LINSEED OIL FILMS PERMEABILITY, ADSORPTION, AND SOLUBILITY HENRY FLEMING PAYNE American Cyanamid Company, Stamford, Conn., and Polytechnic Institute, Brooklyn, N. Y.
Large differences in permeability, adsorption, and solubility are found between films made from untreated alkali-refined linseed oil and films made from the oil after heat treatment. The increase in time of heat treatment does not produce so much difference in these film properties as is shown between the untreated and relatively short heattreated oils. The difference in these properties of films made from oils which have been heat-treated in air and those heat-treated in vacuum is relatively small. The water adsorption of films made from highacid oils is greater than that of films made from low-acid oils, but the diffusion of moisture through a film is retarded by the metallic soaps formed in high-acid oils so that the permeability to moisture of the high-acid oil 6lms was lower than the lowacid oil films. The effect of oxygen absorption, with consequent decomposition products in air-dried films, is to lower their water resistance as compared with 6lms which are baked. It is not possible to relate directly the physical and chemical characteristics of a series of oils to the physical properties of films made from these oils because of the large number of variables involved.
INSEED oil, when spread out into a relatively thin film, will dry; that is, it will change from the liquid t o the solid state. This change of state is the result of both chemical and physical reactions. Many workers have shown that linseed oil dries by a combination of oxidation and polymerization, and that the relative extent of each is modified by the pretreatment of the oil. It has also been found (8) that, if drying were purely a matter of oxygen absorption, the molecules of linolenic and a-eleostearic glycerides should absorb the same amount of oxygen, because they are isomers which differ only in position and arrangement of the double bonds. The difference in gelation time and amount of oxygen absorbed shows that association or polymerization is taking place coincident with oxidation:
L
Glyceride
Gel Time
Grams Oz/Gram Oil
Linolenic a-Eleostearic
3 hr. 39 min. 2 16
0 1030 0.0534
It was also found that linseed oils with different degrees of unsaturation absorbed nearly the same weight of oxygen up to the gel point; this indicates that gelation does not correspond to complete oxidation but occurs when a certain size, complexity, or polarity of the molecule is reached. The importance of molecular complexity is again indicated when the methyl ester absorbs 30 per cent more oxygen than the glyceride but does not gel, and the pentaerythritol ester absorbs only 29 per cent as much oxygen and gels much faster. The ultimate analysis of linseed oil films and gels of different ages showed (9) that they have nearly the same composition. This suggested that the solid phase of the film is of definite composition and complexity, and that variations in film properties are due to the liquid or adsorbed phase. Evidence in support of the existence of a liquid phase in the film structure is furnished by extraction with solvents (4, 5, 9). The variation in solubility with different solvents (4) indicated that the liquid or soluble portion of the film structure is present as a mixture of polymerides. This statement was modified when it was found that the acetone-insoluble residue treated with acetone in a closed tube a t 100” C. dissolved almost completely. This indicates that solvents do not merely remove from the film certain low-order polymerides but may exert a depolymerizing effect, depending on conditions of extraction. It is apparent that certain properties of the film would be due to the liquid phase, but this mould not apply to all film properties. It was shown (7) that the ultimate tensile strength of linseed oil films is reached between molecular weights of 1100 and 1336 on the oil. The ultraviolet absorption of an untreated linseed oil film was found (15) to be considerably less than that of a heatbodied oil film. The untreated oil film allows ultraviolet penetration to a considerable distance before it is absorbed completely, but the ultraviolet is absorbed almost entirely a t the surface of a heat-bodied oil film. These properties are dependent more on the molecular complexity and physical structure of the film than on the adsorbed liquid phase.
The resistance of films to water and organic solvents is closely related t o the amount and condition of the adsorbed phase because of selective adsorption and solubility and, to a lesser extent, to the molecular complexity or purely physical structure of the film. The imbibition pressure developed in gel structures by adsorptive processes is resisted by the cohesive forces operating between the micelles and micellar aggregates. An indication of the extent of these forces may be obtained by “initial permeability measurement” (IS) and by the rate of swelling of the film (1, 14). The swelling, or increase in volume of a film when immersed in a liquid, is difficult to measure directly; and when adsorption values are used, they are complicated by a coincident loss of soluble material from the film. The swelling caused by intermicellar adsorption would be proportional to the weight of water adsorbed, but this would not apply to the water held by intramicellar adsorption because of the tremendous pressures developed. It has been stated (14) that “swelling depends on so many processes that it cannot be calculated quantitatively”. The ratio of oxidation to polymerization in the drying process produces marked differences in the properties of the resulting film. This ratio is determined by pretreatment of the oil and by variations in the drying conditions. It has been stated (9) that “the final film structure may be composed of fundamental physical units which are identical irrespective of the condition of the original oil”, but the manner in which these units are formed in films is of extreme importance and is dependent on the condition of the oil. 737
738
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 32, NO. 5
same degree. The lower polarity of this surface would resist water adsorption to a greater degree than the highly polar, oriented film from the untreated oil. An interesting study (3) of the surface structure of linseed oil films showed that, as the oil absorbs oxygen, a gradual orientation of carbon-chain molecules normal to the surface occurs, and that complete orientation does not exist until the film has dried completely. This takes place with oils of all viscosities but to a more marked degree with oils of very low viscosity. This arrangement a t the air-oil interface was considered to be the result of the formation of polar products in the drying oil which are oriented by the electric field set up. The rate of adsorption of water a t such surfaces would depend on the extent and particularly the depth of the oriented layer. The infrared and ultraviolet absorption studies of polymeric bodies present interesting new methods which will assist in the elucidation of the complicated phenomenon of drying oil convertibility, but i t must be apparent that correlation of isolated data cannot be satisfactory until rigid standard conditions of test are established.
