Adhesives from Renewable Resources - American Chemical Society

Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch008

Chapter 8 Effects of Phenol-Formaldehyde Copolymer on Gluebond Performance of Lignin-Phenolic Resin Systems Chung-Yun

H s e and

QiQing

Hong

1

Southern Forest Experiment Station Forest Service U . S . Department of Agriculture Pineville, LA 71360

A series of experiments was conducted to optimize 1) molar ratio of formaldehyde/phenol, 2) sodium hydroxide catalyst, and 3) reactant concentration of phenolic copolymer to lignin in terms of providing the best performance of lignin-phenolic resin systems for structural flakeboard panels. A t 25/75 (w/w) mixture of phenolic/lignin, a methylolated lignin blended with phenolic resin synthesized with a formaldehyde/phenol ratio of 3 consistently resulted in higher bond strength, lower thickness swell, and smaller linear expansion of structural flakeboard. Gluebond performance improved as the NaOH/phenol ratio increased from 0.2 to 0.7. Further increases in sodium hydroxide adversely affected gluebond performance. Panel strength properties decreased with increasing resin solids content. Adhesives formulated with 75% of methylolated lignins as substi tutes for phenolic resins can be used to make structural flakeboards with acceptable properties. I n c o r p o r a t i o n o f l i g n i n i n t o phenol-formaldehyde resins h a s been one o f t h e p r i m a r y areas o f research i n l i g n i n u t i l i z a t i o n . W h e n l i g n i n is used d i r e c t l y as a replacement for p h e n o l , t h e m a x i m u m acceptable level o f replacement is about 2 0 % (1). However, a higher degree o f replacement c a n be achieved u s i n g m o d i f i e d l i g n i n (2-7). O f a l l l i g n i n m o d i f i c a t i o n t r e a t m e n t s , those t h a t increase c h e m i c a l r e a c t i v i t y o r reactive sites, such as p h e n o l a t i o n o r m e t h y l o l a t i o n , seem t o be the most p r o m i s i n g . α

Ο η study leave from Nanjing Forestry University, Nanjing,China This chapter not subject to U.S. copyright Published 1989 American Chemical Society

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


8.

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97

I n f o r m u l a t i n g l i g n i n - p h e n o l i c resin adhesives for f a b r i c a t i o n of w o o d c o m posites, t h e i m p o r t a n c e o f the c o m p a t i b i l i t y o f a 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 for l i g n i n often has not been f u l l y recognized. R e c e n t l y , C a l v e a n d S h i e l d s (8) i n d i c a t e d t h a t l i g n i n c o p o l y m e r i z e d w i t h a n a c i d - c u r e d p h e n o l i c showed the best p o t e n t i a l i n w a f e r b o a r d p r o d u c t i o n ; whereas, l i g n i n c o p o l y m e r i z e d w i t h a n a l k a l i n e - c u r i n g p h e n o l i c was m o s t s u i t a b l e for p l y w o o d . H o w e v e r , n o c o m prehensive studies have been p u b l i s h e d o n the effect o f r e s i n v a r i a b l e s o n the p r o p e r t i e s a n d b o n d performances o f l i g n i n - p h e n o l i c resin systems. T h e experi m e n t s r e p o r t e d here p r o v i d e i n f o r m a t i o n o n s t r e n g t h p r o p e r t i e s o f s t r u c t u r a l flakeboards b o n d e d w i t h l i g n i n - p h e n o l i c r e s i n adhesives as affected b y 1) the m o l a r r a t i o o f f o r m a l d e h y d e / p h e n o l , 2) the a m o u n t of s o d i u m h y d r o x i d e c a t a l y s t , a n d 3) the solids content o f p h e n o l i c resins. T h e o b j e c t i v e of the research was t o o p t i m i z e l i g n i n - p h e n o l i c c o p o l y m e r resin systems. Experimental

