Room-Temperature Curing Adhesives Based on Lignin and

Chapter 10 Room-Temperature Curing Adhesives Based on Lignin and Phenoloxidases Downloaded by UNIV OF PITTSBURGH on May 3, 2015 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch010

Annegret Haars, Alireza Kharazipour, H e l m u t Z a n k e r , and A l o y s H u t t e r m a n n 1

Institute of Forest Botany University of Gottingen Busgenweg 2, D-3400 Gottingen Federal Republic of Germany

A n effective adhesive for wood materials, e.g. particleboards, con sists of spray-dried lignin, particularly lignosulfonate, and a phe noloxidase containing culture fluid of filamentous fungi grown on dilute lignin solutions in the presence of cheap C and Ν sources in a fermenter. Wood laminates bonded with this two-component room -temperature curing adhesive had tensile strengths above 2.0 M P a . The underlying reaction mechanism is the crosslinking of lignin via oxidative polymerization catalyzed by the phenoloxidase. The pro duction of this adhesive includes the total utilization of waste lignins a) directly as one component of the binding system and b) indirectly as nutrient source of the phenoloxidase-producing fungi. T h e p u l p i n g i n d u s t r y releases a b o u t 40 m i l l i o n tons o f l i g n i n a n n u a l l y , w h i c h are s t i l l far f r o m b e i n g u t i l i z e d effectively. Indeed, o n l y 2 0 % o f t h i s vast p o t e n t i a l is used f o r v a r i o u s i n d u s t r i a l purposes, t h e rest b e i n g b u r n t . Irrespective o f SO2 e m i s s i o n d u r i n g the b u r n i n g o f waste p u l p i n g effluents, the process represents a n enormous d i s s i p a t i o n o f a renewable raw m a t e r i a l t h a t c o u l d b e better u t i l i z e d . A m o n g t h e m a n y considerations r e g a r d i n g l i g n i n u t i l i z a t i o n , t w o seem t o be very i m p o r t a n t t o any increase i n l i g n i n ' s m a r k e t value: 1. A p p l i c a t i o n s s h o u l d m a k e use o f the p o l y m e r i c s t r u c t u r e o f l i g n i n . 2. T h e m a r k e t has t o be large enough t o absorb e n o r m o u s q u a n t i t i e s of lignin. C u r r e n t address: G . A . Pfleiderer, Postfach 14 80, D-8430 Neumarkt/Opf. 0097-6156/89/0385-0126$06.00/0 ·

1989 American Chemical Society

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

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T h e a l r e a d y large tonnage of l i g n i n s p r o d u c e d i n p u l p i n g w o o d w i l l f u r t h e r increase because of the i n c r e a s i n g need for h i g h - v a l u e c h e m i c a l p u l p a n d because the m a i n use t o d a y - t h e f o o d i n d u s t r y - w i l l need m u c h less l o w - v a l u e l i g n i n as a p e l l e t i z i n g agent.

Downloaded by UNIV OF PITTSBURGH on May 3, 2015 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch010

