High-strength easy-to-process polypropylene and preparation method and application thereof

Abstract

The application discloses a kind of high-strength easy-to-process polypropylene and its preparation method and application. By double reactor series process, the kettle alloy comprising polyolefin component A (low entanglement ultrahigh molecular weight polypropylene) and polyolefin component B (conventional molecular weight polypropylene) is prepared, weight average molecular weight is at 50-3000 kg / mol, melt index is at 0.001-2.0 g / 10 min. Among them, the weight average molecular weight of polyolefin component A is greater than or equal to 1000 kg / mol, the weight average molecular weight of polyolefin component B is at 50-400 kg / mol, and the isotacticity of the two components is all greater than or equal to 95%. The initial storage modulus in rheological sweep test of polyolefin component A is at 20000-100000 Pa, and after 24 hours of rheological test, the storage modulus is more than 150% of the initial storage modulus. The preparation method can flexibly adjust the preparation order of two components. High-strength easy-to-process polypropylene has the characteristics of high strength, high toughness and easy processing.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials, and relates to a polyolefin material. Specifically, this invention relates to a high-strength, easily processed polypropylene, its preparation method, and its application. Background Technology

[0002] Polypropylene (PP), a widely used polymer material, has performance characteristics closely related to its molecular weight and molecular weight distribution. While ordinary polypropylene exhibits good processing fluidity, its low molecular weight and wide molecular weight distribution result in insufficient strength and low melt strength, limiting its application in fields with high mechanical performance requirements, such as automotive parts, appliance housings, and rail transportation. Ultra-high molecular weight polypropylene (UHMWPP), on the other hand, displays excellent strength, abrasion resistance, and impact resistance due to its long molecular chains, narrow molecular weight distribution, and high degree of entanglement. However, its extremely high melt viscosity makes it extremely difficult to process and mold, hindering large-scale production through conventional extrusion and injection molding processes.

[0003] In the prior art, patent application CN102516655B discloses a reinforced and toughened polypropylene composite and its preparation method. The components are mixed evenly and then added to a screw extruder for melt blending and extrusion granulation to obtain the composite. This involves an in-situ grafting reaction between multifunctional monomers and polypropylene during melt blending. Patent application CN111117073A discloses a method for preparing a blended ultra-high molecular weight polypropylene / polypropylene alloy. This method prepares the alloy by melt blending a small amount of ultra-high molecular weight polypropylene with polypropylene. While this improves processing performance to some extent, its ability to control molecular weight distribution is limited, and problems such as poor uniformity, melt blend phase separation, and unstable performance still exist. Patent application CN102174225A discloses a multiphase copolymerized polypropylene in-reactor alloy and its preparation method. This method uses a Ziegler-Natta / metallocene composite catalyst to simultaneously generate a polypropylene resin phase and an ethylene / α-olefin rubber phase in a polymerization reactor, utilizing block copolymers as compatibilizers to achieve two-phase dispersion. Patent application CN102127176A discloses a method for preparing high melt strength polypropylene. Utilizing a Ziegler-Natta / metallocene composite catalyst system, it achieves one-step polymerization of high melt strength polypropylene through a simple polymerization method, enabling the in-reactor polymerization of linear polypropylene and long-chain branched polypropylene blends. However, this process requires precise control of the catalyst ratio (e.g., the Al / Ti molar ratio needs to be maintained between 100-10000), and the high cost of preparing the composite catalyst limits its industrial application. In summary, existing technologies for preparing high-strength polypropylene materials generally face the technical bottleneck of balancing high strength and processability. On the one hand, the high molecular weight leads to extensive entanglement between molecular chains, making processing and molding difficult; on the other hand, balancing processing performance and usability often results in sacrificing the material's mechanical properties to achieve better processing performance. Therefore, developing a preparation method that retains the high strength advantage of ultra-high molecular weight polypropylene while improving the processing performance of polypropylene materials through process optimization has become an urgent technical challenge to be solved in this field. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a high-strength, easily processed polypropylene, a method for preparing high-strength, easily processed polypropylene, and applications of high-strength, easily processed polypropylene.

