Preparation of Nanocellulose Aerogel from the Poplar (Populus tomentosa) Catkin Fiber

Abstract

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...

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