Effect of Chemicals on
Phenol Resin Bonded Laminated
TI ith sodium silicate, and photographic film development equipment. Such applications indicate that the material has possibilities in resisting corrosive effects which are fully as great as its value as an insulator. The versatility of the general reaction between phenols and aldehydes resulting in the formation of resins, and the many modifications possible for specialized uses are reflected in the types of laminated available. No single resin or varnish combines all the properties for the best performance under all conditions of use. Likewise, no single filler meets the requirements for all purposes: neither will a set method of processing resin or varnish and filler into the finished laminated sheet result in an all-purpose product. Therefore, this paper will be devoted to a brief review of the physical properties of all laminated and a report of the effect of some common chemicals on canvas-base laminated which is bonded with a phenolic resin developed particularly for chemical resistance. Later papers will discuss the chemical resistance of paper base laminated and various other laminated in which the bond consists of other types of phenolic resins which are available for the purpose.
Preparation and Physical Properties Because of the nature of the filler, which may be highly absorbent and readily attacked by chemicals, the inertness of the laminated to chemical attack depends on the protection of the fibers by the resin bond. The usual method of protecting the fibers is to pass the fibrous base materials through a solution of the resin dissolved in solvents and then to evaporate the solvents from the impregnated sheet in heated ovens. By varying the type or amount of resin in the solution and the speed of impregnation and temperature of the oven, the impregnated sheet may have a corresponding variety of properties. To prepare flat panels, the impregnated web is cut into sheets of the desired size. A number of these sheets are superimposed, placed in a hydraulic press, and subjected to heat and pressure. Tubes are prepared by winding the impregnated web onto a mandrel and subjecting to heat with or without pressure. Rods may be prepared in much the same manner. Heat polymerizes or cures the resin to the insoluble, infusible condition; usually, the longer the cure, the more inert the resin becomes. Pressure compacts the mass to a hard, dense, more or less rigid structure. During the cure and before the resin sets, the resin fluxes and flows, penetrating every crevice of the fibrous structure and also forming a protective film on the surfaces of the sheets. Phenol resin bonded laminated products (sold under such trade names as Synthane, Formica, Phenolite, Micarta, Textolite, Panelyte, Lamicoid, Spauldite, and Dilecto) may be obtained in sheets, tubes, and rods which may be further fabricated into desired shapes by sawing, drilling, tapping, or punching. The tubes and rods may also be threaded. Simple objects of uniform cross section may be obtained without the need of further processing, or the laminated may be combined with other types of phenolic molding compounds to make more intricate pieces. The variety of properties available is governed by the amount and type of phenolic resin bond and by the type of filler. Considered as a sheet, the laminated is a comparatively dense, uniform solid, stronger than wood and metal in many applications and, because of its resiliency, less likely to fracture than various metal alloys. Table I gives data which may be considered indicative of the physical properties of phenol resin laminated made with the several types of filler and various amounts of resin bond. The values given do not represent a range of test data on a single sample but are the extremes noted in data covering numerous samples.
H. E. RILEY Bakelite Corporation, Research and Development, Bloomfield, N. J.
The data show that, within limits of concentration of chemical and elevation of temperature, the phenol resin bonded laminated tested is sufficiently inert to be used in a number of applications requiring chemical resistance. CanvasLase laminated, exposed to widely differing types and concentrations of chemicals and temperatures, shows a surprising uniformity in maximum weight increase. This maximum for a 50 per cent resin bond is almost identical with known data for the 100 per cent resin structure.
