I
MACK F. FULLER Burnside Laboratory, Explosives Department, E. 1. du Pont de Nemours & Co., Inc., Penns Grove,
N. J.
N,N'-Dimethyl=N,W=dinitrosotqrep hthalamide Blowing Agent Preparation, Properties, and General AppIications This nitrogen-releasing compound overcomes most performance difficulties of earlier materials for pr e paring c e IIu Ia r p o Iy (viny I c hIor ide) prod u ct s
ORGANIC
compounds that decompose upon heating to give one or more gaseous products have been used extensively for about 15 years in the production of cellular rubber and plastics products. Most of these compounds have been of the nitrogen-releasing type. Nitrogen is a relatively inert gas chemically, and the permeability of most common polymers to nitrogen is less than to oxygen, carbon dioxide, ammonia, etc., which can be generated economically from organic compounds (72). Organic compounds generally are preferred to inorganic compounds because of better dispersibility in organic polymers. Commercially available blowing agents such as dinitrosopentamethylenetetramine (7, 8, 9 ) and several sulfonyl hydrazides were generally acceptable for use in preparing expanded elastomers such as natural rubber, GR-S (butadienestyrene), and neoprene. Available blowing agents were operable but not completely satisfactory for expanding poly(vinyl chloride), because they led to discoloration and odor development in this type of polymer during decomposition or failed to produce products in a wide range of physical properties, both in highpressure and atmospheric-pressure blowing processes.
Nitrosoamides as Blowing Agents A new nitrogen-releasing compound, N,?!iLT' dimethyl N,N' dinitrosoterephthalamide, appeared to over-
-
722
-
-
come most of the performance deficiencies of earlier materials for the preparation of cellular poly(viny1 chloride) products. The N-methyl-N-nitrosoamides of succinic and adipic acids had been mentioned in the patent literature as blowing agents (I, 9 ) ) but these aliphatic nitrosoamides performed particularly poorly in the preparation of foamed poly(viny1 chloride) products at atmospheric pressure, in comparison with N,N'-dimethylN,N'-dinitrosoterephthalamide. Difference in performance of these three nitrosoamides when used to prepare open-cell poly(viny1 chloride) foam at atmospheric pressure employing a typical foam plastisol formulation is summarized as follows: Procedure 1. 2.
Formulation foamed in oven at 100' C. Foam fluxed 0.5 hour in oven at 162' C.
Formulation Parts by
wt. Geon
121 [ dispersion-grade, poly(viny1 chloride) resin] Dow 276-V-2 (a-methylstyrene trimer resin) Paraplex G-62 (epoxy polyester) Paraplex G-SO (polymeric polyadipate) Ohopex Q-10 (octyl fatty phthalic acid esters) Advastab BC-105 (liquid bariumcadmium stabilizer) Tipure R-610 (titanium dioxide) Calcium Petronate (petroleum sulfonate salt) White mineral oil Nitrosoamide
loo'%
100 20 8 36
36 2 2 3.6 3 5 . 7 to 7
Results NitrosoTime amide/ Required Degree 100 G. toFoam, of PVC Min. expansion 5.7a 40 8.5X
Nitrosoamide N,N' Dimethyl N,N' - dinitrososuccinamide N,N' Dimethyl N,N' di7 ' 18 8X nitrosoadipamide N,N' - Dimethyl N,N' di12 13X nitrosoterephthalamide Theoretically equivalent in releasable nitrogen.
INDUSTRIAL AND ENGINEERING CHEMISTRY
-
-
-
Product
Color Cream Cream Brilliant white
Cell structure Poor, contained fissures Poor, contained fissures Fine, uniform
Preparation
-
-
N,N' - Dimethyl iV,iV' dinitrosoterephthalamide was prepared in high yield by nitrosation of N,N'-dirnethylterephthalamide in nitric acid solution. N,N'-Dimethylterephthalamide was prepared by reaction of methylamine with terephthalic acid, terephthaloyl chloride, or dimethylterephthalate. The reactions involved in the preparation starting with dimethylterephthalate are :
was determined a t 60" C., because tke stability at this temperature appeared to be an accelerated means of estimating the long-term stability of the compounds under ambient-temperature storage conditions. Furthermore, 60" C. is a temperature which occasionally might be reached in the storage and shipment of a blowing agent. To determine stability, a sample of the
In mixtures with other materials A7,lV'dimethyl-lY,N'-dinitrosoterephthalamide
was usually less stable thermally than when pure. The blowing agent was much less stable in solution than in the solid state, its stability in solution depending upon the chemical nature of the solvent-the nitrosoamide dissolved in mono- or polyhydroxy compounds such as isopropyl alcohol or ethylene glycol decomposed completely in a few hours at room temperature, as compared with 0 0 several days when dissolved in a nonpolar // // solvent such as benzene. Certain solids, C-NHClls C-OCHa normally considered relatively inert chemically, reduced the stability of the nitrosoamide significantly. For example, in a 40/60 nitrosoamide-poly(viny1 chloride) resin mixture, the nitrosoamide had a half life at 60" C. of only about 50 hours, compared with no significant deDimethylterephthalate