Degradation and stability of polyaniline on exposure to electron beam irradiation (structure-property relationship)

Polyaniline (PAni) was prepared by electrochemical polymerization and subjected to different doses of electron beam (EB) irradiation. The effect of EB irradiation causes both chain scission and cross-linking process in PAni, which depends on irradiation dose. The degree of chain scission and cross-linking in PAni by EB irradiation is characterized through XRD, TGA, DSC, solubility, EPR and electrical properties measurement. The results reveal that with increase in EB irradiation dose from 0 to 150 kGy DC and AC conductivity and dielectric constant are found to increase mainly due to the chain scission or further doping in PAni. Due to irradiation there is change in the structure of PAni, such as decrease in the d-spacing, inter-chain separation, thermal stability and T_g but increase in the percent crystallinity and solubility. With further increase in the EB irradiation dose from 150 kGy onwards the DC and AC conductivity and dielectric constant are decreased due to the cross-link formation or dedoping in PAni, which causes the decrease in percentage of crystallinity and solubility and increase in d-spacing, inter-chain separation, thermal stability and T_g of PAni.     

A mild method of amine-type adsorbents syntheses with emulsion graft polymerization of glycidyl methacrylate on polyethylene non-woven fabric by pre-irradiation

A mild pre-irradiation method was used to graft glycidyl methacrylate (GMA) onto polyethylene (PE) non-woven fabric (NF). The polymer was irradiated by electron beam in air atmosphere at room temperature. The degree of grafting (D_g) was determined as a function of reaction time, absorbed dose, monomer concentration and temperature. After 30 kGy irradiation, with 5% GMA, surfactant Tween 20 (Tw-20) of 0.5% at 55 °C for 15 min, the trunk polymer was made grafted with a D_g of 150%. Selected PE-g-PGMA of different D_g was modified with aminated compounds such as ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA) and tetraethylenepentamine (TEPA). The obtained amine-type adsorbents were prepared to remove copper and uranium ions from solution. It was shown that at least 90% of copper and 60% of uranium with the initial concentration from 3 to 1000 ppb can be removed from water.     

Effect of electron beam radiation dose on the foam formation in pre-ceramic polymer

Methylsilicone resin as a polymer precursor for a SiOC ceramic material was cured and foamed by electron beam (EB) irradiation in air prior to the pyrolysis under an inert atmosphere. Methylsilicone foams were obtained without additional foaming agent when exposed to accelerated electrons with radiation doses up to 9 MGy and dose rate of 2.8 kGy/s. During irradiation the polymer was melted and simultaneously gaseous products were formed by the methyl group oxidation and by the poly-condensation crosslinking reactions. The formed gases could not escape from the molten polymer and began to aggregate into bubbles. The effect of the radiation dose on the polymer foam molecular structure, the gel fraction and the ceramic yield was analyzed. The results indicate that the maximum amount of crosslinking in methylsilicone, when EB radiation is used, occurred between 1.0 and 2.0 MGy radiation dose. Methylsilicone foams were pyrolysed in N₂ atmosphere at temperatures of 1200 and 1500 °C, resulting in amorphous SiOC and partially crystalline ceramic foams, respectively. A porosity of ~84% was achieved in the pyrolyzed foams, with cell size ranging from 30 to 300 μm and density of about 0.31 g cm^?3.     

Preparation of block copolymer of poly(trimethylene carbonate) with oligo(ethylene glycol) and the surface properties of the dip coated film

To persuade the stent coating materials for the better sustainable development, a block copolymer composed of hydrophobicity of poly(trimethylene carbonate) (PTMC) and hydrophilicity of PTMC bearing ethylene glycol chains was synthesized as a potential candidate. The result of thermal stability of the polymer was analyzed which reached up to 206 °C (T₁₀) and it is considered that sufficient for sterilization during the treatment. Moreover, the dip coated films of polymer were coated on polyethylene (PE) and stainless steel (SS) substrates in order to stimulate the stability upon the physiological environment. In addition, the preliminary in vitro test of the films were evaluated by protein adsorption and blood platelet adhesion tests. Hence, this study tends to convince that the synthetic block copolymer based on PTMC derivatives were approached for stent coating materials.     

