Correlation between Properties of
Alkyds and Composition of Modifying Fattv Acids d
EFFECT OF VARIOUS OIL-RESIN RATIOS D. T. JIOORE Fatty Acids and Esters Laboratory, Emery Industries, Inc., Cincinnati, Ohio
I
N A prior publication on this subject ( 2 ) , there were shown some relationships bet,ween the drying times, hardnesses, and color retentions of several groups of alkyd resins and the compositions of the fatty acid mixtures with which they were modified. Specifically, the data presented therein supported the generalixations that: 1. For any particular ratio between conjugated and nonconjugated fatty acids, the drying t,imes of the alkyds are generally related hyperbolically to the total content of polyenoic acids. 2 . The presence of conjugated unsaturation, up t o a limit of about one half of the total unsaturation, has a beneficial effect on drying time. 3. Ultimate hardness of the alkyl film is proportional to the total polyenoic acid content and is not appreciably affected by the ratio between dienoic and trienoic acids nor by the ratio between conjugated and nonconjugat'ed forms. 4. Afteryellon-ing is a function of fatty acid composition, with suitable weight being assigned to the various degrees of unsaturation, etc. 5 . Afteryellowing increases TTith time a t such a rate that a logarithmic plot versus the reciprocal of the duration of test is a straight line. However, these relationships, potentially useful though they may be, all referred to alkyds of one particular oil length, containing 2 1 / 2 equivalents of dibasic acid (phthalic anhydride) per equivalent of monobasic acid (fatty acid). It was felt that their full utility would be realized only after it was determined to what extent they might be applied to alkyds of other oil-resin ratios t>hatare used by the protective coatings industry. Accordingly, the present paper deals with the results of applying tests similar t,o those detailed before to alkyds in which the rat,io between dibasic and monobasic acids was 1 1 / ~to 1, 2 to 1, and 3 to 1.
These, blended as required with oleic acid, were used to prepai e the fatty acid mixtures shown in Table I. Each of the 20 mixtures shown in Table I was used in the preparation of an alkyd at each of threeoil lengths: A , a pentaerythritol alkyd containing ll/z equivalents of phthalic anhydride per equivalent of fatty acid; B , it pentaergthritol-glycerine ( 2 to 1) alkyd containing 2 equivalents of phthalic anhydride per equivalent of fatty acid; and C , a glycerine alkyd containing 3 equivalenth of phthalic anhydride per equivalent of fatty acid. To each of the 60 alkyds were added the usual cobalt and lead riaphthenate driers and the drying time, hardness (6 weeks), and afteryellowing (3 months) were determined. Details of the apparatus and method used in the preparation of the alkyds and of the preparation and testing of the films may be found by reference to (2).
Drying times of the alkyds are shown in Figure 1, the nonconjugated alkyds being in the upper graph and the conjugated alkyds in the lower. The hardness results are given in Table I1 and the afteryellowing figures in Table 111. I n the upper graphs of Figure 2 (oil length A ) , Figure 3 (oil length B ) , and Figure 4 (oil length C), the reciprocals of the
EXPERIMENTAL
'.
840
30
I 60
I 90
I 120
"
0"
I
I
180. 210
240
60 90 120 150 180 210 DRYING TIME MINUTES Figure 1. Drying Times of Alkyds
240
150
The fatty acids used in the alkyds covered in this report were derived from soya oil, largely dienoic with little conlugation; linseed oil, largely trienoic with little conjugation; dehydrated castor oil, largely dienoic Kith considerable conjugation; and a tung-linseed oil blend, largely trienoic with considerable conjugation. The compositions (determined spectrophotometricallp) of the four starting materials were as given in the folloning table:
Soya oil Linseed oil Dehydrated castor oil Tung-linseed oil blend
NonNonConjugated conjugated Conjugated conjugated Oleic plus Trienoio Trienoio Dienoic Dienoic Saturates 0.1 6.3 1.8 61.0 30.8 0.2 48.5 2.3 18.2 30.8
...
