阅读说明：本技术 一种聚偏氟乙烯树脂的制备方法 (Preparation method of polyvinylidene fluoride resin ) 是由 周晓勇 陈振华 卢泉轩 蔡怀勋 姜澜 于 2020-10-21 设计创作，主要内容包括：本发明公开了种聚偏氟乙烯树脂的制备方法,包括偏氟乙烯单体聚合、热处理以及后处理,聚合步骤中按重量份数,将去离子水100份,分散剂0.005-0.02份,引发剂0.05-0.2份,链转移剂0.1-1份,VDF单体15-30份加入聚合釜,在低温下聚合反应至压降特定值后,回收VDF单体至聚合釜压力为微正压,进一步对聚合釜加热至较高温度,加入0.03-0.1份还原剂进行原位热处理一定时间后,收集物料,采用冷水热水交替洗涤树脂,然后干燥得到纯净的PVDF树脂成品。由此制得的PVDF树脂不但具有很高的结晶度,而且具有很好的热稳定性。(The invention discloses a preparation method of polyvinylidene fluoride resin, which comprises polymerization, heat treatment and post-treatment of vinylidene fluoride monomer, wherein in the polymerization step, 100 parts of deionized water, 0.005-0.02 part of dispersing agent, 0.05-0.2 part of initiator, 0.1-1 part of chain transfer agent and 15-30 parts of VDF monomer are added into a polymerization kettle according to parts by weight, after polymerization reaction is carried out at low temperature to a specific pressure drop value, the VDF monomer is recovered to the polymerization kettle with the pressure of micro positive pressure, the polymerization kettle is further heated to higher temperature, 0.03-0.1 part of reducing agent is added for in-situ heat treatment for a certain time, materials are collected, cold water and hot water are adopted to alternately wash the resin, and then the pure PVDF resin finished product is obtained after drying. The PVDF resin prepared by the method not only has high crystallinity, but also has good thermal stability.)

1. A preparation method of polyvinylidene fluoride resin comprises polymerization, heat treatment and post-treatment of vinylidene fluoride monomers, and is characterized in that in the polymerization step, 100 parts of deionized water, 0.005-0.02 part of dispersing agent, 0.05-0.2 part of initiator, 0.1-1 part of chain transfer agent and 15-30 parts of VDF monomer are added into a polymerization kettle according to parts by weight, after polymerization reaction is carried out at low temperature to a specific pressure drop value, the VDF monomer is recovered to the polymerization kettle with the pressure of micro positive pressure, the polymerization kettle is further heated to a higher temperature, 0.03-0.1 part of reducing agent is added for in-situ heat treatment for a certain time, materials are collected, cold water and hot water are adopted to alternately wash the resin, and then the resin is dried to obtain a pure PVDF resin finished product.

2. The method for preparing polyvinylidene fluoride resin according to claim 1, characterized in that: the dispersant and the chain transfer agent are well known in the industry, for example, the dispersant is cellulose or polyethylene glycol water-soluble polymer, and the chain transfer agent is ethyl acetate, acetone, diethyl carbonate and the like.

3. The method for preparing polyvinylidene fluoride resin according to claim 1, characterized in that: the low-temperature polymerization temperature is 0-30 ℃.

4. The polyvinylidene of claim 1The preparation method of the vinyl fluoride resin is characterized by comprising the following steps: the initiator is a low-temperature high-activity initiator with half-life period of T_10h≤50℃。

5. The method for preparing polyvinylidene fluoride resin according to claim 1, characterized in that: the reaction pressure drop is 0.1-1.5 Mpa.

6. The method for preparing polyvinylidene fluoride resin according to claim 1, characterized in that: and after the polymerization reaction reaches specified pressure drop, recovering and decompressing the VDF monomer in the polymerization kettle to micro positive pressure, further heating and adding a reducing agent for in-situ heat treatment.

7. The method for preparing polyvinylidene fluoride resin according to claim 6, characterized in that: the micro positive pressure is 0.1-0.5 Mpa.

8. The method for preparing polyvinylidene fluoride resin according to claim 6, characterized in that: the reducing agent is one or a mixture of sulfite, hypochlorite and ferrous salt.

