Permeation of Water Vapour Through Organic Solids

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Permeation of Water Vapour Through Organic Solids

NATIONAL RESEARCH COUNCIL

CANADA

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! THE

PERMEATION

OF WATER

VAPOUH

THROUGH

ORGANIC SOLIDS

I

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i

by

J.

Harris and R. Lundall

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A N A L Y Z E D i i. t I

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Report No.

37

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_{of the}

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Division of Building Research

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Ottawa

December 1954

----..--__I-.Y._I__%-.-*---".?*w----m -"..-"w,-.-.-wm*.~~~-m.~ ", "%., - ." " -

.

7 -

,':or>lcini; v'C tti r u b b e r scuuplc s

,

T a y l o r :, rlerr;i~ann and

I<ecip sho7,~ed tt1;:t t h e peri-[leak! i l i . t g c o n s t o . n t i n c r e a s e d w i t h

i f i c r e a s i i . ~ i . ; t h i ~ ~ r n e s s . I t i s n e c e s s a r y , t h e r e f o r e , t h a t tlse

v a r i a t i o n of' p e r m e a l ! i l . i t y c o n s t a n t w i t h f4il1:; t h i c k n e s s be

d e t e r m i r ~ e d f 01- t.he m a t e r i a l u n d e r t e s t .

3

0 -- . E f f e c t of' Va!>our l're s s u r e

I t h a s Feen shown

(5')

t h a t f o r a m a t e r i a l which

s o r b s l i t t l e rsater (pol)::; t y r e n e ) t h e perl-:ioal. l . l i t < y c o n s t a n t

d i d n o t va1.y r%:ith t h e rolclt;i.\.?c vapoi;lr p r e s s u r e i n c o n t a c t ;$ zh.

t h e s u r f a c e of t h e f i l m , For r , u b s t a n c e s sue?!. a s p o l y v i n y l alcok::~!!;

n y l o n a r d r e g e n e r a t ~ e d c e % l u l o s e , i t h a s been sh.own (11-3 t h a t

perme,il.-il.j.ty c o l i s t a n t i n c r e a s e s w i t h t h e r e l a t i v e h.uniiditg, I n

t h e s e t e s t s t h e r e l s t i v e llumrdity was ;riaint,a:ined a t z e r o on one

s i d e of t h e .fill-rLq, I:.l a l l c a s e s t h e ii-ltie-pendence of' perrnen7ei1.itg

c o n s t a n t or? t h e r e l a t i v e hurtiidity seerils t o h o l d below 5'0 p e r ten?

r e l a - t r i v e humid-ity, The p e r r ! i e a b i l i t y c o n s t a n t o f w a t e r - s e n s i . t , i v e

f i l m s i n c r e a s e s a s t h e r e l a t i v e h u m i d i t y r i s e s above

50

p e r c e r , , t ,

The s o r p t i o n i s o t t l e r m s o f Kuuscr show s i m i l a r behavi-our (11)"

4.

Nl'fect of' T e n l p r a t u r e -

As vapour p r e s s u r e i s t e m p e r a t i r e de!>endent tt1.e

amount of w a t e r perrneat:ing; a filril s h o u l d b e e x p e c t e d t o i n c r e a s e w i t h terl..perature i f t h e vapour p r e s s u r e d i f f e r e n c e a l o n e i s

c o n s i d e r e d . Edwards and ;dray

(14)

m a i n t a i n e d a c o n s t a n t m o i s t u r e

c o n t e n t on t h e n i o i s t sride of t h e f i l m and found t h e p e r n i e a k i l i t y

d e c r e a s e d w i t h t e m p e r a t u r e . 'Thls b e h a v i o u r , t h e y assumed, was

due t o t h e s o r p t i o n of l e s s w a t e r a t h i ~ ; h e r t e m p e r a t u r e s ,

IIermmn, Ta;ylor and Kemp

( 5 )

found t h a t t h e permeabi1.it-y c o n s t a n t

f n c r e a s e d w i t h t e m p e r a t u r e and a s c r i b e d t h e i n c r e a s e t o c h a n g e s

of s t r u c t u r e i n t h e f i l m . Doty, Aiken and Mark

( 1 5 ) ,

u s i n g f i l m s

whose p e r n ~ e n b i l i t y c o n s t a n t s were i n d e p e n d e n t of vapour p r e s s u r e

and t h i c k n e s s , found i n a l l c a s e s , e x c e p t t h a t of p o l y s t y r e n e , , t h a t t h e r e was an e x p o n e n t i a l dependence of t h o permeabT1:ity constra;it on t e r ~ l p e r a t u r e a c c o r d i n g t o t h e e q u a t i o n : :

where

PP

i s t h e permout1ilit;li- c o n s t a n t a t z e r o d e g r e e s a b s c l i ~ t , e :

En i s trje energ;-;.j of a c t , i v a t i o n f o r p e r m e a t i o n , and T t h e a b s o l u t e

t e i l . ; p e r a t ~ l r e . Ep i s t h e a l g e b r a i c s m of t h e h e a t of s o l u t i o n

[ = - A F T ) and t h e e n e r g y of' a c t i v a t i o n f o r d i f : r u s i o n

(Z,,

)

.

