CN110607046A - Flame-retardant polyvinyl alcohol aerogel and preparation method thereof - Google Patents
Flame-retardant polyvinyl alcohol aerogel and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a flame-retardant polyvinyl alcohol aerogel which is prepared by the cross-linking reaction of polyvinyl alcohol and phosphorylated cellulose. The preparation method comprises the following steps: s1, adding cellulose and phosphorous acid into molten urea, reacting for 4-8h at 140-180 ℃, adding water and ethanol, and separating out precipitate to obtain phosphorized cellulose; s2, ultrasonically dispersing the phosphated cellulose in water; s3, dissolving polyvinyl alcohol in water at 80-95 ℃; s4, adding a phosphorized cellulose solution into a polyvinyl alcohol aqueous solution, then adding a cross-linking agent aqueous solution, and reacting at the temperature of 60-85 ℃ for 1-4 h to prepare a polyvinyl alcohol/phosphorized cellulose cross-linked hydrogel; s5, freeze-drying the hydrogel for 24-72 hours to obtain the flame-retardant polyvinyl alcohol aerogel. The polyvinyl alcohol aerogel disclosed by the invention has excellent flame retardant property and excellent mechanical property because the phosphorized cellulose contains a large amount of P elements.
Description
Technical Field
The invention relates to the technical field of composite materials, in particular to a flame-retardant polyvinyl alcohol aerogel and a preparation method thereof.
Background
Polyvinyl alcohol (PVA) is a common polyhydroxy water-soluble high molecular polymer, and the synthetic raw material is vinyl acetate (VAc). The polyvinyl acetate is obtained by a suspension polymerization method and then is obtained by catalytic alcoholysis of alkali. Some of the physical properties of different types of polyvinyl alcohol differ: the shapes of the particles are different according to different models, and the particles are white flaky, flocculent, granular and the like; the water solubility of the water-soluble polymer also greatly varies according to the model. Because the molecular chain of polyvinyl alcohol contains many polar groups-hydroxy (-OH), and the hydrophilic power of hydroxy group is stronger, so that the water-solubility of polyvinyl alcohol is good, and it can be used as adhesive. The polyvinyl alcohol molecular chain has regular and symmetrical structure and excellent film forming property, can be used for preparing film products, and the film is soft, transparent, wear-resistant and tough, and the tensile strength of the film is increased along with the improvement of the alcoholysis degree and the polymerization degree of the polyvinyl alcohol. Meanwhile, the polyvinyl alcohol also has good biodegradability and is a very safe polymer.
The polyvinyl alcohol aerogel is a porous solid material, has the general property of hydrogel, and has the characteristics of low thermal conductivity, strong insulating capability, low refractive index, low toxicity, good biocompatibility and the like. But due to the defects of high flammability, poor mechanical property and the like, the industrial application is greatly limited. In recent years, with the rise of polyvinyl alcohol aerogel, people try to solve the problems of low strength and flame retardance of the polyvinyl alcohol aerogel by compounding and modifying the polyvinyl alcohol and a phosphorus flame retardant. The application of phosphorus flame retardants to polymer materials has two main ways: one is to incorporate the phosphorus-containing flame retardant into the polymer during production by physical addition; the other is to introduce a covalent bond containing phosphorus on the polymer structure by means of a chemical reaction. By adding the nano particles with specific properties, the polyvinyl alcohol aerogel can have the properties after reaching a certain content, and the appearance of the added nano particles is regulated to ensure that the polyvinyl alcohol aerogel has multiple properties.
Disclosure of Invention
The invention aims to provide a novel flame-retardant polyvinyl alcohol aerogel, which overcomes the problem of flammability of the polyvinyl alcohol aerogel in the prior art.
The invention also aims to provide a preparation method of the flame-retardant polyvinyl alcohol aerogel.
