A method for preparing an engineering plastic reinforced modification

Abstract

The application relates to the technical field of high polymer composite material modification, and specifically discloses a preparation method of engineering plastic reinforcing modification, which comprises the following steps: S1, surface purification and activation treatment are performed on reinforcing fibers to obtain pretreated fibers; S2, the pretreated fibers are immersed in a reaction solution containing a cyclic monomer, a catalyst, an activator and a thermoresponsive non-reactive block regulator to obtain pre-prepared soft shell fibers; S3, the pre-prepared soft shell fibers are melt-blended with engineering plastic matrix resin, so that a gradient interface structure with continuously changed modulus is constructed between the fibers and the matrix, and a blended material is obtained; and S4, the blended material is extruded, cooled and granulated to prepare reinforcing modified engineering plastic particles. The engineering plastic can be used for manufacturing automobile parts and electronic and electrical appliance housings, and has the advantages of good rigidity and toughness balance and excellent wet heat aging resistance.

Description

Technical Field

[0001] This application relates to the field of polymer composite material modification technology, and more specifically, it relates to a method for preparing reinforced and modified engineering plastics. Background Technology

[0002] Engineering plastics such as polyamides, polyphenylene sulfides, and polycarbonates are widely used in automotive manufacturing, electronics, and aerospace due to their advantages of being lightweight, corrosion-resistant, and easy to mold and process. To further improve the mechanical properties of engineering plastics to meet the load-bearing requirements of structural components, they are usually reinforced and modified with glass fibers or carbon fibers. In existing technologies, the fiber surface is often coated with silane coupling agents, or a layer of low molecular weight polymer is coated on the fiber surface using heavy sizing technology to improve the interfacial bonding between the fiber and the matrix resin. These treatment methods can improve the tensile strength and flexural modulus of composite materials to a certain extent, enabling fiber-reinforced engineering plastics to exhibit higher rigidity under static load conditions.

[0003] However, engineering plastics aim for maximum interfacial bond strength between fibers and the matrix. This results in stress concentration in the interfacial region when subjected to impact loads, which cannot be effectively dissipated through the interfacial layer. This leads to brittle delamination between the fibers and the matrix, resulting in decreased toughness and a rigidity-toughness inversion phenomenon where rigidity increases while toughness deteriorates. At the same time, traditional silane coupling agent monolayer interfaces are prone to hydrolysis in humid and hot environments, and the interfacial bonding strength continuously decreases with the extension of service time. This makes it difficult for the composite material to meet the mechanical property retention requirements under long-term humid and hot conditions, thus restricting the further promotion of fiber-reinforced engineering plastics in high-end applications. Summary of the Invention

[0004] To address the problem of decreased material toughness caused by the increased interfacial bonding strength of related engineering plastics, this application provides a method for preparing reinforced and modified engineering plastics.

[0005] This application provides a method for preparing reinforced and modified engineering plastics, using the following technical solution: A method for preparing reinforced and modified engineering plastics includes the following steps: S1. The reinforcing fibers are subjected to surface cleaning and activation treatment to obtain pretreated fibers; S2. The pretreated fiber is immersed in a reaction solution containing cyclic monomers, catalysts, activators and thermally responsive non-reactive block modifiers to carry out an in-situ anionic polymerization reaction, forming a functionalized soft polymer shell with active end groups on the fiber surface to obtain pre-made soft shell fiber. S3. The prefabricated soft shell fiber is melt-blended with the engineering plastic matrix resin. Under high temperature shearing, the active end groups of the shell layer are diffusely welded to the molecular chain end groups of the matrix resin. At the same time, the soft micro-regions are stretched in a direction perpendicular to the fiber surface to form a radial bridging structure, thereby constructing a gradient interface structure with continuously changing modulus between the fiber and the matrix to obtain the blended material. S4. The blended material is extruded, cooled, and pelletized to obtain reinforced modified engineering plastic granules.

[0006] By adopting the above technical solution, since a polymer soft shell layer containing phase-separated soft micro-regions is pre-constructed on the fiber surface, and a modulus gradient interface is formed by diffusion welding and micro-region deformation during melt processing, the soft shell layer of the composite material can dissipate energy through its own deformation and micro-region bridging when under stress, while the chemical bonding of the interface maintains the integrity of the structure. Therefore, the effect of simultaneously improving rigidity and toughness and resisting humid heat aging is achieved.

