The effect of γ-irradiation on optical and electrical properties of polycarbonate

Poly-(bisphenol A carbonate) (PC) samples were exposed to different doses of γ-rays from a ⁶⁰Co source (from 0.05 to 0.3 M rad) at room temperature. Conductivity and dielectric constant as well as optical measurements were carried out. It was noticed that almost no work has been reported on the electrical conductivity of polycarbonate at high temperatures. γ-irradiation of polycarbonate is believed to create free radicals which increases the state of disorder and perturb the orientation of dipoles inside the polymer. At about 95°C, the electrical conductivities of irradiated samples were found to increase by nearly one order of magnitude with respect to the unirradiated one. The dielectric constant, ?, of fresh polycarbonate was nearly temperature independent over a range of ～ 70°C, then it increased with temperature, but for γ-irradiated samples (from 0.05 to 0.3 M rad) the dielectric constant increased continuously with temperature and also with respect to the fresh sample what confirms the effect of γ-irradiation in perturbing the orientation of the dipoles in the polymer. It was found that the UV absorption spectrum has a broad band at 0.280 μm and the absorption intensity was strongly dependent on the dose of γ-irradiation.     

Influence of γ-irradiation on proton spin–lattice relaxation of SBR used as antirads and its ESR investigation

Proton spin–lattice relaxation time t₁ was measured on SBR samples with carbon black or kaolin filler using modified linseed oil. The NMR pulse technique at 90MHz was used in the temperature range from 180 to 400 K. The temperature dependence of t₁ indicates that samples filled with carbon black have similar molecular dynamics to the standard unfilled SBR samples. The activation energy for the motion of the main chain for these samples amounts to 16.4kJ/mol. Samples containing linseed oil modified with para-toluidine showed an activation energy of about 14.6kJ/mol and were not affected by γ-irradiation. Values of the minimum relaxation time t^min₁ were increased by γ-irradiation in comparison with a standard SBR sample. ESR measurements carried out at room temperature by means of an X-band spectrometer indicated that unidentified radicals within the rubber were formed during its mastication with vulcanizing additives. The ESR spectra did not change during the vulcanization process. Samples filled with carbon black showed a broadening of the ESR line; this is consistent with the increase in the electrical conductivity.     

Electrical conductance of irradiated NBR/LDPE conductive blend during swelling in benzene

The effect of γ-irradiation on both the electrical conductance, Y, and diffusion coefficient, D, of acrylonitrile butadiene rubber mixed with different concentrations (1, 3, and 5 phr) of low-density polyethylene (LDPE) that was swollen in benzene, have been studied. The diffusion coefficient decreases with increasing the γ-irradiation dose for loaded samples with 1 and 3 phr of LDPE content, while samples with 5 phr of LDPE show a significant increase of diffusion coefficient with the increase of the radiation dose. The electrical conductance was found to be highly affected by the γ-irradiation dose. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1639–1645, 1997     

Effect of γ-Irradiation on Electrical Conductivity of Metal-Chloride-Treated Polyacrylamide

The electrical conductivity of polyacrylamide (PAAm) before and after treatment with low concentrations of ZnCl₂, NiCl₂, and CoCl₂ was determined at different temperatures. The effects of γ-irradiation on the electrical conductivity and activation energy of the original and the metal-chloride-treated specimens were investigated. The experimentally obtained data revealed that the conduction in PAAm is ionic in nature. The treatment of the polymer with 2% or 4% (w/w) of ZnCl₂, NiCl₂, or CoCl₂, as determined from its weight, either increases or decreases its conductivity according to the nature of the metal ions, concentration of metal chloride, ratio of KOH/metal chloride, and temperature and cycle of measurement. The exposure of PAAm to 2 to 10 Mrad of γ-radiation produces no significant changes in its conductivity. On the other hand, the exposure of the PAAm pretreated with a metal chloride produces considerable changes in its conductivity. Also, the γ-irradiation of PAAm increases its activation energy. The extent of the γ-induced changes in activation energy was influenced by the pretreatment of PAAm with metal chlorides.     

