Rare earth-based nucleating agent for polypropylene and preparation method thereof

Abstract

A rare earth-based nucleating agent for polypropylene is characterized by comprising the following components and their weight ratios: 70-85% cerium nitrate hexahydrate; 15-30% hexamethylenediaminetetramethylenephosphonic acid. The invention also discloses a method for preparing the rare earth-based nucleating agent for polypropylene. The rare earth-based nucleating agent of the invention can significantly improve the high temperature stability and low temperature toughness of polypropylene while ensuring the high strength of polypropylene.

Description

Technical Field

[0001] The invention relates to a modified preparation of polypropylene, in particular to a nucleating agent containing rare earth, which is suitable for the modified preparation of polypropylene. The invention also relates to a preparation method of the nucleating agent. Background Art

[0002] With the rapid development of new energy vehicles, lithium-ion batteries have experienced explosive growth. However, new energy vehicles have experienced frequent spontaneous combustion and explosion incidents, and the safety of lithium-ion batteries has attracted great attention. In the structure of lithium batteries, the battery separator is one of the key inner components and is also a high-value-added material with the highest technical barriers.

[0003] The diaphragm is the core material that ensures the safety of the battery system and affects the battery performance. Since polypropylene has the advantages of low price, excellent mechanical properties and stable electrochemical properties, commercial dry-process diaphragms mainly use polypropylene. However, polypropylene diaphragms sometimes shrink and deform during high-temperature charging and discharging, causing equipment explosions, and become brittle under low-temperature conditions, and are easily pierced by burrs, dendrites, etc., causing short circuits. Chinese dry-process diaphragm companies have accounted for more than 60% of the global market share, but the upstream polypropylene materials of diaphragms are heavily dependent on imports, mainly because domestic polypropylene materials cannot meet the performance requirements of diaphragms.

[0004] Polypropylene lithium-ion battery separators sometimes shrink and deform during high-temperature charging and discharging, causing electric vehicles to spontaneously combust and mobile phones and other devices to explode, seriously endangering human life. Although grafting polymerization, coating and other technologies can improve the thermal stability of polypropylene separators, most of them are still in the research stage and have not yet been applied to large-scale commercial production.

[0005] At present, commercial polypropylene diaphragms mainly use the method of adding nucleating agents to improve the high temperature stability and low temperature toughness of polypropylene. This type of nucleating agent can be roughly divided into inorganic nucleating agents and organic nucleating agents in terms of chemical structure. Inorganic nucleating agents mainly include talc, mica, calcium carbonate, silica, molecular sieves, etc. This type of nucleating agent was developed earlier, and its biggest advantage is that it is cheap and easy to obtain. However, due to the poor compatibility of inorganic powders with polypropylene resins, the transparency and gloss of the products are not greatly improved, which limits its application. Another type of organic nucleating agent has more types and better nucleating effects. It mainly includes carboxylates, sorbitol (DBS), aryl phosphates and rosin acid soaps. Sorbitol and aryl phosphates are currently more widely used, the former is used to increase transparency, and the latter is used to increase rigidity. Due to good nucleating effects and compatibility, organic nucleating agents have become the main development direction of polypropylene nucleating agents.

[0006] The prior art also discloses organic nucleating agents, see Chinese invention patent No. ZL201610513822.9, "A rare earth polypropylene reinforced nucleating agent and its preparation method" (authorization announcement No. CN106084465B), which also uses rare earth complexes. Summary of the invention

[0007] The first technical problem to be solved by the present invention is to provide a rare earth-based nucleating agent for polypropylene in view of the above technical status.

[0008] The second technical problem to be solved by the present invention is to provide a method for preparing a rare earth-based nucleating agent for polypropylene in view of the above technical status.

[0009] The technical solution adopted by the present invention to solve the above-mentioned first technical problem is: a rare earth-based nucleating agent for polypropylene, characterized by comprising the following components and their weight ratios:

[0010] Cerium nitrate hexahydrate 70-85%;

[0011] Hexamethylenediaminetetramethylenephosphonic acid 15-30%.

