Development of silica-rich polyols from rice husk biomass

Rice (Oryza sativa) is one of the most produced and consumed cereals in the world, being the main food for more than half of the world population. It contains, by weight, about 25% of husk and 10% of bran, which represent a high volume of residues. In fact, every year about 30 million tons of solid residues (husk and pulp) are produced, most of them inadequately disposed. The rice husk ash (RHA) has proved to be an important source material for manufacturing value-added silicon carbide, silicon nitride, silicon tetrachloride, magnesium silicide, pure silicon, zeolites, fillers for rubbers and plastic composites, corrosion resistant cements, adsorbents and support of heterogeneous catalysts. The abundant presence of silica is considered an interesting feature of this lignocellulosic residue, which can be exploited in the production of silica-rich polyols. In this context, the oxypropylation of RH will enable the direct obtainment of polyols enriched with silica, which can find application as raw-materials for the synthesis of polyurethanes and other polymeric materials. The incorporation of silica in polyurethanes leads to an increase of crystallinity and polymer chain orientation. Also, the incorporation of nanofillers like silica can provide materials with higher thermal, mechanical, optical properties, and flame retardancy properties. In fact, silica nanoparticles have received much attention due to their mild synthetic preparative conditions, large surface area, smooth nanoporous surface, high adsorption capacity and large pore volume. In this context, and as a preliminary study to the topic, the oxypropylation process of RH will be presented and discussed.POCI-01-0145-FEDER-006984 (LA LSRE-LCM), funded by FEDER, through POCICOMPETE2020 and FCT; UID/AGR/00690/2013 (CIMO), financed by FEDER, through POCI-COMPETE2020; Project NORTE-01-0145-FEDER-000006, funded by NORTE2020 under PT2020, through ERDF. To the CECILIO Group for the supply of the rice husk.