Core-shell structure additive, polylactic acid composite material and preparation method of polylactic acid composite material

Abstract

The invention discloses a core-shell structure additive, a polylactic acid composite material and a preparation method of the polylactic acid composite material, and belongs to the field of flame-retardant polylactic acid composite materials. The core-shell structure additive has a core-shell structure, a phosphorus-containing flame retardant is coated with a bio-based compound to obtain an intermediate product, a metal organic framework is self-grown on the surface of the intermediate product to obtain the core-shell structure additive, and the metal organic framework is ZIF-8. The additive provided by the invention can be well used for flame retardance of polylactic acid, and when the additive is added into polylactic acid and is burnt by flame, molten drops of a composite material are inhibited, and the char forming performance is improved, so that oxygen and heat are better blocked, and the flame-retardant effect is achieved. Meanwhile, the bio-based compound coats the phosphorus-containing flame retardant, so that the compatibility of the flame retardant of the composite material and a matrix is better, and the bio-based compound and the metal organic framework enable the composite material to have high recovery efficiency under an alkaline condition.

Description

Technical Field

[0001] The present invention belongs to the field of flame-retardant polylactic acid composites, and particularly relates to a core-shell structure additive, a polylactic acid composite material and a preparation method thereof. Background Art

[0002] Petroleum-based plastics cause pollution and threats to the environment and ecosystem due to improper treatment. Nowadays, the industry is seeking to reduce dependence on petroleum fuels and products to achieve economic and environmental sustainability. Polylactic acid (PLA) is a bio-based material with the potential for economic and environmental sustainability. However, polylactic acid is extremely flammable when exposed to fire, with a limiting oxygen index of only about 19%, and at the same time, it is prone to produce a large number of molten droplets with fire when ignited, which greatly restricts the expanded application of polylactic acid in fields with flame-retardant requirements. Traditional halogen-based flame retardants have extremely high flame-retardant efficiency. However, due to the strong bioaccumulation and toxicity of the by-products formed after combustion, the use of halogen-based flame retardants is being gradually prohibited and replaced at home and abroad. Among many flame-retardant elements, phosphorus-based flame retardants are considered to be one of the most efficient in halogen-free flame retardants and are widely used for the flame-retardant modification of polylactic acid. However, commercial phosphorus-based flame retardants, such as ammonium polyphosphate (APP), aluminum hypophosphite, etc., have poor compatibility with polylactic acid, which greatly affects the mechanical properties of polylactic acid. Therefore, more and more research inventions tend to use multiple elements to synergistically flame-retard polylactic acid. In addition, although polylactic acid is a biodegradable material, it cannot be rapidly degraded under natural conditions. At 50-60°C, the microbial degradation of polylactic acid usually takes 45 to 60 days. Therefore, based on the problems of easy combustion, difficult degradation of polylactic acid and poor compatibility of commercial flame retardants, it is very necessary to synthesize an additive that is compatible with the polylactic acid matrix and improves the recycling efficiency of polylactic acid. Summary of the Invention

[0003] The purpose of the present invention is to provide a core-shell structure additive, a polylactic acid composite material and a preparation method thereof. The polylactic acid composite material provided by the present invention adopts a halogen-free flame retardant system and has the advantage of being more environmentally friendly. In addition, due to the coating of bio-based compounds, the phosphorus-based flame retardant has good compatibility in the polylactic acid matrix and has basically no influence on the mechanical properties. Finally, in terms of degradation performance, the water absorption effect of bio-based compounds and the catalytic effect of metal ions in metal-organic frameworks promote the rapid hydrolysis of polylactic acid in an alkaline environment, and the final degradation product lactic acid is obtained by purification.

[0004] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0005] The present invention first provides a core-shell structure additive. The core-shell structure additive has a core-shell structure, which is obtained by first coating a bio-based compound on a phosphorus-containing flame retardant to obtain an intermediate product, and then self-growing a metal-organic framework on the surface of the intermediate product to obtain the core-shell structure additive. The metal-organic framework is ZIF-8.

