Electric breakdown resistant polypropylene and preparation method thereof

Abstract

The invention provides electric breakdown resistant polypropylene and a preparation method thereof. The composition consists of isotatic polypropylene with conventional molecular weight, ultra-high molecular weight isotatic polypropylene with aromatic groups on side groups, and a heat stabilizer. The composition has the comprehensive advantages of high breakdown strength, low ash content, good processability, high mechanical strength and the like, the preparation process is simple, convenient and mild, degradation of polypropylene is not easily caused, and the electrical property stability of polypropylene is favorably kept.

Description

Technical Field

[0001] The present invention relates to a polypropylene composition and a preparation method thereof, in particular to a preparation method of a polypropylene composite resistant to electrical breakdown. Background Art

[0002] As a semi-crystalline thermoplastic polymer, polypropylene is widely used in the fields of electronics, automobile manufacturing, and insulation of power equipment due to its excellent electrical insulation, chemical corrosion resistance, light weight, and good processing performance. However, with the increasing requirements of modern industry for material performance, especially in scenarios such as high-voltage power transmission and transformation equipment, new energy vehicle motor windings, and high-frequency capacitors, the electrical breakdown resistance of traditional polypropylene has gradually become difficult to meet the demand. Under the action of high-voltage or high-frequency electric fields, ordinary polypropylene is prone to electrical dendrites or breakdown due to local electric field concentration, charge accumulation, or thermal aging, leading to insulation failure, which seriously threatens the safety and service life of the equipment. Therefore, the development of modified polypropylene materials with high electrical breakdown strength, thermal stability, and mechanical properties has become a research hotspot in the field of insulation materials in recent years.

[0003] In the prior art, the main methods for improving the electrical breakdown resistance of polypropylene include blending modification, inorganic filler composite and chemical grafting modification. For example, the dielectric properties and corona resistance of the material can be effectively improved by introducing inorganic nanofillers (such as silica, aluminum oxide, boron nitride, etc.), but the addition of inorganic substances can easily lead to a decrease in matrix fluidity, deterioration of mechanical properties and an increase in interface defects, which may form breakdown channels. In addition, the inorganic fillers with unmodified surfaces have poor compatibility with the polypropylene matrix and are prone to agglomeration, further exacerbating the unevenness of the dielectric properties. In terms of chemical modification, the use of polar monomers (such as maleic anhydride) to graft polypropylene chains can enhance interfacial bonding, but the grafting process may destroy the crystalline structure of polypropylene, affecting its thermal stability, and the process is complex and the cost is high. In recent years, there have been studies using multilayer composite structures (such as PP / PE alternating layers) or in situ polymerization to prepare nanocomposites. Although they can partially improve the breakdown field strength, they still face problems such as poor process controllability and insufficient long-term stability. Summary of the Invention

[0004] To address the deficiencies in the prior art, the present invention provides an electrical breakdown resistant polypropylene and a method for preparing the same. The polypropylene used in the present invention is ultra-high molecular weight isotactic polypropylene. The resulting polypropylene composition has advantages such as low ash content, good processing performance, and excellent mechanical properties, making it significantly advantageous in the application of electrical breakdown resistant polypropylene resins. Furthermore, the mild preparation conditions effectively avoid the problem of polypropylene degradation easily caused by the melt grafting reaction, thereby facilitating stable polymer performance.

[0005] To achieve the object, the present application provides a polypropylene composition (electric breakdown resistant polypropylene) composed of isotactic polypropylene a, ultrahigh molecular weight isotactic polypropylene b with side groups containing aromatic groups, and thermal stabilizer c; wherein,

[0006] The mass fraction of the isotactic polypropylene a in the composition is 50% to 94%, preferably the mass fraction is 69% to 90%;

[0007] The mass fraction of the ultrahigh molecular weight isotactic polypropylene b with side groups containing aromatic groups in the composition is 5% to 50%, preferably the mass fraction is 9% to 30%;

[0008] The mass fraction of the thermal stabilizer c in the composition is 0.1% to 5%, preferably the mass fraction is 0.3% to 1%.

[0009] The ultrahigh molecular weight isotactic polypropylene b with side groups containing aromatic groups has the following structure:

[0010]

[0011] wherein, R 1 is biphenyl or condensed ring aromatic hydrocarbon (such as biphenyl, naphthyl, anthryl, phenanthryl, benzocyclobutene) containing 8 to 30 carbon atoms, preferably biphenyl or condensed ring aromatic hydrocarbon (such as biphenyl, naphthyl, anthryl, phenanthryl, benzocyclobutene) containing 8 to 20 carbon atoms; or aromatic hydrocarbon containing 4 to 20 carbon atoms and containing heteroatoms (such as benzofuranyl, thienyl, quinolinyl), the heteroatom is one or several of N, S, O, preferably aromatic hydrocarbon containing 4 to 12 carbon atoms and containing heteroatoms (such as benzofuranyl, thienyl, quinolinyl); R 2 is H or CH3; x is an integer of 10000 to 50000, preferably x is an integer of 15000 to 40000; y = 0.001x to 0.1x, preferably y = 0.01x to 0.1x.

