CN111019187A - Flame-retardant aerogel with fire early warning and piezoresistive sensing functions and preparation method thereof - Google Patents
Flame-retardant aerogel with fire early warning and piezoresistive sensing functions and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a flame-retardant aerogel with fire early warning and piezoresistive sensing functions and a preparation method thereof. The preparation method comprises the steps of adding deionized water and the layered nano material into a reaction kettle at room temperature, stirring, and then performing ultrasonic dispersion to uniformly disperse the layered nano material; centrifuging the obtained dispersion at a high speed, and adding ionized water into the centrifuged supernatant to dilute the centrifuged supernatant to form 0.1-10 wt% of stable suspension; adding a chain-shaped natural polymer material, deionized water and a stable suspension into a reaction kettle, and uniformly stirring; adding carbon oxide material or carbon nitride material, ultrasonic dispersing, dripping cross-linking agent, ageing gel and freeze drying. Compared with the prior art, the flame-retardant aerogel prepared by the invention has excellent flame-retardant and heat-insulating properties, has sensitive fire early warning and prominent piezoresistive sensing functions, and can be applied to the fields of heat preservation and heat insulation with higher fire safety requirements, wearable equipment and the like.
Description
Technical Field
The invention relates to a flame-retardant aerogel, in particular to a flame-retardant aerogel with fire early warning and piezoresistive sensing functions and a preparation method thereof.
Background
Aerogel is one of the most rapidly developed lightweight materials at present due to its extremely low density, and particularly organic aerogel has great potential application value in the fields of thermal insulation, wearable devices and the like due to its low thermal conductivity and high flexibility (CN 110183716A). However, the flammability of the organic component and the porous structure of the aerogelThe structure causes organic aerogel (such as polyvinyl alcohol, cellulose aerogel and the like) to be extremely easy to ignite, and the flame spread speed is extremely high, so that the fire safety hazard is serious (Carbohydrate Polymers,2019,221 and 230). Therefore, how to improve the fire safety of the organic aerogel is one of the key problems which needs to be solved urgently at present. While organic-inorganic hybridization is considered to be one of the most effective methods for improving fire safety of organic aerogels (CN 110066495A), namely, by using inorganic filler (such as Silica (SiO)2) The organic aerogel material comprises lamellar montmorillonite (MMT), acicular sepiolite, halloysite, hydroxyapatite, sodium bicarbonate, graphene oxide and the like, has high thermal stability and a synergistic char formation effect with organic components, and can effectively improve the flame retardant property of the organic aerogel and improve the use safety of the organic aerogel (Angewandte chemical Edition,2018,57(17), 4538-.
However, the addition of the inorganic filler does not completely inhibit the thermal degradation of the organic component in a high-temperature environment. Organic-inorganic hybrid aerogels still have the risk of flashing and promoting flame spread during use (especially when applied to the field of high-temperature heat insulation), and still cannot meet the increasing fire safety requirements. Therefore, if the organic-inorganic hybrid aerogel can be endowed with a high-temperature self-warning function, so that the organic-inorganic hybrid aerogel can give an alarm to people in a temperature rise stage before a fire disaster occurs, the fire disaster can be killed in a bud stage, more escape time is won for people on the fire scene, and property loss and casualties are effectively reduced. The oxygen (nitrogen) carbon nanomaterial is the preferred material for preparing the flame-retardant aerogel with the high-temperature self-warning function. On one hand, the oxygen (nitrogen) carbon nanomaterial has high-temperature thermal reduction characteristics, and oxygen (nitrogen) containing groups can be rapidly removed when the carbon nanomaterial encounters high temperature or open fire, and the oxygen (nitrogen) containing groups are reduced to carbon materials with good conductivity, so that the resistance of the aerogel is sharply reduced, and a fire early warning device can be triggered through the change of an electric signal. On the other hand, the oxygen (nitrogen) carbon nanomaterial has good flexibility and does not deteriorate the mechanical properties of the aerogel. However, there are still significant challenges to preparing fire warning aerogels at present: on one hand, the aerogel has high porosity and complex network structure, and the rapid change of the resistance during combustion is difficult to realize (Nanoscale,2019,11(18), 8835-; on the other hand, the addition of a larger amount of filler can destroy the network structure of the aerogel, deteriorate the mechanical properties of the aerogel and increase the density of the aerogel (Chem,2019,5(7), 1871-1812).
Disclosure of Invention
The invention aims to provide a preparation method of a flame-retardant aerogel with a sensitive fire early warning function aiming at the problem of the use safety of the current organic aerogel.
