CN113388151B - Preparation method of nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel - Google Patents
Preparation method of nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel Download PDFInfo
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Abstract
The invention relates to the field of flame retardance, in particular to a preparation method of nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel, the invention firstly adopts lemon juice as an acidolysis agent for chemical pretreatment, and then combines a high-efficiency and low-consumption ball milling technology to extract nano cellulose fiber from pericarp garbage pomelo peel, so that the cost is low, and the preparation method is green and environment-friendly; then, a large amount of hydroxyl carboxyl contained in the sodium alginate can form a large amount of hydrogen bonds and Ca on the surface of the hydroxyapatite with cellulose and the hydroxyapatite 2+ The prepared nano cellulose fiber, hydroxyapatite and sodium alginate are compounded to prepare the flame-retardant aerogel which is efficient in flame retardance and does not harm human bodies and the environment.
Description
Technical Field
The invention relates to the field of flame retardance, in particular to a preparation method of a nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel.
Background
Flame retardants prepared from petroleum materials have poor flame retardancy and single inorganic flame retardants such as silica gels are brittle, so it is imperative to prepare flame retardant materials from renewable resources and compound them with inorganic flame retardant components. The cellulose has wide source, can be obtained from plants, knapsack animals, algae and fungi, has low preparation cost and can be regenerated. The heat insulation performance of cellulose-based materials has attracted great interest in both the scientific and industrial fields, the surface morphology of cellulose increases the penetration or diffusion distance, and cellulose has good heat insulation performance in terms of heat conduction, but cellulose has a low limiting oxygen index, is a very flammable material, and therefore should be endowed with fire resistance for safe use.
Sodium alginate is a natural biodegradable anionic polysaccharide, the molecular chain of the polysaccharide contains a large number of hydroxyl groups and carboxyl groups, and sodium ions on a G unit (alpha-L guluronic acid) are easy to be subjected to certain divalent cationsIon exchange reaction of the seeds, ca 2+ Can generate a stable egg box structure through ion crosslinking reaction with sodium alginate, and has good hydrophilicity. The viscosity of sodium alginate is better, and when the temperature rises, the internal structure of the sodium alginate is changed, and hydroxyl and oxygen are broken to form a group structure without a certain shape, so that the sodium alginate is easy to adhere to each other, the resistance is increased, and the spread of fire is indirectly inhibited. In addition, a carbonization interlayer is formed on the surface of the sodium alginate after the fire disaster happens to prevent the inside from further participating in combustion and pyrolysis,
the hydroxyapatite is widely existed in nature, is an inorganic calcium phosphate material, has excellent thermal stability, has the advantage of certain catalysis carbon formation, is expected to improve the formation speed and carbon formation amount of a carbon layer, and is a high-efficiency flame retardant additive. Hydroxyapatite can also act as a physical barrier to inhibit the diffusion of oxygen to the cellulose fibers, limiting the escape of volatile products and thereby inhibiting the combustion of nanocellulose fibers.
At present, there is still a report about how to prepare composite aerogel by compounding sodium alginate, hydroxyapatite and nano cellulose fiber, so that there is a certain research significance on how to reasonably compound the three materials to obtain the composite aerogel with excellent flame retardance.
Disclosure of Invention
In order to solve the technical problems, the invention provides a preparation method of a nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel. According to the method, lemon juice is adopted as an acidolysis agent to carry out chemical pretreatment, and then a high-efficiency and low-consumption ball milling technology is combined to extract the nano cellulose fiber from the pericarp garbage pomelo peel, so that the cost is low, and the method is green and environment-friendly; then sodium alginate containing a large amount of hydroxyl carboxyl can form a large amount of hydrogen bonds with cellulose and hydroxyapatite and Ca on the surface of the hydroxyapatite 2+ The prepared nano cellulose fiber is compounded with hydroxyapatite and sodium alginate to prepare the flame-retardant aerogel, wherein the flame-retardant aerogel has better affinity with carboxylic acid groups and can have complexation and coulomb interaction with the carboxylic acid groups.
