1. Martin‐Luther‐University Halle‐Wittenberg, Center of Engineering Sciences, , D‐06099 Halle/Saale, Germany;2. University of Rostock, Institute of Physics, , 18051 Rostock, Germany;3. Consiglio Nazionale delle Ricerche, Istituto per i Polimeri, Compositi e Biomateriali – c/o Comprensorio Olivetti – Via Campi Flegrei, , 34 – 80078 Pozzuoli, (NA), Italy
Abstract:
Melting and reorganization of conformationally disordered crystals (α′‐phase) of poly(l ‐lactic acid) (PLLA) are analyzed as a function of the rate of heating in a wide range between about 10?1 and 103 K s?1. It is found for the first time that the reorganization of conformationally disordered α′‐crystals into stable α‐crystals can be suppressed by fast heating. Heating of α′‐crystals of PLLA at a constant rate, faster than 30 K s?1, leads to its complete melting between 150 and 160 °C and suppression of formation of α‐crystals on continuation of heating. Non‐isothermal reorganization of α′‐crystals into α‐crystals only occurs when heating at a rate slower than 30 K s?1. It is evidenced that isothermal reorganization of α′‐crystals into α‐crystals at 150–160 °C proceeds via melting followed by recrystallization rather than a solid–solid phase transition.
