PAPER making! g! FROM THE PUBLISHERS OF PAPER TECHNOLOGY INTERNATIONAL ® Volume 11, Number 3, 2025
COATING “Effects of Precoating Color Formulation with Coarse Ground Calcium Carbonate and Porous Precipitated Calcium Carbonate on Paperboard Properties and Printability”, Sun Goo Kim, Sung Jong Yoo, Yong Kyu Lee & Jin-Ho Seo, BioResources , 2025, 20(1), p888. To identify suitable pigments for the precoating of paperboard, the rheological properties of coating colors and their effects on the surface and printing properties of coated paperboard were evaluated with respect to the type and combination of coating pigments. The investigation included porous precipitated calcium carbonate (PCC) and four types of coarse ground calcium carbonate (GCC) of different sizes. As the GCC particle size increased, the viscosity of the coating color decreased in the lowshear region, and the degree of dehydration increased. Coatings containing PCC, which comprised relatively small and highly porous particles, were found to be less dehydrated than coatings containing only GCC. The surface roughness of the coated paperboard increased as the GCC particle size increased, leading to reduced paper gloss. However, increasing the GCC particle size decreased the binder usage and increased surface strength. In conclusion, it is believed that the use of 55-grade GCC rather than the smaller size of 60-grade GCC can reduce costs and enhance surface strength by reducing binder and energy. “High-strength, self-healable, transparent castor-oil-based waterborne polyurethane barrier coatings enabled by a dynamic acylhydrazone co-monomer”, Guowen Zhou, Yunfeng Zhou, Xiaoqian Zhang, Zepeng Lei & Xiaohui Wang, Green Chemistry , 8 (2025). Castor oil-based waterborne polyurethanes (CWPUs) are recognized as sustainable polymers sourced from renewable materials. However, these polymers often exhibit suboptimal mechanical properties and lack reprocessability due to their soft backbones and irreversible crosslinking structures. Herein, we synthesized a novel rigid diol (VSD) featuring dynamic acylhydrazone covalent bonds, which remain stable even in aqueous environments and can contribute additional hydrogen bonding sites, through the condensation reaction of commercially available succinohydrazide with lignin-derived vanillin. VSD was subsequently introduced into the CWPU system to form colorless and transparent CWPU-VSD films, which exhibited self-healable and reprocessable properties due to the dynamic nature of the acylhydrazone bond. By adjusting the ratio of VSD (the ‘hard’ section) to castor oil (the ‘soft’ section), the mechanical properties of CWPU-VSDs were finely tuned, achieving an optimal tensile strength of 33.9MPa. Moreover, the application of this CWPU as a paper-based functional coating was explored. The coated paper exhibited excellent water and oil resistances, low water vapor permeability, good recyclability and biodegradability, suggesting a promising approach for the development of multifunctional and sustainable paper-based barrier coatings. “Sensitivity of the slip condition and viscoplastic effect of the micropolar-Casson fluid during a non-isothermal blade coating process”, Sabeeh Khaliq, Zaheer Abbas, Muhammad Yousuf Rafiq & Mahammad Sajid, Waves in Random and Complex Media , 35(5), 2025. Blade coating is a technique where blade operates as a typical smoothening tool to coat a fluid layer on the moving substrate. This study presents the heat transfer impact on the blade coating process by employing the micropolar-Casson fluid with slip condition and viscous dissipation. The non-dimensional expressions are simplified by operating the Lubrication Approximation Theory (LAT). Analytical solution of the velocity, temperature, and pressure gradient are obtained while numerical (root finding algorithm) used to acquire the pressure and other mechanical quantities. Impacts of coupling number, slip parameter, Brinkman number, microrotation, and Casson parameter on the various mechanical and flow characteristics are inspected through graphs and in tabular form. Micropolar effects decrease the coating thickness and increase the blade load, whereas viscoplastic effect
Technical Abstracts
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