Mechanical Toughening of Brittle Acrylate Networks with Lignin-Derivable, Semi-Interpenetrating Polymer Networks

Lignin-derivable acrylate thermosets are promising renewable materials, yet their rigid architectures limit stress dissipation and lead to brittle failure. Herein, we demonstrate a toughening strategy using semi-interpenetrating polymer networks (SIPNs) that leverages methoxy substituents in lignin-derivable precursors to promote interphase interaction and energy dissipation. A rigid acrylate thermoset composed of vanillyl alcohol diacrylate (VDA) and n-butyl acrylate (BA) was interpenetrated with a thermoplastic, bisguaiacol F-based non-isocyanate polyurethane (BGF-NIPU) to form SIPNs containing 30-70 wt % cross-linked phase. Mechanical, fractography, and morphological analyses were correlated to elucidate the composition-dependent toughening behavior. The SIPN containing 30 wt % cross-linked phase exhibited ∼90× toughness enhancement compared to the single acrylate network, attributed to improved elongation-at-break and the formation of a continuous linear phase. Comparison with a methoxy-deficient control highlights the role of methoxy groups in enhancing interphase interactions. This work showcases an effective approach for toughening brittle, biobased thermosets through a multicomponent network approach.