Showing papers by "Kin-tak Lau published in 2011"
TL;DR: In this article, a review examines the inspiration for high temperature proton exchange membrane fuel cells (PEMFCs) development, the technological constraints, and recent advances, and a detailed discussion of the synthesis of polymer, membrane fabrication and physicochemical characterizations is provided.
779 citations
TL;DR: In this article, a tensile property test was conducted to examine the mechanical properties of the samples with different nanoclay content, and it was found that the Young's modulus and tensile strength of a composite with 5.5% of nanoclays increased up to 34% and 25% respectively, as compared with a pristine sample.
Abstract: Using organomodified montmorillonite (MMT) (commonly called “Nanoclay”) to reinforce polymer-based composites have raised much attention to academic and industrial sectors due to the addition of small amount of nanoclay could substantially enhance the mechanical properties of pristine polymers. However, most of the works done previously have neglected to comprehensively study the basic reinforcing mechanism of the composites, particular the interaction between nanoclay and surrounding matrix even though high tensile strength and modulus were obtained. In this paper, uniformly-dispersed nanoclay/epoxy composite samples, based on our tailor-made experiment setup were fabricated. A tensile property test was conducted to examine the mechanical properties of the samples with different nanoclay content. It was found that the Young’s modulus and tensile strength of a composite with 5 wt.% of nanoclay increased up to 34% and 25% respectively, as compared with a pristine sample. Images obtained from scanning electron microscopy (SEM) and results extracted from transmission electron microscope (TEM) proved that interlocking and bridging effects did exist in the composites. Nanoclay clusters with the diameter of 10 nm could enhance the mechanical interlocking inside the composites and thus, breaking up the crack propagation. The formation of boundaries between the nanoclay clusters and epoxy can refine the matrix grains and further improve the flexural strength of the composites.
184 citations
TL;DR: A unique nanoarchitecture has been established involving polypyrrole (PPy) and graphene nanosheets by in situ polymerization, suggesting the possible use of the nanocomposite as a supercapacitor electrode.
Abstract: A unique nanoarchitecture has been established involving polypyrrole (PPy) and graphene nanosheets by in situ polymerization. The structural aspect of the nanocomposite has been determined by Raman spectroscopy. Atomic force microscopy reveals that the thickness of the synthesized graphene is ~ 2 nm. The dispersion of the nanometer-sized PPy has been demonstrated through transmission electron microscopy and the electrochemical performance of the nanocomposite has been illustrated by cyclic voltammetry measurements. Graphene nanosheet serves as a support material for the electrochemical utilization of PPy and also provides the path for electron transfer. The specific capacitance value of the nanocomposite has been determined to be 267 F g − 1 at a scan rate of 100 mV s − 1 compared to 137 mV s − 1 for PPy, suggesting the possible use of the nanocomposite as a supercapacitor electrode. After 500 cycles, only 10% decrease in specific capacitance as compared to initial value justifies the improved electrochemical cyclic stability of the nanocomposite.
172 citations
28 Apr 2011
TL;DR: In this article, the effects of natural fiber surface on composite properties are discussed and several fiber surface modification methods are reported and their effects on composites are analysed, and the results of these methods are shown to improve composite properties.
Abstract: Processing of polymer composites by using green source of fibres as reinforcement has increased dramatically in recent years. Advantages of using natural fibre over man-made fibres include low density, low cost, recyclability and biodegradability. These benchmark properties make natural fibre a potential replacement for synthetic fibres in composite materials opening up further industrial possibilities. However, high level of moisture absorption by the fibre leads to poor wettability and insufficient adhesion within the matrix (interfacial adhesion) resulting degradation of composite properties. These properties hinder the potential of these fibres in providing successful reinforcement for polymer composites. In order to expand the use of natural fibres as successful reinforcement in polymer composites the fibre surface needs to be modified to enhance fibre-matrix adhesion. In this review paper, effects of natural fibre surface on composite properties are discussed. Several fibre surface modification methods are reported and their effects on composite properties are analysed. These properties constitute the prime area of research in developing green fibre polymer composite technologies.
68 citations
TL;DR: In this article, Fourier Transform Infrared spectroscopy (FTIR) and X-ray photoelectron spectrograph (XPS) were conducted to analyze the chemical composition between epoxy matrix and nanocomposite.
67 citations
TL;DR: In this article, a study on the mechanical properties and bio-degradability of silk fibre reinforced Poly (lactic-acid) (PLA) composites is conducted, and it has been found that the Young's modulus and flexural modulus of the composites increased with the use of silk fiber reinforcement while their tensile and flexur strengths decreased.
