A carbon-based composite flame retardant and flame-retardant nylon 6 prepared by in-situ polymerization thereof

Abstract

The present invention relates to the technical field of nylon 6 flame retardancy, and specifically to a carbon-based composite flame retardant and flame-retardant nylon 6 prepared by in-situ polymerization. The preparation raw materials thereof at least include: amino-functionalized metal oxide modified carbon nanotubes, compounds containing triazine-based flame retardant groups, p-hydroxybenzaldehyde, and p-aminobenzoic acid. The preparation raw materials of the amino-functionalized metal oxide modified carbon nanotubes at least include an acidified and opened carbon nanotube solution, an alcohol solution of a metal salt, and an amino silane solution. Using carbon nanotubes as the main flame retardant, a composite flame retardant is constructed with other flame retardant components by chemical methods, and an in-situ polymerization method is used to develop a nylon 6 material with comprehensive flame retardancy and difficult spreadability, reducing the risk of fire generation and spread, and having extremely high market application and promotion value.

Description

Technical Field

[0001] The present invention relates to the technical field of nylon 6 flame retardancy, and particularly to a carbon-based composite flame retardant and flame-retardant nylon 6 prepared by in-situ polymerization thereof. Background Art

[0002] Nylon 6 is a thermoplastic resin formed by ring-opening polymerization of the monomer caprolactam and is applied in many industries. It has long faced severe use environments such as high temperature and high voltage. However, nylon 6 itself has poor thermal stability and is often ignited as a combustible material, causing fires. Moreover, it is difficult to self-extinguish during the combustion process and is accompanied by a large amount of molten droplets, leading to the further spread of the fire, threatening personal safety and causing property losses. Therefore, flame-retardant nylon 6 has also received increasing attention in the market, and the flame-retardant modification of nylon 6 has become an issue of social concern.

[0003] At present, the flame-retardant modification of nylon 6 is mainly achieved by adding flame retardants to the nylon 6 system. Commonly used flame retardants include inorganic flame retardants (such as graphite, vermiculite, graphene, carbon nanotubes, etc.) and organic flame retardants (such as cyanuric chloride derivatives, melamine cyanurate, etc.). However, there are still certain problems with the products prepared by addition. Chinese Patent Application (Publication No. CN113845771A) discloses a halogen-free flame-retardant PA66 composite material and its preparation method, in which melamine cyanurate, graphene, and multi-walled carbon nanotubes are simultaneously introduced into the PA66 system to improve the flame-retardant performance of PA66. However, the flame-retardant performance of the product is not stable and has three deficiencies. First, the poor uniform dispersion deteriorates the physical and mechanical properties of the matrix and also causes the carbon layer formed after the combustion of the modified polymer prepared therefrom to be in an island shape with linear separation from each other, affecting the flame-retardant efficiency. Second, it has the effect of anti-dripping, but a large amount of heat accumulates at the non-dripping combustion end, accelerating the generation of the combustion reaction. Third, the anti-mass transfer ability is poor. Due to its nano-scale pore diameter, carbon nanotubes have extremely high capillary pressure, accelerating the transmission of combustible gases or melts and causing the fire spread speed to increase. Summary of the Invention

[0004] In order to solve the above problems, the present invention uses carbon nanotubes as the main flame retardant, constructs a composite flame retardant with other flame-retardant components by chemical methods, and develops a nylon 6 material with comprehensive flame retardancy and difficulty in spreading by in-situ polymerization method, reducing the risk of fire generation and spread, and having extremely high market application and promotion value.

[0005] On the one hand, the present invention provides a carbon-based composite flame retardant, and its preparation raw materials at least include: amino-functionalized metal oxide modified carbon nanotubes, compounds containing triazine-based flame retardant groups, p-hydroxybenzaldehyde, and p-aminobenzoic acid.

[0006] Among them, the amino-functionalized metal oxide modified carbon nanotubes satisfy at least one of the following two conditions:

[0007] (1) The metal oxide is filled inside the carbon nanotubes;

[0008] (2) The metal oxide is loaded on the surface of the carbon nanotubes;

[0009] More preferably, the carbon nanotubes modified with amino-functionalized metal oxide simultaneously satisfy conditions (1) and (2).

[0010] As a preferred technical solution, the raw materials for preparing the carbon nanotubes modified with amino-functionalized metal oxide at least include an acidified and opened carbon nanotube solution, an alcohol solution of metal salt, and an amino silane solution.

[0011] As a preferred technical solution, the volume ratio of the acidified and opened carbon nanotube solution, the alcohol solution of metal salt, and the amino silane solution is (3 - 5):(5 - 10):1, preferably 4:8:1.

[0012] As a preferred technical solution, the mass concentration of the acidified and opened carbon nanotube solution is 10 - 40 g / L, preferably 15 - 30 g / L, more preferably 15 - 25 g / L, and most preferably 20 g / L.

[0013] As a preferred technical solution, the preparation method of the acidified and opened carbon nanotube solution at least includes the following steps: ball-milling the carbon nanotubes and then performing acidification treatment with inorganic strong acid, washing to pH = 6.5 - 7.5 after cooling, and adding water to prepare the acidified and opened carbon nanotube solution.

[0014] Explanation of "opening" in "acidified and opened" in the present invention: Since the carbon nanotubes are sealed at both ends, to fill them, the tube openings of the carbon nanotubes need to be opened. By using a mixed acid of nitric acid and sulfuric acid to act on the carbon nanotubes, carbon nanotubes with both ends opened can be obtained under the reaction conditions and time. At the same time, the opened carbon nanotubes also contain a large number of carboxyl and hydroxyl groups.

[0015] Preferably, the average tube diameter of the carbon nanotubes is 5 - 50 nm, preferably 10 - 25 nm, the model is the FT9000 series powder, and it is sourced from Jiangsu Tiannai Technology Co., Ltd.

[0016] Preferably, the instrument for ball-milling is a ball mill, and the parameter settings of the ball mill include: the rotation speed is 100 - 300 rpm, 5 - 10 min / cycle, and the forward and reverse ball-milling time is 20 - 40 min.

