Advanced Materials Research Vols. 123-125

Abstract: Ammonium polyphosphate (APP) and zinc borate (Zb), as flame retardants were incorporated into sisal fiber/polypropylene (PP) composites. Ratios of APP to Zb were varied. Maleic anhydride grafted polypropylene (MAPP) was used to improve the interfacial adhesion between polypropylene and fillers. Flammability of the composites was examined using a horizontal burning test, a vertical burning test, and a limiting oxygen index test. Morphology and mechanical properties of the composites were also investigated. The composite containing 30 phr of APP and 10 phr of Zb exhibited better flame retardancy than the composites containing other ratios of APP to Zb. The combination of APP and Zb insignificantly changed mechanical properties of the composites. In addition, SEM micrographs of the composites revealed good distribution of flame retardants and sisal fiber in PP matrix.

Abstract: An eight noded isoparametric finite element code is applied to study static bending, free and forced vibration characteristics of composite conoidal shell roofs with complicated boundary conditions which are often encountered in the industry.

Abstract: By means of the wet phase inversion process, the PVDF/silica (SiO2) hybrid membranes with different content of nano-silica (nano-SiO2) were prepared. It was investigated that the pure water flux and retention based on egg albumin solution for different PVDF hybrid membrane samples. The pure water flux and porosity of PVDF/SiO2 hybrid membranes are enhanced simultaneously with increasing SiO2 content in PVDF composite system. When SiO2 content is around 7.5%, the phase separation rate of casting solution increases to peak value, meanwhile, the retention of hybrid membrane achieves the best effect. The SEM micrographs show that the quantity of finger-like pores of PVDF/SiO2 hybrid membranes decreases and the micropores becomes fine compared to PVDF membrane. The results of DSC indicate that there are almost no effects on the melting point, but enhancement the fusion enthalpy and the crystallinity of PVDF along with increasing the SiO2 content.

Abstract: The fracture characterization of Ti–48Al–2Nb-2Cr composites (TANC) with addition of different weight contents of fluoride solid lubricants (LiF, NaF, CaF2 and 38%CaF2-62%BaF2 eutectic solid lubricant (BC) ) were evaluated in the paper. The fracture toughness of composites with different content of fluoride solid lubricants is discussed. The TANC composites with 0-5 wt.% solid lubricant exhibit higher fracture toughness. It can be seen that additions of all fluoride solid lubricants to TANC matrix result in decrease in fracture toughness expect for additions of 5% of that. By adding 5 wt.% BC the fracture toughness of the TANC composites exhibited a maximum value of 12.2MPa m1/2; by addition of 5%CaF2, 11.4 MPa m1/2; 5%LiF, 10.8 MPa m1/2 while 5%NaF, 11.1 MPa m1/2. However, with further increasing of fluoride solid lubricants contents it showed a downward trend. By adding 20 wt.% BC the fracture toughness of the TANC composites exhibited a maximum value of 8.6 MPa m1/2; by addition of 20%CaF2, 8.1 MPa m1/2; 20%LiF, 8.3 MPa m1/2 while 5%NaF, 7.9 MPa m1/2.

Abstract: The increasing demands for indigenous non-toxic friction material for wind mill application with better braking properties is ever expanding and this has motivated the development of non-asbestos brake pads. As an alternative to asbestos friction materials, aramid fibre reinforced phenolic matrix friction composite was developed with fibre content varying from 0 to 7 wt %. Using pin type specimens, their friction and wear behaviour was evaluated against cast iron disc in a pin on disc testing apparatus. The test results at a constant load of 70 N and at two speeds of 1.5 m/s and 5 m/s showed that the coefficient of friction decreased with fibre content and sliding velocity, almost linearly. The wear rate also decreased with increase in fibre content but was following a polynomial relation of third order. A composition which gives frictional coefficient of 0.45 to 0.40 and a minimum wear rate is desirable for the application. The formulation containing 5 wt % aramid fibre exhibited friction in this range and its wear rate was almost closer to the minimal value. Hence, from friction and wear considerations an aramid fibre content of 5 wt % is ideal for this application.

