Low-temperature impact-resistant transparent polypropylene material and preparation method thereof

Abstract

The application relates to the technical field of high polymer materials and rotational molding materials, and discloses a low-temperature impact-resistant transparent polypropylene material and a preparation method thereof. The material comprises polypropylene and a composite elastomer composed of syndiotactic polypropylene elastomer, styrene-ethylene-propylene-styrene block copolymer and ethylene-propylene rubber. During preparation, the components are melt-blended and extruded into granules, and after low-temperature mechanical crushing, short-time plasma spheroidization treatment is carried out in an inert atmosphere. The composite elastomer system is used for improving the low-temperature impact resistance of the polypropylene and reducing the adverse effect of traditional rubber toughening on optical transmission performance, and the spheroidization treatment is used for improving the particle morphology, fluidity and piling performance of the modified powder. The obtained material is suitable for rotational molding products in a low-temperature environment.

Description

Technical Field

[0001] This invention belongs to the technical field of polymer materials and rotational molding materials, specifically relating to a low-temperature impact-resistant transparent polypropylene material and its preparation method, and particularly to a polypropylene composite material prepared by using syndiotactic polypropylene elastomer, styrene-ethylene-propylene-styrene block copolymer and ethylene-propylene rubber to form a composite elastic system, combined with low-temperature pulverization and plasma spheroidization treatment. Background Technology

[0002] Rotational molding is a molding method in which powdered or liquid polymer raw materials are added to a mold, and the mold is rotated around mutually perpendicular axes during heating. This causes the molten material to gradually spread and adhere to the inner wall of the mold, resulting in a hollow product after cooling. Unlike injection molding or extrusion, rotational molding does not involve a continuous high-shear plasticizing process. Therefore, the melting properties of the raw material, the powder morphology, flowability, and the packing state between particles directly affect the spreading, melting, sintering, and product quality of the powder in the mold.

[0003] Polyethylene is a commonly used rotational molding material, but it has certain limitations in terms of heat resistance, rigidity, and some mechanical properties. Polypropylene has better rigidity, heat resistance, and chemical resistance, making it a potential candidate for high-temperature containers, equipment housings, and other rotational molding products. However, at low temperatures, the molecular chain movement of polypropylene is restricted, reducing the material's toughness and making it prone to brittleness during low-temperature transportation, storage, or outdoor use, thus limiting its application in low-temperature rotational molding products.

[0004] To address the issue of insufficient low-temperature toughness in polypropylene, existing technologies typically involve toughening it by introducing flexible materials such as ethylene propylene rubber, polyolefin elastomers, or styrene-based block copolymers. While these elastic components can reduce the low-temperature brittleness of polypropylene, the material's rigidity often decreases as the amount of traditional rubber or elastic components increases. Furthermore, differences in refractive index and dispersion states between different phases may increase light refraction and scattering at the phase interfaces, making it difficult to simultaneously achieve both low-temperature toughness and optical transmittance.

[0005] Syndiotactic polypropylene (SPP) shares structural similarities with conventional polypropylene in terms of molecular backbone. Using SPP elastomers in polypropylene toughening can help mitigate the adverse effects of relatively low optical transmittance of traditional rubber while achieving flexible toughening. However, simply changing the type or proportion of toughening agents cannot solve all the problems encountered in rotational molding.

[0006] To achieve better low-temperature toughness, a certain proportion of flexible components needs to be introduced into polypropylene. After melt blending, the modified polypropylene may still form irregular particles during low-temperature mechanical pulverization, exhibiting strong interlocking and friction between particles, resulting in insufficient flowability and packing properties. For rotational molding, even if the material itself possesses good low-temperature toughness, if the powder is difficult to spread and pack evenly, it may still affect subsequent melt sintering and the quality of the manufactured parts.

[0007] Existing technologies include methods to improve rotational molding performance by altering the morphology of polymer powders, and methods that utilize plasma to rapidly heat and spheroidize polymer powders. However, the melting behavior, viscosity, and thermal stability window of composite elastic modified polypropylene differ from those of ordinary polypropylene: insufficient heat input makes it difficult to generate sufficient flow on the particle surface, limiting the degree of spheroidization; excessive heat input or prolonged residence time may lead to particle adhesion or thermal degradation. Therefore, it is necessary to consider the material composition design in conjunction with subsequent powder processing conditions.

