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2 The Chemical Composition of Wood R O G E R C. P E T T E R S E N
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U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, W I 53705
This chapter includes overall chemical composition of wood, methods of analysis, structure of hemicellulose components and degree of polymerization of carbohydrates. Tables of data are compiled for woods of several countries. Components include: cellulose (Cross and Bevan, holo-, and alpha-), lignin, pentosans, and ash. Solubilities in 1% sodium hydroxide, hot water, e t h a n o l / benzene, and ether are reported. The data were collected at Forest Products Laboratory (Madison, Wisconsin) from 1927-68 and were previously unpublished. These data include both United States and foreign woods. Previously published data include compositions of woods from Borneo, Brazil, Cambodia, Chile, Colombia, Costa Rica, Ghana, Japan, Mexico, Mozambique, Papua New Guinea, the Philippines, Puerto Rico, Taiwan, and the USSR. Data from more detailed analyses are presented for common temperate-zone woods and include the individual sugar composition (as glucan, xylan, galactan, arabinan, and mannan), uronic anhydride, acetyl, lignin, and ash.
THE CHEMICAL COMPOSITION
of w o o d cannot be defined p r e cisely for a g i v e n tree species o r e v e n for a g i v e n tree. C h e m i c a l c o m p o s i t i o n v a r i e s w i t h t r e e p a r t (root, s t e m , o r b r a n c h ) , t y p e o f w o o d (i.e., n o r m a l , tension, or compression) geographic location, c l i mate, a n d soil conditions. Analytical data accumulated from m a n y years of w o r k a n d f r o m m a n y different laboratories have h e l p e d to define average e x p e c t e d values for the c h e m i c a l c o m p o s i t i o n of w o o d . O r d i n a r y c h e m i c a l analysis can d i s t i n g u i s h b e t w e e n h a r d w o o d s (angiosperms) a n d softwoods (gymnosperms). U n f o r t u n a t e l y , such t e c h n i q u e s c a n n o t b e u s e d to i d e n t i f y i n d i v i d u a l tree species b e c a u s e o f the variation w i t h i n each species a n d the similarities a m o n g m a n y s p e c i e s . F u r t h e r i d e n t i f i c a t i o n is p o s s i b l e w i t h d e t a i l e d c h e m i c a l a n a l This chapter not subject to U.S. copyright. Published 1984, of American Chemical Society In The Chemistry Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
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THE CHEMS ITRY OF SOLID WOOD
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y s i s o f e x t r a c t i v e s ( c h e m o t a x o n o m y ) . C h e m o t a x o n o m y is d i s c u s s e d f u l l y e l s e w h e r e i n t h e l i t e r a t u r e ( I , 2). T h e r e are two major c h e m i c a l c o m p o n e n t s i n w o o d : lignin ( 1 8 35%) a n d c a r b o h y d r a t e ( 6 5 - 7 5 % ) . B o t h are c o m p l e x , p o l y m e r i c m a terials. M i n o r amounts of extraneous materials, mostly i n the form o f o r g a n i c e x t r a c t i v e s a n d i n o r g a n i c m i n e r a l s (ash), a r e also p r e s e n t i n w o o d ( u s u a l l y 4 - 1 0 % ) . O v e r a l l , w o o d has a n e l e m e n t a l c o m p o s i tion of about 5 0 % c a r b o n , 6% h y d r o g e n , 4 4 % oxygen, a n d trace amounts of several metal ions. A c o m p l e t e c h e m i c a l analysis accounts for a l l t h e c o m p o n e n t s of t h e o r i g i n a l w o o d s a m p l e . T h u s , i f w o o d is d e f i n e d as p a r t l i g n i n , part c a r b o h y d r a t e , a n d p a r t e x t r a n e o u s m a t e r i a l , analyses for e a c h of these c o m p o n e n t s s h o u l d s u m to 1 0 0 % . T h e p r o c e d u r e b e c o m e s m o r e c o m p l e x as t h e c o m p o n e n t p a r t s a r e d e f i n e d w i t h g r e a t e r d e t a i l . S u m m a t i v e d a t a a r e f r e q u e n t l y a d j u s t e d to 1 0 0 % b y i n t r o d u c i n g c o r r e c t i o n f a c t o r s i n t h e a n a l y t i c a l c a l c u l a t i o n s . W i s e a n d c o w o r k e r s (3) presented an i n t e r e s t i n g study o n the s u m m a t i v e analysis of w o o d and analyses of the carbohydrate fractions. T h e c o m p l e t e analytical r e p o r t a l s o i n c l u d e s d e t a i l s o f t h e s a m p l e , s u c h as s p e c i e s , a g e , a n d l o c a t i o n o f t h e t r e e , h o w t h e s a m p l e w a s o b t a i n e d from t h e t r e e , a n d f r o m w h a t p a r t o f t h e t r e e . T h e t y p e o f w o o d a n a l y z e d is a l s o i m p o r tant; i . e . , c o m p r e s s i o n , t e n s i o n , or n o r m a l w o o d . Vast a m o u n t s o f d a t a a r e a v a i l a b l e o n t h e c h e m i c a l c o m p o s i t i o n o f w o o d . F e n g e l a n d G r o s s e r (4) m a d e a c o m p i l a t i o n f o r t e m p e r a t e z o n e w o o d s . T h i s c h a p t e r is a c o m p i l a t i o n o f d a t a f o r m a n y d i f f e r e n t species f r o m a l l parts of the w o r l d , a n d i n c l u d e s m u c h of the data i n R e f e r e n c e 4. T h e t a b l e s at t h e e n d o f t h i s c h a p t e r s u m m a r i z e t h e s e data.
Chemical Components Carbohydrates. T h e carbohydrate portion of wood comprises cellulose a n d the h e m i c e l l u l o s e s . C e l l u l o s e content ranges f r o m 40 to 5 0 % o f t h e d r y w o o d w e i g h t , a n d h e m i c e l l u l o s e s range f r o m 2 5 to 35%.
CELLULOSE.
C e l l u l o s e is a g l u c a n p o l y m e r c o n s i s t i n g o f l i n e a r c h a i n s o f 1 , 4 - p - b o n d e d a n h y d r o g l u c o s e u n i t s . ( T h e n o t a t i o n 1,4-β describes the b o n d linkage a n d the configuration of the oxygen atom b e t w e e n adjacent glucose units.) F i g u r e 1 shows a structural diagram of a portion of a glucan c h a i n . T h e n u m b e r of sugar units i n one m o l e c u l a r c h a i n is r e f e r r e d to as t h e d e g r e e o f p o l y m e r i z a t i o n ( D P ) . E v e n t h e m o s t u n i f o r m s a m p l e has m o l e c u l a r c h a i n s w i t h s l i g h t l y different D P v a l u e s . T h e average D P for t h e m o l e c u l a r chains i n a g i v e n s a m p l e is d e s i g n a t e d b y D P .
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
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THE CHEMS ITRY OF SOLID WOOD
G o r i n g a n d T i m e l l (5) d e t e r m i n e d t h e D P f o r n a t i v e c e l l u l o s e s from several sources of plant material. T h e y used a nitration isolation p r o c e d u r e that a t t e m p t s to m a x i m i z e the y i e l d w h i l e m i n i m i z i n g the depolymerization of the cellulose. These molecular weight d e t e r m i nations, done b y light-scattering experiments, indicate w o o d c e l l u l o s e h a s a D P o f at l e a s t 9 , 0 0 0 - 1 0 , (XX), a n d p o s s i b l y as h i g h as 1 5 , 0 0 0 . A D P of 10,000 w o u l d m e a n a linear chain length of approximately 5 μπι i n w o o d . T h e D P o b t a i n e d f r o m l i g h t - s c a t t e r i n g e x p e r i m e n t s is b i a s e d u p w a r d because light scattering increases exponentially w i t h molecular s i z e . T h e v a l u e o b t a i n e d is u s u a l l y r e f e r r e d t o as t h e w e i g h t e d D P o r D P . T h e n u m b e r a v e r a g e d e g r e e o f p o l y m e r i z a t i o n ( D P ) is u s u ally obtained from o s m o m e t r y measurements. These measurements are l i n e a r w i t h respect to m o l e c u l a r size a n d , therefore, a m o l e c u l e is c o u n t e d e q u a l l y as o n e m o l e c u l e r e g a r d l e s s o f i t s s i z e . T h e r a t i o o f D P t o D P is a m e a s u r e o f t h e m o l e c u l a r w e i g h t d i s t r i b u t i o n . T h i s r a t i o is n e a r l y o n e f o r n a t i v e c e l l u l o s e i n s e c o n d a r y c e l l w a l l s o f p l a n t s (6). T h e r e f o r e , t h i s c e l l u l o s e is m o n o d i s p e r s e a n d c o n t a i n s m o l ecules o f o n l y o n e size. C e l l u l o s e i n t h e p r i m a r y w a l l has a l o w e r D P a n d is t h o u g h t t o b e p o l y d i s p e r s e . (See R e f e r e n c e 7 f o r a d i s c u s s i o n of molecular w e i g h t d i s t r i b u t i o n i n synthetic polymers.)
