coatings
Article Kaolin-Filled Styrene-Butadiene-Based Dispersion Coatings for Paper-Based Packaging: Effect on Water, Moisture, and Grease Barrier Properties Andrea Marinelli 1,2, * , Maria Vittoria Diamanti 1,2, * , MariaPia Pedeferri 1,2 and Barbara Del Curto 1,2
1 Department of Chemistry, Materials and Chemical Engineering “Giulio Natta”, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milan, Italy 2 National Interuniversity Consortium of Materials Science and Technology (INSTM), Via Giuseppe Giusti 9, 50121 Firenze, Italy * Correspondence: andrea.marinelli@polimi.it (A.M.); mariavittoria.diamanti@polimi.it (M.V.D.); Tel.: +39-0223993137 (M.V.D.) Abstract: Dispersion coating may represent an alternative technology to extrusion coating, currently dominating the market of coated paper-based packaging. Being processed as inks, dispersion coatings can be applied with conventional equipment, achieving lower dry coat grammages. In this work, two styrene-butadiene-based (T g1 ∼ = 0 ◦ C; T g2 ∼ = 15 ◦ C) dispersion coatings filled with different amounts of kaolin were developed and rod-coated on two different paper substrates. The samples were tested for water, moisture, and grease barrier properties. Kaolin-containing formulations showed moisture barrier as low as 15 g/(m 2 · day), as well as grease barrier higher than 24 h. The best formulation involved 20% by weight of kaolin, whereas higher amounts were detrimental for water barrier, beneficial for moisture barrier, and slightly detrimental for grease barrier properties. Benchmarked to two commercial grades, kaolin-filled coatings strongly improved grease barrier, yet achieving similar moisture barrier.
Keywords: paper packaging; clay; dispersion; barrier coating; latex
Citation: Marinelli, A.; Diamanti, M.V.; Pedeferri, M.; Del Curto, B. Kaolin-Filled Styrene-Butadiene- Based Dispersion Coatings for Paper-Based Packaging: Effect on Water, Moisture, and Grease Barrier Properties. Coatings 2023 , 13 , 195. https://doi.org/10.3390/ coatings13010195
1. Introduction Recently, cellulosic substrates gained much interest from the packaging industry as they are regarded to be much more sustainable solutions compared with polymeric solutions. However, cellulosic substrates cannot guarantee barrier properties that are comparable to polymeric counterparts without any functionalization. In particular, due to the highly hydrophilic nature of cellulose, water barrier properties represent a crucial limit [1]. Barrier improvement can be achieved in different ways, such as internal sizing, surface sizing, and surface coating [2–4], yet numerous packaging solutions on the market are surface-coated. Extrusion coating, lamination, and dispersion coatings represent three main surface coating technologies, despite that only the first two are dominating the market [5]. Dispersion coatings can be defined as (water-based) colloidal dispersions of polymeric particles, plus other additives, such as defoamers, dispersants, and possible functional fillers [6,7]. Early studies and applications date back to the 1940s [8]; despite being widely used for printing paper grades, it was only recently that dispersion coatings gained much interest in the industry for barrier purposes, boosted by the transition from plastic to paper-based packaging. Additionally, such technology was boosted by stringent directives increasingly asking for the reduction of noncellulosic content in the packaging to fulfill design guidelines for improved recyclability [9–11]. Several companies are producing on an industrial scale polymeric latices used in coating formulations. Such products are generally based on styrene-butadiene and styrene- acrylate latices, as reported in the literature [12]. Previous literature [13–19] widely focused
Academic Editor: Isabel Coelhoso
Received: 28 December 2022 Revised: 11 January 2023 Accepted: 12 January 2023 Published: 15 January 2023
Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
Coatings 2023 , 13 , 195. https://doi.org/10.3390/coatings13010195
https://www.mdpi.com/journal/coatings
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