Polyurethane Foams from the Reaction of Bark and Diisocyanate

16 Polyurethane Foams from the Reaction of Bark and Diisocyanate SEYMOUR H A R T M A N

Downloaded by UNIV LAVAL on July 12, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0043.ch016

Champion International Corp., U . S. Plywood Technical Center, Brewster, N.Y. 10509

The major areas for bark utilization can be broken down into three groups: 1 - as a source of energy production 2 - as an environment and pollution control product and 3 - as a source for materials or chemicals Bark, a complex chemical mixture of many organic compounds has been used as a power fuel in the Forest Products Industry as a means of conserving the burning of natural fuel (oil and natural gas). Now especially, with the increase of fuel prices, the use of bark as a fuel has increased. Its use as an environmental and pollution control product has been for erosion control and slope stabilization. Bark has also been used as a potential oil pollutant scavenger in oil spills as well as a potential odor scavenger in sulfate pulp mills. As a source for materials, bark has found use in horticultural applications as a mulch growth media containing f e r t i l i z e r s , pesticides and herbicides for container growth plants, as well as a soil conditioner. As a source for chemicals, numerous papers have been written [1] [2], [3] and many patents [4], [5] have been issued on the chemistry of bark and on the isolation of its components. One outstanding early work was that of Kurth [6] who classified the principal chemical components present in barks as listed in Table I. Numerous patents [7], [8], [9], [10], [11], have been issued detailing the preparation of alkali bark extract and also the preparation of alkali bark and its use as extenders in phenol formaldehyde resin adhesive systems. With a l l the research activity in the areas cited, not one research activity has viewed bark as a base chemical or as a raw material or as a reactive component in a chemical reaction. More specifically, as a monomer in a polymerization reaction. As we see in Table I, bark does contain organic compounds possessing hydroxyl components. Since diisocyanate is one of the active components of polyurethanes, and unique in that i t possesses a high degree of reactivity and will react with any chemical compound containing an 257

Goldstein; Wood Technology: Chemical Aspects ACS Symposium Series; American Chemical Society: Washington, DC, 1977.

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258

TECHNOLOGY:

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ASPECTS

TABLE I PRINCIPAL CHEMICAL COMPONENTS OF BARK


1. 2.

L i g n i n - the m a t e r i a l i n s o l u b l e i n concentrated mineral a c i d s Cork - c u t o s e , s u b e r i n , and suberic a c i d ( 1 , 6, hexanedicarboxylic acid) 3. Carbohydrates - h o l o c e l l u l o s e , the t o t a l carbohydrate fraction A. C e l l u l o s e B. Hemicel1uloses-arabans, x y l a n s , mannans, glucosans, and uronic a c i d substances 4. Extraneous m a t e r i a l s A. V o l a t i l e a c i d s and o i l s B. N o n - v o l a t i l e f a t t y o i l s ( f a t s and f a t t y a c i d s ) , higher a l c o h o l s , r e s i n s , and hydrocarbons C. C o l o r i n g matters D. Tannins and the r e l a t e d w a t e r - i n s o l u b l e phlobaphenes E. P o l y s a c c h a r i d e s , g l u c o s i d e s , p e c t i n s , and sugars F. Organic n i t r o g e n compounds G. Mineral matters H. Other organic components-saponins, m a n n i t o l , d u l c i t o l , e t c . a c t i v e hydrogen, I decided to use Bark as a chemical r e a c t a n t , possessing the a c t i v e hydrogen to produce a polyurethane foam. Thus my o b j e c t i v e i n t h i s study was to use bark as the major or s o l e polyol i n the r e a c t i o n with d i i s o c y a n a t e to produce a p o l y urethane and more s p e c i f i c a l l y to produce polyurethane foams. Polyurethane f o r m a t i o n , whether i t be a foam, a c o a t i n g , or an adhesive, i s the r e s u l t of a s e r i e s o f complex chemical bonds and linkages other than the urethane group. The basic chemical r e a c t i o n s t a k i n g place during foam formation have been c i t e d i n the l i t e r a t u r e [ 1 2 ] , [13] and are summarized i n Figure 1. A l l the chemical r e a c t i o n s shown i n Figure 1 may occur simultaneously and very 1 i k e l y do. For s i m p l i c i t y the chemical r e a c t i o n s i n the equations shown are presented i n t h e i r monofunctional f o r m , although I am sure you are a l l aware that a l l the r e a c t i v e components must be d i f u n c t i o n a l o r g r e a t e r to produce a polymeric structure. The two most important chemical r e a c t i o n s i n the p r e p a r a t i o n of polyurethane foam are the r e a c t i o n between isocyanate and hydroxyl compound to form a urethane 1inkage: R-N =C=0 + R'-OH