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W
W
n
n
N a t i v e c e l l u l o s e is p a r t i a l l y c r y s t a l l i n e . X - R a y d i f f r a c t i o n e x p e r i m e n t s i n d i c a t e c r y s t a l l i n e c e l l u l o s e (Valonia ventricosa) has space g r o u p s y m m e t r y P 2 ! w i t h a = 16.34, b = 15.72, c = 10.38 Â, a n d 7 = 9 7 . 0 ° (8). T h e u n i t c e l l c o n t a i n s e i g h t c e l l o b i o s e m o i e t i e s . T h e m o l e c u l a r chains pack i n layers that are h e l d together b y w e a k v a n d e r W a a l s ' f o r c e s ( F i g u r e 2a). T h e l a y e r s c o n s i s t o f p a r a l l e l c h a i n s o f anhydroglucose units, a n d the chains are h e l d together b y i n t e r m o l e c u l a r h y d r o g e n b o n d s . T h e r e are also i n t r a m o l e c u l a r h y d r o g e n b o n d s b e t w e e n t h e a t o m s o f a d j a c e n t g l u c o s e r e s i d u e s ( F i g u r e 2b). T h i s s t r u c t u r e is c a l l e d c e l l u l o s e I . T h e r e a r e at l e a s t t h r e e o t h e r s t r u c t u r e s r e p o r t e d f o r m o d i f i e d c r y s t a l l i n e c e l l u l o s e . T h e m o s t i m p o r t a n t is c e l l u l o s e I I , o b t a i n e d b y m e r c e r i z a t i o n o r r e g e n e r a t i o n o f n a t i v e c e l l u l o s e . Mercerization is t r e a t m e n t o f c e l l u l o s e w i t h s t r o n g a l k a l i . Regeneration is t r e a t m e n t o f c e l l u l o s e w i t h s t r o n g a l k a l i a n d c a r b o n d i s u l f i d e to f o r m a s o l u b l e x a n t h a t e d e r i v a t i v e . T h e d e r i v a t i v e is c o n v e r t e d b a c k t o c e l l u l o s e a n d r e p r e c i p i t a t e d as r e g e n e r a t e d c e l l u l o s e . T h e s t r u c t u r e o f c e l l u l o s e I I ( r e g e n e r a t e d ) h a s s p a c e g r o u p s y m m e t r y Ρ2χ w i t h a = 8 . 0 1 , b = 9.04, c = 10.36 Â, a n d 7 = 117.1°, a n d t w o c e l l o b i o s e m o i e t i e s p e r u n i t c e l l (9). T h e p a c k i n g a r r a n g e m e n t is m o d i f i e d i n c e l l u l o s e I I , a n d p e r m i t s a m o r e intricate h y d r o g e n - b o n d e d n e t w o r k that extends b e t w e e n l a y e r s as w e l l as w i t h i n l a y e r s ( F i g u r e 3). T h e r e s u l t is a
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
PETTERSEN
The Chemical Composition of Wood
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2.
Figure 2. Axial projection (top) and planar projection (bottom) of the crystal structure of ceUuhse I. The planar projection shows the hydrogenbonding network within the layers. (Reproduced with permission from Ref. 8. Copyright 1974, Elsevier Scientific Publishing Company, Amsterdam.)
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
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Figure 3. Axial projection of the crystal structure of cellulose II. (Repro duced with permission from Ref 10. Copyright 19/8, Butterworth ir Co. (Publishers) LtdT) m o r e t h e r m o d y n a m i c a l l y stable substance. E v i d e n t l y , all native c e l luloses have t h e s t r u c t u r e o f cellulose I. C e l l u l o s e is i n s o l u b l e i n m o s t s o l v e n t s i n c l u d i n g s t r o n g a l k a l i . I t is d i f f i c u l t t o i s o l a t e f r o m w o o d i n p u r e f o r m b e c a u s e i t is i n t i m a t e l y associated w i t h the l i g n i n a n d hemicelluloses. A n a l y t i c a l methods of cellulose preparation are discussed i n the section on " A n a l y t i c a l P r o cedures."
HEMICELLULOSES.
H e m i c e l l u l o s e s are m i x t u r e s of polysaccha rides s y n t h e s i z e d i n w o o d a l m o s t e n t i r e l y f r o m g l u c o s e , m a n n o s e , galactose, xylose, arabinose, 4 - O - m e t h y l g l u c u r o n i c a c i d , a n d galacturonic acid residues. S o m e h a r d w o o d s c o n t a i n trace amounts of rhamnose. G e n e r a l l y , hemicelluloses are of m u c h l o w e r m o l e c u l a r w e i g h t than cellulose a n d s o m e are b r a n c h e d . T h e y are i n t i m a t e l y a s s o c i a t e d w i t h c e l l u l o s e a n d a p p e a r t o c o n t r i b u t e as a s t r u c t u r a l c o m p o n e n t i n the plant. S o m e hemicelluloses are present i n abnor m a l l y l a r g e a m o u n t s w h e n t h e p l a n t is u n d e r s t r e s s ; e . g . , c o m p r e s s i o n w o o d h a s a h i g h e r t h a n n o r m a l g a l a c t o s e c o n t e n t as w e l l as a h i g h e r lignin content (II). H e m i c e l l u l o s e s are soluble i n alkali a n d easily h y d r o l y z e d b y acids. T h e s t r u c t u r e o f h e m i c e l l u l o s e s c a n b e u n d e r s t o o d b y first c o n s i d e r i n g t h e c o n f o r m a t i o n o f t h e m o n o m e r u n i t s ( F i g u r e 4). T h e r e a r e t h r e e e n t r i e s u n d e r e a c h m o n o m e r i n F i g u r e 4. I n e a c h e n t r y , the l e t t e r d e s i g n a t i o n s D a n d L refer to a s t a n d a r d c o n f i g u r a t i o n for the two optical isomers of glyceraldehyde, the simplest carbohydrate. T h e G r e e k l e t t e r s α a n d β r e f e r to t h e c o n f i g u r a t i o n of the h y d r o x y l g r o u p at c a r b o n a t o m 1. T h e t w o c o n f i g u r a t i o n s a r e c a l l e d anomers. T h e first e n t r y is a s h o r t e n e d f o r m o f t h e s u g a r n a m e . T h e s e c o n d e n t r y i n d i c a t e s t h e r i n g s t r u c t u r e . P y r a n o s e refers to a s i x - m e m b e r e d ring i n t h e c h a i r o r b o a t f o r m a n d f u r a n o s e r e f e r s to a five-membered r i n g . T h e t h i r d e n t r y is a n a b b r e v i a t i o n c o m m o n l y u s e d for t h e s u g a r residue in polysaccharides.
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
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2.
PETTERSEN
The Chemical Composition of Wood
/3-D-Glucose 0-D-Glucopyranose £-D-Glup
/3-D-Mannose /3-D-Mannopyranose 0-D-Manp
/3-D-Qalactose /3-D-Galactopyranose 0-D-Galp
£-D-XyIose /3-D-Xylopyranose 0-D-Xylp
H
OH
Η
63
μ
.Ο. CH,0 OH
ΗΟΗΧ Η α-L-Arab i nose of-L- Arabinof uranose a-L-Araf
OH 4-0- MethyIgucuronic acid 4-O-Methylglucopyranosyluronic acid 4-O-Me-a-D-GlupA
Figure 4. Monomer components of wood hemicelluloses.
F i g u r e 5 shows a partial structure of a c o m m o n h a r d w o o d h e m i cellulose, O-acetyl-4-O-methylglucuronoxylan. T h e entire molecule c o n s i s t s o f a b o u t 2 0 0 β-D-xylopyranose r e s i d u e s l i n k e d i n a l i n e a r c h a i n b y (1 —> 4) g l y c o s i d i c b o n d s . A p p r o x i m a t e l y 1 o f 10 o f t h e x y l o s e residues hasa 4 - O - m e t h y l g l u c u r o n i c acid residue b o n d e d to it t h r o u g h t h e h y d r o x y l a t t h e 2 ring p o s i t i o n . A p p r o x i m a t e l y 7 o f 1 0 of the xylose residues have acetate groups b o n d e d to e i t h e r t h e 2 o r 3 r i n g p o s i t i o n . T h i s c o m p o s i t i o n is s u m m a r i z e d i n F i g u r e 5 i n a n abbreviated structure diagram. H a r d w o o d xylans contain a n average of two xylan b r a n c h i n g chains p e r macromolecule. T h e branches are p r o b a b l y q u i t e s h o r t (12). Table I lists t h e m o s t a b u n d a n t o f t h e w o o d h e m i c e l l u l o s e s . T h e
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
Downloaded by MONASH UNIV on May 4, 2015 | http://pubs.acs.org Publication Date: May 5, 1984 | doi: 10.1021/ba-1984-0207.ch002
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
Softwood
Larch wood
Hardwood
Hardwood
Arabinoglucuronoxylan
Arabinogalactan
Glucuronoxylan
Glucomannan 2--5
1 5 -- 3 0
5- -35
7- -10
10-- 1 5
5--8
β-D-Manp β-D-Glup
Acetyl
β-D-GlupA β-D-Xylp 4-O-Me-a-DGlupA
a-L-Ara/ β-L-Arap
β-D-Galp
a-L-Ara/
β-D-Xylp 4-O-Me-a-DGlupA
β-D-Manp β-D-Glup a-D-Galp Acetyl
/\ceiyi
aβ-D-Glup -D-Galp
β-D-Manp
Units
1-2
2/3 1/3 Little 10 1 7
1.3 6
4 1 0.1 1 10 2
3 1 1
Molar Ratios
Composition
b
0
n
1 -> 4
1 —• 4
H ->
1 —> 3 1 3, 1 -> 6 1 6 1 —> 3 1 —» 6 4 1 —» 2 1
1 —» 4 1 -» 2
4 1 4 1 -> 6
1
4 1 -> 4 1 -» 6
1
Linkage
Components
T h e asterisk represents a partial soluhility. D P is the n u m b e r average d e g r e e o f p o l y m e r i z a t i o n , usually obtained b y osmometry. ( R e p r o d u c e d with p e r m i s s i o n from Ref. 6. C o p y r i g h t 1981, A c a d e m i c Press.)
