Lignin-Derived Polyols, Polyisocyanates, and ... - ACS Publications

21 Lignin-Derived Polyols, Polyisocyanates, and Polyurethanes 1

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Downloaded by UNIV OF PITTSBURGH on September 24, 2013 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0172.ch021

W. G. GLASSER, Ο. H.-H. HSU , D. L. REED , R. C. FORTE , and L. C.-F. WU Department of Forest Products and Department of Chemical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Lignin. Lignin is a natural polymer of plants which is ex ceeded in abundance only by cellulose. Plants gain the ability of lignifying when they acquire the need for developing "woody tissues." This need may be triggered by the requirement for mechanical support (reinforcing fibers by binding them together with a glue-like substance, lignin); the requirement for a sealed water-conducting system; or the requirement for an im proved natural decay resistance. In response to such require ments, lignin is deposited as a polyphenolic, three-dimensionally cross linked network polymer by maturing plants. Lignin contents range from 20 to 30% by weight of plant materials, or between 30 and 45% by enthalpy (1,2). In the common process of making paper by chemical means, lignin is separated from mostly cellulosic fibers by dissolution processes which often involve structural modification and macromolecular breakdown (1). Pulp and paper mills generate approxi mately 24 million tons of dissolved lignin annually in the Uni ted States (2,3,4), and this compares to a combined total pro duction of all synthetic organic materials of approximately 18.5 million tons per year in the U.S. in 1975 (5). Only about 3%, or 1.5 billion pounds per year, of solubilized lignin from spent pulping liquors are marketed, mostly (ca. 95%) as lignin sulfonic acids for roughly 6-8φ per pound, and the remaining 5% as kraft lignin for approximately 20φ per pound (6). T o t a l market value f o r l i g n i n products i s estimated at roughly $ 1 0 0 m i l l i o n p e r year i n the United S t a t e s ( 6 ) . The supply o f k r a f t l i g n i n i s l i m i t e d by the need o f pulp m i l l s t o i n c i n e r a t e t h e i r l i g n i n and chemicals c o n t a i n i n g spent 1 2 3

Current address: Masonite Corp., St. Charles, IL. Current address: Hammermill Paper Co., Erie, PA. Current address: Kimberly-Clark of Canada, Ltd., St. Catherines, Ontario. 0097-6156/81/0172-0311 $06.75/0 © 1981 American Chemical Society In Urethane Chemistry and Applications; Edwards, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