[0007] Preferably, in step S1, the reinforcing fiber is carbon fiber or glass fiber; the surface cleaning and activation treatment is as follows: first, an organic solvent is used to clean and remove impurities from the surface of the reinforcing fiber, and then plasma surface treatment is used to introduce active reaction sites.

[0008] By adopting the above technical solution, carbon fiber or glass fiber is selected as the reinforcement, and the surface contaminants of the fiber are removed by organic solvent cleaning and plasma treatment, and active functional groups are generated. This improves the surface energy of the fiber and provides a basis for the uniform anchoring and firm bonding of the soft shell layer in the subsequent in-situ polymerization reaction.

[0009] Preferably, in step S2, the cyclic monomer is caprolactam or p-dichlorobenzene.

[0010] By adopting the above technical solution, since the selected cyclic monomer has chemical similarity or reaction compatibility with the target engineering plastic matrix resin, the formed soft shell layer and the matrix can achieve diffusion and chain extension of molecular chain segments, thereby improving the interfacial welding strength.

[0011] Preferably, in step S2, when the cyclic monomer is caprolactam, the catalyst is sodium caprolactam and the activator is N-acetylcaprolactam; when the cyclic monomer is p-dichlorobenzene, the reaction solution also contains sodium sulfide.

[0012] By adopting the above technical solution, a highly active catalytic initiation system is matched for specific monomers, enabling rapid anionic polymerization at low temperatures and suppressing side reactions. This ensures that the molecular weight and structure of the soft shell polymer are controllable and structurally regular, resulting in stable and consistent shell performance.

[0013] Preferably, in step S2, the polyamide segment of the thermoresponsive non-reactive block modifier is a polycaprolactam segment, the polyetheramine segment is an inert polyether segment, and the end group of the polyamide segment is an active end group capable of participating in the in-situ anionic polymerization reaction; the amount of the thermoresponsive non-reactive block modifier is 1% to 10% of the mass of the cyclic monomer.

[0014] By adopting the above technical solution, the polyamide segment of the block regulator is anchored in the shell network through the participation of end groups in polymerization, while the inert polyetheramine segment undergoes in-situ phase separation due to thermodynamic incompatibility, forming diffuse nanoscale soft micro-regions inside the shell. The appropriate dosage ratio ensures that the micro-regions develop without destroying the continuity of the shell, thus laying a morphological foundation for constructing multi-level energy-consuming structures in subsequent processing.

[0015] Preferably, in step S2, the temperature of the in-situ anionic polymerization reaction is 110–125°C, and the time is 90–150 seconds; the thickness of the formed functionalized soft polymer shell is 10–500 nanometers.

[0016] By adopting the above technical solution, the polymerization temperature and time are controlled, so that the reaction is limited to the fiber surface and a thin shell with a thickness in the nanometer range is generated, avoiding fiber adhesion caused by excessive polymerization. The shell with this thickness range can efficiently transfer loads and dissipate energy by plastic deformation under impact, while retaining the high strength characteristics of the fiber body.

[0017] Preferably, in step S2, the reaction solution is prepared as follows: the cyclic monomer is heated to 70-90°C to melt it, the catalyst and activator are added and stirred for 5-15 minutes until homogeneous, the thermoresponsive non-reactive block modifier is added and stirring is continued for 10-20 minutes until uniformly dispersed.

[0018] By adopting the above technical solution, the step-by-step feeding and thorough stirring preparation method ensures the uniform dispersion of catalyst, activator and block modifier in monomer melt, avoids reaction differences caused by uneven local concentration, and thus ensures the consistency of composition and microstructure of the soft shell layer formed on the surface of each fiber.

[0019] Preferably, in step S3, the engineering plastic matrix resin is polyamide, polyphenylene sulfide, or polycarbonate; the processing temperature for melt blending is set to be 10–50°C higher than the melting point of the engineering plastic matrix resin.

