PP / PBAT composite material and preparation method thereof

Abstract

The application discloses a kind of PP / PBAT composite material and preparation method thereof, it is related to composite material field, raw material includes the following components according to mass fraction: polypropylene: 55~75 parts;Polybutylene adipate terephthalate: 25~45 parts;Maleic anhydride grafted polypropylene: 2~5 parts;Epoxy functional compatibilizer and / or epoxy functional chain extension agent: 0.2~1.5 parts;Antioxidant stabilizing system: 0.2~0.8 parts;The antioxidant stabilizing system at least includes hindered phenol antioxidant and phosphite antioxidant.The application can improve the compatibility of polypropylene and polybutylene adipate terephthalate, enhance interface bonding force while also improve the toughness and processing stability of composite material.

Description

Technical Field

[0001] This invention relates to the field of composite materials, specifically to a PP / PBAT composite material and its preparation method. Background Technology

[0002] Polypropylene (PP), a widely used thermoplastic resin, has advantages such as low density, chemical resistance, and ease of processing. However, it also has inherent defects in practical applications, such as insufficient toughness and significant low-temperature brittleness. Especially in the processing of films, sheets, and complex structural parts, the material's ductility is limited, and its performance is prone to degradation after repeated melting and processing.

[0003] To improve the mechanical properties of polypropylene, existing technologies attempt to introduce polybutylene terephthalate (PBAT) as a modifying component. This polyester material possesses both aliphatic flexible segments and aromatic rigid segments, theoretically enhancing the flexibility and impact resistance of the composite system. However, polypropylene and PBAT differ significantly in molecular polarity and thermodynamic compatibility, making it difficult to form a stable interfacial structure when directly blended. Although existing technologies employ maleic anhydride-grafted polypropylene or epoxy functional group additives for interfacial compatibilization, the synergistic reaction mechanism between compatibilizers and chain extenders has not been effectively established, resulting in insufficient interfacial chemical bonding and difficulty in simultaneously improving material toughness and rheological stability. Furthermore, the particle size control precision of the dispersed phase is limited, making it prone to thermo-oxidative aging or molecular chain breakage during secondary melt processing, leading to rapid deterioration of material properties and severely restricting the recycling of scrap materials and the adaptability to multiple product lines.

[0004] Therefore, how to achieve efficient blending of polypropylene and polybutylene terephthalate (PET) while simultaneously improving the toughness, processing stability, and secondary processing performance retention of the material is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This invention can solve one of the technical problems in related technologies to a certain extent. Therefore, this invention provides a PP / PBAT composite material and its preparation method, which can improve the compatibility of polypropylene and polybutylene terephthalate (PET), enhance interfacial bonding, and also improve the toughness and processing stability of the composite material.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A PP / PBAT composite material, the raw materials of which comprise the following components by mass parts: Polypropylene: 55-75 parts; Polybutylene terephthalate-adipate: 25-45 parts; Maleic anhydride-grafted polypropylene: 2-5 parts; Epoxy functional compatibilizer and / or epoxy functional chain extender: 0.2-1.5 parts; Antioxidant stabilizing system: 0.2-0.8 parts; The antioxidant stabilizing system includes at least hindered phenolic antioxidants and phosphite antioxidants.

[0007] In this application, through the synergistic effect of polypropylene, polybutylene terephthalate (PET), maleic anhydride-grafted polypropylene, epoxy functional compatibilizer, and antioxidant stabilizing system, the components of this composite material work together to solve the problems of insufficient toughness, large fluctuations in processing performance, and degradation of secondary processing performance in existing polypropylene materials. Compared with the simple blending of polypropylene and PET in the prior art, this application constructs a more efficient and stable interfacial compatibilization system by introducing a combination of maleic anhydride-grafted polypropylene and epoxy functional compatibilizer. Maleic anhydride-grafted polypropylene first establishes preliminary compatibility between polypropylene and PET, while the epoxy functional compatibilizer further strengthens the interfacial bonding, forming a tight chemical bond. This multiple compatibilization mechanism enables the PET dispersed phase to achieve a more uniform and fine dispersion in the polypropylene matrix, avoiding the common problems of two-phase separation, large particle size, and uneven distribution of the dispersed phase in the prior art. Furthermore, the antioxidant stabilizing system introduced into the composite material of this application, particularly the synergistic use of hindered phenolic antioxidants and phosphite antioxidants, provides comprehensive thermo-oxidative protection for the composite material, inhibiting polymer degradation during processing and thus improving the shortcomings of existing polypropylene materials, such as large fluctuations in processing performance and performance degradation after secondary processing. Moreover, after secondary melt reprocessing, the performance retention rate of this composite material remains at a high level, and the change rate of melt flow rate is effectively controlled. Therefore, through optimized component formulation and synergistic effects, this composite material not only significantly improves the toughness and impact resistance of the composite material, solving the inherent brittleness problem of PP materials, but also ensures the stability of the composite material during complex processing and its performance retention after multiple recycling and reprocessing.

[0008] Optionally, the polybutylene terephthalate (PET) is distributed as a dispersed phase in the composite material; the volume fraction of the dispersed phase is 20% to 50%, the particle size distribution D10 is ≥ 0.2 μm, the particle size distribution D90 is ≤ 6 μm, and the median particle size is 0.3 to 5.0 μm.

[0009] Optionally, the crystallinity of the composite material is 35% to 60%.

[0010] Optionally, after the composite material undergoes secondary melting and solidification, its notched impact strength retention rate is ≥70%, its tensile elongation at break retention rate is ≥60%, and its melt flow rate change rate is ≤20%.

[0011] Optionally, the melt flow rate of the polypropylene is 1-30 g / 10 min at 230°C and 2.16 kg load; the melt flow rate of the polybutylene terephthalate is 1-20 g / 10 min at 190°C and 2.16 kg load; and the epoxy equivalent of the epoxy functional compatibilizer and / or the epoxy functional chain extender is 150-1200 g / eq.

[0012] Optionally, the amount of the hindered phenolic antioxidant added is 0.05 to 0.30 parts, and the amount of the phosphite antioxidant added is 0.05 to 0.30 parts.

[0013] Optionally, the composite material is used to manufacture film products, the thickness of the film products being 20–200 μm, the tensile elongation at break being ≥350%, and the notched impact strength of the film products being ≥8 kJ / m²; the composite material is used to manufacture injection molded parts, the dimensional change rate of the injection molded parts being ≤1%.

[0014] Furthermore, this invention also provides a method for preparing a PP / PBAT composite material, comprising: S1, polypropylene is added to the pre-extrusion section of a twin-screw extruder for melting to obtain a pre-melt; S2, polybutylene terephthalate-adipate and maleic anhydride-grafted polypropylene are added to the pre-melt in the middle extrusion section of the twin-screw extruder for compatibilization reaction to obtain a compatibilized blend material; S3, epoxy functional compatibilizer and / or epoxy functional chain extender and antioxidant stabilizing system are added to the compatibilized blend material in the rear extrusion section of the twin-screw extruder for melt mixing, extrusion granulation to obtain granules; wherein, the granules are the aforementioned PP / PBAT composite material; the extrusion temperature of the twin-screw extruder is 160-220℃, the screw speed is 100-600rpm, and the material residence time is 20-180s.

[0015] Optionally, step S2 specifically includes: first preparing a premixed masterbatch from the polybutylene terephthalate-adipate and the maleic anhydride-grafted polypropylene, and then adding the premixed masterbatch into the premelt from the side feed port of the extrusion section.

[0016] Optionally, in step S3, the pressure fluctuation of the compatibilizing blend is ≤15%, and the melt flow rate uniformity of the granules is ≥95%.

[0017] These features and advantages of the present invention will be disclosed in detail in the following specific embodiments and accompanying drawings. The preferred embodiments or means of the present invention will be shown in detail in conjunction with the accompanying drawings, but are not intended to limit the technical solutions of the present invention. In addition, each of these features, elements and components appearing in the following text and drawings is a plurality of, and different symbols or numbers are used for convenience of representation, but all represent parts with the same or similar construction or function. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the preparation method of the PP / PBAT composite material in this invention. Detailed Implementation

[0019] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described are intended to explain the present invention and should not be construed as limiting it.

[0020] The terms "an embodiment," "example," or "trademark" used in this specification refer to a particular feature, structure, or characteristic described in connection with the embodiment itself that may be included in at least one embodiment disclosed in this patent. The phrase "in an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0021] In a mixture of polypropylene and polybutylene terephthalate (PET), polypropylene is a non-polar semi-crystalline polymer, while PET contains polar functional groups such as ester groups in its molecular chain. The poor thermodynamic compatibility between the two leads to large and unevenly distributed dispersed phase particles, resulting in insufficient interfacial bonding in the composite material. This, in turn, reduces stress transfer efficiency, decreases mechanical property stability, increases melt flow fluctuations during processing, and increases surface defects in the finished product. Furthermore, the interfacial structure of this composite material is easily damaged by thermo-oxidative aging and molecular chain breakage during secondary melting and reprocessing, causing performance degradation.

