A method for preparing degradable flame-retardant foam beads

Abstract

The present invention discloses a method for preparing degradable flame-retardant foam beads, belonging to the technical field of degradable foam materials. The present invention forms a base material by melt-blending PLA and PBAT, constructs a micro-crosslinked network structure in combination with a modified chain extender and a flame retardant, and adopts a supercritical carbon dioxide foaming process to prepare the foam beads. The present invention synthesizes a branched chain extender body by reacting bio-based polyisocyanate with glycyrrhetinic acid, forms a composite chain extension system by nanorectorite loading, strengthens the interaction force between molecular chains and improves the compatibility of the flame retardant. The chain extender can accelerate the overall biodegradation of the foam beads, and the nanorectorite layered structure forms a phosphorus-silicon synergistic flame retardant mechanism with the phosphorus-based flame retardant, and generates a dense silicate carbon layer during combustion to inhibit free radical reactions. The flame retardant is uniformly dispersed by extrusion, and a fine closed-cell structure is formed by supercritical carbon dioxide foaming combined with gradient aging. The foam beads obtained have the characteristics of biodegradability and uniform and dense pores.

Description

Technical Field

[0001] The invention belongs to the technical field of degradable foaming materials, and in particular relates to a method for preparing degradable flame-retardant foaming beads. Background Art

[0002] The widespread use of traditional petroleum-based plastics has brought tremendous convenience to modern industrial production and daily life. Petroleum-based plastics such as polyethylene, polypropylene, and polystyrene, with their excellent processing properties and diverse applications, have penetrated numerous fields, including packaging, building materials, and electronics. However, due to their resistance to degradation, these plastic products are gradually accumulating as solid waste that pollutes soil and water bodies. At the same time, global oil reserves are becoming increasingly depleted. As a non-renewable resource, the uncertain and limited supply of oil has led to a growing interest in raw materials derived from renewable sources. Against this backdrop, PLA (polylactic acid) has emerged as a fully biodegradable and environmentally friendly material. Made from renewable plant resources such as corn and cassava, PLA boasts significant advantages such as environmental friendliness, full biodegradability, and food contact safety, demonstrating its enormous potential for application in areas such as environmentally friendly packaging and biomedical materials.

[0003] With the booming express delivery industry, demand for foam beads in applications such as cushioning and packaging has skyrocketed. PLA foam beads, with their advantages in compression molding to create foam products in various shapes and their environmentally friendly biodegradable properties, have become an ideal alternative to traditional foam materials. However, PLA itself has significant drawbacks. Its brittleness and poor tensile strength significantly limit its widespread use in a wider range of applications. To address this, the use of other monomers in PLA production for co-polymerization and foaming has emerged as a solution. This approach maximizes PLA's inherent environmental benefits while effectively improving the impact resistance and toughness of PLA foam materials.

[0004] Although copolymerization and foaming have improved some of PLA's properties to a certain extent, PLA's shortcomings of high flammability and poor heat resistance continue to seriously hinder its further application. Given the growing market demand for PLA foam beads, the development of flame-retardant PLA foam beads is particularly necessary. Currently, PLA foam beads primarily achieve flame retardancy by adding various flame retardant compounds. However, while this additive approach imparts excellent flame retardancy, the poor compatibility of the flame retardant compounds with the PLA substrate negatively impacts the foam's mechanical properties. Furthermore, over time, the additives migrate, resulting in a decrease in the foam's flame retardancy. This presents a significant obstacle to the development of flame-retardant PLA foam beads. Summary of the Invention

[0005] In view of the above situation, in order to overcome the defects of the prior art, the present invention prepares a foaming bead with the advantages of safe raw materials, non-toxicity, biodegradability and flame retardancy.

[0006] In order to achieve the above object, the following technical solution is adopted: The present invention provides a method for preparing degradable flame retardant foam beads, comprising the following steps:

[0007] S1. PLA and PBAT were pre-mixed in proportion, added to a twin-screw extruder for melt blending, the melt temperature was controlled at 170-190° C., the screw speed was 200-300 rpm, and extrusion granulation was performed to obtain a PLA / PBAT blend base material;

[0008] S2. Add PLA / PBAT blend base, modified chain extender, and flame retardant into a high-speed mixer, and add antioxidant and nucleating agent at the same time, and mix well;

[0009] S3. Use a twin-screw extruder for secondary blending, with the temperature zones being 160°C in the feed section, 175-185°C in the melting section, and 170°C in the die head, and the screw speed being 150-200 rpm, and extrusion granulation is performed to obtain foamable masterbatch;

[0010] S4, placing the foamable masterbatch in a high-pressure reactor, injecting supercritical carbon dioxide as a foaming agent, and foaming;

[0011] S5. Place the foamed beads in a steam box, mature them by gradient heating, and vacuum dry them after maturation to obtain the degradable flame-retardant foamed beads.

