Full-degradable high-temperature-resistant foaming material

Abstract

The invention discloses a full-degradable high-temperature-resistant foaming material which comprises a low-density system, a medium-density system and a high-density system, the low-density system comprises the following components: stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, poly (butylene succinate), surface radiation modified straw fibers, talcum powder, nano clay and supercritical carbon dioxide; the medium-density system comprises the following components: stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, poly (butylene succinate), plasticized starch, an AC foaming agent, zinc oxide and citric acid; the high-density system comprises the following components: stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, polyhydroxybutyrate, surface radiation modified straw fibers, sodium bicarbonate and a DCP dynamic cross-linking agent. The full-degradable high-temperature-resistant foaming material provided by the invention has the advantages of high temperature resistance, good mechanical property, complete degradation and the like.

Description

Technical Field

[0001] The invention relates to the technical field of foaming materials, in particular to a fully degradable and high temperature resistant foaming material. Background Art

[0002] With the enhancement of environmental awareness and the promotion of the concept of sustainable development, the research and application of degradable materials have become a hot topic. As agricultural waste, it is of great significance to realize its resource utilization.

[0003] In the early days, the large-scale utilization of straw was mainly concentrated in papermaking, fuel or simple pressing of boards, etc. For example, the "Straw Steam Explosion Modification Processing Technology" jointly developed by the Chinese Academy of Sciences and Heze Lvlu Company in 2006 used high-temperature and high-pressure steam to achieve natural bonding of straw to produce fully degradable decorative boards, but did not solve the mechanical and temperature resistance problems of foaming materials.

[0004] In the 2010s, domestic and foreign attempts were made to compound straw with bio-based resins such as polylactic acid (PLA) and polybutylene succinate (PBS) to produce biodegradable foaming materials. For example, some people used PLA and straw fiber to compound and improved the interfacial bonding strength through plasma modification, but the temperature resistance was only 70-80°C, and the problem of continuous production was not solved. Some people used plasticized starch-based foaming technology to develop straw shoe trees, but its mechanical strength only met the needs of low-end packaging, and the temperature resistance was less than 60°C.

[0005] It can be seen that the current biodegradable foaming materials have many key technical bottlenecks. In terms of temperature resistance, traditional PLA-based materials soften and deform above 70°C, which cannot meet the needs of scenarios such as cold chain logistics (need to be above 90°C). In terms of interface compatibility, the straw fiber has a weak bonding force with the resin matrix, which causes the foam to crack easily and the compression strength is <100kPa. In terms of technology, the problems of chemical foaming agent residues (such as azodicarbonamide) and thermal degradation of fibers are prominent. These problems seriously limit the application scope and performance improvement of biodegradable foaming materials. Summary of the invention

[0006] In order to overcome the problems of insufficient temperature resistance, poor interface compatibility and uncontrollable process in existing degradable foaming materials, the present invention provides a fully degradable and high-temperature resistant foaming material. The fully degradable and high-temperature resistant foaming material has the advantages of high temperature resistance, good mechanical properties and complete degradation, and the preparation method can effectively solve the bottleneck of the prior art.

[0007] The technical solution of the present invention is as follows: The present invention provides a fully degradable and high temperature resistant foaming material, including a low-density system, a medium-density system and a high-density system; Calculated by weight parts, the low-density system comprises the following components: 35-45 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 30-40 parts of polybutylene succinate, 15-20 parts of straw fiber modified by surface radiation, 1-3 parts of talcum powder, 0.3-0.7 part of nano-clay, and 4-8 parts of supercritical carbon dioxide; Calculated by weight parts, the medium-density system comprises the following components: 35-45 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 40-50 parts of polybutylene succinate, 5-15 parts of plasticized starch, 2-6 parts of AC foaming agent, 0.3-0.7 part of zinc oxide, and 0.2-0.4 part of citric acid; Calculated by weight parts, the high-density system comprises the following components: 30-40 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 35-45 parts of polyhydroxybutyrate, 15-25 parts of straw fiber modified by surface radiation, 1-3 parts of sodium bicarbonate, and 0.2-0.4 part of DCP dynamic crosslinking agent.

[0008] Further, the density of the low-density system is 25 kg / m³, the density of the medium-density system is 50 kg / m³, and the density of the high-density system is 50 kg / m³.

[0009] Further, calculated by weight parts, the low-density system comprises the following components: 45 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 35 parts of polybutylene succinate, 15 parts of straw fiber modified by surface radiation, 2 parts of talcum powder, 0.5 part of nano-clay, and 6 parts of supercritical carbon dioxide.

[0010] Further, calculated by weight parts, the medium-density system comprises the following components: 40 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 45 parts of polybutylene succinate, 10 parts of plasticized starch, 4 parts of AC foaming agent, 0.5 part of zinc oxide, and 0.3 part of citric acid.

