Unexpected role of amphiphilic lignosulfonate to improve the storage stability of urea formaldehyde resin and its application as adhesives.

As the second-largest natural polymer, the utilization of lignin for practical applications has attracted increasing attention. In this study, lignosulfonate was employed to enhance the storage stability of urea formaldehyde (UF) resins. Cryo-scanning electron microscopy was firstly used to observe the influence of lignosulfonate addition on the colloidal morphology of UF resin. Moreover, adding lignosulfonate at different stages during the UF resins synthesis was also investigated to reveal its effect on storage stability. The potential interaction between lignosulfonate and UF resins was then analyzed via FT-IR, 13C CPMAS NMR, and zeta potential. It has been observed that lignosulfonate could increase the electrostatic repulsion of UF resins to avoid aging. No chemical reaction between UF resins and lignosulfonate was observed. After the elucidation of potential interaction, the effect of lignosulfonate on the curing process, thermal stability and adhesive performance of UF resins was systematically evaluated. Finally, as adhesives to fabricate eucalyptus plywood, the shear strength and formaldehyde release of UF resins with 20% addition of lignosulfonate could reach 0.88 MPa and 0.12 mg/L, respectively. Due to the excellent performance, low cost and wide availability of lignosulfonate, it might be industrially used as a stabilizer in the UF resins production.