The specific technical scheme of the invention is as follows: a preparation method of a nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel comprises the following steps:
1) Weighing 6-8.5 g of pretreated shaddock peel, stirring for 3-4 h under heating by using 1-1.5 wt% NaOH solution, wherein the shaddock peel and the NaOH have a certain material-liquid ratio, centrifuging for 7-10 min at 13000-15000 rpm when the shaddock peel and the NaOH are hot, removing supernatant, fully washing precipitates, drying for 6-9 at 75-85 ℃ to obtain powder A, soaking the powder A for 1-1.5 h by using lemon juice, centrifuging for 10-13 min at 12000-13000 rpm to obtain precipitates, directly ball-milling for 20-25 min, washing until the pH is neutral, drying to obtain powder B, and finally using 1.5-1.7 wt% NaClO 2 Soaking the powder B in the solution for 0.5-1 h, washing with deionized water for 3-4 times, drying at 75-85 ℃ for 6-9 h to obtain nano cellulose fibers, and ultrasonically dispersing the nano cellulose fibers in water to prepare a nano cellulose fiber suspension with the mass fraction of 1.5% -1.8% for later use;
the plant cell wall mainly comprises hemicellulose, cellulose and lignin, and the effective removal of the hemicellulose and the lignin is the key for extracting the cellulose from the plant. NaOH aqueous solution can promote a plurality of single water molecules to be generated, and promote alkali liquor to enter the raw materials, so that the valence bonds of the mutual combination among cellulose, hemicellulose and lignin are loosened, and the hydrogen bonds among the cellulose and the hemicellulose can be obviously weakened; naOH can also react with hemicellulose to break acetyl in the hemicellulose so that the acetyl is dissolved in water and removed; furthermore, naOH can also remove part of the lignin: the lignin and the carbohydrate are connected through covalent bonds and are distributed in a complex mode in a cell wall, the lignin is difficult to be clearly separated from biomass, in NaOH solution, OH & lt- & gt can be used as a nucleophilic reagent to destroy beta-O & lt- & gt-4 & lt- & gt ether bonds in macromolecules of the lignin, na & lt + & gt can react with hydroxyl in the lignin to generate soluble phenolate, and meanwhile, hydrophilic groups are introduced into the lignin, so that the lignin after cracking is dissolved in alkali liquor and removed. Under the heating condition, naOH can also saponify ester bonds between lignin and hemicellulose, thereby being beneficial to dissolving out lignin. According to the invention, a sample is pretreated by 1-1.5 wt% NaOH solution under heating conditions, so that on one hand, impurities such as lignin and hemicellulose can be effectively removed, on the other hand, the concentration of the used alkali solution is lower than that of the alkali solution which is researched at present and is used for extracting cellulose, the sample can be completely removed from the sample by washing, and the influence on the environment is small.
The acid has three functions in extracting cellulose from plants 1) H + Can form carbonium ion with oxygen atom on glycosidic bond in hemicellulose, 2) acid can destroy ether bond and carbon-carbon bond in lignin to convert into monocyclic aromatic compound and remove, 3) natural cellulose comprises crystalline region and amorphous region, and dilute acid treatment can react with beta-1, 4 glycosidic bond in amorphous region of cellulose to destroy cellulose in amorphous region, thereby improving crystallinity. The invention uses lemon juice as acidolysis agent, wherein the lemon juice contains common citric acid and ascorbic acid, and two adjacent enol-type hydroxyl groups at the 2 nd and 3 rd positions in the molecule are easy to dissociate to release H + The two acids are simultaneously subjected to acidolysis, so that the required amount is small, the cost is low, and the environmental protection benefit is good.
The invention adopts grinding beads with 3 diameters, can fully contact with a sample and can generate larger shearing force, thereby generating mechanical-chemical effect, destroying the main chain and the side chain of part of biological hemicellulose which is not removed by acid and alkali treatment in the plant cell wall, depolymerizing the hemicellulose, and converting the hemicellulose into water-soluble oligosaccharide and monosaccharide, on the other hand, reducing the rigidity of lignin in the plant cell wall and promoting the lignin to dissociate.
The invention further processes the sample by ball milling, and can obviously reduce and disperse the size of the obtained sample under the condition of not obviously influencing the crystal form and the crystallinity of the extracted cellulose.
The invention adopts NaClO 2 The solution is further used for treating a sample, so that the acid-insoluble lignin can be removed, and the sample can be purified.
2) Modifying hydroxyapatite: weighing 4-6 g of hydroxyapatite A, adding the hydroxyapatite A into 350-450 g of alcohol, performing ultrasonic dispersion for 30-35 min, then adding gamma-glycidyl ether propyl trimethoxy silane (GPTMS) hydrolysate, stirring the obtained mixture for 1.5-2.5 h at 80-85 ℃, then alternately washing the mixture to be neutral by deionized water and ethanol, and drying the washed sample at 90-100 ℃ for later use;
according to the invention, GPTMS hydrolysate is used for modifying hydroxyapatite, so that on one hand, the electrostatic attraction among particles can be reduced, and the agglomeration problem is reduced, on the other hand, epoxy groups are introduced on the surface of hydroxyapatite, GPTMS hydrolysate can cause the conformational change of nearby polymers, the subsequent bonding effect of hydroxyapatite and nano cellulose fiber is improved, and the construction of a cross-linked network structure is promoted.
3) Preparing the nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel: taking 1.5-2.4 g of hydroxyapatite B, 90-100 g of the nano cellulose suspension obtained in the step 1) and a certain amount of sodium alginate, carrying out low-speed ball milling for 30-45 min to uniformly disperse the nano cellulose suspension, taking the mixed liquid after ball milling, and adding a certain amount of CaCl 2 Stirring the solution at 70-75 ℃ for 1-2 h, and drying to obtain the aerogel.
The sodium alginate is a natural biodegradable anionic polysaccharide, the sodium alginate is used as a flame retardant component, when the temperature rises, the internal structure of the sodium alginate is changed, hydroxyl and oxygen groups are broken to form a group structure without a certain shape, and the group structure is easy to adhere to each other, so that the resistance is increased, and the spread of fire is indirectly inhibited. In addition, a carbonization interlayer is formed on the surface of the sodium alginate after a fire disaster occurs to prevent the interior from further participating in combustion and pyrolysis.
The hydroxyapatite is used as another flame-retardant component, has the advantage of catalyzing to form carbon to a certain extent, is expected to improve the forming speed and the carbon forming amount of a carbon layer, and can also be used as a physical barrier to inhibit oxygen from diffusing to cellulose fibers and limit escape of volatile products, thereby inhibiting the combustion of the nano cellulose fibers.
