The method of positron annihilation lifetime (PAL) spectroscopy was first employed to study atomic-deficient free-volume structure of nanocomposites prepared by high-energy mechanical milling of glassy g-As2Se3 in water solution of polyvinylpyrrolidone (PVP). The formalism of x3-x2-CDA (coupling decomposition algorithm) describing conversion of bound positron-electron (positronium Ps) states into positron traps was applied to identify free-volume elements in pelletized PVP-capped g-As2Se3 nanocomposite in respect to parent dry-milled g-As2Se3. Under wet milling, the internanoparticle Ps-decaying sites in preferential PVP environment were shown to replace free-volume positron traps in dry-milled g-As2Se3 with defect-specific positron lifetime of 0.352ns, corresponding to diatomic/triatomic vacancies in g-As-Se matrix. (C) 2019 Society of Plastics Engineers.