Thermodynamic properties of polyvinyl alcohol binder of electrically controlled solid propellant.

The thermodynamic properties of polyvinyl alcohol (PVA) binder of electrically controlled solid propellant with different degrees of polymerization and alcoholysis were studied via multiple thermochemical methods. The combustion heat of three PVA types at 298.15 K were measured by a bomb combustion calorimeter, and the results showed that the combustion heat of PVA increased with the increase of its degrees of polymerization and alcoholysis. According to the results of combustion heat and elemental analysis, the standard molar enthalpy of polymer formation was calculated. The specific heat capacity of high-molecular-weight PVA (146,000 − 186,000) was measured through the differential scanning calorimeter (DSC) method from 293 K to 453 K, and the molar heat capacity was calculated. Through calculation of the heat capacity values, the relationship between the molar heat capacity and temperature was presented as a function of the following polynomial equations: Cp,m (J∙K−1∙mol−1) = 7.21 × 10−4 T3 − 0.63 T2 + 184.58 T − 17,958.71 (293–323 K) and Cp,m (J∙K−1∙mol−1) = −3.64 × 10−7 T4 + 5.62 × 10−4 T3 − 0.322 T2 + 81.83 T − 7692.35 (333–453 K). According to the polynomial equations and thermodynamic relationship, the thermodynamic functions (HT − H298.15) and (ST − S298.15) of the PVA with high molecular weight relative to 298.15 K were calculated in the temperature range of 293–453 K with an interval of 10 K by using the heat capacity data. The thermal stability of the PVA with different molecular weights and alcoholysis were also measured by using the thermogravimetry technique. Results showed that high-molecular-weight PVA had better thermal stability than low-molecular-weight PVA. The volatile degradation products of three PVA types were analyzed by Thermal gravimetric analysis-Fourier transform infrared (TG-FTIR) spectroscopy suggests that water, unsaturated aldehydes and ketone are the dominant products, however, a big amount of acetic acid is also found in the products of PVA with low alcoholysis degree. [ABSTRACT FROM AUTHOR]