A process for uniform mixing of fibers in the preparation of a bio-based material

Abstract

This invention relates to the field of polymer material processing and blending technology, and discloses a fiber uniform mixing process in the preparation of bio-based materials. The process includes: controlling the barrel wall temperature of the main dispersion zone of a co-rotating twin-screw extruder to be lower than the intrinsic melting point of the polylactic acid matrix and turning off the external heater; adding jute fiber bundles and the polylactic acid matrix and controlling the screw speed, utilizing the frictional heat balance temperature difference generated by mechanical shearing to maintain the actual melt temperature above the intrinsic melting point; and conveying the mixture to the secondary diffusion zone as the motor drive torque increases, thereby increasing the barrel wall temperature of the secondary diffusion zone and reducing the screw speed to blend the materials. This invention eliminates temperature control lag, maintains a stable shear flow field, avoids a sudden drop in melt viscosity to improve fiber dispersion uniformity, automatically indicates process stage transitions, avoids material thermal degradation, and improves the stability of the mechanical properties of the finished material.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing and blending technology, and in particular to a fiber uniform mixing process in the preparation of bio-based materials. Background Technology

[0002] Currently, in the mixing process of multiphase heterogeneous materials, the use of the mechanical shear stress field of twin-screw extruders to disperse fiber agglomerates in the polymer matrix is ​​a conventional process. The conventional temperature control method relies on electric heating coils and cooling fluid pipes arranged on the outer wall of the barrel to provide overall heat conduction flow. Under the drive of external thermodynamics, a stepped temperature gradient is constructed. In the early stage of mixing, a high viscosity state is maintained to transfer mechanical shear stress, and in the later stage of mixing, the melt is adjusted to a low viscosity state to wet the fiber surface. However, when the polymer melt applies mechanical shear to the multiphase cross-linked fiber bundles in a high viscosity state, strong viscous dissipation heat is generated instantaneously at the material interface. Due to the low intrinsic thermal conductivity of polymer materials and the thermal hysteresis effect of heat transfer on the metal barrel wall, the external cooling medium cannot instantly remove the frictional heat accumulated at the multiphase interface. This causes the local melt temperature to rapidly exceed the critical rheological temperature zone, and the dynamic viscosity of the melt to drop unexpectedly. This causes the preset high-stress mechanical shear field to decay before the fiber bundles are completely disintegrated and dispersed in space, resulting in fiber agglomeration inside the material and batch-to-batch fluctuations in the mechanical properties of the finished composite material.

[0003] In addition to the inherent limitations of the heat transfer components such as heating and cooling arranged on the outer wall of the barrel in terms of energy transfer and spatial form, the existing processing technology also has shortcomings in software aspects such as control methods. For example, Chinese invention patent application CN106543663A discloses a method for preparing long natural fiber / polylactic acid-based composite materials. The barrel is kept at a constant temperature according to a preset stepped static temperature zone. The above-mentioned static temperature zone control implicitly relies on the underlying objective properties that the heat generation state and rheological characteristics of the material in the mixing process are in a constant and ideal state. However, in high-load, non-homogeneous multiphase continuous processing scenarios, due to the dynamic fluctuations of the intrinsic moisture content, entanglement degree or feeding rate of natural fibers, the viscous heat dissipation and intrinsic frictional resistance of the material in the extruder exhibit nonlinear dynamic evolution. The above-mentioned static temperature zone control is fundamentally mismatched with the dynamic requirements of instantaneous frictional heat generation at the material interface. It is difficult to maintain the continuous stability of the boundary high shear stress field, which can easily induce excessive shear degradation of the matrix macromolecular chains or uneven spatial dispersion of fibers, resulting in batch fluctuations in the mechanical properties of the finished product.

[0004] Therefore, the technical problem to be solved by this invention is how to adjust the thermodynamic boundary conditions by utilizing the energy balance mechanism between the internal shear potential energy of multiphase materials and the thermal enthalpy difference of the barrel wall, and control the mixing rheological state by controlling the driving load change signal caused by the evolution of the intrinsic friction coefficient of the material, so as to achieve a continuous and stable transition from the forced shear physical crushing process to the surface wetting process of low viscosity fluid. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a fiber uniform mixing process in the preparation of bio-based materials, comprising the following steps:

[0006] Step S101: Determine the intrinsic melting point of the polylactic acid matrix;

[0007] Step S102: Control the barrel wall temperature of the main dispersion zone in the co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1 to be 12°C to 18°C ​​below the intrinsic melting point, and turn off the external heater of the main dispersion zone.

[0008] Step S103: 20 to 30 parts by weight of jute fiber bundles and 70 to 80 parts by weight of polylactic acid matrix are quantitatively added to the feed port of the co-rotating twin-screw extruder, wherein the volume moisture content of the jute fiber bundles is less than 2%. The screw speed is controlled at 380 rpm to 420 rpm. The jute fiber bundles and polylactic acid matrix are sheared by a kneading disc assembly set in the main dispersion zone with a staggered angle of 45° to 90°. The actual melt temperature of the polylactic acid matrix is ​​collected in real time by a temperature sensor set in the co-rotating twin-screw extruder, and the actual melt temperature is controlled to be maintained in the range of 3° to 8° above the intrinsic melting point.

[0009] Step S104: Continuously detect the motor drive torque value of the co-rotating twin-screw extruder. When the motor drive torque value is detected to increase by more than 15% within 2 seconds, output a material flow signal and transport the mixture to the secondary diffusion zone.

