Preparation method of nylon rubber and plastic material with high mechanical memory

Abstract

The invention relates to the technical field of polymer composite materials, and discloses a preparation method of a nylon rubber and plastic material with high mechanical memory, which comprises the following steps: respectively carrying out drying pretreatment on nylon 66 resin with specific viscosity and a thermoplastic polyurethane elastomer with specific hardness; the preparation method comprises the following steps: carrying out compatibilization premixing on maleic anhydride grafted POE, a composite antioxidant and a beta crystal form nylon nucleating agent in parts by weight, carrying out melt blending on the premix through a twin-screw extruder, injecting a phenolic resin vulcanizing agent at a set temperature gradient to carry out in-situ dynamic vulcanization, and finally extruding through a high-shear orientation die orifice to obtain the high-strength nylon composite material. The extruded strip-shaped object is subjected to two-stage cooling of shock cooling and slow cooling in sequence and then is cut into particles, the particles are subjected to hot press molding to form sample strips, programmed heating and cooling treatment is carried out under the constraint of a clamp, and the material is endowed with a temporary shape; the prepared material has the advantages of being high in shape recovery rate, accurate in recovery response temperature and excellent in mechanical property, the process is controllable, and the method is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, and in particular to a method for preparing a high mechanical memory nylon rubber-plastic material. Background Technology

[0002] With the rapid development of fields such as intelligent manufacturing, flexible electronics, and biomedicine, the demand for polymer materials with shape memory function is becoming increasingly urgent. Common shape memory materials generally suffer from problems such as insufficient mechanical strength, low recovery accuracy, and difficulty in precisely controlling the response temperature, which limits their application in load-bearing structures or precision applications.

[0003] Nylon (polyamide) series resins, especially nylon 66, are considered ideal structural material matrices due to their excellent mechanical properties, heat resistance, wear resistance and processability. However, as a typical highly crystalline polymer, the shape memory behavior of nylon 66 is limited by its high glass transition temperature and melting point, resulting in a high shape recovery temperature and poor controllability of the recovery process.

[0004] Blending nylon with TPU is a common strategy to improve its toughness and introduce shape memory potential. However, nylon 66 has poor compatibility with TPU, and simple blending can easily lead to interfacial debonding and degradation of shape memory properties during cyclic deformation. In addition, conventional blended materials lack effective control over the microstructure, crystallization behavior and molecular orientation during processing, making it difficult to achieve stable and efficient shape memory properties.

[0005] Currently, most methods for preparing high-mechanical-performance shape memory nylon materials focus on chemically synthesizing novel copolymers or introducing expensive functional monomers. These methods are complex, costly, and difficult to balance large-scale processing and performance stability. Therefore, there is an urgent need to develop a preparation method based on mature commercial raw materials. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing high mechanical memory nylon rubber and plastic materials in order to solve the problems in the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a high mechanical memory nylon rubber-plastic material, comprising the following steps:

[0008] S1, Nylon 66 resin with an intrinsic viscosity of 2.8-3.2 dL / g and thermoplastic polyurethane elastomer with a Shore hardness of 75A-90A are respectively dried and pretreated.

[0009] S2, by weight, weigh 70-75 parts of pretreated nylon 66 resin, 25-30 parts of pretreated thermoplastic polyurethane elastomer, 4-6 parts of maleic anhydride-grafted POE, 1.5-2.5 parts of composite antioxidant containing hindered phenol and phosphite, and 0.3-0.8 parts of β-crystalline nylon nucleating agent and premix them to obtain a premix;

[0010] S3, the premixed material is added to the twin-screw extruder, and a temperature gradient is set in the third to sixth zones: 210℃→225℃→235℃→245℃ and the screw speed is set to 380-420r / min. Phenolic resin vulcanizing agent is injected in the fifth zone, and finally the material is extruded through a high-shear orientation die to obtain a strip extruded material.

[0011] S4, the strip extruded material is first rapidly cooled in a cooling water bath at 40-45℃ in the first temperature zone for 30-45 seconds, and then slowly cooled in a constant temperature oil bath at 75-80℃ in the second temperature zone for 60-90 seconds before being granulated to obtain drum-shaped particles.

[0012] S5, the drum-shaped particles are hot-pressed to form a standard template, and then subjected to programmed heating and cooling under the constraint of a fixture to obtain a finished material with a preset temporary shape.

[0013] The beneficial effects of the technical solution provided by this invention include at least the following:

[0014] This invention, through precise formulation design and synergistic process control, successfully prepared a nylon rubber and plastic material with high shape recovery rate, precise recovery response temperature, and excellent mechanical properties. It can trigger efficient and stable shape recovery in a room temperature environment, significantly expanding the applicable temperature window of shape memory materials in fields such as biomedicine, smart wearables, and daily necessities.

[0015] This invention creatively introduces a β-crystalline nylon nucleating agent into the nylon 66+TPU blend system, and, in conjunction with a staged cooling process, effectively induces the nylon matrix to form a β-crystalline structure. This successfully controls the shape recovery temperature of the material from the traditional high melting point range of nylon 66 to around 45°C. At the same time, through in-situ dynamic vulcanization, a moderate micro-crosslinking network is constructed inside the TPU phase, which greatly enhances the material's elastic recovery and resistance to permanent deformation.

[0016] This invention employs high-shear orientation die extrusion combined with a two-stage cooling process of rapid cooling and slow cooling. High-shear orientation causes nylon molecular chains and micro-crosslinked TPU particles to be highly aligned along the extrusion direction, forming a stable orientation memory framework. The staged cooling strategy enables rapid freezing of the orientation structure, and the controllable isothermal treatment promotes the perfection of β crystals and releases internal stress, ensuring that the material has both excellent dimensional stability and mechanical strength, as well as a clear shape memory triggering and execution mechanism.

