Modifying the thermal and mechanical properties of poly(lactic acid) by adding lithium trifluoromethanesulfonate

Abstract

The effect of the addition of lithium trifluoromethanesulfonate (LiCF3SO3) on the linear viscoelastic properties, crystallization behavior, and mechanical properties of poly(lactic acid) (PLA) was studied. The glass transition temperature (Tg) was enhanced by adding LiCF3SO3, without any loss of transparency of the PLA. This was attributed to the ion-dipole interaction between the lithium cation and oxygen atom in the PLA carbonyl group. The interaction weakened at higher temperature. Consequently, the rheological terminal region was clearly detected, which suggested that the system possessed good melt-processability. The Young’s modulus and yield stress at room temperature were also enhanced by the addition of LiCF3SO3, although the toughness was reduced due to the brittle failure. Finally, the presence of LiCF3SO3 retarded the crystallization of PLA, because the segmental motion of the PLA chains was reduced.