[0010] Step S105: Control the barrel wall temperature of the secondary diffusion zone to be 23°C to 28°C above the intrinsic melting point, and simultaneously control the screw speed in the secondary diffusion zone to be 60 rpm to 100 rpm to blend the polylactic acid matrix and jute fiber bundles.

[0011] Preferably, before feeding the polylactic acid matrix and jute fiber bundles into the co-rotating twin-screw extruder, a material pre-mixing step is also included: feeding the polylactic acid matrix and jute fiber bundles into a high-speed mixer, controlling the impeller speed of the high-speed mixer to be 1000 rpm to 1200 rpm, and mixing for 4 to 6 minutes at a temperature of 20°C to 30°C; the co-rotating twin-screw extruder is equipped with a multi-channel quantitative feeding unit, which continuously and proportionally feeds materials into the feeding port using the multi-channel quantitative feeding unit.

[0012] Preferably, in step S103, the screw speed is adjusted according to the actual melt temperature change rate monitored by the temperature sensor to keep the actual melt temperature stable within a range of 3°C to 8°C above the intrinsic melting point.

[0013] Preferably, in step S105, the barrel wall temperature of the secondary diffusion zone is controlled to be between 188°C and 193°C, and the screw speed in the secondary diffusion zone is controlled to be between 60 rpm and 100 rpm.

[0014] Preferably, in step S103, the jute fiber bundles are broken by the mechanical shearing action of the kneading disc assembly, generating sub-millimeter particles with an average particle size of 0.2 mm to 0.8 mm.

[0015] Preferably, the co-rotating twin-screw extruder is equipped with a forward threaded conveying assembly in the secondary diffusion zone, which provides axial conveying power to the material so that the material is in a low-shear blending state.

[0016] Preferably, step S103 further includes the following auxiliary temperature control sub-steps: Step S1031, when the actual melt temperature of the polylactic acid matrix exceeds 175°C, the external cooling pipes installed on the barrel wall are opened to input the cooling medium; Step S1032, when the actual melt temperature drops to the range of 168°C to 173°C, the external cooling pipes are closed to stop inputting the cooling medium.

[0017] Preferably, after step S105, the following steps are also included: Step S106, the mixed material discharged from the co-rotating twin-screw extruder is introduced into the water-cooled pelletizing unit, and the water temperature is controlled at 15°C to 25°C to solidify the material; Step S107, the solidified material is cut into bio-based composite particles using pelletizing blades.

[0018] Preferably, in step S107, the length of the bio-based composite particles is controlled to be 2 mm to 4 mm by a pelletizing tool, and the weight moisture content of the bio-based composite particles is less than 0.5%.

[0019] The beneficial effects of this invention are:

[0020] 1. In the uniform mixing process of fibers for bio-based material preparation, a sub-melting barrel wall temperature zone below the melting point of the polymer matrix is ​​used in conjunction with a specific rotation speed. This allows the viscous heat dissipation generated by the forced shearing of the fiber agglomerates by the kneading components during the high-dispersion mixing stage to be mutually beneficially compensated with the heat dissipation from the barrel wall, thus constructing a shear flow field with energy balance in the melt itself. The high mechanical frictional heat generated at the material interface is directly converted into the only energy source to maintain the matrix in a viscous flow state, eliminating the thermal hysteresis effect in traditional external heat conduction temperature control methods. This ensures that the high-stress shear field remains stable before the fiber agglomerates are completely disintegrated, avoiding uneven fiber dispersion caused by an unexpected sudden drop in melt viscosity due to local overheating.

[0021] 2. Active rheological control of the mixing stage is achieved by continuously monitoring the driving torque changes of the twin-screw extruder. As the physical entanglement of fiber agglomerates is gradually eliminated during the deconstruction process, the friction coefficient inside the multiphase material system decreases, resulting in the interfacial shear heat generation being lower than the heat dissipation to the barrel wall. Consequently, the melt temperature drops and the polymer matrix viscosity rises rapidly, causing the driving torque curve to show an upward inflection point. This torque change state serves as a direct physical characterization signal of the evolution of material mixing uniformity, automatically indicating the flow switching from the high-viscosity shear zone to the low-viscosity diffusion zone. This eliminates the reliance on experience in traditional timed or quantitative segmented mixing methods and avoids physical thermal degradation of materials due to excessive shearing.

[0022] 3. The high-viscosity spatial fragmentation stage based on material friction dissipation and shear heat generation is deeply coupled with the low-viscosity surface wetting stage based on externally heated melt degradation. In the first half of the mixing process, the fiber bundles in the multiphase heterogeneous material are forcibly stripped by a high shear stress field. After the material enters the secondary diffusion zone triggered by torque feedback, the high fluid diffusion pressure under high temperature and low viscosity conditions guides the molten matrix to densely penetrate the dissociated fiber surface. This achieves the sequential connection between spatial flow field discrete diffusion and multiphase interface penetration, reduces the internal stress concentration phenomenon of composite materials after molding and curing, and improves the batch stability of the mechanical properties of the finished material. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments 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, wherein:

[0024] Figure 1 This is a flowchart of the main steps of the fiber uniform mixing process in the preparation of bio-based materials of the present invention;

[0025] Figure 2 This is a process control diagram for the uniform mixing of fibers in the preparation of bio-based materials according to the present invention. Detailed Implementation

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0027] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0028] The term "one embodiment" or "an embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. An embodiment appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0029] This invention is described in detail with reference to the schematic diagrams. When describing the embodiments of this invention, for ease of explanation, the cross-sectional views of the device structure will be partially enlarged without adhering to the general scale. Moreover, the schematic diagrams are only examples and should not limit the scope of protection of this invention. In addition, in actual manufacturing, the three-dimensional spatial dimensions of length, width and depth should be included.

