Highly flame-retardant polypropylene foamed particles and method for preparing the same

Abstract

The application belongs to the technical field of polypropylene manufacturing, and discloses a kind of high flame-retardant polypropylene foaming particles and preparation method thereof, by mass fraction, including polypropylene 80~90 parts, toughening agent 3~5 parts, filling agent 4~12 parts, stabilizer 0.3~1 parts, lubricant 0.2~2 parts, nucleating agent 0.1~0.5 parts and 3~5 parts composite modified nano flame retardant.The beneficial effects of the application are: polydopamine is embedded in nano flame retardant by its adhesion, forms "nano clothes" to modify the surface of nano particles, so that nano particles show good stability and dispersibility.Ammonium polyphosphate is combined with the catechol group on the surface of dopamine, and ammonium polyphosphate is used to embed polydopamine in nano flame retardant for secondary embedding, to obtain composite modified nano flame retardant.Ammonium polyphosphate is combined with polydopamine, which can reduce the polarity of both and improve the compatibility of composite modified nano flame retardant with polypropylene, and make the composite modified nano flame retardant uniformly dispersed in polypropylene.

Description

Technical Field

[0001] This invention belongs to the field of polypropylene manufacturing technology, and specifically relates to a high flame-retardant polypropylene foamed granule and its preparation method. Background Technology

[0002] Expanded polypropylene (EPP) is a high-performance, highly crystalline polypropylene / CO2 composite material, currently the fastest-growing environmentally friendly new type of pressure-resistant, cushioning, and heat-insulating material. EPP products possess excellent shock absorption and energy absorption properties, high recovery rate after deformation, good heat resistance, chemical resistance, oil resistance, and thermal insulation. Furthermore, its lightweight nature significantly reduces the weight of items. EPP is a green and environmentally friendly material, recyclable, and does not cause white pollution. However, EPP is flammable, with a low ignition point and high combustion temperature, generating significant heat and easily allowing fire to spread further. Improving flame retardancy while maintaining a good cell structure is one of the effective methods to expand the application range of EPP materials.

[0003] The most common flame-retardant modification method is to add flame retardants to PP. There are many types of flame retardants, and nano-flame retardants only require a small amount to significantly reduce the material's combustion performance. Different nano-flame retardants have different flame-retardant mechanisms. Nano-layered flame retardants can act as effective thermal barriers, inhibiting mass loss during thermal degradation. The presence of layered materials slows the escape rate of combustible gases from the matrix to the surface of the nanocomposite material, thereby reducing the amount of combustible gas in the combustion zone; this is also known as the "maze effect." Furthermore, the addition of layered nanomaterials increases the viscosity of the polymer matrix, which helps slow the diffusion rate of oxygen in the polymer melt and the precipitation of degradation products from below. Nano-hydroxides have three main functions: flame retardancy, smoke suppression, and filling. They can be used as flame retardants and smoke suppressants, and are among the most widely used flame retardants. Nano-metal hydroxides decompose and release water molecules when heated; this process is endothermic. In this case, the cooling effect increases the self-extinguishing ability of the nanocomposite material. Aluminum hydroxide (ATH) and magnesium hydroxide (MH) are two typical non-halogenated flame retardant additives. When heated, they undergo an endothermic reaction, interfering with the combustion process. Simultaneously, the water vapor produced during decomposition dilutes combustible gases, thus inhibiting flame spread. However, nano-hydroxide particles are highly polar, especially as the particles become increasingly smaller, making them prone to aggregation. Furthermore, they are difficult to disperse uniformly in polymers and have poor adhesion to the base material, easily causing interfacial defects. This leads to a decline in material properties and affects their effectiveness as flame retardant additives. Summary of the Invention

[0004] The purpose of this invention is to provide a high flame-retardant polypropylene foamed granule and its preparation method, which has the effects of good mechanical properties and good flame-retardant effect.

