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Why is the long chain structure emphasized when preparing Ammonium Polyphosphate (APP-L)?
This material is made of phosphoric acid and ammonia. It is polymerized at a high temperature of 250℃ for six hours to fully extend the molecular chain to form a linear long chain structure with a polymerization degree of 40-50, which is Ammonium Polyphosphate (APP-L). The long chain is like silk, and the molecules are tightly entangled, so the water solubility is extremely low, only 0.3g/100mL at 25℃, which is nearly 20 times lower than XAP-02. The process is like spinning a long line, which needs to be continuously stretched to be tough. It is spray-granulated into particles with a diameter of 1mm, with a smooth surface, good fluidity, and a bulk density of 0.8g/cm³, which is convenient for large-scale equipment feeding. This long chain structure makes it excellent in thermal stability. It does not decompose below 280℃, which is suitable for engineering plastics processed at high temperatures and is a long-lasting flame retardant.
What is the application of Ammonium Polyphosphate (APP-L) in high-temperature engineering plastics?
This product is added to polyamide 66 at a dosage of 20%, supplemented with 5% montmorillonite for synergy. After injection molding at 280℃, the product has no bubbles and a tensile strength of 85MPa, which is only 10% lower than that without addition. The combustion test reaches UL94 V-0 level, and the vertical combustion self-extinguishing time is 2 seconds. The carbon layer is thin but dense and can withstand 300℃ high temperature without collapse. In polyetheretherketone (PEEK), the addition of 15% can meet the flame retardant requirements, and the heat deformation temperature is retained at 280℃, which is suitable for high-temperature parts in the engine compartment. It has good compatibility with glass fiber reinforced plastics, uniform fiber dispersion, and a bending strength of 150MPa. Therefore, it is widely used in high-temperature engineering plastics such as high-speed rail seat frames and aviation components, and can withstand long-term high temperature environments without failure.
How is the chemical corrosion resistance of Ammonium Polyphosphate (APP-L) reflected?
After being immersed in a 30% sulfuric acid solution for 90 days, the weight loss rate was only 0.5%, which is more resistant to acid corrosion than XAP-02's 5%. After being placed in a 10% sodium hydroxide solution for the same period of time, there was no obvious dissolution, indicating that it has excellent acid and alkali resistance. After being in contact with engine oil and hydraulic oil for 6 months, no swelling occurred, so it can be used in plastic parts around automobile engines. It has no corrosion to metals. After immersing iron, copper, and aluminum sheets in its suspension, there is no rust after 30 days. Therefore, it is safe to use in plastic products with metal inserts and does not affect the matching accuracy of parts. This feature makes it suitable for scenes such as chemical equipment housings and tank linings that come into contact with corrosive media, broadening the application range of APP.
What is the difference between Ammonium Polyphosphate (APP-L) and other long-chain APPs?
Compared with APP-2, Ammonium Polyphosphate (APP-L) has a higher degree of polymerization and a more regular long-chain structure, so its thermal stability is improved by 10%, and its thermal weight loss rate at 280°C is only 2%, while APP-2 is 5%. It has better dispersibility in polyamide. Scanning electron microscopy shows that the particles are evenly distributed and there is no agglomeration, so the mechanical properties are better retained. It has low hygroscopicity. After being stored in an environment with a relative humidity of 90% for 30 days, the moisture content is only 0.8%, which is much lower than 2% of APP-2, and it is not easy to agglomerate. Although the cost is 8% higher than APP-2, it has more stable performance and is more cost-effective in high-end engineering plastics, especially suitable for scenarios with high requirements for long-term reliability.
What precautions should be taken for the storage and processing of Ammonium Polyphosphate (APP-L)?
This product needs to be packed in galvanized iron barrels lined with plastic bags, 50kg per barrel, sealed and moisture-proof, stored in ventilated warehouses, the temperature should not exceed 35℃, the stacking height should not exceed 10 layers, to prevent the bottom layer from being compressed and agglomerated. It does not need to be dried before processing, and can be directly mixed with the resin to save energy. In the twin-screw extruder, the speed needs to be controlled at 300 rpm to ensure uniform shearing and avoid long chain breakage, otherwise the flame retardant efficiency will be reduced. If agglomeration is accidentally caused, it needs to be crushed by a crusher and can still be used after passing through an 80-mesh sieve without affecting the performance. It has low dust flying, and ordinary dust masks can be worn during operation. It is easier to manage than ultra-fine APP.