A fully biodegradable plant fiber reinforced micro-foamed express delivery cushioning material and a preparation method thereof

Abstract

The application relates to the technical field of green packaging materials, and discloses a full-biodegradable plant fiber reinforced micro-foaming express buffering material and a preparation method thereof, which comprises polylactic acid resin or polybutylene adipate terephthalate resin, microporous foaming biodegradable masterbatch and functional additives; the above raw materials are put into a high-speed mixer to obtain mixed materials, and then the mixed materials are sent into a granulator to be melt-extruded; preformed particles are filled into a foaming forming mold, the particles are heated and expanded and fused with each other through saturated water vapor heating or mold pressure relief; finally, the whole microporous structure is moved into a curing chamber to be cured under constant temperature and humidity. The physical support network constructed by the surface modified plant fiber in the cell wall limits the cell wall damage and blocks the water permeation, the closed pore rate is improved, the volume water absorption rate is reduced, the functional additives improve the melt strength, and the antistatic and flame-retardant capacities of the material are improved.

Description

Technical Field

[0001] This invention relates to the field of green packaging materials technology, specifically to a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material and its preparation method. Background Technology

[0002] With the continuous expansion of e-commerce, the usage of express delivery packaging materials has increased. Currently, petroleum-based plastic cushioning materials are gradually being replaced by fully biodegradable materials due to their difficulty in degradation and the environmental impact they cause. Biodegradable polyesters such as polylactic acid (PLA) and polybutylene terephthalate (PET) have become a research focus in the field of express delivery cushioning materials due to their excellent biodegradability.

[0003] In existing biodegradable foamed materials, the lack of effective reinforcing structures in the foam matrix during molding easily leads to insufficient cell wall strength and cell breakage, resulting in a decrease in closed-cell rate. Furthermore, when biodegradable resins are directly blended with natural fibers, the difference in interfacial compatibility between the two results in uneven fiber distribution within the matrix, making it difficult to form a stable support structure at the microscopic level. In addition, the hydrophilic properties of biodegradable polyester materials lead to a high volumetric water absorption rate in foamed products, affecting the material's cushioning stability in humid environments.

[0004] On the other hand, biodegradable polyesters are prone to molecular chain breakage during high-temperature processing, leading to reduced melt strength and difficulty in maintaining stable microporous morphology. Existing biodegradable foam materials often have limited functionality, lacking integrated functions such as antistatic and flame retardancy, making it difficult to meet the safety protection requirements of goods such as electronic products during transportation. Therefore, improving the cell wall strength, reducing water absorption, and achieving multifunctional integration of biodegradable foam materials are problems that need to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a fully biodegradable plant fiber reinforced microfoamed express cushioning material and its preparation method, which solves the problems of insufficient cell wall strength, high volume water absorption rate, and lack of multifunctional integration in existing biodegradable foamed materials.

[0006] To address the above problems, the present invention provides the following technical solution: This invention provides a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material, employing the following technical solution: A fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material, made from raw materials comprising the following parts by weight: 50-70 parts of polylactic acid resin or polybutylene terephthalate-adipate resin; 30-50 parts of microporous foamed biodegradable masterbatch containing surface-modified plant fibers; Functional additives: 0.5-15.0 parts; The functional additive is one or a combination of several of the following: polymeric carbodiimide antihydrolysis agent, quaternary ammonium salt antistatic agent, and phosphorus nitrogen-based halogen-free flame retardant.

[0007] By employing the above technical solution, and using the microporous foamed biodegradable masterbatch pre-dispersed with the surface-modified plant fibers as a reinforcing component, uniform dispersion of the surface-modified plant fibers in the biodegradable polyester matrix is ​​achieved. During the foaming and expansion process, the surface-modified plant fibers are subjected to biaxial tensile stress, resulting in a unidirectional alignment along the circumferential direction of the cell walls, thereby constructing a physical support network at the microscale. This network can improve the tensile yield strength of the cell walls, prevent cell rupture and perforation during the high-temperature expansion stage, and ensure the closed-cell ratio of the material. Because the surface-modified plant fibers are hydrophobic after surface modification, combined with the dense cell wall structure, the penetration path of water within the material is prolonged, significantly reducing the volumetric water absorption rate, resulting in a lightweight, supportive, and weather-resistant express cushioning material.

[0008] Preferably, the microporous foamed biodegradable masterbatch is made from the following raw materials in parts by weight: 50-70 parts of polylactic acid resin carrier, 30-50 parts of surface-modified plant fiber with an average length of 10-50 μm, 3-7 parts of epoxy compatibilizer, 5-12 parts of compound foaming agent, and 0.5-1.5 parts of zinc stearate lubricant.

[0009] By employing the above technical solution, surface-modified plant fibers of a specific length range are used in combination with the epoxy compatibilizer. The epoxy groups chemically bond with the hydroxyl groups on the surface of the surface-modified plant fibers and the carboxyl groups at the ends of the biodegradable polyester, enhancing the interfacial adhesion between the fibers and the matrix. The compounded foaming agent is uniformly distributed in the microporous foamed biodegradable masterbatch, acting as heterogeneous core points to induce the formation of numerous fine pores, further optimizing the microstructure of the support network.

