Formaldehyde Release from Wood Products - American Chemical

14

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 19, 2017 | http://pubs.acs.org Publication Date: August 8, 1986 | doi: 10.1021/bk-1986-0316.ch014

Predicting Real-Life Formaldehyde Release by Measurement in the Laboratory M. Romeis Centre Technique du Bois et de l'Ameublement, 10 avenue de Saint-Mande, 75012 Paris, France The purpose of this study was to evaluate laboratory formaldehyde release test methods for predicting real-life formaldehyde air concentrations, human exposure levels, and health risk. Three test methods were investigated: the European perforator test, the gas analysis method at 60°C and 3% RH, and the gas analysis method at 23°C and55%RH. Different types of particle-board bonded with urea-formaldehyde and urea-melamine-formaldehyde resins were tested. The results were used to rank boards as a function of test method, conditioning, short-term humidity, and temperature variations during storage. Additional experiments were conducted in small experimental houses at a Dutch research institute. Our conclusions are that relative ranking of products is influenced by the test method and by change in relative humidity. The relationship between test method and release in real-life situations is not clear. In fact, it seems impossible to use laboratory measurements to predict real-life product performance of board if the board is not fully in equilibrium with the atmosphere. Formaldehyde emission from particleboard has been studied at our laboratory for over 15 years. We search for an answer to the following question: Given the fact that ami no-resin bonded wood products have the ability to release formaldehyde into indoor air when they are in use, what simple and rapid analysis method can be used at the time of manufacture to predict formaldehyde release under use conditions as quantitatively as possible? Obviously, the chosen method needs to be applicable for all types of boards that are available on the market. Background The presence of formaldehyde is due to the necessity to provide for an e x c e s s o f a l d e h y d e , i n o r d e r t o g e t good r e s i n c u r i n g .

I t i s well

0097-6156/86/0316-0188$06.00/0 © 1986 A m e r i c a n C h e m i c a l Society

Meyer et al.; Formaldehyde Release from Wood Products ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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e s t a b l i s h e d t h a t t h e r a t i o o f formaldehyde t o t o t a l n i t r o g e n compounds i s r e l a t e d t o t h e e m i s s i o n tendency o f t h e f i n i s h e d p r o d u c t