[0011] Further, calculated by weight parts, the high-density system comprises the following components: 35 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 40 parts of polyhydroxybutyrate, 20 parts of straw fiber modified by surface radiation, 2 parts of sodium bicarbonate, and 0.3 part of DCP dynamic crosslinking agent.

[0012] Further, the preparation method of the low-density system includes: Step A1, performing vacuum drying on the stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid; Step A2: Soak the straw fiber with NaOH solution, and then perform surface modification on the soaked straw fiber by electron beam radiation; Step A3: First premix the dried stereocomplex polylactic acid and talcum powder at 140 °C, then melt-blend them with polybutylene succinate and nano-clay at 170 °C, and finally add the surface-modified straw fiber in a side-feeding manner to form a polymer melt; Step A4: Use a supercritical carbon dioxide foaming system to foam the polymer melt, and pelletize the foamed polymer melt through the underwater pelletizing module of the supercritical carbon dioxide foaming system; Step A5: Cure the pelletized material in an environment of 45 °C and 20% humidity for 48 h, and modify the surface of the cured material particles by spraying PLA-g-MAH solution in a fluidized bed to form low-density foamed particles.

[0013] Further, in Step A3, the stereocomplex polylactic acid, talcum powder, polyhydroxybutyrate, nano-clay and the surface-modified straw fiber are kneaded for 90 s in a starved feeding mode by a co-rotating twin-screw extruder, and the surface-modified straw fiber is added from the side-feeding port of the co-rotating twin-screw extruder.

[0014] Further, in Step A4, when the supercritical CO2 foaming system foams, the pressure is controlled at 18 MPa, the saturation time is controlled at 4 h, the pressure relief rate is controlled at 120 MPa / s, and the cell density is controlled at 1.2×10 8 cells / cm³; when underwater pelletizing, the water temperature is controlled at 40 - 50 °C, the cutter speed is 3000 rpm, the particle size reaches 1 - 3 mm, the sphericity ≥ 0.85, and an anti-adhesion coating is formed by spraying 0.1% zinc stearate solution.

[0015] Further, the preparation method of the medium density system includes: Step B1: Perform vacuum drying on the stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid; Step B2: Premix starch and epoxidized soybean oil, and perform gradient temperature extrusion to form plasticized starch; Step B3: Add the dried stereocomplex polylactic acid, plasticized starch, polyhydroxybutyrate, AC foaming agent, zinc oxide and citric acid to a two-stage extruder in sequence, and perform the first-stage plasticization treatment and the second-stage foaming treatment in sequence to form a cell structure; Step B4: Perform underwater pelletizing on the cell structure; Step B5: Cure the foamed structure after pelletizing at 45°C and 20% humidity for 48 hours, and modify the surface of the cured foamed structure particles by spraying 0.5% PLA-g-MAH solution through a fluidized bed to form medium-density foamed particles.

