Preparation and characterization of poly(methyltetradecylsiloxane) stationary phases immobilized by gamma radiation onto zirconized silica

The preparation of stationary phases with enhanced chemical stability in alkaline eluents has been the principal objective of many chromatographers. New and improved silica substrates and advanced chemical modification methods are among the possibilities being investigated to reach this objective. The present work has evaluated these two possibilities for new stationary phases. First, the silica surface was modified by reaction with zirconium tetrabutoxide to produce zirconized silica particles having about 21% (w/w) of zirconium. Then poly(methyltetradecylsiloxane) (PMTDS) was immobilized onto this surface using different doses (50-120 kGy) of gamma radiation. These new phases were characterized using elemental analysis and infrared and solid-state (29)Si-nuclear magnetic resonance (NMR) spectroscopies. These new stationary phases presented column efficiencies of about 68,000 plates m(-1), symmetric peaks for apolar compounds and retention factors that depend on the irradiation dose and show improved stability in high pH mobile phases. The separation of several pharmaceuticals at pH 11 is presented.     

Effect of gamma radiation on the physico mechanical properties of recycled HDPE/modified sugarcane bagasse composite

In this work, the sugarcane bagasse (SCB) fibers were used as reinforcing filler for recycled high density polyethylene (rHDPE) to form eco-friendly composite. The SCB surface was chemically modified to improve the compatibility with rHDPE matrix. The SCB fibers were alkali modified using 10% sodium hydroxide (SCBm) and acetylated using acetic anhydride (SCBac). The chemically modified SCB fibers were characterized using Fourier transform infrared (FTIR) and scanning electronic microscopy (SEM). The composites were prepared by mixing of rHDPE with 15 phr (parts per hundred parts rHDPE) of different SCB samples. Neat rHDPE and its composites with SCB were irradiated by gamma radiation dose of 50–250 kGy. The Effect of gamma radiation on the water up-take, mechanical properties and the thermal stability of (rHDPE) and its composites was studied. The effect of gamma radiation on the compatibility between rHDPE and SCB was also investigated. The results showed that the combination between the chemical modification of fibers and the irradiation of polymer composites were more effective in compatibility improvement than chemical modification alone. The irradiated (at 100 kGy) composite containing of SCBac gave the best mechanical properties, lowest water up-take and the highest thermal stability.     

Preparation of Co/Pd alloy particles dispersed multiwalled carbon nanotube supported nanocatalysts via gamma irradiation

New multiwalled carbon nanotube/silica supported cobalt-palladium bimetallic nanocatalysts (MWNT@silica/Co–Pd NPs) were prepared by a simple one step gamma irradiation method. The method involves the in-situ surface modification of MWNT with silica (MWNT@silica) and simultaneous formation of Co–Pd bimetallic NPs using gamma irradiation. The bimetallic NPs were stabilized by silica particles formed over the surface of MWNT. Extensive characterization studies have been performed on structural, morphological, and electrochemical, aspects of MWNT@silica/Co–Pd NPs. MWNT@silica/Co–Pd NPs were characterized by field emission scanning microscopy (FESEM), UV–visible spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Raman spectroscopy. The influence of irradiation dosage levels on the stabilizing effect of silica particles has been studied. The electrolytic activities of the MWNT@silica/Co–Pd NPs were investigated by cyclic voltammetry.     

Gel production, oxidative degradation and dielectric properties of isotactic polypropylene irradiated under various atmospheres

In this work, changes in structure and physical properties of stabilized isotactic polypropylene (iPP) were created by gamma irradiation, up to a dose of 700 kGy, in different media: air, deionised distilled (DD) water and acetylene. Gel and infrared (IR) spectroscopy measurements were used to determine the changes in the degree of network formation and oxidative degradation, respectively. Sol-gel analysis was studied in detail using the Charlesby-Pinner (C-P) equation. The radiation-induced changes in the structure and evolution of oxygen-containing species were also studied through dielectric loss (tan δ) analysis in a wide temperature and/or frequency range. Evolution of low temperature dielectric relaxations with gamma irradiation was investigated. In the case of dielectric relaxation measurements, the polar groups that were introduced by irradiation in non-polar iPP were considered as tracer groups. Conclusions derived according to different methods were compared.     

