Advanced Materials Research Vols. 123-125

Abstract: In a previous study, we have proposed a model that describes the non-Arrhenius ionic conduction behavior in superionic glasses. In the present report, the model is applied to analyze the conductivity behavior of a wide variety of solid electrolytes that include crystals, glasses, polymers, composites and mixed ionic-electronic conductors. From the analysis of the model, the physical factor responsible for the non-Arrhenius behavior has been extracted and discussed.

Abstract: The application of polymer electrolyte fuel cell (PEMFC) to the electrical vehicles is restricted by high material cost and complicated manufacturing process. The epoxy based graphite composite has been prepared with various additives. The possibility for bipolar plate material at PEMFC was investigated by electrical and thermal properties. Density of bipolar plate with graphite composite was decreased from 5.40 to 2.57 as 80 w/o of graphite content were changed to 50 w/o of graphite content and 30 w/o of expanded graphite. The percolation thresholds showed around 75 w/o of graphite content was varied by molding pressure. From the TGA analysis, the glass transition temperatures were shown around 250 degrees and less that 3% of weight loss was found at 150 degree. The surface conductivity of epoxy/graphite bipolar plate showed from 4.5 S/cm to 87 S/cm and the highest value of conductivity was obtained using expanded graphite powder only. The improvement of thermal stability and electrical properties was accomplished by addition of expanded graphite powder.

Abstract: Wastes such as saw dust (Pinus Radiata) and milk bottles (High Density Polyethylene - HDPE) are available in abundance. Composite decking materials, consisting of different weight percentages (60%, 70% and 80%) of saw dust and recovered HDPE, were extruded using a co-rotating, conical, twin screw extruder with a decking-profile die. The extruded decking materials were evaluated on their surface finish and shape conformance. The extruded decking materials were tested in accordance with the appropriate ASTM standards to determine their water absorption, thickness swell, static coefficient of friction, weathering and flexural (four-point bending) properties after they met the required quality ratings.

Abstract: A variety of natural fibers have been on research over the past years to develop alternative echo friendly materials that have comparable performance as their synthetic counter parts for use in composite materials. In this study, two different forms of date palm tree fibers were used as reinforcement materials to develop composite materials with polypropylene (PP) matrix. These two different date palm fibers are namely Date palm fiber (DPF) & Date Palm twigs (DPT). These fibers were surface modified using alkali treatment. Two different Percentages of PP (50%, 75%) were mixed with the each type of fibers to form composite pellets using double screw extruder. The mechanical properties of the different fibers reinforced composite, in treated and untreated condition were investigated. The effect of different weight fraction of Polypropylene matrix reinforced DPF or Twigs fiber composite was investigated. The results indicate that untreated DPF-PP composites possess better mechanical properties compared to all untreated & treated DPT-PP composites. Mechanical interlocking between untreated fibers and the matrix showed some increase in the mechanical properties of the untreated DPF-PP compared to the treated one. In both cases, composites having 75% PP has better mechanical properties than the 50%PP composites. This is due to the lack of compatibility between the fibers and the matrix.

Abstract: Carbon fiber-reinforced polymer (CFRP) composites are thin laminates that are externally bonded to broken concrete specimens using an epoxy system to increase their load-carrying capacity in this study. This paper reports the test results of broken concrete specimens strengthened with CFRP sheets and subjected to two aggressive environments including ultraviolet (UV) and freeze-thaw cycles. Test results revealed that three different CFRP layers are effective in retrofit on the broken compressive or flexural concrete specimens. The broken concrete specimens repaired with an epoxy and CFRP system could improve their compressive strength, flexural strength or ductility. Both aggressive environment tests didn’t cause obvious degradation to hardness index, compressive or flexural strength. The flexural specimens used half-U coating and anchorage systems were much higher strength than those only wrapped with CFRP sheets on the flat surface.

