Crystallization of poly(L-lactic acid)/poly(D-lactic acid) blend induced by organic solvents

Crystallization of amorphous poly(L-lactic acid) (PLLA)/poly(D-lactic acid) (PDLA) blend has been investigated by immersion in various organic solvents, acetone, ethyl acetate, tetrahydrofuran (THF), toluene, o-xylene, o-dichlorobenzene, and benzene. Crystalline structure of the blend samples was studied by wide angle X-ray diffraction pattern and differential scanning calorimetry measurement. Immersion of the amorphous blend sample in the solvents, except o-xylene, induced the crystallization of both the homo- and stereocomplex (SC) crystals of PLA. Among the used solvents, benzene, THF, and acetone were effective to form the SC crystal. Increase in the conducting temperature accelerated the formation of the SC crystal. The crystallization of the amorphous PLLA/PDLA blend has been also investigated by exposing to vapor of some organic solvents, acetone, THF, benzene, and chloroform. The vapor of chloroform induced crystallization of the SC crystal effectively. High compatibility, close solubility parameter, of PLA and the solvent should be essential to induce effective formation of the SC crystal by the vapor of the solvents.