Preparation and characterization of chitosan derivatives and their application as flame retardants in thermoplastic polyurethane.

Our previous work has demonstrated that chitosan (CS) can be directly used as charring agents. In this paper, efforts were made to further improve the thermal stability and charring ability of CS by reacting with benzaldehyde, salicylaldehyde and hydroxybenzaldehyde respectively to obtain different CS derivatives. CS derivatives in association with ammonium polyphosphate (APP) was then introduced into thermoplastic polyurethane (TPU) to prepare flame retardant TPU composites. The sample containing 18.75% APP and 6.25% salicylaldehyde modified CS (SCS) achieved the maximal limiting oxygen index of 29.5%, passed the V-0 rating and significantly decreased the peak heat release rate from 840.8kW/m2 of neat TPU to 206.2kW/m2. Thermogravimetric analysis and char morphology observation demonstrated that SCS/APP could promote the char formation to form more intact intumescent char structure. It was proposed that the synergism between CS derivatives and APP might be responsible for the improvement of flame retardancy.