Lightweight electrically conductive fire-retardant polypropylene expanded beads, process for their preparation and use

Abstract

The application discloses a kind of light conductive flame-retardant polypropylene foaming beads in the field of polypropylene foaming material and its preparation method and application, the steps of preparation method include: taking matrix PP resin, conductive masterbatch, flame-retardant masterbatch, nucleating agent, interface compatilizer and filling agent, into stirrer, then LiNbO3 Nanowire is added, and stirring is mixed until uniform, to obtain intermediate product;Take intermediate product, and it is treated by argon plasma;Again send into screw extruder, while supercritical CO2 is added, to form homogeneous saturated system;After being discharged by mouth die, complete foaming under the influence of pressure relief, then water ring hot cutting granulation and drying, sieve, obtain immediately.The application uses argon plasma to bombard intermediate product, improves the interface bonding force of filler, improves the conductive and flame-retardant performance, and LiNbO3 Nanowire is added in raw material, local electric field is generated under ultrasonic field in the stage of extrusion homogenization, the conductive network is optimized, and the conductive performance is further improved.

Description

Technical Field

[0001] This invention relates to the field of polypropylene foam materials, specifically to a lightweight, conductive, flame-retardant polypropylene foam bead, its preparation method, and its application. Background Technology

[0002] Expanded polypropylene (EPP) beads are a high-performance closed-cell foam material with excellent impact resistance, heat resistance, thermal insulation, lightweight, and recyclability. They are widely used in automotive parts (bumper cores, headrests, toolboxes), packaging (electronic products, precision instruments), sporting goods, toys, and construction. The typical components of EPP beads include polypropylene resin, physical foaming agents (butane, CO2, and other supercritical fluids), nucleating agents (calcium carbonate, talc, silica, mica, etc.), and modifiers for desired functions (lubricants, antioxidants, light stabilizers, antistatic agents, colorants, etc.).

[0003] Among them, lightweight conductive and flame-retardant polypropylene foam beads (EPP) have important applications in high-end electronics and semiconductor fields, military and aerospace, new energy vehicles and high-end automotive electronics, medical and laboratory equipment and other fields. Existing lightweight conductive and flame-retardant polypropylene foam beads, such as the patent document with publication number CN107828134B, disclose a method for preparing highly conductive and highly flame-retardant polypropylene foam beads, which is made by mixing, screw extrusion, high pressure and high temperature treatment, and pressure release foaming of polypropylene A, conductive filler, modified inorganic flame retardant, organic flame retardant, nucleating agent masterbatch, aqueous dispersion medium, dispersant, foaming agent and other components. This existing solution has the following defects: (1) The compatibility between conductive filler, flame retardant and other components and the matrix PP resin is poor, which will affect the mechanical properties and conductive and flame-retardant properties of the final foamed material. (2) The conductive filler is randomly arranged in the homogeneous saturated system, which is not conducive to the formation of conductive network, thus leading to unsatisfactory conductivity. Summary of the Invention

[0004] The purpose of this invention is to provide a lightweight, conductive, flame-retardant polypropylene foamed bead, its preparation method, and its application. It solves the problems of unsatisfactory conductivity and flame-retardant properties of existing polypropylene foamed beads due to poor compatibility between conductive fillers, flame retardants, and the matrix PP resin, as well as the disordered arrangement of conductive fillers in a homogeneous saturated system, which is not conducive to the formation of a conductive network.

[0005] The present invention achieves the above objectives through the following technical solutions:

[0006] A method for preparing lightweight, conductive, flame-retardant polypropylene foam beads, the method comprising the following steps:

[0007] S1. Weigh the base PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer and filler according to the proportion, put them into the mixer, and then add 0.1-0.3% of LiNbO3 nanowires according to the mass of the base PP resin. Stir and mix until uniform to obtain PP foaming intermediate product.

[0008] S2. Take the intermediate product of PP foaming and treat it with argon plasma.

[0009] S3. Then, take the PP foaming intermediate product and feed it into the screw extruder. Control the feeding speed to 8-12 kg / h. At the same time, add supercritical CO2 into the screw extruder through the filling port of the extruder. Control the adding speed to 600-800 g / h. After the supercritical CO2 and the PP foaming intermediate product are mixed and melted, a homogeneous saturated system is formed.

[0010] Specifically, in the homogenization section of the screw extruder, a power of 20-32 kHz is applied perpendicular to the screw direction, with a power density of 4-5 W / cm³. 2 Ultrasonic waves are used to activate the piezoelectric effect of LiNbO3 nanowires to generate a local electric field, inducing the alignment of the conductive masterbatch.

[0011] S4. Adjust the extruder die temperature to 120-130℃ and the pressure to 10-12MPa. After the homogeneous saturated system is discharged through the die, it completes foaming under the influence of pressure relief to obtain a foamed body.

[0012] S5. After discharge, the foamed body is subjected to water ring hot cutting granulation and drying, and finally vibrated and sieved to obtain lightweight conductive flame-retardant polypropylene foamed beads.