[0020] By adopting the above technical solution, since the selected matrix resin covers a variety of thermoplastic engineering plastics and the processing temperature is moderately higher than the melting point, it not only ensures the complete plasticization of the matrix resin and the ability of molecular chain movement, but also avoids the thermal degradation of the shell polymer at excessively high temperatures. This provides rheological conditions for diffusion welding reaction and micro-area shear deformation, enabling the formation of a gradient interface structure.

[0021] Preferably, in step S3, an antioxidant is also added, wherein the antioxidant is a hindered phenolic antioxidant or a phosphite antioxidant.

[0022] By adopting the above technical solution, the addition of antioxidants during the melt blending process inhibits the oxidative chain scission of the matrix resin and shell polymer under high-temperature shear, maintains the reactivity of the molecular chain end groups, thereby ensuring the diffusion welding reaction between the shell active end groups and the matrix molecular chains, and enhancing the chemical bonding stability of the interface.

[0023] Preferably, in step S4, the extrusion temperature is higher than the melting point of the matrix resin by a certain range. In step S4, the extrusion temperature is 10-50°C above the melting point of the engineering plastic matrix resin, and the cooling is water cooling with a cooling water temperature of 20-40°C. The pelletizing is done by traction pelletizing with a pellet length of 2-5mm.

[0024] By adopting the above technical solution, due to the reasonable extrusion temperature setting, the material has good fluidity and no degradation. The water cooling process provides uniform and rapid cooling and shaping, avoiding interfacial stress caused by slow crystallization. The pellet size is controlled consistently, so that the resulting pellets can be fed smoothly and plasticized uniformly during subsequent injection molding or extrusion molding, thus ensuring the quality stability of the final product.

[0025] In summary, this application has the following beneficial effects: 1. Because this application uses a polymer soft shell layer containing phase-separated soft micro-regions pre-constructed on the surface of reinforcing fibers, and forms a modulus gradient interface structure through diffusion welding and micro-region deformation during melt processing, the soft shell layer deforms and dissipates energy first when the composite material is subjected to external force. The micro-region bridging structure provides multi-level energy dissipation channels, while the chemically bonded interface prevents crack propagation. Therefore, the effect of simultaneously improving rigidity and toughness and resisting humid heat aging is achieved.

[0026] 2. In this application, polyetheramine-polyamide diblock copolymer is preferably used as a thermally responsive non-reactive block modifier. Since the polyamide segment of the modifier is anchored in the shell network through the participation of end groups in polymerization, and the inert polyetheramine segment spontaneously separates during the polymerization process to form nanoscale soft microdomains, stress concentration dissipation sites are pre-constructed inside the shell, providing a basis for the formation of radial bridging structures in subsequent processing.

[0027] 3. The method of this application introduces active reaction sites on the fiber surface by performing organic solvent cleaning and plasma activation treatment on the reinforcing fiber, so that the soft shell layer generated by in-situ polymerization forms a chemical bond anchor between it and the fiber, thus obtaining a stable interface bond and hydrolysis resistance.

[0028] 4. In this application, it is preferred to add hindered phenolic or phosphite antioxidants during the melt blending stage. The antioxidants effectively inhibit the oxidative degradation of the matrix resin and the shell polymer under high-temperature shear conditions, maintain the reactivity of the molecular chain end groups, thus ensuring the full completion of the diffusion welding reaction between the shell and the matrix, and enhancing the chemical bonding stability of the gradient interface. Attached Figure Description

[0029] Figure 1 This is a flowchart of a method for preparing reinforced and modified engineering plastics according to this application; Figure 2 This is a schematic diagram showing the tensile strength test results of the embodiments and comparative examples in this application; Figure 3 This is a schematic diagram of the elongation at break test results of the embodiments and comparative examples in this application; Figure 4 This is a schematic diagram showing the notch impact strength test results of a simply supported beam in the embodiments and comparative examples of this application; Figure 5 This is a schematic diagram showing the test results of the mechanical property retention rate after damp heat aging in the embodiments and comparative examples of this application. Detailed Implementation

[0030] The present application will be further described in detail below with reference to the accompanying drawings and embodiments.

