Preparation method of high-compatibility PBAT bamboo powder composite master batch

Abstract

The invention relates to the technical field of polymer composition modification, and discloses a high-compatibility PBAT bamboo powder composite master batch preparation method, which comprises: mixing sulfonated PBAT, a PBAT-g-GMA graft, activated bamboo powder and an auxiliary agent to obtain a mixed dry material; the viscosity difference between the graft and the matrix is utilized in the melting section of double-screw extrusion, so that the graft melt permeates and fills tracheid micropores in the bamboo powder; in the reaction mixing section, epoxy groups in the graft are chemically bonded with sulfonic acid groups and hydroxyl groups to form an interface anchoring structure, in-situ chain extension and esterification reaction of the components in micropores are utilized, micro-nano molecular anchor points of a cross-phase boundary are constructed, the compatibility of biomass fibers and a polyester matrix under the high filling amount is effectively improved, and the compatibility of the biomass fibers and the polyester matrix is improved. The self-agglomeration trend of the filler is inhibited, and the mechanical property and service stability of the composite material are improved.

Description

Technical Field

[0001] This invention relates to a method for preparing highly compatible PBAT bamboo powder composite masterbatch, belonging to the field of polymer composition modification technology. Background Technology

[0002] In current biodegradable polymer composite material production practices, melt blending poly(butylene adipate / terephthalate) with natural plant fibers such as bamboo powder to prepare composite materials is a common method to achieve low cost and high bio-based content in products. This composition utilizes the good toughness of the polyester matrix and the rigid support of natural fibers, and has wide application value in the fields of green packaging materials and agricultural mulch films. However, as the bamboo powder filling content increases to more than 30%, the composite system faces the risk of interfacial adhesion failure. Due to the low density of polar groups in the adipic acid / butylene terephthalate molecular chain, it has poor wettability with the surface of bamboo powder rich in polar hydroxyl groups. During melt extrusion, the filler particles are driven by surface energy differences to generate physical agglomeration, resulting in stress concentration at the interface between the two phases, which in turn reduces the mechanical strength and impact resistance of the product.

[0003] To improve interfacial compatibility, the industry typically uses silane coupling agents to modify the surface of bamboo powder or adds maleic anhydride grafts as compatibilizers. These modification methods only form a transition layer on the outer surface of the bamboo powder particles, representing surface physical coverage or shallow chemical bonding. Because bamboo powder is a typical anisotropic biomass material with numerous tracheid micropores and vessel cavities, high-viscosity polyester melt, limited by extruder residence time, finds it extremely difficult to overcome rheological resistance and penetrate these micron-sized pores. This discontinuity in the core-shell structure results in a large amount of unwetted surface stress defects remaining inside the fiber. Conventional modification methods are insufficient to solve the problem of poor interfacial bonding. Therefore, developing specialized chemical additives is crucial. To regulate interfacial polarity, for example, Chinese invention patent CN119505212B discloses an integrated PBAT / bamboo powder compatibility and crosslinking agent, its preparation method, and its application. By synthesizing a PBAT-g-AGEMUANTA multi-component grafting agent, a network of hydrogen bonds and chemical bonds is constructed at the interface using polar groups. However, in actual continuous extrusion production, it is difficult to achieve deep penetration of the melt. The grafting agent is highly polar, and it is easy for local phase separation to occur between the grafting agent and the matrix in the high-temperature melting section, or premature crosslinking is induced by shear temperature rise before entering the micropores. This leads to the accumulation of modified components at the fiber opening, forming a physical blockage. The modification effect is limited to the outer boundary of the fiber, and it is difficult to eliminate interfacial stress concentration.

[0004] Therefore, the technical problem to be solved by this invention is how to utilize the natural capillary structure of bamboo powder to guide reactive components to penetrate deeply, construct a geometric anchoring structure that crosses phase boundaries and forms an interpenetrating network, thereby improving the interfacial stress transfer efficiency while maintaining a high filling rate. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A method for preparing highly compatible PBAT bamboo powder composite masterbatch, comprising the following steps: Step 101: Mix 55% to 70% by weight of sulfonated PBAT, 3% to 8% of PBAT-g-GMA graft, 25% to 40% of activated bamboo powder, 0.1% to 0.5% of lubricant, and 0.1% to 0.3% of antioxidant to obtain a mixed dry material; the sulfonated PBAT is poly(butylene adipate) / poly(terephthalate) containing sulfonic acid groups in its molecular chain, and the activated bamboo powder is bamboo powder fiber with a silane coupling agent coating layer containing epoxy groups on its surface; Step 102: The mixed dry material is fed into the melt conveying section of the twin-screw extrusion system. The set temperature of the melt conveying section is controlled to be 140°C to 170°C, so that the mixed dry material melts at the set temperature. The melt viscosity of the PBAT-g-GMA graft is lower than that of the sulfonated PBAT, so that the molten PBAT-g-GMA graft fills the tracheid micropores inside the activated bamboo powder. Step 103: Activated bamboo powder filled with PBAT-g-GMA graft is fed into the reaction mixing section of a twin-screw extrusion system. Under the condition of a set temperature of 170°C to 190°C, the epoxy groups in PBAT-g-GMA graft react with the sulfonic acid groups in sulfonated PBAT and the hydroxyl groups on the surface of activated bamboo powder to undergo a ring-opening esterification reaction, forming an interfacial anchoring structure in the tracheid micropores where PBAT-g-GMA graft is chemically bonded to the inner wall of the micropores. Step 104: The reacted melt is extruded through a die head and then water-cooled and pelletized in sequence to obtain highly compatible PBAT bamboo powder composite masterbatch.

