Lignin-derivable, thermoplastic, non-isocyanate polyurethanes with increased hydrogen-bonding content and toughness vs. petroleum-derived analogues.

Jignesh S MahajanZachary R HintonEduardo Nombera BuenoThomas H EppsLa Shanda T J Korley
Published in: Materials advances (2024)
The functionality inherent in lignin-derivable bisguaiacols/bissyringols can improve the processability and performance of the resulting polymers. Herein, non-isocyanate polyurethanes (NIPUs) were synthesized from bisguaiacols/bissyringols with varying degrees of methoxy substitution and differing bridging groups. Notably, the presence of increasing numbers of methoxy groups (0, 2, and 4) in bisphenol F (BPF)-, bisguaiacol F (BGF)-, and bissyringol F (BSF)-NIPUs led to higher percentages of hydrogen-bonded -OH/-NH groups ( i.e. , ∼65%, ∼85%, ∼95%, respectively). Increased hydrogen bonding between chains improved the elongation-at-break ( ε break ) and toughness of lignin-derivable NIPUs over their petroleum counterparts without a reduction in Young's moduli and tensile strengths. For example, BSF-NIPU exhibited the highest ε break ∼210% and toughness ∼62 MJ m -3 , followed by BGF-NIPU ( ε break ∼185% and toughness ∼58 MJ m -3 ), and then BPF-NIPU ( ε break ∼140% and toughness ∼42 MJ m -3 ). Similar trends were found in the dimethyl-substituted analogues, particularly for the bisphenol A-NIPU and bisguaiacol A-NIPU. Importantly, the melt rheology of the lignin-derivable NIPUs was comparable to that of the petroleum-derived analogues, with a slightly lower viscosity ( i.e. , improved melt flow) for the bio-derivable NIPUs. These findings suggested that the added functionalities (methoxy groups) derived from lignin precursors improved thermomechanical stability while also offering increased processability. Altogether, the structure-property-processing relationships described in this work can help facilitate the development of sustainable, performance-advantaged polymers.