Advanced Materials Research Vols. 47-50

Abstract: Natural fibres, such as sisal, flax and woodfibres, are relatively inexpensive and originate from renewable resources. Thermoplastic polymers, such as polypropylene (PP), high density polyethylene (HDPE) and waste plastics, possess shorter manufacturing cycle times and reprocessability. Natural fibre-reinforced thermoplastic composite materials exhibit favourable values of modulus and strength when the fibres are properly compounded with the polymers. Common methods for manufacturing natural fibre-reinforced thermoplastic composites, injection moulding and extrusion, require pre-compounding of the fibres and the thermoplastic due to the large difference in densities of the loose fibres and thermoplastic materials. Development and analysis of a screwless extruder that employs a reliable and low technology process for melt blending natural fibres and thermoplastic polymers is the main objective of this study.

Abstract: A good method for dispersing Multi-walled carbon nanotubes (MWNTs) in LDPE matrix by melt processing technique had been developed. The surface of MWNTs was modified by HNO3, then, treated with γ-aminopropyltriethoxy Silane. The surface-modified MWNTs homogeneous LDPE composites with 0-0.35 mass fraction MWNTs loading had been evaluated for electrical conductivity. The composites’ electrical conductivity (σDC) was improved for the good dispersion of MWNTs in LDPE matrix. The values of σDC obeyed a percolation power law with MWNTs concentration threshold 0.10 mass fraction. 10-2 s/cm conductivity for 0.15 mass fraction MWNTs loading indicated that the composites could be used as lightweight electrostatic shielding materials.

Abstract: In order to study the potential of increasing the weather stability of natural rubber latex for use as a water-based contact adhesive, the natural rubber latex was modified by graft copolymerization with n-butyl acrylate (BA) and methyl methacrylate (MMA). The grafting reaction was carried out using emulsion polymerization at 60°C. Potassium persulfate was used to initiate polymerization. Four different weight percentage ratios of BA to MMA used in this work were 80:20, 70:30, 60:40 and 50:50. Percentage conversion of the monomer of all latexes prepared was ≥ 79.8 %. The grafting efficiency of grafted natural rubber latexes with a different monomer ratio tended to decrease with an increase of MMA. The adhesion property was characterized by 90° peel strength and 180° lap shear tests. The shear strength value of grafted natural rubber latexes increased with an increase of MMA content. The grafted latex with the monomer ratio of 50:50 possessed higher shear strength than natural rubber latex. The peel strength value of grafted natural rubber latexes seemed to lower than that of natural rubber latex. The weather stability of the modified latex was characterized using thermogravimetric analysis (TGA) and also the peel samples were left in the open air for 45 days before testing. The results showed that grafted natural rubber latex had a higher weather stability than natural rubber latex.

Abstract: The research is aimed to investigate the influence of spherical nanoparticles on the fracture behavior of glass fiber/epoxy composites. Two different contents of silica nanoparticles, 10wt% and 20wt %, were introduced into the composite samples. Through a sol-gel technique, the silica particles with diameter of 25 nm were dispersed uniformly into the epoxy matrix. Subsequently, the silica epoxy mixtures were impregnated into the unidirectional glass fiber mat by means of a vacuum hand lay-up process to form the unidirectional glass fiber/epoxy laminate. During the fabrication, a porous film was inserted into the mid-plane of the laminate to generate the pre-crack. The Mode I fracture toughness of the composites with different nanoparticles contents were then determined form the double cantilever beam (DCB) specimens. Based on the experimental observations, it was found that the glass fiber/epoxy composites with silica nanoparticles exhibit superior fracture toughness than those that do not contain any silica particles. Scan Electronic Microscopy (SEM) observations on the failure surfaces indicated that the enhanced fracture toughness could be due to the improved interfacial bounding in conjunction with the nanoparticle debonding from the surrounding epoxy. In general, such failure mechanisms may complicate the fracture process, dissipating more fracture energy.