[0005] The above-mentioned technical objective of the present invention is achieved by the following technical solution: by mass parts, it includes 80-90 parts of polypropylene, 3-5 parts of toughening agent, 4-12 parts of filler, 0.3-1 parts of stabilizer, 0.2-2 parts of lubricant, 0.1-0.5 parts of nucleating agent and 3-5 parts of composite modified nano flame retardant.

[0006] A further provision of the present invention is that the preparation method of the composite modified nano flame retardant includes the following steps: S1. Mix 5 parts of nano flame retardant with distilled water, add dispersant, disperse using ultrasound, then add 0.5~1 parts of dopamine hydrochloride to the dispersion, adjust the pH value to 8.5 with NaOH solution, stir continuously for 2~3 hours, use centrifuge to achieve solid-liquid separation, wash the centrifuged product with ethanol and dry it to obtain polydopamine-encapsulated nano flame retardant; S2. The polydopamine-encapsulated nano flame retardant is mixed at high speed with deionized water, water-based coupling agent and water-based dispersant, and then ultrasonically dispersed into a polydopamine-encapsulated nano flame retardant nano suspension. S3. Mix 0.5~1 part of ammonium polyphosphate with deionized water and water-based dispersant at high speed and disperse it ultrasonically to form an ammonium polyphosphate nano suspension. S4. The polydopamine-encapsulated nano flame retardant nano suspension and the ammonium polyphosphate nano suspension are mixed at high speed to obtain a composite modified nano flame retardant suspension, and the particle size is controlled to have a 90% pass rate of 80-110 nm.

[0007] A further provision of the present invention is that the nano flame retardant includes one or more of nano aluminum hydroxide, nano titanium dioxide, nano silicon dioxide, nano zinc oxide, and carbon nanotubes.

[0008] The present invention is further configured such that: the toughening agent comprises at least one of ethylene-butene copolymer, ethylene-octene copolymer, and propylene-based elastomer; the stabilizer comprises at least one of hindered phenolic heat stabilizer, phosphite heat stabilizer, and hindered amine light stabilizer; and the lubricant comprises at least one of calcium stearate, PE wax, zinc stearate, ethylene bis-stearamide, and erucamide.

[0009] A further provision of the present invention is that the filler comprises at least one of zeolite, diatomaceous earth, and silica activated by a coupling agent.

[0010] A further provision of the present invention includes the following steps: S1. Add polypropylene resin, toughening agent, filler, stabilizer, lubricant, nucleating agent and composite modified nano flame retardant to a high-speed mixer and mix evenly at 10~20℃ to obtain polypropylene foam material. S2. Add polypropylene foam material to a three-screw extruder for plasticizing and mixing. Then, inject supercritical fluid into the homogenization section of the three-screw extruder, control the die pressure to 5~25Mpa and the die temperature to 110~160℃, and then release the pressure through the die instantly to foam and obtain ultrafine microporous foamed polypropylene. S3. Ultrafine microporous foamed polypropylene is granulated by water heat exchange on the mold surface, dried, and sieved to obtain polypropylene resin foamed granules.

[0011] A further feature of the present invention is that the supercritical fluid is supercritical CO2, and the amount added is 2% to 10% of the mass of the polypropylene foaming material.

[0012] The beneficial effects of this invention are: 1. Polydopamine encapsulates nano-flame retardants through its adhesive properties, forming a "nanocoat" that modifies the surface of the nanoparticles. The numerous catechol groups distributed on the polydopamine surface give the nanoparticles a negative charge, and the strong electrostatic repulsion results in good stability and dispersibility for the polydopamine-encapsulated nanoparticles. Multiple nano-flame retardants are modified by dopamine encapsulation; polydopamine has good film-forming properties, and the bond between dopamine and the nano-flame retardant is tight, preventing the modifier from easily detaching.

[0013] 2. Adding nano flame retardants to polypropylene is beneficial because nano flame retardants have a high specific surface area and pore capacity. Introducing nano flame retardants into the polymer matrix can help improve the shortcomings of flame retardants such as easy migration and loss, thereby effectively improving the flame retardancy and mechanical properties of the polymer.

