CN100579638C - A modified polyvinyl chloride hollow fiber microporous membrane and its preparation method - Google Patents

Abstract

The invention discloses a hollow microporous membrane of a modified polychloroethylene and process for preparation. The hollow microporous membrane of the modified polychloroethylene has a spongy structure, the bore diameter of a microporous is 0.01-1.0 um, the porosity rate of the membrane is 40-80%, wall thickness of the membrane is 0.10-0.30 mm, and the external diameter of the membrane is 1.0-3.0mm, wherein the main components of the hollow microporous membrane of the modified polychloroethylene are polychloroethylene and toughening agent. The preparing method is realized on the basis of thermal separation process. The hollow microporous membrane of the improved polychloroethylene which is made by the invention has the advantages of narrow bore diameter distribution, high intensity, and good structural repeatability and the like, and the bore diameter is easy to be controlled. The invention is a filter membrane material for water process which has high performance, low cost and long service life.

Description

A modified polyvinyl chloride hollow fiber microporous membrane and its preparation method

technical field

The invention relates to membrane separation technology, in particular to a polyvinyl chloride hollow fiber microporous filter membrane material and a preparation method thereof.

Background technique

Due to the advantages of high efficiency, simple equipment, convenient operation, energy saving and environmental protection, membrane separation technology has shown great application potential in the industrial field, and its application range has been extended to biology, medicine, environmental protection, energy, seawater desalination, wastewater treatment, etc. field. Membrane materials are the core basic materials of membrane separation technology. Among them, ultrafiltration membranes and microfiltration membranes are the most widely used microporous membrane materials. Among the two types of membrane materials, inorganic membranes (mainly ceramic membranes and metal membranes) and organic polymers, polymer membranes occupy a dominant position; in the most important application field of membrane separation technology - water treatment, polymer ultrafiltration membranes And the morphology of microfiltration membrane is mainly hollow fiber membrane. At present, the polymer hollow fiber microporous membranes that have been commercialized are mostly made of polysulfone (PS), polyvinylidene fluoride (PVDF), polyethersulfone (PES), polyacrylonitrile (PAN) and other materials. However, due to the relatively high cost of raw materials, PVDF, PES, PS, etc. lead to high membrane manufacturing costs, while PAN, etc., have limited their application in many industries due to their relatively low strength. Therefore, finding and realizing the preparation of low-cost, high-performance polymer hollow fiber microporous membranes from the aspects of material selection and membrane formation method is the main way out for the development of microfiltration and ultrafiltration membrane technology.

As we all know, polyvinyl chloride is the second general-purpose plastic after polyethylene among the three synthetic resins (polypropylene, polyethylene and polyvinyl chloride) with the largest output. It is rich in sources, low in price, and is a chemically stable Well, traditional polymer materials with high mechanical strength. Since polyvinyl chloride also has the advantages of bacteria resistance, acid and alkali resistance, and chemical corrosion resistance necessary for separation membrane materials, the potential significance of polyvinyl chloride separation membrane materials - especially microporous microfiltration/ultrafiltration membranes - has attracted people's attention .

At present, there are reports at home and abroad about polyvinyl chloride microfiltration membranes and ultrafiltration membranes and their preparation methods. More representative ones are: Chinese Patent (Patent No. CN1188207C) proposes a large-flux polyvinyl chloride hollow fiber membrane and its preparation method. At first, this method uses vinyl chloride as the main raw material, 1-methyl-2-pyrrolidone As a solvent, polyethylene glycol is used as an additive to prepare a film-forming solution (wherein the weight percentage of polyvinyl chloride is 16 to 19%, and the weight ratio of the solvent to the additive is controlled to be 50 to 58: 43 to 50), and then dry- The polyvinyl chloride hollow fiber membrane is formed by wet spinning process. In the phase inversion method reported in the Chinese patent (patent number: CN1621434A), a superhydrophobic porous polyvinyl chloride film with a surface microstructure of micron and nanoscale particles and its preparation method is reported, and the contact angle between the film and water is greater than 150° , has good superhydrophobic properties, but the membrane is not intended for water treatment. Chinese patent (Patent No.: CN1415407) reported that a high-flux polyvinyl chloride hollow fiber ultrafiltration membrane was prepared by phase inversion method. The porosity of the membrane was 90%, and the pure water flux was 400 L/m ² h. In CN1247295C, a high-throughput polyvinyl chloride/polyvinyl acetal polymer blend film is prepared by phase inversion method. A Chinese patent (patent number: CN1579600A) reports a polyvinyl chloride/vinyl chloride-vinyl acetate-maleic anhydride terpolymer alloy hollow filter membrane and a preparation method thereof.

