Revisiting cellulosic fibrils in papermaking: from ancient papermaking principles to room-temperature engineering of "plastic-like" paper via in-situ fibril-derived additives.

Papermaking, one of ancient China's greatest innovations, shaped human civilization through the creation of true paper, widely attributed to Cai Lun during the Eastern Han Dynasty. A defining feature of this invention was the formation of fibrillated microstructures during fibre processing, which promoted fibre bonding and sheet formation. Inspired by this principle, the present work revisits the structural role of cellulosic fibrils and explores their potential as functional building blocks for materials innovation. By enhancing fibrillation through controlled pulp refining, a straightforward room-temperature strategy was developed to produce "plastic-like" paper, herein referring to cellulosic paper combining high wet strength, flexibility, and liquid barrier performance while retaining its fibrous structure. During treatment with a non-derivatizing zinc chloride-based solvent system, accessible fibrillated structures are proposed to undergo partial dissolution and subsequently regenerate within the fibre network, forming in-situ fibril-derived additives. The resulting fibril-derived material acts as an in-situ binding phase within the paper structure, bridging adjacent fibres and filling interfibre voids, thereby consolidating the network while preserving the overall fibrous architecture. As a result, the treated paper exhibits plastic-like high wet strength, improved liquid barrier performance, and antibacterial activity associated with residual zinc species. Because fibrillated microstructures are widely present in refined pulps, the approach also shows potential for application to different papermaking fibres. Rooted in the principles of papermaking wet-end chemistry and chemical additives, this work reinterprets cellulosic fibrils as in-situ functional additives and highlights new opportunities for designing multifunctional sustainable materials.