[0010] Preferably, the functional additives include one or more of the following components by weight: 0.5-2.0 parts of polymeric carbodiimide antihydrolysis agent, 2.0-3.0 parts of quaternary ammonium salt antistatic agent, and 5.0-15.0 parts of phosphorus-nitrogen halogen-free flame retardant.

[0011] By adopting the above technical solution, the polymeric carbodiimide can repair the molecular chain breakage of biodegradable polyester during high-temperature processing through chain extension, thereby improving the melt strength of the material. The addition of the quaternary ammonium salt antistatic agent and the phosphorus-nitrogen halogen-free flame retardant meets the safety requirements of express delivery materials under different transportation environments.

[0012] Preferably, the microporous foamed biodegradable masterbatch consists of particles with a diameter of 2.0-3.0 mm.

[0013] By adopting the above technical solution, the particle size specification can ensure that the microporous foamed biodegradable masterbatch and the polylactic acid resin or polybutylene terephthalate adipate resin have similar bulk density and flowability during the mixing process, avoid component segregation during the feeding process, and ensure the stability of the final product performance.

[0014] This invention also provides a method for preparing a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material, using the following technical solution: A method for preparing a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material includes the following steps: Polylactic acid resin or polybutylene terephthalate-adipate resin, microporous foaming biodegradable masterbatch and functional additives are put into a high-speed mixer and mixed to obtain a mixture. The mixture is fed into a granulator for melt extrusion, and then pelletized by a pelletizing device to obtain expandable cushioning material preforms with an average diameter of 1.0-1.5 mm. The expandable cushioning material preformed particles are filled into a foaming mold, and heated by saturated steam or depressurized by molding. The expandable cushioning material preformed particles expand and fuse together to form an integral microporous structure. The entire microporous structure is removed and moved into a curing chamber for curing under constant temperature and humidity conditions to obtain the fully biodegradable plant fiber reinforced microfoamed express cushioning material.

[0015] By adopting the above technical solution, and through the process logic of first preparing the microporous foamed biodegradable masterbatch and then performing secondary extrusion granulation, secondary dispersion of the reinforcing component in the matrix is ​​achieved. The expandable buffer material preformed particles undergo phase change and volume expansion upon heating within the foaming mold. Under the influence of heat, the surface polymer chains diffuse and physically entangle, forming a monolithic material with a continuous interface and uniform microporous structure, ensuring the uniformity of the buffering properties.

[0016] Preferably, in the step of preparing the mixture, the high-speed mixer rotates at 400-1200 rpm and the mixing time is 4-15 min; in the step of obtaining the expandable buffer material preformed particles, the body temperature of the granulator is controlled at 120-170℃.

[0017] By adopting the above technical solutions, the precise setting of mixing parameters ensures the mechanical stirring effect between components, while the segmented temperature-controlled extrusion process avoids the thermal degradation of biodegradable resin and ensures that the melt viscosity of the material is within a suitable range for shear dispersion.

[0018] Preferably, the microporous foamed biodegradable masterbatch is prepared by the following method: Plant fibers were placed in an ethanol solution of silane coupling agent with a mass concentration of 1%-5%, stirred at 25-65℃ for 30-90 min, and dried at 60-100℃ for 6-12 h to obtain surface-modified plant fibers. The surface-modified plant fibers, polylactic acid resin carrier, epoxy compatibilizer, compound foaming agent and zinc stearate lubricant are put into a high-speed mixer and mixed to obtain masterbatch premix; The masterbatch premix is ​​fed into a twin-screw extruder and melt-mixed, extruded, stretched, cooled and pelletized at a temperature of 140-190°C to obtain the microporous foamed biodegradable masterbatch.

[0019] By employing the above technical solution, the surface of plant fibers is modified using the silane coupling agent, reducing the surface polarity of the fibers and enabling them to have good mechanical interlocking force and affinity with non-polar or weakly polar biodegradable carriers, which is beneficial for constructing the physical support network. The high shear force of the twin-screw extruder further breaks down the fiber bundles, achieving uniform coating of individual fibers within the microporous foamed biodegradable masterbatch.

[0020] Preferably, in the step of preparing the masterbatch premix, the high-speed mixer rotates at 500-1500 rpm and the mixing time is 5-15 min; in the step of obtaining the microporous foamed biodegradable masterbatch, the screw speed of the twin-screw extruder is 150-450 rpm.

[0021] By adopting the above technical solution, high-speed mixing enables the zinc stearate lubricant to form a uniform film on the fiber surface, and precise control of the screw speed balances the shear strength and material residence time, ensuring that the fiber length is not excessively cut and preserving the fiber's aspect ratio advantage.

[0022] Preferably, in the step of forming the integral microporous structure, the pressure of the saturated steam heating is 0.1-0.3 MPa, and the heating time is 10-30 s; the molding temperature for the molding and depressurization is 120-160℃, the pressure inside the foaming mold is 0.5-2.0 MPa, and the pressure is maintained for 30-90 s before the foaming mold is opened to instantly depressurize.

[0023] By employing the above technical solution, the expansion ratio of the cells can be controlled by adjusting the steam pressure or the pressure difference at the moment of depressurization. The pressure drop generated by instantaneous depressurization induces the precipitation and nucleation of dissolved gases inside the material, forming uniformly sized fine pores under the constraint of the fiber support network.

[0024] Preferably, in the curing process, the ambient temperature of the curing chamber is controlled at 40-60℃, the relative humidity at 40%-60%RH, and the curing time at 6-24h.