Softwood
(Galacto)Glucomannan
Occurrence
Softwood
Type
Galactoglucomannan
Hemicellulose
Amount (% of wood)
Table I. T h e M a j o r Hemicellulose
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0
borate
Alkaline
borate
Alkali, dimethyl sulfoxide*
Alkali, dimethyl sulfoxide, * water* Water
Alkaline
Alkali, water*
Solubility
200
200
200
100
100
100
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m e t h o d s u s e d for the isolation a n d s t r u c t u r a l c h a r a c t e r i z a t i o n o f each of these materials are b e y o n d the scope of this chapter (13-15). Lignin. L i g n i n is a p h e n o l i c s u b s t a n c e c o n s i s t i n g o f a n i r r e g u l a r array of variously b o n d e d h y d r o x y - a n d methoxy-substituted p h e n y l p r o p a n e units. T h e precursors of l i g n i n biosynthesis are p-eoum a r y l a l c o h o l (I), c o n i f e r y l a l c o h o l (II), a n d s i n a p y l a l c o h o l (III). I is
OCH.
0CH
CH o 3
o
OH I
II
III
a m i n o r p r e c u r s o r o f s o f t w o o d a n d h a r d w o o d l i g n i n s ; I I is t h e p r e d o m i n a n t p r e c u r s o r of softwood l i g n i n ; a n d II a n d III are b o t h p r e c u r s o r s o f h a r d w o o d l i g n i n (15). T h e s e a l c o h o l s a r e l i n k e d i n l i g n i n b y e t h e r a n d c a r b o n - c a r b o n b o n d s . F i g u r e 6 (15) is a s c h e m a t i c s t r u c t u r e o f a s o f t w o o d l i g n i n m e a n t to i l l u s t r a t e t h e v a r i e t y o f s t r u c tural components. The 3,5-dimethoxy-substituted aromatic ring n u m b e r 13 o r i g i n a t e s f r o m s i n a p y l a l c o h o l , I I I , a n d is p r e s e n t o n l y i n t r a c e a m o u n t s ( < 1 % ) (16). F i g u r e 6 d o e s n o t s h o w a l i g n i n - c a r b o h y d r a t e c o v a l e n t b o n d . T h e r e has b e e n m u c h c o n t r o v e r s y c o n c e r n i n g t h e e x i s t e n c e o f this b o n d , b u t e v i d e n c e has b e e n a c c u m u l a t i n g i n i t s s u p p o r t (15, 17). A s t r u c t u r e p r o p o s e d f o r h a r d w o o d l i g n i n (Fagus silvatica L . ) is s i m i l a r t o t h a t o f F i g u r e 6, e x c e p t t h a t t h e r e a r e t h r e e t i m e s as m a n y s y r i n g y l p r o p a n e u n i t s as g u a i a c y l p r o p a n e u n i t s (18). T h e s e m o i e t i e s are d e r i v e d f r o m I I I a n d I I , r e s p e c t i v e l y . T h e ratio of s y r i n g y l to g u a i a c y l m o i e t i e s is o f t e n o b t a i n e d b y m e a s u r i n g t h e r e l a t i v e a m o u n t s of syringaldehyde (3,5-dimethoxy-4-hydroxybenzaldehyde) and va n i l l i n ( 4 - h y d r o x y - 3 - m e t h o x y b e n z a l d e h y d e ) g e n e r a t e d as p r o d u c t s o f n i t r o b e n z e n e o x i d a t i o n o f l i g n i n (19). A b e t t e r m e t h o d is t o d e t e r m i n e the products f o r m e d from the two types of moieties on permanganate o x i d a t i o n o f m e t h y l a t e d l i g n i n s (20). L i g n i n can be isolated b y one of several methods. A c i d h y d r o l y s i s o f w o o d i s o l a t e s K l a s o n l i g n i n , w h i c h c a n b e q u a n t i f i e d (see " A n a l y t i c a l P r o c e d u r e s " ) , b u t is t o o s e v e r e l y d e g r a d e d f o r u s e i n s t r u c t u r a l s t u d i e s . B j o r k m a n ' s (21) m i l l e d w o o d l i g n i n p r o c e d u r e y i e l d s a l i g n i n t h a t is m u c h l e s s d e g r a d e d a n d i s , t h u s , m o r e u s e f u l
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
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for s t r u c t u r a l s t u d i e s . T h e f o l l o w i n g are e x a m p l e s o f t h e w e i g h t av erage m o l e c u l a r w e i g h t of l i g n i n s isolated b y u s i n g the m i l l e d w o o d l i g n i n p r o c e s s : s p r u c e [Picea abies ( L . ) K a r s t ] , 1 5 , 0 0 0 ; a n d s w e e t g u m (Liquidambar styraciflua L . ) , 1 6 , 0 0 0 (22). T h e s e v a l u e s a r e l o w e r than the molecular weight of the original lignin because fragmenta tion of the lignin molecules results from the ball m i l l i n g procedure. L i g n i n for s t r u c t u r a l s t u d i e s c a n also b e o b t a i n e d b y e n z y m a t i c h y d r o l y s i s o f t h e c a r b o h y d r a t e (23). W o o d is g r o u n d i n a v i b r a t o r y b a l l m i l l and then treated w i t h cellulytic enzymes. T h e isolated lignin contains 1 2 - 1 4 % carbohydrate. M e t h o x y l c o n t e n t is u s e d t o c h a r a c t e r i z e l i g n i n s . E l e m e n t a l a n d m e t h o x y l a n a l y s i s o f s p r u c e (Picea abies ( L . ) K a r s t . ) m i l l e d w o o d l i g n i n i n d i c a t e s a c o m p o s i t i o n C H . 9 2 0 . 4 o ( O C H ) . 9 2 (15, 24). B e e c h (Fagus silvatica L . ) m i l l e d w o o d l i g n i n has a c o m p o s i t i o n C H 7 . 4 9 0 2 . 5 3 ( O C H 3 ) 9 (24). T h i s i n f o r m a t i o n h e l p s l i g n i n c h e m i s t s u n d e r s t a n d w h a t p r e c u r s o r s w e r e u s e d for the biosynthesis of l i g n i n . A n e x c e l l e n t , c o m p r e h e n s i v e b o o k o n l i g n i n is e d i t e d b y S a r k a n e n a n d L u d w i g (25). Extraneous C o m p o n e n t s . T h e extraneous c o m p o n e n t s (extrac t i v e s a n d ash) i n w o o d a r e t h e s u b s t a n c e s o t h e r t h a n c e l l u l o s e , h e m i c e l l u l o s e s , a n d l i g n i n . T h e y d o n o t c o n t r i b u t e to t h e c e l l w a l l s t r u c ture, a n d most are soluble i n neutral solvents. T h e detailed c h e m i s t r y o f w o o d e x t r a c t i v e s c a n b e f o u n d e l s e w h e r e (26). A r e v i e w o f e x t r a c t i v e s i n e a s t e r n U . S . h a r d w o o d s is a v a i l a b l e (27). 9
9
7
2
3
0
h3
Extractives — the extraneous material soluble i n neutral sol v e n t s — c o n s t i t u t e 4 - 1 0 % of the d r y w e i g h t of n o r m a l w o o d of species t h a t g r o w i n t e m p e r a t e c l i m a t e s . T h e y m a y b e as m u c h as 2 0 % o f the w o o d of t r o p i c a l species. E x t r a c t i v e s are a variety of organic c o m p o u n d s i n c l u d i n g fats, w a x e s , a l k a l o i d s , p r o t e i n s , s i m p l e a n d c o m p l e x phenolics, s i m p l e sugars, pectins, mucilages, gums, resins, terpenes, starches, glycosides, saponins, a n d essential oils. M a n y of these func t i o n as i n t e r m e d i a t e s i n t r e e m e t a b o l i s m , as e n e r g y r e s e r v e s , o r as part of the tree's defense m e c h a n i s m against m i c r o b i a l attack. T h e y c o n t r i b u t e to w o o d p r o p e r t i e s s u c h as c o l o r , o d o r , a n d d e c a y r e s i s tance. Ash is t h e i n o r g a n i c r e s i d u e r e m a i n i n g a f t e r i g n i t i o n at a h i g h t e m p e r a t u r e . I t is u s u a l l y l e s s t h a n 1 % o f w o o d f r o m t e m p e r a t e z o n e s . It is s l i g h t l y h i g h e r i n w o o d f r o m t r o p i c a l c l i m a t e s .
Carbohydrate and Lignin Distribution Carbohydrates. T h e m o r p h o l o g i c a l parts of the cell w a l l of a c o n i f e r a r e s h o w n i n C h a p t e r 1, F i g u r e l b . M o s t o f w o o d c a r b o h y d r a t e is i n t h e m a s s i v e s e c o n d a r y w a l l , p a r t i c u l a r l y i n S . Y o u n g t r a c h e i d s h a v e b e e n i s o l a t e d (28) at v a r i o u s stages o f c e l l w a l l d e v e l o p 2
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
2.