[0022] For example, when using polypropylene / polybutylene terephthalate (PP / PBAT) composite materials to prepare film products on a film blow molding production line, the PP / PBAT dispersed phase often forms localized stress concentration points due to poor particle size control. During extrusion, melt pressure fluctuations exceed process tolerances, leading to fisheyes and holes on the film surface. The material is also prone to breakage during stretching, failing to meet the requirements for film thickness uniformity and thus limiting production efficiency. Furthermore, this phenomenon is even more pronounced in injection molding of complex structural parts, where uneven dispersion of the dispersed phase causes a decrease in dimensional stability and a deterioration in the surface finish of the parts, affecting the assembly accuracy of the final product.

[0023] If the above problems are not solved, the interfacial chemical bonding efficiency of PP / PBAT composite materials will continue to decrease during the cyclic processing, and the mechanical properties will deteriorate rapidly, making it impossible to maintain the performance stability after multiple recycling and reprocessing. At the same time, the wide particle size distribution of the dispersed phase will lead to uncontrollable rheological behavior, making it difficult to match the processing requirements of different products and limiting the application of this composite material in many fields such as films, sheets, injection molding and blow molding.

[0024] Example: This example presents a PP / PBAT composite material, the raw materials of which include the following components by mass parts: Polypropylene: 55-75 parts; Polybutylene terephthalate (PET): 25-45 parts; Maleic anhydride-grafted polypropylene: 2-5 parts; Epoxy functional compatibilizer and / or epoxy functional chain extender: 0.2 to 1.5 parts; Antioxidant stabilizing system: 0.2–0.8 parts; The antioxidant stabilizing system includes at least hindered phenolic antioxidants and phosphite antioxidants.

[0025] In this embodiment, the PP / PBAT composite material is a polymer blend mainly composed of polypropylene (PP) and polybutylene terephthalate (PBAT). It combines the advantages of both polymers to obtain a novel material with a specific balance of properties, such as improved toughness, processing stability, and recyclability. The preparation of this composite material involves the precise proportioning of various components. Polypropylene is the matrix component of this composite material, characterized by low density, chemical resistance, excellent electrical insulation properties, and low cost. It provides rigidity and heat resistance in the composite material. The mass fraction of polypropylene as the matrix material ranges from 55 to 75 parts. Homopolymer or copolymer polypropylene with different melt flow rates can be selected; for example, polypropylene with a melt flow rate of 5 g / 10 min or 6 g / 10 min can be used. By adjusting the polypropylene content, the overall rigidity and cost of the composite material can be controlled.

[0026] Polybutylene terephthalate (PET) is the dispersed phase component of this composite material. It exhibits high elongation at break, good flexibility and processability, and possesses certain biodegradability, thus enhancing the toughness and impact resistance of the composite material. Specifically, PET is used as the dispersed phase, with a mass fraction ranging from 25 to 45 parts. PET can be selected from polyesters with different melt flow rates; for example, PET with a melt flow rate of 12 g / 10 min or PET with a melt flow rate of 10 g / 10 min can be used to impart good flexibility and biodegradability to the composite material.

[0027] Maleic anhydride-grafted polypropylene is a grafted compatibilizer formed by grafting maleic anhydride onto the polypropylene molecular chain. It improves the interfacial compatibility between polypropylene and polybutylene terephthalate (PET), promoting uniform dispersion and interfacial bonding between the two phases. Specifically, the mass fraction of maleic anhydride-grafted polypropylene ranges from 2 to 5 parts. As an interfacial compatibilizer, it promotes the compatibility between non-polar polypropylene and polar PET. For example, maleic anhydride-grafted polypropylene can be directly blended with polypropylene and PET to form physical or chemical interactions at the interface between the two phases, thereby improving the distribution of the dispersed phase.

[0028] Epoxy functional compatibilizers and / or epoxy functional chain extenders are both oligomers or copolymers containing epoxy groups. The mass fraction range of the epoxy functional compatibilizers and / or epoxy functional chain extenders is 0.2 to 1.5 parts. Both contain reactive epoxy groups, capable of reacting with the end groups or ester bonds of polybutylene terephthalate (PET). Epoxy functional compatibilizers enhance interfacial bonding, while epoxy functional chain extenders increase the molecular weight of the polymer through chain extension reactions. For example, epoxy functional compatibilizers or epoxy chain extenders can be selected and directly added to the blend system.

[0029] Antioxidant stabilizing systems protect composite materials from degradation caused by heat, oxygen, and other factors during processing and use. By inhibiting free radical reactions, they maintain the molecular structural integrity of the composite material, thereby ensuring its mechanical properties and processing stability. Specifically, the mass fraction of the antioxidant stabilizing system ranges from 0.2 to 0.8 parts. This system protects the composite material from oxidative degradation during high-temperature processing and long-term use. For example, only one antioxidant can be added, or a combination of multiple antioxidants can be used.

[0030] In addition, the antioxidant stabilization system includes at least hindered phenolic antioxidants and phosphite antioxidants. Hindered phenolic antioxidants are primary antioxidants that interrupt the oxidation chain reaction by capturing free radicals, providing long-lasting thermo-oxidative stability. Phosphite antioxidants are secondary antioxidants that prevent further free radical reactions by decomposing hydroperoxides, providing thermal stability during processing. The two work synergistically to provide more comprehensive antioxidant protection. Furthermore, the hindered phenolic antioxidant, as the primary antioxidant, mainly captures free radicals; the phosphite antioxidant, as the secondary antioxidant, mainly decomposes hydroperoxides. For example, 0.1 parts of hindered phenolic antioxidant and 0.1 parts of phosphite antioxidant, or 0.2 parts of hindered phenolic antioxidant and 0.2 parts of phosphite antioxidant, can be added respectively. The synergistic effect of the two antioxidants provides more comprehensive thermo-oxidative stability to the composite material, thereby extending the material's service life and improving processing stability.

[0031] Polybutylene terephthalate (PET) is distributed as the dispersed phase in the composite material; the volume fraction of the dispersed phase is 20% to 50%, the particle size distribution D10 ≥ 0.2 μm, the particle size distribution D90 ≤ 6 μm, and the median particle size is 0.3 to 5.0 μm.

[0032] If the dispersion and particle size distribution of polybutylene terephthalate (PET) in the composite material are poor, the mechanical properties of the composite material, especially its toughness and ductility, may not meet expectations, affecting its performance as a film product or injection molded part. Therefore, in this embodiment, PET is distributed as a dispersed phase in the composite material, that is, PET exists in a discrete and discontinuous phase state in the polypropylene matrix. The formation of this dispersed phase is due to the incompatibility of the two polymers. As a dispersed phase, PET can absorb and disperse stress, thereby improving the toughness and impact resistance of the composite material. This dispersed phase can be achieved by controlling blending process parameters, such as shear rate, temperature, and residence time, and by adding compatibilizers to adjust the interfacial tension between the two phases, promoting the uniform dispersion of PET in the polypropylene matrix. Another approach is to select polymer components with appropriate viscosity ratios so that polybutylene terephthalate (PET) can be sheared into fine droplets during processing and maintain this dispersion after cooling and solidification.

[0033] Specifically, the volume fraction of the dispersed phase is 20%–50%, meaning that polybutylene terephthalate (PET) accounts for 20%–50% of the total volume of the composite material. This volume fraction range ensures that the composite material maintains the excellent properties of the polypropylene matrix while fully utilizing the toughening effect of PET. If the volume fraction is too low, the toughening effect will be insignificant; if the volume fraction is too high, it may lead to a decrease in the rigidity of the material, or even a phase transformation, affecting the overall mechanical balance of the material. It should be noted that this volume fraction can be achieved by controlling the amount of PET added, for example, by using a metering feeding system to ensure that each component is added in a preset ratio. Alternatively, the volume fraction can be indirectly calculated and verified by adjusting the density of the composite material and the density of each component.

[0034] The dispersed phase has a particle size distribution D10 ≥ 0.2 μm, a particle size distribution D90 ≤ 6 μm, and a median particle size of 0.3–5.0 μm. These particle size parameters collectively define the size range and uniformity of the dispersed phase. D10 indicates that 10% of the dispersed phase particles have a particle size smaller than this value, and D90 indicates that 90% of the dispersed phase particles have a particle size smaller than this value. In this application, the dispersed phase has D10 ≥ 0.2 μm, D90 ≤ 6 μm, and a median particle size of 0.3–5.0 μm. For example, D10 ≥ 0.2 μm means that the value of D10 is greater than or equal to 0.2 μm. Since D10 is defined as "10% of the particles have a particle size smaller than this value", D10 ≥ 0.2 μm means that 10% of the particles may have a particle size of 0.2 μm, or it may have a particle size of 0.3, 0.4, etc. A median particle size of 0.3–5.0 μm indicates that 50% of the dispersed phase particles have a particle size less than or equal to this value.

