γ‐Irradiation effects on the thermal and structural characteristics of modified,grafted polypropylene

The effects of both the degree of grafting and γ irradiation on the thermal stability and structural characteristic of polypropylene‐graft‐polyvinylpyrrolidone and polypropylene‐graft‐polyvinylpyrrolidone modified with α‐cyano‐δ‐(2‐thienyl) crotononitrile were investigated. The employed techniques were thermogravimetric analysis, differential thermogravimetry, and X‐ray diffraction. The thermal stability of various polymeric substrates was investigated through the determination of the degradation temperature and activation energy of degradation. The effects of different parameters on the structural characteristics of different films were investigated through the determination of possible changes in the degree of ordering of the polymeric substrates. The results revealed that the thermal stability of the trunk polymer, grafted polymer, and polymer modified by α‐cyano‐δ‐(2‐thienyl) crotononitrile increased progressively with an increasing degree of grafting. The increase was, however, more pronounced for the sample undergoing the lowest degree of grafting. The activation energy of the thermal degradation process remained almost unchanged, and this indicated that the degradation processes of the different films followed almost the same mechanism. The γ irradiation at a dose of 60 kGy of the sulfur‐treated polymeric films [i.e., the polymeric films treated with α‐cyano‐δ‐(2‐thienyl) crotononitrile] reduced their thermal stability. This conclusion was reached by the consideration of the changes observed in the pre‐exponential factor of the Arrhenius equation due to different chemical and γ‐irradiation treatments. The degree of ordering, evidenced by X‐ray diffraction measurements of the trunk polymer, grafted polymer, and modified polymer, suffered a significant drop. This drop was much more pronounced for the sulfur‐containing polymeric materials. The observed drop in the degree of ordering of the polymeric substrates was taken as a measure of the structure collapse due to a certain treatment (degree of grafting and sulfur inclusion). The γ irradiation of the sulfur‐containing polymeric materials greatly increased their degree of ordering, which reached a value greater than that measured for the trunk polymer. Therefore, it was concluded that the thermal stability increased as the degree of ordering decreased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 506–515, 2006     

Encapsulation of titanium dioxide in styrene/n‐butyl acrylate copolymer by miniemulsion polymerization

Miniemulsion copolymerization of styrene/n‐butyl acrylate was investigated as a means of encapsulating hydrophilic titanium dioxide (TiO₂) in a film‐forming polymer. Dispersion studies of the TiO₂ were first carried out to determine the choice of stabilizer, its concentration, and the dispersion process conditions for obtaining stable TiO₂ particles with minimum particle size. Through screening studies of various functional stabilizers and shelf‐life stability studies at both room and polymerization temperatures, Solsperse 32,000 was selected to give relatively small and stable TiO₂ particles at 1 wt % stabilizer and with 20–25 min sonification. The subsequent encapsulation of the dispersed TiO₂ particles in styrene/n‐butyl acrylate copolymer (St/BA) via miniemulsion polymerization was carried out and compared with a control study using styrene monomer alone. The lattices resulting from the miniemulsion encapsulation polymerizations were characterized in terms of the encapsulation efficiencies (via density gradient column separations; DGC) and particle size (via dynamic light scattering). Encapsulation efficiencies revealed that complete encapsulation of all of the TiO₂ by all of the polymer was not achieved. The maximum encapsulation efficiencies were 79.1% TiO₂ inside 61.7% polystyrene and 63.6% TiO₂ inside 38.5% St/BA copolymer. As the density of the particles collected from the DGC increased from one layer to another, both the average particle size and the number of the TiO₂ particles contained in each latex particle increased. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3479–3486, 2006     

Biodegradation of low‐density polyethylene/thermoplastic starch foams before and after electron beam irradiation

Foamy low‐density polyethylene/plasticized starch (LDPE/PLST) blends at different compositions were produced in the presence of azodicarbonamide (ACA) compound as foaming agent. The LDPE/PLST blends before and after electron beam irradiation were investigated in terms of mechanical properties, bulk density, and structure morphology. Moreover, the biodegradability of these materials was evaluated by the soil burial test for 2 months, in which the buried sheets were also examined by scanning electron microscopy (SEM). The results showed that the increase of PLST content from 24 to 30% was accompanied by a decrease in the yield and break stresses of 10 and 20% for the unirradiated blends without the foaming agent, respectively. Further decrease in these mechanical parameters was observed after the foaming process. The bulk density, void fraction, cell size measurements as well as the examination by SEM illustrate clearly the cell growth of the foam structure. The soil burial test and SEM micrographs indicate the growth of microorganisms overall the blend sheets and that the blend was completely damaged after two months of burying. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Investigation of conductivity characteristics of nitrile butadiene rubber vulcanizates filled with semiconducting carbide ceramic

SiC‐ and B₄C‐filled NBR rubber composites were prepared with various volume fractions of filler by a conventional roll‐mill method. The morphological structures of the NBR–SiC and NBR–B₄C composites were analyzed by scanning electron microscopy. The dependence of room‐temperature volume resistivity (ρ_v) on the concentration of filler in the two systems was studied. In addition, variation in the number of current carriers (n), mobility carriers (μ), dielectric constant (ε), and dielectric loss factor (tan δ) on filler concentration in the two systems were investigated in detail. The applicability of composites as negative temperature coefficient (NTCR) linear thermistors was studied by the dependence of volume resistivity on temperature. The resistivity showed negative temperature dependence and changed linearly with temperature parallel. The conduction mechanism of the conductivity of the two composites was analyzed in terms of the computed activation energy and hopping energy. Change in volume resistivity as a function of frequency for the two systems was also investigated. Finally, the dependence of volume resistivity on applied pressure and possible real applications of these composites as transducers in pressure sensors were also studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2158–2165, 2007     

Electrical conductivity of concrete containing silica fume

The influence of silica fume on concrete properties represents an important technical research. In general, silica fume tends to improve both mechanical characteristics and durability of concrete. Thus the electrical properties of concrete containing silica fume can be studied to clarify its physical performance during hydration. The electrical conductivity of neat cement, mortar and concrete pastes was measured during setting and hardening. The ordinary Portland cement was partially replaced by different amounts of silica fume by weight. The changes in the electrical conductivity were reported during setting and hardening after gauging with water. The results of this study showed that the electrical conductivity can be used as an indication for the setting characteristics as well as the structural changes of the hardened pastes made with and without silica fume.     