[0005] A method for preparing high-strength, easily processable polypropylene (PP) directly produces an in-reactor alloy containing a specific-structure polyolefin component A (ultra-high molecular weight polypropylene) and component B (conventional molecular weight polypropylene) through a dual-reactor tandem process. This effectively solves the core technical bottleneck of the difficulty in processing high-strength PP materials and the challenge of simultaneously achieving optimal mechanical properties. This dual-reactor tandem process allows for the preparation of either polyolefin component A or polyolefin component B first, with flexible adjustment of the order. It is also compatible with various reactors used in industrial production, efficiently producing high-strength, easily processable PP. High-strength, easily processable PP can be processed using conventional twin-screw extrusion, injection molding, or blow molding processes. The processed products exhibit significant improvements in strength, rigidity, and toughness, such as enhanced impact resistance, environmental stress cracking resistance, flexural strength, tensile strength, and tensile modulus.

[0006] The method for preparing high-strength, easily processable polypropylene using a dual-reactor tandem process described in this invention differs significantly from the fixed polymerization flow in existing patents, offering substantial technical advantages. The process can either first prepare ultra-high molecular weight component A (UHMWPP) followed by conventional molecular weight component B, or vice versa. For example, when A is prepared first and then B, component B acts as a "plasticizing phase" to encapsulate component A, improving overall melt flowability; when B is prepared first and then A, the high-strength network of component A can be uniformly dispersed in the continuous phase of B, optimizing mechanical properties. This flexibility allows for switching product specifications in industrial production without equipment modifications, significantly reducing process conversion costs. It also enables precise control of the two-phase structure and distribution based on the differentiated strength-processability requirements of various applications, such as automotive parts and appliance casings.

[0007] This invention provides a high-strength, easily processed polypropylene, which is prepared by a series process. The high-strength, easily processed polypropylene has a weight-average molecular weight of 50-3000 kg / mol, a melt index of 0.001-2.0 g / 10min, a tensile strength ≥40 MPa, and an impact strength ≥12 kJ / m². 2 The high-strength, easily processed polypropylene includes polyolefin component A and polyolefin component B; wherein, polyolefin component A is ultra-high molecular weight polypropylene with a weight-average molecular weight ≥ 1000 kg / mol; and polyolefin component B is polypropylene with a weight-average molecular weight of 50-400 kg / mol.

[0008] Preferably, in the high-strength, easily processed polypropylene, the isotacticity of polyolefin component A is ≥95%, and the melt index is 0.001-0.1 g / 10 min; the isotacticity of polyolefin component B is ≥95%, and the melt index is 0.1-150 g / 10 min.

[0009] Preferably, in the high-strength, easily processed polypropylene, the polyolefin component A accounts for 3 wt%-60 wt% by weight, the polyolefin component B accounts for 40 wt%-97 wt% by weight, and the molecular weight distribution index of the high-strength, easily processed polypropylene is 30-500.

[0010] Preferably, in the high-strength, easily processed polypropylene, the polyolefin component A is a low-entanglement ultra-high molecular weight polypropylene; the initial storage modulus of the polyolefin component A in the rheological sweep frequency test is 20,000-100,000 Pa, and after 24 h of rheological testing, the storage modulus is more than 150% of the initial storage modulus.

[0011] This invention provides an application of the high-strength, easily processed polypropylene, which can be used alone or for the modification of general polyolefin materials, and is widely used in automobiles, home appliances, rail transportation, consumer electronics, communication equipment and other fields.

[0012] This invention provides a method for preparing high-strength, easily processed polypropylene, wherein the high-strength, easily processed polypropylene is prepared using a dual-reactor series process; the preparation method includes: S1, adding a catalyst, a co-catalyst, an electron donor, and propylene; S2, preparing the high-strength, easily processed polypropylene powder containing polyolefin component A and polyolefin component B; S3, granulating the high-strength, easily processed polypropylene powder to obtain high-strength, easily processed polypropylene granules.

