Adhesives from Renewable Resources - American Chemical Society

Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch007

Chapter 7 Soda Bagasse Lignin Adhesives for Particleboard Preliminary Results Antonio Pizzi, Flora-Ann Cameron, and G e r r i t H. van der K l a s h o r s t National T i m b e r Research Institute Council for Scientific and Industrial Research P . O . Box 395, Pretoria 0001 Republic of South Africa

The development and application of low-cost adhesives for interior-gradeparticleboard and for exterior-grade structural glulam derived from soda bagasse lignin are very advanced. Laboratory results and optimum conditions of application of these adhesives for particleboard manufacture have been evaluated. The results satisfy the requirements of the relevant standard specifications. This research project is now at the pilot-plant stage, and initial tests indicate that considerable potential exists for commercial utilization of these types of grass lignins. M a n y examples o f l i g n i n - b a s e d w o o d adhesives have been presented i n the scientific l i t e r a t u r e i n the last few decades ( i ) . W h i l e u n d o u b t e d l y m a n y interesting adhesive f o r m u l a t i o n s a n d uses have been devised, t h e l i g n i n - b a s e d adhesives t h a t have been proposed o r even i n d u s t r i a l l y used for l i m i t e d periods o f t i m e have always suffered f r o m some serious d r a w b a c k s , sometimes t e c h n i c a l , sometimes economical. C e r t a i n l y , t h e most w i d e l y investigated avenue is t h e u t i l i z a t i o n o f l i g n i n i n phenol-formaldehyde ( P F ) w o o d adhesives. However, t o date n o i n d u s t r i a l l i g n i n has f o u n d a p p l i c a t i o n i n these p r o d u c t s i n such a m a n n e r t h a t t h e l i g n i n c o u l d s u b s t i t u t e for the m a j o r p o r t i o n o f the s y n t h e t i c r e s i n . T h i s is due t o t h e low n u m b e r o f sites o n t h e l i g n i n fragments t h a t are reactive t o f o r m a l d e h y d e under a l k a l i n e - c a t a l y z e d c o n d i t i o n s . T h i s c o n s t r a i n t h a s l e d t o a n u m b e r o f i n n o v a t i o n s t o increase t h e n u m b e r o f reactive sites o n t h e l i g n i n fragments. D e m e t h y l a t i o n o f the m e t h o x y groups o f t h e l i g n i n , for e x a m p l e , affords 3,40097-6156/89/0385-0082$06.00/0 ·

1989 American Chemical Society

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

7.

83

Soda Bagasse Lignin Adhesives

P i z z i ET A L .

d i h y d r o x y p h e n y l p r o p a n o i d structures (see F i g u r e 1). T h e 2- a n d 6-positions o n these u n i t s are s i t u a t e d ortho a n d para to the n e w l y i n t r o d u c e d a r o m a t i c 3h y d r o x y l g r o u p a n d thus y i e l d the required r e a c t i v i t y (2).

Alternatively, lignin

fragments o f a h i g h m o l e c u l a r mass c a n be separated f r o m those of low m o l e c u l a r mass b y u l t r a f i l t r a t i o n (3).

T h e s e m o d i f i c a t i o n s a g a i n have some d r a w b a c k s ,

such as cost or the fact t h a t o n l y p a r t of the l i g n i n source is u t i l i z e d . R e c e n t l y , however, a n i n d u s t r i a l l i g n i n was described t h a t shows a m u c h larger n u m b e r of sites reactive t o f o r m a l d e h y d e t h a n the average i n d u s t r i a l l i g n i n


(4).

T h i s l i g n i n is o b t a i n e d f r o m the s o d a p u l p i n g of sugarcane bagasse.

The

i n d u s t r i a l p u l p i n g of bagasse is done at the r e l a t i v e l y m i l d c o n d i t i o n s o f 170 ° C for o n l y 15 m i n u t e s ( t y p i c a l l y also employed for other grassy m a t e r i a l s s u c h as s t r a w ) .

T h e bagasse l i g n i n is consequently not extensively condensed

and

c o n t a i n s a h i g h n u m b e r of u n s u b s t i t u t e d 5-positions ( F i g u r e 1) t h a t c a n react w i t h formaldehyde.

I n T a b l e I, the m o l e c u l a r f o r m u l a a n d n u m b e r o f u n s u b -

s t i t u t e d 5-positions o n p h e n o l i c p h e n y l p r o p a n o i d u n i t s of s o d a bagasse l i g n i n are c o m p a r e d w i t h those of a t y p i c a l k r a f t l i g n i n a n d a n extensively

condensed

s o d a / A Q hardwood lignin.

