Rice waste /polymer composites

In the last century, production of petrochemical-based materials and their usage have caused many adverse effects such as greenhouse effects, environmental pollution, and dangerous diseases such as asthma, lung cancer, etc. On the other hand, wood-based materials have destroyed forests which has intensified these problems. In recent decades, international community concerns have developed a new generation of materials and products. Today, bio-based materials have been replaced by petrochemical-based materials in many applications. Bio-composites, also known as “Green Composites” are designed ​​to achieve this goal. Bio-composites include one type of polymer as matrix and natural fibers and fillers as reinforcement. Because of their unique advantages such as renewability, biodegradability, low cost, low density (light weight), enhanced energy recovery, low energy consumption, availability in a variety of forms throughout the world, recyclability, greater deformability, less abrasion to equipment, safe working environment, high specific properties, abundance, high level of filler loading, absence of associated health hazards, natural fibers and fillers have been dramatically applied in production of bio-composites.

Rice husk, as a lignocellulosic material, offers many advantages such as abundant renewable source, low price, biodegradability, and high specific strength and stiffness. n the majority of rice producing countries, the husk produced from the processing of rice is either burnt or dumped as waste. Burning rice husk can produce thermal energy about 4000 kcal/kg which can substitute wood. It can also generate gases for drying processes. In recent years, rice husk has been used to generate energy, but that will release large amounts of greenhouse gases. Rice husk is an excellent insulator with thermal conductivity of not more than 0.29 W/m.k, therefore, it can be used in industrial processes such as steel foundries and as insulator for houses and refractory bricks. Rice husk has been also applied to produce mesoporous molecular sieves ,which performed as catalysts for various chemical reactions, supports for drug delivery systems, and adsorbents in waste water treatment. Rice husk ash is rich in silica (77%-96%) and can be an economically viable raw material for production of silica gels and powders.

From the data available, the quantity of rice straw produced per year in the world is probably about 570 million tons. Large amount of rice straw throughout the world is annually burnt after paddy harvest, contributing to local pollution problems. Some of rice straw used as fuel caused environmental and health concerns. It  is also used in paper production and as animal feed. The most promising annual plant waste materials for manufacturing MDF (Medium density fiberboard) are wheat and rice straw. Rice straw fiber can be considered as good reinforcement for polymers in producing green composites. Rice straw has a high thermal resistance. Low density rice straw panels have already been suggested for applications in thermal and acoustic insulation. Since rice straw has a similar composition to that of rice husk, it can be generally used in the same applications as rice husk.