The invention also aims to provide the multifunctional flame-retardant heat-insulation aerogel, and the aerogel provided by the invention can be applied to the fields of heat preservation and insulation, wearable equipment and the like with higher requirements on fire safety.
Aiming at the defects, the invention adopts the chain natural polymer material, the layered nano material and the carbon oxide material or the carbon nitride material as the main raw materials of the aerogel, and the crosslinked polymer material not only can form the framework of the aerogel, but also can be used as a good binder, so that the layered nano material and the carbon oxide material or the carbon nitride material are adhered to the hole walls of the aerogel to form a continuous three-dimensional network structure, thereby being beneficial to the rapid change of the resistance during combustion. Research results show that the aerogel not only has outstanding flame retardant performance and sensitive flame retardant early warning function, but also has excellent piezoresistive sensing function.
The invention mainly and uniformly disperses the layered nano material, the carbon oxide material or the carbon nitride material and the cross-linkable chain-shaped natural polymer material in deionized water to prepare the flame-retardant heat-insulating aerogel with the fire early warning and piezoresistive sensing functions. The layered nano material has excellent thermal stability and barrier property, the chain-like natural high polymer material has excellent char-forming property, the chain-like natural high polymer material can quickly generate a charring reaction when encountering flame or being in a high-temperature environment, the charring product can bond the layered nano material together to form a layered porous carbon layer with excellent thermal stability and barrier property, the efficient flame-retardant heat-insulating effect is exerted, and the aerogel is endowed with excellent fire safety. In addition, the oxygen (nitrogen) carbon nanomaterial in the aerogel can be quickly reduced into a carbon nanomaterial with good conductivity in a high-temperature environment due to the degradation of oxygen (nitrogen) groups, so that the resistance of the aerogel is sharply reduced, a fire early warning device connected with the aerogel is triggered, and an ultra-sensitive fire early warning effect is exerted. In addition, due to the unique thin-wall three-dimensional porous structure and good flexibility of the aerogel, when the aerogel is subjected to external weak stress, the contact point of the carbon nano material in the aerogel can be obviously changed, so that the resistance is changed, and the aerogel provided by the invention has a sensitive piezoresistive sensing function. In conclusion, the flame-retardant aerogel with fire early warning and piezoresistive sensing functions provided by the invention has excellent fire safety and has wide application prospects in the fields of heat preservation, heat insulation, wearable equipment and the like.
The purpose of the invention can be realized by the following technical scheme:
the preparation method of the flame-retardant aerogel with the fire early warning and piezoresistive sensing functions comprises the following steps:
1) stripping the layered nano material: adding deionized water and the layered nano material into a reaction kettle at room temperature, stirring, and performing ultrasonic dispersion to uniformly disperse the layered nano material; centrifuging the obtained dispersion at a high speed, and adding ionized water into the centrifuged supernatant to dilute the centrifuged supernatant to form 0.1-10 wt% of stable suspension;
2) have fire early warning and the fire-retardant aerogel of pressure drag sensing function concurrently: adding a chain-shaped natural polymer material, deionized water and the stable suspension prepared in the step 1) into a reaction kettle, and uniformly stirring; adding a carbon oxide material or a carbon nitride material, performing ultrasonic dispersion, then dropwise adding a cross-linking agent, aging the gel, and then freeze-drying to obtain the flame-retardant aerogel with fire early warning and piezoresistive sensing functions;
the chain-shaped natural high polymer material is one or more of carboxymethyl chitosan, hydroxypropyl chitosan, hydroxyethyl chitosan, carboxymethyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose and hydroxypropyl methyl cellulose;
the carbon oxide material or the carbon nitride material is one or more of a carboxylated single-walled carbon nanotube, a hydroxylated single-walled carbon nanotube, an aminated single-walled carbon nanotube, a carboxylated multi-walled carbon nanotube, a hydroxylated multi-walled carbon nanotube, an aminated multi-walled carbon nanotube, a graphene oxide nanobelt and a graphene oxide nanosheet.
To further achieve the object of the present invention, preferably, the layered nano-material is one or more of montmorillonite, kaolin, hydrotalcite, sericite, double metal hydroxide and layered phosphate.
Preferably, the mass ratio of the layered nano material to the chain-like natural polymer material is 1: 0.1-1: 10, and the total solid content of the layered nano material and the chain-like natural polymer material in the flame-retardant aerogel is 50-99 wt%; the carbon oxide material or the carbon nitride material accounts for 1-50% of the total solid content of the aerogel.