312

URETHANE CHEMISTRY AND APPLICATIONS

p u l p i n g l i q u o r s f o r the purpose o f r e c o v e r i n g i n o r g a n i c p u l p i n g chemicals. Thus, the p r a c t i c a l a v a i l a b l e supply o f k r a f t l i g n i n i n the United S t a t e s i s probably l e s s than 2 m i l l i o n tons per year. However, a d d i t i o n a l sources o f l i g n i n are l i k e l y t o become a v a i l a b l e i n the f u t u r e i f any o f the novel biomass-to-ethanol conversion processes designed f o r a g r i c u l t u r a l r e s i d u e s , waste paper, newsprint, o r v a r i o u s types o f wood sources, ever m a t e r i a l i z e . Such l i g n i n sources w i l l probably be s i m i l a r i n nature to k r a f t l i g n i n ( 6 ) . PoZyuJizthan&A. Polyurethanes are a v e r s a t i l e group o f p o l y mers which span a wide range o f p h y s i c a l p r o p e r t i e s and a p p l i c a t i o n s . Polyurethane markets are p r e d i c t e d to grow at an annual r a t e o f 7-10% i n the next 10 years ( 7 ) . Many polyurethane a p p l i c a t i o n s are f o r network polymers, and these have been reviewed elsewhere i n t h i s t r e a t i s e ( 7 ) . There have been s e v e r a l accounts i n the l i t e r a t u r e f o r the involvement o f wood o r wood components i n polyurethane systems. Thus, Senzyu and Ishikawa o x y a l k y l a t e d wood w i t h ethylene oxide i n the presence o f a l k a l i i n 1948 ( 8 ) . Using a p p r o p r i a t e l i g n i n l i k e model compounds, Ishikawa, 0ki~and F u g i t a (9) observed t h a t p h e n o l i c h y d r o x y l groups r e a c t q u a n t i t a t i v e l y w i t h ethylene oxide i f the s i d e chains do not c o n t a i n carbonyl groups or other unsat u r a t e d m o i e t i e s . P h e n o l i c h y d r o x y l groups o f model compounds w i t h unsaturated s i d e chains e x h i b i t e d great r e s i s t a n c e to hyd r o x y l - e t h y l a t i o n , probably r e f l e c t i n g the reduced n u c l e o p h i l i c i t y o f the r e s u l t i n g phenoxide anions. In another s e r i e s o f experiments w i t h model compounds, K r a t z l e t a l . (10) s t u d i e d the r e a c t i v i t y o f the v a r i o u s f u n c t i o n a l groups which are present i n l i g n i n and which may r e a c t w i t h isocyanate and d i i s o c y a n a t e s . Since the a l c o h o l i c and p h e n o l i c h y d r o x y l groups d i f f e r i n react i v i t y towards i s o c y a n a t e s , K r a t z l et a l . (10) were able t o prepare both a mono- and diurethane from g u a i a c y l propanol-2 u s i n g a phenyl i s o c y a n a t e . With hexamethylene d i i s o c y a n a t e , slower r e a c t i o n s were observed and s e l e c t i v i t y between a l c o h o l i c and p h e n o l i c h y d r o x y l model compounds y i e l d e d o n l y p o l y m e r i c o i l y or t a r r y products. However, naphthalene d i i s o c y a n a t e y i e l d e d d i urethanes i n every case. When these s t u d i e s were a p p l i e d t o t e c h n i c a l h y d r o l y s i s l i g n i n s , r e a c t i o n s w i t h i s o c y a n a t e s were d e s c r i b e d as very poor. This r e a c t i o n behavior was i n c o n t r a s t to the b e h a v i o r o f k r a f t and s u l f i t e l i g n i n s i n combinations w i t h commercial p o l y o l s (11,12). Moorer, Dougherty and B a l l (13) have employed l i g n i n i n the formation o f polyurethane foams by d i s s o l v i n g i t i n g l y c o l s which are r i c h i n a c t i v e h y d r o x y l groups, and then r e a c t i n g i t w i t h d i i s o c y a n a t e s . The r e a c t i o n was d e s c r i b e d as the isocyanate a c t i n g as a b r i d g e substance l i n k i n g the two k i n d s o f p o l y o l together. The p h e n o l i c h y d r o x y l groups i n l i g n i n were assumed to p l a y a key r o l e i n t h i s r e a c t i o n . However, r e s u l t s showed t h a t most l i g n i n by-products y i e l d e d urethanes o f i n f e r i o r qual i t y when compared w i t h products made w i t h p o l y e t h y l e n e g l y c o l .

In Urethane Chemistry and Applications; Edwards, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


21.

GLASSER ET AL.

