A flame retardant, heat-insulating biodegradable composite material and its preparation method and application

Abstract

The present application provides a flame-retardant, heat-insulating bio-based degradable composite material and its preparation method and application, which relates to the field of polymer composite materials. The preparation method of the flame-retardant, heat-insulating bio-based degradable composite material of the present application adopts low-molecular-weight polylactic acid with end hydroxyl groups having biodegradable properties as raw material, and after modifying the end group of the flame retardant molecule DDP, it is used to extend the chain of the low-molecular-weight polylactic acid to obtain high-molecular-weight intrinsic flame-retardant polylactic acid, so that the polylactic acid has both excellent flame-retardant properties and mechanical properties. Polyethylene glycol with excellent heat-insulating properties is used as a phase change material, and its end group is modified so that it has a strong intermolecular force with the intrinsic flame-retardant polylactic acid, thereby preventing the loss of phase change components during the foaming process. After being evenly mixed in an internal mixer, the flame-retardant, phase-change heat-insulating polylactic acid composite material is foamed by supercritical carbon dioxide to form a continuous microporous structure, reduce the thermal conductivity, and further improve the heat-insulating performance.

Description

Technical Field

[0001] The present application relates to the field of polymer composite materials, and specifically to a flame-retardant, heat-insulating bio-based degradable composite material and its preparation method and application. Background Art

[0002] Polylactic acid (PLA), as an important bio-based degradable plastic, has become one of the most commercially successful and widely used bio-based degradable materials because of its renewable raw material source (all biomass), rapid biodegradation under specific industrial composting conditions, and excellent thermoplastic processing properties.

[0003] However, like most biodegradable plastics, polylactic acid (PLA) suffers from inherent brittleness, limiting its application in applications requiring high toughness. More critically, its mechanical properties (such as strength and toughness) generally rely on a high molecular weight, while its ideal rapid degradation performance favors a lower molecular weight. This conflicting molecular weight requirements make it difficult to simultaneously optimize both the mechanical properties and degradation rate of PLA, hindering its development in many applications requiring both. Furthermore, PLA's flammability and the high thermal conductivity resulting from its high crystallinity severely restrict its application as a building insulation material.

[0004] Therefore, there is an urgent need to develop a new composite material that has good biodegradable properties, excellent flame retardant properties and outstanding thermal insulation capabilities to overcome the above-mentioned shortcomings of existing polylactic acid materials. Summary of the Invention

[0005] The purpose of this application is to provide a composite material that has good biodegradable properties, excellent flame retardant properties and outstanding thermal insulation capabilities.

[0006] The technical problem solved by the present application is achieved by adopting the following technical solutions: First, a method for preparing a flame-retardant and heat-insulating bio-based degradable composite material is provided, comprising:

[0007] Under the first protective atmosphere, adding flame retardant DDP to the thionyl chloride solution for reflux reaction to obtain acyl chloride DDP;

[0008] Providing a first mixture and a second mixture, and adding the second mixture to the first mixture under a second protective atmosphere for mixed reaction to obtain intrinsic flame retardant polylactic acid;

[0009] wherein the first mixture comprises dihydroxy-terminated polylactic acid, an acid-binding agent and a first solvent, and the second mixture comprises the chlorinated DDP and a second solvent;

[0010] Under a third protective atmosphere, mixing phenyl isocyanate and polyethylene glycol to react to obtain benzene ring-terminated polyethylene glycol;

[0011] The intrinsic flame-retardant polylactic acid and the benzene-terminated polyethylene glycol are mixed and kneaded to obtain a flame-retardant and heat-insulating bio-based degradable composite material.

[0012] Optionally, in some embodiments of the present application, the molar ratio of thionyl chloride in the thionyl chloride solution to the flame retardant DDP is 2 to 3:1; and / or, the solvent in the thionyl chloride solution is selected from one or more of dichloromethane, dichloroethane, dichloropropane, chloroform and trichloroethane; and / or,

[0013] The concentration of the thionyl chloride solution is 1.0-2.5 mol / L; and / or the first protective atmosphere is selected from an atmosphere formed by one or more of nitrogen, helium, neon, and argon; and / or the reflux reaction time is 4-10 hours.

