Iranian Journal of Wood and Paper Industries

Iranian Journal of Wood and Paper Industries

Evaluation of nano-sized fraction index as a benchmark parameter for cellulose nanofiber production

Document Type : Research Paper

Authors
ُSeyedeh Faegheh Mousavi 1
َAmir Khosravani 2
Pejman Rezayati Charani 3
1 Wood and Paper Science and Technology Department, Natural Resources Faculty, Tarbiat Modares University, Noor, Mazandaran, Iran.
2 Wood and Paper Science and Technology Department, Natural Resources Faculty, Tarbiat Modares University, Noor, Mazandaran,Iran
3 Department of Forestry and Cellulose Industry, Faculty of Natural Resources, Behbahan Khatam Alanbia University of TechnologyWood and Paper Science and Technology Department, Natural Resources Faculty, Behbehan Khatam Alanbia University, Iran.
10.22034/ijwp.2025.2070159.1724
Abstract
Problem definition and objectives: To produce cellulose nanofibers, a wide variety of chemical and enzymatic pretreatments have been applied to various raw materials through numerous mechanical fibrillation methods. This has led to the development of a broad spectrum of cellulose and lignocellulose nanofibers with diverse functional properties. Consequently, over the past decade, numerous methods have been developed to characterize and provide criteria for the quantitative assessment of various types of cellulose nanofibers, which are referred to as benchmarking parameters. Accordingly, in this study, by producing several cellulose nanofiber samples from a specific raw material and by examining the nano-sized fraction index and comparing it with the results of electron microscope images and the tensile strength of the produced film, some advantages and weaknesses of the nano-sized fraction index in nanofiber benchmarking were investigated. Therefore, the main goal of this paper was to study some positive and negative points of nano-sized fraction index for benchmarking of cellulose nanofibrils and the efficiency range of this index compared to common evaluation methods such as film tensile strength, and morphological studies by electron microscope images.
Methodology: To produce pulp and prepare it for cellulose nanofiber production, kraft pulp obtained from poplar wood chips was produced using 14% alkalinity, liquor/wood ratio of 6:1, temperature: 170°C, sulfidity: 25%, and a cooking time: 120 minutes. After washing the resulted brown pulp, to delignify and remove residual lignin, treatment with sodium hypochlorite and alkaline extraction using sodium hydroxide was employed. The pulp consistency was 10%, bleaching time was 45 minutes, and the pH during bleaching was maintained within the range of 9 to 10. Additionally, alkaline extraction was performed using 2% sodium hydroxide, and the pH at this stage was kept within the range of 10 to 11. The production process of nanofibrillated lignocellulose was carried out using an ultra-fine grinder at two various fibrillation intensities: high fibrillation intensity (HC-CNF) and low fibrillation intensity (LC-CNF). The chemical composition of the pulp, X-ray diffraction, and transmission electron microscope images were evaluated. The nano-sized fraction index, used for comparing nanofibrillation quality, was evaluated by centrifuging a dilute nanofiber suspension (0.02% w/w) at 3500 rpm for 15 minutes. Cellulose nanofiber films with a grammage of 30 g/m² were prepared by the vacuum filtration method, and their tensile strength was evaluated.
Results: The chemical composition of the used fibers was 98.2% holocellulose with an average degree of polymerization of 637. The average diameter of HC-CNF was 18.9 nm with a distribution of 5.0-47.2 nm, a crystallinity index of 73.79%, a nano-material percentage index of 26.71%, and a tensile strength of 110 MPa, indicating better fibrillation, lower crystallinity, higher tensile strength, and a higher nano-sized fraction index. However, for LC-CNF, the average diameter was 20.4 nm with a dispersion of 5.2-75 nm, a crystallinity index of 73.79%, a nano-sized fraction index of 18.54%, and a tensile strength of 106 MPa.
Conclusion: Considering the fact that the evaluation and benchmarking of produced nanofibers are necessary for comparing and converting qualitative results into reliable numerical indices, commonly, morphological evaluation indices of produced nanofibers and the tensile strength of films fabricated from nanofiber are suggested. However, evaluation through electron microscope images is very time-consuming and costly. Furthermore, by this type of evaluation, an extremely small portion of the total volume of produced nanofibers is examined, making its generalization to the entire produced nanofiber batch not entirely accurate. Also, the results of this evaluation depend on the operator and the researcher. On the other hand, examining the strengths of nanofiber films, in addition to being very time-consuming, involves multiple errors in film production and measurement methods. However, in a specific nanofiber production process, the nano-sized fraction index demonstrated greater numerical differentiation capability, and significantly lower cost and time compared to other characterization methods investigated in this study. An increase in the number of passes through the ultra-fine grinder resulted in an 8% difference in average diameter and a 4% difference in tensile strength. Nevertheless, this parameter led to an increase of over 44% in the nano-sized fraction index, indicating superior differentiation capability for this particular index.
Keywords
Benchmarking
nano-sized fraction index
cellulose nanofiber
nanofibril

Subjects

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Iranian Journal of Wood and Paper Industries
Volume 16, Issue 4
Winter 2026
Pages 577-589