Structural modifications of polymers under the impact of fast neutrons

Fast neutron irradiations were performed at room temperature on a series of 13 polymer matrixes having great practical and academic interest. Polymers were irradiated with very low doses of 14 MeV neutrons deposited at reduced dose rate. The modifications of chemical structure of the polymeric matrixes resulting from irradiation were analyzed at the molecular scale by infrared and UV-visible spectroscopy. Particular attention was given to the oxidation occurring in irradiated matrixes during storage in the absence of light at room temperature. In addition the effects of irradiation on the chain arrangements in the polymers were analyzed by Differential Scanning Calorimetry.The most significant result obtained in this preliminary work was evidence that neutron irradiation with very low doses in the range ≈130-320 cGy could provoke structural changes. Indeed, depending on the matrixes, the formation of oxidation products along the macromolecular chains or the evolution of the polymer architecture, evidenced by changes of the T_g or of the crystallinity, was observed. The perspectives of this preliminary work are discussed.     

Characterization of irradiation-induced crosslink of epoxidised natural rubber/ethylene vinyl acetate (ENR-50/EVA) blend

The effect of irradiation on tensile, dynamic mechanical properties, thermal properties and morphology of ENR-50, EVA and ENR-50/EVA blend was investigated. All the samples were irradiated using a 3.0 MeV electron beam (EB) machine with doses ranging from 20 to 100 kGy. Results indicate that the gel fraction of ENR-50, EVA and ENR-50/EVA blend increases with irradiation dose. Concerning tensile properties, it can be seen that EB radiation increases the tensile strength of all the samples, increases the elongation at break of ENR-50 and ENR-50/EVA blend, reduces the elongation at break of EVA, increases M200 (modulus at 200% strain) of ENR-50 and EVA, while decreases M200 of the ENR-50/EVA blend. For dynamic mechanical studies, it was found that EB radiation increases the T_g of all the samples due to the effect of irradiation-induced crosslinking. The compatibility of ENR-50/EVA blend also found to be improving upon irradiation. In the case of thermal properties, it was detected that T_m, T_c and the degree of crystallinity of ENR-50/EVA blend increase with an increase in irradiation dose. This was due to the perfection in the crystal growth occurring upon radiation. Morphology changes play a major role in the changes of the properties of ENR-50/EVA blend. Finally, it can be concluded that ENR-50/EVA blend can be vulcanized by EB radiation.     

Effect of gamma irradiation on microbial decontamination,and chemical and sensory characteristic of lycium fruit

Lycium fruit, popular traditional Chinese medicine and food supplement generally is ingested uncooked, was exposed to several doses of gamma irradiation (0–14 kGy) to evaluate decontamination efficiency, changes in chemical composition, and changes in sensory characteristic. In this study, lycium fruit specimens contained microbial counts of 3.1×10³–1.7×10⁵ CFU/g and 14 kGy was sufficient for microbial decontamination. Before irradiation, the main microbe isolated from lycium fruit was identified as a strain of yeast, Cryptococcus laurentii. After 10 kGy of irradiation, a Gram-positive spore-forming bacterium, Bacillus cereus, was the only survivor. The first 90% reduction (LD₉₀) of C. laurentii and B. cereus was approximately 0.6 and 6.5 kGy, respectively, the D₁₀ doses of C. laurentii and B. cereus was approximately 0.6 and 1.7 kGy, respectively. After 14 kGy irradiation, except the vitamin C content, other chemical composition (e.g., crude protein, β-carotene, riboflavin, fructose, etc.) and the sensory characteristic of lycium fruit specimens did not have significant changes. In conclusion, 14 kGy is the optimal decontamination dose for lycium fruit for retention of its sensory quality and extension of shelf life.     

Radiation resistances and decontamination of common pathogenic bacteria contaminated in white scar oyster (Crassostrea belcheri) in Thailand

In Thailand, white scar oyster (Crassostrea belcheri) was ranked for premium quality, being most expensive and of high demand. This oyster is often eaten raw, hence it may pose health hazards to consumers when contaminated with food-borne pathogens. As limited alternative methods are available to sterilize the oyster while preserving the raw characteristic, irradiation may be considered as an effective method for decontamination. In this study, the radiation resistance of pathogenic bacteria commonly contaminating the oyster and the optimum irradiation doses for sterilization of the most radiation resistant bacteria were investigated. The radiation decimal reduction doses (D₁₀) of Salmonella Weltevreden DMST 33380, Vibrio parahaemolyticus ATCC 17802 and Vibrio vulnificus DMST 5852 were determined in broth culture and inoculated oyster homogenate. The D₁₀ values of S. Weltevreden, V. parahaemolyticus and V. vulnificus in broth culture were 0.154, 0.132 and 0.059 kGy, while those of inoculated oyster homogenate were 0.330, 0.159 and 0.140 kGy, respectively. It was found that among the pathogens tested, S. Weltevreden was proved to be the most resistant species. An irradiation dose of 1.5 kGy reduced the counts of 10⁵ CFU/g S. Weltevreden inoculated in oyster meat to an undetectable level. The present study indicated that a low-dose irradiation can improve the microbial quality of oyster and further reduce the risks from the food-borne pathogens without adversely affecting the sensory attributes.     