The flame-retardant polyvinyl alcohol aerogel provided by the invention is prepared by carrying out a crosslinking reaction on polyvinyl alcohol and phosphorylated cellulose. The weight ratio of the polyvinyl alcohol to the phosphorylated cellulose is 50-120: 0.5-35.
The phosphorized cellulose is prepared by modifying cellulose with phosphorous acid and urea. Adding cellulose and phosphorous acid into molten urea, reacting for 4-8h at 140-180 ℃, then adding water and ethanol, and separating out precipitate to obtain the phosphorized cellulose. The length-diameter ratio of the phosphorized fiber is 100-300. The cellulose is one of microfibrillated cellulose, nanocrystalline cellulose and bacterial nano cellulose, and the length-diameter ratio of the cellulose is 50-600.
The polyvinyl alcohol is one of polyvinyl alcohol 1788, polyvinyl alcohol 1799, polyvinyl alcohol 2099, polyvinyl alcohol 2488 and polyvinyl alcohol 2499.
A preparation method of flame-retardant polyvinyl alcohol aerogel comprises the following steps:
s1, preparing the phosphated cellulose, comprising the following steps:
s11, heating 40-150 parts by weight of urea to 130-150 ℃ until the urea is molten;
s12, sequentially adding 10-25 parts by weight of cellulose and 50-170 parts by weight of phosphorous acid into molten urea for full dissolution, then raising the temperature to 140-180 ℃, and reacting at constant temperature for 4-8 h;
s13, dissolving the product obtained in the step S12 in water, then adding 100-500 parts by weight of absolute ethyl alcohol to separate out white precipitate, and drying the precipitate at 60-90 ℃ to obtain the phosphorylated cellulose.
S2, ultrasonically dispersing 0.5-35 parts by weight of phosphorized cellulose in 50-100 parts by weight of water for 30-60min to obtain a phosphorized cellulose solution.
S3, dissolving 50-120 parts by weight of polyvinyl alcohol in 2000 parts by weight of water at 80-95 ℃ for 5-10h to obtain the polyvinyl alcohol aqueous solution.
S4, adding the phosphorized cellulose solution into a polyvinyl alcohol aqueous solution, uniformly mixing, then adding a cross-linking agent aqueous solution, and reacting for 1-4 hours at the temperature of 60-85 ℃ to obtain the polyvinyl alcohol/phosphorized cellulose cross-linked hydrogel. The cross-linking agent aqueous solution is prepared by dissolving 13-40 parts by weight of cross-linking agent in 50-100 parts by weight of water, wherein the cross-linking agent is one of paraformaldehyde, glutaraldehyde, borax salt, maleic anhydride, phthaloyl chloride, phthalic anhydride, succinic anhydride, phthalic acid, epichlorohydrin, potassium permanganate and copper hydroxide.
S5, freeze-drying the cross-linked hydrogel of the polyvinyl alcohol/the phosphorized cellulose for 24-72 hours to obtain the flame-retardant polyvinyl alcohol aerogel.
Compared with the prior art, the invention has the advantages that:
firstly, the polyvinyl alcohol/phosphorized cellulose (PVA/PCF) aerogel prepared by the invention adopts phosphorized cellulose reaching the nanometer level, can be uniformly dispersed in an aqueous solution, and forms aerogel with a three-dimensional network structure after freeze drying of a mixed solution of the phosphorized cellulose and the polyvinyl alcohol through the action of hydrogen bonds generated between the phosphorized cellulose and the polyvinyl alcohol, thereby improving the mechanical property of the polyvinyl alcohol aerogel. Due to the fact that the phosphorized cellulose contains a large amount of P elements, the polyvinyl alcohol/phosphorized cellulose aerogel has flame retardant performance. The urea can promote the dissolution of cellulose, and simultaneously, N in the urea reacts with hydroxyl on the cellulose to finally form a P-N system, thereby further improving the flame retardant effect.