[0017] The method of this invention is based on mature plastic processing equipment, with clear and highly controllable process parameters. All raw materials are commercially available high-molecular-weight, high-strength, wear-resistant TPU sub-materials and additives. The prepared material not only has excellent shape memory properties, but also inherits the good elasticity of Nylon 66. As a smart structural material with excellent comprehensive performance, it has a wide range of applications and market prospects. Attached Figure Description

[0018] To more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart of a method provided in an embodiment of the present invention. Detailed Implementation

[0020] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a method for preparing a high mechanical memory nylon rubber-plastic material according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0023] The following describes in detail, with reference to the accompanying drawings, a specific scheme for preparing a high mechanical memory nylon rubber and plastic material provided by the present invention.

[0024] Please see Figure 1 The diagram illustrates a method flow chart for preparing a high mechanical memory nylon rubber-plastic material according to an embodiment of the present invention. The method includes the following steps:

[0025] S1, Nylon 66 resin with an intrinsic viscosity of 2.8-3.2 dL / g and thermoplastic polyurethane elastomer with a Shore hardness of 75A-90A are respectively dried and pretreated.

[0026] S2, by weight, weigh 70-75 parts of pretreated nylon 66 resin, 25-30 parts of pretreated thermoplastic polyurethane elastomer, 4-6 parts of maleic anhydride-grafted POE, 1.5-2.5 parts of composite antioxidant containing hindered phenol and phosphite, and 0.3-0.8 parts of β-crystalline nylon nucleating agent and premix them to obtain a premix;

[0027] S3, the premixed material is added to the twin-screw extruder, and a temperature gradient is set in the third to sixth zones: 210℃→225℃→235℃→245℃ and the screw speed is set to 380-420r / min. Phenolic resin vulcanizing agent is injected in the fifth zone, and finally the material is extruded through a high-shear orientation die to obtain a strip extruded material.

[0028] S4. The strip extruded material is first cooled by passing it through a cooling water bath at 40-45℃ in the first temperature zone for 30-45 seconds, and then slowly cooled by passing it through a constant temperature oil bath at 75-80℃ in the second temperature zone for 60-90 seconds before being granulated to obtain drum-shaped granules.

[0029] S5, the drum-shaped particles are hot-pressed to form a standard sample, and then subjected to programmed heating and cooling under the constraint of a fixture to obtain a finished material with a preset temporary shape.

[0030] In one embodiment of the present invention, the step of drying and pretreating nylon 66 resin with an intrinsic viscosity of 2.8-3.2 dL / g and thermoplastic polyurethane elastomer with a Shore hardness of 75A-90A respectively includes:

[0031] Nylon 66 resin with an intrinsic viscosity of 2.8-3.2 dL / g was placed in a vacuum drying device and dried for 6-8 hours at a temperature of 100-110℃ and a vacuum degree of ≤0.095MPa.

[0032] The thermoplastic polyurethane elastomer with a Shore hardness of 75A-90A was placed in a dehumidifying drying oven and treated with dry air circulation at a temperature of 80-85℃ for 3-4 hours with a dew point ≤-40℃.

[0033] The treated nylon 66 resin and thermoplastic polyurethane elastomer were transferred to sealed containers filled with dry nitrogen and cooled to 25-30°C for later use.

[0034] It should be noted that Nylon 66 is a semi-crystalline polymer, and its crystallization behavior and morphology have a decisive influence on the material's mechanical properties, dimensional stability, and shape memory recovery ability. In shape memory cycling, the crystalline phase of Nylon 66, especially the crystal form induced by a specific nucleating agent, serves as the memory stationary phase to lock the temporary shape after the material is deformed and cooled. In addition, its glass transition temperature (Tg) and melting point (Tm) are the main temperature reference points for the material's shape recovery response, and its crystallization perfection can be controlled through subsequent formulation and processes.

[0035] Thermoplastic polyurethane elastomer (hereinafter referred to as TPU) has a molecular chain composed of alternating hard segments (used to provide physical crosslinking points, determining the material's strength and melting point) and soft segments (used to provide elasticity and low-temperature performance). In this material, they act as dispersed phases or island phases, giving the material excellent elasticity and high elongation at break. In the shape memory process, the soft segments of TPU usually act as reversible phases, so that the material has a significant modulus change near the recovery temperature. When the temperature is higher than its transformation temperature, the molecular chain segment mobility is enhanced, the material becomes softer and easier to deform under external force. When the temperature decreases, the molecular chain segment mobility is frozen, and the material fixes its deformation. The hard-soft two-phase structure is the classic model for constructing shape memory polymers (SMP).

[0036] In this embodiment, the moisture content of nylon 66 after drying is reduced to <0.02%, and the moisture content of thermoplastic polyurethane elastomer is reduced to <0.05%. The moisture content can be determined using conventional methods in the art. For example, the moisture content of nylon 66 resin is determined by Karl Fischer titration or thermogravimetric analysis according to GB / T12006.2 standard, and the moisture content of thermoplastic polyurethane elastomer is determined by Karl Fischer titration according to GB / T6283 standard.

[0037] After drying, the nylon 66 resin and thermoplastic polyurethane elastomer are quickly transferred to sealed containers pre-filled with dry nitrogen. Dry nitrogen refers to nitrogen with a dew point ≤ -40℃ and a purity ≥ 99.99%. The sealed containers should be kept well sealed before filling with dry nitrogen. The filling process can be carried out by displacement method to ensure that the container is in a dry and inert atmosphere. The cooled raw materials should be sealed and stored in this atmosphere until they are used in the next step.

