Wood Technology: Chemical Aspects

9 Dimensional Stabilization of W o o d with Furfuryl Alcohol Resin

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 19, 2016 | http://pubs.acs.org Publication Date: June 1, 1977 | doi: 10.1021/bk-1977-0043.ch009

ALFRED J. STAMM School of Forest Resources, Department of Wood and Paper Science, North Carolina State University, P.O. Box 5516, Raleigh, N.C. 27607

A number of methods have been developed i n the l a s t f o r t y years f o r the dimensional s t a b i l i z a t i o n o f wood ( 1 2 ) , Un f o r t u n a t e l y none of these have proved to be economically success f u l on a l a r g e s c a l e . One of the methods, i n v o l v i n g the t r e a t ment w i t h f u r f u r y l a l c o h o l (3) was shown by G o l d s t e i n (4, 5) to impart both alkali as w e l l as a c i d r e s i s t a n c e to wood, g i v i n g i t a distinctive black c o l o r . This treatment i s of renewed i n t e r e s t at the present time because f u r f u r y l a l c o h o l i s made from the renewable r e s o u r c e , corn cobs, and can a l s o be made from the h y d r o l i z a t e of hardwood waste ( 6 ) . G o l d s t e i n and Dreher ( 7 ) , have shown t h a t five parts of the c a t a l y s t z i n c c h l o r i d e or organic di-or tri-basic acids, such as citric acid, gave s o l u t i o n s i n 5 p a r t s of water added to 90 p a r t s of f u r f u r y l a l c o h o l t h a t remain s t a b l e f o r a month or more a t room temperature without a significant amount of p o l y m e r i z a t i o n , whereas they polymerize to g i v e high y ields of r e s i n when heated f o r a day at 100°C, This makes p o s s i b l e the impregnation o f wood with t h i s l i q u i d i n conventional t r e a t i n g c y l i n d e r s , d r a i n i n g o f f the excess 1 i q u i d f o r r e u s e , and then heat c u r i n g the r e s i n w i t h i n the wood. In t h i s way an a n t i s h r i n k e f f i c i e n c y (1 - % swel1ing of t r e a t e d wood χ 100) of 63 was obtained at % s w e l l i n g of untreated wood 48% r e s i n content and 70 at 120% r e s i n content w i t h Idaho pine cross s e c t i o n s (4, _7), The toughness of southern pine s t i c k s (0.5 by 0.5 by 4 i n c h span) as shown by the Charpy impact t e s t at 68% r e s i n content was, however, reduced from 69 to 27 f o o t pounds ( r elative toughness 0 , 3 9 ) . I t thus appeared d e s i r a b l e to determine if the use of l e s s c a t a l y s t would improve the toughness and if the long tie up of an oven or dr y k i l n f o r the cure of the resin could be a v o i d e d . p

Experimental Douglas f i r , l o b l o l l y p i n e , and Engelmann spruce specimens 4.5 by 4.5 cm i n the r a d i a l and t a n g e n t i a l d i r e c t i o n s were cut i n t o a s e r i e s of end matched cross s e c t i o n s 3 mm t h i c k f o r 141

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


142

WOOD TECHNOLOGY;