[0025] By adopting the above technical solution, the curing treatment can promote the release of residual stress, balance the pressure of the cell walls inside the material with the external environment, prevent the material from shrinking and deforming during storage, and induce the crystallization of biodegradable polyester, thereby improving the dimensional stability of the finished material.

[0026] This invention provides a fully biodegradable plant fiber-reinforced microfoamed express cushioning material and its preparation method. It possesses the following beneficial effects: 1. This invention pre-disperses surface-modified plant fibers in polylactic acid resin or polybutylene terephthalate-adipate resin through microporous foaming biodegradable masterbatch. The physical support network constructed by the oriented distribution of surface-modified plant fibers within the cell wall during the foaming process restricts cell wall damage and blocks water penetration, thereby improving the closed-cell rate and reducing the volume water absorption rate of the fully biodegradable plant fiber reinforced microfoamed express buffer material.

[0027] 2. This invention utilizes epoxy compatibilizers to enhance the interfacial adhesion between surface-modified plant fibers and polylactic acid resin carriers, and combines them with compound foaming agents as heterogeneous core points to induce the generation of uniformly distributed cell structures. This optimizes the microstructure of the fully biodegradable plant fiber-reinforced microfoamed express buffer material while enhancing the tensile yield strength of the cell wall and the overall structural support performance.

[0028] 3. This invention, by adding functional additives including polymeric carbodiimide anti-hydrolysis agent, quaternary ammonium salt antistatic agent and phosphorus nitrogen-based halogen-free flame retardant to the raw materials, not only repairs the broken molecular chains of polylactic acid resin or polybutylene terephthalate resin and improves melt strength, but also endows the fully biodegradable plant fiber reinforced microfoamed express cushioning material with antistatic and flame retardant functions, thereby improving the safety of the material in the application environment. Attached Figure Description

[0029] Figure 1 This is a diagram showing the test results of microstructure parameters according to an embodiment of the present invention; Figure 2 This is a static compressive stress-strain response diagram according to an embodiment of the present invention; Figure 3 This is a graph showing the variation of peak acceleration due to continuous drop impact according to an embodiment of the present invention. Figure 4 This is a surface resistivity fluctuation curve of one embodiment of the present invention; Figure 5 This is a graph showing the rate of mass loss due to thermal decomposition according to an embodiment of the present invention. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a microporous foamed biodegradable masterbatch A containing modified plant fibers, comprising the following steps: Plant fibers with an average length of 10 μm and an aspect ratio of 10 were placed in a 1% (w / w) silane coupling agent ethanol solution and stirred at 25 °C for 30 min. The treated plant fibers were then transferred to a drying oven and dried at 60 °C for 6 h to obtain surface-modified plant fibers. By weight, take 70 parts of polylactic acid resin carrier, 30 parts of surface-modified plant fiber, 3 parts of epoxy compatibilizer, 5 parts of compound foaming agent, and 0.5 parts of zinc stearate lubricant. Put the above materials into a high-speed mixer and mix at 500 rpm for 5 minutes to ensure thorough mixing. The mixed material is added to a twin-screw extruder, and the temperature of each heating zone is set to 140℃ to 150℃, while the screw speed is controlled at 150 rpm. After melt mixing, extrusion, stranding, and cooling, the material is cut into granules with a particle size of 2.0 mm by a pelletizer, thus obtaining foaming masterbatch A.

[0032] Preparation Example 2: This preparation example provides a microporous foamed biodegradable masterbatch B containing modified plant fibers, comprising the following steps: Plant fibers with an average length of 30 μm and an aspect ratio of 30 were placed in a 3% (w / w) silane coupling agent ethanol solution and stirred at 45 °C for 60 min. The treated plant fibers were then transferred to a drying oven and dried at 80 °C for 9 h to obtain surface-modified plant fibers. By weight, take 60 parts of polylactic acid resin carrier, 40 parts of surface-modified plant fiber, 5 parts of epoxy compatibilizer, 8 parts of compound foaming agent, and 1.0 part of zinc stearate lubricant. Put the above materials into a high-speed mixer and mix at 1000 rpm for 10 minutes to ensure thorough mixing. The mixed material is added to a twin-screw extruder, and the temperature of each heating zone is set to 155℃ to 170℃, while the screw speed is controlled at 300 rpm. After melt mixing, extrusion, stranding, and cooling, the material is cut into granules with a particle size of 2.5 mm by a pelletizer, thus obtaining foaming masterbatch B.

[0033] Preparation Example 3: This preparation example provides a microporous foamed biodegradable masterbatch C containing modified plant fibers, comprising the following steps: Plant fibers with an average length of 50 μm and an aspect ratio of 50 were placed in a 5% (w / w) silane coupling agent ethanol solution and stirred at 65 °C for 90 min. The treated plant fibers were then transferred to a drying oven and dried at 100 °C for 12 h to obtain surface-modified plant fibers. By weight, take 50 parts of polylactic acid resin carrier, 50 parts of surface-modified plant fiber, 7 parts of epoxy compatibilizer, 12 parts of compound foaming agent, and 1.5 parts of zinc stearate lubricant. Put the above materials into a high-speed mixer and mix at 1500 rpm for 15 minutes to ensure thorough mixing. The mixed material is added to a twin-screw extruder, and the temperature of each heating zone is set to 175℃ to 190℃, while the screw speed is controlled at 450 rpm. After melt mixing, extrusion, stranding, and cooling, the material is cut into granules with a particle size of 3.0 mm by a pelletizer, thus obtaining foaming masterbatch C.

