Blends of hydroxypropyl methylcellulose and poly(1-vinylpyrrolidone-co-vinyl acetate): Miscibility and thermal stability

The miscibility, kinetic parameters, and mechanism associated with the thermal degradation of hydroxypropyl methylcellulose/poly(1-vinylpyrrolidone-co-vinyl acetate) (HPMC/P(VP-co-VAc)) blends, were analysed. The presence of only one glass transition temperature (Tg) in the blend, intermediate between those for the pure polymers, the shift of the bands in the region of 3430 cm−1 and the disappearance of the band at 1647 cm−1 from the infrared spectra, suggest miscibility between the components. The thermogravimetric curves associated with the temperature of maximum degradation rate (Tmax) indicate a higher thermal stability for the blend with 30% HPMC and for the pure copolymer. This conclusion was supported by the activation energy (E) values which increased to ca. 190 and 170 kJ mol−1 for the blend with 30% HPMC and the pure copolymer, respectively. The E-values for the studied systems suggested a degradation mechanism associated with a random scission of the chain. The FTIR spectra of the solid residues from the thermal degradation reaction of both systems suggest the formation of alcohol and unsaturated hydrocarbons as reaction products. For the HPMC system, CO2, CO, aldehydes, alcohols and ethers were detected as volatile products. Volatile products such as, acetic acid, CO2, CO and NH3 were detected for P(VP-co-VAc).