[0038] In one embodiment of the present invention, the steps of weighing 70-75 parts by weight of pretreated nylon 66 resin, 25-30 parts by weight of pretreated thermoplastic polyurethane elastomer, 4-6 parts by weight of maleic anhydride-grafted POE, 1.5-2.5 parts by weight of a composite antioxidant containing hindered phenol and phosphite, and 0.3-0.8 parts by weight of β-crystalline nylon nucleating agent for compatibilization premixing to obtain the premix include:

[0039] The mixing chamber of a high-speed mixer is preheated to 20±2℃, and cooling water is continuously circulated into its jacket;

[0040] Add 70-75 parts of pretreated nylon 66 resin and 25-30 parts of pretreated thermoplastic polyurethane elastomer to a high-speed mixer and dry mix at 300-500 r / min for 2-3 minutes.

[0041] 4-6 parts of maleic anhydride-grafted POE, 1.5-2.5 parts of a composite antioxidant containing hindered phenol and phosphite, and 0.3-0.8 parts of β-crystalline nylon nucleating agent are manually stirred and premixed at 20-25℃ for 30-60 seconds to form an additive premix.

[0042] Add the premixed additives evenly into the high-speed mixer and mix for 8-12 minutes at a speed of 800-1200 r / min, while controlling the material temperature in the high-speed mixer to be below 45℃ during the process.

[0043] After high-speed mixing is complete, reduce the speed to 100-200 r / min and continue mixing for 1-2 minutes. Then discharge the resulting premix and immediately transfer it to a sealed container.

[0044] It should be noted that before feeding the materials, the mixing chamber of the high-speed mixer (such as a high-speed kneader) should be preheated to 20±2℃, which is slightly higher than the room temperature, to prevent the materials from absorbing moisture due to contact with cold metal surfaces. At the same time, circulating cooling water at 10-15℃ should be continuously introduced into the jacket of the mixing chamber to prevent the thermoplastic polyurethane elastomer (TPU) from softening and sticking to the wall too early, and to prevent nylon 66 from pre-crystallizing or the additives from thermally decomposing.

[0045] POE is an ethylene-octene copolymer elastomer with excellent toughness and low-temperature performance. It is obtained by grafting maleic anhydride (hereinafter referred to as MAH) onto its molecular chain, introducing highly polar anhydride functional groups. The anhydride groups of MAH readily react with the amino groups (-NH_2) at the end of nylon 66 to form imide bonds at the processing temperature. At the same time, the olefin segments of POE have good compatibility with the soft segments or amorphous regions of TPU. One end of the MAH-g-POE molecule is connected to nylon 66 by chemical bonds, and the other end is combined with TPU by physical entanglement or compatibility. This greatly improves the interfacial adhesion between nylon 66 and TPU, which originally had poor compatibility, thereby significantly improving the impact toughness and shape memory cycle stability of the blend material.

[0046] In composite antioxidants containing hindered phenols and phosphites, hindered phenols (such as antioxidant 1010) are the main antioxidants, used to capture free radicals generated by polymers during processing and use due to heating, oxidation and shearing, interrupting the chain oxidation reaction to prevent polymer molecular chain degradation or cross-linking. Phosphites (such as antioxidant 168) are auxiliary antioxidants, used to decompose hydroperoxides (ROOH) generated during oxidation into stable non-free radical products. The composite antioxidants are used to effectively inhibit the thermal oxidative degradation of nylon 66 and TPU in the high temperature and high shear environment of twin-screw extruders, and continuously provide antioxidant protection during the subsequent hot pressing, shape programming and long-term use of the materials.

[0047] β-crystal nylon nucleating agents are special nucleating agents (such as certain aromatic amide compounds) that can selectively induce nylon 66 to crystallize into the β-crystal form. Unlike the most common α-crystal form of nylon 66, the β-crystal form is a metastable crystal form, and its melting temperature range is usually slightly lower than that of the α-crystal. This helps to precisely control the shape recovery temperature (Tr) of the material within a comfortable or easily triggered range of 45±3℃, rather than near the higher melting point (about 260℃) of the α-crystal of nylon 66. This makes the shape recovery process smoother and avoids violent or uncontrollable recovery caused by the sudden melting of the α-crystal.

[0048] In one embodiment of the present invention, the premixed material is added to a twin-screw extruder, a temperature gradient is set in zones three to six: 210℃→225℃→235℃→245℃, and the screw speed is set to 380-420 r / min. A phenolic resin vulcanizing agent is injected in zone five. Finally, the material is extruded through a high-shear orientation die to obtain a strip-shaped extrudate.

[0049] The premixed material is fed into the twin-screw extruder through the main feed port and passes through zones one through six in sequence, including:

[0050] When the premixed material arrives at the first to second zones of the twin-screw extruder, it is melt-plasticized at a temperature of 190-205°C.

[0051] When the premixed material after being melted and plasticized reaches the third, fourth, fifth and sixth zones of the twin-screw extruder, it is homogenized and mixed with temperature gradients of 210℃, 225℃, 235℃ and 245℃ respectively, and with a screw speed of 380-420r / min.

[0052] At the high-shear orientation die outlet of a twin-screw extruder, the oriented melt is smoothly extruded under a die pressure of 2.5-3.5 MPa to form a continuous strip-shaped extrudate.

[0053] It should be noted that this step is the core of the material's microstructure shaping and performance determination. By precisely controlling the temperature gradient, screw speed, vulcanizing agent injection timing, and high-shear die of the twin-screw extruder, the synergistic and integrated completion of melt blending, in-situ dynamic vulcanization, and shear-induced orientation is achieved.

