Flame-retardant lightweight EPP / polyurea composite material as well as preparation method and application thereof

Abstract

The invention discloses a flame-retardant lightweight EPP / polyurea composite material as well as a preparation method and application thereof. The composite material takes an EPP foamed bead molding body as a base material, a flame-retardant polyurea coating is compounded on the surface, the thickness of the coating is 0.5-3.0 mm, and the composite material is prepared from the following components: aliphatic diisocyanate, aromatic diamine, aliphatic polyether amine, an intumescent flame retardant system, nano filler and the like. The preparation method comprises the four steps of EPP base material surface pretreatment, flame-retardant polyurea component preparation, spraying or dipping compounding and curing forming. The density of the composite material is only 0.08-0.25 g / cm < 3 >, the limit oxygen index reaches 32-38%, the vertical combustion reaches V-0 level, the heat release rate peak value is reduced by 55-70%, the multiple impact energy absorption retention rate is greater than or equal to 82%, and the composite material has the advantages of light weight, excellent flame retardance and impact resistance. The method is suitable for preparing unmanned aerial vehicle performance packaging boxes, urban park outdoor sculptures and the like, and has the advantages of simple process, low cost and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polymer composites, and particularly relates to a flame-retardant lightweight EPP / polyurea composite material, a preparation method thereof and application thereof BACKGROUND

[0002] Expanded polypropylene (EPP) is a closed-cell bead foamed material with excellent performance, and has excellent energy absorption performance, multiple impact resistance, thermal insulation, buoyancy, water and chemical resistance, extremely high strength-to-weight ratio, and 100% recyclability. EPP can be made into various specifications with a density of 15 g / L to 200 g / L, and can be converted into final products with a density of 18 g / L to 260 g / L through a steam forming process. Due to its lightweight, high-strength and environmentally friendly properties, EPP is widely used in the fields of automobiles, packaging and consumer products.

[0003] With the rapid development of emerging application scenarios such as unmanned aerial vehicle performances and outdoor exhibitions, higher requirements are put forward for lightweight protective materials. For example, unmanned aerial vehicle formation performances are often combined with fireworks and other activities, and in this scenario, the unmanned aerial vehicle packaging box needs to meet the performance requirements of lightweight, impact resistance and flame retardance at the same time; in the application of outdoor sculptures in city parks, the material needs to have multiple functions such as lightweight, aesthetic, weather resistance and fire safety. However, the oxygen index of traditional EPP materials is relatively low (usually 18-20%), and they are easy to burn in the presence of open flames, which limits their application in these scenarios with higher safety requirements.

[0004] In the prior art, a carbon fiber reinforced polypropylene composite material for unmanned aerial vehicles and a preparation method thereof are disclosed in Chinese Patent No. CN118755198A, which comprises 110-130 parts of polypropylene resin, 20-40 parts of modified carbon fiber, 0.3-0.5 parts of initiator and 6-10 parts of paraffin wax. A modifier containing a Schiff base structure, a hindered phenol structure and a Si-N flame-retardant structure is prepared through a complex organic synthesis route, grafted to the surface of pitch-based carbon fiber, and then a composite material is prepared through melt blending. Although this technical solution can improve the flame-retardant performance and mechanical strength of the material, it has the following disadvantages: 1. The synthesis route of the modifier is complex, and needs to go through four steps of organic synthesis reaction, including Schiff base condensation, silylation reaction, nucleophilic substitution and amidation reaction, which is complicated and costly; 2. The material uses solid polypropylene as the matrix, and has a relatively high density (about 0.9-1.2 g / cm 3 ), which does not meet the requirement of extreme lightweight; 3. The introduction of carbon fiber can improve the mechanical properties, but increases the brittleness of the material, and micro-cracks are easy to occur after multiple impacts; 4. The melt blending process has a destructive effect on the length of carbon fibers, affecting the full play of the reinforcing effect; 5. The technical solution mainly aims at unmanned aerial vehicle structural parts, without considering the special needs of packaging protection and outdoor decoration application scenarios.

[0005] Therefore, it is urgent to develop a process simple, excellent performance of flame retardant lightweight composite material, to meet the emerging application scenarios of lightweight, flame retardant, impact resistance and weatherability of the comprehensive requirements of the material. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art, provide a flame-retardant lightweight EPP / polyurea composite material and its preparation method and application, in order to solve the shortcomings of the existing materials in lightweight, flame retardancy, multiple impact resistance.

