High-strength low-water-absorption polyamide engineering plastic and preparation method thereof

Abstract

The application relates to the technical field of high polymer material compositions, and discloses a high-strength low-water-absorption polyamide engineering plastic and a preparation method thereof, which comprises the following steps: setting a non-monotonic temperature path in a double-screw extruder, applying high shear to make a hydrophobic phase forcibly cover the surface of solid polyamide particles below the melting point of a polyamide matrix, and constructing a core-shell intermediate phase state; then, the polyamide core part is melted by temperature rising, an in-situ grafting of a pre-set compatibility agent at the interface is triggered, and the intermediate phase state is chemically fixed. The application constrains the controlled path of subsequent chemical reactions through physical shaping, constructs an ordered hydrophobic network phase, can form effective physical enclosure to a hydrophilic matrix, and establishes an efficient stress transmission path, so that the material can realize low water absorption and simultaneously improve strength and toughness.

Description

Technical Field

[0001] This invention relates to a high-strength, low-absorption polyamide engineering plastic and its preparation method, belonging to the technical field of polymer material composition. Background Technology

[0002] Polyamide engineering plastics occupy an important position in the field of polymer material compositions due to their excellent comprehensive mechanical properties, wear resistance, and heat resistance. They are widely used in various harsh engineering environments. However, the molecular chain structure of polyamide materials makes them highly hydrophilic. In humid and hot environments, polyamide compositions are prone to absorbing water, which leads to dimensional swelling of the material. At this time, its key mechanical properties such as tensile strength and flexural modulus will decrease significantly, which will limit the use of the material in applications requiring high dimensional stability and environmental tolerance.

[0003] To eliminate this defect, melt blending extrusion is commonly used in the field, which involves introducing hydrophobic polymers or reinforcing fillers into a polyamide matrix. However, conventional melt blending processes have a common problem, especially a process setting where the temperature increases monotonically from the feed zone to the die zone. The purpose of this setting is simply to melt all polymer components as quickly as possible. When this process is used in intrinsically incompatible systems such as polyamide and polypropylene, problems arise. At high temperatures, the physical transformation of the components in the system and the chemical reactions at the interfaces occur simultaneously and uncontrollably. This leads to disorder and randomness in the dispersion of the toughening phase, the distribution of the filler, and the interfacial reactions of the compatibility agent.

[0004] This disordered and random process path inevitably leads to an uneven and difficult-to-control microstructure of the composite product. In such products, the hydrophobic toughening phase does not form an effective water-blocking network. Instead, it is randomly dispersed in the polyamide matrix in the form of isolated islands. This island structure brings two serious problems: 1. It is impossible to achieve a low water absorption rate. Water molecules can easily bypass these islands and penetrate into the material through the continuous channels of the hydrophilic matrix; 2. It is difficult to effectively transfer stress. The interface bonding formed by random collisions between the phases is very weak, and efficient stress transfer cannot be achieved. For example, Chinese invention patent CN115181416B discloses a polyamide engineering plastic and its preparation method and application. It uses a chain extender to prepare a high molecular weight modified polyamide as a toughening agent, and then physically blends it with a conventional polyamide matrix. Although this method avoids compatibility issues, its process is still essentially random blending, and it is also difficult to form an ordered and controllable microstructure.

[0005] Therefore, how to prepare a polyamide engineering plastic composition that combines high strength, high toughness and low water absorption is the technical problem to be solved by this invention. Summary of the Invention

[0006] This invention provides a high-strength, low-absorption polyamide engineering plastic and its preparation method. Its main purpose is to solve the problem that the process parameters cannot be precisely controlled in the existing monotonous heating melt blending process.

