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IRVING S. GOLDSTEIN and WILLIAM A. DREHER Research Department, Koppers Co., Inc., Verona, Pa.
Stable Furfuryl Alcohol Impregnating Solutions Monomeric furfuryl alcohol impregnating solutions for porous materials should have long storage life and give high resin yields when cured. Use of selected catalysts permits premixing of the impregnating solution so it is always ready for use
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Storage-stable monomeric furfuryl alcohol solutions which give high yields of furfuryl alcohol resin when heated may be prepared by using zinc chloride or organic acids such as tartaric, citric, and malic as catalyst. These solutions of low viscosity may be used to impregnate such fine-pored materials as wood, brick, and carbon to increase their chemical resistance and improve physical properties.
IMPREGNATING
solutions of polymerized furfuryl alcohol resins have not been widely used because simple dilutions of such resins can be used only with material of large pores. Fine-pored substances such as wood, brick, or carbon shapes require monomeric solutions of low viscosity for deep penetration. Many acidic compounds catalyze polymerization of furfuryl alcohol (7, 3-6, 8-70, 72-74). However, formulations where viscosity does not increase significantly give unsatisfactory resin yields and those giving high resin yields are not stable. I n the work described here, storage stability for a large number of catalyzed furfuryl alcohol solutions was measured, together with resin yields. Several new stable solutions which give high resin yields were obtained.
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Experimental Five parts of the catalyst suspended in 5 parts of water was added to 90 parts of furfuryl alcohol. Water sometimes aided solubility of the catalyst and exerted a moderating effect on the catalyst. Furfural has also been used as a diluent and moderator in impregnating solutions (2, 7, 77), but both the resin yield and chemical resistance are decreased as the proportion of furfural increases. T h e bulk of each formulation prepared was stored a t room temperature for evaluation of storage stability. Storage life was defined as the length of time required to reach a viscosity empirically
borderline stability, has a dissociation As the dissociaconstant of 10 X tion constant of the acids decreases, storage life increases and resin yield decreases. Malic acid with K1 of0.4 X provides good resin yield; succinic acid with XIof 6.5 X 10-6 is not satisfactory. T h e amine hydrochlorides show a confused picture as far as correlation of activity with base strength is concerned. Because the amine salts are prepared by neutralization, a slight excess of either acid or amine in the salt would have a profound effect on acidity and therefore on its utility as a catalyst.
established as too high for complete impregnation of fine-pored material. Resin yield was determined by heating a 10.0-gram portion of each formulation in a 25-ml. Erlenmeyer flask a t 100' C. for 24 hours. Somewhat higher yields are obtained in flasks than in watch glasses or Petri dishes.
Results Adequate storage stability is a flexible requirement depending upon the specific application and the rate at which the catalyzed solution is consumed. For classification purposes a storage life of less than 10 days and a resin yield of less than 60% have been arbitrarily designated as unsatisfactory. O n the basis of these criteria the catalysts tested have been separated into two groups, suitable and unsuitable. All of the so-called suitable catalysts are not of equal utility. T h e zinc chloride is in a class by itself in providing indefinite storage life for the catalyzed solutions. After 3 months' storage the viscosity remained unchanged a t 9 cp. (25' (2.). The other inorganic salts in Table I give considerably less storage life and are more expensive. Evaluation of the organic dibasic and tribasic acids shows a correlation between dissociation constant and catalyst activity. Maleic acid, which provides ~~
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Applications The low viscosity of the catalyzed monomeric furfuryl alcohol solution allows ready penetration of fine-pored materials with conventional vacuum-pressure techniques, T h e furfuryl alcohol resin may then be formed in the impregnated article by curing a t elevated temperatures. Good cures are obtained in 24 hours at 100' C. Higher temperatures may cause excessive exudation of resin and fracture of the impregnated article by trapped steam. Wood. Wide variations in resin content are possible with wood because of the large number of species and densities available. At 35y0 resin content impregnated southern yellow pine has ~~
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Table 1. These Satisfactory Catalysts for Furfuryl Alcohol Impregnating Solutions Provide Storage Stable Solutions Capable of Providing High Resin Yields Storage Life at Room Resin Yield Dissociation Temp., Days at 1000 c.,70 Constant, K I 79 Cd(N0a)t. 4Hn0 SV-6 CO(NO8)r.6Hzo Ni(N0a)z. 6Hz0 Zn(N0s)~.6HaO ZnClz Maleic acid Malonic acid Tartaric acid Citric acid Malic acid SV = slightly viscous.
