A polypropylene composition, its preparation method and application

Abstract

The present invention belongs to the field of polypropylene materials, and specifically discloses a polypropylene composition, a preparation method and an application thereof. The polypropylene composition of the present invention comprises the following components in parts by weight: 55-80 parts of polypropylene resin, 10-20 parts of long-chain branched low-density polyethylene resin, 5-15 parts of filler, 2-10 parts of compatibilizer, and 1-5 parts of processing aid. The polypropylene composition system of the present invention has good compatibility, which not only makes the polypropylene composition have strong environmental stress cracking resistance, but also has excellent mechanical properties.

Description

Technical Field

[0001] The invention belongs to the field of polypropylene materials, and in particular relates to a polypropylene composition and a preparation method and application thereof. Background Art

[0002] With the rapid development of the automobile industry in recent years, lightweight, quality, energy-saving, environmental protection, and functionalization have become the main goals of the current automobile industry. Polypropylene is a general-purpose thermoplastic with excellent comprehensive performance. It has the characteristics of low price, light weight, solvent resistance, easy recycling, and non-toxicity. It is one of the most important lightweight materials for automobiles. It can reduce the weight of automobile parts by about 40% and has been widely used in automobile decorations. Functionalized polypropylene materials are also increasingly used in automobiles.

[0003] In the field of automobile manufacturing, a fuel tank specifically refers to a device for storing fuel oil on a machine driven by a diesel engine or a gasoline engine. In order to achieve lightweight automobiles, most existing automobile manufacturing processes use plastic fuel tanks to hold gasoline. The material used for the plastic fuel tank needs to have good barrier properties or low permeability to fuel. Moreover, automobile fuel tanks are exposed to vibrations caused by bumpy road conditions for a long time, and need to be loaded with high-temperature automobile fuel containing various components for a long time. In such a complex use environment for a long time, the environmental stress cracking resistance of the material is also required to be high.

[0004] Patent document CN115584087A discloses a polypropylene composite material and its preparation method and application. The polypropylene composite material includes the following components by weight: 42-76 parts of polypropylene resin; 10-20 parts of low-density polyethylene; 10-30 parts of nylon resin; 3-5 parts of compatibilizer; 1-3 parts of processing aid; the melt strength of the polypropylene resin is 90-200mN, and the test condition is 210℃; the elongation at break of the nylon resin after reaching moisture absorption equilibrium is ≥80%, and the test conditions of moisture absorption equilibrium are: temperature is -40℃, relative humidity is 50%, and storage time is 72h. Through the synergistic effect of polypropylene with a certain melt strength, low-density polyethylene resin and nylon resin, the polypropylene composite material not only has excellent fuel barrier properties, but also effectively improves the environmental stress cracking resistance of the polypropylene composite material. However, in the above technical solution, even if a compatibilizer is added, due to the poor compatibility of nylon resin and polyethylene, the fuel tank will show obvious performance degradation during long-term use due to the oil vapor pressure inside the tank and the external bumpy stress environment, including material aging, embrittlement and damage, thereby shortening the actual service life of the fuel tank. Summary of the invention

[0005] Aiming at the technical problems involved in the prior art such as poor compatibility of components in polypropylene composites and shortened actual service life, the purpose of the present invention is to provide a polypropylene composition, its preparation method and application. The polypropylene composition material of the present invention has good compatibility performance inside itself, and at the same time, it can meet the performance requirements in terms of environmental stress cracking resistance.

[0006] To achieve the above object, the specific technical solutions include the following:

[0007] A polypropylene composition, comprising the following components in parts by weight: 55 - 80 parts of polypropylene resin, 10 - 20 parts of long-chain branched low-density polyethylene resin, 5 - 15 parts of filler, 2 - 10 parts of compatibilizer, and 1 - 5 parts of processing aid.

[0008] Long-chain branched low-density polyethylene is a polymer material with special structure and properties, which is prepared by subjecting low-density polyethylene to a long-chain branching reaction to form a long-chain branched structure. The long-chain branched low-density polyethylene resin in the present invention is prepared by initiating the long-chain branching reaction of the matrix LLDPE with rLLDPE. Since the branched structure on its long chain is conducive to better entanglement and is not prone to phase separation structure, it appears more dispersed and uniform in the overall structure. Therefore, this long-chain branched low-density polyethylene resin can form a uniform dispersed phase in the polypropylene matrix, avoiding the occurrence of phase separation and phase separation phenomena. Through experimental research and analysis by the inventors, this uniform dispersed phase structure helps to improve the crack propagation resistance and environmental stress cracking resistance of the polypropylene composition. Moreover, due to the existence of the long-chain branched structure prepared by the long-chain branching reaction of rLLDPE and LLDPE, this long-chain branched low-density polyethylene resin exhibits higher strength and toughness than ordinary LLDPE at the same molecular weight. The improvement of this strength and toughness can further enable the polypropylene composition to resist environmental stress and cracking tendency to a greater extent.