APER and cloth sheets when laminatedthat is, bonded by the combined action of heat and pressure with various types of phenol resins and thus combining high mechanical strength and good electrical insulating qualities-have been used for many years almost exclusively in the electrical insulating field. In recent years, however, uses of these laminated products have been expanded to such diverse applications as breaker strips on mechanical refrigerators, plating barrels and conveyor chains in cyanide plating baths, pump valves and disks in deep oil wells, and table tops and bar tops in hotels and restaurants which are subject to contact with various foods, drinks, and cleansing preparations. Other uses are as vanes in a pump handling corrosive mine water, housings for steam sterilizers, gears in scrubbing machines, links of the conveyor of an automatic dishwasher, .piping handling chemicals in a paper mill, rollers in a pastlng machine in contact 919
ISDUSTRIAL A S D ENGINEERING CHEMISTRY
VOL. 28. NO. 8
GRAPHI. HIGH(20) PERCESTACIDTYPES 77a F. 1. Sulfuric acid, zinc chloride,
8. 9.
ferric chloride Nitric acid 3. Hydrochloric acid 4. Hydrofluoric acid 5 . Phosphoric acid 6 . -4cetio acid, citric acid 7. Aluminum chloride
in.
2.
11. 12.
13. 14. 15.
140' F. Sulfuric acid Nitric acid Hydrochloric acid Phosphoric acid Acetic acid Citric acid Aluminum chloride Ferric chloride, zinc chlcride
0
GRAPH11. Low (ONE) PERCENT ID TYPES 77O F. 16. Sulfuric acid, nitric acid, hydrofluoric acid (30 days only) 17. Chromic acid 18. Hydrochloric acid, phosphoric acid 19. Acetic acid, citric acid 20. Aluminum ohloride, zinc chloride, ierric chloride
140° F. Sulfuric acid Nitric acid Chromic acid Hydrochloric acld 25. Phosphoric acid 26. Acetic acid, citric acid 21. Aluminum chloride, zinc chloride, ferric chloride 21. 22. 23. 24.
0
ASD GRAPH111. HIGHPERCENTOXIDIZING TYPES
% 20 Sodium hydroxide 7 1 Potassium permanganate 13 5 Potassium dichromate 20 Sodium carbonate 13 7 Trisodium phosphate 20 Sodium sulfite; sodium thiosulfate (hypo)
GRAPHIv.
ALKALISE
770 F
140' F
h B
G
n
C
I
D E
.J
Ii
€
L
L O W P E R CENT OXIDIZING, -4LK.ILINE AXD
MISCELLAXEOUS
% 1 Sodium hydroxide 0 . 3 5 Potassium permanganate; 0 . 6 7 potassium dichromate Sodium hypochlorite solution (1% available chlorine) Sodium carbonate; sodium sulfite: SO1 dium thiosulfate (hypo); 0.68 trisodium phosphate: water Ethyl lactate
7 7 O F.
140°
11
R
N
S
0
T
P
I!
Q
v
F
ISDUSTRIAL AND ENGINEERING CHEMISTRY
AUGLST, 1936
TABLEI. PHYSICAL PROPERTIES Specific gravity
Minimum 1 32
Maximum 1.41
30 70
40 94
0,00002 8,500
0.00003 24,000
1,000,000
2,500,000
15,000 15,000
30,000 24,000
30,000 18,000
43,000 35,000
400 400 170 250
900 1,400 700 1,000 6.0 10.0
Re;Jitanee to heat (safe lim Hardness (sample flatwise) : Brinell Scleroscope Coefficient of expansion (sample lengthwise) per C. Cltimate t e n d e strength,b lb./sq. in. Mpdulus of elasticity (from tensile test), lb./sq. in. Bending te8t.b ultimate strength, lb./sq. in.: Sample flatwise Sample edgewise Compression test,b ultimate strength, lb./sq. in.: Sample flatwise S a m d e edgewise Dielectric stiength,b volts/mil thickness: '/E in. sample (instantaneous) ','win. sample (instantaneous) l/s-in. sample (step) '/win. sample (step) Dielectric constant5 ' Power factorb (106 cycles), % Vol. resistirity,b ohm cm. a
b
4 5 3 0 109
10'8
Water absorption vaiies. depending upon size, shape, etc., of sample. l l e t h o d p according to A . S.T. M.
