Rheological behavior of cellulose nanowhisker suspension under magnetic field

Uniformly aligned flexible magnetic films from bacterial nanocelluloses for fast actuating optical materials

Naturally derived biopolymers have attracted great interest to construct photonic materials with multi-scale ordering, adaptive birefringence, chiral organization, actuation and robustness. Nevertheless, traditional processing commonly results in non-uniform organization across large-scale areas. Here, we report magnetically steerable uniform biophotonic organization of cellulose nanocrystals decorated with superparamagnetic nanoparticles with strong magnetic susceptibility, enabling transformation from helicoidal cholesteric (chiral nematic) to uniaxial nematic phase with near-perfect orientation order parameter of 0.98 across large areas. We demonstrate that magnetically triggered high shearing rate of circular flow exceeds those for conventional evaporation-based assembly by two orders of magnitude. This high rate shearing facilitates unconventional unidirectional orientation of nanocrystals along gradient magnetic field and untwisting helical organization. These translucent magnetic films are flexible, robust, and possess anisotropic birefringence and light scattering combined with relatively high optical transparency reaching 75%. Enhanced mechanical robustness and uniform organization facilitate fast, multimodal, and repeatable actuation in response to magnetic field, humidity variation, and light illumination.

Naturally derived biopolymers attracted great interest to construct photonic materials but traditional processing commonly results in non-uniform organization across largescale areas. Here, the authors report a uniform biophotonic organization of cellulose nanocrystals decorated with superparamagnetic nanoparticles enabling transformation from helicoidal cholesteric to uniaxial nematic phase with near-perfect orientation.

Spin-Induced Organization of Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) are composed of chiral cellulose units, which form chiral nematic liquid crystals in water that, upon drying, self-assemble to more complex spiral chiral sheets. This secondary structure arrangement is found to change with an external magnetic or electric field. Here, we show that one of the basic organization driving forces is electron spin, which is produced as the charge redistributes in the organization process of the chiral building blocks. It is important to stress that the electron spin-exchange interactions supply the original driving force and not the magnetic field per se. The results present the first utilization of the chiral-induced spin selectivity (CISS) effect in sugars, enabling one to regulate the CNC bottom-up fabrication process. Control is demonstrated on the organization order of the CNC by utilizing different magnetization directions of the ferromagnetic surface. The produced spin is probed using a simple Hall device. The measured Hall resistance shows that the CNC sheets' arrangement is affected during the first four hours as long as the CNC is in its wet phase. On introducing the 1,2,3,4-butanetetracarboxylic acid cross-linker into the CNC sheet, the packing density of the CNC helical structure is enhanced, presenting an increase in the Hall resistance and the chiral state.

Role of the Exchange Interactions in the Stability of the Cellulose

The problem of the origin of biochirality and the related problem of the initial monomers' selection are still under discussion, and the main point here is not the mechanics of...

Rheological Aspects of Cellulose Nanomaterials: Governing Factors and Emerging Applications

Cellulose nanomaterials (CNMs), mainly including nanofibrillated cellulose (NFC) and cellulose nanocrystals (CNCs), have attained enormous interest due to their sustainability, biodegradability, biocompatibility, nanoscale dimensions, large surface area, facile modification of surface chemistry, as well as unique optical, mechanical, and rheological performance. One of the most fascinating properties of CNMs is their aqueous suspension rheology, i.e., CNMs helping create viscous suspensions with the formation of percolation networks and chemical interactions (e.g., van der Waals forces, hydrogen bonding, electrostatic attraction/repulsion, and hydrophobic attraction). Under continuous shearing, CNMs in an aqueous suspension can align along the flow direction, producing shear-thinning behavior. At rest, CNM suspensions regain some of their initial structure immediately, allowing rapid recovery of rheological properties. These unique flow features enable CNMs to serve as rheological modifiers in a wide range of fluid-based applications. Herein, the dependence of the rheology of CNM suspensions on test protocols, CNM inherent properties, suspension environments, and postprocessing is systematically described. A critical overview of the recent progress on fluid applications of CNMs as rheology modifiers in some emerging industrial sectors is presented as well. Future perspectives in the field are outlined to guide further research and development in using CNMs as the next generation rheological modifiers.

A review on processing techniques of bast fibers nanocellulose and its polylactic acid (PLA) nanocomposites

The utilization of nanocellulose has increasingly gained attentions from various research fields, especially the field of polymer nanocomposites owing to the growing environmental hazardous of petroleum based fiber products. Meanwhile, the searching of alternative cellulose sources from different plants has become the interests for producing nanocellulose with varying characterizations that expectedly suit in specific field of applications. In this content the long and strong bast fibers from plant species was gradually getting its remarkable position in the field of nanocellulose extraction and nanocomposites fabrications. This review article intended to present an overview of the chemical structure of cellulose, different types of nanocellulose, bast fibers compositions, structure, polylactic acid (PLA) and the most probable processing techniques on the developments of nanocellulose from different bast fibers especially jute, kenaf, hemp, flax, ramie and roselle and its nanocomposites. This article however more focused on the fabrication of PLA based nanocomposites due to its high firmness, biodegradability and sustainability properties in developed products towards the environment. Along with this it also explored a couple of issues to improve the processing techniques of bast fibers nanocellulose and its reinforcement in the PLA biopolymer as final products.

