Carbon particle, nickel-cobalt hydrotalcite and tea polyphenol organic-inorganic hybrid flame retardant and preparation method thereof

Abstract

The invention discloses a carbon particle-coated nickel-cobalt hydrotalcite-tea polyphenol organic-inorganic hybrid flame retardant and a preparation method thereof.The preparation method comprises the steps that carbon particles (HCCFD) prepared from calcium carbide furnace dust (CCFD) serve as a core, nickel-cobalt hydrotalcite (NiCo-LDH) prepared from a metal organic framework material ZIF-67 serving as a precursor serves as a shell, the surface of the carbon particle-coated nickel-cobalt hydrotalcite is subjected to organic modification through tea polyphenol (TP), and the carbon particle-coated nickel-cobalt hydrotalcite-tea polyphenol organic-inorganic hybrid flame retardant is obtained; the double-shell organic-inorganic hybrid flame retardant (HCCFD (at) NiCo-LDH (at) TP) is successfully prepared, the interfacial compatibility and dispersity of the HCCFD (at) NiCo-LDH (at) TP and polypropylene (PP) are improved, and the flame retardant property and the mechanical property can be effectively balanced through multi-component synergistic modification and interface regulation; and the flame retardant and smoke suppression properties of the PP composite material are improved while the deterioration of the mechanical properties of the PP matrix due to the addition of the flame retardant is reduced as much as possible.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flame retardants, and particularly relates to a carbon particle-nickel cobalt hydrotalcite-tea polyphenol organic-inorganic hybrid flame retardant and a preparation method thereof. BACKGROUND

[0002] In recent years, the emergence and continuous evolution of polymer materials have brought unprecedented convenience to people's life and are widely used in various fields, such as clothing, construction, electronics, medical equipment, automobile industry and various home textiles, and polymer materials have excellent processing performance and low cost-effectiveness. Polymer materials are generally highly flammable, generate toxic gas smoke during combustion, and release heat during combustion, which can cause immeasurable damage to human life and property. Therefore, strict flame retardant requirements should be put forward for the use of polymer materials. Although traditional flame retardant methods have achieved some ideal effects, there are still deficiencies, and the existing system is difficult to simultaneously achieve high-efficiency flame retardation of the flame-retardant material, reduce the release of smoke and toxic gas, and more importantly, not deteriorate or even improve the overall performance of the polymer. In recent years, some advanced flame retardant methods have been developed to improve the flammability of polymers or provide new strategies for the design of flame-retardant polymer materials.

[0003] Polypropylene (PP) is a semi-crystalline thermoplastic polymer synthesized by the polymerization of propylene monomers, which is considered an important polymer material with high tensile strength and low cost. In the past 10 years, the global consumption of PP has continued to grow, and it has been widely used in electrical and electronic appliances, automobile manufacturing, packaging materials and building materials. However, PP is a thermoplastic polymer with a low ignition point, and a large amount of heat is released during combustion, and importantly, molten droplets may cause the occurrence of "secondary fire", which has greatly limited the development of PP applications. With the rapid development of household appliances and the automobile industry, not only has the demand for advanced manufacturing materials of PP continued to rise, but the performance requirements have also become increasingly stringent. Under this background, flame retardant modification has become a mandatory requirement for the application of PP materials to effectively reduce fire risk. At present, melt blending is the main method to improve the flame retardant performance of materials by compounding flame retardants with polymers. This method not only avoids the complex adjustment of the synthesis process of polymers, but also has the advantages of simple process and easy industrial production, and therefore is widely favored in the industrial field. From the perspective of material science, this modification method not only maintains the excellent processing performance and mechanical properties of PP, but also significantly improves its flame retardant grade. Therefore, adding flame retardants to PP is an effective way to improve its flame retardant performance. SUMMARY

[0004] In order to solve the problems in the prior art, the purpose of the present application is to provide a carbon particle-nickel cobalt hydrotalcite-tea polyphenol organic-inorganic hybrid flame retardant and a preparation method thereof, wherein carbon particles (HCCFD) prepared by acidizing calcium carbide furnace dust (CCFD) are used as cores, nickel cobalt hydrotalcite (NiCo-LDH) prepared by using metal organic framework material ZIF-67 as a precursor is used as a shell, and the surface of the carbon particle-nickel cobalt hydrotalcite is organically modified by using tea polyphenol (TP), so that an organic-inorganic hybrid double-layer core-shell structure flame retardant (HCCFD@NiCo-LDH@TP) with HCCFD as the core, NiCo-LDH as the shell and TP as the outer layer is successfully constructed, the interfacial compatibility and dispersibility of HCCFD@NiCo-LDH@TP and polypropylene (PP) are improved, and the multi-component synergistic modification and interface regulation can effectively balance the flame retardant performance and mechanical properties, so that the mechanical performance deterioration of the PP matrix caused by the addition of the flame retardant is reduced as much as possible, and the flame retardant and smoke suppression performance of the PP composite material is improved.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0006] A preparation method of a carbon particle-nickel cobalt hydrotalcite-tea polyphenol organic-inorganic hybrid flame retardant comprises the following steps:

[0007] (1) calcium carbide furnace dust is added into a hydrochloric acid solution, and after sufficient stirring and reaction, solid-liquid separation is performed to obtain carbon particles (HCCFD);

[0008] (2) ZIF-67 and the carbon particles are ultrasonically dispersed in anhydrous ethanol to obtain a dispersion liquid A; Ni(NO3)2·6H2O is ultrasonically dispersed in anhydrous ethanol to obtain a dispersion liquid B; the dispersion liquid B is added into the dispersion liquid A, and after sufficient stirring and reaction, solid-liquid separation is performed to obtain carbon particle-nickel cobalt hydrotalcite (HCCFD@NiCo-LDH);

[0009] (3) the carbon particle-nickel cobalt hydrotalcite is ultrasonically dispersed in deionized water to obtain a dispersion liquid C; tea polyphenol (TP) is ultrasonically dispersed in anhydrous ethanol to obtain a dispersion liquid D; the dispersion liquid D is added into the suspension liquid C, and after heating and stirring and reaction, solid-liquid separation is performed to obtain a carbon particle-nickel cobalt hydrotalcite-tea polyphenol organic-inorganic hybrid flame retardant (HCCFD@NiCo-LDH@TP).

[0010] In the present application, HCCFD has a unique graphite layered structure and porous characteristics, and its own carbon skeleton can resist the heat of combustion, providing an ideal substrate for the loading of NiCo-LDH and tea polyphenol, wherein the layered structure and transition metal characteristics of NiCo-LDH can catalyze the polymer carbonization and promote the formation of dense carbon layers, and the introduction of tea polyphenol not only improves the compatibility of the interface between HCCFD@NiCo-LDH and PP, but also synergistically promotes the formation of dense carbon layers together with NiCo-LDH, and the carbon layer structure becomes stable, greatly enhancing the barrier effect of the carbon layer during the combustion process, effectively improving the flame retardant and smoke suppression performance of the PP composite material.

[0011] In summary, the present application uses carbon particles (HCCFD) as the "core", and constructs an organic-inorganic hybrid flame retardant HCCFD@NiCo-LDH@TP through inorganic modification of nickel-cobalt hydrotalcite and organic modification of tea polyphenol, which not only significantly improves the flame retardant performance, but also improves the hydrophobic performance and compatibility between the flame retardant and the PP matrix, while reducing the deterioration of the mechanical properties of the PP matrix caused by the addition of the flame retardant, the flame retardant and smoke suppression performance of the PP composite material is improved.

[0012] Preferably, in step (1), the mass-volume ratio of calcium carbide furnace dust to hydrochloric acid is 1g:10-20mL; the concentration of the hydrochloric acid solution is 1-3mol / L.

[0013] Preferably, in step (2), the mass-volume ratio of ZIF-67, HCCFD and anhydrous ethanol in dispersion A is 0.05-0.2g:0.01-0.1g:100mL, and the mass-volume ratio of Ni(NO3)2·6H2O and anhydrous ethanol in dispersion B is 0.2-0.5g:10mL.

[0014] Preferably, in step (3), the concentration of HCCFD@NiCo-LDH in dispersion C is 0.005-0.015g / mL, and the mass-volume ratio of TP and anhydrous ethanol in dispersion D is 0.02-0.05g:10mL.

[0015] Preferably, in step (3), the heating temperature is 40-60℃.

[0016] The present application also provides a carbon particle@nickel-cobalt hydrotalcite@tea polyphenol hybrid flame retardant prepared by the above preparation method.

[0017] The advantages of the present application are:

[0018] 1. In the present invention, HCCFD has a unique graphite layered structure and porous properties. Its own carbon skeleton can resist the heat of combustion, providing an ideal substrate for the loading of NiCo-LDH and tea polyphenols. The layered structure and transition metal properties of NiCo-LDH can catalyze the carbonization of the polymer, and synergistically promote the formation of a dense carbon layer together with tea polyphenols. The carbon layer structure becomes stable, greatly enhancing the barrier effect of the carbon layer during combustion, and effectively improving the flame retardant and smoke suppression properties of the PP composite material.

[0019] 2. The introduction of tea polyphenols in the present invention can significantly improve the hydrophobic properties of the flame retardant (HCCFD and HCCFD@NiCo-LDH are both inorganic flame retardants, so their WCA values ​​are 8.3° and 32.7°, respectively, while the WCA value of HCCFD@NiCo-LDH@TP is 48.6°), improve the compatibility between HCCFD@NiCo-LDH and the PP interface, and thus improve the flame retardant properties of the PP composite material.