Change in the enzymatic dual function of the peroxiredoxin protein by gamma irradiation

PP1084 protein was exposed to gamma irradiation ranging from 5 to 500 kGy. Native PAGE showed minor structural changes in PP1084 at 5 kGy, and major structural changes at >15 kGy. Size-exclusion chromatography (SEC) showed the formation of a new shoulder peak when the protein was irradiated with 15 and 30 kGy, and a double peak appeared at 100 kGy. The results of PAGE and SEC imply that PP1084 protein is degraded by gamma irradiation, with simultaneous oligomerization. PP1084 chaperone activity reached the highest level at 30 kGy of gamma irradiation, and then, decreased in a dose-dependent manner with increasing gamma irradiation. However, the peroxidase activity significantly decreased following exposure to all intensities of gamma irradiation. The improvement of chaperone activity using gamma irradiation might be promoted by the oligomeric structures containing covalently cross-linked amino acids. Consequently, PP1084 modification using gamma irradiation could elevate chaperone activity by about 3–4 folds compared to the non-irradiated protein.     

Influence of surface characteristics of carbon blacks on cure and mechanical behaviors of rubber matrix compoundings

In this work, the effect of chemical modification on the surface energetics and cure kinetics of carbon blacks (CBs) modified with KOH and C6H6 was investigated by contact angle and rheometer measurements, respectively. Also, the resulting mechanical properties of the CBs/styrene-butadiene composites were studied in terms of tensile and dynamic mechanical analysis. As experimental results, the polar basic and nonpolar chemical treatments showed an increase of the London dispersive component (gamma(S)(L)) of gamma(S) of the CBs without significantly changing the surface properties and microstructures that resulted from the deaggregation of microstructures and decrease of the swollen weight of the sample in the equilibrium state. Also, it was clearly revealed that the increase of gamma(S) of the CBs could largely affect the vulcanization and mechanical properties of the composites, resulting from the increase in gamma(S)(L) of the CBs. These results were evident that the mechanical properties of the composites were controlled more by the gamma(S)(L) of gamma(S) than by the specific (or polar) component (gamma(S)(SP)), including electron acceptor and donor parameters on CB surfaces in an organic matrix composite system.     

Fracture toughness of gamma irradiated polycarbonate sheet using the essential work of fracture

Polycarbonate (PC), a ductile polymer, has been found by both linear elastic fracture mechanics and impact tests to present a ductile-brittle transition, which depends on notched specimen thickness, test speed and gamma irradiation. Owing to large amounts of plastic deformation, fracture toughness measurements by these test methods are not precise. In the present communication, a better method, the Essential Work of Fracture (EWF), to assess the fracture characteristics in plane state of stress was for the first time used to evaluate the fracture toughness of PC sheets subjected to gamma irradiation dose. Three-points bend tests of sharp pre-cracked specimens with different ligament lengths were 340 kGy gamma irradiated. EWF results showed that the total fracture work increased linearly with length for both non-irradiated and gamma irradiated conditions. A significant decrease in EWF fracture toughness was associated with brittleness promoted by gamma irradiation. This brittleness was also confirmed by macro and microscopy (SEM) evidence.     

Surface species produced in the radiolysis of zirconia nanoparticles

Modifications to water-zirconia nanoparticle interfaces induced by gamma irradiation have been examined using diffuse reflection infrared Fourier transform (DRIFT), Raman scattering, and electron paramagnetic resonance (EPR) techniques. Spectroscopy with in situ heating was used to probe variations in the dissociatively bound chemisorbed water on the zirconia nanoparticles following evaporation of the physisorbed water. DRIFT spectra show that the bridged Zr-OH-Zr species decreases relative to the terminal Zr-OH species upon irradiation. No variation is observed with Raman scattering, indicating that the zirconia morphology is unchanged. EPR measurements suggest the possible formation of the superoxide ion, presumably by modification of the surface OH groups. Trapped electrons and interstitial H atoms are also observed by EPR.     

