The Chemical Composition of Wood - Advances in Chemistry (ACS

2 The Chemical Composition of Wood R O G E R C. P E T T E R S E N

Downloaded by MONASH UNIV on May 4, 2015 | http://pubs.acs.org Publication Date: May 5, 1984 | doi: 10.1021/ba-1984-0207.ch002

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 The data were collected at Forest Products Laboratory (Madison, Wisconsin) from 1927-68 and were previously unpublished.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.

58

THE CHEMS ITRY OF SOLID WOOD


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.



60


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.)


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


PETTERSEN

The Chemical Composition of Wood

61


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.)


62



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.



2.

PETTERSEN


/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





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


0

borate

Alkaline

borate

Alkali, dimethyl sulfoxide*

Alkali, dimethyl sulfoxide, * water* Water

Alkaline

Alkali, water*

Solubility

200

200

200

100

100

100

66



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




68



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


2.

PETTERSEN

69


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



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.


2.

FETTERSΕΝ


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


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.


72


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


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.


2.

WOOD SOLUBILITY IN 1 % 1% N a O H

73


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


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).


74


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 ) .


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


2.

PETTERSEN

The Chemical

Composition

of Wood

75


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 -



(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



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


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


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


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


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


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


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


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)


—

—

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

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The Chemical Composition of Wood - Advances in Chemistry (ACS

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