A method for preparing high-strength flame-retardant cellulose film

Abstract

The present invention relates to a method for preparing a high-strength flame-retardant cellulose film, comprising the following steps: (1) mixing a sodium lignin sulfonate aqueous solution and a polyamide epichlorohydrin crosslinker aqueous solution at a volume ratio of 1:1 to 1.5 to form a mixed solution A; (2) adding a cellulose aqueous dispersion and an ammonium polyphosphate aqueous solution with a polymerization degree of less than 20 to the mixed solution A of step (1), and stirring the mixed solution B sufficiently; (3) filtering the mixed solution B obtained in step (2) to form a film, and heating and drying the mixed solution to obtain a high-strength flame-retardant cellulose film. The preparation method of the present invention does not use an organic solvent, is green and environmentally friendly, and the obtained high-strength flame-retardant cellulose film not only has good flame retardant properties, but also has significantly improved mechanical properties, and has good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of cellulose membranes and relates to a method for preparing a high-strength flame-retardant cellulose membrane. Background Art

[0002] Cellulose membranes have been widely used in fields such as paper and diaphragms due to their green, environmentally friendly and biodegradable properties. However, the poor mechanical properties and easy flammability of pure cellulose membranes have hindered the application and development of cellulose. To improve the strength of cellulose, existing research mostly uses methods of compounding with nanoparticles, nanofibers, microfibers, and pretreating cellulose using the TEMPO method to improve the mechanical strength of cellulose membranes. In addition, using lignin and its derivatives to mimic the composition of trees to improve strength is also a common method. However, there is an electrostatic repulsion between lignin and cellulose, which is not conducive to the solution mixing of the two. To solve this electrostatic repulsion problem, some research has introduced PEI, which can form electrostatic attraction with cellulose and lignin, as a cross-linking agent, which can well solve the dispersion problem of the mixed solution and improve the mechanical strength of cellulose membranes. Similarly, to improve the flame-retardant properties of cellulose membranes, most are by adding organic and inorganic flame retardants. Ammonium polyphosphate (APP) is a commonly used phosphorus-based flame retardant. However, most existing research uses high-polymerization-degree APP, which is insoluble in water, while cellulose is mostly in an aqueous dispersion. Therefore, there is also a problem of uneven dispersion in the mixing of high-polymerization-degree APP and cellulose. At the same time, existing research on improving the mechanical and flame-retardant properties of cellulose membranes mostly studies them separately, and adds various functional substances to achieve performance improvement.

[0003] Therefore, there is an urgent need to develop a method in which the components added during the preparation process can be well mixed with the cellulose solution and can simultaneously improve the mechanical properties and flame-retardant properties of cellulose membranes. Summary of the Invention

[0004] The object of the present invention is to solve the above problems existing in the prior art and provide a method for preparing a high-strength flame-retardant cellulose membrane.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a high-strength flame-retardant cellulose membrane, comprising the following steps:

[0007] (1) Mix an aqueous solution of sodium lignosulfonate and an aqueous solution of a cross-linking agent to form a mixed solution A;

[0008] (2) Add a cellulose aqueous dispersion and an aqueous solution of ammonium polyphosphate to the mixed solution A in step (1), and stir well to obtain a mixed solution B;

[0009] (3) Filter the mixed solution B obtained in step (2) to form a film, and heat and dry it (covalent cross-linking will occur between sodium lignosulfonate-polyamide epichlorohydrin and cellulose during the heating and drying process) to obtain a high-strength flame-retardant cellulose film;

[0010] In step (1), the cross-linking agent is polyamide epichlorohydrin (selecting polyamide epichlorohydrin cross-linking agent not only makes the mixed solution A electropositive, but also covalently cross-links with cellulose to increase the mechanical strength of the composite film). The volume ratio of the sodium lignosulfonate aqueous solution to the cross-linking agent aqueous solution is 1:1 to 1.5. Within this range, the mixed solution A is electropositive. If the amount of sodium lignosulfonate is too large, the solution will be electronegative. If it is electronegative, it will repel the negatively charged cellulose dispersion, and they cannot be tightly combined;