Abstract: There has been increasing awareness of the use of intuitional imaging techniques to describe a damage event in the engineered structures. A Lamb wave-based diagnostic imaging approach was developed in this study, by fusing the prior probabilities established by the sensors of an active sensor network at different spatial positions of the structure under inspection. Rather than pinpointing the damage location and shape with definitive parameters, such an approach was intended to probabilistically predict the occurrence of a damage event, which is in nature more consistent with the implication of ‘estimating’ damage in SHM than traditional approaches. As validation, the approach was employed to detect mono- and dual-delamination in CF/EP laminates, and the results were represented in probability contour diagrams, where the structural damage became intuitional. Other major benefits of the approach include the independence of its effectiveness on the number of damage and enhanced tolerance to noise/uncertainties.

Abstract: BT resins composed of 4,4’-bismaleimidodiphenylmethane (BMI) and 2,2’-bis-(4-cyanatophenyl)propane (BCE) were modified by octa(maleimidophenyl) silsesquioxane (OMPS). It was found that the curing reaction of BCE were accelerated by OMPS, and the onset temperature of the cyclotrimerization was reduced up to 95.5°C (by DSC). As demonstrated by DSC and FT-IR, there was no evidence indicated the co-reaction between maleimide and cyanate ester. 2,2’-diallyl bisphenol A (DBA) and diglycidyl ether of bisphenol A (E-51) were also used to enhance the toughness of BT resins, and the formulated BTA and BTE resins were obtained. The results of DMA and TG show that the BT, BTA, and BTE resins containing 1wt% of OMPS exhibit enhanced thermal properties in comparison with pristine BT0, BTA0, and BTE0 resins, while more content of OMPS may impair the polymer matrix, though the effect of OMPS was slight. The dielectric constant of these hybrid materials were reduced by incorporation of OMPS, while overmuch contents of OMPS were disadvantageous for dielectric constant due to the aggregation of OMPS.

Abstract: Polycarbonate - carbon nanofibers, containing various concentrations of filler ranging from 0 % to 10 % wt. have been investigated by electron spin resonance. The as obtained electron spin resonance spectra are complex due to the overlap of several resonances originating from the conducting electrons delocalized over the metallic domains of nanotubes, from the free radicals generated within the polymeric matrix during the processing step, from insulating graphite particles, and from catalyst residues (observed as magnetic impurities). The effect of the filler on the resonance line shape is analyzed in detail. The shape of resonance spectrum demonstrates that the resonance line located near g=2.00 originates from conducting electrons delocalized over the metallic domains of nanotubes. Thos line was accurately fitted by a Lorentzian line shape.

Abstract: Partially aligned and oriented polyacrylonitrile(PAN)-based nanofibers were electrospun from PAN and CNTs/PAN in the solution of dimethylformamide(DMF) to manufacture the carbon nanofibers. The as-spun nanofibers were hot-stretched in a temperature controlled oven to enhance its crystallinity and molecular orientation. Therefore it were stabilized at 250 ( under a stress, and carbonized at 1000 ( in N2 atmosphere by fixing the length of the stabilized nanofiber to convert them into carbon nanofibers. With the hot-stretched process and with the content of CNTs, the mechanical properties will be enhanced correspondingly. The crystallinity of the stretched fibers confirmed by X-ray diffraction has also increased. For PAN nanofibers, the improved fiber alignment and crystallinity resulted in the increased mechanical properties, such as the modulus and tensile strength of the nanofibers. It was concluded that the hot-stretched nanofiber and the CNTs/PAN nanofibers can be used as a potential precursor to produce high-performance carbon composites.

Abstract: In this paper, an attempt has been made to understand the electric field distribution in the Representative Volume Element (RVE) of the Macro Fiber Composite (MFC) using interdigitated electrodes IDEs. Since the magnitude of the electric field within the Representative Volume Element (RVE) using the IDEs is not uniform, an electrostatic study of the electric field behavior is carried out. An approximate RVE model with conventional electrodes, which is useful for the analytical solution, has been proposed instead of the RVE model with IDEs. Finally, the results obtained by the proposed analytical solution are compared to those obtained numericaly using the RVE model with IDEs.

Abstract: 2D metal oxide fractal structures with different appearance and composition are successfully grown on the silicon (100) substrates from their colloidal solutions at room temperature. These films display very high surface coverage on the substrates and abundant structures. The results demonstrate the appearances and dimensions of these structures are dependent on the properties and composition of their constituent particles and the substrates. This work may have potential applications in the fabrication of gas sensors, photon-receivers and catalyst carriers which are not easy made by other methods at RT.