Polymerization electron beam process

Electron beam processing of solvenf-free liquid systems for coatings, inks, and paints involves essentially polymerizahon and cross-linking using electrons with energies between 120 and 300 keV. Initiation by electrons leads primarily to free radical reactions. Cationic polymerization is only found in rare cases. ... 

Major Commercial Applications of Electron Beam Processing of Polymeric Materials... 

Alessi et al. (2005) examined the y-irradiation and electron-beam processing of an epoxy-resin system in the presence of a photoinitiator. They showed that increasing the irradiation dose frequency and photoinitiator concentration greatly increases the temperature reached by the samples. The increase in temperature of the system during irradiation is related to the balance between the heat-evolution rate, due to both polymerization reaction and radiation absorption, and the rate of heat release towards the environment. High dose rates and high photoinitiator concentmtions increase the reaction rate and the difference between the heat produced and the heat released to the environment (Alessi et al. (2005). 

Polymerization, electron beam EB polymerization is a slow irradiating process. Monomeric materials that have been irradiated to produce plastic films include silicone, butadiene, styrene, methyl methacrylate, and epoxy. However the lack of selectivity of this energy source can result in contamination. Film properties can be tailored by varying the acceleration voltage. >coating, vacuum... 

It is clear from this discussion that the dose requirement and unit cost will be lower if the material has a higher molar mass M and the reaction has a high G value. Thus, the best candidates will be a polymeric material and a chain reaction. Quite often, a free-radical irradiation is used. The radiation source of choice is usually a 60Co - y facility, although electron beam irradiation is also used. Since most radiation-chemical reactions used in industry can also be brought about by other conventional means such as thermal, or photochemical processes, the processing cost must be below 10irradiation cost one has to include the cost of operation, maintenance, and the like. (Danno, 1960). 

A number of new resist materials which provide very high sensitivities have been developed in recent years [1-3]. In general, these systems owe their high sensitivity to the achievement of chemical amplification, a process which ensures that each photoevent is used in a multiplicative fashion to generate a cascade of successive reactions. Examples of such systems include the electron-beam induced [4] ringopening polymerization of oxacyclobutanes, the acid-catalyzed thermolysis of polymer side-chains [5-6] or the acid-catalyzed thermolytic fragmentation of polymer main-chains [7], Other important examples of the chemical amplification process are found in resist systems based on the free-radical photocrosslinking of acrylated polyols [8]. 

The hybridizing component can also be formed directly on the surface of a pristine or modified nanocarbon using molecular precursors, such as organic monomers, metal salts or metal organic complexes. Depending on the desired compound, in situ deposition can be carried out either in solution, such as via direct network formation via in situ polymerization, chemical reduction, electro- or electroless deposition, and sol-gel processes, or from the gas phase using chemical deposition (i.e. CVD or ALD) or physical deposition (i.e. laser ablation, electron beam deposition, thermal evaporation, or sputtering). 

The other types of ionizing radiation mentioned above are also used in processing of polymeric systems, but not as frequently as electron beams and mainly for specialized applications. 

This reaction is based on a stoichiometric reaction of multifunctional olefins (enes) with thiols. The addition reaction can be initiated thermally, pho-tochemically, and by electron beam and radical or ionic mechanism. Thiyl radicals can be generated by the reaction of an excited carbonyl compound (usually in its triplet state) with a thiol or via radicals, such as benzoyl radicals from a type I photoinitiator, reacting with the thiol. The thiyl radicals add to olefins, and this is the basis of the polymerization process. The addition of a dithiol to a diolefin yields linear polymer, higher-functionality thiols and alkenes form cross-linked systems. 

Radiation processing of monomers and polymers by electron beam, such as polymerization and copolymerization of monomers, cross-linking, grafting, and degradation of polymers, is induced by these different chemically reactive species. ... 

Plastics are by far the largest group of polymeric materials being processed by electron beam irradiation. Cross-linking of polyolefins, PVC, polyesters, polyurethanes, fluoropolymers, and fiber-reinforced composites is a common practice. 

But vitrification may be a problem when the cure is started at room temperature and no external heat source is provided (the only source of heat generation is the polymerization reaction). This is the case of UV (ultraviolet radiation), EB (electron beam), or X-ray curing processes. 

Cross-linking — A reaction during which chemical links are formed between polymeric chains. The process can be carried out by chemical agents (e.g., organic peroxides), reactive sites on the polymeric chains, or high energy radiation (e.g., electron beam). 

Electron beam (EB) cure — A process using high energy (accelerated) electrons to promote reactions in a polymeric material (cross-linking, polymerization). The reaction is instantaneous. The voltage range used in this process is typically from hundreds of kilovolts to several megavolts. 

In terms of paper conservation, this work is of value since it is an attempt to determine (i) if UV and EB grafting times for cellulose copolymerization can be shortened significantly by the inclusion of appropriate additives and (ii) if such a process is capable of incorporating into cellulose properties required for preservation, particularly wet and dry strength and flexibility. These studies also should indicate the feasibility of extrapolating data from the present solvent grafting systems to processes based on solvent-free, rapid-cure UV and electron beam (EB) which are the ideal polymerization conditions for preservation applications. 

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