Preparation of natural bio-based Eucommia ulmoides gum/styrene-butadiene rubber composites and the evaluation of their damping and sound absorption properties

To achieve effective sound absorption in wide frequency bands under high pressures, Eucommia ulmoides gum (EUG) as one of the natural biopolymers was incorporated into styrene-butadiene rubber (SBR) to prepare sound absorption materials. The morphology, crystalline structure, and macro-performance (damping, sound absorption, and mechanical properties) of the as-produced composites were systemically investigated. When the EUG content was less than 30 phr, the EUG was dispersed in the SBR matrix as nanocrystallites primarily existed in the β-crystal form, which is demonstrated by wide-angle X-ray diffraction (WAXD) and polarizing microscope (POM). The dynamic mechanical thermal analyzer (DMA) results expressed that EUG had two dynamic mechanical loss peaks, i.e. the glass transition peak (Peak 1, -60–40°C) and melting transition peak (Peak 2, 30–60°C). Thus, the addition of EUG improved the damping performance of the composites in high-temperature areas to some extent. Moreover, in comparison to the neat SBR, the average sound absorption coefficient of SBR/EUG (70/30) composite increased by 24.23% in the frequency range of 3–8 kHz under 2.5 MPa, which show the excellent sound absorption properties. And since the EUG nanocrystallites played the role of physical crosslingking points, the SBR/EUG (70/30) composite also had outstanding comprehensive mechanical properties. The SBR/EUG composites may be applied to underwater sound absorption materials.