[0016] Furthermore, the preparation method of the high-density system includes: Step C1: Vacuum dry the stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid. Step C2: Immerse the straw fiber in NaOH solution, then modify the surface of the immersed straw fiber by electron beam radiation, spray 1% silane coupling agent on its surface, and finally control the length of the treated straw fiber to 300 - 500 μm. Step C3: Pre-crystallize polyhydroxybutyrate at 100°C for 2 hours. Step C4: First, put the dried stereocomplex polylactic acid, pre-crystallized polyhydroxybutyrate, treated straw fiber, sodium bicarbonate and DCP dynamic cross-linking agent into a mixer for mixing and kneading, and then extrude the kneaded material through a single-screw extrusion foaming machine to form a foamed structure. Step C5: Underwater pelletize the foamed structure. Step C6: Cure the foamed structure after pelletizing at 45°C and 20% humidity for 48 hours, and modify the surface of the cured foamed structure particles by spraying PLA-g-MAH solution through a fluidized bed to form high-density foamed particles.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By adopting different component combinations and modification means in different density systems, the heat distortion temperature of the material is greatly improved; among them, the heat distortion temperature of the low-density system can reach 90°C - 100°C, the medium-density system can reach 95°C - 105°C, and the high-density system exceeds 100°C, far exceeding the 70 - 80°C of traditional PLA-based materials, meeting the requirements of high-temperature scenarios such as cold chain logistics; in the low-density system, after the stereocomplex polylactic acid is crystallized and modified with talcum powder and nanoclay, and then combined with the polybutylene succinate cross-linking network, the thermal stability is improved; in the medium-density system, high temperature resistance is achieved through the synergistic effect of the stereocomplex polylactic acid and other components; in the high-density system, polyhydroxybutyrate is used to replace part of the stereocomplex polylactic acid, combined with the characteristics of the stereocomplex polylactic acid itself to improve the heat resistance, so that the foamed material can meet the application scenarios with strict requirements for high temperature resistance such as cold chain logistics and high-temperature industrial packaging. 3. In the low-density system and the high-density system, on the premise of ensuring the material properties, the weight fraction of straw fiber is increased to 15-25 parts (the weight fraction of straw fiber in traditional PLA-based materials is less than 10 parts), and the amount of polylactic acid is reduced to 30-45 parts (the weight fraction of polylactic acid in traditional PLA-based materials is 50-70 parts). The comprehensive cost is reduced by about 30%. Moreover, straw, as agricultural waste, is efficiently utilized, which not only reduces the raw material cost but also realizes the recycling of resources, meeting the concept of sustainable development. 4. In the low-density system and the high-density system, the straw fiber is modified by electron beam radiation (replacing traditional alkali treatment), forming active free radicals on the fiber surface, which form covalent bonds with PLA and PBS, enabling the interfacial shear strength to be increased by more than 50%. By increasing the weight fraction of straw fiber to 15-20 parts (the weight fraction of straw fiber in traditional PLA-based materials is less than 10 parts) and reducing the amount of polylactic acid to 35-45 parts (the weight fraction of polylactic acid in traditional PLA-based materials is 50-70 parts), the comprehensive cost can be reduced by about 30%. 5. The low-density system avoids the problem of chemical blowing agent residues (no harmful substances such as formamide are detected) through supercritical carbon dioxide physical foaming technology, meets the food contact-grade packaging standard, and has good pore size uniformity (CV≤8%), enabling precise control of the cell structure and improving the material properties. 6. In the low-density system, the melt blending and dynamic crosslinking of stereocomplex polylactic acid and straw fiber are synchronously completed by a co-rotating twin-screw extruder, and in the high-density system, the straw dispersion, PLA and PBS melting, and DCP crosslinking reaction are synchronously completed in a mixer using a dynamic crosslinking blending process. The process time is shortened to 1 / 3 of the traditional step-by-step method, improving the production efficiency. Detailed implementation manners

[0018] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention will be further described in detail below.

[0019] It should be noted that the terms "comprising" and "having" in the specification and claims of the present invention and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally further includes steps or units not listed, or optionally further includes other steps or units inherent to these processes, methods, products or devices.

[0020] An embodiment of the present invention provides a fully degradable and high temperature resistant foaming material, including a low-density system, a medium-density system and a high-density system. The density of the low-density system is 25kg / m³, the density of the medium-density system is 50kg / m³, and the density of the high-density system is 50kg / m³.

[0021] In the embodiment of the present invention, the low-density system includes the following components, calculated by weight: 35-45 parts of stereocomposite polylactic acid formed by mixing poly-L-lactic acid (PLLA) and poly-D-lactic acid (PDLA), 30-40 parts of polybutylene succinate, 15-20 parts of surface radiation-modified straw fiber, 1-3 parts of talcum powder, 0.3-0.7 parts of nanoclay, and 4-8 parts of supercritical carbon dioxide. Among them, the stereocomposite polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid is used to improve crystallinity and thermal stability, polybutylene succinate is used for toughening and compensating for strength loss, surface radiation-modified straw fiber is used to enhance the mechanical properties of the material, talcum powder and nanoclay are used to improve material properties, and supercritical carbon dioxide is used as a physical foaming agent.

[0022] The preparation method of the low-density system comprises the following steps: Step A1, vacuum drying the stereocomposite polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid at 80°C to make its moisture content ≤0.02%; this step can remove moisture from the stereocomposite polylactic acid to prevent bubbles from being generated during processing or polymer hydrolysis from occurring due to moisture evaporation, thereby affecting material properties.

[0023] Step A2, soaking the straw fiber in 2% NaOH solution for 4 hours, and then surface modifying the soaked straw fiber by 5 kGy electron beam radiation to form active free radicals on the fiber surface; in this step, the NaOH solution treatment can remove impurities and part of the lignin on the surface of the straw fiber, increase the surface roughness and active groups, and the radiation modification further enhances the hydrogen bonding effect between the electron beam radiation and the stereocomplex polylactic acid and polybutylene succinate, and the contact angle is reduced to 65°, thereby enhancing the interfacial bonding force.

