Lightweight conductive flame-retardant polypropylene foamed bead as well as preparation method and application thereof

Abstract

The invention discloses a lightweight conductive flame-retardant polypropylene foamed bead and a preparation method and application thereof in the field of polypropylene foamed materials, and the preparation method comprises the following steps: taking matrix PP resin, a conductive master batch, a flame-retardant master batch, a nucleating agent, an interfacial compatibilizer and a filler, putting into a stirrer, then adding LiNbO3 nanowires, and stirring and mixing uniformly to obtain an intermediate product; taking the intermediate product, and carrying out argon plasma treatment on the intermediate product; feeding into a screw extruder, and adding supercritical CO2 at the same time to form a homogeneous saturated system; and after being discharged through a mouth mold, completing foaming under the influence of pressure relief, and then carrying out water ring hot cutting granulation, drying and sieving, thereby obtaining the product. According to the preparation method, argon plasma is adopted to bombard an intermediate product, the interface bonding force of the filler is improved, the conductivity and flame retardance are improved, LiNbO3 nanowires are added into the raw materials, a local electric field is generated under an ultrasonic field in the extrusion homogenization stage, a conductive network is optimized, and the conductivity is further improved.

Description

Technical Field

[0001] The invention relates to the field of polypropylene foam materials, and in particular to lightweight conductive and flame-retardant polypropylene foam beads, a preparation method and application thereof. Background Art

[0002] Expanded polypropylene beads (EPP) are high-performance closed-cell foam materials with excellent impact resistance, heat resistance, thermal insulation, lightweight construction, and recyclability. They are widely used in automotive parts (bumper cores, headrests, tool boxes), packaging (electronic products, precision instruments), sports equipment, toys, and construction. The typical ingredients of EPP include polypropylene resin, a physical blowing agent (supercritical fluids such as butane and CO2), a nucleating agent (calcium carbonate, talc, silica, mica, etc.), and functional modifiers (lubricants, antioxidants, light stabilizers, antistatic agents, colorants, etc.).

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

[0004] The object of the present invention is to provide lightweight conductive flame-retardant polypropylene foam beads and their preparation method and application, which solve the problem that the conductive fillers, flame retardants and the like of the existing polypropylene foam beads have poor compatibility with the matrix PP resin, and the conductive fillers are arranged in a disorderly manner in a homogeneous saturated system, which is not conducive to the formation of a conductive network.

[0005] The present invention achieves the above-mentioned purpose through the following technical solutions:

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

[0007] S1. Weigh the base PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interfacial compatibilizer and filler in proportion, put them into a blender, then add LiNbO3 nanowires accounting for 0.1-0.3% of the mass of the base PP resin, stir and mix until uniform, to obtain a PP foaming intermediate product;

[0008] S2, taking the PP foaming intermediate product and subjecting it to argon plasma treatment;

[0009] S3, then take the PP foaming intermediate product and feed it into the screw extruder, control the feeding rate to 8-12kg / h, and at the same time add supercritical CO2 to the screw extruder through the filling port of the extruder, control the addition rate to 600-800g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system;

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

[0011] S4, adjusting the extruder die temperature to 120-130 ° C and the pressure to 10-12 MPa, and the homogeneous saturated system is discharged from the die and then foamed under the influence of pressure relief to obtain a foamed body;

[0012] S5. The discharged foamed body is granulated and dried by water ring heat cutting, and finally vibrated and sieved to obtain lightweight conductive and flame-retardant polypropylene foam beads.

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

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

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

[0016] The nucleating agent is selected from one of talc, nano calcium carbonate or silicon dioxide;

[0017] The interfacial 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 hollow glass microspheres or hollow ceramic microspheres.

[0019] A further improvement is that in step S1, the mass ratios of the base PP resin, the conductive masterbatch, the flame retardant masterbatch, the nucleating agent, the interfacial compatibilizer and the filler are 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: taking LiOH·H2O, Nb2O5 and KOH powders with a molar ratio of 2:1:11 as raw materials, mixing the raw materials and adding them into deionized water accounting for 5-8 times the total mass of the raw materials, magnetically stirring for 50-60 minutes, then pouring the stirred mixture into a reactor, sealing the reactor and placing it in an oven at a temperature of 145-150°C to react for 6-7 days. After the reaction is completed, taking out the white flocculent precipitate in the reactor, washing it with deionized water multiple times and centrifuging it, the resulting product is LiNbO3 nanowires.

