Learn how chemical attack degrades rubber products – and how to stop it before it starts.
Rubber products are used to seal and insulate heavy equipment, military land systems, mass transit vehicles, and electronic enclosures – just to name a few applications. When rubber seals or gaskets fail, the resulting fluid leaks, pressure losses, and environmental contamination can put assets at risk and disrupt operations.
Seals and gaskets fail for a variety of reasons, but over-compression and mechanical wear are often to blame. But don’t overlook chemical attack. It’s easy to confuse this failure mode with other forms of material degradation, and there’s a complex relationship between temperature and chemical exposure.
This article from Elasto Proxy describes chemical attack and how incompatible chemicals interact with the molecular structure of rubber. It also explains how to identify the signs of chemical degradation, and what you need to know about the interaction of heat and chemicals. You’ll also find some tips you can use to prevent problems before they occur.
Keep reading to learn more and contact Elasto Proxy for sealing and insulation solutions.
What is Chemical Attack?
In industrial sealing, chemical attack refers to the irreversible degradation of a rubber material caused by exposure to incompatible fluids, gases, cleaning agents, or environmental substances. It does not refer to weapons or warfare, but the effects of chemical attack on rubber products can be catastrophic.
When rubber experiences a true chemical attack, its molecular structure changes. Unlike metal parts that experience surface corrosion or pitting, rubber products absorb, react with, and degrade internally when they’re exposed to incompatible chemicals.
Physical Interaction or Chemical Attack?
At the molecular level, rubber materials consist of long, flexible polymer chains that are linked together (cross-linked) during vulcanization – a chemical process that hardens the raw, sticky rubber into a durable, elastic material.
The density of these cross-links, among other factors, determines the chemical resistance of a rubber material. The polymer chains also determine whether physical interaction or chemical attack occurs when a chemical is encountered.
- Physical Interaction: If the rubber product is compatible with the chemical, the chemical penetrates the spaces between the polymer chains. This doesn’t necessarily break its bonds; however, it can cause swelling and a loss of tensile strength.
- Chemical Attack: Incompatible chemicals break the bonds within either the main polymer backbone or the vulcanized crosslinks that help hold the structure together. If this happens, rubber can lose its elasticity and other material properties.
What Does Chemical Attack Look Like?
There are visual and mechanical indicators of chemical attack in rubber products.
Volume Expansion and Distortion
A seal or gasket that’s exposed to an incompatible fuel, hydraulic fluid, or solvent absorbs the medium and expands significantly. This isn’t physical interaction, however. In bulb trim or edge trim, this swelling causes the rubber product to buckle, ripple, or push away from its mounting flange.
Hardening and Surface Cracking
Exposure to strong acids, bases, or oxidizing agents like ozone breaks rubber’s cross-links. As a result, the rubber increases in durometer (hardness) and develops fine, deep cracks along stress points, especially on the radiused corners of gaskets.
Softening, Stickiness, and Disintegration
Some organic solvents and aggressive chemical compounds reduce rubber to a sticky, gummy substance. The causes the seal or gasket to loses its structural integrity so that even at low pressure, the rubber part can be sheared off or wiped away.
Blistering and Delamination
Rubber can absorb volatile liquids under pressure and then become rapidly heated or depressurized When this happens, the trapped chemical can vaporize inside the matrix of cross-links. This results in internal voids, surface blisters, and physical delamination.
When Thermal Aging and Chemical Attack Occur Together
In industrial sealing applications, chemical exposure rarely happens in isolation. Machinery, engine bays, and processing equipment all expose rubber seals and gaskets to chemicals and high operating temperatures at the same time.
Thermal aging in rubber is the irreversible breakdown of a material’s physical and chemical properties caused by long-term exposure to high heat. It’s different than chemical attack, but the two failure modes work together.
The results include:
- Increased Absorption Rates: Heat expands the free volume between polymer chains, allowing chemicals to penetrate deeper and faster into the rubber material.
- Thermal Oxidation Acceleration: Atmospheric oxygen or dissolved oxygen in fluids attacks polymer chains and leads to rapid embrittlement.
- Leaching of Plasticizers and Additives: High heat and chemicals remove internal plasticizers, flame retardants, and processing aids. When these protective additives leach out, the rubber shrinks, hardens, and loses compression.
That’s not all. For every 10°C (18°F) increase in operating temperature, the rate of chemical reaction doubles. As a result, a rubber that’s rated for chemical resistance at 23°C (73°F) could suffer severe degradation at 80°C (176°F) from the same chemical.
Preventing Chemical Attack: Design Tips for Engineers
Selecting the right rubber is the first step in preventing chemical attack in seals and gaskets. Elasto Proxy can help you with this and uses a framework called MTAP to guide material selection. MTAP stands for Media (M), Temperature (T), Application (A), and Pressure (P).
When designing seals and gaskets, follow these guidelines as well.
Map Full Chemical Exposure
Do not evaluate chemical compatibility based on exposure to a single substance, such engine oil in an engine bay. Consider washdown agents, industrial detergents, airborne vapors, and lubricants applied during assembly.
Consider Continuous Immersion vs. Intermittent Splash
A gasket that’s exposed to intermittent fluid splashes may perform reliably if it’s made from a commodity-grade rubber. However, continuous immersion may require a spec-grade material. To avoid over-specifying a material or under-protecting the system, understand the exposure.
Account for Physical Swell in Profile Geometry
If mild volume swell is expected, account for it in your seal design. In other words, make sure that the gasket channel or enclosure lip has enough room to expand. Otherwise, swollen rubber could result in problems like fastener displacement.
Review Thermal-Chemical Limits
When reviewing chemical compatibility tables, look at actual maximum operating temperatures rather than ambient conditions. If your application approaches thermal-chemical limits, you may need a high-performance material.
Partner with Elasto Proxy for Engineered Sealing Solutions
Preventing chemical failure requires evaluating the complete application environment, including chemical concentration, operating temperature, and mechanical load. At Elasto Proxy, we help engineers navigate compound selection, but we don’t stop there.
As part of the value-added gasket fabrication that we provide, Elasto Proxy can also recommend profiles and joining methods. With our water jet cutting capabilities, we can also supply you with prototypes that you can test in your application.
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