Polypropylene composite material, and preparation method and application thereof

Abstract

The application belongs to the technical field of high polymer materials, and specifically discloses a polypropylene composite material, which comprises the following components in parts by weight: 25-45 parts of polypropylene resin, 10-25 parts of ammonium polyphosphate, 10-20 parts of bamboo powder, 5-15 parts of DOPO or a derivative thereof, and 1-8 parts of PLA. The application precisely controls the acid source release temperature by wrapping the ammonium polyphosphate with the PLA and matches the temperature window of the DOPO gas source; meanwhile, the bamboo powder is used to catalyze the carbonization, so that the gas-solid dual-phase flame-retardant synergy is realized. The polypropylene composite material has the advantages of high efficient flame retardation, high mechanical property retention and environmental friendliness, and can be used for preparing household appliance shells or automobile interiors.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and specifically relates to a polypropylene composite material. Background Technology

[0002] Polypropylene (PP) has become a core material for automotive interiors, home appliance housings, and electronic device components due to its excellent processing performance, chemical stability, and cost advantages, with annual global consumption exceeding 70 million tons. However, its limiting oxygen index (LOI) is only 17-18%, classifying it as a highly flammable material (UL94 HB grade). When it thermally decomposes at 380-400℃, it produces a large amount of flammable alkane fragments (such as propane and butane), with a calorific value as high as 46 MJ / kg (ASTM D5865), seriously threatening the safety performance of its applications.

[0003] Existing polypropylene flame retardant technologies suffer from three major technical problems:

[0004] (1) Environmental risks of toxic flame retardant systems: Although halogenated flame retardants (such as decabromodiphenyl ether) can increase the LOI to 24-26%, they release hydrogen bromide and polybrominated dibenzodioxins during combustion, with a toxicity equivalent factor (TEF) as high as 0.5 (referring to WHO standards). The EU RoHS Directive (2011 / 65 / EU) explicitly restricts the application of brominated flame retardants in electronic and electrical appliances, leading to compliance risks for material exports.

[0005] (2) Temperature mismatch of flame retardant components leads to synergistic failure: Intumescent flame retardant systems (such as APP / pentaerythritol compound) rely on the synchronous action of acid source, gas source, and carbon source. However, the initial decomposition temperature of APP (250±5℃) is much lower than the activation window of the gas source flame retardant DOPO (300-350℃), resulting in a short gas-acid reaction time window. As a result, the char residue rate is less than 20% (800℃ TGA), and the porosity of the char layer is >80% (microscopic CT), which fails the UL94 V-1 level test.

[0006] (3) Thermal degradation defects of natural fiber reinforcement: Although bamboo fiber filling can improve mechanical strength, its main component α-cellulose undergoes molecular chain breakage above 160℃, resulting in a decrease in tensile strength of composite material >30% (ISO 527-1), while releasing small aldehyde molecules (such as furfural) to exacerbate odor problems.

[0007] Therefore, developing PP composite materials that combine high flame retardancy, high mechanical property retention, and environmental friendliness is a core requirement of the industry. Summary of the Invention

[0008] The purpose of this invention is to solve the above-mentioned technical problems and provide a polypropylene composite material that is highly efficient in flame retardancy, has high mechanical property retention, and is environmentally friendly.

[0009] Another object of the present invention is to provide a preparation process for the above-mentioned polypropylene composite material.

[0010] Another object of the present invention is to provide applications of the above-mentioned propylene composite material.

[0011] This invention is achieved through the following technical solution:

[0012] A polypropylene composite material, comprising the following components by weight:

[0013] 25-45 parts of polypropylene resin;

[0014] 10-25 parts of ammonium polyphosphate;

[0015] 10-20 parts bamboo powder;

[0016] 5-15 parts of DOPO or its derivatives;

[0017] PLA 1-8 copies.

[0018] The molecular weight range of PLA described in this invention is 50,000-150,000 g / mol.

[0019] The PLA described in this invention has a glass transition temperature (Tg) of 58-62℃, a melting temperature (Tm) of 155-300℃ (DSC test ISO 11357-1), a melt flow rate of 1-20 g / 10 min (190℃ / 2.16 kg, ISO 1133), a crystallinity of 0-40% (XRD method ASTM D3899), and a density of 1.24-1.28 g / cm³ (ISO 1183).