E p i s

z e r o f c r pol;yst.grene and p o : : i t i v e f o r t h e o t h e r m a t e r i a l s of' t h i s

inves.,ti;:ation. The perme ai;:rility c o n s t a n t f o r p o l y s t y r e n e i s

independei?t of tei:.~per:ltcu'e; i t i n c r e a s e s w i t h t e r a p e r a t u r e f o r t h e

o t h e r ?n::.t;erials. I f n

H

fs g r e a t e r t h a n E D

,

one c o u l d expect, t h e

p e ~ m e 8 ? - ~ i l ? t y c o n s t a n t t o d e c r e a s e w i t h t e m p e r a t u r e , T h i s d e c r e a . s e

i-s sl:ro~%~!l f o r po1yviri;yl ' ~ : u t y r a l i n t h e work o f I-Iauser a!?d ibiclaren

(11)

.

Dot;7, Aileen au;d It'larlc ( 1 5 ) showed t h a t c r y s t a l l i n i t y (;r,iv.es

c o l ? s t , a - ~ t . I t . l u s t be rcr:ieri!k~ereb t h a t . t h e work o f I;)ot;y9 A i k e i ~

e;id ;';lar!-r a p q l i s s t o f i 1:;;:; tha.t bchnve i d e a l l y .

5'.

-

E f f e c t of i'ip;ments ,

.-I t i s assur-tred u a u e l l g t h a t w a t e r vapour d o e s n o t

d i f f u s e t h r o u ~ h t h e pii;rnent i n a p a i n t f i l m ( 1 6 ) . The pigment

c o n c e n t r a t i o n , d i . s p e r s i . o r ~ , p m t i c l e s h a p e ant1 r e a c t i v i t y w i t h

t h e vek:.fcle, w i l l . deter11:iile the ef'f?ri.cielicy i n . r e t a r d i n g n i o i s t u r e

f l o w . >dray- and Van Vorzst si-:owed t h . a t t h e f i n e r p a r t i c l e s i z e

pigwisnt o l i f e r e d t h c '::,etter n i c i s t u r e irnpeda:zce ( 1 6 ) . They a l s o concluZed t l l e ~ t a p i g n e n t of' eranu1e.r form ofl'er:; l e s s r e s i s t a r l c e t k a n oRe of f l a k e f'orrii. beca.\ise of' t h e o v e r l a p p i n g o f t h e l a t t e r .

For a given v e h i c l e and pi(;lnent t h e r e i s a c r i - t i c a l pigment-

v e h i c l e volume r a t i o which g i v e s optimu'n m o i s t u r e impedance

( 1 7 ) .

ImpeGance i n c r e a s e s wi.tl.1 i n c r e a s i n g p i g ~ ~ e n t c o n c e n t r a t i o n unti.1

tllc c r i . t i c a l c o n c e n t r a t i o n i s r e a c h e d ; above t h i s c c ~ n c e n t r a t i o n ,

p o r o s i t y o c c u r s . "The c r i t : ~ c a l ~ o i n t i s l a r g e l y a f u n c t i o n 02'

pigment r a t h e r t h a n ve!?iclel'

( 1 7 ) .

The a f f i n i t y of a .pippen.t

f o r rjater. rnay i n f l u e n c e clois t u r e excluc?.irq< e f f i c i e n c y

.

Cherniczlly r e a c t i v e p i g m e n t s rnay d e c r e a s e permeabi.1.i.t.y b : r t h e f o r n a t i o n of' s o a p s which d i f f u s e t h r o u g h t h e f i l m or by

a i d i n g d r g i - n g . They may i n c r e a s e p e r m e a t : i l i t y t h r c u g h t h e r e a . c t l o n

of 1;a.sj.c pi:;ments w i t h : i c l d i c o x i d a t i o n prociucts ( 2 ) .

L i t t l e i n v e s t i i ; ; a t i o n h a s b e a n c a r r i e d o u t on t h e

e f f e c t o f a g i n g on p t : r m e a I ) i l i ty . D e c r e a s e i n p e r m e a t i i l . l t g w f t h

a c i n z , h o x e v e r , has been shown

( 1 8 ) .

