Structural adhesives, also known as load-bearing adhesives, are substances that harden and fasten two similar or dissimilar substrate elements with high-modulus, high-strength, and permanent bonds. These adhesives are capable of withstanding forces and holding the bonded surfaces efficiently, even under shock, vibration, temperature, and chemical changes. Common substrate materials include metals, plastics, glass, ceramics, and rubbers, among others.
According to a report published by Allied Market Research, the global structural adhesives market is projected to reach $27.9 billion and exhibit a considerable CAGR from 2021-2030. Material bonding technology has seen significant advantages that have led to an increase in global demand for adhesively bonded structures. The advantages of structural adhesives, such as curing flexibility and durability, will contribute to the growth of the global market to a great extent.
Growth is expected in several applications. For example, automotive parts can be bonded with epoxy adhesives that enable them to absorb high energy at variable temperatures. Acrylic and polyurethane structural adhesives are widely used in several building and construction applications, including ceramic tile fixing and lamination. Structural adhesives are also used for some decorative applications and insulation foams.
Chemistries and Developments
Epoxy, polyurethane, polyimide, silicone, and acrylic, are a few common structural adhesive chemistries. Typical properties include:
- Epoxy adhesives—highly resistant to temperature and can be structurally bonded to metals, ceramics, woods, and plastics. These are generally converted into viscous liquids or pastes and are less sensitive to slight differences in mix ratio. Epoxy needs nearly 24 hrs at room temperature to reposition and develop its final properties. It can withstand temperatures from 40-205˚C.
- Polyurethane adhesives—polymer-based, polyurethanes offer strong bonding, high flexibility, and permanent elasticity. These adhesives are commonly used for construction purposes.
- Polyimide adhesives—used for coating or electronic insulation, these adhesives are strong and resistant to chemicals. They are well-known for performance in extremely high temperatures (up to 500˚C).
- Silicone adhesives—can be formulated for both high and low electric and thermal conductivities. Silicones possesses less cohesive strength than all other structural adhesives. However, this property makes these adhesives an excellent choice for repair and rework purposes in electrical, electronic, automotive, domestic, and construction applications.
- Acrylic adhesives—comprise methyl acrylic polymers and offer extremely strong and efficient bonding, which makes them widely used for construction purposes. These adhesives, which give a visual indication by changing color during cure, are effective up to 205˚C.
- Urethane adhesives—sensitive to moisture and can be formulated with much less viscosity than epoxy and acrylic adhesives. Urethanes provide resiliency and flexibility and can withstand temperatures up to 120˚C. Urethane adhesives are mostly used for composites, thermoplastics, natural materials, and prepared metals.
In a recent technological development, researchers have created new durable structural adhesives for affordable housing and next-generation infrastructure. These structural adhesives are specially designed to withstand the environmental factors and structural demands found in concrete buildings.
Externally bonded fiber-reinforced polymers (EBFRPs) strengthen structures made of concrete materials, and the durability of EBFRPs can be improved by enabling adhesive bonding to concrete. These new adhesives can be used to attach prefabricated structural elements to combine 3D-printed concrete layers, which can foster structural integrity and enable the transfer of loads easily through the structure.
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