Recovery method of polyphenylene sulfide oligomer

Abstract

The invention discloses a method for recovering polyphenylene sulfide oligomer, which is characterized by comprising the following steps of: mixing slurry obtained after filtering polyphenylene sulfide high polymer in a reacted system with washing waste liquid of the polyphenylene sulfide high polymer, centrifugally separating, and discarding supernatant to obtain a polyphenylene sulfide oligomer crude product, the washing waste liquid of the polyphenylene sulfide polymer comprises organic washing waste liquid and washing waste liquid. According to the method, the organic washing waste liquid and the washing waste liquid for washing the polyphenylene sulfide high polymer are mixed with the polyphenylene sulfide oligomer, and then the polyphenylene sulfide oligomer is recycled, so that the polyphenylene sulfide oligomer in the organic washing waste liquid and the washing waste liquid can be recycled at the same time, the recycling rate is increased, the washing cost is reduced, and the economical efficiency is high. Besides, after the organic washing waste liquid and the water washing waste liquid for washing the polyphenylene sulfide high polymer are mixed with the slurry together, rapid solid-liquid layering can be realized in a centrifugal sedimentation manner, and supernatant is discarded, so that a polyphenylene sulfide oligomer crude product can be obtained, and the operation is simple.

Description

Technical Field

[0001] This invention relates to the field of polymer separation technology, and in particular to a method for recovering polyphenylene sulfide oligomers. Background Technology

[0002] Polyphenylene sulfide (PPS), composed of repeating thiophenyl units, is a high-performance engineering plastic with excellent heat resistance, corrosion resistance, and electrical insulation. It is widely used in automotive manufacturing, aerospace, electronics, new energy, chemical, pharmaceutical, and environmental protection industries. Its structural formula is shown in Formula I.

[0003] Formula I Polyphenylene sulfide (PPS) can be produced by various methods, among which the sodium sulfide method is widely used in large-scale industrial production due to its advantages such as good stability, high reproducibility, high yield, and low cost. The sodium sulfide method typically uses sodium sulfide and p-dichlorobenzene as raw materials, an alkali metal catalyst, and N-methylpyrrolidone as a solvent, undergoing a polycondensation reaction under high temperature and pressure. The reaction equation is shown in Equation II:

[0004] Formula II During the synthesis and precipitation of polyphenylene sulfide (PPS), particles of varying sizes are formed due to differences in chain length. These differences in particle size result in variations in product performance. Therefore, it is necessary to separate PPS particles of different sizes. Large PPS particles (such as those filtered through a sieve of 50 mesh or larger) are washed and dried to become the final product, while small PPS particles are treated as oligomers.

[0005] Polyphenylene sulfide (PPS) oligomers have low melting points and crystallinity, and good solubility in polar organic solvents. They can be used as copolymer modification raw materials, charge transfer agents in optoelectronic semiconductors, and plastic additives, exhibiting high economic value. Patents CN106279692A and CN107936250A involve re-introducing recycled PPS oligomers into a high-pressure reactor, adding catalysts and solvents, and controlling reaction conditions to repolymerize the PPS oligomers, thereby obtaining PPS polymers. Patents CN111825862A and CN116178955A involve chemically cross-linking recycled PPS oligomers with high-molecular-weight PPS molecules, effectively increasing the molecular weight of PPS to meet downstream application requirements. Patent CN113652046A introduces an aqueous solution of polyvinyl alcohol (PVA) to allow the thioether bonds in the polyphenylene sulfide (PPS) oligomer to form hydrogen bonds with the hydroxyl groups of PVA, thereby obtaining a PVA-PPS composite material with shape memory properties and realizing the effective utilization of PPS oligomers. Patent CN119931062A, on the other hand, adds a chain extender to the PPS oligomer, effectively increasing the molecular chain length and branching degree of the PPS oligomer through chemical crosslinking.

