Chemical resistance is a key factor to consider when choosing an epoxy system. Different epoxies are developed for specific classes of chemicals, and selection depends on the expected exposure duration and degree of chemical attack.
Durcon Epoxy upholds NSF Standards and is UL certified Greenguard Gold for lower VOC emissions and healthier indoor environments. Our epoxy is also abrasion and impact resistant.
Abrasion Resistance
Abrasion resistance is a big deal for many epoxy applications. For example, industrial environments where concrete repairs are needed due to water and cleaning solutions abrading the surface of a drain, or in heavy machinery that grinds up parts. It can also let you choose from numerous colors and patterns. The good news is that there are a number of coatings that are formulated for this type of work, including epoxy urethanes.
A basic abrasion test involves pushing a hard object across the surface of an epoxy coated substrate. The force required to cause any damage to the coating is measured in pounds of pressure per square inch (psi). This force, also known as a stress/strain curve, can be used to determine an epoxy’s abrasion resistance. The closer to the linear portion of the curve, the more abrasion resistant a coating is.
An abrasion-resistant coating can be even more effective when it incorporates reinforcement fabrics designed to absorb impact energy. A popular fabric for this purpose is Kevlar, an aramid fiber. It is popular for powerboats because it resists puncture from impact and abrasion. Another reinforcement option is Xynole, another aramid fiber. It is more affordable than Kevlar but still offers excellent abrasion resistance. Other choices are Spectra(tm), a polymer fiber traditionally used in soft and hard body armor applications, and fiberglass.
In addition to these reinforcement materials, choosing a tough epoxy system and adding additives can improve an epoxy’s abrasion resistance. WEST SYSTEM epoxy systems like the 105 System are great for this purpose, as is G/flex 650 Toughened Epoxy Adhesive. Many customers also choose to blend G/flex 650 with the 105 System to create an even more tough laminate.
A study using underwater steel ball grinding to examine the abrasion resistance of elastic epoxy resins found that when hygroscopically conditioned, an epoxy showed obvious physical yield at a lower strain rate. However, it also demonstrated that most of the impact mechanical energy was absorbed by the hygroscopically conditioned epoxy’s elastic deformation. This resulted in much less damage when compared to the dry epoxy plate.
Impact Resistance
As an engineering material, epoxy is frequently used to build structures that must be able to withstand impact forces. When exposed to high-velocity projectiles, it is essential that these structures are capable of absorbing and resisting the kinetic energy of the impacts without being penetrated or cracked. Impact resistance is a vital property that needs to be considered when designing composites or coatings.
Adding silk fibre reinforcements can dramatically improve the impact strength of epoxy composites. In fact, the silk composites are so tough that they display ductile behaviour in response to impact.
The improved impact resistance of the SFRPs is attributed to their better elasticity, ductility and interfacial toughness. In addition, the hygroscopic conditioning effect of MC also contributes to their superior impact performance.
Hygroscopic conditioned SFRPs are characterised by lower elastic deformation and dissipation, and a greater ductility than dry plates. The ductility enhancement is caused by the higher crosslink density of a wet epoxy system, which promotes chain segment mobility. This leads to more bridging between polymer molecules and the formation of stronger diffraction peaks in the tensile, flexural, and short beam flexure tests.
In addition, a wet epoxy system has a much higher impact resistance. The difference is attributed to the tighter network structure and greater chemistry of the epoxy, which provides resistance to chemical attack. A tighter network and a higher chemistry also increases the crosslinking density of the epoxy system, which also contributes to its resistance to specific chemicals.
For example, TECHNO BOND 8106 is a rubber-toughened epoxy system that has excellent impact and abrasion resistance. It can be used to seal seams, gouges and cracks in walls, floors, ceilings, roofs, and other structural surfaces. It is especially good at filling expansion joints in industrial areas or damaged concrete sections, providing protection and stabilization. It can be applied with a trowel or by spray application, making it ideal for surface repairs and new construction projects in a wide variety of environments.
Chemical Resistance
Chemical resistance is a major requirement for thermoset epoxy coatings, especially those used in areas where spills and splashes of varying chemicals occur. This includes food plants, electronics production facilities and other commercial or industrial applications where diluted acids and other chemicals may be splashed or poured. Typically, a higher crosslink density will provide superior chemical resistance compared to a lower one.
The chemistry and network structure of the epoxy resin play a major role in the overall chemical resistance of the system. During chemical attack, a coating’s polymer network is subject to swelling and chemical diffusion followed by degradation or chemical reaction. A tighter network will provide better resistance to swelling and chemical diffusion, and also generally provides superior chemical resistance compared to a looser one.
During impact testing, the most common cause for poor chemical resistance in epoxy systems is water trapped inside the polymer network or unreacted amine curing agent from improper mixing and/or inadequate cure conditions. This essentially reduces the crosslink density of the epoxy to a point where it cannot protect the substrate as effectively. Incremental improvements are often possible by utilizing proper curing methods, increasing the film thickness or by using a solvent-based epoxy formulation.
Another factor impacting chemical resistance is the amount of methanol (MC) present in the epoxy formulation. MC increases the elastic limit of the epoxy and enhances its ductility. This allows more of the impact energy to be dissipated during the test and less damage to the composite.
For those demanding exceptional chemical resistance, Master Bond has formulated EP21AR, a two-component, 100% solids epoxy that can withstand extended immersion in harsh environments. This product can withstand up to 96-98% sulfuric acid and 36% hydrochloric acid for over a year, and has an extremely low coefficient of thermal expansion. This makes it an ideal choice for lining, bonding and coating in areas that require exceptional chemical resistance.
Aside from the above, a cured epoxy’s resistance to chemicals is heavily influenced by temperature. High-temperature exposure will typically decrease a system’s chemical resistance as the amine groups in the epoxy react with the hot surface and lose their plasticizing ability, which results in the formation of carbonyl compounds and loss of chemical resistance. Fortunately, this effect can be mitigated by using a curing agent with more than 2 amine groups, or by adding rubber tougheners to the mixture.
Temperature Resistance
The temperature resistance of epoxy is the ability of the resin to withstand high temperatures without warping, brittleness or a chemical degradation. The temperature resistance of epoxy is a function of the type of epoxy and the level of additives and reinforcements in the resin. In addition, the temperature resistance of epoxy is also influenced by the curing process and the ambient temperature.
During the curing process, epoxy resin undergoes an exothermic reaction that generates heat. While this is a good thing for the strength and durability of the finished product, it can have an impact on the resin’s temperature resistance. The temperature resistance of epoxy can also be reduced by solvents or improperly measured and mixed resin components.
When working with epoxy, it is important to follow the manufacturer’s instructions for mixing the product correctly. The right amount of time and the proper temperature can significantly improve the epoxy’s temperature resistance.
In order to determine the effect of hygroscopic condition on impact-resistance of carbon fiber/epoxy quasi-isotropic composite plates, low-velocity impact tests were performed on dry and hygroscopically conditioned carbon fiber/epoxy plates. The results show that absorbed MC enhances the elastic deformation capacity of the composite plate and overall less damage is induced on the hygroscopically conditioned plate compared with the dry one. This improvement in the elastic limit of the composite is attributed to the chain segmental mobility promoted by absorbed MC and improved interfacial bond between the carbon fibers and the matrix resin.
For applications where epoxy needs to withstand high temperatures, it is important to choose a product designed for the application. For example, the CHILL EPOXY line of products can withstand up to 350F without warping, melting or losing its hardness and is ideal for countertops. It is also recommended that you use hot pads and coasters to protect the epoxy from direct contact with hot items, especially metal.