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

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

[0023] A further improvement is that in step S3, the speed of the screw extruder is 450-480 rpm, the screw extruder is divided into a feeding section, a melting section, a supercritical injection section and a homogenization section in sequence, and the temperature is controlled at 160±2°C, 185±2°C, 170±2°C and 165±2°C in sequence, and the pressure is controlled at 0.8±0.2MPa, 10±1MPa, 25±1MPa and 20±1MPa in sequence.

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

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

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

[0027] The beneficial effects of the present invention are:

[0028] (1) The present invention uses argon plasma to bombard the PP foaming intermediate product, introducing oxygen-containing polar groups (carboxyl and hydroxyl groups) on the PP surface, significantly improving the interfacial bonding strength of fillers (such as nickel-plated carbon fibers). At the same time, the polar groups can capture free radicals generated by combustion, thereby increasing the limiting oxygen index (LOI) and improving flame retardancy.

[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 affected by the electric field lines, which helps to form a stable conductive network, thereby greatly improving the conductive performance. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0031] The present application is described in further detail below in conjunction with the accompanying drawings. It is necessary to point out that the following specific implementation methods are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Technicians in this field can make some non-essential improvements and adjustments to the present application based on the above application content.

[0032] 1. Main materials and equipment

[0033] Base PP resin: PPB-M02, purchased from Yuyao Fulin Plastic Chemical 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 Hisili Extrusion Equipment Co., Ltd.

[0036] 2. Implementation of the Experiment

[0037] Example 1

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

[0039] S1. Weigh the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interfacial compatibilizer and filler in proportion, put them into a blender, add LiNbO3 nanowires accounting for 0.1% of the mass of the matrix PP resin, and stir and mix (temperature of 22°C, rotation speed of 300 rpm, time of 6 min) until uniform, to obtain a 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 interfacial compatibilizer is maleic anhydride grafted polypropylene, and the filler is hollow glass microspheres. The mass ratios of the matrix PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interfacial compatibilizer and filler are 100:12:20:1:3:4, respectively;

[0040] The LiNbO3 nanowires have an aspect ratio of 50-60 and are prepared by taking LiOH·H2O, Nb2O5, and KOH powders in a molar ratio of 2:1:11 as raw materials, mixing the raw materials and adding them into deionized water that is 5 times the total mass of the raw materials, magnetically stirring for 50 minutes, pouring the stirred mixture into a reactor, sealing the reactor and placing it in an oven at a temperature of 145°C for 7 days, and after the reaction is completed, removing the white flocculent precipitate from the reactor, washing it with deionized water multiple times, and centrifuging it to obtain the LiNbO3 nanowires.

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

[0042] S3, then take the PP foaming intermediate product and feed it into the screw extruder, control the feeding rate to 8kg / h, and at the same time add supercritical CO2 to the screw extruder through the filling port of the extruder, control the addition rate to 600g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system;

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

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

[0045] S4, adjusting the extruder die temperature to 120 ° C and the pressure to 10 MPa, and the homogeneous saturated system is discharged from the die and then foamed under the influence of pressure relief to obtain a foamed body;

[0046] S5. The discharged foamed body is granulated by water ring hot cutting (water ring temperature is 72°C, cutter speed is 3400rpm) and dried (fluidized bed hot air drying at 50°C), 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 preparation method comprising the following steps:

[0049] S1. Weigh a matrix PP resin, a conductive masterbatch, a flame retardant masterbatch, a nucleating agent, an interfacial compatibilizer, and a filler in proportion, put them into a blender, add LiNbO3 nanowires accounting for 0.2% of the mass of the matrix PP resin, and stir and mix (temperature 24°C, rotation speed 350 rpm, time 5 min) until uniform, to obtain a 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 interfacial compatibilizer is maleic anhydride grafted polyolefin elastomer, and the filler is hollow ceramic microspheres; the mass ratios of the matrix PP resin, the conductive masterbatch, the flame retardant masterbatch, the nucleating agent, the interfacial compatibilizer, and the filler are 100:15:18:2:4:5, respectively;

