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In light of the difficulties and disagreements in determining the property-processing structure relations of lignin-based polymers, dielectric analysis was used to identify the thermal and rheological characteristics of a lignin-based polycondensate and the pristine lignin. Using dielectric analysis, the pristine lignin with Mw=6000 g/mol, was clearly identified as giving the wet glass transition temperature (Tg,wet) and the evolution of gases (i.e., burning) at around 80 oC to 125 oC followed by subsequent cross-linking reactions over 150 oC to give the dry glass transition temperature (Tg,dry) of lignin at around 130 oC to 140 oC. Connecting the lignin macromers using sequential condensation reactions with caprolactone and sebacoyl chloride, the lignin based polycaprolactone (LigPCL) polycondensates were synthesized as a thermoplastic polymer composed of lignin macromers and aliphatic polyester chains with Mw=10500 g/mol. The synthesized LigPCL presented good thermal stability and rheological melting behavior without evolving odor or fumes. In particular, the T2% (defined at 2% of weight loss) of the LigPCL and pristine lignin were 200 oC and 80 oC, respectively. The melt viscosity was measured at 103Pa.s at 120 oC, ensuring facile melt-blending processing with various commodity polymers to be used in eco-friendly polymer composite development.

Chemical and Rheological Characteristics of Thermally Stable Kraft Lignin Polycondensates Analyzed by Dielectric Properties