[0006] However, due to the small particle size and high viscosity of polyphenylene sulfide (PPS) oligomers in NMP solvent, their separation is quite challenging. Patent CN120271823A improves the yield and purity of PPS oligomers by adding diethanolamine and 1,3-dimethyl-2-imidazolinone to the mother liquor and using pressure candle filtration. However, this method introduces new substances into the mother liquor, increasing post-processing costs and complicating subsequent solvent recovery and waste salt treatment. Patent CN116328418A uses a combination of a horizontal screw centrifuge and a candle filter to effectively separate the solvent mother liquor from the PPS oligomers. However, this method is complex, requires multiple devices, and is costly, making it unsuitable for industrial production. Patents JP4848688B2 and JP2007106784A reduce the viscosity of the reaction slurry by adding an organic solvent and then removing the solvent by heating, thus obtaining the oligomer residue. This method is costly and unsuitable for industrial production. Furthermore, the resulting oligomers have a high ash content, hindering subsequent utilization. Additionally, the crude polyphenylene sulfide oligomers after separation contain large amounts of impurities such as sodium chloride, NMP, and water, requiring further impurity removal. Patent CN111100294A uses a multi-stage water washing method to obtain solid recycled oligomers, which has some economic value. However, the polyphenylene sulfide oligomers obtained solely through water washing have a high ash content, failing to meet downstream application requirements.

[0007] It should also be noted that although patents CN106279692A and CN107936250A achieve the repolymerization of oligomers to obtain polyphenylene sulfide polymers, the reaction conditions of this method are difficult to control, resulting in low product stability. Patents CN111825862A, CN116178955A, CN113652046A, and CN119931062A also achieve increased polymerization degree, molecular chain length, and molecular chain branching through chemical crosslinking, but all require the introduction of additional crosslinking agents, which is not only cumbersome but also increases the cost of oligomer recycling.

[0008] Therefore, it is essential to develop a simpler, more efficient, and more economical method for recycling polyphenylene sulfide oligomers. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a method for recycling polyphenylene sulfide oligomers, which is simple to operate, has high recycling efficiency, is economical, and the obtained polyphenylene sulfide oligomers have low ash content, making them suitable for subsequent applications.

[0010] To solve the above-mentioned technical problems, the present invention provides a method for recovering polyphenylene sulfide oligomers, which includes filtering the polyphenylene sulfide polymer from the reaction system, mixing the slurry after filtering the polyphenylene sulfide polymer with the washing waste liquid of the polyphenylene sulfide polymer, centrifuging and separating, discarding the supernatant, and obtaining crude polyphenylene sulfide oligomer, wherein the washing waste liquid of the polyphenylene sulfide polymer includes organic washing waste liquid and water washing waste liquid.

[0011] In this invention, to recover polyphenylene sulfide oligomers from the slurry after filtering out the polyphenylene sulfide polymer, a mixture of organic washing waste liquid and water washing waste liquid used to wash the polyphenylene sulfide polymer is mixed with the polyphenylene sulfide oligomers before recovery. The water washing waste liquid facilitates the precipitation of the polyphenylene sulfide oligomers for recovery, helps remove impurities to reduce ash content, and helps reduce the viscosity of the slurry for separation. The organic washing liquid helps reduce the viscosity of the slurry for separation. Simultaneously, the addition of both organic washing waste liquid and water washing waste liquid... The residual polyphenylene sulfide oligomers in the machine washing wastewater and water washing wastewater are also recovered, thereby improving the recovery rate of polyphenylene sulfide oligomers. The organic washing wastewater contains approximately 1wt%-2wt%, and the water washing wastewater (especially primary water washing wastewater) contains approximately 0.1wt%-0.5wt%. After mixing, centrifugal sedimentation can achieve rapid solid-liquid separation. The supernatant is discarded to obtain crude polyphenylene sulfide oligomers. This method has low recovery cost, high economic efficiency, high recovery efficiency of polyphenylene sulfide oligomers, and is simple to operate and widely applicable. It should be noted that no special requirements are placed on the centrifugation conditions in this invention; solid-liquid separation is sufficient. Centrifugation speeds are, for example, between 3000-20000 rpm (e.g., 3000 rpm, 5000 rpm, 8000 rpm, 10000 rpm, 20000 rpm), and centrifugation times are, for example, 5-20 min (e.g., 5 min, 10 min, 15 min, 20 min).

