aspect, a peroxide cross-linked polyethylene pipe is provided, comprising the following components in parts by weight: 99-101 parts of polyethylene resin, 0.7-1.6 parts of a peroxide cross-linking agent, 0.4-1.3 parts of a co-cross-linking agent, 0.25-0.6 parts of an antioxidant, and 0.15-0.35 parts of a lubricant;

[0006] The polyethylene resin includes high-density polyethylene and ultra-low-density polyethylene, and the density of the high-density polyethylene is 0.955-0.970 g / cm 3 The density of the ultra-low density polyethylene is 0.860-0.900 g / cm 3 ;

[0007] The auxiliary cross-linking agent is a polymer containing a borate ester bond, N,N'-m-phenylene bismaleimide and trimethylolpropane trimethacrylate.

[0008] In some embodiments, the mass ratio of the high-density polyethylene to the ultra-low-density polyethylene is (7-9): (1-3);

[0009] In some embodiments, the high-density polyethylene has a melt index of 0.6-1.8 g / 10 min;

[0010] In some embodiments, the ultra-low density polyethylene has a melt index of 1.2-3.5 g / 10 min.

[0011] In some embodiments, the mass ratio of the borate ester bond-containing polymer, N,N'-m-phenylene bismaleimide, and trimethylolpropane trimethacrylate is (0.5-1.2):(1-1.5):(1-1.5).

[0012] In some embodiments, the preparation method of the boronate ester bond-containing polymer is:

[0013] reacting a polyol, an unsaturated acid, and an acidic catalyst in an inert atmosphere at a temperature of 80-120° C. for 4-8 hours to obtain an esterification product;

[0014] After cooling the esterification product to 60-80° C., adding a boron-containing compound and a complexing agent, reacting at a temperature of 80-100° C. for 2-4 hours, removing impurities, and obtaining a polymer containing borate ester bonds.

[0015] In some embodiments, the molar ratio of the polyol to the unsaturated acid is 1:(3-4.5).

[0016] In some embodiments, the mass of the acidic catalyst is 0.5-2% of the total mass of the polyol and the unsaturated acid.

[0017] In some embodiments, the molar ratio of the polyol to the boron-containing compound is 1:(0.8-1.2).

[0018] In some embodiments, the molar ratio of the polyol to the complexing agent is 1:(0.9-1.1).

[0019] In some embodiments, the polyol is at least one of pentaerythritol, dipentaerythritol, polyethylene glycol, and trimethylolpropane;

[0020] In some embodiments, the unsaturated acid is at least one of acrylic acid, methacrylic acid, maleic anhydride, and itaconic acid;

[0021] In some embodiments, the boron-containing compound is at least one of boric acid, borax, and phenylboric acid;

[0022] In some embodiments, the acidic catalyst is p-toluenesulfonic acid;

[0023] In some embodiments, the complexing agent is at least one of ethanolamine and triethanolamine.

[0024] In some embodiments, the peroxide crosslinking agent is at least one of benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane;

[0025] In some embodiments, the antioxidant is at least one of a hindered amine antioxidant and a thioester antioxidant;

[0026] In some embodiments, the lubricant is at least one of low molecular weight esters, metal soaps, stearic acid complex esters, and amides.

[0027] In some embodiments, the peroxide crosslinking agent is benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and the mass ratio of benzoyl peroxide to 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane is (1-1.5):(1-1.5).

[0028] In some embodiments, the antioxidant is a hindered amine antioxidant and a thioester antioxidant, and the mass ratio of the hindered amine antioxidant to the thioester antioxidant is (2-2.5): (1-1.5).

[0029] In some embodiments, the lubricant is ethylene bisstearamide and silicone powder, and the mass ratio of ethylene bisstearamide to silicone powder is (1-1.5): (1-1.5).

[0030] In a second aspect, a method for preparing the peroxide cross-linked polyethylene pipe is provided, comprising the following steps:

[0031] Mix the components uniformly in proportion to obtain a premix;

[0032] The premix is ​​added into a screw extruder for melt extrusion to obtain a pipe blank;

[0033] The pipe blank is subjected to a pre-crosslinking treatment and a main crosslinking treatment in sequence under infrared irradiation, and the obtained crosslinked pipe is cooled and post-treated to obtain a peroxide crosslinked polyethylene pipe.

[0034] In some embodiments, the mixing parameters satisfy at least one of the following: temperature below 38° C., rotation speed of 1000-1400 r / min, and time of 15-25 min.

[0035] In some embodiments, the melt extrusion parameters satisfy at least one of the following: screw aspect ratio of 28-30:1, temperature of 140-180° C., screw speed of 30-40 r / min, and feeding rate of 150-200 kg / h.

[0036] In some embodiments, the pre-crosslinking treatment is performed at a temperature of 185-230° C. for a time of 9-15 seconds.

[0037] In some embodiments, the main cross-linking treatment is performed at a temperature of 230-280° C. for a time of 9-15 seconds.

[0038] In some embodiments, the cooling end point temperature is 20-30°C, and the cooling rate is 5-10°C / min.

[0039] In some embodiments, the post-treatment temperature is 70-100° C. and the time is 20-30 h.

[0040] In some embodiments, during the melt extrusion, the setting temperatures of the screw extruder from the feed port to the die head are: zone 1 temperature 140-150°C, zone 2 temperature 150-160°C, zone 3 temperature 160-170°C, zone 4 temperature 150-160°C, zone 5 temperature 160-170°C, zone 6 temperature 160-180°C;

[0041] In some embodiments, the pre-crosslinking treatment includes a first pre-crosslinking treatment, a second pre-crosslinking treatment, and a third pre-crosslinking treatment performed sequentially, wherein the temperature of the first pre-crosslinking treatment is 185-195° C., the temperature of the second pre-crosslinking treatment is 195-205° C., and the temperature of the third pre-crosslinking treatment is 205-230° C.; the time for the first pre-crosslinking treatment, the second pre-crosslinking treatment, and the third pre-crosslinking treatment is each independently 3-5 s, and the heating rate is each independently 5-10° C. / s;

[0042] In some embodiments, the primary crosslinking treatment includes a first primary crosslinking treatment, a second primary crosslinking treatment, and a third primary crosslinking treatment performed sequentially, wherein the temperature of the first primary crosslinking treatment is 240-250° C., the temperature of the second primary crosslinking treatment is 260-280° C., and the temperature of the third primary crosslinking treatment is 230-245° C.; and the time for the first primary crosslinking treatment, the second primary crosslinking treatment, and the third primary crosslinking treatment is each independently 3-5 seconds;

[0043] In some embodiments, the cooling includes a first cooling treatment, a second cooling treatment and a third cooling treatment performed sequentially, wherein the endpoint temperature of the first cooling treatment is 70-85°C, the endpoint temperature of the second cooling treatment is 40-55°C, and the endpoint temperature of the third cooling treatment is 20-30°C.

[0044] In a third aspect, a system for preparing the peroxide cross-linked polyethylene pipe is provided, comprising a twin-screw extruder, a loading and unloading system, a cross-linking infrared furnace, a vacuum tank, a cooling water tank, a haul-off machine, and a winder; the unloading end of the loading and unloading system is connected to the feeding end of the twin-screw extruder, and the twin-screw extruder, the cross-linking infrared furnace, the vacuum tank, the cooling water tank, the haul-off machine, and the winder are connected in sequence;

[0045] The cross-linking infrared furnace includes a pre-cross-linking mechanism and a main cross-linking mechanism connected in sequence; the pre-cross-linking mechanism is used to perform a pre-cross-linking treatment, and the main cross-linking mechanism is used to perform a main cross-linking treatment;

[0046] The pipe blank extruded from the twin-screw extruder passes through a traction mechanism of a traction machine in sequence through a cross-linking infrared furnace, a vacuum tank, and a cooling water tank, and is wound up by a winder.