Polyols, Polyisocyanates, and Polyurethanes 313

The conversion o f the p h e n o l i c h y d r o x y l groups t o a l i p h a t i c hy d r o x y l f u n c t i o n s was recognized as an important step toward the a c t i v a t i o n o f f u n c t i o n a l hydroxyl groups by A l l a n (14) and by C h r i s t i a n e t a l . (15) . Reactions w i t h ethylene o x i d e , propylene o x i d e , and an a l k y l s u l f i d e were shown t o produce o i l s w i t h v i s c o s i t i e s and h y d r o x y l numbers s u i t a b l e f o r mixing and r e a c t i n g w i t h d i i s o c y a n a t e s i n the formation o f r i g i d polyurethane foams. B r i t t l e n e s s , h i g h water a b s o r p t i o n and low s t r e n g t h appeared t o c o n s t i t u t e the main drawbacks o f the r e s u l t i n g o x y a l k y l a t e d l i g nin-urethane foams. These d i f f i c u l t i e s could l a r g e l y be over come by a c a r b o x y l a t i o n ρretreatment w i t h maleic anhydride (16). C a r b o x y l - r i c h l i g n i n s were converted i n t o e s t e r - r i c h p o l y o l s by o x y a l k y l a t i o n , and these were employed f o r the p r e p a r a t i o n o f polyurethane foams (17), adhesives, and coatings (18) w i t h ac ceptable p r o p e r t i e s . The enrichment o f l i g n i n w i t h c a r b o x y l i c f u n c t i o n a l i t y has a l s o been accomplished by carboxymethylation w i t h bromoacetic a c i d (19). Approach and ÛbjZctiveA. In g e n e r a l , i n h e r e n t disadvantages o f l i g n i n i n regard t o i t s u t i l i z a t i o n f o r m a t e r i a l s concern (a) i t s r e s i s t a n c e t o degradative d e p o l y m e r i z a t i o n t o low molecular weight chemical f e e d s t o c k s , and (b) i t s s t r u c t u r a l complexity which presents d i f f i c u l t i e s i n a l t e r i n g , c o n t r o l l i n g , and manip u l a t i n g the chemical and p h y s i c a l p r o p e r t i e s o f polymeric l i g n i n - d e r i v e d m a t e r i a l s v i a s t r u c t u r a l f e a t u r e s . In a d d i t i o n , polymeric uses o f l i g n i n are burdened by an i n h e r e n t resource v a r i a b i l i t y , which, when i t f i n d s entrance t o end product char a c t e r i s t i c s , gives r i s e t o i n t o l e r a b l e performance v a r i a t i o n s (2). Therefore, a l i g n i n u t i l i z a t i o n approach was e x p l o r e d which promised t o s a t i s f y the f o l l o w i n g p r e r e q u i s i t e s : (a) t h a t l i g n i n be used i n i t s polymeric form f o r products which depend i n t h e i r performance on typical Hgviin ckanact&LU>tZcA ( s t r u c t u r a l r e i n forcement, a n t i o x i d a n t behavior, e t c . ) ; (b) t h a t the chemical treatment o r treatments i n v o l v e d i n the u t i l i z a t i o n scheme amount to a homogmation capable o f a l l e v i a t i n g some o f t h e n a t u r a l v a r i a b i l i t i e s ; (c) t h a t the chemical m o d i f i c a t i o n ( s ) i n t r o d u c e s a measure o f f l e x i b i l i t y w i t h regard t o end product c h a r a c t e r i s t i c s , such t h a t i t becomes p o s s i b l e t o taltoK-makd l i g n i n - d e r i v e d m a t e r i a l s f o r s p e c i f i c end uses; and (d) t h a t the end product type belongs t o a gfiowtk ma/ikoX i n which l i g n i n can conquer a s i z a b l e market share without d i s p l a c i n g other raw m a t e r i a l s . Various types o f l i g n i n - d e r i v e d polyurethane products and t h e i r p r e c u r s o r s appeared t o s a t i s f y these c o n s t r a i n t s . This paper summarizes experimental e f f o r t s aimed a t developing l i g n i n d e r i v e d p o l y o l , p o l y i s o c y a n a t e , and polyurethane products. Results and D i s c u s s i o n LZgyvin-OoXiv^d VolyolM. Polyhydroxy ( p o l y o l ) components may be prepared from l i g n i n u s i n g a one-, two-, o r t h r e e - s t e p modi-



