This paper describes the mechanical and thermal characterisation of cross‐linked glycidyl azide polymer (GAP) and GAP–hydroxyl terminated polybutadiene (HTPB) networks. Cross‐linked GAP and GAP–HTPB networks were prepared by reacting GAP diol and GAP–HTPB diol mixture with different diisocyanates. The physical and mechanical characteristics were found to be influenced by the type of isocyanate curing agents, [NCO]/[OH] equivalent ratios and concentration of GAP. For all the three types of curing agents, GAP–HTPB blends of 50 : 50 to 30 : 70 ratios show higher mechanical strength over the virgin networks of GAP or HTPB. Thermal decomposition of cross‐linked GAP–HTPB networks was evaluated by thermogravimetric analysis (TGA). The kinetic parameters for the decomposition of GAP–HTPB blends were found to be dependant on the concentration of GAP and HTPB in the blend. The cross‐linked GAP–HTPB blends were subjected to dynamic mechanical analysis (DMA). The glass transition characteristics of the blends were evaluated by DMA and it was found that blends prepared with GAP content up to 30% showed single transition in the loss tangent trace indicating no phase separation in the cured network.
Four different samples of ferrocene-grafted hydroxyl-terminated polybutadiene (Fc-HTPB), containing 0.20, 0.52, 0.90, and 1.50 wt % iron, were synthesized by the Friedel-Crafts alkylation of ferrocene with hydroxyl-terminated polybutadiene (HTPB) in the presence of AlCl 3 as a (Lewis acid) catalyst. The effects of the reaction conditions on the extent of ferrocene substitution were investigated. The Fc-HTPBs were characterized by IR, ultraviolet-visible, 1 H-NMR, and 13 C-NMR spectra. The iron content and number of hydroxyl groups were estimated, and the properties, including thermal degradation, viscosity, and propellant burning rates (BRs), were also studied. The thermogravimetric data indicated two major weight loss stages around 395 and 500 C. These two weight losses were due to the depolymerization and decomposition of the cyclized product, respectively, with increasing temperature. The Fc-HTPB was cured with toluene diisocyanate and isophorone diisocyanate separately with butanediol-trimethylolpropane crosslinker to study their mechanical properties. Better mechanical properties were obtained for the gumstock of Fc-HTPB polyurethanes with higher NCO/OH ratios. The BRs of the ammonium perchlorate (AP)-based propellant compositions having these Fc-HTPBs (without dilution) as a binder were much higher (8.66 mm/s) than those achieved with the HTPB/ AP propellant (5.4 mm/s).
Reactions between hydroxyl-terminated glycidyl azide polymer (GAP) and different isocyanate curatives such as toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and methylene diicyclohexyl isocyanate (MDCI) at various temperatures viz. 30, 40, 50, and 608C were followed by Fourier transform infra red spectroscopy. The reactions were found to follow second-order kinetics. With TDI and IPDI at 308C, a two-stage reaction was observed. For GAP-TDI system, the second stage was slower than the first while for GAP-IPDI system, the second stage was faster than the first indicating dominance of autocatalytic effect. The stage separation occurred due to the difference in reactivity of the isocyanate groups and was found to narrow down with increase in temperature. The viscosity build up due to the curing reaction was followed for GAP-TDI system for comparison. The stage separation was evident in the viscosity build up also. Rheokinetic analysis done based on data generated showed a linear correlation between viscosity build up and fractional conversion. The kinetic and activation parameters evaluated from the data showed the relative difference in reactivity of the three diisocyanates with GAP. Both the approaches suggested that the reactivity of the isocyanates employed for the present study could be arranged as TDI > IPDI ) MDCI.
In this study, the authors investigated antimicrobial activity of TiO2 nanoparticles (NPs) synthesised by sol-gel method. As synthesised TiO2 NPs were characterised by X-ray diffraction, scanning electron microscopy and ultraviolet-visible absorption spectroscopy. The antimicrobial activity of calcined TiO2 nanoparticle samples was examined in day light on Gram positive bacteria (Staphylococcus aureus, Streptococcus pneumonia and Bacillus subtilis), Gram negative bacteria (Proteus vulgaris, Pseudomonas aeruginosa and Escherichia coli) and fungal test pathogen Candida albicans. The synthesised TiO2 NPs were found to be effective in visible light against Streptococcus pneumonia, Staphylococcus aureus, Proteus vulgaris, Pseudomonas aeruginosa and Candida albicans.
Glycidyl azide polymer (GAP) has been evaluated for use as binder for solid propellants. The effects of various parameters like cross-linking conditions, concentration of crosslinker, and the ratio of isocyanate to hydroxyl functional groups (NCO/OH ratio) on the mechanical properties were studied in detail. It was observed that the type of curing agent and the NCO/OH ratio have a strong influence on the gum-stock properties. Similar impact was seen for cross-linker concentration also. The swelling characteristics of the cross-linked binder prepared with different NCO/OH ratios were evaluated with toluene and tetrahydrofuran (THF). The polarity and the solubility parameter of the solvents were found to influence the swelling of GAP. The NCO/OH ratio and cross-linker concentration of the polymer were also found to affect the swelling characteristics. The sol fraction determined for the polymer was found to follow a similar pattern. The cross-link density and average molecular weight between crosslinks (Mc) were determined from the swelling studies and also from the stress-strain relationship. The Mc values were found to be influenced by the NCO/ OH ratio. Finally, the Mc values determined from the swelling data were correlated to the gum-stock properties, and the model parameters were estimated.
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