Experimental Procedure FIGURE 1. CONSTAXT RATE-OF-KITHDRAWAL hl ACHINE
The phenomenon of the drying of linseed oil is necessarily complicated because of the large number of variables involved. The oil is a natural product and, as such, is subject to some variation; the use of various catalysts and conditions of drying complicate the situation and produce differences in the properties of the resulting film. This paper presents a comparison of certain properties of films made from linseed oil which was heat-treated under different conditions. The samples of oil were made available through the kindness of Technical Committee No. 19 of the New York Paint and Varnish Production Club, J. J. Mattiello, chairman.
It has been shown (4) that the untreated linseed oil adds oxygen with the formation of peroxides. Subsequent decomposition of the peroxides yields a variety of soluble and volatile compounds and also some molecular aggregates formed by oxygen linkage. The polarity or oxygen activation of these large units induce polymerization or association, the system becomes immobilized, and the rigid gel structure or film is formed. In heat-treated oils molecular aggregates are also formed, but they are addition and condensation polymers produced by the thermal treatment. These molecuThe original alkali-refined linseed oil was heat-bodied in air and in vacuum at three temperatures and t o widely different lar aggregates have been separated from the oil and have viscosities. The methods of heating and determinations of the molecular weights indicating dimers to tetramers ( 5 ) . It is physical characteristics of the oils are described in detail elseapparent that thin liquid films of the heat-bodied oils require where (IO). Films of the oils were prepared on glass cloth (1.2) the absorption of much less oxygen to immobilize the system and dried by baking and also by air drying under normal room conditions. The films were tested under room conditions, and and form the dry, rigid film. This results in a correspondingly therefore the results are comparable to those which may be smaller amount of soluble product in the film with consequent obtained from paint films when applied in the regular manner. greater resistance to water and organic solvents. The following physical properties of the films were determined: It has been postulated (2, 6) that “drying is the conversion change in weight during air drying; permeability and adsorption of moisture; and solubility in water, acetone, methanol, and of a linear structure to a cross-linked or three-dimensional benzene. structure”. That is, polymeric bodies which may be conThe samples of oil as received from J. J. Mattiello were not verted to the insoluble, infusible condition are three dimenlarge enough to immerse the pieces of glass cloth; therefore, sional in structure. and those which remain Dermanently blends viere made of two and in a few cases of three samples. soluble or fusible ‘are two dimensional. The‘ heat-bodied oils have been found (5, 10) to contain varying amounts of acetone-insoluble rnateCHARACTERISTICS OF LINSEED OIL SAMPLES TABLE I. PHYSICAL rial, depending on the time and temperature of RefracIp~o1. % heating. Therefore, the liquid film of a heatTemp. and Acid Iodine Yiscqsity. JIol. Sp. tive in Condition Oil bodied oil is a two-phase system containing inof Bodying No. No. KO. Poises Weight Gr. Index Acetone soluble three-dimensional bodies dispersed in a Entreated 1 0.28 186.2 0.23 738 0.9327 1.4792 0 liquid two-dimensional phase. Relatively few 1.4869 42.5 1246 0.9595 142.3 12.6 2 4.48 In air, 1.4893 68.5 1722 0.9688 65.5 134.7 3 6.15 27g°C. intermolecular oxygen linkages immobilize this 1.4902 72.8 1920 0,9713 133.6 138 5 4 7.8 (534OF.) system with rapid sol-gel transition. This pro1.4866 38.7 0.9600 12.2 1184 140.7 5 6.41 In air. 1.4898 64.2 1635 0.9707 82.7 6 10.67 134.2 302OC. duces a dry film, although oxygen absorption 1.4905 69.7 1729 0.9727 132.6 180.1 7 12.27 (576’F.) continues