Le Van Hai

Cellulose long fibers fabricated from cellulose nanofibers and its strong and tough characteristics

Cellulose nanofiber (CNF) with high crystallinity has great mechanical stiffness and strength. However, its length is too short to be used for fibers of environmentally friendly structural composites. This paper presents a fabrication process of cellulose long fiber from CNF suspension by spinning, stretching and drying. Isolation of CNF from the hardwood pulp is done by using (2, 2, 6, 6-tetramethylpiperidine-1-yl) oxidanyl (TEMPO) oxidation. The effect of spinning speed and stretching ratio on mechanical properties of the fabricated fibers are investigated. The modulus of the fabricated fibers increases with the spinning speed as well as the stretching ratio because of the orientation of CNFs. The fabricated long fiber exhibits the maximum tensile modulus of 23.9 GPa with the maximum tensile strength of 383.3 MPa. Moreover, the fabricated long fiber exhibits high strain at break, which indicates high toughness. The results indicate that strong and tough cellulose long fiber can be produced by using ionic crosslinking, controlling spinning speed, stretching and drying.

Green all-cellulose nanocomposites made with cellulose nanofibers reinforced in dissolved cellulose matrix without heat treatment

Green all-cellulose nanocomposites were fabricated by adding reinforcing cellulose nanofiber (CNF) to a matrix of dissolved cellulose. CNFs were isolated from one dried native hardwood bleached Kraft pulp and office waste recycled deinked copy/printing paper (DIP) by using the TEMPO oxidation method. The cellulose was dissolved by using DIP and DMAc/LiCl solvent without heat treatment and solvent exchange to form a matrix of the all-cellulose nanocomposites. The DIP was not only selected for CNF isolation, but also for the cellulose matrix. The isolated CNFs and the all-cellulose nanocomposites were characterized by atomic force microscopy, thermogravimetry–differential thermal analysis, X-ray diffraction and mechanical tensile testing. The green all-cellulose nanocomposites made without heat treatment offered better thermal stability, crystallinity and mechanical properties than the heat treated ones. CNFs isolated from two resources show similar reinforcement capacity in all-cellulose nanocomposites. All-cellulose nanocomposite fabrication by dissolving cellulose without heat treatment and solvent exchange is a simple way that saves energy and chemicals.

Properties of micro-nanofibrillated-chitin/bamboo-cellulose nanofiber composite

This paper reports an eco-friendly nanocomposite made with bamboo cellulose nanofiber and chitin micronanofibers. Bamboo has antibacterial property and is beneficial for human living environment meanwhile chitin is safe for food packaging, highly toxic resistant and able to absorb heavy metals. Chitin was micro-nano fibrillated (CT-MNF) by using aqueous counter collision (ACC) physical method. Cellulose nanofiber (CNF) was isolated from bamboo by treating it with 2,2,6,6-tetramethylpiperidine-1-oxylradical (TEMPO)-oxidation followed by ACC method. Bamboo cellulose nanofiber (BA-CNF) was blended with CT-MNF to form BA-CNF nanocomposite. The morphology of BA-CNF and CT-MNF was determined by an atomic force microscopy and field emission scanning electron microscopy. CT-BA nanocomposites were made with different ratios of BA-CNF and CT-MNF. Properties of CT-BA nanocomposites were investigated by using thermogravimetric analysis, UV-visible spectra, and tensile test. The UV-Vis visible spectrum shows better transmittance of the CT-BA nanocomposite with high BA-CNF content. CT-BA nanocomposite has better surface smoothness. By blending BA-CNF with CT-MNF, CT-BA nanocomposite shows improved mechanical properties.

Alignment of cellulose nanofibers by high-DC magnetic field

The fabrication of cellulose long-fiber (CL) is necessary for eco-friendly and high strength composites development. CL can be made with cellulose nanofiber (CNF) that has high mechanical strength and modulus. However, the mechanical properties of CL in early studies were shown to be lower than those of original CNF. An idea of fabricating strong CL is to align CNFs so as to make strong hydrogen bond between CNFs. To achieve this, alignment of CNF is very important. In this study, high dc magnetic field is introduced to align the CNFs. The CNFs are aligned perpendicular to the direction of dc magnetic field due to its negative diamagnetic anisotropy. CNFs isolated by TEMPO oxidation and aqueous counter collision method are used in this experiment. The CNF emulsion is located in the high dc magnetic field and cured. Alignment of CNF is investigated by using optical microscopy, scanning electron microscopy and mechanical tensile test.