[0020] Preferably, the peak decomposition temperature of the PLA is 270-290℃.

[0021] The peak decomposition temperature of PLA matches the synergistic window of ammonium polyphosphate and DOPO, thus improving the flame retardant effect.

[0022] Preferably, the melt flow rate of the polypropylene resin is 3-15 g / 10 min, the testing conditions are: 230℃, 2.16 kg, and the testing standard is GB / T3682.1-2018. The melt flow rate of the polypropylene resin described in this invention can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 g / 10 min, or any range formed by any two of the above values.

[0023] Polypropylene has a high melt flow rate, which can reduce the temperature during material processing. However, an excessively high melt flow rate will lead to uneven dispersion of the components.

[0024] More preferably, the melt flow rate of the polypropylene resin is 5-12 g / 10 min.

[0025] In the polypropylene composite material of the present invention, the content of polypropylene resin is not less than 30 wt%. The weight parts of polypropylene resin of the present invention can be: 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45 parts, or any range formed by any two of the above values.

[0026] The ammonium polyphosphate described in this invention has an inorganic polycondensation phosphate structure and a general chemical formula of (NH4). n+2 P n O 3n+1 In the formula, the degree of polymerization n ≥ 1000.

[0027] The ammonium polyphosphate has a particle size distribution D50 of 5-20 μm (laser particle size analyzer ISO 13320:2020).

[0028] The weight parts of ammonium polyphosphate described in this invention can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25 parts, or any range formed by any two of the above values.

[0029] The weight parts of bamboo powder described in this invention can be 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 parts, or any range formed by any two of the above values.

[0030] Preferably, the bamboo powder has a particle size D50 of 30-70µm.

[0031] Preferably, the bamboo powder is treated with phosphoric acid and ferric chloride to obtain iron-phosphated bamboo powder.

[0032] Specifically, the process is as follows: 80-90wt% phosphoric acid is mixed with 0.03-0.1mol / ml FeCl3 to obtain a pretreatment solution. The pretreatment solution is then mixed with bamboo powder at 70-90℃ and stirred for 20-40 minutes at a stirring speed of 150-200r / min. After drying, iron-phosphated bamboo powder is obtained.

[0033] The present invention describes the in-situ deposition of 20-50 nm iron pyrophosphate compounds on the surface of iron-phosphated bamboo powder.

[0034] The chemical structural formula of the iron pyrophosphate compound is: Fe2P2O7⋅xH2O, where x=0-2. Preferably, the iron-phosphated bamboo powder has a specific surface area ≥10 m² / g and a surface iron pyrophosphate particle size of 20-50 nm.

[0035] The working principle of the iron-containing phosphated bamboo powder is as follows:

[0036] Fe²⁺ / Fe³⁺ acts as a Lewis acid catalyst, combining with polyphosphoric acid produced from the decomposition of ammonium polyphosphate to form the active intermediate iron pyrophosphate, which catalyzes the dehydration of cellulose to char and the release of water vapor: Fe₂P₂O₇ + H₄P₂O₇ → Fe₂P₄O 13 The highly active iron polyphosphate generated by 2H2O further catalyzes the dehydration and crosslinking of cellulose molecules. The polyphosphate produced in this process continuously catalyzes the dehydration reaction, significantly improving the expansion ratio and thermal stability of the expanded carbon layer. At the same time, Fe³⁺ forms an ionic crosslinking network with the cellulose hydroxyl groups, which improves the tensile strength of the composite material.

[0037] The DOPO derivatives described in this invention include, but are not limited to:

[0038] DOPO-HQ: Synthesized from DOPO and p-benzoquinone.

[0039] DOPO-ITA: Synthesized from DOPO and itaconic acid.

[0040] The weight parts of DOPO or its derivatives described in this invention can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 parts, or any range formed by any two of the above values.

[0041] Those skilled in the art may add 0.01-5 parts by weight of additives to the present invention as needed. The additives include, but are not limited to, at least one of the following: anti-dripping agents, heat stabilizers, light stabilizers, antioxidants, lubricants, release agents, antistatic agents, plasticizers, nucleating agents, foaming agents, rheology modifiers, filler dispersants, crosslinking agents, flame retardants, and UV stabilizers. The processing aids are not limited to the types of additives listed above. Those skilled in the art may increase or decrease the types and / or content of additives as needed.