[0012] It should be noted that in this invention, the reaction is a reaction to prepare polyphenylene sulfide using sodium sulfide and p-dichlorobenzene as raw materials; the filtration is filtering the system after the reaction is completed through a 50-200 mesh sieve (e.g., 50 mesh, 100 mesh, 150 mesh, 200 mesh), and the filter cake is polyphenylene sulfide polymer. The reaction system for preparing polyphenylene sulfide using sodium sulfide and p-dichlorobenzene as raw materials may also include, for example, organic solvents, additives, alkali metal catalysts, etc., wherein the organic solvent includes N-methylpyrrolidone (NMP), etc. The organic washing liquid for the polyphenylene sulfide polymer is preferably the same solvent as the reaction solvent; for example, when the reaction solvent is NMP, the organic washing liquid is also NMP. However, it is not desirable to be limited by this. In the prior art, organic washing liquids used in the reaction to prepare polyphenylene sulfide using sodium sulfide and p-dichlorobenzene as raw materials, and in washing polyphenylene sulfide polymers, are all applicable to this invention.

[0013] In one specific embodiment, the mass ratio of the slurry to the washing waste liquid of the polyphenylene sulfide polymer is 1:0.5-2, for example, 1:0.5, 1:1, 1:1.5, or 1:2. The mass ratio of the organic solvent washing waste liquid to the water washing waste liquid is 1:1-3, for example, 1:1, 1:2, 1:3.

[0014] In one specific embodiment, when the polyphenylene sulfide polymer is washed using a multi-stage cross-flow washing method, the washing wastewater is designated as primary washing wastewater. Understandably, the primary washing wastewater also contains a certain amount (approximately 0.1 wt%-0.5 wt%) of polyphenylene sulfide oligomers, thereby improving the recovery rate of polyphenylene sulfide oligomers while simultaneously utilizing the wastewater. However, if not wishing to be constrained by this, secondary, tertiary, or other stages of washing wastewater are also applicable to this invention.

[0015] In one specific embodiment, the recycling method further includes: sequentially acid washing, water washing, and drying of the crude polyphenylene sulfide oligomer to obtain the polyphenylene sulfide oligomer.

[0016] Preferably, the pickling solution is hydrochloric acid with a mass fraction of 0.1%-10%, such as 0.1%, 0.3%, 0.5%, 0.8%, 1.0%, 2.0%, 3.0%, 5.0%, or 10%. More preferably, the pickling is performed at least once (e.g., once, twice, or three times), the pickling temperature is 15℃-40℃ (e.g., room temperature), and the pickling time is generally 25-50 minutes, such as 25 minutes, 30 minutes, 32 minutes, 35 minutes, 40 minutes, or 50 minutes. The water washing is a multi-stage cross-flow washing process with 2-4 washing stages, preferably 3 stages. The water washing temperature is between 80℃ and 90℃. The drying conditions are vacuum drying at 80℃-120℃, such as 80℃, 82℃, 85℃, 90℃, 100℃, 110℃, or 120℃.

[0017] Preferably, the mass ratio of the crude polyphenylene sulfide oligomer to the washing liquid in a single acid wash is 1:1.5-5, for example, 1:1.5, 1:2, 1:2.5, 1:3, 1:4, or 1:5; the mass ratio of the crude polyphenylene sulfide oligomer to the washing liquid in each stage of water washing is 1:3-8, for example, 1:3, 1:4, 1:5, 1:6, or 1:8.

[0018] In this specific implementation plan, because the crude polyphenylene sulfide oligomer has a high ash content and still contains other impurities, its utilization value is often small. Therefore, further processing is required. First, acid washing can effectively reduce the ash content in the polyphenylene sulfide oligomer and increase the crystallization temperature of the product. At the same time, the acid washing process can change the end groups of the polyphenylene sulfide oligomer, for example, by exchanging the sodium ions of the end groups for hydrogen ions, which helps to improve the crosslinking efficiency.

[0019] In one specific embodiment, the recycling method further includes: subjecting the polyphenylene sulfide oligomer to solid-state thermo-oxidative crosslinking to obtain a crosslinked polyphenylene sulfide oligomer product.

