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

Abstract

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 (;.e., burning) at around 80 °C to 125 °C followed by subsequent cross-linking reactions over 150 °C to give the dry glass transition temperature (Tg,dry) of lignin at around 130 °C to 140 °C. 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 °C and 80 °C, respectively. The melt viscosity was measured at 103Pas at 120 °C, ensuring facile melt-blending processing with various commodity polymers to be used in eco-friendly polymer composite development.