[0012] As the best, it includes the following components and their weight ratios:

[0013] Cerium nitrate hexahydrate 20%;

[0014] Hexamethylenediaminetetramethylenephosphonic acid 80%.

[0015] Preferably, the purity of the cerium nitrate hexahydrate is ≥99.95%; the purity of the hexamethylenediaminetetramethylenephosphonic acid is ≥98%.

[0016] The technical solution adopted by the present invention to solve the above second technical problem is: a method for preparing a rare earth-based nucleating agent for polypropylene, characterized by comprising the following steps:

[0017] ① Dissolve hexamethylenediaminetetramethylenephosphonic acid in deionized water, start stirring at room temperature for 8 to 15 minutes, until no suspended matter is visible to the naked eye in the deionized water, to obtain an aqueous solution of hexamethylenediaminetetramethylenephosphonic acid;

[0018] ② dissolving cerium nitrate hexahydrate in deionized water to obtain an aqueous solution of cerium nitrate hexahydrate, and adding the aqueous solution of cerium nitrate hexahydrate dropwise into the stirred aqueous solution of hexamethylenediaminetetramethylenephosphonic acid;

[0019] ③ After the addition is complete, turn on the heating and react at 70-90°C for 24-48 hours to obtain a mixed solution;

[0020] ④ Then transfer the mixed solution to a high-pressure reactor and perform a constant temperature hydrothermal reaction at 80-100° C. for 24-72 hours;

[0021] ⑤Finally, wash repeatedly with deionized water, centrifuge, and finally obtain the rare earth-based nucleating agent.

[0022] Preferably, the conditions for dropping the aqueous solution of cerium nitrate hexahydrate in step ② are as follows: dropping at a rate of 5 to 7 mL / min through a constant pressure dropping funnel.

[0023] Preferably, the drying temperature in step ⑤ is 80-110°C.

[0024] The rare earth-based nucleating agent is used to prepare a polypropylene material with high temperature stability and low temperature toughness. The preferred preparation method is as follows: a rare earth-based nucleating agent for polypropylene is melt-blended with polypropylene to prepare a polypropylene material with high temperature stability and low temperature toughness containing the rare earth-based nucleating agent. The weight percentage of the rare earth-based nucleating agent for polypropylene in the polypropylene material is 0.1-0.5%, and the polypropylene is one of homopolymer polypropylene, copolymer polypropylene, etc.

[0025] Compared with the prior art, the advantages of the present invention are: the rare earth element cerium (Ce) in the rare earth-based nucleating agent has an empty 4f electron orbit and has the ability to capture free radicals. Under high temperature conditions, it can react with the molecular chain segments of polypropylene that are degraded at high temperature to prevent the free radical chain degradation reaction of polypropylene from further occurring, thereby improving the high temperature stability of the polypropylene material.

[0026] EDTMP can form coordination with rare earth elements, so that rare earth elements are connected with a large number of organic groups, thereby improving the dispersibility of rare earth compounds in polypropylene. The surface of the obtained rare earth-based nucleating agent has a large number of organic groups, which makes it easy to disperse in polypropylene and not easy to agglomerate. Moreover, the rare earth-based nucleating agent is in the form of nano-scale spherical and can be used as a nano-scale nucleating agent in polypropylene, which can induce polypropylene to form a microcrystalline structure and is not easy to produce large spherulites, which is beneficial to the formation of uniformly distributed microcrystals in the polypropylene material, ensuring the stability of performance and size.

[0027] The rare earth-based nucleating agent of the present invention has a large number of flexible organic groups on its surface, and due to its nano-scale small molecule structure, it can enter between the polypropylene macromolecular chains when melt-blended with polypropylene, destroying the entanglement structure of the polypropylene macromolecular chains, thereby reducing the interaction between the polypropylene macromolecules and greatly improving its low-temperature toughness.

[0028] Experiments have shown that the rare earth-based nucleating agent of the present invention can significantly improve the high-temperature stability and low-temperature toughness of polypropylene while ensuring the high strength of polypropylene. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the infrared spectrum of the rare earth-based nucleating agent obtained in Example 2.

