Document Type : Research Paper
Authors
1 Associate Professor, Department of Wood and Paper Engineering, Savadkooh Branch, Islamic Azad University, Savadkooh, I.R. Iran.
2 Department of Wood Industry, National University Skill (NUS), Tehran, Iran.
Abstract
Background and objectives: Fruit packaging cardboard protects fruits from impacts, pressure, and damage during transportation, while helping to maintain their freshness and quality. To achieve these objectives, it is essential to enhance the strength of the cardboard and minimize the interaction between its interior and exterior. At the same time, it must be biodegradable, durable, and environmentally friendly. Kraft paper is recognized as a suitable option for preserving the quality of fruits. Therefore, this research aims to improve the barrier and mechanical properties of cardboard by applying coatings of nano-graphene, fluorine, and zein, both separately and in combination, to provide consumers with higher quality cardboard
Methodology: The brown kraft liner paper with a basis weight of 120 grams was obtained from the Mazandaran Wood and Paper Company. The nanographene type AO-4 was sourced from Graphene Supermarket in the USA, zein protein from Sigma Aldrich, and fluorine from Mine Kavaran Production Group. For coating, the nanographene, zein, and fluorine were weighed in specified weight percentages and mixed with 100 grams of distilled water for 30 minutes at 50 degrees Celsius, 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 added as a retention aid to enhance the coating. The coating solutions were applied to the paper sheets using an Auto Bar Coater (GBC - A4 GIST Co., Ltd). The physical and mechanical properties were measured according to TAPPI and ISO standards. The experimental design was completely randomized, and data analysis was performed using one-way ANOVA and Duncan's test at a 95% confidence level.
Results: The one-way ANOVA analysis indicated that there are significant differences at the 5% level among the thickness, water absorption, and porosity of the 8 types of paper. The greatest thickness was observed in the brown liner paper coated with graphene and fluorine, while the lowest thickness was found in the control sample, with a difference of 27% between the maximum and minimum thickness. The lowest water absorption was noted in the brown liner paper coated with zein, fluorine, and nano-graphene, with a difference of 647.5% between the maximum and minimum water absorption. Additionally, the least porosity was attributed to the paper coated with nano-graphene, showing a difference of 7365.8% between the maximum and minimum porosity. Density analysis revealed that the highest density was observed in the sample coated with zein and nano-graphene, with a difference of 14.5% between the maximum and minimum density. Furthermore, the highest surface smoothness was recorded in the paper coated with nano-graphene and zein, with a difference of 23.9% between the maximum and minimum surface smoothness. For the tensile and tear resistance index, no significant difference was observed at the 5% level, with differences of 15.5% and 26.4% between the maximum and minimum tensile and tear resistance indices, respectively. However, for burst resistance, the lowest value was found in the paper coated with fluorine and zein, with a difference of 14.2% between the maximum and minimum burst resistance. In terms of ring crush test, the highest resistance was related to the paper coated with zein, fluorine, and nano-graphene, with a difference of 16.1% between the maximum and minimum ring crush test.
Conclusion: The goal of food packaging is to extend shelf life and protect against spoilage factors. Paper and cardboard, as packaging materials, have specific advantages and disadvantages, including a lack of resistance to moisture. This research addresses the improvement of the physical and mechanical properties of kraft liner paper for fruit packaging and has demonstrated that coating increases thickness and reduces water absorption. These coatings enhance the prevention of water absorption by penetrating the pores of the paper. Various factors affect water permeability, including the paper structure and the type of coating. The use of nano-graphene and zein leads to a reduction in paper porosity and an improvement in its mechanical properties. In this study, coating the paper with nano-graphene and zein significantly increased barrier properties and improved paper quality. Additionally, the results indicate that these compounds can help reduce water absorption and porosity of the paper.
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