Castor oil–multiwalled carbon nanotubes based waterborne nanocomposite polyurethane emulsion adhesive

Numerous studies have reported the polymerization and stabilization of castor oil (CO) with isocyanates for the synthesis of polyurethanes (PUs) intended for adhesive applications. In this work, we propose a novel strategy for stabilizing PU emulsions, employing modified styrene-co-maleic anhydride (SMA) copolymers as surfactants, in combination with carbon nanotubes (CNTs). We synthesized emulsified PU nanocomposites using isophorone diisocyanate and 4,4′-dicyclohexylmethane diisocyanate (H12MDI), which were reacted with CO as the polyol source. Stabilization of the PU adhesives was achieved by emulsifying the resulting PUs in the presence of a modified SMA copolymer, functionalized via imidization reaction with tallow amine with two different styrene and maleic anhydride ratios, along with water and functionalized CNTs. The resulting material is a stable, flowable PU emulsion capable of effectively bonding wood substrates. Lap shear tests were performed to evaluate the adhesive bonding strength showing values of 1.2 MPa. The presence of the SMA-based plays a crucial role in emulsion stability, as it reduces the oil–water interfacial tension by approximately 40%. The combination of CNTs and SMA copolymers resulted in emulsions that remained stable for over ten months after preparation exhibiting droplet sizes smaller than 2 µm in diameter, maintaining their performance as adhesive materials.