Permanent antistatic PA composite material and preparation method thereof

Abstract

The invention relates to a permanent antistatic PA composite material and a preparation method thereof, and belongs to the technical field of high polymer materials. The permanent antistatic PA composite material comprises the following components in parts by weight: 70-90 parts of PA resin, 30-60 parts of polyethylene, 5-15 parts of polythiophene, 1-5 parts of a modified antistatic agent, 1-5 parts of a modified flame retardant, 1-3 parts of a flexibilizer, 1-3 parts of a dispersant and 1-3 parts of a lubricant, a compound containing an alkanolamide bond in the modified antistatic agent forms a conductive layer on the surface of the material, the resistivity is reduced, and the pre-product enhances the hydrophilicity of the material and accelerates the transfer and dissipation of charges; diphenyl chlorophosphate in the modified flame retardant forms an expanded carbon layer in the combustion process, absorbs heat, dilutes combustible gas and isolates flames, and cooperates with the phosphorus-nitrogen flame retardant to reinforce the carbon layer, so that the flame retardant property of the material is remarkably improved; the permanent antistatic PA composite material prepared by the invention not only has a good antistatic effect, but also has an excellent flame retardant effect.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and particularly relates to a permanent antistatic PA composite material and a preparation method thereof. Background Art

[0002] PA (nylon), as an important engineering plastic, occupies a dominant position in the market due to its excellent performance and is widely used in automobiles, aircraft, electronics, petrochemicals, medical treatment, textiles, packaging, transportation and other fields.

[0003] However, nylon engineering plastics tend to accumulate static electricity during use, which is difficult to eliminate. This not only causes the plastic to absorb dust from the air, affecting its appearance, but can also damage sensitive components within electronic devices during the plastic manufacturing process. Furthermore, the accumulation of static electricity can cause safety hazards such as electric shock, equipment failure, and even fire. Furthermore, nylon materials are inherently flammable. In the event of a fire, they not only burn quickly but also release a large amount of heat, making it difficult to extinguish themselves. This is accompanied by billowing smoke, posing a significant threat to the safety of personnel and public property, and posing a significant risk to social stability and security. Therefore, the development of permanent antistatic PA composite materials with excellent performance is of great practical significance and application value. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a permanent antistatic PA composite material and a preparation method thereof.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A permanent antistatic PA composite material and a preparation method thereof, comprising the following raw materials in parts by weight: 70-90 parts of PA resin, 30-60 parts of polyethylene, 5-15 parts of polythiophene, 1-5 parts of modified antistatic agent, 1-5 parts of modified flame retardant, 1-3 parts of toughening agent, 1-3 parts of dispersant, and 1-3 parts of lubricant; The toughening agent is EVA-g-MAH; The dispersant is talc; The lubricant is paraffin.

[0006] The modified antistatic agent is prepared by the following method: Step A1: Mix lauric acid, diethanolamine, and sodium methoxide evenly, stir under nitrogen for 5 minutes, slowly heat to 170-180°C, react for 2-3 hours, filter, wash, and dry to obtain a compound; Furthermore, the mass ratio of lauric acid, diethanolamine, and sodium methoxide is 0.01-0.03 mol: 0.01-0.03 mol: 0.05-0.15 g; First, the amino group of diethanolamine reacts with the carboxyl group of lauric acid to prepare the compound; Step A2: Mix the compound, 4-chloromethylstyrene, and triethylamine, raise the temperature to 70°C under a nitrogen atmosphere, and react for 12 hours. After the system is cooled to 40°C, wash, filter, and vacuum dry at 40°C to obtain a pre-product; Furthermore, the ratio of the compound, 4-chloromethylstyrene, and triethylamine is 0.01-0.03 mol: 0.01-0.03 mol: 2 mL; Secondly, the chlorine atom of 4-chloromethylstyrene reacts with the amino group of the compound to form a quaternary ammonium salt to obtain a positively charged pre-product; Step A3: The pre-product, N-vinyl pyrrolidone, glycidyl methacrylate and acetonitrile were mixed uniformly, stirred for 10 minutes, and then azobisisobutyronitrile was added. The mixture was stirred for 30 minutes and reacted at 70°C for 3 hours. After the reaction was completed, the mixture was rotary evaporated and vacuum dried at 50°C for 12 hours to obtain a modified antistatic agent. Furthermore, the ratio of the pre-product, N-vinyl pyrrolidone, glycidyl methacrylate, acetonitrile, and azobisisobutyronitrile is 0.01-0.03 mol: 0.01-0.03 mol: 0.01-0.03 mol: 2 mL: 0.25-0.35 g; Finally, the modified antistatic agent was prepared by copolymerizing the carbon-carbon double bond of the pre-product, N-vinyl pyrrolidone and glycidyl methacrylate.