[0050] The LiNbO3 nanowires have an aspect ratio of 50-60 and are prepared by taking LiOH·H2O, Nb2O5, and KOH powders in a molar ratio of 2:1:11 as raw materials, mixing the raw materials and adding them into deionized water that is 6 times the total mass of the raw materials, magnetically stirring for 55 minutes, pouring the stirred mixture into a reactor, sealing the reactor and placing it in an oven at a temperature of 148°C for 7 days, and after the reaction is completed, removing the white flocculent precipitate from the reactor, washing it with deionized water multiple times, and centrifuging it to obtain the LiNbO3 nanowires.

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

[0052] S3, then take the PP foaming intermediate product and feed it into the screw extruder, control the feeding rate to 10kg / h, and at the same time add supercritical CO2 to the screw extruder through the filling port of the extruder, control the addition rate to 700g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system;

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

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

[0055] S4, adjusting the extruder die temperature to 125 ° C and the pressure to 11 MPa, and the homogeneous saturated system is discharged from the die and then foamed under the influence of pressure relief to obtain a foamed body;

[0056] S5. The discharged foamed body is granulated by water ring hot cutting (water ring temperature is 75°C, cutter speed is 3500rpm) and dried (fluidized bed hot air drying at 52°C), 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 preparation method comprising the following steps:

[0059] S1. Weigh a matrix PP resin, a conductive masterbatch, a flame retardant masterbatch, a nucleating agent, an interfacial compatibilizer, and a filler in proportion, put them into a blender, add LiNbO3 nanowires accounting for 0.3% of the mass of the matrix PP resin, and stir and mix (temperature 26°C, rotation speed 400 rpm, time 4 min) until uniform, to obtain a PP foaming intermediate product; wherein, the conductive masterbatch is conductive graphene, the flame retardant masterbatch is an organosilicon flame retardant, the nucleating agent is silica, the interfacial compatibilizer is maleic anhydride grafted styrene elastomer, and the filler is hollow ceramic microspheres; the mass ratios of the matrix PP resin, the conductive masterbatch, the flame retardant masterbatch, the nucleating agent, the interfacial compatibilizer, and the filler are 100:18:15:3:5:6, respectively;

[0060] The LiNbO3 nanowires have an aspect ratio of 50-60 and are prepared by taking LiOH·H2O, Nb2O5, and KOH powders in a molar ratio of 2:1:11 as raw materials, mixing the raw materials and adding them into deionized water that accounts for 8 times the total mass of the raw materials, magnetically stirring for 60 minutes, then pouring the stirred mixture into a reactor, sealing the reactor and placing it in an oven at a temperature of 150°C for 6 days. After the reaction is completed, taking out the white flocculent precipitate in the reactor, washing it with deionized water multiple times, and centrifuging it to obtain the LiNbO3 nanowires.

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

[0062] S3, then take the PP foaming intermediate product and feed it into the screw extruder, control the feeding rate to 12kg / h, and at the same time add supercritical CO2 to the screw extruder through the filling port of the extruder, control the addition rate to 800g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system;

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

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

[0065] S4, adjusting the extruder die temperature to 130° C. and the pressure to 12 MPa, and the homogeneous saturated system is discharged from the die and then foamed under the influence of pressure relief to obtain a foamed body;

[0066] S5. The discharged foamed body is granulated by water ring hot cutting (water ring temperature is 78°C, cutter speed is 3600rpm) and dried (fluidized bed hot air drying at 55°C), 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 preparation method comprising the following steps:

[0069] S1. Weigh a matrix PP resin, a conductive masterbatch, a flame retardant masterbatch, a nucleating agent, an interfacial compatibilizer, and a filler in proportion, put them into a blender, add LiNbO3 nanowires accounting for 0.2% of the mass of the matrix PP resin, and stir and mix (temperature 24°C, rotation speed 350 rpm, time 5 min) until uniform, to obtain a 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 interfacial compatibilizer is maleic anhydride grafted polyolefin elastomer, and the filler is hollow ceramic microspheres; the mass ratios of the matrix PP resin, the conductive masterbatch, the flame retardant masterbatch, the nucleating agent, the interfacial compatibilizer, and the filler are 100:15:18:2:4:5, respectively;