a t a diminished rate for some time. 8 8.22 139.0 12.2 1231 0.9603 1.4868 37.2 In air, 1480 0.9711 1.4898 67.5 From these considerations i t is apparent that 316OC. 9 14.22 131.4 78.7 (601OF.) 10 15.6 132.1 125.9 1560 0,9728 1.4905 66.0 the structural units of untreated oil films are 1.4866 4 2.3 1235 0.9589 143.9 12.3 0.95 Invacuum, 11 1.4887 65.5 1601 0,9671 produced from oxygen linkages, followed by as136.9 51.0 0.85 27D0 C. 12 1.4904 7 3.6 0.9715 2073 173.3 135.3 0.91 13 sociation a t viscosities low enough and with suffi1.4875 40.5 0.9628 1336 18.7 137.3 2.26 Invacuum, 14 cient time to permit considerable orientation a t 1.4893 61.2 0.9680 1554 54.3 133.2 2.09 302O C. 15 1.4902 78.0 0.9716 1794 137.5 132.7 1.52 16 the film-air interface. In contrast, the low oxyInvacuum. 17 2.28 138.5 13.1 1241 0.9604 1.4869 44.7 gen requirements and rapid rate of gel formation 1499 0.9671 1.4889 67.: 316O C. 18 2.21 132.8 45.7 2037 0,9701 1.4901 74., 19 2.32 130.3 122.5 in high-viscosity oils immobilize the structure so quickly that orientation cannot take place to the
INDUSTRIAL AND ENGINEERING CHEXTISTRY
M A Y , 1940
739
a
8 0 VI
9 VI
W
?-f Y V
A N 0 1.2 GM.
0
5
FIGURE2 .
10
15
CH4NGE IN WEIGHT O F
20
25 TIME IN DAYS
30
LINSEEDOIL FILMSWITH
The physical characteristics of the oils as shown in Table I are additive, and when two samples were mixed, the average value was used. Table I shows that the nineteen oils vary most with respect to acid number, viscosity, molecular weight, and per cent insoluble in acetone. There is a relatively large drop in iodine number from oil 1 to the other samples. An attempt was made to select three oils from each bodying condition which have approximately the same viscosity and also to have a wide range of viscosity in each set of three oils. The molecular weights do not vary in the same ratio as the viscosities. DRIERS.Soluble naphthenate driers were added to the oils in the ratio of 0.6 per cent lead, 0.06 per cent manganese, and 0.006 per cent cobalt as metal to oil. The driers were mixed thoroughly and allowed to stand 3 days before use. A slight turbidity developed in oils 2 to 10, inclusive; the others were quite clear. This turbidity resulted in some precipitation on prolonged standing, but care was taken to apply the oils to the glass cloth before this occurred. APPLICATION.The oils were applied to the strips of glass cloth by immersion with subsequent withdrawal at a constant rate by the apparatus shown in Figure 1. It consists of a directcurrent motor, the current to which is controlled by two resistances; one ensures a uniform current on the line, and the other adjusts the operating voltage desired. This type of application produces very uniform films except for a short distance from the top and bottom of the panel. The rate of withdrawal is adjusted so that there is no drip from the bottom of the panel. The oils described in Table I, with the exception of oil 1, were too viscous to apply without thinning and were therefore thinned with benzene in the following ratio (per cent by weight):
35
40
45
TIhfE OF A I R DRYING
Oil Original oil Low-viscosity oils Medium-viscosity, oils Heavy-viscosity oils
Benzene 0 33 43 50
100 67 57 50
The glass cloth has been described (18)and for this work was cut so as to give coated dimensions of 8 X 12.5 cm. The dipping application saturates the cloth, and both sides present a drying surface so that the total area exposed is 200 sq. cm. Slight variations in flowing qualities and viscosities produced variations in weight of coating on the 200 sq. cm. from 0.9 to 1.2 grams of oil. This corresponds to approximately 50 to 60 microns, or 2 t o 2.4 mils, which is a normal film thickness. Some objection may be raised to the use of film thickness because of the presence of the glass cloth; therefore results will be expressed on the weight of oil on a specified area. All determinations were made in duplicate, and good agreement was obtained in the large majority of cases.
