ZnO nanoparticles were synthesized from chitosan and zinc chloride by a precipitation method. The synthesized ZnO nanoparticles were characterized by Fourier transform infrared spectroscopy, X-ray diffraction peak profile analysis, Scanning electron microscopy, Transmission electron microscopy and Photoluminescence. The X-ray diffraction results revealed that the sample was crystalline with a hexagonal wurtzite phase. We have investigated the crystallite development in ZnO nanoparticles by X-ray peak profile analysis. The Williamson-Hall analysis and size-strain plot were used to study the individual contributions of crystallite sizes and lattice strain e on the peak broadening of ZnO nanoparticles. The parameters including strain, stress and energy density value were calculated for all the reflection peaks of X-ray diffraction corresponding to wurtzite hexagonal phase of ZnO lying in the range 20°-80°using the modified form of Williamson-Hall plots and size-strain plot. The results showed that the crystallite size estimated from Scherrer's formula, Williamson-Hall plots and size-strain plot, and the particle size estimated from Transmission electron microscopy analysis are very much inter-correlated. Both methods, the X-ray diffraction and Transmission electron microscopy, provide less deviation between crystallite size and particle size in the present case.

The viscoelastic behavior and reinforcement mechanism of nano ZnO reinforced natural rubber (NR) nanocomposites were investigated in this study. Dynamic mechanical analysis was performed to investigate the nature of the constrained polymer region in NR−nano ZnO nanocomposites, and the constrained polymer region is responsible for the reinforcement mechanism. The viscoelastic and tensile properties of NR nanocomposites were investigated with respect to the effect of nanofiller loading. All the nanocomposites showed a significant increase in storage modulus in the glassy and rubbery regions, the shift of the tan δ peak to the higher temperature region, and the lowering of the tan δ peak intensity compared to neat NR. The enhancement in the modulus is related to the weight % of the added nano ZnO as well as the volume of the constrained rubber chains in the proximity of ZnO nanoparticles. The study of the constrained volume of the polymer indicates that the structure of the nanocomposite possesses a moderately strong interfacial interaction between rubber chains and ZnO nanoparticles. The type of rubber−nanofiller interaction strongly influences the amount and modulus of the constrained region and contributes to the enhancement in the storage modulus of the resulting nanocomposites. The volume fraction of the constrained region of the NR nanocomposites was found to have good linear correlation with the weight % of nano ZnO. It was also understood that there should exist an optimum cross-linking density for a certain nanofiller reinforced rubber system, as well as partial physical adsorption of macromolecular rubber chains on the nanofiller surface. An optimum nanofiller loading is necessary for moderately strong rubber−nanofiller interaction and hence for the enhancement in the mechanical properties of the NR nanocomposites. A core−shell morphology model and constrained polymer model have been proposed to explain the constrained polymer chains in the NR−nano ZnO nanocomposite system on the basis of these results.

Zinc oxide (ZnO) nanoparticles of size 20–90 nm and surface area 9.56 m2/g were synthesized from ZnCl2 and Chitosan and characterized by X‐ray diffraction, high resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM). Natural rubber (NR) vulcanizates containing nano ZnO was prepared by mill mixing and characterized by SEM, energy dispersive X‐ray analysis (EDAX), and HRTEM. Cure characteristics, free volume studies, bound rubber, crosslink density, and dynamic mechanical properties were evaluated and compared with that of NR vulcanizate containing conventional micro ZnO. Considering the cure characteristics, it was found that NR vulcanizate with 0.5 phr (parts per 100 g rubber) of nano ZnO showed low values of optimum cure time (t90) and very high cure rate index compared with 5 phr of conventional micro ZnO. The study shows that micro ZnO can be successfully replaced with nano ZnO for accelerated sulfur vulcanization process in NR, and preparation of vulcanizate containing nano ZnO with better properties as that of micro ZnO. The optimum dosage of nano ZnO as a cure activator in NR vulcanization was found to be 0.5 phr compared with conventional grade micro ZnO. This will lead to substantial cost reduction in the manufacture of rubber products and alleviate environmental pollution due to excess ZnO in rubber compounds. POLYM. ENG. SCI., 2013 © 2013 Society of Plastics Engineers

In this article we study the optical properties of ZnO nanoparticles. This paper describes cost effective, high yield, and a facile synthetic method for the synthesis of ZnO nanoparticles from precursors viz. linear polysaccharide, chitosan, and ZnCl2 by a precipitation method. The synthesized ZnO nanoparticles were characterized by surface area, pore size, and UV-visible measurements. The optical band gap and the Urbach energy were also calculated and the optical band gap energy of the synthesized ZnO nanoparticles was found to be 3.26 eV and the nature of the optical transition has been identified as direct allowed.

ABSTRACT:We studied the stress-relaxation behavior of natural rubber (NR)/polystyrene (PS) blends in tension. The effects of strain level, composition, compatibilizer loading, and aging on the stress-relaxation behavior were investigated in detail. The dispersed/matrix phase morphology always showed a two-stage mechanism. On the other hand, the cocontinuos morphology showed a singlestage mechanism. The addition of a compatibilizer (NR-g-PS) into 50/50 blends changed the blend morphology to a matrix/dispersed phase structure. As a result, a two-step relaxation mechanism was found in the compatibilized blends. A three-stage mechanism was observed at very high loadings of the compatibilizer (above the critical micelle concentration), where the compatibilizer formed micelles in the continuous phase. The aged samples showed a two-stage relaxation mechanism. The rate of relaxation increased with strain levels. The aging produced interesting effects on the relaxation pattern. The rate of relaxation increased with temperature due to the degradation of the samples.