The Crosslink Density of Ethylene-Vinyl-Acetate Copolymer/Triallylcyanurate Mixture Cross-linked by Electron Processing

Abstract

ABSTRACT. Vulcanization by electron beam (EB) irradiation involves the interaction of electron energy and an elastomer. The interaction results in formation of free radicals by dissociation of molecules in the excited state or by interaction of molecular ions. The free radicals or molecular ions can react by connecting directly to the polymer chains or by initiating grafting reactions. The chemistry of the process is based on macroradical formation from elastomer chains, which recombine causing structuring. This paper presents the effect of ionizing radiation on mixtures based on ethylene-vinyl acetate copolymer (EVA) and triallylcyanurate (TAC). Samples were subjected to electron beam treatment with doses ranging between 50 kGy and 500 kGy. The induced crosslinking of EVA/TAC samples was evaluated with gel fraction (crosslinked polymer content) and crosslink density determination. The cross-linking density of the samples was determined on the basis of equilibrium solvent-swelling measurements (in toluene at 23-25°C) by applying the well-known modified Flory-Rehner equation for tetra functional networks, where values of the solubility parameter were calculated according to Small, Hoy and Krevelen. Sol-gel analyses and crosslink density have shown that samples tend to cross-link as a result of electron beam irradiation. As EB dose increases, there is an increase of gel fraction, of volume fractions of polymer in the samples at equilibrium swelling (í2m) and of cross-link density (í), and a decrease of swelling ratio G (toluene soluble polymer quantity). The highest value of crosslinking rate was obtained for the sample irradiated with a dose of 350 kGy. KEY WORDS: ethylene-vinyl-acetate-copolymer, triallylcyanurate, cross-linking, electron beam DENSITATEA DE RETICULARE A UNOR AMESTECURI COPOLIMER ETILEN-VINIL-ACETAT/TRIALILCIANURAT RETICULATE PRIN PROCESAREA CU ELECTRONIACCELERAÞI REZUMAT. Vulcanizarea prin iradiere cu electroni acceleraþi (EA) se bazeazã pe interacþiunea dintre energia electronilor ºi elastomerul supus acestui tratament. În urma acestei interacþiuni se obþin radicali liberi formaþi prin disocierea moleculelor aflate în stare excitatã sau prin interacþiunea ionilor moleculari. Radicalii liberi sau ionii moleculari pot reacþiona prin legarea directã de lanþul polimeric sau prin iniþierea reacþiilor de grefare. Chimia procesului se bazeazã pe formarea de macroradicali pe lanþul elastomeric, care se recombinã determinând structura finalã. În aceastã lucrare este prezentat efectul radiaþiei ionizante asupra unor amestecuri pe bazã de copolimer etilen-vinil-acetat (EVA) ºi trialilcianurat (TAC). Probele au fost supuse tratamentului cu electroni acceleraþi cu doze cuprinse între 50 kGy ºi 500 kGy. Reticularea prin iradiere a probelor EVA/TAC a fost evaluatã prin determinarea fracþiei de gel ºi a densitãþii de reticulare. Densitatea de reticulare a probelor a fost determinatã pe baza mãsurãtorilor gradului de gonflare în solvent (toluen) la 23-25°C, prin aplicarea bine cunoscutei ecuaþii modificate Flor...