Flame Retardant Polypropylene Compound

This material is made of copolymer polypropylene (PP, melt flow rate 15g/10min, ethylene content 8%, melting temperature 165℃) as the matrix, and mixed with ammonium polyphosphate (APP-4, polymerization degree 1000, phosphorus content 31%), pentaerythritol (purity 98%, hydroxyl value 410mgKOH/g), melamine (industrial grade, nitrogen content 66.7%), talcum powder (particle size 3μm, whiteness 95%) and antioxidant (1076 and 168 are compounded at a ratio of 1:2) according to the precise mass ratio of 50:30:12:5:3. At the beginning of preparation, PP particles were first put into a 1000L high-speed mixer, the heating device was turned on to raise the temperature to 90°C, and premixed at 1000 rpm for 3 minutes to preheat the surface of the particles evenly to avoid agglomeration due to temperature difference when adding flame retardants later. Then the components were added in stages: APP-4 was added first, because it accounted for the largest proportion (30%), and it was necessary to stir for 2 minutes to make it initially dispersed; then pentaerythritol and melamine were added, the speed was adjusted to 800 rpm, and mixed for 5 minutes to allow the carbon source and gas source to fully contact; finally, talcum powder and antioxidant were added, and mixing continued for 12 minutes until the material color was uniform and no particles were visible to the naked eye. The mixed materials are fed into a twin-screw extruder through a screw feeder. The screw length-diameter ratio of the machine is 36:1. The temperature is controlled in four zones: 165℃ in zone 1, 180℃ in zone 2, 195℃ in zone 3, and 185℃ in zone 4. The screw speed is 320 rpm. The materials are cut into 2×3mm cylindrical particles through a water ring pelletizer, namely Flame Retardant Polypropylene Compound. According to the test, the density is 1.02g/cm³, the melt flow rate is 8g/10min (230℃, 2.16kg), the oxygen index is 29% (GB/T 2406), the flame retardant performance reaches UL94 V-0 level (3.2mm thickness), the vertical combustion self-extinguishing time is an average of 1.8 seconds, and there is no melting dripping phenomenon. This process is like mixing soup in a pot. The ratio of the matrix and the flame retardant must be accurate: APP-4 provides an acid source and releases phosphoric acid at high temperature; pentaerythritol, as a carbon source, reacts with phosphoric acid to form a carbon layer by esterification; melamine, as a gas source, releases ammonia gas when heated to expand the carbon layer. The three work together to form a honeycomb thermal insulation barrier; talcum powder is like a skeleton, enhancing the dimensional stability of the carbon layer, so that a product with both flame retardant and mechanical properties can be obtained, laying a solid foundation for subsequent processing and application.

This product is widely used in automotive interiors. Taking a 2.5mm thick automotive door panel interior panel as an example, its injection molding process parameters have been optimized for multiple rounds: mold temperature 45℃, injection pressure 120MPa, holding pressure 65MPa, injection time 3 seconds, cooling time 25 seconds, product surface finish reaches 60GU, no weld marks and shrinkage marks. Mechanical performance tests show that its tensile strength is 26MPa (GB/T 1040), flexural strength is 40MPa (GB/T 9341), and simply supported beam impact strength is 4.2kJ/m² (GB/T 1043), which fully meets the requirements of QC/T 252 "General Technical Conditions for Automobile Plastic Parts". The combustion performance has passed a number of rigorous tests: in the FMVSS 302 horizontal combustion test, the burning speed is less than 100mm/min, and there is no melting dripping phenomenon; in the ISO 3795 automobile interior material combustion test, the afterburning time is less than 10 seconds, which meets the vehicle safety standards. The environmental performance is also excellent. According to the HJ/T 400-2007 standard test, its VOC (volatile organic compound) volatility is less than 50μgC/g, and harmful gases such as benzene, toluene, and xylene are not detected, which meets the GB/T 27630 "Guidelines for Passenger Car Interior Air Quality Evaluation". After being exposed to the sun in a 65℃ constant temperature box for 72 hours, it was taken out and left to stand for 2 hours in a 25℃ environment. It was found that there was no irritating odor and the air quality test in the car met the standard. In view of the use needs in cold areas, the -40℃ low-temperature impact test showed that its impact strength retention rate reached 60% (3.2kJ/m²), which is much better than the 45% of pure PP, and it is not easy to crack in low temperature environment. Compared with traditional filled PP, its heat deformation temperature (under 1.82MPa load) reaches 120℃ (GB/T 1634), which is 25℃ higher than pure PP. It can still maintain dimensional stability in the high temperature environment near the engine compartment and will not warp or deform due to heat. Therefore, it is used in interior parts such as automobile dashboards, pillar trims, seat guards, etc., which can not only meet the flame retardant safety requirements, but also ensure driving comfort and service life. It is an ideal choice for automotive interior materials.

