Direct Radiation Method Research Articles

Research on Dielectric Focusing Lens Antenna for HPM Atmospheric Breakdown Experiments

To distinguish the dielectric surface breakdown from the atmospheric breakdown, one method for atmospheric breakdown experiment by loading dielectric focusing lens is proposed. The focusing characteristics of dielectric focusing lens are investigated for the microwave frequency on the order of 1.3GHz to 9.3GHz, the lens focal length on the order of 0.3m to 0.9m and the dielectric constant on the order of 0.3 to 0.9. Simulations show that higher frequency, shorter focal length, and fitter dielectric constant result in better focus effect that the rising and falling edges of electric field strength change faster near the focus which is closer to the theoretical value. A dielectric focusing lens for the S-band is optimally designed with the polytetrafluoroethylene of 0.32m thickness, 0.6m diameter, and 0.4m focal length. The focus indicator of dielectric lens is measured and the atmospheric breakdown experiment is carried out. The experimental values of atmospheric breakdown are consistent with the theoretical values. The electric field strength with the lens at the focus is 5-6 times greater than that without focusing lens. The image of atmospheric breakdown by the dielectric lens focusing method experiment is clearer than that by the direct radiation method.

Grafting of thermo-sensitive N-vinylcaprolactam onto silicone rubber through the direct radiation method

The modification of silicone rubber films (SR) was performed by radiation-induced graft polymerization of thermosensitive poly(N-vinylcaprolactam) (PNVCL) using gamma rays from a Co-60 source. The graft polymerization was obtained by a direct radiation method with doses from 5 to 70kGy, at monomer concentrations between 5% and 70% in toluene. Grafting was confirmed by infrared, differential scanning calorimetry, thermogravimetric analysis, and swelling studies. The lower critical solution temperature (LCST) of the grafted SR was measured by swelling and differential scanning calorimetry.

Effects of cobalt and potassium doping on thermal stability and electrical properties of radiation grafted acrylic acid onto poly(tetrafluoroethylene ethylene) copolymer films

AbstractGrafted copolymer of poly(tetrafluoroethylene ethylene) (ET) with acrylic acid (AAc) was prepared by direct radiation method. The obtained films were modified by treating with small amounts of Co2+ and K+ ions (1.0 wt %). The effects of such treatment on the thermal stability and electrical conductivity of these films were studied. Cobalt treatment did not much affect the thermal degradation of the films. The results obtained revealed that k+ treatment enhanced the thermal degradation of ET‐g‐PAAc, which started 273 K lower than that observed in the case of the untreated and Co2+‐treated films. Potassium and cobalt treatment of the investigated films increased their electrical conductivity (σ) and decreased the activation energy ΔEσ. The increase in σ values was, however, more pronounced in the case of K+‐treated film. These results were discussed in terms of the effective increase in the hydrophilicity of the films, especially those treated with potassium. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 867–871, 2005

Radiation-induced grafting polymerization of MMA onto polybutadiene rubber latex

The grafting of methyl methacrylate (MMA) onto polybutadiene rubber latex by the direct radiation method was carried out. The effects of monomer concentration, absorbed dose and dose rate of gamma rays on the grafting yield were investigated. The graft copolymers were characterized by transmission electron microscopy (TEM), FTIR spectroscopy, and differential scanning calorimetry. TEM photographs revealed that the core–shell structures of latex particles are formed at low MMA content, and with the increasing of MMA content, the semi-IPN-like structure with core–shell could be developed due to the high gel fraction of polybutadiene (PBD) seed particles. In addition, infrared analysis confirmed that MMA could be grafted onto PBD molecular chains effectively under appropriate irradiation conditions. The interfacial adhesion between PBD rubber (core) and PMMA (shell) phases could be enhanced with the increase of MMA concentration.