[0030] Furthermore, in the description of this invention, it should be noted that the terms such as "upper," "lower," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or component referred to has a specific orientation, or is constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention. In addition, the terms "first," "second," or "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] Unless otherwise explicitly specified and limited, the terms installation, connection, and linking in this invention should be interpreted broadly. For example, they can refer to fixed connection, detachable connection, or integrated connection; similarly, they can refer to mechanical connection, electrical connection, or direct connection, or indirect connection through an intermediate medium, or internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] A fiber homogenization process for the preparation of bio-based materials includes the following steps:

[0033] Step S101: Determine the intrinsic melting point of the polylactic acid matrix;

[0034] Step S102: Control the barrel wall temperature of the main dispersion zone in the co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1 to be 12°C to 18°C ​​below the intrinsic melting point, and turn off the external heater of the main dispersion zone.

[0035] Step S103: 20 to 30 parts by weight of jute fiber bundles and 70 to 80 parts by weight of polylactic acid matrix are quantitatively added to the feed port of the co-rotating twin-screw extruder, wherein the volume moisture content of the jute fiber bundles is less than 2%. The screw speed is controlled at 380 rpm to 420 rpm. The jute fiber bundles and polylactic acid matrix are sheared by a kneading disc assembly set in the main dispersion zone with a staggered angle of 45° to 90°. The actual melt temperature of the polylactic acid matrix is ​​collected in real time by a temperature sensor set in the co-rotating twin-screw extruder, and the actual melt temperature is controlled to be maintained in the range of 3° to 8° above the intrinsic melting point.

[0036] Step S104: Continuously detect the motor drive torque value of the co-rotating twin-screw extruder. When the motor drive torque value is detected to increase by more than 15% within 2 seconds, output a material flow signal and transport the mixture to the secondary diffusion zone.

[0037] Step S105: Control the barrel wall temperature of the secondary diffusion zone to be 23°C to 28°C above the intrinsic melting point, and simultaneously control the screw speed in the secondary diffusion zone to be 60 rpm to 100 rpm to blend the polylactic acid matrix and jute fiber bundles.

[0038] Preferably, before feeding the polylactic acid matrix and jute fiber bundles into the co-rotating twin-screw extruder, a material pre-mixing step is also included: feeding the polylactic acid matrix and jute fiber bundles into a high-speed mixer, controlling the impeller speed of the high-speed mixer to be 1000 rpm to 1200 rpm, and mixing for 4 to 6 minutes at a temperature of 20°C to 30°C; the co-rotating twin-screw extruder is equipped with a multi-channel quantitative feeding unit, which continuously and proportionally feeds materials into the feeding port using the multi-channel quantitative feeding unit.

[0039] Preferably, in step S103, the screw speed is adjusted according to the actual melt temperature change rate monitored by the temperature sensor to keep the actual melt temperature stable within a range of 3°C to 8°C above the intrinsic melting point.

[0040] Preferably, in step S105, the barrel wall temperature of the secondary diffusion zone is controlled to be between 188°C and 193°C, and the screw speed in the secondary diffusion zone is controlled to be between 60 rpm and 100 rpm.

[0041] Preferably, in step S103, the jute fiber bundles are broken by the mechanical shearing action of the kneading disc assembly, generating sub-millimeter particles with an average particle size of 0.2 mm to 0.8 mm.

[0042] Preferably, the co-rotating twin-screw extruder is equipped with a forward threaded conveying assembly in the secondary diffusion zone, which provides axial conveying power to the material so that the material is in a low-shear blending state.

[0043] Preferably, step S103 further includes the following auxiliary temperature control sub-steps: Step S1031, when the actual melt temperature of the polylactic acid matrix exceeds 175°C, the external cooling pipes installed on the barrel wall are opened to input the cooling medium; Step S1032, when the actual melt temperature drops to the range of 168°C to 173°C, the external cooling pipes are closed to stop inputting the cooling medium.

[0044] Preferably, after step S105, the following steps are also included: Step S106, the mixed material discharged from the co-rotating twin-screw extruder is introduced into the water-cooled pelletizing unit, and the water temperature is controlled at 15°C to 25°C to solidify the material; Step S107, the solidified material is cut into bio-based composite particles using pelletizing blades.

[0045] Preferably, in step S107, the length of the bio-based composite particles is controlled to be 2 mm to 4 mm by a pelletizing tool, and the weight moisture content of the bio-based composite particles is less than 0.5%.

[0046] Example 1: In the continuous blending extrusion molding process of a multiphase non-homogeneous material consisting of 70 to 80 parts by weight of polylactic acid matrix and 20 to 30 parts by weight of jute fiber bundles in a co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1, the local temperature of the melt rises due to heat dissipation caused by the viscosity of the multiphase interface. Furthermore, the heat transfer time is delayed due to the radial thermal resistance from the metal barrel wall to the center of the material, which restricts the temperature control by heat conduction. This causes the shear stress flow state in the main dispersion zone to change before the jute fiber bundles are completely disintegrated and dispersed. Local fiber agglomeration occurs in the material, resulting in fluctuations in the mechanical properties of the finished product.

