Optimizing recycled and recyclable PET felt lightweight formulations for best acoustic insulation as poroelastic springs with minimum weight

For sustainability reasons, the automotive market is requesting 100% mono-material noise treatments, particularly for the end-of-life recycling without any part separation operation. But also, the OEMs require super light, highly performance insulating noise treatments for electric vehicles in order to extend vehicle autonomy. PP meltblown fiber felts present good mono-material characteristics with very good absorption, but generally not so good insulation properties behind an airtight barrier due to lack of stiffness. Moreover, these PP meltblown fiber felts are relatively expensive and not thermoformable, thus obliging to use them as 2D die-cut parts behind existing hard or soft trims classically. The optimization approach proposes to return to 100% thermoformable recycled and recyclable PET formulations blending unusual coarse mechanical specific fibers, in order to optimize the viscothermal exchanges, while maintaining good mechanical properties, with microfibers for best dissipation properties bonded by bi-component fibers. The insulation properties obtained as poroelastic spring behind a barrier allow a weight reduction of -50% compared to cotton felt while being 1 dB better for the Insertion Loss values (2 dB compared to a flexible foam) and perform as well as best PP meltblown fiber felts while being more competitive as well as thermoformable. It is possible to adjust the sound insulation properties, sound absorption and hardness (static compressibility) using optimal PET fibers formulations but also thanks to felt verticalization processes. These optimization levers will be illustrated in this paper.