[0009] The addition of the filler can increase the rigidity and strength of the polypropylene composition and further improve the mechanical properties of the composition, which helps to reduce the cracking tendency of the plastic fuel tank under stress conditions.

[0010] By adjusting the ratio of the two resins, namely polypropylene resin and long-chain branched low-density polyethylene resin, better compatibility and interaction can be achieved in the polypropylene composition to meet the optimization requirements of the modified material.

[0011] Preferably, the ratio of the melt flow rate M1 of the long-chain branched low-density polyethylene resin at 190 °C and a load of 10 kg to the melt flow rate M2 at 190 °C and a load of 2.16 kg is M1 / M2 = 10 - 20.

[0012] Further preferably, the ratio of the melt flow rate M1 of the long-chain branched low-density polyethylene resin at 190 °C under a load of 10 kg to the melt flow rate M2 at 190 °C under a load of 2.16 kg is M1 / M2 = 13-18.

[0013] The melt flow rate ratio of the long-chain branched low-density polyethylene resin under different load conditions at the same temperature is a commonly used indicator for judging the long-chain branching and shear sensitivity of materials. In the present invention, the melt flow rates M1 and M2 of 10 kg load and 2.16 kg load at 190 °C are selected as indicators according to GB / T3682-2000, and the melt flow rate ratio is defined as M1 / M2. The higher this ratio, the more long-chain branches the material contains and the more sensitive it is to shear. To a certain extent, increasing the long-chain branching degree can improve the toughness and impact resistance of the composition. By introducing a branched structure, the movement of polymer chains is restricted, enabling the material to better absorb energy and extend and deform when stressed, thereby improving the impact resistance. However, too high a long-chain branching value will lead to an increase in the melt viscosity of the material and a deterioration in melt fluidity, resulting in an increase in melt non-uniformity, bubble generation, flaws and defects during injection molding or extrusion, thus reducing the molding quality, and the decline in molding quality will also have an adverse effect on the use effect of the final fuel tank.

[0014] Preferably, the long-chain branched low-density polyethylene resin is prepared by a long-chain branching reaction of rLLDPE and LLDPE, and the mass ratio of rLLDPE to LLDPE is (0.1-3):(9.9-7).

[0015] Further preferably, the mass ratio of rLLDPE to LLDPE is (0.5-2):(8-9.5).

[0016] Further preferably, the mass ratio of rLLDPE to LLDPE is (1-1.5):(8.5:9).

[0017] Preferably, the melt flow rate of the LLDPE is 0.5-3 g / 10 min when tested according to the GB / T 3682-2000 standard at 190 °C under a condition of 2.16 kg.

[0018] Further preferably, the melt flow rate of the LLDPE is 1-2.5 g / 10 min at 190 °C under a condition of 2.16 kg.

[0019] Within the above melt flow rate (MFR value) range, thermal decomposition and bubble generation of the melt during injection molding or extrusion can be reduced, thereby reducing the generation of flaws and defects; at the same time, better filling and holding forces can also be provided, contributing to the formation of a uniform and dense product structure.

[0020] Preferably, the processing aid includes at least one of a nucleating agent and a lubricant.

[0021] Preferably, the nucleating agent includes a β-crystal nucleating agent.

[0022] The introduction of the β-crystal nucleating agent helps to improve the environmental stress cracking resistance of the composition. By promoting the crystallization behavior, the crystalline structure of the material can be improved, the rate and degree of crack propagation can be reduced, and the crack resistance of the material can be enhanced.

[0023] In the processing aid, adding substances such as lubricants can improve the processing performance and fluidity of the composition, ensuring uniform material distribution and good molding performance during production. This helps to reduce the defects and stress concentration introduced during the manufacturing process, thereby reducing the risk of environmental stress cracking.

[0024] Preferably, the compatibilizer includes polypropylene grafted maleic anhydride.