[0013] Wherein, S2 includes step S AB Or step S BA ;

[0014] Step S AB The process includes: initiating homopolymerization of propylene in a first reactor using a catalyst to obtain polyolefin component A; then, initiating homopolymerization of propylene or copolymerization of propylene with other olefin monomers in a second reactor to prepare polyolefin component B, thereby obtaining the high-strength, easily processable polypropylene powder containing polyolefin component A and component B.

[0015] Step S BA The process includes: initiating the homopolymerization of propylene or copolymerization of propylene with other olefin monomers in a first reactor to prepare the polyolefin component B; the polyolefin component B enters a second reactor to initiate the homopolymerization of propylene to prepare the polyolefin component A, thereby obtaining the high-strength, easily processable polypropylene powder containing the polyolefin component A and the polyolefin component B.

[0016] Preferably, in step S3, during the granulation process, an additive is added in a twin-screw extruder or a single-screw extruder. The additive includes one or more of antioxidants, acid absorbents, lubricants, nucleating agents, antistatic agents, and antibacterial agents. The total amount of the additive added accounts for ≤1% of the total weight of the high-strength, easily processed polypropylene.

[0017] Preferably, the first reactor and the second reactor are one or more of the following: horizontal stirred bed reactor, vertical stirred tank reactor, gas phase fluidized bed reactor, loop reactor, and single multi-zone circulating reactor, and the types of the first reactor and the second reactor can be the same or different.

[0018] Preferably, in the method for preparing high-strength, easily processed polypropylene according to the present invention:

[0019] The preparation temperature of polyolefin component A is 50-80℃, the propylene pressure is 0.5-3.0 MPa, and the time is 0.5-5h; the preparation temperature of polyolefin component B is 50-100℃, and the propylene pressure is 0.1-3.0 MPa; when preparing polyolefin component B, hydrogen gas at a pressure of 0.01-0.5 MPa is introduced into the reactor as a molecular weight regulator for 0.1-5h.

[0020] The catalyst is one or more of the following: supported ZN catalyst, supported metallocene catalyst, supported non-metallocene catalyst, and supported FI catalyst;

[0021] The co-catalyst is selected from one or more of alkylaluminum, methylaluminoxane and modified methylaluminoxane, preferably one or more of methylaluminoxane, modified methylaluminoxane, triethylaluminum, triisobutylaluminum, diethylaluminum chloride, dichloroethylaluminum, tributylaluminum, trihexylaluminum, and trioctylaluminum.

[0022] The electron donor is selected from one or more of silanes, carboxylic acid esters, and ethers, preferably one, two, or three of methylcyclohexyldimethoxysilane, dicyclopentyldimethoxysilane, diisobutyldimethoxysilane, tetraethoxysilane, and other organosilanes.

[0023] Preferably, the method for preparing high-strength, easily processable polypropylene further includes a catalyst prepolymerization step: in step S1, a prepolymerization solvent is added to a prepolymerization reactor, followed by the addition of the co-catalyst, the electron donor, the catalyst, and the propylene, and a prepolymerization reaction is carried out for 0.1-2.0 h; wherein the catalyst prepolymerization temperature is 0-30℃, the prepolymerization pressure is 0.1-4.0 MPa, the prepolymerization time is 0.1-2.0 h, and the degree of prepolymerization is 2-100 g / g; the prepolymerization reactor is one of a loop reactor or a vertical stirred tank reactor; the prepolymerization solvent is selected from one or more of n-pentane, isopentane, n-hexane, 2-methylpentane, n-heptane, methylcyclohexane, and 2-methylhexane.

[0024] The present invention has the following outstanding gain effects:

[0025] (1) The high-strength, easily processed polypropylene of the present invention is prepared by a dual-reactor series process. The high-strength, easily processed polypropylene is a polypropylene in-reactor alloy. Polyolefin component A and polyolefin component B are the continuous phase and the dispersed phase, respectively. During blending, the molecular chain interaction between polyolefin component A and polyolefin component B is stronger, which enables the high-strength, easily processed polypropylene to efficiently absorb and disperse energy when subjected to impact, thereby significantly improving the impact toughness of the material while maintaining the good rigidity of polypropylene. Therefore, the high-strength, easily processed polypropylene has stronger tensile strength and impact strength, which is significantly better than that of physically blended polypropylene products.