Secondly, the prepared polyvinyl alcohol/phosphorized cellulose aerogel has good flame retardant property, mechanical strength and thermal stability, and the problem of poor comprehensive performance of the polyvinyl alcohol aerogel is solved.
And thirdly, in the preparation process of the material, the dispersion medium is water, so that the material is non-toxic, pollution-free, ecological and environment-friendly, and conforms to the development trend of current environment-friendly materials. Moreover, the preparation process is simple, the cost is low, the industrial production is easy, and the method has great practical value and popularization value.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Drawings
FIG. 1 is an infrared absorption spectrum (FTIR) of the cellulose described in example 1 and the phosphorylated cellulose described in example 1.
Figure 2 is a stress strain plot of the flame retardant polyvinyl alcohol aerogel described in example 2 versus the neat polyvinyl alcohol aerogel described in comparative example 1.
Fig. 3 is a Scanning Electron Microscope (SEM) image of the flame retardant polyvinyl alcohol aerogel described in example 2 and the pure polyvinyl alcohol aerogel described in comparative example 1.
Figure 4 is a thermogravimetric analysis (TGA) plot of the flame retardant polyvinyl alcohol aerogel described in example 2 versus the pure polyvinyl alcohol aerogel described in comparative example 1.
Detailed Description
The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.
The performance test related in the embodiment of the invention is carried out according to the following method:
(1) infrared absorption spectrometer
A Nicolet FTIR 6700 infrared spectrometer manufactured by Nicolet Inc. of America was used. At 2cm-1The chemical structures of the cellulose powder and the phosphated cellulose were analyzed. Each sample was at 400-4000cm-1An in-range scan.
(2) Compression performance test
The test was carried out by using a CMT6104 microcomputer controlled universal tester. And wiping water on the pure polyvinyl alcohol hydrogel and the flame-retardant polyvinyl alcohol hydrogel sample, wherein the thickness of each sample is 20mm, the compression speed is set to be 2mm/min, and five samples in each group are subjected to a parallel test to determine the compression performance of the hydrogel sample.
(3) Scanning Electron Microscope (SEM)
The microscopic structure of the aerogel is observed by a JEOL JSM-7500FA scanning electron microscope. And spraying gold on the sample to be tested before testing.
(4) Thermogravimetric analysis (TGA)
Thermal properties of the pure polyvinyl alcohol aerogel and the flame-retardant polyvinyl alcohol aerogel were measured using a thermogravimetric analyzer (TA instrument Q500). The sample is in nitrogen atmosphere, and the gas flow rate is 20 ml/min; the heating rate is 10 ℃/min, and the testing temperature range is 40-800 ℃.
(5) Limiting Oxygen Index (LOI) and vertical burn (UL-94)
And (3) measuring the limiting oxygen indexes of the pure polyvinyl alcohol aerogel and the flame-retardant polyvinyl alcohol aerogel by using an oxygen index tester (HC-2). The dimensions of the sample were 10mm by 150 mm.
The vertical combustion rating of the pure polyvinyl alcohol aerogel and the flame retardant polyvinyl alcohol aerogel was determined using a vertical combustor (CZF-2). Aerogel samples were tested according to ASTM D3801 and had sample sizes of 10mm by 15mm by 150 mm.
Example 1
A preparation method of flame-retardant polyvinyl alcohol aerogel comprises the following steps:
s1, adding 55 parts by weight of urea into a three-neck flask provided with a thermometer, an electronic constant speed stirrer and a reflux condenser, and heating to 132 ℃ until the urea is molten; adding 10 parts by weight of cellulose with the length-diameter ratio of 100 (nanocrystalline cellulose) and 70 parts by weight of phosphorous acid into the melted urea melt, fully dissolving, then raising the temperature to 140 ℃, and reacting for 4 hours at the temperature; dissolving the product obtained by the reaction in water, then adding 200 parts by weight of absolute ethyl alcohol to obtain white precipitate, and drying the precipitate at 60 ℃ to obtain the phosphorized cellulose.
