K.S.S. Sarma

High energy electron irradiation effects on polystyrene films

The effect of an 8 MeV electron-beam on the structural, optical and dielectric properties of polystyrene films has been investigated respectively by means of Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–VIS) spectroscopy and electrical impedance (LCR) analysis over a radiation dose in the range of 50–250 kGy using a Microtron accelerator. The FTIR spectral analysis shows no change in the overall structure of the irradiated polystyrene films, except a minor change in the intensity of a few peaks in the FTIR spectrum, indicating that polystyrene is resistant to electron-beam irradiation over the range of radiation doses investigated. The optical band gap analysis using the UV–VIS absorption spectra of the polystyrene shows a small decrease in the optical band gap (E g) and the activation energy with an increase in electron doses. Further, the dielectric measurements over a frequency range of 100 Hz to 1 MHz for the electron-beam-irradiated polystyrene films show that both the dielectric constant and the dielectric loss increase with an increase in electron radiation dose, which may be ascribed to the formation of defect sites in the band gap of polystyrene as a consequence of molecular chain scission in the polymer films upon irradiation.

Designing a single superabsorbent for separating oil from both layered as well as micron/submicron size emulsified oil/water mixtures by gamma radiation assisted grafting

Separation of oil–water from either its layered mixtures or emulsions is an extremely important challenge in this modern era. Commercially available polyurethane (PU) sponge does not have selectivity towards liquid. In this article, we introduce a rapid, single step, scalable, economic and sustainable route to introduce super selectivity towards oily liquid to the sponge upon modification via gamma radiation assisted grafting of a low surface energy molecule (dodecyl 2-methacrylate). The covalent bond formed through grafting process, provides a highly durable special wettable property (superhydrophobicity and superoleophilicity) to the material without compromising its inherent mechanical property. We demonstrate that single the ‘super’-oil-absorbent (modified PU sponge) is highly efficient to separate quickly both layered oil–water mixtures and emulsions (micron and submicron size), which is unprecedented in the literature. Here, the reported material provides an energy efficient and more convenient approach to separate oil–water from both layered and emulsified oil/water mixture. SEM image indicates the formation of a rough surface on a modified PU sponge with some micron, submicron and nanosize hemispheres or bumps (ups and downs) due to the gamma-radiation based grafting of DMA, which is the cause behind this transformation. Moreover, the same piece of this modified PU sponge can be repetitively used in separation of oil–water for more than 100 times at least without compromising its mechanical & physical (special wetting) properties.

Electron-beam-induced changes in ultra-high-molecular weight polyethylene

Post-irradiation studies have been carried out to elucidate the effects of electron beam irradiation on the structural, optical, dielectric and thermal properties of ultra-high-molecular weight polyethylene (UHMWPE) films. The modifications in the optical band gap, activation energy, oscillator strength, and transition dipole moment have been investigated as a function of electron radiation dose using UV–Vis absorption spectra of UHMWPE films. The spectral analysis showed a decrease in both the optical band gap and activation energy, whereas the oscillator strength and the transition dipole moment increased with the increase in electron radiation doses. Further, the dielectric measurements indicated a slight increase in the dielectric constant and the ac conductivity of the UHMWPE films upon electron irradiation. The thermal analysis carried out by differential scanning calorimeter and thermo-gravimetric analyzer revealed that the melting temperature, degree of crystallinity and thermal stability of the UHMWPE films increased, obviously, due to the predominant cross-linking following high doses of electron radiation.

Electron-beam irradiation effects on poly(ethylene-co-vinyl acetate) polymer

Poly(ethylene-co-vinyl acetate) (EVA) films were irradiated with a 1.2 MeV electron beam at varied doses over the range 0–270 kGy in order to investigate the modifications induced in its optical, electrical and thermal properties. It was observed that optical band gap and activation energy of EVA films decreased upon electron irradiation, whereas the transition dipole moment, oscillator strength and number of carbon atoms per cluster were found to increase upon irradiation. Further, the dielectric constant, the dielectric loss, and the ac conductivity of EVA films were found to increase with an increase in the dose of electron radiation. The result further showed that the thermal stability of EVA film samples increased upon electron irradiation.

