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°C), cooling rates (2, 5, 10, 20, and 50°C/min) and heating rates (5, 10, 20, 30, 40, and 50°C/min) have been investigated. The lower endothermic peak (Tm1) representing the original crystals prior to DSC scan, while the higher one (Tm2) is attributed to the melting of the crystals formed by recrystallization. Thermomechanical analysis (TMA) was used to evaluate the original melting temperature (Tmelt) and glass transition temperature (Tg) 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 Tm1. 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.