Change i n Weight of Oil Films with Air Drying The strips of glass cloth were weighed before coating, again after application of the oil, and periodically as shown in Figure 2. The original oil was the only one applied without solvent so that its change in weight was recorded at short time periods immediately after application with the following results : Time, hours Increase in weight, 70 Time, hours Increase in n-eight, %
1 0.75 30 6.97
0
5.53 30 6.67
3 6.64 40 6.64
4 6.79 50 6.35
i)
6.87
INDUSTRIAL AND ENGINEERING CHEMISTRY
740
Oils 2 to 19, inclusive, contained solvent and were not weighed until it had evaporated. A 20-hour period was considered ample for this purpose. For the same reason it was impossible to express the change in weight of these oils as the percentage of the original weight because the original could not be determined. The changes in weight were recorded periodically for 42 days, and were found to be practically constant for all the oils after that time. They were then plotted as shown in Figure 2. The curves were spaced one division apart, which equals 0.005 gram or approximately 0.5 per cent of the oil film. The percentage change in weight may be estimated in this way, and any significant changes between the various oils would be apparent. The flms were kept under normal laboratory conditions, with diffused north light, during June and July. It was hoped in this way to be able to relate any changes which take place to the various phenomena which are known to occur in paint films when drying under normal application conditions. The typical stepwise curves obtained indicate a rapid initial increase in weight followed by a gradual decrease. The oils all show a loss from the maximum weight of 1.6 to 1.9 per cent; and although the time required to reach the maximum weight is practically the same for all the heattreated oils, there is a considerable difference between this time and that required for the original untreated oil. This is related to the greater unsaturation and consequent oxidation of the untreated oil with its attendant liberation of oxidation-decomposition products. Any significant differences which occur between the oils take place in the first 3-day period, followed by stepwise changes which become quite uniform. This suggests that the changes are due to surface conditions rather than specific characteristics of the oils. For example, the rapid increase in weight in the 17-19 day period was undoubtedly due to the high humidity which prevailed a t that time. This increase varies between 0.6 and 0.8 per cent, and is lost a t approximately the same rate by all the oil films. This is somewhat surprising in view of the significant differences between the oils before drying, and it would suggest the possible similarity of the final gel structure, irrespective of the original oil. The results from the solubility of the films (Table V) modify this theory with respect to the untreated and heat-treated oils. The change-in-weight curves do not indicate the amount of oxygen absorbed because of the coincident liberation of volatile decomposition products.
VOL. 32, NO. 5
Permeability to 3Ioisture The permeability of a film is the rate a t which water will pass through it. The permeability was determined by the New York Paint and Varnish Production Club method (11) which specifies the Payne cup (12) having an exposed film area of 10 sq. cm., a test temperature of 38" C. ( l O O O F . ) , and phosphorus pentoxide in the desiccator. Three sets of films were tested, one set after being airdried 3 weeks, another after 6 weeks, and the third set after being baked for 8 hours a t 121O C. (250' F.). The results are shown in Table 11. TABLE 11. PERMEABILITY OF FILMS TO MOISTURE~ Baked Baked Oil 8 Hr. a t ---Air-DriedOil 8 Hr. a t -Air-Dried3 weeks 6 weeks No. 2.50' E'. h-0. 250' F. 3 weeks 6 weeks 11 1 0.826 1.22 1.04 0.761 0.932 1.16 2 12 0.754 1.05 0.901 0.782 0.986 0.926 0.735 0.910 13 1.09 0.893 3 0.876 0.728 14 0.941 4 0.698 0.863 0.841 0.786 1.04 0.760 0.913 0.713 16 1.18 0.952 5 0.901 0.780 6 16 0.921 0.866 0.674 1.03 0.862 17 0.862 0.650 1.18 0.902 7 0.848 0.692 18 0.705 0.875 0.828 0.703 1.06 0.864 8 19 0.695 0.880 0.842 0.643 1.20 0.830 9 0.612 0.823 0.812 10 a T h e milligrams of water which pass through 1 gram of oil on s 10-sq. am. area i n 1 day, under the specified conditions of the test.
Table I1 does not show marked differences in permeability of the films from the various oils, either air-dried or baked. This again suggests a similarity of fundamental units in the gel structure of these films. The similarity is greater between the baked films because of the decreased oxidation effects. The films air-dried for 6 weeks show a slight reduction in permeability from the 3-week films owing to a gradual densification of the film structure. The lower permeability of the air-bodied oil films is not what might have been expected, considering their higher acid number with consequent increase in polarity and decrease in water resistance. This condition is more than offset by the formation of metallic soaps which diffuse throughout the film and are known to be very water repellent. These soaps precipitated in the retained wet samples of the air-bodied oils but were not present in the vacuum-bodied oils. This is another illustration of the complexity of the problem of paint film behavior because of the many variables involved. It would also be expected that the heavy-bodied oil films would have considerably lower permeabilities than the light-
AFTER IMMERSIOS TABLE 111. CHANGEIN WEIGHTOF FILMS
-Baked
8 Hr. a t 250'
Yo Change in Wt.
7
7
24 hr. 6.05 6.40 5.25 5.83 7.40 5.95 6.33
Oil No. 1 2
3
4
5 6
0
8
6.24
9 10
6.80 6.56
12 13
11
6.23 5.17 5.00
14 15 16
6.43 6.00 5.26
17 18 19
6.77 5.62 5.04
240 hr. 7.35 3.16 2.56 4.05 4.83 3.89 3.44 4.92 3.5s 4.54 2.75 1.97 2.30 2.36 3.57 3.80 3.15 2.91 3.04
.