The preparation methods of the above-mentioned vinyl chloride microporous membranes are all realized based on the principle of submerged precipitation phase inversion. However, in the general immersion precipitation phase inversion method or its deformed microporous membrane preparation technology, there are the following problems due to the limitation of the principle: (1) There are many factors affecting the membrane structure in the membrane production process, and the phase change membrane process Involving material exchange, the structure and performance of the membrane are difficult to control; (2) The membrane production process forms a large amount of organic wastewater that is difficult to harmless and recycle, resulting in high membrane production costs and environmental pollution; (3) The internal structure of the membrane is mostly large finger-shaped holes, and the strength of the membrane is low, which is not suitable for application in water treatment projects with high hydraulic impact strength; (4) Due to the intrinsic nature of the PVC material, the PVC membrane High brittleness and poor toughness can easily cause damage to the end of the membrane module and shorten the service life of the membrane. For PVC films, the solution to these problems needs to be realized from two aspects: film making method and film composition improvement.

Essentially, the principle of thermally induced phase separation is another major method for preparing polymeric microporous membranes. Different from the immersion precipitation phase inversion method in which the non-solvent induces phase separation to form pores, the thermally induced phase separation method is a method in which the phase separation is driven by temperature change. The main process is to first combine the polymer with the appropriate High boiling point small molecule compounds or oligomers (diluents) form a homogeneous solution at elevated temperatures; then lower the temperature to solidify into a film, and at the same time solid-liquid or liquid-liquid phase separation occurs in the film (wherein the polymer, diluent Form a double continuous phase); Finally, the diluent in the cured film is extracted with a solvent to obtain a polymer microporous film. Compared with the immersion precipitation phase inversion method, the membrane technology based on the principle of thermally induced phase separation has a large selection of polymers, a high porosity of the obtained membrane, and strong controllability of the membrane pore size (especially the internal spongy structure, membrane No cortex or ultra-thin cortex), high strength of the membrane, etc. At the same time, there are few types of raw materials used in the membrane production process, the composition of waste liquid is simple, and it is easy to separate and recycle. Since the thermally induced phase separation mechanism was proposed in the early eighties of the 20th century, there have been some reports on the preparation of polymer microporous materials and flat membranes by thermally induced phase separation, such as U.S. patents (patent numbers: US3423491, US4020230, US4247498, US4490431, US4726989) and Chinese patent (Patent No.: CN1265048A) respectively reported the technology of polyethylene, polypropylene, polyvinylidene fluoride hollow fiber or flat microporous membrane prepared by thermal phase separation principle, wherein polyethylene, Polypropylene, polyvinylidene fluoride, etc. are mainly crystalline or semi-crystalline polymers, but no report has been found on the preparation of amorphous PVC microporous membranes using the principle of thermally induced phase separation.

It is different from the existing polyvinyl chloride hollow fiber microporous membrane materials and their preparation methods based on the principle of phase inversion, and also different from other crystalline polymer microporous membranes and their preparation techniques based on the principle of thermally induced phase separation, combined with the characteristics of polyvinyl chloride itself , this patent discloses a high-performance modified polyvinyl chloride hollow fiber microporous filtration membrane and its high-efficiency preparation method based on the principle of thermally induced phase separation on the basis of sufficient experiments and success. The disclosed modified polyvinyl chloride hollow fiber microporous membrane has the advantages of narrow membrane pore size distribution, high strength, good toughness, stable structure and performance, and is suitable for various membrane water treatment equipment and projects. The disclosed preparation method , has the characteristics of strong controllability of membrane structure and performance during the preparation process, low manufacturing cost, and clean production (for example, the formed waste liquid can be recycled and harmlessly discharged through a simple low-energy process).

Contents of the invention

The object of the present invention is to provide a modified polyvinyl chloride hollow fiber microporous membrane and its preparation method based on the principle of thermally induced phase separation.