[0054] In this embodiment, the temperature gradient of the third to sixth zones of the twin-screw extruder is set as: 210℃→225℃→235℃→245℃. This gradual heating strategy is designed based on the material composition characteristics and includes:

[0055] 210℃ (Zone 3): Slightly higher than the initial melting temperature of Nylon 66 (the melting point of Nylon 66 is about 255℃, but the blended system will melt and plasticize at a lower temperature due to compatibilizers and shear action), to ensure that Nylon 66 melts completely, while avoiding excessive thermal degradation of TPU at this temperature;

[0056] 225℃→235℃ (Zones 4 and 5): Continue to raise the temperature, mainly for the following two purposes:

[0057] (1) Further reduce the melt viscosity and enhance the fluidity, providing good conditions for homogenization and mixing and dispersion of vulcanizing agent;

[0058] (2) Provide the most suitable reaction temperature window for in-situ dynamic vulcanization reaction (zone 5). Phenolic resin vulcanizing agents usually need 210-240℃ to effectively initiate the micro-crosslinking reaction of TPU, and 225-235℃ is the ideal range to balance the reaction rate and side reactions.

[0059] 245℃ (Zone 6): This is the final preparation for the melt to enter the high-shear orientation die. The slightly higher temperature helps the melt obtain more uniform rheological properties at the die and partially compensates for the instantaneous temperature rise (shear heat) that may be caused by high shear to prevent local overheating and degradation. At the same time, it ensures that the Nylon 66 molecular chains have sufficient mobility to be oriented under subsequent high shear.

[0060] In this embodiment, the screw speed of the twin-screw extruder is 380-420 r / min. The purpose is to apply high shear force and strong dispersion and mixing effect during melt delivery, including:

[0061] (1) It helps to shear, stretch, and break down the TPU elastomer phase (and the subsequently formed micro-crosslinked particles) into micron or submicron-sized dispersed phases in the Nylon 66 continuous phase;

[0062] (2) It helps the phenolic resin vulcanizing agent injected in the fifth zone to be instantly and uniformly dispersed in the melt, and intensifies the movement of molecular chains, promotes its contact and reaction with TPU, and achieves efficient in-situ dynamic vulcanization.

[0063] (3) In the strong shear flow field of the third to sixth regions, the long chain molecules of nylon 66 begin to undergo a certain degree of pre-stretching and orientation in order to establish orientation precursors.

[0064] In one embodiment of the present invention, when the melt-plasticized premix reaches the fifth zone of the twin-screw extruder:

[0065] Weigh out 1.5-2.5% of the phenolic resin curing agent by mass of the thermoplastic polyurethane elastomer, and inject the phenolic resin curing agent into the melt flow in a pulse injection manner using a high-pressure metering pump.

[0066] The melt pressure in the fifth zone is controlled at 4.0-6.0 MPa to carry out in-situ dynamic vulcanization reaction, resulting in micro-crosslinked elastomer particles;

[0067] The twin-screw extruder is equipped with a high-shear kneading block element in the fifth zone, which allows the melt to be subjected to high shear in this zone.

[0068] It should be noted that phenolic resin vulcanizing agents (usually alkylphenolic resins, such as the SP-1045 series) are highly efficient elastomer crosslinking agents. They are characterized by high reactivity with polar groups such as urethane groups and urea groups in TPU, good crosslinking efficiency, and have virtually no effect on the nylon 66 matrix. In this embodiment, they are used to achieve selective vulcanization of TPU.

[0069] The dosage control of phenolic resin vulcanizing agent (1.5-2.5% of TPU mass) includes:

[0070] Lower limit (1.5%): Ensure sufficient cross-linking points to form, enabling the TPU phase to achieve significant elastic recovery and resistance to permanent deformation. If it is too low, the cross-linking density will be insufficient, and an effective physical network cannot be formed.

[0071] Upper limit (2.5%): To prevent excessive cross-linking from causing TPU particles to harden and become brittle, losing elasticity, and potentially interfering with melt flow stability due to the exothermic cross-linking reaction or a sharp increase in viscosity, or even causing abnormal increase in screw torque or material scorching.

[0072] At this dosage, a moderate three-dimensional network structure is formed inside the TPU. Its particles can still be dispersed and refined under strong shearing, but it has sufficient elastic memory inside, making it an ideal structure for obtaining high shape fixation rate and high recovery rate.

[0073] High-pressure metering pumps are used to overcome melt back pressure (4.0-6.0 MPa) to deliver viscous liquid or molten phenolic resin vulcanizing agents. The vulcanizing agent is injected into the high-viscosity polymer melt in the form of intermittent high-pressure jets. Compared with continuous and gentle injection, high-pressure pulse jets can penetrate the melt more effectively, which helps the vulcanizing agent to achieve primary macro-mixing with the melt at the moment of injection. This avoids uneven surface spreading caused by excessive viscosity. The pulse interval provides time for the injected vulcanizing agent to be quickly carried away and dispersed by the screw shear element, preventing it from accumulating near the injection port and causing excessive cross-linking or gelation of TPU.

[0074] The melt pressure is mainly established by the conveying resistance of the melt in front of the fifth zone, the resistance generated by the high-shear kneading block element configured in this zone, and the configurable reverse thread element. The high-shear kneading block element consists of multiple staggered or juxtaposed kneading discs, which can generate strong squeezing, stretching, shearing and folding effects on the material.

[0075] In one embodiment of the present invention, the high-shear orientation die of the twin-screw extruder has a parallel slit structure with a slit gap of 0.5-1.0 mm and a length-to-diameter ratio of 10:1 to 20:1.

[0076] When the melt flows through the high-shear orientation die, it experiences an instantaneous shear rate of ≥500s^-1 at the slit gap, which causes the nylon molecular chains and micro-crosslinked elastomer particles to align in the extrusion direction.