F.yo water sol. 9.35 3.47 3.16 3.01 3.25 3.26 2.77 4.25 3.55 4.04 2.92 2.60 1.98 2.60 2.42 3.05 3.27 2.00 2.92
---
3 Weeks
% Change in Wt.
I
24 hr. 5.87 5.80 3.53 2.03 5.50 3.40 2.66 5.34 3.85 3.16 4.85 2.67 2.32 3.29 2.64 1.68 2.93 2.38 1.68
. 240 hr.
5.60 2.05 0.15 -1.20b 4.60 0.72 0.50 6.75 2.65 1.75 2.44 0.0 -0.55b 1.60 0.40 -0.75b 1.89 0.23 -0.80b
6-
% water sol. 16.1 7.91 6.07 7.20 7.84 6.30 6.84 8.79 7.52 7.60 8.01 6.64 6.20 7.16 6.20 6.50 7.43 6.65 6.88
Films Air-Dried
% Change in Weight 6 hr. 9.50 7.90 5.70 5.73 9.50 5.80 9.14 10.1 6.65 8.20 7.41 6.40 5.30 7.36 6.16 5.22 6.15 5.84 6.32
24 hr. 4.92 5.25 4.10 2.75 6.47 4.32 4.18 5.95 4.77 5.10 4.56 3.42 2.95 4.06 3.11 2.31 4.31 4.41 3.79
-
Weeks
I
240 hr. 3.27 1.36 0.11 -0.146 2.42 1.43 0.38 2.50 1.90 1.60 1.76 0.49 -0.24) 0.97 0 -0.59b 1.50 0.88 0.31
% water sol. 13.1 7.13 5.88 6.85 7.25 5.85 6.75
9.50 6.95 7.91 6.93 6.26 6.08 7.51 6.50 6.85 6.81 5.79 6.73
YOwater removed by desiccation0 0.86 0.82 0.73 0.72 0.76 0.76 0.60 0.63 0.60 0.66 0.48 0.70 0.74 0.61 0.72 0.76 0.82 0.78 0.68
Films dried over phosphoric anhydride for 72 hours. loss from film.
b T h e minus sign indicates per cent
I
INDUSTRIAL AND ENGINEERING CHEMISTRY
MAY, 1940
bodied oil films; but although the permeability is generally lower, it is not of the order anticipated. Permeability is the rate of moisture movement through a film and does not necessarily indicate the water resistance as measured by the degree of softening or whitening of a film. The water immersion test showed the light-bodied oil films to be considerably swollen and very soft compared with the heavy-bodied oil films. A comparison of Tables 11, 111, and IV shows that permeability (the rate of moisture movement through a film) is not proportional to water resistance as measured by standard test methods. Tater Adsorption and Solubilit? The water adsorption and per cent soluble of the various oil films were determined by immersion of the coated glass cloth in water a t 30” C. with periodic weighing, followed by removal from the water and subsequent drying and weighing. In order t o obtain check results from the adsorption determination, a definite procedure must be maintained. The immersed films were removed from the water and pressed between heavy blotting paper to remove surface adhering water, and a stop watch was started. The films were placed on the balance pan, and the weight was recorded after 1 minute. The per cent soluble is the loss in weight from the film after immersion for 10 dags and subsequent drying to constant weight for 72 hours. The maximum loss from the film occurs in from 6 to 8 days and then remains constant. The results are shown in Tables I11 and IV. TABLE IV. WATERADSORPTION AFTER 240 H O U R S ~ -%
Films Baked 8 Hr. a t 250° F.
Oil Yo.