[0013] A further improvement is made in step S1:

[0014] The conductive masterbatch is selected from one of acetylene black, nickel-plated carbon fiber, conductive furnace black, or conductive graphene.

[0015] The flame retardant masterbatch is selected from one of the following: phosphorus-nitrogen intumescent flame retardant, aluminum diethylphosphinate, melamine cyanurate, melamine polyphosphate, or organosilicon flame retardant.

[0016] The nucleating agent is selected from talc, nano-calcium carbonate, or silicon dioxide.

[0017] The interface compatibilizer is selected from one of maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyolefin elastomer, or maleic anhydride-grafted styrene elastomer.

[0018] The filler is selected from either hollow glass microspheres or hollow ceramic microspheres.

[0019] A further improvement is that, in step S1, the mass ratio of the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer and filler is 100:12-18:15-20:1-3:3-5:4-6, respectively.

[0020] A further improvement is that, in step S1, the aspect ratio of the LiNbO3 nanowires is 50-60, and the preparation steps are as follows: LiOH·H2O, Nb2O5 and KOH powders in a molar ratio of 2:1:11 are used as raw materials. The raw materials are mixed and added to deionized water accounting for 5-8 times the total mass of the raw materials. The mixture is magnetically stirred for 50-60 minutes. The stirred mixture is then poured into a reaction vessel. The reaction vessel is sealed and placed in an oven at a temperature of 145-150℃ for 6-7 days. After the reaction is completed, the white flocculent precipitate in the reaction vessel is taken out, washed and centrifuged multiple times with deionized water, and the obtained product is LiNbO3 nanowires.

[0021] A further improvement is that, in step S1, the stirring and mixing temperature is 22-26℃, the rotation speed is 300-400rpm, and the time is 4-6min.

[0022] A further improvement is that, in step S2, the power of the argon plasma treatment is 80-100W, the pressure is 40-50Pa, and the time is 80-100s.

[0023] A further improvement is that, in step S3, the screw extruder rotates at 450-480 rpm, and the screw extruder is divided into a feeding section, a melting section, a supercritical injection section, and a homogenization section, with the temperatures controlled sequentially at 160±2℃, 185±2℃, 170±2℃, and 165±2℃, and the pressures controlled sequentially at 0.8±0.2MPa, 10±1MPa, 25±1MPa, and 20±1MPa.

[0024] A further improvement is that, in step S5, the water ring temperature of the water ring hot cutting granulation is 72-78℃, the cutting speed is 3400-3600rpm, and the drying is carried out using fluidized bed hot air drying at 50-55℃.

[0025] The present invention also provides lightweight conductive flame-retardant polypropylene foam beads, which are prepared by the aforementioned preparation method.

[0026] The present invention also provides an application of the aforementioned lightweight conductive and flame-retardant polypropylene foam beads in the preparation of conductive and flame-retardant material products, such as electronic products, automotive parts, and medical devices, to leverage their lightweight, conductive, and flame-retardant properties.

[0027] The beneficial effects of this invention are as follows:

[0028] (1) In this invention, argon plasma is used to bombard the intermediate product of PP foaming, and oxygen-containing polar groups (carboxyl and hydroxyl groups) are introduced on the surface of PP, which significantly improves the interfacial bonding force of fillers (such as nickel-plated carbon fiber). At the same time, the polar groups can capture free radicals generated by combustion, thereby increasing the limiting oxygen index (LOI) and improving the flame retardant performance.

[0029] (2) The present invention adds LiNbO3 nanowires to the raw materials, which have a high Curie temperature and piezoelectric coefficient. When an ultrasonic field is applied during the extrusion homogenization stage, the piezoelectric effect of LiNbO3 can be activated to generate a local electric field, and the conductive masterbatch is subjected to the electric field lines, which helps to form a stable conductive network, thereby greatly improving the conductivity. Attached Figure Description

[0030] Figure 1 This is a scanning electron microscope image of the polypropylene foam beads prepared in Example 2 of the present invention. Detailed Implementation

[0031] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0032] I. Main Materials and Equipment

[0033] Matrix PP resin: PPB-M02 type, purchased from Yuyao Fulin Plastics Co., Ltd.;

[0034] Plasma instrument: HD-1B model, purchased from Jiangsu Changzhou Shitai Plasma Development Co., Ltd.;

[0035] Screw extruder: TSE-35A / 600-15-48, purchased from Nanjing Haisi Extrusion Equipment Co., Ltd.

[0036] II. Conducting the Experiment

[0037] Example 1

[0038] A method for preparing lightweight, conductive, flame-retardant polypropylene foam beads, the method comprising the following steps:

[0039] S1. Weigh out the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer, and filler according to the proportion, put them into a mixer, and then add 0.1% of LiNbO3 nanowires according to the mass of the matrix PP resin. Stir and mix (temperature 22℃, speed 300rpm, time 6min) until uniform to obtain PP foaming intermediate product; wherein, the conductive masterbatch is acetylene black, the flame retardant masterbatch is phosphorus nitrogen intumescent flame retardant, the nucleating agent is talc, the interface compatibilizer is maleic anhydride grafted polypropylene, and the filler is hollow glass microspheres. The mass ratio between the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer, and filler is 100:12:20:1:3:4 respectively.