Abstract: Sisal fiber reinforced polypropylene composites were prepared using an internal mixer. Heat treatred sisal fibers were performed by heating the fibers in an oven at 150, 170, and 200°C under an atmospheric pressure and a presence of air. The composites prepared at a fiber content of 20 wt% were molded by an injection molding machine for mechanical tests including tensile and impact properties. Morphologies of the composites were examined using a scanning electron microscope (SEM). Viscosity at various shear rate of the composites were also investigated. Tensile strength and impact strength of heat treated sisal fiber/polypropylene composites were slightly higher than that of the untreated sisal fiber/polypropylene composite. However, no remakable effect of treatment temperatures on the mechanical and rheological properties of the composites was observed. SEM micrographs revealed that the heat treatment improved adhsion between the fiber and PP matrix.

Abstract: Jute fabrics reinforced polypropylene (PP) composites were prepared by compression molding. Tensile strength (TS), tensile modulus (TM), bending strength (BS), bending modulus (BM) and impact strength (IS) of the composites were studied. To investigate the effect of oxidizing agents on the properties of the composites, jute fabrics were treated separately with the aqueous solutions of (0.005-0.05%w/v) potassium dichromate (K2Cr2O7) and (0.0025-0.04%w/v) potassium permanganate (KMnO4). The highest values of mechanical properties were reported for 0.02% K2Cr2O7 and 0.01% KMnO4 treatment. Thermal analysis of PP, treated and untreated jute fabrics and composites revealed that KMnO4 treatment lowers the thermal stability of the jute fabrics and composite. On the other hand, K2Cr2O7 treatment increases the stability of the fibers and composites. Hydrophilic nature of the treated composites was also reduced significantly.

Abstract: In this study, wear behaviours of fiber-reinforced and matrix composite materials are experimentally investigated under different speeds, loads and temperature. Composite materials were made of Kevlar-epoxy resin, glass fibre-epoxy resin and glass fibre -polyester resin materials. Tests were conducted for speeds of 0.390 and 0.557 m/s at two different loads of 5N and 10N respectively. Wear in the experiments was determined as lost in mass.In addition, the wear behaviour of samples was investigated through the SEM observation.

Abstract: . This paper deals with the mechanical characterization of short bamboo fiber reinforced green composites (BFGC). The effects of thermal shock on the mechanical properties of BFGC were investigated. Their flexural strength was evaluated by 3-point bending test, and Vickers hardness and elastic modulus were evaluated by a nano-indentation method. The fracture surfaces and microstructure of BFGC were examined by SEM. The results of evaluated mechanical properties (3-point bending test) after thermal shock indicated that the strength of BFGC decreased below 40°C, however the strength became constant above 40°C. The Vickers hardness and modulus of elasticity evaluated from the nano-indentation tests also represented a similar trend to that of flexural strength. The fracture surface of thermal shocked BFGC after bending tests indicated the pull-outed bamboo fibers. This might be responsible for insufficient bonding between bamboo fiber and resin.

Abstract: In this study, the effects of weave type and fiber content on the physical properties of woven sisal fiber/epoxy composites were investigated. Sisal fibers used in this work were obtained from Nakhon Ratchasima, Thailand. Both untreated and alkali-treated fibers were employed. The woven sisal fibers were manufactured by hand weaving process. The fiber content in sisal fiber/epoxy composites were 3 wt.%, 5 wt.% and 10 wt.%. The composites were cured at room temperatures. In order to determine mechanical properties of the composites, flexural and impact tests were applied. Flexural strength and flexural modulus of all composites were higher than those of pure epoxy resin and tended to increase with increasing fiber content. The impact strength of all composites was lower than that of pure epoxy resin. The composites containing 10 wt.% sisal fibers showed the highest impact strength. There was no definite influence of weave type on flexural properties of the composites. At 3 and 5 wt.% fiber, the composites containing plain weave fibers seemed to show a higher impact strength than the composites containing other weave types.