[0012] In the polypropylene composition of the present application, the isotactic polypropylene a is isotactic polypropylene with conventional molecular weight, which is polypropylene with a melt index of 1 to 100 g / 10 min (230℃, 2.16 kg) and a weight average molecular weight of 100 to 500 million g / mol, preferably polypropylene with a melt index of 10 to 50 g / 10 min (230℃, 2.16 kg) and a weight average molecular weight of 150 to 300 million g / mol;

[0013] The ultrahigh molecular weight polypropylene b with side groups containing aromatic groups is a polypropylene with a melt index of 0.5-10 g / 10 min (230°C, 21.6 kg) and a weight average molecular weight of 1-5 million g / mol, preferably a polypropylene with a melt index of 0.5-5 g / 10 min (230°C, 2.16 kg) and a weight average molecular weight of 2-5 million g / mol.

[0014] The polypropylene composition according to the present application, the isotactic polypropylene a is a polypropylene powder with an isotacticity greater than or equal to 95%, preferably a polypropylene powder with an isotacticity greater than or equal to 98%;

[0015] The ultrahigh molecular weight polypropylene b with side groups containing aromatic groups is a polypropylene powder with an isotacticity greater than or equal to 95%;

[0016] The heat stabilizer c is at least one of a hindered phenol antioxidant, a phosphite antioxidant or a thioester antioxidant; further, the heat stabilizer c is selected from one or more of antioxidant 1010, antioxidant 1076, antioxidant 264, antioxidant 2246, antioxidant 330, antioxidant 300, antioxidant 168, antioxidant TPP, antioxidant TNP, antioxidant DLTP, antioxidant DSTP; preferably, the heat stabilizer c is selected from one or more of antioxidant 1010, antioxidant 1076, antioxidant 264, antioxidant 2246, antioxidant 168, antioxidant TPP, antioxidant DSTP; more preferably, the heat stabilizer c is selected from one or more of antioxidant 1010, antioxidant 1076, antioxidant 168, antioxidant DSTP, for example, a combination of antioxidant 1010 and antioxidant 168 (e.g. a mass ratio of antioxidant 1010 to antioxidant 168 is 1:2).

[0017] The ultrahigh molecular weight polypropylene b with side groups containing aromatic groups in the polypropylene composition according to the present application is prepared by the following steps:

[0018] In the first step, a mixture of an ultrahigh molecular weight isotactic polypropylene powder with a melt index of 0.5-10 g / 10 min (230°C, 21.6 kg) and a weight average molecular weight of 1-5 million g / mol (preferably an ultrahigh molecular weight isotactic polypropylene powder with a melt index of 0.5-5 g / 10 min (230°C, 2.16 kg) and a weight average molecular weight of 2-5 million g / mol), a swelling liquid d, a heat stabilizer e is pretreated to obtain a first step pretreated product;

[0019] In the second step, the first step pretreated product is reacted with an aromatic olefin g having the following structure in the presence of an initiator f to obtain a second step reaction product;

[0020] In the third step, the reaction product of the second step is washed in eluent h and then dried to obtain the ultrahigh molecular weight isotactic polypropylene b having aromatic groups in the side groups.

[0021]

[0022] wherein R 1 is biphenyl or condensed ring aromatic hydrocarbon having 8 to 30 carbon atoms, or aromatic hydrocarbon having 4 to 20 carbon atoms and containing N, S and the like heteroatoms; R 2 is H or CH3.

[0023] In the preparation of the ultrahigh molecular weight isotactic polypropylene b having aromatic groups in the side groups, in the first step, the mass ratio of the swelling liquid d to the ultrahigh molecular weight isotactic polypropylene powder is 0.1 to 100:1, preferably 1 to 10:1; the mass ratio of the thermal stabilizer e to the ultrahigh molecular weight isotactic polypropylene powder is 1:100 to 1000, preferably 1:100 to 500; the pretreatment temperature is 20°C to 100°C, preferably 50°C to 80°C; and the pretreatment time is 10 min to 120 min, preferably 30 min to 90 min.

[0024] In the second step, the mass ratio of the initiator f to the ultrahigh molecular weight isotactic polypropylene powder of the first step is 1:10 to 1000, preferably 1:100 to 500; the mass ratio of the aromatic olefin g to the ultrahigh molecular weight isotactic polypropylene powder of the first step is 1:5 to 500, preferably 1:5 to 100; the reaction temperature is 60°C to 120°C, preferably 80°C to 110°C; and the reaction time is 0.5 h to 10 h, preferably 2 h to 6 h.

[0025] In the third step, before the reaction product of the second step is washed in eluent h, a filtration treatment can be performed or the elution can be directly performed; the mass ratio of the eluent h to the ultrahigh molecular weight isotactic polypropylene powder of the first step is 1 to 10:1, preferably 2 to 6:1; the washing temperature is 20°C to 100°C, preferably 40°C to 80°C; and the washing time is 5 h to 50 h, preferably 10 h to 30 h.