Methodology

T h e b o n d performances of l i g n i n - p h e n o l i c resin systems were s t u d i e d t h r o u g h a series o f e x p e r i m e n t s , each designed to e l u c i d a t e a facet o f the p r o b l e m . T h e resin p r e p a r a t i o n a n d p a n e l f a b r i c a t i o n procedures were, however, m a i n t a i n e d as u n i f o r m l y as possible. T h u s , unless otherwise specified, the e x p e r i m e n t a l procedures described below were used i n the s t u d y . R e s i n P r e p a r a t i o n . A l l p h e n o l i c resins were p r e p a r e d i n the l a b o r a t o r y . R e s i n p r e p a r a t i o n s were r e p l i c a t e d one t i m e . T o prepare each r e s i n , a l l p h e n o l a n d water were p l a c e d i n a r e a c t i o n k e t t l e . T h e f o r m a l d e h y d e was a d d e d i n three steps: 1) t o t a l f o r m a l d e h y d e less 1 m o l e o f f o r m a l d e h y d e was a d d e d at the b e g i n n i n g ; 2) the b a l a n c e was d i v i d e d i n t o t w o e q u a l p a r t s (i.e., 0.5 m o l e each), one o f w h i c h was a d d e d 1 h o u r after the r e a c t i o n b e g a n ; a n d 3) the r e m a i n d e r of f o r m a l d e h y d e was a d d e d 20 m i n u t e s l a t e r . T h e s o d i u m h y d r o x i d e was a d d e d as c a t a l y s t i n four steps (i.e., four e q u a l p a r t s at 10-minute i n t e r v a l s ) . T o i n i t i a t e the r e a c t i o n , the m i x t u r e was heated a n d m a i n t a i n e d at 75 ° C . A l l reactions were t e r m i n a t e d at the e n d o f 100 m i n u t e s . G e l t i m e , p H , viscosity, s o l i d content, a n d specific g r a v i t y were d e t e r m i n e d . T h e general c o n d i t i o n s for resin p r e p a r a t i o n were:

N a O H / p h e n o l r a t i o - 0.3 S o l i d s content - 4 2 % R e a c t i o n t e m p e r a t u r e - 75 ° C R e a c t i o n t i m e - 100 m i n u t e s

G e l - P e r m e a t i o n C h r o m a t o g r a p h y . A W a t e r A s s o c i a t e s H P L C w i t h four S h o d e x G P C - A D - 8 0 2 S c o l u m n s was used w i t h d i m e t h y l f o r m a m i d e at a flow rate o f 1 m L / m i n u t e . T h e gel is p o l y s t y r e n e - d i v i n y l benzene c o p o l y m e r a n d has e x c l u s i o n l i m i t o f 8,000 b y p o l y s t y r e n e m o l e c u l a r weight. S a m p l e i n j e c t i o n


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ADHESIVES F R O M RENEWABLE RESOURCES


v o l u m e was 100 μL at a c o n c e n t r a t i o n of 1% ( w t / v ) , i f n o t specified. C o l u m n s were c a l i b r a t e d w i t h s t a n d a r d m o l e c u l a r weight p o l y e t h y l e n e glycols (i.e., 3,000, 1,500,1,000, 600, 400, a n d 300), 2,2/- a n d 4 , 4 / - d i h y d r o x y p h e n y l m e t h a n e , 2- a n d 4 - h y d r o x y m e t h y l p h e n o l , a n d p h e n o l . M a t h e m a t i c a l a p p r o x i m a t i o n of the G P C c a l i b r a t i o n curve was m a d e b y e x p o n e n t i a l fit of m o l e c u l a r weight v s . e l u t i o n volumes o f the s t a n d a r d s . T h e n u m b e r a n d weight average m o l e c u l a r weight were c a l c u l a t e d b y the m e t h o d described b y N a v a s ( 0 ) . M e t h y l o l a t i o n o f K r a f t L i g n i n . S o u t h e r n p i n e k r a f t l i g n i n was o b t a i n e d f r o m the W e s t v a c o C o r p o r a t i o n . T h e acidified l i g n i n ( a p p r o x i m a t e l y 9 7 % solids a n d ash content of less t h a n 1%) was I n d u l i n A T . M e t h y l o l a t i o n was p e r f o r m e d a c c o r d i n g t o the m e t h o d developed i n a previous s t u d y (10). B r i e f l y , the l i g n i n was dissolved i n d i l u t e s o d i u m h y d r o x i d e s o l u t i o n a n d allowed t o m i x for 75 m i n u t e s at 80 ° C . T h e r e s u l t i n g s o l u t i o n was adjusted t o p H 12.0. T h e t e m p e r ature was t h e n a d j u s t e d t o 50 ° C , a n d f o r m a l d e h y d e s o l u t i o n (50%) was a d d e d s l o w l y t o t h e l i g n i n s o l u t i o n . T h e m e t h y l o l a t i o n r e a c t i o n was allowed t o proceed for a n h o u r w i t h c o n t i n u o u s s t i r r i n g . T h e m o l a r r a t i o o f f o r m a l d e h y d e t o l i g n i n ( m o l e c u l a r weight of l i g n i n was assumed t o be 180) was 1 / 1 , a n d the ingredients i n p a r t s b y weight were: W a t e r - 1,200 K r a f t l i g n i n (97%) - 600 F o r m a l d e h y d e (50%) - 192 S o d i u m h y d r o x i d e (50%) - 185 B l e n d i n g o f L i g n i n - P h e n o l i c R e s i n S y s t e m . T h e m e t h y l o l a t e d l i g n i n was b l e n d e d w i t h the p h e n o l i c resins at a s o l i d weight r a t i o of 7 5 / 2 5 a n d at r o o m t e m p e r a t u r e . T h e m i x t u r e was m e c h a n i c a l l y s t i r r e d for 15 m i n u t e s . T h e gel t i m e , p H , a n d solids content were d e t e r m i n e d for each resin s y s t e m . E v a l u a t i o n o f G l u e b o n d Q u a l i t y . S t r u c t u r a l flakeboard panels were p r e p a r e d i n the l a b o r a t o r y w i t h s w e e t g u m flakes 3 inches l o n g , 0.015 inches t h i c k , a n d v a r i a b l e w i d t h s . G e n e r a l c o n d i t i o n s for p a n e l p r e p a r a t i o n were: P a n e l size - 1/2 b y 22 b y 24 i n . P a n e l density - 43 lbs per c u . ft. R e s i n content - 5 % of ovendry weight wood