[0008] Therefore, how to improve the low-temperature impact resistance of polypropylene while reducing the adverse effects of traditional rubber toughening on optical transmittance, and further enable the composite modified polypropylene to obtain a powder flow and stacking state suitable for rotational molding, are technical problems that still need to be solved in this field. Summary of the Invention

[0009] In view of this, the present invention proposes a low-temperature impact-resistant transparent polypropylene material and its preparation method. By using syndiotactic polypropylene elastomer as the main component in the composite elastic system and combining it with styrene-ethylene-propylene-styrene block copolymer and ethylene-propylene rubber, the polypropylene obtains low-temperature toughness while reducing the adverse effects of traditional rubber toughening systems on the optical transmittance of the material. Furthermore, the modified polypropylene obtained by melt blending is subjected to low-temperature mechanical pulverization and short-time plasma spheroidization treatment to improve the particle morphology, flowability and packing state of the modified polypropylene powder.

[0010] The technical solution of the present invention is implemented as follows: The present invention provides a low-temperature impact-resistant transparent polypropylene material, which, by mass parts, comprises 80-84 parts of polypropylene and 15-19 parts of a composite elastomer, wherein the sum of the mass parts of the polypropylene and the composite elastomer is 99 parts; the composite elastomer is composed of syndiotactic polypropylene elastomer, styrene-ethylene-propylene-styrene block copolymer and ethylene-propylene rubber, wherein the syndiotactic polypropylene elastomer comprises 7-11 parts, the styrene-ethylene-propylene-styrene block copolymer comprises 5 parts, and the ethylene-propylene rubber comprises 1-5 parts.

[0011] The syndiotactic polypropylene elastomer referred to in this invention refers to a polypropylene material with propylene structural units as the main body, a syndiotactic arrangement of molecular chains in its stereostructure, and exhibiting elastomeric behavior. This syndiotactic arrangement can be confirmed by methods commonly used in the art, such as 13C-NMR. The ethylene-propylene rubber referred to is a binary ethylene-propylene rubber, abbreviated as EPR. The styrene-ethylene-propylene-styrene block copolymer referred to is abbreviated as SEPS. The above terms remain consistent throughout the specification.

[0012] In some embodiments, the polypropylene may be selected from propylene homopolymers or copolymers with propylene as the main structural unit; the syndiotactic polypropylene elastomer may be selected from those with a melt flow rate of 0.1–10 g / 10 min (230°C, 2.16 kg) and a density of 0.85–0.90 g / cm³. 3 The materials are as follows: SEPS is a thermoplastic elastomer with a styrene-ethylene-propylene-styrene block structure, and EPR is a binary rubber formed from ethylene and propylene. All the above raw materials can be commercially available materials, and the raw material grades and batches are kept consistent in the same set of comparative tests.

[0013] In some embodiments, the polypropylene is 82 parts, the syndiotactic polypropylene elastomer is 10 parts, the styrene-ethylene-propylene-styrene block copolymer is 5 parts, and the ethylene-propylene rubber is 2 parts.

[0014] In some embodiments, the total amount of the composite elastomer is 15 parts, 17 parts, or 19 parts. During the screening of the composite elastomer formulation, the mass ratio of syndiotactic polypropylene elastomer, ethylene propylene rubber, and styrene-ethylene-propylene-styrene block copolymer can be set to 6:2:2, 6:1:3, 5:2:3, or 4:3:3 to compare the effects of different elastic phase compositions on the material's low-temperature toughness, rigidity, and optical transmittance. A total composite elastomer amount of 17 parts, with a mass ratio of syndiotactic polypropylene elastomer, ethylene propylene rubber, and styrene-ethylene-propylene-styrene block copolymer of 6:1:3, can be considered a preferred performance balance scheme. Performance comparisons of different composite elastomer ratios and different total composite elastomer amounts are as follows: Figure 1 and Figure 2 As shown.

[0015] In some embodiments, the material further includes 1 part by weight of a polypropylene flame retardant containing melamine polyphosphate. The flame retardant is an additional component selected based on the requirements of the final product and does not constitute a necessary condition for achieving the low-temperature toughening and powder processing performance control of this invention; the flame retardant may not be added when evaluating the effect of the toughening system itself on optical transmittance.

