Materials Science Forum Vol. 757

Abstract: Oleochemicals offer viable choices to replace petrochemicals in a wide range of applications such as fuels, lubricants and surfactants. Many of the conversions require the use of suitable solid acids as the catalysts. The chemical and physical properties of the feedstock in oleochemical processes often result in difficulties and challenges that limit the success. Large amount of free fatty acids and high water content create barriers towards the successful use of broad range of oleochemicals as raw materials. To overcome this problem, efforts have been dedicated to the development of new technologies involving new types of catalyst. Solid acid catalysts based on heteropolyacids (HPAs) for various oleochemical conversions especially esterification reaction of fatty acids and transesterification of vegetable oils have been successfully developed. This type of catalyst already secured a tangible success in solving some problems associated with the earlier types of catalyst leading to higher productivity in the process while satisfying the needs of sustainable and environmental friendly industrial processes. Incorporation of HPAs active component into mesoporous supports can produce heterogeneous catalysts with high acid sites dispersion, stability to high temperature, recyclable and they usually demonstrate low leaching of active components in the reaction medium. This article reviews common oleochemical processes where various HPA catalysts already found successful application with some insight into the specific characteristics of the catalysts. Their advantages and drawbacks as well as specific process behaviors in few important oleochemical conversions of industrial importance will be discussed.

Abstract: Modern sun protective means (SPM) represent complex compositions of substances which provide effective protection of a person’s skin against sunlight. Organic and inorganic sun protective filters (sunscreens) or combinations of them are used as the active components of SPM. Organic sunscreens absorb ultraviolet radiation due to the presence of chromophores in their structure; while action of inorganic sunscreens is based on physical mechanism of protection, such as dispersion, absorption and reflection of ultraviolet (UV) radiation by inorganic particles. Silicon nanocrystals have attracted increasing attention as a new promising sun protective agent. They possess extremely high extinction coefficient in UV region of the spectrum and at the same time are transparent for visible light. The combination of physical properties related to the quantum size effect of silicon nanoparticles and their biological compatibility allows the development of highly effective sun protective skincare compositions. Efficiency and quality of SPM depend on many factors. The variety of known sunscreens allows finding optimum structures for creation of the most effective sun protective means. The review of the literature presented is devoted to consideration of existing SPM, their characteristics and effective properties. Then a comparative analysis of a totally new sun protective material based on silicon nanocrystals with known, widely used UV protectors is performed.

Abstract: Sulfated Zirconia (SZ) has opened up a very interesting area for application predominantly as catalyst for various acid catalyzed organic syntheses and transformation reactions. Catalytic properties of SZ vary with methods of preparation. Lot of efforts is made to modify SZ to increase reactivity and stability of the catalyst. This review focuses on the individual synthesis routes to prepare nano-sized and –crystalline SZ, short discussion on its characterization and exhaustive survey on its utility in organic chemistry for the development of new synthetic methodologies, which provide simple direction having enormous practical significance. As can be realized, the nano-sized and –crystalline SZ as solid acid catalyst exhibits exceptionally better catalytic activity and selectivity for the synthesis of trisubstituted and tetrasubstituted imidazoles, acetyl salicylic acid, dypnone, esterification of acetic acid, caprylic acid and so on.

Abstract: Solution combustion synthesis technique is one of the novel techniques used to prepare nanoparticles, multi-component ceramic oxides and nanocomposites with properties better than conventionally prepared one and these materials have been used for various applications such as sensors, catalysts, and materials for solid oxide fuel cell (SOFCs). In the present work, the method has been used to prepare nanoparticles of 10 mol% Gd doped ceria (GDC) and Cu and its oxides. The oxidant to fuel (O/F) ratio is found to affect the powder properties and even compositional homogeneity. In glycine-nitrate combustion synthesis of GDC, as revealed by XRD studies, phase pure nanoparticles with crystallite size in the range 9-12nm were obtained for all the O/F ratios. TEM measurements of calcined powder showed hexagonal shaped particles of roughly 20nm size. The exothermicity was increased with the oxidant to fuel ratio resulting in high surface area and soft agglomerates. A slightly lean O/F ratio gives surface area of 73 m²/g and soft agglomerates (D₅₀ = 5.34 mm), which eventually results into high sintering density at low temperature. Raman Spectra of GDC showed a sharp and intense peak at 467 cm⁻¹ which corresponds to CeO₂ due to F_2g symmetry of the cubic phase. In combustion synthesis of copper nitrate and citirc acid, the compositional homogenity and phase purity was affected by the oxidant to fuel ratio. The combustion at stoichiometric O/F ratio gives Cu nano particles, lean O/F ratio gives nanoparticles of Cu, CuO and Cu₂O and rich ratio gives pure CuO nanoparticles. These nanoparticles have been studied with different characterization techniques like XRD, TG-DTA, SEM, TEM, FT-IR and Raman.