[0035] Appropriate particle size distribution is crucial for the mechanical properties of composite materials. Particles that are too small may not effectively absorb energy, resulting in minimal toughening; while particles that are too large may become stress concentration points, reducing the material's strength and toughness. Therefore, controlling the particle size of the dispersed phase can optimize stress transmission, thereby improving the toughness and impact resistance of the composite material. Achieving an ideal particle size distribution can be done in several ways. For example, adjusting the screw configuration, shear strength, and rotational speed of the twin-screw extruder can provide sufficient shear force to refine the dispersed phase. Additionally, selecting appropriate types and amounts of compatibilizers, such as maleic anhydride-grafted polypropylene, can reduce interfacial tension, inhibit agglomeration of the dispersed phase, and thus stabilize the fine dispersed phase particle size.

[0036] In summary, this application achieves control over the microstructure of the composite material by distributing polybutylene terephthalate (PET) as the dispersed phase in the composite material and controlling the volume fraction of this dispersed phase between 20% and 50%, while limiting its particle size distribution to D10 ≥ 0.2 μm, D90 ≤ 6 μm, and median particle size of 0.3–5.0 μm. During melt blending, PET forms discrete island-like structures in the polypropylene matrix. Maleic anhydride-grafted polypropylene, as a compatibilizer, reduces the interfacial tension between polypropylene and PET, promoting the refinement and uniform dispersion of PET in the polypropylene matrix. Epoxy functional compatibilizers further enhance the interfacial bonding between the two phases, and epoxy functional chain extenders can also increase the molecular weight of PET through reactions with its end groups, thereby stabilizing the morphology of the dispersed phase. Furthermore, by controlling the volume fraction of the dispersed phase within the range of 20% to 50%, sufficient polybutylene terephthalate (PET) can be ensured to provide a toughening effect, while avoiding a significant decrease in material rigidity due to excessive PET content. More importantly, by precisely controlling the particle size distribution of the dispersed phase—D10 ≥ 0.2 μm, D90 ≤ 6 μm, and a median particle size of 0.3–5.0 μm—the dispersed phase particles exist at an optimal size. This allows the PET particles to absorb a large amount of impact energy when the composite material is under stress, thereby preventing crack propagation. Consequently, the toughness and ductility of the composite material are significantly improved, overcoming the problem of insufficient mechanical properties that may result from simple blending.

[0037] The crystallinity of the composite material is 35% to 60%.

[0038] The overall mechanical properties of composite materials are often significantly influenced by their internal microstructure, especially their crystallization behavior. Improper crystallinity control can lead to unsatisfactory overall performance, such as insufficient rigidity or decreased toughness, affecting their performance in specific applications. Therefore, in this embodiment, the crystallinity of the composite material is limited. Crystallinity refers to the proportion of crystalline regions in the polymer material; this value measures the degree of order in the material's internal structure. The level of crystallinity directly affects the material's mechanical, thermal, and processability properties. Furthermore, crystallinity can be determined using techniques such as differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), or density methods. For example, DSC can measure the heat of fusion of the material and compare it with the heat of fusion of a fully crystalline polymer to calculate the crystallinity. Further details are omitted here.

[0039] Specifically, the crystallinity of composite materials can be controlled in various ways. For example, during the preparation of composite materials, the crystallinity can be affected by controlling the cooling rate; a slower cooling rate promotes higher crystallinity, while a faster cooling rate tends to result in lower crystallinity. Furthermore, the crystallization process can be promoted by adding nucleating agents, thereby affecting crystal size and crystallinity. Nucleating agents can provide more crystal nuclei, increasing the number of crystals while reducing their size, thus affecting the overall crystallinity. Simultaneously, processing parameters such as melt temperature, shear rate, and subsequent heat treatments (such as annealing) also significantly influence the crystallization behavior of composite materials.

[0040] Furthermore, this application controls the crystallinity of the composite material within the range of 35% to 60%, enabling the polypropylene matrix to form a moderately crystalline structure. This ensures that the composite material maintains good toughness and impact resistance while possessing sufficient rigidity and strength. If the crystallinity is too low, the resulting composite material may be too soft, leading to insufficient mechanical strength; if the crystallinity is too high, the material may become brittle and hard, reducing its impact toughness. Therefore, this crystallinity range, combined with the specific volume fraction and particle size distribution of polybutylene terephthalate (PET) as the dispersed phase, jointly optimizes the microstructure of the composite material, thereby achieving a comprehensive mechanical property that balances rigidity and toughness. This synergistic effect allows the composite material to better adapt to the stringent performance requirements of various application scenarios, and this can not be determined by a limited number of experiments.

[0041] Specifically, the crystallinity of the composite material can be controlled during the cooling process after extrusion granulation. For example, after extrusion granulation in a twin-screw extruder, the molten composite material strands are introduced into a temperature-controlled cooling water bath. By adjusting the temperature of the water bath (e.g., maintained between 20°C and 50°C) and the residence time of the strands in the water bath, the cooling rate of the composite material can be controlled, thereby affecting its crystallization process. Alternatively, an appropriate amount of nucleating agent, such as talc or a specific organic nucleating agent, can be introduced into the composite material formulation to promote heterogeneous nucleation of the polypropylene phase, thereby controlling the crystallinity of the composite material within the range of 35% to 60% under set cooling conditions.

[0042] After the aforementioned composite material undergoes secondary melting and solidification, its notched impact strength retention rate is ≥70%, its tensile elongation at break retention rate is ≥60%, and its melt flow rate change rate is ≤20%.

[0043] In practical applications, composite materials may require multiple processing or recycling processes, such as secondary melt-forming. During these processes, the material often degrades due to thermal history and shear stress, leading to a significant decrease in its mechanical properties and processing stability, thus limiting its application range and recycling value. However, the PP / PBAT composite material provided in this embodiment exhibits excellent secondary processing performance. After secondary melt-reprocessing, its notched impact strength retention rate is ≥70%, tensile elongation at break retention rate is ≥60%, and melt flow rate change rate is ≤20%, indicating that the material's performance degradation is significantly reduced during recycling and reprocessing, demonstrating good recyclability and cycle processing stability. This is beneficial for the recycling of scrap materials and meets environmental protection and sustainable development requirements.

[0044] "After secondary melting and solidification of composite materials" refers to the process where, after a composite material has undergone primary molding, it is heated to a molten state and then cooled and solidified. This process can simulate the recycling or multiple processing scenarios of composite materials. For example, composite material products (such as scraps or waste parts) after initial molding can be crushed, granulated, and then subjected to injection molding, extrusion, or blow molding. Under laboratory conditions, the secondary melting process can also be simulated through multiple melt flow index tests or cyclic extrusion using a small extruder.

[0045] "Notched impact strength retention rate ≥70%" indicates that after secondary melting and solidification, the composite material's ability to resist impact loads, even in the presence of stress concentration (notches), shows minimal loss relative to its initial properties, maintaining high toughness. By optimizing the composite material's composition, such as adjusting the type and amount of compatibilizer and improving the effectiveness of the antioxidant stabilization system, it is possible to suppress polymer chain degradation during secondary melting, maintain the material's molecular weight, and ensure stable impact performance, thereby achieving the goal of "notched impact strength retention rate ≥70%".

[0046] "Tensile elongation at break retention ≥60%" indicates the ability of a composite material to undergo plastic deformation under tensile load until fracture after secondary melting and solidification, with minimal loss of initial properties and still exhibiting good flexibility and resistance to deformation. Specifically, by selecting polymer matrices and dispersed phases with good thermal stability and incorporating an efficient antioxidant stabilizing system to reduce thermal oxidative degradation, the polymer chain structure can be protected, maintaining its ductility, thereby achieving the goal of "tensile elongation at break retention ≥60%".

[0047] "Mel flow rate change rate ≤ 20%" indicates that the processing fluidity of the composite material changes little relative to its initial properties after secondary melting and solidification. Melt flow rate (MFR) is an important indicator for measuring the processing fluidity of polymers. A change rate ≤ 20% indicates that the material maintains good stability in processing performance after secondary melting, avoiding abnormal fluidity caused by a significant decrease in molecular weight or cross-linking. By precisely controlling the composition and dosage of the antioxidant stabilizing system, degradation or cross-linking reactions of the polymer during high-temperature melting can be suppressed, stabilizing the molecular weight of the material and thus achieving the ideal melt flow rate change rate.

[0048] In summary, after secondary melting and solidification, the aforementioned composite material exhibits consistent retention rates of notched impact strength, tensile elongation at break, and melt flow rate, ensuring performance stability during repeated processing and recycling. During the composite material preparation process, precise control of the proportions of polypropylene, polybutylene terephthalate-adipate, maleic anhydride-grafted polypropylene, epoxy functional compatibilizer and / or epoxy functional chain extender, and antioxidant stabilizing system ensures excellent overall performance from the initial molding stage. When the composite material undergoes secondary melting and solidification, its internal antioxidant stabilizing system effectively inhibits thermal oxidative degradation of the polymer chains under high temperature and shear stress, thereby protecting the molecular weight and structural integrity of the polymer. Meanwhile, epoxy functional compatibilizers and / or epoxy functional chain extenders can, to some extent, repair or inhibit the decrease in molecular weight caused by degradation, and may even increase the molecular weight through chain extension, further stabilizing the mechanical and processing properties of the composite material. This ensures that the notched impact strength and tensile elongation at break of the material remain at a high level after secondary processing. Furthermore, strictly controlling the melt flow rate change indicates that the molecular weight and rheological behavior of the material remain relatively stable after secondary processing, facilitating subsequent molding and processing.

