Theses & Dissertations

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https://hdl.handle.net/20.500.14170/194

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Now showing 1 - 5 of 243
  • Publication
    Deep eutectic solvents(DES) pretreatment of Leucaena leucocephala for production of the bioethanol using Kluyveromyces marxianus UniMAP 1-1
    ( 2024)
    Mohammad Zulhilmi Ishak
    Cellulosic bioethanol production using deep eutectic solvents (DESs) as the pretreatment solvent is a promising step in producing fermentable sugars. It can overcome the drawbacks of using conventional acid and alkaline pretreatment that could be harmful to the environment. Moreover, DESs are capable of solubilizing lignin, opening up the complex biomass matrix, thus allowing enzymatic attack towards the cellulose and hemicellulose structure. However, wide range of DESs combination need to be chosen wisely due to the suitability and compatibility of DESs were strongly depend on the specific biomass and process involved. In addition, non-identical optimum condition between hydrolysis and fermentation have hindered simultaneous saccharification and fermentation (SSF) to be successful in bioethanol production. Hence, this study was conducted to screen the suitable combination of DES mixture to be used in pretreatment of Leucaena leucocephala. In order to effectively pretreat L. leucocephala, several factors that influence the pretreatment and enzymatic hydrolysis need to be optimized before being used in fermentation process, thus the yield of bioethanol can be evaluated. In this work, 30 combination of DESs were synthesized and screened through several criteria such as their physicochemical properties and the stability and compatibility towards L. leucocephala, cellulase enzyme and Kluyveromyces marxianus UniMAP 1-1. After that, the best selected DES was then underwent several pretreatment processes to optimized factors influencing pretreatment process such as solid loading, water addition and enzyme concentration. The optimized conditions were then used in the fermentation process using K. marxianus via SSF and the yield of bioethanol produced was evaluated using high performance liquid chromatography (HPLC). The best screened DES was ChCl:Gly at 1:2 molar ratio with conductivity at 1.86 mS/cm, viscosity at 258.3 cP and pH 4.11. ChCl:Gly (1:2 M) also shows remarkable compatibility and stability with cellulase enzyme by retaining most of cellulase activity at 7.6 FPU during 48 h incubation. It also shows potential compatibility towards L. leucocephala and K. marxianus by showing an optimal adaptation in both conditions. The optimum solid loading was at 10% (w/v), water addition at 25% (v/v) and enzyme concentration at 30 FPU were necessary to obtain the highest glucose possible. The maximum bioethanol yield from this study was at 0.162 g/g with 31.68 % conversion efficiency which showed that this newly isolated K. marxianus can be used in fermentation process. In short, DESs could serve as a great option in biorefineries, not only capable in solubilizing lignin, but also effectively improve subsequent cellulose digestion and glucose yields, thus providing alternative route to achieve consolidated bioprocessing (CBP) strategy.
  • Publication
    Effect of nickel microalloying on the microstructure and properties of In-35 wt%Sn low temperature solder
    ( 2024)
    Chang May Shin
    As the microelectronics industry faces challenges in sustaining Moore's Law due to physical limitations in component miniaturization, the reliability and performance of solder joints in electronic assemblies becomes crucial. The adoption of lead-free solder materials has raised concerns related to processing temperatures inducing dynamic warpage, reduced yield, and reliability concerns. To address these challenges, this thesis investigates the use of low temperature solder (LTS), specifically In-35Sn (wt%) solder with 0.05 wt% nickel (Ni) microalloying. Various techniques, including synchrotron Xray radiography imaging (SXRI), scanning electron microscope (SEM), transmission electron microscope (TEM), differential scanning calorimeter (DSC), and high-speed shear (HSS) testing are employed to comprehensively analyze the prepared solder, microstructure and soldering behavior. In-situ real-time SXRI observations reveal complex interactions during the solidification of the alloy, providing insights into how Ni suppresses primary arm growth by a factor of 0.652 and reduces secondary arm spacing by a factor of 0.502, impacting microstructure evolution. These interactions are challenging to observe using conventional methods that provide micrographs of solidified microstructures. Furthermore, the thesis explores microstructure evolution during solidification and the formation of interfacial Cu3(Sn,In) intermetallic compounds (IMCs) in In-35Sn solder alloys on copper (Cu) substrates. The SXRI observations reveal Ni microalloying providing nucleation sites for the β-In3Sn phase and reducing the degree of undercooling to near zero. Additionally, the TEM observations reveal that Ni microalloying results in refining microstructures of interfacial IMCs formation in In- 35Sn solder on Cu substrates, and improving mechanical properties by increasing shear strength by 5.62% and 3.45%, respectively, and increasing fracture initiation energy by 4.35% and 18.55%, compared to the reference solder joint during shear at speeds of 100 mm/s and 2000 mm/s. Furthermore, the thesis investigates how multiple reflow cycles during assembly processes impact primary Cu2(In,Sn) particles, the interfacial Cu3(Sn,In) layer, and solder joint shear strength. The findings validate nucleation and solidification kinetics and demonstrate a 60 % refinement of Cu2(In,Sn) particles and increased energy absorption of the solder joint by 20.77%, 35.40%, and 6.85% during the first, third, and sixth reflows. Collectively, the results show that Ni microalloying profoundly impacts alloy solidification, interfacial reactions, and phase formation. This approach effectively modifies microstructure and enhances the properties of In-35Sn solder joints on Cu substrates. The findings not only deepen the understanding of alloy behavior but also offer practical implications for the design of novel LTS compositions. This work contributes to the advancement of microelectronics packaging, bridging the gap between scientific understanding and industrial applicability, paving the way for improved and reliable LTS joint solutions in the development of Pb-free electronics assembly.
