Advanced Materials Research Vol. 701

Abstract: As electric insulators of the copper conductors in the electric generators of alternative current or in electric motors of high tension, there are used with priority the composite crosslinked mica-epoxy. Pre-impregnated band with solvent was introduced, the impregnation being performed with phenolic-novolac resin. The studied material got superior dielectric properties at function temperatures corresponding to the insulation class F(155C). Its main components are: mica paper (53%), glass cloth (13%) and the basic epoxy phenolic-novolac resin. The complex permittivity and conductivity were determined with the Time Domain Spectrometer (TDS); the apparatus allows the determination of the electric values in the domain of frequencies: very large domain of frequencies. The temperature varied in the domain 23-190C with the help of an oven. The purpose of this article is to report the dielectric properties of mica-epoxy-novolac composite insulator, for which very few data have so far been published.

Abstract: In this Investigation, the influence of two kind of polymers (Urea-formaldehyde and Polypropylene) mixed with natural fibre (Kenaf) were studied for their sound absorption coefficients. Four samples were made; Samples A1 and A2 are made of Kenaf core fibre with adhesive of high emission Urea-formaldehyde resin (HN 100) with 51.6 % solid content. The fabrication of the particle board was done using a hot press for 6 minutes under the pressure of 40 Ton at 180°C for different fibre lengths 1 mm (Sample A1) and 0.6 mm (Sample A2) with weight fraction of 80%. Sample B1 and B2 are made of Kenaf core fibre with polypropylene matrix materials with coupling agent of polyvinyl alcohol. The fabrication of the sample was done using hot press for 30 minutes under the pressure of 1000 Psi at 180°C for different lengths of 1 mm (Sample B1) and 0.6 mm (Sample B2) with weight fraction of 20%. The sound absorption coefficients of samples were measured according to American society for Testing Materials (ASTM E1050 10) two microphone method. It is evident that type of polymer influences the sound absorption coefficients.

Abstract: This study was undertaken to investigate mechanical and morphological properties of rubber toughened polyester composite filled with kenaf and was exposed in varying natural weathering and difference environmental condition (Artificial Sea Water (SW), Distilled Water (DS), Environment Exposure (EX) and Soil Exposure (SL)). Rubber-toughened polyester-kenaf fibre composites were prepared by adding 25% of kenaf fibre in unsaturated polyester resin and cross linked with a mixture of methyl ethylketone peroxide and cobalt octanoate. Three percent (3%) of liquid natural rubber (LNR) were added as a toughening agent. The sample was prepared using compression molding technique. It was found that the samples that being immersed in seawater (SW) had lower mechanical properties values as compare with other conditions. The value of flexural modulus and flexural strength were decrease by 35.9 % , 12.5% but the value of impact strength had slightly increase by 34% .The microstructures of the composites fracture surface were examined using a scanning electron microscope (SEM).

Abstract: Plastic resistance to be degraded by microbial activity has led to serious waste and landfill problems. Thus a study has been constructed to replace the non renewable and non degradable material with natural and synthetic biodegradable resources commonly available, namely Sago Starch and Polyvinyl alcohol (PVA). Hybrid blend consists of Sago Starch (SS), Polyvinyl Alcohol (PVA) and LLDPE has been developed and thermal and mechanical properties of this blend have been investigated. DSC plot for blend of various composition of PVA and SS formulated with fixed amount of LLDPE reported series of different gelation and melting temperature for SS and LLDPE. Tensile strength for all hybrid samples were found to have higher strength than pure SS blend, range from 4-6 Mpa compared to 1-2 Mpa. Modulus of Hybrid samples were range from 54.469 243.066. Increase the starch loading deceases the modulus of the blends. FTIR spectrums for all samples showed peaks at 3301 cm^-1 -3322 cm^-1 and 1462 cm^-1 indicating that hydroxyl groups and CH₂ bending vibration were presents in the blends.

