Novel beta crystal form compound nucleating agent for improving toughness of polypropylene and application thereof

Abstract

The invention belongs to the technical field of polypropylene nucleating agents, and relates to a novel beta-crystal-form compound nucleating agent for improving the toughness of polypropylene and application of the novel beta-crystal-form compound nucleating agent. The composite nucleating agent disclosed by the invention is formed by compounding imidazolyl bis (trifluoromethanesulfonate) ionic liquid and a rare earth beta nucleating agent WBG-II, and the conversion rate and toughness of a beta crystal form in a polypropylene (PP) material can be remarkably improved. The imidazolyl bis (trifluoromethanesulfonate) ionic liquid is in a liquid state at room temperature and has excellent thermal stability, so that the imidazolyl bis (trifluoromethanesulfonate) ionic liquid can be uniformly dispersed in PP resin in the processing process, the problem that a traditional powdery nucleating agent is easy to agglomerate is avoided, and meanwhile, WBG-II is used as a beta nucleating agent and has excellent performance in the aspect of promoting PP to form a beta crystal form.

Description

Technical Field

[0001] The invention belongs to the technical field of polypropylene nucleating agents and relates to a novel β-crystal composite nucleating agent for improving the toughness of polypropylene and application thereof. Background Art

[0002] Polypropylene (PP) is a thermoplastic formed by addition polymerization of propylene monomers. It is widely used in many fields due to its non-toxic, colorless, translucent properties, good economy and versatility. It is used to manufacture medical devices, automotive parts, pipelines, fiber products, chemical containers, food and pharmaceutical packaging, etc.

[0003] The physical properties of PP depend largely on its crystal structure. The most common crystal forms of PP are α-crystal and β-crystal. α-crystal PP has high strength but poor toughness, while β-crystal exhibits higher toughness, i.e., impact strength. In order to improve the mechanical properties of PP, especially the impact resistance at low temperatures, nucleating agents are usually added to control the crystal morphology, thereby improving the material properties.

[0004] The application of β-nucleating agents is an effective way to improve the toughness of PP. It can induce the transformation of PP from α-crystalline to β-crystalline, thereby enhancing the impact resistance of the material. Currently, there are limited types of β-nucleating agents on the market, mainly including condensed ring compounds with quasi-planar structures, organic acids and their salts, rare earth substances, and aromatic amide substances. Aromatic amide β-nucleating agents such as N,N'-dicyclohexylbenzamide (DCHT) have been shown to significantly improve the toughness of PP, and some patent technologies have expired, allowing these chemicals to be used more widely.

[0005] As a new type of modification additive, ionic liquids have begun to be used in the modification research of PP. They can affect the crystallization behavior and mechanical properties of PP by interacting with the PP molecular chain. For example, some imidazolyl ionic liquids can maintain the tensile strength of PP while improving its toughness when added in large amounts, but He Fei et al. found that for ionic liquids, large additions will cause the impact strength and tensile strength of PP to decrease at the same time. Guo et al. found that polyether imidazolyl ionic liquids (PIIL) can significantly improve the tensile strength, flexural strength and impact strength of PP at a specific concentration. However, β-nucleating agents also face challenges in practical applications. For example, powdered nucleating agents are prone to agglomeration in PP pellets, which affects their dispersibility and nucleation efficiency. Therefore, future research may focus on developing more effective dispersion techniques and new types of nucleating agents to ensure better processing performance and finished product quality. In addition, as more research on β-nucleating agents and ionic liquid modification deepens, more innovative methods and technologies are expected to emerge to further expand the application range of PP and improve its performance.

[0006] The Chinese patent application document (publication number: CN114085425A) discloses a β-crystal composite nucleating agent and its application. The composite nucleating agent is formed by compounding the fluidity and thermal stability of imidazolyl bis(trifluoromethanesulfonyl)imide salt ionic liquid with aromatic amide β-nucleating agent (TMB-5). After adding polypropylene modification, the conversion rate of polypropylene β-crystal will be greatly improved. Although this patent greatly improves the conversion rate of β-crystal, the toughness improvement of modified PP is only 52%. For some application scenarios that require extremely high toughness, such improvement may still be insufficient. Summary of the invention

[0007] The purpose of the present invention is to address the above-mentioned problems existing in the prior art and propose a new type of β-crystal composite nucleating agent for improving the toughness of polypropylene. After being added to PP modification, the conversion rate of β-crystals will be increased, greatly improving the toughness of polypropylene materials.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] A novel β-crystal composite nucleating agent for improving the toughness of polypropylene. The nucleating agent comprises the following raw materials in parts by weight: 0.05-0.3 parts of a rare earth β-nucleating agent and 0.5-3 parts of an imidazolyl bis(trifluoromethanesulfonyl)imide salt ionic liquid.