[0007] To achieve the above purpose, the first aspect of the present application provides a flame-retardant lightweight EPP / polyurea composite material, which is based on an EPP foamed bead forming body, and the surface is compounded with a flame-retardant polyurea coating, characterized in that the thickness of the flame-retardant polyurea coating is 0.5-3.0mm, which is prepared from the following components: A component (isocyanate component): aliphatic diisocyanate: 100 parts by mass; catalyst: 0.05-0.3 parts by mass; B component (curing agent component): aromatic diamine: 30-60 parts by mass; aliphatic polyether amine: 40-70 parts by mass; intumescent flame retardant: 20-40 parts by mass; nano filler: 2-8 parts by mass; interface reinforcing agent: 1-5 parts by mass.

[0008] Preferably, the density of the EPP foamed bead forming body is 40-120g / L, preferably 60-100g / L.

[0009] Preferably, the aliphatic diisocyanate is selected from one or more of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (H 12 MDI).

[0010] Preferably, the aromatic diamine is selected from one or more of diethyl toluene diamine (DETDA), 4,4'-methylene bis(2-chloroaniline) (MOCA), 4,4'-diamino diphenyl sulfone (DDS), 4,4'-diamino diphenyl methane (MDA); the aliphatic polyether amine is an amino-terminated polyether with a number average molecular weight of 2000-4000g / mol.

[0011] Preferably, the intumescent flame retardant system comprises: acid source: ammonium polyphosphate (APP), 10-20 parts by mass; carbon source: pentaerythritol or dipentaerythritol, 5-12 parts by mass; gas source: melamine or melamine cyanurate, 5-10 parts by mass.

[0012] Preferably, the nanofiller is selected from expandable graphite, layered double hydroxide (LDH), graphene oxide (GO), nano-aluminum hydroxide, nano-magnesium hydroxide, or a combination thereof; preferably, the nanofiller is a composite of expandable graphite and layered double hydroxide, with a mass ratio of (1-3):1.

[0013] Preferably, the interfacial reinforcing agent is selected from silane coupling agent, maleic anhydride grafted polypropylene (PP-g-MAH), epoxidized natural rubber, or a combination thereof.

[0014] Preferably, the catalyst is selected from dibutyltin dilaurate, stannous octoate, triethylenediamine, or a combination thereof.

[0015] The second aspect of the present application provides a preparation method of the flame-retardant lightweight EPP / polyurea composite material, characterized in that it comprises the following steps: Step 1: EPP substrate pretreatment The EPP foamed bead body is surface treated, the surface is activated by flame treatment, plasma treatment or chemical treatment method to improve the surface energy and wettability; after treatment, the surface is cleaned to remove oil stains and impurities; Step 2: Preparation of flame-retardant polyurea component A: mixing the aliphatic diisocyanate in component A with the catalyst uniformly; mixing the aromatic diamine, aliphatic polyether amine, intumescent flame retardant (acid source, carbon source, gas source), nanofiller and interfacial reinforcing agent in component B, and mixing them uniformly by using high-speed dispersion or planetary stirring equipment, and ultrasonic dispersion for 30-60 min to ensure uniform dispersion of the nanofiller; Step 3: Polyurea coating composite Flame-retardant polyurea is coated on the surface of the EPP substrate by spraying or dipping method: spraying method: using two-component spraying equipment, mixing and spraying component A and component B by high-pressure impact at a volume ratio of 1:1, spraying pressure is 15-25 MPa, spraying temperature is 60-80℃, control spraying distance is 40-60 cm, multi-pass spraying forms uniform coating; dipping method: dipping the EPP substrate into the mixture of pre-mixed component A and component B (gel time after mixing is 15-30 s), dipping time is 3-8 s, and standing after lifting for solidification; Step 4: Curing forming The composite material is cured at room temperature for 4-24 h to obtain a flame-retardant lightweight EPP / polyurea composite material; post-curing treatment can be carried out at 60-80℃ for 2-4 h to further improve the performance.

[0016] Preferably, the surface treatment method in step 1 is as follows: Flame treatment: using an oxidizing flame, with a flame temperature of 800-1200℃ and a treatment time of 1-3s; Plasma treatment: using a plasma power of 300-600W and a treatment time of 30-90s; Chemical treatment: using a potassium permanganate solution or a chromic acid mixture with a mass fraction of 5-15% for 2-5min.

[0017] Preferably, the nanofiller in step 2 is subjected to surface modification treatment. The modifier includes one or more of silane coupling agents, titanate coupling agents, or phosphate esters, and the amount of modifier is 1-3% of the mass of the nanofiller.

[0018] A third aspect of the invention provides the application of the flame-retardant lightweight EPP / polyurea composite material in the preparation of drone packaging boxes.

[0019] The fourth aspect of this invention provides the application of the flame-retardant lightweight EPP / polyurea composite material in the preparation of outdoor sculptures.