[0014] 3. Ammonium polyphosphate combines with the catechol groups on the surface of dopamine. The polydopamine nano flame retardant is then encapsulated with ammonium polyphosphate to obtain a composite modified nano flame retardant. The combination of ammonium polyphosphate and polydopamine can simultaneously reduce the polarity of both, improve the compatibility of the composite modified nano flame retardant with polypropylene, and enable the composite modified nano flame retardant to be uniformly dispersed in polypropylene.

[0015] 4. Ammonium polyphosphate is also a good flame retardant. It expands (carbonizes) when heated, isolates (air), and provides insulation (lowers the ignition point). APP decomposes upon heating to produce poly / polyphosphoric acid (a strong dehydrating agent), promoting dehydration and carbonization of organic surfaces. Upon heating, the non-volatile phosphorus oxides and polyphosphoric acid cover the substrate surface, isolating it from air and thus achieving flame retardancy. The synergistic effect of ammonium polyphosphate with nano-flame retardants can improve the flame retardant effect and reduce the amount of flame retardant used. Detailed Implementation

[0016] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Example 1

[0017] The preparation method of the composite modified nano flame retardant includes the following steps: S1. Mix 5 parts of nano aluminum hydroxide with distilled water, add a dispersant, disperse using ultrasound, then add 1 part of dopamine hydrochloride to the dispersion, adjust the pH value to 8.5 using NaOH solution, stir continuously for 2-3 hours, separate solid and liquid using a centrifuge, wash the centrifuged product with ethanol and dry it to obtain polydopamine-encapsulated nano flame retardant. S2. The polydopamine-encapsulated nano flame retardant is mixed at high speed with deionized water, water-based coupling agent and water-based dispersant, and then ultrasonically dispersed into a polydopamine-encapsulated nano flame retardant nano suspension. S3. Mix 0.5 parts of ammonium polyphosphate with deionized water and an aqueous dispersant at high speed and then ultrasonically disperse the mixture into an ammonium polyphosphate nano suspension. S4. The polydopamine-encapsulated nano flame retardant nano suspension and the ammonium polyphosphate nano suspension are mixed at high speed to obtain a composite modified nano flame retardant suspension, and the particle size is controlled to have a 90% pass rate of 80-110 nm.

[0018] A method for preparing highly flame-retardant polypropylene foamed granules includes the following steps: S1. Add 90 parts of polypropylene, 5 parts of ethylene-butene copolymer, 12 parts of zeolite activated by coupling agent, 0.3 parts of hindered phenolic heat stabilizer, 2 parts of calcium stearate, 0.1 parts of cerium stearate complex and 5 parts of composite modified nano flame retardant to a high-speed mixer and mix evenly at 10~20℃ to obtain polypropylene foam material. S2. Add polypropylene foam material to a three-screw extruder for plasticizing and mixing. Then, inject supercritical fluid into the homogenization section of the three-screw extruder, control the die pressure at 5~25 MPa and the die temperature at 110~160℃, and then release the pressure through the die instantaneously to foam, thereby obtaining ultra-fine microporous foamed polypropylene. The supercritical fluid is supercritical CO2, and the addition amount is 2%~10% of the mass of the polypropylene foam material. S3. Ultrafine microporous foamed polypropylene is granulated by water heat exchange on the mold surface, dried, and sieved to obtain polypropylene resin foamed granules. Example 2