The molecular chain of sodium alginate contains a large amount of hydroxyl and carboxyl, and forms a large amount of hydrogen bonds with cellulose and hydroxyapatite, and Ca on the surface of the hydroxyapatite 2+ Has better affinity with carboxylic acid groups, has complexation and coulomb interaction with the carboxylic acid groups, and in addition, sodium ions on the G unit (alpha-L guluronic acid) of sodium alginate are easy to react with Ca 2+ Producing stable egg box knot by ion cross-linking reactionAdding CaCl 2 The solution facilitates this crosslinking, resulting in improved mechanical properties of the final aerogel.
Preferably, the shaddock ped pretreatment in the step 1) is as follows: removing yellow peel from fresh pericarpium Citri Grandis, cleaning, drying in a forced air drying oven at 75-85 deg.C for 24-32 hr, pulverizing the dried sample in a pulverizer, and sieving with 35-45 mesh sieve.
Preferably, in the step 1), the material-liquid ratio of the NaOH solution to the shaddock peel is 38-40, and the heating condition is that the shaddock peel powder soaked by the NaOH solution is placed in an oil bath kettle at 95-110 ℃ and the stirring speed is 200-220 r/min.
Preferably, the intensive washing process in the step 1) is specifically as follows: adding deionized water into the precipitate, stirring at 300-400 rpm for 5 min to make water fully contact with the precipitate, centrifuging at 13000-15000 rpm for 7-10 min, and repeating the step for 4-6 times.
Preferably, the lemon juice in step 1) is prepared by peeling fresh lemon, removing seeds, squeezing, filtering, collecting filtrate, centrifuging the filtrate at 14000-15000 rpm for 15-20 min, discarding precipitate, and storing supernatant in 6-8 deg.C refrigerator.
Preferably, in the step 1), the material-liquid ratio of the lemon juice to the powder A is 1.
Preferably, the ball milling in the step 1) is carried out, wherein the ball-to-material ratio is 1-1, three types of milling beads are used, the diameters of the milling beads are respectively 2 mm, 6 mm and 10 mm, the quantity ratio of the milling beads is (5.9-6.1): (1.4-1.6): 1, the total volume of the milling beads is not more than 1/3 of the volume of the ball milling tank, and the frequency of the ball mill is set to be 25-30 HZ.
Preferably, in step 1), naClO is added 2 The material-liquid ratio of the solution to the powder B is 1.
Preferably, in step 2), the hydroxyapatite a may be prepared according to the published patents (juenge, liheng, wujin, hydroxyapatite nanowires, nanowire assembly networks, and a method for preparing the same. ) Preparation and slight adjustment: at room temperature, 0.222 g of CaCl 2 Dissolving in 25 ml deionized water to obtain solution A, and dissolving 2.440 g of sodium oleate in 25 ml deionized water to obtain solution BDropwise adding the solution A into the solution B while stirring to prepare a reaction precursor, continuously stirring at room temperature for 30 minutes, then adding 25 ml of 0.072 mol/L sodium dihydrogen phosphate solution, transferring the mixture into a hydrothermal reaction kettle (the volume is 100 ml), sealing, carrying out hydrothermal treatment at 200 ℃ for 36 hours, and carrying out freeze drying for 12-15 hours to obtain the hydroxyapatite A.
Preferably, the specific preparation method of the gamma-glycidyl ether propyl trimethoxy silane (GPTMS) hydrolysate in the step 2) comprises the following steps: adding 10-15 g of GPTMS into 4-6 g of deionized water and 36-54 g of alcohol, and then dropwise adding 35-40% of dilute citric acid to adjust the pH value to 4.5-5.5, thereby obtaining GPTMS hydrolysate.
Preferably, in the step 3), the adding amount of the sodium alginate is 4-8 wt% of the total adding amount of the nano cellulose fiber and the hydroxyapatite A.
Preferably, the ball milling parameters in step 3) are as follows: the ball-material ratio is 1.
Preferably, 5-8 mL of 3 wt% CaCl are added in step 3) 2 And (3) solution.
Preferably, the stirring rate in step 3) is 200-300 rpm.
Preferably, the specific drying manner in step 3) is as follows: freezing the stirred mixed suspension in liquid nitrogen, placing the frozen mixed suspension in a sleeve of a Soxhlet extractor, adding 60-70 mL of acetone into an extraction bottle, heating at 60-70 ℃ for 2-4 h, transferring the suspension in the sleeve into a beaker, and drying in a vacuum drying oven at 110-115 ℃ for 25-30 min.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention combines chemical pretreatment and mechanical ball milling to extract nano cellulose fiber from the peel garbage. The used alkali and bleaching agent are low in concentration, can be removed after being washed by water, and other impurities are not introduced, and the lemon juice is adopted as the acidolysis agent, so that the cost is low, the efficiency is high, and the environmental protection benefit is good; the size is reduced by ball milling and the cellulose is further purified, so that the consumption is low and the efficiency is high; the method for preparing the nano cellulose fiber has the advantages of simple equipment, no corrosion to equipment, low cost and environmental protection.