The d e c r e a s e .Ls Inore

n o t i c e a t ~ l e f o r t h o s e f i l m s which d r y s l o w l y ,

6. P r e p a r a t i o n o f T e s t Specimens

One a s p e c t o f p e r r n e a L i l i t y s t u d y which h a s r e c e i v e d

much a t t e n t i o n i s t h a p r e p a r a t i o n o f the f i l m s p e c i m e n s . R e s e ~ v c h

b a s 'uel:n done on f r e e i ' i l n . 1 ~ o r f i l r t s c ~ s t e t l on parclmient, a?"._l.l.:,

:?ata.l,~:r, 1-!1:2+:3.1 sc:pc.e;.i ( l g ) , , 1q00d m-id g l a s s s l o t h . F r e e f i l : . r ~ s :ii?s

of-i;sll n r e p a r e d b y - c o a t i n g a::i;~lsslr.:ited t i : - ~ ' - . ; ~ l i ~ t e by d i p - e o a t l . c-lg:,

d~nwin!.; w i t h . a i o c t 3 r ~ - b l n c J - e 9 o r s p r a y i n g . ?'?la d r y fi-lms m e

r 3 : , . ~ o ~ . r : ~ ~ ~ i easily fro:,. t;).~; 1;nneis nnii u n i f o r m s,w,,zples ,arc oktairiecl.

p L o i , ~ e v e r , so,:le qi~es.t:iorl a ~ . i s e s ~ ~ i i - t h r e g a r d t o the d e p o s i t _ro.:~ai:llnc;

o : ~

t h e f i l m , Unsupporteii i'illns have beeii p r e p a r e d i j , ) ~ c o a t i n g

s i i - v s r e d - g l a s s and a~~::ilg~-::!,iatt ng t h e s i l v e r l a y e r ( 1 7 )

.

S e v s r a l

i m s n t i s f a c t o r y ati;;;!..lp-t s :lel.o mado usiizg s i l ~ e ~ e d . . ~ g l . a s s . 1LlLi;Lough

l'll.:;s 'r;a.:e been y)rzphi.)ecl t ; y soalc:ing c o a t e d g l a s s p a n e l s iii ( : i f s t i l l e d

i - ~ ~ i - t e r , t h i s j7roce:lure 3.s a l s o q~le:;tio:tlnble.

kl.though f 1 . e ~ f i l n s g i v e more s c i t ? n t l f i c a l l y c o r l - e c t

~ e r n e a h i l i - t g r e s u l t s , their p i - a c t i c a l a p p l i c a t i - c n s a r e l i r n i t e d ,

7 ,

r L i i ; t e l b ? r ~ e r (20) s t a t e s t h a t p e r m a $ - , i i i t y nleasmie-

; ! l ~ i l . k s rilade on f : i l : . s s!ilp;,o~c.-k,2..,d o n t h e s s ~ i e s u b s t r a - i ; e a s t h a t f c r

rri L i - I tilie p:iL:.?Z; i s i n t z n d e d a r c o f t h e ,nos

t

p r a c J c i . c a l v a l u e ,

,-I

:.,oa;;etl ::ii.sc:.; ~ i a g b e s e a l - a d i n a cuy) . v ~ i ' t k : e i . t a c r ti-15 11ainI;ed o r

1.1npain-Led sicte S'aci ,.- 1 ~ . t . h e h i g h ::lulnidi. t y d - e p e n d i n g upon t h e w a l l

c o : ~ d i t i o n s ~.rl?lch a r e t o 1:z s i . : n u l a t e d . F i l m t i ; i c I c . ~ l e s s rnay b e

c a l c u l a t e d froia w e i g l ~ t of f i l m , a r e a , and d e n s i t y . T h i s method

::-rives a goo6 m e a s u r e o f per.ileance f o r t h e s y s t e m , however, it

0

doas n o t g i v e a gcod rrleasLtre of' t h e peri.;leance o f t h e f i l m .

I C i t t e l b e r g e r a l l o w a d f o r t h e ? e f i ' c c t o f t h e wood b y u s i n g t h e

f ' o l l o w i n f ; f ~ r i - i l u l a :

per cni:Jili =

21;

c h : i . t ~ ~ e f o r p a i n t e d p a t i e l

x

1 0 0

(4)

v r t , c h a n s e o f u n p a i n t g d n a n e l

'The p r e s e n c e o f t h e wood trl-lick1 a b s o r b s w a t e r r e a d i l y a f f e c t s t h e

v a p o u r p r e s s u r e d i - f ' f s r e n c e sii(!L t h e r e f o r e a f i ' e c t s t h e f i l m per~;ii:ance. 50 a b s o l u t e v a l u e o f p e r r a e a L i l i t y rimy b e d e r i v e d , , I t i s d i . f . ' f ' i c i ~ l t t o s e c u r e wcod p a n e l s w h i c h a r e u.niforrn, Pal;npar, a v e g e t a b l e parc'c~rnent, h a s b e e n x i d e l y u s e d a s a f i l ~ i ~ s u p p o r t . F i l m s c o a t e d o n p a t a p a r b y d i p p i n c showed a p e r - c l e a 1 : i l i t y v n r y i n c ; a , p r o x i : n a t e l g