[0007] The modified flame retardant is prepared by the following method: Step B1: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and anhydrous ethanol were mixed uniformly, placed in an oil bath, and heated to 85°C while stirring. Then, formaldehyde solution was added dropwise. After reacting for 8 hours, the mixture was cooled to room temperature, filtered, washed, and dried in vacuo at 80°C to obtain an intermediate. Furthermore, the dosage ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, anhydrous ethanol, and formaldehyde solution is 0.01-0.03 mol:40-60 mL:0.01-0.03 mol, and the volume ratio of formaldehyde to water in the formaldehyde solution is 2:5; First, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is reacted with formaldehyde to prepare an intermediate; Step B2: Under nitrogen protection, the intermediate and acetonitrile were mixed uniformly, stirred in an ice-water bath for 6 hours, triethylamine was added, and stirring was continued in an ice-water bath for 1 hour, and then diphenyl chlorophosphate was added. The mixture was reacted at room temperature for 12 hours, filtered, washed, distilled under reduced pressure, and dried to obtain a modified flame retardant; Furthermore, the usage ratio of the intermediate, acetonitrile, triethylamine, and diphenyl chlorophosphate is 0.01-0.03 mol: 20-30 mL: 14-20 mL: 0.01-0.03 mol; Finally, the modified flame retardant is prepared by utilizing the reaction between the hydroxyl group of the intermediate and the chlorine atom of diphenyl chlorophosphate.

[0008] A method for preparing a permanent antistatic PA composite material comprises the following steps: S1. Evenly mixing PA resin, polyethylene, polythiophene, modified antistatic agent, modified flame retardant, toughening agent, dispersant and lubricant to prepare a mixed material; S2. Add the mixed material into a twin-screw extruder and extrude and granulate to obtain a permanent antistatic PA composite material; the temperatures of each section in the twin-screw extruder are: 170-190°C in zone 1, 230-240°C in zone 2, 230-240°C in zone 3, 220-230°C in zone 4, 180-190°C in zone 5, 180-190°C in zone 6, 180-190°C in zone 7, 210-220°C in zone 8, 220-230°C for die head, and 190-350r / min for screw speed.

[0009] Beneficial effects of the present invention: The permanent antistatic PA composite material of the present invention has a good antistatic effect and also has an excellent flame retardant effect, further extending the service life.

[0010] The modified antistatic agent prepared by the present invention exhibits antistatic performance that surpasses traditional small-molecule antistatic agents by virtue of its advantages as a macromolecular polymer. In the modified antistatic agent, the compound containing an alkanolamide bond can form a conductive layer on the material surface, reducing resistivity, accelerating the dissipation of static charge, achieving an antistatic effect, and imparting lubricity to the material, thereby reducing friction and reducing static electricity generation. Simultaneously, the quaternary ammonium salt pre-product can enhance the hydrophilicity of the material and promote moisture absorption. The ions in the water film formed after moisture absorption act as a conductive medium, accelerating the transfer and dissipation of charge, and preventing static electricity from negatively impacting production and product quality. Furthermore, the polymerized N-vinyl pyrrolidone contains a hydrophilic group, and the epoxy groups in the polymerized glycidyl methacrylate can react with the hydroxyl groups in PA, enhancing intermolecular forces, improving material toughness, and forming a conductive network, further reducing surface resistivity. The quaternary ammonium salt synergistically enhances the conductive efficiency of ions on the material surface, reducing static electricity accumulation.

