Heat-resistant polypropylene composition and method for producing the same

Abstract

This invention discloses a heat-resistant polypropylene composition and its preparation method, relating to the field of polymer material modification technology. The heat-resistant polypropylene composition comprises: homopolymer polypropylene, a composite nucleating agent, an amorphous olefin copolymer, and ammonium polyphosphate. The composite nucleating agent is a compound system of an α-crystalline nucleating agent and a phosphate ester salt nucleating agent. The preparation method includes: melting and extruding the raw materials using a twin-screw extruder at 180-210℃, granulation, and drying. This invention induces PP grain refinement through the composite nucleating agent, while simultaneously utilizing the interaction between the amorphous olefin copolymer and ammonium polyphosphate to form an organic-inorganic hybrid network, constructing a multi-level heat-resistant barrier of "crystal refinement + network anchoring". Under conditions completely independent of glass fiber, the heat distortion temperature is ≥145℃, with good processing fluidity, no warping or fiber floating problems, and it can be used for automotive engine peripheral parts, heat-resistant components of household appliances, and electronic appliance housings.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, and more specifically to a heat-resistant polypropylene composition and its preparation method. Background Technology

[0002] Polypropylene (PP), one of the five major general-purpose thermoplastics, is widely used in automobiles, home appliances, electronics, packaging, and other fields due to its abundant sources, low price, and excellent comprehensive performance. However, although the regular structure of the polypropylene molecular chain gives it a high degree of crystallinity, the van der Waals forces between the molecular chains are relatively weak, resulting in a heat distortion temperature (HDT) that is usually between 80-100℃. This defect seriously restricts the use of polypropylene in applications that require high temperatures, such as automotive engine peripheral parts, LED lighting heat dissipation components, and microwave oven tableware. These fields typically require a heat distortion temperature of 120-150℃.

[0003] To improve the heat resistance of polypropylene, existing technologies mainly focus on the following aspects:

[0004] First, inorganic filler modification. This involves adding inorganic rigid particles such as talc, calcium carbonate, and mica, utilizing the modulus difference between the filler and the matrix to restrict the movement of polypropylene molecular chains at high temperatures. Talc is the most commonly used filler due to its layered structure, which allows it to simultaneously act as a heterogeneous nucleator. However, simple filler modification has significant technical bottlenecks: on the one hand, while high filler content can increase the heat distortion temperature, it severely deteriorates the material's processing fluidity; on the other hand, the interfacial bonding between inorganic fillers and the polypropylene matrix is ​​weak, easily leading to interfacial debonding near the heat distortion temperature and premature material failure.

[0005] Second, fiber-reinforced modification. Glass fiber, due to its high modulus and high strength, is widely used for reinforcing polypropylene. Short-cut glass fibers can form a physical skeleton to restrict molecular chain movement, while long glass fibers can construct a three-dimensional network structure to further improve high-temperature creep resistance. However, fiber reinforcement also faces many problems: the directional arrangement of glass fibers during injection molding can lead to anisotropic shrinkage of the product, causing warping deformation; the surface roughness caused by exposed glass fibers limits its application in paint-free products; and high fiber content causes severe wear on processing equipment.

[0006] Third, nucleating agent modification. Nucleating agents provide additional nucleation sites, inducing polypropylene molecular chains to form finer and more complete crystal structures, thereby increasing crystallinity and crystallization temperature, and thus improving heat resistance. Studies have shown that α-crystalline nucleating agents can significantly increase the crystallization temperature and rigidity of polypropylene, and there is a synergistic effect between different nucleating agents; compounding can achieve better results than using a single nucleating agent. However, the increase in heat distortion temperature obtained by modifying solely with nucleating agents is limited, usually only in the range of 5-15℃, which is insufficient to meet heat resistance requirements above 120℃.

[0007] Fourth, the current application status of amorphous olefin copolymers (APAO). In existing technologies, APAO (also known as atactic polypropylene) is mainly used as a matrix resin for hot melt adhesives, or as a carrier for filler masterbatches to enhance the plasticity of polypropylene and polyethylene and reduce raw material costs. In this traditional application, APAO acts as a "promoter" and "flow enhancer," and does not itself serve to improve heat resistance.

[0008] Fifth, the current application status of ammonium polyphosphate (APP). APP is a phosphorus-nitrogen-based halogen-free flame retardant. Its conventional application in polypropylene is to impart flame retardant properties to the material. Its decomposition temperature is greater than 220℃, and at high temperatures, it can promote the dehydration of the polymer surface to form char and a protective layer.

