Organosolv Lignin-Modified Phenolic Resins - ACS Publications

their effects on resin adhesive properties are also briefly described. ... Both maple block .... 111. 138. 169. T G A (weight loss):. 50°C. %. 1. 0. ...
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Chapter 24

Organosolv Lignin-Modified Phenolic Resins Phillip M . Cook and Terry Sellers, Jr. 1

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1

2

Eastman Kodak Company, Eastman Chemicals Division, P.O. Box 1972, Kingsport, TN 37662 Forest Products Utilization Laboratory, P.O. Drawer FΡ, Mississippi State, MS 39762 2

An adhesive system for structural wood panels is demon­ strated in which at least 35% of the resin solids of a phenol-formaldehyde resin are successfully replaced with organosolv hardwood lignin. The bulk properties of the lignin were characterized before and after its purifica­ tion with aqueous sodium bicarbonate solution. Phenolic resins are described that have been prepared from both purified and non-purified (crude) lignin. The nature of residues removed from the lignin during purification and their effects on resin adhesive properties are also briefly described. Evaluations of the lignin-modified phenolic resins were carried out on a small scale by measuring the lap-shear strength of parallel laminated maple blocks, and on a large scale by performing strength and dimen­ sional tests on southern pine flake boards (waferboard or strandboard types). Flake board tests included internal bond, static bending (modulus of rupture, M O R ) , water absorption, and thickness swelling. The M O R was mea­ sured on both dry specimens and specimens subjected to accelerated aging wet-dry cycles. Both maple block and flakeboard evaluations included available commer­ cial phenolic resins as controls. L i g n i n makes u p a b o u t one-quarter o f the weight o f d r y w o o d a n d is sec­ o n d o n l y t o cellulose as t h e most a b u n d a n t n a t u r a l l y o c c u r r i n g p o l y m e r . P u l p i n g m e t h o d s w h i c h use o r g a n i c solvents are p a r t i c u l a r l y well-suited t o solubilize the lignins for l i g n i n isolation a n d are r e a d i l y c o u p l e d w i t h solvent recovery (1). D e s p i t e these facts, there are n o large v o l u m e o r g a n o s o l v p u l p ­ i n g processes or c o m m e r c i a l p r o d u c t s based u p o n organosolv l i g n i n ( O S L ) i n the U n i t e d States. 0097-6156/89/0397-0324$06.00/0 © 1989 American Chemical Society

In Lignin; Glasser, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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24.

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Organosolv Lignin-Modified Phenolic Resins