[0034] Examples 1-5: Example 1: This embodiment provides a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material, including the following steps: S01. By mass, add 60 parts of polybutylene terephthalate (PBAT) resin, 40 parts of foaming masterbatch B and 1.25 parts of polymeric carbodiimide anti-hydrolysis agent into a high-speed mixer, set the speed to 800 rpm and mix at room temperature for 8 minutes. S02. The mixed material is fed into a single screw granulator for melt extrusion. The machine body temperature is controlled at 150℃. The expandable cushioning material preforms with an average diameter of 1.2mm are obtained by underwater pelletizing device. S03. Fill the pre-formed particles into the foaming mold, and introduce saturated water vapor at a pressure of 0.2MPa into the mold cavity for heating for 20s, so that the particles expand a second time due to heat and fuse together to form an integral structure. S04. Take out the molded cushioning material and place it in a curing room with a temperature of 50℃ and a relative humidity of 50%RH for constant temperature and humidity curing for 12 hours to obtain the cushioning material.

[0035] Example 2: This embodiment provides a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material, including the following steps: S01. By mass, add 50 parts of polylactic acid (PLA) resin, 50 parts of foaming masterbatch C and 3.0 parts of quaternary ammonium salt antistatic agent into a high-speed mixer, set the speed to 1200 rpm and mix at room temperature for 12 min. S02. The mixed material is fed into a single screw extruder, kneaded at a melting temperature of 160°C and extruded into a preheated calendering die to ensure that the melt fills the cavity. S03. Close the mold, set the molding temperature to 160℃, apply an internal pressure of 2.0MPa, maintain the pressure and mold for 90 seconds, then open the mold to release the pressure instantly, allowing the material to expand and solidify in situ using the foaming agent it contains. S04. Take out the molded cushioning material and place it in a curing room with a temperature of 60℃ and a relative humidity of 60%RH for constant temperature and humidity curing for 24 hours to obtain the cushioning material.

[0036] Example 3: This embodiment provides a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material, including the following steps: S01. By mass, add 70 parts of polylactic acid (PLA) resin, 30 parts of foaming masterbatch A and 2.0 parts of quaternary ammonium salt antistatic agent into a high-speed mixer, set the speed to 400 rpm and mix at room temperature for 4 minutes. S02. The mixed material is fed into a single screw extruder, kneaded at a melting temperature of 120°C and extruded into a preheated calendering die to ensure uniform material distribution. S03. Close the mold, set the molding temperature to 120℃, apply an internal pressure of 0.5MPa, maintain the pressure and mold for 30 seconds, then open the mold to release the pressure instantly, inducing the formation of microporous structures and completing the molding process. S04. Take out the molded cushioning material and place it in a curing room with a temperature of 40℃ and a relative humidity of 40%RH for constant temperature and humidity curing for 6 hours to obtain the cushioning material.

[0037] Example 4: This embodiment provides a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material, including the following steps: S01. By mass, add 50 parts of polybutylene terephthalate (PBAT) resin, 50 parts of foaming masterbatch C, 2.0 parts of polymeric carbodiimide anti-hydrolysis agent and 15.0 parts of phosphorus nitrogen-based halogen-free flame retardant into a high-speed mixer, set the speed to 1000 rpm, and mix at room temperature for 15 minutes. S02. The mixed material is fed into a granulator for melt extrusion. The machine body temperature is maintained at 170℃. The preformed particles of expandable flame-retardant cushioning material with an average diameter of 1.5mm are obtained by underwater pelletizing. S03. Fill the pre-formed particles into the foaming mold, and introduce saturated steam at a pressure of 0.3MPa for 30 seconds to heat it continuously, so that the flame-retardant functional particles can complete the expansion ratio conversion and interface bonding under the action of high-temperature steam. S04. Take out the molded cushioning material and place it in a curing room with a temperature of 60℃ and a relative humidity of 60%RH for constant temperature and humidity curing for 24 hours to obtain the cushioning material.

[0038] Example 5: This embodiment provides a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material, including the following steps: S01. By mass, add 70 parts of polybutylene terephthalate (PBAT) resin, 30 parts of foaming masterbatch A, 0.5 parts of polymeric carbodiimide anti-hydrolysis agent and 5.0 parts of phosphorus-nitrogen halogen-free flame retardant into a high-speed mixer, set the speed to 600 rpm, and mix at room temperature for 6 minutes. S02. The mixed material is fed into a granulator for melt extrusion. The machine body temperature is set to 130℃. The pelletizing device produces expandable preformed particles with an average diameter of 1.0mm. S03. Fill the pre-formed particles into the foaming mold, introduce saturated steam at a pressure of 0.1MPa and heat for 10s, control the amount of steam so that the particles can achieve controlled foaming and molding under low pressure. S04. Take out the molded cushioning material and place it in a curing room with a temperature of 40℃ and a relative humidity of 40%RH for constant temperature and humidity curing for 6 hours to obtain the cushioning material.

