Flame-retardant toughening agent for polypropylene material and preparation method of flame-retardant toughening agent

Abstract

The invention discloses a flame-retardant toughening agent for a polypropylene material and a preparation method of the flame-retardant toughening agent, and relates to the technical field of flame-retardant toughening agents. The flame-retardant toughening agent for the polypropylene material is prepared from the following raw materials: a polypropylene carrier, ethylene-octylene elastomer grafted maleic anhydride, a modified polypropylene compatilizer, modified ammonium polyphosphate, pentaerythritol, melamine cyanurate, a zinc oxide-zinc borate compound synergist, polytetrafluoroethylene micro powder, nano silicon dioxide and a hindered phenol antioxidant. The composition comprises a phosphate antioxidant, oxidized polyethylene wax, calcium stearate, a nucleating agent and an ammonium molybdate smoke suppressant. According to the invention, a polypropylene carrier is taken as a matrix, ethylene-octylene elastomer grafted maleic anhydride and a modified polypropylene compatilizer are introduced synergistically to construct a plurality of raw materials such as a polar gradient interface, so that synergic improvement of flame retardance and toughening performance is realized on the premise of not significantly sacrificing flow and strength; it is expected that a stable vertical combustion rating and higher carbon layer integrity and impact resistance retention rate can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flame-retardant toughening agent, in particular to a flame-retardant toughening agent for polypropylene material and a preparation method thereof. BACKGROUND

[0002] Polypropylene is widely used in electrical, automotive and building components due to its low specific gravity, high chemical resistance and high molding efficiency, but its limiting oxygen index is low, it is easy to drip during burning and has high heat release rate, and usually only reaches UL-94 HB; at the same time, its toughness under low temperature and with notches is insufficient. In order to meet the dual requirements of flame retardation and impact resistance, an intumescent flame-retardant system is often used together with an elastomer in engineering. However, polypropylene is a non-polar matrix, and the flame-retardant powder is mostly hydrophilic and polar, so the interface compatibility and dispersion stability become limiting factors, which easily causes the decline of mechanical properties and the fluctuation of flame-retardant failure, and there are also problems of difficulty in balancing flame retardation and toughening, and insufficient long-term stability and manufacturing consistency. SUMMARY

[0003] In view of the deficiencies of the prior art, the present application provides a flame-retardant toughening agent for polypropylene material and a preparation method thereof to solve the problems in the background art.

[0004] To achieve the above-mentioned purpose, the present application provides the following technical scheme: The first object of the present application is to provide a flame-retardant toughening agent for polypropylene material, which comprises the following raw materials by weight: 20-60 parts of polypropylene carrier; 20-80 parts of ethylene-octene elastomer grafted maleic anhydride; 5-20 parts of modified polypropylene compatibilizer; 40-120 parts of modified ammonium polyphosphate; 10-35 parts of pentaerythritol; 10-40 parts of melamine cyanurate; 2-8 parts of zinc oxide-zinc borate compound synergist; 0.5-2.0 parts of polytetrafluoroethylene micro powder; 1-5 parts of nano-silicon dioxide; 0.2-1.0 parts of hindered phenol antioxidant; 0.2-1.0 parts of phosphate ester antioxidant; 1-6 parts of oxidized polyethylene wax; 0.5-3.0 parts of calcium stearate; 0.2-1.5 parts of nucleating agent; 0.5-3.0 parts of ammonium molybdate smoke suppressant.

[0005] Further optimization of the technical solution, the polypropylene carrier is based on homopolymer polypropylene particles, obtained by melt homogenization and particle size control, the preparation process is as follows: Select polypropylene resin with melt mass flow rate of 10-40 g / 10 min, first hot air drying at 80-90 ℃ for 2-4 h to ensure the moisture content is less than 0.2 wt%; Then melt homogenization in a twin-screw extruder, the temperature zone is set to 170 / 180 / 190 / 195 / 200 ℃, screw speed is 200-300 rpm, the actual temperature of the melt is controlled at 195-205 ℃; In the melt state, the low molecular and residual moisture are removed by vacuum exhaust section, the extruded strip is rapidly cooled in a cooling water tank, and the granulator is cut into uniform particles with a particle size of 2-3 mm to obtain the polypropylene carrier.

[0006] Further optimization of the technical solution, the preparation process of ethylene-octene elastomer grafted maleic anhydride is as follows: Select ethylene-octene elastomer with melt mass flow rate of 0.5-3.0 g / 10 min, pre-dry at 70-80 ℃ for 1-2 h; Maleic anhydride is injected into the twin-screw side feed port through a metering pump at a proportion of 0.5-1.2 wt%, and an initiator is added, the initiator is dicumyl peroxide, the amount is 0.02-0.08 wt% relative to the elastomer; The temperature zone of the extruder is controlled at 170 / 180 / 185 / 190 / 195 ℃, the screw speed is 150-300 rpm, and the actual temperature of the melt is maintained at 185-195 ℃, and vacuum exhaust is used to remove unreacted monomers to obtain the final product.

[0007] Further optimization of the technical solution, the preparation process of pentaerythritol is as follows: First, mix formaldehyde and acetaldehyde in a molar ratio of 2-3:1-2 in a reaction kettle, in the presence of alkali catalyst sodium hydroxide, generate trihydroxymethyl acetaldehyde intermediate at 50-60 ℃; Then, in a high-pressure hydrogenation reactor, under the action of Raney nickel catalyst, hydrogenate at 4-5 MPa hydrogen pressure and 100-120 ℃, the reaction liquid is concentrated under reduced pressure, crystallized and precipitated, and the filter cake is dried at 80 ℃ under vacuum to obtain pentaerythritol.

[0008] Further optimization of the technical solution, the melamine cyanurate is prepared by precipitation method: Dissolve melamine in deionized water, the concentration is 5-10 wt%, form a uniform solution at 70-80 ℃; Take cyanuric acid suspension, concentration 5-10 wt%, keep temperature 25-30 ℃, slowly add melamine solution into cyanuric acid suspension under stirring condition, control molar ratio 1:1, adjust pH to 6.5-7.5 during reaction; maintain stirring for 1-2 h, generate white precipitate; After filtration and washing, the obtained precipitate is dried at 80 ℃ under vacuum for 6-8 h to obtain melamine cyanurate.