[0006] Preferably, in step 102, the melt flow rate of the PBAT-g-GMA graft is greater than that of the sulfonated PBAT; the PBAT-g-GMA graft fills and seals the pit channels inside the activated bamboo powder.

[0007] Preferably, the activated bamboo powder has a particle size of 800 mesh to 1200 mesh and an average pore size of 0.1 μm to 3 μm for the tracheid micropores; the silane coupling agent coating layer is formed by a condensation reaction of 3-glycidyl etheroxypropyltrimethoxysilane or 3-glycidyl etheroxypropylmethyldiethoxysilane.

[0008] Preferably, the grafting rate of the PBAT-g-GMA graft is 2% to 5%, and its weight-average molecular weight is 30% to 50% of the weight-average molecular weight of sulfonated PBAT; in step 102, the average filling depth of the PBAT-g-GMA graft inside the tracheid micropores is not less than 20% of the radial depth of the tracheid micropores.

[0009] Preferably, the molar amount n of epoxy groups in the PBAT-g-GMA graft is... EP The molar amount n of sulfonic acid groups in sulfonated PBAT SA The following relationship must be satisfied: 1.2 ≤ n EP / n SA ≤2.5; where n EP n is the total molar amount of epoxy groups calculated based on the amount of PBAT-g-GMA graft material fed and the grafting rate in step 101. SA The total molar amount of sulfonate groups is calculated based on the amount of sulfonated PBAT fed in step 101 and the degree of substitution of sulfonate groups.

[0010] Preferably, the degree of substitution of sulfonic acid groups in sulfonated PBAT is 1% to 3%; in step 103, the sulfonic acid groups serve as catalytic sites to guide the PBAT-g-GMA graft to form a cross-linked network inside the tracheid micropores.

[0011] Preferably, the lubricant is selected from zinc stearate, stearamide, or polyethylene wax; the antioxidant is selected from antioxidant 1010 or antioxidant 168.

[0012] Preferably, the screw length-to-diameter ratio of the twin-screw extrusion system is 40:1 to 48:1; the screw of the twin-screw extrusion system includes a conveying thread element for mixing and plasticizing dry materials and a kneading block element for generating radial extrusion stress in step 103 to assist the components in penetrating into the micropores of the tracheids.

[0013] Preferably, the screw speed of the twin-screw extrusion system is 300 r / min to 500 r / min to promote ring-opening esterification reaction in the reaction mixing section.

[0014] Preferably, after step 104, the following step is also included: Step 105: The pelletized masterbatch is placed in a vacuum drying unit and dried at 45°C to 55°C for 4 to 6 hours, so that the moisture content of the highly compatible PBAT bamboo powder composite masterbatch is less than 0.1%.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. In the preparation of PBAT bamboo powder composite masterbatch, the strong polar environment provided by sulfonated poly(adipic acid) / butylene terephthalate, together with the epoxy groups in the graft and the silane layer on the surface of the bamboo powder, form a triple chemical synergistic mechanism. In the melt blending stage, the capillary driving force of the tracheids inside the bamboo powder is used to fill the micropores inside the fiber with the low viscosity reaction precursor first. In the subsequent temperature rise process, in-situ chain extension and ring-opening esterification reactions occur to construct a molecular anchoring structure that crosses the phase boundary, improves the interfacial adhesion between the filler and the matrix, and improves the interfacial delamination between biomass fiber and polyester matrix caused by modulus mismatch under high filler ratio.

[0016] 2. By introducing sulfonate groups into the matrix molecular chain to enhance the polarity of the matrix, and in conjunction with the shielding effect of the grafted material on the hydroxyl groups on the activated bamboo powder surface, the surface energy of the filler is reduced. Combined with the rheological gradient control during melt extrusion, the self-agglomeration tendency of bamboo powder when added in a high proportion is suppressed, so that the bamboo powder is uniformly distributed in the continuous phase in a micron-sized form, eliminating stress concentration points at the phase interface, and improving the tensile strength and impact toughness of the composite material while maintaining good processing fluidity.

[0017] 3. By utilizing the pre-wetting effect of low-viscosity components before the melting section, the duct cavities and pit structures inside the bamboo powder are pre-filled and sealed, blocking the path of water penetration into the fiber interior. Combined with the sealing of the terminal carboxyl groups of the grafted epoxy groups, the chemical stability of the composite material under humid and hot conditions is improved, and the interfacial failure caused by the water absorption and swelling of natural fibers is mitigated. The process relies on conventional twin-screw extrusion equipment. Through precise control of the temperature zones from the feeding section to the die head, chemical reaction, micropore wetting and physical shearing are combined. Without changing the original production cycle, the reliability and mechanical properties of the composite material are improved. Attached Figure Description

[0018] Figure 1 This is a flowchart of the dynamic process closed-loop control based on real-time feedback of rheological state according to the present invention. Figure 2 This is a diagram showing the multi-role synergistic operation and reaction mechanism correlation in the masterbatch preparation process of this invention. Detailed Implementation

[0019] The specific embodiments of the present invention will be described in detail below with reference to the technical solution of the present invention. The following description is intended to explain the present invention and is not intended to limit the scope of protection of the present invention.

