One of the most popular questions we receive from customers is providing advice and recommendations on the strongest adhesive for their application. In this post, we explore the best adhesives for bonding metals, glass, plastics and composites.
If we look at tensile strength, epoxy adhesives could be classed as the strongest adhesive. Tensile strength refers to how strong the cured adhesive is, in relation to how much internal strength it has to resist external forces on the bond line. One component epoxy adhesives have the highest tensile strength of approximately 35-41 N/mm (5100-6000 psi).
Strongest adhesives for bonding metals, glass, plastics and composites
What are the best adhesives for bonding metals?
One component epoxy adhesives
When bonding metals, one component epoxy adhesives offer high shear, impact and peel strength, making them ideal for replacing metal soldering and brazing. The shear strength can reach 41 N/mm² (6000 psi) on steel. The surface treatment of the steel and gap size can affect the overall strength.
Most one component epoxies require a heat cure where using an industrial oven will speed up the adhesive curing process. One component epoxies provide excellent resistance to chemicals and temperatures.
Two component epoxy adhesives
Two component epoxy adhesives have a hardener that accelerates the curing process to form high strength structural bonds on ferrous metals, aluminium, copper, zinc, brass and galvanised metals. These epoxy adhesives have a tensile strength of approximately 20-30 N/mm² (2900-4400psi).
The benefits are two component epoxy adhesives will cure at room temperature, making them fast setting adhesives. Other properties include high temperature and chemical resistance (up to 190°c) making them suitable for harsh and high-stress environments.
Structural acrylic adhesives
Structural acrylic adhesives such as Methyl methacrylate (MMA) provide high tensile strength and good adhesion to metals and ferrites. These adhesives are commonly chosen due to their ability to bond surfaces with minimal or no preparation at all. They provide greater flexibility over epoxy adhesives with good impact strength and high fatigue resistance. The drawback is that some of these structural acrylic adhesives, particularly MMA’s have a distinct odour making it unsuitable for certain work environments.
Structural acrylic adhesives have a high resistance to chemicals and temperatures. Depending on the type and grade of the adhesive, the tensile strength can be over 28N/mm² (4000psi).
Cyanoacrylate adhesives have exceptional strength on steel with 30 N/mm² (4400psi), however they do not have good chemical and temperature resistance compared to epoxies and acrylic adhesives. Epoxies and acrylic adhesives also provide better impact resistance than cyanoacrylates. Cyanoacrylate adhesives are ideal for smaller assemblies and fast moving production lines.
Anaerobic adhesives and sealants
Anaerobic adhesive and sealants such as the Permabond range can be used for metal bonding and are often used as threadlockers, retaining compounds, thread sealants and form in place gaskets. These adhesives will not cure without a metal and require oxygen to be present.
What are the best adhesives for bonding glass?
UV curable adhesives
UV curable adhesives are used for most glass to glass applications. UV curable adhesives have several features that make it suitable for bonding glass including curing on demand, stress absorption within the joint and producing clear transparent bonds for aesthetics. Some grades of epoxies and structural acrylics can bond well to glass however they do not have a fast cure and the aesthetics are not as good compared to UV curable adhesives.
What are the best adhesives for bonding plastics?
There are many adhesives for bonding different types of plastic:
UV curable adhesives
UV curable adhesives provide excellent adhesion to most plastics and are chosen for its aesthetic properties. Many plastics are UV stabilized to prevent yellowing but speciality UV adhesives for bonding plastics can cure within visible light. One of the plastics must be light transmitting.
Cyanoacrylate adhesives have a high shear strength and can bond most plastics including PVC, ABS and PC. If bonding polyolefin and silicone, these may require a primer prior to bonding. Known as instant adhesives, cyanoacrylates are fast setting and cure by reacting to the moisture on the surface of the components.
Structural acrylic adhesives
Structural acrylic adhesives are suitable for bonding low surface energy plastics such as polypropylene and polyethylene. MMA’s can provide high strength on plastics and can be used in tough environments.
What are the best adhesives for composite bonding?
Epoxies, Methyl methacrylates and polyurethanes such as the Araldite range of adhesives can be used to bond composite materials including carbon fibre and dissimilar metals.
If you are unsure about what the best adhesive is for your application, we can provide advice on adhesive selection including product testing and trials to ensure the product is right for your needs.