Chemically grafted modified PBAT / EVA composite foaming material and its preparation method

Abstract

This invention relates to the field of foam materials technology, specifically to a chemically grafted modified PBAT / EVA composite foam material and its preparation method. The invention involves grafting polar monomers onto PBAT using a free radical grafting method to improve its elongation at break and ductility. A biodegradable PBAT / EVA composite foam material is then prepared using the modified PBAT. Under the action of a crosslinking agent, the system forms a stable covalent chemical crosslinking network. Simultaneously, the carboxyl groups on the grafted chains form dynamic reversible hydrogen bonds with the ester groups in the PBAT and EVA molecular chains through intermolecular forces. These two types of crosslinking synergistically construct a strong and tough crosslinking network structure, which not only endows the foam material with better tensile and compressive strength but also strengthens the cell walls and significantly increases the cell density. This invention is suitable for large-scale industrial production and can be directly implemented using plastic processing methods such as internal mixers, injection molding machines, and extruders.

Description

Technical Field

[0001] This invention belongs to the field of foam materials technology. Specifically, it relates to a chemically modified PBAT / EVA composite high-performance foam material and its preparation method. Background Technology

[0002] Polymer foams, due to their low density and lightweight properties, have shown broad application prospects in modern technology fields, including sensors, electromagnetic shielding, and shock absorption. Currently, foam materials need to possess excellent physical properties, thermal stability, and biodegradability to meet the demands of diverse application scenarios. In engineering applications, polymer foams often withstand mechanical deformations such as tension, bending, and torsion, especially repeated mechanical loads. However, most traditional foam materials are prone to significant plastic deformation and structural collapse, mainly due to molecular chain deentanglement and chemical bond breaking. These two factors severely restrict the practical application of polymer foams.

[0003] Polybutylene adipate / terephthalate (PBAT), as a typical biodegradable polyester, is a core matrix material for biodegradable foams due to its excellent toughness and processability. However, PBAT has inherent defects such as low melt strength, easy cell collapse during foaming, and poor resilience under cyclic loading, which urgently require performance breakthroughs through modification technology. This invention introduces a large number of carboxyl groups into the side chains of PBAT through chemical grafting modification. Subsequently, the grafted material is melt-blended with EVA. Under the action of a crosslinking agent, the system forms a stable covalent chemical crosslinking network. At the same time, the carboxyl groups on the grafted chains and the ester groups in the PBAT and EVA molecular chains form dynamic reversible hydrogen bonds through intermolecular forces. These two types of crosslinking synergistically construct a strong and tough crosslinking network structure. Furthermore, the grafted branches increase the entanglement between molecular chains, improve the viscoelasticity of the melt, effectively inhibit cell coalescence during foaming, and effectively encapsulate EVA and other blended components and bamboo powder fillers, inhibiting phase separation and producing high-performance foam materials.

[0004] Chinese patent CN116478442B discloses an application of chain-extended modified PBAT foam material, providing a preparation technology for multifunctional PBAT foam material that improves PBAT melt strength. This technology utilizes the reaction of polyhydroxy sugars with functionalized groups, and employs a chain extender to extend the chain of PBAT, thereby improving the tensile, resilience, and tear resistance properties of the PBAT foam material. However, the chain-extended PBAT in this foam material exhibits poor compatibility with EVA matrix during blending. It relies solely on the chain extension reaction to construct a covalent cross-linked network, lacking dynamic and reversible interfacial interactions. Under repeated compression, tension, and other cyclic loading, the covalent bonds are prone to irreversible breakage, and the molecular chain de-entanglement is difficult to recover, leading to rapid decay of foam resilience and continuous accumulation of plastic deformation. This makes it unsuitable for applications requiring repeated deformation and shock absorption. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a PBAT / EVA composite high-performance foam material based on chemical grafting modification technology and its preparation method, which has better tensile and compressive strength, higher cell density, and lower cell diameter, while alleviating the environmental burden caused by the non-degradability of traditional foam.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The preparation method of chemically grafted modified PBAT / EVA composite foam material includes the following steps:

[0008] Step 1: The dried PBAT is melt-blended with polar monomers and initiators under heating and shearing, cooled, pelletized and dried to obtain PBAT grafted material;

[0009] Step 2: After thoroughly mixing the PBAT grafted material with EVA (ethylene-vinyl acetate copolymer), POE (ethylene octene copolymer), filler, foaming agent, crosslinking agent, and foaming aid, the mixture is blended under heating and shearing to obtain a compound, wherein the PBAT grafted material, EVA, and POE are used as the main materials.