[0009] Further optimize the technical solution, the modified polypropylene compatibilizer is based on homopolymer polypropylene, and the polarity modification is realized by maleic anhydride grafting. The preparation process is as follows: First, select polypropylene particles with a melt mass flow rate of 10-40 g / 10 min, dry at 80 ℃ for 3 h, and ensure that the water content is less than 0.2 wt%; In the twin-screw reaction extruder, the amount of maleic anhydride is 0.4-1.0 wt%, and the initiator is dicumyl peroxide, the amount is 0.02-0.06 wt%; The temperature zone is set to 175 / 185 / 190 / 195 / 200 ℃, the screw speed is 200-280 rpm, and the vacuum exhaust is -0.08 MPa to remove residual monomers. After cooling and granulation of the grafted product, the modified polypropylene compatibilizer is obtained.

[0010] Further optimize the technical solution, prepare polyphosphoric acid ammonium by polycondensation reaction process, and modify the polyphosphoric acid ammonium: Mix the prepared polyphosphoric acid ammonium in ethanol-water mixed solvent, add 0.5-1.5 wt% γ-aminopropyl triethoxysilane, stir at 70-80 ℃ for 0.5-1 h, filter and dry, residual solvent ≤0.2 wt%, to obtain modified polyphosphoric acid ammonium.

[0011] Further optimize the technical solution, the zinc oxide-zinc borate complex synergist is prepared by two-step method of liquid phase precipitation and solid phase compounding; The liquid phase precipitation specifically includes: Take zinc oxide powder, prepare 30-40 wt% uniform slurry according to solid-liquid ratio 1:6-1:8, under stirring condition, add boric acid solution dissolved in hot water, control the molar ratio of Zn:B=1:1.2-1.5; the reaction temperature is maintained at 60-85 ℃, the reaction time is 1.5-3 h, and the system pH is stabilized at 7.0-7.8. In this process, the suspension of basic zinc borate precipitate is generated; The suspension is filtered and washed to a conductivity < 50 µS / cm to remove free ions, the wet filter cake is dried at 100-110 ℃ for 6-8 h, and then air-jet milled to obtain zinc borate powder with an average particle size D50 = 1-5 µm.

[0012] Further optimization of the present technical solution, the solid phase recombination specifically includes: The dry zinc borate powder is recombined with zinc oxide powder at a molar ratio of ZnO:ZnB of 1:3-1:5, and stirred at 800-1000 rpm for 15-30 min using a high-speed mixer; Surface treatment is performed using 0.5-1.0 wt% silane coupling agent, refluxing in an ethanol solution at 70-80 ℃ for 0.5-1 h, and then filtering and drying to obtain the zinc oxide-zinc borate recombination synergist.

[0013] The second object of the present application is to provide a preparation method of the flame-retardant toughening agent as described above, comprising the following specific steps: S1, raw material pretreatment and drying; S2, raw material weighing and premixing; S3, melting plasticization and main feeding; S4, side feeding, segmented addition and synergistic dispersion; S5, granulation and post-treatment; S6, process quality control and sample retention.

[0014] Compared with the prior art, the present application provides a flame-retardant toughening agent for polypropylene material and a preparation method thereof, which has the following beneficial effects: The flame-retardant toughening agent for polypropylene material, by taking polypropylene carrier as the matrix, synergistically introducing ethylene-octene elastomer grafted maleic anhydride and modified polypropylene compatibilizer to construct a polar gradient interface; using modified ammonium polyphosphate, pentaerythritol, melamine cyanurate to form an expanded carbon layer system; using zinc oxide-zinc borate recombination synergist and nano-silicon dioxide to realize carbon layer mineralization-skeleton composite; using polytetrafluoroethylene powder to suppress dripping; using hindered phenolic antioxidant and phosphate antioxidant to improve processing and long-term heat and oxygen stability; and using oxidized polyethylene wax, calcium stearate, nucleating agent and ammonium molybdate smoke suppressant to optimize rheology, crystallization and smoke suppression. Thus, without significantly sacrificing flow and strength, the flame-retardant and toughening properties are synergistically improved, and stable vertical burning rating, higher carbon layer integrity and impact retention rate are expected, which meets the manufacturing consistency requirements of multi-cavity and regeneration conditions. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0016] Figure 1 A preparation process schematic diagram of a flame-retardant toughening agent for a polypropylene material is provided for the present application. DETAILED DESCRIPTION

[0017] In order to make the above-mentioned purposes, features and advantages of the present application more apparent and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the drawings of the specification.

[0018] In the following description, a large number of specific details are set forth in order to facilitate a thorough understanding of the present application, but the present application can also be implemented in other ways different from the description, and those skilled in the art can make similar generalizations without departing from the connotation of the present application, therefore the present application is not limited by the specific embodiments disclosed below.

[0019] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor does it mean an embodiment that is separate or selectively excluded from other embodiments.

[0020] A flame-retardant toughening agent for a polypropylene material includes the following raw materials by weight: 20-60 parts of polypropylene carrier; as a matrix and rheological adjustment platform, providing processing fluidity and thermal stability, ensuring uniform dispersion and molding consistency of the flame-retardant phase and the toughening phase.

[0021] 20-80 parts of ethylene-octene elastomer grafted maleic anhydride; as a toughening and interface polarity transition phase, improving notch impact and low-temperature brittle fracture resistance, and improving adhesion with intumescent flame-retardant powder.

[0022] 5-20 parts of modified polypropylene compatibilizer; establishing a chemical / physical bridge between polypropylene and the polar flame-retardant system, reducing interfacial tension, and inhibiting phase separation and strength loss.

[0023] 40-120 parts of modified ammonium polyphosphate; providing an acid source and generating polyphosphoric acid to promote carbonization and expansion when heated, significantly reducing heat release and flame propagation.

[0024] 10-35 parts of pentaerythritol; as a carbon source and foaming skeleton donor, participating in the formation of the expanded carbon layer, making the carbon layer dense, complete and improving the heat insulation.

[0025] 10-40 parts of melamine cyanurate; providing nitrogen source and gas phase dilution effect, synergistically suppressing smoke and building intumescent char layer with acid / carbon source.