[0020] This invention provides a method for preparing highly compatible PBAT bamboo powder composite masterbatch. By controlling the rheological gradient of each component under the temperature field of twin-screw extrusion, micro- and nano-scale molecular anchors are constructed in the micropores of the tracheids inside the bamboo powder. Addressing the technical deficiency of weak interfacial adhesion between poly(butylene adipate / terephthalate), i.e., PBAT, and bamboo powder, this method utilizes the dual coupling effect of chemical bonding and geometric interlocking to improve the mechanical strength of the composite material. Specifically, the dynamic formulation calculation module employs a step-by-step compensation strategy for the deviation of the bamboo powder moisture content from the baseline value. For every 0.5% increase in moisture content, a 2°C thermal compensation increment is added to the set temperature of the melting conveying section (145°C to 170°C), until the moisture content is reduced to below 0.1% through vacuum drying. Simultaneously, to address fluctuations in the hydroxyl concentration on the bamboo powder surface, the system adjusts the feed ratio through a preset discrete ratio mapping table. When the concentration of PBAT-g-GMA grafts was increased from 2.5 mmol / g to 4.8 mmol / g, the weight percentage of PBAT-g-GMA grafts was simultaneously increased linearly from 3% to 8% to maintain the balance of reactive sites within the system. To improve the wettability of PBAT resin and polar cellulose, this invention prepares sulfonated PBAT through a melt free radical grafting reaction. The specific operation process is as follows: 55% to 70% by weight of PBAT resin, 5% to 8% by weight of sodium methacrylate sulfonate, and 0.1% to 0.3% by weight of antioxidant are fed into a twin-screw extruder, and the grafting reaction is carried out at a temperature of 175 to 195°C. In the resulting sulfonated PBAT, the degree of substitution of sulfonic acid groups is maintained in the range of 1% to 3%. As polar sites, sulfonic acid groups increase the electrostatic attraction at the interface between the matrix and the filler, and provide catalytic centers for subsequent ring-opening esterification reactions.

[0021] To address the physical specifications of the micropores in bamboo powder tracheids, this invention prepares a PBAT-g-GMA graft with specific rheological properties as an interfacial bridging unit. The preparation process involves selecting dried PBAT, glycidyl methacrylate (GMA), and a peroxide initiator, and performing melt grafting at 160 to 190°C. The weight-average molecular weight of the PBAT-g-GMA graft is set to 30% to 50% of the weight-average molecular weight of sulfonated PBAT, and its grafting rate is controlled within the range of 2% to 5%. Under this molecular weight distribution, the PBAT-g-GMA graft exhibits superior flowability in the molten state compared to the matrix resin, enabling it to be readily adaptable to various applications in a short time. This invention overcomes the rheological resistance inside micropores; it performs surface activation treatment on bamboo powder to reduce its surface energy and introduce reactive sites; the treatment steps are as follows: γ-glycidoxypropyltrimethoxysilane is dissolved in a mixed solvent of ethanol and water to obtain a coupling agent solution, which is then sprayed onto bamboo powder with a water content of less than 1%; the solution is stirred and dried at 65 to 85°C to form a coating layer with epoxy groups on the surface of the bamboo powder; the amount of silane coupling agent used is 0.2% to 0.5% of the weight of the bamboo powder; the activated bamboo powder exhibits improved dispersion characteristics and provides chemical sites for binding with compatibilizers during the composite process; torque stability threshold. The quantitative determination of the interface coverage coefficient λ includes acquiring the drive motor torque signal of a co-rotating twin-screw extruder running unloaded for 10 minutes at a set screw speed, calculating the standard deviation σ of the signal fluctuation, and selecting twice its value to determine the interface coverage coefficient λ. It is used to identify and shield mechanical vibration interference signals during the production process, and measures the hydroxyl concentration C on the surface of activated bamboo powder by conductivity titration. OH By measuring the specific surface area using nitrogen adsorption, the theoretical molar amount of silane coupling agent required to cover the surface of activated bamboo powder monolayer was calculated. Combined with the adsorption conversion efficiency calibrated experimentally, λ was set in the range of 0.08 to 0.12.

