The Effect of Glass Transition Temperature on Adhesives and Sealants

The Effect of Glass Transition Temperature on Adhesives and Sealants 

Polymers have physical properties that are important in adhesion. The chemical structure of the base polymer of the adhesive or sealant and the various formulating agents used in modification of the polymer control the physical characteristics. The glass transition temperature (Tg) is a physical property measurement that reflects the behaviour of polymers. Tg gives us an understanding of the molecular motion that occurs in a polymer system the higher the molecular movement the softer the material. 

When considering adhesion, cohesion, and other properties of adhesives and sealants the amount of molecular freedom is an important aspect. At low temperatures they exhibit solid characteristics however, as the temperature increases the material starts to soften and exhibits viscous flow. The temperamre at which this occurs is called the glass transition temperature, and signifies a transition of the polymer from a glassy to a rubbery state. Raising the temperamre further above its Tg, allows the molecules more freedom of movement until the material melts into liquid flow. 

Polymeric materials have transition phases above and below normal room temperature. Many polyurethane elastomers show a Tg — 50 C while structural foams show a Tg 83°C. 

The transition phase of a polymeric material does not occur at a single unique temperature. Usually, the phase change happens over a short temperature range, the Tg is the approximate mid-point temperamre of that range. 

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