Ultrasonic Production of Nano-Structured Cellulose

Nanocellulose, a remarkable high-performance additive, has gained prominence for its versatile applications as a rheology modifier, reinforcing agent, and key component in various advanced materials. These nano-structured fibrils, derived from any cellulose-containing source, can be efficiently isolated through high-power ultrasonic homogenization and milling. This process, known as sonication, significantly enhances fibrillation, resulting in a higher yield of nanocellulose and producing finer, thinner fibers. Ultrasonic technology surpasses conventional manufacturing methods, thanks to its ability to generate extreme cavitational high shear forces, making it an exceptional tool for nanocellulose production.

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 a Hielscher probe-type sonicator 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 the Hielscher sonicator model 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.

Ultrasonic Dispersion of Nanocellulose

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, power ultrasound is the preferrable technology to formulate nanocellulosic suspensions as the coupling of high-power ultrasound into liquids creates extreme shear forces.
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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.

Ultrasonically Improved Dewatering of Cellulose Nanofibers

Ultrasonically enhanced dewatering of cellulose nanofibers is a cutting-edge technique that significantly improves the efficiency of water removal – making cellulose nanofibers an highly attractive additive for nanopaper production. Nanocellulose fibers, typically requires time-intensive dewatering due to its high water retention capacity. By applying ultrasonic waves, this process is accelerated through the generation of intense cavitational forces, which disrupt the water matrix and facilitate faster, more uniform water expulsion. This not only reduces drying time but also enhances the structural integrity and mechanical properties of the resulting cellulose nanofibers, making it a highly effective method in the production of high-quality nanopapers and other nanomaterials.
Learn more about ultrasonic dewatering of nanopaper!

Industrial Nanocellulose Production using Power Ultrasound

Hielscher Ultrasonics offers a comprehensive range of powerful and reliable ultrasonic solutions, from small lab-scale ultrasonicators to large-scale industrial systems, ideal for the commercial processing of nanocellulose. The key advantage of Hielscher industrial probe-type sonicators lies in their ability to deliver optimal ultrasonic conditions through their flow-through sonoreactors, which come in various sizes and geometries. These reactors ensure that the ultrasound energy is applied consistently and uniformly to the cellulose material, leading to superior processing outcomes.

Hielscher bench-top sonicators, such as the UIP1000hdT, UIP2000hdT, and UIP4000hdT, are capable of producing several kilograms of nanocellulose daily, making them suitable for mid-scale production needs. For large-scale commercial production, the full industrial units like the UIP10000 and UIP16000hdT can handle extensive mass streams, enabling the efficient production of high volumes of nanocellulose.

One of the most significant advantages of Hielscher ultrasonic systems is their linear scalability. Both bench-top and industrial ultrasonicators can be installed in clusters, providing virtually unlimited processing capacity, making them an ideal choice for operations requiring high throughput and reliable performance in the production of nanocellulose.