[0070] The LiNbO3 nanowires have an aspect ratio of 50-60 and are prepared by taking LiOH·H2O, Nb2O5, and KOH powders in a molar ratio of 2:1:11 as raw materials, mixing the raw materials and adding them into deionized water that is 6 times the total mass of the raw materials, magnetically stirring for 55 minutes, pouring the stirred mixture into a reactor, sealing the reactor and placing it in an oven at a temperature of 148°C for 7 days, and after the reaction is completed, removing the white flocculent precipitate from the reactor, washing it with deionized water multiple times, and centrifuging it to obtain the LiNbO3 nanowires.

[0071] S2, take the PP foaming intermediate product and feed it into a screw extruder, control the feeding rate to be 10kg / h, and at the same time, add supercritical CO2 into the screw extruder through the filling port of the extruder, control the addition rate to be 700g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system;

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

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

[0074] S3, adjusting the extruder die temperature to 125 ° C and the pressure to 11 MPa, and the homogeneous saturated system is discharged from the die and then foamed under the influence of pressure relief to obtain a foamed body;

[0075] S4. The discharged foamed body is granulated by water ring hot cutting (water ring temperature is 75℃, cutter speed is 3500rpm) and dried (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 preparation method comprising the following steps:

[0078] S1. Weigh a base PP resin, a conductive masterbatch, a flame retardant masterbatch, a nucleating agent, an interfacial compatibilizer, and a filler in proportion, put them into a blender, and stir and mix them (temperature 24°C, rotation speed 350 rpm, time 5 min) until uniform, to obtain a 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 interfacial compatibilizer is maleic anhydride grafted polyolefin elastomer, and the filler is hollow ceramic microspheres; the mass ratios of the base PP resin, the conductive masterbatch, the flame retardant masterbatch, the nucleating agent, the interfacial compatibilizer, and the filler are 100:15:18:2:4:5, respectively;

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

[0080] S3, then take the PP foaming intermediate product and feed it into the screw extruder, control the feeding rate to 10kg / h, and at the same time add supercritical CO2 to the screw extruder through the filling port of the extruder, control the addition rate to 700g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system;

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

[0082] The power applied perpendicular to the screw direction in the homogenizing section of the screw extruder is 25kHz and the power density is 4W / cm 2 Ultrasound;

[0083] S4, adjusting the extruder die temperature to 125 ° C and the pressure to 11 MPa, and the homogeneous saturated system is discharged from the die and then foamed under the influence of pressure relief to obtain a foamed body;

[0084] S5. The discharged foamed body is granulated by water ring hot cutting (water ring temperature is 75°C, cutter speed is 3500rpm) and dried (fluidized bed hot air drying at 52°C), 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 preparation method comprising the following steps:

[0087] S1. Weigh a matrix PP resin, a conductive masterbatch, a flame retardant masterbatch, a nucleating agent, an interfacial compatibilizer, and a filler in proportion, put them into a blender, add LiNbO3 nanowires accounting for 0.2% of the mass of the matrix PP resin, and stir and mix (temperature 24°C, rotation speed 350 rpm, time 5 min) until uniform, to obtain a 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 interfacial compatibilizer is maleic anhydride grafted polyolefin elastomer, and the filler is hollow ceramic microspheres; the mass ratios of the matrix PP resin, the conductive masterbatch, the flame retardant masterbatch, the nucleating agent, the interfacial compatibilizer, and the filler are 100:15:18:2:4:5, respectively;

[0088] The LiNbO3 nanowires have an aspect ratio of 50-60 and are prepared by taking LiOH·H2O, Nb2O5, and KOH powders in a molar ratio of 2:1:11 as raw materials, mixing the raw materials and adding them into deionized water that is 6 times the total mass of the raw materials, magnetically stirring for 55 minutes, pouring the stirred mixture into a reactor, sealing the reactor and placing it in an oven at a temperature of 148°C for 7 days, and after the reaction is completed, removing the white flocculent precipitate from the reactor, washing it with deionized water multiple times, and centrifuging it to obtain the LiNbO3 nanowires.