S2, ultrasonically dispersing 20 parts by weight of phosphated cellulose with the length-diameter ratio of 200 in 67 parts by weight of water for 40min to obtain a phosphated cellulose solution;
s3, dissolving 100 parts by weight of polyvinyl alcohol 1799 in 1500 parts by weight of water at 95 ℃ for 5 hours to obtain a polyvinyl alcohol aqueous solution;
s4, adding a phosphorized cellulose solution into a polyvinyl alcohol solution, magnetically stirring at 300rpm for 5 hours to prepare a polyvinyl alcohol/phosphorized cellulose mixed solution, dissolving 28 parts by weight of a cross-linking agent into 100 parts by weight of water, adding into the polyvinyl alcohol/phosphorized cellulose mixed solution, and magnetically stirring at 300rpm for 20 minutes at 25 ℃ to prepare a polyvinyl alcohol/phosphorized cellulose/cross-linking agent mixed solution; reacting the mixed solution of polyvinyl alcohol/phosphorized cellulose/cross-linking agent for 2.5h at the temperature of 60 ℃ to prepare the cross-linked hydrogel of polyvinyl alcohol/phosphorized cellulose;
s5, freeze-drying the cross-linked hydrogel of the polyvinyl alcohol/the phosphorized cellulose for 48 hours to obtain the polyvinyl alcohol/the phosphorized cellulose aerogel, namely the flame-retardant polyvinyl alcohol aerogel.
FIG. 1 is a graph of the infrared contrast of the raw cellulose and the corresponding phosphated cellulose of example 1. As can be seen from the figure, 3480cm of the infrared spectrum of the raw material cellulose in example 1-1The vibration peak at (B) corresponds to the vibration absorption peak of the-OH group, 1000cm-1The two characteristic spectra on the left and right are the C-O-C oscillation peaks of the glucoside units or of the b- (1-4) -glucosidic bonds. The phosphoric acid group of the cellulose is substituted for the hydrogen in the hydroxyl group bonded to the carbon atom in the cellulose structure in the phosphorylation reaction, and thus 1210cm in the infrared spectrum of the phosphorylated cellulose in example 1-1The position of (B) shows an absorption peak of P ═ O bond at 858cm-1The absorption peak of the P-O-C group appears. Example 1 Infrared Spectrum of phosphorylated cellulose, 2393cm-1The vibration peak appeared at the position corresponds to the P-H absorption peak, 1063cm-1The peak of vibration at (A) is the absorption peak of P-OH. From the infrared analysis, step S1 succeeded in preparing a phosphorylated cellulose.
Example 2
A preparation method of flame-retardant polyvinyl alcohol aerogel comprises the following steps:
s1, adding 150 parts by weight of urea into a three-neck flask provided with a thermometer, an electronic constant speed stirrer and a reflux condenser, and heating to 140 ℃ until the urea is molten; adding 25 parts by weight of cellulose with the length-diameter ratio of 200 (microfibrillated cellulose) and 170 parts by weight of phosphorous acid into the melted urea melt, fully dissolving, then raising the temperature to 150 ℃, and reacting for 5 hours at the temperature; dissolving the product obtained by the reaction in water, then adding 500 parts by weight of absolute ethyl alcohol to obtain white precipitate, and drying at 65 ℃ to obtain the phosphorized cellulose.
S2, ultrasonically dispersing 35 parts by weight of phosphorized cellulose with the length-diameter ratio of 200 in 100 parts by weight of water for 40min to obtain a phosphorized cellulose solution.
S3, dissolving 120 parts by weight of polyvinyl alcohol 2488 in 2000 parts by weight of water at 95 ℃ for 5 hours to obtain a polyvinyl alcohol aqueous solution.