[0040] The aspect ratio of the LiNbO3 nanowires is 50-60, and the preparation steps are as follows: LiOH·H2O, Nb2O5 and KOH powders with a molar ratio of 2:1:11 are taken as raw materials, the raw materials are mixed and added to deionized water accounting for 5 times the total mass of the raw materials, and magnetically stirred for 50 min. Then the stirred mixture is poured into a reaction vessel, the reaction vessel is sealed and placed in an oven at 145℃ for 7 days. After the reaction is completed, the white flocculent precipitate in the reaction vessel is taken out, washed and centrifuged multiple times with deionized water, and the product obtained is LiNbO3 nanowires.

[0041] S2. Take the intermediate product of PP foaming and treat it with argon plasma (power 80W, pressure 40Pa, time 100s).

[0042] S3. Then, the PP foaming intermediate product is fed into the screw extruder, and the feeding speed is controlled at 8 kg / h. At the same time, supercritical CO2 is added to the screw extruder through the filling port of the extruder, and the adding speed is controlled at 600 g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system.

[0043] The screw extruder rotates at 450 rpm and is divided into a feeding section, a melting section, a supercritical injection section, and a homogenization section. The temperatures are controlled at 160±2℃, 185±2℃, 170±2℃, and 165±2℃, respectively, and the pressures are controlled at 0.8±0.2MPa, 10±1MPa, 25±1MPa, and 20±1MPa, respectively.

[0044] Specifically, in the homogenization section of the screw extruder, a power of 20 kHz is applied perpendicular to the screw direction, with a power density of 4 W / cm³. 2 Ultrasonic waves are used to activate the piezoelectric effect of LiNbO3 nanowires to generate a local electric field, inducing the alignment of the conductive masterbatch.

[0045] S4. Adjust the extruder die temperature to 120℃ and the pressure to 10MPa. After the homogeneous saturated system is discharged through the die, it completes foaming under the influence of pressure relief to obtain a foamed body.

[0046] S5. The discharged foam is subjected to water ring hot cutting granulation (water ring temperature is 72℃, cutter speed is 3400rpm) and drying (fluidized bed hot air drying at 50℃), and finally vibrated and sieved to obtain lightweight conductive flame-retardant polypropylene foam beads.

[0047] Example 2

[0048] A method for preparing lightweight, conductive, flame-retardant polypropylene foam beads, the method comprising the following steps:

[0049] S1. Weigh out the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer, and filler according to the proportion, put them into a mixer, and then add 0.2% of LiNbO3 nanowires according to the mass of the matrix PP resin. Stir and mix (temperature 24℃, speed 350rpm, time 5min) until uniform to obtain PP foaming intermediate product; wherein, the conductive masterbatch is nickel-plated carbon fiber, the flame retardant masterbatch is aluminum diethylphosphinate, the nucleating agent is nano calcium carbonate, the interface compatibilizer is maleic anhydride-grafted polyolefin elastomer, and the filler is hollow ceramic microspheres. The mass ratio between the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer, and filler is 100:15:18:2:4:5 respectively.

[0050] The aspect ratio of the LiNbO3 nanowires is 50-60, and the preparation steps are as follows: LiOH·H2O, Nb2O5 and KOH powders with a molar ratio of 2:1:11 are used as raw materials. The raw materials are mixed and added to deionized water accounting for 6 times the total mass of the raw materials. The mixture is magnetically stirred for 55 minutes. The stirred mixture is then poured into a reaction vessel. The reaction vessel is sealed and placed in an oven at 148°C for 7 days. After the reaction is completed, the white flocculent precipitate in the reaction vessel is taken out and washed and centrifuged multiple times with deionized water. The product obtained is LiNbO3 nanowires.

[0051] S2. Take the intermediate product of PP foaming and treat it with argon plasma (power 90W, pressure 45Pa, time 90s).

[0052] S3. Then, the PP foaming intermediate product is fed into the screw extruder, and the feeding speed is controlled at 10 kg / h. At the same time, supercritical CO2 is added to the screw extruder through the filling port of the extruder, and the adding speed is controlled at 700 g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system.

[0053] The screw extruder rotates at 460 rpm and is divided into a feeding section, a melting section, a supercritical injection section, and a homogenization section. The temperatures are controlled at 160±2℃, 185±2℃, 170±2℃, and 165±2℃, respectively, and the pressures are controlled at 0.8±0.2MPa, 10±1MPa, 25±1MPa, and 20±1MPa, respectively.

[0054] Specifically, in the homogenization section of the screw extruder, a power of 25 kHz is applied perpendicular to the screw direction, with a power density of 4 W / cm³. 2 Ultrasonic waves are used to activate the piezoelectric effect of LiNbO3 nanowires to generate a local electric field, inducing the alignment of the conductive masterbatch.

