A process for the preparation of a pa510 / 6 block polyamide material

Abstract

The application discloses a preparation method of PA510 / 6 block polyamide material and belongs to the field of high polymer materials. The preparation method comprises the following steps: (1) adding sebacic acid pentamethylene salt and caprolactam into a reaction kettle, stirring, and then introducing a protective gas, sealing the reaction kettle, raising the temperature to 180-200 DEG C under an initial pressure of 0.2-0.5 MPa, adjusting the pressure to 1.6-2.0 MPa, and performing heat preservation and pressure preservation reaction for 1-3 h; (2) releasing the pressure to normal pressure, continuously introducing the protective gas, adding an initiator, raising the temperature to 220-240 DEG C, and performing reaction for 1-1.5 h; and (3) vacuumizing, performing vacuum polycondensation reaction for 0.5-1.5 h under a vacuum degree of 0-900 Pa and a temperature of 220-240 DEG C, and obtaining a PA510 / 6 initial product. The application controls the time of caprolactam ring opening based on the difference between the caprolactam ring opening temperature and the sebacic acid pentamethylene salt polymerization temperature, and prepares the block copolymer bio-based polyamide PA510 / 6 with regular chain segments.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, specifically relating to a method for preparing PA510 / 6 block polyamide material. Background Technology

[0002] Polyamides, as important polymers, are widely used in the automotive, aerospace, and electronics industries due to their excellent mechanical properties and chemical resistance. Currently, most commercially available polyamides are petroleum-based. Petroleum is a non-renewable resource, and its depletion has led to environmental pollution. Therefore, scientists are dedicated to solving the problems of polyamide materials at their source, exploring ways to replace traditional products with polyamide products made from biomass. This innovative approach means shifting from the traditional method of extracting raw materials such as diamines, diacids, and lactams from petroleum products to the production of more environmentally friendly and sustainable biomass-based polyamide products. These biomass-based polyamide products are expected to replace traditional polyamide products in terms of properties and uses, promoting the sustainable development and environmentally friendly manufacturing of polyamide materials.

[0003] Bio-based polyamides are made from renewable resources. First, bio-based polyamide monomers are obtained through bio-fermentation or vegetable oil pyrolysis, and then further condensed to prepare bio-based polyamides. This green and environmentally friendly material originates from plant components such as glucose, cellulose, castor oil, oleic acid, or linoleic acid. Its renewable properties help reduce carbon emissions, meeting the current urgent societal demand for environmental protection and sustainable development.

[0004] PA510 is a novel, fully bio-based polyamide material with excellent anti-friction and low-temperature resistance, widely used in the apparel and textile industries. Compared to traditional petroleum-based nylons such as PA66 and PA6, PA510's raw materials, pentanediamine and sebacic acid, are both bio-based, giving it significant environmental benefits. However, PA510 suffers from relatively weak mechanical properties, a high melting point, poor processing performance, and low overall production capacity, which greatly limits its applications. To address these issues, existing technologies improve its performance through copolymerization with other components. However, multi-component copolymerization often results in high molecular chain segment disorder, leading to lower mechanical properties and molecular weight. Furthermore, the raw material caprolactam in the reaction is a cyclic lactam, requiring the addition of an initiator for ring-opening. Traditional initiators are mostly phosphoric acid, phosphorous acid, metal salts, or polyesters. The addition of these initiators introduces new impurities, and the existing synthesis methods use a "one-pot" addition method, resulting in poor ring-opening effects, a high number of oligomers, a wide molecular weight distribution, and low yield. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a method for preparing PA510 / 6 block polyamide material.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0007] A method for preparing PA510 / 6 block polyamide material includes the following steps:

[0008] (1) Add pentanediamine sebacate and caprolactam to the reactor, stir and purge with nitrogen protective gas. Purge with nitrogen to replace the air in the reactor 2 to 3 times, then seal the reactor. Raise the temperature to 180 to 200°C at an initial pressure of 0.2 to 0.5 MPa, adjust the pressure to 1.6 to 2.0 MPa, and maintain the temperature and pressure for 1 to 3 hours.

[0009] (2) Depressurize to atmospheric pressure, add initiator under continuous nitrogen protection gas, heat to 220-240℃, and react for 1-1.5h;

[0010] (3) Vacuum is drawn and vacuum polycondensation reaction is carried out at a vacuum degree of 0 to 900 Pa for 0.5 to 1.5 h to obtain the initial product PA510 / 6.