[0016] In some embodiments, the material may further include an antioxidant, which is added during melt blending to reduce the thermo-oxidative degradation of polypropylene during melt blending and subsequent rotational molding. The antioxidant is an optional additive and does not alter the composition of the aforementioned composite elastic system.

[0017] The present invention also provides a method for preparing the above-mentioned low-temperature impact-resistant transparent polypropylene material, including melt blending, low-temperature mechanical pulverization and plasma spheroidization treatment.

[0018] In some embodiments, polypropylene, syndiotactic polypropylene elastomer, styrene-ethylene-propylene-styrene block copolymer, and ethylene-propylene rubber are added to a twin-screw extruder in a predetermined ratio for melt blending, followed by extrusion, cooling, and granulation. The temperatures of each zone of the twin-screw extruder from the feed inlet to the die head are sequentially 140°C, 160°C, 190°C, 190°C, 190°C, 190°C, 190°C, 190°C, and 180°C.

[0019] In some embodiments, the modified polypropylene granules after melt blending and granulation are subjected to low-temperature mechanical pulverization at -80 to -100°C; further, the low-temperature mechanical pulverization temperature is -100°C.

[0020] In some embodiments, the modified polypropylene material undergoes thermal and rheological property analysis before determining the plasma spheroidization conditions. The modified polypropylene material has a peak melting temperature of approximately 165°C and an initial decomposition temperature of approximately 415°C; at 300°C and a shear frequency below 0.1 Hz, the melt viscosity is approximately 135 Pa·s. Based on the melting, flow, and thermal stability of the material, short-duration plasma treatment is employed to ensure sufficient fluidity of the powder particles while avoiding prolonged exposure to high temperatures.

[0021] In some embodiments, the plasma spheroidization process is performed under an inert atmosphere. The processing chamber is evacuated to a gauge pressure of -40 kPa relative to atmospheric pressure, argon gas is introduced, and the radio frequency plasma generator is activated. The power and frequency of the radio frequency power supply are adjusted according to the equipment specifications to stabilize the outer flame processing area of ​​the plasma torch at 300–430°C. After the plasma torch stabilizes, modified polypropylene powder is transported to the processing area using argon gas as the powder carrier gas.

[0022] In some embodiments, the plasma generating gas flow rate is 40 slpm, the protective gas flow rate is 65 slpm, the powder-carrying gas flow rate is 3 slpm, and the powder supply rate is 50 g / min; where slpm represents liters per minute under standard conditions.

[0023] In some embodiments, the powder is conveyed via a transport conduit with a cooling jacket. The transport conduit has a concentric annular jacket structure, and cooling water is circulated within the jacket to reduce softening and adhesion of the powder before it enters the plasma processing zone. The outlet of the transport conduit is located in the outer flame region of the plasma torch. For details on the plasma spheroidization equipment and powder processing process, please refer to [link to relevant documentation]. Figure 5 .

[0024] In some embodiments, after the powder enters the outer flame region of the plasma torch at a temperature of 300–430°C, it is first heated to 300°C within 0.2–0.25 s to form molten particles. Subsequently, the molten particles continue to travel in the plasma torch for 0.2–0.25 s, transforming from an irregular shape to a spherical shape under the action of surface tension. After completing spheroidization, they leave the high-temperature region and enter the cooling section for rapid cooling and shaping, finally entering the collection area. Here, 300–430°C refers to the temperature range of the outer flame treatment region of the plasma torch, while 300°C refers to the target temperature reached by the powder during the heating and melting stage; the two represent different temperature objects.

[0025] In some embodiments, the modified polypropylene powder after plasma spheroidization treatment has an average sphericity of 0.93, with particle sizes mainly distributed between 100 and 120 μm. The average sphericity can be obtained through analysis of two-dimensional projection images of the particles, with the sphericity of a single particle characterized by 4πA / P², where A is the projected area of ​​the particle and P is the projected perimeter of the particle. The average sphericity of multiple particles is then calculated. The morphology, sphericity, and particle size distribution of the powder after spheroidization treatment are as follows: Figure 4 As shown.