  • Publication
    Fabrication of polylactic acid/chitosan/cellulose nanocrystal incorporated with essential oil for Harumanis mango postharvest application
    ( 2023)
    Raja Hasnida Raja Hashim
    ‘Harumanis’ mango is the leading commercial cultivar on north Peninsular Malaysia, which also refer as “king of mangoes” in Malaysia and have the maximum consumer demand. The major challenges face by Harumanis mango’s farmer is mango postharvest diseases. The application Polylactic acid and Chitosan biopolymer as packaging during postharvest could provide an eco-friendly alternative to those conventional approaches. However, due to higher costs, poor mechanical strength, poor water and gas barrier and poor antioxidant antimicrobial activity of the films, biopolymer packaging is still relatively limited. The purpose of adding nanofillers (cellulose nano crystals) and essential oils to films is to improve their properties. The ability of essential oils to retain and additives to prevent water and gas transfer between product and environment produce a layer that allows for the control of chemical barriers and serves as an additional barrier to improve the overall quality and stability of fruit. Hence, the aim of this research is to incorporate Cellulose nanocrystal (CNC) and Coleus aromaticus essential oil (CAEO) and their constituents into a new packing material of poly-lactic acid (PLA)/ Chitosan (Cs) and to examine the effect of CNC and CAEO on the properties of PLA/Cs films as fruit packaging. The films are fabricated via solvent casting technique. The obtained films' antimicrobial, antioxidant, microstructural, and mechanical properties were studied. Mechanical properties studies showed the incorporation of CNC indicated higher Tensile strength (TS) value by incorporation of 2% of CNC. However, the PLA/Chitosan-CNC films at 3% and 4% CNC concentration exhibited a decreased TS value. PLA/Cs films were improved with the addition of a small amount of CNC. On the other hand, when the CAEO was added, it improves the elongation breaks which reflect on its flexibility properties. Scanning electron microscopy (SEM) analysis revealed that SEM analysis showed that the surface of PLA/Cs films smoother when 1% and 2 % of CNC and start to produce bubbles and crack on 3 % and 4 %. The surface of films became rougher when CAEO was incorporated into the film. Antioxidant activity of biopolymer film significantly increased (p< 0.05) with increasing CAEO. In-vitro and in-vivo tests were used to evaluate the inhibitory effect of the film against isolated fungi from mango (Curvularia sp.) by comparing the film with different concentration of essential oil with the treatment of control. Disk diffusion was used to evaluate mycelial growth inhibition, which the film incorporated with 1.2 wt% CAEO showed the best result. For in-vivo with wounded mango, the disease incidence was successfully reduced by the film incorporated with 1.2 wt% CAEO. All FTIR spectra of PLA/Cs/CNC and CAEO blends displayed the characteristic bands of PLA-based materials. TEM analysis shows the presence of CAEO, and homogeneity of oil droplets was detected in the PLA/Cs/CNC matrix. The results indicate the biopolymer film incorporated with CAEO could be used as active packaging in fruit industry and be a promising alternative to current control treatment that used for controlling postharvest disease on Harumanis mango.