[0020] In summary, the present invention uses carbon particles (HCCFD) as the "core" and constructs an organic-inorganic hybrid flame retardant HCCFD@NiCo-LDH@TP through inorganic modification of nickel-cobalt hydrotalcite and organic modification of tea polyphenols. This not only significantly improves the flame retardant properties, but also improves the hydrophobic properties and its compatibility with the PP matrix. While minimizing the deterioration of the mechanical properties of the PP matrix caused by the addition of the flame retardant, it also improves the flame retardancy and smoke suppression properties of the PP composite material. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 are the SEM images of CMSs (a), CMSs (b) and HCCFD.

[0022] Figure 2 These are digital photos of carbon residues of pure PP, PP / CMSs (a), PP / CMSs (b) and PP / HCCFD composites.

[0023] Figure 3 SEM images of the microstructure of carbon residues of pure PP, PP / CMSs (a), PP / CMSs (b) and PP / HCCFD composites.

[0024] Figure 4 Raman spectra of residual carbon in PP / CMSs (a), PP / CMSs (b) and PP / HCCFD composites.

[0025] Figure 5 3 is an XRD comparison chart of HCCFD prepared in Comparative Example 1, HCCFD@NiCo-LDH prepared in Comparative Example 2, and HCCFD@NiCo-LDH@TP prepared in Example 1.

[0026] Figure 6 is the FT-IR contrast diagram of HCCFD@NiCo-LDH prepared in Comparative Example 2 and HCCFD@NiCo-LDH@TP prepared in Example 1.

[0027] Figure 7 is the SEM and TEM diagram of HCCFD prepared in Comparative Example 1, HCCFD@NiCo-LDH prepared in Comparative Example 2 and HCCFD@NiCo-LDH@TP prepared in Example 1.

[0028] Figure 8 is the water contact angle diagram of HCCFD prepared in Comparative Example 1, HCCFD@NiCo-LDH prepared in Comparative Example 2 and HCCFD@NiCo-LDH@TP prepared in Example 1.

[0029] Figure 9 is the cross-section SEM diagram of PP / HCCFD, PP / HCCFD@NiCo-LDH and PP / HCCFD@NiCo-LDH@TP composite materials.

[0030] Figure 10 is the digital photo of residual carbon of pure PP, PP / HCCFD, PP / HCCFD@NiCo-LDH and PP / HCCFD@NiCo-LDH@TP composite materials.

[0031] Figure 11 is the micro-morphology SEM diagram of residual carbon of pure PP, PP / HCCFD, PP / HCCFD@NiCo-LDH and PP / HCCFD@NiCo-LDH@TP composite materials.

[0032] Figure 12 is the Raman spectrum diagram of residual carbon of PP / HCCFD, PP / HCCFD@NiCo-LDH and PP / HCCFD@NiCo-LDH@TP composite materials. DETAILED DESCRIPTION

[0033] The application will be further described below in combination with the drawings and examples.

[0034] 1. Preparation of carbon "core"

[0035] (1) Preparation of carbon microspheres CMSs(a)

[0036] First, 300 mL of 0.4 mol / L xylose aqueous solution was prepared, and after ultrasonic dissolution, the solution was transferred to a 500 mL hydrothermal kettle, which was reacted in an oven at 180℃ for 12 h. After the reaction, the product was repeatedly washed and filtered with deionized water, and the obtained sample was dried in a vacuum at 80℃ for 8 h, which was recorded as CMSs(a).

[0037] (2) Preparation of carbon microspheres CMSs (b)

[0038] First, 6 g of cellulose and 1 g of citric acid were poured into a 500 mL beaker. Then, 300 mL of deionized water was added to the beaker. After ultrasonic dissolution, the solution was transferred to a 500 mL hydrothermal autoclave. The hydrothermal autoclave was reacted in an oven at 210 °C for 12 h. After the reaction, the sample was repeatedly washed with deionized water and vacuum-dried at 80 °C for 8 h. It was recorded as CMSs (b).

[0039] (3) Preparation of spherical carbon particles HCCFD

[0040] Weigh a certain amount of CCFD (calcium carbide furnace dust), pour it into a beaker, and add hydrochloric acid solution (2 mol / L) at a solid-liquid ratio (g:mL) of CCFD: hydrochloric acid (1:15), add it to the beaker, and stir in a water bath at 60°C for 60 minutes. After the end, let the black suspension in the beaker stand for 10 minutes, then filter it through a Buchner funnel, wash with deionized water, and vacuum dry it at 80°C for 8 hours. It is recorded as HCCFD.

