Role of Cellulose Nanofibrils in Structure Formation of Pigment Coating Layers

Preparation of Tung Oil Microcapsule and Its Effect on Wood Surface Coating

Through the optimized preparation of tung oil microcapsules, five kinds of microcapsules containing different core material content were obtained to explore the influence of microcapsules on water-based paint film and the self-healing ability of microcapsules. The results showed that the microcapsules had good appearance, and the microcapsules were successfully prepared. The color difference in the paint film increased with the increase in microcapsule content, and the gloss decreased gradually. The mechanical test showed that adding microcapsules increased the toughness of the paint film to a certain extent, and the performance of the paint film was unchanged or better. The results showed that paint film with the core–wall ratio of 0.78:1 had the best performance and self-healing function when microcapsules were added.

Rheological Behavior of Spectrally Selective Coatings for Polymeric Solar Absorbers

Since the world’s energy demands are growing rapidly, there is a constant need for new energy systems. One of the cleanest, most abundant, and renewable natural resources available is solar energy; therefore, the development of surfaces with high absorption of solar radiation is increasing. To achieve the best efficiency, such surfaces are coated with spectrally selective coatings, which are strongly influenced by the pigments and resin binders. Spectrally selective paints have a very specific formulation, and since the applied dry coatings should exhibit high spectral selectivity, i.e., high solar absorptivity and low thermal emissivity, the rheological properties of liquid paints are of great importance. In the present work, we studied the effect of the rheological properties of liquid thickness-insensitive spectrally selective (TISS) paints on the spectral selectivity and adhesion of dry coatings on a polymeric substrate. The results showed that the functional and adhesion properties of dry coating on polymeric substrates is strongly dependent on the rheological properties of the binder and catalyst used for the preparation of the liquid paints. It was shown that the paints with good spectral selective properties (thermal emissivity eT < 0.36 and solar absorptivity aS > 0.92) and good adhesion (5B) can be prepared for polymer substrates.

Boosted output performance of nanocellulose-based triboelectric nanogenerators via device engineering and surface functionalization

Triboelectric nanogenerators (TENGs) provide promising potential to sustainably power modern portable electronic devices through harvesting mechanical energy from the environment. There is a need to further improve the sustainability credentials of TENGs by reducing the usage of non-renewable materials. Nanocellulose possessing outstanding properties, can partially replace non-renewable materials used in TENGs. Here, main sources and types of nanocellulose and methods of forming nanocellulose-based 2D/3D configurations used as triboelectric layers of TENGs are introduced. Cellulose has relatively weak tribopositivity and this review describes effective strategies of amplifying the output performance of TENGs possessing a nanocellulose-based tribopositive layer. Furthermore, efforts made to change the polarity of nanocellulose structures in order to use them as both positive and negative triboelectric layers are reviewed and their output performance is compared to that of all-synthetic polymer-based TENGs. Finally, requirements expected to be met in near future for development of commercial green nanocellulose-based TENGs are highlighted.

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.

The Effect of a Polymer-Stabilized Latex Cobinder on the Optical and Strength Properties of Pigment Coating Layers

Coated paper with a porous coating layer may have enhanced light-scattering ability and thus favorable optical properties. However, the increased porosity of such a coating layer is likely to decrease the strength of the coated paper, thereby adversely affecting the quality of the paper in the printing and converting processes. In this research, polymer-stabilized (PS) latex was prepared and used as a cobinder for the pigment coating of the paper. The PS latex particles were colloidally stabilized by a 3:1 mixture of starch and polyvinyl alcohol. The influence of the PS latex cobinder on the viscosity, sedimentation, and consolidation of coating colors was investigated. In addition, the effect of the cobinder on the properties of coating layers, namely, their porosity and surface, optical, and tensile properties, was examined. The results revealed that the PS latex cobinder formed microstructures in the coating colors and affected their viscosity. The addition of PS latex also led to enhanced interactions between coating color components, which affected the consolidation of the coating color, resulting in the formation of dried coating layers with greater porosity and improved optical properties (i.e., higher brightness and opacity) relative to coatings without the PS latex cobinder. Furthermore, the addition of PS latex improved the tensile strength of the coating layers, which was attributable to the small size and the polymeric protective shell of the cobinder particles. Thus, these results show that this PS latex cobinder has the potential to be used for the production of high-quality coated paper products.