Preferably, the stirring in the step 1) and the step 2) is magnetic stirring, and the stirring speed is 1000-3000 r/min; stirring for 2-6 h in the step 1); the stirring time in the step 2) is 0.5-1 h.
Preferably, the rotation speed of the high-speed centrifugation treatment in the step 1) is 3000-.
Preferably, the freeze drying in the step 2) is to remove water in the gel through a freeze dryer at a temperature of between 20 ℃ below zero and 80 ℃ below zero to obtain the aerogel; the vacuum degree of freeze drying is 10-300 Pa, and the time is 12-24 h.
Preferably, the aging of the gel in the step 2) is to form the gel through the reaction of a cross-linking agent and a chain-like natural high polymer material at the temperature of 30-60 ℃, and form a stable cross-linked network structure after aging for 3-6 hours.
Preferably, the cross-linking agent in the step 2) is one or more of citric acid, maleic acid, malic acid, itaconic acid, tartaric acid, polymaleic acid and glutaraldehyde, and the mass ratio of the dosage of the cross-linking agent to the chain-shaped high polymer material is 1: 10-1: 1.
Preferably, the power of the ultrasonic dispersion in the step 1) and the step 2) is 300-500W, and the time of the ultrasonic dispersion is 0.5-1 h.
The flame-retardant aerogel with fire early warning and piezoresistive sensing functions is prepared by the preparation method.
The invention skillfully utilizes the thermal resistance change of the carbon oxide material or the carbon nitride material to prepare the flame-retardant aerogel with the fire early warning function. When encountering flame, the carbon oxide material or the carbon nitride material in the aerogel is quickly reduced into the carbon material with good conductivity, so that the resistance of the aerogel is sharply reduced, an early warning device connected with the aerogel is triggered, and high-sensitivity fire early warning is realized. Besides the fire early warning function, the aerogel disclosed by the invention also has excellent flame-retardant heat insulation and sensitive piezoresistive sensing functions.
Compared with the prior art, the invention has the following advantages:
1. the flame-retardant aerogel provided by the invention has a sensitive fire early warning function and excellent heat insulation performance. When encountering flame, the carbon oxide material or the carbon nitride material can generate rapid thermal reduction reaction, so that the resistance of the aerogel is sharply reduced, an early warning device connected with the aerogel is triggered, and high-sensitivity fire early warning is realized. In addition, the porous structure of the aerogel itself imparts excellent thermal insulation properties to the aerogel of the present invention.
2. When the flame-retardant aerogel provided by the invention is at high temperature or is combusted, the chain natural high polymer material in the flame-retardant aerogel can quickly generate a carbonization reaction, and the carbonization product can bond the layered nano material together, so that a layered porous carbon layer with excellent thermal stability and barrier property is formed, and the high-efficiency flame-retardant effect is exerted.
3. The aerogel provided by the invention has a unique thin-wall three-dimensional porous structure and good flexibility, and when the aerogel is subjected to external weak stress, the contact point of the carbon nano material in the aerogel can be obviously changed, so that the resistance is changed, and the aerogel provided by the invention has a sensitive piezoresistive sensing function.
Drawings
Fig. 1 is a cross-sectional SEM photograph of the flame retardant aerogel prepared in example 1. Where A is a cross-sectional view of the aerogel and B is a further enlargement (20.0k times) of the aerogel cross-section.
FIG. 2 is a graph showing the resistance change of the aerogel in the fire early warning test of example 6.
FIG. 3 is a graph showing the real-time change in resistance of the aerogel under different strains in example 4.
FIG. 4 is a graph showing the real-time variation of the resistance of the aerogel in example 4 in monitoring the bending and jumping of human fingers. Wherein A is the crooked resistance real-time change picture of aerogel monitoring human finger, and B is the crooked resistance real-time change picture of aerogel monitoring human body when jumping.
FIG. 5 is the temperature change curve of three points (Sp1, Sp2, Sp3) on the back surface and the temperature difference between the front and back surfaces of example 2 in 30min when the surface is subjected to the burning of butane burner (temperature about 1200 ℃). Wherein A is the temperature change curve of three points (Sp1, Sp2 and Sp3) on the back surface of the aerogel along with time when the surface of the aerogel is burned by a butane torch, and B is the temperature comparison and temperature difference diagram of the front surface and the back surface of the aerogel in 30min after being burned by the butane torch.
Detailed Description
For a better understanding of the present invention, the present invention will be further described with reference to the following drawings and examples, but the embodiments of the present invention are not limited thereto.