[0019] The preparation method of the composite modified nano flame retardant includes the following steps: S1. Mix 5 parts of nano-titanium dioxide with distilled water, add a dispersant, disperse using ultrasound, then add 0.5 parts of dopamine hydrochloride to the dispersion, adjust the pH value to 8.5 using NaOH solution, stir continuously for 2-3 hours, separate solid and liquid using a centrifuge, wash the centrifuged product with ethanol and dry it to obtain polydopamine-encapsulated nano flame retardant. S2. The polydopamine-encapsulated nano flame retardant is mixed at high speed with deionized water, water-based coupling agent and water-based dispersant, and then ultrasonically dispersed into a polydopamine-encapsulated nano flame retardant nano suspension. S3. Mix 1 part of ammonium polyphosphate with deionized water and aqueous dispersant at high speed and disperse it ultrasonically to form an ammonium polyphosphate nano suspension. S4. The polydopamine-encapsulated nano flame retardant nano suspension and the ammonium polyphosphate nano suspension are mixed at high speed to obtain a composite modified nano flame retardant suspension, and the particle size is controlled to have a 90% pass rate of 80-110 nm.

[0020] A method for preparing highly flame-retardant polypropylene foamed granules includes the following steps: S1. Add 80 parts of polypropylene, 10 parts of ethylene-octene copolymer, 4 parts of diatomaceous earth activated by coupling agent, 1 part of phosphite heat stabilizer, 0.2 parts of PE wax, 0.5 parts of cerium stearate complex and 3 parts of composite modified nano flame retardant to a high-speed mixer and mix evenly at 10~20℃ to obtain polypropylene foam material. S2. Add polypropylene foam material to a three-screw extruder for plasticizing and mixing. Then, inject supercritical fluid into the homogenization section of the three-screw extruder, control the die pressure at 5~25 MPa and the die temperature at 110~160℃, and then release the pressure through the die instantaneously to foam, thereby obtaining ultra-fine microporous foamed polypropylene. The supercritical fluid is supercritical CO2, and the addition amount is 2%~10% of the mass of the polypropylene foam material. S3. Ultrafine microporous foamed polypropylene is granulated by water heat exchange on the mold surface, dried, and sieved to obtain polypropylene resin foamed granules. Example 3

[0021] The difference between Example 3 and Example 1 is that the preparation method of the composite modified nano flame retardant includes the following steps: S1. Mix 5 parts of nano aluminum hydroxide with distilled water, add a dispersant, disperse using ultrasound, then add 1 part of dopamine hydrochloride to the dispersion, adjust the pH to 8.5 using NaOH solution, stir continuously for 2-3 hours, and use a centrifuge to achieve solid-liquid separation. After centrifugation, wash the product with ethanol and dry it to obtain polydopamine-encapsulated nano flame retardant. Example 4

[0022] The difference between Example 4 and Example 1 is that the flame retardant used is 4 parts of nano aluminum hydroxide. Example 5

[0023] The difference between Example 5 and Example 1 is that no flame retardant was added.

[0024] Test data Polypropylene foamed granules were prepared according to the steps in Examples 1-5, and the mechanical and flammability properties of the polypropylene foamed granules were tested. Mechanical properties included tensile strength, flexural strength, and notched impact strength. Tensile property testing was performed according to GB / TG 1040.2-2006 standard. Flammability: The limiting oxygen index (LOI) of EPP materials with different formulations was determined using an FTT oxygen index meter, according to GB / T 2406.2—2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics". The test data are shown in Table 1 below:

[0025] The experimental data show that the polypropylene foamed particles in Examples 1 and 2 have good mechanical and flame-retardant properties. In Example 3, the flame retardant did not use ammonium polyphosphate for secondary encapsulation, resulting in lower mechanical properties and limiting oxygen index of the polypropylene foamed particles. This indicates that ammonium polyphosphate and the nano-flame retardant have a synergistic flame-retardant effect. Simultaneously, the combination of ammonium polyphosphate and polydopamine can reduce the polarity of both, improve the compatibility of the composite modified nano-flame retardant with polypropylene, and allow the composite modified nano-flame retardant to be uniformly dispersed in the polypropylene, thereby effectively improving the flame retardancy and mechanical properties of the polymer. The flame retardant in Example 4 used… The data for Example 5, which uses an unmodified nano-flame retardant, shows that both the mechanical and flame retardant properties of polypropylene are reduced. This indicates that the dopamine-modified nano-flame retardant has good dispersibility and can improve the flame retardancy and mechanical properties of the polymer. In Example 5, no flame retardant was added, and the limiting oxygen index was significantly reduced. However, the mechanical property parameters were higher than those in Examples 4 and 5, but slightly lower than those in Examples 1 and 2. This suggests that adding flame retardants with poor dispersibility or poor compatibility with polypropylene will negatively affect the mechanical strength of foamed polypropylene. Only by using a composite modified nano-flame retardant with good dispersibility and good compatibility with polypropylene can both flame retardancy and mechanical properties be improved simultaneously.

