Nitroparaffins and Derivatives as Heat Sensitizers for

Rubber Latices ARTHUR WILLIAM CAMPBELL'

Commercial Solvents Corporation, Terre Haute, Ind.

ECEKT research has made various nitroparaffins and their derivatives available in commercial quantities (3, 4) , and large-scale applications for the materials

are rapidly being found. A considerable number of these com- pounds cause heat sensitization in rubber latices ( I ) , a phenomenon that has been produced in the past by a number of materials (8, 5, 6) and is used extensively a t present in the In the course of experiments on the use of nitroparaffins manufacture of foamed-rubber products. The use of nitro- and their derivatives as heat sensitizers, two different samples paraffins in this application is quite new, however, and has of latex were used: Concentrated F, from the Heveatex recently been the subject of extensive experimentation in this Corporation, and Lotol NC-957, from the Naugatuck Chemi- laboratory. cal Company. Both had been concentrated to 60 per cent

In compounded latices it is rubber content by centri- not unusual to find three or fuging, and the former had more different materials, each The nitroparaffins and their derivatives been protected against coagu- with a definite purpose. In a have been found to be heat sensitizers for lation by the addition of study such as this, the use of

The compound to be tested completely latices of compounds recently made commercially was prepared in the follow- mould unduly complicate the problem; so an effort was made nitroethane produces gels ing manner: The latex was to avoid these complications quickly, and 2-nitro-2-methyl-l-propano1, stirred well, strained through by running preliminary tests on while somewhat less active, produces a mix cheesecloth, and weighed. theindividualingredientsalone that may be stored for long periods at 150 c. The proper amount of zinc in a latex-nitroparaffin mix. without oxide dimersion was added It was found that gelling could

For use in subsequent tests a sample of zinc oxide dispersion was prepared by ball milling a composition prepared by the following recipe (in grams) :

Zinc oxide (New Jersey Zinc Co. Horsehead Red XX4) 50 2

Water 60

R Dispersing Agent (Darvan, R. T: Vanderbilt Go.)

latices containing zinc oxide. Of the group ammonia*

not be produced by a nitro- paraffin alone, even though the test mixtures were heated for considerable periods a t 80-90" C. However, addition of a small proportion of zinc oxide to these mixes quickly induced gelling. It was also found that the oxides and hydroxides of the elements of Periods 2-6 of the Second Group of the Periodic Table gave results similar to those obtained with zinc oxide:

Formula: Lotol NC-957

Temperature

Nitroethane Metallio compound

83 grams

500 c. 1 1

Compounds that roduoed no elling: Group I NaOIf, KOH, Cuz%, AgCaHa02

I1 BeOb I11 BnOs Al& Laz(SOS8 I V TiOz: ZrOi,'Sn(S,Oa)n, CeO, PbO, Th(N0s)r V H3vO4 AszOa Biz03

V I CrOa, IhoOs, iVa~WO~, NanUOa, UOa VI1 bInOz

VI11 COO, FeO, NiO a Barium hydroxide always produced gelling when added to latex, even

b A 0.17 BUS ension in water was used. When carefully added t o a blank in the abience of nitroethane.

(no nitroet%aneY, this suspension produced gelling in 108 minutes.

1 Present address, Thermatomic Carbon Company, Terre Haute, Ind.

to give 2.grams of the oxide per 100 grams of dry rubber.

The compounds to be tested as heat sensitizers were then added slowly to the latex with rapid stirring.

The determination of the gelling time was carried out in the following way: Forty milliliters of the prepared latex were poured into a 25 X 200 mm. Pyrex test tube. An iron wire 20 om. long with a hook of about 1 cm. radius was placed in the latex. This assembly was stoppered with a cork having a groove down one side, through which the wire extended. The test tube was placed in a thermostat at the desired tem- perature, and a t intervals the liquid was tested for gelling by moving the wire gently up and down. Vigorous stirring was avoided, since this occasionally induced gelling. When the mass slipped readily in the tube, it was considered to be gelled, and the elapsed time was recorded.

In Table I the results of tests on a number of nitroparaffins and nitroparaffin derivatives are presented. All are shown to be heat sensitizers.

In another series of tests the highly water-soluble crystalline compound, 2-nitro-2-methyl-1-propanol, was used to study the effect of heat-sensitizer concentration on the rate of gelling under various conditions. The results are listed in Table 11. Table I1 shows that compounds with a nitroalcohol concen- tration of three parts per hundred are stable enough a t room temperature for most process requirements, and other tests have shown that they can be stored a t 15" C. for more than a month Tyithout gelling.