[0026] 2-8 parts of zinc oxide-zinc borate synergistic agent; promoting char layer mineralization and inorganic skeleton formation, enhancing char layer strength and buffering acidity, stabilizing flame retardant efficiency.

[0027] 0.5-2.0 parts of polytetrafluoroethylene micro powder (Teflon® MP 1100); in situ fiberization under melt shear to suppress dripping, improving UL-94 rating stability of intumescent system.

[0028] 1-5 parts of nano-silica (AEROSIL® R972); building inorganic nano skeleton and suppressing melt flow, enhancing char layer density and heat resistance stability.

[0029] 0.2-1.0 parts of hindered phenolic antioxidant (Irganox® 1010); as primary antioxidant, chain scission and free radical scavenging, improving processing and long-term thermal-oxidative stability.

[0030] 0.2-1.0 parts of phosphate ester antioxidant (Irganox® 168); as secondary antioxidant, decomposing hydroperoxide, synergistically inhibiting thermal degradation and discoloration with hindered phenolic system.

[0031] 1-6 parts of oxidized polyethylene wax (Honeywell A-C® 316A); as internal and external lubricant and demolding aid, regulating melt viscosity and improving extrusion, injection molding rheology.

[0032] 0.5-3.0 parts of calcium stearate (industrial grade CaSt-1); providing internal and external lubrication and acid capture effect, reducing shear heating and adhesion, improving surface and dimensional stability.

[0033] 0.2-1.5 parts of nucleating agent (Millad® NX-8000); increasing crystallization rate and crystallinity, improving rigidity and transparency and shortening molding cycle.

[0034] 0.5-3.0 parts of ammonium molybdate smoke suppressant ((NH4)2MoO4, industrial grade); promoting carbonization and suppressing smoke and harmful gas generation during pyrolysis, enhancing flame retardant synergistic effect.

[0035] The polypropylene carrier is based on homopolymer polypropylene particles, obtained by melt homogenization and particle size control, and the preparation process is as follows: Select polypropylene resin with melt mass flow rate of 10–40 g / 10 min, first hot air drying at 80–90 ℃ for 2–4 h to ensure the moisture content is less than 0.2 wt%; Subsequently melt homogenization in a twin-screw extruder, temperature zone is set to 170 / 180 / 190 / 195 / 200 ℃ in turn, screw speed is 200–300 rpm, the actual temperature of the melt is controlled at 195–205 ℃; In the molten state, the low molecular and residual moisture are removed by vacuum exhaust section (-0.08~-0.095 MPa), the extruded strip is rapidly cooled in a cooling water tank, and then cut into uniform particles with a particle size of 2–3 mm by a granulator to obtain a polypropylene carrier. The obtained polypropylene carrier has good fluidity and thermal stability, providing a basic masterbatch platform for embedding of subsequent functional additives.

[0036] The preparation process of the ethylene-octene elastomer grafted maleic anhydride is as follows: Select ethylene-octene elastomer with a melt mass flow rate of 0.5–3.0 g / 10 min, and dry it at 70–80 ℃ for 1–2 h in advance; Maleic anhydride is injected into the twin-screw side feed port through a metering pump at a proportion of 0.5–1.2 wt%, and an initiator is added at the same time. The initiator is dicumyl peroxide (DCP), and its dosage is 0.02–0.08 wt% relative to the elastomer; The temperature zone of the extruder is controlled at 170 / 180 / 185 / 190 / 195 ℃, the screw speed is 150–300 rpm, the actual temperature of the melt is maintained at 185–195 ℃, and vacuum exhaust is used to remove unreacted monomers to obtain the final product. This material can significantly improve the compatibility and impact toughness as an interface regulator of the toughening phase and the flame retardant system.

[0037] The preparation process of the pentaerythritol is as follows: First, mix formaldehyde and acetaldehyde in a molar ratio of 2–3:1–2 in a reaction kettle, and generate a trihydroxymethyl acetaldehyde intermediate in the presence of a base catalyst sodium hydroxide at 50–60 ℃; Subsequently, hydrogenate in a high-pressure hydrogenation reactor under the action of Raney nickel catalyst at a hydrogen pressure of 4–5 MPa and a temperature of 100–120 ℃. After the reaction solution is concentrated under reduced pressure and crystallized, the filter cake is dried at 80 ℃ under vacuum to obtain pentaerythritol. The particle size of the obtained pentaerythritol is controlled at 50–150 µm. This material can significantly improve the char yield and flame retardant efficiency as a carbon source in the polypropylene flame-retardant toughener and cooperates with modified ammonium polyphosphate and melamine cyanurate.

[0038] The melamine cyanurate is prepared by a precipitation method. The melamine is dissolved in deionized water with a concentration of 5-10 wt%, and a uniform solution is formed at 70-80 ℃; Another cyanuric acid suspension is prepared with a concentration of 5-10 wt%, and the temperature is maintained at 25-30 ℃. The melamine solution is slowly added to the cyanuric acid suspension under stirring, and the molar ratio is controlled to be 1:1. The pH is adjusted to 6.5-7.5 during the reaction. The stirring is maintained for 1-2 h, and a white precipitate is formed; The obtained precipitate is filtered, washed, and dried at 80 ℃ under vacuum for 6-8 h to obtain melamine cyanurate. The final product has a particle size distribution D50=3-8 µm and a specific surface area of 6-12 m² / g. As a nitrogen source and smoke suppressant, the material can be used in combination with modified ammonium polyphosphate and pentaerythritol to form a dense and expanded carbon layer, thereby improving the flame retardant properties of polypropylene.

[0039] The modified polypropylene compatibilizer is based on homopolymer polypropylene, and the polarity modification is achieved by grafting maleic anhydride. The preparation process is as follows: First, polypropylene particles with a melt mass flow rate of 10-40 g / 10 min are selected, dried at 80 ℃ for 3 h, and the water content is ensured to be less than 0.2 wt%; In a twin-screw reaction extruder, the amount of maleic anhydride is 0.4-1.0 wt%, and the initiator is dicumyl peroxide with a dosage of 0.02-0.06 wt%; The temperature zone is set to 175 / 185 / 190 / 195 / 200 ℃, the screw speed is 200-280 rpm, and the vacuum exhaust is -0.08 MPa to remove residual monomers. After cooling and granulation, the grafted product is obtained. Through this modification, the polypropylene matrix can maintain good compatibility when compounded with the phosphorus-nitrogen flame retardant system, avoiding interface delamination and stress concentration, thereby improving the overall stability of the flame retardant toughener.