I n t h i s respect, the m o s t i m p o r t a n t f u t u r e a p p l i c a t i o n o f l i g n i n w i l l be as a n a t u r a l p l a s t i c i n the field of general p o l y m e r a p p l i c a t i o n s , especially as adhe sives for w o o d composites. T h e adhesive properties o f l i g n i n , its r e a c t i v i t y w i t h f o r m a l d e h y d e , a n d i t s s t r u c t u r a l s i m i l a r i t y w i t h p h e n o l i c adhesives i n v i t e d i n v e s t i g a t i o n of the a p p l i c a b i l i t y o f l i g n i n i n adhesive resin systems. Therefore, d u r i n g the past several years, n u m e r o u s a t t e m p t s have been m a d e to replace the expensive p e t r o c h e m i c a l resins t o t a l l y or p a r t i a l l y w i t h the renewable r a w m a t e r i a l l i g n i n (1). H o w e v e r , the polydisperse character a n d the a c c o m p a n y i n g i m p u r i t i e s cre a t e d significant p r o b l e m s for the u t i l i z a t i o n o f t e c h n i c a l b y p r o d u c t l i g n i n s ( f r o m spent sulfite l i q u o r a n d k r a f t b l a c k l i q u o r ) as extenders for p e t r o c h e m i c a l resins. P h e n o l i c resins, for e x a m p l e , react p r i m a r i l y w i t h the low m o l e c u l a r weight l i g nosulfonates so t h a t the percentage o f phenolics t h a t c o u l d be replaced r e m a i n e d r a t h e r l o w . T h i s disadvantage was c i r c u m v e n t e d b y the " K a r a t e x " adhesive de veloped b y Forss a n d coworkers (2). E v e n i n t h i s a d v a n c e d process ( w h i c h produces a n n u a l l y n e a r l y 4,000 tons of adhesive), the h i g h m o l e c u l a r weight l i g n i n f r a c t i o n , o b t a i n e d b y u l t r a f i l t r a t i o n , c a n replace o n l y « 4 0 % o f p h e n o l i c resins. A n o t h e r p r o b l e m for the u t i l i z a t i o n o f l i g n o s u l f o n a t e as a n adhesive is the h i g h content o f sulfonate groups, w h i c h causes a hygroscopic character a n d t h u s prevents t h e i r conversion t o a water-resistant p o l y m e r . K r a f t l i g n i n seems t o be b e t t e r s u i t e d because o f i t s water i n s o l u b i l i t y . However, f r o m the esti m a t e d a n n u a l p r o d u c t i o n o f 2 χ 1 0 tons, o n l y 0 . 1 % is i s o l a t e d a n d m a r k e t e d (3). M a n y of the m i l l s b u r n i n g black l i q u o r for recovery o f the chemicals are a l r e a d y o p e r a t i n g above recovery furnace capacity, so a use for t h i s l i g n i n w o u l d help t o u n b u r d e n t h e i r o p e r a t i o n s . 7

F i n a l l y , i t s h o u l d be s t a t e d t h a t the processes t h a t use l i g n i n alone as t h e r m o s e t t i n g resin i n p a r t i c l e b o a r d s (4-6) d i d not find i n d u s t r i a l a p p l i c a t i o n , whereas, the processes u s i n g l i g n i n i n c o m b i n a t i o n w i t h s y n t h e t i c resins (2,7) are e c o n o m i c a l l y feasible t h o u g h the r e m a i n i n g p r o p o r t i o n o f s y n t h e t i c resin is still relatively high (60%). O n e reason for the l i m i t e d o p p o r t u n i t i e s for r e p l a c i n g p h e n o l i c resins w i t h l i g n i n is the r a t h e r low content of p h e n o l i c groups (0.6 a n d 0.3 p h e n o l i c O H groups p e r m o n o m e r i n K r a f t a n d sulfite l i g n i n , respectively (8)). Therefore, new developments focus o n the " a c t i v a t i o n " o f the l i g n i n m o l e c u l e , for e x a m ple, b y the synthesis o f h y d r o x y a l k y 1 derivatives for use i n c o m b i n a t i o n w i t h m e l a m i n e or isocyanate (9). O t h e r new a n d i n t e r e s t i n g i n v e s t i g a t i o n s i n t o the use o f m o r e " a c t i v e " l i g n i n i n c o m b i n a t i o n w i t h s y n t h e t i c resins, i n a d d i t i o n t o o u r c h a p t e r , are r e p o r t e d elsewhere i n t h i s b o o k .