[0055] S4. Adjust the extruder die temperature to 125℃ and the pressure to 11MPa. After the homogeneous saturated system is discharged through the die, it completes foaming under the influence of pressure relief to obtain a foamed body.

[0056] S5. The discharged foam is subjected to water ring hot cutting granulation (water ring temperature is 75℃, cutter speed is 3500rpm) and drying (fluidized bed hot air drying at 52℃), and finally vibrated and sieved to obtain lightweight conductive flame-retardant polypropylene foam beads.

[0057] Example 3

[0058] A method for preparing lightweight, conductive, flame-retardant polypropylene foam beads, the method comprising the following steps:

[0059] S1. Weigh the base PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer, and filler according to the proportion, put them into a mixer, and then add 0.3% of LiNbO3 nanowires according to the mass of the base PP resin. Stir and mix (temperature 26℃, speed 400rpm, time 4min) until uniform to obtain PP foaming intermediate product; wherein, the conductive masterbatch is conductive graphene, the flame retardant masterbatch is organosilicon flame retardant, the nucleating agent is silicon dioxide, the interface compatibilizer is maleic anhydride grafted styrene elastomer, and the filler is hollow ceramic microspheres. The mass ratio between the base PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer, and filler is 100:18:15:3:5:6 respectively.

[0060] The aspect ratio of the LiNbO3 nanowires is 50-60, and the preparation steps are as follows: LiOH·H2O, Nb2O5 and KOH powders with a molar ratio of 2:1:11 are used as raw materials. The raw materials are mixed and added to deionized water accounting for 8 times the total mass of the raw materials. The mixture is magnetically stirred for 60 minutes. The stirred mixture is then poured into a reaction vessel. The reaction vessel is sealed and placed in an oven at 150℃ for 6 days. After the reaction is completed, the white flocculent precipitate in the reaction vessel is taken out and washed and centrifuged multiple times with deionized water. The product obtained is LiNbO3 nanowires.

[0061] S2. Take the intermediate product of PP foaming and treat it with argon plasma (power 100W, pressure 50Pa, time 80s).

[0062] S3. Then, the PP foaming intermediate product is fed into the screw extruder, and the feeding speed is controlled at 12 kg / h. At the same time, supercritical CO2 is added to the screw extruder through the filling port of the extruder, and the adding speed is controlled at 800 g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system.

[0063] The screw extruder rotates at 480 rpm and is divided into a feeding section, a melting section, a supercritical injection section, and a homogenization section. The temperatures are controlled at 160±2℃, 185±2℃, 170±2℃, and 165±2℃, respectively, and the pressures are controlled at 0.8±0.2MPa, 10±1MPa, 25±1MPa, and 20±1MPa, respectively.

[0064] Specifically, in the homogenization section of the screw extruder, a power of 32 kHz is applied perpendicular to the screw direction, with a power density of 5 W / cm³. 2 Ultrasonic waves are used to activate the piezoelectric effect of LiNbO3 nanowires to generate a local electric field, inducing the alignment of the conductive masterbatch.

[0065] S4. Adjust the extruder die temperature to 130℃ and the pressure to 12MPa. After the homogeneous saturated system is discharged through the die, it completes foaming under the influence of pressure relief to obtain a foamed body.

[0066] S5. The discharged foam is subjected to water ring hot cutting granulation (water ring temperature is 78℃, cutter speed is 3600rpm) and drying (fluidized bed hot air drying at 55℃), and finally vibrated and sieved to obtain lightweight conductive flame-retardant polypropylene foam beads.

[0067] Comparative Example 1

[0068] A method for preparing lightweight, conductive, flame-retardant polypropylene foam beads, the method comprising the following steps:

[0069] S1. Weigh out the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer, and filler according to the proportion, put them into a mixer, and then add 0.2% of LiNbO3 nanowires according to the mass of the matrix PP resin. Stir and mix (temperature 24℃, speed 350rpm, time 5min) until uniform to obtain PP foaming intermediate product; wherein, the conductive masterbatch is nickel-plated carbon fiber, the flame retardant masterbatch is aluminum diethylphosphinate, the nucleating agent is nano calcium carbonate, the interface compatibilizer is maleic anhydride-grafted polyolefin elastomer, and the filler is hollow ceramic microspheres. The mass ratio between the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer, and filler is 100:15:18:2:4:5 respectively.

[0070] The aspect ratio of the LiNbO3 nanowires is 50-60, and the preparation steps are as follows: LiOH·H2O, Nb2O5 and KOH powders with a molar ratio of 2:1:11 are used as raw materials. The raw materials are mixed and added to deionized water accounting for 6 times the total mass of the raw materials. The mixture is magnetically stirred for 55 minutes. The stirred mixture is then poured into a reaction vessel. The reaction vessel is sealed and placed in an oven at 148°C for 7 days. After the reaction is completed, the white flocculent precipitate in the reaction vessel is taken out and washed and centrifuged multiple times with deionized water. The product obtained is LiNbO3 nanowires.