[0025] Polypropylene grafted maleic anhydride has good compatibility and can form good interfacial interactions between polypropylene and other components. It can effectively reduce the interfacial tension between polypropylene and other components, increasing their compatibility. This helps to improve the compatibility between polypropylene and other components (such as fillers, resins, etc.), enhancing the uniformity and consistency of the material.

[0026] Preferably, the filler includes at least one of precipitated barium sulfate and precipitated barium carbonate.

[0027] Preferably, the mesh number of the filler is 1000 - 3000 mesh.

[0028] Precipitated barium sulfate has a relatively high melting point and thermal stability, and can play a certain role in fuel barrier in the composition matrix. By adding precipitated barium sulfate filler, the heat resistance and high-temperature resistance of the composition material can be improved. In addition, precipitated barium sulfate with a mesh number of 1000 - 3000 has a small particle size and a narrow particle size distribution range, which helps to provide the dimensional stability of the material. The uniform dispersion of filler particles can reduce the shrinkage and expansion of the material, improving the dimensional accuracy and consistency of the product.

[0029] The present invention also provides a method for preparing a polypropylene composition, comprising the following steps:

[0030] (1) Irradiating the LLDPE raw material with γ-rays or electron beams from a 60Co source to obtain rLLDPE;

[0031] (2) Mixing the rLLDPE and LLDPE in proportion and adding them to an extruder for reactive extrusion, with an extrusion temperature of 160 - 200 °C, to obtain a long-chain branched low-density polyethylene resin;

[0032] (3) Mix the polypropylene resin, long-chain branched low-density polyethylene resin, filler, compatibilizer, and processing aid evenly, and obtain the polypropylene composition through melt blending, extrusion granulation, and drying.

[0033] Preferably, the dose of the irradiation is 5 - 8 kGy / h.

[0034] Preferably, the time of the irradiation is 0.5 - 5 h.

[0035] In the present invention, controlling the irradiation dose of rLLDPE within the range of 5 - 8 kGy is an appropriate range. An appropriate irradiation dose can achieve a suitable degree of crosslinking, improve the strength and durability of the material, and at the same time avoid brittleness or performance degradation caused by excessive crosslinking, and can achieve a good irradiation effect.

[0036] Preferably, in order to improve the pretreatment efficiency, the LLDPE raw material is processed as a powder.

[0037] Preferably, the temperature of the extrusion granulation is 200°C - 230°C.

[0038] The application of the above polypropylene composition in the preparation of automotive fuel tank materials is also within the protection scope of the present invention.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The polypropylene composition of the present invention uses long-chain branched low-density polyethylene resin as the raw material for increasing the environmental stress cracking resistance performance, and uses long-chain branched low-density polyethylene resin and filler as the reinforcing raw materials. This system has good compatibility, so that the polypropylene composition has strong environmental stress cracking resistance performance and excellent mechanical properties;

[0041] (2) The technical solution of the present invention has a lower cost compared with the selection of nylon materials, the preparation method is simple and easy to implement, and the production process is simple and suitable for mass production. Specific Embodiments

[0042] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described through specific embodiments below. The test methods used in the embodiments and / or comparative examples are all conventional methods unless otherwise specified; the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0043] Some of the reagents selected in the embodiments and comparative examples of the present invention are described as follows:

[0044] Polypropylene resin:

[0045] Copolymerized PP: Melt flow rate (230°C / 2.16 kg) is 3.0 g / 10 min, model: PPH-T03, manufacturer: Beihai Refining & Chemical Co., Ltd.;

[0046] LLDPE1: Melt flow rate (190°C / 2.16 kg) is 2.0 g / 10 min, model: FZ201-0, manufacturer: Sumitomo Chemical Co., Ltd., Japan;

[0047] LLDPE2: Melt flow rate (190°C / 2.16 kg) is 2.7 g / 10 min, model: 18H27DX, manufacturer: Maoming Petrochemical Company;

[0048] LLDPE3: Melt flow rate (190°C / 2.16 kg) is 2.2 g / 10 min, model: 3224, manufacturer: Hanwha Chemical Corporation, South Korea;

[0049] LLDPE4: Melt flow rate (190°C / 2.16 kg) is 1.0 g / 10 min, model: 118N, manufacturer: SABIC;

[0050] LLDPE5: Melt flow rate (190°C / 2.16 kg) is 0.78 g / 10 min, model: 9085, manufacturer: Tianjin United Chemical Co., Ltd.;

[0051] Compatibilizer: Polypropylene grafted maleic anhydride, model: 18722, manufacturer: Arkema France;

[0052] Precipitated calcium carbonate: Mesh number: 3000, manufacturer: Anda;

[0053] Precipitated barium sulfate: Mesh number: 3000, manufacturer: Baifeng;

[0054] β-crystalline nucleating agent: Model: NP-328; Manufacturer: JihaiChuan;

[0055] Lubricant: Zinc stearate, manufacturer: HuijinChuan Chemical Industry.