[0014] Optionally, in some embodiments of the present application, the molar ratio of the acid binding agent to the bishydroxy-terminated polylactic acid is 1.5-3; and / or the acid binding agent is selected from one or more of triethylamine, N,N-diisopropylethylamine, and pyridine; and / or the first solvent is selected from one or more of N,N-dimethylformamide, tetrahydrofuran, toluene, and dimethyl sulfoxide; and / or the ratio between the amount of the bishydroxy-terminated polylactic acid and the mass of the first solvent is 0.05 mol: (300-500) g; and / or the second solvent is selected from one or more of N,N-dimethylformamide, tetrahydrofuran, toluene, and dimethyl sulfoxide; and / or the ratio between the amount of the acyl chloride DDP and the volume of the second solvent is (1.0-2.5) mol: 1 L; and / or the ratio between the amount of the bishydroxy-terminated polylactic acid in the first mixture and the amount of the acyl chloride DDP in the second mixture is 0.98-1.02: 1.

[0015] Optionally, in some embodiments of the present application, adding the second mixture to the first mixture for mixed reaction under the second protective atmosphere comprises:

[0016] In a second protective atmosphere and under ice bath conditions, the second mixture is added dropwise to the first mixture, and then the mixing reaction is continued under ice bath conditions, wherein the temperature of the ice bath conditions is 0-10° C. and the mixing reaction time is 4-10 h.

[0017] Optionally, in some embodiments of the present application, the polyethylene glycol is selected from polyethylene glycol 4000, the chemical structure of which is , wherein n is an integer from 60 to 120; and / or,

[0018] The ratio of the amount of polyethylene glycol to the amount of phenyl isocyanate is 0.4-0.6:1; and / or,

[0019] The third protective atmosphere includes an atmosphere formed by one or more of nitrogen, helium, neon, and argon; and / or,

[0020] The temperature of the mixed reaction of phenyl isocyanate and polyethylene glycol is 55-65° C.; and / or,

[0021] The time for the mixing reaction of the phenyl isocyanate and the polyethylene glycol is 3 to 5 hours.

[0022] Optionally, in some embodiments of the present application, the mixing and reacting phenyl isocyanate with polyethylene glycol under a third protective atmosphere comprises: dissolving the polyethylene glycol in a third solvent, and then adding the phenyl isocyanate;

[0023] Wherein, the third solvent is selected from one or more of N,N-dimethylformamide, tetrahydrofuran, toluene, and dimethyl sulfoxide; and / or,

[0024] The mass ratio of the polyethylene glycol to the volume of the third solvent is (0.8-1.2) g:1 mL.

[0025] Optionally, in some embodiments of the present application, the mass ratio of the intrinsic flame retardant polylactic acid to the benzene ring terminated polyethylene glycol is (1.5-9):1; and / or,

[0026] The mixing temperature is 160-200° C. and the mixing time is 2-5 min; and / or,

[0027] The internal kneading is carried out in a torque rheometer, and the rotation speed of the torque rheometer is 40-60 rpm.

[0028] Optionally, in some embodiments of the present application, after mixing and kneading the intrinsically flame-retardant polylactic acid and the benzene-terminated polyethylene glycol, the process further comprises:

[0029] The composite material obtained after mixing and kneading is subjected to hot pressing and / or cold pressing to obtain a finalized sample;

[0030] The shaped sample is subjected to supercritical carbon dioxide foaming treatment.

[0031] In a second aspect, a flame-retardant and heat-insulating bio-based degradable composite material is provided, which is prepared by the above-mentioned preparation method.

[0032] Thirdly, the present invention provides applications of the composite material in building insulation, food and medicine packaging, and agriculture.

[0033] Compared with the prior art, this application has the following beneficial effects:

[0034] The present application provides a method for preparing a flame-retardant, heat-insulating biodegradable composite material. The method uses low-molecular-weight polylactic acid (PLA) with biodegradable terminal hydroxyl groups as a raw material. The flame retardant DDP (DDP) end groups are modified and then used to chain-extend the low-molecular-weight PLA to produce a high-molecular-weight, intrinsically flame-retardant PLA, resulting in a PLA with both excellent flame retardancy and mechanical properties. Polyethylene glycol (PEG), which exhibits excellent heat-insulating properties, is used as a phase-change material. Its end groups are modified to create strong intermolecular forces between the end groups and the intrinsically flame-retardant PLA, thereby preventing loss of the phase-change component during foaming. After being uniformly mixed in an internal mixer, the flame-retardant, phase-change, heat-insulating PLA composite is foamed with supercritical carbon dioxide to form a continuous microporous structure, reducing thermal conductivity and further improving heat-insulating properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0036] Figure 1 This is a schematic flow chart of an embodiment of a method for preparing a composite material provided in this application;

[0037] Figure 2 This is a flow chart of another embodiment of a method for preparing a composite material provided in this application. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0039] The technical solutions provided by this application will be described in detail below. It should be noted that the order of description of the following embodiments does not limit the preferred order of the embodiments. In addition, in the description of this application, the term "including" means "including but not limited to". The various embodiments of this application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and simplicity and should not be understood as a rigid limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range.

