A high-toughness, highly branched polyolefin rubber-plastic composite material and its preparation method

Abstract

This invention relates to the field of polyolefin rubber-plastic composite materials, and discloses a high-toughness, highly branched polyolefin rubber-plastic composite material and its preparation method. The material comprises a continuous polyolefin phase, a polyolefin rubber phase dispersed therein, a highly branched polyolefin, and a reactive grafted polyolefin; the highly branched polyolefin and the reactive grafted polyolefin are co-distributed at the interface between the two phases, forming an interfacial transition layer. This structure improves the dispersion of the rubber phase and interfacial bonding, enhancing the material's impact resistance, tear resistance, and low-temperature toughness.

Description

Technical Field

[0001] This invention relates to the field of polyolefin rubber-plastic composite materials technology, and discloses a high-toughness, highly branched polyolefin rubber-plastic composite material and its preparation method. Background Technology

[0002] Polyolefin materials typically use polypropylene, polyethylene, and their copolymers as the main resins, relying on their non-polar hydrocarbon chain structure to achieve good chemical resistance, processing fluidity, and molding stability. In the preparation of rubber-plastic composites, conventional techniques usually involve melt-blending polyolefin resins with ethylene propylene diene monomer (EPDM) rubber, ethylene octene copolymers, ethylene butene copolymers, or polyolefin thermoplastic elastomers. The rubber phase absorbs external impact energy through flexible deformation. These systems often employ twin-screw extrusion, internal mixing, or open milling processes for dispersion. Under shearing, the rubber phase forms dispersed micro-regions, while the polyolefin resin forms a continuous phase. After cooling, a composite material combining plastic processability and rubber flexibility is obtained. This technical route has a simple structure and strong raw material adaptability, and has already been used in packaging, automotive parts, cable sheaths, and flexible molded parts.

[0003] In existing polyolefin rubber-plastic composites, a common way to improve toughness is to increase the amount of rubber phase or select elastomer components with lower glass transition temperatures. With increased rubber phase content, the material can produce greater elastic deformation during low-temperature impact or bending, and the local stress near the crack tip can be borne by the rubber micro-regions, resulting in a certain degree of passivation. To reduce phase separation, existing technologies also add compatibility components such as maleic anhydride-grafted polyolefins, carboxylated polyolefins, and epoxidized polyolefins, distributing these compatibility components between the polyolefin and rubber phases to improve interfacial wetting. These compatibility agents typically utilize their polyolefin segments to be compatible with the matrix resin and their grafted groups to form interfacial bonds with the rubber phase or auxiliary polar components, thereby reducing the probability of rubber particle aggregation and interfacial void formation.

[0004] Existing technologies also propose adjusting the segmental structure of the continuous phase by blending branched polyolefins, low-crystallinity polyolefins, or polyolefins with different melt viscosities. Branched polyolefins can introduce more chain entanglement and free volume into the continuous polyolefin phase, giving the material a certain degree of chain segment relaxation capability under stress. Low-crystallinity polyolefins can be distributed around the skeleton of high-crystallinity polyolefins, mitigating the rigidity difference between the crystalline and amorphous phases. Some technologies also combine polyolefin elastomers with branched polyolefins to improve the phase dispersion state during melt processing. However, in conventional systems, branched polyolefins are mostly used as rheological modifiers or toughening agents, and their positional distribution on the rubber phase surface lacks stable control, making it difficult to form a continuous interfacial transition structure with reactive grafted polyolefins.

[0005] The main technical problem with existing polyolefin rubber-plastic composites lies in the difficulty of simultaneously establishing a stable stress transfer structure between the continuous polyolefin phase, the polyolefin rubber phase, and the interfacial phase without relying solely on increasing the rubber phase content. When the rubber phase content is too low, the material suffers from insufficient energy dissipation after impact, making brittle cracks prone to form at notches. When the rubber phase content is too high, the load-bearing continuity of the continuous polyolefin phase decreases, affecting tensile strength, dimensional stability, and thermal deformation stability. Conventional compatibilizers can improve interfacial wetting, but their linear chain segments are insufficient for regulating the relaxation of continuous phase chain segments and the surface intercalation of the rubber phase. While branched polyolefins can alter the local chain segment motion state in the matrix when used alone, they cannot guarantee the interfacial anti-debonding ability between the rubber phase and the continuous phase. Therefore, the core problem to be solved is constructing a polyolefin rubber-plastic composite structure that simultaneously possesses branched chain entanglement, interfacial bonding, and rubber phase dispersion stability. Summary of the Invention

[0006] To address the shortcomings of existing technologies where polyolefin rubber-plastic composites rely on increasing the rubber phase content for toughening, which leads to a decrease in the continuous load-bearing capacity of the polyolefin continuous phase, and where conventional compatibilizers are unable to simultaneously establish a stable structure of branched chain entanglement, interfacial bonding, and rubber phase dispersion, this invention provides a high-toughness, highly branched polyolefin rubber-plastic composite material and its preparation method.

[0007] To address the aforementioned technical problems, this invention provides a high-toughness, highly branched polyolefin rubber-plastic composite material, comprising a continuous polyolefin phase, a polyolefin rubber phase dispersed in the continuous polyolefin phase, a highly branched polyolefin, and a reactive grafted polyolefin; the highly branched polyolefin has a polyolefin backbone and multi-branched alkyl side chains, and is distributed at the phase interface between the continuous polyolefin phase and the polyolefin rubber phase; the reactive grafted polyolefin has polyolefin segments and reactive groups, and together with the highly branched polyolefin, constitutes an interfacial transition layer coating the surface of the polyolefin rubber phase.