314

URETHANE CHEMISTRY AND

APPLICATIONS

f i c a t i o n procedure i n v o l v i n g copolymerization w i t h maleic anhyd r i d e ( o p t i o n a l ) , s a p o n i f i c a t i o n or s o l v e n t e x t r a c t i o n ( o p t i o n a l ) , and o x y a l k y l a t i o n w i t h propylene oxide. The general react i o n sequence i s i l l u s t r a t e d i n Figure 1. The r e s u l t o f t h i s l i g n i n m o d i f i c a t i o n i s a l i q u i d p o l y o l w i t h unique f u n c t i o n a l i t y i n regard to r e a c t i v i t y w i t h isocyanates. This t r a n s f o r m a t i o n o f l i g n i n v i a s e v e r a l chemical m o d i f i c a t i o n steps o f f e r s f l e x i b i l i t y i n terms o f degree of c a r b o x y l a t i o n ; c o n c e n t r a t i o n o f e s t e r groups; concentration of a l i p h a t i c e t h e r s ; r a t i o of aromatic vs. a l i p h a t i c polymer components; and extent of network vs. chain polymer c o n s t i t u e n t s . P o l y o l c h a r a c t e r i s t i c s may be i n f l u e n c e d by v a r i a t i o n s i n the r e a c t i o n o f l i g n i n with maleic anhydride; by the method of copolymer p u r i f i c a t i o n ; and by the c o n d i t i o n s o f the o x y a l k y l a t i o n r e a c t i o n . Copolymer p u r i f i c a t i o n may i n v o l v e solvent e x t r a c t i o n , s a p o n i f i c a t i o n (NaOH), or r e p r e c i p i t a t i o n ; and o x y a l k y l a t i o n may be v a r i e d v i a r e a c t i o n time and/or temperature, type o f c a t a l y s t ( a c i d i c or b a s i c ) , and presence o f i n i t i a t o r (ethylene g l y c o l ) . The e f f e c t o f the maleic anhydride content i n the copolym e r i z a t i o n r e a c t i o n mixture on the degree of c a r b o x y l a t i o n i s i l l u s t r a t e d by the data i n Table I . C a r b o x y l a t i o n of k r a f t l i g n i n and l i g n i n s u l f o n a t e s may e a s i l y reach l e v e l s o f 0.7 to 0.8 maleic anhydride u n i t s per l i g n i n - b u i l d i n g Cg-unit, i f the l i g n i n to maleic anhydride r a t i o i n the r e a c t o r increases to 2:1. The degree of copolymerization of the carboxylated l i g n i n w i t h propylene oxide, and the degree of homopolymerization o f propylene oxide, can be expected to vary w i t h the r e a c t o r pressure at the end of the o x y a l k y l a t i o n r e a c t i o n . A t y p i c a l pressure-temperature diagram of t h i s r e a c t i o n i s presented i n Figure 2. P o l y m e r i z a t i o n u s u a l l y commences between 165 and 185°C as i s i n d i c a t e d by a r e t a r d a t i o n of the temperature r i s e and a d i s t i n c t peaking o f the r e a c t o r pressure. The e n t i r e r e a c t i o n i s complet e d a f t e r three to four hours, when the f i n a l pressure d e c l i n e s to around 180 p s i . Parameters which i n f l u e n c e the f u n c t i o n a l i t y of the r e s u l t i n g p o l y o l s i n c l u d e the r a t i o o f copolymer to propylene oxide, and the presence and concentration o f c a t a l y s t and i n i t i a t o r . The i n f l u e n c e of those parameters on hydroxyl number, carboxyl number, and p o l y o l y i e l d are summarized i n Tables I I and I I I . Low copolymer to propylene oxide r a t i o s make i t o b v i o u s l y d i f f i c u l t to t o t a l l y l i q u e f y l i g n i n , Table I I . Such c o n d i t i o n s , however, seem to favor p o l y o l s w i t h low t o t a l hydroxyl numbers. The o x y a l k y l a t i o n r e a c t i o n appears to r e q u i r e c a t a l y z a t i o n by z i n c c h l o r i d e or base c a t a l y s t s i n concentrations o f about 10% or l e s s f o r s u c c e s s f u l completion. The presence o f an i n i t i a t o r (ethylene g l y c o l ) helps completion o f the r e a c t i o n i n p a r t i c u l a r when the unhydrolyzed copolymer i s used as substrate (Table I I I ) . The degree to which p h y s i c a l p r o p e r t i e s o f p o l y o l s depend on the nature and p r i o r treatment o f the l i g n i n employed i n the o x y a l k y l a t i o n r e a c t i o n i s i n d i c a t e d i n Table IV. P o l y o l s pre-


21.

Polyols, Poly isocyanates, and Polyurethanes

GLASSER ET AL.

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Ratio of Lignin to M a l e i c Anhydride

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Semi-Empirical Formula

Semi-Empirical Formulas and M a l e i c A c i d Contents o f L i g n i n s and L i g n i n - M a l e i c Anhydride Copolymers

Table I

0.79

0.48

0.29

0.27

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0.67

0.38

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Content o f Maleic Acid/C


9

GLASSER ET AL.



21.

Figure 2. Pressure-temperature diagram for an oxyalkylation reaction of a c boxylated kraft lignin.


318



Table I I P o l y o l F u n c t i o n a l i t y i n R e l a t i o n t o Method o f P r e p a r a t i o n - R a t i o o f L i g n i n Copolymer t o Propylene Oxide ( A l l Reactions: 4 h r s . r e a c t i o n time; temperature: 200-250°C)

Lignin Preparation Unhydrolyzed K r a f t L.-M.A. (2:1) Copolymer

Ratio o f Propylene Oxide to L i g n i n Copolymer

Catalyst System A B 1

z

OH Number

COOH Number

9

333

12: 1

X

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309±2%

11±2%

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430±2%

13±12%

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X

tt

6:13

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X

tt

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tt

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Unhydrolyzed L. S u l f o nates-M.A. (2:1) Copolymer

10: 1

X

3

X X

X

362

12

289

26

307

18

167

36

260

32

509

9

C a t a l y s t System A: 10% c a t a l y s t ( Z n C l ) and 10% i n i t i a t o r (ethylene g l y c o l ) . 2

2

C a t a l y s t System B: 10% c a t a l y s t and 30% i n i t i a t o r .

