Flame-retardant low-VOCs automotive trim PP / EPDM thermoplastic elastomer and preparation method thereof

Abstract

The invention discloses a flame-retardant low-VOCs automotive interior PP / EPDM thermoplastic elastomer and a preparation method thereof, and relates to the technical field of automotive interior materials. A bio-based hyperbranched polymer containing multiple carboxyl and amino functional groups is adopted as a multifunctional modifier, and trace food-grade zinc oxide is combined, so that the flame-retardant low-VOCs automotive interior PP / EPDM thermoplastic elastomer is prepared. A reversible dynamic coordination cross-linked network is formed in the melt blending process, the network can enhance the compatibility and melt strength of PP and EPDM and improve the mechanical property of the material, sulfur-containing, nitrogen-containing and oxygen-containing micromolecular VOCs generated in the anchoring processing process can be chelated through the coordination effect of zinc ions, meanwhile, a halogen-free flame retardant is introduced to achieve the flame retardant function, and the flame retardant property of the material is improved. Finally, the automotive interior material with excellent synergism of flame retardant property, mechanical property and low VOCs (Volatile Organic Compounds) performance is obtained, can be widely applied to automotive interior parts, and has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of automotive interior materials technology, specifically to a flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer and its preparation method. Background Technology

[0002] With the rapid development of the automotive industry and the increasing health awareness of consumers, the performance requirements for automotive interior materials are becoming increasingly stringent. In terms of environmental protection, it is necessary to strictly control the release of volatile organic compounds, such as benzene, formaldehyde, and ethylbenzene, during the processing and use of materials. These small molecules not only produce pungent odors but also harm human health. In terms of safety, automotive interior materials must meet flame retardant requirements to address fire risks and ensure passenger safety. At the same time, materials must also possess good comprehensive performance to ensure the normal use of components and good melt strength to meet processing and molding requirements. PP / EPDM thermoplastic elastomers combine the rigidity and processability of PP with the elasticity and weather resistance of EPDM and are widely used in automotive dashboards, door panels, seats, headliners, and other components. However, existing PP / EPDM thermoplastic elastomers still face many challenges in meeting the above stringent requirements.

[0003] Existing PP / EPDM thermoplastic elastomers suffer from two major problems. First, the poor compatibility between PP and EPDM leads to insufficient mechanical properties, such as low tensile strength, impact strength, and melt strength, which in turn affects processing and molding, making it difficult to guarantee the quality of interior parts. Second, during processing and use, the materials release small-molecule VOCs containing sulfur, nitrogen, and oxygen, adversely affecting the air quality inside vehicles. To address these issues, existing technologies have adopted a series of measures, but all have significant shortcomings. For example, compatibilizers are often added to improve the compatibility between PP and EPDM; however, compatibilizers have a single function, only improving compatibility and failing to achieve long-term control of VOCs. Adsorbents are used to adsorb VOCs, but adsorbents are physical adsorption agents with limited adsorption capacity, are easily saturated, and affect the mechanical and processing properties of the material. In addition, existing modifiers are mostly petroleum-based products, which do not conform to the trend of green and environmentally friendly development and are difficult to achieve synergistic improvement in mechanical enhancement, VOC control, and flame retardant properties. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer and its preparation method. This invention utilizes a bio-based hyperbranched polymer containing multiple carboxyl and amino functional groups as a multifunctional modifier, combined with trace amounts of food-grade zinc oxide, to form a reversible dynamic coordination crosslinking network during melt blending. This network enhances the compatibility and melt strength of PP and EPDM, improves the material's mechanical properties, and chelates and anchors sulfur-, nitrogen-, and oxygen-containing small-molecule VOCs generated during processing through zinc ion coordination. Simultaneously, a halogen-free flame retardant is introduced to achieve flame retardant functionality. Ultimately, this results in an automotive interior material with excellent synergistic properties of flame retardancy, mechanical properties, and low VOCs, which can be widely used in automotive interior components and has promising application prospects.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: On one hand, a flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer, comprising, by weight, 40-60 parts PP resin, 20-35 parts EPDM rubber, 3-8 parts bio-based hyperbranched polymer, 0.1-1.0 parts food-grade zinc oxide, 10-25 parts halogen-free flame retardant, 0.2-0.8 parts antioxidant, and 0.3-0.9 parts lubricant; The bio-based hyperbranched polymer is a bio-based hyperbranched polymer containing multiple carboxyl and amino functional groups, with a number-average molecular weight of 5000-20000, a carboxyl content of 2.5-5.0 mmol / g, and an amino content of 1.0-2.5 mmol / g. It is prepared by amidation and polymerization of terminal amino aliphatic bio-based compounds with carboxylic acids or anhydrides containing unsaturated double bonds. The food-grade zinc oxide has a particle size of 20-50 nm and a purity of ≥99.5%. The halogen-free flame retardant is one or a mixture of two or more of magnesium hydroxide, aluminum hydroxide, and phosphorus-based flame retardants, wherein the phosphorus-based flame retardant is a phosphate ester or ammonium polyphosphate flame retardant.