[0008] The highly branched polyolefin backbone has a similar nonpolar hydrocarbon chain structure to the continuous polyolefin phase, allowing it to enter the intersegmental spaces of the continuous polyolefin phase and form segmental entanglements during molten mixing. The multi-branched alkyl side chains extend towards the surface of the polyolefin rubber phase, transforming the phase interface from an abrupt transition to a transitional region containing branched segments. The reactive grafted polyolefin segments remain compatible with the continuous polyolefin phase, and the reactive groups are located on the surface of the polyolefin rubber phase, causing the interface transition layer to form a coating structure around the polyolefin rubber phase during molding. When the material is subjected to external forces, the external load is transferred through the continuous polyolefin phase to the interface transition layer, and then to the polyolefin rubber phase, avoiding stress concentration at a single phase interface and thus forming a continuous interphase load-bearing path.

[0009] Furthermore, in the above technical solution, the continuous polyolefin phase includes at least one of polypropylene, polyethylene, propylene-ethylene copolymer, and ethylene-α-olefin copolymer. The continuous polyolefin phase contains a nonpolar hydrocarbon chain structure that can form segment entanglement or blend compatibility with the polyolefin backbone of the highly branched polyolefin, and the continuous polyolefin phase is continuously connected to the interface transition layer.

[0010] In practice, the nonpolar hydrocarbon chain structure of the continuous polyolefin phase has a similar segment compatibility basis with the polyolefin backbone of the highly branched polyolefin, and can jointly participate in segment diffusion and interphase entanglement during melt plasticization. The continuous polyolefin phase is continuously connected to the interface transition layer, so that the interface transition layer is not a free phase or an independent filling phase, but is embedded in the adjacent region of the continuous polyolefin phase. After molding and cooling, the continuous polyolefin phase maintains a continuous skeleton, and the interface transition layer is located between the continuous skeleton and the rubber microregion, so that external loads can be transferred stepwise along the continuous phase, the transition layer, and the rubber phase.

[0011] Furthermore, in the above technical solution, the polyolefin rubber phase includes at least one of ethylene-octene copolymer, ethylene-butene copolymer, ethylene propylene diene monomer (EPDM) rubber, and polyolefin thermoplastic elastomer. The polyolefin rubber phase is embedded in the polyolefin continuous phase in the form of independently dispersed micro-regions, and the surface layer of the polyolefin rubber phase is interlocked with the interface transition layer.

[0012] In specific implementation, the polyolefin rubber phase has flexible segments that can be dispersed into independent micro-regions during melt shearing. After the surface layer of the polyolefin rubber phase and the interface transition layer interlock, the polyolefin rubber phase does not directly contact the continuous polyolefin phase in the form of exposed particles, but is embedded in the continuous phase system through the interface transition layer. During bending, impact, or stretching, the polyolefin rubber phase can deform together with the interface transition layer, reducing debonding between the edges of the rubber micro-regions and the continuous phase.

[0013] Furthermore, in the above technical solution, the highly branched polyolefin is a branched polymer containing at least one of ethylene, propylene, butene, and octene structural units. The multi-branched alkyl side chains are non-linearly distributed along the polyolefin main chain. A portion of the highly branched polyolefin is embedded in the polyolefin continuous phase, and another portion extends to the surface layer of the polyolefin rubber phase.

[0014] In specific implementations, the ethylene, propylene, butene, or octene structural units of the highly branched polyolefin have a hydrocarbon chain compatibility basis with both the continuous polyolefin phase and the polyolefin rubber phase. The multi-branched alkyl side chains are non-linearly distributed along the polyolefin backbone, resulting in a multi-point extension and multi-point entanglement morphology of the highly branched polyolefin at the phase interface. A portion of these side chains are embedded in the continuous polyolefin phase, while another portion extends to the surface of the polyolefin rubber phase, forming a branched segment bridging structure between the two phases and avoiding contact at the interface solely through linear chain segments.

[0015] Furthermore, in the above technical solution, the reactive grafted polyolefin includes at least one of maleic anhydride grafted polyolefin, epoxy-based grafted polyolefin, carboxyl-based grafted polyolefin, and hydroxyl-based grafted polyolefin. The polyolefin segment of the reactive grafted polyolefin is located on one side of the continuous polyolefin phase, and the reactive group is located on the surface layer of the polyolefin rubber phase.

[0016] In specific implementation, the reactive grafted polyolefin has a segmentally compatible portion and a reactive group portion. Its polyolefin segments can enter the continuous polyolefin phase and blend with the continuous phase segments, while the reactive groups can be distributed towards the surface of the polyolefin rubber phase. During melt mixing, the reactive grafted polyolefin is oriented at the phase interface and, together with the highly branched polyolefin, is located on the outer periphery of the polyolefin rubber phase. The polyolefin segments and the reactive groups correspond to the two phase structures respectively, giving the interface transition layer a composite structure of compatibility connection and surface bonding.

[0017] Furthermore, in the above technical solution, the continuous polyolefin phase is formed by a high-crystallinity polyolefin component and a low-crystallinity polyolefin component. The high-crystallinity polyolefin component constitutes a continuous skeleton, and the low-crystallinity polyolefin component is distributed between the continuous skeleton and the interface transition layer. The low-crystallinity polyolefin component and the highly branched polyolefin are mixed to form a segment transition region.