[0010] In the above-mentioned novel β-crystal composite nucleating agent for improving the toughness of polypropylene, the nucleating agent comprises the following raw materials in parts by weight: 0.05-0.3 parts of rare earth β-nucleating agent and 0.5-3 parts of imidazolyl bis(trifluoromethanesulfonyl)imide salt ionic liquid.

[0011] In the above-mentioned novel β-crystal composite nucleating agent for improving the toughness of polypropylene, the mass ratio of the rare earth β-nucleating agent to the imidazolyl bis(trifluoromethanesulfonyl)imide salt ionic liquid is 1:(20-30).

[0012] In the above-mentioned novel β-crystal composite nucleating agent for improving the toughness of polypropylene, the rare earth β-nucleating agent is the nucleating agent WBG-Ⅱ.

[0013] In the above-mentioned novel β-crystal composite nucleating agent for improving the toughness of polypropylene, the imidazolyl bis(trifluoromethylsulfonyl)imide salt ionic liquid is 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide (EMIMTFSI).

[0014] The present invention also provides a polypropylene composite material, which comprises the novel β-crystal composite nucleating agent for improving the toughness of polypropylene.

[0015] In the above-mentioned polypropylene composite material, the β crystal form accounts for ≥90% of the polypropylene.

[0016] In the above-mentioned polypropylene composite material, the polypropylene comprises the following raw materials in parts by weight: 80-120 parts of polypropylene, 0.05-0.3 parts of rare earth β-nucleating agent, and 0.5-3 parts of imidazolyl bis(trifluoromethanesulfonyl)imide salt ionic liquid.

[0017] In the present invention, strict control of the addition amount of rare earth β-nucleating agent and ionic liquid is crucial for the optimal performance of modified polypropylene (PP) materials. The amount of rare earth β-nucleating agent must be precisely controlled: excessive use will lead to high crystallization of PP, which will not only greatly reduce the transparency of the product and affect its appearance quality, but also change other physical properties of the material, such as toughness and processability. On the contrary, if the rare earth β-nucleating agent is not added enough, it will not be able to effectively induce sufficient β-crystal formation, resulting in the product's toughness improvement effect is not obvious, and it cannot meet the needs of high-performance applications.

[0018] Similarly, the amount of ionic liquid added also needs to be handled with caution. Although an appropriate amount of ionic liquid can significantly improve the dispersibility of the nucleating agent in the PP matrix, increase the β-crystal conversion rate, and enhance the toughness of the material, excessive use will bring a series of problems. First, the cost of ionic liquids is relatively high, and excessive addition will significantly increase production costs, which is not conducive to economic feasibility. Secondly, too much ionic liquid will have a negative impact on the toughness of PP materials, and may even cause the material to become brittle, which runs counter to the intended goal. In addition, when the amount of ionic liquid added is too small, its effect on improving the dispersibility of the nucleating agent is limited, and its synergistic effect cannot be fully exerted, which in turn affects the performance optimization of the final product.

[0019] Therefore, in the application of compound nucleating agents, it is key to find the ideal addition ratio of rare earth β nucleating agents and ionic liquids. This not only involves the optimal concentration of each of the two, but also needs to consider the interaction between them and their overall impact on the crystallization behavior of PP. The present invention can maximize the performance of the material by finely adjusting the ratio of the two components, ensuring that while maintaining or improving the transparency of the product, the ideal mechanical properties and processing properties are obtained, so that the PP material is better suitable for various high-demand application fields.

[0020] In the above-mentioned polypropylene composite material, the polypropylene is at least one of homopolymer polypropylene, random copolymer polypropylene and block copolymer polypropylene.

[0021] The present invention also provides a method for preparing the above-mentioned polypropylene composite material, the method comprising the following steps:

[0022] S1, prepare the above raw materials;

[0023] S2. The raw materials are melt-blended and extruded and granulated to obtain a polypropylene composite material.

