Gamma irradiation under vacuum

Table 3. Yield of evolved gases from aromatic polymers by gamma irradiation under vacuum...

Table 11.20. Effect of gamma irradiation under vacuum on LLDPE/PA-6 blends [Spadaro et al., 1993 Valenza et al., 1994]...

The samples were irradiated under vacuum or in air at the desired temperature using 60Co gamma radiation (Nordian Gammacell-220) at a dose rate of approximately 7 kGy h"1. 

Rizzo et al. [1983] investigated changes in the physico-chemical properties caused by gamma irradiation of LDPE/PP blends (100 0, 75 25, 50 50, 25 75, and 0 100) (Table 11.9). On irradiation of the individual polymers with 1500 kGy dose, the gel fraction was obtained as 95% in LDPE and 65% in PP. On irradiation of the blends the gel fraction increased with the LDPE-content and dose. On irradiation under vacuum, the crosslinking reactions predominated in LDPE, as discussed in Section 11.3.1. In the case of PP, accumulation of unsaturation with increasing dose contributes to extensive crosslinking at the high dose used here (1500 kGy), as discussed in Section 11.3.2. 

The change of wear resistance by rubbing test was shown in Figure 12.11 for a PSF sheet specimen irradiated by gamma rays under vacuum. The wear resistance increased with a dose at a small... 

The molecular modifications induced in an isotactic PP gamma-irradiated in vacuum under a complete set of experimental conditions are studied by means of calorimetric analysis. The influence of the irradiation parameters, the total absorbed dose, D, and the dose rate, 1, has previously been analysed and a simple kinetic model based on the rates of the main reactions occurring during irradiation, i.e. beta-scission, addition to double bonds and termination, was also discussed. It is shown how thermal analysis confirms the model forecasts and in particular the existence of the inversion conditions below them the main effect is molecular degradation, while above them the main effects are chain-branching and crosslinking. 12 refs. 

Irradiation Conditions. The gamma (cobalt-60) radiation facility and the source calibration are described by Holm and Jarrett (4). Irradiation temperature was 21 (initial) - 40°C (final). The gamma source was calibrated with the ferrous sulfate/cupric sulfate dosimeter for a dose rate of 8 X 102 rads per second. Pouches were fabricated from multilayered materials and then irradiated while empty. The container used to hold the multilayered materials and the empty pouches during irradiation was a large size, flexible package that was sealed under vacuum prior to the irradiation. 

Powdered samples for cobalt-60 7-irradiation were evacuated for 24 hr and sealed under vacuum. They were then irradiated at ambient temperature in a Co-60 Gamma Cell-220 radiation unit operating at a dose rate of 0.210 Mrad/hr. 

The polymer was dissolved in acetone, precipitated into methanol, and then dried in a vacuum oven at 35 "C for 24 hr. The powdered polymers (20-40 mg) were placed in glass ampoules, degassed at less than 10 4 mm Hg for 40 hr at ambient temperature and then sealed under vacuum. The samples were irradiated in a 60Co Gamma-cell at a dose rate of 0.29 Mrad/hr at ambient temperatures (25-30 C). Absorbed doses up to 10 Mrad were used. 

Mixtures of sulfur dioxide (S02) and 2-methyl-1-pentene (2M1P) were prepared by (1) bubbling sulfur dioxide into a NMR tube containing 2-methyl-1-pentene at -78 °C, and (2) condensing sulfur dioxide and 2-methyl-1-pentene into a NMR tube which was sealed under vacuum. Mole ratios for the 2M1P/S02 mixtures of 20 1 (method (1) above) and 1 1 (method (2)) were prepared and the samples irradiated in the Co gamma-cell. 

Irradiation. All irradiations were performed at the University of Maryland with a 25,000 curie cobalt 60 gamma source. The absorbed dose rate of 1.2 Mrad per hr was determined by ferrous sulfate dosimetry. All samples were irradiated under secondary electron equilibrium conditions. Following irradiation, all samples irradiated in vacuum were annealed in vacuum at 380 K for 24 hours this treatment reduces the long-lived radical concentration to undetectable levels. 

