I
L. H. BROWN,
D.
D. WATSON, and K. J. SIEGFRIED
John Stuart Research Laboratories, The Quaker Oats Co., Barrington, 111.
Furfurylated Novolak Resins Applications in laminates, coatings, and molding powders G R I N D A m E , chemically resistant intermediate resins, curable without acids, can have numerous industrial usese.g., in molding powders and laminates which are used in pipes and tanks for chemical equipment. Furfuryl alcohol-formaldehyde resins can be made grindable, but they require acid catalysts for curing to high alkali resistance. Phenol-formaldehyde-furfury1 alcohol resins have been made only as liquids, most of which cure with acids (7, 2, 4, 5). They have good resistance to alkalies, and all use phenol or a n alkaline-condensed, one-stage phenolic resin. They may be considered as derivatives of polymethylol phenols. Reaction products of furfuryl alcohol and novolaks, and evaluation of their end products are discussed in this article.
Experimental Resin Preparations. Ten moles of phenol (940 grams) and 29.25 grams of 9.65% sulfuric acid (0.3% H,SO4 based on phenol) were mixed at about 45" C. in a 3-liter resin kettle equipped with a thermometer, a reflux condenser, and an anchor-tYPe stirrer. The solution was heated to 100' C., and then 7.5 moles of 37% formalin (608 grams) were added dropwise for 30 minutes: without external heating. After adding all of the formaldehyde, heat was applied and the batch was held at reflux temperature for 5 hours. After this time the formaldehyde odor had disappeared, so the acid catalyst was partially neutralized with 22.8 ml. of lOyo sodium hydroxide. pH of the aqueous layer was 2.6. The water was removed by distillation. Ten moles of furfuryl alcohol (980 grams) were added over a 20-minute period, at temperatures from 115' C. (initial) to 80' C. (final). The condenser was arranged for azeotropic distillation by adding a Barrett trap, and 170 of benzene was added to the reaction mixture. Water was removed as formed, and the reaction was allowed to proceed until no more water was being formed (about 3 hoyrs, pt temperatures up to 117' C.). The resin was neutralized further with 0.32 gram of sodium hydroxide dissolved in a minimum of water and mixed with 15 ml. of furfuryl alcohol. Benzene, water, and furfuryl alcohol were removed by distilling. Melting point of the resin was 70' to 80' c. The theoretical yield for the f&furylation step would be 958 grams of novolak plus 980 grams of furfural alcohol, minus 180 grams of water, or a total of 1758 grams; the actual yield is 1697 grams, or 97y0 of the theoretical.
amyl alcohol, and in 75-25 vol. % ethanol-methyl ethyl ketone were applied to black iron and tin-plated panels. The resins were catalyzed with 12% hexamethylenetetramine, and applied in thicknesses up to 6 mils. The baking cycle used was 30 minutes at 75" C., 10 minutes at 115 ' C., and 60 minutes at 150 'C. Spot tests were run overnight at room temperature with 10% sodium hydroxide and 95% sulfuric acid. The samples were covered with watch glasses. Resin 224-87 (Table I) appeared resistant to both acid and alkali, and had about 0.9 mole of furfuryl alcohol combined per mole of phenol, judging from water evolved during preparation. Resin 22497, in which about 0.8 mole furfuryl alcohol had combined, had good resistance to acid but only fair resistance to alkali. Resin 199-176, made from 1.5 moles of furfuryl alcohol per mole of phenol, had only fair resistance to acid and alkali. All coatings were brittle and had poor adhesion to tin plate. The latter property was partially remedied by use of Du Pont's Submarine Primer.
I n making some of the resins, water of condensation was removed as formed by a different distillation method; the benzene azeotrope was not used. The kettle was fitted with a steam-heated condenser followed by a water-cooled one, to allow refluxing of furfuryl alcohol and distillation of water. This method has some ,production advantages, but some furfuryl alcohol distills with the water of reaction as indicated in Tables I and 11.
Evaluations Laminates. Alcohol-benzene solutions of the resins, catalyzed with hexamethylenetetramine, were used to make canvas-based laminates. Precuring temperatures were 90' to 110' C., and curing cycles were 17 to 30 minutes a t 160' C. and 500 p.s.i. The resulting laminates with 40 to 50% resin content, appeared resistant to short contact with acetone, pyridine, 10% sodium hydroxide, and concentrated sulfuric acid. Shore D hardness was 90, and flexural strength was about 18,000 p.s.i. Coatings. Solutions of resins in 5040-10 vol. % benzene-isopropyl alcohol-
Table I.