27.4
1.0
29.6
52.1
17.3
29.1
3.6
16.3
23.6
8 30
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sigmoid shape in the curves from the nonconjugated fatty acid alkyds, whereas the curves from the NonNonconjugated fatty acid alkyds are approximately Oleic plus Conjugated conjugated conjugated Conjugated hyperbolic. I n both cases, these curves also a p Dienoic Saturated Trienoic Dienoic Trienoic proach a limiting value as the polyenoic acid conSoya 30.8 6.3 1.8 61.0 la 0.1 tent increases. 40.6 5.5 1.5 52.3 lb 0.1 lo 0.1 4.7 1.3 43.6 50.3 It has been pointed out by Earhart ( 1 ) that very 60.1 3.9 1.0 34.9 Id 0.1 le 0.1 3.1 0.7 26.2 69.9 short alkyds show an apparent drying time that is primarily a function of solvent release, true hardLinseed 2& 0.2 48.5 2.3 18.2 30.8 ening occurring very $lowly because of the com2b 0.2 41.4 2.0 15.9 40.5 20 0.1 34.3 1.6 13.6 50.4 paratively small number of fatty acid radicals 0.1 27.1 1.2 11.4 60.2 2d 0.1 20.0 0.9 9.1 69.9 available for cross linking. In agreement with this 2e observation is the fact that for alkyds of oil length Dehydrated castor 3a ... 0.9 23.7 42.3 33.1 C, the apparent drying time is almost constant 3b ... 0.9 20.0 36.1 43.0 30 ... 0.9 16.3 30.0 52.8 among the various fatty acid types. I n the longer 3d ... 0.9 12.6 23.8 62.7 3e ... 0.9 8.9 17.8 72.4 alkyds, however, the expected differences beta-een dienoic and trienoic acids and between conjugated Tung-linseed 4a 23.3 24.9 3.1 14.3 34.4 and nonconjugated forms are apparent. 4b 19.4 21.0 2.6 12.4 44.6 40 15.7 17.2 2.1 10.6 54.4 The hardness values for each oil length are in 4d 12.1 13.4 1.6 8.9 64.0 4e 8.2 9.4 1.1 7.0 74.3 good agreement with the conclusions of ( 2 ) . As before, within the limits of accuracy of the measuring instrument, the hardness is dependent on total polyenoic acid content, without regard to the Sward hardness values are plotted against the per cent of total linoleic-linolenic ratio or the conjugated-nonconjugatedratio, and polyenoic acids. The dotted lines divide those results that lie the hardness may be related to the total polyenoic acids by an within f 1 unit of a line, H ( A - P ) = B, where H = Sward equation of the form H ( K - P ) = K’, where H = the Sward hardness, P = % ’ polyenoic acids, and A , B are constants, from those which are more than one unit off. The lower graphs of Figures 2, 3, and 4 show plots of the degree TABLE 11. HARDNESS OF ALKYD FILMS of afteryellowing Hunter reflectometer, A against afuncOF FATTY ACIDMIXTURES TABLE I. COMPOSITION
(
~
+
+
c ”)
5T 3C, where D = % dition of fatty acid composition, D enoic acids, T = % trienoic acids, and C = % conjugated acids.
Numbera
la
2a 3a 4a 2b lb 3b 4b lo 2C 30 40 Id 2d 3d 4d
DISCUSSION
The drying time curves in Figure 1 are similar to those shown in the earlier report. As before, there is a distinct suggestion of a
a
(Decreasing order of polyenoic acid content) Total Polyenoic Oil Length Oil Length Acids A B 69.2 15 25 69.2 15 22 66.9 13 23 65.6 13 23 59.5 14 20 59.4 13 19 57.0 12 19 55.4 14 17 49.7 12 18 49.6 11 16 47.2 11 15 45.6 12 14 39.9 10 14 39.8 9 14 37.3 9 12 36.0 9 12
% POLYENOIC ACIDS Numbera la 3a lb I C
3b Id 30 le 2a 3d 4a 3e 2b 4b 20 40 2d 2e 4d 4e
Hardness and Yellowing of Alkyds
A alkyds a s defined in Tables I1 and I11
C
23 22 23 22 19 21 20 18 18 18 16 15 14 15 12 12
See Table I.
TABLE 111.
Figure 2.