1106

September, 1942 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 1107

TABLE I. NITROPARAFFINS AND DERIVATIVES hS HEAT SENRI- TIZERS

(Formula: Concentrated F latex, .l.67 grams; e n 0 dispersion, 4: heat sensitizer. 2)

-Gelling Time, Hr.- Compound 28' C. 50' C. 800 c.

Nitroparaffins Blank No gel Nitromethane 48 Nitroethane 24 1-Nitropropane 48 2-Nitropropane 48 1-Nitro-2-methylpropane ' 96 2-Nitro-2-methylpropane 144 1-Nitrobutane 96 2-Nitrobutane 96 I-Phenyl-1-nitroethane No gel

Chlor onitromethane 1-Chloro-1-nitroethane 1,l-Dichloro-1-nitroethane 1-Chloro-1-nitropropane 1,l-Dichloro-1-nitropropane 2-Chloro-2-nitro~rotane 3-Chlo;o-l-njtropropane 1-Bromo-1-nitro ropane I-Chloro-2-nitrogutane

2-Nitro-2-propanol

i-Nitro-2-butanol Nitro-2-methyl-1-propanol

.............. 4-Nitro-3-hexanol 3-Nitro-4-heptanol 5-Nitro-4-octanol

Halonitroparaffins 288

48 No eel

48 No gel No gel

24 48 24

Nitroalcohols* 120 240 288 192 288 120 192 120 96 72

120 144 216 312 264 264 264

6.17 0.13 0.22 0.05 0.22 0.07 0.45 0.07 0.43 0.07 0.55 0.10 0.75 0.10 1.82 0.08 1.12 0.08 2.77 0.08

1.17 0.07 0.50 0.10 4.60 0.08 0.50 0.10 4.60 0.10 1.35 0.10 0.20 0.05 0.35 0.08 0.35 0.08

2.20 0.10 3.33 0.10 4.63 0.08 4.53 0.12 4.53 0.12 2.13 0.08 0.47 0.08 4.03 0.10 4.03 0.12 0.65 0.08 0.53 0.10 0.53 0.08 0.90 0.12 2.78 0.07 0.37 0.17 2.42 0.12 3.25 0.12

a The nitroalcohols were added as 10% aqueous solutions, t o prevent local coagulation; if added directly, coagulation occurred.

Nitroethane was tested in a series of artificial latices and was found to be a vigorous heat-sensitizing agent for these compounds, none of which would gel without it. The results are listed in Table 111.

The true rate of gelling a t elevated temperatures is some- what faster than the tables indicate, owing to poor heat transfer through the latex. Thin layers may be gelled quickly. When a test tube full of water a t 100" C. was

TABLE 11. EFFECT OF CONCENTRATION OF 2-NITRO-2-METHYL- PROPANOL ON GELLING RATE

(Formula: Lotol NC-957, 167 grams: ZnO dispersion, 4: 2-nitro-2-methyl- 1-propanol 88 specified)

Nitroalcohola -Gelling Time, Hr.- G./100 G. Dry Ribber 28' C. 50' C. 800 c.

0.25 0.60 1.00 2.00 3.00 4.00 5.00

0 Added as a 25% aqueous solution.

TABLE 111. EFFECT OF NITROETHANE ON VARIOUS DISPERSIONS . . . 200 . . . . . . . . . ...

4 2

0.08

. . .

. . . 100 . . . . . . ... ...

1 45

. . . . . . . . . 100 ... ... . . .

1 1

. . . . . . . . . io6 . . . . . .

1 1

. . . . . .

. . . 208

10 2 6

a The zinc compounds present in the reclaims were sufficient for the test so none were added.

dipped into a sensitized latex and withdrawn after 5 minutes, its outer surface was coated with a layer of gelled rubber that was 23.8 per cent heavier than the layer deposited by a nonsensitized latex.

I n another test, a 25 X 200 mm. Pyrex test tube was filled with a sensitized latex to a depth of 50 mm. and was immersed in a thermostat at 90" C. At the end of 5 minutes the latex had gelled (according to the test described a t the beginning of this paper), but the center of the mass had not yet reached 75" C. The true time of gelling a t 90" C. must therefore be appreciably less then 5 minutes.

Literature Cited (1) Commercial Solvents Corp., U. S. Patent applioation. (2) Dunlop Rubber Co., Brit. Patent 351,937 (1930). (3) Gabriel, C. L., IND. ENQ. CHBM., 32, 887 (1940). (4) Hass, H. B., Hodge, E. B., and Vanderbilt. B. M., Ibid., 28.

339 (1936). (5) Pestalozza, U.,S. Patent 1,717,248 (1929). (6) Ibid., 1,750,540 (1930).

ROTARY BURNER IN WHICH SULFUR Is BURNED TO SULFUR

DIOXIDE

Courtesy, C o n p a w Uulf Sulphur