[0011] In step (2), the ammonium polyphosphate belongs to oligomeric ammonium polyphosphate with a degree of polymerization < 20; oligomeric ammonium polyphosphate with a degree of polymerization < 20 is extremely soluble in water, with a solubility > 90 g in 100 ml of water. Medium ammonium polyphosphate with a degree of polymerization of 30 - 50 has a solubility < 4 g in 100 ml of water, and higher ammonium polyphosphate with a larger degree of polymerization is insoluble in water. Although higher ammonium polyphosphate is insoluble in water, it has better thermal stability. Therefore, when only aiming to achieve the flame-retardant function, higher ammonium polyphosphate is more often selected as the flame-retardant additive. In existing flame-retardant technologies, most use ammonium polyphosphate with a degree of polymerization greater than 1000 because if oligomeric ammonium polyphosphate is used as the flame retardant, the washing fastness will be very poor. And cellulose is usually in the form of an aqueous dispersion. Selecting oligomeric ammonium polyphosphate with good water solubility can better achieve the mixing with cellulose. In addition, oligomeric ammonium polyphosphate can quickly melt at a lower temperature and penetrate into the surface of the cellulose material, hindering the contact between the fiber and air. Therefore, the flame-retardant sensitivity of oligomeric ammonium polyphosphate is higher. At the same time, due to the existence of chemical bonding in the high-strength flame-retardant cellulose film of the present invention, the washing fastness of the cellulose film is relatively good;

[0012] In step (2), the Zeta potential of the mixed solution B < -30 and there is no precipitation, indicating that the components in the mixed solution are evenly mixed.

[0013] As a preferred technical solution:

[0014] For the preparation method of a high-strength flame-retardant cellulose film as described above, in step (1), the mass fraction of the sodium lignosulfonate aqueous solution is 0.8 - 1%, and the mass fraction of the cross-linking agent aqueous solution is 1 - 1.3%.

[0015] For the preparation method of a high-strength flame-retardant cellulose film as described above, in step (2), the mass fraction of the cellulose aqueous dispersion is 7 - 10%, and the mass fraction of the ammonium polyphosphate aqueous solution is 1 - 5%.

[0016] A preparation method of a high-strength flame-retardant cellulose film as described above. In step (2), the volume ratio of the cellulose aqueous dispersion, the ammonium polyphosphate aqueous solution, and the mixed solution A is 50-80:7-45:7-45; since cellulose is the base material, it needs to account for the largest proportion. If there is too much cellulose and too little of other components, the improvement of strength and flame-retardant performance is not obvious; when there is too little cellulose, film formation cannot occur, when there is too little ammonium polyphosphate, the flame retardancy decreases, and when there is too little mixed solution, the improvement of mechanical properties is low.

[0017] A preparation method of a high-strength flame-retardant cellulose film as described above. The specific process of step (3) is: suction-filter the mixed solution B to form a composite film, and after taking out the composite film, heat it at a certain temperature for a certain time to obtain the high-strength flame-retardant cellulose film (suction-filtering the solution to form a composite film is a prior art, and process parameters such as the suction-filtering amount and time can be adjusted according to the size of the suction-filtering device and the formed thickness).

[0018] A preparation method of a high-strength flame-retardant cellulose film as described above. The certain temperature is 130-150 °C, and the certain time is 30-60 min. Compared with the prior art, the drying temperature of the present invention is increased by 20-40 °C, and the time is extended by 15-30 min, aiming to ensure the complete cross-linking of the cross-linking agent and cellulose and improve the performance of the high-strength flame-retardant cellulose film.

[0019] A preparation method of a high-strength flame-retardant cellulose film as described above. The tensile fracture strength of the high-strength flame-retardant cellulose film is 50-70 MPa, the elongation at break is 6-10%, and the heat release rate is 70-100 KW / m 2 ,and the total combustion release is 20-30 MJ / m 2 (In the prior art, the tensile fracture strength of the cellulose film is 20-30 MPa, the elongation at break is 2-4%, the heat release rate is 130-150 KW / m 2 ,and the total combustion release is 60-80 MJ / m 2 ); the limiting oxygen index of the high-strength flame-retardant cellulose film is 30-37%.

[0020] A preparation method of a high-strength flame-retardant cellulose film as described above. After ultrasonic oscillation water washing for 2 h and drying, the retention rate of the tensile fracture strength of the high-strength flame-retardant cellulose film is not less than 96.5%.

[0021] In the prior art, it is prepared by compounding three substances, namely cellulose, sodium lignosulfonate, and polyamide epichlorohydrin. The addition of polyamide epichlorohydrin is to solve the electrostatic repulsion between cellulose and sodium lignosulfonate and improve the mechanical strength, but it does not have a flame retardant function. In the present invention, ammonium polyphosphate oligomer is selected and added to these three substances. The addition of ammonium polyphosphate oligomer not only endows the cellulose membrane with a flame retardant function, but also can greatly improve the mechanical strength of the composite membrane of the original three substances. That is, there are electrostatic attractions, covalent bond crosslinking, hydrogen bonds and other interactions among the original three substances. When ammonium polyphosphate oligomer is added, it will not only not destroy the original interactions, but also the mixed dispersion liquid is more stable (the Zeta potential value is larger), and ammonium polyphosphate oligomer also has electrostatic attraction and hydrogen bonds with these three substances, making the mechanical strength further significantly improved.