[0010] Step 3: Add the mixture to the open mill for mixing, roll it into strips and take it out to obtain the open mill material;

[0011] Step 4: Place the open-mixed material into a mold of a press machine for hot pressing and foaming to obtain chemically grafted modified PBAT / EVA composite foam material.

[0012] Preferably, the PBAT melt index is 1-50 g / 10 min, the EVA content is 10-30%, and the POE melt index is 20-50 g / 10 min; the melt index test temperature is 190℃, and the test load is 2.16 kg; the mass ratio of the PBAT graft material, EVA, and POE is 10-40:40-90:10-20.

[0013] Preferably, the polar monomer in step one is one or more of itaconic acid, maleic acid, and citraconic acid, and its mass is 0.5%-3% of the mass of PBAT.

[0014] Preferably, the initiator in step one is any one or more of dicumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide, and its mass is 0.1%-1% of the mass of PBAT.

[0015] Preferably, the filler in step two is 100-1200 mesh bamboo powder, accounting for 4%-10% of the main material mass; the foaming agent in step two is azodicarbonamide, accounting for 1%-3% of the main material mass; the crosslinking agent in step two is one or more of bis-tert-butyl peroxide diisopropylbenzene or tert-butyl peroxide, accounting for 0.5%-2% of the main material mass; and the foaming aid in step two is one or more of zinc oxide or zinc stearate, accounting for 1.5%-4% of the main material mass.

[0016] Preferably, the high temperature condition in step one is 150℃-170℃, the shearing condition is 50r / min-70r / min, and the reaction time is 6min-9min.

[0017] Preferably, the high temperature condition in step two is 120℃-140℃, and the shearing condition is 50r / min-70r / min.

[0018] Preferably, the temperature of the open mill in step three is 60-80℃, and the number of coiling times is 3-5.

[0019] Preferably, the hot-pressing temperature in step four is 170℃-190℃, the hot-pressing time is 10min-13min, and the pressure is 10MPa-20MPa.

[0020] The present invention also provides a chemically grafted modified PBAT / EVA composite foam material prepared by the above preparation method.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] (1) This invention effectively combines polar monomers with PBAT molecular chains via melt grafting. Under high shear, thermal initiation, and the action of free radical initiators, the double bonds of the monomers open and undergo a free radical grafting reaction with the PBAT molecular chains to obtain PBAT grafted material. Subsequently, the grafted material is melt-blended with EVA. Under the action of a crosslinking agent, a stable covalent chemical crosslinking network is formed in the system. At the same time, the carboxyl groups on the grafted chains and the ester groups in the PBAT and EVA molecular chains form dynamic reversible hydrogen bond crosslinks through intermolecular forces. The two types of crosslinking synergistically construct a strong and tough crosslinking network structure, which is then foamed to obtain a high-performance foam material. This preparation method is simple and efficient, requiring no complex synthesis steps or toxic organic solvents. It can be mass-produced using conventional internal mixers, open mills, extruders, injection molding machines, and flat vulcanizing machines, fully meeting the needs of industrial mass production. Moreover, the entire preparation process is free of pollutant emissions, which aligns with the concepts of green manufacturing and sustainable development.