325

L i g n i n s are p h e n o l i c - l i k e p o l y m e r s t h a t f r o m t i m e t o t i m e have been considered for use as a p h e n o l replacement i n p h e n o l - f o r m a l d e h y d e ( P F ) resins. T o d a y , however, very l i t t l e l i g n i n is used i n p h e n o l i c resins. P u r i f i e d k r a f t l i g n i n s have been suggested as a p h e n o l s u b s t i t u t e , b u t the price o f such l i g n i n s has been s t r u c t u r e d to be e q u a l to t h a t of p h e n o l , a n d resin adhesive suppliers have resisted i t s use. V e r y l i t t l e has been p u b l i s h e d o n the use of O S L i n phenolic adhesives despite the fact t h a t these l i g n i n s are generally f o u n d to have a higher p u r i t y a n d r e a c t i v i t y t h a n l i g n i n s f r o m conventional p u l p i n g methods. T h e most p r o m i n e n t w o o d adhesives used over the last q u a r t e r of a c e n t u r y have been a m i n o p l a s t a n d p o l y p h e n o l i c types (2). I n the U n i t e d States, p o l y p h e n o l i c adhesives continue t o be p r e d o m i n a n t l y used for p r o d u c t i o n of weather-resistant w o o d p r o d u c t s , such as s t r u c t u r a l p l y w o o d s and flake boards (3). P h e n o l i c r e s i n prices have increased over the past decade, generally p a r a l l e l i n g p h e n o l prices. T h i s increase has o c c u r r e d i n p a r t due to a c o n t i n u i n g erosion of U n i t e d States p h e n o l m a n u f a c t u r i n g c a p a c i t y a n d the c o r r e s p o n d i n g increase i n a v a i l a b i l i t y o f p h e n o l f r o m other countries. A n y significant increase i n the price of o i l (the source of phenol) itself or i n t e r r u p t i o n i n s u p p l y w i l l o n l y c o m p o u n d the p r o b l e m a n d raise p h e n o l prices even higher. T h e o b j e c t i v e o f t h i s w o r k was to d e m o n s t r a t e the u t i l i t y o f organosolv red oak l i g n i n (a projected cheaper p o l y p h e n o l t h a n phenol) i n p h e n o l i c adhesives for w o o d composites. T h i s w o r k i n v o l v e d three stages: 1. A n a l y t i c a l c h a r a c t e r i z a t i o n of red oak O S L . 2. R e s i n synthesis of O S L - m o d i f i e d p h e n o l - f o r m a l d e h y d e resins. 3. E v a l u a t i o n of l i g n i n - m o d i f i e d resins used to b o n d m a p l e blocks a n d s o u t h e r n p i n e flake boards. Results and Discussion Analytical Characterization. A s expected, red oak O S L c o n t a i n s m u c h less sulfur a n d ash b u t more c a r b o h y d r a t e s t h a n k r a f t l i g n i n ( T a b l e I) (kraft l i g n i n i n c l u d e d for c o m p a r i s o n ) . T h e m o l e c u l a r weight a n d p o l y d i s p e r s i t y ( T a b l e II) are less for red oak O S L t h a n for k r a f t l i g n i n ( I n d u l i n A T , W e s t vaco, C h a r l e s t o n , S C ) , a n d O S L has g o o d s o l u b i l i t y i n o r g a n i c solvents ( T a b l e I). S o l u b i l i t y i n r e f l u x i n g methylene chloride was s u r p r i s i n g l y h i g h . P u r i f i c a t i o n of the O S L b y aqueous r e s l u r r y i n 1 0 % s o d i u m b i c a r b o n a t e s o l u t i o n increases the softening t e m p e r a t u r e ( T a b l e II). T h e r m o g r a v i m e t r i c weight loss for the O S L is s i m i l a r to t h a t of k r a f t l i g n i n . E x c e p t for a s l i g h t l y elevated m e t h o x y l content, the N M R a n d d e g r a d a t i o n results i n T a b l e II are w i t h i n the expected range for a h a r d w o o d lignin. OSL Impurities. It was also of interest to d e t e r m i n e the i m p u r i t i e s removed f r o m crude O S L b y r e s l u r r y i n aqueous s o d i u m b i c a r b o n a t e , w h i c h was done to i m p r o v e its usefulness i n p h e n o l i c resins ( C o o k , P . M . , E a s t m a n K o d a k at K i n g s p o r t , T N , p e r s o n a l c o m m u n i c a t i o n s , 1987). E x t r a c t i o n a n d acetyl a t i o n procedures, i n v o l v i n g methylene c h l o r i d e , acetic a n h y d r i d e p y r i d i n e

In Lignin; Glasser, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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326

T a b l e I. L i g n i n c h a r a c t e r i z a t i o n ( b u l k a n d soi l u b i l i t y properties) Amount Kraft Lignin

Crude OSL

% %

97

97

97

A s h , 775°C

1.94

1.13

3.48

Carbohydrates: (Extraction-HPLC)

%

3.0

1.1

0.7

Combustion: C H Ν S

% % % %

59.85 5.87 0.27 0.24

60.94 5.63 Trace 0.04

61.99 5.65 0.52 1.68

E x t r a c t i o n (weight loss): E t h e r , reflux H e p t a n e , reflux M e t h y l e n e chloride, reflux Water, 25°C Water, 60°C W a t e r , 100°C

% % % % % %

6 < 1 50 5 12 5*

Non-volatiles

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Purified OSL

Basis

A n a l y t i c a l Text

* S a m p l e agglomerates S o l u b i l i t y (25° C ) : Methanol Ethanol n-Propanol 2-Propanol Acetic A c i d Acetone 2-Butanone Acetonitrile E t h y l Acetate