SV-6 SV-6 VSV-6 Indef. 12 14 25
Over 1 mo. Over 1 mo. VSV = very slightly viscous.
78 79 78 72 71 71 76 75 73
VOL. 52, NO. 1
1.0 1.4
x x
10-2
4
x
10-4
10-3 9 . 6 X lo-' 8 . 7 x 10-4
0
JANUARY 1960
57
modified bending properties, and its flexibility and impact strength have been decreased to about half that of untreated wood. Hardness has been increased by 90% and crushing strength perpendicular to grain 260% in the wet condition. I n static bending the resinimpregnated wood shows an increase of 100% in stress a t proportional limit, an increase of 25% in modulus of elasticity, an increase of 300% in work to proportional limit, and a decrease of 50% in work to maximum load.
T h e chemical resistance is excellent. After exposure to boiling 10% sulfuric acid for 8 days, the resin-impregnated pine (35% resin content) had a wet crushing strength a t proportional limit of 700 p.s.i. compared to 500 p.s.i. for untreated unexposed wood and 180 p.s.i. for untreated wood exposed to the same conditions. After exposure to refluxing 5% sodium hydroxide for 8 days the resin-impregnated pine had a wet crushing strength of 450 p.s.i. compared to 100 p.s.i. for untreated exposed wood.
With These Catalysts, Viscosity Increases Too Fast or Resin Yields Are Too LOW Violent Polymerization at Room Temperature Polymerization Time, Min. ShCI,
10
15 30
60
FeCt.6Hz0 HCl Hzso4
90
EP EP EP
"03
Unstable Solutions at Room Temperature Dissociation Constant of Acid or Base
Storage Life at Room Temp. 5 min. 5 min. 2 hr. 2 days 40 hr. 30 min. 50 min. 60 min. 90 min. 5-40 hr. 2 days 6 days 9 days V-12 hr.; TP, 0
p-Toluenesulfonic Benzenesulfonic Dichloroacetic 5 x 10-2 Trichloroacetic 1.3 X 10-1 Oxalic 6.5 X Hydroxylamine. HC1 1.1 x 10-8 Aniline. HCI 3.8 X p-Chloroaniline HCl 8.5 x 10-5 p-Toluidine. HCI 2 x 10-9 Ethylenediamine. HCl 8.5 X Benzylamine. HCI 2.0 x 10-5 Quinoline. HCl 6.3 X Ethanolamine. HCI 2.8 X %PO4 AgN03 so SnClz.2H20 so Alcls. 6RzO VO, S-4 days AI(N0a)s.9H20 VO, 5-4 days CrCla. 6H20 VO, S-4 days Cu(NOz)*.3H10 VO, 5-4 days FedS04)a.XKO VO, S-4 days NHaN03 5-4 days CoCla. 6Hz0 TP-4 days MnCl?.4Hzo TP-4 days NiC12.6H20 TP-4 days NHdCl V-9 days No Polymerization at Room Temperature (Insoluble in Furfuryl Alcohol) Al~(S0n)a. 18HzO NaH2P04.H 2 0 CdClz. 2'/zHz0 (NHA)~SOA 3CdS04.8HzO NiSOa. 6H20 COS0~.7HzO Pb(NO8)z CUSOA. 5HzO ZnS04.7Hzo MnSO4.4H20 Stable Homogeneous Solutions with Poor Resin Yields Dissociation Resin Yield Constant at looo c., % Chloroacetic acid 1.4 x 10-3 33 1.1 x 10-3 59 Salicylic acid 1.8 x 10-4 47 Formic acid Benzoic acid 6.3 X 28 1 . 8 x 10-6 20 Acetic acid 7 x 10-6 29 Furoic acid 9.3 x 10-4 ( K ~ ) 54 Fumaric acid Succinic acid 6.5 X 10" (Ki) 46 Dimethylamine.HC1 5.1 x 10-4 33 41 NH~HIPO~ 48 NRiSCN viscous, 0 = overnight, S = solid, TP = two phases, E P = explosive polymerization. V