[0022] The lubricant uses stearamide components to reduce the internal friction between the sulfonated PBAT melt and the activated bamboo powder particles. When the lubricant weight percentage is less than 0.1%, the material experiences fluctuations in the matrix melt index due to frictional heat accumulation under the radial extrusion stress generated by the kneading block. When its dosage exceeds 0.5%, the excessive lubricant component forms a physical isolation layer at the phase interface, hindering the penetration of the PBAT-g-GMA graft into the deep tracheid micropores and reducing the density of the interfacial anchoring structure. The antioxidant uses a hindered phenolic and phosphite compound system to eliminate free radicals generated during the melt grafting of glycidyl methacrylate, ensuring the quality of the masterbatch during preparation and subsequent processing. The invention utilizes a temperature gradient to guide the orderly penetration of components during the preparation of the composite functional masterbatch, ensuring thermal oxidation stability. Sulfonated PBAT, PBAT-g-GMA graft, activated bamboo powder, and additives are fed into a twin-screw extruder, with the temperature of the melt conveying section controlled at 140 to 170°C. Since the melt viscosity of the PBAT-g-GMA graft is lower than that of the sulfonated PBAT at this temperature, the graft melt fills the tracheid micropores inside the bamboo powder under capillary driving force. The average pore size of the tracheid micropores is 0.1 μm to 3 μm, and the average filling depth of the graft inside the micropores is not less than 20% of the radial depth of the tracheid micropores. In the temperature gradient control of the melt conveying section, the criterion is dM / dT < 0.05. Characterizing the rheological equilibrium between PBAT-g-GMA graft and sulfonated PBAT, the control unit collects the sliding average torque percentage M, which has been filtered by mean, at fixed intervals. avg Calculate its rate of change as the set temperature T increases. When the absolute value of the rate of change remains below the torque stability threshold for 5 minutes... At that time, the low viscosity grafted component was determined to be under capillary driving force P. c Driven by the filling of the cavities inside the tracheid micropores, the screw generates radial compressive stress to assist the graft material in penetrating deep into the tracheid micropores, providing physical wetting for the subsequent construction of interface anchoring structures in the reaction mixing section.

[0023] As the material enters the reaction mixing section at a temperature of 170 to 190°C, the epoxy groups in the grafted material undergo ring-opening esterification with the sulfonic acid groups in the matrix and the hydroxyl groups on the surface of the bamboo powder; the molar amount n of the epoxy groups in the PBAT-g-GMA grafted material... EP The molar amount n of sulfonic acid groups in sulfonated PBAT SA The following relationship must be satisfied: 1.2 ≤ n EP / n SA ≤2.5; where n EP n represents the total molar amount of epoxy groups. SAThe total molar amount of sulfonic acid groups; this molar ratio ensures that the interfacial reaction proceeds fully and forms a chemically bonded anchoring structure inside the tracheid micropores; the melt after the reaction is extruded through a die head and then subjected to water cooling and pelletizing operations in sequence; the obtained masterbatch is vacuum dried at 45 to 55°C for 4 to 6 hours to make the final moisture content of the masterbatch less than 0.1%.

[0024] Example 1: In the production of agricultural mulch films with high bio-based content, when the weight percentage of bamboo powder in the composition is increased to 35%, secondary agglomeration of filler particles occurs during the twin-screw extrusion process, resulting in crystal points and holes in the blown film. The tensile strength of the film also decreases from 35 MPa of pure PBAT resin to below 12 MPa. Due to the modulus mismatch between the filler and the matrix, stress concentration occurs at the interface between the two phases, leading to deterioration of the material's mechanical properties. Sulfonated PBAT with a weight percentage of 60% and a sulfonic acid group substitution degree of 2%, PBAT-g-GMA graft with a weight percentage of 5% and a grafting rate of 3.5%, and activated bamboo powder with a weight percentage of 35% were selected. The temperature in the melt conveying section of the twin-screw extruder was set to 155℃. Since the weight average molecular weight of the PBAT-g-GMA graft is 40% of the weight average molecular weight of the matrix resin, the melt viscosity of the graft at the temperature is lower than that of the matrix resin.

[0025] Under capillary driving force P c Under the action of the agent, the low-viscosity graft component permeates into the tracheid micropores with an average pore size of 0.8 μm inside the bamboo powder. This permeation process is completed before the matrix macromolecular chains are embedded, allowing the graft to enter the deep structure of the fiber. The material enters the reaction mixing section with the temperature set at 185℃. In this section, the epoxy groups in the PBAT-g-GMA graft undergo a ring-opening reaction with the sulfonic acid groups in the sulfonated PBAT, and form chemical bonds with the epoxy silane layer on the surface of the activated bamboo powder. By adjusting the molar ratio n of the epoxy groups to the sulfonic acid groups... EP / n SA When set to 1.8, chemical cross-linking points are generated at the interface, where n EP n represents the total molar amount of epoxy groups. SA The total molar amount of sulfonic acid groups, the ring-opening reaction forms mechanical interlocking nodes inside the fiber pores, and constructs a molecular chain entanglement network that crosses the boundary at the phase interface. During the stress process, the molecular chain deformation inside the fiber tracheids absorbs energy. The tensile strength of the obtained masterbatch after blown film processing is 26 MPa, and the elongation at break is 280%. The bamboo powder particles are in a uniformly dispersed state in the PBAT matrix. By adjusting the rheological gradient between components, the interface is guided to be deeply fixed, and the mechanical properties are improved synchronously with the filling ratio.