1

3 < 1 11 2 6 3*

severely. g/L g/L g/L g/L g/L g/L g/L g/L g/L

-

105 53 35 15 108 104 96 86 59

-

-

-

-

I n d u l i n A T b y Westvaco, C h a r l e s t o n , S C ; a purified pine l i g n i n . a n d water, were followed w h i c h p r o d u c e d three residues f r o m the i m p u r i ­ ties a n d each was s u b m i t t e d for G C / M S a n d H N M R analyses. R e s i d u e 1 proved to be nearly a l l l i g n i n - r e l a t e d p r o d u c t s . Residues 2 a n d 3 were f o u n d p r i n c i p a l l y to c o n t a i n f u l l y acetylated m o n o m e r i c C5 a n d Ce sugars w h i c h were also C i alcoholic glycosides. R e s u l t s of G C / M S investigations of the residues i n d i c a t e d t h a t the l o w - m o l e c u l a r - w e i g h t i m p u r i t i e s (e.g., m o n o - f u n c t i o n a l l i g n i n - r e l a t e d species, waxes, a n d c a r b o h y d r a t e s ) s h o u l d be removed to i m p r o v e the O S L r e a c t i v i t y . T h e extent of i m p u r i t y r e m o v a l can be a p p r o x i m a t e d by m e a s u r i n g gelation t i m e (i.e., the higher the i m p u ­ r i t y content, the longer the gel t i m e ) . F o r e x a m p l e , the g e l a t i o n t i m e (using 1

In Lignin; Glasser, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

24.

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327

Organosolv Lignin-Modified Phenolic Resins

T a b l e II. P h y s i c a l a n d c h e m i c a l c h a r a c t e r i z a t i o n of l i g n i n Amount

Basis

Crude OSL

Purified OSL

Kraft Lignin

softening-initial: (TMA)

°C

89

124

124

softening-final : (TMA)

°C

111

138

169

% % % % % %

1 3 5 18 44 55

0 1 2 10 38 49

1 3 6 12 26 51

2227 906 2.46

2030 925 2.19

2479 523 4.32

22.04 (1.55) 1.33

-

13.70 (0.81) < 1

0.60-0.65 0.55-0.60 1.90-1.95 3.60-3.70 1.15-1.25

-

0.57-0.62 0.70-0.72 2.50-2.55 4.25-4.30 1.35-1.40

A n a l y t i c a l Test T

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T

T G A (weight loss): 50°C 100°C 200°C 300°C 400°C 500°C

G P C m o l e c u l a r properties: (CH C1 /HFIP, Styragel Col.) M 2

1

2

W

M

N

M /M W

N M R analysis: OCH

%

3

Syringyl/guaiacyl Bonds: OH (Phenolic) O H (Aliphatic) H (Aromatic) H (Aliphatic) H (Hydroxyl)

N

(bonds/Cg unit) ratio per per per per per

C9 C9 C9 C9 C9

unit unit unit unit unit

Source: G l a s s e r , W . G . R e p o r t to P . M . C o o k . L o c a t e d at E a s t m a n C h e m i c a l D i v i s i o n , Research L a b o r a t o r y , P . O . B o x 1972, K i n g s p o r t , T N 27662 (1984). 1

I n d u l i n A T b y Westvaco, C h a r l e s t o n , S C ; a purified pine l i g n i n .

a S u n s h i n e G e l Tester) at 100°C (212°F) was 21 minutes for a P F resin sol u t i o n , 26 minutes for a purified O S L / P F resin b l e n d , a n d 53 m i n u t e s for an u n p u r i f i e d O S L / P F resin b l e n d . T h e procedure involves b l e n d i n g d r y l i g n i n solids w i t h a P F resin s o l u t i o n to a 2 3 % l i g n i n c o n c e n t r a t i o n a n d a d j u s t i n g w i t h water a n d 5 0 % s o d i u m h y d r o x i d e to the p H (e.g., 1 1 . 1 ± ) a n d viscosity (e.g., 500 ± 50 c P ) of the P F resin. Block Lap-Shear Results. F o r l a m i n a t e d m a p l e w o o d , this w o r k i n d i c a t e d a m a x i m u m of 4 0 % of the P F resin solids can be replaced w i t h O S L w i t h o u t