[0017] Preferably, the inorganic strong acid at least includes concentrated sulfuric acid and nitric acid; the volume ratio of the concentrated sulfuric acid and nitric acid is (1 - 5):1, preferably (2 - 4):1, and most preferably 3:1.

[0018] Preferably, the acid treatment is specifically as follows: the ball-milled carbon nanotubes are put into an inorganic strong acid and stirred and reacted at 60-80 °C for 3-5 h.

[0019] Preferably, the cleaning is specifically as follows: washing with deionized water at 0-5 °C until the pH = 6.5-7.5.

[0020] As a preferred technical solution, the alcohol solution of the metal salt includes at least a metal salt and an alcohol solvent, and the mass concentration of the alcohol solution of the metal salt is 10-40 g / L, preferably 18-32 g / L.

[0021] Preferably, the metal salt includes at least an iron salt, and the iron salt is selected from at least one of ferric sulfate salt, ferric chloride salt, ferric nitrate salt, and ferric carbonate salt, preferably ferric nitrate salt.

[0022] Preferably, the metal salt is ferric nitrate nonahydrate.

[0023] Preferably, the alcohol solvent is absolute ethanol.

[0024] As a preferred technical solution, the amino-silane solution includes at least an amino-silane and an ethanol aqueous solution.

[0025] Preferably, the amino-silane includes at least KH550 (γ-aminopropyltriethoxysilane).

[0026] Preferably, the mass concentration of the ethanol aqueous solution is 80-95%.

[0027] As a preferred technical solution, the preparation method of the amino-functionalized metal oxide modified carbon nanotubes includes at least the following steps: adding the acid-opened carbon nanotube solution into the alcohol solution of the metal salt, stirring and mixing, and then drying to obtain a sample, and performing heat treatment on the sample; after cooling, putting it into the amino-silane solution for reaction, cooling and filtering, and drying to constant weight to obtain the amino-functionalized metal oxide modified carbon nanotubes.

[0028] Preferably, the preparation method of the amino-functionalized metal oxide modified carbon nanotubes includes at least the following steps: adding the acid-opened carbon nanotube solution into the alcohol solution of the metal salt, heating to 40-60 °C, ultrasonically treating for 0.5-2 h under mechanical stirring, naturally drying, and then putting it into a vacuum drying oven at 50-70 °C for vacuum drying. After vacuum drying, the sample is heated to 300-500 °C under nitrogen protection and maintained for 3-5 h; after cooling to 20-30 °C, it is put into the amino-silane solution, heated to 100-150 °C, and reacted for 1-3 h under a nitrogen atmosphere, cooled and filtered, and dried at 50-70 °C to constant weight to obtain the amino-functionalized metal oxide modified carbon nanotubes.

[0029] Preferably, the rotation speed of the mechanical stirring is 300 - 500 rpm, preferably 300 - 400 rpm, and most preferably 350 rpm.

[0030] Preferably, the ultrasonic frequency is 40 - 50 kHz.

[0031] As a preferred technical solution, the compound containing a triazine-based flame retardant group is selected from at least one of cyanuric chloride and its derivatives, melamine and its derivatives, and is preferably cyanuric chloride.

[0032] The present invention uses amino-functionalized metal oxide modified carbon nanotubes, a compound containing a triazine-based flame retardant group, p-hydroxybenzaldehyde, and p-aminobenzoic acid as raw materials to prepare a carbon-based composite catalyst with carbon nanotubes as the carbon-based main body and metal oxides and a triazine-based flame retardant group containing Schiff base as synergistic components to ensure the subsequent application effect. In particular, iron oxide and a cyanuric chloride derivative flame retardant group containing Schiff base are used as synergistic components. The synergistic components are respectively carried with hydroxyl or carboxyl functional groups, reducing the surface inertness of carbon nanotubes and improving the dispersibility of carbon nanotubes in polymers. At the same time, the dicarboxyl groups can participate in the polymerization reaction, further improving the compatibility between carbon nanotubes and nylon 6 materials, solving the defect of unstable flame retardancy efficiency caused by insufficient dispersibility of carbon nanotubes, and reducing the impact of flame retardants on the mechanical properties of nylon 6.

[0033] Specifically, the present invention designs iron oxide modified carbon nanotubes, and the iron oxide endows carbon nanotubes with good ability to block mass transfer. The iron oxide filled inside reduces the capillary action of the carbon tubes themselves by physical hindrance, and improves the catalytic carbonization rate of the melt inside the carbon nanotubes by means of the space effect inside the carbon nanotubes. After carbonization, the transmission path is truncated, and under the dual action, the conduction speed of gas and melt inside the tubes is reduced, eliminating the mass transfer effect from the inside of the combustion zone to the combustion surface and from the unburned zone to the combustion zone during the combustion of nylon 6, greatly reducing the speed of fire spread and enhancing the fire resistance to spread.

[0034] Furthermore, the carbon nanotubes are grafted with a cyanuric chloride derivative flame retardant group containing a Schiff base structure. This flame retardant group contains an aromatic Schiff base structure synthesized from p-hydroxybenzaldehyde and p-aminobenzoic acid. This structure can undergo self-crosslinking at high temperatures as a special flame retardant structure. With the excellent heat conduction of carbon nanotubes and iron oxide, the aromatic Schiff base structure in the unburned area undergoes self-crosslinking in advance, improving the thermal stability of the material. At the same time, the heat accumulated in the combustion zone is transferred, prolonging the decomposition time of the nylon 6 at the combustion end, and thus delaying the flame spread speed until it goes out.