[0022] The principle of the present invention is as follows:

[0023] Cellulose has a large number of polar groups such as hydroxyl and carboxyl groups, and its aqueous solution is electronegative; sodium lignosulfonate contains many negatively charged groups (such as phenolic hydroxyl, alcoholic hydroxyl, sulfonic acid group, etc.), and its aqueous solution is electronegative; the crosslinking agent polyamide epichlorohydrin has an amino group, and the N atom of the amino group has a pair of lone pair electrons, which can combine with H + ionized by water to form a positively charged species, and its aqueous solution is electropositive; the aqueous solution of water-soluble ammonium polyphosphate oligomer is electronegative.

[0024] In the present invention, the aqueous solution of sodium lignosulfonate is first mixed with the aqueous solution of the crosslinking agent to form a mixed solution A. When the volume ratio of the aqueous solution of sodium lignosulfonate to the aqueous solution of the crosslinking agent is 1:1 to 1.5, the mixed solution A is electropositive; then the aqueous solution of cellulose and the aqueous solution of ammonium polyphosphate are added to the mixed solution A for mixing, and the whole solution shows a dispersed and stable state (the reason why the whole solution shows a highly dispersed and stable state is that, firstly, each component is an aqueous solution and is convenient for mixing, and secondly, there is an electrostatic attraction among the components in the solution instead of repulsion, which can make the components dispersed and stable in the solution. The dispersion stability is judged by observing no precipitation and no layering phenomena, and secondly, according to the absolute value of the Zeta potential. If it is greater than 30, it indicates a stable dispersion system).

[0025] In addition to the electrostatic attraction between sodium lignosulfonate-polyamide epichlorohydrin and cellulose, and between sodium lignosulfonate-polyamide epichlorohydrin and ammonium polyphosphate, there are also covalent bond (ester bond) crosslinking and hydrogen bond interactions between sodium lignosulfonate-polyamide epichlorohydrin and cellulose; there is also a hydrogen bond interaction between sodium lignosulfonate-polyamide epichlorohydrin and ammonium polyphosphate; there is also a hydrogen bond interaction between cellulose and ammonium polyphosphate (it can be determined whether it is electrostatic attraction or electrostatic repulsion based on the positive and negative charges measured by Zeta potential, the covalent bond is obtained by infrared testing, and the hydrogen bond is obtained based on the presence of polar functional groups such as hydroxyl and amino groups on each substance). Sodium lignosulfonate-polyamide epichlorohydrin, cellulose and ammonium polyphosphate form a three-dimensional crosslinked structure, interact with each other, achieve synergistic enhancement, and have a flame retardant function.

[0026] Beneficial effects:

[0027] (1) The method for preparing a high-strength flame-retardant cellulose film of the present invention, involving methods such as aqueous solution mixing, suction filtration, heating and drying, etc., is simple and easy to operate, without organic solvents, and is green and environmentally friendly;

[0028] (2) The high-strength flame-retardant cellulose film prepared by the method of the present invention not only has good flame retardant properties, but also has significantly improved mechanical properties and has good application prospects. Description of the drawings

[0029] Figure 1 It is a schematic diagram of the interaction of each component;

[0030] Figure 2 It is the Zeta potential of each solution in Example 8 of the present invention;

[0031] Figure 3 It is the infrared spectra of a pure cellulose film, a composite film without ammonium polyphosphate prepared from a mixed solution without ammonium polyphosphate, the high-strength flame-retardant cellulose film prepared in Example 8 of the present invention, and ammonium polyphosphate oligomer particles. Specific embodiments

[0032] The following further elaborates the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0033] The sources of the substances used in the present invention are as follows:

[0034] (1) Sodium lignosulfonate: sourced from Shanghai Macklin Biochemical Co., Ltd., CAS No. 8061-51-6;

[0035] (2) Aqueous solution of polyamide epichlorohydrin: sourced from Jinhua Sheng Paper Co., Ltd., with a pH value of 3.0 - 6.0 and a viscosity of 30 - 120 mPa·s;

[0036] (3) Cellulose: sourced from Guilin Qihong Technology Co., Ltd.;

[0037] (4) Ammonium polyphosphate: sourced from Shanghai Macklin Biochemical Co., Ltd., with a CAS number of 68333 - 79 - 9, and its infrared spectrum is as Figure 3 shown.