[0024] In the above-mentioned method for preparing a polypropylene composite material, the melt blending temperature in step S2 is 175-185° C., the time is 5-10 min, and the rotation speed is 55-60 r / min.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The composite nucleating agent of the present invention is compounded with imidazolyl trifluoromethanesulfonate ionic liquid and rare earth β-nucleating agent WBG-Ⅱ, which can significantly improve the conversion rate and toughness of β-crystal in polypropylene (PP) material. Imidazolyl trifluoromethanesulfonate ionic liquid is liquid at room temperature and has excellent thermal stability, which enables it to be evenly dispersed in PP resin during processing, avoiding the problem of easy agglomeration of traditional powdered nucleating agents. At the same time, WBG-Ⅱ, as a β-nucleating agent, performs well in promoting the formation of β-crystal in PP;

[0027] 2. When the present invention mixes the imidazolyl trifluoromethanesulfonate ionic liquid and the rare earth β-nucleating agent WBG-Ⅱ in a specific ratio and adds them to the PP modification process, they show obvious synergistic effects: the ionic liquid not only enhances the dispersibility and activity of WBG-Ⅱ, but also improves the distribution of the nucleating agent in the entire polymer matrix through its unique fluidity. The experimental results show that when the addition amount of WBG-Ⅱ is 0.1wt% and the addition amount of ionic liquid is 2.5wt%, the conversion rate of β-crystal reaches 84.5%, and the proportion of β-crystal is as high as 94.74%, which means that the compound nucleating agent greatly promotes the transformation of PP to a tougher β-crystal, thereby greatly improving the overall performance of the material. This improvement is crucial for applications that require high toughness and impact strength, such as automotive parts, medical devices, and packaging materials.

[0028] 3. Due to the good coordination between the ionic liquid and WBG-Ⅱ, this composite nucleating agent is expected to simplify the production process and reduce production costs, while ensuring that the PP material has better mechanical properties, making it more suitable for applications with strict performance requirements. The development of this technology indicates that PP materials will show greater application potential in more fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 X-ray diffraction patterns of PP materials prepared in the embodiments and comparative examples of the present invention;

[0030] Figure 2 DSC first temperature drop (a) and second temperature rise (b) curves of the PP materials prepared in the examples and comparative examples of the present invention. DETAILED DESCRIPTION

[0031] The following are specific embodiments of the present invention, which further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0032] Embodiment 1:

[0033] S1. Prepare the raw materials according to the following mass proportions: 100 parts of homopolymer polypropylene (T30S), 0.1 parts of WBG-Ⅱ, and 0.5 parts of EMIMTFSI, wherein WBG-Ⅱ was purchased from Guangdong Weilinna New Materials Technology Co., Ltd.;

[0034] S2. Place EMIMTFSI, PP and WBG-Ⅱ into HaaKe torque rheometer for melt blending for 8 minutes, with the temperature controlled at 180°C and the rotation speed at 60 r / min.

[0035] S3. After completion, the molten blended material is placed into the mold according to the test requirements, and the mold is placed in a flat plate vulcanizer for molding for 8 minutes at a pressure of 20 MPa. Finally, it is cold pressed in a flat plate vulcanizer of the same model for 8 minutes at a pressure of 10 MPa to obtain the sample PP / W / 0.5E-ILs.

[0036] Embodiment 2:

[0037] S1. Prepare the raw materials according to the following mass proportions: 100 parts of homopolymer polypropylene (T30S), 0.1 parts of WBG-Ⅱ, and 1.0 parts of EMIMTFSI, wherein WBG-Ⅱ was purchased from Guangdong Weilinna New Materials Technology Co., Ltd.

[0038] S2. Place EMIMTFSI, PP and WBG-Ⅱ into HaaKe torque rheometer for melt blending for 8 minutes, with the temperature controlled at 180°C and the rotation speed at 60 r / min.

[0039] S3. After completion, the molten blended material is placed into the mold according to the test requirements, and the mold is placed in a flat plate vulcanizer for molding for 8 minutes at a pressure of 20 MPa. Finally, it is cold pressed in a flat plate vulcanizer of the same model for 8 minutes at a pressure of 10 MPa to obtain the sample PP / W / 1E-ILs.

[0040] Embodiment 3:

[0041] S1. Prepare the raw materials according to the following mass proportions: 100 parts of homopolymer polypropylene (T30S), 0.1 parts of WBG-Ⅱ, and 1.5 parts of EMIMTFSI, wherein WBG-Ⅱ was purchased from Guangdong Weilinna New Materials Technology Co., Ltd.