[0077] It should be noted that in this embodiment, a slit gap of 0.5-1.0 mm is set to force the melt stream from the larger cross-sectional area die head to converge rapidly, and mainly generate two strong flow fields, including a strong tensile flow field in the inlet area and a strong shear flow field in the slit channel. The 0.5-1.0 mm gap is an optimized balance between ensuring that a sufficiently high shear rate (≥500 s^-1) is generated and avoiding excessive extrusion pressure that could cause melt rupture, and shortening the residence time of the melt in the die orifice to minimize the risk of molecular chain retraction due to relaxation.

[0078] The aspect ratio (L / H, 10:1 to 20:1) is set to provide a stable shear flow region, where L refers to the slit length (flow direction) and H refers to the slit gap (thickness direction). After the molecular chains and particles initially oriented due to the strong stretching flow field in the inlet region enter the straight section with a large aspect ratio, they are aligned along the flow direction under the action of continuous and uniform strong shear force to ensure the uniformity and thoroughness of orientation. This avoids the problem of uneven orientation or excessive difference between the surface and core layers that may be caused by inlet stretching alone. In addition, a sufficient aspect ratio helps to stabilize the melt flow, eliminate inlet disturbances, and obtain a continuous strip with a smooth surface and stable dimensions.

[0079] Shear rate γ is a key physical quantity describing the intensity of the flow field and characterizing the magnitude of the orientation driving force. For a parallel slit, the maximum shear rate in its central region can be approximately estimated as follows:

[0080] γ≈6Q / (W×H^2)

[0081] In the formula, Q is the volumetric flow rate, W is the slit width, and H is the slit gap;

[0082] The basis for setting a shear rate ≥500 s^-1 includes: for flexible chain polymers such as Nylon 66, the molecular chains need to overcome a critical shear rate to transform from a random coil state to a significantly oriented state. Below this value, Brownian motion-induced disorientation dominates, while above this value, hydrodynamic force-driven orientation dominates. A shear rate ≥500 s^-1 is much higher than the critical value of 10^2 s^-1 for such materials under conventional extrusion, which is sufficient to forcibly induce a high degree of orientation of the molecular chains. This intensity of shear field can also act on dispersed micro-crosslinked elastomer particles, causing their overall shape or the local flow field at the particle-matrix interface to undergo preferential alignment along the flow direction, forming an ordered dispersed structure. In addition, this shear rate value is matched with the aforementioned screw speed (380-420 r / min) and actual feed rate, and can be achieved by designing reasonable die dimensions (W, H) and aspect ratio.

[0083] In one embodiment of the present invention, the steps of first rapidly cooling the strip extrudate through a first temperature zone (40-45°C) cooling water bath for 30-45 seconds, then slowly cooling it through a second temperature zone (75-80°C) constant temperature oil bath for 60-90 seconds, and finally pelletizing it to obtain drum-shaped granules include:

[0084] The strip extruded material is drawn out at a constant speed of 5-8 m / min by the first pair of traction rollers;

[0085] The drawn strip extruded material is completely immersed in a cooling water bath with a temperature zone of 40-45℃ for rapid cooling, and held for 30-45 seconds.

[0086] The strip extruded material that has been quenched is removed and suspended in room temperature air at 20-30°C for 5-10 seconds. Then, the strip extruded material is completely immersed in a constant temperature hot oil bath at 75-80°C in the second temperature zone for slow cooling for 60-90 seconds.

[0087] The strip extruded material, which has undergone slow cooling, is drawn out by the second pair of traction rollers and fed into a pelletizer, where it is cut into drum-shaped particles with a diameter of 2-3 mm and a length of 3-4 mm, and collected in a moisture-proof container.

[0088] It should be noted that in this embodiment, the traction speed of the first pair of traction rollers is set to 5-8 m / min. This speed range is matched with the output of the twin-screw extruder and the die extrusion speed to ensure that the strip extruded material is straight, without stretching or accumulation, so as to maintain the orientation structure obtained during extrusion.

[0089] The first temperature zone cooling water bath temperature is 40-45℃: Cooling water in this temperature range is used for rapid cooling, which allows the surface of the highly oriented melt, which is extruded from the high shear die and is at a high temperature of about 245℃, to be rapidly cooled and solidified. This freezes the orientation state of the Nylon 66 molecular chains and the arrangement structure of the micro-crosslinked TPU particles to the greatest extent, preventing the molecular chains from loosening and losing orientation due to slow cooling. In addition, rapid cooling allows the extrudate to pass through the maximum crystallization temperature range of Nylon 66 (about 180-220℃) quickly, which greatly inhibits the formation of large α-crystal spherulites.

[0090] The strip extruded material is held in the first temperature zone for 30-45 seconds to ensure that its core is also fully cooled to below the crystallization temperature (e.g., below 100°C) to complete the solidification of the main body and prevent it from absorbing moisture due to prolonged soaking.

[0091] After the strip extruded material is removed from the first temperature zone, it is suspended for 5-10 seconds to allow the moisture adhering to the surface to evaporate or drip off in the air. This allows for brief natural convection cooling, making the cross-sectional temperature of the strip more uniform. This alleviates the problem of excessive core-surface temperature difference and internal stress concentration caused by excessively rapid water cooling, and provides a buffer for switching cooling media.

