The effects of chemical pretreatment on the purification of poplar (Populus tomentosa) catkin fiber and the effect of ultrasonic time for the microfibrillarization of poplar catkin fiber (PCF) were studied. The nanocellulose aerogels were prepared by freeze drying the cellulose solutions. The density, porosity, micro morphology, thermal stability and mechanical properties of the aerogels were analyzed. It was found that the dewaxing time of PCF is shorter than that of unsonicated nanocellulose. After the treatment of 0.5 wt% sodium chlorite for 2 h, the lignin of PCF was removed. After the chemical purification, the PCF was treated with 2 and 5 wt% NaOH solution and ultrasonicated for 5 and 10 min, respectively. When the ultrasonic time was 10 min, the diameter of the nanocellulose was 20-25 nm. When the ultrasonic time was 5 min, the aerogels with porous honeycomb structure can be prepared by using the nanocellulose sol of PCF as raw material. The density of the aerogels was only 0.3-0.4 mg/cm 3 and the porosities of the aerogels were all larger than 99%. The difference between the pyrolysis temperature of aerogels was small, the elastic modulus of aerogels was 30-52 kPa, and the compressive strength was 22-27 kPa. With the increase of the concentration of NaOH solution (5 wt%) and ultrasonic time (10 min), the elastic modulus of aerogels increased gradually and reached the maximum value of 52 kPa, while the compressive strength reached the maximum value of 27 kPa when the PCF being treated in 5 wt% NaOH solution and was ultrasonicated for 5 min. microstructure and chemical composition of the PCF make a large difference to its properties [1]. Thus studying the structure and chemical composition of PCF may play a vital role in the use of PCF in high value-added fields such as cellulose.Cellulose exists in the cell wall of plants in the form of microfibrils with a diameter of 3-5 nm. Microfibrils can aggregate to form cellulose aggregates with a diameter of several tens of nanometers and a length of several tens of micrometers, which is called cellulose nanofibers (CNFs). Compared to the microfibrillated cellulose and nanocellulose whiskers, its unique supramolecular structure and morphology make it possess excellent mechanical, optical and small molecular physical barrier properties [3]. It has broad application prospects in new biomaterials, medicine, information and other industrial fields [4]. At present, the source of nanocellulose is mainly from wood, but due to the long growth cycle and wide use of wood, it is urgent to find more suitable raw materials for high value-added nanocellulose. The scholars of related field have done a lot of researches to prepare the nanocellulose by using the cheap raw materials such as bamboo [5,6], tobacco stalk [7], cotton pulp [8-10], sisal fibers [11], crop straw [12,13], peanut shell [14], soybean hulls [15], banana peel and rod [16], coconut shell [17], cactus peel [18] and beet root [19].CNF aerogel (CNFA) is a natural polymer aerogel material. It not only has the advant...

In this study, the microstructure and mechanical properties of poplar (Populus tomentosa) catkin fibers (PCFs) were investigated using field emission scanning electron microscope, atomic force microscopy (AFM), X-ray diffraction, and nanoindentation methods. Experimental results indicated that PCFs had a thin-wall cell structure with a large cell lumen and the hollow part of the cell wall took up 80 percent of the whole cell wall. The average diameters of the fiber and cell lumen, and the cell wall thickness were 5.2, 4.2, and 0.5 µm, respectively. The crystallinity of fibers was 32%. The AFM images showed that the orientation of microfibrils in cell walls was irregular and their average diameters were almost between 20.6-20.8 nm after being treated with 2 and 5 wt.% potassium hydroxide (KOH), respectively. According to the test of nanoindentation, the average longitudinal-reduced elastic modulus of the PCF S 2 layer was 5.28 GPa and the hardness was 0.25 GPa.Poplar (Populus tomentosa) catkin fiber (PCF) is a cotton-like catkin fiber covering the seeds of white poplar trees [7]. Poplar is a kind of fast-growing tree species with a short growth cycle and low price. It is mainly concentrated in the northeast, north China, and northwest areas. The total area of poplar forest in China exceeds 70,000 km 2 , and it increases year by year. Each poplar tree can harvest about 25 kg of catkins. The tassel fiber is mainly composed of cellulose and hemicellulose, as well as lignin, with a thin cell wall and large lumen [8]. During the period from April to June each year, PCFs float in the air, causing great trouble for the environment and residents' health. Zhang et al. [9] focused on poplar (Populus tomentosa) catkin fiber as a new resource for bioethanol production via enzymatic hydrolysis. Yin et al.[10] studied the water absorption and oil absorption of poplar catkins. They studied how to inhibit the production of PCFs, but not how to utilize them. There are few studies on the microstructure and mechanical properties of PCFs.In recent years, microscopic imaging and spectral characterization methods have been used in nanostructure and chemical composition analyses of cell walls of plant fibers like wood fibers [11][12][13][14][15][16], bamboo fibers [17][18][19][20][21][22], and cotton fibers [23,24]. Chen et al. [25] characterized the aggregation of microfibrils in the cross-section of thin-wall cells using the atomic force microscopy (AFM) technique. Xiao et al. [26] and Hao et al. [24] investigated the cell wall layer structure of kapok fibers using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) through formulating an efficient organic solvent system to isolate cellulose from lignin and concluded that both kapok and cotton fibers had similar multi-wall layer structures. Fernandes et al. [27] investigated the nanostructures of spruce fibers using a series of spectroscopic techniques, such as small angle neutron ray scanning (SANS) and wide-angle X-ray scattering (WAXS).Oliver and Pharr.[28]...

The large diameter metal shell component (LDMSC) is an important part of gas insulated (metal-enclosed) switchgear (GIS). The LDMSC with multi branches is filled with gas under certain pressure. The plastic forming process is an efficient approach to manufacturing the high reliability LDMSC. The warm flanging process has been widely used to form LDMSC using aluminum alloy. The forming process is characterized by local heating, and the distribution of temperature is strongly inhomogeneous. Although the wall thickness of the shell is 10 mm to 20 mm, the ratio of outer diameter to thickness is more than 40. These present some difficulties in the flanging process and result in some forming defects. Detailed forming characteristics are hard to obtain by analytical and experimental methods. Thus, the through-process finite element (FE) modeling considering heating, forming, unloading, and cooling is one of the key problems to research the manufacturing process of LDMSC. In this study, the through-process FE modeling of the warm flanging process of LDMSC using aluminum alloy was carried out based on the FORGE. The thermo-mechanical coupled finite element method was adopted in the modeling, and the deformation of the workpiece and the die stress were considered together in the modeling. A full three-dimensional (3D) geometry was modeled due to inhomogeneous distribution in all directions for the temperature field. The simulation data of local flame heating could be transferred seamlessly to the simulations of the deforming process, the unloading process, and the cooling process in the through-process FE model. The model was validated by comparison with geometric shapes and forming defects obtained from the experiment. The developed FE model could describe the inhomogeneous temperature field along circumferential, radial, and axial directions for the formed branch as well as the deformation characteristic and the unloading behavior during the warm flanging process. By using the FE model, the forming defects during the flanging process and their controlling characteristics were explored, the evolution of the temperature field through the whole process was studied, and deformation and springback characteristics were analyzed. The results of this study provide a basis for investigating deformation mechanisms, optimizing processes, and determining parameters in the warm flanging process of a large-diameter aluminum alloy shell component.