[0024] Step A3: First, premix the dried stereocomplex poly(lactic acid) and talc at 140 °C for 10 min to evenly disperse the talc in the stereocomplex poly(lactic acid), enhancing the rigidity and dimensional stability of the material. Then, melt-blend it with poly(butylene succinate) and nanoclay at 170 °C to increase the crystallinity of the material to ≥40%. Finally, add the surface-modified straw fiber in a side-feeding manner to form a polymer melt. Specifically, in this step, the stereocomplex poly(lactic acid), talc, polyhydroxybutyrate, nanoclay, and surface-modified straw fiber are kneaded for 90 s through the starved feeding mode (feeding rate ≤70%) of a co-rotating twin-screw extruder. The surface-modified straw fiber is added from the side-feeding port of the co-rotating twin-screw extruder to avoid high-temperature degradation of the straw fiber. The starved feeding mode of the co-rotating twin-screw extruder allows the materials to be fully mixed in the screw, ensuring uniform dispersion of each component and improving the material properties. The melt-blending and dynamic cross-linking of the stereocomplex poly(lactic acid) and straw fiber are completed synchronously by the co-rotating twin-screw extruder, and the process time can be shortened to 1 / 3 of the traditional step-by-step method.

[0025] Step A4: Use a supercritical carbon dioxide foaming system to foam the polymer melt and pelletize the foamed polymer melt through the underwater pelletizing module of the supercritical carbon dioxide foaming system. Specifically, in this step, when the supercritical CO2 foaming system foams, the pressure is controlled at 18 MPa, the saturation time is controlled at 4 h, and the pressure relief rate is controlled at 120 MPa / s. The supercritical carbon dioxide dissolves in the polymer melt under high pressure. When the pressure rapidly decreases, the supercritical carbon dioxide escapes to form uniformly distributed pores, and the pore density is controlled at 1.2×10 8 cells / cm³. When underwater pelletizing, the water temperature is controlled at 40 - 50 °C, the cutter speed is 3000 rpm, the particle size reaches 1 - 3 mm, the sphericity is ≥0.85, and a 0.1% zinc stearate solution is sprayed to form an anti-sticking coating to prevent the agglomeration of the pelletized materials.

[0026] Step A5: First, cure the pelletized materials in an environment at 45 °C and 20% humidity for 48 h, which can eliminate the internal stress of the material, increase the rebound rate by 20%, stabilize the material properties, and improve the dimensional stability. Then, modify the surface of the cured material particles by spraying a 0.5% PLA-g-MAH solution through a fluidized bed to improve the fluidity and molding properties of the particles, facilitating subsequent processing into various products, and finally forming low-density foamed particles.

[0027] The above method for preparing a low-density system can raise the heat distortion temperature (HDT) of the material to 90°C - 100°C by crystallizing and modifying stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid with talcum powder and nano-clay, and then combining it with a polybutylene succinate cross-linked network, far exceeding that of traditional PLA-based materials (70 - 80°C), breaking through the temperature resistance bottleneck of PLA, and realizing the application of fully degradable materials in high-temperature scenarios; the straw fiber is modified by electron beam radiation (replacing traditional alkali treatment) to form active free radicals on the fiber surface, which form covalent bonds with PLA and PBS, reducing the water absorption rate of the material while increasing the interfacial shear strength; by increasing the weight fraction of straw fiber to 15 - 20 parts (the weight fraction of straw fiber in traditional PLA-based materials is less than 10 parts) and reducing the amount of polylactic acid to 35 - 45 parts (the weight fraction of polylactic acid in traditional PLA-based materials is 50 - 70 parts), the comprehensive cost can be reduced by about 30%; the supercritical carbon dioxide physical foaming technology avoids the problem of residual chemical foaming agents (zero detection of harmful substances such as formamide), meets the food contact grade packaging standard, and has good pore size uniformity (CV ≤ 8%), can accurately control the cell structure, making the closed cell rate of the material ≥ 95% and the water absorption rate ≤ 2% (ASTM D570 test method), improving the material properties.

[0028] In the embodiment of the present invention, calculated by weight, the medium-density system includes the following components: 35 - 45 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 40 - 50 parts of polybutylene succinate, 5 - 15 parts of plasticized starch, 2 - 6 parts of AC blowing agent, 0.3 - 0.7 parts of zinc oxide, and 0.2 - 0.4 parts of citric acid. Among them, the stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid is used to improve the crystallinity and thermal stability, polybutylene succinate is used to toughen and compensate for the strength loss, starch replaces part of poly-L-lactic acid to reduce the cost, the AC blowing agent is used for foaming, and zinc oxide and citric acid form a compound system to reduce the decomposition temperature of the AC blowing agent (from 210°C to 160°C), reducing the risk of polylactic acid thermal degradation.

[0029] Among them, the preparation method of the medium-density system includes: Step B1: Vacuum-dry the stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid at 80°C to make its moisture content ≤ 0.02%; Step B2: First, pre-mix starch with 3% epoxidized soybean oil in a mixer at a rotational speed of 800 rpm for 5 minutes. The epoxidized soybean oil serves as a plasticizer, reducing the water absorption rate of starch from 12% to 5% and forming a coating structure to improve the compatibility between starch and other polymers, enhancing the processing performance and mechanical properties of the material. Then, extrude the coated structure by gradually increasing the temperature according to 135°C in the feeding section, 165°C in the kneading section, and 150°C in the die head section to form plasticized starch. By means of gradually increasing the temperature for extrusion, carbonization of starch can be prevented.