S4, adding a phosphorized cellulose solution into a polyvinyl alcohol solution, magnetically stirring at 300rpm for 5 hours to prepare a polyvinyl alcohol/phosphorized cellulose mixed solution, dissolving 40 parts by weight of a cross-linking agent into 80 parts by weight of water, adding into the polyvinyl alcohol/phosphorized cellulose mixed solution, and magnetically stirring at 300rpm for 20 minutes at 25 ℃ to prepare a polyvinyl alcohol/phosphorized cellulose/cross-linking agent mixed solution; the mixed solution of polyvinyl alcohol/phosphorized cellulose/cross-linking agent reacts for 2.5 hours at the temperature of 60 ℃ to prepare the cross-linked hydrogel of polyvinyl alcohol/phosphorized cellulose.
S5, freeze-drying the cross-linked hydrogel of the polyvinyl alcohol/the phosphorized cellulose for 48 hours to obtain the polyvinyl alcohol/the phosphorized cellulose aerogel, namely the flame-retardant polyvinyl alcohol aerogel.
Example 3
A preparation method of flame-retardant polyvinyl alcohol aerogel comprises the following steps:
s1, adding 40 parts by weight of urea into a three-neck flask provided with a thermometer, an electronic constant speed stirrer and a reflux condenser tube, and heating to 145 ℃ until the urea is molten; adding 15 parts by weight of cellulose with the length-diameter ratio of 100 (bacterial nano-cellulose) and 50 parts by weight of phosphorous acid into the melted urea melt, fully dissolving, then raising the temperature to 150 ℃, and reacting for 5 hours at the temperature; dissolving the product obtained by the reaction in water, then adding 400 parts by weight of absolute ethyl alcohol to obtain white precipitate, and drying at 65 ℃ to finally obtain the phosphorylated cellulose.
S2, ultrasonically dispersing 0.5 part by weight of phosphated cellulose with the length-diameter ratio of 200 in 50 parts by weight of water for 30min to obtain a phosphated cellulose solution.
S3, 50 parts by weight of polyvinyl alcohol 1788 is dissolved in 350 parts by weight of water at 85 ℃ for 6 hours to obtain a polyvinyl alcohol aqueous solution.
S4, adding the phosphorized cellulose solution into the polyvinyl alcohol solution, and magnetically stirring at 400rpm for 5 hours to prepare a polyvinyl alcohol/phosphorized cellulose mixed solution; dissolving 13 parts by weight of cross-linking agent in 50 parts by weight of water, adding the cross-linking agent into the mixed solution of polyvinyl alcohol and phosphorized cellulose, and magnetically stirring the mixture for 15min at the temperature of 20 ℃ and the speed of 400rpm to prepare mixed solution of polyvinyl alcohol/phosphorized cellulose and cross-linking agent; reacting the mixed solution of polyvinyl alcohol/phosphorized cellulose/cross-linking agent for 3h at the temperature of 75 ℃ to prepare the polyvinyl alcohol/phosphorized cellulose cross-linked hydrogel.
S5, freeze-drying the polyvinyl alcohol/phosphated cellulose crosslinked hydrogel for 36 hours to obtain the polyvinyl alcohol/phosphated cellulose aerogel.
Example 4
A preparation method of flame-retardant polyvinyl alcohol aerogel comprises the following steps:
s1, adding 70 parts by weight of urea into a three-neck flask provided with a thermometer, an electronic constant speed stirrer and a reflux condenser pipe, and heating to 150 ℃ until the urea is molten; adding 13 parts by weight of cellulose with the length-diameter ratio of 600 (microfibrillated cellulose) and 100 parts by weight of phosphorous acid into the melted urea melt, fully dissolving, then raising the temperature to 180 ℃, and reacting for 8 hours at the temperature; dissolving the product obtained by the reaction in water, then adding 100 parts by weight of absolute ethyl alcohol to obtain white precipitate, and drying at 90 ℃ to finally obtain the phosphorylated cellulose.