[0031] Technical concept: A method for preparing reinforced and modified engineering plastics is disclosed. The method includes the following steps: S1, surface cleaning and activation treatment of reinforcing fibers to obtain pretreated fibers; S2, immersing the pretreated fibers in a reaction solution containing cyclic monomers, catalysts, activators, and thermally responsive non-reactive block modulators to obtain pre-formed soft-shell fibers; S3, melt-blending the pre-formed soft-shell fibers with an engineering plastic matrix resin to construct a gradient interface structure with continuously changing modulus between the fibers and the matrix, thereby obtaining a blend; S4, extruding, cooling, and pelletizing the blend to obtain reinforced and modified engineering plastic granules.

[0032] This application employs a polymer soft shell layer containing phase-separated soft microregions pre-constructed on the surface of reinforcing fibers, and a modulus gradient interface structure is formed through diffusion welding and microregion deformation during melt processing. This allows the soft shell layer to deform and dissipate energy first when the composite material is subjected to external forces. The microregion bridging structure provides multi-level energy dissipation channels, while the chemically bonded interface prevents crack propagation. Therefore, the effect of simultaneously improving rigidity and toughness and resisting humid heat aging is achieved.

[0033] Example 1: This example provides a method for preparing reinforced and modified engineering plastics, comprising the following steps: S1. The reinforcing fibers are subjected to surface cleaning and activation treatment to obtain pretreated fibers.

[0034] Among them, carbon fiber is selected as the reinforcing fiber, and the specific operation of surface purification and activation treatment is as follows: first, acetone is used to clean and remove impurities from the surface of carbon fiber, and then air plasma surface treatment is used to introduce active reaction sites.

[0035] S2. The pretreated fiber is immersed in a reaction solution containing cyclic monomers, catalysts, activators and thermally responsive non-reactive block modifiers to carry out in-situ anionic polymerization reaction, forming a functionalized soft polymer shell with active end groups on the fiber surface, thus obtaining pre-made soft shell fiber.

[0036] In this process, caprolactam is selected as the cyclic monomer, sodium caprolactam is selected as the catalyst, N-acetylcaprolactam is selected as the activator, and the thermoresponsive non-reactive block modifier is selected with a structure in which the polyamide segment is a polycaprolactam segment and the polyetheramine segment is an inert polyether segment, and the end group of the polyamide segment is an active end group that can participate in the in-situ anionic polymerization reaction. Its amount is 1% of the mass of caprolactam. The temperature of the in-situ anionic polymerization reaction is set to 110℃, the reaction time is set to 90 seconds, and the thickness of the functionalized soft polymer shell is controlled to be 10 nanometers. The reaction solution is prepared as follows: caprolactam is heated to 70℃ to melt it, sodium caprolactam and N-acetylcaprolactam are added and stirred for 5 minutes until uniform, then the thermoresponsive non-reactive block modifier is added and stirred for another 10 minutes until uniformly dispersed.

[0037] S3. The pre-fabricated soft shell fiber is melt-blended with the engineering plastic matrix resin. Under high temperature shearing, the active end groups of the shell layer diffusely weld with the molecular chain end groups of the matrix resin. At the same time, the soft micro-regions are stretched in a direction perpendicular to the fiber surface to form a radial bridging structure, thereby constructing a gradient interface structure with continuously changing modulus between the fiber and the matrix to obtain the blended material.

[0038] The engineering plastic matrix resin is polyamide, and the melting blending processing temperature is set to be 10°C higher than the melting point of polyamide. Antioxidants are also added during the blending process, and hindered phenolic antioxidants are selected.

[0039] S4. The blended material is extruded, cooled, and pelletized to obtain reinforced modified engineering plastic granules.

[0040] The extrusion temperature is set to 10°C above the melting point of polyamide, cooling is achieved by water cooling with a water temperature of 20°C, and pelletizing is achieved by traction pelletizing with a pellet length of 2mm.

[0041] Example 2: This example provides a method for preparing reinforced and modified engineering plastics, comprising the following steps: S1. The reinforcing fibers are subjected to surface cleaning and activation treatment to obtain pretreated fibers.

[0042] Among them, glass fiber is selected as the reinforcing fiber, and the specific operation of surface purification and activation treatment is as follows: first, ethanol is used to clean and remove impurities from the surface of the glass fiber, and then oxygen plasma surface treatment is used to introduce active reaction sites.

