Structure−Adhesion Relationship in Citric Acid-Crosslinked Cellulose Based Adhesives

Abstract

Understanding how molecular architecture and rheological properties govern crosslinking behavior of cellulose derivatives is essential for designing high-performance biobased adhesive systems. This study investigates citric acid (CA)-mediated crosslinking in carboxymethyl cellulose (CMC) and hydroxypropyl methyl cellulose (HPMC) to elucidate the molecular mechanisms governing bioadhesive performance. High- and low-viscosity grades of both polymers were examined under controlled viscosity and concentration conditions to decouple the effects of molecular architecture from flow behavior. FTIR and XPS results supported curing-induced spectral and thermal changes consistent with possible ester-type interactions and network formation. DSC further showed broad endothermic transitions associated with curing-related thermal processes, while TGA results indicated enhanced thermal stability and higher char yields in all CA-modified samples, particularly for H-CMC, reflecting the formation of thermally stable network-like structures. Lap shear adhesion tests revealed an optimal viscosity window (∼103−104 mPa·s), within which high-viscosity polymers exhibited superior adhesion, achieving shear strengths of ∼4.5−5 MPa, likely due to their greater chain length, higher hydroxyl density, and stronger intermolecular entanglement. Excessive viscosity, however, reduced wood penetration and interfacial bonding, thus reducing the bonding strength. Overall, these results offer new insights into the design of fully biobased, formaldehyde-free wood adhesives.