[0011] In step (1), the molar ratio of sebacic acid pentanediamine salt to caprolactam is (1-9):(1-9).

[0012] As a preferred option, the molar ratio of sebacic acid pentanediamine salt to caprolactam in step (1) is (7:3) to (1:9).

[0013] Specifically, the initiator in step (2) is one or more of 6-aminohexanoic acid, 5-aminovaleric acid, and 10-aminodecanoic acid; the amount of initiator added is 5-10 wt% of caprolactam. These initiators are either homologous to the raw material of pentanediamine sebacate or are products after caprolactam ring-opening. Choosing such initiators can avoid the introduction of phosphorous acid, metal salts, or ester impurities, which may lead to incomplete ring-opening of caprolactam or cause the system to form dimers and prematurely end-cap, resulting in a large molecular weight distribution.

[0014] In addition, an antioxidant was added to the reactor in step (1). The antioxidant was one or more of antioxidant 1076, antioxidant 1098, and BHT (264), and the amount added was 0.2 to 1 wt% of the total weight of pentanediamine sebacate and caprolactam.

[0015] After obtaining the initial PA510 / 6 product in step (3), the product is further processed: the initial PA510 / 6 product is extruded and pelletized, and then placed at 230-240℃ for solid-phase thickening. After that, water is added for extraction to remove oligomers, and the product is dried to obtain the finished product.

[0016] The solid-phase thickening pressure is -0.1MPa to 0.1MPa, and the time is 0.5 to 1h; the water extraction temperature is 60 to 80℃, and the extraction time is 3 to 6h.

[0017] The initial PA510 / 6 product underwent solid-phase thickening in a vacuum oven, which greatly improved the polymer molecular weight and viscosity, and also resulted in better product uniformity.

[0018] The stirring speed changes during the preparation of the product of this invention: In step (1), before the temperature is raised to 80-100℃, the stirring speed is 20-50 r / min; then the stirring speed is increased to 80-100 r / min, and the temperature is raised to 180-200℃; in step (2), when the temperature is raised to 220-240℃, the stirring speed is reduced to 40-60 r / min.

[0019] Before the reactor temperature reaches 80-100°C, the stirring speed is 20-50 r / min. Since no additional solvent is added to the reaction system of this invention, the raw materials melt during the heating process. At this stage, a lower stirring speed makes it easier to mix the raw materials evenly. If the stirring speed is too high, the material will splash onto the reactor wall and top, resulting in material loss and uneven mixing. When the temperature reaches 80-100°C, the raw materials are fully melted, the water contained in the raw materials evaporates, and the material concentration increases. At this time, increasing the stirring speed is beneficial for better heat transfer. When the temperature reaches 220-240°C, the stirring speed is reduced, which is beneficial for the ring-opening polycondensation of caprolactam. As the temperature rises, the molecular chain movement becomes more intense, and a lower stirring speed ensures that the molecular chain completes the polycondensation reaction in a more stable environment.

[0020] Beneficial effects of this invention:

[0021] (1) The raw material addition method of this invention is stepwise addition. Based on the difference between the ring-opening temperature of caprolactam and the polymerization temperature of pentanediamine sebacate, pentanediamine sebacate is first prepolymerized, and then an initiator is added to raise the temperature to open the caprolactam ring. By controlling the ring-opening time of caprolactam, the purpose of controlling the copolymerization reaction segment structure is achieved, and a bio-based polyamide PA510 / 6 with regular chain segments is prepared. The bio-based copolyamide PA510 / 6 prepared by this invention is a block copolymer, which reduces the disorder of the copolymerization system and reduces the large molecular weight distribution caused by random copolymerization.

[0022] (2) The present invention uses a polyamide material based on fully bio-based PA510. The raw material has renewable characteristics, which helps to reduce carbon emissions and meets the current urgent needs of society for environmental protection and sustainable development.