[0012] The modified chain extender is prepared by the following steps: under nitrogen protection, glycyrrhetinic acid, bio-based polyisocyanate and DMF are mixed, the temperature is raised to 70°C, an amine catalyst is added dropwise, and the reaction is carried out at a constant temperature for 4-6 hours, and then the nanorectorite powder is added to the reaction solution in multiple times. After each addition, ultrasonic dispersion is performed at 40kHz for 15 minutes. After all the addition is completed, mechanical stirring is continued at 500rpm for 1 hour to ensure that the nanoparticles are evenly dispersed. The reaction solution is then evaporated to remove the solvent, and 10 times the volume of petroleum ether is added. The solid is stirred to precipitate, and the solid is collected by centrifugation and washed twice with cold petroleum ether to obtain the modified chain extender.

[0013] The mass ratio of the glycyrrhetinic acid, bio-based polyisocyanate, amine catalyst, nano-rectorite powder and DMF is 70-100:15-25:0.05-0.5:1.5-4.5:100-200.

[0014] In the preparation of the modified chain extender, glycyrrhetinic acid is reacted with bio-based polyisocyanate to generate a branched chain extender, whose molecular chain contains both hydrophobic fused rings and degradable ester bonds, replacing traditional petroleum-based chain extenders. The ester bonds in the chain extender can be preferentially degraded by microbial action, thereby increasing the overall degradation rate of the material.

[0015] Furthermore, the PLA and PBAT are premixed at a mass ratio of 50-70:30-50.

[0016] Furthermore, the addition amount of the modified chain extender is 5-10wt% of the PLA / PBAT blend base material, the addition amount of the flame retardant is 15-25wt% of the PLA / PBAT blend base material, and the addition amount of the antioxidant is 0.5-2wt% of the PLA / PBAT blend base material.

[0017] Furthermore, the bio-based polyisocyanate is one of 1,5-pentane diisocyanate or L-lysine diisocyanate.

[0018] Among them, 1,5-pentamethylene diisocyanate (PDI) is a new type of aliphatic diisocyanate, also known as "pentamethylene diisocyanate". It is an isocyanate whose raw materials are derived from biomass (such as corn straw). It has high reactivity and environmental advantages.

[0019] L-lysine diisocyanate (LDI), an amino acid derivative, is biocompatible and easily degradable.

[0020] Furthermore, the amine catalyst is one of ethylenediamine, triethylenetetramine or diethanolamine.

[0021] Furthermore, the flame retardant is a combination of one or more of dimethyl methylphosphonate, trishydroxymethylphosphine oxide, DOPO, triphenyl phosphate, diethyl aluminum phosphinate or ammonium polyphosphate.

[0022] The flame retardant used in the present invention is a phosphorus-containing flame retardant. Through the synergistic effect of nanorectorite and phosphorus-based flame retardants, a phosphorus-silicon synergistic flame retardant effect is formed. The nanorectorite layered structure forms a dense silicate carbon layer during combustion, and its surface hydroxyl groups react with the phosphorus-based flame retardant to form a phosphate-silicon glassy substance, which inhibits free radical chain reactions and plays a multiple flame retardant role.

[0023] Furthermore, the antioxidant is a combination of one or more of antioxidant 1010, antioxidant 168, antioxidant 1076 or antioxidant 1098.

[0024] Furthermore, the nucleating agent is one of talc powder and nano-silicon dioxide, and the particle size of the nucleating agent is 50-200 nm.

[0025] Furthermore, the immersion pressure in the foaming step is 10-12 MPa, the immersion temperature is 45-55° C., the immersion time is 3-4 hours, and the injection rate of the supercritical carbon dioxide is 5-8 kg / h.