9. The method for preparing polyvinylidene fluoride resin according to claim 6, characterized in that: the temperature of the in-situ heat treatment is 50-150 ℃.

10. The method for preparing polyvinylidene fluoride resin according to claim 6, characterized in that: the in-situ heat treatment time is 0.5-4 h.

Technical Field

The invention relates to a preparation method of polyvinylidene fluoride (PVDF) resin, in particular to a preparation method of a high-crystallinity and high-thermal stability PVDF polymer.

Background

PVDF is a high molecular material with excellent performance, and has excellent mechanical property, creep resistance, high and low temperature resistance, weather resistance, radiation resistance, chemical corrosion resistance and low flammability. The lithium ion battery is widely applied to the fields of petrifaction, metallurgy, pharmacy, construction, lithium batteries, water treatment, military industry, aerospace and the like. At present, the production modes of PVDF mainly include emulsion polymerization, suspension polymerization, solution polymerization, supercritical polymerization and the like, wherein the emulsion polymerization and the suspension polymerization are the most common in industrial production.

PVDF is a crystalline polymer, the crystallinity of which is mainly determined by the molecular structure of the resin, and the higher the regularity of the molecular chain, the higher the crystallinity of the resin, and the higher the corresponding material strength. Conversely, the higher the defective structure of the molecular chain, the lower the crystallinity of the resin, and the defective structure of PVDF generally includes a branched structure, a head-head (or tail-tail) structure. In fact, reverse addition of the VDF monomer to the growing polymer chain occurs easily during the polymerization process, generating a head-to-head or tail-to-tail structure. The abnormal structure has great influence on the weather resistance, toughness, mechanical strength, impact strength and the like of the polyvinylidene fluoride. Therefore, the production of polyvinylidene fluoride with high chain regularity is a prerequisite for improving the product quality.

Patent CN 101434670a discloses a method for preparing PVDF resin with high chain regularity, wherein the initiator used in the polymerization is redox initiator, the oxidant is cumene peroxide, and the reducing agent is uranium hypochlorite, but it is known that the benzene ring structure is liable to develop color inherently, and the color of PVDF resin is affected finally.

Patent CN 103146101a discloses a preparation method of PVDF resin with high crystallinity, which is a physical method, wherein the PVDF resin is subjected to heat treatment, and the molecular crystallization process is controlled to obtain the PVDF resin with high crystallinity.

Patent CN 104710550 discloses a high molecular weight polyvinylidene fluoride resin and a preparation method thereof, which adopts a suspension polymerization process, firstly reacts for 1-20 hours at 20-30 ℃, and then is polymerized for 5-24 hours at the temperature of 35-70 ℃. In the heating reaction stage of the method, a large amount of VDF monomers are still in a polymerization kettle, a large amount of low-molecular PVDF resin with higher defect structures is easily generated, the crystallinity and the mechanical property of the resin are influenced, and the high-temperature thermal stability of the resin is also influenced by the existence of a large amount of small molecules.

On the other hand, poor thermal stability is also a common problem of PVDF resin, and the main reasons are easily-developed double bonds formed in the polymerization process and insufficient resin cleanliness, which causes the resin to generate complex chemical reaction when being heated at high temperature during processing, so that the generated developed groups are colored, and therefore how to solve the thermal stability of PVDF resin is also a common concern in the industry.

In patent CN 102336854B, magnesium hydroxide is used as a dispersant to perform suspension polymerization to obtain PVDF resin with good thermal stability, but the protection capability of magnesium hydroxide on monomer droplets is poor, and finally, the PVDF resin with regular particles cannot be obtained.

Patent CN 1526744A adopts ZC_nF_2nCOOM (Z is chlorine or fluorine) type surfactant, sodium acetate and potassium alkyl sulfonate are added at the beginning of polymerization, during polymerization or after polymerization to improve the thermal stability of the resin, but the addition of metal salt in the method can cause excessive metal ions (sodium and potassium) in the system, and the electrical property of the PVDF resin is influenced.