[0047] When adjusting the flow state, the intrinsic melting point of the polylactic acid matrix was determined using a differential scanning calorimeter. In a co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1 and a barrel wall temperature in the main dispersion zone of the extruder at 165℃, the temperature is lower than the intrinsic melting point. The barrel wall temperature of the main dispersion zone is set to 150℃, ranging from 12℃ to 18℃, and the external heater of the main dispersion zone is turned off to cut off the external heat input. 25 parts by weight of jute fiber bundles with a volume moisture content of less than 2% and 75 parts by weight of polylactic acid matrix are continuously and quantitatively added to the feed port of the co-rotating twin-screw extruder through a multi-channel quantitative feeding unit. The screw speed of the co-rotating twin-screw extruder is adjusted to 400 rpm. A kneading disc assembly with a staggered angle of 60° is used in the main dispersion zone to apply shear force to the jute fiber bundles and polylactic acid matrix. A temperature sensor installed in the co-rotating twin-screw extruder continuously collects the actual melt temperature of the polylactic acid matrix online. According to the actual melt temperature The screw speed is finely adjusted using the time derivative. The control unit continuously reads the actual melt temperature Ta at a sampling frequency of 10Hz and calculates the average temperature change slope in a sliding time window of 2.0 seconds. When the average temperature change slope is greater than the preset 0.5℃ / s, a decreasing control level signal is output to the main drive motor, gradually decreasing the screw speed in fixed steps of 5 rpm. When the actual melt temperature Ta drops to 168℃ and the average temperature change slope is less than 0℃ / s, an increasing control level signal is output to the main drive motor, gradually increasing the screw speed in steps of 5 rpm, thus reducing the actual melt temperature... Maintaining the temperature in the range of 168°C to 173°C, which is above the intrinsic melting point. Between 3°C and 8°C, the mechanical frictional heat at the material interface becomes the energy source to maintain the matrix in a fluid state. The kneading disc assembly applies mechanical shear force to the jute fiber bundles, breaking them down into particles with an average particle size of 0.5 mm. During this primary dispersion and mixing stage, the control system collects the motor drive torque values ​​of the co-rotating twin-screw extruder online. When jute fiber bundles disperse and dissociate with an average particle size of 0.5 mm, the intrinsic friction coefficient of the multiphase system decreases. The heat dissipation from the material to the barrel wall in the main dispersion zone exceeds the local shear heat generation, causing a decrease in melt temperature and an increase in the dynamic viscosity of the polylactic acid matrix. The data acquisition module continuously reads the no-load running resistance value of the main drive shaft and establishes a residual background baseline. A five-point moving average algorithm is applied to the raw torque data source continuously collected during the mixing period to remove alternating high-frequency noise data with an amplitude less than 2.0 N·m. The residual background baseline is then simultaneously subtracted from the filtered dataset to extract the net torque value that independently characterizes the viscous flow resistance of the multiphase material. During this rheological evolution, because the jute fiber bundles are forcibly sheared to the sub-millimeter scale, their huge specific surface area instantly exposes a large amount of high-viscosity torque. The polar hydroxyl groups on the surface energy undergo rapid physical entanglement and hydrogen bonding with the polylactic acid macromolecular chains in a viscous flow state at the multiphase interface. This high-density interfacial entanglement network at the surface scale strongly hinders the relative slippage of the macromolecular chains. The mechanical resistance response transmitted to the overall flow field is much faster than the overall thermal conduction rate of the metal barrel. Therefore, the aforementioned viscosity increase is not solely due to the slow heat dissipation and cooling of the barrel as a whole, but rather to the nonlinear spatial abrupt change in local apparent viscosity caused by the instantaneous large-area cross-linking at the surface interface. This physical mechanism supports the system's ability to encounter and detect a dramatic surge in the rheological resistance of the driving rotor within an extremely short timescale of 2 seconds. The increase in the motor driving torque value M is determined by the net torque value; when the motor driving torque value is detected... When the torque increases by 17% within 2 seconds, exceeding the preset torque increase threshold of 15%, the control module sends a 100% duty cycle drive voltage signal to the discharge actuator, driving the electromagnetic reversing valve at the tail of the main dispersion zone to open to the maximum degree, establishing a physical discharge connection path, and the control system outputs a material flow signal to continuously transport the mixture to the secondary diffusion zone.

[0048] After the mixture enters the secondary diffusion zone, the cylinder wall heating assembly is activated to control the cylinder wall temperature in the secondary diffusion zone to be above the intrinsic melting point. Within the range of 23℃ to 28℃, the barrel wall temperature of the secondary diffusion zone is controlled to be maintained within the range of 188℃ to 193℃. Simultaneously, the transmission system is adjusted to reduce the screw speed in the secondary diffusion zone to 80 rpm, placing it within the shear range of 60 rpm to 100 rpm. The forward threaded conveying assembly within the secondary diffusion zone provides stable axial conveying power to the blended material, keeping it in a low-shear blending state. Temperature adjustment reduces the dynamic viscosity of the material, and the high fluid diffusion pressure under high temperature and low viscosity conditions guides the molten polylactic acid matrix to compact into the pores of the dissociated jute fiber bundles. After the low-shear blending process is completed, the mixed composite flow material continuously discharged from the discharge port of the co-rotating twin-screw extruder is directly introduced into the water-cooled pelletizing unit. The water temperature in the water-cooled pelletizing unit is controlled to be maintained between 15°C and 25°C to solidify the material. The solidified material is then cut into bio-based composite particles with a length of 2mm to 4mm and a weight moisture content of less than 0.5% by the pelletizing blade. This completes the connection between spatial flow field discrete diffusion and multiphase interface penetration, reduces the internal stress concentration of the material after molding and curing, and reduces batch fluctuations in the mechanical properties of the finished bio-based composite material.