[0026] This invention does not simply list low-temperature toughening and powder spheroidization as independent technical measures. The composite elastic system is first used to solve the problems of insufficient toughness of polypropylene under low-temperature conditions and the significant impact of traditional rubber toughening on optical transmittance. On this basis, to address the insufficient powder morphology and processing adaptability of composite elastic modified polypropylene after mechanical crushing, the powder morphology is controlled by short-time plasma treatment that matches its melting, rheological, and thermal stability states. This forms a continuous technical route from material composition design to adjustment of rotational molding powder processing performance.

[0027] This invention offers the following advantages over existing technologies: It uses syndiotactic polypropylene elastomer as the main component of a composite elastic system, combined with styrene-ethylene-propylene-styrene block copolymer and ethylene-propylene rubber. This improves the low-temperature impact resistance of polypropylene without solely relying on increasing the amount of traditional rubber toughening agents, while also mitigating the adverse effects of traditional rubber toughening on the material's optical transmittance. Furthermore, it employs short-time plasma spheroidization treatment on the composite-toughened and cryogenically pulverized polypropylene powder, transforming irregular powder particles into more regular morphologies. This reduces mechanical interlocking and movement resistance between particles, improving powder flowability and packing properties, thereby enhancing its adaptability to rotational molding. A more harmonious balance is achieved between low-temperature performance, optical properties, and rotational molding performance. The spheroidized powder exhibits a more uniform spreading and packing state within the rotational molding mold, facilitating gas expulsion during melting and sintering, and reducing the likelihood of bubbles and voids formed due to irregular particle overlap and poor venting. Attached Figure Description

[0028] Figure 1 A comparison chart of material properties under different composite elastomer ratios; Figure 2 A comparison chart of material properties under different total amounts of composite elastomer; Figure 3 This is a comparison of the transmittance of different toughening system samples at 800 nm wavelength without the addition of flame retardants. Figure 4 The images show the morphology and particle size of the powder after plasma spheroidization treatment, where (a) is the surface morphology of the powder, (b) is the sphericity distribution of the powder, and (c) is the particle size distribution of the powder. Figure 5 This is a schematic diagram of a plasma spheroidization device and a powder processing process. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments. The following embodiments are used to illustrate the technical solution of the present invention and are not intended to limit the scope of protection of the present invention. Unless otherwise stated, the amounts of each component are expressed in parts by mass; in the same group of comparative experiments, except for the factors being compared, the batches of raw materials, sample preparation conditions, and testing conditions remain consistent.

[0030] In the embodiments, syndiotactic polypropylene elastomer is abbreviated as sPP elastomer, styrene-ethylene-propylene-styrene block copolymer is abbreviated as SEPS, and ethylene propylene rubber is abbreviated as EPR; the flame retardant is a commonly used polypropylene flame retardant, the main component of which is melamine polyphosphate (MPP). This invention only relates to EPR and does not relate to ethylene propylene diene monomer (EPDM) rubber. Depending on the actual thermal history requirements of rotational molding, commonly used antioxidants in polypropylene processing can also be added during melt blending.

[0031] Test methods Tensile properties were tested according to GB / T 1040.1-2025 and GB / T 1040.2-2022, determining tensile strength and elongation at break; flexural properties were tested according to GB / T 9341-2008, determining flexural strength and flexural modulus. All examples and comparative examples used the same sample preparation and testing conditions.

[0032] During the low-temperature drop ball test, the rotomolded sample is placed in an environment of -30℃. After the overall temperature of the sample reaches the test temperature, a small ball with a mass of 800 g is dropped freely from a height of 1 m above the sample to impact it. Samples that do not break or suffer penetrating damage after impact are considered to have passed. The low-temperature drop ball pass rate is the percentage of the number of passed samples out of the total number of tested samples.

[0033] The powder properties were evaluated using a comprehensive powder characteristic test method, which measured the powder flowability index, angle of repose, angle of plate, loose packing density, and tapped density. Among these, the angle of repose, angle of plate, loose packing density, and tapped density were used as direct measurement indicators. The powder flowability index was a comprehensive evaluation value obtained based on parameters such as the angle of repose, degree of compression, and angle of plate, using the same comprehensive powder characteristic tester and calculation program. It was only used for relative comparisons between various examples and comparative examples and was not considered the sole characterization parameter of the material.

[0034] The peak melting temperature was determined by differential scanning calorimetry, and the initial decomposition temperature was determined by thermogravimetric analysis. The rheological properties were determined by measuring the melt viscosity at different temperatures and shear frequencies using a rotational rheometer to determine the appropriate short-time spheroidization treatment window.