3

R e s u l t e d i n incomplete s o l u b i l i z a t i o n o f the lignin-M.A. copolymer.


21.

GLASSER ET AL.

Polyols, Ρolyisocyanales, and Polyurethanes

319


Table I I I P o l y o l F u n c t i o n a l i t y i n R e l a t i o n t o Method o f P r e p a r a t i o n I n i t i a t o r and C a t a l y s t Concentrations ( A l l Reactions: 4hrs. r e a c t i o n time; R a t i o o f Propylene Oxide: L i g n i n 10:1; Temperature: 220-250°C) Lignin Preparation Unhydrolyzed K r a f t L.-M.A. ( 2 : 1 ) Copoly mer 1

n2 H

Initiator (%)

Catalyst (%)

OH Number

COOH Number

Polyol Yield

0.8

12

4

0

0

318

3.3

3.3

295

10

0

354

2

11

10

67

If

0

10

419

10

79

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10

10

315

11

72

Il3

10

10

289

26

54

n3

10

30

56

36

19

tt 3

30

10

307

18

74

Reaction time o f 2 h r s . Reaction time o f 6 h r s . Propylene o x i d e : l i g n i n r a t i o 6:1. L i q u i d p o l y o l obtained a f t e r d i s s o l v i n g / s u s p e n d i n g r e a c t o r content i n methanol, f i l t r a t i o n o f methanol s o l u t i o n / s u s p e n s i o n , and evaporation o f f i l t r a t e a t 80°C and 2 5 mm Hg; i n % o f t o t a l r e a c t o r content.


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21.

GLASSER ET AL.

Polyols, Polyisocyanates, and Polyurethanes

321

pared w i t h the hydrolyzed copolymer have apparently a l e s s p o l a r s o l u b i l i t y c h a r a c t e r than those p o l y o l s prepared w i t h the unhyd r o l y z e d copolymer or the uncarboxylated l i g n i n . S i m i l a r d i f f e r ences are detected f o r chemical f u n c t i o n a l i t y , v i s c o s i t y , and c o l o r (Table I V ) . S u i t a b l e l i q u e f a c t i o n d u r i n g o x y a l k y l a t i o n seems to r e q u i r e a r a t i o o f propylene oxide to copolymer (or l i g n i n ) o f 4:1 or g r e a t e r . This epoxide excess p r e s e n t l y c o n s t i t u t e s the g r e a t e s t c o n s t r a i n t f o r o p t i m i z i n g the 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 a polyurethane product. A p o l y o l prepared w i t h such an excess o f propylene oxide w i l l not c o n t a i n more than 25% l i g n i n assuming t h a t a l l propylene oxide polymerizes. LsÎgyLÎn-VQAÂvzd pQ&yZ6ocyanatQj>: E f f o r t s to i n c r e a s e the 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 polyurethane products have concent r a t e d on t r a n s f o r m i n g polymeric l i g n i n s i n t o p o l y i s o c y a n a t e s u s e f u l f o r r e a c t i n g w i t h p o l y o l s . Two a l t e r n a t i v e r e a c t i o n pathways have been explored w i t h the three l i g n i n - l i k e model compounds shown i n Figure 3. These models were v a n i l l i c a c i d or a d e r i v a t i v e t h e r e o f (Model Type A); a d e r i v a t i v e o f t e t r a l i n d i c a r b o x y l i c anhydride (Model Type B); and a d e r i v a t i v e o f a s t y rene-maleic anhydride copolymer (Model Type C). The two r e a c t i o n pathways s t u d i e d i n v o l v e a route from the c a r b o x y l i c a c i d to the isocyanate v i a the a c y l c h l o r i d e and azide (Sodium Azide Pathway, Pathway A ) , Figure 4; and a route from the c a r b o x y l i c a c i d to the isocyanate v i a the hydrazide (Hydrazide Pathway, Pathway Β), Figure 5. The r e a c t i o n s were monitored by i s o l a t i n g the intermediate r e a c t i o n products and c h a r a c t e r i z i n g them by m e l t i n g p o i n t s , elemental composition, or IR s p e c t r o s copy. The sodium azide pathway (Pathway A ) , Figure 4, begins w i t h a t h i o n y l c h l o r i d e treatment o f the f r e e a c i d to form the a c y l c h l o r i d e . Subsequent treatment w i t h sodium azide may i n v o l v e a non-aqueous environment (1,2-dimethoxy ethane, "dry method"), or an aqueous medium ("wet method"). The organic a z i d e i s recovered from the r e a c t i o n mixture and converted i n t o the isocyanate by the C u r t i u s rearrangement. This may be accomplished i n s o l i d form ("dry method"), or i n a non-aqueous s o l v e n t l i k e dioxane or DMF ( " s o l u t i o n method"). The hydrazide pathway (Pathway Β ) , Figure 5, was f i r s t a t tempted by t r e a t i n g the a c y l c h l o r i d e w i t h h y d r a z i n e . Since t h i s r e a c t i o n , however, produced the secondary hydrazide i n almost q u a n t i t a t i v e y i e l d s , t h i s approach was abandoned i n f a v o r o f one employing the methyl e s t e r d e r i v a t i v e . H y d r a z i n o l y s i s o f the e s t e r , formed by r e f l u x i n g the f r e e a c i d i n anhydrous methanol/ H2SO4, proceeded i n dry methanol to the hydrazide i n good y i e l d . Subsequent r e a c t i o n o f the hydrazide w i t h n i t r o u s a c i d , which was generated i n the presence o f the hydrazide i n aqueous acetone/HCl s o l u t i o n at 0-5°C, y i e l d e d the o r g a n i c a z i d e . T h i s , a g a i n , was rearranged e i t h e r dry o r i n s o l u t i o n t o the i s o c y a n a t e .