[0020] The fifth aspect of the present invention provides the application of the flame-retardant lightweight EPP / polyurea composite material in the preparation of protective equipment, sporting goods or transportation cushioning components.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Lightweight design: Using low-density EPP foam as the matrix, the overall density of the composite material is only 0.08-0.25 g / cm³. 3 Compared to the carbon fiber reinforced polypropylene composite material in the comparative document (density approximately 0.9-1.2 g / cm³), 3 Weight reduction of 65-91% achieves ultimate lightweighting; 2. Excellent flame retardant properties: By introducing an intumescent flame retardant (IFR) system and a synergistic flame retardant mechanism with nanofillers into the polyurea matrix, the limiting oxygen index (LOI) of the composite material can reach 32-38%, which is much higher than the 18-20% of pure EPP material and the 26-28% of the materials in the comparison document. The vertical burning test reaches V-0 level, the peak heat release rate (PHRR) is reduced by 55-70%, and the total heat release (THR) is reduced by 40-55%, effectively preventing the spread of flames; 3. Resistant to repeated impacts: The closed-cell structure of the EPP substrate and the high elasticity of the polyurea coating work synergistically to give the composite material excellent energy absorption capacity in repeated impacts. After 10 impacts, the energy absorption rate still remains above 85% of that in the first impact, while carbon fiber reinforced composite materials are prone to microcracks after 3-5 impacts, resulting in a significant decrease in performance. 4. Good mechanical properties and hardness: Polyurea coating provides surface hardness and wear resistance, with a Shore D hardness of 50-70, tensile strength of 15-35 MPa, and elongation at break of 200-500%, combining strength and toughness; 5. Simple process and low cost: Compared with the comparative paper's process for preparing modifiers that requires four complex organic synthesis steps, this invention uses commercial raw materials and can be prepared through simple mixing and spraying or impregnation processes, resulting in high production efficiency and a cost reduction of 40-60%; 6. Excellent interfacial bonding: Through surface pretreatment and the introduction of interfacial reinforcing agents, the polyurea coating forms a good mechanical interlock and chemical bond with the EPP substrate, achieving an adhesion level of 4-5 (GB / T 9286 standard) and is not easily peeled off; 7. Excellent weather resistance: The aliphatic polyurea system has excellent UV resistance and aging resistance, making it suitable for long-term outdoor use. After 2000 hours of accelerated aging test, the mechanical properties retention rate is ≥80%, and the color change ΔE is ≤3. 8. Environmentally friendly: EPP material is 100% recyclable, polyurea coating does not contain halogens, heavy metals or other harmful substances, and the flame retardant uses an intumescent halogen-free flame retardant system, resulting in low smoke density and low toxicity during combustion, meeting environmental protection requirements; 9. Wide range of applications: It can be used for protective packaging boxes in drone performance scenarios (flame retardant, lightweight, impact resistant), as well as outdoor sculptures in urban parks (lightweight, beautiful, weather resistant, fireproof), and can also be extended to multiple fields such as protective equipment, sporting goods, and automotive interiors. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below through specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] The raw materials used in the examples are sourced as follows: EPP foamed beads: JSP Corporation, Japan, model P-Block, density 80 g / L; Hexamethylene diisocyanate (HDI): Covestro, Germany, industrial grade; Isophorone diisocyanate (IPDI): Evonik Industries, Germany, industrial grade; Diethyltoluene diamine (DETDA): Albemarle, USA, industrial grade; 4,4'-Methylenebis(2-chloroaniline) (MOCA): Tokyo Chemicals, Japan, industrial grade; Amino-terminated polyether (D2000): Huntsman, USA, number average molecular weight approximately 2000 g / mol; Amino-terminated polyether (D4000): Huntsman, USA, number average molecular weight approximately 4000 g / mol; Ammonium polyphosphate (APP): Shandong Changsheng Flame Retardant New Material Co., Ltd., degree of polymerization >1000; Pentaerythritol: industrial grade, purity ≥98%; Melamine: industrial grade, purity ≥99%; Expandable graphite (EG): Qingdao Tianshengda Graphite Co., Ltd., expansion ratio ≥ 200 times / g; Magnesium-aluminum layered bimetallic hydroxide (Mg-Al LDH): self-made, Mg / Al molar ratio 2:1; Graphene oxide (GO): Nanjing Xianfeng Nanomaterials Technology Co., Ltd., sheet thickness 0.8-1.2nm; Maleic anhydride grafted polypropylene (PP-g-MAH): grafting rate 0.8-1.2%; γ-aminopropyltriethoxysilane (KH550): Nanjing Shuguang Chemical Group Co., Ltd.; Dibutyltin dilaurate (DBTDL): industrial grade; Other chemical reagents: all analytical grade.