[0023] (2) The topology of the hydrogen bond cross-linked network prepared by the present invention has good controllability and can be precisely controlled by the grafting rate of the grafted monomers: as the grafting rate increases, the number of carboxyl groups in the system increases, the number of hydrogen bond cross-linking points increases, and the network structure becomes more compact; the network cross-linking density can also be precisely controlled by adjusting the amount of initiator and the processing parameters, thereby precisely optimizing the overall performance of the composite foam, meeting the differentiated requirements of different application scenarios for material properties, and broadening the application range of PBAT.

[0024] (3) The system prepared by the present invention significantly optimizes the cell structure of the composite foam, effectively suppresses the collapse and merging of cells during the foaming process, and makes the foam form a uniform and dense microporous morphology without pore cracks (the average cell diameter can be controlled within 200 μm and the cell uniformity is ≥90%). The elastic biodegradable composite material constructed thereby successfully balances stable mechanical properties and excellent flexibility. Its mechanical strength and elastic recovery ability are comparable to non-degradable elastic foam materials.

[0025] (4) This invention uses biodegradable materials as the matrix material and replaces talc powder with natural renewable bamboo powder as a filler, making it an environmentally friendly biodegradable material. It also possesses excellent shock absorption and energy absorption capabilities. The synergistic effect of these performance advantages allows this biodegradable composite foam to be widely used in wearable flexible sensor substrates, environmentally friendly cushioning packaging materials, lightweight shock-absorbing structural components, and other scenarios, possessing extremely high industrialization value and market prospects. Attached Figure Description

[0026] Figure 1 The NMR spectra are those of Example 4 and Comparative Example 2 of the present invention.

[0027] Figure 2 The infrared spectra of Embodiment 1, Embodiment 4, and Comparative Example 2 of the present invention are shown.

[0028] Figure 3 The compression performance of the composite foam in Examples 1, 4, and 2 of this invention is shown.

[0029] Figure 4 The stress retention of the composite foam in Example 4 and Comparative Example 1 of this invention under 500 cycles of compression.

[0030] Figure 5 These are scanning electron microscope (SEM) images of the composite foams of Example 4, Comparative Example 1, and Comparative Example 2 of the present invention.

[0031] Figure 6 This is a schematic diagram illustrating the grafting modification principle and chemical foaming process of the present invention. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. However, the described embodiments are only some embodiments of the present invention, and not all embodiments. In the embodiments and comparative examples, PBAT and POE were dried in a drying oven at 50°C for 12 hours before use.

[0033] The raw materials and sources of the following comparative examples and embodiments:

[0034] Polybutylene adipate / terephthalate (PBAT, melt index 13 g / 10min, Lanshan Tunhe), vinyl acetate-vinyl acetate (EVA, VA content 26%, Plastics Industry Co., Ltd.), and polyolefin elastomer (POE, 875L, melt index: 5 g / 10min, SK Group Co., Ltd.) were selected as matrix resins. Zinc oxide (ZnO, analytical grade, white granules, Zhiyuan Chemical Reagent Co., Ltd.), stearic acid (Hst, analytical grade, white powder, Wengjiang Chemical Reagent Co., Ltd.), and zinc stearate (ZnSt, analytical grade, colorless transparent liquid, Liyue Trading Co., Ltd.) were used as additives, and commercial bamboo powder was used as filler. The crosslinking agent used was benzoyl peroxide, and the foaming agent was AC.

[0035] Comparative Example 1

[0036] 165g EVA, 33g POE, 8.5g bamboo powder, 2.5g ZnSt, and 5g ZnO were thoroughly mixed. The mixture was then added to a torque rheometer at 140℃ and run at a constant speed of 60 r / min for approximately 4 minutes for melt blending. After the torque of the torque rheometer stabilized, 1.5g BPO and 5g AC were added and the mixture was allowed to continue for 30 seconds. After the melt blending step was completed, the resulting blend was transferred to an open mill at 80℃ for further plasticizing and homogenization. The blend was rolled three times to ensure uniform dispersion of all components. 100g of the blend was then weighed and placed into the foaming mold cavity of a flat vulcanizing machine. The equipment was set to a temperature of 170℃ and a pressure of 15MPa, and the foaming process lasted for 13 minutes.