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

[0090] S3, then take the PP foaming intermediate product and feed it into the screw extruder, control the feeding rate to 10kg / h, and at the same time add supercritical CO2 to the screw extruder through the filling port of the extruder, control the addition rate to 700g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system;

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

[0092] S4, adjusting the extruder die temperature to 125 ° C and the pressure to 11 MPa, and the homogeneous saturated system is discharged from the die and then foamed under the influence of pressure relief to obtain a foamed body;

[0093] S5. The discharged foamed body is granulated by water ring hot cutting (water ring temperature is 75°C, cutter speed is 3500rpm) and dried (fluidized bed hot air drying at 52°C), 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 preparation method comprising the following steps:

[0096] S1. Weigh a matrix PP resin, a conductive masterbatch, a flame retardant masterbatch, a nucleating agent, an interfacial compatibilizer, and a filler in proportion, put them into a blender, add LiNbO3 nanoparticles accounting for 0.2% of the mass of the matrix PP resin, and stir and mix (temperature 24°C, rotation speed 350 rpm, time 5 min) until uniform, to obtain a 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 interfacial compatibilizer is maleic anhydride grafted polyolefin elastomer, and the filler is hollow ceramic microspheres; the mass ratios of the matrix PP resin, the conductive masterbatch, the flame retardant masterbatch, the nucleating agent, the interfacial compatibilizer, and the filler are 100:15:18:2:4:5, respectively;

[0097] The preparation steps of the LiNbO3 nanoparticles are as follows: dissolving 40 mmol / L niobium ethanol in 10 mL of benzyl alcohol and stirring for 30 minutes to obtain a light yellow solution; then adding 100 μL of triethylamine to the solution and stirring again for 30 minutes; then adding 40 mmol / L of lithium hydroxide and continuing to stir for 10 hours; finally, transferring the mixed solution to an autoclave and heating it at 220°C for 60 hours to obtain LiNbO3 nanoparticles;

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

[0099] S3, then take the PP foaming intermediate product and feed it into the screw extruder, control the feeding rate to 10kg / h, and at the same time add supercritical CO2 to the screw extruder through the filling port of the extruder, control the addition rate to 700g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system;

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

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

[0102] S4, adjusting the extruder die temperature to 125 ° C and the pressure to 11 MPa, and the homogeneous saturated system is discharged from the die and then foamed under the influence of pressure relief to obtain a foamed body;

[0103] S5. The discharged foamed body is granulated by water ring hot cutting (water ring temperature is 75°C, cutter speed is 3500rpm) and dried (fluidized bed hot air drying at 52°C), and finally vibrated and sieved to obtain lightweight conductive flame retardant polypropylene foam beads.

[0104] 3. Performance Testing

[0105] The lightweight conductive flame-retardant polypropylene foam beads samples prepared in the above-mentioned Example 2 and Comparative Examples 1-4 were taken and processed into foam materials by the same process. The specific process steps were as follows: (1) Pre-foaming treatment: the foamed beads were placed in a pre-foaming machine, saturated steam at 110°C was introduced, the pressure was maintained at 0.2 MPa, and pre-foaming was performed for 10 minutes; (2) Ripening and aging: the pre-foamed beads were placed in a ventilated environment at 50°C for 24 hours to eliminate internal stress and balance the gas pressure between the beads; (3) Compression molding: the matured beads were filled into the mold cavity, steam at 130°C was introduced, the pressure was 0.5 MPa, and the beads were foamed for the second time and welded into shape; (3) Cooling and shaping: the product was cooled to below 40°C by water cooling, and after demolding, trimming, polishing and other post-processing were performed to obtain a foam material sample.

[0106] In order to verify the success of the foam material of the present invention, a foam material sample prepared in Example 2 of the present invention was immersed in liquid nitrogen for 3 minutes, quenched to obtain a fresh cross section, and then fixed on a sample table. It was then subjected to gold spraying for 120 seconds. After the gold sprayed sample was removed, the cross-sectional morphology was observed using a scanning electron microscope (Hitachi S4800). The scanning electron microscope image is shown as follows: Figure 1 As shown, it can be seen that the foamed material prepared in Example 2 has a high internal cell density (a large number of cells per unit area), uniform cell size, a smooth surface, and basically no cell rupture phenomenon is observed, indicating good feasibility.