[0092] The second temperature zone uses a constant temperature oil bath at 75-80℃. A heat-conducting oil that does not cause swelling or hydrolysis of the polymer is selected for slow cooling. The slow cooling time is 60-90 seconds. The pre-cured material is then placed in a temperature field slightly below the glass transition temperature of Nylon 66 (about 50-60℃) but much higher than room temperature for controlled isothermal treatment. This process allows molecular chain segments to gain a certain degree of mobility, promoting partial relaxation of the non-equilibrium conformations and internal stresses frozen during the rapid cooling process, thereby improving the dimensional stability of the material. In addition, this temperature (75-80℃) is a favorable temperature window for the nucleation and growth of β-crystal Nylon 66. Under the action of the β-crystal nucleating agent in the early stage, this slow cooling process is conducive to the formation of a more stable β-crystal structure.

[0093] The drum-shaped particles obtained from the cutting process have a diameter of 2-3 mm and a length of 3-4 mm. This size design ensures that the particles have a high volumetric surface area, which facilitates rapid and uniform melting during subsequent hot pressing. The drum-shaped (short cylindrical) shape is conducive to uniform filling in the mold and is less prone to bridging. After cutting, the particles should be placed in a sealed moisture-proof container to prevent nylon 66 from absorbing moisture.

[0094] In one embodiment of the present invention, the steps of hot-pressing drum-shaped particles to obtain a standard sample strip, and then performing programmed heating and cooling under the constraint of a fixture to obtain a finished material with a preset temporary shape include:

[0095] The drum-shaped particles are evenly spread into the standard sample mold, and hot-pressed in a hot press at a temperature of 240-245℃ and a pressure of 12-15MPa for 8-10 minutes. Then, the sample is cooled to below 60℃ at a rate of 10-15℃ / min to demold it, and a homogeneous standard sample is obtained.

[0096] The homogeneous standard sample is mounted on a programming fixture and moved as a whole into a constant temperature chamber. The temperature inside the constant temperature chamber is uniformly raised to 50±1℃ at a heating rate of 2-3℃ / min and held at the constant temperature for 15-20 minutes.

[0097] While maintaining the fixture constraints, the temperature inside the constant temperature chamber was uniformly reduced from 50±1℃ to below 20℃ at a rate of 1-2℃ / min.

[0098] Remove the programming fixture from the constant temperature chamber and unload it to obtain the finished material.

[0099] It should be noted that, in this embodiment, the hot pressing molding parameters and specific effects are as follows:

[0100] Temperature 240-245℃: Ensures that the nylon 66 matrix is ​​completely melted, eliminates the interface between the drum-shaped particles to form a dense whole, and at the same time, the TPU micro-crosslinked particles do not melt, maintaining their elastic network structure.

[0101] Pressure 12-15MPa: Eliminate air bubbles in the melt to completely fill the mold cavity and obtain a homogeneous standard sample with no pores and a smooth surface;

[0102] Time 8-10 minutes: Ensure that the material reaches thermal equilibrium after being fully plasticized under the set temperature and pressure;

[0103] Cooling rate 10-15℃ / min: to prevent the formation of excessively large spherulites in Nylon 66 and to avoid generating excessive internal stress;

[0104] Demolding temperature <60℃: Ensure that the homogeneous standard specimens are cooled to below the material's operating temperature before demolding.

[0105] The parameters and specific effects of procedural shape settings (programming) are as follows:

[0106] The target temperature for heating is 50±1℃, which is slightly higher than the material's recovery response temperature (Tr=45±3℃). This activates the movement of the amorphous region and some β crystal chain segments of Nylon 66, enhances the elasticity of TPU particles, and reduces the overall modulus of the material, allowing it to enter a flexible and deformable state.

[0107] Heating rate 2-3℃ / min: Ensure uniform temperature of the entire specimen and avoid inconsistent deformation or internal stress concentration due to temperature difference;

[0108] Maintain constant temperature for 15-20 minutes: Under the target temperature and fixture constraints, the stress generated by deformation inside the material is fully relaxed and redistributed. The Nylon 66 molecular chains adjust their conformation under thermal motion and external constraints, forming an ordered structure that adapts to the temporary shape. The TPU particle network is fully stretched or compressed, storing elastic potential energy.

[0109] This embodiment uses a sinusoidal curved surface fixture: the complex curvature constraint allows the material to undergo multiple modes of deformation such as bending and stretching at the same time, which can fully verify and endow it with shape memory ability to cope with complex deformation.

[0110] Cooling rate 1-2℃ / min (maintaining constraint): slow cooling achieves stable curing, gradually freezing the molecular conformation and ordered structure of nylon 66 that matches the temporary shape formed during the heating stage, and locking the elastic potential energy stored in TPU particles.

[0111] Cooling endpoint temperature <20℃: Allows the material to cool completely below the glass transition temperature, completely fixing the temporary shape and entering a dimensionally stable state for use.

[0112] The response and final performance when recovery is triggered are as follows:

[0113] Triggering condition: Heating to above the response temperature Tr (45±3℃), for example, 50℃;

[0114] Internal material response: The frozen chain segments in Nylon 66 recover their motion, and their entropic elasticity drives the molecular chains to retract to the random coil conformation corresponding to the standard spline shape determined by hot pressing, simultaneously releasing the elastic potential energy stored in the TPU.

[0115] A high mechanical memory nylon rubber-plastic material prepared by the above method has a shape recovery rate Rr≥95% and a recovery response temperature Tr of 45±3℃ after standard thermomechanical cycling test.

[0116] It should be noted that, in order to objectively verify and quantify the high mechanical memory of the material prepared by this invention, this embodiment employs standard thermomechanical cycling tests. Through a precisely controlled strain-temperature-time program, its shape retention rate, shape recovery rate, and recovery response temperature are measured, including:

[0117] Prepare the testing equipment and fixtures: dynamic thermomechanical analyzer and double cantilever beam bending and tensile fixture. The fixture consists of two parallel clamps to ensure that the homogeneous standard specimen is held evenly. The gauge length (L_0) is accurate to 50 mm. The entire fixture is placed in a programmable temperature controlled environment chamber with a temperature control accuracy of ±0.5℃.

