Phase transitions of lignin-based polycaprolactones and their polyurethane derivatives

Alcoholysis and kraft lignin-based polycaprolactones (LigPCL) were synthesized by the polymerization of ε-caprolactone which was initiated by the hydroxyl (OH) group in lignin. LigPCL-based polyurethanes were also prepared from LigPCL. The caprolactone (CL)/OH ratio of the CAPCLs was changed from 1 to 25 mol mol−1. Thermal properties of the LigPCL and LigPCL-based polyurethane (PU) sheets were studied by differential scanning calorimetry (DSC). Glass transition temperature (Tg), heat capacity difference at Tg (ΔCp) cold crystallization temperature (Tcc) and melting temperature (Tm), were determined by DSC. The main chain motion of lignin is observed in the whole CL/OH ratio. When CL/OH ratio exceeds 5 mol mol−1 in the LigPCL samples and 10 mol mol−1 in the LigPCL-based PU samples, the crystalline region which is organized by the PCL chain association is observed. It was found that PCL chain association is controlled by both chain length and chemical cross linking.