Formaldehyde Release from Wood Products - American Chemical

3 Formaldehyde Release from Wood Panel Products Bonded with Phenol Formaldehyde Adhesives J. A. Emery Downloaded by GEORGE MASON UNIV on December 19, 2014 | http://pubs.acs.org Publication Date: August 8, 1986 | doi: 10.1021/bk-1986-0316.ch003

American Plywood Association, 7011 South 19th Street, Tacoma, WA 98466 Both the published literature and previously unpublished information obtained by the structural panel industry indicate that formaldehyde levels associated with panel products glued with phenol formaldehyde adhesives are extremely low. Large dynamic chamber tests which simulate conditions that might be found in tightly sealed residences indicate consistently that formaldehyde levels associated with freshly manufactured phenolic panel products are less than 0.1 parts per million. The data, as well as theoretical considerations, also indicate that the amount of formaldehyde contributed to the environment by phenolic panel products should rapidly approach zero as the small quantity of formaldehyde initially present in the products is released. Virtually all wood panel products such as plywood and particleboard are manufactured using either urea formaldehyde or phenol formaldehyde adhesives. Urea formaldehyde adhesives are used in hardwood plywood and in certain types of particleboards. These adhesives are not waterproof, and products made with them are normally used indoors for paneling, furniture, shelving and floor underlayment. Phenol formaldehyde, on the the other hand, is used to make the waterproof adhesives that are used in structural wood panel products such as softwood plywood, oriented strand board, waferboard and exterior (phenolic) particleboard. These products are commonly used for roof, floor and wall sheathings, exterior sidings, concrete forms and in pallets and numerous other products. Although formaldehyde emissions from some products glued with urea formaldehyde adhesives can cause indoor air quality problems under certain conditions, such problems have not been associated with phenol formaldehyde-bonded (phenolic) products. Unfortunately, however the commonplace usage of the generic terms "particleboard" and "plywood" has failed to distinguish between product types and has led to a great deal of confusion among consumers. Because phenolic panels have not presented formaldehyde-related problems in the marketplace, there has not been much need to develop information on formaldehyde emissions from these products. 0097-6156/86/0316-0026$06.00/0 © 1986 A m e r i c a n C h e m i c a l Society

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

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N e v e r t h e l e s s , a c o n s i d e r a b l e amount o f i n f o r m a t i o n has been g e n e r a t e d to s a t i s f y c u r i o s i t y and t o answer i n q u i r i e s c o n c e r n i n g e m i s s i o n s from p h e n o l i c p a n e l p r o d u c t s . T h i s i n f o r m a t i o n i s summarized i n t h i s paper under t h r e e p r i m a r y s u b j e c t h e a d i n g s : (1) T h e o r e t i c a l C o n s i d e r a t i o n s ; (2) L i t e r a t u r e Review; (3) P r e v i o u s l y U n p u b l i s h e d Information.

Downloaded by GEORGE MASON UNIV on December 19, 2014 | http://pubs.acs.org Publication Date: August 8, 1986 | doi: 10.1021/bk-1986-0316.ch003

Theoretical Considerations The c h e m i c a l and p h y s i c a l c h a r a c t e r i s t i c s o f p h e n o l i c r e s i n s and a d h e s i v e s made from them suggest t h a t formaldehyde e m i s s i o n s s h o u l d be v e r y minor (_1_) . One r e a s o n f o r p r e d i c t i n g low e m i s s i o n s i s t h a t v e r y l i t t l e r e s i d u a l f r e e formaldehyde i s p r e s e n t i n p r e p a r e d phenolic resins. T h i s low f r e e formaldehyde c o n t e n t i s due t o b o t h t h e use o f low formaldehyde t o phenol mole r a t i o s i n r e s i n p r e p a r a t i o n and t o t h e tendency o f n e a r l y a l l t h e formaldehyde t o r e a c t i r r e v e r s a b l y with the phenol. Another r e a s o n f o r p r e d i c t i n g low e m i s s i o n s i s t h a t t h e s m a l l amount o f r e s i d u a l formaldehyde t h a t might be p r e s e n t i n t h e p r e p a r e d r e s i n i s d i m i n i s h e d even f a r t h e r by r e a c t i o n s which o c c u r when t h e r e s i n c u r e s . P h e n o l i c r e s i n s a r e c u r e d under heat and p r e s s u r e i n a h o t - p r e s s , u s u a l l y under h i g h l y a l k a l i n e c o n d i t i o n s . C u r i n g temperat u r e s a r e u s u a l l y i n t h e range o f 130-220°C. Under t h e s e c o n d i t i o n s , u n r e a c t e d formaldehyde c o n t i n u e s t o r e a c t w i t h phenol t o form l a r g e r p h e n o l formaldehyde polymers. A l s o , some formaldehyde r e a c t s w i t h v a r i o u s c h e m i c a l c o n s t i t u e n t s i n the wood. Moreover, some f o r m a l d e hyde i s p r o b a b l y c o n v e r t e d t o methyl a l c o h o l and f o r m i c a c i d by way of the C a n n i z z a r o r e a c t i o n (JO . A t h i r d r e a s o n f o r p r e d i c t i n g v e r y low e m i s s i o n s o f formaldehyde from p h e n o l i c p a n e l s i s t h a t t h e c u r e d r e s i n i s e x t r e m e l y s t a b l e and does n o t break down t o r e l e a s e a d d i t i o n a l formaldehyde, even under e x t r e m e l y h a r s h e n v i r o n m e n t a l c o n d i t i o n s ( 2 ) . The h i g h r e s i s t a n c e o f p h e n o l i c r e s i n s t o d e t e r i o r a t i o n under s e v e r e s e r v i c e c o n d i t i o n s i s , of c o u r s e , a p r i n c i p a l r e a s o n they a r e used so w i d e l y i n making ext e r i o r types o f wood p a n e l p r o d u c t s . Because o f t h e i r c h e m i c a l s t a b i l i t y the U.S. E n v i r o n m e n t a l P r o t e c t i o n Agency has d e c l a r e d t h a t p h e n o l formaldehyde r e s i n s r e p r e s e n t a "consumptive u s e " o f f o r m a l d e hyde, meaning t h a t formaldehyde i s i r r e v e r s i b l y consumed i n i t s r e a c t i o n w i t h p h e n o l so t h a t the formaldehyde l o s e s i t s c h e m i c a l i d e n t i t y (3). Any formaldehyde t h a t might be p r e s e n t i n i t i a l l y i n f r e s h p h e n o l i c p a n e l s , would be e x p e c t e d t o d i m i n i s h t h r o u g h t i m e , s i n c e a d d i t i o n a l formaldehyde i s n o t r e l e a s e d from a breakdown o f t h e r e s in. Thus, b a r r i n g c o n t a m i n a t i o n from o t h e r s o u r c e s , formaldehyde e m i s s i o n s a s s o c i a t e d w i t h t h o r o u g h l y aged p h e n o l i c p a n e l s s h o u l d be nil. L i t e r a t u r e Review The formaldehyde e m i t t i n g p o t e n t i a l o f wood p a n e l p r o d u c t s c a n be e v a l u a t e d i n numerous ways, i n c l u d i n g the use o f dynamic chamber t e s t s ( t e s t s i n v o l v i n g chambers which a r e v e n t i l a t e d and s i m u l a t e r e a l - w o r l d c o n d i t i o n s ) ; s t a t i c ( u n v e n t i l a t e d ) t e s t s , such as


