Long-time creep in a pure-gum rubber vulcanizate: influence of humidity and atmospheric oxygen

Abstract

Lo ng-tim e c ree p of na tura l rubbe r c ure d with a s u lfur-a cc el e rator rec ipe co ntaining no fill e r ca n be co nv e ni e ntl y rep rese nt ed by a plot of (E-EI )/E I = flE /EI with a double-abscissa sca le show in g log 1 and I. E is th e e lo ngati o n at any tim e I, aft e r app li ca tio n of th e load , and EI its value a t unit tim e.Expe rim e ntal data co nform to the equationexce pt fo r a mo re rap id ri se precedin g rupture. Th e co nst a nts A a nd B ca n be e valuat e d from o n ly three obse rvati o ns -a t th e lo nges t t ime (abo ut 70 da ys), at o ne minute, a nd at a n inte rme di ate tim e . t:..E/EI is ap proximat e ly lin ea r with log 1 whe n 1 is less th a n O.I (A/ B) a nd a pprox ima te ly lin e ar with 1 wh e n 1 is gr ea te r than 4. 343(A/B). Th e obse rved modu lus wa s abo ut 1.4 MPa a nd A was about 2.4 perce nt /(u nit log t) wh e n th e a tm osphe re was a vac uum , dry N" or dry air. Th e modulu s was lo we re d ve r y s li ght ly a nd A beca me about 4 pe rce nt./( unit log t ) whe n th e a ir was saturat e d with water. B was raised from a bo ut 2 X 10 -5 pe rce nt / min to a bo ut 20 X 10 -5 pe rce nt/ min whe n th e va c uum or dry N, was re placed by dry a ir a nd to a bo ut 50 X 10 -5 pe rce nt/ min wh e n th e air was saturate d with mois ture. A is co ns ide red to be re lat ed to ph ys ica l relax a tio n, whi le B co rres pond s to a che mi ca l reacti o n, probably ox idativ e d egradatio n.Key word s : Co mplian ce of rubbe r ; c ree p , long-time, in rubb e r; humidit y, e frec t of, o n c ree p of rubber; modu lus of rubb e r, effec t uf humidit y; uxyge n, inAu e nce of, o n c ree p of rubb e r ; rubbe r, nat ura l, c ree p; tim e, e ffect of, o n co mplia nce of rubbe r.