A comprehensive review on hydrophobicity in cellulosic natural fibers: Trends, techniques, and future directions

Cellulosic natural fibers have gained significant attention as sustainable and biodegradable alternatives for reinforcing polymer composites and producing environmentally friendly materials. However, their intrinsic hydrophilicity, originating from the abundant hydroxyl groups on the cellulose backbone, poses critical limitations in applications that require water resistance, dimensional stability, and strong interfacial bonding with hydrophobic matrices. This review explores the origin of hydrophilicity in cellulosic fibers and its impact on various applications, including packaging, textiles, and composite reinforcement. Comprehensive strategies to enhance fiber hydrophobicity are examined, including chemical modifications, physical treatments, and surface engineering techniques. Key characterization methods such as contact angle measurement, Fourier transform infrared, scanning electron microscopy, X-ray diffraction, and thermal analyses are discussed to evaluate the effectiveness of hydrophobic modification. Furthermore, the review highlights advanced applications of hydrophobically modified fibers in water-repellent textiles, filtration materials, and moisture-resistant biocomposites. Finally, current challenges such as environmental concerns, mechanical property trade-offs, and scalability are outlined, along with future research directions aimed at developing multifunctional, durable, and eco-friendly fiber systems.