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d e s i c c a t o r and " e q u i l i b r i u m j a r " methods; and c h e m i c a l e x t r a c t i o n t e s t s , such as the European P e r f o r a t o r T e s t . T h i s r e v i e w w i l l emphas i z e the r e s u l t s from dynamic chamber t e s t s , e s p e c i a l l y the " l a r g e s c a l e " dynamic chamber t e s t , s i n c e the r e s u l t s o f such t e s t s can g e n e r a l l y be compared and s i n c e the r e s u l t s are more r e p r e s e n t a t i v e of r e a l - w o r l d s i t u a t i o n s than are the r e s u l t s o f o t h e r t e s t s . Data from s t a t i c t e s t s and c h e m i c a l e x t r a c t i o n t e s t s a r e more a b s t r a c t than the r e s u l t s o f dynamic chamber t e s t s , and such d a t a must t h e r e f o r e be c o r r e l a t e d w i t h some type o f dynamic t e s t i n o r d e r t o be usef u l i n terms o f e v a l u a t i n g a c t u a l p o t e n t i a l e x p o s u r e s . N e s t l e r (4) t h o r o u g h l y reviewed the worldwide l i t e r a t u r e on formaldehyde e m i s s i o n s from wood p r o d u c t s p u b l i s h e d through J a n u a r y , 1977. A c c o r d i n g to B l o m q u i s t (1_) , N e s t l e r s l i t e r a t u r e r e v i e w i n c l u d e s o n l y t h r e e c i t a t i o n s which even mention p h e n o l i c a d h e s i v e s , and none o f t h e s e c i t a t i o n s made s p e c i f i c mention o f any problems a s s o c i a t e d w i t h the use o f p h e n o l i c p a n e l s . S i n c e N e s t l e r s r e v i e w was p u b l i s h e d , some a d d i t i o n a l i n f o r m a t i o n on formaldehyde e m i s s i o n s from p h e n o l i c p a n e l s has appeared i n the l i t e r a t u r e . I n f o r m a t i o n o b t a i n e d u s i n g dynamic t e s t chambers i s summarized i n T a b l e I . P e r f o r a t o r and two-hour d e s i c c a t o r d a t a are summarized i n T a b l e I I . As i n d i c a t e d i n T a b l e I , dynamic chamber t e s t d a t a have been o b t a i n e d i n i n v e s t i g a t i o n s u s i n g chambers r a n g i n g i n s i z e from 0.003 m (0.1 f t ) t o 28 m (1000 f t ) . B e s i d e s t h i s l a r g e chamber s i z e v a r i a t i o n , the s t u d i e s a l s o v a r i e d w i d e l y w i t h r e s p e c t t o the t e m p e r a t u r e s , r e l a t i v e h u m i d i t i e s , l o a d i n g r a t e s , and a i r exchange r a t e s used f o r t e s t i n g . Because o f the wide v a r i a t i o n s among the s t u d i e s w i t h r e s p e c t t o t h e s e t e s t parameters, i t i s not p o s s i b l e t o make many i n f e r e n c e s from the d a t a p r e s e n t e d . However, some g e n e r a l t r e n d s a r e e v i d e n t , and c e r t a i n r e l a t i o n s h i p s developed from s t u d i e s i n v o l v i n g u r e a formaldehyde systems make i t p o s s i b l e t o make a few g e n e r a l i z e d o b s e r v a t i o n s c o n c e r n i n g the d a t a . A l t h o u g h T a b l e I i n d i c a t e s t h a t formaldehyde l e v e l s r a n g i n g from 0.01 - 0.3 p a r t s per m i l l i o n (ppm) have been o b s e r v e d i n s t u d i e s u s i n g dynamic t e s t chambers, v a l u e s o f 0.1 ppm or lower were o b s e r v e d i n most o f the i n v e s t i g a t i o n s . Those s t u d i e s i n which the h i g h e r l e v e l s were found ( i . e . , the f i r s t two s t u d i e s summarized i n the t a b l e ) used v e r y s m a l l t e s t chambers (0.003 m ) and r e l a t i v e l y h i g h t e m p e r a t u r e s , h u m i d i t i e s , and l o a d i n g r a t e s . Lower l e v e l s are shown f o r t h o s e s t u d i e s w h e r e i n the t e s t parameters approximated "realw o r l d " c o n d i t i o n s ( l a r g e t e s t chambers u s i n g t e m p e r a t u r e s , h u m i d i t i e s , l o a d i n g r a t e s , and v e n t i l a t i n g r a t e s a p p r o x i m a t i n g those found in l i v i n g areas). The h i g h e r formaldehyde l e v e l s a s s o c i a t e d w i t h the f i r s t two s t u d i e s summarized i n T a b l e I can p r o b a b l y be a t t r i b u t e d p r i m a r i l y to the r e l a t i v e l y h i g h temperatures employed. Numerous i n v e s t i g a t i o n s have shown t h a t formaldehyde l e v e l s i n c r e a s e e x p o n e n t i a l l y w i t h temperature (_5-_7) . S e v e r a l s t u d i e s have shown t h a t formaldehyde l e v e l s a s s o c i a t e d w i t h wood p a n e l p r o d u c t s can i n c r e a s e by more than a f a c t o r o f 3 as the temperature i n c r e a s e s from 25°C t o 40°C ( 8 ) . The e x p o n e n t i a l f u n c t i o n d e v e l o p e d by Berge, e t . a l , (5) i s commonly used t o a d j u s t formaldehyde d a t a f o r temperature (9^ . I f t h i s funct i o n were a p p l i e d t o the d a t a o f T a b l e I i n o r d e r t o a d j u s t a l l formaldehyde l e v e l s t o a common temperature o f 25°C, the c o r r e c t e d l e v e l s


