Excellent toughness and adhesive strength

The toughness of heat curing epoxy resins can be increased substantially with Albipox®. Furthermore, the adhesion to difficult substrates can also be improved significantly. Other important adhesive properties such as tensile strength and modulus remain unaffected.  

Product overview
Improvements to properties
How it works

Product overview [back]

Technical data (no specification)

In many heat curing structural adhesives, the use of Albipox® 1000 or 2000 in the formulation is standard. With Albipox® 2002, higher filler contents can be realized with the same performance. As a ready-for-use type, Albipox® 3001 does not have to be preheated and blended.

Improvements to properties [back]

Epoxy resins have a substantial disadvantage: Their brittleness. This disadvantage can be more than compensated by an elastomer modification (so-called "toughening" or impact resistance modification). In contrast to an elastification, the elongation of the cured modified resin normally remain under 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 flexibilizers significantly impairs a number of important properties such as tensile strength and modulus, thermal and chemical resistance as well as thermodimensional stability.

These negative effects can be avoided by toughening with copolymers based on reactive rubbers (adducts). However, pure liquid rubbers are only slightly miscible with epoxy resins, if at all.

The different Albipox® grades are reaction products between epoxy resins and elastomeric copolymers. Hereby, the epoxy resin forming the base of the different products are reacted with an excess amount of reactive liquid rubber. After the reaction, the elastomer molecules are epoxy functional and chemically bonded to the resin matrix during curing.

After the chemical transformation, an almost unlimited miscibility of these concentrates with all epoxy resins in any ratio is possible.

The products of the Albipox® series can be used by epoxy resin formulators as 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 adhesion. Optimum adhesive properties are found at approx. 15 % copolymer content (corresponds to around 30 % addition of e.g. Albipox® 2000).

As the glass transition temperature of the liquid rubbers used is in the range  -40 °C to -50 °C, the significantly improved properties are also found at correspondingly low temperatures. In addition to significantly increased impact resistance, an improved adhesion to metallic substrates (e.g. oil-treated steels, aluminium alloys) as well as to mineral substrates is achieved. Hence, the use of reactive liquid rubbers in heat curing structural adhesives is almost standard today.

Figure 1:  Improvement in adhesive properties through reactive copolymers

How it works [back]

During curing, a phase separation occurs independently of the chemical nature of the hardener and the curing temperatures. This results in finely dispersed "rubber domains" which are homogenously distrib-uted across the resin. As can be seen in Figure 2, the resultant domains typically lie in the range between 0.2 – 4 µm. For the most part, the rubber domains consist of the relatively long molecules of the elastomer used, and are chemically bonded to the matrix via their epoxy 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 already occurred, this is prevented from tearing further: The elastomer particles stretch perpendicular to the direction of the tear and are not torn out, as they are bonded chemically with the matrix (see Figures 2 and 3).

Figure 3: Schematic representation of the rubber domain under stress

For further details, please contact our application specialists.