[0039] Comparative Examples 1-6: Comparative Example 1: Compared with Example 1, the difference is that the foaming masterbatch B obtained in Preparation Example 2 is not used. Instead, the same mass fractions of base resin, unmodified raw wood flour fibers (average length of 250 μm) and equal amounts of foaming agent are directly mixed and processed. All other parameters and steps are the same.

[0040] Comparative Example 2: Compared with Example 1, the difference is that the mass ratio of base resin to foaming masterbatch B in the formulation is adjusted to 85:15, while the other parameters and steps are the same.

[0041] Comparative Example 3: Compared with Example 1, the difference is that no polymeric carbodiimide anti-hydrolysis agent is added to the formulation, while the other parameters and steps are the same.

[0042] Comparative Example 4: This comparative example uses commercially available ordinary polyethylene (EPE) pearl cotton foam material as a control sample, and its product density is similar to that of the product obtained in Example 1.

[0043] Comparative Example 5: Compared with Example 2, the difference is that the foaming masterbatch C obtained in Preparation Example 3 is not used. Instead, the same mass parts of base resin, unmodified raw wood flour fiber and 3.0 mass parts of quaternary ammonium salt antistatic agent are directly mixed and processed. All other parameters and steps are the same.

[0044] Comparative Example 6: Compared with Example 4, the difference is that the foaming masterbatch C obtained in Preparation Example 3 is not used. Instead, the same mass parts of base resin, unmodified raw wood flour fiber and 15.0 mass parts of phosphorus nitrogen-based halogen-free flame retardant are directly mixed and processed. All other parameters and steps are the same.

[0045] Test Examples 1-4: Test Example 1: Experimental description: This test case aims to evaluate the microstructure quality of microfoamed materials. Through correlation analysis between closed-cell rate and water absorption rate, it verifies the contribution of modified plant fiber masterbatch to cell integrity. The testing equipment includes a fully automated true density analyzer and a high-precision electronic balance. The testing standards refer to GB / T10799-2008 Determination of Open and Closed-Cell Volume Percentage of Rigid Foamed Plastics and GB / T8810-2005 Determination of Water Absorption Rate of Rigid Foamed Plastics.

[0046] Experimental steps: A cube sample with dimensions of 20mm x 20mm x 20mm was cut from the center position of the cushioning material products obtained from Examples 1 to 5 and Comparative Examples 1 and 2. Use compressed air to clean the surface of the sample to remove any remaining debris from the cutting process, and then place the sample in a drying oven at 45°C for 4 hours to eliminate the interference of environmental moisture. The dried sample is placed in the test chamber of the true density analyzer, and high-purity helium is introduced as a medium. The apparent volume and solid volume of the sample are determined by the gas expansion method, and then the closed-pore ratio is calculated. After completing the closed-cell rate test, the sample was immersed in distilled water at 23°C. The sample was fixed with a stainless steel mesh cage so that its top surface was 50 mm below the water surface. After soaking for 24 hours, the sample was taken out, the surface water was quickly dried, and the sample was weighed. The volumetric water absorption rate of the sample was calculated by combining the change in mass before and after soaking with the apparent volume of the sample. Each sample group was tested 5 times, and the arithmetic mean was taken after removing the values ​​with large deviations.

[0047] Experimental data: Table 1. Summary of Microstructural Parameter Test Results for Each Sample Group

[0048] Experimental conclusion: Based on the test data in Table 1 and the appendix Figure 1 Analysis shows that the closed-cell ratio of the samples obtained in Examples 1 to 5 remained at a high level, while the volumetric water absorption rate showed a significant decreasing trend. (Appendix) Figure 1 The diagram illustrates the correspondence between sample group numbers and structural parameters. The bar chart corresponds to the percentage of closed-cell rate represented by the left vertical axis, while the line graph corresponds to the percentage of volumetric water absorption rate represented by the right vertical axis. Example 2 exhibited excellent structural stability across all test groups, achieving a closed-cell rate of 94.38% and a water absorption rate of only 0.49%. This demonstrates that under specific formulation and process conditions, the material can form a more dense cell wall structure.

[0049] The superior performance of Example 2 is attributed to the use of a rationally proportioned modified plant fiber masterbatch and matching molding process parameters. The modified microfibers achieved uniform distribution within the resin matrix, and the transition layer formed at the fiber-cell wall interface effectively alleviated localized stress during foaming and expansion. During foaming, the microfibers aligned oriented within the cell wall, increasing the compressive strength of the cell wall and thus maintaining the integrity of the cell structure. This stable microstructure directly restricts external moisture from entering the material through openings or cracks, resulting in a significantly lower water absorption rate compared to other groups, reflecting the improved interfacial adhesion performance of the masterbatch process.

[0050] Data from Examples 1, 4, and 5 further demonstrate that by adjusting the masterbatch addition ratio and molding parameters, the closed-cell structure of the material can be effectively controlled, enabling the material to possess good physical isolation properties under different application environments. In contrast, groups lacking masterbatch pretreatment, such as Comparative Example 1, cannot maintain normal closed-cell characteristics due to fiber puncture effects, resulting in poor adhesion. Figure 1 The columnar height was significantly reduced, while the zigzag height was significantly increased. Experimental results confirm that this invention, through fiber aspect ratio control and masterbatch pre-dispersion treatment, effectively solves the technical defect of natural fiber-reinforced foam materials being prone to pore absorption, ensuring the functional stability of the cushioning material in humid environments.