[0026] Example 2: In the interfacial mechanical stability verification test of poly(butylene adipate) / butylene terephthalate (PET) and bamboo powder at a filler weight percentage of 35% to 40%, the test platform adopted a co-rotating twin-screw extruder with an aspect ratio of 45:1. This equipment was equipped with a torque sensor with an accuracy of 0.1% and a heating unit with a temperature control accuracy of ±1℃. Test data were acquired through a laboratory physical acquisition system. To simulate signal disturbances caused by mechanical vibration in an industrial environment, Gaussian white noise with a signal-to-noise ratio of 20dB was injected into the pressure acquisition channel, and 50Hz power frequency interference was superimposed. The core of the test was to verify n EP / n SA The influence of molar ratio on the formation of interfacial anchoring structures was investigated. The molar ratio value needs to balance the crosslinking point density of the interfacial reaction and the degradation effect of the matrix caused by initiator overload. If the molar ratio is lower than 1.2, continuous chemical bonding cannot be formed inside the tracheids. If the molar ratio exceeds 2.5, the compatibilizer component will homopolymerize, leading to interfacial embrittlement. Therefore, the optimal working window was determined to be between 1.2 and 2.5, and the screw speed was set to 450 r / min to meet the shear requirements of the permeation coefficient k. The experiment was carried out according to the gradient temperature control method of the specific implementation method. The dried raw materials were mixed and fed into the extruder conveying section. The temperature was controlled at 155℃ so that the low viscosity PBAT-g-GMA graft material could penetrate into the micropores of bamboo powder tracheids under the capillary driving force Pc. Monitoring showed that the treated melt exhibited a stable pressure curve after suppressing signal interference.

[0027] According to the experimental results of the electronic universal testing machine based on the GB / T1040.2-2006 standard, different component ratios had a significant impact on the properties of the composite material: under the condition that the filler weight percentage was 35%, the control sample group without compatibilizer (n) EP / n SA With a molar ratio of 0, its tensile strength is only 11.45 MPa, and its impact strength is 4.23 kJ / m. 2 When the molar ratio was increased to 1.2 (test group 1) and 1.8 (test group 2) within the protection range, the tensile strength increased to 22.31 MPa and 26.48 MPa, respectively, and the impact strength increased to 10.56 kJ / m. 2 and 14.12 kJ / m 2 When the molar ratio further reaches the upper limit of 2.5 (test group 3), the tensile strength is 25.12 MPa and the impact strength is 13.45 kJ / m. 2 Among them, the tensile strength of experimental group 2 (1.8 molar ratio) increased by more than 131% compared with the control group, confirming the synergistic effect of deep wetting guided by rheological gradient and in-situ chemical bonding. In contrast, if the molar ratio deviated to 0.8 (out of range control group 1), the tensile strength dropped to 13.24 MPa and the impact strength decreased to 5.67 kJ / m.2 This indicates that the grafting point density is insufficient to form molecular anchors; and when the molar ratio is excessively increased to 3.2 (out of range control group 2), although the tensile strength remains at 21.56 MPa, the excessive epoxy groups induce local branching or cross-linking of the matrix molecular chains, resulting in impaired flexibility and a drop in impact strength to 11.89 kJ / m. 2 .

[0028] Example 3: This embodiment combines Figures 1 to 2 A method for preparing a highly compatible PBAT bamboo powder composite masterbatch is described, such as... Figure 1 As shown, based on the B1 standard process formula library, the benchmark model is retrieved, and combined with the bamboo powder hydroxyl value and moisture content data uploaded by the laboratory testing terminal, the corrected feed ratio and benchmark temperature are calculated in the dynamic formula calculation module. The calculation result is transmitted to the segmented temperature field control unit, which outputs the heating zone power and screw speed setting instructions to the extruder PLC control terminal. During operation, the real-time torque data stream generated by the extruder PLC control terminal is fed back to the rheological state analysis module, which generates temperature fine-tuning instructions and uses them for penetration optimization. The signals are then transmitted back to the segmented temperature field control unit to form a closed-loop regulation. Finally, the segmented temperature field control unit generates a process parameter snapshot and stores it in the B2 production process history library.

[0029] like Figure 2 As shown, process engineers are responsible for setting the reaction stoichiometry ratio nEP / nSA, configuring segmented temperature fields and rheological gradients, and monitoring torque feedback to determine permeation. Production line operators are mainly responsible for raw material activation and mixing, twin-screw reactive extrusion, pelletizing, and vacuum drying. During twin-screw reactive extrusion, surface behaviors such as physical anchoring of permeable tracheid micropores using viscosity differences and in-situ chemical anchoring of interfacial bonds occur simultaneously within the system. Laboratory quality control personnel are responsible for verifying the mechanical properties and dispersibility of the final product.