2. Sodium alginate containing a large amount of hydroxyl carboxyl can form a large amount of hydrogen bonds with cellulose and hydroxyapatite and Ca on the surface of the hydroxyapatite 2+ The prepared nano cellulose fiber is compounded with hydroxyapatite and sodium alginate to prepare the flame-retardant aerogel, wherein the flame-retardant aerogel has better affinity with carboxylic acid groups and can have complexation and coulomb interaction with the carboxylic acid groups. The flame-retardant material is efficient in flame retardance and does not cause harm to human bodies and the environment.
3. The invention prepares the flame retardant material by compounding the nano cellulose fiber extracted from the peel garbage with the hydroxyapatite and the sodium alginate, changes waste into valuable, has simple used equipment, low energy consumption and high environmental protection benefit, and accords with sustainable development.
Detailed Description
The present invention will be further described with reference to the following examples.
Example 1:
1) Preparing nano cellulose fiber: removing yellow peel from fresh pomelo peel, cleaning, drying in a forced air drying oven at 75 ℃ for 28 h, crushing the dried sample in a crusher, and sieving with a 35-mesh sieve to obtain the pretreated pomelo peel. Weighing 6 g of pretreated shaddock peel, stirring and treating the shaddock peel with 1.2 wt% of NaOH solution at 100 ℃ for 3.5 h at 200 r/min, wherein the material-liquid ratio of the shaddock peel to the NaOH is 38: adding deionized water into the precipitate, stirring at 320 rpm for 5 min to ensure that water is fully contacted with the precipitate, centrifuging at 13000 rpm for 9 min, repeating the step for 5 times, drying at 80 ℃ for 8 h to obtain powder A, removing peel and seeds of fresh lemons, juicing, filtering, collecting filtrate, centrifuging the filtrate at 15000 rpm for 15 min, discarding the precipitate to obtain lemon juice, soaking the powder A with the lemon juice for 1h, wherein the material-liquid ratio of the lemon juice to the powder A is 1, and centrifuging at 12000 rpm for 12 min to obtain the precipitate, and directly performing ball milling for 23 min, wherein the ball milling parameters are as follows: ball material ratio1, using three types of grinding beads, 2 mm, 6 mm and 10 mm in diameter, respectively, in a quantity ratio of 6 2 Soaking powder B in the solution for 0.5 h, wherein the powder is NaClO 2 The material-liquid ratio of the solution to the powder B is 1;
2) At room temperature, 0.222 g of CaCl 2 Dissolving the mixture in 25 ml of deionized water to form solution A, dissolving 2.440 g of sodium oleate in 25 ml of deionized water to form solution B, dropwise adding the solution A into the solution B while stirring to prepare a reaction precursor, continuously stirring the mixture at room temperature for 30 minutes, then adding 25 ml of 0.072 mol/L sodium dihydrogen phosphate solution, transferring the mixture into a hydrothermal reaction kettle (the volume is 100 ml), sealing the reaction kettle, carrying out hydrothermal treatment at 200 ℃ for 36 hours, and carrying out freeze drying for 13.5 hours to obtain the hydroxyapatite A. Weighing 4.5 g of hydroxyapatite A, adding into 360 g of alcohol, and performing ultrasonic dispersion for 32 min to obtain hydroxyapatite dispersion; adding 12 g of GPTMS into 5 g of deionized water and 45 g of alcohol, and then dropwise adding 35% diluted citric acid to adjust the PH to 5.2, so as to obtain GPTMS hydrolysate; adding the hydroxyapatite dispersion liquid into GPTMS hydrolysate, mixing, stirring the obtained mixture at 82 ℃ for 1.8 h, then alternately washing the mixture with deionized water and ethanol to be neutral, and drying the washed sample at 90 ℃ to obtain hydroxyapatite B;
3) Preparing the nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel: taking 1.6 g of hydroxyapatite B, 100 g of the nano cellulose suspension obtained in the step 1) and 0.155 g of sodium alginate, and carrying out low-speed ball milling for 32 min to uniformly disperse the nano cellulose suspension, wherein the ball milling parameters are as follows: the ball-to-material ratio was 1. Taking the mixed liquid after ball milling, adding 6 mL of 3 wt% CaCl 2 The solution was stirred at 200 rpm for 1h at 70 ℃. Freezing the stirred mixed suspension in liquid nitrogen, placing the frozen mixed suspension in a sleeve of a Soxhlet extractor, adding 60 mL of acetone into an extraction bottle, heating at 65 ℃ for 205 h, transferring a colloidal object in the sleeve into a beaker, and drying in a vacuum drying oven at 110 ℃ for 28 min to obtain the aerogel.
The prepared sample is subjected to cone calorimetry, and the maximum heat release rate is 17.81 kW/m 2 The heat release amount is 1.12 MJ/m 2 The maximum heat release rate (324 kW/m) of the flame-retardant material prepared by directly freeze-drying the nano-cellulose fiber 2 ) And amount of heat release (9.25 MJ/m) 2 ) The smaller the size, the composite material has stronger inhibition effect on the combustion process.
