Evaluation of thermal, morphological and flame-retardant properties of thermoplastic polyurethane/polyphosphazene blends

A polydichlorophosphazene was prepared by thermal ring-opening polymerization of hexachlorophosphonitrile (trimer). The functionalization of polydichlorophosphazene was done via substituting the chlorine groups with sodium salt of trifluroethanol and furfuryl alcohol and then structural properties of functionalized polyphosphazene (PPZ) was confirmed by GPC, FT-IR and NMR spectroscopic analysis. The PPZ was further blended with thermoplastic polyurethane (TPU) using solution casting method in anhydrous tetrahydrofuran solvent. The miscibility behavior of TPU/PPZ blends was observed via FTIR spectroscopy which unfolded the reason of compatibility of the blends due to intermolecular Hydrogen bonding interaction between the TPU and PPZ. Further, the thermal properties of the casted films were analyzed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) which revealed the increase in onset of degradation temperature of TPU with the increase of PPZ content. Also the char yields of TPU blends at 600 °C were increased upon increasing the amount of polyphosphazene from 5 to 20 wt%. The appearance of crystallinity in the TPU/PPZ blend due to heteronucleation effect by PPZ was analyzed by X-ray diffractometer. Besides this, the morphological changes of the TPU/PPZ blended films were investigated by scanning electron microscopy which exposed the homogeneity in the blend (d). The flame-retardant properties were evaluated using limiting oxygen index (LOI) analyzer and UL-94 (vertical burning test) showing the rating of V0 with achieved LOI value of 31.4% for the blend (d). Moreover, the films were characterized in terms of mechanical properties (as per relevant ASTM standards) using UTM which demonstrated that the addition of 20 wt% PPZ in the blend enhanced the tensile strength by about 110% and decreased the elongation at break by nearly 13%.