S2, ultrasonically dispersing 10 parts of phosphated cellulose with the length-diameter ratio of 300 in 80 parts of water for 60min to obtain a phosphated cellulose solution.
S3, dissolving 85 parts by weight of polyvinyl alcohol 2099 in 500 parts by weight of water at 90 ℃ for 10 hours to obtain a polyvinyl alcohol aqueous solution.
S4, adding the phosphorized cellulose solution into the polyvinyl alcohol solution, and magnetically stirring at 600rpm for 10 hours to prepare a polyvinyl alcohol/phosphorized cellulose mixed solution; dissolving 20 parts by weight of cross-linking agent in 60 parts by weight of water, adding the cross-linking agent into the mixed solution of polyvinyl alcohol and phosphorized cellulose, and magnetically stirring the mixture for 30min at the temperature of 40 ℃ and the speed of 600rpm to prepare mixed solution of polyvinyl alcohol/phosphorized cellulose and cross-linking agent; reacting the mixed solution of polyvinyl alcohol/phosphorized cellulose/cross-linking agent for 4h at the temperature of 85 ℃ to prepare the polyvinyl alcohol/phosphorized cellulose cross-linked hydrogel.
S5, freeze-drying the cross-linked hydrogel of the polyvinyl alcohol/the phosphorized cellulose for 24 hours to obtain the polyvinyl alcohol/the phosphorized cellulose aerogel.
Example 5
A preparation method of flame-retardant polyvinyl alcohol aerogel comprises the following steps:
s1, adding 100 parts by weight of urea into a three-neck flask provided with a thermometer, an electronic constant speed stirrer and a reflux condenser pipe, and heating to 130 ℃ until the urea is molten; adding 20 parts by weight of cellulose with an aspect ratio of 500 (microfibrillated cellulose) and 150 parts by weight of phosphorous acid to the melted urea melt, sufficiently dissolving, subsequently raising the temperature to 170 ℃, and reacting at this temperature for 7 hours; dissolving the product obtained by the reaction in water, then adding 300 parts by weight of absolute ethyl alcohol to obtain white precipitate, and drying at 96 ℃ to finally obtain the phosphorylated cellulose.
S2, ultrasonically dispersing 15 parts by weight of phosphorized cellulose with the length-diameter ratio of 400 in 80 parts by weight of water for 35min to obtain a phosphorized cellulose solution.
S3, 110 parts by weight of polyvinyl alcohol 2499 is dissolved in 1600 parts by weight of water at 98 ℃ for 7 hours to obtain a polyvinyl alcohol aqueous solution.
S4, adding the phosphorized cellulose solution into the polyvinyl alcohol solution, and magnetically stirring at 450rpm for 7 hours to prepare a polyvinyl alcohol/phosphorized cellulose mixed solution; dissolving 35 parts by weight of cross-linking agent in 90 parts by weight of water, adding the cross-linking agent into the mixed solution of polyvinyl alcohol and phosphorized cellulose, and magnetically stirring the mixed solution at the temperature of 30 ℃ and the speed of 450rpm for 25min to prepare mixed solution of polyvinyl alcohol/phosphorized cellulose and cross-linking agent; the mixed solution of polyvinyl alcohol/phosphorized cellulose/cross-linking agent reacts for 3.5 hours at the temperature of 67 ℃ to prepare the cross-linked hydrogel of polyvinyl alcohol/phosphorized cellulose.
S5, freeze-drying the cross-linked hydrogel of the polyvinyl alcohol/the phosphorized cellulose for 30 hours to obtain the polyvinyl alcohol/the phosphorized cellulose aerogel.