N , N '-Dimethylterephthalamide composition of the nitrosoamide alone 0 0 during the same time. // // C--N-CH ,i C-NHCHn Alkaline materials lowered the stability of N,N'-dimethyl-N,N'-dinitrosoterephthalamide in proportion to their alkalinity and dissolving power for the nitrosoamide. A strong amine solvent It such as ethylenediamine caused the N 'O 0 nitrosoamide to decompose instantaneN,N'-Dimethyl-N,N '-dinitrosoterephthalamide ously when the two materials were mixed proper weight to generate 0.01 mole of together at room temperature. AnLaboratory Preparation of Nitrosoamide. Fifty grams of N,N'-dimethylnitrogen was charged to a glass tube held hydrous sodium hydroxide intimately in a water bath at 60" C. The rate of terephthalamide was dissolved in 603 blended with the nitroscamide induced gas evolution, as measured by collection grams of 6670 nitric acid, and the soluslow decomposition a t room temperature, of the gas in a buret which read per cent tion was cooled to 10" C. A solution of but when the sodium hydroxide was in decomposition directly, was considered a 69 grams of sodium nitrite in 150 grams an alcoholic solution, the effect was the same as that induced by the organic gage of the inherent thermal stability of of water was added over a period of 1.7 the compound, A comparison of the hours to the agitated nitric acid-amide amine. therma I stability of N ,N'-d imethyl-N ,N 'solution at 5" to 15" C. The mixture The effect of acids upon the stability of dinitrosoterephthalamide with the therwas held a t this temperature for 15 N,N' dimethyl - N,N' dinitrosomal stability of several analogous nitrominutes after completion of the nitrite terephthalamide was less pronounced than the effect of alkalies. Mineral acids soamides assmeasured by this test is shown addition. The product was filtered and in Figure 1. No gas was evolved from washed free of acid with water. After in aqueous solution promoted the hydrolthe nitrosoterephthalamide during apdrying a t room temperature, the crude ysis of the nitrosoamide to terephthalic proximately 140 hours at the test temproduct weighed 62.5 grams, or 95.7% acid. The acidic salt, anhydrous zinc of theory. The product contained 22.1% perature. chloride, a t 0.5% concentration by Of particular interest were the obof nitrogen in comparison with a theoretweight in a 70/30 nitrosoamide-mineral ical 22.4y0. McKay, Park, and Viron servations that N,N'-dimethyl-N,N'-dioil mixture improved the thermal nitrosoisophthalamide was more than earlier had used a nitric acid medium stability of the mixture, as determined by 6OY0 decomposed within 40 hours at for the nitrosation of ethylene urea and 2the gas evolution from the mixture stored 60" C., and N,N'-diethyl-N,N'-dinitronitramino-2-imidazoline (7). at 60" C. Low concentrations of nitric Purification by neutralization of ocsotereplithalamide was so unstable at acid-Le., less than o.25y0 by weightcluded nitric acid by aqueous sodium bi60' C. that it decomposed violently exerted no observable deleterious effect within a few hours after initiation of the on the stability of the nitrosoamide in the carbonate was sufficient for N,N'-ditest. N,N' -Dimethyl N,N' dinitrosonear-anhydrous state. Water was nearly me thyl-N,N'-dinitrosoterephthalamide to be used as a blowing agent. Purification hexahydroterephthalamide (trans isomer) neutral in its effect on the stability of the of the compound by recrystallization from was more than 30% decomposed within nitrosoamide. All the esters, including 40 hours a t 60" C. Attempts to nitroa mixture of acetone and ethyl alcohol such solid esters as dicyclohexyl phthalate was demonstrated. sate fl,N'-dimethyl-O-phthalamide unand dimethylterephthalate, studied in der the conditions described were unsucN,N' Dimethyl AT," dinitrosoconnection with their effect on the cessful, and N-alkyl-N-nitrosoterephthal-. thermal stability of the nitrosoamide terephthalamide is an odorless, yellow crystalline solid melting with decomposiamides in which thealkyl group conactivated its decomposition in varying tion at 118" C. tained more than two carbon atoms such degrees, the liquid esters exerting the as N-propyl and N-butyl were obtained most pronounced effect. with difficulty and in low yield. It was The approximate effect of temperature Thermal and Chemical Stability concluded that the aromatic ring, the Non the half life of the nitrosoamide in a N,N' Dimethyl N,N' dinitrosomethyl substitution, and the para position liquid ester medium, dioctyl phthalate, at terephthalamide was more stable in of the 2 N-alkyl-N-nitroso groups com80") 80°, loo", 120°, and 150" C. at heated storage than any analogous nitrobine to make N,N'-dimethyl-N,N'-diniatmospheric pressure is shown in Figure soamides with which it was compared. trosoterephthalamide unusually stable 2. The decomposition rates delineated The stability of blowing agent candidates a t 60" C. for this class of compounds. were obtained by charging 0.35 gram of I
8
-
L.