Patent CN 103467631a discloses a method for preparing vinylidene fluoride polymer, which adds an acidic substance into the polymer slurry during post-treatment to improve the resistance of PVDF resin to coloration at high temperature, but this method increases the post-treatment step of PVDF resin, resulting in higher production cost and lower efficiency.

The number of the PVDF molecular defect structures mainly depends on the polymerization process conditions, and generally, the higher the polymerization reaction temperature is, the more defect structures are generated (mainly head-head or tail-tail structures), and the lower the resin crystallinity is; the lower the reaction temperature, the less defective structures are formed and the higher the crystallinity of the resin. Thus, in general, emulsion polymerization temperatures are higher than in suspension polymerization, and the resulting resins therefore have lower crystallinity than in suspension polymerization. The present inventors have conducted intensive studies on the thermal stability of PVDF resin, and found that the main factors affecting the thermal stability of PVDF resin include two aspects, one of which is the color development of double bonds formed during polymerization during processing; secondly, the initiator and other additives are remained, and complex reaction can further occur in the processing process, so that the thermal stability of the resin is influenced. Therefore, how to reduce the generation of double bonds and the residue of auxiliary agents such as an initiator as much as possible is the key to improve the thermal stability of the PVDF resin. The present inventors have found that the high temperature polymerization is more likely to generate a double bond defect structure due to the reaction severity, but the low temperature polymerization requires a larger amount of initiator than the high temperature polymerization, resulting in a much larger amount of final residue than the high temperature polymerization. Thus lowering the polymerization temperature, while somewhat reducing the production of double bonds, somewhat increases initiator residues in the final resin.

Disclosure of Invention

The invention aims to provide a preparation method of PVDF resin, and the prepared PVDF resin not only has high crystallinity, but also has good thermal stability.

In order to solve the technical problems, the invention adopts the following technical scheme:

a preparation method of polyvinylidene fluoride resin comprises polymerization, heat treatment and post-treatment of vinylidene fluoride monomers, and is characterized in that in the polymerization step, 100 parts of deionized water, 0.005-0.02 part of dispersing agent, 0.05-0.2 part of initiator, 0.1-1 part of chain transfer agent and 15-30 parts of VDF monomer are added into a polymerization kettle according to parts by weight, after polymerization reaction is carried out at low temperature to a specific pressure drop value, the VDF monomer is recovered to the polymerization kettle with the pressure of micro positive pressure, the polymerization kettle is further heated to a higher temperature, 0.03-0.1 part of reducing agent is added for in-situ heat treatment for a certain time, materials are collected, cold water and hot water are adopted to alternately wash the resin, and then the resin is dried to obtain a pure PVDF resin finished product.

Preferably, the dispersant is cellulose or polyethylene glycol water-soluble polymer, and the chain transfer agent is one or a mixture of ethyl acetate, acetone and diethyl carbonate.

Preferably, the low temperature polymerization temperature is from 0 to 30 deg.C, preferably from 2 to 25 deg.C, more preferably from 5 to 20 deg.C (excluding 20 deg.C).

Preferably, the initiator is a highly reactive initiator, so that the amount of the initiator can be reduced as much as possible during low temperature reaction, and the half-life is T_10hLess than or equal to 50 ℃, preferably T_10h45 ℃ or less, more preferably T_10hIs less than or equal to 40 ℃. Preferably, the initiator is diisobutyryl peroxide (T)_10h-23 ℃) of cumyl peroxyneodecanoate (T)_10h38 deg.C), 1,3, 3-tetramethylbutyl peroxyneodecanoate (T)_10h40 deg.c), and the like, and combinations thereof.

Preferably, the pressure drop of the reaction is from 0.1 to 1.5MPa, preferably from 0.4 to 1.2MPa, more preferably from 0.6 to 1.0 MPa. The reaction pressure drop refers to the pressure drop caused by the consumption of gas-phase monomer dissolved in water phase after the suspension polymerization liquid-phase monomer droplets are reacted, the pressure drop is too low, the polymerization conversion rate is too low, the pressure drop is too high, the reaction time in the pressure drop stage is long, and the production efficiency is influenced, so the pressure drop needs to be reasonably controlled.