[0024] Example 1 Step 1: Pretreatment of EPP substrate Take EPP foamed beads with dimensions of 300mm×300mm×30mm (density 80g / L), and activate the surface using a flame treatment method: adjust the flame to an oxidizing flame, the flame temperature to approximately 1000℃, and the flame distance from the EPP surface to approximately 5-8cm. Move the flame gun uniformly at a speed of approximately 10cm / s for approximately 2 seconds to ensure slight melting of the EPP surface and increase surface energy. Immediately after treatment, blow the surface clean with compressed air and allow it to cool to room temperature.

[0025] Step 2: Flame-retardant polyurea compound preparation Group A allocation: Hexamethylene diisocyanate (HDI): 100g; Dibutyltin dilaurate (catalyst): 0.15g Mix the above components thoroughly in a dry environment and store them in a sealed container for later use.

[0026] Group B formulation: Diethyltoluene diamine (DETDA): 45g; Amino-terminated polyether D2000: 55g; Ammonium polyphosphate (APP): 25g; Pentaerythritol: 8g; Melamine: 7g; Expandable graphite (EG): 3g; Magnesium-aluminum layered bimetallic hydroxide (Mg-Al LDH): 2g; Maleic anhydride-grafted polypropylene (PP-g-MAH): 3g The above components were added to a high-speed disperser. The solid powders (APP, pentaerythritol, melamine, EG, LDH) were first thoroughly mixed with PP-g-MAH. Then, the liquid amine components (DETDA and D2000) were added and dispersed at 1500 rpm for 30 min. The mixture was then transferred to an ultrasonic disperser and ultrasonically treated for 45 min (power 400W) to ensure uniform dispersion of the nanofiller and to obtain a uniform B component slurry.

[0027] Step 3: Polyurea coating lamination Coating lamination was performed using a spray coating method: A two-component high-pressure spray coating system (Graco, USA, Reactor E-20) was used. Component A and component B were added to the two separate tanks of the system. The system parameters were set as follows: Tank temperature: 70℃ (preheating to reduce viscosity); Spray pressure: 20MPa; A / B component volume ratio: 1:1; Spraying distance: 50cm; Spray gun movement speed: approximately 30-40cm / s. The pretreated EPP substrate is fixed on the spraying table. A first coat is applied to form a base coat of approximately 0.3-0.5 mm. After waiting 30 seconds, a second coat is applied to form a mid-coat of approximately 0.5-0.7 mm. After another 30 seconds, a third coat is applied to form a top coat of approximately 0.3-0.5 mm, ensuring a total coating thickness of 1.2-1.5 mm. During the spraying process, components A and B are mixed under high pressure at the spray gun tip, reacting instantaneously to form a polyurea coating.

[0028] Step 4: Curing and molding The sprayed composite material was left to cure at room temperature (25℃) for 24 hours, with a gel time of approximately 20 seconds, an initial curing time of approximately 5 minutes, and a complete curing time of 24 hours. To further improve performance, the material could be placed in an oven and post-cured at 70℃ for 3 hours. The final product was a flame-retardant, lightweight EPP / polyurea composite material.

[0029] Example 2 The difference between this embodiment and Embodiment 1 is that: EPP substrate: EPP foamed beads with a density of 60g / L are used.

[0030] Surface treatment: Plasma treatment method is adopted, with a plasma power of 500W and a treatment time of 60s.

[0031] Component B formulation adjustment: 4,4'-Methylenebis(2-chloroaniline) (MOCA): 50g; Amino-terminated polyether D4000: 50g; Ammonium polyphosphate (APP): 30g; Dipentaerythritol: 10g; Melamine cyanurate: 8g; Expandable graphite (EG): 4g; Graphene oxide (GO): 2g; γ-aminopropyltriethoxysilane (KH550): 2g Coating thickness: Control the total coating thickness to 2.0-2.2mm.

[0032] The remaining steps are the same as in Example 1.

[0033] Example 3 The difference between this embodiment and Embodiment 1 is that: EPP substrate: EPP foamed beads with a density of 100g / L are used.

[0034] Isocyanate component: Isophorone diisocyanate (IPDI) is used instead of HDI.

[0035] Component B formulation adjustment: Diethyltoluene diamine (DETDA): 40g; 4,4'-Diaminodiphenyl sulfone (DDS): 10g; Amino-terminated polyether D2000: 50g; Ammonium polyphosphate (APP): 35g; Pentaerythritol: 9g; Melamine: 9g; Expandable graphite (EG): 5g; Magnesium aluminum layered bimetallic hydroxide (Mg-Al LDH): 2g; Maleic anhydride grafted polypropylene (PP-g-MAH): 4g Coating thickness: Control the total coating thickness to 2.5-2.8mm.