[0047] Compared with the prior art, the beneficial effects of the present disclosure are:

[0048] The present invention adopts high-density polyethylene and ultra-low-density polyethylene, combined with antioxidants and lubricants, to improve the heat resistance, flexibility, creep resistance, environmental stress cracking resistance, radiation resistance and oxidation resistance of the peroxide cross-linked polyethylene pipe, so that the peroxide polyethylene pipe can adapt to more demanding use environments; in addition, a specific auxiliary cross-linking agent is used to improve the cross-linking uniformity of the peroxide polyethylene pipe, effectively avoid the difference in local cross-linking, significantly improve the stability of the peroxide polyethylene pipe, and extend the service life of the peroxide polyethylene pipe. At the same time, the polymer containing borate bonds can also give the peroxide polyethylene pipe a certain radiation resistance. The BOC bond in the polymer containing borate bonds gives the auxiliary cross-linking agent a dynamic reversible cross-linking ability, enhances the self-repairing ability of the cross-linked network in the peroxide polyethylene pipe, and significantly improves the heat resistance, durability, aging resistance and mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a system diagram for preparing the peroxide cross-linked polyethylene pipe of the present invention;

[0050] Figure 2 This is a schematic structural diagram of a twin-screw extruder and a loading and unloading system according to an embodiment of the present invention;

[0051] Figure 3 This is a schematic structural diagram of a cross-linking infrared furnace according to an embodiment of the present invention;

[0052] Figure 4 This is a schematic structural diagram of a vacuum tank according to an embodiment of the present invention;

[0053] Figure 5 This is a schematic structural diagram of a cooling water tank according to an embodiment of the present invention;

[0054] Figure 6 This is a schematic structural diagram of a traction machine and a winder according to an embodiment of the present invention;

[0055] Figure 1-6 Among them, 100 twin-screw extruder, 101 loading and unloading system, 102 cross-linking infrared oven, 103 vacuum tank, 104 cooling water tank, 105 haul-off machine, 106 winder, 107 peroxide cross-linked polyethylene pipe, 200 pre-cross-linking mechanism, 201 first heating element, 202 second heating element, 203 third heating element, 300 main cross-linking mechanism, 301 fourth heating element, 302 fifth heating element, 303 sixth heating element;

[0056] Figure 7 This is a cross-sectional view of the peroxide cross-linked polyethylene pipe in Example 1;

[0057] Figure 8 This is a cross-sectional view of the peroxide cross-linked polyethylene pipe of Comparative Example 3. DETAILED DESCRIPTION

[0058] To facilitate understanding of the present disclosure, a more comprehensive description will be given below. However, the present disclosure can be implemented in many different forms and is not limited to the embodiments described herein. Rather, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present disclosure.

[0059] As used herein:

[0060] "Prepared from" is synonymous with "comprising." As used herein, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0061] The conjunction "consisting of" excludes any unspecified element, step, or component. If used in a claim, this phrase renders the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the body of a claim, rather than immediately following the subject matter, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0062] When amount, concentration or other value or parameter are represented with range, preferred range or the range that a series of upper preferred value and lower preferred value limit are expressed, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, and no matter whether this scope is disclosed separately.For example, when disclosing scope " 1-5 ", described scope should be interpreted as including scope " 1-4 ", " 1-3 ", " 1-2 ", " 1-2 and 4-5 ", " 1-3 and 5 " etc.When numerical range is described in this article, unless otherwise stated, otherwise this scope is intended to include its end value and all integers and fractions within this range.

[0063] In these examples, parts and percentages are by mass unless otherwise indicated.

[0064] "Parts by mass" refers to the basic unit of measurement used to express the mass ratio of multiple components. One part can represent any unit of mass, such as 1g or 2.689g. If we say that the mass of component A is a parts and the mass of component B is b parts, this means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, we could say that the mass of component A is aK and the mass of component B is bK (where K is an arbitrary number representing a multiplication factor). It's important to note that, unlike parts by mass, the sum of the mass of all components is not limited to 100 parts.

[0065] "And / or" is used to indicate that one or both of the stated situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0066] To further illustrate the present invention, the peroxide cross-linked polyethylene pipe provided by the present invention, its preparation method and application are described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0067] In a first aspect, a peroxide cross-linked polyethylene pipe is provided, comprising the following components in parts by weight: 99-101 parts of polyethylene resin, 0.7-1.6 parts of a peroxide cross-linking agent, 0.4-1.3 parts of a co-cross-linking agent, 0.25-0.6 parts of an antioxidant, and 0.15-0.35 parts of a lubricant;

[0068] The polyethylene resin includes high-density polyethylene and ultra-low-density polyethylene, and the density of the high-density polyethylene is 0.955-0.970 g / cm 3 The density of the ultra-low density polyethylene is 0.860-0.900 g / cm 3 ;

[0069] The auxiliary cross-linking agent is a polymer containing a borate ester bond, N,N'-m-phenylene bismaleimide (HVA-2) and trimethylolpropane trimethacrylate (TMPTMA).

[0070] Specifically, the weight portion of the peroxide crosslinking agent can be, but is not limited to, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, or 1.6 parts;

[0071] Specifically, the weight portion of the auxiliary cross-linking agent can be, but is not limited to, 0.4 parts, 0.45 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 parts, 1.1 parts, 1.2 parts, and 1.3 parts;

[0072] Specifically, the weight portion of the antioxidant may be, but is not limited to, 0.25 part, 0.3 part, 0.35 part, 0.4 part, 0.45 part, 0.5 part, 0.55 part, or 0.6 part;

[0073] Specifically, the weight portion of the lubricant may be, but is not limited to, 0.15 parts, 0.17 parts, 0.2 parts, 0.23 parts, 0.25 parts, 0.27 parts, 0.3 parts, 0.33 parts, or 0.35 parts.

[0074] The present invention adopts high-density polyethylene and ultra-low-density polyethylene, combined with antioxidants and lubricants, to improve the heat resistance, flexibility, creep resistance, environmental stress cracking resistance, radiation resistance and oxidation resistance of the peroxide cross-linked polyethylene pipe, so that the peroxide polyethylene pipe can adapt to more demanding use environments; in addition, a specific auxiliary cross-linking agent is used to improve the cross-linking uniformity of the peroxide polyethylene pipe, effectively avoid the difference in local cross-linking, significantly improve the stability of the peroxide polyethylene pipe, and extend the service life of the peroxide polyethylene pipe. At the same time, the polymer containing borate bonds can also give the peroxide polyethylene pipe a certain radiation resistance. The BOC bond in the polymer containing borate bonds gives the auxiliary cross-linking agent a dynamic reversible cross-linking ability, enhances the self-repairing ability of the cross-linked network in the peroxide polyethylene pipe, and significantly improves the heat resistance, durability, aging resistance and mechanical properties.

