Thermophysical properties of bacterial poly(3-hydroxybutyrate): Characterized by TMA, DSC, and TMDSC

The melting, isothermal and nonisothermal crystallization behaviors of poly(3-hydroxybutyrate) (PHB) have been studied by means of temperature modulated differential scanning calorimetry (TMDSC) and conventional DSC. Various experimental conditions including isothermal/annealing temperatures (80, 90, 100, 105, 110, 120, 130, and 140 degrees C), cooling rates (2, 5, 10, 20, and 50 degrees C/min) and heating rates (5, 10, 20, 30, 40, and 50 degrees C/min) have been investigated. The lower endothermic peak (T-m1) representing the original crystals prior to DSC scan, while the higher one (T-m2) is attributed to the melting of the crystals formed by recrystallization. Thermomechanical analysis (TMA) was used to evaluate the original melting temperature (T-melt) and glass transition temperature (T-g) as comparison to DSC analysis. The multiple melting phenomenon was ascribed to the melting-recrystallization-remelting mechanism of the crystallites with lower thermal stability showing at T-m1. Different models (Avrami, Jeziorny-modified-Avrami, Liu and Mo, and Ozawa model) were utilized to describe the crystallization kinetics. It was found that Liu and Mo's analysis and Jeziorny-modified-Avrami model were successful to explain the nonisothermal crystallization kinetic of PHB. The activation energies were estimated in both isothermal and nonisothermal crystallization process, which were 102 and 116 kJ/mol in respective condition. (c) 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42412.