In Lignin; Glasser, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

LIGNIN: PROPERTIES AND MATERIALS

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d e t r i m e n t a l l y affecting adhesive properties ( T a b l e III) ( C o o k , P . M . , E a s t m a n K o d a k at K i n g s p o r t , T N , p e r s o n a l c o m m u n i c a t i o n s , 1987). O r g a n o solv l i g n i n - P F resins were at least equivalent t o the c o m m e r c i a l (control) resin a n d o u t - p e r f o r m e d k r a f t l i g n i n - b a s e d P F resins at the 3 5 % a n d 4 0 % solids replacement levels ( T a b l e I I I ) . P u r i f i e d O S L generally y i e l d e d better results t h a n u n p u r i f i e d . A d i s t r a c t i n g q u a l i t y of k r a f t l i g n i n resins is the s u l f u r - l i k e odor p r o d u c e d d u r i n g resin p r e p a r a t i o n a n d p a n e l hot pressing. Use o f O S L alleviates t h i s p r o b l e m . T h e reasons w h y O S L o u t - p e r f o r m e d k r a f t l i g n i n i n t h i s w o r k are not clear, b u t are likely r e l a t e d to the m o l e c u l a r weight characteristics of the O S L a n d its ease of s o l u b i l i z a t i o n . B a s e d u p o n the p r o p o s e d s t r u c t u r e s of h a r d w o o d a n d softwood l i g n i n s , the c o n t r a r y w o u l d have been p r e d i c t e d (i.e., the higher s y r i n g y l / g u a i a c y l r a t i o s of h a r d w o o d w o u l d be expected to be more d e t r i m e n t a l to b o n d i n g ) . T a b l e I I I . Selected m a p l e b l o c k test results Dry Bond

4-Hour Boil

Strength Lignin Shear Wood Shear Wood Retention Replacement Strength Failure Strength Failure ( D r y / W e t ) (%) (MPa) (%) (MPa) (%) (%)

Resin T y p e

1

Control P F OSL-PF (crude l i g n i n )

0

5.18

80

3.08

0

60

24

4.99

100

2.54

30

51

OSL-PF (CH C1 extracted)

34

5.35

100

3.02

40

57

Kraft L - P F (Indulin A T )

35

4.25

90

1.83

0

43

OSL-PF (NaHC0 washed)

40

5.60

60

3.37

30

60

40

4.14

40

1.90

10

46

45

2.68

20

1.00

0

37

2

2

2

3

Kraft L - P F (Indulin A T ) OSL-PF (crude l i g n i n ) 1

2

2

M u l t i p l y M P a b y a factor of 145 to convert to p s i . T h i s resin also contained 1% m e l a m i n e .

Flake Board Test Results. R e s u l t s f r o m i n i t i a l screening tests l o o k e d p r o m i s i n g for the use of k r a f t pine l i g n i n a n d organosolv h a r d w o o d l i g n i n at 2 5 % s u b s t i t u t i o n for p h e n o l i n P F resins used to b o n d flake boards. Therefore, t h i s s t u d y was designed to concentrate o n i m p r o v i n g the O S L - P F cook p r o cedure, increase the p h e n o l s u b s t i t u t i o n to 3 5 % , a n d measure these effects b y e x p a n d i n g the b o a r d test c r i t e r i a (4). I n general, the p u r i f i e d O S L - P F

In Lignin; Glasser, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

COOK & SELLERS

24.

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resins as well as the u n p u r i f i e d O S L - P F resins p e r f o r m e d e q u a l t o , or b e t ­ ter t h a n , the c o n t r o l c o m m e r c i a l resins a n d the c o n t r o l resins c o n t a i n i n g c o m p a r a b l e s u b s t i t u t i o n a m o u n t s of p e c a n shell flour (vs. O S L ) i n a l l test p a n e l properties e x a m i n e d (Table I V ) .

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T a b l e I V . Selected test results of flake boards

Physical Property

L a b o r a t o r y Test R e s u l t s Sampling of F o u r Control Resin Β 35% O S L USA Mills 100% P F 3 5 % P S Purified Crude (1986)

Units

Density

avg.

kg/m

1

3

650-700

(average o f boards was 753)

Internal bond M o d u l u s of rupture

avg.

kPa

340-460

510

386

717

538

avg.