[0075] In some embodiments, the mass ratio of the high-density polyethylene to the ultra-low-density polyethylene is (7-9): (1-3); for example, it can be but not limited to 7:3, 8:2, 9:1, 7:1, 8:3;

[0076] In some embodiments, the melt index of the high-density polyethylene is 0.6-1.8 g / 10min; for example, it can be but not limited to 0.6 g / 10min, 0.8 g / 10min, 1.2 g / 10min, 1.6 g / 10min, 1.8 g / 10min; the test method is ASTM D1238-20, and the test conditions are 190°C / 5kg.

[0077] In some embodiments, the melt index of the ultra-low density polyethylene is 1.2-3.5 g / 10min, for example, it can be but not limited to 1.2 g / 10min, 1.5 g / 10min, 1.8 g / 10min, 2.1 g / 10min, 2.4 g / 10min, 2.7 g / 10min, 3g / 10min, 3.3 g / 10min, 3.5 g / 10min, and the test method is ASTM D1238-20, and the test conditions are 190°C / 2.16kg.

[0078] When the melt index of the high-density polyethylene and the low-density polyethylene and the mass ratio therebetween are within the above ranges, the comprehensive performance of the peroxide cross-linked polyethylene pipe is improved.

[0079] In some embodiments, the mass ratio of the borate ester bond-containing polymer, N,N'-m-phenylene bismaleimide and trimethylolpropane trimethacrylate is (0.5-1.2):(1-1.5):(1-1.5); for example, it can be but is not limited to 0.8:1:1, 0.8:1.2:1, 0.8:1.5:1, 0.8:1:1.2, 0.8:1:1.5, 1:1:1, 0.5:1:1.5, 1:1.2:1.2, 0.8:1.5:1; preferably, it is (0.8-1):(1-1.5):(1-1.5).

[0080] When the mass ratio of the borate-containing polymer, N,N'-m-phenylene bismaleimide and trimethylolpropane trimethacrylate is within the above range, the comprehensive performance of the peroxide cross-linked polyethylene pipe is improved.

[0081] In some embodiments, the preparation method of the boronate ester bond-containing polymer is:

[0082] reacting a polyol, an unsaturated acid, and an acidic catalyst in an inert atmosphere at a temperature of 80-120° C. for 4-8 hours to obtain an esterification product;

[0083] After cooling the esterification product to 60-80° C., adding a boron-containing compound and a complexing agent, reacting at a temperature of 80-100° C. for 2-4 hours, removing impurities, and obtaining a polymer containing borate ester bonds.

[0084] The present invention forms a BOC bond by complexing the hydroxyl group in the esterification product with the boron-containing compound, thereby imparting dynamic reversible cross-linking ability to the polymer containing the borate ester bond.

[0085] The invention determines the end point of the complexation reaction by detecting the formation rate and content of the BO characteristic peak in the borate ester bond-containing polymer through FT-IR.

[0086] In some embodiments, the molar ratio of the polyol to the unsaturated acid is 1:(3-4.5), for example, but not limited to, 1:3, 1:3.3, 1:3.5, 1:3.8, 1:4, 1:4.3, 1:4.5;

[0087] In some embodiments, the mass of the acidic catalyst is 0.5-2% of the total mass of the polyol and the unsaturated acid; for example, it can be but not limited to 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%;

[0088] In some embodiments, the molar ratio of the polyol to the boron-containing compound is 1:(0.8-1.2);

[0089] In some embodiments, the molar ratio of the polyol to the complexing agent is 1:(0.9-1.1);

[0090] In some embodiments, the polyol is at least one of pentaerythritol, dipentaerythritol, polyethylene glycol, and trimethylolpropane; preferably, the polyol is pentaerythritol; the functionality of the polyol ≥ 3 can increase the esterification product to have multiple active sites, which is conducive to the formation of more BOC bonds, thereby improving the cross-linking efficiency of the peroxide polyethylene pipe.

[0091] In some embodiments, the unsaturated acid is at least one of acrylic acid, methacrylic acid, maleic anhydride, and itaconic acid; preferably, the unsaturated acid is acrylic acid; acrylic acid has high reactivity and is conducive to esterification reaction with polyols.

[0092] In some embodiments, the boron-containing compound is at least one of boric acid, borax, and phenylboric acid; preferably, the boron-containing compound is boric acid.

[0093] In some embodiments, the acidic catalyst is p-toluenesulfonic acid.

[0094] In some embodiments, the complexing agent is at least one of ethanolamine and triethanolamine.

[0095] In some embodiments, the peroxide crosslinking agent is at least one of benzoyl peroxide (BPO) and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane (DBPH);

[0096] In some embodiments, the antioxidant is at least one of a hindered amine antioxidant and a thioester antioxidant;

[0097] In some embodiments, the lubricant is at least one of low molecular weight esters, metal soaps, stearic acid complex esters, and amides.

[0098] In some embodiments, the peroxide crosslinking agent is benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and the mass ratio of benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane is (1-1.5):(1-1.5); for example, it can be but not limited to 1:1.5, 1.2:1.3, 1.3:1.2, 1.5:1; the mass ratio of benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane is within the above range, which improves the comprehensive performance of the peroxide cross-linked polyethylene pipe.

[0099] In some embodiments, the antioxidant is a hindered amine antioxidant and a thioester antioxidant, and the mass ratio of the hindered amine antioxidant to the thioester antioxidant is (2-2.5): (1-1.5); for example, it can be but not limited to 2:1.5, 2.2:1.3, 2.4:1.1, 2.5:1; the hindered amine antioxidant and the thioester antioxidant are used in combination to exert antioxidant effects at different stages, effectively inhibiting the oxidative degradation of peroxide polyethylene pipes during processing and use.

[0100] In some embodiments, the lubricant comprises ethylene bisstearamide (EBS) and silicone powder, with the mass ratio of ethylene bisstearamide to silicone powder being (1-1.5):(1-1.5); examples include, but are not limited to, 1:1.5, 1.2:1.3, 1.3:1.2, and 1.5:1. The combination of ethylene bisstearamide and silicone powder can effectively reduce friction between the material and the equipment, improving the smoothness of extrusion molding.

[0101] In a second aspect, a method for preparing the peroxide cross-linked polyethylene pipe is provided, comprising the following steps:

[0102] Mix the components uniformly in proportion to obtain a premix;

[0103] The premix is ​​added into a screw extruder for melt extrusion to obtain a pipe blank;

[0104] The pipe blank is subjected to a pre-crosslinking treatment and a main crosslinking treatment in sequence under infrared irradiation, and the obtained crosslinked pipe is cooled and post-treated to obtain a peroxide crosslinked polyethylene pipe.

[0105] The present invention is beneficial to improving the crosslinking uniformity and stability of the peroxide polyethylene pipe by performing pre-crosslinking treatment and main crosslinking treatment on the pipe blank.

[0106] In some embodiments, the mixing parameters meet at least one of the following: temperature below 38°C, rotation speed of 1000-1400 r / min, and time of 15-25 min; the above mixing conditions can ensure that the components are fully and evenly mixed, thereby improving the cross-linking effect of the peroxide polyethylene pipe.

[0107] In some embodiments, the melt extrusion parameters satisfy at least one of the following: screw aspect ratio of 28-30:1, temperature of 140-180° C., screw speed of 30-40 r / min, and feeding rate of 150-200 kg / h.

[0108] Specifically, during the melt extrusion, the set temperatures of the screw extruder from the feed port to the die head are: zone 1 temperature 140-150°C, zone 2 temperature 150-160°C, zone 3 temperature 160-170°C, zone 4 temperature 150-160°C, zone 5 temperature 160-170°C, and zone 6 temperature 160-180°C.