[0042] S2. Place EMIMTFSI, PP and WBG-Ⅱ into HaaKe torque rheometer for melt blending for 8 minutes, with the temperature controlled at 180°C and the rotation speed at 60 r / min.

[0043] S3. After completion, the molten blended material is placed into the mold according to the test requirements, and the mold is placed in a flat plate vulcanizer for molding for 8 minutes at a pressure of 20 MPa. Finally, it is cold pressed in a flat plate vulcanizer of the same model for 8 minutes at a pressure of 10 MPa to obtain the sample PP / W / 1.5E-ILs.

[0044] Embodiment 4:

[0045] S1. Prepare the raw materials according to the following mass proportions: 100 parts of homopolymer polypropylene (T30S), 0.1 parts of WBG-Ⅱ, and 2.0 parts of EMIMTFSI, wherein WBG-Ⅱ was purchased from Guangdong Weilinna New Materials Technology Co., Ltd.

[0046] S2. Place EMIMTFSI, PP and WBG-Ⅱ into HaaKe torque rheometer for melt blending for 8 minutes, with the temperature controlled at 180°C and the rotation speed at 60 r / min.

[0047] S3. After completion, the molten blended material is placed into the mold according to the test requirements, and the mold is placed in a flat plate vulcanizer for molding for 8 minutes at a pressure of 20 MPa. Finally, it is cold pressed in a flat plate vulcanizer of the same model for 8 minutes at a pressure of 10 MPa to obtain the sample PP / W / 2E-ILs.

[0048] Embodiment 5:

[0049] S1. Prepare the raw materials according to the following mass proportions: 100 parts of homopolymer polypropylene (T30S), 0.1 parts of WBG-Ⅱ, and 2.5 parts of EMIMTFSI, wherein WBG-Ⅱ was purchased from Guangdong Weilinna New Materials Technology Co., Ltd.

[0050] S2. Place EMIMTFSI, PP and WBG-Ⅱ into HaaKe torque rheometer for melt blending for 8 minutes, with the temperature controlled at 180°C and the rotation speed at 60 r / min.

[0051] S3. After completion, the molten blended material is placed into the mold according to the test requirements, and the mold is placed in a flat plate vulcanizer for molding for 8 minutes at a pressure of 20 MPa. Finally, it is cold pressed in a flat plate vulcanizer of the same model for 8 minutes at a pressure of 10 MPa to obtain the sample PP / W / 2.5E-ILs.

[0052] Embodiment 6:

[0053] S1. Prepare the raw materials according to the following mass proportions: 100 parts of homopolymer polypropylene (T30S), 0.1 parts of WBG-Ⅱ, and 3.0 parts of EMIMTFSI, wherein WBG-Ⅱ was purchased from Guangdong Weilinna New Materials Technology Co., Ltd.

[0054] S2. Place EMIMTFSI, PP and WBG-Ⅱ into HaaKe torque rheometer for melt blending for 8 minutes, with the temperature controlled at 180°C and the rotation speed at 60 r / min.

[0055] S3. After completion, the molten blended material is placed into the mold according to the test requirements, and the mold is placed in a flat plate vulcanizer for molding for 8 minutes at a pressure of 20 MPa. Finally, it is cold pressed in a flat plate vulcanizer of the same model for 8 minutes at a pressure of 10 MPa to obtain the sample PP / W / 3E-ILs.

[0056] Comparative Example 1:

[0057] The only difference from Example 4 is that the raw material is only homopolypropylene (T30S) and the sample is marked as purePP.

[0058] Comparative Example 2:

[0059] The only difference from Example 4 is that the raw materials are only homopolypropylene (T30S) and WBG-Ⅱ, and the sample is marked as PP / W.

[0060] Comparative Example 3:

[0061] The only difference from Example 4 is that the raw materials are only homopolypropylene (T30S) and EMIMTFSI, and the samples are marked as PP / E-ILs.

[0062] Comparative Example 4:

[0063] The only difference from Example 4 is that the added amount of WBG-Ⅱ is 0.01 parts.

[0064] Comparative Example 5:

[0065] The only difference from Example 4 is that the added amount of WBG-Ⅱ is 0.5 parts.

[0066] Comparative Example 6:

[0067] The only difference from Example 4 is that the raw materials are prepared according to the following mass parts: 100 parts of homopolypropylene (T30S), 0.1 parts of TMB-5, and 2.0 parts of EMIMTFSI.