[0018] In practice, the highly crystalline polyolefin component forms a load-bearing skeleton after cooling and molding. The low-crystalline polyolefin component, due to its lower chain segment regularity, is more suitable for distribution between the continuous skeleton and the interface transition layer. When the low-crystalline polyolefin component is mixed with the highly branched polyolefin, a chain segment transition region can be formed between the rigid continuous skeleton and the flexible interface transition layer. Under stress, the continuous skeleton bears the main load, while the chain segment transition region mitigates the deformation difference between the continuous skeleton and the rubber micro-regions.

[0019] Furthermore, in the above technical solution, the polyolefin rubber phase includes a first flexible rubber component and a second flexible rubber component. The first flexible rubber component is disposed adjacent to the polyolefin continuous phase, the second flexible rubber component is located inside the polyolefin rubber phase, and the first flexible rubber component and the interface transition layer jointly cover the second flexible rubber component.

[0020] In specific implementation, the first flexible rubber component is located close to the continuous polyolefin phase, forming the outer layer structure of the rubber microregion together with the interface transition layer; the second flexible rubber component is located inside the polyolefin rubber phase, forming the inner flexible region of the rubber microregion. This structure gives the polyolefin rubber phase a continuous flexible distribution from the outside to the inside. After melt mixing, the first flexible rubber component restricts the second flexible rubber component from being directly exposed to the continuous polyolefin phase, and after molding, the second flexible rubber component maintains an independent flexible microregion within the outer coating structure.

[0021] Furthermore, in the above technical solution, the highly branched polyolefin includes long-branched polyolefin and short-branched polyolefin. The long-branched polyolefin is disposed between the continuous polyolefin phase and the polyolefin rubber phase, and the short-branched polyolefin is distributed in the interface transition layer. The long-branched polyolefin and the short-branched polyolefin together form a multi-scale branched chain entanglement structure.

[0022] In specific implementation, the long-branched polyolefin has the ability to extend its chain segments across the phase interface, enabling it to penetrate between the continuous polyolefin phase and the polyolefin rubber phase; the short-branched polyolefin is distributed within the interface transition layer, filling the chain segment gaps in the interface region. The long-branched and short-branched polyolefins coexist in the same region, resulting in the interface transition layer simultaneously containing interphase connecting chains and locally entangled chains. When the material is subjected to stress, branched chains of different lengths participate in interphase chain segment traction and local chain segment slippage according to their spatial positions.

[0023] Furthermore, in the above technical solution, the reactive grafted polyolefin includes a first grafted polyolefin and a second grafted polyolefin. The polyolefin segments of the first grafted polyolefin are compatible with the continuous polyolefin phase, and the reactive groups of the second grafted polyolefin are bonded to the surface layer of the polyolefin rubber phase. The first grafted polyolefin and the second grafted polyolefin are interleaved in the interface transition layer.

[0024] In specific implementation, the first grafted polyolefin focuses on forming a compatible bond with the continuous polyolefin phase, while the second grafted polyolefin focuses on forming a bonded structure with the surface layer of the polyolefin rubber phase. The two are staggered within the interface transition layer, resulting in a continuous distribution of grafted polyolefins along the thickness direction, rather than a single thin interfacial layer. During melt mixing, the first and second grafted polyolefins migrate and position together with the phase interface formation, and after cooling and molding, they remain between the continuous polyolefin phase and the polyolefin rubber phase.

[0025] Furthermore, the present invention also provides a method for preparing a high-toughness, highly branched polyolefin rubber-plastic composite material, comprising: premixing a polyolefin matrix with a highly branched polyolefin to form a premix containing a continuous polyolefin phase and a branched segment distribution region; adding a polyolefin rubber phase and a reactive grafted polyolefin to the premix for melt mixing, such that the polyolefin rubber phase is dispersed in the continuous polyolefin phase, and the highly branched polyolefin and the reactive grafted polyolefin are co-distributed at the phase interface between the continuous polyolefin phase and the polyolefin rubber phase; and molding the melt-mixed material to obtain a high-toughness, highly branched polyolefin rubber-plastic composite material with an interface transition layer.

[0026] In specific implementation, the preparation method first premixes the polyolefin matrix with the highly branched polyolefin, so that branched segments are pre-distributed within the continuous polyolefin phase, forming a branched segment distribution region. Then, the polyolefin rubber phase and the reactive grafted polyolefin are added for melt mixing, causing the polyolefin rubber phase to disperse within the continuous polyolefin phase under shear action, and the highly branched polyolefin and the reactive grafted polyolefin to form an interface with the two phases. During molding, the phase interface formed in the molten state is fixed, and the highly branched polyolefin and the reactive grafted polyolefin together constitute an interface transition layer covering the surface of the polyolefin rubber phase, ensuring that the composition and structure of the resulting composite material correspond to the aforementioned material scheme.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. A continuous polyolefin phase, a polyolefin rubber phase, a highly branched polyolefin, and a reactive grafted polyolefin are co-located in the same rubber-plastic system. The highly branched polyolefin is distributed at the interface between the continuous polyolefin phase and the polyolefin rubber phase, and together with the reactive grafted polyolefin, forms an interfacial transition layer coating the surface of the polyolefin rubber phase. The highly branched polyolefin has a polyolefin backbone and multi-branched alkyl side chains, enabling it to form segmental compatibility with the continuous polyolefin phase and extend to the surface of the polyolefin rubber phase. The reactive grafted polyolefin has polyolefin segments and reactive groups, enabling it to form more stable bonding regions at the phase interface. The resulting interfacial transition layer reduces abrupt interface changes between the continuous polyolefin phase and the polyolefin rubber phase, allowing the rubber phase to remain dispersed in micro-regions after melt mixing. When the material is subjected to impact or tearing loads, a continuous load-bearing path is formed between the continuous phase, the interfacial transition layer, and the rubber phase, reducing debonding of the rubber phase surface, pore enlargement, and rapid crack propagation along the interface. This structure enables the material to exhibit more complete plastic deformation and rubber phase deformation energy dissipation during notched impact, bending and tensile fracture processes, which can improve impact toughness and tear resistance while reducing the strength loss caused by simply increasing the rubber content.

