Sustainable acoustic insulation: perforated recycled PET foam-honeycomb sandwich structure with improved half-absorption bandwidth

Limited absorption bandwidth and lack of sustainable solutions remain key challenges in acoustic insulation building materials. While perforated metallic closed-cell foams have been studied to a limited extent, the acoustic performance of perforated recycled polyethylene terephthalate (r-PET) foam remains unexplored. This study presents the first experimental characterization of perforated r-PET foam. It demonstrates a novel multi-layer structure combining perforated r-PET foam with honeycomb sandwich having graded-microperforation facesheets. The honeycomb core is made of fully recyclable polypropylene while the facesheet is made of fiberglass/PP composite, a sustainable option compared to conventionally used brick masonry. Experimental testing of r-PET foam samples with perforation ratios of 2.6%, 3.7%, and 4.8% revealed tunable absorption peaks at 967-2100 Hz with less than one octave bandwidth. Finite element model simulations show that the complete multi-layer foam-honeycomb structure achieves a half-absorption bandwidth of 2450 Hz (1350-3800 Hz), while the honeycomb subsystem with optimized heterogeneous microperforated facesheets alone provides 1060 Hz bandwidth (990-2050 Hz). This represents a significant improvement over single-layer perforated foams while utilizing sustainable materials from the 19 million tons of annual PET waste. The design maintains thermal insulation properties through limited perforation (<5%) and offers superior manufacturability compared to hierarchical honeycomb structures. This work establishes perforated r-PET foam as a viable sustainable alternative for building acoustic applications.