[0011] The diphenyl chlorophosphate in the modified flame retardant prepared by the present invention can form an expanded carbon layer during the combustion process, which can absorb heat, dilute combustible gases, isolate flames, and suppress flame spread. It synergistically strengthens the carbon layer with the phosphorus-nitrogen flame retardant, significantly improving the flame retardant properties of the material, as well as the tensile strength and smoke suppression properties. At the same time, the phosphorus element in the diphenyl chlorophosphate can form a phosphate protective layer, which decomposes to produce acidic substances such as phosphoric acid, captures free radicals in the combustion reaction, and suppresses the combustion chain reaction. In addition, the phosphorus-nitrogen flame retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, as a phosphaphenanthrene compound with high thermal stability, promotes the formation of a dense and continuous carbon layer during combustion, isolates oxygen, blocks the exchange of heat and combustible gases, enhances the flame retardant effect, and extends the service life of the material. In addition, the modified flame retardant prepared by the present invention is halogen-free, can reduce pollution to the environment and damage to the ecosystem, is harmless to human health, and achieves sustainable development. DETAILED DESCRIPTION

[0012] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0013] Example 1: A method for preparing a permanent antistatic PA composite material, comprising the following steps: S1. Weigh the raw materials by weight: 70 parts of PA resin, 30 parts of polyethylene, 5 parts of polythiophene, 1 part of modified antistatic agent, 1 part of modified flame retardant, 1 part of toughening agent, 1 part of dispersant, and 1 part of lubricant; mix the PA resin, polyethylene, polythiophene, modified antistatic agent, modified flame retardant, EVA-g-MAH, talc and paraffin to obtain a mixed material; S2. The mixture was added to a twin-screw extruder and extruded into granules to obtain a permanent antistatic PA composite material; the temperatures of each section in the twin-screw extruder were: 170° C. in zone 1, 230° C. in zone 2, 230° C. in zone 3, 220° C. in zone 4, 180° C. in zone 5, 180° C. in zone 6, 180° C. in zone 7, 210° C. in zone 8, the die head was 220° C., and the screw speed was 190 r / min; The modified antistatic agent is prepared by the following method: Step A1: 0.01 mol of lauric acid, 0.01 mol of diethanolamine, and 0.05 g of sodium methoxide were uniformly mixed, stirred under a nitrogen atmosphere for 5 minutes, slowly heated to 170° C., reacted for 2 hours, filtered, washed, and dried to obtain a compound; Step A2: Mix 0.01 mol of the compound, 0.01 mol of 4-chloromethylstyrene, and 2 mL of triethylamine. Heat to 70°C under nitrogen atmosphere and react for 12 h. Cool the system to 40°C, wash, filter, and vacuum dry at 40°C to obtain a pre-product. Step A3: 0.01 mol of the pre-product, 0.01 mol of N-vinyl pyrrolidone, 0.01 mol of glycidyl methacrylate, and 2 mL of acetonitrile were mixed uniformly, stirred for 10 min, and then 0.25 g of azobisisobutyronitrile was added. The mixture was stirred for 30 min and reacted at 70°C for 3 h. After the reaction was completed, the mixture was rotary evaporated and dried in vacuum at 50°C for 12 h to obtain a modified antistatic agent. The modified flame retardant is prepared by the following method: Step B1: Mix 0.01 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 40 mL of anhydrous ethanol, place in an oil bath, and heat to 85°C while stirring. Then, add 0.01 mol of formaldehyde solution dropwise. After reacting for 8 hours, cool to room temperature, filter, wash, and vacuum dry at 80°C to obtain an intermediate. The volume ratio of formaldehyde to water in the formaldehyde solution is 2:5. Step B2: Under nitrogen protection, 0.01 mol of the intermediate and 20 mL of acetonitrile were mixed evenly, stirred in an ice-water bath for 6 h, 14 mL of triethylamine was added, and stirring was continued in an ice-water bath for 1 h. Then 0.01 mol of diphenyl chlorophosphate was added, and the mixture was reacted at room temperature for 12 h. The mixture was filtered, washed, distilled under reduced pressure, and dried to obtain a modified flame retardant.