[0038] The present invention adopts the following test methods:

[0039] (1) Zeta potential: The Zeta potential of the solution is measured using a Zeta potential analyzer from MarvernPanalytical;

[0040] (2) Tensile fracture strength: The composite film is cut into rectangular strips of 4 cm × 1 cm, and both ends are clamped on an Instron universal tensile testing machine to measure the tensile fracture strength at a rate of 20 mm / min;

[0041] (3) Elongation at break: The composite film is cut into rectangular strips of 4 cm × 1 cm, and both ends are clamped on an Instron universal tensile testing machine to measure the elongation at break at a rate of 20 mm / min;

[0042] (4) Heat release rate: Using an FTT0001 micro calorimeter from FTT Company in the UK, weigh 5 - 10 mg of the sample in a crucible, and measure it with the micro calorimeter. Heat it in a mixed atmosphere (80% nitrogen, 20% oxygen) at a heating rate of 1℃ / s to measure the heat release rate;

[0043] (5) Total combustion release: Using an FTT0001 micro calorimeter from FTT Company in the UK, weigh 5 - 10 mg of the sample in a crucible, and measure it with the micro calorimeter. Heat it in a mixed atmosphere (80% nitrogen, 20% oxygen) at a heating rate of 1℃ / s to measure the total combustion release.

[0044] (6) Limiting oxygen index: Cut the composite film into samples of 100 mm × 10 mm, vertically fix the sample in a glass combustion tube, connect its base to a device that can generate a nitrogen - oxygen mixed gas stream, ignite the top of the sample, and the oxygen concentration in the mixed gas stream will continuously decrease until the flame goes out;

[0045] (7) Tensile fracture strength retention rate: After ultrasonic cleaning and drying the high - strength flame - retardant cellulose film in an ultrasonic oscillator for 2 h, measure the tensile fracture strength retention rate. The ultrasonic frequency is 40 KHz, and the drying temperature is 30℃.

[0046] The pure cellulose membrane involved in the present invention is prepared by fully stirring a cellulose aqueous dispersion, followed by suction filtration to form a membrane and heating and drying. The infrared spectrum of the prepared pure cellulose membrane is as Figure 3 shown.

[0047] Example 1

[0048] A preparation method of a high-strength flame-retardant cellulose membrane is as Figure 1 shown, and it includes the following steps:

[0049] (1) Mix an aqueous solution of sodium lignosulfonate with a mass fraction of 0.8% and an aqueous solution of polyamide epichlorohydrin with a mass fraction of 1.3% to form a mixed solution A;

[0050] Among them, the volume ratio of the aqueous solution of sodium lignosulfonate to the aqueous solution of polyamide epichlorohydrin is 1:1;

[0051] (2) Add an aqueous dispersion of bacterial cellulose with a mass fraction of 10% and an aqueous solution of ammonium polyphosphate (degree of polymerization < 20) with a mass fraction of 1% to the mixed solution A in step (1), and fully stir to obtain a mixed solution B with a Zeta potential of -33, and no precipitation occurs;

[0052] Among them, the volume ratio of the cellulose aqueous dispersion, the aqueous solution of ammonium polyphosphate, and the mixed solution A is 50:15:7;

[0053] (3) Filter the mixed solution B obtained in step (2) to form a composite membrane. After taking out the composite membrane, heat and dry it at 150 °C for 60 min to obtain a high-strength flame-retardant cellulose membrane with a thickness of 27 μm;

[0054] The tensile fracture strength of the prepared high-strength flame-retardant cellulose membrane is 58 MPa, the elongation at break is 7.8%, the retention rate of the tensile fracture strength after ultrasonic oscillation washing with water for 2 h and drying is 96.5%, the heat release rate is 96 KW / m 2 , the total combustion release is 29 MJ / m 2 , and the limiting oxygen index is 32%.

[0055] Comparative Example 1

[0056] A preparation method of a composite membrane without ammonium polyphosphate is basically the same as that of Example 1, except that the aqueous solution of ammonium polyphosphate is not added in step (2);

[0057] The Zeta potential of the mixed solution B obtained after full stirring in step (2) is -35, and no precipitation occurs;

[0058] The tensile fracture strength of the prepared composite film without ammonium polyphosphate is 36 MPa, the elongation at break is 2.7%, the retention rate of the tensile fracture strength after ultrasonic oscillation washing for 2 h and drying is 99%, and the heat release rate is 133 KW / m 2 , and the total combustion release is 64 MJ / m 2 , the limiting oxygen index is 19%, and the infrared spectrum of the prepared composite film without ammonium polyphosphate is as Figure 3 shown.

