Effect of Certain Organic Bases in Plasticized Nitrocellulose Films


shortened the life of a lacquer film. Pyridine is known to have a deleterious effect in lacquers; in fact, a manufacturer of nitrocellulose advises ag...
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July, 1927

INDUSTRIAL A N D ENGINEERING CHEMISTRY Conclusions

1-The optimum conditions for the phenol fusion are: (a) a temperature of 350” C.; ( b ) an amount of caustic soda 15 per cent in excess of that theoretically required to react with the sulfonate; (c) a 15-minute period of heating after the addition of the sulfonate; (d) exclusion of air from the melt; (e) avoidance of local excess of sulfonate due to too rapid feeding, insufficient stirring, or large lumps. 2-Under the conditions described above, a yield of 96 per cent of the theoretical may be attained. 3-Yields practically as high as those obtained under the optimum conditions may be secured a t as low a temperature

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as 300” C., but only by increasing the amount of soda and the time of heating. 4-The yield of phenol is very markedly lowered if the melt is exposed to air. &Among the oxidation products formed are dihydroxydiphenyls and, if the oxidizing conditions are severe, carbon dioxide. The carbon dioxide may neutralize the excess alkali and some of the phenolate and cause further loss of phenol by vaporization. 6-In the presence of an excess of sulfonate, diphenyl ether and thiophenol are produced in considerable quantitieq. The formation of either of theqe products results in decreased yields, while the thiophenol is an objectionable impurity in the finished phenol.

Effect of Certain Organic Bases in Plasticized Nitrocellulose Films’” By L. L. Steele NATIONAL BUREXUOF STANDARDS, WASHINGTON, D. C.

UKLIGHT is known to be a very important factor in the decay of oil-varnish films exposed outdoors. The destructive action of sunlight, often ascribed to the ultra-violet rays, is perhaps even more marked in the case of clear nitrocellulose lacquer films exposed to the weather. I n the case of the oil varnish it is probable that brittleness of the film, which causes cracking and eventual failure, is due to a slow, continuous oxidation of the drying oil originally present under the catalytic effect of the sun’s rays. Lacquers do not dry through oxidation as do oil varnishes; therefore, their failure in the weather can hardly arise from overoxidation. Their failure is probably caused mainly by hydrolytic splitting of the cellulose ester. Kitric acid is a product of such hydrolysis and would be expected to act as a catalyst in the splitting of additional portions of the cellulose ester, so that once decomposition starts it would be expected to proceed rapidly. The evident effect of sunlight in splitting nitric acid from the nitrocellulose in a lacquer film was indicated in the following simple experiment: To a commercial clear lacquer there was added approximately one per cent by weight of dimethylaniline. Films of this mixture were prepared on sheets of clean steel. These films showed no appreciable coloration after several hours in the laboratory but developed a characteristic green color within 5 minutes when placed in direct sunlight. Photographic prints were obtained by placing a negative over one of the lacquer films and exposing to sunlight. This indicated that the green coloration was produced by light rays and was not due to a heating effect. A plausible explanation for the green coloration is that oxides of nitrogen were liberated in the film through the action of sunlight and combined with the dimethylaniline present to form the green derivative, p-nitrosodimethylaniline.3

S

Stabilizers

The use of a stabilizer (or anti-acid) for guncotton and allied explosives is well established. Diphenylamine seems to have been used very commonly for the purpose. This 1

Received February 17, 1927. by permission of the Director, National Bureau of Stand-