[0006] Furthermore, the PP resin is homopolymer PP or copolymer PP with a melt index of 10-30 g / 10 min; the EPDM rubber has a Mooney viscosity of 40-80, an ethylene content of 45%-65%, and a third monomer content of 3%-8%.

[0007] Furthermore, the antioxidant is a compound system of hindered phenolic antioxidants and phosphite antioxidants, with a compound mass ratio of 1:1-2; the lubricant is one or a mixture of two or more of stearic acid, butyl stearate, and polyethylene wax.

[0008] Furthermore, the preparation method of the bio-based hyperbranched polymer includes the following steps: Using terminal amino-based aliphatic bio-based compounds and unsaturated double-bond compounds containing acid anhydrides and carboxylic acids as raw materials, and toluene as solvent, the mixture was heated under reflux at 65-110℃ for 2-5 hours, and then separated after cooling to obtain amide compounds containing unsaturated double bonds. The obtained amide compound containing unsaturated double bonds was mixed with a carboxylic acid monomer containing double bonds, and an initiator and a molecular weight regulator were added in deionized water as solvent. The mixture was reacted at 40-95℃ for 3-5 hours, and the resulting product was obtained by rotary evaporation.

[0009] Furthermore, the molar ratio of the terminal amino aliphatic bio-based compound to the unsaturated double bond compound containing anhydride and carboxylic acid is 1:2.0-4.0; the mass ratio of the amide compound containing unsaturated double bond to the carboxylic acid monomer containing double bond is (20-40):(40-60), the initiator accounts for 5-10% of the mass of the carboxylic acid monomer containing double bond, and the molecular weight regulator accounts for 2-6% of the mass of the carboxylic acid monomer containing double bond.

[0010] Furthermore, the unsaturated double-bond compound containing anhydride and carboxylic acid is one or a mixture of maleic acid, itaconic acid, maleic anhydride, and itaconic anhydride; the carboxylic acid monomer containing double bond is one or a mixture of acrylic acid, methacrylic acid, and maleic acid; the initiator is one or a mixture of ammonium persulfate, potassium persulfate, and sodium bisulfite; and the molecular weight regulator is one or a mixture of isopropanol and dodecyl mercaptan.

[0011] On the other hand, a method for preparing a flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer is characterized by comprising the following specific steps: Raw material pretreatment: Place PP resin and EPDM rubber separately into a forced-air drying oven and dry at 80-100℃ for 2-4 hours. Stir once every 1 hour during the drying process to ensure uniform removal of moisture. After drying, cool to room temperature for later use. Place bio-based hyperbranched polymer, food-grade zinc oxide, halogen-free flame retardant, antioxidant, and lubricant into a high-speed mixer. Adjust the mixer speed to 800-1200 r / min, the mixing time to 10-15 min, and the mixing temperature to 40-50℃ to obtain a uniform mixture of additives for later use. Melt blending: Select a twin-screw extruder with a screw length-to-diameter ratio of 36:1-40:1. First, preheat the temperature of each section of the twin-screw extruder to the set value for 20-30 minutes to ensure temperature stability. Add the dried PP resin and EPDM rubber to the feed port of the twin-screw extruder in proportion, adjust the screw speed to 300-500 r / min and the feed rate to 20-30 kg / h. After melting and plasticizing for 3-5 minutes, add the mixing additives at a uniform rate through the side feed port and continue melt blending for 5-10 minutes. During this period, control the pressure inside the extruder barrel to 10-15 MPa. During the melt blending process, zinc ions form a reversible dynamic coordination crosslinking network with the carboxyl groups on the bio-based hyperbranched polymer and the oxygen-containing groups on the PP / EPDM chains generated by heat and oxygen. Extrusion granulation: The melt-blended material is extruded through the die head of a twin-screw extruder. The extruded melt strip is cooled by a water cooling tank and then fed into a pelletizer. The pelletizer speed is adjusted to 200-300 r / min and the pellet length is 2-3 mm to obtain flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer granules. The granules are placed in a forced-air drying oven and dried at 70-80℃ for 1-2 hours to remove surface moisture. Unqualified granules are screened out and packaged for later use.

[0012] Furthermore, the temperatures of each section of the twin-screw extruder are 160-170℃, 170-180℃, 180-190℃, and 185-190℃ respectively, and the die head temperature is 180-185℃.

[0013] Furthermore, the water temperature in the water-cooling tank is 20-30℃, and the cooling time is 5-10 seconds.