[0040] This application provides a method for preparing a composite material. Figure 1 , Figure 1 This is a flow chart of an embodiment of a method for preparing a composite material provided by the present application, which specifically includes the following steps:

[0041] Step S10: adding the flame retardant DDP to the thionyl chloride solution under a first protective atmosphere for reflux reaction to obtain DDP chloride;

[0042] Step S20: providing a first mixture and a second mixture, and adding the second mixture to the first mixture under a second protective atmosphere for mixed reaction to obtain intrinsic flame retardant polylactic acid;

[0043] wherein the first mixture comprises dihydroxy-terminated polylactic acid, an acid-binding agent and a first solvent, and the second mixture comprises the chlorinated DDP and a second solvent;

[0044] Step S30: Under a third protective atmosphere, mixing phenyl isocyanate and polyethylene glycol to react to obtain benzene-terminated polyethylene glycol;

[0045] Step S40: mixing and kneading the intrinsically flame-retardant polylactic acid and the benzene-terminated polyethylene glycol to obtain a flame-retardant and heat-insulating bio-based degradable composite material.

[0046] In the step S10:

[0047] The chemical structure of flame retardant DDP is: .

[0048] In some embodiments, the solvent in the thionyl chloride solution is selected from one or more of dichloromethane, dichloroethane, dichloropropane, chloroform, and trichloroethane. The concentration of the thionyl chloride solution is 1.0 to 2.5 mol / L, specifically 1.0 mol / L, 1.3 mol / L, 1.6 mol / L, 2.0 mol / L, 2.5 mol / L, etc.

[0049] In this step, the first protective atmosphere is selected from one or more atmospheres selected from nitrogen, helium (He), neon (Ne), and argon (Ar).

[0050] In some embodiments, the molar ratio of thionyl chloride in the thionyl chloride solution to the flame retardant DDP is 2-3:1, specifically 2-2.2:1, 2.2-2.5:1, 2.5-3:1, etc.

[0051] In some embodiments, the reflux reaction time can be 4 to 10 hours, specifically 4 to 6 hours, 6 to 8 hours, 8 to 10 hours, etc.

[0052] Generally speaking, the reflux reaction temperature needs to be equal to or higher than the boiling point of the reaction system solvent. Specifically, the reflux temperature can be 5-20°C higher than the boiling point of the solvent.

[0053] In some embodiments, the chemical reaction formula of step S10 is as follows:

[0054] .

[0055] It is understood that after the reaction in this step is completed, the solvent and unreacted thionyl chloride and other reaction raw materials can be removed by rotary evaporation, and an organic solvent such as dichloromethane can be used for washing and drying to obtain light yellow acyl chloride DDP.

[0056] In step S20:

[0057] In some embodiments, the chemical reaction formula of step S20 is as follows:

[0058] ;

[0059] Wherein, m represents the degree of polymerization of the dihydroxy-terminated polylactic acid, which is an integer of 20 to 60; n represents the degree of polymerization of the intrinsic flame retardant polylactic acid, which is an integer of 50 to 100.

[0060] In this step, dihydroxy-terminated polylactic acid is also called dihydroxy PLA, CAS number: 26100-51-6, and the chemical structure is as follows:

[0061] ; Wherein, m is an integer between 30 and 100.

[0062] In some embodiments, the acid-binding agent can be selected from one or more of triethylamine, N,N-diisopropylethylamine (DIEA), pyridine, etc. The first solvent is selected from one or more of organic solvents such as N,N-dimethylformamide (DMF), tetrahydrofuran (THF), toluene, and dimethyl sulfoxide.

[0063] It is understandable that the reaction in this step needs to be controlled in a dry and anhydrous environment, so the acid-binding agent and the first solvent used need to be anhydrous reagents.

[0064] In some embodiments, the molar ratio of the acid-binding agent to the dihydroxy-terminated polylactic acid is 1.5-3:1, specifically 1.5-2:1, 2-2.5:1, 2.5-3:1, etc.

[0065] In some embodiments, the ratio of the amount of the dihydroxy-terminated polylactic acid to the mass of the first solvent is 0.05 mol: (300-500) g, specifically 0.05 mol: 300 g, 0.05 mol: 400 g, 0.05 mol: 500 g, etc.

[0066] In some embodiments, the dihydroxy-terminated polylactic acid, the acid-binding agent, and the first solvent are mixed at room temperature until the dihydroxy-terminated polylactic acid is completely dissolved to obtain the first mixture.