[0037] Comparative Example 2

[0038] Mix 66g PBAT, 99g EVA, 33g POE, 8.5g bamboo powder, 2.5g ZnSt, and 5g ZnO thoroughly. Add the mixture to a torque rheometer at 140℃ and run it at a constant speed of 60 r / min for approximately 4 minutes for melt blending. After the torque of the torque rheometer stabilizes, add 1.5g BPO and 5g AC for 30 seconds. After completing the melt blending step, transfer the resulting blend to an open mill at 80℃ for further plasticizing and homogenization. Roll the blend three times to ensure that all components are evenly dispersed. Take out 100g of the blend and place it into the foaming mold cavity of a flat vulcanizing machine. Set the equipment temperature to 170℃ and the pressure to 15MPa, and let the foaming process last for 13 minutes.

[0039] Comparative Example 3

[0040] 100g of PBAT was completely melted for 1 minute at 170℃ under shear force (70 r / min) in a torque rheometer. Then, 2.5g of N-phenylmaleimide and 0.25g of dicumyl peroxide were added for a free radical grafting reaction for 210 seconds. The resulting modified PBAT was then removed from the rheometer and allowed to cool naturally to room temperature. Next, 66g of the modified PBAT, 99g of EVA, 33g of POE, 8.5g of bamboo powder, 2.5g of ZnSt, and 5g of ZnO were thoroughly mixed. The mixture was then added to a torque rheometer at 140℃ and run at a constant speed of 60 r / min for approximately 4 minutes for melting and blending. After the torque of the torque rheometer stabilized, 1.5g of BPO and 5g of AC were added and the process continued for 30 seconds. After completing the melt blending step, the resulting blend is transferred to an open mill at 80°C for further plasticization and homogenization. After rolling three times to ensure that all components are evenly dispersed, 100 grams are taken out and placed into the foaming mold cavity of the flat vulcanizing machine. The equipment is set to a temperature of 170°C and a pressure of 15 MPa. The foaming process lasts for 13 minutes.

[0041] Example 1

[0042] 100g of PBAT was completely melted for 1 minute at 170℃ under shear force (70 r / min) in a torque rheometer. Then, 2.5g of itaconic acid and 0.1g of dicumyl peroxide were added for a free radical grafting reaction for 210 seconds. The resulting PBAT-ITA was then removed from the rheometer and allowed to cool naturally to room temperature. Next, 66g of PBAT-ITA, 99g of EVA, 33g of POE, 8.5g of bamboo powder, 2.5g of ZnSt, and 5g of ZnO were thoroughly mixed. The mixture was added to a torque rheometer at 140℃ and run at a constant speed of 60 r / min for approximately 4 minutes for melting and blending. After the torque of the torque rheometer stabilized, 1.5g of BPO and 5g of AC were added and the process continued for 30 seconds. After completing the melt blending step, the resulting blend is transferred to an open mill at 80°C for further plasticization and homogenization. After rolling three times to ensure that all components are evenly dispersed, 100 grams are taken out and placed into the foaming mold cavity of the flat vulcanizing machine. The equipment is set to a temperature of 170°C and a pressure of 15 MPa. The foaming process lasts for 13 minutes.

[0043] Example 2

[0044] 100g of PBAT was completely melted for 1 minute at 170℃ under shear force (70 r / min) in a torque rheometer. Then, 2.5g of itaconic acid and 0.15g of dicumyl peroxide were added for a free radical grafting reaction for 210 seconds. The resulting PBAT-ITA was then removed from the rheometer and allowed to cool naturally to room temperature. Next, 66g of PBAT-ITA, 99g of EVA, 33g of POE, 8.5g of bamboo powder, 2.5g of ZnSt, and 5g of ZnO were thoroughly mixed. The mixture was added to a torque rheometer at 140℃ and run at a constant speed of 60 r / min for approximately 4 minutes for melting and blending. After the torque of the torque rheometer stabilized, 1.5g of BPO and 5g of AC were added and the process continued for 30 seconds. After completing the melt blending step, the resulting blend is transferred to an open mill at 80°C for further plasticization and homogenization. After rolling three times to ensure that all components are evenly dispersed, 100 grams are taken out and placed into the foaming mold cavity of the flat vulcanizing machine. The equipment is set to a temperature of 170°C and a pressure of 15 MPa. The foaming process lasts for 13 minutes.