[0014] Compared with existing technologies, this flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer and its preparation method have the following advantages: This invention utilizes a bio-based hyperbranched polymer containing multiple carboxyl and amino functional groups and trace amounts of food-grade zinc oxide to construct a reversible dynamic coordination crosslinking network. This not only significantly improves the compatibility of PP and EPDM, resulting in a substantial increase in the tensile strength and impact strength of the materials, but also achieves long-term chemical anchoring of sulfur-, nitrogen-, and oxygen-containing small-molecule VOCs during processing through the coordination effect of zinc ions, effectively reducing VOC release. The synergistic effect of the introduced halogen-free flame retardant and the dynamic coordination network significantly enhances flame retardancy while maintaining the excellent mechanical properties and low VOCs characteristics of the materials. The selection of bio-based hyperbranched polymers and food-grade zinc oxide makes the materials green and environmentally friendly, with no release of harmful impurities. This synergistic optimization of flame retardancy, low VOCs, and mechanical properties has broad application prospects.

[0015] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0017] Figure 1 A flowchart illustrating a method for preparing a flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer; Figure 2 This is a flowchart illustrating a method for preparing a flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer bio-based hyperbranched polymer. Detailed Implementation

[0018] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0019] Example 1

[0020] A flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer, with the following raw material composition by weight: 45 parts of PP resin (copolymer PP, melt index 20g / 10min), 30 parts of EPDM rubber (Mounney viscosity 60, ethylene content 55%, third monomer content 5%), 5 parts of bio-based hyperbranched polymer, 0.5 parts of food-grade zinc oxide (particle size 30nm, purity 99.8%), 18 parts of halogen-free flame retardant (magnesium hydroxide), 0.5 parts of antioxidant (a blend of hindered phenolic antioxidant and phosphite antioxidant, mass ratio 1:1.5), and 0.6 parts of lubricant (stearic acid).

[0021] Among them, such as Figure 2 As shown, the preparation method of bio-based hyperbranched polymers is as follows: Take 0.1 mol of the terminal amino aliphatic bio-based compound, add 100 mL of toluene as solvent, then add 0.3 mol of maleic anhydride, heat under reflux at 85 °C for 3 h, cool to room temperature and separate to obtain an amide compound containing unsaturated double bonds; Take 0.1 mol of the above-mentioned amide compound containing unsaturated double bonds, add 100 mL of deionized water as solvent, add ammonium persulfate (8% of the mass of acrylic acid) as initiator, add isopropanol (4% of the mass of acrylic acid) as molecular weight regulator, and then add 0.2 mol of acrylic acid. React at 80 °C for 4 h. After rotary evaporation, a multi-carboxyl and multi-amino bio-based hyperbranched polymer is obtained with a number average molecular weight of 12000, a carboxyl content of 3.8 mmol / g, and an amino content of 1.8 mmol / g.

[0022] like Figure 1 As shown, the preparation method of this flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer is as follows: PP resin and EPDM rubber were dried at 90℃ for 3 hours to remove moisture; bio-based hyperbranched polymer, food-grade zinc oxide, magnesium hydroxide, antioxidant, and stearic acid were mixed evenly to obtain a mixed additive. The dried PP resin and EPDM rubber were added to a twin-screw extruder (screw length-to-diameter ratio 38:1) and melt-plasticized at 170-185℃ and 400 r / min. Then, mixing additives were added, and the melt blending continued for 8 min. During this process, zinc ions formed a reversible dynamic coordination crosslinking network with the carboxyl groups on the bio-based hyperbranched polymer and the oxygen-containing groups on the PP / EPDM chains. The extrusion section temperatures of the twin-screw extruder were 165℃, 175℃, 185℃, and 188℃, and the die head temperature was 182℃. The melt-blended material is extruded, stretched, cooled, and pelletized to obtain flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer granules.

[0023] Example 2

[0024] A flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer, with the following raw material composition by weight: 50 parts of PP resin (homogeneous PP, melt index 15g / 10min), 25 parts of EPDM rubber (Mounney viscosity 50, ethylene content 50%, third monomer content 4%), 6 parts of bio-based hyperbranched polymer, 0.3 parts of food-grade zinc oxide (particle size 20nm, purity 99.5%), 20 parts of halogen-free flame retardant (ammonium polyphosphate), 0.4 parts of antioxidant (a blend of hindered phenolic antioxidant and phosphite antioxidant, mass ratio 1:1), and 0.5 parts of lubricant (polyethylene wax).

[0025] The preparation method of the bio-based hyperbranched polymer is as follows: Take 0.1 mol of the terminal amino aliphatic bio-based compound, add 100 mL of toluene as solvent, then add 0.25 mol of itaconic acid, heat under reflux at 75 °C for 4 h, cool to room temperature and separate to obtain an amide compound containing unsaturated double bonds; Take 0.1 mol of the above-mentioned amide compound containing unsaturated double bonds, add 100 mL of deionized water as solvent, add a mixture of potassium persulfate and sodium bisulfite (7% of the mass of methacrylic acid) as initiator, add dodecyl mercaptan (3% of the mass of methacrylic acid) as molecular weight regulator, and then add 0.25 mol of methacrylic acid. React at 75 °C for 5 h, and after rotary evaporation, obtain a multi-carboxyl and multi-amino bio-based hyperbranched polymer with a number average molecular weight of 10,000, a carboxyl content of 3.2 mmol / g, and an amino content of 1.5 mmol / g.