[0042] The present invention also provides a method for preparing the above-mentioned polypropylene composite material, comprising the following steps: mixing all components uniformly according to the proportions, and then performing melt blending, extrusion, and granulation.

[0043] Preferably, a twin-screw extruder is used for extrusion.

[0044] Preferably, the twin-screw extruder has a length-to-diameter ratio of 30:1-40:1, a screw speed of 180-220 rpm, and a melt temperature of 160-180℃ during melt blending.

[0045] Preferably, ammonium polyphosphate is preheated, PLA is dissolved in ethyl acetate solution, and sprayed through atomizing nozzles in a fluidized bed. The atomized PLA-ethyl acetate solution is evenly distributed in the fluidized bed by airflow and combines with ammonium polyphosphate particles. Vacuum desolventizing is performed to obtain PLA@APP. PLA@APP is then mixed evenly with other components and melt-extruded.

[0046] The present invention also provides applications of the above-mentioned polypropylene composite material for the preparation of appliance housings or automotive interiors, etc.

[0047] The present invention provides a household appliance housing comprising the aforementioned polypropylene composite material.

[0048] The present invention provides an automotive interior, comprising the aforementioned polypropylene composite material.

[0049] Compared with the prior art, the present invention has the following advantages:

[0050] By introducing PLA into the system to match the temperature window of the DOPO gas source, and simultaneously utilizing bamboo powder to catalyze char formation, a gas-solid two-phase flame retardant synergy is achieved. Its core mechanism is as follows:

[0051] 1. By reconstructing the decomposition behavior of ammonium polyphosphate (APP) using PLA, a gas-acid synergistic flame retardant with precise temperature matching is provided. The glass transition temperature of PLA maintains a rigid structure at the processing temperature, preventing premature decomposition of APP; at the critical temperature, the shell decomposes, enabling the controlled release of APP; the released APP decomposition product, polyphosphoric acid, couples with the DOPO gas source on a spatiotemporal scale, forming a continuous gas-acid synergistic window, significantly extending the flame retardant effect time.

[0052] 2. Iron-catalyzed interfacial char formation enhancement mechanism: Iron-containing phosphated bamboo powder has dual functions: surface iron pyrophosphate acts as a Lewis acid catalyst, which significantly reduces the activation energy of polyphosphate ammonium decomposition products catalyzing the dehydration of bamboo fibers into char, promoting the formation of a continuous and dense char layer; iron ions complex and crosslink with cellulose hydroxyl groups to construct an Fe-OC covalent network in the char layer, which improves the thermal shock resistance and mechanical support strength of the char layer; the closed-pore structure generated during the expansion of the char layer effectively blocks heat and oxygen transfer and inhibits the diffusion of combustible gases.

[0053] 3. Environmentally friendly closed-loop design, halogen-free system: Eliminates bromine / antimony flame retardants, eliminating persistent dioxin-like pollutants at the source; PLA can be completely mineralized into CO2 / H2O under composting conditions, meeting the ISO 17556 degradation standard; Resource recycling: Bamboo fiber comes from renewable resources, and its carbon footprint is reduced by at least half compared to glass fiber.

[0054] This invention breaks through the industrial dilemma of traditional flame retardant systems being unable to simultaneously achieve high-efficiency flame retardancy, high mechanical property retention, and environmental friendliness, opening up new possibilities for the application of high-end polypropylene composite materials in the automotive and electronics fields. Detailed Implementation

[0055] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0056] The raw materials used in this invention are sourced from:

[0057] Polypropylene resin 1: PP HP500N, melt flow rate of 12 g / 10min (test conditions: 230℃, 2.16kg, test standard: GB / T3682.1-2018), LyondellBasell.

[0058] Polypropylene resin 2: HP561X, melt flow rate of 7 g / 10 min (test conditions: 230℃, 2.16 kg, test standard: GB / T3682.1-2018), LyondellBasell.