[0023] (3) This invention prepares polyamide materials with controllable mechanical, thermodynamic, and weather resistance properties by changing the proportion of the fully bio-based polyamide salt (pentanediamine sebacate) in the copolymerization system. The prepared PA510 / 6 block polyamide material has a melting point range of 159–207℃, a glass transition temperature of 16–30℃, and significantly improved low-temperature resistance; an absolute viscosity of 2.5–3.6, a number-average molecular weight of 18,000–22,000 g / mol, and a molecular weight distribution <1.6, indicating a more complete reaction; a tensile strength of 60–90 MPa, an elongation at break of 420%–750%, a flexural strength of 50–70 MPa, and an impact strength of 10.4–12.6 kJ / m. 3 The light transmittance is 65%–95%. Attached Figure Description

[0024] Figure 1 These are the NMR spectra of PA510 / 6 products prepared by different initiator addition orders;

[0025] Figure 2 These are infrared images of PA510 / 6 products prepared with different proportions of raw materials. Detailed Implementation

[0026] The method described in this invention will be explained in detail below with specific examples.

[0027] Example 1: Effect of Initiator Addition Order on the Properties of PA510 / 6 Block Polyamide Material

[0028] I. Preparation of PA510 / 6 product

[0029] (a) Reference samples PA510 and PA6

[0030] The reference samples PA510 and PA6 of this invention are both from Shanghai Aladdin Reagent Co., Ltd.

[0031] (II) Preparation of PA510 / 6 using the method provided in this invention

[0032] A method for preparing PA510 / 6 block polyamide material includes the following steps:

[0033] (1) Take 761.1g (2.5mol) of bio-based pentanediamine sebacate, 282.9g (2.5mol) of caprolactam, and 5.6g of antioxidant 1076 and add them to the reactor. Set the stirring speed to 40r / min, purge the air in the reactor with nitrogen 2-3 times, then seal the reactor. Heat the reactor at an initial pressure of 0.3MPa. After the temperature reaches 80℃, increase the stirring speed to 80r / min and continue to heat the reactor to 180℃. Adjust the pressure to 1.8MPa and maintain the temperature and pressure for 1h.

[0034] (2) Depressurize to atmospheric pressure, add 6-aminohexanoic acid as an initiator under continuous purging of protective gas, the amount of initiator added is 14.2g; heat to 220℃, reduce the stirring speed to 40r / min, and react for 1h;

[0035] (3) Vacuum was applied to 300 Pa, and the temperature inside the reactor was maintained at 220 °C. Vacuum polycondensation reaction was carried out for 1 h to obtain the initial product of PA510 / 6. The initial product of PA510 / 6 was post-processed: the initial product of PA510 / 6 was extruded and granulated, and placed in a vacuum oven at 240 °C for solid-phase thickening at -0.1 MPa for 1 h. Then, water was added for extraction to remove oligomers. The aqueous solution temperature was 50 °C and the time was 4 h. The PA510 / 6 block polyamide material was dried to obtain the finished product, which was marked as sample 1.

[0036] (III) Preparation of PA510 / 6 control sample 1 using the "one-pot method"

[0037] The one-pot method for preparing PA510 / 6 control samples includes the following steps:

[0038] (1) Take 761.1g of bio-based sebacic acid pentanediamine salt, 282.9g of caprolactam powder, 14.2g of 6-aminohexanoic acid, and 5.6g of antioxidant 1076 and add them to the reactor. Set the stirring speed to 80r / min, purge the air in the reactor with nitrogen 2-3 times, then seal the reactor. Heat the reactor at an initial pressure of 0.3MPa. When the reactor temperature reaches 180℃, adjust the pressure to 1.8MPa and maintain the temperature and pressure for 1h.

[0039] (2) Depressurize to atmospheric pressure, heat to 220℃, and react for 1 hour;

[0040] (3) Vacuum was drawn to 300 Pa, and the temperature inside the reactor was maintained at 220 °C. Vacuum polycondensation reaction was carried out for 1 h to obtain the initial product of bio-based PA510 / 6. The initial product of PA510 / 6 was post-processed: the initial product of PA510 / 6 was extruded and granulated, and then water was added for extraction to remove oligomers. The temperature of the aqueous solution was 50 °C and the time was 4 h. The product was dried to obtain the finished product, which was marked as control sample 1 (PA510 / 6).