MPa

22-38

33

33

34

34

Accelerated aging

%of dry M O R

50-70

76

75

77

70

Water absorption

%

25-34

33

35

25

19

Thickness swell

%

12-15

16

25

15

11

R e s i n solids applied

%

3-5

5

3.25

5

5

These panels were b o n d e d w i t h a r e s i n s o l u t i o n c o n t a i n i n g 6 5 % P F and 3 5 % p e c a n shell ( P S ) flour, d e l i v e r i n g 3.25% resin solids to the furnish. N o t e : T o convert m e t r i c to E n g l i s h u n i t s — k g / m to l b / f t , m u l t i p l y b y a factor of 0.0624; k P a to p s i , m u l t i p l y b y a factor of 0.145; M P a to p s i , m u l t i p l y b y a factor of 145.

1

3

3

Use of p o w d e r e d l i g n i n s as a n extender at 2 5 % to 3 5 % replacement of P F solids i n l i q u i d c o m m e r c i a l resins is i m p r a c t i c a l because of p r o b l e m s of d i s p e r s i o n , viscosity, a n d s t a b i l i t y w h i c h h i n d e r subsequent u n i f o r m resin s p r a y a p p l i c a t i o n . However, s u b s t i t u t i o n of l i g n i n for p h e n o l at levels of 35 weight percent, or higher, i n cooked l i g n i n - p h e n o l - f o r m a l d e h y d e c o p o l y m e r s is p r a c t i c a l . W h i l e i m p u r e (crude) O S L cooked into a P F resin a n d used to b o n d flake boards y i e l d e d s i m i l a r b o a r d properties to cooked p u r i f i e d O S L i n P F resins, the i m p u r e l i g n i n was troublesome d u r i n g the cook procedures, f o r m i n g gels u p o n l o n g m e t h y l o l - l i g n i n c o n d e n s a t i o n . I m p u r e l i g n i n was m o r e g r i t t y t h a n purified l i g n i n a n d some extraneous m a t e r i a l m a y have settled r a t h e r t h a n dissolve or suspend i n the cooked resins. I m p u r e l i g n i n required a n a d j u s t m e n t i n the water i n b o t h steps of the cook t o y i e l d a satisfactory n o n - v o l a t i l e solids content. If a n y coarse l i g n i n settled i n the cooked resin, t h i s m a y p a r t i a l l y e x p l a i n the lower percent n o n - v o l a t i l e solids p h e n o m e n o n w i t h resins i n c o r p o r a t i n g i m p u r e l i g n i n .

In Lignin; Glasser, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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Conclusions It has been d e m o n s t r a t e d t h a t red oak O S L c o u l d be used t o replace 3 5 % to 4 0 % o f the p h e n o l (or phenolic resin solids) i n p h e n o l - f o r m a l d e h y d e resins used t o l a m i n a t e m a p l e w o o d a n d t o b o n d s o u t h e r n p i n e flake b o a r d s (waferb o a r d a n d / o r s t r a n d b o a r d ) w i t h o u t adversely affecting the p h y s i c a l b o n d p r o p e r t i e s . W h i l e t h i s p u l p i n g process a n d b y - p r o d u c t l i g n i n do not c o m m e r c i a l l y exist at t h i s t i m e i n the U n i t e d States, lignins f r o m such processes are projected to cost 4 0 % to 5 0 % less t h a n p h e n o l as a p o l y m e r r a w m a t e rial. It is r e c o m m e n d e d t h a t a r e s l u r r y of crude O S L i n a n organic s o l vent or 1 0 % aqueous salt (e.g., N a H C O a ) s o l u t i o n be p e r f o r m e d to remove l o w - m o l e c u l a r - w e i g h t (mono-functional) species, waxes, a n d c a r b o h y d r a t e s . T h i s p u r i f i c a t i o n leads to a n i m p r o v e m e n t i n O S L r e a c t i v i t y a n d c o n t r i b u t e s to the usefulness of O S L as a P F resin extender or P F c o p o l y m e r r a w m a t e r i a l . It is presumed t h a t extraneous removed m a t e r i a l s i n the crude l i g n i n react w i t h f o r m a l d e h y d e b u t do not lead to p r o d u c t i v e c r o s s - l i n k i n g p o l y mer f o r m a t i o n . T h e success o b t a i n e d i n t h i s s t u d y o n b o n d i n g flake b o a r d a n d m a p l e blocks s u p p o r t s the p o s s i b i l i t y of u s i n g O S L i n resins for b o n d i n g crosswise l a m i n a t e s (i.e., p l y w o o d ) . Subsequent research conducted at the M i s s i s s i p p i Forest P r o d u c t s U t i l i z a t i o n L a b o r a t o r y o n O S L - P F resins for b o n d i n g p l y w o o d has been e q u a l l y successful.