[0014] Example 2: A method for preparing a permanent antistatic PA composite material, comprising the following steps: S1. Weigh the raw materials by weight: 80 parts of PA resin, 45 parts of polyethylene, 10 parts of polythiophene, 3 parts of modified antistatic agent, 3 parts of modified flame retardant, 2 parts of toughening agent, 2 parts of dispersant, and 2 parts of lubricant; uniformly mix the PA resin, polyethylene, polythiophene, modified antistatic agent, modified flame retardant, EVA-g-MAH, talc and paraffin to prepare a mixed material; S2. The mixture was added to a twin-screw extruder and extruded into granules to obtain a permanent antistatic PA composite material; the temperatures of each section in the twin-screw extruder were: 180° C. in zone 1, 235° C. in zone 2, 235° C. in zone 3, 225° C. in zone 4, 185° C. in zone 5, 185° C. in zone 6, 185° C. in zone 7, 215° C. in zone 8, the die head was 225° C., and the screw speed was 220 r / min; The modified antistatic agent is prepared by the following method: Step A1: 0.02 mol of lauric acid, 0.02 mol of diethanolamine, and 0.10 g of sodium methoxide were uniformly mixed, stirred under a nitrogen atmosphere for 5 min, slowly heated to 175° C., reacted for 2.5 h, filtered, washed, and dried to obtain a compound; Step A2: 0.02 mol of the compound, 0.02 mol of 4-chloromethylstyrene, and 2 mL of triethylamine were mixed, heated to 70°C under a nitrogen atmosphere, and reacted for 12 h. The mixture was cooled to 40°C, washed, filtered, and dried in vacuo at 40°C to obtain a pre-product. Step A3: 0.02 mol of the pre-product, 0.02 mol of N-vinyl pyrrolidone, 0.02 mol of glycidyl methacrylate and 2 mL of acetonitrile were mixed evenly, stirred for 10 min, and then 0.3 g of azobisisobutyronitrile was added. The mixture was stirred for 30 min and reacted at 70°C for 3 h. After the reaction was completed, the mixture was rotary evaporated and dried in vacuum at 50°C for 12 h to obtain a modified antistatic agent. The modified flame retardant is prepared by the following method: Step B1: Mix 0.02 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 50 mL of anhydrous ethanol, place in an oil bath, and heat to 85°C while stirring. Then, add 0.02 mol of formaldehyde solution dropwise. After reacting for 8 hours, cool to room temperature, filter, wash, and vacuum dry at 80°C to obtain an intermediate. The volume ratio of formaldehyde to water in the formaldehyde solution is 2:5. Step B2: Under nitrogen protection, 0.02 mol of the intermediate and 25 mL of acetonitrile were mixed evenly, stirred in an ice-water bath for 6 h, 17 mL of triethylamine was added, and stirring was continued in an ice-water bath for 1 h. Then, 0.02 mol of diphenyl chlorophosphate was added, and the mixture was reacted at room temperature for 12 h. The mixture was filtered, washed, distilled under reduced pressure, and dried to obtain a modified flame retardant.