PETTERSEN
69
The Chemical Composition of Wood
m e n t , a n d t h e n the s e p a r a t e d fractions w e r e a n a l y z e d for the five w o o d sugars. Table II lists t h e results o b t a i n e d b y u s i n g this m e t h o d o n b i r c h (Betula verrucosa E h r h . ) a n d S c o t s p i n e (Pinus sylvestris L . ) (29) f i b e r s . T h e v a l u e s a r e r e l a t i v e a n d s u m to 1 0 0 % f o r a g i v e n m o r p h o l o g i c a l p a r t . T h i s m e t h o d has d i f f i c u l t y i n d i s t i n g u i s h i n g t h e presence of the v e r y t h i n S . A tentative v o l u m e ratio was d e t e r m i n e d 3
for t h e l i g n i n - f r e e l a y e r s o f t h e p i n e a n d b i r c h f i b e r s b y u s i n g p h o t o m i c r o g r a p h s of transverse sections. T a k i n g the p r o p o r t i o n to b e m i d d l e l a m e l l a + p r i m a r y c e l l w a l l ( M L + P ) : S : S : S , the values are 2 : 1 0 : 7 8 : 1 0 f o r p i n e fibers (28) a n d 3 : 1 5 : 7 6 : 6 f o r b i r c h (29). A s s u m i n g the d e n s i t y of t h e c e l l w a l l to b e constant, t h e v o l u m e ratios b e c o m e a comparison of amounts of polysaccharide i n each layer. Downloaded by MONASH UNIV on May 4, 2015 | http://pubs.acs.org Publication Date: May 5, 1984 | doi: 10.1021/ba-1984-0207.ch002
1
2
3
Lignin. T h e d i s t r i b u t i o n of lignin i n the different m o r p h o l o g ical regions of w o o d m i c r o s t r u c t u r e has b e e n s t u d i e d u s i n g U V m i c r o s c o p y (30). I n s p r u c e (Picea mariana M i l l . ) t r a c h e i d s , i t w a s d e t e r m i n e d that 7 2 % a n d 8 2 % of the l i g n i n was i n the secondary c e l l w a l l s o f e a r l y w o o d a n d l a t e w o o d , r e s p e c t i v e l y (31). T h e r e m a i n d e r was located i n the m i d d l e l a m e l l a a n d c e l l corners. I n b i r c h w o o d (Betula papyrifera M a r s h . ) , 7 1 . 3 % of the l i g n i n was of the s y r i n g y l t y p e a n d w a s f o u n d i n t h e s e c o n d a r y w a l l s o f t h e fibers ( 5 9 . 9 % ) a n d ray cells (11.4%). A n a d d i t i o n a l 1 0 . 9 % of the l i g n i n was of the guaiacyl type a n d was f o u n d i n the secondary walls of the vessels (9.4%) a n d t h e v e s s e l m i d d l e l a m e l l a (1.5%). T h e r e m a i n d e r (17.7%) w a s m i x e d s y r i n g y l - a n d g u a i a c y l - t y p e a n d w a s i n t h e fiber m i d d l e l a m e l l a (32). C a u t i o n is n e e d e d i n i n t e r p r e t i n g t h e s y r i n g y l / g u a i a c y l distribution i n h a r d w o o d lignins; m e t h o x y l analyses of isolated m o r p h o l o g i c a l p a r t s o f o a k fibers a n d v e s s e l s i n d i c a t e s a r a t h e r u n i f o r m s y r i n g y l / g u a i a c y l c o n t e n t (33).
Analytical Procedures Carbohydrates. T h e r e are a n u m b e r of analytical d e t e r m i n a tions associated w i t h the carbohydrate p o r t i o n of w o o d .
HOLOCELLULOSE.
H o l o c e l l u l o s e is t h e t o t a l p o l y s a c c h a r i d e ( c e l l u l o s e a n d h e m i c e l l u l o s e s ) c o n t e n t o f w o o d , a n d m e t h o d s f o r its d e t e r m i n a t i o n seek to r e m o v e a l l o f the l i g n i n f r o m w o o d w i t h o u t d i s t u r b i n g t h e c a r b o h y d r a t e s . T h e p r o c e d u r e g e n e r a l l y u s e d (34) w a s a d o p t e d as T a p p i S t a n d a r d T 9 m ( n o w u s e f u l m e t h o d 2 4 9 ) , a n d as A S T M S t a n d a r d D 1 1 0 4 . E x t r a c t e d w o o d m e a l is t r e a t e d a l t e r n a t e l y w i t h c h l o r i n e gas a n d 2 - a m i n o e t h a n o l u n t i l a w h i t e r e s i d u e ( h o l o c e l l u l o s e ) r e m a i n s . T h e a c i d c h l o r i t e m e t h o d is a l s o u s e d (3). T h e J
2
T a p p i standards are m a i n t a i n e d b y the T e c h n i c a l Association o f P u l p a n d Paper Industry, Atlanta, G a . A S T M standards are m a i n t a i n e d b y the A m e r i c a n Society for Testing Materials, P h i l a d e l p h i a , Pa. 1
2
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
Also contains a h i g h p e r c e n t a g e of pectic a c i d . ( R e p r o d u c e d w i t h p e r m i s s i o n from Ref. 29. C o p y r i g h t 1961,
a
20.1 35.5 7.7 29.4 7.3
Galactan Cellulose Glucomannan Arabinan Glucuronoarabinoxylan
1
S Ehrh.) 0.7 48.0 2.1 1.5 47.7 L.) 1.6 66.5 24.6 0.0 7.4
2
S (outer
J o h n W i l e y & Sons.)
verrucosa 1.2 49.8 2.8 1.9 44.1 P i n e (Pinus sylvestris 5.2 61.5 16.9 0.6 15.7
B i r c h (Betula
a
+ P
part) 2
S (inner
3.2 47.5 27.2 2.4 19.4
0.0 60.0 5.1 0.0 35.1
part)
of Polysaccharides i n the Different L a y e r s of the F i b e r W a l l
16.9 41.4 3.1 13.4 25.2
Ml
Percentages
Galactan Cellulose Glucomannan Arabinan Glucuronoxylan
Polysaccharide
T a b l e Π.
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2.
FETTERSΕΝ
The Chemical Composition of Wood
71
p r o d u c t , c a l l e d c h l o r i t e h o l o c e l l u l o s e , is s i m i l a r t o c h l o r i n e h o l o c e l lulose. T h e chlorite m e t h o d removes a fraction more of the h e m i celluloses than the chlorine m e t h o d . A l p h a c e l l u l o s e is o b t a i n e d a f t e r t r e a t m e n t o f t h e h o l o c e l l u l o s e w i t h 1 7 . 5 % N a O H (see A S T M S t a n d a r d D 1103). This procedure removes most, but not all, of the hemicelluloses. BE Cross and B e v a n cellulose con sists l a r g e l y o f p u r e c e l l u l o s e , b u t a l s o c o n t a i n s s o m e h e m i c e l l u l o s e s . It is o b t a i n e d b y c h l o r i n a t i o n o f w o o d m e a l , f o l l o w e d b y w a s h i n g w i t h 3 % S 0 a n d 2 % s o d i u m s u l f i t e ( N a S 0 ) w a t e r s o l u t i o n s . T h e final s t e p is t r e a t m e n t i n b o i l i n g N a S 0 s o l u t i o n . T h e a b s e n c e o f a c h a r acteristic r e d (angiosperm) or b r o w n (gymnosperm) color d e v e l o p e d in the presence of c h l o r i n a t e d l i g n i n signals c o m p l e t e l i g n i n r e m o v a l . F o r a d i s c u s s i o n o f t h e m e t h o d a n d its m o d i f i c a t i o n s , see R e f e r e n c e 35. K u r s c h n e r c e l l u l o s e is o b t a i n e d b y r e f l u x i n g t h e w o o d s a m p l e t h r e e t i m e s f o r 1 h w i t h a 1:4 v o l u m e m i x t u r e o f c o n c e n t r a t e d n i t r i c a c i d a n d e t h y l a l c o h o l (37). T h e w a s h e d a n d d r i e d r e s i d u e is w e i g h e d as K u r s c h n e r c e l l u l o s e . T h e p r o d u c t contains a small amount of hemicelluloses. [The cellulose d e t e r m i n e d f o r t h e G h a n a n a n d R u s s i a n w o o d s (see i n T a b l e s V I a n d X I ) is K u r s c h n e r c e l l u l o s e ] . T h e m e t h o d is n o t w i d e l y u s e d b e c a u s e i t d e s t r o y s s o m e o f t h e c e l l u l o s e a n d t h e n i t r i c a c i d / a l c o h o l m i x t u r e is p o t e n t i a l l y explosive.
ALPHA CELLULOSE. CROSS AND
VAN CELLULOSE.
2
2
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2
3
3
KURSCHNER CELLULOSE.
PENTOSAN.
Pentosan analysis measures the amount of fivec a r b o n sugars p r e s e n t i n w o o d (xylose a n d arabinose residues). A l t h o u g h t h e h e m i c e l l u l o s e s c o n s i s t o f a m i x t u r e o f five- a n d s i x - c a r b o n s u g a r s (see d i s c u s s i o n o f h e m i c e l l u l o s e s ) , t h e p e n t o s a n a n a l y s i s r e p o r t s t h e x y l a n a n d a r a b i n a n c o n t e n t as i f t h e five-carbon s u g a r s w e r e p r e s e n t as p u r e p e n t a n s . P e n t o s e s a r e m o r e a b u n d a n t i n h a r d w o o d s t h a n s o f t w o o d s ; t h e d i f f e r e n c e is d u e t o a h i g h e r x y l o s e c o n t e n t i n h a r d w o o d s (see T a b l e X I I I f o r e x a m p l e s ) . T a p p i s t a n d a r d Τ 223 o u t l i n e s the p r o c e d u r e for p e n t o s a n a n a l y s i s . B r i e f l y , w o o d m e a l is b o i l e d i n 3 . 8 5 Ν H C l w i t h s o m e N a C l a d d e d . F u r f u r a l is g e n e r a t e d a n d d i s t i l l e d i n t o a c o l l e c t i o n f l a s k . T h e f u r f u r a l is d e t e r m i n e d c o l o r i m e t r i c a l l y w i t h o r c i n o l - i r o n ( I I I ) c h l o r i d e r e a g e n t . A n o t h e r m e t h o d a l s o g e n e r a t e s f u r f u r a l , a n d t h e f u r f u r a l is determined gravimetrically by precipitation with 1,3,5-benzenetriol. These a n d other methods of pentosan analysis are d e s c r i b e d a n d d i s c u s s e d i n B r o w n i n g ' s b o o k (36). T h i s analysis r e q u i r e s a c i d h y d r o l y s i s o f t h e p o l y s a c c h a r i d e to y i e l d a s o l u t i o n m i x t u r e o f t h e five w o o d s u g a r m o n o m e r s , i . e . , g l u c o s e , x y l o s e , g a l a c t o s e , a r a b i n o s e , a n d m a n n o s e . T h e s o l u t i o n is n e u t r a l i z e d , filtered,
CHROMATOGRAPHIC ANALYSIS OF WOOD SUGARS.