[0020] Preferably, the solid-state thermo-oxidative crosslinking temperature is 180℃-350℃, and air is continuously introduced during the solid-state thermo-oxidative crosslinking process; the solid-state thermo-oxidative crosslinking time is 2-12h, wherein the solid-state thermo-oxidative crosslinking temperature is, for example, 180℃, 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, 350℃, and the solid-state thermo-oxidative crosslinking time is, for example, 2h, 4h, 6h, 8h, 10h, 12h.

[0021] In this specific solution, due to the low molecular weight and low degree of polymerization of polyphenylene sulfide oligomers, the application scenarios are limited. Therefore, further crosslinking is carried out to increase the molecular weight and crystallization temperature, thereby expanding the application scenarios. Moreover, the solid-state thermo-oxidative crosslinking of the present invention does not require the introduction of new substances such as crosslinking agents. It can be carried out directly by passing air in the temperature range of 180℃-350℃, which is simple to operate and has a good crosslinking effect. Attached Figure Description

[0022] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is the washing and drying process flow of polyphenylene sulfide polymer of the present invention; Figure 2 This is the washing and drying process of polyphenylene sulfide oligomers in Embodiment 1 of the present invention. Detailed Implementation

[0024] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] In this embodiment of the invention, polyphenylene sulfide (PPS) polymers are prepared using a sodium sulfide polymerization process. NMP is used as the solvent. After the reaction, the reaction system is passed through a 100-mesh sieve to obtain PPS polymers on the sieve and a slurry containing PPS oligomers below the sieve. The PPS polymers are first washed with NMP as the washing liquid, and the NMP washing waste liquid is collected for later use. Then, the NMP-washed PPS polymers are washed using a three-stage countercurrent water washing process. The washing process is as follows: Figure 1 As shown, primary washing waste liquid is collected for later use. Example

[0026] Take 50 parts by weight of slurry, 25 parts by weight of NMP washing waste liquid and 25 parts by weight of water washing waste liquid (first-level water washing waste liquid) and mix them evenly. Centrifuge the mixture at 10,000 speed for 10 min. After discarding the supernatant, 2.8 parts by weight of crude polyphenylene sulfide oligomer product are obtained, of which the ash content is 35%.

[0027] Take 1 part by weight of crude polyphenylene sulfide oligomer and mix it with 2.5 parts by weight of 0.5% wt hydrochloric acid solution. Wash the mixture at room temperature for 30 minutes. After acid washing, wash the mixture again using a three-stage countercurrent water washing process (refer to...). Figure 2 As shown), the washing temperature is maintained at 80℃-90℃, and the washing time is 30 minutes. During the water washing, 5 parts by mass of water washing solution are added for each stage of water washing (usually, the water washing solution for the first two stages can be the circulating water from the previous batch of washing, and the water washing solution for the third stage is clean deionized water; however, clean deionized water can also be used for all three stages). After the water washing is completed, it is vacuum dried at 80℃ to obtain a white powder (polyphenylene sulfide oligomer). Its ash content is determined to be 0.4%, the crystallization temperature is 209℃, and the molecular weight is 2588.

[0028] Take 0.5 parts by mass of dried polyphenylene sulfide oligomer and place it in a forced-air drying oven. Perform solid-state thermo-oxidative crosslinking at 220℃ for 8 hours to obtain a brown polyphenylene sulfide oligomer crosslinked product. The ash content is 0.4%, the crystallization temperature is 220℃, and the molecular weight is 6311.

[0029] Take 0.5 parts by mass of dried polyphenylene sulfide oligomer and place it in a forced-air drying oven. Perform solid-state thermo-oxidative crosslinking at 260℃ for 8 hours to obtain a brown polyphenylene sulfide oligomer crosslinked product. The ash content was determined to be 0.4% and the crystallization temperature was 216℃.

[0030] As can be seen, the ash content of the polyphenylene sulfide oligomer obtained in this embodiment is significantly reduced after acid washing. After further solid thermo-oxidative crosslinking, the molecular weight and crystallization temperature of the polyphenylene sulfide oligomer are significantly increased, which facilitates further application. Example

[0031] Referring to Example 1, the difference is that the mass fraction of the primary washing waste liquid is increased to 50 parts by mass, and the mass concentration of the pickling solution is 2%wt.

