Réactions de Réticulation du Polyéthylène Haute Pression

Abstract

SynopsisThe crosslinking of polyethylenes by free radicals, produced by complete decomposition of crosslinking a g e n t s tert-butyl peroxide and tertbutyl perbenzoate, w a s carried out in a Brabender Plastograph, which gave continuous viscosity-time curves and s o permitted the crosslinking to be measured a t the same time. T h e soluble fraction and Brabender viscosity were determined simultaneously; the latter represents an exact measure of the variation in degree of crosslinking under the given conditions. A great number of reactions with different quantities of peroxides were carried out. A quantitative equation relating degree of crosslinking and Brabender viscosity w a s established. With the u s e of equations valid in radiation crosslinking some equations relating degree of crosslinking to molecular weight and other characteristics were established. T h e s e lead to the analytical fractionation of polyethylene a n d the establishment of polydispersity curves. Crosslinking by macroradicals obtained by the mechanicochemical degradation of polyethylene of molecular weight 3,000,000 w a s followed in the same way.La reticulation du polythhylkne a suscit; c e s derniers temps un intdrgt particulier du point de w e pratique e t thgorique (1). P a r diffikence a v e c le caoutchouc dont la vulcanisation au soufre e s t f a i t e sur la b a s e d e s doubles liaisons existentes, d a n s le c a s de la macromoldcule du polydthylkne le nombre d e c e s doubles liaisons &ant extrgmement re'duit (0,6-1,s doubles liaisons pour 1000 atomes de carbone) la r6ticulation n e c e s s i t e l'intervention d e certains radicaux libres produits par un agent ext6rieur.Du point de vue pratique la r6ticulation du polydthylkne est possible d e trois manikres diffe'rentes: par lumikre ultraviolette, par radiations ionisantes e t I'aide de peroxydes organiques. L e s deux derniGres mithodes ont trouve c e s derniers temps des applications industrielles.Chacun de c e s proce'de's a son avantage e t son ddsavantage. La me'thode radiochimique, plus perfectionnge thgoriquement a i n s i qu'exp6rirnentalement, pre'sente le ddsavantage d e ndcessiter d e s conditions complexe s de travail e t en ge'ne'ral l e processus a un caractkre superficiel. La + P r e s e n t a d r e s s -Cornbinatul Petrochimic P i t e s t i -Arges t P r e s e n t a d r e s s -Polytechnical Institute -C a l e a Victoriei 149 Bu care s t