[0041] like Figure 1 As shown in the figure, CMSs(a), CMSs(b) and HCCFD were characterized by SEM test. The CMSs(a) prepared by xylose had a smooth surface, uniform particle size, and a particle size distribution of approximately 0.5 to 2 μm; the carbon microspheres prepared by cellulose had a small particle size, different shapes, and aggregated distribution, with a particle size of approximately less than 1 μm; and the HCCFD prepared by calcium carbide furnace dust showed a spherical particle morphology with a rough surface and tiny pores.

[0042] CMSs(a), CMSs(b) and HCCFD were melt-blended with PP by melt blending to prepare PP composite materials PP / CMSs(a), PP / CMSs(b) and PP / HCCFD with a flame retardant mass fraction of 10 wt%. The flame retardancy and mechanical properties of the composite materials were tested.

[0043] The LOI value of pure PP is 17.2%, and it does not meet any UL-94 rating. This indicates that pure PP is easily flammable and is accompanied by the occurrence of dripping during combustion, which can easily lead to "secondary fires." Therefore, the flame retardant properties of PP need to be improved. Whether it is PP / CMSs (a), PP / CMSs (b), or PP / HCCFD composites, the LOI value and UL-94 rating show an upward trend with increasing flame retardant addition. Compared to 22.2% and HB rating for the PP / CMSs (a) composite and 22.8% and HB rating for the PP / CMSs (b) composite, the LOI value of the PP / HCCFD composite reaches 23.5%, passing the UL-94 rating V-2.

[0044] Digital photos of carbon residues of pure PP, PP / CMSs (a), PP / CMSs (b) and PP / HCCFD composites Figure 2 As shown in the figure. From the digital photos, it can be observed that after the pure PP is burned, only a small amount of residual carbon remains on the edge of the tin foil, indicating that there is almost no residue left after the PP is burned. After the addition of flame retardants, the yield of residual carbon in PP composite materials increases. For the two groups of composite materials PP / CMSs (a) and PP / CMSs (b), the amount of residual carbon generated after combustion is relatively small. However, when the HCCFD flame retardant is added, a thin layer of residual carbon is left on the tin foil after combustion of the PP / HCCFD composite material. Compared with the PP / CMSs (a) and PP / CMSs (b) composite materials, the residual carbon is greater, indicating that the graphitized structure of HCCFD is conducive to the formation of residual carbon.

[0045] Further analysis of the morphology of residual carbon was carried out by scanning the carbon residue after burning pure PP and PP composite materials through SEM. The results are as follows: Figure 3 As shown in the SEM image of pure PP, almost no residual carbon is observed, indicating that the residual carbon produced during PP combustion cannot block the heat generated during combustion. The residual carbon in the PP / CMSs (a) composite has a certain carbon layer structure compared to pure PP, but the carbon layer is discontinuous and not dense, and has many small pores, indicating that the carbon layer generated by the PP / CMSs (a) composite cannot effectively isolate the transfer of oxygen and combustible gases and effectively block heat. The carbon layer in the PP / CMSs (b) composite is discontinuous and porous, similar to the PP / CMSs (a) composite. The residual carbon in the PP / HCCFD composite is more dense and continuous than that of pure PP and the above two composites, but pores are still present. It is worth noting that the SEM micromorphology of the three PP composites reveals numerous small spherical particles embedded in the carbon layer, indicating that during combustion, some carbon microspheres and spherical carbon particles resist the high temperature and form a carbon skeleton during the combustion of the PP matrix, which can prevent the escape of heat and gas generated by the PP reaction. The advantage of HCCFD as a carbon skeleton is more obvious.

[0046] The graphitization degree of residual carbon in PP / CMSs(a), PP / CMSs(b) and PP / HCCFD composites was analyzed by Raman spectroscopy. Figure 4 As shown in the Raman spectra of residual carbon in PP / CMSs (a), PP / CMSs (b) and PP / HCCFD composites, the carbon residue at 1365 cm -1 and 1595cm -1There are two strong absorption peaks, corresponding to D band and G band respectively. Generally speaking, the degree of graphitization of residual carbon can be evaluated by the relative intensity ratio of D and G bands (ID / IG). The lower the ID / IG ratio, the higher the degree of graphitization of the carbon layer, and the better the quality of the carbon layer. Test results show that the ID / IG values of the residual carbon of PP / CMSs(a), PP / CMSs(b) and PP / HCCFD composites are 1.37, 1.65 and 0.77 respectively. Among them, the ID / IG value of the PP / HCCFD composite is the lowest, indicating that the residual carbon has the highest degree of graphitization, and the carbon layer structure is more compact and orderly. This high-quality graphitized carbon layer can more effectively block the transfer of heat and the diffusion of flammable gas, thereby significantly improving the thermal stability of the carbon layer and providing better protection for the interior of the matrix.