[0026] In the preparation of the ultrahigh molecular weight isotactic polypropylene b having aromatic groups in the side groups, the ultrahigh molecular weight isotactic polypropylene powder has a melt index of 0.5 to 10 g / 10 min (230°C, 21.6 kg) and a weight average molecular weight of 1 million to 5 million g / mol, preferably a melt index of 0.5 to 5 g / 10 min (230°C, 2.16 kg) and a weight average molecular weight of 2 million to 5 million g / mol;

[0027] The swelling liquid d is an aliphatic hydrocarbon or an aromatic hydrocarbon, selected from one or more of n-pentane, isopentane, n-hexane, cyclohexane, n-heptane, n-octane, n-decane, petroleum ether, benzene, toluene, xylene, and ethylbenzene; preferably, the swelling liquid d is selected from one or more of n-hexane, cyclohexane, n-heptane, n-octane, n-decane, petroleum ether, toluene, and xylene; more preferably, the swelling liquid d is selected from one or more of n-hexane, n-heptane, petroleum ether, toluene, and xylene, such as a combination of n-hexane and toluene (e.g., a volume ratio of n-hexane to toluene of 1:1).

[0028] The heat stabilizer e is at least one of a hindered phenol antioxidant, a phosphite antioxidant or a thioester antioxidant; the heat stabilizer e may be the same as or different from the heat stabilizer c; further, the heat stabilizer e is selected from one or more of antioxidant 1010, antioxidant 1076, antioxidant 264, antioxidant 2246, antioxidant 330, antioxidant 300, antioxidant 168, antioxidant TPP, antioxidant TNP, antioxidant DLTP, and antioxidant DSTP; preferably, the heat stabilizer e is selected from one or more of antioxidant 1010, antioxidant 1076, antioxidant 264, antioxidant 2246, antioxidant 168, antioxidant TPP, and antioxidant DSTP; more preferably, the heat stabilizer e is selected from one or more of antioxidant 1010, antioxidant 1076, antioxidant 168, and antioxidant DSTP.

[0029] The initiator f is a thermal decomposition free radical initiator, selected from one or more of organic peroxide initiators and azo initiators, preferably one or more of alkyl peroxides, alkynyl peroxides, hydroperoxides, acyl peroxides and peroxycarbonates. Further, the initiator f is selected from one or more of benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, azobisisoheptonitrile, ammonium persulfate, potassium persulfate, diisopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, 2,5-dimethyl-2,5-di-tert-butylperoxyhexane, 2,5-dimethyl-2,5-di-tert-butylperoxy-3-hexyne; preferably, the initiator is peroxide Benzoyl, diisopropyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, azobisisoheptonitrile, diisopropyl peroxydicarbonate and dicyclohexyl peroxydicarbonate, 2,5-dimethyl-2,5-di-tert-butylperoxyhexane, 2,5-dimethyl-2,5-di-tert-butylperoxy-3-hexyne; more preferably, the initiator is one or more of benzoyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile and azobisisoheptonitrile.

[0030] The aromatic olefin g is an olefin having an aromatic ring (e.g. biphenyl, naphthalene ring, anthracene ring, phenanthrene ring, benzocyclobutene, pyridine, benzofuran, benzothiophene, quinoline) structure substituent, selected from one or more of 4-vinylbiphenyl, 2-vinyl naphthalene, 9-vinyl anthracene, 9-vinyl phenanthrene, 4-vinylbenzocyclobutene, 4-styrylpyridine, 2-vinylbenzofuran, 2-vinylbenzothiophene, 2-vinylquinoline; preferably the aromatic olefin g is selected from one or more of 4-vinylbiphenyl, 2-vinyl naphthalene, 9-vinyl anthracene, 9-vinyl phenanthrene, 4-vinylbenzocyclobutene, 4-styrylpyridine, 2-vinylquinoline; more preferably the aromatic olefin g is selected from one or more of 4-vinylbiphenyl, 2-vinyl naphthalene, 9-vinyl anthracene, 4-styrylpyridine, 2-vinylquinoline.

[0031] The eluent h is an organic ketone compound, selected from one or more of acetone, methyl ethyl ketone, cyclohexanone, butanone, phenone, hydroxyacetone, benzoylacetone, acetylacetone, propionylacetone, methyl acetoacetate, phenylpropionic acid; preferably the eluent h is selected from one or more of acetone, cyclohexanone, butanone, hydroxyacetone, benzoylacetone, acetylacetone, propionylacetone, methyl acetoacetate; more preferably the eluent h is selected from one or more of acetone, cyclohexanone, benzoylacetone, acetylacetone, methyl acetoacetate.

[0032] The method for preparing the polypropylene composition of the present application comprises the following steps:

[0033] The isotactic polypropylene a, the ultrahigh molecular weight isotactic polypropylene b having side groups containing aromatic groups, and the heat stabilizer c are uniformly mixed to obtain a powdery composition. Preferably, the mixing is carried out at room temperature, and the mixing time is 10-120 minutes, preferably 20-50 minutes; preferably, the mixing is carried out in a double-cone mixer.

[0034] The use of the polypropylene composition of the present application in the preparation of polypropylene shaped articles, especially puncture-resistant polypropylene articles, in particular electric puncture-resistant polypropylene articles.