Example 2:
1) Preparing nano cellulose fiber: removing yellow peel from fresh pomelo peel, cleaning, drying in a forced air drying oven at 80 ℃ for 26 h, crushing the dried sample in a crusher, and sieving with a 40-mesh sieve to obtain the pretreated pomelo peel. Weighing 6.5 g of pretreated shaddock peel, stirring and treating the shaddock peel with 1.2 wt% of NaOH solution at 95 ℃ for 4h at 210 r/min, wherein the material-liquid ratio of the shaddock peel to the NaOH is 39: adding deionized water into the precipitate, stirring at 350 rpm for 5 min to ensure that water is fully contacted with the precipitate, centrifuging at 14000 rpm for 8 min, repeating the step for 6 times, drying at 85 ℃ for 6 h to obtain powder A, removing peel and seeds of fresh lemons, juicing, filtering, collecting filtrate, centrifuging the filtrate at 15000 rpm for 16 min, discarding the precipitate to obtain lemon juice, soaking the powder A in the lemon juice for 1.3 h, wherein the material-liquid ratio of the lemon juice to the powder A is 1: ball to material ratio of 1 2 Soaking the powder B in the solution for 0.6 hNaClO 2 The material-liquid ratio of the solution to the powder B is 1;
2) At room temperature, 0.222 g of CaCl 2 Dissolving the mixture in 25 ml of deionized water to form solution A, dissolving 2.440 g of sodium oleate in 25 ml of deionized water to form solution B, dropwise adding the solution A into the solution B while stirring to prepare a reaction precursor, continuously stirring the mixture at room temperature for 30 minutes, then adding 25 ml of 0.072 mol/L sodium dihydrogen phosphate solution, transferring the mixture into a hydrothermal reaction kettle (the volume is 100 ml), sealing the reaction kettle, carrying out hydrothermal treatment at 200 ℃ for 36 hours, and carrying out freeze drying for 15 hours to obtain the hydroxyapatite fiber A. Weighing 5 g of hydroxyapatite A, adding into 400 g of alcohol, and performing ultrasonic dispersion for 35 min to obtain hydroxyapatite dispersion; adding the hydroxyapatite dispersion liquid into GPTMS hydrolysate, mixing, stirring the obtained mixture at 85 ℃ for 1.5 h, then alternately washing the mixture with deionized water and ethanol to be neutral, and drying the washed sample at 95 ℃ to obtain hydroxyapatite B;
3) Preparing the nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel: 2 g of hydroxyapatite B, 95 g of the nano cellulose suspension obtained in the step 1) and 0.246 g of sodium alginate are subjected to low-speed ball milling for 41 min to be uniformly dispersed, wherein the ball milling parameters are as follows: ball to material ratio 1, 12, using three types of grinding beads, 2 mm, 6 mm and 10 mm in diameter, respectively, in a quantity ratio of 4.5. Adding 7 mL of 3 wt% CaCl into the mixed liquid after ball milling 2 The solution was stirred at 72 ℃ for 1.5 h. Freezing the stirred mixed suspension in liquid nitrogen, placing the frozen mixed suspension in a sleeve of a Soxhlet extractor, adding 66 mL of acetone into an extraction bottle, heating at 66 ℃ for 3 hours, transferring the suspension in the sleeve into a beaker, and drying in a vacuum drying oven at 112 ℃ for 30 min to obtain the aerogel.
The prepared sample is subjected to cone calorimetry, and the maximum heat release rate is 18.21 kW/m 2 The heat release amount is 1.21 MJ/m 2 The maximum heat release rate (324 kW/m) of the flame-retardant foam is higher than that of the flame-retardant foam prepared by directly freeze-drying only the nano-cellulose fiber 2 ) And amount of heat release (9.25 MJ/m) 2 ) The smaller the size, the composite material has a strong inhibiting effect on the combustion process.
Example 3:
1) Preparing nano cellulose fiber: removing yellow peel from fresh pomelo peel, cleaning, drying in a forced air drying oven at 82 ℃ for 26 h, crushing the dried sample in a crusher, and sieving with a 40-mesh sieve to obtain the pretreated pomelo peel. Weighing 7.5 g of pretreated shaddock peel, stirring and treating the shaddock peel with 1.3 wt% of NaOH solution at 102 ℃ for 4h at 210 r/min, wherein the material-liquid ratio of the shaddock peel to the NaOH is 39: adding deionized water into the precipitate, stirring at 330 rpm for 5 min to ensure that water is fully contacted with the precipitate, then centrifuging at 13500 rpm for 8 min, repeating the step for 6 times, drying at 83 ℃ for 8.5 h to obtain powder A, removing peel and seeds of fresh lemons, juicing, filtering, collecting filtrate, centrifuging the filtrate at 15000 rpm for 16 min, discarding the precipitate to obtain lemon juice, soaking the powder A with the lemon juice for 1.2 h, wherein the material-liquid ratio of the lemon juice to the powder A is 1, and directly ball-milling the precipitate obtained by centrifuging at 13000 rpm for 11min for 25 min, wherein the ball-milling parameters are: ball-to-material ratio of 1 2 The material-liquid ratio of the solution to the powder B is 1;
2) At room temperature, 0.222 g of CaCl 2 Dissolving the mixture in 25 ml of deionized water to form solution A, dissolving 2.440 g of sodium oleate in 25 ml of deionized water to form solution B, dropwise adding the solution A into the solution B while stirring to prepare a reaction precursorContinuously stirring the mixture at room temperature for 30 minutes, then adding 25 ml of 0.072 mol/L sodium dihydrogen phosphate solution, transferring the mixture into a hydrothermal reaction kettle (the volume is 100 ml), sealing, carrying out hydrothermal treatment at 200 ℃ for 36 hours, and carrying out freeze drying for 14.5 hours to obtain hydroxyapatite fiber A; weighing 5.2 g of hydroxyapatite A, adding into 420 g of alcohol, and performing ultrasonic dispersion for 33 min to obtain hydroxyapatite dispersion liquid; adding the hydroxyapatite dispersion into GPTMS hydrolysate, mixing, stirring the obtained mixture at 84 ℃ for 2 h, then alternately washing the mixture with deionized water and ethanol to be neutral, and drying the washed sample at 95 ℃ to obtain hydroxyapatite B;
3) Preparing the nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel: 2.2 g of hydroxyapatite B, 90 g of the nano cellulose suspension obtained in the step 1) and 0.149 g of sodium alginate are subjected to low-speed ball milling for 34 min to be uniformly dispersed, wherein the ball milling parameters are as follows: ball to material ratio 1, 11, using three types of grinding beads, 2 mm, 6 mm and 10 mm in diameter, respectively, in a quantity ratio of 4.6. Taking the mixed liquid after ball milling, adding 8 mL of 3 wt% CaCl 2 The solution was stirred at 74 ℃ for 1.5 h. Freezing the stirred mixed suspension in liquid nitrogen, placing the frozen mixed suspension in a sleeve of a Soxhlet extractor, adding 63mL of acetone into an extraction bottle, heating at 65 ℃ for 3.5 hours, transferring the suspension in the sleeve into a beaker, and drying in a vacuum drying oven at 115 ℃ for 25 min to obtain the aerogel.