[0026] (2) The high-strength, easily processable polypropylene of the present invention has a molecular weight distribution of 30-500. The wide or extremely wide molecular weight distribution gives the polypropylene material lower viscosity and easy processing characteristics. In order to balance processing performance and performance, the content of polyolefin component A in the high-strength, easily processable polypropylene can be higher, thereby further improving the performance of the high-strength, easily processable polypropylene.

[0027] (3) Polyolefin component A in high-strength, easily processed polypropylene is ultra-high molecular weight polypropylene (UHMWPP), which exhibits low entanglement characteristics. In the rheological sweep frequency test, the initial storage modulus of polyolefin component A is 20,000-100,000 Pa. After 24 h of rheological testing, the storage modulus is more than 150% of the initial storage modulus. The low-entanglement aggregated structure gives polyolefin component A better molecular chain structure mobility. During high-temperature processing, the low-entanglement polyolefin component A molecular chains can form an interpenetrating network structure more quickly, thereby improving the rigidity and toughness of high-strength, easily processed polypropylene.

[0028] (4) In high-strength, easily processed polypropylene, polyolefin component A is low-entanglement UHMWPP. When modifying other general-purpose polyolefin materials, low-entanglement UHMWPP can form more entangled network structures and ligated molecular structures more quickly, thereby improving the melt strength of the blended material. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a graph showing the molecular weight distribution of the product in Example 1.

[0031] Figure 2 The graph shows the change of the storage modulus of polyolefin component A over time in the rheological test of Example 4.

[0032] Figure 3 This is a stress-strain curve of the product in Example 4. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0035] Characterization methods for polymer structure and properties:

[0036] (1) Melt index: determined according to GB / T 3682-2000.

[0037] (2) Tensile strength: determined according to GB / T 1040-2006.

[0038] (3) Impact strength: determined according to GB / T 1843-2008.

[0039] (4) Weight-average molecular weight and molecular weight distribution: determined by high-temperature permeation gel chromatography.

[0040] (5) Isotacticity: determined according to GB / T 2412-2008.

[0041] Example 1

[0042] The first reactor, second reactor, and prepolymerization reactor were purged with high-purity nitrogen to remove moisture and oxygen from the reactors. A hexane solution (prepolymerization solvent) was added to the prepolymerization reactor, followed by the sequential addition of triethylaluminum (co-catalyst), methylcyclohexyldimethoxysilane (electron donor), and a supported Zn catalyst, and prepolymerization was carried out in the prepolymerization reactor. The prepolymerization temperature was controlled at 15°C, the propylene monomer pressure was maintained at 3.0 MPa during prepolymerization, the prepolymerization reaction time was 0.12 h, and the degree of prepolymerization was adjusted to 5 g / g.

[0043] After prepolymerization, the material was transferred to the first reactor to prepare polyolefin component A. The reaction temperature was controlled at 58°C, the propylene pressure at 1.1 MPa, and the reaction time at 3 h, initiating homopolymerization of propylene to obtain low-entanglement ultra-high molecular weight polypropylene. The material was then transferred to the second reactor to prepare polyolefin component B. Hydrogen gas at a pressure of 0.2 MPa was first introduced into the reactor, followed by propylene. The propylene pressure was controlled at 1.0 MPa, the reaction temperature at 72°C, and the reaction time at 2 h, initiating homopolymerization of propylene.

[0044] After the reaction is complete, the product is discharged, and 0.5 wt% of composite additives (containing antioxidants and acid absorbents in a ratio of 3:1) are added during the granulation process to obtain high-strength, easily processed polypropylene P1.