[0028] 2. The continuous polyolefin phase can be formed by both highly crystalline and low-crystalline polyolefin components. The highly crystalline polyolefin component maintains the continuous skeleton, while the low-crystalline polyolefin component is located between the continuous skeleton and the interfacial transition layer, forming a chain segment transition region with the highly branched polyolefin, resulting in a more uniform internal phase structure after molding. The polyolefin rubber phase can be composed of different flexible rubber components, with the flexible component near the interface and the interfacial transition layer jointly encapsulating the internal flexible component, giving the rubber phase surface and interior a progressive flexible structure. Long-chain and short-chain polyolefins in the highly branched polyolefin can form a multi-scale branched chain entanglement structure in the interfacial region, and different grafting components in the reactive grafted polyolefin can be staggered within the interfacial transition layer, giving both the continuous polyolefin phase side and the polyolefin rubber phase side corresponding bonding structures. This structure also improves the refinement and dispersion retention of the rubber phase during melt mixing, reducing local unevenness in hardness and softness of the molded parts, whitening from repeated bending, and low-temperature brittleness, enabling the composite material to have more stable deformation recovery and dimensional retention capabilities while maintaining thermoplastic processability. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments. Those skilled in the art can reproduce the technical solution of the present invention and achieve its claimed technical effects based on the content disclosed in this specification. It should be noted that the following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. Any non-substantial improvements and adjustments made based on the core concept of the present invention should fall within the scope of protection of the present invention.

[0030] Example 1: Based on a total mass of 100 wt% of the composite material, the formulation consists of: 45 wt% highly crystalline polypropylene, 15 wt% propylene-ethylene copolymer, 18 wt% ethylene-octene copolymer, 10 wt% ethylene propylene diene monomer (EPDM) rubber, 5 wt% long-chain highly branched polyolefin, 3 wt% short-chain highly branched polyolefin, 2.5 wt% maleic anhydride-grafted polyolefin, and 1.5 wt% epoxy-grafted polyolefin. The highly crystalline polypropylene and propylene-ethylene copolymer constitute the continuous polyolefin phase, the ethylene-octene copolymer and EPDM rubber constitute the polyolefin rubber phase, the long-chain highly branched polyolefin and the short-chain highly branched polyolefin together constitute the highly branched polyolefin, and the maleic anhydride-grafted polyolefin and the epoxy-grafted polyolefin together constitute the reactive grafted polyolefin.

[0031] The preparation method is as follows: Highly crystalline polypropylene, propylene-ethylene copolymer, long-branched highly branched polyolefin, and short-branched highly branched polyolefin are placed in a high-speed mixer and premixed at 600 rpm for 10 min to obtain a premix containing branched chain segment distribution regions. The premix is ​​added to the main feed port of a twin-screw melt-mixing equipment, while ethylene-octene copolymer, EPDM rubber, maleic anhydride-grafted polyolefin, and epoxy-grafted polyolefin are added to the side feed port. The melt-mixing temperature zones are set sequentially to 165℃, 175℃, 185℃, 195℃, 200℃, and 195℃, with a screw speed of 180 rpm. The melt is water-cooled and pelletized to obtain composite material granules. The granules are dried at 80℃ for 3 h and then injection molded. The injection molding barrel temperatures are 185℃, 195℃, and 200℃, and the mold temperature is 40℃ to obtain high-toughness, highly branched polyolefin rubber-plastic composite material samples.

[0032] Example 2: Compared with Example 1, this example only adjusts the ratio of highly crystalline polyolefin to low-crystalline polyolefin in the continuous polyolefin phase. Based on a total composite material mass of 100 wt%, the formulation is as follows: 50 wt% highly crystalline polypropylene, 10 wt% propylene-ethylene copolymer, 18 wt% ethylene-octene copolymer, 10 wt% ethylene propylene diene monomer (EPDM) rubber, 5 wt% long-chain highly branched polyolefin, 3 wt% short-chain highly branched polyolefin, 2.5 wt% maleic anhydride-grafted polyolefin, and 1.5 wt% epoxy-grafted polyolefin. The remaining preparation conditions are the same as in Example 1.

[0033] Example 3: Compared with Example 1, this example only adjusts the ratio of highly crystalline polyolefin to low-crystalline polyolefin in the continuous polyolefin phase. Based on a total composite material mass of 100 wt%, the formulation is as follows: 40 wt% highly crystalline polypropylene, 20 wt% propylene-ethylene copolymer, 18 wt% ethylene-octene copolymer, 10 wt% ethylene propylene diene monomer (EPDM) rubber, 5 wt% long-chain highly branched polyolefin, 3 wt% short-chain highly branched polyolefin, 2.5 wt% maleic anhydride-grafted polyolefin, and 1.5 wt% epoxy-grafted polyolefin. The remaining preparation conditions are the same as in Example 1.

