Showing papers by "Kishor Kumar Sadasivuni published in 2013"

Synergistic effect of multi walled carbon nanotubes and reduced graphene oxides in natural rubber for sensing application

Abstract: Utilizing the electrical properties of polymer nanocomposites is an important strategy to develop high performance solvent sensors. Here we report the synergistic effect of multi walled carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) in regulating the sensitivity of the naturally occurring elastomer, natural rubber (NR). Composites were fabricated by dispersing CNTs alone and together with exfoliated RGO sheets (thermally reduced at temperatures of 200 and 600 °C ) in NR by a solution blending method. RGO exfoliation and the uniform distribution of fillers in the composites were studied by atomic force microscopy, Fourier transformation infrared spectroscopy, X-ray diffraction, transmission electron microscopy and Raman spectroscopy. The solvent sensitivity of the composite samples was noted from the sudden variation in electrical conductivity which was due to the breakdown of the filler networks during swelling in different solvents. It was found that the synergy between CNTs and RGO exfoliated at 200 °C imparts maximum sensitivity to NR in recognizing the usually used aromatic laboratory solvents. Mechanical and dynamic mechanical studies reveal efficient filler reinforcement, depending strongly on the nature of filler–elastomer interactions and supports the sensing mechanism. Such interactions were quantitatively determined using the Maier and Goritz model from Payne effect experiments. It is concluded that the polarity induced by RGO addition reduces the interactions between CNTs and ultimately results in the solvent sensitivity.

Interrelated shape memory and Payne effect in polyurethane/graphene oxide nanocomposites

Abstract: We report the fabrication of graphene oxide (GO) based polyurethane (PU) nanocomposites by a simple method of mixing and their shape memory properties at different temperatures. Both the polymer and the filler were synthesized in the laboratory by simple and easy methods – PU by pre-polymer method and GO by improved graphene oxide synthesis method. High molecular level dispersion of GO platelets within the PU matrix and thus good mechanical properties were maintained by the improved PU/GO interfacial interaction. The structure of the polymer composites was investigated by scanning electron microscopy and X-ray diffraction studies revealed a highly dispersed morphology of graphene oxide sheets in PU. The improvement in shape memory obtained for the nanocomposites was then quantitatively analysed using the Payne effect. The crosslink density calculated using the Maier and Goritz model (Payne effect) was found to be dependent on the thermal transitions of the composites and it varied with the filler concentration. Accordingly a nice correlation was established between the temperature dependence of shape memory and the crosslink density. Composite behaviour was further analysed by the dynamic measurements such as rheology, stress relaxation and Mullins effect. To the best of our knowledge, the quantification of shape memory in terms of physical crosslinks and filler–polymer entanglements of the PU/GO nanocomposite system has not been addressed before and is introduced in this work.

Effect of molecular interactions on the performance of poly (isobutylene-co-isoprene)/graphene and clay nanocomposites

Abstract: Poly(isobutylene-co-isoprene) (IIR)/graphene and cloisite10A nanocomposites were prepared successfully and the resulting mechanical, rheological and barrier properties were carefully evaluated and compared. Chemical treatments like maleic anhydride grafting were used to improve the dispersion of the clay in the IIR matrix. Blends with different loading (20, 40, 60, and 80 %) of maleic anhydride grafted poly(isobutylene-co-isoprene) (MA-g-IIR) and IIR were made to maintain a balance between the beneficial polarity induced by MA grafting and the inevitable decrease in molecular weight (due to chain scission) induced by the free radical grafting process. The highest moduli, tensile strength and elongation at break were achieved in the case of a 60:40 ratio of MA-g-IIR (grafting degree 0.75)/IIR mixture with 5 phr of cloisite 10A. IIR/graphene nanocomposites exhibited higher reinforcement (Young’s moduli) and lower gas permeability compared to the optimized clay nanocomposites with same weight percentage. The filler–elastomer and filler–filler interactions deduced from rheology, stress relaxation and Payne effect experiments emphasize the reinforcing ability in IIR/graphene and MA-g-IIR/clay. XRD, SEM and TEM results further substantiated the results from the obtained micro structure of the nanocomposites. The improved performances of IIR/MA-g-IIR/clay and IIR/graphene were successfully correlated with interactions between the filler platelets and elastomer chains occurring in the nanocomposites.

Special Purpose Elastomers: Synthesis, Structure-Property Relationship, Compounding, Processing and Applications

Abstract: Elastomers are notable as very special class of polymers due to their multifunctional applications. The superior mechanical properties, high flexibility, resilience and good viscoelastic behaviour make this class applicable in a wide range of technology and industry. Depending on the various properties and general applications elastomers are classified in to a number of categories. This particular chapter deals with a very important class of special purpose elastomers. The synthesis, structure, different properties, mode of vulcanization, processing and applications of most of the synthetic elastomers are discussed. Apart from providing a basic understanding about the materials, this chapter can facilitate wide information about the technical details and industrial importance of this class of rubbers.