Author(s): Vinicius Guedes, Waleska Hirschfeld and Ubiratan Itaborai

Abstract: Dashboard panels in compact vehicles are among the largest interior surfaces exposed to engine and road noise, yet environmental regulations increasingly push manufacturers to replace steel and virgin-polymer components with recycled-content alternatives. This research evaluated the vibro-acoustic performance of sandwich panels made from post-consumer recycled polypropylene (rPP) as a potential substitute for a conventional 0.8 mm steel dashboard backing in a B-segment hatchback. Three panel configurations were tested: the original steel sheet, a sandwich panel with virgin-PP skins and a virgin-PP honeycomb core, and an equivalent sandwich panel with 100% post-consumer rPP skins and core. Each panel was bonded to a 12 mm melamine acoustic-foam backing layer. Sound transmission loss (STL) was measured in a coupled reverberation-anechoic room facility across the 125 to 4,000 Hz one-third-octave band range, and surface vibration velocity was recorded by scanning laser vibrometry at 143 grid points. The steel baseline achieved an STC rating of 28 and a mass-per-unit-area of 6.27 kg/m². The virgin-PP sandwich reached STC 26 at 3.84 kg/m² a 38.8% mass saving with a 2 dB STC reduction. The rPP sandwich scored STC 25 at 3.91 kg/m², losing one additional STC point relative to the virgin panel. The STL deficit of the rPP panel relative to steel was largest at low frequencies (3.3 dB at 125 Hz) and narrowed to 1.4 dB at 4,000 Hz, where the foam backing's absorption compensated for the lower surface density. Vibration velocity maps showed that the rPP panel's damping loss factor (0.034 at 1 kHz) sat 8.1% below the virgin panel's value (0.037), which is consistent with the slightly coarser crystalline morphology of the recycled resin. A cost analysis found that rPP feedstock was 34% cheaper per kilogram than virgin PP, giving the rPP sandwich a 22.7% lower material cost despite the marginally thicker core needed to match stiffness. These results indicate that rPP sandwich panels offer a viable mass-and-cost-saving route for dashboard noise attenuation, provided that the 1 to 3 dB low-frequency STL penalty is acceptable within the vehicle's overall acoustic package.

DOI: https://www.doi.org/10.22271/27078205.2026.v7.i2a.82

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