CDT h i s e x c e s s aldehyde may be p r e s e n t i n d i f f e r e n t c h e m i c a l s t a t e s . V a r i o u s h y p o t h e s i s e x i s t about t h e s e : 1. Formaldehyde i s i n a f r e e s t a t e , and we may p r e d i c t i t s e m i s s i o n by means o f w e l l known p h y s i c a l laws. 2. Formaldehyde i s combined w i t h wood and may be d i s p l a c e d by o t h e r r e a g e n t s , such a s water. I n t h i s c a s e , water a d d i t i o n w i l l cause a l d e h y d e r e l e a s e . 3. Formaldehyde i s absorbed i n t h e water absorbed i n t h e wood c e l l w a l l ; i t may be r e l e a s e d when t h e water v a p o r i z e s from t h e board. 4. Formaldehyde i s an i n t e g r a l chemical p a r t o f t h e c u r e d a d h e s i v e ; i t may be r e l e a s e d by h y d r o l y s i s . Whatever t h e h y p o t h e s i s , i t always i n v o l v e s e x c e s s a l d e h y d e . T h i s i s t o say t h a t : 1. The formaldehyde c o n t e n t d i m i n i s h e s w i t h t i m e . 2. A n a l y s i s o f t h e t o t a l e x c e s s aldehyde w i l l g i v e t h e maximum q u a n t i t y o f formaldehyde a board may r e l e a s e d u r i n g i t s l i f e , and 3. A n a l y s i s p e r m i t s e s t i m a t i o n o f t h e r a t e o f i t s r e l e a s e , and, t a k i n g i n t o a c c o u n t t h e maximum v a l u e found above, p r e d i c t i o n o f t h e r e l e a s e r a t e o f t h e board. Exper imentaI Numerous p r e v i o u s s t u d i e s have l e d t o e q u a t i o n s p e r m i t t i n g p r e d i c t i o n s o f formaldehyde r e l e a s e r a t e s , b u t none o f t h e s e were based on boards manufactured i n F r a n c e , p a r t i c u l a r l y not me I amineurea-formaIdehyde a d h e s i v e bonded boards. I t was i n t e r e s t i n g t o us t o a p p l y t h e s e t e s t i n g methods t o French boards. We s e l e c t e d i n d u s t r i a l p a n e l s f o r t h i s s t u d y , s o t h a t t h e r e s u l t s have p r a c t i c a l v a l u e . U n f o r t u n a t e l y , t h i s c h o i c e p r e s e n t s drawbacks i n t h a t i n t h e comparison o f i n d u s t r i a l p a n e l s s e v e r a l parameters may vary from one panel t o a n o t h e r . From t h e numerous p o s s i b l e methods a v a i l a b l e , t h r e e were s e l e c t e d , because they had a l r e a d y g i v e n good c o r r e l a t i o n s i n o t h e r European s t u d i e s . These methods a r e : 1. The p e r f o r a t o r method, European S t a n d a r d CEN EN 120 ( 2 ) : T h i s method uses c u b i c specimens, 2 x 2 cm x board t h i c k n e s s . T h i s i s a t o l u e n e t o t a l e x t r a c t i o n method and t h e formaldehyde i s determined by t i t r a t i o n w i t h i o d i n e . The r e s u l t i s e x p r e s s e d i n HCHO mg/100 g board. Two g a s f l o w methods: These methods a p p l y t o l a r g e r specimens, up t o 9 x 50 cm x board t h i c k n e s s f o r our a p p a r a t u s . Board edges may be s e a l e d . The aldehyde i s d r i v e n o f f by n i t r o g e n f l o w , r e c o v e r e d i n w a t e r , and d e t e r m i n e d p h o t o m e t r i c a l l y w i t h c h r o m o t r o p i c a c i d . The chosen methods a r e : 2. The FESYP Gas f l o w method, u s i n g n i t r o g e n a t 60 C, 3% r e l a t i v e h u m i d i t y , 120 L/hour n i t r o g e n . The r e s u l t i s e x p r e s s e d i n HCHO ug/kg board x hour ( 3 ) , and 3. The European D r a f t s t a n d a r d ( 4 ) , u s i n g n i t r o g e n a t 23 C, 5 5 % RH, 20 t o 60 L/hour n i t r o g e n . The r e s u l t i s e x p r e s s e d i n HCHO ug/n i t r o g e n I i t e r . 0


190

F O R M A L D E H Y D E RELEASE F R O M WOOD PRODUCTS

We used e i g h t b o a r d s , s e e T a b l e I . A l l boards were 19 mm t h i c k . Each method w i l l p r o v i d e as a r e s u l t a formaldehyde q u a n t i t y . Thus, i t i s p o s s i b l e t o rank t h e boards i n o r d e r o f i n c r e a s i n g v a l u e s , presumably c o r r e s p o n d i n g t o i n c r e a s i n g " p o l l u t i o n " .

T a b l e I . Board Samples Used i n t h i s Study


Type

Fl F2 F3 F4 Rl R2 R3 R4

Wood S p e c i e s

Mixed Hardwoods

Adhesive

Year o f Manufacture

UF #1; low F/NH + scavenger UF #1; w i t h o u t scavenger UF #2; h i g h F/NH Melamine-UF; higfi F/NH UF #3; low F/NH UF #4; e q u i v a l e n t t o #1 UF #5; F/NH between #4 ft #2 Melamine-UF^ 9