Tensile, flexural and morphological properties of electron beam-crosslinked LDPE–EPDM blends

The effect of electron beam (EB) irradiation on the tensile, flexural and morphological properties of low-density polyethylene (LDPE)/ethylene-propylene diene elastomer (EPDM) blends had been studied in the absence and presence of crosslink promoters, such as trimethylolpropane triacrylate (TMPTA) and triallyl cyanurate (TAC). Blends were prepared by melt mixing of LDPE and EPDM followed by EB irradiation at various doses. The gel fraction (%) of irradiated blends was increased with an increase in EPDM content as well as EB irradiation dose and consequently the tensile and flexural properties of the blends increased. The incorporation of crosslinking promoters accelerated the gel formation and improved the properties upon irradiation more efficiently. The phase morphology of fractured surface displayed immiscibility with a rough appearance before irradiation. But after irradiation, the surface became fine, smooth and uniform, which went on increasing upon irradiation, supporting the steady increase in mechanical properties. Surface appeared even smoother in the presence of TMPTA and TAC.

A study on beam profile of an industrial electron accelerator

ABSTRACT Experimental evaluation of electron beam profile of a recently upgraded industrial electron accelerator has been carried out to study characteristics of the beam required for the irradiation of various industrial products. Calibrated cellulose triacetate (CTA) film strip dosimeters were used for the measurement of dose profile along and transverse to the scanning direction at different distances in air under the beam extraction window in dynamic (conveyor) and static mode of operation. Two-dimensional dose distribution mapping under the beam has also been measured by using a large number of CTA strip dosimeters. The obtained result shows that the electron beam emerging out from scanning horn has a good uniformity along the scanning direction within 90% of the average maximum dose. Also, the paper reports depth dose distribution in unit density material under the 4.5 MeV beam. Using this study, area affecting dose to the product is controlled within the limit for the irradiation.

Electron beam modified nylon 6-clay nanocomposites: morphology and water absorption behavior

Abstract A series of nylon 6-clay nanocomposites were prepared by melt mixing, followed by electron beam (EB) crosslinking at various doses. Effects of crosslinking on clay dispersion, gel content, crystallinity and water absorption properties (hygrothermal) were studied. No change of the dispersion pattern of clay in nanocomposites was observed after crosslinking [from X-ray diffraction (XRD) and transmission electron microscopy (TEM)]. Gel content, i.e., degree of crosslinking is seen to keep on increasing with irradiation dose, although clays hinder crosslinking of polymers to some extent. Crystallinity of polymers is reduced after incorporation of clay as well as crosslinks. However, water absorption rate and maximum water content of nanocomposites are found to increase and saturation time to decrease with clay content. However, these changes become opposite after crosslinking of polymers. The water absorption for all samples is noticed to increase with temperature. Thus, EB crosslinking, without affecting the nanocomposite morphology, i.e., properties derived from nano interface generation, decreases the water absorption properties of nanocomposites.

Thermoluminescence glow-curve characteristics of LiF phosphors at high doses of gamma radiation

High doses of ionising radiation are becoming increasingly common for radiation-processing applications of various medical, agricultural and polymer products using gamma and electron beams. The objective of this work was to study thermoluminescence (TL) glow-curve characteristics of commonly used commercial LiF TL phosphors at high doses of radiation with a view to use them in dosimetry of radiation-processing applications. The TL properties of TLD 100 and 700 phosphors, procured from the Thermo-Scientific (previously Harshaw) company, have been studied in the dose range of 1–60 kGy. The shift in glow peaks was observed in this dose range. Integral TL responses of TLD 100 and TLD 700 were found to decrease as a linear function of dose in the range of 5–50 kGy. The paper describes initial results related to the glow-curve characteristics of these phosphors.