The Influence of Drying Conditions of Clay-Based Polymer Coatings on Coated Paper Properties

Coatings based on pigment and polymer binders are applied on paper surfaces to improve their surface, optical, and printing properties. Besides the coating composition, the structure and properties of the coated papers are influenced by the coating layer consolidation upon drying. In this study, the influence of drying conditions on the structure and properties of coating layers based on natural pigments (clay) and polymer binders (butadiene acrylonitrile latex) has been analyzed. Using a laboratory rod Mayer device, the coatings were applied as thin layer (about 15–16 g/m2) on the paper surface and samples of coated paper were dried at 20 and 105 °C temperatures. The optical, structural, and water absorption properties of the coating layer were evaluated by the measurement of gloss, opacity, void fraction, light scattering, and contact angle. The obtained results highlighted that both the drying temperature and latex content in the coating color have a synergic effect on the coated paper quality.

The Application of Polysaccharides and Their Derivatives in Pigment, Barrier, and Functional Paper Coatings

As one of the most abundant natural polymers in nature, polysaccharides have the potential to replace petroleum-based polymers that are difficult to degrade in paper coatings. Polysaccharide molecules have a large number of hydroxyl groups that can bind strongly with paper fibers through hydrogen bonds. Chemical modification can also effectively improve the mechanical, barrier, and hydrophobic properties of polysaccharide-based coating layers and thus can further improve the related properties of coated paper. Polysaccharides can also give paper additional functional properties by dispersing and adhering functional fillers, e.g., conductive particles, catalytic particles or antimicrobial chemicals, onto paper surface. Based on these, this paper reviews the application of natural polysaccharides, such as cellulose, hemicellulose, starch, chitosan, and sodium alginate, and their derivatives in paper coatings. This paper analyzes the improvements and influences of chemical structures and properties of polysaccharides on the mechanical, barrier, and hydrophobic properties of coated paper. This paper also summarizes the researches where polysaccharides are used as the adhesives to adhere inorganic or functional fillers onto paper surface to endow paper with great surface properties or special functions such as conductivity, catalytic, antibiotic, and fluorescence.

Development and Application of Nanosized Polymer-Stabilized Cobinders and Their Effect on the Viscoelastic Properties and Foaming Tendencies of Coating Colors

Polymer latexes have long been used as coating binders by various branches of industry due to their capacity to adhere coating components and increase the strength of the dried final coatings. In addition, these latexes have been known to affect the rheology of coating dispersions. Currently, emulsion polymerization is the most widely used method of producing polymer latexes. While the stability of these latexes is primarily provided by electrostatic repulsion between surfactants, this property also causes foaming problems during coating processes. In this research, these problems were addressed by preparing polymer-stabilized (PS) latexes that contained different concentrations of acrylic acid. Steric protection of the latexes was provided by a protective shell consisting of starch and poly(vinyl alcohol) (PVA). The viscosity, particle size, ζ-potential, and viscoelastic behavior of the prepared latexes were investigated as a function of pH, and their surface tension and foaming tendencies were evaluated. The latexes were applied as coating cobinders in calcium carbonate and clay coating dispersions, and the viscoelastic properties, surface tensions, and foaming tendencies of these mixtures were studied. The presence of acrylic acid monomers was found to be an important factor affecting the viscosity, particle size, and ζ-potential of the PS latexes prepared in this work, which were further found to generate less foam than comparable emulsion-polymerized latexes. Finally, coating color viscoelastic properties were modified via the partial substitution of styrene-butadiene (S/B) latexes with PS latexes.

Structural Changes of the Coating Layer by Styrene/Acrylate Latex with Hydroxyethyl Methacrylate

The coating structure is directly related to quality of coated paper, especially printability. Its structure mainly consists of pigment, binder, and additives. Binder has a significant influence on the coating structure because it is involved in the structure forming process and takes a key role in maintaining the structure. In this study, styrene acrylate (S/A) latex with hydroxyethyl methacrylate (HEMA) as a comonomer was used as a binder, and the influence of HEMA contents on latex swelling and coating structure was investigated. The S/A latex particle swelled more with an increasing HEMA content, which significantly influenced coating color and coating layer characteristics. The viscosity of coating color became thick, and the dewatering of coating color was suppressed. The HEMA monomer that swelled latex particle allowed the coating layer to consolidate rapidly, which made the coating layer more porous and more uniform.