9

9

Mixed Softwoods

A

9

0

1983 1981ft1983 1981 1981 1984 1984 1984 1984

R e s u l t s and D i s c u s s i o n I t i s f i r s t n e c e s s a r y t o check i f t h e r e l a t i v e r a n k i n g o f t h e samples i s t h e same f o r a l l a n a l y t i c a l methods. I f t h i s i s n o t t h e c a s e , then i t w i l l be n e c e s s a r y t o t a k e i n t o a c c o u n t t h e e m i s s i o n r a t e . I f t h i s does n o t e x p l a i n p o s s i b I e d i s c r e p a n c i e s , i t becomes n e c e s s a r y t o c o n s i d e r t h e i n f l u e n c e of s t o r a g e o r c o n d i t i o n i n g , i . e . t h e h i s t o r y of t h e board from t h e t i m e o f m a n u f a c t u r i n g i n t h e p r e s s and t h e i n f l u e n c e o f sudden changes o f e n v i r o n m e n t a l c o n d i t i o n s . The r e s u l t s o b t a i n e d w i t h t h e t h r e e ana l y t i c l a I methods a r e shown i n T a b l e I I . Table I I .

Board

Fl F2 F3 F4 Rl R2 R3 R4

1981 1983 1981 1983

R e s u l t s O b t a i n e d by Three A n a l y t i c a l Methods

Perforator mg/lOOg board

16 28 28 73 64 61 10 16 21 38

Gas f l o w FESYP 60°C; 3% RH HCHO mg/kg board h r

Gas f l o w CEN 23°C; 5 5 % RH HCHO mg/L n i t r o g e n

1 .02 8 9 1 .83 3 8 10 9 1 .33 1 .88 1 .83 2 .87 1 .08


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The absence o f any c o r r e l a t i o n between t h e t h r e e methods can be seen immediately. I n p a r t i c u l a r , i f we compare t h e r e s u l t s o b t a i n e d w i t h t h e p e r f o r a t o r and t h e gas f l o w method a t 23 C, 5 5 % RH which i s c l o s e t o normal use c o n d i t i o n s , we note t h e i n c o n s i s t e n t r e s u l t s shown i n F i g u r e I. I n f a c t , i f we c a l c u l a t e t h e r a t i o , p e r f o r a t o r r a t e t o gas f l o w r a t e , we o b t a i n t h e f o l l o w i n g approximate r a t i o s :


B o a r d s R l , R2, and R3: B o a r d s F l and F2: B o a r d s F4, and R4:

R a t i o o f P e r f o r a t o r t o Gas Flow R a t i o o f P e r f o r a t o r t o Gas Flow R a t i o o f P e r f o r a t o r t o Gas Flow

= 7 =15 =40

T h i s r a i s e s doubts about t h e r e l i a b i l i t y o f p r e d i c t i n g formaldehyde e m i s s i o n by u s i n g t h e p e r f o r a t o r . However, on t h e o t h e r hand, each group o f p r o d u c t s c o r r e s p o n d s t o a g i v e n a d h e s i v e . T h i s means t h a t f o r a g i v e n a d h e s i v e a c o n s t a n t r e l a t i o n s h i p e x i s t s between t h e p e r f o r a t o r r a t e and t h e e m i s s i o n , a s has been a l r e a d y demonstrated i n e a r l i e r s t u d i e s . Thus, t h i s r e l a t i o n v a r i e s from one a d h e s i v e t o another. N e v e r t h e l e s s , i t w i l l be necessary t o c a r r y o u t f u r t h e r t e s t s i n order t o confirm t h a t p o i n t . The e m i s s i o n v e l o c i t y method proposed t o CEN i s based on t h e work of H o e t j e r ( 5 ) . T h i s method c o n s i s t s i n drawing a s t r a i g h t l i n e t h r o u g h e x p e r i m e n t a l p o i n t s o b t a i n e d by p l o t t i n g on t h e o r d i n a t e t h e r e c i p r o c a l v a l u e o f t h e formaldehyde c o n c e n t r a t i o n , o b t a i n e d a t 22 C, 55% RH ( c : formaldehyde c o n c e n t r a t i o n i n n i t r o g e n ) , and on t h e a b s c i s s a t h e r a t i o n/a, where n i s t h e a i r exchange r a t e p e r hour and a i s t h e ^ b o a r d load f a c t o r i n t h e chamber i n m board per chamber volume m . T h i s s h o u l d y i e l d a c o r r e c t p r e d i c t i o n o f t h e e m i s s i o n f o r a l l t h e n/a v a l u e s . The c u r v e s o b t a i n e d from boards a f t e r 4 weeks of c o n d i t i o n i n g a r e shown i n F i g u r e 2. We have t o note t h a t t h e two me I amine-urea-formaIdehyde b o a r d s do not s a t i s f y i n g t h i s t h e o r y . T h i s d i f f i c u l t y e x c e p t e d , t h e c u r v e family obtained f i t s without f a u l t . However, we can say t h a t f o r a l o a d i n g r a t e o f 0.5, near t h a t used i n t h e f o r e g o i n g t e s t , we s h o u l d o b t a i n a s i m i l a r r a n k i n g , i n s p i t e o f an i n v e r s i o n between two p a n e l s . However, a c o r r e l a t i o n f a c t o r between t h e two gas a n a l y s i s methods does n o t e x i s t , because t h e v a l u e s a r e a s f o l l o w s : Board Board Board Board

