Crosslinking of rigid PVC by ionizing radiation to improve its thermal properties

Rigid PVC formulations containing two different stabilizer systems (tin and Ca/Zn) and TMPTMA as a crosslinking agent were treated with ionizing radiation (gamma and electron beam) at different doses and irradiation atmospheres. The objective was to increase thermal and mechanical properties of this material. Polyene formation was followed through the yellowing index (YI), the extent of crosslinking by gel percentage, thermal resistance by Vicat temperature and the mechanical properties by DMA. Both formulations became colored with irradiation, especially with gamma as a result of a longer treatment time; the gel formation and the Vicat temperature were also higher for gamma treated samples, suggesting that values were enhanced by oxidation. However, DMA elastic modulus traces were almost similar for both treatments. The main difference observed for Ca/Zn samples compared with traditional tin samples was the lower ability of the former system in protecting the material against processing conditions.     

Radiation-induced crosslinking of collagen gelatin into a stable hydrogel

Gelatin, the low molecular weight collagen derivative from porcine skin was transformed into a stable permanent hydrogel by γ-radiation. A series of samples with 3% gelatin solution in water were irradiated at doses of 12, 25, 50, 100, 150, 200 kGy at room temperature in the absence of air with a dose rate of 2.2 kGy/h. At low dose gelatin hydrogels incorporating all the available water were obtained. At higher doses above 50 kGy, the gelatin hydrogel samples show a curious shrinking phenomenon due to the relatively high crosslinking density level achieved, so part of the available water is squeezed out from the gel cage. The gelatin hydrogel samples were studied by mass fractionation analysis, by spectrophotometric and polarimetric analysis. Further characterization was made by FT-IR spectroscopy and by thermal analysis (DSC, DTA and TGA) of the dried gelatin samples after irradiation in comparison to a reference untreated sample.     

Formation of monomer residues in PS,PC, PA-6 and PVC upon γ-irradiation

Food packaging polymers, polystyrene (PS), polycarbonate (PC), polyamide-6 (PA-6), and polyvinylchloride (PVC), were irradiated with dose in the range 5–200 kGy. The quantities of corresponding monomer residues (styrene monomer, bisphenol-A, ε-caprolactam, vinyl chloride) released from target materials were analyzed using a SIM mode of GC/MSD. Styrene monomer in PS showed a slight increase from 740 to 777 ppm at 5–30 kGy and then decreased as the dose increased from 30 to 200 kGy. Bisphenol-A in PC was dose independent at the low doses, 5, 10 and 30 kGy, but its level increased from 173 to 473 ppm at 30 kGy and thereafter remained unchanged through 200 kGy. ε-Caprolactam in PA-6 was also dose independent, in the range of 5–200 kGy, but its level (122–164 ppm) was found to be higher than those (71 ppm) of non-irradiated sample. As for PVC, the quantity of vinyl chloride tended to increase from 8 to 18 ppm at 5–200 kGy.     

Degradation behavior of poly (l-lactide-co-glycolide) films through gamma-ray irradiation

Gamma-ray irradiation is a very useful tool to improve the physicochemical properties of various biodegradable polymers without the use of a heating and crosslinking agent. The purpose of this study was to investigate the degradation behavior of poly (l-lactide-co-glycolide) (PLGA) depending on the applied gamma-ray irradiation doses. PLGA films prepared through a solvent casting method were irradiated with gamma radiation at various irradiation doses. The irradiation was performed using 60Co gamma-ray doses of 25–500 kGy at a dose rate of 10 kGy/h.The degradation of irradiated films was observed through the main chain scission. Exposure to gamma radiation dropped the average molecular weight (M_n and M_w), and weakened the mechanical strength. Thermograms of irradiated film show various changes of thermal properties in accordance with gamma-ray irradiation doses. Gamma-ray irradiation changes the morphology of the surface, and improves the wettability. In conclusion, gamma-ray irradiation will be a useful tool to control the rate of hydrolytic degradation of these PLGA films.     

Preparation of the crosslinked polyethersulfone films by high-temperature electron-beam irradiation

The radiation-crosslinked polyethersulfone (RX-PES) films were prepared by means of electron-beam irradiation under nitrogen atmosphere at 230 °C, where the temperature is around the glass transition temperature of PES (222 °C). The gel formation of RX-PES films was observed when the absorbed doses exceeded 300 kGy, which indicated the crosslinking structure formation. The G(S) of 0.10 and G(X) of 0.23 were calculated according to the Y-crosslinking mechanism. The irradiation was also performed at ambient temperature for comparison. There was no gel formation of the irradiated films even for the absorbed doses as high as 2250 kGy. The thermal properties of the original and irradiated PES films were measured by means of DSC and TGA analyses. The chemical structure of the original and the irradiated films was analyzed by means of FT-IR ATR and UV-vis spectroscopies.     

