Ultrastrong, closed-loop recyclable bio-based composite foams with hierarchical plant fibers

The global demand for sustainable materials with structural and functional performance drives research into bio-based and recyclable polymeric foams. Among these, poly(lactic acid) (PLA) has emerged as a promising thermoplastic matrix because of its biodegradability and moderate mechanical and thermal properties; however, its high production costs and limited strength still restrict its use in industrial applications. To address this limitation, a green methodology for recyclable hierarchical biocomposite foams is presented, incorporating the dual-scale natural reinforcements jute fiber (JF) and microfibrillated cellulose (MFC) into a PLA matrix via compression molding and a particulate leaching process. Particulate leaching with sieved NaCl templates a semi-open-cell architecture with precise morphological control, while room-temperature processing preserves fiber geometry and avoids thermal degradation. This combination of controlled cellular architecture and dual-scale fiber reinforcement enables concurrent tuning of airflow resistivity, energy dissipation, and mechanical stiffness. Rheological optimization and compositional tuning identify an optimal JF:MFC ratio of 1:2 that yields a 2.15-fold increase in stress at 40% strain and a 2.06-fold increase in specific energy absorption relative to pure PLA foam. Acoustic measurements show a 1.38-fold increase in average absorption in the mid-frequency range. The enhancements stem from a hierarchical interfiber network that promotes efficient stress transfer and enhances viscoelastic damping through synergistic interactions between JF and MFC. Recyclability tests show retention of performance, with 97.6% of the stress at 40% strain and 94.4% of the sound absorption retained after reprocessing. The approach provides a viable, environmentally conscious alternative to petroleum-derived foams for lightweight structural and poroacoustic applications.