Microfibrillated Cellulose Suspension and Its Electrorheology

Comparison of thermal, rheological properties of Finnish Pinus sp. and Brazilian Eucalyptus sp. black liquors and their impact on recovery units

Black liquor (BL) is the major bioproduct and biomass fuel in pulp mill processes. However, the high viscosity of BL makes it a challenging material to work with, resulting in issues with evaporators and heat exchangers during its transport and processing. The thermal and rheological properties of BLs from Pinus sp. (PBL) and Eucalyptus sp. (EBL) were studied. FTIR spectra revealed the presence of the characteristic functional groups and the chemical composition in liquors. TGA/DTG curves showed three characteristic degradation stages related to evaporation of water, pyrolysis of organic groups, and condensation of char. Rheologically, liquors are classified as non-Newtonian and with comportment pseudoplastic. Their rheological dynamic shear properties included a linear viscoelastic region up to 1% shear strain, while frequency sweeps showed that storage modulus (G') > loss modulus (G''), thus confirming the solid-like behavior of both BLs. The rheological study demonstrated that increasing the temperature and oscillatory deformations of PBL and EBL decreased their degree of viscoelasticity, which could favor their pumping and handling within the pulp mill, as well as the droplet formation and swelling characteristics in the recovery furnace.

Transformation of Cellulose via Two-Step Carbonization to Conducting Carbonaceous Particles and Their Outstanding Electrorheological Performance

In this study, cellulose was carbonized in two-steps using hydrothermal and thermal carbonization in sequence, leading to a novel carbonaceous material prepared from a renewable source using a sustainable method without any chemicals and, moreover, giving high yields after a treatment at 600 °C in an inert atmosphere. During this treatment, cellulose was transformed to uniform microspheres with increased specific surface area and, more importantly, conductivity increased by about 7 orders of magnitude. The successful transition of cellulose to conducting carbonaceous microspheres was confirmed through SEM, FTIR, X-ray diffraction and Raman spectroscopy. Prepared samples were further used as a dispersed phase in electrorheological fluids, exhibiting outstanding electrorheological effects with yield stress over 100 Pa at an electric field strength 1.5 kV mm⁻¹ and a particle concentration of only 5 wt%, significantly overcoming recent state-of-the-art findings. Impedance spectroscopy analysis showed clear interfacial polarization of this ER fluid with high dielectric relaxation strength and short relaxation time, which corresponded to increased conductivity of the particles when compared to pure cellulose. These novel carbonaceous particles prepared from renewable cellulose have further potential to be utilized in many other applications that demand conducting carbonaceous structures with high specific surface area (adsorption, catalyst, filtration, energy storage).

Rheological and Tribological Properties of Nanocellulose-Based Ecolubricants

Based on the response surface methodology, a rheological and tribological study carried out on eco-friendly lubricants is described. Such ecolubricants consisted of fibrillated or crystalline nanocellulose in vegetable oil (castor oil, high oleic sunflower oil or their mixtures). Cellulose nanoparticles showed noticeable friction-reducing and anti-wear properties within the boundary and mixed lubrication regimes, which were found to be dependent on nanocellulose concentration, base oil composition and applied normal force. In general, both types of nanocellulose performed equally well. An excellent tribological performance, with large wear scar diameter reductions, was achieved with 3.3 wt.% (or higher) nanocellulose dispersions in castor oil-rich mixtures. The observed behavior was explained on the basis of enhanced viscosity of castor oil-rich suspensions and the preferential action of the most polar components, nanocellulose and ricinoleic acid, in the vicinity of the contact surfaces.

Preparation of Cellulose/Laponite Composite Particles and Their Enhanced Electrorheological Responses

Cellulose, as a natural polymer with an abundant source, has been widely used in many fields including the electric field responsive medium that we are interested in. In this work, cellulose micron particles were applied as an electrorheological (ER) material. Because of the low ER effect of the raw cellulose, a composite particle of cellulose and Laponite was prepared via a dissolution–regeneration process. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) were used to observe the morphologies and structures of the composite particles, which were different from pristine cellulose and Laponite, respectively. The ER performances of raw cellulose and the prepared composite were measured by an Anton Paar rotational rheometer. It was found that the ER properties of the composite were more superior to those of raw cellulose due to the flake-like shapes of the composite particles with rough surface. Moreover, the sedimentation stability of composite improves drastically, which means better suspension stability.

On the Electro-Active Control of Nanocellulose-Based Functional Biolubricants

This research work aims to explore the development of functional nanocellulose-based biolubricants, which allow for an electro-active control of the friction behavior. With this purpose, the influence of both nanocellulose concentration and electric field strength on the lubricant's electrorheological behavior was analyzed. Electric field strengths up to 4 kV/mm were imposed and two different kinds of nanocellulose were studied as the polarizable particulate phase: cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs). Nanocellulose particles were added to castor oil at weight fractions ranging from 0 to 6 wt %. All dispersions exhibited a noticeable variation in their dielectric constant, but not in their conductivity, within a wide frequency range between 1 Hz and 200 kHz, and their dielectric behavior was significantly affected by the particle weight fraction. Noteworthily, it was found that the critical value of nanocellulose concentration, 4 wt %, at which the electro-viscous effect displayed by these dispersions was constrained, yielding a limiting electrorheological (ER) behavior. In addition, the dynamic yield stress dependence on the electric field strength showed a critical value within the interval of 0.8-1.2 kV/mm, suggesting a nonlinear conduction model for these nanocellulose-based ER dispersions. Finally, a maximum leak current intensity for 1 wt % CNF or CNC dispersions and an asymptotic decay at higher concentrations were observed. We conclude that both CNC and CNF nanoparticles have demonstrated that they can endow castor oil with significant ER properties, which remarkably reduced the friction coefficient within the boundary and mixed lubrication regions at electric field strengths lower than 40 V.