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Method for determining the gas permeability of urea formaldehyde
foam insulation samples
NATIONAL RESEARCH COUNCIL OF CANADA DIVISION OF BUILDING RESEARCH
DBR INTERNAL REPORT NO. 499
METHOD FOR DETERMINING THE GAS PERMEABILITY OF UREA FORMALDEHYDE FOAM INSULATION SAMPLES
by S. J . R o l f e and P . J . S e r e d a
Checked by: Approved by: L.W. Gold Date: A p r i l 1985
Prepared for: Records P u r p o s e s
ABSTRACT
The r e s i s t a n c e t o a i r f l o w w a s measured f o r UFFI and o t h e r i n s u l a t i n g materials u s i n g a s i m p l e t e s t d e v e l o p e d f o r t h i s p u r p o s e . The r e s i s t a n c e t o a i r f l o w of a foam s p e c i m e n may g i v e an i n d i c a t i o n of i t s s t r u c t u r e and t h e amount of d e g r a d a t i o n t h a t h a s o c c u r r e d . When compared t o o t h e r i n s u l a t i n g m a t e r i a l s , W F I had a h i g h r e s i s t a n c e i n most c a s e s .
METHOD FOR DETERMINING THE GAS PERMEABILITY OF UREA FORMALDEHYDE FOAM INSULATION SAMPLES
S.J. Rolfe and P.J. Sereda
I t was b e l i e v e d t h a t t h e g a s p e r m e a b i l i t y of u r e a formaldehyde foam i n s u l a t i o n (UFFI) was an i m p o r t a n t m a t e r i a l p r o p e r t y t h a t c o u l d p r o v i d e t h e b a s i s f o r an a s s e s s m e n t of t h e e x t e n t and e f f e c t i v e s i z e of foam c e l l
i n t e r c o n n e c t i o n s , and t h e r e f o r e t h e e a s e of removal of o f f - g a s e s by a i r f l o w t h r o u g h t h e foam.
P r e l i m i n a r y t e s t s e s t a b l i s h e d ' t h a t a l i n e a r r e l a t i o n s h i p e x i s t e d
between t h e volume of a i r f l o w i n g t h r o u g h a g i v e n t h i c k n e s s and a r e a of foam and t h e p r e s s u r e d r o p r e q u i r e d t o s u s t a i n t h e flow. It was t h e r e f o r e
p o s s i b l e t o d e t e r m i n e t h e r e s i s t a n c e - t o - f l o w f a c t o r t h a t would c h a r a c t e r i z e t h e g i v e n sample. The f o l l o w i n g r e l a t i o n s h i p was developed:
*
( p r e s s u r e d r o p p e r u n i t l i n e a r v e l o c i t y p e r u n i t t h i c k n e s s of sample) Where: P1 i s t o t a l p r e s s u r e d r o p , mm Hg P 2 i s t o t a l p r e s s u r e drop a c r o s s empty f u n n e l s , mm Hg V i s volume of a i r p e r u n i t t i m e , t , (mm)3/min A i s c r o s s - s e c t i o n a l a r e a of sample, (mm)2 h i s sample t h i c k n e s s , cmT h i s n o t e d e s c r i b e s t h e proposed t e s t method and g i v e s some t y p i c a l r e s u l t s . T h i s may p r o v i d e t h e b a s i s f o r comparison between d i f f e r e n t foams and o t h e r i n s u l a t i n g m a t e r i a l s .
EXPERIMENTAL
Sample P r e p a r a t i o n
The sample f o r t e s t i n g uust be an u n d i s t u r b e d p i e c e of UFFI. From t h i s , a c o r e was t a k e n w i t h a t h i n - w a l l e d t u b e ( s i m i l a r t o a c o r k b o r e r ) a s shown i n F i g u r e 1 t o p r o v i d e a c y l i n d r i c a l specimen a b o u t 2 mm g r e a t e r i n d i a m e t e r t h a n t h e i n s i d e d i a m e t e r of t h e f u n n e l i n t o which i t i s pressed.
It was i m p o r t a n t t h a t t h e s i z e s of t h e specimen and t h e f u n n e l were s u c h t h a t t h e r e was an a i r t i g h t s e a l between t h e foam and t h e f u n n e l s o t h a t a i r d i d n o t bypass t h e sample.