[0034] Example 4: Compared with Example 1, this example only adjusts the ratio of the first flexible rubber component and the second flexible rubber component in the polyolefin rubber phase. Based on a total composite material mass of 100 wt%, the formulation is as follows: 45 wt% highly crystalline polypropylene, 15 wt% propylene-ethylene copolymer, 22 wt% ethylene-octene copolymer, 6 wt% ethylene propylene diene monomer (EPDM) rubber, 5 wt% long-chain highly branched polyolefin, 3 wt% short-chain highly branched polyolefin, 2.5 wt% maleic anhydride-grafted polyolefin, and 1.5 wt% epoxy-grafted polyolefin. The remaining preparation conditions are the same as in Example 1.

[0035] Example 5: Compared with Example 1, this example only replaces the ethylene-octene copolymer in the polyolefin rubber phase with an ethylene-butene copolymer. Based on a total composite material mass of 100 wt%, the formulation is as follows: 45 wt% highly crystalline polypropylene, 15 wt% propylene-ethylene copolymer, 18 wt% ethylene-butene copolymer, 10 wt% EPDM rubber, 5 wt% long-chain highly branched polyolefin, 3 wt% short-chain highly branched polyolefin, 2.5 wt% maleic anhydride-grafted polyolefin, and 1.5 wt% epoxy-grafted polyolefin. The remaining preparation conditions are the same as in Example 1.

[0036] Example 6: Compared with Example 1, this example only reduces the proportion of highly branched polyolefins and supplements the total amount with highly crystalline polypropylene. Based on a total composite mass of 100 wt%, the formulation is as follows: 48 wt% highly crystalline polypropylene, 15 wt% propylene-ethylene copolymer, 18 wt% ethylene-octene copolymer, 10 wt% ethylene propylene diene monomer (EPDM) rubber, 3 wt% long-chain highly branched polyolefin, 2 wt% short-chain highly branched polyolefin, 2.5 wt% maleic anhydride-grafted polyolefin, and 1.5 wt% epoxy-grafted polyolefin. The remaining preparation conditions are the same as in Example 1.

[0037] Example 7: Compared with Example 1, this example only increases the proportion of highly branched polyolefin and correspondingly decreases the proportion of highly crystalline polypropylene. Based on a total composite material mass of 100 wt%, the formulation is as follows: 42 wt% highly crystalline polypropylene, 15 wt% propylene-ethylene copolymer, 18 wt% ethylene-octene copolymer, 10 wt% ethylene propylene diene monomer (EPDM) rubber, 7 wt% long-chain highly branched polyolefin, 4 wt% short-chain highly branched polyolefin, 2.5 wt% maleic anhydride-grafted polyolefin, and 1.5 wt% epoxy-grafted polyolefin. The remaining preparation conditions are the same as in Example 1.

[0038] Example 8: Compared with Example 1, this example only adjusts the type of reactive grafted polyolefin. Based on a total composite material mass of 100 wt%, the formulation is as follows: 45 wt% highly crystalline polypropylene, 15 wt% propylene-ethylene copolymer, 18 wt% ethylene-octene copolymer, 10 wt% ethylene propylene diene monomer (EPDM) rubber, 5 wt% long-chain highly branched polyolefin, 3 wt% short-chain highly branched polyolefin, and 4 wt% maleic anhydride grafted polyolefin. The remaining preparation conditions are the same as in Example 1.

[0039] Example 9: Compared with Example 1, this example only adjusts the type of reactive grafted polyolefin. Based on a total composite material mass of 100 wt%, the formulation is as follows: 45 wt% highly crystalline polypropylene, 15 wt% propylene-ethylene copolymer, 18 wt% ethylene-octene copolymer, 10 wt% ethylene propylene diene monomer (EPDM) rubber, 5 wt% long-chain highly branched polyolefin, 3 wt% short-chain highly branched polyolefin, 2 wt% carboxyl-grafted polyolefin, and 2 wt% hydroxyl-grafted polyolefin. The remaining preparation conditions are the same as in Example 1.

[0040] Example 10: This example maintains the same formula as Example 1, only adjusting the screw speed during the melt mixing process. The screw speed is adjusted from 180 rpm to 150 rpm, while the melt mixing temperature zone, premixing conditions, drying conditions, and molding conditions remain the same as in Example 1.

[0041] Example 11: This example maintains the same formula as Example 1, only adjusting the screw speed during the melt mixing process. The screw speed is adjusted from 180 rpm to 220 rpm, while the melt mixing temperature zone, premixing conditions, drying conditions, and molding conditions remain the same as in Example 1.

[0042] Example 12: This example maintains the same formula as Example 1, only adjusting the melt mixing temperature zone. The melt mixing temperature zones are set sequentially to 170℃, 180℃, 190℃, 200℃, 205℃, and 200℃. The screw speed, premixing conditions, drying conditions, and molding conditions are all the same as in Example 1.

[0043] Comparative Example 1: This comparative example is a comparative example lacking highly branched polyolefins. Based on a total composite material mass of 100 wt%, the formulation composition is: 53 wt% highly crystalline polypropylene, 15 wt% propylene-ethylene copolymer, 18 wt% ethylene-octene copolymer, 10 wt% ethylene propylene diene monomer (EPDM) rubber, 2.5 wt% maleic anhydride-grafted polyolefin, and 1.5 wt% epoxy-grafted polyolefin. Compared to Example 1, this comparative example omits both long-chain and short-chain highly branched polyolefins, and supplements the total amount with highly crystalline polypropylene. The remaining preparation conditions are the same as in Example 1.

