Room-Temperature Curing Adhesives Based on Lignin and

D-8430 Neumarkt/Opf. 0097-6156/89/0385-0126$06.00/0 · 1989 American Chemical Society ... ical resins totally or partially with the renewable raw ...
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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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HAARS E T AL.

Room-Temperature Curing Adhesives

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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.

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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 .

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

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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

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

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

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.

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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:

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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

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

2

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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).

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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

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Results a n d Discussion

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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 .

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

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

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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 .

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

134

ADHESIVES F R O M RENEWABLE RESOURCES

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.

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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

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