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would a l l be 0.1 ppm or lower. Such an adjustment would make the e m i s s i o n d a t a from the s m a l l chamber t e s t s s i m i l a r t o those from the l a r g e chamber t e s t s summarized i n the t a b l e . I t i s i m p o r t a n t t o note here t h a t h i g h e r temperatures probably i n c r e a s e e m i s s i o n s from p h e n o l i c p a n e l s s i m p l y by a c c e l e r a t i n g the r e l e a s e o f t h a t s m a l l amount o f r e s i d u a l formaldehyde t h a t o r i g i n a t e s from the a d h e s i v e and s u b s e q u e n t l y becomes adsorbed t o the wood subs t a n c e and water i n the wood. Because p h e n o l i c r e s i n s are v e r y s t a b l e c h e m i c a l l y , any t e m p e r a t u r e - r e l a t e d i n c r e a s e i n e m i s s i o n s would not be e x p e c t e d to be a s s o c i a t e d w i t h r e s i n d e g r a d a t i o n . C o n s e q u e n t l y , temperature would be e x p e c t e d t o e x e r t much l e s s i n f l u e n c e on e m i s s i o n s from p a n e l s which have been a i r e d out than from f r e s h p a n e l s . Indeed, t h i s t r e n d i s shown by the d a t a , as d i s c u s s e d below. The i n f o r m a t i o n p r e s e n t e d i n T a b l e I a l s o i n d i c a t e s t h a t the l o a d i n g and v e n t i l a t i o n r a t e s f o r those two s t u d i e s i n which the h i g h e r formaldehyde l e v e l s were found (8,10) were h i g h e r than f o r the o t h e r s t u d i e s summarized. The i n f l u e n c e o f t h e s e f a c t o r s on formaldehyde l e v e l s has not been c l e a r l y e x p l a i n e d , however, s i n c e the amount o f d a t a p e r t a i n i n g t o p h e n o l i c p a n e l s i s so l i m i t e d and s i n c e the l i t e r a t u r e appears to be c o n t r a d i c t o r y . S t u d i e s o f u r e a formaldehyde-bonded systems g e n e r a l l y i n d i c a t e t h a t e m i s s i o n s i n c r e a s e w i t h h i g h e r l o a d i n g s and d e c r e a s e w i t h h i g h e r v e n t i l a t i o n r a t e s (6,11). Moreover, Meyers (11) has shown t h a t t h e r e i s o f t e n a good r e l a t i o n s h i p between the r a t i o o f v e n t i l a t i o n and l o a d i n g r a t e s (N/L r a t i o s ) and formaldehyde c o n c e n t r a t i o n i n c o n t r o l l e d chamber experiments. Indeed, the d a t a p r e s e n t e d i n two o f the s t u d i e s summarized i n T a b l e I (10,12) appear t o be i n g e n e r a l agreement w i t h t h e s e t r e n d s , s i n c e the d a t a show d e c r e a s e s i n formaldehyde l e v e l s c o r r e s p o n d i n g t o i n c r e a s e d v e n t i l a t i o n a t c o n s t a n t l o a d i n g . However, o t h e r s t u d i e s have i n d i c a t e d t h a t e m i s s i o n l e v e l s from v e r y low e m i t t i n g p r o d u c t s a r e not i n f l u e n c e d s i g n i f i c a n t l y by l o a d i n g or v e n t i l a t i o n r a t e s (6^). More r e s e a r c h on t h e s e r e l a t i o n s h i p s i s needed. The e f f e c t o f p a n e l age on formaldehyde r e l e a s e was i n v e s t i g a t e d i n the f i r s t study summarized i n T a b l e I , and t h i s v a r i a b l e was e v i d e n t l y v e r y i m p o r t a n t w i t h r e s p e c t t o the formaldehyde l e v e l s measured. As n o t e d i n the Remarks column i n the t a b l e , formaldehyde l e v e l s ranged from 0.1 - 0.3 ppm f o r f r e s h l y manufactured specimens, w h i l e l e v e l s i n the range o f o n l y 0.05 - 0.1 ppm were a s s o c i a t e d w i t h matched specimens t h a t had been a i r e d out f o r 90 days a t 23°C and 44% r e l a t i v e h u m i d i t y . T h i s a g i n g e f f e c t i s c o n s i s t e n t w i t h the t h e o r e t i c a l c o n s i d e r a t i o n s d i s c u s s e d e a r l i e r and w i t h t e s t r e s u l t s to be p r e s e n t e d l a t e r i n t h i s r e p o r t . The two-hour d e s i c c a t o r and P e r f o r a t o r t e s t r e s u l t s shown i n T a b l e I I a r e a l s o i n d i c a t i v e o f v e r y low formaldehyde l e v e l s f o r phenolic panels. As w i t h most o f the r e s u l t s o b t a i n e d i n dynamic chamber t e s t s , the u n i f o r m i t y o f these t e s t r e s u l t s , b o t h w i t h i n and between s t u d i e s , i n d i c a t e s t h a t the v a r i o u s p h e n o l i c p a n e l p r o d u c t s are q u i t e s i m i l a r with r e s p e c t to t h e i r e m i t t i n g p o t e n t i a l . Twenty-four hour d e s i c c a t o r t e s t s were a l s o conducted i n some o f the s t u d i e s summarized i n T a b l e s I and I I ( 8 , 1 0 ) , but the r e s u l t s are not shown s i n c e d i f f e r e n t t e s t p r o c e d u r e s were used i n each o f the s t u d i e s and the d a t a a r e , t h e r e f o r e , not comparable.