[0026] Furthermore, the specific steps of the gradient temperature aging are: the temperature is maintained at 80-90°C for 5-10 minutes at the initial stage, then the temperature is increased to 110°C at a rate of 2°C / min, the pressure is increased from 0.1MPa to 0.3MPa, and maintained at 110°C for 15-20 minutes.

[0027] The beneficial effects of the present invention are:

[0028] (1) The foam beads prepared by the present invention have the advantages of safe raw materials, non-toxicity, biodegradability and flame retardancy. The present invention uses bio-based polyisocyanates to replace traditional petroleum-based chain extenders, and combines renewable glycyrrhetinic acid as a reaction component, so that the modified chain extender itself has degradable properties. Glycyrrhetinic acid has a pentacyclic triterpenoid skeleton, and its complex condensed ring structure can be gradually decomposed by microbial action during the degradation process, solving the problem that traditional petroleum-based chain extenders are difficult to degrade;

[0029] (2) Through the condensation reaction between bio-based polyisocyanate and the oxygen active sites of glycyrrhetinic acid, a chain extender with a branched structure is formed. The layered surface of the nanorectorite is rich in hydroxyl groups, which can chemically bond with the isocyanate group to form a load structure for the chain extender. This composite structure can not only enhance the interaction between molecular chains through chemical cross-linking during melt blending, but also form physical cross-linking points through nanosheet intercalation, thereby constructing a micro-cross-linked network and effectively improving the melt strength of the PLA / PBAT blend.

[0030] (3) The layered structure of nanorectorite can form a dense carbonized isolation layer during combustion. Its surface active hydroxyl groups and the phosphorus components in the flame retardant can produce a synergistic flame retardant effect of phosphorus and silicon. The chain extender molecules grafted on its surface can improve the compatibility with the PLA / PBAT matrix and prevent the agglomeration of chain extender particles during melt blending. At the same time, the hydrophobic fused ring structure of glycyrrhetinic acid can delay the migration of the flame retardant to the surface of the material, anchoring the flame retardant component in the polymer matrix through intermolecular forces, solving the problem of easy migration and failure of traditional additives.

[0031] (4) The present invention can effectively stabilize the pore structure during the supercritical carbon dioxide foaming process through the micro-crosslinked network. The lamellar structure of the nanorectorite acts as a heterogeneous nucleation point and synergizes with the talc / silica nucleating agent to promote the formation of a fine and uniform closed-cell structure, ultimately obtaining dimensionally stable foamed beads with a high closed-cell ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a macroscopic image of the carbon residue after combustion of Example 3 of the present invention;

[0033] Figure 2 This is a macroscopic image of the carbon residue after combustion of Comparative Example 1 of the present invention;

[0034] Figure 3 This is a macroscopic image of the carbon residue after combustion of Comparative Example 2 of the present invention.

[0035] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods and materials similar or equivalent to those described herein can be applied to the present invention. The preferred embodiments and materials described herein are for illustrative purposes only and are not intended to limit the scope of this application.

[0038] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and the experimental materials used in the following examples, unless otherwise specified, are all purchased from commercial channels.

[0039] Example 1. A method for preparing degradable flame-retardant foam beads, comprising the following steps:

[0040] S1. PLA and PBAT were pre-mixed in a mass ratio of 50:50, added to a twin-screw extruder for melt blending, the melt temperature was controlled at 170°C, the screw speed was 200 rpm, and extrusion granulation was performed to obtain a PLA / PBAT blend base;

[0041] S2. Add the PLA / PBAT blend base, modified chain extender, and flame retardant (dimethyl methylphosphonate, trishydroxymethylphosphine oxide, and DOPO in a mass ratio of 3:1:3) into a high-speed mixer. Simultaneously, add an antioxidant (antioxidant 1010) and a nucleating agent (talc, with a particle size of 50-200 nm) and mix them evenly. The added amounts of the modified chain extender and flame retardant antioxidant are 5wt%, 15wt%, and 0.5wt% of the PLA / PBAT blend base, respectively.