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Experimental

Methodology

T h e a p p r o a c h we used t o m a k e l i g n i n a s u i t a b l e " p a r t n e r " i n a n adhesive f o r m u l a t i o n is based o n the f o l l o w i n g considerations. O u r i d e a was t o use the l i g n i n not m e r e l y as f i l l i n g m a t e r i a l , where i t is o b v i o u s l y inferior t o the m o r e active p h e n o l i c resins because o f the few p h e n o l i c groups a n d condensed s t r u c t u r e of l i g n i n . R a t h e r , we t h o u g h t t h a t lignosulfonate itself c o u l d be a g o o d b i n d i n g agent even w i t h o u t a d d i t i o n of s y n t h e t i c resins, i f new a c t i v e sites were i n t r o d u c e d . " A c t i v e sites" means, for e x a m p l e , the d i s i n t e g r a t i o n of the condensed s t r u c t u r e , the a d d i t i o n o f p h e n o l i c h y d r o x y l s , the s p l i t t i n g o f m e t h y l ethers so t h a t new p h e n o l i c groups are f o r m e d , the i n t r o d u c t i o n o f new f u n c t i o n a l groups (for e x a m p l e , c a r b o x y l groups), a n d last b u t not least, the f o r m a t i o n o f r a d i c a l s t h a t t h e n c o u l d react t o f o r m a n o x i d a t i v e p o l y m e r i z a t e . B o t h the a c t i v a t i o n o f l i g n i n a n d i t s c r o s s l i n k i n g to f o r m a b i n d e r for w o o d m a t e r i a l c o u l d be p e r f o r m e d b y a single b i o t e c h n o l o g i c a l process based o n the o b s e r v a t i o n t h a t enzymes are often m u c h m o r e powerful c a t a l y s t s i n the c o n version o f n a t u r a l l y o c c u r r i n g p o l y m e r molecules t h a n m a n m a d e chemicals can ever be. T h e b i n d i n g c a p a c i t y o f the l i g n i n - b a s e d e n z y m a t i c adhesive is based o n the f o l l o w i n g reactions (10-12). T h e e n z y m e used is a p h e n o l o x i d a s e , also c a l l e d " l a c c a s e " , classified b y I U P A C as m o n o p h e n o l , d i h y d r o x y - L - p h e n y l a l a n i n e : o x y gen oxido-reductase ( E . C . 1.14.18.1). T h i s r e l a t i v e l y unspecific c o p p e r - c o n t a i n i n g e n z y m e catalyzes the one-electron o x i d a t i o n of a r o m a t i c substrates (e.g., phenols) b y c o u p l i n g t o the four-electron r e d u c t i o n o f m o l e c u l a r o x y g e n t o w a ter. I n o u r case, the p h e n o l i c substrate is l i g n i n . T h e i n i t i a l one-electron o x i d a t i o n o f l i g n i n b y phenoloxidase, peroxidase a n d oxygenase y i e l d s r a d i c a l c a t i o n i n t e r m e d i a t e s t h a t c a n react i n t w o ways: 1. T h e y react w i t h water t o f o r m new p h e n o l i c groups (e.g.), v i a d e m e t h y l a t i o n . T h i s r e a c t i o n represents the " a c t i v a t i o n " o f the l i g n i n m o l e c u l e because new active p h e n o l i c groups, w h i c h c a n be f u r t h e r o x i d i z e d , are f o r m e d (13). 2. T h e y react w i t h each other t o f o r m a n o x i d a t i v e p o l y m e r i z a t e . T h i s r e a c t i o n represents t h e c r o s s l i n k i n g , a n d t h u s t h e a c t u a l g l u i n g process. T h u s , the a c t i v a t i o n a n d c r o s s l i n k i n g of the l i g n i n are p e r f o r m e d i n one step. I n t h i s way, the a p p a r e n t average m o l e c u l a r weight of l i g n o s u l f o n a t e is increased u p t o 1 χ 1 0 D a l t o n s ( F i g u r e 1). W e measured t h i s by Sepharose G P C a n d c a l i b r a t e d the c o l u m n b y m o l e c u l a r weight d e t e r m i n a t i o n s o f several f r a c t i o n s i n a n a n a l y t i c a l u l t r a c e n t r i f u g e (14). T h e curve w i t h the b r o a d d i s t r i b u t i o n i n F i g u r e 1 shows n a t i v e l i g n o s u l f o n a t e ; the s h a r p peak is the same l i g n o s u l f o n a t e after e n z y m a t i c p o l y m e r i z a t i o n . T h i s p o l y m e r i z a t e was s t i l l water-soluble because 6



