Elevation of charring level of polyamide-6,6 films via ionic introduction of phosphoric acid and boric acid esters

Phosphorus and boron containing materials have the feature of increasing char formation, which can be effectively used as flame retardants especially in textiles. This paper discusses the ionic addition of phosphorus and boron esters to polyamide-6,6 (PA66), and its effect on the charring level. A mixture of phosphoric acid–boric acid ester at different degrees of esterification (ED) was prepared and two theoretical mechanisms for the esterification reaction were suggested. Ionically grafted polymer films were prepared by introducing the ester of highest ED to PA66–formic acid solution via three different processes: open air (cold) grafting, ultraviolet irradiation grafting, and hot vacuum oven grafting. Thermogravimetry was conducted for all synthesized esters and films, and the formation of new bonds between the ester and PA66 was verified using Fourier transform infrared spectroscopy.