Can the expired polyurethane adhesive still be used?

The answer is no. 

 

Polyurethane adhesives that have exceeded their shelf life have undergone irreversible chemical changes. Using them forcefully will pose significant risks and performance hazards. The specific reasons are as follows: 

 

1.The curing effect does not meet expectations.

The curing of Polyurethane Adhesive relies on the cross-linking reaction between the isocyanate component in the adhesive and moisture in the air or curing agent. After expiration, there may already be a small amount of moisture seeping into the sealed packaging, causing some effective components to react prematurely and fail. During use, there will be situations such as slower curing speed, incomplete curing, sticky surfaces or a constantly honeycomb-like soft elasticity inside, resulting in a bonding strength far below the design standard. 

 

2. Significant decline in physical properties

Even though it may seem to be solidified on the surface, the adhesion, flexibility, weather resistance and aging resistance of expired adhesive will significantly deteriorate. When subjected to vibrations, temperature changes or long-term stress, the brittle adhesive layer is prone to cracking and falling off, thus failing to ensure the long-term stability of the structural components. 

 

3. Operational Risks

For single-component wet-curing polyurethane, expired products often experience abnormal increases in viscosity due to incomplete reactions, which can affect the leveling of the construction process and even result in particles or lumps appearing within the container. For two-component products, there may be issues such as layering, crystallization, or severe mismatch in the reaction activities of the two components, preventing the formation of a uniform adhesive layer.