[0045] Testing revealed that the high-strength, easily processable polypropylene P1 contained polyolefin component A with a weight ratio of 30 wt%, a weight-average molecular weight of 1800 kg / mol, isotacticity of 97%, and a melt index of 0.03 g / 10min; polyolefin component B with a weight ratio of 69.5 wt%, a weight-average molecular weight of 120 kg / mol, isotacticity of 97%, and a melt index of 8 g / 10min; the product had a molecular weight distribution of 40.2, a tensile strength of 41.2 MPa, an impact strength of 25.1 kJ / m², and good resistance to environmental stress cracking.

[0046] Example 2

[0047] The first reactor, second reactor, and prepolymerization reactor were purged with high-purity nitrogen to remove moisture and oxygen from the reactors. An isopentane solution was added to the prepolymerization reactor, followed by the sequential addition of methylaluminoxane (co-catalyst), dicyclopentyldimethoxysilane (electron donor), and a supported metallocene catalyst, and prepolymerization was carried out in the prepolymerization reactor. The prepolymerization temperature was 10℃, the propylene monomer pressure was maintained at 2.5 MPa during prepolymerization, the prepolymerization reaction time was 0.2 h, and the degree of prepolymerization was adjusted to 20 g / g.

[0048] After prepolymerization, the material is transferred to the first reactor to prepare polyolefin component A. The reaction temperature is controlled at 60℃, the propylene pressure at 1.4 MPa, and the reaction time at 2.5 h, initiating homopolymerization of propylene to obtain low-entanglement ultra-high molecular weight polypropylene. The material is then transferred to the second reactor to prepare polyolefin component B. Hydrogen gas at a pressure of 0.03 MPa is first introduced into the reactor, followed by propylene. The propylene pressure is controlled at 1.0 MPa, the reaction temperature at 65℃, and the reaction time at 1.5 h, initiating homopolymerization of propylene. After the reaction, the product is discharged, and 0.6 wt% of a composite additive (containing antioxidant, nucleating agent, and antistatic agent in a 2:1:1 ratio) is added during granulation to obtain high-strength, easily processable polypropylene P2.

[0049] Testing revealed that the high-strength, easily processable polypropylene P2 contains polyolefin component A with a weight percentage of 20 wt%, a weight-average molecular weight of 2200 kg / mol, an isotacticity of 96%, and a melt index of 0.03 g / 10min; and polyolefin component B with a weight percentage of 79.4 wt%, a weight-average molecular weight of 210 kg / mol, an isotacticity of 97%, and a melt index of 3.6 g / 10min. The product exhibits a molecular weight distribution of 61.7, a tensile strength of 45.1 MPa, and an impact strength of 18.2 kJ / m², demonstrating good processing and mechanical properties.

[0050] Example 3

[0051] The first reactor, second reactor, and prepolymerization reactor were purged with high-purity nitrogen to remove moisture and oxygen from the reactors. A n-pentane solution was added to the prepolymerization reactor, followed by the sequential addition of triisobutylaluminum (co-catalyst), diisobutyldimethoxysilane (electron donor), and a supported non-metallocene catalyst. Prepolymerization was then carried out in the prepolymerization reactor. The prepolymerization temperature was 3°C, the propylene monomer pressure was maintained at 0.5 MPa, the prepolymerization reaction time was 1.8 h, and the degree of prepolymerization was adjusted to 15 g / g.

[0052] After prepolymerization, the material is transferred to the first reactor to prepare polyolefin component B. Hydrogen gas at a pressure of 0.08 MPa is introduced into the reactor, the reaction temperature is controlled at 85°C, the propylene pressure at 2.0 MPa, and the reaction time is 1 h to initiate homopolymerization of propylene. The material is then transferred to the second reactor to prepare polyolefin component A. Propylene is introduced, the propylene pressure is controlled at 2.5 MPa, the reaction temperature at 61°C, and the reaction time is 1.2 h to initiate homopolymerization of propylene to obtain low-entanglement ultra-high molecular weight polypropylene.

[0053] After the reaction is complete, the product is discharged, and 0.8 wt% of a composite additive (containing lubricant, nucleating agent and antibacterial agent in a ratio of 2:2:1) is added during granulation to obtain high-strength, easily processed polypropylene P3.