Effects of enzymes and gamma irradiation on the tensile strength and morphology of poly(p-dioxanone) fibers

The objective of this study was to examine how and to what extent a new degradable polymeric fiber, poly(p-dioxanone), used as a surgical suture material, degrades in the presence of enzymes and after γ-irradiation. The degradation of the fiber was studied mechanically using an Instron and morphologically by SEM. Both esterase and trypsin enzymes and their corresponding buffer controls were used. The fibers were γ-irradiated at the dosages ranging from 0 to 20 Mrad, immersed in the solution for up to 70 days, and then removed for tensile strength and morphological examinations. It was found that γ-irradiation alone lowered the tensile strength of PDS fibers and made them more susceptible to hydrolysis. Esterase and trypsin did not accelerate the hydrolytic degradtion of this fiber to any significant level. Both γ-irradiation and enzymes influenced the gross morphological characteristic of PDS fibers when they were subjected to hydrolysis. The most important morphological observations were the formation of surface cracks and chips on the fibers and the subsequent peeling of the chips. Enzyme-treated PDS fibers exhibited similar morphological findings but the size of the chips was smaller. The morphological observations of PDS fibers were consistent with the tensile strength data.     

Irradiation of solvent-treated cotton fibers

The infrared spectra and dielectric properties of cotton fibers pretreated for one day with toluene, methanol, and mixtures of the two have been investigated after drying the samples for 1 and 4 days. The effect of γ-radiation on the crystallinity and dielectric properties of the solvent-treated was examined. The samples were irradiated in air and also in the presence of the solvents. The data obtained indicate that the addition of toluene to methanol increases the rate of uptake of methanol by cotton. Moreover, it is found that irradiation of cotton fibers in the presence of toluene assists the oxidation of the cotton while irradiation in the presence of methanol reduces the oxidation effects of γ-radiation.     

Effect of γ-Radiation on the Dielectric Behaviour of Some Agricultural Wastes

Abstract

Dielectric properties of some agricultural wastes e.g., cotton stalks, Cs, rice straw, Rs and bagasse, B, are studied. The chemical constituents as well as the morphology of these material play a big roll on their dielectric properties. The effect of γ-irradiation on the dielectric properties of these lignocellulosic materials is also investigated. Grafting of these raw materials with acrylamide using γ-irradiation at dose of 20 M rad is also studied. Dielectric properties of these grafted materials and its complexes with Co⁺⁺ is clarified. The mechanism of the interaction of γ-radiation with the investigated samples is also studied.     

A systematic study on the effects of doping agents on polypyrrole coating of fabrics

Polypyrrole is widely used as coating to produce electrically conductive textiles. Counter‐ions (i.e. doping agents) were embedded in polypyrrole to improve electrical conductivity. Good electrical performances are required for several applications, such as microwave attenuation/electro‐magnetic interference shielding, heat generation, electro‐static discharge protection, sensing, and energy storage. In this work, a systematic study was carried out on the effects of doping agents in coating cotton fabrics with a thin polypyrrole layer. A total of 11 compounds were selected and compared as counter‐ions. The electrical performances of the coated fabrics were assessed with measures of electrical conductivity. Moreover, evenness and morphology of the resulting polypyrrole layer were discussed. As the final result, the best performances in terms of electrical conductivity (i.e. low surface resistivity) were measured using on dicyclohexyl sulfosuccinate, 2,6‐naphthalenedisulfonate or 1,5‐naphthalenedisulfonate as doping agents. The weight increases after polypyrrole deposition on the fabrics were greater than 15% and polypyrrole deposited on the fibers as a uniform film. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42831.     

Preparation and characterization of poly (ethylene glycol) grafted Ca-alginate fibers by γ-irradiation for biomedical applications

Radiation processing, being a physical process, is an environmentally friendly alternative to chemical modifications. It is economically viable, safe, and possesses several advantages over other conventional methods employed for modification and grafting. To improve the physico-mechanical properties of Ca-alginate fiber (CaAF), poly (ethylene glycol) (PEG) was grafted by applying γ-radiation of different intensities. The effect of γ-irradiation on the physico-mechanical, thermal, morphological, thermal and water aging, water, and simulated body fluid (SBF) uptake were evaluated. FT-IR results confirmed that PEG was successfully grafted onto Ca-alginate fibers by γ-irradiation. From the detailed experimental results, irradiation doses and PEG concentration were optimized for grafting processes. The results showed that 50% PEG and 2.5?kGy irradiation dose yielded the highest tensile strength. Differential scanning calorimetric (DSC) analysis showed that with increasing γ-intensity a decrease of dehydration temperature of the fibers had occurred. On the other hand, the glass transition temperature (T _g) increased with increasing irradiation dose. The tensile cracked surfaces of the grafted alginate fibers were analyzed by scanning electron microscope (SEM) in order to monitor their surface morphologies. The SEM images of the cracked surfaces demonstrated that spherical shape rods were present for irradiated fiber sample while no such rods were observed for non-irradiated fibers. The characteristic data obtained from SBF and water uptake, and water and thermal aging experiments indicated that CaAF grafted with 50% PEG by applying 2.5?kGy γ-irradiation can be potentially employed for biomedical purposes, such as surgical suture.     