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

[0108] (1) Apparent density test

[0109] According to ISO 1183-1987, the apparent density test is performed using Mettler's BT224S density tester. The specific test process is as follows: take an appropriate amount of foam material sample and cut it into appropriate size. Use a density balance to first weigh the mass M1 of the foam material sample. After the balance is reset, immerse the foam material sample in water and weigh its mass M2 after excluding the same volume of water. The apparent density of the foam material sample is calculated as the ratio of M1 to M2, in units of g / cm 3 .

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

[0111] According to GB / T2408-2008, foam material samples were cut into strips measuring 100 mm × 13 mm × 1.6 mm and placed in the fixture of a vertical combustion instrument (Vouch5402, Suzhou Yangyi Co., Ltd.). Two flames were ignited, each for 10 seconds. The time it took for the flame to extinguish was observed and recorded. Five specimens were tested for each group of foam material samples, and the final data was averaged. The vertical combustion level was evaluated by referring to Table 1 below:

[0112] Table 1: Vertical Burning Levels

[0113]

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

[0115] According to the GB / T2406.2-2009 standard, foam material samples were cut into long strips measuring 100 mm × 6.5 mm × 1.6 mm and placed in the fixture of a limiting oxygen index instrument (Vouch5801A, Suzhou Yangyi Co., Ltd.). Simultaneously, the concentration of the O2 and N2 mixed gas flow was adjusted. After the mixed gas flow stabilized, the propane gas was ignited. The time it took for the flame to extinguish was observed, and the corresponding LOI value was recorded. Five specimens were tested for each group of foam material samples, and the final data were averaged.

[0116] (4) Conductivity test

[0117] According to GB / T 31838.2-2019, the volume resistance, average thickness and other data of the foam material sample are tested, and the volume resistivity is calculated according to the following formula:

[0118]

[0119] Where: ρ is the volume resistivity, unit is Ω·m, R x is the measured volume resistance, unit Ω, A is the effective area of ​​the electrode, unit m 2 , h is the average thickness of the sample, unit is m.

[0120] (5) Mechanical properties test

[0121] Tensile properties: According to ISO 527-2, the foam material samples were cut into standard specimens of 35 mm in length and tensile tests were performed using a universal testing machine (Instron 5567, Instron Corporation, USA) at a tensile speed of 20 mm / min. Five specimens were tested for each group of foam material samples, and the final data were averaged.

[0122] 4. Results Analysis

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

[0124] Table 2: Performance test results of each group

[0125]

[0126] As can be seen from Table 2 above, Example 2 of the present invention exhibits excellent flame retardancy and electrical conductivity, achieving a V-0 vertical flame test rating, a limiting oxygen index (LOI) of 33.4, and a low volume resistivity of 25.64 Ω / cm. Furthermore, it exhibits the advantages of lightweight and high strength. Comparative Examples 1-4 are modifications of Example 2. Comparative Example 1 does not utilize argon plasma bombardment on the PP foam intermediate, resulting in a significant reduction in the vertical flame test rating to V-1 and the LOI to 26.6, compared to Example 2. Furthermore, the volume resistivity increases to 29.95 Ω / cm, and the tensile strength decreases to 29.8 MPa, likely due to the combined properties of the fillers. Comparative Example 2 removes LiNbO3 nanowires from the raw materials, and Comparative Example 3 eliminates the ultrasonic field during the homogenization stage. Both significantly reduce the volume resistivity compared to Example 2, while maintaining no significant change in flame retardancy. This demonstrates that the LiNbO3 nanowires and the ultrasonic field treatment during the homogenization stage work together to enhance electrical conductivity. In Comparative Example 4, LiNbO3 nanowires were replaced with LiNbO3 nanoparticles, and it was found that the conductive performance was significantly worse than that of Example 2, which shows the importance of using a nanowire structure.