-
-
-
-
-
-
-
-
-
VOL. 49, NO. 4
APRIL 1957
723
T I M E - HOURS Figure 1 . Thermal stability of N,N'-dimethyl-N,N'-dinitrosoterephthalamide analogous N-alkyl-N-nitrosoamides at 60" C. NTA NSA 112 NTA HHNTA NAA NIA NOA NETA
N,N'-Dimethyl-N,N'-dinitrosoterephthalamide
N,N'-Dimethyl-N,N'-dinitrososuccinamide p-N-Methyl-N-nitrosocarbomethoxybenzamide N,N'-Dimethyl-N,N'-dinitrosohexahydroterephthaiamide N,N'-Dimethyl-N,N'-dinitrosoadipamide N,N'-Dimethyl-N,N'-dinitrosoisophthaiamide N,N'-Dimethyl-N,N'-dinitrosooxamide N,N'-Diethyl-N,N'-dinitrosoterephthalamlde
iY,,Y'- dimethyl
-
-
N,lV' dinitrosoterephthalamide and 10 grams of di-2ethylhexylphthalate to a 50-ml. distilling flask attached to a tube for collecting gas over water in an inverted 100-ml. graduated cylinder. The distilling flask was lowered into an agitated oil bath at the desired temperature, and the time required to evolve one half of the total releasable gas was recorded. Determinations were made in triplicate and the results averaged.
Course of Thermal Decomposition
with
consisting of poly(viny1 chloride) resin, di-2-ethylhexyl phthalate, and basic lead carbonate in a closed bomb reaching a maximum temperature of 177" C. was 99+% nitrogen, with traces of water and carbon dioxide. These results were obtained by mass spectrographic analysis. The total gas evolved by decomposing h,N' dimethyl iV,N' dinitrosoterephthalamide in a toluene solution at 70" C. to the reflux temperature of toluene or in several poly(viny1 chloride) plastisols (compounded for foaming at atmospheric pressure) over a temperature range of 60" to 100' C. failed to show in-
-
-
~
which is sensitive to impact and friction. Therefore, for use as a blowing agent it was coated with approximately 30% by weight of white mineral oil, which adequately desensitized it with minimal lowering of its storage stability or its blowing performance in most applications. However, some lowering of stability is effected by admixture of the mineral oil with the nitrosoamide-for example, a 70/30 mixture of nitrosoamideoil decomposed in the 60' C. test to the extent of about 2 to 3% within 96 hours. in comparison with no decomposition in the same time when the nitrosoamide was moiled. A sample of 70/30 nitrosoamide-oil mixture retained 94y0 of its gas-generating potential after storage for 2 years under the ambient temperature conditions existing in an unheated building at Penns Grove, N. J. Ar,N' Dimethyl - iV,.V' - dinitrosoterephthalamide was easily ignited by sparks or flame and burned rapidly. A 70,/'30 nitrosoamide-mineral oil blend in a copper trough a t a depth of 0.5 inch burned a t the rate of 0.8 foot per second. Either the pure nitrosoamide or nitrosoamide-oil blend eventually ignited when held on a surface at a temperature of thr order of 80" C. or higher, as a result 01 the heat generated when the compound underwent uncontrolled decomposition. Certain materials (other than water. which is a very effective flame retardant in low concetrations) such as salt hydrates which release water upon heating-e.g., magnesium sulfate heptahydrate, boric acid, magnesium borate (and other borates)-in 50/50 admixture with the nitrosoterephthalamide great1)reduced its flammability but were not blended with the nitrosoamide for general blowing agent applications because of interference with the blowing of poly(vinyl chloride) plastisols at atmospheric pressure. N,iV' Dimethyl N,S' dinitrosoterephthalamide, according to animal feeding tests, has a low order of acute oral toxicity. Such tests also indicated that the nitrosoamide is a minor skin irritant, for which a sensitivity may be developed.