[0042] S3. Use a twin-screw extruder for secondary blending, with the temperature zones being 160°C in the feed section, 175°C in the melting section, and 170°C in the die head, and the screw speed being 150 rpm, and extrusion granulation is performed to obtain foamable masterbatch;

[0043] S4. Place the foamable masterbatch in a high-pressure reactor, inject supercritical carbon dioxide as a foaming agent, and foam. The immersion pressure is 10 MPa, the immersion temperature is 45° C., the immersion time is 3 hours, and the injection rate of supercritical carbon dioxide is 5 kg / h;

[0044] S5. Place the foamed beads in a steam box and use gradient temperature increase for aging. In the initial stage of aging, the temperature is maintained at 80°C for 5 minutes, then the temperature is increased to 110°C at a rate of 2°C / min, the pressure is increased from 0.1MPa to 0.3MPa, and the temperature is maintained at 110°C for 15 minutes. After aging, vacuum drying is performed to obtain the degradable flame-retardant foamed beads.

[0045] The modified chain extender is prepared by the following steps: under nitrogen protection, glycyrrhetinic acid, bio-based polyisocyanate (1,5-pentane diisocyanate) and DMF are mixed, the temperature is raised to 70°C, an amine catalyst (the amine catalyst is one of ethylenediamine, triethylenetetramine or diethanolamine) is added dropwise, and the reaction is carried out at a constant temperature for 4-6 hours. Then, nanorectorite powder is added to the reaction solution in multiple times, and after each addition, ultrasonic dispersion is carried out at 40kHz for 15 minutes. After all the powder is added, mechanical stirring is continued at 500rpm for 1 hour to ensure that the nanoparticles are evenly dispersed. Then, the reaction solution is evaporated to remove the solvent, and 10 times the volume of petroleum ether is added. The solid is stirred to precipitate, and the solid is collected by centrifugation and washed twice with cold petroleum ether to obtain the modified chain extender.

[0046] The mass ratio of the glycyrrhetinic acid, bio-based polyisocyanate, amine catalyst, nano-rectorite powder and DMF is 70:15:0.05:1.5:100.

[0047] Example 2. A method for preparing degradable flame-retardant foam beads, comprising the following steps:

[0048] S1. PLA and PBAT were pre-mixed in a mass ratio of 70:30, added to a twin-screw extruder for melt blending, the melt temperature was controlled at 190° C., the screw speed was 300 rpm, and extrusion granulation was performed to obtain a PLA / PBAT blend base material;

[0049] S2. Add the PLA / PBAT blend base, modified chain extender, and flame retardant (the flame retardant is a combination of tris(hydroxymethyl)phosphine oxide, DOPO, triphenyl phosphate, and aluminum diethylphosphinate in a mass ratio of 2:3:1:1) into a high-speed mixer. Simultaneously, add an antioxidant (the antioxidant is a combination of antioxidant 168 and antioxidant 1076 in a mass ratio of 2:1) and a nucleating agent (nano-silica, with a particle size of 50-200 nm) and mix them evenly. The added amounts of the modified chain extender and flame retardant antioxidant are 10 wt%, 25 wt%, and 2 wt% of the PLA / PBAT blend base, respectively.

[0050] S3. Use a twin-screw extruder for secondary blending, with the temperature zones being 160°C in the feed section, 185°C in the melting section, and 170°C in the die head, and the screw speed being 200 rpm, and extrusion granulation is performed to obtain foamable masterbatch;

[0051] S4. The foamable masterbatch is placed in a high-pressure reactor, and supercritical carbon dioxide is injected as a foaming agent to foam. The immersion pressure is 12 MPa, the immersion temperature is 55° C., the immersion time is 4 hours, and the injection rate of supercritical carbon dioxide is 8 kg / h.

[0052] S5. Place the foamed beads in a steam box and use gradient temperature increase for aging. In the initial stage of aging, the temperature is maintained at 90°C for 10 minutes, then the temperature is increased to 110°C at a rate of 2°C / min, the pressure is increased from 0.1MPa to 0.3MPa, and the temperature is maintained at 110°C for 20 minutes. After aging, vacuum drying is performed to obtain the degradable flame-retardant foamed beads.

[0053] The modified chain extender is prepared by the following steps: under nitrogen protection, glycyrrhetinic acid, bio-based polyisocyanate (L-lysine diisocyanate) and DMF are mixed, the temperature is raised to 70°C, an amine catalyst (triethylenetetramine) is added dropwise, and the reaction is carried out at a constant temperature for 6 hours. Then, nanorectorite powder is added to the reaction solution in multiple times. After each addition, ultrasonic dispersion is performed at 40kHz for 15 minutes. After all the powder is added, mechanical stirring is continued at 500rpm for 1 hour to ensure that the nanoparticles are evenly dispersed. Then, the reaction solution is evaporated to remove the solvent, and 10 times the volume of petroleum ether is added. The solid is stirred to precipitate, and the solid is collected by centrifugation and washed twice with cold petroleum ether to obtain the modified chain extender.