Example 1
1) Stripping montmorillonite: under the condition of room temperature, adding 250g of deionized water and 7.0g of montmorillonite into a 500mL beaker, stirring for 6h at 1000r/min, and continuing to perform ultrasonic dispersion for 6h to uniformly disperse the montmorillonite; centrifuging the obtained dispersion liquid at a high speed of 3000r/min for 3 times, and adding deionized water into the centrifuged supernatant to form 2.0 wt% of montmorillonite suspension.
2) Have fire early warning and piezoresistive sensing function's fire-retardant aerogel's preparation concurrently: adding 1.0g of carboxymethyl chitosan, 100mL of deionized water and 5.0g of the montmorillonite suspension prepared in the step 1) into a 250mL beaker, and stirring for 0.5h for full dispersion; and then adding 0.11g of aminated single-walled carbon nanotube, ultrasonically dispersing for 1h under the power of 300W, then dropwise adding 0.1g of glutaraldehyde for crosslinking, carrying out gel aging for 3h at the temperature of 30 ℃, and carrying out freeze drying for 12h under the conditions of-40 ℃ and the vacuum degree of 100Pa to obtain the flame-retardant aerogel with the fire early warning and piezoresistive sensing functions. The results of the vertical combustion, limiting oxygen index, fire alarm and thermal conductivity tests of the aerogel obtained in this example are shown in table 1.
Example 2
1) Exfoliation of layered double hydroxide: under the condition of room temperature, adding 30.0g of layered double hydroxide and 200g of deionized water into a 500ml beaker, stirring for 3.5h at 2000r/min, and continuing to perform ultrasonic dispersion for 4.5h to uniformly disperse the double hydroxide; and centrifuging the obtained solution at a high speed of 4500r/min for 4 times, and adding deionized water into the supernatant to form 8.0 wt% of double metal hydroxide solution.
2) Have fire early warning and piezoresistive sensing function's fire-retardant aerogel's preparation concurrently: adding 2.3g of hydroxyethyl chitosan, 100mL of deionized water and 1.25g of the layered double hydroxide solution prepared in the step 1) into a 200mL beaker, and stirring for 1 hour to fully disperse the materials; and then adding 0.5g of carboxylated multi-walled carbon nanotubes, ultrasonically dispersing for 0.6h under the power of 360W, then dropwise adding 2.3g of tartaric acid for crosslinking, carrying out gel aging for 5h at the temperature of 60 ℃, and carrying out freeze drying for 15h under the conditions of-20 ℃ and the vacuum degree of 300Pa to obtain the flame-retardant aerogel with the fire early warning and piezoresistive sensing functions. The results of the vertical combustion, limiting oxygen index, fire alarm and thermal conductivity tests of the aerogel obtained in this example are shown in table 1, and the test methods are the same as those of example 1.
Example 3
The present embodiment is different from embodiment 1 in that:
replacing montmorillonite in the step 1) with layered phosphate, shortening the stirring and ultrasonic dispersion time to 2h, replacing the stirring rotating speed with 3000r/min, replacing the centrifugal rotating speed with 5000r/min, and forming the mixed solution with the concentration of 5.0 wt%;
in the step 2), 1.0g of carboxymethyl chitosan is replaced by 0.1g of carboxymethyl cellulose, the stirring time is prolonged to 0.8h, 5.0g of montmorillonite suspension is replaced by 20.0g of layered phosphate dispersion, 0.1g of glutaraldehyde is replaced by 0.05g of citric acid, the aminated single-walled carbon nano-tube is replaced by a hydroxylated multi-walled carbon nano-tube, the ultrasonic dispersion time is shortened to 0.5h, the ultrasonic dispersion power is replaced by 500W, the gel aging temperature is increased to 50 ℃, the gel aging time is prolonged to 6h, the freeze drying time is increased to 24h, the vacuum degree is reduced to 10Pa, and the temperature is reduced to-80 ℃.
The results of the vertical combustion, limiting oxygen index, fire alarm and thermal conductivity tests of the aerogel obtained in this example are shown in table 1, and the test methods are the same as those of example 1.
Example 4
The present embodiment is different from embodiment 1 in that:
the stirring speed of the step 1) is replaced by 2500r/min, the stirring and ultrasonic time is shortened to 3h, and the montmorillonite suspension is replaced by sericite suspension; in the step 2), 1.0g of carboxymethyl chitosan is replaced by 0.5g of hydroxypropyl cellulose, 0.1g of glutaraldehyde is replaced by 0.03g of itaconic acid, 0.1g of aminated single-walled carbon nanotube is replaced by 0.006g of graphene oxide nanobelt, the stirring time is prolonged to 0.6h, the ultrasonic dispersion time is shortened to 0.85h, the ultrasonic dispersion power is replaced by 425W, the gel aging temperature is increased to 40 ℃, the gel aging time is prolonged to 4.5h, the freeze drying time is increased to 20h, and the vacuum degree is reduced to 30 Pa.