[0041] II. Product Testing

[0042] 1. Performance Testing

[0043] Performance tests were conducted on Sample 1 and Comparative Sample 1, and the results are shown in Table 1. Under the same raw material dosage, the PA510 / 6 products prepared by different initiator addition orders showed significant performance differences. The product prepared by stepwise initiator addition was superior to the product prepared by the "one-pot method" in terms of mechanical properties, thermodynamic properties, and weather resistance. Furthermore, the product prepared by stepwise initiator addition had a smaller molecular weight distribution and higher yield.

[0044] Table 1 Product Parameter Table for Example 1

[0045] Parameter testing Sample 1 Comparison Sample 1 Melting point / °C 164 160 Glass transition temperature / °C 19.6 22.9 Absolute viscosity 2.9 1.8 Number average molecular weight (g / mol) 19000 19000 Molecular weight distribution 1.2 3.2 Tensile strength / MPa 65.6 48.3 Elongation at break / % 750 420 Bending strength / MPa 50.2 50.2 <![CDATA[Impact strength / (kJ / m 3 )]]> 12.6 8.6 Light transmittance / % 94 92 Yield / % 78 55

[0046] 2. Structural Confirmation

[0047] NMR analysis was performed on sample 1, control sample 1, reference sample PA510, and reference sample PA6. The NMR spectra are shown below. Figure 1 As shown, the molecular chain of sample 1 is divided into PA510 and PA6 segments. Three chemical shifts of hydrogen appear at position d, which is due to the fact that the hydrogen protons of the block copolymer PA510 and PA6 segments do not affect each other. This can be proven by the NMR chemical shifts of PA510 and PA6 at position d. In contrast, in the NMR spectrum of the comparison sample 1, the pentanediamine, sebacic acid, and 6-aminohexanoic acid segments are randomly arranged, and the chemical shifts of hydrogen protons are affected by adjacent amide bonds, resulting in a red or blue shift. Four characteristic peaks of hydrogen protons appear at position d. This demonstrates that the present invention, by adjusting the ring-opening temperature of caprolactam, changing the type of initiator, and the addition stage, controls the segmental structure of the reaction product, preparing a block copolymer PA510 / 6 with regular molecular chains, while PA510 / 6 prepared by the "one-pot method" is a random copolymer.

[0048] Example 2: Effect of different raw material ratios on the properties of PA510 / 6 block polyamide material

[0049] As demonstrated in Example 1, PA510 / 6, prepared using the stepwise initiator addition method provided by this invention, yields a block polymer. This example will further explore the effects of different amounts of pentanediamine sebacate and caprolactam added on the product performance.

[0050] The product preparation method follows the experimental scheme of distribution addition in Example 1. The molar ratios of bio-based sebacate pentanediamine salt and caprolactam were set to 9:1, 7:3, 5:5, 3:7, and 1:9, corresponding to PA510 / 6, respectively. 0.1 PA510 / 6 0.3 PA510 / 6 0.5 PA510 / 6 0.7 PA510 / 6 0.9The product is labeled with caprolactam percentages of 10%, 30%, 50%, 70%, and 90%. Performance tests were conducted on PA510 / 6 products with different raw material ratios, and the results are shown in Table 2. Table 2 shows that with increasing caprolactam content, the melting point, tensile properties, flexural strength, and light transmittance of PA510 / 6 initially decreased and then increased, while the elongation at break and impact strength initially increased and then decreased. The glass transition temperature decreased monotonically. This is because the introduction of caprolactam segments altered the regularity of the PA510 chain segments, changing its crystallinity and hydrogen bond density. Furthermore, due to the block structure and the process control of this invention, the product has a higher viscosity, larger molecular weight, and narrower molecular weight distribution, thus optimizing the material properties of PA510 / 6.

[0051] Table 2 Product Parameter Table for Example 2

[0052] Parameter testing <![CDATA[PA510 / 6 0.1 ]]> <![CDATA[PA510 / 6 0.3 ]]> <![CDATA[PA510 / 6 0.5 ]]> <![CDATA[PA510 / 6 0.7 ]]> <![CDATA[PA510 / 6 0.9 ]]> Melting point / °C 207 203 164 159 204 Glass transition temperature / °C 29.4 22.3 19.6 19.2 16.9 Absolute viscosity 3.2 3.1 2.9 3.6 2.8 Number average molecular weight (g / mol) 20000 18000 19000 22000 20000 Molecular weight distribution 1.5 1.3 1.2 1.4 1.5 Tensile strength / MPa 70.4 65.8 65.6 76.5 81.7 Elongation at break / % 420 577 750 647 509 Bending strength / MPa 58.7 54.1 50.2 62.4 66.3 <![CDATA[Impact strength / (kJ / m 3 )]]> 10.4 11.3 12.6 11.8 11.3 Light transmittance / % 69.3 86.4 94 92.3 92 Yield / % 78 80 78 79 75