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In a d d i t i o n t o the s t u d i e s summarized i n T a b l e s I and I I , Meyer (13) measured formaldehyde e m i s s i o n s from samples o f p h e n o l i c p l y wood, w a f e r b o a r d and p a r t i c l e b o a r d u s i n g a m o d i f i e d v e r s i o n o f the Japanese I n d u s t r i a l S t a n d a r d , which i s a type of 24-hour d e s i c c a t o r test. E m i s s i o n s from wood veneer and a u r e a formaldehyde-bonded p a r t i c l e b o a r d w i t h known e m i s s i o n c h a r a c t e r i s t i c s were a l s o measured. T h i s r e s e a r c h e r used the d e s i c c a t o r t e s t r e s u l t s , a l o n g w i t h i n f o r m a t i o n from the l i t e r a t u r e , t o e s t i m a t e the maximum amount o f f o r m a l d e hyde t h a t might p o t e n t i a l l y be c o n t r i b u t e d by p h e n o l i c p a n e l p r o d u c t s t o i n d o o r a i r . Assuming a l o a d i n g f a c t o r of 1.18-m^/m and rio vent i l a t i o n , c a l c u l a t i o n s showed t h a t p h e n o l i c p a n e l s would c o n t r i b u t e l e s s t h a n 0.05 ppm. Assuming a v e n t i l a t i o n r a t e o f o n e - h a l f a i r change per h o u r , c a l c u l a t e d l e v e l s were below 0.0025 ppm. The t e s t s a l s o i n d i c a t e d t h a t formaldehyde l e v e l s a s s o c i a t e d w i t h wood veneer a l o n e ( w i t h o u t any added a d h e s i v e ) were about the same as l e v e l s a s sociated with phenolic panels. No background formaldehyde l e v e l s were r e p o r t e d , however; and c o n s i d e r i n g the f i n d i n g s o f s t u d i e s which a r e d i s c u s s e d l a t e r , background l e v e l s c o u l d e a s i l y have been as h i g h as those r e p o r t e d f o r b o t h the veneer and the p h e n o l i c products. R e g a r d l e s s of background l e v e l c o n s i d e r a t i o n s , the s t u d y g e n e r a l l y i n d i c a t e s t h a t p h e n o l i c p a n e l s emit e x t r e m e l y low l e v e l s of f o r m a l d e hyde, thus c o r r o b o r a t i n g the f i n d i n g s o f the s t u d i e s d i s c u s s e d earlier.


