A new article out of a collaboration between Dr. Ning Yan and Dr. Jing Chen’s labs has been published in Science of The Total Environment written by Xiaozhen Ma, Shuqi Li, Fan Wang, Jialong Wu, Yeyan Chao, Xu Chen, Peng Chen, Jin Zhu, Ning Yan and Jing Chen.
You can find the article here.
Here a new strategy of catalyst-free direct synthesis of covalent adaptable network polyurethanes (LPUs) from lignin with editable shape memory effect is reported. Using unmodified lignin, PEG, and isocyanate under the condition of the isocyanate index less than 1.0 (NCO/OH <1.0), a variety of LPUs were obtained. When NCO/OH=0.8, a stable cross-linked network could be formed (ex. the gel content of LPU50-0.8 was 98 ± 0.3 %). The activation energy (Ea) value of LPUs was similar to that of polyhydroxyurethanes (PHUs), at around 110 kJ/mol. With an increase of lignin content, the LPUs showed a transition from ductile fracture to brittle fracture mode. And the mechanical properties of LPUs were significantly enhanced after extrusion processing, with the maximum modulus reaching 649 ± 26 MPa and the maximum toughness up to 9927 ± 111 kJ/m3. The improvement in mechanical properties was due to the homogenization of complex cross-linked network under the powerful external force of the extruder and the lignin that originally was free in the system participated in the exchange reactions. Moreover, LPUs could also be prepared continuously in one step by using an extruder as the reactor. In addition, LPU50-0.8 had an editable shape memory effect. This study developed a novel method for the synthesis of LPU from lignin with NCO/OH<1.0, showcasing new possibilities for value-added utilization of lignin, and expanding the bio-based products portfolio from biomass feedstock to help meet future green manufacturing demands.