Synthesis and Evaluation of Eleven Novel Renewable Plasticizers for Polylactic Acid (PLA): Linking Molecular Structure to Performance

The development of bio-based plasticizers is increasingly important due to regulatory restrictions on several phthalates, growing concerns over plasticizer migration and toxicity, and the demand for renewable materials. In this work, eleven novel furfural-derived bio-based plasticizers were synthesized and evaluated in polylactic acid (PLA) at 15 wt% loading via melt compounding. Their influence on the thermomechanical properties of PLA was investigated, enabling the establishment of structure–property relationships. Hansen Solubility Parameters (HSPs) were used to predict plasticizer–PLA compatibility and correlate theoretical predictions with experimental performance. All developed bio-plasticizers exhibited onset degradation temperatures exceeding 225 °C, ensuring suitability for melt processing with PLA. Increasing the alkyl chain length in the diester bio-plasticizers reduced plasticization efficiency, consistent with lower predicted compatibility based on HSP analysis. The most promising candidates, namely 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid 2,3-dihexyl ester (F/MA-C6), 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid 2,3-dioctyl ester (F/MA-C8), and 1,1′-[oxybis(1-methyl-2,1-ethanediyl)]bistetrahydrofuroate (Bis-THF), substantially enhanced polymer chain mobility, reducing the glass transition temperature to approximately 28–35 °C compared to 60 °C for neat PLA. These bio-plasticizers also demonstrated outstanding plasticizing efficiency, achieving elongations at break exceeding 245%, compared with 4.5% for neat PLA. These results demonstrate that furfural-derived plasticizers are promising sustainable alternatives to conventional fossil-based plasticizers for flexible PLA applications.