The prepared sample is subjected to cone calorimetry, and the maximum heat release rate is 17.94 kW/m 2 The heat release amount is 1.16 MJ/m 2 Maximum heat release rate (324 kW/m) over the flame retardant foam made by direct freeze-drying of nanocellulose fibers alone 2 ) And amount of heat release (9.25 MJ/m) 2 ) The smaller the size, the composite material has a strong inhibiting effect on the combustion process.
Example 4:
1) Preparing nano cellulose fiber: removing yellow peel from fresh pericarpium Citri Grandis, cleaning, drying at 79 deg.C in forced air drying oven for 25 hr, and pulverizing the dried sampleCrushing in a crusher, and sieving with a 35-mesh sieve to obtain the pretreated shaddock peel. Weighing 6.5 g of pretreated pomelo peel, stirring and treating the pomelo peel with 1.4 wt% of NaOH solution at 105 ℃ for 3.5 h at 200 r/min, wherein the material-liquid ratio of the pomelo peel to the NaOH is 40: adding deionized water into the precipitate, stirring at 360 rpm for 5 min to make water fully contact with the precipitate, then centrifuging at 13800 rpm for 10 min, repeating the step for 4-6 times, drying at 83 ℃ for 7.5 h to obtain powder A, removing peel and seeds of fresh lemon, juicing, filtering, collecting filtrate, centrifuging the filtrate at 14800 rpm for 18 min, discarding the precipitate to obtain lemon juice, soaking the powder A with the lemon juice for 1.2 h, wherein the material-liquid ratio of the lemon juice to the powder A is 1: ball-to-material ratio of 1 2 Soaking the powder B in the solution for 1h, wherein the powder is NaClO 2 The material-liquid ratio of the solution to the powder B is 1;
2) At room temperature, 0.222 g of CaCl 2 Dissolving the mixture in 25 ml of deionized water to form solution A, dissolving 2.440 g of sodium oleate in 25 ml of deionized water to form solution B, dropwise adding the solution A into the solution B while stirring to prepare a reaction precursor, continuously stirring the mixture at room temperature for 30 minutes, then adding 25 ml of 0.072 mol/L sodium dihydrogen phosphate solution, transferring the mixture into a hydrothermal reaction kettle (the volume is 100 ml), sealing the reaction kettle, carrying out hydrothermal treatment at 200 ℃ for 36 hours, and carrying out freeze drying for 13.5 hours to obtain hydroxyapatite fiber A; weighing 6 g of hydroxyapatite A, adding into 450 g of alcohol, and performing ultrasonic dispersion for 35 min to obtain hydroxyapatite dispersion liquid; adding hydroxyapatite dispersion into GPTMS hydrolysate, mixing, and heating to 84 deg.CStirring for 2.2 h, then alternately washing with deionized water and ethanol to be neutral, and drying the washed sample at 100 ℃ to obtain hydroxyapatite B;
3) Preparing the nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel: taking 1.5 g of hydroxyapatite B, 92 g of the nano cellulose suspension obtained in the step 1) and 0.149 g of sodium alginate, and carrying out low-speed ball milling for 38 min to uniformly disperse the nano cellulose suspension, wherein the ball milling parameters are as follows: the ball-to-material ratio was 1. Taking the mixed liquid after ball milling, adding 6 mL of 3 wt% CaCl 2 The solution was stirred at 70 ℃ for 2 h. Freezing the stirred mixed suspension in liquid nitrogen, placing the frozen mixed suspension in a sleeve of a Soxhlet extractor, adding 65 mL of acetone into an extraction bottle, heating the mixture at 70 ℃ for 2 hours, transferring the suspension in the sleeve into a beaker, and drying the mixture in a vacuum drying oven at 110 ℃ for 30 min to obtain the aerogel.
