A method for preparing heat-resistant modified polyethylene composite pipe

Abstract

The present invention relates to the field of polyethylene technology, and discloses a preparation method of a heat-resistant modified polyethylene composite pipe. The present invention mixes 100 parts by weight of polyethylene, 15-25 parts by weight of ammonium polyphosphate, 5-20 parts by weight of a nitrogen-rich carbonizing agent, 10-20 parts by weight of a filler, and the like, and extrude the mixture to obtain a heat-resistant modified polyethylene composite pipe. Ammonium polyphosphate is used as an acid source, the nitrogen heterocycle in the nitrogen-rich carbonizing agent is used as a gas source, and the aromatic ring is used as a carbon source to form an intumescent flame retardant. When burned, a foam carbon layer is formed on the surface of the polyethylene pipe, which has the effects of heat insulation and oxygen isolation, smoke suppression, and anti-melting dripping, thereby significantly improving the flame retardant properties of the polyethylene material. As a macromolecular polymer, the nitrogen-rich carbonizing agent has good heat resistance and contains a thermally stable phenylimide structure, which significantly increases the initial thermal decomposition temperature and the maximum thermal decomposition rate temperature of the polyethylene pipe, thereby improving heat resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of polyethylene, in particular to a method for preparing a heat-resistant modified polyethylene composite pipe. Background Art

[0002] Polyethylene pipes feature simple molding processes, high mechanical strength, and excellent corrosion resistance, making them widely used in gas transportation, biogas projects, and industrial pipelines. However, traditional polyethylene and its pipe products suffer from poor flame retardancy, limiting their practical applications. Ammonium polyphosphate (AMP) is a high-performance halogen-free flame retardant, offering advantages such as high flame retardancy, environmental friendliness, and minimal impact on the mechanical properties of materials. It can improve the flame retardancy of polymers such as polyethylene, polyvinyl chloride (PVC), polyurethane, and polylactic acid. However, AMP has a low thermal decomposition temperature, and its addition to polymers like polyethylene can affect their heat resistance.

[0003] Ammonium polyphosphate is compounded with carbonizing agents such as triazines and pentaerythritol to obtain an intumescent flame retardant that can achieve a better flame retardant effect. Patent No. CN114773707B discloses β-cyclodextrin microencapsulated ammonium polyphosphate intumescent flame-retardant low-density polyethylene and its preparation method. β-cyclodextrin microencapsulated ammonium polyphosphate and tris (2-hydroxyethyl) isocyanurate are used as intumescent flame retardants to improve the flame retardant properties of polyethylene. However, this patent does not improve the heat resistance of polyethylene. Guanine is a cheap and readily available nitrogen-rich compound with broad application prospects in carbonizing agents and flame retardants. For example, Chinese patent CN109400957B, an alkaloid phosphate flame retardant and its preparation method, both report that guanine can be used as a flame retardant additive to improve the flame retardant properties of materials. Summary of the Invention

[0004] (1) Technical problems to be solved: In view of the deficiencies of the existing technology, the present invention provides a method for preparing a modified polyethylene composite pipe with good heat resistance and excellent flame retardancy.

[0005] (II) Technical solution: A method for preparing heat-resistant modified polyethylene composite pipe:

[0006] (1) Add pyromellitic anhydride and guanine to N,N-dimethylformamide, heat to 130-140°C, react for 12-18 hours, distill under reduced pressure, wash with methanol, and recrystallize the product from dichloromethane to obtain pyromellitic imide guanine.

[0007] (2) Add trimesoyl chloride, trimesoylguanine and triethylamine to N,N-dimethylformamide, react at 20-30°C for 18-24 hours, filter, wash with water and dichloromethane, and dry to obtain a nitrogen-rich carbon-forming agent.

[0008] (3) 100 parts by weight of polyethylene, 15-25 parts by weight of ammonium polyphosphate, 5-20 parts by weight of nitrogen-rich carbon-forming agent, 0.6-1.2 parts by weight of external lubricant, 0.3-0.7 parts by weight of internal lubricant, 10-20 parts by weight of filler, and 2-6 parts by weight of compatibilizer are added to a mixer and mixed. The mixture is placed in an extruder and extruded to obtain a heat-resistant modified polyethylene composite pipe.

