On the Thermal Features of Polystyrene-Polyvinylidene Fluoride Blends

Polystyrene-Polyvinylidene Fluoride (PS-PVDF) blends of various compositions were prepared by melt-mixing. Their thermal features were studied by thermogravimetric analysis (TGA). TGA measurements were performed under nitrogen atmosphere in the range 50 to 1000 ^oC, at a heating rate of 10 ^oC/min. The thermograms of homopolymers showed a single sigmoid-like shape. The blends showed more complex thermograms defined as two superimposed sigmoidal shapes.

The derivatives of the thermograms with respect to the temperature show two almost independent gaussians, thus allowing a good separation between the degradation of PS and PVDF in PS-PVDF blends. This approach allowed us the introduction of a pair of inflection points with the inflection temperature and the fraction of residual sample at the inflection temperature, for PS and PVDF. The experimental data showed that the inflection temperature for each phase (PS and PVDF) depends weakly on the composition of the blend. Additionally, two new parameters representing the width of the thermal degradation for PS and PVDF were introduced. The dependence of the widths of the degradation derivatives on composition is reported for each phase. Tentatively, a procedure to calculate the activation energy for the thermal degradation is proposed.