[0051] Test Example 2: Experimental description: This test case aims to evaluate the static cushioning capacity and structural stability of fully biodegradable plant fiber-reinforced microfoamed materials under continuous impact loading. The test verifies the enhancing effect of modified plant fibers on the microporous structure by recording the stress-strain response during static compression and the peak acceleration changes during multiple dynamic drops. The experimental equipment used was a universal testing machine and a dynamic pressure testing system. The testing standards referenced GB / T8168-2008 Static Compression Test Method for Packaging Cushioning Materials and GB / T8167-2008 Dynamic Compression Test Method for Packaging Cushioning Materials.

[0052] Experimental steps: Cube samples with dimensions of 50mm x 50mm x 50mm were cut from Examples 1 to 5 and Comparative Examples 1 and 4. The sample is placed in the center of the pressure plate of the universal testing machine. The compression rate is set to 10 mm / min. The load is continuously applied until the sample deformation reaches 75% and then stopped. The system automatically collects and records the compression stress-strain curve data. Another set of specimens of the same specifications were prepared for dynamic impact testing. A fixed mass hammer was dropped from a height of 60cm to impact the specimens using a drop tester. The acceleration time history curve during the impact process was obtained by an acceleration sensor installed on the hammer. Three consecutive repeated drop impact tests were performed on the same sample, with an interval of 1 minute between each impact. The peak acceleration value generated by each impact was recorded sequentially. The yield plateau stress values ​​in static compression and the peak acceleration of each impact in dynamic impact testing were summarized. The performance degradation ratio of each sample group after multiple impacts was calculated. The arithmetic mean was taken after each sample group was tested 5 times.

[0053] Experimental data: Table 2. Buffer performance and resistance to repeated impacts test data for each sample group

[0054] Experimental conclusion: Combined with Table 2 and Appendix Figure 2 and appendix Figure 3 The test results shown indicate that Examples 1 to 5 all exhibit a significant synergistic enhancement effect in terms of static energy absorption efficiency and dynamic impact resistance stability. (Appendix) Figure 2 The stress-strain response of the sample group under static compression is shown in the figure. The horizontal axis represents the strain percentage, and the vertical axis represents the compressive stress value. (See attached figure.) Figure 3The figure reflects the peak acceleration variation trend during continuous drop impact. The three bars corresponding to each sample group in the figure represent the first, second, and third impact results from left to right. Example 2 exhibits excellent energy absorption characteristics. Its stress-strain curve has a flat and broad yield plateau in the strain range of 10% to 60%, which means that the material can absorb more impact energy under small stress fluctuations, thereby providing stable protection for the contents.

[0055] This resistance to repeated impacts is attributed to the reinforcing support structure formed within the cell wall by the modified plant fibers in this design. During compression, the plant fibers distributed within the cell wall bear part of the stress through their high modulus properties, inhibiting premature yielding of the cell walls. In Example 2, due to the use of modified fibers with a large aspect ratio, a stable physical entanglement is formed between the fibers and the matrix resin. (See attached...) Figure 3 As shown, in Example 2, after three consecutive impacts, the height of the corresponding columnar strip did not increase significantly, remaining at around 70.5g. This indicates that the material can dissipate energy through the micro-slippage of fibers upon impact, and the porous structure possesses good elastic recovery capability after unloading, preventing performance degradation caused by structural collapse.

[0056] Data from Examples 1, 4, and 5 further confirm that by controlling the aspect ratio of the fibers in the masterbatch and optimizing the molding process, the material prepared by this invention can improve the brittleness of natural fiber-reinforced systems. In contrast, Comparative Example 1, due to the direct use of unmodified plant fibers, exhibits insufficient bonding strength between the fiber and resin interface, making it prone to interfacial debonding under impact. (Appendix) Figure 3 In Comparative Example 1, the height of the columnar strips showed a significant step increase after the third impact, reflecting irreversible physical damage to its microporous structure under continuous impact. In summary, the process of this invention improves the mechanical durability of the fully biodegradable material, enabling it to achieve performance levels that are, in some aspects, superior to, traditional petroleum-based cushioning materials.

[0057] Test Example 3: Experimental description: This test example assesses the conductivity stability of fully biodegradable plant fiber-reinforced microfoamed materials by measuring the surface resistivity, and verifies the influence of the microstructure constructed by the foaming masterbatch on the dispersion state of the antistatic agent. The testing instrument used was a high-resistivity meter and a three-electrode system. The experimental environment was strictly controlled at a temperature of 23℃ and a relative humidity of 50%. The testing standard referenced GB / T1410-2006, "Test Methods for Volume Resistivity and Surface Resistivity of Insulating Materials".

[0058] Experimental steps: Thin plate samples with dimensions of 100mm x 100mm x 5mm were randomly cut from the surface of the cushioning material products obtained in Examples 2, 3 and Comparative Example 5. The sample surface was wiped with anhydrous ethanol to remove surface impurities, and the sample was placed in a constant temperature and humidity chamber for 48 hours to eliminate environmental interference. The treated sample was placed in the center of the three-electrode test stage, the test voltage was set to 100V, and the surface resistivity value was read by the instrument after 60s of pressure application. Ten evenly distributed test sites were selected on the surface of each sample for cyclic measurement, and the resistance data of each site were recorded in detail to evaluate the uniformity of spatial distribution. Calculate the arithmetic mean and standard deviation of resistivity for each sample group. Repeat the test 5 times for each sample group and take the final average value.