Modification of poly(vinyltrimethylsilane) by radiation-induced graft polymerization

The modification of polyvinyltrimethylsilane (PVTMS) has been carried out using the radiation-induced graft polymerization. PVTMS is applied as a basis for gas-separating membranes. Acrylonitrile, acrolein, ethyl acrylate, acrylic acid and acrylamide were used as monomers. The grafting was performed both from vapour and liquid phase of monomers and their solutions by the direct radiation method. Some kinetic regularities of radiation graft polymerization of monomers and the character of distribution of grafted polymers along the thickness of PVTMS films were studied. It was shown that grafting improves the chemical resistance, the selective permeability of gases and some mechanical properties of PVTMS films.

Surface modification of MgO filler by radiation

Direct radiation method has been used to graft methyl methacrylate(MMA) onto magnesium oxide(MgO) powder. The graft products were characterized by FT-IR, X-ray diffraction. Their surface properties were studied by ESCA, SEM and determination of water contact angle. The grafted MgO was used as a filler of HDPE. The experimental results showed that the dispersibility of MgO in polymer matrix is remarkably improved, when the MgO is grafted with MMA. The tensile strength and elongation percentage at break of HDPE filled the modified MgO were higher than those of unmodified. When the HDPE was filled by modified MgO, its thermal stability was remarkably improved.

Relations entre la structure et les proprietes des membranes de polytetrafluoroethylene greffe—II. Membranes bifonctionnelles

Bifunctional membranes containing both carboxylic and pyridine groups are obtained by successive grafting of acrylic acid and 4-vinylpyridine onto thin films of PTFE. Homogeneous membranes with a random distribution of grafting chains have been prepared by the direct radiation method. Mosaic membranes containing geometrically well defined acid and basic zones are made by pre-irradiation with X-rays using two absorbing shields; the two monomers are grafted in successive steps. The equilibrium and transport properties of these membranes have been determined. They can either result from the addition of the properties of each component (in the case of conductivity) or give rise to a new properties (e.g. abnormal negative osmosis). Whatever the structure of the bifunctional membrane (homogeneous or mosaic), this negative osmosis occurs within a pH range in which the membrane potential varies greatly i.e. when the ionic character of the membrane changes. Experimental data are discussed on the basis of thermodynamics of irreversible phenomena. The phenomenological coefficients characteristic for a membrane belonging to each of the two types (mono- and bi-functional) have been calculated. The reflection coefficient σ is negative: this suggests a potential application of these membranes in piezodialysis.

Greffage de l'acide acrylique et du styrene sur des films de polytetrafluoroethylene preirradie en presence d'air

Styrene (St) and acrylic acid (AA) were grafted onto 0 · 1 mm thick PTFE films pre-irradiated in air. The kinetics were investigated at different temperatures and radiation doses. The results show that the grafting process exhibits a strong auto-catalytic character due to the progressive diffusion of the monomer and to the “gel effect”. The active centres which initiate grafting appear to be asymmetric diperoxides containing a perfluorinated polymeric chain and a small fluorinated fragment. The swelling of the films grafted with AA was investigated in water, KOH and HCl. It was found that the films grafted by the pre-irradiation method have a better stability than those prepared by the direct radiation method.

Extraction selective de films de poly(chlorure de vinyle) greffes par la methode radiochimique directe

PVC films grafted by the direct radiation method were subjected to selective solvent extraction. All samples were converted into a fine powder by a special precipitation technique. PVC samples grafted with MMA were extracted with acetone. They did not contain any PMMA homopolymer and all fractions had a MMA content close to 85 per cent. This result is explained by a strong transfer of PVC with respect to the growing MMA chain. Samples grafted with St were extracted with toluene at different temperatures and with toluene+dichloroethane mixtures at 25°. The first treatment led to a fractionation according to compositions and the second to a fractionation according to molecular weights. A sample grafted with a 50/50 mixture of (St+AN) was extracted with different mixtures of toluene+dichloroethane. The various results are discussed.