-%
Water rldsorbedaFilms Baked Films Air-Dried --,Oil 8 Hr. a t 3 weeks 6 weeks 6 weeks KO. 250’ F. 10 45 8.69 11 5.67 6.75 6 64 12 4.57 5 65 5.84 13 4.28 8.48 8 76 14 4.96 6 60 6.50 15 5.99 6.26 5 75 16 6.85 9 32 8.31 17 6.42 6 88 6.67 18 4.91 7.04 6.08 19 5.96
Water Adsorbed”--
Films Air-Dried
I
I
3 weeks
and per cent adsorbed a t 240 hours
The amount of water adsorbed by a film should be a measure of the degree of smelling of the film structure, but if the determination is made by immersion, then the amount of water-soluble material dissolved from the film must be con-
74 1
sidered also. Table I11 shows the change in weight of the films after immersion and weighing as described above, and Table IV shows the algebraic sum of the water-soluble content and per cent adsorbed after 240-hour immersion. Table IV is titled “Water Adsorption” on the assumption that the recorded increase in weight should be greater by the amount dissolved out of the film. 5 = original film weight y = weight after immersion (240 hr.) = x m z = weight after drying = x - n m = increase due to water addition n = loss due t o soluble material Adsorption of water A in film Z is the difference between Y and Z: A = Y - Z A = (Z m) - (X - n) A=m+n Table I11 shows that the adsorption of water by linseed oil films takes place quite rapidly upon immersion. The leaching out of the film of soluble material takes place simultaneously with adsorption so that, unless a quantitative determination of each is made, the amount adsorbed a t any time period is not significant. The per cent adsorbed and per cent soluble were measured after 10-day immersion, and a t least one adsorption measurement was made in the early stages of immersion. -4comparison of the untreated and heat-treated oils again shows a relatively large difference in their film properties. The high percentage of water-soluble material in the untreated oil is the result of the greater oxidation taking place in this film, with the consequent formation of low-molecular-weight decomposition products which are water soluble. These acidic materials react with certain pigments and cause difficulties with gloss retention in paint films which are dried under high humidity conditions. Table I11 shows that the normal amount of water on the surface of the film is about 0.7 per cent, and Figure 2 shows that the increase in weight due t o a high humidity condition is also about 0.7 per cent. The total surface water a t high humidity is therefore about 1.4 per cent of the oil, and this is sufficient to promote considerable reactivity. Tables I11 and IV show the essential difference between the films from the low- and high-viscosity oils. The permeability data indicate that the rate of moisture movement through these films is practically the same, and Table I11 indicates only a slight difference in the per cent water soluble; but the amount adsorbed after 240-hour immersion varies con-
+
+
-
OF FILMS IN FOUR LIQUIDS TABLEV. SOLCBILITY Oil No.
a
Soly. of F a m s Baked 8 H r . a t 250’ F. in: Water Aoetone Methanol Benzene
Water
Solubility of Films Air-Dried for:__ 3 Weeks 6 Weeks-Acetone Methanol Benzene Water Aoetone Methanol
.
7 -
Benzene
%
%
%
%
%
%
%
%
%
%
%
%
1
9.35
14.45
17.38
13.52
16.1
46.1
50.5
36.7
13.1
39.1
31.2
23.4
2 3 4
3.47 3.16 3.01
11.85 11.28 9.77
13.90 11.95 11.82
11.51 10.20
7.91 6.07 7.20
39.4 36.5 35.4
42.6 36.7 36.4
5 6 7 8 9 10
3.25 3.26 2.77 4.25 3.55 4.04
11.48 11.05 12.68 12.47 12.49 12.52
14.60 13.38 13.12 15.47 14.57 14.65
11.55 11.35 12.06 12.68 12.30 12.25
7.84 6.30 6.84 8.79 7.52 7.60
26.6 25.8 23.1 27.3 27.6 20.8
2.92 2.60 1.98 2.60 2.42 3.05
11.07 10.10 10.48
11.25 10.33 9.75 10.90 10.02 10.75
8.01 6.64 6.20 7.16 6.20 6.50
26.9 29.4 29.7 26.9 23.8 22.2
25.0 23.0 22.8 26.5 25.0 24.8 27.6 21.0 26.9 25.7 22.6 21.1
10.8U 10.78 9.71
13.23 12.22 11.50 12.45 9.75 $1.45
44.9 39.2 39.0 47.3 43.6 43.3 43.0 37.3 33.1
35.6 32.8 31.9 37.3 36.0 34.8
11 12 13 14 15 16
43.0 38.6 38.1 45.0 42.5 41.8 40.4 35.5 33.3 39.0 36.2 33.7
31.2 26.9 27.6 30.8 28.7 28.2 34.1 31.7 31.3 30.7 32.3
11.37 10.71 10.62
10.54 10.18 9.87
12.15 11.92 10.65
7.43 6.65 6.88
40.1 37.0 34.0
17 3.27 18 2.00 19 2.92 Apparently too high.
7.13 5.88 6.85 7.23 5.S5
6.75 9.500 6.95 7.65
25.4
6.26 6.08
41.0 38.9 40.1 36.5 31.2 29.6
41.5 37.6 35.C
30.2 27.1 26.8
7.51 6.50 6.85
34.3 32.0 30.1
20.6 25.3 23.0
25.4 24.0 23.1
42.5 38.2 34.7
29.8 27.5 28.2
6.81 5.79 6.73
35.2 34.3 32.6
26.4 25.9 23.9
26.0 23 3 23.0
6.93
742
INDUSTRIAL AND ENGINEERIKG CHEMISTRY
siderably. In every case the low-viscosity oil films adsorb more than the high-viscosity oil films, which indicates a greater degree of swelling of the low-viscosity oil films. This result was also shown by their greater softness and whitening after water immersion. It will be noted that these observations do not apply to the baked films. The numerical values obtained for adsorption and water-soluble content are considerably lower than those recorded by other workers ( I , I,$), but this may be accounted for by experimental differences. These would include differences in original oil, drier content, conditions of drying, and type of support for the film. The last item is of particular importance because it is impossible to remove the wat,er which accumulates between the base and the film when the base is a glass plate or metal panel. This condition does not develop when the base is glass cloth because the film is substantially a free film reenforced with glass fibers. The fibers do not offer any resistance to the normal swelling of the film.
