J. Soc. Cosmetic Chemists, 19, 149-158 (Mar. 4, 1968)

Conductometric Testing and Corrosion Study of Nonanhydrous Ethanol Systems for Hair Spray

STANLEY BOHAC, M.S.*

Presented before the Midwest Chapter, April I l, 196'7, Chicago

Synopsis---It was found that nonanhydrous ethanol in cmnbination with nitromethane gives the same life stability in most hair spray products as anhydrous ethanol. Formulations with different resins, various amounts of air in the cans, and various concentrations of nitromethane with nonanhydrous (95 and 90% by wt) and anhydrous ethanol are compared at elevated (48øC = 120øF) and at room temperatures. A conductometric method, which is very useful for testing in the hair spray field, is used for evaluation of this broad corrosion study.

INTRODUCTION

The purpose of this study was to clarify certain pertinent questions and to verify the possible use of nonanhydrous ethanol with nitromethane in aerosol hair spray in combination with Freon 11. From the standpoint of corrosion, different resins (PVP/VA E-735, } Resyn 25-1310, :• VEM, õ Gantrez AN-3152, [I shellac base, • and also ethanol alone) were compared. Ethanol (40-A) and Freon 12/11 as a solvent and propellent, respectively,

* Barr-Stalfort Co., Div. Pittway Corp., Niles, Ill. 60648. t PVP/VA, Antara Chemicals, Division of General Aniline and Fihn Corp., New York,

N.Y.

:• Resyn is a registered trademark of National Starch and Chemical Corp., Resin Division, New York, N. Y.

õ VEM is a registered trademark of Barr-Stalfort Co., Div. Pittway Corp., Niles, Ill. [I Gantrez AN, General Aniline and Fihn Corp., Dyestuff & Chemical Division, Ne•v York,

N.Y.

41Shellac Base, The Mantrose Co., Division of Millmaster Chemical Corp., New York, N.Y.

149

150 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

were used. Each of these formulas was tested with various amounts of

air in 8-oz, three-piece tinplated cans. Results of these combinations of variables were then compared with those obtained with the same for- mulations containing nitromethane as a corrosion inhibitor. The very same tests were also performed with nonanhydrous ethanol, both with and without nitromethane, to determine the effect of a certain amount of water on free radical reaction between Freon 11 and ethanol. For-

mulas with a different amount of nitromethane, as well as formulas with perfumes, were also employed. To accelerate the reaction, elevated temperature (48øC = 120øF) was used. Certain formulas were also tested at room temperature for shelf life comparison. Earlier studies related to corrosion are listed in the references (1-14).

CONDUCTOMETRY

The prindple of this method is to measure conductance as the re- ciprocal of resistance using a Wheatstone Bridge. Conductometry, a useful analytical tool in aerosol technology, was found adequate to evaluate the systems given below.

The acid numbers of unneutralized as well as neutralized, carbox- ylic-type, hair spray resins can be determined (Fig. 1).

The purity of an amine, or the amount of it, used for neutralization of hair spray resin, can also be determined (Fig. 2). By titrating two iden- tical samples of neutralized resin, one with NaOH and the other with HC1, the degree of neutralization of carboxylic groups can be calculated. If the slope of the line before neutralization is negative (in titration of the sample of neutralized carboxylic-type resin with HC1), it shows a strong base was used for neutralization.

Can corrosion of a hair spray product which has ethanol and Freon 12/11 is caused by HC1 formed by decomposition from Freon 11. This is indicated by increased conductivity of the solution (Fig. 3). The amount of HC1 could be titrated conductometrically, but, for practical purposes, measuring the conductivity of samples at certain time inter- vals is preferable.

One advantage of this method is that small samples (approximately 3 ml) can be used each time and contents of the same can may be tested repeatedly, providing a chronological evaluation of the condition of the product over a required period of time, without opening the container. Another, even greater, advantage of conductometry is that the corrosion results are expressed in numerical values, which other known methods do not provide.

CONDUCTOMETRIC TESTING AND CORROSION STUDY OF HAIR SPRAY 1.51

5OO

• 4oo

E •oo

• •oo ._

• •oo o

t o o I 2

---'-ml IN Na0H

Figure I

3 4 2 3 4 5

oo[ 4oo F

-•.