[0006] Preferably, the bio-based compound is chitosan, tannic acid or polydopamine.

[0007] Preferably, the phosphorus-containing flame retardant is ammonium polyphosphate, aluminum hypophosphite or aluminum diethyl hypophosphite.

[0008] The present invention also provides a preparation method of the core-shell structure additive, including:

[0009] Step 1: Add a bio-based compound solution to a phosphorus-containing flame retardant dispersion and react to obtain an intermediate product;

[0010] Step 2: Dissolve the intermediate product obtained in Step 1 in a solvent to obtain a dispersion, and then add a Zn(NO3)2 solution and a 2-methylimidazole solution to the above dispersion and stir to obtain the core-shell structure additive.

[0011] Preferably, the reaction temperature in Step 1 is 80 °C, and the reaction time is 4-6 h.

[0012] Preferably, the mass ratio of the bio-based compound to the phosphorus-containing flame retardant in Step 1 is 1:(5-10).

[0013] The present invention also provides a polylactic acid composite material, including the above core-shell structure additive.

[0014] Preferably, the polylactic acid composite material, by weight, includes 93-97 parts of polylactic acid and 3-7 parts of the core-shell structure additive.

[0015] The present invention also provides a preparation method of the polylactic acid composite material, including:

[0016] Dry and mix the core-shell structure additive and polylactic acid evenly to obtain a mixed material, and carry out internal mixing on the above mixed material to obtain the polylactic acid composite material; the processing temperature of the internal mixing is: zone 1 180 ± 10 °C, zone 2 180 ± 10 °C, zone 3 180 ± 10 °C; the screw speed is 50 revolutions / min, and the processing time is 6-20 min.

[0017] The present invention also provides the application of the above polylactic acid composite material in the preparation of mechanical, automotive, electronic and electrical, building, textile and packaging products.

[0018] Advantages of the present invention

[0019] The present invention provides a core-shell structure additive, a polylactic acid composite material and a preparation method thereof. The additive has a core-shell structure. First, a biobased compound is used to coat a phosphorus-containing flame retardant to obtain an intermediate product, and then a metal-organic framework is self-grown on the surface of the intermediate product to obtain the core-shell structure additive. The metal-organic framework is ZIF-8. The biobased compound and the metal-organic framework act as a shell to coat the phosphorus-containing flame retardant. The additive provided in the present invention can be well used for the flame retardancy of polylactic acid. When added to polylactic acid and subjected to flame combustion, the melt dripping of the composite material is inhibited, and the char-forming performance is improved, so as to better block oxygen and heat and achieve the flame retardant effect. At the same time, the biobased compound coating the phosphorus-containing flame retardant can make the compatibility between the flame retardant and the matrix of the composite material better. Moreover, the biobased compound and the metal-organic framework enable the composite material to have a high recovery efficiency under alkaline conditions. Compared with commercial phosphorus-based flame retardants, the advantages of the present invention are better compatibility with the polylactic acid matrix, the composite material taking into account various mechanical properties, higher flame retardant efficiency, and excellent degradation and recovery performance, obtaining a flame-retardant polylactic acid composite material with excellent flame retardancy and degradation and recovery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the preparation process of a core-shell structure additive of the present invention;

[0021] Figure 2 Infrared spectra of the core-shell structure additives prepared in Examples 1-3 of the present invention;

[0022] Figure 3 Microscopic morphology diagrams of the core-shell structure additives prepared in Examples 1-3 of the present invention;

[0023] Figure 4 Test results of LOI and UL-94 and sample melt temperature curve diagrams of Comparative Example 1, Example 3 and Comparative Example 4 of the present invention;

[0024] Figure 5 Schematic diagram of the degradation process of Comparative Example 1, Example 3 and Comparative Example 4 of the present invention in a NaOH solution (10 wt%); DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention first provides a core-shell structure additive. The core-shell structure additive has a core-shell structure. First, a biobased compound is used to coat a phosphorus-containing flame retardant to obtain an intermediate product, and then a metal-organic framework is self-grown on the surface of the intermediate product to obtain the core-shell structure additive. The metal-organic framework is ZIF-8.