R-NH-C-O-R* II

0 urethane and the r e a c t i o n between isocyanate and water. The f i r s t step of t h i s r e a c t i o n i s the formation of an unstable carbamic a c i d , which decomposes to form an amine and carbon d i o x i d e . This r e -


16.

Polyurethane

H A R T M A N

R-N=C=0 + H 0 +

Foams

259

R-NH-C-OH

2

R'NH + C 0 2

2

6 carbamic a c i d a c t i o n i s r e s p o n s i b l e f o r foam formation through the l i b e r a t i o n of carbon d i o x i d e . Another r e a c t i o n t a k i n g place i s the formation of a d i s u b s t i t u t e d urea from the r e a c t i o n of the preceeding amine and isocyanate: R-N=C=0 + R'NH

R-NH-C-NH-R*

2


II

0 d i s u b s t i t u t e d urea Other r e a c t i o n s are the formation of allophanate l i n k a g e s atom of the urethane

which lead to branching and c r o s s - l i n k i n g allophanate and b i u r e t l i n k a g e s . The occurs when the hydrogen on the n i t r o g e n group r e a c t s with an i s o c y a n a t e :

R-N=C=0 + R-NH-C-O-R* II

0

R-NH-C-N-C-O-R* II

II

I

0 R 0 allophanate

The b i u r e t 1inkage o c c u r r i n g when the hydrogens on the n i t r o g e n atoms i n the d i s u b s t i t u t e d urea r e a c t s w i t h i s o c y a n a t e : R-N=C=0 + R-NH-C-NH-R* - * II

0

R-NH-C-N-C-NH-R* II

I

II

0 R 0 biuret

Since the isocyanate r e a c t i o n s i n Figure 1 are u s u a l l y slow, the p r e p a r a t i o n of polyurethane foams r e q u i r e s besides a d i i s o cyanate and a p o l y o l , a blowing agent, a s u r f a c t a n t and a catalyst. The blowing agents used can be water (as seen i n Figure 1) or t r i c h l o r o f l u o r o methane and/or d i c h l o r o d i f l u o r o methane, commonly known as Freons. The s u r f a c t a n t s which act as foam s t a b i l i z e r s and which c o n t r o l the c e l l s i z e of the foam produced are u s u a l l y s i 1icones, such a s , s i l i c o n e g l y c o l c o polymers, or copolymers of dimethylpolysi1oxane and p o l y a l k y l e n e e t h e r s . The c a t a l y s t s normally used to speed up the r e a c t i o n are t e r t i a r y amines and/or organotin compounds. T e r t i a r y amines included i n t h i s group a r e : t r i e t h y l e n e d i a m i n e , Ν,Ν,Ν'Ν', t r i ethylamine, N-methyl or N-ethyl morpholine. The organotin c a t a l y s t s normally used are d i b u t y l t i n d i l a u r a t e , stannous o c t o a t e , d i b u t y l t i n d i - ( 2 e t h y l ) hexoate. Combinations of t e r t i a r y amines and organotin compounds can a l s o be used. Since the p r o p e r t i e s of a polyurethane foam i n the r e a c t i o n between a p o l y o l and an d i i s o c y a n a t e depends somewhat on the



urethane

1

R -OH

Figure 1.