[0049] Example 2: A process test environment was constructed using a mechanical blending rheological testing platform. The platform included a co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1 and independent temperature control components for each zone; a transmission sensor for continuously acquiring torque changes with a measurement range of 0 to 200 N·m and a sampling frequency set to 50 Hz; and a temperature control sensor for measuring the actual temperature inside the barrel and melt with a measurement accuracy of ±0.1℃. In the material feeding section, periodically fluctuating jute fiber bundles with varying volume moisture content were continuously added to the feeding system through the feeding port as a dynamic moisture interference source. The volume moisture content varied sinusoidally within the range of 0.5% to 4.5%, generating torque fluctuation loads. The load control system is equipped with a mean filtering module to perform a five-point moving average calculation on the collected raw drive torque signal to eliminate high-frequency load fluctuations and extract the trend of drive torque variation rate. The main dispersion zone of the co-rotating twin-screw extruder is equipped with a kneading disc assembly with a staggered angle of 60° to apply shear force to the jute fiber bundles and polylactic acid matrix. By adjusting the barrel wall temperature of the main dispersion zone and controlling the screw speed of the co-rotating twin-screw extruder, the jute fiber bundles are dissociated before the polylactic acid matrix is ​​completely melted. When the dynamic intrinsic frictional resistance of the material decreases due to the uniform dispersion of the multiphase and the motor drive torque reaches an inflection point, the control system automatically adjusts the material flow according to the drive torque variation rate.

[0050] In the process data testing, one experimental group and eight control groups were set up. The barrel wall temperature in the main dispersion zone of the experimental group was set to 150℃, the torque increase trigger threshold was set to 15%, the barrel wall temperature in the secondary diffusion zone was set to 190℃, and the screw speed in the secondary diffusion zone was set to 80 rpm. Control group one maintained the temperature and speed of the main dispersion zone when the drive torque variation rate reached 15%, without any flow within the process temperature zone. Control group two had a constant barrel wall temperature of 190℃ throughout the entire process, without setting a sub-melting temperature zone in the main dispersion zone. Control group three had a barrel wall temperature of 13℃ in the main dispersion zone. The temperature of the barrel wall in the main dispersion zone of control group 4 was set at 5℃; the temperature of the barrel wall in the secondary diffusion zone of control group 5 was set at 162℃; the temperature of the barrel wall in the secondary diffusion zone of control group 6 was set at 25%; the temperature of the barrel wall in the secondary diffusion zone of control group 7 was set at 175℃; and the temperature of the barrel wall in the secondary diffusion zone of control group 8 was set at 210℃. The experimental group and control groups 1 to 8 were operated under process conditions with jute fiber bundle volume moisture content of 0.5%, 1.8% and 4.5%, respectively. The mechanical properties of the molded and cured specimens were measured using a universal testing machine and a cantilever beam impact testing machine.

[0051] All experimental and control groups (1-8) used 75 kg of polylactic acid matrix and 25 kg of jute fiber bundles as the feeding standard. Online data acquisition showed that when the injected moisture content was 4.5% (excessive moisture), the original drive torque signal without mean filtering exhibited transient alternating fluctuations with an amplitude of 8.2 N·m. After processing by the mean filtering module, the experimental group extracted a torque trend curve that continuously changed with the spatial dissociation of the fiber bundle. In material melting control, the experimental group collected the motor drive torque value after running in the main dispersion zone for 14.2 minutes. The torque increased continuously from an initial 42.3 N·m to 49.5 N·m when the control system calculated the motor drive torque value. When the rate of change reaches 17.1% within 2 seconds, the control loop sends a cascade flow control signal to the conveying assembly, continuously feeding the mixture into the secondary diffusion zone. At this time, the actual melt temperature collected by the temperature control sensor... The intrinsic melting point of polylactic acid matrix is ​​171.2℃. The pre-determined temperature was 165℃. After material flow, it continuously flowed and uniformly penetrated in the secondary diffusion zone with a wall temperature of 190℃ and a screw speed of 80 rpm, relying on the forward screw conveyor assembly. The morphology of the impact section of the material was characterized by scanning electron microscopy. The results showed that jute fiber monofilaments were three-dimensionally randomly oriented and dispersed in the polylactic acid matrix, and the average width of the gap between the fiber monofilaments and the matrix interlayer was 0.12 μm. In control group one, because the extrusion state was not changed when the torque increased, the material residence time in the main dispersion zone exceeded 30 minutes. The tensile strength of the formed sample decreased from 62.4 MPa in the experimental group to 31.5 MPa. The weight-average molecular weight measured by gel electrophoresis decreased from 135,000 to 61,000, indicating that the material molecular chains underwent macromolecular chain breakage. Control groups two and four did not operate below the intrinsic melting point. Initial crushing was performed within a submelting shear window of 12℃ to 18℃. Scanning electron microscopy images revealed undissociated fiber aggregates with a size of 120μm to 240μm inside the matrix, which became crack initiation sites under load. The cantilever beam notched impact strength decreased from 8.6kJ / m² in the experimental group to 2.4kJ / m². Data from control groups five, six, seven, and eight showed that when the torque was increased to trigger threshold or deviated from the secondary diffusion temperature, the mechanical properties of the specimens increased more slowly and entered a flat saturation zone. In the continuous stable blending extrusion molding process, the submelting friction temperature-controlled crushing in the main dispersion zone of the co-rotating twin-screw extruder was sequentially connected with the low-viscosity fluid penetration in the secondary diffusion zone. The standard deviation of the batch mechanical strength of the solidified composite particles decreased from 8.4% to 0.6%, and the tensile strength deviation of the specimens in the direction parallel to the extrusion axis and perpendicular to the extrusion axis was less than 1.5%.