The modified polyvinyl chloride hollow fiber microporous membrane according to the present invention has a spongy structure, preferably a symmetrical spongy microporous structure, with a micropore diameter of 0.01-1.0 μm, a membrane porosity of 40-80%, and a membrane wall The thickness is 0.10-0.30mm, the outer diameter of the film is 1.0-3.0mm, and its main components are polyvinyl chloride and toughening agent. The toughening agent is selected from dibutyl phthalate, dioctyl phthalate, nitrile rubber, thermoplastic polyurethane and ethylene-vinyl acetate copolymer. The modified polyvinyl chloride hollow fiber microporous membrane according to the present invention includes 70-95% polyvinyl chloride and 5-30% toughening agent. The degree of polymerization of the polyvinyl chloride is preferably between 600-3600.

The preparation method of modified polyvinyl chloride hollow fiber microporous membrane according to the present invention comprises the following steps:

(1) Preparation of film-making material: polyvinyl chloride, diluent, toughening agent and thermal stabilizer are mixed, melt blended into a uniform film-making material, wherein the weight percentage of the above components is: polyvinyl chloride: 10 -50%, Thinner: 40-85%, Toughener: 0.5-10%, Heat Stabilizer: 0.1%-1%;

(2) Precursor hollow fiber membrane forming: using diluent as the core liquid, extrude the above-mentioned membrane-making material through a spinneret under high pressure to form a tubular liquid film, and the liquid film enters a cooling bath to solidify after passing through an air gap. A polyvinyl chloride precursor hollow fiber membrane, wherein the core liquid is the same as the diluent in the film-making material; the cooling bath is the diluent or water in the film-making material;

(3) Extraction to form pores: soak and extract the precursor hollow fiber membrane of polyvinyl chloride in the extractant, and then dry it in the air to obtain the polyvinyl chloride hollow fiber microporous membrane.

Preferably, it is melted at 130-200°C in preparing the film-making material.

In the molding of the precursor hollow fiber membrane, it is preferable to use a diluent at 30-60°C as the core liquid, the high-pressure range is preferably 0.1-0.4MPa, the temperature of the spinneret is preferably 120-190°C, and the length of the air gap is preferably 10 ~50cm, the temperature of the cooling liquid is preferably 20~70°C.

During extraction to form pores, the temperature of the extract solution is preferably 20-50° C., and the extraction time is preferably 24-48 hours.

The main raw materials used in the preparation method of the modified polyvinyl chloride hollow fiber microporous membrane are: polyvinyl chloride, preferably with a degree of polymerization between 600 and 3600; diluent, preferably selected from diphenyl ether, γ-1,4 - butyrolactone, sulfolane and oleic acid; tougheners, preferably selected from dibutyl phthalate, dioctyl phthalate, nitrile rubber, thermoplastic polyurethane and ethylene-vinyl acetate copolymer; stabilizers , preferably selected from methyl tin mercaptide, dibutyl tin dilaurate and di-n-octyl tin dilaurate; core liquid, which is the same as the diluent in the film-making material; cooling bath; it is water or The diluent in the film material is the same.

Invention effect

The modified polyvinyl chloride hollow fiber microporous membrane disclosed by the present invention adopts the thermally induced phase separation method in the membrane making process, so the membrane porosity is high, the membrane has no skin layer or the skin layer is ultra-thin, which is beneficial to the improvement of flux; The pore size is controllable in the range of 0.01-1.0 microns, and the pore size distribution is narrow, which can accurately control the retention performance of the membrane;

In addition, the preparation method of the modified polyvinyl chloride hollow fiber microporous membrane disclosed by the present invention has simple process, convenient operation, high efficiency, diversified pore structures can be obtained by changing few process parameters, and the controllability of the membrane structure is good. , good production repeatability;

In addition, the use of the toughening agent in the modified polyvinyl chloride hollow fiber microporous membrane disclosed by the present invention can greatly improve the mechanical properties of the membrane, so that the membrane can be used under higher pressure or hydraulic impact;

In addition, the modified polyvinyl chloride hollow fiber microporous membrane disclosed by the present invention has a sponge-like structure inside and high tensile strength;

In addition, in the preparation method of the modified polyvinyl chloride hollow fiber microporous membrane disclosed by the present invention, the used diluent and the waste liquid formed by the organic extractant are simple in composition, can be recycled and used, and have less pollutant discharge;

In addition, the toughening agent disclosed in the present invention has good compatibility with polyvinyl chloride, will not be lost during the process of film making and use, and ensures the long-lasting stability of the composition, physical structure and performance of the film.