[0040] The polyphosphoric acid ammonium is prepared by a condensation reaction process, and the polyphosphoric acid ammonium is modified: The prepared polyphosphoric acid ammonium is mixed in an ethanol-water mixed solvent, 0.5-1.5 wt% γ-aminopropyl triethoxysilane is added, and stirred at 70-80 ℃ for 0.5-1 h. After filtration and drying, the residual solvent is ≤0.2 wt%, and the modified polyphosphoric acid ammonium is obtained. The prepared modified polyphosphoric acid ammonium has the characteristics of thermal decomposition temperature ≥300 ℃ and moisture absorption rate ≤0.6 wt%, and can form a stable expanded carbon layer in the flame retardant toughener.

[0041] The zinc oxide-zinc borate complex synergist is prepared by a two-step method of liquid phase precipitation and solid phase compounding.

[0042] Liquid phase precipitation, specifically including: Zinc oxide powder (purity ≥ 99%, average particle size D50 = 0.5-1.0 µm) is weighed and prepared into a uniform slurry of 30-40 wt% according to the solid-liquid ratio of 1:6-1:8. Under stirring conditions, boric acid solution dissolved in hot water is added to the slurry. The molar ratio of Zn:B is controlled at 1:1.2-1.5. The reaction temperature is maintained at 60-85 ℃, the reaction time is 1.5-3 h, and the pH of the system is stabilized at 7.0-7.8. During this process, a suspension of basic zinc borate precipitate is generated; The suspension is filtered and washed until the conductivity is < 50 µS / cm to remove free ions. The wet filter cake is dried at 100-110 ℃ for 6-8 h, and then ground by airflow to obtain zinc borate powder with an average particle size D50 = 1-5 µm.

[0043] Solid phase recombination, specifically including: The dry zinc borate powder is recombined with zinc oxide powder at a molar ratio of ZnO:ZnB of 1:3-1:5. A high-speed mixer is used to stir at 800-1000 rpm for 15-30 min. Surface treatment is performed using 0.5-1.0 wt% silane coupling agent (γ-aminopropyl triethoxysilane) in an ethanol-water (7 / 3) solution at 70-80 ℃ under reflux for 0.5-1 h. After filtration and drying, the zinc oxide-zinc borate recombination synergist is obtained. The particle size distribution is concentrated (D90 ≤ 8 µm), and the dispersibility in the polypropylene matrix is good. When used in combination with modified ammonium polyphosphate, pentaerythritol, and melamine cyanurate, the material can promote the mineralization of the intumescent carbon layer and significantly improve the thermal stability and smoke suppression performance of the flame-retardant system.

[0044] Reference Figure 1 , the preparation method of the flame-retardant toughening agent for polypropylene material, specifically including: S1, raw material pretreatment and drying; Modified ammonium polyphosphate, pentaerythritol, melamine cyanurate, and nano-silicon dioxide are hot air dried at 80-90 ℃ for 2-4 h, with a target moisture content of ≤0.2 wt%. Sieving is performed to D90 ≤ 30 µm (nano-silicon dioxide maintains the original dispersion). Polypropylene carrier, ethylene-octene elastomer grafted maleic anhydride, modified polypropylene compatibilizer, polytetrafluoroethylene powder, zinc oxide-zinc borate recombination synergist, nucleating agent, and ammonium molybdate smoke suppressant are stored at room temperature and protected from moisture. Hindered phenolic antioxidant and phosphate antioxidant are stored in airtight and light-proof conditions. Oxidized polyethylene wax and calcium stearate are stored at room temperature in a sealed state to prevent caking and moisture absorption.

[0045] S2, raw material weighing and premixing; The raw materials are weighed according to the proportions. Group A: polypropylene carrier, ethylene-octene elastomer grafted maleic anhydride, modified polypropylene compatibilizer, oxidized polyethylene wax, calcium stearate, hindered phenolic antioxidant, phosphate antioxidant, planetary mixing for 3-5 min. Group B: modified ammonium polyphosphate, pentaerythritol, melamine salt, zinc oxide-zinc borate complex synergist, nano-silicon dioxide, polytetrafluoroethylene powder, nucleating agent, ammonium molybdate smoke suppressant, low-speed stirring for 2-3 min to avoid powder scattering. Ensure that the batch-to-batch deviation is ≤±0.2 parts; record the ambient humidity ≤55% RH.

[0046] S3, melt plasticization and main feeding; The twin-screw extruder L / D ≥ 40, temperature zone 185 / 190 / 195 / 200 / 200 ℃, screw speed 200-300 rpm, vacuum exhaust -0.08~-0.095 MPa. Continuously add Group A to the main feeding port to form a stable phase of ethylene-octene elastomer grafted maleic anhydride and modified polypropylene compatibilizer; adjust the rheology of oxidized polyethylene wax and calcium stearate. The target melt temperature is 195-205 ℃, specific torque ≤65% of the rated value, and melt pressure fluctuation ≤±5 bar, to ensure uniform plasticization of the matrix phase and provide sufficient coating conditions for the flame-retardant phase.

[0047] S4, side feeding and synergistic dispersion; Side feeding 1 adds modified ammonium polyphosphate and pentaerythritol in the middle section, and the local shear of the screw is increased to 1.2-1.4 times the baseline; side feeding 2 adds melamine salt, zinc oxide-zinc borate complex synergist, and nano-silicon dioxide; polytetrafluoroethylene powder is added through a small-scale metering port at the end (in the form of a small-ratio master batch containing 10-20 wt%). The hindered phenolic antioxidant and phosphate antioxidant are placed in the post-melt zone to reduce thermal degradation. The online control melt temperature is 200-205 ℃, residence time 45-90 s; torque alarm threshold 70%, to prevent agglomeration and over-shearing.