[0043] S2. The pretreated fiber is immersed in a reaction solution containing cyclic monomers, catalysts, activators and thermally responsive non-reactive block modifiers to carry out in-situ anionic polymerization reaction, forming a functionalized soft polymer shell with active end groups on the fiber surface, thus obtaining pre-made soft shell fiber.

[0044] In this process, p-dichlorobenzene is selected as the cyclic monomer, sodium sulfide is also included as a reactant in the reaction solution, ferric chloride is selected as the catalyst, N-methylpyrrolidone is selected as the activator, and the thermoresponsive non-reactive block modifier is selected with a polyamide segment consisting of a polycaprolactam segment and an inert polyetheramine segment, and the end group of the polyamide segment is an active end group that can participate in the in-situ anionic polymerization reaction. Its amount is 5.5% of the mass of p-dichlorobenzene. The temperature of the in-situ anionic polymerization reaction is set at 117.5℃, the reaction time is set at 120 seconds, and the thickness of the functionalized soft polymer shell is controlled at 255 nm. The reaction solution is prepared as follows: p-dichlorobenzene is heated to 80℃ to melt it, ferric chloride and N-methylpyrrolidone are added and stirred for 10 minutes until uniform, then the thermoresponsive non-reactive block modifier is added and stirring is continued for 15 minutes until uniformly dispersed.

[0045] S3. The pre-fabricated soft shell fiber is melt-blended with the engineering plastic matrix resin. Under high temperature shearing, the active end groups of the shell layer diffusely weld with the molecular chain end groups of the matrix resin. At the same time, the soft micro-regions are stretched in a direction perpendicular to the fiber surface to form a radial bridging structure, thereby constructing a gradient interface structure with continuously changing modulus between the fiber and the matrix to obtain the blended material.

[0046] The engineering plastic matrix resin is polyphenylene sulfide, and the processing temperature for melt blending is set to be 30°C higher than the melting point of polyphenylene sulfide. Antioxidants are also added during the blending process, and phosphite antioxidants are selected.

[0047] S4. The blended material is extruded, cooled, and pelletized to obtain reinforced modified engineering plastic granules.

[0048] The extrusion temperature is set to 30°C above the melting point of polyphenylene sulfide, cooling is achieved by water cooling with a water temperature of 30°C, and pelletizing is performed by traction pelletizing with a pellet length of 3.5mm.

[0049] Example 3: This example provides a method for preparing reinforced and modified engineering plastics, comprising the following steps: S1. The reinforcing fibers are subjected to surface cleaning and activation treatment to obtain pretreated fibers.

[0050] Among them, carbon fiber is selected as the reinforcing fiber, and the specific operation of surface purification and activation treatment is as follows: first, isopropanol is used to clean and remove impurities from the surface of carbon fiber, and then argon plasma surface treatment is used to introduce active reaction sites.

[0051] S2. The pretreated fiber is immersed in a reaction solution containing cyclic monomers, catalysts, activators and thermally responsive non-reactive block modifiers to carry out in-situ anionic polymerization reaction, forming a functionalized soft polymer shell with active end groups on the fiber surface, thus obtaining pre-made soft shell fiber.

[0052] In this process, caprolactam is selected as the cyclic monomer, sodium caprolactam is selected as the catalyst, N-acetylcaprolactam is selected as the activator, and the thermoresponsive non-reactive block modifier is selected with a structure in which the polyamide segment is a polycaprolactam segment and the polyetheramine segment is an inert polyether segment. The end group of the polyamide segment is an active end group that can participate in the in-situ anionic polymerization reaction. Its amount is 10% of the mass of caprolactam. The temperature of the in-situ anionic polymerization reaction is set at 125℃, the reaction time is set at 150 seconds, and the thickness of the functionalized soft polymer shell is controlled at 500 nanometers. The reaction solution is prepared as follows: caprolactam is heated to 90℃ to melt it, sodium caprolactam and N-acetylcaprolactam are added and stirred for 15 minutes until uniform, then the thermoresponsive non-reactive block modifier is added and stirred for another 20 minutes until uniformly dispersed.