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
72
THE CHEMS ITRY OF SOLID WOOD
a n d the sugars c h r o m a t o g r a p h i c a l l y separated a n d q u a n t i f i e d . G e n e r a l l y t h i s m e t h o d is a c c e p t e d as t h e s t a n d a r d o f h y d r o l y s i s (37). I n t h i s p r o c e d u r e , w o o d m e a l is t r e a t e d w i t h 7 2 % H S 0 at 3 0 ° C f o r 1 h to d e p o l y m e r i z e the c a r b o h y d r a t e s . R e v e r s i o n p r o d u c t s ( r e c o m b i n e d s u g a r m o n o m e r s ) a r e f u r t h e r h y d r o l y z e d i n 3 % H S 0 at 1 2 0 ° C f o r 1 h . T h e s o l u t i o n is t h e n filtered, a n d t h e s o l i d r e s i d u e is w a s h e d , d r i e d , a n d w e i g h e d as K l a s o n l i g n i n (see " L i g n i n " l a t e r ) . T h e f i l t r a t e is n e u t r a l i z e d w i t h b a r i u m ( I I ) h y d r o x i d e o r i o n e x c h a n g e r e s i n . T h e i n d i v i d u a l s u g a r s a r e s e p a r a t e d b y p a p e r , l i q u i d , o r gas c h r o m a t o g r a p h y ( G C ) . P a p e r c h r o m a t o g r a p h y has b e e n t h e s t a n d a r d m e t h o d for m a n y years a n d a l l the i n d i v i d u a l sugar data a n d h e m i cellulose data r e p o r t e d i n the tables of this chapter w e r e o b t a i n e d b y t h i s m e t h o d [ a d o p t e d as T a p p i P r o v i s i o n a l Test M e t h o d Τ 2 5 0 (37)]. T h i s m e t h o d u s e s a m o d i f i e d f o r m o f t h e S o m o g y i c o l o r i m e t r i c assay f o r r e d u c i n g s u g a r s (38). T i m e l l (39) r e p o r t s a c o l o r i m e t r i c m e t h o d i n w h i c h the r e d u c i n g sugars are reacted w i t h 2 - a m i n o b i p h e n y l h y d r o c h l o r i d e . T h e r e a r e m a n y o t h e r assay m e t h o d s f o r r e d u c i n g s u g a r s . 2
4
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2
4
Sugar separation b y G C requires the preparation of volatile de rivatives. T a p p i Test M e t h o d Τ 249 p m - 7 5 uses t h e a l d i t o l acetate d e r i v i t i z a t i o n (40). P e r a c e t y l a t e d a l d o n i t r i l e (41) o r t r i m e t h y l s i l a n e (42, 43) d e r i v a t i v e s c a n a l s o b e p r e p a r e d a n d s e p a r a t e d b y G C . W o o d sugar analysis b y G C m a y b e u s e f u l for s p e c i a l i z e d p r o b l e m s , b u t the d e r i v i t i z a t i o n steps m a k e it a t i m e - c o n s u m i n g m e t h o d for r o u t i n e work. H i g h p e r f o r m a n c e l i q u i d c h r o m a t o g r a p h y ( H P L C ) is c u r r e n t l y the most efficient m e a n s for r o u t i n e separation a n d quantification of t h e five w o o d s u g a r s (44). I n t h i s c a s e , n o d e r i v i t i z a t i o n is n e c e s s a r y , a n d s e p a r a t i o n is a c h i e v e d u s i n g w a t e r as a n e l u e n t . D e t e c t i o n is b y a differential refractometer.
UROMC ACID.
U r o n i c a c i d is d e t e r m i n e d b y m e a s u r i n g c a r b o n d i o x i d e ( C 0 ) g e n e r a t i o n w h e n w o o d is b o i l e d w i t h 1 2 % H C 1 (45). Results from this m e t h o d m a y be somewhat h i g h because of C 0 evolution from material containing carboxyl groups other than uronic a c i d . A m e t h o d d e v e l o p e d b y S c o t t (46) is r a p i d a n d s e l e c t i v e . T h e s a m p l e is t r e a t e d w i t h 9 6 % H S 0 at 7 0 ° C , a n d a p r o d u c t , 5 - f o r m y l 2 - f u r a n c a r b o x y l i c a c i d , is d e r i v e d f r o m u r o n i c a c i d s . T h i s c o m p o u n d reacts s e l e c t i v e l y w i t h 3 , 5 - d i m e t h y l p h e n o l to y i e l d a c h r o m o p h o r e a b s o r b i n g at 4 5 0 n m . 2
2
2
4
ACETYL CONTENT.
T h e a c e t y l c o n t e n t o f w o o d is d e t e r m i n e d b y saponification of the sample i n 1 Ν N a O H , followed b y acidification, quantitative distillation of the acetic acid, a n d titration of the distillate w i t h s t a n d a r d N a O H (47). A m o d i f i c a t i o n h e r e ( F o r e s t P r o d u c t s L a b oratory) enables acetic a c i d d e t e r m i n a t i o n b y u s i n g G C w i t h p r o p a n o i c a c i d as a n i n t e r n a l s t a n d a r d . T h i s m o d i f i c a t i o n e l i m i n a t e s t h e tedious, t i m e - c o n s u m i n g distillation step.
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
2.
WOOD SOLUBILITY IN 1 % 1% N a O H
73
The Chemical Composition of Wood
PETTERSEN
NAOH.
W o o d extraction procedures i n
( T a p p i S t a n d a r d Τ 212) e x t r a c t m o s t e x t r a n e o u s
compo
nents, some lignin, and low molecular weight hemicelluloses
and
degraded cellulose. T h e percent of alkali-soluble material increases as t h e w o o d d e c a y s (48). T h e e x t r a c t i o n is d o n e i n a w a t e r b a t h m a i n t a i n e d at 1 0 0 ° C . Lignin.
T h e l i g n i n contents of w o o d s p r e s e n t e d i n the tables
of this c h a p t e r are K l a s o n l i g n i n , t h e r e s i d u e r e m a i n i n g after s o l u bilizing the carbohydrate w i t h strong m i n e r a l acid. T h e usual p r o c e d u r e , as i n T a p p i S t a n d a r d Τ 2 2 2 o r A S T M S t a n d a r d D 1 1 0 6 , is t o treat f i n e l y g r o u n d w o o d w i t h 7 2 % H S 0 2
b y d i l u t i o n to 3 % H S 0
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2
4
4
f o r 2 h at 2 0 ° C , f o l l o w e d
a n d b o i l i n g o r r e f l u x i n g for 4 h . A n e q u i v
alent b u t shorter m e t h o d treats the sample w i t h 7 2 % H S 0 2
for
1 h , f o l l o w e d b y 1 h at 1 2 0 ° C i n 3 % H S 0 2
4
at 3 0 ° C
(50). I n b o t h c a s e s
4
t h e d e t e r m i n a t i o n is g r a v i m e t r i c . Softwood l i g n i n s are i n s o l u b l e i n 7 2 % H S 0 2
4
and Klason lignin
provides an accurate measure of total lignin content. H a r d w o o d lig nins are s o m e w h a t soluble i n 7 2 % H S 0 , a n d the acid-soluble p o r 2
4
t i o n m a y a m o u n t t o 1 0 - 2 0 % o f t h e t o t a l l i g n i n c o n t e n t (51). T h e soluble (51,
lignin
acid-
c a n b e d e t e r m i n e d s p e c t r o p h o t o m e t r i c a l l y at 2 0 5 n m
(Table X I V c o n t a i n s l i g n i n v a l u e s t h a t a d d t h e a c i d - s o l u b l e
52).
c o m p o n e n t m e a s u r e d at 2 0 5 n m t o t h e K l a s o n l i g n i n . L i g n i n c o n t e n t s of hardwoods in a l l the other tables are low).
METHOXYL.
m e t h o d (53).
M e t h o x y l groups are d e t e r m i n e d b y a m o d i f i e d
M e t h y l i o d i d e is f o r m e d b y h y d r o l y s i s o f t h e m e t h o x y l
g r o u p s o f w o o d l i g n i n i n h y d r i o d i c a c i d a n d is d i s t i l l e d u n d e r
C 0
2
into a solution of b r o m i n e a n d potassium acetate i n glacial acetic acid. B r o m i n e o x i d i z e s i o d i d e to i o d a t e w h i c h is t h e n t i t r a t e d w i t h s t a n d a r d t h i o s u l f a t e . T h e m e t h o d is d i f f i c u l t a n d t i m e - c o n s u m i n g , a n d s o m e e x p e r i e n c e is n e c e s s a r y b e f o r e s a t i s f a c t o r y r e s u l t s c a n b e D e t a i l s are i n A S T M
Standard D
obtained.
1166 a n d T a p p i S t a n d a r d Τ
( w i t h d r a w n i n N o v e m b e r 1979). A d d i t i o n a l d i s c u s s i o n c a n b e in Reference
209
found
54.
Extraneous Components W o o d Solubility.
T h e s o l u b i l i t y o f w o o d i n v a r i o u s s o l v e n t s is
a measure of the extraneous components
content. N o single solvent
is a b l e t o r e m o v e a l l o f t h e e x t r a n e o u s m a t e r i a l s . E t h e r is r e l a t i v e l y n o n p o l a r a n d e x t r a c t s fats, r e s i n s , o i l s , s t e r o l s , a n d t e r p e n e s . E t h a n o l / benzene
is m o r e p o l a r a n d e x t r a c t s m o s t o f t h e e t h e r - s o l u b l e s p l u s
most of the organic materials i n s o l u b l e i n water. H o t w a t e r extracts s o m e i n o r g a n i c salts a n d l o w m o l e c u l a r w e i g h t p o l y s a c c h a r i d e s i n c l u d i n g g u m s a n d starches. W a t e r also r e m o v e s
certain hemicellu
l o s e s s u c h as t h e a r a b i n o g a l a c t a n g u m p r e s e n t i n l a r c h w o o d (see T a b l e I).