[0109] Appropriate screw aspect ratio, screw speed, feeding rate and temperature of multi-stage melt extrusion can ensure that the material is fully plasticized and evenly mixed during the extrusion process, thereby improving the molding quality of the pipe.

[0110] In some embodiments, the pre-crosslinking treatment is performed at a temperature of 185-230° C. for a time of 9-15 seconds;

[0111] Specifically, the pre-crosslinking treatment includes a first pre-crosslinking treatment, a second pre-crosslinking treatment and a third pre-crosslinking treatment performed sequentially, wherein the temperature of the first pre-crosslinking treatment is 185-195° C., the temperature of the second pre-crosslinking treatment is 195-205° C., and the temperature of the third pre-crosslinking treatment is 205-230° C.; the time of the first pre-crosslinking treatment, the second pre-crosslinking treatment and the third pre-crosslinking treatment is each independently 3-5 s, and the heating rate is each independently 5-10° C. / s;

[0112] In some embodiments, the main cross-linking treatment is performed at a temperature of 230-280° C. for a time of 9-15 seconds;

[0113] The main cross-linking treatment includes a first main cross-linking treatment, a second main cross-linking treatment and a third main cross-linking treatment performed in sequence, wherein the temperature of the first main cross-linking treatment is 240-250°C, the temperature of the second main cross-linking treatment is 260-280°C, and the temperature of the third main cross-linking treatment is 230-245°C; and the time of the first main cross-linking treatment, the second main cross-linking treatment and the third main cross-linking treatment is each independently 3-5s.

[0114] The present invention adopts a multi-stage temperature-variable treatment process to carry out pre-crosslinking treatment and main crosslinking treatment. The combination of the two makes the crosslinking reaction more controllable and uniform, effectively avoids local crosslinking differences, and significantly improves the stability of the overall performance of the peroxide crosslinked polyethylene pipe. Specifically, the first pre-crosslinking treatment causes the peroxide crosslinking agent to begin to slowly decompose, triggering a partial crosslinking reaction and forming a small number of crosslinking points; the second pre-crosslinking treatment further promotes the progress of the crosslinking reaction and increases the number of crosslinking points; the third pre-crosslinking treatment makes the crosslinking structure initially stable and reduces stress concentration; the first main crosslinking treatment causes the crosslinking reaction to proceed rapidly, a large number of crosslinking points are formed and begin to connect into a crosslinked network structure; the second main crosslinking treatment further improves the crosslinking network structure and increases the crosslinking degree of the peroxide crosslinked polyethylene pipe; the third main crosslinking treatment ensures that the crosslinking reaction is fully completed and forms a uniform and firm three-dimensional crosslinked network.

[0115] Specifically, during the pre-crosslinking treatment and the crosslinking treatment, the temperature difference between adjacent stages is 10-20°C;

[0116] Precise temperature difference and heating and cooling rates can effectively control the progress and uniformity of the cross-linking reaction, making the network cross-linking structure in the peroxide cross-linked polyethylene pipe more dense and stable.

[0117] In some embodiments, the cooling end point temperature is 20-30°C, and the cooling rate is 5-10°C / min;

[0118] Specifically, the cooling includes a first cooling treatment, a second cooling treatment and a third cooling treatment performed in sequence, wherein the terminal temperature of the first cooling treatment is 70-85°C, the terminal temperature of the second cooling treatment is 40-55°C, and the terminal temperature of the third cooling treatment is 20-30°C.

[0119] Specifically, the time for the first cooling treatment, the second cooling treatment and the third cooling treatment is independently 3-5 minutes.

[0120] The cooling rate and multi-stage cooling process ensure the dimensional stability and internal structural uniformity of the peroxide-cross-linked polyethylene pipe. Specifically, the first cooling process rapidly cools the peroxide-cross-linked polyethylene pipe while avoiding the internal stress caused by sudden cooling. The second cooling process further reduces the temperature of the peroxide-cross-linked polyethylene pipe and stabilizes the cross-linked structure. The third cooling process allows the peroxide-cross-linked polyethylene pipe to reach room temperature, completing the cooling and setting.

[0121] Specifically, before cooling, it also includes a vacuum shaping treatment, in which negative pressure is formed by evacuating air from the vacuum tank, so that the tube blank can be quickly shaped before cooling to avoid deformation caused by gravity or thermal expansion; the vacuum pressure makes the tube blank close to the shaping mold, ensuring that the outer diameter and wall thickness of the tube are uniform, while eliminating surface defects after melt extrusion (such as bubbles and wrinkles), and improving the surface smoothness of the tube. Furthermore, the vacuum shaping treatment can also assist cooling, reduce internal stress concentration of the tube blank, and improve the structural density of the tube.

[0122] In some embodiments, the post-treatment temperature is 70-100° C. and the time is 20-30 h.

[0123] Within the above-mentioned post-treatment parameter range, the residual internal stress of the peroxide cross-linked polyethylene pipe can be eliminated, and at the same time, appropriate secondary cross-linking can be carried out, thereby improving the performance stability of the peroxide cross-linked polyethylene pipe; in addition, the post-treatment can also eliminate residual peroxides and reaction by-products and odors, ensuring hygienic performance.

[0124] In order to avoid the influence of moisture and volatile impurities, the polyethylene resin needs to be dried before the raw materials are mixed. The drying temperature is 90-100°C and the time is 6-8 hours.

[0125] Thirdly, as Figure 1-6 As shown, a preparation system for the peroxide cross-linked polyethylene pipe is provided, comprising a twin-screw extruder 100, a loading and unloading system 101, a cross-linking infrared furnace 102, a vacuum tank 103, a cooling water tank 104, a tractor 105, and a winder 106; the unloading end of the loading and unloading system 101 is connected to the feeding end of the twin-screw extruder 100, and the twin-screw extruder 100, the cross-linking infrared furnace 102, the vacuum tank 103, the cooling water tank 104, the tractor 105, and the winder 106 are connected in sequence;

[0126] The interior of the cross-linking infrared furnace includes a pre-cross-linking mechanism 200 and a main cross-linking mechanism 300 connected in sequence; the pre-cross-linking mechanism 200 is used to perform a pre-cross-linking process, and the main cross-linking mechanism 300 is used to perform a main cross-linking process;

[0127] The pipe blank extruded from the twin-screw extruder 100 passes through a cross-linking infrared furnace 102 , a vacuum tank 103 , and a cooling water tank 104 in sequence through a traction mechanism of a traction machine 105 , and is wound up by a winder 106 .

[0128] Specifically, the pre-crosslinking mechanism 200 includes a first chamber, a second chamber, and a third chamber, which are sequentially connected by through-holes. The first, second, and third chambers are isolated from each other so that they can be maintained at preset temperatures. The through-holes are used for the passage of tubing, and the tubing blank passes through the first, second, and third chambers in sequence through the through-holes. A first heating element 201 is connected to the first chamber, a second heating element 202 is connected to the second chamber, and a third heating element 203 is connected to the third chamber. The first heating element 201 is used to adjust the temperature of the first pre-crosslinking treatment, the second heating element 202 is used to adjust the temperature of the second pre-crosslinking treatment, and the third heating element 203 is used to adjust the temperature of the third pre-crosslinking treatment.