[0035] The preparation method of the carbon-based composite flame retardant at least includes the following steps:

[0036] (1) Mix the amino-functionalized metal oxide modified carbon nanotubes with organic solvent A to obtain solution A; mix the compound containing triazine-based flame retardant groups with organic solvent B to obtain solution B; drop solution B into solution A while dropping an alkaline solution to maintain the pH of the reaction system at 5.0 - 7.0, control the temperature of the reaction system at 0 - 5 °C, and stir and react for 1 - 3 h;

[0037] (2) Mix p-hydroxybenzaldehyde with organic solvent C to obtain solution C; raise the temperature of the reaction system in step (1) to 30 - 50 °C, drop solution C while dropping an alkaline solution to maintain the pH of the reaction system at 6.0 - 7.0, and stir and react for 1 - 3 h; continue to raise the temperature to 60 - 80 °C, drop solution C while dropping an alkaline solution to maintain the pH of the reaction system at 7.0 - 7.5, and stir and react for 3 - 5 h to obtain a mixture. After the mixture is cooled, filtered, washed, and vacuum dried, aldehyde-functionalized iron oxide modified carbon nanotubes are obtained;

[0038] (3) Disperse the aldehyde-functionalized iron oxide modified carbon nanotubes and p-aminobenzoic acid in dioxane respectively to obtain an aldehyde-functionalized iron oxide modified carbon nanotube solution and a p-aminobenzoic acid solution. Mix the aldehyde-functionalized iron oxide modified carbon nanotube solution and the p-aminobenzoic acid solution and then carry out a heating reaction. After washing, suction filtration, and drying, the carbon-based composite flame retardant is obtained.

[0039] As a preferred technical solution, the mass ratio of the amino-functionalized metal oxide modified carbon nanotubes, the compound containing triazine-based flame retardant groups, and p-hydroxybenzaldehyde is (5 - 10) : 3 : 4, preferably (6 - 7.2) : 3 : 4.

[0040] As a preferred technical solution, the mass ratio of the aldehyde-functionalized iron oxide modified carbon nanotubes and p-aminobenzoic acid is (2 - 5) : 1, preferably 3 : 1.

[0041] As a preferred technical solution, organic solvent A, organic solvent B, and organic solvent C are each selected from at least one of acetone, ethanol, and ether, preferably acetone.

[0042] As a preferred technical solution, the alkaline solution is an aqueous sodium hydroxide solution, and the mass concentration of the aqueous sodium hydroxide solution is 10 - 30%.

[0043] The carbon-based composite flame retardant provided by the present invention combines multiple flame retardant elements of carbon, nitrogen, silicon, and iron into one body, and can achieve double flame retardancy in the condensed phase and the gas phase. Especially in the condensed phase, the carbon particles catalyzed by the surface iron oxide fill the voids of the carbon nanotube network structure, improving the continuity and density of the carbon layer, enabling nylon 6 to achieve the effect of zero melt dripping during combustion, preventing the spread of molten droplets that act as ignition heat sources, and preventing the spread of fire.

[0044] On the other hand, the present invention provides a flame-retardant nylon 6 prepared by in-situ polymerization of a carbon-based composite flame retardant. The raw materials for preparing the flame-retardant nylon 6 at least include caprolactam, 6-aminocaproic acid, and a carbon-based composite flame retardant.

[0045] As a preferred technical solution, the mass ratio of caprolactam, 6-aminocaproic acid, and the carbon-based composite flame retardant is 40:(0.3 - 1):(0.1 - 1), preferably 40:(0.3 - 0.5):(0.2 - 0.5), and more preferably 40:(0.37 - 0.4):(0.25 - 0.47).

[0046] The caprolactam is from BASF (China) Co., Ltd. and its specification is industrial grade.

[0047] As a preferred technical solution, the preparation method of the flame-retardant nylon 6 at least includes the following steps:

[0048] Add caprolactam and the carbon-based composite flame retardant into a container. After ultrasonic treatment, add 6-aminocaproic acid, and use the in-situ polymerization method to prepare the flame-retardant nylon 6.

[0049] As a preferred technical solution, the preparation method of the flame-retardant nylon 6 at least includes the following steps:

[0050] Step 1: Add caprolactam and the carbon-based composite flame retardant into a container. After ultrasonic treatment, add 6-aminocaproic acid, introduce nitrogen to stabilize for 30 - 45 min, turn on mechanical stirring, and control the system temperature to rise from 20 - 30 °C to 200 - 250 °C in a programmed manner, and pre-polycondense for 2 - 3 h;

[0051] Step 2: Raise the temperature to 255 - 270 °C in a programmed manner, keep the temperature constant for the post-polycondensation reaction. When the stirring speed is lower than 90 r / min, turn off the mechanical stirring, and continue the constant-temperature reaction for 1 - 3 h to obtain a composite product. During the reaction process, it is necessary to ensure that the container is in a nitrogen environment and isolated from oxygen;

[0052] Step 3: Mechanically crush the composite product and put it into distilled water, boil for 4 - 5 h, and change the distilled water every 1 - 2 h during this period to obtain a semi-finished product;

[0053] Step 4: Dry the semi-finished product to obtain the flame-retardant nylon 6.

[0054] As a preferred technical solution, the temperature of the ultrasonic treatment in Step 1 is 90 - 110 °C, and the time is 0.5 - 2 h.

[0055] As a preferred technical solution, the rotation speed of the mechanical stirring in Step 1 is 120 - 170 r / min.

[0056] As a preferred technical solution, the heating rate of the programmed temperature rise in step 1 is 2-3 °C / min, preferably 2.5 °C / min.

[0057] As a preferred technical solution, the heating rate of the programmed temperature rise in step 3 is 5-8 °C / min, preferably 6 °C / min.

[0058] As a preferred technical solution, the drying in step 4 is specifically as follows: the semi-finished product is dried in a forced air drying oven at 70-90 °C for 1-3 h, and then transferred to a vacuum drying oven at 100-120 °C for drying for 12-24 h.

[0059] The flame-retardant nylon 6 provided by the present invention introduces a carbon-based composite flame retardant through in-situ polymerization, fully exerts the synergistic effect of iron oxide and cyanuric chloride derivatives, solves the problem of insufficient dispersibility of the carbon nanotube flame retardant, eliminates the negative effect of carbon nanotubes promoting the spread of fire, enables the flame-retardant nylon 6 material to reach the level of being difficult to burn, the flame retardant grade reaches HB level, reduces the speed of fire spread, provides more sufficient escape and rescue time in case of fire, and protects life and property safety.