[0056] Examples 1-14 and Comparative Examples 2-3

[0057] The long-chain branched low-density polyethylene resin 1-8 of the present invention is prepared through the following process:

[0058] (1) The LLDPE raw material is processed into powder, and then irradiated with 60Co source γ-rays at room temperature for 1.5 hours to obtain LLDPE powder, where the irradiation dose is 4 kgy / h;

[0059] (2) The rLLDPE and LLDPE raw materials were pre-mixed evenly according to the proportions in Table 1 and then added to a twin-screw extruder for reactive extrusion. The temperatures of each section of the extruder from the feed inlet to the die were 170, 170, 175, 170, 160, 180, and 200 °C in sequence. The length-diameter ratio of the processing screw was 40, the main machine speed was 400 r / min, and the extruded product was pelletized after being cooled by a water bath and dried by hot air to obtain long-chain branched low-density polyethylene resin.

[0060] Table 1

[0061]

[0062] The polypropylene compositions of the examples and comparative examples of the present invention were prepared through the following process:

[0063] The polypropylene resin, long-chain branched low-density polyethylene resin, filler, compatibilizer, and processing aid were mixed evenly to obtain a premix. The premix was added to the main feed port of the extrusion equipment, and after melt blending and extrusion granulation, the extrusion temperature of the extrusion equipment was 200 °C - 230 °C, and after extrusion granulation and drying, a polypropylene composition was obtained.

[0064] This example provides a series of polypropylene compositions, and their formulations are shown in Tables 2 and 3.

[0065] Table 2 Formulations of Examples 1 - 14 (parts by weight)

[0066]

[0067]

[0068] Table 3 Formulations of Comparative Examples 2 - 3 (parts by weight)

[0069]

[0070] Comparative Example 1

[0071] The polypropylene composite material obtained according to the preparation method of Example 1 recorded in the literature with the patent publication number CN115584087A.

[0072] The performance test methods and standards of the polypropylene compositions of each example and comparative example of the present invention are as follows:

[0073] (1) Melt flow rate ratio: The melt flow rates M1 and M2 at 190 °C and a load of 10 kg and at 190 °C and a load of 2.16 kg were measured respectively, and the melt flow rate ratio was M1 / M2;

[0074] (2) Tensile strength: Tested in accordance with ISO 527~2~2016, with a tensile speed of 50 mm / min;

[0075] (3) Izod impact strength of the cantilever beam: Tested according to the ISO 180-2000 standard;

[0076] (4) Fuel barrier property: Inject fuel containing 50 wt% aromatic hydrocarbons into the fuel tank, weigh the total mass M0 of the fuel tank and the fuel, after placing it in an environment of 40 °C for 56 days, weigh the total mass M1 of the fuel tank and the fuel at this time, and finally obtain the average daily leakage amount △M of the fuel, △M = (M0 - M1) / 56; the smaller △M is, the better the fuel barrier property of the material;

[0077] (5) Environmental stress cracking resistance test: The test standard is ASTM D1693-2015 F50, the test temperature is 30 °C, and the test medium is 10% nonylphenol polyoxyethylene ether (TX10); the longer the environmental stress cracking resistance time is, the better the environmental stress cracking resistance;

[0078] (6) Environmental stress cracking resistance test after box simulation: Inject a small 3L box by injection molding, fill it with 80% capacity of fuel, clamp it and vibrate it up and down, the experimental temperature is 50 °C, after one week, take the material of the box to do the environmental stress cracking resistance test, and compare the ratio of the time change before and after.

[0079] Determine the properties of the polypropylene compositions of each example and comparative example according to the methods mentioned above, and the results are shown in Table 4.

[0080] Table 4 Performance test results of each example and comparative example

[0081]

[0082]

[0083] As can be seen from Table 4, the polypropylene compositions obtained in Examples 1-14 of the present invention all have high mechanical strength, excellent fuel vapor barrier performance and environmental stress cracking resistance performance. In addition, compared with Comparative Example 1, it can be known that after the box simulation test of the polypropylene composition of the present invention, its environmental stress cracking resistance performance changes little, which further shows that good compatibility and interaction are achieved in the composition, and there will be no obvious performance decline during the use process.