[0030] Step B3: Add the dried stereocomplex poly(lactic acid), plasticized starch, polyhydroxybutyrate, AC blowing agent, zinc oxide, and citric acid to a twin-screw extruder in sequence, and conduct the first-stage plasticization treatment and the second-stage foaming treatment in sequence to form a cell structure. When the twin-screw extruder is conducting the first-stage plasticization treatment, the temperature control is at 150°C to preliminarily melt and mix the raw materials. When conducting the second-stage foaming treatment, the temperature is controlled at 145°C, and the screw speed ratio is 1:2.5 to avoid premature foaming and ensure that the AC blowing agent decomposes at a suitable temperature to generate uniform cells.

[0031] Step B4: Conduct underwater pelletizing on the cell structure. Specifically, during underwater pelletizing, the water temperature is controlled at 40 - 50°C, and the cutter speed is 3000 rpm to make the particle size reach 1 - 3 mm, with a sphericity ≥ 0.85, and spray a 0.1% zinc stearate solution to form an anti-adhesion coating to prevent the agglomeration of the pelletized material.

[0032] Step B5: First, cure the pelletized cell structure in an environment of 45°C and 20% humidity for 48 hours, which can eliminate the internal stress of the material, increase the rebound rate by 20%, stabilize the material performance, and improve the dimensional stability. Then, modify the surface of the cured cell structure particles by spraying a 0.5% PLA-g-MAH solution through a fluidized bed to enhance the fluidity and molding property of the particles, facilitating subsequent processing into various products, and finally forming medium-density foamed particles.

[0033] In the above preparation method of the medium-density system, through the synergistic effect of the stereocomplex poly(lactic acid) formed by mixing poly(L-lactic acid) and poly(D-lactic acid) with other components, the heat distortion temperature (HDT) of the material can be increased to 95°C - 105°C, far exceeding that of traditional PLA-based materials (70 - 80°C), breaking through the temperature resistance bottleneck of PLA and realizing the application of fully biodegradable materials in high-temperature scenarios; by replacing part of the poly(L-lactic acid) with starch, the raw material cost is reduced on the premise of ensuring the basic performance of the material; by using a compound system composed of zinc oxide and citric acid, the decomposition temperature of the AC blowing agent is reduced from 210°C to 160°C. Combining with the temperature and screw speed control of the twin-screw extruder, premature foaming is avoided, ensuring that the AC blowing agent decomposes at 145°C during the second-stage foaming treatment to generate uniform cells and improving the foaming quality.

[0034] In the embodiments of the present invention, calculated by weight parts, the high-density system comprises the following components: 30-40 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 35-45 parts of polyhydroxybutyrate, 15-25 parts of surface-radiation-modified straw fiber, 1-3 parts of sodium bicarbonate, and 0.2-0.4 parts of DCP dynamic crosslinking agent. Among them, the stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid is used to improve the crystallinity and thermal stability. Polyhydroxybutyrate (with a melting point of 175°C) replaces part of the stereocomplex polylactic acid, significantly improving the temperature resistance of the material to above 100°C. The surface-radiation-modified straw fiber is used to enhance the mechanical properties of the material. Sodium bicarbonate serves as a foaming agent. The DCP dynamic crosslinking agent is used to initiate crosslinking reactions, construct a three-dimensional network structure, and enhance the comprehensive properties of the material.

[0035] Among them, the preparation method of the high-density system includes: Step C1: Vacuum-dry the stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid at 80°C to make its moisture content ≤ 0.02%. This step can prevent the generation of bubbles or polymer hydrolysis due to water vaporization during processing, which may affect the material properties by removing the moisture in the stereocomplex polylactic acid.

[0036] Step C2: First, soak the straw fiber in 2% NaOH solution for 4 h, then perform surface modification on the soaked straw fiber by 5 kGy electron beam radiation to form active free radicals on the fiber surface, and spray 1% silane coupling agent on its surface to improve the compatibility with polyhydroxybutyrate. Finally, control the length of the treated straw fiber to 300-500 μm to facilitate its uniform distribution under the shearing and heating of the internal mixer and enhance the material properties. In this step, the treatment with NaOH solution can remove the surface impurities and part of the lignin of the straw fiber, increase the surface roughness and active groups, while the radiation modification further enhances the hydrogen bond interaction between the electron beam radiation and the stereocomplex polylactic acid and polybutylene succinate, reducing the contact angle to 65° and enhancing the interfacial bonding force.