5

p e r c e n t frorn t h a t o f f r e e

f i l n a

( 1 8 )

because o f a b s o r p t i o n o f w a t e r , The p r e c i s i o r ~ was

be.t.t,er f o r ~ . e s n l t s fro:n s ~ x p p o r t e d ~ . ' L ~ I T ~ s t h a n f o r t h o s e f r o m f r e e i s The d i s c r e p a n c y x a y b e s l i x i n a t e d by c o a t i n g one s i d e o f the p a t a p a r artd p l a c i n g t h e s i . r p ~ o r t t o ~ ~ r a r d s t h e d r y s i d s ( d r y - c u p l a n t h o f - l ) , P a t a p n r was f o u n d urisa'i;isT'actory f o r e x p o s u r e b e c a u s e i t s w e l l s ancl s l ~ r i n k s cons:i..derai;l;y p ~ ~ o c l u c i n ~ c r a c k s i n b r i t t l e ~ ; i a t ~ e r i r . ^ l s . Pa-y;le ( 2 1 ) c o r l s i d e r s g l a s s c l o t h ( f i b e r z l a s c - l o t h i.!o, 01--175) a n imn~ove.:nsni; o v e r j s a t a p a r f o r t h e p ~ e p a r a t i o n o f

s u p p o y t e d fi1:ns. 1;'ilms inay b e p r e p a r e 6 b y d i p . . . ~ c o n t i n g , and t h e

t';iic2:llesu d e t e r - n ~ i r l e i i froin t h e r . e l a t i o n o f r . ~ e i g h . t : , a r e a and

d e n s i z y . The : ; l a s s c l o t i i was u s e d f o r fj.11n.s w h i c h w e r e baiced a t

t l i ~ h teiclpertl-tu~raes

wf

t h e x c e l l e n t r e s u l t s ,

; le:+-!cds o r beterrrliilinp, . d a t e r Vapour

7

*

- - -

.---

--

-

'Irdnter vnpourl p e r : . n a a i - , i l i t y r i ~ e t t l o d s ma; b e d i v i d e d i n t a

t k e e b a s i z c l a s s e s . The f i r s t x e a s u r e s t h e we1y;h-l; gain of a n

a.bsorbinc; s u b s t a n c e c o a t e d w i t h +:,be f i l m m a t e r i a l , t h e s e c o n d

.:-ceesurc;; t h e xei.[;tit or' r r ~ . o - i s t ~ ~ . r e p e r i : n c a t i n g tl...rc:n,r;h a ~ ? . e r n t r a ~ ~ e

s e a l e t l i i l a cu-p, su.ch as t h e Pa7,rn~ p . c ; . r m e a S i l f t y cr.lp, and t h e t h i r d

m e a s u r e s t h e c k a n ~ e c f va:.jour p r e s s u r e i n an e v a c u a t e d systerr, a s

l;!le v a p o u r p a s s e s t h r o u g t ~ . t h e m e n b r a n e f r o x one h a l f o f a c e l l

c n t , : . a l t ~ l n ~ i.iater v a p c u r a t a kilota~n p r e s s m e ,

An e x ' m p l e o f t h e f ' i r s t c l a s s i s t h e f;'ol-cst P r o d u c t s

L a b o r a t o r y method. The .wej.ght oi' w z t e r s o r b e d by c a r c f r l l l g c h o s e n

ni.1~1 c c n d l ~ t i o n c d . b i r c h p a n e l s wtl.ich a r e p a i n t e d o n a l l s i d e s a n d

p l a c e d i n s co:is-t.an

t

t e i r p e r z l t u r e a n d h u z i i d i t y c a b i n e t i s x e a s i l r e d .

r77 ! - h i s rfiet,hr,d s~.~~'i.'e~-s t h e :31:.:;ativanta;.:es rnentiorled p r e v i o u s l y f o r

P1 L

l l l e c u p ;zel;l!ods are a l s o q u i t e s i m p l e . The f i i r n i s

s s a l e c ' ; o v e r t h e H I . O L ~ ~ ' L ~ i ' t h e cu,p c o n t a i n i n i ; e i t h e r a d e s i c c a n t

(dr.;;- cl-1p aietklod) o r a s o l u t i o n o r lcrlown v a p o u r p r e s s u r e o r p u r e

- , l a t e r ( w e t c u p tiiethod). 'i'hc ?;a-1.n o r l o s s o f w e i g h t i s m e a s u r e d

17eriodica:Lly. I n t h e Y l r s t xe-t-.l;od. th e cup i s p l a c e d i n a c o n t r o l l e d

E.i~~rriiiiitg at~i:,osl.~hel-e ; i n t h o s e c o n d , t h e clup t s u s u a l l y p l a c e d i n

a d e s i c c a t o r , ho~,re-ver,

i t

rmjr b e p l a c e d i n a l o w i i u r n i d i t y a t m o s p h e r e ,

Z i g i d , t e i - c p e r a t u r c contra01 i s n e c e s s a r y . I n % h e d r y c u ! ~ r n e t h ~ d ,

Ix?L!;h. h m l i d i t i e s .;Tag l e a d t o e r r o r t h r o u g h c o n d e n s a t i o n o n t h e f i l m .