322


C0 H 2

ΤΥΡΙ:

Λ

CH 0 Downloaded by UNIV OF PITTSBURGH on September 24, 2013 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0172.ch021

3

OR R=H , Ac , C H

3

TYPE C

R=H,Ac,CH

Figure 3.

3

Lignin-like model compounds.

CO CI

C0 H 2

SO CIOCH,

6

*OCH,

OR

OR

aq.NaN,

R=CH or Ac 3

CON,

NCO HEAT

OCH,

OCH, OR

OR

PATHWAY A Figure 4.

Reaction scheme of the sodium azide pathway.


GLASSER ET AL.



21.



324


Model Type A, v a n i l l i c a c i d and i t s a c e t y l a t e d o r methylated d e r i v a t i v e , generated the expected isocyanate without major prob lems e i t h e r v i a the sodium azide o r the hydrazide pathway. Y i e l d s and a n a l y s i s r e s u l t s are summarized i n Table V. IR spec t r a o f the v a r i o u s i n t e r m e d i a r y r e a c t i o n products are given i n Figure 6. Formation o f the organic azide by the wet method from the a c y l c h l o r i d e was s u p e r i o r t o "dry" formation; but h y d r a z i n o l y s i s o f the methyl e s t e r f o l l o w e d by HNO2-treatment worked s a t i s f a c t o r i l y as w e l l . Model Type Β (Figure 3 ) , t e t r a l i n d i c a r b o x y l i c a c i d and i t s d e r i v a t i v e s , f a i l e d t o form a s t a b l e f r e e a c i d . I t s anhydride regenerated c o n s i s t e n t l y from i t s sodium s a l t , which was tempo r a r i l y formed i n aqueous a l k a l i n e s o l u t i o n , upon a c i d i f i c a t i o n . Therefore, conversion attempts w i t h t h i s model were abandoned. Model Type C, a copolymer formed by the r e a c t i o n o f i s o eugenol o r i t s methyl e t h e r w i t h maleic anhydride a t 170°C i n an autoclave and p u r i f i e d by p r e c i p i t a t i n g i t s e t h y l acetate s o l u t i o n from e t h e r , was r e a c t e d f o l l o w i n g both pathways. The r e s u l t s i n Table VI i n d i c a t e t h a t , although eventual formation o f azide groups can be documented a t l e a s t f o r the sodium a z i d e and probably a l s o f o r the hydrazide pathway, the accumulation o f im p u r i t i e s along the m u l t i - s t e p conversion pathways present mount i n g problems. Incomplete t r a n s f o r m a t i o n o f f u n c t i o n a l i t i e s o f i n t e r m e d i a r y steps i s i n d i c a t e d i n the sodium azide pathway by the r e t e n t i o n o f c h l o r i n e a f t e r treatment w i t h sodium azide and i n the hydrazide pathway by incomplete m e t h y l a t i o n and incomplete hydrazide t r a n s f o r m a t i o n t o azide by HN0 , r e s u l t i n g i n a product w i t h low N-content. Model Type C, the isoeugenol-maleic anhydride copolymer, forms an organic azide and isocyanate by the sodium a z i d e path way as i s i n d i c a t e d by the IR s p e c t r a (A and B) o f F i g u r e 7. However, o v e r a l l isocyanate y i e l d s remain low. Another approach a t i n t r o d u c i n g isocyanate f u n c t i o n a l i t y i n t o polymeric l i g n i n d e r i v a t i v e s concentrated on "capping" hy dro x y l groups o f l i g n