[0037] Step C3: Pre-crystallize polyhydroxybutyrate at 100°C for 2 h. Pre-crystallization can make the molecular chains of polyhydroxybutyrate more regular, improve the melt strength (from 15 kPa·s to 28 kPa·s), facilitate maintaining the shape stability of the material during subsequent processing, and prevent deformation or collapse during the foaming and molding processes.

[0038] Step C4: First, put the dried stereocomplex polylactic acid, pre-crystallized polyhydroxybutyrate, treated straw fiber, sodium bicarbonate, and DCP dynamic cross-linking agent into a mixer for mixing and kneading. During the kneading process, the raw materials are fully mixed under the action of high temperature and mechanical shear force, and the dispersion degree of the straw fiber is ≥88%; then, the kneaded material is extruded through a single-screw extrusion foaming machine to form a cell structure; among them, when the mixer works, the kneading temperature is controlled at 170 °C, the kneading time is controlled at 8 min, the DCP dynamic cross-linking agent is injected at the end of the melting section, and the residence time is ≤15 s. The DCP dynamic cross-linking agent initiates a cross-linking reaction at 170 °C to form a three-dimensional network structure. When the single-screw extrusion foaming machine works, it is extruded according to the temperature gradient of 155 °C - 160 °C - 145 °C, and the die head pressure is controlled at 10 MPa; the setting of the temperature gradient of the single-screw extrusion foaming machine can not only ensure the full plasticization and mixing of the material during extrusion, but also control the decomposition rate of the foaming agent and the formation of cells, and the 10 MPa die head pressure helps to maintain the stability of the cell structure, so that the final product has a uniform cell distribution and good appearance quality.

[0039] Step C5: Carry out underwater pelletizing on the cell structure. Specifically, during underwater pelletizing, the water temperature is controlled at 40 - 50 °C, the cutter speed is 3000 rpm, so that the particle size reaches 1 - 3 mm, the sphericity is ≥0.85, and a 0.1% zinc stearate solution is sprayed to form an anti-sticking coating to prevent the material after pelletizing from sticking.

[0040] Step C6: First, cure the pelletized cell structure in an environment of 45 °C and 20% humidity for 48 h, which can eliminate the internal stress of the material, increase the resilience rate by 20%, stabilize the material properties, and improve the dimensional stability; then, modify the surface of the cured cell structure particles by spraying 0.5% PLA-g-MAH solution through a fluidized bed to improve the fluidity and molding property of the particles, facilitate subsequent processing into various products, and finally form high-density foamed particles.

[0041] The above-mentioned high-density system preparation method, by replacing part of the stereocomposite polylactic acid with polyhydroxybutyrate (melting point 175°C), combined with the role of stereocomposite polylactic acid in improving crystallinity and thermal stability, greatly improves the temperature resistance of the material to above 100°C, far exceeding the traditional PLA-based materials (70-80°C), breaking through the temperature resistance bottleneck of PLA, and realizing the application of fully degradable materials in high-temperature scenarios; the mechanical properties of the straw fiber reinforced material modified by surface radiation, and the construction of a three-dimensional network structure by the cross-linking reaction initiated by the DCP dynamic cross-linking agent, enhance the comprehensive mechanical properties of the material such as tensile strength, compressive strength and wear resistance The performance makes the compression strength of the high-density system reach 280-320kPa, which can withstand greater pressure and is suitable for products with strict strength requirements; by increasing the weight of straw fiber to 15-25 parts (the weight of straw fiber in traditional PLA-based materials is less than 10 parts), the amount of polylactic acid is reduced to 30-40 parts (the weight of polylactic acid in traditional PLA-based materials is 50-70 parts), and the overall cost can be reduced by about 30%; straw dispersion, PLA and PBS melting, and DCP cross-linking reaction are completed simultaneously in the internal mixer, and the process time is shortened to 1 / 3 of the traditional step-by-step method.

[0042] In a specific embodiment of the present invention, the low-density system includes the following components, calculated by weight: 45 parts of a stereocomplex polylactic acid formed by a mixture of poly-L-lactic acid and poly-D-lactic acid, 35 parts of polybutylene succinate, 15 parts of surface radiation-modified straw fibers, 2 parts of talc, 0.5 parts of nanoclay, and 6 parts of supercritical carbon dioxide.

[0043] Calculated by weight, the medium density system includes the following components: 40 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 45 parts of polybutylene succinate, 10 parts of plasticized starch, 4 parts of AC foaming agent, 0.5 parts of zinc oxide, and 0.3 parts of citric acid.

[0044] Calculated by weight, the high-density system includes the following components: 35 parts of stereocomposite polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 40 parts of polyhydroxybutyrate, 20 parts of surface radiation-modified straw fiber, 2 parts of sodium bicarbonate, and 0.3 parts of DCP dynamic crosslinking agent.