The results of the vertical combustion, limiting oxygen index, fire alarm and thermal conductivity tests of the aerogel obtained in this example are shown in table 1, and the test methods are the same as those of example 1.
Example 4
The present embodiment is different from embodiment 1 in that:
in the steps 1) and 2), 1.0g of carboxymethyl chitosan is replaced by 2.0g of hydroxyethyl cellulose, and 5.0g of montmorillonite suspension is replaced by 20.0g of kaolin suspension; the ultrasonic dispersion time in the step 1) is shortened to 2.5 h;
the stirring time in the step 2) is prolonged to 0.9h, the aging temperature of the gel is increased to 60 ℃, the aging time of the gel is prolonged to 5.5h, the freeze-drying time is increased to 20h, and the vacuum degree is increased to 250 Pa.
The results of the vertical combustion, limiting oxygen index, fire alarm and thermal conductivity tests of the aerogel obtained in this example are shown in table 1, and the test methods are the same as those of example 1.
Example 5
The present embodiment is different from embodiment 1 in that:
in the step 2), 1.0g of carboxymethyl chitosan is replaced by 0.01g of hydroxypropyl methyl cellulose, 5.0g of montmorillonite suspension is replaced by 5.0g of hydrotalcite suspension, glutaraldehyde is replaced by malic acid, the gel aging temperature is increased to 55 ℃, the gel aging time is prolonged to 3.8h, the freeze drying time is increased to 18h, and the vacuum degree is increased to 210 Pa.
The results of the vertical combustion, limiting oxygen index, fire alarm and thermal conductivity tests of the aerogel obtained in this example are shown in table 1, and the test methods are the same as those of example 1.
Example 6
The present embodiment is different from embodiment 1 in that:
the aminated single-walled carbon nanotube in the step 2) is replaced by an aminated multi-walled carbon nanotube, carboxymethyl chitosan is replaced by carboxymethyl cellulose, and glutaraldehyde is replaced by polymaleic acid.
The results of the vertical combustion, limiting oxygen index, fire alarm and thermal conductivity tests of the aerogel obtained in this example are shown in table 1, and the test methods are the same as those of example 1.
Example 7
The present embodiment is different from embodiment 1 in that:
the centrifugation frequency in the step 1) is increased to 5 times, the centrifugation rotating speed is increased to 4000r/min, 0.11g of aminated carbon nano tube in the step 2) is replaced by 0.011g of graphene oxide nano sheet, the ultrasonic dispersion time is shortened to 0.8h, and 0.1g of glutaraldehyde is replaced by 0.38g of maleic acid.
The results of the vertical combustion, limiting oxygen index, fire alarm and thermal conductivity tests of the aerogel obtained in this example are shown in table 1, and the test methods are the same as those of example 1.
Example 8
The present embodiment is different from embodiment 1 in that:
the stirring speed of the seed in the step 1) is increased to 2500r/min, 200g of deionized water and 50.0g of hydrotalcite are added into a 500ml beaker, the mass fraction is increased to 10 wt%, the speed of centrifugal treatment is increased to 4800r/min, and the centrifugation frequency is 5 times. Replacing the carboxymethyl chitosan in the step 2) with hydroxyethyl cellulose, increasing the gel aging time to 4.6h, reducing the freeze-drying temperature to-47 ℃, reducing the vacuum degree to 120Pa, and increasing the freeze-drying time to 15 h.
The results of the vertical combustion, limiting oxygen index, fire alarm and thermal conductivity tests of the aerogel obtained in this example are shown in table 1, and the test methods are the same as those of example 1.
Example 9
The present embodiment is different from embodiment 1 in that:
the stirring speed in the step 1) is increased to 1900r/min, 200g of deionized water and 41.0g of montmorillonite are added into a 500ml beaker, the mass fraction is increased to 6.5 wt%, the speed of centrifugal treatment is increased to 3800r/min, and the centrifugation frequency is reduced to 2 times. Replacing the carboxymethyl chitosan in the step 2) with hydroxypropyl chitosan, increasing the gel aging time to 5.8h, replacing 0.1g of glutaraldehyde with 0.86g of tartaric acid, freezing and drying at-60 ℃, reducing the vacuum degree to 25Pa, and increasing the freezing and drying time to 22 h.
