Preparation and characterization of microcapsulated red phosphorus and its flame-retardant mechanism in halogen-free flame retardant polyolefins

Microcapsulated red phosphorus (MRP), with a melamine-formaldehyde resin coating layer, was prepared by two-step coating processes. The physical and chemical properties of MRP were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) and other measurements. The flame retardant action and mechanism of MRP in the halogen-free flame retardant (HFFR) polyolefins (PO) blends have been studied using cone calorimeter, limiting oxygen index (LOI), thermogravimetric analysis (TGA) and dynamic FTIR spectroscopy. The results show that the MRP, which is coated with melamine-formaldehyde resin, has a higher ignition point, a considerably lower amount of phosphine evolution and of water absorption compared with red phosphorus (RP) itself. The data observed by cone calorimeter, LOI and TGA measurements from the PO/HFFR blends demonstrated that the MRP can decrease the heat release rate and effective heat of combustion, and increase the thermostability and LOI values of PO materials. The dynamic FTIR results revealed the flame-retardant mechanism that RP can promote the formation of charred layers with the P-O and P-C complexes in the condensed phase during burning of polymer materials. (C) 2003 Society of Chemical Industry.