In addition, the preparation method of the modified polyvinyl chloride hollow fiber microporous membrane disclosed by the invention has low raw material prices, low cost of obtaining the membrane, and high cost performance.

Description of drawings

Fig. 1 is the preparation process and flow chart of precursor hollow fiber membrane;

Fig. 2 (a) is the spinneret flow chart of preparing hollow fiber microporous membrane;

Fig. 2(b) is a diagram of the internal structure of the spinneret for preparing the hollow fiber microporous membrane.

Fig. 3 (a) is the polyvinyl chloride hollow fiber filter membrane scanning electron micrograph (surface) among the embodiment 7-B;

Fig. 3(b) is a scanning electron micrograph (section) of the polyvinyl chloride hollow fiber filter membrane in Example 7-B.

Detailed ways

For the improvement according to the present invention, which is mainly composed of polyvinyl chloride and toughening agent, has a pore size of 0.01-1.0 μm, a porosity of 40-80%, a film wall thickness of 0.10-0.30 mm, and a film outer diameter of 1-3 mm. The composition and structure control of the microporous polyvinyl chloride hollow fiber membrane is achieved by a preparation method based on the principle of thermally induced phase separation.

The preparation process of the membrane in the invention consists of three steps: preparation of membrane material, molding of precursor hollow fiber membrane and extraction to form holes. The preparation of the membrane-making material is to mix polyvinyl chloride, diluent, toughener and heat stabilizer, and then melt and blend to form a uniform membrane-making material; the forming of the hollow fiber membrane is to pass the molten membrane-making material through the hollow fiber molding process 1. Use water or diluent as a cooling bath to solidify into a precursor hollow fiber membrane (see Figure 1); the extraction of holes is to use an organic solvent to extract the diluent in the precursor hollow fiber membrane, and the dense structure of the precursor hollow fiber The membrane is converted to a hollow fiber microporous membrane. The three steps can be continuous or intermittent.

The composition of polyvinyl chloride hollow fiber microporous membrane among the present invention (being mainly the ratio of polyvinyl chloride and toughening agent), is determined by the ratio of polyvinyl chloride and toughening agent in the film-making liquid, and the aperture of membrane , porosity, thickness, outer diameter and other physical structure and retention performance are mainly determined by the membrane material formula and the molding process conditions of the hollow fiber membrane.

The polymer used in the present invention is polyvinyl chloride, and its degree of polymerization is preferably between 700 and 3000. It can also be used as a film-making material after blending polyvinyl chlorides with different degrees of polymerization in proportion according to the needs of processing and practical applications. raw material. In addition, since the preparation of the film-making liquid in the process of thermally induced phase separation is carried out at high temperature, and the stability of polyvinyl chloride at high temperature is very poor, it is necessary to add a certain amount of heat to the film-making liquid. Stabilizer to prevent thermal degradation of PVC. The heat stabilizer can be selected from stearic acid, organotin or lead compounds. In the present invention, methyl tin mercaptide, dibutyl tin dilaurate or di-n-octyl tin dilaurate are used. The added amount of the stabilizer is preferably 0.1% to 1.0%.

The diluent in the process of thermally induced phase separation membrane preparation is an organic solvent that can dissolve the polymer to form a homogeneous solution at high temperature and undergo phase separation at low temperature. In order to keep the composition of the homogeneous solution unchanged at high temperature, the diluent is required to have good stability at high temperature, low volatility and low toxicity. The diluent used in the present invention is diphenyl ether, γ-1,4-butyrolactone, sulfolane or oleic acid.

In the present invention, the polyvinyl chloride as the main material of the membrane belongs to a kind of brittle material, and the defect of this poor toughness greatly limits the application of polyvinyl chloride in the membrane separation technology, so select dibutyl phthalate, ortho Dioctyl phthalate, nitrile rubber, thermoplastic polyurethane or ethylene-vinyl acetate copolymer are used as toughening agents to achieve toughening modification of the film.

The porosity of the polyvinyl chloride hollow fiber microporous membrane in the present invention is mainly determined by the content of the diluent in the film-making material. The general principle is that when preparing a high-porosity membrane, the content of the diluent is high. On the other hand, when the content of the diluent is too high, the strength of the film will decrease. At this time, it is suitable to use polyvinyl chloride raw materials with a high degree of polymerization. In order to obtain a polyvinyl chloride hollow fiber microporous membrane with a porosity of 40-80%, the dosage of the diluent in the present invention is 40-85% of the weight of the total membrane-making material.