Preferably, after the polymerization reaction reaches the specified pressure drop, recovering and decompressing the VDF monomer in the polymerization kettle to a micro positive pressure, further heating and adding a reducing agent for in-situ heat treatment. The micro positive pressure refers to the pressure formed by a small amount of VDF monomers still remaining in the polymerization kettle after the VDF monomers are recovered, and at the moment, if the pressure is too high, the VDF residual amount of the polymerization kettle is large, and the defect structure of the resin generated by the polymerization reaction in the high-temperature treatment is large, so that the crystallinity of the whole PVDF resin in the polymerization kettle is influenced, and the pressure needs to be reasonably controlled.

Preferably, the micro-positive pressure is from 0.1 to 0.5MPa, preferably from 0.15 to 0.4MPa, more preferably from 0.2 to 0.25 MPa.

Preferably, the reducing agent is one or a mixture of sulfite, hypochlorite and ferrous salt.

Preferably, the in-situ heat treatment temperature is 50-150 ℃.

Preferably, the in-situ heat treatment time is 0.5-4 h.

Due to the adoption of the technical scheme, the invention has the following beneficial effects:

1. the low-temperature suspension polymerization process is adopted, and the polymerization pressure is greatly lower than that of high-temperature polymerization, so that the requirement on the pressure grade of a polymerization kettle is low, and the method is more suitable for industrial amplification;

2. the resin obtained by low-temperature polymerization has few defect structures, high crystallinity and good mechanical property;

3. the monomer recovered after low-temperature polymerization is adopted for high-temperature in-situ heat treatment, the obtained resin has low auxiliary agent residue and less generation amount of low molecular weight PVDF, so that the obtained resin has good high-temperature yellowing resistance, and the thermal decomposition temperature of the resin is greatly improved.

Detailed Description

The present invention will be further illustrated with reference to the following specific examples.

Example 1

Adding 3000g of deionized water, 0.5g of a dispersant system, 1.5g of diisobutyronitrile peroxide, 5g of ethyl acetate and 600g of VDF monomer into a 5L vertical kettle with a double-layer double-blade inclined paddle, raising the temperature of the reaction kettle to 10 ℃ for polymerization reaction, recovering the monomer to the pressure of 0.2MPa of the polymerization kettle when the reaction pressure is reduced by 0.6MPa, raising the temperature of the polymerization kettle to 70 ℃, and adding 2g of sodium bisulfite for heat treatment for 2 hours. And collecting the obtained resin, alternately washing the resin by cold water and hot water, and drying the resin to obtain a PVDF finished product. The results of the finished product testing are shown in table 2.

Example 2

Adding 3000g of deionized water, 0.5g of a dispersant system, 3g of cumyl peroxyneodecanoate, 5g of ethyl acetate and 600g of VDF monomer into a 5L vertical kettle with double-layer double-blade inclined paddles, raising the temperature of the reaction kettle to 15 ℃ for polymerization reaction, recovering the monomer to the pressure of 0.2MPa of the polymerization kettle when the reaction pressure is reduced by 0.8MPa, raising the temperature of the polymerization kettle to 85 ℃, and adding 1g of sodium hypochlorite for heat treatment for 1.7 hours. And collecting the obtained resin, alternately washing the resin by cold water and hot water, and drying the resin to obtain a PVDF finished product. The results of the finished product testing are shown in table 2.

Example 3

Adding 3000g of deionized water, 0.5g of a dispersing agent system, 4g of 1,1,3, 3-tetramethyl butyl peroxyneodecanoate, 5g of ethyl acetate and 600g of VDF monomer into a 5L vertical kettle with double-layer double-blade inclined paddles, raising the temperature of the reaction kettle to 19 ℃ for polymerization reaction, recovering the monomer until the pressure of the polymerization kettle is 0.25MPa when the reaction pressure is reduced by 1.0MPa, raising the temperature of the polymerization kettle to 100 ℃, and adding 2g of sodium bisulfite for heat treatment for 1.5 hours. And collecting the obtained resin, alternately washing the resin by cold water and hot water, and drying the resin to obtain a PVDF finished product. The results of the finished product testing are shown in table 2.

