A method for optimizing the morphology of high efficiency initiated polyvinyl chloride resin particles

Abstract

The application belongs to the technical field of polyvinyl chloride resin production, and specifically provides a method for optimizing and efficiently initiating the particle morphology of polyvinyl chloride resin, which comprises the following steps: mixing a buffer, soft water, a dispersing agent and a surfactant, adding monomers and increasing the temperature to the polymerization temperature, adding a high-efficiency initiator to perform polymerization, adding a small amount of defoaming agent after the reaction is completed, and then performing filtration, washing and drying to obtain the PVC resin. In the preparation of the PVC resin, the surfactant is added to enhance the lipophilicity of the dispersion system and strengthen the colloidal protection of the primary particles, which is conducive to improving the uniformity of the primary particle size and porosity. The PVC resin prepared by the method has high porosity, narrow particle size distribution and regular particle morphology.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyvinyl chloride resin production, and particularly relates to a method for optimizing and efficiently initiating polymerization of polyvinyl chloride resin particles. BACKGROUND

[0002] Polyvinyl chloride resin (PVC) is a polymer formed by free radical polymerization of vinyl chloride monomer under the action of an initiator, has low price and excellent performance, and is widely used in building materials, industrial products, daily necessities, electric wires and cables, fibers, and the like, and is the second largest general-purpose polymer resin in global production capacity. There are many polymerization methods for polyvinyl chloride resin, which can be divided into the following categories: bulk polymerization, emulsion polymerization, suspension polymerization, and solution polymerization, among which, suspension polymerization is the most important polymerization method, accounting for more than half of the total polyvinyl chloride production. In the process of preparing polyvinyl chloride resin by using the suspension polymerization method, many additives need to be added, including initiators, plasticizers, stabilizers, blowing agents, pigments, and the like, which can affect the processing performance and finished product performance of polyvinyl chloride resin. Due to the wide application of polyvinyl chloride, in order to improve market competitiveness, polyvinyl chloride resin manufacturers are striving to improve production efficiency and improve resin quality.

[0003] The production efficiency can be improved by reducing the polymerization reaction time, and generally, based on the heat removal capacity of the polymerization kettle, one or more high-efficiency initiator systems composed of one or more initiators are used to shorten the reaction time. Generally, one or more high-activity initiators with a half-life of less than 1 hour at 60℃ are continuously or semi-continuously added to the polymerization kettle, but inevitably, due to the too fast generation speed of primary particles, the traditional dispersion and stirring system cannot effectively protect the primary particles, resulting in severe Brownian motion of the primary particles, rapid aggregation of the primary particles to form primary particle agglomerates, large PVC particle size, wide particle size distribution, and a large number of small particles adhering to the surface of the PVC resin particles.

[0004] The PVC resin particles generated under the high-efficiency initiator system have large particle size, wide particle size distribution, irregular particle morphology, and a large number of small particles adhering to the surface, which not only affects the quality of PVC products, but also greatly affects the downstream processing and application, showing uneven plasticization and poor product quality. Patent CN102453175 discloses a preparation method of polyvinyl chloride resin, which adds C4-C 10Alkanes as functional aids improve the morphology of polyvinyl chloride resin particles, the obtained resin is loose and porous inside, has high porosity and uniform pore distribution, and high oil absorption rate. Patent CN114478882A discloses a preparation method of PVC resin, by adding chloroethane functional aid, which does not participate in the reaction of chloroethylene, but plays a dispersing effect, speeds up the dispersion of chloroethylene monomer, in the polymerization process, chloroethane is removed from the polymerized chloroethylene chain to support the skin film formed on the chain surface, resulting in a thin skin film, and finally removing the broken skin film to form a large number of pores, improve the porosity of the final PVC resin product, improve the oil absorption rate of polyvinyl chloride resin, plasticizer absorption effect, and shorten the removal of residual chloroethylene in PVC resin. CN102443085A provides a preparation method of chlorinated special polyvinyl chloride resin, by the combined action of a water-soluble dispersant and an oil-soluble surfactant, a loose and low-skin polyvinyl chloride resin with large specific surface area is synthesized, but there is no obvious effect of improving the pore performance of the particle inside.