In the present invention, after the tubular liquid film extruded from the film-making material melt through the spinneret (see Figure 2) enters the cooling bath in the air, the liquid-liquid phase separation process occurs first, and then the solid-liquid phase separation process occurs . Depending on the polymer concentration and cooling rate, the mechanism of the liquid-liquid phase separation process is different, resulting in the formation of hollow fiber microporous membranes with different structures and properties. When the polymer concentration is high or the cooling rate is low, the liquid-liquid phase separation process proceeds through the nucleation growth mechanism, and a honeycomb pore structure is generated; when the polymer concentration is low or the cooling rate is high, the liquid-liquid When the phase separation process is carried out through the spinodal phase separation mechanism, the interpenetrating sponge-like pore structure is generated. Different polymer concentrations and cooling rates can be selected according to the needs of actual applications during production.

In the forming process of the precursor hollow fiber membrane of the present invention, the extrusion of the film-making material melt can be melted in the kettle and extruded under nitrogen pressure. The viscosity of the body is related to the phase separation behavior of the system. In the system determined in the present invention, preferably, the melt temperature used is 130-200°C.

In the molding process of the precursor hollow fiber membrane of the present invention, the diluent is used as the core liquid for hollow molding, and the tubular liquid film extruded from the spinneret enters the diluent or water cooling bath after a certain air gap to make the membrane The liquid film is solidified. At this stage, the temperature of the diluent, the distance of the air gap and the temperature of the cooling bath have an important influence on the pore structure of the final hollow fiber microporous membrane. The general rule is: when the temperature of the diluent increases, the distance of the air gap decreases or the temperature of the cooling bath increases, the membrane The micropore diameter is larger. In order to prepare a polyvinyl chloride hollow fiber microporous membrane with a pore size of 0.01-1.0 μm, preferably, the temperature of the diluent core liquid used in the present invention is 30-60°C, the air gap distance is 10-50 cm, and the cooling bath The temperature is 20-70°C, wherein the diluent is the same as the diluent in the film-making material.

In the present invention, pore formation is achieved by extracting the diluent in the precursor hollow fiber membrane with a solvent (extractant). The principle of extractant selection is not to affect the phase separation structure in the precursor hollow fiber membrane, only to extract the continuous phase formed by the diluent and convert this region into micropores. In the system proposed by the present invention, ethanol, methanol, isopropanol or cyclohexane can be used as the extractant. Considering the cost and safety of practical application, ethanol is the best diluent. In order to ensure that the diluent is fully extracted, the present invention proposes a process of soaking in the extractant at 20-50°C for 24-48 hours.

The following are examples of the modified polyvinyl chloride hollow fiber microporous membrane and its preparation method, but the examples do not constitute a limitation to the present invention.

The implementation conditions of the embodiments, the implementation steps of all the embodiments are the same as the aforementioned implementation steps, and the raw materials used are products supplied in large quantities on the market.

Example

Example 1

(1) Preparation of film-making materials: polyvinyl chloride (polymerization degree of 3600), diphenyl ether, dibutyl phthalate, and di-n-octyl tin dilaurate in a ratio of 15:79:5:1 Add it into the melting material kettle, heat the material to 140°C under stirring and nitrogen protection, melt and form a uniform film-making material for 1 hour, and then let it stand for defoaming.

(2) Precursor hollow fiber membrane forming: using diphenyl ether as the core liquid, extruding the melt of the film-making material through the spinneret under a certain pressure to form a tubular liquid film, the liquid film enters the water after passing through an air gap. Solidified into a precursor hollow fiber membrane in a cooling bath;

(3) Extraction to form pores: soak the precursor hollow fiber membrane in ethanol extractant at 20° C. for 24 hours, take it out and dry it in the air to obtain the polyvinyl chloride hollow fiber microporous membrane.

The various implementation conditions and the structure and properties of the obtained polyvinyl chloride hollow fiber microporous membrane are shown in Table 1.

Table 1

Example 2

The preparation steps are the same as in Example 1, and the various implementation conditions and the structure and performance of the obtained polyvinyl chloride hollow fiber microporous membrane are shown in Table 2.

Table 2

Example 3

The preparation steps are the same as in Example 1, and the various implementation conditions and the structure and performance of the obtained polyvinyl chloride hollow fiber microporous membrane are shown in Table 3.

table 3

Example 4

The preparation steps are the same as in Example 1, and the various implementation conditions and the structure and properties of the obtained polyvinyl chloride hollow fiber microporous membrane are shown in Table 4.

