Repair and adhesive bonding on fiber composites

Adhesive films and coatings based on benzoxazine - storage-stable and non-meltable

Repairing fiber composite components is often time-consuming and requires multiple processing steps and curing cycles of the resin. Typical restoration of the function or appearance of a damaged area is carried out using a wet lamination process or application of reinforcing structures on the surface. Therefore, if an adhesive film or coating based on benzoxazines is used instead this enables comparatively simpler repair and adhesive bonding, with final strength being achieved within 30 minutes.


Benzoxazine vitrimers: new possibilities in repairing of FRP

The benzoxazine-based adhesive film developed by Fraunhofer IFAM is based on a duromersystem featuring vitrimeric properties. That means, it does not melt and there is no (typical) reactive resin system, as would be the case, for example, in the wet lamination process. The main advantages result from vitrimeric nature: The resin is already polymerized and a crosslinked plastic. The adhesion of benzoxazine-based adhesive films is generated via pressure and thermally induced chemical exchange reactions (vitrimer). Hence, it also ensures greater occupational safety because there is no need to handle reactive hazardous substances.

The resin system used for the adhesive film allows a flexibility in terms of design and layout, since the benzoxazine system could already be present as a coating on a repair patch. The cured film enables the conformity to the final contour of the damaged component. Unlike prepregs or conventional duromer-based adhesive films, refrigerated storage is not required to inhibit premature curing. Thus, the benzoxazine-based adhesive film is stable in storage at room temperature and is not sticky.

Due to the flexibility and possibilities of benzoxazine chemistry, this technology can also be realized with bio-based and more sustainable raw materials in the future and it opens up various application possibilities in diverse industries, such as the automotive industry, the aerospace sector and for maritime technologies.