[0005] Although improvements have been made to solve the problem of poor particle morphology of high-efficiency initiated polyvinyl chloride resin, but still cannot meet the polyvinyl chloride resin with high porosity, regular particle morphology and uniform particle size distribution. Therefore, it is of great practical significance to optimize the production method of polymerized polyvinyl chloride resin. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a method for optimizing the particle morphology of high-efficiency initiated polymerized polyvinyl chloride resin. The polyvinyl chloride resin prepared by the method has high porosity, regular particle morphology and uniform particle size distribution.

[0007] The purpose of the present application can be achieved by the following technical solutions:

[0008] A method for optimizing the particle morphology of high-efficiency initiated polymerized polyvinyl chloride resin, comprising the following steps:

[0009] Step one, coating the polymerization kettle with coating kettle liquid;

[0010] Step two, add buffer, soft water, composite dispersant and surfactant to the polymerization kettle and mix uniformly;

[0011] Step three, discharge the air in the kettle, add chloroethylene monomer, and heat to the polymerization temperature;

[0012] Step four, add high-activity initiator for reaction;

[0013] Step five, add terminating agent to terminate the reaction and add defoaming agent;

[0014] Step six, obtain polyvinyl chloride resin after post-treatment.

[0015] The present application adds surfactant in the production process, enhances the lipophilicity of the dispersion system, makes the dispersant mainly disperse on the surface of the vinyl chloride droplets, stabilizes the primary particles, improves the uniformity of the primary particle size and porosity, makes up for the deficiencies of the prior art, and makes the obtained polyvinyl chloride resin have high porosity, regular particle morphology and uniform particle size distribution, which is beneficial to downstream post-processing.

[0016] Further, in step one, the coating liquid, i.e., the anti-sticking kettle agent, is selected from any one or mixture of several of dyes, inorganic reducing agents, and nitrite salts; preferably, it is the Italian yellow anti-sticking kettle agent.

[0017] The polymerization kettle is coated with the above-mentioned coating liquid, which is an alkaline solution, and a dense protective layer is formed on the inner surface and the surface of the internal components of the polymerization kettle to prevent or reduce sticking.

[0018] Further, in step one, the amount of the coating liquid is preferably 0.01% to 1.0% of the mass of vinyl chloride, further preferably 0.02% to 0.1%, and more preferably 0.025% to 0.05%.

[0019] Further, in step two, the buffering agent is a pH regulator selected from any one or mixture of several of calcium hydroxide aqueous solution, sodium bicarbonate aqueous solution, and ammonium bicarbonate aqueous solution, and is further preferably sodium bicarbonate aqueous solution or ammonium bicarbonate aqueous solution, and more preferably ammonium bicarbonate aqueous solution. The addition of the buffering agent can maintain the pH value in the polymerization kettle within the neutral range, which is beneficial to the stability of the colloid.

[0020] Further, in step two, the concentration of the buffering agent is preferably 0.1% to 2%, further preferably 0.5% to 1%, and more preferably 0.8%; and the dry basis amount of the buffering agent is preferably 0.001% to 1.0% of the mass of vinyl chloride, further preferably 0.002% to 0.1%, and more preferably 0.0025% to 0.05%.

[0021] Further, in step two, the amount of the soft water is preferably 50% to 500% of the mass of vinyl chloride, more preferably 75% to 400%, and most preferably 100% to 300%. The soft water is not only a dispersion medium for suspension polymerization, but also a heat transfer medium for removing reaction heat.

[0022] Further, in step two, the composite dispersant is selected from one or more of cellulose ethers, partially alcoholized polyvinyl alcohol, maleic anhydride, styrene, or vinyl acetate alternating copolymer, and is further preferably three polyvinyl alcohols with different alcoholization degrees, and more preferably polyvinyl alcohols with alcoholization degrees of 72%, 80%, and 40%.

