An Ionomeric Renewable Thermoplastic from Lignin-Reinforced Rubber

An ionomeric, leathery thermoplastic with high mechanical strength is prepared by a new thermal processing method from a soft, melt-processable rubber. Compositions made by incorporation of equal-mass lignin, a renewable oligomeric feedstock, in an acrylonitrile-butadiene rubber often yield weak rubbers with large lignin domains (1-2 µm). The addition of zinc chloride (ZnCl₂ ) in such a composition based on sinapyl alcohol-rich lignin during a solvent-free synthesis induces a strong interfacial crosslinking between lignin and rubber phases. This compositional modification results in finely interspersed lignin domains (<100 nm) that essentially reinforce the rubbery matrix with a 10-22 °C rise in the glassy-to-rubbery transition temperature. The ion-modified polymer blends also show improved materials properties, like a 100% increase in ultimate tensile strength and an order of magnitude rise in Young's modulus. Coarse-grained molecular dynamics (MD) simulations verify the morphology and dynamics of the ionomeric material. The computed result also confirms that the ionomers have glassy characteristics.