Interfacial engineering of a "soft-hard" layer interface via cardanol-mediated chemical interlocking for high-performance soundproofing multilayer PLA-based composite foams.

The inherent brittleness of polylactic acid (PLA) restricts expand its functional applications. This study innovatively constructs a sustainable multilayer composite PLA-based foam featuring a "soft-hard" layer interface. The high-toughness polypropylene carbonate (PPC) was employed into the PLA matrix to regulate macromolecular chain mobility and form new covalent bonds, successfully reducing crystallinity from 50.87% to 20.94%. The 30 wt% PPC/PLA composite foam with optimized the melt index achieved 4.52 × 106 cells/cm3 of high cell density and uniform cell structure by the supercritical carbon dioxide foaming technology. Furthermore, a "chemical interlocking" mechanism was established via covalent and hydrogen bonding between the "soft" (PPC/PLA) and "hard" (PLA) layers by employing bio-derived cardanol as an interfacial compatibilizer. This engineered interface for "soft- hard" layer interface boasts a bonding strength of 9.73 MPa, effectively broadens stress transmission pathways and promotes acoustic energy dissipation. Consequently, the multilayer composite foam exhibited a 13% enhancement in compressive strength and achieved a superior low-frequency sound transmission loss of 39 dB compared to corresponding single-layer sample. This research offers a robust theoretical reference for designing high-performance of fully biodegradable functional foams.