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Wherever wood is now used in chemical process equipment such as filter press plates and frames, vacuum filter leaves, tanks, tank covers, and agitators, longer service can be obtained by use of furfuryl alcohol resin-impregnated wood. Brick. Chemically resistant bricks (Duro Dot) were given a double impregnation with a furfuryl alcohol impregnating solution. After exposure to 10% sodium hydroxide a t 300' to 350' F. for 2 weeks, untreated brick had a weight loss of about 1870 while the treated brick lost only 13%. O n exposure to 20% sulfuric acid at 415' to 460' F. for 2 weeks, untreated brick picked u p 10% of its weight of acid while treated brick picked u p only 3.5%. Carbon. Carbon rods with an original porosity of 28,2y0 and apparent density of 1.35 grams per cc. xere given a double impregnation with a furfuryl alcohol impregnating solution. The first impregnation reduced the apparent porosity to 9.8% and the second to 1.6% with an apparent density of 1.68 grams per cc. T h e treated carbon, unlike the untreated, did not chip or flake when cut. Impact strength, hardness, and resistance to oxidation were increased by the resin treatment.
Acknowledgment T h e bricks were impregnated and tested by Thomas M. Davis and the carbon by William J. Oberley.
literature Cited (1) British Thomson-Houston Co., Ltd., Brit. Patent 549,515 (Nov. 25, 1942). (2) Campbell, J. A. ( t o Kewaunee Mfg. Co.), U. S. Patent 2,333,151 (Nov. 2, 1943). (3) Dunlop, A. P., Stout, P. R. (to Quaker Oats Co.), Ibid.,2,584,681 (Feb. 5,1952). (4) Harvey, M. T., Durst, R. F. (to Harvel Research Corp.), Ibid., 2,383,793 (Aug. 28, 1945). (5) Hebcrer, A. J., Marshall, W. R. (to Glidden Co.), Ibid., 2,095,250 (Oct. 12, 1937). ( 6 ) Hersh, H. I. (to Owens-Illinois Glass Co.), Ibid.,2,432,890 (Dec. 16, 1947). (7) Kiefer, E. F. (to National Carbon Co.), Zbid.,2,174,887 (Oct. 3, 1939).
(8) Korten, E. (to General Aniline and Film Corp.), Ibid., 2,321,493 (June 8, 1943). ( 9 ) Meiler, J. G. (to Marathon Paper Mills), Ibid.,2,243,481 (May 27, 1941). (10) Nordlander, B. W. (to General Electric C o . ) , Ibid., 2,399,055 (April 23, 1046) -, .",. (11) Reineck, E. A . (to Kewaunee Mfg. Co.), Ibid.,2,367,312, (Jan. 16! 1945). (12) Root, F. B., Virgm, C. W. (to EllisFoster Co.), Ibid., 2,368,426 (Jan. 30, 1945). (13) Trickey, J. P., Miner, C. S. (to Quaker Oats Co.), Ibid., 1,665,235 (Xpril 10, 1928). (14) White, E., Smucker, C. A . (to Owens-Corning Fiberqlas), Ibtd., 2,397,453 (March ZG,1946): RECEIVED for review May 20, 1959 ACCEPTED September 8 , 1959
