Adhesive strength refers to the ability of an adhesive to adhere to one surface and bond two surfaces together. It is measured by evaluating the maximum tensile stress required to separate or unwind the adhesive perpendicular to the substrate.
Adhesive strength is the maximum possible tensile stress at the interface. When using solvent-borne coatings, it is affected by coating thickness and solvent retention.
When an adhesive bonds to an item or surface, many physical, mechanical and chemical forces come into play and they may interact with each other.
Adhesive strength is a measure of the adhesion or adhesion between an adhesive and a substrate. This can happen mechanically, where the adhesive enters the pores of the substrate, or by one of several chemical mechanisms.
Bond strength depends on many factors, including how it occurs. Bonding methods include:
A chemical bond may occur between the adhesive and the substrate.
Like static electricity, electrostatic forces hold matter together.
Van der Waals forces may arise between molecules.
The adhesive diffuses into the substrate with the help of moisture and then hardens.
For example, pressure sensitive adhesives (PSAs) form bonds by applying light pressure to seal the adhesive to an adherend. The bond is formed because the adhesive is soft enough to flow onto the adherend. Bonds have strength because the adhesive is strong enough to resist flow when stress is applied to the bond. Once the adhesive and adherend are in close proximity, molecular interactions such as van der Waals forces enter into the bond, significantly increasing its strength.
Some high-performance irreversible PSAs have very high adhesion values, capable of supporting several kilograms per square centimeter of contact area, even at elevated temperatures. Removable adhesives have low adhesion and typically cannot hold significant weight.
The determination of the point of failure is very important for the use of materials and adhesives. There are a large number of different adhesive products that require different test methods to characterize the properties of the material.
Testing can be done for quality control purposes, but is more commonly done to comply with industry standards and customer specifications. Even during the application of an established coating, many factors can affect the bond strength of the coating. Seemingly small changes in process parameters can have a major impact on the ultimate bond strength between coating and substrate.