[0060] Beneficial effects

[0061] 1. The present invention uses carbon nanotubes as the main flame retardant, constructs a composite flame retardant with other flame retardant components by chemical methods, and develops a nylon 6 material with comprehensive flame retardancy and difficult spread by in-situ polymerization method, reducing the risk of fire generation and spread, and having extremely high market application and promotion value.

[0062] 2. The present invention prepares a carbon-based composite catalyst with carbon nanotubes as the carbon-based main body and metal oxides and triazine-based flame retardant groups containing Schiff base as synergistic components by using amino-functionalized metal oxides modified carbon nanotubes, compounds containing triazine-based flame retardant groups, p-hydroxybenzaldehyde, and p-aminobenzoic acid as raw materials to ensure the subsequent application effect.

[0063] 3. The present invention uses iron oxide and cyanuric chloride derivatives containing Schiff base flame retardant groups as synergistic components. The synergistic components are respectively carried with hydroxyl or carboxyl functional groups, reducing the surface inertness of carbon nanotubes, improving the dispersibility of carbon nanotubes in polymers. At the same time, the dicarboxyl groups can participate in the polymerization reaction, further improving the compatibility between carbon nanotubes and nylon 6 materials, solving the defect of unstable flame retardancy efficiency caused by insufficient dispersibility of carbon nanotubes, and reducing the influence of the flame retardant on the mechanical properties of nylon 6.

[0064] 4. The carbon-based composite flame retardant provided by the present invention combines multiple flame retardant elements such as carbon, nitrogen, silicon, and iron into one, achieving double flame retardancy in the condensed phase and the gas phase. Especially in the condensed phase, the voids of the carbon nanotube network structure are filled with carbon particles catalyzed by iron oxide on the surface, enhancing the continuity and density of the carbon layer, enabling nylon 6 to achieve the effect of zero melt dripping during combustion, preventing the spread of melt droplets that serve as an ignition heat source, and preventing the spread of fire.

[0065] 5. The flame-retardant nylon 6 provided by the present invention introduces a carbon-based composite flame retardant through in-situ polymerization, giving full play to the synergistic effect of iron oxide and cyanuric chloride derivatives, solving the problem of insufficient dispersion of carbon nanotube flame retardants and eliminating the negative effect of carbon nanotubes promoting the spread of fire, enabling the flame-retardant nylon 6 material to reach the level of flame retardancy and the flame retardant grade to reach HB, reducing the speed of fire spread, providing more sufficient escape and rescue time in case of fire, and protecting life and property safety. Brief Description of the Drawings

[0066] Figure 1 It is a schematic structural diagram of the carbon-based composite flame retardant prepared in the embodiment.

[0067] Figure 2 It is a TEM characterization diagram of amino-functionalized metal oxide modified carbon nanotubes. Detailed Description of the Embodiments

[0068] Example 1

[0069] See Figure 1 , on the one hand, Example 1 of the present invention provides a carbon-based composite flame retardant, and its preparation raw materials include: amino-functionalized metal oxide modified carbon nanotubes, compounds containing triazine-based flame retardant groups, p-hydroxybenzaldehyde, and p-aminobenzoic acid.

[0070] See Figure 2 , the amino-functionalized metal oxide modified carbon nanotubes simultaneously meet the following two conditions:

[0071] (1) Metal oxide is filled inside the carbon nanotubes;

[0072] (2) Metal oxide is loaded on the surface of the carbon nanotubes;

[0073] Through the TEM image, it can be clearly seen that the metal oxide is uniformly dispersed inside and outside the carbon nanotubes.

[0074] The preparation raw materials of the amino-functionalized metal oxide modified carbon nanotubes include an acidified and opened carbon nanotube solution, an alcohol solution of metal salt, and an amino silane solution.

[0075] The volume ratio of the acidified and opened carbon nanotube solution, the alcohol solution of metal salt, and the amino silane solution is 4:8:1.

[0076] The mass concentration of the acidified and opened carbon nanotube solution is 20 g / L.

[0077] The preparation method of the acidified and opened carbon nanotube solution comprises the following steps: ball-milling the carbon nanotubes and then performing acidification treatment with an inorganic strong acid, washing with water until the pH = 7 after cooling, and adding water to prepare the acidified and opened carbon nanotube solution.

[0078] The average tube diameter of the carbon nanotubes is 10 - 25 nm, the model is the FT9000 series powder, and they are sourced from Jiangsu Tiannai Technology Co., Ltd.

[0079] The instrument for ball-milling is a ball mill, and the parameter settings of the ball mill include: rotation speed 200 rpm, 5 min / cycle, and forward and reverse ball-milling time 30 min.

[0080] The inorganic strong acid is a combination of concentrated sulfuric acid (AR. concentration ≥ 99.0%) and nitric acid (AR. concentration 65.0% - 68.0%); the volume ratio of the concentrated sulfuric acid to the nitric acid is 3:1.

[0081] The acidification treatment is specifically: putting 4 g of the ball-milled carbon nanotubes into 500 mL of the inorganic strong acid, and stirring and reacting at 70 °C for 4 h.

[0082] The washing is specifically: washing with deionized water at 4 °C until the pH = 7.

[0083] The alcoholic solution of the metal salt includes a metal salt and an alcohol solvent, and the mass concentration of the alcoholic solution of the metal salt is 18 g / L.

[0084] The metal salt is a ferric nitrate salt, and the metal salt is ferric nitrate nonahydrate.

[0085] The alcohol solvent is absolute ethanol.

[0086] The amino silane solution includes an amino silane and an ethanol aqueous solution.

[0087] The amino silane is KH550 (γ-aminopropyltriethoxysilane).

[0088] The mass concentration of the ethanol aqueous solution is 95%.

