CN115716882B - Modified cellulose nanocrystalline and preparation method and application thereof - Google Patents
Modified cellulose nanocrystalline and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to a modified cellulose nanocrystal and a preparation method and application thereof. The preparation method of the modified cellulose nanocrystalline comprises the following steps: (1) Dispersing microcrystalline cellulose in a sodium periodate aqueous solution, then reacting at 60-80 ℃ for 70-90min, cooling to room temperature after the reaction is finished, washing and drying to obtain cellulose nanocrystals; (2) Dispersing cellulose nanocrystalline in water, then adding melamine water solution, reacting for 10-30min at 60-80 ℃, then adding phytic acid water solution, reacting for 10-30min at 60-80 ℃, cooling to room temperature after the reaction is finished, washing, and drying to obtain modified cellulose nanocrystalline. The modified cellulose nanocrystalline prepared by the invention is a novel flame retardant integrating a carbon source, an air source and an acid source, has high thermal stability and excellent flame retardant property, and is simple in preparation process, environment-friendly and low in cost.
Description
Technical Field
The invention belongs to the technical field of material modification, and particularly relates to a modified cellulose nanocrystal and a preparation method and application thereof.
Background
Synthetic polymers are the primary raw materials for manufacturing industrial and consumer products. Flammability of petroleum derived polymers has been recognized as an important safety issue. The most widely used thermoplastic polymers, such as Polyethylene (PE), polypropylene (PP), polystyrene (PS), poly (methyl methacrylate) (PMMA) and Acrylonitrile Butadiene Styrene (ABS), have poor fire resistance without flame retardant. Their limiting oxygen index is lower than 19% (the average atmospheric oxygen content is 21%). Polyolefins can degrade, decompose, and produce toxic gases when exposed to high temperatures. Flame retardants are often added to polymeric materials as additives or active materials. Inorganic reactive fillers and halides are widely used for flame resistance of fiber reinforced polymer composites. Widely used metal hydroxides require loading levels of 60% or more, which can have a detrimental effect on viscosity and mechanical properties. The inorganic filler has the defects of poor compatibility, easy leaching, low mechanical property and the like. Halogenated flame retardants release toxic gases upon combustion, causing 80% of the fires to die. In addition, a wide variety of other toxic substances, most notably HBr and brominated phenols/benzene, are produced. With the increasing attention of people to sustainable ecosystems and environmental protection, renewable energy sources and abundant natural resources are used as raw materials of flame retardants to gradually develop, so that the damage to the environment can be reduced, and non-renewable resources are saved. These factors indicate that a safer, more effective and environmentally friendly flame retardant system is highly desirable.
The Intumescent Flame Retardants (IFRs) are composed of a carbon source, an acid source and an air source, and have the advantages of low smoke, low toxicity, environmental protection, high efficiency and the like, so that the IFRs become one of research hotspots in the domestic and foreign fields at present. Cellulose is one of the most abundant biodegradable polymers in the world, and has unique characteristics of no toxicity, low price, renewable resources, temperature resistance, stability of pH value change and the like. Cellulose has a rich molecular structure of polyhydroxy groups, and can form a crosslinked carbon layer in the combustion process. However, the flammability of cellulose limits its further use as a flame retardant.
Disclosure of Invention
Based on the above-mentioned drawbacks and deficiencies of the prior art, it is an object of the present invention to at least solve one or more of the above-mentioned problems of the prior art, in other words, to provide a modified cellulose nanocrystal satisfying one or more of the above-mentioned needs, and a method for preparing the same and an application thereof.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
the preparation method of the modified cellulose nanocrystalline comprises the following steps:
(1) Dispersing microcrystalline cellulose in a sodium periodate aqueous solution, then reacting at 60-80 ℃ for 70-90min, cooling to room temperature after the reaction is finished, washing and drying to obtain cellulose nanocrystals;
(2) Dispersing cellulose nanocrystalline in water, then adding melamine water solution, reacting for 10-30min at 60-80 ℃, then adding phytic acid water solution, reacting for 10-30min at 60-80 ℃, cooling to room temperature after the reaction is finished, washing, and drying to obtain modified cellulose nanocrystalline.
In the preferred scheme, in the step (1), the solid-liquid mass ratio of the microcrystalline cellulose to the sodium periodate aqueous solution is 1: (90-110).
Preferably, the concentration of the sodium periodate aqueous solution is 0.5-1M.
In the step (2), the solid-liquid mass ratio of melamine to water in the aqueous solution of melamine is (1-2): 20.
preferably, in the step (2), the mass fraction of the phytic acid in the phytic acid aqueous solution is 60-70%.
As a preferable scheme, in the step (2), the mass part ratio of the cellulose nanocrystalline, the melamine aqueous solution and the phytic acid aqueous solution is 1: (1-3): (1-3).
