Effect of latex on surface structure and wetting of pigment coatings

Study of tobacco-derived proteins in paper coatings

Replacing synthetic polymers with renewable alternatives is a critical challenge for the packaging industry. This research investigated the use of leaf-based proteins as a sustainable co-binder in the coating formulations for paper-based packaging and other applications. Protein isolates from tobacco leaf and alfalfa concentrates were characterized using the Pierce protein assay, Kjeldahl nitrogen, and gel electrophoresis. The proteins were tested as co-binders in a typical latex-based paper coating formulation. The rheology and water retention properties of the wet coating and the surface, optical, structural, and strength properties of coated papers were measured. The coating performance was affected by the purity, solubility, and molecular weight of the tobacco protein and exhibited a shear-thinning behavior with lower water retention than soy protein. Analysis by scanning electron microscopy and time of flight secondary ion mass spectroscopy on the dried coating layer containing tobacco protein showed enhanced porosity (advantageous for package glueability) relative to the control latex coating. The tobacco protein offers adequate coverage and coating pigment distribution, indicating that this protein can be a suitable option in coatings for packaging applications.

Matt Polyurethane Coating: Correlation of Surface Roughness on Measurement Length and Gloss

Matt polyurethane coating was successfully prepared through the synergistic effect of castor oil and phenolic epoxy resin into polyurethane backbone. The formation mechanism may be ascribed to the modulus mismatch between the partially modified epoxy polyurethane and partially unmodified polyurethane. Scanning electron microscopy (SEM) was used to observe the micro-rough surface morphologies. Atomic force microscopy (AFM) and three-dimensional (3D) surface profilometer were applied to calculate a series of surface roughness parameters in different dimensions, such as S_a, S_q, S_p, S_v, S_z, S_ku, S_sk, etc. The exciting results of this paper—the correlation of surface roughness on measurement length and gloss—are explored in detail. It reveals the extrinsic property of measured roughness with measurement length and provides guidance for what kind of incident angle gloss meters (20°, 60°, and 85°) best describe the gloss of matt polyurethane coating.

Development of paper substrate for paper spray MS in high-sensitivity analysis of biological samples

Paper spray (PS) has demonstrated a promising future for direct mass spectrometric analysis. In the process of PS, paper substrate has been demonstrated as a crucial factor in determining the final performance of PS-MS, and therefore much attention is paid to modification of paper substrate. In this review, we systematically introduce the development of paper substrate for PS. Various commercial and modified papers are comprehensively reviewed, and much effort is focused on some physical and chemical approaches for modification of paper substrate. The application of modified paper substrates to biological sample analyses is discussed. The future promising directions of paper substrate for PS are highlighted.

Characterization of the Interface Between Coating and Fibrous Layers of Paper

Coated paper is an example of a multi-layer porous medium, involving a coating layer along the two surfaces of the paper and a fibrous layer in the interior of the paper. The interface between these two media needs to be characterized in order to develop relevant modeling tools. After careful cutting of the paper, a cross section was imaged using focused ion beam scanning electron microscopy. The resulting image was analyzed to characterize the coating layer and its transition to the fibrous layer. Such image analysis showed that the coating layer thickness is highly variable, with a significant fraction of it being thinner than a minimum thickness required to keep ink from invading into the fibrous layer. The overall structure of the coating and fibrous layers observed in this analysis provide insights into how the system should be modeled, with the resulting conclusion pointing to a specific kind of multi-scale modeling approach.

Droplet Imbibition into Paper Coating Layer: Pore-Network Modeling Simulation

Liquid penetration into thin porous media such as paper is often simulated using continuum-scale single-phase Darcy's law. The underlying assumption was that a sharp invasion front percolates through the layer. To explore this ambiguous assumption and to understand the controlling pore-scale mechanisms, we have developed a dynamic pore-network model to simulate imbibition of a wetting phase from a droplet into a paper coating layer. The realistic pore structures are obtained using the FIB-SEM imaging of the coating material with a minimum resolution of 3.5 nm. Pore network was extracted from FIB-SEM images using Avizo software. Data of extracted pore network are used for statistically generating pore network. Droplet sizes are chosen in the range of those applicable in inkjet printing. Our simulations show no sharp invasion front exists and there is the presence of residual non-wetting phase. In addition, penetration of different sizes of droplets of different material properties into the pore network with different pore body and pore throat sizes are performed. We have found an approximately linear decrease in droplet volume with time. This contradicts the expected t -behavior in vertical imbibition that is obtained using macroscopic single-phase Darcy's law. With increase in flow rate, transition of imbibition invasion front from percolation-like pattern to a more sharper one with less trapping of non-wetting phase is also reported. Our simulations suggest that the single-phase Darcy's law does not adequately describe liquid penetration into materials such as paper coating layer. Instead Richards equation would be a better choice.

Surface characterization of trimethoxysilane-containing high-solid hydroxyl acrylic resin films

In recent years, organosilane-containing copolymers have attracted much attention in antifouling coatings, automotive coatings, fiber, composite materials, biomedical materials, and latex and protection coatings against corrosion owing to their excellent weathering and low surface energy. Trimethoxysilane-containing high-solid hydroxyl acrylic resin used for automotive coatings was prepared by in situ free radical polymerization. The surfaces of the resin film were characterized by solid surface energy, atomic force microscopy and X-ray photoelectron spectroscopy (XPS) measurements. With the increase in silicone content from 0 to 2.5 wt.%, the surface energy of trimethoxysilane-containing hydroxyl acrylic copolymer films decreased from 49 to 40 mN/N and the surface roughness (Rms) on the surface of thin films increased from 0.427 to 0.887 Å. The XPS result indicated that the surface accumulation phenomena of silicone occurred in the surface of the thin films. The phenomena can explain the reason why the incorporation of trimethoxysilane (MPS) into acrylic copolymer by in situ polymerization can decrease its surface energy and increase its outdoor weathering.

Liquid spreading on solid surfaces and penetration into porous matrices: Coated and uncoated papers

Liquid spreading on solid surfaces and penetration into porous matrices (powders and coated papers) are investigated. The influence of chemical and structural heterogeneity on equilibrium and dynamic surface wetting is evaluated both experimentally and theoretically. Single capillary systems are used to identify the predominating mechanisms for acceleration, momentum, inertial and viscous liquid penetration. Different stages of vertical and horizontal penetration of liquids from non-limited, restricted (sessile drop) and cut-off sources into powders and papers are evaluated with reference to a range of frequently used models. For all types of liquid transport power-law exponents are used to relate all observations. The applicability of models from which the exponents are derived is discussed. Results are compared to theoretical predictions for liquid penetration. Models are of general validity, but the focus is placed on probe liquid spreading on and penetrating into coated and uncoated papers. This sets a particular challenge, since papers are heterogeneous layered composites of powder compacts on fibrous network. For the evaluation of models published results are supported by extended original results.

A silica coated paper substrate: development and its application in paper spray mass spectrometry for rapid analysis of pesticides in milk

A novel silica coated paper substrate has been developed, which demonstrated a high capacity for direct analysis of pesticides in paper spray mass spectrometry.