The antibacterial behavior of HA-Ag (silver-doped hydroxyapatite) nanopowder and their composite coatings were investigated against Escherichia coli (DH5a). HA-Ag nanopowder and PEEK (polyether-ether-ketone)-based HA-Ag composite powders were synthesized using in-house powder processing techniques. Bacteria culture assay of HA-Ag nanopowder and their composite powders displayed excellent bacteriostatic activity against E. coli. The antibacterial activity increased with increasing concentration of HA-Ag nanoparticle in these composite powders. These nanocomposite powders were subsequently used as feedstock to generate antibacterial coatings via cold spray technology. The ratios of HA-Ag to PEEK in their composite powders were 80:20, 60:40, 40:60, and 20:80 (wt.%). Microstructural characterization and phase analysis of feedstock powders and as-deposited coatings were carried out using FESEM/EDX and XRD. Antibacterial nanocomposite HA-Ag/PEEK coatings were successfully deposited using cold spraying parameters of 11-12 bars at preheated air temperature between 150 and 160°C. These as-sprayed coatings of HA-Ag/PEEK composite powders comprising varying HA-Ag and PEEK ratios retained their inherent antibacterial property as verified from bacterial assay. The results indicated that the antibacterial activity increased with increasing HA-Ag nanopowder concentration in the composite powder feedstock and cold-sprayed coating.

The purpose of this study was to examine how the presence of crystals can retard electron‐beam (e‐beam) radiation degradation, and their effects on the thermal and morphological properties of poly(lactide‐co‐glycolide) (PLGA) upon e‐beam irradiation. Isothermal annealing at 115 °C was carried out on PLGA films and the effect of different annealing times on the degree of crystallinity (DOC) of PLGA was recorded. The DOC increased with annealing time to a maximum value, and remained unchanged with further annealing. The annealed films were then e‐beam irradiated at doses of 5, 10, 20 and 30 Mrad. The degradation of the films was studied by measuring the changes in their molecular weight, DOC, thermal properties and FTIR spectra. It was observed that, regardless of the DOC of the films, the molecular weight of PLGA generally decreased with increasing radiation dose, indicating that chain scission is dominant. However, the extent of degradation is less for the films with a higher DOC. The thermal properties of PLGA also decreased with increasing radiation dose. Radiation increases the DOC for films with initial crystallinity below 5 % but decreases the DOC for films with initial crystallinity above 5 %. Crystals in PLGA films decreased the extent of radiation degradation. Copyright © 2005 Society of Chemical Industry

Thermites belong to a class of energetic material comprising of a metal as a fuel and a metal oxide as the oxidizer. The research on nano-thermites has significantly emerged in the last two decades and novel ways to harness their energy with improved reactivity, reduced sensitivity and high stability remains highly desirable to date. In this work, Al/NiO nano-thermite system was studied due to their relatively gasless reaction. Gasless thermite reactions could offer potential in applications requiring little flow disturbances and vibrations. A novel self-assembly technique to promote better intermixing of the fuel-oxidizer system through surface functionalization with complimentary functional groups as well as the addition of an energetic polymer binder to reduce the sensitivity were studied. The heat release characteristics and reaction mechanism of Al/NiO nano-thermites were studied. n-Al/n-NiO with different equivalence ratio (ER) were prepared and their heat of reactions measured using a bomb calorimeter. The heat of reaction increased from a fuel lean formulation to a slightly fuel rich formulation at ER 1.2, yielding an optimized heat of reaction of 3649 J/g. Their highly exothermic nature was studied using a Differential Scanning Calorimeter (DSC). The reaction products during the different stages of the decomposition were analyzed using a powder X-ray Diffraction (XRD) to understand the reaction mechanism of this alumino-thermic reaction. Surface functionalization of n-Al and n-NiO using organosilanes with complimentary end groups (epoxide/ amino) to bring about the fuel-oxidizer self-assembly were performed. The self-assembled n-Al/n-NiO showed a better intermixing of the binary composite powder from their Scanning Electron Microscopy/Energy Dispersive X-ray (SEM/EDX) photographs. The self-assembled system displayed a larger heat release before aluminum melting as well as an increased heat release rate from their DSC profiles. The preference for reaction prior to aluminum melting (or solid-state reaction) is an indication of intimate interaction between the fuel and oxidizer. The self-assembly process was shown to increase the energy release rate of organosilane-functionalized nano-thermites in their pressure studies. The overall energy release rate of the functionalized n-Al/n-NiO was, however, not better than unfunctionalized n-Al/n-NiO.

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