[0071] S2. Take the PP foaming intermediate product and feed it into the screw extruder. Control the feeding speed to 10 kg / h. At the same time, add supercritical CO2 into the screw extruder through the extruder's filling port. Control the adding speed to 700 g / h. So that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system.

[0072] The screw extruder rotates at 460 rpm and is divided into a feeding section, a melting section, a supercritical injection section, and a homogenization section. The temperatures are controlled at 160±2℃, 185±2℃, 170±2℃, and 165±2℃, respectively, and the pressures are controlled at 0.8±0.2MPa, 10±1MPa, 25±1MPa, and 20±1MPa, respectively.

[0073] Specifically, in the homogenization section of the screw extruder, a power of 25 kHz is applied perpendicular to the screw direction, with a power density of 4 W / cm³. 2 Ultrasonic waves are used to activate the piezoelectric effect of LiNbO3 nanowires to generate a local electric field, inducing the alignment of the conductive masterbatch.

[0074] S3. Adjust the extruder die temperature to 125℃ and the pressure to 11MPa. After the homogeneous saturated system is discharged through the die, it completes foaming under the influence of pressure relief to obtain a foamed body.

[0075] S4. The discharged foam is subjected to water ring hot cutting granulation (water ring temperature is 75℃, cutter speed is 3500rpm) and drying (fluidized bed hot air drying at 52℃), and finally vibrated and sieved to obtain lightweight conductive flame-retardant polypropylene foam beads.

[0076] Comparative Example 2

[0077] A method for preparing lightweight, conductive, flame-retardant polypropylene foam beads, the method comprising the following steps:

[0078] S1. Weigh out the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer and filler according to the proportion, put them into a mixer, and stir and mix (temperature 24℃, speed 350rpm, time 5min) until uniform to obtain PP foaming intermediate product; wherein, the conductive masterbatch is nickel-plated carbon fiber, the flame retardant masterbatch is aluminum diethylphosphinate, the nucleating agent is nano calcium carbonate, the interface compatibilizer is maleic anhydride grafted polyolefin elastomer, and the filler is hollow ceramic microspheres. The mass ratio between the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer and filler is 100:15:18:2:4:5 respectively.

[0079] S2. Take the intermediate product of PP foaming and treat it with argon plasma (power 90W, pressure 45Pa, time 90s).

[0080] S3. Then, the PP foaming intermediate product is fed into the screw extruder, and the feeding speed is controlled at 10 kg / h. At the same time, supercritical CO2 is added to the screw extruder through the filling port of the extruder, and the adding speed is controlled at 700 g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system.

[0081] The screw extruder rotates at 460 rpm and is divided into a feeding section, a melting section, a supercritical injection section, and a homogenization section. The temperatures are controlled at 160±2℃, 185±2℃, 170±2℃, and 165±2℃, respectively, and the pressures are controlled at 0.8±0.2MPa, 10±1MPa, 25±1MPa, and 20±1MPa, respectively.

[0082] Specifically, in the homogenization section of the screw extruder, a power of 25 kHz is applied perpendicular to the screw direction, with a power density of 4 W / cm³. 2 Ultrasound;

[0083] S4. Adjust the extruder die temperature to 125℃ and the pressure to 11MPa. After the homogeneous saturated system is discharged through the die, it completes foaming under the influence of pressure relief to obtain a foamed body.

[0084] S5. The discharged foam is subjected to water ring hot cutting granulation (water ring temperature is 75℃, cutter speed is 3500rpm) and drying (fluidized bed hot air drying at 52℃), and finally vibrated and sieved to obtain lightweight conductive flame-retardant polypropylene foam beads.

[0085] Comparative Example 3

[0086] A method for preparing lightweight, conductive, flame-retardant polypropylene foam beads, the method comprising the following steps:

[0087] S1. Weigh out the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer, and filler according to the proportion, put them into a mixer, and then add 0.2% of LiNbO3 nanowires according to the mass of the matrix PP resin. Stir and mix (temperature 24℃, speed 350rpm, time 5min) until uniform to obtain PP foaming intermediate product; wherein, the conductive masterbatch is nickel-plated carbon fiber, the flame retardant masterbatch is aluminum diethylphosphinate, the nucleating agent is nano calcium carbonate, the interface compatibilizer is maleic anhydride-grafted polyolefin elastomer, and the filler is hollow ceramic microspheres. The mass ratio between the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer, and filler is 100:15:18:2:4:5 respectively.

[0088] The aspect ratio of the LiNbO3 nanowires is 50-60, and the preparation steps are as follows: LiOH·H2O, Nb2O5 and KOH powders with a molar ratio of 2:1:11 are used as raw materials. The raw materials are mixed and added to deionized water accounting for 6 times the total mass of the raw materials. The mixture is magnetically stirred for 55 minutes. The stirred mixture is then poured into a reaction vessel. The reaction vessel is sealed and placed in an oven at 148°C for 7 days. After the reaction is completed, the white flocculent precipitate in the reaction vessel is taken out and washed and centrifuged multiple times with deionized water. The product obtained is LiNbO3 nanowires.