[0049] The verification process for the retention rate of the composite material's secondary processing properties is as follows: First, the composite material is injection molded or extruded into standard samples, and its initial notched impact strength, tensile elongation at break, and melt flow rate are tested. Then, these initially molded composite material samples are pulverized and subjected to secondary melt granulation using a twin-screw extruder to simulate the recycling process. The granulated material is then injection molded again into new standard samples. These secondary-molded samples are then tested again for notched impact strength and tensile elongation at break, and their melt flow rate is measured. By comparing the properties after secondary molding with the initial properties, the retention rate and change rate of each property are calculated. For example, if the initial notched impact strength is 10 kJ / m², and after secondary melting it is 7.5 kJ / m², the retention rate is 75%, meeting the requirement of ≥70%. Similarly, the changes in tensile elongation at break and melt flow rate should also meet the corresponding retention rate and change rate requirements.

[0050] The melt flow rate of polypropylene is 1–30 g / 10 min at 230 °C and 2.16 kg load; the melt flow rate of polybutylene terephthalate is 1–20 g / 10 min at 190 °C and 2.16 kg load; and the epoxy equivalent of the epoxy functional compatibilizer and / or chain extender is 150–1200 g / eq.

[0051] In the actual preparation process of this composite material, if the rheological properties and reactivity of each component are not precisely controlled, uneven melt blending and insufficient compatibility may occur, thereby affecting the processing performance, microstructure, and mechanical properties and stability of the final product. Melt flow rate is an indicator of the fluidity of a polymer in its molten state under specific temperature and load conditions, reflecting the polymer's molecular weight and processing performance. In this embodiment, the melt flow rate of polypropylene is limited to 1–30 g / 10 min, ensuring suitable fluidity during melt processing. If the melt flow rate is too low, the polypropylene melt viscosity will be too high, potentially leading to mixing difficulties, excessive shear heat, or even degradation. Conversely, if the melt flow rate is too high, the polypropylene melt viscosity will be too low, potentially resulting in insufficient shear force in the blend system, making it difficult to form a fine dispersed phase structure, and possibly affecting the mechanical properties of the final material. Therefore, selecting polypropylene within this range ensures good operability during extrusion, injection molding, and other processing, and facilitates uniform mixing with other components. For example, general-purpose polypropylene with a melt flow rate of 5-15 g / 10 min can be selected, or high-flowability polypropylene with a melt flow rate of 15-25 g / 10 min can be selected. It should be noted that "the melt flow rate of polypropylene at 230℃ and a load of 2.16 kg is 1-30 g / 10 min" means that when polypropylene is heated to 230℃ and a 2.16 kg weight is applied downwards, the mass flowing out within 10 minutes is measured to be 1-30 grams. Similarly, "the melt flow rate of polybutylene terephthalate (PET) at 190℃ and a load of 2.16 kg is 1-20 g / 10 min" means that when PET is heated to 190℃ and a 2.16 kg weight is applied downwards, the mass flowing out within 10 minutes is measured to be 1-20 grams.

[0052] The melt flow rate of polybutylene terephthalate (PET) is also used to measure its melt flowability. In this embodiment, the melt flow rate range of PET is limited to 1–20 g / 10 min. This ensures that its melt viscosity matches that of polypropylene when blended, thereby forming a uniform and appropriately sized dispersed phase under shear. If the melt flow rate of PET is too low, its melt viscosity may differ too much from that of polypropylene, leading to difficulty in dispersion and the formation of a coarse dispersed phase. If the melt flow rate is too high, PET may be over-dispersed under shear or easily agglomerate during subsequent processing, affecting the toughness of the final material. Therefore, selecting this range of PET is beneficial for optimizing the viscosity ratio of the two phases, promoting good dispersion of PET in the polypropylene matrix, and thus improving the overall performance of the composite material. For example, polybutylene terephthalate with a melt flow rate of 5 to 10 g / 10 min or polybutylene terephthalate with a melt flow rate of 10 to 15 g / 10 min can be selected.

[0053] Epoxy equivalent refers to the number of grams of epoxy resin containing 1 mol of epoxy groups, reflecting the content and reactivity of epoxy functional groups. The epoxy equivalent of epoxy functional compatibilizers and / or epoxy functional chain extenders is limited to 150–1200 g / eq to ensure suitable reactivity, allowing for sufficient reaction with the end groups of polypropylene and polybutylene terephthalate (PPT) or the functional groups grafted onto polypropylene with maleic anhydride, achieving compatibilization or chain extension. If the epoxy equivalent is too low and the reactivity is too high, the reaction may be too vigorous, leading to local crosslinking or degradation that is difficult to control; if the epoxy equivalent is too high and the reactivity is insufficient, it will be difficult to form an interfacial compatibility layer or achieve chain extension, resulting in poor compatibilization. Therefore, selecting an epoxy equivalent within this range ensures that the compatibilizer and / or epoxy functional chain extender can react appropriately during melt blending, improving the interfacial bonding between polypropylene and PTT and enhancing the mechanical properties of the composite material. For example, epoxy functional compatibilizers with an epoxy equivalent of 200-500 g / eq can be selected, or epoxy functional chain extenders with an epoxy equivalent of 600-1000 g / eq can be selected.

[0054] This application optimizes the melt processing behavior and compatibility of PP / PBAT composites by controlling the melt flow rates of polypropylene and polybutylene terephthalate (PP-PBAT), as well as the epoxy equivalent of the epoxy functional compatibilizer and / or epoxy functional chain extender. Specifically, limiting the melt flow rate of polypropylene to 1–30 g / 10 min ensures good processing fluidity in the molten state, avoiding mixing difficulties due to excessively high viscosity or insufficient shear due to excessively low viscosity. Simultaneously, limiting the melt flow rate of PP-PBAT to 1–20 g / 10 min maintains a suitable ratio between its melt viscosity and that of polypropylene at the processing temperature. This viscosity matching is crucial for forming a uniform PP-PBAT dispersion with appropriate particle size under shear stress, preventing the dispersion from being too large or too small, thus contributing to improved composite toughness. Based on this, by controlling the epoxy equivalent of the epoxy functional compatibilizer and / or epoxy functional chain extender at 150–1200 g / eq, moderate reactivity is ensured. This compatibilizer and / or epoxy functional chain extender can react with the anhydride groups on maleic anhydride-grafted polypropylene and the terminal hydroxyl or carboxyl groups of polybutylene terephthalate (PET) during melt blending to form copolymers or grafts. This creates an effective interfacial layer at the interface between the polypropylene and PET phases, enhancing the bonding between the two phases and stabilizing the morphology of the dispersed phase. Through the combined effect of the specific parameters of the above components, the composite material can achieve more uniform blending, finer phase dispersion, and stronger interfacial bonding during processing, thereby significantly improving the overall performance of the composite material.

[0055] The amount of hindered phenolic antioxidant added is 0.05 to 0.30 parts.

[0056] Although the antioxidant stabilizing system is specified to include at least hindered phenolic antioxidants and phosphite antioxidants, the lack of clarity regarding the specific addition amounts of these two key antioxidants may lead to difficulties in precisely controlling the processing stability of the composite material in practical applications, thereby affecting the overall performance and service life of the material. Hindered phenolic antioxidants, as the main antioxidants, can capture free radicals generated during polymer degradation, thereby interrupting the oxidation chain reaction and providing excellent long-term thermal stability to the composite material, especially at high temperatures. For example, pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] or octadecyl-β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate can be selected. By controlling the addition amount of hindered phenolic antioxidants within the range of 0.05 to 0.30 parts, sufficient antioxidant capacity of the composite material can be ensured during long-term use, while avoiding precipitation, migration, or adverse effects on other material properties that may be caused by excessive addition. This embodiment also proposes an addition amount of phosphite antioxidants of 0.05 to 0.30 parts. Phosphite antioxidants, acting as auxiliary antioxidants, can decompose hydroperoxides formed during polymer oxidation. Therefore, phosphite antioxidants can provide melt stabilization during polymer processing (such as melt extrusion), preventing degradation of the composite material under high-temperature shear conditions. For example, tris(2,4-di-tert-butylphenyl) phosphite or bis(2,4-dicumylphenyl)pentaerythritol diphosphite can be used. Controlling the amount of phosphite antioxidant added within the range of 0.05–0.30 parts can inhibit material degradation during processing, maintain melt viscosity stability, and form a synergistic effect with hindered phenolic antioxidants, jointly improving the antioxidant properties of the composite material.

