Sustainable recycling of polymer nanocomposites: Challenges and innovations

Polymer nanocomposites (PNCs) offer lightweight materials with enhanced mechanical, thermal, barrier, and functional properties, but their complex architectures pose significant challenges for sustainable end-of-life (EoL) management. This review provides a critical and comparative analysis of current recycling strategies for PNCs incorporating inorganic, carbon-based, in-situ generated polymeric, and hierarchically structured nanofillers. Mechanical, chemical, solvent-based, and emerging thermal approaches are systematically evaluated with respect to property retention, morphological stability, and nanofiller behaviour during repeated processing cycles. Beyond summarizing existing methods, this review identifies key structure–recyclability relationships that govern performance loss, filler migration, and phase instability, highlighting how nanofiller chemistry, dimensionality, and interfacial interactions dictate recyclability outcomes. Particular emphasis is placed on all-polymer nanocomposites (APNCs), which are critically assessed as a promising pathway toward closed-loop recycling due to their intrinsic chemical compatibility, while also addressing unresolved challenges related to fibrillar morphology preservation during reprocessing. By comparing recycling efficiencies across nanofiller classes and processing routes, this review delineates design principles for recyclable nanocomposites and identifies gaps that limit industrial implementation. The analysis demonstrates that optimized nanofiller loading, compatibilization strategies, and controlled processing histories can significantly mitigate degradation and enable functional reuse. Overall, the review provides actionable insights for designing next-generation PNCs aligned with circular economy principles rather than treating recyclability as an afterthought.