[0023] Further, the polyvinyl alcohol is added in the form of an aqueous solution, with a concentration of 1% to 10%, preferably 5%; the dry basis amount of 70% to 75% alcoholysis degree polyvinyl alcohol is preferably 0.005% to 1.0%, further preferably 0.01% to 0.5%, more preferably 0.015% to 0.1% of the mass of the vinyl chloride; the dry basis amount of 78% to 85% alcoholysis degree polyvinyl alcohol is preferably 0.01% to 1.0%, further preferably 0.02% to 0.5%, more preferably 0.03% to 0.1% of the mass of the vinyl chloride; the dry basis amount of 35% to 50% alcoholysis degree polyvinyl alcohol is preferably 0.005% to 1.0%, further preferably 0.01% to 0.5%, more preferably 0.015% to 0.1% of the mass of the vinyl chloride.

[0024] The dispersant has a dual role of reducing interfacial tension and colloidal protection in the suspension polymerization, and an organic dispersant is currently often used in the production of PVC by suspension method, mainly cellulose ethers, partially alcoholized polyvinyl alcohol or a combination of the two, and the present application selects a mixture of polyvinyl alcohol with high and low alcoholysis degrees as a composite dispersant, which can achieve more excellent dispersing effect, thereby improving the performance of the final product PVC resin.

[0025] Further, in step three, the polymerization temperature is 30 to 70°C, preferably 40 to 60°C, more preferably 50 to 60°C; the reaction time is 1 to 40h, preferably 1 to 30h, further preferably 2 to 20h.

[0026] Further, in step four, the surfactant is sorbitan fatty acid ester surfactant, preferably any one or a mixture of several of sorbitan monolaurate (Span-20, hydrophilic-lipophilic balance HLB = 8.6), sorbitan monopalmitate (Span-40, HLB = 6.7), sorbitan monostearate (Span-60, HLB = 4.7), sorbitan tristearate (Span-65, HLB = 2.1), sorbitan monooleate (Span-80, HLB = 4.3) and sorbitan trioleate (Span-85, HLB = 1.8), more preferably a mixture of Span-60 and Span-80, with a mixing mass ratio of 0.1 to 10:1, preferably 0.5 to 2:1. The total amount of the surfactant is preferably 0.001% to 0.5%, further preferably 0.001% to 0.25%, more preferably 0.001% to 0.015% of the mass of the vinyl chloride.

[0027] The present application adds surfactant on the basis of dispersant, enhances the lipophilicity of dispersion system, makes the dispersant mainly disperse on the surface of vinyl chloride droplets, can stabilize the primary particles, improve the uniformity of primary particle size and porosity, through controlling the addition type and amount of surfactant, can improve the resin porosity, and control the resin particle size and particle size distribution in the optimal range, finally get the PVC resin with optimal particle morphology, which is beneficial to the downstream post-processing.

[0028] Further, in step four, the high-activity initiator is any one of peroxide or azo compound, preferably a mixture of diisobutyryl peroxide, cumyl phenyl peroxide, di-3-methoxy butyl peroxide carbonate, 1,1,3,3-tetramethyl butyl peroxide neodecanoate, preferably diisobutyryl peroxide or cumyl phenyl peroxide, and further preferably diisobutyryl peroxide.

[0029] Further, in step four, the high-activity initiator is added in the form of emulsion, the concentration is 0.1%-5%, preferably 0.5%-2%; the ratio of the dry base amount to the mass of vinyl chloride monomer in the kettle is 0.0001-0.002, preferably 0.00015-0.0015, and further preferably 0.0002-0.001.

[0030] The high-activity initiator can be continuously added after heating to the polymerization temperature, or can be added semi-continuously after the addition of buffer, soft water, monomer, dispersant and surfactant, but is preferably continuously added.

[0031] Further, in step five, the defoaming agent is selected from at least one of polyether, silicone oil, preferably polyoxypropylene glycerol ether, polyoxyethylene polyoxypropylene pentaerythritol ether and phenylethyl phenol polyoxyethylene ether, and more preferably polyoxypropylene glycerol ether.

