Lignin-liquid crystalline elastomeric composites for shape memory applications and their thermomechanical properties

Liquid crystalline elastomers (LCEs) are stimuli-responsive materials with potential use in shape memory applications. Though particularly suited for shape memory, the LCEs however have some drawbacks such as low shape fixity (Rf) and slow recovery time. To overcome these limitations, new lignin-filled elastomeric liquid crystalline (ELC) composite materials were fabricated. The lignin used is a by-product of Kraft pulping process, which was obtained from renewable resources abundant in nature. Here, we show that the aromatic structure of lignin increases the netpoints density at the microscopic level in the ELC composite systems. Shape memory effects are enhanced by incorporating up to only 7 wt% of lignin, resulting in an Rf of 97% for the composites. Concurrently, these composites were able to maintain their shape recovery (Rr) of nearly 100%. The recovery time of the composites reduces with increasing lignin content due to the higher elastic energy released from the netpoints based on the lignin structure. The ELC composites with 7 wt% lignin could fully recover within 70 s, while the neat LCE counterpart took 100 s. Morphological features of dispersed lignin shows that even without surface modification and only a moderate quality of dispersion in LCE matrix, both shape memory and dynamic mechanical properties of the resultant composites can be significantly improved.