[0036] The remaining steps are the same as in Example 1.

[0037] Example 4 The difference between this embodiment and Embodiment 1 is that: EPP substrate: EPP foamed beads with a density of 120g / L are used for high-strength applications.

[0038] Surface treatment: The EPP substrate is immersed in a 10% potassium permanganate solution for 3 minutes using a chemical treatment method, then rinsed thoroughly with deionized water and dried for later use.

[0039] Component A: A mixture of HDI and IPDI (mass ratio 1:1).

[0040] Component B formulation adjustment: Diethyltoluene diamine (DETDA): 55g; Amino-terminated polyether D2000: 45g; Ammonium polyphosphate (APP): 32g; Pentaerythritol: 10g; Melamine: 8g; Expandable graphite (EG): 4g; Graphene oxide (GO): 1g; Nano-aluminum hydroxide: 2g; Maleic anhydride-grafted polypropylene (PP-g-MAH): 3g; Epoxidized natural rubber: 2g Coating thickness: Control the total coating thickness to 2.8-3.0 mm.

[0041] The remaining steps are the same as in Example 1.

[0042] Example 5 The difference between this embodiment and Embodiment 1 is that the coating is applied using an impregnation method: After flame treating the EPP substrate, components A and B are rapidly mixed at a volume ratio of 1:1 (gel time approximately 25 seconds after mixing). The EPP substrate is immediately and completely immersed in the mixture for 5 seconds. After lifting, it is held vertically to allow excess slurry to flow off. After 30 seconds, the coating is initially cured, forming a polyurea coating with a thickness of approximately 1.8-2.0 mm. After curing at room temperature for 24 hours, it is further cured at 70°C for 3 hours to obtain the composite material.

[0043] The remaining steps are the same as in Example 1.

[0044] Comparative Example 1 The EPP substrate (density 80 g / L) of Example 1 was used, but without polyurea coating, and was directly used as pure EPP material for performance testing.

[0045] Comparative Example 2 The method of Example 1 was used, but the intumescent flame retardant (APP, pentaerythritol, melamine) and nanofiller (EG, LDH) were not added to the flame retardant polyurea formulation. Only a pure polyurea coating (composed of 100g HDI, 50g DETDA, and 50g D2000) was used, and the other steps were the same.

[0046] Comparative Example 3 The formulation of Example 7 in patent CN118755198A was adopted: 130g of polypropylene resin was placed in a forced-air constant temperature drying oven and dried at 80°C for 48h. Then, it was mixed with 40g of modified carbon fiber, 0.5g of lauroyl peroxide, and 10g of paraffin wax, and fed into a twin-screw extruder for melt blending. After extrusion, the mixture was dried in a forced-air constant temperature drying oven at 80°C for 48h to obtain carbon fiber reinforced polypropylene composite material. Samples of this material were prepared according to the same dimensions as in the example for performance comparison testing.

[0047] The materials from Examples 1-5 and Comparative Examples 1-3 were prepared into specimens of corresponding shapes according to different testing standards, and the following performance tests were conducted: 1. Density test: The apparent density of the composite material was determined in accordance with GB / T 6343-2009 "Determination of apparent density of foamed plastics and rubber".

[0048] 2. Flame retardant performance testing: Limiting oxygen index (LOI): determined according to GB / T 2406.2-2009 "Determination of flammability by oxygen index method for plastics - Part 2: Room temperature test"; Vertical burning test: determined according to GB / T 2408-2008 "Determination of flammability of plastics - Horizontal and vertical methods", with sample size of 125mm × 13mm × thickness, and flammability rating evaluated; Cone calorimetry test: conducted according to ISO 5660-1 standard, with a radiant heat flux density of 50kW / m³. 2 Parameters such as peak heat release rate (PHRR), total heat release (THR), and ignition time (TTI) were measured.

[0049] 3. Mechanical property testing: Tensile properties: Tensile strength and elongation at break were determined according to GB / T 1040.3-2006 "Determination of tensile properties of plastics"; Hardness testing: Shore D hardness was determined according to GB / T 2411-2008 "Shore hardness test method for plastics"; Impact energy absorption: Energy absorption efficiency was determined using a drop hammer impact tester according to GB / T 8813-2008 "Determination of compressive properties of rigid foamed plastics". The same sample was subjected to 10 repeated impacts, and the energy absorption rate of each impact was recorded.

[0050] 4. Coating adhesion test: The adhesion between the polyurea coating and the EPP substrate was determined according to GB / T 9286-2021 "Cross-cut test of paint and varnish film".