[0054] Testing revealed that the high-strength, easily processable polypropylene P3 contained polyolefin component A at a weight ratio of 40 wt%, with a weight-average molecular weight of 3300 kg / mol, isotacticity of 95%, and a melt index of 0.01 g / 10 min; polyolefin component B at a weight ratio of 59.2 wt%, with a weight-average molecular weight of 60 kg / mol, isotacticity of 96%, and a melt index of 45 g / 10 min; the product's molecular weight distribution was 118 (e.g., ...). Figure 1 As shown in the figure, the tensile strength is 47.5 MPa, the impact strength is 20.8 kJ / m², and the overall performance is excellent.

[0055] Example 4

[0056] The first reactor, second reactor, and prepolymerization reactor were purged with high-purity nitrogen to remove moisture and oxygen from the reactors. A heptane solution was added to the prepolymerization reactor, followed by the sequential addition of diethylaluminum chloride (co-catalyst), tetraethoxysilane (electron donor), and a supported FI catalyst, to carry out prepolymerization. The prepolymerization temperature was 25°C, the propylene monomer pressure was maintained at 0.8 MPa, the reaction time was 0.3 h, and the degree of prepolymerization was adjusted to 100 g / g.

[0057] After prepolymerization, the material was transferred to the first reactor to prepare polyolefin component A. The reaction temperature was controlled at 71℃, the propylene pressure at 0.5 MPa, and the reaction time at 0.3 h, initiating homopolymerization of propylene to obtain low-entanglement ultra-high molecular weight polypropylene (the rheological storage modulus of this low-entanglement ultra-high molecular weight polypropylene as a function of time is shown in the figure). Figure 2 (As shown). The material was then transferred to a second reactor to prepare polyolefin component B. Hydrogen gas at a pressure of 0.1 MPa was first introduced into the reactor, followed by propylene and ethylene. The propylene pressure was controlled at 0.6 MPa, the ethylene pressure at 0.1 MPa, the reaction temperature at 90°C, and the reaction time at 0.9 h to initiate propylene copolymerization.

[0058] After the reaction is complete, the product is discharged, and 0.3 wt% of a composite additive (containing antioxidant, acid absorbent and antistatic agent in a ratio of 1:2:1) is added during granulation to obtain high-strength and easy-to-process polypropylene P4.

[0059] Testing revealed that the high-strength, easily processable polypropylene P4 contained polyolefin component A at a weight ratio of 5 wt%, with a weight-average molecular weight of 1100 kg / mol, isotacticity of 95%, and a melt index of 0.11 g / 10 min; polyolefin component B comprised 94.7 wt%, with a weight-average molecular weight of 80 kg / mol, isotacticity of 97%, and a melt index of 60 g / 10 min; the product had a molecular weight distribution of 62.1 and a tensile strength of 41.9 MPa (e.g., ...). Figure 3 As shown in the figure, the impact strength is 18.6 kJ / m², and the processing performance is good.

[0060] Example 5

[0061] The first and second reactors were purged with high-purity nitrogen to remove moisture and oxygen from the reactors. An isopentane solution was added to the first reactor, followed by the sequential addition of triethylaluminum (co-catalyst), methylcyclohexyldimethoxysilane (electron donor), and a supported Zn catalyst. Polyolefin component A was prepared in the first reactor under controlled conditions of 63°C, propylene pressure 1.5 MPa, and reaction time 2.2 h, initiating homopolymerization of propylene to obtain low-entanglement ultra-high molecular weight polypropylene. The material was then transferred to the second reactor to prepare polyolefin component B. Hydrogen gas at a pressure of 0.05 MPa was first introduced into the reactor, followed by propylene, controlled at a propylene pressure of 1.0 MPa, reaction temperature 75°C, and reaction time 1.5 h, initiating homopolymerization of propylene.

[0062] After the reaction is complete, the product is discharged, and 0.6 wt% of a composite additive (containing antioxidant, nucleating agent and antistatic agent in a ratio of 2:1:1) is added during granulation to obtain high-strength, easy-to-process polypropylene P5.

