Adhesives from Renewable Resources - American Chemical Society

Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch017

Chapter 17 Modification of Diisocyanate-Based Particleboard and Plywood Glues with Natural Polymers Polyphenols, Carbohydrates, and Proteins B r i g e t t e D i x and R a i n e r M a r u t z k y Fraunhofer-Institute for W o o d Research Bienroder Weg 54 Ε D-3300 Braunschweig Federal Republic of Germany

Investigations aimed at finding some fast-setting glues for exterior plywood and particleboard based on diisocyanates in combination with compounds from renewable resources like tannins, proteins, and starches revealed the following: T h e mechanical properties of parti cleboard bonded with unmodified tannin extracts from spruce (Picea abies) and pine (Pinus sylvestris) were inferior. T h e fortification of the tannin extracts with diisocyanate increased the bonding strength and reduced the thickness swelling. W i t h one exception, parti cleboards bonded with nonemulsifiable diisocyanate modified with glutin or maize starch (extender content up to 20%) had exterior -grade quality (German standard V100 for flat-pressed boards). Ve neer plywood, which is conditionally weatherproof (German stan dard A W ) , can be produced by applying diisocyanate together with tannins or starches. T h e veneer wood species, the glue mixtures, the pressing conditions, and the fillers have to be adjusted to the diisocyanate type and to the extender. Modified, emulsifiable diiso cyanate gave plywood with better strength and wood failure than glue formulations with nonemulsifiable diisocyanate. W o o d - b a s e d p a n e l p r o d u c t s are u s u a l l y b o n d e d w i t h s y n t h e t i c adhesives based o n condensates o f p h e n o l , r e s o r c i n o l , u r e a , o r m e l a m i n e w i t h f o r m a l d e h y d e . P a r t i c l e b o a r d s a n d f i b e r b o a r d s c a n also b e b o n d e d w i t h m i n e r a l b i n d e r s like cement o r g y p s u m . W o o d adhesives derived f r o m n a t u r a l p r o d u c t s have m o r e 0097-6156/89A)385-0229$06.00A)

c

1989 American Chemical Society

In Adhesives from Renewable Resources; Hemingway, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

230

ADHESIVES F R O M RENEWABLE RESOURCES


h i s t o r i c a l i m p o r t a n c e . N o w a d a y s , o n l y t a n n i n - b a s e d adhesives are used i n i n d u s t r i a l p r o d u c t i o n of p a n e l p r o d u c t s l i m i t e d to c e r t a i n areas (e.g., A u s t r a l i a , S o u t h A f r i c a , a n d some countries i n S o u t h A m e r i c a ) . T e c h n i c a l disadvantages of t a n n i n adhesives are so d o m i n a n t t h a t the glue f o r m u l a t i o n s generally have t o be fortified by s y n t h e t i c resins. A r e l a t i v e l y new s y n t h e t i c adhesive for p a n e l p r o d u c t s is the d i i s o c y a n a t e . D i i s o c y a n a t e s have been used i n d u s t r i a l l y w i t h success i n W e s t G e r m a n y i n p a r t i c l e b o a r d p r o d u c t i o n for m o r e t h a n 10 years. A d v a n t a g e s of the diisocyanates are: h i g h r e a c t i v i t y , b i n d i n g q u a l i t i e s for exterior-grade p a n e l p r o d u c t s , a n d no f o r m a l d e h y d e e m i s s i o n p o t e n t i a l after c u r i n g . F u r t h e r m o r e , diisocyanates do not c o n t a i n hygroscopic salts like phenolic resins. D i s a d v a n t a g e s o f d i i s o cyanates are the higher price a n d higher t o x i c i t y of the u n c u r e d glue i n c o m p a r i s o n w i t h other w o o d adhesives. T h e properties of n a t u r a l glues are opposite to those o f diisocyanates; h i g h viscosity, m o s t l y l o w r e a c t i v i t y , a n d inferior b i n d i n g qualities. A t t e m p t s t o combine the n a t u r a l glues w i t h diisocyanates have l e d t o success. S e v e r a l t a n n i n adhesive f o r m u l a t i o n s fortified w i t h diisocyanates for p a r t i c l e b o a r d s a n d b e e c h w o o d have been described i n the l i t e r a t u r e (1-4)· D i i s o c y a n a t e s have also generated interest as adhesives for p l y w o o d , b u t they have m a i n l y f a i l e d i n use because of economics a n d adhesive a p p l i c a t i o n p r o b lems (adhesive d i s t r i b u t i o n , p e n e t r a t i o n i n t o veneer, etc.). F u r t h e r e x p e r i m e n t s have s h o w n t h a t m i x t u r e s of diisocyanates w i t h the u s u a l fillers a n d extenders have a very short p o t l i f e or give nonhomogeneous glues (5,6). Research