[0053] S3. The pre-fabricated soft shell fiber is melt-blended with the engineering plastic matrix resin. Under high temperature shearing, the active end groups of the shell layer diffusely weld with the molecular chain end groups of the matrix resin. At the same time, the soft micro-regions are stretched in a direction perpendicular to the fiber surface to form a radial bridging structure, thereby constructing a gradient interface structure with continuously changing modulus between the fiber and the matrix to obtain the blended material.

[0054] The engineering plastic matrix resin is polycarbonate, and the melting blending processing temperature is set to be 50°C higher than the melting point of polycarbonate. Antioxidants are also added during the blending process, and hindered phenolic antioxidants are selected.

[0055] S4. The blended material is extruded, cooled, and pelletized to obtain reinforced modified engineering plastic granules.

[0056] The extrusion temperature is set to 50°C above the melting point of polycarbonate, cooling is achieved by water cooling with a water temperature of 40°C, and pelletizing is achieved by traction pelletizing with a pellet length of 5mm.

[0057] Comparative Example 1: This comparative example refers to the content of Example 1, except that no thermally responsive non-reactive block modifier is added in step S2, and the rest is the same as Example 1.

[0058] Comparative Example 2: This comparative example refers to the content of Example 1, except that in step S2, an in-situ anionic polymerization reaction is not carried out to form a functionalized soft polymer shell. Instead, the pretreated fiber is directly immersed in a conventional silane coupling agent solution for surface coating treatment. The rest of the content is the same as in Example 1.

[0059] Comparative Example 3: This comparative example refers to the content of Example 1, except that in step S1, only acetone cleaning is used to remove impurities from the carbon fiber surface, and plasma surface treatment is not performed to introduce active reaction sites. The rest of the content is the same as in Example 1.

[0060] Comparative Example 4: This comparative example is the same as that in Example 1, except that hindered phenolic antioxidants are not added in step S3. The rest of the content is the same as that in Example 1.

[0061] Comparative Example 5: This comparative example refers to the content of Example 2, except that the thermally responsive non-reactive block modifier used in step S2 is replaced with homopolymer polyamide, that is, the modifier does not contain inert polyetheramine segments, and the rest is the same as Example 2.

[0062] Comparative Example 6: This comparative example is the same as that in Example 3, except that N-acetylcaprolactam activator is not added in step S2. The rest of the content is the same as that in Example 3.

[0063] Performance testing Sample preparation: The reinforced modified engineering plastic granules obtained in Examples 1 to 3 and Comparative Examples 1 to 6 were dried to constant weight in a forced-air drying oven at a suitable temperature. Then, each dried granule was injection molded into standard tensile test specimens, standard impact test specimens, and standard bending test specimens using an injection molding machine. The injection temperature was set according to the processing temperature range of each matrix resin, and the injection pressure and holding time were kept consistent. The number of test specimens in each group met the requirements of the corresponding test standard for parallel samples.

[0064] Tensile property testing: Tensile properties of each group of standard tensile specimens were tested using a universal testing machine. The tests were conducted at room temperature with a constant tensile rate. The tensile strength and elongation at break of the specimens were recorded. Multiple parallel samples were tested for each group of specimens, and the average value was taken. Tensile properties were tested according to GB / T1040 standard.

[0065] Impact performance testing: A pendulum impact testing machine was used to test the notched impact strength of each group of standard impact specimens. Before testing, a V-notch of a specified size was machined in the middle of the specimen using a notch cutter. The test was conducted at room temperature. The impact energy absorbed when the specimen fractured was recorded and the impact strength was calculated. Multiple parallel samples were tested for each group of specimens, and the average value was taken. The impact performance was tested according to GB / T1043 standard.

[0066] Bending performance testing: A universal testing machine was used to perform three-point bending tests on each group of standard bending specimens. The tests were conducted at room temperature with a constant loading rate. The bending strength and bending modulus of the specimens were recorded. Multiple parallel samples were tested for each group of specimens, and the average value was taken. The bending performance was tested according to GB / T9341 standard.

[0067] Test for retention rate of mechanical properties after damp heat aging: Standard tensile and impact specimens were placed in a constant temperature and humidity chamber for damp heat aging treatment. The chamber temperature and relative humidity were set to the specified values, and the aging treatment lasted for the specified duration. After removal, the specimens were allowed to stand at room temperature for a specified time to eliminate thermal stress. Subsequently, the tensile and impact properties were tested according to the conditions described above. The retention rate of tensile strength and impact strength after damp heat aging relative to their pre-aging values ​​was calculated. The damp heat aging conditions were conducted according to GB / T12000 standard, and the mechanical property tests after aging were conducted according to GB / T1040 and GB / T1043 standards, respectively.

