蚕茧内部微结构特征与其隔热性能的关系以及隔热机理研究

Silkworm cocoons own excellent two-directional heat-insulating property, which enables the silkworm chrysalis to survive in both extremely high and low environmental temperatures. Investigating the relationship between the microstructural characteristics of the cocoon and its heat-insulating property as well as the mechanism is of great significance to develop the new style biomimetic heat-insulating fabrics. In this project, we initially obtained the internal microstructure images of cocoons in-situ by using the electronic computer X-ray tomography technique and then quantified the microstructural characteristics. Thereafter, we adopted the fractal theory to establish the relationship between the microstructural characteristics and heat transfer property of cocoons , and used the finite volume method to solve it. The theoretical model takes full consideration of the heat conductivity of silk fibers (affected by temperatures), radiative heat absorption and radiative heat scattering by fibers as well as the conductive and radiative heat transfer through air pores formed by fibers. We then verified the model by testing the inner and outer temperatures of the cocoons and their variation with time in both high (using ovens) and low environmental temperatures (using refrigerating system). Finally, based on the model, we revealed the key microstructural characteristics that account for cocoon’s excellent two-directional -insulating property, analyzed the mechanism, and presented the proposal for designing the biomimetic heat-insulating fabrics and trial-produced a fabric. In one word, this project was not only efficiently helpful to explore heat-insulating mechanism of cocoons but also to design new style heat-insulating fabrics.

蚕茧具有优异的双向隔热性能，可保护蚕蛹在极端高温与低温环境下不被热死或冻死。研究蚕茧内部微结构特征与其隔热性能的关系、进行隔热机理分析对于开发新型仿生隔热织物具有重要意义。本项目首先采用X射线断层扫描技术无损、原位地获得蚕茧内部微结构图像，明晰并定量表达了微结构特征；采用分形学理论构建了蚕茧内部微结构与其传热过程关系模型：综合考虑纤维相热传导（受温度影响）、纤维对辐射热的吸收和散射以及通过纤维间孔隙相的热传导与热辐射，采用有限体积法求解；利用高温烘箱与超低温箱体分别测量高温与低温环境下蚕茧内外层温度以及温度随时间的变化，并验证理论结果；在此基础上，揭示蚕茧具有优异隔热性的关键微结构特征并深入分析隔热机理，提供仿蚕茧结构织物的设计方案并试制织物。该项目的成功实施不仅可以理解蚕茧具有优异双向隔热性的本质原因，更为开发新型隔热织物提供理论基础和依据。

蚕茧具有优异的双向隔热性能，可保护蚕蛹在极端高温与低温环境下不被热死或冻死。研究蚕茧内部微结构特征与其隔热性能的关系、进行隔热机理分析、揭示关键结构参数对于开发新型仿生隔热织物具有重要意义。本项目首先采用X射线断层扫描技术无损、原位地获得桑蚕茧和野蚕茧内部微细结构图像，采用分形理论定量表达了其微细结构特征；接着，利用自行研制的热线法导热系数测试装置研究了几种蚕茧在不同温度环境下的导热系数，构建了蚕丝纤维和温度的关系模型；结合蚕茧内部微细结构特征，综合考虑纤维相热传导、纤维对辐射热的吸收和散射以及孔隙相的热传导与热辐射，采用分形理论与能量守恒方程构建了蚕茧内部微结构与其传热过程关系模型。将高温和低温环境下的蚕茧内部温度变化理论值和实验值对比，获得了较好的吻合结果。在此基础上，研究了微细结构参数对蚕茧隔热性能的影响，发现垂直于厚度方向上的不同层次的分形维数、厚度方向上的孔隙曲折度及孔隙率是影响蚕茧隔热性能的关键结构参数。另外，研究了蚕茧的稳态隔热性能，发现其导热系数和分形维数线性相关。最后，设计了仿蚕茧结构隔热织物，并证明了其优异的隔热性能，同时提出了一种仿蚕茧结构生物基复合材料的制备方法。该研究揭示了蚕茧双向优异隔热性能的深层次原因，同时为新型隔热材料的开发提珙理论基础和依据。