i n - d e r i v e d p o l y o l s w i t h d i i s o c y a n a t e s . Re s u l t s o f these experiments, which employed anhydrous benzene so l u t i o n s o f p o l y o l s and excess HDI, are given i n Table V I I . That t h i s method o f i n t r o d u c i n g N-containing f u n c t i o n a l i t y i n t o p o l y o l s i s h i g h l y s u c c e s s f u l i s i n d i c a t e d by the h i g h n i t r o g e n con t e n t s o f capped p o l y o l s A and B. A s t r o n g NCO band i n the IR spectrum o f the d e r i v a t i z e d p o l y o l , Figure 7C, suggests t h a t t h i s p o l y o l has been s u c c e s s f u l l y transformed i n t o a p o l y i s o c y anate. This simple p o l y o l conversion may e l i m i n a t e the d i f f i c u l t i e s a s s o c i a t e d w i t h the formation o f a p o l y i s o c y a n a t e from l i g n i n by m u l t i - s t e p t r a n s f o r m a t i o n procedures a p p l i e d t o carboxyl a t e d l i g n i n d e r i v a t i v e s , which are caused by the accumulation of m u l t i p l e f u n c t i o n a l i t i e s . Llgyiin-Vz/UvzcL VolyiVKitkoLViQA. The manufacture o f p o l y u r e thane foams, adhesives and coatings from l i g n i n - d e r i v e d p o l y e s t e r - e t h e r - p o l y o l s and v a r i o u s commercial d i i s o c y a n a t e s has been accomplished and r e p o r t e d e a r l i e r (16,17,18). Foam p r o p e r t i e s 2


21.

Polyols,

GLASSER ET AL.

Ρolyisocyanales, and

ο

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325

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Polyurethanes

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326


(μ)

WAVELENGTH

(μ)


WAVELENGTH

4000

2800

1800

WAVENUMBER Figure 6.

1200

800

1

(cm- )

Infrared spectra of isocyanate formation of model Type A (R = CH ) via the sodium azide and the hydrazide pathways.


S


Η

Ν

CI

0CH 3

9

Mai. Acid/ C 9

COOH/ C CI/ COOH

1.27 1.38 4.25 3.23 16.44

13.70 12.86 4.13 7.51 8.13

9.74 7.31

1.32 2.24

3

2.64 4.48 0.53 0.38

61.70 60.72 55.60 56.3

5.42 6.00 5.31 5.92

9.76 3.63 (max) —

-

17.90 29.73 15.54 16.91

1.71

3.42

HYDRAZIDE PATHWAY - MODEL TYPE C (R = CH ) - ANHYDRIDE

5.97 5.39 3.91 4.31 3.93 4.12 2.49

SODIUM AZIDE PATHWAY - MODEL TYPE C (R = CH3CO) -- ACID

55.87 57.28 48.00 50.43 54.04 54.73 33.68

C

Determined by IR-spectroscopy.

Anhydride Methylester Hydrazide Azide

Acid - A ( l . t r i a l ) B(2.trial) Acid Chloride - A Β Azide-Wet Method-A -B Azide-Dry Method-B

Compound

Elemental A n a l y s i s (%)

0.49

COOH

OCH3/

Ester-

Functionality

Elemental A n a l y s i s and F u n c t i o n a l i t y Data o f Model Type C Intermediates

Table VI


0.44

Hydra zide/ COOH

1

O.O

0.10 0.05 0.21

3

N/ COOH

328



WAVELENGTH 2.5

3

3.5

4

5

{μ)

6

7

8

9

I

I

1

I

ι

1

I

4000

3400

2800

2200

1800

1500

1200

WAVENUMBER

II

I

900

1

(cm" )

Figure 7. Infrared spectra of isocyanate formation of model Type C (R = CH ) (Spectrum A, azide and Spectrum B, isocyanate) and of capped lignin-derived polyol S



21.