[0052] Example 3: When a co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1 continuously processes multiphase heterogeneous materials under high load, the melt shear field in the main dispersion zone becomes unstable due to transient disturbances in the feed rate. Local pressure fluctuations in the feed channel and the non-uniform aggregation and interweaving of jute fiber bundles cause the transmission system to be subjected to non-periodic resistance impacts. Conventional static control methods cannot deconstruct the mechanical oscillation noise of the transmission chain in the drive torque signal, resulting in phase lag. This causes the material in the main dispersion zone to leak out prematurely before reaching the preset dispersion fineness due to control system malfunctions, or the polymer chains are thermally degraded due to excessive shearing, resulting in a significant decline in the interlayer peel mechanical strength of the continuously extruded molded parts.

[0053] To eliminate background noise from variable loads in the signal path controlling material transport, the data processing module within the control system employs a time-domain sliding sampling window. This window is set to 3.2 seconds with a sampling frequency of 50Hz. Within this window, raw motor drive torque data output from the drive sensor is continuously acquired. The built-in mean filtering module then performs a five-point sliding average of the raw motor drive torque data to eliminate high-frequency load fluctuations and extract the trend of the drive torque variation rate. An offline temperature calibration regression equation is used to determine the torque increase trigger threshold. This equation is established based on the physical law of screw axial shear energy dissipation rate varying with material viscosity. The input receives the intrinsic melting point of the polylactic acid matrix. The value is 165℃ and the current actual melt temperature. The control unit calculates the monotonic extreme point of the corresponding material's dynamic intrinsic resistance turning point in real time based on the input data. In the specific data processing steps, the system's built-in calculation module calculates the transient pure thermodynamic temperature difference by subtracting the actual melt temperature from the intrinsic melting point, and then divides this temperature difference by the intrinsic melting point to convert it into a dimensionless thermodynamic deviation ratio. This dimensionless ratio is multiplied by the inherent proportionality constant reflecting the shear rheological properties of a specific polymer material, and then accumulated with the basic resistance base set by the material ratio. When the internal dispersion state of the material changes from initial agglomeration under shear action... When the process transitions to uniform dispersion, the dynamic time derivative curve of the accumulated values ​​will rise rapidly from a flat range and reach a peak with the steepest slope. The system identifies the monotonic extreme point representing the physical turning point of intrinsic resistance by capturing the zero-crossing moment when the first derivative changes from positive to negative. Based on this, it outputs a quantitative control limit value and calculates a torque increase trigger threshold of 15% under specific test sample conditions. When multiphase materials undergo continuous strong mechanical shearing in the main dispersion zone of a co-rotating twin-screw extruder through a kneading disc assembly with a 60° staggered angle, and the temperature sensor monitors the actual melt temperature... When the temperature reaches 171.2℃, the free radicals generated by the spatial fragmentation and dissociation of jute fiber bundles undergo local covalent entanglement with the polymer melt interface, causing a nonlinear increase in rheological viscosity in the later stage of main dispersion. When the mean filtering module calculates the smoothed motor drive torque value... When the continuously increasing rate of change within 2 seconds reaches 17.1% and crosses the quantitative control threshold of 15%, in order to eliminate the mathematical time domain conflict between the long-term sliding sampling window and the short-term abrupt change judgment condition, the system executes a dual-track processing logic of long and short windows when calculating this continuously increasing rate of change. Specifically, a buffered data sequence of up to 3.2 seconds is used to fit the low-frequency residual resistance baseline of the current operating cycle, while the mean filtering module only performs a moving average calculation on the five discrete data points acquired at the latest moment. Since the sampling frequency is as high as 50Hz, the actual physical time spanned by this filtering action is only an extremely short 0.1 seconds, so that the smoothed signal after noise reduction still retains a very high transient time resolution. The control unit directly extracts the short-window smoothed torque value at this moment and performs an algebraic comparison calculation with the baseline historical data accurately backtracked to 2 seconds ago, thereby overcoming the algorithm contradictions of different time scales and realizing the accurate identification and capture of the overall viscosity jump action. The control system instantly issues a flow channel switching command to guide the sub-melted blend material to the secondary diffusion zone at a constant extrusion flow rate.