of

H o t press t e m p e r a t u r e - 193 ° C Press closing t i m e - 45 sec. H o t press t i m e - 6 m i n . T o prepare each p a n e l , w o o d f u r n i s h was weighed o u t a n d p l a c e d i n a r o t a t i n g blender. T h e required a m o u n t of resin was t h e n weighed a n d a p p l i e d to the w o o d p a r t i c l e s b y a i r - a t o m i z i n g nozzles. T h e b l e n d e d p a r t i c l e s were t h e n carefully felted i n t o the final m a t w i t h a f o r m i n g box. T h e m a t was transferred



8.

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i m m e d i a t e l y t o a single o p e n i n g h o t press heated at 193 ° C . A l l panels were c o n d i t i o n e d at r o o m t e m p e r a t u r e for 24 h o u r s . A f t e r c o n d i t i o n i n g , each p a n e l was t r i m m e d a n d cut i n t o 2-inch w i d e s t r i p s . A b e n d i n g s p e c i m e n a n d t w o I B blocks were cut f r o m each s t r i p . T h r e e b e n d i n g specimens were selected at r a n d o m for d e t e r m i n a t i o n o f d r y M O R a n d M O E a n d three specimens were selected f r o m each p a n e l for d e t e r m i n a t i o n o f b o n d d u r a b i l i t y . T e n I B specimens were selected at r a n d o m f r o m each p a n e l . B e n d i n g a n d i n t e r n a l b o n d tests were p e r f o r m e d i n accordance w i t h A S T M s t a n d a r d s for e v a l u a t i n g p r o p e r t i e s o f w o o d - b a s e d fiber a n d p a r t i c l e p a n e l m a t e r i a l s ( D 1037-72). T h e b o n d d u r a b i l i t y was e v a l u a t e d by a v a c u u m - p r e s s u r e soak test ( O D V P S ) u n d e r the f o l l o w i n g c o n s t r a i n t s : 1) specimens were d r i e d at 102 ° C for 24 h o u r s ; 2) t h e y were p l a c e d i n pressure c y l i n d e r a n d flooded w i t h t a p w a t e r ; 3) the s y s t e m was s u b j e c t e d t o a v a c u u m 27 ± 2 inches o f m e r c u r y for 1 h o u r a n d t h e n pressure > 90 ± 10 p s i for 2 h o u r s . T h i s procedure was developed b y the 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 a n d designated as Α Ρ Α Test M e t h o d P - l . L i n e a r e x p a n s i o n ( L E ) a n d thickness swell ( T S ) values are based o n the change f r o m the o v e n d r y c o n d i t i o n t o the e n d o f the O D V P S cycle. B e n d i n g a n d I B o f O D V P S specimens received the a d d i t i o n a l t r e a t m e n t o f d r y i n g i n a n oven for 24 h o u r s followed b y at least 48 hours o f c o n d i t i o n i n g at 5 0 % r e l a t i v e h u m i d i t y before e v a l u a t i o n . Experiment 1. Effect of Molar Ratio of Formaldehyde/Phenol on Strength Properties of Lignin-Phenolic Resin System. P h e n o l i c resins, w i t h f o r m a l d e h y d e i n excess o f 2 moles per 1 m o l e p h e n o l , have p r o v e d t o be m o s t useful for g l u i n g p l y w o o d a n d flakeboard. I n g e n e r a l , a d d i t i o n a l f o r m a l d e h y d e (i.e., h i g h e r m o l a r ratios) w i l l not react effectively, a n d t h u s c o n t r i b u t e s l i t t l e t o resin p e r f o r m a n c e . W h e n the r a t i o o f f o r m a l d e h y d e t o p h e n o l is less t h a n 2 m o l e s , the r e a c t i v i t y or g e l a t i o n t i m e o f the resin is lengthened. H o w e v e r , i n l i g n i n - p h e n o l i c resin systems, the o p t i m u m r a t i o o f f o r m a l d e h y d e t o p h e n o l has not been c l e a r l y defined. T h i s e x p e r i m e n t was designed t o o p t i m i z e the f o r m a l d e h y d e / p h e n o l r a t i o o f the resin s y s t e m . T h e v a r i a b l e s were four levels o f f o r m a l d e h y d e / p h e n o l r a t i o s - 2 . 0 , 2.5, 3.0, a n d 3.5. Experiment 2. Effect of Molar Ratio of Sodium Hydroxide to Phenol of Phe nolic Resin on Strength Properties of Lignin-Phenolic Resin Adhesives. S o d i u m h y d r o x i d e has been the p r e d o m i n a n t c h e m i c a l used as a c a t a l y s t i n resol resin technology. T h r o u g h v a r i a t i o n i n the a m o u n t s o f the c a t a l y s t a n d the m e t h o d o f c a t a l y s t a d d i t i o n , a w i d e v a r i e t y of resin systems c a n be f o r m u l a t e d . T h i s e x p e r i m e n t e x a m i n e d the properties of p h e n o l i c resins f o r m u l a t e d w i t h v a r i ous s o d i u m h y d r o x i d e / p h e n o l r a t i o s a n d t h e i r effects o n the b o n d properties of s t r u c t u r a l flakeboards m a d e w i t h l i g n i n - p h e n o l i c resin adhesive systems. V a r i ables for resin p r e p a r a t i o n were four m o l a r r a t i o s of s o d i u m h y d r o x i d e / p h e n o l (i.e., 0.2, 0.45, 0.7, a n d 0.95). T h e f o r m a l d e h y d e / p h e n o l r a t i o a n d solids content were fixed at 3 / 1 a n d 4 2 % , respectively. Experiment 3. Effect of Phenolic Resin Solid Content on Strength Properties of Lignin-Phenolic Resin System. P a s t experience has s h o w n t h a t the o p t i m u m solids content o f t y p i c a l p h e n o l i c resin f o r m u l a t i o n s is between 4 0 % t o 5 0 % .