[0032] Further, the amount of the defoaming agent is preferably 0.005%-1.0% of the mass of vinyl chloride, further preferably 0.01%-0.5%, and more preferably 0.015%-0.1%. The defoaming agent is added after the completion of the polymerization reaction, which can inhibit the foam generated in the processes of polymerization discharge recovery and discharge, ensure the heat transfer effect and prevent pipeline blockage, etc.

[0033] Further, in step five, the terminating agent is selected from any one of acetone thiosemicarbazone, bisphenol A, diethyl hydroxylamine, nitrous acid, more preferably acetone thiosemicarbazone or diethyl hydroxylamine, and further preferably acetone thiosemicarbazone; the amount is preferably 0.01%-1.0% of the mass of vinyl chloride, further preferably 0.015%-0.5%, and more preferably 0.02%-0.2%.

[0034] Further, in step five, the post-treatment step comprises: cooling after the reaction, vacuumizing, centrifugal filtering, washing, and drying.

[0035] Compared with the prior art, the present application has the following beneficial effects:

[0036] 1) The present application provides a method for optimizing the particle morphology of the polymerized polyvinyl chloride resin, and the polyvinyl chloride resin prepared by the method has high porosity, regular particle morphology, and uniform particle size distribution.

[0037] 2) The surfactant is added on the basis of the dispersant, which enhances the lipophilicity of the dispersion system, makes the dispersant mainly disperse on the surface of the chloroethylene droplets, stabilizes the primary particles, and improves the uniformity of the primary particle size and porosity. By controlling the type and amount of the surfactant, the resin porosity can be improved, and the resin particle size and particle size distribution can be controlled in an optimal range, so that the polyvinyl chloride resin with optimal particle morphology is finally obtained, which is beneficial to downstream processing. DETAILED DESCRIPTION

[0038] The following non-limiting examples can enable those of ordinary skill in the art to more fully understand the present application, but in no way limit the present application. The following content is only an exemplary description of the scope of the present application, and those skilled in the art can make various changes and modifications to the application disclosed herein, which should also be within the scope of the present application.

[0039] In addition, the terms used in the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular form is also intended to include the plural form unless the context clearly indicates otherwise. It will be further understood that when the terms "comprise", "have" and "include" are used in the present disclosure, they specify the presence of the features, numbers, steps, components or combinations thereof mentioned, but do not exclude the presence or addition of one or more other features, numbers, steps, components or combinations thereof.

[0040] The term "dry basis amount" in the present application refers to the amount of material added in the dry state. The buffer, composite dispersant and high activity initiator in the present application are added in the form of solution or emulsion, and the dry basis amount refers to the amount of the material in the solution or emulsion. The term "soft water" refers to water with a hardness of less than 8 degrees. The term "high activity initiator" refers to an initiator with a half-life of less than 1 hour at 60℃. The term "alcoholysis degree" refers to the percentage of hydroxyl groups in the original groups in the product obtained after alcoholysis.

[0041] The present application will be further described below in the form of specific examples. The various chemical reagents used in the examples of the present application are obtained through conventional commercial channels unless otherwise specified.

[0042] Example 1

[0043] A method for optimizing the morphology of high efficiency initiated polymerized polyvinyl chloride resin particles comprising the following steps:

[0044] Step one, coating the polymerization reactor (5L) with 0.4g of Italy yellow anti-sticking agent;

[0045] Step two, adding 1050g of soft water, 4.3g of 0.8% sodium bicarbonate aqueous solution, 3.6g of 5% 72% alcoholysis degree polyvinyl alcohol solution, 14.8g of 5% 80% alcoholysis degree polyvinyl alcohol solution, 6.2g of 5% 40% alcoholysis degree polyvinyl alcohol solution into the polymerization reactor, adding 0.05g of Span-60, and mixing uniformly;

[0046] Step three, pressurizing with nitrogen to 9.38bar to observe whether there is leakage, and if no leakage is observed, vacuumizing and pressurizing with nitrogen to 3bar three times to substantially blow out all air, adding 1000g of vinyl chloride monomer, and heating to 56℃;

[0047] Step four, continuously adding 30g of diisobutyryl peroxide (used as a 1% concentration aqueous emulsion), and circulating water into the circulating pump to maintain the temperature of the reaction;

[0048] Step five, observing the pressure drop to 0.1MPa, adding 0.5g of acetone thiosemicarbazone to terminate the reaction, and discharging the suspension in the reactor into the discharge tank with the assistance of a filter and a discharge pump, and adding 0.5g of polyoxypropylene glycol ether to reduce the carryover amount;

[0049] Step six, vacuumizing after cooling to 25℃, centrifugal filtering, washing, and drying to obtain the polyvinyl chloride resin.