[0047] Example 1

[0048] (1) A certain amount of CCFD (calcium carbide furnace dust) was weighed and poured into a beaker, and the amount of hydrochloric acid solution (2 mol / L) was added to the beaker with a solid-liquid ratio (g:mL) of CCFD:hydrochloric acid (1:15), and a glass rod was used to stir the reaction to obtain a black suspension. The black suspension in the beaker was placed in a 60°C water bath for stirring for 60 min, and after the end, the black suspension in the beaker was left still for 10 min, then filtered through a Buchner funnel, washed with deionized water, and dried at 80°C under vacuum for 8 h to obtain spherical carbon particles HCCFD.

[0049] (2) 1 mmol of Co(NO3)2·6H2O and 4 mmol of 2-methylimidazole were dissolved in 25 mL of methanol and 20 mL of methanol respectively, and after ultrasonic dissolution, the transparent solution with 2-methylimidazole was poured into the pink solution with Co(NO3)2·6H2O, mixed, and then left to age for 24 h. The purple solid was collected by filtration, washed with methanol 3 times, and dried at room temperature to obtain ZIF-67.

[0050] (3) 0.1 g of ZIF-67 and 0.05 g of HCCFD were dispersed in 100 mL of anhydrous ethanol, and ultrasonic was applied for more than 15 min. After uniform dispersion, the HCCFD suspension and the ZIF-67 suspension were mixed, and then the beaker was placed in a heat collecting constant temperature heating magnetic stirrer for magnetic stirring at room temperature for 1 h. 0.6 g of Ni(NO3)2·6H2O was dissolved in 20 mL of anhydrous ethanol, and then poured into the beaker in the heat collecting constant temperature heating magnetic stirrer, and then magnetic stirred at room temperature for 2 h. The liquid was centrifuged, washed with deionized water and anhydrous ethanol 3 times, vacuum dried, and ground to obtain HCCFD@NiCo-LDH.

[0051] (4) Take 1 g of HCCFD@NiCo-LDH dispersed in 100 mL of ethanol, 0.1 g of TP (tea polyphenol) dispersed in 25 mL of ethanol, after ultrasonic dissolution, mix the above two solutions in a three-necked flask, under nitrogen atmosphere, put the three-necked flask into the heat collecting constant temperature heating magnetic stirrer at 50℃ for 6h, after the reaction is finished, take the sample solution for filtration treatment, wash with deionized water and anhydrous ethanol for 3 times, dry, grind the sample to obtain HCCFD@NiCo-LDH@TP.

[0052] Comparative Example 1

[0053] A certain amount of CCFD (calcium carbide furnace dust) was weighed and poured into a beaker, and the amount of hydrochloric acid solution (2 mol / L) was added to the beaker at a solid-liquid ratio (g:mL) of CCFD:hydrochloric acid (1:15), and the reaction was fully stirred with a glass rod to obtain a black suspension. The black suspension in the beaker was placed in a 60℃ water bath for stirring for 60 min, and after the reaction was completed, the black suspension in the beaker was left to stand for 10 min, and then filtered through a Buchner funnel, washed with deionized water, and dried at 80℃ under vacuum for 8h to obtain spherical carbon particles HCCFD.

[0054] Comparative Example 2

[0055] (1) A certain amount of CCFD (calcium carbide furnace dust) was weighed and poured into a beaker, and the amount of hydrochloric acid solution (2 mol / L) was added to the beaker at a solid-liquid ratio (g:mL) of CCFD:hydrochloric acid (1:15), and the reaction was fully stirred with a glass rod to obtain a black suspension. The black suspension in the beaker was placed in a 60℃ water bath for stirring for 60 min, and after the reaction was completed, the black suspension in the beaker was left to stand for 10 min, and then filtered through a Buchner funnel, washed with deionized water, and dried at 80℃ under vacuum for 8h to obtain spherical carbon particles HCCFD.

[0056] (2) 1 mmol of Co(NO3)2·6H2O and 4 mmol of 2-methylimidazole were dissolved in 25 mL of methanol and 20 mL of methanol respectively, after ultrasonic dissolution, the transparent solution with 2-methylimidazole was poured into the pink solution with Co(NO3)2·6H2O, after mixing, the solution was left to stand for 24h, the purple solid was collected by filtration, washed with methanol for 3 times, and dried at room temperature to obtain ZIF-67.

[0057] (3) Take 0.1 g ZIF-67, 0.05 g HCCFD respectively dispersed in 100 mL of anhydrous ethanol, ultrasonic for 15 min above, after uniform dispersion, mix the above HCCFD suspension and ZIF-67 suspension, then put the beaker into the heat collecting constant temperature heating magnetic stirrer, magnetic stirring at room temperature for 1 h, 0.6 g Ni(NO3)2·6H2O is dissolved in 20 mL of anhydrous ethanol, then poured into the beaker in the heat collecting constant temperature heating magnetic stirrer, then magnetic stirring at room temperature for 2 h, the liquid is centrifuged, washed with deionized water and anhydrous ethanol for 3 times, vacuum drying, grinding sampling to obtain HCCFD@NiCo-LDH.