[0009] In summary, the existing technology lacks a polypropylene composition and its preparation method that can achieve a significant increase in heat distortion temperature (HDT ≥ 145℃) while maintaining good processing fluidity. Therefore, overcoming the technical deficiencies in the existing technology and providing a polypropylene composition with excellent heat resistance and good processing fluidity is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0010] In view of this, the present invention develops a heat-resistant polypropylene composition and its preparation method, overcoming the contradiction between heat resistance and processability in existing heat-resistant polypropylene materials, and providing a polypropylene composition with an ultra-high heat distortion temperature (heat distortion temperature ≥145℃) without significantly affecting processing fluidity. Simultaneously, the present invention also solves the technical problem of weak interfacial bonding between inorganic fillers and the polypropylene matrix, and easy debonding and failure at high temperatures, in the prior art. By introducing amorphous olefin copolymers, nanoscale dispersion of fillers in the matrix is ​​achieved.

[0011] To solve the above-mentioned technical problems, this application adopts the following technical solution:

[0012] The primary objective of this application is to provide a heat-resistant polypropylene composition comprising, by weight, the following raw materials: 100 parts homopolymer polypropylene, 0.05-0.3 parts composite nucleating agent, 5-15 parts amorphous olefin copolymer, and 8-20 parts ammonium polyphosphate.

[0013] In the above scheme, the homopolymer polypropylene, as the matrix resin, has higher crystallinity and regularity than copolymer polypropylene, and can form a more perfect crystal structure under the action of nucleating agent. This is the basis for achieving ultra-high heat resistance.

[0014] As a preferred technical solution, the composite nucleating agent is a compound system of α-crystal nucleating agent and phosphate salt nucleating agent, with a mass ratio of 1:0.5-2.

[0015] As a preferred technical solution, the α-crystal nucleating agent is selected from NP-657 nucleating agent; the phosphate ester salt nucleating agent is aluminum hydroxydi[2,2'-methylene-bis(4,6-di-tert-butylphenoxy)phosphate] (abbreviated as APAl-OH).

[0016] The choice to combine an α-crystalline nucleating agent with APAl-OH is based on the following considerations: While a single α-crystalline nucleating agent can increase the crystallization rate, its effect on increasing the crystallization temperature is limited; while a single APAl-OH has excellent nucleation efficiency, its dispersibility is poor, and it is prone to agglomeration in the matrix. The combination of the two can produce a synergistic effect—the α-crystalline nucleating agent first induces the polypropylene molecular chains to form a large number of fine crystal nuclei, while APAl-OH further promotes the growth and perfection of the crystal nuclei, resulting in smaller, more uniformly distributed, and more crystallized grains.

[0017] As a preferred technical solution, the amorphous olefin copolymer (APAO) is a propylene-based amorphous olefin copolymer with a glass transition temperature of -20℃ to -10℃ and a weight-average molecular weight of 5000-20000. APAO is a low-molecular-weight amorphous copolymer obtained by polymerizing monomers such as propylene, ethylene, and 1-butene through a special catalyst. Unlike conventional polypropylene, APAO has extremely low crystallinity and excellent flowability.

[0018] It is particularly important to note that the function of APAO in this invention is completely different from that in the prior art. In traditional applications, APAO is only used as a filler masterbatch carrier to reduce costs and increase production; those skilled in the art have no incentive to use it to improve the heat resistance of polypropylene. This invention discovers for the first time that APAO plays three entirely new roles in the heat resistance modification of polypropylene:

[0019] Firstly, it functions as a compatibilizer and dispersant. APAO's molecular chain structure is similar to that of polypropylene, exhibiting good compatibility with the polypropylene matrix. Simultaneously, the amorphous regions distributed along its molecular chain can interact with polar inorganic fillers (ammonium polyphosphate) (especially through hydrogen bonding), thereby improving the uniformity of the inorganic filler's dispersion within the polypropylene matrix. This amphiphilic characteristic makes it an ideal interfacial bridge connecting the non-polar polymer matrix and the polar inorganic filler.

[0020] Secondly, it acts as a flow promoter. APAO's low molecular weight and high fluidity can reduce the melt viscosity of the entire system, improve processing performance, and effectively offset the negative impact of ammonium polyphosphate on the system's fluidity. This is key to achieving a balance between "high heat resistance and easy processing".

