Recycled Nitrocellulose-Treated Fe ₃ O ₄ for Microwave Absorption

Industrially sole-phase magnetic powders for microwave absorption (MA) purposes rely mainly on magnetic loss, restricting better impedance matching. Concurrently, the massive disposal of single-use industrial products, such as medical diagnostics, presents a pressing environmental challenge. Herein, we introduce a cross-industrial strategy to transform waste nitrocellulose (NC) membranes from medical lateral flow assay (LFA) strips into functional MA materials via dimethyl sulfoxide (DMSO)-induced structural reconstruction. The dissolved NC transforms from a porous network into a condensed binding matrix, enabling the fabrication of two distinct product forms: (1) flexible, transparent, and magnetic Fe3O4/NC hybrid films, and (2) Fe3O4 aggregates bonded by NC. DMSO concentration was revealed as a factor regulating the microstructure and MA behavior of the NC-treated Fe3O4 aggregates. With improved impedance matching, the NC-treated Fe3O4 aggregates show good MA properties, e.g., a minimum reflection loss (RL) of −38.94 dB at 11.57 GHz (70 wt % filler/paraffin), −42.31 dB at 15.55 GHz (60 wt % filler/paraffin), and −47.02 dB at 6.54 GHz (50 wt % filler/paraffin). This work establishes a scalable strategy for designing MA materials from discarded medical resources.