Effects of D-lactide content and molecular weight on the morphological, thermal, and mechanical properties of electrospun nanofiber polylactide mats

In this study, the effects of both D-lactide content, that is, the change in PLA crystallizability, and molecular weight of polylactide (PLA) on its electrospinning behavior, along with thermal and mechanical properties of the electrospun mats were investigated. Although the effect of D-lactide content on processability of PLA has been studied in extrusion, thermoforming, foaming, and melt spinning, it has not been explored in electrospinning. The current study aimed to analyze electrospinnability of three different PLA grades; two amorphous with high and low molecular weights (i.e., aPLA-H and aPLA-L) and a semicrystalline with a high molecular weight (cPLA-H). PLAs were dissolved at different concentrations in chloroform (CHL)/dimethylformamide (DMF) at various volume ratios. Due to its high crystallizability and molecular weight, coarser nanofibers of cPLA-H were produced from solvents with high CHL content (≥75%), resulting in highest water vapor transmission rate (50,000 g/m ² .day) of mats. aPLA-H revealed coarser nanofibers than that of aPLA-L due to its higher molecular entanglement. Although the increase in DMF content in the solvent hindered dissolving and electrospinning of cPLA-H, it caused the refinement of nanofibers in amorphous PLAs. Despite similar tensile strength, cPLA-H showed higher elongation at break (∼69%) than that of aPLA-H (∼59%) possibly due to the existence of some beads within the fibers in aPLA-H. Storage modulus of electrospun cPLA-H was also higher (∼15MPa) than that of other samples (∼10–12 MPa) due to high content of crystallinity (∼37%) while aPLA-L revealed the lowest storage modulus (∼10MPa) due to its amorphous structure and low molecular entanglement.