Characteristics of thermoplastics containing electrically conducting asymmetric particles: Anisotropic electrical conductivity of injection molded parts and extrusion behavior

The characteristics of compounds of acrylonitrile-buta-diene-styrene and high impact polystyrene resins, filled with carbon fibers, steel fibers, carbon black, and aluminum flakes have been investigated with special emphasis on electrical conductivity and flow behavior in a capillary rheometer. Compression and injection molded compounds were found to be highly electrically anisotropic. The components of the electrical conductivity tensor, K₁₁, K₂₂ and K₃₃, were measured, Generally K₁₁, the flow direction conductivity, has the highest value and the thickness direction, and K₃₃ has the lowest. The injection molded parts were usually electrically heterogeneous with the conduetivities highest at the greatest distances from the gate. The results were interpreted in terms of particle orientation and distribution. Shear viscosities were measurable for all but the aluminum flake compounds which exhibited fluctuating pressure drops. The flow of these compounds through dies was investigated. Examination of material from the die entrance indicated streamline flow without entrance vortices. Sometimes high entrance concentration of particulates were observed especially for the aluminum flakes. Extrudates were found to contain oriented particles.     

Molecular weights and molecular weight distributions of irradiated cellulose fibers by gel permeation chromatography

Radiation degradation of cellulose fibers was investigated by gel permeation chromatography (GPC). Scoured cotton of Mexican variety (cellulose I), Polynosic rayon (cellulose II), and their microcrystalline celluloses obtained by hydrolysis of the original fibers were irradiated by Co-60 γ-rays under vacuum or humid conditions. The irradiated samples were then nitrated under nondegradative conditions. The molecular weights and molecular weight distributions were measured by GPC using tetrahydrofran as solvent. The relationship between molecular weight and elution count was obtained with cellulose trinitrate standards fractionated by preparative GPC. The degree of polymerization of the fibers decreased with increasing irradiation dose, but their microcystalline celluloses were only slightly degraded by irradiation, especially in microcrystalline cellulose from cellulose I. Degradation of the fibers irradiated under humid conditions was less than that irradiated under vacuum. It was found that the G-values for main-chain scission for the irradiated cellulose I, cellulose II, microcrystalline cellulose I, and microcrystalline cellulose II were 2.8, 2.9, less than 1, and 2.9, respectively, but the G-value for main-chain scission for the irradiated cellulose II was increased to 11.2 at irradiation doses above 3 Mrad. Consequently, it is inferred that cellulose molecules in the amorphous regions are degraded more readily, and the well-aligned molecules in crystalline regions are not as easily degraded by irradiation.     

Electrical Conductivity of Inhomogeneous Cu2O–10CuAlO2–xCu Cermets

Cu₂O–10CuAlO₂– x Cu cermets, as candidate inert anode materials for Al production, were prepared via hot-pressing (HP) technology, and their electrical conductivity was studied. The results show that the Cu₂O–10CuAlO₂– x Cu cermet materials can act as an electrical conductor when the Cu content is higher than 15 wt%. The electrical conductivity of the cermet material depends on the content, the particle size of the metal phase, and also on the porosity of the cermet material. The electrical conductivity increases with the decrease of particle size of the metal phase and the porosity. The particle size of the metal phase decreases with the increase of HP pressure, while it increases with increase of the HP temperature. The mathematic relationship connecting electrical conductivity and the influence factors was found.     