[0057] In summary, by clearly defining the addition amounts of hindered phenolic antioxidants and phosphite antioxidants, the processing stability and long-term thermal oxidation stability of PP / PBAT composites are improved while maintaining their original excellent properties. This avoids problems such as molecular weight reduction, mechanical property loss, and melt flow rate fluctuations caused by oxidative degradation during high-temperature processing, ensuring the uniformity and stability of product quality. Simultaneously, this approach significantly extends the service life of composite products, enabling them to better resist performance degradation caused by environmental factors during long-term service, thereby improving the reliability and application value of the material.

[0058] The above-mentioned composite material is used to manufacture film products with a thickness of 20-200 μm, a tensile elongation at break of ≥350%, and a notched impact strength of ≥8 kJ / m². The composite material is also used to manufacture injection molded parts with a dimensional change rate of ≤1%.

[0059] In this embodiment, the composite material can be used to manufacture film products. These film products require materials with good processing flowability, excellent flexibility, and sufficient mechanical strength. This can be achieved through methods including, but not limited to, blown film extrusion, cast film extrusion, or calendering. The thickness of the manufactured film products is 20–200 μm, defining a typical thickness range. Within this thickness range, the composite material needs to possess good melt strength and tensile properties to ensure that it maintains structural integrity and mechanical properties even at thin dimensions. This thickness range can be achieved by precisely controlling extrusion process parameters (e.g., die gap, draw ratio, and blow-up ratio) and optimizing the material's rheological properties. A tensile elongation at break ≥350% characterizes the material's ductility and toughness. High tensile elongation at break helps prevent premature film breakage under stress or deformation. Achieving this property depends on optimizing the phase structure in the polymer blend, such as the formation of a fine and uniform dispersed phase of polybutylene terephthalate (PET) in a polypropylene matrix, and good interfacial bonding between the two phases. The notched impact strength of thin film products is ≥8 kJ / m², reflecting the material's resistance to impact and puncture. High notched impact strength is crucial for improving the durability and reliability of thin films. This performance is achieved through optimized phase structure, enhanced interfacial adhesion, and the inherent toughness of polybutylene terephthalate (PET).

[0060] Composite materials can be used to manufacture injection-molded parts. Injection-molded parts require materials with good flowability, dimensional stability, and sufficient mechanical strength, which can be achieved through methods including but not limited to standard injection molding processes. A dimensional change rate of ≤1% in the manufactured injection-molded parts characterizes the dimensional stability of the part after molding. A low dimensional change rate (including shrinkage and warpage) is crucial for meeting the tolerance requirements of precision components. This performance can be achieved by controlling the material's crystallization behavior, minimizing internal stress, and optimizing injection molding parameters (such as temperature, pressure, and cooling rate).

[0061] By applying the aforementioned PP / PBAT composite material to specific products and strictly defining its performance, the problem of insufficient performance of existing composite materials in specific high-requirement applications is solved. Specifically, the components of this composite material (polypropylene, polybutylene terephthalate-adipate, maleic anhydride-grafted polypropylene, epoxy functional compatibilizer and / or epoxy functional chain extender, and antioxidant stabilizing system) are optimized in proportion, allowing polybutylene terephthalate-adipate to be dispersed in the polypropylene matrix in a controlled manner, and enhancing the interfacial bonding between the two phases through the action of the compatibilizer. The optimized microstructure endows the composite material with excellent toughness and ductility, enabling it to achieve high performance indicators such as tensile elongation at break ≥350% and notched impact strength ≥8kJ / m² when preparing film products with a thickness of 20-200μm. The high tensile elongation at break ensures that the film is not easily broken during stretching or deformation, while the high notched impact strength improves the film's puncture resistance and impact resistance. Meanwhile, for injection molded parts, the good flowability and controlled crystallization behavior of this composite material help reduce internal stress during the molding process, thereby ensuring that the injection molded parts have excellent dimensional stability with a dimensional change rate of ≤1%, meeting the dimensional accuracy requirements of precision parts.

[0062] like Figure 1 As shown in the figure, this embodiment also provides a method for preparing PP / PBAT composite material, which can solve the technical problems in the prior art such as poor compatibility between polypropylene and polybutylene terephthalate, large and uneven particle size of dispersed phase, insufficient interfacial bonding force, and rapid decay of performance after secondary melting and reprocessing. The preparation method includes the following steps: First, polypropylene is added to the front section of a twin-screw extruder for melting to obtain a pre-melt; second, polybutylene terephthalate-adipate and maleic anhydride-grafted polypropylene are added to the pre-melt in the middle section of the twin-screw extruder for compatibilization reaction to obtain a compatibilized blend; finally, epoxy functional compatibilizer and / or epoxy functional chain extender and antioxidant stabilizing system are added to the compatibilized blend in the rear section of the twin-screw extruder for melt mixing, extrusion granulation, and obtaining granules; wherein, the granules are the above-mentioned PP / PBAT composite material; the extrusion temperature of the twin-screw extruder is 160-220℃, the screw speed is 100-600rpm, and the material residence time is 20-180s.

[0063] This embodiment combines a staged addition of polypropylene, polybutylene terephthalate (PET), and maleic anhydride-grafted polypropylene with a reaction compatibilization process, and introduces an epoxy functional compatibilizer and / or epoxy functional chain extender and an antioxidant stabilizing system in the later stage of the twin-screw extruder. This achieves uniform and fine dispersion of the PET phase in the polypropylene matrix and interfacial chemical bonding. Specifically, the pre-extrusion stage is used only for melt polypropylene to avoid thermal degradation caused by premature addition of PET; the mid-extrusion stage adds PET and maleic anhydride-grafted polypropylene for interfacial reaction compatibilization, promoting fine dispersion of the PET phase and forming preliminary interfacial bonding; the post-extrusion stage adds an epoxy functional compatibilizer and / or epoxy functional chain extender to further strengthen interfacial chemical bonding, while the antioxidant stabilizing system inhibits thermo-oxidative degradation. In addition, by controlling the extrusion temperature, screw speed and material residence time, the median particle size of the polybutylene terephthalate dispersion phase can be ensured to be 0.3 to 5.0 μm, and the interfacial chemical bonding efficiency is high, thereby significantly improving the toughness, processing stability and the retention rate of secondary melt reprocessing performance of the composite material.

[0064] During implementation, the polypropylene can be selected as homopolymer or copolymer polypropylene at 230℃ and 2.16kg conditions, with a yield of 1–30 g / 10 min. The polybutylene terephthalate (PET) can be selected as a biodegradable polyester at 190℃ and 2.16kg conditions, with a yield of 1–20 g / 10 min. The epoxy equivalent of the epoxy functional compatibilizer and / or epoxy functional chain extender is 150–1200 g / eq. The amount of hindered phenolic antioxidant and phosphite antioxidant added to the antioxidant stabilization system is 0.05–0.30 parts. Furthermore, to improve interfacial reaction efficiency and reduce side reactions, PET and maleic anhydride grafted polypropylene can be pre-prepared as a masterbatch and fed into the intermediate section. During the extrusion process, the melt pressure fluctuation must be controlled to be no more than 15% to ensure that the particle size distribution of the polybutylene terephthalate-adipate dispersed phase is D10≥0.2μm and D90≤6μm, forming a uniform phase distribution structure.

[0065] Adding these two components directly to the high-temperature polypropylene premelt in solid form, either separately or simultaneously, may lead to uneven feeding, excessively high local concentrations, or insufficient dispersion, thereby affecting the efficiency of the reaction compatibilization and the performance stability of the final composite material. Therefore, in this embodiment, step S2 specifically includes: first preparing a premixed masterbatch from polybutylene terephthalate-adipate and maleic anhydride-grafted polypropylene, and then adding the premixed masterbatch to the premelt from the side feed port of the extrusion section.

[0066] Premixed masterbatch refers to an intermediate product formed by pre-mixing two or more components evenly. By pre-preparing polybutylene terephthalate (PET) and maleic anhydride-grafted polypropylene into masterbatch, it is ensured that these two key reactive components reach a highly uniform mixing state before being added to the extruder. This helps avoid insufficient or excessive local reactions caused by uneven feeding or poor dispersion during extrusion. Methods for preparing premixed masterbatch include, but are not limited to, dry mixing using a high-speed mixer or melt blending and granulation. The side feed port is an auxiliary feed port on a twin-screw extruder used to add material into the screw barrel during extrusion. The side feed port is located in the middle section of the extruder. Adding premixed masterbatch through the side feed port allows for precise material delivery, avoiding potential blockages at the main feed port, especially for materials with poor flowability or powdery forms, ensuring a continuous and stable material supply. In addition, the side feed port is usually located in the area where the premelt has been formed and has a certain shear force, which is conducive to the rapid dispersion of the premixed masterbatch and full contact with the premelt, thereby promoting the subsequent reaction and compressibility process.

