Excellent toughness and adhesive strength

Product overview
Improvements to properties
How it works

Product overview [back]

Technical data (no spezification)

Improvements to properties [back]

Besides their many excellent properties, epoxy resins have a substantial disadvantage: Their brittleness. This disadvantage can be more than compensated through an elastomer modification (so-called "toughening" or impact resistance modification). In contrast to an elastification, the elongations of the cured resin normally remain below 10 %.

The toughening of epoxy resins proves to be difficult, however. Thus, for example, the use of flexible hardeners or the addition of non-reactive flexibilisers significantly impairs a range of important properties such as tensile strength and modulus, thermal and chemical resistances as well as thermodimensional stability.

These negative effects can be avoided by toughening with reactive rubbers. However, pure liquid rubbers are only slightly, if at all, miscible with epoxy resins. The products of the Albipox® series represent elastomer-modified epoxy resins.

Here, the epoxy resins forming the base of the different products are reacted with a high proportion of reactive liquid rubber. After the chemical transformation, an almost unlimited miscibility of these elastomer-epoxy pre-adducts with all epoxy resins in any ratio is possible.

The products of the Albipox® series can be used by epoxy resin formulators like a modular system. There are no limitations in respect to the resins and hardeners that can be used.

Figure 1 shows the effects of such a resin modification on the fracture energy. The flat curve represents an adduct of the first generation, which could be improved considerably by the currently marketed adduct of the second generation (steeper curve, Albipox® 2000).

Figure 1:  Improvement of fracture toughness through the use of toughened epoxy resins

How it works [back]

The products of the Albipox® series consist of various epoxy resins or epoxy resin combinations, which are modified with suitable liquid rubbers (mostly based on acrylonitrile-butadiene-copolymers). The elastomer molecules have epoxy functionality and are bonded chemically in the resin matrix during curing.

Any miscibility with all epoxy resins is possible before curing. During the curing, a phase separation occurs independently of the chemical nature of the hardener and the curing temperatures. Homogenously distributed, finely disperse, so-called "rubber domains" now result through the complete mixing which occurred previously. As can be seen in Figure 2, the resultant domains typically lie in the range between 0.2 – 4 µm.

The rubber domains for the most part consist of the relatively long molecules of the elastomer used, but are chemically bonded to the resin matrix via their epoxy end groups at the phase boundary. If a force is now applied to the cured resin system, it can be dissipated uniformly in all directions when encountering a rubber domain.

Figure 2:  Scanning electron microscope images of rubber-modified epoxy resins

If a tear has occurred, it is prevented from propagating: The elastomer particles stretch perpendicular to the direction of tear and are not torn out, as they are bonded chemically with the matrix (see also Figure 3).

Figure 3: Schematic representation of the rubber domains under stress

For further details, please contact our application specialists.