Iranian Journal of Wood and Paper Industries

Iranian Journal of Wood and Paper Industries

Evaluation of the properties of recycled liner paper coated with nanolignin

Document Type : Research Paper

Authors
Masoumeh Seyednaseredin 1
Sahab Hedjazi 2
Majid Azizi 1
Ali Abdulkhani 1
Alireza Ashori 3
Arash Dourandish 4
1 Dept. of Wood and Paper Science and Technology, Faculty of Natural Resources, University of Tehran
2 Associate Professor- Gorgan University of Agricultural Sciences and Natural Resources- Faculty of Wood and Paper Engineering- Dept. of Paper Science and Engineering
3 Department of Chemical Technologies Iranian Research Organization for Science and Technology (IROST)
4 Dept. of Agricultural Economy, Faculty of Agriculture, University of Tehran
10.22034/ijwp.2026.2076313.1738
Abstract
Problem definition and objectives: The packaging industry is facing significant environmental challenges due to its reliance on non-biodegradable petroleum-based polymers. Paper and cardboard, as biodegradable alternatives, require appropriate coating due to their porous structure and high moisture absorption. Starch, a conventional coating agent, has limitations such as mechanical weakness and being a food resource. Lignin, an abundant and inexpensive biopolymer byproduct from the pulp and paper industry, with barrier and antibacterial properties, is a promising renewable resource. However, despite extensive research on lignin valorization, practical applications of lignin at the nanoparticle scale in paper coating remain largely unknown and less investigated. The aim of this research is to extract and convert lignin to nanolignin and investigate its application in the coating of recycled liner paper to improve the physical, barrier, and mechanical properties of the paper.
Methodology: Recycled liner paper without any sizing was obtained from Kaveh Paper Manufacturing Company and anionic starch from Glucosan Company. Lignin was extracted from kraft black liquor using the acid precipitation method (pH = 1.5-2) with 30% sulfuric acid and purified with 98% ethanol. Nanolignin was produced by the anti-solvent precipitation method, where lignin was dissolved in ethylene glycol as a polar solvent and precipitated by adding hydrochloric acid as an antisolvent. The dialysis solution and nanoparticles were separated by centrifugation and, after applying ultrasound waves, freeze-dried, and converted into powder. The morphology of nanolignin was evaluated using field emission scanning electron microscopy (FE-SEM). Coating solutions containing nanolignin, lignin, and starch with different percentages were prepared along with carboxymethyl cellulose as a crosslinking agent. The coating was applied at a concentration of 5-7 g/m2 using an automatic coater (30-micron rod), and the samples were stored under standard conditions after drying in an oven. Physical properties (thickness, grammage and density), barrier properties (resistance to water absorption, resistance to air penetration), and mechanical properties (burst, tear, and tensile indices) were measured according to corresponding TAPPI standards. Statistical analysis was performed using ANOVA and Duncan tests.
Results: FE-SEM images confirmed the successful formation of nanolignin with particle sizes of 50-150 nm, whereas the original lignin exhibited particles in the range of 1-5 micrometers. The results demonstrated that nanolignin coatings did not significantly alter the bulk structural properties, such as thickness, grammage and density (P>0.05); however, they significantly influenced surface properties. In the water absorption test, pure nanolignin demonstrated the best performance with a 30% reduction (39.9 g/m²) compared to the uncoated control. This superiority is attributed to the reduction in particle size and the increase in specific surface area. In the air resistance test, highly significant differences were observed among the coatings (P<0.01), with nanolignin significantly enhancing air impermeability. Conversely, mechanical indices (burst, tear, and tensile strength) showed no statistically significant differences among the coatings (P>0.05), indicating that these properties are mainly controlled by the properties of the base paper, fiber network, and interfiber bonds rather than surface coatings. The slight increase tensile index observed for the nanolignin-coated samples (24.36 Nm/g) compared to the control paper (22.49 Nm/g), although not statistically significant, may be attributed to surface-related effects of the coating and limited data fluctuations, indicating that the nanolignin coating does not have a negative effect on the mechanical properties of the paper.
Conclusion: This research investigated the application of nanolignin as a sustainable coating to replace starch in liner paper. Nanolignin extracted from Kraft black liquor was synthesized via antisolvent precipitation method and compared with conventional coatings. Results demonstrated that nanolignin coatings significantly improved air resistance and water absorption resistance, which is of great importance with respect to air permeability in food packaging applications, while mechanical properties (tensile, burst, and tear indices) remained essentially unchanged. These findings introduce nanolignin as a promising bio-based coating material for enhancing the barrier properties of recycled papers, which can provide a foundation for starch replacement and advancing environmental sustainability in the packaging industry.
Keywords
Nanolignin
Sustainable coating
Barrier properties
Kraft lignin
Paper packaging
Subjects
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Iranian Journal of Wood and Paper Industries
Volume 17, Issue 2
Summer 2026
Pages 235-251