Abstract: Electronic device that subjected to various effects by radiations can cause small interferences such as noises in the circuit. These effects are especially critical in operating environment such as outer space, where radiation comes in stronger and more frequent. In this research, analytical study on the effects of ionizing radiation induced by ⁶⁰Co gamma (γ) rays in bipolar junction transistor (BJT) devices had been performed. It was found that the high energy of the radiation allows more valence electrons to be excited to the conduction band in the BJT. This leads to the production of a large number of excited atoms and increases the holes in the valence band. The increase of holes in the base region due to trapping will increase the probability of recombination and reducing the number of electrons that reaches the collector region. This ionizing radiation effect was found to arouse either a permanent or temporarily damage in the devices depending on their current drives and total dose absorbed.

Abstract: The paper presents the determination of fatigue life of 316L stainless steel at room temperature. Plenty of steel in the world has been investigated for a lot of application in the science and technology market. The mechanisms of fatigue of 316L stainless steels were studied and investigated. Fatigue tests of specimens were performed in accordance with ASTM E466-96. The fatigue tests were performed in constant load amplitude, constant frequency of 5 Hz with load ratio R=0.1. Fracture surface of specimens were examined by using Scanning Electron Microscope (SEM). The results showed that the endurance fatigue limit of 316L stainless steel was 146.45 MPa.

Abstract: The purposes of this study are to investigate the effect on variation of the specimens tube length and annealing temperature on the amount of energy absorption of Aluminium tubes (AA 6061) towards inversion collapse mode. The tests were performed on the Aluminium tubes using compression test according to ASTM E8 standard procedure. In this study, a quasi-static inversion tests were conducted in order to obtain the energy absorbed during inversion stages. It was found that the energy absorbed by Aluminium tubes were increased by increasing the tube length but decreased with annealing temperature.

Abstract: Self-healing has usually an emphasis on special materials that is metallic materials. When there is a minor damage, almost all biological organisms, even complex ones, have the ability to repair themselves. Recently, a novel field of materials science is constituted by self-healing in organic materials or material systems and it is rapidly expanding. These materials have a particular ability to heal themselves. The initial crack is healed to the point that upon reloading, a new crack is formed next to the original, rather than the original crack reopening. Only simple heating can reverse transformation and cause reinforcement for these cracks. The shape memory alloy wires are activated by heating the system and therefore the healing begins. Due to the heat, the wires relapse to their original shape at the shape change in martensite to austenite transition temperature. The concentration of most of the studies so far has been on polymers and ceramics and the reason is that it includes self-healing in non-metallic materials. Also, they are more convenient than including it in metallic materials. In this review paper the design principles of self-healing materials and their improvement methods are investigated.

Abstract: The primary aim of this paper is to provide an insight on the effect of chitosan compounds on the properties of polypropylene/chitosan composite fiber prepared by melt spun process. Three types of chitosan powder including ball mill prepared chitosan, spray dry prepared chitosan, and soybean oil-g-chitosan were employed for the preparation of chitosan compounds using polypropylene as polymer matrix. Then, chitosan compounds were incorporated into polypropylene fibers by melt spinning process. Polypropylene fibers containing chitosan particle loadings of 0.5 wt%, 1 wt%, and 3 wt% were prepared. Tensile strength, thermal property, morphology of chitosan compounds and fibers were investigated. The soybean oil-g-chitosan particles were found well distributed in PP matrix due to the compatibility of hydrophobic interfaces. However, spray dry-chitosan exhibited the best reinforcement effect by imparting the highest toughness compared to the others.

Abstract: Cryogel based oil encapsulation was attempted with a ternary system of colloidal chitosan, κ-carrageenan, and carboxymethylcellulose sodium salt (NaCMC). Favourable formulations of this ternary system that caused irreversible sol-gel transition by freezing (cryogelation) were found in this study, and the oil phase that contained a selected model food ingredient (curcumin) was successfully encapsulated in this prepared cryogel matrix. The encapsulation yields were found to vary from ca 89 to 99%, and the values were influenced by the cooling protocol used during freezing, thereby indicating that the gel formation kinetics was intimately related to the degree of encapsulation. The release behaviours of the ingredient were investigated in aqueous systems. The release curves showed that both a burst release and a first order release were achieved simply by changing the freezing condition. Freezing could modify the gel formation of the present cryogel, and the resulting structural modification evidently controlled the oil encapsulation manner. The prepared cryogels were found to be sensitive to the ambient pH. It was suggested that the ternary system of chitosan, κ-carrageenan, and NaCMC is an interesting matrix for designing controlled release system.