Fl R2 R3 Rl

Ratio Ratio Ratio Ratio

1.40 1.51 1.67 2.78

A f u r t h e r experiment w i t h 4 boards was made, T a b l e I I I . Two s e r i e s of measurements were c a r r i e d o u t on t h e s e boards: One was t h e a p p l i c a t i o n of t h e CEN d r a f t s t r a i g h t l i n e method, and t h e second were a i r l e v e l measurements i n s m a l l e x p e r i m e n t a l houses, where t h e boards were used i n r o o f s o f f i t s , a s i t would be i n p r a c t i c e . A t t h i s p o i n t o f t h e study i t i s n o t p o s s i b l e t o improve o u r knowledge o f t h e e m i s s i o n t r e n d s w i t h t h i s method. However, g i v e n t h a t t h e formaldehyde e m i s s i o n from a p a r t i c l e b o a r d must d e c r e a s e w i t h t i m e , we d e c i d e d t o measure t h i s e f f e c t . Two s e t s o f e x p e r i m e n t s were c a r r i e d o u t p a r a l l e l t o each o t h e r f o r one y e a r a t 23 C and 6 5 % RH, 80% RH, o r 3 0 % RH. The boards were t e s t e d a t r e g u l a r i n t e r v a l s by both t h e p e r f o r a t o r method and t h e gas f l o w


192

FORMALDEHYDE RELEASE FROM WOOD PRODUCTS

R3

R4

F4


R2

l 0

F i g u r e 2.

1

1

0,5

1

1

1

1,5

2

1

2,5

1

n

3

3,5

1

4

1 5

w*. n

/

a

R a t i o o f t h e gas a n a l y s i s methods a t 23°C; 5 5 % RH.


14.

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Table I I I .