[0067] The present application describes a method that pre-prepares a homogeneous premixed masterbatch from polybutylene terephthalate (PET) and maleic anhydride-grafted polypropylene (MPP), and then adds it to the polypropylene premelt via a side feed port in the middle section of a twin-screw extruder. This achieves precise, stable, and uniform introduction of the compatibilizing components. Specifically, the preparation of the premixed masterbatch ensures that PET and MPP are ideally mixed before entering the extruder, avoiding potential localized unevenness that might occur with direct mixing inside the extruder. Subsequently, the homogeneous premixed masterbatch is added to the already molten polypropylene premelt through the side feed port, avoiding feeding instability or material bridging problems that might occur with the main feed port. Simultaneously, the side feed port is typically located in the middle section of the extruder, where the polypropylene is fully melted and has good fluidity, and the shearing action of the screw has begun to take effect. This allows the premixed masterbatch to be quickly wetted and dispersed by the premelt, ensuring sufficient contact with it and providing initial conditions for subsequent compatibilization. This precisely controlled addition method makes the reaction between polybutylene terephthalate (PET) and maleic anhydride-grafted polypropylene, as well as the process of improving their compatibility with the polypropylene matrix, more uniform and efficient. This is beneficial for obtaining PP / PBAT composite materials with finer phase dispersion structure and more stable performance.

[0068] In summary, pre-preparing polybutylene terephthalate (PET) and maleic anhydride-grafted polypropylene into a premixed masterbatch and adding it through the side feed port in the middle of the extrusion section solves the problems of uneven feeding, poor dispersion, and insufficient local reaction that may occur when adding directly. This ensures that the reactive components can be more evenly dispersed in the polypropylene premelt after entering the extruder, thereby promoting a more complete and stable reaction compatibilization process.

[0069] In step S3 of the above preparation method, the pressure fluctuation of the compatibilized blend is controlled to be below 15%, and the melt flow rate uniformity of the granules reaches or exceeds 95%.

[0070] Pressure fluctuation refers to the fluctuations in melt pressure over time during the extrusion process within a twin-screw extruder. Smaller pressure fluctuations indicate more stable melt flow and more consistent shear forces. Maintaining low pressure fluctuations in compatibilized blends helps ensure the stability and homogeneity of the composite material during extrusion. Pressure fluctuations can be controlled by optimizing the extruder screw configuration, adjusting screw speed, controlling the feed rate, and precisely controlling the extrusion temperature. For example, a special screw combination can be used to provide more uniform shearing and mixing; or pressure sensors can be installed to monitor melt pressure in real time, thereby keeping pressure fluctuations within the target range. Meanwhile, melt flow rate uniformity reflects the consistency of melt flow rate between the same or different batches of pellets. Higher uniformity indicates better batch stability and less material property fluctuation. A melt flow rate uniformity of 95% or higher indicates high batch stability of the prepared composite material. High uniformity can be achieved by ensuring uniform mixing of components during extrusion or by optimizing the cooling and pelletizing processes.

[0071] In the preparation of PP / PBAT composite materials, a twin-screw extruder with a screw length-to-diameter ratio of 48 can be used. In step S1, polypropylene is added to the front section of the extruder through the main feed port for melting. Subsequently, in step S2, a pre-prepared premixed masterbatch of polybutylene terephthalate-adipate and maleic anhydride-grafted polypropylene is added to the middle section of the extruder through a side feed port to react and compatibilize with the polypropylene pre-melt. In step S3, an epoxy functional compatibilizer and an antioxidant stabilizing system are added to the rear section of the extruder through another side feed port or a forced feeder for thorough melt mixing. Specifically, to better control the pressure fluctuation of the compatibilized blend material to ≤15%, a screw configuration with a three-stage mixing zone (e.g., consisting of a kneading block and a reverse thread element) can be used, combined with a melt pressure sensor to monitor the pressure in front of the extruder die or pre-die in real time. When pressure fluctuations exceed the preset range, the automatic control system fine-tunes the screw speed or feeding rate to maintain pressure stability. Simultaneously, to ensure a melt flow rate uniformity of ≥95% for the pellets, an underwater pelletizing system can be employed, controlling the pelletizer speed and water temperature to obtain pellets of uniform size. During production, samples can be taken at regular intervals to test the melt flow rate of the pellets and calculate their uniformity to ensure they meet requirements.

[0072] Preparation Example 1: This preparation example provides a method for preparing PP / PBAT composite material, including:

[0073] 1. Raw material preparation The raw material composition of this embodiment, by weight, is as follows: 65 parts waste polypropylene with a melt flow rate of 5 g / 10 min (230℃ / 2.16 kg); 35 parts polybutylene terephthalate adipate with a melt flow rate of 12 g / 10 min (190℃ / 2.16 kg); 3 parts maleic anhydride-grafted polypropylene; 1 part epoxy functional compatibilizer; 0.2 parts hindered phenolic antioxidant; 0.2 parts phosphite antioxidant. Polypropylene and polybutylene terephthalate (PET) were placed separately in an oven and dried at 80°C for 4 hours until their moisture content was below 0.1%. The dried materials were then cut into granules of approximately 5 mm for later use.

[0074] 2. Preparation of premixed masterbatch Polybutylene terephthalate (PET) and maleic anhydride-grafted polypropylene are mixed in the above mass ratio to prepare a premixed masterbatch, which can be uniformly fed into the middle section of the extruder for subsequent processing.

[0075] 3. Segmented extrusion compounding The process involves segmented extrusion using a twin-screw extruder (screw length-to-diameter ratio of 48:1), and the steps are as follows: (1) Front section: Polypropylene is added to the front section of the twin-screw extruder and melted and plasticized at 180-200℃. The screw speed is 300rpm and the residence time is about 60s to obtain a pre-melt. (2) Middle section: Premixed masterbatch is added to the middle section of the twin-screw extruder and reacted with the pre-melt to compatibilize and blend, so that the poly(butylene adipate) phase is finely dispersed in the polypropylene matrix. (3) Back section: Epoxy functional compatibilizer and antioxidant stabilizing system are added to the back section of the twin-screw extruder and melt-blended to form a uniform blend melt. During extrusion, the melt pressure fluctuation does not exceed 15%. After extrusion, the material is granulated to obtain composite material granules. Testing revealed that the median particle size D50 of the polybutylene terephthalate (PET) dispersion is 1.2 μm, the particle size distribution D10 is 0.4 μm, and the D90 is 2.5 μm.

[0076] 4. Granulation and Cooling The extruded material was granulated using a cold water cooling system to obtain granules with a particle size of 3–5 mm. Testing showed that the crystallinity of the granules was 42%.

[0077] 5. Product molding The above-mentioned granules were directly used for film blow molding to produce a film product with a thickness of 50 μm. Testing showed that the film had a tensile elongation at break of 380% and a notched impact strength of 9.2 kJ / m².

[0078] 6. Secondary processing performance test The aforementioned film products were pulverized, remelted and granulated using a twin-screw extruder, and then injection molded into standard samples. Testing showed that the tensile elongation at break of the material after secondary processing retained ≥72%, and the melt flow rate changed ≤18%.

[0079] Preparation Example 2: This preparation example provides a method for preparing PP / PBAT composite material, including:

[0080] 1. Raw material preparation The raw material composition of this embodiment, by weight, is as follows: 70 parts waste polypropylene with a melt flow rate of 6 g / 10 min (230℃ / 2.16 kg); 30 parts polybutylene terephthalate adipate with a melt flow rate of 10 g / 10 min (190℃ / 2.16 kg); 3 parts maleic anhydride-grafted polypropylene; 1 part epoxy chain extender; 0.25 parts hindered phenolic antioxidant; 0.25 parts phosphite antioxidant. Polypropylene and polybutylene terephthalate (PET) were placed separately in an oven and dried at 80°C for 4 hours until their moisture content was below 0.1%. The dried materials were then cut into granules of approximately 5 mm for later use.

[0081] 2. Preparation of premixed masterbatch Polybutylene terephthalate (PET) and maleic anhydride-grafted polypropylene are mixed in the above mass ratio to prepare a premixed masterbatch for uniform feeding into the middle section of the extruder.

[0082] 3. Segmented extrusion compounding The process involves segmented extrusion using a twin-screw extruder (screw length-to-diameter ratio of 48:1), and the steps are as follows: (1) Front section: Polypropylene is added to the front section of the twin-screw extruder and melted and plasticized at 175-190℃. The screw speed is 350rpm and the residence time is about 60s to obtain a pre-melt. (2) Middle section: The premixed masterbatch is added to the middle section of the twin-screw extruder and reacted with the pre-melt to compatibilize and blend, so that the poly(butylene adipate) phase is finely dispersed in the polypropylene matrix. (3) Back section: The epoxy chain extender and antioxidant stabilizing system are added to the back section of the twin-screw extruder and melt-blended to form a uniform blended melt. During extrusion, the melt pressure fluctuation does not exceed 15%. After extrusion, the material is granulated to obtain composite material granules. Testing revealed that the median particle size D50 of the polybutylene terephthalate (PET) dispersion is 1.5 μm, the particle size distribution D10 is 0.5 μm, and the D90 is 3.0 μm.

[0083] 4. Granulation and Cooling The extruded material was granulated using a cold water cooling system to obtain granules with a particle size of 3–5 mm. Testing showed that the crystallinity of the granules was 38%.

[0084] 5. Product molding The above-mentioned granules were directly used for film blow molding to produce a film product with a thickness of 120 μm. Testing showed that the film had a tensile elongation at break of 380% and a notched impact strength of 8.5 kJ / m².

