عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The effects of magnesium hydroxide and l-lactide dimer as additives on thermal properties and morphology of poly(l-lactide) (PLLA) films were studied. Hence, neat PLLA films and films containing additives (10% w/w) were prepared in dichloromethane at room temperature via solution casting. To evaluate thermal history on polymer properties, PLLA films were annealed by different processes. In one process, designated as A, PLLA films were heated from 20 up 140oC, then held for 1 h and cooled to room temperature. In another process, designated as B, melted PLLA samples
which had been maintained at 200oC for 5 min were cooled with a rate of -20oC/min to 140oC and annealed for 1 h before being cooled to room temperature. In the next process designated as C, the melted PLLA samples after
5 min of staying at 200oC were being quenched to 0oC. Then the samples were heated to 140oC followed by annealing for 1 h before being cooled to room temperature. The crystallization and morphology properties of PLLA
films were studied using polarized optical microscopy and differential scanning calorimetry. It is found that the percentage of crystal and spherulitic formation inside PLLA films were influenced by thermal history and presence
of the additives. The type of additives did not affect melting point (Tm) of the films annealed through different processes of A to C, while they had influence on Tm of the films, significantly. It is to be noted that some spherulites
were formed in films during B process. During C process, however, the nucleation rate increased due to quenching which enhanced the spherulites formation.