Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to provide the triazine-based organic covalent skeleton modified hydrotalcite-based flame retardant and the preparation method thereof, wherein the triazine-based organic covalent skeleton is generated by in-situ polymerization reaction on the surface of MgAl-LDH, so that the stability and hydrophobicity of hydrotalcite are improved, the agglomeration performance of hydrotalcite and the compatibility with a polymer matrix are improved, and the mechanical performance and the flame retardant performance of a composite material are obviously improved.
In order to achieve the technical purpose, the invention adopts the following technical scheme:
a preparation method of a triazine-based organic covalent skeleton modified hydrotalcite-based flame retardant comprises the following steps:
(1) Placing melamine and MgAl-LDH in DMF, and carrying out ultrasonic stirring to obtain slurry A; placing the trichlorohydrogen in DMF, and carrying out ultrasonic stirring to obtain slurry B;
(2) Slowly dripping the slurry B into the slurry A under the stirring condition, and then adding triethylamine to obtain slurry C; and (3) carrying out heating reaction on the slurry C to obtain the triazinyl organic covalent skeleton modified hydrotalcite-based flame retardant.
According to the invention, the triazinyl organic covalent skeleton is generated by in-situ polymerization reaction on the MgAl-LDH surface, and the surface morphology of the MgAl-LDH is obviously changed while nitrogen element is introduced, so that the stability and hydrophobicity of hydrotalcite are improved, and meanwhile, the agglomeration performance of hydrotalcite and the compatibility with a polymer matrix are improved. Moreover, the inventor also unexpectedly found that in the reaction process, the addition sequence and the mixing process of raw materials can obviously influence the surface morphology and the performance of the finally generated triazine-based organic covalent skeleton modified hydrotalcite-based flame retardant. Only when the method is adopted to firstly mix MgAl-LDH with melamine and then add the addition sequence and the mixing mode of the melamine, the MgAl-LDH is easier to surface modify, and the self-stacking condition of the MgAl-LDH is obviously improved. And other methods are adopted, such as mixing melamine and melamine chloride, and then adding MgAl-LDH; or the three are directly mixed, the surface of the obtained hydrotalcite-based flame retardant is relatively smooth, and the self-stacking condition is not improved. This is also evident in the mechanical properties and flame retardant properties of the finally obtained flame retardant composite.
Further, in the step (1), the mass ratio of MgAl-LDH to melamine is 2-3:1, a step of; in the slurry A, the concentration of MgAl-LDH is 10-20g/L; in the slurry B, the concentration of the trichlorohydrogen is 20-30g/L.
Further, in the step (2), in the slurry C, the mass ratio of MgAl-LDH to trichlorohydrogen is 3-5:1, the mass volume ratio of MgAl-LDH to triethylamine is 0.3-0.6g:1ml.
Further, in the step (2), the temperature of the heating reaction is 70-90 ℃ and the time is 8-12h.
The invention also provides the triazine-based organic covalent skeleton modified hydrotalcite-based flame retardant prepared by the preparation method.
The invention has the advantages that:
according to the invention, by strictly controlling the adding sequence and mixing process of the reaction raw materials, the triazinyl organic covalent skeleton is generated by in-situ polymerization reaction on the surface of MgAl-LDH, and the surface morphology of the MgAl-LDH is obviously changed while nitrogen element is introduced, so that the stability and hydrophobicity of hydrotalcite are improved, the agglomeration performance of hydrotalcite and the compatibility with a polymer matrix are improved, and the mechanical performance and flame retardant performance of the composite material are obviously improved.
Detailed Description
The invention will be further described with reference to the drawings and examples.
In the invention, mgAl-LDH is conventional magnesium-aluminum hydrotalcite and is prepared by the existing method, for example:
firstly, the molar ratio of magnesium-aluminum cations is 3:1 weighing 0.03mol of Mg (NO 3 ) 2 ·6H 2 O and 0.01mol of Al (NO) 3 ) 3 ·6H 2 O, dissolving the two into 200ml deionized water, and ultrasonically forming a mixed salt solution for standby. Accurately weighing urea with the total molar number of metal cations being 3.3 times, placing the urea into 200ml of deionized water, and performing ultrasonic dissolution for later use. The two materials are transferred into a 500ml hydrothermal reaction kettle with a polytetrafluoroethylene lining, fully mixed and transferred into an electric heating constant temperature drying oven for reaction for 24 hours at 110 ℃. Finally, carrying out suction filtration, washing, drying and grinding on the obtained product, and obtaining the product, namely the magnesium aluminum hydrotalcite (MgAl-LDH).
Example 1
(1) 3g of magnesium aluminum hydrotalcite (MgAl-LDH) and 1.11g of melamine are weighed and ultrasonically dispersed in 200ml of DMF to obtain slurry A, and the slurry A is transferred into a 500ml three-necked flask;
(3) And (3) weighing 0.75g of trichlorohydrogen, ultrasonically dispersing the trichlorohydrogen in 30ml of DMF to obtain slurry B, slowly dripping the slurry B into a three-necked flask, finally dripping 6ml of triethylamine to obtain slurry C, reacting at 90 ℃ for 12 hours, stirring the reaction process, and carrying out suction filtration, washing, drying and grinding on the obtained target product after the reaction is finished to obtain the triazinyl organic covalent skeleton modified magnesium aluminum hydrotalcite-based flame retardant, namely LDH@TOF.