--• ml IN HCI

Figure 2 Conductometric titration

A--2.4 g Resyn 28-1310 in 100 ml anhydrous ethanol B--2.71 g Rcsyn 28-1310 90% neutr. with AEPD in 1()0 ml anhydrous ethanol C--0.31 g AEPD in 100 ml anhydrous ethanol

2OO

Figure $. Conductivity of a hair spray product during its lifetime

This method is useful not only for hair sprays but also for any aerosol products having low conductivity, where the conductivity of the con- tents substantially changes by forming HC1 from Freon 11, or by reac- tion with the metal of the container.

EXPERIMENTAL

Method and .•1 pparatus

For evaluation of results, the Conductivity Bridge,* Model 1t5 B2, was used. This was equipped with a glass-type cell (0.1 cell constant) having black platinized platinum electrodes. Approximately 3 ml of the liquid sample was collected by spraying out of the 3-piece 8 oz tinplated aerosol can into a test tube, and after four hours of condi- tioning at room temperature (24 øC) the conductivity was measured.

* Industrial Instruments, Inc.

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

o 20

o I I I I I I 0 I 2 3 4 5 6 7

• Time (hrs.)

Figure 4. Conductivity of a hair spray sample at different times after spraying out

of a container

4 6 8 I0

No, of runs

Figure 5. Air concentration in vapor space in container without dip tube at consecutive

determinations

/ 0 I0 20 30 40 / 0 I0 20 30 40 • Time (days} • Time (days}

200 ,oo ,ooL

I , , f o I•"T"F , , , o• / o IO 2o $o 4o o IO 2o $o 4o

, Time (doys} • Time (doys}

Figure 6 Figure 7

Comparison of value of pH and conductivity as they relate to corrosion at similar times (at 48øC = 120øF)

Conc.: 3(• VEM-9 (90% neutr. with AMPD) in 90% by wt. ethanol Fill: Fig. 6--35t)• conc., 65% F12/11 35/65

Fig. 7--35% conc., 65% F12/11S 35/65 A--less than 0.5% air in vapor space B--approx. 8% air in vapor space

CONDUCTOMETRIC TESTING AND CORROSION STUDY OF HAIR SPRAY 153

The amount of air in the vapor space in some of the cans was deter- mined. These cans, made without a dip tube, were evaluated in the upright position using a gas chromatograph equipped with a 12-ft di-2- ethylhexyl sebacate column.

RESULTS

The conductivities of liquids sprayed out of the aerosol containers will vary due to a rapid evaporation of F-12 and F-11, which changes the relative concentrations of the conductive components. A certain amount of F-11 will still be found dissolved in ethanol, even after a con- siderable length of time, as the evaporation process continues. After approximately four hours of standing at room temperature, the con- ductivity results obtained are sufficiently constant to be used for the evaluation of results (Fig. 4).

When dealing with determination of air concentration in the vapor space in the container, one must pay particular attention to the manner in which the container is connected to the gas chromatograph and to the amount of the sample taken, both of which may influence the results (Fig. 5).

Figures 6 and 7 show a comparison of pH values and conductivity determined on the same samples checked simultaneously at the same stage of corrosion. In some corrosion cases (probably when the me- tallic salt of HC1 is formed instantly), the pH measurement cannot pro- vide a correct picture of the condition of the container's contents.

The effect of the amount of air in the vapor space on the rapidity of corrosion at 48 øC is apparent from Fig. 8. When similar tests were con- ducted at room temperature for three and one-half years, no change in initial conductivity (3 mmhos) was observed.

The corrosion inhibiting influence of nitromethane was also deter- mined. Freon IlS, which is Freon 11 containing 0.3% of nitromethane, was used. Experiments similar to those described above (except that Freon 11S replaced Freon 11) indicated that cans containing from 0.21ø•o-0.54% air showed no change in conductivity when exposed to either room temperature or 48 øC for up to two years. Similar results were obtained when hair spray resins were tested in cases where pH values were not exceedingly low (under pH 6).

Figures 9 and 10 show comparisons of formulations with ethanol only, and Resyn 28-1310, both without any additives, at 48 øC. One hundred per cent, 95%, and 90% by wt. ethanol was used. Also included are the effects of air and nitromethane.

154

Figure 8.