Preferably, the cellulose nanocrystal is in a nanosphere structure.
The invention also provides modified cellulose nanocrystals prepared by the preparation method according to any one of the schemes.
Preferably, the modified cellulose nanocrystalline is a petal-shaped nano lamellar structure.
The invention also provides the use of modified cellulose nanocrystals according to any one of the above schemes as flame retardants.
Compared with the prior art, the invention has the beneficial effects that:
the invention uses melamine as a gas source, and generates a large amount of nonflammable nitrogen-containing gas NH in the combustion process 3 、N 2 And NO 2 And the combustible volatile is diluted; the phytic acid is used as an acid source, and phosphoric acid substances generated by heating and dehydrating the phytic acid promote the dehydration of the high polymer into carbon; the cellulose nanocrystalline is used as a carbon source, and under the synergistic effect of the cellulose nanocrystalline, melamine and phytic acid, a compact carbon layer is formed, so that the carbon layer can not only prevent external heat and oxygen from entering the material to play a barrier role, but also effectively inhibit the release of heat and smoke.
The modified cellulose nanocrystal prepared by the invention is a novel flame retardant integrating a carbon source, an air source and an acid source, has high thermal stability, excellent flame retardant property, simple preparation process, environment friendliness and low cost, and has wide application prospects in the fields of nano-composite and reinforcing materials, biomedicine, textiles and the like.
Drawings
FIG. 1 is a scanning electron microscope image of a cellulose nanocrystal of example 1 of the present invention;
FIG. 2 is a scanning electron microscope image of modified cellulose nanocrystals of example 1 of the present invention;
FIG. 3 is an infrared spectrum of the cellulose nanocrystals and modified cellulose nanocrystals of example 1 of the present invention;
FIG. 4 is a thermogravimetric plot of modified cellulose nanocrystals of example 1, modified cellulose nanocrystals of comparative examples 1-4, and cellulose nanocrystal CNC of the present invention.
Detailed Description
The technical scheme of the invention is further explained by the following specific examples.
Example 1:
the preparation method of the modified cellulose nanocrystalline in the embodiment comprises the following steps:
(1) Dispersing 2 parts of microcrystalline cellulose in 100 parts of 0.5M sodium periodate aqueous solution, then reacting for 90min at 60 ℃, cooling to room temperature after the reaction is finished, washing and drying to obtain cellulose nanocrystalline containing aldehyde groups;
(2) Dispersing 1 part of cellulose nanocrystalline in deionized water, then adding 1 part of melamine aqueous solution (the solid-liquid mass ratio of melamine to water is 1:20), reacting for 10min at 80 ℃, then adding 2 parts of phytic acid aqueous solution (the mass fraction of phytic acid is 70%), reacting for 30min at 80 ℃, cooling to room temperature after the reaction is finished, centrifugally separating, washing and drying to obtain modified cellulose nanocrystalline CNC@MEL@PA.
As shown in FIG. 1, the cellulose nanocrystalline containing aldehyde groups is of a nanosphere structure, and the modified cellulose nanocrystalline CNC@MEL@PA presents a petal-shaped nano lamellar structure due to the fact that a nano layer is generated under the action of p-p accumulation and hydrogen bonds.
As shown in FIG. 2, the cellulose nanocrystalline is 1500-2000cm -1 Carbon-oxygen double bonds (c=o) occur; subsequent Schiff base reaction with amino group of melamine at 1500cm -1 The new peak appears at the left and right is vibration of triazine ring structure after grafting, 1080cm -1 And 1190cm -1 The left and right represent P-O and p=o, respectively, indicating success of the grafting modification.
Example 2:
the preparation method of the modified cellulose nanocrystalline in the embodiment comprises the following steps:
(1) Dispersing 2 parts of microcrystalline cellulose in 100 parts of 0.5M sodium periodate aqueous solution, then reacting for 90min at 60 ℃, cooling to room temperature after the reaction is finished, washing and drying to obtain cellulose nanocrystalline containing aldehyde groups;
(2) Dispersing 1 part of cellulose nanocrystalline in deionized water, then adding 1 part of melamine aqueous solution (the solid-liquid mass ratio of melamine to water is 1:20), reacting for 10min at 80 ℃, then adding 1 part of phytic acid aqueous solution (the mass fraction of phytic acid is 70%), reacting for 30min at 80 ℃, cooling to room temperature after the reaction is finished, centrifugally separating, washing and drying to obtain modified cellulose nanocrystalline CNC@MEL@PA.