The specimens were made by r o t a t i n g t h e s h a r p c u t t e r a s i t was g e n t l y p r e s s e d i n t o t h e foam. The ends of t h e specimen were c u t f l a t w i t h a s h a r p k n i f e t o make t h e specimen 50 mm l o n g . The c u t t i n g was done w h i l e t h e
Apparatus
The a p p a r a t u s f o r t h e s e e x p e r i m e n t s was made f r o m s t a n d a r d l a b o r a t o r y equipment ( F i g u r e 2). UFFI specimens were h e l d between two s i n t e r e d g l a s s f u n n e l s (Pyrex 36060, 60
mL,
c o a r s e f r i t ) s e a l e d t o g e t h e r w i t h PVCe l e c t r i c a l t a p e . The p r e s s u r e d r o p a c r o s s t h e specimen was measured w i t h a mercury f i l l e d U-tube manometer w i t h a m i r r o r e d s c a l e c a l i b r a t e d i n mm. Flow r a t e was measured w i t h a r o t a m e t e r ( F i s h e r and P o r t e r S t a b l - V i s
F l o w r a t o r #LK-7355) and p r e s s u r e was c o n t r o l l e d w i t h a g a s r e g u l a t o r . A l l
c o n n e c t i o n s were made w i t h Tygon t u b i n g . T e s t P r o c e d u r e
P r i o r t o t h e t e s t i n g of foam s p e c i m e n s , t h e assembly of t h e two f u n n e l s ( w i t h o u t a specimen) was c o n n e c t e d i n t o t h e a p p a r a t u s . P r e s s u r e a c r o s s t h e . f u n n e l s was a d j u s t e d u s i n g t h e r e g u l a t o r t o d i f f e r e n t v a l u e s i n d i c a t e d on t h e manometer, and t h e s e were r e c o r d e d w i t h t h e c o r r e s p o n d i n g f l o w r a t e a s p o i n t s on a graph. T h i s measurement r e p r e s e n t e d a b l a n k v a l u e , n e c e s s a r y t o c o r r e c t v a l u e s o b t a i n e d w i t h t h e specimen.
T h i s t e s t was r e p e a t e d i n d u p l i c a t e f o r e a c h specimen t o check f o r changes t h a t might have o c c u r r e d on i n c r e a s e and d e c r e a s e of p r e s s u r e .
I£ a
change o c c u r r e d between t h e f i r s t and s e c o n d t e s t s , i t i n d i c a t e d t h a t t h e s e a l i n g of t h e sample i n t h e f u n n e l had changed, a l l o w i n g a i r t o bypass t h e specimen around i t s edges. Once samples were s a t i s f a c t o r i l y p u t i n t o t h e f u n n e l s , c r a c k i n g and s p l i t t i n g were n o t a problem.RESULTS AND DISCUSSION
I n a l l c a s e s , t h e p r e s s u r e vs. f l o w c u r v e s were s t r a i g h t l i n e s w i t h v e r y l i t t l e s c a t t e r ( F i g u r e 3). The p e r m e a b i l i t y ( p ) of a specimen was d e f i n e d t o be t h e s l o p e of t h i s l i n e minus t h e s l o p e of t h e l i n e p l o t t e d f o r empty f u n n e l s . The r e s i s t a n c e of a sample t o a i r f l o w (Rf) c o u l d t h e n be c a l c u l a t e d f r o m p a f t e r measuring t h e specimen d i a m e t e r and t h i c k n e s s .
I n i t i a l measurements were done u s i n g f u n n e l s chosen a t random from l a b s t o c k . Some of t h e s e measurements showed a d e c r e a s e i n r e s i s t a n c e t o a i r f l o w w i t h r e p e a t e d a p p l i c a t i o n s of p r e s s u r e ( F i g u r e 4 1 , and r e s i s t a n c e
i n c r e a s e d when t h e specimen was compacted.
To check t h e p o s s i b i l i t y t h a t a i r p a s s e d between e d g e s of t h e foam and t h e f u n n e l r a t h e r t h a n t h r o u g h t h e foam, t h e measurements were r e p e a t e d w i t h h i g h vacuum s t o p c o c k g r e a s e on t h e i n s i d e of t h e f u n n e l s t o s e a l t h e e d g e s of t h e specimen. The measurements done i n t h i s manner were r e p r o d u c i b l e even a f t e r a p p l i c a t i o n of a 75 mm Hg p r e s s u r e d i f f e r e n c e , and t h e r e s i s t a n c e d e c r e a s e d when t h e sample was compacted. F u r t h e r i n v e s t i g a t i o n showed t h a t some f u n n e l s had a s l i g h t l y l a r g e r i n s i d e d i a m e t e r t h a n t h e mean of t h e l a b s t o c k (one mm s m a l l e r i n s i d e d i a m e t e r t h a n t h e i n s i d e d i a m e t e r of t h e
c u t t e r ) , s o t h e s e were removed f r o m t h e s t o c k . With s m a l l e r f u n n e l s ( a t l e a s t 2 mm s m a l l e r i n s i d e d i a m e t e r t h a n t h e i n s i d e d i a m e t e r of t h e c u t t e r ) , t h e r e was no e v i d e n c e of a i r b y p a s s i n g specimens a t p r e s s u r e s up t o
100 mm Hg. Subsequent measurements were done w i t h t h e s m a l l e r d i a m e t e r f u n n e l s and n o g r e a s e .
