Waterproofing of cellulosic materials by hydrophobization with oleic acid: Thermochemical modification and structural insights.

Cellulosic paper is naturally porous and hydrophilic due to the presence of free hydroxyl groups, which limit its effectiveness in wet environments. Consequently, the industry faces ongoing challenges in developing environmentally friendly and sustainable methods to produce hydrophobic cellulosic paper. In this study, we produced a smooth hydrophobic paper by grafting long-chain oleic acid (OA) onto the cellulose surface through an esterification reaction via a thermochemical process. The chemical composition and surface morphology of the hydrophobic paper were extensively characterized using FTIR, solid-state 13C NMR, XRD, scanning electron microscopy, and X-ray nano-tomography. This allows the best grafting conditions to be determined (200 °C for 30 min). The functionalized paper exhibited a water contact angle of 123°, with a significant reduction in surface free energy to 4.59 mJ.m-2. Dynamic vapor sorption (DVS) and full immersion tests were conducted to assess the interaction between the modified paper and water. The DVS results confirmed that the paper's ability to absorb water vapor remained unchanged, despite the strong liquid water repellency introduced by OA grafting. This demonstrates that while OA effectively repels liquid water, it does not compromise the material's capacity for vapor uptake, offering a sustainable approach for hydrophobic paper production.