Chitosan-Based Functional Films and Nanocomposites for Sustainable Electronics: A Structure–Property–Function Systematic Review

Chitosan-based films and nanocomposites have attracted growing attention as renewable, biodegradable, and chemically adaptable materials for sustainable electronics. This systematic review synthesizes evidence on chitosan-containing functional films, membranes, polymer electrolytes, dielectric substrates, optoelectronic nanocomposites, electrochemical sensors, impedance sensors, and smart-device interfaces. This review adopts a structure–property–function perspective, examining molecular interactions, crystallinity, amorphous fraction, morphology, filler dispersion, processing routes, and interfacial architecture in relation to optical, electrical, dielectric, electrochemical, and sensing performance. The literature was identified using Scopus-oriented Boolean searches combining chitosan/chitin terms with thin-film or membrane descriptors, electronic-function terms, and structure–property terminology. Relevant studies were grouped into four themes: structural engineering and processing, dielectric/electrical/impedance properties, optoelectronic and band-gap engineering, and electrochemical/impedance-sensing applications. The synthesis shows that chitosan becomes electronically functional when its semi-crystalline, hydrogen-bonded matrix is modified through salt doping, plasticization, blending, conductive polymers, carbon materials, metal oxides, metal–organic frameworks, or noble metal nanoparticles. Reported advances include ionic conductivities up to 10−3 S/cm, improved dielectric behavior, band-gap reduction, and low detection limits. However, inconsistent reporting of material source, molecular weight, degree of deacetylation, film thickness, humidity, stability, and sustainability metrics limits comparability.