[0059] Experimental data: Table 3. Test data on surface resistivity and spatial distribution uniformity of each sample group.

[0060] Experimental conclusion: Based on the test data in Table 3 and the appendix Figure 4 Analysis shows that both Examples 2 and 3 achieved stable static dissipation effects with the addition of a low proportion of antistatic agent, maintaining a surface resistivity of 10. 8 Up to 10 9 Ohm range. (Appendix) Figure 4 The resistivity fluctuation curves of different groups at multiple test sites are shown. The horizontal axis represents the test site number on the sample surface, and the vertical axis represents the commonly used logarithmic value of surface resistivity. Example 2 exhibits excellent conductivity stability, with its corresponding dotted curve fluctuating slightly between 8.1 and 8.2, and the curvature change is gentle, reflecting the high uniformity of the charge transport channels on the material surface.

[0061] This stable antistatic effect stems from the reinforcing network constructed within the foamed cell walls by the modified plant fiber masterbatch in this solution. Because the fibers undergo surface modification and pre-dispersion during pretreatment, these microfibers align oriented within the cell walls during compression molding, providing a physical deposition carrier for the antistatic agent. The antistatic agent molecules tend to oriented along the fiber surface and cell wall interface, thus forming a continuous permeation network even at low concentrations. Data from Example 2 shows that when the masterbatch addition amount and antistatic agent content are appropriately matched, the material can form a dense conductive pathway, avoiding the depletion of the additive in localized areas.

[0062] In contrast, Comparative Example 5, due to the absence of a masterbatch process, resulted in uneven dispersion of the directly added antistatic agent within the resin matrix, leading to poor adhesion. Figure 4 The corresponding solid line shows significant and dramatic fluctuations, with resistivity deviations spanning orders of magnitude at different sites. Data from Example 3 further validates the effectiveness of this structure; even with reduced antistatic agent content, its resistivity fluctuation curve remains relatively flat. Experimental results confirm that the fiber-reinforced network achieved through masterbatch pretreatment in this invention can significantly improve the utilization efficiency and performance stability of functional additives, effectively solving the technical problem that the antistatic properties of traditional foamed materials easily fluctuate with spatial location.

[0063] Test Example 4: Experimental description: This test case aims to evaluate the fire safety and flame retardant stability of fully biodegradable plant fiber-reinforced microfoamed materials. Through limiting oxygen index (LOI) determination and vertical burning rating assessment, the synergistic effect mechanism of modified plant fibers and flame-retardant components under masterbatch processing is verified. The testing instruments used include an oxygen index meter and a vertical burning test apparatus. The experimental environment meets the requirements of a standard laboratory. The testing standards refer to GB / T2406.2-2008 Determination of Combustion Behavior by Oxygen Index Method for Plastics and GB / T2408-2021 Determination of Combustion Performance of Plastics.

[0064] Experimental steps: Strip samples with dimensions of 125mm x 13mm x 3.2mm were cut from the cushioning material products obtained in Examples 2, 3 and Comparative Example 6. The sample was placed in a standard laboratory environment for 48 hours to ensure that the internal moisture of the material reached equilibrium and to eliminate the influence of ambient humidity on the combustion process. The sample was vertically fixed inside the combustion chamber of the oxygen index meter. The mixing ratio of nitrogen and oxygen was adjusted to find the lowest oxygen concentration value that could sustain the sample burning for 3 minutes or when the burning length reached 50 mm after ignition. Another set of samples was tested for vertical combustion. The flame burning time and flameless burning time of the samples were recorded after the flame was removed. It was observed whether any burning droplets ignited the degreased cotton below. The flame retardant level was evaluated based on the experimental phenomena. The residual char products after combustion were collected, and the mass of the residual char was weighed using a precision electronic balance and the residual char rate was calculated. Five samples were selected from each sample group for parallel testing, and the experimental data were summarized.

[0065] Experimental data: Table 4. Summary of Flame Retardant Performance and Charring Stability Test Results for Each Sample Group

[0066] Experimental conclusion: Based on the test data in Table 4 and the appendix Figure 5Analysis shows that Examples 2 and 3 exhibited significant flame-retardant characteristics after the addition of flame-retardant components, with limiting oxygen indices exceeding 28%. (Appendix) Figure 5 The graph shows the trend of mass loss rate of the sample group over time during the thermal decomposition process. The horizontal axis represents heating time, and the vertical axis represents the mass residue rate. Example 2 exhibits excellent thermal stability, which is shown in the figure. Figure 5 The solid line in the middle shows a slower rate of mass decrease in the early stage of heating, and the final residual mass percentage remains at a high level, which indicates that the material can form a continuous and dense protective layer under high temperature conditions.

[0067] This superior flame-retardant performance is attributed to the synergistic charring mechanism formed within the cell walls of the modified plant fibers and flame-retardant components in this design. Because the fibers are surface-modified and pre-dispersed in the foaming masterbatch, the uniformly distributed microfibers act as a skeletal support during combustion, inducing directional cross-linking of flame-retardant decomposition products at the cell wall interface. Data from Example 2 demonstrates that when the masterbatch process ensures microscopic contact between components, the material can form a high-strength composite char layer. This char layer exhibits significant oxygen-barrier and heat-insulating functions, effectively blocking heat transfer to the internal pore structure, thereby inhibiting the continuous degradation of the matrix resin.

