Yeoh Cheow Keat
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Preferred name
Yeoh Cheow Keat
Official Name
Cheow Keat, Yeoh
Alternative Name
Yeoh, C. K.
Yeoh, Cheow Keat
Yeoh, Cheow-Keat
Main Affiliation
Scopus Author ID
16231574200
Researcher ID
EGP-0633-2022

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Effect of printing parameters on tensile, dynamic mechanical, and thermoelectric properties of FDM 3D printed CABS/ZnO composites

2018-03-22 , Yah Yun Aw , Yeoh Cheow Keat , Mohd Asri Idris , Teh Pei Leng , Khairul Amali Hamzah , Shulizawati Aqzna Sazali

Fused deposition modelling (FDM) has been widely used in medical appliances, automobile, aircraft and aerospace, household appliances, toys, and many other fields. The ease of processing, low cost and high flexibility of FDM technique are strong advantages compared to other techniques for thermoelectric polymer composite fabrication. This research work focuses on the effect of two crucial printing parameters (infill density and printing pattern) on the tensile, dynamic mechanical, and thermoelectric properties of conductive acrylonitrile butadiene styrene/zinc oxide (CABS/ZnO composites fabricated by FDM technique. Results revealed significant improvement in tensile strength and Young's modulus, with a decrease in elongation at break with infill density. Improvement in dynamic storage modulus was observed when infill density changed from 50% to 100%. However, the loss modulus and damping factor reduced gradually. The increase of thermal conductivity was relatively smaller compared to the improvement of electrical conductivity and Seebeck coefficient, therefore, the calculated figure of merit (ZT) value increased with infill density. Line pattern performed better than rectilinear, especially in tensile properties and electrical conductivity. From the results obtained, FDM-fabricated CABS/ZnO showed much potential as a promising candidate for thermoelectric application.

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Thermoelectric properties of Sm doped CaMnO₃ using density functional theory method

2020-09 , Abdullah Chik , Ruhiyuddin Mohd Zaki , Akeem Adekunle Adewale , Faizul Che Pa , Yeoh Cheow Keat

The electronic structure and thermoelectric properties of CaMnO₃ doped with 8% and 17% f block element Sm using first principles calculations and semi-classic Boltzmann theory were presented in this paper. The G-type AFM phase is most stable among five phases for CaMnO3, however, with 8% and 17% Sm doping, these compounds became nonmagnetic phases. CaMnO₃ calculated electronic band structure shows an indirect band gap of 0.523 eV, which is underestimated by the density functional theory (DFT) calculations but the band gap explains the semiconducting behavior. However, with 8% and 17% Sm doping, the electronic bandstructure of these compounds exhibit metallic behavior, with Sm 4f and Mn 3d electrons contributing to conduction band, increasing the magnitude of conductivity for doped compounds. All temperature dependence Seebeck coefficient plots show n-typed conduction for all compound with reduced magnitude of Seebeck coefficient for doped compounds. The temperature dependence thermal conductivity plot shows overall thermal conductivity is reduced in Sm doped compound. CaMnO₃ with 17% Sm doping exhibit much higher ZT of 0.32 at 800 K showing enhanced thermoelectric properties at high temperature and suitability or high temperature energy conversion devices.

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Properties of epoxy/LNR foam using sodium bicarbonate as a gas generator

2022-05-18 , Hussein M.S. , Teh Pei Leng , Zainuddin F. , Rahmat A.R. , Yeoh Cheow Keat

A series of porous epoxy foams toughened by liquid natural rubber (LNR) were fabricated by sodium bicarbonate (SB) as chemical foaming agent and finding the optimal composition ensuring both high porosity and mechanical strength. In this research, we studied the properties of epoxy foam by adding LNR as toughening agent in contents of (5 to 25 vol%) with adding 15 phr of SB as an optimal content foaming agent. The flexural, fracture toughness, compression, cross-link density, morphology and thermal stability properties of epoxy foam was characterized. Cellular plastics keep mechanical strength loss and plastic weight to a minimum through cells inside the foam. Increasing the content of LNR retarded the crosslinking reaction by increasing the expansion and affected the mechanical strength. A suitable expansion and mechanical strength were observed for epoxy-foam containing 10 to 15 vol% LNR. Densities of the foams can be tuned in a range of up to 0.760 g/cm3 by changing the content of LNR from 5 to 25vol%. The compressive strength was decreased from 8.62 and 4.15 MPa.

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Effect of infill density with ZnO concentration on the mechanical properties of 3D printed PLA/ZnO composites

2022-05-18 , Tan M.A. , Yeoh Cheow Keat , Teh Pei Leng , Nor Azura Abdul Rahim , Song C.C. , Mansor N.S.S. , Lim J.H.