Comparative example 1
Preparing a phosphated cellulose free polyvinyl alcohol aerogel: 120 parts by weight of polyvinyl alcohol was dissolved in 2000 parts by weight of water at 80 ℃ for 7 hours to obtain an aqueous polyvinyl alcohol solution. Dissolving 25 parts by weight of cross-linking agent in 200 parts by weight of water, adding the solution into polyvinyl alcohol solution, and magnetically stirring the solution at the temperature of 35 ℃ and the rpm of 300 for 20min to prepare polyvinyl alcohol/cross-linking agent mixed solution. And (3) reacting the polyvinyl alcohol/cross-linking agent mixed solution for 2 hours at the temperature of 80 ℃ to obtain the polyvinyl alcohol hydrogel. And (4) freeze-drying the polyvinyl alcohol hydrogel for 36 hours to obtain pure polyvinyl alcohol aerogel.
Performance test analysis:
fig. 2 is a graph showing the compression performance test of the flame retardant polyvinyl alcohol aerogel of example 2 and the pure polyvinyl alcohol aerogel of comparative example 1. From the figure, when the compression ratios are all 45%, the stress of the flame-retardant polyvinyl alcohol aerogel is obviously higher than that of pure polyvinyl alcohol aerogel, and the flame-retardant polyvinyl alcohol aerogel is proved to have better compression performance.
Fig. 3 is a scanning electron microscope image of the flame retardant polyvinyl alcohol aerogel of example 2 and the pure polyvinyl alcohol aerogel of comparative example 1. As can be seen from the figure, the aerogel of example 2 has more porous structures and more uniform pore sizes compared to comparative example 1. Meanwhile, tiny phosphorylated cellulose is distributed around the pore structure, which shows that the fiber and the polyvinyl alcohol are well connected.
Fig. 4 is a thermogravimetric analysis chart of the flame retardant polyvinyl alcohol aerogel of example 2 and the pure polyvinyl alcohol aerogel of comparative example 1. As seen from the figure, the initial decomposition temperature of the flame-retardant polyvinyl alcohol aerogel is 256 ℃, the maximum weight loss rate temperature is 285 ℃, and the carbon residue rate at 550 ℃ is 23%; the initial decomposition temperature of the pure polyvinyl alcohol aerogel is 310 ℃, the maximum weight loss rate temperature is 383 ℃, and the carbon residue rate at 550 ℃ is 7%. The decomposition temperature of the flame-retardant polyvinyl alcohol aerogel is advanced, the residual carbon rate is higher than that of pure polyvinyl alcohol aerogel, the number of carbon layers on the surface of the material is increased, the exchange of oxygen and heat is favorably prevented, the overflow of thermal decomposition products can be prevented, the combustion reaction is inhibited, and the thermal stability of the material is improved.
Table 1 shows the Limiting Oxygen Index (LOI) and vertical burn (UL-94) test data for the flame retardant polyvinyl alcohol aerogel of example 2 versus the pure polyvinyl alcohol aerogel of comparative example 1. The LOI value of the pure polyvinyl alcohol aerogel is 18, the L0I value of the flame-retardant polyvinyl alcohol aerogel is 32, and the LOI value is increased by 78% compared with the L0I value of the pure polyvinyl alcohol aerogel, so that the flame retardant property of the polyvinyl alcohol aerogel can be obviously improved by the phosphorized cellulose.
LOI and UL-94 test data for the aerogels of Table 1, example 2, and the neat polyvinyl alcohol aerogel of comparative example 1
In conclusion, the polyvinyl alcohol/phosphorized cellulose aerogel disclosed by the invention not only has good flame retardant property, but also has good mechanical strength and thermal stability, and the problem of poor comprehensive performance of the polyvinyl alcohol aerogel is solved.
Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (9)
1. The flame-retardant polyvinyl alcohol aerogel is characterized by being prepared by carrying out a crosslinking reaction on polyvinyl alcohol and phosphorylated cellulose; the phosphorized cellulose is prepared by modifying cellulose with phosphorous acid and urea.
2. The flame-retardant polyvinyl alcohol aerogel according to claim 1, wherein the weight ratio of the polyvinyl alcohol to the phosphorylated cellulose is 50 to 120: 0.5-35.