High radiation tolerance of electrocaloric (1-x)Pb(Mg1/3Nb2/3)O3–xPbTiO3

High radiation tolerance of functional materials in harsh environments is the key requirement for the operation of particle accelerators, medical devices, nuclear power plants, satellites, and spacecraft. Neutron and gamma (γ) radiation can seriously affect the functional properties of the irradiated materials and thus the performance of the entire device. In this work, the feasibility of using (1-x)Pb(Mg_1/3Nb_2/3)O₃–xPbTiO₃ (PMN–100xPT) electrocaloric materials in applications where the material is exposed to high neutron and γ-radiation is investigated. For this purpose, three different compositions of PMN–100xPT ceramics (x = 0, 0.1, and 0.35) were prepared and their dielectric, ferroelectric and electrocaloric properties were investigated before and after neutron and γ-irradiation. The samples were irradiated with a neutron fluence of 10¹⁵ to 10¹⁷ neutrons cm^?2 with an energy of 1 MeV, which exceeds the largest expected neutron irradiation in the European Council for nuclear Research (CERN) and simultaneously exposed to γ-irradiation. The neutron and γ-radiation partially affect the functional properties of the PMN–35PT, the ceramic with distinct ferroelectric and weakened relaxor features, with some differences observed in the domain switching behavior, measured by conventional polarization versus electric field (P–E) hysteresis, at the highest radiation dose of 10¹⁷ neutrons cm^?2. In contrast, the functional properties of the irradiated PMN and PMN–10PT samples with relaxor behavior are quite similar to those of the pristine samples, therefore, we conclude that these materials can be used as working materials in EC coolers exposed to such harsh environments.     

Electron spin resonance studies of γ-irradiated cellulose. I. Free radicals in decrystallized cellulose

The types of free radicals formed in decrystallized cellulose prepared from cellulose I and II after γ-irradiation in nitrogen atmosphere at room temperature were studied by ESR spectroscopy. X-Ray diffraction revealed that decrystallized cellulose I and II have the same microstructure. The ESR spectra obtained with the γ-irradiated decrystallized samples are simple. By contacting the irradiated sample with moisture in nitrogen atmosphere, the ESR spectrum changed to a narrow singlet, which gradually decreased in intensity until the spectrum completely disappeared. It was found that the types of free radicals generated in the decrystallized cellulose by γ-irradiation consist of the overlap of singlet and doublet. The singlet spectrum is mainly attributed to alkoxyl radical formed by the rupture of glycosidic linkage at the C 1 or C 4 position, and the doublet spectrum is ascribed to radical formed by hydrogen abstraction from the C 1 position in cellulose molecule.     

The in situ polymerization of vinyl monomers in polyester yarns

The effects of a pretreatment of polyester (PET) yarns with a strongly interacting solvent such as dimethylformamide (DMF) on vinyl monomer incorporation were investigated. When the DMF pretreatment is carried out at high temperatures (above 120°C), the swollen PET structure is stabilized by solvent-induced secondary crystallization. This substrate is highly suitable for the incorporation of vinyl monomers. In situ polymerization of vinyl monomers in DMF-treated PET was investigated using chemical and γ-irradiation polymerization techniques, both in the presence and in the absence of excess monomer outside the PET fibers. When polymerization was carried out in a system in which a constant supply of free radicals was available from the outside of the PET fibers, lower initiator concentrations and smaller γ-irradiation doses were necessary. These results are attributed to a low efficiency of the initiator inside the PET fiber due to mobility restrictions. Water uptake and moisture regain of PET yarns containing poly(hydroxyethyl methacrylate) and poly(acrylic acid) were also investigated. When most of the vinyl polymer was inside the PET fiber, water absorption was limited. The changes in mechanical properties of the PET yarns resulting from the DMF pretreatment were partially reversed by in situ polymerization of vinyl monomers.     

Modulus-Graded Interphase Modifiers in E-Glass Fiber/Thermoplastic Composites

A process for coating E-glass fibers with polystyrene–polyethyleneimine (PEi) core–shell particles was developed, and uniform monolayers of particles of 143 and 327 nm diameter were covalently bonded to the glass surface. The effect of the particle coatings on the mechanical properties of fiber-reinforced composites of poly(vinyl butyral) (PVB) was investigated. The interfacial shear strength (IFSS) was measured for specimens containing one to 20 fibers each using the tensile fiber fragmentation test, and significant enhancements were found, in particular for samples containing larger numbers of fibers. The smaller-particle (143 nm) coatings in the 20-fiber specimens produced approximately a 100% enhancement in IFSS over equivalent specimens with bare or aminosilane-treated fibers, while the 327 nm particle coatings produced only approximately a 25% enhancement. The greater effectiveness of the smaller particles was attributed, at least in part, to the larger effective interfacial area they provide and their relatively greater shell-to-core ratio, providing greater interphase stiffness. The greater enhancements achieved for the multi-fiber vs single-fiber specimens suggest that the coatings produce a more uniform fiber–fiber spacing and, therefore, a more thorough wetting of the fibers by the resin in the multi-fiber samples. Composites formed using fiber tows of 3200 fibers each showed more than a 100% increase in composite toughness and 35% increase in ultimate tensile strength as compared to samples with bare fibers due to the presence of the 143 nm particle coatings, and somewhat more modest increases for the 327 nm particle coatings.     