Experimental Wood Pulping and Lignin Purification. T h e w o o d p u l p i n g i n v o l v e d red oak w o o d c h i p s , aqueous organic solvent, a n d a n a c i d c a t a l y s t , w h i c h were p r o cessed at 120 to 140°C. T h e r e s u l t a n t p u l p was washed w i t h more aqueous solvent, w a t e r - s l u r r i e d a n d cooled. T h e l i g n i n was i s o l a t e d by r e m o v i n g the solvent under v a c u u m , replacement of solvent w i t h water, l i g n i n prec i p i t a t i o n , filter cake water w a s h i n g , a n d d r y i n g . T h e l i g n i n was p u r i f i e d b y s l u r r i n g one p a r t of d r y O S L i n five p a r t s of a 1 0 % aqueous s o d i u m b i c a r b o n a t e s o l u t i o n at 6 0 ° C for one h o u r . T h e s l u r r y was cooled to r o o m t e m p e r a t u r e a n d filtered. T h e filter cake was washed w i t h water u n t i l the filtrate was less t h a n 7.5 p H . T h e filter cake was then d r i e d i n a forced-air oven at 50 to 5 5 ° C , w i t h a weight y i e l d of 9 0 % to 9 5 % . T h e r e s u l t a n t d r y and loose l i g n i n was used w i t h o u t further processing such as g r i n d i n g . Analytical Characterization. T h e l i g n i n s were characterized a n a l y t i c a l l y by the f o l l o w i n g m e t h o d s : H N M R s p e c t r a , gel p e r m e a t i o n c h r o m a t o g r a p h y (5), gas c h r o m a t o g r a p h y (6), t h e r m a l measurements, e l e m e n t a l a n a l y s i s , sugar content, e x t r a c t i o n s , s o l u b i l i t y , a n d c o m b u s t i o n properties. 1

Resin Preparation. T w o approaches to resin p r e p a r a t i o n were used w i t h regard t o the i n i t i a l stages of condensation, d e p e n d i n g o n w h e t h e r the resin was i n t e n d e d for l a m i n a t i n g m a p l e blocks or for b o n d i n g s o u t h e r n pine flake boards. F o r m a p l e block resins, the steps i n v o l v e d were as follows: a d d i t i o n of water, s o d i u m h y d r o x i d e ( o p t i o n a l ) a n d l i g n i n , w h i c h were heated a n d

In Lignin; Glasser, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

COOK & SELLERS

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h e l d u n t i l a homogeneous m i x t u r e was o b t a i n e d ; a d d i t i o n of either 1 0 0 % of the p h e n o l or 1 0 % to 2 0 % of the formaldehyde r e q u i r e d i n the cook a n d heated t o 75 t o 9 0 ° C for 30 to 90 m i n u t e s ; a d d i t i o n of the r e m a i n d e r of the p h e n o l (unless a l l was a d d e d i n i t i a l l y ) , a n d f o r m a l d e h y d e , h o l d i n g at 60 to 7 5 ° C for 30 t o 90 m i n u t e s . F o r m a p l e block b o n d i n g , a series o f cooks were m a d e i n w h i c h 2 4 % to 4 5 % of the resin solids were replaced w i t h O S L or k r a f t l i g n i n . F o r flake b o a r d resins the steps i n c l u d e d the f o l l o w i n g : a p r e p o l y m e r synthesis of m e t h y l o l - l i g n i n condensation for 30 to 90 m i n u t e s , t h e n a sequential m e t h y l o l - l i g n i n , p h e n o l - f o r m a l d e h y d e c o n d e n s a t i o n (resin synthesis) step, w h i c h varied f r o m 3 to 5 hours cook t i m e (4). F o r flake b o a r d resins, cooks were m a d e w i t h 2 5 % a n d 3 5 % of the p h e n o l replaced w i t h p u r i f i e d a n d u n p u r i f i e d O S L . V a r i o u s properties of the resins were d e t e r m i n e d b y s t a n d a r d m e t h o d s , i n c l u d i n g n o n - v o l a t i l e solids, viscosity, p H , free f o r m a l d e h y d e , free p h e n o l , alkalinity, a n d gel t i m e . I n b o t h studies, c o m m e r c i a l resins were o b t a i n e d a n d used as controls. T a b l e V provides t y p i c a l s t o i c h i o m e t r i c d a t a of resin reactants i n v e s t i g a t e d for b o t h resin types. T a b l e V . T y p i c a l s t o i c h i o m e t r i c properties of resin reactants A m o u n t by Resin T y p e Reactant

