Physical properties of natural and modified cotton cellulose grafted with acrylate monomers

Natural, cyanoethylated, and formaldehyde-crosslinked cotton cellulose has been grafted with methyl, ethyl, and n-butyl acrylate and methyl methacrylate monomers. Various physical properties such as density, moisture regain, birefringence, and mechanical properties were studied. The results indicate that the density and moisture regain of the grafted fibers are less than those of natural cotton. The birefringence of grafted fibers is also less than that of natural cotton. The variation in birefringence with percent graft-on depends on the monomer. Parameters such as orientation factor, helix angle, and refractive power of fibers were calculated from the birefringence data and the results discussed. It was observed that due to grafting of both natural and crosslinked cotton, there is a decrease in tensile strength, increase in elongation at break, and decrease in the initial modulus. Attempts are made to understand these changes in the properties of cotton in terms of the changes occurring in the fine structure of the fiber.     

Effect of boric acid on thermal dehydrogenation of ammonia borane: Mechanistic studies

Ammonia borane (AB, NH₃BH₃) is a promising hydrogen storage material for use in proton exchange membrane (PEM) fuel cell applications. In this study, the effect of boric acid on AB dehydrogenation was investigated. Our study shows that boric acid is a promising additive to decrease onset temperature as well as to enhance hydrogen release kinetics for AB thermolysis. With heating, boric acid forms tetrahydroxyborate ion along with some water released from boric acid itself. It is believed that this ion serves as Lewis acid which catalyzes AB dehydrogenation. Using boric acid, we obtained high H₂ yield (11.5 wt% overall H₂ yield, 2.23 H₂ equivalent) at 85 °C, PEM fuel cell operating temperatures, along with rapid kinetics. In addition, only trace amount of NH₃ (20–30 ppm) was detected in the gaseous product. The spent AB solid product was found to be polyborazylene-like species. The results suggest that the addition of boric acid to AB is promising for hydrogen storage, and could be used in PEM fuel cell based vehicles.     

Forced convection subcooled boiling of binary mixtures

A mode based on an additive mechanism of heat transfer is proposed for forced convection subcooled boiling of binary mixtures. The contributing modes of heat transfer are: (i) the heat transferred as latent heat by the rising bubbles, (ii) the heat transferred as the heat contained in the superheated thermal layer that is removed from the surface in the wake of the rising bubbles and (iii) the single phase forced convection heat transfer from the heating surface not influenced by the bubbles. Experimental data from the literature on binary systems show good agreement with the model, validating the postulated mechanism.     

High-temperature X-ray structural,thermal and dielectric characteristics of ferroelectric Bi2VO5.5

The X-ray powder diffraction, dielectric and thermal studies of bismuth vanadate (Bi₂VO_5.5) ceramic have been carried out as a function of temperature (300–900 K). The hightemperature X-ray studies, supported by differential scanning calorimetry, clearly demonstrate that Bi₂VO_5.5 undergoes two major phase transitions at 730 and 835 K. It was found that the one at 730 K is associated with both the ferroelectric and the crystallographic transition, while at 835 K, Bi₂VO_5.5 undergoes only the crystallographic transition. Anomalies in both the dielectric constant and specific heat curves have been observed at 730 and 835 K. The total heat, Q, and entropy, S, associated with the transition at 730 K were found to be higher than those at 835 K.     

Dielectric behaviour of dysprosium oxide films

The dielectric properties of vacuum-deposited dysprosium oxide films have been studied in the audio-frequency range (10²–10⁴ Hz) at various temperatures (78–373 K). The dielectric constant (6.7) was independent of film thickness for thicker films (d > 1000 Å). The capacitance was dependent both on temperature and frequency, but became constant for all frequencies at low temperature. Tan δ showed a frequency minimum and its variation with frequency and temperature was in agreement with the model proposed earlier by Goswami and Goswami. The breakdown field (≌10⁶ V cm^-1) followed the Forlani-Minnaja relation. The activation energy and the refractive index of these films were also measured.     