[0021] Thirdly, it serves as a building block for hybrid networks. This is the core technological discovery of this invention. APAO and ammonium polyphosphate can form a stable organic-inorganic hybrid network structure through non-covalent interactions such as hydrogen bonding. Specifically, the ammonium polyphosphate molecular chain contains a large number of P=O and PO- groups, which can form hydrogen bonds with the polar groups on the APAO molecular chain; at the same time, the amorphous structure of APAO provides sufficient chain segment mobility, allowing this hydrogen-bonded network to be fully formed during melt blending. This hybrid network acts as an "anchor" between the crystalline and amorphous regions of polypropylene. When the material is heated, this network can effectively restrict the movement of polypropylene molecular chains, thereby significantly increasing the heat distortion temperature.

[0022] As a preferred technical solution, the degree of polymerization of the ammonium polyphosphate is greater than 1000, and its mass ratio to the amorphous olefin copolymer in the composition is 1:0.5-1.5. Ammonium polyphosphate (APP) is a phosphorus-nitrogen-based halogen-free flame retardant that decomposes at high temperatures to generate polyphosphoric acid or polymetaphosphoric acid, which can promote the dehydration and char formation of the polymer surface. In this invention, the role of APP is not only flame retardant, but more importantly, it forms a stable organic-inorganic hybrid network in the polypropylene matrix through its interaction with APAO. Unlike the prior art where APP is only used as a flame retardant, this invention is the first to use APP as a core component for heat-resistant modification, utilizing the polar groups in its molecular structure to form a hydrogen bond network with APAO, thereby achieving a significant improvement in heat resistance.

[0023] Another object of this application is to provide a method for preparing the heat-resistant polypropylene composition, comprising the following steps:

[0024] (1) Homopolymer polypropylene, composite nucleating agent, amorphous olefin copolymer and ammonium polyphosphate are added into a high-speed mixer according to the proportion and mixed evenly to obtain a mixture;

[0025] (2) Add the mixture to a twin-screw extruder for melt extrusion;

[0026] (3) The extruded strip is cooled, granulated and dried to obtain a heat-resistant polypropylene composition.

[0027] The key process control point of the above preparation method is the processing temperature: compared with conventional polypropylene modification, the processing temperature of the present invention is lower (maximum only 205°C), which is to avoid premature decomposition of ammonium polyphosphate at high temperature, and also to protect the nucleation activity of the composite nucleating agent.

[0028] As a preferred technical solution, the processing temperature of the twin-screw extruder in step (2) is 180-210℃, the screw speed is 200-400 rpm, and the vacuum degree is less than -0.06 MPa.

[0029] Another object of this application is to provide the application of the heat-resistant polypropylene composition or the heat-resistant polypropylene composition prepared by the preparation method in automotive engine peripheral parts, heat-resistant parts of household appliances, and electronic and electrical housings.

[0030] Another object of this application is to provide: a method for increasing the heat distortion temperature of polypropylene, using homopolymer polypropylene as the matrix, and adding 0.05-0.3 parts of a composite nucleating agent, 5-15 parts of an amorphous olefin copolymer, and 8-20 parts of ammonium polyphosphate for blending modification, wherein the composite nucleating agent is a compound system of α-crystal nucleating agent and phosphate ester salt nucleating agent.

[0031] As a preferred technical solution, the amorphous olefin copolymer and ammonium polyphosphate form an organic-inorganic hybrid network structure during melt blending, which together with the refined grains induced by the composite nucleating agent to construct a multi-level heat-resistant barrier.

[0032] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) Significantly improved the heat distortion temperature of polypropylene

[0034] This invention achieves a significant improvement in heat distortion temperature by constructing a triple composite heat-resistant system consisting of "nucleation-induced grain refinement - APAO compatibilization and dispersion - APP / APAO hybrid network". Experimental data show that the polypropylene composition prepared by this invention can achieve a heat distortion temperature of 146-152℃ under a load of 1.8MPa, which is 53-57℃ higher than that of unmodified homopolymer polypropylene (95℃), and also higher than that of conventional talc / glass fiber filled modification (approximately 118-128℃).

[0035] (2) Achieved a synergistic improvement in heat resistance and processability.

[0036] Traditional heat-resistant modification methods (such as high-filled inorganic fillers) often come at the cost of sacrificing processing fluidity. In this invention, low molecular weight APAO also acts as a flow promoter, effectively compensating for the negative impact of ammonium polyphosphate on the system's fluidity. The melt index (230℃ / 2.16kg) is maintained between 10.8-13.5 g / 10min, significantly higher than that of traditional glass fiber / talc-filled modified systems (comparative examples 4-6 are 8.2-9.5 g / 10min). This indicates that the APP / APAO system achieves high heat resistance while having less negative impact on processing fluidity, demonstrating good processing adaptability.