[0059] Ammonium polyphosphate: Exolit AP422, thermal decomposition temperature 275℃, Clariant Germany.

[0060] DOPO: Hanfeng Technology Co., Ltd.

[0061] PLA: Ingeo™ 4032D, NatureWorks LLC.

[0062] FeCl3·6H2O: Analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0063] Phosphoric acid: 85wt%, GR grade, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0064] Ethyl acetate: AR grade, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0065] Bamboo powder: ZF50, average particle size 300 micrometers, Zihao Wood Industry Co., Ltd.

[0066] Additive: Polytetrafluoroethylene, DF-102, average particle size 300-600 micrometers, Guangzhou Huigui Composite Materials Co., Ltd.

[0067] Test methods:

[0068] (1) Tensile strength, ISO 527-1:2019. In the test, a standard strip specimen with a length of 115 mm, a width of 10 mm, and a thickness of 4 mm is used. The test is conducted using a ZWICK BT2-FR020TEW-A50 tensile testing machine. During the test, the specimen is stretched at a specified rate (usually 50 mm / min) until the specimen breaks. The test result is expressed in MPa, representing the maximum tensile strength of the material.

[0069] (2) Limiting Oxygen Index (LOI), ISO 4589-2:2017. In the test, the sample, with a length of 80 mm, a width of 10 mm, and a thickness of 4 mm, is placed in a mixed atmosphere of oxygen and nitrogen, ignited under specified conditions, and the minimum oxygen concentration required for ignition is recorded. The LOI value of the material can be obtained through this test, expressed as a percentage (%).

[0070] (3) UL-94 flame retardancy rating, UL 94-2020. In the test, the sample is placed under a flame source according to the standard size (usually 125 mm × 13 mm × 1.5 mm) and ignited. The duration of combustion, whether there are burning drips, and the self-extinguishing condition after combustion are observed. According to the test results, the sample is rated as V-0, V-1, V-2 or HB.

[0071] (4) Carbon residue rate, ISO 11358-1:2022, the sample particles (10 mg by weight) are heated to 700°C using a thermogravimetric analyzer (TGA) under a specified nitrogen or oxygen atmosphere, and the mass loss of the material is recorded. After the test, the carbon residue rate is the ratio of the mass of the carbonized material remaining after heating to the original mass, expressed as a percentage (%).

[0072] The embodiments 1-9 of this invention are obtained by the following method:

[0073] All components are mixed evenly according to the formula and extruded using a twin-screw extruder with a length-to-diameter ratio of 30:1-40:1 and a screw speed of 180-220 rpm. The melt temperature during melt blending is 160-180℃.

[0074] The iron-containing phosphated bamboo powder in Examples 9-10 of this invention is obtained through the following methods:

[0075] A pretreatment solution is prepared by mixing 80-90 wt% phosphoric acid with 0.03-0.1 mol / ml FeCl3. The pretreatment solution is then mixed with bamboo powder at 70-90℃ and stirred for 20-40 min at a stirring speed of 150-200 r / min. After drying, iron-phosphated bamboo powder is obtained.

[0076] The present invention, in Example 10, is prepared by the following method:

[0077] Ammonium polyphosphate is preheated, PLA is dissolved in ethyl acetate solution, and sprayed through atomizing nozzles in a fluidized bed. The atomized PLA-ethyl acetate solution is evenly distributed in the fluidized bed by airflow and combines with ammonium polyphosphate particles. Vacuum desolventizing is performed to obtain PLA@APP. The above PLA@APP is mixed evenly with other components and melt-extruded.

[0078] Table 1. Weight parts of each component and test results for Examples 1-10

[0079] Components / parts by weight Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Polypropylene resin 1 25 35 45 Polypropylene resin 2 25 30 35 40 45 35 35 Ammonium polyphosphate 10 20 20 25 20 10 20 20 20 20 bamboo powder 10 15 15 20 20 10 15 20 Iron-phosphated bamboo powder 15 15 DOPO 5 10 10 15 15 5 10 15 10 10 PLA 2 5 5 8 8 2 5 8 5 5 Additives 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 1.5mm flame retardant rating (UL-94) V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-0 Limiting Oxygen Index (LOI) (%) 25 28 29 31 30 25 29 32 33 35 Carbon residue rate 700℃ (%) 21 23 24 28 27 22 24 29 31 33 Tensile strength (MPa) 42 41 40 38 37 43 40 36 44 46