F i g u r e 1. M o l e c u l a r weight d i s t r i b u t i o n ( d e t e r m i n e d b y Sepharose C L 6 B G P C ) o f l i g n o s u l f o n a t e before (filled circles) a n d after (open circles) i n c u b a t i o n w i t h phenoloxidase.


130


of the sulfonate groups. However, water-soluble organosol ν l i g n i n f r a c t i o n s be came w a t e r - i n s o l u b l e after e n z y m a t i c p o l y m e r i z a t i o n , a n d t h i s is i m p o r t a n t for a w a t e r - r e s i s t a n t adhesive (11). O f course, a n e n z y m e a p p l i e d t o a t e c h n i c a l process i n such a d i m e n s i o n as adhesives for w o o d m a t e r i a l s has t o have c e r t a i n p r o p e r t i e s . It m u s t be:


1. P r o d u c i b l e i n large q u a n t i t i e s o n cheap n u t r i e n t s . 2. 3. 4. 5.

H i g h l y reactive w i t h t e c h n i c a l l i g n i n s . S t a b l e at r o o m t e m p e r a t u r e . M o r e t h e r m o t o l e r a n t t h a n enzymes u s u a l l y are. A p p l i c a b l e as a crude p r e p a r a t i o n w i t h o u t f u r t h e r p u r i f i c a t i o n .

W e f o u n d t h a t a l l these c o n d i t i o n s were fulfilled b y e x t r a c e l l u l a r p h e n o l o x i dases p r o d u c e d b y a g r o u p of filamentous f u n g i called w h i t e - r o t basidiomycetes (15). A m o n g the m a n y species a n d s t r a i n s tested, the fungus Trametes versi color, a frequent i n h a b i t a n t of the woods of the N o r t h e r n H e m i s p h e r e , showed the m o s t active e n z y m e p r o d u c t i o n . It was a n especially g o o d c a n d i d a t e for our purposes because i t c o u l d be a d a p t e d to very cheap n u t r i e n t sources. T h e s u l fite l i q u o r itself, c o n s i s t i n g m a i n l y of lignosulfonate a n d sugars, was s u i t a b l e i n d i l u t e f o r m for g r o w t h of the fungus a n d for i n d u c i n g phenoloxidase p r o d u c t i o n . T h e e n z y m e a c t i v i t y was d e t e r m i n e d u s i n g 2 , 6 - d i m e t h o x y p h e n o l as the s u b strate (16). T h e phenoloxidase a c t i v i t y o b t a i n e d w h e n t h i s fungus was g r o w n o n d i l u t e sulfite l i q u o r was 12 t o 15 U / m L , w h i c h was a m u l t i p l e of the p r o d u c t i o n o n sole c a r b o h y d r a t e w i t h o u t l i g n i n (11 17). F o r use as a n adhesive c o m p o n e n t , t h i s e n z y m e s o l u t i o n has to be f u r t h e r c o n c e n t r a t e d , b y u l t r a f i l t r a t i o n or e v a p o r a t i o n . T o save energy, i t was desirable t o increase the e n z y m e p r o d u c t i o n of the fungus. W e tested m a n y phenols a n d l i g n i n s a n d f o u n d t h a t l i g n i n s o b t a i n e d b y a n organosol ν p u l p i n g process h a d a n e a r l y t e n f o l d c a p a c i t y for e n z y m e i n d u c t i o n (12). T h e s e results were o b t a i n e d i n 5 0 0 - m L s h a k i n g c u l tures. T h e next step was t o transfer the e n z y m e p r o d u c t i o n t o a larger scale. W e were able t o grow the fungus Trametes versicolor i n a 3 0 - L fermenter scale o n 0 . 1 % organosol ν l i g n i n i n the presence of a cheap a d d i t i o n a l C-source p r o d u c i n g 70 U / m L of e x t r a c e l l u l a r phenoloxidase. A f t e r r e m o v a l of the m y c e l i u m by filtration a n d subsequent sterile filtration of the e n z y m e - c o n t a i n i n g n u t r i e n t b r o t h , t h i s p r e p a r a t i o n was stable at r o o m t e m p e r a t u r e for at least a m o n t h a n d c o u l d be used w i t h o u t f u r t h e r p u r i f i c a t i o n as a c o m p o n e n t i n the l i g n i n - b a s e d adhesive. T h e t h e r m o s t a b i l i t y of the phenoloxidase was u n u s u a l l y h i g h c o m p a r e d t o m o s t enzymes; even h e a t i n g u p t o 65 ° C d i d not destroy the a c t i v i t y . C o n s i d e r i n g t h a t lignosulfonate contains 0.3 p h e n o l i c O H - g r o u p s per m o n o m e r a n d t h a t the K value of phenoloxidase t o w a r d phenols lies between 1 0 " a n d 1 0 " M , a n e n z y m e c o n c e n t r a t i o n of 400 U / m L i n the aqueous s o l u t i o n of 45 t o 5 0 % l i g n i n s h o u l d be sufficient t o cause the a c t i v a t i o n a n d c r o s s l i n k i n g w i t h i n a reasonable t i m e , so t h a t a sufficient b i n d i n g c a p a c i t y is o b t a i n e d ( T a b l e I). }

