Electron beam treatment

FIGURE 3.64 Reactions on hydrocarbon pol3mer chains induced by e-beam radiation. 

The electron beam technique has often been utilized for surface modification and properly improvement of polymer materials like fibers, films, plastics, and composites in recent decades [104-107]. It may remove surface impurities and alter surface chemical characteristics at an appropriate irradiation condition. Electron beam processing is a dry, dean, and cold method with advantages such as energysaving, high throughput rate, uniform treatment, and envirorunental safety. 

The cellulose component of natural fibers may be degraded or cross-linked upon electron beam irradiation of high energy [108]. The chain sdssion of cellulose may occur at higher irradiation dosage and it may cause deterioration in the mechanical properties of natural fibers [14,109,110]. The irradiation may considerably change the structure, reactivity, physicochemical, and mechanical properties of cellulose. 

Electron beam treatment of natural fibers of interest is carried out before biocomposite fabrication. A relatively large amount of raw natural fibers, bundles, and/or woven fabrics contained and spread in a polyethylene bag can be irradiated separately or simultaneously. Different levels of electron beam dosages, for example, from 1 to 100 kGy, or even higher, may be applied. Use of too high intensity of electron beam may cause some damages and microstructural defects of the natural fibers, resulting in deterioration of their mechanical properties. Eventually, the treatment effect on the property improvement of biocomposites may depend on the treatment level, as reported earlier with different natural fiber/polymer biocomposite systems by Cho et al. [105, 107-110, 112]. The electron beam irradiation processes can normally be performed at ambient temperature in air. 

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Some physical techniques can be classified into flame treatments, corona treatments, cold plasma treatments, ultraviolet (UV) treatment, laser treatments, x-ray treatments, electron-beam treatments, ion-beam treatments, and metallization and sputtering, in which corona, plasma, and laser treatments are the most commonly used methods to modify silicone polymers. In the presence of oxygen, high-energy-photon treatment induces the formation of radical sites at surfaces these sites then react with atmospheric oxygen forming oxygenated functions. 

Fig. 1 also shows the chemical reaction mechanism of 80, and NO c in air for producing acid rain [2]. The radicals (O, OH, and HO2) produced in air play an important role in oxidizing 80, and to produce sulfuric acid and nitric acid, which are the main components of acid rain. 8ome of these reactions also occur in a reaction chamber of electron beam treatment of flue gas. 

The energy, or power, of electron beam induced in the flue gas is divided and absorbed by their gas components roughly depending on their electron fraction. Therefore almost all the energy is absorbed by the main components of the flue gas, namely, N2, O2, CO2, and H2O. Table 2 shows a typical concentration of the components in coal-fired flue gas in Japan. The ratio of the total number of electrons in each gas components is also listed in the same table. The energy absorbed directly by the toxic components (SO2 and NO) is negligibly small. For electron beam treatment of flue gas, ammonia gas is added to the flue gas before the irradiation. The amount of ammonia is usually set as stoichiometrically, i.e., 2A[S02] + A[NO], where A[S02] and A[NO] are the concentrations of SO2 and NO intended to be treated, respectively. The concentration of ammonia is usually higher than the initial concentration of SO2 and NO however, it is still far lower than that of the main components. 

These positive ions are the main source of the OH radical, which is one of the most important radicals for electron beam treatment of flue gas as will be discussed in the next section. 

The flue gas from municipal waste incinerator boilers contains SO2, and HCl. To remove these harmful components simultaneously by dry process, electron beam treatment method was investigated. The pilot-scale test was conducted in Matsudo, Japan, in 1992 with a flue gas of 1000 m /hr [34]. Recently, dioxins, namely, poly-chlorinated-di-benzo-paradioxins (PCDDs) and poly-chrorinated-di-benzo-furan (PCDFs), from incinerators have become a very serious problem because of their high toxicity. Pilot-scale tests to decompose dioxins by electron beam irradiation were conducted in Karlsruhe, Germany [35], and in Takahama, Japan [36], using almost the same capacity of flue gas, 1000 m /hr. Very promising results were obtained with decomposing more than 90% of dioxins. 

