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Rubber compounds play an instrumental role in the built environment, as they are flexible and durable materials that construct many products, structures, and vehicles. The physical properties of these compounds are controlled by specific formulations developed in the rubber compounding process, which aims to optimize the performance of each compound for its intended application. |
In rubber compounding, physical properties such as Young’s modulus, tensile strength, tear resistance, viscosity, hardness, and more are influenced using additives called processing aids. Oil-based processing aids, known as processing oils, are commonly used to improve mold fill performance by lubricating rubber and elastomer compounds and reducing their viscosity. This, in turn, creates better flowability, facilitates better dispersion of ingredients, and makes the compound formulation easier to mix and cure. While processing oils improve mold fill performance, they can detract from several physical properties mentioned above.
EPOLENE® Rubber Processing Aid Additives
Westlake developed processing aids designed to enhance mold fill performance and processability while maintaining or improving the physical properties of rubbers and elastomers. These processing aids, known as
EPOLENE®, are low–molecular weight polyethylene polymers used to optimize both natural rubber and synthetic rubber compounds. These include nitrile, butyl, SBR, EPDM, and neoprene-based compounds. In general, EPOLENE® polymers are used to imbue compounds with the following suite of performance benefits:
- Improved mixing of compound ingredients
- Decreased shrinkage
- Reduced tackiness
- Enhanced mold fill
- Increased scorch time
- Optimized physical properties
EPOLENE® Processing Aids versus Oil Processing Aids
To illustrate the performance benefits above, a case study compared the use of the
EPOLENE® N-14 polymer versus a processing oil in an EPDM compound dispersion. First, the effect of processing aid on compound mold fill performance was evaluated, as shown below.
 |
 |
 |
| Control containing 25 phr oil |
Addition of +5 phr EPOLENE® |
Addition of +10 phr oil |
“phr” stands for parts per hundred rubber
The control formulation above containing 25 phr processing oil did not exhibit good mold fill compared to the other samples; it failed to fill sections of the rubber part. In comparison, the sample that contained an additional 5 phr of EPOLENE® N-14 and the sample containing an addition of 10 phr of processing oil exhibited good mold fill properties that were visually identical. Although the parts containing +5 phr EPOLENE® N-14 and +10 phr oil had good mold fill properties, their physical properties were not the same. Several physical properties were evaluated for comparison, with the results shown below.
*Ts2 values exceeded 120% of the control, where +10 phr oil provided 143% improvement and +5 phr EPOLENE® N-14 provided 125% improvement
Using the control formulation as a baseline, the data indicate that many physical properties were maintained or enhanced by the formulation containing +5 phr of EPOLENE® N-14. In comparison, the formulation containing +10 phr oil reduced physical properties such as tensile strength, Young’s modulus, durometer hardness, and tear resistance, which are critical for rubber parts that require high durability and flexibility.
EPOLENE® Processing Aid Grades
| EPOLENE® Grade |
Form |
Drop Point (°C) |
Density at 25°C (g/cm3) |
Brookfield Thermosel Viscosity at 125°C (cPs) |
| N-11 |
Pellet |
111 |
0.921 |
350 |
| N-14 |
Pellet |
108 |
0.920 |
150 |
| N-34 |
Pellet |
104 |
0.910 |
450 |
| N-11P |
Powder |
111 |
0.921 |
350 |
| N-14P |
Powder |
108 |
0.920 |
150 |
| N-34P |
Powder |
104 |
0.910 |
450 |
Summary
Compounders of natural and synthetic rubbers often use additives like processing oils to improve mold fill performance and enhance dispersion workability. However, these oil-based processing aids degrade physical properties, such as Young’s modulus, tensile strength, durometer hardness, and tear resistance, which are critical for rubber compound durability and performance. EPOLENE® polymer processing aids are a better option to improve mold fill performance and workability while preserving or improving many physical properties. Click below to discuss your rubber compounding application and request a sample of an EPOLENE® processing aid today.