3

Sundin (14) a l s o measured formaldehyde e m i s s i o n s from a sample o f p h e n o l i c plywood i n a s t a t i c chamber (no a i r exchange) w i t h a volume o f 15 m . The temperature was m a i n t a i n e d a t 20°C and the l o a d i n g r a t e was 1 m^/m . R e l a t i v e h u m i d i t y was not c o n t r o l l e d , but was r e p o r t e d to be g e n e r a l l y i n the range o f 30-50%. The exact forma l d e h y d e l e v e l measured i n the chamber was not r e p o r t e d , but the a u t h o r c o n c l u d e d t h a t ... "the e m i s s i o n from phenol formaldehyde (PF) - g l u e d plywood i s e x t r e m e l y low and i n p r a c t i c e i s n e g l i g i b l e ... " A graph i s p r e s e n t e d t h a t i n d i c a t e s the l e v e l was below 0.2 ppm. As i n d i c a t e d i n T a b l e I I , a P e r f o r a t o r v a l u e o f 0.6 mg/lOOg was a l s o r e p o r t e d f o r t h i s plywood. R o f f a e l (15) measured formaldehyde e m i s s i o n s from a p h e n o l i c p a r t i c l e b o a r d u s i n g the "WKI-Method" which i n v o l v e s s u s p e n d i n g s m a l l samples over 50 cm o f d i s t i l l e d water i n t i g h t l y c l o s e d polyethylene b o t t l e s and measuring formaldehyde l e v e l s i n the water a f t e r v a r y i n g times. Temperatures were m a i n t a i n e d at 42°C. T h i s work i n d i c a t e d t h a t formaldehyde r e l e a s e from the p h e n o l i c p a r t i c l e b o a r d s ceased a f t e r a r e l a t i v e l y s h o r t r e a c t i o n p e r i o d ( a p p r o x i m a t e l y 96 h o u r s ) . T h i s f i n d i n g i s c o n s i s t e n t w i t h the r e s i n s t a b i l i t y c o n s i d e r a t i o n s d i s c u s s e d p r e v i o u s l y under t h e o r e t i c a l c o n s i d e r a t i o n s . 3

3

3

P r e v i o u s l y Unpublished

Information

Much o f the i n f o r m a t i o n p e r t a i n i n g to formaldehyde e m i s s i o n s from p h e n o l i c p a n e l s has been o b t a i n e d by m a n u f a c t u r e r s o f t h e s e p r o d u c t s but has not been p u b l i s h e d p r e v i o u s l y i n the open l i t e r a t u r e . This i n f o r m a t i o n has been o b t a i n e d p r i m a r i l y t o form a b a s i s f o r answering consumer i n q u i r i e s .

A m e r i c a n Plywood A s s o c i a t i o n Study. P r o b a b l y the most e x t e n s i v e s t u d y o f p h e n o l i c p a n e l e m i s s i o n s was conducted by W. F. Lehmann o f Weyerhaeuser Company f o r the American Plywood A s s o c i a t i o n . In t h i s



3.