[0089] S2. Take the intermediate product of PP foaming and treat it with argon plasma (power 90W, pressure 45Pa, time 90s).

[0090] S3. Then, the PP foaming intermediate product is fed into the screw extruder, and the feeding speed is controlled at 10 kg / h. At the same time, supercritical CO2 is added to the screw extruder through the filling port of the extruder, and the adding speed is controlled at 700 g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system.

[0091] The screw extruder rotates at 460 rpm and is divided into a feeding section, a melting section, a supercritical injection section, and a homogenization section. The temperatures are controlled at 160±2℃, 185±2℃, 170±2℃, and 165±2℃, respectively, and the pressures are controlled at 0.8±0.2MPa, 10±1MPa, 25±1MPa, and 20±1MPa, respectively.

[0092] S4. Adjust the extruder die temperature to 125℃ and the pressure to 11MPa. After the homogeneous saturated system is discharged through the die, it completes foaming under the influence of pressure relief to obtain a foamed body.

[0093] S5. The discharged foam is subjected to water ring hot cutting granulation (water ring temperature is 75℃, cutter speed is 3500rpm) and drying (fluidized bed hot air drying at 52℃), and finally vibrated and sieved to obtain lightweight conductive flame-retardant polypropylene foam beads.

[0094] Comparative Example 4

[0095] A method for preparing lightweight, conductive, flame-retardant polypropylene foam beads, the method comprising the following steps:

[0096] S1. Weigh out the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer, and filler according to the proportion, put them into a mixer, and then add 0.2% of LiNbO3 nanoparticles according to the mass of the matrix PP resin. Stir and mix (temperature 24℃, speed 350rpm, time 5min) until uniform to obtain PP foaming intermediate product; wherein, the conductive masterbatch is nickel-plated carbon fiber, the flame retardant masterbatch is aluminum diethylphosphinate, the nucleating agent is nano calcium carbonate, the interface compatibilizer is maleic anhydride-grafted polyolefin elastomer, and the filler is hollow ceramic microspheres. The mass ratio between the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer, and filler is 100:15:18:2:4:5 respectively.

[0097] The preparation steps of the LiNbO3 nanoparticles are as follows: Niobium ethanol with a concentration of 40 mmol / L is dissolved in 10 mL of benzyl alcohol and stirred for 30 min to obtain a light yellow solution. Then, 100 μL of triethylamine is added to the solution and stirred for another 30 min. Then, 40 mmol / L of lithium hydroxide is added and stirred for another 10 h. Finally, the above mixed solution is transferred to an autoclave and heated at 220 °C for 60 h to obtain LiNbO3 nanoparticles.

[0098] S2. Take the intermediate product of PP foaming and treat it with argon plasma (power 90W, pressure 45Pa, time 90s).

[0099] S3. Then, the PP foaming intermediate product is fed into the screw extruder, and the feeding speed is controlled at 10 kg / h. At the same time, supercritical CO2 is added to the screw extruder through the filling port of the extruder, and the adding speed is controlled at 700 g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system.

[0100] The screw extruder rotates at 460 rpm and is divided into a feeding section, a melting section, a supercritical injection section, and a homogenization section. The temperatures are controlled at 160±2℃, 185±2℃, 170±2℃, and 165±2℃, respectively, and the pressures are controlled at 0.8±0.2MPa, 10±1MPa, 25±1MPa, and 20±1MPa, respectively.

[0101] Specifically, in the homogenization section of the screw extruder, a power of 25 kHz is applied perpendicular to the screw direction, with a power density of 4 W / cm³. 2 Ultrasonic waves are used to activate the piezoelectric effect of LiNbO3 nanowires to generate a local electric field, inducing the alignment of the conductive masterbatch.

[0102] S4. Adjust the extruder die temperature to 125℃ and the pressure to 11MPa. After the homogeneous saturated system is discharged through the die, it completes foaming under the influence of pressure relief to obtain a foamed body.

[0103] S5. The discharged foam is subjected to water ring hot cutting granulation (water ring temperature is 75℃, cutter speed is 3500rpm) and drying (fluidized bed hot air drying at 52℃), and finally vibrated and sieved to obtain lightweight conductive flame-retardant polypropylene foam beads.

[0104] III. Performance Testing

[0105] The lightweight conductive flame-retardant polypropylene foamed bead samples obtained in Example 2 and Comparative Examples 1-4 were processed into foamed materials using the same process. The specific process steps are as follows: (1) Pre-foaming treatment: The foamed beads were placed in a pre-foaming machine, 110℃ saturated steam was introduced, and the pressure was maintained at 0.2MPa for 10min; (2) Curing and aging: The pre-foamed beads were placed in a 50℃ ventilated environment for 24h to eliminate internal stress and balance the gas pressure between the beads; (3) Molding: The cured beads were filled into the mold cavity, 130℃ steam was introduced, and the pressure was maintained at 0.5MPa for 5min to allow the beads to foam a second time and be fused into shape; (4) Cooling and shaping: The product was cooled to below 40℃ by water cooling, and after demolding, it was trimmed, polished and other post-processing to obtain foamed material samples.