[0067] In some embodiments, the second solvent is selected from one or more organic solvents such as N,N-dimethylformamide (DMF), tetrahydrofuran, toluene, and dimethyl sulfoxide.

[0068] The ratio between the amount of the DDP acyl chloride and the volume of the second solvent is (1.0-2.5) mol:1 L, specifically (1.0-1.5) mol:1 L, (1.5-2.0) mol:1 L, (12.0-2.5) mol:1 L, etc.

[0069] In some embodiments, the ratio of the amount of the dihydroxy-terminated polylactic acid in the first mixture to the amount of the chlorinated DDP in the second mixture is 0.8 to 1.2:1, specifically 0.8:1, 1:1, 1.1:1, 1.2:1, etc.

[0070] In some embodiments, adding the second mixture to the first mixture for mixed reaction under a second protective atmosphere includes: adding the second mixture dropwise to the first mixture under an ice bath condition in the second protective atmosphere, and then continuing the mixed reaction under an ice bath condition, wherein the temperature of the ice bath condition is approximately between 0 and 10° C., and the mixing reaction time is 4 to 10 hours, specifically 4 to 6 hours, 6 to 8 hours, 8 to 10 hours, etc.

[0071] It is understandable that after the reaction in this step is completed, a filtrate can be obtained by filtration, and deionized water can be added to the filtrate to precipitate the intrinsic flame-retardant polylactic acid.

[0072] Step S30:

[0073] In some embodiments, the chemical reaction formula of step S30 is as follows:

[0074] .

[0075] In some embodiments, the polyethylene glycol is selected from polyethylene glycol 4000 (PEG-4000), the chemical structure of which is , where n is an integer between 60 and 120.

[0076] Among them, the chemical structural formula of phenyl isocyanate is .

[0077] In some embodiments, the molar ratio of the polyethylene glycol to the phenyl isocyanate is 0.4-0.6:1, specifically 0.4:1, 0.5:1, 0.6:1, etc.

[0078] In some embodiments, the third protective atmosphere includes an atmosphere formed by one or more of nitrogen, helium, neon, and argon.

[0079] In some embodiments, reacting phenyl isocyanate with polyethylene glycol under a third protective atmosphere specifically includes dissolving polyethylene glycol in a third solvent and adding the phenyl isocyanate. The third solvent is selected from one or more organic solvents such as N,N-dimethylformamide (DMF), tetrahydrofuran (THF), toluene, and dimethyl sulfoxide. The ratio of the polyethylene glycol mass to the third solvent volume is (0.8-1.2) g:1 mL, specifically 0.8 g:1 mL, 1 g:1 mL, 1.2 g:1 mL, and so on.

[0080] In some embodiments, the temperature of the mixing reaction is 55-65° C., and the time is 3-5 hours.

[0081] It is understood that after the reaction in this step is completed, the solvent and unreacted reaction reagents can be removed by rotary evaporation, and post-treatment such as solvent washing and drying can be performed to obtain benzene ring-terminated polyethylene glycol.

[0082] The step S40:

[0083] The mass ratio of the intrinsic flame-retardant polylactic acid to the benzene ring-terminated polyethylene glycol is (1.5-9):1, and can specifically be (1.5-2.3):1, (2.3-4):1, (4-9):1, etc.

[0084] In some embodiments, the banburying temperature is 160-200° C., specifically 160-180° C., 180-200° C., etc.; the banburying time is 2-5 min, specifically 2 min, 3 min, 5 min, etc.

[0085] In a specific embodiment, the internal kneading is performed in a torque rheometer, and the rotation speed of the torque rheometer is 40-60 rpm, specifically 40 rpm, 50 rpm, 50 rpm, etc.

[0086] In some embodiments, see Figure 2 , Figure 2This is a flow diagram of another embodiment of a composite material preparation method provided herein. Following step S40, step S50 may also be included: hot pressing and / or cold pressing the composite material obtained after mixing and kneading to obtain a finalized sample. The cold pressing temperature may be 20-30°C for a holding time of 3-5 minutes; the hot pressing temperature may be 160-200°C for a holding time of 5-10 minutes.

[0087] Furthermore, after step S50, step S60 may be included: subjecting the molded sample to supercritical carbon dioxide foaming. Specifically, the molded sample may be placed in an autoclave for supercritical carbon dioxide foaming, connected to a carbon dioxide aerator, with the temperature set to 60-70°C and the pressure set to 10-15 MPa. When the reactor reaches the set temperature and pressure, the aerator is closed, and the pressure holding time is started. After 2-3 hours, the exhaust valve is opened to quickly release the gas to release the pressure to atmospheric pressure.

