酚—纖維素—甲醛樹脂製作氣凝膠及碳氣凝膠之性質

The properties of aerogels and carbon aerogels prepared with phenol-cellulose-formaldehyde resin

本研究以酚及福馬林為原料，纖維素為添加物，於90°C密封環境下製作酚-纖維素-甲醛（Phenol-cellulose-formaldehyde；PCF）水凝膠（Hydrogel），將水凝膠經-20°C凍結後，利用冷凍乾燥脫水使其形成氣凝膠（Aerogels），再於700°C密封通氮氣環境下加熱形成碳氣凝膠（Carbon aerogel），探討纖維素添加量對PF樹脂（Phenol-formaldehyde resin；PF）凝膠化速度及所製作PCF氣凝膠及碳氣凝膠性質之影響。由試驗結果得知，添加纖維素粉末對PF樹脂凝膠化時間之影響不明顯，而將纖維素先溶解於尿素/氫氧化鈉/蒸餾水混合液後再與酚及福馬林混合，則PF樹脂之凝膠化時間延長。PCF氣凝膠在加熱過程因熱裂解造成的重量損失及重量損失速率大於PF氣凝膠，且隨纖維素添加比例提高，PCF氣凝膠之重量損失增加，熱抵抗性降低。PF及PCF碳氣凝膠的氮氣等溫吸脫附曲線均符合IUPAC（International Union of Pure and Applied Chemistry）分類之Type IV（a）型，其碳氣凝膠同時具備微孔及中孔結構。添加纖維素可提高碳氣凝膠之比表面積，而隨纖維素添加量增加，PCF碳氣凝膠之微孔表面積提高，但中孔的體積及表面積則減少。

In this study, phenol-cellulose-formaldehyde (PCF) hydrogels were prepared at 90°C under a sealed environment with phenol and formalin as raw materials and cellulose as an additive. The hydrogels were frozen at -20°C and dehydrated by freeze-drying to form aerogels, followed by heating at 700°C under a sealed nitrogen environment to form carbon aerogels. The effect of the amount of cellulose on the gelling speed of Phenol-formaldehyde resin (PF) and the properties of PCF aerogels and carbon aerogels was investigated. The experimental results showed that the gelation speed of PF resin was not affected by the addition of cellulose powder. However, when the cellulose was dissolved in a mixture of urea/ sodium hydroxide/distilled water and mixed with phenol and formalin, the gelation time of the PF resin was prolonged. The weight loss rate and weight loss speed of PCF aerogels due to the thermal degradation were greater than those of PF aerogel during the heating process. With the increase of cellulose addition, the weight loss of PCF aerogel increased, and the properties of thermal-resistance decreased. The nitrogen isothermal adsorption and desorption curves of PF and PCF carbon aerogels were in accordance with Type IV(a) of IUPAC (International Union of Pure and Applied Chemistry) classification, which had both microporous and mesoporous structures. The specific surface area of the carbon aerogel increased when cellulose was added. As the cellulose content increased, the micropore surface area of the PCF carbon aerogels increased, but the volume and surface area of mesopores decreased.