May 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
Table VI. Mill Stability and HC1 Escape Rate
Stabilizer Dibasic lead phthalate Dibasic lead phosphite Dibut 1 tin maleate Monogydrous tribasic lead sulfate Coprecipitated lead orthosilicate and silica gel Epoxidized soybean oil Dibutyl tin dilaurate n-Hexyl epoxy stearate Normal lead salicylate Calcium stearate
Trade Name Dythal Dyphos
.....
HCl Escape Reflectance a t 60 Min., at 450 mp Mg.HC1/1000 after 20 Min. Sq. Cm./Hr. Milling, % ’ 0.0 80 0.0 80 0.0 80
Tribase
0.0
77
Plumb-0-Si1 B Paraplex G-60 D-22
0.0 0.47 0.0 4.3 0.0
76 71 68 66 55
..... .....
Normasal
0.78
43
took place, and chloride ions were found. T h e glass wool did not affect hydrogen chloride in t h e effluent stream since a calcium stearate stabilized sample gave identical escape curves in t h e presence and absence of the trap. Many of the other stabilizers tested are not efficient hydrogen chloride acceptors since they allow hydrogen chloride to escape. Barium stearate does not allow quite as high a n escape rate as calcium stearate. Among the least efficient of the hydrogen chloride accepting stabilizers are the epoxides. D a t a are given for epoxidized soybean oil (Paraplex G-60) and n-hexyl epoxy stearate. The epoxidized soybean oil is a fair hydrogen chloride acceptor, comparable in this respect t o calcium and barium stearates. %-Hexyl epoxy stearate, on the other hand, is a very poor hydrogen chloride acceptor. I n fact, the results indicate that only a small portion of the hydrogen chloride given off by the resin reacts with the epoxy stearate. At 60 minutes the hydrogen chloride escape rate for the stabilizer is 4.3 mg. of HC1/1000 sq. cm./hour. T h e results given previously on dibasic lead, calcium, and cadmium stearate stabilized samples (Figures 6, 7, and 8) show t h a t the rate of hydrogen chloride formation is close to 0.0055 mg. of HCl/min./gram of sample. For a 0.012-inch film, this corresponds t o 6.6 mg. of HC1/1000 sq. cm./hour. Since n-hexyl epoxy stearate would not be expected to affect the rate of resin dehydrochlorination t o any great extent, it is apparent that a large fraction of the hydrogen chloride formed by the resin escapes from the compound. Escape rate data obtained in this manner were used t o test the hypothesis t h a t t h e concentration of hydrogen chloride in the resin compound is t h e major factor influencing t h e color stability. Table VI compares t h e hydrogen chloride escape rate at 60 minutes with the color of di(2-ethylhexyl) phthalate compounds milled for 20 minutes at 170” C. T h e mill stabilities were obtained on compounds with t h e formulation: Bakelite vinyl resin QYNA Di(2-ethylhexyl) phthalate Anatase T i 0 2 Stearic acid Stabilizer
ride as does n-hexyl epoxy stearate can give reasonably good color stability. I n this connection it is probably significant t h a t epoxy stabilizers are generally used in combination with other stabilizers. A small amount of cadmium stearate with an epoxy compound gives excellent color stability. This improvement may be due in part to the improved hydrogen chloride pickup when cadmium stearate is present. I t has also been shown recently by Lewis ( 5 )t h a t the reaction between phenoxypropene oxide and hydrogen chloride is strongly catalyzed by chloride ions. Phenoxypropene oxide i s used as an hydrogen chloride scavenger in chlorinated transformer oils. This suggests t h a t a similar type of catalysis may improve the hydrogen chloride scavenging action of epoxy stabilizers during milling on an iron mill. It appears certain t h a t such an effect must be acting to reduce the hydrogen chloride concentration during milling. Otherwise, it would be expected t h a t hydrogen chloride would attack the iron mill surface with formation of iron chloride dehydrochlorination catalysts. Milling an unstabilized stock at these temperatures invariably results in rapid blackening with copious evolution of hydrogen chloride fumes. From the foregoing it is apparent that the mechanism by which vinyl chloride resin compounds discolor is very complex. Many factors influence the color stability, and one of these is probably the efficiency of the hydrogen chloride pickup by the stabilizer. It is not always the major factor, however, since poor color stability is sometimes obtained with good hydrogen chloride scavengers. ACKNOWLEDGMENT
The advice of M. C. Reed and the late W. J. Jebens on several aspects of this work has been very helpful. Thanks are also due t o M. C. Reed and W. J. Frissell for permission to quote data obtained by them. LITERATURE CITED
(1) Boyer, R. F., J . Phys. & Colloid Chem., 51, 80-106 (1947). (2) Druesedow, D., and Gibhs, C. F., National Bureau of Standards, Circ. 525. DD. 69-80 (U. S. Government Printine: Office. Washington 25, -D. C . ) [Modern Plastics, 30, 123 (1953) ]. (3) Kenyon, A. S., Ibid., pp. 81-94. (4) Kolthoff, I. PI.,and Laitinen, H. A , , “pH and Electrometric Titrations,” p. 113, Wiley, New York. ( 5 ) Lewis, C. W., IND.ENG.CHEM..46, 366-9 (1954). (6) Marvel, C. S., and Homing, E. C., in “Organic Chemistry, An Advance Treatise” (Henry Gilman, editor), Vol. 1, 2nd ed., chapt. 8, p. 754, Wiley, Kew York, 1943. (7) National Lead Co., 111 Broadway. Xew York, N. Y . Handbook
on Stabilizers for Vinyl Resins, revised ed., 1952.
RECEIVED for review July 6, 1954.
Parts 100 45
After 20 minutes of milling at 170” C., the samples were removed, and the visible reflectance was obtained with a General Electric spectrophotometer. Reflectance values a t 450 millimicrons are used as a measure of the degree of yellowing t h a t has taken place. These data indicate that efficiency of the hydrogen chloride accepting reaction is certainly not the only factor determining the discoloration obtained with a stabilizer. All the best color stabilizers are efficient hydrogen chloride acceptors but, on the other hand, a good acceptor can give poor color stability-e.g., normal lead salicylate. Normal lead salicylate has been reported t o be an antioxidant (7), and its poorer color stabilizing efficiency may therefore be due to inhibition of oxidative polyene bleaching. It is also surprising that a material t h a t reacts as slowly with hydrogen chlo-
4CCEPTED
December 10, 1954.
Corrections
1
0.5 2
1019
I n the article, “Some Physical Properties of Activated BauxEKG.CHEW., 38, 839 (1946)], the following corrections ite” [IND. apply t o Table 11: Activation Temp.,
F.
450
Arkansas Bauxite 1
700
Void Vol.. CC./G. 0.26 0.44
Voids,
%
Pore Vol., CC./G.
Pores,
0128
47
%
34 , ,
I n the article, “Thermal Activation of Attapulgus Clay” [IND. ENG.CHEM., 42, 529 (1950)], the following corrections apply to Table VII: Activation (Da) Bulk Temp., Density, F G./CC. Attapulgus clay, natural
400
0.563
(Di)True
Pore Vol.,
Density G./CC.’
CC./G.
Pores,
%
2.56
0.583
58.5