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
74
THE CHEMS ITRY OF SOLID WOOD
ETHANOL/BENZENE.
T h e solubility of w o o d i n E t O H / b e n z e n e ( b e n z e n e is a k n o w n c a r c i n o g e n ; t o l u e n e c a n b e s u b s t i t u t e d ) i n a 1 : 2 v o l u m e ratio w i l l give a measure of the extractives content. T h i s p r o c e d u r e is T a p p i S t a n d a r d Τ 2 0 4 a n d A S T M S t a n d a r d D 1 1 0 7 . T h e w o o d m e a l is r e f l u x e d 6 - 8 h i n a S o x h l e t f l a s k , a n d t h e w e i g h t loss o f t h e e x t r a c t e d , d r i e d w o o d is m e a s u r e d . S o m e t i m e s t h e l i g n i n , c a r b o h y d r a t e , a n d o t h e r c o m p o n e n t s are d e t e r m i n e d o n w o o d that h a s b e e n e x t r a c t e d p r e v i o u s l y w i t h E t O H / b e n z e n e (see T a b l e X I I I ) .
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DIETHYL ETHER.
T h e s o l u b i l i t y o f w o o d i n d i e t h y l e t h e r is d e t e r m i n e d i n t h e s a m e w a y as E t O H / b e n z e n e s o l u b i l i t y . Ash Analysis. A s h a n a l y s i s is p e r f o r m e d a c c o r d i n g to T a p p i Standard Τ 1 5 a n d A S T M S t a n d a r d D 1 1 0 2 . I n these standards ash is d e f i n e d as t h e r e s i d u e r e m a i n i n g a f t e r d r y i g n i t i o n o f t h e w o o d at 5 7 5 ° C . E l e m e n t a l c o m p o s i t i o n o f t h e a s h is d e t e r m i n e d b y d i s s o l v i n g the residue i n strong H N 0 and analyzing the solution by atomic absorption or atomic emission. T h e inorganic elemental composition of w o o d can be d e t e r m i n e d directly b y n e u t r o n activation analysis. (Table X V c o n t a i n s e l e m e n t a l d a t a u s i n g b o t h m e t h o d s ) . 3
Silica ( S i 0 ) content i n w o o d can be d e t e r m i n e d by treating the a s h w i t h h y d r o f l u o r i c a c i d ( H F ) to f o r m t h e v o l a t i l e c o m p o u n d s i l i c o n t e t r a f l u o r i d e ( S i F ) . T h e w e i g h t loss is t h e a m o u n t o f s i l i c a i n t h e a s h . S i l i c a is r a r e l y p r e s e n t i n m o r e t h a n t r a c e a m o u n t s i n t e m p e r a t e c l i m a t e w o o d s , b u t c a n v a r y i n t r o p i c a l w o o d s f r o m a m e r e t r a c e to as m u c h as 9 % . M o r e t h a n 0 . 5 % s i l i c a i n w o o d is h a r m f u l t o c u t t i n g tools ( 5 5 ) . 2
4
Moisture Content. T h e m o i s t u r e c o n t e n t o f w o o d is d e t e r m i n e d b y m e a s u r i n g t h e w e i g h t loss a f t e r d r y i n g t h e s a m p l e at 1 0 5 °C. U n l e s s specified otherwise, the percent of all other c h e m i c a l c o m p o n e n t s i n w o o d is c a l c u l a t e d o n t h e b a s i s o f m o i s t u r e - f r e e w o o d . M o i s t u r e c o n t e n t is d e t e r m i n e d o n a s e p a r a t e p o r t i o n o f t h e s a m p l e not u s e d for the o t h e r analyses.
Recent Improvements in Techniques T h e data reported i n this chapter w e r e obtained using standard methods. T h e m e t h o d s are r o u t i n e b u t r e q u i r e m u c h care a n d t i m e . S o m e methods have b e e n r e p l a c e d b y better, m o r e efficient methods. F o r e x a m p l e , t h e h o l o c e l l u l o s e , c e l l u l o s e , a n d p e n t o s a n tests h a v e b e e n r e p l a c e d b y t h e s i n g l e five-sugar c h r o m a t o g r a p h i c t e s t . T h e five-sugar test p r o c e d u r e gives m o r e d e t a i l e d i n f o r m a t i o n i n a shorter t i m e . T h e r e c e n t c h a n g e f r o m p a p e r c h r o m a t o g r a p h y t o H P L C has i m p r o v e d t h e efficiency o f this test. T h e test for K l a s o n l i g n i n r e m a i n s i n u s e , as d o t h e a c e t y l , m e t h o x y l , a n d u r o n i c a c i d t e s t s . A n a l y t i c a l i n s t r u m e n t s a n d d a t a p r o c e s s o r s h a v e h e l p e d to r e m o v e s o m e o f t h e t e d i u m a n d to s h o r t e n analysis t i m e . T h e r e s u l t has b e e n a n i n c r e a s e i n t h e n u m b e r o f a n a l y s e s p e r f o r m e d . M o r e
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
2.
PETTERSEN
The Chemical
Composition
of Wood
75
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s i g n i f i c a n t is t h e d e t a i l p o s s i b l e w i t h a d v a n c e d i n s t r u m e n t s . F o r e x ample, H P L C can separate a n d quantitate i n d i v i d u a l u r o n i c acids. This provides more detail of hemicellulose composition. T h e struc ture of l i g n i n can b e p r o b e d f u r t h e r b y mass spectrometry a n d h i g h resolution N M R spectrometry. W o o d extractives can be isolated a n d c h a r a c t e r i z e d b y c a p i l l a r y G C / m a s s spectrometry. A n e w mass spec t r o m e t e r has t w o o r m o r e mass analyzers a n d e l i m i n a t e s the often l i m i t i n g chromatographic separation step. M o r e systematic w o o d composition studies are n e e d e d i n the future. It w o u l d b e useful to s t u d y the c o m p o s i t i o n of a select n u m b e r of p r o m i n e n t species a n d note the content variability w i t h tree parts, c l i m a t e , soil c o n d i t i o n s , a n d age.
Tables of Composition Data Tables I I I - X I V are o r g a n i z e d geographically a n d list c h e m i c a l c o m p o s i t i o n d a t a f o r w o o d s f r o m v a r i o u s c o u n t r i e s . T h e d a t a as p u b l i s h e d o r i g i n a l l y w e r e o f i n t e r e s t to the l o c a l p u l p a n d p a p e r i n d u s tries. T h i s c o m p i l a t i o n p r o v i d e s a w o r l d w i d e v i e w of w o o d c o m p o sition. M o s t o f t h e d a t a w e r e o b t a i n e d u s i n g s i m i l a r test m e t h o d s ( T a p p i S t a n d a r d s ) . W h e n i t is k n o w n t h a t o t h e r t e s t m e t h o d s w e r e u s e d , t h e m e t h o d is f o o t n o t e d i n t h e t a b l e s . M o s t o f t h e v a l u e s r e p o r t e d f r o m a l l s o u r c e s h a d o n e o r t w o figures b e y o n d t h e d e c i m a l p o i n t . E x c e p t for t h e e t h e r s o l u b i l i t y a n d a s h v a l u e s (usually less t h a n 1%), v a l u e s h a v e b e e n r o u n d e d o f f t o t h e n e a r e s t p e r c e n t b e c a u s e t h i s r e f l e c t s t h e p r e c i s i o n o f t h e s a m p l i n g a n d assay m e t h o d s . T h e data i n Table III have not b e e n p u b l i s h e d previously. T h e same test m e t h o d s w e r e u s e d for a l l tree species i n Table I I I . M o s t o f t h e s e m e t h o d s w e r e d e v e l o p e d at t h e l a b o r a t o r y a n d w e r e l a t e r a d o p t e d as T a p p i s t a n d a r d s . T a b l e s I V - X I I c o n t a i n s i m i l a r d a t a o b t a i n e d i n m a n y test laboratories. T h e t h r e e Taiwanese sources c o n t a i n data for m o r e t h a n 4 0 0 trees. T h e trees s e l e c t e d for i n c l u s i o n i n Table X w e r e those d e s c r i b e d i n a book p u b l i s h e d b y the C h i n e s e F o r e s t r y A s s o c i a t i o n (56). T a b l e X I I c o n t a i n s d a t a o n t r e e s o f u n r e c o r d e d o r i g i n . E x c e p t f o r Tectonia grandia, the species r e p o r t e d do not appear in the other tables. Tables X I I I a n d X I V p r e s e n t m o r e d e t a i l e d analyses of woods: Table X I I I contains data o n 30 N o r t h A m e r i c a n species, a n d Table X I V contains data o n 32 species f r o m the southeastern U n i t e d States. T h e lignin values i n Table X I V are the s u m of K l a s o n a n d acid-soluble l i g n i n s . P e c t i n ( T a b l e X I V ) is m a i n l y g a l a c t u r o n i c a c i d . I t is t h e m e a sured total uronic acid value m i n u s the estimated glucuronic acid value. G l u c u r o n i c acid content can be estimated from the xylan con t e n t b y a s s u m i n g a r a t i o o f x y l o s e to 4 - O - m e t h y l g l u c u r o n i c a c i d o f 10:1 (see T a b l e I and F i g u r e 5). T h e r e p o r t e d v a l u e s o f t h e c a r b o -
