Laccase-Mediated Coupling of Nonpolar Chains for the Hydrophobization of Lignocellulose

We investigate the use of laccase enzymes to couple short nonpolar chains containing aromatic groups onto flax fibers and nanofibrillated cellulose (NFC) with different lignin contents. Trametes villosa, Pycnoporus cinnabarinus, and Myceliophthora thermophila were used to facilitate surface coupling and to produce materials with different levels of hydrophobicity. Heat treatment of fiber webs after lacccase-mediated coupling markedly increased the resistance to water absorption. The highest hydrophobization levels of flax fibers was achieved by coupling dodecyl 3,4,5-trihydroxybenzoate (HB-C₁₂), which yielded water contact angles (WCAs) of 80–96 degrees and water absorption times (drop tests) of ca. 73 min. The results from apparent aromatic content and FTIR analyses confirmed the laccase-mediated coupling of HB-C₁₂ onto the cellulose fibers. Ultrathin films of NFC were also used as substrates for enzyme-mediated hydrophobization with HB-C₁₂. In these cases, WCAs in the range of 87–104 degrees were achieved, depending on the conditions. Quartz crystal microgravimetry (QCM) was used to study the dynamics and the extent of the coupling process onto cellulose. The results help to better understand the mechanisms involved in laccase-mediated hydrophobization and provide a proof of a biotechnological platform for the development of value-added fiber products