Blocks (mol)

Flake Board (mol)

W a t e r (sufficient for desired n o n - v o l a t i l e solids) Phenol Formaldehyde Organosolv l i g n i n Sodium hydroxide Urea

1.00 1.8-3.0 0.25-0.80 0.40-0.65 -

1

1

1.00 2.98 0.25 0.64 0.09

A s s u m e a m o l e equivalent u n i t of 200 for organosolv l i g n i n , based o n a t y p i c a l a n a l y z e d C9 l i g n i n u n i t .

Maple Block Screening Method. A series of e x p e r i m e n t a l procedures were p e r f o r m e d o n b o n d i n g m a p l e block w o o d ( C o o k , P . M . , E a s t m a n K o d a k at K i n g s p o r t , T N , p e r s o n a l c o m m u n i c a t i o n s , 1987). T h e procedure a d o p t e d was the A S T M D 905 s t a n d a r d , m o d i f i e d as follows: S u g a r m a p l e (Acer saccharum) w o o d , 76 b y 25 b y 5.7 m m i n size (3 inches l o n g , 1 i n c h w i d e , and 0.25 i n c h t h i c k ) , w i t h 6% m o i s t u r e content was p l a n e d to o b t a i n fresh surfaces for b o n d i n g . T h e desired a m o u n t of resin ( w i t h no m i x additives) was weighed (58.6 g / m , 12 l b / 1 0 0 0 f t , resin solids basis) a n d a p p l i e d t o one block surface a n d t h e n a second clean block was o v e r l a p p e d so t h a t 25 square m m (1 square inch) surface area c o m m o n to each block was coated. T h e resin coated blocks were placed d i r e c t l y i n the hot press (no c l a m p t i m e ) . T h e blocks were hot pressed at 177°C (350°F) for 4 to 6 m i n u t e s at 3.44 M P a (500 p s i ) . A l l b o n d e d blocks were allowed to 2

2

In Lignin; Glasser, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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LIGNIN: PROPERTIES AND MATERIALS