Studies on Sand-Unsaturated Polyester Composite Materials

The influence of unsaturated polyester resin to sand ratios as well as γ-irradiation on the physico-mechanical properties of the sand-polyester composite has been investigated. The samples were prepared at different ratios ranging from 5% to 30% of unsaturated polyester to sand, then subjected to γ-irradiated between 10 and 100 kGy. The effect on the compressive strength, total porosity, and water absorption, in addition to infrared spectroscopy and thermogravimetric analysis (TGA) were studied. The results indicate that the compressive strength increases with the increase of unsaturated polyester resin and the γ-irradiated dose, whereas the total porosity and water absorption values were decreased. These are attributed to adhesion between the sand and unsaturated polyester under the effect of γ-irradiation. Infrared spectra showed the appearance of new bands as a result of the formation of the Si=C bond. Also, TGA showed that the thermal stability of the composite increases with the increase of exposure dose.     

Electrical properties of gamma-irradiated,pure, and nickel chloride-doped polyvinyl alcohol films

The electrical transport properties, such as direct current (dc) electrical conductivity (σ), dielectric constant (ε′), and dc current–time characteristics of unirradiated and γ-irradiated pure and NiCl₂-doped PVA were studied in the temperature range of 26–155°C. Quantitative analysis was carried out to determine the thermal activation energy of the conduction process, drift mobility, and carrier concentration. The thermally activated mobility of charge carriers is confirmed from calculations of drift mobility at different γ-doses and temperatures. The results obtained revealed that γ-irradiation enhances the conductivity. The dielectric constant data at different temperatures before and after irradiation can be attributed mainly to the changes in the intra- and intermolecular interactions. The dc conductivity at 30 and 40°C, activation energy in low temperature region I, and proved to be dose-dependent. The obtained data suggests that these materials may have an application in dosimetry. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:687–698, 1998     

The growth of FeOOH microcrystals and chemisorption rate of NO

The adsorption of NO over a period of 1 ms–1 min on α- and γ-FeOOH with different degrees of crystallization has been examined in order to clarify the fast chemisorption phenomenon. The FeOOH crystals were prepared under the conditions of various reaction temperatures and ageing times. The changes in X-ray diffraction patterns, particle size, specific surface area and electrical conductivity were examined. The fast chemisorption rate constant, k_f, for NO was obtained at 30°C from the conductivity change in the initial stage of NO adsorption. The α-FeOOH aged for 2 days and 6 days, the crystallite size of which approximately 100 Å gave the highest k_f and the greatest amount of chemisorption; the high activity is assumed to be caused by a special surface structure accepting NO molecules. The maximum k_f for α-FeOOH was also for a crystallite size of approximately 100 Å. As the change of k_f with crystal growth for γ-FeOOH is similar to that of electrical conductivity, an electronic factor seems to be most important in the fast chemisorption process of NO on γ-FeOOH.     

Interaction of Aluminum with Detonation Products

A method of electrical conductivity and an analysis of recovered explosion products are used to study interaction of aluminum with detonation products of condensed high explosives. The electrical conductivity of HMX/Al and RDX/Al mixtures is inhomogeneous; a region with the maximum electrical conductivity is adjacent to the detonation front, whereas the electrical conductivity decreases with distance from the front. If the wave is incident onto a wall, the electrical resistance of the composite high explosive increases, which indicates that the high-conducting zone disappears. The electrical conductivity, resistance of the conducting zone, and the time of resistance growth are found as functions of the particle size of the additive. The results obtained confirm the reaction of the metal additive with detonation products in a microsecond range of time. An analysis of condensed explosion products shows that the reaction of aluminum with detonation products proceeds on the particle surface. The amount of reacted aluminum and the oxide-layer thickness are estimated. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 1, pp. 120–129, Jnuary–February, 2006.