[0009] Preferably, the molar ratio of pyromellitic anhydride to guanine in (1) is 1:(2-2.1).

[0010] Preferably, the molar ratio of trimesoyl chloride, pyromellitic imide guanine, and triethylamine in (2) is 1:(1.5-1.6):(3-3.3).

[0011] Preferably, the filler in (3) is calcium carbonate, hematite or barium sulfate.

[0012] Preferably, the compatibilizer in (3) is maleic anhydride grafted polyethylene or maleic anhydride grafted polyethylene wax.

[0013] Preferably, (3) the external lubricant is calcium stearate or zinc stearate, and the internal lubricant is white oil.

[0014] (III) Technical effects of the present invention: The present invention utilizes the imino group of pyromellitic imide guanine to react with pyromellitic trimesic chloride to polymerize and obtain a nitrogen-rich carbon-forming agent containing a phenylimide ring and a guanine structure, which is then blended with polyethylene, ammonium polyphosphate, hematite and other fillers, maleic anhydride grafted polyethylene and other compatibilizers to obtain a heat-resistant modified polyethylene composite pipe. Ammonium polyphosphate serves as an acid source, the nitrogen heterocycle in the nitrogen-rich carbon-forming agent serves as a gas source, and the aromatic ring serves as a carbon source to form an intumescent flame retardant. When burned, it produces non-combustible gases such as nitrogen. At the same time, ammonium polyphosphate pyrolyzes to generate phosphoric acid substances, which promote the dehydration of the nitrogen-rich carbon-forming agent to form carbon, forming a foam carbon layer on the surface of the polyethylene pipe. This layer has the functions of heat insulation, oxygen isolation, smoke suppression, and anti-melting dripping, significantly improving the limiting oxygen index, UL94 rating and flame retardant properties of the material.

[0015] The nitrogen-rich carbon-forming agent of the present invention is a macromolecular polymer with good heat resistance and contains a thermally stable phenylimide structure. When added to polyethylene pipes, it significantly increases the initial thermal decomposition temperature and the maximum thermal decomposition rate temperature, thereby improving the heat resistance of the pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the reaction formula for preparing pyromellityl imide guanine.

[0017] Figure 2 This is the reaction formula for preparing nitrogen-rich carbon-forming agent. DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto. Example 1

[0019] (1) Add 60 mmol of pyromellitic anhydride and 120 mmol of guanine to 100 mL of N,N-dimethylformamide, heat to 140°C, react for 12 h, distill under reduced pressure, wash with methanol, and recrystallize the product from dichloromethane to obtain pyromellitic imide guanine.

[0020] (2) Add 40 mmol of trimesoyl chloride, 60 mmol of guanine tetracarboxylic acid imide, and 126 mmol of triethylamine to 700 mL of N,N-dimethylformamide, and react at 25°C for 24 h. After filtering, wash with water and dichloromethane, and dry, a nitrogen-rich carbon-forming agent is obtained.

[0021] (3) Add 2 kg of polyethylene, 500 g of ammonium polyphosphate, 100 g of nitrogen-rich carbonizing agent, 20 g of external lubricant zinc stearate, 8 g of internal lubricant white oil, 320 g of filler barium sulfate (average particle size 1250 mesh), and 100 g of compatibilizer maleic anhydride grafted polyethylene into a mixer and mix for 30 minutes. Place the mixture in an extruder with a melt temperature of 180 ° C and a screw speed of 80 r / min for extrusion molding to obtain a heat-resistant modified polyethylene composite pipe.

[0022] Comparative Example 1: The difference between this comparative example and Example 1 is that no nitrogen-rich carbon-forming agent is added.