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
(Wangenh.) K . K o c h / Bitternut h i c k o r y Carya glaubra ( M i l l . ) Sweet/ Pignut h i c k o r y Carya ovata ( M i l l . ) K . K o c h / Shagbark h i c k o r y
Acer macrophyllum Pursh/ Bigleaf m a p l e Acer negundo L . / B o x e l d e r Acer rubrum L . / R e d m a p l e Acer saccharinum L./Silver maple Acer saccharum Marsh./Sugar maple Alnus rubra B o n g . / R e d a l d e r Arbutus menziesii P u r s h / Pacific m a d r o n e Betula alleghaniensis Britton/ Yellow b i r c h Betula nigra L . / R i v e r b i r c h Betula papyrifera Marsh./ Paper b i r c h Carya cordiformus
0
44
— 64 (2) 57 63 (3)
—
73
78 (2)
44 49 (2) 48
56
— —
—
71 (2)
71
45(5)
47(2) 41
44(3)
45
60
74 (2)
42
56
—
47(3)
46 45 61 (2)
b
Alpha Cellulose
77 (3)
0
Holocellulose
Cross and Bevan Cellulose
Carbohydrate
18
17(2)
19
23(5)
23 (2) 23
23
20 (3)
17
19
18(3)
22 20
Hardwoods
1
sans'
Pento-
21
24 (2)
25
18(5)
21(2) 21
21
22 24(3)
21
25 30 21 (3)
Klason Lignin
18
17(2)
16
17(4)
16(2) 21
23
16(3)
15
21
16(3)
10
18
1% NaOH
5
5(2)
5
2(4)
2(2) 4
5
3 3(3)
4
3(3)
2
Hot Water
3
4(2)
4
3(4)
2(2) 2
7
2(3)
3
3
2(3)
3
EtOHl Benzene
Solubility
0.4
0.4 (2)
0.5
1.4 (4)
1.2 (2) 0.5
0.4
0.5 (3)
0.5
0.6
0.7 (3)
0.7 0.4
Ether
0.6
0.8 (2)
—
0.3 (2)
0.7 (2)
0.7
0.2 0.3 (3)
—
0.4 (3)
0.5
Ash
T a b l e III. C h e m i c a l C o m p o s i t i o n o f U . S . W o o d s as D e t e r m i n e d at U . S . F o r e s t Products L a b o r a t o r y f r o m 1927 to 1968
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In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
triacanthos
H o n e y locust Laguncuhria racemosa (L.) Gaertn./White mangrove Liquidambar styraciflua L./ Sweetgum Liriodendron tulipifera L . / Yellow-poplar Lithocarpus densiflorus (Hook. & A m . ) R e h d . / Tanoak Milalenca quinquenervia (Cav.) S. T . B l a k e / C a j e p u t Nyssa aquatica L./Water tupelo Nyssa sylvatica M a r s h . / B l a c k tupelo Populus alba L . / W h i t e p o p l a r Populus deletoides Bartr. ex M a r s h . / E a s t e r n cotton w o o d
Gleditsia
L./
pennsylvanica
M a r s h . / G r e e n ash
Fraxinus
f./— Fagus grandifolia Ehrh./ American beech Fraxinus americana L./White ash
Mockernut hickory Celtis laevigata W i l l d . / Sugarberry Eucalyptus gigantea H o o k .
Carya pallida (Ashe) E n g l . & G r a e b n . / S a n d hickory Carya tomentosa (Poir.) N u t t . /
51
—
46(3)
45(2) 45(5) 52
60 (3) 62
— 56 59 (2) 57(4) 67 64(3)
—
—
71(2)
—
—
—
—
72
45
52
—
47(3)
43
46 (4)
40
— 52
40 (4)
41
49 (2)
49
(2)
—
53(4)
61(2)
77 (2)
—
—
40
48
— 54
50
—
72
71 (2)
69
18(3)
17(4) 23
16(2)
19
20 (2)
19
20 (4)
19
22
18(4)
15
20 (2)
14
22
18 (2)
17
23 (3)
27(5) 16
24 (2)
27
19 (3)
20
21(4)
23
21
26(4)
26
22 (2)
22
21
21(2)
23
15(3)
15(5) 20
16(2)
21
20 (3)
17
15(4)
29
19
19 (4)
16
14 (2)
16
23
17(2)
18
2(3)
3(5) 4
4(2)
4
5(2)
2
3(3)
15
—
7(4)
7
2(2)
7
6
5(2)
7
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2(3)
2(5) 5
3(2)
2
3(2)
1
2(4)
6
—
5(4)
5
2(2)
4
3
4(2)
4
Continued
0.8
0.4 0.9
0.6
0.5
0.4
0.2
0.7
2.1
0.4
0.4
0.5
0.8
0.3
0.3
0.4
0.4
(2)
(5)
(2)
(2)
(3)
(4)
(2)
0.4
0.5
0.6
—
0.7
1.0
0.3
—
—
—
—
0.4
0.2
—
0.6
(2)
(2)
(3)
(2)
on next page
(2)
1.0
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
Michx./
Name
42 37 43
44 47
— — — — 57
— — 55
69
60 70
—
—
76
69
—
Quercus marylandica M u e n c h h . / B l a c k j a c k oak Quercus prinus L . / C h e s t n u t oak
Quercus rubra L . / N o r t h e r n r e d oak
Wangenh./
fobata N e e / V a l l e y oak lyrata W a l t . / O v e r c u p
Quercus stellata Post oak
Quercus Quercus oak
41
46
40
40
—
46
59
Quercus fahata M i c h x . / Southern r e d oak Quercus kelloggii N e w b . / California black oak
Hook &
—
47 (2)
63
45
60
—
(20)
85 67 (2)
49
49
—
(13)
0
—
65
Quercus douglasii A r n . / B l u e oak
Ehrh./Black
78 (9)
13
Alpha Cellulose
Quercus alba L . / W h i t e oak Quercus coccinea M u e n c h h . / Scarlet oak
Prunus serotina cherry
Populus trichocarpa Ton*. & Gray/Black cottonwood
Populus tremoides Q u a k i n g aspen
Scientific Name/Common
Holocellufose°
Cross and Bevan Cellulose
Carbohydrate
18
22
19
20
18
23 19
20
22
18
e
e
e
20 (2)
20
19
19 (19)
1
24
24
24
26
28
26 19
25
27
28
27 (2)
21
21
19 (22)
Lignin
Klason
Continued
Pentosans'
T a b l e III.
21
22
21
15
24
26 23
17
23
20
19 (2)
18
18
18 (15)
1% NaOH Hot
8
6
7
5
9
10 5
6
11
6
6(3)
4
3
3(15)
EtOHl
4
5
5
4
5
5 7
4
5
3
3(2)
5
3
3(14)
Benzene
Solubility
Water
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0.5
1.2
0.6
0.6
1.2
1.5 1.0
0.3
1.4
0.4
0.9 0.5
0.7
1.2
(2)
(15)
Ether
1.2
0.4
0.4
0.3
0.4 0.9
0.4
1.4
0.4
0.1
0.5
0.4
(11)
Ash
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
Nutt./Cedar
L./American
Vent./
Torr./
W h i t e spruce
Picea engelmanni Parry ex E n g e l m . / E n g e l m a n spruce Picea gfauca ( M o e n c h ) Voss/
Incense cedar
W e s t e r n larch Libocedrus decurrens
Chamaecyparis thyoides ( L . ) B . S . P./Atlantic white c e d a r Juniperus deppeana S t e u d . / Alligator j u n i p e r Larix larcina ( D u Roi) Κ. Koch/Tamarack Larix occidentalis Nutt./
fir
(Hook.) Nutt./
S u b a l p i n e fir Abies procera R e h d . / N o b l e
W h i t e fir Abies lasiocarpa
Abies amabilis D o u g l . ex Forbes/Pacific silver fir Abies balsamea (L.) M i l l . / Balsam fir Abies concolor ( G o r d . & G l e n d . ) L i n d l . ex H i l d e b r . /
elm Ulmus crassifolia elm
willow Tilia heterophyUa Bas s w o o d Ulmus americana
Quercus velutina Lam./Black oak Salix nigra M a r s h . / B l a c k
—
69
(4) 61
60
—
(8)
(2) 43(8)
45(6)
37
48
56
65
56
44(3)
—
64(3) (3)
40
—
57
(3)
41
53
(2)
(16)
46(4) 43
49
42
44(3)
50
50(3)
48
46(2)
48
—
— —
—
66
67(4) 61
58
— (16)
61(3)
61(3)
—
73
65
61(2)
—
77
—
71
(16)
13(7)
10(6)
(6)
(3)
(3)
(4)
(16)
(3)
(3)
29(8)
28
34
27
9(3) 12
26
34
33
29 29
28
29
29
27
22
20
21(2)
24
8(3)
5
9
9(4) 9
6
11
10(3)
Softwoods
19
17(3)
17
19(2)
20
(16)
12(8)
11(6)
3(8)
2(6)
3
6(3)
16(3) 9
7
3
3
3(4) 2
5
4(16)
3(3)
3(3)
2
4(2)
6
14(3)
16
16
12(4) 10
13
11
11(3)
14
16(3)
20
19 (2)
18
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2(8)
2(6)
3
2(3)
3(3)
7
6
3(4) 3
2
(3)
0.8
1.1
(2)
0.4
(2) (2)
0.2 0.3
0.3
(2)
(4)
(15)
0.3
0.3
—
0.5 0.4
0.4
0.4
0.4
0.4
0.7
—
0.2
on next page
(8)
1.1(6)
0.8
(3)
(4)
(16)
(3)
(3)
(2)
0.9
2.4
2.4
0.6 0.6
0.3
1.0
0.7
0.3
0.5
2.1
0.6
0.2
Continued
3(16)
3(3)
2(3)
4
2(2)
5
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
Name/Common
Name
Le mm./
(Bong.) C a r r . /
64(3)
69 (3)
—
Pinus monticola D o u g l . ex D . Don/Western white pine
Pinus palustris pine
D o u g l . ex
Laws./Ponderosa pine
Pinus ponderosa
Mill./Longleaf
68
69
Engelm./Slash
Pinus elliottii pine
(11)
(13)
58
59 (7)
61(4)
59
60(8)
59 (7)
57(3)
—
68
58
66 (6)
(25)
(19)
—
62
60
1
—
—
—
1
Loud./Lodgepole pine Pinus echinata M i l l . / S h o r t l e a f pine
Knobcone pine Pinus banksiana L a m b . / J a c k pine Pinus clausa ( C h a p m . ex E n g e l m . ) Vasey ex S a r g . / Sand p i n e Pinus contorta D o u g l . ex
Picea sitchensis Sitka spruce Pinus attenuata
Picea mariana ( M i l l . ) B . S . P . / Black spruce
Scientific
Holocellulose'
Cross and Bevan Cellulose ' 0
(27)
(20)
(11)
(15)
41
(2)
44(5)
43(7)
46
45(9)
45
44 (4)
43
47
45
43
Alpha Cellulose
Carbohydrate
(27)
(19)
(11)
(15)
9(2)
12 (7)
9(7)
11
12(9)
10
11(4)
13
14
7
12
(27)
(20)
(11)
(15)
26 (2)
30 (6)
25(7)
27
28(9)
26
27(4)
27
27
27
27
Klason Lignin
Continued
Pentosans*
T a b l e III.