[0030] Figure 2 This is a scanning electron microscope image of the rare earth-based nucleating agent obtained in Example 2.

[0031] Figure 3 This is an optical micrograph of polypropylene film.

[0032] Figure 4 This is an optical microscope image of a film prepared by melt blending a rare earth-based nucleating agent with polypropylene in Example 2. DETAILED DESCRIPTION

[0033] The present invention is further described in detail below in conjunction with the embodiments of the accompanying drawings, but the present invention is not limited to the following embodiments.

[0034] Embodiment 1:

[0035] 4.00 g of EDTMP was dissolved in 100 mL of deionized water, and stirred at room temperature for 8 min. 9.68 g of Ce(NO)3·6H2O was dissolved in 100 mL of deionized water, and added dropwise to the stirred EDTMP aqueous solution at a rate of 5 mL / min through a constant pressure dropping funnel. After the addition was completed, heating was started and the mixture was reacted at 90°C for 24 h. The mixed solution was then transferred to a high pressure reactor and subjected to a constant temperature hydrothermal reaction at 100°C for 24 h.

[0036] Finally, the product is repeatedly washed with deionized water, centrifuged and dried to finally obtain a rare earth-based nucleating agent.

[0037] The prepared rare earth-based nucleating agent is placed in an internal mixer with a rare earth-based nucleating agent weight percentage of 0.1% (the rest of the substances are polypropylene), a melting temperature of 160°C, a rotation speed of 55r / min, and melt blending for 10 minutes to obtain polypropylene containing a rare earth-based nucleating agent with high temperature stability and low temperature toughness.

[0038] Embodiment 2:

[0039] 3.15 g of hexamethylenediaminetetramethylenephosphonic acid (EDTMP) was dissolved in 100 mL of deionized water, and stirring was started at room temperature for 10 min. 12.60 g of cerium nitrate hexahydrate (Ce(NO)3·6H2O) was dissolved in 100 mL of deionized water, and added dropwise to the stirred EDTMP aqueous solution through a constant pressure dropping funnel at a rate of 6 mL / min. After the addition was completed, heating was started, and the mixture was reacted at 80° C. for 36 h. The mixed solution was then transferred to a high-pressure reactor, and subjected to a constant temperature hydrothermal reaction at 90° C. for 48 h. Finally, the mixture was repeatedly washed with deionized water, centrifuged, and dried (at a temperature of 80 to 110° C.), and a rare earth-based nucleating agent was finally obtained.

[0040] like Figure 1 As shown in the figure, by comparing the infrared spectra of CeEDTMP and EDTMP, it can be found that EDTMP is easy to dissociate in aqueous solution, has strong coordination ability, and can react with metal ions. -1 There is a strong broad absorption band at 1658cm -1 The peak at 3035cm is the bending vibration peak of water molecules, indicating that there is crystal water inside EDTMP. -1 and 3007cm -1 The absorption peak of CeEDTMP and EDTMP is between 1500-1000cm -1 The peaks in the region vary greatly, and this region corresponds to the characteristic peak of -P(O)(OH)2, indicating that the phosphonate reacts and coordinates with Ce, indicating that CeEDTMP is synthesized.

[0041] like Figure 2 As shown, CeEDTMP presents a nearly spherical three-dimensional structure with a particle size of about 100 nm.

[0042] The prepared rare earth-based nucleating agent is placed in an internal mixer with a rare earth-based nucleating agent weight percentage of 0.3% (the rest of the substances are polypropylene), a melting temperature of 170°C, a rotation speed of 60r / min, and melt blending for 10 minutes to obtain polypropylene containing a rare earth-based nucleating agent with high temperature stability and low temperature toughness.

[0043] like Figure 3 and Figure 4 As shown, the polypropylene film forms scattered large spherulites, while the film prepared by melt blending the rare earth-based nucleating agent with polypropylene forms a uniformly distributed microcrystalline structure.