* Published

ards. a Subsequent t o the experiment outlined above, the author found that

weak organic base is supposed to combine with traces of nitrous or nitric acid and prevent the extensive catalytic splitting effect of these acids on nitrocellulose. Very little has been written about the use of stabilizers in nitrocellulose lacquers. Wilson4 advises the use of small percentages of urea in certain formulas. Sproxton6 mentions the use of urea or dicyandiamide as a n anti-acid in certain airplane dopes. I n some preliminary experiments with lacquers it was found that diphenylamine prolonged to a marked degree the life of a clear lacquer exposed to the weather. On the other hand, it was observed that pyridine and quinoline shortened the life of a lacquer film. Pyridine is known to have a deleterious effect in lacquers; in fact, a manufacturer of nitrocellulose advises against the use of completely denatured alcohol in lacquers because of its pyridine content. Wilson mentions the use of pyridine to reduce the viscosity of nitrocellulose solutions “whereby the action of the pyridine seems to be progressive and results in rapid decomposition of the film.” a

Experimental

It seemed desirable to study a wider range of organic compounds in respect to their effect on nitrocellulose films. Forty organic compounds containing nitrogen were so selected a s to include aliphatic amines, primary, secondary, and tertiary aromatic amines, cyclic amines, amides, and several miscellaneous compounds. A simple plasticized nitrocellulose solution was prepared of the following composition : Nitrocellulose (I/* second R. S.) Dibutyl phthalate Ethyl acetate Butyl acetate Toluene

200

It was recognized that this mixture did not represent a typical present-day lacquer because of the absence of resins, but it was considered advisable to cut down the number of variables. T o portions of the above mixture 1 per cent by weight of the various selected organic compounds shown in Table I was added. I n most cases the added compound dissolved readily in the mixture. Exceptions are noted in

J. Walter, 2. angew. Chem., 24, 62 (1911). has observed that guncotton or celluloid moistened with dimethylaniline develops a color ranging from green to blue and suggests the possibility of coloring celluloid in this manner.

Parts 100 33.3 100 100

”Pyroxylin Enamels and Lacquers,” p. 146, D . Van Nostrand Company. 6

“Cellulose Ester Varnishes,” p. 127, D. Van Nostrand Company.

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1NDUSTRIAL A N D ENGINEERING CHEMISTRY T a b l e I-Data

ORGANIC COMPOUND NO. ADDED I Iso-allylamine

COXDITION OF SOLUTION Clear

Vol. 19, No. 7

on Nitrocellulose Solutions and Exposure of Films COLOR OF COLOR OF FILM UNEXPOSED AFTER 2 HOURS IN SOLUTION FILM SUNLIGHT COLOR OF

DAY5 FOR COMPLETE

FAILURE 29

CONDITION O F FILMS NOT FAILING I N 170 DAYS

Light red

Light yellow

Light yellow

2 3 4

Benzylamine Piperin e Quinoline

Clear Clear Clear

Red None Light yellow

Light brown None Light yellow

None Yellow Light yellow

32 32 32

... ... ... ...

5 6

Diphenylguanidine Piperidine

Clear Clear

Red Red

Light yellow Light brown

Light yellow None

39 39

... ...

7

0-Anisidine

$-Toluidine Xylidine

Clear Clear Clear

Red Red Red

Light tan Light red Light tan

Brown Tan Light tan

47 47 47

10

Acetotoluide

Clear

None

Sone

Kone

63

11

4-Amino-1,3-dimethylbenzene Di&&yltoluidine Hippuric acid Oxamide Pyridine

Clmr

Red

12 13 14 15

Clear Undissolved crystals Undissolved crystals Clear

None None None None

Light t a n Sone None h-one None

Light t a n None None Brown spots None

64 64 64 64

16 17

Aniline Diethylaniline

Clear Clear

Light red None

Light red None

Light t a n Brown-yellow

18 19 20 21 22 23 24 25 26

None added (original soiution) Acetanilide Asparagine Dichloroaniline Dimethylaniline Formanilide Monoethylaniline Urea Urethane

Clear Clear Undissolved crystals Clear Clear Clear Clear Undissolved crystals Clear