[0129] Specifically, the primary cross-linking mechanism 300 includes a fourth chamber, a fifth chamber, and a sixth chamber, interconnected by through-holes. These chambers are isolated from each other to maintain preset temperatures. The through-holes allow the tubing to pass through, with the tubing passing through the fourth, fifth, and sixth chambers in sequence. A fourth heating element 301 is connected to the fourth chamber, a fifth heating element 302 is connected to the fifth chamber, and a sixth heating element 303 is connected to the sixth chamber. The fourth heating element 301 is used to adjust the temperature of the first primary cross-linking treatment, the fifth heating element 302 is used to adjust the temperature of the second primary cross-linking treatment, and the sixth heating element 303 is used to adjust the temperature of the third primary cross-linking treatment.

[0130] In the present invention, the cross-linking infrared furnace has multiple heating elements, through which the temperature and time of the pre-cross-linking reaction and the main cross-linking reaction can be independently controlled, and the progress of the cross-linking reaction of the peroxide cross-linked polyethylene pipe can be accurately controlled. Among them, the pre-cross-linking mechanism realizes a pre-cross-linking reaction with step-by-step heating, and the main cross-linking mechanism adopts a three-stage temperature control of high temperature-heating-cooling to realize a high-temperature main cross-linking reaction and cooling curing, so that the peroxide cross-linked polyethylene pipe forms a dynamic cross-linking network; it solves the problem of uneven cross-linking of peroxide cross-linked polyethylene pipes in traditional technologies, and significantly improves the heat resistance and mechanical properties of peroxide cross-linked polyethylene pipes.

[0131] Specifically, the cooling water tank 104 includes a first cooling element, a second cooling element and a third cooling element connected in sequence. The first cooling element is used to control the temperature of the first cooling process, the second cooling element is used to control the temperature of the second cooling process, and the third cooling element is used to control the temperature of the third cooling process.

[0132] After the cross-linking infrared furnace, the pipes are sequentially subjected to vacuum shaping (vacuum tank) and three-stage gradient cooling (cooling water tank) to avoid stress concentration in the peroxide cross-linked polyethylene pipes and improve the overall performance of the peroxide cross-linked polyethylene pipes.

[0133] Specifically, the method for preparing a peroxide cross-linked polyethylene pipe using the peroxide cross-linked polyethylene pipe preparation system comprises the following steps:

[0134] After the components are mixed evenly, the obtained premix is ​​transported to the twin-screw extruder 100 through the discharge end of the loading and unloading system 101 for melt plasticization and extrusion to obtain a pipe blank. The pipe blank enters the pre-crosslinking mechanism 200 through the traction mechanism of the traction machine 105 for pre-crosslinking treatment, and then enters the main crosslinking mechanism 300 for main crosslinking treatment, and then enters the vacuum tank 103 for vacuum setting, and then enters the cooling water tank 104 for cooling and setting, and then is wound by the winder 106 to obtain a semi-finished product. The obtained semi-finished product is post-processed to obtain a peroxide cross-linked polyethylene pipe 107.

[0135] The raw materials used in the examples and comparative examples are described below, but are not limited to these materials:

[0136] High-density polyethylene A: density 0.953 g / cm³, melt index 0.7 g / 10 min at 190°C and 5 kg, Lupolen 5461B Q471 B (Basel);

[0137] High-density polyethylene B: density 0.965 g / cm³, melt index 1.2 g / 10 min at 190°C and 5 kg, ExxonMobil HDPE HDZ-100;

[0138] Ultra-low-density polyethylene A: density 0.880 g / cm³, melt index 2.0 g / 10 min at 190°C and 2.16 kg, Dow ATTANE™ 4203 (Dow Chemical);

[0139] Ultra-low-density polyethylene B: density 0.890 g / cm³, melt index 2.5 g / 10 min at 190°C and 2.16 kg, Mitsui ULDPE SP0540 (Mitsui Chemicals);

[0140] Linear low-density polyethylene: density 0.920 g / cm³, melt index 1.0 g / 10 min at 190°C and 2.16 kg, ExxonMobil LLDPE LL 1001;

[0141] The borate ester-containing polymer was prepared in-house. The following preparation method was used: pentaerythritol and acrylic acid were added to a reactor at a molar ratio of 1:3, along with p-toluenesulfonic acid, with the mass of the p-toluenesulfonic acid being 1% of the total mass of the pentaerythritol and acrylic acid. The reaction was then heated to 100°C under nitrogen protection, stirred, and an esterification reaction was carried out. The water generated by the esterification reaction was removed through a water separator. The esterification reaction was terminated when the acid value of the reaction product was ≤5 mg KOH / g, yielding an esterified product.

[0142] The esterification product was cooled to 80°C, and after adding boric acid, triethanolamine was added dropwise at a dropwise rate of 1 mL / min. The reaction was carried out at 80°C for 4 hours. The resulting reaction product was subjected to reduced pressure distillation to remove low-boiling substances, and then dissolved in acetone. The resulting solution was filtered and dried to obtain a polymer A containing a borate ester bond; wherein the molar ratio of triethanolamine to boric acid was 1:1.

[0143] Hindered amine antioxidant: Succinic acid and (polymer of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinol), abbreviated as antioxidant GW-622, commercially available;

[0144] Thioester antioxidant: dilauryl thiodipropionate, abbreviated as antioxidant DLTP, commercially available;

[0145] Hindered phenol antioxidant: pentaerythritol tetrakis (3,5-di-tert-butyl-4-hydroxyhydrocinnamate), commercially available;

[0146] Except for the above specific instructions, the components used in the parallel examples and comparative examples (such as high-density polyethylene, peroxide cross-linking agent, antioxidant and lubricant, etc.) are all the same commercially available or homemade varieties.

[0147] Examples 1-13 and Comparative Examples 1-5

[0148] The components of the peroxide cross-linked polyethylene pipes described in Examples 1-13 and Comparative Examples 1-5 are shown in Tables 1 and 2;

[0149] The method for preparing the peroxide cross-linked polyethylene pipe described in Example 1 comprises the following steps:

[0150] Add the components according to the weight parts in Table 1 into a high-speed mixer and stir at a temperature of 25°C and a speed of 1200 r / min for 20 min to obtain a premix;

[0151] The premix is ​​conveyed to a co-rotating twin-screw extruder at a feeding rate of 150 kg / h through a loading and unloading system for melt extrusion to obtain a pipe blank; wherein the twin-screw aspect ratio is 30:1, the screw speed is 35 r / min, and during melt extrusion, the set temperatures of the twin-screw extruder from the feed port to the die are: zone 1 temperature 140-150°C, zone 2 temperature 150-160°C, zone 3 temperature 160-170°C, zone 4 temperature 150-160°C, zone 5 temperature 160-170°C, and zone 6 temperature 160-180°C;

[0152] The pipe blank is placed in a pre-crosslinking mechanism and sequentially subjected to a first pre-crosslinking treatment, a second pre-crosslinking treatment, and a third pre-crosslinking treatment to obtain a pre-crosslinked pipe, wherein the temperature of the first pre-crosslinking treatment is 195°C, the time is 5s; the temperature of the second pre-crosslinking treatment is 200°C, the time is 5s, and the heating rate is 5°C / s; the temperature of the third pre-crosslinking treatment is 230°C, the time is 5s, and the heating rate is 30°C / s;

[0153] The pre-crosslinked pipe is added to the main crosslinking mechanism and sequentially subjected to the first main crosslinking treatment, the second main crosslinking treatment and the third main crosslinking treatment to obtain a crosslinked pipe; wherein the temperature of the first main crosslinking treatment is 245°C, the time is 5s; the temperature of the second main crosslinking treatment is 275°C, the time is 5s, and the heating rate is 30°C / s; the temperature of the third main crosslinking treatment is 235°C, the time is 5s, and the cooling rate is 30°C / s;

[0154] The cross-linked pipe is placed in a vacuum tank for vacuum setting, and the obtained pipe is placed in a cooling water tank for a first cooling treatment, a second cooling treatment, and a third cooling treatment in sequence, and then stretched by a stretching machine and collected by a winder to obtain a semi-finished product; wherein, the end temperature of the first cooling treatment is 75°C, and the time is 5 minutes; the end temperature of the second cooling treatment is 50°C, and the time is 5 minutes, and the cooling rate is 10°C / min; the end temperature of the third cooling treatment is 25°C, and the time is 5 minutes, and the cooling rate is 10°C / min;

[0155] The semi-finished product was placed in a hot air circulation oven and heat treated at 85° C. for 24 hours to obtain a peroxide cross-linked polyethylene pipe.