[0068] Interface morphology observation: Impact fracture surfaces of each group of reinforced modified engineering plastic particles were collected, surface-sprayed with gold, and then the morphology of the fracture surfaces was observed using a scanning electron microscope. The focus was on observing the interfacial bonding state between the fibers and the matrix resin, the fiber pull-out length, and the plastic deformation traces of the matrix resin. Interface morphology observation was conducted in accordance with GB / T36422 standard.

[0069] Table 1: Test results of tensile and impact properties of composite materials

[0070] Table 2: Test results of bending properties and mechanical property retention rate of composite materials after damp heat aging

[0071] Table 3: Summary of Observation Results of Composite Material Interface Morphology

[0072] Example Conclusion: As can be seen from Examples 1-3 and Comparative Example 1, and Tables 1 and 3, the thermally responsive non-reactive block modifier is a key component for constructing phase-separated soft microregions and radial bridging structures. Without this modifier, the shell cannot form pre-defined stress concentration dissipation sites, and the interface undergoes brittle peeling under impact load. The rigidity and toughness of the composite material cannot be improved simultaneously. However, the examples with the addition of this modifier achieve a balance between rigidity and toughness through a multi-level energy dissipation mechanism.

[0073] As can be seen from Examples 1-3 and Comparative Example 2, and Tables 1 and 2, the functionalized soft polymer shell formed by in-situ anionic polymerization has a fundamental advantage over conventional silane coupling agent coating treatment. Coupling agents can only form physically adsorbed monolayer interfaces and cannot undergo diffusion welding reactions with the matrix resin during melt processing to form chemical bonds. The interfacial bonding is insufficient and it is prone to hydrolysis failure in humid and hot environments. In contrast, the chemically bonded gradient interface constructed in this application shows improved mechanical properties and resistance to humid and hot aging.

[0074] As can be seen from Examples 1-3 and Comparative Example 3, and Tables 2 and 3, the active reaction sites introduced by plasma surface activation treatment are a prerequisite for achieving chemical bonding and anchoring between the soft shell and the fiber surface. Without this treatment step, the shell and fiber only have physical adhesion, and the interfacial bonding is not strong enough. During the wet heat aging process, moisture penetrates along the interface, causing further deterioration of the bonding and a significant reduction in the retention rate of mechanical properties. In contrast, the examples that have undergone activation treatment have achieved a stable interfacial bonding and resistance to hydrolysis.

[0075] Based on Examples 1-3 and Comparative Example 4, and in conjunction with Tables 1 and 2, it can be seen that the addition of hindered phenolic or phosphite antioxidants effectively inhibited the oxidative degradation of the matrix resin and shell polymer during high-temperature shear melt blending. In the absence of antioxidants, the molecular chain end genes oxidize and break down, resulting in inactivation. The diffusion welding reaction cannot be fully completed, the interfacial chemical bond density decreases, and the mechanical properties of the composite material and the performance retention rate after damp heat aging are adversely affected. In contrast, the examples with added antioxidants ensured the chemical integrity and performance stability of the gradient interface structure.

[0076] Combining Example 2 and Comparative Example 5 with Tables 1 and 3, it can be seen that after homopolymer polyamide replaces polyetheramine-polyamide diblock copolymer, the regulator lacks inert polyetheramine segments. During polymerization, in-situ phase separation cannot occur inside the shell to form soft microregions, and the shell exhibits a homogeneous structure. During melt shearing, it cannot form a radial bridging structure, and the interfacial energy dissipation capacity is significantly reduced, resulting in a significant decrease in impact toughness. In contrast, the example using diblock copolymer achieves excellent impact toughness while maintaining high tensile strength.