Optimization of electron beam crosslinking of wire and cable insulation

The computer simulations based on Monte Carlo (MC) method and the ModeCEB software were carried out in connection with electron beam (EB) radiation set-up for crosslinking of electric wire and cable insulation. The theoretical predictions for absorbed dose distribution in irradiated electric insulation induced by scanned EB were compared to the experimental results of irradiation that was carried out in the experimental set-up based on ILU 6 electron accelerator with electron energy 0.5–2.0 MeV.The computer simulation of the dose distributions in two-sided irradiation system by a scanned electron beam in multilayer circular objects was performed for various process parameters, namely electric wire and cable geometry (thickness of insulation layers and copper wire diameter), type of polymer insulation, electron energy, energy spread and geometry of electron beam, electric wire and cable layout in irradiation zone. The geometry of electron beam distribution in the irradiation zone was measured using CTA and PVC foil dosimeters for available electron energy range. The temperature rise of the irradiated electric wire and irradiation homogeneity were evaluated for different experimental conditions to optimize technological process parameters. The results of computer simulation are consistent with the experimental data of dose distribution evaluated by gel-fraction measurements. Such conformity indicates that ModeCEB computer simulation is reliable and sufficient for optimization absorbed dose distribution in the multi-layer circular objects irradiated with scanned electron beams.     

Correlation of processing parameters and in situ temperatures for electron beam irradiated polycarbonate

Temperature measurements were performed for polycarbonate samples under electron beam irradiation for a total dose of 200 kGy at different dose fractionations. The samples were irradiated with a commercial electron beam accelerator and total dose was applied at different number of passes under the beam. Peak temperatures by beam heating obtained during irradiation varied significantly with different amounts of energy deposited per pass. For one-pass irradiation (200 kGy), the peak temperature recorded exceeded the polycarbonate's glass transition temperature.     

Evaluation of protein content, lysine and sulfur-containing amino acids content and electrophoretic patterns of soluble proteins for gamma-irradiated semolina before and after milling of durum wheat

Influenced of gamma irradiation (0, 0.25, 1, 2.5, 5 and 10 kGy) on total nitrogen, lysine and sulfur-containing amino acids content and electrophoretic patterns of soluble proteins of semolina was studied. The effect of irradiation before and after milling on previous parameters was also investigated. Protein content of semolina was not affected with gamma irradiation before and after milling. Up to 10 kGy dose, cystine and methionine were not significantly changed, although they increased slightly with increasing irradiation dose. Lysine content decreased significantly (P≤0.05) at irradiation dose higher than 5 kGy. At 10 kGy dose, lysine decreased 5% and 14% for irradiated semolina and that obtained from irradiated wheat grains, respectively. The bands number and intensity of soluble proteins decreased with increasing irradiation dose higher than 5 kGy, as shown on SDS-PAGE electrophoresis. Irradiated semolina and semolina obtained from irradiated wheat grains at 10 kGy showed 13 and 15 bands, respectively. Unirradiated sample showed 19 bands.     

Effect of gamma irradiation on linear low density polyethylene/magnesium hydroxide/sepiolite composite

Radiation crosslinking is generally used to improve the thermo-mechanical properties of the composites. A study has been carried out to investigate the effect of gamma radiation on the thermo-mechanical properties of linear low density polyethylene containing magnesium hydroxide (MH) and sepiolite (SP) as non-halogenated flame retardant additives. The developed composites are irradiated at different doses upto maximum of 150 kGy. Infrared spectra of the irradiated composites reveal the reduction in the intensity of O-H band with increase in the absorbed doses, thus indicates a distinct structural change in MH at higher doses. The thermogravimetric analysis results of unirradiated and composites irradiated at low doses (≤75 kGy) show two steps weight loss, which is changed to single step at higher doses with lower thermal stability. The melting temperature (T_m) and crystallization temperature (T_c) of irradiated composites are lowered with irradiation whereas Vicat softening temperature (VST) is increased. The increasing trend in gel content with increase in the absorbed dose confirms the presence of crosslinked network. The mechanical properties, results show significant improvement in the modulus of irradiated composites. The results also confirm that MH gradually loses its OH functionality with irradiation.     