[0048] S5, granulation and post-processing; Water-cooled pull strips or water ring cutting are used for granulation, with a target particle size of 2-3 mm; after centrifugal air drying, secondary drying is performed with hot air at 60-70 ℃ for 30-60 min to make the moisture content of the finished product ≤0.10 wt%. Online screening is performed to remove large particles and fine powder (screen aperture 2.5-3.0 mm). A small amount of oxidized polyethylene wax (≤0.2 parts) can be sprayed on the surface to improve flow and prevent moisture from blocking. The finished product is packaged in double-layer aluminum-plastic composite bags, with an additional moisture-proof barrel seal, and stored at a temperature of 15-30 ℃ and a relative humidity of ≤50% RH, to avoid long-term coexistence with acid, alkali, and amine-containing environments.

[0049] S6, process quality control and sample retention; Detection is performed on a batch basis, and ≥500 g of sample is retained for each batch, with a storage period of 12 months.

[0050] Example 1 (low-end amount, flow and toughness): A flame-retardant toughening agent for polypropylene material, comprising the following raw materials by weight: 40 parts of polypropylene carrier; 20 parts of ethylene-octene elastomer grafted maleic anhydride; 5 parts of modified polypropylene compatibilizer; 40 parts of modified ammonium polyphosphate; 10 parts of pentaerythritol; 10 parts of melamine cyanurate; 2 parts of zinc oxide-zinc borate compound synergist; 0.5 parts of polytetrafluoroethylene powder; 1 part of nano silicon dioxide; 0.5 parts of hindered phenol antioxidant; 0.5 parts of phosphate antioxidant; 1 part of oxidized polyethylene wax; 0.5 parts of calcium stearate; 0.2 parts of nucleating agent; 0.5 parts of ammonium molybdate smoke suppressant.

[0051] The polypropylene carrier is based on homopolymer polypropylene particles, obtained by melt homogenization and particle size control, and the preparation process is as follows: Select a polypropylene resin with a melt mass flow rate of 40 g / 10 min, first dry it at 90 ℃ for 4 h to ensure that the moisture content is less than 0.2 wt%; Subsequently, melt homogenization is carried out in a twin-screw extruder, with temperature zones set at 170 / 180 / 190 / 195 / 200 ℃, screw speed at 300 rpm, and melt actual temperature controlled at 205 ℃; In the molten state, low molecular and residual moisture are removed by vacuum exhaust section (-0.08 to -0.095 MPa), the extruded strip is rapidly cooled in a cooling water tank, and the particles are cut into uniform particles of 2-3 mm in diameter by a granulator, obtaining the polypropylene carrier.

[0052] The preparation process of the ethylene-octene elastomer grafted maleic anhydride is as follows: Select an ethylene-octene elastomer with a melt mass flow rate of 3.0 g / 10 min, and dry it at 80 ℃ for 2 h in advance; Maleic anhydride is injected into the twin-screw side feed port through a metering pump at a proportion of 1.2 wt%, and an initiator is added, which is dicumyl peroxide (DCP), with a dosage of 0.08 wt% relative to the elastomer; The extruder temperature zone is controlled at 170 / 180 / 185 / 190 / 195 ℃, the screw speed is 300 rpm, the melt actual temperature is maintained at 195 ℃, and vacuum exhaust is used to remove unreacted monomers, obtaining the final product.

[0053] The preparation process of the pentaerythritol is as follows: First, mix formaldehyde and acetaldehyde in a molar ratio of 2:1 in a reaction kettle, in the presence of an alkali catalyst sodium hydroxide, at 60 ℃ to generate a trihydroxymethyl acetaldehyde intermediate; Subsequently, hydrogenation was carried out in a high-pressure hydrogenation reactor under the action of a Raney nickel catalyst at a hydrogen pressure of 5 MPa and a temperature of 120°C. After the reaction solution was concentrated under reduced pressure, crystallization was carried out, and the filter cake was dried at 80°C under vacuum, pentaerythritol was obtained. The particle size of the obtained pentaerythritol was controlled to be 50-150 µm.

[0054] The melamine cyanurate is prepared by a precipitation method. Melamine was dissolved in deionized water at a concentration of 10 wt%, and a uniform solution was formed at 80°C. Another cyanuric acid suspension was prepared at a concentration of 10 wt%, and the temperature was maintained at 30°C. The melamine solution was slowly added to the cyanuric acid suspension under stirring, and the molar ratio was controlled to be 1:1. The pH was adjusted to 7.5 during the reaction. Stirring was maintained for 2 h, and a white precipitate was formed. The obtained precipitate was filtered, washed, and dried at 80°C under vacuum for 8 h to obtain melamine cyanurate. The particle size distribution of the final product was D50=3-8 µm, and the specific surface area was 6-12 m² / g.

[0055] The modified polypropylene compatibilizer is based on homopolymer polypropylene, and the polarity modification is achieved by grafting maleic anhydride. The preparation process is as follows: First, polypropylene particles with a melt mass flow rate of 40 g / 10 min were selected, dried at 80°C for 3 h, and the water content was ensured to be less than 0.2 wt%; In a twin-screw reaction extruder, the amount of maleic anhydride was 1.0 wt%, and the amount of initiator was 0.06 wt%, and the initiator was selected as dicumyl peroxide. The temperature zone was set to 175 / 185 / 190 / 195 / 200°C, the screw speed was 280 rpm, and the vacuum exhaust was -0.08 MPa to remove residual monomers. After the grafted product was cooled and granulated, the modified polypropylene compatibilizer was obtained.

[0056] The polyphosphoric acid ammonium salt is prepared by a condensation reaction process, and the polyphosphoric acid ammonium salt is modified. The prepared polyphosphoric acid ammonium salt was mixed in an ethanol-water mixed solvent, 1.5 wt% γ-aminopropyl triethoxysilane was added, and stirring was carried out at 80°C for 1 h. After filtration and drying, the residual solvent was ≤0.2 wt%, and the modified polyphosphoric acid ammonium salt was obtained.

[0057] The zinc oxide-zinc borate complex synergist is prepared by a two-step method of liquid phase precipitation and solid phase compounding.