m

4


2

10.

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T h e e n z y m e s o l u t i o n represents one c o m p o n e n t o f the t w o - c o m p o n e n t w o o d adhesive s y s t e m . T h e second c o m p o n e n t is m e r e l y s p r a y - d r i e d sulfite l i q u o r . T h e adhesive p r e p a r a t i o n was as follows. T h e b i o c o m p o n e n t is m i x e d w i t h t h e s p r a y - d r i e d sulfite l i q u o r at a r a t i o o f a p p r o x i m a t e l y 2 p a r t s o f sulfite l i q u o r a n d a p p r o x i m a t e l y 1 p a r t o f aqueous e n z y m e s o l u t i o n , so t h a t t h e d r y m a t t e r content o f the adhesive is between 50 a n d 6 0 % . T h i s m i x t u r e is h o m o g e n i z e d a n d heated u p t o 50 ° C t o reduce i t s viscosity. T h e test b o a r d s were p r o d u c e d b y m i x i n g 150 g o f adhesive w i t h 1 k g o f w o o d chips a n d pressing t h e m a t a t a t e m p e r a t u r e of 190 ° C for 5 m i n u t e s at 30 k g / c m . It has t o be kept i n m i n d t h a t t h e h e a t i n g process is not necessary for g l u i n g w i t h t h i s p h e n o l o x i d a s e - l i g n i n adhesive. O f course, t h e p o l y m e r i z a t i o n is c a r r i e d o u t at r o o m t e m p e r a t u r e . T h e h e a t i n g serves o n l y t o remove t h e water w i t h i n a short t i m e . W e b o n d e d b o a r d s at 24 ° C , a n d t h e y h a d t h e same tensile s t r e n g t h as u r e a - f o r m a l d e h y d e a n d p h e n o l f o r m a l d e h y d e b o n d e d b o a r d s t h a t m u s t be pressed at a b o u t 200 ° C t o o b t a i n polymerization (Table I).


