Elastomeric compositions with improved chemical, water and heat resistance

An elastomeric composition of the type used as a jacketing material for electrical wires and cables is shown having improved chemical, water and heat resistance. An ethylene/acrylic elastomer comprising a terpolymer of ethylene, methyl acrylate, and a cure site monomer is used as the base polymer and has blended therewith a polybutadiene. The polybutadiene has greater than 50% 1,2 polymerized units and has a molecular weight between about 1,500 and 25,000 grams/mole.

BACKGROUND OF THE INVENTION 
The present invention relates generally to elastomeric compositions having 
improved chemical, water and heat resistance and, specifically, to an 
elastomeric jacketing composition for use at elevated temperatures and 
under extreme pressures which can withstand exposure to oil, water and 
chemical environments such as are found in oil and gas wells. 
Wire and cable constructions of the type employed in oil and gas wells, 
such as the cables running to submerged pumps, must be able to withstand 
exposures to pressures of 2000 psi or higher and temperatures in excess of 
250.degree. F. in contact with crude oil, brines, and hot gases. Various 
synthetic olefin polymers have been employed in the manufacture of 
electric wire and cable as jacketing or insulating materials including 
ethylene-propylene copolymer rubbers and ethylene-propylene-diene monomer 
terpolymers. These materials ae useful in many applications because of 
their ease of compounding, good extrudability and excellent electrical 
characteristics. However, because these materials flow or distort at 
elevated temperatures and under extreme pressures and are sensitive to 
swelling and dissolving in various hydrocarbon solvents and oils, their 
use has been limited to moderate environmental conditions. Where these 
materials are used in the extreme environmental conditions of oil and gas 
wells, the materials must generally be chemically modified or protected by 
added layers of secondary barrier materials, with a resulting increase in 
manufacturing difficulty and cost. 
The ethylene/acrylic elastomers have also been used in the manufacture of 
electrical wires and cables in the oil and gas industries. The combination 
of the two major monomers, ethylene and methyl acrylate, in 
ethylene/acrylic elastomers provides a balance of oil resistance and good 
heat resistance. Unfortunately, ethylene/acrylic elastomers alone are 
sensitive to water, aromatic hydrocarbons, and sulfide contaminants such 
as are often encountered in oil and gas wells. 
There exists a need, therefore, for an elastomeric jacketing composition 
which possesses the heat and oil resistance of an ethylene/acrylic 
elastomer but which has improved resistance to water, aromatic 
hydrocarbons, and sulfide contaminants. 
There exists a need for such a jacketing composition which can alleviate 
the need for secondary barrier materials when employed in oil and gas well 
wire and cable applications and which can be easily compounded and 
manufactured. 
SUMMARY OF THE INVENTION 
The present elastomeric compositions having improved chemical, water, and 
heat resistance comprise an ethylene/acrylic elastomer having blended 
therewith a polybutadiene having greater than 50% 1, 2 polymerized units 
and having a molecular weight between about 1,500 and 25,000 grams/mole. 
Preferably, the ethylene/acrylic elastomer is a terpolymer of ethylene, 
methyl acrylate, and a cure site monomer. The preferred ethylene/acrylic 
elastomer is a normally solid composition which is blended with a normally 
liquid polybutadiene, the polybutadiene having 65-95%, 1,2 polymerized 
units and having a molecular weight between about 1,500 and 25,000 
grams/mole. The preferred elastomeric composition of the invention has 
about 70 to 90% by weight of elastomeric composition of an 
ethylene/acrylic elastomer and 30 to 10 percent by weight of elastomeric 
composition of normally liquid polybutadiene blended with the 
ethylene/acrylic elastomer, the polybutadiene having at least 80% 1,2 
polymerized units and having a molecular weight between about 1,500 and 
25,000 grams/mole. 
Additional objects, features and advantages will be apparent in the written 
description which follows.

DETAILED DESCRIPTION OF THE INVENTION 
The base polymer employed in preparing the elastomeric compositions of the 
present invention are ethylene/acrylic elastomers. The preferred base 
polymer is an ethylene/acrylic elastomer which is a copolymer of ethylene 
and methyl acrylate plus a third monomer containing carboxylic curing 
sites. The preferred ethylene/acrylic elastomer base polymers have the 
following structural formula: 
##STR1## 
The methods of preparing ethylene/acrylic elastomers are known and a 
suitable ethylene/acrylic elastomer which can be used in practicing the 
present invention is commercially available under the tradename "VAMAC" 
from the DuPont company. The published product description for VAMAC gives 
the following properties: 
______________________________________ 
Polymer Content (Wt %) 81 
Specific Gravity 1.12 .+-. 0.03 
Mooney Viscosity at 100.degree. C. 
