Enzymatic surface engineering of cellulose nanofibrils for Pickering emulsions and thin films

The intrinsic hydrophilicity of cellulose nanofibrils (CNFs) restricts their application in moisture-sensitive and non-polar systems. To address this limitation, an efficient and scalable enzymatic route was developed to graft butanoic acid onto CNFs using an immobilized lipase system. Because solvent exchange critically influences the reaction environment and overall process efficiency, a systematic assessment was conducted between vacuum filtration and successive centrifugation to identify the pre-treatment that most effectively reduced water activity and supported subsequent esterification. Vacuum filtration proved superior, achieving lower water activity (1.78% vs. 4.76%) while reducing processing time by 62% and energy consumption by 64% (7.88 vs. 21.91 kWh/kg). The subsequent lipase-mediated esterification significantly enhanced surface hydrophobicity without compromising nanofibril morphology. The modification promoted a transition toward surface amphiphilicity, evidenced by an increase in water contact angle from 39.7° (unmodified CNFs) to 79.9° (modified CNFs), remaining stable over 200 s, whereas control group films showed rapid wetting (final contact angle 16.4°). In application testing, the functionalized CNFs demonstrated exceptional performance as Pickering emulsion stabilizers, maintaining a creaming index >90% after 28 days, compared to <60% for unmodified CNFs. Additionally, thin films produced from functionalized CNFs exhibited a twofold increase in porosity (62.3% vs. 28.9%) and reduced density while retaining optical translucency. These findings establish a greener, energy-efficient pathway for tailoring CNF amphiphilicity, unlocking new potential in stable emulsions and advanced barrier materials.