[0030] Example 4: In a masterbatch preparation process for bamboo powder from different origins, the porosity of the bamboo powder tracheids in the raw material fluctuates within the range of 15% to 25%. This uncertainty in physical properties causes a shift in the permeability coefficient k, resulting in fluctuations in the penetration depth of the components into the tracheid micropores within the melt conveying section, affecting the construction quality of the interface anchoring structure. This embodiment uses a torque feedback-based process adjustment method to determine the permeation operation temperature. 65% by weight of sulfonated PBAT, 6% by weight of PBAT-g-GMA graft, and 28% by weight of activated bamboo powder are mixed and fed into a twin-screw extruder. The torque percentage of the drive motor, i.e., the torque value M, is monitored in real time. The initial temperature of the melt conveying section is set to 145℃. The temperature of this section is increased at a rate of 2℃ / min. The torque value M shows a monotonically decreasing change with increasing temperature. The logical criterion for determining the critical permeation state is as follows: |dM / dT| < Where M represents the torque percentage and T represents the melting zone temperature in °C. As the torque stability threshold, in this embodiment The value is 0.05% / ℃. The physical basis of this criterion is that the increase in interfacial friction torque generated by the low viscosity compatibilizer melt during the filling of bamboo powder micropores tends to be stable. When the PBAT-g-GMA graft melt fills to 20% of the radial depth of the tracheid micropores, its real-time contribution to the macro torque fluctuates and decreases to below 0.05%. At this time, the system determines that the preliminary physical wetting is completed. When the torque change rate meets the above criterion, the corresponding temperature of 158℃ is determined as the penetration operation temperature of this batch of raw materials.

[0031] At the infiltration operating temperature, the low-viscosity component is driven by capillary force P. c Under the influence of the torque, the material penetrates deep into the micropores of the tracheids; it enters the reaction mixing section at a temperature of 185℃, where the ring-opening esterification reaction causes the viscosity of the system to rise and generates a secondary torque increment ΔM. This increment reflects the degree of construction of the interfacial molecular chain entanglement network. The control algorithm monitors the upward gradient of this increment in real time. When the absolute value of the secondary torque increment reaches 5% of the stable torque value of the melting section, the system determines that the degree of in-situ chemical bonding at the interface has reached more than 85%, and outputs a step increment command to the main control PLC to synchronously reduce the screw speed in increments of 10 r / min. This aims to increase the residence time of the material in the reaction mixing section to complete the final anchoring. The masterbatch obtained by the above torque feedback control has tensile strengths ranging from 25.5 MPa to 29.0 MPa in different batches, and the strength deviation between batches has been reduced from 15% to less than 3%, with the best value in a single test reaching 28.5 MPa.

[0032] Example 5: In testing the performance stability of biomass fiber raw materials with different growth cycles, the hydroxyl group distribution density on the surface of bamboo powder fluctuates between 2.5 mmol / g and 4.8 mmol / g. This difference in chemical properties leads to uneven epoxy group density after surface activation. To balance the interfacial coverage density and the effective utilization rate of active groups, the surface hydroxyl group concentration C of the bamboo powder sample was measured by conductivity titration before activation pretreatment. OH The weight percentage W of the epoxy silane coupling agent was set according to the stoichiometric relationship. SC Satisfying the following relationship: W SC =λ C OH Among them, W SC C represents the weight percentage of the epoxy silane coupling agent. OH The concentration of hydroxyl groups was measured in mmol / g. λ is the interface coverage coefficient, with a value ranging from 0.08 to 0.12. This coefficient was calibrated based on the average surface area of ​​bamboo powder (6.5 m²) measured by nitrogen adsorption at 77 K. 2 / g, the theoretical coefficient value required for full monolayer coverage was calculated by the cross-sectional area of ​​silane molecules, which is 0.07. Combined with the capillary adsorption loss of the coupling agent solution by the tracheid micropores, and the surplus of 20% to 70%, it was found that the process adjusts the interface coverage to make the bamboo powder exhibit a dispersed state without obvious agglomeration under the filling condition of 35% by weight.

[0033] When the initiator activity deviates due to temperature differences in the storage environment, the grafting efficiency of sulfonated PBAT decreases, leading to a reduction in the density of sulfonic acid groups at the interface. To balance grafting rate stability and production continuity, during the start-up phase of sulfonated PBAT preparation, the intensity of the characteristic infrared absorption peak corresponding to the sulfonic acid groups in the extrudate is detected. SA With carbonyl absorption peak intensity I CO The ratio R g To characterize the degree of substitution of the sulfonic acid group, where R g I represents the ratio of the intensity of the characteristic infrared absorption peaks. SA The characteristic infrared absorption peak intensity of sulfonic acid groups, I CO The intensity of the carbonyl absorption peak is determined by R. g The deviation from the target degree of substitution is adjusted by regulating the feed rate of the peroxide initiator in the feeding unit of the twin-screw extruder. In this closed-loop control, the sensor monitors the intensity of the symmetric stretching vibration peak of the sulfonic acid group in the wavenumber range of 1045 cm⁻¹ to 1055 cm⁻¹ in real time. Using this as an input variable, the intensity is calculated by comparing it with the intensity of the internal standard peak of the ester carbonyl group in the wavenumber range of 1710 cm⁻¹ to 1730 cm⁻¹. This eliminates the interference of the sample protonation degree on the detection results and ensures the uniqueness of the substitution degree feedback signal.