[0085] 6. Secondary processing performance test The aforementioned film products were pulverized, remelted and granulated using a twin-screw extruder, and then injection molded into standard samples. Testing showed that the tensile elongation at break of the material after secondary processing retained ≥70%, and the melt flow rate changed ≤20%.

[0086] Preparation Example 3: This preparation example provides a method for preparing PP / PBAT composite material, including:

[0087] 1. Raw material preparation The raw material composition of this embodiment, by weight, is as follows: 60 parts waste polypropylene with a melt flow rate of 4 g / 10 min (230℃ / 2.16 kg); 40 parts polybutylene terephthalate adipate with a melt flow rate of 12 g / 10 min (190℃ / 2.16 kg); 4 parts maleic anhydride-grafted polypropylene; 1.5 parts epoxy chain extender; 0.3 parts hindered phenolic antioxidant; 0.3 parts phosphite antioxidant. Polypropylene and polybutylene terephthalate (PET) were placed separately in an oven and dried at 80°C for 4 hours until their moisture content was below 0.1%. The dried materials were then cut into granules of approximately 5 mm for later use.

[0088] 2. Preparation of premixed masterbatch Polybutylene terephthalate (PET) and maleic anhydride-grafted polypropylene are mixed in the above mass ratio to prepare a premixed masterbatch for uniform feeding into the middle section of the extruder.

[0089] 3. Segmented extrusion compounding The process involves segmented extrusion using a twin-screw extruder (screw length-to-diameter ratio of 48:1), and the steps are as follows: (1) Front section: Polypropylene is added to the front section of the twin-screw extruder and melted and plasticized at 185-200℃. The screw speed is 280rpm and the residence time is about 60s to obtain a pre-melt. (2) Middle section: The premixed masterbatch is added to the middle section of the twin-screw extruder and reacted with the pre-melt to compatibilize and blend, so that the poly(butylene adipate) phase is finely dispersed in the polypropylene matrix. (3) Back section: The epoxy chain extender and antioxidant stabilizing system are added to the back section of the twin-screw extruder and melt-blended to form a uniform blended melt. During extrusion, the melt pressure fluctuation does not exceed 15%. After extrusion, the material is granulated to obtain composite material granules. Testing revealed that the median particle size D50 of the polybutylene terephthalate (PET) dispersion is 1.0 μm, the particle size distribution D10 is 0.3 μm, and the D90 is 2.0 μm.

[0090] 4. Granulation and Cooling The extruded material was granulated using a cold water cooling system to obtain granules with a particle size of 3–5 mm. Testing showed that the crystallinity of the granules was 50%.

[0091] 5. Product molding The above-mentioned granules were used for injection molding to produce injection molded parts. Testing showed that the dimensional change rate ΔL / L of the injection molded parts was ≤1%, the tensile elongation at break was 370%, and the notched impact strength was 8.8 kJ / m².

[0092] 6. Secondary processing performance test The injection-molded parts were crushed, remelted and granulated using a twin-screw extruder, and then injection-molded again to form standard samples. Testing showed that the tensile elongation at break of the material after secondary processing retained ≥73%, and the melt flow rate changed ≤19%.

[0093] Preparation Example 4: This preparation example provides a method for preparing PP / PBAT composite material, including:

[0094] 1. Raw material preparation The raw material composition of this embodiment, by weight, is as follows: 75 parts waste polypropylene with a melt flow rate of 7.5 g / 10 min (230℃ / 2.16 kg); 25 parts polybutylene terephthalate adipate with a melt flow rate of 2.5 g / 10 min (190℃ / 2.16 kg); 3 parts maleic anhydride-grafted polypropylene; 1 part epoxy chain extender; 0.15 parts hindered phenolic antioxidant; 0.15 parts phosphite antioxidant. Polypropylene and polybutylene terephthalate (PET) were placed separately in an oven and dried at 80°C for 4 hours until their moisture content was below 0.1%. The dried materials were then cut into granules of approximately 5 mm for later use.

[0095] 2. Preparation of premixed masterbatch Polybutylene terephthalate (PET) and maleic anhydride-grafted polypropylene are mixed in the above mass ratio to prepare a premixed masterbatch for uniform feeding into the middle section of the extruder.

[0096] 3. Segmented extrusion compounding The process of segmented extrusion using a twin-screw extruder (length-to-diameter ratio of 48:1) is as follows: (1) Front section: Polypropylene is added to the front section of the twin-screw extruder and melted and plasticized at 160-180℃. The screw speed is 320rpm and the residence time is about 60s to obtain a pre-melt. (2) Middle section: The premixed masterbatch is added to the middle section of the twin-screw extruder and reacted with the pre-melt to compatibilize and blend, so that the poly(butylene adipate) phase is finely dispersed in the polypropylene matrix. (3) Back section: The epoxy chain extender and antioxidant stabilizing system are added to the back section of the twin-screw extruder and melt-blended to form a uniform blended melt. During extrusion, the melt pressure fluctuation does not exceed 15%. After extrusion, the material is granulated to obtain composite material granules. Testing revealed that the median particle size D50 of the polybutylene terephthalate (PET) dispersion is 1.8 μm, the particle size distribution D10 is 0.7 μm, and the D90 is 3.5 μm.

[0097] 4. Granulation and Cooling The extruded material was granulated using a cold water cooling system to obtain granules with a particle size of 3–5 mm. Testing showed that the crystallinity of the granules was 35%.

[0098] 5. Product molding The above-mentioned granules were directly used for film blow molding to produce a film product with a thickness of 80 μm. Testing showed that the film had a tensile elongation at break of 355% and a notched impact strength of 8.0 kJ / m².

[0099] 6. Secondary processing performance test The aforementioned film products were pulverized, remelted and granulated using a twin-screw extruder, and then injection molded into standard samples. Testing showed that the tensile elongation at break of the material after secondary processing retained ≥71%, and the melt flow rate changed ≤18%.

[0100] Preparation Example 5: This preparation example provides a method for preparing PP / PBAT composite material, including the following steps:

[0101] 1. Raw material preparation The raw material composition of this embodiment, by weight, is as follows: 68 parts waste polypropylene with a melt flow rate of 6.8 g / 10 min (230℃ / 2.16 kg); 32 parts polybutylene terephthalate adipate with a melt flow rate of 3.2 g / 10 min (190℃ / 2.16 kg); 3 parts maleic anhydride-grafted polypropylene; 1 part epoxy chain extender; 0.2 parts hindered phenolic antioxidant; 0.2 parts phosphite antioxidant. Polypropylene and polybutylene terephthalate (PET) were placed separately in an oven and dried at 80°C for 4 hours until their moisture content was below 0.1%. The dried materials were then cut into granules of approximately 5 mm for later use.

[0102] 2. Preparation of premixed masterbatch Polybutylene terephthalate (PET) and maleic anhydride-grafted polypropylene are mixed in the above mass ratio to prepare a premixed masterbatch for uniform feeding into the middle section of the extruder.

[0103] 3. Segmented extrusion compounding The process of segmented extrusion using a twin-screw extruder (length-to-diameter ratio of 48:1) is as follows: (1) Front section: Polypropylene is added to the front section of the twin-screw extruder and melted and plasticized at 170-210℃. The screw speed is 300 rpm and the residence time is about 90s to obtain a pre-melt. (2) Middle section: The premixed masterbatch is added to the middle section of the twin-screw extruder and reacted with the pre-melt to compatibilize and blend, so that the poly(butylene adipate) phase is finely dispersed in the polypropylene matrix. (3) Back section: The epoxy chain extender and antioxidant stabilizing system are added to the back section of the twin-screw extruder and melt-blended to form a uniform blended melt. During extrusion, the melt pressure fluctuation does not exceed 15%. After extrusion, the material is granulated to obtain composite material granules. Testing revealed that the median particle size D50 of the polybutylene terephthalate (PET) dispersion is 1.3 μm, the particle size distribution D10 is 0.5 μm, and the D90 is 2.8 μm.

[0104] 4. Granulation and Cooling The extruded material was granulated using a cold water cooling system to obtain granules with a particle size of 3–5 mm. Testing showed that the crystallinity of the granules was 45%.

[0105] 5. Product molding The above-mentioned granules were directly used for film blow molding to produce a film product with a thickness of 60 μm. Testing showed that the film had a tensile elongation at break of 365% and a notched impact strength of 8.7 kJ / m².

[0106] 6. Secondary processing performance test The aforementioned film products were pulverized, remelted and granulated using a twin-screw extruder, and then injection molded into standard samples. Testing showed that the tensile elongation at break of the material after secondary processing retained ≥72%, and the melt flow rate changed ≤19%.

[0107] Comparative Example 1: This comparative example provides a method for preparing PP / PBAT composite material, including the following steps:

[0108] 1. Raw material preparation The raw material composition of this comparative example, by weight parts, is as follows: 65 parts waste polypropylene, 35 parts polybutylene terephthalate-adipate, and 3 parts maleic anhydride-grafted polypropylene. No epoxy chain extenders or antioxidant stabilizers are added. Polypropylene and polybutylene terephthalate (PET) were placed separately in an oven and dried at 80°C for 4 hours until their moisture content was below 0.1%. The dried materials were then cut into granules of approximately 5 mm for later use.