,

0

allophanate

0

Chemistry of urethane foam formation

d i s u b s t i t u t e d urea

I

Il

O

R- NH-C-NH.-R'

1

i


biuret

R-INH-C-N-C-NHI-R'

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Polyurethane

Foams

261

s t o i c h i o m e t r i c r e l a t i o n s h i p of these components, the hydroxyl number of the bark used had to be determined. Results of the a n a l y s i s of the two bark m a t e r i a l s s t u d i e d , namely, Ponderosa Pine and Douglas F i r are given Table I I . The amount of d i i s o TABLE II BARK ANALYSIS


Bark Ponderosa Pine Douglas F i r

% Hydroxy 12.56 13.35

Hydroxyl Number 414.48 440.55

cyanate r e q u i r e d to r e a c t w i t h the bark was then c a l c u l a t e d on the basis of the t o t a l c o n c e n t r a t i o n o f the hydroxyl number of the bark and water when used. An excess of isocyanate over the amount r e q u i r e d by s t o i c h i o m e t r i c c a l c u l a t i o n s was used. A f t e r much experimentation with v a r i o u s c a t a l y s t s and s u r f a c t a n t systems, a t y p i c a l formula f o r our foam preparation i s set f o r t h i n Table I I I . TABLE

III

GENERAL FORMULA OF A BARK - DIISOCYANATE POLYURETHANE FOAM Reactants Bark Catalyst Surfactant Diisocyanate (crude) MDI

H2O

Parts i n Grams 50 1-2 .5-3 100 2-10

The foams were prepared by f i r s t mixing the bark and the i s o c y a n a t e , the other components ( c a t a l y s t , s u r f a c t a n t , and blowing agent) were pre-mixed and added to t h i s bark - isocyanate mix, and the mixing was continued to y i e l d a homogeneous blend which began to r i s e and y i e l d a foam product. The r a t e of foaming was a f u n c t i o n of the c a t a l y s t used. A number of b a r k - d i i s o c y a n a t e polyurethane foams were p r e pared. An area which I f e l t had to be explored was whether I was producing a polyurethane foam from the r e a c t i o n of bark and diisocyanate. I n i t i a l attempt to e l u c i d a t e or c o n f i r m a urethane l i n k a g e i n the prepared foams, was made by the I n f r a - r e d a n a l y s i s on a s e r i e s of three prepared polyurethane foam f o r m u l a s , wherein the bark was the v a r y i n g f a c t o r . The three prepared foam formulations s t u d i e d are shown i n Table IV. I n f r a - r e d a n a l y s i s was conducted on the three foam f o r m u l a t i o n s 1 i s t e d i n Table IV. The r e s u l t i n g curves are shown i n Figure 2. The three IR curves shown i n Figure 2 , when i n t e r p r e t e d revealed the presence of urea 1inkages i n Formula 1. The p r è s -


Figure 2



16.

H A R T M A N

Polyurethane

263

Foams

TABLE IV BARK-DIISOCYANATE - POLYURETHANE FOAM FORMULATIONS USED FOR INFRA-RED (IR) AND FOR THERMOGRAVIMETRIC ANALYSIS (TGA)


Formulations Ponderosa Pine Bark Douglas F i r Bark C a t a l y s t - T-6 S u r f a c t a n t L-5420 Freon Water MDI (crude)