[0051] 5. Weather resistance testing was conducted according to GB / T 16422.2-2014 "Laboratory Light Source Exposure Test Methods for Plastics - Part 2: Xenon Arc Lamp", with an artificial accelerated aging test and an irradiation intensity of 0.51 W / (m²). 2 The blackboard temperature was (65±3)℃, the relative humidity was (50±5)%, and the aging time was 2000h. The mechanical property retention rate and color change (ΔE) before and after aging were tested.

[0052] The test results are shown in Tables 1 and 2: Table 1 Comparison of basic material properties and flame retardant properties Sample Density (g / cm 3 )]]> LOI(%) Vertical Burning Rating TTI(s) PHRR (kW / m 2 ) THR (MJ / m 2 ) PHRR Reduction Rate(%) THR Reduction Rate(%) Example 1 0.12 35.2 V-0 35 142 22.5 64.5 48.6 Example 2 0.10 36.8 V-0 38 128 19.8 68.0 54.7 Example 3 0.15 33.5 V-0 32 155 24.3 61.2 44.5 Example 4 0.18 32.1 V-0 30 168 26.7 58.0 39.0 Example 5 0.13 34.8 V-0 34 148 23.1 63.0 47.2 Comparative Example 1 (Pure EPP) 0.08 19.3 No Rating 8 400 43.8 - - Comparative Example 2 (Pure Polyurea Coating) 0.11 22.6 V-2 12 325 38.2 18.8 12.8 Comparative Example 3 (Carbon Fiber / PP) 1.05 27.5 V-1 15 265 32.5 - - Note: The PHRR reduction rate and THR reduction rate are calculated based on Comparative Example 1 (pure EPP).

[0053] Table 2 Comparison of material mechanical properties and weather resistance Sample Shore D Hardness Tensile Strength (MPa) Elongation at Break (%) First Impact Energy Absorption Rate (%) Energy Absorption Retention Rate (%) after 10 Impacts Coating Adhesion (Scale) Mechanical Retention Rate (%) after 2000h Aging ΔΕ after 2000h Aging Example 1 62 24.5 320 88 87 5 85 2.3 Example 2 58 18.2 450 90 89 5 88 2.1 Example 3 68 32.8 280 86 84 5 83 2.5 Example 4 70 35.6 250 84 82 4 82 2.7 Example 5 60 22.3 340 89 88 5 86 2.2 Comparative Example 1 (Pure EPP) 45 2.8 15 85 83 - 75 4.5 Comparative Example 2 (Pure Polyurea Coating) 55 20.5 380 87 86 4 70 5.2 Comparative Example 3 (Carbon Fiber / PP) 85 68.5 8 72 45 - 78 3.8 The data in Tables 1 and 2 show that: 1. Significant weight reduction effect: The density of the composite materials in Examples 1-5 is 0.10-0.18 g / cm³. 3 Compared to the carbon fiber reinforced polypropylene composite material of Comparative Example 3 (1.05 g / cm³), 3 It reduces weight by 81-90%, achieving an ultra-lightweight design that meets the lightweight requirements of drone packaging boxes and outdoor sculptures.

[0054] 2. Excellent flame retardant performance: The LOI values ​​of Examples 1-5 reached 32.1-36.8%, and the vertical burning test all achieved V-0 rating, which is far superior to Comparative Example 1 (pure EPP, LOI 19.3%, no rating) and Comparative Example 3 (carbon fiber / PP, LOI 27.5%, V-1 rating); the cone calorimetry test showed that the PHRR reduction rate of the materials in the examples reached 58.0-68.0%, and the THR reduction rate reached 39.0-54.7%, proving that the synergistic flame retardant mechanism of intumescent flame retardant and nanofiller effectively inhibited the combustion and heat release of the materials; the ignition time (TTI) was significantly extended to 30-38s, providing valuable time for personnel evacuation and property transfer in fire scenarios; Comparative Example 2 showed that when only pure polyurea coating was used without adding flame retardant, the flame retardant effect was limited (LOI 22.6%, V-2 rating), proving that the introduction of flame retardant is the key to achieving excellent flame retardant performance.

[0055] 3. Excellent mechanical properties and resistance to repeated impacts: The Shore D hardness of the materials in the examples reaches 58-70, which is significantly improved compared to pure EPP (hardness 45), meeting the surface hardness requirements for packaging and sculpting applications; the tensile strength is 18.2-35.6 MPa, and the elongation at break is 250-450%, combining strength and toughness; repeated impact tests show that the energy absorption retention rate of the materials in the examples still reaches 82-89% after 10 impacts, proving that the synergistic effect of the closed-cell structure of EPP and the high elasticity of polyurea endows the materials with excellent resistance to repeated impacts; in contrast, although the carbon fiber reinforced composite material of Comparative Example 3 has a higher initial impact energy absorption rate (72%), the retention rate after 10 impacts is only 45%, proving that fiber reinforced composite materials are prone to microcracks under repeated impacts, leading to performance degradation.