[0023] (1) 2 kg polyethylene, 500 g ammonium polyphosphate, 20 g external lubricant zinc stearate, 8 g internal lubricant white oil, 320 g filler barium sulfate (average particle size 1250 mesh), and 100 g compatibilizer maleic anhydride grafted polyethylene were added to a mixer and mixed for 30 min. The mixture was placed in an extruder with a melt temperature of 180 ° C and a screw speed of 80 r / min for extrusion molding to obtain a modified polyethylene composite pipe.

[0024] Comparative Example 2: The main difference between this comparative example and Example 1 is that guanine is used instead of the nitrogen-rich carbon-forming agent.

[0025] (1) 2 kg polyethylene, 500 g ammonium polyphosphate, 100 g guanine, 20 g external lubricant zinc stearate, 8 g internal lubricant white oil, 320 g filler barium sulfate (average particle size 1250 mesh), and 100 g compatibilizer maleic anhydride grafted polyethylene were added to a mixer and mixed for 30 min. The mixture was placed in an extruder with a melt temperature of 180 ° C and a screw speed of 80 r / min for extrusion molding to obtain a modified polyethylene composite pipe.

[0026] Comparative Example 3: The main difference between this comparative example and Example 1 is that guanine is used instead of pyromellityl guanine when preparing the nitrogen-rich carbon-forming agent.

[0027] (1) Add 40 mmol of trimesoyl chloride, 60 mmol of guanine, and 126 mmol of triethylamine to 700 mL of N,N-dimethylformamide, and react at 25°C for 24 h. After filtering, wash with water and dichloromethane, and dry, a nitrogen-rich carbonizing agent is obtained.

[0028] (2) 2 kg polyethylene, 500 g ammonium polyphosphate, 100 g nitrogen-rich carbonizing agent, 20 g external lubricant zinc stearate, 8 g internal lubricant white oil, 320 g filler barium sulfate (average particle size 1250 mesh), and 100 g compatibilizer maleic anhydride grafted polyethylene were added to a mixer and mixed for 30 min. The mixture was placed in an extruder with a melt temperature of 180 ° C and a screw speed of 80 r / min for extrusion molding to obtain a modified polyethylene composite pipe.

[0029] Comparative Example 4: The main difference between this comparative example and Example 1 is that melamine is used instead of pyromellitimide guanine when preparing the nitrogen-rich carbon-forming agent.

[0030] (1) Add 40 mmol of trimesoyl chloride, 40 mmol of melamine, and 126 mmol of triethylamine to 700 mL of N,N-dimethylformamide, and react at 25°C for 24 h. After filtering, wash with water and dichloromethane, and dry, a nitrogen-rich carbonizing agent is obtained.

[0031] (2) 2 kg polyethylene, 500 g ammonium polyphosphate, 100 g nitrogen-rich carbonizing agent, 20 g external lubricant zinc stearate, 8 g internal lubricant white oil, 320 g filler barium sulfate (average particle size 1250 mesh), and 100 g compatibilizer maleic anhydride grafted polyethylene were added to a mixer and mixed for 30 min. The mixture was placed in an extruder with a melt temperature of 180 ° C and a screw speed of 80 r / min for extrusion molding to obtain a modified polyethylene composite pipe. Example 2

[0032] (1) Add 60 mmol of pyromellitic anhydride and 126 mmol of guanine to 110 mL of N,N-dimethylformamide, heat to 130°C, react for 18 h, distill under reduced pressure, wash with methanol, and recrystallize the product from dichloromethane to obtain pyromellitic imide guanine.

[0033] (2) Add 40 mmol of trimesoyl chloride, 64 mmol of guanine tetracarboxylic acid imide, and 132 mmol of triethylamine to 800 mL of N,N-dimethylformamide, and react at 20°C for 24 h. After filtering, wash with water and dichloromethane, and dry, a nitrogen-rich carbon-forming agent is obtained.