Claims

1. A high flame-retardant polypropylene foam granule, characterized in that: By weight, it includes 80-90 parts of polypropylene, 3-5 parts of toughening agent, 4-12 parts of filler, 0.3-1 part of stabilizer, 0.2-2 parts of lubricant, 0.1-0.5 parts of nucleating agent and 3-5 parts of composite modified nano flame retardant; The preparation method of the composite modified nano flame retardant includes the following steps: S1. Mix 5 parts of nano flame retardant with distilled water, add dispersant, disperse using ultrasound, then add 0.5~1 parts of dopamine hydrochloride to the dispersion, adjust the pH value to 8.5 with NaOH solution, stir continuously for 2~3 hours, use centrifuge to achieve solid-liquid separation, wash the centrifuged product with ethanol and dry it to obtain polydopamine-encapsulated nano flame retardant; S2. The polydopamine-encapsulated nano flame retardant is mixed at high speed with deionized water, water-based coupling agent and water-based dispersant, and then ultrasonically dispersed into a polydopamine-encapsulated nano flame retardant nano suspension. S3. Mix 0.5~1 part of ammonium polyphosphate with deionized water and water-based dispersant at high speed and disperse it ultrasonically to form an ammonium polyphosphate nano suspension. S4. The polydopamine-encapsulated nano flame retardant nano suspension and the ammonium polyphosphate nano suspension are mixed at high speed to prepare a composite modified nano flame retardant suspension, and the particle size is controlled to have a 90% pass rate of 80-110 nm. The nano flame retardant includes one or more of nano aluminum hydroxide, nano titanium dioxide, nano silicon dioxide, nano zinc oxide, and carbon nanotubes.

2. The high flame-retardant polypropylene foam granules according to claim 1, characterized in that: The toughening agent comprises at least one of ethylene-butene copolymer, ethylene-octene copolymer, and propylene-based elastomer; the stabilizer comprises at least one of hindered phenolic heat stabilizer, phosphite heat stabilizer, and hindered amine light stabilizer; the lubricant comprises at least one of calcium stearate, PE wax, zinc stearate, ethylene bis-stearamide, and erucamide.

3. The high flame-retardant polypropylene foam granules according to claim 1, characterized in that: The filler comprises at least one of zeolite, diatomaceous earth, and silica activated by a coupling agent.

4. The method for preparing high flame-retardant polypropylene foamed granules according to claim 1, characterized in that: Includes the following steps: S1. Add polypropylene resin, toughening agent, filler, stabilizer, lubricant, nucleating agent and composite modified nano flame retardant to a high-speed mixer and mix evenly at 10~20℃ to obtain polypropylene foam material. S2. Add polypropylene foam material to a three-screw extruder for plasticizing and mixing. Then, inject supercritical fluid into the homogenization section of the three-screw extruder, control the die pressure to 5~25Mpa and the die temperature to 110~160℃, and then release the pressure through the die instantly to foam and obtain ultrafine microporous foamed polypropylene. S3. Ultrafine microporous foamed polypropylene is granulated by water heat exchange on the mold surface, dried, and sieved to obtain polypropylene resin foamed granules.

5. The method for preparing high flame-retardant polypropylene foamed granules according to claim 4, characterized in that: The supercritical fluid is supercritical CO2, and the amount added is 2% to 10% of the mass of the polypropylene foam material.

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