[0088] It is understood that in order to ensure a more complete reaction in each step, stirring or ultrasonication may be performed in each step involving mixing or a mixed reaction process to promote mixing uniformity and reaction uniformity and accelerate the reaction rate. After each mixing reaction is completed, post-processing operations such as washing, purification, and drying may also be performed.

[0089] The present application provides a method for preparing a flame-retardant, heat-insulating biodegradable composite material. The method uses low-molecular-weight polylactic acid (PLA) with biodegradable terminal hydroxyl groups as a raw material. The flame retardant DDP (DDP) end groups are modified and then used to chain-extend the low-molecular-weight PLA to produce a high-molecular-weight intrinsically flame-retardant PLA, resulting in a PLA with both excellent flame retardancy and mechanical properties. Polyethylene glycol (PEG) with excellent heat-insulating properties is then used as a phase-change material. Its end groups are modified to create strong intermolecular forces between the end groups and the intrinsically flame-retardant PLA, thereby preventing loss of the phase-change component during foaming. After uniform mixing in an internal mixer, the flame-retardant, phase-change, heat-insulating PLA composite material is foamed with supercritical carbon dioxide to form a continuous microporous structure, reducing thermal conductivity and further improving heat-insulating properties.

[0090] This application also provides a flame-retardant, heat-insulating biodegradable composite material, prepared by the preparation method described above. The composite material provided in this application, while being biodegradable, also possesses excellent flame-retardant properties and outstanding heat-insulating capabilities, and has broad application prospects in the fields of building insulation, food and pharmaceutical packaging, and agriculture.

[0091] The present application also provides applications of the flame-retardant and heat-insulating bio-based degradable composite materials in the fields of building insulation, food and pharmaceutical packaging, and agriculture, and can be specifically applied to flame-retardant and heat-insulating materials.

[0092] The technical solutions and technical effects of the present application are described in detail below through specific embodiments, comparative examples and experimental examples. The following embodiments are only some embodiments of the present application and do not specifically limit the present application.

[0093] The reagents used in the various examples and comparative examples can be purchased commercially. The names, English abbreviations, chemical structures and related information of some of the reagents are as follows:

[0094] Dihydroxy terminated polylactic acid (dihydroxy PLA) , number average molecular weight = 5000, purchased from Hubei Yamaide Biopharmaceutical Co., Ltd.;

[0095] Flame retardant DDP: , molecular weight = 346.27;

[0096] Thionyl chloride: , molecular weight = 118.97;

[0097] Triethylamine: Molecular weight = 101.19;

[0098] Polyethylene glycol 4000 (PEG-4000): , n is an integer from 60 to 120, number average molecular weight = 4000;

[0099] Phenyl isocyanate: , molecular weight = 119.12;

[0100] Example 1

[0101] This embodiment provides a composite material and a preparation method thereof.

[0102] The preparation method of the composite material includes:

[0103] Step 1: Add 29.7g of thionyl chloride (0.25mol) and 150ml of dichloromethane to a 250ml three-necked flask, add 34.6g of flame retardant DDP (0.1mol), and flow nitrogen protection. Connect a spherical condenser to reflux. React at room temperature for 6 hours until the system becomes a transparent liquid. After the reaction is completed, rotary evaporate at 20°C to remove the dichloromethane in the system. Then, rotary evaporate at 70°C to remove the excess thionyl chloride in the system, obtaining a light yellow liquid, which is DDP chloride with a molecular weight of 383.27. Its specific structural formula and reaction equation are shown below:

[0104] .

[0105] Step 2: Weigh 250g of dihydroxy-terminated polylactic acid (dihydroxy PLA, 0.05mol), 10.1g (0.1mol) of anhydrous triethylamine (acidifying agent) and 400g of anhydrous DMF into a 1L three-necked flask, stir at room temperature until the dihydroxy PLA is completely dissolved, and introduce circulating nitrogen for protection; take 19.2g of the acyl chloride DDP obtained in step 1 (0.05mol) and dissolve it in 30ml of anhydrous DMF. In an ice bath, gradually add it dropwise to the three-necked flask through a constant pressure funnel. After the addition is completed, react for 6h in an ice bath. After the reaction is completed, filter to remove the by-product triethylamine hydrochloride, and pour the filtered reaction solution into excess deionized water to precipitate the product. Its specific structural formula and reaction equation are shown in the figure below:

[0106] ;

[0107] Wherein m represents the degree of polymerization of the dihydroxy-terminated polylactic acid, which is an integer of 20 to 60; n represents the polymerization of the intrinsic flame retardant polylactic acid.