[0026] The preparation method of this flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer is as follows: PP resin and EPDM rubber were dried at 85℃ for 3.5h to remove moisture; bio-based hyperbranched polymer, food-grade zinc oxide, ammonium polyphosphate, antioxidant, and polyethylene wax were mixed evenly to obtain a mixed additive. The dried PP resin and EPDM rubber were added to a twin-screw extruder (screw length-to-diameter ratio 36:1) and melt-plasticized at 165-180℃ and 350 r / min. Then, mixing additives were added, and the melt blending continued for 7 min. During this process, zinc ions formed a reversible dynamic coordination crosslinking network with the carboxyl groups on the bio-based hyperbranched polymer and the oxygen-containing groups on the PP / EPDM chains. The extrusion section temperatures of the twin-screw extruder were 160℃, 170℃, 180℃, and 185℃, and the die head temperature was 180℃. The melt-blended material is extruded, stretched, cooled, and pelletized to obtain flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer granules.

[0027] Example 3

[0028] A flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer, with the following raw material composition by weight: 55 parts of PP resin (copolymer PP, melt index 25g / 10min), 22 parts of EPDM rubber (Mounney viscosity 70, ethylene content 60%, third monomer content 6%), 4 parts of bio-based hyperbranched polymer, 0.7 parts of food-grade zinc oxide (particle size 40nm, purity 99.7%), 15 parts of halogen-free flame retardant (mixture of magnesium hydroxide and phosphate ester flame retardant, mass ratio 1:1), 0.6 parts of antioxidant (component of hindered phenolic antioxidant and phosphite antioxidant, mass ratio 1:2), and 0.8 parts of lubricant (butyl stearate).

[0029] The preparation method of the bio-based hyperbranched polymer is the same as that in Example 1.

[0030] The preparation method of this flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer is as follows: PP resin and EPDM rubber were dried at 95℃ for 2.5h to remove moisture; bio-based hyperbranched polymer, food-grade zinc oxide, mixed flame retardant, antioxidant, and butyl stearate were mixed evenly to obtain mixed additives. The dried PP resin and EPDM rubber were added to a twin-screw extruder (screw length-to-diameter ratio 40:1) and melt-plasticized at 175-190℃ and 450 r / min. Then, mixing additives were added, and the melt blending continued for 9 min. During this process, zinc ions formed a reversible dynamic coordination crosslinking network with the carboxyl groups on the bio-based hyperbranched polymer and the oxygen-containing groups on the PP / EPDM chains. The extrusion section temperatures of the twin-screw extruder were 170℃, 180℃, 190℃, and 190℃, respectively, and the die head temperature was 185℃. The melt-blended material is extruded, stretched, cooled, and pelletized to obtain flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer granules.

[0031] Comparative Example 1 A type of PP / EPDM thermoplastic elastomer for automotive interiors, differing from Example 1 in that it does not contain bio-based hyperbranched polymers and food-grade zinc oxide. The raw material composition (parts by weight) is as follows: 45 parts of PP resin (copolymer PP, melt index 20 g / 10 min), 30 parts of EPDM rubber (Mounney viscosity 60, ethylene content 55%, third monomer content 5%), 18 parts of halogen-free flame retardant (magnesium hydroxide), 0.5 parts of antioxidant (a blend of hindered phenolic antioxidant and phosphite antioxidant in a mass ratio of 1:1.5), and 0.6 parts of lubricant (stearic acid).

[0032] Preparation method: PP resin and EPDM rubber were dried at 90℃ for 3 hours to remove moisture; magnesium hydroxide, antioxidant, and stearic acid were mixed evenly to obtain a mixed additive. The dried PP resin and EPDM rubber were added to a twin-screw extruder (screw length-to-diameter ratio 38:1) and melt-plasticized at 170-185℃ and 400 r / min. Then, mixing additives were added, and the mixture was melt-blended for another 8 minutes (without the formation of a dynamic coordination crosslinking network). The extrusion section temperatures of the twin-screw extruder were 165℃, 175℃, 185℃, and 188℃, and the die head temperature was 182℃. The melt-blended material is extruded, stretched, cooled, and pelletized to obtain PP / EPDM thermoplastic elastomer granules for automotive interiors.