[0026] According to the present invention, the bio-based compound is preferably chitosan, tannic acid or polydopamine, more preferably chitosan, and the deacetylation degree of the chitosan is preferably 95%; the phosphorus-containing flame retardant is preferably ammonium polyphosphate, aluminum hypophosphite or aluminum diethyl hypophosphite, more preferably ammonium polyphosphate, and the polymerization degree of the ammonium polyphosphate is preferably greater than 1000.

[0027] The present invention also provides a preparation method of a core-shell structure additive, comprising:

[0028] Step 1: Adding a bio-based compound solution to a phosphorus-containing flame retardant dispersion for reaction to obtain an intermediate product;

[0029] Step 2: Dissolving the intermediate product obtained in Step 1 in a solvent to obtain a dispersion, and then adding a Zn(NO3)2 solution and a 2-methylimidazole solution to the above dispersion and stirring to obtain a core-shell structure additive.

[0030] According to the present invention, first dissolve the bio-based compound in an acetic acid aqueous solution (1 wt%) to obtain a bio-based compound solution, disperse the phosphorus-containing flame retardant in water to obtain a phosphorus-containing flame retardant dispersion, and then add the bio-based compound solution to the phosphorus-containing flame retardant dispersion for reaction. The reaction temperature is preferably 80°C, and the reaction time is preferably 4-6 h. After filtration, washing and drying, an intermediate product is obtained; the mass ratio of the bio-based compound to the phosphorus-containing flame retardant is preferably 1:(5-10), more preferably 1:5.

[0031] According to the present invention, dissolve the above intermediate product in a solvent to obtain a dispersion. The solvent is preferably methanol. Dissolve 2-methylimidazole and Zn(NO3)2·6H2O in methanol respectively to obtain a Zn(NO3)2 solution and a 2-methylimidazole solution. Add the Zn(NO3)2 solution and the 2-methylimidazole solution to the dispersion and stir. The stirring temperature is preferably room temperature, and the stirring time is preferably 2-4 h. After centrifugation, washing and drying, a final product is obtained. The mass ratio of the bio-based compound, Zn(NO3)2 and 2-methylimidazole is preferably 1:0.8:0.75.

[0032] The present invention also provides a polylactic acid composite material comprising the above core-shell structure additive.

[0033] Preferably, the polylactic acid composite material, by weight, comprises 93-97 parts of polylactic acid and 3-7 parts of the core-shell structure additive, more preferably 93 parts of polylactic acid and 7 parts of the core-shell structure additive.

[0034] The present invention also provides a preparation method of a polylactic acid composite material, comprising:

[0035] The core-shell structure additive and polylactic acid are dried and then mixed evenly to obtain a mixed material, and the above-mentioned mixed material is subjected to internal mixing to obtain a polylactic acid composite material. The processing temperature of the internal mixing is preferably: zone 1 180±10°C, zone 2 180±10°C, zone 3 180±10°C; the screw speed is 50 revolutions / min, and the processing time is 6-20 min.

[0036] According to the present invention, the raw materials in the synthesis process of the polylactic acid and the additive are all commercially obtained. The sources of the polylactic acid resin are, for example, Nature 3053D from the United States, Total LX175 from Thailand, etc. The ammonium polyphosphate and zinc nitrate hexahydrate are of chemical purity and are purchased from Shanghai Aladdin Reagent Co., Ltd.; the chitosan and 2-methylimidazole are of analytical purity and are purchased from Shanghai Macklin Co., Ltd.

[0037] The present invention also provides the application of the above-mentioned polylactic acid composite material in the preparation of mechanical, automotive, electronic and electrical, building, textile and packaging products.

