冷冻干燥法制备纤维素基多孔材料的研究

Study on the Preparation of Cellulose-based Porous Material by Freeze-drying Process

关键词:  植物纤维  冷冻干燥  多孔材料  悬浮液浓度  冷冻温度

Key Words:plant fibers  freeze-drying  porous material  the solid content of fiber suspension  freeze-temperature

摘要:以植物纤维为原料，研究了利用冷冻干燥法制备纤维素基多孔材料过程中纤维悬浮液浓度和冷冻温度对多孔材料微观结构和性能的影响，并探讨了冷冻过程中冰晶对纤维的作用方式和多孔材料微观结构的形成机制。结果表明，随着纤维悬浮液浓度的升高，冰晶的结构从平面状演变为层状，导致多孔材料的Z向微观形貌从各向同性转变为各向异性层状孔隙结构，有助于提高其抗欧拉失稳能力，使应力-应变曲线平压区缩短，密实化区向低应变点偏移。随着冷冻温度降低，冰晶凝固前沿处纤维受到的黏滞阻力增大，从而使其被冰晶吞没而均匀分散，材料两面差减少；另外，降低冷冻温度可降低层状冰晶的厚度，使多孔材料Z向孔隙尺寸减小，有助于提高其抵抗应力变形的能力，使应力-应变曲线中的密实化区向低应变点偏移。

Abstract:In this study, a cellulose-based porous material was prepared from plant fibers by freeze-drying technique. The effect of the solid content of fiber suspension and freeze-temperature on the microstructure and properties of the prepared porous materials was investigated. Meanwhile, the action and formation mechanisms of ice crystal on the fibers during freezing process and the microstructure of final porous material were discussed. The results revealed that the increase of solid content of fiber suspension could transform the Z direction microstructure of final porous material from an isotropic architecture to an anisotropic lamellar porous structure which could prevent Euler buckling of porous materials, leading to the shortening of plateau curve and the shiftment of densification curve to lower strain percentage in stress-strain curve. With the decreasing of freeze-temperature, the viscous resistance acting on the fibers at the solidification front of ice crystal was enhanced, thus the fibers had uniform distribution as it were swallowed by ice crystal and resulting in the porous materials with less two-sidedness. In addition, porous material produced at lower freeze-temperature owned smaller pores due to the thickness of lamellar ice crystal was reduced, which improved its ability to resist stress and deformation, leading to the densification region in stress-strain curve occurred at lower strain point．