[0050] Example 2

[0051] Another method for optimizing the morphology of high efficiency initiated polymerized polyvinyl chloride resin particles, the amounts of components and steps of which are basically the same as those of Example 1, except that the amount of the surfactant Span-60 in Step two is 0.10g.

[0052] Example 3

[0053] Another method for optimizing the morphology of high efficiency initiated polymerized polyvinyl chloride resin particles, the amounts of components and steps of which are basically the same as those of Example 1, except that the amount of the surfactant Span-60 in Step two is 0.15g.

[0054] Example 4

[0055] Another method for optimizing the morphology of the particles of the polymerized polyvinyl chloride resin, which is basically the same as that of Example 1, except that the amount of the surfactant Span-60 in step 2 is 0.20 g.

[0056] Example 5

[0057] Another method for optimizing the morphology of the particles of the polymerized polyvinyl chloride resin, which is basically the same as that of Example 1, except that the surfactant in step 2 is replaced by 0.05 g of Span-20.

[0058] Example 6

[0059] Another method for optimizing the morphology of the particles of the polymerized polyvinyl chloride resin, which is basically the same as that of Example 1, except that the surfactant in step 2 is replaced by 0.05 g of Span-80.

[0060] Example 7

[0061] Another method for optimizing the morphology of the particles of the polymerized polyvinyl chloride resin, which is basically the same as that of Example 1, except that the surfactant in step 2 is replaced by 0.025 g of Span-60 and 0.025 g of Span-80.

[0062] Comparative Example 1

[0063] Another method for optimizing the morphology of the particles of the polymerized polyvinyl chloride resin, which is basically the same as that of Example 1, except that the surfactant Span-60 in step 2 is replaced by 1 g of a 40% alcoholysis degree polyvinyl alcohol having a concentration of 5%.

[0064] Comparative Example 2

[0065] Another method for optimizing the morphology of the particles of the polymerized polyvinyl chloride resin, which is basically the same as that of Example 1, except that the complex dispersant in step 2 is replaced by 3.6 g of a 72% alcoholysis degree polyvinyl alcohol solution having a concentration of 5%, 14.8 g of an 80% alcoholysis degree polyvinyl alcohol solution having a concentration of 5%, and 6.2 g of hydroxypropyl methylcellulose having a concentration of 5%.

[0066] Comparative Example 3

[0067] Another method for optimizing the morphology of the particles of the polymerized polyvinyl chloride resin, which is basically the same as that of Example 1, except that the complex dispersant in step 2 is replaced by 12.4 g of hydroxypropyl methylcellulose having a concentration of 5%.

[0068] Experimental Examples

[0069] The polyvinyl chloride resins prepared in the above examples and comparative examples were subjected to the following performance tests, wherein the apparent density was tested in accordance with the standard GB-T 20022-2005, the oil absorption was tested in accordance with the standard GB / T 3400-2002, and the volume average diameter (i.e. d[4,3]) and the particle size distribution (i.e. the ratio of (d90-d10) / d50) of the resins were tested by using a laser particle size analyzer, and the results are shown in Table 1 below.