EMERY

Wood Panel Products

Bonded

with Phenol Formaldehyde

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33

i n v e s t i g a t i o n , formaldehyde e m i s s i o n s from r e p r e s e n t a t i v e samples o f all major t y p e s o f p h e n o l i c p a n e l s were measured u s i n g a L a r g e - S c a l e Dynamic Chamber (LSDC) and two-hour d e s i c c a t o r t e s t s . P a n e l types i n c l u d e d s o u t h e r n p i n e and D o u g l a s - f i r plywood, o r i e n t e d s t r a n d board from two d i f f e r e n t m a n u f a c t u r e r s , waferboard, and a p h e n o l i c p a r t i c l e b o a r d . For each p r o d u c t t y p e , f i v e 1.2m x 2.4m (4 f t x 8 f t ) p a n e l s were o b t a i n e d d u r i n g a s i n g l e s h i f t . The p a n e l s were kept s t a c k e d t o g e t h e r d u r i n g s h i p p i n g and s t o r a g e u n t i l t h r e e days p r i o r to t e t i n g , when they were p l a c e d i n r a c k s i n o r d e r to a l l o w a i r c i r c u l a t i o n around each p a n e l . S t r i p s measuring 15.2 cm i n w i d t h were cut from the c e n t e r s o f f o u r o f the f i v e p a n e l s , p a r a l l e l to the s h o r t e r p a n e l d i m e n s i o n . Four 2-hour d e s s i c a t o r t e s t specimens, each measuring 7 cm x 12.7 cm (2-3/4 i n . x 5 i n . ) , were c u t from each s t r i p and c o n d i t i o n e d o v e r night. Two d e s i c c a t o r t e s t s were conducted f o r each p r o d u c t t y p e , w i t h each d e s i c c a t o r c o n t a i n i n g e i g h t specimens. T e s t s were p e r formed i n accordance w i t h s t a n d a r d p r o c e d u r e FTM 1 ( 1 6 ) . Specimens f o r the LSDC t e s t s were p r e p a r e d from the l e f t o v e r p o r t i o n s o f the f o u r p a n e l s which were cut f o r d e s i c c a t o r t e s t s p e c i mens and a l s o from the f i f t h p a n e l sampled f o r each p r o d u c t t y p e . Most o f the p r o d u c t s were t e s t e d r e l a t i v e l y soon a f t e r m a n u f a c t u r e and a g a i n a f t e r they were a i r e d out f o r 3 or more months by p l a c i n g them on s t i c k e r s t o a l l o w a i r c i r c u l a t i o n between i n d i v i d u a l panels. The time a l l o w e d f o r a i r i n g i s to be d i s t i n g u i s h e d from p a n e l age o r a g e i n g , s i n c e formaldehyde l e v e l s tend t o remain c o n s t a n t f o r p a n e l s which a r e s t a c k e d t i g h t l y t o g e t h e r ; whereas, l e v e l s d e c r e a s e q u i t e r a p i d l y d u r i n g a i r i n g out (10) . Thus, a i r i n g time i s more c r i t i c a l than a c t u a l p a n e l age when c o n s i d e r i n g f o r m a l dehyde e m i s s i o n s . S i n c e the p a n e l s f o r each o f the p r o d u c t s s t u d i e d were kept s t a c k e d t o g e t h e r u n t i l they were c o n d i t i o n e d f o r the i n i t i a l t e s t i n g , a l l p r o d u c t s were r e l a t i v e l y " f r e s h " , i n one sense, r e g a r d l e s s o f the time which had e l a p s e d s i n c e t h e i r m a n u f a c t u r e . In the dynamic chamber t e s t s , the l a r g e chamber (55.4 m ) was l o a d e d a t a r a t e o f 0.43 m^/m , and the v e n t i l a t i o n r a t e was maint a i n e d a t 0.5 a i r changes per hour. The t e s t temperature was 25 _+ 1°C, and the r e l a t i v e h u m i d i t y was h e l d a t 50 _+ 5%. A i r sampling was a c c o m p l i s h e d w i t h t h r e e s e t s o f double impingers a t one l i t e r per minute f o r 60 m i n u t e s , t w i c e per day f o r two days. Formaldehyde was a n a l y z e d u s i n g the a c e t y l a c e t o n e p r o c e d u r e ( 1 0 ) . The r e s u l t s o f the s t u d y are summarized i n T a b l e I I I which p r o v i d e s 2-hour d e s i c c a t o r v a l u e s and dynamic chamber v a l u e s f o r b o t h f r e s h and a i r e d out p a n e l s . For most o f the p r o d u c t t y p e s , b o t h empty chamber and l o a d e d chamber formaldehyde v a l u e s a r e p r o v i d e d , the empty chamber v a l u e s r e p r e s e n t i n g "background" measurements t a k e n j u s t b e f o r e the chamber was l o a d e d . These background l e v e l s r e p r e s e n t r e s i d u a l formaldehyde p r e s e n t i n the chamber from previous t e s t i n g . The d a t a i n d i c a t e t h a t the l o a d e d chamber v a l u e s were below 0.1 ppm f o r a l l p r o d u c t s and, a l s o , t h a t the background l e v e l s ( i n the empty chamber) were on the same o r d e r o f magnitude as the l e v e l s observed with panels present. In f a c t , the d a t a show t h a t the background l e v e l s i n some cases were as h i g h as the l e v e l s measured when the chamber was f u l l y l o a d e d , e s p e c i a l l y a f t e r the p a n e l s had been 3

3


In Formaldehyde Release from Wood Products; Meyer, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986. Empty (ppm)t4)

Chamber (3) Re-Test Storage W/Panels (ppm)(4) Time (Mo.)

L a r g e - S c a l e Dynamic

Products

Empty (ppm)t4)

—

—

—

—

3

—

—

—

—

—

—

—

SPP, 13 mm, 4-ply 32 0.08 0.04(5) 0.01 0.03 0.02 4 DFP, 14 mm, 0.18 1 8 5-ply 0.05 0.01 0.05 0.05 OSB No. 1, 12 mm 0.14 19 0.07 0.01 OSB No. 2, (Sample 1 ) , 12 mm 21 0.02 0.07 3 0.07 0.02 0.04 OSB No. 2, (Sample 2 ) , 12 mm 21 0.03 0.09 WB (Sample 1 ) , 12 mm 0.17 0.08 0.03 55 8 0.01 0.01 WB (Sample 2 ) , 12 mm 21 0.03 0.06 0.03 PB, 19 mm, hot-melt c o a t i n g 16 0.15 0.08 0.03 0.01 9 (1) SPP = s o u t h e r n p i n e plywood; DFP = D o u g l a s - f i r plywood; OSB = o r i e n t e d s t r a n d b o a r d ; WB = w a f e r b o a r d ; PB = p a r t i c l e b o a r d . (2) Micrograms o f formaldehyde per ml d i s t i l l e d w a t e r . In t h i s t e s t , 25 ml d i s t i l l e d water i n a p e t r i d i s h i s p l a c e d i n a d e s i c c a t o r w i t h e i g h t 7 cm x 12.7 cm specimens f o r 2 h o u r s , and the water i s t h e n a n a l y z e d f o r formaldehyde ( 1 6 ) . (3) Test conditions: 25 +_ 1°C, 50 +_ 5% RH, 0.5 a i r changes per h o u r , 0.43 m^/m loading (panel surface area/volume). (4) Amount o f f o r m a l d e h y d e , p a r t s per m i l l i o n p a r t s o f a i r i n the t e s t chamber, volume b a s i s . (5) The sample was r e t e s t e d a t 0 a i r changes p e r h o u r , and formaldehyde c o n c e n t r a t i o n was found t o be 0.06 ppm.