[0035] Compared with the prior art, the advantages of the present application include the following:

[0036] (1) using ultra-high molecular weight isotactic polypropylene powder as raw material to carry out solid phase grafting modification, aromatic substituent groups (especially fused ring type, heterocyclic type) are introduced on the surface of the ultra-high molecular weight isotactic polypropylene, which can introduce a large number of deep traps in the polymer, thereby inhibiting the migration ability of carriers and significantly improving the DC breakdown strength of the material; the chain entanglement degree of the ultra-high molecular weight isotactic polypropylene is significantly higher than that of ordinary molecular weight polypropylene, so when the amorphous region is attacked by electrons and part of the molecular chain is broken, the remaining large number of entanglements can prevent the local density of polypropylene from being reduced due to chain scission, thereby inhibiting the electrical breakdown phenomenon caused by low-density regions, and significantly improving the AC breakdown strength of the material.

[0037] (2) combining conventional molecular weight isotactic polypropylene a with ultra-high molecular weight isotactic polypropylene b containing aromatic groups in the side groups: the conventional molecular weight isotactic polypropylene has a high melt index and does not contain any modified groups, so the molecular chain is regular, crystallization is fast, and the crystallinity is high, which is beneficial to the stability of the electrical properties of the material matrix; the conventional molecular weight isotactic polypropylene is easy to process, and after being combined with the ultra-high molecular weight isotactic polypropylene, the melt processing performance of the composition can also be improved.

[0038] (3) using the method of swelling first and grafting later to realize the low-temperature modification of the side groups of the ultra-high molecular weight isotactic polypropylene, which effectively solves the problem that the ultra-high molecular weight isotactic polypropylene is difficult to realize melt grafting modification due to its extremely high melt viscosity, and also avoids the problem that the melt modification of polypropylene causes serious degradation of polypropylene; the method also uses a ketone solvent for post-treatment, which effectively reduces the residual ash in the polypropylene and significantly improves the breakdown resistance of the polymer.

[0039] (4) the composition has the comprehensive advantages of high breakdown resistance, low ash content, good processing performance, high mechanical strength, and the preparation process is simple and mild, which is not easy to cause degradation of polypropylene and is beneficial to maintaining the stability of the electrical properties of polypropylene. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 NMR spectra of the comparative examples and examples. DETAILED DESCRIPTION

[0041] The present application proposes the following examples as further illustration, but not as a limitation of the scope of protection of the claims of the present application.

[0042] 2-vinyl naphthalene: purchased from Macklin Chemical (CAS: 827-54-3).

[0043] 4-vinyl biphenyl: purchased from Macklin Chemical (CAS: 2350-89-2).

[0044] 9-vinyl anthracene: purchased from Macklin Chemical (CAS: 2444-68-0).

[0045] 2-Vinylbenzofuran: purchased from TCI (Shanghai) Chemicals Co., Ltd. (CAS: 7522-79-4).

[0046] 2-Vinylquinoline: purchased from Angene Chemicals (CAS: 772-03-2).

[0047] Isotactic polypropylene a1-a3: all are commercial isotactic polypropylene, and the powder without melt granulation was used.

[0048] (1) Isotactic polypropylene powder a1: brand T30S, melt index 3.0 g / 10 min (230℃, 2.16 kg), weight average molecular weight 310,000 g / mol;

[0049] (2) Isotactic polypropylene powder a2: brand 1900, melt index 40 g / 10 min (230℃, 2.16 kg), weight average molecular weight 190,000 g / mol;

[0050] (3) Isotactic polypropylene powder a3: brand K7760, melt index 60 g / 10 min (230℃, 2.16 kg), weight average molecular weight 150,000 g / mol.

[0051] Ultra-high molecular weight isotactic polypropylene was synthesized according to the literature: Polymer Testing, 2017, 60, 260-265.

[0052] (1) Ultra-high molecular weight isotactic polypropylene powder b1: melt index 3.3 g / 10 min (230℃, 21.6 kg), weight average molecular weight 1,600,000 g / mol;

[0053] (2) Ultra-high molecular weight isotactic polypropylene powder b2: melt index 1.2 g / 10 min (230℃, 21.6 kg), weight average molecular weight 4,400,000 g / mol.

[0054] The melt index of the polypropylene resin in the application was determined according to GB / T 3682.1-2018.

[0055] The ash content of the polypropylene resin in the application was determined according to GB / T 9345.1-2008.

[0056] The dielectric breakdown strength of the polypropylene resin in the application was determined according to GB / T 1408.1-2016.

[0057] The impact strength of the polypropylene resin in the application was determined according to GB / T 1043.2-2018.

[0058] The flexural modulus of the polypropylene resin in the application was determined according to GB / T 9341-2008.

[0059] Example 1

[0060] In a 500 mL reactor purged with nitrogen, 100 g of the ultra-high molecular weight isotactic polypropylene powder b1, 50 mL of toluene, 50 mL of n-hexane, 0.5 g of antioxidant 1010 were added and swelled at 60°C for 60 min; next, 1 g of initiator benzoyl peroxide, 8 g of aromatic olefin 2-vinylnaphthalene were added and reacted at 90°C for 4 h; finally, 300 mL of acetylacetone was added and washed at 60°C for 24 h; the product in the reactor was filtered and dried to obtain the ultra-high molecular weight isotactic polypropylene b containing aromatic groups in side groups.