[0034] (3) 2 kg of polyethylene, 430 g of ammonium polyphosphate, 200 g of nitrogen-rich carbonizing agent, 24 g of external lubricant calcium stearate, 6 g of internal lubricant white oil, 200 g of filler hematite (average particle size 800 mesh), and 40 g of compatibilizer maleic anhydride grafted polyethylene were added to a mixer and mixed for 30 min. The mixture was placed in an extruder with a melt temperature of 180 ° C and a screw speed of 80 r / min for extrusion molding to obtain a heat-resistant modified polyethylene composite pipe. Example 3

[0035] (1) Prepare pyromellitic imide guanine according to the method of Example 1.

[0036] (2) Add 40 mmol of trimesoyl chloride, 60 mmol of guanine tetracarboxylic acid imide, and 132 mmol of triethylamine to 700 mL of N,N-dimethylformamide, and react at 25°C for 18 h. After filtering, wash with water and dichloromethane, and dry, a nitrogen-rich carbon-forming agent is obtained.

[0037] (3) 2 kg of polyethylene, 370 g of ammonium polyphosphate, 300 g of nitrogen-rich carbonizing agent, 12 g of external lubricant zinc stearate, 14 g of internal lubricant white oil, 400 g of filler barium sulfate (average particle size 1250 mesh), and 120 g of compatibilizer maleic anhydride grafted polyethylene were added to a mixer and mixed for 30 min. The mixture was placed in an extruder with a melt temperature of 180 ° C and a screw speed of 80 r / min for extrusion molding to obtain a heat-resistant modified polyethylene composite pipe. Example 4

[0038] (1) Prepare pyromellitic imide guanine according to the method of Example 1.

[0039] (2) Add 40 mmol of trimesoyl chloride, 60 mmol of guanine tetracarboxylic acid imide, and 120 mmol of triethylamine to 700 mL of N,N-dimethylformamide, and react at 30°C for 18 h. After filtering, wash with water and dichloromethane, and dry, a nitrogen-rich carbon-forming agent is obtained.

[0040] (3) Add 2 kg of polyethylene, 300 g of ammonium polyphosphate, 400 g of nitrogen-rich carbonizing agent, 20 g of external lubricant calcium stearate, 8 g of internal lubricant white oil, 280 g of filler calcium carbonate (average particle size 1500 mesh), and 90 g of compatibilizer maleic anhydride grafted polyethylene wax into a mixer and mix for 30 minutes. Place the mixture in an extruder with a melting temperature of 180 ° C and a screw speed of 80 r / min for extrusion molding to obtain a heat-resistant modified polyethylene composite pipe.

[0041] 10 mg of polyethylene composite pipe was weighed and placed in a thermogravimetric analyzer for thermogravimetric analysis. The atmosphere was nitrogen, the heating rate was 10°C / min, and the maximum test temperature was 600°C.

[0042] Oxygen index was tested according to GB / T 2406.1-2008. Vertical burning performance was tested according to UL94.

[0043] Table 1 Pipe performance test

[0044]

[0045] After testing, the polyethylene pipe of Comparative Example 1 only added ammonium polyphosphate, the limiting oxygen index of the pipe was low, the UL94 grade was only V-2, the flame retardancy was poor, and after the addition of ammonium polyphosphate, the heat resistance of the pipe deteriorated, and the initial thermal decomposition temperature and the maximum thermal decomposition rate temperature were low.

[0046] In Example 1-4, ammonium polyphosphate is added as an acid source, the nitrogen heterocycle in the nitrogen-rich carbon-forming agent is used as a gas source, and the aromatic ring is used as a carbon source to form an intumescent flame retardant. When burned, non-combustible gases such as nitrogen are generated. At the same time, ammonium polyphosphate is pyrolyzed to generate phosphoric acid substances, which promotes the dehydration of the nitrogen-rich carbon-forming agent to form carbon, forming a foam carbon layer on the surface of the polyethylene pipe. It has the functions of heat insulation, oxygen isolation, smoke suppression, and anti-melting dripping, and significantly improves the limiting oxygen index, UL94 grade and flame retardant performance of the material. In addition, as a macromolecular polymer, the nitrogen-rich carbon-forming agent itself has good heat resistance, and it also contains a thermally stable phenylimide structure ( ), added to polyethylene pipes, significantly increased the thermal decomposition temperature and improved heat resistance.