100


T h e m o s t p o p u l a r is the 4 0 % solids content f a m i l y , since i t seems t o give a l i t t l e better c o s t / p e r f o r m a n c e r e l a t i o n s h i p . T h i s e x p e r i m e n t e x a m i n e d the effect of p h e n o l i c resin solids o n the properties of s t r u c t u r a l flakeboards b o n d e d w i t h the l i g n i n - p h e n o l i c resin s y s t e m . T h e v a r i a b l e s were three levels o f p h e n o l i c resin solids content - 3 9 % , 4 6 % , a n d 5 4 % . T h e f o r m a l d e h y d e / p h e n o l r a t i o a n d N a O H / p h e n o l r a t i o were 3 / 1 a n d 0 . 7 / 1 , respectively.


Results and Discussion Characteristics of Methylolated Kraft Lignin. m e t h y l o l a t e d k r a f t l i g n i n are s u m m a r i z e d as follows:

T h e basic p r o p e r t i e s

of

pH-12 V i s c o s i t y - 2 1 6 cps as d e t e r m i n e d o n a B r o o k f i e l d viscometer w i t h s p i n d l e N o . 2 at 25 ° C a n d 20 r p m Specific g r a v i t y - 1 . 2 Free f o r m a l d e h y d e - 1 . 8 % w i t h f o r m a l d e h y d e / l i g n i n r a t i o o f 1/1 after r e a c t i o n for 1 h o u r at 50 ° C , and 0 . 4 6 % w i t h f o r m a l d e h y d e / l i g n i n r a t i o of 0 . 5 / 1 after r e a c t i o n for 1 h o u r at 50

0

C

P h e n o l i c R e s i n P r o p e r t i e s . A v e r a g e p h y s i c a l a n d c h e m i c a l properties of phen o l i c resins as affected b y m o l a r r a t i o of f o r m a l d e h y d e / p h e n o l are s u m m a r i z e d as follows: CH 0/Phenol Ratio

pH

2.0/1 2.5/1 3.0/1 3.5/1

9.64 9.86 9.78 9.78

2

Viscosity

Solids Content

Specific Gravity

(cps) 18 20

(%) 43 41

(g/cc) 1.16 1.16

20 23

40 39

1.16 1.17

Gel Time (min) 62 38 27 26

A s expected, the gel t i m e decreased consistently as f o r m a l d e h y d e / p h e n o l r a t i o increased t o 3 . 0 / 1 ; thereafter, f u r t h e r increase i n f o r m a l d e h y d e / p h e n o l r a t i o h a d l i t t l e effect o n the gel t i m e . T h e effects of f o r m a l d e h y d e / p h e n o l r a t i o o n p H , viscosity, s o l i d content, a n d specific g r a v i t y were n o t s i g n i f i c a n t . F i g u r e 1 shows the G P C c h r o m a t o g r a m s o f p h e n o l i c resins reacted at different f o r m a l d e h y d e / p h e n o l r a t i o s . I n general, the c h r o m a t o g r a m is d i v i d e d i n t o


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

< χ 10

ML)

G P C c h r o m a t o g r a m s o f p h e n o l i c resins reacted at different p h e

nol/formaldehyde ratios.