2

Table I. Tensile Strengths of Lignin-Based Two-Component Wood Bonding Systems Compared to Synthetic Resins Versai Tensile Strength Type of Resin a. Synthetic resins: Urea-formaldehyde Phenol-formaldehyde

c. Lignin-phenoloxidase resins: S A i + 320 U / m L (CA++) S A + 320 U / m L (CA++/Mg++) S A + 320 U / m L (Mg++) S A i -f organosol ν lignin + 320 U / m L

£C£

0.52 0.62

190 190

0.25 0 0.25

24 24 24

0.64

24 24 24 24

2

3

3

Temperature

(MPa)

b. Controls (only one component): Spray-dried sulfite liquor S A i Lyophilized enzyme (320 U / m L ) Spray-dried S A i - f denaturated enzyme

2

1

0.51 0.60 0.05

^ h e minimum standard requirement for 19-mm V20 particleboards is 0.35 M P a . M e a n values of 10 replicates tested by DIN 52365. S A = sulfite liquor.

2

3


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Results a n d Discussion


I n a l l cases, the m i n i m u m G e r m a n s t a n d a r d requirement of 0.35 M P a is exceeded by l i g n i n - p h e n o l o x i d a s e resins ( T a b l e I). I n m o s t cases, the break o c c u r r e d i n the w o o d a n d n o t i n the g l u e l i n e . A s c a n be seen i n S e c t i o n Β of the t a b l e , no c o m p o n e n t alone, w h e t h e r the e n z y m e or the sulfite l i q u o r , is capable of m e e t i n g s t a n d a r d r e q u i r e m e n t s . A synergistic effect is o b t a i n e d i f the c o m p o n e n t s are m i x e d . T h e c a t i o n of the sulfite l i q u o r has n o significant effect o n the tensile s t r e n g t h ; c o m p a r a b l e results were o b t a i n e d b o t h w i t h m a g n e s i u m a n d c a l c i u m sulfite l i q u o r s . T h o u g h the contact area between adhesive a n d w o o d is m u c h larger i n p a r t i cleboards t h a n i n w o o d l a m i n a t e s , o n l y 7 5 % of the tensile s t r e n g t h was o b t a i n e d w h e n the l i g n i n - b a s e d adhesive was a p p l i e d as t h e r m o s e t t i n g s y s t e m i n p a r t i cleboards ( T a b l e I I ) . T h e f o l l o w i n g reasons m a y be a p p l i c a b l e : 1. T h e c u r i n g t i m e at r o o m t e m p e r a t u r e under pressure was m u c h longer (8 h) i n the c o l d - s e t t i n g s y s t e m t h a n i n the p a r t i c l e b o a r d p r o d u c t i o n ( T a b l e I I ) . Indeed, the tensile s t r e n g t h c o u l d be increased w h e n the p a r t i c l e b o a r d was pressed at r o o m t e m p e r a t u r e for some h o u r s . H o w e v e r , t h i s procedure is of course not a p p l i c a b l e i n a t e c h n i c a l process. 2. Besides the shorter c u r i n g t i m e , the s p r a y i n g procedure also p l a y s a role i n d e t e r m i n i n g tensile s t r e n g t h . T h e r e l a t i v e l y h i g h v i s c o s i t y of the adhesive caused some p r o b l e m s t h a t c a n , however, easily be overcome i n a t e c h n i c a l process.

T a b l e I I . V e r s a i Tensile S t r e n g t h of L i g n i n - B a s e d A d h e s i v e U s e d t o B o n d P a i r s of W o o d Laminates and W o o d Chips (Particleboard) 1

Procedure and Properties 1) M i x i n g procedure of the adhesive: time and temperature

Wood Laminates

Wood Chips

10 m i n - 2 2 ° C

30 m i n - 2 2 ° C

8 h-22°C

5 mi n - 1 9 0 ° C

0.55 M P a

0.22 M P a

2) P r e s s i n g procedure: time and temperature 3) Tensile s t r e n g t h

C o m p o s i t i o n of the adhesive: O n e p a r t s p r a y - d r i e d , m i l l e d sulfite l i q u o r c o n t a i n i n g c a . 2 0 % sugar a n d 1.5 p a r t s concentrated c u l t u r e filtrate of Trametes versicolor (grown o n 0 . 1 % organosolv l i g n i n i n a 25 L fermenter), c o n t a i n i n g 420 U / m L phenoloxidase a c t i v i t y .