Solubility in Water, Acetone, Methanol, and Benzene The per cent soluble in these four liquids was determined by immersing two weighed strips of coated glass cloth (3 X 1 inch, or 7.6 X 2.5 cm.) in 200 ml. of the liquid for 10 days with water and 1 day with the other three liquids, and then drying to constant weight. The drying was complete in 48 hours, but 72 hours was allowed in all cases. This method may not completely remove all of the soluble material, and the results would probably be higher if the films had been refluxed with the solvent until no further soluble was obtained. The possibility also exists that considerable dissociation of the gel structure would take place under continued reflLxing. The present study is a comparison of a particular series of oils, and the results obtained by the method used are therefore directly comparable within the series. Table V shows the large decrease in solubility of the films which were baked (heat-polymerized) as compared with the more highly oxidized air-dried films. The baked films also show less difference between the low- and high-viscosity oils. The effect of increasing acidity in the oils bodied in air may be seen in the films dried under the three different conditions. The increase in acidity produces a greater increase in solubility in water and acetone than in methanol and benzene, which might be expected from the relative polarity of these materials. An apparent lack of relationship between permeability (Table 11) and solubility may be shown from the data presented, but a consideration of the methods used for these determinations would explain some of the discrepancies. Immersion in water gives the water-soluble materials an opportunity to leach out of the film and show high solubility, but the permeability determination is made with water vapor in contact with the film; and although this condenses to liquid water, it is retained in the film. The saturated solution in the film would retard the vapor movement and also lower the rate of evaporation from the film, both of which would lower the permeability. The solubility of the baked films in acetone, methanol, and benzene is so nearly alike that it might suggest the desorption of a lom-molecularweight constituent from the gel structure. The acetone and benzene swelled the films considerably so that they were difficult to handle, but the methanol gave no indication of swelling although the films were very soft. This need not affect the desorption hypothesis, because if only a definite amount of adsorbed material was contained in the film, no more than this could be desorbed, irrespective of the extent of film swelling or disruption. The large decrease in solubility in methanol as compared
VOL. 32, XO. 5
with the small decrease in lyater and acetone from the 3-6 week drying of the films is significant of considerable change in the film structure. This change is also indicated by the larger drop in solubility of the original oil film as compared with the heat-treated oils. An interesting comparison may be made between the per cent insoluble in acetone in the oils (Table I) and the per cent soluble in acetone in the films (Table V). The large differencesin Table I become more nearly equalized in Table V, which points clearly to the fact that acetone insolubility is a measure of the extent of polymerization. The baked films contain less acetone-soluble material than the original oils, and the air-dried films show the greatest change in solubility where the degree of polymerization has been greatest. This is apparently contradictory because the untreated oil, which has the greatest degree of oxidation, has the greatest acetonesoluble change. This may be considered as further evidence that oxidation is only a necessary step to polymerization in untreated oils. The actual increase in acetone-soluble material in the high-viscosity oil films as compared to the oil itself is no doubt due to oxidation-decomposition products in the film. Summary Glass cloth is a satisfactory support for linseed oil films which are to be investigated for permeability, adsorption, and solubility characteristics. No difficulty was encountered from water blistering in immersion tests, which is a source of error on glass or metal panels. The measurement of the change in weight of untreated and heat-treated linseed oil films while air drying shows that there is a sharp difference in the rate of change in the first 3-day period, followed by a gradual decrease which is practically equal in the various oils. Variations in temperature and humidity while drying produce a stepmise curve. The increase in weight due to high humidity may be greater than the change produced by absorption of oxygen and liberation of volatile decomposition products after the first 3-5 day period. The surface moisture on the films under normal room conditions during summer weather is approximately 0.7 per cent, which may be increased during periods of high humidity to 1.4 per cent of the weight of the oil. This is sufficient to cause considerable reactivity between the watersoluble acidic decomposition products from the drying oil and certain basic pigments. This has been found to be related to the loss of gloss on paint films containing these materials when dried under conditions of high humidity. The permeability to moisture is greater for the untreated than for the heat-treated oil films, and also for the air-dried as compared with the baked films, but the differences are not of the numerical order which might be anticipated from the large differences in oil characteristics. The increase in acid number of the heat-bodied oils with consequent increase in polarity and decrease in water resistance was more than compensated for by the formation of water-repellent metallic soaps from the metal driers and free acid; therefore, the higher acid oils gave lower permeability values. The permeability to moisture gives the rate a t which moisture vi11 pass through a film under specific conditions, but this is not necessarily proportional to the degree of softening or whitening of a iilm when immersed in water. The complete picture of the water resistance of a film requires permeability, water immersion, and adsorption as well as loss of electrical resistance data, but the specific use for which the film is intended will dictate the number of the above tests necessary for evaluation The water adsorbed by a film after immersion for a given period is considered t o be the algebraic sum of the change in
