Surface modification of bamboo fibers by diammonium phosphate and their applications in flame retardant thermoplastic polyurethane

Bamboo fibers (BF) were used as charring agent in thermoplastic polyurethane (TPU), together with ammonium polyphosphate (APP) to prepare intumescent flame retardant composites. In order to improve the dispersibility and flame retardant efficiency, BF was grafted with diammonium phosphate (DAP), named as modified bamboo fibers (M-BF). By the presence of 8 wt% APP and 2 wt% M-BF, the sample could achieve the maximal limiting oxygen index (LOI) value of 30.5% and V-0 rating in UL-94 test. The peak heat release rate for TPU/8APP/2 M-BF is 190 kW/m(2), which is 86.0% lower than that of neat TPU. Besides, TPU/8APP/2 M-BF sample presented a tensile strength of 23.0 MPa, which was slightly lower than neat TPU sample. The thermogravimetric analysis for TPU composites and the morphology observation of the char demonstrated that APP and M-BF took effects on condensed phase through promoting the formation of intumescent char structure and free radical trapping. Meanwhile, it could release inert gases in gas phase. Therefore, M-BF exhibited great potential in applying as renewable charring agent for alleviating the depletion of petroleum resources.