T h e cun method h a s b e e n mociTfied f o r u s e w i t h m a t e r i a l s o r low

p e r a l e a t i l i t y ( 2 2 ) . f.l. l n e cup i s e n c l o s e d i n a g l a s s j a r a n d t h e

d e s l . c c a n t i s s u s p e n d e d o v e r t h e cup o n a c a l i b r a t e d q u a r t z s p r i n g .

?'he e x t e n s i o n o f t h e s p r i n g i s a Yceasure o f t h e w e i g h t o f w a t e r

p a s s i n g t h r o u g h t h e

rilrn.

The 1 ; ' e d e r a t i o n o f P a i n t and V a r n i s h P r o d u c t i o n C l u b s

h.as su?;:xitteci 2 s t a n d a r d :,erii:ea!-;ili~ t y m e t h o d b a s e d o n t h e c u p

; n e t h o d t c t h e J o i n t ."ederation-A

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(24)

u s e d a c e l l d i v i d e d i n t o

t w o h a l v e s betwee:? ~ , ~ h i c h . t h e filrrl was p l a c e d . B o t h h a l v e s r,Jere

e v e c u a t e d , a ca?sl.:le o f w a t e r was bro!!:en on one s i d e o f t;he f i l m ,

a:ld t h e chan[.;e o f p r e s s u r e or, t h e o t h e r s i d e was r a e a s u r e d w i t h a

mc:rcury alanome t e r

.

I-tl t h e s t u d j o r t h e e f f e c t o f t e m p e r a t u r e , r e l a t i v e

? ~ u m i d i t y and t h i c k n e s s v a r i a t , i o n s o n p e r m e a b i l i t y , D o t y , A i k e n

a d T4ark

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15)

made u s e o f a : ~ a p p a r a t u s b a s e d on c h a n g e o f

v-apourx p r e s s u r e i n all e v a c u a t e d sy-stern. P r e s s u r e chanlges w e r e

xnsasurecl ~ . . r i t h a I-;cLeod g a u g e ,

I n t h e me:;!-:ads d e s c r i b e d a b o v e

i t

i s c u s t o m a r y +c. p l o t

t h e c h a n g e o f w e i g h t o r p r e : : s a r e a g a i n s t t i m e . A f t e r an I . n i t i a . 1

period d u r i n g whicli s o r p t i o n e q u i l i b r i u m i s e s t a ! ) l i s h e d , t h e r a t e

of p e r m e a t i o n becoines c o n s t a n t . The w e i g h t o r p r e s s u r e chanp;e i n

u n i t tiyce inay t h e n b e d e t e r n l i n e c l f'rorn t h e l i n e a r p o r t i o n o f t h e c u r v e .

P r o f e s s o r

F.A.

J o y ( 2 5 ) , r e a l i z i n g t h e c o n f u s i o n a r i . s i n g

f r o m t h e interchanp:ea!rle u s e of' p e r m e a n c e a n d p e r m e a b i l i t y , h a s

ciefil-~ecl p e r m e a n c e ' ( 1 4 ) a s t h e r?rei[:,l-it o f w a t e r ~ e r r q e nl-.in(.. t h r o u g h u n i t

ar-ea of n l a t e r i a l i n u n i t tivie unde.?- unit ;ore ssure difference.

Yotrever, he i n t r o d u c e s Tilore c o n f u s i o n b y s t a t i n g t h a t t h e t e r m s

-pc>rrl:eance a-1.-:d perrnea1r)ili t y a r e ari a l o g o u s t o t h e t e r m s c o n d u c t a n c e

and c o n d u c t i v i t y ( e l e c t r i c a l c o l ~ d u c t a n c e i s s i m p l y t h e q u a n t i t y o f

a l e c i - r 8 t c l . t y p a s s i n s t h r o u g h a sa:.:;:le o f m a t - e r i a l oI" a n y dimensrions

pei,....,i7 L, t; a . : - B i i i ' L T '.. , as dei'iaed. b y J o y - - , w e i ~ , h t o f wa1;cr 17erliieating t h y o u p ; l ~

ul?;r.t, a r e a ci" u n i t t h i c k r i e s s i n u n i t ti!ile u n d e r u n i t p r e s s u r e

dii".?ere_n-ce

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a,ntl c o : x i u c - t i v i t g i s v a l i d . I n a l l c a s e s t h e world

irmpedal:.ce h a s r e f e r r e d t o t h e r e c i . p r o c a l o f perni'sance. T h e r e i s no t e r m c,ori-.es:?onciin.g t o t h e r e c i p r o c a l o f t h e p e r r n e a l , i l l . t y c f , ,

r e s i s t i v i t y .