1 8

#2 25 25 2 1 8

80

80

#1 50

-2 -

-

#3

-

50 2 1

-

7 100

ence of urethane and urea 1inkages were found i n Formula 2 , which contained a mixture of Douglas F i r and Ponderosa Pine bark. While Formula 3 , which contained Douglas F i r bark, revealed the presence o f urethane 1inkages. A l l three foams showed the p r e s ence of isocyanate l i n k a g e s . The l a c k of d i s t i n c t urethane l i n k a g e r e s o l u t i o n i n the formula c o n t a i n i n g Ponderosa Pine bark could well be due to two factors: 1 - the inherent h i g h l y r i g i d polymeric system formed and 2 - the p o s i t i o n of the urethane 1inkage a b s o r p t i o n band. Since the absorption bands i n IR spectrum are at frequencies r e l a t e d to the v i b r a t i o n of the f u n c t i o n a l groupings p r e s e n t , h i g h l y r i g i d polymeric m a t e r i a l s do not v i b r a t e as much as non h i g h l y r i g i d s t r u c t u r e s , t h e r e f o r e , d i s t i n c t r e s o l u t i o n of s p e c i f i c groupings (urethane) may not be t h a t v i s i b l e i n the IR spectrum. Furthermore, the urethane 1inkage absorption band i s at about 5.8 microns, and the other groupings or l i n k a g e s assoc i a t e d with polyurethane f o r m a t i o n , namely, the d i s u b s t i t u t e d u r e a , b i u r e t , a l l o p h a n a t e , u r e t i d i o n e , and i s o c y a n u r a t e s , are a l l i n c l o s e p r o x i m i t y to t h i s absorption band. This can be seen i n Table V, [14]. Any one of these groupings or l i n k a g e s and more p a r t i c u l a r l y the d i s u b s t i t u t e d u r e a , which y i e l d s a strong s h o u l d e r , can wash out the urethane l i n k a g e . Niederdellmann, et a l . [ 1 5 ] , i n t h e i r study of polyurethane and polyurea foam mixtures by IR a n a l y s i s , found t h a t small concentrations of p o l y urethane l i n k a g e s cannot be e a s i l y determined or detected i n the presence of l a r g e amounts of polyurea l i n k a g e s . Thus we see that due to the p o s s i b l e wash out of the polyurethane l i n k a g e and a l s o due to the p o s s i b l e h i g h l y r i g i d polymeric system formed, when Ponderosa Pine bark was used as the p o l y o l , more d e f i n i t e c o n f i r m a t i o n of the polyurethane grouping was sought. In t h i s b e h a l f , Thermogravimetric A n a l y s i s (TGA) was used, s i n c e i t would provide (a) information on the composition of the i n i t i a l sample, (b) i n f o r m a t i o n on the composition of any intermediate compounds t h a t may be formed and (c) information on the composit i o n of the residue i f any was formed. This a n a l y t i c a l method,


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264

Figure 3.

Figure 4.

TGA—Thermogram—Formula

TGA—Thermogram—Formula

TECHNOLOGY:

CHEMICAL

1

2


ASPECTS

16.

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265

TABLE V WAVELENGTHS FOR CHARACTERIZATION OF ISOCYANATE DERIVITIVES


Group

Wavelength

(micron) -NCO - i n isocyanates 4.40-4.46 -N=C=Ν - i n carbodiimides 4.72 5.61-5.65 - C - 0 - i n u r e t i d i o n e r i n g (dimer) -C=0 - i n isocyanurate r i n g ( t r i m e r ) 5.85-5.92 -C=0 - i n carbamates (urethane) 5.75-5.88 -C=0 - i n allophanates 5.71-5.81° 5.81-5.90 5.99-6.13 - 0 0 - i n ureas 5.81-5.92° -C=0 - i n b i u r e t s -NH - deformation (Amide II bond) 6.41-6.58 -NH - s t r e t c h (bonded) 2.94-3.13 -NH - s t r e t c h ( f r e e ) 2.86-2.94 -C=N - i n carbodiimide dimer 5.95 5.99 -C=N - i n carbodiimide t r i m e r °= Higher frequency band i s more intense

