Halogen Free Flame Retardant for Polypropylene

This product is specially designed for polypropylene and has good adaptability to homopolymer PP, copolymer PP and even modified PP, especially PP varieties with a melt flow rate of 8-20g/10min (230℃, 2.16kg). In homopolymer PP (isotacticity 96%, melting temperature 165℃), adding 25% can make the product reach UL94 V-0 level (1.6mm thickness), and the oxygen index rises to 30%; for copolymer PP (ethylene content 5-8%), due to the better toughness of the matrix, the addition amount can be reduced to 22%, the oxygen index is still over 30%, and the impact strength retention rate is increased by 5%. For high melt flow rate PP (20g/10min), 0.3% maleic anhydride grafted PP is required as a compatibilizer. Its polar group can improve the interface bonding between flame retardant and PP to prevent precipitation during processing. After the torque rheometer test, the mixing torque is stable at 45-50N・m, the dispersed particle size is <20μm, and there is no agglomeration phenomenon. For low melt flow rate PP (8g/10min), due to the high melt viscosity, it can be added directly without additional adjustment. After mixing, the melt flow rate can still be maintained at 6-7g/10min, meeting the process requirements of injection molding, extrusion, etc. The test shows that its compatibility score with PP is 4.5 points (out of 5 points). In modified materials such as PP for automobile bumpers and PP for home appliance shells, there is no precipitation on the surface of the product after adding it, and the color is uniform, so it can adapt to a variety of PP substrates and broaden the scope of application.

This product is based on a phosphorus-nitrogen composite system, and is compounded in a ratio of 3:2:1 by ammonium polyphosphate (APP, degree of polymerization 1000), melamine cyanurate (MCA) and nano magnesium hydroxide (particle size 50nm), and contains 0.5% silane coupling agent (KH550) to improve dispersion. When exposed to fire, the components work together to form a three-dimensional flame retardant barrier: when the temperature rises to 250℃, APP first decomposes to release phosphoric acid, which acts as an acid source to catalyze the dehydration and carbonization reaction of the PP molecular chain; MCA decomposes at 300℃, releasing ammonia and carbon dioxide, which act as a gas source to expand and foam the generated carbon layer to form a honeycomb structure; nano magnesium hydroxide undergoes a dehydration reaction at around 340℃, absorbing a large amount of heat (about 1.5kJ/g), reducing the surrounding temperature, and the generated magnesium oxide particles fill the pores of the carbon layer to enhance the structural stability. Within 30 seconds of burning, the thickness of the carbon layer can reach 20 times that of the original product, the porosity is 85%, the thermal conductivity is reduced to 0.02W/(m・K), and it can block more than 90% of heat transfer. Compared with traditional single flame retardants, its carbonization rate is 30% faster, the carbon layer can still maintain structural integrity at a high temperature of 800℃, and the oxidation resistance is significantly improved, so the flame retardant performance is more durable. And there is no halogen involved in the whole process, the smoke density rating (SDR) during combustion is <40, which is 50% lower than that of brominated flame retardant PP, and the toxicity index (according to NBS smoke box method) is reduced by 60%, achieving the dual advantages of high-efficiency flame retardancy and low toxicity and low smoke.

Adding 25% of this product to homopolymer PP, the product has a tensile strength of 28MPa, which is 88% of pure PP; the flexural strength is 42MPa, with a retention rate of 85%; the simply supported beam unnotched impact strength is 3.8kJ/m², which is 15% lower than pure PP, but better than the 20% drop of similar halogen-free flame retardants. After mixing through a twin-screw extruder (length-to-diameter ratio 36:1, speed 300 rpm), the melt flow rate is 7g/10min, which meets the requirements of injection molding, and the surface finish of the product reaches 55GU, with no obvious shrinkage marks. For low temperature environments, the -20℃ impact test shows that its impact strength retention rate is 70% (2.7kJ/m²), which is higher than 60% of pure PP, and is suitable for outdoor products in cold areas. If compounded with 15% chopped glass fiber (length 3mm), the impact strength can be increased to 6.5kJ/m², the bending modulus reaches 3500MPa, and the mechanical property loss is further reduced, which can meet the strength requirements of structural parts. In the PP material of automobile door panels, after adding 23% of this product, its tensile strength is 26MPa, which meets the QC/T 252 standard, and the heat deformation temperature (1.82MPa) is increased from 100℃ to 125℃, an increase of 25℃, which enhances the dimensional stability at high temperature. Therefore, this flame retardant can retain the mechanical properties of PP to the maximum extent while being highly flame retardant, balancing the needs of flame retardancy and performance.

This product has excellent thermal stability. Thermogravimetric analysis (nitrogen atmosphere, heating rate 10℃/min) shows that the initial decomposition temperature is greater than 320℃, and there is almost no weight loss at the PP processing temperature (180-220℃), ensuring that it will not decompose and fail during processing. After being placed in a 120℃ oven at a constant temperature for 1000 hours, its flame retardant performance has no obvious attenuation, the oxygen index remains at 31%, and the UL94 test still reaches V-0 level, indicating that the performance is stable in a long-term high temperature environment. In the water resistance test, the product was immersed in 25℃ distilled water for 7 days, taken out and wiped dry and weighed, the weight loss rate was less than 0.3%, and there was no swelling phenomenon; after drying at 80℃ for 2 hours, the flame retardant performance test showed that the vertical combustion self-extinguishing time was still less than 3 seconds, no dripping occurred, and the V-0 level was maintained. For humid environments, after being placed in a constant temperature and humidity chamber at 85°C and 85% relative humidity for 500 hours, there was no white frost on the surface of the product, the tensile strength retention rate was 90%, and the bending strength retention rate was 88%, which is suitable for humid scenes such as bathroom appliance housings and kitchen storage boxes. In addition, its weather resistance test (QUV aging for 1000 hours) showed that the mechanical property retention rate was 85%, and the flame retardant performance was not degraded, so it can also be used as PP products for outdoor use such as outdoor clothes drying racks and garden tools.

No pre-drying is required before processing, because its moisture content is less than 0.2%, it can be directly mixed with PP. When mixing, first put PP into a high-speed mixer (speed 800 rpm), preheat it to 80°C, then slowly add the flame retardant, mix for 10 minutes until the color is uniform, and avoid dust flying. When the twin-screw extruder is used, the temperature is set to: 170℃ in zone 1, 185℃ in zone 2, 195℃ in zone 3, and 185℃ in zone 4, and the screw speed is 300 rpm to ensure that the material is fully melted and dispersed. Microscopic observation shows that the dispersed particle size of the flame retardant particles is less than 15μm. During injection molding, the mold temperature is controlled at 50℃, the injection pressure is 100MPa, the holding pressure is 60MPa, and the holding time is 18 seconds, which can reduce the shrinkage and warping of the product. Storage is packaged in kraft paper bags lined with PE film, 25kg per bag, the bag mouth is heat-sealed, and the outer woven bag is moisture-proof. It is placed in a warehouse with a temperature of less than 30℃ and a relative humidity of less than 50%. The stacking height does not exceed 8 bags, and the bottom is padded with a wooden pallet (height 10cm), ≥50cm from the wall, and the shelf life is 18 months. If the particles accidentally absorb moisture and form lumps, they can be placed in a 60℃ oven for 3 hours. After screening with a 60-mesh sieve, 95% of the particles can be restored to dispersibility, and the flame retardant performance remains unchanged. During operation, workers need to wear KN95 dust masks and goggles, and the workshop is equipped with a dust removal system with an air volume of 2000m³/h to ensure that the dust concentration is less than 5mg/m³, which meets occupational health standards.