Epoxy–lignin polyblends: Correlation between polymer interaction and curing temperature

Abstract A bisphenol A–polyamine hardener based epoxy adhesive (EP) was modified by polyblending with Kraft lignin (L). EP–L polyblends with an L content up to 40% by weight were cured at room temperature or above their glass transition temperature (T g ). Previous data have shown that the thermal and viscoelastic properties, as well as adhesive performance of the EP–L polyblends, are influenced by the curing temperature and by the L content in thermally cured polyblends. A reasonable explanation for the different behavior of EP–L polyblends as function of the curing temperature and their L content could be the enhanced degree of bonding between L and the EP network taking place at elevated temperature. This bonding was specifically considered to take place between L and possible unreacted amine groups of the hardener. Characterization of the EP–L polyblends was performed to search for evidence of irreversible chemical bonding between L and the EP network in thermally cured EP–L polyblends. FTIR studies, L extractibility from the crosslinked, polyblends, and quantitative data concerning the reactivity of L toward the polyamine hardener are discussed.