F i g u r e 1.

E LUT ΙΟΝ



102


two groups o f peaks. A t a n e a r l y stage o f r e a c t i o n several peaks are observed. T h e peak between 45 a n d 50 m L e l u t i o n v o l u m e is t h a t o f p h e n o l , a n d the negative peak between 40 a n d 45 m L is due t o f o r m a l d e h y d e a n d water i n the s a m p l e . T h e s e i d e n t i f i c a t i o n s were m a d e b y c o m p a r i n g G P C c h r o m a t o g r a m s o f p h e n o l i c resins before a n d after a d d i t i o n o f p h e n o l a n d f o r m a l d e h y d e t o the s a m p l e . T h e assignments agree w i t h those o f p r e v i o u s workers (10-13). O t h e r peaks e v i d e n t at e a r l y stages o f the r e a c t i o n (i.e., those between e l u t i o n v o l u m e s 32 a n d 45 m L ) m a y be m o n o m e r s a n d d i m e r s o f p o l y m e t h y l o l p h e n o l . T h e s e p e a k s c a n be i n t e g r a t e d together ( G r o u p A ) as a n estimate o f low m o l e c u l a r weight p r o d u c t s . I n l a t e r stages o f the c o o k peaks develop at lower r e t e n t i o n v o l u m e s t h a t c a n be i n t e g r a t e d together ( G r o u p B ) t o represent a measure o f the higher m o l e c u l a r weight p r o d u c t s o b t a i n e d b y c o n d e n s a t i o n reactions. It is n o t e d t h a t , at the same r e a c t i o n t i m e , the free p h e n o l content decreased as the f o r m a l d e h y d e / p h e n o l r a t i o increased. A s e x p e c t e d , o n l y a s m a l l a m o u n t of h i g h m o l e c u l a r weight f r a c t i o n ( G r o u p B ) f o r m e d at f o r m a l d e h y d e / p h e n o l r a t i o s below 2 / 1 ( F i g u r e 1). T h e result i n d i c a t e d t h a t there was not e n o u g h f o r m a l d e h y d e t o p r o m o t e the c o n d e n s a t i o n r e a c t i o n o f the r e s i n . T h e n u m b e r average m o l e c u l a r weight increased s l i g h t l y as the m o l e r a t i o increased f r o m 2.0 t o 3.0 w i t h h i g h m o l e c u l a r weight f r a c t i o n d r o p p i n g s l i g h t l y at the 3.5 r a t i o ( F i g u r e 2). T h e result i n d i c a t e s t h a t the excess f o r m a l d e h y d e was n o t effective i n p r o m o t i n g c o n d e n s a t i o n o f the r e s i n . F o r m a l d e h y d e t o P h e n o l R a t i o . T h e effect o f f o r m a l d e h y d e / p h e n o l r a t i o o n p H , viscosity, a n d gel t i m e o f the l i g n i n - p h e n o l i c resin s y s t e m is s u m m a r i z e d as follows:

CH 0/Phenol Ratio

Methylolated Lignin/Phenolic Resin Ratio

2.0/1.0 2.5/1.0 3.0/1.0 3.5/1.0

75/25 75/25 75/25 75/25

2

Viscosity

pH

Gel Time

11.15 10.95 10.95 11.15

(min) 64 45 32 30

(cps) 120 112 112 114

It is n o t e d t h a t the gel t i m e decreased as the f o r m a l d e h y d e / p h e n o l r a t i o of the p h e n o l i c resin i n the s y s t e m increased. F u r t h e r m o r e , the gel t i m e curve o f t h e l i g n i n - p h e n o l i c s y s t e m was, i n general, s i m i l a r t o t h a t o f p h e n o l i c resins m e a s u r e d i n the p r e v i o u s section. T h e s i m i l a r i t y o f the gel t i m e curves ( F i g u r e 3) m a y i n d i c a t e t h a t the p h e n o l i c resin p l a y s the m a j o r role i n affecting the cure speed o f the l i g n i n - p h e n o l i c resin s y s t e m even t h o u g h the p h e n o l i c resin consisted o f o n l y 2 5 % b y weight i n the s y s t e m . A v e r a g e p h y s i c a l a n d m e c h a n i c a l properties o f the flakeboards are s u m m a r i z e d i n T a b l e I. O n the average, panels b o n d e d w i t h the l i g n i n / p h e n o l i c resin


HSE AND HONG

Phenol-Formaldehyde Copolymer

103


8.