Valence stabilization of polyvalent ions during gamma irradiation of their aqueous solutions by sacrificial protection. III-Valence stabilization of Fe(II) ions by organic additives

Valence stabilization of polyvalent ions in gamma irradiated aqueous solutions is sometimes necessary in some chemical operations. In previous publications, valence stabilization of some polyvalent ions in solution upon gamma irradiation was achieved by using inorganic additives capable of interacting with the oxidizing or reducing species formed during water radiolysis. The results showed that the nature and duration of valence stabilization of Fe(II) depend on the concentration of the inorganic additives used. In the present work, a series of some organic additives has been used to investigate their capability in inducing valence stabilization of polyvalent iron ions, taken as an indicator, in aqueous acidic solutions when subjected to extended gamma irradiation. The results showed that the efficiency of valence stabilization depends on the amount and chemical structure of the organic additive used.     

Stress-induced increase in the amounts of maysin and maysin derivatives in world premium natural compounds from centipedegrass

The red leaves of centipedegrass are known to produce compounds with stronger antibiotic effects than those produced by green leaves. Therefore, the aim of this study was to identify if stress methods (e.g., gamma irradiation, UV-B irradiation, and wounding) could effectively convert green leaves to red leaves, and thereby increase the production of maysin and maysin derivatives that have been known for antibiotic properties. Our results showed differential concentration changes for different compounds using these stress methods. The concentrations of luteolin increased from 0.014% to 0.019%, 0.022%, and 0.028% following gamma irradiation, UV-B irradiation, and wounding, respectively. The concentration of isoorientin increased from 0.898% to 1.938% and 2.538%, while the concentration of mixed rhamnosylisoorientin and orientin increased from 0.303% to 0.474% and 0.690%, following UV-B irradiation and wounding, respectively. Gamma irradiation produced concentrations of isoorientin, rhamnosylisoorientin, and orientin similar to those found in red leaves. The concentrations of derhamnosylmaysin increased from 0.004% to 0.009%, 0.015%, and 0.024% by gamma irradiation, UV-B irradiation, and wounding, respectively. The concentration of maysin increased from 0.515% to 0.714%, 0.583%, and 0.777% by gamma irradiation, UV-B irradiation, and wounding, respectively, while the concentration of luteolin-6-C-boivinopyranoside increased from 0.324% to 0.834%, 0.979%, and 1.493% by gamma irradiation, UV-B irradiation, and wounding, respectively. According to these results, wounding and gamma irradiation are promising methods for increasing the concentrations of maysin and maysin derivatives.     

A facile and novel process for the preparation of <Superscript>147</Superscript>Pm source

Aiming the selective recovery of palladium from high level radioactive liquid waste (HLW), a chelating thiamide type sorbent, CWP–TU, was prepared by the modification of Japanese cedar wood powder (CWP). Convection oven and microwave heating were separately used for modification purpose and found that microwave heating is more effective over oven heating. CWP–TU was extensively studied for the adsorption of Pd(II) from nitric acid medium. The batch test showed that nitric acid concentration of 3 M or higher is favorable for Pd(II) loading. Consistent adsorption of Pd(II) under gamma irradiation condition demonstrated the feasibility of using CWP–TU in real HLW. Also, Pd(II) only adsorption from simulated HLW solution verified the palladium only selectivity of the sorbent as well as the lack of influence of coexisting metal ions on its affinity toward Pd(II). CWP–TU holds maximum Pd(II) loading capacities of 0.98 mol/kg at 30 °C and 1.04 mol/kg under gamma irradiation. A comparative study using some ion exchange resins revealed that the resins are either ineffective in nitrate medium or lack stability under irradiation.     