[0054] After the mixture enters the secondary diffusion zone, the temperature control component adjusts the cylinder wall heating component to stabilize the cylinder wall temperature in the secondary diffusion zone between 188℃ and 193℃. The transmission system adjusts the drive motor to control the screw speed in the secondary diffusion zone to maintain 80 rpm. Under the drive of high flow diffusion pressure, the polylactic acid matrix in the molten state overcomes the mass transfer grain boundary resistance and densely penetrates and wets the pores of the dissociated jute fiber monofilaments. The uniformly blended multiphase viscous fluid material is directly extruded through the discharge port into the water-cooled pelletizing unit with a constant cooling temperature of 20℃ for instantaneous solidification and locking. It is uniformly cut into finished pellets with a length of 3mm by the pelletizing blade, completing the flow switching between high-stress phase deconstruction and low-flow-rate interface wetting in the flow field channel transformation sequence. This eliminates the phenomenon of internal stress deformation concentration caused by melt fracture at the extrusion die of the composite material, and improves the batch stability of the mechanical strength of the cured bio-based composite material.

[0055] Example 4: When the system faces the condition of a co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1 experiencing changes in no-load resistance due to flow channel wear, the shear flow field within the flow channel shifts. The control system collects the no-load torque before material input. Under no-load conditions, the main screw runs at 400 rpm for 300 seconds. The mean filtering module collects the raw torque data stream and determines the baseline value of the inherent residual resistance torque by calculating the average value of the last 50 sampling points. The control system will use the inherent residual resistance torque reference value Stored in a register, the total torque signal is differentially canceled during the mixing stage to eliminate the interference of mechanical transmission dissipation on resistance determination.

[0056] When the system faces a situation where the initial resistance deviates from the baseline due to the replacement of different batches of jute fiber bundles, the friction coefficient of the material in the main dispersion zone undergoes a sudden change. The control system uses the weighing component to obtain the bulk density parameter of this batch of material. When the screw rotates at low speed, the feeding device delivers 500g of material to the feed channel. The transmission sensor collects the peak resistance value at the moment the material contacts the kneading disc and subtracts the inherent residual resistance torque baseline value. The intrinsic shear resistance constant of the material is calculated; the control system adjusts the torque to increase the trigger threshold boundary based on the intrinsic shear resistance constant; after the parameter adjustment, the flow channel valve is closed, and the material is driven to cross the phase melting zone by mechanical friction shear heat generation under the corrected boundary constraints, and the homogeneous material is continuously and stably output to the downstream conveying temperature zone.

[0057] Example 5: When the system faces the situation of deviation between the axial conveying power and radial stress field of multiphase non-homogeneous materials in a co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1 due to the tonnage change and model switching of a large-scale production line, the extrusion load and flow heat generation in the main dispersion zone fluctuate. Before the jute fiber bundles and polylactic acid matrix are introduced, an initial channel calibration procedure is carried out. A geometric measuring instrument is selected to measure the spatial distance from the end face of the kneading disc assembly in the main dispersion zone to the inner wall of the barrel to determine the radial clearance value of the kneading channel. Adjusting the center positioning component of the main screw will pinch the radial clearance value of the flow channel. To maintain a stable flow boundary of 0.15 mm, the feeding unit was activated to prepare multiple test feed sets containing 75 parts by weight of polylactic acid matrix and 25 parts by weight of jute fiber bundles, with the total feed flow rate increasing from 20 kg / h to 100 kg / h in 20 kg / h increments. Continuous extrusion was driven under an adjustment window of 400 rpm screw speed and 150°C barrel wall temperature in the main dispersion zone. The actual melt temperature of the test feed sets flowing through the main dispersion zone was continuously collected using a temperature sensor. The data processing module calculates the shear heat loss caused by load variations under different feed flow rates based on energy conversion relationships. A torque bias matrix corresponding to different flow rate gradients is established, and the torque increase trigger threshold correction coefficient for adjusting the flow boundary of the temperature zone under different processing capacities is calculated. Specifically, the torque bias matrix preset within the control data processing module is a two-dimensional lookup mapping table storing different nominal feed flow rates and corresponding equipment no-load resistance offset constants. During system operation, the main control unit collects the current total feed flow rate data in real time and performs linear interpolation retrieval in this mapping table to extract the accurate resistance offset constant. The system uses its internal arithmetic logic unit to perform a weighted algebraic sum calculation on the previously measured basic torque increase trigger limit value and this resistance offset constant, and then performs spatial normalization on the value to accurately calculate the aforementioned correction coefficient. This processing logic successfully transforms the abstract flow fluctuation interference into a definite mathematical adjustment parameter, providing a clear system derivation path for the adaptive execution of thresholds under subsequent large-scale production conditions.