[0035] Powder sphericity was determined by two-dimensional projection analysis using particle microscopic images. The sphericity of a single particle was calculated using 4πA / P² and the average value was taken. Particle size was obtained through particle size testing.

[0036] Rotational molding sample preparation conditions The same rotational molding conditions were used for comparing the performance of the parts in all embodiments and comparative examples of this application. To demonstrate that the powder of this invention can be used to prepare test parts using conventional rotational molding methods in the art, in one specific embodiment, 250 g of powder can be added to a 100 mm × 100 mm × 100 mm metal mold, heated for 30 min at an oven temperature of 290°C and a rotation speed of 7 rpm, and then the mold is kept rotating and cooled for 30 min before demolding. For biaxial rotational molding equipment, the ratio of the main and auxiliary shaft speeds can be adjusted according to the mold size and the amount of material, but the ratio should be kept consistent for each comparative group. The above rotational molding conditions are used to illustrate the feasibility of the material of this invention, and the specific equipment conditions can be conventionally adjusted without changing the material technical solution.

[0037] Example 1 The polypropylene material in this embodiment consists of 82 parts polypropylene, 10 parts sPP elastomer, 5 parts SEPS, 2 parts EPR and 1 part MPP flame retardant.

[0038] The above components were weighed and mixed according to the formula, and then added to a twin-screw extruder for melt blending. The temperatures of each zone of the extruder from the feed inlet to the die head were 140℃, 160℃, 190℃, 190℃, 190℃, 190℃, 190℃, 190℃, and 180℃, respectively. The extrudate was granulated after being water-cooled at room temperature. The resulting granules were then subjected to low-temperature mechanical pulverization at -100℃ to obtain modified polypropylene powder.

[0039] The processing chamber was evacuated to a gauge pressure of -40 kPa relative to atmospheric pressure, argon gas was introduced, and the radio frequency plasma torch was ignited. The plasma generating gas flow rate was 40 slpm, the protective gas flow rate was 65 slpm, the powder-carrying gas flow rate was 3 slpm, and the powder supply rate was 50 g / min. The powder entered the outer flame region of the plasma torch at a temperature of 300–430℃ through a delivery conduit with a cooling jacket. It was first heated to 300℃ within 0.2–0.25 s to form molten particles, and then continued to operate in the molten state for another 0.2–0.25 s to complete spheroidization. After leaving the high-temperature region, it was rapidly cooled and shaped before being collected. The plasma spheroidization equipment and powder processing process are described in [reference needed]. Figure 5 .

[0040] The powder obtained in Example 1 had a powder flowability index of 84.5, an angle of repose of 32.30°, a flatness angle of 38.49°, and a bulk density of 0.51 g / cm³. 3 The tap density is 0.60 g / cm³. 3 The obtained powder was used to prepare parts under the same rotational molding process. The tensile strength of the parts was 15.6 MPa, the elongation at break was 560%, the flexural strength was 16.5 MPa, the flexural modulus was 380 MPa, and the drop ball pass rate at -30℃ was 100%.

[0041] Examples 2-6 The preparation steps of Examples 2 to 6 are the same as those of Example 1, except that the ratio of polypropylene and composite elastomer is different. The specific composition is shown in Table 1.

[0042]

[0043] Table 1. Formulation composition of Examples 1-6 The properties of the powders obtained after low-temperature mechanical pulverization and plasma spheroidization treatment in each embodiment are shown in Table 2.

[0044]

[0045] Table 2 Powder properties of Examples 1-6 The powders in each embodiment were prepared into parts under the same rotational molding conditions. The mechanical properties and low-temperature drop ball properties of the resulting parts are shown in Table 3.

[0046]

[0047] Table 3 Performance of rotationally molded parts from Examples 1-6 As shown in Table 3, changes in the total amount of the composite elastomer and the ratio among the three elastic components affect the material's rigidity, elongation, and low-temperature impact performance. With the increase of the flexible component, the overall elongation at break increases, while tensile strength and flexural properties decrease to some extent. This indicates that the present invention aims for a comprehensive balance between low-temperature toughness and rigidity, rather than a simultaneous improvement in all mechanical properties.