Kurucz, C., Cooper, W.J., Nickelsen, M.G., and Waite, T.D., Full-scale electron beam treatment of hazardous waste, in Proc. of the 45th Industrial Waste Conference, Purdue University, West Lafayette, IN, 1990, pp. 539-545. 

Tobien T, Cooper WJ, Nickelsen MG, Pernas E, O Shea KE, Asmus K-D. Odor control in wastewater treatment the removal of thioanisole from water— a model case study by pulse radiolysis and electron beam treatment. Environ Sci Technol 2000 34 1286-1291. 

In the preceding sections, the reader got acquainted with a few basic concepts on the remediation of water pollution by injecting energy in water and its latest developments. The Electron beam treatment is a physico-chemical method which pursues the rehabilitation of polluted waters by the oxidative action of the OH radical, and we saw that the methods for OH generation distinguishe various Advanced Oxidation Processes. 

The thioether alone at room temperature does not protect polypropylene from loss of physical properties after electron-beam treatment, although irradiated samples that are subsequently heated to 150°C are apparently protected from thermal oxidation. 

As a generalisation, electron beam treatment creates similar effects to gamma irradiation, but usually on slightly reduced scale, since depth of penetration is less. 

Several reactor types have been suggested for industrial application. One of the best designs is shown in O Pig- 23.15. The injected wastewater forms a wide continuous layer, which is irradiated by a transverse electron beam. The thickness of the water jet is tied to the beam energy, i.e., to the penetration of the accelerated electrons. The width of the water jet corresponds to the width of the beam window. The water jet type reactor makes possible electron beam treatment at high rates of wastewater flow (Haji-Saeid 2007). 

Emmi SS, Takacs E (2008) Water remediation by electron-beam treatment. In Spotheim-Maurizot M, Mostafavi M, Douki T, Belloni J (eds) Radiation chemistry from basics to applications in material and life scienas. EDP Sciences, Paris, pp 87—95 Farkas J (2004) Food irradiation. In Mozumder A, Hatano Y (eds) Charged particle and photon interactions with matter chemical, physicochemical and biological consequences with applications. N cel Dekker, New York, pp 785-812 Farkas J (1988) Irradiation of dry food ingredients. CRC, Boca Raton... 

A final technique that has been utilized to chemically remove residual styrene in PS is radiation treatment. Both beta (e-beam) and gamma radiation have been tried. E-beam appears to be the most effective form of radiation and is most suitable for continuous use (319,320). The e-beam ruptures C—H bonds, resulting in the formation of PS radicals. These radicals are very reactive and scavenge unreacted monomer. However, if no styrene is in the vicinity of the PS radical, it can do other things such as couple with another PS radical or react with oxygen. Currently, electron beam treatment of polymers is used commercially for elastomer cross-linking (wire/cable coatings) but not for monomer reduction. 

The purpose of this chapter is to focus on controlled surface modifications of polymers, with emphasis on the advances achieved during the past decade or so. The commonly used techniques generally mentioned include corona discharge, plasma, UV, laser, and electron beam treatments. Lateral patterning techniques utiUzing soft hthography, which is the collective name for a number of techniques where a patterned elastomer is used as mold, stamp or mask to generate or transfer patterns with sub-micrometer resolution, will not be covered in this chapter, since several comprehensive reviews focused on these techniques have been recently pubhshed [46,47]. 

The surface relief and structure peculiarities of steel 45 (C<0.45 wt %) after electroexplosive copper plating and subsequent electron beam treatment are investigated by methods of scanning and transmission electron microscopy. It is established that the copper concentration in surface layer is increased in two times with the growth of electron beam pulses number. The high speed crystallization on of modified layer is accompanied by hardness growth of surface layer. 

FIGURE 10.3 Change in the copper concentration in the surface layer of steel 45, subjected to electoexplosive alloying and subsequent electron-beam treatment with varying of electron beam energy density (50 ps, 0.3 Hz, 10 pis.). 

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