[0061] 30 g of the ultra-high molecular weight isotactic polypropylene b containing aromatic groups in side groups prepared above, 70 g of isotactic polypropylene powder a2, 0.9 g of heat stabilizer powder c (0.3 g of antioxidant 1010 + 0.6 g of antioxidant 168) were mixed in a double-cone mixer at room temperature for 30 min to prepare a powdered polypropylene composition, the composition and properties of which are shown in Table 1.

[0062] Example 2

[0063] In a 500 mL reactor purged with nitrogen, 100 g of the ultra-high molecular weight isotactic polypropylene powder b2, 80 mL of toluene, 0.2 g of antioxidant 1010 and 0.4 g of antioxidant 168 were added and swelled at 80°C for 60 min; next, 1 g of initiator benzoyl peroxide, 10 g of aromatic olefin 9-vinylanthracene were added and reacted at 100°C for 6 h; finally, 350 mL of methyl acetylacetate was added and washed at 60°C for 24 h; the product in the reactor was filtered and dried to obtain the ultra-high molecular weight isotactic polypropylene b containing aromatic groups in side groups.

[0064] 30 g of the ultra-high molecular weight isotactic polypropylene b containing aromatic groups in side groups prepared above, 70 g of isotactic polypropylene powder a2, 0.9 g of heat stabilizer powder c (0.3 g of antioxidant 1010 + 0.6 g of antioxidant 168) were mixed in a double-cone mixer at room temperature for 30 min to prepare a powdered polypropylene composition, the composition and properties of which are shown in Table 1.

[0065] Example 3

[0066] In a 500 mL reaction vessel filled with nitrogen, 100 g of the ultra-high molecular weight isotactic polypropylene powder b2, 120 mL of n-heptane, 0.2 g of the antioxidant 1010 and 0.4 g of the antioxidant 168 were swelled at 90 °C for 120 min; next, 1.5 g of the initiator azobisisobutyronitrile, 10 g of the aromatic olefin 4-vinylbiphenyl were reacted at 80 °C for 12 h; finally, 300 mL of acetylacetone was added and washed at 80 °C for 36 h; the product in the reaction vessel was filtered and dried to obtain the ultra-high molecular weight isotactic polypropylene b having aromatic groups in the side groups.

[0067] The 20 g of the ultra-high molecular weight isotactic polypropylene b having aromatic groups in the side groups prepared above, 80 g of the isotactic polypropylene powder a2, 0.9 g of the heat stabilizer powder c (0.3 g of the antioxidant 1010 + 0.6 g of the antioxidant 168) were mixed in a double-cone blender at room temperature for 30 min to prepare a powdered polypropylene composition, the composition and properties of which are shown in Table 1.

[0068] Example 4

[0069] In a 500 mL reaction vessel filled with nitrogen, 100 g of the ultra-high molecular weight isotactic polypropylene powder b2, 120 mL of n-heptane, 0.2 g of the antioxidant 1010 and 0.4 g of the antioxidant 168 were swelled at 90 °C for 120 min; next, 1.5 g of the initiator azobisisobutyronitrile, 10 g of the aromatic olefin 4-vinylbiphenyl were reacted at 80 °C for 12 h; finally, 300 mL of acetylacetone was added and washed at 80 °C for 36 h; the product in the reaction vessel was filtered and dried to obtain the ultra-high molecular weight isotactic polypropylene b having aromatic groups in the side groups.

[0070] The 20 g of the ultra-high molecular weight isotactic polypropylene b having aromatic groups in the side groups prepared above, 80 g of the isotactic polypropylene powder a2, 0.9 g of the heat stabilizer powder c (0.3 g of the antioxidant 1010 + 0.6 g of the antioxidant 168) were mixed in a double-cone blender at room temperature for 30 min to prepare a powdered polypropylene composition, the composition and properties of which are shown in Table 1.

[0071] Example 5

[0072] In a 500 mL reaction vessel filled with nitrogen, 100 g of the ultra-high molecular weight isotactic polypropylene powder b2, 120 mL of n-heptane, 0.2 g of the antioxidant 1010 and 0.4 g of the antioxidant 168 were swelled at 90 °C for 120 min; next, 1.5 g of the initiator azobisisobutyronitrile, 10 g of the aromatic olefin 4-vinylbiphenyl were reacted at 80 °C for 12 h; finally, 300 mL of acetylacetone was added and washed at 80 °C for 36 h; the product in the reaction vessel was filtered and dried to obtain the ultra-high molecular weight isotactic polypropylene b having aromatic groups in the side groups.

[0073] A mixture of 15 g of the above prepared ultrahigh molecular weight polypropylene b having aromatic group-containing side groups, 85 g of isotactic polypropylene powder a3, 0.9 g of heat stabilizer powder c (0.3 g of antioxidant 1010 + 0.6 g of antioxidant 168) was mixed in a double-cone blender for 30 minutes at room temperature to prepare a powdered polypropylene composition, the composition and properties of which are shown in Table 1.

[0074] Example 6

[0075] In a 500 mL reaction vessel filled with nitrogen, 100 g of ultrahigh molecular weight polypropylene powder b1, 500 mL of toluene, 0.2 g of antioxidant 1010 and 0.4 g of antioxidant 168 were swelled at 90°C for 60 minutes; next, 1 g of initiator benzoyl peroxide, 8 g of aromatic olefin 2-vinylnaphthalene, 8 g of aromatic olefin 2-vinylquinoline were reacted at 90°C for 6 hours; finally, 300 mL of acetylacetone was washed at 80°C for 24 hours, and the product in the reaction vessel was filtered and dried to obtain ultrahigh molecular weight isotactic polypropylene b having aromatic group-containing side groups.