Quality of fresh-cut Iceberg lettuce and spinach irradiated at doses up to 4 kGy

Fresh-cut Iceberg lettuce packaged in modified atmosphere packages and spinach in perforated film bags were irradiated with gamma rays at doses of 0, 1, 2, 3, and 4 kGy. After irradiation, the samples were stored for 14 days at 4 °C. O₂ levels in the packages of fresh-cut Iceberg lettuce decreased and CO₂ levels increased with increasing radiation dose, suggesting that irradiation increased respiration rates of lettuce. Tissue browning of irradiated cut lettuce was less severe than that of non-irradiated, probably due to the lower O₂ levels in the packages. However, samples irradiated at 3 and 4 kGy had lower maximum force and more severe sogginess than the non-irradiated control. In addition, ascorbic acid content of irradiated lettuce was 22–40% lower than the non-irradiated samples after 14 days of storage. The visual appearance of spinach was not affected by irradiation even at a dose of 4 kGy. Consumer acceptance suggested that more people would dislike and would not buy spinach that was treated at 3 and 4 kGy as compared to the non-irradiated sample. Overall, irradiation at doses of 1 and 2 kGy may be employed to enhance microbial safety of fresh-cut Iceberg lettuce and spinach while maintaining quality.     

Radiation-induced degradation of butyl rubber vulcanized by three different crosslinking systems

Butyl rubber (IIR) is an isobutylene/isoprene copolymer and is provided with good properties including low permeability to gases, good thermal stability and high resistance to oxygen and ozone action, among others. It is well known that the major effect of ionizing radiations on butyl rubber is chain scission accompanied with a significant reduction in molar mass. This work aimed to study the effects of gamma radiation on the properties of butyl rubbers vulcanized by three different curing systems, such as, the ones based on sulfur, sulfur donor and phenolic resin to identify which curing system is the most stable under irradiation. The butyl rubber vulcanized by three different systems was gamma irradiated with doses of 25 kGy, 50 kGy, 100 kGy, 150 kGy and 200 kGy. Irradiated and non-irradiated samples were characterized by the following techniques: tensile, elongation and hardness. It was observed that doses higher than 150 kGy practically destroy the assessed properties for all butyl compounds, irrespective of the vulcanization system used; however compounds cured with phenolic resin showed a decrease in properties proportional to the dose.     

Effect of ionizing radiation on physicochemical and mechanical properties of commercial monolayer and multilayer semirigid plastics packaging materials

Tensile testing, overall migration tests and sensory tests were used to evaluate the effects of gamma irradiation (5–60 kGy) on six commercial semirigid packaging materials. The monolayer and multilayer materials in sheet or bottle form were: polystyrene (PS), polypropylene (PP), polyvinyl chloride/high-density polyethylene (PVC/HDPE), polyethylene terepthalate (PET), HDPE/polyamide (HDPE/PA) and HDPE. In terms of mechanical strength, PET was the most radiation-resistant material, while the HDPE monolayer and multilayer showed some degradation after 60 kGy. PS was slightly affected after 30 kGy, whereas PP was severly degraded and became very brittle. Generally, there was no change in overall migration at lower doses; at higher doses migration from PP tended to increase, while migration from HDPE/PVC tended to decrease. Odor and taste transfer as well as discoloration were observed with most plastics, especially at higher doses, and it is concluded that these tests are a sensitive and important quality control tool for evaluating irradiated packaging materials.     

Polypropylene nanogel: “Myth or reality”

The objective of this work is the investigation of the nanogel and microgel formation in modified PP. The modified PP in pellets was synthesized by gamma irradiation of pristine PP under a crosslinking atmosphere of acetylene in dose of 5, 12.5 and 20 kGy, followed by thermal treatment for radical recombination and annihilation of the remaining radicals. The thin film gel of the polypropylenes was obtained by extraction in boiling xylene for period of 12 h at 138 °C, followed by decantation in beaker at room temperature of 25 °C with the total volatilization of the xylene and deposition of dried material film on glass substrate under agitation by Settling process. The thin film gel formed of pristine PP and modified PP (i.e., irradiated) was characterized using scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and differential scanning calorimetry (DSC). The PP morphology indicated the nanogels and microgel formation with increase of spherulitic concentration and crystallinity at dose of 12.5 kGy.     

Physico-chemical changes taking place in gamma irradiated bovine globulins studied by thermal analysis

Structural transformations induced in gamma and alpha globulins under influence of gamma irradiation using doses of 2.5 and 24 kGy were studied by differential scanning calorimetry (DSC) and thermogravimetry (TG, DTG). Thermal decomposition of the globulins irradiated in water suspensions occurs at higher temperatures, in comparison to the reference non-irradiated samples. This was related to formation of covalent linkages in the irradiated proteins, apart to chemical changes induced in amino-acids. Essential modification of thermal decomposition was detected already after irradiation with a dose of 2.5 kGy performed for water suspensions. Irradiation of solid native proteins induces decrease in decomposition temperature and gives evidence of proteins degradation.     