[0089] The preparation method of the amino-functionalized metal oxide modified carbon nanotubes comprises the following steps: adding the acidified and opened carbon nanotube solution into the alcohol solution of the metal salt, heating to 50 °C, ultrasonicating for 1 h under mechanical stirring, naturally drying for 12 h, then putting into a vacuum drying oven at 60 °C and 19 kPa for vacuum drying. The vacuum-dried sample is transferred to a muffle furnace, heated to 400 °C under nitrogen protection at a heating rate of 3 °C / min, and kept for 3 h. After cooling to 25 °C, it is put into the amino-silane solution, heated to 120 °C, and reacted for 2 h under nitrogen atmosphere, then cooled, filtered, and dried at 60 °C to constant weight, thus obtaining the amino-functionalized metal oxide modified carbon nanotubes.

[0090] The rotation speed of the mechanical stirring is 350 rpm, and the ultrasonic frequency is 45 Hz.

[0091] The compound containing triazine-based flame retardant groups is cyanuric chloride.

[0092] The preparation method of the carbon-based composite flame retardant comprises the following steps:

[0093] (1) Mixing 1.5 g of the amino-functionalized metal oxide modified carbon nanotubes with 180 mL of organic solvent A to obtain solution A; mixing 0.75 g of the compound containing triazine-based flame retardant groups with 30 mL of organic solvent B to obtain solution B; dropping solution B into solution A, and simultaneously dropping 30 wt% sodium hydroxide aqueous solution to keep the pH of the reaction system at 6.0, controlling the temperature of the reaction system at 4 °C, and stirring and reacting for 2 h;

[0094] (2) Mixing 1 g of p-hydroxybenzaldehyde with 40 mL of organic solvent C to obtain solution C; heating the reaction system in step (1) to 40 °C, dropping 20 mL of solution C, and simultaneously dropping 30 wt% sodium hydroxide aqueous solution to keep the pH of the reaction system at 6.5, stirring and reacting for 2 h; continuing to heat to 70 °C, dropping 20 mL of solution C, and simultaneously dropping 10 wt% sodium hydroxide aqueous solution to keep the pH of the reaction system at 7.0, stirring and reacting for 4 h to obtain a mixture. After the mixture is cooled, filtered, washed, and vacuum dried, aldehyde-group-functionalized iron oxide modified carbon nanotubes are obtained;

[0095] (3) Dispensing 3.6 g of the aldehyde-group-functionalized iron oxide modified carbon nanotubes and 1.2 g of p-aminobenzoic acid in 100 mL of dioxane and 120 mL of dioxane respectively to obtain the aldehyde-group-functionalized iron oxide modified carbon nanotube solution and the p-aminobenzoic acid solution. After mixing the aldehyde-group-functionalized iron oxide modified carbon nanotube solution and the p-aminobenzoic acid solution, carrying out a heating reaction, washing, suction filtration, and drying to obtain the carbon-based composite flame retardant.

[0096] The organic solvent A, organic solvent B, and organic solvent C are all acetone.

[0097] On the other hand, Embodiment 1 of the present invention provides a flame-retardant nylon 6 prepared by in-situ polymerization of a carbon-based composite flame retardant. The raw materials for preparing the flame-retardant nylon 6 include caprolactam, 6-aminocaproic acid, and a carbon-based composite flame retardant.

[0098] The mass ratio of the caprolactam, 6-aminocaproic acid, and the carbon-based composite flame retardant is 40:0.4:0.47.

[0099] The caprolactam is from BASF (China) Co., Ltd. and its specification is industrial grade.

[0100] The preparation method of the flame-retardant nylon 6 includes the following steps:

[0101] Step 1: Add caprolactam and the carbon-based composite flame retardant into a container. After ultrasonic treatment, add 6-aminocaproic acid, introduce nitrogen to stabilize for 45 min, turn on mechanical stirring, and control the system temperature to be programmed from 25°C to 220°C for pre-polycondensation for 2.5 h.

[0102] Step 2: Program the temperature to 265°C and keep it at a constant temperature for post-polycondensation reaction. After constant-temperature reaction for 3.4 h, turn off mechanical stirring and continue the constant-temperature reaction for 2 h to obtain a composite product. During the reaction process, it is necessary to ensure that the container is in a nitrogen environment and is isolated from oxygen.

[0103] Step 3: Mechanically crush the composite product and put it into distilled water, boil it for 4.5 h, and change the distilled water every 1.5 h to obtain a semi-finished product.

[0104] Step 4: Dry the semi-finished product to obtain the flame-retardant nylon 6.

[0105] The temperature of the ultrasonic treatment in Step 1 is 100°C and the time is 1 h.

[0106] The rotation speed of the mechanical stirring in Step 1 is 150 r / min.

[0107] The rate of programmed temperature increase in Step 1 is 2.5°C / min.

[0108] The rate of programmed temperature increase in Step 3 is 6°C / min.

[0109] The drying in Step 4 is specifically as follows: Dry the semi-finished product in a forced-air drying oven at 80°C for 2 h, and then transfer it to a vacuum drying oven at 110°C for drying for 16 h.

[0110] Embodiment 2

[0111] Example 2 of the present invention provides a carbon-based composite flame retardant and flame-retardant nylon 6 prepared by in-situ polymerization thereof. The specific implementation manner is the same as that of Example 1, except that the mass ratio of caprolactam, 6-aminocaproic acid, and carbon-based composite flame retardant is 40:0.37:0.25; the preparation method of the flame-retardant nylon 6 includes the following steps:

[0112] Step 1: Add caprolactam and carbon-based composite flame retardant into a container. After ultrasonic treatment, add 6-aminocaproic acid, introduce nitrogen to stabilize for 40 min, turn on mechanical stirring, and control the system temperature to be programmed from 25 °C to 220 °C for pre-polycondensation for 2.5 h.

[0113] Step 2: Program the temperature to 265 °C and keep it at a constant temperature for post-polycondensation reaction. After 3.1 h of constant-temperature reaction, turn off mechanical stirring and continue the constant-temperature reaction for 2 h to obtain a composite product. During the reaction process, it is necessary to ensure that the container is in a nitrogen environment and isolated from oxygen.