[0045] Example 3

[0046] 100g of PBAT was completely melted for 1 minute at 170℃ under shear force (70 r / min) in a torque rheometer. Then, 2.5g of itaconic acid and 0.2g of dicumyl peroxide were added for a free radical grafting reaction for 210 seconds. The resulting PBAT-ITA was then removed from the rheometer and allowed to cool naturally to room temperature. Next, 66g of PBAT-ITA, 99g of EVA, 33g of POE, 8.5g of bamboo powder, 2.5g of ZnSt, and 5g of ZnO were thoroughly mixed. The mixture was added to a torque rheometer at 140℃ and run at a constant speed of 60 r / min for approximately 4 minutes for melting and blending. After the torque of the torque rheometer stabilized, 1.5g of BPO and 5g of AC were added and the process continued for 30 seconds. After completing the melt blending step, the resulting blend is transferred to an open mill at 80°C for further plasticization and homogenization. After rolling three times to ensure that all components are evenly dispersed, 100 grams are taken out and placed into the foaming mold cavity of the flat vulcanizing machine. The equipment is set to a temperature of 170°C and a pressure of 15 MPa. The foaming process lasts for 13 minutes.

[0047] Example 4

[0048] 100g of PBAT was completely melted for 1 minute at 170℃ under shear force (70 r / min) in a torque rheometer. Then, 2.5g of itaconic acid and 0.25g of dicumyl peroxide were added for a free radical grafting reaction for 210 seconds. The resulting PBAT-ITA was then removed from the rheometer and allowed to cool naturally to room temperature. Next, 66g of PBAT-ITA, 99g of EVA, 33g of POE, 8.5g of bamboo powder, 2.5g of ZnSt, and 5g of ZnO were thoroughly mixed. The mixture was added to a torque rheometer at 140℃ and run at a constant speed of 60 r / min for approximately 4 minutes for melting and blending. After the torque of the torque rheometer stabilized, 1.5g of BPO and 5g of AC were added and the process continued for 30 seconds. After completing the melt blending step, the resulting blend is transferred to an open mill at 80°C for further plasticization and homogenization. After rolling three times to ensure that all components are evenly dispersed, 100 grams are taken out and placed into the foaming mold cavity of the flat vulcanizing machine. The equipment is set to a temperature of 170°C and a pressure of 15 MPa. The foaming process lasts for 13 minutes.

[0049] Example 5

[0050] 100g of PBAT was completely melted for 1 minute at 170℃ under shear force (70 r / min) in a torque rheometer. Then, 2.5g of itaconic acid and 0.3g of dicumyl peroxide were added for a free radical grafting reaction for 210 seconds. The resulting PBAT-ITA was then removed from the rheometer and allowed to cool naturally to room temperature. Next, 66g of PBAT-ITA, 99g of EVA, 33g of POE, 8.5g of bamboo powder, 2.5g of ZnSt, and 5g of ZnO were thoroughly mixed. The mixture was added to a torque rheometer at 140℃ and run at a constant speed of 60 r / min for approximately 4 minutes for melting and blending. After the torque of the torque rheometer stabilized, 1.5g of BPO and 5g of AC were added and the process continued for 30 seconds. After completing the melt blending step, the resulting blend is transferred to an open mill at 80°C for further plasticization and homogenization. After rolling three times to ensure that all components are evenly dispersed, 100 grams are taken out and placed into the foaming mold cavity of the flat vulcanizing machine. The equipment is set to a temperature of 170°C and a pressure of 15 MPa. The foaming process lasts for 13 minutes.

[0051] Performance testing: The test results are shown in Table 1.

