Intumescent flame-retardant liquid suitable for ethylene-vinyl acetate copolymer, preparation method and application of intumescent flame-retardant liquid

Abstract

The invention discloses an intumescent flame retardant liquid suitable for ethylene-vinyl acetate copolymer, and a preparation method and application thereof, the flame retardant liquid is composed of ammonium polyphosphate, nanofiber, pentaerythritol and water, during preparation, pentaerythritol is dissolved in water under heating and stirring conditions; and then sequentially adding the nano cellulose and the ammonium polyphosphate, and continuously stirring and dissolving. The flame retardant liquid can be used for modifying an ethylene-vinyl acetate copolymer. Ammonium polyphosphate is used as an acid source and a gas source of an intumescent flame-retardant system, pentaerythritol is used as a carbon source of the intumescent flame-retardant system, nano-cellulose is used as a charring agent and a framework of the intumescent flame-retardant system, and the ammonium polyphosphate, the pentaerythritol and the nano-cellulose have a synergistic effect, so that a compact and firm carbon layer can be formed on the surface of the material in a flame-retardant process; and molten drops are effectively prevented from being generated during combustion, the LOI of EVA is remarkably improved, and the heat release rate and the total heat release amount are greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant technology, and relates to the modification of ethylene-vinyl acetate copolymer, specifically to an intumescent flame retardant liquid suitable for ethylene-vinyl acetate copolymer, its preparation method and its application. Background Technology

[0002] Ethylene-vinyl acetate copolymers are widely used in footwear, packaging, wire and cable, and hot melt adhesives due to their excellent flexibility, transparency, adhesion, and processability. However, these materials are highly flammable, have a low limiting oxygen index (LOI), and release large amounts of heat and smoke when burning, posing a serious fire hazard. Therefore, flame-retardant modification is crucial.

[0003] Traditional flame retardant treatment methods include additive flame retardancy (adding flame retardants during processing) and reactive flame retardancy (integrating flame retardant elements into the polymer chain through chemical reactions). For pre-formed EVA foam or films, impregnation is an effective and convenient post-processing flame retardant modification method. Currently, commonly used impregnation flame retardants are mostly halogen-containing systems. Although they have high flame retardant efficiency, they produce a large amount of toxic and corrosive gases during combustion, causing secondary hazards to the environment and user safety. Halogen-free intumescent flame retardant systems (IFR) have become a research hotspot due to their high efficiency, low smoke, and low toxicity.

[0004] Halogen-free intumescent flame retardant systems typically consist of three parts: an acid source, a carbon source, and a gas source. They work synergistically to form a uniform, dense, porous carbon layer on the material surface during combustion, providing insulation, oxygen barrier, smoke suppression, and prevention of molten dripping. However, existing halogen-free intumescent flame retardant impregnation solutions have some shortcomings, such as poor adhesion between the flame retardant components and the substrate, easy migration and precipitation, poor water resistance, and uneven treatment due to the tendency of nano-components to agglomerate. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide an intumescent flame retardant liquid suitable for ethylene-vinyl acetate copolymers, its preparation method, and its application, thereby solving the technical problems of poor adhesion between flame retardant components and substrates, easy migration and precipitation, poor water resistance, and uneven treatment caused by easy agglomeration of nano-components in existing halogen-free intumescent flame retardant systems.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: An intumescent flame retardant liquid suitable for ethylene-vinyl acetate copolymers comprises the following components: ammonium polyphosphate as an acid source and gas source; nanocellulose as a charring agent and binder; pentaerythritol as a carbon source; and water as a solvent.

[0007] The mass ratio of ammonium polyphosphate, nanocellulose, pentaerythritol and water is (2.5-20):(0.5-2.5):(1-8):40; preferably (5-10):(1-1.5):(2-4):40.

[0008] The present invention also has the following technical features: Specifically, the average degree of polymerization of the ammonium polyphosphate is 1400 to 1600.

[0009] Specifically, the nanocellulose has a diameter of 4–10 nm and a length of 180–220 nm.

