Circular Strategies for Polylactic Acid Waste: A Pathway to Advanced Thermosets

Due to its degradable nature and origin from natural feedstock, polylactic acid (PLA) stands out as a promising alternative to traditional fossil-based plastics in response to the environmental crisis. However, the slow degradation rate of PLA underscores the necessity of introducing efficient recycling methods. The approach proposed herein involves the degradation of the macromolecular chains with the insertion of unsaturations into telechelic PLA-based oligomers, leading to renewable chemical building blocks that are useful for the preparation of novel PLA-based networks. One-pot reactions involving PLA waste, maleic anhydride, and different diols (ethylene glycol or 1,4-benzenedimethanol) were conducted under neat conditions at 170 °C and using titanium isopropoxide as a catalyst. Gel permeation chromatography measurements showed the reduction in molecular weight over time; by varying the amounts of the reactants, unsaturated oligomers with molecular weights spanning from 700 to 4000 Da were obtained. The oligomers were characterized by1H nuclear magnetic resonance (NMR) and diffusion-ordered spectroscopy (DOSY) NMR spectroscopy and then used for the preparation of polymeric networks by thermal or chemical cross-linking through the use of divinylbenzene and radical initiators. The thermoset materials formed were characterized by1H magic angle spinning (MAS) NMR and13C cross-polarization MAS (CPMAS) NMR.