Oil Length
a See Table
.4FTERYELLOWING O F P I G M E N T E D kiLKYDB
(Increasing order of yellowing index) Yellowing Index, Oil Length A, Oil Length B , Oil Length C , D 5T 3C ( A B ) / G ( A - B)/G ( A - B)/G 45 138 139 91 58 139 144 92 59 140 142 97 73 149 152 98 79 154 157 103 87 151 154 101 100 160 158 111 101 158 157 113 114 165 161 115 121 162 166 116 124 175 176 118 142 171 172 118 153 180 171 131 179 185 193 136 193 194 187 146 231 205 20 6 157 232 209 202 155 272 224 224 174 283 226 229 181 338 246 246 196
+ +
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.I. Q i
Bd
I
I
I
I
I
I 55
35
25
45 % POtYENOC
I 65
I
ACIDS
/'
/% /O o / / O A O / .
p" pB
46
I
!
I
I
I
I
240
I60
80
I 320
D + 5 T + X Figure 3.
Hardness and Yellowing of Alkrcls
B alkl-ds as defined in Tables 11 and 111
+
+
35
45
hardness, P = the per cent of polyenoic acids, and K and K' = constants. Further, the value of K is the same, in all three cases, as the value previously obtained, although the value of K' changes with the oil length, as would be expected. Not only are the longer alkyds less hard than those reported previously, despite their increased pentaerythritol content, but this is true of the shortest series also, I n part this may be due to the fact that the shortest series contains no pentaerythritol, but it seems probable that part of the effect is due to the comparatively small opportunity for cross linking afforded by the fatty acids. Afteryello~~-ing a t each of the three oil lengths is proportional to 3C) that the same function of fatty acid composition ( D 5T was developed in the earlier work, the average deviation being of approximately the same magnitude. It may be noted that the values for oil lengths A aiid B are virtually equal. Since the degree of afteryellowing developed in a particular exposure is presumably influenced by the weather conditions (mean temperature, hours, and intensity of sunlight, etc.) prevailing a t the time, the values reported here are not directly and numerically comparable to those reported before. Hovever, a t the same time that the present data were obtained, repeat exposure of four enamels from the previous work was made. If these four repeat exposures are used as a basis for adjusting the previous data to the conditions prevailing a t the time of exposure of the present groups, it is found that not only do those results lie between the lines shown in Figures 2 (or 3) and 4 but also t h a t the slope of the line defined thereby is the same as the slopes in the present graphs. It appears, therefore, t h a t in the formula for afteryel57' 3C) K', the value of K is deterlowing, Y = K ( D mined solely by the conditions of test and only K' varies with changes in the alkyds' oil length.
+
+
+
+
+
CONCLUSIOKS
+
55 % POLYENOIC ACIDS
25
f
Vol. 44, No. 11
65
The generalizations contained in the previous publication are confirmed by the data in this report, and in addition it may be suggested t h a t the drying rate of alkyds is inversely proportional to the oil-resin ratio, except that a t very small oil-resin ratios the apparent drying rate is misleading and the time for real hardening again increases. As the oil-resin ratio decreases, the hardness of the alkyd film rises to a maximum (at some medium-short oil length) and then decreasps to someTThat lower values. In the equation t h a t relates hardness to polyenoic acid content, H ( K - P ) = K', the value of K' is determined by the oil-resin ratio, the value of K rpmaining const,ant. The degree of afteryellowing of the pigmented alkyd film is related to the oil-resin ratio but appears t o approach a limiting value as the oil-resin ratio increases. I n the equation relating after5T 3C) yellowing to fattv acid composition, Y = K ( D K', the value of K is determined solely bv the environment prevailing during test and only K' changes as the oil-resin ratio is varied.
+
+
+
ACKNOWLEDGMENT
The constructive criticisms and the suggestions received from
It. G. Kadesch and V. J. Muckerheide have been very helpful. Thanks are also due to B. R.Krabacher, who assisted with the experimental work and the preparation of the graphs, and to W. C. Clark, who made the spectrophotometric analyses. LITERATURE CITED
0
80
Figure 4.
160
240
320
D+ST+SC Hardness and Yellowing of Alkyds
C alkyds as defined in Tablea 11 and I11
(1) Earhart, K. A., IND.EXG.CEEM.,41, 716 (1949). ( 2 ) Moore, D. T., Ibid., 43,2348 (1951). RECEIVED for review April 17, 1952. ACCEPTED June 2, 1962. Presented before the Division of Paint, Varnish, and Plastics Chemistry at CHEMICAL SOCIETY, Milwaukee, Wis. the 121st Meeting of the AMERICAN