1

Products^ )

I n i t i a l Test W/Panels P a n e l Age (ppm)(4) (Days)

Summary o f Formaldehyde T e s t Data f o r V a r i o u s P h e n o l i c - B o n d e d P a n e l

2 Hour Desiccator Jug/ml)(2)

Table I I I .


70

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O

70

D

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O

O

70

m r m > en m ti

To

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3

3.

EMERY

Wood Panel Products

Bonded

with Phenol Formaldehyde

Adhesives

35


aired. Because o f the complex e q u i l i b r i a i n v o l v e d , i t i s not p o s s i b l e t o s i m p l y c o r r e c t the p a n e l t e s t d a t a f o r background l e v e l s . T h e r e f o r e , i t i s not f e a s i b l e to use the r e s u l t s t o d e r i v e an e x a c t e m i s s i o n v a l u e f o r any o f the p r o d u c t s o r t o compare the v a r i o u s pane l products. I n s t e a d , i t i s p r o b a b l y most prudent t o s i m p l y c o n c l u d e from t h i s study t h a t the upper l i m i t on e m i s s i o n s from a l l types o f p h e n o l i c p a n e l s , as d e t e r m i n e d i n the l a r g e t e s t chamber, i s l e s s than 0 . 1 ppm. A l t h o u g h the h i g h l e v e l s o f " n o i s e " due to background f o r m a l d e hyde l e v e l s p r e c l u d e m e a n i n g f u l s t a t i s t i c a l comparisons between e m i s s i o n s f o r v a r i o u s p r o d u c t t y p e s , c e r t a i n o t h e r comparisons can be made. F o r example, a s t a t i s t i c a l t - t e s t i n v o l v i n g a p p r o p r i a t e l y p a i r e d o b s e r v a t i o n s i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e a t the 1% c o n f i d e n c e l e v e l between l o a d e d and empty chamber v a l u e s f o r the fresh panels. T h i s d i f f e r e n c e i n d i c a t e s t h a t the p a n e l s were proba b l y c o n t r i b u t i n g some formaldehyde t o the t e s t chamber, a l t h o u g h i t i s not p o s s i b l e t o determine how much, due t o the complex e q u i l i b r i a involved. A s i m i l a r a n a l y s i s o f the d i f f e r e n c e between l o a d e d and empty chamber v a l u e s f o r a i r e d p a n e l s , however, shows a b a r e l y s i g n i f i c a n t t - v a l u e a t the 5 p e r c e n t c o n f i d e n c e l e v e l . Thus, the a i r e d p a n e l s were p r o b a b l y c o n t r i b u t i n g v e r y l i t t l e , i f any, formaldehyde to the ambient atmosphere i n the chamber. E v i d e n t l y , the s m a l l amount o f formaldehyde p r e s e n t i n i t i a l l y i n phenolic panels d i s s i p a t e s as the p a n e l s a i r o u t , so t h a t l o a d e d chamber l e v e l s approach background l e v e l s . I f background l e v e l s a r e i g n o r e d , a t - t e s t i n v o l v i n g p a i r e d o b s e r v a t i o n s r e p r e s e n t i n g those 5 s e t s o f p a n e l s t h a t were t e s t e d b o t h b e f o r e and a f t e r the p a n e l s were a i r e d i n d i c a t e s t h a t f r e s h p a n e l s emit more formaldehyde than a i r e d p a n e l s (5% c o n f i d e n c e level). A l t h o u g h such a s t a t i s t i c a l comparison i s tenuous because of the c o n f o u n d i n g e f f e c t s o f the background l e v e l s , i t i s s u p p o r t e d by the c o n c l u s i o n s drawn above — i . e . , t h a t f r e s h p a n e l s were appar e n t l y i n c r e a s i n g the l e v e l s o f formaldehyde i n the chamber t o a s i g n i f i c a n t degree, w h i l e a i r e d p a n e l s were c o n t r i b u t i n g v e r y l i t t l e , i f any, formaldehyde to the chamber. The two-hour d e s i c c a t o r v a l u e s shown i n T a b l e I I I a r e s i m i l a r to t h o s e a s s o c i a t e d w i t h the s t u d i e s c i t e d e a r l i e r i n t h i s r e p o r t , and they a r e a l s o i n d i c a t i v e o f e x t r e m e l y low formaldehyde e m i s s i o n s from the p a n e l s . O t h e r U n p u b l i s h e d Data. T a b l e IV summarizes a d d i t i o n a l e m i s s i o n d a t a which have been s u p p l i e d t o the American Plywood A s s o c i a t i o n by v a r i o u s phenolic panel manufacturers. Data from b o t h l a r g e - s c a l e dynamic chamber t e s t s and 2-hour d e s i c c a t o r t e s t s a r e p r o v i d e d . This i n f o r m a t i o n agrees w i t h t h a t p r o v i d e d i n the s t u d y d e s c r i b e d above and a g a i n demonstrates t h a t formaldehyde e m i s s i o n s from p h e n o l i c p a n e l s a r e e x t r e m e l y low. In f a c t , f o r most o f the p r o d u c t s , the chamber background l e v e l s were as h i g h as the l e v e l s d u r i n g t e s t i n g , s u g g e s t i n g t h a t the p r o d u c t s p r o b a b l y were not even c o n t r i b u t i n g any formaldehyde t o the chamber environment. These d a t a a g a i n demons t r a t e t h a t p h e n o l i c p a n e l s are such weak e m i t t e r s t h a t background formaldehyde l e v e l s can e a s i l y i n t e r f e r e w i t h t e s t i n g .