10.

HAARS ET AL.

133

Room-Temperature Curing Adhesives

A p r o b l e m t h a t s t i l l has t o be solved is the deficiency o f w a t e r resistance. T h e sulfonate groups are so p o l a r t h a t the p o l y m e r i z a t e is s t i l l w a t e r - s o l u b l e . A s was m e n t i o n e d before, w a t e r - s o l u b l e f r a c t i o n s o f o r g a n o s o l v l i g n i n s b e c a m e i n s o l u b l e i n water after e n z y m i c p o l y m e r i z a t i o n (11).

T h e r e f o r e , we h o p e d t h a t

a n a d d i t i o n o f p h e n o l - r i c h organosolv l i g n i n w o u l d i m p r o v e t h e w a t e r resistance However, as c a n be seen i n the last l i n e of T a b l e I, t h i s is n o t the case. T h e e n z y m e c o n c e n t r a t i o n was not the r a t e - l i m i t i n g f a c t o r i n the s y s t e m , because a n increase o f a c t i v i t y u p to 1,000 U / m L d i d n o t l e a d t o a higher tensile s t r e n g t h or a b e t t e r w a t e r resistance.

C u r r e n t l y , we are i n v e s t i g a t i n g


several m i x t u r e s o f less p o l a r lignosulfonates a n d k r a f t l i g n i n s . Because these studies are b e i n g c o n d u c t e d c o o p e r a t i v e l y w i t h a n i n d u s t r i a l p a r t n e r , t h e results m u s t b e considered c o n f i d e n t i a l at t h i s t i m e . Conclusions F u n g a l p h e n o l o x i d a s e enzymes p r o d u c e d o n waste l i g n i n c o n t a i n i n g effluents were s u i t a b l e b i o c o m p o n e n t s i n c o l d - s e t t i n g a n d t h e r m o s e t t i n g l i g n i n - b a s e d a d hesives. T h e p h e n o l o x i d a s e - l i g n i n bio-adhesive w i l l be s u i t a b l e as t h e r m o s e t t i n g glue 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 i f the w a t e r resistance o f the b o a r d s c a n be increased.

R e s u l t s i n t h i s area have a l r e a d y been o b t a i n e d .

T h e properties

of l i g n i n - p h e n o l o x i d a s e - b o n d e d p a r t i c l e b o a r d s revealed several advantages c o m p a r e d t o s y n t h e t i c resins:

1. T h e l i g n i n p h e n o l o x i d a s e adhesive i m p l i e s the t o t a l u t i l i z a t i o n o f waste l i g n i n , d i r e c t l y as one c o m p o n e n t o f the adhesive a n d i n d i r e c t l y as n u t r i e n t o f the p h e n o l o x i d a s e - p r o d u c i n g fungus. 2. T h e p r o d u c t i o n of e n z y m e - l i g n i n - b o n d e d p a r t i c l e b o a r d is m u c h less h a z a r d o u s t h a n the p r o d u c t i o n o f i s o c y a n a t e - b o n d e d

particle-

b o a r d , for e x a m p l e . 3. T h e bio-adhesive consists o f renewable r a w m a t e r i a l , so the p r o d u c t i o n does n o t d e p e n d o n the o i l m a r k e t . 4. T h e p h e n o l o x i d a s e - l i g n i n - b o n d e d p a r t i c l e b o a r d s are free o f a n y emission. 5. T h e p h e n o l o x i d a s e - l i g n i n adhesive is n o t o n l y a p p l i c a b l e as t h e r m o s e t t i n g adhesive b u t also as a c o l d - c u r i n g s y s t e m . A ckno wledgment s

P a r t o f t h i s w o r k was p e r f o r m e d as a n R & D p r o j e c t i n c o o p e r a t i o n w i t h the G . A . Pfleiderer C o m p a n y , N e u m a r k t , w i t h s u p p o r t o f the G e r m a n M i n i s t r y of R e s e a r c h a n d T e c h n o l o g y a n d the C o m m i s s i o n o f the E u r o p e a n C o m m u n i t y .


