Plasticization of Poly-L-lactide with L-Lactide, D-Lactide, and D,L-Lactide Monomers

Poly-L-lactide (PLLA) is being widely considered for repair of damaged tissues, for controlled antibiotic release, and also as scaffolds for cultured cells. PLLA was blended with the lactide monomer in its two enantiomeric forms: D-lactide (D-la) and L-lactide (L-la) and with the cyclic dimmer D,L-la, in order to enhance its flexibility and thereby overcome its inherent problem of brittleness. In this work, the crystallization, phase structure, and tensile properties of PLLA and PLLA plasticized with 5, 10, 15, and 20 wt% of D-la, L-la, and D,L-la are explored. The three plasticizers used were effective in lowering the glass transition temperature (T-g) and the melting temperature (T-m) of PLLA, around 20 degrees C for a plasticizer content of 20 wt%. The tensile strength and modulus of the blends decreased following the increasing content of plasticizers from approximately 58 MPa to values below 20 MPa, and from 1667 to 200 MPa, respectively. Aging the blends at storage ambient temperature revealed that the enhanced flexibility as well as the morphological stability was lost over time due to the migration of the plasticizer to the surface, this being less marked in the case of D-la as a result of interactions between the polymer and its enantiomeric monomer of complementary configuration. POLYM. ENG. SCI., 53:2073-2080, 2013. (c) 2013 Society of Plastics Engineers