-
-
0 KO
NO 0
0
__
__
Dimethylterephthalate
h',S'-Dimethyl-N,N'-dinitrosoterephthalamide
The evidence for this course of decomposition was obtained as follows: iV,:tT' Dimethyl N,N' - dinitrosoterephthalamide, recrystallized from acetone-ethyl alcohol, was decomposed in hot (70" C. to reflux temperature) toluene and the toluene removed by distillation. A white solid residue was obtained having the same melting point and neutral equivalent values as dimethylterephthalate-Le., 140" C. and 97. The gas evolved by the decomposition of the nitrosoamide in a plastisol
-
724
-
0
Potential Hazards
I n common with other .V-methyl-.Vnitrosoamides, when A',n"-dimethyl-.V,N'-dinitrosoterephthalamide was decomposed in the presence of strong alkalies, diazomethane was evolved. As diazomethane is a highly toxic, explosive gas, extreme caution was used when this type of nitrosoamide was employed for expanding basic compositions. N,N' - Dimethyl - K,.V' - dinitrosoterephthalamide is a weak explosive
INDUSTRIAL AND ENGINEERING CHEMISTRY
-
-
Heat of Decomposition
The heat liberated by iY,A"-dimethylN,iZ"-dinitrosoterephthalamide upon decomposition is estimated by bond energy calculations to be 234 kcal. per mole. By comparison, the calculated heats of decomposition for two commercially established blowing agents, dinitrosopentamethylenetetramine and cu,a'-azobisisobutyronitrile (77), are 306 and 238 kcal. per mole, respectively. Applications
-
-
N,N' Dimethyl N N ' - dinitrosoterephthalamide diluted with white min-
P O L Y ( V I N Y L CHLORIDE) FOAMS era1 oil (distributed by E. I. du Pont de Nemours & Co. under the code name BL-353) was used in the preparation of cellular products from a variety of plastics and elastomers; its blowing performance was particularly suitable for expanding vinyl chloride homopolymer and copolymer resins both in high pressure molds and in open or vented molds at atmospheric pressure. Unicellular Expanded Poly(viny1 Chloride) Compositions
Large sections of unicellular expanded poly(viny1 chloride) of brilliant whiteness and with little or no odor were prepared by using the nitrosoamide as a blowing agent. Expanded products resisted discoloration by sunlight to approximately the same degree as unblown poly(viny1 chloride) compositions. T h e use of N,N‘-dimethyl-N,N’-dinitrosoterephthalamide for preparing expanded unicellular poly(viny1 chloride) by the general method developed in Germany during World War I1 (5) and widely used commercially in this country since the war is illustrated in the following examples. These formulations yielded soft unicellular expanded products.
Formulation A Parts by
Wt. Poly(viny1 chloride) 100 Epoxy polyester plasticizer 10 Tricresyl phosphate 90 Dyphos (dibasic lead phosphite stabilizer) 2 Ferro 1203 (barium-cadmium liquid stabilizer) 3.5 70/30 AT,”-dimethyl-N,N’-di-
nitrosoterephthalamide-white 25
mineral oil (i
Formulation B Poly(viny1 chloride) Chlorowax 40 (chlorinated paraffin, 40y0 C1) Butyl isodecyl phthalate Dibasic lead silicate (stabilizer) Kalite (calcium carbonate filler) 70/30 N,N‘-dimethyl-N,N’-dinitrosoterephthalamide-white mineral oil
100 20 80
TIME TO EVOLVE ONE HALF OF NITROGEN, MINUTES
Figure 2. Variation of half life of N,N’-dimethyl-N,N’-dinitrosoterephthalamide in a dioctylphthalate medium with varying temperature
mold was covered with a n aluminum or stainless steel plate about 3 / 3 2 inch thick and was then clamped between the platens of a hydraulic press capable of exerting a pressure of 3200 pounds per square inch on a 3I/~-inch ram. The mold was heated for 15 minutes with steam a t 120 pounds per square inch gage in the platens and then cooled by cold water running through the platens for 20 minutes. The press was opened, the partially expanded plastic removed from the mold, and the expansion completed by heating the plastic 1 hour in a circulating-air oven a t 100” C. The blown sample was expanded about 11 times the volume of the mold, had a slight pleasant odor, was free of discoloration, and had a very fine uniform cell structure. T h e density of the sample after cooling was 6 to 6.5 pounds per cubic foot. A photograph of unicellular expanded poly(viny1 chloride) based on Formulation A is shown in Figure 3. Hard, expanded unicellular poly(viny1 chloride) was made from the following composition :
10 10 25
Unicellular Poly(viny1 Chloride) Parts
The ingredients were mixed together, passed once through a tight three-roll paint mill, and mixed again with a turbine-type stirrer after passage through the paint mill. A stainlesssteel mold 11/4 inches deep, 3 inches in diameter, with side walls inch thick was filled with the plastisol so that the meniscus of the liquid was even with the top of the mold. The
Poly(viny1 chloride) [ dispersiongrade 100% poly(viny1 chloride) resin or 95/5 vinyl chloride-vinyl acetate copolymer resin] Di-2-ethylhexyl phthalate Dythal 1 (dibasic lead phthalate stabilizer) Tribase (tribasic lead sulfate stabilizer) 70/30 N,N’-dimethyl-N,N’-dinitrosoterephthalamide-white mineral oil
The ingredients were partially blended and the mixture was milled for 10 minutes on a water-cooled 2-roll rubber mill. The flaked composition was packed in the 3 X 11/4inch mold, so that the mold was slightly overfilled. The steps of heating under pressure, cooling, and expanding were followed in cellular product formation from this mixture. The product obtained was similar to those obtained from the composition containing 100 parts of plasticizer but was much harder. Expansion efficiency was greater if a temporary plasticizer was employed in the composition to be blown (70). The final unicellular product could be completely unplasticized. The following example illustrates the preparation of snowwhite, odorless, unplasticized unicellular expanded poly(viny1 chloride) with fine cell structure having a density of 2 to 2.5 pounds per cubic foot.
