Isolation and Performance Evalaution of Microcrystalline Cellulose from Ethiopian Teff (Eragrostis tef) Straw for the Enhancement of Thermo Mechanical Properties of Polyvinyl Alcohol Based Bio Degradable Polymer
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Date
2024-07
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Addis Ababa University
Abstract
Traditional plastics come from fossil fuels, harm the environment, and don't break down easily. Here, the study explores using a natural material, microcrystalline cellulose (MCC), from Teff straw (TS), an abundant agricultural residue in Ethiopia. The research aims to isolate MCC from TS and evaluate its effectiveness as a reinforcing agent in PVA to create improved eco-friendly plastic. This research is divided into three main parts.
In the first part of this study, developing a method to produce cellulose-rich pulp from TS and characterization of the achieved material was done. A two stage pre-treatment(alkaline and chlorine-free bleaching treatments) for TS fibers was used which can bring about internal defibrillation in the fibers through cleavage of the hydrogen bonding that holds the hemicellulose - cellulose micro fibril network. The first alkaline treatment stage termed as the alkaline delignification was optimized by a single effect design with a three independent variables [i.e. temperature (60–95 °C at the interval of 10°C except for the last level (at 5°C interval)), time (30–150 min at the interval of 30 min), and NaOH concentration (2–8 wt. % at the interval of 1.5 wt. %)] targeted at predict their effect on lignin decomposition and fiber yield. The second stage bleaching treatment was conducted using a preheated mixture of hydrogen peroxide (20%) and sodium hydroxide (5%) at a temperature of 65 °C for 90 min. The bleaching treatment was focused on obtaining a cellulose-rich pulp with minimal lignin content for microcrystalline cellulose production.
Chemical composition analysis shows that the raw TS has 40.44%, 29.44%, and 18.05% of cellulose, hemicellulose, and lignin respectively. Furthermore, the TS cellulose-rich pulp obtained after the two-stage pre-treatment had cellulose, hemicelluloses, and lignin content of 85.5%, 11.98%, and 2.52%, respectively, which confirmed the significant decrease in the percentage of non-cellulosic components. In addition, the extraction procedure yielded purified cellulose with crystallinity, Onset temperature (Ton), and maximum decomposition temperature (Tmax), of 65.51%, 255 °C, and 365.5 °C. The results indicated that two-stage alkali hydrogen peroxide treatment was beneficial for producing cellulose-rich pulp, while TS is a promising new source of raw material to produce cellulose for application in microcrystalline cellulose production.In the second part, the cellulose was converted to microcrystalline cellulose via transition metal salts assisted dilute acid hydrolysis. The products were characterized by FT-IR, SEM, XRD, and TGA. XRD results indicated that Cr (NO3)3 assisted acid hydrolysis produced MCCs presented the highest crystallinity index (CrI) values (73.34%), as compared to both FeCl3 (67.58%), and Fe (NO3)3 (66.69%) catalyzed acid treatments. Furthermore, from the TGA analysis, It was interesting to note that, the thermal degradation starting temperature (Ton) obtained for Cr (NO3)3, FeCl3, and Fe (NO3)3 assisted dilute acid hydrolysis were 285, 273, and 275 °C, respectively which indicate the higher thermal stability of these fibers.
After successfully isolating MCC from Teff straw, its ability was further explored to act as a reinforcing agent in PVA polymer in the last part of this research work. The processing of PVA /MCCs composites employed solvent based fabrication methods (solution casting) by mixing the pre-dispersing MCCs in a 5% PVA solution and then performing a film. The effects of filler-matrix compatibility on the composites mechanical, thermal properties were investigated. The mechanical properties of the composites were remarkably enhanced by the incorporation of MCC into the PVA matrix at lower MCC content without negatively affecting its important properties. The tensile strength of the PVA films increased by up to 49%, 71%, and 67% when Cr(III)-MCC, Fe(III)Cl-MCC and Fe(III)-MCC was incorporated at a level of 5%, respectively. Additionally, MCCs obtained using different catalysts (Cr(III)-MCC, Fe(III)Cl-MCC, and Fe(III)-MCC) showed different reinforcement effects for the PVA composite films.
MCC addition also increased the thermal stability of the composites compared to pure PVA (295°C). Notably, the onset temperatures reached 305°C for Cr(III)-MCC, 308°C for Fe(III)Cl-MCC, and 303°C for Fe(III)-MCC-based PVA films. SEM analysis also revealed that the MCC fibers were dispersed in the PVA matrix, indicating that there was good interaction between the two materials. Overall, the results of this study suggest that Teff straw MCCs could be used as a low-cost reinforcement additive to produce biodegradable films with enhanced mechanical properties and thermal stability. These films could be used for a variety of applications, such as food packaging.
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Keywords
Teff straw, cellulose, microcrystalline cellulose, composites, hydrolysis, polyvinyl alcohol, pre-treatments, characterization