Thermal Properties of Polyvinyl Alcohol by Fast Scanning Calorimetry

Polyvinyl alcohol crystallizes from the melt so rapidly that it is difficult to obtain fully amorphous glassy polymer. To study thermal properties of fully amorphous PVA, we use fast scanning calorimetry (FSC) to heat and cool at rates ranging from 1000 K/s up to 600,000 K/s. We determine the critical cooling rate, β_c, needed to quench PVA from the melt into an amorphous glass as |β_c| = 20,000 K/s. Using FSC in combination with conventional differential scanning calorimetry (DSC), we evaluate the temperature dependent liquid state heat capacity, c_p^Liquid(T) = ((0.0016 ± 0.0002)* T + (2.3 ± 0.2)) J/(gK). The specific heat capacity increment at T_g for fully amorphous PVA is Δc_p^amor(T_g) = (1.005 ± 0.002) J/(gK). For the semi-crystalline samples used in this study, PVA obeys a two phase model in which the rigid amorphous fraction, φ_RA ~ 0. The approaches used in this work are applicable to any semicrystalline polymer or biopolymer which degrades upon heating, or crystallizes so rapidly from the melt that a fully amorphous material cannot be realized at conventional DSC rates.