[0118] The test is conducted in a complete "deformation-fixation-restoration" cycle, including the following steps:

[0119] Step 1: Record the strain (ε), temperature (T) and time (t). Install the spline in the fixture, set the gauge length L_0=50mm, and stabilize it at a low temperature T_1=20℃ for 5 minutes. At this time, the strain ε_0=0%.

[0120] Step 2: Heat from T_1 to a high temperature T_2=70℃ at a rate of 2℃ / min. After reaching T_2, keep the temperature constant for 2 minutes to make the sample uniform. Apply tension to the sample at a constant rate through the clamp at T_2 until the preset maximum strain ε_m=50% is reached. Record the load at this time.

[0121] Step 3: Keep ε_m constant, cool from T_2 back to T_1 at a rate of 3℃ / min. After reaching T_1, keep the temperature constant for 5 minutes to stabilize the sample temperature and internal stress. Reduce the load to zero, measure and record the fixed strain ε_x of the sample at T_1.

[0122] Step 4: Under no external force (fixture) constraint, reheat from T_1 (20℃) to T_2 at a rate of 2℃ / min. Record the change of spline strain with temperature and time throughout the process and plot the strain-temperature recovery curve. Record the final residual strain ε_r at high temperature after the free recovery is completed.

[0123] Repeat steps 2-4 to perform multiple thermomechanical cycles and calculate the performance parameters:

[0124] Shape fixation rate Rf = (ε_x / ε_m) × 100%;

[0125] Shape recovery rate Rr=[(ε_m-ε_r) / ε_m]×100%=[(ε_x-ε_r) / ε_x]×100%;

[0126] From the strain-temperature recovery curve, the temperature corresponding to the inflection point of the recovery process curve is taken and denoted as Tr. In the free recovery stage of step 4, the strain starts to decrease from ε_x as the temperature increases, and a sharp drop plateau appears near the temperature Tr, eventually tending to a stable value ε_r.

[0127] In this embodiment, the following data was obtained after a certain cycle test:

[0128] Given ε_m = 50%, ε_x = 48.5%, and ε_r = 1.5%, the calculation yields:

[0129] Shape fixation rate Rf = (48.5% / 50%) × 100% = 97%;

[0130] Shape recovery rate Rr = [(50% - 1.5%) / 50%] × 100% = 97%;

[0131] Furthermore, when the temperature rises to the range of ~44℃ to 47℃, the strain drops sharply from about 48.5% to close to ε_r. Taking the temperature corresponding to a recovery rate of 50%, Tr≈45.5℃ is calculated.

[0132] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preparing a high mechanical memory nylon rubber-plastic material, characterized in that, The method includes: S1, Nylon 66 resin with an intrinsic viscosity of 2.8-3.2 dL / g and thermoplastic polyurethane elastomer with a Shore hardness of 75A-90A are respectively dried and pretreated. S2, by weight, weigh 70-75 parts of pretreated nylon 66 resin, 25-30 parts of pretreated thermoplastic polyurethane elastomer, 4-6 parts of maleic anhydride-grafted POE, 1.5-2.5 parts of composite antioxidant containing hindered phenol and phosphite, and 0.3-0.8 parts of β-crystalline nylon nucleating agent and premix them to obtain a premix; S3, the premixed material is added to the twin-screw extruder, and a temperature gradient is set in the third to sixth zones: 210℃→225℃→235℃→245℃ and the screw speed is set to 380-420r / min. Phenolic resin vulcanizing agent is injected in the fifth zone, and finally the material is extruded through a high-shear orientation die to obtain a strip extruded material. S4, the strip extruded material is first rapidly cooled in a cooling water bath at 40-45℃ in the first temperature zone for 30-45 seconds, and then slowly cooled in a constant temperature oil bath at 75-80℃ in the second temperature zone for 60-90 seconds before being granulated to obtain drum-shaped particles. S5, the drum-shaped particles are hot-pressed to form a standard template, and then subjected to programmed heating and cooling under the constraint of a fixture to obtain a finished material with a preset temporary shape.

2. The method for preparing a high mechanical memory nylon rubber-plastic material according to claim 1, characterized in that: The step of drying and pretreating nylon 66 resin with an intrinsic viscosity of 2.8-3.2 dL / g and thermoplastic polyurethane elastomer with a Shore hardness of 75A-90A respectively includes: The nylon 66 resin with an intrinsic viscosity of 2.8-3.2 dL / g was placed in a vacuum drying device and dried for 6-8 hours at a temperature of 100-110℃ and a vacuum degree of ≤0.095MPa. The thermoplastic polyurethane elastomer with a Shore hardness of 75A-90A was placed in a dehumidifying drying oven and treated with dry air circulation at a temperature of 80-85℃ for 3-4 hours with a dew point ≤-40℃. The treated nylon 66 resin and thermoplastic polyurethane elastomer were transferred to sealed containers filled with dry nitrogen and cooled to 25-30°C for later use.