Test Conditions In purely mechanical or insulating applications the physical properties of laminated may be considered fairly stable, although in the latter application low moisture absorption is a prime requisite. Physical properties, however, are not always indicative of the behavior of laminated when exposed to the corrosive effectsof many chemicals and solutions. The present uses of laminated under conditions of chemical attack are an indication of its usefulness. The chemist or engineer, however, may not find in the examples the application which approximates his own problems, and he will be interested in specific data on the extent of chemical attack (if any), weight change, and dimension change as an aid to his choice of materials. Because of the many types of phenol resin varnishes which have been developed for use in the bonding of filler sheets to make laminated articles, it seemed desirable to confine this paper to the effect of chemicals on laminated made from one type of varnish and one type of filler only. The laminated samples were comparable to a type of the commercially available supply and were limited to the C grade with 10-ounce canvas duck filler, impregnated with the Bakelite resin already mentioned. The resin content of the samples was approximately 50 per cent. Specimens measuring x 1 X 3 inches for all tests were cut from a single large sheet, so that all results iTere comparable. The size of the test pieces is that recommended by the A. S. T. hl. Method D229-31T for the determination of water absorption of laminated. The pieces were not conditioned before the tests started. The size was also convenient for individual tests, and each piece was completely immersed in its solution in a 11/4X 5 inch test tube which was kept closed during the test. Tests were made a t room temperature and a t 140" F. The chemicals were those commonly used in many industries, and water was included for purposes of comparison; ethyl lactate, a medium-boiling solvent, was included as representing in solvent properties both alcohols and esters : Mineral acids, oxidizing Mineral acids
Organic acids
Acid salts Strong alkali Oxidizing agents Alkaline salts Water Organic solvent
%So4 "01 HzCrO4 HC1, H F , H d O , Acetic, citric Alc11, ZnClt, FeCL NaOH KMnO4 KzCrz01 NaClO NazCOa,' NasPOcilHnO, Na?StOa,5H?O,Na?SOa Salt water tap water Ethyl 1act;te
92 1
Water solutions of 1 and 20 per cent concentrations of the chemicals were used, except with those chemicals of limited solubility. Potassium permanganate was used in concentrations of 7.1 and 0.35 per cent; potassium dichromate, 13.5 and 0.67 per cent; trisodium phosphate, 13.7 and 0.68 per cent; and sodium hypochlorite in solution containing 1 per cent available chlorine. The salt water corresponded to sea water. Before placing the test pieces in the solutions, they were weighed and measured for thickness. The samples were examined a t various intervals, and inspection consisted of noting the weight change, measuring the thickness (at 10 days only), and noting the condition of surface, laminations, and edges. Before each weighing the pieces were rinsed in water and dried as thoroughly as possible with a cloth. They were immediately replaced in the chemical solution after each inspection. The tests ran a total of 180 days.
Discussion of Test Results Weight change may ordinarily be considered a measure of the permeability of the sample and an indication of the degree of protection of the fiber by the resin bond. Graphs I to IV present the weight changes observed as the tests progressed. Where several chemicals of the same concentration were found t o cause increase in weight in the same range, it was convenient to average the values and construct a composite curve. I t \vas also Convenient to use a semilogarithmic scale for the abscissas of the curves for clearer presentation of the slowing down of rate of weight change with unit time, as the saturation point was approached. With several exceptions the most striking feature of the curves is the similarity of total weight change which lies generally in the range 2.5 to 