[0059] Comparing Comparative Example 1 with Example 1, it can be found that the tensile fracture strength and elongation at break of Comparative Example 1 are lower than those of Example 1, and the heat release rate and total combustion release are higher than those of Example 1. This is because no aqueous solution of oligomeric ammonium polyphosphate is added, and only sodium lignosulfonate itself and intermolecular covalent crosslinking enhance the strength of the film in the film, and no flame retardant is added, resulting in an increase in the heat release rate and total combustion heat release of the film combustion.

[0060] Comparative Example 2

[0061] A preparation method of a composite film is basically the same as that of Example 1, except that the oligomeric ammonium polyphosphate in step (2) is replaced with medium ammonium polyphosphate (the degree of polymerization is 30 < n < 50);

[0062] The Zeta potential of the mixed solution B obtained after sufficient stirring in step (2) is -22, and no precipitation occurs;

[0063] The tensile fracture strength of the prepared composite film is 21 MPa, the elongation at break is 2.2%, the retention rate of the tensile fracture strength after ultrasonic oscillation washing for 2 h and drying is 97%, and the heat release rate is 63 KW / m 2 , and the total combustion release is 18 MJ / m 2 , and the limiting oxygen index is 35%.

[0064] Comparing Comparative Example 2 with Example 1, it can be found that the tensile fracture strength and elongation at break of Comparative Example 2 are significantly lower than those of Example 1. This is because after adding medium ammonium polyphosphate, the mixed solution is not stable, and when forming the film, medium ammonium polyphosphate cannot be well fused with cellulose to produce an effective effect, but instead blocks the effective interaction between other components, resulting in a decrease in the mechanical properties of the composite film.

[0065] Comparative Example 3

[0066] A preparation method of a composite film, the specific steps are basically the same as those of Example 1, except that the oligomeric ammonium polyphosphate in step (2) is replaced with high ammonium polyphosphate (the degree of polymerization > 1500);

[0067] The Zeta potential of the mixed solution B obtained after sufficient stirring in step (2) is 26, and no precipitation occurs;

[0068] The tensile breaking strength of the obtained composite film is 28 MPa, the elongation at break is 3.5%, the retention rate of the tensile breaking strength after ultrasonic oscillation washing with water for 2 h and drying is 96%, and the heat release rate is 61 KW / m 2 , and the total combustion release is 17 MJ / m 2 , and the limiting oxygen index is 36%.

[0069] Comparing Comparative Example 3 with Example 1, it can be found that the tensile breaking strength and elongation at break of Comparative Example 3 are significantly lower than those of Example 1. This is because after adding ammonium polyphosphate, the mixed solution is not stable, and when the film is formed, ammonium polyphosphate cannot be well fused with cellulose to produce an effective effect, but instead blocks the effective interaction between other components, resulting in a decrease in the mechanical properties of the composite film.

[0070] Example 2

[0071] A preparation method of a high-strength flame-retardant cellulose film, as Figure 1 shown, includes the following steps:

[0072] (1) Mix an aqueous solution of sodium lignosulfonate with a mass fraction of 0.8% and an aqueous solution of polyamide epichlorohydrin with a mass fraction of 1.3% to form a mixed solution A;

[0073] Among them, the volume ratio of the aqueous solution of sodium lignosulfonate to the aqueous solution of polyamide epichlorohydrin is 1:1.5;

[0074] (2) Add an aqueous carboxylated nanocellulose dispersion with a mass fraction of 7% and an aqueous solution of ammonium oligophosphate (degree of polymerization < 20) with a mass fraction of 5% to the mixed solution A in step (1), and stir well to obtain a mixed solution B with a Zeta potential of -31 and no precipitation;

[0075] Among them, the volume ratio of the cellulose aqueous dispersion, the ammonium oligophosphate aqueous solution and the mixed solution A is 80:45:35;

[0076] (3) Filter the mixed solution B obtained in step (2) to form a composite film. After taking out the composite film, heat and dry it at 130 °C for 30 min to obtain a high-strength flame-retardant cellulose film with a thickness of 32 μm;

[0077] The tensile breaking strength of the obtained high-strength flame-retardant cellulose film is 51 MPa, the elongation at break is 6.2%, the retention rate of the tensile breaking strength after ultrasonic oscillation washing with water for 2 h and drying is 97%, and the heat release rate is 91 KW / m 2 , and the total combustion release is 27 MJ / m 2 , and the limiting oxygen index is 36%.

