Construction of an Asymmetric Structure to Enhance the Sound Absorption and Mechanical Properties of PUF/Polypropylene Honeycomb Composites

Polypropylene honeycomb (PPHC) has the advantages of being lightweight and having high strength. However, the thin-walled structure is susceptible to buckling under compression loading, and the hollow structure leads to almost no sound absorption properties. These problems seriously hinder the application of PPHC in the automotive, construction, and other fields. In this study, the filled honeycomb composite structure using a low-cost polyurethane foam (PUF) is an effective route to resolve the aforementioned problems. In order to further enhance the sound absorption and mechanical properties of the composite structure, the PUF-filled PPHC composites with an asymmetric structure were constructed by the closed-mold foaming method. In this study, the effects of different structures on acoustic behavior and the effects of the self-generated skin structure on the comprehensive properties of the composite structure were studied. The results demonstrated that the asymmetric structure overcame the constraints of the conventional symmetric structure with regard to sound absorption and mechanical properties. Compared to bare PPHC, the average sound absorption coefficient of PUF/PPHC-2 (160–6400 Hz) reached 0.63, which was improved by 530.00%. Meanwhile, PUF and bare PPHC also showed a significant synergistic effect in mechanical properties. The peak strength and energy absorption of PUF/PPHC-2 under an axial compression loading reached 2.67 MPa and 22.01 J, which were 56.96% and 93.41% higher than the sum of PPHC and PUF, respectively.