29 .+-. 5 
Physical form, Bale Stud Pack 
25 Kg 
Color Black 
Odor Mild Acrylic 
Storage Stability Excellent 
______________________________________ 
The liquid 1, 2 polybutadiene which is used in practicing the present 
invention is characterized as a low molecular weight polymer of butadiene 
wherein greater than 50% of the monomer units are present in the 1,2 
configuration. As is well known, the 1, 3 butadiene monomer may be 
polymerized by a variety of techniques to give polymers having a high 
proportion of units having 1, 4 attachment in the cis and trans 
configuration. Certain commercial techniques based upon anionic 
polymerization technology are also well known whereby the 1,2 butadiene 
monomer may be polymerized to give polymers having a high proportion 1,2 
attachment, viz: 
##STR2## 
Such polymers can be produced in a variety of molecular weight ranges and 
with varying proportions of 1,2 to 1,4 units. For the purposes of this 
invention, only those materials having molecular weights low enough to be 
liquid or semi-solid, when at room temperature and solvent free, and 
containing not less than 50 mole percent units having 1,2 attachment, the 
remaining fraction being units with 1,4 attachment are useful. While the 
molecular weight of these materials may vary somewhat depending on the 
proportion of 1,2 and 1,4 attachments and remain liquid, it has been found 
that the most desirable materials have molecular weights in the range of 
about 1,500 to 25,000 grams/mole. Although called liquid resins, many of 
these materials are extremely viscous having viscosities in excess of 
10,000 cps at room temperature, becoming truly pourable only when heated. 
The level of liquid polybutadiene employed in the blend of the elastomeric 
compositions of the invention is preferably between about 10 to 30 parts 
per hundred parts ethylene/acrylic elastomer. The preferred range of 
liquid polybutadiene used is between about 15 and 25 parts per hundred 
parts ethylene/acrylic elastomer with the most preferred amount being 
about 20 parts per hundred polybutadiene. While lesser amounts of liquid 
polybutadiene may be employed where exposure to extreme conditions is not 
contemplated, blends containing as little as 10 parts polybutadiene per 
hundred parts ethylene/acrylic elastomer are considered to be too 
sensitive to hot oil, water and other contaminants found in the oil and 
gas well environment. The flexibility of the resulting blend is greatly 
affected by increased levels of polybutadiene and it has been found that 
blends containing greater than about 25 to 30 parts liquid polybutadiene 
per hundred parts ethylene/acrylic elastomer are too rigid, hard, and 
inflexible when cured to be used as wire and cable insulating materials. 
A suitable curing agent or agents must be provided to effect the necessary 
curing and cross-linking of the compounded material. The higher 
temperature peroxides such as dicumyl peroxide and .alpha., .alpha.', bis 
(t-butylperoxy)-di isopropyl benzene are well suited for the practice of 
the present invention in accomplishing a rapid and complete cure. The 
amount of peroxide curing agent employed can vary between about 7 to 14 
parts per hundred parts ethylene/acrylic elastomer with the most preferred 
amount being about 10 parts per hundred peroxide based on the weight of 
the total blend. Very low levels of curing agents are undesirable since 
the degree of cross-linking affects solvent and environmental resistance 
of the cured compound. Higher levels of cross-links result in higher cure 
and consequently a more rigid inflexible material which is undesirable for 
use as wire and cable insulation. 
The blending of the ethylene/acrylic elastomer and the liquid polybutadiene 
resin can be accomplished by any of the common rubber compounding methods 
including roll milling and the like. Additional materials including the 
curing agents, lubricants, fillers, antioxidants and carbon blacks 
commonly employed in the electrical insulating resins may also be added, 
either at this point or during a later compounding step. A phenolic filler 
material supplied commercially under the tradename "DUREZ 12687" by the 
Durez Division, Hooker Chemical Corporation has been found to be 
especially useful. DUREZ 12687 is a phenolic resin containing 8% 
hexamethylenetetramine which is commonly used in rubber compounding and 
which cures rapidly to a hard, inflexible, heat resisting product which is 
insoluble in oils, acids, alkalies, and organic solvents. The range of 
phenolic filler used in the present blend is between about 20 to 90 parts 
phenolic filler per hundred parts ethylene/acrylic elastomer. The 
preferred range of phenolic filler is between about 30 to 60 parts with 
the most preferred amount of phenolic filler being about 50 parts phenolic 
filler per hundred parts of ethylene/acrylic elastomer. 