Example 3:
the preparation method of the modified cellulose nanocrystalline in the embodiment comprises the following steps:
(1) Dispersing 2 parts of microcrystalline cellulose in 100 parts of 0.5M sodium periodate aqueous solution, then reacting for 90min at 60 ℃, cooling to room temperature after the reaction is finished, washing and drying to obtain cellulose nanocrystalline containing aldehyde groups;
(2) Dispersing 1 part of cellulose nanocrystalline in deionized water, then adding 1 part of melamine aqueous solution (the solid-liquid mass ratio of melamine to water is 1:20), reacting for 10min at 80 ℃, then adding 3 parts of phytic acid aqueous solution (the mass fraction of phytic acid is 70%), reacting for 30min at 80 ℃, cooling to room temperature after the reaction is finished, centrifugally separating, washing and drying to obtain modified cellulose nanocrystalline CNC@MEL@PA.
Comparative example 1:
the preparation method of the modified cellulose nanocrystals of this comparative example is different from that of example 1 in that: no phytic acid modification was performed.
Specifically, the preparation method of the modified cellulose nanocrystalline of the comparative example comprises the following steps:
(1) Dispersing 2 parts of microcrystalline cellulose in 100 parts of 0.5M sodium periodate aqueous solution, then reacting for 90min at 60 ℃, cooling to room temperature after the reaction is finished, washing and drying to obtain cellulose nanocrystalline containing aldehyde groups;
(2) Dispersing 1 part of cellulose nanocrystalline in deionized water, then adding 1 part of melamine aqueous solution (the solid-liquid mass ratio of melamine to water is 1:20), reacting for 10min at 80 ℃, cooling to room temperature after the reaction is finished, centrifuging, washing and drying to obtain CNC@MEL.
Comparative example 2:
the preparation method of the modified microcrystalline cellulose of the comparative example comprises the following steps:
dispersing 1 part of microcrystalline cellulose (MCC) in deionized water, adding 1 part of melamine aqueous solution (the solid-liquid mass ratio of melamine to water is 1:20), reacting at 80 ℃ for 10min, adding 2 parts of phytic acid aqueous solution (the mass fraction of phytic acid is 70%), reacting at 80 ℃ for 30min, cooling to room temperature after the reaction is finished, centrifuging, washing, and drying to obtain the modified microcrystalline cellulose MCC@MEL@PA.
Comparative example 3:
the preparation method of the flame retardant of the comparative example comprises the following steps:
(1) Dissolving chitosan powder in acetic acid water solution to prepare CS solution; diluting 1 part of nano cellulose dispersion liquid with water to obtain CNF dispersion liquid; then, after uniformly mixing and stirring CS solution and CNF dispersion liquid according to the mass ratio of (1:3), freezing unmodified CNF aqueous suspension liquid at the temperature of minus 20 ℃, and then freezing for 3 days at the temperature of minus 50 ℃;
(2) 1 part of Melamine (MEL) is dissolved in deionized water at 80 ℃ (the solid-liquid mass ratio of melamine to water is 1:20) until the melamine is completely dissolved; then adding CNF aerogel into MEL solution, gradually adding Phytic Acid (PA) (1/6 mole MEL) into the solution within 25min, reacting for 30min at 80 ℃, cooling to room temperature after the reaction is finished, centrifuging, washing and drying to obtain CNF@MEL@PA.
Comparative example 4:
the preparation method of the modified microcrystalline cellulose of this comparative example is different from that of example 1 in that: the addition sequence of the melamine and the phytic acid is opposite, namely, firstly adding the phytic acid for reaction, and then adding the melamine for reaction;
the other steps are the same as in example 1.
The thermal stability performance of the product was evaluated using a thermogravimetric analyzer (TG 209F 1, netzsch), and the thermal weights of the Cellulose Nanocrystals (CNC), example 1, and comparative examples 1-4 are shown in fig. 4. Comparative example 1 compared to CNC, T max Increasing the char residue from 29.4% to 34.9% at 600 ℃ from 208.8 ℃ to 225.8 ℃ suggests that melamine acts as a source of intumescent flame retardant, and the release of inert gas (ammonia) produced may promote the formation of an expanded char layer. Example 1 compared to CNC, T max The maximum mass loss rate of the CNC@MEL@PA is reduced by increasing the carbon residue amount at 600 ℃ from 29.4% to 44.9% from 208.8 ℃ to 440 ℃, because the mass transfer speed is slowed down by the carbon layer, the thermal resistance of the CNC@MEL@PA is greatly improved, and further degradation of the matrix is prevented. Example 1 compared to comparative example 4, the thermal stability and limiting oxygen index ratio of example 1 were compared, although the materials were the same, except that the order of addition of melamine and phytic acid was differentExample 4 is high, because melamine is added first, the amino group of melamine can react with the aldehyde group of cellulose nanocrystalline to generate Schiff base reaction, and after the full reaction is finished, phytic acid is added, and the phosphate group of phytic acid can further interact with the amino group of melamine; if phytic acid is added first, then melamine is added, thus melamine reacts with the phytic acid and aldehyde groups of cellulose nanocrystals simultaneously, and the load of MEL@PA on CNC is reduced; while an increase in mel@pa loading favors the formation of carbon residues, the results indicate: the modified cellulose nanocrystals of example 1 had more excellent thermal stability.
