Molecular Dynamics Simulation Considering Covalent Bond Dissociation for Lignin-based Composite Materials

Although epoxy resin is widely used as a structural material such as transportation vehicles, replacing these materials with bio-based materials or its composites would greatly contribute to achieving a carbon-neutral society. Lignin produced from wood has been attracting attention as one of the naturally derived materials. Toward the application of lignin in composite materials, molecular dynamics simulations are performed on the mechanical characteristics of lignin/epoxy polymers, which are expected to be important candidates for the matrix of biobased composites. This study prepares two types of lignin/epoxy polymers with and without polyethylene glycol (PEG) sidechains, and effects of these side chains on the material characteristics are investigated through uniaxial tensile test and analysis of interfacial stability between lignin/epoxy polymer and functionalized graphene. Our calculation results show that PEG side chains improve Young's modulus, strength and toughness, which may be induced by increasing the number of entanglement points between side chains. Further, the PEG side chains also improve the interfacial stability by forming hydrogen bonds between PEG and charge-biased functional groups on graphene sheet. We investigate molecular-scale mechanisms of interface stability difference between these models through analysis with radial distribution functions. In addition, by using an MD simulation algorithm that takes into account bond dissociation within the polymer chain, the stress-strain relationship of thermosetting polymers in the crosslinked state can be predicted.