Comparative example 1

As in example 1, the only difference was that the reaction was stopped by directly recovering the monomer when the pressure drop of the reaction was 0.6 MPa. And collecting the obtained resin, alternately washing the resin by cold water and hot water, and drying the resin to obtain a PVDF finished product. The results of the finished product testing are shown in table 2.

Comparative example 2

As in example 1, the only difference is that the reaction is stopped after heating the polymerization to 80 ℃ by adding 2g of sodium bisulfite directly after the reaction pressure drops to 0.6MPa for 1.7 hours. And collecting the obtained resin, alternately washing the resin by cold water and hot water, and drying the resin to obtain a PVDF finished product. The results of the finished product testing are shown in table 2.

Comparative example 3

3000g of deionized water, 0.5g of a dispersant system, 1.5g of diisopropyl peroxydicarbonate, 5g of ethyl acetate and 600g of VDF monomer are added into a 5L vertical kettle with a double-layer double-blade inclined paddle, the temperature of the reaction kettle is raised to 60 ℃ for polymerization reaction, and the monomer is recovered when the reaction pressure is reduced by 0.6Mpa to stop the reaction. And collecting the obtained resin, alternately washing the resin by cold water and hot water, and drying the resin to obtain a PVDF finished product. The results of the finished product testing are shown in table 2.

The specific test method is as follows:

(1) measurement of resin crystallinity

The crystallinity of the resin was calculated by measuring the enthalpy of fusion of the resin using Differential Scanning Calorimetry (DSC) according to the national Standard GB/T19466.3-2004 as follows:

PVDF resin crystallinity (%) (. DELTA.H/104.7). times.100%

In the above formula 104.7 is the theoretical enthalpy of fusion when the PVDF resin is 100% crystalline.

(2) Testing of resin defect structures

And measuring and calculating the defect degree of the PVDF resin by adopting nuclear magnetic fluorine spectrum (19FNMR), and calculating the content of the defect structure of the resin according to the peak areas of different chemical shifts. Different sequence structures are in¹⁹The peak positions on the F NMR spectrum were-92 ppm (A) and-94.8 ppm (B), respectively,-92.5ppm (A'), -113.7ppm (C) and-116.2 ppm (D). Wherein C, D is head-head structure, and B is tail-tail structure. Degree of defect (mol%) < 1- (S)_A+S_A’)/(S_A+S_A’+S_B+S_C+S_D)×100％

(3) Testing of thermal stability of resins

Approximately 15g of polymer powder was weighed into a 20ml container and heated in an oven at 230 ℃ for 30 min. A HunterLab LabScan XE yellow index instrument is selected for testing, the yellow index (YID1925) is used for representing the yellowing degree, and the lower the index is, the better the thermal stability is.

(4) Measurement of thermal decomposition temperature of resin

The thermal decomposition temperature of the resin was tested using thermogravimetric analysis (TGA). Weighing about 5-15mg of resin sample, placing the resin sample in a platinum disk, raising the temperature from room temperature to 650 ℃ at the speed of 10 ℃/min in the air atmosphere, recording a weight loss curve, and calculating the temperature when the weight loss is 5% according to the curve to evaluate the high temperature resistance stability of the resin.

(5) Testing of tensile Properties of resins

The resin was hot-pressed into a sheet having a thickness of 1mm by a press vulcanizer, cut into a dumbbell shape by a cutter, and the mechanical properties of the resin were measured at 23 ℃.

The testing speed of the tensile strength is 50mm/min, 5 parallel samples are tested, and the average value is taken;

the tensile modulus test speed was 5mm/min, and 5 replicates were tested and averaged.

Table 1: reaction conditions of examples 1 to 3 and comparative examples 1 to 3

Table 2: test results of examples 1 to 3 and comparative examples 1 to 3

YI value of standard white board is 3.85

The results clearly show that the polyvinylidene fluoride resin provided by the invention has very low defect degree and very high crystallinity, and simultaneously has excellent heat resistance and mechanical properties.

The above is only a specific embodiment of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions or modifications made on the basis of the present invention to solve the same technical problems and achieve the same technical effects are all covered in the protection scope of the present invention.