[0080] Table 2. Weight parts of each component and test results for Comparative Examples 1-4

[0081] Components / parts by weight Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Polypropylene resin 2 35 35 35 35 Ammonium polyphosphate / 20 20 20 bamboo powder 15 / 15 15 DOPO 10 10 / 10 PLA 5 5 5 / Additives 0.1 0.1 0.1 0.1 1.5mm flame retardant rating (UL-94) HB V-1 V-2 V-1 Limiting Oxygen Index (LOI) (%) 18 23 21 22 Carbon residue rate 700℃ (%) 14 18 17 16 Tensile strength (MPa) 45 33 43 37

[0082] As shown in Examples 1-8, the polypropylene composite material provided by this invention utilizes a synergistic system of PLA controlled-release acid source, bamboo powder, and DOPO, achieving a UL-0 flame retardant rating (UL-94) of 1.5mm thickness, a limiting oxygen index (LOI) ≥25%, and a char residue rate ≥20% at 700℃, demonstrating excellent thin-wall flame retardant performance; furthermore, its tensile strength is ≥36MPa. Building upon Example 3, Example 9 introduced iron-containing phosphated bamboo powder, achieving even better results. Based on Example 9, Example 10 involved fluidized bed treatment of PLA, combining it with ammonium polyphosphate particles to obtain PLA@APP, which was then mixed with the other components. Example 10 exhibited better results than Example 9.

[0083] The polypropylene composite material provided by this invention has both high flame retardant effect and high mechanical property retention.

[0084] As can be seen from Comparative Examples 1-4, the absence of any one of the following components—ammonium polyphosphate (Comparative Example 1), bamboo powder (Comparative Example 2), DOPO (Comparative Example 3), or PLA (Comparative Example 4)—cannot achieve a flame retardant rating (UL-94) of V-0 for 1.5mm thick walls, with a limiting oxygen index (LOI) < 25% and a char residue rate of < 20% at 700℃, indicating that it does not have a good thin-wall flame retardant effect.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A polypropylene composite material, characterized in that, By weight, it includes the following components: 25-45 parts of polypropylene resin; 10-25 parts of ammonium polyphosphate; 10-20 parts bamboo powder; 5-15 parts of DOPO or its derivatives; PLA 1-8 copies.

2. The polypropylene composite material according to claim 1, characterized in that, The melt flow rate of the polypropylene resin is 3-15 g / 10 min, and the testing conditions are: 230℃, 2.16 kg, with a preferred melt flow rate of 5-12 g / 10 min.

3. The polypropylene composite material according to claim 1, characterized in that, The molecular weight of the PLA is in the range of 50,000-150,000 g / mol.

4. The polypropylene composite material according to claim 1, characterized in that, The bamboo powder is treated with phosphoric acid and ferric chloride to obtain iron-phosphated bamboo powder.

5. A polypropylene composite material according to claim 4, characterized in that, The iron-containing phosphated bamboo powder has an in-situ deposition of 20-50 nm iron pyrophosphate compounds on its surface.

6. A polypropylene composite material according to claim 1, characterized in that, It also includes 0.01-5 parts by weight of additives.

7. A method for preparing a polypropylene composite material according to any one of claims 1-7, characterized in that, Includes the following steps: All components are mixed evenly according to the formula, and then granulated by melt blending and extrusion.

8. A method for preparing a polypropylene composite material according to any one of claims 7, characterized in that, Ammonium polyphosphate is preheated, PLA is dissolved in ethyl acetate solution, and sprayed through atomizing nozzles in a fluidized bed. The atomized PLA-ethyl acetate solution is evenly distributed in the fluidized bed by airflow and combines with ammonium polyphosphate particles. Vacuum desolventizing is performed to obtain PLA@APP. The above PLA@APP is mixed evenly with other components and melt-extruded.

9. The application of a polypropylene composite material according to any one of claims 1-6 for the manufacture of appliance housings or automotive interior trim.

10. An automotive interior, characterized in that, The invention comprises a polypropylene composite material according to any one of claims 1-6.