Cellulose microfibrils: A novel method of preparation using high shear refining and cryocrushing

Abstract

This paper describes a novel technique to produce cellulose microfibrils through mechanical methods. The technique involved a combination of severe shearing in a refiner, followed by high-impact crushing under liquid nitrogen. Fibers treated in this way were subsequently either freeze-dried or suspended in water. The fibers were characterized using SEM, TEM, AFM, and high-resolution optical microscopy. In the freeze-dried batch, 75% of the fibrils had diameters of 1 μm and below, whereas in the water dispersed batch, 89% of the fibrils had diameters in this range. The aspect ratio of the microfibrils ranged between 15 and 55 for the freeze-dried fibrils, and from 20 to 85 for the fibrils dispersed in water. These measurements suggest that the microfibrils have the potential to produce composites with high strength and stiffness for high-performance applications. The microfibrils in water were compounded with polylactic acid polymer to form a biocomposite. Laser confocal microscopy showed that the microfibrils were well dispersed in the polymer matrix.

Toward Industrially Feasible Methods for Following the Process of Manufacturing Cellulose Nanofibers

“…Microscopy has indeed been widely utilized to determine the lateral dimensions and lengths of cellulose nanofibers. The most common methods are fieldemission scanning electron microscopy (FE-SEM) (Zimmermann et al 2004;Chakraborty et al 2005;Abe et al 2007;Iwamoto et al 2007;Wang and Sain 2007;Alemdar and Sain 2008;Kaushika and Singh 2011;Qua et al 2011), transmission electron microscopy (TEM) (Alemdar and Sain 2008;Chakraborty et al 2005;Kaushika and Singh 2011;Pääkkö et al 2007;Qua et al 2011;Saito et al 2009;Wang and Sain 2007;Zimmermann et al 2004), and atomic force microscopy (AFM) (Chakraborty et al 2005;Pääkkö et al 2007;Wang and Sain 2007;Kaushika and Singh 2011;Helander et al 2012). Although veracious size measurements can be performed at the nano-scale, only a limited field of view is visualized, often overlooking larger structures (Chinga-Carrasco 2013).…”

Effect of nanocellulose isolation techniques on the formation of reinforced poly(vinyl alcohol) nanocomposite films

“…While for mechanical methods, which include high intensity ultrasonication [13], high pressure refiner [14] or grinder treatment [15], the main product generated is not a single fiber and has been referred as nanofibrils. However, these two techniques of extracting nanocellulose from plants are time consuming and very costly [1].…”

Advanced Cellulosic Nanocomposite Materials

“…A typical procedure to prepare cellulose nanocrystals has five steps: hydrolysis by acid, centrifugation and neutralization, rinsing with deionized water by centrifuge, dispersion by ultrasonic irradiation, and ultrafiltration to remove any remaining ions (Choi and Simonsen, 2006). Cellulose whiskers or nanocrystals have been obtained from many cellulosic materials, such as wood fibers, cotton, ramie, tunicate mantles, sugar beet pulp, and bacterial cellulose (Beck-Candanedo et al, 2005;Chakraborty et al, 2005;Dufresne et al, 1997b;Edgar and Gray, 2002;Kvien et al, 2005;Lu et al, 2005;Pu et al, 2007;Zimmermann et al, 2004). In terms of mechanical methods, a process using highintensity ultrasonication (HIUS) was developed at the Center for Renewable Carbon to isolate fibrils from several cellulose resources, which is discussed in Section 3.3.…”

“…Several tools can be used for morphological observation, such as a scanning electron microscope (SEM), an atomic force microscope (AFM), and a transmission electron microscopy (TEM) (Bhatnagar and Sain, 2005;Bondeson et al, 2006;Chakraborty et al, 2005;Choi and Simonsen, 2006;Wang and Sain, 2007;Zimmermann et al, 2004). The degree of fibrillation of the fibers used to isolate MFC/microfibrils/aggregates by mechanical methods may be evaluated by water retention value (WRV) (Cheng et al, 2007a;Cheng et al, 2010a, b;Herrick et al, 1983;Turbak et al, 1983;Wang and Cheng, 2009;Yano and Nakahara, 2004).…”