[0108] Step 3: Accurately weigh 200g (0.05mol) of PEG-4000 and 200ml of anhydrous THF and add them to a 500ml three-necked flask. Heat to 60°C and start stirring. After PEG-4000 is completely dissolved, introduce nitrogen protection. Add 11.9g of phenyl isocyanate (0.1mol) and react at 60°C for 4h. After the reaction is completed, remove THF from the system by rotary evaporation. Pour the concentrated solution after rotary evaporation into a glass dish while it is still hot. After it cools and solidifies, benzene-terminated polyethylene glycol is obtained. Its specific structural formula and reaction equation are shown in the figure below:

[0109] ;

[0110] Step 4: 45g of the intrinsically flame-retardant polylactic acid obtained in Step 2 and 5g of the product obtained in Step 3 were added to a small torque rheometer and mixed at a mixing temperature of 180°C and a rotation speed of 50 rpm for 3 minutes. The mixture was removed while still hot. The mixed composite material was hot-pressed and then cold-pressed to produce test strips for subsequent flame retardancy testing. The hot-pressing temperature was 180°C for a 5-minute hold, and the cold-pressing temperature was 25°C for a 3-minute hold. The resulting flame-retardant test strips were placed in an autoclave for supercritical carbon dioxide foaming. Connected to a CO2 aerator, the temperature was set to 65°C and the pressure to 10 MPa. When the reactor reached the set temperature and pressure, the aerator was closed and the hold time was started. After 2 hours, the exhaust valve was opened to rapidly release the air. Once the pressure returned to atmospheric pressure, the autoclave was opened and the sample removed.

[0111] Example 2

[0112] This embodiment provides a composite material and a preparation method thereof.

[0113] The preparation method of the composite material provided in this embodiment is basically the same as that in Example 1, except that in step 4, 40 g of the intrinsic flame-retardant polylactic acid obtained in step 2 and 10 g of the product obtained in step 3 are added to a small torque rheometer for internal mixing.

[0114] Example 3

[0115] This embodiment provides a composite material and a preparation method thereof.

[0116] The preparation method of the composite material provided in this embodiment is basically the same as that in Example 1, except that: in step 4, 35 g of the intrinsic flame-retardant polylactic acid obtained in step 2 and 15 g of the product obtained in step 3 are added to a small torque rheometer for internal mixing.

[0117] Example 4

[0118] This embodiment provides a composite material and a preparation method thereof.

[0119] The preparation method of the composite material provided in this embodiment is basically the same as that in Example 1, except that in step 4, 30 g of the intrinsic flame-retardant polylactic acid obtained in step 2 and 20 g of the product obtained in step 3 are added to a small torque rheometer for internal mixing.

[0120] Comparative Example 1

[0121] This comparative example provides a composite material and its preparation method. The composite material preparation method comprises: adding 40g of commercially available polylactic acid (PLA LX175, purchased from Total Corbivir Polylactic Acid Co., Ltd.) and 10g of PEG-4000 to a small torque rheometer for internal kneading at a temperature of 180°C and a rotation speed of 50 rpm for 3 minutes. After internal kneading, the material is removed while still hot. The internal kneaded composite material is then hot-pressed and cold-pressed to produce test strips for subsequent flame retardancy testing. The hot-pressing temperature is 180°C with a holding time of 5 minutes, and the cold-pressing temperature is 25°C with a holding time of 3 minutes. The resulting flame-retardant test strips are placed in an autoclave for supercritical carbon dioxide foaming. Connected to a carbon dioxide aerator, the temperature is set to 65°C and the pressure is set to 10 MPa. When the reactor reaches the set temperature and pressure, the aerator is closed and the hold time is started. After 2 hours, the exhaust valve is opened for rapid release of air. Once the pressure drops to atmospheric pressure, the autoclave is opened and the sample is removed.

[0122] Comparative Example 2

[0123] This comparative example provides a composite material and its preparation method. The composite material preparation method comprises: adding 30g of commercially available polylactic acid (PLA LX175, purchased from Total Corbivir Polylactic Acid Co., Ltd.) and 20g of PEG-4000 to a small torque rheometer for internal kneading at a temperature of 180°C and a rotation speed of 50 rpm for 3 minutes. After internal kneading, the material is removed while still hot. The internal kneaded composite material is then hot-pressed and cold-pressed to produce test strips for subsequent flame retardancy testing. The hot-pressing temperature is 180°C with a holding time of 5 minutes, and the cold-pressing temperature is 25°C with a holding time of 3 minutes. The resulting flame-retardant test strips are placed in an autoclave for supercritical carbon dioxide foaming. Connected to a carbon dioxide aerator, the temperature is set to 65°C and the pressure is set to 10 MPa. When the reactor reaches the set temperature and pressure, the aerator is closed and the holding time is started. After 2 hours, the exhaust valve is opened for rapid release of air. Once the pressure drops to atmospheric pressure, the autoclave is opened and the sample is removed.