[0156] The method for preparing the peroxide cross-linked polyethylene pipe described in Example 2 comprises the following steps:

[0157] Add the components according to the weight parts in Table 1 into a high-speed mixer and stir at a temperature of 25°C and a speed of 1200 r / min for 20 min to obtain a premix;

[0158] The premix is ​​conveyed to a co-rotating twin-screw extruder at a feeding rate of 150 kg / h through a loading and unloading system for melt extrusion to obtain a pipe blank; wherein the twin-screw aspect ratio is 30:1, the screw speed is 35 r / min, and during melt extrusion, the set temperatures of the twin-screw extruder from the feed port to the die are: zone 1 temperature 140-150°C, zone 2 temperature 150-160°C, zone 3 temperature 160-170°C, zone 4 temperature 150-160°C, zone 5 temperature 160-170°C, and zone 6 temperature 160-180°C;

[0159] The pipe blank is placed in a pre-crosslinking mechanism and sequentially subjected to a first pre-crosslinking treatment, a second pre-crosslinking treatment, and a third pre-crosslinking treatment to obtain a pre-crosslinked pipe, wherein the temperature of the first pre-crosslinking treatment is 200°C, the time is 5s; the temperature of the second pre-crosslinking treatment is 205°C, the time is 5s, and the heating rate is 5°C / s; the temperature of the third pre-crosslinking treatment is 240°C, the time is 5s, and the heating rate is 35°C / s;

[0160] The pre-crosslinked pipe is added to the main crosslinking mechanism and sequentially subjected to the first main crosslinking treatment, the second main crosslinking treatment and the third main crosslinking treatment to obtain the main crosslinked pipe; wherein, the temperature of the first crosslinking treatment is 250°C, the time is 5s; the temperature of the second crosslinking treatment is 280°C, the time is 5s, and the heating rate is 30°C / s; the temperature of the third crosslinking treatment is 240°C, the time is 5s, and the cooling rate is 40°C / s;

[0161] The cross-linked pipe is placed in a vacuum tank for vacuum setting, and the obtained pipe is placed in a cooling water tank for a first cooling treatment, a second cooling treatment, and a third cooling treatment in sequence, and then stretched by a stretching machine and collected by a winder to obtain a semi-finished product; wherein, the end temperature of the first cooling treatment is 75°C, and the time is 5 minutes; the end temperature of the second cooling treatment is 50°C, and the time is 5 minutes, and the cooling rate is 10°C / min; the end temperature of the third cooling treatment is 25°C, and the time is 5 minutes, and the cooling rate is 10°C / min;

[0162] The semi-finished product was placed in a hot air circulation oven and heat treated at 85° C. for 24 hours to obtain a peroxide cross-linked polyethylene pipe.

[0163] The preparation method of the peroxide cross-linked polyethylene pipe of Examples 3-13 and Comparative Examples 1-5 comprises the following steps:

[0164] Add the components according to the weight parts of Table 1 and Table 2 into a high-speed mixer, and stir at a temperature of 25°C and a speed of 1200 r / min for 20 min to obtain a premix;

[0165] The premix is ​​conveyed to a co-rotating twin-screw extruder at a feeding rate of 150 kg / h through a loading and unloading system for melt extrusion to obtain a pipe blank; wherein the twin-screw aspect ratio is 30:1, the screw speed is 35 r / min, and during melt extrusion, the set temperatures of the twin-screw extruder from the feed port to the die are: zone 1 temperature 140-150°C, zone 2 temperature 150-160°C, zone 3 temperature 160-170°C, zone 4 temperature 150-160°C, zone 5 temperature 160-170°C, and zone 6 temperature 160-180°C;

[0166] The pipe blank is placed in a pre-crosslinking mechanism and sequentially subjected to a first pre-crosslinking treatment, a second pre-crosslinking treatment, and a third pre-crosslinking treatment to obtain a pre-crosslinked pipe, wherein the temperature of the first pre-crosslinking treatment is 195°C, the time is 5s; the temperature of the second pre-crosslinking treatment is 200°C, the time is 5s, and the heating rate is 5°C / s; the temperature of the third pre-crosslinking treatment is 230°C, the time is 5s, and the heating rate is 30°C / s;

[0167] The pre-crosslinked pipe is added to the main crosslinking mechanism and sequentially subjected to the first main crosslinking treatment, the second main crosslinking treatment and the third main crosslinking treatment to obtain a crosslinked pipe; wherein the temperature of the first main crosslinking treatment is 245°C, the time is 5s; the temperature of the second main crosslinking treatment is 275°C, the time is 5s, and the heating rate is 30°C / s; the temperature of the third main crosslinking treatment is 235°C, the time is 5s, and the cooling rate is 30°C / s;

[0168] The cross-linked pipe is placed in a vacuum tank for vacuum setting, and the obtained pipe is placed in a cooling water tank for a first cooling treatment, a second cooling treatment, and a third cooling treatment in sequence, and then stretched by a stretching machine and collected by a winder to obtain a semi-finished product; wherein, the end temperature of the first cooling treatment is 75°C, and the time is 5 minutes; the end temperature of the second cooling treatment is 50°C, and the time is 5 minutes, and the cooling rate is 10°C / min; the end temperature of the third cooling treatment is 25°C, and the time is 5 minutes, and the cooling rate is 10°C / min;

[0169] The semi-finished product was placed in a hot air circulation oven and heat treated at 85° C. for 24 hours to obtain a peroxide cross-linked polyethylene pipe.

[0170] Table 1

[0171]

[0172] Table 2

[0173]

[0174] Example 14

[0175] The composition of the peroxide cross-linked polyethylene pipe in this embodiment is the same as that in Example 1.

[0176] The method for preparing the peroxide-crosslinked polyethylene pipe in this embodiment differs from the method for preparing the peroxide-crosslinked polyethylene pipe in Example 1 only in that the pre-crosslinking treatment step in the preparation method is different. The pre-crosslinking treatment step in this embodiment is as follows: the pipe blank is added to the pre-crosslinking mechanism and sequentially subjected to a first pre-crosslinking treatment, a second pre-crosslinking treatment, and a third pre-crosslinking treatment to obtain a pre-crosslinked pipe, wherein the temperature of the first pre-crosslinking treatment, the second pre-crosslinking treatment, and the third pre-crosslinking treatment are all 210° C., and the time is all 5 seconds.

[0177] Example 15

[0178] The composition of the peroxide cross-linked polyethylene pipe in this embodiment is the same as that in Example 1.