Polylactic acid (PLA) plastics are biodegradable materials manufactured from PLA resin by melt spinning and solvent spinning methods. PLA is widely applied in textile fabric, non-woven, masks and sanitary napkins applications due to excellent safety, environmental protection and good mechanical properties. The process of 3D printing is continuous and able to produce complex three-dimensional structures. PLA/ZnO composite samples were fabricated by a 3D printer. ZnO acts as filler in PLA/ZnO composites to obtain the excellent properties like specific tensile properties and density. However, ZnO agglomeration occurred at higher concentration when viewed via SEM. Printing parameters such as infill density, raster orientation and infill pattern can influence the mechanical properties of 3D samples as well. The objective of this paper is to determine the effect of infill density with different ZnO concentration on the mechanical properties of 3D printed PLA/ZnO composites. Tensile and density measurement were carried out to determine the mechanical properties of composites. The influence of 80%, 90%, 100% infill rate and ZnO concentration varied by 1 and 5 mol. As a result, higher infill rate (100%) and optimum filler concentration (1 mol ZnO) give the excellent properties thus can be used for future applications.

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Effect of zinc oxide suspension on the overall filler content of the PLA/ZnO composites and cPLA/ZnO composites

2023-01-01 , Tan M.A. , Yeoh Cheow Keat , Teh P.L. , Nor Azura Abdul Rahim , Song C.C. , Voon Chun Hong

This work aimed to study the effect of zinc oxide (ZnO) filler suspension on the mechanical, electrical, and thermal properties of polylactic acid (PLA)/ZnO and cPLA/ZnO. Fused deposition modelling, one of the additive manufacturing methods, was used to fabricate the PLA specimen. PLA was used as the main material in this project, and the ZnO suspension was added during the printing process. The speed of the dispenser (low speed = 1,000 rpm, medium speed = 1,400 rpm, and high speed = 1,800 rpm) was the parameter that was varied to control the filler content of the composite. All the samples underwent a tensile test to determine the mechanical properties, followed by the scanning electron microscopy (SEM) test to analyse the fracture surface properties of the tensile test. SEM observations showed the PLA samples' inherent smooth appearance, but the PLA/ZnO composite showed a rougher surface. PLA and cPLA composites showed an enhanced storage modulus but lower loss modulus than the pure samples. Because of the high thermal and electrical conductivity of carbon black and ZnO, cPLA composites had higher electrical and thermal conductivity than PLA composites.

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Microwave welding with SiCNW/PMMA nanocomposite thin films: enhanced joint strength and performance

2025-01 , Phey Yee Foong , Voon Chun Hong , Lim Bee Ying , Foo Wah Low , Teh Pei Leng , Nor Azizah Parmin , Subash Chandra Bose Gopinath , Veeradasan Perumal , Yeoh Cheow Keat , Nor Azura Abdul Rahim

Most previously reported susceptors for microwave welding are in powder form. In this study, a thin-film susceptor was employed due to its uniform heating rate and ease of handling. Silicon carbide nanowhisker (SiCNW) were incorporated into a poly(methyl methacrylate) (PMMA) matrix to create a nanocomposite thin film, which served as the susceptor. The microwave welding process involved three straightforward steps: fabrication of the PMMA/SiCNW nanocomposite thin film, application of the nanocomposite film to the target area, and subsequent microwave heating. Upon cooling, a robust microwave-welded joint was formed. The mechanical properties and microstructure of the welded joints were characterized using single-lap shear tests, three-point bending tests, and scanning electron microscopy. Results demonstrated that the shear strength and elastic modulus of the welded joints were optimized with increased heating time and SiCNW filler loading. This optimization is attributed to the formation of a SiCNW-filled polypropylene (PP) nanocomposite layer of increasing thickness at the welded joint interface. However, the incorporation of SiCNW also constrained the mobility of the PP chains, reducing the joint’s flexibility. Furthermore, the welded joint formed with the PMMA/SiCNW nanocomposite thin-film susceptor exhibited an 18.82% improvement in shear strength compared to joints formed with a powdered SiCNW susceptor. This study not only demonstrates the potential of PMMA/SiCNW nanocomposite thin films as efficient susceptors for microwave welding but also paves the way for developing high-performance polymer-based composite joints with improved mechanical properties for applications in the automotive, aerospace, and construction industries.

