Daniel Karthik

The Joule heating behavior of carbon-based materials obtained by the process of carbonization of industrial para-aramid fabric wastes are investigated in the present work. Carbonization involves a process of thermally decomposing organic material, thereby altering its physical and chemical properties to obtain carbon-rich materials that are electrically conductive and display Joule heating behavior. The principle of Joule heating is based on the intrinsic electrical resistance of the material across an applied voltage. Here, para-aramid woven fabric wastes are converted into activated carbon materials through straightforward, controlled, single-step thermal treatments by three different kinds of atmosphere, i.e., in the CO₂ evolved from charcoal, a mixture of gases from ammonium bicarbonate salt (NH₄HCO₃), and Nitrogen gas (N₂), respectively, inside a high-temperature furnace. The carbonization temperatures were varied from 800 to 1100 °C. The carbonization process variables were optimized to obtain carbon-rich materials with lower electrical resistivity. The results of electrical resistivity measurements show that for all three methods, the electrical resistivity decreases with increasing carbonization temperatures. An experimental setup consisting of an infrared (IR) camera, positioned over the surface of the fabric specimen to record the surface temperature of the material connected to a DC power supply, was employed. The kinetics of Joule heating and subsequent cooling were also analyzed at a fixed voltage of 5 V by recording the changes in surface temperature with respect to time. The heating–cooling cycle is described by a simple kinetic model of first order.

Electric and electronic devices are mainly emitting electromagnetic radiation, and shielding from radiation is essential. Electrically conductive materials are suitable for radiation shielding applications. The designing of the textile material for the radiation shielding is challenging because of its open area and design. In general, more open area has transmit the radiations tend to lesser in shielding. Another factor is the laying angle of the textile material also plays important role beyond open area. In this study, the effect of laying angle and open area was analysed for effective utilization of conductive materials. The conductive nonwoven fabric was used to form as strips to simulate the various textile structures for shielding application. The Cu/Ni coated ultrathin polyester nonwoven fabric sample is taken to form two-layers strips and test for electromagnetic shielding effectiveness. In experimental design, three factors of strips which are strips laid angle, strip thickness, and gap between the strips are taken at three levels. The strip cover area and aperture area were calculated geomentrically for each design and significant difference on shielding effectiveness was noticed.

The aim of this research was the preparation and characterization of hybrid prepreg tapes from glass multifilament roving (circular cross-section). The fiber, roving, and tape strength distribution was characterized by exploratory data analysis tools (especially quantile-quantile plot) and modeled by the three parameters’ Weibull distribution. For estimation of Weibull model parameters, the noniterative technique based on the so-called Weibull moments was used. It was shown that the prepared hybrid prepreg tapes prepared by controlled mechanical spreading technology developed by the authors improved mechanical tensile properties and can be used for the preparation of composites of complicated forms by robotic winding.

Pyrolysis in an inert atmosphere involves elimination of moisture and volatile components from fibrous materials followed by cleavage of molecular bonds to finally obtain carbon rich residues. Over the years there have been numerous studies on the pyrolysis of 1,4 phenylene terephthalamide (Kevlar) and characterization of volatile products by using various analytical techniques. The main objectives of this work were to exhibit a simple and straightforward pyrolysis method using a smelting furnace and to condense the volatile products on a cold surface, thereafter, using UV-Vis spectroscopy to get information progressive changes in concentrations of decomposition products and their difference in volatility and also demonstrate an interesting algorithm for separation of mixture spectra. Variations in concentration of major elements (C, N, S, and O) were also monitored as a function of pyrolysis temperature. An increase in the concentration of volatile products was observed above 500°C, reaches maximum at 700°C and then gradually decreases progressing towards the final temperature of 1100°C. Separation of mixture spectra was attempted using the concept of spectral matrix decomposition to decompose measured spectra into possible spectra of individual components.

The augmented demands of textile materials over time have brought challenges in the disposal of substantial volumes of waste generated during the processing and end of life of such materials. Taking into consideration environmental safety due to discarding of textile waste, it becomes critical to recuperate useful products from such waste for economic reasons. The present work deals with the preparation of porous and electrically conductive activated carbon fabric by a novel single stage method of simultaneous carbonization and physical activation of Kevlar feedstock material procured from local industries, for effective electromagnetic (EM) shielding applications. The Kevlar fabric waste was directly carbonized under a layer of charcoal without any intermediate stabilization step at 800 °C, 1000 °C, and 1200 °C, with a heating rate of 300 °C/h and without any holding time. The physical and morphological properties of the activated carbon, influenced by carbonization process parameters, were characterized from EDX, X-ray diffraction, SEM analysis, and BET analysis. Furthermore, the electrical conductivity was analyzed. Finally, the potential application of the activated material for EM shielding effectiveness was analyzed at low (below 1.5 GHz) and high (2.45 GHz) frequencies. The phenomena of multiple internal reflections and absorption of electromagnetic radiations was found dominant in the case of activated carbon fabric produced at higher carbonization temperatures.