LAUSR

Abstract Crystallization behaviors on two-step isothermal crystallization at T c 1 and T c 2 ( T c 1 ) were examined by fast scanning calorimetry for poly(butylene terephthalate) in order to identify the dominant process during the secondary stage of crystallization at T c 1 after the completion of spherulitic growth under isothermal condition. From the difference between the melting peaks obtained before and after the low-temperature crystallization step at T c 2 , the distinction of the following two processes became realizable: the growth of crystals formed at T c 2 and the stabilization of crystals formed at T c 1 . The dependences on T c 2 and the duration of times Δ t c 1 and Δ t c 2 revealed the following: The formation and growth of new crystals are controlled by thermodynamic driving force determined by supercooling, and hence are suppressed at T c 1 higher than T c 2 . The crystal stabilization is controlled by the mobility of polymer chains, and became more pronounced at T c 1 . Therefore, the dominant process of the secondary crystallization under isothermal condition at T c 1 should be the stabilization of crystals formed in the primary stage and the formation of new crystals will only have a secondary effect.