Plasticization of Polylactide Using Biobased Epoxidized Isobutyl Esters Derived from Waste Soybean Oil Deodorizer Distillate

Abstract

A series of epoxidized isobutyl esters (EIE) derived from soybean oil deodorizing distillate (SODD) were synthesized via esterification with isobutanol followed by epoxidation. Epoxidized isobutyl soyate (EIS), epoxidized isobutyl soyate distillate (EISD), as well as the epoxidized esters of the main fatty acids contained in SODD, namely, epoxidized isobutyl linoleate (EIL), and epoxidized isobutyl oleate (EIO) were also synthesized and assessed as environmentally friendly plasticizers for polylactide (PLA). A comparison of the plasticizing efficiency of 10 wt.% of these EIE on PLA properties is addressed in this work. The effects of the different EIE on mechanical properties (tensile and impact tests) at 21 ºC, thermal transitions and thermal degradation, dynamic-mechanical thermal properties and dimensional change with temperature, and morphology are evaluated and compared with commercial epoxidized soybean oil (ESBO), and acetyl tributyl citrate (ATBC). Tensile tests indicate that EIE provide increased elongation at break from 8.8% (neat PLA), up to 10–32%, depending on the EIE. EIE seem to be more compatible with PLA as observed by field emission scanning electron microscopy (FESEM) since they do not give evidence of phase separation, or plasticizer saturation, which is clearly observed with ESBO. Regarding thermal properties, all EIE provide a noticeable decrease in the glass transition temperature (T_g) from 61.6 ºC (neat PLA), down to values ranging from 42 to 48 ºC, remarkably lower than the decrease provided by ESBO with a T_g value of 56.6 ºC. These findings reveal that EIE are promising plasticizers for PLA with balanced properties and contribute to improve its intrinsic brittleness by increasing the impact toughness.