Synthesis and properties of a nano-silica modified environmentally friendly polyurethane adhesive

In this study, a nano-SiO2 modified waterborne polyurethane (WPU) adhesive with remarkably low VOC content and high adhesion performance was successfully synthesized via in situ polymerization. The influence of nano-silica concentration on different properties of the aqueous-based adhesive and the casted films was carefully investigated. When the concentration of nano-SiO2 was in the range of 2.0–2.5%, the performance of the adhesive reached the optimum. When the nano-silica content is about 2.0 wt%, the appearance of the emulsion was milky white with a blue light. The T-peel and shear strength of the nano-modified adhesive showed essential improvement compared with pure-WPU adhesive. The results of shear adhesion failure temperature tests showed that the thermo-tolerance temperature of the adhesive was higher than 175 °C. The tensile strength, elongation at break and water swelling of the casted films were about 21.3 MPa, 890% and 2.7%, respectively. Finally, other properties of the water-based adhesive were investigated using FTIR, SEM, molecular weight, pH, mean particle size and solid content measurements.