The flame retardant properties of the above samples were evaluated as shown in table 1.
Table 1 LOI index of each sample
| Sample of | LOI index (%) |
| CNC | 28.9 |
| Example 1 | 36.6 |
| Comparative example 1 | 31.2 |
| Comparative example 2 | 30.6 |
| Comparative example 3 | 32.3 |
| Comparative example 4 | 33.9 |
As can be seen from table 1, the modified cellulose nanocrystals of example 1 have excellent flame retardant properties, and can be used as flame retardants in nanocomposite and reinforcement materials, biomedical, textile and other fields.
In the above embodiment and the alternatives thereof, in the preparation process of the cellulose nanocrystalline, the solid-liquid mass ratio of the microcrystalline cellulose to the aqueous solution of sodium periodate may be 1: 90. 1: 95. 1: 105. 1:110, etc., the concentration of the aqueous sodium periodate solution may be 0.6M, 0.7M, 0.8M, 0.9M, 1.0M, etc., the reaction temperature may be 65℃and 70℃and 75℃and 80℃and the reaction time may be 70min, 75min, 80min, 85min, etc.
In the above embodiment and its alternatives, the solid-liquid mass ratio of melamine to water in the aqueous melamine solution may be 1.2: 20. 1.5: 20. 1.7: 20. 2:20, etc.
In the above embodiment and its alternative, after adding the aqueous melamine solution, the reaction temperature may be 60 ℃, 65 ℃, 70 ℃, 75 ℃, and the like, and the reaction time may be 12min, 15min, 20min, 25min, 30min, and the like.
In the above embodiments and alternatives, the mass fraction of the phytic acid in the phytic acid aqueous solution may also be 60%, 62%, 65%, 68%, 70%, etc.
In the above embodiment and its alternative, the reaction temperature may be 60 ℃, 65 ℃, 70 ℃, 75 ℃ and the like, and the reaction time may be 10min, 12min, 15min, 20min, 25min, 28min and the like after the addition of the phytic acid aqueous solution.
In the above embodiments and alternatives thereof, the mass part ratio of the cellulose nanocrystals, the aqueous melamine solution, and the aqueous phytic acid solution may be 1:3: 1. 1:2: 2. 1:2: 3. 1:3:3, etc.
In view of the numerous embodiments of the present invention, the experimental data of each embodiment is huge and is not suitable for the one-by-one listing and explanation here, but the content of the verification needed by each embodiment and the obtained final conclusion are close.
The foregoing is only illustrative of the preferred embodiments and principles of the present invention, and changes in specific embodiments will occur to those skilled in the art upon consideration of the teachings provided herein, and such changes are intended to be included within the scope of the invention as defined by the claims.
Claims (5)
1. The preparation method of the modified cellulose nanocrystalline is characterized by comprising the following steps:
(1) Dispersing microcrystalline cellulose in a sodium periodate aqueous solution, then reacting at 60-80 ℃ for 70-90min, cooling to room temperature after the reaction is finished, washing and drying to obtain cellulose nanocrystals;
(2) Dispersing cellulose nanocrystalline in water, then adding melamine aqueous solution, reacting for 10-30min at 60-80 ℃, then adding phytic acid aqueous solution, reacting for 10-30min at 60-80 ℃, cooling to room temperature after the reaction is finished, washing, and drying to obtain modified cellulose nanocrystalline;
in the step (1), the solid-liquid mass ratio of the microcrystalline cellulose to the sodium periodate aqueous solution is 1: (90-110);
the concentration of the sodium periodate aqueous solution is 0.5-1M;
in the step (2), the solid-liquid mass ratio of melamine to water in the melamine aqueous solution is (1-2): 20, a step of;
in the step (2), the mass fraction of the phytic acid in the phytic acid aqueous solution is 60-70%;
in the step (2), the mass part ratio of the cellulose nanocrystalline, the melamine aqueous solution and the phytic acid aqueous solution is 1: (1-3): (1-3).
2. The method of claim 1, wherein the cellulose nanocrystals are nanosphere structures.
3. Modified cellulose nanocrystals produced by the production process according to any one of claims 1 to 2.
4. The modified cellulose nanocrystal of claim 3, wherein the modified cellulose nanocrystal is a petal-shaped nanolayered structure.
5. Use of modified cellulose nanocrystals according to claim 3 or 4 as flame retardant.
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