[0032] The crude polyphenylene sulfide oligomer obtained was 3 parts by mass, with an ash content of 30%. The obtained white polyphenylene sulfide oligomer had an ash content of 0.25% and a crystallization temperature of 236℃.

[0033] In this embodiment, compared to Embodiment 1, the precipitation of polyphenylene sulfide oligomers is increased by increasing the amount of water washing waste liquid, thereby improving the crude product recovery rate and reducing the ash content of the crude product to a certain extent. At the same time, the ash content of the product is significantly reduced by increasing the concentration of the pickling solution. In addition, it can be seen that the crystallization temperature of the white polyphenylene sulfide oligomers obtained in this embodiment is significantly increased. This may be because a higher concentration of pickling solution can improve the end-group conversion rate, which is conducive to increasing the crystallization temperature and facilitating the expansion of application scenarios.

[0034] Comparative Example 1 Referring to Example 2, the difference is that the acid washing step is omitted, and a white powder (polyphenylene sulfide oligomer) is obtained. Its ash content is measured to be 1.51%, and the crystallization temperature is 181°C.

[0035] It is evident that, by omitting the pickling step, the ash content of the polyphenylene sulfide oligomer is significantly increased compared to Example 2, and the crystallization temperature is also much lower than that of Example 2. This indicates that pickling has a significant impact on ash content and crystallization temperature. Adding the pickling step is beneficial for reducing ash content and increasing crystallization temperature.

[0036] Comparative Example 2 Referring to Example 1, the difference is that centrifugation was replaced by vacuum filtration, and the filtration time was 12 hours, yielding 2.8 parts by mass of white powder (polyphenylene sulfide oligomer).

[0037] It can be seen that the solid-liquid separation method of Comparative Example 2 is different from that of Example 1. The amount of polyphenylene sulfide oligomer obtained is the same as that of Example 1, indicating that the centrifugal separation method is applicable to the solid-liquid separation of the present invention and will not affect the recovery rate. However, the centrifugal separation method is simple to operate, the separation time is greatly shortened, and the separation efficiency is high. Therefore, it is superior to vacuum filtration.

[0038] Comparative Example 3 Referring to Example 1, the difference is that before centrifuging the slurry, only 25 parts by mass of NMP washing waste liquid (i.e., no water washing waste liquid is added) are added, and the centrifugation time needs to be increased to 15 minutes. Finally, 2.5 parts by mass of crude polyphenylene sulfide oligomer is obtained, of which the ash content is 40%.

[0039] Comparative Example 4 Referring to Example 1, the difference is that before centrifuging the slurry, neither NMP washing waste liquid nor water washing waste liquid is added. 50 parts by mass of the slurry are directly centrifuged, and the centrifugation time needs to be increased to 15 minutes. Finally, 2.2 parts by mass of crude polyphenylene sulfide oligomer is obtained, with an ash content of 40%.

[0040] Comparative Example 5 Referring to Example 1, the difference is that only 25 parts by mass of primary water washing waste liquid are added (no organic washing waste liquid is added). During centrifugation, the centrifugation time does not need to be extended, that is, separation can be achieved in 10 minutes, and 2.4 parts by mass of crude polyphenylene sulfide oligomer is obtained, of which the ash content is 34%.