Thermal,tensile and rheological properties of linear low density polyethylene (LLDPE) irradiated by gamma-ray in different atmospheres

The aim of this paper is to investigate structural changes of linear low density polyethylene (LLDPE) modified by ionizing radiation (gamma rays) in different atmospheres. The gamma radiation process for modification of commercial polymers is a widely applied technique to promote new physical–chemical and mechanical properties. Gamma irradiation originates free radicals which can induce chain scission or recombination, providing its annihilation, branching or crosslinking. This polymer was irradiated with gamma source of ⁶⁰Co at doses of 5, 10, 20, 50 or 100 kGy at a dose rate of 5 kGy/h. The changes in molecular structure of LLDPE, after gamma irradiations were evaluated using thermogravimetric analyzer (TGA) and tensile machine and oscillatory rheology. The results showed the variations of the properties depending on the dose at each atmosphere.     

Effects of gamma irradiation on poly(ethylene isophthalate)

Radiation methods are largely used for polymerisation and polymer modification, since irradiation induces transformations in the structure of materials which can be exploited to improve their performance. On the other hand, combined action of ionising radiation and oxygen may lead to degradation of the polymer, with worsening of properties such as mechanical strength or electrical insulation resistance. Therefore, the change of the chemical and physical properties of polymers under irradiation is a dynamic topic of research. In this work there are discussed data on the physical features of a polyester, poly(ethylene isophthalate) (PEI), subjected to gamma irradiation up to 1 MGy. PEI is a semicrystalline polymer with a structure similar to polyethylene terephthalate. Viscosity and differential scanning calorimetry measurements were carried out which allowed the monitoring of changes in the structure in terms of variations in the molecular weight, as well as of the percentage crystallinity depending on the dose. Furthermore, positron annihilation lifetime spectroscopy supplied information on the free volume present in the amorphous phase of the irradiated polymer.     

Catalytic properties of nickel–yttrium mixed oxides and the influence of ionizing radiation

Some physico-chemical and catalytic properties of NiO–Y₂O₃ cataysts containing various amounts of components in the range 0–100 wt% of one component have been studied before and after 1 MGy gamma or accelerated electron irradiation in air or in water using the hydrogen peroxide decomposition as a test reaction. Both kinds of irradiation led only to a change in surface oxidative ability but did not lead to modification of the catalytic activity of the catalysts. The reduction of the catalysts led to a creation of new kind of catalytic sites.     

Vinyl acetate polymerization by ionizing radiation

For this work an irradiation system to be used in the polymerization of the vinyl acetate in methylethylketone and in ethyl alcohol solution using the gamma radiation as initiator was projected and built. The molecular weights of the polymers obtained by irradiation with gamma rays in methylethylketone and in ethyl alcohol solution were 33,000 and 44,000 g/mol, respectively. From the characterization by infrared spectroscopy it was possible to verify that the polymers obtained in two studied cases actually correspond to poly(vinyl acetate).     

Study of the morphology,thermal and mechanical properties of irradiated isotactic polypropylene films

Thin films of isotactic polypropylene (iPP) are of great economical importance and their production is quite challenging due to the need of very fast uniaxial or biaxial expansion. During the expansion, critical problems usually arise, like structure disruption, shear thinning, causing material, energy and time losses. This work aims to study the surface morphology and compare the thermal, mechanical properties of PP films irradiated by gamma ray in an acetylene atmosphere after uniaxial expansion. PP films were made by compression molding at 190 °C with cooling in water at room temperature and irradiated by gamma ray, at (5, 12.5 and 20 kGy) under acetylene atmosphere. After irradiation the samples were submitted to thermal treatment at 90 °C for 1 h and then stretched out at 170 °C using an Instron machine. The surface of PP films, pristine and modified, (i.e., irradiated), was studied using optical microscopy (OM) and scanning electron microscopy (SEM). The changes in morphology, crystallinity and tensile parameters, like yield stress, rupture stress and elongation strain of the PP with irradiation dose were investigated. The results showed some evidences of gel formation due to crosslinking and/or long chain branching induced by radiation.     

