TEMPO氧化和高频超声下埃米级厚度纤维素纳米纤丝的制备

通过不同TEMPO氧化体系对商品竹浆进行氧化处理,经高频超声纳米纤丝化后,可以制得长度在数百纳米,宽度小于5.0 nm,厚度仅为几个埃的纤维素纳米纤丝(TEMPO-oxided cellulose nanofibrils,TOCNs).这种纳米带状(nanostrip)的TOCNs是由纤维素片层构成的.本文通过场发射扫描电子显微镜(FE-SEM)探究了原料和2组TOCNs样品的形貌变化,利用透射电子显微镜(TEM)和原子力显微镜(AFM)对2组TOCNs样品的三维尺寸(长、宽、厚)进行测量统计.通过不同氧化体系产物的TOCNs三维尺寸差异,并结合傅里叶红外吸收光谱(FTIR)、X射线衍射(XRD)及交叉极化和魔角旋转13C固态核磁共振光谱(CP/MAS 13C-NMR)揭示了不同氧化体系对纤维素Iβ层内氢键及长轴方向的作用机理.

High Frequency Ultrasound Preparation of TEMPO-oxided Ultrafine Cellulose Nanofibrils of Angstrom-scale

The commercial bleached bamboo was oxidized to TEMPO-oxidized cellulose nanofibrils (TOCNs) with hundreds of nanometers in length,less than 5 nm in width and the thickness less than 1 nm,which was done through TEMPO (2,2,6,6-tetramethylpiperidine-l-oxyl radical)-mediated oxidation and successive mild disintegration in water solution combined with high frequency ultrasonic treatment.The shape and dimensions of these sheets (termed "nanoribbons" hereafter),composed of many mono-and multi-layered molecular sheets,were analyzed by scattering and spectroscopy techniques to understand the structural changes.The morphology of the raw material and two types of TOCNs nanoribbons were characterized by field emission scanning electron microscope (FESEM).And the three-dimensional morphologies of the same two TOCNs samples were measured through transmission electron microscope (TEM) and atomic force microscope (AFM).The results revealed that the TEMPO-mediated oxidization systems processed in cellulose Iβ intra-layer hydrogen bonds and the long axis direction of elementary fibrils (composed by 36 cellulose chains),which was explained based on the three dimensional size difference and the change of the crystalline structure in TOCNs nanoribbons.The structures of different nanoribbons were analyzed by Fourier infrared absorption spectrum (FTIR),X-ray diffraction (XRD) and cross polarization and magic angle spinning solid-state 13C nuclear magnetic resonance (CP/MAS 13C-NMR).FTIR analysis indicated that structure of the cellulose nanofibrils was changed during oxidization,significant amount of C6 carboxylate groups were selectively formed on each cellulose nanofibril surface by TEMPO-mediated oxidation without any changes to the original crystalline structure.XRD analysis indicated that the cellulose elementary fibrils were broken mainly along its (101) planes in TEMPO/NaClO/NaC1O2 and TEMPO/NaC1O/NaBr oxidized systems under high frequency ultrosonic treatment,while the Iβ crystalline structure was retained.CP/MAS 13C-NMR results were in accordance with the analyses from XRD and Raman spectra.Moreover,the oxidization scheme was important to explain the structures of the final products.This research has important significance for design,development and application of ultrafine biomass cellulose nanoribbons.