[0063] Testing revealed that the high-strength, easily processable polypropylene P5 contained polyolefin component A with a weight percentage of 25 wt%, a weight-average molecular weight of 2000 kg / mol, an isotacticity of 98%, and a melt index of 0.03 g / 10min; and polyolefin component B with a weight percentage of 74.4 wt%, a weight-average molecular weight of 150 kg / mol, an isotacticity of 97%, and a melt index of 6.8 g / 10min. The product exhibited a molecular weight distribution of 73.2, a tensile strength of 43.5 MPa, and an impact strength of 18.0 kJ / m², demonstrating good processing and mechanical properties.

[0064] Comparative Example 1

[0065] Polypropylene material was prepared by melt blending: ultra-high molecular weight polypropylene (weight average molecular weight 1300 kg / mol, isotacticity 97%, melt index 0.09 g / 10min), conventional molecular weight polypropylene (weight average molecular weight 120 kg / mol, isotacticity 97%, melt index 9 g / 10min), and composite additives (including antioxidants and acid absorbents in a ratio of 3:1) were melt blended and granulated in a twin-screw extruder at a weight ratio of 30:69.5:0.5. The extrusion temperature was 200℃ and the speed was 100 r / min to obtain polypropylene P6.

[0066] Polypropylene P6 was tested and found to have a molecular weight distribution of 28.5, a tensile strength of 35.1 MPa, and an impact strength of 10.5 kJ / m². It also showed obvious phase separation and poor melt flow during processing. Compared with Example 1, its mechanical properties and processing performance were significantly different.

[0067] Table 1. Physical properties of high-strength, easily processed polypropylene in Examples 1-5

[0068]

[0069] The high-strength, easily processed polypropylene P1-P5 prepared in Examples 1-5 of this invention have higher tensile strength, impact strength, and environmental stress cracking (ESCR) resistance than polypropylene P6 in Comparative Example 1. This indicates that they can be used alone in fields such as automobiles, rail transportation, and home appliances where strength, toughness, and durability are required.

[0070] Compared to Example 4, the high-strength, easily processed polypropylene in Example 1 has a higher content of polyolefin component A, and its tensile strength, impact strength, and environmental stress cracking (ESCR) index are all better than those of Example 4, indicating that the increased content of polyolefin component A improves the performance of the high-strength, easily processed polypropylene.

[0071] Example 6

[0072] The high-strength, easily processed polypropylene P1-P5 from Examples 1-5 were added sequentially to general-purpose polypropylene (grade M1600K) at a rate of 25 wt%, and modified polypropylene GP1-GP5 was obtained by injection molding. Its mechanical properties are shown in Table 2.

[0073] Comparative Example 2

[0074] The polypropylene P6 in Comparative Example 1 was added to general-purpose polypropylene (grade M1600K) at a rate of 25 wt%, and modified polypropylene GP6 was obtained by injection molding. Its mechanical properties are shown in Table 2.

[0075] Table 2. Physical properties of modified polypropylene in Examples 6-10

[0076]