Comparison of electron beam and gamma ray irradiations effects on ruminal crude protein and amino acid degradation kinetics,and in vitro digestibility of cottonseed meal

This study was conducted to compare effects of electron beam (EB) and gamma ray (GR) treatments at doses of 25, 50 and 75 kGy on ruminal degradation kinetics of crude protein (CP), amino acid (AA), and in vitro digestibility of cottonseed meal (CSM). Ionizing radiations of EB and GR had significant effects (P<0.05) on CP and AA ruminal degradability characteristics of CSM. Effective ruminal degradability (ERD) of CP was lower in EB and GR irradiated CSM (P<0.05) than in unirradiated CSM. GR and EB treatments had the same effects on ERD decreasing of CP (P>0.05). Irradiation processing caused decrement in AA degradation after 16 h of ruminal incubation (P<0.05). EB irradiation was more effective than GR irradiation in lessening the ruminal degradability of AA (P<0.05). EB and GR treatments at a dose of 75 kGy increased in vitro digestibility of CSM numerically. This study showed that EB could cause CP and AA bypass rumen as well as GR. Therefore, ionizing irradiation processing can be used as an efficient method in improving nutritional value of CSM.     

Preparation of N-doped and oxygen-deficient TiO2 microspheres via a novel electron beam-assisted method

Nitrogen-doped and oxygen-deficient TiO₂ microspheres (NT) with large specific surface were prepared by a solvothermal method and following with electron beam (EB) irradiation under various doses (140–500 kGy). XPS results show that under the EB irradiation, nitrogen ions have been doped into the TiO₂ lattice successfully, as well as part of Ti⁴⁺ on the surface of the samples changed to Ti³⁺. Photocatalytic performance was tested by decomposing Rhodamine B in the aqueous phase under visible light irradiation. The prepared materials under the EB irradiation at dose of 140 kGy (NT-140) exhibit the best visible light photocatalytic activity. It is attributed to the large specific surface (138.4 m²/g) and a synergistic effect between substitutional nitrogen dopants and oxygen defects in NT-140. The results obtained may provide a new sight for the application of EB-assisted preparation of nanomaterials.     

Effect of gamma irradiation on Burkholderia thailandensis (Burkholderia pseudomallei surrogate) survival under combinations of pH and NaCl

This study evaluated the effect of gamma irradiation on Burkholderia thailandensis (Burkholderia pseudomallei surrogate; potential bioterrorism agent) survival under different levels of NaCl and pH. B. thailandensis in Luria Bertani broth supplemented with NaCl (0–3%), and pH-adjusted to 4–7 was treated with gamma irradiation (0–0.5 kGy). Surviving cell counts of bacteria were then enumerated on tryptic soy agar. Data for the cell counts were also used to calculate D₁₀ values (the dose required to reduce 1 log CFU/mL of B. thailandensis). Cell counts of B. thailandensis were decreased (P<0.05) as irradiation dose increased, and no differences (P≥0.05) in cell counts of the bacteria were observed among different levels of NaCl and pH. D₁₀ values ranged from 0.04 to 0.07 kGy, regardless of NaCl and pH level. These results indicate that low doses of gamma irradiation should be a useful treatment in decreasing the potential bioterrorism bacteria, which may possibly infect humans through foods.     

Preparation of poly(methyl acrylate)/phosphate/composites and its possible use as storage medium for radioactive isotopes

The distribution of ¹³⁷Cs, ¹⁵²Eu, ²³⁸U, and ⁸⁵Sr in a solid/aqueous system (poly(methyl acrylate)/phosphate/composite in contact with groundwater, was investigated using γ-Spectrometry and flourometry. The results were compared with earlier results with mineral phosphate in the solid phase. The effect of contact time, pH and the concentration of concurrent element were studied. The ability of the prepared polymer composites to keep the studied radioisotopes in the solid phase is much higher than mineral phosphate. The used polymer composites have been prepared consisting of natural phosphate powder and the monomer methyl acrylate using gamma irradiation. The yield of polymerization was followed up with respect to the irradiation dose using thermogravimetric analyzer (TGA). A thermomechanical analyzer (TMA) was used to locate the area of the glass transition temperatures (T _g ) using the mode with alternative variable force; the mode with constant force was used to determine the T _g of the pure polymer and the polymer composite prepared at the same irradiation dose. The T _g of the pure poly(methyl acrylate) is 13 ± 3 °C, and the T _g of poly(methyl acrylate)/phosphate/composites is 8 ± 3 °C. The T _g were also determined using the DSC technique, and similar values were found.     