[0010] The present invention also protects a method for preparing an intumescent flame retardant liquid as described above, the method comprising: firstly dissolving pentaerythritol in water under heating and stirring conditions; then sequentially adding nanocellulose and ammonium polyphosphate, continuing to stir and dissolve, and finally obtaining an intumescent flame retardant liquid suitable for ethylene-vinyl acetate copolymer.

[0011] Specifically, the heating and stirring conditions are as follows: stirring at a temperature of 60–90 °C and a speed of 1200 rad / min for 20–40 min.

[0012] The present invention also protects the use of the intumescent flame retardant liquid described above in the modification of ethylene-vinyl acetate copolymer.

[0013] Specifically, the application includes: first, drying the ethylene-vinyl acetate copolymer, then immersing the ethylene-vinyl acetate copolymer in an intumescent flame retardant liquid and performing impregnation treatment under vacuum or normal pressure conditions; and finally, drying and curing after impregnation.

[0014] Specifically, the drying and curing conditions for the ethylene-vinyl acetate copolymer are as follows: drying at a temperature of 60–90 °C for 30–120 min, preferably 30–90 min.

[0015] Specifically, the vacuum conditions are: a vacuum degree of not less than -0.08 MPa.

[0016] Specifically, the immersion treatment time is 30–120 min, preferably 30–90 min.

[0017] Compared with the prior art, the present invention has the following technical effects: (I) This invention uses ammonium polyphosphate as the acid source and gas source of the intumescent flame retardant system, pentaerythritol as the carbon source of the intumescent flame retardant system, and nanocellulose as the char-forming agent and skeleton of the intumescent flame retardant system. The three work together to form a dense and solid carbon layer on the surface of the material during the flame retardant process, effectively preventing the generation of molten droplets during combustion, significantly improving the LOI of EVA, and greatly reducing the heat release rate (HRR) and total heat release (THR).

[0018] (II) The anionic nanocellulose contained in the intumescent flame retardant system of this invention has a large number of carboxyl and hydroxyl groups, which can form hydrogen bonds with pentaerythritol in the flame retardant system and also have good affinity with EVA substrate, effectively preventing the flame retardant from failing due to migration or precipitation during use and improving durability. At the same time, due to the nano-size effect and extremely high specific surface area of ​​nanocellulose, it can penetrate into the intumescent char layer to form a skeleton, significantly enhancing the strength, density and continuity of the char layer, thereby more effectively insulating heat and oxygen.

[0019] (III) All components in the intumescent flame retardant system of the present invention are halogen-free, low-toxicity and environmentally friendly materials. They do not produce toxic and corrosive gases when burning, which is in line with the development direction of modern green flame retardant materials.

[0020] (IV) The impregnation process provided by the present invention is simple, requires low equipment, and is applicable to, but not limited to, post-flame retardant treatment of EVA products with complex shapes (such as foam and fabric). Attached Figure Description

[0021] Figure 1 The formulation and impregnation process of the flame retardant liquid, as well as the synergistic mechanism of the flame retardant, are demonstrated.

[0022] Figure 2 Microstructure diagrams of the combustion residues of Examples 1-5 and Comparative Example 1; Figure 2 In the examples: (a) Example 1, (b) Example 2, (c) Example 3, (d) Example 4, (e) Example 5, (f) Comparative Example 1.

[0023] Figure 3 These are photographs of Examples 1-5 and Comparative Example 1 after vertical combustion in air for different times; Figure 3 In the examples: (a) Example 1, (b) Example 2, (c) Example 3, (d) Example 4, (e) Example 5, (f) Comparative Example 1.

[0024] Figure 4 The values ​​are the LOI measurements for Examples 1-5 and Comparative Example 1.

[0025] Figure 5 The tensile stress-tensile strain curves are for Examples 1-5 and Comparative Example 1.

[0026] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0027] It should be noted that all raw materials used in this invention, unless otherwise specified, are those known in the art. For example: Ammonium polyphosphate was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with product number MKL-A823395-2.5kg, an average degree of polymerization of approximately 1500, and CAS code 68333-79-9.

