Sulfanilic acid-functionalized kraft lignin as a multifunctional additive for poly(vinyl acetate)-based wood adhesives and composite film applications

Many domestic and industrial applications, particularly wood adhesives and polymer composite films, continue to depend on petroleum-derived additives, which pose environmental and health risks. To overcome these challenges, the present study introduces a novel formulation using sulfanilic acid-functionalized kraft lignin (SA-f-Lig) as a multifunctional bio-additive in poly(vinyl acetate) (PVAc). PVAc/SA-f-Lig composite resins were prepared by incorporating SA-f-Lig into an aqueous PVAc emulsion and cured by solvent evaporation to produce composite films. FTIR analysis suggested the presence of hydrogen-bonding interactions between SA-f-Lig and PVAc, which likely contributed to the observed improvements in the composite properties. The tensile strength of pristine PVAc increased from 8.9 ± 2.3 MPa to 21.92 ± 4 MPa for PVAc containing 3.5 wt% SA-f-Lig, corresponding to an approximately 146% increase. The thermal stability and antioxidant activity of PVAc were significantly improved as the SA-f-Lig content increased. Furthermore, the PVAc/SA-f-Lig (5 wt%) resin exhibited about a 125% increase in dry lap shear strength compared to pure PVAc. The developed PVAc/SA-f-Lig composite resins exhibited significantly improved mechanical strength, thermal stability, antioxidant activity, and wood adhesive performance in dry environments, highlighting their potential as multifunctional and sustainable alternatives to conventional synthetic adhesive systems.