Formaldehyde

193

Release

C o r r e l a t i o n Between L a b o r a t o r y and F i e l d Measurements

Content measured i n Exper i menta1 homes

C o n t e n t c a l c u l a t e d from t h e CEN method mg/a i r

Board


Real-Life

Rl

0.231

0.079

R2

0.246

0.217

R3

0.239

0.196

R4

0.306

0.209

method a t 60oC, 3% RH. R e s u l t s a r e shown i n F i g u r e s 3 and 4. Two d i s t i n c t phenomena a r e o b s e r v e d : 1. A d e c r e a s e w i t h t i m e , t o g e t h e r w i t h a c e r t a i n s t a b i l i z a t i o n a f t e r t h r e e t o f o u r months i n a low h u m i d i t y atmosphere, b u t r e s u l t s were i n c o h e r e n t , and 2. An a b r u p t drop i n r e l e a e under h i g h h u m i d i t y c o n d i t i o n , t h e t h r e e boards p r o n i n g t o g i v e t h e same r e s u l t s a f t e r one y e a r . S i n c e t h e i n f l u e n c e o f ambient a i r h u m i d i t y i s v e r y s i g n i f i c a n t , we extended t h i s s t u d y . Two t e s t s were c a r r i e d o u t on boards t h a t were f i r s t f u l l y c o n d i t i o n e d i n a chamber a t 23 C and 5 5 % RH: F i r s t , s h o r t term v a r i a t i o n s were s t u d i e d over a p e r i o d o f 1 week, and, second, c o n t i n u o u s measurements were t a k e n d u r i n g sudden m o i s t u r e uptakes. The r e s u l t s a r e as f o l l o w s :

T a b l e IV.

I n f l u e n c e of Short-term Moisture V a r i a t i o n s

P e r f o r a t o r (mg HCHO/lOOg board)

Start Resin

12 weeks 20°C 65%RH

+1 wk +1 wk 23°C 23°C 85%RH 30%RH

Gas f l o w (mg/kg board h r )

Start

12 weeks 20°C 60%RH

+1 wk +1 wk 23°C 23°C 85RH% 30%RH

F2 1981 UF

28

21

27

16

8.9

2.3

2.0

2.4

UF

73

53

69

55

3.8

4.7

3.5

8.2

F4 1981 UFMe I ami ne

64

71

54

57

10.9

4.5

4.7

5.8

F3




194

F i g u r e 3. P e r f o r a t o r method. Samples c o n d i t i o n e d a t : (a) 25 C; 85% RH; (b) 25°C; 30% RH; (c) 20°C; 6 5 % RH.


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ug HCHO/H/kg b o a r d

40

weeks

ug HCHO/H/kg b o a r d

weeks F i g u r e 4. Gas f l o w method. Samples c o n d i t i o n e d a t (a) 25°C; 8 5 % RH; (b) 20°C; 6 5 % RH; ( c ) 25°C; 3 0 % RH



196


One week v a r i a t i o n s : A f t e r 3 months o f s t a b i l i z a t i o n , t h e boards a r e p l a c e d one week i n a 23 C, 8 5 % RH chamber, then another week i n a 23 C, 3 0 % RH chamber. The formaldehyde c o n t e n t was determined a t t h e end o f each p e r i o d w i t h t h e p e r f o r a t o r and t h e gas f l o w a t 60 C, 3$ RH. The r e s u l t s a r e shown i n T a b l e I V . The passage i n t o wet c o n d i t i o n s i n c r e a s e s t h e c o n t e n t measured w i t h t h e p e r f o r a t o r f o r urea-formaldehyde boards, b u t d e c r e a s e s i t f o r me I amine-ureaformaldehyde boards. On t h e o t h e r hand, w i t h gas f l o w a t 60 C, t h e r e i s an i n c r e a s e o n l y f o r one urea-formaldehyde board i n d r y c o n d i t o n s . C o n t i n u o u s Measurements: I n o r d e r t o be a s c l o s e a s p o s s i b l e t o p r a c t i c a l c o n d i t i o n s , measurements were conducted a t 23 C. The n i t r o g e n m o i s t u r e c o n t e n t was suddenly i n c r e a s e d d u r i n g t h e t e s t and t h e v a r i a t i o n s o f t h e formaldehyde e m i s s i o n were observed a t t h e same time.