[0058] The liquid phase precipitation specifically includes: Zinc oxide powder (purity ≥ 99%, average particle size D50 = 0.5-1.0 µm) was weighed out, and a uniform slurry of 40 wt% was prepared according to a solid-liquid ratio of 1:7. Under stirring conditions, boric acid solution dissolved in hot water was added to the slurry, and the molar ratio of Zn:B was controlled to be 1:1.5. The reaction temperature was maintained at 85 ℃, the reaction time was 3 h, and the pH of the system was stabilized at 7.8. During this process, a suspension of basic zinc borate precipitate was generated; The suspension was filtered and washed until the conductivity was < 50 µS / cm to remove free ions. The wet filter cake was dried at 110 ℃ for 8 h, and then air-jet pulverized to obtain zinc borate powder with an average particle size D50 = 1-5 µm.

[0059] Solid-phase recompounding, specifically including: The dry zinc borate powder was recompounded with zinc oxide powder at a molar ratio of ZnO:ZnB of 1:4, and stirred at 1000 rpm for 30 min using a high-speed mixer; Surface treatment was performed using 1.0 wt% silane coupling agent (γ-aminopropyl triethoxysilane) in an ethanol-water (7 / 3) solution at 80 ℃ under reflux for 1 h. After filtration and drying, zinc oxide-zinc borate recompounded synergist was obtained.

[0060] Method for preparing flame-retardant toughening agent for polypropylene material, comprising: S1, raw material pretreatment and drying; The modified ammonium polyphosphate, pentaerythritol, melamine cyanurate, and nano-silicon dioxide were hot air dried at 90 ℃ for 4 h, with a target moisture content of ≤0.2 wt%. The materials were sieved to D90 ≤ 30 µm (nano-silicon dioxide was maintained at the original fraction). The polypropylene carrier, ethylene-octene elastomer grafted maleic anhydride, modified polypropylene compatibilizer, polytetrafluoroethylene powder, zinc oxide-zinc borate recompounded synergist, nucleating agent, and ammonium molybdate smoke suppressant were stored at room temperature under moisture-proof conditions. The hindered phenol antioxidant and phosphate antioxidant were stored in airtight and light-proof conditions. The oxidized polyethylene wax and calcium stearate were stored at room temperature under sealed conditions.

[0061] S2, raw material weighing and premixing; The raw materials were weighed according to the proportions. Group A: polypropylene carrier, ethylene-octene elastomer grafted maleic anhydride, modified polypropylene compatibilizer, oxidized polyethylene wax, calcium stearate, hindered phenol antioxidant, and phosphate antioxidant were mixed for 5 min using a planetary mixer. Group B: modified ammonium polyphosphate, pentaerythritol, melamine cyanurate, zinc oxide-zinc borate recompounded synergist, nano-silicon dioxide, polytetrafluoroethylene powder, nucleating agent, and ammonium molybdate smoke suppressant were gently stirred for 3 min at low speed to avoid powder dispersion.

[0062] S3, melt plasticization and main feeding; Twin-screw extruder L / D≥40, temperature zone 185 / 190 / 195 / 200 / 200℃, screw rotation speed 300 rpm, vacuum exhaust -0.095 MPa. Continuously add Group A through main feeding port, so that ethylene-octene elastomer grafted maleic anhydride and modified polypropylene compatibilizer form a stable phase; oxidized polyethylene wax and calcium stearate adjust rheology. Target melt temperature 195-205℃, specific torque ≤65% of rated value, melt pressure fluctuation ≤±5 bar, to ensure that the base phase is uniformly plasticized and provide sufficient coating conditions for the flame-retardant phase to enter.

[0063] S4, side-feeding segmented addition and synergistic dispersion; Side-feeding 1 adds modified ammonium polyphosphate and pentaerythritol in the middle segment, and the local shear of the screw is increased to 1.4 times the reference value; side-feeding 2 adds melamine cyanurate, zinc oxide-zinc borate complex synergist and nano-silicon dioxide; polytetrafluoroethylene powder is added through a small metering port at the end (in the form of a small proportion of master batch containing 10-20 wt%). Hindered phenolic antioxidant and phosphate antioxidant are placed in the melt zone of the later stage to reduce thermal degradation. The melt temperature is controlled online at 205℃, and the residence time is 90s; the torque alarm threshold is 70%, to prevent agglomeration and over-shearing.

[0064] S5, granulation and post-treatment; Water-cooled pull strips or water ring cutting are used for granulation, with a target particle size of 2-3 mm; after centrifugal air drying, hot air secondary drying is performed at 70℃ for 60 min, so that the moisture content of the finished product is ≤0.10 wt%. On-line screening is performed to remove large particles and fine powder (screen aperture 3.0 mm). A small amount of oxidized polyethylene wax (≤0.2 parts) can be sprayed on the surface to improve flow and prevent moisture from blocking. The finished product is double-packaged in an aluminum-plastic composite bag, with an additional moisture-proof barrel seal, and stored at a temperature of 30℃ and a relative humidity of ≤50% R.

[0065] S6, process quality control and sample retention; Detection is performed on a batch basis, and ≥500 g of sample is retained for each batch, with a storage period of 12 months.

[0066] Example 2 (intermediate amount, balanced performance): A flame-retardant toughening agent for a polypropylene material, comprising the following raw materials by weight: 40 parts of polypropylene carrier; 50 parts of ethylene-octene elastomer grafted maleic anhydride; 12 parts of modified polypropylene compatibilizer; 80 parts of modified ammonium polyphosphate; 22 parts of pentaerythritol; 22 parts of melamine cyanurate; 5 parts of zinc oxide-zinc borate complex synergist; 1.2 parts of polytetrafluoroethylene powder; 3 parts of nano-silicon dioxide; 0.7 parts of hindered phenolic antioxidant; 0.7 parts of phosphate antioxidant; 3 parts of oxidized polyethylene wax; 1.5 parts of calcium stearate; 0.8 parts of nucleating agent; 1.5 parts of ammonium molybdate smoke suppressant.

[0067] The preparation method of the raw materials is the same as in Example 1.