I n the p a i n t i n d u s t r y , a teri:; w i d e l y u s e d i s s p e c i f i c

p e r : n e a t : j . : ~ . i t y l , the-: :xLlli;3rz!!s ~ i ' wa.ker p e r i n e a t i n g t h r o u g h one

squ8.i-e cei-itimet.i..c;t o.C m a t e r i a l one n ~ i l l i m e t r e t h i c k i - n t w e n t y - f o u r

E-~ocrs u n d e r a va:?ou.r p r e s s u r e d i i ' f ' e r e n c e of' f i f t y m i l l i m e t r e s o f

IneIacury ( 26)

.

l'hc Ga.:Ll..cll-~lg i n d u s t r y f a v o u r s t h e p e r n - i n c h , t h e

@ r a i n s of' w a t e r p e r m s cl;,ing one s q u a r e f o o t o f lna t e r i a l o n e - i n c h

t h i c k i n one h o u r u n d e r a va-:-,our p r e s s u r e d i f ' f e r e r i c e o f one i n c h

or" n l e r c u r y . P e r ! j : c a b l l i t g c o n s t a r l t s i n w h i c h t h e q v a n t i t y o f

krater v a P o u r kiss 1 een e x p r e s s e d i n m o l e s o r cu'riic c e n t i m ? t r e s a t

stanciarcl t e r ~ p c r a t u r e and p r e s s u r e h a v e b e e n u s e d 2 . P e r ~ n c a t i o n m e a s u r e x e n t s h a v e a l s o tiean r e p o r t e d i n tsr::ls c f n l o i s t ~ ~ r e e x c l u d i n g e i ' f i c i e n c g 3 and w a t e r v a n o u r t r a n s n l i s s i o n I lli-1 i

t

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t i n - p l a t e p a n e l s wkLich h a d b e e n p r e v i o u s l y analgama-~.;ed, The t i n -

p l a t e wasa:~:algamhteci by rubbi.ric; a s m a l l alz.ount of' rriercury o v e r t n e

s u r l ' a c e . k . f t e r t h e T i l r t i s beca:;:e d r y e n o u g h t o h a n d l e , t h e y vrers

s t r i p p e d frcrn the p a n e l s and a l l o ~ ~ ~ e d t o ap;e f o r a s r ~ e c i f i e d p e r i o d .

Tile f i l i n t h i c k n e s s e s w e r e m e a s u r e d a f t e r t h e co.lidi-

t i o i l i n s p e r i o d . irxoecil.ntelg b e f o r e m o u n t i n g . The fi.l-r;ls w e r e mouilted

i n ca:ps s u p - p l i e d b y t h e Duil.diri{; S e r v i c e s S e c t i o n , D i . v i s i o ~ - : of

Buildi;?!;; l~icsea~zt-: ,z.n.c-l s e a l e d w:i.th wax. 'The d e s i c c a n t , c a l c i u m

c h l o r i d e d e h ; j ~ l r a t e h e a t e d a t 1 1 G " C . , was prev:i.ously- p l a c e d i n tine

C U F t o r ~ ~ i t h i n

1/4.

i n c h o f .'itla l e v e l of' t l i e f i l m . A c i r c u 1 a . r pilece

of o o t t . o n b a t t i n g was ~ l u c e c l o v e r t h e c a l c i u m c h l o r a i d e t o p i 9 n v e : > t

d.otr~a,-,e t o the f'fir:l,

The p3ri;leafice m.easurernen.t was c a r r i e d o u t by t h e

B u i l d i n g S e r v i c e s S e c t i o n , The \ r a t e r v a p c u r perlne a - ~ c e was d e t e r i n ? - n e d

i ~ aecordar:ce r r i t h T A F P I X e t h o d T2+!.\.8-M!.~9, W a t e r 'Ja:-lour P e r m e a l - j i l i . t y i

o f P a p e r and P a p s r b o a r d , T e c h n i c a l A s s o c i a t i o n o f t h e P u l p and

F s p c r I n d u s t r y .

Tlle c;:;~s rrere p l a c o d i.il a n i n v e r t e d p o s i t i o n i n t h e

c , ~ i l t r o l l c d i:,an~pcrat-;ul-.e and humiclity c a b i n e t . 'l.'lie c o n d i t i o n s

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elernelits. G e s i c c z n t

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c n l c i u ~ n c h l o r i d e d i h g t l r a t e .

