On the production and application of functional branched oligomers by PLA upcycling using a green solvent-based approach

The main goal of this work was to develop an environmentally friendly method for upcycling poly (lactic acid) (PLA) into functionalized oligomers, as well as to propose an innovative strategy enabling their direct use within the reaction environment. To this end, the investigated reaction—an alcoholysis based on the use of reagents derived from renewable sources—was carried out in the green solvent dihydrolevoglucosenone (Cyrene®, Cy). Indeed, upon the addition of virgin polymer, a PLA/oligomer mixture was obtained, providing a suitable system for the direct preparation of porous films. Specifically, the alcoholysis process, carried out using pentaerythritol (PE) as the polyalcohol and zinc stearate as the catalyst was optimized by monitoring the viscosity of the reaction mixture over time. 1H NMR analysis of the resulting oligomers confirmed a decrease in molecular weight and the formation of a branched structure, attributed to the multifunctionality of the polyalcohol and dependent on the amount of PE added. These structural characteristics significantly affected the thermal behaviour of the oligomers, as demonstrated by DSC and TGA analyses. Porous films, prepared via the Non-solvent Induced Phase Separation (NIPS) technique using the reaction mixture directly as the casting solution, exhibited a leaf-like structure that was unaffected by the presence of oligomers in the mixture, as observed by FE-SEM analysis. The enzymatic hydrolysability and retention capacity were evaluated using Humicola insolens cutinase (HiC) as the enzyme and pararosaniline hydrochloride (PARA) as a cationic organic dye, selected to mimic the behavior of amino-terminated drugs. The results indicated that, compared to neat PLA films, those incorporating the developed oligomers exhibited enhanced dye retention capacity and faster degradation rate. These phenomena were attributed to the high functionality of the branched additives obtained through the alcoholysis process. Finally, a closed-loop process for Cy recovery through distillation was established, enabling its reuse and improving the overall sustainability of the process.