[0052] Grafting rate test: Weigh 0.5g PBAT-ITA and heat to dissolve in 70 mL xylene. Then add 10 mL of 0.1 mol / L trichloroacetic acid-xylene standard solution. After heating and refluxing for 2 h, add 2 drops of phenolphthalein indicator (10g / L) and titrate to the endpoint with 0.1 mol / L KOH-ethanol standard solution. Perform a blank experiment and calculate the grafting rate according to the following formula. The test results are shown in Table 1.

[0053] (1)

[0054] Where GD is the grafting degree (%), N is the concentration of KOH / CH3OH solution used in the titration process (mol / L), V2 and V1 are the volumes (mL) of KOH / CH3OH solution consumed in the titration of the blank sample and the titration of PBAT-ITA, respectively, M is the molecular weight of the polar monomer (g / mol), and m is the mass of PBAT-ITA titrated (g).

[0055] Tensile strength test: The tensile speed is 500 mm / min, and dumbbell-shaped specimens are used for testing; each sample is tested at least 5 times, and the ratio of stress intensity to material density is the specific tensile strength.

[0056] Cell density: The average cell density is calculated using the following formula:

[0057] (2)

[0058] Where N is the bubble density (10)10 / cm 3 ); n is the number of bubbles in the scanning electron microscope image; M is the magnification; A is the area of ​​the selected scanning electron microscope region.

[0059] Compression performance test: The specimen was cut into rectangular blocks of 25×25×20 mm, and its compression stress-strain curve was measured under the conditions of compression speed of 100 mm / min, compression ratio of 50%, and load of 900 Newtons; the compressive strength of the specimen was determined based on the compression strain curve.

[0060] Cyclic compression performance test: The specimen was cut into rectangular blocks of 25×25×20 mm and cyclically compressed 500 times under the conditions of a compression speed of 100 mm / min, a compression ratio of 50%, and a load of 900 Newtons. The compression stress-compression cycle curve was then measured. The stress retention rate was determined by the ratio of the real-time stress to the maximum stress.

[0061] Table 1: Test results of Examples 1-5 and Comparative Examples 1-3 of the present invention.

[0062]

[0063] Table 1 shows that the grafting rate of PBAT-ITA gradually increased with the increase of initiator dosage in Examples 1-4, indicating that the amount of initiator can promote the grafting rate of ITA on the PBAT backbone. However, the increasing trend of grafting rate in Example 5 decreased, because excessive initiator led to the formation of a large amount of gel, affecting the grafting rate. Meanwhile, the changes in the mechanical properties and cell density of the foam material were positively correlated with the grafting rate. At the highest grafting rate in Example 4, the tensile strength was approximately 12% higher than in Comparative Example 1, indicating that the hydrogen-bonded crosslinking network structure of PBAT-ITA can effectively improve the mechanical properties of the material. In Comparative Example 2, the mechanical strength of the foam material prepared using pure PBAT decreased because the fragile cell structure was prone to collapse, leading to a significant decrease in cell density, which in turn affected the tensile strength of the foam. In Comparative Example 3, N-phenylmaleimide was used as the grafting monomer. Although it also possesses a double bond structure and can be successfully grafted, it lacks a carboxyl functional group. Therefore, after grafting onto the PBAT backbone, it cannot form a dynamic, reversible hydrogen bond structure through carboxyl-ester or carboxyl-hydroxyl groups. Furthermore, N-phenylmaleimide contains a rigid benzene ring structure, resulting in significant steric hindrance during melt grafting. This makes it difficult to effectively combine with the free radicals of the PBAT molecular chain, easily leading to self-homogenization. The actual grafting rate is far lower than that of the dicarboxyl monomer. Simultaneously, the rigid structure destroys the intrinsic flexibility of PBAT, restricting molecular chain movement and causing a decrease in the specific tensile strength of the foam material.