[0070] Table 1 Properties of polyvinyl chloride resins

[0071] Group Apparent density (g / mL) Volume average diameter (μm) Particle size distribution (μm / μm) Oil absorption (g / g) Example 1 0.436 203.2 0.668 30.65 Example 2 0.423 233.8 0.709 30.83 Example 3 0.414 212.1 0.717 33.92 Example 4 0.377 249.9 0.787 61.22 Example 5 0.441 231.4 0.782 29.04 Example 6 0.490 197.3 0.643 28.87 Example 7 0.462 198.7 0.651 30.01 Comparative Example 1 0.502 188.4 0.771 28.30 Comparative Example 2 0.487 172.6 0.683 26.82 Comparative Example 3 0.450 153.2 0.891 19.26

[0072] As can be seen from Table 1, in Comparative Example 1, no surfactant was added, and the obtained polyvinyl chloride resin had a high apparent density, a small volume average diameter, a large particle size distribution, and a low oil absorption, which indicated that the porosity of the obtained resin was low and the pore size was uneven. However, when the surfactant was added (Examples 1-4), the apparent density of the obtained resin was significantly reduced, the volume average diameter was increased, the particle size distribution was narrowed, and the oil absorption was improved, which indicated that the addition of the surfactant helped to enhance the lipophilicity of the dispersion system, so that the dispersant was mainly dispersed on the surface of the vinyl chloride droplets, which could stabilize the primary particles, improve the uniformity of the primary particle size and porosity, and thus obtain a resin with a more uniform particle size distribution and improve the oil absorption of the resin. As can be seen from Comparative Examples 1-4, when the amount of Span-60 surfactant was increased, the oil absorption of the resin was further improved, but the particle size distribution tended to be wider, and the apparent density gradually decreased. When the amount was 0.005%, the particle size distribution was the narrowest, and the oil absorption and apparent density were better than those of the resin of Comparative Example 1. When the amount was further increased to 0.015%, the oil absorption was increased to the highest of 33.92 g / 100 g PVC, but the particle size distribution of the resin was significantly wider than that when the amount of the surfactant was 0.05% of the mass of vinyl chloride.

[0073] In addition, as can be seen from the results of Comparative Examples 1, 6 and 7, the type of surfactant also had a significant effect on the resin. When a composite additive was used (Example 7), the particle size distribution was narrower than when Span 60 was used alone, although the oil absorption was slightly reduced, but the apparent density was significantly improved, i.e. the polyvinyl chloride resin particles prepared by using a composite surfactant were more uniform.

[0074] In addition, from the results of Example 1 and Comparative Examples 2 and 3, it can be seen that the component ratio of the composite dispersant greatly affects the properties of the resin, and compared with using hydroxypropyl methyl cellulose instead of 40% alcoholysis degree polyvinyl alcohol as the composite dispersant, or using only hydroxypropyl methyl cellulose as the dispersant, the composite dispersant using three alcoholysis degrees provided by the present application can obtain more excellent glue retention and dispersion effect, thereby improving the properties of the final product PVC resin.

[0075] The above description of the embodiments is to facilitate the understanding and use of the present application by those of ordinary skill in the art. Those skilled in the art can obviously make various modifications to these embodiments and apply the general principles described herein to other embodiments without having to undergo creative labor. Therefore, the present application is not limited to the above-described embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present application without departing from the scope of the present application should be within the scope of protection of the present application.

Claims

1. A method for optimizing the morphology of polyvinyl chloride resin particles, characterized in that, Includes the following steps: Step 1: Coat the polymerization reactor with a coating solution; Step 2: Add buffer, soft water, composite dispersant, and surfactant to the polymerization reactor and mix thoroughly. Step 3: Purge the air from the reactor, add vinyl chloride monomer, and heat to the polymerization temperature; Step 4: Add a highly active initiator to initiate the reaction; Step 5: Add a terminator to stop the reaction, and add an antifoaming agent; Step 6: After post-treatment, polyvinyl chloride resin is obtained; The highly active initiator is any one or a mixture of several of the following: diisobutyryl peroxide, cumyl peroxyneodecanate, di-3-methoxybutyl peroxydicarbonate, and 1,1,3,3-tetramethylbutyl peroxyneodecanate; the highly active initiator is added in the form of an emulsion at a concentration of 0.1%-5%; the ratio of its dry basis dosage to the mass of vinyl chloride monomer in the reactor is 0.0001-0.002; The composite dispersant is polyvinyl alcohol with 72%, 80%, and 40% degree of hydrolysis; the polyvinyl alcohol is added in the form of an aqueous solution at a concentration of 1%-10%; wherein the dry basis amount of the 72% hydrolyzed polyvinyl alcohol is 0.005%-1.0% of the mass of vinyl chloride; and the dry basis amount of the 80% hydrolyzed polyvinyl alcohol is 0.01-1.0% of the mass of vinyl chloride. The dry basis dosage of 40% hydrolyzed polyvinyl alcohol is 0.005%-1.0% of the mass of vinyl chloride; The surfactant is any one or a mixture of several of Span-20, Span-40, Span-60, Span-65, and Span-80; the amount of surfactant used is 0.001%-0.5% of the mass of vinyl chloride.

