Document Type : Pulp and Paper
Authors
1 Associate Professor, Department of Wood and Paper Engineering, Savadkooh Branch, Islamic Azad University, Savadkooh, I.R. Iran.
2 Assistant prof., Department of Wood Industry, National University Skill (NUS), Tehran, Iran
Abstract
Paper and cardboard, as biodegradable and lightweight materials, are widely used in the packaging of various industries. Coating paper improves its properties and enhances print quality. Biopolymer coatings have advantages over conventional polymers due to their biodegradability and non-toxicity. The aim of this study is to prepare a coated cardboard sheet with nanomaterials and mineral compounds as a packaging tool and to evaluate the physical properties and printability of white liner paper from Mazandaran Wood and Paper Company. Various amounts of three materials—nanographene, zein protein, and fluorine—along with an acrylamide resin were used for coating the paper using a blade method. The properties examined included thickness, ash paper content, air permeability, roughness, opacity, whiteness, brightness, yellowness, gloss, optical density, and adhesion. This research investigates the effect of surface coating of cardboard (top liner) with nanographene, protein solutions, and mineral materials. Therefore, the goal of this study is to create a barrier against air permeation by coating the outer surface of the cardboard (top liner) with one or more layers of coating that include nanographene, protein solutions, and mineral materials. This coating is designed as the first layer of the cardboard that is in direct contact with the outside, aiming not only to reduce the interaction between the inside and outside of the cardboard but also to enhance printability.
Methodology: The white liner paper with a basis weight of 110 grams was obtained from the Mazandaran Wood and Paper Company. The AO-4 type nanographene was sourced from Graphene Supermarket in the USA, zein protein from Sigma Aldrich, and fluorine from the Minekavan production group. For coating, nanographene, zein, and fluorine were weighed according to specified weight percentages and mixed with 100 grams of distilled water at 50 degrees Celsius for 30 minutes, depending on the treatment conditions. Then, 2.5 grams of styrene-butadiene latex and 0.5 grams of dispersant D200 were added to the mixture and homogenized for 20 minutes at 1500 RPM. A 5% cationic starch solution was also used as a retention aid to enhance the coating. The physical and optical properties were measured according to standard methods. The experimental design was completely randomized. Data analysis was performed using one-way analysis of variance and Duncan's test at a 95% confidence level.
Results: The results of the one-way analysis of variance indicated that there is not a significant difference in thickness, ash content, air permeability, roughness, opacity, whiteness, brightness, yellowness, gloss, and optical density of these papers at a 5% probability level. The greatest thickness is associated with the white liner paper coated with zein and fluorine, while the least thickness belongs to the control sample. Regarding ash content, the highest amount is found in the white liner paper coated with fluorine and graphene. For air permeability, the paper coated with fluorine and nanographene shows the best performance. Roughness results indicate that the white liner paper coated with zein and fluorine has the highest roughness. Additionally, the lowest levels opacity and whiteness are related to the white liner paper coated with zein, nanographene, and fluorine. The adhesion test showed that the coated layers and flexo composite adhered well to the paper.
The results obtained from microscopic studies showed that the addition of nanographene, zein, and fluorine improved the quality of the fiber coating on the paper, and using the laboratory coating method allowed for a more uniform surface to be created on the paper. A significant increase in paper thickness was observed, attributed to changes in the thickness of the base paper. Air permeability increased significantly with coating, and in some cases, this resistance was so high that it could not be measured. The use of fluorine and zein resulted in maximum roughness, while nanographene produced the least roughness. Additionally, the opacity of the papers decreased after coating. Furthermore, optical density improved in the composite coatings, indicating better print quality. The results suggest that the adhesion of the coating layer to the flexo ink was excellent, and compared to the uncoated samples, the amount of paper delamination was lower.
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