Abstract: Silk fibre is one kind of well recognized animal fibres for bio-medical engineering and surgical operation applications because of its biocompatible and bio-resorbable properties. Recently, the use of silk fibre as reinforcement for some bio-polymers to enhance the stiffnesses of scaffolds and bone fixators has been a hot research topic. However, their mechanical and biodegradable properties have not yet been fully understood by many researchers, scientists and bio-medical engineers although these properties would govern the usefulness of resultant products. In this paper, a study on the mechanical properties and bio-degradability of silk fibre reinforced Poly (lactic-acid) (PLA) composites is conducted. It has been found that the Young’s modulus and flexural modulus of the composites increased with the use of silk fibre reinforcement while their tensile and flexural strengths decreased. This phenomenon is attributed to the disruption of inter- and intra-molecular bonding on the silk fibre with PLA during the mixing process, and consequent reduction of the silk fibre strength. Moreover, bio-degradability tests showed that the hydrophilic properties of the silk may alter the biodegradation properties of the composites compared to that of a pristine PLA sample.
66 citations
TL;DR: In this article, the reinforcement efficiency was determined from the composite flexural and impact properties with the correlation to the morphological structure and interfacial bonding effect via scanning electron microscopy (SEM) and X-ray diffraction.
Abstract: Epoxy composites reinforced with zinc oxide nanoparticles, alumina microparticles and nanoclays at 1, 3, 5 and 8 wt% were fabricated by combined mechanical stirring and ultrasonication processes. The reinforcement efficiency was determined from the composite flexural and impact properties with the correlation to the morphological structure and interfacial bonding effect via scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results reveal the moderate enhancement of composite modulus up to a maximum 27% for 8 wt% alumina inclusions; flexural strengths increase quite marginally or even show a decreasing trend with increasing the particle content by weight. The comparison between a series of mathematical models and experimental data of flexural moduli indicates the applicabilities of Paul model for alumina and zinc oxide reinforcements, and Kerner model and Ishai–Cohen model for nanoclays. The appropriate micro/nanoparticle selection due to different shapes and sizes is critical for the better mechanical performance of their composite materials.
39 citations
TL;DR: In this article, the constitutive relation and the electromechanical stability of compressible isotropic dielectric elastomers undergoing large deformation are investigated by applying a new kind of free energy model, which consists of elastic strain energy, composed of the Varga model as the volume conservative energy and the Blatz-Ko model as a volume non-conservative energy, and electric field energy with constant permittivity.
Abstract: The constitutive relation and the electromechanical stability of Varga–Blatz–Ko-type compressible isotropic dielectric elastomers undergoing large deformation are investigated in this paper. Free energy in any form, which consists of elastic strain energy and electric field energy, can be applied to analyze the electromechanical stability of dielectric elastomers. The constitutive relation and the electromechanical stability are analyzed by applying a new kind of free energy model, which consists of elastic strain energy, composed of the Varga model as the volume conservative energy and the Blatz–Ko model as the volume non-conservative energy, and electric field energy with constant permittivity. The ratio between the principal planar stretches, the ratio between the thickness and length direction stretches, and the power exponent of the stretch are defined to characterize the mechanical loading behavior and compressible behavior of the dielectric elastomer. Along with the increase of these parameters, which determine the shape or volume of the elastomer, and the Poisson ratio, the critical nominal electric field is higher, which indicates a more stable dielectric elastomer electromechanical system. In contrast, with the decrease of the dimensionless material parameter α of the Varga elastic strain energy, the critical nominal electric field increases. The coupling system becomes more stable. We further demonstrate that the critical nominal electric field of the compressible dielectric elastomer electromechanical coupling system is significantly influenced by the ratio between the principal planar stretches.
27 citations
TL;DR: In this article, the thermal properties of a multi-walled carbon nanotube (MWNT)-reinforced thermoplastic natural rubber (TPNR) nanocomposite were studied using a melt blending method.
Abstract: This article studies the thermal properties of a multi-walled carbon nanotube (MWNT)-reinforced thermoplastic natural rubber (TPNR) nanocomposite. The nanocomposite was prepared using a melt blending method. Various percentages (1, 3, 5, and 7 wt%) of MWNTs were added into TPNR to improve its thermal properties. The laser flash technique was also employed to determine the thermal conductivity, thermal diffusivity, and specific heat capacity of the nanocomposite. The DMA result showed that the glass transition temperature (Tg) increased with the increase in MWNT content. TEM micrographs also demonstrated that a good dispersion of MWNTs was achieved in the TPNR environment.
15 citations
01 Jan 2011
TL;DR: In this paper, a cleaner and environmental friendly surface modification technique of tussah silk was under investigated, and the effectiveness of parameters of degumming on Tussah Silk such as surface purity, surface purity and temperature was discussed.
