Browsing by Subject "Nanocomposites"
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Item Characterization of the Cellulosic Fiber Obtained from Nepalese Lokta Bushes and Explore its Novel Applications(Institute of Science and Technology, 2024-05) Aryal , Girja ManiIn 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.Item Investigation of micromechanical properties and strain sensing behavior of electrically conducting and Piezoresistive flexible copolyester/Carbon Nanotubes Nanocomposites(Institute of Science and Technology, Chemistry, 2022) Dhakal, Kedar NathVarious concentration of multiwalled carbon nanotubes (MWCNT) as conductive filler was incorporated into poly(butylene adipate-co-terephthalate) (PBAT), a flexible biodegradable copolyester by melt-mixing followed by compression moulding. Deformation behavior of electrically conductive nanocomposites was correlated with piezoresistivity, leading to their strain sensing behavior. Structural and morphological characterization of the materials were determined by Fourier transform infrared (FTIR) spectroscopy and microscopic techniques while thermal stability and crystallization behavior were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. Comparative analysis of FTIR spectra of PBAT and PBAT/MWCNT nanocomposites suggested a physical matrix-filler binding force to form the composite microstructures. Microscopic techniques revealed an entangled CNT-network uniformly spread in the polymer matrix. Increased thermal stability of the materials was suggested by TGA, attributed to a good filler-matrix interfacial interaction. DSC results revealed the retarded crystallization process of the polymer with the formation of less perfect crystals. Increasing tensile modulus, Martens Hardness (HM) and indentation modulus (EIT ), and decreasing maximum indentation depth (hmax ) (by 50%, 50%, 100% and 32% on incorporation of 5 wt-% of fillers, respectively) confirmed the mechanical reinforcement of composites by MWCNT. Volume resistivity observed in the nanocomposites suggested the suitability of nanocomposites for strain sensing applications. An exponential-like increment of relative resistance change (ΔR/R0 ) of the nanocomposites as a function of strain confirmed their piezoresistivity. Applicability of nanocomposites as low-strain sensing materials was suggested by their reproducible ΔR/R0 values from 2% to 8% strain during cyclic strain test. Electron beam (EB) irradiation induced crosslinking of the nanocomposites was employed as a strategy to improve the strain sensing behavior of the nanocomposites. Cyclic strain test of irradiated samples (dose: 150 and 200 kGy) exhibited the improvement (up to 10% strain), attributed to their enhanced elastic deformability. The nanocomposites irradiated with the highest dose (300 kGy) exhibited no correlation between ΔR/R0 and strain, attributed to the formation of a 3D network of polymer crosslinks restricting the homogeneous deformation of the CNT-network. Moderate degree of EB irradiation induced crosslinking of polymer nanocomposites can be a strategy to improve their strain sensing behavior. Keywords: nanocomposites, biodegradability, electrical conductivity, piezoresistivity, strain sensing, electron beam irradiation, crosslinking