3. The flame retardant polyvinyl alcohol aerogel according to claim 2, wherein the aspect ratio of the phosphorylated fibers is 100-300.
4. The flame-retardant polyvinyl alcohol aerogel according to claim 1, wherein the cellulose is one of microfibrillated cellulose, nanocrystalline cellulose and bacterial nanocellulose, and the aspect ratio of the cellulose is 50 to 600.
5. The preparation method of the flame retardant polyvinyl alcohol aerogel according to any one of claims 1 to 4, comprising the following steps:
s1 preparation of phosphated cellulose
Adding cellulose and phosphorous acid into molten urea, reacting for 4-8h at 140-180 ℃, then adding water and ethanol, and separating out precipitate to obtain phosphorized cellulose;
s2, ultrasonically dispersing the phosphorized cellulose in water to obtain a phosphorized cellulose solution;
s3, dissolving polyvinyl alcohol in water at 80-95 ℃ to obtain a polyvinyl alcohol aqueous solution;
s4, adding the phosphorized cellulose solution into a polyvinyl alcohol aqueous solution, uniformly mixing, then adding a cross-linking agent aqueous solution, and reacting at the temperature of 60-85 ℃ for 1-4 h to prepare the polyvinyl alcohol/phosphorized cellulose cross-linked hydrogel;
s5, freeze-drying the cross-linked hydrogel of the polyvinyl alcohol/the phosphorized cellulose for 24-72 hours to obtain the flame-retardant polyvinyl alcohol aerogel.
6. The method according to claim 5, wherein the step S1 specifically comprises the following steps:
s11, heating 40-150 parts by weight of urea to 130-150 ℃ until the urea is molten;
s12, sequentially adding 10-25 parts by weight of cellulose and 50-170 parts by weight of phosphorous acid into molten urea for full dissolution, then raising the temperature to 140-180 ℃, and reacting at constant temperature for 4-8 h;
s13, dissolving the product obtained in the step S12 in water, then adding 100-500 parts by weight of absolute ethyl alcohol to separate out white precipitate, and drying the precipitate at 60-90 ℃ to obtain the phosphorylated cellulose.
7. The method for preparing the flame-retardant polyvinyl alcohol aerogel according to claim 6, wherein the step S2 specifically comprises: 0.5-35 parts by weight of phosphorized cellulose is ultrasonically dispersed in 50-100 parts by weight of water for 30-60min to obtain a phosphorized cellulose solution.
8. The method according to claim 7, wherein the step S3 is specifically carried out by: 50-120 parts by weight of polyvinyl alcohol is dissolved in 2000 parts by weight of water at the temperature of 80-95 ℃ for 5-10h to obtain the polyvinyl alcohol aqueous solution.
9. The method for preparing the flame-retardant polyvinyl alcohol aerogel according to claim 8, wherein the aqueous solution of the crosslinking agent is prepared by dissolving 13 to 40 parts by weight of the crosslinking agent in 50 to 100 parts by weight of water, and the crosslinking agent is one of paraformaldehyde, glutaraldehyde, borax salt, maleic anhydride, phthalic acid chloride, phthalic anhydride, succinic anhydride, phthalic acid, epichlorohydrin, potassium permanganate and copper hydroxide.
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| CN111995835A (en) * | 2020-08-28 | 2020-11-27 | 盐城工学院 | Preparation method of green flame-retardant polyvinyl alcohol aerogel |
| CN112175229A (en) * | 2020-09-03 | 2021-01-05 | 昆明理工大学 | Two-dimensional material composite flame-retardant polyvinyl alcohol aerogel and preparation method thereof |
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| CN112898625A (en) * | 2021-02-25 | 2021-06-04 | 山东省科学院新材料研究所 | Underwater elastic cellulose aerogel and preparation method and application thereof |
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