Toughening Up Without Sacrificing Big on Other Properties

FORTEGRA Epoxy Tougheners from Dow improve
fracture toughness with minimal impact on critical
performance attributes such as corrosion resistance.

Sometimes, the remedy is almost as bad as the disease. For decades, fabricators of corrosion-resistant composites have struggled with the brittle nature of epoxy-based materials, resorting to adding high-viscosity rubber additives like carboxyl terminated butadiene-acrylonitrile (CTBN) to improve toughness. These treatments come with undesirable side effects - most often higher viscosity, longer cure times, and reduced corrosion and chemical resistance.

Dow recently developed and introduced FORTEGRA™ Epoxy Tougheners, low viscosity materials for use in amine, DICY, anhydride and phenolic cured epoxy systems. These tougheners are designed to virtually eliminate the need for additives such as CTBN.

"We've created a material that is epoxy-phylic and epoxy-phobic at the same time," explains Steve Hoyles, Dow technical service and development representative. "When suspended in an epoxy resin matrix, one side of the molecule balls up, refusing to interact with the epoxy, while the other side stabilizes the system."

"The result is a composite or coating that retains all of the benefits imparted by the epoxy resin without the drawbacks of aliphatic modifiers or other additives."

First Steps - Overcoming Traditional Practices
As with any new solution, the first step is implementing trial programs to show the effectiveness of the new system.

"Traditional remedies such as CTBN or aliphatic modifiers have become commonplace in the industry. Most formulators have just accepted the negative properties they impart," Hoyles says. "Our biggest challenge is getting fabricators and formulators to accept the fact that they do not have to give anything up to get the toughness they want.

"There is usually a give and take associated with epoxy formulation," he continues. "To improve one property you generally give another up. This isn't the case with FORTEGRA Epoxy Tougheners. Once formulators try it, the benefits are obvious."

75 Percent More Fracture Toughness
FORTEGRA Epoxy Tougheners work similarly to traditional additives. Dow tests show that these epoxy tougheners, in ratios of five to 10 percent by volume, have increased the fracture toughness of the resulting composite or coating by 75 percent, reducing crack propagation and improving impact resistance to levels comparable with formulations using CTBN or aliphatic modifiers.

Some tests have shown that ratios as low as three percent by volume can double the fracture toughness.

Introducing the FORTEGRA Epoxy Toughener Family
The FORTEGRA family consists of a toughening agent, known as FORTEGRA 100 Toughening Agent, and three toughened epoxy resins:

• FORTEGRA 383-50, a 50 weight percent blend of the toughening material in D.E.R.™ 383 Liquid Epoxy Resin
• FORTEGRA 383-5, a 5 weight percent blend of the toughening material, also in D.E.R. 383 Liquid Epoxy Resin
• FORTEGRA 664-12, a 12 weight percent blend of the toughening material in D.E.R. 664 Solid Epoxy Resin, which is used mainly in powder coatings

Having these choices makes it easier for customers to incorporate FORTEGRA Epoxy Tougheners into their formulations. 

FORTEGRA 100 Epoxy Toughening Agent should be added to the epoxy side of formulations. When post-added to a system, the product must be blended with the epoxy before adding the hardener.

More information about FORTEGRA Epoxy Tougheners can be found at www.dowfortegra.com.

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