Characterization of pulp derived nanocellulose hydrogels using AVAP® technology

Bioinspiration from hierarchical structures found in natural environments has heralded a new age of advanced functional materials. Nanocellulose has received significant attention due to the demand for high-performance materials with tailored mechanical, physical and biological properties. In this study, nanocellulose fibrils, nanocrystals and a novel mixture of fibrils and nanocrystals (blend) were prepared from softwood biomass using the AVAP® biorefinery technology. These materials were characterized using transmission and scanning electron microscopy, and atomic force microscopy. This analysis revealed a nano- and microarchitecture with extensive porosity. Notable differences included the nanocrystals exhibiting a compact packing of nanorods with reduced porosity. The NC blend exhibited porous fibrillar networks with interconnecting compact nanorods. Fourier transform infrared spectroscopy and X-ray diffraction confirmed a pure cellulose I structure. Thermal studies highlighted the excellent stability of all three NC materials with the nanocrystals having the highest decomposition temperature. Surface charge analysis revealed stable colloid suspensions. Rheological studies highlighted a dominance of elasticity in all variants, with the NC blend being more rigid than the NC fibrils and nanocrystals, indicating a double network hydrogel structure. Given these properties, it is thought that these materials show great potential in (bio)nanomaterial applications where careful control of microarchitecture, surface topography and porosity are required.

Effect of Cationic Surface Modification on the Rheological Behavior and Microstructure of Nanocrystalline Cellulose

In the present work, the microstructure and rheological behavior of nanocrystalline cellulose (NCC) and cationically modified NCC (CNCC) were comparatively studied. The resultant CNCC generally showed improved dispersion and higher thermal stability in comparison to the un-modified NCC. The rheological behavior demonstrated that the viscosity of the NCC suspension substantially decreased with the increasing shear rate (0.01–100 s⁻¹), showing the typical characteristics of a pseudoplastic fluid. In contrast, the CNCC suspensions displayed a typical three-region behavior, regardless of changes in pH, temperature, and concentration. Moreover, the CNCC suspensions exhibited higher shear stress and viscosity at a given shear rate (0.01–100 s⁻¹) than the NCC suspension. Meanwhile, the dynamic viscoelasticity measurements revealed that the CNCC suspensions possessed a higher elastic (G′) and loss modulus (G″) than NCC suspensions over the whole frequency range (0.1–500 rad·s⁻¹), providing evidence that the surface cationization of NCC makes it prone to behave as a gel-like structure.

Controlling the Photonic Properties of Cholesteric Cellulose Nanocrystal Films with Magnets

The self-assembly of cellulose nanocrystals is a powerful method for the fabrication of biosourced photonic films with a chiral optical response. While various techniques have been exploited to tune the optical properties of such systems, the presence of external fields has yet to be reported to significantly modify their optical properties. In this work, by using small commercial magnets (≈ 0.5-1.2 T) the orientation of the cholesteric domains is enabled to tune in suspension as they assemble into films. A detailed analysis of these films shows an unprecedented control of their angular response. This simple and yet powerful technique unlocks new possibilities in designing the visual appearance of such iridescent films, ranging from metallic to pixelated or matt textures, paving the way for the development of truly sustainable photonic pigments in coatings, cosmetics, and security labeling.

Benchmarking Cellulose Nanocrystals: From the Laboratory to Industrial Production

The renewability, biocompatibility, and mechanical properties of cellulose nanocrystals (CNCs) have made them an attractive material for numerous composite, biomedical, and rheological applications. However, for CNCs to shift from a laboratory curiosity to commercial applications, researchers must transition from CNCs extracted on the bench scale to material produced on an industrial scale. There are a number of companies currently producing kilogram to ton per day quantities of sulfuric acid-hydrolyzed CNCs as well as other nanocelluloses, as described herein. With the recent intensification of industrially produced CNCs and the variety of cellulose sources, hydrolysis methods, and purification procedures, the characterization of these materials becomes critical. This has further been justified by the past two decades of research that demonstrate that the CNC stability and behavior are highly dependent on the surface chemistry, surface charge density, and particle size. This work outlines key test methods that should be employed to characterize these properties to ensure a "known" starting material and consistent performance. Of the sulfuric acid-extracted CNCs examined, industrially produced material compared well with laboratory-made CNCs, exhibiting similar charge density, colloidal and thermal stability, crystallinity, morphology, and self-assembly behavior. In addition, it was observed that further purification of CNCs using Soxhlet extraction in ethanol had minimal impact on the nanoparticle properties and is unlikely to be necessary for many applications. Overall, the current standing of industrially produced CNCs is positive, suggesting that the evolution to commercial-scale applications will not be hindered by CNC production.

Cooperative Ordering and Kinetics of Cellulose Nanocrystal Alignment in a Magnetic Field

Cellulose nanocrystals (CNCs) are emerging nanomaterials that form chiral nematic liquid crystals above a critical concentration (C*) and additionally orient within electromagnetic fields. The control over CNC alignment is significant for materials processing and end use; to date, magnetic alignment has been demonstrated using only strong fields over extended or arbitrary time scales. This work investigates the effects of comparatively weak magnetic fields (0-1.2 T) and CNC concentration (1.65-8.25 wt %) on the kinetics and degree of CNC ordering using small-angle X-ray scattering. Interparticle spacing, correlation length, and orientation order parameters (η and S) increased with time and field strength following a sigmoidal profile. In a 1.2 T magnetic field for CNC suspensions above C*, partial alignment occurred in under 2 min followed by slower cooperative ordering to achieve nearly perfect alignment in under 200 min (S = -0.499 where S = -0.5 indicates perfect antialignment). At 0.56 T, nearly perfect alignment was also achieved, yet the ordering was 36% slower. Outside of a magnetic field, the order parameter plateaued at 52% alignment (S = -0.26) after 5 h, showcasing the drastic effects of relatively weak magnetic fields on CNC alignment. For suspensions below C*, no magnetic alignment was detected.