[0078] Example 3

[0079] A preparation method of a high-strength flame-retardant cellulose film is as follows Figure 1 shown, and it includes the following steps:

[0080] (1) Mix an aqueous solution of sodium lignosulfonate with a mass fraction of 0.9% and an aqueous solution of polyamide epichlorohydrin with a mass fraction of 1.1% to form a mixed solution A;

[0081] Among them, the volume ratio of the aqueous solution of sodium lignosulfonate to the aqueous solution of polyamide epichlorohydrin is 1:1.1;

[0082] (2) Add an aqueous dispersion of microfibrillated cellulose with a mass fraction of 8% and an aqueous solution of ammonium oligophosphate (degree of polymerization < 20) with a mass fraction of 2% to the mixed solution A in step (1), and stir well to obtain a mixed solution B with a Zeta potential of -42 and no precipitation;

[0083] Among them, the volume ratio of the cellulose aqueous dispersion, the ammonium oligophosphate aqueous solution and the mixed solution A is 65:26:26;

[0084] (3) Filter the mixed solution B obtained in step (2) to form a composite film. After taking out the composite film, heat and dry it at 140 °C for 45 min to obtain a high-strength flame-retardant cellulose film with a thickness of 29 μm;

[0085] The tensile fracture strength of the obtained high-strength flame-retardant cellulose film is 53 MPa, the elongation at break is 6.4%, the retention rate of the tensile fracture strength after ultrasonic oscillation washing with water for 2 h and drying is 100%, and the heat release rate is 85 KW / m 2 and the total combustion release is 26 MJ / m 2 , and the limiting oxygen index is 34%.

[0086] Example 4

[0087] A preparation method of a high-strength flame-retardant cellulose film is as follows Figure 1 shown, and it includes the following steps:

[0088] (1) Mix an aqueous solution of sodium lignosulfonate with a mass fraction of 0.9% and an aqueous solution of polyamide epichlorohydrin with a mass fraction of 1.2% to form a mixed solution A;

[0089] Among them, the volume ratio of the aqueous solution of sodium lignosulfonate to the aqueous solution of polyamide epichlorohydrin is 1:1.2;

[0090] (2) Add an aqueous dispersion of hydroxyethyl cellulose with a mass fraction of 8% and an aqueous solution of ammonium polyphosphate (degree of polymerization < 20) with a mass fraction of 2% to the mixed solution A in step (1), and stir well to obtain a mixed solution B with a Zeta potential of -46 and no precipitation;

[0091] Among them, the volume ratio of the cellulose aqueous dispersion, the ammonium polyphosphate aqueous solution, and the mixed solution A is 60:20:30;

[0092] (3) Filter the mixed solution B obtained in step (2) to form a composite membrane. After taking out the composite membrane, heat and dry it at 140 °C for 45 min to obtain a high-strength flame-retardant cellulose membrane with a thickness of 36 μm;

[0093] The tensile fracture strength of the obtained high-strength flame-retardant cellulose membrane is 61 MPa, the elongation at break is 6.8%, the retention rate of the tensile fracture strength after ultrasonic oscillation washing with water for 2 h and drying is 98.3%, and the heat release rate is 73 KW / m 2 , and the total combustion release is 23 MJ / m 2 , and the limiting oxygen index is 33%.

[0094] Example 5

[0095] A preparation method of a high-strength flame-retardant cellulose membrane, as Figure 1 shown, includes the following steps:

[0096] (1) Mix an aqueous solution of sodium lignosulfonate with a mass fraction of 0.9% and an aqueous solution of polyamide epichlorohydrin with a mass fraction of 1.2% to form a mixed solution A;

[0097] Among them, the volume ratio of the sodium lignosulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution is 1:1.2;

[0098] (2) Add an aqueous dispersion of bacterial cellulose with a mass fraction of 8% and an aqueous solution of ammonium polyphosphate (degree of polymerization < 20) with a mass fraction of 3% to the mixed solution A in step (1), and stir well to obtain a mixed solution B with a Zeta potential of -49 and no precipitation;

[0099] Among them, the volume ratio of the cellulose aqueous dispersion, the ammonium polyphosphate aqueous solution, and the mixed solution A is 70:30:20;

[0100] (3) Filter the mixed solution B obtained in step (2) to form a composite membrane. After taking out the composite membrane, heat and dry it at 140 °C for 55 min to obtain a high-strength flame-retardant cellulose membrane with a thickness of 33 μm;

[0101] The tensile fracture strength of the obtained high-strength flame-retardant cellulose membrane is 70 MPa, the elongation at break is 9.4%, the retention rate of the tensile fracture strength after ultrasonic oscillation washing with water for 2 h and drying is 97%, and the heat release rate is 76 KW / m 2 , and the total combustion release is 23 MJ / m 2 , and the limiting oxygen index is 32%.