[0048] Comparative Example 1: Traditional Polypropylene Rotational Molding Powder Comparative Example 1 uses the company's existing conventional polypropylene rotational molding powder and employs the same rotational molding sample preparation and testing conditions as the Example 1 for overall performance comparison. Comparative Example 1 is used to characterize the comprehensive performance difference between the company's existing conventional rotational molding material and the Example 1 of this invention, and is not used as a single variable attribution basis for the technical effect of a specific component or single step. The test results of Comparative Example 1 and Example 1 are shown in Table 4.

[0049] Table 4. Performance comparison between Example 1 and traditional polypropylene rotational molding powder.

[0050] As shown in Table 4, compared with the company's existing traditional polypropylene rotational molding materials, Example 1 exhibits different comprehensive performance characteristics in terms of low-temperature ball drop performance, elongation at break, and powder flow and packing properties, while its tensile strength and flexural properties are somewhat reduced. This comparison is used to illustrate the overall performance orientation of the material of the present invention in low-temperature use and rotational molding processing; the specific effects of each distinguishing technical feature will be analyzed in conjunction with the comparison of the same formulation before and after spheroidization and the comparison of optical transmittance properties described later.

[0051] Comparative Example 2: Same formulation without plasma spheroidization treatment Using the same formulation and melt blending method as in Example 1, the granulated modified polypropylene was subjected to low-temperature mechanical pulverization at -100°C to obtain modified polypropylene powder, but without plasma spheroidization treatment. This powder was compared with the spheroidized powder of the same formulation from Example 1, and the results are shown in Table 5.

[0052] Table 5. Powder properties before and after spheroidization for the same formulation.

[0053] As shown in Table 5, the polypropylene powder modified with composite elasticity and subjected to low-temperature mechanical pulverization did not naturally acquire good rotational molding powder flowability. After short-time plasma spheroidization treatment, the powder flowability index improved, the angle of repose and angle of plate decreased, and the loose density and tap density increased. Therefore, spheroidization treatment is not an additional step unrelated to material toughening, but rather a further adjustment to address the insufficient processing adaptability of the composite elastic modified powder.

[0054] Comparison of optical transmission performance To evaluate the effect of different toughening routes on the optical transmittance of polypropylene, sPP elastomer-modified samples and conventional rubber-toughened modified samples were prepared without the addition of MPP flame retardant. Both groups of samples were tested under the same thickness, molding method, and spectral conditions, and their transmittance was measured at 800 nm. The results showed that the transmittance of the sPP elastomer-modified sample at 800 nm was approximately 85%, while that of the conventional rubber-toughened modified sample was approximately 40%. This result indicates that, under the comparative conditions used in this application, the toughening system containing sPP elastomer exhibits a higher single-wavelength transmittance at 800 nm. Since the specific toughening formulations of the two types of samples do not involve changing only a single variable, this comparison is used to illustrate the trend of optical performance changes under different toughening routes and is not considered the sole causal basis for the effect produced by a single component. The aforementioned 800 nm single-wavelength transmittance is not equivalent to the total transmittance across the entire visible light spectrum. The corresponding 800 nm transmittance comparisons are as follows: Figure 3 As shown.

[0055] morphology of spheroidized powder After plasma spheroidization treatment in Example 1, the modified polypropylene powder had a smoother surface and more regular particle morphology, with an average sphericity of 0.93 and a particle size mainly distributed between 100 and 120 μm. As shown in Table 5, the improvement in particle morphology corresponds to the improvement in powder flowability and packing properties. The corresponding powder morphology, sphericity, and particle size distribution are shown in Table 5. Figure 4 .

[0056] In summary, this invention first improves the low-temperature toughness of polypropylene through a composite elastic system with sPP elastomer as the main component, and reduces the adverse effects of traditional rubber toughening on optical transmittance. Subsequently, addressing the powder flow and accumulation problems that still exist after low-temperature pulverization of the composite modified polypropylene, a short-time plasma treatment matching the melting, rheological, and thermal stability states of the modified material is used to spherize the powder. These two technical measures form a continuous technical relationship between material properties and rotational molding processing performance.

[0057] The above description is merely a specific embodiment of the present invention. Those skilled in the art can make conventional adjustments to the specific process parameters based on actual raw materials and equipment conditions without departing from the technical concept of the present invention; any equivalent substitutions or conventional modifications that can be directly obtained based on the disclosure of the present invention should be determined by the scope of protection defined by the claims.