CHEMICAL

ASPECTS

treatment. Yellow poplar s t i c k s 1 by 1 cm i n the r a d i a l and t a n g e n t i a l d i r e c t i o n s by 40 cm long were a l s o t r e a t e d . A l l s p e c i mens were s t r e s s r e l i e v e d by s w e l l i n g i n water f o l l o w e d by a i r and then oven d r y i n g . P a r t of the s t i c k s were cut i n t o f o u r end matched s t i c k s 9.5 cm long f o r treatment and toughness t e s t s . Three d i f f e r e n t c a t a l y s t s were used. F i v e p a r t s by weight of z i n c c h l o r i d e or of c i t r i c a c i d were d i s s o l v e d i n 5 parts o f water and added to 90 parts by weight o f f u r f u r y l a l c o h o l , g i v i n g 5% c a t a l y s t c o n c e n t r a t i o n s . Zinc c h l o r i d e was a l s o used i n one f i f t h and one twenty f i f t h of the former c o n c e n t r a t i o n . Formic a c i d was used i n 5% by weight concentrations w i t h no water p r e s e n t . The presence of the small amounts of water i n the case of the two s o l i d c a t a l y s t s a i d i n t h e i r s o l u t i o n and cause almost as r a p i d s w e l l i n g of wood as i n water a l o n e , whereas the s w e l l i n g i n w a t e r - f r e e f u r f u r y l a l c o h o l i s extremely slow. Formic a c i d a c c e l e r a t e s the r a t e of s w e l l i n g of wood i n f u r f u r y l a l c o h o l , s i m i l a r to the e f f e c t of water. The h i g h l y permeable l o b l o l l y pine and Engelmann spruce cross s e c t i o n s were t r e a t e d by merely immersing the a i r dry specimens i n the t r e a t i n g s o l u t i o n s f o r 5 seconds. The much denser Douglas f i r heartwood cross s e c t i o n s were t r e a t e d by p u l l i n g a vacuum f o r 30 seconds over the s o l u t i o n immersed specimens. The 9.5 cm long y e l l o w poplar s t i c k s were t r e a t e d by immersing them f o r 10 minutes under vacuum i n the t r e a t i n g s o l u t i o n s . The 40 cm long y e l l o w poplar s t i c k s were t r e a t e d i n g l a s s tubes by p u l l i n g a vacuum of 0.1 mm of mercury on the oven dry specimens, running i n the t r e a t ing s o l u t i o n under vacuum and holding f o r one minute (8), The t r e a t e d specimens were wrapped i n aluminum f o i l and held at room temperature f o r one day to a l l o w f o r e q u i l i z a t i o n of the s o l u t i o n through the s t r u c t u r e by c a p i l a r i t y and d i f f u s i o n . The specimens were then weighed and the r a d i a l and t a n g e n t i a l dimensions determined. They were again wrapped i n aluminum f o i l and heat cured at 120°C f o r e i t h e r 18 or 6 hours. The specimens were weighed and measured, oven d r i e d f o r 2 hours to remove unpolymerized v o l a t i l e s and again weighed and measured. The specimens were then immersed i n d i s t i l l e d water f o r a t l e a s t two days, measured, a i r d r i e d f o l l o w e d by oven d r y i n g , weighing and measuri n g . Specimens that were w e l l cured l o s t l i t t l e weight and dimensions between the heat cured c o n d i t i o n and the f i r s t and second oven d r y i n g . A n t i - S h r i n k and P o l y m e r i z a t i o n E f f i c i e n c i e s A n t i s h r i n k e f f i c i e n c i e s (ASE) f o r the t r e a t e d specimens were c a l c u l a t e d from the changes i n cross s e c t i o n s between the o r i g i n a l untreated water swollen and oven dry c o n d i t i o n s and the t r e a t e d water swollen and second oven dry c o n d i t i o n . Figure 1 i s a p l o t of the ASE f o r the three species of cross sections and the y e l l o w poplar s t i c k s versus the r e s i n c o n t e n t . The ASE values increase approximately 1 i n e a r l y w i t h an increase i n r e s i n content as r e s i n



9.

Stabilization

S T A M M

with Furfuryl

Alcohol

Resin

143

i s formed w i t h i n the c e l l w a l l s to bulk the f i b e r . Above about 40% r e s i n content by weight, r e s i n i s deposited w i t h i n the natural v o i d s t r u c t u r e with l i t t l e i n c r e a s e i n ASE. This p o i n t corresponds to an optimum bulked volume of 32.5% as the s p e c i f i c g r a v i t y of c a s t f u r f u r y l r e s i n was found to be 1.23 by the sus pension method i n an aqueous z i n c c h l o r i d e s o l u t i o n (1 pg 55). This value i s o n l y s l i g h t l y g r e a t e r than the f i b e r s a t u r a t i o n p o i n t or optimum b u l k i n g of untreated wood by water, 30%. The f u r f u r y l a l c o h o l - c a t a l y s t s o l u t i o n s swel1ed the wood 6 to 8% beyond the s w e l l i n g i n water. The b u l k i n g by the s o l u t i o n s was thus 31.6 to 32.4%. This i n d i c a t e s a r e a l high e f f i c i e n c y of d i f f u s i o n of r e s i n forming chemicals i n t o the c e l l w a l l s of wood under the c o n d i t i o n s used. The e f f i c i e n c y w i t h which r e s i n i s formed from the weight of r e s i n forming m a t e r i a l taken up w i t h i n the wood was c a l c u l a t e d on the basis of one mole of water being l o s t f o r each mole of f u r f u r y l a l c o h o l polymerized (0.815) and a l l c a t a l y s t and water l o s t as vapor or from l e a c h i n g subsequent to the f i n a l water soak. The e f f i c i e n c y of p o l y m e r i z a t i o n i s then the f i n a l r e s i n content of the wood i n weight percent, d i v i d e d by the o r i g i n a l s o l u t i o n content of the wood before p o l y m e r i z a t i o n times one minus the i n i t i a l f r a c t i o n a l moisture content of the wood times the f r a c t ion of the weight of the t r e a t i n g s o l u t i o n t h a t was f u r f u r y l alcohol times 0.815. These e f f i c i e n c i e s together with the a n t i s h r i n k e f f i c i e n c i e s are given i n Table I f o r the matched y e l l o w poplar s t i c k s 9.5 cm long and i n Table II f o r the Douglas f i r and Engelman spruce cross s e c t i o n s . Under c o n d i t i o n s where p o l y m e r i z a t i o n was v i r t u a l l y complete (18 h r . cure) the e f f i c i e n c i e s were 90% or b e t t e r using both z i n c c h l o r i d e and c i t r i c a c i d catalysts. When formic a c i d was used as the c a t a l y s t , the e f f i c i e n c y was s i g n i f i c a n t l y lower. When the c u r i n g time was reduced to 6 hours high e f f i c i e n c y of p o l y m e r i z a t i o n r e s u l t e d only at z i n c c h l o r i d e concentrations of 1% and 5%, Mechanical