[0058] As shown in Figure 5 , HCCFD only has a relatively obvious and wide diffraction powder at about 2θ = 26.2°, which is the graphite (002) crystal face of HCCFD. Observing and analyzing the XRD pattern of HCCFD@NiCo-LDH, several peaks appear at 2θ = 11.1°, 22.5°, 34.1° and 60.1°, which are mainly attributed to the diffraction peaks of NiCo-LDH, corresponding to the crystal face diffraction peaks of (003), (006), (009) and (110), and the graphite (002) crystal face of HCCFD, and no new diffraction peak appears, indicating that NiCo-LDH and HCCFD are only physically adsorbed, and no new chemical reaction occurs. However, for TP modified HCCFD@NiCo-LDH, it still shows the crystal face diffraction peaks of NiCo-LDH, and the graphite (002) crystal face of HCCFD, indicating that the modification does not affect the crystal structure of HCCFD@NiCo-LDH. However, due to the addition of TP, the XRD pattern of HCCFD@NiCo-LDH@TP is different from that of HCCFD@NiCo-LDH, the diffraction peak intensity of HCCFD@NiCo-LDH@TP is lower, and the baseline is unstable, which is mainly due to the decrease of the crystallinity of HCCFD@NiCo-LDH caused by the non-crystalline organic tea polyphenol core-shell wrapping.

[0059] As shown in Figure 6 , HCCFD has a relatively wide vibration peak at 3400-3600 cm –1 , which is attributed to the stretching vibration of the hydroxyl group (v-OH) group, indicating that the surface has a hydroxyl group, and the vibration peak appears at about 2900 cm –1 , which is derived from the stretching vibration peak of C-H bond, appearing at 1580 cm –1 , 1076 cm –1 characteristic peaks, which are respectively attributed to the C=N bending vibration peak and C-C stretching vibration peak in HCCFD. In the graph of HCCFD@NiCo-LDH, the wide band is at 1634 cm –1The absorption band centered is due to the bending vibration of water molecules between NiCo-LDH layers; due to NO3 - The vibration of the NO band, as well as the MO and MOM lattice vibrations (M represents Ni or Co), the absorption peak of NiCo-LDH is located at 1389 cm –1 , the characteristic absorption wave number is between 500 and 800 cm –1 There is a strong absorption peak between 1580cm –1 、1076cm –1 It is attributed to the C=N bending vibration peak and CC stretching vibration peak in HCCFD. At the same time, in addition to the characteristic peaks of HCCFD and NiCo-LDH, new characteristic peaks appear in HCCFD@NiCo-LDH@TP, specifically, at 1500~1000cm –1 The bands are mainly attributed to the C=C vibration peak of aromatic hydrocarbons in TP, the presence of benzene ring structure in TP, and the characteristic peaks of CO (phenol and ether bond). In addition, HCCFD@NiCo-LDH@TP has a peak at 3400~3600 cm –1 The strong absorption on the left and right is caused by the stretching vibration of the -OH group. These newly appeared peaks indicate that TP is successfully wrapped on the surface of HCCFD@NiCo-LDH.

[0060] like Figure 7 As shown in the SEM image of HCCFD, the morphology of spherical particles is shown, the surface of the spheres is rough, and there are tiny pores on the surface of the HCCFD spherical carbon particles. For HCCFD@NiCo-LDH, it can be observed that compared with the pores and roughness on the surface of HCCFD spherical particles, HCCFD@NiCo-LDH is more manifested in the adsorption of nanoparticles on the surface of the spheres. After TP modification, the surface of the spherical carbon particles is still rough, but the nano-sheet structure is not significant, and the particle size is slightly increased. Combined with TEM analysis, HCCFD presents a hollow sphere morphology with a clear outline. After modification with NiCo-LDH and TP, the hollow structural characteristics of HCCFD are significantly masked, the surface of the sphere is wrapped by a layer of material, the morphology becomes rough and the boundaries are blurred, and small particles can be observed distributed on the surface of the sphere.

[0061] like Figure 8As shown, in general, the lower the WCA value of the material, the stronger its hydrophilicity, and the higher the WCA value, the stronger its hydrophobicity; since the HCCFD spherical carbon particles are exposed on the outside, and the surface of the sphere can contain a large number of hydrophilic groups, the WCA thereof is 8.3°, exhibiting strong hydrophilicity; after modification by NiCo-LDH, the hydrophilic groups of HCCFD@NiCo-LDH are reduced, and the hydrophobicity is improved to 32.7°, but it still belongs to a hydrophilic material. To further optimize its performance, organic modification is performed by tea polyphenol, and the hydrophobicity of HCCFD@NiCo-LDH@TP is improved to 48.6°, which can be due to the fact that the hydrophobic groups in the tea polyphenol cover the surface of HCCFD@NiCo-LDH. With the gradual advancement of the modification process, the hydrophobicity of the material is continuously improved, which has a positive effect on enhancing the interfacial interaction between the flame retardant and the PP matrix, and helps to stably improve the flame retardant performance of the PP material.