[0064] Figure 1The NMR spectra of pure PBAT from Comparative Example 2 and PBAT-ITA from Example 4 are presented. The key proton signals are assigned as follows: signals in the range of 8.0–8.2 ppm correspond to hydrogen atoms (Ha) on the primary carbon atoms of the main chain. Peak integration analysis shows that the integrated area of ​​Ha in Example 4 is smaller than that in Comparative Example 2—clearly indicating that the grafting reaction occurs at the primary carbon site. Meanwhile, the newly emerging peak at 3.8–3.95 ppm corresponds to the (-CH-ITA-) grafted segment, providing direct evidence for successful ITA grafting and the formation of the branched PBAT structure.

[0065] Figure 2 The Fourier transform infrared spectra of pure PBAT in Comparative Example 2 and Examples 1 and 4 are shown. When ITA was introduced into the PBAT molecular chain, the infrared spectrum of PBAT-ITA was at approximately 3335 cm⁻¹. -1 A new characteristic peak appeared. This peak is attributed to the stretching vibration of the hydroxyl (-OH) group grafted with ITA, and its intensity increases significantly with increasing ITA grafting degree. These results further confirm the successful grafting of ITA onto the PBAT molecular chain.

[0066] Figure 3 The compressive stress of the composite foams in Example 4, Comparative Example 1, and Comparative Example 2 at 50% compressive strain is shown. In Comparative Example 2, the addition of pure PBAT reduced the melt strength of the material, making it difficult to form a stable cell structure, resulting in a decrease in the compressive strength of the composite foam compared to Comparative Example 1. In contrast, the hydrogen-bonded cross-linked network structure of the composite foam in Example 4 significantly improved its compressive strength, with a compressive stress of 0.30 MPa, significantly higher than the 0.22 MPa of the composite foam in Comparative Example 1, representing an improvement of approximately 36%.

[0067] Figure 4 The stress retention performance curves of the composite foams of Example 4 and Comparative Example 1 after 500 cycles of cyclic compression at 50% compressive strain are shown. The X-axis represents the number of cycles, and the Y-axis represents the stress. Comparative Example 1 exhibits rapid and significant stress decay during cyclic compression, with a peak stress retention rate of only about 75% after 500 cycles. This indicates irreversible cell collapse and wall fatigue cracking, resulting in significantly insufficient fatigue resistance and structural stability. In contrast, Example 4, through a multi-layered network constructed with grafted hydrogen-bonded physical crosslinks and covalent chemical crosslinks, maintains a peak stress retention rate of over 82% after 500 cycles, with a stress decay rate far lower than that of Comparative Example 1. The foam experiences minimal permanent deformation, and the multi-layered crosslinked network effectively suppresses cell collapse and fatigue damage. During cyclic deformation, the dynamic and reversible breakage and reconstruction of hydrogen bonds efficiently dissipates energy and maintains structural integrity, achieving excellent fatigue resistance and structural stability.

[0068] Figure 5Scanning electron microscope (SEM) images and average pore size distributions of the composite foams of Comparative Example 1, Comparative Example 2, and Example 4 are presented. The images show that the composite foam of Example 4 has a standard continuous closed-cell structure with smooth pore walls. In contrast, the foam of Comparative Example 2 exhibits pore wall fractures, a wide pore size distribution (40-240 μm), and a large average pore size (99.5 ± 5.7 μm). This brittle structure is easily destroyed under mechanical action. The composite foam of Example 4 has a more uniform pore size distribution (40-180 μm) and a smaller average pore size (75.5 ± 1.2 μm). This is due to the enhanced physical entanglement of the ITA side chains on the molecular chains: during foaming, the highly oriented molecular chains return to a coiled state, causing pore shrinkage, enabling the overall structure of the composite foam to withstand various mechanical loads to meet the requirements of complex applications.

