PAPER making! FROM THE PUBLISHERS OF PAPER TECHNOLOGY INTERNATIONAL ® Volume 8, Number 2, 2022
study addresses the question of how the difference in mechanical properties of the individual layers in a multi-ply commercial paperboard affects the outcome of the tray- forming operation. Two commercially produced paperboards with nearly identical mechanical properties when conventionally tensile tested were considered. These boards are produced on different machines with the same target grammage and density. Despite the similar mechanical properties, their performance in a given tray-forming operation was drastically different, with one of the boards showing an unacceptable failure rate. To investigate the difference seen during converting operations, a detailed multi-ply finite element model was built to simulate the converting operation. The present model considers a critical area of the paperboard known to exhibit failures. To derive the constitutive relations for each ply in the sub-model, both boards were split to single out individual plies which were then tensile tested. Including the properties of individual plies revealed large differences between the boards when it comes to the distribution of the properties in the thickness direction. In particular, the top plies differed to a large extent. This is attributed to the difference in refining energies for the plies. The results from the three-ply sub-model demonstrated the importance of including the multi-ply structure in the analysis. Weakening of the top ply facing the punch by using lower refining energy considerably increased the risk of failure of the entire board. These results suggest that there is room for optimizing the board performance by adjusting the refining energy at the ply level. “Improving water vapor barrier of cellulose based food packaging using double layer coatings and cellulose nanofibers”, Mohammed Z. Al -Gharrawi, Jinwu Wang & Douglas W. Bousfield, Food Packaging and Shelf Life , Vol.33, 100895 (Sept. 2022). Paper based packaging has the potential to replace many plastic-based systems if the required barrier properties can be obtained. Water borne barrier coatings have the potential to generate good barrier layers, but their performance is often less than expected. Recent work has shown improved performance of these coatings when applied on paper that has a cellulose nanofiber layer. Here, papers with a cellulose nanofiber layer were coated with barrier coatings at different coat weights applied as single-layers, as double-layers, and single-layers pressed together in a hot press in order to generate a packaging system that has good barrier properties. The performance of double-layer samples resulted in moisture transmission rates that were 40 – 70% of the value of the single-layer systems. Surprisingly, the hot-pressing of two dry layers showed no advantage compared to the single-layer system. A barrier pigment added to one formulation improved the performance further and followed the same trends. Three dimensional models of diffusion through layers that have defects help explain the results. The work shows a potential path to produce paper-based packaging that has both good oxygen and water vapor barrier properties. PAPERMAKING “ Janus particles stabilized alkenyl succinic anhydride emulsion as internal sizing agent ”, Hongzhen Wang, Jujie Sun, Yongxian Zhao, Zhongqin Zhang & Shijie Cheng, Cellulose , Vol.29, pp.6361-6372 (2022). Alkenyl succinic anhydride (ASA) is widely used in papermaking industry as an internal sizing agent. In situ emulsification of ASA using cationic starch is conventionally practiced because of the low shelf life of ASA emulsion. We synthesized Janus particles by surfactant-free seeded polymerization to stabilize ASA emulsion. The morphology evolution and anisotropic compositions of Janus particles were confirmed by transmission electron microscopy. The Janus particles showed a strong tendency to adsorb at the ASA – water interface and enhanced the stability of ASA emulsion. The droplet size of ASA emulsion decreased and emulsion
Technical Abstracts
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