Papers by Author: S. Kanagaraj

Abstract: The usage of polymers is increased in order to replace the conventional metals because of their low cost and weight. As the processing technique of polymers plays a vital role in their properties, Polypropylene (PP) and multi walled carbon nanotubes (MWCNTs) were chosen as a matrix and reinforcement, respectively in order to confirm the effective processing method to prepare nanocomposites. The PP/MWCNTs nanocomposites with different concentration of reinforcement such as 0, 0.5, 1.0, 1.5 and 2.0 wt. % were prepared by melt mixing technique through (i) an injection molding (IM) process and (ii) the twin-screw extruder followed by an injection moulding process (TSE). It is observed that the mechanical properties of PP were found to be increased with MWCNTs concentration irrespective of the processing methods, where the optimum concentration was observed to be 1.5 wt. % of MWCNTs. It is also observed that the mechanical properties of polymer processed through TSE process was found to be less than that of the sample processed by IM process. However, an opposite trend was observed when the reinforcement was done. It is concluded that the PP/MWCNTs nanocomposites processed through TSE were found to have enhanced mechanical properties compared to that of the sample prepared through IM process.

Abstract: The property of high oxygen storage capacity (OSC) of Ceria is an important component in three-way catalysts (TWC), which depends on the low reduction temperature, high surface area and stable crystalline structure. These are required to be improved using mixed oxides for the increased OSC of TWC. Though a good number of literature is available in Ceria-Zirconia mixed oxides, optimization of the composition of oxides based on OSC is very much limited. Hence, an attempt was made to optimize the composition of Ce_xZr_1-xO₂ (0.4 x 0.8) (CZ) based on the OSC using thermogravimetric technique. The CZ solid solution was prepared by co-precipitation (COP) method using Ceria nitrate, and Zirconia oxy-choloride precursors, where the freshly prepared metal hydroxide precipitates were continuously stirred at 45 °C for 60 minutes followed by washing and drying to obtain the nanosized CZ particles. The formation of single nanocrystallite with less than 8 nm size solid solution was identified by XRD, and the same was confirmed by Micro Raman studies. It is observed that the trend of OSC in CZ solid solution was based on the ratio of Ce to Zr in the starting aqueous solution, where the OSC was found to be maximum at 1.5 and the corresponding OSC of the compound was about 0.14 μmol per gram of Ceria.

Abstract: Crosslinking of UHMWPE by gamma irradiation has been the prime choice to improve the wear resistance of the polymer. However, it is always associated with few setbacks like degradation of material properties during the shelf ageing period. In the present work, nanocomposites were prepared using ball milling process and then compression moulding process where UHMWPE was reinforced by MWCNTs with 0.20 and 0.40 wt. %. The samples were gamma irradiated using ⁶⁰Co at 25 and 50 kGy sterilizing doses in air without any post irradiative treatments and then shelf aged for 240 days. The mechanical properties of the composites were studied using small punch technique according to ASTM F2183 standards. Both toughness and hardness of the composites were found to be improved with an increase of irradiation dosage and MWCNT concentration. It is observed that the percentage reduction in Young’s modulus, yield stress and % strain at fracture of 0.4% composite at 50 kGy dose are 6.4%, 8.8% and 12.7%, respectively compared to that of virgin UHMWPE irradiated at same dosage. It is concluded that presence of MWCNTs in UHMWPE prevents the degradation of material properties during the shelf ageing period after irradiation.

Abstract: In this work, nanocomposites of ultrahigh molecular weight polyethylene (UHMWPE) reinforced with multiwalled carbon nanotubes (MWCNTs) were evaluated for their ability to produce nanocomposites with superior mechanical properties. As homogeneity of the nanocomposite plays an important role into final mechanical properties, mechanical ball-milling is used to prepare homogeneous UHMWPE/MWCNTs powders, where special emphasis is given to milling-time optimization. Mechanical ball-milling seems to be a suitable and rather simple technique for preparing nanocomposites even outside laboratory conditions and it is presented here as an interesting technique for nanoscience industrial applications. A fact that is worth noting since the great majority of research breakthroughs fail due to lack of industrial accomplishment. The powder mixture was further processed through compression moulding in a hot plate press. The impact of milling time on mechanical properties of the nanocomposites was evaluated. Nanocomposites with different volume fractions of MWCNTs were prepared using the optimized milling time, processed via compression moulding and their mechanical properties were evaluated. It was observed an enhancement of the Young’s modulus of about 80%, for higher volume fractions of MWCNTs (1.0%), as compared with the pure UHMWPE.

