Adhesive Education Series: Physical Properties of Adhesives

Below you can find several common physical properties of our adhesives with a brief definition.

Viscosity: Viscosity is the measure of an adhesive’s “thickness” and the magnitude of internal friction. All being equal, an adhesive with higher viscosity will appear thicker and won’t flow as easily. For example, honey is more viscous than water. Viscosity can be measured, depending on test method, through the use of a viscometer or rheometer. For adhesive application, it is important to understand that viscosity can vary by temperature as well as shear rate.

Density and Specific Gravity: Density represents the degree of compactness of a material measured in mass per unit of volume. A higher density will mean the end product is heavier. Specific gravity is closely related to density, but it is dimensionless since it is a ratio of the density of one material versus the density of a chosen reference material. A material with a specific gravity >1 will be more dense and heavier than the reference material. Density is important because an understanding of density will help you understand what volume or thickness of adhesive you are applying.

Melting Point: Melting point refers to the temperature at which a material distinctly changes state from a solid to a liquid under normal atmospheric pressure. At a temperature below the melting point, the material is a solid. Beyond the melting point, the material is a liquid. Highly crystalline materials, like ice, will have a distinct melting point; however, many adhesives are semi-crystalline or amorphous in nature and do not have a distinct change point.

Softening Point: Another measure used to use to determine when an adhesive will begin to flow, especially those adhesives without a distinct melting point, is the softening point In the Ring and Ball test, a common method for determining softening point of an adhesive, a weighted ball is placed on top of a disc of adhesive and the temperature at which the ball falls through adhesive is measured. All being equal, this test can relate to the temperature resistance of the adhesive but it is most effectively used when compared relatively to other physical and rheological properties of the adhesive.

No matter the adhesive need or application, Bostik’s chemists can help answer all your technical questions. Looking for adhesive specific information? Click here be put in touch with one of our adhesive experts.