As shown in fig. 1, ldh@tof showed characteristic diffraction peaks of (003), (006), (009), (015), (018) unique to the hydrotalcite material, indicating that it still retains the layered structure of LDH. Compared with the diffraction peak of LDH, the LDH@TOF presents a plurality of new diffraction peaks, all characteristic diffraction peaks of the new diffraction peaks can simultaneously correspond to the diffraction peaks of the LDH and the TOF (triazinyl organic covalent skeleton), and the peak shape is still sharp and strong, which indicates that the LDH still maintains a good crystal form after modification.
As shown in FIG. 2, not only the vibration peak of LDH but also 1664cm appears in the FT-IR spectrum of LDH@TOF -1 And 1536cm -1 The oscillation peak of TOF triazine ring appears nearby, further demonstrating the successful synthesis of LDH@TOF.
As shown in fig. 3, both LDH (upper) and ldh@tof (lower) exhibit a sheet structure, typically a magnesium aluminum hydrotalcite structure. The LDH surface is smooth, the particle size is uniform, the edge is smooth, the LDH@TOF surface is rough and covered by a layer of substance, which shows that the triazinyl organic covalent skeleton generated by in-situ reaction of melamine and cyanuric chloride is successfully modified and acted on the LDH surface.
Comparative example 1
(1) 3g of magnesium aluminum hydrotalcite (MgAl-LDH) is weighed and ultrasonically dispersed in 200ml of DMF and transferred into a 500ml three-necked flask;
(2) 1.11g of melamine and 0.75g of melamine are weighed and dispersed in 30ml of DMF together by ultrasonic, then slowly added dropwise into a three-necked flask, finally 6ml of triethylamine is added dropwise, the reaction is carried out at 90 ℃ for 12 hours, stirring is kept in the reaction process, and after the reaction is finished, the obtained target product is subjected to suction filtration, washing, drying and grinding to obtain the triazinyl organic covalent skeleton modified magnesium aluminum hydrotalcite-based flame retardant, which is marked as D1.
Comparative example 2
(1) 3g of magnesium aluminum hydrotalcite (MgAl-LDH), 1.11g of melamine and 0.75g of trichlorohydrogen are weighed and dispersed in 200ml of DMF together by ultrasonic, and then transferred into a 500ml three-necked flask;
(2) 6ml of triethylamine is measured and dripped into a three-necked flask, the reaction is carried out for 12 hours at 90 ℃, stirring is kept in the reaction process, and after the reaction is finished, the obtained target product is subjected to suction filtration, washing, drying and grinding to obtain the triazinyl organic covalent skeleton modified magnalium hydrotalcite-based flame retardant, which is marked as D2.
As shown in fig. 4, the ldh@tof prepared in example 1 had significantly higher surface modification rate than D1 prepared in comparative example 1 and D2 prepared in comparative example 2, and D1 and D2 had smooth surface morphology and severe self-stacking.
The LDH, the ldh@tof prepared in example 1, the D1 prepared in comparative example 1, and the D2 prepared in comparative example 2 were melt-blended with polypropylene (PP) in a mass fraction of 20wt% of a flame retardant by a melt blending method to prepare PP composite materials, and flame retardant and mechanical properties were tested, and the results are shown in table 1:
TABLE 1 flame retardant and mechanical Property test results for different PP composites
From table 1, after adding the flame retardants LDH and ldh@tof, the tensile strength and elongation at break of the PP/LDH and PP/ldh@tof composite materials all show a tendency to decrease, and compared with the aggregation phenomenon of pure LDH in the PP matrix, after adding ldh@tof, the compatibility of ldh@tof and the PP matrix is greatly improved, and the decrease of mechanical performance parameters is obviously relieved. Pure PP is a material which is quite flammable, and after the flame retardant is added, the LOI value and the UL-94 grade of the PP composite material show rising trend, and the peak heat release rate and the total heat release rate are correspondingly reduced. And under the same load, the LOI value and the UL-94 grade of the PP/LDH@TOF are obviously better than those of the PP/LDH, which shows that the flame retardant property of the LDH@TOF is obviously stronger than that of the LDH, namely, after being modified by a triazinyl organic covalent skeleton, the flame retardant property of the LDH is obviously improved.
Further, as is clear from a comparison of the flame retardant properties and mechanical properties of the PP composite material obtained by adding the ldh@tof prepared in example 1, the D1 prepared in comparative example 1, and the D2 prepared in comparative example 2 as flame retardants, the order and mixing manner of raw materials used in example 1 (i.e., mgAl-LDH is mixed with melamine before adding melamine), and the order and mixing manner of raw materials used in comparative example 1 and comparative example 2 (i.e., melamine and melamine are mixed before adding MgAl-LDH or directly mixing the three) are significantly better than those of the PP composite material obtained by adding the ldh@tof prepared in example 1 as flame retardant.