[0077] The high-strength, easily processed polypropylene P1-P5 prepared in this invention was modified with general-purpose polypropylene M1600K. The modified polypropylene GP1-GP5 materials obtained after modification showed significantly improved tensile strength, impact strength, and environmental stress cracking (ESCR) performance, and the improvement was significantly better than that of the modified polypropylene GP6 material in Comparative Example 2. This indicates that high-strength, easily processed polypropylene can be used to modify polyolefin materials and can be applied in fields such as automobiles, rail transportation, home appliances, consumer electronics, and communication equipment where strength, toughness, and durability are required.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength, easily processed polypropylene, characterized in that, The high-strength, easily processed polypropylene is prepared by a dual-reactor series process; the high-strength, easily processed polypropylene has a weight-average molecular weight of 50-3000 kg / mol, a melt index of 0.001-2.0 g / 10min, a tensile strength ≥40 MPa, and an impact strength ≥12 kJ / m. 2 The high-strength, easily processed polypropylene comprises polyolefin component A and polyolefin component B; wherein, polyolefin component A is ultra-high molecular weight polypropylene with a weight-average molecular weight of 1100-3300 kg / mol; polyolefin component B is polypropylene with a weight-average molecular weight of 50-400 kg / mol; the isotacticity of polyolefin component A is ≥95%, and the melt index is 0.001-0.1 g / 10 min; the isotacticity of polyolefin component B is ≥95%, and the melt index is 0.1-150 g / 10 min; the weight percentage of polyolefin component A is 3 wt%-60 wt%, the weight percentage of polyolefin component B is 40 wt%-97 wt%, and the molecular weight distribution index of the high-strength, easily processed polypropylene is 30-118. The polyolefin component A is low-entanglement ultra-high molecular weight polypropylene; the initial storage modulus of the polyolefin component A in the rheological sweep frequency test is 20,000-100,000 Pa, and after 24 h of rheological testing, the storage modulus is more than 150% of the initial storage modulus. The method for preparing the dual-reactor series process includes: S1, adding a catalyst, a co-catalyst, an electron donor, and propylene; S2, preparing the high-strength, easily processed polypropylene powder containing polyolefin component A and polyolefin component B; S3, granulating the high-strength, easily processed polypropylene powder to obtain the high-strength, easily processed polypropylene granules. S2 includes: initiating homopolymerization of propylene in a first reactor with a catalyst to obtain polyolefin component A; the polyolefin component A enters a second reactor to initiate homopolymerization of propylene or copolymerization of propylene with other olefin monomers to prepare polyolefin component B, thereby obtaining the high-strength, easily processable polypropylene powder containing polyolefin component A and polyolefin component B.

2. The application of the high-strength, easily processed polypropylene as described in claim 1, characterized in that, The applications include the modification of polypropylene.

3. The high-strength, easily processed polypropylene according to claim 1, characterized in that, In step S3, an auxiliary agent is added during the granulation process; the auxiliary agent includes one or more of antioxidants, acid absorbents, lubricants, nucleating agents, antistatic agents, and antibacterial agents, and the total amount of the auxiliary agent added accounts for ≤1% of the total weight of the high-strength, easily processed polypropylene.

4. The high-strength, easily processed polypropylene according to claim 1, characterized in that, The first reactor and the second reactor are one or more of the following: horizontal stirred bed reactor, vertical stirred tank reactor, gas phase fluidized bed reactor, loop reactor, and single multi-zone circulating reactor.

5. A high-strength, easily processed polypropylene according to claim 1, characterized in that, The preparation temperature of polyolefin component A is 50-80℃, the propylene pressure is 0.5-3.0 MPa, and the time is 0.5-5 h; the preparation temperature of polyolefin component B is 50-100℃, and the propylene pressure is 0.1-3.0 MPa; when preparing polyolefin component B, hydrogen gas at a pressure of 0.01-0.5 MPa is introduced into the reactor as a molecular weight regulator for 0.1-5 h. The catalyst is one or more of the following: supported ZN catalyst, supported metallocene catalyst, supported non-metallocene catalyst, and supported FI catalyst; The co-catalyst is selected from one or more of alkylaluminum, methylaluminoxane, and modified methylaluminoxane; The electron donor is selected from one or more of silanes, carboxylic acid esters, and ethers.

6. A high-strength, easily processed polypropylene according to claim 5, characterized in that, The method for preparing the product using the dual-reactor series process further includes a catalyst prepolymerization step: in step S1, a prepolymerization solvent is added to the prepolymerization reactor, followed by the addition of the co-catalyst, the electron donor, the catalyst, and the propylene, and a prepolymerization reaction is carried out for 0.1-2.0 h; wherein the catalyst prepolymerization temperature is 0-30℃, the prepolymerization pressure is 0.1-4.0 MPa, and the degree of prepolymerization is 2-100 g / g; the prepolymerization reactor is one of a loop reactor or a vertical stirred tank reactor; the prepolymerization solvent is selected from one or more of n-pentane, isopentane, n-hexane, 2-methylpentane, n-heptane, methylcyclohexane, and 2-methylhexane.

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