Parts Poly(viny1 chloride) (dispersion grade resin) Acetone Dyphos (dibasic lead phosphite stabilizer) 70/30 N,N’-dimethyl-N,N’-di-
nitrosoterephthalamide-white mineral oil
100
70 10
25
100 30 6 6
25
The poly(viny1 chloride), stabilizer, and 70/30 nitrosoamide-oil were thoroughly blended on a cold two-roll rubber mill. T h e acetone was blended with the cold-milled mixture, and this blend was passed once through the twoVOL. 49, NO. 4
*
APRIL 1957
725
Expansion of Plastisols at Atmospheric Pressure The favorable decomposition rate of N,iQ' dimethyl N,N' dinitrosoterephthalamide dispersed in poly(viny1 chloride) plasticizers, in conjunction with the formation of odorless and colorless decomposition products, made this nitrosoamide useful for foaming plastisols at atmospheric pressure. The following example illustrates the use of the blowing agent for making open-cell poiy(viny1 chloride) foam at atmospheric pressure in slab form: Formulation
-
-
-
Parts Poly(viny1 chloride) (Geon 121) Paraplex G-62 (epoxy polyester plasticizer) Paraplex G-50 (polyadipate plasticizer) Ohopex Q-IO (fatty phthalic acid esters) Advastab BC-105 (bariumcadmium stabilizer) Neutral calcium Petronate (petroleum sulfonate foaming aid) 70130 N,N'-dimethyl-N,N/-dinitrosoterephthalamide - white mineral oil
Figure 3. Soft unicellular expanded poly(viny1 chloride) prepared with dimethyl-N,N'-dinitrosoterephthalamide
roll mill. A stainless steel mold 3 inches in diameter and "4 inch deep was filled with the composition, and the mold was covered with a 3/32-in~haluminum plate, clamped in a hydraulic press, and heated for 10 minutes with steam at 100 pounds per square inch gage. The mold was cooled for 10 minutes, and the partially
N,N'-
expanded sample removed. Expansion was completed by heating the plastic 1 5 to 20 minutes in a circulating-air oven at 100" C. A photograph of hard, unplasticized, unicellular expanded poly(vinyl chloride) prepared in this manner is shown in Figure 4. Other unicellular specimens are shown in Figure 5 .
LOO
8
46
46
2 3.6 10
The ingredients were stirred together and passed once through a tight three-roll paint mill. The plastisol was stirred further by means of a turbine-type agitator and then poured to a depth of slightly over l / g inch (166 grams of composition) into an 8 X 8 X 2 inch aluminum pan. It was heated for about 25 minutes in a circulating-air oven set at 100" C., or until the composition changed from yellow to white. The resulting fragile foam was then fluxed by heating for 20 minutes in a circulatingair oven at 177' C. (350' F.). (An alternative method of fluxing, if the foaming was carried out in a mold of low electrical loss characteristics-Le., borosilicate glass-was by use of a dielectric heater, which reduced the fluxing period to a small fraction of the time required by convection heating.) The white opencell foam thus obtained was highly resilient and had a fine uniform cell structure and a density of approximately 7.5 pounds per cubic foot. Slabs of poly(viny1 chloride) foam prepared in a similar fashion are shown in Figure 6. Molded objects were produced also by the use of N,N'-dimethyl-N,N'-dinitrosoterephthalamide as a blowing agent. For example, an automobile poly(viny1 chloride) foam arm rest was made in the following manner : Plastisol Composition Part3 Poly(viny1 chloride) resin ( G e m 121)
Figure 4. Hard, unplasticized, unicellular expanded poly(viny1 chloride) prepared with N,N'-dimethyl-N,N'-dinitrosoterephthalamide
726
INDUSTRIAL AND ENGINEERING CHEMISTRY
Triithylene glycol dipelargonate Paraplex G-50 (polyadipate) Epoxy plasticizer (Admex 710) Di-2-ethylhexyl hexahydrophthalate Didecyl phthalate 70/30 N,N'-dimethyl-N,N'-dinitrosoterephthalamide - white mineral oil
100
20 20 20 20
20 4
POLY(VINYL CHLORIDE) F O A M S The ingredients were blended by stirring with a turbine-type agitator and given one pass through a tight three-roll mill. A cast aluminum mold was filled with enough plastisol to cause slight emersion of foam from the vent holes on top of the mold when the foaming was complete. The volume of plastisol loaded to the mold was about one fifth the volume of the mold cavity. The mold was heated for '/z hour in a hot-air oven a t 177' C. (350' F.) to effect foaming and fluxing of the foam. The complete foam thus produced was strong and highly resilient and had a fine uniform cell structure. Arm rests and other molded automotive components prepared in a similar manner by the use of the nitrosoamide blowing agent are shown in Figure 7.