Electrical behaviour of butyl acrylate/methyl methacrylate copolymer films irradiated with 1.5 MeV electron beam

Electrical conductivity and dielectric parameters of the (BuA/MMA) copolymer films irradiated with 1.5 MeV electron beam (EB) have been studied. The samples were irradiated with different doses of the electron beam: 5, 10, 50, 125 and 200 kGy. The electrical conductivity of the samples was found to decrease as the irradiation dose increases. The temperature dependence of the direct current (dc) conductivity for unirradiated and irradiated samples has been obtained over a temperature range from 293 to 373 K. The activation energy values were calculated for all samples. Moreover, measurements of the dielectric constant, dielectric loss and alternating current (ac) conductivity were performed at a frequency range from 100 Hz to 5 MHz at room temperature. The results indicated that the EB irradiation has formed some traps in the energy gap, which reduce the movement of the charge carriers. Furthermore, a direct proportional relationship between the activation energy and the irradiation dose was estimated in two regions: below and above the glass transition temperature of the polymer. Dipole relaxation was observed in the samples, and the dose effect was found to shift this relaxation towards higher frequencies.     

Sorption of europium on a MX-80 bentonite sample: experimental and modelling results

The EDXRF technique offers simultaneous detection and determination of multiple trace elements in F₃ generation seed of Cicer arietinum L. plant, developed from irradiated group of 0.05, 0.10, 0.15 kGy and 0.20 kGy using ⁶⁰Co gamma source (0.12 kGy/h). The accumulations of elements in edible seeds were significantly different (p ≤ 0.05) in different absorbed dose. Out of 14 elementals (S, Cl, K, P, Ca, V, Mn, Fe, Co, Cu, Zn, Rb, Sr and Cd), the accumulations of K, P, Ca, S, Cu, Zn, Mn, Fe, Cd, Rb, Sr and Cl were increased in seed with in the dose range of 0.15–0.20 kGy, except V and Co. Also, the yielding potentials of seeds were increased with in the dose range of 0.15–0.20 kGy.     

Effect of electron beam irradiation on dynamic mechanical,thermal and morphological properties of LLDPE and PDMS rubber blends

The effect of electron beam irradiation on the blends of linear low-density polyethylene (LLDPE) and poly dimethyl siloxane rubber (PDMS) prepared over a wide range of compositions starting from 70:30 to 30:70 (LLDPE: PDMS) by varying the radiation doses from 50 to 300 kGy has been studied. The dynamic modulii and dielectric strength of the blends increase on irradiation at 100 kGy as compared to that for the unirradiated blends. Degree of crystallinity and melting behaviour remain unchanged upon irradiation upto a dose of 100 kGy, beyond which it decreases. Thermal stability increases with increase in the proportion of PDMS rubber in the blend as well as on irradiation at 100 kGy. The phase morphology of the blends examined under the SEM exhibit two phase morphology before electron beam irradiation, whereas single phase morphology is observed after electron beam irradiation due to intra- as well as inter-molecular crosslinking leading to a miscible system.     

High-energy radiation forming chain scission and branching in polypropylene

The degradation of high molecular weight isotactic polypropylene (iPP) subjected to gamma rays irradiation up to 100 kGy in inert atmosphere was analyzed. The investigation relied upon complex viscosity, elastic modulus, gel fraction, morphology of the insoluble fraction and deconvoluted molecular weight distribution (MWD) curves. At low irradiation doses, already at 5 kGy, the MWD curve is strongly shifted to the low molecular weight side showing chain scission, which is confirmed using the calculated chain scission distribution function (CSDF). At high dose levels, the appearance of a shoulder in the high molecular weight side of the MWD curve indicates the formation of chain branching. The presence of a considerable insoluble fraction at these high dose levels indicates also the formation of cross-linking, which has different morphology then the insoluble fraction present in the original iPP. The rheological results show changes in the molecular structure of irradiated samples in agreement with the gel content data. The chromatographic and rheological data has shown that gamma irradiation of iPP produces chain scission, branching and cross-linking.     

Determination of the changes of antifungal properties of Satureja hortensis,Thymus vulgaris and Thymbra spicata exposed to gamma irradiation

In this research, changes in the antifungal activity of the extract of Satureja hortensis, Thymus vulgaris and Thymbra spicata exposed to gamma irradiation against two aflatoxigenic moulds Aspergillus parasiticus NRRL 2999 and 465 were investigated. The samples of dry plant leaf powder were irradiated with doses of 1.2, 3.0, 5.1 kGy. While the antifungal activity of S. hortensis with 0 and 1.2 kGy dose irradiation against A. parasiticus NRRL 2999 was found to be similar, it decreased with 3.0 and 5.1 kGy irradiation doses (P<0.05). On the contrary, antifungal activity of T. spicata increased until 3.0 kGy and then it decreased with 5.1 kGy irradiation dose (P<0.05). For T. vulgaris, an increase of irradiation dose resulted in a decrease of antifungal activity against aflatoxigenic moulds. This research shows that antifungal properties of some spices can be changed by gamma 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.