F i g u r e 3. G e l t i m e curves of p h e n o l i c a n d l i g n i n - p h e n o l i c resins as affected formaldehyde/phenol ratio.


by

104



s l i g h t l y higher s t r e n g t h properties before a n d after the O D V P S t r e a t m e n t . T h e O D V P S t r e a t m e n t resulted i n a n average of m o r e t h a n 6 6 % r e d u c t i o n i n M O E , 3 9 % i n M O R , a n d 2 2 % i n I B . S i m i l a r t o the s t r e n g t h properties, the panels b o n d e d w i t h the P / F r a t i o 3:1 resins also were s u p e r i o r i n d i m e n s i o n a l s t a b i l i t y a n d e x h i b i t e d less water a b s o r p t i o n ( W A , T a b l e I). B a s e d o n these e v a l u a t i o n s , the P / F r a t i o 3:1 seems t o p r o v i d e consistently better performance a n d was chosen for the second phase, the e x p e r i m e n t o n o p t i m i z i n g the N a O H / p h e n o l ratio.

T a b l e I. A v e r a g e P h y s i c a l a n d M e c h a n i c a l P r o p e r t i e s o f F l a k e b o a r d s CH / Lignin Phenol Phenolic Ratio Resin 2

Ratio

2.0/1 2.5/1 3.0/1 3.5/1

75/25 75/25 75/25 75/25

After O D V P S Treatment IB

MOR

(psi)

(psi)

66 72 80 69

6475 5167 7318 6133

MOE (10

3

IB

psi) (psi)

875 798 915 814

48 60 60 55

MOR (psi)

MOE (10

3726 3078 4211 4212

3

L E TS

psi) (%)

373 345 437 412

0.19 0.27 0.23 0.27

WA

(%)

(%)

37 44 33 34

106 107 99 104

M o l a r R a t i o s o f S o d i u m H y d r o x i d e / P h e n o l . T a b l e II s u m m a r i z e s the effect of v a r y i n g m o l a r ratios of N a O H / p h e n o l o n p H , viscosity, s o l i d content, specific g r a v i t y , gel t i m e , a n d m o l e c u l a r weight of the resins. T h e G P C c h r o m a t o g r a m s of the p h e n o l i c resins reacted at different N a O H / p h e n o l r a t i o s are given i n F i g u r e 4.

T a b l e I I . Effect of M o l a r R a t i o of N a O H / P h e n o l o n P h y s i c a l a n d C h e m i c a l P r o p e r t i e s of P h e n o l i c R e s i n s Molar Ratio NaOH/Phenol

Gel Time

PH

(min) 0.20/1 0.45/1 0.70/1 0.95/1

39 25 24 92

9.41 10.06 10.38 10.70

Viscosity

Specific Solid Content

Gravity

(cps)

(%)

(g/cm )

20 22 24 26

40 40 39 42

1.15 1.18 1.19 1.20

3

T h e significant effect of N a O H / p h e n o l r a t i o o n gel t i m e is p l o t t e d i n F i g ure 5. T h e fastest g e l a t i o n rate occurred between N a O H / p h e n o l m o l a r r a t i o s



nol ratios.

F i g u r e 4. G P C c h r o m a t o g r a m s of p h e n o l i c resins reacted at v a r i o u s N a O H / p h e -