Cellulose nanofibers isolated by TEMPO-oxidation and aqueous counter collision methods

In this research, cellulose nanofiber (CNF) was isolated by the combination of chemical 2,2,6,6-tetramethylpiperidine-1-oxylradical (TEMPO)-oxidation and physical aqueous counter collision (ACC) methods The combination of TEMPO-oxidation and ACC is an efficient method to isolate CNFs by reducing chemical usage in TEMPO-oxidation and saving energy in ACC along with controlling the size of CNFs. Two cellulose sources, hardwood bleached kraft pulp (HW) and softwood bleached kraft pulp (SW), were used for the CNF isolation with different TEMPO oxidation time and a defined number of ACC pass. The CNF properties were investigated and compared in term of morphology, crystallinity index, transparency and birefringence. The width of the isolated CNFs from HW is in the range of 15.1 nm-17.5 nm, and that of the SW CNFs is between 18.4 nm and 22 nm depending on the TEMPO oxidation time. This difference is due to the fact that SW is less oxidized than HW under the same chemical dosage, which results in larger width of SW-CNFs than HW-CNFs. The HW-CNF treated with TEMPO for over 2 h and isolated using ACC with 5 pass offers almost 90% transparency. Birefringence of CNFs exhibits that HW-CNFs show better birefringence phenomenon than SW-CNFs. The combination of TEMPO-oxidation and ACC methods is useful for isolating CNFs with its size control.

Properties of TEMPO-oxidized cellulose nanofiber by using aqueous counter collision

Cellulose nanofiber (CNF) isolation from different resources influences the characteristics of the CNF. There are two methods to isolate CNFs, chemical and physical methods. This paper deals with a 2,2,6,6-tetramethylpiperidine- 1-oxylradical (TEMPO-oxidation) chemical method and aqueous counter collision physical method to isolate CNFs. TEMPO-oxidized cellulose nanofiber was isolated using an aqueous counter collision method from two cellulose resource including Softwood bleached kraft pulp (SW) and Hardwood bleached kraft pulp (HW) resources. The CNFs properties were studied by atomic force microscopy, cross-polarize light and UV visible spectrometer. The width of the isolated CNFs is in the range of 15 nm to 20 nm and the length of cellulose nanofibers is around 1000 nm. The HW-CNF offers better transmittance than the SW-CNF. High transmittance of CNF films from both SWCNF and HW-CNF was observed. In addition, the birefringence of CNFs was observed under cross polarized light. The SW-CNF and HW-CNF films showed birefringence phenomenon. More clear iridescence color of HW-CNF sample than that of SW-CNF case.

Characterization of cellulose nanocrystal obtained from electron beam treated cellulose fiber

Cellulose nanocrystals (CNCs) from electron beam treated cellulose sources such as cotton linter and bleached softwood kraft pulp were isolated using the acid method. Their crystallinity index, cupriethylene diamine (CED) viscosities and morphology properties were evaluated using X-ray diffraction, a capillary viscometer and both field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM), respectively. CNC fibers were obtained with average diameter of 10 to 30 nm and several hundred nm in length. The CNCs isolated from cotton linter had a lower aspect ratio than those CNCs produced from softwood. As electron beam dosage increased, the lengths and the aspect ratios of CNCs decreased. Electron beam treatment decreased yields, crystallinity index, α-cellulose contents, CED viscosities and thermal stability of cellulose sources and their CNCs. Interestingly, circular self-assembly of nanocellulose from all treated sample were observed by FE-SEM clearly. However, electron beam treatment did not affect the self-assembly behavior of CNCs. ADDRESSES OF THE AUTHORS: Le Van Hai (levanhai121978@gmail.com), Dept. of Pulp and Paper Technology, Phutho College of Industry and Trade, Phutho, Vietnam and Yung Bum Seo (ybseo@cnu.ac.kr) Dept. of Bio-based Materials, College of Agriculture and Life Science, Chungnam National University, Daejeon, South Korea. Corresponding author: Le Van Hai