Claims

1. A low-temperature impact-resistant polypropylene material, characterized in that, The product comprises, by weight, 80-84 parts of polypropylene and 15-19 parts of composite elastomer, wherein the sum of the weights of the polypropylene and the composite elastomer is 99 parts; the composite elastomer is composed of syndiotactic polypropylene elastomer, styrene-ethylene-propylene-styrene block copolymer and ethylene-propylene rubber, wherein the syndiotactic polypropylene elastomer comprises 7-11 parts, the styrene-ethylene-propylene-styrene block copolymer comprises 5 parts, and the ethylene-propylene rubber comprises 1-5 parts, wherein the sum of the weights of the three comprises 15-19 parts.

2. The low-temperature impact-resistant polypropylene material according to claim 1, characterized in that, The mass ratio of the syndiotactic polypropylene elastomer, ethylene propylene rubber, and styrene-ethylene-propylene-styrene block copolymer is 6:1:

3.

3. The low-temperature impact-resistant polypropylene material according to claim 1, characterized in that, The polypropylene comprises 82 parts, the syndiotactic polypropylene elastomer comprises 10 parts, the styrene-ethylene-propylene-styrene block copolymer comprises 5 parts, and the ethylene-propylene rubber comprises 2 parts; the material also includes 1 part of polypropylene flame retardant, which contains melamine polyphosphate.

4. The low-temperature impact-resistant polypropylene material according to any one of claims 1 to 3, characterized in that, The material is a composite powder for rotational molding, and the average sphericity of the composite powder is 0.

93.

5. A method for preparing a low-temperature impact-resistant polypropylene material, characterized in that, Includes the following steps: S1. Polypropylene and composite elastomer are melt-blended and extruded into granules, wherein the polypropylene is 80-84 parts by mass, the composite elastomer is 15-19 parts by mass, and the sum of the mass parts of the polypropylene and the composite elastomer is 99 parts. The composite elastomer is composed of 7-11 parts by mass of syndiotactic polypropylene elastomer, 5 parts by mass of styrene-ethylene-propylene-styrene block copolymer, and 1-5 parts by mass of ethylene propylene rubber. S2. The granules obtained in step S1 are subjected to low-temperature mechanical pulverization at -80 to -100°C to obtain modified polypropylene powder. S3. Under an inert atmosphere, the modified polypropylene powder obtained in step S2 is fed into a plasma treatment area with a temperature of 300-430°C for spheroidization treatment, and then removed from the high-temperature area and cooled for collection.

6. The preparation method according to claim 5, characterized in that, In step S1, a twin-screw extruder is used for melt blending, and the temperatures of each zone from the feed inlet to the die head are 140℃, 160℃, 190℃, 190℃, 190℃, 190℃, 190℃, 190℃ and 180℃ respectively; the low-temperature mechanical crushing temperature in step S2 is -100℃.

7. The preparation method according to claim 5 or 6, characterized in that, In step S3, the processing chamber is evacuated to a gauge pressure of -40 kPa relative to atmospheric pressure, and argon is used as the plasma reaction gas and powder carrier gas.

8. The preparation method according to claim 7, characterized in that, The plasma generating gas flow rate was 40 slpm, the protective gas flow rate was 65 slpm, the powder carrier gas flow rate was 3 slpm, and the powder supply rate was 50 g / min.

9. The preparation method according to claim 8, characterized in that, The powder is fed into the outer flame region of the plasma torch through a delivery conduit equipped with a cooling jacket, through which cooling water is circulated. After entering the outer flame region, the powder heats up to 300°C within 0.2 to 0.25 seconds to form molten particles. The molten particles continue to run in the plasma torch for 0.2 to 0.25 seconds to complete spheroidization.

10. A rotationally molded part, characterized in that, The rotationally molded part is obtained by rotational molding of polypropylene composite powder for rotational molding; the polypropylene composite powder for rotational molding includes, by mass, 80-84 parts of polypropylene, 7-11 parts of syndiotactic polypropylene elastomer, 5 parts of styrene-ethylene-propylene-styrene block copolymer and 1-5 parts of ethylene propylene rubber, and the sum of the mass parts of polypropylene, syndiotactic polypropylene elastomer, styrene-ethylene-propylene-styrene block copolymer and ethylene propylene rubber is 99 parts.

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