Analysis of MWCNT/epoxy composites at microwave frequency: reproducibility investigation

A wide-band microwave characterization of nanocomposites based on commercial multiwalled carbon nanotubes (MWCNTs) and epoxy resin is presented. The sample preparation method is discussed in detail. Field emission scanning electron microscopy is used for morphological sample analysis of nanocomposites and MWCNTs. The complex permittivity is measured in a wide frequency band (3 to 18 GHz) using a commercial dielectric probe (Agilent 85070D) and a network analyzer (E8361A). A statistical analysis based on one-way analysis of variance (ANOVA) technique is performed. The aim of this statistical analysis is to investigate the influence of concentration of nanoparticles inside the polymer matrix on the complex permittivity. This can be significantly different in nanocomposites even if the samples have similar electrical properties.     

Fused Deposition Modeling for Unmanned Aerial Vehicles (UAVs): A Review

Additive Manufacturing (AM) is a game changing production technology for aerospace applications. Fused deposition modeling is one of the most widely used AM technologies and recently has gained much attention in the advancement of many products. This paper introduces an extensive review of fused deposition modeling and its application in the development of high performance unmanned aerial vehicles. The process methodology, materials, post processing, and properties of its products are discussed in details. Successful examples of using this technology for making functional, lightweight, and high endurance unmanned aerial vehicles are also highlighted. In addition, major opportunities, limitations, and outlook of fused deposition modeling are also explored. The paper shows that the emerge of fused deposition modeling as a robust technique for unmanned aerial vehicles represents a good opportunity to produce compact, strong, lightweight structures, and functional parts with embedded electronic.

     

Investigating the acoustical properties of carbon fiber‐, glass fiber‐, and hemp fiber‐reinforced polyester composites

Wood is one of the main materials used for making musical instruments due to its outstanding acoustical properties. Despite such unique properties, its inferior mechanical properties, moisture sensitivity, and time‐ and cost‐consuming procedure for making instruments in comparison with other materials (e.g., composites) are always considered as its disadvantages in making musical instruments. In this study, the acoustic parameters of three different polyester composites separately reinforced by carbon fiber, glass fiber, and hemp fiber are investigated and are also compared with those obtained for three different types of wood specimens called poplar, walnut, and beech wood, which have been extensively used in making Iranian traditional musical instruments. The acoustical properties such as acoustic coefficient, sound quality factor, and acoustic conversion factor were examined using some non‐destructive tests based on longitudinal and flexural free vibration and also forced vibration methods. Furthermore, the water absorption of these polymeric composites was compared with that of the wood samples. The results reveal that the glass fiber‐reinforced composites could be used as a suitable alternative for some types of wood in musical applications while the carbon fiber‐reinforced composites are high performance materials to be substituted with wood in making musical instruments showing exceptional acoustical properties. POLYM. COMPOS., 35:2103–2111, 2014. © 2014 Society of Plastics Engineers     

Effect of the lateral substituent on the mesomorphic behavior of side-chain liquid-crystalline polymers containing a Schiff base ester

New polymerizable macromers containing a Schiff base ester linkage have been synthesized. These macromers were used to synthesize side-chain liquid-crystalline polymers (SCLCPs) by radical polymerization. The chemical structures of the macromers and polymers were characterized by spectroscopic techniques (FTIR, ¹H NMR, and ¹³C NMR). The mesomorphic properties of the macromers as well as the polymers were studied by polarized optical microscopy (POM) and differential scanning calorimetry (DSC) and confirmed by powder X-ray diffraction (PXRD). POM and DSC studies revealed that all of the macromers and polymers showed liquid crystal behavior, with their nematic phases occurring in different mesophase ranges. The macromer without a lateral unit in the mesogen (M1) showed a thermal transition at a relatively high temperature (181.4 °C), whereas the macromer with a lateral unit in the mesogen (M2) showed a thermal transition at a relatively low temperature (101.8 °C). The SCLCP from macromer M1 (HPM1) also showed a comparatively high-temperature thermal transition compared to that of the polymer from macromer M2 (HPM2). The thermal properties of the polymers were studied by thermogravimetric analysis (TGA). The polymer from the macromer with a lateral unit in the mesogen (M2) showed higher thermal stability than the polymer from the macromer without a lateral unit (M1).