[0045] The performance of the low-density system, medium-density system and high-density system of the above embodiment is tested in terms of compression strength, rebound rate, energy absorption, heat deformation temperature, heat deformation temperature and degradation cycle. The results are shown in Table 1.

[0046] Table 1 Performance test results As can be seen from the above table, the fully degradable and high temperature resistant foaming material of this embodiment has the advantages of high temperature resistance, good mechanical properties, and complete degradation, which effectively solves the problems existing in the prior art, has good application prospects, and can be applied to cold chain logistics packaging and precision instrument buffering. Among them, cold chain logistics packaging: temperature resistance ≥90℃, resistance to condensation water erosion (water absorption rate of low-density system ≤2%), replacing EPS insulation box; precision instrument buffer: compression strength gradient design (80-300kPa), energy absorption efficiency is higher than EPE pearl cotton.

[0047] In another specific embodiment of the present invention, the low-density system includes the following components, calculated by weight: 35 parts of stereocomplex polylactic acid formed by a mixture of poly-L-lactic acid and poly-D-lactic acid, 30 parts of polybutylene succinate, 15 parts of surface radiation-modified straw fibers, 1 part of talc, 0.3 parts of nanoclay, and 4 parts of supercritical carbon dioxide.

[0048] Calculated by weight, the medium density system includes the following components: 35 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 40 parts of polybutylene succinate, 5 parts of plasticized starch, 2 parts of AC foaming agent, 0.3 parts of zinc oxide, and 0.2 parts of citric acid.

[0049] Calculated by weight, the high-density system includes the following components: 30 parts of stereocomposite polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 35 parts of polyhydroxybutyrate, 15 parts of surface radiation-modified straw fibers, 1 part of sodium bicarbonate, and 0.2 parts of DCP dynamic crosslinking agent.

[0050] In another specific embodiment of the present invention, the low-density system includes the following components, calculated by weight: 45 parts of stereocomplex polylactic acid formed by a mixture of poly-L-lactic acid and poly-D-lactic acid, 40 parts of polybutylene succinate, 20 parts of surface radiation-modified straw fibers, 3 parts of talc, 0.7 parts of nanoclay, and 8 parts of supercritical carbon dioxide.

[0051] Calculated by weight, the medium density system includes the following components: 45 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 50 parts of polybutylene succinate, 15 parts of plasticized starch, 6 parts of AC foaming agent, 0.7 parts of zinc oxide, and 0.4 parts of citric acid.

[0052] Calculated by weight, the high-density system includes the following components: 40 parts of stereocomposite polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 45 parts of polyhydroxybutyrate, 25 parts of surface radiation-modified straw fibers, 3 parts of sodium bicarbonate, and 0.4 parts of DCP dynamic crosslinking agent.

[0053] It should be understood that those of ordinary skill in the art can make modifications or transformations based on the above description, and all such modifications and transformations shall fall within the protection scope of the appended claims of the present invention.

[0054] The above has given an exemplary description of the present invention patent. Obviously, the implementation of the present invention patent is not limited by the above-mentioned manner. As long as various modifications are made by adopting the method concept and technical solution of the present invention patent, or the concept and technical solution of the present invention patent are directly applied to other occasions without modification, they are all within the protection scope of the present invention.

Claims

1. A fully degradable and high temperature resistant foaming material, characterized in that: Including low-density system, medium-density system and high-density system; The low-density system comprises the following components, calculated by weight: 35-45 parts of stereocomposite polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 30-40 parts of polybutylene succinate, 15-20 parts of surface radiation-modified straw fiber, 1-3 parts of talc, 0.3-0.7 parts of nanoclay, and 4-8 parts of supercritical carbon dioxide; The medium density system comprises the following components calculated by weight: 35-45 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 40-50 parts of polybutylene succinate, 5-15 parts of plasticized starch, 2-6 parts of AC foaming agent, 0.3-0.7 parts of zinc oxide, and 0.2-0.4 parts of citric acid; Calculated by weight, the high-density system includes the following components: 30 to 40 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 35 to 45 parts of polyhydroxybutyrate, 15 to 25 parts of surface radiation-modified straw fibers, 1 to 3 parts of sodium bicarbonate, and 0.2 to 0.4 parts of DCP dynamic crosslinking agent.

2. The fully degradable and high temperature resistant foaming material according to claim 1, characterized in that: The density of the low-density system is 25kg / m³, the density of the medium-density system is 50kg / m³, and the density of the high-density system is 50kg / m³.

3. The fully degradable and high temperature resistant foaming material according to claim 1, characterized in that: Calculated by weight, the low-density system includes the following components: 45 parts of stereocomposite polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 35 parts of polybutylene succinate, 15 parts of surface radiation-modified straw fiber, 2 parts of talc, 0.5 parts of nanoclay, and 6 parts of supercritical carbon dioxide.