[0127] The above-described embodiments merely illustrate several implementations of the present invention. 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 a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements 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 steps of the preparation method include: S1. Weigh the base PP resin, conductive masterbatch, flame retardant masterbatch, nucleating agent, interfacial compatibilizer and filler in proportion, put them into a blender, then add LiNbO3 nanowires accounting for 0.1-0.3% of the mass of the base PP resin, stir and mix until uniform, to obtain a PP foaming intermediate product; S2, taking the PP foaming intermediate product and subjecting it to argon plasma treatment; S3, then take the PP foaming intermediate product and feed it into the screw extruder, control the feeding rate to 8-12kg / h, and at the same time add supercritical CO2 to the screw extruder through the filling port of the extruder, control the addition rate to 600-800g / h, so that the supercritical CO2 and the PP foaming intermediate product are mixed and melted to form a homogeneous saturated system; The power applied perpendicular to the screw direction in the homogenizing section of the screw extruder is 20-32kHz, and the power density is 4-5W / cm 2 Ultrasonic waves are used to activate the piezoelectric effect of LiNbO3 nanowires to generate a local electric field, inducing alignment of the conductive masterbatch; S4, adjusting the extruder die temperature to 120-130 ° C and the pressure to 10-12 MPa, and the homogeneous saturated system is discharged from the die and then foamed under the influence of pressure relief to obtain a foamed body; S5. The discharged foamed body is granulated and dried by water ring heat cutting, and finally vibrated and sieved to obtain lightweight conductive and flame-retardant polypropylene foam 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 carbon black, nickel-plated carbon fiber, conductive furnace black or conductive graphene; The flame retardant masterbatch is selected from one of phosphorus-nitrogen intumescent flame retardant, aluminum diethylphosphinate, melamine cyanurate, melamine polyphosphate or organosilicon flame retardant; The nucleating agent is selected from one of talc, nano calcium carbonate or silicon dioxide; The interfacial 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 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 ratios of the base PP resin, the conductive masterbatch, the flame retardant masterbatch, the nucleating agent, the interfacial compatibilizer and the filler are 100:12-18:15-20:1-3:3-5:4-6, respectively.

4. The method for preparing lightweight conductive flame-retardant polypropylene foam beads according to claim 1, characterized in that: In step S1, the aspect ratio of the LiNbO3 nanowires is 50-60, and the preparation steps are: taking LiOH·H2O, Nb2O5 and KOH powders with a molar ratio of 2:1:11 as raw materials, mixing the raw materials and adding them into deionized water accounting for 5-8 times the total mass of the raw materials, magnetically stirring for 50-60 minutes, then pouring the stirred mixture into a reactor, sealing the reactor and placing it in an oven at a temperature of 145-150°C for 6-7 days. After the reaction is completed, taking out the white flocculent precipitate in the reactor, washing it with deionized water multiple times and centrifuging it to obtain the product, which is LiNbO3 nanowires.

5. The method for preparing lightweight conductive flame-retardant polypropylene foam beads according to claim 1, characterized in that: In step S1, the stirring and mixing is performed at a temperature of 22-26° C., a rotation speed of 300-400 rpm, and a time of 4-6 min.

6. The method for preparing lightweight conductive flame-retardant polypropylene foam beads according to claim 1, characterized in that: In step S2, the argon plasma treatment has a power of 80-100 W, a pressure of 40-50 Pa, and a time of 80-100 s.

7. The method for preparing lightweight conductive flame-retardant polypropylene foam beads according to claim 1, characterized in that: In step S3, the speed of the screw extruder is 450-480 rpm, and the screw extruder is divided into a feeding section, a melting section, a supercritical injection section and a homogenization section in sequence, and the temperature is controlled at 160±2°C, 185±2°C, 170±2°C and 165±2°C, and the pressure is controlled at 0.8±0.2MPa, 10±1MPa, 25±1MPa and 20±1MPa, respectively.

8. 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°C, the cutter speed is 3400-3600rpm, and the drying adopts fluidized bed hot air drying at 50-55°C.

9. A lightweight, conductive, flame-retardant polypropylene foam bead, characterized in that: The invention discloses a novel novel polyol according to claim 1 , wherein the polyol is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the lightweight conductive fire-retardant polypropylene foam beads according to claim 9 in preparing conductive fire-retardant material products.

Images