[0068] Example 3 (high amount, flame retardant reinforcement): A flame-retardant toughening agent for polypropylene material comprises the following raw materials by weight: 20 parts of polypropylene carrier; 80 parts of ethylene-octene elastomer grafted maleic anhydride; 20 parts of modified polypropylene compatibilizer; 120 parts of modified ammonium polyphosphate; 35 parts of pentaerythritol; 40 parts of melamine cyanurate; 8 parts of zinc oxide-zinc borate compound synergist; 2.0 parts of polytetrafluoroethylene micro powder; 5 parts of nano silicon dioxide; 1.0 parts of hindered phenol antioxidant; 1.0 parts of phosphate antioxidant; 6 parts of oxidized polyethylene wax; 3.0 parts of calcium stearate; 1.5 parts of nucleating agent; 3.0 parts of ammonium molybdate smoke suppressant.

[0069] The raw materials and the preparation method of the flame-retardant toughening agent for polypropylene material are the same as in Example 1.

[0070] Comparative Example A (without polytetrafluoroethylene micro powder): A flame-retardant toughening agent for polypropylene material comprises the following raw materials by weight: 40 parts of polypropylene carrier; 50 parts of ethylene-octene elastomer grafted maleic anhydride; 12 parts of modified polypropylene compatibilizer; 80 parts of modified ammonium polyphosphate; 22 parts of pentaerythritol; 22 parts of melamine cyanurate; 5 parts of zinc oxide-zinc borate compound synergist; 3 parts of nano silicon dioxide; 0.7 parts of hindered phenol antioxidant; 0.7 parts of phosphate antioxidant; 3 parts of oxidized polyethylene wax; 1.5 parts of calcium stearate; 0.8 parts of nucleating agent; 1.5 parts of ammonium molybdate smoke suppressant.

[0071] The raw materials and the preparation method of the flame-retardant toughening agent for polypropylene material are the same as in Example 1 (remove polytetrafluoroethylene micro powder).

[0072] Comparative Example B (without zinc oxide-zinc borate compound synergist): A flame-retardant toughening agent for polypropylene material comprises the following raw materials by weight: 40 parts of polypropylene carrier; 50 parts of ethylene-octene elastomer grafted maleic anhydride; 12 parts of modified polypropylene compatibilizer; 80 parts of modified ammonium polyphosphate; 22 parts of pentaerythritol; 22 parts of melamine cyanurate; 1.2 parts of polytetrafluoroethylene micro powder; 3 parts of nano silicon dioxide; 0.7 parts of hindered phenol antioxidant; 0.7 parts of phosphate antioxidant; 3 parts of oxidized polyethylene wax; 1.5 parts of calcium stearate; 0.8 parts of nucleating agent; 0 parts of ammonium molybdate smoke suppressant.

[0073] The raw materials and the preparation method of the flame-retardant toughening agent for polypropylene material are the same as in Example 1 (remove zinc oxide-zinc borate compound synergist).

[0074] Based on the above examples and comparative examples, a plurality of tests were conducted, and the results are shown in Table 1.

[0075] Table 1

[0076] From the results of Table 1, it can be seen that: Example 1 uses lower amounts of modified ammonium polyphosphate, pentaerythritol and melamine cyanurate, combined with polytetrafluoroethylene micro-powder and zinc oxide-zinc borate complex synergist, to achieve basic flame retardant performance while maintaining good flowability and processing stability. The test results show that UL-94 can reach V-0, limiting oxygen index 28.5%, notched impact strength 11.2 kJ / m², carbon residue 23%, total afterflame time 6s, and no dripping. This shows that under low flame retardant system content, through the action of synergist and compatibilizer, the polypropylene flame retardant toughening agent can still meet safety standards, while also taking into account higher tensile strength and processing flowability (MFR 12.0 g / 10 min), suitable for application scenarios with moderate flame retardant requirements but higher requirements for processing rheology and toughness. Example 2 achieves a balance between flame retardancy and mechanics: UL-94 reaches V-0, LOI 30.2%, notched impact Izod 13.8 kJ / m², and total afterflame time only 4s, showing that modified ammonium polyphosphate, pentaerythritol, melamine cyanurate, and zinc oxide-zinc borate complex synergist, nano-silicon dioxide together form a dense "mineralized carbon layer-nano skeleton". Example 3 increases the content of modified ammonium polyphosphate, pentaerythritol, melamine cyanurate and synergist, LOI increases to 32.1%, carbon residue 29.8%, and dripping inhibition is best, but MFR and tensile strength decrease slightly, reflecting the influence of high flame retardant formulation on rheology and strength. Comparative Example A deletes polytetrafluoroethylene micro-powder and appears obvious dripping, UL-94 decreases to V-2, total afterflame time increases, proving the key role of polytetrafluoroethylene micro-powder in suppressing dripping. Comparative Example B lacks zinc oxide-zinc borate complex synergist, carbon residue decreases and smoke density increases, showing that this synergist has a significant contribution to carbon layer mineralization and smoke suppression. Overall, examples containing polytetrafluoroethylene micro-powder and zinc oxide-zinc borate complex synergist perform stably in terms of flame retardant grade, carbon layer integrity and smoke suppression, and achieve synergistic improvement without significantly sacrificing toughness.

[0077] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application, which should be covered by the claims of the present application.

Claims

1. A flame retardant flexibilizer for polypropylene materials, characterized in that, The raw materials include the following weight parts: ​ 20-60 parts of polypropylene carrier; 20-80 parts of ethylene-octene elastomer grafted maleic anhydride; 5-20 parts of modified polypropylene compatibilizer; 40-120 parts of modified ammonium polyphosphate; 10-35 parts of pentaerythritol; 10-40 parts of melamine cyanurate; 2-8 parts of zinc oxide-zinc borate compound synergist; 0.5-2.0 parts of polytetrafluoroethylene micro powder; 1-5 parts of nano silicon dioxide; 0.2-1.0 parts of hindered phenol antioxidant; 0.2-1.0 parts of phosphate antioxidant; 1-6 parts of oxidized polyethylene wax; 0.5-3.0 parts of calcium stearate; 0.2-1.5 parts of nucleating agent; 0.5-3.0 parts of ammonium molybdate smoke suppressant.