[0034] Example 6: In production scenarios involving twin-screw extrusion systems with a background noise level of 20 dB, the original torque signal of the drive motor is subject to high-frequency random disturbances due to mechanical vibration. If the original data is directly applied to determine the penetration state criterion |dM / dT| < This causes a shift in the control logic. To establish a stable control reference, the sampling frequency f of the torque sensor is selected before starting the calibration program. s The frequency was set to 100Hz, and a sliding window containing 50 consecutive sampling points was selected for mean filtering to obtain the moving average torque percentage M. avg M avg The calculation formula is as follows: M avg =1 / N∑ i=1 N M i Among them, M avg M represents the percentage of the sliding average torque. i Here, N represents the measured torque value at the i-th sampling point, and N is the total number of sampling points within the sliding window. In this embodiment, N is 50. The above filtering logic suppresses signal glitches caused by power frequency interference, ensuring that the calculation accuracy of the torque change rate in temperature field adjustment meets the preset threshold. The testing standards.

[0035] When the extrusion system faces a non-linear change in penetration resistance due to screw element wear, in order to maintain the penetration depth of the compatibilizer component in the bamboo powder tracheids at no less than 20% of the radial depth, a structural compensation process is performed when switching material batches on the production line. This involves setting the staggered angle of the kneading block elements in the twin-screw extruder to 45 degrees. Or 60 A multi-level pressure gradient field is constructed, and the radial extrusion stress generated by the kneading element assists in filling micropores with an average pore size of 1.2 μm with low viscosity components. The torque change rate after filtering is monitored in real time. When the system operates at the permeation operation temperature and M... avg When the fluctuation range is within ±0.1% for 5 consecutive minutes, the system is considered to have reached rheological equilibrium. This process is used to calibrate batches of raw materials and equipment under wear conditions. The mechanical property deviation of the resulting composite material is within the tolerance range of 2.1%.

[0036] The standardized process for preparing highly compatible PBAT bamboo powder composite masterbatch includes the following steps: Activated bamboo powder with a moisture content of less than 1% is added to the premixing unit. Lubricant and antioxidant are added at a speed of 800 r / min and mixed for 3 minutes. Sulfonated PBAT and PBAT-g-GMA grafts that have undergone vacuum drying are added. The mixing temperature is controlled below 35℃ to prevent particle agglomeration. The uniformly mixed material is fed into a co-rotating twin-screw extruder through a metering and weighing system. Melt blending and interfacial chemical bonding reactions are carried out under the temperature field and speed parameters of each zone. The melt after reaction is filtered through a 150-200 mesh stainless steel filter screen to remove impurities and then extruded from the die head. It is cooled to 40℃ in a constant temperature water cooling tank while the traction speed is kept constant within the range of 15 m / min to 20 m / min. Finally, it is cut into masterbatch particles with a specification of 3×3 mm by a rotary pelletizer.

[0037] To further verify the technical effects of the process of this invention, Comparative Examples 1-3 were set up for comparison. Comparative Example 1: 65% by weight of sulfonated PBAT, 6% by weight of PBAT-g-GMA graft, 28% by weight of untreated raw bamboo powder, and 1% by weight of additives were mixed and fed into a twin-screw extruder. Extrusion, cooling, and pelletizing were performed under conditions of 158°C in the melt conveying section and 185°C in the reaction mixing section. Comparative Example 2: 65% by weight of sulfonated PBAT, 6% by weight of PBAT-g-GMA graft, 28% by weight of activated bamboo powder, and 1% by weight of additives were mixed and fed into a twin-screw extruder. The extrusion process was set to a constant temperature of 185°C throughout, without rheological temperature gradient control. Comparative Example 3: 71% by weight of sulfonated PBAT, 28% by weight of activated bamboo powder, and 1% by weight of additives were mixed. The mixture was prepared without adding PBAT-g-GMA grafts. All other process parameters and material handling methods were consistent with those in Example 4. The mixture was fed into a twin-screw extruder and extruded, cooled, and pelletized under the conditions of a melt conveying section temperature of 158°C and a reaction mixing section temperature of 185°C. Considering the intermediate properties of the masterbatch of the present invention as a high-loading component, the masterbatches obtained in Example 4 and the above comparative examples 1-3 were melt diluted and blended with pure PBAT resin at a mass ratio of 1:3 to 1:4 (preferably 1:3). Experiments showed that the diluted composite system had better tensile strength and impact performance than the undiluted masterbatch itself or conventional direct blends due to the uniform expansion of its interfacial anchoring structure in the matrix. The diluted mixture was injection molded into standard tensile and impact test specimens, and the test results are shown in the table below.

[0038] Table 1: Test results of mechanical properties of PBAT / bamboo powder composite material.

[0039]

[0040] According to Table 1 above, the data and mechanical property test results show that the bamboo powder at the impact fracture surface of the composite material is tightly coated by the polymer, with few pull-out marks and blurred interface, showing excellent interfacial adhesion. In contrast, the bamboo powder surface in the fracture surface of each comparative sample is smooth, and the holes left after pull-out are clearly visible, indicating severe interfacial debonding. This shows that the present invention can improve the mechanical properties of the high-filling system through the synergistic mechanism of guiding micropore penetration and in-situ chemical bonding by rheological gradient.

