From Cellulose to Nanocellulose: Functionalization Strategies and Applications in Biomedicine, Ecology, and Energy

The growing demand for sustainable and high-performance materials has positioned cellulose as a key biopolymer for next-generation functional systems. Beyond its traditional use, cellulose undergoes a qualitative transformation at the nanoscale, where increased surface area, interfacial dominance, and tunable chemistry enable functions unattainable in bulk form. This review provides a critical and integrative analysis of functionalization strategies governing the transition from structural modification to application-specific performance in cellulose and nanocellulose-based materials. A unified structure-property-function-process (SPFP) framework is introduced to systematically connect modification approaches with resulting structural features, physicochemical properties, and functional outcomes. Chemical, physical, and surface/interface modification strategies are comparatively evaluated with respect to their efficiency, scalability, and environmental trade-offs. Rather than cataloguing methods, the review emphasizes cross-domain synthesis and identifies key limitations, including high energy demand, reagent consumption, structural instability, and challenges in large-scale implementation. Particular attention is given to applications in biomedicine, environmental remediation, and energy technologies, where performance is governed by surface reactivity, accessibility, and hierarchical organization. The analysis highlights that no single modification strategy is universally optimal, and that effective material design requires balancing performance, sustainability, and process feasibility. By integrating conceptual frameworks, comparative analysis, and emerging design principles, this review provides a forward-looking perspective on the development of cellulose-based functional materials, supporting their transition from laboratory-scale demonstrations to application-ready technologies.