[0068] Crystallinity test: The mixed pellets of the above-mentioned Examples 1-6 and Comparative Examples 1-4 were prepared into films using a hot press, and the films were tested using an X-ray diffractometer. A Cu target was used. The scanning range was 10°-30°, the scanning speed was 4° / min, and the wavelength was 0.154nm. Method 2: Differential Scanning Calorimetry (DSC): Weigh 5-8 mg of the sample and put it into an aluminum crucible for compaction, and then put the crucible into a differential scanning calorimeter for the experiment. Under the protection of a nitrogen atmosphere, the sample was heated from 30°C or room temperature to 180°C at a rate of 10°C / min, and then cooled to about 50°C at a rate of 5°C / min, and kept at this temperature for 10 minutes to eliminate the thermal history, and then heated to 180°C for the second time at a rate of 10°C / min, and the experimental data was recorded and the β-crystal conversion rate K was calculated at the same time. β .

[0069] Figure 1The X-ray diffraction diagram of the PP material prepared in the embodiment of the present invention and the comparative example; it can be seen from the figure that the α-crystal diffraction peaks α(110), α(040) and α(130) appear when 2θ is 14.05°, 16.8° and 18.4°. The β-crystal diffraction peaks β(300) and β(301) of polypropylene exist when 2θ is 16° and 21°. By calculating the peak area of ​​each diffraction peak in the X-ray diffraction diagram, the relative content of the β-crystal of each sample can be obtained by calculation. Using the measured data, the relative content of the β-crystal can be calculated according to the formula obtained by the research of M.CORTAZAR et al., as can be seen from formula (1):

[0070]

[0071] Where:

[0072] I β(300) Etc.——the peak area of ​​the corresponding diffraction peak.

[0073] K β ——Relative content of polypropylene β crystal

[0074] The results calculated according to formula 1 are shown in Table 1

[0075] Table 1: β-crystal content calculated by XRD test

[0076] sample <![CDATA[K β (%)]]> PP 32.28 PP / W 26.41 PP / E-ILs 89.75 PP / W / 0.5E-ILs 88.14 PP / W / 1E-ILs 87.93 PP / W / 1.5E-ILs 83.90 PP / W / 2E-ILs 85.30 PP / W / 2.5E-ILs 88.42 PP / W / 3E-ILs 89.55

[0077] According to the data in the table, it can be seen that the compound nucleating agent of WBG-Ⅱ and EMIMTFSI can effectively induce the β-crystal crystallization of PP. According to the calculation, when the amount of ionic liquid added reaches 1.5wt%, the relative content of β-crystal suddenly drops to 83.9%, but with the subsequent increase in the amount of ionic liquid added, the relative content of β-crystal of the sample gradually increases and is basically the same as the sample with low content of ionic liquid added. It can be concluded that the addition of nucleating agent has a significant effect on increasing the relative content of β-crystal of PP, but when the amount of ionic liquid added reaches about 1.5wt%, this effect will be inhibited, but this inhibitory effect will disappear with the increase in the amount of ionic liquid added.

[0078] Figure 2 The DSC first cooling curve (a) and the second heating curve (b) of the PP materials prepared in the examples of the present invention and the comparative examples. The crystallization temperature of different samples can be read from the DSC first cooling curve, and it can be seen from the second heating curve that during the heating process, the melting peak near 150°C represents the melting point of β crystals, while the peak near 162°C represents the melting point of α crystals. Based on the areas of these two peaks, X i and K β . Analyze and calculate each curve, and formula (2) can be seen.

[0079]

[0080] Where:

[0081] X α ——α crystallinity

[0082] X β ——β crystal crystallinity.

[0083] The crystallinity of the crystal form is calculated according to formula (3):

[0084]

[0085] Where:

[0086] △H i —Relative to the crystal form peak area.

[0087] △H standard—PP standard melting enthalpy value.