4 per cent for all concentrations of chemical solution and for normal and elevated temperatures. In addition, the rate of increase in weight is initially more rapid at elevated temperatures and the maximum ie reached in fewer days, but the final, more or less stable condition of absorption is only slightly different from that obtained a t normal temperatures. Other experience with the phenolic resins indicates that pure resin alone will generally increase in weight about 3 or 4 per cent when immersed over long periods in water. If the time of exposure in the present tests may be considered sufficient t o reach that maximum in pure resins, it is evident that the absorbent filler has been exceptionally well protected. The rate and amount of absorption depend to some extent on the ratio of the area of cut surface to total area exposed. The specimens had a total of 8 square inches of surface exposed, of which 2 square inches were cut surface. There is no hard and fast rule by which the effect of this ratio may be expressed, but in general the greater the area of cut surface to the total area, the higher will be the absorption. In the present tests no attempt was made to protect the cut edges, but chemical-resistant varnishes could be applied for this purpose. Visible signs of absorption were evident in all samples and appeared as a slight increase in thickness, much like a ring extending along the edges of the specimens and gradually striking deeper into the samples as tests continued. Table I1 shows this thickness change in per cent after 10-day immersion, with the corresponding weight change. The percentage change is the average of three or four measurements taken a t uniform intervals over the surfaces of the test pieces. The increase in thickness generally follows the increase in weight, and the dilute solutions show a greater increase in thickness than concentrated solutions. The reason for this behavior is obscure, but we might surmise that the presence of larger quantities of chemicals in the
TABLE 11. EFFECTO F IMMERSION O F
LAMIN.4TED
Chemical
Concn
% His04
HNOs
HgCrO,
HC1
HF Hap04
.4cetic acid
Citric acid
AlClr
ZnClz
FeCh
NaOH
KIvInOa
NaClO
VOL. 28, NO. 8
INDUSTRIAL AND ENGISEERING CHEMISTRY
922
1 1
IN
CAKVAS-BASE P H E X O L RESINBONDED VARIOUS CHEMICALS
SOLUTIONS O F
Increase after --lo DaysThickWeight Temp ness F. % % 1.20 1,88 77 2.00 3.07 140
20 20
77 140
0.39 1.54
1.05 1.82
1 1 20
77 140 77
1.15 2.26 2.68
1,50 2.52 1 57
20
140
7.28
5.34
1 1 20
77 140 77
1.93 2.69
1.25 3.07
20 1 1
140 77 140
..
..
1.56 2.29
1.46 2.60
20 20
77 140
0.77 1.92
0.60 1.36
1 20 1 1 20
77 77 77 140 77
1.94 1.16 1.95 1.50 1.15
1.68 1.78 1.55 2.59 1.25
20
140
1.13
2.13
1 1 20 20 1 1 20 20 1 1
77 140 77 140 77 140 77 140 77 140
1.57 1.50 1.56 2.63 1.90 1.12 1.95 1.12 1.97 1.90
1.43 2.05 1.19 2.35 1.42 2.56 1.31 2.32 1.48 2.59
20 20 1 1 20 20 1 1
77 140 77 140 77 140 77 140
0.41 1.15 2.68 2.21 1.19 1.53 1.10 2.29
0.67 1.04 1.34 2.74 1.12 2.25 1.84 2.78
20 20 1 1 20
77 140 77 140 77
1.55 1.53 1.58 2.27 3.53
0.96 1.99 1.89 2.92 2.16
20
140
..
11.8
..
9.43
0 . 3 5 77 0.35 140 7.1 77
2.33 2.24 2.36
1.82 2.91 2.57
7.1
140
1.87
3.70
77 140 77 140
1.55 2.26 1.56 2.32
1.44 2.68 1.48 2.85
0.67 0.67 13.5 13.5 1.% available Ch 1 1 20 20 0.68 0.68 13.7 13.7 1 1 20 20 1
Condition of Sample a t 180 Days“ Slightly darkened and dulled Dark, dull, mottled, no attack apparent but slight loss in wt. Darkened Blistered and losing wt. a t 106 days; removed Slightly pimpled Surface fibers swollen P i m d e d and verv- rough - a t 60 davs; re‘moved Surface soft and mushy a t 10 days, a t . increase 5.3%; removed Slightly rough No attack apparent Surface soft, losing wt. a t 1 day: removed Same Dull and darkened Dull and darkened, mottled, slight wt. loss Blistered a t 106 days. removed Blistered and losing a t . after 10 days: removed No change 30 days; test stopped Same Slightly rough Dark. dull. mottled. slieht wt. loss Slightly rough, no a a a c k apparent: final wt. increase, 4.8% Dark dull mottled loss of wt. after 30 da& bub no a t t i c k apparent; final wt. gain 2.6% Surface rough Dark, dull, and mottled Slightly rough Dark. dull. and mottled