[0015] Example 3: A method for preparing a permanent antistatic PA composite material, comprising the following steps: S1. Weigh the raw materials by weight: 90 parts of PA resin, 60 parts of polyethylene, 15 parts of polythiophene, 5 parts of modified antistatic agent, 5 parts of modified flame retardant, 3 parts of toughening agent, 3 parts of dispersant, and 3 parts of lubricant; uniformly mix the PA resin, polyethylene, polythiophene, modified antistatic agent, modified flame retardant, EVA-g-MAH, talc and paraffin to prepare a mixed material; S2. The mixture was added to a twin-screw extruder and extruded into granules to obtain a permanent antistatic PA composite material; the temperatures of each section in the twin-screw extruder were: 190° C. in zone 1, 240° C. in zone 2, 240° C. in zone 3, 230° C. in zone 4, 190° C. in zone 5, 190° C. in zone 6, 190° C. in zone 7, 220° C. in zone 8, the die head was 230° C., and the screw speed was 350 r / min; The modified antistatic agent is prepared by the following method: Step A1: 0.03 mol of lauric acid, 0.03 mol of diethanolamine, and 0.15 g of sodium methoxide were uniformly mixed, stirred under a nitrogen atmosphere for 5 min, slowly heated to 180° C., reacted for 3 h, filtered, washed, and dried to obtain a compound; Step A2: 0.03 mol of the compound, 0.03 mol of 4-chloromethylstyrene, and 2 mL of triethylamine were mixed, heated to 70°C under a nitrogen atmosphere, and reacted for 12 h. The mixture was cooled to 40°C, washed, filtered, and dried in vacuo at 40°C to obtain a pre-product. Step A3: 0.03 mol of the pre-product, 0.03 mol of N-vinyl pyrrolidone, 0.03 mol of glycidyl methacrylate, and 2 mL of acetonitrile were mixed evenly, stirred for 10 min, and then 0.35 g of azobisisobutyronitrile was added. The mixture was stirred for 30 min and reacted at 70°C for 3 h. After the reaction was completed, the mixture was rotary evaporated and dried in vacuum at 50°C for 12 h to obtain a modified antistatic agent. The modified flame retardant is prepared by the following method: Step B1: Mix 0.03 mol of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 60 mL of anhydrous ethanol, place in an oil bath, and heat to 85°C while stirring. Then, add 0.03 mol of formaldehyde solution dropwise. After reacting for 8 hours, cool to room temperature, filter, wash, and vacuum dry at 80°C to obtain an intermediate. The volume ratio of formaldehyde to water in the formaldehyde solution is 2:5. Step B2: Under nitrogen protection, 0.03 mol of the intermediate and 30 mL of acetonitrile were mixed evenly, stirred in an ice-water bath for 6 h, 20 mL of triethylamine was added, and stirring was continued in an ice-water bath for 1 h. Then, 0.03 mol of diphenyl chlorophosphate was added, and the mixture was reacted at room temperature for 12 h. The mixture was filtered, washed, distilled under reduced pressure, and dried to obtain a modified flame retardant.

[0016] Comparative Example 1: This comparative example is a permanent antistatic PA composite material. The difference from Example 3 is that an equal amount of carbon black is used instead of the modified antistatic agent prepared in Example 3, and the rest are the same.

[0017] Comparative Example 2: This comparative example is a permanent antistatic PA composite material. The difference from Example 3 is that an equal amount of magnesium hydroxide is used instead of the modified flame retardant prepared in Example 3. The rest are the same.

[0018] Performance testing: The permanent antistatic PA composite materials prepared in Examples 1-3 and Comparative Examples 1-2 were cut into standard test sizes and tested for surface resistivity according to GB / T 1410-2006. Vertical burning performance was tested using the GB / T 2048-1996 plastics combustion performance test method. Tensile strength was tested according to GB / T 1040-2018. The test results are shown in Table 1 below: Table 1

[0019] It can be seen from the test data in Table 1 that the permanent antistatic PA composite material prepared by the present invention has a good flame retardant effect. It can also be seen from Table 1 that the permanent antistatic PA composite material prepared by the present invention has a good antistatic effect and prolongs the service life.