[0114] Step 3: Mechanically crush the composite product and put it into distilled water, boil it for 4.5 h, and change the distilled water every 1.5 h during this period to obtain a semi-finished product.

[0115] Step 4: Dry the semi-finished product to obtain flame-retardant nylon 6.

[0116] The rotation speed of the mechanical stirring in Step 1 is 140 r / min.

[0117] Example 3

[0118] Example 3 of the present invention provides a carbon-based composite flame retardant and flame-retardant nylon 6 prepared by in-situ polymerization thereof. The specific implementation manner is the same as that of Example 1, except that the mass concentration of the metal salt alcohol solution is 32 g / L, the mass of the amino-functionalized metal oxide modified carbon nanotubes in the preparation method of the carbon-based composite flame retardant is replaced with 1.8 g, and the preparation method of the flame-retardant nylon 6 includes the following steps:

[0119] Step 1: Add caprolactam and carbon-based composite flame retardant into a container. After ultrasonic treatment, add 6-aminocaproic acid, introduce nitrogen to stabilize for 40 min, turn on mechanical stirring, and control the system temperature to be programmed from 25 °C to 220 °C for pre-polycondensation for 2.5 h.

[0120] Step 2: Program the temperature to 265 °C and keep it at a constant temperature for post-polycondensation reaction. After 3.5 h of constant-temperature reaction, turn off mechanical stirring and continue the constant-temperature reaction for 2 h to obtain a composite product. During the reaction process, it is necessary to ensure that the container is in a nitrogen environment and isolated from oxygen.

[0121] Step 3: Mechanically crush the composite product and put it into distilled water, boil it for 4.5 h, and change the distilled water every 1.5 h during this period to obtain a semi-finished product.

[0122] Step 4: After drying the semi-finished product, flame-retardant nylon 6 is obtained.

[0123] In step 1, the rotation speed of mechanical stirring is 155 r / min.

[0124] Example 4

[0125] Example 4 of the present invention provides a carbon-based composite flame retardant and flame-retardant nylon 6 prepared by in-situ polymerization thereof. The specific implementation manner is the same as that of Example 1, except that the mass concentration of the metal salt alcohol solution is 32 g / L, the mass of the amino-functionalized metal oxide modified carbon nanotubes in the preparation method of the carbon-based composite flame retardant is replaced by 1.8 g, and the mass ratio of caprolactam, 6-aminocaproic acid, and the carbon-based composite flame retardant is 40:0.37:0.33; The preparation method of the flame-retardant nylon 6 includes the following steps:

[0126] Step 1: Add caprolactam and the carbon-based composite flame retardant into a container, after ultrasonic treatment, add 6-aminocaproic acid, introduce nitrogen to stabilize for 40 min, turn on mechanical stirring, and control the system temperature to be programmed from 25 °C to 220 °C for pre-polycondensation for 2.5 h;

[0127] Step 2: Program the temperature to 265 °C, keep it at a constant temperature for post-polycondensation reaction. After 3.0 h of constant temperature reaction, turn off mechanical stirring, and continue the constant temperature reaction for 2 h to obtain a composite product. During the reaction process, it is necessary to ensure that the container is in a nitrogen environment and isolated from oxygen.

[0128] Step 3: Mechanically crush the composite product and put it into distilled water, boil it for 4.5 h, and change the distilled water every 1.5 h to obtain a semi-finished product.

[0129] Step 4: After drying the semi-finished product, flame-retardant nylon 6 is obtained.

[0130] In step 1, the rotation speed of mechanical stirring is 165 r / min.

[0131] Comparative Example 1

[0132] Comparative Example 1 of the present invention provides a preparation method of ordinary nylon, including the following steps:

[0133] Step 1: Add caprolactam into a container, add 6-aminocaproic acid, introduce nitrogen to stabilize for 40 min, turn on mechanical stirring, and control the system temperature to be programmed from 25 °C to 220 °C for pre-polycondensation for 2.5 h;

[0134] Step 2: Program the temperature to 265 °C, keep it at a constant temperature for post-polycondensation reaction. After 3.0 h of constant temperature reaction, turn off mechanical stirring, and continue the constant temperature reaction for 2 h to obtain a composite product. During the reaction process, it is necessary to ensure that the container is in a nitrogen environment and isolated from oxygen.

[0135] Step 3: Mechanically crush the composite product and put it into distilled water, boil it for 4.5 h, and replace the distilled water every 1.5 h during boiling to obtain a semi-finished product;

[0136] Step 4: Dry the semi-finished product to obtain the flame-retardant nylon 6.

[0137] The rotation speed of the mechanical stirring in Step 1 is 165 r / min.

[0138] The heating rate of the programmed temperature rise in Step 1 is 2.5 °C / min.

[0139] The heating rate of the programmed temperature rise in Step 3 is 6 °C / min.

[0140] The drying in Step 4 is specifically as follows: Dry the semi-finished product in a forced-air drying oven at 80 °C for 2 h, and then transfer it to a vacuum drying oven at 110 °C and dry it for 16 h.

[0141] Comparative Example 2

[0142] Comparative Example 2 of the present invention provides a preparation method of flame-retardant nylon 6 modified with ordinary carbon nanotubes, including the following steps:

[0143] Step 1: Put caprolactam and carbon nanotubes into a container, after ultrasonic treatment, add 6-aminocaproic acid, introduce nitrogen to stabilize for 40 min, turn on mechanical stirring, and control the temperature of the system to rise from 25 °C to 220 °C by programmed temperature rise, and pre-polycondense for 2.5 h;

[0144] Step 2: Raise the temperature to 265 °C by programmed temperature rise, keep the temperature constant for the post-polycondensation reaction, turn off the mechanical stirring after the constant-temperature reaction for 3.0 h, and continue the constant-temperature reaction for 2 h to obtain a composite product. During the reaction process, it is necessary to ensure that the container is in a nitrogen environment and isolated from oxygen.