[0037] (3) Non-obviousness of technical solutions – APAO’s functional transformation

[0038] The technological innovation of this invention is primarily reflected in the novel application of APAO in the heat resistance modification of polypropylene. APAO is conventionally used as a matrix resin in hot melt adhesives or as a carrier for filler masterbatches. Those skilled in the art know that it can be used to "enhance the plasticity of polypropylene and polyethylene and reduce costs," but in this application, APAO is only used as an "increaser" and does not itself contribute to improving heat resistance. Those skilled in the art lack the technical motivation to use APAO to improve the heat resistance of polypropylene because:

[0039] APAO itself is an amorphous low molecular weight polyolefin with a low glass transition temperature (-20℃ to -10℃) and does not have the ability to provide high-temperature stability.

[0040] In conventional understanding, low molecular weight components are usually regarded as "impurities" or "diluents" that reduce rather than improve the heat resistance of materials;

[0041] Combining APAO and APP to form a hybrid network requires overcoming the technical bias that "low molecular weight components = performance degradation".

[0042] This invention unexpectedly reveals that APAO and APP can form a stable hybrid network through interactions such as hydrogen bonding. This network acts as a "thermal barrier" in the polypropylene matrix, making the low molecular weight, low Tg APAO a key component for improving heat resistance. This discovery overturns conventional understanding in those skilled in the art and is of non-obvious nature.

[0043] (4) Non-obviousness of the technical solution – Proof of collaboration between “APP+APAO”

[0044] The technological innovation of this invention is also reflected in the indispensability of the "APP+APAO" system. To demonstrate this, the invention specifically includes the following comparative experiment:

[0045] Comparative Example 8: Using only APP (without APAO) + composite nucleating agent → HDT was 117℃

[0046] Comparative Example 9: APAO alone (without APP) + composite nucleating agent → HDT of 113℃

[0047] Comparative Example 3: APP + APAO (neither with added nucleating agent) → HDT of 123℃

[0048] Experimental results show that when APP (Comparative Example 8) or APAO (Comparative Example 9) are used alone, the heat distortion temperature does not exceed 120℃, which is much lower than 152℃ when both are used together with the addition of a composite nucleating agent (Example 2). This indicates that APP and APAO are "indispensable"—the absence of either component makes it impossible to achieve a significant increase in heat distortion temperature.

[0049] (5) The composite nucleating agent and the APP / APAO system produced unexpected technical effects.

[0050] When using the composite nucleating agent alone (Comparative Example 2), the heat distortion temperature of polypropylene is 108°C; when using the APP / APAO system alone (Comparative Example 3), the heat distortion temperature is 123°C; and when the two are used in combination (Example 2), the heat distortion temperature reaches 152°C.

[0051] If only a simple addition is used, the expected heat distortion temperature of the two combined can be calculated as follows: based on 95°C for pure PP (Comparative Example 1), the contribution of the composite nucleating agent is 108-95=13°C, and the contribution of the APP / APAO system is 123-95=28°C. The expected value for simple addition is 95+13+28=136°C. However, the actual heat distortion temperature of Example 2 reached 152°C, exceeding the expected value by 16°C. Even if the higher of Comparative Example 2 and Comparative Example 3 is used for estimation, the expected value is only 123°C, and Example 2 is still 29°C higher.

[0052] This synergistic effect far exceeds the simple sum of the individual effects of each component, and is a "1+1>2" effect that could not have been foreseen by those skilled in the art.

[0053] (6) Excellent overall performance

[0054] In addition to its heat resistance, the polypropylene composition of this invention also exhibits excellent dimensional stability. As shown in Table 1, the shrinkage rates (longitudinal / transverse) of Examples 1-3 are 0.4% / 0.9%, 0.3% / 0.8%, and 0.4% / 1.0%, respectively, significantly better than the 1.2% / 1.5% of Comparative Example 1 (pure PP). Most importantly, the technical approach of this invention does not rely on glass fiber reinforcement at all, fundamentally avoiding the warping and surface fiber floating problems caused by glass fiber reinforcement schemes, resulting in products with excellent appearance quality. Detailed Implementation

[0055] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0056] Experimental materials

[0057] Homopolymer polypropylene: Grade Z30S, produced by Qingyang Petrochemical, CAS No.: 9003-07-0, melt index (230℃ / 2.16kg) is 15-25g / 10min, isotacticity ≥96%;

[0058] α nucleating agent: NP-657, commercially available, CAS No.: 135861-56-2, melting point approximately 220℃;

[0059] Phosphate ester nucleating agent: Nucleating agent NA-21 (chemical name: bis[2,2'-methylene-bis(4,6-di-tert-butylphenoxy)phosphate]aluminum hydroxyl), CAS No.: 151841-65-5, produced by Shanxi Provincial Chemical Research Institute;

[0060] Amorphous olefin copolymer (APAO): Produced by Eastman Chemical Company, USA, grade P1010PL, CAS No.: 68131-77-1, glass transition temperature approximately -15℃, weight average molecular weight approximately 10,000.