2. The flame-retardant toughening agent for polypropylene material according to claim 1, characterized in that, The polypropylene carrier is based on homopolymer polypropylene particles, obtained by melt homogenization and particle size control, and the preparation process is as follows: Select polypropylene resin with a melt mass flow rate of 10-40 g / 10 min, first dry it with hot air at 80-90 ℃ for 2-4 h to ensure that the moisture content is less than 0.2 wt%; Then melt homogenize it in a twin-screw extruder, with temperature zones set at 170 / 180 / 190 / 195 / 200 ℃, screw speed at 200-300 rpm, and melt actual temperature controlled at 195-205 ℃; In the molten state, remove low molecular and residual moisture with vacuum exhaust section, rapidly cool the extruded strip in a cooling water tank, and cut it into uniform particles of 2-3 mm in diameter with a granulator to obtain the polypropylene carrier.

3. The flame-retardant toughening agent for polypropylene material according to claim 1, characterized in that, The preparation process of the ethylene-octene elastomer grafted maleic anhydride is as follows: Select ethylene-octene elastomer with a melt mass flow rate of 0.5-3.0 g / 10 min, and dry it at 70-80 ℃ for 1-2 h in advance; Inject maleic anhydride at a proportion of 0.5-1.2 wt% into the twin-screw side feed port through a metering pump, while adding an initiator, which is dicumyl peroxide, at a dosage of 0.02-0.08 wt% relative to the elastomer; Control the extruder temperature zones at 170 / 180 / 185 / 190 / 195 ℃, with screw speed at 150-300 rpm, and melt actual temperature maintained at 185-195 ℃, and use vacuum exhaust to remove unreacted monomers to obtain the final product.

4. The flame-retardant toughening agent for polypropylene material according to claim 1, characterized in that, The preparation process of the pentaerythritol is as follows: First, mix formaldehyde and acetaldehyde in a molar ratio of 2-3:1-2 in a reaction kettle, and in the presence of an alkali catalyst, sodium hydroxide, react at 50-60 ℃ to generate a trihydroxymethyl acetaldehyde intermediate; Then, in a high-pressure hydrogenation reactor, under the action of a Raney nickel catalyst, hydrogenate at a hydrogen pressure of 4-5 MPa and a temperature of 100-120 ℃, concentrate the reaction liquid under reduced pressure, and crystallize to precipitate, then dry the filter cake at 80 ℃ under vacuum to obtain pentaerythritol.

5. The flame-retardant toughening agent for polypropylene material according to claim 1, characterized in that, The melamine cyanurate is prepared by a precipitation method: Dissolve melamine in deionized water at a concentration of 5-10 wt%, and form a uniform solution at 70-80 ℃; Another cyanuric acid suspension, concentration 5-10 wt%, temperature 25-30 ℃, slowly add melamine solution to cyanuric acid suspension under stirring, control molar ratio 1:1, adjust pH to 6.5-7.5 during reaction; maintain stirring for 1-2 h, white precipitate is generated; The obtained precipitate is filtered, washed, and dried at 80 ℃ under vacuum for 6-8 h to obtain melamine cyanurate.

6. The flame-retardant toughening agent for polypropylene material according to claim 1, characterized in that, The modified polypropylene compatibilizer is based on homopolymer polypropylene, which is modified by grafting maleic anhydride to achieve polarity modification, and the preparation process is as follows: First, select polypropylene particles with a melt mass flow rate of 10-40 g / 10 min, dry at 80 ℃ for 3 h to ensure that the water content is less than 0.2 wt%; In a twin-screw reaction extruder, the amount of maleic anhydride is 0.4-1.0 wt%, and the initiator is dicumyl peroxide, with a dosage of 0.02-0.06 wt%; The temperature zone is set to 175 / 185 / 190 / 195 / 200 ℃, the screw speed is 200-280 rpm, and the vacuum exhaust is -0.08 MPa to remove residual monomers. After the grafted product is cooled and granulated, the modified polypropylene compatibilizer is obtained.

7. The flame-retardant toughening agent for polypropylene material according to claim 1, characterized in that, Polyphosphoric acid ammonium is prepared by condensation reaction process, and polyphosphoric acid ammonium is modified: The prepared polyphosphoric acid ammonium is mixed in an ethanol-water mixed solvent, 0.5-1.5 wt% γ-aminopropyl triethoxysilane is added, stirred at 70-80 ℃ for 0.5-1 h, filtered and dried, residual solvent ≤0.2 wt%, to obtain modified polyphosphoric acid ammonium.

8. The flame-retardant toughening agent for polypropylene material according to claim 1, characterized in that, The zinc oxide-zinc borate complex synergist is prepared by a two-step method of liquid phase precipitation and solid phase compounding; The liquid phase precipitation specifically includes: Take zinc oxide powder, prepare 30-40 wt% uniform slurry according to solid-liquid ratio 1:6-1:8, under stirring, add boric acid solution dissolved in hot water, control the molar ratio Zn:B=1:1.2-1.5; the reaction temperature is maintained at 60-85 ℃, the reaction time is 1.5-3 h, and the system pH is stable at 7.0-7.8, during which the suspension of basic zinc borate precipitate is generated; The suspension is filtered and washed to a conductivity <50 µS / cm to remove free ions, the wet filter cake is dried at 100-110 ℃ for 6-8 h, and then air-jet pulverized to obtain zinc borate powder with an average particle size D50=1-5 µm.

9. The flame-retardant toughening agent for polypropylene material according to claim 8, characterized in that, The solid phase compounding specifically includes: Compound the dry zinc borate powder with zinc oxide powder according to the molar ratio ZnO:ZnB 1:3-1:5, and stir with a high-speed mixer at 800-1000 rpm for 15-30 min. Surface treatment with 0.5-1.0 wt% silane coupling agent, reflux in ethanol solution at 70-80 ℃ for 0.5-1 h, filter and dry to obtain zinc oxide-zinc borate complex synergist.

10. A process for the preparation of a flame retardant flexibilizer for polypropylene materials as claimed in any one of claims 1 to 9, characterized in that, The process includes the following specific steps: S1, raw material pretreatment and drying; S2, raw material weighing and premixing; S3, melt plasticization and main feeding; S4, side feeding, segmented addition and synergistic dispersion; S5, granulation and post-treatment; S6, process quality control and sample reservation.

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