Table 4

Example 5

The preparation steps are the same as in Example 1, and the various implementation conditions and the structure and properties of the obtained polyvinyl chloride hollow fiber microporous membrane are shown in Table 5.

table 5

Example 6

The preparation steps are the same as in Example 1, and the various implementation conditions and the structure and performance of the obtained polyvinyl chloride hollow fiber microporous membrane are shown in Table 6.

Table 6

Example 7

The preparation steps are the same as in Example 1, the various implementation conditions and the structure and performance of the polyvinyl chloride hollow fiber microporous membrane are shown in Table 7, and the electron microscope photo of the hollow fiber microporous membrane in Example 7-B is shown in Figure 3 .

Table 7

Example 8

The preparation steps are the same as in Example 1, and the various implementation conditions and the structure and performance of the obtained polyvinyl chloride hollow fiber microporous membrane are shown in Table 8.

Table 8

Example 9

The preparation steps are the same as in Example 1, and the various implementation conditions and the structure and properties of the obtained polyvinyl chloride hollow fiber microporous membrane are shown in Table 9.

Table 9

Claims (10)

1. modified polyvinyl chloride hollow fiber microporous membrane, it is characterized in that described modified polyvinyl chloride hollow fiber microporous membrane has spongelike structure, micropore size is at 0.01～1.0 μ m, membrane porosity is 40～80%, membranous wall is thick to be 0.10～0.30mm, the film external diameter is 1.0～3.0mm, and wherein, the key component of described modified polyvinyl chloride hollow fiber microporous membrane is the polyvinyl chloride of 70～95 weight % and the flexibilizer of 5～30 weight %.

2. modified polyvinyl chloride hollow fiber microporous membrane as claimed in claim 1, the degree of polymerization that it is characterized in that described polyvinyl chloride is between 600～3600.

3. modified polyvinyl chloride hollow fiber microporous membrane as claimed in claim 1 is characterized in that described polyvinyl chloride is the mixture with polyvinyl chloride of different polymerization degree.

4. as each described modified polyvinyl chloride hollow fiber microporous membrane of claim 1-3, it is characterized in that described flexibilizer is selected from dibutyl phthalate, dioctyl phthalate, acrylonitrile-butadiene rubber, thermoplastic polyurethane and ethylene-vinyl acetate copolymer.

5. the preparation method of modified polyvinyl chloride hollow fiber microporous membrane as claimed in claim 1, it comprises the steps:

(1) preparation system coating materials: polyvinyl chloride, diluent, flexibilizer are mixed with heat stabilizer, melt blending becomes system coating materials uniformly, wherein the weight percentage of said components is: polyvinyl chloride: 10-50%, diluent: 40-85%, flexibilizer: 0.5-10% and heat stabilizer: 0.1%-1%;

(2) precursor hollow-fibre membrane moulding: with the diluent is core liquid, above-mentioned system coating materials under high pressure is extruded into the tubulose liquid film through spinning head, this liquid film enters after through one section the air gap and is solidified into polyvinyl chloride precursor hollow-fibre membrane in the cooling bath, wherein, described core liquid is identical with the kind of diluent in the system coating materials; Described cooling bath is diluent or water in the system coating materials;

(3) extraction pore-forming: with the precursor hollow-fibre membrane of polyvinyl chloride in extractant, soaks extract after, in air, dry and obtain described polyvinyl chloride hollow fiber microporous membrane.

6. preparation method as claimed in claim 5, the degree of polymerization that it is characterized in that described polyvinyl chloride is between 600-3600.

7. preparation method as claimed in claim 5 is characterized in that described polyvinyl chloride is the mixture with polyvinyl chloride of different polymerization degree.

8. preparation method as claimed in claim 5 is characterized in that described diluent is selected from diphenyl ether, γ-1,4-butyrolactone, sulfolane and oleic acid.

9. preparation method as claimed in claim 5 is characterized in that described flexibilizer is selected from dibutyl phthalate, dioctyl phthalate, acrylonitrile-butadiene rubber, thermoplastic polyurethane and ethylene-vinyl acetate copolymer.

10. preparation method as claimed in claim 5 is characterized in that described heat stabilizer is selected from thiol methyl tin, dibutyl tin dilaurate and di-n-octyl two laurate tin.

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