Wave Number (cm-1) 2270-2240 2120 1783-1770 1709-1689 1739-1700 1751-1721 1721-1695 1670-1630 1720-1690 1560-1520 3400-3200 3500-3400 1681 1669

when compared to I n f r a - r e d a n a l y s i s , i s a l s o u s e f u l i n the i d e n t i f i c a t i o n and c h a r a c t e r i z a t i o n of m a t e r i a l s . In TGA, the mass of a sample i s c o n t i n u o u s l y recorded as a f u n c t i o n of temperature. The thermogram produced represents the temperature a t which the mass changes, with a peak temperature representing the maximum mass change. TGA was run on the same prepared foam samples shown i n Table I V , using a F i s h e r Thermal Analyzer #442, i n a Helium atmosphere a t 50 m l . / m i n . and a t a r a t e of 10°/min. The thermograms produced are set f o r t h i n Figures 3 , 4 and 5. The i n t e r p r e t a t i o n of these thermograms were based on comparing them w i t h confirmed polyurea and polyurethane foam thermograms. They showed, as d i d the IR a n a l y s i s , the p r e s ence of urea 1inkages i n Formula I ; the presence of urea and urethane l i n k a g e s i n Formula 2 ; and the presence o f urethane l i n k a g e s i n Formula 3 . A summary o f the instrumental a n a l y s i s (IR and TGA) i s presented i n Table V I . From the three f o r m u l a t i o n s s t u d i e d , I would have expected to f i n d the presence of urea 1inkages, i f anywhere, i n Formula 1 , s i n c e t h i s foam was prepared w i t h water as the blowing agent, and as seen i n Figure 1 , the production of d i s u b s t i t u t e d urea s t r u c tures can be produced from the r e a c t i o n o f water and d i i s o c y a n a t e . Why the appearance of u r e a - l i n k a g e s when using Ponderosa Pine bark as the p o l y o l with Freon, as the blowing agent, i s d i f f i c u l t to e x p l a i n a t t h i s t i m e . Compressive strengths were performed on a number o f foam samples i n accordance w i t h ASTM #1621. The r e s u l t s obtained were comparable to other polyurethane foams prepared from conventional p o l y o l s and d i i s o c y a n a t e s .



WOOD TECHNOLOGY:

Figure 5.

CHEMICAL

TGA—Thermogram— Formula 3


ASPECTS

16.

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267

TABLE VI


INFRA-RED (IR) THERMOGRAVIMETRIC ANALYSIS (TGA) OF DIFFERENT BARK-POLYURETHANE FOAM FORMULATIONS Formulations Ponderosa Pine-bark Douglas F i r - b a r k C a t a l y s t - T-6* S u r f a c t a n t - L-5420** Freon Water MDI (crude) Infra-red analysis

#2 25 25 2 1 8

J i 50 2 1 8

#3

-

50 2 1

-

-

7 100 80 unreacted NCO urethane plus urethane and urea

80 unreacted NCO plus high con c e n t r a t i o n of urea TGA a n a l y s i s urea - plus urea - no urethane urethane * M&T - stannous s a l t of long f a t t y a c i d * * Union Carbide S i l i c o n e

urethane

When the F l a m m a b i l i t y Test of P l a s t i c Sheeting and C e l l u l a r P l a s t i c s i n accordance w i t h ASTM #D-1692-68 was performed on a s e r i e s of foams, the foams were found to have (a) a high degree of thermal s t a b i l i t y and to possess (b) a high degree of f i r e retardancy ( s e l f - e x t i n g u i s h i n g ) . The average r e s u l t obtained u t i l i z i n g t h i s procedure on a s e r i e s of prepared foams i s given i n Table V I I . TABLE VII ASTM - D-1692-68 FLAMMABILITY OF PLASTIC SHEETING AND CELLULAR PLASTICS burning extent - - - - - - - burning or e x t i n g u i s h i n g time burning r a t e (BR) - — - - - BR = d i s t a n c e burned ( i n . ) χ 60 burning time ( s e c . ) Burning C h a r a c t e r i s t i c s of Foam intumescence self-extinguishing

2 inches 70 seconds 1.71 inches/mi η.

