Flame-Retardant Cellulosic Fiber Nanocomposite Based on Aluminum Tetraborate and Aluminum Tungstate

Nanoaluminum tetraborate (Al۲(B۴O۷)۳) and nanoaluminum tungstate (Al۲(WO۳)۳) were prepared by in situ precipitation method on the surface of cellulosic fibers to achieve flame retardant nanocomposite fibers. The prepared nanocomposite fibers were characterized by several techniques such as XRD, SEM, TEM, EDS, and FTIR. Al۲(B۴O۷)۳ and Al۲(WO۳)۳ with less than ۱۰۰ nm in size were dispersed throughout on the surface of the fibers without the formation of large aggregates which showed effective flame retardancy properties. It was found that loading ۲.۶۰% Al۲(B۴O۷)۳ and ۴.۹۵% Al۲(WO۳)۳ onto the cellulosic fibers improved greatly the flame retardancy behavior of  nanocomposite fibers which was approved by vertical flame test and limiting oxygen index (LOI) values. The thermal stability and amount of heat release of untreated and flame retardant fibers were evaluated by thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyses. The results showed that the flame retardancy mechanism of the obtained flame retardant nanocomposite fibers probably is a condensed-phase phenomenon due to the formation of a protective char layer that acts as a mass transport barrier and a thermal insulator.