Abstract: Ultrahigh molecular weight polyethylene (UHMWPE) is a unique polymer with outstanding physical and mechanical properties that makes it particularly attractive to fabricate the bearing surface for artificial joints. Despite the requirement of visco-elastic properties of the UHWMPE and its composites, the characterization of them has received relatively little attention. The objective of this work is concerned with the studies on visco-elastic behaviour of UHMWPE and nanocomposites, which were prepared at optimized ball milling time with different cooling techniques. It is observed that stiffness of the materials increases appreciably at 0.2wt.% CNTs with an increase of frequency till 30Hz which confirms the reinforcing effect of CNTs in composites. The loss modulus of the sample is observed to be converged at higher temperature irrespective of frequency. The damping effect of the sample could be kept within the limit of polymer at any frequency range when the temperature is low and it is also possible at any temperatures at higher frequencies except LN2 cooled sample. The relaxation fraction increases with an increase of temperature and decreases with an increase of frequency. It is concluded that air cooled sample could be used wherever modulus is the main criteria irrespective of temperature and frequency, LN2 cooled sample can be used where more damping is required and water cooled samples may be used where more strength and toughness are required.

Abstract: The research work presented here intends to contribute to the overall research effort towards nanofluids engineering and characterization. To accomplish the latter, multiwalled carbon nanotubes (MWCNTs) are added to an ethylene glycol (EG) based fluid. Different aspects concerning the nanofluids preparation and its thermal characterization will be addressed. The study considers and exploits the relative influence of CNTs concentration on EG based fluids, on the suspension effective thermal conductivity and viscosity. In order to guarantee a high-quality dispersion it was performed a chemical treatment on the MWCNTs followed by ultrasonication mixing. Furthermore, the ultrasonication mixing-time is optimized through the UV-vis spectrophotometer to ensure proper colloidal stability. The thermal conductivity is measured via transient hot-wire within a specified temperature range. Viscosity is assessed through a controlled stress rheometer. The results obtained clearly indicate an enhancement in thermal conductivity consistent with carbon nanotube loading. The same trend is observed for the viscosity, which decreases with temperature rise and its effect is nullified at higher shear rates.

Abstract: Carbon nanotubes (CNTs) – perhaps the most enticing class of nano-materials, can be added in small volume fractions to enhance the thermal properties of fluids when process intensification or even device miniaturization is required. This work reports on the results obtained when measuring viscosity, and thermal conductivity of homogenous CNTs – water based nanofluids. The influence of CNTs volume concentration on the nanofluid thermo-physical properties is studied and measurements are undertaken at different temperatures, ranging from 283.15 K to 333.15 K. The nanofluids have been prepared by adding different volume concentrations of treated CNTs to water. The latter has been then sonicated for one hour and the colloidal stability monitored via UV – vis spectrophotometer. The absorbance of the nanofluid was observed at 263 nm, and the average concentration of CNTs was maintained at 9.35 mg/l, even after 200 hours, over 97% when compared with the initial concentration. The viscosity was measured using a controlled stress rheometer, and the measurements were performed in the shear rate ranging from 0 to 600 sec-1. At the same shear rate and temperature, the viscosity was observed to rise with increasing CNTs volume concentration. In what concerns thermal conductivity, it was assessed with a KD2 pro thermal property tester from Decagon Devices and the results clearly show that thermal conductivity rises with CNTs volume fraction, reaching its maximum at 2.5%vol where it represents more than 100% enhancement when the comparison is established with the corresponding value for the base fluid, at the same temperature conditions (i.e. 283.15 – 303.15 K). Furthermore, at higher temperatures (i.e. 313.15 – 333.15 K), the latter, for up to 1%vol concentration represents a 70% enhancement in thermal conductivity.