The low burning r e s u l t and the s e l f - e x t i n g u i s h i n g charac t e r i s t i c obtained were not s u r p r i s i n g . I say t h i s i n h i n d s i g h t , f o r the inherent f l a m m a b i l i t y of polyurethane foam, i n g e n e r a l , i s almost e n t i r e l y a f u n c t i o n of the chemical composition of the s o l i d polymer; and one route used to produce flame r e t a r d a n t polyurethane foams has been to a l t e r the s t r u c t u r e of the u r e -



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thane molecule. Stepniczka [16] has reported t h a t the flamma b i l i t y o f polyurethane foams can be reduced by u s i n g : 1 - components w i t h a high degree of a r o m a t i c i t y . 2 - high molecular weight p o l y o l s . 3 - p o l y o l s w i t h high f u n c t i o n a l i t y - a t l e a s t 4. 4 - aromatic isocyanate w i t h f u n c t i o n a l i t y of 2.3 to 3 . 2 . 5 - c y c l i c r a t h e r than open chain p o l y o l s . From Table 1 , we can see that bark components do possess many of the above inherent f i r e r e t a r d a n t f e a t u r e s . Thus the f i r e r e t a r d a n t p r o p e r t i e s obtained should not have been a s u r p r i s e but rather an expected r e s u l t which I can a t t r i b u t e to the design of the components used. In c o n c l u s i o n , I have attempted to demonstrate t h a t bark can be used as the s o l e polyol component i n the production of r i g i d polyurethane foam. These foams possess good p h y s i c a l as w e l l as inherent f i r e r e t a r d a n t p r o p e r t i e s . With the a v a i l a b i l i t y of bark as a r e a c t i v e p o l y o l , I can see a means o f u t i l i z i n g bark as a cheap raw m a t e r i a l i n producing economical polyurethane foam products. Acknowledgement: I wish to thank Mr. David L . W i l l i a m s of Upjohn Chemical C o . , f o r h i s a n a l y t i c a l help i n performing the IR and TGA a n a l y s i s , and f o r h i s i n t e r p r e t a t i o n s of the r e s u l t i n g c u r v e s . Furthermore, I wish to thank Mr. R. R. K i r k , Mobay Chemical C o . , f o r h i s IR interpretations.

"Literature Cited" 1 - Kurth, E. F., Tappi, (1953), 36 (7). 2 - Hergert, H. L. and Kurth, E. F., Tappi, (1953), 36 (3). 3 - Graham, H. M. and Kurth, E.F., Industrial and Engineering Chemistry, (1949), 41 (2). 4 - Brink, D. L., Dowd, L. E. and Root, E. F., U. S. Patent No. 3,234,202, (1966). 5 - Dowd, L. E . , U. S. Patent No. 3,255,221, (1966). 6 - Kurth, E. F., Oregon State College Research Paper #106, School of Science, Dept. of Chemistry, (1948). 7 - Herrick, F. W. and Bock, L. H., U. S. Patent No. 3,025,250, (1962). 8 - Herrick, F. W. and Bock, L. H., U. S. Patent No. 3,053,784, (1962) 9 - Herrick, F. W. and Bock, L. H., U. S. Patent No. 3,223,667, (1965). 10 - Klein, J. A. and Poletika, N.V., U. S. Patent No. 3,213,045, (1965). 11 - Heritage, C. C., U. S. Patent No. 2,574,785, (1947). 12 - Saunders, J . Η., and Frisch, K. C., "Polyurethanes": Chem istry and Technology (Part 1: Chemistry), Interscience Pub


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lishers, New York, (1962). 13 - Ferrigno, T. H . , "Rigid Plastics Foams", 2nd Edition, Reinhold Publishing Company, New York, (1967). 14 - David, D. J . and Staley, Η. Β., "Analytical Chemistry of the Polyurethanes", Part III, Interscience, John Wiley, New York (1969). 15 - Niederdellman, G., Lauerer, D. and Merten, Κ., Central Research Lab., Farbenfabriken Bayer, A. G., private communi cations, November, 1965. 16 - Stepniczka, H. Ε., JFF/Fire Retardant Chemistry, (1974), 1 (5).


Polyurethane Foams from the Reaction of Bark and Diisocyanate

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