Influence of Post-Synthesis Heat Treatments on the Molecular Structure and Thermal Stability of Phosphatized Starch

The threat of fires necessitates effective flame retardants (FR) to safeguard human life and property. In response to the demand for sustainable options, bio-based FR have emerged, with phosphatized starch (PS) standing out as a promising candidate. This study explores the influence of post-synthesis heat treatments on the molecular structure of PS to enhance its thermal stability for processing in polymeric matrix materials. The molecular structure of the flame-retardant PS is characterized via solid state and solution nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, and differential scanning calorimetry. Through a comprehensive analysis of results from thermo-gravimetric analysis, thermo-gravimetric Fourier-transform infrared spectroscopy, and elemental analysis, the thermal stability and thermal decomposition mechanisms of PS are investigated. The post-synthesis heat treatment leads to the decomposition of residual urea and carbamate groups, as well as to the formation of ammonium polyphosphates. By employing thermal modification, the thermal stability and phosphorus-content are enhanced.