[0038] The following 4 examples and 3 comparative examples of the present invention are given to more clearly illustrate the present invention, rather than the scope of the present invention, to help those skilled in the art have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0039] Comparative Example 1

[0040] This comparative example provides a preparation method of pure PLA:

[0041] The PLA is baked at 80°C for 5 h to remove the moisture therein, and a dried material is obtained. According to the weight fraction, 100 parts of PLA resin are added to an internal mixer, and through the processes of melt blending, cooling and drying, a pure PLA material is obtained; the pure PLA masterbatch is made into a PLA material spline through an injection molding machine. The processing temperature of the Harp internal mixer is: zone 1 180±10°C, zone 2 180±10°C, zone 3 180±10°C, the screw speed is 50 revolutions / min, and the processing time is 10 min.

[0042] Example 1

[0043] This example provides a preparation method of a novel flame-retardant and recyclable PLA composite material: as Figure 1 shown.

[0044] Dissolve 1 g of chitosan in 100 mL of acetic acid aqueous solution (1 wt%), and disperse 5 g of ammonium polyphosphate in an appropriate amount of water. Then add the chitosan solution to the ammonium polyphosphate dispersion solution, react at 80 °C for 4 hours, filter, wash, and dry to obtain the intermediate product CH@APP. Then disperse CH@APP in 100 mL of methanol. Dissolve 0.80 g of 2-methylimidazole and 0.75 g of zinc nitrate hexahydrate in 50 mL of methanol respectively. Then add the Zn(NO3)2 solution and the 2-methylimidazole solution to the intermediate product dispersion solution, and stir at room temperature for 4 hours. Centrifuge, wash, and dry to obtain the core-shell structure additive ZIF-8@CH@APP.

[0045] According to the stated weight parts, it is composed of the following raw materials in parts: 97 parts of PLA resin and 3 parts of ZIF-8@CH@APP. Specifically: Dry the PLA resin and the additive ZIF-8@CH@APP at 80 °C for 4 h respectively to remove the moisture therein, and obtain the dried components; After fully mixing the PLA resin and the additive evenly, obtain the premix; Add the premix into a mixer, and through the processes of melt blending, cooling and drying, obtain the flame-retardant recyclable PLA composite material. Make the masterbatch of the flame-retardant recyclable PLA composite material into a new type of flame-retardant recyclable PLA spline through an injection molding machine. The processing temperature of the Hapu mixer is: zone 1 180 ± 10 °C, zone 2 180 ± 10 °C, zone 3 180 ± 10 °C, the screw speed is 50 revolutions / min, and the processing time is 10 min.

[0046] Example 2

[0047] This example provides a preparation method for a new type of flame-retardant and recyclable PLA composite material:

[0048] Dissolve 1 g of chitosan in an appropriate amount of 100 mL of acetic acid aqueous solution (1 wt%), and disperse 5 g of ammonium polyphosphate in an appropriate amount of water. Then add the chitosan solution to the ammonium polyphosphate dispersion solution, react at 80 °C for 4 h, filter, wash, and dry to obtain the intermediate product CH@APP. Then disperse CH@APP in 100 mL of methanol. Dissolve 0.80 g of 2-methylimidazole and 0.75 g of zinc nitrate hexahydrate in 50 mL of methanol respectively. Then add the Zn(NO3)2 solution and the 2-methylimidazole solution to the intermediate product dispersion solution, and stir at room temperature for 4 hours. Centrifuge, wash, and dry to obtain the core-shell structure additive ZIF-8@CH@APP.

[0049] According to the said weight parts, it is composed of the following parts of raw materials: 95 parts of PLA resin and 5 parts of ZIF-8@CH@APP. Specifically: The PLA resin and the additive ZIF-8@CH@APP are dried at 80 °C for 4 h respectively to remove the moisture therein, and then the dried components are obtained; after the PLA resin and the additive are fully mixed evenly, a premix is obtained; the premix is added into a mixer, and through the processes of melt blending, cooling and drying, a flame-retardant recyclable PLA composite material is obtained. The masterbatch of the flame-retardant recyclable PLA composite material is made into a new type of flame-retardant recyclable PLA spline through an injection molding machine. The processing temperature of the Hap mixer is: zone 1 180 ± 10 °C, zone 2 180 ± 10 °C, zone 3 180 ± 10 °C, the screw speed is 50 revolutions per minute, and the processing time is 10 min.