[0061] Ammonium polyphosphate (APP): Degree of polymerization >1000, CAS No.: 68333-79-9, commercially available;

[0062] Talc powder: Golden Monkey brand, 1250 mesh, CAS No.: 14807-96-6;

[0063] Short-cut fiberglass: Produced by Chongqing International, length 3mm, CAS No.: 65997-17-3;

[0064] LDPE: Produced by Sichuan Chemical Industry Group, grade 7042, CAS No.: 9002-88-4;

[0065] Compatibilizer KT-1: Manufactured by Koton, CAS No.: 47487-05-8;

[0066] POE (Polyolefin Elastomer): Brand name ENGAGE™ 8107, manufactured by Dow Chemical in the United States, CAS No.: 26221-73-8 (General CAS for ethylene-octene copolymers), commercially available.

[0067] Performance testing methods

[0068] The performance of the products obtained in each embodiment and comparative example was tested according to the following methods:

[0069] (1) Heat distortion temperature: tested according to ISO 75-1 standard, load 1.8MPa, span 62mm, spline size 80mm×10mm×4mm;

[0070] (2) Melt flow index: Tested according to ISO 1133 standard, temperature 230℃, load 2.16kg;

[0071] (3) Shrinkage rate: Tested according to ISO 294-4 standard, sample size 60mm×60mm×2mm.

[0072] Example 1

[0073] A heat-resistant polypropylene composition formulation (parts by weight):

[0074] Homopolymer polypropylene: 100 parts;

[0075] Composite nucleating agent (NP-657:APAl-OH = 1:0.8): 0.1 parts;

[0076] APAO: 8 copies;

[0077] APP: 12 copies.

[0078] Preparation method:

[0079] (1) Weigh each raw material according to the proportion, put them into a high-speed mixer, and mix at room temperature for 8 minutes until the materials are evenly mixed;

[0080] (2) Add the mixture to the main feed port of the twin-screw extruder for melt extrusion. The temperature of each section of the extruder is set as follows: Zone 1 180℃, Zone 2 190℃, Zone 3 200℃, Zone 4 200℃, Zone 5 195℃, Die head temperature 205℃, screw speed 300 rpm, vacuum degree -0.08 MPa.

[0081] (3) The extruded strip is cooled in a water tank, air-dried, and granulated. Finally, it is dried at 80°C for 3 hours to obtain the final product.

[0082] Example 2

[0083] A heat-resistant polypropylene composition formulation (parts by weight):

[0084] Homopolymer polypropylene: 100 parts;

[0085] Composite nucleating agent (NP-657:APAl-OH=1:1): 0.15 parts;

[0086] APAO: 10 copies;

[0087] APP: 15 copies.

[0088] Preparation method: Same as in Example 1.

[0089] Example 3

[0090] A heat-resistant polypropylene composition formulation (parts by weight):

[0091] Homopolymer polypropylene: 100 parts;

[0092] Composite nucleating agent (NP-657:APAl-OH = 1:1.2): 0.2 parts;

[0093] APAO: 12 portions;

[0094] APP: 10 copies.

[0095] Preparation method: Same as in Example 1.

[0096] Comparative Example 1 (Unmodified pure PP)

[0097] Formula: 100 parts homopolymer polypropylene.

[0098] Preparation method: Homopolymer polypropylene was directly added to a twin-screw extruder for melt extrusion granulation, and the processing conditions were the same as in Example 1.

[0099] Comparative Example 2 (with only composite nucleating agent added)

[0100] formula:

[0101] Homopolymer polypropylene: 100 parts;

[0102] Composite nucleating agent (NP-657:APAl-OH=1:1): 0.15 parts.

[0103] Preparation method: Same as in Example 1.

[0104] Comparative Example 3 (only APP / APAO system added, no composite nucleating agent added)

[0105] formula:

[0106] Homopolymer polypropylene: 100 parts;

[0107] APAO: 10 copies;

[0108] APP: 15 copies.

[0109] Preparation method: Same as in Example 1.

