Polymers by Electron Beam

MODIFICATION OF POLYMERS BY ELECTRON BEAM Preparation of Tile Compounds 

The plastic or rubber samples are mixed with the sensitizer at the desired level in a Brabender Plasticorder or an internal mixer. The speed and the temperature of mixing depend on the nature of polymer. A temperature of 120 C may be used for polyethylene and ethylene vinyl acetate copolymer. A higher temperature is needed for crystalline plastics. 

These compounds may be molded under compression to prepare sheets of various dimensions. The compounded sample may be extruded in a single screw extruder to make tubes or cables. The inner liner compounds in the industry may be calendered first to a thickness of 1-2 mm before irradiation. 

The mechanisms of crosslinking and grafting reactions are studied with the help of infrared spectroscqiy, photoelectnm spectroscopy, reflectitHi 

A difference in the absolute value of the ultimate properties was observed if the type of filler component was changed. The tensile strength of zeolite-filled composite demonstrates a maximum for the highest concentrations of BMI and zeolite in the chosen experimental range. This fact indicates that degree of interaction between PP and zeolite is directly proportional to the concentration of filler for a BMI concentration of about 2.5 wt%. 

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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. ... 

The cost of polymer irradiation depends on the type of polymer, formulation, and shape of the fabricated polymer. Upgrading polymers by electron beam radiation costs about 1 to 4 cents per pound. Some of this cost can be equalized through material saving in view of property improvement. Surface treatment might be as low as 0.1 to 0.2 cents per pound. 

I) Generation of a regular dot pattern of polymer by electron beam polymerization (top view)... 

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. 

For all three diallyl phthalate isomers, gelation occurs at nearly the same conversion DAP prepolymer contains fewer reactive allyl groups than the other isomeric prepolymers (36). More double bonds are lost by cyclisation in DAP polymerisation, but this does not affect gelation. The heat-distortion temperature of cross-linked DAP polymer is influenced by the initiator chosen and its concentration (37). Heat resistance is increased by electron beam irradiation. 

Silicone acrylates (Fig. 5) are again lower molecular weight base polymers that contain multiple functional groups. As in epoxy systems, the ratio of PDMS to functional material governs properties of release, anchorage, transfer, cure speed, etc. Radiation induced radical cure can be initiated with either exposure of photo initiators and sensitizers to UV light [22,46,71 ] or by electron beam irradiation of the sample. 

However, Pacansky and his coworkers77 studied the degradation of poly(2-methyl-l-pentene sulfone) by electron beams and from infrared studies of the products suggest another mechanism. They claim that S02 was exclusively produced at low doses with no concomitant formation of the olefin. The residual polymer was considered to be essentially pure poly(2-methyl-l-pentene) and this polyolefin underwent depolymerization after further irradiation. However, the high yield of S02 requires the assumption of a chain reaction and it is difficult to think of a chain reaction which will form S02 and no olefin. 

Chattopadhyay S., Chaki T.K., and Bhowmick A.K., New thermoplastic elastomers from poly(ethyle-neoctene) (engage), poly(ethylene-vinyl acetate) and low-density polyethylene by electron beam technology structural characterization and mechanical properties. Rubber Chem. TechnoL, 74, 815, 2001. Roy Choudhury N. and Dutta N.K., Thermoplastic elastomeric natural rubber-polypropylene blends with reference to interaction between the components. Advances in Polymer Blends and Alloys Technology, Vol. 5 (K. Finlayson, ed.), Technomic Publishers, Pensylvania, 1994, 161. 

Figure 13. Outline of the pattern generation for integrated circuits provided by electron beam writing on chemically suitable polymer films, which are thus sensitized for development.

Polyethylene may be crosslinked by electron beams or by free-radical initiators. These polymers have elastic memory, i.e., stretched crosslinked Aims or tubing shrinks to the original dimensions when heated. 

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. 

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.)... 

Polymers of MMA, AAc, and MAA were grafted onto an ultrahigh molecular weight polyethylene (UHMWPE) fiber surface after pretreatment with electron beam irradiation [31]. Sundell et al. [32] pretreated a PE film with electron beams to facilitate the graft polymerization of vinyl benzylchloride onto the substrate. The inner surface of porous PE hollow fiber had also been modified by grafting of glycidyl methacrylate (GMA) polymer after electron beam irradiation [33]. 

Fluorosilicone polymers can be cross-linked by ultraviolet radiation or by electron beam, but these methods are not commonly used69... 

Fig. 5 Synthesis of PVME particles by irradiation of phase-separated solutions. Above the phase transition temperature Tc, the polymer chains collapse to globular aggregates. The collapsed structures are fixed by electron beam irradiation to yield temperature-sensitive microgel particles...

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