A combined experimental and molecular dynamic studies of curing of shape memory lignin-liquid crystalline elastomeric composites

Elastomeric liquid crystalline (ELC) composites have recently been developed to be utilised as thermomechanically activated shape memory materials. To extend their utility for a range of industrial applications, understanding the curing behaviour of this composite system is critical, which could pave the way for their processability through advanced manufacturing methods. This work has investigated the curing behaviour of these composites using a combination of laboratory experiments and molecular dynamic (MD) simulations. The results show that the addition of higher loading of lignin increases the activation energy and hence retards the curing conversion of the composites due to its steric hindrance in the polymerisation process. To arrive at an upper limit of lignin content, for the benefit of maximising the shape memory effects and to improve the thermomechanical properties while reducing the overall cost of the composites, rheological characteristics were studied through MD. The maximum packable lignin content achieved in the composite was 20 wt%. The inter- and intramolecular interactions of this composite material were identified using FTIR analysis. Using MD simulations, the calculated radial distribution functions (RDF) indicated that lignin could have intermolecular hydrogen bonding with liquid crystalline structures. The calculation of the flow behaviour of the uncured composite mixtures showed temperature- and shear-rate-dependent behaviours. The presence of lignin increases the computed viscosity of the composite system, confirming the increase in the activation energy of the system. These findings provided insight into the influence of lignin filler on the curing of the ELC composite polymer system.