[0054] The mass ratio of the glycyrrhetinic acid, bio-based polyisocyanate, amine catalyst, nano-rectorite powder and DMF is 100:25:00.5:4.5:200.

[0055] Example 3. A method for preparing degradable flame-retardant foam beads, comprising the following steps:

[0056] S1. PLA and PBAT were pre-mixed in a mass ratio of 60:40, added to a twin-screw extruder for melt blending, the melt temperature was controlled at 180° C., the screw speed was 250 rpm, and extrusion granulation was performed to obtain a PLA / PBAT blend base;

[0057] S2. Add the PLA / PBAT blend base, modified chain extender, and flame retardant (the flame retardant is a combination of DOPO, triphenyl phosphate, aluminum diethylphosphinate, and ammonium polyphosphate in a mass ratio of 3:1:2:1) into a high-speed mixer. Simultaneously, add an antioxidant (the antioxidant is a combination of antioxidant 1076 and antioxidant in a mass ratio of 2:1) and a nucleating agent (nano-silica, with a particle size of 50-200 nm) and mix them evenly. The added amounts of the modified chain extender, flame retardant, and antioxidant are 8wt%, 20wt%, and 1wt% of the PLA / PBAT blend base, respectively.

[0058] S3. Use a twin-screw extruder for secondary blending, with the temperature zones being 160°C in the feed section, 180°C in the melting section, and 170°C in the die head, and the screw speed being 180 rpm, and extrusion granulation is performed to obtain foamable masterbatch;

[0059] S4. The foamable masterbatch is placed in a high-pressure reactor, and supercritical carbon dioxide is injected as a foaming agent to foam. The immersion pressure is 10 MPa, the immersion temperature is 50° C., the immersion time is 3.5 hours, and the injection rate of supercritical carbon dioxide is 6 kg / h;

[0060] S5. Place the foamed beads in a steam box and use gradient temperature increase for aging. In the initial stage of aging, the temperature is maintained at 80-90°C for 8 minutes, then the temperature is increased to 110°C at a rate of 2°C / min, the pressure is increased from 0.1MPa to 0.3MPa, and the temperature is maintained at 110°C for 18 minutes. After aging, vacuum drying is performed to obtain the degradable flame-retardant foamed beads.

[0061] The modified chain extender is prepared by the following steps: under nitrogen protection, glycyrrhetinic acid, bio-based polyisocyanate (L-lysine diisocyanate) and DMF are mixed, the temperature is raised to 70°C, an amine catalyst (diethanolamine) is added dropwise, and the reaction is carried out at a constant temperature for 4-6 hours. Then, nanorectorite powder is added to the reaction solution in multiple times. After each addition, ultrasonic dispersion is performed at 40kHz for 15 minutes. After all the powder is added, mechanical stirring is continued at 500rpm for 1 hour to ensure uniform dispersion of the nanoparticles. Then, the reaction solution is evaporated to remove the solvent, and 10 times the volume of petroleum ether is added. The solid is stirred to precipitate, and the solid is collected by centrifugation and washed twice with cold petroleum ether to obtain the modified chain extender.

[0062] The mass ratio of the glycyrrhetinic acid, bio-based polyisocyanate, amine catalyst, nano-rectorite powder and DMF is 80:20:0.1:3:150.

[0063] Example 4. A method for preparing degradable flame-retardant foam beads. In this example, the amount of the modified chain extender added is 5 wt % of the PLA / PBAT blend base material, the amount of the flame retardant added is 25 wt % of the PLA / PBAT blend base material, and the amount of the antioxidant added is 0.5 wt % of the PLA / PBAT blend base material. The rest is the same as in Example 3.

[0064] Example 5. A method for preparing degradable flame-retardant foam beads. In this example, the amount of the modified chain extender added is 10 wt % of the PLA / PBAT blend base material, the amount of the flame retardant added is 15 wt % of the PLA / PBAT blend base material, and the amount of the antioxidant added is 2 wt % of the PLA / PBAT blend base material. The rest is the same as in Example 3.