Abstract: HALE (High Altitude Long Endurance) UAVs are aircraft systems for surveillance and reconnaissance for over 25 hours. Most of UAVs consist of fuselage and high aspect ratio wing because of long-endurance flight mission. The structural weight of HALE UAV is one of the most critical design requirements. In addition, the structural stiffness for the high aspect ratio wing is another critical design requirement because the UAV has to keep the minimum clearance between wing tip and ground when the UAV is being towed. For above design requirements, the wing structure of the UAV has been designed by intermediate modulus Gr/Ep composite materials. The goal of this research is to present the optimized design concepts for the composite wing structure of the UAV. Although there are many design parameters for the composite structure of the aircraft, this research is focused on composite structure strength and buckling analysis for the plate type structures, such as cover panel skins and spar webs, which are loaded in in-plane shear and/or compression. This research presents that the wing structural weight can be reduced when the material allowables based on tape laminate are applied instead of unidirectional lamina allowables. For the buckling analysis, this report has a trade off study to find an optimized lay-up design and stacking sequence with 0°, ±45° and 90° plies. This research shows that the critical buckling load is a function of the number of ±45° plies and the position of the ±45° plies through the laminate thickness using a typical Gr/Ep composite tape material. The structural design of the UAV composite wing regarding buckling analysis is more effective when the laminates are stacked up with high percent of ±45° plies and the ±45° plies are located toward outside through the laminate.

Abstract: In recent decades, stretchable conductive polymers have gained extensive interest of researchers because of their hi-tech applications in electronics, textiles and medicine devices. In this study, carbon nanotubes and carbon nanospheres, as the chemically stable dopants, were uniformly dispersed in a polyurethane matrix to develop a highly elastic and stretchable conductive polymer composite film. The nanocomposite film inherited the advantageous properties from its constituents, namely the high conductivity from carbon nanotubes and nanospheres, and the elastomeric mechanical properties from the polyurethane. The conductive polymer nanocomposite film can be uniaxially and biaxially stretched up to 50% without clearly mechanical or electrical changes. Stretching beyond 50% would result in the conductivity decreasing gradually. Therefore, the as-prepared stretchable conductive polymer nanocomposites possessed both the high conductivity and the high elasticity, which would have greater application potential in high-performance electronic circuits.

Abstract: The solvent-based exfoliation of graphite, including into graphene and/or graphene-like platelets, is an important challenge. Here, we report a “direct” Friedel-Crafts acylation reaction between graphite and 4-ethylbenzoic acid (EBA) to afford edge-functionalized graphite (EFG). Unlike, for example, graphite oxide (GO), the functionalization is at the edges of the graphite and thus, the basal plane of individual layers in EFG is not functionalized. The EFG can be easily dispersed and exfoliated in common organic solvents to concentrations as high as 0.8 mg/mL. Large-are uniform films can be produced by solution-casting such dispersions on substrates and conductivities as high as 125 S/cm can be obtained by subsequent heat treatment at 900 °C under argon atmosphere. Hence, a few layers graphene obtained from annealing under argon atmosphere show the potential to replace Indium tin oxide (ITO).

Abstract: A simple and versatile method has been invented to fabricate conducting polymer hydrogels via supramolecular self-assembly between polymers and multivalent cations. As-prepared hydrogels composed of poly(3,4-ethylenedioxythiophene) and poly(styrenesulfonate) (PEDOT-PSS) exhibit expanded-coil conformation in polymer chains, phase-separate at nanometer scale, possess controllable microstructure, and is responsive to external stimulus. The conducting PEDOT-PSS hydrogels have then been introduced into multiple-network hydrogels to obtain composite hydrogels combining enhanced mechanical strength and excellent electrical activity. Triple-network (TN) and special double-network (sDN) hydrogels, containing poly(acrylic acid) (PAA) and poly(acrylamide) (PAAm) as the matrix respectively, are successfully prepared. Finally, PEDOT-PSS hydrogels with self-strengthening function are directly fabricated via a one-step process under optimized conditions. The strengthening mechanisms for each kind of hydrogels are proposed, and the applicability in electrosensors, supercapacitors and electromechanical actuators are briefly demonstrated.

Abstract: Sulphoaluminate cement and Lead Niobium-Magnesium Zirconate Titanate ceramic [P(MN)]ZT were used as matrix and functional phase respectively to fabricate 1-3-2 cement-based piezoelectric composites by dice and filling technique. The influences of base thickness on piezoelectric properties, electromechanical properties and acoustic impedance properties of the composites were discussed. The results show that as the base thickness increases, the piezoelectric stain factor d33 increases gradually, while the piezoelectric voltage factor g33 decreases. The planar electromechanical coupling coefficient Kp exhibits the trend of decrease, while the thickness electromechanical coupling coefficient Kt and acoustic impedance show the increasing trend. The mechanical quality factor Qm reaches the minimum (1.49) when base thickness is 2.00 mm. The results reveal that the 1-3-2 piezoelectric composite will be suitable for application by changing the base thickness.