[0041] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing highly compatible PBAT bamboo powder composite masterbatch, characterized in that, Includes the following steps: Step 101: Mix 55% to 70% by weight of sulfonated PBAT, 3% to 8% of PBAT-g-GMA graft, 25% to 40% of activated bamboo powder, 0.1% to 0.5% of lubricant, and 0.1% to 0.3% of antioxidant to obtain a mixed dry material; the sulfonated PBAT is poly(butylene adipate) / poly(terephthalate) containing sulfonic acid groups in its molecular chain, and the activated bamboo powder is bamboo powder fiber with a silane coupling agent coating layer containing epoxy groups on its surface; Step 102: The mixed dry material is fed into the melt conveying section of the twin-screw extrusion system. The set temperature of the melt conveying section is controlled to be 140°C to 170°C, so that the mixed dry material melts at the set temperature. The melt viscosity of the PBAT-g-GMA graft is lower than that of the sulfonated PBAT, so that the molten PBAT-g-GMA graft fills the tracheid micropores inside the activated bamboo powder. Step 103: Activated bamboo powder filled with PBAT-g-GMA graft is fed into the reaction mixing section of a twin-screw extrusion system. Under the condition of a set temperature of 170°C to 190°C, the epoxy groups in PBAT-g-GMA graft react with the sulfonic acid groups in sulfonated PBAT and the hydroxyl groups on the surface of activated bamboo powder to undergo a ring-opening esterification reaction, forming an interfacial anchoring structure in the tracheid micropores where PBAT-g-GMA graft is chemically bonded to the inner wall of the micropores. Step 104: The reacted melt is extruded through a die head and then water-cooled and pelletized in sequence to obtain highly compatible PBAT bamboo powder composite masterbatch.

2. The method for preparing a highly compatible PBAT bamboo powder composite masterbatch according to claim 1, characterized in that, In step 102, the melt mass flow rate of the PBAT-g-GMA graft is greater than that of the sulfonated PBAT. PBAT-g-GMA grafts fill and seal the pit channels inside activated bamboo powder.

3. The method for preparing a highly compatible PBAT bamboo powder composite masterbatch according to claim 1, characterized in that, The activated bamboo powder has a particle size of 800 to 1200 mesh, and the average pore size of the tracheid micropores is 0.1 μm to 3 μm; the silane coupling agent coating layer is formed by the condensation reaction of 3-glycidyl etheroxypropyltrimethoxysilane or 3-glycidyl etheroxypropylmethyldiethoxysilane.

4. The method for preparing a highly compatible PBAT bamboo powder composite masterbatch according to claim 1, characterized in that, The grafting rate of the PBAT-g-GMA graft is 2% to 5%, and its weight-average molecular weight is 30% to 50% of the weight-average molecular weight of sulfonated PBAT; in step 102, the average filling depth of the PBAT-g-GMA graft inside the tracheid micropores is not less than 20% of the radial depth of the tracheid micropores.

5. The method for preparing a highly compatible PBAT bamboo powder composite masterbatch according to claim 1, characterized in that, The molar amount n of epoxy groups in PBAT-g-GMA graft EP The molar amount n of sulfonic acid groups in sulfonated PBAT SA The following relationship must be satisfied: 1.2 ≤ n EP / n SA ≤2.5; where n EP n is the total molar amount of epoxy groups calculated based on the amount of PBAT-g-GMA graft material fed and the grafting rate in step 101. SA The total molar amount of sulfonate groups is calculated based on the amount of sulfonated PBAT fed in step 101 and the degree of substitution of sulfonate groups.

6. The method for preparing a highly compatible PBAT bamboo powder composite masterbatch according to claim 1, characterized in that, The degree of substitution of sulfonic acid groups in sulfonated PBAT is 1% to 3%; in step 103, the sulfonic acid groups act as catalytic sites to guide the PBAT-g-GMA graft to form a cross-linked network inside the tracheid micropores.

7. The method for preparing a highly compatible PBAT bamboo powder composite masterbatch according to claim 1, characterized in that, The lubricant is selected from zinc stearate, stearamide or polyethylene wax; the antioxidant is selected from antioxidant 1010 or antioxidant 168.

8. The method for preparing a highly compatible PBAT bamboo powder composite masterbatch according to claim 1, characterized in that, The screw length-to-diameter ratio of the twin-screw extrusion system is 40:1 to 48:1; the screw of the twin-screw extrusion system includes a feed thread element for mixing and plasticizing dry materials and a kneading block element for generating radial extrusion stress in step 103 to assist the components in penetrating into the micropores of the tracheids.

9. The method for preparing a highly compatible PBAT bamboo powder composite masterbatch according to claim 1, characterized in that, The screw speed of the twin-screw extrusion system is 300 r / min to 500 r / min to promote the ring-opening esterification reaction in the reaction mixing section.

10. The method for preparing a highly compatible PBAT bamboo powder composite masterbatch according to claim 1, characterized in that, After step 104, the following steps are also included: Step 105: Place the pelletized masterbatch in a vacuum drying unit and dry it at 45°C to 55°C for 4 to 6 hours to make the moisture content of the highly compatible PBAT bamboo powder composite masterbatch less than 0.1%.

Images