Simultaneously reinforcing and toughening of shape-memory epoxy resin with carboxylated lignosulfonate: Facile preparation and effect mechanism

To improve the compatibility and reactivity of lignosulfonate (LS) with epoxy oligomers, the LS was firstly functionalized with anhydride via the carboxylation reaction. The carboxylated lignosulfonate (CLS) reinforced epoxy resin with excellent mechanical and shape memory performance was prepared facilely via distributing the CLS into the combined epoxy monomers of DGEBA and PEGDGE with the aid of water, rather than using the normal organic solvents. The incorporated CLS promoted the curing reaction of epoxy resin. A typical sea-island structure was formed in the cured sample at the CLS content of 5 phr, exhibiting the highest increases in tensile strength, modulus, elongation at break and toughness by 23.8 %, 18.2 %, 217 % and 113 %, respectively, relative to neat epoxy. Interestingly, the incorporation of CLS at a proper amount led to the simultaneous strengthening and toughing effects on cured epoxy resin, which could be attributed to the rigid structure of CLS covalently introduced in the epoxy resin network and the heterogeneous structure formed in the epoxy matrix. The rigid CLS component also restrained the movement of chain segments, consequently, the mechanical stability was enhanced and the fast shape recovery rate of epoxy resin network was slowed down to some extent.