Biobased plasticizers derived from fumaric acid for ductility improvement in injection-molded polylactide

The intrinsic brittleness of poly(lactide) (PLA) remains a major limitation for applications requiring a suitable balance between stiffness and toughness. In this work, four bio-based fumaric acid esters with different alkyl-chain lengths and architectures, namely diethyl fumarate (DEF), diisopropyl fumarate (DPF), dibutyl fumarate (DBF), and bis(2-ethylhexyl) fumarate (DEHF), were evaluated as plasticizers for PLA. Formulations containing 10 and 20 wt% of each fumarate were prepared by melt extrusion followed by injection molding and characterized in terms of their mechanical, morphological, chemical, thermal, viscoelastic, thermomechanical, and migration behavior. At 10 wt%, none of the fumarates induced a brittle-to-ductile transition, and the formulations largely retained the rigid and brittle mechanical response of neat PLA. In contrast, the incorporation of 20 wt% of DEF, DPF, and DBF produced pronounced plasticization, with substantial reductions in stiffness and glass transition temperature and an increase in elongation at break from 6.7% for neat PLA to 212.9–326.0%. Conversely, PLA formulations plasticized with DEHF exhibited a markedly different behavior. Even at 20 wt%, DEHF retained comparatively high stiffness, showed a smaller reduction in glass transition temperature, and maintained good dimensional stability, while improving Charpy impact strength from 4.8 to 8.5 kJ m −2 . Overall, the results demonstrate that the plasticization efficiency and retention of fumaric acid esters are strongly governed by their molecular architecture. Short- and medium-chain fumarates provide highly ductile PLA formulations, whereas the bulky and branched structure of DEHF promotes enhanced toughness while preserving comparatively high rigidity.