t
Expansion of Vulcanizable Elastomers
-
-
-
N,N' Dimethyl N,N' dinitrosoterephthalamide was shown to be a nonstaining, nondiscoloring blowing agent for elastomers such as natural rubber, GR-S, neoprene, acrylonitrile rubber, and chlorosulfonated polyethylene. A careful choice of accelerators was necessary, as certain intermediate decomposition products of the nitrosoamide react with many organic compounds widely used as accelerators--e.g., thiols and thiazoles-deactivating the accelerators and producing unpleasant odors. The nitrosoamide was apparently soluble in most elastomer polymers at elevated temperatures, as expanded products of very fine uniform cell structure usually were obtained. A light-colored, fine-celled, naturalrubber, open-cell sponge which was nearly odorless was made by the conventional procedure from the following composition :
Figure 5. Unicellular expanded poly(viny1 chloride) fish net floats, soft sheet stock and low-density unplasticized specimens prepared with N,N'-dimethyl-N,N'-dinitrosoterephthalamide
porous canvas heavily powdered with talc to prevent adhesion of the rubber to canvas. The mold was sandwiched between aluminum sheets and heated between the platens of a hydraulic press with steam a t 60 pounds per square inch for 25 minutes. The sponge obtained was
expanded to about 2.5 times the volume of the stock charged. The following compositions are illustrative of the type of formulations which were used to prepare unicellular expanded products based on a variety of elastomer polymers. ,
Sponge Composition Parts Pale crepe 85-P Zinc oxide Whiting Titanium dioxide Stearic acid Process oil Sulfur Zinc dimethyl dithiocarbamate Tetramethylthiuram monosulfide 70/30
100 5 30
30 10 10 3
0.22 0.45
N,N'-dimethyl-N,N'-dinitra-
soterephthalamide-mineral oil
1.5
The pale crepe was banded on a tworoll rubber mill, and the other ingredients were incorporated by continued milling. Forty grams of the milled composition was cut to fit a circular picture-frame mold z7/8 X inches deep. The top and bottom of the mold were covered with
Figure 6. Open-cell poly(viny1chloride) foam prepared at atmospheric pressure with N,N'-dimethyl-N,N'-dinitrosoterephthalamide VOL. 49, NO. 4
0
APRIL 1957
727
L m a E ARM RESTS COURTESY DRYDEN RUBBER DIVISION. INO.;
V A L V E COVERS COURTESY U
SHELLER MANUFACTURINO
CORP.,
SMALL A R M REST COURTESY FOAM K I N G ,
S . RUBBER CO.
Figure 7. Molded automotive components prepared a t atmospheric pressure with N,N'-dimethyl-N,N '-dinitrosoterephthalamide
Trial
Natural rubber (pale crepe 85-P) GR-S-50 (1001) Neoprene Type GN GR-I (butyl rubber) Hycar OR-25 (acrylonitrile rubber) Hypalon chlorosulfonated polyethylene 70/30 nitrosoamide-oil Zinc oxide Magnesium oxide Petrolatum Stearic acid Titanium dioxide Whiting Dixie clay Antioxidant 2246 (phenolic type) Ethex (zinc dimethyl dithiocarbamate) Tetrone A (dipentamethylene thiuram tetrasulfide) Diphenylguanidine (DPG) Sulfur Process oil Diisodecyl adipate Di-2-ethylhexyl phthalate Piccolastic A-5 (styrenesubstituted styrene resin) Wood rosin Precure time, min. Platen steam pressure, lb./ sq. inch gage Expansion, vol. 70
728
A 100
... ... ...
... ... 7 5
... 3 3 20
...
Parts by Weight c D
B
... 100
... ... ... ... 7 5
...
... ... 100
...
... ... 7 5 4 3
7 5
... *..
20
20
20
30
30 25
...
...
1
1
2
1
...
...
... ... ... ... 20 ... ... ... ...
6
7
60 425
60 4 90
... ... ... ...
... ...
...
60
3.5 20
100
3 3
60
.*. ...
... ... ...
2
...
... 20
... ... I . .
INDUSTRIAL AND ENGINEERING CHEMISTRY
5
E
... ...
... ...
100
... 7 5
...
... 5 ... 80 ... ... 2
6
... ... 10
5
...
I
.
.
... 2 ...
... 75
...
5
... ...
6
8
5
60 540
60 540
60 3 70
_F
... ... ... ... ... 100 3.5
...
20
... ... ... 80 ... ... 1
0.5
... ... ...
