Nonlinear determination of the equilibrium melting temperature from initial nonreorganized crytals of poly(3-hydroxybutyrate)

In this article a procedure for the determination of the equilibrium melting temperature (Tm 0 ) of polymers whose crystals reorganize during heating with a melting/recrystallization mechanism is presented and discussed. The procedure is completely based on data obtained by calorimetry and does not require measurements with nonroutine techniques. From the extrapolated melting temperatures of initial nonreorganized crystals, the Tm 0 of poly(3-hydroxybutyrate) is calculated through the Thomson-Gibbs equation via a nonlinear regression method. The value of Tm0 here determined (511 K) is higher than previous data obtained with the commonly used Hoffman-Weeks procedure, which confirms that the latter method provides an underestimation of the equilibrium melting point, similar to the data reported for a number of other semicrystalline polymers.