Ultrasonic Production of Nano-Structured Cellulose
- Nanocellulose is a high-performance additive which is successfully used as rheology modifier, reinforcing agent and additive in manifold high-performance materials and applications.
- The nano-structured fibrils can be very efficiently isolated from any cellulose-containing source by high-power ultrasonic homogenization and milling.
- By sonication, a higher degree of fibrillation, higher nanocellulose yield, and thinner fibers can be achieved.
- The ultrasonic technology excels conventional methods of nanocellulose manufacture due to extreme cavitational high shear forces.
Ultrasonic Manufacture of Nanocellulose
High power ultrasonics contributes to the extraction and isolation of micro- and nano-cellulose from various sources of cellulosic materials such as wood, lignocellulosic fibers (pulp fibers), and cellulose containing residues.
To release the plant fibres from the source material, ultrasonic grinding and homogenization is a powerful and reliable method, that allows to process very large volumes. The pulp is fed into an inline sonoreactor, where ultrasonic high-shear forces break the cell structure of the biomass so that the fibrillous matter becomes available.
Figure 1 below shows a TEM image of “Never Dried Cotton” (NDC) submitted to enzymatic hydrolysis and sonicated with Hielscher’s UP400S for 20 minutes. [Bittencourt et al. 2008]
Figure 2 below shows a SEM image of a film of viscose, submitted to the enzymatic hydrolysis, followed by sonication with UP400S. [Bittencourt et al. 2008]
Ultrasonic nanocellulose processing can be also successfully combined with the TEMPO-oxidized fiber treatment. In the TEMPO-process, cellulose nanofibers are produced by an oxidation system using 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) as catalyst, and sodium bromide (NaBr) and sodium hypochlorite (NaOCl). Research has proven that the oxidation efficiency is significantly improved when the oxidation is conducted under ultrasonic irradiation.
Nanocellulose dispersions demonstrate an extraordinary rheological behaviour due to its high viscosity at low nanocellulose concentrations. This makes nanocellulose a very interesting additive as rheological modifier, stabilizer and gellant for various applications, e.g. in the coating, paper, or food industry. To express its unique properties, nanocellulose must be
Ultrasonic dispersing is the ideal method to obtain fine-size, single-dispersed nanocellulose. As nanocellulose is highly shear-thinning, ultrasound is the preferrable technology to formulate nanocellulosic suspensions as the coupling of high-power ultrasound into liquids creates extreme shear forces. (Click here to learn more about ultrasonic cavitation in liquids!)
After the synthesis of nanocrystalline cellulose, the nanocellulose is often ultrasonically dispersed into a liquid medium, e.g. a non-polar or polar solvent such as dimethylformamide (DMF), to formulate a final product (e.g. nanocomposites, rheological modifier etc.) As CNFs are used as additives in manifold formulations, a reliable dispersing is crucial. Ultrasonication produces stable and uniformly dispersed fibrils.
Industrial Ultrasonic Processing
Hielscher Ultrasonics supplies powerful and reliable ultrasonic technology from small lab ultrasonicators to bench-top systems and full-commercial industrial plant equipment. In Hielscher’s flowthrough sonoreactors, which are available at different sizes and geometries, optimal ultrasound condition are achieved as the optimized reaction conditions are applied focused and uniform to the cellulose matter.
With Hielscher’s ultrasonic bench-top devices such as the UIP1000hdT, UIP2000hdT or UIP4000hdT, several kilogram of nanocellulose can easily produced per day. The full industrial units such as the UIP10000 and UIP16000 handle very large mass streams and allow for the full commercial production of high production volumes. As all of Hielscher’s bench-top and industrial ultrasonicators can be installed as clusters, there is virtually no limit to the ultrasonic process capacity.
- high degree of fibrillation
- high nanocellulose yield
- thin fibers
- detangled fibers
- E. Abraham, B. Deep, L.A. Pothan, M. Jacob, S. Thomas, U. Cvelbar, R. Anandjiwala (2011): Extraction of nanocellulose fibrils from lignocellulosic fibres: A novel approach. Carbohydrate Polymers 86, 2011. 1468–1475.
- E. Bittencourt, M. de Camargo (2011): Preliminary Studies on the Production of Nanofibrils of Cellulose from Never Dried Cotton, using Eco-friendly Enzymatic Hydrolysis and High-energy Sonication. 3rd Int’l. Workshop: Advances in Cleaner Production. Sao Paulo, Brazil, May 18th – 20th 2011.
- L. S. Blachechen, J. P. de Mesquita, E. L. de Paula, F. V. Pereira, D. F. S. Petri (2013): Interplay of colloidal stability of cellulose nanocrystals and their dispersibility in cellulose acetate butyrate matrix. Cellulose 2013.
- A. Dufresne (2012): Nanocellulose: From Nature to High Performance Tailored Materials. Walter de Gruyter, 2012.
- M. A. Hubbe; O. J. Rojas; L. A. Lucia, M. Sain (2008): Cellulosic Nanocomposites: A Review. BioResources 3/3, 2008. 929-980.
- S. P. Mishra, A.-S. Manent, B. Chabot, C. Daneault (2012): Production of Nanocellulose from Native Cellulose – Various Options using Ultrasound. BioResources 7/1, 2012. 422-436.
- V. K. Thakur (2014): Nanocellulose Polymer Nanocomposites: Fundamentals and Applications. Wiley & Sons, 2014.
Nanocellulose includes different types of cellulose nanofibers (CNF), which can be distinguished in microfibrillated cellulose (MFC), nanocrystalline cellulose (NCC), and bacterial nanocellulose. The latter refers to nano-structured cellulose produced by bacteria.
Nanocellulose shows outstanding properties such as an extraordinary strength and stiffness, high crystallinity, thixotropy, as well as a high concentration of hydroxyl group on its surface. Many of the high performance characteristics of nanocellulose are caused by its high surface/mass ratio.
Nanocelluloses are widely used in medicine and pharmaceuticals, electronics, membranes, porous materials, paper, and food because of their availability, biocompatibility, biological degradability, and sustainability. Due to its high performance characteristics, nanocellulose is an interesting material for reinforcing plastics, the improvement of the mechanical properties of e.g. thermosetting resins, starch-based matrixes, soy protein, rubber latex, or poly(lactide). For composite applications, nanocellulose is used for coatings and films, paints, foams, packaging. Furthermore, nanocellulose is a promising component to make aerogels and foams, either in homogeneous formulations or in composites.
Nanocrystalline Cellulose (NCC)
Cellulose Nanofibers (CNF)
Microfibrillated Cellulose (MFC)
Nanocellulose Whiskers (NCW)
Cellulose Nanocrystals (CNC)