List of papers presented (oral and poster) at the Third Asian Photochemistry Conference (APC-2002) incorporating the Sixth Trombay Symposium on Radiation (original) (raw)
Related papers
Polymerization Reactions and Modifications of Polymers by Ionizing Radiation
Polymers, 2020
Ionizing radiation has become the most effective way to modify natural and synthetic polymers through crosslinking, degradation, and graft polymerization. This review will include an in-depth analysis of radiation chemistry mechanisms and the kinetics of the radiation-induced C-centered free radical, anion, and cation polymerization, and grafting. It also presents sections on radiation modifications of synthetic and natural polymers. For decades, low linear energy transfer (LLET) ionizing radiation, such as gamma rays, X-rays, and up to 10 MeV electron beams, has been the primary tool to produce many products through polymerization reactions. Photons and electrons interaction with polymers display various mechanisms. While the interactions of gamma ray and X-ray photons are mainly through the photoelectric effect, Compton scattering, and pair-production, the interactions of the high-energy electrons take place through coulombic interactions. Despite the type of radiation used on mat...
Progress in radiation processing of polymers
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2005
Modification in polymeric structure of plastic material can be brought either by conventional chemical means or by exposure to ionization radiation from ether radioactive sources or highly accelerated electrons. The prominent drawbacks of chemical cross-linking typically involve the generation of noxious fumes and by products of peroxide degradation. Both the irradiation sources have their merits and limitations. Increased utilization of electron beams for modification and enhancement of polymer materials has been in particular witnessed over the past 40 years. The paper highlights several recent cases of EB utilization to improve key properties of selected plastic products. In paper is provided a survey of radiation processing methods of industrial interest, encompassing technologies which are already commercially well established, through developments in the active R&D stage which show pronounced promise for future commercial use. Radiation cross-linking technologies discussed include: application in cable and wire, application in rubber tyres, radiation vulcanization of rubber latex, development of radiation crosslinked SiC fiber, polymer recycling, development of gamma compatible pp, hydrogels etc. Over the years, remarkable advancement has been achieved in radiation processing of natural polymers. Role of radiation in improving the processing of temperature of PCL for use as biodegradable polymer, in accelerated breakdown of cellulose into viscose and enhancement in yields of chitin/chitosan from sea-food waste, is described.
Effects of Gamma Radiation on Polymer in Solution. II. Poly(Vinyl Methyl Ether)
Bulletin of the Institute for Chemical Research, Kyoto University, 1962
Dilute aqueous solutions of poly(acrylic acid) in acid form and in sodium-salt form have been irradiated with gamma-rays from a Co-60 source both in the presence and in the absence of air. Changes in gelation dose and viscosity have been measured. On irradiation in the absence of air, gel-formation was observed, and both the gelation dose and the critical concentration for gel-formation increased as the degree of neutralization of polymers increased. The critical concentrations were 0.25, 0.30, 0.56 and 1.0 wt. %, for polymers with degrees of neutralization of 0, 5, 10 and 20%, respectively. When NaC1 was added to the solution for irradiation so as to diminish the ionization of carboxyl groups, gelation occurred more readily with increasing NaC1 concentration, if the NaC1 concentration was relatively low. However, as the concentration of NaC1 became higher than O.O1N, gel-formation was increasingly suppressed with increasing NaC1 concentration. This fact demonstrates that there is an optimum expansion of polyion for crosslinking in aqueous solution. On irradiation in the presence of air, the polymer appeared to degrade exclusively. The higher the degree of neutralization, the higher the degree of degradation. If, however, NaCl was present sufficiently in the solution for irradiation, degradation did not occur practically.
Bulletin of the Institute For Chemical Research Kyoto University, 1963
When polyvinyl acetate (PVAc) was subjected to gamma radiation in various organic solvents at a concentration of 10 weight %, the polymer resulted in crosslinking in methanol and benzene, but in many other organic solvents degradation occurred predominantly. As the solvents became poorer, crosslinking was promoted at low concentrations but retarded at high concentrations of the polymer. The most optimum concentration for crosslinking of the polymer in methanol solution was about 20%, where it was found that degradation hardly ever occurred. When PVAc was irradiated in methanol-organic solvent mixtures, the rate of crosslinking was retarded as the solubility of the polymer in solution was raised. However, in methanol-water mixtures, no correlation was observed between the radiation-induced changes and the solubility, but the rate of crosslinking increased monotonically with increasing water content in the mixtures, which may indicate that water is a very effective solvent for crosslinking. The radiation-induced changes were very slight during irradiation at-50°C but relatively large at 70°C. The minimum doses needed for gelation in the 10% benzene solutions were inversely proportional to the degree of polymerization of the initial polymer. It was directly confirmed that the density of crosslinked units was proportional to the radiation dose, and that crosslinks were formed not only from the main chain radicals (not end radicals), but also from the side chain radicals.