Grafting of Radiation-Peroxidized Lignin

Lignin is subject to easy radiation-peroxidation. In the case of pine hydrochloric acid lignin, irradiation of 1.92 Megarads of γ-ray in air gave rise to 3×1019 peroxide per gram of lignin. When the peroxidized lignin was allowed to stand in air, the peroxide contents diminished in 25 days to 40%, which was, thereafter, invariable for 250 days. When styrene or methyl methacrylate was used as monomer in the grafting there was reaction of 36 parts of styrene or of 39 parts of methyl methacrylate to 100 parts of lignin, but it was not the case with ligninsulfonic acid. Up to 1.92 Megarads of dose amount applied, the peroxide concentration in lignin increased proportionally with the radiation period, but the grafting ratio indicated maximum value at the point of a peroxide content of 1.89×1019 per gram of lignin. When polystyrene branches propagated up to Pn of 100, the corresponding grafting ratio reached to 35 in the radiation-peroxidation method and 200 in the case of direct radiation method respectively. This means that. in the case of radiation-peroxidation method, the number of active centers for grafting is one-sixth compared with those which appeared in the direct radiation grafting. From the so far known structure of lignin and the experimental results obtained here, it is to be concluded that the peroxides produced in the lignin molecules by pre-irradiation were mostly hydroperoxide arising from C-H scission at tertiary carbon, and less in diperoxide.

Structure and properties of cellulose graft copolymers. I. Radiation‐induced rayon–styrene graft copolymer

AbstractRayon–styrene graft copolymers were prepared by the direct radiation method, with the use of the preswelling technique, by irradiation with γ‐rays from 60Co. The grafting was carried out in bulk styrene and in styrene–solvent mixtures, such as styrene–methanol and styrene–acetone, to study their effect on the graft copolymerization reaction and the structure of the resulting graft copolymer. The effects of carbon tetrachloride, a chain‐transfer agent, was also investigated. Three different types of rayon yarn were used; Fortisan, a modifier‐type high wet‐modulus rayon, and a high‐tenacity tire yarn, in order to study the effect of rayon microstructure on the grafting reaction. The molecular structure of the rayon–styrene graft copolymers was studied by hydrolyzing away the cellulose backbone and measuring the molecular weights of the grafted polystyrene branches. For grafting in bulk styrene, the molecular weights of the grafted polystyrene ranged from 400,000 to 1,000,000, while those of the polystyrene homopolymer formed in the outside solution were of the order of 30,000–50,000. The molecular weights of the grafted polystyrene branches tended to increase with per cent grafting in the graft copolymer. For grafting in styrene–methanol and styrene–acetone mixtures, the molecular weights of the polystyrene branches decreased with increasing solvent content. The addition of carbon tetrachloride to bulk styrene resulted in a sharp decrease in the molecular weights of the grafted branches. The grafting frequency or number of polystyrene branches per cellulose chain was calculated from the per cent grafting and the molecular weights of the polystyrene branches. The morphology of the rayon–styrene graft copolymers and some of their physical properties are discussed.

Electron Microscopic Observations on Cellulose Graft Copolymers: Radiation Induced Rayon-Styrene Graft Copolymers1

Three types of commercial rayon (Fortisan, high-tenacity tire yarn, and modifier- type, high wet modulus yarn) were grafted with styrene, using the direct radiation method with gamma-rays from Co-60. The grafted filaments were examined in the electron microscope to investigate their morphology and fine structure, the location and distribution of polystyrene in the fiber, and whether the polystyrene was truly grafted. In all three grafted fibers, the polystyrene was distributed throughout the cross sec tion of the filament and also appeared on the surface. As a result, the filaments expanded isometrically during grafting, but retained their original shape. The polystyrene grafted to the surface of the filament followed the original surface striations of the rayon and appeared as protruding ridges and valleys, rather than as uniform surface layers. The polystyrene inside the filament could not be removed hy exhaustive extraction of the intact yarn with benzene, but some of it could be removed by extracting the ultra-thin cross sections (ca. 500 Å thick) used for electron microscopic observations. The main portion of these ultri-thin sections was insoluble in solvents for both polystyrene and cellulose and is considered to be a true cellulose-styrene graft. The changes induced in the fine structure of the cross sections by alternate extraction with solvents for polystyrene and cellulose were followed, using the electron microscope. From a macroscopic viewpoint, it was concluded that the styrene grafted rayons are homogeneous. At a molecular level, however, they consist of a gross heterogeneous mixture of polystyrene homopolymer, cellulose, and true cellulose-styrene graft co polymer.