Design strategies of polyvinyl alcohol-based composites for EMI shielding: from matrix modulation to structural engineering.

Polyvinyl alcohol (PVA) is widely used as the polymer matrix in electromagnetic interference (EMI) shielding composites due to its excellent film-forming properties, abundant hydroxyl active sites and good biocompatibility. However, PVA's intrinsic hydrophilicity makes it prone to water absorption and swelling under high-humidity conditions, leading to the destabilisation of the conductive network. Furthermore, conductive nanofillers such as MXene and graphene are prone to agglomeration, whilst high-conductivity inorganic fillers can cause interfacial impedance mismatch, resulting in significant electromagnetic wave reflection losses, which limit the improvement of the overall performance of shielding materials. This paper provides a systematic review of the influence of PVA synthesis processes and its molecular chain structure on the microstructure and electrical properties of composite systems. It focuses on elucidating the latest research findings on three major categories of PVA-based shielding materials-films, aerogels/foams and hydrogels-and analyses the mechanisms of synergy between different conductive fillers and the PVA matrix, as well as the patterns of electromagnetic loss in different structures. Finally, the paper outlines future research directions for the design and engineering applications of PVA in high-performance absorptive electromagnetic shielding composites.