【作者】 杨雯；

【导师】 何飞；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2014， 硕士

【摘要】 SiO2气凝胶是一种具有低热导率的隔热材料，但是其纤细的网络多孔结构导致材料具有较高脆性，严重制约该材料实际应用。因此，对SiO2气凝胶进行有效的柔韧化具有重要的研究与实用价值。作为第三代气凝胶材料，纤维素气凝胶在继承传统SiO2气凝胶、有机聚合物气凝胶性能的基础上，又融入了自身很多优异的性能。针对此问题，本论文综合考虑了纤维素气凝胶和SiO2气凝胶的特点，以纤维素气凝胶为模板，原位生成纤维素-SiO2有机—无机杂化复合气凝胶，并对其组织结构与力学行为进行表征和分析。以碱解纤维素为模板，分别以SiO2水溶胶和醇溶胶为再生液，采用冷冻干燥工艺方法，原位合成了纤维素-SiO2复合气凝胶。研究了纤维素含量、再生时间、再生液类型以及干燥条件等对气凝胶复合过程的影响。结果显示，纤维素-SiO2复合气凝胶具有多孔特征。当纤维素含量为3.2%时，复合气凝胶呈现较高的孔隙率。随着纤维素含量的增加，复合气凝胶中可结合更多的SiO2凝胶颗粒。无机SiO2颗粒引入可提高纤维素材料的热稳定性。当再生时间达到6h时，纤维素构建的交联网络骨架、表面网络孔结构最完善。SiO2醇溶胶作为再生液以及冷冻干燥工艺方法更易获得多孔结构的纤维素-SiO2复合气凝胶。制得的纤维素-SiO2复合气凝胶同时具有I型纤维素和II型纤维素的晶向特征。参与复合的非晶态SiO2凝胶颗粒随着再生时间的延长而增多，并且与纤维素之间的键合作用随再生时间的延长而加强。纤维素再生时，在纤维素分子内和分子间的氢键作用下，使无规则的微晶纤维素平行排列并聚合，逐渐形成片层状多孔结构。SiO2凝胶上的Si–OH基团实现了与纤维素表面–OH的脱水缩合作用，从而实现SiO2与纤维素间的有机—无机杂化。复合气凝胶具有更高的比表面积和更小的平均孔径与最可几孔径，这与介孔的SiO2凝胶颗粒填充到纤维素凝胶中有关。力学行为表征结果显示，SiO2凝胶颗粒的引入使纤维素-SiO2复合气凝胶的力学特性得以提高。短时再生条件下，复合气凝胶的强度主要源于微晶纤维素构成的骨架结构，包裹于纤维素表面的SiO2凝胶颗粒以及颗粒间的聚合使复合气凝胶的强度高于纯纤维素气凝胶。长时再生条件下，严重团聚的SiO2凝胶颗粒成为材料脆化的主要来源，使复合气凝胶的力学行为下降。更多还原

【Abstract】 SiO2aerogels are a kind of low thermal conductivity functional materials. Theirslight porous network structures, however, result in high brittleness, which is aserious restriction for the practical applications. Therefore, it is very valuable andsignificative to realize the flexibility of aerogels. As new third generation materials,cellulose aerogels possess many excellent performances besides traditional featuresof aerogels. In this paper, based on the features of silica and cellulose aerogels, thecellulose/silica aerogels were in-situ synthesized and the structural characteristicsand mechanical behavior were analyzed.The cellulose/silica aerogels were in-situ synthesized by means of freeze-dryingmethod. In the preparative process, the original celluloses were dissolved in alkalisolution. The silica aqueous solution and alcoholic solution were chosen asregenerative coagulants, respectively. The influences of the cellulose content,regenerative time, the types of coagulants and drying methods were discussed. Theresults show that the cellulose/silica aerogels possess porous characteristics. Whenthe content of the cellulose is3.2%, the cellulose/silica aerogels present highporosity. With the increase of the cellulose contents, more silica particles wereintroduced into the cellulose/silica aerogels. The addition of inorganic silicaparticles can improve the thermal stability of cellulose materials. The cellulosesrender the optimal crosslink ing network structures when the regenerative time is6h.It is an easier process to obtain the cellulose/silica aerogels by using silicaalcoholic solution as a regenerative coagulant and by means of freeze-dryingmethod.It is noted that two kinds of crystal structure of cellulose I and II co-exist in thecellulose/silica aerogels. The amorphous silica particles increase and the bondingactions between silica and cellulose strengthen with the extension of regenerativetime. The microcrystalline celluloses self-assemble and then render parallelarrangements under the actions of hydrogen bonds in intra-and inter-molecular.Ultimately, the layered porous structures are formed. The dehydration andcondensation between Si–OH groups originating from silica gels and–OH groupson the surfaces of cellulose are the main actions to realize organic- inorganic hybrids. The cellulose/silica aerogels possess high specific surface areaand small average pore diameter, which is related with the filling of silica particlesinto cellulose gels.The mechanical properties of the cellulose/silica aerogels were improved by theintroduction of the silica particles. In the condition of short regenerative time, thestrengths of the cellulose/silica aerogels mainly generate from skeleton structures ofmicrocrystalline celluloses. The silica particles wrapping on the surfaces ofcellulose and the condensation among silica particles are the main reasons to furtherimprove the strength of aerogels. In the condition of long regenerative time, seriousaccumulational silica particles result in the brittleness of aerogels, which decreasedthe mechanical characteristics of the cellulose/silica aerogels.更多还原