efecto de la irradiación en elastómeros.pdf

7/28/2019 Efecto de la irradiacin en elastmeros.pdf

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Radiation Effects on PolymericSystemsElastoDlers


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Radiation Vulcanization ofElastomersCommercial Process Most elastomers can be radiation vulcanized togive crosslinked products similar to thoseobtained by conventional thermal vulcanization Some radiation vulcanization on commercial scaleis being done

Conventional formulations can be radiationvulcanized Optimizina the formulations for radiationvulcanization gives better productsBradley (1984)


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Radiation Vulcanization ofElastomersFree Radical Mediated

Radiation crosslinking of natural rubber (cis-1,4polyisoprene) and gutta percha (trans-1,4polyisoprene) is infiibited by oxygen Gamma irradiation requires inert atmosphere Electron irradiation can be done in air

Radiation crosslinking of EPDM proceeds moreefficiently than that ofEPR Crosslinking efficiency of EPDM depends on itsethylene content, and also varies with thecrosslinking aQent present e.g., ENS (5-ethylidene2-norbornene) IS very efficient

Radiation crossl inking of polybutadiene is quiteefficient


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Radiation Vulcanization ofElastomersWide Applicability

Radiation vulcanization of polychloroprene,polychloroprene/polyethylene blend, vinylidenefluoride based fluoroelastomers, silicone rubbers,and blends of conjugated diene butyl rubber withpolyethylene and polybutylene, also proceeds well In contrast, polyisobutylene and butyl rubberdegrade on irradiation


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Radiation Vulcanization ofNRL(RVNRL) Much simpler than thermal vulcanization Requires flushing with nitrogen and stirring Crosslinking promoters 5%) added, e.g., CCI4,mono- or multi-functional acrylates Dose required, 10-30 kGy Product has very low cytotoxicity Nitrosamines, sulfur and zinc oxide eliminated(potential health risks) RVNRL safer than thermally vulcanized NRL


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Properties ofThermally Cured NRL and RVNRLProperty RVNRL1 ThermallyCured NRLTensile Strength (Tb)' MPa 38 41Elongation at Break (Eb), % 900 870Acid Resistance (10% HCI, 48h)Tb, MPa 23 33Eb, % 900 850Alkali Resistance (10% NaOH, 48h)

~ , M ~ 32 35Eb, % 920 920Ageing Resistance (70oC, 48h)Tb, MPa 37 41Combustion:Gas Production, mg/g 58.5 346.3Ash, wt.% 0.5 2.2Ignition Temperature, C 348 3331 Crosslinking promoter, mixture of 2-ethylhexyl acrylate and ammonia;dose, 12 kGy


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Tire ManufactureSynergy with Conventional Technology Radiation crosslinkina of innerliner has helpedmake tire manufacturing a more efficient andeconomical process It is an electron irradiation application (1-3 MeV) Irradiation of the green rubber innerliner allows aprecise control of its strength and tack This enables precise assembly of the multi-layeredtire, and the tack of the innerliner results in goodadhesion between layers during conventionalvulcanization


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Economics of Irradiation inTire Manufacture(Bradley, 1984)Orginialliner 24" wide x .047" thick x 72" long x p 1.2=3.5 Ibs =1.59 kgReduced liner 24" wide x .040" thick x 72" longx p 1.2=2.91bs =1.32 kgMaterial savings of 0.6 Ibs or 270 g/tireCost savings are based on $0.35/lb for the inner linerMaterial cost saving is approx. $0.20/tireIrradiation cost is approx. $0.03/tireActual savings $0.17/tire


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Product Throughput(Bradley, 1984)

800 kV electron accelerator, 31.25 kW 40 kGy dose 1077 Tires (innerliners)/h


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Conclusions Crosslinking of elastomers is very important forthe final mechanical properties of theirproducts Radiation crosslinking has carved out a place inthis industryWith focussed R&D and involvement ofvisionary entrepreneurs, the use of radiationprocessing in the elastomer industry shouldincrease

efecto de la irradiación en elastómeros.pdf

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