In order to fully verify its chemical corrosion resistance, this product was made into a standard test piece of 50×50×2mm, and immersed in four typical media for testing: 30% sulfuric acid solution (simulating acidic environment), 10% sodium hydroxide solution (simulating alkaline environment), 92# gasoline (simulating fuel contact) and household detergent (simulating daily cleaning). After standing for 24 hours at 25℃±2℃, it was taken out, rinsed with deionized water and wiped dry, and the weight loss rate was measured by weighing, and the surface state changes were observed. The results showed that the weight loss rate in sulfuric acid solution was only 0.2%, and there was no corrosion mark or discoloration on the surface; the weight loss rate in sodium hydroxide solution was 0.3%, and there was no swelling or cracking; the weight loss rate in gasoline was 0.15%, and there was no sign of dissolution; the weight loss rate in detergent was 0.08%, and the surface was as smooth as before. In the further wipe resistance test, a cotton cloth dipped in 95% alcohol was used to wipe the surface of the test piece back and forth 500 times with a force of 500g. The surface was not white or scratched, and the gloss retention rate reached 90% (initial gloss 60GU), indicating that its surface solvent resistance is excellent. In the harsh environment test simulating the engine compartment of an automobile, the product was immersed in a mixture of engine oil and antifreeze at 120°C (volume ratio 1:1) for 6 months. After being taken out, it was found that its tensile strength decreased by less than 5%, and its bending strength decreased by less than 4%. The flame retardant performance still maintained the UL94 V-0 level, and the oxygen index only decreased by 0.5 percentage points, with no obvious attenuation. This is due to the good compatibility of flame retardant and PP matrix. The surface of flame retardant particles treated with coupling agent is evenly wrapped by resin, and the molecules are tightly bound to form a dense protective structure, making it difficult for chemical reagents to penetrate into the interior. Therefore, it is suitable for scenes that are exposed to a variety of chemical media, such as automobile engine peripheral parts, plastic accessories for chemical plants, etc., with stable and reliable performance.

After this product is compounded with reinforced materials, the performance can be improved by leaps and bounds, which can meet the high-strength requirements of different scenes. Taking the composite of 15% chopped glass fiber (length 3mm, diameter 13μm, silane coupling agent treatment) as an example, the two are mixed by a twin-screw extruder, and the extrusion temperature is 5℃ higher than that of pure material (170℃ in zone 1, 185℃ in zone 2, 200℃ in zone 3, and 190℃ in zone 4), and the screw speed is 300 rpm to ensure that the glass fiber is evenly dispersed. The mechanical properties of the composited products are significantly enhanced: the bending strength reaches 85MPa, an increase of 112% compared with the unreinforced 40MPa; the tensile strength is 38MPa, an increase of 46%; the impact strength is 7.5kJ/m², an increase of 67%, which fully meets the strength requirements of structural parts. The flame retardant performance does not decrease due to the addition of glass fiber, and it still reaches UL94 V-0 level at a thickness of 2.0mm. The vertical combustion self-extinguishing time is less than 3 seconds. Because the glass fiber is interspersed in the carbon layer, it enhances the structural stability of the carbon layer like a skeleton, and the flame erosion resistance time is extended by 30%, which can better withstand continuous high temperature. When compounded with 20% mica powder (particle size 5μm, flaky structure), the dimensional shrinkage rate of the product is reduced from 1.5% to 0.8% (GB/T 15585), and the heat deformation temperature reaches 140℃, which is 17% higher than the pure material. It is suitable for precision parts with high dimensional accuracy requirements, such as automobile air-conditioning outlet frames, dashboard brackets, etc. To improve compatibility, 0.5% maleic anhydride grafted PP is added as a compatibilizer during compounding. Its polar groups can form chemical bonds with the hydroxyl groups on the surface of glass fiber and mica powder, which increases the interfacial bonding strength by 40%. Scanning electron microscopy shows that the surface of glass fiber and mica powder is evenly wrapped by resin, without obvious debonding, and stress can be effectively transmitted when subjected to force. Therefore, the composite material can be flexibly matched with a variety of reinforcing materials to meet the performance requirements of different scenarios and broaden the scope of application.

During the processing of this product, by optimizing the process and management measures, the loss can be controlled at an extremely low level, significantly improving the economic benefits. During injection molding, the residual material in the barrel needs to be thoroughly cleaned with pure PP particles before stopping the machine. The cleaning amount is 1.5 times the volume of the barrel, and it is added in three times: the first time, 1/3 of the amount is added, the screw speed is 100 rpm, and the residual material is pushed out; the second time, 1/3 of the amount is added, the speed is 150 rpm, and further cleaning is performed; the last time, 1/3 of the amount is added, the speed is 200 rpm, to ensure that the flame retardant is completely discharged, to prevent the residual material from decomposing and deteriorating at high temperature, and contaminating the new material when the machine is started next time. This step can increase the cleanliness of the barrel to 99%. For the scraps (such as gates and waste products) generated during the production process, they are crushed by a crusher (screen aperture 5mm), screened to remove impurities, and can be mixed back into new materials at a ratio of 20%. After testing, the tensile strength retention rate of the mixed material is 97%, the impact strength retention rate is 95%, the flame retardant performance still reaches V-0 level, and the oxygen index is retained at 28%, which is only 1 percentage point lower than that of pure new materials, fully meeting the use requirements of non-critical components. Every ton of scraps recycled can save about 3,000 yuan in costs. In the production of extruded sheets, by accurately controlling the matching of traction speed and extrusion volume (traction speed 1.5m/min corresponds to extrusion volume 20kg/h), installing an online thickness detector (accuracy ±0.01mm), and adjusting the traction speed in real time, the thickness deviation of the sheet is controlled within ±0.1mm, reducing scrap caused by uneven thickness, and the scrap rate can be controlled below 3%. The storage link is also critical. The product is packaged in moisture-proof kraft paper bags, 25kg per bag, lined with polyethylene film, and sealed with a heat sealer. The pallet stacking height does not exceed 8 layers, and the bottom is padded with a 10cm high wooden pallet to prevent moisture. The warehouse is equipped with a temperature and humidity recorder to control the temperature <35℃ and the relative humidity <55%. It is equipped with a dehumidifier (dehumidification capacity 50L/day) to ensure a stable storage environment and a shelf life of 18 months. Before expiration, sampling is required to test the melt index and flame retardant properties. If the melt index change rate is <10% and the flame retardant level is still V-0, it can be downgraded for products with lower performance requirements (such as trash cans and storage boxes). Through these measures, the comprehensive processing loss can be controlled within 5%. With an annual consumption of 1,000 tons, the cost can be saved by about 150,000 yuan, with significant economic benefits.