T a b l e I. Different L i g n i n M o l e c u l a r F o r m u l a e (4) Reactive Lignin

Molecular Formulae

Points Per C

9

Soda/ AQ

C H^ H« Oo.56(OH)^ (OH)« 9

1 0

9 6

7 7

(OMe)

5 4

1 2 9

0.1

Soda bagasse

C H^ 9

0 5

H«3 Oo.63(OH)^ 6

6 3

(OH)«

7 6

(OMe

) . 0

8 5

0.7

Kraft pine

C H^ 9

4 8

H«

7 5

Oo.

3 9

(OH)^

6 2

(OH)«

9 9

( O M e VeeSo.os

0.3

T h e u n i q u e h i g h r e a c t i v i t y of the i n d u s t r i a l bagasse l i g n i n was s u b s e q u e n t l y u t i l i z e d i n the development o f c o l d - c u r i n g adhesives ( 5 ) . B o t h c o l d - s e t t i n g a n d f a s t - s e t t i n g w o o d adhesives were developed a n d are c u r r e n t l y b e i n g e v a l u a t e d o n p i l o t p l a n t scale. A s u m m a r y of the s t r e n g t h properties o f some of the c o l d s e t t i n g bagasse l i g n i n adhesives is l i s t e d i n T a b l e I I . T h e a b i l i t y o f t h i s l i g n i n to s u b s t i t u t e for three-quarters of the solids i n the c o l d - s e t t i n g adhesives c l e a r l y underlines the c o m p a t i b i l i t y of the reactive bagasse l i g n i n w i t h P F resins.



84

ADHESIVES F R O M RENEWABLE RESOURCES

and

= P o s s i b l e l i n k a g e to o t h e r phenyl propanoic! u n i t s

F i g u r e 1. P h e n y l propanoic! u n i t s of l i g n i n .


7.

85


Pizzi E T A L .

In t h i s chapter, the development of a t h e r m o s e t t i n g adhesive f r o m s o d a bagasse l i g n i n is described. T h e research has concentrated o n the development of i n t e r i o r - g r a d e adhesives for p a r t i c l e b o a r d . T h e l o c a l m a r k e t for exterior b o a r d s is s m a l l e r t h a n t h a t for the interior panels, a n d adhesives for exterior b o a r d s are a l r e a d y covered b y a n excellent range of t a n n i n - b a s e d adhesives.

T a b l e I I . S t r e n g t h of C o l d - S e t t i n g W o o d A d h e s i v e s P r e p a r e d Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch007

f r o m I n d u s t r i a l Bagasse L i g n i n Adhesive

D r y Test Wood Failure

Strength (N)

(%)

24-hour C o l d Soak Wood Strength Failure (N) (%)

(5) 6-hour B o i l Wood Strength Failure (N) (%)

Cold set

1

BS

2

Fingerjoint 3

SABS 1

3,338

33

2,473

95

1,870

80

-

-

2,200

75

1,500

75

2,250

100

2,343

100

2,237

100

-

-

1,400 2,800

90-100 30-40

1,400 2,800

90-100 30-40

4

L i g n i n - b a s e d c o l d - s e t t i n g adhesives evaluated o n beech s t r i p s ( 7 4 % l i g n i n ;

2 6 % resorcinol). 2

B S 1204-1965, p a r t 2 specification for s y n t h e t i c adhesives for m a r i n e - g r a d e

wood. 3

L i g n i n - b a s e d fast-set as component Β a n d c o m m e r c i a l P R F as c o m p o n e n t A

(1:1); e v a l u a t e d by 4

S A B S 970-1976

Experimental

finger-joint.

finger-joint

requirement.

Methodology

L i g n i n was o b t a i n e d f r o m a n i n d u s t r i a l s o d a bagasse spent l i q u o r as before ( 5 ) . T h e l i g n i n was i n i t i a l l y e v a l u a t e d as a t h e r m o s e t t i n g adhesive b y the beech s t r i p test. P r i o r to its a p p l i c a t i o n as adhesive, the l i g n i n was reacted w i t h f o r m a l d e hyde i n a l k a l i at t e m p e r a t u r e s below 60 ° C to afford a h y d r o x y m e t h y l a t e d l i g n i n (6). T h e h y d r o x y m e t h y l a t i o n r e a c t i o n was done at p H 12 a n d 13, a n d samples of the r e a c t i o n m i x t u r e s were evaluated o n beech strips w i t h overlaps of 25 χ 25 m m , cured for 4 hours at 90 ° C a n d 1 2 % e q u i l i b r i u m m o i s t u r e content. One-layer p a r t i c l e b o a r d s were prepared f r o m E u c a l y p t u s chips w i t h a resin content of 10 percent o n d r y chips. T h e boards were f o r m e d 1 2 - m m t h i c k o n a l a b o r a t o r y press w i t h the press platens at 170 ° C for press t i m e s of 15 m i n u t e s .


