高力学强度细菌纤维素气凝胶纤维的连续化制备

Continuous Bacterial Cellulose Aerogel Fibers with High Strength

气凝胶纤维因其高外表面积和高柔韧性在能量管理系统中具有潜在应用而引起了广泛关注.但是,目前制备的气凝胶纤维力学强度较低,限制了其实际应用.为提高气凝胶纤维力学性能,在始终保持细菌纤维素(BC)纳米纤维处于湿态下,利用NaOH/尿素/硫脲复合溶剂直接低温溶解原生BC,获得透明的BC纺丝原液;通过湿法纺丝制备了BC水凝胶纤维,经过水洗和冷冻干燥后处理,制得BC气凝胶纤维.采用偏光显微镜(POM)、13C核磁共振(13C-NMR)和高级旋转流变仪研究BC在复合溶剂中的溶解过程与状态;利用全反射傅里叶变换红外吸收光谱(ATR-FTIR)、X射线衍射(XRD)和热失重(TG)研究BC溶解前后结构与性能变化;利用场发射扫描电镜(FESEM)、全自动比表面积和孔径分布分析仪、单丝强力仪对获得的BC气凝胶纤维结构与性能进行表征.结果表明,复合溶剂在−15℃条件下可以直接溶解原生湿态BC,最高溶解浓度为3 wt%;采用湿法纺丝制得高度多孔的连续BC气凝胶纤维,比表面积高达192 m^2/g且具有优异的力学性能,断裂强度和杨氏模量高达(9.36±1.68)MPa和(176±17.55)MPa,如0.4 mg BC气凝胶纤维可以支撑高于其本身质量5×10^4倍的重物.

Aerogel fibers have attracted increasing interests due to their high outside specific surface area and high flexibility for applications in energy management systems.However,aerogel fibers usually suffer from weak mechanical properties and complicated fabrication process,thus severely restricting their broad application.In this paper,the never-dried bacterial cellulose(BC)with high molecular weight was firstly dissolved in NaOH/urea/thiourea aqueous solution at−15°C.Followed by wet spinning,solvent exchange and freeze-drying,the BC aerogel fiber with high mechanical properties was simply obtained.The dissolution process was observed by polarized optical microscope(POM),13C nuclear magnetic resonance(NMR)and viscoelastic measurements.The variations of structure and properties on original BC and regenerated BC aerogel fibers were characterized by attenuated total reflection-Fourier transform infrared spectrometry(ATR-FTIR),X-ray diffraction(XRD)and thermogravimetric analysis(TGA).The structure and properties of BC aerogel fiber were studied by field emission scanning electron microscopy(FESEM),specific surface area and pore size distribution analyzer(BET)and fiber strength tester.The results show that the never-dried BC can be dissolved in NaOH/urea/thiourea solution at low temperature.The maximum concentration of BC in the solution reaches up to 3 wt%.The resulted BC solution behaves as pseudoplastic fluid and stays stabe at room temperature.To fabricate BC aerogel fibers,wet-spinning technology and freeze-drying were utilized using BC solution as spinning dope.After regeneration,the crystal structure of BC transforms from I to II without derivatization.Meanwhile,highly porous structure in axial alignment with a high specific area of 192 m2/g was demonstrated in the BC aerogel fibers.Due to the high molecular weight of BC,strong intramolecular and intermolecular interactions,and molecular chain orientation,the tensile strength and Young’s modulus of BC aerogel fibers could reach up to(9.36±1.68)MPa and(176±17.55)MPa,which are higher than those of state-of-the-art aerogel fibers.The lightweight BC aerogel fiber can withstand a load of more than 5×104 times its own weight.Such BC aerogel fibers show high potentials in flexible biological scaffolds,drug carriers,bio-adsorbents and advanced thermal insulation textiles.