'
MAY. 1940
INDUSTRIAL AND ENGINEERING CHEhIISTRT
weight recorded after immersion and removal of surfaceadhering water, and the weight of any soluble material dissolved from the film during the immersion period. The degree of swelling of a film may be estimated from the adsorption data, but a quantitative expression for swelling is impossible because of solubility and inter- and intramicellar adsorption. The per cent water adsorbed is no criterion of the degree of softening of the film. Low-viscosity heattreated oil films adsorb slightly more than high-viscosity oil films, but the degree of softening is much greater with the low-viscosity oil films. Increase in acid number of the oil gives increase in adsorption by the film but not to the extent which might be expected because of several modifying factors. The difference in water adsorption of baked and air-dried films is not large, but the greatest difference is between the low-viscosity oil films. The amount of soluble material in linseed oil films is affected by conditions of drying, type of driers, and methods of extraction. Films which have been baked contain considerably less soluble material than air-dried films. Film from oils of widely different viscosities and percentages of acetone-soluble material appear to approach each other in per cent soluble after drying. The amount of soluble material decreases with age of the film a t a different rate for different solvents. Films from oils of high acid number show slightly greater solubility than films from oils of low acid number. The experimental values obtained in this paper are comparative for the particular series of oils under the given test conditions. Therefore they are not absolute values but
743
indicate clearly the reawns for some of the phenomena Fhich are of interest to the surface coating industry.
Acknowledgment The author's appreciation is due the American Cyanamid Company for support of this work and permission t o publish it, and to Walter B. Hartley for asqistance in making the physical measurements. The forethought of J. J. Mattiello in preserving sufficient samples of the oils so that research could be done nith them other than that for which the oils were originally intended, is especially appreciated.
Literature Cited Blom, A. V., J. Oil Colour Chem. Assoc., 22, 104 (1939). Bradley, T.F., IXD.EXQ.CHEM.,29,440 (1937). Clewell, D. H., Ibid., 29, 650 (1937). Elm, A. C., Ibid., 23, 881 (1931). Elod, E., and Mach, V., Kolloid-Z., 75, 338 (1937). Kienle, R. H., J. SOC.Chem. Ind., 55, 229 (1936). Long, J. S.,and Arner, W. J., IXD.ENQ.CHEM.,18, 1252 (1926). Long, J. S., and McCarter, W. S W., Ibid., 23, 786 (1931). Long, J. S., Zimmermann, E. K., and Nevins, S. C., Ibid., 20, 806 (1928).
Natl. Paint, Varnish & Lacquer Assoc., Circ. 523, 410 (1936). Ibid., 546, 368 (1937). Payne, H. F., IXD.EXO.CHEW,Anal. Ed., 11,453 (1939). Payne, H. F., and Gardner, W. H., IND.ENO.CHEU,29, 893 (1937). Rinse, J., and Wiebols, TV. H. G., Ihid., 29, 1149 (1937); 30, 1043 (193s). Stutz, G. F. A., Ibid., 19, 897 (1927).
PRESENTED before the Division of Paint and Varnish Chemistry a t the 98th Meeting of the American Chemical Society, Boston, Mass.
Phase Equilibria in Hydrocarbon Systems 0
J
J
Methane-Decane System' The volumetric behavior of six mixtures of methane and decane was determined at five temperatures between 70" and 250" F. The experimental work included measurements in the condensed liquid and twophase regions at pressures as high as 4500 pounds per square inch absolute. From these primary data the partial volumetric behavior of methane and decane has been calculated for the liquid phase. The results are presented in tabular and graphical form. 1 This is the twenty-ninth paper i n this series. Previous articles appeared in 1934, 1935, 1936, 1937, 1938, 1939, and in January and March, 1940.
B. H. SAGE, H. M. LAVENDER, AND W. N. LACEY California Institute of Technology, Pasadena, Calif.
XPERIMENTAL information relating to binary hydro-
E
carbon systems is of value in the prediction of the complex behavior of naturally occurring hydrocarbon mixtures. A number of binary systems containing methane have been investigated experimentally, but there appears to be no information available concerning the volumetric or phase behavior of the methane-decane system. For this reason the specific volumes of six mixtures of methane and decane were determined in the liquid and two-phase regions a t pressures as high as 4500 pounds per square inch. The experimental work was carried out a t five temperatures between 70' and 250 O F.
Method The a paratus and methods used in this investigation were describef previously ( 6 ) . In principle the procedure involved the addition of known weights of methane and decane to a container whose effective volume was varied by the addition and withdrawal of mercury. The volume of the mixture was deter-