[0179] The method for preparing the peroxide-crosslinked polyethylene pipe of this embodiment differs from the method for preparing the peroxide-crosslinked polyethylene pipe of Example 1 only in that the main crosslinking treatment step in the preparation method is different. The main crosslinking treatment steps in this embodiment are as follows: the pre-crosslinked pipe is added to the main crosslinking mechanism and sequentially subjected to the first main crosslinking treatment, the second main crosslinking treatment, and the third main crosslinking treatment to obtain the crosslinked pipe; wherein the temperature of the first crosslinking treatment, the second crosslinking treatment, and the third crosslinking treatment are all 250°C, and the time is all 5 seconds.

[0180] Example 16

[0181] The composition of the peroxide cross-linked polyethylene pipe in this embodiment is the same as that in Example 1.

[0182] The method for preparing the peroxide-cross-linked polyethylene pipe of this embodiment differs from the method for preparing the peroxide-cross-linked polyethylene pipe of Example 1 only in that the cooling and shaping step in the preparation method is different. The cooling and shaping step in this embodiment is as follows: the cross-linked pipe is placed in a vacuum tank for vacuum shaping, the obtained pipe is placed in a cooling water tank for cooling treatment, and then stretched by a stretching machine and collected by a winder to obtain a semi-finished product; wherein, the end temperature of the cooling is 25°C, the cooling time is 15 minutes, and the cooling rate is 10°C / min.

[0183] Performance Testing

[0184] The peroxide cross-linked polyethylene pipes obtained in the examples and comparative examples were subjected to performance tests, and the test methods were as follows:

[0185] (1) Degree of cross-linking: ASTM D2765-16 (2024) (xylene extraction method), calculate the mass fraction of insoluble matter;

[0186] (2) Tensile strength: ISO 6529-2:2020, test speed 50 mm / min, dumbbell-shaped specimen;

[0187] (3) Heat deformation temperature: ISO 75-2:2013, temperature at load 0.45 MPa and deformation 2 mm;

[0188] (4) Environmental stress cracking time: ASTM D1693-15, polyoxyethylene (9) nonylphenyl ether (CAS No. 68412-54-4) solution with a mass volume concentration of 50 g / mL, type A specimen, notch depth of 0.3 mm, cracking time was recorded at 80°C;

[0189] (5) Radiation resistance: ASTM D1879-06 (2023), using cobalt-60 gamma ray irradiation, a dose rate of 5 kGy / h, a total absorbed dose of 200 kGy, to test the tensile strength retention and surface morphology changes after irradiation;

[0190] (6) Antioxidant properties: ISO 11346:2014 (oxidation induction time method, OIT), test conditions: 200 °C, oxygen flow rate 50 mL / min, record the oxidation induction time (minutes), which reflects the antioxidant ability of the material.

[0191] The test results are shown in Table 3.

[0192] Table 3

[0193]

[0194] It can be seen from the experimental data in Table 3 that the peroxide cross-linked polyethylene of the present invention has a crosslinking degree of greater than or equal to 70%, a tensile strength of greater than or equal to 23 MPa, a heat deformation temperature of greater than or equal to 105° C., and an environmental stress cracking resistance time of greater than or equal to 500 h. After radiation, the tensile strength retention rate is greater than or equal to 85%, and the antioxidant performance is greater than or equal to 35 min.

[0195] From the experimental data of Example 1 and Example 4-5, it can be seen that the peroxide crosslinking agents are benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and the obtained peroxide cross-linked polyethylene has a crosslinking degree greater than or equal to 85%, a tensile strength greater than or equal to 28 MPa, a heat deformation temperature greater than or equal to 120°C, and an environmental stress cracking resistance time ≥800h. After radiation, the tensile strength retention rate is greater than or equal to 95%, and the antioxidant performance is greater than or equal to 45min, indicating that the compound use of benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane can improve the overall performance of peroxide cross-linked polyethylene.

[0196] From the comparison of Example 1 and Examples 6-8, it can be seen that the antioxidants are hindered amine antioxidants and thioester antioxidants; the obtained peroxide cross-linked polyethylene has a crosslinking degree greater than or equal to 85%, a tensile strength greater than or equal to 28 MPa, a heat deformation temperature greater than or equal to 120°C, and an environmental stress cracking resistance time greater than or equal to 800 h. After radiation, the tensile strength retention rate is greater than or equal to 95%, and the antioxidant performance is greater than or equal to 45 min, indicating that the combined use of hindered amine antioxidants and thioester antioxidants can improve the overall performance of peroxide cross-linked polyethylene.

[0197] From the experimental data of Examples 1 and 9-10, it can be seen that the lubricant is ethylene bisstearamide and silicone powder; the crosslinking degree of the obtained peroxide cross-linked polyethylene is greater than or equal to 85%, the tensile strength is greater than or equal to 28 MPa, the heat deformation temperature is greater than or equal to 120°C, the environmental stress cracking resistance time is greater than or equal to 800h, and after radiation, the tensile strength retention rate is greater than or equal to 95%, and the antioxidant performance is greater than or equal to 45min, indicating that the compound use of ethylene bisstearamide and silicone powder can improve the overall performance of peroxide cross-linked polyethylene.

[0198] From the experimental data of Example 1 and Examples 11-13, it can be seen that when the mass ratio of the borate-containing polymer, N,N'-m-phenylene bismaleimide, and trimethylolpropane trimethacrylate is (0.8-1):(1-1.5):(1-1.5), the obtained peroxide-crosslinked polyethylene has a crosslinking degree greater than or equal to 84%, a tensile strength greater than or equal to 27 MPa, a heat deformation temperature greater than or equal to 119°C, and an environmental stress cracking resistance time greater than or equal to 770 h. After irradiation, the tensile strength retention rate is greater than or equal to 93%, and the antioxidant performance is greater than or equal to 43 min. This indicates that when the mass ratio of the borate-containing polymer, N,N'-m-phenylene bismaleimide, and trimethylolpropane trimethacrylate is (0.8-1):(1-1.5):(1-1.5), the overall performance of the peroxide-crosslinked polyethylene can be improved.

[0199] By comparing Example 1 with Examples 14-16, it can be seen that the use of single-temperature treatment for pre-crosslinking treatment, main crosslinking treatment or cooling treatment will lead to a decrease in the overall performance of peroxide cross-linked polyethylene, indicating that the pre-crosslinking treatment, main crosslinking treatment and cooling treatment adopt multi-stage variable temperature treatment. The multi-stage variable temperature process controls the crosslinking rate in stages, avoids local stress concentration, improves material uniformity, and improves the overall performance of peroxide cross-linked polyethylene.

[0200] By comparing Example 1 with Comparative Examples 1-4, it can be seen that when a single co-crosslinking agent is used, the crosslinking degree of the obtained peroxide cross-linked polyethylene is less than or equal to 70%, the tensile strength is less than or equal to 20 MPa, the heat deformation temperature is less than or equal to 100°C, and the environmental stress cracking resistance time is less than or equal to 300h. After radiation, the tensile strength retention rate is less than or equal to 50%, and the antioxidant performance is less than or equal to 8min, indicating that there is a synergistic effect between N,N'-m-phenylene bismaleimide, trimethylolpropane trimethacrylate and the polymer containing borate bonds. The three components synergistically enhance the dynamic reversibility and self-repair ability of the cross-linked network, effectively improving the overall performance of the peroxide cross-linked polyethylene pipe.