T h e pe2:ncance was r e p o r t e d i n perms, i . e . , g r a i n s of

u a t e r p e r m e a t i n g througll one s q u a r e f o o t of matex7inl i n one

l i ~ ~ - l r under a xr:,.:>o~.~r; p r e s s u r e d i f f e r e n c e o f one i n c h of mercury.

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z l s o a s " p e r l a e a b i l i t y c o n s t t ? n t s l '

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-- or1 t > ~ . e coTr2el:.:-l;i(jll

o r

ph;:-:;ical i ~ r o p c l - ~ t i e s 01' p~'.iilt - .

.

1 . YI.!s:;e p e r r i l e s l ~ i l i t y d-cterii,1inction.a

,

.:, -. . --. :,. ,>, ..;

.

L , u _ L . \.,:~ .., :,:yn'i; ~ ~ b e r i n c loi.11, T.:..T~:..E: pl.op~.c'::ii t o relate

I-) _{- .} 2

l:.i.cl;p';r.J,-ic>:; :;1lci,. 2 2 .,.,yi,jo>:'uili-l-?- i,. , r;cLjlesiolL znc

' J 9 rl ;I; i l e i; -p i..!. r Ll :: ti:

oz : ; , - , u s e i,zL?j-i;t f ilL;ls to t i l e i p a j i l - j - . t ~ j - to p e : ; i s t b l i s t e r i ~ ~ . 0 ,.." 7 c..;LLb (3'~:-. (2 1'

r:',

5 _{1 ~ 1 . 6} 3 --

.

O f f i c i a l i;iiyest L >

1 C : ? 6

9 297, (1-1 i,ayne?, iL. I .-) 7 .

,

? , i ; . P r o t e c t l v c ; . n d L!ecorative C o a t i n g s , iiol. l i i : . , a t ; t i e l l o . ; 2' :.L rl';- ; ; F '; -

,, -a, ) ~ ; a >me

,

? .].I, ' "~

.

,., Cr;:.lidner. I . n . Cherri. 29,

893

(

1 5 3 7 )

8

.,

(Li.) s ~ . i ; g - ,

.

I , ' i 1 . a n

.

i . t i i x l

.

1 6 ,

oct3 ( l C j L C L C )

.

:

I I'lr

t

3

';,

- c - i ~ l o ~ ~ , Y,

I,.

,

. ileI>r;l..,r - ,~ar?-:i, !;'.A. and

A.R.

I;emp. I b i d ,

28,

1255

( Ly.:j b ! e ( : 9 1:. 7::. D i f f ; U S i O l l i l l ~ , n c ; l;hrou;S1? s o l i d s , Cai-<Lb~:id,:..e

.

. .. . 8.-> ~ . ; n ~ v ~ l : s i t y I:pess l ~ < l . , - - / / ( G c l r . 2 ~ l c r ,

.

In(:.

b11~. Chern.

23,

1402

( 1 9 3 1 ) .

1 1 - , L i l ; i c i .

25,

437

( 1 9 3 6 ) .

(5)

I : , i . _{i b i i i ,}

30,

_4-09

(lc)38).

( 0 ) P , 1 . TYt.u13. Far. Soc.

35,

628 ( 1 7 3 9 ) .

v ,.

( 11) I i a u s e r , I-.. i.!. a n 6 1). i ; i c l Z ~ e n , Ind. Ant;. Chern. //.Us 1 1 2 (

191ii'l)

.

( 1 2 ) r I . J. i bid. 28,

786

( 1936)

.

( 1 3 )

Goa:::r, C . L . nnd . L L . J. I . ; i l l e r , I b i d . , Anal. b c l .

15,

737

( 1 9 4 3 ) .

( 1 ) . J . . r 1.

I?.

a I 28,

54.9

( 1936)

.

(13)

Yjcty, i?.i;i., i.ilien, . . I < . a n d 11. Hark. I b i d .

3 8

788

(1C)Ik6je

( i b ) y 1.2. ::.nu I : . L ~ . van Vorst. I b i d . 25,

84.2

(1933)

( 7 )

I

.

O:I-1,iciul i j i g e s t 1947,

197.

( 3 )

, ,;o&

r~-j:lt

and

'iJg.jl?ish yr.ocjuci;ion Club, '.ilechr_ical

C o ~ n r ~ i t t e e PaJ.nt a n d Vel:nish P r o c e e d i n g s of t h e

i:c:i : : : l t i f ' i c :;ect-ion, 1939.

.' 7 r ~ ' ) , iF !,jcc3py 11. ..!. and ,.F. Iiickson. Bur. S t a n d . J . R e s e a r c h 1,

1, ( 1 9 2 5 )

.

,

-.

1 . j e , .

.

2'. I ' i ~ i d . ii n a l . iid.. 11,

453

( 1 9 3 9 )

.

( 2 2 ) liurr,.;z:inn, i~.,i. d e l l ~ a b . Fiecord

13,

4.5

( 1 9 3 4 ) .