[0102] Example 6

[0103] A preparation method of a high-strength flame-retardant cellulose film, as Figure 1 shown, includes the following steps:

[0104] (1) Mix an aqueous solution of sodium lignosulfonate with a mass fraction of 1% and an aqueous solution of polyamide epichlorohydrin with a mass fraction of 1% to form a mixed solution A;

[0105] Among them, the volume ratio of the aqueous solution of sodium lignosulfonate to the aqueous solution of polyamide epichlorohydrin is 1:1.3;

[0106] (2) Add an aqueous dispersion of bacterial cellulose with a mass fraction of 9% and an aqueous solution of oligomeric ammonium phosphate (degree of polymerization < 20) with a mass fraction of 3% to the mixed solution A in step (1), and stir well to obtain a mixed solution B with a Zeta potential of -38 and no precipitation;

[0107] Among them, the volume ratio of the cellulose aqueous dispersion, the oligomeric ammonium phosphate aqueous solution and the mixed solution A is 50:35:15;

[0108] (3) Filter the mixed solution B obtained in step (2) to form a composite film, take out the composite film and heat and dry it at 145 °C for 35 min to obtain a high-strength flame-retardant cellulose film with a thickness of 40 μm;

[0109] The tensile fracture strength of the obtained high-strength flame-retardant cellulose film is 55 MPa, the elongation at break is 6.5%, the retention rate of the tensile fracture strength after ultrasonic oscillation washing with water for 2 h and drying is 96.5%, and the heat release rate is 79 KW / m 2 and the total combustion release is 24 MJ / m 2 The limiting oxygen index is 32%.

[0110] Example 7

[0111] A preparation method of a high-strength flame-retardant cellulose film, as Figure 1 shown, includes the following steps:

[0112] (1) Mix an aqueous solution of sodium lignosulfonate with a mass fraction of 1% and an aqueous solution of polyamide epichlorohydrin with a mass fraction of 1% to form a mixed solution A;

[0113] Among them, the volume ratio of the aqueous solution of sodium lignosulfonate to the aqueous solution of polyamide epichlorohydrin is 1:1.3;

[0114] (2) Add an aqueous dispersion of methyl cellulose with a mass fraction of 9% and an aqueous solution of oligomeric ammonium phosphate (degree of polymerization < 20) with a mass fraction of 4% to the mixed solution A in step (1), and stir well to obtain a mixed solution B with a Zeta potential of -37 and no precipitation;

[0115] Among them, the volume ratio of the cellulose aqueous dispersion, the ammonium polyphosphate aqueous solution, and the mixed solution A is 55:40:45;

[0116] (3) Filter the mixed solution B obtained in step (2) to form a composite membrane. After taking out the composite membrane, heat and dry it at 135 °C for 40 min to obtain a high-strength flame-retardant cellulose membrane with a thickness of 36 μm;

[0117] The tensile fracture strength of the obtained high-strength flame-retardant cellulose membrane is 52 MPa, the elongation at break is 6.4%, the retention rate of the tensile fracture strength after ultrasonic oscillation washing with water for 2 h and drying is 99%, and the heat release rate is 71 KW / m 2 , the total combustion release is 21 MJ / m 2 , and the limiting oxygen index is 36%.

[0118] Example 8

[0119] A preparation method of a high-strength flame-retardant cellulose membrane, as Figure 1 shown, includes the following steps:

[0120] (1) Mix an aqueous solution of sodium lignosulfonate with a mass fraction of 1% and an aqueous solution of polyamide epichlorohydrin with a mass fraction of 1% to form a mixed solution A;

[0121] Among them, the volume ratio of the sodium lignosulfonate aqueous solution to the polyamide epichlorohydrin aqueous solution is 1:1.4, and the Zeta potential of the sodium lignosulfonate aqueous solution, the polyamide epichlorohydrin aqueous solution, and the mixed solution A is as Figure 2 shown;

[0122] (2) Add an aqueous dispersion of bacterial cellulose with a mass fraction of 9% and an aqueous solution of ammonium polyphosphate (degree of polymerization < 20) with a mass fraction of 4% to the mixed solution A in step (1), and stir well to obtain a mixed solution B with a Zeta potential of -50 (as Figure 2 shown), and no precipitation occurs;

[0123] Among them, the volume ratio of the cellulose aqueous dispersion, the ammonium polyphosphate aqueous solution, and the mixed solution A is 75:7:40, and the Zeta potential of the cellulose aqueous dispersion and the ammonium polyphosphate aqueous solution is as Figure 2 shown;

