On the upcycling of PCL to produce building blocks for the development of PCL-PLA copolymers

Despite its many advantages over other bioplastics, poly(ε-caprolactone) (PCL) still faces limited applications and a lack of sustainable chemical recycling routes that could extend its life cycle, reduce its carbon footprint, and enhance its applicability. In this work, to address this gap, a novel bulk alcoholysis process was developed for upcycling PCL into functional hydroxyl-terminated oligomers using two bio-based fatty alcohols, 1-dodecanol and 1,12-dodecandiol, in the presence of zinc stearate as a catalyst. This approach enables precise control over the final properties of the resulting oligomers by varying the type and the concentration of the alcohol, yielding mono- and difunctional telechelic structures suitable for further synthesis. The prepared PCL-based oligomers were used directly, without purification, as macroinitiators for the ring-opening polymerization (ROP) of L-lactide to synthesize well-defined diblock (PCL-PLA) and triblock (PLA-PCL-PLA) copolymers with a PCL/PLA ratio of 1 and tailored chain lengths. These copolymers were then applied in two different scenarios. The diblock copolymers were tested as compatibilizers for PLA/PCL blends, where they enhanced the elongation at break by improving interfacial adhesion between the two polymer phases. Moreover, two telechelic systems, namely a PCL oligomer and a PLA-PCL-PLA copolymer, were used in the preparation of thermoplastic polyurethanes (TPUs) via chain-extension reactions with methylene diphenyl diisocyanate (MDI), leveraging the residual catalyst and demonstrating efficient polymerization. Overall, the developed approach provides a robust, solvent-free, scalable, and effective strategy for valorizing PCL waste, establishing a platform for producing sustainable, functional polyester-based building blocks.