... ... 2.5 4 60 330
The general procedure employed was conventional (2-4). The components of the composition were blended on a tworoll rubber mill a t a temperature below 50" C. and sheeted from the mill at a thickness of about 3 / 8 inch. The sheet was cut to fit a stainless steel mold 1/4 inch deep and 3 inches in diameter with a bottom inch thick and side uall l / ~ inch thick. The mold was covered lvith a I/le-inch thick stainless steel plate and clamped in a platen press with the application of 3200 pounds per square inch hydraulic pressure. The mold was heated sufficiently long in the press with 60 pounds per square inch gage platen steam pressure to decompose the blowing agent and precure the composition to a resilient fully expanded composition when the press was opened hot a t the temperature of cure. The unicellular expanded elastomer was cured further in the press in a mold l,'2 inch deep and 6 inches in diameter or in an oven for the same length of time and a t the same temperature as the precure to effect dimensional stabilization of the expanded specimen. The expanded products varied in color from near-white to cream. The odors varied from slight (but not unpleasant) for natural rubber to pungent and somewhat unpleasant for GR-I synthetic rubber. All specimens were characterized by very fine uniform cell structure. .t',.V' Dimethyl N,N' dinitrosoterephthalamide was also suitable for the expansion of elastomer compositions of the newer types such as the polyurethane and silicone rubbers, in which the usual types of sulfur-containing accelerators are normally not employed. A fine-celled, cream-colored, odorless specimen of unicellular urethane rubber expanded by means of iV,;2"-dimethyl.$7,,t"-dinitrosoterephthalamide is shown in Figure 8. -V,N' Dimethyl 'V,N' dinitrosoterephthalamide was used for expanding silicone rubber compounds designed specifically for the production of expanded unicellular products ( 6 ) . The blowing agent was incorporated into the silicone rubber during the fresheningforming step. After the blowing agent was incorporated, the silicone compounds were blown and cured to optimum expansion in 10 to 20 minutes a t temperatures as low as 300" F. The compounds could also be extruded for free-expansion or mold-expansion processes and expanded to fill mold volumes with curing in one operation. As the 70/30 A-,iV'-dimethyl -iV,iV'- dinitrosoterephthalamideoil was varied from 2 to 670 by weight, free expansion varied from 350 to 700% and mold expansion from 280 to 45070. After extrusion, higher expansion percentages were obtained. This information on the use of the nitrosoamide blowing agent in silicone rubber was developed at General Electric laboratories. Silicone rubber sponge blown with Ar,AV'-di-
-
~
-
~
-
-
POLYtVlNYL CHLORIDE1 FOAMS
Figure 8. Unicellular expanded urethane rubber prepared with N,N’-dimethylN,N’-dinitrosoterephthalamide
Formulation Parts by
Wt. 50
Epon 828 (liquid epoxy resin) Versamide 115 (liquid polyamide resin) 50 Bentone 34 (dimethyl dihexadecyl ammonium bentonite) 10 70/30 iV,N’-dimethyl-N,A’’-dinitrosoterephthalamide-oil 2.5
The epoxy resin, polyamide, and Bentone 34 were blended on a three-roll paint mill. The basic polyamide was incorporated last by means of a laboratory turbine-type agitator, and the liquid composition poured into an aluminum foil-lined galvanized steel mold G inches square and 2 inches deep. The composition foamed completely within about 30 minutes. The foam was tack-free after 1 to 2 hours and was hard and strong The foam had after 18 to 24 hours. a fine cell structure and a density of about 12.5 pounds per cubic foot. The use of 5 parts of blowing agent instead of 2.5 parts per hundred parts of resin led to foaming in about 10 minutes and a foam of 7 pounds per cubic foot. The preparation of a foam from a basic system of this type was accompanied by the release of diazomethane. N,N’ Dimethyl N,N’ dinitrosoterephthalamide was explored briefly for preparation of expanded polystyrene. Powdered polystyrene obtained by evaporating a water emulsion of poIystyrene (Koppers Emulsion M) to dryness was pulverized and passed through a 100mesh sieve. One hundred parts by weight of the powder and 25 parts by weight of di-2-ethylhexyl phthalate were blended and then heated ,in a pressure mold a t 100’ C. The composition was transferred to a two-roll mill heated by 65’ to 70’ C. water passing through the rolls and banded on the mill. Twenty parts by weight of 70/30 nitrosoamide-oil was incorporated into the composition, which was then sheeted from the mill. A stainless steel open-faced mold 3 inches in inside diameter, l / 4 inch deeD. with I/sinch side wall thickness was Xlled with the composition, covered with a I/lG-inch
-
-
Figure 9. Extruded and molded silicone rubber expanded with N,N’-dimethylN,N’-dinitrosoterephthalamide
-
Figure 1 0. Foamed-in-place epoxy resin-polyamide cellular product prepared with N,N’-dimethyl-N,N’-dinitrosoterephthalamide VOL. 49, NO. 4
APRIL 1957
729
stainless steel plate, and clamped in a platen press by the application of 3200 pounds per square inch hydraulic pressure. The mold was heated for 4 minutes a t 177’ C. (120 pounds per square inch gage platen steam pressure), and was cooled to room temperature before the press was opened. The polystyrene specimen was heated briefly in an oven a t 70’ C. to complete expansion. The product expanded to 4.4 times the mold size, was white, had a fine uniform cell structure, and possessed a faint styrenelike odor. The specimen was rigid and somewhat brittle.
