Green aerogels from rice straw for thermal, acoustic insulation and oil spill cleaning applications

For the first time, a versatile, novel and environmentally-friendly aerogel was successfully fabricated from rice straw – one of the most abundant agricultural waste in South-east Asia. The final product is able to be applied in a wide range of applications including oil-spill cleaning, thermal insulation and acoustic absorption. The fabrication process is simple, cost-efficient and totally green without disposal of harmful by-products into the environment. Specifically, rice straw fibers were dispersed along with reinforcers (PVA or cationic starch) followed by freeze-drying to form shaped aerogels. Those samples were then turned into hydrophobic by coating with MTMS using chemical vapor deposition (CVD) method to produce aerogels with exceptional water repellency (WCA exceeding 1500). The morphology, pore structure and physical properties of the aerogels were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), thermal conductivity, water contact angle (WCA) measurements, oil adsorption and sound absorption measurements. The aerogel samples exhibit extremely low densities (0.05–0.06 g/cm3), high porosities (~97%), excellent heat reduction properties with low thermal conductivities (0.034–0.036 W/m.K), good mechanical properties (Young modulus up to 47 kPa) and oil adsorption efficiency proven with the capacity up to 13 g/g. In addition, huge potential of rice straw aerogels in sound absorption applications is also demonstrated with high noise reduction coefficient (up to 0.6). The samples still retain their thermal insulation, sound insulation capability and hydrophobicity after 2-month exposure in ambient environment.