[0062] Performance test:

[0063] By melt blending, the flame retardants prepared in Example 1 (S1) and Comparative Examples 1 and 2 (D1, D2) are melt blended with polypropylene (PP) to prepare a PP composite material with a flame retardant mass fraction of 10wt%, as shown in Figure 9 As shown in the PP / HCCFD diagram, it can be observed that HCCFD has obvious agglomeration in PP, the surface is rough and has large particles protruding, the interface between HCCFD and the PP matrix is obvious, and at the same time, it can be observed that HCCFD is unevenly dispersed on the PP material, which can be due to the poor compatibility between the inorganic HCCFD and the organic PP matrix. After modification by NiCo-LDH, the small particles of HCCFD@NiCo-LDH are obviously reduced, and the agglomeration phenomenon is weakened, and the interface is blurred, but there are still small particles unevenly dispersed on the surface. Based on this, after organic modification by tea polyphenol, the agglomeration of HCCFD is effectively inhibited, the particles are not obvious on the cross section, and HCCFD@NiCo-LDH@TP can effectively embed into the PP material, which indicates that the compatibility and dispersibility of HCCFD@NiCo-LDH@TP and PP are obviously improved, which can be due to the fact that the improvement of the hydrophobicity of HCCFD@NiCo-LDH@TP improves the compatibility of the flame retardant and the PP material.

[0064] The flame retardant performance and mechanical property test results of different PP composites are shown in Table 1:

[0065] Table 1 Flame retardant performance and mechanical property test results of different PP composites

[0066]

[0067]

[0068] As shown in Table 1, the tensile strength and elongation at break of pure PP were 25.2 MPa and 106%, respectively. Due to the significant difference in structure and composition between the flame retardant and the PP matrix, the tensile strength and elongation at break of the PP composite decreased to some extent after the flame retardant was added to the PP matrix. When the addition amount of the flame retardant was 10 wt%, the tensile strength of the PP / HCCFD and PP / HCCFD@NiCo-LDH composites decreased to 16.1 MPa and 16.6 MPa, respectively. The mechanical properties of these two composites decreased so dramatically because the compatibility between HCCFD and HCCFD@NiCo-LDH and the PP matrix was not ideal, that is, there was a significant separation phenomenon between HCCFD and HCCFD@NiCo-LDH and the PP matrix. After TP modification, the mechanical properties of the PP / HCCFD@NiCo-LDH@TP composite had improved, and the tensile strength and elongation at break of the PP / HCCFD@NiCo-LDH@TP composite had increased to 17.3 MPa and 61%, respectively.

[0069] The LOI value of pure PP was 17.2%, and the UL-94 did not reach any level, indicating that pure PP was flammable and accompanied by the occurrence of melt dripping phenomenon during combustion, which was extremely easy to cause the occurrence of "second fire", so the flame retardant performance of PP needed to be improved. With the increase of the addition amount of the flame retardant, the LOI value and UL-94 level of all the PP composites showed different degrees of improvement. When the addition amount reached 10 wt%, the LOI value of the PP / HCCFD@NiCo-LDH@TP composite increased to 26.7%, and passed the UL-94 V-1 level test, reaching the level of difficult flammable materials. Compared with the PP / HCCFD and PP / HCCFD@NiCo-LDH composites, the flame retardant performance of the PP / HCCFD@NiCo-LDH@TP composite was significantly improved, which was mainly due to the surface modification of tea polyphenol (TP) and the synergistic effect between HCCFD and NiCo-LDH. This synergistic effect could effectively delay the combustion rate, inhibit the flame spread, and reduce the melt dripping phenomenon during the combustion process of the composite, thereby significantly improving the overall flame retardant performance of the material.

