Upcycling Waste Bamboo Residues into Mechanically Enhanced TOCNF/Quaternized Cellulose Composite Films

Steam explosion processing of bamboo generates substantial quantities of granular residues that are often discarded, leading to resource waste and potential secondary pollution. In this study, a sustainable upcycling strategy was developed to convert these residues into mechanically reinforced cellulose-based composite films. Cellulose isolated from steam-exploded bamboo residues was separately converted into negatively charged TEMPO-oxidized cellulose nanofibrils (TOCNFs) and positively charged quaternized cellulose (QCell), with the latter prepared through modification using 2,3-epoxypropyltrimethylammonium chloride. The oppositely charged cellulose components were subsequently assembled into TOCNF/QCell composite films through electrostatic interactions. At an optimal TOCNF-to-QCell mass ratio of 3:1, the resulting composite film exhibited a tensile strength of 134 MPa, representing an improvement of 23.09% compared with that of the corresponding unmodified TOCNF1/Cell1 film. SEM observations revealed that the enhanced interfacial interactions facilitated the formation of a dense and compact network structure, thereby contributing to the improved mechanical performance. Although quaternization exerted little influence on the equilibrium moisture uptake of the films, it markedly reduced moisture sorption–desorption hysteresis, indicating enhanced structural reversibility during humidity cycling without substantially altering their overall hydrophilicity. FTIR and XPS analyses confirmed the successful chemical modification of cellulose, while thermogravimetric analysis demonstrated that the thermal stability of the cellulose-based films was largely preserved. Overall, these findings provide a sustainable and effective route for valorizing steam-exploded bamboo residues into high-performance cellulose-based materials.