[0007] To achieve the above objectives, the present invention provides a method for preparing high-strength, low-absorption polyamide engineering plastic. The method involves melt-blending the composition in a twin-screw extruder that forms a shearing and shaping zone and a first plasticizing reaction zone under preset process conditions along the material conveying direction. The composition comprises: 60 to 70 parts by weight of polyamide 66, 15 to 20 parts by weight of block copolymer polypropylene, 15 to 20 parts by weight of magnesium sulfate whiskers, and 3 to 6 parts by weight of maleic anhydride functionalizing compatibility agent. The melt blending step is achieved through a process path that constrains subsequent chemical reaction steps by a physical structure building step. The process path includes: Step a, Physical structure construction step: In the shearing and shaping zone, the temperature of the shearing and shaping zone is controlled within the range of 230°C to 240°C, which is higher than the melting temperature of block copolymer polypropylene and lower than the melting temperature of polyamide 66; at the same time, a shearing action is applied to the material by one or more sets of strong shear screw assemblies configured in this zone, and the applied shearing rate is not less than 5000 / s, so that the molten polypropylene phase carrying maleic anhydride functionalized compatibilizer is forcibly coated on the surface of the still solid or semi-solid polyamide 66 particles, thus constructing an intermediate phase structure with polyamide 66 particles as the core and a mixture of polypropylene and magnesium sulfate whiskers as the shell; Step b, constrained chemical reaction step: The material carrying the mesophase structure is conveyed to the first plasticizing reaction zone, and the temperature of the first plasticizing reaction zone is raised to 260°C to 265°C, which is higher than the melting temperature of polyamide 66. This causes the core of the mesophase structure to melt and triggers an in-situ grafting reaction between the maleic anhydride functionalized compatibilizer pre-placed at the core-shell interface and the end groups of polyamide 66 exposed due to melting, thereby chemically bonding and fixing the mesophase structure.

[0008] Preferably, the material residence time t in the shearing and shaping zone shear The material residence time t in the first plasticizing reaction zone anchor Between these conditions, the process control rules defined by the following relationship apply: 1.2≤t shear / t anchor ≤2.5, where t shear t is the total time it takes for the material to pass through the shearing and shaping zone. anchor The total time for the material to pass through the first plasticizing reaction zone; and t shear With t anchorThe ratio is achieved by configuring a preset number and configuration of screw assemblies in the shearing and shaping zone and the first plasticizing reaction zone.

[0009] Preferably, the high-shear screw assembly includes at least one screw assembly consisting of multiple large-angle kneading blocks, the screw assembly being coordinated with the screw speed of the twin-screw extruder to apply a shear rate of not less than 5000 / s to the material in the shearing and shaping zone.

[0010] Preferably, the method further includes a filler pretreatment step prior to the melt blending step, wherein the filler pretreatment step is as follows: placing magnesium sulfate whiskers with an aspect ratio greater than 20 in an ethanol solution containing a silane coupling agent and sonicating them, followed by drying, to form a silane coupling agent coating layer on the surface of the magnesium sulfate whiskers.

[0011] Preferably, the intermediate phase structure formed in step a has a shell that forms a physical enclosure on the surface of polyamide 66 as the core, the shell has an average thickness of 100 nanometers to 500 nanometers, and the shell constitutes a continuous or semi-continuous network phase in the microstructure of the finally prepared polyamide engineering plastic.

[0012] Preferably, the twin-screw extruder includes, in sequence along the material conveying direction, a feeding zone, a second plasticizing reaction zone, a shearing and shaping zone, a first plasticizing reaction zone, and a homogenizing and metering zone. The temperature of each zone is set as follows: 70°C for the feeding zone, 220°C for the second plasticizing reaction zone, and 260°C for the homogenizing and metering zone.

[0013] Preferably, the method further includes a calibration procedure prior to the melt blending step. The calibration procedure includes: measuring the melt viscosity curve of the mixture of block copolymer polypropylene and maleic anhydride functionalized compatibility agent at the target temperature in the shear shaping zone using an offline capillary rheometer; inputting the viscosity data and the geometric configuration parameters of the screw assembly in the shear shaping zone of the twin-screw extruder into polymer processing simulation software to calculate the minimum screw speed value corresponding to a shear rate of not less than 5000 / s, and using it as the benchmark operating parameter.

[0014] Preferably, the method further includes online process stability assurance measures, including: installing an online melt viscosity sensor between the end of the shearing and shaping zone and the beginning of the first plasticizing reaction zone of the twin-screw extruder to monitor the melt viscosity value leaving the shearing and shaping zone in real time; when the monitored viscosity value deviates from a reference viscosity value to a preset threshold, the control system automatically adjusts the screw speed until the viscosity value returns to the range of the reference viscosity value.