[0076] A mixture of 20 g of the above prepared ultrahigh molecular weight polypropylene b having aromatic group-containing side groups, 80 g of isotactic polypropylene powder a1, 0.6 g of heat stabilizer powder c (0.2 g of antioxidant 1010 + 0.4 g of antioxidant 168) was mixed in a double-cone blender for 30 minutes at room temperature to prepare a powdered polypropylene composition, the composition and properties of which are shown in Table 1.

[0077] Comparative Example 1

[0078] In a 500 mL reaction vessel filled with nitrogen, 100 g of isotactic polypropylene powder a1, 120 mL of n-heptane, 0.2 g of antioxidant 1010 and 0.4 g of antioxidant 168 were swelled at 90°C for 120 minutes; next, 1.5 g of initiator azobisisobutyronitrile, 8 g of styrene were reacted at 80°C for 12 hours; finally, 300 mL of hexane was washed, and the product in the reaction vessel was filtered and dried to obtain the product.

[0079] A mixture of 100 g of the above prepared product, 0.9 g of heat stabilizer powder c (0.3 g of antioxidant 1010 + 0.6 g of antioxidant 168) was mixed in a double-cone blender for 30 minutes at room temperature to prepare a powdered polypropylene composition, the composition and properties of which are shown in Table 1.

[0080] Comparative Example 2

[0081] In a 500 mL reaction vessel filled with nitrogen, 100 g of isotactic polypropylene powder a1, 500 mL of toluene, 0.2 g of antioxidant 1010 and 0.4 g of antioxidant 168 were added, and swelled at 90°C for 60 min; next, 1 g of initiator benzoyl peroxide, 8 g of aromatic olefin 2-vinylnaphthalene, 8 g of aromatic olefin 2-vinylquinoline were added, and reacted at 90°C for 6 h; finally, 300 mL of acetylacetone was added, and washed at 80°C for 24 h, and the product in the reaction vessel was filtered and dried to obtain isotactic polypropylene b' having aromatic groups in the side groups.

[0082] In a double-cone blender, 20 g of the isotactic polypropylene b' having aromatic groups in the side groups prepared above, 80 g of isotactic polypropylene powder a1, 0.6 g of heat stabilizer powder c (0.2 g of antioxidant 1010 + 0.4 g of antioxidant 168) were mixed at room temperature for 30 min, and a powdered polypropylene composition was prepared, the composition and properties of which are shown in Table 1.

[0083] Comparative Example 3

[0084] In a 500 mL reaction vessel filled with nitrogen, 100 g of isotactic polypropylene powder a1, 500 mL of toluene, 0.2 g of antioxidant 1010 and 0.4 g of antioxidant 168 were added, and swelled at 90°C for 60 min; next, 1 g of initiator benzoyl peroxide, 8 g of aromatic olefin 2-vinylnaphthalene, 8 g of aromatic olefin 2-vinylquinoline were added, and reacted at 90°C for 6 h; finally, 300 mL of acetylacetone was added, and washed at 80°C for 24 h, and the product in the reaction vessel was filtered and dried to obtain isotactic polypropylene b' having aromatic groups in the side groups.

[0085] In a double-cone blender, 20 g of the isotactic polypropylene b' having aromatic groups in the side groups prepared above, 80 g of isotactic polypropylene powder a1, 0.6 g of heat stabilizer powder c (0.2 g of antioxidant 1010 + 0.4 g of antioxidant 168) were mixed at room temperature for 30 min, and a powdered polypropylene composition was prepared, the composition and properties of which are shown in Table 1.

[0086] Comparative Example 4

[0087] In a double-cone blender, 20 g of the isotactic polypropylene b' having aromatic groups in the side groups prepared above, 80 g of isotactic polypropylene powder a1, 0.6 g of heat stabilizer powder c (0.2 g of antioxidant 1010 + 0.4 g of antioxidant 168) were mixed at room temperature for 30 min, and a powdered polypropylene composition was prepared, the composition and properties of which are shown in Table 1.

[0088] Comparative Example 5

[0089] The 1000 g of the ultra-high molecular weight isotactic polypropylene powder b2, 2 g of the antioxidant 1010, 4 g of the antioxidant 168, 15 g of the initiator azobisisobutyronitrile, 100 g of the aromatic olefin 4-vinylbiphenyl were mixed in a double-cone mixer at room temperature for 30 min, and then were added into a twin-screw extruder to be melt-extruded and granulated at 210°C to obtain the ultra-high molecular weight isotactic polypropylene b containing aromatic groups in side groups.

[0090] The 20 g of the ultra-high molecular weight isotactic polypropylene b containing aromatic groups in side groups prepared above, 80 g of the isotactic polypropylene powder a2, and 0.9 g of the heat stabilizer powder c (0.3 g of the antioxidant 1010 + 0.6 g of the antioxidant 168) were mixed in a double-cone mixer at room temperature for 30 min to prepare a polypropylene composition, the composition and properties of which are shown in Table 1.