[0053] Infrared spectroscopy was performed on PA510 / 6 with different raw material ratios prepared in Example 2 and the reference sample. The results are as follows: Figure 2 As shown, 3296cm -1 The absorption peaks at 2933 and 2858 cm⁻¹ are the stretching vibration absorption peaks of -NH. -1 The absorption peak at 1633 cm⁻¹ is the stretching vibration of -CH₂-. -1 The absorption peak at 1535 cm⁻¹ is the C=O group of the amide group. -1 The peak at this position represents the stretching vibration absorption peak of CN in the amide group. Furthermore, the shaded area in the spectrum represents the amide III band, signifying the -CH2-NH- stretching vibration of different PA510 / 6 copolyamide components. The characteristic peaks in the infrared spectrum confirm the successful preparation of each PA510 / 6 group.

[0054] Example 3: Effect of different initiators on the properties of PA510 / 6 product

[0055] A method for preparing PA510 / 6 includes the following steps:

[0056] A method for preparing PA510 / 6 block polyamide material includes the following steps:

[0057] (1) Take 761.1g (2.5mol) of bio-based pentanediamine sebacate, 282.9g (2.5mol) of caprolactam, and 5.6g of antioxidant 1076 and add them to the reactor. Set the stirring speed to 40r / min, purge the air in the reactor with nitrogen 2-3 times, then seal the reactor. Heat the reactor at an initial pressure of 0.3MPa. After the temperature reaches 80℃, increase the stirring speed to 80r / min and continue to heat the reactor to 180℃. Adjust the pressure to 1.8MPa and maintain the temperature and pressure for 1h.

[0058] (2) Depressurize to atmospheric pressure, add 2g of sodium hypophosphite as an initiator while continuously introducing protective gas, heat to 220℃, reduce stirring speed to 40r / min, and react for 1h.

[0059] (3) Vacuum was applied to 300 Pa, and the temperature inside the reactor was maintained at 220 °C. Vacuum polycondensation reaction was carried out for 1 h to obtain the initial product of PA510 / 6. The initial product of PA510 / 6 was post-processed: the initial product of PA510 / 6 was extruded and granulated, and placed in a vacuum oven at 240 °C for solid-phase thickening at -0.1 MPa for 1 h. Then, water was added for extraction to remove oligomers. The aqueous solution temperature was 50 °C and the time was 4 h. The PA510 / 6 block polyamide material was dried to obtain the finished product, which was marked as control sample 2.

[0060] The performance of the comparative sample 2 obtained in this embodiment was tested. The obtained PA510 / 6 product had a melting point of 204℃, a glass transition temperature of 42℃, an absolute viscosity of 2.6, a number-average molecular weight of 15000 g / mol, a molecular weight distribution of 3.9, a tensile strength of 70 MPa, an elongation at break of 280%, a flexural strength of 55 MPa, and an impact strength of 7.5 kJ / m. 3 The light transmittance was 65%, the yield was 60%, and the yield after extraction was 43%.

[0061] In Example 3, sodium hypophosphite was used as an initiator. The ring-opening rate of caprolactam was low, resulting in a high molecular weight distribution of the product and a large number of small molecular weight segments, which reduced the yield. In addition, the small molecular weight segments also affected the macroscopic properties of PA510 / 6, such as mechanical and thermal properties.

[0062] Example 4: Effect of different raw material types on the properties of PA510 / 6 product

[0063] A method for preparing PA510 / 6 includes the following steps:

[0064] (1) Mix 81.6g pentanediamine (0.8mol), 161.6g sebacic acid (0.8mol), 90.4g caprolactam powder (0.8mol), 2.3g antioxidant 1010, 0.5g amino silicone oil, and 0.3g benzoic acid evenly and add them to the reactor. Maintain a constant rotation speed of 80r / min and introduce nitrogen into the reactor to replace the air in the reactor 2-3 times. Then close the exhaust valve of the reactor and heat the reactor at an initial pressure of 0.2MPa. When the reactor reaches 200℃, the pressure reaches 1.2MPa. Maintain the temperature and pressure for 2 hours.

