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

Le Dai Duong, Nguyen Dang Luong, Nguyen Thi Thanh Binh, In-Kyung Park, Seong Hoon Lee, Dea Sik Kim, Yong Sang Lee, Young Kwan Lee, Byung Woo Kim, Kwang Ho Kim, Ho Kyu Yoon, Ju Ho Yun, Jae-Do Nam

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 (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.

Keywords


Lignin; Polycondensate; Polycaprolactone; Biodegradable polymer; Eco-friendly

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