[0068] In contrast, Comparative Example 6, lacking a masterbatch pretreatment process, exhibits a sharp decline in its corresponding dashed line. Due to uneven component distribution, Comparative Example 6 fails to construct a complete protective char layer during combustion, allowing the flame to easily spread inward through the fiber-matrix separation interface, resulting in a significantly lower char residue rate compared to the Example group. Data from Example 3 further confirms that even with a low flame retardant content, a high oxygen index can still be maintained by optimizing the fiber aspect ratio and dispersion state. Experimental results demonstrate that the fiber-reinforced system constructed using masterbatch technology in this invention significantly improves flame retardant efficiency and ensures the fire safety of the biodegradable buffer material in its application environment.

Claims

1. A fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material, characterized in that, Made from the following ingredients in parts by weight: 50-70 parts of polylactic acid resin or polybutylene terephthalate-adipate resin; 30-50 parts of microporous foamed biodegradable masterbatch containing surface-modified plant fibers; Functional additives: 0.5-15.0 parts; The functional additive is one or a combination of several of the following: polymeric carbodiimide antihydrolysis agent, quaternary ammonium salt antistatic agent, and phosphorus nitrogen-based halogen-free flame retardant.

2. The fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material according to claim 1, characterized in that, The microporous foamed biodegradable masterbatch is made from the following raw materials in parts by weight: The mixture consists of 50-70 parts polylactic acid resin carrier, 30-50 parts surface-modified plant fibers with an average length of 10-50 μm, 3-7 parts epoxy compatibilizer, 5-12 parts compound foaming agent, and 0.5-1.5 parts zinc stearate lubricant.

3. The fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material according to claim 1, characterized in that, The functional additives specifically include one or a combination of the following in parts by weight: Polymeric carbodiimide anti-hydrolysis agent: 0.5-2.0 parts; 2.0-3.0 parts of quaternary ammonium salt antistatic agent; 5.0-15.0 parts of phosphorus-nitrogen halogen-free flame retardant.

4. The fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material according to claim 2, characterized in that, The microporous foamed biodegradable masterbatch consists of particles with a diameter of 2.0-3.0 mm.

5. A method for preparing a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material, characterized in that, The application of the fully biodegradable plant fiber reinforced microfoamed express cushioning material as described in claims 1-4 includes the following steps: Polylactic acid resin or polybutylene terephthalate-adipate resin, microporous foaming biodegradable masterbatch and functional additives are put into a high-speed mixer and mixed to obtain a mixture. The mixture is fed into a granulator for melt extrusion, and then pelletized by a pelletizing device to obtain expandable cushioning material preforms with an average diameter of 1.0-1.5 mm. The expandable cushioning material preformed particles are filled into a foaming mold, and heated by saturated steam or depressurized by molding. The expandable cushioning material preformed particles expand and fuse together to form an integral microporous structure. The entire microporous structure is removed and moved into a curing chamber for curing under constant temperature and humidity conditions to obtain the fully biodegradable plant fiber reinforced microfoamed express cushioning material.

6. The method for preparing a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material according to claim 5, characterized in that, In the step of preparing the mixture, the high-speed mixer rotates at 400-1200 rpm and the mixing time is 4-15 min; In the step of preparing the expandable cushioning material preformed particles, the body temperature of the granulator is controlled at 120-170℃.

7. The method for preparing a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material according to claim 5, characterized in that, The microporous foamed biodegradable masterbatch is prepared by the following method: Plant fibers were placed in an ethanol solution of silane coupling agent with a mass concentration of 1%-5%, stirred at 25-65℃ for 30-90 min, and dried at 60-100℃ for 6-12 h to obtain surface-modified plant fibers. The surface-modified plant fibers, polylactic acid resin carrier, epoxy compatibilizer, compound foaming agent and zinc stearate lubricant are put into a high-speed mixer and mixed to obtain masterbatch premix; The masterbatch premix is ​​fed into a twin-screw extruder and melt-mixed, extruded, stretched, cooled and pelletized at a temperature of 140-190°C to obtain the microporous foamed biodegradable masterbatch.

8. The method for preparing a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material according to claim 7, characterized in that, In the step of preparing the masterbatch premix, the high-speed mixer rotates at 500-1500 rpm and the mixing time is 5-15 min; In the step of preparing the microporous foamed biodegradable masterbatch, the screw speed of the twin-screw extruder is 150-450 rpm.

9. The method for preparing a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material according to claim 5, characterized in that, In the step of forming the overall microporous structure, the pressure of the saturated steam heating is 0.1-0.3 MPa, and the heating time is 10-30 s; The molding temperature for the compression molding and depressurization process is 120-160℃, and the pressure inside the foaming mold is 0.5-2.0MPa. After maintaining the pressure for 30-90 seconds, the foaming mold is opened to instantly depressurize.

10. The method for preparing a fully biodegradable plant fiber reinforced microfoamed express delivery cushioning material according to claim 5, characterized in that, In the curing process, the ambient temperature of the curing chamber is controlled at 40-60℃, the relative humidity is controlled at 40%-60%RH, and the curing time is controlled at 6-24h.

Images