[0020] The above content is merely an example and explanation of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a permanent antistatic PA composite material, characterized in that: The specific steps include: S1. Weigh the raw materials by weight: 70-90 parts of PA resin, 30-60 parts of polyethylene, 5-15 parts of polythiophene, 1-5 parts of modified antistatic agent, 1-5 parts of modified flame retardant, 1-3 parts of toughening agent, 1-3 parts of dispersant, and 1-3 parts of lubricant; uniformly mix the PA resin, polyethylene, polythiophene, modified antistatic agent, modified flame retardant, toughening agent, dispersant, and lubricant to prepare a mixed material; S2. The mixture is added to a twin-screw extruder and extruded into granules to obtain a permanent antistatic PA composite material; the temperatures of each section in the twin-screw extruder are: zone 1 170-190°C, zone 2 230-240°C, zone 3 230-240°C, zone 4 220-230°C, zone 5 180-190°C, zone 6 180-190°C, zone 7 180-190°C, zone 8 210-220°C, die head 220-230°C, screw speed 190-350r / min; The modified antistatic agent is prepared by the following method: Step A1: Mix lauric acid, diethanolamine, and sodium methoxide evenly, stir under nitrogen for 5 minutes, slowly heat to 170-180°C, react for 2-3 hours, filter, wash, and dry to obtain a compound; Step A2: Mix the compound, 4-chloromethylstyrene, and triethylamine, raise the temperature to 70°C under a nitrogen atmosphere, and react for 12 hours. After the system is cooled to 40°C, wash, filter, and vacuum dry at 40°C to obtain a pre-product; Step A3: The pre-product, N-vinyl pyrrolidone, glycidyl methacrylate and acetonitrile were mixed evenly, stirred for 10 minutes, and then azobisisobutyronitrile was added, and the stirring was continued for 30 minutes. The reaction was carried out at 70°C for 3 hours. After the reaction was completed, the mixture was rotary evaporated and vacuum dried at 50°C for 12 hours to obtain a modified antistatic agent.

2. The method for preparing a permanent antistatic PA composite material according to claim 1, characterized in that: In step A1, the mass ratio of lauric acid, diethanolamine, and sodium methoxide is 0.01-0.03 mol: 0.01-0.03 mol: 0.05-0.15 g.

3. The method for preparing a permanent antistatic PA composite material according to claim 1, characterized in that: In step A2, the usage ratio of the compound, 4-chloromethylstyrene, and triethylamine is 0.01-0.03 mol: 0.01-0.03 mol: 2 mL.

4. The method for preparing a permanent antistatic PA composite material according to claim 1, characterized in that: In step A3, the usage ratio of the pre-product, N-vinyl pyrrolidone, glycidyl methacrylate, acetonitrile, and azobisisobutyronitrile is 0.01-0.03 mol: 0.01-0.03 mol: 0.01-0.03 mol: 2 mL: 0.25-0.35 g.

5. The method for preparing a permanent antistatic PA composite material according to claim 1, characterized in that: The modified flame retardant is prepared by the following method: Step B1: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and anhydrous ethanol were mixed uniformly, placed in an oil bath, and heated to 85°C while stirring. Then, formaldehyde solution was added dropwise. After reacting for 8 hours, the mixture was cooled to room temperature, filtered, washed, and dried in vacuo at 80°C to obtain an intermediate. Step B2: Under nitrogen protection, the intermediate and acetonitrile were mixed evenly, stirred in an ice-water bath for 6 hours, triethylamine was added, and stirring was continued in an ice-water bath for 1 hour. Then, diphenyl chlorophosphate was added, and the mixture was reacted at room temperature for 12 hours. The mixture was filtered, washed, distilled under reduced pressure, and dried to obtain a modified flame retardant.

6. The method for preparing a permanent antistatic PA composite material according to claim 5, characterized in that: In step B1, the usage ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, anhydrous ethanol, and formaldehyde solution is 0.01-0.03 mol:40-60 mL:0.01-0.03 mol, and the volume ratio of formaldehyde to water in the formaldehyde solution is 2:

5.

7. The method for preparing a permanent antistatic PA composite material according to claim 5, characterized in that: The usage ratio of the intermediate, acetonitrile, triethylamine, and diphenyl chlorophosphate in step B2 is 0.01-0.03 mol: 20-30 mL: 14-20 mL: 0.01-0.03 mol.

8. The method for preparing a permanent antistatic PA composite material according to claim 1, characterized in that: The toughening agent is EVA-g-MAH, the dispersant is talc, and the lubricant is paraffin.

9. A permanent antistatic PA composite material, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 8.

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