Abstract: This work presents the synthesis of acrylic copolymer and trimer of isophorone diisocyanate (IPDI) for preparation of polyurethane (PU) coatings. Further we have studied the effect of silane modified nano montmorillonite (MMT) on the properties of PU coatings. Nano MMT was modified by vinyltriethoxysilane (TEVS) coupling agent and incorporated in PU coatings made from acrylic copolymers and trimer of IPDI. Acrylic copolymer was synthesized in the laboratory using butyl acrylate (BA), methyl methacrylate (MMA), styrene and hydroxyl ethyl acrylate (HEA) monomers. Coating properties of prepared PU coatings studied are gloss, impact resistance, flexibility, cross hatch adhesion and physicochemical properties include chemical resistance. The experimental results revealed that polyurethane coatings based on MMT based acrylic polyol and IPDI trimer showed good gloss and excellent adhesion. Thermal stability of these PU samples was found upto 229 °C. Physicochemical properties reflected that these PU have excellent chemical and solvent resistance.

Abstract: Enhanced thermal conductivity of nanofluids compared to that of the base fluid has received attention of many researchers in the last one decade. Experimental data on thermal conductivity of nanofluids using varied nanoparticles in the size range 10-100 nm have been reported. However, there is lot of variance in the data and needs critical analysis. Many models have been proposed by various research groups for predicting the thermal conductivity of nanofluids. Due to complexity of various parameters involved (size, % volume fraction, specific surface area and the type of nano particles, pH of nano fluid, thermal conductivity and viscosity of base fluid) no single model can be used for predicting the thermal conductivity of nanofluids. Inconsistent and conflicting results are reported on the enhanced thermal conductivity of nanofluids. Further, insufficient understanding and inconclusive mechanism behind enhanced thermal conductivity requires further attempt to work in this field. This article critically reviews the available literature on thermal conductivity of nanofluids.

Abstract: It has long been established that a suspension of nanosized solid particles in liquids provide useful advantages in industrial heat transfer fluid systems. Numerous investigations on nanofluids show a significant enhancement in thermal conductivity over the base fluid in which these nanoparticles are dispersed. However, the stability of the suspension is critical in the development and application of these new kind of heat transfer fluids. Rather, high discrepancy in the published data for the same nanoparticles on the physical and thermal characteristics of nanofluids is primarily due to different methods adopted by different researchers to obtain stable nanofluids. Sedimentation and agglomeration of nanoparticles in nanofluids and their dispersion stability has not been well addressed in the literature. Hence, there is a need to establish a standard method of preparation of these nanofluids so as to obtain a unified data which can eventually be utilized for the application of nanofluids. This chapter focuses on the stability of nanofluids prepared via two step process. Different parameters that affect the stability of nanofluids have been discussed. Different techniques that have been used for the evaluation of the stability characteristics of nanofluids have been elucidated.

Abstract: Polypropylene filament incorporating carbon nanofibre has been spun using conventional fibre processing route. Nanocomposite filament with very high dynamic modulus of 29 GPa and tenacity of 770 MPa could be obtained at 1% loading of nanofibres. The Nanocomposite filament exhibits higher thermal stability. Influence of carbon nanofibres on the morphology, mechanical and thermal properties of the nanocomposite filament have been studied.

Abstract: This article provides the brief overview on effect of dopant on the performance of zinc oxide (ZnO) as photocatalysts for the degradation of dye wastewaters. ZnO itself is a semi conductor having wide band gap (3.37eV), thus requiring high energy to work as a photocatalyst. To decrease the band gap or to alter its requirement of high energy from light sources like UV to visible (solar), surface modification or doping of ZnO is necessary. This paper discusses how dopant modifies the characteristics of ZnO which helps in degradation of dyes in colored wastewaters.