[0015] Preferably, the method for determining the preset threshold is as follows: under the stable operating state of the extruder, the signal of the online melt viscosity sensor is continuously collected, the natural fluctuation peak of the signal is recorded, and the value between 1.5 times and 2.0 times the peak value is set as the preset threshold; the adjustment step size of the screw speed is calculated and determined by applying a small step disturbance to the screw speed under the stable operating state and recording the response time and change of the melt viscosity value.

[0016] A high-strength, low-absorption polyamide engineering plastic is prepared by a method for preparing high-strength, low-absorption polyamide engineering plastic.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. In the preparation of polyamide engineering plastics, by setting a non-monotonic temperature path, the preparation process of polymer composition is transformed from the random thermodynamic mixing of traditional melt blending into a controlled process of stepwise synergy between physical shaping and chemical anchoring. By utilizing the difference in melting points of components, an ordered intermediate phase structure is forcibly constructed first below the melting point of the matrix resin through high shear. The subsequent high-temperature zone is only used to trigger in-situ chemical reactions at the interface, fixing the previously constructed topological structure and forming a highly ordered and stable polymer composite material base.

[0018] 2. The topological structure constructed in this invention guides the formation of a continuous or semi-continuous network phase by a hydrophobic toughening phase, which physically encloses the hydrophilic polyamide matrix. This alters the penetration and migration pathways of water molecules within the composite material, effectively hindering water molecule penetration and suppressing water absorption while maintaining high strength. Simultaneously, it establishes an efficient internal stress transfer path. When the material is subjected to external loads, the stress is flexibly transferred from the high-modulus polyamide core through chemically bonded interfaces to the toughening shell surrounding it. From there, the stress is uniformly dispersed to the high-strength reinforcing filler anchored within the flexible shell. This avoids stress concentration problems caused by interfacial incompatibility or rigid fillers in conventional composite materials, thus achieving a synergistic balance of rigidity, strength, and toughness in the material.

[0019] 3. By coupling the filler pretreatment step with the physical structure construction step, the surface-modified reinforcing filler, due to the change in surface polarity, preferentially anchors itself in the molten hydrophobic toughening phase in the shear-forming zone, and together with it forms a composite coating shell on the surface of the polyamide particles; not only is the reinforcing effect of the filler utilized, but it also becomes part of the hydrophobic network, further strengthening the physical blockage of water molecule permeation channels, and realizing the synergistic effect of the reinforcing filler and the hydrophobic toughening phase. Attached Figure Description

[0020] Figure 1 This is a flowchart of the step-by-step process of physical shaping and chemical anchoring in this invention; Figure 2 This is a graph showing the relationship between the core process temperature and material properties of this invention. Figure 3 This is a diagram showing the relationship between the four core elements of this invention and their microstructure. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to specific embodiments. However, it should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the scope of protection of the invention.

[0022] This invention discloses a high-strength, low-absorption polyamide engineering plastic and its preparation method, comprising a pretreatment step of surface modification of reinforcing filler, a melt blending step in which the physical structure building step and the subsequent chemical reaction step are carried out in a twin-screw extruder in a stepwise synergistic manner, and a finished product obtained through granulation and drying processes; the initial step is a filler pretreatment step, which targets magnesium sulfate whiskers as reinforcing filler, with an initial aspect ratio greater than 20; in a container equipped with an ultrasonic generator, the magnesium sulfate whiskers are placed in an ethanol solution containing a silane coupling agent for ultrasonic treatment, followed by drying, using the silane coupling agent to form a coating layer on the surface of the whiskers, reducing the polarity of the magnesium sulfate whisker surface, improving the dispersibility of the subsequent low-polarity polypropylene phase, and enhancing the interfacial bonding between the phase and the polymer matrix; after the pretreatment, the surface-modified magnesium sulfate whiskers are physically premixed with polyamide 66 as the matrix resin, block copolymer polypropylene as the toughening phase, and maleic anhydride functionalized compatibilizer as a compatibilizer to prepare a uniform raw material for subsequent melt blending extrusion.