4. The fully degradable and high temperature resistant foaming material according to claim 1, characterized in that: Calculated by weight, the medium density system includes the following components: 40 parts of stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 45 parts of polybutylene succinate, 10 parts of plasticized starch, 4 parts of AC foaming agent, 0.5 parts of zinc oxide, and 0.3 parts of citric acid.

5. The fully degradable and high temperature resistant foaming material according to claim 1, characterized in that: Calculated by weight, the high-density system includes the following components: 35 parts of stereocomposite polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid, 40 parts of polyhydroxybutyrate, 20 parts of surface radiation-modified straw fibers, 2 parts of sodium bicarbonate, and 0.3 parts of DCP dynamic crosslinking agent.

6. The fully degradable and high temperature resistant foaming material according to claim 1, characterized in that: The preparation method of the low-density system comprises: Step A1, vacuum drying the stereocomplex polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid; Step A2, soaking the straw fibers with a NaOH solution, and then performing surface modification on the soaked straw fibers by electron beam radiation; Step A3, premixing the dried stereocomposite polylactic acid with talc at 140° C., then melt-blending with polybutylene succinate and nanoclay at 170° C., and finally adding the surface-modified straw fiber by side feeding to form a polymer melt; Step A4, foaming the polymer melt using a supercritical carbon dioxide foaming system, and pelletizing the foamed polymer melt using an underwater pelletizing module of the supercritical carbon dioxide foaming system; Step A5, ripening the pelletized material at 45° C. and 20% humidity for 48 h, and modifying the surface of the ripened material particles by spraying PLA-g-MAH solution on a fluidized bed to form low-density foamed particles.

7. The fully degradable and high temperature resistant foaming material according to claim 6, characterized in that: In step A3, stereocomposite polylactic acid, talc, polyhydroxybutyrate, nanoclay and surface-modified straw fibers are mixed for 90 seconds by the starvation feeding mode of the co-rotating twin-screw extruder, wherein the surface-modified straw fibers are added from the side feeding port of the co-rotating twin-screw extruder.

8. The fully degradable and high temperature resistant foaming material according to claim 6, characterized in that: In step A4, when the supercritical CO2 foaming system is foaming, the pressure is controlled to 18 MPa, the saturation time is controlled to 4 h, the pressure release rate is controlled to 120 MPa / s, and the cell density is controlled to 1.2×10 8 cells / cm³; during underwater pelletizing, the water temperature is controlled at 40-50℃, the cutter speed is 3000rpm, the particle size reaches 1-3mm, the sphericity is ≥0.85, and 0.1% zinc stearate solution is sprayed to form an anti-adhesion coating.

9. The fully degradable and high temperature resistant foaming material according to claim 1, characterized in that: The preparation method of the medium density system comprises: Step B1, vacuum drying the stereocomposite polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid; Step B2, premixing starch and epoxidized soybean oil, and extruding them by gradient heating to form plasticized starch; Step B3, adding the dried stereocomposite polylactic acid, plasticized starch, polyhydroxybutyrate, AC foaming agent, zinc oxide and citric acid to a two-stage extruder in sequence, and performing a first-stage plasticizing treatment and a second-stage foaming treatment in sequence to form a cellular structure; Step B4, underwater pelletizing the cell structure; Step B5, ripening the pelletized cell structure at 45° C. and 20% humidity for 48 h, and modifying the surface of the ripened cell structure particles by spraying 0.5% PLA-g-MAH solution on a fluidized bed to form medium-density foamed particles.

10. The fully degradable and high temperature resistant foaming material according to claim 1, characterized in that: The preparation method of the high-density system comprises: Step C1, vacuum drying the stereocomposite polylactic acid formed by mixing poly-L-lactic acid and poly-D-lactic acid; Step C2, soaking the straw fiber with a NaOH solution, then surface-modifying the soaked straw fiber by electron beam radiation, spraying a silane coupling agent on the surface, and finally controlling the length of the treated straw fiber to 300-500 μm; Step C3, pre-crystallizing the polyhydroxybutyrate at 100° C. for 2 hours; Step C4, firstly put the dried stereocomposite polylactic acid, pre-crystallized polyhydroxybutyrate, treated straw fiber, sodium bicarbonate and DCP dynamic crosslinking agent into an internal mixer for mixing and kneading, and then extrude the kneaded materials through a single screw extruder foaming integrated machine to form a cellular structure; Step C5, performing underwater pelletizing on the cell structure; Step C6, ripening the pelletized cellular structure at 45° C. and 20% humidity for 48 hours, and modifying the surface of the ripened cellular structure particles by spraying PLA-g-MAH solution in a fluidized bed to form high-density foamed particles.