The results of the vertical combustion, limiting oxygen index, fire alarm and thermal conductivity tests of the aerogel obtained in this example are shown in table 1, and the test methods are the same as those of example 1.
Comparative example 1
In order to verify that the flame-retardant heat-insulating aerogel with fire early warning and piezoresistive sensing functions prepared by the invention can play a high-efficiency flame-retardant role, only aerogel splines made of chain-shaped natural high polymer materials are added for comparison. The results of the vertical burn and limiting oxygen index tests are shown in Table 1, and the test methods are the same as in example 1.
Test method
1. Scanning Electron Microscope (SEM): the measurement was carried out on a thermal field emission scanning electron microscope (Calzaisi, Germany, model: Merlin). And adhering the sample on a sample table through conductive adhesive, and performing surface gold spraying treatment. And (4) scanning and imaging by using an electron beam with the accelerating voltage of 5kV, and observing the surface appearance of the sample.
2. And (3) testing the flame retardant property: limiting Oxygen Index (LOI) the test was performed according to ASTM D2863 with sample dimensions of 100mm by 10 mm; the vertical burning (UL-94) test was carried out according to ASTM D635, with specimen dimensions of 120mm by 10 mm.
3. Fire early warning test: the sample is connected with an early warning lamp and a direct current power supply (12V) through a lead, then the sample is placed 20mm above the alcohol lamp, the sample is exposed to the flame of the alcohol lamp with the height of 40mm, the flame is removed after 40s, and the time for triggering the early warning lamp by the sample is recorded.
4. And (3) piezoresistive sensing test: copper wires are adhered to two ends of the aerogel by silver paste, the copper wires are connected with a four-probe resistivity measuring system (RTS-9, 4 probe, China) and a digital multimeter (DMM 650061/2, Keithley instrument in USA), a certain pressure is applied to a sample to enable the sample to generate certain deformation, or the sample is adhered to a finger joint or a knee joint, the change of resistance in the pressure applying process, the finger bending process and the jumping process is recorded, and the size of the sample is 10mm multiplied by 10 mm.
5. Thermal infrared imaging test: the sample was fixed between a heat source and a thermal imager (butane burner flame) and subjected to a flame resistance test, the sample size being 100mm × 100mm × 10 mm. A thermal imaging video is taken for 30min by using a thermal infrared imager Fotric 226s, and a change curve of the sample temperature which is not exposed to the flame side in the time zone is made to obtain an average temperature.
6. And (3) testing thermal conductivity: thermal conductivity was obtained at room temperature by TPS 2500(Hot Disk, Sweden) measurement. The measurement parameters are as follows: heating power of 5mW, time of 10s, and 3.189mm nickel wire sensor. Measurements were made using four samples, the average of which was taken.
7. Testing the change of the fire early warning resistance in real time: copper wires are adhered to two ends of the aerogel by utilizing silver paste, and the copper wires are connected with a four-probe resistivity measurement system (RTS-9, 4 probes, China) to study the change process of the resistance of the copper wires along with the burning of a fire disaster. Wherein the sample size is 60mm × 10mm × 10 mm.
As can be seen from the data of the embodiments 1 to 9 in the table 1, under different process conditions, the aerogel prepared by using different chain-like natural polymer materials, layered nano materials and carbon oxide materials or carbon nitride materials has an ultra-sensitive fire early warning function, excellent flame retardant and heat insulation properties and a sensitive piezoresistive sensing function.
As can be seen from Table 1, the flame-retardant aerogel with fire early warning and piezoresistive sensing functions provided by the invention has excellent flame-retardant performance. As example 1, the aerogel provided by the invention has the limiting oxygen index as high as 30.5 percent and reaches the UL-94V-0 grade, and shows excellent flame retardant performance. However, the aerogel to which only the chain-like natural polymer material was added (comparative example 1) had a limiting oxygen index of only 19.0%, failing the vertical burning test. Fig. 1 is a scanning electron micrograph of a cross section of the flame retardant aerogel prepared in example 1, wherein a shows that the flame retardant aerogel in the present invention has a porous structure, and an enlarged view (20.0k times) of the cross section of the aerogel B shows that the flame retardant aerogel in the present invention has a structure in which layers are tightly stacked in the cross section, which is attributed to spontaneous co-assembly of chain-like natural polymer materials and layered nanomaterials. When encountering flame, the chain natural high polymer material in the aerogel can quickly generate carbonization reaction, and the carbonization product bonds the layered nano montmorillonite with lamellar barrier effect together to form a layered compact carbon layer with excellent thermal stability and barrier property, thereby playing a role of high-efficiency flame retardance.