None None None None None None None h-one None

h-one None None Very light green Kone None N-one Sone

None None None Light t a n Green None Light t a n None None

27 28

BenEamide Formamide

Clear Clear

None Very light yellow

Sone Brown spots

Light buff Brown spots

102 102

29 30 31 32 33 34 35

Acridine Anthranilic acid @-Naphthylamine Diphenylthiourea Ethylbenzylaniline p-Amidobenzoic acid p-Bromoaniline

Clear .~~~~ Clear Clear Clear Clear Clear Clear

Light brown Light brown Red Very light yellow None Light yellow Light red

Light Light Red &-one None 1,ight Light

Yellow Brown Red Light yellow Brown-yellow Tan Tan

117 117 117 117 117 117 117

36

a-Naphthylamine

Clear

Red

Reddish

Wine red

130

8 9

~

. Clear

N o._. ne .

yellow tan

tan tan

64



79 79

80

...

... ...

...

...

... . ..

... ... ...

...

...

... ... ... ... ... ... ... ...

... ...

37

Carbazole

None

None

Greenish yellow

More than 170 days

Dull and consider-

38

m-Nitroaniline

Clear

Light red

Green-yellow

Yellow-brown

More than 170 days

Dull able arust n d considerable rust Dull a n d considerable rust Dull and considerable rust Somewhat dull; rust a t edges of panel only

39

Methyldiphenylamine

Clear

None

None

Greenish yellow

hlore than 170 days

40

Phenyl-a-naphthylamine

Clear

Red

Faint tan

Red

More than 170 days

41

Diphenylamine

Clear

None

None

Golden-brown

More than 170 days

Table I. Duplicate clean, bright, cold-rolled steel panels were coated with each of the forty different lacquer mixtures. Panels were also prepared with the original solution containing no added organic base. Two coats were applied in each case by the dipping method draining each coat vertically but in opposite directions. The color of the solutions, if any, was noted, as well as the color of the films after a drying period of 24 hours. The panels were exposed to the weather on June 7, 1926, a t an angle of 45 degrees facing south. The color of the films was noted after a 2-hour exposure to sunlight. The data on the color observations are given in Table I. The panels were subjected to an artificial spray of rain for 20 minutes daily (rainy days and Sundays excepted). Inspection of the exposed panels was made nearly every day for the first 80 days and then at intervals of a week. Failure for the coatings was arbitrarily taken to be the point at which two-thirds of the film surface had disintegrated to an extent that no further protection was offered to the metal. Results

I n Table I are listed the various organic derivatives in the order in which the respective coatings failed. The isoallylamine showed a life of 29 days, the standard nitrocellulose film with no added organic compound, 80 days, while diphenylamine did not show failure after 170 days. I n general it was found that the very strong bases, such as iso-allylamine, benzylamine, piperidine, etc., were detri-

mental in the nitrocellulose film. Many compounds appeared to have no effect on the life of the film. Urea and asparagine are in this class, but it should be noted that these compounds did not dissolve completely in the solvents present in the lacquer. Hippuric acid and oxamide appeared to accelerate decomposition although they were only partially dissolved. It is interesting to note that aniline appeared to be neutral in its effect in the nitrocellulose film while bromoaniline and especially m-nitroaniline appeared to have a beneficial effect. The greater vapor pressure of aniline might account for this difference. The most effective compound in prolonging the life of the nitrocellulose film was diphenylamine. This is noteworthy in view of the use of this material for the stabilization of smokeless powder. The brown coloration of the film containing diphenylamine caused by sunlight would probably be a serious drawback to its use as a stabilizer in commercial lacquers. Other derivatives which appeared to act as stsbilizers also showed a similar defect of discoloration in sunlight. New Nitrate Works in Poland-It has been practically decided t o break ground soon for Poland’s second nitrate factory, near Tarnow in Galicia or southern Poland. A delegation has recently returned from a visit to Italy and France, where a study was made of manufacturing methods and equipment. The necessary machinery has not yet been purchased. Further details, together with the name of the official to be addressed, may be procured from the U. S. Department of Commerce.