[0033] Comparative Example 2 A type of PP / EPDM thermoplastic elastomer for automotive interiors, differing from Example 1 in that it does not contain halogen-free flame retardants. The raw material composition (parts by weight) is as follows: 45 parts of PP resin (copolymer PP, melt index 20g / 10min), 30 parts of EPDM rubber (Mounney viscosity 60, ethylene content 55%, third monomer content 5%), 5 parts of bio-based hyperbranched polymer, 0.5 parts of food-grade zinc oxide (particle size 30nm, purity 99.8%), 0.5 parts of antioxidant (a blend of hindered phenolic antioxidant and phosphite antioxidant, mass ratio 1:1.5), and 0.6 parts of lubricant (stearic acid).

[0034] Preparation method: PP resin and EPDM rubber were dried at 90℃ for 3 hours to remove moisture; bio-based hyperbranched polymer, food-grade zinc oxide, antioxidant, and stearic acid were mixed evenly to obtain a mixed additive. The dried PP resin and EPDM rubber were added to a twin-screw extruder (screw length-to-diameter ratio 38:1) and melt-plasticized at 170-185℃ and 400 r / min. Then, mixing additives were added, and the melt blending continued for 8 min. During this process, zinc ions formed a reversible dynamic coordination crosslinking network with the carboxyl groups on the bio-based hyperbranched polymer and the oxygen-containing groups on the PP / EPDM chains. The extrusion section temperatures of the twin-screw extruder were 165℃, 175℃, 185℃, and 188℃, and the die head temperature was 182℃. The melt-blended material is extruded, stretched, cooled, and pelletized to obtain PP / EPDM thermoplastic elastomer granules for automotive interiors.

[0035] Comparative Example 3 A type of PP / EPDM thermoplastic elastomer for automotive interiors differs from Example 1 in that it uses maleic anhydride-grafted PP as a compatibilizer to replace the bio-based hyperbranched polymer and does not contain food-grade zinc oxide. The raw material composition (parts by weight) is as follows: 45 parts of PP resin (copolymer PP, melt index 20 g / 10 min), 30 parts of EPDM rubber (Mounney viscosity 60, ethylene content 55%, third monomer content 5%), 5 parts of maleic anhydride-grafted PP (grafting rate 1.2%), 18 parts of halogen-free flame retardant (magnesium hydroxide), 0.5 parts of antioxidant (a mixture of hindered phenolic antioxidant and phosphite antioxidant in a mass ratio of 1:1.5), and 0.6 parts of lubricant (stearic acid).

[0036] Preparation method: PP resin, EPDM rubber, and maleic anhydride-grafted PP were dried at 90°C for 3 hours to remove moisture; magnesium hydroxide, antioxidant, and stearic acid were mixed evenly to obtain a mixed additive. The dried PP resin, EPDM rubber, and maleic anhydride-grafted PP were added to a twin-screw extruder (screw length-to-diameter ratio 38:1) and melt-plasticized at 170-185℃ and 400 r / min. Then, mixing additives were added, and the mixture was melt-blended for another 8 minutes (no dynamic coordination crosslinking network was formed; compatibility was improved only through maleic anhydride-grafted PP). The extrusion section temperatures of the twin-screw extruder were 165℃, 175℃, 185℃, and 188℃, respectively, and the die head temperature was 182℃. The melt-blended material is extruded, stretched, cooled, and pelletized to obtain PP / EPDM thermoplastic elastomer granules for automotive interiors.

[0037] Performance testing A comprehensive performance test was conducted on the PP / EPDM thermoplastic elastomers prepared in Examples 1-3 and Comparative Examples 1-3: Mechanical property testing: Tensile strength test: The test was conducted using an electronic universal testing machine. Each specimen was injection molded into a Type I standard tensile specimen, and 5 parallel specimens were prepared for each group. The specimens were placed in a constant temperature and humidity environment of 23±2℃ and 50±5% relative humidity for 24 hours to eliminate internal stress. During the test, the two ends of the specimen were clamped in the upper and lower clamps of the testing machine, the tensile speed was set to 50 mm / min, the testing machine was started, and the test continued until the specimen broke. The maximum tensile force of each specimen was recorded, and the tensile strength was calculated according to the formula σ=F / A (where σ is the tensile strength, F is the maximum tensile force, and A is the cross-sectional area of ​​the specimen), and two decimal places were retained. The test results of the 5 parallel specimens were averaged, and a tensile strength ≥15MPa was considered qualified.

[0038] Impact strength test: A simply supported beam impact testing machine was used for testing. Each specimen was injection molded into a standard impact specimen without notches, and 5 parallel specimens were prepared for each group. The specimens were placed in a constant temperature and humidity environment of 23±2℃ and 50±5% relative humidity for 24 hours to equilibrate. During the test, the specimens were placed stably on the support of the testing machine, the impact velocity was set to 3.5m / s, the testing machine was started, and the impact energy of each specimen was recorded. The impact strength was calculated according to the formula α=W / A (where α is the impact strength, W is the impact energy, and A is the cross-sectional area of ​​the specimen), and one decimal place was retained. The test results of the 5 parallel specimens were averaged, and an impact strength ≥50kJ / m² was considered qualified.

