酚－木質素－甲醛樹脂製作氣凝膠及碳氣凝膠之性質

本研究以酚和福馬林為原料，碳酸鈉為催化劑，木質素為添加物，設定甲醛/酚莫耳比3/1、碳酸鈉/酚莫耳比1/3、木質素添加量為樹脂固形分重0～30%，反應物濃度20%，並在90℃密封環境下凝膠化製作酚-木質素-甲醛樹脂（phenol-lignin-formaldehyde resin; PLF）水凝膠（hydrogel）。隨後將經-20℃凍結之水凝膠利用冷凍乾燥脫水形成氣凝膠（aerogels），再以700℃加熱形成碳氣凝膠（carbon aerogels），探討木質素添加量對所製作水凝膠、氣凝膠及碳氣凝膠性質之影響。由試驗結果得知，木質素添加量15%以下不影響其凝膠化速度，添加量15%以上則隨木質素比例增加，凝膠化時間延長，並出現相分離現象。孔隙分析顯示氣凝膠之內部孔隙結構以中孔為主，經碳化處理所得碳氣凝膠則同時具備微孔與中孔，且其比表面積大幅增加，平均孔隙直徑則明顯減小，其氮氣等溫吸脫附曲線屬於IUPAC（International Union of Pure and Applied Chemistry）分類之Type IV(a)型。不同木質素添加量比較，以添加量2%之PLF-2碳氣凝膠有最大的比表面積、微孔體積及微孔表面積。 In this study, phenol and formalin were used as raw materials, sodium carbonate and lignin were used as the catalyst and additive, respectively. The phenol-lignin-formaldehyde resin (PLF) hydrogel was prepared with the formaldehyde/phenol molar ratio of 3/1, sodium carbonate/phenol molar ratio of 1/3, 0~30% of lignin (based on the weight of the solid content of resin), and gelled at 90℃ under a sealed environment. After the hydrogel was froze at -20℃, it was dehydrated by freeze-drying to form an aerogel, followed by heating at 700℃ to form a carbon aerogel. The properties of hydrogel, aerogel and carbon aerogel affected by the amount of lignin added was investigated. The results showed that the addition of lignin below 15% did not affect the gelation rate. However, when more than 15% of lignin were added, the gelation time prolonged with the amount of lignin increased and phase separation occured. Porosity analysis showed that the internal pore structure of aerogel was dominated by mesopores. After carbonization, the carbon aerogel had both micropores and mesopores, the specific surface area was greatly increased, whereas the average pore diameter was significantly reduced. Thire nitrogen isothermal adsorption desorption curves fit the Type IV (a) of the IUPAC (International Union of Pure and Applied Chemistry) classification. Compared with the addition of lignin, the PLF-2 carbon aerogel with 2% of lignin had the largest specific surface area, micropore volume and micropore surface area.