[0091] Table 1 Composition and properties of the polypropylene composition

[0092]

[0093] From the data in Table 1, it can be seen that the polypropylene composition prepared in the present application has the following characteristics:

[0094] (1) Taking Example 3 as an example, the aromatic group monomer is successfully grafted onto the side groups of the ultra-high molecular weight isotactic polypropylene, which can be confirmed from the nuclear magnetic hydrogen spectrum of the product, as shown in Table 2: Figure 1 The characteristic peak of benzene ring appearing between the chemical shifts of 7.1-7.5 ppm indicates that the 4-vinylbiphenyl is introduced into the side groups of the polypropylene, and the polypropylene composition prepared by mixing the ultra-high molecular weight isotactic polypropylene b containing biphenyl groups in side groups with the isotactic polypropylene a and the heat stabilizer c also clearly shows the presence of the biphenyl groups. However, the nuclear magnetic spectrum of Comparative Example 4 (without adding the aromatic olefin g for grafting reaction, but only mixing the ultra-high molecular weight isotactic polypropylene, the isotactic polypropylene a, and the heat stabilizer c) only contains the characteristic peak of the polypropylene backbone.

[0095] (2) The polypropylene without any functional treatment (Comparative Example 4) has a DC breakdown strength of about 375 kV / mm and an AC breakdown strength of about 218 kV / mm; after the normal molecular weight isotactic polypropylene is grafted with styrene (Comparative Examples 1 and 2), the DC breakdown strength can be increased to about 470-495 kV / mm and the AC breakdown strength can be increased to about 270-285 kV / mm; and by grafting biphenyl, polyphenyl, fused ring aromatic hydrocarbon or aromatic hydrocarbon containing N, S and other heteroatoms on the ultra-high molecular weight isotactic polypropylene and then combining with the normal molecular weight isotactic polypropylene (Examples 1-6), the DC breakdown strength can be further significantly increased to about 525-575 kV / mm and the AC breakdown strength can be increased to about 332-375 kV / mm, which can meet the demand of the material breakdown resistance of the ultra-high voltage power transmission.

[0096] (3) Since the organic ketone compound is used for elution treatment after the functional group is grafted on the ultra-high molecular weight isotactic polypropylene in the present application, the ash content in the polypropylene can be significantly reduced compared with the conventional alkane and aromatic eluent. As can be seen from the polymers of Comparative Example 3 and Example 3, since the polarity of the eluent acetylacetone used in Example 3 is significantly higher than that of the eluent hexane used in Comparative Example 3, the ash content in the product is significantly different: the ash content of the product of Example 3 is only 15 ppm, while the ash content of the product of Comparative Example 3 is 236 ppm, and the high ash content reduces the breakdown strength of the material.

[0097] (4) The combination of the ultra-high molecular weight isotactic polypropylene and the normal molecular weight isotactic polypropylene used in the present application significantly improves the processability of the ultra-high molecular weight isotactic polypropylene and also improves the mechanical properties of the composition. For example, 30 parts of the ultra-high molecular weight isotactic polypropylene with a melt index of 1.2 g / 10 min (230°C, 21.6 kg) is combined with 70 parts of the normal molecular weight isotactic polypropylene with a melt index of 40 g / 10 min (230°C, 2.16 kg) to obtain a composition with a melt index of 3.9 g / 10 min (230°C, 2.16 kg), which has a processability comparable to that of Comparative Example 1 (melt index 3.0 g / 10 min (230°C, 2.16 kg)), but the impact strength and flexural modulus of Example 2 are significantly improved, which is due to the significant improvement of the strength of the material by the high molecular weight polypropylene.

[0098] (5) The grafting temperature adopted by the present application is low, which can effectively avoid thermal degradation of the ultrahigh molecular weight isotactic polypropylene. Compared with Example 3 under the same formula, the melt index of Comparative Example 5 prepared by using the traditional melt grafting method is significantly improved (i.e. the molecular weight is obviously decreased), which indicates that the degradation of ultrahigh molecular weight polypropylene by high temperature processing cannot be ignored. In addition, since the melt extrusion processing is difficult to sufficiently wash the grafting product, the ash content in the product is extremely high, which seriously affects the electrical properties of the material.

Claims

1. A polypropylene composition, characterized in that: The composition comprises isotactic polypropylene (a), ultra-high molecular weight isotactic polypropylene (b) with aromatic side groups, and a heat stabilizer (c); wherein the mass fraction of the isotactic polypropylene (a) in the composition is 50% to 94%, the mass fraction of the ultra-high molecular weight isotactic polypropylene (b) with aromatic side groups in the composition is 5% to 50%, and the mass fraction of the heat stabilizer (c) in the composition is 0.1% to 5%. The ultra-high molecular weight isotactic polypropylene b with aromatic side groups has the following structure: Among them, R 1 is a biphenyl or condensed aromatic hydrocarbon containing 8 to 30 carbon atoms, or an aromatic hydrocarbon containing 4 to 20 carbon atoms and containing heteroatoms, wherein the heteroatoms are one or more of N, S, and O; R 2 is H or CH3; x is an integer from 10000 to 50000; y = 0.001x to 0.1x.