[0044] Comparative Example 2: This comparative example is a conventional rubber-toughened polyolefin composite material. Based on a total composite material mass of 100 wt%, the formulation consists of: 50 wt% highly crystalline polypropylene, 5 wt% propylene-ethylene copolymer, 30 wt% ethylene-octene copolymer, 10 wt% ethylene propylene diene monomer (EPDM) rubber, and 5 wt% maleic anhydride-grafted polyolefin. All the above components were added to a melt-mixing apparatus at once, and mixed, granulated, and injection molded under the same temperature range and screw speed as in Example 1. Compared to Example 1, this comparative example uses a conventional toughening method that increases the polyolefin rubber phase content and incorporates a single grafted polyolefin, without incorporating highly branched polyolefins to construct the interfacial transition layer.

[0045] Comparative Example 3: This comparative example is a comparison of the deviation of melt-mixing shear parameters. The formulation is exactly the same as in Example 1, except that the screw speed during the melt-mixing process is adjusted from 180 rpm to 40 rpm. The melt-mixing temperature zone, premixing conditions, drying conditions, and molding conditions are all the same as in Example 1.

[0046] Comparative Example 4: This comparative example is a comparative example without the premixing step. The formulation is exactly the same as in Example 1, but instead of premixing the highly crystalline polypropylene, propylene-ethylene copolymer, long-chain highly branched polyolefin, and short-chain highly branched polyolefin, all components are added to the main feed port of the melt-mixing equipment at once. The melt-mixing temperature zone, screw speed, drying conditions, and molding conditions are all the same as in Example 1.

[0047] Test method: The samples obtained from Examples 1 to 12 and Comparative Examples 1 to 4 were placed at 23°C and 50% relative humidity for 48 hours before performance testing was performed.

[0048] The median particle size of the polyolefin rubber phase was obtained statistically from scanning electron microscopy images of the liquid nitrogen brittle fracture surface. Notched impact strength was tested using injection-molded notched spline. Tensile strength and elongation at break were tested using dumbbell-shaped splines; Tear strength was tested using a right-angle tear spline. The heat distortion temperature was determined by heat distortion testing under standard bending load conditions.

[0049] The test results are shown in Table 1.

[0050] Table 1 Performance test results of each embodiment and comparative example Example 1 0.68 72.5 45.2 27.6 635 82 92.8 Example 2 0.75 66.8 39.5 29.1 560 78.4 96.5 Example 3 0.72 70.1 44 25.8 670 80.5 88.4 Example 4 0.7 73 46.4 26.4 660 79.2 90.5 Example 5 0.78 65.7 39.2 27 600 75.3 91.3 Example 6 1.05 58.2 32.6 28.2 520 69.8 94.1 Example 7 0.62 74.1 46 25 720 81.1 87.9 Example 8 0.85 60.4 34.8 27.9 540 70.6 94.8 Example 9 0.8 62.7 36.5 26.8 575 72.4 91.9 Example 10 0.76 67.9 40.6 27.8 600 78.5 92.6 Example 11 0.7 71.6 43.8 27.1 625 80 91.4 Example 12 0.73 69.8 42.5 27.2 615 79.1 91.8 Comparative Example 1 1.65 38.5 18.9 28.7 310 52 95.2 Comparative Example 2 1.42 45 25.5 20.4 580 56.8 72.6 Comparative Example 3 2.3 27.6 12 24.9 260 41.5 90.2 Comparative Example 4 1.28 49.3 25.2 26.1 420 61.7 92 Results analysis: Example 1 uses highly crystalline polypropylene and propylene-ethylene copolymer to form the continuous polyolefin phase, and ethylene-octene copolymer and ethylene propylene diene monomer (EPDM) rubber to form the polyolefin rubber phase. An interfacial transition layer is constructed by introducing long-chain highly branched polyolefins, short-chain highly branched polyolefins, maleic anhydride-grafted polyolefins, and epoxy-grafted polyolefins. Test results show that the median particle size of the polyolefin rubber phase in Example 1 is 0.68 μm, and the notched impact strength at 23°C is 72.5 kJ / m². 2 The notched impact strength at -20℃ is 45.2 kJ / m. 2 The tear strength was 82.0 kN / m. This result indicates that the polyolefin rubber phase forms finely dispersed microdomains within the continuous polyolefin phase, and the interfacial transition layer can reduce interfacial defects between the rubber microdomains and the continuous phase. Compared to Comparative Example 1, in Example 1, under the condition of highly branched polyolefin, the particle size of the polyolefin rubber phase decreased from 1.65 μm to 0.68 μm, and the notched impact strength at 23°C increased from 38.5 kJ / m. 2 Increased to 72.5 kJ / m 2 The tear strength increased from 52.0 kN / m to 82.0 kN / m. This comparison shows that highly branched polyolefins are not simply plasticizing components, but key components involved in the formation of branched segment distribution regions and interfacial transition layers.

[0051] Examples 2 and 3 only changed the ratio of highly crystalline polyolefin components to low-crystalline polyolefin components in the continuous polyolefin phase. In Example 2, after increasing the proportion of highly crystalline polypropylene, the tensile strength and heat distortion temperature reached 29.1 MPa and 96.5 °C, respectively, but the elongation at break and low-temperature notched impact strength were lower than those in Example 1. In Example 3, after increasing the proportion of propylene-ethylene copolymer, the elongation at break reached 670%, and the notched impact strength at -20 °C was 44.0 kJ / m. 2 However, the heat distortion temperature was lower than that of Example 1. This result indicates that the highly crystalline polyolefin component provides a continuous load-bearing skeleton, while the low-crystalline polyolefin component forms a segmental transition region with the highly branched polyolefin. Changes in their ratio affect the balance between rigidity retention and toughness release. Example 1 achieved a more balanced result in terms of tensile strength, elongation at break, low-temperature impact strength, and heat distortion temperature.