[0056] 4. Good coating adhesion: The polyurea coating of the material in the example achieved an adhesion level of 4-5, proving that the surface pretreatment and the introduction of the interface enhancer effectively enhanced the interfacial bonding between the coating and the EPP substrate, and the coating was not easy to peel off.

[0057] 5. Excellent weather resistance: After 2000 hours of artificial accelerated aging, the mechanical properties of the material in the example retained 82-88%, and the color change ΔE was 2.1-2.7, which is far superior to that of Comparative Example 2 (pure polyurea coating, retention rate 70%, ΔE 5.2). This proves that the synergistic effect of the aliphatic polyurea system and aromatic diamine endows the material with excellent UV resistance and aging resistance, making it suitable for long-term outdoor use.

[0058] 6. Significant process advantages: Compared with Comparative Example 3, which requires four complex organic synthesis steps to prepare the modifier and then melt blending to prepare the composite material, this invention uses commercial raw materials and can be prepared through simple mixing and spraying or impregnation processes, resulting in high production efficiency and a cost reduction of 40-60%.

[0059] In summary, the flame-retardant and lightweight EPP / polyurea composite material prepared by this invention exhibits excellent performance in terms of lightweight, flame retardancy, resistance to repeated impacts, mechanical properties, and weather resistance. Compared with existing technologies, it has significant advantages and is very suitable for applications such as protective packaging boxes for drone performances (requiring flame retardancy, lightweight, and impact resistance) and outdoor sculptures in urban parks (requiring lightweight, aesthetics, weather resistance, and fire resistance). It can also be extended to multiple fields such as protective equipment, sporting goods, and automotive interiors, showing broad application prospects.

[0060] Application Example 1: Packaging Box for Drone Shows Using the flame-retardant, lightweight EPP / polyurea composite material prepared in Example 2, a special packaging box for drone performances was designed and manufactured. The box has internal dimensions of 600mm × 500mm × 400mm, a wall thickness of 30mm, and an overall weight of only 1.8kg, capable of accommodating a single drone and its accessories. This packaging box underwent practical application testing during a large-scale fireworks display event. Test scenario: A nighttime drone formation performance is combined with fireworks. After the performance, the drones land inside a packaging box on the ground, and sparks from the fireworks may land on the surface of the packaging box.

[0061] Test results: The packaging box surface did not ignite upon contact with a spark, only showing slight charring. The material stopped burning after the spark was extinguished. After three demonstrations and more than 30 loading and unloading operations, the packaging box maintained good structural integrity, with no cracks, deformations, or coating peeling. Compared to traditional ABS plastic packaging boxes (weighing approximately 5.5 kg), the weight is reduced by 67%, significantly reducing the handling burden for on-site personnel.

[0062] User review: This packaging box perfectly meets the comprehensive requirements of drone performance scenarios for flame retardancy, lightweight, and impact resistance. It provides reliable safety protection, especially in high-risk scenarios such as fireworks displays, and has been highly recognized by the performance teams.

[0063] Application Example 2: Outdoor Sculptures in Urban Parks Using the flame-retardant, lightweight EPP / polyurea composite material prepared in Example 3, a set of outdoor decorative sculptures (cartoon animal shapes, 1.5-2.0m in height) for urban parks were designed and fabricated. The sculptures were decorated with colored polyurea topcoat, presenting vibrant colors and a smooth texture.

[0064] Application scenario: Located in a children's playground in a city center park, the sculpture is exposed to the outdoor environment for a long time and needs to withstand the test of sun exposure, rain, and temperature changes.

[0065] Follow-up evaluation (18 months after installation): The sculpture maintains a good appearance, with vibrant colors and no obvious fading or yellowing; the surface coating is intact, without cracking, peeling, or powdering; it has withstood the test of high summer temperatures (maximum 42℃) and low winter temperatures (minimum -15℃), and the material has not cracked or deformed due to thermal expansion and contraction; after being washed by multiple heavy rains, the material has not absorbed water, and the internal EPP structure remains dry; the sculpture is lightweight (approximately 15-25kg per sculpture), facilitating installation, movement, and adjustment; it has passed the fire retardant performance test by the fire department, meeting the fire safety requirements for public places.