The prepared sample is subjected to cone calorimetry, and the maximum heat release rate is 19.01 kW/m 2 The heat release amount is 1.26 MJ/m 2 Maximum heat release rate (324 kW/m) over the flame retardant foam made by direct freeze-drying of nanocellulose fibers alone 2 ) And amount of heat release (9.25 MJ/m) 2 ) The smaller the size, the composite material has stronger inhibition effect on the combustion process.
Example 5:
1) Preparing nano cellulose fiber: removing yellow peel from fresh pomelo peel, cleaning, drying in a forced air drying oven at 85 ℃ for 24h, crushing the dried sample in a crusher, and sieving with a 45-mesh sieve to obtain the pretreated pomelo peel. Weighing 8.5 g of pretreated pomelo peel, stirring and treating the pomelo peel with 1.5 wt% of NaOH solution at 100 ℃ for 4h at 200 r/min, wherein the material-liquid ratio of the pomelo peel to the NaOH is 39: adding deionized water into the precipitate, stirring at 400 rpm for 5 min to make water contact with the precipitate, centrifuging at 15000 rpm for 9 min, repeating the steps for 4 times, and collecting the precipitate and the deionized waterRemoving peel and seeds of fresh lemon, juicing, filtering and collecting filtrate, centrifuging the filtrate for 17 min at 14000 rpm, discarding precipitate to obtain lemon juice, soaking the powder A in the lemon juice for 1.5 h, wherein the material-liquid ratio of the lemon juice to the powder A is 1: ball to material ratio of 1 2 Soaking the powder B in the solution for 0.5 h, wherein the powder is NaClO 2 The material-liquid ratio of the solution to the powder B is 1;
2) At room temperature, 0.222 g of CaCl 2 Dissolving the mixture in 25 ml of deionized water to form solution A, dissolving 2.440 g of sodium oleate in 25 ml of deionized water to form solution B, dropwise adding the solution A into the solution B while stirring to prepare a reaction precursor, continuously stirring the mixture at room temperature for 30 minutes, then adding 25 ml of 0.072 mol/L sodium dihydrogen phosphate solution, transferring the mixture into a hydrothermal reaction kettle (the volume is 100 ml), sealing the reaction kettle, carrying out hydrothermal treatment at 200 ℃ for 36 hours, and carrying out freeze drying for 14 hours to obtain hydroxyapatite fiber A; weighing 4 g of hydroxyapatite A, adding into 350 g of alcohol, and performing ultrasonic dispersion for 30 min to obtain hydroxyapatite dispersion; adding the hydroxyapatite dispersion into GPTMS hydrolysate, mixing, stirring the obtained mixture at 80 ℃ for 2.5h, then alternately washing with deionized water and ethanol to be neutral, and drying the washed sample at 98 ℃ to obtain hydroxyapatite B;
3) Preparing the nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel: 2.4 g of hydroxyapatite B, 100 g of the nano cellulose suspension obtained in the step 1) and 4.2 g of sodium alginate are subjected to low-speed ball milling for 45 min to be uniformly dispersed, wherein the ball milling parameters are as follows: ball to feed ratio of 1Bead sizes, 2 mm, 6 mm and 10 mm in diameter, respectively, in a quantity ratio of 4.7. Adding 8 mL of 3 wt% CaCl into the mixed liquid after ball milling 2 The solution was stirred at 70 ℃ for 2 h. Freezing the stirred mixed suspension in liquid nitrogen, placing the frozen mixed suspension in a sleeve of a Soxhlet extractor, adding 70 mL of acetone into an extraction bottle, heating the mixture at 60 ℃ for 3 hours, transferring the suspension in the sleeve into a beaker, and drying the mixture in a vacuum drying oven at 113 ℃ for 28 min to obtain the aerogel.
The prepared sample is subjected to cone calorimetry, and the maximum heat release rate is 17.25 kW/m 2 The heat release amount is 1.14 MJ/m 2 Maximum heat release rate (324 kW/m) over the flame retardant foam made by direct freeze-drying of nanocellulose fibers alone 2 ) And amount of heat release (9.25 MJ/m) 2 ) The smaller the size, the composite material has a strong inhibiting effect on the combustion process.
The raw materials and equipment used in the invention are common raw materials and equipment in the field if not specified; the methods used in the present invention are conventional in the art unless otherwise specified.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, alterations and equivalents of the above embodiments according to the technical spirit of the present invention are still within the protection scope of the technical solution of the present invention.