3. The method for preparing a high mechanical memory nylon rubber-plastic material according to claim 1, characterized in that: The step of weighing 70-75 parts by weight of pretreated nylon 66 resin, 25-30 parts by weight of pretreated thermoplastic polyurethane elastomer, 4-6 parts by weight of maleic anhydride-grafted POE, 1.5-2.5 parts by weight of a composite antioxidant containing hindered phenols and phosphites, and 0.3-0.8 parts by weight of a β-crystalline nylon nucleating agent for compatibilization premixing to obtain the premix includes: The mixing chamber of a high-speed mixer is preheated to 20±2℃, and cooling water is continuously circulated into its jacket; Add 70-75 parts of the pretreated nylon 66 resin and 25-30 parts of the pretreated thermoplastic polyurethane elastomer to a high-speed mixer and dry mix at 300-500 r / min for 2-3 minutes. The 4-6 parts of maleic anhydride-grafted POE, 1.5-2.5 parts of a composite antioxidant containing hindered phenol and phosphite, and 0.3-0.8 parts of β-crystalline nylon nucleating agent are manually stirred and premixed at 20-25°C for 30-60 seconds to form an additive premix. The premixed additive is uniformly added to the high-speed mixer and mixed at a speed of 800-1200 r / min for 8-12 minutes, during which the material temperature in the high-speed mixer is controlled to be below 45℃. After high-speed mixing is complete, reduce the speed to 100-200 r / min and continue mixing for 1-2 minutes. Then discharge the resulting premix and immediately transfer it to a sealed container.

4. The method for preparing a high mechanical memory nylon rubber-plastic material according to claim 1, characterized in that: The steps of adding the premixed material to a twin-screw extruder, setting a temperature gradient in zones three to six: 210℃→225℃→235℃→245℃ and setting the screw speed to 380-420 r / min, injecting a phenolic resin vulcanizing agent in zone five, and finally extruding through a high-shear orientation die to obtain a strip extrudate include: The premixed material is fed into a twin-screw extruder through the main feed port and passes sequentially through zones one to six, including: When the premixed material reaches the first to second zones of the twin-screw extruder, it is melt-plasticized at a temperature of 190-205°C. When the premixed material after being melted and plasticized reaches the third, fourth, fifth and sixth zones of the twin-screw extruder, it is homogenized and mixed with temperature gradients of 210°C, 225°C, 235°C and 245°C respectively, and with a screw speed of 380-420 r / min. At the high-shear orientation die outlet of the twin-screw extruder, the oriented melt is smoothly extruded under a die pressure of 2.5-3.5 MPa to form a continuous strip-shaped extrudate.

5. A method for preparing a high mechanical memory nylon rubber-plastic material according to claim 1 or 4, characterized in that: When the premixed material that has undergone melt plasticization reaches the fifth zone of the twin-screw extruder: Weigh 1.5-2.5% of the phenolic resin curing agent by mass of the thermoplastic polyurethane elastomer, and inject the phenolic resin curing agent into the melt flow in a pulse injection manner through a high-pressure metering pump. The melt pressure in the fifth zone is controlled at 4.0-6.0 MPa to carry out in-situ dynamic vulcanization reaction, resulting in micro-crosslinked elastomer particles; The twin-screw extruder is equipped with a high-shear kneading block element in the fifth zone, which allows the melt to be subjected to high shear in this zone.

6. A method for preparing a high mechanical memory nylon rubber-plastic material according to claim 1 or 4, characterized in that: The high-shear orientation die of the twin-screw extruder has a parallel slit structure with a slit gap of 0.5-1.0 mm and a length-to-diameter ratio of 10:1 to 20:

1. When the melt flows through the high-shear orientation die, it experiences an instantaneous shear rate of ≥500s^-1 at the slit gap, which causes the nylon molecular chains and micro-crosslinked elastomer particles to align in the extrusion direction.

7. The method for preparing a high mechanical memory nylon rubber-plastic material according to claim 1, characterized in that: The steps of first rapidly cooling the strip extrudate through a first temperature zone (40-45℃) cooling water bath for 30-45 seconds, then slowly cooling it through a second temperature zone (75-80℃) constant temperature oil bath for 60-90 seconds, and finally pelletizing it to obtain drum-shaped granules include: The strip extruded material is drawn out at a constant speed of 5-8 m / min by the first pair of traction rollers; The drawn strip extruded material is completely immersed in a cooling water bath with a temperature zone of 40-45℃ for rapid cooling, and held for 30-45 seconds. The strip extruded material that has been quenched is removed and suspended in room temperature air at 20-30°C for 5-10 seconds. Then, the strip extruded material is completely immersed in a constant temperature hot oil bath at 75-80°C in the second temperature zone for slow cooling for 60-90 seconds. The strip extruded material, which has undergone slow cooling, is drawn out by the second pair of traction rollers and fed into a pelletizer, where it is cut into drum-shaped particles with a diameter of 2-3 mm and a length of 3-4 mm, and collected in a moisture-proof container.

8. The method for preparing a high mechanical memory nylon rubber-plastic material according to claim 1, characterized in that: The step of hot-pressing the drum-shaped particles into standard templates and then subjecting them to programmed heating and cooling under fixture constraints to obtain a finished material with a preset temporary shape includes: The drum-shaped particles are evenly spread into a standard sample mold, and hot-pressed for 8-10 minutes at a temperature of 240-245℃ and a pressure of 12-15MPa on a hot press. Then, the sample is cooled to below 60℃ at a rate of 10-15℃ / min to demold it, and a homogeneous standard sample is obtained. The homogeneous standard sample is mounted on a programming fixture and moved as a whole into a constant temperature chamber. The temperature inside the constant temperature chamber is uniformly raised to 50±1℃ at a heating rate of 2-3℃ / min and kept constant for 15-20 minutes. While maintaining the constraint of the fixture, the temperature inside the constant temperature chamber is uniformly reduced from 50±1℃ to below 20℃ at a rate of 1-2℃ / min. Remove the programming fixture from the constant temperature chamber and unload it to obtain the finished material.

9. A high mechanical memory nylon rubber-plastic material prepared by the method according to any one of claims 1-8, characterized in that: Through standard thermomechanical cycling tests, the shape recovery rate Rr of the high mechanical memory nylon rubber and plastic material is ≥95%, and the recovery response temperature Tr is 45±3℃.

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