Acrylonitrile, styrene, and isobutylene were irradiated at low temperatures in binary mixtures with either low molecular weight compounds or polymers. The reagents were mixed at room temperature, sealed under vacuum, and the resulting liquid or swollen polymer was rapidly cooled to the irradiation temperature. Irradiations were carried out with cobalt-60 gamma-rays at a dose rate of 2000 rads/min. After irradiation the samples were warmed to room temperature under two different standard conditions. The sealed ampoules were either immersed in a water bath at 25 °C. immediately after irradiation or first opened at —196°C. and then stirred in a large excess of warm acetone. The polymer was separated and dried to constant weight. 

Torikai et al. [1994] compared the effects of gamma irradiation of films of PS/PMMA blends and PS-PMMA copolymer (co-PS-PMMA) (Table 11.9). Polymer films were cast from methylene chloride solutions and were dried under vacuum. Based on the UV and FTIR spectroscopy, and viscosity measurements, Torikai et al. [1994] concluded that whereas the presence of PS in the copolymer provided protection against radiation-induced degradation to the PMMA units, similar... 

Nguyen and Kausch [1984] found that the presence of phenyl groups in poly(styrene-co-acrylo-nitrile), SAN, protects PMMA in the blend, during radiolysis (Table 11.9). SAN and PMMA were dissolved in dimethyl formamide, 50- J,m-thick films were cast, and then dried under vacuum. Transparent bar specimens were compression-molded from the film. Mixing the polymers by co-precipitation from methanol resulted in opaque samples. Gamma irradiations were done in evacuated and sealed glass tubes, at a dose rate of 3 kGy/h. Comparison of freshly irradiated samples with irradiated and annealed ones showed the absence of any post-irradiation effects. 

The samples for SANS were prepared by dissolving 30 wt% PSD and 70 wt% PVME in toluene. A thin film (0.1 mm) was cast and dried under vacuum. Disks were cut from the film, stacked and hot pressed at 120°C into spacer rings. The disks were sealed under high vacuum and gamma irradiated to 1250 kGy at 45°C. 

The samples for crosslinking kinetic studies were cast into thicker films (0.5 mm), sealed under high vacuum and gamma irradiated to 40 kGy. GPC (gel permeation chromatography) analyses of the irradiated samples suggested that chain scission for both PSD and PVME was minor. FTIR analyses indicated mutual grafting of PSD and PVME. The inverse of the spinodal temperatures obtained (Table 11.57) varies linearly with dose, and inversely with (number of monomers between crosslinks), as predicted by de Gennes... 

Gas Evolution from Polycarbonate by °Co Gamma Ray Irradiation with a Dose Rate of 10 kGy/h at 25 C and 150°C under Vacuum... 

Generally, the irradiation effects of polymers under vacuum or in an inert gas atmosphere are not different between gamma rays and accelerated EB irradiation. For PC, it was confirmed that the irradiation effects including hardness and wear resistance by EB were the same with those by gamma ray irradiation even at 150°C. However, the dose profile was different between gamma rays and EB for thick polymer materials, because the EB penetration depth into polymer materials depends on the EB acceleration voltage. 

Besides the normal hazards associated with liquid hydrogen there is the possibility of air leaking into the vacuum space and solidifying on the outside of the moderator chamber, which under gamma irradiation could lead to the production of ozone and a spontaneous ozone explosion followed by a liquid-hydrogen explosion. To prevent damage to the reactor such an explosion must be contained by the vacuum vessel and vented to the outside of the reactor shield. 

Controlled preparation of thin films of P(DiAc)s can be obtained by topochemical (solid state) polymerization of thin films of monomer previously deposited by evaporation under high vacuum, followed by UV or gamma irradiation [569] such thin films possess high order and alignment. Variation of the substrate crystallinity yields thin films or crystals of varying crystallinity [569]. Innovative methods, such as application of pressure on a mobile monomer phase between two optical plates... 

This work shows the application of quantitative pyrolysis-gas chromatography coupled with infrared spectroscopy and electron impact mass spectrometry in the study of radiation-induced scission of bisphenol-A polycarbonate (PC). PC under vacuum was gamma-irradiated using a 60Co source in the dose range from 0.125 to 1.0 MGy. This was followed by flash pyrolysis under an inert atmosphere observed by GC-FTIR-MS. Pyrolysis of the irradiated PC gave different products depending on the dose. Yields of carbon dioxide and methane decreased with dose whereas those of phenol and 4-methylphenol increased. The yields of benzene and toluene were unaffected by irradiation. Analysis of the products in this study helped to infer two main pathways for the radiation-induced scission of PC that involve carbonate bond rupture or aliphatic-aromatic bond rupture. 30 refs. 

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