[0124] (3) Filter the mixed solution B obtained in step (2) to form a composite membrane. After taking out the composite membrane, heat and dry it at 140 °C for 50 min to obtain a high-strength flame-retardant cellulose membrane with a thickness of 34 μm, and its infrared spectrum is as Figure 3 shown;

[0125] The tensile breaking strength of the prepared high-strength flame-retardant cellulose film is 65 MPa, the elongation at break is 8.4%, the retention rate of the tensile breaking strength is 97.8% after ultrasonic oscillation washing for 2 h and drying, and the heat release rate is 70 KW / m 2 , and the total combustion release is 20 MJ / m 2 , and the limiting oxygen index is 37%.

[0126] In addition, Figure 3 From top to bottom are the infrared spectra of the pure cellulose film, the polyammonium phosphate-free composite film prepared in Comparative Example 1, the high-strength flame-retardant cellulose film prepared in Example 8, and the polyammonium phosphate used in Examples 1-8; compared with the pure cellulose spectrum, the polyammonium phosphate-free composite film and the high-strength flame-retardant cellulose film have a characteristic peak of the C=O bond at 1715 cm -1 , which confirms that covalent cross-linking occurs between sodium lignosulfonate-polyamide epichlorohydrin and cellulose during the heat drying process to produce an ester bond; the high-strength flame-retardant cellulose film and the oligoammonium phosphate have a P-O-P characteristic peak at 883 cm -1 , which is the characteristic peak of polyammonium phosphate, indicating that the high-strength flame-retardant cellulose film contains polyammonium phosphate.

Claims

1. A method for preparing a high-strength flame-retardant cellulose film, characterized in that The steps include: (1) mixing an aqueous solution of sodium lignin sulfonate and an aqueous solution of a cross-linking agent to form a mixed solution A; (2) adding the cellulose aqueous dispersion and the ammonium polyphosphate aqueous solution to the mixed solution A of step (1), and stirring thoroughly to obtain a mixed solution B; (3) filtering the mixed solution B obtained in step (2) to form a membrane, and heating and drying to obtain a high-strength flame-retardant cellulose membrane; In step (1), the crosslinking agent is polyamide epichlorohydrin, and the volume ratio of the sodium lignin sulfonate aqueous solution to the crosslinking agent aqueous solution is 1:1 to 1.5; The degree of polymerization of the ammonium polyphosphate in step (2) is less than 20; the Zeta potential of the mixed solution B is less than -30, and no precipitation is generated.

2. The method for preparing a high-strength flame-retardant cellulose film according to claim 1, characterized in that: In step (1), the mass fraction of the sodium lignin sulfonate aqueous solution is 0.8-1%, and the mass fraction of the cross-linking agent aqueous solution is 1-1.3%.

3. The method for preparing a high-strength flame-retardant cellulose film according to claim 2, characterized in that: In step (2), the mass fraction of the cellulose aqueous dispersion is 7-10%, and the mass fraction of the ammonium polyphosphate aqueous solution is 1-5%.

4. The method for preparing a high-strength flame-retardant cellulose film according to claim 3, characterized in that: In step (2), the volume ratio of the cellulose aqueous dispersion, the ammonium polyphosphate aqueous solution and the mixed solution A is 50-80:7-45:7-45.

5. The method for preparing a high-strength flame-retardant cellulose film according to claim 1, characterized in that: The specific process of step (3) is as follows: the mixed solution B is filtered to form a composite membrane, and the composite membrane is taken out and heated at a certain temperature for a certain time to obtain a high-strength flame-retardant cellulose membrane.

6. The method for preparing a high-strength flame-retardant cellulose film according to claim 5, characterized in that: The certain temperature is 130-150°C, and the certain time is 30-60 minutes.

7. The method for preparing a high-strength flame-retardant cellulose film according to any one of claims 1 to 6, characterized in that: The thickness of the high-strength flame-retardant cellulose film is 25 to 50 μm.

8. The method for preparing a high-strength flame-retardant cellulose film according to claim 7, characterized in that: The tensile strength of the high-strength flame-retardant cellulose film is 50-70MPa, the elongation at break is 6-10%, and the heat release rate is 70-100KW / m 2 The total amount of combustion release is 20~30MJ / m 2 , the limiting oxygen index is 30-37%.

9. The method for preparing a high-strength flame-retardant cellulose film according to claim 8, characterized in that: The tensile breaking strength retention rate of the high-strength flame-retardant cellulose film after ultrasonic vibration washing for 2 hours and drying is not less than 96.5%.

Images