,., - \

-

( L ; , _ zr:e;..:ition :;tc7.:-rda:.-d 9-47, i ! ' e ~ ~ :I'orlr ? a i n t a n d ii'crnish

I'ro6uct;ion Cl-ilb. i c iii;e s t

1147,

479.

( 2 3 c.l~:-a;l;i]rer:, ;., t l x l f i

L

Ipe 1, ,

_-

,-. .uson, Ir~c.:

.

l,rq;. <Jle~:l. 21,

15c

-,

( 1Cj2c;, )

( ' r : _, )

,

A . p=rnn.

:,!

n -L;z G o l l e g e , - - kcp. . , t a t i o n , ' I ' e c h n i c a l

%per IT?.

85.

(26)

Ljunn, L.J. Jr. O f ~ ' i c ; i n l _-- ~ ; : ' ~ g , e s t 1952, 365.

(

27)

Chcng, ;i. C. 2nd. i i . 3. I:'i?~tclleon. 12cr;f 01-mance o f L e s i c c a n t s i n

t--le Dry Fan T e s t f o r .Jai;er Vapor Perrneance of 1kiernbr:lnes.

gar^. J. of [Pechnology, 31:175-192. S e p t . 1953.

(23)

:!nCel ;n:~tic;nt.l i ; ~ - i . ' i i c u l T ~ ~ b l e s 1101. 111, p.

305.

T i,

( 2 J ~ r ; n o y , ... c~. jA;ncr:icz.n Paint J o u r n a l

36,

ido. 32, 82, 81/.-07

APPENDIX

-..--

Note

A

It is unfortunate that the term specific permeability has

been adopted for this quantity. It would be logical to consider

specific permeability and permeability as synonymous, the units

depending upon the system of measurement.

Specific permeability is,

however, a particular reas1Lr.e of permeability.

Note

B

Hauser and McLaren

(11)

expressed the quantity of water in

moles; the permeakility is

~ f v e n

as tho permeability constant,

N

=

number of moles

1

=

thickness in centimetres

A =

area in square centimetres

L L ~ =

vapour pressure difference in centimetres of mercury

t

=

time in seconds,

Doty, Aiken and Mark

(4)

expressed the quantity of moisture

vapour in cubic centimetres at standard temperature and

pr

essure; the

permeability is given as the permeability constant,

The quantities A , h p and t are expressed in the units of Hauser and

McLaren, however, the thickness

1, is measured in millimetres.

The

eonstznt used by Hauser and FbLaaren may be converted to cc,'s-m.

per cma2-cm. of Hg.-sec.

by multiplying by

2.24

x lo5 (one mole of

gas o o c ~ ~ ~ i e s

2.24

x

104

cz.

at S.T.P.).

Values of Permeabtlity Constant Expressed in

cc,

-me

cm,L-cm.~g,-sec,

for Polyethylene

Hauser and McLaren

5.9

x

loo8

Doty, Aiken and Mark

4.0

x loo8 (cast)

6.1

x log8

(calendered)

Note

C

Percentaze moisturle

excluding efficiency is equal to

A-B

x 100.

--

A

A i s

the weight gain of unpainted panel.

App. 2.

-..,

: : j ~ - a e ~ t Proi!acts Ls.:.jora'torg perciea t i o n r e ~ , u l t s a r e e x p r e s s e d

--

~ - , ~ ~ : c e n t a ; . ~ e ?. iizoris'tur;e e x c l u d i n g e f f i c i e n c y .

- .

~ : i t ( i i . 'J't~pour 'Tr;insi;;ission U n i t s a r e u n i t s i n which

. "

;:.: r:::en t i o n

re::

i-il-;s :lye e x p r o ,,ded r c - sj-~tiply a:: weight p e r u n i t

z r e a I r i u l l i t t i i : ~ e .

'Tl-lic:lcnesz l;i.ezsu-rcimnts were :nade on t h r e e s e t s

of

.I;!-:I~ p:il.ct r"il!.;zcc w : i t l l

rn

1'il;les din1 ;?luge a f t e r t h e t e s t s were

ccncl~..;ded a ~ i d t h e f i l ! ~ ~ : : \Jeri

dr

l r : d ii? n d e s i c c n t o r . I n a l l

c:!.:_:e s :.he t l l i c l r ~ e s s ,?::oslled a corls iclcrable i n c r e a s e o v e r t h a t

.;let:

:;ur

ec]. on enr dl~ie - - 1 thtcliiie s s gauige. T15.s d i f f e r e n c e c a n

i j e explcLir.led a ~2 :incr,e'l '.,ec. in thiclcness of f i l m because of

oxidcti-ve p o l g i i i ( > ~ i ~ ~ i t i o n o r a dii'f cr:ence i n c a l i b r a t i o n of t h e

'a'

.p