TABLE 1 LOI, UL-94 and fire warning trigger time characteristic parameters for flame retardant aerogels
In fig. 5, a is a temperature curve of three points (Sp1, Sp2, Sp3) on the back of the aerogel collected by a thermal infrared imager as a function of time when the surface of the aerogel is burned by a butane torch flame which is 10cm away from the sample, and B is a temperature comparison and a temperature difference between the front and back of the aerogel within 30min after being burned by the butane torch. As can be seen from table 1 and fig. 5, the flame retardant aerogel provided by the present invention exhibits excellent fire resistance and thermal insulation properties. As in example 2, the thermal conductivity was only 0.026 W.m-1·K-1And the thermal conductivity of the material is similar to that of air at room temperature. Furthermore, when the front side of the aerogel was exposed to a butane torch flame at temperatures up to 1200 ℃, the temperature change at three points (Sp1, Sp2, Sp3) on the back side was as shown in B in fig. 5, and it can be seen that the average temperature at three points was only 280 ℃ and the difference between the front and back sides was up to 920 ℃. It can be seen from A in FIG. 5 that the aerogel has a back temperature of about 2min when the front surface is burned by a torch flame up to 1200 deg.CThe temperature rises to the maximum and then stabilizes at 350 ℃, 280 ℃ and 180 ℃ respectively. Therefore, the aerogel provided by the invention can effectively inhibit heat transfer and can play an excellent heat preservation and insulation role in an extremely severe environment (such as ultrahigh temperature).
As can be seen from the table 1 and the figure 2, the flame-retardant heat-insulating aerogel with the fire early warning and piezoresistive sensing functions provided by the invention has an ultra-sensitive fire early warning function. As in example 6, the aerogel of the present invention rapidly decreases in resistance after encountering a flame and triggers a fire alarm device within 0.97s, and the alarm response time is much shorter than that of the current infrared alarm and smoke alarm (>100s, ACS Nano 2017,12(1),416- "424). This is because: in a high-temperature environment, the aminated multi-walled carbon nanotube in the aerogel can be rapidly degraded to remove a side chain group, is reduced into a carbon nanotube with good conductivity, and a chain-shaped natural polymer is rapidly carbonized, is bonded with a layered nano material, and is connected with the carbon nanotube obtained by reduction in series in an aerogel structure to form a conductive path, so that the resistance of the aerogel is sharply reduced (as shown in figure 2), and an early warning device connected with the aerogel is triggered to realize ultra-sensitive fire early warning.
FIG. 3 is a graph showing the real-time variation of the electrical resistance of the aerogel under different strains in example 4; FIG. 4 is a graph showing the real-time variation of the resistance of the aerogel in example 4 in monitoring the bending and jumping of human fingers. Wherein A is the crooked resistance real-time change picture of aerogel monitoring human finger, and B is the crooked resistance real-time change picture of aerogel monitoring human body when jumping. As can be seen from fig. 3 and 4, the flame retardant aerogel provided by the present invention has an excellent piezoresistive sensing function. As can be seen from fig. 3, the aerogel provided by the present invention exhibits different rates of resistance change at different strains of 10% to 50% in example 4, with the greater the strain, the greater the rate of resistance change. When the aerogel of the invention is used for monitoring human body movement, as can be seen from fig. 4, the aerogel can sensitively monitor a signal of finger bending and is distinguished from a signal of jumping. Moreover, the resistance change of the finger bending and jumping shows a certain regularity, and the highest resistance change rate hardly changes after several cycles, and shows excellent fatigue resistance. Therefore, the aerogel provided by the invention has great potential application value in the aspects of human health monitoring, electronic skin and the like.
In conclusion, the chain-like natural polymer material and the layered nanomaterial in the flame-retardant aerogel provided by the invention can cooperatively form a three-dimensional porous carbon layer with excellent thermal stability and barrier property, so that the flame-retardant and heat-insulating effects are achieved. In addition, the carbon oxide material or the carbon nitride material in the aerogel can be quickly reduced due to the degradation of oxidation or nitridation groups in a high-temperature environment, so that the resistance of the aerogel is sharply reduced, a fire early warning device connected with the aerogel is triggered, and an ultrasensitive fire early warning effect is exerted. In addition, the carbon oxide material or the carbon nitride material in the aerogel also endows the aerogel with an excellent piezoresistive sensing function. Therefore, the flame-retardant aerogel with fire early warning and piezoresistive sensing functions, provided by the invention, has excellent fire safety, and can be applied to the fields of heat preservation and insulation, wearable equipment and the like with higher requirements on fire safety.
