Poly(itaconic acid)-functionalized kraft lignin (PIA-f-Lig) and chitosan derived fully biocomposite with enhanced water resistance, mechanical strength, wet wood adhesion, and antioxidant activity.

A fully biobased composite adhesive system exhibiting superior water resistance along with good storage stability was developed by incorporating 5-20 wt% poly(itaconic acid)-functionalized kraft lignin (PIA-f-Lig) into a chitosan matrix. The integration was enabled by nanoscale mixing, supported by hydrogen bonding between -OH groups, and ionic crosslinking between -COO⁻ groups of PIA-f-Lig and -NH₃⁺ groups of chitosan. Zeta potential measurements confirmed the ionic interactions, while FTIR, WAXS, and TGA analyses highlighted the interfacial compatibilization of the composite. Mechanical testing of films showed a noticeable increase in tensile strength, reaching 75 ± 2.5 MPa at 15 wt% PIA-f-Lig compared to 59 ± 3 MPa for pure chitosan. The incorporation of PIA-f-Lig also imparted strong radical scavenging activity, enhancing durability against oxidative degradation. Adhesion studies demonstrated that at 15 wt% PIA-f-Lig loading, dry bond strength and elongation improved by ∼91.6% and ∼62.7%, respectively, relative to pure chitosan. In contrast to pure chitosan, which lacks wet adhesion even after 3 h, the Ch/PIA-f-Lig 15% composite preserved bonding strength of approximately 1.7 ± 0.7 MPa and 2.39 ± 0.45 MPa under wet and re-dry conditions, respectively, after 6 h of immersion. The synergistic improvements in contact angle measurements, water resistance, mechanical robustness, antioxidant activity, and both dry and wet wood adhesion demonstrate that the chitosan/PIA-f-Lig composites are promising multifunctional and sustainable alternatives to petroleum-based adhesives and active packaging films.