We note a t each i n c r e a s e o f t h e m o i s t u r e o f t h e gas stream an i n c r e a s e o f t h e formaldehyde r e l e a s e , more o r l e s s marked a c c o r d i n g t o t h e boards. I f t h e same m o i s t u r e c o n t e n t i s m a i n t a i n e d , t h e r e i s a s t a b i l i z a t i o n o f t h e r e l e a s e , sometimes a d e c r e a s e o f t h e l e v e l , a f t e r 3 o r 4 hours. No more v a r i a t i o n s a r e observed a f t e r w a r d s d u r i n g 36 hours, t h e maximum d u r a t i o n o f our t e s t . The mean v a l u e s o f t h e r e s u l t s o b t a i n e d d u r i n g t h i s s t a b i l i z a t i o n p e r i o d a r e g i v e n i n T a b l e V. We can s e e a s t r o n g i n c r e a s e f o r one urea-formaldehyde g l u e and a l e s s e r i n c r e a s e o r n o t h i n g a t a l l f o r the other glues.

T a b l e V.

Mean Formaldehyde E m i s s i o n w i t h V a r i a b l e Humidity (HCHO/hour; N i t r o g e n a t 2 3 C , 20 L/hour) U

Board

Nitrogen 55%

Fl F2 1983 F4 Rl R2 R3 R4

0.98 2.03 2.28 1.08 1.39 1.87 2.04

humidity 80%

0.86 2.93 2.18 2.39 3.91 2.72 3.79

R e l a t i v e increase of t h e emission f r o m 5 5 % t o 80% RH

0 +45 0 •121 •181 •45 •86

Summary The c o n c l u s i o n i s s i m p l e : I t i s n o t p o s s i b l e t o p r e d i c t a t t h e p r e s e n t s t a t e o f knowledge, w i t h o u t e r r o r s , t h e r i s k i n p r a c t i c e o f formaldehyde e m i s s i o n from any p a r t i c l e b o a r d f o r any use by means o f o n l y one s i m p l e l a b o r a t o r y measurement. As a m a t t e r o f f a c t we f i n d that:



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197

1. In the case of the analysis of "total" formaldehyde by the perforator method, the ratio of perforator content/emission differs notably from one board type to another, even though for a given type of board, known wood species and glue, the./comparison is valid. The latter condition holds only in the case of quality control during manufacture, and not in product use. 2. In the case of emission measurement, more realistic, it is necessary to take into account the board emission as a function of time. Measurements should be done only after stabilization, of several months if necessary. 3. The great sensitivity to pressure variations may produce sudden and immediate increase of the emission. For example, a consumer taking a shower may experience a blast of formaldehyde release from the shower stall. Thus it is necessary to take into account the final use of the board. A board which releases little formaldehyde at 65% RH may double emission instantaneously when the relative humidity increases to 85%. This type of board should not be recommended for uses in which there is a risk of moisture intake, such as bathrooms or kitchens. This is to say that in practice for a given particleboard, we have to determine the emission at 23oC and 55% RH, and the influence of humidity in order to classify the board for the appropriate use category. Ack now Iedgment This paper was edited for the ACS Proceedings format by M. M. Kapsa. Literature Cited 1. 2. 3.

4. 5. 6. 7.

Mayer, J. In "Spanplatten - Heute und Morgen"; Weinbrenner, Ed.; DRW Verlag: Stuttgart, 1978, p. 102. "Particleboard-Determination of Formaldehyde Content-Extraction Method Called Perforator Method," European Standard EN-120-1982, European Committee for Standardization, Brussels, 1982. "Particleboards - Determination of Formaldehyde Under Specified Conditions. Method Called: Formaldehyde Emission Method," European Committee for Standardization, CEN Situation Report N 76 E, Brussels, 1984. Determination of Formaldehyde by Gas Analysis, DIN Standard 52 368, 1984. Beuth Publishers, Berlin, 1984. Hoetjer, J. J; Koerts, F. Holz Roh-Werkstoff, 1981, 39, 391. Korf, C. Institute for Surface Technology, Haarlem, Holland, unpublished data, 1985 Roffael, E. "FormaIdehydabgabe von Spanplatten und anderen Werkstoffen"; DRW Publishers: Stuttgart, 1982.

RECEIVED September 20, 1985


Formaldehyde Release from Wood Products - American Chemical

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