[0039] VOCs content test: Benzene and ethylbenzene test: Detection is carried out by thermal desorption-gas chromatography, using a gas chromatograph and a thermal desorption instrument; each sample is pressed into a sheet sample with dimensions of 100 mm×100 mm×3 mm, and the mass of each sample is controlled at 50±2 g; the sample is placed in a 10L sealed Tedlar bag, and the air in the bag is replaced with high-purity nitrogen (purity ≥99.999%) three times. After each replacement, it is kept sealed for 10 minutes to ensure that there is no air residue in the bag; the sealed Tedlar bag is placed in an environment at 23±2°C and a relative humidity of 50±5% for 24 hours of equilibration to make the VOCs released by the sample reach a stable state; after equilibration, the gas in the bag is sampled by the thermal desorption instrument, and the thermal desorption conditions are set as: desorption temperature 120°C, desorption time 30 minutes, desorption gas flow rate 50 mL / min; the desorbed gas is separated by an HP-5 capillary column, and the detection conditions of the gas chromatograph are: initial column temperature 60°C, held for 2 minutes, then heated to 150°C at a rate of 10°C / min and held for 5 minutes; the detector is a flame ionization detector, the detector temperature is 250°C, the carrier gas is nitrogen, and the flow rate is 1.0 mL / min; a standard curve of benzene and ethylbenzene is drawn, and the content of benzene and ethylbenzene in the sample is calculated according to the standard curve. Three parallel tests are set for each sample, and the average value is taken, retaining three decimal places; benzene ≤ 0.005 mg / m³ and ethylbenzene ≤ 0.020 mg / m³ are regarded as qualified.

[0040] Formaldehyde test: Detection is carried out by high performance liquid chromatography, using a high performance liquid chromatograph; the sample preparation, sealing and equilibration conditions are the same as those for the benzene and ethylbenzene tests; after equilibration, 5 mL of the gas in the bag is extracted, 1 mL of 2,4-dinitrophenylhydrazine derivatization reagent is added, and the reaction is carried out in the dark at 25°C for 30 minutes to make formaldehyde react fully with the derivatization reagent to form hydrazone derivatives; after the reaction, it is filtered through a 0.45μm filter membrane, and the filtrate is injected into the high performance liquid chromatograph. The chromatographic column uses a C18 column, the mobile phase is methanol-water (volume ratio 60:40), the flow rate is 1.0 mL / min, the detection wavelength is 354 nm, and the column temperature is 30°C; a formaldehyde standard curve is drawn, and the content of formaldehyde in the sample is calculated according to the standard curve. Three parallel tests are set for each sample, and the average value is taken, retaining three decimal places; formaldehyde ≤ 0.05 mg / m³ is regarded as qualified.

[0041] Flame retardant performance test: Oxygen Index Test: An oxygen index meter was used for testing. Each sample was cut into standard specimens of 120mm × 10mm × 4mm, and three parallel specimens were prepared for each group. The specimens were placed in an environment of 23±2℃ and 50±5% relative humidity for 24 hours to equilibrate. During the test, the specimens were vertically installed in the combustion chamber of the oxygen index meter, ensuring that the bottom of the specimen was 10mm away from the igniter. The oxygen concentration was adjusted, starting from a low concentration and gradually increasing. After each adjustment, the top of the specimen was ignited with the igniter, and the combustion was observed until the lowest oxygen concentration at which the specimen could burn continuously for 3 minutes or the burning length reached 50mm was determined. This lowest oxygen concentration was the oxygen index, which was retained to one decimal place. The average value of the test results of the three parallel specimens was taken, and an oxygen index ≥ 24% was considered qualified.

[0042] Horizontal burning rate test: Using a horizontal burning tester, each sample was cut into standard specimens of 360mm×100mm×4mm, and three parallel specimens were prepared for each group. The specimens were placed in an environment of 23±2℃ and 50±5% relative humidity for 24h to equilibrate. During the test, the specimen was placed horizontally on the specimen support of the tester, with one end of the specimen fixed and the other end suspended. The igniter was lit, and the flame was aimed at the edge of the suspended end of the specimen. The ignition time was 15s. Then the igniter was removed, and the burning distance and corresponding burning time of the specimen were recorded. The burning rate was calculated according to the formula v=L / t (where v is the horizontal burning rate, L is the burning distance, and t is the burning time). The test results of the three parallel specimens were averaged, and a horizontal burning rate ≤50mm / min was considered qualified.