No attack Dark and mottled n o attack apparent but slight loss id wt. No attack Dark and mottled Dark and dull Surface fibers slightly swollen Dark and dull Same No attack Dark, dull, and mottled; slight losa in wt. No attack Same Rough. ed es showed slight erosion Dark i n d full Swelled and blistered, 5.3% ,wt. increase a t 30 days 14 wt. increase a t 106 da 8 ; r e m b v e r Rough anc? blistered a t 10 days, greatly swollen; removed Slightly rough Dark coating fibers slightly swollen Slightly rough dark coating; removed a t 106 day: because of loss of liquid from teRt tube Dark coat’ removed a t 30 days because of ioss of liquid from test tube Dull and darkened Dull darkened and mottled D a r i and motiled Dark, mottled, and dull
1.62 Slightly rough 1.54 77 Slightly rough, dark, dull 2.55 2.68 140 Dark and mottled 1.42 1 . 1 7 77 NazCOJ N o attack 2.26 2.67 140 Dark and mottled 1.11 1.62 77 Dark, mottled, and dull 2.08 1.12 140 1.61 No attack apparent 1.58 77 Same 2.80 2.61 140 1.51 Same 1.97 77 Same 2.30 2.83 140 Dull dark and mottled 1.37 1.14 77 Dull’and dark 2.00 3.16 140 1.15 Dull, dark, and mottled 0.87 77 Same 1.18 2.17 140 Same 1.46 1.57 77 Same 2.68 2.75 1 140 Same 1.27 1.19 20 77 Same 2.20 20 140 1.96 Dull and dark 1.50 1.98 .. 77 Salt water Same 1.96 2.67 .. 140 Dull, dark, and mottled 1 . 4 1 2.30 77 T a p water Same 2.37 2.87 140 0.10 Same 0.00 . 77 Ethyl lactate Dull s n d darkened 0.70 0.79 140 Weight loss refers to a decrease from the maximum weight gained.
.. ..
...
solutions, within limits, has an increasingly large inhibiting effecton osmotic absorption of moisture, or may cause actual physical changes in the sample which limit absorption. Table I1 also tabulates the condition of the samples as observed after 180-day exposure, or less if by reason of attack or other cause the samples were removed. The exceptions to the similarity of total weight change are confined to the higher concentrations of those chemicals which might be expected to have the greatest chemical effects. Here again the tests a t elevated temperatures show a more pronounced initial change in weight. Of these chemicals, chromic acid has by far the most rapid and destructive effect. Based on these results the use of laminated in contact with solutions of this acid more concentrated than 1 per cent should not be considered. Nitric acid and sodium hydroxide also appear to attack the laminated rapidly, and absorption is quite high. Such attack, however, does not necessarily entirely impair the usefulness of the laminated as illustrated by the following applications. A canvas-base laminated frame is being used for holding halftone etchings in a bath of 20 per cent nitric acid a t about room temperature. The acid is constantly agitated and air is blown through to remove fumes. The laminated frames have a useful life of about 9 months. Metal frames under the same conditions must be replaced every 3 or 4 weeks. In another case a canvasbase laminated bearing ring must run in contact with 10 to 15 per cent sodium hydroxide solution a t elevated temperatures. After 2 yearr the ring looks badly eroded but has retained its strength and shape and is still in use. Metal rings in the same application had a t best a useful life of only a few months. In considering laminated for applications requiring chemical resistance, the following factors should be given their due weight: (1) relative lightness as compared to metal; (2) retention of strength in spite of chemical attack; (3) relative length of useful life under corrosive conditions as compared to other materials; and (4)cost and ease of replacement. RECEIVED March 14, 1936.
Correction In the article on ‘‘Temperature in Industrial Furnaces” [IND. ENG.CHEM.,28, 70810 (1936)]by H. C. Hottel, F. W. Meyer, and I. Stewart, the connection of Mr. Ian M. Stewart was not properly given. Although he is now doing graduate work a t the Mmsachusetts Institute of Technology, he is the Walter and Eliza Hall Travelling Scholar from the University of Queensland, Commonwealth of Australia.? H. C. HOWEL
