多级网络结构纳米纤维素气凝胶的可控构筑及热湿耦合导热机制研究

Traditional building thermal insulation materials such as polystyrene have the limitations of high energy consumption and high pollution processing. Therefore, new type of green thermal insulation materials with high energy efficiency, light weight and environmental protection have become the research hotspot in the field of building thermal insulation. Nanocellulose can be used to prepare multistage network structure aerogel with high thermal insulation, but its forming mechanism is not clear at present, so it is difficult to realize its controllable preparation.The heat transfer mechanism of traditional aerogel is mostly based on the isopore model, and the research on the heat transfer process of nanocellulose aerogel in humidity environment is less.This project attempts to study the fracture mechanism of straw cellulose macromolecules and reveal the regulation rules of nanocellulose size. The dynamic evolution process of migration and mesh formation of cellulose macromolecular during drying will be studied, the internal correlation between size adaptability and mesh aperture and structure will be analyzed, and the forming mechanism and the regulation law of mechanical properties will be revealed，to realize the controllable preparation of the multistage network structure. Based on the microstructure model of aerogel multistage network structure, the heat transfer mechanism under the coupled effect of heat and humidity will be studied. Finally, a kind of high-performance green thermal insulation material with controllable structure will be obtained. This project will significantly improve the thermal insulation performance of cellulosic insulation materials, which is of great significance for environmental protection and effective utilization of resources.

聚苯乙烯等传统建筑保温隔热材料存在高能耗、高污染加工的局限性，因此高效节能、轻质环保的新型绿色保温材料成为当前建筑隔热领域的研究热点。纳米纤维素可用于制备高效保温的多级网络结构气凝胶，但目前对其成型机制尚不清晰，难以实现其可控制备；传统气凝胶传热机制多基于等孔径模型，针对湿度环境下纳米纤维素气凝胶的传热过程研究较少。本项目尝试开展秸秆纤维素大分子的断裂机制研究，揭示纳米纤维素尺度调控规律；研究纤维素干燥过程中大分子迁移及成网的动态演变过程，分析其纳米纤维素尺寸适配性与气凝胶成网孔径及结构间的内在关联，揭示气凝胶多级网络结构的成型机制和力学性能调控规律，实现多级网络结构气凝胶的可控制备；在气凝胶多级网络结构微观模型的基础上，探索研究其热湿耦合作用下多级网络结构传热机制，获得一种结构可控的高性能绿色保温材料。本课题将显著提升纤维素基保温材料的隔热性能，对环境保护、资源有效利用具有重要意义。

纳米纤维素气凝胶材料，不仅具有轻质多孔、超低导热系数和高比表面积等特点，还具有原料来源广、可再生、良好的生物相容性等优点，在保温隔热领域中应用潜力巨大。本项目以水稻秸秆为原料，采用超声波辅助纤维素酶解法提取水稻秸秆纳米纤维素，研究结果表明：双相水溶液法制备的水稻秸秆纤维在外观色泽、长度、细度以及拉伸性能等方面均优于传统碱煮法获得的纤维。采用超声波辅助酶解法制得的纳米纤维素由于纤维素酶在秸秆纤维上进行靶向磨蚀，产生定位断裂点，使其长径比小、尺寸离散度小、分散稳定性好。因此，该制备方法可实现纳米纤维素尺度和稳定性的可控制备。采用层层自组装法和定向冷冻工艺，制备多级网络结构气凝胶，探究了其成型机制，研究结果表明：纳米纤维素粒径、浓度、搅拌时间、冷冻方式对气凝胶隔热性能影响显著，搅拌转速对气凝胶隔热性能影响较小。在结构上，发现通过调节纳米纤维素的浓度可以实现对孔径结构和比表面积的调控，且多级结构的气凝胶结构更加规则有序。在力学性能上，发现在相同粒径的情况下，多级结构样品的压缩回弹性要优于常规结构样品，并且在多级结构样品中，若气凝胶浓度梯度的起始浓度越高，其压缩回弹性也越高，在一定浓度梯度范围内，随着纤维素粒径的增加，其压缩回弹呈逐渐增加的趋势。与冰箱冷冻、液氮冷冻相比，冰模板定向冷冻法制备的纳米纤维素气凝胶在径向上形成了层状结构，而且层状之间有孔相连，是一种调控纳米纤维素气凝胶结构的有效手段。并基于冰模板法制备的多级网络结构模型，建立了不等孔径模型的传热数值模型，解析了热湿耦合作用下的传热机制。本项目的开展明晰了秸秆纤维素的靶向断裂机制，实现了秸秆纳米纤维素尺寸性、稳定性的可控制备，明晰了多级网络结构气凝胶的成型机制，以及热湿耦合导热机制，开发了一种结构可控的高性能绿色保温材料，对环境保护、资源有效利用具有重要意义。