Development of macroporous silicone rubber composites by internal emulsion templating for acoustic applications

This work reports synthesis of macroporous silicone rubber (MPSR) composites using room temperature vulcanizable liquid silicone rubber (LSR), comparatively non-hazardous pore-generator (oil-in-water emulsion) and hexagonal boron nitride (h-BN). Besides, effects of pore generators and filler incorporation (~0.1–0.3 wt. % hexagonal boron nitride, h-BN) on acoustic properties (sound absorption coefficient and transmission loss) have been investigated. Microstructural study revealed that pore size distribution, porosity content and fraction of interconnected pores in MPSR samples were significantly affected by addition of pore generators and h-BN filler, which finally influenced their acoustic properties. MPSR samples synthesized with optimal content of pore generators displayed an average sound absorption coefficient (SAC) of ∼0.41 and transmission loss (TL) of 5 − 42 dB in the frequency range of 63–6300 Hz. Interestingly, incorporation of only 0.2 wt.% h-BN in this optimized MPSR sample further improved the sound-absorbing capability (average SAC ~0.44) at a frequency higher than 1000 Hz and transmission loss over the entire frequency range (> 100 Hz). This was ascribed to the decrease in pore size, increase in interconnected pores and possibility of enhanced mechanical energy dissipation at polymer matrix-h-BN interface by interfacial sliding.