[0043] UL94 Flame Retardant Rating Test: A horizontal combustion tester is used for testing. The sample preparation and equilibrium conditions are the same as for the horizontal combustion rate test. The sample is cut into standard specimens of 127mm × 12.7mm × 4mm, and three parallel specimens are prepared for each group. During the test, the specimen is vertically clamped on the support of the tester, with the bottom of the specimen 50mm away from the ignition plate. The igniter is lit, and the flame is directed at the bottom of the specimen. The ignition time is 10s. The igniter is then removed, and the burning time of the specimen, whether it drips, and whether the drips ignite the filter paper are recorded. Based on the burning performance of the specimen, the flame retardant rating is determined according to the UL94 standard (divided into four levels: HB, V-2, V-1, and V-0). Only when all three parallel specimens meet the requirements of the corresponding level can the specimen be determined as that level. A UL94 rating of V-0 or V-1 is considered qualified.

[0044] Compatibility test: The cross-sectional morphology of the material is observed by scanning electron microscopy; each sample is fractured in liquid nitrogen, and the cross-section is sputter-coated with gold using a gold sputtering machine. Then, the cross-sectional morphology is observed under a scanning electron microscope at an accelerating voltage of 10kV to determine the degree of phase separation between PP and EPDM; if the cross-section is smooth and there is no obvious phase separation interface, it is considered to have good compatibility; if the cross-section is rough and there is an obvious phase separation area, it is considered to have poor compatibility; if the cross-section has slight traces of phase separation but no obvious interface, it is considered to have average compatibility.

[0045] The test results are shown in the table below: Test sample Tensile strength (MPa) Impact strength (kJ / m²) Example 1 18.2 58.6 Example 2 17.5 56.3 Example 3 18.8 60.2 Comparative Example 1 12.3 32.5 Comparative Example 2 18.0 57.8 Comparative Example 3 14.6 45.2 Table 1 Test sample Benzene (mg / m³) Formaldehyde (mg / m³) Ethylbenzene (mg / m³) Example 1 0.003 0.042 0.015 Example 2 0.004 0.045 0.017 Example 3 0.002 0.038 0.014 Comparative Example 1 0.012 0.113 0.035 Comparative Example 2 0.003 0.043 0.016 Comparative Example 3 0.008 0.078 0.028 Table 2 Test sample Oxygen index (%) Horizontal combustion rate (mm / min) UL94 flame retardant rating Compatibility Example 1 26.8 38 V-0 Good, phase separation is not obvious. Example 2 27.2 35 V-0 Good, phase separation is not obvious. Example 3 26.5 40 V-0 Good, phase separation is not obvious. Comparative Example 1 26.7 39 V-0 Poor, phase separation is obvious. Comparative Example 2 19.5 85 HB Good, phase separation is not obvious. Comparative Example 3 26.6 37 V-0 Generally, slight phase separation exists. Table 3 The test results above show that the flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomers prepared in Examples 1-3 of this invention have excellent mechanical properties, with a tensile strength ≥17.5MPa and an impact strength ≥56.3kJ / m². They also exhibit good flame-retardant performance, with benzene content ≤0.004mg / m³, formaldehyde content ≤0.045mg / m³, ethylbenzene content ≤0.017mg / m³, an oxygen index ≥26.5%, a horizontal burning rate ≤40mm / min, and a UL94 flame retardant rating of V-0. Furthermore, the materials have good compatibility and minimal phase separation.

[0046] Comparative Example 1, without the addition of bio-based hyperbranched polymer and food-grade zinc oxide, showed a significant decrease in mechanical properties, a substantial exceedance of VOC content, and poor compatibility. Comparative Example 2, without the addition of halogen-free flame retardant, exhibited severely insufficient flame retardant performance, with an oxygen index of only 19.5% and a flame retardant rating of only HB. Comparative Example 3, using a traditional compatibilizer to replace the bio-based hyperbranched polymer and without the addition of food-grade zinc oxide, showed inferior mechanical properties and low VOC performance compared to the embodiments of the present invention, and also exhibited a certain degree of compatibility.

[0047] In summary, this invention, through innovative modified system design, achieves synergistic improvement in flame retardancy, low VOCs, and mechanical properties, solving many problems in the prior art and showing promising application prospects.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer and its preparation method, characterized in that, By weight, the elastomer composition includes: 40-60 parts PP resin, 20-35 parts EPDM rubber, 3-8 parts bio-based hyperbranched polymer, 0.1-1.0 parts food-grade zinc oxide, 10-25 parts halogen-free flame retardant, 0.2-0.8 parts antioxidant, and 0.3-0.9 parts lubricant. The bio-based hyperbranched polymer is a bio-based hyperbranched polymer containing multiple carboxyl and amino functional groups, with a number-average molecular weight of 5000-20000, a carboxyl content of 2.5-5.0 mmol / g, and an amino content of 1.0-2.5 mmol / g. It is prepared by amidation and polymerization of terminal amino aliphatic bio-based compounds with carboxylic acids or anhydrides containing unsaturated double bonds. The food-grade zinc oxide has a particle size of 20-50 nm and a purity of ≥99.5%. The halogen-free flame retardant is one or a mixture of two or more of magnesium hydroxide, aluminum hydroxide, and phosphorus-based flame retardants, wherein the phosphorus-based flame retardant is a phosphate ester or ammonium polyphosphate flame retardant.