(27)
(20)
(11)
(15)
16 (2)
12 (7)
13(6)
13
12(9)
13
12(2)
13
11
12
11
1% NaOH
(26)
(20)
4(2)
3(5)
4(6)
3(15)
2(9)
4(11)
2(2)
3
3
4
3
(20)
5(2)
4(7)
4(6)
4(15)
4(9)
3(11)
3(2)
5(27)
1
4
2
EtOHl Benzene
Solubility Hot Water
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5.5
1.4
2.3
3.3
2.9
1.6
1.0
3.0
—
0.7
1.0
(2)
(7)
(6)
(15)
(9)
(11)
(26)
(20)
Ether
0.5
—
0.2
0.2
0.4
0.3
0.4
0.3
0.2
—
0.3
Ash
(3)
(3)
(2)
(11)
(7)
(19)
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
—
—
43
7
27
—
60
(22)
29
(22)
9
(22)
42
58
67 (2)
(22)
33 (7)
9(4)
41 (7)
32
30
55 (7)
e
33
33 33
12
5
5
(22)
4
(22)
4
14
(22)
3(7)
14
6
5
10 —IrHCNI
ι—I CM
oq I I CD
oq
N C O O Î H N M N O O O O I O l > l > l > 00 t> l > CD t> 00 l > 00
O O 00 00
00 Η I i n CD
oq CD
ε
s
1
S
I
ι 00
2
« a i t -i e ^ „ et ^ Q ^ ^ δ
bn
J
N
δ ο ·»5 σ ί>
CD E S
,3
'3D
ι O
| | cq Η
I-H
2:
S -S
i—J CD ^
3
sS **·«» co
in ^
1
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-s
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O
CM
I> CD
!>
oo CD
CD
24.2 ± 3.4(46) 8.8 ± 2.5(12)
28.6 ± 3.6(39)>
28.5 ±
31.7 ± 3.8(10)>
9.8 ± 2.2(35)
19.3 ± 2.2(49)
N O T E : Values are m e a n ± standard d e v i a t i o n ( n u m b e r o f data). H o l o c e l l u l o s e is t h e total carbohydrate content o f w o o d . A l p h a cellulose is nearly p u r e cellulose. Pentosans are the total anhydroxylose a n d arabinose residues i n w o o d . Cross a n d B e v a n cellulose is largely p u r e cellulose b u t contains some hemicelluloses. K u r s c h n e r cellulose is nearly p u r e cellulose. f O n e value o f 4 . 6 % not i n c l u d e d . M o d i f i e d K u r s c h n e r cellulose. M o d i f i e d C r o s s a n d B e v a n cellulose. ' P u r e glucan calculated from glucose a n d m a n n o s e content. H e m i c e l l u l o s e s c a l c u l a t e d from five-sugar, acetyl, a n d u r o n i c a c i d content. Klason l i g n i n + a c i d - s o l u b l e l i g n i n . O n e value o f 5 . 4 % not i n c l u d e d .
Hardwoods Softwoods
—
—
Softwoods
U . S . A . (Table X I V ) U . S . S . R . (Table XI)
—
Hardwoods
(Table XIII)
U . S . A . and Canada
71.7 ± 5.7(25)
6 4 . 5 ± 4.6(22)
Hardwoods
Softwoods
U . S . A . (Table III)
Table X V I . Continued
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23.0 ± 3.0(40)
1.8(11)
21.9 ± 3.2(47) 29.0 ± 1.6(15)
24.5 ± 3.0(39)*
29.2 ± 2.0(19)
22.5 ±
28.8 ± 2.6(35)
0.6 ± 0.4(45)' 0.5 ± 0.4(16)
0.4 ± 0.3(39)
0.3 ± 0.2(19)
0.4 ± 0.2(11)
0.3 ± 0.1(30)
0.5 ± 0.3(34)
X2
m
X
H
to to
2.
PETTERSEN
The Chemical Composition of Wood
123
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hydrate components i n Table X I V have b e e n adjusted b y a hydrolysisloss factor. T h i s f a c t o r w a s c a l c u l a t e d f o r e a c h s p e c i e s , s u c h t h a t t h e s u m of total extractives, lignin, cellulose, hemicellulose, a n d ash equals 1 0 0 % . T h e hemicellulose components were calculated using t h e a d j u s t e d v a l u e o f t h e five i n d i v i d u a l s u g a r s a n d t h e m e a s u r e d values for acetyl a n d u r o n i c acid. Table V I I reports t h e trace e l e m e n t composition of some woods. C a l c i u m , potassium, magnesium, a n d phosphorus are the principal trace elements i n t e m p e r a t e woods. T h e three tropical w o o d s have a higher potassium a n d magnesium content a n d a lower calcium con tent than the temperate woods. Table X V I is a s u m m a r y o f average w o o d c o m p o s i t i o n i n 13 c o u n tries. T h e m e a n , standard deviation, a n d n u m b e r o f data are t a b u lated for carbohydrate, l i g n i n , a n d ash compositions. H a r d w o o d s a n d softwoods are separated w h e n b o t h are available. A l l other values are o n l y for hardwoods. B e careful c o m p a r i n g values b e t w e e n countries because techniques a n d m e t h o d s vary. F o r e x a m p l e , t h e m e a n h o l o c e l l u l o s e c o n t e n t o f C o s t a R i c a n h a r d w o o d s is 7 8 . 1 % , h i g h e r t h a n that o f w o o d s f r o m B r a z i l (71.7%) a n d M e x i c o (67.8%). T h e h o l o c e l lulose d e t e r m i n e d for the C o s t a Rican hardwoods probably contained s o m e l i g n i n . T h e m e a n v a l u e o f Taiwanese h a r d w o o d h o l o c e l l u l o s e is obviously h i g h (83.3%) because t h e means for holocellulose a n d l i g n i n s u m to 1 0 8 % .
Literature Cited 1. Hegnauer, R. "Chemotaxonomie der Pflanzen," Volumes I - V I ; Birkhäuser Verlag: Basel and Stuttgart, 1962-1973. 2. Gibbs, R. Darnley "Chemotaxonomy of Flowering Plants," Volumes 1-4; McGill-Queens University Press: Montreal and London, 1974. 3. Wise, L. E.; Murphy, M.; D'Addieco, A. A. Pap. Trade J. 1946, 122(2), 35-43. 4. Fengel, Dietrich; Grosser, Dietger Holz Roh- Werkst. 1975, 33(1), 32-34. 5. Goring, D. A. I.; Timell, T. E. Tappi 1962, 45(6), 454-60. 6. Sjöström, Eero "Wood Chemistry. Fundamentals and Applications"; Academic Press: New York, 1981; p. 56, 65. 7. Billmeyer, F. W., Jr. J. Polym. Sci., Part C 1965, No. 8, 161-78. 8. Gardner, Κ. H.; Blackwell, J. Biochim. Biophys. Acta 1974, 343, 232-37. 9. Kolpak, F. T.; Blackwell, J. Macromolecules 1976, 9(2), 273-78. 10. Kolpak, F. J.; Weik, M.; Blackwell, J. Polymer 1978, 19, 123-31. 11. Timell, T. E. Wood Sci. Technol. 1982, 16, 83-122. 12. Timell, T. E. Wood Sci. Technol. 1967, 1, 45-70. 13. Timell, T. E. Adv. Carbohydr. Chem. Biochem. 1964, 19, 247-302. 14. Timell, T. E. Adv. Carbohydr. Chem. Biochem. 1965, 20, 409-83. 15. Adler, Erich Wood Sci. Technol. 1977, 11, 169-218. 16. Leopold, B.; Malmström, I. L. Acta Chem. Scand. 1952, 6, 49-54. 17. Obst, John R. Tappi 1982, 65(4), 109-12. 18. Nimz, H. Angew. Chem., Int. Ed. Engl. 1974, 13, 313-21. 19. Creighton, R. N. J.; Hibbert, H. J. Am. Chem. Soc. 1944, 66, 37-38. 20. Larsson, Sam; Miksche, Gerhard E. Acta Chem. Scand. 1967, 21(7), 1970-71.
In The Chemistry of Solid Wood; Rowell, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1984.
124
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Κ.
T H E CHEMISTRY O F SOLID W O O D
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