[0023] The subsequent melt blending step is carried out in a twin-screw extruder that sequentially includes a feeding zone, a second plasticizing reaction zone, a shearing and shaping zone, a first plasticizing reaction zone, and a homogenizing and metering zone along the material conveying direction. This melt blending step is configured as a non-monotonic thermodynamic process path where the physical structure building step constrains the subsequent chemical reaction steps. The physical structure building step is carried out in the shearing and shaping zone, where the temperature is set in a range higher than the melt temperature of block copolymer polypropylene but lower than the melt temperature of polyamide 66, specifically 230°C to 240°C. Under these temperature conditions, polyamide 66 particles with an intrinsic viscosity of 2.4 dL / g to 2.6 dL / g remain in a solid or semi-solid state, while the melt index is 15 g / 10 min to... 20g / 10min of block copolymer polypropylene has been completely melted; simultaneously, one or more sets of high-shear screw assemblies composed of multiple large-angle kneading blocks are configured in this zone, and in conjunction with the screw speed of the twin-screw extruder, the shear rate applied to the material in this zone is not less than 5000 / s. This mechanical shear force extends, stretches, and forms a coating on the surface of the solid polyamide 66 particles, which are already molten and carry compatibilizer, and anchors the surface-treated magnesium sulfate whiskers from the previous step into this coating layer. This physically constructs an intermediate phase structure with polyamide 66 particles as the core and a mixture of polypropylene and magnesium sulfate whiskers as the shell. To ensure the full formation of this core-shell structure, the material residence time t in the shearing and shaping zone is... shear The material residence time t in the subsequent first plasticizing reaction zone anchor Between, it is set to satisfy 1.2≤t shear / t anchor Relationships ≤2.5.

[0024] Material carrying the intermediate phase structure is conveyed to the first plasticizing reaction zone for a constrained chemical reaction step. The temperature in this zone is raised to above the melting temperature of polyamide 66, specifically set at 260°C to 265°C. At this high temperature, the core polyamide 66 of the intermediate phase structure melts rapidly, exposing the end groups of its molecular chains at the newly formed melt interface. Since maleic anhydride-grafted polypropylene, which serves as a maleic anhydride functionalizing compatibilizer, has been pre-placed at the core-shell interface in the previous step, the maleic anhydride functional groups it carries can undergo an in-situ grafting reaction with the end groups of polyamide 66 exposed by melting. This chemical reaction forms a chemical bond at the core-shell interface, fixing the microscopic topology constructed in the first step. By separating physical shaping and chemical anchoring into steps, the continuous or semi-continuous network composed of block copolymer polypropylene forms a physical enclosure relative to the polyamide 66 core.

[0025] By synergistically utilizing the principles of rheology-driven phase selection and forced stacking of high-solids-content phases, in the shear-forming region (230℃-240℃), the system consists of high-viscosity solid / semi-solid PA66 particles (as the dispersed phase) and low-viscosity molten PP phase (as the flow medium). Under a high shear field (≥5000 / s), the enormous shear force drives the low-viscosity melt to flow and encapsulate the high-viscosity particles, reducing the total interfacial energy consumption and forming an initial unit with PA66 particles as the core and PP melt as the shell. The volume fraction of PA66 is much higher than the dispersed phase content in general toughening modifications, reaching 60-70 wt%. Under this high solids content, PA66 particles... Under the powerful conveying and kneading of the screw, the PP particles are not freely suspended in the PP melt, but are in a state of compression and compaction. Their packing density is close to or has reached the percolation threshold. As a minority phase, the PP melt fills all the narrow gaps between these compactly packed PA66 particles. The high shear and extrusion not only coat the PP on the particle surface to form a shell, but also extrudes and welds these shells together at the contact points of the particles, forming a three-dimensional continuous network that runs through the gaps in the PA66 skeleton. Therefore, the continuity of the PP network does not depend on its own volume fraction to achieve percolation, but is determined by the gap topology of the high volume fraction PA66 skeleton.