Goals

P l y w o o d b o n d i n g is u s u a l l y restricted t o adhesives based o n phenolics a n d a m i n o p l a s t s . P h e n o l i c s often have low r e a c t i v i t y a n d u n f a v o r a b l e hygroscopic properties. A m i n o p l a s t s , t h o u g h t h e y have higher r e a c t i v i t y , e m i t f o r m a l d e hyde even years after p r o d u c t i o n a n d lack d u r a b i l i t y i n adverse e n v i r o n m e n t s [i.e., h i g h t e m p e r a t u r e s >150 ° F (65 ° C ) ] a n d c y c l i c w e t t i n g a n d d r y i n g . T o e x p a n d the range of p l y w o o d adhesives, the F r a u n h o f e r - I n s t i t u t e for W o o d R e search has s t a r t e d t o develop f o r m u l a t i o n s based o n diisocyanates i n c o m b i n a t i o n w i t h c o m p o u n d s f r o m renewable resources like t a n n i n s , l i g n i n s , p r o t e i n s , a n d starches. T h e a i m of the research was the development of the c o m b i n a t i o n of fasts e t t i n g glues for exterior p l y w o o d ( T y p e A W , D I N 68 705, p a r t 2) w i t h suffic i e n t l y h i g h v i s c o s i t y b u t w i t h o u t f o r m a l d e h y d e e m i s s i o n . S o m e of these adhesive f o r m u l a t i o n s were tested i n p a r t i c l e b o a r d p r o d u c t i o n . A l l tests were done o n a l a b o r a t o r y scale, t a k i n g i n t o c o n s i d e r a t i o n the l i m i t s given b y the t e c h n o l o g y a n d economics i n the i n d u s t r y . T h e results presented i n t h i s chapter are p a r t of a comprehensive research p r o g r a m a f f i r m i n g the benefits of n a t u r a l p r o d u c t s i n adhesive f o r m u l a t i o n s for w o o d - b a s e d p a n e l p r o d u c t s .


17.