Optimum pH Range Is 2.4 to 3.3
(Furfuryl alcohol-phenol ratio, I; formaldehyde-phenol ratio, 0.75) Resin Number
PH
Time, Min.
224-62 224-64 22497 224-87 224-80 224-85 199-17811
1.5 2.4 2.6 2.75 3.0 3.2 4.2
25 105 240 285 360 540 120
a
O
Per mole of furfuryl alcohol charged.
Table II.
Water Formed, Molea
Temp.,
c.
... 108-123
... 0.92b
115-117 104-131 115-135 120-135 125-135
0.79 0.92 0. gob 0.91 0.0
''
Yield,
%
Gelled 95 97 92 97 101 No reaction
Melting Range,
c.
75-85 70-80 52-62 58-68 55-65
Includes some furfuryl alcohol.
CHzO-Phenol Ratio of 0.75 Is Optjmum tFurfuryl alcohol-phenol ratio, 1)
Resin Number
CH20/
224-58 224-64 199-174 199-173 224-87 199-179
0.66 0.75 0.80 0.85 0.75
i:;
0.75 0.80
pH
... 2.4 2.4 2.4 2.75 2.70 3.2 3.3
Time, Min.
Temp.,
300 105 43 75 285 120 540 210
100-125 108-123 122-116 106120 104-131 133-110 120-135 115-132
' Per mole of furfuryl alcohol charged.
''
O
c.
Water Mole'
Yield,
0.64 0.92b 0.39* 0.66'' 0.92 0.44 0.91 0.83
90 95
%
... .10192. . . a .
97
Melting 'Range, O
c.
50-60 75-85 Gelled Gelled 52-62 Almost gelled 55-65 43-53
Includes some furfuryl alcohol.
VOL. 50,
NO. 11
4
NOVEMBER 1958
1675
An unmodified novolak, cured with hexamethylenetetramine, gave a film which was attacked almost instantly by 10% sodium hydroxide. Furfuryl alcohol polymer, cured with acid, was attacked by 95% sulfuric acid overnight. An unmodified epoxy resin, cured with an aromatic diamine, was attacked in a few minutes by 95% sulfuric acid. Several blends were prepared from furfurylated novolaks and Bakelite Epoxy ERL 2774, a viscous resin with an epoxy assay of 185 to 200 grams per gram-mole of epoxy. The proportions tested were equal parts by weight, and 10 parts of furfurylated phenolic to 15.8 parts of epoxy. Solvents used were dioxane and methyl ethyl ketone. Good cures were obtained in the baking cycles used for unmodified resins with either 12% hexamethylenetetramine, 2% n-tributylamine, or 17.5% methylenedianiline (based on the resin). Resin 224-82 appeared to be compatible with poly(viny1 acetate) (Vinylite AYAF), poly(viny1 butyral) (Vinylite XYHL), vinyl chloride-acrylonitrile copolymer (Vinyon N), and GR-S. Molding Compounds. Molding compounds were prepared from furfurylated phenolic resins using the following formu1.a :
Parts by Weight Resin Wood flour Shell flour Hy-flo (a diatomaceous earth) Nigrosine (alcohol soluble) Stearic acid Hexamethylenetetramine Boric acid
44.3 42.6 13.6 3.4 1.9 1.1 4.4 4.4
The compounds were milled on a small set of plastic milling rolls a t a front roll temperature of 180’ F. and a back roll temperature of 230’ F. They were molded a t 350’ F. and 2000 p.s.i. Molded bars had a flexural strength of 11,000 p.s.i., with either an unmodified or a furfurylated novolak.
Reaction Variables Fufuryl Alcohol-Phenol Ratio. Good yields were obtained for all molar ratios between 0.5 to 1.5:
Rwin Number 1919-175
224-70 224-64
199-176
Ratio FAa t o Phenol 0.50 0.75 1.0
1.5
Yield, % 96 100 95 85
The Quaker Oats Co.’s brand of furfuryl alcohol. a
1 676
Reaction pH. The most critical point in making a furfurylated novolak resin is adjustment of p H prior to dehydration of the initial phenol-formaldehyde condensate (Table I). The reaction time is that which elapsed between addition of furfuryl alcohol and neutralization. The water formed is a minimum value because furfuryl alcohol reacted is always less than that charged, and removing all water from the resin is difficult. According to refraction indices, water which separated from the system to which benzene had been added was reasonably pure. Thus, if corrected, about 1 mole of water would be obtained for each mole of furfuryl alcohol which reacts. If the reaction were intermolecular condensation of furfuryl alcohol this value would be unlikely without gelation. The optimum p H range is 2.4 to 3.3. Below this, cross linking occurs and above the reaction is too slow. At p H 4.2, no reaction is obtained. Formaldehyde-Phenol Ratio. A formaldehyde-phenol ratio of about 0.75 appears to be optimum (Table 11). At lower ratios, the products are low melting, and at higher ratios, premature gelation is obtained. Removal of all free phenol from a novolak made with 0.75 mole ratio gave gelation at an early stage in the reaction with furfuryl alcohol -even at a relatively high pH. Using a formaldehyde-phenol ratio of 0.75, resins were made successfully at p H 2.4, 2.7, and 3.2. Only at pH 3.2, however, could a resin be obtained with a mole ratio of 0.80 or higher.
