Production of Carbon Foams from Rice Husk

The production of a material with rigid, multifunctional three-dimensional porous structure at a low cost is still challenging to date. In this work, a light and rigid carbon foam was prepared using rice husk as the basic element through a simple fermentation process followed by carbonization. For the fermentation process, the amount of biological yeast (7.5 g for the carbon foam CA-1P and 5 g for the carbon foam CA-2P) was used to evaluate its influence on the morphology of the foams. In order to prove that the heat treatment made in the foam alters the hydrophilic character of the rice husk foam, a chemical treatment with steam deposition was carried out. The foams were characterized by the following analyzes: apparent density, micrograph, thermogravimetry, contact angle, water sorption capacity and thermal conductivity. Visually, the CA-1P foams presented a structure with larger pores due to the greater amount of yeast used in its formulation. The heat treatment of rice potato foams proved to be as efficient as the chemical treatment for water contact angle above 90º, proving the ability of the foams to repel water/moisture. The thermal conductivity of the foams (0.029 and 0.026 W m-1 K-1 for CA-1P and CA-2P, respectively) was close to the conductivity of polyurethane foams (0.032 W m-1 K-1). Thus, the method used in the production of the carbon foams produced from the rice husk proved to be effective. In addition, the foams produced have the potential to be used for thermal insulation.

低成本制备兼具刚性与多功能性的三维多孔结构材料，至今仍是一项挑战性课题。本研究以稻壳为基础原料，通过简易发酵工艺结合碳化过程，成功制备出轻质刚性碳泡沫（carbon foam）。在发酵工艺中，通过调控生物酵母（biological yeast）的添加量（制备碳泡沫CA-1P时为7.5 g，制备CA-2P时为5 g），考察其对泡沫形貌的影响。为验证热处理可改变稻壳基泡沫的亲水特性，本研究采用蒸汽沉积（steam deposition）法开展化学改性处理。通过表观密度、显微形貌、热重分析（thermogravimetry）、接触角（contact angle）、吸水性能及导热系数等测试手段对所制备泡沫进行表征。视觉观察结果显示，由于CA-1P配方中酵母添加量更高，其泡沫孔隙尺寸更大。研究表明，稻壳基泡沫经热处理后，水接触角可达90°以上，疏水性能与化学改性处理相当，证明该泡沫具备拒水拒湿的能力。所制备泡沫的导热系数分别为0.029 W·m⁻¹·K⁻¹（CA-1P）与0.026 W·m⁻¹·K⁻¹（CA-2P），接近聚氨酯泡沫（polyurethane foam）的导热系数（0.032 W·m⁻¹·K⁻¹）。综上，本研究所采用的稻壳基碳泡沫制备方法切实有效。此外，所制备的泡沫具备用作隔热材料的应用潜力。