[0050] Example 3

[0051] This example provides a preparation method of a new type of flame-retardant and recyclable PLA composite material:

[0052] Dissolve 1 g of chitosan in an appropriate amount of 100 mL of acetic acid aqueous solution (1 wt%), and disperse 5 g of ammonium polyphosphate in an appropriate amount of water. Then add the chitosan solution to the ammonium polyphosphate dispersion solution, react at 80 °C for 4 h, filter, wash, and dry to obtain an intermediate product CH@APP. Then disperse CH@APP in 100 mL of methanol. Dissolve 0.80 g of 2-methylimidazole and 0.75 g of zinc nitrate hexahydrate in 50 mL of methanol respectively. Then add the Zn(NO3)2 solution and the 2-methylimidazole solution to the intermediate product dispersion solution, and stir at room temperature for 4 hours. Centrifuge, wash, and dry to obtain the core-shell structure additive ZIF-8@CH@APP.

[0053] According to the said weight parts, it is composed of the following parts of raw materials: 93 parts of PLA resin and 7 parts of ZIF-8@CH@APP. Specifically: The PLA resin and the additive ZIF-8@CH@APP are dried at 80 °C for 4 h respectively to remove the moisture therein, and then the dried components are obtained; after the PLA resin and the additive are fully mixed evenly, a premix is obtained; the premix is added into a mixer, and through the processes of melt blending, cooling and drying, a flame-retardant recyclable PLA composite material is obtained. The masterbatch of the flame-retardant recyclable PLA composite material is made into a new type of flame-retardant recyclable PLA spline through an injection molding machine. The processing temperature of the Hap mixer is: zone 1 180 ± 10 °C, zone 2 180 ± 10 °C, zone 3 180 ± 10 °C, the screw speed is 50 revolutions per minute, and the processing time is 10 min.

[0054] Comparative Example 2

[0055] This comparative example provides a preparation method of a flame-retardant PLA composite material:

[0056] According to the said parts by weight, it consists of the following raw materials in parts: 97 parts of PLA resin and 3 parts of flame retardant (APP). After fully mixing and homogenizing the said flame retardant, it is stirred and then added into a mixer. Through the processes of melt blending, cooling, and drying, a flame-retardant PLA composite material is obtained. Specifically: The PLA resin and the flame retardant APP are respectively dried at 80°C for 4 hours to remove the moisture therein, and then the dried components are obtained; after fully mixing and homogenizing the PLA resin and the flame retardant, a premix is obtained; the premix is added into a mixer, and through the processes of melt blending, cooling, and drying, a flame-retardant recyclable PLA composite material is obtained. The masterbatch of the said flame-retardant PLA composite material is made into a flame-retardant PLA spline through an injection molding machine. The processing temperature of the Hap mixer is: Zone 1: 180±10°C, Zone 2: 180±10°C, Zone 3: 180±10°C, the screw speed is 50 revolutions per minute, and the processing time is 10 minutes.

[0057] Comparative Example 3

[0058] This comparative example provides a preparation method of a flame-retardant PLA composite material:

[0059] According to the said parts by weight, it consists of the following raw materials in parts: 95 parts of PLA resin and 5 parts of flame retardant (APP). After fully mixing and homogenizing the said flame retardant, it is stirred and then added into a mixer. Through the processes of melt blending, cooling, and drying, a flame-retardant PLA composite material is obtained. Specifically: The PLA resin and the flame retardant APP are respectively dried at 80°C for 4 hours to remove the moisture therein, and then the dried components are obtained; after fully mixing and homogenizing the PLA resin and the flame retardant, a premix is obtained; the premix is added into a mixer, and through the processes of melt blending, cooling, and drying, a flame-retardant recyclable PLA composite material is obtained. The masterbatch of the said flame-retardant PLA composite material is made into a flame-retardant PLA spline through an injection molding machine. The processing temperature of the Hap mixer is: Zone 1: 180±10°C, Zone 2: 180±10°C, Zone 3: 180±10°C, the screw speed is 50 revolutions per minute, and the processing time is 10 minutes.