Dielectric properties of Poly(vinylidene fluoride)/CaCu3Ti4O12 composites

The possibility of obtaining relatively high dielectric constant polymer–ceramic composite by incorporating the giant dielectric constant material, CaCu₃Ti₄O₁₂ (CCTO) in a Poly(vinylidene fluoride) (PVDF) polymer matrix by melt mixing and hot pressing process was demonstrated. The structure, morphology and dielectric properties of the composites were characterized using X-ray diffraction, Thermal analysis, scanning electron microscope, and impedance analyzer. The effective dielectric constant (ε_eff) of the composite increased with increase in the volume fraction of CCTO at all the frequencies (100 Hz–1 MHz) under study. The dielectric loss did not show any variation up to 40% loading of CCTO, but showed an increasing trend beyond 40%. The room temperature dielectric constant as high as 95 at 100 Hz has been realized for the composite with 55 vol.% of CCTO, which has increased to about 190 at 150 °C. Theoretical models like Maxwell’s, Clausius–Mossotti, Effective medium theory, logarithmic law and Yamada were employed to rationalize the dielectric behaviour of the composite and discussed.     

On the development of an apatitic calcium phosphate bone cement

Development of an apatitic calcium phosphate bone cement is reported. 100 μ Particles of tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD) were mixed in equimolar ratio to form the cement powder. The wetting medium used was distilled water with Na₂HPO₄ as accelerator to manipulate the setting time. The cement powder, on wetting with the medium, formed a workable putty. The setting times of the putty were measured using a Vicat type apparatus and the compressive strength was determined with a Universal Testing Machine. The nature of the precipitated cement was analyzed through X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR) and energy dispersive electron microprobe (EDAX). The results showed the phase to be apatitic with a calcium-to-phosphorous ratio close to that of hydroxyapatite. The microstructure analysis using scanning electron microscopy (SEM) showed hydroxyapatite nano-crystallite growth over particulate matrix surface. The structure has an apparent porosity of ∼ 52%. There were no appreciable dimensional or thermal changes during setting. The cement passed the in vitro toxicological screening (cytotoxicity and haemolysis) tests. Optimization of the cement was done by manipulating the accelerator concentration so that the setting time, hardening time and the compressive strength had clinically relevant values.     

Parametric sensitivity and runaway in chemical reactors

In certain regions of operating conditions, chemical reactors may exhibit parametric sensitivity; i.e., small changes in one or more of the reactor input parameters lead to much larger changes in the output variables. Since such behaviour leads to deleterious performance, it is of practical interest to identify regions of parametric sensitivity in the reactor parameter space. Until recently, this could be done only to describe thermal runaway, and only for those systems where a temperature profile could be defined. Both of these limitations can be removed by consideringthe generalized criterion for parametric sensitivity, whereby sensitivity ofany output of the model toany input can be treated. Applications of the generalized criterion are discussed, with specific examples including pseudohomogeneous and heterogeneous model tubular reactors, a nonisothermal CSTR, and a polymerization reactor. Dedicated to Dr L K Doraiswamy — Gentleman, Scholar, Friend — on his sixtieth birthday.     

Greener assembling of MoO3 nanoparticles supported on gum arabic: cytotoxic effects and catalytic efficacy towards reduction of p-nitrophenol

Clean Technologies and Environmental Policy - An economical and easy one-step method for the biosynthesis of highly stable molybdenum trioxide (MoO3) nanoparticles was developed using gum arabic as...     

Hydroxyapatite filled chitosan-polyacrylic acid polyelectrolyte complexes

Chitosan (CHI) has been complexed with polyacrylic acid (PAA) in the presence of hydroxyapatite (HAP) to prepare composites intended for bone substitute applications. Thermogravimetric analysis of the composite showed that the presence of HAP had little effect on the degradation profile of the polyelectrolyte complex (PEC), except for the onset of degradation. Optimum compressive strength was observed for 70-weight percentage HAP filled PEC. The morphological analysis revealed that the HAP particles were uniformly distributed in the PEC matrix. The results indicate that HAP filled PEC of CHI and PAA could be prepared following the proposed simple route.