Claims (10)
1. A preparation method of a nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel is characterized by comprising the following steps:
1) Weighing 6-8.5 g of pretreated shaddock peel, stirring for 3-4 h under heating by using 1-1.5 wt% NaOH solution, centrifuging for 7-10 min at 13000-15000 rpm while hot, removing supernatant, fully washing precipitate, drying for 6-9 h at 75-85 ℃ to obtain powder A, soaking the powder A for 1-1.5 h by using lemon juice, centrifuging for 10-13 min at 12000-13000 rpm to obtain precipitate, directly ball-milling for 20-25 min, washing until the pH value is neutral, and drying to obtain powder BAnd finally using 1.5-1.7 wt% of NaClO 2 Soaking the powder B in the solution for 0.5-1 h, washing with deionized water for 3-4 times, drying at 75-85 ℃ for 6-9 h to obtain nano cellulose fibers, and ultrasonically dispersing the nano cellulose fibers in water to prepare a nano cellulose fiber suspension with the mass fraction of 1.5% -1.8% for later use;
2) Modifying hydroxyapatite: weighing 4-6 g of hydroxyapatite A, adding the hydroxyapatite A into 350-450 g of alcohol, performing ultrasonic dispersion for 30-35 min, then adding gamma-glycidyl ether propyl trimethoxy silane hydrolysate, stirring the obtained mixture at 80-85 ℃ for 1.5-2.5 h, then alternately washing the mixture with deionized water and ethanol to be neutral, and drying the washed sample at 90-100 ℃ to obtain hydroxyapatite B;
3) Preparing the nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel: taking 1.5-2.4 g of hydroxyapatite B, 90-100 g of the nano cellulose fiber suspension obtained in the step 1) and sodium alginate, performing low-speed ball milling for 30-45 min to uniformly disperse the nano cellulose fiber suspension, taking the mixed liquid after ball milling, and adding CaCl 2 Stirring the solution at 70-75 ℃ for 1-2 h, and drying to obtain the aerogel.
2. The preparation method of the nano cellulose fiber-sodium alginate-hydroxyapatite flame retardant aerogel as claimed in claim 1, wherein in the step 1):
the shaddock peel pretreatment comprises the following steps: removing yellow peel from fresh pericarpium Citri Grandis, cleaning, drying at 75-85 deg.C in a forced air drying oven for 24-32 h, pulverizing the dried sample in a pulverizer, and sieving with 35-45 mesh sieve;
the material-liquid ratio of the NaOH solution to the shaddock peel is 38-40, and the heating condition is that the shaddock peel powder soaked by the NaOH solution is placed in an oil bath kettle at the temperature of 95-110 ℃ and the stirring speed is 200-220 r/min;
the full washing process is as follows: adding deionized water into the precipitate, stirring at 300-400 rpm for 5 min to ensure that water is fully contacted with the precipitate, then centrifuging at 13000-15000 rpm for 7-10 min, and repeating the step for 4-6 times;
the lemon juice is prepared by peeling fresh lemon, removing seed, squeezing, filtering, collecting filtrate, centrifuging at 14000-15000 rpm for 15-20 min, discarding precipitate, and storing supernatant in 6-8 deg.C refrigerator.
3. The preparation method of the nano cellulose fiber-sodium alginate-hydroxyapatite flame retardant aerogel according to claim 1, wherein in the step 1), the ratio of the lemon juice to the powder A is 1.
4. The preparation method of the nano cellulose fiber-sodium alginate-hydroxyapatite flame retardant aerogel as claimed in claim 1, wherein the ball milling in the step 1) is performed at a ball-to-material ratio of 1 to 12 to 1, three types of milling beads are used, the diameters of the three types of milling beads are respectively 2 mm, 6 mm and 10 mm, the number ratio of the three types of milling beads is (5.9 to 6.1): (1.4 to 1.6): 1, the total volume of the milling beads is not more than 1/3 of the volume of the ball milling tank, and the frequency of the ball mill is set to be 25 to 30 HZ.
5. The preparation method of the nano cellulose fiber-sodium alginate-hydroxyapatite flame retardant aerogel as claimed in claim 1, wherein in the step 1), naClO is adopted 2 The material-liquid ratio of the solution to the powder B is 1.
6. The preparation method of the nano cellulose fiber-sodium alginate-hydroxyapatite flame-retardant aerogel as claimed in claim 1, wherein the specific preparation method of the gamma-glycidyl ether propyl trimethoxy silane hydrolysate in the step 2) comprises: adding 10-15 g of gamma-glycidyl ether propyl trimethoxy silane into 4-6 g of deionized water and 36-54 g of alcohol, and then dropwise adding 35-40% of dilute citric acid to adjust the pH to 4.5-5.5 to obtain gamma-glycidyl ether propyl trimethoxy silane hydrolysate.
7. The method for preparing the nano cellulose fiber-sodium alginate-hydroxyapatite flame retardant aerogel as claimed in claim 1, wherein in the step 3), the amount of sodium alginate added is 4-8 wt% of the total amount of nano cellulose fiber and hydroxyapatite A added.
8. The preparation method of the nano cellulose fiber-sodium alginate-hydroxyapatite flame retardant aerogel as claimed in claim 1, wherein the ball milling parameters in the step 3) are as follows: the ball-material ratio is 1.
9. The preparation method of the nano cellulose fiber-sodium alginate-hydroxyapatite flame retardant aerogel as claimed in claim 1, wherein 5-8 mL of 3 wt% CaCl is added in the step 3) 2 And (3) solution.
10. The preparation method of the nano cellulose fiber-sodium alginate-hydroxyapatite flame retardant aerogel as claimed in claim 1, wherein in the step 3):
the stirring speed is 200-300 rpm;
the drying mode is as follows: freezing the stirred mixed suspension in liquid nitrogen, placing the frozen mixed suspension in a sleeve of a Soxhlet extractor, adding 60-70 mL of acetone into an extraction bottle, heating at 60-70 ℃ for 2-4 h, transferring the suspension in the sleeve into a beaker, and drying in a vacuum drying oven at 110-115 ℃ for 25-30 min.
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