[0026] Subsequently, in the first plasticizing reaction zone, the PA66 core melts and undergoes in-situ chemical bonding with the compatibilizer at the interface. This chemical anchoring step permanently locks in the non-equilibrium structure where the kinetic process constructs a tightly packed PA66 framework and a PP filling network coexist. The resulting microstructure retains the mechanically and thermally dominant framework formed by the mutual contact and support of PA66 particles (ensuring high HDT), while also solidifying the hydrophobic PP isolation network filling all interface channels of this framework. This makes the water molecule penetration path extremely tortuous and difficult, inhibiting water molecule penetration and achieving an ultra-low water absorption rate. To obtain the target mechanical properties and water absorption rate combination required for specific application scenarios, the material residence time t in the shear-forming zone is... shear The material residence time t in the first plasticizing reaction zone anchorThe ratio of residence time to the final average shell thickness can be determined through the following engineering calibration procedure: Key performance indicators of the final product, such as tensile strength and notched impact strength, are set as target response variables. At least three residence time ratios are selected, adjusted by increasing or decreasing the number of specific screw components within the shearing zone of the twin-screw extruder. Simultaneously, at least two block copolymer polypropylene raw materials with different melt index specifications are selected to obtain different melt viscosities. A test matrix containing multiple test points is established based on the above variables. During each test, in addition to testing the performance of the final sample, the sample cross-section is observed using a scanning electron microscope, and the average shell thickness is measured. This yields a quantitative dataset that correlates the combination of process parameters (residence time ratio, raw material melt index) with intermediate structural characteristics (shell thickness) and final macroscopic properties (mechanical properties). Based on this dataset, a combination of process parameters and raw material specifications that meets specific performance requirements is selected as the benchmark production procedure for this specific application scenario.

[0027] In continuous production, to maintain the stability of the rheological behavior of the molten blend, key parameters in the online melt viscosity feedback control loop need to be tuned on-site. The method for determining the trigger threshold of the control response is as follows: under stable extruder operation, continuously collect online melt viscosity sensor signals for at least 30 minutes, record the natural fluctuation peak of the signal without external intervention, and set the value between 1.5 and 2.0 times this peak as the control threshold to avoid excessive response of the control system to normal process noise. For the screw speed adjustment step size, under stable operation, apply a known small step disturbance to the screw speed, such as increasing it by 10 rpm, and record the response time and change in melt viscosity from the initial state to the new stable state. Based on this response time and change, calculate the speed adjustment value that effectively returns the viscosity value to the target range without causing system oscillation due to excessive single adjustment, and set this as the adjustment step size. For example, 5 rpm in this embodiment is an effective value determined through this procedure.

[0028] Example 1: In applications for manufacturing automotive engine intake manifolds, this component operates under conditions of prolonged high temperature, high humidity, and continuous mechanical vibration. Manifolds made from conventional glass fiber reinforced polyamide 66 material, due to the water absorption of their matrix material, experience dimensional changes in high humidity environments, leading to leaks at the sealing connection with the engine cylinder head. Under continuous vibration loads, stress concentration easily occurs at the interface between the reinforcing fibers and the matrix, inducing fatigue cracks and ultimately affecting the component's service life. To address this condition, the intake manifold component is manufactured using the method of this invention. Its raw material composition, based on 100 parts by total weight, includes 65 parts by weight of polyamide 66, 18 parts by weight of block copolymer polypropylene, and 16 parts by weight of pre-treated with a silane coupling agent. The mixture consisted of magnesium sulfate whiskers and 4.5 parts by weight of maleic anhydride-grafted polypropylene. During melt blending, the temperature of the shearing zone of the twin-screw extruder was set at 240°C. This temperature allowed the block copolymer polypropylene, which served as the toughening phase, to completely melt while the polyamide 66 particles remained solid. This provided the necessary conditions for subsequent physical structure construction. The high shear applied in this zone caused the molten polypropylene phase to uniformly coat the surface of the solid polyamide 66 particles, creating an intermediate phase structure. The subsequent first plasticizing reaction zone raised the temperature to 265°C, melting the polyamide 66 core and triggering an in-situ grafting reaction at the interface. The preceding physical shaping provided an ordered reaction interface for the subsequent chemical reaction, while the subsequent chemical anchoring solidified this ordered structure.

[0029] The material prepared by this method forms a core-shell structure in which a hydrophobic polypropylene phase acts as a continuous network, physically enclosing the hydrophilic polyamide 66 phase region, thus blocking the path of water molecules to penetrate into the polyamide 66 matrix. When the component is subjected to external vibration loads, the stress is transferred from the polyamide 66 core to the flexible polypropylene shell surrounding it through chemical bonding at the interface, and then dispersed from the shell to the embedded magnesium sulfate whiskers. This gradient transition structure makes the interface a region that can dissipate energy, avoiding the stress concentration problem that is prone to occur at the interface in conventional rigid filler reinforced materials.