[0145] Step 3: Mechanically crush the composite product and put it into distilled water, boil it for 4.5 h, and replace the distilled water every 1.5 h during boiling to obtain a semi-finished product.

[0146] Step 4: Dry the semi-finished product to obtain the flame-retardant nylon 6.

[0147] The temperature of the ultrasonic treatment in Step 1 is 100 °C and the time is 1 h.

[0148] The rotation speed of the mechanical stirring in Step 1 is 165 r / min.

[0149] The heating rate of the programmed temperature rise in Step 1 is 2.5 °C / min.

[0150] The heating rate of the programmed temperature rise in Step 3 is 6 °C / min.

[0151] The drying in step 4 is specifically as follows: The semi-finished product is dried in a forced-air drying oven at 80°C for 2 h, and then transferred to a vacuum drying oven at 110°C for 16 h.

[0152] Comparative Example 3

[0153] Comparative Example 3 of the present invention provides a carbon-based composite flame retardant and flame-retardant nylon 6 prepared by in-situ polymerization thereof. The specific implementation manner is the same as that of Example 4, except that the amino-functionalized metal oxide modified carbon nanotubes are replaced by amino-functionalized carbon nanotubes. The preparation method of the amino-functionalized carbon nanotubes includes the following steps:

[0154] Step 1: Put 4 g of ball-milled carbon nanotubes into 500 mL of inorganic strong acid, stir and react at 60°C for 4 h, wash with deionized water at 4°C until pH = 7, add water to prepare an acidified and opened carbon nanotube solution, and the mass concentration of the acidified and opened carbon nanotube solution is 20 g / L.

[0155] Step 2: Put 6.4 g of acidified carbon nanotubes into 200 mL of ethanol aqueous solution, add KH550, heat up to 120°C and react under a nitrogen atmosphere for 2 h, cool and filter, and dry at 60°C to constant weight to obtain amino-functionalized carbon nanotubes.

[0156] Comparative Example 4

[0157] Comparative Example 4 of the present invention provides a carbon-based composite flame retardant and flame-retardant nylon 6 prepared by in-situ polymerization thereof. The specific implementation manner is the same as that of Example 4, except that the raw materials for preparing the carbon-based composite flame retardant include: amino-functionalized metal oxide modified carbon nanotubes, p-aminobenzoic acid;

[0158] The preparation method of the carbon-based composite flame retardant includes the following steps: Disperse 3.6 g of amino-functionalized metal oxide modified carbon nanotubes and 1.2 g of p-aminobenzoic acid in 100 mL of dioxane and 120 mL of dioxane respectively to obtain an aldehyde-functionalized iron oxide modified carbon nanotube solution and a p-aminobenzoic acid solution. Mix the aldehyde-functionalized iron oxide modified carbon nanotube solution and the p-aminobenzoic acid solution, carry out a heating reaction, wash, filter by suction, and dry to obtain the carbon-based composite flame retardant.

[0159] The mass ratio of the amino-functionalized metal oxide modified carbon nanotubes to p-aminobenzoic acid is 3:1.

[0160] Performance test method

[0161] The flame-retardant nylon 6 provided in the examples and comparative examples is tested as follows. The test results are shown in Table 1.

[0162] (1)Mechanical properties: The dried nylon 6 chips at 125 °C in vacuum were injection-molded into standard specimens according to the test standard of ISO527-1:2012, and the tensile strength and elongation at break were tested by an electronic universal material testing machine.

[0163] (2)Burning rate: The dried nylon 6 chips in vacuum were injection-molded into standard specimens with dimensions of 128 mm × 13.2 mm × 3.0 mm for testing according to the test standard of GB / T2408-2008.

[0164] (3)Oxygen index test: The dried nylon 6 chips in vacuum were injection-molded into standard specimens with dimensions of 120 mm × 10 mm × 4 mm for testing according to the test standard of GB / T2406.2-2009.

[0165] Table 1

[0166]

[0167] As can be seen from Table 1 above: In Comparative Examples 3 and 4, the flame retardant CNTs were modified separately with transition metal oxide ferric oxide or triazine-based flame retardant groups to prepare flame retardants for preparing flame retardant nylon 6. It was judged by the limiting oxygen index that neither of them reached the level of flame-retardant materials. However, in Examples 1 to 4, after the carbon nanotubes were co-modified with transition metal oxides and triazine-based flame retardants, the limiting oxygen indices obtained through the test method in the standard GBT 2406.2-2009 "Plastics - Determination of burning behavior by the oxygen index method - Part 2: Ambient temperature test" were all greater than 32. Generally, it is considered that materials with a limiting oxygen index greater than 32 are flame-retardant materials. Therefore, ferric oxide, cyanuric chloride derivatives and carbon nanotubes have a synergistic effect during the flame retardant process, making the flame retardant effect of nylon 6 reach the level of flame-retardant materials.

[0168] The burning rates of the flame retardant nylon 6 in Examples 1 to 4 were reduced by 58.6%, 51.7%, 69.0%, and 55.2% respectively compared with that of the ordinary nylon 6 in Comparative Example 1. While in Comparative Example 2 where carbon nanotubes were used alone for flame retardant modification of nylon 6, the burning rate increased by 7% compared with that of the ordinary nylon 6 in Comparative Example 1. This shows that the flame retardant prepared by the present invention eliminates the speed at which carbon nanotubes promote the spread of the fire of nylon 6, and there is no molten dripping but greatly reduces the spread speed of the flame, which greatly curbs the spread of the fire when nylon 6 burns.

