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Chapter 22 Utilization of Soda Bagasse Hemicellulose As Corrugated Board Adhesive G e r r i t H. van der Klashorst National Timber Research Institute Council for Scientific and Industrial Research P. O. Box 395, Pretoria, 0001 Republic of South Africa
Large quantities of hemicellulose are produced as a waste byproduct during chemical pulping of sugarcane bagasse. The hemicellulose present in soda bagasse spent liquors has a high molecular weight that enables its easy reclamation and gives it good potential for use in polymeric products. A corrugated board adhesive was developed from industrial soda bagasse hemicellulose and evaluated on laboratory scale. The gel properties of the adhesive were similar to those of commercial starch binders. The adhesive gave a ply adhesion comparable to that obtained with conventional starch-based adhesive. L a r g e q u a n t i t i e s o f hemicellulose a n d l i g n i n are p r o d u c e d as waste p r o d u c t s d u r i n g the s o d a p u l p i n g o f w o o d or other p l a n t m a t e r i a l . T h e l i g n i n p r o d u c e d b y t h e i n d u s t r i a l p u l p i n g o f sugarcane bagasse was s h o w n t o have a n e x c e p t i o n a l l y h i g h reactivity m a k i n g i t useful as a r a w m a t e r i a l for t h e p r e p a r a t i o n o f c o l d set a n d t h e r m o s e t t i n g adhesives ( F i g u r e 1). T h i s p r o p e r t y o f the l i g n i n results p a r t i a l l y f r o m the m i l d c o n d i t i o n s used for t h e i n d u s t r i a l p u l p i n g o f bagasse. T h e m i l d p u l p i n g c o n d i t i o n s also cause o n l y s u p e r f i c i a l d e g r a d a t i o n o f t h e h e m i c e l lulose. T h e r e s u l t i n g hemicellulose i n the spent p u l p i n g l i q u o r consequently has a r e l a t i v e l y h i g h m o l e c u l a r weight, w h i c h enables i t s easy r e c l a m a t i o n . S o d a bagasse spent l i q u o r thus contains t w o useful renewable p o l y m e r i c c h e m i c a l feedstocks: hemicellulose a n d l i g n i n . T h e uses developed so f a r for these m a t e r i a l s are depicted g r a p h i c a l l y i n F i g u r e 1. T h e use o f t h e h e m i c e l l u lose as a c o r r u g a t e d b o a r d adhesive is discussed i n t h i s chapter. 0097-6156/89/0385-0305$06.00/0 © 1989 American Chemical Society
In Adhesives from Renewable Resources; Hemingway, Richard W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
In Adhesives from Renewable Resources; Hemingway, Richard W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Novel c o l d set adhesive I (2)
1(4)
|wood a d h e s i v e I
Thermoset-
(1)
—
I Paper I surface I size 1(5)
r ICorrugaI ted Iboard I adhesive
HEMICELLULOSE
Briquette binder
I
j
|
|
(2)
Recovered re-use
for
PULPING CHEMICALS
F i g u r e 1. P r o d u c t s f r o m i n d u s t r i a l s o d a s u g a r c a n e bagasse s p e n t p u l p i n g l i q u o r s .
LIGNIN
LIQUOR
SPENT
SEPARATION (2)
BAGASSE
SODA
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22.
VAN DER K L A S H O R S T
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Experimental
307
Soda Bagasse Hemicellulose Adhesive
Methodology
H e m i c e l l u l o s e was r e c l a i m e d f r o m i n d u s t r i a l s o d a bagasse spent p u l p i n g l i q u o r by p r e c i p i t a t i o n w i t h m e t h a n o l as was done i n earlier studies (2-5). T h e h e m i cellulose p r e c i p i t a t e o b t a i n e d was s u b m i t t e d t o different degrees of w a s h i n g w i t h 5 0 % aqueous m e t h a n o l , r e s u l t i n g i n hemicellulose p r e p a r a t i o n s c o n t a i n i n g differ ent q u a n t i t i e s o f ash a n d l i g n i n . T h e p H of the hemicellulose was a d j u s t e d a n d b o r a x or C a C b a d d e d , after w h i c h i t was d r i e d a n d b a l l - m i l l e d t o the i n d i c a t e d p a r t i c l e sizes. T h e K l a s o n l i g n i n content was d e t e r m i n e d b y the T A P P I procedure ( 0 ) , a n d the ash content was d e t e r m i n e d at 750 ° C . V i s c o s i t y d e t e r m i n a t i o n s o n a n u m b e r of hemicellulose p r e p a r a t i o n s i n d i c a t e d a n average degree of p o l y m e r i z a t i o n of between 60 a n d 70 ( 7 ) . G e l f i l t r a t i o n of the hemicellulose was done o n a G - 5 0 S e p h a d e x c o l u m n w i t h water as eluent b y the N a t i o n a l F o o d R e s e a r c h I n s t i t u t e o f the C S I R . N e u t r a l ized samples were a p p l i e d to the c o l u m n a n d f r a c t i o n s (6 m L ) collected, o f w h i c h 1 - m L a l i q u o t s were assayed by the p h e n o l - s u l f u r i c a c i d test (