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

The effect of air in vapor space on container's life. Cone.' auhydrous ethanol without any additives; fill: 35% cone., 65% F12/11 35:65.

• 01: I .• o 0 L.;...._. • ._• •_ I I

1.0,.2 4 6t 0 2 4 6 Time (mo$,) / ' Time (mo$.)

no•ir 4øø I ! no•irl 2OO 2OO ! NM

, oL." .... , Time(mos.) / ----'- Time (mos.)

Figure 9. Ethanol only

400= . , . , 400

200 /I 2øør .,,: NM X old', , I oL.'"------- / o 2 4 6 } o 2 4 6 • • Time(mos.) ß Time(mos.)

Time (mos.) • • Time(mos.)

Figure 10. Resyn 28-1310 (90% neutr. with AMPD)

The effects of air in vapor space, nitromethane, and water on conductivity vs. time at 48øC Where NM is mentioned, F 11S was used (0.3% of nitromethane based on Fll) Air = approx. 8% of air in vapor space No air = less than 0.5% of air in vapor space Cone.: 3% of resin solids (without any additives) in 1()0• ( ), 95(/0 (---) and 90% (' ß ß )

by wt. ethanol

Under the same conditions shown in Figs. 9 and 10, tests were also conducted with the following resins: 90% neutralized VEM-640 with AMPD, PVP/VA E-735, 6% neutralized Gantrez AN-3152 with AMPD, and 90% neutralized Shellac base with AMPD.

The results indicated that, from the standpoint of corrosion, there is no visible difference between all tested hair spray resins.

Similar experiments, conducted with commercial products, indicate that in some eases it may be difficult to predict the effect of perfumes, since certain components of the perfume may act as corrosion accelera- tors, while components in others may act as inhibitors.

CONDUCTOMETRIC TESTING AND CORROSION STUDY OF HAIR SPRAY 155

200

• 200 /•o.•5 % NM -- /•0.15 % NM /L• 0.:30% NM 0.:30 % NM

/ ,oor / /0.15% NM 0.15% NM

F/r•0.30 % NM g 0• NM •0.30%

I I I I 0 I I 6 12 18 2 [ 12 18 Time (mos.} ß Time (mos:)

24

Figure 11. Veto-640 (9()• neutr. with AMPD)

Figure 12. Resyn 28-1310 (90% neutr. with AMPD)

The effects of various amounts of nitromethane on formulas with different resins in 93% (---) and 95% (--) by wt. ethanol. 0.15% and 0.30% o[ nitro•nethane based on Fll was used

Amount of air in vapor space--approx. 8% Fill: 36% cone. with 3% of resin solids, 65% F12/ll 35/65

•200 • 200 . 0% NM

I' • %NM • .

,oo %;:

I i / 0 6 12 18 24 0 6 12 18 24 • , Time (mos.] • Time

Figure 13. Commercial formula with E-735 Figure 14. Commercial formula with Resyn 28-1310

The effects of various amounts o[ nitromethane (based on Fll) on commercial [ormulas in 95% by wt. ethanol at 48øC

Amount of air in vapor space--approx. 8% Filh 35% cone. with 3% o[ resin solids, 65% F12/tl 35/65

The influence of nitromethane on inhibiting corrosion of various for- mulations containing 93% by wt. and 93% by wt. ethanol with VEM-640 and Resyn 28-1310 is shown in Figs. 11 and 1.2. Similar tests were per- formed on commercial products containing E-735 (Fig. 13) and Resyn 28-1310 (Fig. 14) resins. Distilled water and nitromethane were added to the can to obtain the desired combination of components.

Before making general conclusions from these results, it must be remembered that perfume components may act as corrosion inhibitors or

156 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

'- 200 E E

• •oo

I ø 2.0 40 60 80

Time (days)

Figure 15. The effects of various a•nounts of water on conductivity of commercial hair spray containing Veto-640 resin without •fitromethane at 48øC. Amount of air in vapor space-- approx. 8%

• 60 - o

_

> _

-• 20

I 2

Time (mos.)

perfume A•=• ,'• perfume B

4 6

Figure 16. Comparison of the effects of two different perfumes (A and B) on the conductivi- ties of formulas containing Vem-640 resin in 95% by wt. ethanol with nitromethane at 48øC Fill: 35% cone. with 3% resin solids, 65% F12/11S 35/65 Amount of air in vapor space--approx. 8%

accelerators. This fact could change the comparative corrosion rapidity between elevated and room temperatures. Figure 15 shows a case in which a particular perfume component acted as a stabilizer of corrosion, thus formulations with up to 5% by wt. of water were stable.