[0084] It can be known from the examples and comparative examples of the present invention that:

[0085] (1) It can be known from Examples 1-3 and Comparative Example 2 that the change in the amount of long-chain branched low-density polyethylene resin affects the mechanical strength, fuel vapor barrier performance and environmental stress cracking resistance performance of the polypropylene composition.

[0086] (2) By comparing Example 1 and Example 4, it can be found that the use of precipitated barium sulfate can further improve the heat resistance and high-temperature resistance of the polymer material, and further extend the test time of the environmental stress cracking resistance of the material.

[0087] (3) By comparing Example 1 and Example 5, it can be found that the use of β-crystalline nucleating agent can improve the mechanical properties of the polymer material and the test time of the environmental stress cracking resistance.

[0088] (4) From Example 1 and Comparative Example 3, it can be seen that long-chain branched low-density polyethylene resin can significantly improve the mechanical strength, fuel vapor barrier performance and environmental stress cracking resistance of the polypropylene composition compared with conventional LLDPE. And from Example 1 and Examples 6 - 12, it can be seen that the higher the M1 / M2 ratio, the more long-chain branches the material contains, and the more sensitive it is to shear action. The increase in long-chain branching degree can improve the toughness and impact resistance of the composition to a certain extent, that is, by introducing a branched structure, the movement of polymer chains is restricted, so that the material can better absorb energy and extend and deform when stressed, thereby improving the impact resistance. However, too high a long-chain branching value will lead to an increase in the melt viscosity of the material and a deterioration in melt fluidity, resulting in an increase in melt non-uniformity, bubble generation, defects and flaws during injection molding or extrusion, thus reducing the molding quality. The decrease in molding quality will also have an adverse effect on the use effect of the final fuel tank. Therefore, the M1 / M2 ratio is preferably 10 - 19, and more preferably the M1 / M2 ratio is 13 - 18.

[0089] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A polypropylene composition, characterized in that, It comprises components in the following parts by weight: 55 - 80 parts of polypropylene resin, 10 - 20 parts of long-chain branched low-density polyethylene resin, 5 - 15 parts of filler, 2 - 10 parts of compatibilizer, and 1 - 5 parts of processing aid; the long-chain branched low-density polyethylene resin is prepared by a long-chain branching reaction of rLLDPE and LLDPE, and the melt flow rate of the LLDPE is 0.78 - 3 g / 10 min; the ratio of the melt flow rate M1 of the long-chain branched low-density polyethylene resin under a load of 10 kg at 190°C to the melt flow rate M2 under a load of 2.16 kg at 190°C is M1 / M2 = 10 - 20.

2. The polypropylene composition according to claim 1, wherein The ratio of the melt flow rate M1 of the long-chain branched low-density polyethylene resin under a load of 10 kg at 190°C to the melt flow rate M2 under a load of 2.16 kg at 190°C is M1 / M2 = 13 - 18.

3. The polypropylene composition according to claim 1, characterized in that, The mass ratio of the rLLDPE to the LLDPE is (0.1 - 3):(9.9 - 7).

4. The polypropylene composition according to claim 3, characterized in that, The mass ratio of the rLLDPE to the LLDPE is (0.5 - 2):(8 - 9.5).

5. The polypropylene composition according to claim 1, characterized in that, It comprises at least one of the following: The filler comprises at least one of precipitated barium sulfate and precipitated calcium carbonate; The mesh number of the filler is 1000 - 3000 meshes; The processing aid comprises at least one of a nucleating agent and a lubricant.

6. The polypropylene composition according to claim 1, characterized in that, The compatibilizer comprises polypropylene grafted maleic anhydride.

7. A method for preparing the polypropylene composition according to any one of claims 1 to 6, characterized in that, It comprises the following steps: (1) Irradiate the LLDPE raw material with a 60Co source γ-ray or electron beam to obtain rLLDPE; (2) Mix the rLLDPE and LLDPE in proportion and add them to an extruder for reactive extrusion, and the extrusion temperature is 160 - 200°C to obtain the long-chain branched low-density polyethylene resin; (3) Mix the polypropylene resin, long-chain branched low-density polyethylene resin, filler, compatibilizer, and processing aid evenly, and through melt blending, extrusion granulation, and drying, obtain the polypropylene composition.

8. Use of the propylene composition according to any one of claims 1 to 6 in the preparation of an automotive fuel tank material.

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