[0110] Comparative Example 4 (using talcum powder instead of APP)

[0111] formula:

[0112] Homopolymer polypropylene: 100 parts;

[0113] Composite nucleating agent (NP-657:APAl-OH=1:1): 0.15 parts;

[0114] APAO: 10 copies;

[0115] Talc powder (1250 mesh): 15 parts.

[0116] Preparation method: Same as in Example 1.

[0117] Comparative Example 5 (using chopped glass fiber instead of APP)

[0118] formula:

[0119] Homopolymer polypropylene: 100 parts;

[0120] Composite nucleating agent (NP-657:APAl-OH=1:1): 0.15 parts;

[0121] APAO: 10 copies;

[0122] Short-cut glass fiber (3mm): 15 parts.

[0123] Preparation method: Same as in Example 1.

[0124] Comparative Example 6 (using the glass fiber / talc / LDPE system from the background art)

[0125] Formulation (refer to typical formulations in the background art):

[0126] Homopolymer polypropylene: 100 parts;

[0127] Talc powder: 10 parts;

[0128] Short-cut fiberglass: 5 parts;

[0129] POE: 5 copies;

[0130] Compatibilizer KT-1: 3 parts.

[0131] Preparation method: Same as in Example 1.

[0132] Comparative Example 7 (Single nucleating agent replacing composite nucleating agent)

[0133] formula:

[0134] Homopolymer polypropylene: 100 parts;

[0135] Alpha nucleating agent NP-657 (single): 0.15 parts;

[0136] APAO: 10 copies;

[0137] APP: 15 copies.

[0138] Preparation method: Same as in Example 1.

[0139] Comparative Example 8 (Verification that both APP and APAO are indispensable - using only APP, without APAO)

[0140] formula:

[0141] Homopolymer polypropylene: 100 parts;

[0142] Composite nucleating agent (NP-657:APAl-OH=1:1): 0.15 parts;

[0143] APP: 15 copies (excluding APAO).

[0144] Preparation method: Same as in Example 1. Without APAO, APP has poor dispersibility in the PP matrix, and obvious particle agglomeration occurs during extrusion.

[0145] Phenomenon: The surface of the extruded strip is rough, and the uneven dispersion of APP leads to obvious brittleness of the material.

[0146] Results Analysis: The heat distortion temperature of Comparative Example 8 was only 117℃, far lower than 152℃ of Example 2. This indicates that using APP alone (without APAO) cannot achieve a significant improvement in heat resistance. The reason is that without the compatibilizing and dispersing effect of APAO, APP forms micron-sized aggregates in the PP matrix, failing to form an effective hybrid network structure; simultaneously, the interfacial bonding between APP and the PP matrix is ​​weak, making it prone to interfacial debonding under heat.

[0147] Comparative Example 9 (Verification that "both APP and APAO are indispensable" - using only APAO, without APP)

[0148] formula:

[0149] Homopolymer polypropylene: 100 parts;

[0150] Composite nucleating agent (NP-657:APAl-OH=1:1): 0.15 parts;

[0151] APAO: 15 copies (excluding APP).

[0152] Preparation method: Same as in Example 1.

[0153] Phenomenon: The material has good fluidity, but insufficient rigidity at high temperatures.

[0154] Results Analysis: The heat distortion temperature of Comparative Example 9 was only 113℃, far lower than 152℃ in Example 2. This indicates that using APAO alone (without APP) also cannot achieve a significant improvement in heat resistance. The reason is that without the rigid network support of APP, APAO only plays a role in compatibilization and flow promotion. Although it improves processing performance, because APAO itself is an amorphous low molecular weight polymer, its low Tg characteristic actually softens the matrix to some extent, failing to provide high-temperature stability.

[0155] Comparative Examples 8 and 9 together demonstrate that APP and APAO are "indispensable"—the absence of either component makes it impossible to achieve the leapfrog increase in heat distortion temperature from below 120°C to above 150°C. This fully demonstrates the synergistic effect and indispensability of the "APP+APAO" system.

[0156] The performance test results of each embodiment and comparative example are summarized in Table 1:

[0157] Table 1 Performance test results for different groups

[0158] serial number Heat distortion temperature (°C) Melt index (g / 10min) Shrinkage rate (longitudinal / transverse %) Example 1 148 12.3 0.4 / 0.9 Example 2 152 10.8 0.3 / 0.8 Example 3 146 13.5 0.4 / 1.0 Comparative Example 1 95 18.5 1.2 / 1.5 Comparative Example 2 108 17.2 1.0 / 1.2 Comparative Example 3 123 11.2 0.5 / 1.0 Comparative Example 4 118 9.5 0.6 / 1.1 Comparative Example 5 128 8.2 0.8 / 1.4 Comparative Example 6 113 11.2 0.6 / 1.1 Comparative Example 7 135 11.5 - Comparative Example 8 117 9.6 - Comparative Example 9 113 13.5 -

[0159] Note: "—" indicates that the index was not measured, as the main experimental purpose of comparative examples 7-9 was to verify the heat resistance synergistic effect, and shrinkage rate was not a necessary test item.