86


T h e final density of the boards was a p p r o x i m a t e l y 700 k g / m . Different r a t i o s of c o m m e r c i a l P F a n d U F resins were a d d e d to h y d r o x y m e t h y l a t e d l i g n i n . 3

Results and Discussion


T h e results presented i n F i g u r e 2 clearly i n d i c a t e d t h a t the bagasse l i g n i n can be used t o prepare a t h e r m o s e t t i n g adhesive of h i g h s t r e n g t h . T h e s t r e n g t h of the adhesive increased w i t h increasing h y d r o x y m e t h y l a t i o n t i m e s , w h i c h were as l o n g as 15 h o u r s . I m p r o v e m e n t of the performance of the l i g n i n adhesive was subsequently a t t e m p t e d by the a d d i t i o n of several c r o s s l i n k i n g agents. T h e s e m a t e r i a l s are capable of f u r t h e r i m p r o v i n g the degree of c r o s s l i n k i n g of the l i g n i n adhesive ( T a b l e I I I ) . T h e a d d i t i o n of p h e n o l ( T a b l e I I I , entries 1-3) resulted o n l y i n s m a l l increases i n the d r y s t r e n g t h results. T h e a d d i t i o n of a P F resol resin to fixed-time h y d r o x y m e t h y l a t e d bagasse l i g n i n resulted i n a s u b s t a n t i a l i m p r o v e m e n t i n the adhesive performance ( T a b l e I I I , entries 13-18), whereas, a d d i t i o n of p h e n o l to the P F r e s i n / l i g n i n c o m b i n a t i o n d i d n o t i m p r o v e the d r y s t r e n g t h of the b o n d e d j o i n t s over the c o n t r o l . T h e s t r e n g t h of the adhesive o b t a i n e d by the a d d i t i o n of 3 3 % resol resin b y mass (ent r y 15) p r a c t i c a l l y complies w i t h requirements of the S o u t h A f r i c a n a n d B r i t i s h S t a n d a r d specifications for i n t e r i o r t y p e s y n t h e t i c adhesives for w o o d , a n d i t is not t o o far f r o m the exterior-grade requirements. T h e a d d i t i o n of a resol resin to h y d r o x y m e t h y l a t e d bagasse l i g n i n therefore constitutes a versatile adhesive p r e p a r a t i o n . E m p l o y i n g more resol resin i n the adhesive m i x t u r e , o n the other h a n d , results i n a t h e r m o s e t t i n g adhesive t h a t m a r g i n a l l y complies w i t h the S o u t h A f r i c a n a n d B r i t i s h specification for exterior-grade resins. T h e a d d i t i o n of the n i t r o g e n - c o n t a i n i n g c r o s s l i n k i n g agents, m e l a m i n e , u r e a , a n d urea-formaldehyde ( U F ) resin, resulted i n a s u b s t a n t i a l increase i n s t r e n g t h ( T a b l e I I I , entries 7-12). T h e best results were o b t a i n e d b y the m e l a m i n e crosslinked adhesives. T h e a d d i t i o n of 3 3 % m e l a m i n e resulted i n a n adhesive w i t h s t r e n g t h values w e l l w i t h i n exterior-grade adhesive specifications. F u r t h e r o p t i m i z a t i o n of the l i g n i n adhesive was a t t e m p t e d b y m i x i n g different p r o p o r t i o n s of a c o m m e r c i a l P F resin w i t h h y d r o x y m e t h y l a t e d s o d a bagasse l i g n i n a n d p a r a f o r m a l d e h y d e as hardener. It must be p o i n t e d out t h a t a c o m m e r c i a l P F resin has not been engineered to f u n c t i o n as a l i g n i n adhesive fortifier b u t t o cure by itself. It is thus not a n i d e a l f o r t i f y i n g r e s i n . T h e results presented i n F i g u r e 3 i n d i c a t e d t h a t o p t i m u m s t r e n g t h was o b t a i n e d at 60:40 P F . l i g n i n . T h i s is, however, not i d e a l as a n e c o n o m i c p r o p o s i t i o n . E c o n o m i c considerations d i c t a t e d t h a t a lower level of c o m m e r c i a l P F f o r t i f i c a t i o n h a d t o be e m p l o y e d for the screening w o r k .


