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Zastosowanie chemii radiacyjnej w modyfikacji materiałów i ochronie środowiska

Chmielewski A.G.

Wiadomości Chemiczne

2007

[Z] 61, 7-8

515-546

Radiation chemistry is a part of the physical chemistry similary like photo-chemistry, plasma-chemistry, ultrasonic-chemistry etc. Ionizing radiation produces abundant secondary electrons. Following these primary events, the ions, secondary electrons and excited molecules undergo further transformations, exchanging charges and energy and reacting with surrounding molecules, thereby producing free radicals and other reactive species which finally evolve into new stable products. Three main sources of radiation are applied for radiation processing]. These are electron accelerators], gamma sources and X-ray unit based on e-/X conversion process. Radiation processing was used early on for polymer modification. The intermediates formed during material irradiation can follow several reaction paths that result in disproportion, hydrogen abstraction, arrangements and/or the formation of new bonds. Nowadays, the modification of polymers covers radiation cross-linking, radiation-induced polymerization (graft polymerization and curing) and the degradation of polymers. Some polymers predominantly undergo crosslinking other degradation. However new techniques allow crosslinking of polymers which were considered to be degradable only, like PTFE and cellulose derivatives. Regarding natural polymers the biggest application concerns rubber pre-crosslinking in tire industry. The processing of natural polymers is also being developed to elaborate new biodegradable materials. The radiation crosslinked wires and cables show excellent heat resistance (long-term thermal stability and short-term thermal stability) as well as abrasion resistance. Other big application is crosslinking of XLPE type pipes which are widely used for hot water and floor heating. Polybutelene terephtalate (PBT), which is a plastic for electronic industry, can be crosslinked by radiation and lead free soldering materials can be applied in such a case. This method of crosslinking is also applied to manufacture thermoshrinkable tubes and types possessing "memory effect". Through radiation, grafting metal adsorbents and ion exchange membranes can be developed. Radiation is early applied tool in the area of nanomaterials engineering; arrangement of atoms and ions has been performed using ion or electron beams for many years. New trends concern surface curing and development of ion track membranes and controlled release drug-delivery systems. Finally, radiation processing concerns gem stones colorization, development of high temperature resistant fibers (SiC) and semiconductor modification. Over the past few years, radiation processing technologies aimed at ensuring the safety of gaseous and liquid effluents discharged to the environment have been developed. It has been demonstrated that radiation processing based technologies for flue gas treatment (SOX and NOX removal), wastewater purification, and sludge hygienization can be effectively deployed to mitigate environmental degradation. Electron beam technology is among the most promising advanced technologies of new generation. This is a dry-scrubbing process of simultaneous SO2 and NOx removal, where no waste except the fertilizer by-product are generated.The other possibility is application of the process for VOC removal. Tests at the pilot plant constructed at a coal-fired power station were performed with the purpose of estimating the influence of electron beam on VOCs present in flue gas, during SO2 and NOx removal. The removal efficiencies have been ranged from 40% up to 98%. The chlorocarbons including dioxins may be removed with high efficiency as well. During the radiolysis of water reactive radicals of strong oxidizing or reducing properties are formed that can transform the pollutants in the liquids wastes. A large number of substances such as hard surfactants, lignin, pesticides cannot be degraded by conventional biochemical methods and thus escape from decomposition in biological treatment. Research and industrial treatments testify significant improvement of pollutant biodegradability after radiation-oxidation in aerated wastewater.