[0069] This invention constructs a covalent chemical crosslinking and reversible hydrogen bond crosslinking structure within PBAT / EVA composite materials. Replacing the graft monomer with citraconic acid or maleic acid and employing the same process flow, the mechanical properties exhibit the same characteristics as the grafting rate. Similar grafting rates achieve tensile strength and cell density comparable to those obtained with itaconic acid grafting modification. By dynamically responding to external forces such as heat and force throughout the foaming process, the elongation at break of the composite material is improved, addressing the core pain points of thin, easily broken cell walls and low cell density in foam materials. Simultaneously, using bamboo powder as a filler, a biodegradable composite foam with excellent tensile and compressive strength and a stable cell structure was successfully prepared. Grafting modified PBAT not only enhances the composite foam network structure but also contributes to the retention of elastic properties. This provides guidance for the design and preparation of next-generation environmentally friendly high-performance composite foams and has broad application prospects.

[0070] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any person skilled in the art can make more possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the scope of the present invention. Therefore, all equivalent changes made based on the concept of the present invention without departing from the scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a PBAT / EVA composite foamed material based on chemical graft modification, characterized in that, Includes the following steps: Step 1: The dried PBAT is melt-blended with polar monomers and initiators under heating and shearing, cooled, pelletized and dried to obtain PBAT grafted material; Step 2: After thoroughly mixing the PBAT grafted material with EVA, POE, filler, foaming agent, crosslinking agent and foaming aid, the mixture is blended under heating and shearing to obtain a compound, wherein the PBAT grafted material, EVA and POE are used as the main materials; Step 3: Add the mixture to the open mill for mixing, roll it into strips and take it out to obtain the open mill material; Step 4: Place the open-mixed material into a mold of a press machine for hot pressing and foaming to obtain chemically grafted modified PBAT / EVA composite foam material.

2. The preparation method of the chemically grafted modified PBAT / EVA composite foam material according to claim 1, characterized in that, The PBAT melt index is 1-50 g / 10 min, the VA content of EVA is 10-30%, and the POE melt index is 20-50 g / 10 min; the test temperature for the melt index is 190℃, and the test load is 2.16 kg; the mass ratio of the PBAT graft material, EVA, and POE is 10-40:40-90:10-20.

3. The preparation method of the chemically grafted modified PBAT / EVA composite foam material according to claim 1, characterized in that, The polar monomer in step one is one or more of itaconic acid, maleic acid, and citraconic acid, and its mass is 0.5%-3% of the mass of PBAT.

4. The preparation method of the PBAT / EVA composite foam material based on chemical grafting modification according to claim 1, characterized in that, The initiator in step one is any one or more of dicumyl peroxide, benzoyl peroxide, and di-tert-butyl peroxide, with a mass of 0.1%-1% of the mass of PBAT.

5. The preparation method of the chemically grafted modified PBAT / EVA composite foam material according to claim 1, characterized in that, The filler in step two is 100-1200 mesh bamboo powder, accounting for 4%-10% of the main material's mass. The foaming agent in step two is azodicarbonamide, and its mass is 1%-3% of the main material mass. The crosslinking agent in step two is one or more of bis-tert-butyl peroxide diisopropylbenzene or tert-butyl peroxide, and its mass is 0.5%-2% of the main material mass; The foaming agent in step two is one or more of zinc oxide or zinc stearate, and its mass is 1.5%-4% of the main material mass.

6. The method for preparing the chemically grafted modified PBAT / EVA composite foam material according to claim 1, characterized in that, The high temperature conditions in step one are 150℃-170℃, the shearing conditions are 50r / min-70r / min, and the reaction time is 6min-9min.

7. The preparation method of the chemically grafted modified PBAT / EVA composite foam material according to claim 1, characterized in that, The high temperature conditions in step two are 120℃-140℃, and the shearing conditions are 50r / min-70r / min.

8. The preparation method of the chemically grafted modified PBAT / EVA composite foam material according to claim 1, characterized in that, In step three, the temperature of the open mill is 60-80℃, and the number of coiling times is 3-5.

9. The preparation method of the chemically grafted modified PBAT / EVA composite foam material according to claim 1, characterized in that, The hot-pressing temperature in step four is 170℃-190℃, the hot-pressing time is 10min-13min, and the pressure is 10MPa-20MPa.

10. A chemically grafted modified PBAT / EVA composite foam material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 9.

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