00

106



of 0.45 a n d 0.70; a n d the gel t i m e increased s h a r p l y at b o t h extremes of the N a O H / p h e n o l r a t i o s . T h e G P C c h r o m a t o g r a m showed t w o d i s t i n c t m o l e c u l a r weight f r a c t i o n s (i.e., a h i g h m o l e c u l a r weight f r a c t i o n between e l u t i o n v o l u m e s o f 20 a n d 30 m L a n d a low m o l e c u l a r weight f r a c t i o n between e l u t i o n v o l u m e s o f 35 a n d 45 m L ) . T h e l o w N a O H content o f 0.2 resulted i n s i g n i f i c a n t l y lower percentage o f h i g h m o l e c u l a r weight f r a c t i o n ( T a b l e I I I , c o l u m n 2). T h i s result m a y i n d i c a t e insufficient c a t a l y s t t o effectively p r o m o t e c o n d e n s a t i o n . T h e h i g h N a O H content o f 0.95 resulted i n a s u b s t a n t i a l l y lower average m o l e c u l a r weight ( T a b l e I I I , c o l u m n s 3 a n d 4 ) . T h e effect o f h i g h caustic c o n tent o n average m o l e c u l a r weight m a y be a t t r i b u e d t o the C a n n i z z a r o r e a c t i o n as s h o w n i n a p r e v i o u s s t u d y (15). T h e f o r m a l d e h y d e deficiency m a y have l i m i t e d m e t h y l o l groups t o sufficiently p r o l o n g the c o n d e n s a t i o n , r e s u l t i n g i n lower average m o l e c u l a r weight. A v e r a g e p h y s i c a l a n d m e c h a n i c a l properties o f the flakeboards are s u m m a r i z e d i n T a b l e I V . T h e caustic content level o f 0.2 c o n s i s t e n t l y resulted i n the smallest s t r e n g t h (i.e., I B , M O R , a n d M O E ) , whereas, t h a t of 0.45 r e s u l t e d i n s l i g h t l y h i g h e r M O R , 0.7 gave the highest I B , a n d 0.95 the highest M O E . A s e x p e c t e d , the O D V P S t r e a t m e n t reduced a l l s t r e n g t h values s u b s t a n t i a l l y . Nevertheless, the differences a m o n g the v a r i o u s N a O H contents were n o t s i g n i f i c a n t . T h e effect o f caustic content o n s t a b i l i t y o f the panels shows the r a t i o o f 0.7 r e s u l t e d i n m o s t stable panels w i t h less l i n e a r e x p a n s i o n ( L E ) a n d thickness swell ( T S ) . B a s e d o n t h i s e x p e r i m e n t , i t was c o n c l u d e d t h a t the m o l a r r a t i o of N a O H / p h e n o l at 0.7 s h o u l d be chosen for the subsequent e x p e r i m e n t .

T a b l e I I I . Effect o f N a O H C o n t e n t o n C o n t e n t o f H i g h Molecular Weight Fraction and Average Molecular Weight NaOH/ Phenol

Content of H i g h Molecular Weight

0.20 0.45 0.70 0.95

19 25 26 26

After O D V P S Weight Average Number Average 1488 1688 1685 845

488 508 491 294

R e s i n S o l i d s C o n t e n t . A v e r a g e p h y s i c a l a n d c h e m i c a l p r o p e r t i e s o f t h e resins are s u m m a r i z e d i n T a b l e V . T h e effect o f resin solids content o n p H a n d specific g r a v i t y was n o t significant. H o w e v e r , the gel t i m e decreased a n d v i s c o s i t y increased as the resin solids content increased. Figure 6 the p h e n o l i c u l a r weight distribution

shows the G P C c h r o m a t o g r a m s o f the p h e n o l i c resins. O t h e r t h a n r e s i n at 4 6 % , resin s o l i d content r e s u l t e d i n s l i g h t l y h i g h e r m o l e c ( T a b l e V ) , the effect o f resin s o l i d content o n m o l e c u l a r weight was n o t significant.



8.

HSE AND HONG

107

Phenol-Formaldehyde Copolymer

0 20 NAOH

0.45

0.70

I PHENOL

0.95

RATIO

F i g u r e 5. Effect o f N a O H / p h e n o l r a t i o o n gel t i m e o f p h e n o l i c resins.

RESIN SOLID CONTENT UJ

-

3 9 °/

0

CO

CO UJ

ct ct Ο Ο UJ κ UJ

α 4 ELUTION

VOLUME

5-2

3

(X10ML)

F i g u r e 6. G P C c h r o m a t o g r a m s o f p h e n o l i c resins at various resin s o l i d contents.


108



P h y s i c a l a n d m e c h a n i c a l properties of the flakeboards are s u m m a r i z e d i n T a b l e V I . O n average, a l l s t r e n g t h properties decreased as the p h e n o l i c resin solids increased, w i t h one e x c e p t i o n (i.e., M O E at 4 6 % resin s o l i d s ) . T h e effect of p h e n o l i c resin s o l i d o n the s t a b i l i t y o f the flakeboard was not significant ( T a b l e VI). T a b l e I V . Effect of C a u s t i c C o n t e n t o n P h y s i c a l a n d M e c h a n i c a l P r o p e r t i e s of F l a k e b o a r d s NaOH/

Lignin/

Phenol Phenolic Ratio

Resin

0.20/1 0.45/1 0.70/1 0.95/1

75/25 75/25 75/25 75/25


MOR

(psi)

(psi)

58 72 77 70

5081 6706 5680 5918

MOE (10

IB

MOR

psi) (psi)

3

746 794 762 821

(psi)

50 52 54 53

MOE (10

3503 3874 3580 3275

LE

psi) (%)