[0047] In Comparative Example 2, ammonium polyphosphate and guanine were added. Guanine, as a small molecule compound, has poor thermal stability, which reduces the initial thermal decomposition temperature and the maximum thermal decomposition rate temperature of the polyethylene pipe, and deteriorates the heat resistance.

[0048] Comparative Example 3 utilizes the amino and imino groups of guanine to react with trimesoyl chloride to produce a nitrogen-rich char-forming agent. The resulting polymerization does not contain a thermally stable phenylimide structure, does not significantly increase the thermal decomposition temperature of the polyethylene pipe, and exhibits lower heat resistance than Example 1. Furthermore, the char-forming performance of the char-forming agent is inferior to that of Example 1, resulting in a lower limiting oxygen index.

[0049] Comparative Example 4: The nitrogen-rich char-forming agent obtained by reacting the amino group of melamine with trimesoyl chloride does not contain a thermally stable phenylimide structure, does not significantly increase the thermal decomposition temperature of the polyethylene pipe, and has lower heat resistance than Example 1. Furthermore, the char-forming performance of the char-forming agent is lower than that of the nitrogen-rich char-forming agent in Example 1, resulting in a lower limiting oxygen index.

[0050] The present invention is not limited to the above-mentioned embodiments. Any modification, improvement, or substitution that can be conceived by those skilled in the art without departing from the essential content of the present invention shall fall within the scope of the present invention.

Claims

1. A method for preparing a heat-resistant modified polyethylene composite pipe, characterized in that: The preparation method is: Step 1: adding trimesoyl chloride, pyromellitic imide guanine and triethylamine to N,N-dimethylformamide, filtering after reaction, washing and drying to obtain a nitrogen-rich carbon-forming agent; The structural formula of the pyromellityl imide guanine is as follows: ； Step 2: Add 100 parts by weight of polyethylene, 15-25 parts by weight of ammonium polyphosphate, 5-20 parts by weight of nitrogen-rich carbon-forming agent, 0.6-1.2 parts by weight of external lubricant, 0.3-0.7 parts by weight of internal lubricant, 10-20 parts by weight of filler, and 2-6 parts by weight of compatibilizer into a mixer and mix them. Place the mixture in an extruder and extrude it to obtain a heat-resistant modified polyethylene composite pipe.

2. The method for preparing the heat-resistant modified polyethylene composite pipe according to claim 1, characterized in that: The reaction temperature in step 1 is 20-30° C., and the reaction time is 18-24 h.

3. The method for preparing the heat-resistant modified polyethylene composite pipe according to claim 1, characterized in that: In the step 1, the molar ratio of trimesoyl chloride, pyromellitic imide guanine, and triethylamine is 1:(1.5-1.6):(3-3.3).

4. The method for preparing the heat-resistant modified polyethylene composite pipe according to claim 3, characterized in that: The preparation method of pyromellitic anhydride guanine comprises: adding pyromellitic anhydride and guanine to N,N-dimethylformamide, heating to 130-140° C., reacting for 12-18 hours, performing reduced pressure distillation, washing with methanol, and recrystallizing the product in dichloromethane to obtain pyromellitic anhydride guanine.

5. The method for preparing the heat-resistant modified polyethylene composite pipe according to claim 4, characterized in that: The molar ratio of pyromellitic anhydride to guanine is 1:(2-2.1).

6. The method for preparing the heat-resistant modified polyethylene composite pipe according to claim 1, characterized in that: The filler in step 2 is calcium carbonate, hematite or barium sulfate.

7. The method for preparing the heat-resistant modified polyethylene composite pipe according to claim 1, characterized in that: The compatibilizer in step 2 is maleic anhydride grafted polyethylene or maleic anhydride grafted polyethylene wax.

8. The method for preparing the heat-resistant modified polyethylene composite pipe according to claim 1, characterized in that: In the step 2, the external lubricant is calcium stearate or zinc stearate, and the internal lubricant is white oil.

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