The r e s i s t a n c e t o a i r f l o w of f o u r specimens e a c h of f o u r UFFI samples was measured, and t h e a v e r a g e r e s u l t s a r e g i v e n i n T a b l e 2. The r e s i s t a n c e t o a i r f l o w of foam specimens v a r i e d by 20% t o 50% f o r e a c h foam sample. Three of t h e samples (foams A, B and D) had h i g h r e s i s t a n c e t h a t d e c r e a s e d when t h e specimens were compacted. This i n d i c a t e d t h a t c e l l w a l l s i n foam s t r u c t u r e were f r a c t u r e d l e a d i n g t o an i n c r e a s e i n t h e e f f e c t i v e s i z e of i n t e r c o n n e c t i n g c h a n n e l s . Foam D was an e x c e p t i o n b e c a u s e i t s r e s i s t a n c e d e c r e a s e d and t h e n i n c r e a s e d i n e x p l i c a b l y on compaction.
An e x c e p t i o n t o t h i s behaviour was Foam C. It had a low i n i t i a l r e s i s t a n c e t h a t i n c r e a s e d when t h e foam was compacted. In t h i s c a s e ,
compaction tended t o d e c r e a s e t h e e f f e c t i v e s i z e of i n t e r c o n n e c t i n g c h a n n e l s which must have been l a r g e t o s t a r t w i t h - (The m i c r o s t r u c t u r e of UFFI i s r e p o r t e d i n a n o t h e r n o t e ) .
I t i s r e a l i z e d t h a t compaction may i n c r e a s e t h e p a t h l e n g t h p e r u n i t t h i c k n e s s and t h a t a f a c t o r may need t o be a p p l i e d i f compacted samples were t o be u s e d -
When t h e r e s i s t a n c e of UFFI t o a i r f l o w was compared t o t h e r e s i s t a n c e of o t h e r i n s u l a t i o n t y p e s ( T a b l e 3 1 , UFFI appeared r e l a t i v e l y impermeable, e x c e p t Foam C.
CONCLUSION
The r e s i s t a n c e t o a i r f l o w was measured f o r UFFI and o t h e r i n s u l a t i n g m a t e r i a l s u s i n g a s i m p l e t e s t developed f o r t h i s purpose. The r e s i s t a n c e t o a i r f l o w of a foam specimen may g i v e an i n d i c a t i o n of i t s s t r u c t u r e and t h e amount of d e g r a d a t i o n t h a t h a s o c c u r r e d . When compared t o o t h e r i n s u l a t i n g m a t e r i a l s , UFFI had a h i g h r e s i s t a n c e i n most c a s e s .
TABLE 1. R e s i s t a n c e Measurements of UFFI Showing Bypass of Air Around Sample
Foam T h i c k n e s s * (cm) R e s i s t a n c e (Rf (m Hg/(mm/min)/cm)
*
Compacted f r o m 5 c m t h i c k n e s s .TABLE 2. R e s i s t a n c e t o A i r Flow of UFFI Samples Foam R e s i s t a n c e (R )
T h i c k n e s s * (mm Hg/(mm/min)/cm~ x
(cm) Foam A Foam B Foam C Foam D
-
*
Compacted f r o m 5.0 cm t h i c k n e s s . TABLE 3. R e s i s t a n c e of V a r i o u s I n s u l a t i n g M a t e r i a l s t o A i r Flow - R e s i s t a n c e M a t e r i a l (mm Hg/(mm/min)/cm) F i b r e g l a s s B a t t 0.036 x 1 0 ' ~ F i b r e g l a s s S h e a t h i n g 0.15 x lo-3 Blown C e l l u l o s e 0.15 x l o - 3 UFFI ( A v e r a g e ) 8 1 0 ' ~SHARPENED CUTTING EDGE F I G U R E 1 S P E C I M E N C O R E C U T T E R F O R M A K l N G U F F l S P E C I M E N S R LAB A I R Y 1 :
<
PYREX SINTERED GLASS FUNNELS F I G U R E 2 T E S T A P P A R A T U S F O R P E R M E A T I O N M E A S U R E M E N T SP R E S S U R E A C R O S S S A M P L E , m m H g F I G U R E 3
P R E S S U R E A C R O S S S A M P L E , m m Hg F I G U R E 4
FLOW RATE V S P R E S S U R E D R O P FOR UFF l S P E C I M E N S H O W I N G B Y P A S S OF A I R . N U M B E R S I N D I C A T E THE ORDER I N W H I C H THE M E A S U R E M E N T S WERE M A D E