Abstract: Silk fibre is well recognized as an outstanding material for bio-medical engineering application because of its superior mechanical and bioresorbable properties. However, when producing silk fibre reinforced polymer composites, hydrophilic sericin has been found to cause poor interfacial bonding with polymer. Besides, sericin on the fibre surface is a major cause of adverse problems with biocompatibility and hypersensitivity to silk for implant application. Therefore, certain treatment should be proposed for sericin removal. Degumming is a surface modification process which allows for a wide control of the silk fibre's properties, making silk possible to be used for the development and production of novel bio-composites. In this paper, a cleaner and environmental friendly surface modification technique of tussah silk was under investigated. The effectiveness of parameters of degumming on tussah silk such as surface purity, degumming time and temperature is discussed. The evaluation of the data was carried out through the measurement of the tensile properties and surface morphology of the samples. The findings of this research provide an environmental friendly degumming method which is one of the most important steps on preparation of silk fibre reinforced composite.
4 citations
TL;DR: In this article, the dynamic mechanical and thermal properties of degraded and non-degraded silk fibre reinforced Polylactic acid (PLA) composites are discussed, as well as their properties with the biodegradable properties.
Abstract: Silk fibre has been popularly used for bio-medical engineering and surgically-operational applications because of its biocompatible and bio-resorbable properties for centuries. Using silk fibre as reinforcement for some bio-polymers to enhance the stiffness of scaffolding and bone implant plates has been developed. However, its dynamic mechanical properties with the biodegradable properties have not yet well understood. In this paper, the dynamic mechanical and thermal properties of degraded and non-degraded silk fibre reinforced Polylactic acid (PLA) composites are discussed.
TL;DR: In this paper, reaction injection molding process of phenolic foam sandwich plate was introduced in order to resolve the difficulties in repetitive continuous manufacturing process of such product, which have uniform pore diameter, good fireproof property and there need not any glue between phenolic foams and color steel plate which could make it a potential building material instead of polysterol sandwich plate.
Abstract: Reaction injection molding process of phenolic foam sandwich plate was introduced in order to resolve the difficulties in repetitive continuous manufacturing process of such product. The phenolic foam produced here have uniform pore diameter, good fireproof property and there need not any glue between phenolic foam and color steel plate which could make it a potential building material instead of polysterol sandwich plate.
15 Jan 2011
TL;DR: In this paper, a fully biodegradable thermoplastic composite made from silkworm silk fibres and poly-lactic acid (PLA) was used to form a composite, which was examined through tensile and flexural properties and Izod impact tests.
Abstract: Chopped silkworm silk fibres and Poly-lactic acid (PLA) were mixed to form a fully biodegradable thermoplastic composite. Injection moulding process was used to mix these constituents together at a controlled temperature range. The mechanical properties of the composite were examined through tensile and flexural property and Izod impact tests. It was found that the Young's and flexural moduli of the composite increased while their strengths and impact resistance decreased during the tests as compared with a PLA sample. Early fibre fractures observed from micrographs explain the reasons of enhanced moduli and reduction of strengths.
01 Aug 2011
TL;DR: Alkalization, acetylation, and the combination were used in this paper to treat the hemp fiber and the effects of the chemical treatments on the fibre and the hemp fibre reinforced composites were investigated.
Abstract: Glass or carbon fibres are traditionally used as reinforcement in engineering composites. The increasing ecological and environmental concerns have led to the use of natural fibres as renewable alternatives. Among them, hemp fibre offers the best mechanical properties as well as abundant availability. However, the hemp fibre, same as other natural fibres, has the issues of fiber/matrix bonding and moisture absorption. Hydrophilic nature of hemp fibre causes a weak bonding with hydrophobic polymers matrix and the property deterioration during service.
Chemical treatments are needed to modify the surface of fibre, aiming at improving the adhesion with polymer matrix and reducing the hydrophilicity of the fibre. Alkalization, acetylation and the combination were used in this study to treat the hemp fibre. The effects of the chemical treatments on the fibre and the hemp fibre reinforced composites were investigated.
TL;DR: In this article, a flow-through plate silencer is constructed for low frequency noise control by using new reinforced composite panels with light weight and high bending stiffness, and the performance of two plate silencers with the stopband from 229 to 618Hz is analyzed.
Abstract: A compact flow-through plate silencer is constructed for low frequency noise control by using new reinforced composite plates. The concept comes from the previous theoretical study [1] that in a duct, a clamped supported plate covered with a rigid cavites. The structural property of the very light plate with high bending stiffness is very crucial element in such plate silencer. In this study, an approach to fabricate new reinforced composite panel with light weight and high bending stiffness is developed in order to realize the function of this plate silencer practically. The performance of two plate silencer with the stopband from 229 to 618Hz in which the transmission loss is higher than 10 dB over the whole frequency band can be achieved.
TL;DR: In this paper, X-ray photoelectron spectroscopy (XPS) was conducted to analyze the chemical composition between epoxy matrix and nanocomposite, which revealed that a chemical bonding at an interface between the matrix and the nanoclay of the composites did exist.