Bulletin of the Institute for Chemical Research, Kyoto University, 1962
Dilute aqueous solutions of poly(acrylic acid) in acid form and in sodium-salt form have been irradiated with gamma-rays from a Co-60 source both in the presence and in the absence of air. Changes in gelation dose and viscosity have been measured. On irradiation in the absence of air, gel-formation was observed, and both the gelation dose and the critical concentration for gel-formation increased as the degree of neutralization of polymers increased. The critical concentrations were 0.25, 0.30, 0.56 and 1.0 wt. %, for polymers with degrees of neutralization of 0, 5, 10 and 20%, respectively. When NaC1 was added to the solution for irradiation so as to diminish the ionization of carboxyl groups, gelation occurred more readily with increasing NaC1 concentration, if the NaC1 concentration was relatively low. However, as the concentration of NaC1 became higher than O.O1N, gel-formation was increasingly suppressed with increasing NaC1 concentration. This fact demonstrates that there is an optimum expansion of polyion for crosslinking in aqueous solution. On irradiation in the presence of air, the polymer appeared to degrade exclusively. The higher the degree of neutralization, the higher the degree of degradation. If, however, NaCl was present sufficiently in the solution for irradiation, degradation did not occur practically.
Radiation and environmental biophysics, 2018
The present article focuses on the influence of gamma irradiation and post-irradiation storage conditions on FT-IR spectra of 1 mm thick polystyrene irradiated with 51, 77 and 129 kGy. The increase in amplitude corresponding to 3600, 3400 and 2100 cm stretching frequencies clearly showing the formation of O-H and C=O bonds (~ 25%). On prolonged storage (2160 h) in the dark, there is an increase in O-H group (~ 28%). The electron cloud facilitates the formation of hydroxyl group in irradiated polystyrene. The post-irradiation treatment with heat conversely showed a reduction of O-H, C-H and C=O (9-16%) groups due to radical-radical recombination at higher temperatures and light intensities. This investigation finds its applications in memory devices, optical sensors, radiation dosimetry and different space and radiation facilities.
The study of gamma irradiation effects on poly (glycolic acid)
Radiation Effects and Defects in Solids, 2015
We have investigated the effects of gamma irradiation on chemical structure, thermal and morphological properties of biodegradable semi-crystalline poly (glycolic acid) (PGA). PGA samples were subjected to irradiation treatment using a 60 Co gamma source with a delivered dose of 30, 60 and 90 kGy, respectively. Gamma irradiation induces cleavage of PGA main chains forming ∼ OĊH 2 andĊH 2 COO ∼ radicals in both amorphous and crystalline regions. The free radicals formed in the amorphous region abstract atmospheric oxygen and convert them to peroxy radicals. The peroxy radical causes chain scission at the crystal interface through hydrogen abstraction from methylene groups forming the ∼ĊHCOO ∼ (I) radical. Consequently, the observed electron spin resonance (ESR) doublet of irradiated PGA is assigned to (I). The disappearance of the ESR signal above 190°C indicates that free radicals are formed in the amorphous region and decay below the melting temperature of PGA. Fourier transform infrared and optical absorption studies confirm that the COO [-C-O-] O groups are not influenced by gamma irradiation. Differential scanning calorimetry (DSC) studies showed that the melting temperature of PGA decreased from 212°C to 202°C upon irradiation. Degree of crystallinity increased initially and then decreased with an increase in radiation as per DSC and X-ray diffraction studies. Irradiation produced changes in the physical properties of PGA as well as affecting the morphology of the material.
Ionizing Radiation-Induced Polymerization
Ionizing Radiation Effects and Applications, 2018
Ionizing radiation can induce some kinds of reactions, other than polymerization, such as dimerization, oligomerization, curing, and grafting. These reactions occur through a regular radical chain causing growth of polymer by three steps, namely, initiation, propagation, and termination. To understand ionizing radiation-induced polymerization, the water radiolysis must be taken into consideration. This chapter explores the mechanism of water molecules radiolysis paying especial attention to the basic regularities of solvent radicals' interaction with the polymer molecules for forming the crosslinked polymer. Water radiolysis is the main engine of the polymerization processes, especially the "freeradical polymerization." The mechanisms of the free-radical polymerization and crosslinking will be discussed in detail later. Since different polymers respond differently to radiation, it is useful to quantify the response, namely in terms of crosslinking and chain scission. A parameter called the G-value is frequently used for this purpose. It represents the chemical yield of crosslinks, scissions and double bonds, etc. For the crosslinked polymer, the crosslinking density increases with increasing the radiation dose, this is reflected by the swelling degree of the polymer while being immersed in a compatible solvent. If crosslinking predominates, the crosslinking density increases and the extent of swelling decreases. If chain scission predominates, the opposite occurs. A further detailed discussion of these aspects is presented throughout this chapter.
Radiation Processing of Polymers for Medical and Pharmaceutical Applications
Macromolecular Symposia, 2015
The use of ionizing radiation for the preparation of polymeric biomaterials is one of the examples of the application of atomic energy for the benefit of humanity. Radiation processing is based on the use of high energy ionizing radiation to induce chemical and biological changes in irradiated systems. High energy electron (EB) under 10 keV and gamma irradiation are the most frequently used of ionizing radiation for synthesis, modification of polymers, and sterilization of medical devices. Potential biomedical and pharmaceutical applications of these polymers are implants, topical dressings, injectable formulations, drug delivery devices, diagnostic assays, and immobilized enzyme. Through radiation crosslinking or degradation processes, polymers with specific characteristics can be prepared. The advantages of radiation processing include the absent of any chemical residues (since no chemical additives are requires to initiate the reactions), can be used at all temperatures, can be limited to the surface only and in certain cases, the synthesis/modification of materials can be combined with sterilization.