2. The flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer according to claim 1, characterized in that, The PP resin is homopolymer PP or copolymer PP with a melt index of 10-30 g / 10 min; the EPDM rubber has a Mooney viscosity of 40-80, an ethylene content of 45%-65%, and a third monomer content of 3%-8%.

3. The flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer according to claim 1, characterized in that, The antioxidant is a compound system of hindered phenolic antioxidants and phosphite antioxidants, with a compound mass ratio of 1:1-2; the lubricant is one or a mixture of two or more of stearic acid, butyl stearate, and polyethylene wax.

4. The flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer according to claim 1, characterized in that, The preparation method of the bio-based hyperbranched polymer includes the following steps: Using terminal amino-based aliphatic bio-based compounds and unsaturated double-bond compounds containing acid anhydrides and carboxylic acids as raw materials, and toluene as solvent, the mixture was heated under reflux at 65-110℃ for 2-5 hours, and then separated after cooling to obtain amide compounds containing unsaturated double bonds. The obtained amide compound containing unsaturated double bonds was mixed with a carboxylic acid monomer containing double bonds, and an initiator and a molecular weight regulator were added in deionized water as solvent. The mixture was reacted at 40-95℃ for 3-5 hours, and the resulting product was obtained by rotary evaporation.

5. The flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer according to claim 4, characterized in that, The molar ratio of the terminal amino aliphatic bio-based compound to the unsaturated double bond compound containing anhydride and carboxylic acid is 1:2.0-4.0; the mass ratio of the amide compound containing unsaturated double bond to the carboxylic acid monomer containing double bond is (20-40):(40-60), the initiator accounts for 5-10% of the mass of the carboxylic acid monomer containing double bond, and the molecular weight regulator accounts for 2-6% of the mass of the carboxylic acid monomer containing double bond.

6. The flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer according to claim 4, characterized in that, The unsaturated double-bond compound containing anhydride and carboxylic acid is one or a mixture of maleic acid, itaconic acid, maleic anhydride, and itaconic anhydride; the carboxylic acid monomer containing double bond is one or a mixture of acrylic acid, methacrylic acid, and maleic acid; the initiator is one or a mixture of ammonium persulfate, potassium persulfate, and sodium bisulfite; and the molecular weight regulator is one or a mixture of isopropanol and dodecyl mercaptan.

7. A method for preparing a flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer as described in any one of claims 1-4, characterized in that, The specific steps include the following: Raw material pretreatment: Place PP resin and EPDM rubber separately into a forced-air drying oven and dry at 80-100℃ for 2-4 hours. Stir once every 1 hour during the drying process to ensure uniform removal of moisture. After drying, cool to room temperature for later use. Place bio-based hyperbranched polymer, food-grade zinc oxide, halogen-free flame retardant, antioxidant, and lubricant into a high-speed mixer. Adjust the mixer speed to 800-1200 r / min, the mixing time to 10-15 min, and the mixing temperature to 40-50℃ to obtain a uniform mixture of additives for later use. Melt blending: Select a twin-screw extruder with a screw length-to-diameter ratio of 36:1-40:

1. First, preheat the temperature of each section of the twin-screw extruder to the set value for 20-30 minutes to ensure temperature stability. Add the dried PP resin and EPDM rubber to the feed port of the twin-screw extruder in proportion, adjust the screw speed to 300-500 r / min and the feed rate to 20-30 kg / h. After melting and plasticizing for 3-5 minutes, add the mixing additives at a uniform rate through the side feed port and continue melt blending for 5-10 minutes. During this period, control the pressure inside the extruder barrel to 10-15 MPa. During the melt blending process, zinc ions form a reversible dynamic coordination crosslinking network with the carboxyl groups on the bio-based hyperbranched polymer and the oxygen-containing groups on the PP / EPDM chains generated by heat and oxygen. Extrusion granulation: The melt-blended material is extruded through the die head of a twin-screw extruder. The extruded melt strip is cooled by a water cooling tank and then fed into a pelletizer. The pelletizer speed is adjusted to 200-300 r / min and the pellet length is 2-3 mm to obtain flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer granules. The granules are placed in a forced-air drying oven and dried at 70-80℃ for 1-2 hours to remove surface moisture. Unqualified granules are screened out and packaged for later use.

8. The method for preparing a flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer according to claim 1, characterized in that, The temperatures of each section of the twin-screw extruder are 160-170℃, 170-180℃, 180-190℃, and 185-190℃ respectively, while the die head temperature is 180-185℃.

9. The method for preparing a flame-retardant, low-VOCs automotive interior PP / EPDM thermoplastic elastomer according to claim 1, characterized in that, The water cooling tank has a cooling water temperature of 20-30℃ and a cooling time of 5-10 seconds.

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