DIX A N D MARUTZKY

Experimental

Modification of Diisocyanate-Based Glues

231

Procedures


N o n e m u l s i f i a b l e a n d emulsifiable p o l y m e r i c m e t h y l e n e diisocyanates ( D e s m o d u r V P P U 1520 A 31 a n d 1520 E , M e s s r s . B a y e r , West G e r m a n y ) were c o m b i n e d w i t h m a i z e s t a r c h a n d s o l u t i o n s of t a n n i n e x t r a c t or p r o t e i n . T h e g l u i n g e x p e r i m e n t s were done w i t h c o m m e r c i a l l y a v a i l a b l e s t a r c h , p r o teins (casein, g l u t i n ) a n d t a n n i n s o f m i m o s a (Acacia s p p . ) , Pinus radiata, a n d quebracho (Schinopsis spp.) a n d w i t h t a n n i n s e x t r a c t e d f r o m the b a r k o f spruce (Picea abies) a n d c o m m o n pine (Pinus sylvesiris). T h e e x t r a c t i o n s were c a r r i e d out w i t h w a t e r or o r g a n i c solvents u n d e r a l k a l i a n d / o r s u l p h i t e c o n d i t i o n s o n a l a b o r a t o r y scale a i m i n g at o p t i m i z a t i o n o f y i e l d a n d p o l y p h e n o l i c e x t r a c t c o n tent. A f t e r e x t r a c t i o n , the s o l u t i o n s were concentrated u n d e r reduced pressure a n d freeze d r i e d . O n e pine b a r k e x t r a c t was m o d i f i e d w i t h p h e n o l . A s u m m a r y of the t a n n i n e x t r a c t s a n d t h e i r properties is g i v e n i n T a b l e I . F o r the p l y w o o d glues, the r a t i o P M D I / e x t e n d e r was 7:3 or 6:4 ( w / w ) . T h e glue d i d not c o n t a i n further a d d i t i v e s i f not otherwise m e n t i o n e d . T h r e e - p l y panels were pressed f r o m spruce (100 m m χ 85 m m χ 1.8 m m ) , beech (100 m m χ 85 m m χ 1.5 m m ) , a n d g a b u n veneers (100 m m χ 85 m m χ 1.6 m m ) ; the m o i s t u r e content o f the veneers was 8 t o 9 . 5 % . P l y w o o d m a n u f a c t u r i n g c o n d i t i o n s are given i n T a b l e I I . W i t h each glue f o r m u l a t i o n , seven panels were m a d e . F r o m the panels, 20 test specimens were c u t . T h e shear s t r e n g t h a c c o r d i n g t o b u i l d i n g veneer p l y w o o d ( D I N 68 705, p a r t 3) a n d the w o o d f a i l u r e ( d e l a m i n a t i o n test, D I N 53 255) o f test specimens were assessed. P r e t r e a t m e n t s were a c o l d water storage for 24 h o u r s a n d a b o i l i n g - d r y - b o i l i n g test ( b o i l i n g i n water for 4 h o u r s , storage at 60 ° C i n a n oven for 16 to 20 h o u r s , b o i l i n g i n water for another 4 h o u r s ) . A c c o r d i n g t o the G e r m a n s t a n d a r d for w e a t h e r p r o o f b u i l d i n g veneer p l y w o o d (type B F U 100, D I N 68 705, p a r t 3), the m i n i m u m shear s t r e n g t h is 1 M P a . A c c o r d i n g to the G e r m a n s t a n d a r d for exterior-grade p l y w o o d for general use ( t y p e A W , D I N 68 705, p a r t 2), the q u a l i t y o f the b o n d i n g m u s t be at least grade 3 (see r e m a r k i n T a b l e I I I ) . P a r t i c l e b o a r d m a n u f a c t u r i n g c o n d i t i o n s are given i n T a b l e I V . W i t h each glue f o r m u l a t i o n , t w o p a r t i c l e b o a r d s were m a d e . T h e G e r m a n s t a n d a r d for flatpressed b o a r d s for b u i l d i n g s w i t h o u t w o o d preservatives ( D I N 68 763) d i s t i n guishes t y p e V 2 0 ( b o n d i n g not stable at h i g h m o i s t u r e ) a n d t y p e V I 0 0 ( b o n d i n g stable a t h i g h m o i s t u r e ) . T h e l i m i t s for s t r e n g t h a n d thickness s w e l l i n g are given in Tables I V and V . R e s u l t s and

Discussion

A d h e s i v e s f r o m D i i s o c y a n a t e s and T a n n i n s . T h e t a n n i n e x t r a c t s were m i x e d as powders or s o l u t i o n s w i t h nonemulsifiable or emulsifiable d i i s o c y a n a t e . T h e p o t l i f e o f the f o r m u l a t i o n s o f e x t r a c t powders w i t h n o n e m u l s i f i a b l e d i i s o cyanate was sufficient; the viscosities of the m i x t u r e s r e m a i n e d n e a r l y constant for m o r e t h a n 5 h o u r s . W i t h e x t r a c t s o l u t i o n s , the v i s c o s i t y of the glue increased



1

3

2

Commercial Product

Quebracho

Q

F o r m a l d e h y d e reactive p o l y p h e n o l i c c o m p o u n d s ( S t i a s n y n u m b e r ) . E x t r a c t m o d i f i e d w i t h 2 % p h e n o l (ovendry weight). N E : N o t estimated.

90.6

4.9

5.7

84.2

Commercial Product

Mimosa

M

NE 73.9

5% N a O H

Ethanol/ W a t e r (3:2)

Pine

PII

NE

68.0

2% N a O H

Ethanol/ W a t e r (3:2)

Spruce

SII

3

NE

(% D r y W t . )

Hydroxyl Content %

61.2

2

7% N a O H

Water

Pine

PI

3

1

NE

2

Polyphenol 55.0

Chemicals

Extraction 1% N a O H / 1 % N a S 0

Solvent Water

Spruce

Bark/Wood

SI

Code

Extract

T a b l e I. E x t r a c t i o n C o n d i t i o n s a n d P r o p e r t i e s of T a n n i n E x t r a c t s


17.