[0028] Pentaerythritol was purchased from Tianjin Bodi Chemical Co., Ltd., CAS code 115-77-5.

[0029] Nanocellulose was purchased from Shanghai McLean Biochemical Technology Co., Ltd., with product number C916412. Its diameter ranges from 4 to 10 nm and its length is approximately 200 nm.

[0030] The weight-average molecular weight of ethylene-vinyl acetate copolymer (EVA) is 100,000 to 400,000, and its CAS code is 24937-78-8.

[0031] Following the above technical solutions, specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0032] Example 1 This embodiment provides a method for preparing an intumescent flame retardant suitable for ethylene-vinyl acetate copolymers, which specifically includes the following steps: Step 1, Flame Retardant Liquid Preparation: Take 100 g ammonium polyphosphate, 10 g nanocellulose, 20 g pentaerythritol, and 400 ml deionized water. First, heat the deionized water to 60 ℃, then add pentaerythritol while stirring at 1200 rad / min, and stir for 60 min until completely dissolved. Then, add nanocellulose and ammonium polyphosphate sequentially, and continue stirring for 60 min to obtain a homogeneous flame retardant liquid.

[0033] Step 2, Sample processing: EVA strips measuring 125 mm × 13 mm × 1 mm were dried in an oven at 60 ℃ for 30 min; then placed in a beaker, ensuring the flame retardant liquid completely submerged the sample, and impregnated for 10 min, serving as vertical burning test strips. EVA strips measuring 150 mm × 10 mm × 4 mm were dried in an oven at 60 ℃ for 30 min; then placed in a vacuum impregnation tank (vacuum degree not less than -0.08 MPa), ensuring the flame retardant liquid completely submerged the sample, and vacuum impregnated for 40 min, serving as oxygen index test strips. Dumbbell-shaped EVA strips, 4 mm thick, were cut using a type 1 cutter, dried in an oven at 60 ℃ for 30 min; then placed in a vacuum impregnation tank, ensuring the flame retardant liquid completely submerged the sample, and vacuum impregnated for 40 min, serving as tensile strength test strips.

[0034] Step 3, post-processing: Remove the sample and drain it; then dry it at 60 ℃ for 40 min to obtain flame-retardant EVA strips.

[0035] Verification of the effect of Example 1: by Figure 2 (a) It can be seen that the sample formed a porous structure ranging from approximately 5 to 150 μm after combustion. The cavities, ranging from tens to hundreds of micrometers, are the main units for heat insulation; the enclosed air and non-combustible gases inside effectively block heat transfer. Smaller pores are distributed on the carbon walls of the larger pores, forming a finer microstructure. These increase the specific surface area of ​​the carbon layer, enhance its rigidity, and prevent the large pores from easily breaking under thermal impact. Figure 3 (a) shows that the sample self-extinguishes after being removed from the flame, exhibiting good flame-retardant properties. From Figure 4 It can be seen that the LOI of the oxygen index test strip obtained in this embodiment is 40.6%. Figure 5 (a)-(c) and Figure 5 (p)-(r) shows that the tensile strength of the specimens hardly changes before and after impregnation.

[0036] Example 2 This embodiment provides a method for preparing an intumescent flame retardant suitable for ethylene-vinyl acetate copolymers, which specifically includes the following steps: Step 1, Flame Retardant Liquid Preparation: Take 100 g ammonium polyphosphate, 15 g nanocellulose, 20 g pentaerythritol, and 400 ml deionized water. First, heat the deionized water to 60 ℃, then add pentaerythritol while stirring at high speed, and stir for 60 min until completely dissolved. Then, add nanocellulose and ammonium polyphosphate sequentially, and continue stirring for 60 min to obtain a homogeneous flame retardant liquid.