Tests were also conducted with at least two different perfumes with all the listed hair spray resins. Figure 16 stresses that the only unpre- dieted factor in the use of formulations with 95% by wt. ethanol in com- bination with nitromethane is the possible role of the perfume as an accelerator of corrosion. For this reason, each formulation should be

scrutinized individually for these effects before production filling. The effect on corrosion of different degrees of neutralization of car-

boxylic types of resin in anhydrous and nonanhydrous ethanol was also studied using VEM resin. Formulas with 0 to 90% (in 10% incre-

CONDUCTOMETRIC TESTING AND CORROSION STUDY OF HAIR SPRAY 157

merits) neutralized resin using AMPD were tested. No significant difference was found. The same results were obtained with Resyn 28-1310, 70% and 90% neutralized with AMPD.

CONCLUSIONS

It is evident that it is possible in most formulations to use 95% by wt. ethanol in combination with F-11 in hair sprays, if nitromethane is added as a corrosion inhibitor. The products obtained have the same shelf life as those containing anhydrous ethanol without the nitro- methane.

Until the reaction between certain perfume components and nitro- methane in the presence of 95•o by wt ethanol and F-11 is thoroughly explored, it will be necessary to test every product to determine sta- bility. It was found that in some cases certain ingredients in perfumes have practically the same effect as nitromethane. In other instances, however, a reaction probably occurs between a particular perfume com- ponent and nitromethane, which can accelerate corrosion.

The known effect on corrosion of the amount of air in the vapor space in a can with anhydrous ethanol (which plays an important r61e in contemporary hair spray products) is substantially minimized if nitro- methane is used.

Conductivity, as a method of evaluating corrosion, proved to be very useful because of its numerical expression of results, and also for the ability to evaluate corrosion results of the product in the can, without opening' the can for visual examination.

(Received April 18, 1967)

REFERENCES

(1) Root, M. J., Corrosion o[ aerosol metal containers, Proc. 42nd Ann. Meeting, C.S.M.A., Dec., 1955.

(2) Johnson, H. T., McAlpin, A. W., and Schenck, A.M., S•me Aspects o[ Canning Soft Drinks, Food Technol., 12,643 (1955).

(3) Root, M. J., and Maury, M. J., Corrosion testing of aerosol products, J. Soc. Cosmetic Chemists, 10,403 (1959).

(4) Sanders, P. A., Mechanism o[ the reaction between trichloromonofluoromethane and ethyl alcohol, Proc. 46th Mid-Year Meeting, C.S.M.A., May, 1960.

(5) Bower, F. A., and Long, L. J., Stabilization o[ alcohol-based aerosols, Proc. 47th Mid- Year Meeting, C.S.M.A., May, 1961.

(6) U.S. Pat. 3,085,116, Stabilized chlorofluoroalkanes, D. E. Kvalnes and C. Ford, assignor to E. I. dupont de Nemours & Co., Inc. Patented Apr. 9, 1963.

(7) Hoffmann, B., The question about the utility of nitromethane as stability agent in aerosol [ormulations, Aerosol Rept., 2• 17 (1963).

158 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

(8) Sanders, P. A., Nitromethane in aerosol formulations, Ibid., 2, 178 (1963). (9) Hoffmann, B., Nitromethane in aerosol formulations, Ibid., 2,182 (1963).

(10) Hoffmann, B., The use of alcohols in aerosols, Ibid., 4, 71 (1965). (11) Sanders, P. A., Corrosion in aerosols, Soap Chem. Specialties, 43, 74 (July, 1966). (12) Sanders, P. A., Corrosion pitfalls in fornmlating aerosols, Proc. 52nd Mid- Year Meeting,

C.S.M..4., May, 1966. (13) Reed, A. B., Testing for corrosion in aerosol packages, Ibid. (14) Johnson, H. T., Polarization methods applied to corrosion studies in aerosol products,

Ibid.