[0065] Comparative Example 1: In this comparative example, only the modified chain extender is replaced by the petroleum-based chain extender ADR-4370, and the rest are the same as Example 3.

[0066] Comparative Example 2: In this comparative example, the modified chain extender is not added with nanorectorite powder, and the rest is the same as Example 3.

[0067] Result Analysis

[0068] The performance of the expanded beads prepared in each embodiment and comparative example was analyzed, specifically including:

[0069] Density: tested according to ASTM D 792;

[0070] Expansion ratio: calculated by density ratio, expansion ratio = density of unfoamed masterbatch / density of foamed beads. The density of unfoamed masterbatch is determined according to ASTM D 792.

[0071] Limiting oxygen index: tested according to GB / T 2406.2-2009;

[0072] Vertical burning grade: tested according to standard ASTMD 3801-10;

[0073] Melt index: tested according to ASTM D 1238, test conditions are 190℃ / 2.16kg;

[0074] Closed-cell ratio: Refer to ASTM D 6226 test and use the gas specific gravity method to calculate the closed-cell ratio;

[0075] Degradation rate: According to ISO 14855-1:2012 standard, the material was tested in a composting environment at 58℃±2℃ and 50%±5% humidity for 180 days, and the mass loss rate was calculated.

[0076] The above test results are shown in Table 1.

[0077] Table 1. Comparative table of performance analysis results of the expanded beads prepared in various embodiments and comparative examples

[0078] project Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 <![CDATA[Density (g / cm 3 )]]> 0.41 0.50 0.47 0.42 0.44 0.58 0.55 Foaming ratio 3.12 3.25 3.15 2.89 3.05 2.85 2.46 Limiting oxygen index (%) 33.5 33.2 34.3 35.0 31.2 26.8 28.1 Vertical combustion level V0 V0 V0 V0 V0 V0 V1 Melt index (g / 10min) 4.2 3.8 3.8 3.6 4.3 4.7 4.9 Closed cell rate (%) 88.5 92.3 91.2 90.7 89.5 78.5 80.3 Degradation rate (%) 69.5 62.5 72.3 68.8 64.6 66.9 54.3

[0079] As can be seen from Table 1, the limiting oxygen index of Examples 1 to 5 is greater than 30%, and the vertical combustion level reaches V0, indicating that the flame retardancy of Examples 1 to 5 is significantly better than that of Comparative Examples 1 and 2. This is attributed to the synergistic effect of the nanorectorite and the phosphorus-based flame retardant in the modified chain extender: the nanorectorite layered structure forms a dense silicate carbon layer during combustion, and its surface hydroxyl groups react with the phosphorus-based components to form a phosphate silicon glassy substance, which inhibits the free radical chain reaction. The closed porosity of Examples 1 to 5 is greater than 88%, and the density is ≤0.5g / cm 3 , the foaming ratio is greater than 2.8, and the melt index is also relatively low. This is because the modified chain extender forms a micro-crosslinked network through nanorectorite intercalation, which improves the melt strength and enables the cells to grow stably during supercritical foaming. Example 3 has the highest degradation rate, which is 8% higher than that of Comparative Example 1. This is due to the synergistic degradation mechanism of the hydrophobic fused ring of glycyrrhetinic acid and the bio-based chain extender, while the petroleum-based chain extender in Comparative Example 1 is difficult to biodegrade, which slows down the overall degradation rate.

[0080] The macroscopic morphology of the carbon residue after combustion of Example 3, Comparative Example 1 and Comparative Example 2 are shown in FIG. Figure 1-Figure 3 ,from Figure 1-Figure 3 It can be seen that the carbon residue formed in Example 3 is continuous and dense, with only a small number of microcracks on the surface, while the carbon residues in Comparative Examples 1 and 2 all show cracks to varying degrees, indicating that the poor compatibility between the oil-based chain extender and the flame retardant leads to a fragile carbon layer structure and reduced flame retardant efficiency. Due to the skeleton support effect of the nanorectorite, the flame retardant cannot form an effective isolation layer.