[0030] Example 2: To verify the effect of the preparation method of the present invention in improving the comprehensive performance of polyamide engineering plastics, the following comparative experiment was set up. The experimental equipment was a twin-screw extruder with a length-to-diameter ratio of 40:1 and segmented independent temperature control function, with a temperature control accuracy of ±1℃ for each temperature zone. All test samples were melt-blended on this equipment and then prepared into standard specimens for performance testing using an injection molding machine with a clamping force of 150 tons under the same injection molding process parameters. This experiment set up the sample group of the present invention and three control groups. The raw material composition and preparation process of the sample group of the present invention were consistent with the process parameters in Example 1. Control group 1 used the exact same raw material composition as the sample group of the present invention, but its melt blending step adopted a monotonically increasing temperature process, that is, the temperature of the twin-screw extruder increased linearly from the feeding zone to the homogenization and metering zone, and the temperature of the shearing and shaping zone and the control group were adjusted accordingly. The temperature of the first plasticizing reaction zone was set at 265℃. Control group 2 used the same raw material composition and process parameters as the sample group of the present invention, but without adding maleic anhydride functionalized compatibilizer to the raw material. Control group 3 was based on the formula and process of the sample group of the present invention, but omitted the step of silane coupling agent pretreatment of magnesium sulfate whiskers, that is, directly used untreated magnesium sulfate whiskers. The standard samples prepared by each sample group were tested according to the corresponding test standards. The tensile strength was tested according to ASTM D638, the flexural modulus was tested according to ASTM D790, the 24-hour water absorption rate was tested according to ASTM D570, and the heat distortion temperature was tested according to ASTM D648 under a load of 1.82MPa. The main performance test data of each sample group are recorded in Table 1.

[0031] Table 1: Comparison of Performance Test Data for Each Sample Group Sample of the present invention 132 18800 0.009 265 Control group 1 95 11500 0.65 240 Control group 2 88 10200 0.011 263 Control group 3 110 15500 0.52 258 Referring to Table 1, comparing the data of the present invention sample group with control group 1, under the same raw material composition, the present invention sample group using a non-monotonic thermodynamic process path has higher tensile strength, flexural modulus, and heat distortion temperature than control group 1 using a monotonic heating process, and the water absorption rate is significantly reduced from 0.65% in control group 1 to 0.009%, a reduction of more than 70 times. Comparing the data of the present invention sample group with control group 2, the tensile strength and flexural modulus of the material decrease in the absence of a compatibilizer, indicating a weakening of the interfacial bonding between the two phases. Comparing the present invention sample group with control group 3, the untreated magnesium sulfate whiskers result in inferior mechanical properties and water absorption performance compared to the present invention sample group, indicating that surface treatment of the filler plays a role in improving its dispersibility and interfacial compatibility in the matrix. To further verify the differences between the present invention sample group and the control group... 1. Regarding the differences in microstructure, injection-molded samples of both were subjected to brittle fracture in liquid nitrogen, and the fracture surfaces were sputtered with gold. The morphology was then observed using scanning electron microscopy (SEM). The results showed that the cross-section of the control group 1 (monotropic heating process) exhibited a typical island structure, with the PA66 matrix (sea) and PP (island) randomly dispersed and the interface between the two phases blurred. In contrast, the cross-section of the sample group of this invention clearly showed a highly ordered micro-topological structure: PA66 formed multiple core regions, while the block copolymer polypropylene (PP) constituted a continuous or semi-continuous network phase, which physically enclosed these PA66 cores. SEM evidence proved that the non-monotropic thermodynamic path of this invention successfully constructed an intermediate phase structure before the PA66 cores melted, and fixed the structure through in-situ chemical reaction after the PA66 melted, ultimately forming a core-shell network structure.

[0032] Example 3: This example combines Figures 1 to 3 This document describes a high-strength, low-absorption polyamide engineering plastic and its preparation method, such as... Figure 1 As shown, magnesium sulfate whiskers, used as reinforcing fillers, first undergo a separate filler pretreatment step to obtain surface-modified whiskers. PA66, used as the matrix resin, polypropylene, used as the toughening phase, and compatibility agent enter the raw material storage area from the raw material supply end for physical premixing. These two materials then enter the physical structure construction step, where an intermediate phase structure material is formed under specific thermodynamic and kinetic conditions. This material then enters the chemical reaction anchoring step, where the ordered structure constructed in the previous step is fixed through in-situ chemical reaction, ultimately forming a high-strength, low-water-absorption polyamide product, which is then stored in the finished product warehouse.