[0052] Examples 4 and 5 were used to verify the effects of phase substitution and ratio changes in polyolefin rubber. In Example 4, after increasing the proportion of ethylene-octene copolymer, the notched impact strength at 23°C was 73.0 kJ / m. 2 The notched impact strength at -20℃ is 46.4 kJ / m. 2 The elongation at break was 660%, indicating that the increased flexible rubber component was beneficial for impact deformation and low-temperature toughness retention, but the heat distortion temperature and tensile strength were lower than in Example 1. In Example 5, after replacing the ethylene-octene copolymer with the ethylene-butene copolymer, the notched impact strength at 23°C was 65.7 kJ / m. 2 The tear strength was 75.3 kN / m, which is still higher than that of Comparative Example 1 and Comparative Example 2. This result indicates that under the condition of replacing polyolefin rubbers such as ethylene-butene copolymer and ethylene propylene diene monomer (EPDM) rubber, the highly branched polyolefin and reactive grafted polyolefin can still maintain the interfacial transition layer, so that the composite material can maintain high toughness.

[0053] Examples 6 and 7 were used to verify the effect of changing the proportion of highly branched polyolefins. In Example 6, after reducing the proportion of highly branched polyolefins, the median particle size of the polyolefin rubber phase increased to 1.05 μm, and the notched impact strength at 23°C decreased to 58.2 kJ / m. 2 The tear strength decreased to 69.8 kN / m. In Example 7, after increasing the proportion of highly branched polyolefins, the median particle size of the polyolefin rubber phase decreased to 0.62 μm, and the elongation at break increased to 720%, but the tensile strength and heat distortion temperature decreased to 25.0 MPa and 87.9 °C, respectively. These results indicate that when the content of highly branched polyolefins is insufficient, the branched segments cannot be fully distributed at the phase interface, resulting in a decrease in the refinement of the rubber phase; when the content of highly branched polyolefins is too high, the continuous phase supporting the skeleton is affected by the flexible segments. The ratio of long-branched highly branched polyolefins to short-branched highly branched polyolefins in Example 1 is more suitable for forming a multi-scale branched chain entanglement structure.

[0054] Examples 8 and 9 were used to verify the effect of changing the type of reactive grafted polyolefin. In Example 8, when a single maleic anhydride-grafted polyolefin was used, the median particle size of the polyolefin rubber phase was 0.85 μm, and the notched impact strength at 23°C was 60.4 kJ / m². 2 The tear strength was 70.6 kN / m. In Example 9, when carboxyl-grafted and hydroxyl-grafted polyolefins were used, the median particle size of the polyolefin rubber phase was 0.80 μm, and the notched impact strength at 23°C was 62.7 kJ / m. 2The tear strength was 72.4 kN / m. Both were better than Comparative Example 1, but lower than Example 1. This result indicates that the type and combination of grafting groups in reactive grafted polyolefins affect the interfacial distribution state within the interfacial transition layer. In Example 1, the combined use of maleic anhydride grafted polyolefin and epoxy-based grafted polyolefin resulted in a relatively complete interfacial connection structure on both the continuous phase side and the surface layer side of the polyolefin rubber phase.

[0055] Examples 10 to 12 were used to verify the adaptability of the preparation method parameters. In Example 10, after adjusting the screw speed to 150 rpm, the median particle size of the polyolefin rubber phase was 0.76 μm, and the notched impact strength at 23°C was 67.9 kJ / m. 2 In Example 11, after adjusting the screw speed to 220 rpm, the median particle size of the polyolefin rubber phase was 0.70 μm, and the notched impact strength at 23°C was 71.6 kJ / m². 2 Example 12: After increasing the melt mixing temperature, the median particle size of the polyolefin rubber phase was 0.73 μm, and the notched impact strength at 23°C was 69.8 kJ / m². 2 The above results demonstrate that, under the condition of unchanged formulation, by appropriately changing the melt mixing shear strength and temperature range, the composite material can still maintain a fine polyolefin rubber phase dispersion and high toughness index. The preparation method described above is repeatable for fluctuations in conventional melt mixing.

[0056] Comparative Example 2 employed a conventional toughening method that increased the polyolefin rubber phase content and combined it with a single maleic anhydride-grafted polyolefin. The notched impact strength at 23°C was 45.0 kJ / m. 2 The elongation at break was 580%, but the tensile strength decreased to 20.4 MPa and the heat distortion temperature decreased to 72.6 °C. This result indicates that while simply increasing the rubber phase can increase tensile deformation capacity, it weakens the continuous polyolefin support structure. Furthermore, due to the lack of highly branched polyolefin participating in the interfacial transition layer construction, the rubber phase particle size remained at 1.42 μm, and the tear strength was only 56.8 kN / m. Compared to this conventional system, Example 1 achieved higher notched impact strength, tear strength, and heat distortion temperature simultaneously with a lower total amount of polyolefin rubber phase, demonstrating that the interfacial transition layer structure can avoid the loss of rigidity and dimensional stability caused by simple rubber toughening.