Yield response of lentil to directly applied and residual phosphorus in a Mediterranean environment

The response of lentil grown under rainfed conditions to directly applied and residual phosphorus (P) was described by a modified Mitscherlich equation, accounting for the effects of rainfall on (1) potential yield, and (2) the availability of soil-P to the crop. The response of lentil yield to directly applied and residual P was studied in two-course cereal–lentil rotational trials under rainfed conditions in a Mediterranean-type environment. Cereal crops were grown at different P application rates during 4 growing seasons at 3 sites, representing different rainfall zones in northwest Syria. Lentil (Lens culinaris Med.) was grown during 4 seasons at the same sites, each lentil crop following a cereal crop. In 3 out of 4 lentil-growing seasons, additional P was applied to lentil in subplots to compare the residual and direct effects of P application. The initial contents of extractable soil-P (P-Olsen) were low at all sites, in the range of 2–5 ppm P. Under the conditions of the experiments, lentil appeared to benefit slightly more from P applied to the preceding wheat crop (residual P) than from directly applied P. It is shown that the modified Mitscherlich equation could be used as a basis for P fertilizer recommendations for rainfed farming. As for lentil, it was concluded that a single application of P to the wheat crop in a wheat/lentil rotation could reduce the cost of lentil production, without reducing lentil yield.     

Synthesis and Polymerization of Cationic bis(cyclopentadienyliron)arene Complexes Containing Arylazo Dyes

The synthesis of the title complexes was achieved via the reaction of -p-dichlorobenzene- -cyclopentadienyliron cations with 4,4′-bis(4-hydroxyphenyl)valeric acid to produce the diiron complexes which were then reacted with a number of arylazo dyes to give cationic bis(cyclopentadienyliron)arene complexes containing the arylazo dyes. These iron-containing monomers were subsequently polymerized via nucleophilic aromatic substitution using 1,8-octanedithiol, 4,4′-thiobisbenzenethiol, or bisphenol A to produce the desired coloured cationic organoiron polymers. The weight – average molecular weights were estimated to range from 11,800 to 31,600. UV–vis studies conducted in dimethylformamide (DMF) showed that the metallated polymers exhibited of 412–491 nm. Addition of HCl to the polymer solution caused a bathochromic shift into the range of 515–530 nm. Thermogravimetric analysis (TGA) revealed that the iron moieties were cleaved between 205 and 248 °C while the polyether/thioether backbone degraded between 380 and 613 °C. Differential scanning calorimetry (DSC) showed that the polymers exhibited glass transition temperatures (Tg) ranging from 106 to 184°C.This paper is dedicated to Professor Richard J. Puddephatt in recognition of his outstanding contribution to the field of metal-containing polymers.     

Organoiron Polyelectrolytes: Synthesis and Characterization of Cationic Cyclopentadienyliron Complexes of Polyarylether-Imines

The synthesis of an aromatic ether complex of cyclopentadienyliron containing two terminal aldehyde groups was achieved via metal-mediated nucleophilic aromatic substitution reactions. This dialdehyde monomer was subsequently reacted with a variety of aliphatic and aromatic diamines to produce the corresponding soluble cationic organoiron polyether-imines. These cationic organometallic polymers were characterized using IR, ¹H, and ¹³C NMR, viscosity and thermogravimetric analysis. Viscosity measurements showed that these polymers exhibited polyelectrolyte effects in DMSO solutions. Thermogravimetric analysis showed that decoordination of the iron moieties occurred at about 300°C for polymers with aliphatic spacers in their backbones, while the cyclopentadienyliron moieties were cleaved from the polymers with aromatic spacers in their backbones at about 200°C. Photolytic demetallation of the organoiron polymers resulted in the removal of the pendent cyclopentadienyliron moieties and allowed for the isolation of their organic analogs. While the organoiron polymers were soluble in polar organic solvents, the corresponding organic polymers exhibited very limited solubilities or were insoluble. The organic polymers had glass transition temperatures between 101 and 120°C     

Time optimization of ultraviolet–ozone pretreatment for improving wool fabrics properties

Wool fabrics were exposed to ultraviolet (UV)–ozone treatment for different periods. After exposure, the fabrics were analyzed by Fourior transform infrared spectroscopy (FTIR). Also, the crystallinity and amorphousity regions were followed by an X‐ray diffraction technique. The results were correlated by mechanical properties measurements. After a certain period of exposure, the dyeability and printability were improved because these abilities are strongly related to the percentage ratio of crystallinity regions to amorphousity regions in wool fabrics. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1469–1476, 2002     

Cryptanalysis of an embedded systems’ image encryption

Multimedia Tools and Applications - Recently, a new image encryption-scheme for embedded systems based on continuous third-order hyperbolic sine chaotic system, has been proposed. The...