[0033] like Figure 2As shown, the influence of the shear-forming zone temperature on tensile strength (MPa), flexural modulus (×100MPa), and water absorption (×10%) is plotted on the x-axis and the macroscopic performance values ​​of the material on the y-axis. The curves in the figure show that when the shear-forming zone temperature is set around 240℃, the tensile strength and flexural modulus of the material reach their peak values, while the water absorption remains at a very low and stable level. Figure 3 As shown, the first aspect is the core process parameters, specifically including high-temperature triggering in the reaction zone, low-temperature control in the shearing and shaping zone, step-by-step physical shaping / chemical anchoring, non-monotonic thermodynamic path, and high shear rate. The second aspect is the key raw material components, covering magnesium sulfate whiskers (reinforcing filler) pretreated on the filler surface, polyamide 66 (matrix), block copolymer polypropylene (hydrophobic toughening phase), and maleic anhydride functionalized compatibility agent (interfacial bonding). The third aspect is the equipment and control, indicating that the synergistic effect of the three elements—twin-screw extruder, high-shear screw assembly, segmented independent temperature control, and online melt viscosity sensing and feedback—ultimately constructs an ordered microstructure characterized by reinforcing filler anchored to the shell, in-situ chemical bonding at the interface, physical enclosure of the hydrophobic shell network, and core-shell topology.

[0034] Example 4: When applied to different batches of raw materials or different specifications of equipment, a standardized calibration procedure can be performed for key process parameters in the shearing and shaping zone. The goal of this procedure is to convert the requirement of a shear rate of not less than 5000 / s into a settable equipment operating parameter, namely the screw speed. The specific steps are as follows: First, the melt viscosity curve of the current batch of block copolymer polypropylene and maleic anhydride functionalized compatibility agent mixture at the target temperature in the shearing and shaping zone, such as 230°C, is measured using an offline capillary rheometer. This viscosity data, along with the geometric configuration parameters of the screw assembly in the shearing and shaping zone of the twin-screw extruder, is input into the polymer processing simulation software. The minimum screw speed value corresponding to a shear rate of 5000 / s under this screw configuration is obtained through calculation, and this speed value is used as the benchmark operating parameter when this batch of raw materials is produced on this equipment.

[0035] In continuous production, to address potential slight fluctuations in upstream raw material supply, this method also includes an online process stability assurance measure. An online melt viscosity sensor is installed between the end of the shearing and shaping zone and the beginning of the first plasticizing reaction zone of the twin-screw extruder to monitor the melt viscosity value leaving the shearing and shaping zone in real time. During production, if the viscosity value detected by the sensor deviates from the reference viscosity value determined by the aforementioned calibration procedure by a preset threshold, such as ±5%, the control system will automatically fine-tune the screw speed. Specifically, when the detected viscosity value is lower than the reference value by -5%, it indicates that the shearing action on the material may be insufficient. At this time, the control system will gradually increase the screw speed in steps of 5 rpm until the viscosity value returns to the reference range, and vice versa. Through this closed-loop feedback adjustment, it is ensured that even with slight fluctuations in raw material, the shearing environment in the shearing and shaping zone can be stably maintained within the target process window.

[0036] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a high-strength, low-water-absorption polyamide engineering plastic, wherein the composition is melt-blended in a twin-screw extruder; The composition comprises: The polyamide 66 comprises 60 to 70 parts by weight, block copolymer polypropylene 15 to 20 parts by weight, magnesium sulfate whiskers 15 to 20 parts by weight, and maleic anhydride functionalizing compatibility agent 3 to 6 parts by weight. The feature is that the melt blending step is achieved through a process path where the subsequent chemical reaction steps are constrained by a physical structure building step. The process path includes: Step a: In the shearing and shaping zone, the temperature of the shearing and shaping zone is controlled within the range of 230°C to 240°C, which is higher than the melting temperature of block copolymer polypropylene and lower than the melting temperature of polyamide 66. At the same time, a shearing action is applied to the material by one or more sets of strong shear screw assemblies configured in this zone, and the applied shear rate is not less than 5000 / s. The molten polypropylene phase carrying maleic anhydride functionalized compatibilizer is forcibly coated on the surface of the polyamide 66 particles that are still in a solid or semi-solid state, thus constructing an intermediate phase structure with polyamide 66 particles as the core and a mixture of polypropylene and magnesium sulfate whiskers as the shell. Step b involves conveying the material carrying the intermediate phase structure to the first plasticizing reaction zone, raising the temperature of the first plasticizing reaction zone to 260°C to 265°C, which is higher than the melting temperature of polyamide 66. This causes the core of the intermediate phase structure to melt and triggers an in-situ grafting reaction between the maleic anhydride functionalized compatibilizer pre-placed at the core-shell interface and the end groups of polyamide 66 exposed due to melting, thereby chemically bonding and fixing the intermediate phase structure.