Effects of Annealing on the Properties of Gamma-Irradiated Sago Starch

The increase in health and safety concerns regarding chemical modification in recent years has caused a growing research interest in the modification of starch by physical techniques. There has been a growing trend toward using a combination of treatments in starch modification in producing desirable functional properties to widen the application of a specific starch. In this study, a novel combination of gamma irradiation and annealing (ANN) was used to modify sago starch (Metroxylon sagu). The starch was subjected to gamma irradiation (5, 10, 25, 50 kGy) prior to ANN at 5 °C (T_o-5) and 10 °C (T_o-10) below the gelatinization temperature. Determination of amylose content, pH, carboxyl content, FTIR (Fourier Transform Infrared) intensity ratio (R_1047/1022), swelling power and solubility, thermal behavior, pasting properties, and morphology were carried out. Annealing irradiated starch at T_o-5 promoted more crystalline perfection as compared to T_o-10, particularly when combined with 25 and 50 kGy, whereby a synergistic effect was observed. Dual-modified sago starch exhibited lower swelling power, improved gel firmness, and thermal stability with an intact granular structure. Results suggested the potential of gamma irradiation and annealing to induce some novel characteristics in sago starch for extended applications.     

The influence of nano silica particles on gamma-irradiation ageing of elastomers based on chlorosulphonated polyethylene and acrylonitrile butadiene rubber

The goal of this work was to study gamma irradiation ageing of rubber blends based on acrylonitrile butadiene rubber (NBR) and chlorosulphonated polyethylene rubber (CSM) reinforced by silica nano particles. The NBR/CSM compounds (50: 50, w/w) filled with different content of filler (0–100 phr) were crosslinked by sulfur. The vulcanization characteristics were assessed using the rheometer with an oscillating disk. The vulcanizates were prepared in a hydraulic press. The obtained materials were exposed to the different irradiation doses (100, 200, 300 and 400 kGy). The mechanical properties (hardness, modulus at 100% elongation, tensile strength and elongation at break) and swelling numbers were assessed before and after gamma irradiation ageing.     

Surface modification of poly(tetrafluoroethylene) with benzophenone and sodium hydride by ultraviolet irradiation

Poly(tetrafluoroethylene) (PTFE) films were surface modified in a solution of benzophenone and sodium hydride in dry dimethylformamide by ultraviolet (UV) light irradiation. The extent of surface modification was characterized after durations of UV light irradiation from 5–20 min at temperatures from 19–60°C. The modified films were analyzed by electron spectroscopy for chemical analysis, diffuse reflectance ultraviolet-visible light spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, dynamic contact angle measurement, and low-voltage scanning electron microscopy. PTFE surfaces produced by this modification demonstrated extensive defluorination, oxygen incorporation, surface unsaturation, and reduction in both advancing and receding dynamic water contact angles in a manner that was more extensive at long durations of irradiation and at high temperatures. Morphological damage depended upon treatment conditions, but extensive surface modification could be obtained without substantial morphological damage to PTFE films. Control experiments indicated that the surface modification proceeded by photoexcitation of either diphenyl ketyl radical anion or benzhydrol anion, the products of reaction of benzophenone with sodium hydride. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1499–1514, 1997     

A study of transcrystallinity in polypropylene in the presence of wood irradiated with gamma rays

The interest in lignocellulosic composites has been growing in recent years because of their specific properties. In this study, a new technique of wood treatment using γ-irradiation was used. This research focuses on the influence of the gamma irradiation on the chemical composition of wood and on the nucleation ability of polypropylene matrice. The inner morphology of the transcrystalline layer was investigated using hot stage optical microscopy. Differential scanning calorimetry was used to investigate the kinetic parameters of polypropylene crystallization in the presence of wood surface. The results showed that the gamma irradiation can decrease the content of the cellulose in the wood, but it has a slightly negative effect on the transcrystallization process of polypropylene. This treatment also affects the crystal conversion and the half-time of PP crystallization. These results suggested that the gamma irradiation of wood may play a useful role in changing the microstructure of the matrice near the wood. It was observed that the nucleation of the wood surface was selective, indicating that the chemical characteristics of the lignocellulosics might have influence on the polypropylene crystallization. A possible mechanism for the appearance of transcrystallinity involving chemical composition of lignocellulosic is also proposed.