Synthesis, thermal properties, rheological and mechanical behaviors of lignins-grafted-poly(ε-caprolactone)

Original macromolecular architectures based on lignin, a promising biobased building block or macromer, have been elaborated and analyzed. Different soda lignins-grafted-poly(ε-caprolactone) were synthesized by ROP of ε-caprolactone (CL) initiated by the hydroxyl groups (OH) brought by the lignins, and catalyzed by stannous octanoate. The influence of polycaprolactone (PCL) grafted chains onto lignin was investigated with a large range of CL/OH molar ratios, from 5 to 100. Based on analyses carried out by FT-IR and DSC, it was found that PCL chain organization was controlled by both intermolecular bonding and chain length. A semi-crystalline structure was observed for samples with a CL/OH ratio from 10 to 100 mol.mol−1 which implicated the formation of a well arranged structure between PCL chains grafted around lignin. However, specific behavior has been observed at a CL/OH ratio equal to 5 due to the absence of crystallinity and specific intermolecular bonding. Mechanical tensile tests and rheological analyses were performed additionally to highlight the remarkable elastomer-like behavior of this new lignin-based material.