[0160] Results analysis:

[0161] (1) Verification that APP and APAO are "indispensable"

[0162] The HDT of Comparative Example 8 (APP only, without APAO) was 117°C, the HDT of Comparative Example 9 (APAO only, without APP) was 113°C, while the HDT of Example 2 (APP + APAO) reached 152°C. Neither APP nor APAO alone could raise the heat distortion temperature (HDT) above 120°C, but when used together, the HDT exceeded 150°C. This result indicates that APP and APAO constitute an inseparable functional unit in this invention, and their synergistic effect is a key prerequisite for achieving ultra-high heat resistance.

[0163] (2) Synergistic effect of composite nucleating agent and APP / APAO system

[0164] The heat distortion temperature of Comparative Example 2 (composite nucleating agent only) was 108°C, and that of Comparative Example 3 (APP / APAO only) was 123°C. If simply added together, the expected heat distortion temperature for the combined use of both would be approximately 108 + (123 - 95) = 136°C. However, the actual heat distortion temperature of Example 2 reached 152°C, exceeding the expected value by 16°C, resulting in a net synergistic effect of 16°C. This result indicates a strong positive synergistic effect between the composite nucleating agent and the APP / APAO system, and this effect far exceeds the reasonable expectations of those skilled in the art.

[0165] (3) Advantages of composite nucleating agents compared to single nucleating agents

[0166] A comparison between Comparative Example 7 and Example 2 shows that, under the same conditions of other components, replacing the single α-nucleating agent with a composite nucleating agent (NP-657+APAl-OH) increased the heat distortion temperature from 135°C to 152°C, an increase of 17°C. This indicates that the composite nucleating agent system used in this invention has a significant advantage in increasing the heat distortion temperature of polypropylene.

[0167] (4) Advantages of APP compared to traditional inorganic fillers

[0168] The heat distortion temperatures of Comparative Example 4 (talc) and Comparative Example 5 (glass fiber) were 118°C and 128°C, respectively, significantly lower than 152°C in Example 2. This indicates that APP does not simply act as a filler reinforcement, but rather provides a unique heat resistance mechanism by forming a hybrid network structure with APAO. Furthermore, both the talc and glass fiber systems resulted in a significant decrease in melt flow index (down to 9.5 and 8.2, respectively), while Example 2 of this invention had a melt flow index of 10.8, superior to the aforementioned comparative schemes, indicating that the APP / APAO system has a relative advantage in improving processing fluidity.

[0169] (5) Comparison with existing technologies

[0170] The heat distortion temperature of the existing technology (glass fiber / talc / POE system) represented by Comparative Example 6 is only 113°C, which is far lower than the 146-152°C of the present invention. More importantly, the heat distortion temperature of the existing technology is close to its technical limit (about 110-120°C) when it reaches 113°C, while the technical solution of the present invention still has room for further improvement (by optimizing the nucleating agent ratio and APAO / APP ratio).

[0171] (6) Dimensional stability analysis

[0172] As shown in Table 1, the longitudinal shrinkage rates of Examples 1-3 of the present invention are 0.4%, 0.3%, and 0.4%, respectively, and the transverse shrinkage rates are 0.9%, 0.8%, and 1.0%, respectively, all significantly lower than the 1.2% / 1.5% of Comparative Example 1 (pure PP). This indicates that the hybrid network formed by APP / APAO can effectively limit the shrinkage behavior of polypropylene molecular chains during the cooling process.

[0173] Compared to traditional reinforcement systems, the present invention also exhibits advantages in dimensional stability. The shrinkage rates of Comparative Example 4 (talc replacing APP) were 0.6% / 1.1%, Comparative Example 5 (glass fiber replacing APP) was 0.8% / 1.4%, and Comparative Example 6 (prior art) was 0.6% / 1.1%, while the shrinkage rate of Example 2 of the present invention was as low as 0.3% / 0.8%. Furthermore, the glass fiber system (Comparative Example 5) suffers from a much greater lateral shrinkage rate than longitudinal shrinkage rate due to the directional arrangement of the glass fibers, exhibiting anisotropy of 0.6%, making the product prone to warping and deformation; the present invention, however, is completely independent of glass fiber, fundamentally avoiding this problem.

