Preparation, characterization and its flame retardance performance of microencapsulated ammonium polyphosphate/bridged polysesquisiloxane polyurethane composites

A core shell material consisting of ammonium polyphosphate as core and 4,4-oxydianiline-formaldehyde resin as shell was prepared through a situ microencapsulation technology. The monomer of the polyurethane (PU) was modified to form bridged polysesquisiloxane. The purpose of modification is to improve the thermal stability of polyurethane matrix through the formation of networks. The degree of the networks was evaluated by solid state Si-29-nuclear magnetic resonance. The structure and hydrophobic property of microencapsulated flame retardant were characterized using X-ray photoelectron spectroscopy and water solubility. The results indicated that the microencapsulation of APP with 4,4'-oxydianiline-formaldehyde resin (OF resin) resulted in improved hydrophobicity. The thermal properties of final flame retardant were systematically analyzed through thermogravimetric analysis. Limiting oxygen index and UL-94 test were used to classfied the flame retardant properties of varying the composition of APP and OFAPP in silanol-terminated polyurethane composites. Pure PU exhibited an LOI of 17 % and failed the UL-94 test. The LOI values of the 40 % OFAPP-added composites can reach 41 % and pass V-0 level. The results revealed that the microcapsulation of commercial flame retardant can improve the flame retardance of the composites.