[0041] In conjunction with Example 1 and Comparative Examples 3 to 5: In terms of centrifugation time, without adding water washing waste liquid, the centrifugation time needs to be increased to 15 minutes, indicating that adding water washing waste liquid helps to shorten the centrifugation time. Regarding the amount of crude product precipitated, Example 1 yielded 2.8 parts by mass, Comparative Example 3 yielded 2.5 parts by mass, Comparative Example 4 yielded 2.2 parts by mass, and Comparative Example 5 yielded 2.4 parts by mass. Compared to Example 1, Comparative Example 3 showed a reduction of 0.3 parts by mass in crude product quantity. Considering the very low content of polyphenylene sulfide oligomers in the washing waste liquid (approximately 0.025-0.125 parts by mass in 25 parts by mass of washing waste liquid), it can be seen that the amount of polyphenylene sulfide oligomers precipitated from the slurry has decreased. This indicates that the washing waste liquid is beneficial in promoting the precipitation of polyphenylene sulfide oligomers in the slurry and improving the recovery rate of polyphenylene sulfide oligomers in the slurry (this can also be seen from the comparison of crude product quantities obtained from Example 1 and Example 2). (Technical effect); Compared with Example 1, Comparative Example 5 showed a reduction of 0.4 parts by mass in the amount of crude product, while the content of polyphenylene sulfide oligomers in 25 parts by mass of organic washing waste liquid was approximately 0.25-0.5 parts by mass. The reduction in crude product was comparable to the content of polyphenylene sulfide oligomers in the organic washing waste liquid. Therefore, it can be further concluded that the addition of washing waste liquid is beneficial for the full precipitation of polyphenylene sulfide oligomers in the slurry. Similarly, compared with Comparative Example 5, Comparative Example 4 showed a reduction of 0.2 parts by mass in the amount of crude product, while the content of polyphenylene sulfide oligomers in 25 parts by mass of washing waste liquid was approximately between 0.025-0.125 parts by mass, which is less than 0.2 parts by mass. Therefore, it also shows that the addition of washing waste liquid is beneficial for promoting the precipitation of polyphenylene sulfide oligomers in the slurry.

[0042] In terms of ash content, the ash content of Example 1 is 35%, the ash content of Comparative Example 3 is 40%, the ash content of Comparative Example 4 is 40%, and the ash content of Comparative Example 5 is 34%, indicating that adding water washing waste liquid is beneficial to reducing the ash content in the crude product.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recovering polyphenylene sulfide oligomers, characterized by, The slurry after filtering the polyphenylene sulfide high polymer of the reaction completed system is mixed with the washing waste liquid of the polyphenylene sulfide high polymer, and after centrifugal separation, the supernatant is discarded to obtain the polyphenylene sulfide low polymer crude product, wherein the washing waste liquid of the polyphenylene sulfide high polymer comprises organic washing waste liquid and water washing waste liquid.

2. The recycling method of claim 1, wherein, The reaction is the reaction for preparing the polyphenylene sulfide by using sodium sulfide and p-dichlorobenzene as raw materials. The filtering is filtering the reaction completed system by using a 50-200 mesh screen, and the filter cake is the polyphenylene sulfide high polymer.

3. The recycling method of claim 1, wherein, The mass ratio of the slurry to the washing waste liquid of the polyphenylene sulfide high polymer is 1:0.5-2. The mass ratio of the organic washing waste liquid to the water washing waste liquid is 1:1-3.

4. The recycling method of claim 3, wherein, When the polyphenylene sulfide high polymer is washed by multi-stage cross-flow washing, the water washing waste liquid is a first-stage water washing waste liquid.

5. The recycling method of claim 1, wherein, The recovery method further comprises: sequentially subjecting the polyphenylene sulfide low polymer crude product to acid washing, water washing and drying to obtain the polyphenylene sulfide low polymer.

6. The recycling method of claim 5, wherein, The washing liquid of the acid washing is hydrochloric acid with a mass fraction of 0.1%-10%; The water washing is multi-stage cross-flow washing, and the washing stage number is 2-4 stages; The drying condition is vacuum drying at 80-120℃.

7. The recycling method of claim 6, wherein, The washing number of the acid washing is at least 1 time, and the washing temperature is 15-40℃. The washing stage number of the water washing is 3 stages, and the washing temperature is 80-90℃.

8. The recovery method according to any one of claims 7, wherein The mass ratio of the polyphenylene sulfide low polymer crude product to the washing liquid of the acid washing is 1:1.5-5; The mass ratio of the polyphenylene sulfide low polymer crude product to the washing liquid of each stage of water washing is 1:3-8.

9. The recycling method of claim 2, wherein, The recovery method further comprises: subjecting the polyphenylene sulfide low polymer to solid state thermal oxygen crosslinking to obtain a polyphenylene sulfide low polymer crosslinked product.

10. The recycling method of claim 9, wherein, The temperature of the solid state thermal oxygen crosslinking is 180-350℃, and air is continuously introduced during the solid state thermal oxygen crosslinking process; The time of the solid state thermal oxygen crosslinking is 2-12h.

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