THERMAL-ANALYSIS OF THE DEHYDRATION PROCESS OF CROSS-LINKED POLYVINYLPYRROLIDONE AND ITS MIXTURES WITH NAPROXEN

Ways of finding kinetic parameters useful for pharmaceutical formulato rs from thermal analytical methods (TGA, DSC) under both isothermal an d non-isothermal conditions are suggested. We considered as an example those followed to determine the first-order kinetics of dehydration o f cross-linked polyvinylpyrrolidone (PVP XL). PVP XL samples differing in particle size (granulometric fractions in the 250 mu m to 63 mu m range) and/or equilibrium moisture content (12 to 32 g(H2O)/100 g) sho w activation energy values in the 43 to 54 kJ mol(-1) (non-isothermal TGA) and 48 to 61 kJ mol(-1) (non-isothermal DSC) ranges. The weight f raction of water present may influence the activation energy of the de hydration process whilst the particle size of PVP XL seems not to affe ct this parameter. The low interaction energy between PVP XL and water suggests that the interaction mainly occurs within the porous agglome rates of the polymer particles, at the intraparticulate surface level (surface-type interaction). The influence of an admired drug (naproxen ) on the thermodynamic and kinetic parameters of PVP XL dehydration su ggests that analogous surface phenomena are probably involved in the s olid-state interaction between the amorphous polymer and the crystalli ne drug.