[0088] Table 2: Crystal content and β-crystal ratio of modified PP with different nucleating agent contents calculated by DSC test

[0089] Example <![CDATA[X β (%)]]> <![CDATA[X α (%)]]> <![CDATA[K β (%)]]> Comparative Example 1 0 87.2 0 Comparative Example 2 0 85.98 0 Comparative Example 3 79.69 10.05 88.68 Comparative Example 4 3 85.3 3 Comparative Example 5 93.52 2.13 97.79 Comparative Example 6 85.3 4.2 95.3 Example 1 80.76 6.55 92.5 Example 2 83.03 7.64 91.57 Example 3 79.9 15.55 83.71 Example 4 81.01 11.03 88.02 Example 5 84.5 4.69 94.74 Example 6 84.1 5.73 93.62

[0090] As can be seen from Table 2, the relative content of β-crystals added with ionic liquid alone did not change compared with pure PP, indicating that ionic liquids cannot induce the production of β-crystals, which is consistent with the above XRD test results. In the subsequent groups, with the addition of ionic liquids, the highest relative content of β-crystals can be obtained, with a value of 94.74%. And we found that when the amount of ionic liquid added was 1.5wt%, the β-crystal content dropped sharply, but as the amount of ionic liquid added increased, it returned to the same level as the low concentration group. This is consistent with the analysis obtained by XRD, but due to different crystallinity test methods, the specific crystallinity will be slightly different, but the trend is consistent.

[0091] Mechanical properties test: The test was carried out 48 hours after the specimens were prepared. Six impact specimens and six dumbbell specimens were selected from the specimens for impact and tensile tests. The simply supported beam impact strength test was carried out according to GB / T 1843-1996; the tensile test was carried out according to GB / T 1040.2-2006, and the tensile rate was set to 50 mm / min.

[0092] Table 3: Physical property test results of polypropylene composite materials prepared in Examples and Comparative Examples

[0093]

[0094] From Table 3, we can see that the impact strength of PP is improved after adding ionic liquid and nucleating agent, which shows that the compound nucleating agent modified by ionic liquid β nucleating agent is effective in toughening PP. When the amount of ionic liquid added is 2.5wt%, the impact strength is 6.5KJ / m 2 This is consistent with the decrease in the tensile strength of the sample. Combined with Table 2, it is found that the impact strength of PP / W, PP / W / 0.5E, and PP / W / 1E at room temperature is similar to the K β The positive correlation between the size of β crystals indicates that the higher the content of β crystals, the stronger the toughness of polypropylene. β The difference is not big, both are around 88%, but the toughness is very different. The impact strength of PP / W at room temperature is 5.6KJ / m 2 , but the impact strength of PP / W / 2E-ILs is as high as 9KJ / m 2 , it can be seen that the ionic liquid does not affect its K β In this case, it also has a toughening effect within a certain addition amount.

[0095] Comparative Example 4 is a case where the amount of nucleating agent added is too little, resulting in insufficient β crystals produced, which fails to improve the toughness of PP. Comparative Example 5 is a case where the amount of nucleating agent added is too much, which will cause the product to be highly crystallized, thereby significantly reducing the transparency, haze and tensile properties of the product.

[0096] The amount of nucleating agent added has a crucial impact on the performance of the final product, which can be more clearly understood through the results of Comparative Examples 4 and 5. As can be seen from Comparative Example 4, when the amount of nucleating agent added is insufficient, it is not enough to induce the formation of a large number of β-crystals. This is because the main function of the nucleating agent is to act as a "nucleus" in the heterogeneous nucleation crystallization process, guiding and accelerating the growth of a specific crystal. If the amount of nucleating agent is not enough to cover the entire PP matrix, the amount of induced β-crystals will be limited and the overall structure of the material cannot be significantly changed. As a result, the toughness improvement effect of the PP material is not good and the expected modification target is not achieved. As can be seen from Comparative Example 5, when the nucleating agent is added excessively, too much β-crystal will be produced, which will also have a negative impact on the material performance. Specifically, 1. Transparency decreases: As the amount of β-crystal increases, the crystal structure inside the PP material becomes more complex, and more scattering occurs when light passes through, resulting in a significant decrease in transparency. For some applications, such as food packaging or medical devices, transparency is a very critical property, and its decline will directly affect the market acceptance of the product. 2. Increased haze: Associated with transparency is an increase in haze. Too much β crystals will increase the light scattering effect, making the product look more hazy, which is particularly unfavorable for applications that require high clarity. 3. Decreased tensile strength: Although β crystals generally improve the toughness of materials, excessive presence will make the material brittle. This is because too many β crystals will interfere with the normal formation of α crystals, destroying the original balance, thereby reducing the tensile strength and other mechanical properties of the material. In addition, excessive nucleating agents may also cause stress concentration inside the material, further weakening its mechanical properties.