2. The method for preparing a high-strength, low-absorption polyamide engineering plastic according to claim 1, characterized in that, Material residence time t in the shearing and shaping zone shear The material residence time t in the first plasticizing reaction zone anchor Between these conditions, the process control rules defined by the following relationship apply: 1.2≤t shear / t anchor ≤2.5, where t shear t is the total time it takes for the material to pass through the shearing and shaping zone. anchor The total time for the material to pass through the first plasticizing reaction zone; and t shear With t anchor The ratio is achieved by configuring a preset number and configuration of screw assemblies in the shearing and shaping zone and the first plasticizing reaction zone.

3. The method for preparing a high-strength, low-absorption polyamide engineering plastic according to claim 1, characterized in that, The high-shear screw assembly includes at least one set of screws consisting of multiple large-angle kneading blocks.

4. The method for preparing a high-strength, low-absorption polyamide engineering plastic according to claim 1, characterized in that, The method also includes a filler pretreatment step prior to the melt blending step, wherein magnesium sulfate whiskers with an aspect ratio greater than 20 are placed in an ethanol solution containing a silane coupling agent and sonicated, and then dried to form a silane coupling agent coating layer on the surface of the magnesium sulfate whiskers.

5. The method for preparing a high-strength, low-absorption polyamide engineering plastic according to claim 1, characterized in that, The intermediate phase structure formed in step a has a shell that forms a physical enclosure on the surface of polyamide 66 as the core. The average thickness of the shell is 100 nanometers to 500 nanometers, and the shell constitutes a continuous or semi-continuous network phase in the microstructure of the final polyamide engineering plastic.

6. The method for preparing a high-strength, low-absorption polyamide engineering plastic according to claim 1, characterized in that, The twin-screw extruder includes, in sequence along the material conveying direction, a feeding zone, a second plasticizing reaction zone, a shearing and shaping zone, a first plasticizing reaction zone, and a homogenizing and metering zone. The temperature settings for each zone are as follows: 70°C for the feeding zone, 220°C for the second plasticizing reaction zone, and 260°C for the homogenizing and metering zone.

7. The method for preparing a high-strength, low-absorption polyamide engineering plastic according to claim 1, characterized in that, The method also includes a calibration procedure prior to the melt blending step, which includes: measuring the melt viscosity profile of the mixture of block copolymer polypropylene and maleic anhydride functionalized compatibility agent at the target temperature in the shear shaping zone using an offline capillary rheometer; inputting the viscosity data and the geometric configuration parameters of the screw assembly in the shear shaping zone of the twin-screw extruder into polymer processing simulation software to calculate the minimum screw speed value, and using it as the benchmark operating parameter.

8. The method for preparing a high-strength, low-absorption polyamide engineering plastic according to claim 1, characterized in that, The method also includes online process stability assurance measures, including: installing an online melt viscosity sensor between the end of the shearing and shaping zone and the beginning of the first plasticizing reaction zone of the twin-screw extruder to monitor the melt viscosity value leaving the shearing and shaping zone in real time; when the monitored viscosity value deviates from a reference viscosity value to a preset threshold, the control system automatically adjusts the screw speed until the viscosity value returns to the range of the reference viscosity value.

9. The method for preparing a high-strength, low-absorption polyamide engineering plastic according to claim 8, characterized in that, The method for determining the preset threshold is as follows: under the stable operation of the extruder, continuously collect the signal from the online melt viscosity sensor, record the natural fluctuation peak of the signal, and set the value between 1.5 times and 2.0 times the peak value as the preset threshold.

10. A high-strength, low-absorption polyamide engineering plastic, characterized in that, It is made by the preparation method of a high-strength, low-absorption polyamide engineering plastic as described in claim 1.

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