life of thermally unstable compounds; J. P. Swed, Du Pont Eastern Laboratory, for work on the impact and friction sensitivity of blowing agent candidates; L. S. Bake and Andrew Mitchell, Du Pont Rubber Laboratory, for advice on rubber compounding; the Du Pont Haskell Laboratory for toxicity studies; and W. F, Filbert, Burnside Laboratory, for advice on all phases of the developmental program. Literature Cited
(1) Briggs, A. S., Scharff, G. E. (to Imperial Chemical Industries), U. S. Patent 2,491,709 (Dec. 20, 1949). ( 2 ) Cooper, L.: Bascom, R., Roberts, D. (to Rubatex Products), Ibid., 2,299,593(Oct. 20, 1942). 13’1 L.. Roberts..D. (to Rubatex . , CooDer. Prodhctsj, Zbid., ‘2,283,316 (May 19,1942). ( 4 ) Cuthbertson, G. R. (to U. S. Rubber C o . ) , Zbid., 2,291,213 (July 28, 1942).
Acknowledgment
The author wishes to thank H. SV. Bradley, Du Pont Jackson Laboratory, and H. D. SVilliams and R. E. Barnhart, Du Pont Burnside Laboratory, for their assistance in the synthesis of new blowing agent candidates; PaulVanFossen, Burnside Laboratory, for studies on the shelf
( 5 ) Debell, J. M.,Goggin, W. C., Gloor, W. E., “German Plastics Practice,” p. 458, Debell & Richardson, Springfield, Mass., 1946. ( 6 ) General Electric Go., “Silicone Rubber Sponge Compounds 81597 and 81601,” Preliminary Product Data Sheet, March 15,1956. (7) McKay, A. F., Park, W. R. R., Viron, S. J., J. Am. Chem. Suc. 72, 3659-61 (1950). (8) hfaver, F.,Ber. 21, 2888 (1888). ( 9 ) Muller, E., Peterson, S., Loblein, F. (to Fabriken Bayer A. G.), U. S. Patent 2,683,696(July 13, 1954). (10) Sprague, G. R., Scantlebury, F. M. (to Sponge Rubber Products Co.), Brit. Patent 714,606 (Sept. 1,1954). (11) Thiele, J., Heuser, R., Ann. 290, 30 (1896); Belgian Patent 449,032 (to I. G.Farbenindustrie) (Feb. 3, 1943). ~.. - ,(12) Van Amerongen, G. J., J . Ap@. Phys. 17, 972-89 (1946).
RECEIVED for review November 5, 1955 ACCEPTED October 4, 1956 Division of Paint, Plastics, and Printing Ink Chemistry, 128th Meeting, ACS, Minneapolis, Minn., September 1955.
MACK F. FULLER Burnside Laboratory, Explosives Department, E. I. du Pont de Nemours
& Co., Inc., Penns Grove, N. J.
N,N‘-Dimethyl- ,PI’-dinitros lowing Agent Preparation
o f oIy(vinyI
Chloride)
~ o a mat Atmospheric Pressure
A method for producing slab stock foam, batchwise or continuously, several inches thick, c o r d foam, foam formed on and bonded to substrata such as vinyl sheet and fabrics, and miscellaneous molded objects
P a Y ( \ m x CHLORIDE) compositions have been expanded by cherrical blowing agents for more than a decade. However, most early developments involved the preparation of a unicellular expanded product in closed, high-pressure molds. Expanded plasticized poly(viny1 chloride) structures usually having an open or continuous cell structure have since been prepared a t ataospheric pressure in open or vented molds. The more recently developed product has many of the physical characteristics of
730
foam and sponge rubber and is useful where the pressure-blown product is unsuited or too costly. Two general methods utilizing chemical blowing agents may be employed to expand poly(viny1 chloride) compositions at atmospheric pressure. One method utilizes an agent such as unactivated dinitrosopentamethylenetetramine or azodicarbonamide (7, 6), which does not decompose appreciably until fusion of the vin)-l composition is well advanced. Under these conditions, de-
INDUSTRIAL AND ENGINEERING CHEMISTRY
composition of the blowing agent causes foaming of the molten fluxed vinyl composition. This process is useful where a poly(viny1 chloride) composition is to be gelled into a substrate and is adequate for a thin layer of relatively high-density foam-e.g., foamlined vinyl overshoes, but is not generally satisfactory for producing thicker, more highly blown foam. The second method is more satisfactory for preparing products varying widely in density, thickness, and other