(5)

(4)

(2) (3)

(1)

A A A A B C C C C D D D E

SPP, 18mm, 4 - p l y SPP, 16mm, 5 - p l y SPP, 16mm, 5 - p l y DFP, 13mm PB, 16mm SPP, 16mm, 5 - p l y COMPLY, 16mm WB, 16mm WB, 16mm PB, 19mm PB, 19mm PB, 19mm SPP, 12mm

2

Product Type< )

30 30 22

P a n e l Age at T e s t (Days)

7

2-3 2-3 2-3 2-3 2-3(8) (9) 7(10) 2

8 8

3

0.95 0.95 0.95 0.95 0.49 0.49 0.43 0.52 0.52 0.43 0.43 0.43 0.43

3

4

23 23 23 23 24 24 24 24 24 24 24 24 25

0.5 0.5 0.5 0.5 1 1 1 1 1 1 1 1 1

48 48 48 48 50 50 50 50 50 45 42 42 42 1 1 1 1 1 5 5 5 5 55 48 50 56

Dynamic Chamber T e s t Parameters Precondition Loadin; Rel. Time^ ) Rate< f Temp. Humid. (Days) (m^/m ) (C) (%)

7

0.01 0.01 0.01

0.03-0.04(7) 0.03-0.04( ) 0.03-0.04^7) 0.03-0.04^7)

6

0.015 0.010 0.005( > 0.013

12

6

0.022 0.020 0.01l( > 0.017 0.04 0.03 0.04 0.03 0.05 0.04 0.05 0.04 0.04< )

0.51 0.09 0.13 0.17 0.18 0.22 0.17 0.20 0.34(H)

Formaldehyde L e v e l s Dynamic Chamber Two-Hr. Desiccator Loaded Empty G*g/ml)(5) (ppm) (ppm)

R e s u l t s o f L a r g e - S c a l e Dynamic Chamber T e s t s and Two-Hour D e s i c c a t o r T e s t s on V a r i o u s Types o f P h e n o l i c P a n e l P r o d u c t s ( D

V e n t i l a t i o n r a t e was 0.5 a i r changes per hour f o r a l l t e s t s . C h r o m o t r o p i c a c i d was used f o r HCHO a n a l y s e s , u n l e s s noted o t h e r w i s e . D i f f e r e n t t e s t chambers were used by each o f t h e companies r e p r e s e n t e d . SPP = s o u t h e r n p i n e plywood; DFP = D o u g l a s - f i r plywood; PB = p a r t i c l e b o a r d ; WB = w a f e r b o a r d . Specimens were p r e c o n d i t i o n e d a t the same temperature and r e l a t i v e h u m i d i t y as i s g i v e n f o r t h e t e s t chamber. L o a d i n g i s g i v e n i n terms o f square meters o f p a n e l s u r f a c e p e r c u b i c meter o f a i r volume i n t h e chamber. A l l d e s i c c a t o r t e s t s were performed i n a c c o r d a n c e w i t h t h e p r o c e d u r e s g i v e n by T e s t Method FTM 1-1983 (16) w i t h edges u n s e a l e d u n l e s s noted o t h e r w i s e . V a l u e s r e p r e s e n t micrograms formaldehyde per ml d i s t i l l e d w a t e r . I n t h i s t e s t 25 ml d i s t i l l e d water i n a p e t r i d i s h i s p l a c e d i n a d e s i c c a t o r w i t h e i g h t 7 cm x 12.7 cm specimens f o r 2 h o u r s , and t h e water i s then a n a l y z e d f o r formaldehyde.

Company Code

T a b l e IV.


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(12)

(7) (8) (9) (10) (11)

(6)

(continued)

P a r a r o s a n i l i n e was used f o r formaldehyde a n a l y s i s , r a t h e r than c h r o m o t r o p i c a c i d , u s i n g the same p a n e l specimens as t h o s e used i n the t e s t whose r e s u l t s a r e r e p o r t e d d i r e c t l y above. Range t y p i c a l l y e n c o u n t e r e d a t t h i s t e s t f a c i l i t y . Background formaldehyde l e v e l i n c o n d i t i o n i n g a r e a was 0.08 ppm. Background formaldehyde l e v e l i n c o n d i t i o n i n g a r e a was 0.03 ppm. Background formaldehyde l e v e l i n c o n d i t i o n i n g a r e a was 0.05 ppm. Average o f f o u r t e s t s i n v o l v i n g samples from two s e p a r a t e p a n e l s : f o r each p a n e l , samples f o r one t e s t had s e a l e d edges, w h i l e t h o s e f o r the o t h e r t e s t s were u n s e a l e d . Range = 0.29 - 0.43. Average o f f o u r measurements made on f o u r c o n s e c u t i v e days. Range was 0.02 - 0.05.

T a b l e IV.


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Formaldehyde Release from Wood Products - American Chemical

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