Sulfur-substitution-enhanced crystallization and crystal structure of poly(trimethylene monothiocarbonate)

In this paper, the crystallization behavior of a novel poly(monothiocarbonate), poly(trimethylene monothiocarbonate) (PTMMTC), was investigated and compared with its polycarbonate analogue, poly(trimethylene carbonate) (PTMC). It is found that PTMMTC exhibits strong crystallizability, while unstretched PTMC is amorphous. DSC and DMA results reveal that PTMMTC possesses higher glass transition temperature (T_g) and β-transition temperature (T_β) than PTMC. Simulation based on density functional theory (DFT) shows that, the bond angle of C-S-C is evidently smaller than that of C-O-C, and thus a larger dipole moment. This leads to the stronger intermolecular interaction and more rigid chain conformation in PTMMTC, which is the origin of sulfur-substitution enhanced crystallization. The crystal structure of PTMMTC was preliminarily determined for the first time. PTMMTC has an orthorhombic crystal structure with a planar zig-zag chain conformation. The parameters of unit cell are a = 10.74 Å, b = 4.79 Å, and c (fiber axis) = 7.74 Å.     

Dose dependence of the radiothermoluminescence intensity of polyethylene crystalline regions

The dose dependence for the intensity of all radiothermoluminescence peaks of polyethylene crystalline regions has been studied in the dose (D) range of 1.3?C30 kGy. The initial portion of the dose dependence curve at doses below 5 kGy has the same pattern for all the peaks; the first derivative is dI/dD > 0 at D = 0 and only decreases with the dose. This type of the dependence suggests that charge traps present in the polymer (in intracrystalline regions) at low doses have existed before irradiation. These traps can be regular segments of polymer chains in the crystalline regions. As the dose increases, radiation-induced traps appear and the dose dependence curves for peak intensities become dissimilar. Some of them show a decrease in intensity with the dose, others reach a limiting value and further do not vary in intensity, and the third ones display a permanent intensity rise.     

Electron beam accelerators—trends in radiation processing technology for industrial and environmental applications in Latin America and the Caribbean

The radiation processing technology for industrial and environmental applications has been developed and used worldwide. In Latin America and the Caribbean and particularly in Brazil there are 24 and 16 industrial electron beam accelerators (EBA) respectively with energy from 200 keV to 10 MeV, operating in private companies and governmental institutions to enhance the physical and chemical properties of materials. However, there are more than 1500 high-current electron beam accelerators in commercial use throughout the world. The major needs and end-use markets for these electron beam (EB) units are R and D, wire and electric cables, heat shrinkable tubes and films, PE foams, tires, components, semiconductors and multilayer packaging films. Nowadays, the emerging opportunities in Latin America and the Caribbean are paints, adhesives and coatings cure in order to eliminate VOCs and for less energy use than thermal process; disinfestations of seeds; and films and multilayer packaging irradiation. For low-energy EBA (from 150 keV to 300 keV). For mid-energy EBA (from 300 keV to 5 MeV), they are flue gas treatment (SO₂ and NO_X removal); composite and nanocomposite materials; biodegradable composites based on biorenewable resources; human tissue sterilization; carbon and silicon carbide fibers irradiation; irradiated grafting ion-exchange membranes for fuel cells application; electrocatalysts nanoparticles production; and natural polymers irradiation and biodegradable blends production. For high-energy EBA (from 5 MeV to 10 MeV), they are sterilization of medical, pharmaceutical and biological products; gemstone enhancement; treatment of industrial and domestic effluents and sludge; preservation and disinfestations of foods and agricultural products; soil disinfestations; lignocellulosic material irradiation as a pretreatment to produce ethanol biofuel; decontamination of pesticide packing; solid residues remediation; organic compounds removal from wastewater; and treatment of effluent from petroleum production units and liquid irradiation process to treat vessel water ballast. On the other hand, there is a growing need of mobile EB facilities for different applications in South America.     