[0109] 2. Segmented extrusion compounding The process involves staged extrusion using a twin-screw extruder, with the following steps: Polypropylene is added to the front section of the twin-screw extruder and melt-plasticized at 180–210°C; in the middle section, polybutylene terephthalate-adipate and maleic anhydride-grafted polypropylene are added and blended; no additives are added in the final section. The screw speed is 300 rpm. After extrusion, the mixture is granulated to obtain composite material granules.

[0110] The median particle size D50 of the polybutylene terephthalate-adipate dispersion was found to be 1.8 μm, the particle size distribution D10 was 0.7 μm, and the D90 was 4.0 μm.

[0111] 3. Product molding The above-mentioned granules were used for film blow molding to produce a film product with a thickness of 50 μm. Testing showed that the film had a tensile elongation at break of 320% and a notched impact strength of 7.0 kJ / m².

[0112] 4. Secondary processing performance test The aforementioned film products were pulverized, remelted and granulated using a twin-screw extruder, and then injection molded into standard samples. Testing showed that the tensile elongation at break of the material after secondary processing retained approximately 60%, and the melt flow rate changed by approximately 25%.

[0113] Comparative Example 2: This comparative example provides a method for preparing PP / PBAT composite material, including the following steps:

[0114] 1. Raw material preparation The raw material composition of this comparative example, by weight parts, is as follows: 65 parts waste polypropylene, 35 parts polybutylene terephthalate (PET), and 3 parts commercially available maleic anhydride-grafted polypropylene. No epoxy chain extender or antioxidant stabilizer was added, and the particle size of PET was not controlled. Polypropylene and polybutylene terephthalate (PET) were placed separately in an oven and dried at 80°C for 4 hours until their moisture content was below 0.1%. The dried materials were then cut into granules of approximately 5 mm for later use.

[0115] 2. Segmented extrusion compounding The process involves staged extrusion using a twin-screw extruder, with the following steps: Polypropylene is added to the front section of the twin-screw extruder and melt-plasticized at 170–220°C; in the middle section, polybutylene terephthalate (PET) and commercially available maleic anhydride-grafted polypropylene are added and blended; no additives are added in the final section. The screw speed is 350 rpm. After extrusion, the mixture is granulated to obtain composite material granules.

[0116] The median particle size D50 of the polybutylene terephthalate-adipate dispersion was found to be approximately 2.5 μm, the particle size distribution D10 was 0.5 μm, and the D90 was 5.0 μm.

[0117] 3. Product molding The above-mentioned granules were used for film blow molding to produce a film product with a thickness of 50 μm. Testing showed that the film had a tensile elongation at break of 310% and a notched impact strength of 6.8 kJ / m².

[0118] 4. Secondary processing performance test The aforementioned film products were pulverized, remelted and granulated using a twin-screw extruder, and then injection molded into standard samples. Testing showed that the tensile elongation at break of the material after secondary processing retained approximately 58%, and the melt flow rate changed by approximately 28%.

[0119] Table 1: Comparison of physical properties of composite material articles prepared in Examples 1 to 5 and Comparative Examples 1 to 2

[0120] According to Table 1, the preparation examples of this invention achieved uniform and fine dispersion of polybutylene terephthalate (PET) in a polypropylene matrix through premixed masterbatch and segmented extrusion processes. In Preparation Examples 1 to 5, the median particle size (D50) of the PET dispersed phase was 1.0–1.8 μm, with a concentrated particle size distribution. In contrast, Comparative Example 1 had a median particle size of 1.8 μm but a wider distribution (D10 = 0.7 μm, D90 = 4.0 μm), and Comparative Example 2 had a median particle size of approximately 2.5 μm with an even wider distribution range (D10 = 0.5 μm, D90 = 5.0 μm). This indicates that the method of this invention can effectively control the particle size of the dispersed phase and obtain a uniformly finely dispersed phase structure.

[0121] The mechanical properties of the prepared examples of this invention are significantly superior to those of the comparative examples. In prepared examples 1 to 5, the tensile elongation at break of the film products was 355%–380%, and the notched impact strength was 8.0–9.2 kJ / m²; the dimensional change rate ΔL / L of the injection-molded parts was ≤1%. In contrast, the tensile elongation at break of Comparative Example 1 was only 320%, and the notched impact strength was 7.0 kJ / m²; the tensile elongation at break of Comparative Example 2 was only 310%, and the notched impact strength was 6.8 kJ / m². This indicates that the composite material of this invention has excellent flexibility and impact resistance, and is suitable for various molding processes such as film and injection molding.

[0122] The performance retention rate of the prepared examples of this invention after secondary melt processing is significantly better than that of the comparative examples. In prepared examples 1 to 5, the tensile elongation at break after secondary processing is ≥70%, while that of comparative example 1 is only about 60% and that of comparative example 2 is only about 58%. This indicates that the composite material of this invention exhibits less performance degradation during recycling and reprocessing and has good cyclic processing stability.

[0123] The melt flow rate change rate of the preparation examples of the present invention is ≤20%, while that of Comparative Example 1 is as high as about 25%, and that of Comparative Example 2 is as high as about 28%. This indicates that the composite material of the present invention has small changes in fluidity and good processing stability during secondary processing, which is beneficial for continuous industrial production.

[0124] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that the present invention includes, but is not limited to, the contents described in the accompanying drawings and the specific embodiments above. Any modifications that do not depart from the functional and structural principles of the present invention will be included within the scope of the claims.

Claims

1. A PP / PBAT composite material, characterized in that, Its raw materials, by mass parts, include the following components: Polypropylene: 55-75 parts; Polybutylene terephthalate-adipate: 25-45 parts; Maleic anhydride-grafted polypropylene: 2-5 parts; Epoxy functional compatibilizer and / or epoxy functional chain extender: 0.2-1.5 parts; Antioxidant stabilizing system: 0.2-0.8 parts; The antioxidant stabilizing system includes at least hindered phenolic antioxidants and phosphite antioxidants.

2. The composite material according to claim 1, characterized in that, The polybutylene terephthalate (PET) is distributed as a dispersed phase in the composite material; the volume fraction of the dispersed phase is 20% to 50%, the particle size distribution D10 ≥ 0.2 μm, the particle size distribution D90 ≤ 6 μm, and the median particle size is 0.3 to 5.0 μm.

3. The composite material according to claim 2, characterized in that, The crystallinity of the composite material is 35% to 60%.

4. The composite material according to claim 1, characterized in that, After secondary melting and solidification, the composite material retains a notched impact strength of ≥70%, a tensile elongation at break of ≥60%, and a melt flow rate change of ≤20%.

5. The composite material according to claim 1, characterized in that, The melt flow rate of the polypropylene is 1-30 g / 10 min at 230°C and 2.16 kg load; the melt flow rate of the polybutylene terephthalate is 1-20 g / 10 min at 190°C and 2.16 kg load; and the epoxy equivalent of the epoxy functional compatibilizer and / or the epoxy functional chain extender is 150-1200 g / eq.

6. The composite material according to claim 5, characterized in that, The amount of the hindered phenolic antioxidant added is 0.05 to 0.30 parts, and the amount of the phosphite antioxidant added is 0.05 to 0.30 parts.

7. The composite material according to claim 1, characterized in that, The composite material is used to manufacture film products, the thickness of which is 20-200 μm, the tensile elongation at break is ≥350%, and the notched impact strength is ≥8 kJ / m²; the composite material is also used to manufacture injection molded parts, the dimensional change rate of which is ≤1%.

8. A method for preparing a PP / PBAT composite material, characterized in that, include: S1, polypropylene is added to the pre-extrusion section of a twin-screw extruder for melting to obtain a pre-melt; S2, polybutylene terephthalate-adipate and maleic anhydride-grafted polypropylene are added to the pre-melt in the mid-extrusion section of the twin-screw extruder for compatibilization reaction to obtain a compatibilized blend material; S3, epoxy functional compatibilizer and / or epoxy functional chain extender and antioxidant stabilizing system are added to the compatibilized blend material in the post-extrusion section of the twin-screw extruder for melt mixing, extrusion granulation to obtain granules; wherein, the granules are the PP / PBAT composite material according to any one of claims 1 to 7; the extrusion temperature of the twin-screw extruder is 160-220℃, the screw speed is 100-600rpm, and the material residence time is 20-180s.

9. The preparation method according to claim 8, characterized in that, Step S2 specifically includes: first, preparing a premixed masterbatch from the polybutylene terephthalate-adipate and the maleic anhydride-grafted polypropylene, and then adding the premixed masterbatch into the premelt from the side feed port of the extrusion section.

10. The preparation method according to claim 8, characterized in that, In step S3, the pressure fluctuation of the compatibilizing blend is ≤15%, and the melt flow rate uniformity of the granules is ≥95%.

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