Properties

S t a t i c bending t e s t s were made on nine t r e a t e d y e l l o w pop l a r s t i c k s (40 χ 1 χ 1 cm) (three each w i t h 2.5% z i n c c h l o r i d e , 2.5% c i t r i c a c i d and 5% formic a c i d c a t a l y s t cured f o r 18 h r . a t 120°C), and f o u r c o n t r o l s t i c k s . Loading was i n the t a n g e n t i a l d i r e c t i o n . The r e s i n contents ranged from 40 to 72%, ASE values ranged from 72 to 77% (av. 74%), The average r e l a t i v e s t r e s s to p r o p o r t i o n a l l i m i t was 1 . 3 , the average r e l a t i v e modulus of rupture was 0.89 and the average r e l a t i v e modulus of e l a s t i c i t y was 2 . 0 . The increases i n the s t r e s s to p r o p o r t i o n a l l i m i t and the modulus of e l a s t i c i t y are due to s t i f f e n i n g of the f i b e r s . The l o s s i n modulus of rupture r e s u l t e d from a c i d embrîttlement of the f i b e r s . There was no s i g n i f i c a n t d i f f e r e n c e due to c u r i n g w i t h the d i f f e r e n t c a t a l y s t s except i n the case of the r e l a t i v e modulus of rupture which averaged 0,99 f o r the specimens



9

6

6

6

6

1% c i t r i c a c i d

1% z i n c c h l o r i d e

0.2% z i n c c h l o r i d e



71.2

74.4

73.8

91.8

102,3

91,5

Av. Solution Content Wt,%

6

6

6

18

18

18

hr.

Cure Time

53.7

49.7

20,7

55.9

67.1

51,2

Av. Resin Content Wt.%

53.2

57.6

57.2

59.5

74.3

66.5

Ut.%

Theoretical Resin Content

t

97,3

86.3

36.2

90,7

90.3

77,1

%

Effici

68.8

54,6

27.7

73.4

73,6

70.6

10

ASE

.33

.58

.74

.57

.55

0.78

Av. Relative Toughness-

U, S. Forest Products Lab, toughness t e s t (9) 3 i n c h span top w e i g h t . 30° a n g l e , p u l l i n t a n g e n t i a l direction.

9

Spec,

No.

s

E f f i c i e n c y of F u r f u r y l Alcohol Resin Treatment of End Matched Yellow Poplar S t i c k s (9,5 χ 1,0 χ l 0 cm) Cured at 120°C i n Aluminum F o i l The A n t i s h r i n k E f f i c i e n c y (ASE) and the R e l a t i v e Toughness

5% formic a c i d

Catalyst

Table I .



4

4

4

4

1% c i t r i c a c i d


0.2% z i n c c h l o r i d e


141.0

143.0

124.1

103.9

113,3

55.3

6

6

18

18

18

98.2

66.7

88.1

67.5

62.7

Engelmann Spruce

18

43.3

104.2

90.3

75.7

82.5

56.6

45.8

64.0

97.3

89.5

76.3

97.5

94.5

80.5

%

Efficiency

97.9

4

5% formic a c i d

77.8

18

59.4

wt, %

Theoretical Resin Content

5% z i n c c h l o r i d e 4 149.0 6 106.0 108.5 y O r i g i n a l moisture content of wood before treatment, 6% 2/ Loos Abrader (10)

4


62.9

47.7

wt. %

Av. Resin Content

95.5

4

λ% c i t r i c a c i d

81.5 18

hr.

wt. %

y

Cure Time

Av. Solution Content

102,8

8

Spec.

No.

Douglas F i r

66.7

72.0

61.7

73.6

72.5

69.2

74.1

77.2

73.0

%

ASE

.73

.80

.83

.63

.63

.66

.63

.64

0.71

y

Relative Abrasion Resistance

E f f i c i e n c y of F u r f u r y l Alcohol Resin Treatment of Douglas f i r and Engelmann Spruce cross Sections Cured at 120°C i n Aluminum F o i l , the A n t i s h r i n k E f f i c i e n c y (ASE) and the R e l a t i v e Abrasion R e s i s t a n c e .

5% formic a c i d

Catalyst

Table Γ Ι .


146

WOOD TECHNOLOGY:

CHEMICAL

|l Δ


ω ω

40

/

0

t

0

ο

•

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Δ

Wood Technology: Chemical Aspects

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