3

338 399 396 405

0.33 0.31 0.28 0.32

TS

WA

(%)

(%)

38 37 34 34

110 109 106 103

T a b l e V . Effect of R e s i n S o l i d s C o n t e n t o n P h y s i c a l a n d Mechanical Properties of Phenolic Resins Resin Solid Content

PH

(%) 39 46 54

10.6 10.7 10.8

Specific Gravity

Gel Time

Viscosity

(g/cc)

(min)

(cps)

1.17 1.20 1.24

26.5 21.5 18.5

40 84

Molecular Weight M M„ w

24

468 491 469

972 1293 1086

Table V I . Physical and Mechanical Properties of Flakeboard Phenolic L i g n i n / Resin Phenolic Solids

Resin

Content

Ratio

39 46 54

75/25 75/25 75/25


MOR

(psi)

(psi)

72 66 57

6849 6413 5639

MOE (10

3

IB

psi) (psi)

817 853 723

60 57 49

MOR (psi) 3867 3594 3592

MOE (10

3

L E TS

psi) (%)

436 415 392

0.29 0.29 0.29


WA

(%)

(%)

36 36 35

105 105 110

8.

HSE AND HONG

Phenol-Formaldehyde

109

Copolymer


Conclusions P e r f o r m a n c e o f l i g n i n - p h e n o l i c resin b o n d e d flakeboard is r e l a t e d t o m o l a r r a t i o of f o r m a l d e h y d e t o p h e n o l , a m o u n t o f s o d i u m h y d r o x i d e c a t a l y s t , a n d the solids content o f the b l e n d e d p h e n o l i c resins. A t a 2 5 / 7 5 ( w / w ) m i x t u r e o f p h e n o l i c r e s i n / m e t h y l o l a t e d l i g n i n , the blends f o r m u l a t e d w i t h a p h e n o l / f o r m a l d e h y d e r a t i o o f 1:3 c o n s i s t e n t l y resulted i n higher b o n d s t r e n g t h , lower thickness s w e l l , a n d s m a l l e r l i n e a r e x p a n s i o n . G l u e b o n d performance i m p r o v e d as t h e phen o l / N a O H r a t i o increased f r o m 1:0.2 t o 1:0.7. F u r t h e r increases i n s o d i u m h y d r o x i d e adversely affected p a n e l properties. T h e b o n d s t r e n g t h decreased s l i g h t l y as the resin solids content increased. S t r u c t u r a l flakeboard panels w i t h acceptable s t r e n g t h a n d d u r a b i l i t y c a n b e m a d e u s i n g m e t h y l o l a t e d l i g n i n as 75 percent replacement for p h e n o l i c resins.

Literature Cited

1. Falkehag, S.I. J. Polym. Sci. Appl. Polym. Symp. 1975, 28, 247-257. 2. Holderby, J . M . ; Olson, H.S.; Wegener, W . H . Tappi 1967, 50(9), 92A-94A. 3. Ludwig, G . H . ; Stout, A . W . U.S. Patent 3 658 638, 1972. 4. Enkvist, T. U.S. Patent 3 864 291, 1975. 5. Forss, K . ; Fuhrmann, A . Paperi ja Puu 1976, 11, 817-824. 6. Dolenko, A.J.; Clark, M . R . For. Prod. J. 1978, 28(8), 41-46. 7. Muller, P.C.; Kelley, S.S.; Glasser, W . G. J. Adhesion 1984, 17, 185-206. 8. Calve, L . ; Shields, J . A . Development of Lignin Adhesives. Project C-209. F O R I N T E K Canada Corp. 1982.

Final Report, E N F O R

9. Navas, Alberto A . J. of Liquid Chromatography, 1982, 5(3), 413-423. 10.

Chen, C . C . ; Zhao, L . - W . ; Gratzl, J.S.; Hse, C . - Y . Utilization of Kraft Lignin as Adhesive for the Manufacture of Reconstituted Wood. Final Report FS-SO-4701-19-83-004, 1987.

11.

Duval, M.; Bloch, B.; Kohn, S. J. of Appl. Polym. Sci. 1972, 16, 1585-1602.

12. Rudin, Alfred; Fyfe, C . A . ; Vines, S.M. J. Appl. Polym. Sci. 1983, 28, 2611-2622. 13.

Tsuge, Morio. Nippon SetChaku Kyokai Shi. 1976, 12(7), 256-264.

14. Wagner, G.R.; Greff, R . J . J. Polym. Sci. 1971, P a r t A-1 (9), 2193-2207. 15.

Hse, C . Y . For. Prod. J., 1972, 22(9), 104-108.

R E C E I V E D May 27,

1988


Adhesives from Renewable Resources - American Chemical Society

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