[0077] As can be seen from Example 3 and Comparative Example 6, and from Tables 1 and 2, the activator plays a role in initiating and activating chain growth in the anionic polymerization reaction. Without the activator, the polymerization rate and conversion rate are significantly reduced, the resulting shell polymer has a low molecular weight and insufficient number of active terminal groups, the shell structure is loose and the diffusion welding reaction with the matrix is ​​insufficient, the interfacial bonding strength is weakened, and the mechanical properties of the composite material and the retention rate of mechanical properties after wet heat aging are significantly reduced. In contrast, the example with the addition of the activator ensures the structural integrity of the shell polymer and the interfacial reactivity, thereby obtaining excellent comprehensive mechanical properties and durability.

[0078] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing reinforced and modified engineering plastics, characterized in that, Includes the following steps: S1. The reinforcing fibers are subjected to surface cleaning and activation treatment to obtain pretreated fibers; S2. The pretreated fiber is immersed in a reaction solution containing cyclic monomers, catalysts, activators and thermally responsive non-reactive block modifiers to carry out an in-situ anionic polymerization reaction, forming a functionalized soft polymer shell with active end groups on the fiber surface to obtain pre-made soft shell fiber. S3. The prefabricated soft shell fiber is melt-blended with the engineering plastic matrix resin. Under high temperature shearing, the active end groups of the shell layer are diffusely welded to the molecular chain end groups of the matrix resin. At the same time, the soft micro-regions are stretched in a direction perpendicular to the fiber surface to form a radial bridging structure, thereby constructing a gradient interface structure with continuously changing modulus between the fiber and the matrix to obtain the blended material. S4. The blended material is extruded, cooled, and pelletized to obtain reinforced modified engineering plastic granules.

2. The method for preparing reinforced and modified engineering plastics according to claim 1, characterized in that, In step S1, the reinforcing fiber is carbon fiber or glass fiber; the surface cleaning and activation treatment is as follows: first, organic solvent is used to clean and remove impurities from the surface of the reinforcing fiber, and then plasma surface treatment is used to introduce active reaction sites.

3. The method for preparing reinforced and modified engineering plastics according to claim 1, characterized in that, In step S2, the cyclic monomer is caprolactam or p-dichlorobenzene.

4. The method for preparing reinforced and modified engineering plastics according to claim 3, characterized in that, In step S2, when the cyclic monomer is caprolactam, the catalyst is sodium caprolactam and the activator is N-acetylcaprolactam; when the cyclic monomer is p-dichlorobenzene, the reaction solution also contains sodium sulfide.

5. The method for preparing reinforced and modified engineering plastics according to claim 1, characterized in that, In step S2, the polyamide segment of the thermoresponsive non-reactive block modifier is a polycaprolactam segment, the polyetheramine segment is an inert polyether segment, and the end group of the polyamide segment is an active end group that can participate in the in-situ anionic polymerization reaction; the amount of the thermoresponsive non-reactive block modifier is 1% to 10% of the mass of the cyclic monomer.

6. The method for preparing reinforced and modified engineering plastics according to claim 1, characterized in that, In step S2, the in-situ anionic polymerization reaction is carried out at a temperature of 110–125°C for 90–150 seconds; the thickness of the formed functionalized soft polymer shell is 10–500 nanometers.

7. The method for preparing reinforced and modified engineering plastics according to claim 1, characterized in that, In step S2, the reaction solution is prepared as follows: the cyclic monomer is heated to 70-90°C to melt it, the catalyst and activator are added and stirred for 5-15 minutes until homogeneous, the thermoresponsive non-reactive block modifier is added and stirring is continued for 10-20 minutes until uniformly dispersed.

8. The method for preparing reinforced and modified engineering plastics according to claim 1, characterized in that, In step S3, the engineering plastic matrix resin is polyamide, polyphenylene sulfide, or polycarbonate; the processing temperature for melt blending is set to be 10–50°C higher than the melting point of the engineering plastic matrix resin.

9. The method for preparing reinforced and modified engineering plastics according to claim 1, characterized in that, In step S3, an antioxidant is also added, which is a hindered phenolic antioxidant or a phosphite antioxidant.

10. The method for preparing reinforced and modified engineering plastics according to claim 1, characterized in that, In step S4, the extrusion temperature is 10-50°C above the melting point of the engineering plastic matrix resin, the cooling is water cooling, and the cooling water temperature is 20-40°C; the pelletizing is done by traction pelletizing, and the pellet length is 2-5mm.

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