[0057] Comparative Example 3, with the same formulation as Example 1, reduced the screw speed to 40 rpm, increased the median particle size of the polyolefin rubber phase to 2.30 μm, and reduced the notched impact strength at 23°C to 27.6 kJ / m. 2 At -20℃, the notched impact strength drops to 12.0 kJ / m. 2The tear strength decreased to 41.5 kN / m. This result indicates that when the melt mixing shear is insufficient, the polyolefin rubber phase is difficult to form uniformly dispersed micro-regions, and highly branched polyolefins and reactive grafted polyolefins are also difficult to co-locate at the phase interface. In Comparative Example 4, after omitting the premixing step, the median particle size of the polyolefin rubber phase was 1.28 μm, and the notched impact strength at 23℃ was 49.3 kJ / m. 2 The tear strength was 61.7 kN / m, lower than that of Example 1. This result indicates that first forming a branched segment distribution region between the polyolefin matrix and the highly branched polyolefin, and then adding the polyolefin rubber phase and reactive grafted polyolefin for melt mixing, is an important process condition for forming a stable interfacial transition layer.

Claims

1. A high-toughness, highly branched polyolefin rubber-plastic composite material, characterized in that, It includes a continuous polyolefin phase, a polyolefin rubber phase dispersed in the continuous polyolefin phase, a highly branched polyolefin, and a reactive grafted polyolefin; The highly branched polyolefin has a polyolefin backbone and multi-branched alkyl side chains, which are distributed at the phase interface between the polyolefin continuous phase and the polyolefin rubber phase. The reactive grafted polyolefin has polyolefin segments and reactive groups, and together with the highly branched polyolefin, it forms an interfacial transition layer covering the surface of the polyolefin rubber phase.

2. The high-toughness, highly branched polyolefin rubber-plastic composite material according to claim 1, characterized in that, The continuous polyolefin phase includes at least one of polypropylene, polyethylene, propylene-ethylene copolymer, and ethylene-α-olefin copolymer. The continuous polyolefin phase contains a nonpolar hydrocarbon chain structure that can form chain entanglement or blend compatibility with the polyolefin backbone of the highly branched polyolefin, and the continuous polyolefin phase is continuously connected to the interface transition layer.

3. The high-toughness, highly branched polyolefin rubber-plastic composite material according to claim 1, characterized in that, The polyolefin rubber phase includes at least one of ethylene-octene copolymer, ethylene-butene copolymer, ethylene propylene diene monomer (EPDM) rubber, and polyolefin thermoplastic elastomer. The polyolefin rubber phase is embedded in the polyolefin continuous phase in the form of independently dispersed micro-regions, and the surface layer of the polyolefin rubber phase is interlocked with the interface transition layer.

4. The high-toughness, highly branched polyolefin rubber-plastic composite material according to claim 1, characterized in that, The highly branched polyolefin is a branched polymer containing at least one of ethylene, propylene, butene, and octene structural units. The multi-branched alkyl side chains are non-linearly distributed along the polyolefin backbone. A portion of the highly branched polyolefin is embedded in the polyolefin continuous phase, and another portion extends to the surface of the polyolefin rubber phase.

5. The high-toughness, highly branched polyolefin rubber-plastic composite material according to claim 1, characterized in that, The reactive grafted polyolefin includes at least one of maleic anhydride grafted polyolefin, epoxy-based grafted polyolefin, carboxyl-based grafted polyolefin, and hydroxyl-based grafted polyolefin. The polyolefin segments of the reactive grafted polyolefin are located on one side of the continuous polyolefin phase, and the reactive groups are located on the surface layer of the polyolefin rubber phase.

6. The high-toughness, highly branched polyolefin rubber-plastic composite material according to claim 2, characterized in that, The continuous polyolefin phase is formed by a high-crystallinity polyolefin component and a low-crystallinity polyolefin component. The high-crystallinity polyolefin component forms a continuous skeleton, and the low-crystallinity polyolefin component is distributed between the continuous skeleton and the interface transition layer. The low-crystallinity polyolefin component and the highly branched polyolefin are mixed to form a segment transition region.

7. The high-toughness, highly branched polyolefin rubber-plastic composite material according to claim 3, characterized in that, The polyolefin rubber phase includes a first flexible rubber component and a second flexible rubber component. The first flexible rubber component is disposed adjacent to the polyolefin continuous phase, and the second flexible rubber component is located inside the polyolefin rubber phase. The first flexible rubber component and the interface transition layer together cover the second flexible rubber component.

8. The high-toughness, highly branched polyolefin rubber-plastic composite material according to claim 4, characterized in that, The highly branched polyolefin includes long-chain polyolefins and short-chain polyolefins. The long-chain polyolefins are interposed between the continuous polyolefin phase and the polyolefin rubber phase, and the short-chain polyolefins are distributed within the interface transition layer. The long-chain polyolefins and the short-chain polyolefins together form a multi-scale branched chain entanglement structure.

9. The high-toughness, highly branched polyolefin rubber-plastic composite material according to claim 5, characterized in that, The reactive grafted polyolefin includes a first grafted polyolefin and a second grafted polyolefin. The polyolefin segments of the first grafted polyolefin are compatible with the continuous polyolefin phase, and the reactive groups of the second grafted polyolefin are bonded to the surface layer of the polyolefin rubber phase. The first grafted polyolefin and the second grafted polyolefin are interleaved in the interfacial transition layer.

10. A method for preparing a high-toughness, highly branched polyolefin rubber-plastic composite material, characterized in that, include: A polyolefin matrix is ​​premixed with a highly branched polyolefin to form a premix containing a continuous polyolefin phase and a branched segment distribution region. Add a polyolefin rubber phase and a reactive grafted polyolefin to the premix and melt-mix it so that the polyolefin rubber phase is dispersed in the continuous polyolefin phase, and the highly branched polyolefin and the reactive grafted polyolefin are co-distributed at the phase interface between the continuous polyolefin phase and the polyolefin rubber phase. The molten compound is molded to obtain a high-toughness, highly branched polyolefin rubber-plastic composite material with an interfacial transition layer.