Claims

1. A carbon-based composite flame retardant, characterized in that, The raw materials for its preparation include: amino-functionalized metal oxide modified carbon nanotubes, compounds containing triazine-based flame retardant groups, p-hydroxybenzaldehyde, p-aminobenzoic acid. The compound containing triazine-based flame retardant groups is cyanuric chloride. The raw materials for the preparation of the amino-functionalized metal oxide modified carbon nanotubes include an acid-treated and opened carbon nanotube solution, an alcoholic solution of metal salt, and an amino-silane solution. Among them, the amino-functionalized metal oxide modified carbon nanotubes meet the following two conditions: (1) Metal oxides are filled inside the carbon nanotubes; (2) Metal oxides are loaded on the surface of the carbon nanotubes. The preparation method of the acid-treated and opened carbon nanotube solution includes at least the following steps: ball-milling the carbon nanotubes and then performing acidification treatment with inorganic strong acid, washing to pH = 6.5 - 7.5 after cooling, and adding water to prepare the acid-treated and opened carbon nanotube solution; The alcoholic solution of metal salt includes at least metal salt and an alcohol solvent. The metal salt is ferric nitrate nonahydrate, and the alcohol solvent is absolute ethanol; The amino-silane solution includes at least amino-silane and an ethanol aqueous solution; The average diameter of the carbon nanotubes is 10 - 25 nm; The preparation method of the amino-functionalized metal oxide modified carbon nanotubes includes the following steps: adding the acid-treated and opened carbon nanotube solution to the alcoholic solution of metal salt, heating to 40 - 60 °C, ultrasonicating for 0.5 - 2 h under mechanical stirring, naturally drying, and then placing in a vacuum drying oven at 50 - 70 °C for vacuum drying. After vacuum drying, the sample is heated to 300 - 500 °C under nitrogen protection and maintained for 3 - 5 h; After cooling to 20 - 30 °C, it is placed in the amino-silane solution, heated to 100 - 150 °C, and reacted for 1 - 3 h in a nitrogen atmosphere, cooled and filtered, and dried to constant weight at 50 - 70 °C to obtain the amino-functionalized metal oxide modified carbon nanotubes; The preparation method of the carbon-based composite flame retardant includes the following steps: (1) Mixing the amino-functionalized metal oxide modified carbon nanotubes with acetone to obtain solution A; Mixing the compound containing triazine-based flame retardant groups with acetone to obtain solution B; Adding solution B dropwise to solution A, while adding an aqueous sodium hydroxide solution to maintain the pH of the reaction system at 5.0 - 7.0, controlling the temperature of the reaction system at 0 - 5 °C, and stirring and reacting for 1 - 3 h; (2) Mixing p-hydroxybenzaldehyde with acetone to obtain solution C; Heating the reaction system in step (1) to 30 - 50 °C, adding solution C dropwise, while adding an alkaline solution to maintain the pH of the reaction system at 6.0 - 7.0, and stirring and reacting for 1 - 3 h; Continuing to heat to 60 - 80 °C, adding solution C dropwise, while adding an alkaline solution to maintain the pH of the reaction system at 7.0 - 7.5, and stirring and reacting for 3 - 5 h to obtain a mixture. After the mixture is cooled, filtered, washed, and vacuum dried, aldehyde-group-functionalized iron(III) oxide modified carbon nanotubes are obtained; (3) Dispersing the aldehyde-group-functionalized iron(III) oxide modified carbon nanotubes and p-aminobenzoic acid in dioxane respectively to obtain an aldehyde-group-functionalized iron(III) oxide modified carbon nanotube solution and a p-aminobenzoic acid solution. After mixing the aldehyde-group-functionalized iron(III) oxide modified carbon nanotube solution and the p-aminobenzoic acid solution, heating reaction is carried out, and after washing, suction filtration, and drying, the carbon-based composite flame retardant is obtained.

2. The carbon-based composite flame retardant according to claim 1, wherein The volume ratio of the acidified and opened carbon nanotube solution, the alcoholic solution of metal salt, and the amino silane solution is 4:8:

1.

3. The carbon-based composite flame retardant according to claim 1, wherein The mass concentration of the alcoholic solution of metal salt is 18 - 32 g / L; the mass concentration of the acidified and opened carbon nanotube solution is 20 g / L.

4. The carbon-based composite flame retardant according to claim 1, wherein The mass ratio of the amino-functionalized metal oxide modified carbon nanotubes, the compound containing triazine-based flame retardant groups, and p-hydroxybenzaldehyde is (6 - 7.2):3:

4.

5. The carbon-based composite flame retardant according to claim 1, wherein The mass ratio of the aldehyde-functionalized iron(III) oxide modified carbon nanotubes and p-aminobenzoic acid is 3:

1.

6. A flame-retardant nylon 6 prepared by in-situ polymerization of the carbon-based composite flame retardant according to any one of claims 1-5, characterized in that, The raw materials for preparing the flame-retardant nylon 6 at least include caprolactam, 6-aminocaproic acid, and the carbon-based composite flame retardant.

7. The flame-retardant nylon 6 prepared by in-situ polymerization of the carbon-based composite flame retardant according to claim 6, characterized in that, The mass ratio of caprolactam, 6-aminocaproic acid, and the carbon-based composite flame retardant is 40:(0.37 - 0.4):(0.25 - 0.47).

8. The flame-retardant nylon 6 prepared by in-situ polymerization of the carbon-based composite flame retardant according to claim 7, wherein, The preparation method of the flame-retardant nylon 6 includes the following steps: Step 1, Add caprolactam and the carbon-based composite flame retardant into a container, after ultrasonic treatment, add 6-aminocaproic acid, introduce nitrogen to stabilize for 30 - 45 min, turn on mechanical stirring, and control the system temperature to be programmed from 20 - 30 °C to 200 - 250 °C for pre-polycondensation for 2 - 3 h; Step 2, Program the temperature to 255 - 270 °C, keep the temperature constant for post-polycondensation reaction. When the stirring speed is lower than 90 r / min, turn off the mechanical stirring and continue the constant-temperature reaction for 1 - 3 h to obtain the composite product. During the reaction process, it is necessary to ensure that the container is in a nitrogen environment and isolated from oxygen; Step 3, Mechanically crush the composite product and put it into distilled water, boil for 4 - 5 h, and change the distilled water every 1 - 2 h during this period to obtain the semi-finished product; Step 4, Dry the semi-finished product to obtain the flame-retardant nylon 6.

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