Conformation Directed Mpemba Effect on Polylactide Crystallization

Structures of polymers depend on the degree of polymerization and chain conformation, and the chain conformation plays a key role on the structure formation and structure transition of an existing polymer, especially for the crystalline polymers. DSC and WAXD measurements were performed to investigate crystallization behavior and structure of polylactide (PLA) with different thermal histories. A similar Mpemba effect was found during the crystallization process, which showed that the PLA sample quenched from “hot” crystallizes faster than that quenched from the “cold”. The obtained crystallization half-times of isothermal crystallization, and the crystallization temperatures, glass transition temperatures, and melting points during the cold nonisothermal crystallization process with a high heating rate, decrease with holding temperature. The Mpempa effect was discussed and attributed to the temperature dependent chain conformation or local structure of the amorphous and confined effect on the conformation adjustment before PLA crystallization. The unusual crystallization phenomenon of PLA would be helpful to understand the polymer crystallization and control the crystalline structure of PLA.