2. The polypropylene composition according to claim 1, characterized in that The isotactic polypropylene a is a polypropylene having a melt index of 1 to 100 g / 10 min (230° C., 2.16 kg); the ultra-high molecular weight isotactic polypropylene b having side groups containing aromatic groups is a polypropylene having a melt index of 0.5 to 10 g / 10 min (230° C., 21.6 kg); The isotactic polypropylene a is a polypropylene powder having an isotacticity greater than or equal to 95%; the ultra-high molecular weight isotactic polypropylene b having side groups containing aromatic groups is a polypropylene powder having an isotacticity greater than or equal to 95%; The heat stabilizer C is at least one of a hindered phenol antioxidant, a phosphite antioxidant or a thioester antioxidant.

3. The polypropylene composition according to claim 1, characterized in that The ultra-high molecular weight isotactic polypropylene b having side groups containing aromatic groups is prepared by the following steps: In the first step, a mixture of ultra-high molecular weight isotactic polypropylene powder, swelling liquid d, and thermal stabilizer e is pretreated to obtain a product of the first step pretreatment; In the second step, in the presence of an initiator f, the product pretreated in the first step reacts with an aromatic olefin g having the following structure to obtain a reaction product of the second step; The third step is to wash the reaction product of the second step in an eluent h, and then dry it to obtain an ultra-high molecular weight isotactic polypropylene b having a side group containing an aromatic group; Among them, R 1 is a biphenyl or condensed ring aromatic hydrocarbon containing 8 to 30 carbon atoms, or an aromatic hydrocarbon containing 4 to 20 carbon atoms and containing heteroatoms such as N, S, and O; R 2 is H or CH3.

4. The polypropylene composition according to claim 3, characterized in that ,, characterized by: In the first step, the mass ratio of the swelling liquid d to the ultra-high molecular weight isotactic polypropylene powder is 0.1 to 100:1; the mass ratio of the heat stabilizer e to the ultra-high molecular weight isotactic polypropylene powder is 1:100 to 1000; the pretreatment temperature is 20° C. to 100° C.; and the pretreatment time is 10 min to 120 min. In the second step, the mass ratio of the initiator f to the ultra-high molecular weight isotactic polypropylene powder of the first step is 1:10-1000; the mass ratio of the aromatic olefin g to the ultra-high molecular weight isotactic polypropylene powder of the first step is 1:5-500; the reaction temperature is 60° C.-120° C.; and the reaction time is 0.5 h-10 h. In the third step, the reaction product of the second step is filtered or directly eluted before being washed in the eluent h; the mass ratio of the eluent h to the ultra-high molecular weight isotactic polypropylene powder of the first step is 1 to 10:1; the washing temperature is 20° C. to 100° C.; and the washing time is 5 h to 50 h.

5. The polypropylene composition according to claim 3, characterized in that: The ultra-high molecular weight isotactic polypropylene powder has a melt index of 0.5 to 10 g / 10 min (230° C., 21.6 kg) and a weight-average molecular weight of 1 to 5 million g / mol; the swelling liquid d is an aliphatic hydrocarbon or an aromatic hydrocarbon, selected from one or more of n-pentane, isopentane, n-hexane, cyclohexane, n-heptane, n-octane, n-decane, petroleum ether, benzene, toluene, xylene, and ethylbenzene.

6. The method for preparing ultra-high molecular weight isotactic polypropylene (B) having side groups containing aromatic groups according to claim 3, characterized in that: The heat stabilizer e is at least one of a hindered phenol antioxidant, a phosphite antioxidant or a thioester antioxidant; the heat stabilizer e is the same as or different from the heat stabilizer c.

7. The method for preparing ultra-high molecular weight isotactic polypropylene (B) having aromatic side groups according to claim 3, characterized in that: The initiator f is a thermal decomposition free radical initiator selected from one or more of an organic peroxide initiator and an azo initiator, preferably one or more of an alkyl peroxide, an alkynyl peroxide, a hydroperoxide, an acyl peroxide and a peroxycarbonate; The aromatic olefin g is an olefin having an aromatic ring structure substituent, selected from one or more of 4-vinylbiphenyl, 2-vinylnaphthalene, 9-vinylanthracene, 9-vinylphenanthrene, 4-vinylbenzocyclobutene, 4-styrylpyridine, 2-vinylbenzofuran, 2-vinylbenzothiophene, and 2-vinylquinoline.

8. The method for preparing ultra-high molecular weight isotactic polypropylene (B) having aromatic side groups according to claim 3, characterized in that: The eluent h is an organic ketone compound, selected from one or more of acetone, methyl ethyl ketone, cyclohexanone, butanone, benzophenone, hydroxyacetone, benzoyl acetone, acetylacetone, propionyl acetone, methyl acetylacetonate, and phenylpyruvic acid.

9. The method for preparing the polypropylene composition according to any one of claims 1 to 8, characterized in that: The steps include: The isotactic polypropylene a, the ultra-high molecular weight isotactic polypropylene b having aromatic groups on the side groups, and the thermal stabilizer c are uniformly mixed to prepare a powdery composition.

10. Use of the polypropylene composition according to any one of claims 1 to 9 in the preparation of polypropylene molded products.

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