When there’s a need for an adhesive that will give a very strong, permanent bond, most people reach for the structural adhesives. These are usually made from thermosetting resins, but the resins require either a hardener (curing agent), a catalyst or the application of heat.
Polyurethanes are mega-strength thermosetting elastomers, and they are also counted as structural adhesives. Let’s look at the six main types of structural adhesives, so that you can choose the best one for the job.
Epoxies are highly versatile and provide strong bonding with plastics, glass and metals. They’re the most widely used structural adhesive https://www.adhesives.org/adhesives-sealants/adhesives-sealants-overview/adhesive-technologies/chemically-curing/two-component-(2-c)/epoxy-adhesives). When they have cured, they’ll resist chemicals and temperature extremes, with high cohesion and very low shrinkage. Widely used in industrial applications.
Acrylic adhesives are often called reactive acrylics, to distinguish them from other acrylic resins used when pressure is a key factor. Starting as thin liquids, they can form very strong bonds through the polymerisation process. Acrylics are designed to cure, even in room temperature air, in a matter of minutes or hours. You’ll recognise an acrylic adhesive through its pungent odour – some love it, some can’t abide it.
3. Anaerobic acrylics
These only cure when there’s no air in or around the resin. They mainly consist of (meth)acrylic monomers and are widely used where there’s a requirement for a metal bonding adhesive (www.ct1ltd.com/product-applications/metal-to-metal-adhesive), particularly between tightly fitting metal joints. They can augment the seals on joints or threads, or provide a hold when assemblies are being mechanically joined.
These are the famous “super glues”, beloved of practical jokers everywhere, because they bond and cure in seconds. However, they need moisture to start the polymerisation process and aren’t brilliant at resisting moisture or heat.
Polyurethanes give a tough bond and because they are flexible, they are widely used to bond materials such as foils, films and elastomers. They have good adhesion to sheet moulding materials and perform well at low temperatures. However, you need to apply a primer to get them to bond effectively to metals.
These adhesives have outstanding heat resistance and are able to bond to polyethylene and fluorocarbons. They are used either as pressure sensitive formulations, or as solvent solutions.