[0037] Step two, sample processing: In this embodiment, step two is exactly the same as step two in embodiment 1. Step 3, Post-processing: In this embodiment, step 3 is exactly the same as step 3 in embodiment 1. Verification of the effect of Example 2: by Figure 2 (b) shows that the sample also formed a dense porous structure after combustion. Figure 3 (b) It can be seen that the self-extinguishing performance of the sample weakens with increasing nanocellulose content. From Figure 4 It can be seen that the LOI of the oxygen index test strip obtained in this embodiment is 38.5%. Figure 5 (d)-(f) and Figure 5 (p)-(r) shows that the tensile strength of the specimens hardly changes before and after impregnation.

[0038] Example 3 This embodiment provides a method for preparing an intumescent flame retardant suitable for ethylene-vinyl acetate copolymers, which specifically includes the following steps: Step 1, Flame Retardant Liquid Preparation: Take 50 g ammonium polyphosphate, 10 g nanocellulose, 20 g pentaerythritol, and 400 ml deionized water. First, heat the deionized water to 60 ℃, then add pentaerythritol while stirring at high speed, and stir for 60 min until completely dissolved. Then, add nanocellulose and ammonium polyphosphate sequentially, and continue stirring for 60 min to obtain a homogeneous flame retardant liquid.

[0039] Step two, sample processing: In this embodiment, step two is exactly the same as step two in embodiment 1. Step 3, Post-processing: In this embodiment, step 3 is exactly the same as step 3 in embodiment 1. Verification of the effect of Example 3: by Figure 2 (c) It can be seen that as the ammonium polyphosphate content decreases, the number of small pores after combustion decreases sharply, and the mechanical strength of the entire porous structure decreases significantly. From Figure 3 (c) It can be seen that the self-extinguishing performance of the sample weakens as the ammonium polyphosphate content decreases. From Figure 4 It can be seen that the LOI of the oxygen index test strip obtained in this embodiment is 23.7%. Figure 5 (g)-(i) and Figure 5 (p)-(r) shows that the tensile strength of the specimens hardly changes before and after impregnation.

[0040] Example 4 This embodiment provides a method for preparing an intumescent flame retardant suitable for ethylene-vinyl acetate copolymers, which specifically includes the following steps: Step 1, Flame Retardant Liquid Preparation: Take 100 g ammonium polyphosphate, 10 g nanocellulose, 30 g pentaerythritol, and 400 ml deionized water. First, heat the deionized water to 60 ℃, then add pentaerythritol while stirring at high speed, and stir for 60 min until completely dissolved. Then, add nanocellulose and ammonium polyphosphate sequentially, and continue stirring for 60 min to obtain a homogeneous flame retardant liquid.

[0041] Step two, sample processing: In this embodiment, step two is exactly the same as step two in embodiment 1. Step 3, Post-processing: In this embodiment, step 3 is exactly the same as step 3 in embodiment 1. Verification of the effect of Example 4: by Figure 2 (d) shows that with the increase of pentaerythritol content, the micropores become denser after combustion, and the overall strength of the porous structure is improved. Figure 3 (d) It can be seen that the self-extinguishing performance of the sample increases with the increase of pentaerythritol content. From Figure 4 It can be seen that the LOI of the oxygen index test strip obtained in this embodiment is 37.0%. Figure 5 (j)-(l) and Figure 5 (p)-(r) shows that the tensile strength of the specimens hardly changes before and after impregnation.

[0042] Example 5 This embodiment provides a method for preparing an intumescent flame retardant suitable for ethylene-vinyl acetate copolymers, which specifically includes the following steps: Step 1, Flame Retardant Liquid Preparation: Take 100 g ammonium polyphosphate, 10 g nanocellulose, 40 g pentaerythritol, and 400 ml deionized water. First, heat the deionized water to 60 ℃, then add pentaerythritol while stirring at high speed, and stir for 60 min until completely dissolved. Then, add nanocellulose and ammonium polyphosphate sequentially, and continue stirring for 60 min to obtain a homogeneous flame retardant liquid.

