Toward novel materials by carbonization of cellulosic raw materials

从结晶度损失和产碳率两方面重新考察了纤维素热解的基本特征。纤维素微晶在320℃以上的惰性气氛中降解。所得碳的质量产率低至纯纤维素理论值的1/3-1/4。通过向纤维素中添加少量硫酸，提高了碳收率，达到理论值的80%左右。纤维素衍生化对周期性酸氧化纤维素的产率也有显著的提高作用。通过与胺的反应，双醛纤维素进一步衍生化，导致材料在高水平衍生化时发生异常爆炸性分解。从细菌、被囊动物或藻类中提取的高结晶纤维素样品在1600C以上进行石墨化，所得材料的结晶度与起始材料的结晶度一致。石墨化材料中含有明显来源于纤维素微纤维的微纤维晶体。这种新形式的石墨，碳纳米棒，可能会导致新的应用。因此，通过对纤维素进行冷冻干燥处理、包埋在其他材料中以及包覆微原纤维，努力以更高的产量制备这种材料。镀银有一定效果，但收率没有明显提高。聚乙烯醇是一种具有纤维素结构的聚合物，研究了它在硫酸的作用下的热解碳化反应。与纯材料不同，经过硫酸处理的PVA在250℃左右失重，其失重程度相当于化学计量脱水。所得到的材料被认为含有聚乙炔类结构，并可能导致一种新的导电聚合物。

Basic features of pyrolysis of cellulose were reexamined in terms of loss of crystallinity and carbon yield. Cellulose crystallite was found to degrade at above 320C in inert atmosphere. Mass yield of resulting carbon was as low as 1/3-1/4 of theoritical value for pure cellulose. Imprivement of carbon yield was achieved by addition of small amounts of sulfuric acid to cellulose, the yield reaching about 80% of theoritical value. Derivatization of cellulose also had remarkable effect in increasing the yield, as observed for periodic acid-oxidized cellulose. Further derivatization of dialdehyde cellulose through reactions with amines caused anomalous explosive decomposition of the material at high level of derivatization.Highly crystalline cellulose samples from bacteria, tunicate or algae were graphitized at above 1600C, and crystallinity of the resultant material was in accord with that of starting material. The graphitized material contained microfibrillar crystallite apparently derived from the cellulose microfibril. This new form of graphite, carbon nanorod, may lead to novel applications. Hence efforts were made for preparing this material in higher yields, through processing of cellulose by freeze drying, embedding in other materials, and coating of microfibrils. Coating with silver showed some effect, but significant improvement in yield has not been achieved.As a polymer having cellulose-like structure, poly (vinyl alcohol) was examined for its pyrolytic carbonization with addition fo sulfuric acid. Unlike pure material, PVA with sulfuric acid showed weight loss at around 250C, giving loss levels that correspond to stoichiometric dehydration. The resulting material is considered to contain polyacetylene-like structure and may lead to a novel electroconductive polymer.