[0065] (2) Open the pressure relief valve of the reactor and depressurize to atmospheric pressure within 2 hours, and maintain atmospheric pressure for 2 hours.

[0066] (3) Inflate with nitrogen at 0.2 MPa, open the discharge valve, and vacuum dry the material until the moisture content is less than 0.5% to obtain the finished product, which is marked as control sample 3.

[0067] The comparative sample 3 obtained in this embodiment was tested. The obtained PA510 / 6 product had a melting point of 188℃, a glass transition temperature of 32℃, an absolute viscosity of 1.8, a number-average molecular weight of 11000 g / mol, a molecular weight distribution of 4.2, a tensile strength of 48 MPa, an elongation at break of 400%, a flexural strength of 35 MPa, and an impact strength of 8.9 kJ / m. 3 The light transmittance was 88%, the yield was 55%, and the yield after extraction was 35%.

[0068] Example 4 uses pentanediamine and sebacic acid directly as raw materials instead of pre-forming them into salts. This leads to the volatilization of pentanediamine during the prepolymerization reaction, reducing the ratio of pentanediamine to sebacic acid. This causes premature chain termination, resulting in a lower molecular weight and a wider molecular weight distribution. The prepared product has low mechanical strength, suggesting the formation of a large amount of random copolymers with high molecular disorder and poor crystallinity, thus significantly reducing mechanical strength.

Claims

1. A method for preparing PA510 / 6 block polyamide material, characterized in that, Includes the following steps: (1) Add pentanediamine sebacate and caprolactam to the reactor at a molar ratio of (1-9):(1-9), stir and introduce protective gas, then seal the reactor, raise the temperature to 180-200℃ at an initial pressure of 0.2-0.5 MPa, adjust the pressure to 1.6-2.0 MPa, and maintain the temperature and pressure for 1-3 h. (2) Depressurize to atmospheric pressure, add initiator while continuously introducing protective gas, heat to 220-240℃, and react for 1-1.5 hours. The initiator is one or more of 6-aminohexanoic acid, 5-aminovaleric acid, and 10-aminodecanoic acid; the amount of initiator added is 5 wt%-10 wt% of caprolactam. (3) Vacuum is drawn and vacuum polycondensation reaction is carried out at a vacuum degree of 0-900 Pa and a temperature of 220-240℃ for 0.5-1.5 h to obtain the initial product PA510 / 6.

2. The method for preparing the PA510 / 6 block polyamide material according to claim 1, characterized in that, In step (1), an antioxidant was also added to the reactor. The antioxidant is one or more of antioxidant 1076, antioxidant 1098, and BHT (264).

3. The method for preparing the PA510 / 6 block polyamide material according to claim 2, characterized in that, The amount of antioxidant added is 0.2 wt% to 1 wt% of the total weight of pentanediamine sebacate and caprolactam.

4. The method for preparing the PA510 / 6 block polyamide material according to claim 1, characterized in that, Post-processing of the initial PA510 / 6 product in step (3): extrude and pelletize the initial PA510 / 6 product, place it at 230-240℃ for solid-phase thickening, then add water to extract and remove oligomers, and dry to obtain the finished product.

5. The method for preparing the PA510 / 6 block polyamide material according to claim 4, characterized in that, The solid-phase thickening pressure was -0.1 MPa to 0.1 MPa, and the time was 0.5 to 1 h; the temperature of the aqueous solution during water extraction was 60 to 80 °C, and the extraction time was 3 to 6 h.

6. The method for preparing the PA510 / 6 block polyamide material according to claim 1, characterized in that, In step (1), before heating to 80-100℃, the stirring speed is 20-50 r / min; then the speed is increased to 80-100 r / min, and the temperature is further increased to 180-200℃.

7. The method for preparing the PA510 / 6 block polyamide material according to claim 1, 3, 4, 5, or 6, characterized in that, The protective gas is nitrogen.

8. The method for preparing the PA510 / 6 block polyamide material according to claim 7, characterized in that, In step (1), nitrogen gas is introduced to replace the air inside the reactor 2 to 3 times before sealing the reactor.

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