[0058] After the initial channel calibration procedure is completed, the control system will increase the torque trigger threshold correction factor. The flow control loop is incorporated to compensate for flow fluctuations. When the actual total feed flow rate of the production line changes to 60 kg / h, the control unit adjusts the trigger limit value of the motor drive torque to 18.2%. Jute fiber bundles and polylactic acid matrix are continuously input into the main dispersion zone and undergo breakage and spatial dispersion under the shearing action of the main screw at a speed of 400 rpm. As the jute fiber bundles spatially break and dissociate, the material system experiences a sudden change in rheological viscosity. The mean filtering module continuously moves and averages the collected raw torque data stream to filter out mechanical vibration noise. When the motor drive torque value reflecting the phase change of the material is calculated, the result is obtained. When the rate of change of change reaches 18.5% within 2 seconds and exceeds the trigger threshold of 18.2%, the valve is switched to adjust the flow path and continuously feed the blended material into the secondary diffusion zone. At this time, the actual melt temperature collected by the melt temperature sensor is... The temperature was maintained at 169.5℃ to keep the polylactic acid matrix in a viscous flow state and reduce the thermal breakage and degradation of the polymer chains. The blended material discharged from the discharge port continuously entered the water-cooled pelletizing unit with the water temperature maintained at 20℃ to control the material condensation and solidification. Finally, it was cut into finished pellets with a length of 3mm by the pelletizing blade. The tensile test machine and impact test machine test showed that the standard deviation of the tensile strength of the solidified sample was 0.3% when the total feed flow rate changed. The impact cross section of the sample observed by scanning electron microscopy showed that the jute fiber monofilaments were uniformly and discretely distributed in the continuous phase of the polylactic acid matrix.

[0059] 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, and all such modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A fiber uniform mixing process in the preparation of bio-based materials, characterized in that, Includes the following steps: Step S101: Determine the intrinsic melting point of the polylactic acid matrix; Step S102: Control the barrel wall temperature of the main dispersion zone in the co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1 to be 12°C to 18°C ​​below the intrinsic melting point, and turn off the external heater of the main dispersion zone. Step S103: 20 to 30 parts by weight of jute fiber bundles and 70 to 80 parts by weight of polylactic acid matrix are quantitatively added to the feed port of the co-rotating twin-screw extruder, wherein the volume moisture content of the jute fiber bundles is less than 2%. The screw speed is controlled at 380 rpm to 420 rpm. The jute fiber bundles and polylactic acid matrix are sheared by a kneading disc assembly set in the main dispersion zone with a staggered angle of 45° to 90°. The actual melt temperature of the polylactic acid matrix is ​​collected in real time by a temperature sensor set in the co-rotating twin-screw extruder, and the actual melt temperature is controlled to be maintained in the range of 3° to 8° above the intrinsic melting point. Step S104: Continuously detect the motor drive torque value of the co-rotating twin-screw extruder. When the motor drive torque value is detected to increase by more than 15% within 2 seconds, output a material flow signal and transport the mixture to the secondary diffusion zone. Step S105: Control the barrel wall temperature of the secondary diffusion zone to be 23°C to 28°C above the intrinsic melting point, and simultaneously control the screw speed in the secondary diffusion zone to be 60 rpm to 100 rpm to blend the polylactic acid matrix and jute fiber bundles.

2. The fiber uniform mixing process in the preparation of bio-based materials according to claim 1, characterized in that, Before feeding the polylactic acid matrix and jute fiber bundles into the co-rotating twin-screw extruder, a material pre-mixing step is also included: the polylactic acid matrix and jute fiber bundles are fed into a high-speed mixer, the impeller speed of the high-speed mixer is controlled at 1000 rpm to 1200 rpm, and the mixture is mixed for 4 to 6 minutes at a temperature of 20°C to 30°C; the co-rotating twin-screw extruder is equipped with a multi-way quantitative feeding unit, which continuously and proportionally feeds materials into the feeding port.

3. The fiber uniform mixing process in the preparation of bio-based materials according to claim 1, characterized in that, In step S103, the screw speed is adjusted according to the actual melt temperature change rate monitored by the temperature sensor to keep the actual melt temperature stable within a range of 3°C to 8°C above the intrinsic melting point.

4. The fiber uniform mixing process in the preparation of bio-based materials according to claim 1, characterized in that, In step S105, the barrel wall temperature in the secondary diffusion zone is controlled to be between 188°C and 193°C, and the screw speed in the secondary diffusion zone is controlled to be between 60 rpm and 100 rpm.

5. The fiber uniform mixing process in the preparation of bio-based materials according to claim 1, characterized in that, In step S103, jute fiber bundles are broken by the mechanical shearing action of the kneading disc assembly, generating sub-millimeter particles with an average particle size of 0.2 mm to 0.8 mm.

6. The fiber uniform mixing process in the preparation of bio-based materials according to claim 1, characterized in that, The co-rotating twin-screw extruder is equipped with a forward threaded conveying assembly in the secondary diffusion zone. The forward threaded conveying assembly provides axial conveying power to the material so that the material is in a low-shear blending state.

7. The fiber uniform mixing process in the preparation of bio-based materials according to claim 1, characterized in that, Step S103 also includes the following auxiliary temperature control sub-steps: Step S1031, when the actual melt temperature of the polylactic acid matrix exceeds 175°C, the external cooling pipes installed on the barrel wall are opened to input the cooling medium; Step S1032, when the actual melt temperature drops to the range of 168°C to 173°C, the external cooling pipes are closed to stop inputting the cooling medium.

8. The fiber uniform mixing process in the preparation of bio-based materials according to claim 1, characterized in that, After step S105, the following steps are also included: Step S106, the mixed material discharged from the co-rotating twin-screw extruder is introduced into the water-cooled pelletizing unit, and the water temperature is controlled at 15°C to 25°C to solidify the material; Step S107, the solidified material is cut into bio-based composite particles using pelletizing blades.

9. The fiber uniform mixing process in the preparation of bio-based materials according to claim 8, characterized in that, In step S107, the length of the bio-based composite particles is controlled to be 2 mm to 4 mm by a pelletizing tool, and the weight moisture content of the bio-based composite particles is less than 0.5%.

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