[0070] The digital photos of the residual carbon of pure PP, PP / HCCFD, PP / HCCFD@NiCo-LDH and PP / HCCFD@NiCo-LDH@TP composites are shown in Fig. 6. Figure 10As shown. After combustion, pure PP has almost no residual carbon, indicating that pure PP cannot generate residual carbon that can protect the matrix during combustion. With the addition of HCCFD, HCCFD@NiCo-LDH and HCCFD@NiCo-LDH@TP, the residual carbon residue increases, and the color of the residual carbon becomes darker, indicating that the PP composite material generates a more stable carbon layer structure. Among them, the residual carbon of the PP / HCCFD composite material is loose, and the residual carbon has many pores, and this may be related to the volatilization of combustible degradation products during the combustion process. The carbon blocks of the PP / HCCFD@NiCo-LDH composite material become larger, but the residual carbon is discontinuous and not dense. In contrast, the color of the residual carbon of the PP / HCCFD@NiCo-LDH@TP composite material deepens, and the carbon layer is denser. In order to further analyze the residual carbon structure of the PP composite material, the carbon layer was scanned by SEM, and the results are shown as follows Figure 11 As shown in the figure, it is observed that the residual carbon of the PP / HCCFD@NiCo-LDH@TP composite material becomes dense and continuous. The main reason is that tea polyphenols promote the formation of the carbon layer during combustion, while the catalytic carbonization of the transition metal nickel and cobalt helps to generate a strong carbon layer. In contrast, the residual carbon of PP, PP / HCCFD, and PP / HCCFD@NiCo-LDH composite materials has pores and cracks. At the same time, due to the addition of HCCFD@NiCo-LDH@TP, the residual carbon of the PP / HCCFD@NiCo-LDH@TP composite material transforms from large open pores to small closed pores, and the carbon layer structure becomes stable, which greatly enhances the barrier effect of the carbon layer during combustion, thereby improving the flame retardancy of PP.

[0071] The structure of the carbon layer was verified by Raman spectroscopy, e.g. Figure 12 As shown in Figure 2, the Raman spectra of the carbon residues in the PP / HCCFD, PP / HCCFD@NiCo-LDH, and PP / HCCFD@NiCo-LDH@TP composites show ID / IG values ​​of 0.77, 0.75, and 0.71, respectively, indicating a gradually increasing degree of graphitization. The PP / HCCFD@NiCo-LDH@TP composite exhibits a relatively low ID / IG value, indicating a high degree of graphitization and good thermal stability of the carbon layer, resulting in improved carbon layer quality. This suggests that the carbon residues generated during the combustion of the PP / HCCFD@NiCo-LDH@TP composite provide more effective protection for the matrix material. This is likely due to the inherent graphitic structure of HCCFD, which acts as a carbon skeleton that resists the heat of combustion. As the combustion reaction proceeds, the combined catalytic carbonization of tea polyphenols and NiCo-LDH promotes the generation of more carbon residues from the polymer, which adheres to the HCCFD carbon skeleton. Finally, the decomposition of transition metal oxides and aromatic rings by NiCo-LDH and tea polyphenols further enhances the stability of the carbon layer, forming a strong physical barrier that prevents further combustion.

Claims

1. A method for preparing a carbon particle @ nickel-cobalt hydrotalcite @ tea polyphenol organic-inorganic hybrid flame retardant, characterized in that: The steps include: (1) adding calcium carbide furnace dust to a hydrochloric acid solution, stirring the solution sufficiently for reaction, and then separating the solid and liquid to obtain carbon particles; (2) Ultrasonic dispersion of ZIF-67 and carbon particles in anhydrous ethanol to obtain dispersion A; ultrasonic dispersion of Ni(NO3)2·6H2O in anhydrous ethanol to obtain dispersion B; dispersion B is added to dispersion A, and the mixture is stirred thoroughly for reaction, followed by solid-liquid separation to obtain carbon particles@nickel-cobalt hydrotalcite; (3) Ultrasonic dispersion of carbon particles @ nickel cobalt hydrotalcite in deionized water to obtain dispersion C; ultrasonic dispersion of tea polyphenols in anhydrous ethanol to obtain dispersion D; dispersion D is added to dispersion C, and the mixture is heated and stirred for reaction, followed by solid-liquid separation to obtain a carbon particle @ nickel cobalt hydrotalcite @ tea polyphenols organic-inorganic hybrid flame retardant.

2. The preparation method according to claim 1, characterized in that In step (1), the mass volume ratio of calcium carbide furnace dust to hydrochloric acid is 1g:10-20mL; and the concentration of the hydrochloric acid solution is 1-3mol / L.

3. The preparation method according to claim 1, characterized in that In step (2), the mass volume ratio of ZIF-67, carbon particles and anhydrous ethanol in dispersion A is 0.05-0.2 g: 0.01-0.1 g: 100 mL, and the mass volume ratio of Ni(NO3)2·6H2O and anhydrous ethanol dispersion in dispersion B is 0.2-0.5 g: 10 mL.

4. The preparation method according to claim 1, characterized in that In step (3), the concentration of carbon particles @ nickel-cobalt hydrotalcite in dispersion C is 0.005-0.015 g / mL, and the mass volume ratio of tea polyphenols to anhydrous ethanol in dispersion D is 0.02-0.05 g:10 mL.

5. The preparation method according to claim 1, characterized in that In step (3), the heating temperature is 40-60°C.

6. Carbon particle@nickel-cobalt hydrotalcite@tea polyphenol hybrid flame retardant prepared by the preparation method according to any one of claims 1 to 5.

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