[0124] The samples provided in Examples 1 to 4 and Comparative Examples 1 to 2 were tested for flame retardancy, crystallization performance, thermal insulation performance, and foaming performance, respectively. The test results are shown in Table 1.

[0125] Table 1:

[0126] name Flame retardant grade Thermal conductivity W / (m·K) Melting temperature (℃) Melting enthalpy (J / g) Crystallization temperature (℃) Crystallization enthalpy (J / g) Average pore size (um) <![CDATA[Average density (cells / cm 3 ).]]> Example 1 V0 0.018 48 31.5 41 24.2 73.5 <![CDATA[2.1*10 9 ]]> Example 2 V0 0.021 49 50.7 41 38.7 98.3 <![CDATA[4.3*10 8 ]]> Example 3 V1 0.025 49 70.2 42 56.8 126.7 <![CDATA[3.5.*10 7 ]]> Example 4 V2 0.028 49 99.8 42 85.4 153.8 <![CDATA[5.2*10 6 ]]> Comparative Example 1 HB 0.032 63 45.1 57 35.5 138.3 <![CDATA[6.7*10 5 ]]> Comparative Example 2 HB 0.035 63 88.7 57 76.3 195.1 <![CDATA[2.8*10 4 ]]>

[0127] Among them, the flame retardant performance test is carried out in accordance with the standard UL94.

[0128] Thermal conductivity determination: carried out in accordance with standard GB / T 42919.1-2023.

[0129] Determination of melting and crystallization temperature and enthalpy: in accordance with standard GB / T 19466.3-2004.

[0130] Average pore size and average density test: The foamed sample was soaked in liquid nitrogen for 30 minutes and then taken out for brittle fracture. After the cross section was sprayed with gold, the cross-sectional morphology was characterized using a JSM-7500F scanning electron microscope. The average pore size and average density were calculated using the obtained SEM photos using Image J software. The average density is defined as the number of bubbles per unit volume (cm3).

[0131] The data in Table 1 show that the polylactic acid oligomers are chain extended with DDP having acyl chloride, and the obtained polylactic acid has excellent flame retardant properties. At the same time, the polylactic acids reported in Examples 1 to 4 all have excellent foaming properties, indicating that the polylactic acid after chain extension has a higher molecular weight and higher fluid strength. By comparing the average pore size and the average density of the pores after foaming, it is shown that the lower the content of the phase change component, the easier it is to form a dense microporous structure, and the lower its thermal conductivity. Comparing the melting and crystallization properties of Example 2 and Comparative Example 1, the melting temperature of Example 2 is lower than that of Comparative Example 1, indicating that the end-capping treatment of the phase change component PEG-4000 will destroy its crystallization ability, resulting in a decrease in its melting temperature and crystallization temperature; Example 2 and Comparative Example 1 theoretically have the same content of phase change component. At the same time, the crystallization performance of the phase change component of Example 2 is weaker than that of Comparative Example 1. However, the melting and crystallization enthalpy values ​​of Example 2 are higher than those of Comparative Example 1. This is because there is a strong π-π conjugation effect between the end-group treated PEG-4000 and the polylactic acid molecules, which can effectively avoid leakage of the phase change component during foaming and pressure relief.

[0132] In summary, the present invention provides a flame-retardant and heat-insulating bio-based degradable composite material and its preparation method and application, which is characterized by excellent flame retardant properties and outstanding heat-insulating capacity, and has broad application prospects in the fields of building insulation, food and medical packaging, and agriculture.

[0133] The above is a detailed introduction to the technical solutions provided in the embodiments of the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for those skilled in the art, based on the ideas of the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A method for preparing a flame-retardant and heat-insulating bio-based degradable composite material, characterized in that: include: Under the first protective atmosphere, adding flame retardant DDP to the thionyl chloride solution for reflux reaction to obtain acyl chloride DDP; Providing a first mixture and a second mixture, and adding the second mixture to the first mixture under a second protective atmosphere for mixed reaction to obtain intrinsic flame retardant polylactic acid; wherein the first mixture comprises dihydroxy-terminated polylactic acid, an acid-binding agent and a first solvent, and the second mixture comprises the chlorinated DDP and a second solvent; Under a third protective atmosphere, mixing phenyl isocyanate and polyethylene glycol to react to obtain benzene ring-terminated polyethylene glycol; The intrinsic flame-retardant polylactic acid and the benzene-terminated polyethylene glycol are mixed and kneaded to obtain a flame-retardant and heat-insulating bio-based degradable composite material.