[0044] Embodiment 3:

[0045] 2.00 g of EDTMP was dissolved in 100 mL of deionized water, and stirred at room temperature for 15 min. 11.33 g of Ce(NO)3·6H2O was dissolved in 100 mL of deionized water, and added dropwise to the stirred EDTMP aqueous solution at a rate of 7 mL / min through a constant pressure dropping funnel. After the addition was completed, heating was started and the mixture was reacted at 70°C for 72 h. The mixed solution was then transferred to a high-pressure reactor and subjected to a constant temperature hydrothermal reaction at 80°C for 72 h. Finally, the mixture was repeatedly washed with deionized water, centrifuged, and dried (at a temperature of 80-110°C) to obtain a rare earth-based nucleating agent.

[0046] The prepared rare earth-based nucleating agent is placed in an internal mixer with a rare earth-based nucleating agent weight percentage of 0.5% (the rest of the substances are polypropylene), a melting temperature of 160°C, a rotation speed of 50r / min, and melt blending for 10 minutes to obtain polypropylene containing a rare earth-based nucleating agent with high temperature stability and low temperature toughness.

[0047] The high temperature stability and low temperature toughness test of the embodiment (test conditions: the impact test was conducted according to GB1043-93 standard, the sample size was 70×6×4mm, the notch was 2mm; the tensile test was conducted according to GB1040-89 standard, the sample was made into a dumbbell shape, the gauge length was 25mm, and the tensile rate was 25mm / min; the thermal deformation test was conducted according to GB / T1633 standard, the span size was 64mm, and the heating rate was 5°C / min.) The test results are shown in Table 1. It can be seen from the table that after adding the rare earth-based nucleating agent of the present invention, the notched impact strength and tensile strength of polypropylene at low temperature are significantly improved, and the mechanical properties at room temperature are not much different; moreover, after adding the rare earth-based nucleating agent of the present invention, the thermal deformation temperature of polypropylene is greatly improved, and the maximum can reach 180°C, and good stability can be maintained at high temperature.

[0048] Table 1, performance test results of the embodiments

[0049]

Claims

1. A rare earth-based nucleating agent for polypropylene, characterized in that It includes the following components and their weight ratios: Cerium nitrate hexahydrate 70-85%; Hexamethylenediaminetetramethylenephosphonic acid 15-30%.

2. The rare earth-based nucleating agent for polypropylene according to claim 1, characterized in that It includes the following components and their weight ratios: Cerium nitrate hexahydrate 20%; Hexamethylenediaminetetramethylenephosphonic acid 80%.

3. The rare earth-based nucleating agent for polypropylene according to claim 1, characterized in that The purity of the cerium nitrate hexahydrate is ≥99.95%; the purity of the hexamethylenediaminetetramethylenephosphonic acid is ≥98%.

4. A method for preparing a rare earth-based nucleating agent for polypropylene according to any one of claims 1 to 3, characterized in that The steps include: ① Dissolve hexamethylenediaminetetramethylenephosphonic acid in deionized water and stir at room temperature until no suspended matter is visible to the naked eye in the deionized water to obtain an aqueous solution of hexamethylenediaminetetramethylenephosphonic acid; ② dissolving cerium nitrate hexahydrate in deionized water to obtain an aqueous solution of cerium nitrate hexahydrate, and adding the aqueous solution of cerium nitrate hexahydrate dropwise into the stirred aqueous solution of hexamethylenediaminetetramethylenephosphonic acid; ③ After the addition is complete, turn on the heating and react at 70-90°C for 24-48 hours to obtain a mixed solution; ④ Then transfer the mixed solution to a high-pressure reactor and perform a constant temperature hydrothermal reaction at 80-100° C. for 24-72 hours; ⑤Finally, wash repeatedly with deionized water and centrifuge to finally obtain a rare earth-based nucleating agent.

5. The preparation method according to claim 4, characterized in that The conditions for dropping the cerium nitrate hexahydrate aqueous solution in step ② are as follows: dropping at a rate of 5 to 7 mL / min through a constant pressure dropping funnel.

6. The preparation method according to claim 4, characterized in that In step ⑤, the drying temperature is 80-110°C.

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