134


O r g a n o s o l v l i g n i n was k i n d l y s u p p l i e d b y t h e O r g a n o c e l l C o m p a n y , M u n i c h , F.R.G. Literature Cited 1. Nimz, H . H. Lignin-based wood adhesives. In Wood Adhesives, Chem. and Technol. Pizzi, Α . , E d . ; Marcel Dekker Inc., N Y , 1983.


2. Forss, K . ; Fuhrmann, A. Karatex-the lignin-based adhesive for plywood, particleboard and fiberboard. Paperi ja Puu. 1976, 11, 817-824. 3. Kirkman, A . G.; Gratzl, J. S.; Edwards, L. L. Kraft lignin recovery by ultrafiltration: economic feasibility and impact on the kraft recovery system. Tappi J. 1986, 69(5), 110-114. 4. Pedersen, A . H . F . ; Rasmussen, J . J. Manufacture of chipboard and the like. C a n . Pat. 743 861, 1986. 5. Nimz, H . H . ; Hitze, G . The application of spent sulfite liquors as an adhesive for particleboards. Cell Chem. Technol 1980, 14, 371-38. 6. Shen, K . C.; Calve, L. Ammonium-Based Spent Sulfite Liquor for Waferboard Binder. Reprinted: Adhesive Age, August 1980. 7. Roffael, E. Fortschritte in der Verwendung der Sulfit-ablauge als Bindemittel und Ansatzmittel bei der Herstellung von Holzspanplatten. Adhasion 1979, 23, 368-370. 8. Fengel, D . ; Wegener, G. Wood-Chemistry, Ultrastructure, Reactions, Walter de Gruyter, New York, 1984. 9. Newman, W . H . ; Glasser, W . G . Engineering plastics from lignin. 12 Synthesis and performance of lignin adhesives with Isoxyanate and Melamine. Holzforschung 1985, 39,(6) 345. 10. Haars, Α.; Huttermann, A . Process for producing a binder for wood materials. U.S. Patent 4 432 921, 1984. 11. Haars, Α.; Tautz, D . ; Huttermann, A . Bioconversion of organosoluble lignins by differ ent types of fungi. Resources and Conservation, 1986, 13, 37-51. 12. Haars, Α . ; Kharazipour, Α . ; Huttermann, A. Two-component wood adhesives based on lignin and phenoloxidases. Abstr., 3rd Intl. Conf. Biotechnol. Pulp Paper Industry, Stockholm, 1986. 13. Schoemaker, Η. E.; Harvey, P. J.; Bowen, R. M.; Palmer, J. M. O n the mechanism of enzymatic lignin breakdown. FEBS Letters 1985, 183, 7-12. 14. Huttermann, A . Gelchromatographie von Na-Ligninsulfonaten an Sepharose CL 6B. Holzforschung, 1977, 31(2), 45-50. 15. Kharazipour, A. Optimierung eines Verfahrens zur Herstellung von Bindemitteln fur Holzwerkstoffe auf der Basis von Ligninsulfonat und Laccase. Dissertation, Gottingen, December 1983. 16. Haars, Α . ; Huttermann, A . Function of laccase in the white-rot fungus Fomes annosus. Arch. Microbiol. 1980, 125, 233-237. 17. Huttermann, Α . ; Gebauer, M.; Volger, C.; Rosger, C . Polymerisation und Abbau von Natrium-Ligninsulfonat. Holzforschung, 1977, 31(3), 83-89. R E C E I V E D November 11, 1988


Room-Temperature Curing Adhesives Based on Lignin and

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