[0043] Step two, sample processing: In this embodiment, step two is exactly the same as step two in embodiment 1. Step 3, Post-processing: In this embodiment, step 3 is exactly the same as step 3 in embodiment 1. Verification of the effect of Example 5: by Figure 2 (e) shows that with a further increase in pentaerythritol content, the micropores become more compact after combustion, and the overall strength of the porous structure is further improved. Figure 3 (e) shows that with further increases in pentaerythritol content, the self-extinguishing performance of the sample after flame removal is further enhanced. Figure 4 It can be seen that the LOI of the oxygen index test strip prepared in this embodiment is 34.1%. Figure 5 (m)-(o) and Figure 5 (p)-(r) shows that the tensile strength of the specimens hardly changes before and after impregnation.

[0044] Comparative Example 1 This comparative example provides a method for preparing an ethylene-vinyl acetate copolymer without flame retardants. The method specifically includes the following steps: EVA samples with dimensions of 125 mm × 13 mm × 1 mm and 150 mm × 10 mm × 4 mm are dried in an oven at 60 ℃ for 1 h to obtain vertical burning and LOI test samples without flame retardants. Dumbbell-shaped EVA samples with a thickness of 4 mm are cut using a type 1 cutter as tensile strength test samples.

[0045] Verification of the effect of Example 1: by Figure 2 (f) shows that after burning, the sample without flame retardant produces dense, solid particles. From... Figure 3 (f) shows that the sample without flame retardant is highly flammable and produces a large number of molten droplets. From Figure 4 It can be seen that the LOI of the oxygen index test strip prepared according to Comparative Example 1 is 18.6%. Figure 5 It can be seen that the tensile strength of the specimen without flame retardant is approximately 0.95 MPa.

[0046] As can be seen from Examples 1-5 and Comparative Example 1, this flame retardant can promote the charring of EVA, and the char layer formed on the surface can effectively insulate heat transfer and efficiently prevent the generation of molten droplets. The LOI of pure EVA is only 18.6%, while the LOI of Example 1 is as high as 40.6%, which is far higher than the flame retardant grade (27%).

Claims

1. An intumescent flame retardant liquid suitable for ethylene-vinyl acetate copolymers, characterized in that, It contains the following components: ammonium polyphosphate, as an acid source and gas source; nanocellulose, as a char-forming agent and binder; and pentaerythritol, as a carbon source. The mass ratio of ammonium polyphosphate, nanocellulose and pentaerythritol is (2.5-20):(0.5-2.5):(1-8).

2. The intumescent flame retardant liquid suitable for ethylene-vinyl acetate copolymer as described in claim 1, characterized in that, The average degree of polymerization of the ammonium polyphosphate is 1400-1600.

3. The intumescent flame retardant liquid suitable for ethylene-vinyl acetate copolymer as described in claim 1, characterized in that, The nanocellulose has a diameter of 4–10 nm and a length of 180–220 nm.

4. A method for preparing an intumescent flame retardant liquid as described in any one of claims 1 to 3, characterized in that, include: First, the pentaerythritol is dissolved under heating and stirring conditions; Then add nanocellulose and ammonium polyphosphate in sequence, and continue stirring to dissolve.

5. The method for preparing the intumescent flame retardant liquid as described in claim 4, characterized in that, The heating and stirring conditions are as follows: stirring at a temperature of 60–90 °C and a speed of 1200 rad / min for 20–40 min.

6. The application of the intumescent flame retardant liquid according to any one of claims 1 to 3 in the modification of ethylene-vinyl acetate copolymer.

7. The application as described in claim 6, characterized in that, include: First, the ethylene-vinyl acetate copolymer is dried, and then the ethylene-vinyl acetate copolymer is immersed in an intumescent flame retardant liquid and impregnated under vacuum or normal pressure conditions. After impregnation, the mixture is dried and cured.

8. The application as described in claim 7, characterized in that, The drying and curing conditions for ethylene-vinyl acetate copolymer are as follows: drying at 60–90 °C for 30–120 min.

9. The application as described in claim 7, characterized in that, The vacuum condition is: the vacuum level is not lower than -0.08 MPa.

10. The application as described in claim 7, characterized in that, The immersion treatment time is 30 to 120 minutes.

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