GLASSER ET AL.

329

Polyols, Polyisocyanates, and Ρolyurethanes

Table V I I A n a l y s i s Data o f Two HDI-Capped P o l y o l s

Elemental A n a l y s i s (%) Prepa ration

C

H

Ν

S

Kraft Lignin

_ Total OH

Functionality NCO/OH 1

10.39

Polyol-A

6.23

-B HDI-Capped Polyol^-A -B

9.3 52.01

7.51

13.52

0.69

2.1

52.55

7.48

12.08

0.74

1.5

1

Assuming t h a t one o f the two NCO-groups o f HDI s u r v i v e s the r e a c t i o n as NCO.

2

A n a l y s e s were performed on e t h e r - i n s o l u b l e f r a c t i o n s recovered from the t o t a l r e a c t i o n mixtures i n low ( u n r e p r e s e n t a t i v e ) yields.



330


are summarized i n Table V I I I , where they are compared t o a com m e r c i a l low-density foam and t o a foam prepared from an uncarboxylated l i g n i n - d e r i v e d p o l y e t h e r - p o l y o l . The r e s u l t s demon s t r a t e s u p e r i o r performance c h a r a c t e r i s t i c s o f l i g n i n - p o l y e s t e r ether-polyol-based urethane foams i n terms o f compressive s t r e n g t h , recovery, and d e n s i t y , as compared t o the two other foams. Water s o r p t i o n ranges g e n e r a l l y below 10% f o r l i g n i n p o l y e s t e r - p o l y o l s , and between 10 and 20% f o r the non-carboxyl a t e d k r a f t l i g n i n - p o l y o l foams and the commercial product. Adhesive p r o p e r t i e s are l i s t e d i n Table IX. Shear s t r e n g t h , wood f a i l u r e , and s w e l l i n g data f o r two wood s p e c i e s , southern pine and hard maple, i l l u s t r a t e e x c e l l e n t performance p r o p e r t i e s of l i g n i n - b a s e d urethane products. Urethane coatings f o r wood s u r f a c e s , prepared w i t h l i g n i n based p o l y e s t e r - e t h e r - p o l y o l , have demonstrated e x c e p t i o n a l prop e r t i e s i n terms o f s o l v e n t and chemical r e s i s t a n c e (18), and they provide the coated wood surface w i t h an a t t r a c t i v e appearance. Capped p o l y o l s , prepared by r e a c t i n g p o l y o l s i n non-polar s o l v e n t s (benzene o r e t h y l acetate) w i t h excess d i i s o c y a n a t e (HDI), reacted w i t h c e l l u l o s e f i b e r s a t ambient temperature. Simple immersion o f preformed f i b e r mats ( b l o t t i n g paper) f o l lowed by a i r - d r y i n g r e s u l t e d i n d r a s t i c i n c r e a s e s i n sheet s t r e n g t h p r o p e r t i e s . This i s i n d i c a t e d i n Table X. Economic Conb-LdoAcutLoviA. The economic f e a s i b i l i t y o f pro ducing l i g n i n - d e r i v e d p o l y o l s from carboxylated and o x y a l k y l a t e d k r a f t l i g n i n has been assessed i n a p u b l i c a t i o n s e r i e s e n t i t l e d "How t o Design Chemical P l a n t s on the Back o f an Envelope," by J . P. Clark (20). The r e s u l t s o f t h i s economic e v a l u a t i o n , which was completed i n 1975 and p u b l i s h e d i n 1976, are h i g h l i g h t e d i n Table X I . The "back-of-the-envelope" e v a l u a t i o n concluded t h a t commercial production o f l i g n i n - d e r i v e d p o l y e s t e r - e t h e r - p o l y o l s was commercially f e a s i b l e at t h a t time. Where s i m i l a r p o l y e s t e r p o l y o l s were s e l l i n g f o r 40-60

Lignin-Derived Polyols, Polyisocyanates, and ... - ACS Publications

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