[0060] Comparative Example 4

[0061] This comparative example provides a preparation method of a flame-retardant PLA composite material:

[0062] According to the above weight parts, it is composed of the following raw materials in parts by weight: 93 parts of PLA resin and 7 parts of flame retardant (APP). After fully mixing the flame retardant evenly, it is added to a kneader after stirring, and through the processes of melt blending, cooling, and drying, a flame-retardant PLA composite material is obtained. Specifically: The PLA resin and the flame retardant APP are dried at 80 °C for 4 h respectively to remove the moisture therein, and then the dried components are obtained; after the PLA resin and the flame retardant are fully mixed evenly, a premix is obtained; the premix is added to a kneader, and through the processes of melt blending, cooling, and drying, a flame-retardant recyclable PLA composite material is obtained. The masterbatch of the flame-retardant PLA composite material is made into a flame-retardant PLA spline through an injection molding machine. The processing temperature of the Hap kneader is: zone 1 180 ± 10 °C, zone 2 180 ± 10 °C, zone 3 180 ± 10 °C, the screw speed is 50 revolutions per minute, and the processing time is 10 min.

[0063] The conventional mechanical properties and combustion properties of the polylactic acid composite material are tested according to the following standards, and the results are shown in Table 1.

[0064] Tensile strength: Tested according to the standard of GB / T1040.1-2018, and the test speed is 5 mm / min;

[0065] Combustion performance: Conducted LOI standard test according to the standard of GB / T 2406-2015, and conducted UL-94 standard test according to GB / T2408-2008.

[0066] Figure 2 For the infrared spectra of the additive ZIF-8@CH@APP used in Examples 1-3 and the flame retardant APP used in the comparative example, it can be observed that the characteristic peaks of APP can be found in both APP and ZIF-8@CH@APP, such as the P=O stretching vibration at 1250 cm -1 and the P-O-P stretching vibration at 870 cm -1 . It is worth noting that in the infrared spectrum of ZIF-8@CH@APP, the peak value of NH4 + is weakened compared with APP, and a new absorption peak related to -NH3 -1 appears at 1630 cm + , indicating the formation of -NH3 + O - P-. The absorption peaks of ZIF-8 are located at 2930 cm -1 and 2890 cm -1 , which are attributed to -CH3 and -CH= of 2-methylimidazole respectively. The characteristic peak at 421 cm -1 is caused by the stretching vibration of Zn-N.

[0067] Figure 3Scanning electron microscope photographs of additive ZIF-8@CH@APP used in Examples 1-3. Among them Figure 3 a represents 5 μm, Figure 3 b represents 1 μm. As can be seen from the figure, the surface of ZIF-8@CH@APP becomes rough after CH coating. And ZIF-8 is hexagonal and evenly distributed on the surface.

[0068] Figure 4 Test results of LOI and UL-94 and sample melt temperature curves for Comparative Example 1, Example 3 and Comparative Example 4, where Figure 4 a are the test results of LOI and UL-94, Figure 4 b is the sample melt temperature curve. The key data are shown in Table 1. The LOI of Comparative Example 1 is 19.8 and it cannot pass any UL-94 grade. The flame retardant grade of Comparative Example 4 is V-2, indicating a low flame retardancy efficiency of APP. After adding 7 wt% ZIF-8@CH@APP, the LOI value of the PLA composite material is increased to 28.5, reaching the V-0 grade. ZIF-8@CH@APP can reduce the number of melt droplets generated in the UL-94 test. The melt droplet temperature of Comparative Example 1 rises rapidly to 273.9 °C, which is sufficient to ignite cotton. In a real fire scenario, this may lead to the spread of fire. The melt droplet temperature of Example 3 drops to 156.8 °C, which is 42.8% and 21.2% lower than that of Comparative Example 1 and Comparative Example 4 respectively. The results show that Example 3 can take away heat through melting, but the melting temperature is not sufficient to ignite absorbent cotton. The TSP value of Example 3 drops to 0.2 m 2 . It should be noted that the TSP value of Example 3 is significantly lower than that of Comparative Example 4, indicating that ZIF-8 has significant smoke suppression ability. ZIF-8 has a high specific surface area and pore volume, and can reduce the smoke generation amount by absorbing and delaying the release of volatile substances, thus solving the problem of large smoke generation caused by phosphorus-based flame retardants.

