4.8 Degradation of Elastomers by Heat and/or Radiation

Transcription

1 4.8 Degradatn f Elastmers by Heat and/r Radatn M.It Japan Atmc Energy Research Insttute, Nuclear Educatn Center , Hnkmagme, Bunkyu-ku Tky, 113, JAPAN Abstract Ths artcle studed sme prblems n the degradatn f elastmers by heat and /r radatn. The changes n ultmate elngatn, and the ncrease n C=0 cncentratn shw the exstence f synergstc relatnshp between heat and radatn as the rate cnstant f chemcal stress relaxatn shws. The temperature dependence f radatn nduced degradatn f flurne cntanng elastmers was fund t be small. The flrn cntanng elastmer have less radatn resstant prpertes than apprprately cmpunded EPDM. INTRODUCTION The electrc cable and cmpnents n cntaner vassal f nuclear pwer plant are expsed by radatn and heat smultaneusly durng nrmal servce cndtn and a smulated lss f clant accdent. Elastmers are used as the materals fr the electrc cables and the cmpnents because f t's elastc and flexble prpertes. Therefr, t s mprtant t study the temperature dependence f radatn nduced degradatn f elastmers. The synergstc relatnshp between heat and radatn s the functnal prblem t be als clarfed. It s practcally useful t nvestgate whether heat resstant elastmer have radatn resst prpertes. The artcle studed sme prblems n de degradatn f elastmers by heat and/r radatn mentned abve. EXPERIMENTAL The flurne cntanng elastmers used were AFLAS type(asah glass C. Ltd.) and VITON type (Du pnt). AFLAS type s cplymer f tetraflurethylene wth prpylene, and VITON type s cplymer f hexaflurprpylene wth vnlyden flurde. Each f the cplymers cntans small amunt f termnmer. Table 1 shws cmpundng recepts f thse samples. The recept f ethylene-prpylene dene elastmer(epdm) was shwn elsewhere (It M.,1993). The scknesses f the samples were abut 0.5mm. The rradatn was perfrmed by C-60 ray at the cnstant temperature n ar ven. The mechancal prpertes were measured by the tensle test at rm temperature. The dstance f jwl was 500mm, and the extensn rate was 50mm/mn. The vlume resstvty was measured wth applyng electrcty f 500V

2 Table 1 cmpundng recepts f flurne cntanng elastmers. AFLAS Type Ingredant AFLAS 150 (Asah glass 0 l,3-bs(ter-butyl perxy sprpyl)benzene Trallyl scyanurate Sdume stearate Mstrn vapr talc Parts VITON Type Inqredant VITON B (Du pnt) Lead mnxde DAIAK N.3(Du pnt) Actvated calcum carbnate Parts RESULT AND DISCUSSION Synergstc relatnshp between heat and radatn n the degradatn f elastmers. Fg.l shws ncrease n cncentratn f C=0 f ethylene-prpylene cplymer pure valcanzate by heat and/r radatn. If there s the smple addtvty n the ncrease n C=0 cncentratn by heat and radatn, the smultaneus addtns f each f the deterrate cndtns gves the data n dtted lne. The smultaneus addtn results hgher C=0 cncentratn than the value expected frm the bass f smple addtvty. Therefre the result shws the exstence f a synergsm between heat and radatn. Clugh and Gllen (1981), and It (1981) cncluded that there s a synergstc relatnshp between heat and radatn n the degradatn f plymers. The frmer measured the decrease n ultmate elngatn by heat and/r radatn but they dd nt defne the rate f decrease n ultmate elngatn. On the ther hand, the latter measured the rate f chemcal stress relaxatn. The methd prpsed " ceffcent f synergsm" t express the magntude f synergsm. 0.4 Smpte:EPDM-4 ".3 O A 0.2 Fg.1.- U c 0.0, Tme (h) 150 Increase n cncentratn f C=0 EP07P by heat and/r rradatn. O 7 0 C heat alne 3kGy/h at rm temperature 3kGy/h at 70 C The extraprated lne IOO O Tme (h) Fg.2 Synergsm f Heat nd Rdltln n Elngatn Changes. D Het (110'C ) O Radatn (0.5 Mrad/h t 70*C) Heat andrdltln (0.5 Mrad/h at 110'C)

