Characterization of the Cellulosic Fiber Obtained from Nepalese Lokta Bushes and Explore its Novel Applications
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Institute of Science and Technology
Abstract
In Nepal, Handmade papers (HPs) are made from fibrous biomass of several plant species. Paper fabricated from fibrous biomass obtained from Lokta bushes following the traditional eco-friendly method is called Lokta paper or Nepal Kagaj. Handmade paper fabricated from Lokta bushes is being used to fabricate value-added products. The paper is traditionally believed to be durable and bug and mold-resistant. However, a systematic study on the material properties of this paper is not reported yet. Additionally, material properties of Lokta fiber retted under different conditions; which help to understand the performance of Lokta fiber-derived products is not mentioned in the literature. To increase, trade value it is also equally important to find next generation applications of the Lokta paper. This dissertation work was aimed at understanding the material properties of Lokta paper and fiber, and the fabrication of Lokta paper-derived nanocomposite mat for antimicrobial application.
It was found that the mean caliper, apparent density, Cobb 60, grammage, brightness, opacity equilibrium moisture content, tensile strength, and tensile index values in the paper samples collected from local enterprises (n=10) ranged from ~90‒700µm, 0.2‒0.4 g/cm3, 50‒150 g/m2, 4‒7%, 50‒400 g/m2, 56‒67 %, 83‒98 %, 30‒2900 N/m, and 1‒27 Nm/g; in that order. These data recommended that Lokta paper is a light weight paper having intermediate to high strength, high caliper variation and relatively low brightness. All paper samples exhibited considerably increased tensile strength across the length axis (p<0.05). Distinctive characteristics of hemi‒cellulose, cellulose, and lignin were spotted in the FTIR spectra of all the samples. The amorphous and crystalline cellulosic segments were detected in X‒ray diffraction (XRD) data. Most importantly, electron microscopic showed a properly cross-linked web of entire fibers organizing a parallel layout of microfibrils. These morphological qualities could be responsible for delivering strength and durability to the paper samples.
A comprehensive analysis of material properties of Lokta fiber subjected to 1-9% NaOH (w/v) concentrations at ambient temperature was also performed. The alkali resulted in significant shrinkage of lignin and hemicellulose; thereby increasing the cellulose content. On alkali treatment, fiber width and equilibrium moisture content decreased whilst fiber density, crystallinity index, tensile strength, and thermal stability increased. These changes can be assigned to the deduction of cementing materials from fiber bundles. These findings suggested that processing conditions greatly affect the fiber properties and to get Lokta paper of optical performance fiber chemistry needs to be properly tailored.
Finally, Lokta paper-making process was mimicked in laboratory settings and the physico-chemical properties of lab-made Loka paper were compared with commercially available paper. The Ag/ZnO and Cu nanoparticles were doped in the Lokta paper following hydrothermal and chemical reduction methods. The Lokta paper nanocomposite mat showed promising antimicrobial activity contrary to two bacteria (Escherichia coli and Bacillus subtilis) and a fungal strain (Candida Albicans). These observations suggested that the Lokta paper-derived nanocomposite mat can find potential applications as an antimicrobial packaging material.