[0174] The shrinkage rate of Comparative Example 3 (PP+APAO+APP, without composite nucleating agent) was 0.5% / 1.0%, which was higher than that of Example 2 (0.3% / 0.8%). This indicates that the composite nucleating agent further reduced the shrinkage rate and improved dimensional stability by refining PP grains and providing additional nucleation sites.

[0175] Industrial application

[0176] The heat-resistant polypropylene composition and its preparation method provided by this invention have broad prospects for industrial application, specifically in the following aspects:

[0177] (1) Automotive industry: The product of this invention can be applied to peripheral parts of automobile engines, such as engine cover, intake manifold, radiator fan, etc. These parts need to withstand high temperature environments above 120°C during long-term use.

[0178] (2) Household appliances: microwave ovens, tableware, rice cooker shells, induction cooker coil frames, and other applications requiring heat-resistant polypropylene.

[0179] (3) Electronic and electrical appliances: LED lamp heat dissipation components, power adapter housings and other components that have dual requirements for heat dissipation and heat resistance.

[0180] (4) Industrial pipelines: hot water pipeline systems, chemical pipelines and other application scenarios that require long-term heat aging resistance.

[0181] Furthermore, the preparation process of this invention is simple, does not involve complex equipment modifications, and can be directly implemented on existing twin-screw extrusion granulation production lines. All raw materials used can be routinely sourced in the domestic market, ensuring controllable raw material costs and making it suitable for large-scale industrial production.

[0182] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0183] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A heat-resistant polypropylene composition, characterized in that, The raw materials include the following by weight: 100 parts homopolymer polypropylene, 0.05-0.3 parts composite nucleating agent, 5-15 parts amorphous olefin copolymer, and 8-20 parts ammonium polyphosphate.

2. The heat-resistant polypropylene composition according to claim 1, characterized in that, The composite nucleating agent is a mixture of an α-crystal nucleating agent and a phosphate ester nucleating agent, with a mass ratio of 1:0.5-2.

3. The heat-resistant polypropylene composition according to claim 2, characterized in that, The α-crystal nucleating agent is selected from NP-657 nucleating agent; the phosphate ester nucleating agent is bis[2,2'-methylene-bis(4,6-di-tert-butylphenoxy)phosphate]aluminum hydroxyl.

4. The heat-resistant polypropylene composition according to claim 1, characterized in that, The amorphous olefin copolymer is a propylene-based amorphous olefin copolymer with a glass transition temperature of -20°C to -10°C and a weight-average molecular weight of 5000-20000.

5. The heat-resistant polypropylene composition according to claim 1, characterized in that, The ammonium polyphosphate has a degree of polymerization greater than 1000, and its mass ratio to the amorphous olefin copolymer in the composition is 1:0.5-1.

5.

6. A method for preparing the heat-resistant polypropylene composition according to any one of claims 1-5, characterized in that, Includes the following steps: (1) Homopolymer polypropylene, composite nucleating agent, amorphous olefin copolymer and ammonium polyphosphate are added into a high-speed mixer according to the proportion and mixed evenly to obtain a mixture; (2) Add the mixture to a twin-screw extruder for melt extrusion; (3) The extruded strip is cooled, granulated and dried to obtain a heat-resistant polypropylene composition.

7. The preparation method according to claim 6, characterized in that, The processing temperature of the twin-screw extruder in step (2) is 180-210℃, the screw speed is 200-400 rpm, and the vacuum degree is less than -0.06 MPa.

8. The use of the heat-resistant polypropylene composition according to any one of claims 1-5 or the heat-resistant polypropylene composition prepared by the preparation method according to any one of claims 6-7 in automotive engine peripheral parts, heat-resistant parts of household appliances, and electronic and electrical housings.

9. A method for increasing the heat distortion temperature of polypropylene, characterized in that, The homopolymer polypropylene is used as the matrix, and 0.05-0.3 parts of composite nucleating agent, 5-15 parts of amorphous olefin copolymer and 8-20 parts of ammonium polyphosphate are added for blending modification. The composite nucleating agent is a compound system of α-crystal nucleating agent and phosphate ester salt nucleating agent.

10. The method as described in claim 9, characterized in that, The amorphous olefin copolymer and ammonium polyphosphate form an organic-inorganic hybrid network structure during melt blending, which, together with the refined grains induced by the composite nucleating agent, constructs a multi-level heat-resistant barrier.