[0201] By comparing Example 1 and Comparative Example 5, it can be seen that when linear low-density polyethylene is used instead of ultra-low-density polyethylene, the obtained peroxide cross-linked polyethylene has a cross-linking degree of 65%, a tensile strength of 18 MPa, a heat deformation temperature of 95°C, and an environmental stress cracking time of 150 h. After radiation, the tensile strength retention rate is 40%, and the antioxidant performance is 5 min, indicating that only ultra-low-density polyethylene can improve the overall performance of peroxide polyethylene pipes.

[0202] The fracture morphology of the peroxide cross-linked polyethylene pipes obtained in the examples and comparative examples was observed using a scanning electron microscope. Figure 7-8 As shown. Figure 7-8 It can be seen that the cross-section of the peroxide cross-linked polyethylene pipe obtained in Example 1 presents a uniform dimple structure, indicating that the cross-linked network is uniformly dispersed; the cross-section of the peroxide cross-linked polyethylene pipe obtained in Comparative Example 3 has obvious cracks and voids, indicating that the defects are caused by uneven cross-linking.

[0203] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present disclosure rather than to limit the scope of protection of the present disclosure. Although the present disclosure has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present disclosure may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present disclosure.

Claims

1. A peroxide cross-linked polyethylene pipe, characterized in that: The invention comprises the following components in parts by weight: 99-101 parts of polyethylene resin, 0.7-1.6 parts of peroxide crosslinking agent, 0.4-1.3 parts of auxiliary crosslinking agent, 0.25-0.6 parts of antioxidant and 0.15-0.35 parts of lubricant; The polyethylene resin includes high-density polyethylene and ultra-low-density polyethylene, and the density of the high-density polyethylene is 0.955-0.970 g / cm 3 The density of the ultra-low density polyethylene is 0.860-0.900 g / cm 3 ; The auxiliary cross-linking agent is a polymer containing a borate ester bond, N,N'-m-phenylene bismaleimide and trimethylolpropane trimethacrylate; The mass ratio of the borate ester bond-containing polymer, N,N'-m-phenylene bismaleimide and trimethylolpropane trimethacrylate is (0.5-1.2): (1-1.5): (1-1.5); The mass ratio of the high-density polyethylene to the ultra-low-density polyethylene is (7-9): (1-3); The preparation method of the borate ester bond-containing polymer is as follows: reacting pentaerythritol, an unsaturated acid, and an acidic catalyst in an inert atmosphere at a temperature of 80-120° C. for 4-8 hours to obtain an esterification product; After cooling the esterification product to 60-80°C, adding boric acid and a complexing agent, reacting at 80-100°C for 2-4 hours, removing impurities, and obtaining a polymer containing borate ester bonds; The molar ratio of pentaerythritol to unsaturated acid is 1:3; The mass of the acidic catalyst is 0.5-2% of the total mass of the polyol and the unsaturated acid; The molar ratio of pentaerythritol to boric acid is 1:(0.8-1.2); The molar ratio of the polyol to the complexing agent is 1:(0.9-1.1); The unsaturated acid is at least one of acrylic acid and methacrylic acid; The acidic catalyst is p-toluenesulfonic acid; The complexing agent is at least one of ethanolamine and triethanolamine.

2. The peroxide cross-linked polyethylene pipe according to claim 1, characterized in that: The high-density polyethylene has a melt index of 0.6-1.8 g / 10 min; And / or, the ultra-low density polyethylene has a melt index of 1.2-3.5 g / 10 min.

3. The peroxide cross-linked polyethylene pipe according to claim 1, characterized in that: The peroxide crosslinking agent is at least one of benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane; And / or, the antioxidant is at least one of a hindered amine antioxidant and a thioester antioxidant; And / or, the lubricant is at least one of low molecular weight esters, metal soaps, stearic acid complex esters, and amides.

4. The peroxide cross-linked polyethylene pipe according to claim 3, characterized in that: The peroxide crosslinking agent is benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane, and the mass ratio of the benzoyl peroxide and 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane is (1-1.5):(1-1.5); And / or, the antioxidant is a hindered amine antioxidant and a thioester antioxidant, and the mass ratio of the hindered amine antioxidant to the thioester antioxidant is (2-2.5): (1-1.5); And / or, the lubricant is ethylene bisstearamide and silicone powder, and the mass ratio of ethylene bisstearamide to silicone powder is (1-1.5):(1-1.5).

5. A method for preparing a peroxide cross-linked polyethylene pipe according to any one of claims 1 to 4, characterized in that: The following steps are involved: Mix the components uniformly in proportion to obtain a premix; The premix is ​​added into a screw extruder for melt extrusion to obtain a pipe blank; The pipe blank is subjected to a pre-crosslinking treatment and a main crosslinking treatment in sequence under infrared irradiation, and the obtained crosslinked pipe is cooled and post-treated to obtain a peroxide crosslinked polyethylene pipe.

6. The method for preparing a peroxide cross-linked polyethylene pipe according to claim 5, wherein: The mixing parameters satisfy at least one of the following: temperature below 38°C, rotation speed 1000-1400 r / min, and time 15-25 min; And / or, the melt extrusion parameters meet at least one of the following: screw aspect ratio of 28-30:1, temperature of 140-180°C, screw speed of 30-40 r / min, and feeding rate of 150-200 kg / h; and / or, the pre-crosslinking treatment is performed at a temperature of 185-230° C. and for a time of 9-15 seconds; and / or, the main cross-linking treatment is performed at a temperature of 230-280° C. for a time of 9-15 seconds; And / or, the cooling end temperature is 20-30°C, and the cooling rate is 5-10°C / min; And / or, the post-treatment temperature is 70-100° C. and the time is 20-30 h.

7. The method for preparing a peroxide cross-linked polyethylene pipe according to claim 5, wherein: During the melt extrusion, the setting temperatures of the screw extruder from the feed port to the die head are: zone 1 temperature 140-150°C, zone 2 temperature 150-160°C, zone 3 temperature 160-170°C, zone 4 temperature 150-160°C, zone 5 temperature 160-170°C, zone 6 temperature 160-180°C; And / or, the pre-crosslinking treatment includes a first pre-crosslinking treatment, a second pre-crosslinking treatment, and a third pre-crosslinking treatment performed sequentially, wherein the temperature of the first pre-crosslinking treatment is 185-195° C., the temperature of the second pre-crosslinking treatment is 195-205° C., and the temperature of the third pre-crosslinking treatment is 205-230° C.; the time for the first pre-crosslinking treatment, the second pre-crosslinking treatment, and the third pre-crosslinking treatment is each independently 3-5 s, and the heating rate is each independently 5-10° C. / s; And / or, the main cross-linking treatment includes a first main cross-linking treatment, a second main cross-linking treatment, and a third main cross-linking treatment performed sequentially, wherein the temperature of the first main cross-linking treatment is 240-250° C., the temperature of the second main cross-linking treatment is 260-280° C., and the temperature of the third main cross-linking treatment is 230-245° C.; and the time of the first main cross-linking treatment, the second main cross-linking treatment, and the third main cross-linking treatment is each independently 3-5 seconds; And / or, the cooling includes a first cooling treatment, a second cooling treatment and a third cooling treatment performed in sequence, wherein the endpoint temperature of the first cooling treatment is 70-85°C, the endpoint temperature of the second cooling treatment is 40-55°C, and the endpoint temperature of the third cooling treatment is 20-30°C.

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