ELECTRON BEAM PROCESSING OF POLYMERS

Sujit K. Datta, Tapan K. Chaki and Anil K. Bhowmick Rubber Technology Center, Indian Institute of Technology Kharagpur, INDIA 

The process is very fast, clean and can be controlled precisely. 

There is no permanent radioactivity since the machine can be switched off. 

The electron beam can be steered very easily to meet the requirements of various geometrical shapes of products to be irradiated. This cannot be achieved by X-rays and y-rays. 

The EB radiation process is practically ftee of waste products and hence there is no serious environmental hazard. 

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Natural Rubber and Synthetic Polyisoprene Polybutadiene and Its Copolymers Polyisobutylene and Its Copolymers Ethylene-Propylene Copolymers and Terpolymers Polychloroprene Silicone Elastomers Fluorocarbon Elastomers Fluorosilicone Elastomers Electron Beam Processing of Liquid Systems Grafting and Other Polymer Modifications... 

Das, P.K., Ambatkar, S.U., Sarma, K.S.S., Sabharwal, S., and Banerji, M.S. (2006) Electron beam processing of nylon 6 and hydrogenated nitrile rubber (HNBR) blends 1. Development of high strength heat- and oil-resistant thermoplastic elastomers. Polym. Int, 55 (1), 118-123. 

Radiation processing of polymers was introduced after World War II with the development of the nuclear reactor. In the current years, various radiation sources, e.g.. X-rays (soft and hard), gamma (7) and ultraviolet (UV) rays and electron beam (EB) are being widely used. 

Two-sided irradiation of a wire by electron beam. (Radiation Processing of Polymers (Singh, A., and Silverman, J., Eds.), Carl Hanser Publishers, p. 82 (1992). With permission from Carl Hanser Publishers.)... 

The use of radiation to modify the physical properties of polymers has become a very important industry with products such as electrical cables with insulation capable of withstanding high temperatures and heat-shrinkable polyethylene. However, of direct relevance to this symposium was the recognition in the early 1970 s that electron beam irradiation of pol3mier films could provide an important lithographic tool for the manufacture of microelectronic components. For consideration of the general principles of these processes see, for example, references (66) and (67). The products required In this field are complex requiring both microscopic... 

An example system is PVC and polyethylene wire and cabling irradiated to improve stresscracking resistance, abrasion resistance, high-temperature properties and flame retardance, via controlled electron-beam crosslinking (Loan, 1977). Additionally electron-beam crosslinking is utilized to impart memory into a polymer system, such as crosslinked PE materials for heat-shrinkable films and pipe applications (Baird, 1977). The control of electron-beam processing has advanced the quality of cell size and shape of PE foams via control of crosslink distribution (Paterson, 1984). 

Cleland et al. (2003) reviewed the application of electron beams with various materials however, little process modelling has been developed due to the low industrial usage of electron-beam processing for reactive polymers. However, many researchers are examining cure models for promising materials. 

Figure 11.49 Effect of electron-beam curing of resists based on poly(methacrylate) platform and hybrid methacrylate/alicyclic polymer platform on polygate etch. Electron-beam curing improves etch resistance by up to 50% relative to the control (uncured) sample. Processing was done in a nitrogen environment of the ElectronCure Electron Beam Process Chamber utilizing these electron-beam parameters 3.75 keV, 6 mA, 2000 pC/cm. The wafer temperature of the standard (Std.) process was not controlled, that for the electron-beam standard cure (ESC) process was kept at a medium temperature, that for the low-temperature (LT) process was maintained at a iow temperature, whiie that for the control was at room temperature. [After R. Dammel, Practical resist processing, SPIE Short Course No. SC616 (2005).]...

Radiation processing of polymers can be operated with several types of ionizing radiations e-beam (accelerated electrons generated by an accelerator), gamma rays (photons emitted by a cobalt 60 source), and X-rays (since recently). It acts by a spontaneous ionizing process, in two steps formation of ions that decomposes into free radicals. There is no need to add an initiator like peroxides or photoinitiators. Then, the free radicals can induce some chemical reactions, depending on different parameters that will be considered hereafter. 

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. 

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. 

Now-a-days electron beam radiation processing has wide applications particularly in the wire, cable, coating and the tire industries. This chapter deals with the processing of polymers by electron beam radiation and the properties as well as the applications of modified polymers. 

Clayden N J and Pendlebury R (2001) NMR study of the effect of electron beam processing on a poly(ether-61ocfc-amide), Polymer 42 8373-8377. 

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