[0097] Through the experiment of Comparative Example 6, it was found that although TMB-5 can induce more β-crystals at a lower addition amount, its effect on improving the toughness of PP is limited. The selection of nucleating agent should not be based solely on its ability to induce β-crystals, but also needs to consider its impact on the overall mechanical properties of the material. Although WBG-Ⅱ is not as good as TMB-5 in β-crystal conversion rate, it is more outstanding in improving PP toughness. Because TMB-5 is prone to agglomeration or other poor dispersion during processing, even if it can induce more β-crystals, the effect in practical applications may be greatly reduced. Compared with pure PP, its impact strength is only increased by 52%, while WBG-Ⅱ performs better in this regard, which helps to ensure production stability and consistency of product quality.

[0098] In summary, the composite nucleating agent of the present invention is compounded by imidazolyl bistrifluoromethanesulfonate ionic liquid and rare earth β-nucleating agent WBG-Ⅱ, which can significantly improve the conversion rate and toughness of β-crystal in polypropylene (PP) material. Imidazolyl bistrifluoromethanesulfonate ionic liquid is liquid at room temperature and has excellent thermal stability, which enables it to be evenly dispersed in PP resin during processing, avoiding the problem of easy agglomeration of traditional powdered nucleating agents. At the same time, WBG-Ⅱ, as a β-nucleating agent, performs excellently in promoting PP to form β-crystal.

[0099] The parts of the embodiments herein that are not exhaustive of the midpoint values ​​of the technical scope claimed for protection by the present invention and the new technical solutions formed by equivalent replacement of single or multiple technical features in the technical solutions of the embodiments are also within the scope claimed for protection by the present invention; at the same time, in all the listed or unlisted embodiments of the scheme of the present invention, each parameter in the same embodiment merely represents an example of its technical solution (i.e., a feasible solution), and there is no strict coordination and limitation relationship between the parameters, wherein the parameters can be replaced with each other without violating the axioms and the claims of the present invention, unless otherwise stated.

[0100] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above technical means, but also include technical schemes composed of any combination of the above technical features. The above is a specific implementation of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also regarded as the protection scope of the present invention.

[0101] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A novel β-crystal composite nucleating agent for improving the toughness of polypropylene, characterized in that: The nucleating agent comprises the following raw materials in parts by weight: 0.05-0.3 parts of rare earth beta nucleating agent and 0.5-3 parts of imidazolyl bis(trifluoromethanesulfonyl)imide salt ionic liquid.

2. A novel β-crystal composite nucleating agent for improving the toughness of polypropylene according to claim 1, characterized in that: The mass ratio of the rare earth β-nucleating agent to the imidazolyl bis(trifluoromethanesulfonyl)imide salt ionic liquid is 1:(20-30).

3. A novel β-crystal composite nucleating agent for improving the toughness of polypropylene according to claim 1, characterized in that: The rare earth β nucleating agent is the nucleating agent WBG-Ⅱ.

4. A novel β-crystal composite nucleating agent for improving the toughness of polypropylene according to claim 1, characterized in that: The imidazolyl bis(trifluoromethanesulfonyl)imide salt ionic liquid is 1-ethyl-3-methylimidazolinium bis(trifluoromethanesulfonyl)imide.

5. A polypropylene composite material, characterized in that: The polypropylene composite material comprises the novel β-crystal composite nucleating agent for improving the toughness of polypropylene as claimed in claim 1.

6. A polypropylene composite material according to claim 5, characterized in that: The β crystal form accounts for ≥90% of polypropylene.

7. A polypropylene composite material according to claim 5, characterized in that: The polypropylene comprises the following raw materials in parts by weight: 80-120 parts of polypropylene, 0.05-0.3 parts of rare earth beta nucleating agent, and 0.5-3 parts of imidazolyl bis(trifluoromethanesulfonyl)imide salt ionic liquid.

8. A polypropylene composite material according to claim 7, characterized in that: The polypropylene is at least one of homopolymer polypropylene, random copolymer polypropylene and block copolymer polypropylene.

9. A method for preparing a polypropylene composite material as claimed in claim 7, characterized in that: The method comprises the following steps: S1. Prepare the raw materials according to claim 7; S2. The raw materials are melt-blended and extruded and granulated to obtain a polypropylene composite material.

10. The method for preparing a polypropylene composite material according to claim 9, characterized in that: The melt blending temperature in step S2 is 175-185° C., the time is 5-10 min, and the rotation speed is 55-60 r / min.

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