EXAMPLES 
The invention will be more fully understood by reference to the following 
examples, wherein all ingredients are given in parts per hundred parts 
ethylene/acrylic elastomer. Note that 124 parts of VAMAC are used since 
VAMAC contains approximately 81% active polymer. That is, 124 (0.81) 
equals approximately 100 parts ethylene/acrylic elastomer as the base 
reference. There are then, for instance, 20 parts of 1,2 liquid 
polybutadiene used per hundred parts of ethylene/acrylic elastomer. 
In order to demonstrate the improved properties of the elastomeric 
jacketing compositions of the invention, a sample blend composition was 
formulated by compounding on a two roll mill, cured in slab form having 
about a 0.070 inch thickness by heating at 400.degree. F. for 10 minutes 
in a press, cut into 11/2 inch by 3/4 inch strips and tested. The 
environmental test consisted of placing the sample to be treated into a 
pressure vessel containing a selected test fluid, pressurizing the vessel 
with nitrogen and heating while maintaining the pressure at 4000 psi. 
After 7 days, at the testing temperature, the vessel was cooled to room 
temperature, the pressure was released, and the sample removed. The final 
weight and dimensions of each sample was measured and the % change 
recorded. 
The sample formulation of the improved composition of the invention was: 
______________________________________ 
Parts 
______________________________________ 
Ethylene/acrylic elastomer (VAMAC 124').sup.1 
124 
1,2 Liquid Polybutadiene (RICON 154).sup.2 
20 
Carbon Black Reinforcing Filler (N337).sup.3 
30 
Dicumyl Peroxide Curing Agent (Di Cup R).sup.4 
11 
Processing Lubricant (VAN FRE AP-2).sup.5 
2 
Diak #1.sup.6 Curing Agent (hexamethylene 
1 
diamine carbamate) 
DPG.sup.7 (diphenyl-guanidine accelerator) 
4 
Lubricant (Armeen 18D).sup.8 
0.5 
Stearic Acid Processing Aid.sup.9 
1 
DUREZ 12681.sup. Phenolic Filler 
50 
______________________________________ 
.sup.1 DuPont 
.sup.2 Colorado Chemical Specialities, Inc. 
.sup.3 Continental Carbon 
.sup.4 Hercules, Process Chemicals Division 
.sup.5 RT Vanderbilt 
.sup.6 DuPont 
.sup.7 Monsanto Chemical Co. 
.sup.8 Armak, Industrial Chemicals Division 
.sup.9 Darling 
.sup.10 Hooker Chemical Company 
TABLE I 
______________________________________ 
Duro- 
Tensile meter % 
Strength % (Shore 
Volume 
VAMAC (275.degree. F.) 
(psi) Elongation 
"A") Charge 
______________________________________ 
original 2280 360 78 
water 1 month 1710 200 77 9.5 
3 months 1090 10 93 6.4 
Freezene 
1 month 2370 90 82 6.8 
(Mineral 
3 months 2180 60 89 8.0 
Oil) 
Sulfide 
7 days 1870 240 69 94.4 
Xylene 4 hours 222 
8 hours 239 
24 hours 245 
______________________________________ 
TABLE II 
______________________________________ 
Tensile % % 
SAMPLE Strength Elonga- Duro- Volume 
Composition (psi) tion meter Charge 
______________________________________ 
original 2490 130 88 
water 7 days 4450 20 94 4.8 
(10% at 450.degree. F. 
brine) 
Freezene 7 days 1960 80 78 15.6 
(Mineral at 350.degree. F. 
Oil) 
Sulfide 7 days 2340 80 85 17.7 
at 275.degree. F. 
Xylene 24 hours 121.9 
at 275.degree. F. 
______________________________________ 
As seen from the test results the Sample Composition of the invention 
containing a blend of ethylene/acrylic elastomer and 1,2 polybutadiene 
showed a 20% elongation after 7 days in water at 450.degree. F. indicating 
that the composition would remain flexible when exposed to water. The 
example composition also displayed greatly reduced swelling in water (9.5% 
to -4.8%) and in the presence of sulfide contamination (94.4% to 17.7%). 
The tendency to swell in the presence of xylenes was reduced from 245% to 
121.9%. 
The foregoing examples have been provided by way of illustration, thereby 
demonstrating jacketing materials resistant to destruction by exposure to 
oil, water, and sulfides under high pressure and at elevated temperatures. 
The improved elastomeric jacketing compositions of the invention are 
suitable for use as jacketing and cushioning materials in wires and cables 
used in oil and gas wells. The improved material is also useful as an 
O-ring material and in elastomeric bags and seals of the type used in 
downhole pumps and apparatus for use in oil and gas wells. 
While the invention has been shown in only one of its forms, it should be 
understood that it is not thus limited but is susceptible to various 
changes and modifications without departing from the spirit thereof.