DIX A N D MARUTZKY


T a b l e I I . S t r e n g t h of P l y w o o d B o n d e d w i t h F o r m u l a t i o n s o f N o n e m u l s i f i a b l e D i i s o c y a n a t e a n d S p r u c e or Pine Bark Extracts (40% Solution) Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch017

1

Extract SI

PI

2

(% o n G l u e )

Dry

C o l d W a t e r S o a k (24 h)

0.5

3.1

2.0

3.3

2.3

—

3.0 3.4

N o strength 2.2

2.3 2.9

1.1 2.0

2.6 3.2

0.9 2.8

0.5 PII

_ 0.5

SII

Shear S t r e n g t h ( M P a )

Paraform

_ 0.5

s

3

M a n u f a c t u r e of p l y w o o d : veneer species : beech p a n e l c o n s t r u c t i o n : 3 p l y , each 1.5 m m t h i c k p a n e l size : 80 m m χ 100 m m press t e m p e r a t u r e : 140 ° C pressure : 1.5 M P a press t i m e : 6 m i n prepressing : none 1

assembly t i m e : 5 t o 5 m i n glue s p r e a d : 210 g / m (double glueline) glue : r a t i o d i i s o c y a n a t e / e x t r a c t s o l u t i o n : 7:3 2

2

3

E x t r a c t code, see r e m a r k i n T a b l e I. P a r t l y no strength.


233

234

ADHESIVES F R O M RENEWABLE RESOURCES

T a b l e I I I . S t r e n g t h a n d W o o d F a i l u r e of P l y w o o d B o n d e d w i t h F o r m u l a t i o n s of D i i s o c y a n a t e ( P M D I ) a n d T a n n i n Extracts (50% Solutions)


1

PMDI

Tannin

Veneer

Shear S t r n . ( M P A ) A

Nonemul-

Mimosa

B

4

Wood Fail A

3

0.0

0.0

Spruce

1.5

1.0

Quebracho

Beech Spruce Gabun

1.7 2.3 2.9

0.0 1.6 2.1

Mimosa

Beech Spruce

4.3 2.4

2.7 1.6

2 2

3 4

Quebracho

Beech Spruce Gabun

4.5 2.7 3.3

2.6 2.2 2.8

1 2

2 3

M a n u f a c t u r e o f p l y w o o d : see r e m a r k i n T a b l e I I . J u d g m e n t o f D I N 53 255: 1: excellent b o n d i n g ; 2: g o o d b o n d i n g ; 3: s a t i s f a c t o r y b o n d i n g ; 4: insufficient b o n d i n g . 3

4

B

4

Beech

sifiable

Emulsifiable

3

A : C o l d water soak. B : B o i l i n g test.


2

17.

235


DIX A N D MARUTZKY

T a b l e I V . M e c h a n i c a l P r o p e r t i e s of 1 3 - m m P a r t i c l e b o a r d B o n d e d with Unmodified Tannin Extracts and with Tannin Extracts Diisocyanate ( P M D I ) Formulations 1


2

Extract

Extract

PMDI

Modulus

Internal

Code

Content

Content

of R u p t u r e

B o n d (V20)

(MPa)

(MPa)

--

0.3 0.2

43.3 23.4

-

9.5 10.1 5.8 N o bonding

0.1 because of

54.0 precuring

.10

21.2

3.0 3.0 3.0 4.5 4.5 4.5 4.5 4.5 6.0

13.9 13.8 14.5 16.6 15.6 15.6 15.3 17.2 21.2

0.6 0.5 0.5 0.6 1.0 0.9 0.9 1.0 1.2 1.4

15.9 20.0 22.1 24.1

3

% on D r y Weight SI PI SII PII SI PI SII PII SI PI SII PII

-

10.0 10.0 10.0 10.0 6.0 6.0 6.0 6.0 4.5 4.5 4.5 4.5

--

Thickness Swelling (%/24

15.5 15.5 15.8 17.1 14.1 11.5

R e q u i r e m e n t s of D I N 68 763 ( b o a r d thickness 13...20 m m ) M O R V 2 0 >16; V 1 0 0 >18: I B V 2 0 > 0 . 3 5 : T S V 2 0

Adhesives from Renewable Resources - American Chemical Society

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