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s t a n d (post cure) at a m b i e n t temperatures for 24 hours p r i o r to t e s t i n g . T e n b o n d e d b l o c k s were tested d r y a n d ten were tested after a n acceler­ ated a g i n g regimen (4 h b o i l i n water, cool, a n d test wet) for each r e s i n . T h e lap-tension-shear s t r e n g t h of the test specimens was measured u s i n g a n I n s t r o n m a c h i n e , a n d s u b j e c t i v e estimates of the percent w o o d failure (or b o n d failure) were observed a n d recorded. T h e d a t a were subjected to s t a t i s t i c a l analysis. Flake Board Screening Method. T h i s phase of the s t u d y has been p r e v i ­ o u s l y r e p o r t e d i n more d e t a i l b y Sellers et al. (4) b u t c a n be s u m m a r i z e d as follows. D i s c - c u t s o u t h e r n pine flakes (wafers a n d / o r strands) were o b ­ t a i n e d f r o m c o m m e r c i a l flake b o a r d plants i n the S o u t h e r n U n i t e d States. T h e flakes were a p p r o x i m a t e l y 76 m m (3 i n . ) l o n g , 19 to 38 m m (0.75 to 1.5 i n . ) w i d e , a n d 0.5 to 0.8 m m (0.020 to 0.030 i n . ) t h i c k a n d adjusted to 2 . 5 % m o i s t u r e content at the t i m e of use. E a c h resin t y p e was a p p l i e d at 5 % a n d 7% resin solids rates. T h e m a t c o n f i g u r a t i o n was homogeneous a n d h a n d felted i n sufficient size to o b t a i n a t r i m m e d p a n e l m e a s u r i n g 560 b y 610 b y 12.5 m m (22 b y 24 by 0.5 i n . ) . T h e m a t s were hot pressed at 205°C ( 4 0 0 ° F ) for 6 minutes w i t h a dual-pressure regimen ( 5 . 5 1 / 2 . 7 5 M P a , 8 0 0 / 4 0 0 p s i ) . T h e i n i t i a l h i g h pressure was d r o p p e d after one m i n u t e i n t o the cycle a n d the panels were pressed to 1 2 . 7 - m m (0.5-in.) m e t a l stops i n the hot press. T h e target density was 745 k g / m (46 l b / f t ) . T h r e e panels per resin t y p e a n d a p p l i c a t i o n rate were m a d e . R e s i n types i n c l u d e d the c o n t r o l c o m m e r c i a l resins (no l i g n i n content), l i g n i n - m o d i f i e d P F resins, a n d c o n t r o l P F resins c o n t a i n i n g a n inert filler (pecan shell flour) at the same loads as the l i g n i n s u b s t i t u t e d resins. Screening tests for p a n e l perfor­ m a n c e i n c l u d e d i n t e r n a l b o n d ( I B ) , d r y s t a t i c b e n d i n g ( m o d u l u s of r u p t u r e , M O R ) , accelerated a g i n g M O R (strength r e t e n t i o n after a n A m e r i c a n P l y ­ w o o d A s s o c i a t i o n performance 6-cycle test), a n d d i m e n s i o n a l tests [water a b s o r p t i o n ( W A ) a n d thickness swell ( T S ) ] . T h e s t a t i s t i c a l a n a l y s i s was a two-factor e x p e r i m e n t (resin type-resin a p p l i c a t i o n level), u s i n g a n a n a l ­ ysis of variance a n d Τ tests ( L S D ) for g r o u p i n g for the various p h y s i c a l properties tested. 3

3

Product Disclaimer T h e use of t r a d e , firm, or c o r p o r a t i o n names i n this p u b l i c a t i o n is for the i n f o r m a t i o n a n d convenience of the reader. S u c h use does not c o n s t i t u t e an official endorsement or a p p r o v a l b y the M i s s i s s i p p i Forest P r o d u c t s U t i l i z a ­ t i o n L a b o r a t o r y ( M F P U L ) , M i s s i s s i p p i S t a t e U n i v e r s i t y , or the E a s t m a n K o d a k C o m p a n y of any p r o d u c t or service to the e x c l u s i o n of others w h i c h m a y be s u i t a b l e . A cknowledgment s A p p r e c i a t i o n is expressed to the following M F P U L employees: D r . A . L . W o o t e n (retired) for resin synthesis; G a r y S t o v a l l a n d George M i l l e r for resin a n d flake b o a r d s a m p l e p r e p a r a t i o n a n d t e s t i n g ; a n d L y n n P r e w i t t for G F C work. M a t e r i a l s were d o n a t e d i n s u p p o r t of t h i s project b y B o r d e n

In Lignin; Glasser, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.

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Incorporated, Chembond Corporation, E a s t m a n K o d a k Company, Georgia P a c i f i c C o r p o r a t i o n , L o u i s i a n a Pacific C o r p o r a t i o n , a n d S o u t h e a s t e r n R e ­ d u c t i o n C o m p a n y . T h i s w o r k was s u p p o r t e d by t w o research grants f r o m Eastman Kodak Company.

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Literature

Cited

1. Chemical Week 1984, 134(1), 26, 28. 2. Conner, A . H.; Lorenz, L . F . J. Wood Chem. Technol. 1986, 6(4), 591613. 3. Sellers, T . , Jr. Plywood and Adhesive Technology, Marcel Dekker: New York, 1985; pp. 349-373. 4. Sellers, T . , Jr.; Wooten, A . L . ; Cook, P. M . Proc. Structural Wood Composites: New Technologies for Expanding Markets; Forest Products Research Society, Madison, WI, 1988, Proc. No. 47359, 43-50. 5. Glasser, W . G . ; Glasser, H . R.; Morohoshi, N. Macromol. 1981, 14(2), 252-262. 6. Glasser, W . G . ; Barnett, C . Α.; Sano, Y . J. Appl. Polym. Sci., Appl. Polym. Symp. 1983, 37, 441-460. RECEIVED February 27,1989

In Lignin; Glasser, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.