Photocrosslinking of poly(N-vinylcarbazole): Implementing a complementary set of techniques to characterize the three-dimensional network formation

The crosslinking of poly(N-vinylcarbazole) PVK resulting from UV irradiation (λ > 300 nm) was studied by combining various techniques including infrared spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), swelling ratio, positron annihilation spectroscopy (PAS) and thermoporosimetry. The results obtained from all of these techniques were correlated and allowed a complete monitoring of the crosslinking during irradiation, from the creation of the first crosslinks to the formation and densification of the three-dimensional network. From SEC analysis and determination of swelling ratios, it was demonstrated that crosslinking was the predominant mechanism during the first stages of irradiation. PAS and DSC analyses revealed a good correlation between variations of free volume and increase of glass transition (T_g) of the bulk material. In addition, the development of the polymer architecture shown by the growth of T_g was nicely correlated with the modifications of the chemical structure observed by infrared analysis. Thermoporosimetry allowed the determination of the mesh size distributions within the polymer for the longest irradiation times. Numerical relationships were established and their validity was checked.     

The decontamination of industrial casein and milk powder by irradiation

The efficacy of gamma radiation decontamination of industrial casein, a milk protein utilized as a component of many food and non-food products has been studied. Low-fat milk powder was also included with a purpose to study the microflora survival in protein-rich materials. Microbial analysis of the samples prior to irradiation showed that the initial total viable count was higher than 6.0 log cfu g⁻¹ in both casein and milk powders. The contamination of casein with moulds and yeasts was found to be equal to 3.56 log cfu g⁻¹. The counts of coliforms have not exceeded the value of 2.48 log cfu g⁻¹. Radiation processing of casein and milk powder has substantially reduced the microbial population of all samples. The dose of 5 kGy was sufficient to reduce the total microflora and coliforms counts to the level permitted for food products. Survivals of microorganisms were analyzed by the generalized exponential equation, SF=exp[−D/D_o)^α]. Values of an exponent, α, standing for the dispersion parameter, were equal to 0.65 and 0.70 for microorganisms contaminating casein and milk powders, respectively. The numerical value of the dispersion parameter α<1 indicates the concave dependence of a logarithm of surviving fraction versus radiation dose. No difference in microflora survival in irradiated samples tested immediately and in samples stored for 1-month after irradiation has been noticed.     

Electron irradiation induced microstructural modifications in BaCl2 doped PVA: A positron annihilation study

Thin films of pure and 10 wt% BaCl₂ doped poly(vinyl alcohol) (PVA) were prepared by solution casting method. These films were subjected to electron irradiation for different doses ranging from 0 to 400 kGy in air at room temperature. The effect of electron irradiation on the optical and free volume related microstructures of these polymer films was studied using positron annihilation lifetime spectroscopy, FTIR and UV-vis techniques. The FTIR spectral studies indicate that the electron irradiation induces chemical modifications within the doped PVA, which results in chain scission as well as cross-linking of the polymer. The positron lifetime study on these irradiated polymers shows that the chain scissions and cross-linking within the polymer matrix affect the free volume content and hence the microstructure. The UV-vis optical absorption studies show that the induced microstructural change by electron irradiation also modifies the optical properties. Using UV-vis spectra, the optical energy band gap was estimated and it decreases with increase in electron dose. A correlation between positron results and optical results is obtained and electron irradiation induced microstructure modifications within the doped polymer are understood. The results highlight the usefulness of positron annihilation technique in the study of the microstructure of irradiated polymers.     

Radiation sensitivity of bacteria and virus in porcine xenoskin for dressing agent

In this study, gamma irradiation sensitivities of bacteria and viruses in porcine skin were evaluated to establish the optimum sterilization condition for the dressing material and a xenoskin graft. Escherichia coli and Bacillus subtilis were used as model pathogens and inoculated at 10⁶–10⁷ log CFU/g. As model viruses, porcine parvovirus (PPV), bovine viral diarrhea virus (BVDV), and poliovirus were used and inoculated at 10⁵–10⁶ TCID₅₀/g into porcine skin. The D₁₀ value of E. coli was found to be 0.25±0.1 kGy. B. subtilis endospores produced under stressful environmental conditions showed lower radiation sensitivity as D₁₀ was 3.88±0.3 kGy in porcine skin. The D₁₀ values of PPV, BVDV, and poliovirus were found to be 1.73±0.2, 3.81±0.2, and 6.88±0.3 kGy, respectively. These results can offer the basic information required for inactivating pathogens by gamma irradiation and achieving dressing material and porcine skin grafts.     

Dose rate effect on internal friction and structural transformations in electron-irradiated carbon-armored composites

Temperature dependence of internal friction and specific electric resistance of multi-layer carbon-armored epoxy-based composites is experimentally studied in the temperature range of 20–300 °C before and after irradiation with 2 MeV electrons. It is shown that carbon penetration into the polymer matrix causes intense polymer cross-linking in the basic layers of the composite even at low irradiation doses. The strong effect of dose rate on radiation-induced structural transformations was observed.