2. The method according to claim 1, characterized in that, The buffer is a pH adjuster, selected from any one of calcium hydroxide aqueous solution, sodium bicarbonate aqueous solution, and ammonium bicarbonate aqueous solution.

3. The method according to claim 2, characterized in that, The pH adjuster is an aqueous solution of sodium bicarbonate or an aqueous solution of ammonium bicarbonate.

4. The method according to claim 3, characterized in that, The pH adjuster is an aqueous solution of ammonium bicarbonate.

5. The method according to claim 1, characterized in that, The concentration of the buffer is 0.1%-2%, and the dry basis amount of the buffer is 0.001%-1.0% of the mass of vinyl chloride.

6. The method according to claim 5, characterized in that, The dry basis amount of buffer is 0.002%-0.1% of the mass of vinyl chloride.

7. The method according to claim 6, characterized in that, The dry basis amount of buffer is 0.0025%-0.05% of the mass of vinyl chloride.

8. The method according to claim 1, characterized in that, Polyvinyl alcohol was added in the form of an aqueous solution at a concentration of 5%.

9. The method according to claim 1, characterized in that, The dry basis dosage of 72% hydrolyzed polyvinyl alcohol is 0.01%-0.5% of the mass of vinyl chloride; the dry basis dosage of 80% hydrolyzed polyvinyl alcohol is 0.02%-0.5% of the mass of vinyl chloride. The dry basis dosage of 40% hydrolyzed polyvinyl alcohol is 0.01%-0.5% of the mass of vinyl chloride.

10. The method according to claim 9, characterized in that, The dry basis dosage of 72% hydrolyzed polyvinyl alcohol is 0.015%-0.1% of the mass of vinyl chloride; the dry basis dosage of 80% hydrolyzed polyvinyl alcohol is 0.03%-0.1% of the mass of vinyl chloride. The dry basis dosage of 40% hydrolyzed polyvinyl alcohol is 0.015%-0.1% of the mass of vinyl chloride.

11. The method according to claim 1, characterized in that, The surfactant is a mixture of Span-60 and Span-80.

12. The method according to claim 1, characterized in that, The amount of surfactant used is 0.001%-0.25% of the mass of vinyl chloride.

13. The method according to claim 12, characterized in that, The amount of surfactant used is 0.001%-0.015% of the mass of vinyl chloride.

14. The method according to claim 11, characterized in that, The mixing mass ratio of Span-60 and Span-80 is 0.1-10:

1.

15. The method according to claim 1, characterized in that, The highly active initiator is diisobutyryl peroxide or cumyl peroxide neodecanoate.

16. The method according to claim 15, characterized in that, The highly active initiator is diisobutyryl peroxide.

17. The method according to claim 1, characterized in that, The highly active initiator is added in the form of an emulsion at a concentration of 0.5%-2%; the ratio of the dry basis amount of the highly active initiator to the mass of vinyl chloride monomer in the reactor is 0.00015-0.0015.

18. The method according to claim 17, characterized in that, The ratio of the dry basis amount of the highly active initiator to the mass of vinyl chloride monomer in the reactor is 0.0002-0.

001.

19. The method according to claim 1, characterized in that, The post-processing steps include: cooling after the reaction is completed, vacuuming, centrifugation and filtration, washing, and drying.