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The effect of the GNP-SDS loadings on the properties of the NRL/GNP-SDS composites

2020-07-09 , Che W.M. , Teh Pei Leng , Jalilah Abd Jalil , Yeoh Cheow Keat

Stretchable conductive polymer composites (CPC) are fabricated by incorporating the conductive particles into the polymer matrix. In this paper, CPC was fabricated by incorporating the sodium dodecyl sulfate (SDS) modified graphene nanoplatelet (GNP) into natural rubber latex (NRL) by varying loading from 0phr to 9phr using a simple mechanical stirring method. The effect of the GNP-SDS loadings on the properties of the composites were study by investigated the crosslink density, tensile properties, morphology of the tensile fracture surface and electrical conductivity. The crosslink density of the composites shows a decreased trend. Then, due to the well dispersed GNP-SDS, the tensile strength increased but decreased at high filler loading caused by the agglomeration issue. The tensile modulus also increased with increasing filler loading due to the intrinsic high modulus of GNP and the reduction of chain mobility. However, the electrical properties of the composites improved as GNP-SDS loading increased and achieved a percolation threshold at 7phr.

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Comparison between natural rubber, liquid natural rubber, and recycled natural rubber as secondary matrix in epoxy/natural rubber/graphene nano-platelet system

2023 , K. W. Kam , Teh Pei Leng , Yeoh Cheow Keat

A comparison is made between the effects of natural rubber (NR), liquid natural rubber (LNR), and recycled natural rubber (rNR) in the filled epoxy systems on the physical, mechanical, thermal, and electrical performances of filled epoxy systems. The results show that flexural strength and modulus values were improved. The toughness properties of the filled epoxy system were enhanced with NR phases (72 MPa, 2317 MPa, 4.2 MPa. m1/2), as compared to those with LNR (55 MPa, 2100 MPa, 3.2 MPa. m1/2) and rNR (52 MPa, 2000 MPa, 2.3 MPa. m1/2) at 5 vol.%. Scanning electron micrograph (SEM) analysis revealed that the particle sizes of NR phases dispersed within the epoxy matrix were smaller and more uniform (0.29-1.65 μm) as compared to those with LNR (0.64-3.57 μm) and rNR (≥250 μm) phases. The incorporation of NR, LNR, and rNR phases improved the thermal stability of the filled system. This is attributed to more heat energy being needed to overcome good interfacial bonding between epoxy matrices and the small NR phases. X-ray diffraction analysis results showed that the filled epoxy/NR/GNP system has higher 2θ values, indicating that d-spacing in GNP nano-fillers has the closer distance. Electrical bulk conductivity values of filled epoxy/NR/GNP systems were the highest, 4.50 x 10-3 1/Ω. cm at 20 vol.%. Small NR phases acted as elastomer spacers, which provided better GNP packing efficiency and realigned the GNP nano-fillers to form more effective conductive pathways for electron transport.

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Effect of dispersibility of graphene nanoplatelets on the properties of natural rubber latex composites using sodium dodecyl sulfate

2022-01-01 , Che W.M. , Teh Pei Leng , Yeoh Cheow Keat , Jalilah Abd Jalil , Lim Bee Ying , Rasidi M.S.M.

Natural rubber latex/graphene nanoplatelet (NRL/GNP) composites containing GNP-pristine and GNP-SDS were prepared by a simple mechanical mixing method. The main objective was to study the effect of dispersibility of GNP on the properties in NRL. X-ray diffraction confirmed the adsorption of sodium sulfate dodecyl (SDS) on the GNP surface. The results showed that high filler loading diminished the physical and mechanical properties of the composites but successfully endured to satisfy electrical conductivity to the NRL/GNP composites. Besides, the SDS surfactant-filled system demonstrated better physical, tensile, electrical, and thermal stability properties than the GNP-pristine. The intercalated and dispersed GNP-SDS increased the number of routes for stress and heat transfer to occur and facilitated the formation of conductive pathways as well, leading to the improvement of the properties as compared to NRL/GNP-pristine composites. However, as the GNP-SDS loading exceeded 5 phr, the GNP-SDS localized in the interstitial layer of NRL, restricted the formation of crosslinking, and interfered with the strain-induced crystallization ability of the composites.

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DFT Study of Thermoelectric Performance of SrTiO₃ Doped by Tantalum

2019-10 , Akeem Adekunle Adewale , Abdullah Chik , Ruhiyuddin Mohd Zaki , Faizul Che Pa , Yeoh Cheow Keat , Noorina Hidayu Jamil

This paper deals with enhancement of thermoelectric performance of SrTiO₃ - a perovskite-based material by doping Ti-site with Ta. The electronic and the thermoelectric transport properties of doped SrTiO₃ were studied using the first principle calculation in full-potential of density functional theory. Spin-orbit coupling including Hubbard U parameter influences were observed in the investigation. Energy band structure and electron density of state were determined for electronic properties. The Seebeck coefficients, thermal conductivity, electrical conductivity as well as thermoelectric efficiency ZT were calculated for thermoelectric properties. The results of our calculations revealed that narrowing the bandgap of the material leads to the increase of thermoelectric efficiency ZT. At spin-orbit coupling with DFT+U method, ZT of 0.18 at 750 K were obtained and this is similar to the experimental data reported.

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