[0069] Table 1

[0070]

[0071] The influence of the addition of flame retardants on the mechanical properties of polylactic acid was studied by tensile tests. As a rigid material (tensile strength up to 64.3 MPa), Comparative Example 1 deforms in a brittle manner. The tensile strength of Comparative Example 4 decreases. The tensile strength of Example 3 (59.4 MPa) is slightly higher than that of Comparative Example 4 (53.2 MPa). APP aggregates in the polymer matrix, and there is an obvious gap between APP and the matrix. After adding ZIF-8@CH@APP, there is no obvious gap between the flame retardant and the matrix, indicating good interfacial compatibility between ZIF-8@CH@APP and the matrix. The introduced bio-based shell eliminates the phase separation between the matrix flame retardant and the inorganic flame retardant.

[0072] Figure 5 Schematic diagram of the degradation process of Comparative Example 1, Example 3 and Comparative Example 4 in NaOH solution (10 wt%). There was almost no change in Comparative Example 1 and Comparative Example 4 after 24 h, and the mass loss was small, 9.3 wt% and 14.2 wt% respectively. However, after introducing ZIF-8@CH@APP, the sample degraded rapidly within 6 h, and the sample was almost completely degraded after 12 h, with a mass loss of 91.8%.

[0073] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made on the basis of the above description. It is impossible to enumerate all the implementation manners here. Any obvious changes or variations derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A core-shell structure additive, characterized in that, The core-shell structure additive has a core-shell structure. First, a bio-based compound is used to coat a phosphorus-containing flame retardant to obtain an intermediate product, and then a metal-organic framework is self-grown on the surface of the intermediate product to obtain the core-shell structure additive. The metal-organic framework is ZIF-8.

2. The core-shell structure additive according to claim 1, characterized in that, The bio-based compound is chitosan, tannic acid or polydopamine.

3. The core-shell structure additive according to claim 1, characterized in that, The phosphorus-containing flame retardant is ammonium polyphosphate, aluminum hypophosphite or aluminum diethyl hypophosphite.

4. The preparation method of a core-shell structure additive according to claim 1, characterized in that, It includes: Step 1: Add a bio-based compound solution to a phosphorus-containing flame retardant dispersion and react to obtain an intermediate product. Step 2: Dissolve the intermediate product obtained in Step 1 in a solvent to obtain a dispersion, and then add a Zn(NO3)2 solution and a 2-methylimidazole solution to the above dispersion and stir to obtain the core-shell structure additive.

5. The preparation method of a core-shell structure additive according to claim 4, characterized in that, The reaction temperature in Step 1 is 80 °C, and the reaction time is 4-6 h.

6. The preparation method of a core-shell structure additive according to claim 4, characterized in that, In Step 1, the mass ratio of the bio-based compound to the phosphorus-containing flame retardant is 1:(5-10).

7. A polylactic acid composite material, comprising the core-shell structure additive described in claim 1.

8. The polylactic acid composite material according to claim 7, wherein By weight, it includes 93-97 parts of polylactic acid and 3-7 parts of the core-shell structure additive.

9. A method for preparing a polylactic acid composite material according to claim 7, characterized in that, It includes: Dry and mix the core-shell structure additive and polylactic acid evenly to obtain a mixed material, and carry out internal mixing on the above mixed material to obtain the polylactic acid composite material; the processing temperature of the internal mixing is: zone 1 180±10 °C, zone 2 180±10 °C, zone 3 180±10 °C; the screw speed is 50 revolutions / min, and the processing time is 6-20 min.

10. The application of the polylactic acid composite material described in claim 7 in the preparation of mechanical, automotive, electronic and electrical, building, textile and packaging products.

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