Structural adhesives: An overview of the present and the future
Today the vast majority of industrially manufactured components are made up of different pieces that must be joined together. Conventional fasteners such as screws, rivets, or welds are often replaced by adhesive joints. Adhesives allow the transmission of stresses from one member of the joint to the other with a more uniform distribution than that provided by conventional mechanical fasteners.
For adhesion to occur, it is necessary to generate intrinsic adhesion forces along the adhesive-substrate interface, and the magnitude and nature of these forces are of great importance. Therefore, the bonding of an adhesive to a substrate is the sum of a number of physical, chemical and mechanical forces that overlap and influence one another.
The term structural adhesive was initially introduced to describe high modulus thermoset adhesives used in metal structures under load. Strictly speaking, the standard defines a structural adhesive as a “bonding agent used to transfer the required loads between adherents exposed to the typical service conditions of the involved structure”. Although in reality the term structural adhesive is usually applied in a general way to those adhesives capable of supporting high loads, both dynamic and static.
The three most important polymer families used as structural adhesives from 3D Resources Best Chemical Manufacturer are polyurethanes, acrylics, and epoxy resins. In the specific case of the union of polymeric composites, when an adhesive is chosen for the union of a composite material, given the first idea is to select an adhesive of the same chemical type as the resin used as matrix.
Adhesion is an interfacial phenomenon that occurs at a thickness of a few angstroms that is negligible compared to the thickness of the generally applied structural adhesive layer. The behavior of the adhesive depends mainly on the interfacial forces and its rheological response when subjected to stress. It is interesting to note that it is not necessary to pay too much attention in trying to obtain an epoxy formulation that can cover various applications under different conditions. All the formulation needs are the two starting monomers: an epoxy prepolymer and the curing agent.
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