7.

Pizzi E T A L .


87

WOOD / STRENGTH FAILURE / (Nî


100% /3000-τ

F i g u r e 2. S t r e n g t h a n d w o o d failures o b t a i n e d o n beech s t r i p s g l u e d w i t h l i g n i n h y d r o x y m e t h y l a t e d for different times at p H 13 or 12.


88



T a b l e I I I . Beech S t r i p Strengths o f H y d r o x y m e t h y l a t e d

Bagasse

L i g n i n A d h e s i v e s C r o s s l i n k e d w i t h V a r i o u s Fortifiers Percentage Fortifier Entry

1

Fortifier

Phenol

2 3 4 5 6

Melamine

7

Urea

8 9 10 11 12

U F resin

13

P F resol

A d h e s i v e S t r e n g t h (% W o o d F a i l u r e )

O n Resin Solids

Dry

(%) 8

2,480 ( 96)

15 25

2,290 ( 76) 2,300 ( 81)

1,020 ( 5) 1,040 ( 5) 820 ( 5)

1,160 ( 0) 0(0) 0(0)

11 20 33

2,970 (100) 3,150 (100) 2,700 (100)

2,250 ( 98) 2,170 (100) 2,730 ( 93)

670 ( 2) 1,070 (15) 1,450 (28) 130 ( 0)

Soak

Boil

5

2,510 ( 56)

1,180 ( 17)

10 16

2,570 ( 60) 2,680 ( 90)

1,270 ( 22) 1,370 ( 48)

0(0) 0(0)

11 20 33

2,550 ( 85) 2,830 (100) 2,620 (100)

1,480 ( 2) 1,620 ( 35) 140 ( 97)

0(0) 0(0) 0(0)

20

2,970 ( 86)

1,780 ( 32)

1,259 (66)

25 33

2,720 ( 99)

1,920 ( 64)

1,350 (24)

2,930 (100)

2,090 ( 83)

1,490 (75)

resin 14 15


7.

Pizzi E T A L .


89

T a b l e I I I (cont.). Beech S t r i p Strengths of H y d r o x y m e t h y l a t e d Bagasse L i g n i n A d h e s i v e s C r o s s l i n k e d w i t h V a r i o u s Fortifiers Percentage Fortifier Entry

Fortifier

Solids Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: December 31, 1989 | doi: 10.1021/bk-1989-0385.ch007

A d h e s i v e S t r e n g t h (% W o o d F a i l u r e )

O n Resin Dry

Soak

Boil

(%) 16 17

P F resol resin +15% phenol

18 19

20

21

Hydroxymethylated lignin control w i t h no fortifier National specification (for exterior applications)

10

2,190 ( 89)

990 ( 7)

15

1,960 ( 53)

1,180 ( 12)

25

2,230 ( 61)

1,320 ( 16)

0

2,110 ( 58)

130 ( 0)

2,500 ( 75)

2,200 ( 75)

710 ( 2) 1,120 1,410

(11) (25)

0(0)

1,500

(75)

British specification (for exterior

"(-)

2,200 ( - )

1,450

(-)

applications)

T h e bagasse l i g n i n adhesives were subsequently e v a l u a t e d as p a r t i c l e b o a r d adhesives. T h e results l i s t e d i n T a b l e I V clearly i n d i c a t e t h a t the l i g n i n - b a s e d adhesives do p r o v i d e proper b o n d i n g of p a r t i c l e b o a r d . T h e larger p r o p o r t i o n of l i g n i n used w i t h the P F resin, however, showed a decrease i n i n t e r n a l b o n d s t r e n g t h ( T a b l e I V , entries 1 a n d 2). T h e reverse was evident for the U F l i g n i n adhesives. T h e p o o r performance of the adhesive m i x t u r e c o n t a i n i n g the largest p r o p o r t i o n of U F resin can p r o b a b l y be a t t r i b u t e d to d e g r a d a t i o n of the U F c o m p o n e n t due to the l o n g press times of 15 m i n u t e s .


90



100

Ο

90 10

80 20

70 30

60 AO

50 50

Adhesives from Renewable Resources - American Chemical Society

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