Abstract: In this study, X-ray photoelectron spectroscopy (XPS) was conducted to analyze the chemical composition between epoxy matrix and nanocomposite. This experiment revealed that a chemical bonding at an interface between the matrix and nanoclay of the composites did exist. Thus, such bonding can enhance the mechanical and thermal properties of resultant polymer composites as reported in many literatures.
TL;DR: In this paper, a Nafion-clay nanocomposite membrane has been prepared by dispersing unmodified and acid activated Laponite XLS in 20% dispersion.
Abstract: Nafion-clay nanocomposite membrane has been prepared by dispersing unmodified and acid activated Laponite XLS in Nafion 20% dispersion. The resulting membranes possess better proton conductivity and mechanical strength as compared to the virgin membrane. Acid activation of the nanoclay leads to the in-situ generation of H3PO4 by the hydrolysis of the peptizer present on the surface of the nanoclay. The in-situ generated H3PO4 helps in improving all the technical properties of the nanocomposite including the water uptake and proton conductivity of the nanocomposite, containing acid activated clay compared to the nanocomposite, containing unmodified clay. The maximum proton conductivity of 270.2 mS/cm is achieved at 110 °C for the nanocomposite membrane containing 3% acid-activated Laponite compared to 136.2 mS/cm for the virgin Nafion. Keywords: Nafion, clay, nanocomposite, peptizer, polymer electrolyte membrane fuel cell (FEMFC), proton conductivity, membrane
TL;DR: In this paper, a nanoindentation technique was applied to measure the localized elastic modulus and hardness for interstitial lamellae and osteons of bovine cortical bones at different temperature ranges.
Abstract: Among different sterilization methods, heat-treatment of bone is recognized as one of the simple and practical methods to lower the human immunodeficiency virus (HIV) infection and overcome the risks of rejection and disease transfer from allograft and xenograft during bone transplantation. In order to best characterize the micro-structural mechanical property of bone after heat treatment, the nanoindentation technique was applied in this study to measure the localized elastic modulus and hardness for interstitial lamellae and osteons lamellae of bovine cortical bones at temperature 23°C (room temperature-pristine specimen), 37°C, 90°C, 120°C and 160°C, respectively. The elastic modulus (E) and hardness (H) of interstitial lamellae obtained higher values as compared with osteons lamellae which show that interstitial lamellae are more stiff and mineralized than osteons. Moreover, as a specimen pre-heat treated at 90°C, the E and H values of interstitial lamellae and osteons were closed to a pristine specimen. For a specimen pre-heat treated at 120°C, both interstitial lamellae and osteons obtained an increase in E and H values. As a specimen pre-heat treated at 160°C, the interstitial lamellae and osteons obtained a slight decrease in E and H values. These findings are correlated to results reported by other researchers [1, 2] that calcified collagen molecules starts to degenerate at about 120°C and complete at 160°C. Interestingly, when a specimen was pre-heat treated at 37°C, both interstitial lamellae and osteons obtained significant decreases in E values of 57% and 40%, respectively as compared to the pristine specimen; while in H values, there was a decrease of 27.4% and 15%, respectively. Thus, this paper will investigate the mechanical properties of bovine cortical bones under various temperature ranges by nanoindentation technique.
24 Aug 2011
TL;DR: In this paper, a study of lower cost, high energy absorbent continuous fiber laminates, and in particular, high modulus polypropylene (HMPP)fibers Innegra™ S is the commercial name used by======Innegrity for its HMPP fiber.
Abstract: Advanced fibre composites which were primarily developed for defense and aerospace industries have made inroads into fast growing and high volume civil infrastructure industry nearly a decade ago There are traditional para-aramid synthetic fibres such as Kevlar which are significantly expensive for the use of civil infrastructure construction The recent development of less expensive, high modulus synthetic fibre has opened a new path for the development of cheaper, high performance, impact resistant composites which are affordable for civil infrastructure development This paper details a study of lower cost, high-energy absorbent continuous fiber laminates, and in particular, high modulus polypropylene (HMPP)fibers Innegra™ S is the commercial name used by
Innegrity for its HMPP fiber
TL;DR: In this article, N. Amino-phenylacetamide (B) was firstly immobilized on the single-walled carbon nanotubes and characterized by 1H NMR, IR spectra and TEM images.
Abstract: N-(2-Amino-phenyl)-2-{2-[(2-amino-phenylcarbamoyl)-methoxy]-phenoxy}-acetamide (B) was firstly immobilized on the single-walled carbon nanotubes and characterized by 1H NMR, IR spectra and TEM images. The longer 5D0 fluorescence lifetime was observed in the europium (III) complex of this functionalized carbon nanotube than in the Eu (III) complex of free B.