[0066] Social Benefits: This sculpture group is very popular with citizens, especially children, and has become a landmark of the park. Compared with traditional fiberglass or cement sculptures, sculptures made of this material have significant advantages in terms of lightweight, safety (no sharp edges, flame retardant), color expression, and production cycle, providing a new material option for urban public art.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of protection of the present invention.

Claims

1. A flame-retardant lightweight EPP / polyurea composite material, comprising EPP foamed beads as the substrate and a flame-retardant polyurea coating on the surface, characterized in that... The flame-retardant polyurea coating has a thickness of 0.5-3.0 mm and is prepared from the following components: Component A comprises: 100 parts by weight of aliphatic diisocyanate and 0.05-0.3 parts by weight of catalyst; Component B includes: 30-60 parts by weight of aromatic diamine, 40-70 parts by weight of aliphatic polyether amine, 20-40 parts by weight of intumescent flame retardant, 2-8 parts by weight of nanofiller, and 1-5 parts by weight of interface reinforcing agent.

2. The flame-retardant lightweight EPP / polyurea composite material according to claim 1, characterized in that... The density of the EPP foamed beads is 40-120 g / L.

3. The flame-retardant lightweight EPP / polyurea composite material according to claim 1, characterized in that... The aliphatic diisocyanate is selected from hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, or several thereof; the aromatic diamine is selected from diethyltoluene diamine, 4,4'-methylenebis(2-chloroaniline), 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenylmethane, or several thereof; the aliphatic polyetheramine is an amino-terminated polyether with a number average molecular weight of 2000-4000 g / mol.

4. The flame-retardant lightweight EPP / polyurea composite material according to claim 1, characterized in that... The intumescent flame retardant includes an acid source, a carbon source, and a gas source, wherein the acid source is 10-20 parts by weight of ammonium polyphosphate, the carbon source is 5-12 parts by weight of pentaerythritol or dipentaerythritol, and the gas source is 5-10 parts by weight of melamine or melamine cyanurate.

5. The flame-retardant lightweight EPP / polyurea composite material according to claim 1, characterized in that... The nanofiller is selected from one or more of expandable graphite, layered bimetallic hydroxide, graphene oxide, nano aluminum hydroxide, and nano magnesium hydroxide. The nanofiller is a composite of expandable graphite and layered bimetallic hydroxide with a mass ratio of 1-3:

1. The interface reinforcing agent is selected from one or more of silane coupling agent, maleic anhydride-grafted polypropylene, and epoxidized natural rubber.

6. The flame-retardant lightweight EPP / polyurea composite material according to claim 1, characterized in that... The catalyst is selected from one or more of dibutyltin dilaurate, stannous octoate, and triethylenediamine.

7. The method for preparing the flame-retardant lightweight EPP / polyurea composite material according to any one of claims 1-6, characterized in that... This includes the following steps: Step 1, EPP substrate pretreatment: The EPP foamed bead molded body is surface treated by flame treatment, plasma treatment or chemical treatment to activate the surface; Step 2, Flame-retardant polyurea component preparation: Mix the aliphatic diisocyanate and catalyst in component A evenly; mix the aromatic diamine, aliphatic polyetheramine, intumescent flame retardant, nanofiller and interface reinforcing agent in component B, and mix thoroughly using a high-speed dispersion or planetary stirring device, followed by ultrasonic dispersion for 30-60 minutes; Step 3, Polyurea Coating Lamination: Apply flame-retardant polyurea to the surface of the EPP substrate using a spraying or dipping method; Step 4, Curing and Molding: Cur the composite material at room temperature for 4-24 hours to obtain flame-retardant and lightweight EPP / polyurea composite material.

8. The preparation method according to claim 7, characterized in that... The surface treatment method described in step 1 is flame treatment, with a flame temperature of 800-1200℃ and a treatment time of 1-3s; or plasma treatment, with a plasma power of 300-600W and a treatment time of 30-90s; or chemical treatment, using a potassium permanganate solution or chromic acid mixture with a mass fraction of 5-15% for 2-5min.

9. The preparation method according to claim 7, characterized in that... The process parameters for the spraying method in step 3 are as follows: using a two-component spraying equipment, component A and component B are mixed and sprayed under high pressure with a volume ratio of 1:1, the spraying pressure is 15-25MPa, the spraying temperature is 60-80℃, and the spraying distance is 40-60cm; the process parameters for the immersion method are as follows: immersing the EPP substrate in the pre-mixed mixture of component A and component B for 3-8s.

10. The application of the flame-retardant lightweight EPP / polyurea composite material according to any one of claims 1-6 in the preparation of drone packaging boxes; in the preparation of outdoor sculptures; or in the preparation of protective equipment, sporting goods, or transportation cushioning components.