In this section, we will study several types of structural adhesives which are used for the assembly of composites: Acrylics, Polyesters, and others.
These are also called "engineering acrylics" or "structural acrylics", in order to differentiate it from the non structural acrylics which are used for Pressure sensitive adhesives or Construction and decoration applications.
There are several types but all are based on the same chemistry:
The formulations include methacrylate monomers plus a dissolved rubber polymer added as a toughener, cure accelerator and a free radical generator, sometimes also crosslinking agents. It may be one part adhesive with an activator applied on one of the substrates or 2 part adhesives. These adhesives cure at room temperature by a redox reaction of the accelerator with a free radical source - a peroxide -. This gives free radicals that open the double bonds.
Accelerators may be N-phenyl 2-propyl 3,5 diethyl 2 dihydropyridine, or aromatic amine such as NN dimethyl para toluidine.