  • Publication
    One-part geopolymer binders with sodium-based activators exposed to acid and sulphate environments
    ( 2024)
    Ooi Wan En
    One-part geopolymer (OPG) evolved from traditional geopolymer, intended to substitute the Ordinary Portland cement (OPC) as a construction binder material. OPG is made by mixing of aluminosilicate precursor, solid alkali activator and water. OPG production commonly utilises blends of class F fly ash + ground granulated blast furnace slag (GGBS) as precursors, with Na₂SiO₃ as the solid alkali activator. Addition, limited information regarding the chemical resistance of OPGs, thereby restricting their applications. This research uncovered the influence of solid alkali activators on class C fly ash-based OPGs and their resistance to acid and sulphate attacks. Four OPGs based on were fabricated. The M-OPG (solely sodium metasilicate (Na₂SiO₃)), MH-OPG (Na₂SiO₃ + sodium hydroxide (NaOH)), MA-OPG (Na₂SiO₃ + sodium aluminate (NaAlO₂)) and MC-OPG (Na₂SiO₃ + sodium carbonate (Na₂CO₃)). The optimised mixtures were subjected to 3% and 5% sulphuric (H₂SO₄) solutions, and 5% and 10% magnesium sulphate (MgSO4) solutions. The fluidity, setting time, density, mass, porosity, compressive strength, loss of alkalinity, depth of degradation, leaching behaviour and material characterisation of the OPGs were evaluated. The influence of mix proportions of the OPGs with different solid alkali activators were distinctive. The optimised M-OPG attained the highest compressive strength. For the MH-OPG, the alteration of Na₂SiO₃/NaOH ratio significantly influenced fluidity and setting time but had no impact on compressive strength. The MA-OPG exhibited thixotropic fresh paste. The incorporation of Na₂CO₃ reduced the water demand of the MC-OPG. Optimum mix proportions selected were based on well-balanced fresh properties and compressive strength. The optimum M-OPG, MH-OPG, MA-OPG and MC-OPG exhibited 28-day compressive strength of 83.6, 72.7, 45.1 and 75.1 MPa, respectively. After H₂SO₄ exposure, the compressive strengths of all the OPGs were reduced. Gypsum was precipitated on the out-most layer of the samples, gradually restricting acid migration. After 28 days of exposure to 5% H₂SO₄ solution, the MH-OPG exhibited the most severe degradation, with a 66.0% reduction in compressive strength. The MA-OPG and MC-OPG revealed continuous geopolymerisation reaction, which contributed to significant strength recovery from 7 to 28 days during exposure to 10% H₂SO₄. Brucite and hydromagnesite were identified on the surface of the samples after MgSO₄ exposure. The increasing MgSO4 concentration did not caused more severe deterioration on MC-OPG and MH-OPG. After 5% MgSO₄ solution exposure, the compressive strength of the M-OPG, MH-OPG and MC-OPG decreased, whereas the compressive strength of the MA-OPG increased. The unique properties of solid alkali activators resulted in OPGs with varied potential applications, similar to the diverse uses of different OPC types. This research recommends the pre-cast production of M-OPG for indoor applications, the site-cast production of MH-OPG for indoor use, the pre-cast production of MC-OPG for acidic environments, and the site-cast production of MA-OPG for environments with acid and sulphate exposure.
  • Publication
    Tri-Enzyme immobilized on magnetized multiwall carbon nanotubes for single pot Lignocellulosic biomass hydrolysis
    ( 2024)
    Natasha Yasmin Hasnol Azahari
    Single pot is an innovative idea by combining multi-enzyme in single process for hydrolysis of lignocellulosic biomass. Native enzymes have several drawbacks in the industrial setting, including low enzyme activity, poor stability, uneconomical nature, and challenging separation from the final product. This recent study addresses the co-immobilization of xylanase, laccase, and cellulase on magnetized multiwall carbon nanotubes that have been synthesized and functionalized using an environmentally friendly method that combines water-based synthesis of functionalized multiwall carbon nanotubes with mild acid oxidation of pristine multiwall carbon nanotubes. The immobilized enzymes were characterized in terms of stability and reusability prior to the establishment of a single-pot system for the hydrolysis of paddy straw into reducing sugars (glucose and xylose). Through mild acid treatments, 8 M of acid, 8 h, and 80 °C of reflux time and temperature were examined as ideal working conditions. The establishment of a water-based system in the synthesis of iron oxides on p-MWCNTs was confirmed by energy-dispersive X-ray spectroscopy (EDX), with 10.49% iron detected on the surface of MWCNTs. Immobilization of enzymes on m-MWCNTs was successfully achieved via the adsorption method with > 95% binding efficiency for all enzymes, which was further confirmed with the aid of Fourier-transform infrared spectroscopy (FTIR) peaks, scanning electron microscopy (SEM) images, and EDX analysis. The optimum enzyme concentration for immobilization was recorded at 5 mg/mL for both cellulase and xylanase and 7 mg/mL for laccase. Based on the stability study, the optimum temperature of immobilized cellulase, laccase, and xylanase corresponds to 50, 60, and 70 °C, respectively. The optimum pH of 5 was recorded with immobilized cellulase and laccase, while pH 6 was recorded with immobilized xylanase. A reusability study on model substrate showed all immobilized enzymes retained more than 50% of relative activity after five cycles of analysis, while up to 30% of relative activity was still retained with immobilized cellulase and xylanase that were subjected to the hydrolysis of paddy straw. The detection of a FTIR peak at 1657 cm-1 using paddy straw treated with immobilized laccase on m-MWCNTs indicates successful delignification. As for the single-pot system, the operation was conducted at 50 °C, pH 5, and 100 rpm for 16 h using untreated and acid-pretreated paddy straw. Untreated biomass exhibited higher glucose and xylose content during each cycle of analysis. From high-performance liquid chromatography (HPLC) analysis, 1.03 g/L and 1.04 g/L of glucose and xylose were secreted from untreated biomass through a single-pot system after the third cycle of analysis, highlight the potential of immobilized enzymes on m-MWCNTs synthesized using a water-based for lignocellulosic biomass hydrolysis.