[0106] To verify the success of the foamed material of this invention, a sample of the foamed material prepared in Example 2 of this invention was immersed in liquid nitrogen for 3 minutes. After quenching to obtain a fresh fracture surface, it was fixed on a sample stage and subjected to gold sputtering treatment for 120 seconds. After removing the gold-sputtered sample, the cross-sectional morphology was observed using a scanning electron microscope (Hitachi S4800). The scanning electron microscope image is shown below. Figure 1 As shown, the foamed material prepared in Example 2 has a high internal pore density (a large number of pores per unit area), uniform pore size, smooth surface, and basically no pore rupture phenomenon was observed, indicating good feasibility.

[0107] Next, in order to verify the performance of the foamed material of the present invention, the foamed material samples prepared in Example 2 and Comparative Examples 1-4 were subjected to the following performance comparison tests:

[0108] (1) Apparent density test

[0109] The apparent density was tested according to ISO 1183-1987 standard using a Mettler BT224S density meter. The specific testing procedure was as follows: A suitable amount of foamed material sample was taken and cut to appropriate dimensions. The mass M1 of the sample was first weighed using a density balance. After zeroing the balance, the sample was immersed in water and weighed to remove the same volume of water, resulting in a mass M2. The apparent density of the foamed material sample was then calculated as the ratio of M1 to M2, expressed in g / cm³. 3 .

[0110] (2) Vertical burning test (UL-94)

[0111] According to GB / T2408-2008 standard, the foamed material samples were cut into strips measuring 100mm × 13mm × 1.6mm and placed on the fixture of a vertical combustion instrument (Vouch5402, Suzhou Yangyi Co., Ltd.). The samples were ignited twice, each time for 10 seconds, and the flame extinguishing time was observed and recorded. Five samples were tested for each group of foamed material samples, and the final data was the average. Refer to Table 1 below to evaluate its vertical combustion rating.

[0112] Table 1: Vertical Combustion Rating

[0113]

[0114] (3) Limiting Oxygen Index (LOI) test

[0115] According to GB / T2406.2-2009 standard, the foamed material samples were cut into strips of 100mm×6.5mm×1.6mm and placed in the fixture of the Limiting Oxygen Index (LOI) instrument (Vouch5801A, Suzhou Yangyi Co., Ltd.). At the same time, the concentration of the O2 and N2 mixed gas flow was adjusted. After the mixed gas flow stabilized, the propane gas was ignited, and the flame extinguishing time was observed and the corresponding LOI value was recorded. Five samples were tested for each group of foamed material samples, and the final data was the average value.

[0116] (4) Conductivity test

[0117] According to GB / T 31838.2-2019 standard, the volume resistivity and average thickness of the foamed material samples were tested, and the volume resistivity was calculated according to the following formula:

[0118]

[0119] In the formula: ρ is the volume resistivity, in Ω·m, R x The measured volume resistivity is expressed in Ω, and A is the effective area of ​​the electrode, expressed in m². 2 h is the average thickness of the sample, in meters (m).

[0120] (5) Mechanical property testing

[0121] Tensile properties: According to ISO527-2 standard, the foam material samples were cut into standard strips of 35 mm in length and tensile tests were conducted using a universal testing machine (Instron 5567, Instron Corporation, USA) at a tensile speed of 20 mm / min. Five samples were tested for each group of foam material samples, and the final data was the average value.

[0122] IV. Results Analysis

[0123] The results of the above performance tests are summarized in Table 2 below:

[0124] Table 2: Performance Test Results for Each Group

[0125]

[0126] As shown in Table 2 above, Example 2 of the present invention exhibits excellent flame retardant and electrical conductivity properties. Its vertical burning test rating reaches V-0, its limiting oxygen index (LOI) reaches 33.4, and its volume resistivity is as low as 25.64 Ω / cm. Furthermore, it possesses the advantages of being lightweight and having high strength. Comparative Examples 1-4 are all adjustments made based on Example 2. Specifically, Comparative Example 1 did not use argon plasma bombardment of the PP foaming intermediate product, resulting in a decrease in the vertical burning test rating to V-1 and the limiting oxygen index (LOI) to 26.6, a significant change compared to Example 2. The volume resistivity increased to 29.95 Ω / cm, and the tensile strength decreased to 29.8 MPa, which may be related to the bonding performance of the fillers. Comparative Example 2 removed LiNbO3 nanowires from the raw materials, and Comparative Example 3 removed the ultrasonic field during the homogenization stage. Both resulted in a significant decrease in volume resistivity compared to Example 2, while the flame retardant properties remained unchanged. This indicates that the LiNbO3 nanowires and the ultrasonic field treatment during the homogenization stage need to work synergistically to improve electrical conductivity. Comparative Example 4 replaced the LiNbO3 nanowires with LiNbO3 nanoparticles, and found that the conductivity was significantly worse than that of Example 2, which illustrates the importance of using a nanowire structure.