2. The preparation method according to claim 1, characterized in that The molar ratio of thionyl chloride in the thionyl chloride solution to the flame retardant DDP is 2-3:1; and / or, The solvent in the thionyl chloride solution is selected from one or more of dichloromethane, dichloroethane, dichloropropane, chloroform and trichloroethane; and / or, The concentration of the thionyl chloride solution is 1.0-2.5 mol / L; and / or, The first protective atmosphere is selected from one or more of nitrogen, helium, neon, and argon; and / or The reflux reaction time is 4 to 10 hours.

3. The preparation method according to claim 1, characterized in that The molar ratio of the acid binding agent to the dihydroxy-terminated polylactic acid is 1.5 to 3; and / or, The acid binding agent is selected from one or more of triethylamine, N,N-diisopropylethylamine, and pyridine; and / or, The first solvent is selected from one or more of N,N-dimethylformamide, tetrahydrofuran, toluene, and dimethyl sulfoxide; and / or, The ratio between the amount of the dihydroxy-terminated polylactic acid and the mass of the first solvent is 0.05 mol: (300-500) g; and / or, The second solvent is selected from one or more of N,N-dimethylformamide, tetrahydrofuran, toluene, and dimethyl sulfoxide; and / or, The ratio between the amount of the DDP chloride and the volume of the second solvent is (1.0-2.5) mol:1 L; and / or, The molar ratio of the dihydroxy-terminated polylactic acid in the first mixture to the chlorinated DDP in the second mixture is 0.98-1.02:

1.

4. The preparation method according to claim 3, characterized in that The step of adding the second mixture to the first mixture for mixed reaction under a second protective atmosphere comprises: In a second protective atmosphere and under ice bath conditions, the second mixture is added dropwise to the first mixture, and then the mixing reaction is continued under ice bath conditions, wherein the temperature of the ice bath conditions is 0-10° C. and the mixing reaction time is 4-10 h.

5. The preparation method according to claim 1, characterized in that The polyethylene glycol is selected from polyethylene glycol 4000, and its chemical structural formula is , wherein n is an integer from 60 to 120; and / or, The ratio of the amount of polyethylene glycol to the amount of phenyl isocyanate is 0.4-0.6:1; and / or, The second protective atmosphere includes an atmosphere formed by one or more of nitrogen, helium, neon, and argon; and / or, The third protective atmosphere includes an atmosphere formed by one or more of nitrogen, helium, neon, and argon; and / or, The temperature of the mixed reaction of phenyl isocyanate and polyethylene glycol is 55-65° C.; and / or, The time for the mixing reaction of the phenyl isocyanate and the polyethylene glycol is 3 to 5 hours.

6. The preparation method according to claim 5, characterized in that The mixing and reacting of phenyl isocyanate and polyethylene glycol under the third protective atmosphere comprises: dissolving the polyethylene glycol in a third solvent, and then adding the phenyl isocyanate; Wherein, the third solvent is selected from one or more of N,N-dimethylformamide, tetrahydrofuran, toluene, and dimethyl sulfoxide; and / or, The mass ratio of the polyethylene glycol to the volume of the third solvent is (0.8-1.2) g:1 mL.

7. The preparation method according to claim 1, characterized in that The mass ratio of the intrinsic flame retardant polylactic acid to the benzene ring terminated polyethylene glycol is (1.5-9):1; and / or, The mixing temperature is 160-200° C. and the mixing time is 2-5 min; and / or, The internal kneading is carried out in a torque rheometer, and the rotation speed of the torque rheometer is 40-60 rpm.

8. The preparation method according to claim 1, characterized in that After the intrinsic flame retardant polylactic acid and the benzene ring terminated polyethylene glycol are mixed and kneaded, the method further comprises: The composite material obtained after mixing and kneading is subjected to hot pressing and / or cold pressing to obtain a finalized sample; The shaped sample is subjected to supercritical carbon dioxide foaming treatment.

9. A flame retardant and heat-insulating biodegradable composite material, characterized in that: The method is prepared according to any one of claims 1 to 8.

10. Use of the composite material according to claim 9 in building insulation, food and medicine packaging, and agriculture.

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