Chemistry of Reaction If furfuryl alcohol polymer was formed during the resin preparation, this would account for consumption of furfuryl alcohol and evolution of water. However, less than a mole of water per mole of furfuryl alcohol charged is normally obtained before gelation in making a furfuryl alcohol polymer. I t may be argued that novolak acts as a solvent for the furfuryl alcohol polymer ; but gelled furfuryl alcohol polymer does not dissolve in furfurylated novolak. Liquid furfuryl alcohol polymer in novolak is gummy, and brittle furfuryl alcohol polymers are not known. Furfuryl alcohol polymers are largely insoluble in 10% sodium hydroxide solutions, even when these solutions contain novolaks. As some furfurylated novolaks are soluble in 10% sodium hydroxide before they are cured, it is improbable that these resins contain much furfuryl alcohol polymer. This reaction may follow etherification of hydroxyl groups, which would give extremely high hydroxyl equivalent weights. A number of hydroxyl determinations ( 6 ) have been run on furfurylated novolaks from both phenol and p-cresol. I n
INDUSTRIAL AND ENGINEERING CHEMISTRY
all cases these equivalent weights were in the range as expected if the phenolic hydroxyls were still available. For example, a p-cresol-formaldehyde resin ga>e a hydroxyl equivalent weight of 121, and after reacting half a mole of furfuryl alcohol per mole of p-cresol the equivalent weight was 164. Hachihama and Shono (3) indicated that furfuryl alcohol reacts with phenols in the presence of acids to produce o-furfuryl phenols. An analogous reaction may be obtained with phenolic resins. However, judging from curing properties, this may not be the predominant reaction route. Cross Linking. Curing was investigated by comparing disks made from molding powders containing phenol- and p-cresol-formaldehyde resins and furfurylated novolaks of both types. The resins were made from equimolar quantities of furfuryl alcohol and phenol or p-cresol.
Table 111.
Molding Tests Cure Time,
Resin Type
Min.
Result
Phenol-CHzO p-Cresol-CHz0 FAa-p-cresol-CH~O FA-phenol-CHzO FA-phenol-CHPO
1.0 30.0 30.0 2.0 3.5
Cured Uncured Uncured Uncured Cured
a
Furfuryl alcohol, the Quaker Oats Co
brand.
The first two resins in Table I11 (nonfurfurylated) confirm that cure normally occurs through an open ortho or para position. Failure of the third resin, a furfurylated p-cresol, to cure indicates that the furan ring does not add to the functionality of a resin under these conditions. As the furfurylated phenolformaldehyde resin cures, either the ortho and para positions in the novolak are not substituted, or the furan ring takes part in the cure.
Literature Cited (1) Dunlop, A. P., Reineck, E. A. (to Quaker Oats Co.), U. S. Patent 2,453,704 (Nov. 16, 1948). (2) Ibid., 2,456,628 (Dec. 21, 1948). (3) Hachihama, Y., Shono, T., “Studies
on the Furfuryl Alcohol Resin-I,” Technol. Repts. of Osaka University, Vol. 4, No. 133, pp. 421-2, Osaka, Japan, 1954. (4) Korten, E. (to General Aniline and Film Corp.), U. S. Patent 2,321,493 (June 8, 1943). (5) Lebach, H. H. (to Haveg Corp.), Ibid., 2,471,631 (May 31, 1949). (6) Ogg, C. L., Porter, W. L., Willits, c. o.,IND. ENG. CHEM., ANAL. ED. 17, 394-7 (1945). for review October 26, 1957 RECEIVED ACCEPTEDApril 21, 1958 Division of Paint, Plastics, and Printing Ink Chemistry, 132nd Meeting, ACS, New York, September 1957.
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