The embodiments of the present invention are not limited to the embodiments described above, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and they are included in the scope of the present invention.
Claims (10)
1. The preparation method of the flame-retardant aerogel with the fire early warning and piezoresistive sensing functions is characterized by comprising the following steps:
1) stripping the layered nano material: adding deionized water and the layered nano material into a reaction kettle at room temperature, stirring, and performing ultrasonic dispersion to uniformly disperse the layered nano material; centrifuging the obtained dispersion at a high speed, and adding ionized water into the centrifuged supernatant to dilute the centrifuged supernatant to form 0.1-10 wt% of stable suspension;
2) have fire early warning and the fire-retardant aerogel of pressure drag sensing function concurrently: adding a chain-shaped natural polymer material, deionized water and the stable suspension prepared in the step 1) into a reaction kettle, and uniformly stirring; adding a carbon oxide material or a carbon nitride material, performing ultrasonic dispersion, then dropwise adding a cross-linking agent, aging the gel, and then freeze-drying to obtain the flame-retardant aerogel with fire early warning and piezoresistive sensing functions;
the chain-shaped natural high polymer material is one or more of carboxymethyl chitosan, hydroxypropyl chitosan, hydroxyethyl chitosan, carboxymethyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose and hydroxypropyl methyl cellulose;
the carbon oxide material or the carbon nitride material is one or more of a carboxylated single-walled carbon nanotube, a hydroxylated single-walled carbon nanotube, an aminated single-walled carbon nanotube, a carboxylated multi-walled carbon nanotube, a hydroxylated multi-walled carbon nanotube, an aminated multi-walled carbon nanotube, a graphene oxide nanobelt and a graphene oxide nanosheet.
2. The preparation method of the flame-retardant aerogel with fire early warning and piezoresistive sensing functions according to claim 1, wherein the layered nano material is one or more of montmorillonite, kaolin, hydrotalcite, sericite, double metal hydroxide and layered phosphate.
3. The preparation method of the flame-retardant aerogel with the functions of fire early warning and piezoresistive sensing according to claim 1, wherein the mass ratio of the layered nano material to the chain-shaped natural polymer material is 1: 0.1-1: 10, and the layered nano material and the chain-shaped natural polymer material account for 50-99 wt% of the total solid content of the flame-retardant aerogel; the carbon oxide material or the carbon nitride material accounts for 1-50% of the total solid content of the aerogel.
4. The preparation method of the flame-retardant aerogel with fire early warning and piezoresistive sensing functions according to claim 1, wherein the stirring in the steps 1) and 2) is magnetic stirring, and the stirring speed is 1000-3000 r/min; stirring for 2-6 h in the step 1); the stirring time in the step 2) is 0.5-1 h.
5. The preparation method of the flame-retardant aerogel with fire early warning and piezoresistive sensing functions as claimed in claim 1, wherein the rotation speed of the high-speed centrifugation treatment in the step 1) is 3000-5000r/min, and the centrifugation frequency is 2-5 times.
6. The method for preparing the flame-retardant aerogel with fire early warning and piezoresistive sensing functions according to claim 1, wherein the freeze-drying in the step 2) is to remove water in the gel through a freeze-drying machine at-20 to-80 ℃ to obtain the aerogel; the vacuum degree of freeze drying is 10-300 Pa, and the time is 12-24 h.
7. The preparation method of the flame-retardant aerogel with fire early warning and piezoresistive sensing functions according to claim 1, wherein the aging of the gel in the step 2) is to form the gel through the reaction of a cross-linking agent and a chain-like natural polymer material at 30-60 ℃, and form a stable cross-linked network structure after aging for 3-6 hours.
8. The preparation method of the flame-retardant aerogel with the functions of fire early warning and piezoresistive sensing according to claim 1, wherein the cross-linking agent in the step 2) is one or more of citric acid, maleic acid, malic acid, itaconic acid, tartaric acid, polymaleic acid and glutaraldehyde, and the mass ratio of the cross-linking agent to the chain-shaped polymer material is 1: 10-1: 1.
9. The preparation method of the flame-retardant aerogel with fire early warning and piezoresistive sensing functions according to claim 1, wherein the ultrasonic dispersion power in the steps 1) and 2) is 300-500W, and the ultrasonic dispersion time is 0.5-1 h.
10. A flame-retardant aerogel with fire early warning and piezoresistive sensing functions, which is prepared by the preparation method of any one of claims 1-9.
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