[0127] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing lightweight, conductive, flame-retardant polypropylene foam beads, characterized in that, The preparation method includes the following steps: S1. Weigh the base PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer and filler according to the proportion, put them into the mixer, and then add 0.1-0.3% of LiNbO3 nanowires according to the mass of the base PP resin. Stir and mix until uniform to obtain PP foaming intermediate product. The aspect ratio of the LiNbO3 nanowires is 50-60, and the preparation steps are as follows: LiOH·H2O, Nb2O5 and KOH powders with a molar ratio of 2:1:11 are used as raw materials. The raw materials are mixed and added to deionized water accounting for 5-8 times the total mass of the raw materials. The mixture is magnetically stirred for 50-60 minutes. The stirred mixture is then poured into a reaction vessel. The reaction vessel is sealed and placed in an oven at a temperature of 145-150℃ for 6-7 days. After the reaction is completed, the white flocculent precipitate in the reaction vessel is taken out and washed and centrifuged several times with deionized water. The product obtained is LiNbO3 nanowires. S2. Take the intermediate product of PP foaming and treat it with argon plasma. The argon plasma treatment has a power of 80-100W, a pressure of 40-50Pa, and a time of 80-100s; S3. Then, take the PP foaming intermediate product and feed it into the screw extruder. Control the feeding speed to 8-12 kg / h. At the same time, add supercritical CO2 into the screw extruder through the filling port of the extruder. Control the adding speed to 600-800 g / h. After the supercritical CO2 and the PP foaming intermediate product are mixed and melted, a homogeneous saturated system is formed. Specifically, in the homogenization section of the screw extruder, a power of 20-32 kHz is applied perpendicular to the screw direction, with a power density of 4-5 W / cm³. 2 Ultrasonic waves are used to activate the piezoelectric effect of LiNbO3 nanowires to generate a local electric field, inducing the alignment of the conductive masterbatch. S4. Adjust the extruder die temperature to 120-130℃ and the pressure to 10-12MPa. After the homogeneous saturated system is discharged through the die, it completes foaming under the influence of pressure relief to obtain a foamed body. S5. After discharge, the foamed body is subjected to water ring hot cutting granulation and drying, and finally vibrated and sieved to obtain lightweight conductive flame-retardant polypropylene foamed beads.

2. The method for preparing lightweight, conductive, flame-retardant polypropylene foam beads according to claim 1, characterized in that, In step S1: The conductive masterbatch is selected from one of acetylene black, nickel-plated carbon fiber, conductive furnace black, or conductive graphene. The flame retardant masterbatch is selected from one of the following: phosphorus-nitrogen intumescent flame retardant, aluminum diethylphosphinate, melamine cyanurate, melamine polyphosphate, or organosilicon flame retardant. The nucleating agent is selected from talc, nano-calcium carbonate, or silicon dioxide. The interface compatibilizer is selected from one of maleic anhydride-grafted polypropylene, maleic anhydride-grafted polyolefin elastomer, or maleic anhydride-grafted styrene elastomer. The filler is selected from either hollow glass microspheres or hollow ceramic microspheres.

3. The method for preparing lightweight, conductive, flame-retardant polypropylene foam beads according to claim 1, characterized in that, In step S1, the mass ratio of the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interface compatibilizer and filler is 100:12-18:15-20:1-3:3-5:4-6.

4. The method for preparing lightweight, conductive, flame-retardant polypropylene foam beads according to claim 1, characterized in that, In step S1, the stirring temperature is 22-26℃, the stirring speed is 300-400rpm, and the stirring time is 4-6min.

5. The method for preparing lightweight, conductive, flame-retardant polypropylene foam beads according to claim 1, characterized in that, In step S3, the screw extruder rotates at 450-480 rpm. The screw extruder is divided into a feeding section, a melting section, a supercritical injection section, and a homogenization section, with the temperatures controlled sequentially at 160±2℃, 185±2℃, 170±2℃, and 165±2℃, and the pressures controlled sequentially at 0.8±0.2MPa, 10±1MPa, 25±1MPa, and 20±1MPa.

6. The method for preparing lightweight, conductive, flame-retardant polypropylene foam beads according to claim 1, characterized in that, In step S5, the water ring temperature of the water ring hot cutting granulation is 72-78℃, the cutting speed is 3400-3600rpm, and the drying is carried out using fluidized bed hot air drying at 50-55℃.

7. A lightweight, conductive, flame-retardant polypropylene foamed bead, characterized in that, It is prepared by the method described in any one of claims 1-6.

8. The application of the lightweight conductive and flame-retardant polypropylene foam beads as described in claim 7 in the preparation of conductive and flame-retardant material products.

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