双层定向/随机冷冻对纤维素基气凝胶孔结构及吸水性能的调控

Regulation of Pore Structure and Water Absorption in Cellulose-based Aerogels via a Combined Directional and Random Freezing Strategy

关键词:  气凝胶  随机冷冻  定向冷冻  孔结构  吸水性能

Key Words:aerogels  random freezing  directional freezing  pore structure  water absorption properties

摘要:本研究以羧基化纳米纤维素、聚乙烯醇、分离乳清蛋白为基材，通过调控冷冻温度和方向，开发了一种结合-20 ℃随机冷冻与-196 ℃定向冷冻的双层定向/随机冷冻气凝胶（DF/RF-20），并与-20 ℃慢速随机冷冻（RF-20）、-196 ℃快速随机冷冻（RF-196）、-196 ℃定向冷冻（DF）方式对比，探究了冷冻方式对气凝胶微观结构、密度、孔隙率、力学性能和吸水性能的影响。结果表明，RF-20的孔径大且孔隙分布分散，吸水率为42.21 g/g，但压缩强度较差（44.37 kPa）；DF自下而上形成了有序致密的通孔，压缩性能较好（73.39 kPa），但吸水能力较弱（35.80 g/g）；相比之下，DF/RF-20兼具高压缩性能（73.90 kPa）、优异的湿态压缩强度（含水率500%时达25.75 kPa）与高吸水率（43.30 g/g），表面吸水速率较RF-20提升了约15倍；在25 ℃下干燥12 h，其表现出良好的保水性能（保水率86.76%），且在不同pH和离子环境中也可保持稳定的吸液能力。

Abstract:This study utilized carboxylated nanocellulose, polyvinyl alcohol, and whey protein isolate as matrix materials. By regulating freezing temperature and orientation, a bilayer directional/random frozen aerogel (DF/RF-20) was developed, combining -20 ℃ random freezing and -196 ℃ directional freezing. It was compared with aerogels prepared under -20 ℃ slow random freezing (RF-20), -196 ℃ fast random freezing (RF-196), and -196 ℃ directional freezing (DF), to investigate the effects of freezing methods on the microstructure, density, porosity, mechanical properties, and water absorption performance of the aerogels. The results showed that RF-20 exhibited large pore sizes with a dispersed pore distribution and a water absorption capacity of 42.21 g/g, but poor compressive strength (44.37 kPa). DF showed ordered and dense through-pores formed from bottom to top, with better compressive performance (73.39 kPa) but weaker water absorption ability (35.80 g/g). In comparison, DF/RF-20 combined high compressive strength (73.90 kPa), excellent wet-state compressive strength (25.75 kPa at 500% water content), and good water absorption capacity (43.30 g/g). Its surface water absorption rate was approximately 15 times higher than that of RF-20. After drying at 25 ℃ for 12 h, it demonstrated good water retention performance (water retention rate of 86.76%) and maintained stable liquid absorption capability under different pH and ionic environments.