3 Recently I fund ut that the rate cnstant f decrease n ultmate elngatn can defne fr certan elastmers. As an example, decrease n ultmate elngatn f EPDM-4 by heat and/r radatn s shwn n Fg.2. The rate cnstant f decrease n ultmate elngatn K defned by equatn 1. Lg(e/e) = -Kt (1) where e s elngatn at tme t and e s the ntal elngatn. A synergstc relatnshp exst n the decreasee n ultmate elngatn. The slpe fr the smulatanus addtn f heat and radatn s hgher than that expected frm the bass f smple addtvty. The results suggests that the measurement f C=0 cncentratn and elngatn at break fr the certan elastmers can gve the degree f synergsm. Radatn nduced degradatn f flurne cntanng elastmers at varus temperatures. Fg.3 and 4 shw the relatnshp between the weght f the samples and dse. The weght decreases wth ncreasng dse and temperature. The scssn reactn by rradatn prduced lw mlecular prducts. The dffusn f thse vlatle prducts frm samples t ar results n the weght lss at hgher temperatures. The temperature dependence f the rate f weght lss was fund t be dscrete. The results shw that the rate f scssn reactn des nt affect the weght lss drecdy, but the dffusn f lw mlecular weght prducts frm the sample t ar cntrls the rate f the weght lss. Fg.5 and 6 shw the changes f vlume resstvty by rradatn. At hgher temperatures, rradatn des nt affect the resstvty. Ths s due t the vaprzatn f plar mlecules that decrease the value f resstvty frm the samples at hgher temperatures. The 25% mdulus f tw elastmers ncreases wth ncreasng dse as shwn n Fg.7 and. VITON type dses nt shw the temperature dependence. AFLAS types have temperature dependence, but nt remarkable ne. The decrease n ultmate elngatn by rradatn at varus temperatures was als studed. Fg.9 shws the dse when elngatn at break decreases t 50% and when elngatn decreases the half f ntal values. The result shws that AFLAS type has better radatn resstant prpertes than VITON type. Cmparsn f radatn resstant prperty wth anmer elastmers. Fg 10 shws the decreases n ultmate elngatn f varus elastmers by rradatn. EPDM-3 and acrylc elastmer(ac-l) have better radatn resstant prpertes n the vew pnt f elngatn retaned. Thus, apprprately cmpunded EPDM and acrylc rubber were fund t have excellent radatn resstant prpertes cmpared wth flurne cntanng heat resstant elastmers

4 T 1 1 r B S. -ah c 10 CJ JC -6 Ol 3: B -10 J I Fg.3 Heght chenge f AFUS type elstaner by Irradatn. O 90'C a 120'C A150*C 175*C 200*C "FJg.4 Weght change f VITOH type elastmer by rradatn. O 90'C P 120'C AISO'C 175'C 16.5 r T r Fg.5 j L A. changes f vlume resstvty f AFUS type elastmer by rradatn. O 90*C D 120*C A150*C 175-C 10 1 T T T r Fg.6 Changes f vlune resstvty f yton (0 a 5 a Z3 type elastmer by rradatn. O 90'C 175'C A \A A n V O 120'C J AlSO'C - " Rg.7 changes f 251 mdulus f AFLAS type elastmer by lrrastatln. O 90'C D 120'C A150'C 175'C 200"C r cp Fg.8 Changes f 251 mdulus f YITON type elastmer by Irradatn. O90'C 175'C D 120*C A150'C 'r

5 r e-50 (AFLAS type) 0.25 >.. ID <u n O a e-50x (VITOH type). (AFUS type) _l e/e 0 *0.5 <VIT0N type) a B 3.0 1/T(K)X1000 Rg.9.Relatnshp between crtcal dse and recprcal f temperature. u a 4" Fg.10 Decrease n ultmate' elngatn f varus elastmers by rradatn. ( 3 kgy/h at 70 C ) REFERENCES Cluh R.L. and Gllen K.T.(1981) Radatn-thermal degradatn fpe and PVC mechansm f synergstc and dse rate effect. Radat. Phys. Chem. &I It M Chemrhelgy f rubber under heat and radatn. Radat. Phys. Chem It M, Kusama, Y.,Yag,T.,Okada S., and Ysda K.(1993) The methddlgy study f tme accelerated rradatn f elastmer. Materals Lfe_5_