[0081] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

[0082] The present invention and its embodiments are described above. Such description is not restrictive. The drawings show only one embodiment of the present invention, and actual applications are not limited thereto. In short, if a person skilled in the art is inspired by the above, and does not deviate from the purpose of the present invention, any method and embodiment similar to the technical solution without creative design shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing degradable flame-retardant foam beads, characterized in that: The following steps are involved: S1. PLA and PBAT were pre-mixed in proportion, added to a twin-screw extruder for melt blending, the melt temperature was controlled at 170-190° C., the screw speed was 200-300 rpm, and extrusion granulation was performed to obtain a PLA / PBAT blend base material; S2. Add PLA / PBAT blend base, modified chain extender, and flame retardant into a high-speed mixer, and add antioxidant and nucleating agent at the same time, and mix well; S3. Use a twin-screw extruder for secondary blending, with the temperature zones being 160°C in the feed section, 175-185°C in the melting section, and 170°C in the die head, and the screw speed being 150-200 rpm, and extrusion granulation is performed to obtain foamable masterbatch; S4, placing the foamable masterbatch in a high-pressure reactor, injecting supercritical carbon dioxide as a foaming agent, and foaming; S5, placing the foamed beads in a steam box, aging them by gradient heating, and vacuum drying them after aging to obtain the degradable flame retardant foamed beads; The modified chain extender is prepared by the following steps: under nitrogen protection, glycyrrhetinic acid, bio-based polyisocyanate and DMF are mixed, the temperature is raised to 70° C., an amine catalyst is added dropwise, and the reaction is carried out at a constant temperature for 4-6 hours, and then nanorectorite powder is added to the reaction solution in multiple times, and ultrasonically dispersed at 40 kHz for 15 minutes after each addition. After all the addition is completed, mechanical stirring is continued at 500 rpm for 1 hour to ensure that the nanoparticles are evenly dispersed, and then the reaction solution is evaporated to remove the solvent, and then 10 times the volume of petroleum ether is added, stirred to precipitate solids, and collected by centrifugation and washed twice with cold petroleum ether to obtain the modified chain extender; The mass ratio of the glycyrrhetinic acid, bio-based polyisocyanate, amine catalyst, nano-rectorite powder and DMF is 70-100:15-25:0.05-0.5:1.5-4.5:100-200.

2. The method for preparing degradable flame-retardant foamed beads according to claim 1, wherein: The PLA and PBAT are premixed in a mass ratio of 50-70:30-50.

3. The method for preparing the degradable flame-retardant foamed beads according to claim 1, wherein: The added amount of the modified chain extender is 5-10wt% of the PLA / PBAT blend base material, the added amount of the flame retardant is 15-25wt% of the PLA / PBAT blend base material, and the added amount of the antioxidant is 0.5-2wt% of the PLA / PBAT blend base material.

4. The method for preparing degradable flame-retardant foamed beads according to claim 1, wherein: The bio-based polyisocyanate is one of 1,5-pentamethylene diisocyanate or L-lysine diisocyanate.

5. The method for preparing degradable flame-retardant foamed beads according to claim 1, wherein: The amine catalyst is one of ethylenediamine, triethylenetetramine or diethanolamine.

6. The method for preparing degradable flame-retardant foamed beads according to claim 1, characterized in that: The flame retardant is a combination of one or more of dimethyl methylphosphonate, trishydroxymethylphosphine oxide, DOPO, triphenyl phosphate, aluminum diethylphosphinate or ammonium polyphosphate.

7. The method for preparing degradable flame-retardant foamed beads according to claim 1, characterized in that: The antioxidant is a combination of one or more of antioxidant 1010, antioxidant 168, antioxidant 1076, and antioxidant 1098.

8. The method for preparing degradable flame-retardant foamed beads according to claim 1, characterized in that: The nucleating agent is one of talc powder and nano-silicon dioxide, and the particle size of the nucleating agent is 50-200 nm.

9. The method for preparing degradable flame-retardant foamed beads according to claim 1, wherein: In the foaming step in S4, the immersion pressure is 10-12 MPa, the immersion temperature is 45-55° C., the immersion time is 3-4 hours, and the injection rate of the supercritical carbon dioxide is 5-8 kg / h.

10. The method for preparing degradable flame-retardant foamed beads according to claim 1, characterized in that: The specific steps of the gradient temperature rise aging are: the temperature is maintained at 80-90°C for 5-10 minutes in the initial stage, then the temperature is raised to 110°C at a rate of 2°C / min, the pressure is increased from 0.1MPa to 0.3MPa, and maintained at 110°C for 15-20 minutes.

Images